Power Transmission Reference Guide 2016 by WTWH Media LLC

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April 2016

POWER Transmission REFERENCE GUIDE

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Haydon Kerk® Linear Actuators...

SOLUTIONS IN MOTION High performance, precision linear motion technology Size 17 43 mm2 (1.7-in)2 Double Stack external, non-captive, captive hybrid linear actuator stepper motors

25000 Series G4, can-stack captive, non-captive, external linear actuator steppers 25 mm (1.0-in) diameter

Size 34 87 mm2 (3.4-in)2 captive hybrid linear actuator stepper motor. Non-captive and external linear also available.

Size 17 - 43 mm2 (1.7-in)2 non-captive hybrid linear actuator with programmable IDEA™ stepper motor drive Size 8 21 mm2 (0.8-in)2 captive hybrid linear actuator stepper motor. Also available in Single and Double Stack, non-captive and external linear.

Haydon Kerk Motion Solutions hybrid and can-stack linear actuators continue to offer equipment designers new motion control solutions that provide unmatched performance-to-size ratios, patented technologies and thousands of configuration options, and a vast experience in customized solutions. HYBRID actuators are available in six sizes from Size 8: 21 mm2 (0.8 -in.) to Size 34: 87 mm2 (3.4-in.) – capable of delivering up to 500 pounds (2224 N) of force. Travels per step range from .001524 mm (.00006-in) to .127 mm (.005-in), with micro stepping capability for even finer resolution. An integrated, programmable IDEA™ Drive is also available for Size 17 hybrids. The G4 Series represents the industry’s most robust and most powerful CAN-STACK linear actuators. The G4 Series offers diameters of 20 mm (.79-in), 26 mm (1-in), and 36 mm (1.4-in). The can-stack product line also includes motors with diameters of 15 mm (0.59-in), 20 mm (.79-in) , 26 mm (1-in), 36 mm (1.4-in) and Ø 46 mm (1.8-in), available with captive, non-captive or external linear lead-screws. Haydon Kerk Motion Solutions continues to be an innovative motion control technology company with a global network of people, facilities and services dedicated to engineering and manufacturing the world’s most advanced linear motion solutions. For more information: www.HaydonKerk.com > Linear Actuators

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REFERENCE GUIDE

Power Transmission

LISA EITEL SENIOR EDITOR @DW_LISAEITEL

POWER-TRANSMISSION C CO OM MP PO ON NE EN NT TS S A AR RE E M MA A II N NS S TAY TAY S S POWER-TRANSMISSION MOTION designs continually evolve, but will always rely on mechanical devices, particularly where the drive of an electric motor engages a load to execute machine tasks. In fact, as the technical reviews in this 2016 Power Transmission Reference Guide explain, applications for mechanical motion components only proliferate as technical innovations make them increasingly effective. Consider this Reference Guide’s section on bearings by Associate Editor Mike Santora. The most common bearing applications are in heavy machinery and industrial setups as always, but renewableenergy use is spurring innovations to get higher capacities as turbines push the limits of bearing designs. There’s also increased demand for complete system solutions over components, which is changing the

DESIGN WORLD

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design of linear systems, actuators and gearmotors, as well as subsystems such as conveyors and robotics. Consider the section on gearmotors in this Reference Guide by Senior Editor Miles Budimir. Here, manufacturers are predesigning and assembling more motors than ever with gearboxes upfront, for an ever-expanding array of ac gearmotors and servo gearmotors. Such gearmotors are increasingly accurate as well, particularly those sporting planetary gearsets. That’s thanks in part to how manufacturers are making gearing with the latest approaches in design, machining and assembly. Check out the sections in this Reference Guide covering gear-design consultation, custom gear designs and analysis, as well as general speed reducers, worm gearing, and shaft-mount sets. These articles detail common and custom offerings that optimize inertia matching and speed output. In fact, today’s software now lets designers get design-specific gearing—and other powertransmission components—at lower cost than that of general-purpose offerings from just a decade ago. In fact, today’s moving designs rely on an increasingly diverse array of mechanical components to protect expensive subsystems and change motion-system dynamics to simplify programming. These actuators, ballscrews, bearings, brakes, chains, collars, couplings, gearing, rails and rack-and-pinion sets transmit power in ways that get higher performance than ever. www.designworldonline.com

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So use this Reference Guide as a review of basic component functions or as an update on what’s new in power-transmission designs—and to get instructions on how to make the most of proliferating features to meet evolving motion-system requirements. As mechanical designs change, count on us Design World editors to bring you technology updates to help you specify and integrate the right components. We invite your feedback and requests for technical information. There are innumerable ways to reach us: Email me at leitel@wtwhmedia.com or tweet to @DW_LisaEitel, @Linear_Motion and @Motion_Control. Connect with our Design World Network Facebook page at facebook.com/DesignWorldNetwork, and let us know what designs you’re using or are looking to apply. Also look out for the 2016 Motion Systems Handbook and 2016 Motion Casebook coming to you in August and November for complete coverage of electronic and programming technologies for motion designs, as well as real-world application examples and illustrations to inform your next build. In the mean time, also find all our motion-technology news announcements (as well as technical archives) on our motion tips sites—motioncontroltips. com, linearmotiontips.com, sensortips.com, bearingtips.com and couplingtips.com.

WEBINAR ALERT TRENDS TO WATCH IN MOTION CONTROL

DOWNLOAD ON DEMAND: bit.ly/1Lxaexl

Get a Free Power Basics Poster tlec-2015_power-poster-final-cmyk-HIRES.pdf

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LINE VOLTAGE

Neutral

Line

At any given moment in time, the voltage magnitude is V * sin(α) • V = magnitude of voltage vector • α = angle of rotation, in radians

Line

Neutral

Important to Know • Voltage is stated as “VAC”, but this is really VRMS • Rated Voltage is Line-Neutral • VPEAK = 2 * VAC (or 2 * VRMS ) • 169.7 V in the example below • VPK-PK = 2 * VPEAK • If rectiﬁed and ﬁltered • VDC = 2 * VAC = VPEAK AC Single-Phase “Utility” Voltage Volts (Peak), Line-Neutral

200

120 VAC Example

120VAC

150 100 50 0

Phase Angle freq (Hz)

THREE-PHASE

Voltage value = VX*sin(α) • VX = magnitude of phase voltage vector • α = angle of rotation, in radians

Voltages can be measured two ways: • Line-Line (L-L) • Also referred to as Phase-Phase • e.g. from VA to VB, or VA-B • Line-Neutral (L-N) • Neutral must be present and accessible • e.g. from VA to Neutral, or VA-N • VL-L conversion to VL-N • Magnitude: VL-N * 3 = VL-L • Phase: VL-N - 30° = VL-L

-150

400

0 -200

-800

Time

400 200 0 -200

-400

-800

VRMS =

1 V PK-PK 2 2

VRMS = VAC2

-600

Time

A-N Voltage B-N Voltage C-N Voltage Three-phase Rectiﬁed DC

P≠V*I N

P≠V*I

Apparent Power • |S|, in Volt-Amperes, or VA • = VRMS * IRMS for a given power cycle

9 6 3

Real Power • P, in Watts • = instantaneous V * I for a given power cycle

0 -3 -6

Capacitive load

-12 -15

Period 1 Mi = 18 points

Time A Current B Current C Current

Reactive Power • Q, in Volt-Amperes reactive, or VAr • Q = S2 - P2 • Does not “transfer” to load during a power cycle, just “moves around” in the circuit

10 ARMS Example

Period 2 Mi = 18 points

mi = point 7

mi = point 25

For one power cycle

• The digital samples are grouped into measurement cycles (periods) • For a given cycle index i…. • The digitally sampled voltage waveform is represented as having a set of sample points j in cycle index i • For a given cycle index i, there are Mi sample points beginning at mi and continuing through mi + Mi -1. • Voltage, current, power, etc. values are calculated on each cycle index i from 1 to N cycles.

PT O T A L = VA - N * IA + VB - N * IB + VC - N * IC

IA PT O T A L ≠ VA - N * IA + VB - N * IB + VC - N * IC

V C-N

teledynelecroy.com/motor-drive-analyzer

IRMS

Real Power for each Phase • P, in Watts • = instantaneous V * I for a given power cycle

VRMSi =

IRMSi =

Reactive Power for each Phase • Q, in Volt-Amperes reactive, or VAr • Q = S2 - P2

SB PA

• PTOTAL = PA + PB + PC • STOTAL = SA + SB + SC • QTOTAL = QA + QB + QC

φ φ

PC QC

Line-Line Voltage Sensing Case

B IB VB-C

Current is measured L-N

L-L voltages must be transformed to L-N reference:

VB-N

VA-B

VA-N IA

VC-A

Calculations are straightforward, as described above: • PTOTAL= PA + PB + PC • STOTAL = SA + SB + SC • QTOTAL = QA + QB + QC

φ P

Real Power

Note: Any distortion present on the Line voltage and current waveforms will result in power measurement errors if real power (P) is calculated as |S|*cos(φ). To avoid measurement errors, a digital sampling technique for power calculations should be used, and this technique is also valid for pure sinusoidal waveforms.

Voltage is measured L-L on two phases • Note that the both voltages are measured with reference to C phase

VC-N

mi + Mi - 1 1 V j2 Mi j=mi

mi + Mi - 1 1 I j2 Mi j=mi

Real Power (P, in Watts)

Mathematical assumptions: • Σ(IA + IB + IC) = 0 • Σ(VA-B + VB-C + VC-A) = 0 This is a widely used and valid method for a balanced three-phase system

Pi =

Apparent Power (S, in VA)

Reactive Power (Q, in VAR)

PTOTAL = VA-C * IA + VB-C * IB STOTAL= VRMSA-C * IRMSA + VRMSB-C * IRMSB QTOTAL = STOTAL2 - PTOTAL2

Current is measured on two phases • The two that flow into the C phase

Formulas Used for Per-cycle Digitally Sampled Calculations

VRMS

V A-N

IC V C-N

V A-N

Two Wattmeter Method – 2 Voltages, 2 Currents with Wye (Y or Star) or Delta (∆) Winding

-9

Delta (∆) 3-phase Connection • Neutral is not present in the winding (in most cases)

Voltage is measured L-L • Neutral point may not be accessible, or • L-L voltage sensing may be preferred

Inductive load

Single-phase Real, Apparent and Reactive Power AC Three-Phase "Line" Currents 15 12

B A

φ I

• For inductive loads • The current vector “lags” the voltage vector angle φ • Purely inductive load has angle φ = 90°

Digital Sampling Technique for Power Calculations�

For capacitive and inductive loads • P ≠ V * I since voltage and current are not in phase

120°

A IC

480 VAC Example Three-Phase Winding Connections

For one power cycle

Single-phase, Non-resistive Loads

• Capacitive Loads • The current vector “leads” the voltage vector by angle φ • Purely capacitive load has angle φ = 90°

Important to Know • Current is stated as “lAC”, but this is really IRMS • Line currents can represent either current through a coil, or current into a terminal (see image below) depending on the three-phase winding connection • IPEAK = 2 * IRMS • 14.14A for a 10 ARMS current in the example to the right • IPK-PK = 2 * IPEAK

A-B Voltage B-C Voltage C-A Voltage

480 VAC Example AC Three-Phase “Utility” Voltage 480VAC , Measured Line-Neutral

600

V B-N

Apparent Power for each Phase • |S|, in Volt-Amperes, or VA • = VRMS * IRMS for a given power cycle

Line Current Measurements

-600

800

If a neutral wire is present, three-phase voltages may also be measured Line-Neutral • VL-N = VL-L/ 3 • 277 VAC (VRMS) in this example • VPEAK = 2 * VL-N • 392 V in the example to the right • VPK-PK = 2 * VPEAK

-400

Line-Neutral Voltage Measurements

Wye (Y) 3-phase Connection • Neutral is present in the winding • But often is not accessible • Most common conﬁguration

Neutral

Current value = IX*sin(α) • IX = magnitude of line current vector • α = angle of rotation, in radians

200

As with the single-phase case, Power is not the simple multiplication of voltage and current magnitudes, and subsequent summation for all three phases.

V B-N

Voltage Current

120°

Like voltage, the resulting time-varying “rotating” current vectors appear as three sinusoidal waveforms • Separated by 120° • Of equal peak amplitude for a balanced load

AC Three-Phase “Utility” Voltage 480VAC , Measured Line-Line

600

Three-phase, Non-resistive Loads

For purely resistive loads • PA = VA-N * IA • PB = VB-N * IB • PC = VC-N * IC • PTOTAL = PA + PB + PC

Power Factor (PF, or λ) • cos(φ) for purely sinusoidal waveforms • Unitless, 0 to 1, • 1 = V and I in phase, purely resistive load • 0 = 90° out of phase, purely capacitive or purely inductive load • Not typically “signed” – current either leads (capacitive load) or lags (inductive load) the voltage

800

Three-phase, Resistive Loads

Three-phase, Any Load

ω (rad/s) or freq (Hz)

Like voltage, three-phase current has three different line current vectors that rotate at a given frequency • Typically, 50 or 60 Hz for utility-supplied voltage

VA-N

Important to Know • Voltage is stated as “VAC”, but this is really VRMS • Rated Three-phase voltage is always Line-Line (VL-L) • Line-Line is A-B (VA-B), B-C (VB-C), and C-A (VC-A) • Line-Line is sometimes referred to as Phase-Phase • VPEAK(L-L) = 2 * VL-L • 679 V in the example to the right • VPK-PK(L-L) = 2 * VPEAK(L-L)

Time

“True” RMS

Neutral

120°

Line-Line Voltage Measurements

Resistive load

By deﬁnition, the system is “balanced” • Vectors are separated by 120˚ • Vectors are of equal magnitude • Sum of all three currents = O A at neutral (provided there is no leakage of current to ground)

VA-B

P=V * I

Power Factor

Phase Angle (φ) • Indicates the angular difference between the current and voltage vectors • Degrees: - 90° to +90° • Or radians: -π/2 to + π/2

Line

Neutral

The resulting time-varying “rotating” voltage vectors appear as three sinusoidal waveforms • Separated by 120° • Of equal peak amplitude

If all three phases are rectiﬁed and ﬁltered • VDC = 2 * VL-N * 3 = VPEAK * 3 = 679 V in the example to the right

-50 -100

-200

“Not True” RMS

VPK-PK

For purely resistive loads • P = I2R = V2/R = V * I • The current vector and voltage vector are in perfect phase

120°

Volts (Peak), Line-Line

ω (rad/s) or freq (Hz)

THREE-PHASE

Electric Power • “The rate at which energy is transferred to a circuit” • Units = Watts (one Joule/second)

The resulting time-varying “rotating” current vector appears as a sinusoidal waveform

At any given moment in time, the current magnitude is I*sin(α) • I = magnitude of current vector • α = angle of rotation, in radians

MDA800 Series Motor Drive Analyzers 8 channels, 12-bits, 1 GHz

SINGLE-PHASE

Like voltage, the single-phase current vector rotates at a given frequency • Typically, 50 or 60 Hz

120° Neutral

120°

• 50 Hz in Europe • 60 Hz in US • Either 50 or 60 Hz in Asia • Other frequencies are sometimes used in non-utility supplied power, e.g. • 400 Hz • 25 Hz

mechanical static and dynamic power

ω (rad/s) or freq (Hz)

Typically, the three phases are referred to as A, B, and C, but other conventions are also used: • 1, 2, and 3 • L1, L2, and L3 • R, S, and T The three voltage vectors rotate at a given frequency • Typically, 50 or 60 Hz for utility-supplied voltage

The single-phase voltage vector rotates at a given frequency • Typically, 50 or 60 Hz for utility-supplied voltage

LINE POWER

SINGLE-PHASE

Three-phase line voltage consists of three voltage vectors. • By deﬁnition, the system is “balanced” • Vectors are separated by 120° • Vectors are of equal magnitude • Sum of all three voltages = 0 V at Neutral

Imaginary Power

• Magnitude (voltage) • Angle (phase) Typically, the single-phase is referred to as “Line” voltage, and is referenced to neutral.

The resulting time-varying “rotating” voltage vector appears as a sinusoidal waveform with a ﬁxed frequency

Identify 3-phase electrical and motor

LINE CURRENT THREE-PHASE

Single-phase line voltage consists of one voltage vector with:

Line Current (Peak)

SINGLE-PHASE

Volts (Peak), Line-Neutral

One Instrument, One Solution

Line Voltage, Current, and Power – The Basics

mi + Mi - 1 1 Vj * Ij Mi j=mi

IB VB-C

Power Factor (λ)

IA VA-C

VB-C

λi =

VA-C

Pi Si

Si = VRMSi * IRMSi

magnitude Qi =

S i2 - P i2

Sign of Qi is positive if the fundamental voltage vector leads the fundamental current vector

Phase Angle (φ)

magnitude Φi = cos-1λi Sign of Φi is positive if the fundamental voltage vector leads the fundamental current vector

behaviors. Built on an 8 channel, 12-bit, 1 GHz oscilloscope platform for power section and embedded control debug – complete test capability. Learn more about the MDA800 and sign up to receive a Power Basics Poster for free: teledynelecroy.com/static-dynamic-complete

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REFERENCE GUIDE

Power Transmission

GRAPHICS

EDITORIAL

NEW MEDIA/WEB/ BUSINESS DEVELOPMENT

Director, Creative Services Mark Rook mrook@wtwhmedia.com @wtwh_graphics

Editorial Director Paul J. Heney pheney@wtwhmedia.com @dw_Editor

Web Development Manager B. David Miyares dmiyares@wtwhmedia.com @wtwh_WebDave

Art Director Matthew Claney mclaney@wtwhmedia.com @wtwh_designer

Managing Editor Leslie Langnau llangnau@wtwhmedia.com @dw_3Dprinting

Web Development Specialist Patrick Amigo pamigo@wtwhmedia.com @amigo_patrick

Graphic Designer Allison Washko awashko@wtwhmedia.com @wtwh_allison

Executive Editor Leland Teschler lteschler@wtwhmedia.com @dw_LeeTeschler

Digital Marketing Specialist Andrew Zistler azistler@wtwhmedia.com

Traffic Manager Mary Heideloff mheideloff@wtwhmedia.com

Senior Editor Miles Budimir mbudimir@wtwhmedia.com @dw_Motion

Controller Brian Korsberg bkorsberg@wtwhmedia.com

Production Associate Tracy Powers tpowers@wtwhmedia.com VIDEO

Senior Editor Lisa Eitel leitel@wtwhmedia.com @dw_LisaEitel

Videographer John Hansel jhansel@wtwhmedia.com @wtwh_Jhansel Videographer Kyle Johnston kjohnston@wtwhmedia.com @wtwh_Kyle Videographer Alex Barni abarni@wtwhmedia.com

Senior Editor Mary Gannon mgannon@wtwhmedia.com @dw_MaryGannon

Associate Editor Mike Santora msantora@wtwhmedia.com @dw_MikeSantora Assistant Editor Michelle DiFrangia mdifrangia@wtwhmedia.com @wtwh_Michelle

Business Development Manager Patrick Curran pcurran@wtwhmedia.com @wtwhseopatrick Online Coordinator Jennifer Calhoon jcalhoon@wtwhmedia.com @wtwh_Jennifer

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MARKETING Marketing Manager Stacy Combest scombest@wtwhmedia.com @wtwh_Stacy

2014 Winner

Marketing & Event Coordinator Jen Kolasky jkolasky@wtwhmedia.com @wtwh_Jen Marketing Coordinator Lexi Korsok lkorsok@wtwhmedia.com @medtech_Lexi Digital Marketing Specialist Josh Breuler jbreuler@wtwhmedia.com @wtwh_Joshb Digital Marketing Intern Aly Ryan aryan@wtwhmedia.com @wtwh_Aly

2011 - 2015

CONNECT WITH US!

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DESIGN WORLD — MOTION

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motioncontroltips.com | designworldonline.com

4/29/16 5:34 PM

What’s Inside Matters The PITTMAN Difference ®

On the outside, this looks like an ordinary DC motor. In fact, this particular motor is not a standard off-the-shelf part, but designed exactly to a customer’s specific technical requirements. PITTMAN has an experienced team of engineers focused on providing the perfect motor assembly to our customers demanding motion applications. • • • • •

Special brush formulation for use in a very low humidity environment Bearing system to handle higher than normal axial loads Very tight balancing spec to minimize audible noise and vibration at high speeds Unique magnet charge pattern to minimize cogging at low speeds Specially chosen surface-mount components inside the motor to meet an aggressive EMC requirement • Numerous integrated spur and planetary gearboxes, encoders, brakes and drives

When evaluating DC motor choices, it’s what’s inside that matters.

www.Pittman–Motors.com 343 Godshall Drive, Harleysville, PA 19438 USA: +1 267 933 2105 Europe: +33 2 40 92 87 51 Asia: +86 21 5763 1258

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M OT I O N CO N T R O LT I P S . CO M

INSIDE VOL 2 NO 2

P04

Power-transmission components are mainstays

PTDA Updates ..............................................10 Actuators Electrical ..................................................14 Rigid Chain ..............................................18 Ballscrews .....................................................20 Bearings ......................................................24 Belts, Pulleys ...........................................28 Brakes, Clutches ...................................31 Cabling ................................................32 Chain, Roller, Sprocket .......................34 Compression Springs ........................38 Couplings ..........................................41 Drives ................................................50

Gearing .............................................54 Gearmotors ........................................66 Leadscrews...........................................68 Linear Motion ........................................70 Locking Devices, Shaft Collars .................75 Lubrication ..................................................78 Motors ..........................................................80 Positioning Stages ........................................84 Seals .............................................................86 Shock, Vibration Damping ............................88

Cover photography by Miles Budimir

DESIGN WORLD — MOTION

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5/3/16 10:42 AM

Affordable Power Transmission

high-quality components at low prices!

SureMotion® Drive Couplings

Jaw / Spider Couplings start at $10.50 Double Loop Couplings start at $34.00 Oldham Couplings start at $14.25 Beam-Style Servo Couplings start at $42.00 Bore Reducers start at $7.00

• • • • •

Reduce the unwanted stress caused by shaft misalignment with our new line of high-quality drive couplings. These drive couplings come in a variety of styles, torque ranges and coupling capabilities each designed to enhance system performance and prevent costly failures.

NEW!

Worm Gearboxes

Precision Gearboxes

Synchronous Drives

IronHorse® worm gearboxes are built to withstand the toughest applications while delivering reliable speed reduction and increased torque output.

If it is precision you need, our SureGear family of precision gearboxes is an excellent solution. They are available in a wide range of ratios and styles, and provide high-precision motion control at an incredible price.

Our SureMotion line of synchronous drive components provide dependable speed and torque changes without unwanted slippage and speed variations.

• •

Aluminum gearboxes start at $88.00 Cast Iron gearboxes start at $147.00

•

Servomotor gearboxes start at $398.00

•

Small NEMA motor gearboxes start at $209.00

•

Drive pulleys start at $5.25

•

Drive belts start at $2.00

Research, price, buy at: www.automationdirect.com/power-transmission

AutomationDirect_PTGuide4-16.indd 9

1-800-633-0405

the #1 value in automation

4/29/16 10:32 AM

Power Transmission

REFERENCE GUIDE The PTDA Spring Governance Meetings attracted nearly 90 volunteer senior leaders to Charleston, S.C., along with more than 45 Next-Gen members who took part in the PTDA 2016 Leadership Development Conference. Attendees played Businessopoly, the name PTDA gave to an interactive, hands-on board game that teaches executive management skills.

PTDA

POWER TRANSMISSION D I S T R I B U T O R S A S S O C I AT I O N

UPDATES MIKE SANTORA • ASSOCIATE EDITOR • @DW_MIKESANTORA

2016 LEADERSHIP DEVELOPMENT CONFERENCE The Power Transmission Distributors Association (PTDA) held its 2016 Leadership Development Conference in early March in the Historic District of Charleston, S.C. PTDA members continuously seek ways to bring their future management team up-to-speed so they can step into a supervisory role ready to excel. The 2016 Leadership Development Conference fulfilled that need. Designed for emerging power transmission/motion control leaders who want to enhance their management skills, network in small group settings, and learn best practices that support business results, those that participated in this year’s conference benefited from two sessions: • •

“Ready. Get Set. Lead”—a dinner program by Randy Disharoon, director global accounts, Rexnord Industries, on how to quickly ramp up younger leaders for success to kick-off the conference “Businessopoly”—a full-day, interactive, team-oriented business simulation game, led by industry veteran Michael Cinquemani, president and CEO, Master Power Transmission.

Cinquemani said, “We are going to really challenge people to give them a deeper understanding of their decision-making: how it affects the profit and loss statement, the balance sheet, the statement of cash flows, and then review their results compared to their initial plans.”

DESIGN WORLD — MOTION

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PTDA WELCOMES SIX NEW MEMBERS PTDA has recently welcomed six new member companies. DISTRIBUTOR MEMBER MJ May Material Specialists (South Holland, Ill.) distributes mechanical PT components, bearings, motors, motor/motion control, electrical/electronic drives, material handling, hydraulics/pneumatics, and PT accessories. President Walter Lopez said, “As a small business looking to grow in the power transmission market, it was a nobrainer for us to join. The access to manufacturers and opportunity to strengthen established relationships will greatly benefit us in our quest to become a premier distributor of power transmission products.”

iwis Drive Systems (Indianapolis, Ind.) manufactures chains and sprockets. “iwis joined PTDA to increase our network within the industrial distribution arena. The fact is, we have made significant investments into new products and value added services and PTDA represents a powerful tool for us to capitalize on these initiatives,” said Kody Fedorcha, VP, sales and marketing. Rosta USA Corporation (South Haven, Mich.) is a manufacturer of motor bases. Wittenstein (Bartlett, Ill.) manufactures couplings, gearing, motors, motor/motion control products and linear motion components. Tom Coyle, director of sales NA, said, “We are pleased to be a part of this

association. My goals as a member of PTDA are to leverage the wide network of distributor organizations and contacts, gain access and new perspectives to industry economics and trends, and finally to increase exposure of Wittenstein,” PTDA 2016 CANADIAN CONFERENCE Registration is still open for the PTDA 2016 Canadian Conference, to be held June 9-10, 2016, at The Westin Ottawa in Ottawa, Ontario. For the 15th year, members of the Canadian power transmission/motion control (PT/MC) industry gather for business networking, market-driven education, a manufacturer industry showcase and more. Networking opportunities abound at the PTDA 2016 Canadian Conference. Participants have many opportunities to meet channel partners—both new and established—in comfortable settings such as the Industry Showcase Welcome Reception, featuring tabletop exhibits from every registered PTDA manufacturer member company. Along with networking, business market-driven education takes center stage. Participants will hear information targeted to solve the most vexing needs of the industry including information on corporate culture, hiring, knowledge transfer and an update on the Canadian mining industry. For more information about the Canadian Conference, please visit www.ptda.org/CanadianConference.

MANUFACTURER MEMBERS Auburn Bearing & Manufacturing (Macedon, N.Y.) manufacturers bearings. “We chose to join PTDA because a vast majority of our sales are through an established network of distributors across the marketplace. PTDA will assist us in expanding that network even further,” said Peter Schroth, president. Helical Products Company, a location of MW Industries, (Rosemont, Ill.) manufactures spring couplings and retaining rings. Robert Jack, VP marketing and strategic planning, said, “The opportunity to network with both manufacturers and distributors in our industry is very valuable to us, and we look forward to being an active member and forging many new relationships in the years to come."

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Jim LaHaie, president, W.C. DuComb Co. and John Masek, SVP, Bearing Service Inc., took advantage of PTDA’s complimentary Regional Networking Events and an optional Detroit Tigers game last year. In 2016, complimentary PTDA Regional Networking Events are coming to Minneapolis, Chicago and Cincinnati and are open to any employee of a PTDA member company or a prospective member company.

4 • 2016

DESIGN WORLD — MOTION

4/29/16 10:39 AM

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REFERENCE GUIDE

Power Transmission

ELECTRIC ACTUATORS:

SMART DESIGNS EXCEL LISA EITEL SENIOR EDITOR @DW_LISAEITEL

DESIGN WORLD — MOTION

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MANY

applications call for converting rotary motion into motion that moves in a straight line. For these applications, linear electric or electromechanical actuators handle the task efficiently. In fact, today’s actuators are so efficient that the variety available for different design needs has proliferated. That means that actuators today are easier than ever to integrate into machinery; they’re also less costly. Electric actuators turn an electric motor’s power into linear motion in one of three ways: through a linear motor, belt or screw drive. Linear motors are the most technologically advanced and efficient method of directly transmitting the power of the motor into the motion of the actuator. Instead of the rotor rotating in the stator, the rotor travels in a linear, flat-array fashion along the stator. Belt drive actuators are less costly, but can still move loads at fairly high linear speeds. Because the motor is separate from the drive, the mechanical advantage can increase thrust speed. The disadvantage of belt drives is that they wear over time and require maintenance.

4 • 2016

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4/29/16 10:40 AM

ELECTRIC ACTUATORS

Linear positioning actuators of extremely long stroke lengths — such as this LoPro linear actuator from BishopWisecarver — typically use belt drives. Polyurethane belting is quiet and delivers long mechanical actuation with good accuracy and high speeds. LoPro actuators are three to 8 m long, but units to 15 m are possible.

Most screw drives take the form of either rod-style actuators or rodless cylinders. A motor transmits power through a coupler or pulley arrangement to rotate the screw and translate a nut along the screw axis. Attached to this nut is either the rod or saddle of the actuator. Screw drives can use roller, ball or leadscrews. Electric actuators have several benefits over hydraulic or pneumatic actuators. For one, the operation is cleaner because they operate without the need for fluids or ancillary equipment. They have the ability to integrate power, control and actuation mechanisms into one device. And they combine force, velocity and positioning in a single, compact motion control device. Another advantage is the ability to constantly monitor feedback directly from the motor and adjust performance accordingly. Though not necessary for every application, closed-loop operation has the ability to adjust and correct variances in the operation, resulting in repeatable and accurate motion with every move. Today, the prices for drives for electric actuators have come down, which has opened new application uses for the linear actuator. So, electric actuators are more viable for applications where hydraulic, pneumatic and manual operations once ruled. In many applications, servomotors are replacing induction motors because

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of their performance and energy efficiency. Direct drives are replacing traditional motor-gearbox combinations because of their high dynamic performance, high precision and long life. And electric actuators are replacing pneumatic cylinders in many applications for similar reasons. But the biggest improvements in the last five to ten years can be found in the control systems integrated with electric actuators. Faster bus systems, like industrial Ethernet and real-time communication, make the use of electric actuators simpler. Servo systems require fast communication and exchange of real-time data between the drive and the overlaid machine control. The bus was always the bottleneck in these systems. Now, with the much higher data rates and real-time capacity of industrial Ethernet, the integration and the use of electric actuators is easier. Stepper and servo drive options with Ethernet protocols (Ethernet IP, Modbus, TCP) turn single-axis actuators into simple, low-cost motion devices with infinite positioning, precise control and longer life. Electric linear actuators are an alternative to pneumatic cylinders in several applications because of the flexibility they deliver in the design of production processes and production monitoring systems. In conveying applications, for example, diverting and sorting functions are more frequently controlled using electric actuators. Typically, pneumatic actuators have been used, but the required manual adjustments were often subject to human error. Plus, the pneumatic actuators could only handle a small amount of variability in product sizes. Electric actuators are flexible by design. For example, material handling applications have experienced an increase in the variety and variability of package sizes. In packaging machines, consumer products manufacturers are Tolomatic ERD hygienic all-stainless-steel electric cylinders have a roller-screw option that boosts maximum thrust to 7,868 lbf (35.6 kN) for better life and performance under high duty cycles than ballscrew models.

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REFERENCE GUIDE

Power Transmission

producing more package sizes with the same manufacturing lines, which require equipment to be adaptable enough to handle different product sizes and types. Electric actuators easily handle these variability requirements and, over the life of the motion system, can be less expensive.

SELECTING AN ELECTRIC ACTUATOR The process for selecting an electric actuator is similar to one for hydraulic or pneumatic actuators, with a few differences. Here are the essentials. Start with the motion profile. This establishes the demands for velocity and time as well as force (or torque) and the required travel distance. This is also the place to determine the maximum stroke needed as well as maximum and minimum speed requirements. Then calculate the load. This can have many different components including inertial load, friction load, the external applied load, as well as the gravitational load. Load calculations also depend on the orientation of the actuator itself, whether it’s horizontal or vertical. Duty cycle is another important factor. This is defined as the ratio of operating time to resting time and is usually expressed as a percentage. The cycling rate may be in seconds, minutes, hours or even days, and knowing the operating hours per day may also be necessary. Knowing the duty cycle helps the engineer estimate the system life requirements and can also eliminate problems such as overheating, faster wear and premature component failure due to an incorrectly sized actuator. Know the positional accuracy and precision demanded by the application. The actuator’s precision should meet or exceed the application’s requirements for accuracy, backlash, and straightness and flatness of linear motion. This directly impacts the cost of the system; if the

DESIGN WORLD — MOTION

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NSK’s MCM Series Monocarrier includes a ballscrew, linear guide and supports in one compact structure. It boosts accuracy and reduces installation time, and some versions are available through a Quick Ship Program.

application doesn’t demand high accuracy or precision, then there is no need to buy a more expensive actuator when a less expensive one will satisfy the demands of the application. Aside from the technical specifications mentioned above, there is also the need to select the proper configuration for the actuator in the final design. This includes mounting considerations and the need for any other external components, such as holding brakes and communication and power cables. Lastly, consider the operating environment for the actuator. What are the temperature requirements? Are there any contaminants such as water, oil or abrasive chemicals? Contaminants can affect seals and impact the working life of the actuator. In such cases, selecting the appropriate IP rating for an application can guard against the effects of contaminants.

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4/29/16 10:41 AM

MAINTENANCEfREE OPERATION. WORRy-fREE DESIGN.

nsk k1TM lubricaTion uniT Experience long-term, maintenance-free operation with NSK K1™ Lubrication Units. These patented units provide fresh, continuous oil flow onto the rail or shaft during operation, making them ideal for environments where grease replenishment is undesirable or where grease is easily washed away. Available on NSK linear guides, ball screws, Monocarrier™ actuators and Robot Modules, K1™ Lubrication Units prolong life for up to 5 years or 10,000 km operational distance. 1.800.255.4773

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REFERENCE GUIDE

LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL

MECHANICAL COMPONENTS AT T H E H E A R T O F M O T I O N D E S I G N

RIGID-CHAIN

Power Transmission

actuators work by pairing a drive (usually an electric motor) with a length of chain sporting shoulders on each link. The motor output shaft—fitted with a specialty sprocket or pinion—applies tangential force to the chain. Then the chain comes out and straightens, and its links’ shoulders lock to form a rigid series. When the motor runs in the opposite direction, the chain shoulders disengage and allow for coiling. Inside the actuator body, reaction plates and guides counter thrust resistance and keep the chain on track. Links travel around the pinion to exit the actuator body along the stroke path. Here, the motor’s torque comes to act as forward thrust via the link shoulder to the rest of the links’ shoulders. The last link in the chain before the load has geometry that puts the thrust higher than the articulation axis. This makes a moment that effectively locks the link shoulders. In reverse, pulling force acts along the links’ cross axes. Rigid-chain actuators have the mechanical benefits of conventional chain but can act in horizontal push setups or vertically as jacks. Plus they’re compact. In contrast, traditional chain drives can only pull, so need two drives for bidirectional motion. Traditional screw jacks for vertical power transmission need space for retraction that’s as long as the working stroke itself. Before specifying a rigid-chain actuator, determine the application’s total load, including the transported load, acceleration forces, external environmental forces, and that due to friction—with a coefficient between 0.05 and 0.5 for typical rigid-chain actuator setups. Next, determine what type of actuator body and chain-storage magazine the application can accommodate. Determine whether the chain will need to change direction on its way from the magazine to actuator body. Actuators usually feed chain around 90° or 180° turns. Note that rigid-chain actuators can work alone or in tandem. Twin-chain setups deliver high positioning accuracy and stability where loads are large or bulky.

This is a custom loading-station scissor lift that uses a SERAPID 40 chain actuator. Retractable to table-top level, the platform can smoothly lift a heavy load more than 10 ft. A spacesaving chain storage magazine fits compactly at the bottom.

Common rigid chain has two rows of link plates and shoulders; duplex chain has three; other options abound. Image courtesy iwis Drive Systems

DESIGN WORLD — MOTION

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RIGID CHAIN ACTUATORS

Common rigid-chain arrangements Chain link shoulders

Here, a pushing bar acts as a yoke to keep loads steady, with optional hooks for pulling as well. Optimized geometry has the force vector act on the load’s center for balance. If twin-chain setups are impossible, consider adding framework to guide awkward loads. Guides on the chain also help maintain stability—even over very long strokes—because they address side and buckling forces. Such guides come in different shapes with different crampons and subcomponents to engage the chain. Where use of chain guides is impossible, most designs run the chain

with link shoulders down for moderate stability. Some last design notes: Standard chain is carbon steel to withstand heat to 200° C, but stainless, high-temperature, and coated chain for long life are other options. The required length of chain is total design stroke plus a few links to engage the actuator pinions. As with any powertransmission setup, consult the manufacturer for tips and guidance on determining necessary drive power and other details.

Unguided chain with shoulders up coils downwards ...

... but guided chain is most stable. Actuator body Pinion Input drive shaft Choose a rigid-chain actuator to satisfy the design geometry.

Unguided chain with shoulders up coils downward, which is useful but not always stable enough for long strokes. That with shoulders down (here, bottom) is slightly more stable. Use guided chain wherever space permits.

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LinearBeam guided push-pull Press-mounted dual push-pulls

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REFERENCE GUIDE

BASICS OF

BALLSCREWS

Power Transmission

MILES BUDIMIR • SENIOR EDITOR • @DW_MOTION

BALLSCREWS

are a mainstay of motion actuation. Compared to similar actuation methods such as leadscrews, they typically cost a bit more but are generally more accurate. They also boast higher efficiencies, even though they demand more lubrication because of the use of recirculating balls. The basic components of a ballscrew are a nut, a screw with helical grooves, and balls (often made from steel, ceramic, or hard plastic material) that roll between the nut, the screw and the grooves when either the screw or nut rotates. Balls are routed into a ball return system of the nut and travel in a continuous path to the ball nut’s opposite end. Seals are often used on either side of the nut to prevent debris from compromising smooth motion. Recent advances in manufacturing and materials have improved ballscrew performance so machine designers today can get better linear motion with them at lower cost. Some improvements include the fact that the latest generation of ballscrews has more load density than ever, giving designers higher capacity from a smaller package. There is also a trend toward more miniaturization, but also faster ballscrews with rolled and ground screw manufacturing methods. Ballscrews suit applications needing light, smooth motion, applications requiring precise positioning, and when heavy loads must be moved. Examples include machine tools, assembly devices, X-Y motion, Z motion, and robots. Ballscrews are usually classified according to factors such as lead accuracy, axial play and preload, and life/load relationship. Lead accuracy refers to the degree to which the shaft’s rotational movements are translated into linear movement. With lead accuracy and axial play determined by the manufacturing method of the ballscrew shaft and the assembly of the nut, high lead accuracy and zero axial play is generally

This cutaway, courtesy of Nook Industries, shows the inner workings of a ballscrew, most notably the recirculating balls and the deflector, in relation to the screw assembly.

DESIGN WORLD — MOTION

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REFERENCE GUIDE

A sample ballscrew assembly, such as the Precision Metric Ball Screws (PMBS) series from Nook Industries, features a single nut with flange, uses precision thread-rolling technology and is available in a wide range of leads and diameters.

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associated with relatively higher-cost precision ground ballscrews, while lower lead accuracy and some axial play is associated with lower cost rolled ballscrews. Fabricated by rolling or other means, ballscrew shafts yield a less precise but mechanically efficient and less expensive ballscrew. Axial play is the degree to which a ball nut can be moved in the screw axis direction without any rotation of either nut or screw. Preload is applied to eliminate axial play. The process of preloading removes backlash and increases stiffness. Ball recirculation inside the ball nut can affect precision and repeatability. Thus, ball nuts are available with a range of preload options to reduce or remove the axial play as they rotate around the screw. Minimal axial play allows better accuracy, for example, because no motion is lost from the clearance in the balls as they reengage. There are several techniques for preloading. Some common methods include oversizing the balls inside the nut housing; using the so-called “double-nut” or “tension nut” method; or by using a manufactured offset in the raceway spiral to change the angle of ball engagement (the “lead shift” method) and deliberately force the balls into a preload condition. Each method has its advantages and disadvantages, but all serve to minimize or eliminate backlash between the nut and screw. Perhaps the biggest overall benefit of a ballscrew is that it has high efficiencies that can be well over 90%. By contrast, Acme lead screws average about 50% efficiency or less. There are also minimum thermal effects. Backlash can be eliminated through preloading. 22

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DESIGN WORLD

Ballscrews also offer smooth movement over the full travel range. The higher cost of ballscrews can be offset by decreased power requirements for similar net performance. One drawback to ballscrews is that they require high levels of lubrication. Ballscrews should always be properly lubricated, with the correct type of lubricant, to prevent corrosion, reduce friction, extend operating life, and ensure efficient operation. Because ballscrews are a bearing system, they’ll need some type of lubrication to avoid metal-to-metal contact of the balls in the raceway. While the lubrication choice can be either oil or grease, it’s advisable to avoid solid additives (such as graphite) as they will clog the recirculation system. An NLGI no. 2 type grease is recommended but it should also depend on the application, whether food-grade or another special type of lubrication is required. Ballscrews, especially those used in machine tools, generally require lubricants with EP additives to prevent excessive wear. The lube amount will be fixed, but the frequency of lubrication will vary depending on factors such as the move cycle characteristics, or contamination in the environment. Contaminated lubrication can increase friction. In addition, ballscrews can fail if the balls travel over metal chips or dirt in the ball thread raceway. Using lubricants recommended by machine tool manufacturers can help prevent this effect. Using telescopic covers or bellows can help keep ballscrews clean when used in environments with many contaminants.

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# Zero-Max_full_pgs_r10_Design World 2/12/10 4:02 PM Page 1

Your ball screw Your servomotor Our coupling

Together a winning combination for today’s servomotor applications. Our ServoClass® couplings have been recently redesigned to enable your actuator to go even faster and achieve the positional accuracy that will take your designs to the next level. Our couplings will do all this with low bearing loads. 3 New sizes now available. Now, size, select and see the right ServoClass® coupling solution for your application with Zero-Max 3D CAD files. Check our FAST deliveries.

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REFERENCE GUIDE

Power Transmission

3 times lighter than stainless

REVIEW OF

BEARINGS MIKE SANTORA • ASSOCIATE EDITOR • @DW_MIKESANTORA

IT’S EASY

for bearings to go unnoticed—an out of sight, out of mind mentality. This attitude is common among so many because bearings are simple, internal machine elements. However, that doesn’t make them any less crucial for motion applications. The purpose of a bearing is to reduce frictional forces between two moving parts by giving a surface something to roll on, rather than slide over. There are basic features that all bearings share, but specific application needs demand many different variations of this universal motion system component. A bearing usually consists of smooth rollers or metal balls and the smooth inner and outer surfaces, known as races, that the rollers or balls roll against. These rollers or balls act as the load carrier for the device, allowing it to spin freely. Bearings typically encounter two kinds of load: radial and axial. Radial loads occur perpendicular to the shaft, while axial loads occur parallel to the shaft. Depending on the application the bearing is being used in, some bearings experience both loads simultaneously. There are many different types of bearings, each suitable for different purposes in varying applications.

DryLin® aluminum lead screws with optimized geometry for highefficiency and long service life. Variety of nut types available in 5 materials, including FDA and high-temperature compliant.

BALL BEARINGS One of the most common forms of bearings is the ball bearing. As the name implies, ball bearings use balls to provide a low friction means of motion between two bearing races. Since the contact area between the balls and races is so small, ball bearings cannot support as large a load as other bearing types and are best suited for light to moderate loads. However, their small surface contact also limits the heat generated by friction, meaning that ball bearings can be used in high-speed applications. ROLLER BEARINGS Possibly the oldest form of bearing, roller bearings can be spherically or cylindrically shaped and are commonly used in applications like conveyor belt rollers. Because of their shape, roller bearings have greater surface contact than ball bearings, and are thus able to handle larger loads without deforming. Their shape also allows for a moderate amount of thrust load since the weight is distributed across cylinders instead of spheres.

Learn more at:

www.igus.com/DryLin®

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Tested and Proven 138 million cycles

BEARINGS

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THRUST ROLLER BEARINGS Thrust roller bearings are designed so that the load is transmitted from one raceway to the other, meaning that these bearings can accommodate radial loads. Bearings like these also have a self-aligning capability that makes them immune to shaft deflection and alignment errors. TAPERED ROLLER BEARINGS Tapered roller bearings feature tapered inner and outer ring raceways with tapered rollers arranged between them, angled so the surface of the rollers converge at the axis of the bearing. These bearings are unique in that, unlike most bearings that can handle either axial or radial loads, they can handle large amounts of load in both directions. A single row taper bearing is limited in that it can only take high axial loads from one direction, but if adjusted against a second tapered roller bearing, that axial load is counteracted. This allows the bearings to accept high radial and axial loads from multiple directions. DESIGN WORLD — MOTION

62 t3

THRUST BALL BEARINGS Thrust ball bearings are designed for use in applications with primarily axial loads and are capable of handling shaft misalignment. These bearings are also useful in high-speed applications, such as in the aerospace and automotive industries.

Te s

NEEDLE ROLLER BEARINGS When you need to reduce friction between two moving parts but have very limited space to do so, a needle roller bearing may be just what you’re looking for. A needle roller bearing is a roller bearing with rollers whose length is at least four times their diameter. Despite their low cross section, the large surface area of the needle roller bearing allows them to support extremely high radial loads. They usually consist of a cage, which orients and contains the needle rollers and an outer race, which is sometimes the housing itself. The bearings can often be found in two different arrangements. The first is a radial arrangement, in which the rollers run parallel to the shaft. The second is a thrust arrangement, in which the rollers are placed flat in a radial pattern and run perpendicular to the shaft. These bearings are often used in automotive applications, such as rocker arm pivots, pumps, compressors and transmissions. The drive shaft of a rear-wheel drive vehicle typically has at least eight needle bearings (four in each U joint) and often more if it is particularly long, or operates on steep slopes.

Spherical roller bearings like Koyo’s RZ Spherical Roller Bearing have a greater surface contact than ball bearings, and are thus able to handle larger loads without deforming.

Test 3621: Chainflex® control cable CF98.05.04 Has withstood more than 138 million strokes at a radius of 3.2 x d Test information and details available online:

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REFERENCE GUIDE

Power Transmission

Depending on application requirements, some ball bearing are made with magnetic, lubricant-free motion plastics like this igus xiros M180 which uses a lightweight polymer ball bearing.

The ability of a tapered roller bearing to accommodate angular misalignment of the inner ring in relation to the outer ring is limited to a few minutes of arc. As with other roller bearings, tapered roller bearings must be given a minimum load, especially in high speed applications where the inertial forces and friction can have a damaging effect between the rollers and raceway. LINEAR MOTION BEARINGS Linear motion bearings are specifically designed to allow motion in one direction and are typically used to carry a load on a slide or rail. They can be powered by a motor or by hand and experience over turning moments of force instead of radial and axial loads. PLAIN BEARINGS Plain bearings are the simplest form of bearing available, as they have no moving parts. They are often cylindrical, though the design of the bearing differs depending on the intended motion. Plain bearings are available in three designs: journal, linear and thrust. Journal style bearings are designed to support radial motion where a shaft rotates within the bearing. Linear bearings are often used in applications requiring slide plates, as these bearings are designed to permit motion in a linear motion. Finally, a plain thrust bearing is designed to do the same job as its roller bearing counterpart, but instead of using cone shaped rolling elements, the bearing uses pads arranged in a circle around the cylinder. These pads create wedge-shaped regions of oil inside the bearing between the pads and a rotating disk, which supports applied thrust and eliminates metal-on-metal contact. Out of all the bearing types available, plain bearings tend to be the least expensive. They can be made from a variety of materials including bronze, graphite and plastics, such

DESIGN WORLD — MOTION

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BEARINGS

The greater surface contact of roller bearings enables them to handle larger loads without deforming. Demonstrating just a few of the many types of roller bearings, here we see a needle, spherical, tapered and cylindrical roller bearing. Image courtesy of AST.

as Nylon, PTFE and polyacetal. Improvements in material characteristics have made plastic plain bearings increasingly popular in recent years. Plain bearings of all types, however, are lightweight, compact and can carry a substantial load. As far as lubrication is concerned, some plain bearings require outside lubrication while others are self-lubricating. Plain bearings made of bronze or polyacetal, for example, contain lubricant within the walls of the bearing, but require some outside lubrication to maximize performance. For other plain bearings, the material itself acts as the lubricant. Such is the case with bearings made from PTFE or metalized graphite. The growing popularity of plain plastic bearings and increasingly stringent industry standards has resulted in more consumers requiring the bearings to meet FDA and RoHS standards. There has even been a call for the bearings to meet the standards of EU directive 10/2011/EC, which also takes the material manufacturing process into account.

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APPLICATIONS Bearings are all around us in everyday life and most of the time they go unnoticed. But without them, many of the tasks we undertake would move along much less smoothly. The ball bearings’ simple design, ability to operate at high speeds and relatively lowmaintenance requirements, makes them one of the most common roller bearings found in a variety of industrial applications. For example, deep groove ball bearings are often used in small- to medium-sized electric motors because of their ability to accommodate both high speeds and radial and axial loads. Self-aligning ball bearings, on the other hand, are ideal for use in fans. These bearings have two rows of balls with a common raceway in the outer ring. This design allows for angular misalignment while maintaining running accuracy. They are, however, one of the most difficult bearings to install correctly. Tapered roller bearings are another form of bearing that just about every industry depends on one way or another. They are usually found in applications where support for axial and radial loads is required, such as in a tire hub where the bearing must deal with the radial load from the weight of the vehicle and the axial load experienced while cornering. These bearings are also commonly found in gearboxes where they are generally mounted with a second bearing of the same type in a face-to-face or back-to-back orientation. They provide rigid shaft support, keeping deflection to a minimum. This reduced shaft deflection minimizes gear backlash. Tapered bearings also have the advantage of having less mass but high efficiency, however this Common applications for drawn cup needle does limit their overall speed. roller bearings like this from Koyo include: In applications where bearings are mounted precision gear boxes, machine tool, medical vertically, they are typically oriented in a face-toequipment, precision assembly equipment, robotics, after-market racing equipment and face setup, while horizontal applications use a aerospace. back-to-back setup. Some pumps use this design because of shaft deflection concerns.

4 • 2016

DESIGN WORLD — MOTION

4/29/16 2:36 PM

REFERENCE GUIDE

THE BASICS OF

Power Transmission

BELTS & PULLEYS LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL

Belts and pulleys lift loads, use mechanical advantage to apply forces, and transmit power. They also form the basis of industrial conveyors big and small. Here are the fundamentals of their operation and how to apply them.

INDUSTRIAL

belt drives consist of rubber belts that wrap around drive pulleys, in turn driven by electric motors. In a typical setup, the belt also wraps around one or more idler pulleys that keep the belt taut and on track. The main reasons that engineers pick belt drives over other options is that modern varieties require little if no maintenance; they’re less expensive than chain drives; and they’re quiet and efficient, even up to 95% or more. In addition, the tensile members of today’s belts— cords embedded into the belt rubber that carry the majority of the belt load—are stronger than ever. Made of polyester, aramid, fiberglass or carbon fiber, these tensile cords make today’s belt drives thoroughly modern power-transmission devices. Manufacturers generally describe belts and pulleys with five main geometries. Pitch diameter is the drive pulley’s diameter. Center distance is the distance between the two pulleys’ centers. Minimum wrap angle is a measure of how much the belt wraps around the smallest pulley. Belt length is how long the belt would be if cut and laid flat. Finally, in the case of toothed belts (also called synchronous belts) the pitch is the number of teeth per some length—so a 3-mm pitch means that the belt has one tooth every 3 mm, for example. APPLYING SYNCHRONOUS BELTS Some general guidelines are applicable to all timing belts, including miniature and double-sided belts. First of all, engineers should always design these belt drives with a sufficient safety factor—in other words, with ample reserve horsepower capacity. Tip: Take note of overload service factors. Belt ratings are generally only 1/15 of the belt’s ultimate strength. These ratings are set so the belt will deliver at least 3,000 hours of useful life if the end user properly installs and maintains it. The pulley diameter should never be smaller than the width of the belt.

Shown here is a Gates Carbon Drive CDN system—designed to be lower in cost for new bike applications. It leverages new materials and geometries, with nine carbon cords embedded within engineered polymer belt and a patented 11-millimeter tooth pitch profile for lower tension. Like many new belt applications, it replaces chain drives.

DESIGN WORLD — MOTION

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4/29/16 4:10 PM

BELTS & PULLEYS

Manufacturers of Power Transmission and Motion Control Components

These PowerGrip TruMotion timing belts from Stock Drive Products have nylon tooth facing for longer and quieter running and less dust. Fiberglass tensile cords resist elongation and have a high flex life.

As mentioned, belts are quieter than other powertransmission drive options … but they’re not silent. Noise frequency increases proportionally with belt speed, and noise amplitude increases with belt tension. Most belt noise arises from the way in which belt teeth entering the pulleys at high speed repeatedly compresses the trapped pockets of air. Other noise arises from belt rubbing against the flange; in some cases, this happens when the shafts aren’t parallel. Pulleys are metal or plastic, and the most suitable depends on required precision, price, inertia, color, magnetic properties and the engineer’s preference based on experience. Plastic pulleys with metal inserts or metal hubs are a good compromise. Tip: Make at least one pulley in the belt drive adjustable to allow for belt installation and tensioning. Also note that in a properly designed belt drive, there should be a minimum of six teeth in mesh and at least 60° of belt wrap around the drive pulley.

Concentric Maxi Torque

Other tips: • Pretension belts with the proper recommended tension. This extends life and prevents belt ratcheting or tooth jumping. • Align shafts and pulleys to prevent belt-tracking forces and belt edge wear. Don’t crimp belts beyond the smallest recommended pulley radius for that belt section. • Select the appropriate belt for the design torque. • Select the appropriate belt material for the environment (temperature, chemical, cleaning agents, oils and weather). Belt-and-pulley systems are suitable for myriad environments, but some applications need special consideration. Topping this list are environmental factors. Dusty environments do not generally present serious problems as long as the particles are fine and dry. In contrast, particulate matter can act as an abrasive and accelerates belt and pulley wear. Debris should be prevented from falling into belt drives. Debris caught in the drive is generally either forced through the belt or makes the system stall. In either case, serious damage occurs to the belt and related drive hardware. Light and occasional contact with water—during occasional washdowns, for example—has little serious effect. However,

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American Engineering • American Made DESIGN WORLD — MOTION

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4 • 2016

5/3/16 9:22 AM

REFERENCE GUIDE

Power Transmission

This setup has an electronic warning system from ContiTech to alert operators when a conveyor is elongating or at risk of ripping. Called CONTI PROTECT and most useful on industrial and mining conveyors, the system uses magnetic markings on the belts to track irregularities in the splice length and detects longitudinal rips before they grow. Such monitoring systems are just one example of how belt-drive technologies have kept pace with 21st-centrury design concepts.

Shown here are Baldor-Maska sheaves for V-belt drives,also called friction drives for the way they operate. Minimum allowable sheave diameter depends on the belt shape and material, whether that’s synthetic, neoprene, urethane, or rubber.

DESIGN WORLD — MOTION

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prolonged contact with constant spray or submersion can significantly reduce tensile strength in fiberglass belts and make aramid belts break down and stretch out. In the same way, occasional contact with oils doesn’t damage synchronous belts. But prolonged contact with oil or lubricants, either directly or airborne, significantly reduces belt service life. Lubricants cause the rubber compound to swell, break down internal adhesion systems and reduce felt tensile strength. While alternate rubber compounds may provide some marginal improvement in durability, it’s best to prevent oil from contacting synchronous belts. The presence of ozone can be detrimental to the compounds used in rubber synchronous belts. Ozone degrades belt materials in much the same way as excessive temperatures. Although the bumper materials used in belts are compounded to resist the effects of ozone, eventually chemical breakdown occurs and they become hard and brittle and begin cracking. The amount of degradation depends on the ozone concentration and generation of exposure. Rubber belts aren’t suitable for cleanrooms, as they risk shedding particles. Instead, use urethane timing belts here … keeping in mind that while urethane belts make significantly less debris, most can carry only light loads. Also, none have static conductive construction to dissipate electrical charges.

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4/29/16 2:59 PM

BRAKES & CLUTCHES

BRAKES & CLUTCHES MORE INDISPENSABLE THAN EVER LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL

BRAKES

Shaft-mounted electric clutches from New Torque have a static torque rating from 15 to 202 Nm, voltage of 24 to95 Vdc, and power of 16 to 50 W.

Shown here is an ac solenoid shoe Brake from Ametek. Gemco industrial brakes stop industrial machines in steel mills, gantries, cranes, and commercial laundry equipment. They are tough and long-lasting.

and clutches are a mainstay in motion designs that need to stop, hold or index loads. Especially over the last five years, a technology trend toward application-specific designs has quickened as several industries are pushing the performance envelope of stock components. Brakes are used to stop a load, typically a rotating load, while clutches are used to transfer torque. There are many different types of brakes and clutches. A brake would be used in applications where accurate stopping of the load is needed and the motor will stop as well. A clutch would be used in applications where it’s desirable to engage or disengage a load and motor while leaving the motor to run all the time. When a clutch is used, the load will be allowed to coast to a stop. A clutch and brake combination would be used where the load will be started and stopped while the motor continues to rotate. Both clutches and clutch brakes can mount to a motor shaft or be base-mounted and have input through a belt drive, chain drive or coupling. The motor horsepower and motor frame size play a key role in determining which specific brake or clutch to select. In the case of base-mounted units, it may be necessary to define the RPM at that location. Manufacturers provide quick selection charts where unit size is determined by finding the intersection of motor horsepower and speed at the clutch shaft. The charts are commonly created using the dynamic torque capacity for the product and the torque capacity for the motor plus an overload factor of some value. Using this method presumes that you’ve selected a motor that’s sized appropriately to the application. In applications where cycle rates are considered aggressive for the inertia of the load, it’s a good idea to consult with the application support staff of the manufacturer regarding the heat dissipation capacity. Coil voltage is another consideration. The most common options are 6, 24 and 90 Vdc with 90 V being widely preferred in North American markets, while 24 V is more common in Europe. In both cases, brake and clutch manufacturers can offer power supplies to convert ac to dc if required.

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This is a Force Control Industries coupler brake. In fact, the company’s Posistop and MagnaShear coupler brakes mount between motors and reducers, so engineers can eliminate separate brake motors.

Some clutches and brakes — as the ones from Carlyle Johnson Machine Company shown here — can last 15 years on average, with some products lasting 50 years or more.

DESIGN WORLD

4/29/16 11:14 AM

POWER TRANSMISSION

REFERENCE GUIDE

THE BASICS OF

INDUSTRIAL POWER TRANSMISSION CABLES MARY GANNON • SENIOR EDITOR • @DW_MARYGANNON

ENGINEERS

can use a multitude of cables (including data, coaxial, and instrumentation cables) in industrial settings for control networking, low and mediumvoltage power transmission and distribution, and more. Most cables that distribute power to motors are low-voltage designs rated for 2,000 V and below. That said, some facilities with partial responsibility over the utility power they consume use medium-voltage cables rated for 2,000 to 35,000 V. Available as both single and multi-conductor designs, these power cables must be able to withstand high mechanical loads, speeds and accelerations. Common applications include machine tools, cranes, conveyors, portable designs and stationary heavy-duty equipment. Such cables can supply temporary ac or dc power to motors and generators, and can operate indoors and outdoors, depending on their temperature rating. The proper cable for an application depends on its function and environment. For instance, only use an unshielded cable when it will operate in an enclosed space only accessible by trained professionals. Such enclosures prevent electromagnetic interference and keep plant personnel safely away from potentially live electrical charges. Manufacturers usually construct low-voltage cables with aluminum or copper conductors, insulation and jacketing. Conductors can range anywhere from finely stranded bare copper wires to bunched strands of tinned annealed copper. They come in both shielded and unshielded versions and usually must be flame retardant and oil resistant.

Power cables feature conductors that are either stranded in layers inside or bundled or braided. The stranded design is easier to manufacture so costs less. It features long, layered cores and firm strands wrapped with an extruded jacket. In the bundled or braided design, the conductors are braided around a tension-proof center. By eliminating the layers, a uniform bend radius is ensured. To accommodate the complex and sometimes cramped spaces where they operate, industrial power cables must also have tight bending radii, ranging anywhere from 5 to 15 times the overall cable diameter. Jacketing is also crucial to meet these bending radii requirements. Therefore, the use of flexible materials such as PVC, TPE and CPE not only helps these cables bend and flex but also protects them from environmental damage. Because their materials, shielding and jacketing all vary, so do industrial power cables’ installation techniques. Installers can put cables into fixed duct, shafts, and conduit; direct-bury or even immerse the cables in water in water; or lay cables into open-air applications. Depending on where a cable is manufactured and used, it must meet a variety of approvals, including UL, CSA, TC, AWM, RoHS, CE and more. In the U.S., the National Electrical Code (NEC) sets the standards that designers must usually follow. These codes ensure that the cables have key performance features to satisfy machine requirements—for example, to stop the propagation of flames, satisfy the application’s maximum voltage draw, withstand extreme temperatures, and maintain integrity even when exposed to oil.

Control cables, like this Chainflex continuous flex control design from igus, must be able to withstand high mechanical loads, speeds and accelerations. These Chainflex cables are intended for use in Energy Chain cable carriers and conform to key standards; are capable of torsion—depending on the cable; and can be used in high speeds and accelerations. They are UV resistant, flame retardant, halogen free, and can withstand very high or extremely low temperatures. They are available shielded or unshielded, with a choice of PVC, PUR and TPE outer jackets.

DESIGN WORLD — MOTION

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4 • 2016

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4/29/16 11:15 AM

CMY

• Flexible Control Cables • Continous Flex Cables • Torsion Cables • Halogen-Free Cables • European Cables • Servo Motor Cables

Bus Cables • Data Cables • Tray Cables • Silicone Cables • Cable Accessories • Specialty Cables • Stock Available for Immediate Delivery

SAB NORTH AMERICA 344 Kaplan Drive, Fairfield NJ 07004 Phone: 866-722-2974 • Fax: 973-276-1515 info@sabcable.com • www.sabcable.com

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REFERENCE GUIDE

THE BASICS OF

Power Transmission

SPROCKETS & CHAIN DRIVES LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL

ENGINEERS

have used chains in motion systems for more than a century. They are versatile and reliable components to drive machinery and convey products. Now, advances in precision and technology let designers use chains in more applications than ever. Remote installations benefit from long-life chain that requires no lubrication, for example. Chain-based machinery abounds, but the most common industrial designs use roller chain. This type of chain consists of five basic components: pin, bushing, roller, pin link plate and roller link plate. Manufacturers make and assemble each of these subcomponents to precise tolerances and heat treat them to optimize performance. More specifically, modern roller chains exhibit high wear resistance, fatigue strength and tensile strength. Roller-chain applications generally fall into two categories: drives and conveyors. CHAIN-DRIVE APPLICATIONS Most typical drive applications use an ASME/ANSI roller chain wrapped around a driver sprocket (connected directly to the motor or reducer) and the driven sprocket (often connected to a machine’s conveyor head-shaft). This portion of the drive lets the designer build a system that’s either faster or slower by simply changing the ratio of teeth between the drive and driven sprocket. The ratio of the teeth determines the reduction in rpm … so to reduce rpm, the driven sprocket must be larger than the driver sprocket. For example, if the driver sprocket has 15 teeth and the driven sprocket has 30 teeth, the ratio is 2:1, so the rpm is halved at the driven sprocket.

Shown here is an MPC sprocket from Martin Sprocket and Gear Inc. for use with a curvilinear timing belt. As a side note, synchronous belt drives work as a replacement for roller-chain drive systems where lubrication is unacceptable.

This Morse leaf chain from Power Transmission Solutions of Regal-Beloit America is made of roller-chain-type links and riveted pins for maximum strength for a given width. It works as tension linkage or a lifting device at slow speeds.

DESIGN WORLD — MOTION

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motioncontroltips.com | designworldonline.com

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CHAIN, ROLLER & SPROCKET

This is a Zone Touch case conveyor from Container Handling Systems Corp. (CHSC), which uses chain drives that function as accumulating sections. It has longer life than conventional machines with rollers and fabric belts. It’s also quieter than roller conveyors because its tabletop chain rides lowfriction UHMW wear strips and return ways.

Morse inverted-tooth chain drives from Power Transmission Solutions of Regal-Beloit America come in HV versions for high capacity at high speed. Silent chain is another option to make smooth, silent drives at slower speeds.

Roller-chain selection chart Chain strands 4

900 1,000 700 1,000 800 500 800 600 400 600 400 300 400 300 200 300 200 200 100 100 80 60 40 30

100 80 60

20 10 8 6

10 8 6

4 3

1 0.8

500 400 300 200 100 80 60 40 30 20

10 8 6 4 3

4 3

1 0.8 0.6

2 1 0.8

20 10 8 6 5 4 3

80 60

1 0.8 0.6

0.6

0.4

0.6

0.4

0.3

0.4

0.3

0.2

19 T 19 22 T T 2 25 21T 5T 22 19 T T T 21 25 25 T 25 T 23 23 T T 2 1 T 21 7T 25 T 1 20 40 T T 25 1 9T 0 1 21 7T T 1 21 7T T 16 80 T 25 0 14 23 17 T 0 T T 12 2 15 25 1T 0 T 10 T 17 19 0 T T 19 80 T 23 60 T 15 50 T 40 35

CONVEYOR APPLICATIONS Conveyor chains come in myriad versions to move product horizontally, vertically or even around curved radii. The most common conveyor chains are ASME-style (ANSI-style) attachment chains. These chains include extended pins or plates with tabs onto which parts or product-holding shoes can bolt. Common versions are single-pitch attachment chain, double-pitch attachment chain, hollow-pin chain, curvedattachment chain and plastic-sleeve chain. The attachments let engineers put special fixtures or blocks onto the chain to serve specific conveyor functions. One subtype of conveyor chain is the accumulating conveyor. These stop discrete products even while the chain is still moving, and they do so with minimal friction and wear. Accumulating conveyors are suitable for applications (such as assembly lines) that have products ride through several stations. Tip: Select chain with top rollers or side rollers to let discrete products idle while the conveyor continues to run. Also pick custom attachments or work with manufacturers that make custom fixtures to handle specific parts. Many industries (including the automotive, food and beverage, and consumer-products industries) use custom attachments on their chain-based accumulator conveyors to economically and consistently move.

CHAINS ENDURE SUBOPTIMAL ENVIRONMENTS The environments of many chain applications are less than ideal. Some require clean operation without the lubrication that can contaminate products. Others expose chain-driven machinery to weather, water or chemicals. So, chain manufacturers offer several products to meet these challenges. Consider roller chain: One critical area where roller chains need lubrication is the pin-bushing contact zone. Self-lubricating chains stay cleaner because the exterior of the chain is free of excess lube. These chains

Roller-chain drive capacity (horsepower)

The easiest way to select a roller chain is using horsepower charts. First, obtain the motor horsepower and rpm of the small driver sprocket. From this, determine the chain size and number of teeth for the driver sprocket. Where roller chain must drive applications that need long life without contamination, pick chain with self-lubricating subcomponents. Where roller chain must drive applications that need high precision, pick chain with precision roller bearings at each link connection.

0.4 0.3 0.2

30 20

50 80 200 500 1,000 3,000 7,000 40 60 100 300 700 2,000 5,000 10,000

Speed of roller chain’s small sprocket (rpm)

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DESIGN WORLD — MOTION

4/29/16 11:19 AM

MPC

SYNCHRONOUS SPROCKETS

Direct drop-in for the most popular tooth profile

• Available from stock from over 30 Martin locations throughout North America • MTOs in days not weeks: » QD bushed » MST® bushed » Finished bore

» Stainless steel » Aluminum » And more...

• Over 350 MPC® SKUs on the shelf • Stocked in TB and Minimum Plain Bore • Compatible with all leading Curvilinear Belts

Martin's MPC® Sprockets are manufactured in various sizes, dimensions and capacities to

meet a variety of industrial requirements. These include a wide range of loads, speeds, and demanding applications such as blowers, conveyors, pumps and mixers.

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CHAIN, ROLLER & SPROCKET

Power-transmission and conveyor chain attachment options K1 (B2 one-hole) and K2 (B2 two-hole) chains both have bent attachments on both sides.

A1 chain (sometimes called B1 one-hole chain) has links with one hole and a bent attachment. A2 is similar but always double pitch with two attachment holes per link.

D1 (E1) and D3 (E2) chains have extended pins.

WSK1 (WCS2 one-hole or WM1) and WSK2 (WCS2 two holes or WM2) is wide-contour chain with straight attachments on both sides.

Single-pitch WA1 (WCB1 one hole) chain and wide-contour WA2 (WCB1 two holes) chain both have bent attachments on one side and one or two holes per link.

SK1 chain (sometimes called S2 one-hole or M1 chain) has straight attachments on both sides. SK2 (S2 two holes or M2) is the same but with two holes per link.

WK1 (WCB2 one-hole) and WK2 (WCB2 two holes) is wide-contour chain with bent attachments.

SA1 (S1 one-hole or M35) chain and SA2 (S1 two holes or M35-2) chain both have straight attachments on one side, but the latter has two holes per link.

also attract less dust and particulates than regular chains. Such roller chains are useful where oil contamination is a concern, including paper-product or wood-processing industries.

Roller-chain sprockets come in myriad versions, but most are shaft-ready designs. The sprocket here is from the Power Transmission Solutions division of Regal-Beloit America.

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SPECIALTY COATINGS AND STAINLESS STEEL CAN DELAY OR PREVENT CORROSION Nickel-plated chains offer another alternative for chain coatings, providing some protection for mildly corrosive environments. Stainless-steel chains offer superior corrosion resistance; however, designers must be aware that regular stainless steels cannot be hardened in the same manner as carbon steel. Therefore, the load carrying capacity of stainless steel is lower than carbon steel. Proper chain maintenance requires periodic inspection. All chains must be checked for damage, wear and chemical attack on a regular basis. Another issue is wear elongation. Eventually roller chains wear so much that they necessitate replacement—typically at 1.5 to 2% (12.180 in./ft to 12.240 in./ft) elongation. Chains may work until they reach 3% elongation, but are at increased risk for suboptimal performance.

4 • 2016

DESIGN WORLD — MOTION

4/29/16 11:19 AM

REFERENCE GUIDE

Power Transmission

When hit by an object, oil inside this Zimmer shock absorber floods a spiraling channel from its fat opening to its narrow end. Sold by Intercon Automation Parts, the shock absorber relies on compression springs to return to its extended position after each cycle.

THE BASICS OF

COMPRESSION SPRINGS LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL

ENGINEERS

incorporate compression springs in designs that need linear compressive forces and mechanical energy storage— designs such as pneumatic cylinders and push-button controls, for example. The most conventional compression spring is a round metallic wire coiled into a helical form. The most common compression spring, the straight metal coil spring, bends at the same diameter for its entire length, so has a cylindrical shape. Cone-shaped metal springs are distinct in that diameter changes gradually from a large end to a small end; in other words, they bend at a tighter radius at one end. Cone-shaped springs generally go into applications that need low solid height (the total height when compressed) and higher resistance to surging. Whether cylindrical or cone shaped, helical compression springs often go over a rod or fit inside a hole that controls the spring’s movement. Other configuration types include hourglass (concave), barrel (convex), and magazine (in which the wire coils into a rectangular helix). Most compression springs have squared and ground ends. Ground ends provide flat planes and stability under load travel. Squareness is a characteristic that influences how the axis force produced by the spring can be transferred to adjacent parts. Although open ends may be suitable in some applications, closed ends afford a greater degree of squareness. Squared and ground end compression springs

DESIGN WORLD

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are useful for applications that specify high-duty springs; unusually close tolerances on load or rate; minimized solid height; accurate seating and uniform bearing pressures; and minimized buckling. The key physical dimensions and operating characteristics of these springs include their outside diameter (OD), inside diameter, wire diameter, free length, solid height, and spring rate or stiffness. • •

•

Free length is the overall length of a spring in the unloaded position. Solid height is the length of a compression spring under sufficient load to bring all coils into contact with adjacent coils.  Spring rate is the change in load per unit deflection in pounds per inch (lb/in.) or Newtons per millimeter (N/ mm).

The dimensions, along with the load and deflection requirements, determine the mechanical stresses in the spring. When the design loads a compression spring, the coiled wire is stressed in torsion and the stress is greatest at the wire surface. As the spring is deflected, the load varies, causing a range of operating stress. Stress and stress range affect the life of the spring. The higher the stress range, the lower the maximum stress must be to obtain comparable

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4/29/16 11:21 AM

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REFERENCE GUIDE

Power Transmission 40

life. Relatively high stresses may be used when the stress range is low or if the spring is subjected to static loads only. The stress at solid height must be low enough to avoid permanent damage because springs are often compressed solid during installation. HOW TO SELECT COMPRESSION SPRINGS Here are the most important factors to consider when selecting helical compression springs. The OD of a spring expands under compression. Be sure to consider this if the spring goes into a tube or a bore during assembly. Also remember that the OD of a spring is subject to manufacturing tolerances, just as any mechanical part. If the tolerance range is positive, the spring’s dimensions may be slighter larger and can add to the overall assembly’s envelope size. Most spring suppliers specify work-in-hole diameters for their springs to factor in manufacturing tolerances and the OD’s expected expansion. Look for this information to quickly select from stock spring catalogs, or use this information to better communicate product needs when ordering custom-made springs. Consider loading or travel requirements on the compression spring. The spring rate (also called the spring constant) is the relationship of the force to compress a spring by a unit of length, typically pounds per inch. So with a given load, the product designer can calculate expected spring travel. The further the spring travels, the more stress it endures. So at a critical point, stress can yield the wire material … causing a phenomenon called spring set. After spring set, the spring can’t expand back to its original unloaded length. Even so, in some assemblies, such springs can still function. Stress formulas and online calculators predict spring set. Otherwise, a starting rule of thumb is to avoid solid height by at least 20% (so that there’s always 20% of the spring’s total travel left during the normal range of operation). Compression spring-end types are standard or special. Standard ends are either plain open or closed. Either can be ground or not ground. The ends actually affect the spring rate. So, springs with dissimilar ends that are otherwise identical (with the same total coils, wire size, and OD) have different spring rates. Ground ends require more manufacturing effort. However, combined with closed ends, round ends improve the squareness of the loading force and reduce spring-buckling tendencies. Some manufacturers include closed and ground ends in standard catalog stock design, while some don’t. Be sure to know the difference. Special end examples include reduced coil for screw mounting, offset legs to work as alignment pins, and enlarged coils to snap into ring grooves. Spring materials abound and include everything from carbon steel to exotic alloys. Music wire is a high-carbon spring steel and is the most widely used material. Stainless steel 302 has less strength than music wire, but adds general corrosion resistance. Nickel alloys make a lot of springs branded under various trademarks and are chosen for extreme high or low operating temperatures, specific corrosive environments, and non-magnetic qualities. Springs made of phosphor bronze and beryllium copper are copper alloys for good corrosion resistance and electrical conductivity. DESIGN WORLD

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This concave (hourglass-shaped) compression spring can stay centered, even in large-diameter bores.

This compression spring has a barrel shape for lateral stability.

This compression spring has reduced ends.

Surging is when a spring builds compression-wave motion when subject to vibrations close to its natural frequency. This cone-shaped compression spring resists surging. The larger outer coils collapse before the smaller inner coils, so forces on the spring also increase the spring rate for a natural damping effect. Photo courtesy Lee Spring.

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4/29/16 11:21 AM

COUPLINGS

In these images we see an exploded and fully assembled view of GAM’s KHS metal bellows coupling. The conical hubs, and rotationally symmetric construction allow for speeds up to 30,000RPM and are commonly used for test stands, spindle drives and other high speed applications.

COUPLINGS:

TAC K L I N G T O R Q U E , M I S A L I G N M E N T A N D M O R E MIKE SANTORA • ASSOCIATE EDITOR • @DW_MIKE SANTORA

FOUND

in countless applications, couplings are simple devices that connect two shafts together. Couplings are usually found on rotating equipment such as motors to transmit a number of motion parameters. These parameters include the precise transmission of velocity, angular positioning and torque. However, the simplicity of these devices often serves to obscure their importance. Couplings should be designed to allow for some end movement. Two types are available: rigid and flexible. Flexible couplings compensate for misalignment, while rigid designs are used when shafts are already in alignment. Within these two types exists a variety of coupling styles. Rigid couplings include sleeve-style and clamped, or compression style, and require precise alignment. Flexible couplings include bellows, jaw, Oldham, disc and beam styles. RIGID COUPLINGS Rigid couplings are torsionally stiff and best used when shafts are already in proper alignment; parallel shaft misalignment ideally should be well below one thousandth of an inch. One drawback is that they are susceptible to vibration and cannot be run at high speeds. Sleeve-style rigid couplings are suitable for light- to medium-duty applications. The one-piece sleeve— essentially a tube with an inner diameter that is the same as the shafts it is joining together—has two set-screws to fasten it to the shaft. They are easy to use and offer high torque capacity, stiffness and zero backlash. Clamped, or compression style, couplings come in two parts that completely wrap around the shaft. Like most

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coupling designs, this protects the shaft from damage while providing high torsional holding power. Their advantage comes from their twopiece design, which allows them to be removed for easy maintenance. FLEXIBLE COUPLINGS Flexible couplings can be used where there is a slight amount of misalignment between shafts. They accommodate misalignment while still transmitting torque. Misalignments can be one of several fundamental types, including lateral, axial, angular or skewed. The greater the misalignment, the less efficient the motor is in generating speed and torque. Misalignment also contributes to premature wear including broken shafts, failed bearings and excessive vibration. Flexible couplings are typically the most compliant of components in mechanical motion systems, making torsional stiffness a critical factor in terms of maintaining positional control over a load. Many users of servomotors require the shaft to start and stop multiple times per second, which requires a torsionally stiff coupling to help diminish the settling time between cycles. However, torsionally flexible couplings frequently win out in terms of their

DESIGN WORLD — MOTION

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REFERENCE GUIDE

Power Transmission

Internal leaf springs, like those on this R+W BK-LK serve the purpose of making the coupling axially rigid for rotary / linear applications.

torque capacity in a given body size. Torsionally flexible couplings are naturally better for vibration damping, which is needed just as frequently in continuous motion applications as in cyclic duty applications. Types of motion differ in applications as well. For instance, in manufacturing lines, motion may be either continuous or start and stop. With the latter type, couplings can help dampen all-too-common vibration, diminish the settling time of the system and improve throughput. In contrast, continuous motion applications give greater weight to torsional strength over damping capabilities. Motion applications that require precise motion control, such as in packaging and scanning and inspection, call for zero-backlash couplings. Bellows couplings are commonly used in motion control applications that require precision control and where shaft misalignment is present. If your application requires precision, then it is important to understand the performance factors that are critical for selecting the optimum bellows coupling for the task. There is a difference between backlash—which is a true mechanical clearance, such as that which is found between gear teeth—and torsional deflection, or windup, which everything on earth will exhibit to some degree. Most couplings are preloaded to eliminate backlash or are inherently backlash free, like the bellows coupling. But they all have different levels of torsional stiffness, which is often traded off for lateral flexibility during the coupling selection process. Bellows couplings tend to have the highest torsional stiffness of any servomotor coupling, do not handle quite as much misalignment as others, but also do not impose heavy reaction loads onto the shafts and bearings as they flex.

DESIGN WORLD — MOTION

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Key benefits of bellows couplings include misalignment compensation and precise transmission of velocity, positioning and torque. Bellows couplings are known for their exceptional torsional rigidity, and flexibility in dealing with axial, angular and parallel shaft misalignment. Bellows couplings are typically made from a stainless-steel tube hydroformed to create deep corrugations that make them flexible across axial, angular and parallel shaft misalignments. When coupling shafts, bellows couplings absorb slight misalignments from perpendicularity and concentricity tolerances between the mounting surfaces of the two connected components. Jaw couplings feature two metal hubs and a spider insert, usually made of elastomer, which are fitted together to absorb vibration and shock. The elastomer is available in a variety of hardness and temperature ratings, so the spiders can be chosen for specific applications. Because they are not as torsionally stiff as other couplings, they are better suited to constant motion applications. Jaw couplings are available in two types: straight jaw and curved jaw with zero backlash. Because accuracy of torque transmission can be an issue, straight jaw couplings are not used in most servo applications. Curved jaw couplings, on the other hand, reduce deformation on the spider and the effects of centrifugal forces during high-speed (up to 40,000+

In this image we see R+W’s new SP6 series backlash free precision elastomer couplings. Elastomer couplings like this are often used for high speed spindle applications.

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4/29/16 11:24 AM

Metal Bellows Transfer Pressure or Temperature into into Linear Movement

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Power Transmission

rpm) operation. Both types can easily handle axial motion. If a spider breaks, the driving jaws can still contact the driven jaws directly, maintaining operation, making jaw couplings failsafe designs. Oldham couplings can be preloaded to eliminate backlash and can handle misalignment of all types depending on the disc material. They are being used more often as an alternative to straight jaw couplings on general industrial equipment such as pumps, valves, gearboxes and conveyor systems. They are versatile and offer long lives when misalignment is an issue. Their threepiece design—two hubs and a torquetransmitting center—makes them easy to install and disassemble. Oldham couplings can be specified in a variety of materials to meet the needs of different applications, for example, if zero backlash is required versus vibration reduction. They are best suited when parallel misalignment may be high. And because of their three-piece design, axial motion is limited. Disc couplings are a logical choice for servomotor and other demanding applications because of their ability to transmit high torque, operate at high or changing speeds, and handle misalignment and system loads. While a coupling’s torque, misalignment and speed capacities

DESIGN WORLD — MOTION

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Ringfeder Power Transmission’s Gerwah brand AKN series metal bellows coupling has zero backlash and compensates for angular, axial and radial misalignments. It uses clamping hubs on both sides for shaft connection.

need to be evaluated against a system’s requirements, the disc-pack usually is the most important aspect of the coupling’s construction because it will affect all critical performance aspects of the coupling and the system in which it is used. The most common type of disc-pack is made of metal and can be found in different shapes (straight-sided, scalloped edges, square, and so on). In the case of metal disc couplings, double-flex designs need to be used if there is to be any parallel shaft misalignment. The single-flex variety of metal disc coupling is good for angular misalignment but not parallel. This can be quite advantageous in case a user needs to suspend a load between two single-flex couplings, because their lateral stiffness can support the weight of the intermediate component. Beam, or helical couplings are almost always manufactured of aluminum, but stainless-steel versions are also available for use in corrosive environments and increased torque and stiffness. Their onepiece design makes them easy to maintain. Offering zero backlash, they feature spiral cuts that transmit torque and can handle all types of misalignment and angular, parallel or axial motion. Parallel motion is more of a challenge for the single beam design because it must bend in two directions, which causes stress and possible failure. Two designs exist under this style—single and multiple beams. Single beams are best suited to low-torque applications where no parallel misalignment is present, while multiple-beam designs are stiffer, for higher maximum torque capabilities. SPECIAL COUPLINGS Most disc couplings feature a metal disc-pack. However, some have composite disc-packs that are constructed of a special composite material rather than metal. This composite material provides an alternative to metal disc couplings. The advantages include its ability to absorb shock and vibration, its misalignment capacity, electrical isolation and elimination of fatigue and fretting. Whereas metal disc couplings

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Power Transmission

may be less expensive initially, overall cost of composite disc couplings usually will be lower because they are maintenance free and are rated for long life. The ability to accommodate misalignment is a critical aspect of a flexible disc coupling. Misalignment between coupled shafts often exists due to manufacturing tolerances, improper installation or from loads on the system. Parallel, angular and axial misalignment between coupled shafts should all be examined to see if the coupling selected is up to the task. It is important to know a coupling’s misalignment rating as well as the stiffness rating. The stiffer a coupling, the higher the reaction load misalignment will transmit to the coupled items. These reaction loads will have a negative effect on the life of the system. To limit these reaction loads, composite disc couplings are less radially stiff than metal disc couplings. Therefore, they transmit lower reaction loads on the coupled equipment, thereby increasing the life of connected (and often expensive) components. The amount of misalignment that a system can experience will typically determine the selection between a single-flex (one flexible disc-pack) and a doubleflex (two flexible disc-pack) coupling. While more compact in size than the double-flex variety, a single-flex coupling will have lower misalignment capacity and higher reaction loads. A common misconception is that single-flex disc couplings cannot accommodate parallel misalignment. Although this is true for metal disc couplings, the design of some disc-pack couplings allow single-flex CD couplings to accommodate limited parallel misalignment. This permits designers to implement a single-flex disc coupling into designs that may not have space for a double-flex coupling. Gear couplings are a type of mechanical device designed to transmit torque between two shafts that are not collinear. The coupling typically consists of two flexible joints, one fixed to each shaft. These joints are often connected by a third shaft called the spindle. Each joint generally consists of a 1:1 gear ratio internal/ external gear pair. The tooth flanks and outer diameter of the external gear are crowned to allow for angular displacement between the two gears. Mechanically, the gears are equivalent to rotating splines with modified profiles. They are called gears because of the relatively large size of the teeth. Gear couplings are generally limited to angular misalignments of 4 to 5°. Gear couplings ordinarily come in two variations: flanged sleeve and continuous sleeve. Flanged gear couplings consist of short sleeves surrounded by a

DESIGN WORLD — MOTION

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Jaw couplings like the GWE 5104 from Ringfeder have two metal hubs and a spider insert, usually made of elastomer. This particular coupling is available with elastomeric spiders of different degrees of shore hardness for varying damping levels.

motioncontroltips.com | designworldonline.com

4/29/16 11:25 AM

Linear Mount Products PMK Parallel mounting kit

EPL-H Inline gearbox, with hollow output design for easy mounting to linear actuators

WDS

DL-DC

Bellows style distance coupling

Right angle Dyna Lite gearbox with hollow output design for easy mounting to linear actuators. Includes output adapter tailored to the actuator

For Everything Between the Motor and Actuator Linear Mount Products include gear reducers, couplings, and mounting kits designed to interface specifically with actuators. We don’t make the actuators... We make them better. Toll Free 888.GAM.7117 | www.gamweb.com/linear | info@gamweb.com

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POWER TRANSMISSION

REFERENCE GUIDE

perpendicular flange. One sleeve is placed on each shaft so the two flanges line up face to face. A series of screws or bolts in the flanges hold them together. Continuous-sleeve gear couplings feature shaft ends coupled together and abutted against each other, which are then enveloped by a sleeve. Generally, these sleeves are made of metal, but they can also be made of Nylon. Single-joint gear couplings are used to connect two nominally coaxial shafts. In this application, the device is called a geartype flexible, or flexible coupling. The single joint allows for minor misalignments, such as installation errors and changes in shaft alignment due to operating conditions. These types of gear couplings are generally limited to angular misalignments of 1⁄4 to 1⁄2°. Magnetic couplings are designed to transfer torque from one shaft to another, but they do so without a physical mechanical connection.

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This makes them suitable for fluid pumping applications since the connection can be made through thin barriers, which help maintain a hermetically sealed rotary feed through. Since there are no contacting parts in the coupling, wear is virtually nonexistent and the use of permanent magnets means no external power source is needed. Magnetic couplings also have a built-in safety feature where, in the event of an overload on the coupling, it will shift to the next position and keep going. Magnetic couplings can typically only handle light torque loads and applications with either gradual starts, or low rotational inertia of the driven side of the system. They are also rather large in diameter, considering their relatively light torque load. The couplings also have moderate radial loads on support bearings.

DESIGN WORLD — MOTION

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4/29/16 4:22 PM

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REFERENCE GUIDE

BASICS OF

MOTOR DRIVES

Power Transmission

MILES BUDIMIR • SENIOR EDITOR • @DW_MOTION

ELECTRIC

motors that drive industrial machines need some way to control motor speed. And at its most basic level, a motor drive controls the speed of the motor. Some manufacturers refer to a controller and motor together as a drive system. However, from the electrical side of things, the drive is often specifically the electrical components that make up the variable frequency inverter itself. So drives are the interface between the control signals and the motor and include power electronic devices such as SCRs (silicon controlled rectifiers), transistors and thyristors. Matching the correct drive to the type of motor in an application is critical for getting the best fit. A wide range

Drives continue to offer more performance in smaller packages. For instance, a new line of drives from Yaskawa, the Sigma-7 family, features a smaller footprint, increased bandwidth, and 24-bit encoding that boosts precision. A package of algorithms corrects machine imperfections, including ripple compensation, anti-resonance and friction model compensation.

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of drives is available depending on the needs of the specific application and motor type. In general though, drive types typically fall into two categories: dc and ac. DC DRIVES Dc drives control dc motors. A basic dc drive is similar in operation to an ac drive in that the drive controls the speed of the motor. For dc motor control, a common method is a thyristor-based control circuit. These circuits consist of a thyristor bridge circuit that rectifies ac into dc for the motor armature. And varying the voltage to the armature controls the motor’s speed. AC DRIVES Ac drives control ac motors, such as induction motors and synchronous motors. These drives are sometimes known as variable frequency drives (VFDs) or inverters. Ac drives convert ac to dc, then, using a range of different switching techniques, generate variable voltage and frequency outputs to drive the motor. An adjustable speed drive is a general term used sometimes interchangeably with variable speed drive or variable frequency drive. It controls the motor by varying the frequency of the output power. Again, from an electrical perspective, all of these ultimately refer to the frequency converter circuitry. An ac motor’s speed is determined by the number of poles and the frequency. Thus, as frequency is adjusted, the motor’s speed can be controlled as well. A common way to control frequency is by the use of pulse width modulation (PWM). A PWM drive outputs a train of dc pulses to a motor and by modulating the pulse width, makes it either narrower or wider, which delivers an ac current waveform to the motor. Another drive feature, the ability to slow down or stop a motor, is known as regenerative braking or regen braking. It provides a way of stopping a motor’s rotation by using the same solid-state components that control the motor’s voltage. The energy generated from braking can be channeled back into the ac mains or into a braking resistor. One advantage of regenerative drives include their ability to stop a motor faster than it would normally coast to a stop. motioncontroltips.com | designworldonline.com

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Size matters. Especially with gearmotors... Too small = premature failure Too large = high cost & low efficiency Unsure of your drive size? Then go online to PT Pilot®. Simply enter the parameters of your hoist, conveyor, or travel car. PT Pilot® will automatically calculate the optimal horsepower, speed, and gear unit – with or without a VFD. PT Pilot® also provides documentation, pricing, and a 3D CAD drawing for every selection. Visit ptpilot.com.

ptpilot.com | 864-439-7537

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Power Transmission

The Altivar 320 series of drives from Schneider Electric boast connectivity options including Ethernet (Modbus TCP, Ethernet/ IP, Profinet, EtherCAT) or serial (Modbus RTU, CANopen, Profibus DP, DeviceNet) based networks. They also feature embedded safety solutions for simple application requirements to comply with Machinery Directive 2006/42/ EC and simplify certification.

DESIGN WORLD — MOTION

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VFDs VFDs operate by switching their output devices—which can be transistors, IGBTs (insulated gate bipolar transistors), or thyristors—on and off. VFDs can be either constant voltage or constant current. Constant voltage types are the most common type of VFD. They use PWM to control both the frequency and the voltage applied to the motor. Why use VFDs? They are a powerful way to control the speed of ac induction motors and are fairly simple and easy to use. Among the benefits of using a VFD for motor speed control is the actual energy savings. Controlling the amount of current drawn by the motor can save a lot on energy costs because the motor will not run at full load all of the time. Especially since Congress passed the Energy Independence and Security Act of 2007 (EISA), motor efficiency has become a top design priority. For instance, single-phase induction machines (specifically, permanent splitcapacitor motors) and universal motors, widely used in industrial washers, are managed with simple voltage-control techniques. Contrast this with high-end, high-performance machines where three-phase motors are more common and which use VFDs. Switch reluctance motors (SRMs) are not yet an appropriate alternative because their control schemes are still evolving, but three-phase motors are readily available and may be a smart choice because their VFD control techniques have improved significantly. More importantly, VFD electronics costs have been dropping as well, making them more cost-effective. In the same way, an OEM using a universal motor with simple triac control may now find that a three-phase VFD control will provide better energy efficiency, while OEMs using three-phase/VFD configurations may make the move to technologies like brushless dc motors. Another advantage of VFDs is seen on motor start-up. Without a VFD, an induction motor on start-up has to handle a high initial in-rush current. As the motor speeds up and approaches a constant speed, the current levels off from the peak in-rush values. So with a VFD, the motor’s input starts off with low voltage and a low frequency, avoiding the problem of high in-rush currents. Of course, the main reason any kind of speed control is used on motors is to gain greater and more precise control over motor speed and therefore adjust the motor speed to meet the requirements of the load and reduce energy costs. Another benefit of using a VFD for motor speed control is the reduction of mechanical wear on the motor components. Eliminating the in-rush currents upon start-up gets rid of the excessive torque on the components, and thus increases the life of the motor and reduces maintenance costs and the need for repair. In addition, mechanical stresses on the entire system are greatly reduced. In many cases, mechanical controls such as throttles, valves, dampers and louvers can be removed, thereby reducing mechanical wear and maintenance costs. Further, with reduced mechanical wear, the system output quality may be improved and production times reduced. There are some drawbacks to using VFDs, however. The main one is the possibility of harmonic distortion which can effect the power quality as well as the operation of other machinery. However, VFD manufacturers have developed solutions that mostly eliminate this problem.

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4/29/16 11:31 AM

Power Transmission and Motion Control Solutions for Industrial Applications

The Power Brands in Power Transmission Ameridrives Couplings

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REFERENCE GUIDE

GEARING & GENERAL GEAR DESIGN THE BASICS

Power Transmission

LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL

THE PRIMARY

function of a gear is to mesh with other gears to transmit altered torque and rotation. In fact, gearing can change the speed, torque and direction of motion from a drive source. When two gears with an une qual number of teeth engage, the mechanical advantage makes their rotational speeds and torques different. In the simplest setups, gears are flat with spur teeth (with edges parallel to the shaft) and the input gear’s shaft is parallel to that of the output. Spur gears mostly roll through meshing, so can be 98% or more efficient per reduction stage. However, there is some sliding between tooth surfaces, and initial tooth-to-tooth contact occurs along the whole tooth width at once, causing small shock loads that induce noise and wear. Sometimes lubrication helps mitigate these issues. In slightly more complex setups, parallel-axis gearsets have helical gears that engage at an angle between 90° and 180° for more tooth contact and higher torque capacity. Helical reducers are suitable for higherhorsepower applications where long-term operational efficiency is more important than initial cost. Helical gear teeth engage gradually over the tooth faces for quieter and smoother operation than spur gearsets. They also tend

Worm gear

to have higher load capacities. One caveat: Angled tooth contact generates thrust that the machine frame must resolve. No matter the subtype, most parallel-axis gearsets have gear teeth with tailored involute profiles—customized versions of the rolled trace off a circle with an imaginary string. Here, mating gears have tangent pitch circles for smooth rolling engagement that minimizes slipping. A related value, the pitch point, is where one gear initially contacts its mate’s pitch point. Involute gearsets also have an action path that passes through the pitch point tangent to a base circle. Besides parallel-axis gearsets, there are non-parallel and right-angle gearsets. These have input and output shafts that protrude in different directions to give engineers more mounting and design options. The gear teeth of such gearsets are either bevel (straight, spiral or zerol), worm, hypoid, skew or crossed-axis helical gears. The most common are bevel gearsets with teeth cut on an angular or conical shape. Hypoid gears are much like spiral-bevel gearsets, but the input and output shaft axes don’t intersect, so it’s easier to integrate supports. In contrast, zerol gearsets have curved teeth that align with the shaft to minimize thrust loads.

Spiroid gear ®

Spiroid® or Helicon® gear Helicon® gear Hypoid gear

Spiral bevel gear

DESIGN WORLD — MOTION

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Shown here are Spiroid and Helicon brand gearing. Suitable for right-angle power transmission in applications with high power density requirements, these skew-axis gear forms operate on non-intersecting and non-parallel axes. Compared to traditional right-angel bevel and worm gearing, the gear-centerline offset of Spiroid and Helicon branded gearing allows for more tooth-surface contact and results in higher contact ratios. This boosts torque capacity and smooths motion transmission. Spiroid brand gears use advanced software and tooling to make the proprietary gearing fit specific application requirements. The gearsets are quiet, stiff, and compact, delivering ratios from 3:1 to 300:1 and beyond.

motioncontroltips.com | designworldonline.com

4/29/16 11:34 AM

GEARS Now available factory direct

259 Elm Place, Mineola, NY 11501 Phone: 516.248.3850 | Fax: 516.248.4385 Email: info@khkgears.us

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Common gear options Spur gearsets are simple ...

POWER TRANSMISSION

REFERENCE GUIDE

THE BASICS OF GEARING:

Pitch circle

Reaction force ... but helical gearsets are more efficient. Cross-axis sets are another option.

Planetary gearsets are compact and run to 10,000 rpm. Here, a lightweight Schaeffler differential for a hybrid vehicle has an axial spline to boost efficiency. Zerol bevel gearsets are a special veriation of straight right-angle bevel sets.

Worm gearsets are rugged and don’t let designs backdrive ... which can eliminate the need for brakes. Note there’s some overlap between bevel and worm applications. Case in point: The MS-Graessner DynaGear below is a single-stage bevel gear with a 30:1 ratio.

GENERAL SPEED REDUCERS, SHAFT-MOUNT SETS, WORM DRIVES LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL

GEAR

reducers, also known as speed reducers, are a component of many mechanical, electrical, and hydraulic motors. Essentially it is a gear or series of gears combined in such a manner as to alter the torque of a motor. Typically, the torque increases in direct proportion to the reduction of rotations per unit of time. Speed reducers come in two varieties; base mounted and shaft mounted. Shaftmounted types come in two versions. One is truly shaft mounted in that the input shaft of the drive motor supports it … with a special coupling to address torque reactions. The other mounts to the machine housing so the input shaft doesn’t support the reducer’s weight or address torque reactions. By the American Gear Manufacturers Association (AGMA) definition, engineers apply the term “speed reducer” to units operating at pinion speeds below 3,600 rpm or pitch-line velocities below 5,000 fpm. (The AGMA is an international group of gear manufacturers, gear consultants, academics, and gear users and suppliers.) Reducers operating at speeds higher than these are called high-speed units. Manufacturers base catalog ratings and engineering specifications for speed reducers on these AGMA standards. There are as many types of speed reducers as there are gear types. Consider reducers in which the input and output shafts are at different angles. The most common of these are worm-gear reducers. Worm gear reducers are used in low to moderate-horsepower applications. They offer low initial cost, high ratios, and high output torque in a small package, along

with a higher tolerance for shock loading then helical gear reducers. In a traditional setup, a cylindrical toothed worm engages a disk-shaped wheel gear with teeth on its circumference or face. Most worm gears are cylindrical with teeth of consistent size (for one pitch diameter for the length). Some worm-gear reducers use a double-enveloping tooth geometry, though—with a pitch diameter that goes from deep into short and back to deep—so more teeth engage. No matter the version, most wheel gears in worm-based reducers sport cupped teeth edges that wrap around the worm shaft during engagement. In many cases, the sliding engagement lowers efficiency but extends life, as wormgear mating holds a film of lubricant during operation. The ratio of a worm-gear ratio is the number of wheel teeth to the number of threads (starts or leads) on the worm. A FEW WORDS ON GEARHEADS A gearhead is similar to a gear reducer; however, a gearhead doesn’t just reduce speed. Engineers use them wherever an application calls for high torque at low speed. It reduces a load’s reflected mass inertia, which makes accelerating heavy loads easier, enabling designs to run off smaller motors. Gearheads come in a variety of styles from basic spur gearheads to more complex planetary gearheads and harmonic type gearheads, each with their own characteristics and suitable applications. One caveat: In some applications, gearhead backlash may become an issue. In this case, consider using a gearhead with low or zero backlash.

The ratio of a helical or bevel gearset is simply the number of teeth in the larger gear divided by the number of teeth in the smaller gear. Other gear types such as planetary gears have more complex ratio relationships.

DESIGN WORLD — MOTION

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4/29/16 11:34 AM

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REFERENCE GUIDE

Power Transmission

Interoll conveyors for material handling use power rollers that incorporate precision gearing.

THE BASICS OF GEARING:

GEARBOXES, SPECIALTY GEARHEADS & SERVOGEARSETS LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL

SERVO SYSTEMS

move heavy objects. Speed specifications for gearmotors are normal speed and stall-speed torque. Gearbox: This is a contained gear train … a mechanical are precision-motion setups with unit or component consisting of a series of integrated gears. feedback and (in most cases) fairly Planetary gears are common in integrated gearboxes. stringent accuracy demands. So for Planetary gears: Particularly common in servo systems, these designs, engineers should pick these gearsets consist of one or more outer planet gears that servogear reducers with good torsional revolve about a central, or sun, gear. Typically, the planet stiffness, reliable output torque and gears mount on a movable arm or carrier that rotates relative minimal backlash. OEMs tasked with integrating servo systems should look for to the sun gear. The sets often use an outer ring gear, or annulus, that meshes with the planet gears. quiet reducers that easily mount to the The gear ratio of a planetary set requires calculation, motor and require little or (if possible) no because there are several ways they can convert an input maintenance. In fact, a lot of advanced machinery rotation to an output rotation. Typically, one of these three gear wheels stays stationary; another is an input that provides integrates servogears into applicationspecific electromechanical arrangements, power to the system, and the last acts as an output that receives power from the driving motor. The ratio of input and several of these arrangements are common enough to have specific labels. rotation to output rotation depends on the number of teeth in each gear and on which component is held stationary. Here is a look at some of the most Planetary gearsets offer several advantages over other widespread. gearsets. These include high power density, the ability to Gearmotor: This complete motion get large reductions from a small volume, multiple kinematic component is a gear reducer integrated combinations, pure torsional reactions and coaxial shafting. with an ac or dc electric motor. Usually Another advantage to planetary gearbox arrangements is the motor includes the gears on its power-transmission efficiency. Losses are typically less than output (typically in the form of an assembled gearbox) to reduce speed and 3% per stage, so rather than waste energy on mechanical boost available output torque. Engineers losses inside the gearbox, these gearboxes transmit a high proportion of the energy for productive motion output. use gearmotors in machines that must

DESIGN WORLD — MOTION

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GEARING

Planetary gearbox arrangements distribute load efficiently, too. Multiple planets share transmitted load between them, which greatly increases torque density. The more planets in the system, the greater load ability and the higher the torque density. This arrangement is also very stable due to the even distribution of mass and increased rotational stiffness. Disadvantages include high bearing loads, inaccessibility and design complexity. In servo systems, besides boosting output torque, gearboxes impart another benefit—reducing settling time. Settling time is a problem when motor inertia is low compared to load inertia … an issue that’s the source of constant debate (and regular improvement) in the industry. Gearboxes reduce the reflected inertia at the controls by a factor equal to the gear reduction squared. These are self-lubricating metal-core gears from Intech for applications with frequent start-and-stop stop cycles and high torque that need power-transmission components to resist shock.

DieQua offers more gearboxes Are You Selecting The Right Technology?

For Power Transmission

Whether your application is for precise motion control or for general power transmission, there are several gear technologies that can do the job. But which one does it best? Only DieQua offers the widest range of gearmotors, speed reducers and servo gearheads along with the experience and expertise to help you select the optimal solution to satisfy your needs.

Worm Reducers

Helical Gearmotors

Spiral Bevel Gearboxes

For Motion Control

If you are using gearboxes, you should be talking to DieQua!

Planetary Gearheads

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Servo Worm Gearheads

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REFERENCE GUIDE

THE BASICS OF GEARING:

STRAIN-WAVE GEARING LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL

Power Transmission

STRAIN-WAVE

Circular spline

gearing is a special gear design for speed reduction. It uses the metal elasticity (deflection) of a gear to reduce speed. (Strainwave gearing sets are also known as Harmonic Drives, a registered trademark term of Harmonic Drive Systems Inc.) Benefits of using strain-wave gearing include zero backlash, high torque, compact size and positional accuracy. A strain-wave gearset consists of three components: wave generator, flexspline and circular spline. The wave generator is an assembly of a bearing and steel disk called a wave generator plug. The outer surface of the wave generator plug has an elliptical shape machined to a precise specification. A specialty ball bearing goes around this plug to conform to the same elliptical shape of the wave generator plug. Designers typically use the wave generator as the input (attached to a servomotor). The flexspline— usually acting as the output—is a thinwalled steel cup. Its geometry makes the cup walls radially compliant but torsionally stiff (because the cup has a large diameter). Manufacturers machine the gear teeth into the outer surface near the open end of the cup (near the brim). The cup has a rigid boss at one end for mounting. The wave generator goes inside the

flexspline so the bearing is at the same axial location as the flexspline teeth. The flexspline wall near the brim of the cup conforms to the same elliptical shape of the bearing. This conforms the teeth on the outer surface of the flexspline to the elliptical shape. That way, the flexspline effectively has an elliptical gear-pitch diameter on its outer surface. The circular spline is a rigid circular steel ring with teeth on the inside diameter. It is usually attached to the housing and does not rotate. Its teeth mesh with those of the flexspline. The tooth pattern of the flexspline engages the tooth profile of the circular spline along the major axis of the ellipse. This engagement is like an ellipse inscribed concentrically within a circle. Mathematically, an inscribed ellipse contacts a circle at two points. However, gear teeth have a finite height, so two regions (instead of two points) engage. The pressure angle of the gear teeth transforms the output torque’s tangential force into a radial force acting on the wave-generator bearing. The teeth of the flexspline and circular spline engage near the ellipse’s major axis and disengage at the ellipse’s minor axis. The flexspline has two less teeth than the circular spline, so every time the wave generator rotates one revolution, the flexspline and circular spline shift by two teeth. The gear ratio is: number of flexspline teeth ÷ (number of flexspline teeth - number of circular spline teeth) The tooth engagement motion (kinematics) of the strain wave gear is different than that of planetary or spur gearing. The teeth engage in a manner that lets up to 30% of the teeth (60 for a 100:1 gear ratio) engage at all times. This contrasts with maybe six teeth for a planetary gear, and one or two teeth for a spur gear. In addition, the kinematics enable the gear teeth to engage on both sides of the tooth flank. Backlash is the difference between the tooth space and tooth width, and this difference is zero in strain-wave gearing. As part of the design, the manufacturer preloads the gear teeth of the flexspline against those of the circular spline at the ellipse’s major axis. The preload is such that the stresses are well below the material’s endurance limit. As the gear teeth wear, this elastic radial deformation acts like a stiff spring to compensate for space between teeth that would otherwise increase in backlash. This lets the performance remain constant over the life of the gear. Strain-wave gearing offers high torque-to-weight and torque-to-volume ratios. Lightweight construction and single-stage gear ratios (to 160:1) let engineers use the gears in applications requiring minimum weight or volume ... especially useful for designs with small motors. Another tooth profile for strain-wave gearing is the S tooth design. This design lets more gear teeth engage for a doubling of torsional stiffness and peak torque rating, as well as longer life. The S tooth form doesn’t use the involute tooth curve of a tooth. Instead, it uses a series of pure convex and concave circular arcs that match the loci of engagement points dictated by theoretical and CAD analysis. The increased root filet radius makes the S tooth much stronger than an involute curve gear tooth. It resists higher bending (tension) loads while maintaining a safe stress margin.

Flexspline This is a progression of flex-spline tooth engagement with circular-spline teeth. The profile of Harmonic Drive gear teeth lets up to 30% of the teeth engage ... for higher stiffness and torque than gearsets with involute teeth.

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247 Lynnfield Street, Peabody, MA 01960 â&#x20AC;˘ 800.921.3332 â&#x20AC;˘ www.HarmonicDrive.net Harmonic Drive is a registered trademark of Harmonic Drive LLC. Robonaut image courtesy of NASA/JPL-Caltech.

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REFERENCE GUIDE

Power Transmission

Most of the time, design engineers pair gearsets with electric motors. These setups get a roman-numeral service class number (I, II, or III, for example) that equates to the standalone gear-set service factor (in this case, 1.0, 1.41, or 2.0).

This chart provides values for C-face motor input (flanged) or directly coupled (non-flanged) motors. It lets the design engineer verify that with 15:1 reduction, a 726 flanged gearbox outputs 116.7 rpm … and when used with a 2 hp motor, outputs 994 in.-lb of torque.

DESIGN WORLD — MOTION

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GEARING

THE BASICS OF GEARING:

CONSULTATION, CUSTOM GEAR DESIGN & GEAR ANALYSIS

LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL

CUSTOM

gearboxes are increasingly common, mainly because they’re easier than ever to manufacture to specification. That’s not to say that the design work isn’t challenging. However, modern manufacturing lets some suppliers make gearboxes and components to meet specific application requirements. New supplier approaches to giving engineering support as well as new machine tools, automation and design software now let OEMs and end users get reasonably priced gearing even in modest volumes. When enlisting help from a consultant or manufacturer, an engineer is more likely to get gearing that mounts properly and performs to specification after reviewing the following and answering as many of these questions as possible: • • • •

• •

•

What’s the input speed and horsepower? What’s the gearbox target output speed or output torque? This partially defines the required gear ratio. What are the characteristics of use? How many hours per day will the gearbox run? Will it need to withstand shock and vibration? How overhung is the load? Is there internal overhung load? Remember that bevel gears usually can’t accommodate multiple supports, as their shafts intersect … so one or more gears often overhang. This load can deflect the shaft which misaligns the gears, in turn degrading tooth contact and life. One potential fix here is straddle bearings on each side of the gear. Does the machine need a shaft or hollow-bore input ... or a shaft or hollowbore output? How will the gearing be oriented? For instance, if specifying a right-angle worm gearbox, does the machine need the worm over or under the wheel? Will the shafts protrude from the machine horizontally or vertically? Does the environment necessitate corrosion-resistant paints or stainless-steel housing and shafts?

Service factor: The starting point for most gearbox manufacturers is to define a service factor. This adjusts for such concerns as type of input, hours of use per day, and any shock or vibration associated with the application. An application with an irregular shock (a grinding application, for example) needs a higher service factor than one that’s uniformly loaded. Likewise, a gearbox that runs intermittently needs a lower factor than one used 24 hours a day. Class of service: Once the engineer determines the service factor, the next step is to define a class of service. A gearbox paired to

Shown here is a MS-Graessner PowerGearHS, a high-speed bevel gearbox for dynamic servo drivetrains. Efficiency reaches 98% and torque reaches 45 to 360 Nm (with emergencystop torques of 90 to 720 Nm) depending on the version.

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Power Transmission

Trained machinists run this machine shop to let gear manufacturer NORD Gear Corp. accommodate customerspecific requirements. The Waunakee, Wis. shop processes 20 to 30 specially designed and machined components each day.

as mounting feet for either above or below the body of the gearbox, hollow outputs, and input and output configuration are all possible. All gearbox manufacturers list their mounting options as well as dimensional information in catalogs and websites. Lubricant, seals and motor integration: Most manufacturers can ship gearboxes filled with lubrication. However, most default to shipping units empty to let users fill them on site. For applications where there is a vertical shaft down, some manufacturers recommend a second set of seals. Because many gearboxes eventually mount to a C-frame motor, many manufacturers also offer to integrate motors onto gearboxes and ship assemblies as single units. Work with consultants and even use custom gear designs if the application needs a unique motor-gearbox combination. Some combinations are more efficient. Getting a pre-engineered geamotor ensures that the motor-gearbox combination will perform to specification. Also remember that today’s custom and standard gearing aren’t mutually exclusive. Where fully custom gearboxes aren’t feasible (if quantities aren’t high enough, for example) consider working with manufacturers that sell gearboxes built to order from modular subcomponents. Otherwise, look for manufacturers that leverage the latest CAD and CAM software and machine tools to streamline post-processing work and reduce the cost of one-offs. One final tip: Once the gearmotor has been chosen and installed in the application, perform several test runs in sample environments that replicate typical operating scenarios. If the design exhibits unusually high heat, noise or stress, repeat the gear-selection process or contact the manufacturer.

a plain ac motor driving an evenly loaded, constant-speed conveyor 20 hours per day may have a service class 2, for example. This information comes from charts from gearbox manufacturers that list classes of service. To use these charts, the design engineer must know input horsepower, application type and target ratio. For instance, suppose that an application needs a 2-hp motor with a 15:1 ratio. To use the chart, find the point where 2 hp and 15:1 ratio intersect. In this case, that indicates a size 726 gearbox. According to one manufacturer’s product-number system, size 726 defines a gearbox that has a 2.62 center distance. Such charts also work in reverse, to let engineers confirm the torque or speed of a given gearbox size. Overhung load: After the designer picks a size, the gearbox manufacturer’s catalog or website lists values for the maximum overhung load that is permissible for that sized unit. Tip: If the load in an application exceeds the allowed value, increase the gearbox size to withstand the overhung load. Mounting: At this point, the designer or manufacturer has defined the gearbox size and capability. So, the next step is to pick the mounting. Common mounting configurations abound, and gearbox manufacturers offer myriad options for each unit size. A flanged input with hollow bore for a C-frame motor combined with an output shaft projecting to the left may be the most common mounting, but there are many KHK USA Inc. manufactures gearing to operate in ratchets and pawls, which is mechanical other choices. Options such

gearing that transmits intermittent rotary motion. They only let shafts rotate in one direction.

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速

When second-best is just not good enough. From design to delivery, you can count on us to give you the best gearmotor solution for your application. When your product demands perfect performance every time, call Bodine. visit visit us us at at bodine-electric.com bodine-electric.com || info@bodine-electric.com info@bodine-electric.com BOD designWorld-swoosh-full page.indd 1 Bodine_PTGuide4-16.indd 65

|| 800.726.3463 800.726.3463 (USA) (USA) 3/21/16 9:58 AM 4/29/16 1:33 PM

REFERENCE GUIDE

Power Transmission 66

T E CHN ICAL R E V I E W OF

GEARMOTORS MILES BUDIMIR • SENIOR EDITOR • @DW_MOTION

GEARMOTORS

are a fairly well-established technology. And recently, there is renewed interest in gearmotors, following a trend in integrated systems in general. More specifically, rising energy costs are driving demand for improved process efficiencies. This presents an opening for gearmotors that can be used in a variety of applications and represents a tremendous opportunity for global energy savings. Essentially, a gearmotor is a type of gear reducer based around an ac or dc electric motor. In fact, in a gearmotor, the gear and the motors are combined into one unit. It delivers high torque at low horsepower or low speed. The speed specifications for these motors are normal speed and stall-speed torque. These motors use gears, typically assembled as a gearbox, to reduce speed, which makes more torque available. Gearmotors are most often used in applications that need a lot of force to move heavy objects. By and large, most industrial gearmotors use ac motors, typically fixed-speed motors. However, dc motors can also be used as gearmotors, a lot of which are used in automotive applications. Gearmotors have a number of advantages over other types of motor/gear combinations. Perhaps most importantly, gearmotors can simplify design and implementation by eliminating the step of separately designing and integrating the motors with the gears, thus reducing engineering costs. Another benefit of gearmotors, if sized properly, is that having the right combination of motor and gearing can prolong gearmotor life and allow for optimum power management and use. Also, because gearmotors are integrated units, they eliminate the need for couplings and also eliminate any potential alignment problems. Such problems are common Gearmotors can be simply a motor with a when a separate motor and simple gear attached or as complex as this gear reducer are connected unit from Nord Gear incorporating bevel gears with a 90-degree hollow-shaft output. together and result in more

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An in-line gearmotor design featuring a helical gearset from Nord Gear is one common type of gearmotor.

engineering time and cost as well as the potential for misalignment causing bearing failure and ultimately reduced useful life. Gear reducers, also known as speed reducers, are a component of many mechanical, electrical and hydraulic motors. Essentially, it is a gear or series of gears combined in such a manner as to alter the torque of a motor. Typically, the torque increases in direct proportion to the reduction of rotations per unit of time. A gearbox, or gear train, is a mechanical unit or component consisting of a series of integrated gears. Planetary gears are a common type of integrated gearing in a gearbox. Advances in gearmotor technology include the use of new specialty materials, coatings and bearings, and also improved gear tooth designs that are optimized for noise reduction, increase in strength and improved life, all of which allows for improved performance in smaller packages. Conceptually, motors and gearboxes can be mixed and matched as needed to best fit the application, but in the end, the complete gearmotor is the driving factor. There are a number of motors and gearbox types that can be combined; for example, a right angle wormgear, planetary and parallel shaft gearbox can be combined with permanent magnet dc, ac induction, or brushless dc motors. Though there are a number of different motor and gearbox combinations available, not just any one will work for a specific application. There will be certain combinations that will be more efficient and cost-effective than others. Knowing the application and having accurate ratings for the motor and gearbox is the foundation for successfully integrating a gearmotor into a system.

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YOUR NEEDS. OUR EXPERTISE. Groschopp Inc. 420 15th St. NE Sioux Center, IA 51250 www.groschopp.com

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Phone: 712.722.4135 Toll-free: 800.829.4135 Fax: 712.722.1445 Email: sales@groschopp.com

ÂŠ 2016 Groschopp Inc.

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REFERENCE GUIDE

Power Transmission

Anti-backlash leadscrew assemblies, such as the CMP Series from Haydon Kerk, use a general purpose selfcompensating nut in a small compact package. The standard CMP Series assembly uses a self-lubricating acetal nut, axially preloaded, on a 303 stainless steel screw.

BASICS OF

LEADSCREWS MILES BUDIMIR SENIOR EDITOR @DW_MOTION

DESIGN WORLD — MOTION

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LEADSCREWS

are one of many linear actuator components that also include ballscrews as well as belt and pulley systems, linear motors and belt-drive systems. A leadscrew, also known as a power screw, is a threaded rod or bar that translates rotational motion into linear motion. Leadscrews generate sliding rather than rolling friction between a nut and the screw. Consequently, higher friction means a lower overall efficiency. And efficiency, when talking about leadscrews, is simply the ability to convert torque to thrust while minimizing mechanical losses. Leadscrews are a staple of motion designs, driving axes on machines big and small alike. They usually sport higher ratings than comparable ballscrews thanks to more contact between the nut and screw load surfaces. Now, innovations in materials and helix geometry address old issues associated with leadscrew friction, bringing it down to better than 0.10 in some cases—good for fast and dynamic applications. In fact, there’s also been an uptick in leadscrew use because of proliferating machines for 3D printing, manufacturing and medical applications.

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LEADSCREWS

Industries across the board are adopting new leadscrew components and linear systems. Designers of kiosks and automated retail applications, for instance, are looking for ways to simplify machines, reduce design weight and simplify assembly and maintenance. In a similar way, both additive manufacturing (3D printing) and traditional subtractive processes—plasma cutter, laser and waterjet manufacturing—are driving new leadscrew uses. The same holds true for factory automation. Leadscrew manufacturing processes can determine the performance and cost of the leadscrew. For instance, there are three ways leadscrews can be manufactured; by machining, rolling, or grinding. Ground leadscrews are the most expensive and are generally considered to be the highest performing as well. Another determinant of efficiency is the thread type. Acme threads are the simplest to produce, the most inexpensive, but also among the least efficient. Other types include buttress threads and square threads, which generally have the least amount of friction and higher efficiencies.

Leadscrews have a number of advantages including a relatively high load carrying capacity. They are also compact and simple to design into a system with a minimal number of parts. The motion is also generally smooth and quiet and requires little maintenance. Leadscrews also work well in wash-down environments because the materials used and the lubricant-free operation allows total immersion in water or other fluids. On the other hand, leadscrews do not have high efficiencies. Because of lower efficiency ratings they’re not used in applications requiring continuous power transmission. There’s also a high degree of friction on the threads meaning that the threads can wear quickly. Because a leadscrew nut and screw mate with rubbing surfaces they have relatively higher friction and stiction compared to mechanical parts that mate with rolling surfaces and bearings. There are several parameters that help determine leadscrew performance. These include thrust, speed, accuracy and repeatability. The two most important factors in determining the performance of a leadscrew are the screw pitch and lead. The pitch is the linear distance between the threads while the lead is the linear distance the nut travels. Speed is another critical parameter. Leadscrews have a critical velocity, which is the rotational velocity limit of the screw. Reaching this limit induces vibrations in the leadscrew. Accuracy and repeatability are also important factors. The accuracy of a leadscrew is a measure of how close to a desired end point the assembly can move a load to within a given tolerance. The accuracy of the leadscrew will mostly determine the system’s accuracy. On the other hand, repeatability is a measure of how well a leadscrew assembly can repeatedly move a load to the same position.

Smaller leadscrews have been finding their way into many applications, from vending machines to medical equipment. Miniature leadscrews such as the MINI Series from Haydon Kerk, are designed to minimize backlash with drag torque of less than 1 oz.-in. and in some sizes as low as 0.1 oz.-in.

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Power Transmission

Heavy Duty Slides from HepcoMotion work for long-length transport applications such as pick-and-place or robot-translation stages. V slide rails are made from bearing-grade steel in sections to four meters long. The V slides typically bolt to aluminum extrusions or supporting back plates. A guide wheel bearing with matching V geometry rolls on the V slide raceway. Image courtesy Bishop-Wisecarver

TECHNICAL SUMMARY OF

LINEAR-MOTION GUIDES, RAILS & SYSTEMS LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL

LINEAR-MOTION

This Schaeffler INA assembly has a linear recirculating-ball bearing and guideway. Called the KUVE-B-HS, it has conventional steel rolling elements for speeds to 10 m/sec. Plastic in the recirculation mechanism prevents rollingelement tilting and pulse loads. The guides run on standard guideways.

DESIGN WORLD — MOTION

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systems are essential in all sorts of applications, including everything from manually operated industrial drawers to advanced Cartesian robots. Mechanisms that include the former operate without power, using inertia or manual power to move loads. Components to complete the latter include ready-to-install drive and guidance designs … in the form of self-contained actuators or linear-motion machinery subsections. Some designs simply rely on the rotary-to-linear mechanism or actuator structure for total load support. However, most industrial linear designs have pneumatics, linear motors or motordriven, rotary-to-linear mechanisms to advance attached loads, as well as rails that guide and support the loads. Here, linear rails, rotary rails, guide rails, linear slides and linear ways are just a few options to facilitate single-axis motion. Their main function is to support and guide load with minimal friction along the way. Typical linear-

4 • 2016

motion arrangements consist of rails or shafts, carriages and runner blocks, and some type of moving element. Engineers differentiate these systems by the type of surface interaction (sliding or rolling), the type of contact points, and (if applicable) how the design’s rollingelement recirculation works. In fact, slides and rails are more advanced than ever, with advances in materials and lubrication setups (to help designs last longer in harsh applications), innovative rail geometries (to help designs withstand more misalignment and load than ever), and modular guide mounts (to boost load capacity and minimize deflection). No matter the ultimate installation, linearmotion rails, guides, and ways enable motion along an axis or rail either through sliding or rolling contact. Myriad moving elements can produce either sliding or rolling support: ball bearings, cam roller sliders, dovetail bearings, linear roller bearings, magnetic bearings, fluid bearings, X-Y tables, linear stages and machine slides.

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Power Transmission

One classic rail with sliding contact is a dovetail slide, and one classic rail with rolling contact is a ball rail with a recirculating system. Sliding-contact bearings are the more straightforward type of linear-motion component. These consist of a carriage or slide that rides over a surface known as a rail, way or guide. Sliding contact occurs when the moving part directly contacts the rail section. Older versions of these sliding-contact rails generated considerable friction during movement, so were only suitable for basic applications. However, newer versions have selflubricating sleeves and other features to boost positioning accuracy and repeatability. In contrast, rolling-element linear-motion systems are either recirculating or non-recirculating. Non-recirculating types use rolling elements such as bearing balls, rollers and cam followers for movement. Recirculating types use some type of moving platform that houses a bearing block. This bearing block contains raceways with rolling elements that let the platform move along the rail with little friction. Recirculating types include linear guides and ball-bushing bearings. More specifically, rolling-element linear guides come in two basic versions—those with circular arc grooves and those with Gothic arc grooves. These groove choices are a result of industry evolution that’s enabled new geometries for better load handling. Circular arc grooves contact bearing balls at two points. The Gothic arch contacts the balls at four points for bidirectional load capacity. Another option for rolling-element linear motion is ball bushings that have a bushing nut

lined with recirculating bearing balls. This nut rides along a round shaft to allow axial movement. History lesson: In 1946, the manufacturer Thomson introduced ball bushings, and the technology established the basic mechanism of rollingelement linear-motion bearings. In today’s designs, the bushings may also have integral flanges to support axial loads. SLIDING-CONTACT RAIL GEOMETRIES A distinguishing feature of sliding carriage-and-rail setups is that manufacturers typically incorporate a ground groove in a rectangular track’s geometry (to serve as a working surface). Manufacturers typically build these rails in one of three shapes: • Rails with a boxway shape or square shape are simplest. Square rails excel at carrying large loads without a lot of deflection. Manufacturers often preload square rails, and most linear systems based on square rails do not selfalign. Square rails often have a smaller envelope size; the boxway rails handle the highest loads in all directions. • Rails with a dovetail shape (or twin rail) have male geometry that securely engages female saddle geometry. That boosts stability and load capacity, even in unusual orientations or applications with unsteady loads. • Round rails deflect less under load. In addition, systems based on round rails are inherently self-aligning, so are easier to install than the other options. No matter the type, rails are available in a wide range of sizes and lengths. ROLLING-CONTACT FUNCTIONS AND OPTIONS Rolling-element linear systems need little force to initiate motion. In addition, friction-force variations due to speed are minimal, so these systems can position loads with small and precise steps. The low friction also lets these systems move at high speeds without generating too much heat. That minimizes wear to help machinery maintain a level accuracy for much of the linear system’s operating life. Manufacturers produce rolling-contact guides in several variations. The differences are in rolling element shape (ball or roller); rolling element size; whether the rolling contact is two or four-point; conformity of ball contact; whether the design has two, four, six or some other number of rolling-element rows; contact angle; and how the rolling-element rows are arranged—in an X or O configuration. All these design factors determine load capacity, rigidity and friction. For example, O-shaped arrangements can withstand higher torque than X arrangements. In general, the number of load-bearing rollingelement rows influences the load capacity … so more rail rows means more load capacity and rigidity. However, more rows makes systems more complex and costly. This linear plain bearing is PBC Linear Uni-Guide with a Frelon self-lubricating liner to lower the coefficient of friction, reduce wear, and boost load capacity.

DESIGN WORLD — MOTION

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REFERENCE GUIDE

Power Transmission

Here are more details on these rolling-contact options: • Rolling elements are either linear rollers or balls. Because the rolling elements recirculate in recirculating rolling-element guides, they have a nearly infinite stroke length. They are available on flat guide ways and guide way rails. Flat guide ways are available in single or double row rolling elements. Guide way rails are often square rails. • Non-recirculating roller type units have limited stroke length. Flat guide ways are dominant here and have either a grooved race compatible with crossed rollers, or non-grooved race, which uses cage and roller-type rolling elements. • Recirculating elements (ball or roller bearings) between the rail and the bearing block enable precise linear motion. The coefficient of friction with roller-elementbased systems is much less than with slide based linear motion guides … about 1/50th that of non-recirculating systems. Ball-type rolling element units are also subdivided into recirculating and non-recirculating types. The flat guide ways here typically use double row recirculating rolling elements. The guide way rail can be either round or square. If the raceway is not grooved, the rolling element is typically a linear ball bushing. If the raceway is grooved, the unit usually uses a ball spline. For square rails, the raceway is usually grooved. For ball-type rolling element units that are non-recirculating, the flat guide ways are grooved and use linear ball guides. The guide ways are round rail, without a grooved raceway, and use stroke bearings. QUICK NOTE ON FLUID-FLOATED BEARINGS Less common types of linear systems include hydrostatic or aerostatic linear-motion bearings. Because these systems have no mechanical contact, they are suitable for applications that need extremely accurate or quiet operation. Here’s how they work: A pressure regulator sends pressurized fluid between the rail and carriage. That lifts the carriage off the guideway by about 0.01 mm or so. Aerostatic versions use air as the fluid; hydrostatic linear bearings use specially formulated hydraulic oil. This type of guide is difficult to manufacture and expensive, but damps vibrations and allows for moves to 120 m/min and 10 g—useful for ultra-precision machines.

LINEAR-RAIL LUBRICATION Some linear-motion systems need periodic application of lubricant, but many are available pre-lubricated. In addition, a number of systems use self-lubricated moving elements, eliminating the need for lubrication during the useful life. Note that the rails, ways and guides of linear motion systems tend to pick up dirt and debris from their application environment. For this reason, use carriages and slides with some kind of wiper system to keep the systems clean. When selecting linear systems, engineers should consider space limitations, accuracy needs, stiffness, travel length, magnitude and direction of loads, moving speed and acceleration, duty cycle, and the application’s environment. Note that an excessively large load or an impact load can permanently deform the raceway surface whether the linear guideway is at rest or in motion. Most manufacturers offer tables on the basic dynamic load rating, which can help engineers determine the proper load ratings for a system. Another caveat about friction: Friction measurements are carried out on all profiled rail systems. The friction values are given in tables in the manufacturers’ respective product catalogs. The level of friction depends on load, preload and sealing, taking into account travel speed, lubricant and runner block temperature. The total friction of a runner block includes the associated rolling or sliding friction, lubricant friction, and the friction of any seals.

This Rexroth CKL Compact Module incorporates a linear motor to deliver high force density with a compact package … for travel velocities up to 5 m/sec. A ball rail with central relubrication helps the module deliver precise positioning and zero backlash.

DESIGN WORLD — MOTION

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LOCKING DEVICES

E S S E N T I A L I N F O R M AT I O N F O R

SHAFT COLLARS & LOCKING DEVICES LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL

IN THE

context of motion and machine design, locking devices are mechanical connections that attach powertransmission parts, such as gears, timing-belt pulleys and sprockets, to drive shafts. Locking devices keep rotary drive components secure and machines running. To put locking devices in context, here are common approaches to mount and lock drive components on shafts. • Keyways are notched geometry in a rotary component’s inner diameter to mate with notched geometry in the shaft. In many cases, a key or metal slug plugs into the notches to set the component’s radial orientation. Though prone to backlash and eventual failure, this locking method is still common in industrial applications and some drivetrains in consumer products. • Setscrews mount through the face of a rotary component to tension via threads through the component and shaft surface. These can mount rotary components that output unidirectional rotation in lightweight designs that aren’t subject to any shock. • Shaft collars clamp or screw-set onto shafts to act as mechanical stops and axially locate components and bearings on shafts. Solid versions that use setscrews can gouge shafts unless the engineer specifies flat-machined shaft sections. In contrast, collars with screwtightened tapers that clamp onto shafts are more reliable. One caveat: In applications subject to shock, taper-based collars need an undercut on the shaft to have a positive stop so they don’t turn free. Two-piece designs simplify installation. • Taper-locking devices are any components that use a wedge action from tightening a screw or screws to induce radial locking pressure at a hub and shaft bore. For example, QD bushings (short for quick detachable) are split rings with a screw that bridges the flange and taper opening. Typically (though not always) a few inches in diameter or smaller, screw tensioning clamps the bushing to the shaft and replicates a shrink fit.

This flange coupling from Ringfeder Power Transmission is for heavy-duty applications. It has shrink discs to integrate into machines without making the installer cool or heat the connections.

As a side note, traditional shrink fits are when a mounted component’s inner diameter comes to an interference fit with the shaft on which it mounts. The installer heats the component so it expands; when it cools to room temperature, the ID contracts and locks to the shaft.

This BLC Bearlok Shrink Disc from Whittet-Higgins Co. locks power-transmission components such as gears, conveyor rolls, sheaves, cam shafts, pulleys and sprockets to keyless shafts more securely than conventional collars. It’s balanced for high-speed applications and comes in alloy steel and black-oxide coated versions.

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DESIGN WORLD — MOTION

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POWER TRANSMISSION

RETAINING DEVICES &

Shown here are just some of 3,600 standard shaft collars, couplings, and mounts from Stafford Manufacturing Corp. for packaging machinery. Options include StaffLok hinged collars that simplify opening, closing, and clamping connections by hand, as well as Grip & Go handles that convert standard shaft collars into adjustable locators. The components come in aluminum, steel, stainless steel, and plastic in ODs from 1/4 to 6 in. Options and finishes abound.

maintenance & assembly tools BEARLOK

SHOELOK

BEARLOK Shrink Disc

BEARHUG

CLAMPNUT

TANGENTLOK

LOCKING DEVICE OPERATION AND CAVEATS

PRECISION NUTS & WASHERS

INCH and METRIC THREADS LEFT HANDED as well as RIGHT -HANDED

ADAPTER SLEEVE ASSEMBLIES

Materials of: CARBON, ALLOY and HARDENED ALLOY STEELS Materials of: ALLUMINUM and CORROSION RESISTANT STEEL NUTS & WASHERS

HARDENED TONGUE WASHERS

SPLIT COLLAR

RETHREADING DIES

ADJUSTABLE SPANNER WRENCH

BEARING ASSEMBLY SOCKET

-H

For applications of medium torque and above, double-taper locking devicesâ&#x20AC;&#x201D;more commonly called keyless locking devices or power locks, friction locks or shaft locksâ&#x20AC;&#x201D;connect radial power-transmission components to shafts by interference fit. These have inner and outer rings held together by bolts or capscrews. Internal inclined planes make the rings come together and expand inward (into the shaft) and outward (to the radial componentâ&#x20AC;&#x2122;s hub-bore inner diameter). That makes a two-way gripping force to hold components to shafts in a way thatâ&#x20AC;&#x2122;s rigid and free of backlash. There are some caveats. Locking devices expand to accommodate a range of shaft ODs and component-bore IDs, but design engineers should respect published ranges and pick a locking device thatâ&#x20AC;&#x2122;s sized to the machine application (or change the latter to match a standard locking device). In addition, locking devices only deliver top performance when theyâ&#x20AC;&#x2122;re installed correctly, with a torque wrench in a diametrical pattern â&#x20AC;Ś just as one lugs a tire to a vehicle. When selecting a mounting approach in conjunction with a coupling, match it to the application while remembering that locking devices work well with couplings in high-speed or reversing applicationsâ&#x20AC;&#x201D; engineered disc couplings, for example. (In contrast, locking devices are over-engineered for applications of below-average precision and basic couplings.) In addition, design engineers should specify a shaft finish thatâ&#x20AC;&#x2122;s not overly smoothâ&#x20AC;&#x201D;say, between 40 and 120 Raâ&#x20AC;&#x201D;so the locking device can hold fast, even under maximum load.

WHITTET-HIGGINS manufactures quality oriented, stocks abundantly and delivers quickly the best quality and largest array of adjustable, heavy thrust bearing, and torque load carrying retaining devices for bearing, power transmission and other industrial assemblies; and specialized tools for their careful assembly.

These clamp-style shaft collars are designed and manufactured by Ruland Manufacturing to have high holding power. Suitable for medical equipment, they are often used to guide, space, stop, and align. Precise face to bore perpendicularity is maintained by having TIR of less than or equal to 0.002â&#x20AC;?, which is critical when the collar is used as a load-bearing face or for aligning gears or bearings.

Visit our websiteâ&#x20AC;&#x201C;whittet-higgins.comâ&#x20AC;&#x201C;to peruse the many possibilities to improve your assemblies. Much technical detail delineated as well as 2D and 3D CAD models for engineering assistance. Call your local or a good distributor. 33 Higginson Avenue, Central Falls, Rhode Island 02863 Telephone: (401) 728-0700 â&#x20AC;˘ FAX: (401) 728-0703 E-mail: info@whittet-higgins.com Web: www.whittet-higgins.com

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DESIGN WORLD â&#x20AC;&#x201D; MOTION

4 â&#x20AC;˘ 2016

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Single Source Widest range of shaft collars including over 2,500 standard parts to simplify the design process and ensure the collar you need is available from stock.

carefully Made Shaft collars are manufactured from select north american bar stock in our Marlborough, Ma factory using proprietary processes developed over 75 years.

SHafT collar Hub ruland.com is your source for product specifications, cad models, technical articles, installation videos, live inventory, and application support.

Over

2,500

shaft collars for your

DESIGN.

Find CAD models for your next design at www.ruland.com

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3/21/16 4/29/16 12:16 1:43 PM PM

REFERENCE GUIDE

Power Transmission

The MINIRAIL carriage for this SCHNEEBERGER miniature guideway has a lubricant reservoir carrying LUBE S lubricant. It uses a capillary effect to apply tangential lubrication of the circulating bearings, no matter the installation orientation. So under normal conditions and appropriate loads, the reservoir works to 20,000 km of carriage travel.

REVIEW OF

LUBRICATION BASICS MILES BUDIMIR • SENIOR EDITOR • @DW_MOTION

IN ANY

system with moving parts, no matter how small or large, lubrication is essential. It performs a number of important functions including reducing friction, dissipating heat, and protecting components from corrosion and wear. Lubricants can be classified in a number of different ways, but usually are identified as either one of two kinds; oils or greases. Oil-based lubricants can be made from petroleum sources or newer synthetic oils. Greases have an oil base to which various thickening agents are added.

DESIGN WORLD — MOTION

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The most important parameters for evaluating lubricants include operating temperature, load, speed, viscosity, and application rate. Lubricants are available to accommodate a wide range of application needs. For instance, there are general-purpose greases that handle lubrication needs for general industrial uses as well as greases for special requirements and special applications. For example, there are greases for high temperatures and for low temperatures, as well as greases for high-load applications. There are also greases designed to be biodegradable as well as food-grade greases for use in food and beverage production facilities. Potential problems with lubrication can include two extremes of either using too little lubrication or using too much. Using too little lubrication can increase friction and heat, leading to premature component damage. On the

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4/29/16 11:58 AM

LUBRICATION

other hand, using too much lubrication can also generate additional heat, which can cause lubrication to break down thermally, ultimately leading to more component damage. Sticking to a maintenance schedule can help avoid damage due to improper or inadequate lubrication and ensure against premature equipment failure. LUBRICATION FOR MOTION CONTROL In motion control applications, lubrication plays a critical role, even though sometimes it can be an afterthought or taken for granted. All kinds of components need lubrication; from ballscrews and leadscrews to bearings, gears and motors. Lubrication is used to lubricate bearings in motors, linear motion components such as leadscrews and ballscrews as well as rails, ways and guides.

Leadscrew mechanisms using bronze nuts also need a lubricant, usually a thick damping grease. Leadscrew assemblies with plastic nuts can run well without lubricant due to the internal lubricants in the nut materials, but the use of a gel type lubricant will help increase allowable loading and extend life by reducing friction. If particulates are present, the screw should be cleaned before reapplying lubricant. Scheduled preventative maintenance should occur when there is no visible film remaining on the flanks of the screw thread. Grease should not be used in environments with significant particulate or debris that can load the grease and cause it to become an abrasive slurry. In this type of application, dry film lubricant should be used instead. PTFE coating is a dry film that creates a lubrication barrier between

“LUBRICANTS CAN BE CLASSIFIED IN A NUMBER OF DIFFERENT WAYS, BUT USUALLY ARE IDENTIFIED AS EITHER ONE OF TWO KINDS; OILS OR GREASES.“

Because ballscrews are a bearing system, they’ll need some type of lubrication to avoid metal-to-metal contact of the balls in the raceway. While the lubrication choice can be either oil or grease, it’s advisable to avoid solid additives (such as graphite) as they will clog the recirculation system. An NLGI no. 2 type grease is recommended but it should also depend on the application, whether foodgrade or another special type of lubrication is required. Ballscrews, especially those used in machine tools, generally require lubricants with EP additives to prevent excessive wear. The frequency of lubrication will vary depending on factors such as the move cycle characteristics, or contamination in the environment.

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a metal substrate and a polymer bushing or lead nut. It is well suited for use with plastic nuts and stainless-steel leadscrews. Lubrication maintenance intervals can be eliminated and the coating does not attract particulate like a gel lubricant. There are linear motion systems that require periodic application of a lubricant, but most are available pre-lubricated. In addition, a number of systems use selflubricated moving elements, eliminating the need for lubrication during the useful life. The rails, ways and guides of linear motion systems tend to pick up dirt and debris from their application environment. For this reason, it’s good to use carriages and slides with some kind of wiper system to keep the systems clean.

DESIGN WORLD — MOTION

4/29/16 11:58 AM

REFERENCE GUIDE

BASICS OF

ELECTRIC MOTORS

Power Transmission

MILES BUDIMIR • SENIOR EDITOR • @DW_MOTION

AC MOTORS All electric motors convert electrical energy to mechanical energy. Motors are typically divided into either ac— alternating current, or dc—direct current. The main difference is that ac motors take an input of ac current, while dc motors use dc current. For ac motors, speed control is done by varying the voltage and frequency (along with the number of magnetic poles) while on dc motors control is achieved by varying voltage and current. There is another common way to break down ac motors that is based on the magnetic principle that produces rotation. So there are two fundamental types of ac motors; induction motors and synchronous motors.

In induction motors, the key idea is the rotating magnetic field. The most common source of this in ac motors is the squirrel cage configuration. This is essentially two rings, one at each end of the motor, with bars of aluminum or copper connecting the two ends. Induction motors have properties that make them especially well suited to a number of industrial as well as home appliance applications. For starters, they are simple and rugged motors that are easy to maintain. They also run at constant speed across a wide range of load settings, from zero to full-load. The only drawback is that induction motors are generally not amenable to speed control, although the availability of sophisticated variablefrequency drives means that even induction motors, usually three-phase induction motors, can now be speed controlled as well. The other type of ac motor is a synchronous motor. Synchronous motors are so named because they run synchronously with whatever the frequency of the source is. The motor speed is fixed and doesn’t change with changes to the load or voltage. These motors are primarily used where the requirement is precise and constant speed. Most synchronous motors are used in heavy industrial applications, with horsepower ratings ranging from the low hundreds up to thousands of hp. Synchronous motors can be used in motion control applications, but there are some down sides to using these motors. Because of the rotor size, the motor’s response in incrementing applications is typically not good.

ClearPath brushless servomotors from Teknic include a DSP-based vector servodrive, high-resolution encoder, and controller. The compact motors are low cost to let machine builders replace ac induction, stepper, dc brush, and other servomotors without sacrificing performance.

DESIGN WORLD — MOTION

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MOTORS

Also, because acceleration of inertial loads may not be as high as other motor types, these motors may operate at irregular speeds and produce undesirable noise. And generally, synchronous motors are larger and more costly than other motors with the same horsepower rating. DC MOTORS Motors characterized as dc generate a magnetic field via electromagnetic windings or permanent magnets. According to most common industry naming conventions, there are three dc motor subtypes: brush motors, permanent-magnet (PM) motors, and universal motors. Many larger dc motors still employ brushes and wound fields, but PM motors dominate fractional and integral-horsepower applications below 18 hp. That being said, PM motors are increasingly common in many designs. In a brushed dc motor, the magnet acts as the stator. The armature is integrated onto the rotor and a commutator switches the current flow. The commutator’s function is to transfer current from a fixed point to the rotating shaft. Brushed dc motors generate torque straight from the dc power supplied to the motor by using internal commutation, fixed permanent magnets, and rotating electromagnets. Brushless dc (BLDC) motors, on the other hand, do away with mechanical commutation in favor of electronic commutation, which eliminates the mechanical wear and tear involved with brushed dc motors. In BLDC motors, the permanent magnet is housed in the rotor and the coils are placed in the stator. The coil windings produce a rotating magnetic field because they’re separated from each other electrically, which enables them to be turned on and off. The BLDC’s commutator does not bring the current to the rotor. Instead, the rotor’s permanent magnet field trails the rotating stator field, producing the rotor field. STEPPER MOTORS Stepper motors are one of the most common motors used in motion control applications. They’re used mostly in positioning applications and have the advantage of being able to be accurately controlled for the most precise positioning applications, down to fractions of a degree without the use of feedback devices such as encoders or resolvers. They are operated in open-loop (not closed-loop), without the need for tuning parameters as in closed-loop servo systems. Steppers are generally classified by the number of allowable steps they can be commanded to move. For instance, a 1.8 degree step motor is capable of 200 steps/revolution (1.8 x 200 = 360 degrees, or one full revolution) in full-step mode. If operated in half-step mode, each step becomes 0.9 degrees and the motor can then turn 400 steps/revolution. Another mode called microstepping subdivides the degrees per step even further, allowing for extremely precise movements. There are several different stepper motor technologies including permanent magnet motors, variable reluctance, and hybrid types. The principle of operation for stepper motors is fairly straightforward. Traditional variable reluctance stepper motors have a large number of electromagnets arranged around a central gear-shaped piece of iron. When any individual electromagnet is energized, the geared iron tooth closest to that electromagnet will align with it. This makes them slightly offset from the next electromagnet so when it is turned on and the other switched off, the gear

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REFERENCE GUIDE

Power Transmission

moves slightly to realign. This continues with the energizing and de-energizing of individual electromagnets, thus creating the individual steps of motion. Stepper motors are relatively inexpensive and can be run open loop, requiring no feedback devices. Also, because the speed is proportional to the frequency of the input pulses, a wide range of speeds is attainable. However, while stepper motors are capable of producing high torque at low speeds, they generally are well suited for lower power applications not for applications requiring lots of torque to move heavier loads. They are best for applications requiring the control of rotation angle, speed, and position. A few drawbacks are that not properly controlling the motor can produce undesired resonance in the system. Also, stepper motors are generally not easy to operate at extremely high speeds. And as the motor speed increases, torque decreases. A stepper motor’s low-speed torque varies directly with current. How quickly the torque falls off at higher speeds depends on a number of factors such as the winding inductance and drive circuitry including the drive voltage. Steppers are generally sized according to torque curves, which are typically specified by the manufacturer. SERVOMOTORS The hallmark of any servomotor is the presence of feedback and closed-loop control. Servomotors provide precise control of torque, speed or position using closed-loop feedback. They can also operate at zero speed while maintaining enough torque to maintain a load in a given position. Servomotors have several distinct advantages over other types of motors. For starters, they offer more precise control of motion. This means they can accommodate complex motion patterns and profiles more readily. Also, because the level of precision offered is high, the position error is greatly reduced. The electric motor itself can be either an ac or a dc motor. Under the dc heading,

DESIGN WORLD — MOTION

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brushed dc servomotors are generally less expensive than brushless servos, but do require more maintenance due to the brushes needed for motor commutation. Brushless servomotors are more expensive than brushed dc motors. Generally, these are used in applications requiring higher torque. Brushless dc servomotors are highly reliable and virtually maintenance free. However, the drives for brushless dc servomotors are more complex because the commutation is done electronically rather than mechanically as in the brushed dc motor. Another way to classify servomotors can be as either single-phase or three-phase motors. Motors of the single-phase variety can range from the simple and inexpensive brushed dc motors to voice coils for small microand nano-positioning applications. Servomotors also require a form of feedback, often with the feedback device, such as an encoder, built right into the motor frame. The feedback signal is needed by the control circuitry to close the control loop. It is this closed-loop control that gives servomotors their precise positioning ability. Lastly, the control circuitry typically involves a motion controller, which generates the motion profile for the motor, and a motor drive which supplies power to the motor based on the commands from the motion controller. Servomotors are used in many different industrial applications from machine tools, The MCM series of synchronous packaging machinery, communications servomotors from Lenze are optimized for a range of and robotics applications to newer positioning tasks, including applications such as solar panel control robotics, packaging and a broad range of automation control equipment and handling applications. The diversity of applications systems. Featuring IP65-rated means that servomotors are designed for protection class housings, the motors come in power ratings general-purpose indoor environments but up to 3.35 hp and torque also for specialized situations requiring ratings to 233.66 in-lb. them to withstand extreme temperatures and pressures outdoors as well as the special demands of food processing industries in washdown environments.

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4/29/16 12:05 PM

The Only Coupling To Earn Its Wings

The NEW patented Baldor•Dodge® Raptor takes coupling innovation to greater heights. Utilizing a patented winged element design for higher bond strength and improved fatigue resistance, the Raptor delivers:

• Longer driven equipment life and increased reliability

• Easier installation and reduced maintenance • Drop-in interchangeability The Raptor is backed by over 50 years of natural rubber expertise and an industry leading 5-year warranty. Expect a higher level of reliability with the new Baldor•Dodge Raptor coupling. baldor.com

479-646-4711

Baldor_PTGuide4-16.indd 83

Raptor’s slotted clamp rings offer more clearance at the bolt holes for an easier installation than competitive designs.

Download a QR reader app and scan this code for more information. www.baldor.com/dodgeraptor

4/29/16 1:43 PM

REFERENCE GUIDE

Power Transmission

MILES BUDIMIR • SENIOR EDITOR • @DW_MOTION

BASICS OF

POSITIONING STAGES

Linear stages for extremely fine positioning, such as the V-52x series from Physik Instrumente, feature a voice coil linear motor direct drive with 0.1-micrometer resolution. An integrated optical linear encoder and precision crossed roller bearings with anti-creep cage assist provide high positioning resolution and guiding accuracy.

DESIGN WORLD — MOTION

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POSITIONING

stages and tables are a part of many motion systems. Stages or tables, whether linear or rotary, are complete motion sub-systems themselves. That is, they’re comprised of components such as linear motion elements, motors or actuators, encoders, sensors and controllers. Stages have continued to evolve as their components improve. Some key developments include better mechanical components and innovations in feedback and control that are improving metrology, particularly in high-end stages. As a result, today’s positioning stages can do many things including making moves with incredible accuracy, synchronizing complicated axis commands, and optimizing travel from coarse and fine drives in tandem, closing the loop on one common position feedback. Stages and tables are used in a wide range of high-performance applications such as industrial robots, fiber optics and photonics, vision systems, machine tools, semiconductor equipment, medical component laser machining, micromachining, electronic manufacturing, and other industrial automation applications. Stages can provide one of several different types of motion. They can be linear, rotary, or even lift types (Z-axis positioning stages). Among these, they can be configured in many different ways including movement in one direction (or axis) only, in multiple directions (X-Y positioning), or for extremely small and precise movements, as in nanopositioning applications where moves are in the micro- or nano meter range.

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4/29/16 12:22 PM

PERFORMANCE

POSITIONING STAGES

MATTERS

At Primatics, when we tell you that our precision

The drive mechanisms for positioning stages and tables can also vary significantly, depending on a number of factors including cost and desired accuracy. For instance, stages can be direct-drive types driven by linear servomotors or by a combination of motors and gearing and couplings, and can be linear or rotary actuator driven (either using electric actuators, or even pneumatic of hydraulic actuation). Other methods can include belt and pulley systems, ballscrews or leadscrews. Precision and accuracy requirements can also dictate design decisions such as the components used in assembling a positioning stage. One kind of component used in stages where reliability and high accuracy are desired

4 • 2016

PositioningStages_PTGuide_V2-mb.indd 85

are air bearings. Air bearings support a load with a thin film of pressurized air between the fixed and moving elements. They are typically referred to as aerostatic bearings, because a source of pressure rather than relative motion supplies the film of air. Unlike ordinary bearings, the surfaces of an air bearing do not make mechanical contact, so these systems do not need to be lubricated. Because the surfaces do not wear, the systems don’t generate particulates, which makes them suitable for clean-room applications. When supplied with clean, filtered air, the bearings can operate without failure for many years.

DESIGN WORLD — MOTION

motion products will perform to specification, you can be certain they will do just that. And, we have the data to back it up. We build high performance motion solutions that integrate easily and function seamlessly with complex automated systems. Our clients experience a high correlation between the test data we provide and the performance they are measuring in the field.

When performance matters, Primatics delivers! The PXL33B is small form factor linear stage, optimized for higher accuracy, repeatability, and nanometer level minimum incremental motion.

primatics.com • 541-791-9678 85

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REFERENCE GUIDE

Power Transmission

Image courtesy of Trelleborg Sealing Solutions

REVIEW OF

SEALS

MARY GANNON • SENIOR EDITOR • @DW_MARYGANNON

SEALS

These all-rubber HSS seals are specially developed to protect large size bearings under the tough operating conditions in heavy industrial applications such as metal rolling mills, mining equipment or wind turbines. A well-proven sealing lip design and a new concept of reinforcement provides high stability. Image courtesy of SKF

Seals_PTGuide_V4.indd 86

perform a vital job in any power transmission system—they keep dirt and other ingress materials from entering and damaging critical, internal components. They also have the equally important job of preventing leakage of necessary lubricants, such as oil, grease or hydraulic fluid. Molded seals and v-shaped seals are two of the most common seals found in power transmission applications. V-shaped seals, such as wipers, are used most commonly in fluid power systems to prevent contaminants from entering a system while allowing lubricating oils to return to a system on inward stroke of the hydraulic piston. Molded seals, which are more common in power transmission applications, can be further divided into O-rings, radial lip seals and shaft seals. O-rings are one of the most common types of seals because of their simple and inexpensive construction. They are designed to create a seal

DESIGN WORLD — MOTION

4 • 2016

between the interfaces of two or more components. They generally consist of an elastomer ring with a circular cross section and are usually placed in a groove. They are used frequently in hydraulic components, particularly on cylinder pistons and rotating pump shafts. Mechanical face seals, or heavy-duty seals, are used in extreme applications, such as bearings, gearboxes, turbines and machinery that is used in extremely tough and dirty environments, such as mining and agriculture. They feature two metal seal rings identical in nature that mount separately on a lapped face seal. A flexible, elastomer element centers the metal rings, allowing one half to rotate while the other remains still. While many seals are designed primarily to keep debris from entering a machine, radial lip seals are designed to keep lubricants within a machine that has rotating or oscillating parts. These seals are available as one of two types— spring loaded and non-spring

Some seals — such as this Centritec Seal from the Carlyle Johnson Machine Co. — work even in vertical shafts for rotating machinery. This particular design uses centrifugal pressure and includes a sump to collect lubrication when equipment stops (so there’s no weepage). They’re appropriate for conveyors, gearboxes and heavy equipment.

motioncontroltips.com | designworldonline.com

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SEALS

loaded. Each is suited to a particular type of lubricant, grease or oil. Non-spring loaded seals are suited for applications that use a highly viscous lubricant and operate at slower shaft speeds. Spring-loaded seals are best paired with lubricants with low viscosity and higher speeds. The spring helps the seal lip maintain its contact with the shaft even as the seal material itself breaks down. In addition to keeping contaminants out and fluids in, rotary and shaft seals have the extra benefit of providing low friction and resistance to wear, thus extending component life. When selecting a seal, fluid or lubricant type, material compatibility is critical. The four most commonly used materials for sealing applications are polyurethane (PU), acrylonitrile-butadiene-rubber (NBR), fluoro rubber (FKM), and polytetrafluoroethylene (PTFE). For example, PTFE is common in hydraulic systems for its resistance to high temperatures and corrosive chemicals and fluids. Nitrile rubber provides wear and aging resistance for lower temperature applications. FKM is best in higher temperature applications, or where extremely aggressive fluids are present.

PTFE is one of the most commonly used materials in O-ring seals, particularly in hydraulic systems. They offer resistance to high temperatures and corrosive fluids and chemicals. Image courtesy of Trelleborg Sealing Solutions

MAKE THE CONNECTION

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www.masterbond.com 4 • 2016

DESIGN WORLD — MOTION

4/29/16 12:31 PM

REFERENCE GUIDE

THE BASICS OF

Power Transmission

SHOCK & VIBRATION ABSORBERS MARY GANNON • SENIOR EDITOR • @DW_MARYGANNON

MOTION

is present in almost all industrial automation systems. Stopping or changing the direction of that motion releases kinetic energy, which can cause shock and vibration to occur. Any sudden shock in a system can cause immediate damage to the overall machine and the components it may be manufacturing or processing. And consistent vibration inputs can cause damaging fatigue over time. This is why it’s necessary to decelerate a system smoothly through the use of shock and vibration attenuation components. Based on the type of inputs present in the application, vibration and shock attenuation components can be comprised of shock absorbers, linear dampers, wire rope or spring isolators, elastomeric isolators, air springs, or structural damping treatments. These devices help manufacturers reduce equipment downtime and costly cycle time limitations. These products can be used in a broad range of applications, from the rate control mechanisms that slow the motion of the overhead luggage bin or seat recline on commercial aircraft, to the isolators which keep GPS systems from losing signal or becoming damaged on farm and construction equipment as they harvest crops or pave roadways. Most shock absorbers achieve their damping characteristics through the use of hydraulic fluids. The fluid is pushed by a piston and rod through small orifice holes to create damping, and this action compresses some type of gas. This in turn creates a spring force to return the rod back to its starting position when the load is removed.

RIGHT: Material pads such as these custom Sorbothane components can isolate vibrations. The manufacturer designs and manufactures them in a variety of shapes, sizes and durometers. Each part is specific to the design and function requirements of end products and set client parameters.

DESIGN WORLD — MOTION

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SLABS OF MATERIAL ALSO DAMP VIBRATION Besides mechanical devices, elastomer and other synthetic and rubber pads can also damp vibration and isolate shock loads. These material blocks, tubes, bushings and washers dissipate energy in a variety of applications. Manufacturers usually tailor the geometry, thickness and durometer of the material pieces to meet specific design requirements. Common uses are in lab and testing equipment, aerospace, foundations for presses, plants and machines, under cranes, as impact plates, for pipelines and bridges, and in other heavy-duty applications. In some cases, the manufacturer assembles the material in layers to create strong cushioning plates that protect machinery subsystems against impacts and isolate vibration and structure-borne noise. For example, PAD plates from ACE Controls withstand compressive loads to 10,000 psi (69 N/ mm2) depending on plate form and size. Another custom product called Sorbothane (from a company with the same name) is a thermoset that attenuates shock with near-faultless memory. That means its deformation is elastic and not plastic, so pads of the material reliably return to their original shape. Custom pieces of the material work for vibration damping, acoustic damping and isolation. Sorbothane works by turning mechanical energy into heat as the material is deformed. Molecular friction generates heat energy that translates perpendicularly away from the axis of incidence. Designed to meet specific requirements such as load, area, and natural frequency, many of these padding materials come in soft, rubberlike consistencies that are forgiving in most environments. Predicting the natural frequency of an application lets material manufacturers target known disturbance frequencies to dissipate energy. The lower the ratio of natural system frequency to disturbance frequency, the more it’s possible to isolate problem vibrations. TOP: SLAB damping pads from ACE Controls are made of a viscoelastic PUR and adapt to myriad applications. A calculating tool helps users configure pieces with product engineers.

4 • 2016

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4/29/16 12:51 PM

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Motion Control Custom control of hand forces

Power Transmission

Expect more than Automation Control!

REFERENCE GUIDE

Deceleration & Vibration Technology:

Vibration Control Isolate unwanted vibrations

Industrial shock absorbers are available in a variety of sizes and styles to help prevent the sudden release of kinetic energy in a system, reducing potential and catastrophic machine damage. Photo courtesy ACE Controls

Safety Products Protection for all machine designs under any condition

Shock absorbers and dampers are generally made of highstrength steel to handle the pressures from the internal hydraulic forces. Elastomeric seals prevent the fluid from leaking out of the cylinder, and special plating and coatings keep the units protected from harsh operating environments. Recent and ongoing developments in sealing technologies and in the internal designs of shock absorbers and dampers have allowed for longer service life and more compact designs. Ongoing research in the field of noise attenuation (high frequency, low amplitude vibration) has led to an increased effectiveness in noise reduction technologies. A unique application for these types of hydraulic damping devices has come with the increased awareness for seismic and environmental protection of our infrastructure (buildings and bridges, for example). By adding damping to these critical structures, energy is absorbed by the hydraulic devices instead of damaging the structure. Vibration isolation products rely generally on mechanical designs to achieve their isolation characteristics. A spring function provides support for the mounted equipment, while decoupling it from the vibration source. Friction and elastomeric material properties give the isolators their damping characteristics. Isolators can be made from a variety of materials. Wire rope and spring isolators can be made from carbon steel, stainless steel or aluminum. Elastomeric isolators generally have metallic

Automation Control Optimum tuning for any design

by ACE

More Info? Tel. 800-521-3320 Email: shocks@acecontrols.com

90 Download a CAD fileWORLD or our—product DESIGN MOTION

sizing software at: www.acecontrols.com

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motioncontroltips.com | designworldonline.com

4/29/16 12:52 PM

SHOCK & VIBRATION ABSORBERS

components that function as mounting brackets, separated by an elastomeric material that provides the stiffness and damping desired. Common elastomeric compounds include natural rubber, neoprene and silicone; however, a vast selection of compounds and compound blends can be used to achieve different characteristics specific to the application. Air springs are comprised of metallic end fittings coupled by a composite elastomeric-based bladder that contains the compressed air used to provide isolation. These single-acting designs are comprised of a pressurized bladder and two end plates. As air is directed into the air bladders, they are expanded linearly.

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All of these reusable designs are selfcontained, offering a number of advantages over any other technology that may require outside componentry. For example, hydraulic systems may require plumbing while electrical systems may require wiring and power. Energy or power dissipation is key when selecting a damper or shock-absorbing device. The size and characteristics of the device are based on these inputs, so it is generally the first consideration to make. Dynamic spring rate and damping are the two biggest considerations when selecting an isolator. These characteristics will define the natural frequency (sometimes referred to as resonant frequency) of the isolation system and are important in achieving the desired performance.

4 • 2016

Wire rope isolators reduce system vibration, which can cause damaging fatigue over time. Photo courtesy ITT Enidine

DESIGN WORLD — MOTION

4/29/16 12:55 PM

REFERENCE GUIDE

ACE Controls Inc. ..................................................... 90 All Motion ................................................................. 81 Altra Industrial Motion Corp. .................................... 53 AMETEK PMC ............................................................ 1 AMETEK/DFS (Windjammer) .................................... 21 AutomationDirect ....................................................... 9 Baldor Electric ....................................................83, BC BellowsTech. LLC ...................................................... 43 Bison Gear & Engineering Corp. .............................IBC Bodine Electric Company ......................................... 65 Carlyle Johnson ........................................................ 22 Centa Corporation ................................................... 87 CGI, Inc. ............................................................. 12, 13 Custom Machine and Tool Co. Inc. .......................... 29 DIEQUA Corporation ............................................... 59 Dunkermotoren, part of AMETEK ............................ 71 GAM Gear ................................................................ 47 Groschopp. Inc ......................................................... 67 Harmonic Drive ......................................................... 61 Haydon/Kerk .............................................................. 3 igus, inc. ............................................................. 24, 25 Intech ........................................................................ 63 ITT Enidine ............................................................... 89

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Power Transmission

Ad Index KHK USA Inc. ............................................................ 55 Kuebler Inc. .............................................................. 45 Martin Sprocket ........................................................ 36 Master Bond ............................................................. 87 Neugart USA Corp. .................................................. 57 NSK Precision ........................................................... 17 PBC Linear ................................................................ 73 PITTMAN .................................................................... 7 Primatics, Inc. ........................................................... 85 Promess Inc. ............................................................... 2 Power Transmission Distributors Association ........... 49 R+W America ........................................................... 48 Rotor Clip Company, Inc. ......................................... 39 Ruland Manufacturing .............................................. 77 SAB North America .................................................. 33 Serapid Inc. .............................................................. 19 Servometer ............................................................... 43 SEW Eurodrive .......................................................... 51 Teledyne LeCroy ......................................................... 5 THK America, Inc. .................................................... IFC Whittet-Higgins Co. .................................................. 76 Zero-Max, Inc. ........................................................... 23

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DESIGN WORLD does not pass judgment on subjects of controversy nor enter into dispute with or between any individuals or organizations. DESIGN WORLD is also an independent forum for the expression of opinions relevant to industry issues. Letters to the editor and by-lined articles express the views of the author and not necessarily of the publisher or the publication. Every effort is made to provide accurate information; however, publisher assumes no responsibility for accuracy of submitted advertising and editorial information. Non-commissioned articles and news releases cannot be acknowledged. Unsolicited materials cannot be returned nor will this organization assume responsibility for their care. DESIGN WORLD does not endorse any products, programs or services of advertisers or editorial contributors. Copyright© 2016 by WTWH Media, LLC. No part of this publication may be reproduced in any form or by any means, electronic or mechanical, or by recording, or by any information storage or retrieval system, without written permission from the publisher. Subscription Rates: Free and controlled circulation to qualified subscribers. Non-qualified persons may subscribe at the following rates: U.S. and possessions: 1 year: $125; 2 years: $200; 3 years: $275; Canadian and foreign, 1 year: $195; only US funds are accepted. Single copies $15 each. Subscriptions are prepaid, and check or money orders only. Subscriber Services: To order a subscription or change your address, please email: designworld@halldata.com, or visit our web site at www.designworldonline.com POSTMASTER: Send address changes to: Design World, 6555 Carnegie Ave., Suite 300, Cleveland, OH 44103

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4 • 2016

motioncontroltips.com | designworldonline.com

5/2/16 9:34 AM

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Raptor’s slotted clamp rings offer more clearance at the bolt holes for an easier installation than competitive designs.

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4/29/16 1:46 PM