Sensors, automation and control technology by Faruk Kartal

ifm electronic gmbh Sensors, networking and control technology for automation Training manual

Shaft Encoders

Training manual for shaft encoders (September 2003) Guarantee note: All data published using this medium are ifm's intellectual property or were given to ifm by customers or suppliers for exclusive use. We explicitly point out that no part of this publication may be used (in particular reproduced, distributed and placed in the public domain) nor modified or rearranged without prior written permission by ifm. This manual was written with the utmost care. Nevertheless, we cannot guarantee that the contents are correct and complete. Since errors cannot be avoided despite all efforts we appreciate your comments. ifm electronic gmbh, VTD-STV department, Teichstr. 4, 45127 Essen, phone: +49 201/2422-0, Internet: http://www.ifm-electronic.com

Contents: 1

Introduction........................................................................................................................ 6 1.1

Measuring systems .................................................................................................................. 6 1.1.1

1.2

Applications for shaft encoders ............................................................................................... 6 1.2.1 1.2.2

1.3 1.4 1.5

Application examples of shaft encoders................................................................................... 7 Digital signals.......................................................................................................................... 8 Measuring device and measuring system ................................................................................. 9 On the contents .................................................................................................................... 10

Techniques and methods of electronic linear measurement ............................................... 11 3.1

Analogue systems ................................................................................................................. 11 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5

3.2

Mechanical shaft encoders .......................................................................................................13 Oscillator sensors .....................................................................................................................14 Inductive system.......................................................................................................................14 Photoelectric shaft encoders ....................................................................................................14

Shaft encoders of ifm electronic........................................................................................ 16 4.1 4.2

Potentiometers.........................................................................................................................11 Resolvers ..................................................................................................................................11 Inductive principle ....................................................................................................................12 Magnetic principle ...................................................................................................................12 Capacitive principle ..................................................................................................................13

Digital systems ...................................................................................................................... 13 3.2.1 3.2.2 3.2.3 3.2.4

Rotational movement.................................................................................................................7 Linear movement .......................................................................................................................7

Layout .............................................................................................................................. 10 2.1

Shaft encoders as a standard means of measuring .....................................................................6

DIADUR method ................................................................................................................... 16 Shaft encoder types of ifm electronic..................................................................................... 17

Shaft encoders.................................................................................................................. 18 5.1

Incremental shaft encoders.................................................................................................... 18 5.1.1 5.1.2 5.1.3 5.1.4 5.1.5 5.1.6 5.1.7 5.1.8

5.2

Absolute shaft encoders ........................................................................................................ 30 5.2.1 5.2.2 5.2.3 5.2.4

5.3

Shape and design.....................................................................................................................18 Coded disc ...............................................................................................................................19 Resolution - mechanical ...........................................................................................................20 Signal generation .....................................................................................................................20 Pulse generation and analogue signals .....................................................................................23 Wiring of an incremental encoder ............................................................................................27 Detection of the direction of rotation for the direction of counting..........................................28 Pulse multiplication ..................................................................................................................29 Resolution ................................................................................................................................32 Singleturn shaft encoders.........................................................................................................32 Multiturn shaft encoders ..........................................................................................................34 Code types...............................................................................................................................35

Comparison of absolute shaft encoders and incremental shaft encoders................................ 39

5.4

Data transmission ..................................................................................................................40 5.4.1 5.4.2 5.4.3 5.4.4

5.5

Accuracy of the shaft encoder ...............................................................................................48 5.5.1 5.5.2 5.5.3

Solid shaft encoders ..............................................................................................................51 6.1.1

6.2

7.1 7.2

Connection cable ..................................................................................................................56 Connector .............................................................................................................................57

7.3 7.4

Laying the cable ....................................................................................................................59 Earthing and screening ..........................................................................................................59

Sockets/coupling ......................................................................................................................58

Mechanical data ............................................................................................................... 60 8.1

Maximum mechanical rotational speed ..................................................................................60 8.1.1

8.2 8.3 8.4 8.5 8.6

Mechanical rotational speed of the shaft encoder ....................................................................60

Shaft load..............................................................................................................................61 Shock resistance and vibration resistance ...............................................................................62 Housing material ...................................................................................................................62 Protection rating....................................................................................................................62 Operating temperature ..........................................................................................................62

Electrical data ................................................................................................................... 64 9.1 9.2 9.3 9.4

Voltage supply.......................................................................................................................64 Voltage supply via the external evaluation electronics ............................................................65 Sensor cables for encoders.....................................................................................................65 Current consumption ............................................................................................................66 9.4.1

9.5 9.6

Light-emitting diodes (LEDs) .....................................................................................................66

Current rating of the signal outputs.......................................................................................67 Signal frequency....................................................................................................................67 9.6.1 9.6.2

10 11 12 13

Mounting of hollow shaft encoders..........................................................................................55

Electrical connection ......................................................................................................... 56

7.2.1

Flange types for solid shaft encoders ........................................................................................52

Hollow shaft encoders ...........................................................................................................54 6.2.1

Dividing error ...........................................................................................................................49 Mark-to-space ratio..................................................................................................................49 Phase difference.......................................................................................................................49

Mechanical design ............................................................................................................ 51 6.1

SSI interface on the shaft encoder ............................................................................................40 SSI interface programming via software ...................................................................................43 SSI controller ............................................................................................................................44 Profibus-DP interface................................................................................................................46

Signal frequency and mechanical rotational speed ...................................................................67 Signal frequency and cable length............................................................................................68

Overview shaft encoders................................................................................................... 70 Operating instructions ...................................................................................................... 71 Data sheet........................................................................................................................ 72 Accessories....................................................................................................................... 74

13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9

Couplings for solid shaft encoders......................................................................................... 74 Angle flanges........................................................................................................................ 76 Bearing block ........................................................................................................................ 76 Isolating adapter ................................................................................................................... 77 Pinion and rack ..................................................................................................................... 77 Resilient base ........................................................................................................................ 78 Measuring wheel .................................................................................................................. 78 Fastening clamp .................................................................................................................... 80 Pulse divider, pulse stretcher.................................................................................................. 80 13.9.1 Pulse divider .............................................................................................................................81 13.9.2 Pulse stretcher..........................................................................................................................81

14 Mounting of shaft encoders.............................................................................................. 82 15 Calculation examples ........................................................................................................ 84 15.1 Linear measurement.............................................................................................................. 84 15.2 Switching frequency and mechanical rotational speed ........................................................... 84

16 Handling of shaft encoders ............................................................................................... 85 17 Applications...................................................................................................................... 86 18 Annex............................................................................................................................... 89 18.1 Competitors.......................................................................................................................... 89 18.2 Glossary of technical terms.................................................................................................... 89

19 Type key ........................................................................................................................... 93 19.1 Examples of the use of the type key ...................................................................................... 94

20 List of figures.................................................................................................................... 95 21 Index ................................................................................................................................ 98 22 Source ............................................................................................................................ 100

Introduction

In all areas of technology production and test processes are automated to an increasing extent. If only end stops or reference points are to be monitored, inductive or capacitive proximity switches or photoelectric sensors are the preferred choice.

1.1 Tools of automation

Measuring systems

The mechanical movements of robot arms, linear slides, rotary tables or slides often have to be controlled numerically. Measuring systems for lengths, angles and partial steps provide feedback about these movements to the controller.

1.1.1

Reliable

Shaft encoders as a standard means of measuring

Encoders are needed if high precision and short measuring times are required and if the processing of the information is to be carried out by means of electronic control systems. In the following especially angular and linear measurement will be discussed. There is a variety of measuring methods which will be briefly described below. Shaft encoders are standard units for angular and linear measurement. In many manufacturing and production processes they are indispensable as reliable transducers or pulse pickups. Shaft encoders are used where precise detection of lengths, positions, rotational speed, and angles is required.

Function

Shaft encoders transform mechanical movements into electrical signals.

Resistant

Shaft encoders have shown excellent performance in various applications, even in harsh environments with shock, dirt, changing temperatures and vibration. They are very reliable and have a long life. The photoelectric measuring principle enables high measuring accuracy as well as inexpensive versatile solutions which are especially adapted to automation technology.

Versatile

1.2

Applications for shaft encoders

Typical applications of linear measurement systems are woodworking machines, machine tools, robots and handling machines, textile machines, electronic scales, plotters and printers from the IT area as well as test equipment.

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1.2.1

Rotational movement

Encoders can be used without a lot of mechanical work being required wherever rotating machine parts are present. Flange, fixing holes and grooves enable easy connection to the rotating part.

1.2.2

Linear movement

Nearly every linear movement is connected with a rotational movement, for example a feed function with the rotation of a drive shaft. Furthermore a linear movement can easily be transformed into a rotational movement on the shaft encoder by means of a measuring wheel or a rack with a toothed wheel. Therefore encoders are often used for linear measurement. To convert a rotational angle into a distance a conversion factor is required which results from the geometry of the device as well as any transmission ratio or gear reduction.

1.3

Application examples of shaft encoders

Figure 1, Linear measurement and synchronous movement monitoring

Figure 2, Detection of rotational speed and angle measurement

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Figure 3, Bending systems and X-Y-recorders drawing tables

Figure 4, Level measurement and radar/aerial systems

Figure 5, Industrial robots

1.4

Digital signals

The measured values of angles or distances are in most cases required in digitised form so that they can be further processed in electronics connected downstream, e.g. a plc. For this reason the measurement is carried out digitally. The measuring system in the form of a shaft encoder assigns a digital output value to the analogue measured value as a length or an angle. Thus the output value of the shaft encoder represents the measured quantity in defined digital steps. Most digital length and angle measuring systems are based on standards with a periodic structure. By using different principles of physics periodical electrical signals are generated from which the measured value is derived.

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1.5 Measuring device Measuring system

Measuring device and measuring system

The measuring disc and detection system of the encoder are also called measuring device, sensor, transducer or encoder. They convert lengths or angles into electrical signals. A measuring system consists of the complete measuring chain. It may consist for example of a measuring disc, the scanning unit, the interpolation electronics, and a counter. The electronics and the counter can be integrated as interface electronics in the measuring device or the electronics connected downstream. For angle measurement the coupling between the machine shaft and the measuring device is to be regarded as part of the measuring system as well. ifm offers two different types of unit for the measurement of angles or lengths: incremental encoders absolute encoders Both the absolute and the incremental shaft encoders have advantages when compared with each other. They can also be combined in one unit.

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2 Keywords What does FAQ mean?

For a better understanding a few explanations regarding terms used in the text will be given to make reading the text and finding information easier. Keywords are indicated in the margin on the left, referring to the topic to be dealt with in the following section. This stands for Frequently Asked Questions. This term is used for example in the context of modern electronic media. Almost everybody starting to deal with a new unit faces the same questions. Sometimes an FAQ precedes a section instead of a keyword. To differentiate them from simple keywords, they are written in italics.

2.1

Characteristics of the shaft encoders

ifm-units Applications Annex

Much success!

Training manual

Layout

On the contents

This manual is to provide basic information on shaft encoders. Important terms and correlations are explained, state-of-the-art technology is described and technical data of ifm-units are presented. This results in the following structure. Other types of shaft encoders which are used are mentioned. Then follows a general overview of different encoder systems. This is to facilitate the correct classification of shaft encoders and to decide where they can be used and where they cannot be used. The knowledge of these features, their advantages and disadvantages is a prerequisite for their successful use. Here the data of ifm shaft encoders are stated and explained. Mechanical design, electrical features and use are described. Some units are presented. A few applications with illustrations are briefly described. This manual is to help you with your self-study as well. Therefore important terms are briefly explained again in the glossary of technical terms. The points which are essential for ifm shaft encoders are described in detail in the chapters preceding the glossary. The index will help to look them up. The type key for the ifm-specific units is briefly presented as well. Everybody should have these basics to be able to benefit from the chance this product offers and to use shaft encoders successfully.

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Techniques and methods of electronic linear measurement

Electronic signal processing mainly differentiates between the processing of analogue and digital signals. The information which is supplied by the different measuring systems is also differentiated. It is divided into analogue and digital systems/signal transmitters.

3.1

Analogue systems

3.1.1

Potentiometers

Potentiometers consist of a slide made of resistance material and a wiper contact. The wiper is only ever in contact with a small area of the resistance coil or surface. The position of the wiper contact results in a variable resistance value. Areas of application: Level measurement, measurement of valve positions, temperature measurement by means of a bimetal spring.

Figure 6, Potentiometer

3.1.2

Resolvers

Resolvers are synchro generators which precisely indicate the current position of the rotor. They belong to the group of absolute encoders. The design of the unit is similar to an electric motor or generator. Applications are robots and the military area (aeroplanes, tanks). S4 sine S2

R4 rotor R2 Îą

S1 cosine S3

Figure 7, Resolver

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3.1.3

Inductive principle

The units (well-known are the versions from the company Novotechnik) consist in principle of two ferrite cores which form a magnetic circuit between which printed coils with two closed rings are turned. Areas of application: Machine construction, conveyor technology, robots, printing industry, packaging industry, foundries, and rolling mills.

A M U1

Figure 8, Inductive principle (Novotechnik) A: reference element M: measuring element

3.1.4

Magnetic principle

Small permanent magnets are arranged on the circumference of a disc. The Hall sensor placed in front converts the alternating magnetic fields into electrical signals.

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N S

Figure 9, Magnetic principle

3.1.5

Capacitive principle

Two plates of a capacitor are moved in relation to each other on an axle. The resulting capacitance provides information about the position of the axle.

3.2

Digital systems

3.2.1

Mechanical shaft encoders

Mechanical shaft encoders generate a digital output signal. Switches or contacts on a control shaft are activated by cams. These units are also called cam-operated switchgroups. Areas of application: Conveyor systems with low resolution, transport belts and washing machines.

Figure 10, Mechanical shaft encoder (cam-operated switchgroup) A cam-operated switchgroup is free from wear and tear if the mechanical switches from figure 10 are replaced by inductive proximity switches.

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Figure 11, Cam-operated switchgroup with inductive proximity switches

3.2.2

Oscillator sensors

The oscillator sensors work according to the incremental principle and transmit digital signals. Usually U-shaped sensors are used for non-contact detection of a rack or a coded disc.

3.2.3

Inductive system

With this principle the teeth of a rotating toothed wheel are detected by means of an inductive proximity switch.

Figure 12, Inductive system

3.2.4

Photoelectric shaft encoders

On the edge of a round metal or glass disc transparent slits (segments or increments) are arranged. Binary output signals are generated by means of through-beam sensors in miniature format and subsequent electronics. The number of increments determines the resolution of a full circle.

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Figure 13, Incremental shaft encoder The photoelectric shaft encoders are discussed in this manual.

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Shaft encoders of ifm electronic

ifm electronic offers shaft encoders which function according to the photoelectric principle. In the past ifm electronic cooperated with different partners. Since 1990 ifm has been working with the company Heidenhain in Traunreut.

4.1

DIADUR method

The number of increments (bright and dark fields) on the glass disc are of vital importance for a high resolution of the encoder. The patented DIADUR method of Heidenhain allows to apply very fine structures on a glass disc. The DIADUR method is divided into six steps: 1. 2. 3. 4. 5. 6.

Cleaning of the glass disc (ultrasonic, without contact). Application of photoresist, pre-dried, hardened. Photoresist is a light-sensitive material which is applied in liquid form to a carrier material – in this case glass. The so-called working originals (negatives) are pressed onto the glass plate. The complete glass surface is coated with chromium and exposed via a mask. The chromium is washed off with a chemical solution. Chromium only adheres to the glass plate where the photoresist has been exposed.

Due to the many manufacturing steps the production of a DIADUR glass disc is very time-consuming. The advantages of a DIADUR glass disc are: • • •

Training manual

Very good contour sharpness of the lines. This results in a very high accuracy. The glass disc is largely resistant to chemical and mechanical influences. The system accuracy is approx. ± 1/20 grating mark for coded discs with up to 5,000 increments and ± 12 seconds of an angle for coded discs with more than 5,000 increments.

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4.2

Shaft encoder types of ifm electronic

The following photos show the standard types of shaft encoders of ifm electronic in alphabetical order â&#x20AC;&#x201C; referred to the ifm designation. The sizes of the encoders in the photos are not to correct scale. The designation of the individual shaft encoders always starts with a capital "R". The second capital letter is the designation of the type. It refers to the flange and the type of shaft. Example: RC stands for the type with round flange and solid shaft.

RA, incr., hollow shaft

RM, abs. SSI, hollow shaft

RN, abs., parallel, solid shaft

RB, incr., solid shaft

RM, abs., Profibus DP, solid shaft

RM, abs., SSI, solid shaft

R=, incr., hollow shaft

RU, incr., solid shaft

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RC, incr., solid shaft

RP, incr., hollow shaft

RV, incr., solid shaft

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Shaft encoders

Encoders convert mechanical movements like rotational or linear movements (rotation and translation)into binary/digital voltage values. They are transducers, mainly for rotational movements. In connection with mechanical converters like measuring wheels or racks incremental shaft encoders can also be used for linear measurements. Shaft encoders function according to the principle of photoelectric detection of the fine detection grids. Most shaft encoders are round. Even if the following information may seem superfluous: Shaft encoders have to be driven mechanically from outside on the shaft. Depending on the measuring and evaluation method a differentiation is made between: incremental shaft encoders absolute shaft encoders

5.1

Incremental shaft encoders

5.1.1

Shape and design

The main components of an incremental shaft encoder are shown in figure 14. They are: shaft (solid shaft or hollow shaft) mounting flange ball bearing coded disc detection system (LED, condenser/lens, detection grid, photo elements) electronics for generating the signals electrical connection (cable, connector) housing cap

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Figure 14, Incremental shaft encoder AG: detection rid; PE: photo elements; TS: coded disc; ES: electrical signals; RM: reference mark; KL: ball bearing; MF: mounting flange; WL: shaft; KD: condensor

5.1.2

Increments

Measurement

Coded disc

The core element of the encoder is the coded disc made of hardened and special surface-coated glass, see 4.2. DIADUR-. It is the carrier for the circular graduations or gratings. Due to the special glass it is possible to operate the encoder also at high temperatures without any major changes of the signal quality. On the outer edge of the coded disc there is the radial grid of lines and gaps (light and dark fields). These lines and gaps are called increments and they form the so-called incremental track. This incremental track forms the basis for the measurement of the encoder. With one complete revolution of the coded disc as many electrical signals are transmitted as there are increments on the coded disc. The coded disc is fixed to a shaft which protrudes through the housing.

Figure 15, Coded disc with increments

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5.1.3

Standard resolutions

Resolution - mechanical

The resolution is the number of physical light/dark fields on the coded disc of the encoder which are provided as voltage pulses per revolution of the coded disc. The mechanical resolution of an encoder cannot be modified. The number of increments on the coded disc depends on the resolution required in the application. For standard units there is a large variety of different resolutions per type. It usually starts with five and first continues in small steps, later the distances increase. The small incremental encoder RB for the voltage range of 10 â&#x20AC;&#x201C; 30 VDC for example is offered with the following resolutions in the ifm catalogue: 5, 10, 20, 25, 30, 40, 50, 60, 100, 125, 150, 200, 250, 360, 400, 500, 600 and 1,000. A different resolution always means a different encoder and thus a different article/order number. The maximum resolution which can be shown optically as light â&#x20AC;&#x201C; dark fields is 10,000 increments. The range of the resolution depends on the type. Resolutions deviating from the standard are available on request.

5.1.4

Signal generation

5.1.4.1 Through-beam method The signals are generated by means of the through-beam method. The through-beam method is the principle of photoelectric detection of fine detection grids. This detection principle can be compared to a miniaturised photoelectric through-beam sensor.

Figure 16, Photoelectric detection, through-beam method KD: condensor; AG: detection grid; TS: coded disc; PE: photo elements; RM: reference mark.

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5.1.4.2 Reference mark, zero index The reference mark is on a second track next to the incremental track. Once per revolution it generates a defined pulse, the so-called zero index, on a separate channel. 5.1.4.3 Scanning plate At a short distance opposite the rotatable coded disc with the increments there is a fixed scanning plate. It has a grating on four fields and the reference mark graduating on a further field.

0째

90째

180째

270째

Figure 17, Scanning plate, without reference mark grating Grating period

The four graduations of the scanning plate are shifted against each other by one-fourth of the grating period. One grating period = 360 degrees / resolution. The segments are adapted to the circle of the coded disc and therefore they are slightly curved. 5.1.4.4 Condenser All fields are penetrated by a parallel-orientated light beam which is emitted by a light unit consisting of an LED and a convex lens (condenser).

Lichtquelle

Figure 18, Light source and condenser With one rotation of the coded disc the light is interrupted periodically by the light and dark fields and its intensity is detected by silicon photo diodes. A photo element is assigned to each segment of the scanning plate. Sine wave

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5.1.4.5 Signal generation of the photo elements If a coded disc is rotated the photo elements for the incremental track generate four sinusoidal current signals, each of which is electrically phaseshifted by 90 degrees.

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0°

90°

180°

270°

90°

270°

180°

90°

0°

180°

270°

180°

90°

0°

90°

0°

180°

270°

I3 I1 I2 I4

Figure 19, Sine wave of the photo elements Sine curve I1: segment 0° Sine curve I2: segment 180° Sine curve I3: segment 90° Sine curve I4: segment 270° The photo element for the reference mark or the zero index generate a signal peak. The four sinusoidal photo-element signals are at first symmetrical to the zero line. 5.1.4.6 Photo elements The photo elements are connected in push-pull circuit thus creating two output signals which are electrically phase-shifted by 90°.

Figure 20, Connection of the photo elements DC component

Due to the connection in push-pull circuit the DC component is suppressed. The DC component is generated by scattered light of the adjacent fields of the detection grid. I3-I4

Ie1

I1-I2 Ie2 0°

90°

180°

270°

360°

Figure 21, Signal voltage

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5.1.5

Square-wave pulse train

Pulse generation and analogue signals

5.1.5.1 Square-wave pulse trains The sine curves Ie1 and Ie2 are converted into square-wave pulse trains by means of voltage comparators, thus generating two square-wave pulse trains which are phase-shifted to each other by 90°. The square-wave pulse trains are amplified in the output stage of the encoder and provided as electrical signals in the form of voltage pulses. I3-I4

Ie1

I1-I2 Ie2 0°

90°

180°

270°

360°

180°

90°

180°

Figure 22, Pulse generation 90-degree-shift

Due to the interaction of scanning plate and coded disc the electrical 90degree shift from channel A to channel B has a mechanical origin. This ensures that this shift remains the same for all rotational speeds of the coded disc. For simple counting operations it would be sufficient to only evaluate one output channel, but only by means of the second signal output which is shifted by 90 degrees it is possible to determine the direction of rotation or counting (see 5.1.7). 5.1.5.2 Signal evaluation As a standard an incremental shaft encoder provides three signal outputs: Channel A, channel B and channel 0 (zero index).

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A UB

C B

E E0

AS0

0 0

ASA

G A

ASB

B B

Figure 23, Signal generation, block diagram A: shaft; B: scanning plate; C: coded disc; D: voltage supply; E: signal outputs; AS0, ASA and ASB: signal output stages with inverted and noninverted outputs; E0: infrared reception transistor; F: condenser; G: light source; T0: pulse generation (Schmitt-trigger); V0: direct-current amplifier.

Signal sequence

The mark-to-space ratio of both output signals from channel A and channel B is 1 : 1 at all times. The sequence of voltage levels of the output channels of an incremental shaft encoder is as follows: 1. 2. 3. 4.

LOW level (voltage value zero). Voltage increase from LOW level to HIGH level (positive-going edge). HIGH level (voltage value of the operating voltage). Voltage drop from HIGH level to LOW level (negative-going edge).

If voltage is applied to the incremental shaft encoder it provides for each channel the level value which results from the position of the coded disc. A possible voltage change of a channel from no voltage to operating voltage does not cause any counting operation in the subsequent evaluation electronics. 5.1.5.3 Pulse diagram The duration of the individual pulse (ON/OFF) depends on the rotational speed of the coded disc. Thus it is not possible to indicate a time for the pulse length.

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180°

A 90°

NI 90°

Figure 24, Pulse diagram channels A, B, and zero index (NI)

Measuring step

Therefore the duration of an individual pulse is fixed electrically to the value 360 degrees. The ON pulse is present for the time of (electrically) 180 degrees, for the remaining 180 degrees the pulse has the value zero. The distance between channels A and B is electrically 90 degrees and depends on the speed and direction of rotation of the coded disc. The measuring step is the angular value which results from the distance between two edges of the two square-wave pulse trains of output A and output B. Without previous interpolation of the measured signals the measuring step corresponds to the fourth part of the grating period (90 degrees) of the radial gratings. 5.1.5.4 Zero index, channel 0 The zero index, also called zero pulse or reference mark, is generated only once per revolution of the coded disc. On the complete circumference of the index track there is only one segment. The position of the reference mark on the coded disc is also determined mechanically. As can be seen in figure 24 the relative duration of the HIGH level of the zero index is only half as long as that of channels A and B. Therefore the input circuitry must have an input frequency for the evaluation of the zero index which is four times higher than for the evaluation of channels A and B. With a high number of revolutions of the encoder the length of the zero index is shortened. The distance between the edges becomes shorter. In case of "slow" evaluation electronics/plcs this can lead to the signal not being detected even if the other channels can still be properly read. The zero index can be used to define a switch point, to count the revolutions or to synchronise a connected electronic counter. In addition to the mechanical position of the zero index on the coded disc the signal periods of channels A and B are used as reference values. The standard zero index is 90° long – see figure 24.For the ifm type RB for the voltage range of 10 to 30 V DC the length of the index is 360°.

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180°

B 45°

NI 360°

Figure 25, Zero index 360 degrees long (NI), type RB, 10 – 30 V Reference mark outside

To facilitate the determination of the zero index its approximate position is marked by a reference mark on the outside of some encoder types. For this purpose there is an indentation on the flange near the shaft. The same indentation is also on the front of the shaft. If both indentations are matched, the signal for the zero index is present on the output. For high resolutions the zero index is short and therefore manual positioning is difficult. 5.1.5.5 Inverted output signals For different encoders the three standard output signals (channels A, B and zero index)are additionally provided in the inverted state. The encoder then has six signal outputs in total: channel A and channel Anegated1; channel B and channel B-negated as well as zero index and zero index negated. A

Figure 26, Pulse diagram with inverted channels (NI: Zero index) Suppress interference

Due to the inverted signals it is possible to evaluate the voltage difference. Thus parasitic signals on long connection cables have almost no negative effect. Except for types RA and RB all HTL2 shaft encoders provide the inverted signals. 1

An expression like 'A-negated' is represented as an individual character or word by a line above the character or word (see Figure 26).

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HTL stands for high transistor logic. These are units with an operating voltage higher than 5 V DC.

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5.1.5.6 Sinusoidal signals For some incremental shaft encoders the sinusoidal voltages instead of the square-wave pulse trains are provided for the channels A and B. They can be processed in various ways in the input circuitry. These two sinusoidal increment signals are also phase-shifted by 90 degrees.

1Vss

0°

90°

180°

270°

360°

x Figure 27, Sinusoidal output signals (Vss = Vpp)

1 Volt peak-peak (Vpp)

The reference mark signal for the zero index is also available in analogue form. The voltage step has a nearly triangular shape of approx. 0.5 V. If sinusoidal voltage signals are provided the voltage level is 1 Volt from peak to peak. Cable lengths of up to 150 m are possible. The sinusoidal output signals can be digitised in an input circuitry (comparator). They are specially suitable for pulse multiplication – see below. They can also be used with digital drives to monitor the rotational speed even with very slow movements.

5.1.6

Wiring of an incremental encoder

The individual cores are differentiated by their colours and they have the same meaning for all incremental shaft encoders of ifm electronic. The cores which are available depend on the respective shaft encoder. Wiring of an incremental shaft encoder: brown green grey pink redzero index black blue white brown/green white/green lilac screen

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channel A channel A inverted (A-negated) channel B channel B inverted (B-negated) zero index inverted (zero index L+ (sensor) 0 V (sensor) +Ub (L+) Un (0 V) interference signal (inverted) housing

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5.1.6.1 Interference signal Some encoders have an interference signal as additional signal output. The interference signal indicates malfunctions of the shaft encoder like for example breakage of the supply cores, failure of the light source, soiling of the coded disc or the photo elements. A square-wave pulse train indicates the malfunction. If the wire for the interference signal has a LOW level, there is a malfunction. If the level is HIGH the unit is operational. For cable units the connection core (lilac) must be insulated if the interference signal is not used, in order to avoid any short circuits. Unlike for the useful signals, the output driver for the interference signal is not protected against short circuits.

5.1.7

Signal change

Detection of the direction of rotation for the direction of counting

The electrical 90-degree shift between channels A and B in connection with the dynamic signal changes is used by the subsequent evaluation electronics like programmable logic controllers (plcs) or electronic up/down counters to determine the direction of counting. The signal changes and signal states of channels A and B of the shaft encoder are decisive for the detection of the direction of rotation or counting. If the shaft encoder stands still there is no signal change. Input circuits cannot (yet) decide which is the current direction of counting. If voltage is applied to shaft encoders and evaluation/display electronics a signal change can take place on one or more output channels, depending on the position of the coded disc in the shaft encoder. However, this signal change is suppressed as counting pulse by the evaluation electronics because it was taken into account for the counting process before switching off the supply voltage. This ensures that the direction of counting is correctly determined when the measuring system is switched on and the coded disc starts moving. If the coded disc moves the positive signal change of channel A comes before the positive signal change of channel B and vice versa, depending on the mechanical direction of rotation.

B Figure 28, Signal change Phase discriminator

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The direction of rotation can easily be detected by means of a phase discriminator in evaluation electronics by evaluating the phase position of signal A to signal B.

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5.1.8 Duplication

Pulse multiplication

By means of logic switching elements like AND and OR gates the rising and falling square-wave pulse trains of channels A and B can be connected in such a way that the output signals have a higher resolution than the one determined by the mechanical division of the coded disc. Due to the electrical processing times of the required logic gates it is not possible to increase the number of pulses to any number in this case. A

B A B

& _ >1

A B

Figure 29, Duplication of the pulses

Multiplication (logic gates)

The circuitry from figure 29 can also be implemented with an exclusive-ORgate (XOR). Due to the pulse multiplication with logic gates the electrical 90-degree shift of channels A and B is lost. If the 90-degree shift is required it makes sense to use a shaft encoder with sinusoidal output signals â&#x20AC;&#x201C; see above. A further pulse multiplication is possible with the respective electronics.

Figure 30, Pulse multiplication

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Single evaluation Double evaluation Triple evaluation Quadruple evaluation

Multiplication from sinusoidal signals

Depending on which edge of a channel is evaluated the pulse trains shown in figure 30 and the related pulse multiplication can be implemented. Pulse train X1 represents a single evaluation. A reaction to the to the falling edge of channel A takes place. The number of pulses has not increased. Pulse train X2 is generated if there is a reaction both to the rising edge and to the falling edge of channel A. It is a double evaluation with double symmetrical number of pulses. A triple evaluation is shown in the pulse diagram X3. In addition to the rising and falling edges of channel A it also evaluates the rising edge of channel B. The pulse evaluation is triple, but asymmetric. Diagram X4 shows a quadruple evaluation. The rising and the falling edges of both channels are evaluated. The number of pulses has quadrupled and it is symmetrical. In the limit ranges wrong pulses may occur. The phase position of the channels must be observed exactly. The pulse length after the multiplication is to be set in such a way that with maximum rotational speed the newly generated pulses are about half as long as the original pulses of the output channels. The short signal duration resulting from this causes higher requirements as regards the electronics of the evaluation unit (plc or counter). For shaft encoders which generate sinusoidal signals of 1 Vpp , a multiple number of the mechanical resolution can be achieved (factor 10 and more) by means of linear interpolation. Pulse multiplication with sinusoidal signals as a basis has the advantage of the electrical 90-degree shift between the output channels A and B being maintained.

5.2

Binary numerical values

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Absolute shaft encoders

Absolute measuring systems determine the current absolute position of the measuring system in the form of clear code information by scanning the coded disc. They signal this position to the subsequent electronics as coded value in binary form. The special advantage is that this position value is available unchanged after a power failure. The exact position is also indicated if the encoder has continued to turn when no power was available. Wrong measurements due to wrong pulses and errors which add up are mostly excluded. Absolute shaft encoders convert rotational movements or positions into binary numerical values. Each angular position of the coded disc is provided as a binary numerical value. Binary figures consist of individual bits which can only take the values 1 or 0. For absolute shaft encoders the digital value 1 means that the level of the signal wire is HIGH. Therefore the digital value 0 corresponds to the LOW level. With their HIGH and LOW levels all signal outputs of absolute shaft encoders form a clear binary number. The prerequisite is of course that the signal wires are in the correct order corresponding to their value. The binary numerical value of an absolute shaft encoder consists of up to 13 bits. For each bit a separate signal wire is required. Angular positions, movements and positions can be determined by means of the binary numerical value.

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Figure 31, Coded discs Many tracks

Incremental signals

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In contrast to incremental shaft encoders the coded disc of absolute shaft encoders has considerably more tracks (see figure 31). The graduation carrier of absolute shaft encoders consists of a coded disc made of glass with several code tracks. Each individual track corresponds to one bit within the binary output value â&#x20AC;&#x201C; see above. These absolute shaft encoders also work according to the principle of the photoelectric detection of graduations. Transparent and non-transparent zones are distributed in concentric circles (= tracks)on the coded disc. On a fixed radial reading zone (photoelectric sensors detect the tracks)an exactly determined sequence of light â&#x20AC;&#x201C; dark fields results from each position of the disc. One or several scanning plates are arranged at a short distance to the rotatable coded disc. They have scanning fields which are assigned to the coded tracks. A light beam aligned in parallel illuminates each scanning plate. This light beam is generated by an LED and a capacitor like in the case of the incremental shaft encoder. With the rotation of the coded disc the light beam is modulated and its intensity is detected by the silicon photo elements. For absolute shaft encoders which additionally provide incremental signals four scanning fields are assigned to the finest track. The four graduations of the scanning fields are shifted against each other by one fourth of the grating period like in the case of the incremental shaft encoders.

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Figure 32, Photoelectric detection, through-beam method LQ: light source; KD: condensor; TS: coded disc; PE: photo elements; AG: scanning plate. If voltage is applied to the absolute shaft encoder, the binary value which is caused by the current position of the coded disc is immediately provided at the output channels in the form of HIGH/LOW levels. The number of tracks depends on the requested resolution, the distribution of the light and dark segments on the type of coding selected. Absolute shaft encoders are differentiated as follows: â&#x20AC;˘ â&#x20AC;˘

Singleturn shaft encoders Multiturn shaft encoders

5.2.1

Resolution

The resolution of absolute shaft encoders depends on the number of tracks. Singleturn shaft encoders are available with resolutions of 256 (8 bits), 360, 512 (9 bits), 1,024 (10 bits), 2,048 (11 bits), 4,096 (12 bits), and 8,192 (13 bits). See also chapter 5.2.4 Coding. Multiturn shaft encoders have up to 13 tracks and thus a resolution of 8,192 steps per revolution with 4,096 (12 bits) countable revolutions.

5.2.2

Parallel data output

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Singleturn shaft encoders

Singleturn shaft encoders are absolute shaft encoders. In contrast to the incremental units they provide a coded numerical value for each angular position. After each complete revolution of the axle the numerical value starts with the start value again. If the rotational direction of the shaft changes the counting direction of the output value changes as well. Most singleturn shaft encoders have a parallel data output where each track of the coded disc is assigned a separate data wire. Therefore the number of connection cores to be wired is very high.

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Enable signal

The data of the signal tracks are permanently provided by the shaft encoder if there is a LOW signal or no voltage on the release channels A and B. If a HIGH signal is applied to the release channels all signal outputs are of high impedance and thus they are blocked.

Figure 33, Pulse diagram of the parallel interface The signal outputs are assigned to two release channels â&#x20AC;&#x201C; see figure 33.The number of tracks for the respective release channel is as follows: Release channel A: tracks 3 to 10 tracks 7 to 12 Release channel B: tracks 1 to 2 tracks 1 to 6 LSB and MSB

8, 9 and 10-bit shaft encoders 11 and 12-bit shaft encoders 8, 9 and 10-bit shaft encoders 11 and 12-bit shaft encoders.

Track 1 is the least significant bit (LSB), the last track with the highest index number (e.g. bit 12) is the most significant bit (MSB). If bit 1 (LSB) is not transmitted, the transmission error is smallest; if the last bit (MSB) is not transmitted, the error is largest. The designation of the connections as regards the core colours varies depending on the number of bits. Connection of a 10-bit shaft encoder: brown yellow/brown white white/yellow green yellow white/grey white/green red/blue grey/pink lilac bit 6 black red bit 4 blue pink grey

Ub, plus, 10 - 30 V DC sensor, plus, 10 - 30 V DC Ub, minus, 0 V sensor, minus, 0 V release channel A release channel B bit 10 (MSB) bit 9 bit 8 bit 7 bit 5 bit 3 bit 2 bit 1 (LSB)

The respective connection is indicated on each shaft encoder.

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Multiplex operation

Direction of rotation and counting

Due to the fact that the signal outputs are of high impedance because of the LOW signal at the release channel it is possible to switch the output signals in parallel with other shaft encoders. Therefore a plc for example can operate several shaft encoders with the multiplex method. In that case two or more shaft encoders are wired in parallel on the same channels of the plc input card. Thus only 10 input channels are used for 10bit shaft encoders, irrespective of the number of encoders. The release channels of the shaft encoders are triggered by means of the plc outputs. To do this two output channels per shaft encoder are required. The signal outputs of the individual shaft encoders are read by the plc during operation either one after the other or on demand. It is important that only one shaft encoder at a time is enabled. Depending on the version of the shaft encoder either TTL signals or 24 V DC signals are provided. With shaft encoders it must be possible to differentiate the direction of rotation. Therefore it has been determined that the direction of rotation is always indicated looking at the front of the shaft of the encoder. For the singleturn shaft encoder this means that rotation to the right is clockwise if you look at the shaft. In that case the direction of counting is ascending. Direction of rotation clockwisecounting up Direction of rotation counter-clockwise counting down

5.2.3

Multiturn shaft encoders

Multiturn shaft encoders are also absolute shaft encoders. Like the singleturn shaft encoders they provide a coded numerical value for each angular position of the axle. Multiturn shaft encoders have the same design for determining the position within one revolution as singleturn shaft encoders. In addition the number of completed revolutions of the axle is provided in a further bit combination. In order to distinguish between the number of revolutions permanent magnets embedded in the discs are used which are connected to each other via gears for gear reduction. Detection is made via digital Hall-effect sensors.

Figure 34, Gear box with coded discs and Hall elements HE: Hall element; CS: coded disc; GB: gear box.

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The following diagram shows the pulse characteristics taking the example of a (non-existent) multiturn shaft encoder with four bits for single turn and three bits for multiturn. y 15 0 15

Singleturn 0 - 15

0 15 0 15 0

15 0 15 0

0 15

15 0

Multiturn 0 - 7

Figure 35, Multiturn encoder, 4 bits singleturn, 3 bits multiturn

5.2.4

Code types

In control technology different types of code are used, e.g. Gray code, BCD code or dual code as well as different variants. 5.2.4.1 Dual code (binary code) With the dual code (binary) code each digit is assigned a certain value, starting with 20 for the least significant position and 2n-1 for the most significant position. The dual code can easily be processed from the technical point of view. The optical detection, however, can lead to reading errors as the bit change of several tracks is not carried out exactly time-synchronously or because there is a bit change on several tracks at the same time (see figure 36, values 7 and 8). This can lead to wrong allocations of the position.

Bit 1 (LSB) Bit 2 Bit 3 Bit 4 (MSB) Value

10 11 12 13 14 15

Figure 36, Dual code

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5.2.4.2 BCD code The BCD code has a tetradic design. Each digit of a decimal number is assigned a 4-digit dual figure (tetrad). The BCD code is mainly used if decimal displays are to be triggered directly. Four bits allow numerical values from 0 to 15. For the BCD coding the bits from (binary) 0000 to I00I are required. The bit combinations of I0I0 to IIII are not required because they represent the decimal numbers 10 to 15. Therefore the efficiency of this code is not so high. The figure 3600 is shown as follows: 3 0011

6 0110

0 0000

Thus at least 14 bits are required because the two preceding zeros of the bit combination are not required for the three. The genuine binary code as well as the Gray code only need 12 bits for the same figure. 212 = 4,096 (211 = 2,048). 5.2.4.3 Gray code Absolute shaft encoders often use the Gray code. The advantage is its simple design: It is mirror symmetric and proceeds by one step, i.e. when going from one position (number) to the next only one single bit changes. This minimises the risk of possible reading errors during transmission and further processing.

Bit 1 (LSB) Bit 2 Bit 3 Bit 4 (MSB) Value

10 11 12 13 14 15

Figure 37, Gray code

Reflectible Gray code

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A 4-digit code results in 24 = 16 combinations. As the genuine Gray code counts from 0 to 2n-1 these are the numbers 0 to 15 in the figure above. A 12-digit code (212 = 4,096 combinations) performs a decimal count from 0 to 4,095. The bit information read with the Gray code is converted into a binary code by means of a suitable code converter. It can then be further processed. For further processing of the signals code converters (e.g. code converter Gray code â&#x20AC;&#x201C; dual code) or program modules in programmable controllers can be used. The code values are provided in ascending direction if the shaft of the encoder turns clockwise. As the Gray code is reflectible descending code values can be generated as well with clockwise rotation of the shaft by inverting the most significant bit (MSB).

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5.2.4.4 Symmetrically cut Gray code (Gray excess code) The Gray code proceeding by one step is for resolutions which can be represented as the power of 2 (2, 4, 8, 16,... 256, 512 etc.). If other resolutions, e.g. 360 or 1000 are to be implemented, the section corresponding to the requested even-numbered area is taken from the Gray code â&#x20AC;&#x201C; see figure 38 for the value 10. This ensures that the code proceeds by one step.However, the represented section does not start at zero any more, but it is shifted by a certain amount.

Bit 1 (LSB) Bit 2 Bit 3 Bit 4 (MSB) Value

10 11 12 13 14 15

Gray Excess 10 Code Bit 1 (LSB) Bit 2 Bit 3 Bit 4 (MSB) Value

Figure 38, Gray excess code For the evaluation half of the difference between the original resolution and the reduced resolution is deducted from the generated binary value. Calculation for determining the start value for example with the value 360: 1. The next higher binary value above 360 is 512 (29). 2. The number 360 is deducted from this value, the result is 152. 3. This is divided by 2; the result is 76. The range of numbers starts at 76 and ends at 435. This range from 76 to 435 is shown on the coded disc. The value 76 is converted internally and provided as zero. Accordingly, the internal value 435 is provided as 359.

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511 0 435

A 76

256 Figure 39, Cut Gray code for the value 360 The designation for the code shown in figure 39 is: 512 Gray excess 76 code. With the mechanical resolution only even numbers are possible for the cut Gray code â&#x20AC;&#x201C; like for the normal Gray code. The cut Gray code (also called "reduced Gray code", e.g. 10 Gray excess 3 code) is used if the advantages of a code proceeding by one step are to be used but if resolutions are required which do not correspond to a power of 2. When choosing the resolution it has to be considered that the value can be divided by 2 without any remaining fraction. Other resolutions result in the following positions: 76 to 436 with a required resolution of 360 152 to 872 with a resolution of 720 and 12 to 1,012 with a resolution of 1,000. With the Gray code or cut Gray code the individual bits have no value, like for example with the dual code where each bit combination is directly assigned a decimal number by the power of 2. 5.2.4.5 Decadic Gray excess-3-code This is a combination of the BCD code and the Gray code. Each individual decade is coded in the Gray code in such a way that it counts up to the number 13 starting with the number 3. Following that the second decade starts with the number 3 and the first decade counts down etc. The decimal Gray excess-3-code is a code proceeding by one step and it is mirror-symmetric. A disadvantage is that the conversion is very complex from the point of view of the hardware as well as from the point of view of the software.

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5.2.4.6

Comparison of different code types E D C B A

E D C B A 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

D C B A 0 1 2 3 4 5 6 7 8 9 Decadic Grayexcess-3-Code

D C B A 0 1 2 3 4 5 6 7 8 9 BCD- Code

Dual- Code

Gray- Code

Figure 40, Code types The table shows that only the Gray code and the dual code fully use all possibilities, i.e. there are 2n combinations. With the Gray excess code there are bit combinations which cannot be used.

5.3

Comparison of absolute shaft encoders and incremental shaft encoders

Absolute shaft encoders provide the actual position value immediately after they are switched on or after a power failure. Multiturn shaft encoders can in addition detect the number of revolutions. Thus these absolute shaft encoders have a very wide measuring range. With incremental shaft encoders on the other hand the plant would maybe have be set manually to the basic position or to a reference point. The complexity as regards connection and evaluation is higher for absolute shaft encoders than for incremental shaft encoders. Absolute shaft encoders are also more expensive.

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5.4

Many cores

Data transmission

As mentioned before absolute shaft encoders provide a data word the length of which depends on the resolution. If there is a separate signal output for each track this is called parallel data transmission. In order to transmit the information to the evaluation unit a cable which provides one core for each channel has to be laid. For a multiturn shaft encoder with 12 bits for singleturn and 12 bits for multiturn this would result in 24 cores for the data cable. The respective number of signal inputs is also required at the evaluation electronics, e.g. a plc. With high-resolution units this leads to the wellknown wiring problems: high susceptibility to interference, high cable costs, high installation complexity, thick, inflexible cables. For singleturn shaft encoders with a maximum of 13 bits data this complexity can still be justified. In this case parallel data transmission is still often used. With the 5 V unit multiplex operation with 8 and 4 channels is also possible. This does not reduce the cabling, but inputs on the evaluation unit or the plc.

5.4.1

SSI interface on the shaft encoder

A multiturn shaft encoder can detect 4,096 revolutions (12 bits) with a resolution of 8,192 steps (13 bits). If these data were to be transmitted in parallel 12 + 13 = 25 data wires would be required and in addition the wires for the voltage supply and the sensor.

Figure 41, SSI interface unit RM Few cores

Training manual

Therefore serial data transmission is offered for multiturn shaft encoders. For this purpose the unit has an SSI interface (synchronous-serial interface EIA RS422A or RS485). Only four data cores are required for the data transmission. In contrast to the parallel interface this one requires fewer components and it is less susceptible to interference. Considerably fewer wires than with the parallel interface are needed for the transmission. Furthermore considerably longer cables are possible. These shaft encoders have the following connections in addition to the voltage supply and sensor monitoring:

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Clock and clock inverted TTL-compatible signals for data and data inverted Two sinusoidal increment signals (A and B), 1 Vpp Independent of the unit the data are transmitted either in the dual code or in the Gray code.

Figure 42, SSI, pulse diagram for singleturn shaft encoders

Figure 43, SSI, pulse diagram for multiturn shaft encoders The times for T, t1 and t2 shown in the diagrams above must be observed. They are: Clock T: t1: t2: Function

Training manual

0.9 µs to 11 µs greater than 0.45 µs max. 0.4 µs.

In quiescent condition the clock and data wires are HIGH. The clock is generated by the evaluation electronics (e.g. SSI controller). The first falling clock edge signals the start of the data transmission – the current measured value is stored. Data transfer is carried out with the first rising clock edge. With the following rising clock edges the data are transmitted bit by bit, starting with the MSB. The transmission of a complete data word requires n + 1 rising clock edges (n = resolution in bits). Thus 25 clock edges are required for a 24-bit shaft encoder. After the transmission of a complete data word the data output remains LOW and the clock output remains HIGH until the shaft encoder is ready to transmit the next measured value (t3 – see figure 43). If during this time there is a new request for data output (clock) the data which have already been provided are provided again. In this case the data output is LOW between the LSB of the first data transmission and the MSB of the second data transmission.

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If the data output is interrupted (clock = high for t >= t3) a new measured value is stored with the next clock edge. The input circuitry reads the data with the rising clock edge. The standard signal length is 25 bits (without parity bit), but a version with 24 bits (or with parity bit) is available on request. In addition to the values for the absolute position incremental data can be transmitted as a sine wave in parallel.

A 360° el.

A 0 B 0

90° el.

Figure 44, SSI interface, incremental signal shape The size of the incremental signals is 1 Vpp for a terminating resistor of approximately 120 Ω. The signals for the channels A and B are almost sinusoidal and are also shifted by 90 degrees. The number of increments is limited to 512 per revolution. The evaluation of the serial data of multiturn shaft encoders can be carried out by subsequent electronics – the SSI controller. serial multiturn RM

parallel SSI controller

plc

24 V DC + –

power supply

Figure 45, SSI interface, block diagram The data are updated synchronously with the readout cycle. Thus the data are as current as the time distance between two readouts. Therefore a periodic readout of the shaft encoder is recommended. After a longer readout break and simultaneous rotation of the encoder shaft the data content of the first readout may be obsolete and should be ignored. Connection of a multiturn shaft encoder with SSI interface:

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black red green brown brown lilac clock yellow white/green screen blue/black red/black grey data - negated green/black yellow/black pink data

5.4.2

n. c. (not connected) n. c. n. c. n. c. Ub, plus, 10 - 30 V DC clock - negated Ub, minus, 0 V housing channel B (+) channel B (-) channel A (+) channel A (-)

SSI interface programming via software

Different multiturn shaft encoders with SSI interface can be parameterised via PC (ifm types RM6110 and RM6113). The required programming of the shaft encoder is carried out with a special software via a standard PC. The programming software is for programming as well as for checking the set values. This is especially necessary if units are replaced.

Figure 46, SSI programming software Before setting up new or replaced programmable shaft encoders the correct setting always has to be checked. If the factory setting remains unchanged this may cause serious malfunctions of the plant.

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Figure 47, SSI programming software, connection The programming cable which is available as accessory connects the shaft encoder directly with the COM interface of the PC and serves for voltage supply if the shaft encoder has not yet been connected to a controller/plc. The setting possibilities and operation of the software are very extensive and can be found in the detailed operating instructions supplied with the products. The following features can be set/programmed for example: Output format of the position values in dual or Gray code Transmission format of the data in a triangular structure (SSI) or synchronous-serial right-justified (see chapter 18.2 Glossary of technical terms). Direction of rotation for ascending position values. Singleturn resolution up to max. 8,192 positions per revolution. Multiturn resolution up to max. 4,096 distinguishable revolutions. Offset and preset values. It is also possible to check the shaft encoder by means of the software.

5.4.3

SSI controller

The SSI controller enables the connection of absolute shaft encoders with SSI interface to a plc. shaft encoder +5V line driver

evaluation electronics R2 data + data R2

C2 R1

R1 +5V

R2 clock +

C1 C1 R1

R1 C1 C1

clock R2

Figure 48, SSI interface, circuit example

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The controller converts the serially transmitted Gray-coded data word of the shaft encoder into parallel binary or BCD-coded information. In addition it provides the following functions: • • • • • • •

Monitoring function for voltage errors, Transmission errors (wire break) and incorrect operation Virtual zero point, i.e. the zero point can be defined new at any position Scaling factors, i.e. the number of steps, the resolution, can be freely selected between 1 and 4096, the number of revolutions can be selected between 1 and 4096 by duplicating, thus 2, 4, 8, 16,.... The direction of rotation can be inverted. Code type, i.e. a choice between BCD and Hex code. Parity, i.e. a choice between an encoder with or without parity bit.

Figure 49, SSI controller The pulse frequency for absolute shaft encoders is 100 kHz. The data frequency for binary coded data is 1 kHz, 0.6 kHz in the BCD code. LSB

outputs singleturn

outputs multiturn

LSB

D 00 D 01 D 02 D 03 D 04 D 05 D 06 D 07 D 08 D 09 D 10 D 11 D 12 D 13 D 14 D 15 D 16 D 17 D 18 D 19 D 20 D 21 D 22

24 V supply

UN n.c. n.c. UP-S D

STR RST OEN DAV PYB D 30 D 29 D 28 D 27 D 26 D 25 D 24 D 23

SSI-encoder-input

outputs multiturn

Figure 50, SSI controller, connections Outputs D00 - D15 for singleturn: • •

D00 (=LSB) to D11 (=MSB) with output in binary code D00 (=LSB) to D15 (=MSB) with output in BCD code

Outputs D16 - D30 for multiturn: •

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D16 (=LSB) to D27 (=MSB) with output in binary code

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•

D16 (=LSB) to D30 (=MSB) with output in BCD code

STR

(strobe) input for the signal to call the current encoder value. With a HIGH-LOW edge to STR the last complete encoder value in the output buffer is provided to the plc. (reset) input for external setting of the zero position. (output enable) input for external switching signal which releases or blocks the data outputs (for the use of several controllers on one plc). HIGH releases the data outputs, LOW blocks them. If this input is not connected to the plc the data outputs are permanently free. (Data-valid) If the strobe signal calls the data, these data are valid if the output DAV is HIGH. In case of a LOW signal the following errors might have occurred: • Transmission error of the SSI module • Measured values above the programmed resolution (output for the internal parity information) The parity is formed from singleturn and multiturn by means of the complete data word. In case of an even sum of all HIGH outputs including the parity output this output is HIGH.

RST OEN

DAV

PYB

5.4.4

Profibus-DP interface

Profibus is a further alternative to avoid having to use many cores for data transmission of a multiturn or singleturn shaft encoder.

Figure 51, Profibus DP shaft encoder, type RM Instead of an SSI interface or parallel outputs the shaft encoder has an interface for Profibus DP. The shaft encoder operates as a slave alongside other components on the bus. The expression "DP" stands for decentralized peripherals. Profibus is a manufacturer-independent, open fieldbus standard determined by the international standards EN 50170 and EN 50254. Profibus enables the communication of units of different manufacturers. It is suited for time-critical applications as well as for complex tasks. Further technical and manufacturer- independent information is available on the internet at http://www.profibus.com .

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DP in

shaft encoder

gateway DP out 24 V DC + â&#x20AC;&#x201C; power supply

Figure 52, Profibus DP Absolute shaft encoders with Profibus DP interface are distinguished by their certification by the Profibus user organisation (PNO) and are therefore suitable for unrestricted use in all Profibus DP networks. This means among other things that all possible baud rates, the complete address range and the unit characteristics are supported according to the Profibus unit profile for shaft encoders. The shaft encoder is configured in the Profibus system by means of the socalled device data base file (GSD) for MS Windows. The file can be downloaded free of charge from the internet at http://www.ifmelectronic.com or http://www.profibus.com. The assignment of the addresses and the setting of the terminating resistance are carried out on the unit. The address of the unit can be set from 3 to 126. It is not possible to set the address via the Profibus master. B

B A B

A 5

0 PROFIBUS- DP

+Up -0 V

B/A BUS B/A BUS

Figure 53, Profibus, addressing and terminating resistor The data are transmitted in the dual code. The programming interface has a transmission rate of max. 12 MBaud3. The programming possibilities according to the Profibus profile for shaft encoders class 2 are for example:

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MBaud = megabaud

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• • • • • •

counting direction of the code values resolution zero point limit position HI and LO motion indication separation multiturn and singleturn shaft encoder

Furthermore the following diagnostic possibilities according to the Profibus shaft encoder profile class 2 are available: • alarms • warnings • status • serial number of the shaft encoder. Manual

A comprehensive manual is supplied with the unit. It describes the installation and configuration possibilities. These are for example: • General information about the Profibus technology. • Unit installation as regards cabling, addressing, terminating resistor and GSD file. • Unit configuration consisting of encoder class, operating parameters, data exchange, diagnostic information. • Configuration of the DP-Profibus encoder on a Siemens plc type S7CPU 315-2 DP, version STEP7 V5.X.

5.5

Accuracy of the shaft encoder

There are three types of accuracy as regards a shaft encoder: • • •

dividing error mark to space ratio phase difference

The accuracy of a shaft encoder is indicated in electrical degrees or as part of the grating period. The accuracy of the provided signal sequence of a shaft encoder mainly depends on the following conditions: 1. 2. 3. 4. 5.

Error of the radial gratings of the coded disc. Error in the grating of the detection grid. Eccentricity of the coded disc to the shaft. Radial runout of the bearing. Deviations due to the coupling with rotor couplings (solid shaft encoder). 6. Interpolation error during further processing of the measured signals.

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5.5.1

Dividing error

The dividing error is described as a deviation of any edge to its exact geometric position. It indicates the greatest deviation of the nominal distance between two pulse edges of one or several pulse channels. The dividing error consists of a mechanical rotational error and the electronic repeatability. It does not add up with several revolutions of the shaft encoder. The dividing error is very important with positioning applications which are to be carried out during one revolution of the shaft encoder.

5.5.2

Mark-to-space ratio

The mark-to-space ratio describes the ratio between the rising and the falling pulse edges. It is important for the calculation of the actually required limit input frequency of the input circuit of the evaluation electronics. The accuracy value is indicated for each shaft encoder.

360°

A Figure 54, Mark-to-space ratio Range A in Figure 54 indicates the location of the variation range.

5.5.3

Phase difference

The phase difference describes the variation of two subsequent edges of the two channels A and B by their nominal distance. This distance is to be 90 degrees electrically. The maximum possible deviation is indicated in the data sheet. 360°

A 90°

Figure 55, Phase difference The area A in figure 58 indicates the variation range. For resolutions up to 5,000 the accuracy is ± 1/20 grating period. This is also valid for a detection frequency of one to two kHz and at room temperature.

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If the resolution is above 5,000 the accuracy is indicated in angular seconds. It is approximately Âą 12 angular seconds. The accuracy of the absolute position values is indicated in the technical data sheet of the respective unit.

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Mechanical design

Shaft encoders are differentiated as regards their type of mechanical coupling. There are solid shaft encoders and hollow shaft encoders with different types of flange for mechanical fixing. For the electrical connection there are cable units and connector units, in exceptional cases also units with terminal chamber (e.g. absolute shaft encoder type RM for Profibus connection).

6.1

Solid shaft encoders

Solid shaft encoders are coupled to the machine by means of shafts with a diameter of 6 mm or 10 mm and the respective mechanical couplings. The coupling has to compensate for the vibrations and shocks from the machine.

Figure 56, Solid shaft encoder

Ball bearing

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The shaft at the end of which the coded disc is mounted inside the shaft encoder, is guided by two ball bearings. Depending of the flange size the shafts are in most cases designed in such a way that the same ball bearings can be used for different shaft diameters. The diameter of the shaft in the ball bearing is 10 mm, but outside the shaft only has a diameter of 6 mm. The shaft encoder has two ball bearings positioned behind each other on the shaft in the flange. The ball bearings are closed in order to meet the respective protection rating, i.e. the balls cannot be seen from outside. There is an additional seal in front of the ball bearing. If the mounting tolerances and the maximum rotational speed are observed the ball bearings have an average lifetime of between 25,000 and 120,000 operating hours.

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Figure 57, Ball bearing (K) with sealing ring (D)

Starting torque

The ball bearings are particularly important because their mechanical design is decisive for the smooth running of the shaft. This is especially interesting in cases where the drive for the encoder shaft does not have a high torque or if a high protection rating is required for the shaft encoder. For this reason the starting torque is indicated in the data sheet. It is the minimum impact on the shaft required to start a rotational movement of the shaft from standstill. The value of the starting torque is smaller than 1 Ncm (Newton centimetre) and it is indicated for room temperature. The flange is for the mechanical fixing of solid shaft encoders.

6.1.1 The flange

Flange types for solid shaft encoders

The flange of a shaft encoder is a precise aluminium injection-moulded part. Outside it has the respective profile with the corresponding threaded blind holes for fixing. The inside is for the ball bearings for the shaft, for fixing the housing cap as well as fixing and positioning the LEDs for the through-beam method.

Figure 58, Flange with threaded holes (G)

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The units are distinguished by their individual flange versions. The following flange types are standard: 1. Clamp flange 2. Synchro flange 3. Round flange

Figure 59, Flange types (1, 2, 3 â&#x20AC;&#x201C; see above) The diameter of the flange and the position of the mounting threads are standardised.

Figure 60, Clamp, synchro and round flange In addition to the flange types mentioned above there is also a square flange.

6.2

Hollow shaft encoders

Hollow shaft encoders have their own bearing and a coupling at the stator side. They can be mounted directly on the machine without any special coupling.

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Figure 61, Hollow shaft encoders With an angular acceleration of the shaft the stator coupling must only withstand the torque resulting from the bearing friction. The special stator coupling is the basis for a high natural frequency of the coupling and enables relatively high amplification in the control circuit. The coupling at the stator side allows axial movements of the driving shaft. The maximum permissible axial movement is for types RO ± 1 mm RA ± 0.5 mm RP ± 1.5 mm. The mechanical connection to the shaft is established by tapping off the drive. The hollow shaft of the encoder is put onto this shaft. Additional fixing possibilities on the housing ensure protection against rotation and a secure fit of the housing. Due to the special patented bearing inside the shaft encoder vibrations are compensated for. The hollow shaft versions differ depending on the encoder type. They can be continuous or open on one side (blind hole). The dimensions of the hollow shaft are designed to fit common sizes very precisely. In most cases they have the tolerance H7 according to DIN ISO 286 T2. Common dimensions for the inner diameter are: 6 mm 20 mm 50 mm

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(6 mm to 6.012 mm) (20 mm to 20.021 mm) (50 mm to 50.025 mm)

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Figure 62, Hollow shaft encoder, cut-away view The mounting of the hollow shaft on the shaft of the drive is carried out by means of one or two set screws (n) or a clamping ring. Depending on the type the driving shaft must protrude far enough into the hollow shaft (indication in the data sheet). The shaft of hollow shaft encoders is also only for the transmission of the rotational movement. The use of hollow shaft encoders is cheaper in comparison with solid shaft encoders because additional couplings, mounting devices and other fixing components are not needed. The required mounting space is smaller than for encoders with solid shaft.

6.2.1

Mounting of hollow shaft encoders

Hollow shaft encoders are mounted by means of a stator coupling.

Figure 63, Stator coupling for hollow shaft encoder

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Electrical connection

The electrical connection of shaft encoders can be carried out by means of a connection cable or a connector.

7.1

Cable length

Bending radius

Connection cable

The connection cable at the unit is one or two metres long. Cable lengths of 10 m are also available. At the end of the cable a short section of the insulation is stripped. The cores do not have any wire end ferrules. If a plug and socket connection with a suitable extension lead (cross-section, screening) is used, a max. length of 100 m for the 5-V version and 50 m for the 10 to 30 V version is possible. The cable material is polyurethane (PUR) or polyvinyl chloride (PVC), depending on the unit. The PUR cable is more resistant to oil, hydrolysis and microbes. The permissible bending radii of the connection cables generally depend on the diameter and the material. Guide values for PUR cables with 5 or 6 mm and PVC cables with 5 or 8 mm: r ≥ 20 mm if flexed once, r ≥ 75 mm if flexed continuously.

Screening Temperature ranges

All connection cables of the shaft encoders are screened (metal mesh screening). The screen of the connection cable is fixed internally to the housing cap. The individual connection cores are not screened. Depending on the cable version the encoder cables can be used in the following temperature ranges: for firmly laid cables for frequent flexing

-30° C to 85° C. -10° C to 85° C.

If the cable has a restricted resistance to hydrolysis and microbes, it can be used at up to 100°C for stationary and moving applications.

Figure 64, Cable entry axial (A) and radial (R) The cable entry at the unit can be axial or radial.

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It is implemented by means of a cable gland in most cases. Small shaft encoders do not have a cable gland for reasons of space. In this case the cable entry is radial.

Figure 65, Cable entry for small units The cable entry of a small encoder, like shown in figure 68, allows axial as well as radial connection. Some shaft encoders have a connection cable with cable plug. These units have a cable with a plug mounted at the end.

Figure 66, Cable plug

7.2

Connector

The size of the connector on the unit, the number of pins and their connection depend on the unit version.

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Figure 67, Connector unit In many cases it is a 12-pole connection. 1

7 3

6 4

Figure 68, Pin connection of a plug The pin connection of the plug at the unit is described in detail in the data sheet.

7.2.1

Sockets/coupling

Suitable sockets for the connection of connector units are offered as accessories. The data sheets of the shaft encoders with connector specify the type of connector so that the suitable sockets (coupling with cable) or the suitable couplings for wiring can be selected from the ifm range of accessories. A typical designation for a connector is for example ifm 1001.2.

Figure 69, Coupling, electrical The couplings are rated for operation with DC voltage and have a voltage range of 4.5 V DC to 30 V DC. The temperature range is â&#x20AC;&#x201C;40 degrees Celsius to +140 degrees Celsius. The couplings have the protection rating IP 67. In many cases the housing material is brass with a plastic sheathing.

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7.3

Laying the cable

Connectors or terminal boxes with metal housing should be used for mounting and no other signals should be led through these components. The housing of the encoder, connector, terminal box, and evaluation electronics should be connected with each other via the screening of the cable. The screening should have as low an inductance as possible (short, large surface) and must be connected in the area of the cable entry. The screening system as a whole must be connected to protective earth. The connection cables should be laid separately from any sources of interference (e.g. cables of motors, solenoid valves etc.) In general, a minimum spacing of 20 cm is sufficient. Connections or plugs should not be disconnected while live.

7.4

Earthing and screening

On a cabled unit the screen is directly connected to the encoder housing.

Figure 70, Earthing and screening The screen connected at the encoder should be led directly to the evaluation electronics and be earthed there. This ensures the best possible screening against interference from outside.

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Mechanical data

Shaft encoders are a combination of high-quality mechanics and electronics. With the respective design they can be considered as precise measuring instruments. For this reason the mechanical data are very important. In principle, incremental and absolute shaft encoders have the same mechanical design. The individual components differ in detail. There are differences as regards the coded discs, the number of photo elements and the internal evaluation electronics.

8.1

Maximum mechanical rotational speed

The maximum mechanical rotational speed indicated in the data sheet is stated for permanent operation at the highest temperature. It assumes that the connection between the driving shaft and the encoder has no considerable offset. The maximum rotational speed of the complete system of encoder and evaluation electronics is influenced by three factors: mechanical rotational speed of the shaft encoder limit frequency/maximum output frequency maximum input frequency of the evaluation electronics.

8.1.1

Mechanical rotational speed of the shaft encoder

The maximum permissible mechanical rotational speed is indicated in the data sheet. It results from the mechanical load of the encoder. For most units it is between 10,000 and 12,000 revolutions per minute. Exceptions are hollow shaft encoders with a maximum of 3,000 or 6,000 revolutions per minute. 8.1.1.1

Limit frequency / maximum output frequency of the shaft encoder This is an electrical value for the output stages of the shaft encoder â&#x20AC;&#x201C; see below. The mechanical rotational speed and the maximum output frequency of the signal outputs are in direct correlation with the number of pulses provided per revolution. This means that the rotational speed during operation must not exceed the maximum permissible mechanical rotational speed of the shaft encoder and that the rotational speed must not become so high that it exceeds the maximum permissible output frequency of the output stage because of the number of increments. Example: A shaft encoder has 5,000 increments per revolution and a maximum output frequency of 250,000 Hertz. Thus the shaft encoder may only be operated with max. 50 revolutions per second (3,000 min-1) even if it is rated for 10,000 min-1 so that the maximum output frequency is not exceeded.

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8.1.1.2 Maximum input frequency of the evaluation electronics For the input electronics there are usually details about the maximum frequency taking into account the number of signal edges to be evaluated. In case of pulse duplication or multiplication the pulse length is reduced accordingly. Furthermore the phase difference error must be taken into account. The influences described above should be checked for the concrete application in order to determine the suitability of the shaft encoder. Due to the tolerances a shaft encoder and evaluation electronics should be chosen which can process at least 1.5 times the frequency. 5000 pulses/rev. 2500 pulses/rev.

350 300 250

1000 pulses/rev.

200 150 500 pulses/rev.

100 50

250 pulses/rev.

2000

4000

6000

8000 10000 12000 rot. speed [min-1]

Figure 71, Rotational speed and switching frequency

8.2

Shaft load

The shaft of an encoder is made of stainless steel. The maximum mechanical shaft load is indicated for the outer end of the shaft, i.e. the place with the highest possible leverage. The load of the shaft influences the bearing. Indirectly the shaft load always means the load of the bearing. R

Figure 72, Shaft load, axial (A) and radial (R) Typical values are: axial 10 N (Newton), 20 N, 40 N radial 20 N, 60 N.

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Depending on the ball bearing

The shaft load mainly depends on the design of the bearing. Small units with small ball bearings have lower values for the permissible load. The values for each shaft encoder are indicated in the data sheet.

8.3

Acceleration

Vibration

Shock resistance and vibration resistance

The shock resistance indicates the highest permissible value of an impact or shock which may occur for a short time. For ifm units this value is 100 g for a time of 11 ms (g = gravitational acceleration); type RB is an exception, however. In this case the shock resistance is 30 g for 11 ms. To determine this value the units are connected and mounted according to their specified use (e.g. by means of the fixing holes on the front of the flange). The units are tested in a drop-test machine by dropping them and bringing them to a gentle stop. The acceleration is 100 g (30 g for type RB). The amplitude at which vibration of the unit dies out (attenuation factor) must stop after 11 ms. Despite these high values impacts or shocks with a hammer etc., for example for aligning the system during installation must be avoided. A value is also indicated for vibrations at which the encoder does not show any malfunction or is not destroyed in continuous operation. For ifm units this value is 10 g for the frequency range of 55 to 2,000 Hz. The acceleration values indicated in the technical data sheet of the shaft encoder do not impair the function of the units. They can reduce the accuracy, however.

8.4

Housing material

All shaft encoders have a metal housing. The shaft is made of stainless steel, the flange and the cap are made of aluminium.

8.5

Protection rating

ifm shaft encoders are supplied with the protection rating IP 64 as a standard. This value refers to the shaft entry, not to the housing with cable entry or flange connector. For types RB, RC, RU, and RV the protection rating IP 66 with an additional sealing of the shaft is available on request. It has to be taken into account that the units are slightly stiffer due to the specially sealed bearings. The singleturn shaft encoders have IP 65. The housing (cap), the cable entry and the flange sockets meet the requirements of IP 67.

8.6

Storage temperature

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Operating temperature

Shaft encoders may be used at operating temperatures starting at â&#x20AC;&#x201C;30 degrees Celsius up to +100 degrees Celsius. The temperature range depends on the type of unit. The operating temperature range indicates the limit temperatures of the mounting environment at which the nominal technical data of the encoders are observed (DIN 32 878). Incremental shaft encoders with solid shaft have the widest temperature range. Hollow shaft encoders have the smallest temperature range. Often the storage temperature is also indicated in the data sheet. This is the ambient temperature during storage or transport of the unit in the box.

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Electrical data

In general the current consumption of the shaft encoder increases slightly after approx. 5 to 6 years â&#x20AC;&#x201C; see below.

9.1

Voltage supply

Incremental and absolute shaft encoders are only operated with DC voltage. There are two versions: 1. TTL voltage range, 5 V DC Âą 0.5 V and 2. HTL voltage range, 10 V - 30 V including residual ripple. After the transient condition of the supply voltage the tolerances indicated have to be observed. Ub Upp

5.25 V 5.0 V 4.75 V typ. 500 ms

Figure 73, Transient condition of the TTL voltage Uss = Upp Figure 73 shows that it can take up to 500 ms until the supply voltage is within the tolerances. Internal operating voltage

Residual ripple

The voltage level of the output pulses depends on the supply voltage. The internal operating voltage of the shaft encoder is ensured by built-in voltage regulators. The output pulses are not concerned by this. This means that operation of the shaft encoder is maintained even with a poor supply voltage (voltage dips, high residual ripple). The signal outputs, however, depend on the voltage characteristic of the supply voltage. The shape of the output pulses in case of poor supply voltage can lead to the subsequent evaluation electronics not detecting all pulses. The figure below shows that pulse 2 is below the HIGH level of the controller and can therefore not be detected/counted.

Figure 74, Residual ripple of the signal outputs For linear measurement the pieces to be measured become too long.

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9.2

External power supply

Reference level

Voltage supply via the external evaluation electronics

Many application systems consist of an electronic counter or another evaluation unit (e.g. speed monitor). In such cases the voltage supply of the shaft encoder is often carried out directly via an internal power supply of the evaluation unit (sensor supply). If this is the case it must be ensured that the performance of the power supply of the evaluation electronics is capable of supplying the required energy to the shaft encoder. If the evaluation unit does not provide sufficient power this can result in the problems with the output pulses described above or the evaluation electronics is damaged due to overload. If the sensor supply of the evaluation unit is not sufficient an additional external power supply must be used for the supply of the shaft encoder. When wiring the three units encoder (D), evaluation unit (A) and power supply (N) it must be ensured that the power supply is not switched directly in parallel to the sensor supply â&#x20AC;&#x201C; see figure below. Such cases can lead to compensating currents flowing due to the different internal resistances of the two power supplies. This can damage one of the units. In all cases, however, the negative connections of all units involved have to be connected to each other in order to get a common reference point.

- + A B

- + B A

Figure 75, Encoder supply with external power supply The output voltage of the power supply (N) should have the same level as the sensor supply of the evaluation unit (A) and it should be within the operating voltage range of the shaft encoder.

9.3

Sensor cables for encoders

Long supply cables can lead to insufficient voltage supply of the shaft encoder due to the inherent resistance of the cables. Via the sensor cables the external electronics can detect the voltage at the encoder and adjust it by a suitable control unit if necessary. If the sensor cables are not needed, they can be connected in parallel with the respective supply cable in order to reduce the voltage drop. The sensor cables are designated as 'sensor' in the data sheet and on the type label.

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9.4

Basic consumption

Maximum current consumption

Current consumption

The current consumption of a shaft encoder consists of the current which is required for the actual operation of the shaft encoder (basic consumption) and the current which flows via the output stages of the shaft encoder to the evaluation electronics. The current consumption of a shaft encoder is not constant. It increases with time because the luminosity of the LED(s) has to be re-adjusted for the through-beam method and it depends of course on the number of pulse outputs being triggered at the same time. The data sheet only indicates the current consumption which corresponds to the basic consumption of the shaft encoder. These are typical values, e.g. 95 mA (max. 150 mA). The value in brackets is the highest value for the current consumption. It can be reached if the LEDs have been re-adjusted up to the highest value (see below). Absolute shaft encoders have a higher current consumption than incremental shaft encoders. In many cases only one value is indicated in the data sheet â&#x20AC;&#x201C; the highest possible value. When dimensioning a power supply the highest value for the current consumption of the shaft encoder(s) should always be calculated with.

9.4.1

Light-emitting diodes (LEDs)

In the past miniature incandescent lamps were used in shaft encoders. The lighting area of an incandescent lamp is larger than with LEDs and the luminosity does not decrease so much in the course of time as in the case of LEDs. Disadvantages of the incandescent lamp These incandescent lamps generated white light. The luminous efficiency was low in comparison to the power consumption; the susceptibility to failure was high. LED As the performance of LEDs increased considerably in the past they are now being used in shaft encoders. For this purpose they are aged. This ageing ensures that the luminosity does not decrease very much any more. In addition the luminosity of the LED is automatically re-adjusted electronically if it ages nevertheless or if the coded disc is soiled. Therefore the current consumption of the unit increases with time. Due to the use of LEDs which are bigger and more luminous it has recently been possible to illuminate all photo elements with only one LED and one convex lens (condenser). Therefore the advantages of the LED, i.e. low current consumption, long life and vibration-resistant operation can also be used in the design of shaft encoders.

9.5

Current rating of the signal outputs

The current rating of the signal outputs indicated in the data sheet always refers to one individual signal output. The standard maximum current rating is 20 mA for TTL output stages 50 mA for HTL output stages. For hollow shaft encoders there may be the exception that the HTL output stage can only be rated with 20 mA.

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TTL without protection

This is similar for absolute shaft encoders with parallel signal outputs. In this case the maximum current rating per output is 20 mA, or 6 mA if there are many signal wires. The output stages for the signal outputs of HTL shaft encoders are shortcircuit protected. However, they are not protected against reverse voltages. The voltage supply of these shaft encoders is reverse-polarity protected, but the signal outputs are not. TTL shaft encoders are the most sensitive shaft encoders as regards wrong wiring. The signal outputs are not short-circuit protected and not protected against reverse voltage and the supply voltage is not reverse-polarity protected. The required protective functions, for example a reverse-polarity protection diode cannot be implemented because the minimum levels for TTLoperation might not be reached due to the voltage drops connected with this. The HIGH level is above 2.5 V; the LOW level is below 0.7 V.

9.6

Signal frequency

9.6.1

Signal frequency and mechanical rotational speed

The current signal frequency for incremental shaft encoders results from the product of resolution and mechanical rotational speed. It must not exceed the maximum possible switching frequency indicated in the data sheet in order not to saturate the unit. Especially with shaft encoders with high resolutions it may happen that the maximum permissible switching frequency is exceeded, but not the maximum permissible mechanical rotational speed. Therefore it must be checked in each application if the signal frequency to be expected is not too high. Evaluation electronics to which a shaft encoder is connected must of course be rated for the signal frequencies to be expected. The following diagram shows which rotational speed is permissible for a given resolution.

Y 12000 10000

160 kHz

300 kHz

5000 2000

50 kHz

1000 500 1000 2000

5000 10000 X

Figure 76, Resolution and rotational speed The x-axis in figure 76 shows the resolution, the y-axis the rotational speed.The designations of the three graphs show the maximum possible output frequency of the output stage of the shaft encoder.

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9.6.2

Signal frequency and cable length

If the cable length to the evaluation unit for units with TTL output stage is to be longer than 100 m it has to be taken into account that the maximum output frequency of the shaft encoder cannot be reached any more. In any case the supply voltage of 5 V DC at the shaft encoder should be ensured. Via the sensor cables the external electronics can detect the voltage at the encoder and adjust it by a suitable control unit if necessary. y 300 250 200 150 100 80 60 50 40 30 x

Figure 77, Cable length and output frequency, TTL The x-axis in figure 77 shows the output frequency in kHz; the y-axis shows the cable length in metres. For shaft encoders with HTL-output stage there is an dependence on the supply voltage:

additional

y 300 200 120 100 80 60 50 30 20

Up= 15 V Up= 24 V Up= 30 V

12 10 x

Figure 78, Cable length and output frequency, HTL The x-axis in Figure 78 also shows the output frequency in kHz; the y-axis shows the cable length in metres. With decreasing supply voltage (Up) for the shaft encoder the maximum output frequency decreases as well.

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Overview shaft encoders

Experience has shown that the types offered as standard solutions are sufficient for most positioning problems. There is a choice of different units, depending on which resolution is required, which force is to be applied to the bearing of the shaft and how cable and connector entry are to be designed.

HOLLOW SHAFT

SOLID SHAFT

Incremental shaft encoders Type

Resolution

Operating voltage (TTL/HTL)

Flange (type / Ø in mm)

Shaft (Ø in mm)

Output signals (optional)

Switching frequency in kHz (TTL/HTL)

Max. rot. speed (min-1)

Option connector

5 – 1,000

5 / 10 – 30

R / 36.5

TTL, HTL

300/160

10,000

yes

40 – 512

5 / 10 – 30

R / 58.0

TTL, HTL

300/160

12,000

yes

48 – 10,000

5 / 10 – 30

S / 58.0

TTL, HTL

300/160

12,000

yes

50 – 3,600

5 / 10 – 30

K / 58.0

TTL, HTL

300/160

12,000

yes

10 – 1,000

5 / 10 – 30

- / 36.5

TTL, HTL

300/160

12,000

yes

100 – 5,000

5 / 10 – 30

- / 58.0

TTL, HTL

300/160

12,000

yes

TTL

300

6,000

yes

1,000 – 3,600

HTL

160

3,000

yes

5/- / 877.0 - / 10 – 30

6, open on one side 10, open on one side 20, open on one side 50, open on one side

Flange types: R = round flange; S = synchro flange, K = clamp flange.

Shaft types: V = solid shaft; H = hollow shaft

Absolute shaft encoders

Multiturn

Singleturn

Type

Resolution

Operating voltage

Flange (type / Ø in mm)

Shaft (type / Ø in mm)

256 – 4,096 parallel RN

10 – 30

S / 58

Max. rot. speed (min-1)

Option connexctor

HTL / Gray

10,000

yes

SSI / Gray

1 Vpp / 512

12,000

yes

8,192 x 4,096 serial

10 – 30

S / 58

V / 6 / 10

SSI / Gray

1 Vpp / 512

12,000

yes

max. 8,192 x 4,096 serial, programmable

10 – 30

K / 58

V / 6 / 10

SSI / Gray

1 Vpp / 512

12,000

yes

max. 8,192 x 4,096 programmable, Profibus

10 – 30

S / 58 K / 58

V / 6 / 10

Profibus

12,000

yes

8,192 serial

10 – 30

H / 58

H / 12 (open on one side)

SSI / Gray

1 Vpp / 512

10,000

yes

Flange types: R = round flange; S = synchro flange, K = clamp flange.

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Incremental signals

V / 10

1,024 – 8,192 serial

Output signals (optional)

Shaft types: V = solid shaft; H = hollow shaft

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Operating instructions

All shaft encoders are supplied with detailed operating instructions. Observing the indicated conditions ensures permanent safe use of the unit.

Figure 79, Operating instructions, example The operating instructions are available in several languages (German, English and French).

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Data sheet

The data sheets of shaft encoders provide clear and nearly complete information about the technical data of a shaft encoder. In addition to the important data like article number, type designation, resolution, and output function they contain a technical drawing, a pulse diagram and the connecton.

Figure 80, Data sheet of the shaft encoder RV1009

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Figure 81, Data sheet of the shaft encoder RM6001

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Accessories

Shaft encoders can be mounted easily and operated safely with the corresponding accessories. ifm offers a wide range of accessories.

13.1

Couplings for solid shaft encoders

Incremental shaft encoders (types RC, RU and RV) have their own bearing rated for up to 60 N (radial at the shaft end) for speeds up to 6,000 revolutions per minute. Due to this load capacity it is possible to mount these encoders directly on mechanical transmission elements such as toothed wheels, frictional wheels or pulleys. If the encoders are subjected to higher strain, it is recommended to use a coupling for the shaft-side connection of the drive. The coupling compensates for production and mounting tolerances as well as temperature influences and misalignment between encoder shaft and driving shaft. Thus the bearing of the shaft encoder is not subjected to any additional external stress. The coupling has to meet high demands. It has to be designed in such a way that it withstands the radial and axial forces and transmits the rotational movement without any major delay.

Figure 82, Flexible coupling While in the case of torsion-proof but flexible shaft couplings axial shaft displacement only generates static forces in the coupling, radial and angular displacement results in alternating stress, restoring forces and torques which can strain the shaft bearing of the encoder. There are three different alignment errors when mounting the couplings:

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−δ

+δ

Figure 83, Axial, radial and angular displacement The maximum permissible displacement is indicated in the data sheets of the couplings. Displacement types: • • •

Grub screw

Different axle diameters

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axial displacement radial displacement angular displacement

δ: ± 0.4 mm a: ± 0.25 mm α: ± 3.5 degrees.

These values are valid for 23°C room temperature. The values for radial, angular and axial displacement are maximum values which must not all be reached at the same time during operation. The life of a coupling depends on to what extent the permissible tolerances are used. Couplings can be fixed by means of clamping screws or grub screws (set screw with hexagon socket or slot). For clamping, the front faces of the coupling are slotted. The slot is pressed together on the shaft by means of a through bolt. The grub screws clamp directly onto the shaft. Depending on the material of the screw and the tightening torque indentations on the shaft may occur. Therefore couplings with grub screws for fixing are mainly used on shafts with a flat. Often the hub bore holes in both front faces of the couplings have the same size, e.g. 6 mm. There are also versions with different bore holes for a better adaptation to the machine or to the drive. On one side of the coupling there is e.g. a 10mm bore hole, on the other side a 6-mm bore hole.

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Figure 84, Flexible coupling with different bore holes In addition to the flexible coupling with its excellent mechanical characteristics the spring disc coupling has a further advantage: it is electrically isolating.

Figure 85, Spring disc coupling

13.2

Angle flanges

There are different versions. Their bore holes are designed for the different flanges of the shaft encoders.

Figure 86, Angle flange, example The angle flanges have a height of 80 mm to 100 mm, a width of 90 mm to 110 mm and a depth of 40 mm.

13.3

Bearing block

The bearing block provides a further mounting possibility for hollow shaft encoders. It can withstand high radial stress of the shaft. It is recommended especially for the use with measuring wheels, pulleys or chain wheels. It prevents overload of the encoder bearing.

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Figure 87, Bearing block with angle flange

High resistance

The bearing block has two different shafts. The smaller shaft with a flat on the right in figure 87 has a diameter of 10 mm.The shaft on the left has a diameter of 12 mm. The maximum permissible rotational speed is 6,000 min-1. The shaft can be loaded with 200 N axial and 200 N radial. Thus the shaft load is many times higher than for shaft encoders. A matching angle flange is offered as a further accessory.

13.4

Isolating adapter

The isolating adapter is for shaft encoders with synchro flange. It consists of plastic (PBTP) and provides mechanical as well as isolation protection.

Figure 88, Isolating adapter The cap has a diameter of 63 mm. The diameter of the flange is 82 mm. The depth is 38 mm.

13.5

Pinion and rack

A pinion on the shaft of the encoder in connection with a rack enables direct transmission of linear movements.

Figure 89, Pinion

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The pinion has 20 teeth and a circumference of 50 mm. It is designed for an axle diameter of 6 mm. A pinion with a bore hole of 10 mm is also available.

Figure 90, Rack The rack is 5 mm thick and it is available in lengths of 500 mm and 1,000 mm. Fixing holes have to be drilled by the user. If possible the rack should be mounted with the teeth downwards. Thus malfunctions due to dust or chips can be avoided. Measuring wheels and pinions are usually mounted directly on the encoder shaft without a flexible coupling.

13.6

Resilient base

In order to protect shaft encoders against mechanical overload due to the use of pinions and racks the units can be mounted on a resilient base. A

Figure 91, Resilient base

13.7

Measuring wheel

Measuring wheels are available with circumferences of 200 mm and 500 mm. The measuring wheel with a circumference of 200 mm is available for shaft diameters of 6 or 10 mm, the measuring wheel with a circumference of 500 mm only for a shaft diameter of 10 mm.

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Figure 92, Measuring wheel

Non-slip

Measuring wheels are either completely made of aluminium, the tread is knurled axially (strongly roughened); or they are made of plastics with different surfaces. These can be: rubber, smooth plastic or grooved plastic. For choosing the measuring wheel it is important that the wheel can move on the surface without any slip. Examples: Surface of the measuring distance: Glass Metal Wood rubber

Coating of the measuring wheel:, Rubber Rubber possibly aluminium aluminium

Figure 93, Measuring wheels, rubber, plastic, smooth aluminium, roughened aluminium A disadvantage of rubber is the wear due to abrasion and that the temperature resistance is not very high.

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B C

Figure 94, Measuring wheel on moving arm If a measuring wheel is used it may also be recommendable to place the shaft encoder on a resilient base.

13.8

Fastening clamp

These small discs are for fastening shaft encoders with synchro flange.

Figure 95, Fastening clamp The diameter is only 12 mm. They are 5.5 mm thick. The bore hole has a diameter of 4.2 mm. The lip is 3 mm thick.

13.9

Pulse divider, pulse stretcher

With pulse dividers and pulse stretchers high frequencies or short pulses can be adapted to low input frequencies of evaluation systems and controllers. They modify high signal frequencies or short pulses in such a way that they can be detected by standard inputs of plcs or electronic counters. The use of a pulse divider thus eliminates the need of fast input cards of a plc. Furthermore the pulse divider can be used as level converter of TTL or HTL signals.

13.9.1

Pulse divider

The pulse sequence of incremental shaft encoders can be very fast, depending of the resolution and rotational speed. The input frequency of the standard inputs of a plc or an electronic counter is maybe not high enough to detect all pulses of the shaft encoder. By using a pulse divider the high frequency of the signal outputs of the shaft encoder can be divided so that it can be detected by the plc. The disadvantage is that the accuracy is reduced.

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shaft encoder

E 80102 plc

Figure 96, Pulse divider E80102, connection Depending on the version of the pulse divider the division ratio of the input to the output can be freely selected between 1 and 255 (E80102) or it is fixed to 10:1 (E80100).

13.9.2

Pulse stretcher

The pulse stretcher converts short input pulses into output pulses with a constant length.

Figure 97, Pulse stretcher E80110 The input pulse (IN) length of the pulse stretcher must be at least 0.2 ms. The pulse length on the output (OUT) is 25 ms. There must be at least 28 ms between the input pulses.

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Mounting of shaft encoders

The mounting of shaft encoders is especially important. Misalignment between drive and encoder shaft can considerably impair the operation of the shaft encoder. B

Figure 98, Figure 98: Mounting with coupling The shaft encoder can be mounted by means of: Mounting holes on the front face of the shaft encoder. Fastening clamps Clamping.

Figure 99, Mounting with fastening clamp Not the cap

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Solid shaft encoders must never be fixed outside the flange. The housing cap is made of aluminium and can be deformed relatively easily. It provides no secure hold. Hollow shaft encoders are mounted directly on the driving part, the hollow shaft being connected to the driving shaft.

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Figure 100, Hollow shaft encoder with shaft open on one side

3. SW 3

4x M4

Figure 101, Hollow shaft encoder with continuous hollow shaft

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Calculation examples

15.1

Linear measurement

To calculate the resolution, the circumference of the pinion or the measuring wheel and the requested resolution have to be known. Example: A pinion with a circumference of 50 mm is used, the required resolution is 0.1 mm. With each 0.1 mm-step a pulse is to be generated, this results in a total of 500 pulses for one complete revolution. The shaft encoder in this example needs to have a resolution of 500 increments. For the resolution in millimetres the following applies: Number of increments = circumference (in millimetres).

15.2

Switching frequency and mechanical rotational speed

Correlations between maximum mechanical rotational speed, switching frequency and resolution: Note: With a high resolution the electrical switching frequency is quickly exceeded. The indication of the maximum mechanical rotational speed only refers to the mechanical load of the shaft encoder. Example: Encoder RU1045, type RU-5000-I05/L2 Max. mechanical rotational speed: 12,000 min-1 = 200 s-1 Maximum switching frequency (electr.): 300 kHz A maximum resolution of 5,000 pulses and maximum mechanical rotational speed result in a switching frequency of: 200 s1 X 5,000 = 1,000,000 Hz = 1 MHz. Thus the maximum possible switching frequency of this shaft encoder is exceeded by more than three times.

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Handling of shaft encoders

Better not ...

Figure 102, No overvoltage, do not align with a hammer

Figure 103, Do not clamp into the vice, do not drill into the shaft

Figure 104, Do not saw or grind the shaft

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Applications

Shaft encoders are used in the following industries for example: • • • • • • • • • • • • • • • •

Metallurgical, milling and steelworks equipment Plant and apparatus construction in general (e.g.hydraulics, pneumatics, welding systems, presses, stamping machines, drilling machines) Machine tools Transfer lines Special machines Surface treatment machines Processing machines for wood, paper, plastics Printing and labelling machines Mounting systems Big antenna systems Industrial robots Conveyor and transport systems Construction of lifts, escalators Roller shutter doors Stacking systems Cranes and lifting systems

Figure 105, Measuring wheel for linear measurement Incremental shaft encoders in connection with a counter enable automatic cutting of e.g. sheets of veneer to a specified length.

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Figure 106, High-lift shelves In this case multiturn shaft encoders are used to enable exact positioning of the transport system and automatic loading and unloading. To ensure safe data transmission via longer distances multiturn shaft encoders with SSI interface are used.

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Figure 107, Robots Absolute shaft encoders are used for the precise control of the movement of industrial robots and automatic handling systems. They guarantee further processing e.g. after a power failure without any problems, thus making complex returning to a reference point superfluous.

Figure 108, X-Y-Z-milling system The individual positions and travel lengths of an automatic machining system are detected by incremental encoders with up to 10,000 pulses per revolution. This allows resolutions up to 0.01 mm.

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Annex

18.1

Competitors

There are many competitors on the market for shaft encoders with an optical principle. Heidenhain, Hengstler, Stegmann, Balluff, IVO, TWK, T2R, Litton and Baumer are some of the most important ones.

18.2 Starting torque Absolute shaft encoder Scanning frequency Alarm signal Analogue signal Complementary

ASCII

ASIC Resolution Axial load Baud rate BCD Bimetal Binary Binary code

Bit Byte

Training manual

Glossary of technical terms

The starting torque of a shaft encoder is the torque required to cause the shaft to change from the off position to a rotational movement. Encoder which provides clear, coded information for each measuring step. The number of signal periods per second. The maximum scanning frequency limits the speed of incremental systems. It serves to monitor the shaft encoder as regards malfunctions, e.g. disc breakage, soiling, short circuit of the signal wire, and insufficient supply voltage. A signal which continuously changes its level. Output stage where the inverted signals are provided as well. Electrically the I/O levels are transmitted in the form of voltage differences between two wires. Thus the useful signal (the difference) remains uncorrupted, as interference usually occurs on both wires. The name ASCII stands for ´American Standard Code for Information Interchange´. It is a code standardised in the USA to represent alphanumeric characters. Originally based on a 7-bit coding it enabled the representation of 128 characters. Extended to 8 bits it became the standard code on small computers. Due to this extension 128 characters became possible which are nowadays partly used as checksum or to represent country-specific characters. The ASCII code is currently the standard code to store unformatted text files. User-specific IC. Number of measuring steps (gratings) within a measuring range. Maximum load of the encoder shaft in axial direction – looking at the front face of the shaft in the direction of the flange. Speed of the data transmission (bits per second). Binary-coded-decimal; binary representation of a decimal number (one decade). A bimetal strip consists of two different metals which have a different expansion at different temperatures. Both metal strips are bonded together. These bimetal strips can also be used to manufacture temperature meters. Two logic states (yes/no, ON/OFF, HIGH/LOW). Basis for dual computer systems. The basis for each binary code is a so-called binary system, i.e. a system with only two states, for example ON/OFF, true/false, 0 Volt/5 Volts or the binary code 1/0. The binary code is a code which only works with two characters: the binary zero and the binary one. The basic unit is the bit, a storage place which can only take the values 0 or 1. Eight such bits combined are called byte. Thus one byte can represent 256 characters. Abbreviation for "binary digit"; smallest information unit of a binary system the value of which can be I or 0 (yes/no decision). Sequence of 8 bits. One byte has 8 bits.

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Data transmission, parallel Dual Code Data valid Data bus Data transmission, synchronous-serial

DC DIN Revolution, maximum mechanical Dual code EBCDIC EEPROM EMC Enable EPROM Flange socket Encoder monitoring Encoder supply Encoder accuracy Gray-Code

HTL output Interpolation electronics LSB Mbaud MSB Multiturn shaft encoder Parity bit (even) PC PUR

Training manual

Each individual track has one data wire. The data are either constantly available or they are provided via an enable signal. Example: With a resolution of 4096 steps (12 bits) there are 12 wires. The expression "dual" refers to the representation of numbers. Format of the data transmission. Output for checking the validity of data. System of wires for parallel or serial electronic data transmission. With transmission in this format all data are transmitted in succession on one data wire. Only 4 cable cores are required: Clock, clock negated, data and data negated. In the case of shaft encoders with synchronous-serial interface, the inverted data are provided as well to increase the noise immunity. Depending on the clock frequency cable lengths of up to 100 m are possible. Direct voltage Deutsche Industrie-Norm (German industrial standard). Maximum permissible revolution of the encoder shaft. The maximum value is stated in the data sheet together with the other mechanical data. Natural binary code, code often used with absolute shaft encoders. This abbreviation stands for 'Extended Binary Coded Decimal Interchange Code'. It is used on mainframes to represent characters. This code was introduced by IBM in 1965 and has not changed up to now. Also E2-PROM. Abbreviation for "Electrically Erasable Programmable ReadOnly Memory". Electromagnetic compatibility. Control input via which the data outputs can be enabled. "Erasable Programmable Read-Only Memory"; read-only memory which is erasable with UV light and can therefore be rewritten. Connector which is mounted directly on the encoder housing. see alarm signal The supply voltage to be supplied to the shaft encoder. Deviation between the actual position and the measured position. The Gray code is a different way of representing the binary code. The basis is that two adjacent bit combinations must not differ in more than one bit (0 or 1). This is an advantage especially if as many data as possible are to be stored. A further benefit is the possibility to detect errors in the transmission of such codes more easily because adjacent characters may only differ in one position (valid for Ub of 24 V DC and maximum current rating). Abbreviation for Â´High Threshold LevelÂ´. The output level is more than 21 Volts. The counterpart is the TTL output. It converts a sinusoidal period into several square-wave pulse trains by means of an additional division, thus achieving a considerably higher measuring resolution. Least Significant Bit Megabits per second. Information about a data transmission speed. Most Significant Bit The multiturn shaft encoder does not only count the resolution of a revolution but also the number of revolutions. A parity bit (check bit) is added to the transmitted data in order to achieve an even number of bits. Personal computer. Standard cable material (polyurethane) for all shaft encoders with more than three output signals. According to VDE 0672 the PUR cables are resistant to oil as well as hydrolysis and microbes.

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PVC

Standard material for the sheathing. In order to avoid cable break PVC cables must not be moved if the temperature falls below -5 Â°C. Radial load Maximum load of the encoder shaft in radial direction (parallel to the flange at the outer end of the shaft). RS422/485 Interfaces for serial data transmission with values according to the EIA standard. RS422 Standardised interface for unidirectional point-to-point connection. RS485 Like RS422, but as bidirectional bus interface. Interface Interface point with defined connections, signals and signal sequences. Protection rating IP 50 Complete protection against contact with live parts or internal moving parts. Protection against harmful dust deposits. The ingress of dust is not completely prevented but dust must not penetrate in such quantity as to impair the operation. No special protection against ingress of water. Protection rating IP 64 Complete protection against contact with live parts or internal moving parts. Protection against the ingress of dust and splashing water. Water splashed onto the equipment from any direction shall have no harmful effect. Protecting rating IP 65 Complete protection against contact with live parts or internal moving parts. Protection against the ingress of dust and water jets. A water jet from a nozzle, aimed at the equipment from any direction shall have no harmful effect. Protecting rating IP 66 Complete protection against contact with live parts or internal moving parts. Protection against the ingress of dust and powerful water jets. Water must not penetrate the equipment in harmful quantities in case of temporary powerful water jets. Singleturn encoder The singleturn encoder resolves a mechanical revolution of the shaft into a number of code values corresponding to the resolution. A code value is assigned to each angular position within a revolution. Shock resistance Maximum permissible short-time value of a shock load. Interference signal For 10 to 30 V shaft encoders with axial or radial flange connectors this signal is on PIN 7. It can be used for monitoring the encoder. In case of a problem the signal changes from HIGH to LOW level. Synchronous-serial right-justified format Like with the triangular format (see below) the shaft encoder always provides data bits via 25 clock pulses also in this case. In case of a scaling, however, the 'zeros' are always put before the complete position information. Triangular format (SSI) For SSI transmission of the position values a differentiation is made between multiturn (12 bits) and singleturn (13 bits). Therefore data bits are always read over 25 clock pulses, but the data content may vary. The resolution of the multiturn reduced by means of a scaling is filled with preceding 'zeros'. In case of a reduced singleturn resolution the 'zeros' are added at the end. TTL output "Transistor-transistor-logic" on a 5-Volt basis. The counterpart is the HTL output. Operating temperature Temperature range at which all electrical and mechanical data are met. Vibration The value of a periodical oscillation at which the unit does not show any malfunction or is not destroyed when in permanent operation. It is stated in g for the frequency range 58 â&#x20AC;&#x201C; 2000 Hz. Virtual zero point The SSI controller enables the user to set a zero point independently of the shaft encoder. Shaft load The shaft load is the maximum permissible load on the shaft, referred to the shaft end at maximum mechanical revolution and 20Â°C operating temperature.

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Angular second

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Angle sizes are stated in degrees. One angular second is the 3,600th part of a degree. A full circle with 360 degrees therefore has 1,296,000 angular seconds.

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Type key

May 2004

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19.1

Examples of the use of the type key

A type key is often also described as 'talking type key' because the most important technical data can be read from the type designation by means of the type key. Once fixed, the type key may reach its limits with an increasing variety of unit types. In that case a completely new type key must be created. in general it is useful only to work with the article number. All organisational processes at ifm electronic use the article number. A shaft encoder with the article number RU6071 has the type designation RU-0100-I24/L2E. If the type key is known this type designation provides the following information: Position:

1 2 3 - 7 8 9 10 - 11 12 R U - 0100 - I 24 /

Position 1: Position 2: Positions 3 – 7: Position 8: Position 9: Positions 10 -11: Position 12: Position 13: Position 14: Position 15:

13 L

14 2

15 E

shaft encoder solid shaft encoder ∅ 58 mm with synchro flange standard ∅ 6 mm shaft 100 increments reserve incremental output signals 10 – 30 V DC reserve cable entry axial 2 m cable length protection rating IP66

Another shaft encoder with the article number RM 1102 has the type designation RM-8192-E05/R5B. Position:

1 2 3 - 7 8 9 10 - 11 12 R M - 8192 - E 05 /

Position 1: Position 2: Positions 3 -7: Position 8: Position 9: Positions 10 -11: Position 12: Position 13: Position 14: Position 15:

Training manual

13 R

14 5

15 B

shaft encoder multiturn shaft encoder ∅ 58 mm max. 8192 (25 bits) steps per revolution, 4096 revolutions reserve Profibus interface, connection to gateway 5 V DC (TTL, from the gateway) reserve cable entry radial with cable plug ifm 1001.1 5 m cable length ∅ 10 mm shaft

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List of figures

Figure 1, Linear measurement and synchronous movement monitoring ....................................................................7 Figure 2, Detection of rotational speed and angle measurement...............................................................................7 Figure 3, Bending systems and X-Y-recorders drawing tables....................................................................................8 Figure 4, Level measurement and radar/aerial systems ..............................................................................................8 Figure 5, Industrial robots .........................................................................................................................................8 Figure 6, Potentiometer ..........................................................................................................................................11 Figure 7, Resolver....................................................................................................................................................11 Figure 8, Inductive principle (Novotechnik) ..............................................................................................................12 Figure 9, Magnetic principle....................................................................................................................................13 Figure 10, Mechanical shaft encoder (cam-operated switchgroup)..........................................................................13 Figure 11, Cam-operated switchgroup with inductive proximity switches................................................................14 Figure 12, Inductive system .....................................................................................................................................14 Figure 13, Incremental shaft encoder ......................................................................................................................15 Figure 14, Incremental shaft encoder ......................................................................................................................19 Figure 15, Coded disc with increments ...................................................................................................................19 Figure 16, Photoelectric detection, through-beam method .....................................................................................20 Figure 17, Scanning plate, without reference mark grating.....................................................................................21 Figure 18, Light source and condenser....................................................................................................................21 Figure 19, Sine wave of the photo elements ...........................................................................................................22 Figure 20, Connection of the photo elements .........................................................................................................22 Figure 21, Signal voltage.........................................................................................................................................22 Figure 22, Pulse generation.....................................................................................................................................23 Figure 23, Signal generation, block diagram ...........................................................................................................24 Figure 24, Pulse diagram channels A, B, and zero index (NI)....................................................................................25 Figure 25, Zero index 360 degrees long (NI), type RB, 10 â&#x20AC;&#x201C; 30 V .............................................................................26 Figure 26, Pulse diagram with inverted channels (NI: Zero index) ............................................................................26 Figure 27, Sinusoidal output signals (Vss = Vpp)......................................................................................................27 Figure 28, Signal change.........................................................................................................................................28 Figure 29, Duplication of the pulses ........................................................................................................................29 Figure 30, Pulse multiplication.................................................................................................................................29 Figure 31, Coded discs............................................................................................................................................31 Figure 32, Photoelectric detection, through-beam method .....................................................................................32 Figure 33, Pulse diagram of the parallel interface....................................................................................................33 Figure 34, Gear box with coded discs and Hall elements .........................................................................................34 Figure 35, Multiturn encoder, 4 bits singleturn, 3 bits multiturn..............................................................................35 Figure 36, Dual code ...............................................................................................................................................36 Figure 37, Gray code...............................................................................................................................................36 Figure 38, Gray excess code ....................................................................................................................................37 Figure 39, Cut Gray code for the value 360 ............................................................................................................38 Figure 40, Code types .............................................................................................................................................39 Figure 41, SSI interface unit RM ..............................................................................................................................40 Figure 42, SSI, pulse diagram for singleturn shaft encoders.....................................................................................41 Figure 43, SSI, pulse diagram for multiturn shaft encoders......................................................................................41 Figure 44, SSI interface, incremental signal shape ...................................................................................................42 Figure 45, SSI interface, block diagram ...................................................................................................................42 Figure 46, SSI programming software .....................................................................................................................43 Figure 47, SSI programming software, connection ..................................................................................................44 Figure 48, SSI interface, circuit example ..................................................................................................................44 Figure 49, SSI controller ..........................................................................................................................................45 Figure 50, SSI controller, connections......................................................................................................................45 Figure 51, Profibus DP shaft encoder, type RM .......................................................................................................46

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Figure 52, Profibus DP.............................................................................................................................................47 Figure 53, Profibus, addressing and terminating resistor..........................................................................................47 Figure 54, Mark-to-space ratio ................................................................................................................................49 Figure 55, Phase difference .....................................................................................................................................49 Figure 56, Solid shaft encoder .................................................................................................................................51 Figure 57, Ball bearing (K) with sealing ring (D) .......................................................................................................52 Figure 58, Flange with threaded holes (G) ...............................................................................................................53 Figure 59, Flange types (1, 2, 3 â&#x20AC;&#x201C; see above) ...........................................................................................................53 Figure 60, Clamp, synchro and round flange...........................................................................................................53 Figure 61, Hollow shaft encoders ............................................................................................................................54 Figure 62, Hollow shaft encoder, cut-away view .....................................................................................................55 Figure 63, Stator coupling for hollow shaft encoder................................................................................................55 Figure 64, Cable entry axial (A) and radial (R) ..........................................................................................................56 Figure 65, Cable entry for small units ......................................................................................................................57 Figure 66, Cable plug ..............................................................................................................................................57 Figure 67, Connector unit .......................................................................................................................................58 Figure 68, Pin connection of a plug .........................................................................................................................58 Figure 69, Coupling, electrical .................................................................................................................................58 Figure 70, Earthing and screening ...........................................................................................................................59 Figure 71, Rotational speed and switching frequency..............................................................................................61 Figure 72, Shaft load, axial (A) and radial (R) ...........................................................................................................61 Figure 73, Transient condition of the TTL voltage ....................................................................................................64 Figure 74, Residual ripple of the signal outputs .......................................................................................................64 Figure 75, Encoder supply with external power supply ............................................................................................65 Figure 76, Resolution and rotational speed..............................................................................................................68 Figure 77, Cable length and output frequency, TTL.................................................................................................68 Figure 78, Cable length and output frequency, HTL ................................................................................................69 Figure 79, Operating instructions, example .............................................................................................................71 Figure 80, Data sheet of the shaft encoder RV1009 ................................................................................................72 Figure 81, Data sheet of the shaft encoder RM6001 ...............................................................................................73 Figure 82, Flexible coupling .....................................................................................................................................74 Figure 83, Axial, radial and angular displacement....................................................................................................75 Figure 84, Flexible coupling with different bore holes..............................................................................................76 Figure 85, Spring disc coupling................................................................................................................................76 Figure 86, Angle flange, example ............................................................................................................................76 Figure 87, Bearing block with angle flange..............................................................................................................77 Figure 88, Isolating adapter.....................................................................................................................................77 Figure 89, Pinion .....................................................................................................................................................77 Figure 90, Rack .......................................................................................................................................................78 Figure 91, Resilient base..........................................................................................................................................78 Figure 92, Measuring wheel ....................................................................................................................................79 Figure 93, Measuring wheels, rubber, plastic, smooth aluminium, roughened aluminium .......................................79 Figure 94, Measuring wheel on moving arm ...........................................................................................................80 Figure 95, Fastening clamp......................................................................................................................................80 Figure 96, Pulse divider E80102, connection ...........................................................................................................81 Figure 97, Pulse stretcher E80110 ...........................................................................................................................81 Figure 98, Figure 98: Mounting with coupling.........................................................................................................82 Figure 99, Mounting with fastening clamp..............................................................................................................82 Figure 100, Hollow shaft encoder with shaft open on one side ...............................................................................83 Figure 101, Hollow shaft encoder with continuous hollow shaft .............................................................................83 Figure 102, No overvoltage, do not align with a hammer........................................................................................85 Figure 103, Do not clamp into the vice, do not drill into the shaft ...........................................................................85 Figure 104, Do not saw or grind the shaft...............................................................................................................85

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Figure 105, Measuring wheel for linear measurement.............................................................................................86 Figure 106, High-lift shelves ....................................................................................................................................87 Figure 107, Robots..................................................................................................................................................88 Figure 108, X-Y-Z-milling system.............................................................................................................................88

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Index

9 90-degree-shift

E 22

A Absolute shaft encoders Acceleration Accessories Accuracy of the shaft encoder Angle flanges angular displacement Applikationen axial displacement

29 60 70 47 72 71 82 71

49 35 72 34

80 13 51 34 18 20 32 54 55 33 70 63 63

D Data sheet Data transmission DC component Decadic Gray excess-3-code Detection of the direction DIADUR DIADUR method Direction of rotation Dividing error Dual-Code

Training manual

F FAQ Fastening clamp Flange types

10 76 50

Grating period Gray code Gray excess code Grub screw

20 35 36 71

C Calculation examples Capacitive principle Clamp flange Code types Coded disc Condenser Connection Connection cable Connector counting Couplings Current consumption Current rating

57 54 61 32 62

B Ball bearing BCD code Bearing block Bin채r-Code

Earthing Electrical connection Electrical data Enable signal external evaluation electronics

68 39 21 37 27 18 15 33 47 34

Hall-effect sensors Handling Hollow shaft encoders Housing material hro flange HTL voltage range

33 81 51 60 51 61

I Incremental shaft encoders Increments Inductive principle Inductive system input frequency Interference signal Inverted output signals Isolating adapter

17 18 12 14 59 27 25 73

L Laying the cable LED Light-emitting diodes Limit frequency Linear measurement Linear movement LSB

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56 63 63 58 80 7 32

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M Magnetic principle mark-to-space Mark-to-space ratio Measuring step Measuring wheel Mechanical data Mechanical rotational speed Mechanical shaft encoders Mounting Mounting of shaft encoders MSB Multiplex operation Multiturn shaft encoders

Round flange 12 23 48 24 74 58 58 13 53 78 32 33 33

S Scanning plate screening Sensor cables Shaft encoders Shaft load Shock resistance Signal evaluation Signal frequency Signal generation Signal generation of the photo elements Singleturn shaft encoders Sinusoidal signals Sockets/coupling Solid shaft encoders Square-wave pulse trains SSI controller SSI interface Standard resolutions Starting torque stator coupling Storage temperature system accuracy

O Operating instructions Operating temperature Oscillator sensors

67 60 14

P Phase difference Phase discriminator Photo elements Photoelectric shaft encoders photoresist Potentiometers Profibus-DP interface Protection rating Pulse diagram Pulse divider Pulse multiplication pulse stretcher

48 27 21 14 15 11 45 60 23 76 28 76

Training manual

20 57 62 17 59 60 22 64 19 20 31 26 56 49 22 43 39 19 50 52 60 15

T technical terms Through-beam method transducer TTL voltage range Type key

85 19 9 61 88

R rack radial displacement Reference mark Reference mark outside Reflectible Gray code Residual ripple Resilient base Resolution Resolvers Rotational movement

73 71 20 25 35 61 74 19, 31 11 7

Vibration vibration resistance Voltage supply

60 60 61

W Wiring

Z zero index

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Source

Some diagrams and figures were taken from literature/catalogues of the company Heidenhain.

THE END

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