POWER TRANSMISSION REFERENCE GUIDE
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gearmotor types
gearmotor is a combination of an electric motor and a gear reducer that delivers high torque at low speed. Common motor types include ac permanent magnet or induction and brushless dc, and gears can range from straight and right angle to parallel shaft versions. Gearmotors can be classified in several different ways, but one common method is to divide them into standard and inverter duty. Standard gearmotors are designed to operate over a wide range of conditions producing a range of output speed and torque. However, there are special motor designs aimed at specific applications, such as washdown motors used in food and beverage processing or explosion-proof motors used in hazardous locations. Inverter-duty gearmotors are a bit like this. As the name implies, inverter-duty refers to a gearmotor whose speed is controlled by an inverter, or VFD (variable frequency drive). The difference between an inverter-duty gearmotor and a standard gearmotor is in the construction. These motors are specifically designed to operate at low speeds and not overheat. Because of the special way the windings are insulated, they are better able to withstand the voltage spikes of the fast-switching PWM signals generated by VFDs. The insulation will not break down and cause motor failure. Inverter-duty gearmotors can thus produce a wider constant-torque speed range than a standard gearmotor. Inverter-duty gearmotors are commonly used in applications such as material handling equipment, packaging equipment and conveyors. In short, any application requiring adjustable speed, hence the use of a VFD. A different way of classifying gearmotors is by function – as either controlling position or speed. A good example of position control is in packaging or material handling where a load needs to be picked up or placed at a specified location, or applications with more precise requirements such as micro-positioning in high-precision manufacturing or dispensing. Application requirements will dictate the level of accuracy needed from the gearmotor. For instance, low-accuracy applications are ones where the position can be “good enough,” such as a robotic arm placing boxes on pallets. On the other hand, high-accuracy positioning may require accuracy in thousands of an inch or even at the micron level. In reality, just about any type of gearmotor can be used for position control. The real question is how accurate does the positioning have to be, in which case the focus shifts to the type of gears in the gearmotor. One of the main culprits for inaccuracy in
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DESIGN WORLD — MOTION
Gearmotors — Power Transmission HB 05.19_v2.indd 32
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These H Series gearmotors with inline helical speed reducers from DieQua offer high torque capacity to 14,000 Nm (10,325 ft lbs). The company’s cat4CAD software supports simplified selection and configuration of gearbox and gearmotor systems. gearmotor positioning is backlash in the gears. So, if positioning accuracy is a key variable in the application, make sure that the choice of gearmotor minimizes backlash in the gearing. Manufacturers have several methods for minimizing backlash in gears including preloading and using gears that are designed to minimize or eliminate backlash from the start. Aside from their use in position control applications, gearmotors are used in speed-control applications as well. As with any design problem, the requirements of the unique application will dictate what type of motor is best suited for the job. A good question to ask right off the bat is what are the speed demands. For instance, does the application call for high speed, low speed, or variable speed operation? Another important factor is the type of motor and the associated control. For instance, is a dc or ac gearmotor the right fit? This could depend on the type of power source available as well as the required torque at the load. As for the type of gearing, this too depends on the application needs. Other design considerations may include different frame sizes as well as gear reduction ratios. In the end, the gearmotor selected for the job will ultimately have to satisfy the application’s speed and torque requirements. motioncontroltips.com | designworldonline.com
5/14/19 8:06 AM
