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A motor guide for precision engineering

04 January 2022

When to use a servo motor and the advantages of an accurate precision closed-loop stepper motor are explored by Paul Jepson, New Business Analyst, Oriental Motor (UK).

Traditional servo motors have been a key technology in automation for a long time now. They have been the go-to option if an application requires high speeds and high torque, and/or positional accuracy. There is, however, a more recent introduction: a closed-loop stepper motor. This has all the performance benefits of a servo system, but with the added advantage of incredible positional accuracy, without the need for a proportional-integral-derivative (PID) loop in the driver of the motor to monitor its position.

Traditional servo motors are based on brushless DC (BLDC) technology. There are usually 10 to 16 poles on the motor’s rotor, so each pole covers several degrees of rotation (i.e., 36 degrees per pole for 10-pole motors and 22.5 degrees per pole for 16-pole models). 

If an accurate position, or set point, is required, the position is controlled by a PID loop, which constantly checks the position that the servo motor is in, compares it to the command position, and manipulates the motor position to stay as close to the command position as possible. It has been likened to a circus performer standing on a giant ball; the performer’s head and torso may look stationary but their feet are constantly moving to make little corrections to keep him or her steady. 

Read the full article in DPA's January issue

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