Machine Design – May 2019

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next phase in the process.

more prominent industries, semicon-

ductor and medical device manufac-

turers, there is a clear increase in using

closed-loop stepper motors. Engineers

in these industries must know exactly

where motors have positioned loads or

actuators whether it powers a belt or

ball screw. The closed-loop feedback in

these steppers lets them know exactly

where it is. These steppers can also pro-

vide better performance than servos at

lower speeds.

Generally, any application that needs

guaranteed performance at a lower

cost than a servo motor, and the abil-

ity to run at relatively low speeds is a

good candidate for closed-loop stepper

motors.

Keep in mind, operators do need to

ensure the drive or controls support

closed-loop stepper motors. Histori-

cally, you could get a stepper with an

encoder on the back of it, but the drive

was a standard stepper drive and didn’t

support encoders. The encoder needed

to be taken back to the controller and

position verification would need to

be implemented at the end of a given

move. This is not required with new

closed-loop stepper drives. Closed-

loop stepper drives can dynamically

and automatically handle position and

speed control without involving con-

trollers.

JOHN BROKAW is a Sr. Application En-

gineer for Valin Corp., a leading motion

control and automation company. For more

information, visit http://www.valin.com.

Ser vos or Steppers?

Cross-section of a traditional stepper motor.

Cross-section of a typical servo motor.

54 MAY 2019 MACHINE DESIGN