Bolster Step-Motor Reliability

These tips will help you improve step-motor performance and reliability.

Reliable operation of step-motor systems begins with the sizing and selection process.

Avoid specifying a motor that is too large. You’ll generally end up spending more money than is necessary and/or generating too much heat for an application. If the motor is too small, it may not provide the right amount of torque for reliable motion control. These tips can help you specify a step-motor system that ensures reliable operation for the life of your machine or process.

• Never use the holding-torque specification to size a step motor.
The holding-torque specification defines the amount of torque the motor provides when at rest. Because output torque falls as speed increases, holding torque is a poor indication of the torque the motor produces when rotating.

• Estimate a torque margin when reviewing speed-torque curves.
While torque produced at a specific speed by a step motor is shown in published curves, information represents best-case performance. Pad your torque requirements by 50% to 100% for better results and safeguard against stalls that can stop production.

• Adhere to the supplier’s drive and power-supply recommendations.
The specific drive and power-supply voltage used in creating speed-torque curves is critical to achieving published performance. Whenever possible, use the same drive and power-supply voltages in the machine. The rated supply voltage corresponds to speed, torque, and power. Using a supply voltage other than the published one can result in the motor not achieving expected torque.

• Keep the motor case temperature under 212 F (100 C).
Use the idle-current-reduction feature of the stepper drive to automatically reduce the motor current when the motor is in holding position. While step motors are designed to run hot, surface temperatures that exceed 212 F can lead to motor failure.

• If the step motor vibrates excessively once installed in the machine, it could be due to naturally occurring resonance.
A simple solution to this problem is running the motor a little faster or slower, if possible. Another solution is reducing the current setting on the drive, but not to the point that the motor stalls. A stepper drive with microstepping or anti-resonance also serves as a solution as it will reduce or eliminate the motor’s natural resonance.

Following these tips when sizing, selecting, and operating step motors will increase the success of your application and the long-term reliability of your machine or process. If in doubt about the information presented, contact your step-motor supplier. EP

For more information, contact Applied Motion Products, Watsonville, CA, at applied-motion.com.

—Eric Rice, Applied Motion Products