Thursday, April 25, 2013

Stepping Motors versus Servo Motors

In my view, stepping motors lead the revolution of the use of motion control for machine automation. Microstepping, which allowed stepping motors to be run smoothly and precisely, was developed by Hewlett Packard for use in computer printers. A start-up company in the early 1980’s named Compumotor brought this technology into the industrial market. Combined with simple to use controllers and “plug and play” connections, Compumotor’s stepping motors were used in thousands of applications that previously were either not possible, or required elaborate mechanisms for adjustment and coordination.

As microprocessors and power electronics progressed, the control of brushless servo motors also became commonplace. Today, brushless servo motors have over-taken stepping motors in a wide variety machine automation applications.

So, are stepping motors still a viable choice for automated machines? In short, the answer is, ‘Yes!’

Stepping motors provide very reliable operation, long life, and are inherently stable and precise. They are usually operated open loop (without position feedback) which works well in most applications since they do not require feedback for precise control and positioning. They are relatively simple devices.

If a selected stepping motor is rated for the speed and torque that an application requires and, if the inertia of the motor’s rotor is a good match to the reflected inertia of the mechanism it will drive (called the “inertia ratio”), then a stepping motor may be a very good and economical choice.

The Compumotor stepping motor products are still alive and well as a part of ParkerHannifin’s Automation Group, which also includes brushless servos and precision positioning systems.

Greg Selke
CEO ONExia Inc