STEPPER MOTORS

The stepper motor is a special type of synchronous motor which is designed to rotate through a specific angle called a step for each electrical pulse received by its control unit. The step sizes are 7.5°, 15° or larger. The step motor is used in digitally controlled position control system in open-loop mode. The input command is in the form of a train of pulses to turn a shaft through a specified angle.

Advantages

• Compatible with digital systems.
• No sensors are needed for position and speed sensing as these are directly obtained by counting input pulses and periodic counting input pulses, if speed information is needed.

Application

• As paper feed motors in type writers and printers, positioning of print heads, pens in XY-plotters, recording heads in computer disk drives and in positioning of work tables and tools in numerically controlled machine equipment. The range of these motors is increasing as these motors are becoming available in larger power ratings and with reducing cost.
• Elementary operation of a four-phase stepper motor with a two-pole rotor is illustrated above in figure.