Stepper Motors

Stepper Motor Part 1

       Stepper motor is known by its important property to convert a train of input pulses i.e. a square wave pulses into a precisely defined increment in the shaft position. Each pulse moves the shaft through a fixed angle. So the stepper motor is an electromechanical device which actuates a train of step movements of of shaft in response to train of input pulses. The step movement may be angular or linear. There is one-one relationship between an input pulse and step movement of the shaft. Each pulse input actuates one step movement of the shaft. When a given number of drive pulses are supplied to the motor, the shaft gets turned through a known angle. The angle through which the motor turns or shaft moves for each pulse is known as the step angle, expressed in degrees.

       As such angle is dependent on the number of input pulses, the motor is suitable for controlling position by controlling the number of input pulses. Such system, used to control the position is called position control system. The average motor speed is proportional to the rate at which the input pulse command is delivered. When the rate is low, the motor rotates in steps but for high rate of pulses, due to inertia, it rotates smoothly like d.c. motors. Due to this property it is also used in speed control systems. These motors are available in sub-fractional horse power ratings. As the input command is in pulses, the stepper motor is compatible with modern digital equipments.

       Due to its compatibility with digital equipment, its market is greatly increased in recent times. The stepper motors are widely used in X-Y plotters, floppy disk drives, machine tools, process control systems, robotics, printers, tap drives and variety of other industrial applications.

1.1 Types of Stepper Motors

       The stepper motors can be divided into three categories :

1. Variable Reluctance Stepper Motors

2. Permanent Magnet Stepper Motors

3. Hybrid StepperMotors