Stepper motors
A stepper motor is a special type of d.c motor that produces rotation at equal angles called step's for each digital pulse supplied to its input. For example if a pulse can produce a rotation of 10o then 36 pulses will produce one rotation or 360°. Number and rate of the pulse control the position and speed of the motor shaft. Generally stepper motors are manufactured with steps per revolution of 12, 24, 72, 144, 180 and 200 resulting in shaft increments of 30°, 15°, 5°, 2.5° 2° and 1.8° per step. Special micro-stepping circuitry is sometime provided to allow many more steps per revolution, offer 10,000 steps/revolution or even more.
Performance characteristics
The following are the performance characteristics of a stepper motor.
a. Rotation in both directions
b. Precision angular incremental changes
c. Holding torque at zero speed
d. Capability of digital control
Classification of stepper motor
a. Permanent magnet
b. Variable reluctance and
c. Hybrid type
The other classification are
a. Bipolar stepper motor and
b. Unipolar stepper motor
Permanent magnet stepper motor: In this type the stator consists of wound poles and the rotor poles are permanent magnets. The permanent magnet motor has the advantage of a small residual holding torque called the detent torque even when the stator is not energized.
Fig. 5.62 : Basic concept of step rotation of stepper