21-03-2014, 12:51 PM
INTRODUCTION TO STEP MOTORS
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INTRODUCTION
A Step Motor is defined as a device whose normal shaft motion consists of discrete angular
movements of essentially uniform magnitude when driven from sequentially switched DC
power supply.
A step motor is a digital input-output device. It is particularly well suited to the type of
application where control signals appear as digital pulses rather than analog voltages. One
digital pulse to a step motor drive or translator causes the motor to increment one precise
angle of motion. As the digital pulses increase in frequency, the step movement changes into
continuous rotation.
Types of Step Motors
There are three basic types of step motors in common use:
• Active rotor: permanent magnet (PM)
• Reactive rotor: variable reluctance (VR)
• Combination of VR and PM: Hybrid (HY)
These are brushless electrical machines which rotate in fixed angular
increments when connected to a sequentially switched DC current.
When alternating current is used, the rotation is essentially
continuous.
Permanent Magnet
This type of step motor has a permanent magnet rotor. The stator
can be similar to that of a conventional 2- or 3-phase induction
motor or constructed similar to a stamped motor. The latter is the
most popular type of step motor.
a.) Conventional permanent magnet type. Figure 1
(see page Z-8)shows a diagram of a conventional
permanent magnet rotor step motor. A 2-phase winding
is illustrated. Figure 1a (see page Z-8) shows Phase A
energized with the “A” terminal positive. The field is at 0°.
With the coil wound as shown, the north seeking pole of the
rotor is also at 0°. The motor steps as shown in Table I.