Stepper motor - have a closer look

symbol stepper motor

Stepper motors are often used for positioning without using a sensor, as the actual position can be determined by the specific step angle. Also can this motor apply its full moment even at standstill, without overheating. Or to tell it in other words: its holding torque is the same as its nominal torque. But how does this motor can achieve these outstanding features?

How does a stepper motor work?

Here you see a very simple model of a permanent-magnet bipolar stepper, which is controlled in full step mode. In the following we will explain these terms. In total, you have to switch 4 times until this motor has completed a full 360 ° turn.

Stepper motor - how it works

Parameters which determine the step angle α are:
=> m = Number of stator phases
=> N_r = Number of rotor poles or teeth

The magnitude of step angle for stepper motor is given by:
α =   360°
        2 m N_r

Steps per revolution is given i.e. resolution:  = 360°  =    360°
                                                                        α            2 m N_r

step frequency or Steps per second = rpm * steps per revolution
                                                                           60 s/min

Test your knowledge

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Which of the following statements about a stepper motor are correct? Note: Several statements can also be correct

The starting current of the stepper motor is approximately 7 times the rated current.

If the load is too high, the stepper motor will overheat.

The holding torque of the stepper motor is approximately equal to the nominal torque

The stepper motor is particularly suitable for high speeds.

For simple positioning, a position measuring system is not required when using a stepper motor.

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Example:   A stepper with 2 stator phases and a 4-pole rotor has a rotates at 720 rpm. Calculate
a) the step angle
b) the number of steps per revolution
c) Step frequency