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Stepper Motor

The rotor of a permanent magnet stepper motor consists of permanent magnets and the stator has two pairs of windings. Just as the rotor aligns with one of the stator poles, the second phase is energized. The two phases alternate on and off and also reverse polarity. There are four steps. One phase lags the other phase by one step. This is equivalent to one forth of an electrical cycle or 90°. Poles are formed using a single magnet mounted inline with the rotor axis and two pole pieces with many teeth. The teeth are staggered to produce many poles. The stator poles of a real stepper motor also have many teeth. The teeth are arranged so that the two phases are still 90° out of phase.

Key characteristics of the Stepper Motor:

  • Easy to position – moves in steps based on pulses supplied to the stator windings
  • Direction of rotation is changed by reversing the pulse sequence
  • Speed control is by the frequency of pulses or pulse rate

Stepper Motor

In simplified terms, the rotor of a stepper motor consists of permanent magnets with poles and a stator with windings. The rotor is constructed using a single magnet mounted in line with the rotor axis and two pole pieces with many teeth. The teeth are staggered to produce many salient poles.

The stepper motor is easy to position and moves in steps based on pulses supplied to the stator windings. The direction of rotation is changed by reversing the pulse sequence and speed is controlled by the frequency of pulses or pulse rate. This animation demonstrates this principle for a stepper motor using full step commutation. Just as the rotor aligns with one of the stator poles, the second phase is energized. The two phases alternate on and off, and also reverse polarity. There are four steps. One phase lags the other phase by one step. This is equivalent to one fourth of an electrical cycle or 90°. Stepper motors have a high holding torque but they cannot run at high speeds.

Kilde: microchip.com

 

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