Saturday, October 27, 2018

The Structure and Principle of the Number of Stator Phases

1.Single phase stepper motor
The single phase stepper motor is winding a loop coil on a coils framework, giving it a positive and negative alternating current, and each switching current takes a step in a fixed direction. Because the magnetic conductance of the rotor magnetic path become bigger to change the rotation direction, the single phase stepping motor can only move in one direction, so a single phase stepper motor just only moves in a one direction. In order to ensure the fixed rotation direction, the magnetic conductance takes many measures, for example, to make the stator air pole wider than the rotor, and the working air gap between the stator and rotor is not uniform, and the direction of rotation is in the direction of small reluctance.

The Classification, Structure and Principle of the Number of Stator Phases

2.Two phase stepper motor
The simplest structure of the two phase stepper motor is that Nr=1, Generally ,the number of the stator magnetic pole is a multiplier of 4, at least 4. The rotor is a two pole rotor with one at N pole and one at S pole.

3.Three phase stepper motor
The stepper motor, of which does not use permanent magnet on its rotor, is very early used on three phase stepper motor. In 1986, a Japan servo company developed a stepping motor with permanent magnet and stator magnetic pole with gear, the matching of stator and rotor pitch can achieve higher angular resolution and torque. The main pole number of the stator winding of the three phase stepping motor is multiples of three, so the stator main pole number of the three phase stepping motor is 3, 6, 9, 12 and so on.

4.Four phase stepper motor
According to the formula θs=180°/PNr, if Nr=50, θs=0.9°,then P=4,that is four phase stepper motor. Because of the even phase of the four phase step motor, the power pipe of the driving circuit is 16, the number of the main pole of the stator is 16, all of which are two times of the two phase stepper motor, so the drive structure is complicated and the cost is high, so it is only used for special purpose.

5.Most of stepper motors sold on market are are five phases
The stator structure and drive circuit are simpler than the four phase stepper motor, but more complex than the two phase and three phase stepper motors and the cost is high.

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