Engineering: How Stepper Motors Work

Topics: Electric motor, Magnet, Coil Pages: 4 (1272 words) Published: July 22, 2013
How Stepper Motors Work Stepper motors consist of a permanent magnet rota ng sha , called the rotor, and electromagnets on the sta onary por on that surrounds the motor, called the stator. Figure 1 illustrates one complete rota on of a stepper motor. At posi on 1, we can see that the rotor is beginning at the upper electromagnet, which is currently ac ve (has voltage applied to it). To move the rotor clockwise (CW), the upper electromagnet is deac vated and the right electromagnet is ac vated, causing the rotor to move 90 degrees CW, aligning itself with the ac ve magnet. This process is repeated in the same manner at the south and west electromagnets un l we once again reach the star ng posi on.

Figure 1 In the above example, we used a motor with a resolu on of 90 degrees or demonstra on purposes. In reality, this would not be a very prac cal motor for most applica ons. The average stepper motor's resolu on -- the amount of degrees rotated per pulse -- is much higher than this. For example, a motor with a resolu on of 5 degrees would move its rotor 5 degrees per step, thereby requiring 72 pulses (steps) to complete a full 360 degree rota on. You may double the resolu on of some motors by a process known as "half-stepping". Instead of switching the next electromagnet in the rota on on one at a me, with half stepping you turn on both electromagnets, causing an equal a rac on between, thereby doubling the resolu on. As you can see in Figure 2, in the first posi on only the upper electromagnet is ac ve, and the rotor is drawn completely to it. In posi on 2, both the top and right electromagnets are ac ve, causing the rotor to posi on itself between the two ac ve poles. Finally, in posi on 3, the top magnet is deac vated and the rotor is drawn all the way right. This process can then be repeated for the en re rota on.

Figure 2 There are several types of stepper motors. 4-wire stepper motors contain only two electromagnets, however the opera on is more...
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