Motion Control Stepper Motors
Stepper Motors divide a revolution into discrete steps and can maintain a motors position when not rotating without the need for a positional feedback sensor. The steps are created by sequentially energising the stator's multiple electromagnets causing the rotor to line up each time as shown in the diagram below. The energised magnet is shown in bright green and the angle achieved in yellow. Notice how the rotor teeth only line up with the energised magnet.
Greater resolution can be achieved by energising the electromagnets with some overlapping so that instead of the rotor tooth discretely stepping from one magnet to another, it positions itself in between the two. This is known as Microstepping and the theory is demonstrated in the diagram below where it can be seen that this introduces an intermediate stage between a complete step in normal operation.
Stepper Motors achieve short, precise moves with quick acceleration and no brush maintenance yet generally still remain cheaper than brushless motors. However the rapid energising of electromagnets is inefficient at high speeds and excessive loads can cause the motor to skip its sequence and effectively stall.