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Stepper Fundamentals Slide 7

As stated previously, the basic configuration of a stepper motor can be thought of as a fixed magnet on the rotor and two coils on the stator oriented at 90°. If both coils are energized with the same magnitude of current the resulting magnetic vector will be at 45° and the rotor will move to align with this vector, as shown is state 1 on the slide. By reversing the direction of current flow in the first coil, as shown in state 3, the magnetic vector moves 90° and the rotor will follow. Reversing the direction of current in the second coil will then move the rotor to state 5 and so on. Continuing the step sequence in the 1 3 5 7 order causes the motor to rotate in the forward direction and reversing the order to 7 5 3 1 will cause the motor to rotate in the reverse direction. This drive sequence is commonly referred to as Full Step since each change in the current moves the motor one step. For a simple motor that has only one pole pair on the rotor, there are 4 steps per revolution and one electrical cycle completes one revolution. Real stepper motors, of course, have many more steps per revolution. One common configuration has 7.5° steps which corresponds to 48 steps per revolution for a 12 pole pair motor. Such a motor would require 12 electrical cycles to complete one mechanical revolution. Another common configuration is 1.8° per step with 200 steps per revolution and 25 pole pairs, requiring 25 electrical cycles per revolution. Although other configurations are possible, these are the two most common.

PTM Published on: 2011-12-14