Multistack Variable Reluctance Stepper Motor

What is Multistack Variable Reluctance Stepper Motor

M identical single stack variable reluctance motors are combined to form a multi-stack or m stack variable reluctance stepper motor. One shaft is used to mount the rotor. The Multistack Variable Reluctance Stepper Motor stator and rotor both have the same number of poles, and as a result, have the same pole pitch.

A Multi-Stack motor has perfectly aligned stator poles. However, the rotor poles are separated from one another by 1/m of the pole pitch angle. As the stator pole windings are simultaneously excited, the stator windings of each stack coalesce into a single phase. As a result, there are the same number of phases and stacks.

Consider the cross-sectional view of the three stack motor parallel to the shaft is shown below:

Each stack contains 12 stator and rotor poles. The pole pitch for the 12 pole rotor is 30, and the step angle, or the distance between the rotor pole teeth, is 10 degrees. The result is displayed below:

Let N_r be the number of rotor teeth and m be the number of stacks or phases.

Hence, tooth pitch is represented by the equation shown below:

As there are 12 poles in the stator and rotor, thus the value of N_r = 12. Now, putting the value of N_r in the equation (1) we get,

The value of m = 3. Therefore, the step angle will be calculated by putting the value of m in equation (2)

When the phase winding A is excited the rotor teeth of stack A is aligned with the stator teeth as shown in the figure below:

The rotor teeth of stack B are lined up with the stator teeth when phase A is de-energized and phase B is excited. The anticlockwise rotation of the rotor is about 10 degrees. A change in excitation from stack A to stack B causes the motor to move one step, which is equivalent to one-half of the pole pitch. The stator and rotor teeth’s positions when phase B is excited are depicted in the figure below.

Similarly, now phase B is de-energized, and phase C is excited. The rotor moves another step of 1/3 of the pole pitch in the anticlockwise direction. Again, another change in the excitation of the rotor takes place, and the stator and rotor teeth align it with stack A. However, during this whole process (A – B – C – A ) the rotor has moved one rotor tooth pitch.

Smaller step angles between 2 and 15 degrees can be achieved by using multistack variable reluctance stepper motor. The torque to inertia ratio of variable reluctance motors is high for both the Single Stack and Multi Stack types.