Multi Stack Variable Reluctance ( VR ) Stepper Motor

The construction, step angle, advantages and disadvantages of variable reluctance stepper motor is given in this theory.

Construction of Variable Reluctance Stepper Motor

• Figure shows four stack variable reluctance stepper motor.  
• We can achieve low step angle by multi stack variable reluctance stepper motor. 
• The stator frame and rotor shaft are common in the multi stack variable reluctance stepper motor. 
• Each stack is parallel to shaft axis and its excitation is given by separate winding. 

Step angle in Variable Reluctance Stepper Motor

• The number of stator poles is equal to number of rotor poles. 
• If there are 20 teeth in the four stack VR stepper motor, the step angle becomes 4.5⁰.
• Step angle ( Θ ) = 360⁰ / S

       Where S = 4 ( Number of stacks ) × 20 ( Number of rotor teeth )

                     = 80

• Therefore, Step angle ( Θ ) = 360⁰ / S = 360⁰ / 80 = 4.5⁰

Advantages and Disadvantages of VR Stepper Motor

Advantages

• Higher stepping rate is possible
• Low inertia of rotor
• Light weight
• Freely rotation of rotor

Disadvantages

• Nil detent torque
• Higher efficiency for low stepping rate

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