Correct Answer - Option 2 :
High inertia
Stepper motor: it is a special type of synchronous motor which is designed to rotate through a specific angle (step) for each electrical pulses received by its control unit. The input command is in the form of a train pulse to turn a shaft through a specified angle.
Advantages:
- Compatible with the digital system
- No sensors are needed for position and speed sensing
Types of stepper motor:
Variable – reluctance stepper motor:
- It consists of single or several stacks of stator and rotor.
- Stator have a common frame and rotor have a common shaft.
- Stator and rotor teeth are of same number and size.
- Rotors are unexcited while stators are pulse excited. The static torque acting on the rotor is a function of angular misalignment θ.
- The rotor locks into stator in position θ = 0° or \(\theta = \frac{{360}}{T}\) where T= no of rotor teeth
- Stator teeth of various stacks differ by angular displacement of \(\alpha = \frac{{360}}{{nT}}\) where n= no of stacks.
- Directional control is possible with three or more phases.
Permanent magnet stepper motor:
- The rotor is made of ferrite or rare earth material which is permanently magnetised. Rotor move in steps of 22.5°
- This motor operates at larger steps up to 90° and a maximum response rate of 300 pulses per second.
Hybrid stepper motor:
- This is a permanent magnet stepper motor with the toothed and stacked rotor of the variable reluctance motor.
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Compared to permanent magnet motor finer steps for better resolution are obtained in hybrid motor by increasing the number of stack teeth and also by adding additional stack pans on the rotor.
- As compared to variable reluctance motor a hybrid motor requires less stator excitation current because of the PM excited rotor.
- Compared to a variable reluctance stepper motor it has high inertia.
