Stepper Motor Questions and Answers for Viva

Answer-1: Is it possible to just choose a large motor size?

Answer-2: Inductance is the leading cause for motors losing torque at high speeds. The electrical time constant, t, is the amount of time it takes a motor winding to charge up to 63% of its rated value given a resistance, R, and inductance, L. With t = R/L, at low speeds, high inductance is not an issue since current can easily flow through the motor windings quickly. However, at high speeds, sufficient current cannot pass through the windings quick enough before the current is switched to the next phase, thereby reducing the torque provided by the motor. Therefore, it is the current and number of turns in the windings which determines the maximum output torque in a motor, while the applied voltage to the motor and the inductance value of the winding will affect on the speed at which a given amount of torque can be produced.

Answer-3: Voltage can be viewed as forcing current through the coil windings. By increasing voltage, pressure to force current through the coil also increases. This in turn causes the current to build faster in the winding and is able to produce a larger magnetic field. This larger magnetic field is what produces more torque.

Answer-4: It is possible to increase torque by increasing the current but by doing so, it weakens the motor?s ability to run smoother.

Answer-5: Stepper motors have the capability to run in either parallel or series modes. In a parallel mode, only a four lead motor can be run while in a series mode a six lead motor can be run. Eight lead motors can run in either parallel or series configurations. In applications where more torque is required at higher speeds, a lower inductance value given from a four lead motor is better choice.

Answer-6: A Unipolar wound motor has six lead wires with each winding having a center tap. Most applications implementing Unipolar wound motors require high speed and torque. On the other hand, a bipolar wound motor has four lead wires with having no center tap connections. Most applications implementing bipolar wound motors require high torque at low speeds.

Answer-7: In an open-loop stepper motor controller, no feedback is going from the motor to the controller. This type of controller is effective when the motor is carrying a constant load at a steady speed. A closed-loop motor controller is more applicable in applications where load or speed varies. In comparison to the closed-loop controller, the open-loop controller lacks complexity and is more affordable.

Answer-8: The step angle of the stepper motor depends upon stator and rotor poles and number of phases.

Answer-9: Different types of stepper motor are:
Variable reluctance ( VR ) stepper motor
Permanent magnet ( PM ) stepper motor
Hybrid stepper motor

Answer-10: A regulating mechanism; essentially a DC Power Supply plus power switching with associated circuits for controlling the switching in the proper sequence.

Answer-11: It is defined as the ratio of change in holding torque for particular change in shaft position when the stepper motor is in energized condition.

Answer-12: often referred to as a translator, drives a step motor based on pulses from a clock, pulse generator, or computer. Translates the train of pulses and applied power to the appropriate step motor windings.

Answer-13: The nominal angle through which the shaft of a step motor turns between adjacent step positions. It depends upon the motor and driving sequence (mode of drive).

Answer-14: An indication of step or motion size. Usually this is specified in degrees for a rotary motor and inches or millimeters for a linear motor.

Answer-15: The angular position that the shaft of an unloaded step motor assumes when energized. The step position is not necessarily the same as the detent position.

Answer-16: Projections on both rotor and stator such that when aligned they produce a low reluctance magnetic path.

Answer-17: The stepper motor operation at high speed is called as slewing.

Answer-18: An electrical signal or voltage of short duration, used in conveying intelligence.

Answer-19: The smallest positioning increment that can be achieved. It is frequently defined as the number of steps required for a motor?s shaft to rotate one complete revolution. The reciprocal of the number of steps per revolution of the motor.

Answer-20: The rotating part of the motor (the shaft may be included).

Answer-21:
Full step operation
The operation of the stepper motor with only one phase energized at a time, other two phase remains in the non ? energized condition.
Half step operation
The operation of the stepper motor with only one phase energized at a time, other two phase remains in the non ? energized condition. The second time two phase energized at a time while remaining one phase in the non ? energized condition. Therefore it is combination of one phase ON and two phase ON mode operation.

Answer-22: the stationary magnetic parts of the motor including the windings.

Answer-23: Movement of the rotor from one energized position to the next.

Answer-24: It is stepping mode in which two phases simultaneously on but at the same time the currents in the two phases deliberately made unequal.