15.8 ASSIGNMENT PROBLEMS

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1. A stepper motor is to be used to actuate one joint of a robot arm in a light duty pick and place application. The step angle of the motor is 10 degrees. For each pulse received from the pulse train source the motor rotates through a distance of one step angle.

a) What is the resolution of the stepper motor?

b) Relate this value to the definitions of control resolution, spatial resolution, and accuracy, as discussed in class.

c) For the stepper motor, a pulse train is to be generated by a motion controller. How many pulses are required to rotate the motor through three complete revolutions? If it is desired to rotate the motor at a speed of 25 rev/min, what pulse rate must be generated by the robot controller?

2. Describe the voltage ripple that would occur when using a permanent magnet DC motor as a tachometer. Hint: consider the use of the commutator to switch the polarity of the coil.

3. Compare the advantages/disadvantages of DC permanent magnet motors and AC induction motors.