Drive Sample Questions

1. A closed-loop motion control system has the following parameters:

A brushless DC motor has a speed limit of 12000 rpm. The position sensor is an incremental encoder with a resolution of 1000 pulse-per-revolution (4000 quadrature count per revolution). The encoder frequency is limited to 100 kHz of encoder cycles and the controller limits the encoder frequency to 5*10⁵ quadrature counts per second. The maximum speed that the motor can run at under closed-loop control is:

1. 3600 rpm
2. 377 rpm
3. 5000 rpm
4. 6000 rpm
5. 2400 rpm

2. What most often limits the peak speed of a brushless motor/drive system?

1. the available voltage of the drive
2. the balance of the motor rotor
3. the available current from the drive
4. the torque constant of the motor
5. the commutation rate of the drive

3. Why do stepper motors connected in parallel and using the same driver generally have higher torque at higher speeds than series connected motors?

1. they have lower inductance
2. they have lower resistance
3. they have amp-turns
4. they have less high-speed instability
5. they have higher electrical time constants

Page Revised: July 14, 2003