A Digital Method for DC Motor Speed Control

A motor speed controller is presented using digital techniques to measure, compare, and correct motor speed. In the prototype model, the range of speed control is approximately 200 rpm to 3000 rpm. The digital approach eliminates measurement nonlinearity and makes the speed setting exactly reproducible. The prototype's steady-state error is less that 0.2% of maximum speed, and it is shown how a direct extension of this design concept can easily bring steady-state error to well below 0.1% of maximum speed.