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Pulsewidth modulation (PWM) control of brushless dc motors is implemented with digital servo mechanisms for robotic applications. Under the assumption that the pulse period is much smaller than the motor time-constants, the motor is modeled by a discrete-time transfer function with the pulsewidth playing the role of the control signal. This model enables the application of classical linear control engineering to the design of a digital position servo for the brushless dc steering motors on the CMU Rover. The controller is implemented with a microprocessor and programmable timer to calculate concurrently the actuating signals, time sampling periods, and pulsewidths, as well as to provide commutation. Computer simulation and real-time hardware implementation of the servo demonstrate the efficacy of the approach.
Date of Publication: Aug. 1985