Design and Control of a Closed-Loop Brushless Torque Activator
MASSACHUSETTS INST OF TECH CAMBRIDGE ARTIFICIAL INTELLIGENCE LAB
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This-report explores the design and control issues associated with a brushless actuator capable of achieving extremely high torque accuracy. Models of several different motor - sensor configurations were studied to determine dynamic characteristics. A reaction torque sensor fixed to the motor stator was implemented to decouple the transmission dynamics from the sensor. This resulted in a compact actuator with higher bandwidth and precision than could be obtained with an inline or joint sensor. Quasi-static testing demonstrated a closed-loop torque accuracy within 0.1 over the full range of torques. Torque ripple and friction effects, which accounted for errors of up to 7 in open-loop tests, were virtually eliminated. The mechanical bandwidth of the system approaches 300 Hz, but the current loop in the drive electronics limits the open-loop bandwidth to less than 10 Hz. Compensation techniques were utilized to increase the controllable bandwidth to greater than 200 Hz, demonstrating that the motor response can be drastically improved by closing a high bandwidth torque loop.