Torque Estimation Technique for a Harmonic Drive Robotic Arm

Abstract

This paper presents a double-axes torque estimation model for a harmonic drive actuator robotic arm. Harmonic drives are known for their high gear ratio and relatively compact torque capacities. They have been widely implemented in robot manipulators, where accurate measurement or estimation of torque is necessary. However, the hysteresis property and related disturbances must be addressed when modeling. To model hysteresis, the wave generator and the flexspline were analyzed individually to fully consider their compliance. The structure of the system was carefully analyzed and designed to reduce deformation and exert torque from gravity. The angular displacement and torque can be measured and estimated, which enables the force estimation of the end effector.  The model was numerically verified with constant and sinusoidal input, and the overall system, including the developed sensor, was verified through experiments.