Improved performance of built-in torque sensing for Harmonic Drives

Torque sensing built into Harmonic Drives has advantage in its size and stiffness comparing to the torque sensors added to the robot joints. A relatively high fluctuation signal of a built-in torque sensor Was a drawback in its practical applications. However, in this paper. we present a simple and effective method to compensate the fluctuation signal and thus improve overall accuracy of the Harmonic Drive built-in torque sensing. Different to the previously proposed methods, the new method does not require precise positioning of the strain gauges, does not require on line estimations of the fluctuation signal, and does not increase number of applied strain gauges. It requires initial tuning of the gains for the signals of the separate strain gauges. Two techniques to define the gains are presented in this paper. One is based on a mathematical model of the fluctuation signal, and the other employs a heuristic approach. Practical results show effectiveness and usefulness of the proposed method.