Improved performance of built-in torque sensing for harmonic drives

Torque sensing built into harmonic drives has advantages 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 is a drawback in its practical applications. However, we present a simple and effective method to compensate the fluctuation signal and thus improve an overall accuracy of the harmonic drive built-in torque sensing. The method does not require precise positioning of the strain gauges, does not require online-estimations of the fluctuation signal, and does not increase the 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: one is based on a mathematical model of the fluctuation signal, and the other employs a heuristic approach. Practical results show the effectiveness and usefulness of the proposed method.