Design and Calibration of a Joint Torque Sensor for Robot Compliance Control

Compliance control is one way to achieve compliance for rigid robots and is widely used in cooperative robots, lightweight robots, and exoskeleton robots. Real-time accurate collection of joint torque data is essential for compliance control during dynamic physical interactions with humans or the environment. Therefore, it is highly desirable to develop high-frequency joint torque sensor (JTS) that are accurate and sensitive and that can be properly calibrated. Toward this end, we propose herein a multi-objective optimization design method to improve the elastic strain distribution in the strain gauge working area, thereby improving the sensitivity of JTS. An analysis and comparison of a variety of easily manufactured inner hole spoke structures shows that the circle-rhombus type spoke structure is the most sensitive. An amplifier and low-pass filter circuit are designed for signal acquisition. An analysis of the sensitivity, linearity, hysteresis, repeatability, resolution, zero drift, and mechanical response of the sensor shows that the optimal sensor designed with high sensitivity of 30.5 mV/Nm, ±100 Nm capacity, 0.1 Nm resolution and 78.8 g weight, and the sampling frequency is 2 kHz. The experimental results show that the JTS is lightweight with high sensitivity and resolution, low noise, high dynamic response, all of which satisfy the design requirements. These results lead to an efficient and economical method of customizing JTS.