Design of joint torque sensor with reduced torque ripple for a robot manipulator

Joint torque sensors are widely used in service robots for force control and collision detection. However, commercial torque sensors and amplifiers are too bulky to install inside robots. In this study, we propose an amplifier-embedded torque sensor because placing the amplifier away from the sensor tends to add noise to the output signal. Furthermore, joint torque sensors experience the torque ripple generated by the harmonic drive gear. Therefore, a torque ripple reduction method is also proposed in this study. FEM analysis was conducted to improve the sensitivity of the torque sensor to only torques in the direction of joint rotation. To avoid external noise and excessive wiring, an embedded amplifier, which can be installed inside the joint of the robot arm with the torque sensor, was developed. Also, the torque ripple reduction method based on the change in the installation position of Wheatstone bridges was developed. Through various experiments, the performance of the proposed torque sensor was verified.