Design of joint torque sensor and joint structure of a robot arm to minimize crosstalk and torque ripple

Torque control of a robot arm often requires joint torques which are measured using joint torque sensors. However, a joint torque sensor installed at a robot joint suffers from crosstalk errors and torque ripple. The crosstalk error generated by a moment load induces an offset to the torque sensor output. Furthermore, torque ripple noise generated by a harmonic drive interferes with accurate torque measurement as its amplitude is much higher than electric noise. In this study, novel methods are proposed to reduce crosstalk and torque ripple. The crosstalk is dealt with by specially designing the structure of a robot joint. Torque ripple is reduced by taking an average of two Wheatstone bridges outputs. The performance of the proposed robot joint was verified through various experiments.