Harmonic Drive Friction Loss Based on an Integrated Joint for Collaborative Robots

To investigate the influence of the friction loss generated by the harmonic drive in the integrated robot joint transmission process on the torque control accuracy, this study analyzed the internal friction loss of the harmonic drive by establishing an integrated joint dynamics model based on multi-factor coupling. According to the nonlinear transmission characteristics of the harmonic drive, the effects of hysteresis characteristics, nonlinear friction, transmission error, and temperature on the friction loss of the harmonic drive were analyzed. With rated and peak torques of 0.4[Formula: see text]Nm and 1.44[Formula: see text]Nm, respectively, the theoretical calculations of friction loss inside the harmonic drive and simulations on the co-simulation platform to verify the results were performed. The theoretical analysis yielded friction loss rates of 8.54% and 10.41%, and the co-simulation platform yielded friction loss rates of 9.64% and 12.08%. The simulation results are consistent with the theoretical analysis, and the constructed integrated joint dynamics model is accurate. The scheme used to obtain the joint torque by measuring the deformation of the flexure wheel was found to be feasible; however, the friction loss compensation generated during the transmission process needs to be considered in practical working conditions. By analyzing the friction loss of integrated joints, this study provides the theoretical basis for the torque control of robot joints.