Backlash Elimination Control for Robotic Joints with Dual-Motor Drive

Dual-motor drive is commonly used in heavy-duty robotic joint servo systems. However, the backlash inevitably affects joint accuracy. In this article, a variable bias torque control method is proposed for a dual-motor-driven robotic joint. The variable bias torque varies directly according to the motor current, and the conversion method of the bias compensation torque is presented. A simulation model of the dual-motor drive system in MATLAB/Simulink is established based on the dynamic modeling of a dual-motor drive system, and a robotic joint prototype is also established. The variable bias torque control can achieve a reasonable distribution of the output torque for the whole servo cycle and can effectively reduce the energy consumption of the system to maintain static backlash elimination; the dynamic loading of the bias voltage can be achieved through the setting of the conversion function to complete the smooth transition between the two states of backlash elimination control and common drive control; the dynamic loading of the bias torque improves the torque output capability of the dual-motor system. In the experiment, the steady-state error of the servo system is less than 0.05 degrees, and the error is much smaller than the internal backlash angle (about 2 degrees) of the system, which indicates that the internal backlash of the robot joint has been eliminated. The static backlash elimination bias current of the joint is reduced from about 250 mA to about 110 mA, reducing the energy consumption of the servo system effectively.