A Robotic Manipulator Using Dual-Motor Joints: Prototype Design and Anti-Backlash Control

This letter focuses on the design and control of a novel seven-degree-of-freedom (7-DOF) robotic manipulator (D-Arm) to address the issue of backlash nonlinearity coupling unknown dis- turbance through the dual-motor anti-backlash control technology. Specifically, the first three axes of the D-Arm near the base are implemented as dual-motor joints (DMJs), while the remaining four axes are single-motor joints (SMJs), which achieve a more comprehensive performance. For DMJs, as over-actuated systems, we first discover an internal disturbance phenomenon named servo-conflict and consider it in the controller design. To mitigate the adverse effects of backlash coupling disturbance, an admit- tance control-based position compensator is proposed. Then, after the backlash elimination, a dual-motor linear active disturbance rejection controller is effectively developed for load tracking task of the DMJ. In the presence of unknown backlash and disturbance, the proposed strategy can improve both transient and steady-state position tracking response, reduce energy consumption without requiring any backlash model information. The effectiveness and simplicity of the developed control strategy are verified through comparative experiments on the D-Arm.