Implementation of Gravity Compensation in the Control of a Custom-Designed 2-DOF Manipulator

Abstract

The manipulator presented in this paper has potential to significantly enhance the capability of robots in performing operational tasks, particularly in unstructured and dynamic environments where proximity to humans is a concern. Traditional industrial robots are not well-suited for these conditions, underscoring the importance of studying the fundamentals of manipulator design and control. To explore these concepts, we designed and developed a custom 2-DOF manipulator, applying gravity compensation control as a fundamental and generalized approach for other control strategies. Gravity compensation requires the motor to counteract the torque generated by gravitational forces. We selected DYNAMIXEL XM540-W270-T and XM430-W350-T motors for this application due to their versatility in various control modes and the ability to provide feedback on critical variables. The 2-DOF manipulator was constructed using standard components and 3D-printed parts, with additional end-effector weight introduced via a C-clamp. MATLAB Simulink was employed to compute the dynamic model, simulate the system, and command the torque for each motor. Experimental results demonstrate that gravity compensation was successfully achieved, as the manipulator maintained a steady position while also enabling position adjustments through the application of external force. However, tuning specific parameters to minimize input torque required multiple adjustments. Additionally, challenges were identified in the actuation of the first joint, which relied on shaft friction forces. Despite these issues, the manipulator exhibits considerable potential, although further development is necessary.