Compound control method for reliability of the robotic arms with clearance joint

This study provides a reliability improvement control method for robotic arms with clearance joints. Firstly, the dynamical model of a six-DOF robotic arm with joint clearance is established, and the Archard model is utilized to describe joint wear, considering its effect on clearance evolution. The kinematic and dynamic characteristics of the robotic arm with clearances are analyzed concerning the contact and operation state variations. Then, the influence of clearance wear on the operational reliability of the robotic arm is studied as joint wear in the robotic arm contains interval uncertainty. To provide the uncertainty factors caused by the interval, we introduce Chebyshev functions to describe the dynamic response uncertainty and reliability. The non-probabilistic reliability index is given to evaluate the reliability of the robotic arm based on the stress intensity interference theory. Lastly, to improve operational accuracy and reliability, a novel compound control strategy containing collision force feedforward and PD feedback is carried out. It is compared with the traditional PD control strategy. Also, the sensitivity and robustness of the proposed compound control strategies are discussed. The results show that the proposed control strategy can effectively enhance the dynamics precision and reliability of the robotic arm, with satisfactory robustness. This study provides the control method for joint-worn robotic arms with undesired joint clearance, having significant potential applications for guaranteeing mission reliability in the fields of aerospace and industrial robotics.