Super Twisting Sliding Mode Control-Based Impedance Control for Robot Arm End-Effector Force Tracking

Abstract

Conventional impedance control is essentially used in a wide-ranging industrial robot-environment interaction application. While interacting, the robot arm must regulate the interactive forces to achieve the desired compliance. In this research, the impedance control is designed for a six-degree-of-freedom robot (one-DOF prismatic, telescopic mast, and five-DOF robot manipulator) end-effector force tracking while nuclear power plant's reactor vessel internals (RVI) dismantling operations. Initially, sliding mode control (SMC) was implemented but resulted in chattering in force tracking response. Therefore, super twisting sliding mode control (STSMC)-based force tracking impedance control is designed and implemented for enhanced end-effector force tracking. STSMC is a second-order SMC that does not require system dynamics information. The control input of the STSMC is composed of a continuous and discrete component. Continues control input regulates control performance against uncertainties, whereas discrete provides a switching algorithm. STSMC then eliminates the chattering effect and reduces the force tracking error. Furthermore, the impedance control parameters were auto-tuned using particle swarm optimization (PSO) to get the optimal parameters. The parameters regulation is achieved based on the desired force, current interaction force, and PSO cost-function. The performance of SMC-based and STSMC-based impedance control is compared, and the comparison shows that the STSMC-based impedance control provides enhanced performance.