The Variable Boundary Layer Sliding Mode Control: A Safe and Performant Control for Compliant Joint Manipulators

The control of compliant joint manipulators is challenging for two reasons. First, the elastic elements of the compliant actuators can store an important amount of energy that can be potentially dangerous and needs therefore to be controlled. Second, the compliance introduces nonlinearities and uncertainties in the system. In this paper, we propose a new control scheme, the Variable Boundary layer Sliding Mode Control (VBSMC) for a safe and performant control of compliant joint manipulators. The control method allows achieving various interaction levels while maintaining good tracking performances. This is realized by adjusting the torque limit parameter and the expanding factor of the controller. Tests have been carried on the collaborative robot Baxter in order to compare the tracking performances and the safe behavior of the VBSMC with the internal controller of the robot. Results show that the VBSMC exhibits either similar or higher tracking performances than the robot controller and can achieve different interaction levels.