6D workspace constraints for physical human-robot interaction using invariance control with chattering reduction

For safety in physical human-robot interaction (pHRI) the robot motion must be restricted to an admissible (safe) region. In this work, we propose a systematic approach to guarantee the satisfaction of virtual workspace constraints in 6D for arbitrary manipulator dynamics based on an extended invariance control concept. Invariance control yields a computationally efficient method to render multiple virtual nonlinear workspace boundaries. In order to make the scheme suitable for pHRI we present an approach to reduce chattering by explicitly considering the discrete-time Euler solver output. Orientation constraints are unambiguously represented as unit quaternions. The theoretical results are successfully validated in simulation and experiments on a 7-DoF anthropomorphic manipulator.