Safety-Based Stable Variable Impedance Controller for Interaction Tasks Involving Human Body Surfaces

This paper contributes to the design of Variable Impedance Controllers with safety guarantees in tasks involving contact with a human body surface using a robotic manipulator. Particularly, the work focuses on a bathing task scenario with different contact and free movement phases. Novel modulation laws based on safety criteria are introduced and as safety guarantee an stability and optimality condition is considered. To assess its fulfilment , the controller is formulated in terms of a Linear Parameter Varying (LPV) system such that guarantees can be formulated in terms of Linear Matrix Inequalities (LMI) that define a convex optimisation problem. Results are presented for a 7-DoF WAM robotic manipulator , both in simulation and in the real platform, presenting a comparison against constant impedance and a position-force switching controllers. Assessed Variable Impedance Controller present a stable behaviour while maintaining contact force closer to desired one.