A passivity based control signal guaranteeing joint limit avoidance in redundant robots

In this work we propose a torque control signal that guarantees joint limit avoidance of a redundant arm. Its design is based on the prescribed performance control methodology that enables guarantees on the satisfaction of inequality constraints regarding the system output. It is proved that the proposed signal preserves the passivity of closed loop robot dynamics with respect to joint velocities thus allowing its use with any passive control law designed to attract the robot towards a task goal. Experimental results with a KUKA LWR4+ for a task involving the tip's position motion along a linear path confirm theoretical findings and demonstrate the proposed signal's performance in two scenarios of a feasible and an unfeasible path.