Development and experimental evaluation of a robust contact force control strategy for a 7-DOF redundant manipulator

This paper is concerned with robust contact force control for a 7 degree-of-freedom (DOF) redundant robot arm. An outer-inner loop controller is developed. A 6-DOF force/torque sensor is used to measure the interaction forces and feed them back to the outer-loop controller which implements either a force or an impedance controller in each of the 6-DOF of the tool-frame. The second-order impedance controller causes the end-effector to act as a system of mass-spring-dash-pot with adjustable parameters. The force controller is provided with a force set-point, and desired inertia and damping are introduced in the force control loop to improve transient performance. The inner-loop consists of a PD controller, a redundancy resolution module at the acceleration level, and an inverse dynamics module. Experimental results are given to show the performance of the force controller. The successful application to a typical surface-cleaning scenario is presented.