Parallel active/passive force control of industrial robots with joint compliance

Active force control of an industrial robot with an end-effector force/torque sensor effectively handles compliant industrial tasks like assembly operations, surface finishing jobs, cooperative manipulation, etc. However, the robot still remains intrinsically unsafe for dynamically changing environment where the chances of the links coming in contact with the environment exists. This paper proposes a scheme for active force control at the end-effector using a six-component force/torque sensor through external force-control loop along with steady-state error compensator. In parallel, passive joint compliance was achieved by limiting the currents to joint motors based on an identified model of the robot under study. The proposed method was implemented on a KUKA KR5 ARC industrial robot and tested for passive compliance by colliding with another moving robot in its workspace. Active force control was tested to maintain a desired force on contact to demonstrate the effectiveness of the controller.