Controller Design for Robot Tasks Involving Free and Contact Motion

A controller design strategy is proposed for a task entailing both free and contact motion. Position control is developed in free motion. Using impedance control, force control is then added through the contact force feedback loop. A compensator in this feedback loop helps to reach the target impedance when the end-effector is in contact with the environment. Contact force is assumed to be available from a wrist force (and torque) sensor. Since the force sensor signal may contains inertial force also, a Kalman filter is used to extract contact force from the signal. The development is illustrated in three examples.