Control of generalized contact motion and force in physical human-robot interaction

During human-robot interaction tasks, a human may physically touch a robot and engage in a collaboration phase with exchange of contact forces and/or requiring coordinated motion of a common contact point. Under the premise of keeping the interaction safe, the robot controller should impose a desired motion/force behavior at the contact or explicitly regulate the contact forces. Since intentional contacts may occur anywhere along the robot structure, the ability of controlling generalized contact motion and force becomes an essential robot feature. In our recent work, we have shown how to estimate contact forces without an explicit force sensing device, relying on residual signals to detect contact and on the use of an external (depth) sensor to localize the contact point. Based on this result, we introduce two control schemes that generalize the impedance and direct force control paradigms to a generic contact location on the robot, making use of the estimated contact forces. The issue of human-robot task compatibility is pointed out in case of control of generalized contact forces. Experimental results are presented for a KUKA LWR robot using a Kinect sensor.