Robotic manipulator control of generalized contact force and position

Considers the problem of control of generalized contact forces with a manipulator controller that has traditionally been regarded as a noncontact task trajectory controller. The open-loop control of generalized forces, suitable for tasks in which only crude force control is required, is achieved through the manipulation of the generalized position inputs of the robotic manipulator. An algorithm is proposed which determines the appropriate manipulator generalized inputs, the only input signal available to the position controller, in order to generate prescribed generalized force and position trajectories during contact with the robot work environment. During noncontact motion of the manipulator, the robot is operated in the more usual generalized position control mode. The use of such a method to control generalized contact forces, although in an open-loop manner, permits a single control to be utilized for both noncontact and contact tasks. Thus, issues of stability during the transition to and from contact, as well as stability during sustained contact are avoided. Hence, the utilization of a single control for both noncontact and contact phases of a single task is seen to be advantageous. The stability of the robotic manipulator during object contact, implicitly assumed by the proposed control strategy, is established using the theory of singular perturbations. Experimental results of a two-degree-of-freedom direct drive manipulator during contact with a one-degree-of-freedom linear mechanical impedance illustrate the usefulness of the proposed method