Hybrid force/position control in moving hand coordinate frame

In order to execute complicated tasks involving contact with the environment, the robot manipulator must have force control capabilities. Many strategies for performing constrained motion control have been developed. The major drawback of these strategies is that they can only provide for the control of the interaction forces along fixed task space directions. However, many applications necessitate interaction force control along arbitrary and changing directions. In this paper, a new hybrid force/position controller, implemented in a moving reference frame, which can control the interaction force along arbitrary directions is proposed. Using the proposed controller the robot manipulator can interact with workpieces whose shape is not pre-specified. Thus tasks like milling, deburring, polishing and surface tracking, that involve constrained motion control of the robot manipulator can be performed on a wide variety of workpieces without explicit knowledge of the shape of the workpiece. The design of this new hybrid force/position controller, implemented in the moving hand coordinate frame, is presented and the controller is shown to be stable. Simulation studies for the task of tracking unknown surfaces are also presented.