Fuzzy unidirectional force control of constrained robotic manipulators

The end effector of a robotic arm is required to keep a contact on the contour of the constraint surface in tasks such as deburring and grinding. Being different from contacts resulted from general mechanical pairs, such a contact is unidirectional, or equivalently, the contact force can only act along the outward normal of the constraint surface at the contact point. How to achieve this specification was not addressed explicitly in many position/force control schemes developed so far, instead it was assumed in the development of controllers. In this paper, the unidirectionality of the contact force is explicitly included in modeling and control of constrained robot system. A fuzzy tuning mechanism is developed to generate the impedance model resulted from the continuous contact made by the end effector of the robotic manipulator on the constraint surface while it is in motion. A controller is then developed based on the fuzzy rule bases and the nonlinear feedback technique. The simulation is carried out to verify the effectiveness of the approach.