Localization of hybrid controllers for manipulation on unknown constraints

A robotic control problem is proposed in which a six degree of freedom manipulator is to explore the surface of an object which isa priori unknown to the controller. Choice of an exploration strategy is discussed. The exploration strategy developed uses the maximal freedom of choice allowed under the restrictions of the problem. In particular, it is shown that any admissible reference trajectory can be used, provided it lies in a two-dimensional manifold which maps continuously into the surface. The inverse kinematic velocity problem is then solved using pseudo-inverses which fully exploit the redundancy of the system. The controller used as an example uses computed torque for linearization and compliant motion theory for movement along the desired path. The solution to the inverse kinematic problem together with the on-line generation of selection-mappings constitute a hybrid force/velocity controller. Successful exploration is shown to depend heavily on reliable force control, so PI force feedback is also proposed. Simulation and experimental results demonstrate the effectiveness of the overall design.This work was supported in part by the National Science Foundation under grant No. MSM-8700753 and in part by the Office of Naval Research under grant No. N00014-91-J-1621.