Identification of contact states based on a geometric model for manipulative operations

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Abstract
_A model-based approach to the recognition of contact states is presented. The state of contacts between workpieces varies as the operation proceeds in manipulative tasks such as part-mating and grasping. Adequate control laws and motion strategies of a robot manipulator depend on the contact state. The recognition of contact states is thus required so that the robot can select and modify its motion strategies adequately according to the state. In this paper, we deal with the estimation of contact states by using force information acquired in the mating process, and develop a method for generating the state classifiers based on geometric models of workpieces on a computer. First, a symbolic representation of contact states is addressed. Second, the static behaviour of workpieces at each contact state is analysed by applying the theory of polyhedral convex cones. Next, state classifiers that discriminate contact states are formulated by using the polyhedral convex cones, which directly provide a set of discriminant functions. To reduce real-time computations, the classifiers are simplified to a minimum set by using reduction rules of polyhedral convex cones. The algorithm to generate the state classifiers is then implemented on a computer and a simple experiment to identify the current contact state from the measured reaction force is done to demonstrate the usefulness of the approach.

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