Measurement framework of partial cage quality based on probabilistic motion planning

When an object is caged by a set of fingers, it cannot move arbitrarily far from the caging fingers regardless of what possible rigid motion it takes. Although this condition makes caging an attractive choice for nonprehensile manipulation, directly computing caging configurations is still a complex process. More importantly, using a cage could be too restrictive than necessary in many real cases. This is because some object motions rarely occur in reality. Therefore, some non-caging formations of fingers that only allow these rare escape motions can still effectively be deployed in many caging tasks. This paper introduces a concept of partial cage quality which determine an ability to cage an object of a non-caging formation of fingers, partial cage. We believe that the quality is closely related to possibility of an object escaping from a partial cage. A measurement framework based on motion planning is presented together with experimental results to illustrate and justify the proposed concept.