On computing form-closure grasps/fixtures for non-polygonal objects

Form-closure independent regions are parts of the object edges such that a grasp with a finger in each region ensures a form-closure grasp. These regions are useful to provide some robustness to the grasp in the presence of uncertainty as well as in the design of fixtures. The paper presents a new approach to compute independent regions for four frictionless contacts. A sufficient condition is stated and used to obtain combinations of two contact points that allow a form-closure grasp. Then, selecting one of these combinations, a set of four independent regions on the object boundary is determined. An example of the proposed methodology is included in the paper