Grasping designed for robotic assembly

Mechanical hands are not restricted in physical features in the way human hands are. Therefore, we should not be conned into designing mechanical hands or products and their parts on human limitations. A simultaneous and integrated approach to both the gripper and part design maximises the opportunity for the best mechanical outcome. Force closure formed the basis for a class of finger features aimed at selective restraint to satisfy task requirements. This paper evaluates this set of finger features based on engineering criteria, and ranks them. For the analysis it is assumed that the opposable fingers fitted with the same feature type are applied to the grasping task. The elliptical paraboloid, semi-ellipsoidal and hemispherical ranked significantly better than other feature types. Identifying finger features, which satisfy a broad range of tasks, reduces the need for re-tooling, and improves certainty about part location and relative orientation. Aided by the ability to address a broad range of tasks, design rules are established which assimilate grasps to part design. The approach focuses on minimising undesirable wrenches by alignment of grasp location with the centre of wrenches and the centre of gravity.