Picking, grasping, or scooping small objects lying on flat surfaces: A design approach

Grasping in constrained environments is, to this day, an ongoing research topic. Objects can rarely be grasped from arbitrary directions, hence the need to study the options available to grasp them. This paper proposes a gripper capable of grasping small or thin objects that cannot be directly pinch-grasped. The focus is placed on objects that lie on hard surfaces. The proposed approach uses a quasistatic method referred to as scooping while implementing a passive thumb to compensate for manipulator positioning errors. Hence, the robot arm does not need to be moved while the gripper is grasping an object, similarly to a human hand performing a precision grasp. The design approach is presented and the main design choice, namely the use of epicyclic gear trains instead of conventional revolute joints, is explained. The implementation of the proposed approach to the gripper design is shown. We explain how parallel pinch grasps and large grasping forces are achieved even though the mechanism does not follow the usual parallelogram four-bar implementation of parallel pinch mechanisms. The experimental validation of the proposed concept is then presented by picking up a set of test objects in sequence and demonstrating some variants of the method that expand on the concept.