An underactuated gripper mechanism for picking objects from a tabletop

Abstract

Underactuated grippers that are designed for the pick and place industry tend to pull objects into the gripper when a firm grip is required. This movement within the gripper is sometimes undesired and can damage the object. Therefore, the goal of this study is to design an underactuated gripper mechanism that is able to establish a final and stable grasp without moving the object. The objects are laying on a flat surface and should be grasped from above without damaging the object. By examining the grasping process, we determine the elements needed to create the new gripper mechanism. A mathematical model and simulation tool are developed to study the grasp performance of the gripper. The gripper performance is measured as the feasible grasp range with respect to the complete grasp range. The complete grasp range is determined by an object size range and a horizontal displacement of the object. We optimise the design parameters of the gripper for maximum gripper performance whilst a minimum coefficient of friction is present. With this gripper mechanism, we created a gripper that can cope with large variance in object size and that outperforms a pinch gripper when low contact friction force is required.