Force Controlled Robot Gripper with Flexible Joint for Delicate Assembly Task

For automatic assembly tasks in electronics manufacturing industries, grasping force control for the gripper is required when handling delicate electronic parts, because excessive force could permanently deform or even damage the parts. Furthermore, in order to grasp odd-shaped components, the 'fingers of the gripper should be adaptive to the work-piece's shape in order to maximize the contact area. To meet these requirements, we propose a five-bar linkage gripper design with a compliant finger joint. This under-actuated linkage design can grasp irregular shaped work-piece and maintain the direction of the applied force along the gripper closing direction. The compliant joint design adopts an innovative clamped-and-pivoted flexible beam configuration, with one end of the beam fixed to the finger's tip and the other end rotating with a joint. The angular displacement of the beam, which is a linear function of the grasping force, is measured by a magnetic rotary encoder. Therefore, the grasping force can be controlled by monitoring the angular deflection of the beam. An additional advantage of the compliant linkage design is the gripper can adapt to the centerline misalignment between the gripper and the mating part along the gripper closing direction during an insertion task due to the joint compliance. Based on the mentioned concept, a two-fingered under-actuated gripper is developed. Grasping experiments on objects with different stiffness and shapes, like electromagnetic shield for mobile phone PCB, are conducted to verify the gripper's performance on force control and shape-adaptability. All goals are achieved with satisfactory results.