Anthropomorphic finger mechanism with a nonelastic branching tendon

Abstract

To realize both grasp stability and manipulation dexterity is a central problem in the development of robot hands. In recent years, many underactuated robot hands have been developed that flexibly conform to an object’s surface with simple control. In contrast, it is difficult to realize dexterous manipulation by such underactuated hands in which all degrees of freedom (DoFs) should be controlled. In this research, to realize the dexterous manipulation by simple mechanism and control, we develop a robot gripper comprising of two tendon-driven robotic fingers with nonelastic branching tendons. The branching tendon is a tendon that branches out and connects an actuator to different links. The two joints of this robotic finger are coupled by the nonelastic branching tendon when no external force is exerted. If sufficient external force is applied to the fingertip, one of the tendons slackens and the coupling between the two joints is lost. This means that the two-DoF robotic finger is easily controlled as a single DoF mechanism when reaching toward an object, but when the fingertip is placed on the object, the coupling provided by the branching tendon is released and the finger shifts. Based on this idea, we develop and control a two-DoF robotic finger equipoed with two tendons including a nonelastic branching tendon. We also analyze the conditions, where the branching tendon slacken, and confirmed in an experiment. As the result, the availability of controlling the slack of branched tendon was successfully confirmed.