Development of Gripper to Achieve Envelope Grasping with Underactuated Mechanism Using Differential Gear

In a previous study, we developed a seven-axis multi-joint gripper (MJG) with a mechanism for varying the joint stiffness and showed that it was capable of dexterous grasping. In this research, we expand this design by introducing a hand with several multi-jointed fingers. The mechanism of grasping with this hand involves the use of serially connected differential gear systems (DGSs). The DGSs are controlled by only two actuators: one for driving the joints simultaneously and the other for adjusting the stiffness of all of the joints. The hand is shown to successfully grasp and envelope objects of some shapes without sensory feedback and handle objects by pinching them with the finger tips and subsequently transitioning to an envelope grasp. The mechanism that significantly contributes to this result is the tip roller attached to the fingertip. It is incorporated into the joint drive mechanism using a DGS. These functionalities are considerably advantageous in scenarios where information about the objects to be grasped, such as the shape and precise position, cannot be obtained.