DEVELOPMENT OF MULTI JOINT GRIPPER THAT ACHIEVES TRANSITION FROM PINCHING TO ENVELOPE GRASPING WITH SIMPLE CONTROL

This study proposes a Multi Joint Gripper (MJG) that achieves envelope grasping for unknown shape objects with simple control: In our previous study we have developed the MJG having a number of multi joint fingers. Each finger has back drivability with Variable Stiffness Mechanism (VSM) for adjusting the stiffness of joints. The MJG succeeded envelope grasping of various shape objects with no sensory feedback. We have also showed the MJG is able to handle objects by pinching with the finger tips and to shift into an envelope grasping. However, in some tasks requiring transition from pinching to envelope grasping, it occasionally failed because of difference of mode setting between pinching and grasping. In this paper, we discuss the pinching motion and the transition from pinching to envelope grasping. The finger mechanism we have proposed is mainly composed of a serially connected Differential Gear System (DGS), and it is controlled by only two actuators. One for driving all of the joints simultaneously and the other for VSM of every joints all together. We propose a novel mechanism for transition from pinching to envelope grasping, which requires no change of mechanical mode setting of the DGS. The experiments revealed that the MJG successfully achieves transition from pinching to envelope grasping with very simple control.