Multi-joint gripper - control of envelope gripping -

The study has proposed a multi-joint-gripper (MJG) that achieves envelope grasping for unknown shape objects. The mechanism mainly consists of a serially connected differential gear system (DGS) controlled by only two actuators, one is for driving all of the joints simultaneously and the other is for adjusting stiffness of every joints all together. We have developed the MJG with seven joints and succeeded the envelope grasping of various shape objects with no tactile or pressure sensor on contact surface between gripper and objects for the sake of being used in severe environments. The experiments also revealed necessity to control the stiffness of joints according to grasping conditions such as weight and elasticity of grasping objects. This paper proposes the way to control the joint stiffness followed by being elucidated with some simulation studies and experiments.