Dexterous gripping of a hand with multi-joint fingers

In our previous study we have developed the seven axes multi joint gripper (MJG) having a variable stiffness mechanism and have showed it achieves some dexterous grasping. The mechanism mainly consists of a serially connected differential gear system (DGS) controlled by only two actuators: one for driving all of the joints simultaneously and the other for adjusting stiffness of every joints all together. This paper subsequently shows a method of contact detection using a function of DGS itsself and proposes a way to control contact force and joint stiffness through simulation and experiment results. It also shows a hand consisting of three multi joint fingers (MJF) having four axes developed as the next stage of our MJG research. The hand succeeded envelope grasping of various shape objects with no sensory feedback. The experiments also revealed that the hand with three MJF successfully achieves transition from pinching to envelope grasping. Finally the paper investigates the way to increase the number of contact points and the way to make contact force distribute as evenly as possible.