Development of Five Finger Robot Hand with a Variable Stiffness Mechanism

Abstract

This study deals with a robot hand based on the original finger mechanism consisting of a planetary gear system and serially connected four bar linkages. It also has a mechanism for adjusting stiffness of fingers (VSM: Variable Stiffness Mechanism), which allows to give passive gripping force to a gripping object according to the object's elasticity. The mechanism is merely driven by mechanical elements without sensory feedback from tactile or force sensors attached to fingertip or sole. The total number of motors for driving the robot hand is six, all of which are equipped in the palm. Rotation angle of motor is detected by optical encoder equipped to each motor. The robot hand achieves soft and adaptive gripping action due to VSM that adjusts the joint stiffness of the fingers by changing tension of the spring attached to the planetary gear system equipped in every finger except the thumb. Driving tests show that it achieves typical gripping and pinching motions of a human hand in daily life without any sensory feedback and also show that the VSM works effectively.