A planetary gear based underactuated self-adaptive robotic finger

Different from the traditional using method of one-input-one-output in planetary gear reducer, a concept of one-input-two-output is proposed to drive an underactuated finger. A finger consisting of three degrees of freedom, is driven by two actuators. MP joint is driven by one actuator while PIP and DIP joints are driven by another actuator with power distribution by a planetary gear reducer. When grasping the object, the finger may adapt to its shape automatically through self-motion tuning of the differentially underactuated mechanism. Additionally, when collision between the finger and external objects occurs in the gripping process, the mechanism can absorb the impact energy so as to protect the actuator. Kinematics and statics are analyzed to figure out the related motion relationship among each joint for the underactuated finger. Experiments are conducted to verify the desired characteristics of the finger and the related analysis.