Abstract: To obtain more DOF by fewer actuators with lower control difficulty, under-actuated mechanical fingers are needed, so that a robot hand can grasp objects much better and is more similar to human hand. The design idea on under-actuated fingers is expended, and an experimental under-actuated finger mechanism is developed. As a finger of a robot hand or a part of a finger, this mechanism makes a robot hand have fewer drivers, but more DOF. It can realize passive adaptive grasp to objects of different shapes and sizes without any extra requirements of control precision. With the property of small, light, but reliable, it is easy to produce. Its main parameters for design in detail are described.

Key words: Humanoid robotic finger, Shape adaptation, Under-actuated mechanism