Mechanical Design of a Supernumerary Robotic Finger for Grasping Abilities Compensation

This paper presents the mechanical design, kinematic analysis and tests of a supernumerary robotic finger (SRF). Divided into the executive part and the control part, the device can be used for hand function compensation of stroke patients. This SRF is wearable, small and light, easy to carry. It can be worn on the back of the hand and coordinate with the human fingers to grasp an object through the bionic mechanical finger. The control part obtains the posture of the user’s little finger. It includes a planar four-bar mechanism and several cylindrical pairs, which convert the rotation of the human finger into the rotation of the potentiometer. The executive part is a bionic mechanical finger. It realizes the rotation of two joints driven by the motor through another planar four-bar mechanism and a crossed cable-drive structure, which implements the function of flexion and extension of the SRF. An experiment has been conducted on this device to evaluate its grasping ability. The results show that the SRF can well compensate for the grasping function when it cooperates with human fingers.