Kinematic design of a serial-parallel hybrid finger mechanism actuated by twisted-and-coiled polymer

Abstract Flexible actuators composed of twisted and coiled polymers (TCPs) can provide excellent performance such as high power-to-weight ratios for robotic hands. This paper presents a systematic methodology for the kinematic design of the TCP-actuated finger mechanism. The finger mechanism has a redundant serial-parallel hybrid topology, which is designed for grasping in space. The local and global performance evaluation indices concerning the dexterity and the extreme value of the velocity are first proposed for the optimal design of mechanism dimensions. Moreover, the flexibility matrix, mapping the stiffnesses of flexible elements including active TCP actuators and passive springs into the end-effector's stiffness, is established, and thus the extreme value of the deformation is obtained as the optimization objective function. Therefore, optimal passive stiffness coefficients are achieved by the genetic algorithm. Finally, the prototype of three-fingered robotic hand with the proposed finger mechanism and the control strategy based on TCP power-strain model were developed. Comparisons of experimental and theoretical data validated the kinematic design of the finger mechanism.