Optimal dimensional synthesis of a symmetrical five-bar planar upper-extremity neuromotor device

Abstract

Individuals with hemiplegia suffer from impaired arm movements that appear as a marked change in arm stiffness. A quantitative measure of arm stiffness would characterize rehabilitation therapy effectively, while little mechanism is designed to implement the function. A symmetrical five-bar linkage consisting of two revolute joints and three prismatic joints is presented. Inverse kinematics and forward kinematics are obtained first. Then inverse singularities and direct singularities of the mechanism are gained. Based on the results of kinematics analysis, the global stiffness index is defined. Finally, optimal dimensional synthesis of the mechanism in terms of maximum stiffness is conducted by genetic algorithms. The calculation results shows that when length of both the two linkage a=830 mm, interacting angle of the two guides 2d=4.48 radian, and maximum range of displacement of the two carriers dmax=940 mm, the mechanism achieves highest rigidity and its workspace is singularity-free, which covers the human left and right arm range of motion. The proposed novel mechanism featuring high rigidity and a singularity-free workspace can provides rehabilitation training, but also solves the problem of quantitative measure of arm stiffness.