Optimization design method of upper limb exoskeleton cam mechanism’s motion trajectory model

Abstract

In order to solve the problem caused by the coupling clearance of the upper-limb cam mechanism, based on cam entity structure’s data and motion trajectory characteristics, with the cam axle acceleration αc and the output torque accuracy σT as the optimization targets, a mathematical model of cam mechanism is established in the study. Cam mechanisms was established with the radial basis function (RBF) method to restore the physical model of upper-limb exoskeleton’s motion trajectory model accurately. Then, global optimization was performed with adaptive non-dominated sorting genetic algorithm-II (NSGA-II) to get αc and σT s’ Pareto solution sets and form a data mapping cam mechanism with the dynamic feedback between the motion trajectory model and the entity model. In the verification experiments, the motion trajectory model established with only 37 response points only required a low amount of computation, and the response point verification error was within 3%, indicating the high restoration accuracy. After physical parameters were optimized with NSGA-II, the optimal pareto solution sets of dynamic characteristic parameters of the cam mechanism were obtained. αc and σT were respectively decreased by 52% and 81%. The deviation of αc between the entity model test data and simulation data was 3.84°/s2 and σT was 30.23 N·mm, indicating that cam motion deviation could be adjusted by dynamic data feedback. This study verifies that the dynamic characteristics of the cam mechanism can be optimized by optimizing the material parameters of the rollers, thereby improving the performance of the upper limb exoskeleton.