Optimal design for natural frequency of 6-DOF hydraulic parallel manipulator

Hydraulic branches of six degree-of-freedom (6-DOF) parallel manipulator were considered as virtual single open-loops. Local reference frames (LRFs) of manipulator´s components were established according to the mechanism configurations. RPY angular description was used in transfer matrix to transform components´ stiffness and damping matrix from LRFs to the fixed reference frame (FRF) and vibration differential equation was obtained. Optimal model based on mechanism workspace and cylinder stoke was established to synthetically consider the 6-DOF parallel manipulator resonance frequency. Quasi-Newton algorithm (QNA) and Genetic algorithm (GA) were applied respectively to maximize the minimum frequency of the system. Simulation results show that the minimum resonance frequency and workspace are contradictory factors, and the optimal parameters should be chosen felicitously to satisfy design demands.