Multi-Objective Optimization of Two-Stage Helical Pairs in Helical Hydraulic Rotary Actuator Using Ensemble of Metamodels and NSGA-II

This paper aims to optimize the two-stage helical pairs (TSHPs) in a helical hydraulic rotary actuator (HHRA) in terms of volume, transmission efficiency, and maximum contact stress. Volume and transmission efficiency can be determined through analytical mathematical models. However, calculating the contact stress of helical pairs necessitates complex and time-consuming finite element simulation. To address this issue, a method for predicting the maximum contact stress using an ensemble of metamodels (EMs) is proposed, with an automated finite element simulation process developed for data provision. The superiority of the EMs is validated through comparative analysis with three stand-alone metamodels. The optimization is carried out using the NSGA-II algorithm, including four combinations of the three objectives, and global sensitivity is analyzed over the objectives. The results indicate a trade-off relationship between maximum contact stress and volume in the optimal space. Moreover, considering multiple combinations enhances the robustness of the optimization results. The method is effectively applied to the design of the TSHPs and provides a new idea for the related actuator design.