Research On Identification And Optimal Design Of Weak Parts In 6-DOF Motion Support Mechanism

The motion support mechanism is the core mechanism in the wind tunnel test,and its good stiffness performance can ensure the accuracy of the test results.However,in the process of test,the mechanism is prone to deformation and resonance due to the lack of stiffness performance,which affects the test accuracy.This phenomenon is more obvious in the weak parts of the mechanism.In the actual situation,because the structure of mechanism is complex and its weak parts are difficult to identify,there are some problems in the stiffness optimization design of large-scale mechanism,such as unclear optimization objects and incomplete methods.To solve this problem,taking the series 6-DOF kinematic support mechanism as the research object,combining the topology optimization,size optimization methods and scheme evaluation criteria,this paper proposes a design process method which first analyzes the stiffness matching of the mechanism,and then identifies and optimizes the weak parts.This paper mainly includes the following contents:(1)The overall design and analysis of the organization.Analyzing the wind tunnel test requirements,this paper establishes the scheme model of the motion support mechanism,and the kinematics and dynamics of the mechanism are analyzed based on D-H parameter method and Newton-Euler equation.By comparing the MATLAB programming solution with ADAMS simulation,the correctness of kinematics and dynamics analysis is verified,which lays the foundation for the following research.(2)In order to clarify the optimization object,the identification of weak parts is realized by using the theory of stiffness matching analysis.Based on the stiffness theory,the analysis method of mechanism stiffness matching is deduced.The stiffness process is simulated by gradually changing the elastic modulus of the components,and the matching of each component to the static stiffness and dynamic stiffness of the motion support mechanism is investigated.Based on the change rate of corresponding indexes in the process of component rigidity,the identification criteria of weak components are established,and the Z-axis vertical plate is comprehensively identified as the weak part of the organization.(3)The preliminary structural design is carried out for the Z axis vertical plate.The design target model of Z-axis vertical plate is established based on the variable density theory.The topology iteration is carried out in OPTISTRCT based on the compromise programming method,and the conceptual structure is output.Analyzing the material continuity of the conceptual structure,combining with the layout experience of the ribs of large parts such as machine bed,a variety of schemes are designed.The TOPSIS theory modified by the entropy weight method is established as the evaluation criterion of the optimal scheme,which realizes the quantitative contrast selection of structural schemes.(4)The detailed optimization design is carried out on the basis of the determined preliminary structural scheme.The scale constraints of the motion support mechanism are analyzed.The first and second frequency,the total deformation and the quality of zaxis vertical plate are determined as the optimization objective by harmonic response analysis.And the key variables in the process of optimization design are selected by DOE sensitivity analysis.Based on three single approximation models of RSM,KRG and RBF,a combined approximation model with higher prediction accuracy is constructed by adopting EA method.The structure is optimized by NSGA-II multi-objective genetic algorithm.The Pareto solution set is selected by using the established evaluation criteria of the optimal scheme,and the established schemes are compared by simulations.The results show that the optimization design method proposed in this paper can improve the stiffness performance of the mechanism while realizing the lightweight of weak parts,and the optimization effect is significant.