Vibration Analysis And Error Analysis Of Key Structures Of Hybrid Machine Tools

The development trend of modern machine tools is gradually toward high accuracy,high efficiency and high reliability.There are more and more stringent requirements for the dynamic characteristics of machine tools.The overall performance of machine tools has an extremely important impact on the quality of workpiece processing.In this paper,experimental modal analysis is carried out for the key components of hybrid machine tools and structural optimization is carried out for the weak links.At the same time,the geometric errors of parallel mechanisms,which have the greatest impact on the machining accuracy of machine tools,are modeled and analyzed to provide reference for the subsequent optimization and error compensation of machine tools.The experimental modal analysis of the key structure of hybrid machine tool: moving platform,tool board and gantry frame is carried out.The intelligent data acquisition and signal analysis system developed by Dongfang Institute is used to excite the key structure by force hammer excitation method.The experimental results are analyzed and fitted by PolyLSCF frequency domain method and feature system algorithm respectively.The key of machine tool is determined by comprehensive comparison.The modal parameters of the components: the first four natural frequencies,damp and mode shapes,determine that the beam structure is the weak link of the hybrid machine tool.Aiming at the weakness of hybrid machine tool,the cross beam structure is optimized by multi-objective response surface optimization method based on ANYS Workbench.Five sizes which have the greatest influence on the overall stiffness and quality of the cross beam are selected: the length,width and height of the main body of the cross beam and the length and width of the guide rail seat.The first natural frequency and the maximum deformation of the cross beam are taken as the design variables for optimization.As well as the overall quality as the optimal output,the relevant mathematical model is established and optimized by the multi-objective response surface optimization method.The optimal scheme is selected from 28 sample schemes,and compared with the original structure,the first natural frequency,maximum deformation and overall quality of the beam are ascertained,which not only improves the stiffness of the beam structure,but also achieves the effect of lightweight.The results verify the reliability of the optimization scheme.Taking the geometric errors of serial and parallel structures of machine tools as the research object,the geometric errors of serial and parallel structures are modeled by using the modeling methods based on multi-body system theory and matrix transformation respectively.The geometric errors of parallel structures are emphatically studied and simulated.The theory of multi-body system and the basic principle of matrix transformation are summarized in detail.The error sources of all links of parallel mechanism are analyzed comprehensively,and the forward and inverse solutions of the error model are deduced.Then,the control variable method is used to lock the variation range of each error parameter between the Seven-level tolerance and the eight-level tolerance.The influence of each error parameter on the central position and attitude of the moving platform is observed and analyzed.