Research On Parameter Identification Of Joint Surface In Machine Tools

The CNC machine tool is the foundation of national equipment manufacturing industry and national defense industrial technology.Establishing accurate calculation model of machine tool is an important basis and prerequisite for improving the digital design level of high-grade CNC machine tools.To establish an accurate calculation model of machine tool,an accurate model of joint surface must be established,including the establishment of the equivalent and precise parameter identification.The purpose of this study is to identify the dynamic characteristic parameters of sliding guide joint and ball screw joint,and then establish an accurate calculation model of machine tool.Finally,the sensitivity analysis of the stiffness of each joint is performed to find a joint surface with a greater impact on the overall performance of machine tool,which provides a basis for subsequent optimization.The main work and result can be listed as follows:1.Based on MATLAB and ANSYS,the stiffness and damping of joint are used as design variables,the minimum of relative error between natural frequency and damping ratio of finite element method and their corresponding experimental results is considered as objective function,the genetic algorithm is adopted to identify the parameters of sliding guide joint.Substitute the identified parameters into the finite element model of the sliding guide,and modal analysis is carried out.Compare with the results of the modal tests,the maximum error of the natural frequency is within 10%,the maximum error of the damping ratio is within 15% and modal shape is fairly consistent,so the accuracy of the parameters is validated.2.Experimental modal analysis is used to identify the dynamic characteristic parameters of ball screw joint.Firstly,the single-degree-of-freedom system of the ball screw is established.Then the modal test is carried out and the stiffness and damping of joint are identified based on principal component analysis.At last,a theoretical model of ball screw is established based on Hertz contact theory.3.Substitute the identified parameters of joint into the finite element modal of machine tool,and static analysis,modal analysis and harmonic response analysis are carried out.Compare with the result of the machine tool without joint,and the rule of the effect of joint on the machine tool is obtained.At last,the frequency response function test of machine tool is carried out,and the natural frequency of each low-order modes is obtained.Compare with the result of finite element analysis,the error can be accepted,so the reliability of the identified parameters and the accuracy of machine tool model are validated.4.Based on the sensitivity analysis of stiffness of each joint,the effect of changing the value of stiffness on the performance of machine tool is summarized.And then the weaker joints in the machine tool are found,which provides a basis for subsequent optimization.