Dynamic Load Identification Of Mechanical Structure Based On Frequency Response Function Fitting

To design and analyze the reliability of machine,we should know the dynamic load which is put on the machine.But the structure of some machine are complex,the dynamic load which is put on the machine are hardly to measure.The response of the machine can be easily measured.The reverse method to solve dynamic load by response is a good way.In this paper,the frequency domain method is used to obtain the dynamic load.Before the frequency domain method is used,firstly the frequency response function should be obtained.Then the response in time domain should be measured.The dynamic load can be easily get by the relations between response and frequency response function.In this paper,the content is as follows:(1)Researching the measuring and estimate method of frequency response function.The estimate method is include output noise estimation model---H1 estimation,input noise estimation model---H2 estimation,input output noise estimation model.(2)Researching the fitting method of frequency response function and theory of modal parameter identification.For the single input single output frequency response function fitting,Researching the power polynomial fitting and orthogonal polynomial fitting.For the multi input multi output frequency response function fitting,researching the orthogonal polynomial fitting expression.Deducing converting matrix which can convert the orthogonal polynomial coefficient to power base polynomial coefficient.(3)Obtaining frequency response function of tool holder fixture by simulation of ansys,and fitting it.Solve the modal parameter by the fitting result of frequency response function,establish the frequency response function expression by the modal parameter,and contrast the result with the simulation of frequency response function.The result illustrate that:the relative error between fitting and original frequency response function is little.Then considering the modal truncation's effect to frequency response function.The result illustrate that:the modal truncation without the correction term,the error between truncation and original frequency response function is large.The modal truncation with the correction terms,the error is little.(4)Identifying the dynamic load which is put on the tool holder fixture.Considering the dynamic load as follow situation.Single point single frequency and single point multi frequency dynamic load identification,and multi point single frequency and multi point multi frequency dynamic load identification.The result illustrate that:the method of dynamic load identification can identify the dynamic load and the error is little.