Study On Identification Method Of Modal Parameters Of NC Machine Under Periodic Cutting Excitation

Under high-speed and high-precision conditions,the dynamic characteristics of CNC machine will directly affect the machining quality and efficiency.The machine tool is mainly excited by the periodic cutting force during machining,and the existing machine tool dynamics analysis methods under static and operational conditions cannot effectively cope with this situation.In view of the above problems,this paper analyzes the excitation characteristics of periodic cutting forces,proposes a modal parameter identification scheme and specific methods of the machine under periodic cutting excitation,and realizes the modal parameter identification of the machine tool under cutting machining conditions.In this paper,the following work was mainly carried out:First,the composition and excitation characteristics of the exciting force generated by periodic cutting are analyzed.It is pointed out that the periodic component in the cutting force mainly causes the periodic forced vibration of the machine tool,and the fluctuation component in the cutting force will generate random excitation to the machine tool,the random vibration response caused by the machine structure can be used to extract modal parameters.Secondly,a specific scheme for identifying the modal parameters of a machine tool under periodic cutting excitation is proposed.According to the excitation characteristics of the periodic cutting force,it is pointed out that the fluctuation components in the cutting force can approximately satisfy the excitation requirements of the operational modal analysis.After removing the periodic components in the machining vibration signal,the modal parameters in the machining state of the machine tool can be identified by using a operational modal analysis method.In order to eliminate the severe harmonic interference existing in the processing vibration signal,a method of harmonic frequency elimination of the vibration signal based on the cepstrum editing method is proposed,to directly remove periodic components from the time-domain vibration signal to eliminate harmonic effects.At the same time,the multi-reference least squares complex frequency domain method was introduced and applied to extract the modal parameters from the vibration signal with the periodic component removed.Lastly,static impacting and steady-state machining experiments were performed on the gantry milling machine.Using the proposed method of harmonic frequency removal and parameter identification,the modal parameters of the machine tool are obtained.Combined with the modal shapes acquired by the knocking experiment,the frequency response function of the tool tip point in the machining state was synthesized to predict the cutting stability.Finally,the flutter cutting test was performed to verify the accuracy of the obtained modal parameters.The modal parameter identification method of machine tool under cycle cutting excitation presented in this paper has good pertinence and feasibility,and can meet the needs of machine tool dynamic analysis under machining conditions.