Research On Modal Parameter Identifiication Of CNC Machine Tool Cutting Conditions Based On Response Signal

The machining performance of CNC machine tools is closely related to the structure's dynamic characteristics,so it is of great significance to study the emotion in the design of CNC machine tools.The existing traditional experimental modal analysis can get the machine tool's dynamic characteristics under a static state,but machine tools' dynamic features are different from those in the dormant state.At present,Operational Modal Analysis(OMA)is widely used in various engineering fields,which obtains Modal structural parameters under working conditions through response signals.However,in the machine tool's cutting condition,the vibration response signal usually contains the harmonic component caused by the excitation force of periodic cutting.The direct application of the OMA-based modal parameter identification algorithm will produce many harmonic frequencies that are indistinguishable from the structure's natural frequencies.At the same time,it is very important to improve the identification accuracy of the modal parameter identification algorithm.Aiming at the above problems,this thesis studies eliminating harmonic components and modal parameter identification based on response signals and proposes a modal parameter identification method suitable for CNC machine tools undercutting conditions.The main work of this thesis:1.Given the situation that the cutting vibration signals of machine tools contain harmonic components,this thesis analyzes the influence of periodic excitation on the working modal analysis of machine tools and studies a method of removing harmonic frequency in response signals cepstrum editing.Combined with the dynamic cutting force theory in the milling process,the cutting force was calculated by MATLAB,and the vibration displacement response signal was obtained,which verified the effectiveness of the above method for removing harmonic frequency.2.The identification method of random subspace driven by covariance based on response signal is studied,and an improved algorithm of random subspace driven by covariance based on the row number of Toeplitz matrix is proposed.This article on a five layers framework model in the simulation experiment,the covariance move stochastic subspace,data-driven stochastic subspace built-in N4 SID recognition algorithm and MATLAB three seed space algorithm to identify the natural frequency,damping ratio and modal vibration mode compared the results with the theoretical value,random subspace algorithm is covariance drive in terms of recognition accuracy,and computational efficiency is superior to the rest of the two algorithms.Aiming to select the number of rows of the Toeplitz matrix in the covariance-driven random subspace,the algorithm was improved by introducing the method of condition number to determine the number of rows Toeplitz matrix.The improved covariance-driven random subspace algorithm was simulated in Matlab,and the simulation results proved the enhanced algorithm's effectiveness.3.The hammer test is carried out on the supported beam structure,and the modal parameters of the supported beam are obtained by using Poly LSCF(force measurement method)and OP.Poly LSCF(accident force method)algorithms in the DHDAS dynamic signal acquisition and analysis system.The modal parameters were identified by the improved covariance-driven random subspace method from the vibration response signals of the supported beam.The results were compared with the experimental results of Polyl SCF and OP.Polyl SCF and the reliability of the improved covariance-driven random subspace algorithm were verified.4.Through the finite element analysis of the machine tool,the machine tool system's frequency response functions in X and Y directions are obtained,and the modal parameters of the machine tool in X and Y directions are obtained by the peak fitting method.Through MATLAB calculation of X and Y direction,cutting force and the acceleration response signal is received by static modal parameters of the machine tool,sing the proposed method of harmonic frequency and modal parameter identification,the modal parameters of machine tool cutting state are obtained by response signal,compared with static modal parameters of the machine tool,verify the feasibility of the method is applied to the machine tool structure.