Analysis Of CNC Machine Tool Vibration Using An Instruction-domain Based Approach

Vibration is one of the important factors that affect the machining accuracy and efficiency.How to reasonably select the process parameters according to the vibration characteristics of the machine tool,avoid the resonance points of the structure and the cutting chatter zone,to reduce the machine tool vibration is an important research topic.Based on system analysis theory,this paper takes the CNC G codes associated with process parameters as input,and the corresponding vibration as the response.The machine tool vibration characteristics are obtained by analyzing the response data under typical G code experiments,guiding the machining optimization such as active vibration avoidance and chatter elimination.The main work of this article is as follows:Taking advantage of the correlation between CNC machine tool G commands and cutting process parameters,a signal analysis / expression method for CNC machine tool command domains is proposed.Traditional signal analysis method includes time domain,frequency domain,and time-frequency domain joint analysis etc..But it lacks of the cutting parameters such as spindle speed,depth of cut,postion of the workbench,which makes it difficult to analyze the vibration data and identify the vibration characteristic.The new method realizes the observation with process parameters as the abscissa(domain)and feature quantities as the ordinate.Signal analysis and feature extraction are performed from the instruction domain/process parameter domain,and the instruction waterfall chart,two-dimensional instruction spectrum,and three-dimensional instruction spectrum are used.The analysis method realizes the instruction domain analysis of the CNC machine tool sensor signals.Taking the G command as a special control signal and method,a test analysis method for the command domain of CNC machine tool vibration characteristics is proposed.Unlike manually machine tools,CNC machine tools work under the control of G instructions.To this end,a set of special G instructions is used to control the CNC machine tools to obtain their vibration response and vibration characteristics.The situation is like input pulses signals,step signals and other typical signals in system characteristics identification.A variable speed G instructions is designed to analyze the vibration characteristics related to speed;a set of variable X,Y,and Z position G instructions is designed to analyze the vibration characteristics related to positions;variable cutting parameter instructions is used for cutting chatter analysis.Aiming at the problem of identifying the resonance frequency of high-speed spindles,the variable-speed G instruction is used to control the spindle for gradient up/down speed tests,and a two-dimensional instruction speed spectrum and a instruction waterfall chart are used to analyze the spindle resonance speed.A short-term frequency domain integral displacement measurement method of acceleration data was proposed to realize the rapid measurement of spindle vibration displacement.Aiming at the analysis problems of the chatter lobe diagram,the G instruction method was used with variable cutting depth and variable speed to quickly detect the chatter lobes diagram.In order to improve the measurement accuracy of the vibration spectrum,a micro-frequency shift spectrum refinement method was proposed.A vibration characteristic instruction domain analysis system was completed.The main functions include: instruction domain vibration acquisition,instruction domain machine vibration basic analysis,instruction domain specific function analysis,detection instruction set and other functions.Based on the developed analysis system,tests were performed on a certain type of CNC milling machine,including spindle resonance speed analysis,chatter lobes diagram analysis,and feed axis vibration analysis.The test results of vibration characteristics are consistent with traditional methods such as modal analysis,which proves the correctness of this method.From the perspective of facilitating on-site applications,the new method has many advantages.