Research On Modal Analysis Method Of CNC Machine Tool Based On Operational Impact Excitation

With the rapid development of modern industry and industrial upgrading,machine tool performances such as high machining speed,high machining accuracy,and high reliability have gradually become the development trend of high-end CNC machine tools.The vibration characteristics of the machine structure become an important factor affecting the machining quality and processing efficiency of the machine tool.The traditional experimental modal analysis method can only study the vibration characteristics of machine tools in static state.However,the vibration characteristics of the machine running state are very different from that in static state.CNC machine tool is a complex system composed of many parts.Its movable parts will impact the machine structure during acceleration and deceleration.The excitation force will cause the machine structure to vibrate.By identifying the structural vibration response signal,the modal parameters of the machine under running conditions can be obtained.We call it active excitation modal analysis.However,this method still has some defects in theory and experiment.For example,the study of the incentive principle is not thorough enough,there is no comprehensive design and analysis of the excitation sequence,and there is a problem of insufficient energy for single component impact excitation.To solve these problems,this paper conducts a more comprehensive research on the modal analysis method of CNC machine tools based on operational impact incentives.The main research content is as follows:Based on the active excitation method.Considering the macro rigid body motion of the table and the elastic collision of the screw nut pair,the impact excitation is modeled and analyzed.We introduce a response-based modal identification algorithm.The influence factors of impact excitation energy and frequency band were studied from both theoretical and experimental aspects.We conduct detailed design and research on the incentive sequence of shock incentives.Design three excitation sequences for workbench excitation and spindle excitation,respectively,analyze the vibration response and modal identification of the machine tool structure under different excitation sequences.It is verified that the method does not depend on the specific excitation sequence,as long as it satisfies the random characteristics.Aiming at the problem that the single-component impact excitation does not sufficiently stimulate the machine tool structure,a multi-component joint impact excitation method is proposed.Apply the principle of multi-point excitation technology.Use the workbench and spindle for joint shock excitation.It has verified that multi-component,multi-axis combined excitation has better stimulating effects than single-component and single-axis excitation by experiments.The study results of this paper show that: acceleration and deceleration of movable parts can effectively excite machine modality.Modal parameter analysis method based on impact excitation can effectively identify the mode in which the machine tool is in running state.The excitation energy is related to the machine speed and acceleration factors.The excitation frequency band is related to the structure of the machine tool itself.Different random excitation sequences can excite and identify the machine modality.This method does not depend on the specific excitation sequence.Cycle excitation does not recognize the machine modality.The combined excitation of multi-parts of the worktable and the spindle more fully stimulates the machine tool and identifies more machine modalities.Meanwhile,it is also closer to the actual operating state of the machine tool.