Measurement Of Spindle Rotation Error Of NC Machine Tools Based On Singularity Detection And Compressive Sensing

Spindle unit is the core component of metal cutting machine tools that holds the tools or workpieces in machining process,and the performance of spindle unit has a decisive influence on the machining accuracy and efficiency of the machine tools.Due to the complexity of the error motion of spindle rotation and the high requirements for measurement accuracy,the measurement of spindle rotation error has become an urgent and challenging task.Combined with the latest progress of the technology of signal processing,this thesis made a deep exploration of the measuring method of the radial,axial,and tilt error motion of the spindle in rotation,and the separation method of the roundness error of the artifact used in these measurement,and the main research contents are as follows:(1)The precondition of accurate separation of roundness error by Donaldson reversal method and its realization method in the measurement of NC(Numerical Control)machine tool spindle was studied.In this thesis,a roundness error separation method based on singularity detection and exact-stop of spindle was proposed to perform the measurement of spindle rotation error.The singularity of measured motion is detected using the wavelet transform modulus maximum,to locate the exact-stop and rotating stages of spindle in the measured motion,and the synchronous radial error motion of the spindle is truncated to separate the roundness error of the artifact.This method solves the problems existing in the Donaldson reversal methods,such as the difficulties of accurate repositioning of the sensors and artifacts,and the difficulties of obtaining the signal of spindle encoder.The results of CMM(Coordinate Measuring Machine)show that the proposed method can reduce the measuring error caused by the roundness error of the artifact more than 80%.(2)The radial and axial trajectories of tool points during the rotation of the spindle of NC machine tools are studied.In this thesis,a measuring method based on the compressive sensing and the spectrum line interpolation theory was proposed for the measurement of the radial and axial error motions of spindle rotation.This method decomposed the measured signals into a sparse representation in the frequency domain based on the compressive sensing theory,and suppressed the influence of noise and vibrations by filtering out the tiny spectrum lines.The parameters of the sparse spectrum lines are corrected by double spectrum line interpolation method,and the radial and axial error motion of the spindle rotation are recovered from the corrected sparse spectrum and their error values are calculated eventually.This method overcomes the shortcomings of the existing methods such as considerable theoretical errors,easy to be disturbed by noise,and so on.The simulation experiment shows that the proposed method can reduce the analytic error of the synchronous error motion effectively,and does not depend on the spindle speed information provided by additional sensors.(3)The characteristics of the tilt error motion of spindle axis during the rotation of NC machine tools was studied.In this thesis,a tilt error motion measuring method based on singularity detection and sparse decomposition was proposed.In this method,the spindle error motions are measured on two measuring planes with a certain distance apart.The roundness error of the artifact is removed from the measuring signal based on the roundness error separation method proposed above,and the axis eccentricity error of the artifact is removed based on the foregoing radial error motion decomposition method.Finally,the tilt error motion of the spindle is obtained.The effectiveness of the proposed method was verified by the analysis of separated roundness error of the artifact and axis trajectory of the spindle.(4)The measurement uncertainty caused by the resolution and noise of the measuring system,the roundness error of the artifact,the misalignment of the sensors and the curvature of the artifact was analyzed in detail in this thesis.The uncertainty analysis shows that the extended uncertainty of the measuring system based on the proposed methods is less than 0.4μm,which is better than the current mainstream SPN-300 spindle measuring system.(5)The development of the measuring system for spindle rotation error was completed.The spindle measuring system developed in this thesis was compared with the current mainstream SPN-300 spindle measuring system on three aspects: spindle speed recognition,radial error motion measurement,and axial error motion measurement.It is found that the developed spindle measuring system has higher recognition accuracy of spindle speed and higher measurement accuracy of spindle rotation errors.