Research On Flatness Measurement Technology Based On Interference Fringes Of Multiple Light Sources

With the rapid development of the industrial manufacturing field,the number of workpieces with flatness requirements has increased greatly,and the surface profile accuracy requirements have also reached the sub-micron level.Correspondingly,higher requirements are put forward in terms of accuracy,efficiency and cost of the flatness measurement method.In engineering applications,traditional flatness measurement method is the contact measurement method,such as measuring by a micrometer,three-coordinate measurement,etc.But the precision and efficiency of contact measurement method is low.Optical interferometry is another common way to measure flatness,using an interferometer.This method can effectively improve the measurement efficiency and accuracy,and make up for the shortcomings of contact measurement.However,the interferometers in the current market are generally very expensive.In the face of the rapidly increasing measurement demand,large-scale equipping will greatly increase the measurement cost.Aiming at the above problems,this paper proposes a multi-light source interferometry method.This method uses a white light source combined with narrow-band optical filters of different wavelengths and bandwidths.The method uses the sub-amplitude interference of quasi-monochromatic light with multiple central wavelengths to obtain interference fringes and complete fringe sorting.Taking the method of restoring the surface profile by interference fringes as the main research object.An flatness interferometry system was built.Perform surface profile simulation interferometry measurment and actual workpiece testing,and the measurement results are ideal.This paper provides a low-cost feasible solution for the engineering application of the surface profile measurement of the planar workpiece.The specific research contents are as follows:(1)Use narrow-band optical filters with different center wavelengths and bandwidths,together with LED white light,to obtain a variety of quasi-monochromatic light sources to complete interference.And the effect of changing quasi-monochromatic light central wavelength on interference fringes is analyzed.Studied how to use this effect to accomplish fringes sorting.The measurement range of this method for surface profile measurement is analyzed.Design and build a multi-light source interferometry system.Completed optical path design,structure and hardware design,and software development;(2)In terms of image,the image preprocessing method suitable for the interference fringe pattern collected by the measurement system of this subject is designed.Including image enhancement,fringe enhancement,various noise removal,etc.The boundary recognition and extraction algorithms of different shapes of workpieces are designed and developed.Designed and developed the local fringe sorting algorithms and the global fringe sorting algorithms,they are based on the measurement principle.They are also the core content of the determination of fringe orders.Including expansion search algorithm,deburring algorithm,fringe endpoint correspondence recognition(fringe attitude)algorithm,catch-up search algorithm,fringe angle calculation,sorting algorithm,etc.(3)The Zernike polynomial fitting of the measured surface profile is carried out from the fringes sorting result.Develop algorithms to automatically construct systems of equations based on Zernike polynomials and known discrete data points.And solve the coefficient of each term of the polynomial,and restore the discrete data points into continuous surface data.And the system error is eliminated by the least square method.(4)The simulation interference verification of the measurement principle and the measurement of the actual annular workpiece are carried out,and the measurement results are compared and analyzed.The simulated measurement results are compared with the actual surface profile of the model.Measurements of annular workpieces compared with measurements from commercial flatness meters.It is verified that the measurement system described in this paper still has better measurement accuracy at lower cost.