| Surface topography is an important quality index for manufacturing products and scientific research samples;The dynamic performance of surface topography is an important characterization of the dynamic functional characteristics of products and samples,and an important indicator of their functional quality.Dynamic surface topography measurement is of great significance for surface quality evaluation,functional characteristics analysis and functional quality assurance of products and samples.In this thesis,the simultaneous phase shifting multi wavelength interference dynamic surface topography measurement technology is studied.The main contents include:A single color camera and prism beam-splitting based simultaneous phase shifting three wavelength interference dynamic surface topography measurement system is proposed.The system is based on Linnik interference microscope,combined with polarization interference and multi-channel interference structure of combined prism parallel beam-splitting,to realize prism beam-splitting based simultaneous phase-shift interference with single camera;The RGB three-color LED combined light source and single color camera are used to produce and collect color interferograms,and the simultaneous phase-shifting interferograms of red,green and blue wavelengths are obtained through color decomposition.After interferogram processing and dual or three wavelengths interference phase recovery,the dynamic measurement of continuous surface and non-continuous surface to a certain extent is realized.A method of overall mismatch evaluation and iterative registration of multi-channel phase-shifting interferograms is proposed.It is based on the speed up robust feature(SURF)and random sample consensus(RANSAC)algorithm.Combined with the overall registration requirements of multi-channel images,a step-by-step iterative and incremental reference image registration idea is proposed.The whole process include three steps,in which the second and third steps adopt the iterative registration.The transformation matrix of each iteration is the mean value of the transformation matrix of the registered image relative to all the reference images,and the iteration termination condition is that the standard deviation of the coordinate offset of the registered image relative to all the reference images reaches the minimum.The experimental results of real system registration show that the performance of the new algorithm is better than that of the ordinary registration method,in which the absolute average mismatch is reduced from 0.0868 pixels to 0.0083 pixels,and the standard deviation of mismatch is reduced from 0.587 pixels to0.534 pixels.A method for calculating the wrapped phase of non-ideal simultaneous phase-shifting interference based on parameter pre calibration is proposed,which effectively solves the problem of ripple error caused by uneven light intensity distribution and inaccurate phase shift of the interferogram in the spatial lights-splitting simultaneous phase-shifting interference system.First,the light intensity distribution coefficients of the reference light and the measurement light in the four channels are calibrated based on the light intensity test,and the relative phase shift between the four channel interferograms are calibrated based on the ellipse fitting method.Secondly,these parameters are substituted into the actual four channel simultaneous phase-shift interference intensity equation to calculate the package phase.The verification experiment results based on the prototype system can clearly see the restraining effect of the algorithm on the ripple error.When the object to be tested is a plane mirror and the interference fringe is adjusted to the medium width,the maximum amplitude of the ripple error is about 1 rad for red light and 1.2 rad for green light with the ideal four-step phase-shifting algorithm,while 0.34 rad for red light and 0.42 rad for green light with the proposed algorithm.The reasons of level misjudgment in actual measurement of the equivalent wavelength method commonly used in multi-wavelength interferometry are analyzed,and the unambiguous measurement range and the corresponding single wavelength wrapped phase error tolerance are given.Another phase unwrapping method of multi-wavelength interference is studied,which known as "residual fringe method" and theoretically has a larger unambiguous measurement range than the equivalent wavelength method but is rarely used in practice.The typical unambiguous measurement range and the phase error tolerance of this method are analyzed and given.It is revealed that by increasing the wavelength dimension,the unambiguous measurement range can be further expanded without reducing the error tolerance;Aiming at the problem of large amount of calculation,a fast surface topography recover algorithm based on the geometric distribution information of wrapped phase is proposed.The calculation speed is about 3.8 times that of the traditional table lookup method when the distance between the table lookup points is set to be equivalent to the error of the single wavelength wrapped phase.A prototype system based on the single color camera and prism beam-splitting based simultaneous phase-shifting three wavelength interferometry is established,the system parameter calibration and performance testing are carried out,the residual measurement error is analyzed. |
