| White light interferometry is a method with sub-nanometer precision and millimeter-scale measurement range,which has an irreplaceable role in microscopic measurement.The existing white light interferometer needs to find interference fringes and set the upper and lower limits of the scanning stroke by manual focusing during the measurement,which is time consuming and laborious,and is difficult to meet the automatic measurement requirements in industrial production.Aiming at this problem,this thesis deeply studies the techniques of autofocus,background modeling and phase shift interference,and proposes a new method of three-dimensional measurement with automatically search for interference fringes and automatically set the scan stroke.The method includes a autofocus technique based on quadtree decomposition for obtaining clear images,and a planning strategy based on Vi Be stripe recognition to automatically determine the stroke of the scanning interference.Based on the research of related algorithms,this paper built a white light scanning interference experiment system,and developed a three-dimensional shape measurement software based on Hariharan phase shift method,which realizes automatic and precise measurement of three-dimensional shape,and provides technical support for the application and popularization of white light interferometry in industrial detection.The main contents of this article are summarized as follows:(1)Deeply investigates the measurement methods for surface morphology of ultra-precision optical structures,and compares the principles,structures,advantages and disadvantages of these methods,then discusses the research status of white-light interference technology at home and abroad.Moreover,based on the shortcomings of existing measurement techniques,clears the research direction and research content of this paper.(2)In-depth analysis of the interference characteristics of white light and the measurement principle of white light interference.For the development of research work,selected the relevant hardware,and built a white light scanning interference experiment system.(3)Aiming at the small depth of field of the interference objective,the difficulty of manually focusing and finding the fringe,and the lack of stability of the existing autofocusmethod,this paper carries out research on the key technology of autofocus,and proposes a coarse and fine step evaluation function based on quadtree decomposition,which has better unimodality and higher sensitivity.At the same time,proposes a composite white light interference focus search algorithm to solve the problem of focusing accuracy,speed and stability in deep defocusing in narrow depth of field interferometric objectives.(4)In-depth analysis of the principle and detection process of background modeling technology,based on the characteristics of interference fringe motion,this paper evaluates the interferogram by using stripe modulation degree to avoid the interference problem of ghost phenomenon caused by Vi Be algorithm on stripe recognition,and proposes a planning strategy of scanning stroke based on Vi Be stripe identification,which realizes the extraction of interference fringes after focusing and the automatic determination of the upper and lower limits of the scan stroke.The experimental results show that the proposed planning strategy of the scan stroke can accurately identify the interference fringes,and quickly and automatically determine the range of the scan stroke.(5)Based on the research of several typical white light interference reconstruction methods,this paper focuses on the Hariharan phase shift method based on the maximum modulation degree to realize the three-dimensional reconstruction of white light interferometry.Based on this,the three-dimensional measurement software of white light scanning interference is developed.Finally,the effectiveness of the proposed algorithm and the 3D measurement system is verified by the precision measurement of the standard step block. |
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