Image Acquisition System For Surface Topography Measurement Based On Wavelength Switch And Phase Shift Scanning

High-precision measurement technology for surface topography is urgent required with the improvement of machining precision, the miniaturization of parts and the wide application of microcircuit, micro-optics, etc.. The common used non-contact measurement technology for surface topography are white light phase-shift interferometry, traditional phase-shift interferometry and multi-wavelength interferometry, etc.. Combining the advantages of multi-wavelength interferometry and traditional phase-shift interferometry, an image acquisition system of surface topography measurement based on wavelength switching and phase-shift scanning is studied in this paper.The main research contents are as follows.Firstly, the basic principles, advantages and disadvantages of white light interferometry, phase-shift interferometry and multi-wavelength interference technology are analyzed. An image acquisition of surface topography measurement based on wavelength switching and phase-shift scanning is proposed.Secondly, a multi-wavelength light source which consists of white light LED and three filters with various wavelengths to acquire interference image is designed. A PZT is selected as the phase shifter. The interference microscope optical structure which is based on Mirau interference microscope structure is determined and an image acquisition software is developed by VC++ in order to control the CCD to acquire images.Finally, the three-wavelength interference images are used to calculate the sequence driving phases by gray value extracting algorithm and ellipse fitting algorithm. Then four interference grayscales meeting the four-step phase-shift algorithm are constructed through Lagrange parabolic interpolation, whose phase difference is π/2 successively. The interference phases of every wavelength are calculated using four-step algorithm. On the basis, the phase differences between two close wavelengths and that between two far wavelengths are obtained, and the real phases of every point on interference field could be calculated through multi-wavelength interference algorithm of large scale combining with small scale. The parameters of assessed profile are calculated and the error of measurement system is analyzed. The interference image acquisition system is tested and verified through experiments.