Research On The Surface3D Microcosmic Profile Measurement Based On White Light Phase-shift Interferometry

With the rapid development of optical elements, such as MEMS, and othersurface finishing techniques, demand for surface performance of parts becomesincreasingly high. As a result, greater requirements have been put on themeasurement and evaluation of microstructure and characterization. Althrough thetraditional2D suface measurement and evaluation methods have been mature, it cannot effectively reflect the microstate of part surface and can not establish goodconnection with surface function. As the3D microscopic profile and its roughnessparameters can represent characteristics and qualities of part surface effectively, it isvery important to carry out relative research on them.After analyzing and summarizing the measurement technology of non-contactsurface3D microscopic profile, state-of-the-art technologies of3D microscopicprofile measurement were introduced in this paper. The advantages are to combinetraditional optical measurement methodologies with information optics and signalprocessing technology to measure3D microscopic profile. Until now, white-lightphase-shifting interferometer outperforms other proposed methods with the merits oflarge measuring range, modulation convenience, fastness and real time, highaccuracy and whole field automatic measurement. It has been widely applied tomeasure surface3D microscopic profile. But this technology still exists someproblems, including zero-order fringe phase deviation, profile demodulation errorcaused by phase shift.Aiming at the subject of surface3D microscopic profile measurement, thisthesis focused on the shortcomings of3D microscopic surface detection system withthe help of white-light phase-shifting interferometer technology to solve relatedproblems. According to the principle of white-light phase-shifting interferometer,white light was chosen as interference source and Michelson interferometer was usedin experiments. The measurement system consists of phase shift micro-displacement driving device, CCD camera, image acquisition card, computer and so on.Comprehensive theoretical and experimental research was conducted and the maininnovative contributions and research contents are as follows:1. By analyzing the phase demodulation algorithm, a combination algorithm ofthe digital filter and quadratic curve fitting was proposed in this paper, which cansolve the problem of zero-order fringe phase deviation during white-light phase-shifting interferometer. Compared with other demodulation methods, the proposedmethod can improve the recognizing precision of zero-order fringe position in whitelight interferometer images.2. To reduce the profile demodulation error caused by the phase shift, thecompensation control method was proposed by combining PID close-loop controland creep compensation control. The micro displacement detection circuit includesthe optical leverage and PSD, by which the micro displacement in phase shift wassent back to the control system to achieve closed-loop control. After considering theinfluence of creep properties of piezoelectric ceramics to the measurement process,voltage creep compensation model was established. This model can realizecompensation control using PID close-loop control and creep compensation control,which can control phase shift accurately and improve the measurement precision of3D surface microscopic profile.3. Based on the B spline function of Gaussian filter in the process of surfaceroughness measurement,1D Gaussian approximation filter was designed byintroducing the constraint conditions of variation principles and combining with thecascade characteristics of small scale Gaussian filters. After that, the1D Gaussianfilter was extended to two dimension so that the Gaussian filter base surface wasestatlished to measure roughness. Simulation experiments showed that this filter canachieve high precision and efficiency.4. The application software of surface3D microscopic profile measurement wasdeveloped. After calibrating the surface3D profile measuring system, measurementaccuracy was obtained by measuring the roughness of standard blocks. Experimentsshowed that the measurement error of surface3D profile measuring system is0.003μm and the repeatability of measurement error is0.002μm.