Technology Research Of Gauge Block Length Measurement Based On Interferometry

As a length standard material, gauge block transfers the length unit to almost every step in the manufacture and plays an important role in the product quality assurance program. The measurement and verification of the high grade gauge block is mainly carried out by interferometry. In this dissertation, based on the optical interference theory and the interferometric technique, four digital methods are studied to measure the length of high grade gauge block by means of interference fringes fraction coincident method, which including: the fringe analysis method, the fast Fourier transform (FFT) method, the phase shifting interferometry and the virtual grating moire fringe method. The digital and automated techniques of the interference set are studied. A Twyman-Green interferometer is developed to measure the length of gauge block. The interferometer is a real time image processing instrument which combines different techniques of optics, mechanism, electronics and computer. The digital technique and the analysis algorithm of interference fringe are especially concerned. The automated algorithms on fringe analysis method is put forward to skeleton the fringe and obtain the data points at the fringe center. The following algorithms in FFT method are put forward to pre-processing the interferograms, including the recognition the edge of the gauge block, correction of interferogram's shadow and extrapolation of fringes based on the region spreading of the interferogram. The phase unwrapping algorithm, best seed algorithm, is put forward to retrieve the wavefront from the interferograms. The virtual grating phase shifting moire fringe method is studied to measure the parameters of gauge block which combines the techniques on grating, moire, and phase shifting interferometry. The Damp Least Square method is introduced to fit the radiance of the fringes so as to precisely calibrate the phase shifter on line. The computer-aided interferometric software system based on the WINDOWS platform is established. A series of software are programmed which including the following functions: phase shifter calibration, communication and control, image capture and processing, numerical analysis, figure drawing, results output and software system management. The images are processed with the software built in the equipment. The gauge block is measured with the above methods based on the different theories. The results show that the interferometer we had been set up and the digital interferometric method established in this dissertation...