Research On Measurement Method Of Newton Ring Stress Based On Image Processing

Newton rings are a typical interference phenomenon, with a wide application area, such as controlling the surface quality of optical components, measuring the wavelength of light and curvature radius of lens, testing the surface finish of test specimen, calculating the refractive index of liquids, and measuring the thickness of oxide layer of silicon slice in semiconductor technology, etc. Moreover, the stress on optical glass can be calculated through Newton rings interference technology.Under a relatively strong stress, deformation will occur to the shape of Newton rings, which, as a result, will lead to measuring errors in the traditional way of reading data by human eyes directly. Also, manual reading method is neither suitable for long term and continuous observation nor for storing image data. This thesis has adopted digital image processing in measuring Newton rings and calculating its deformation stress. By stress correction, the precision of Newton rings technology can be boosted in such as measuring curvature radius, etc.In this study, a CMOS image capture device has been installed on the reading microscope in replace of human eyes as a receptor. And it is based on MATLAB as a tool to thoroughly study digital image processing, measurement, and its identification methods, mainly including image binaryzation and smoothing treatment, image intensification and definition processing, and edge processing, etc, based upon which, by Hough transform, a effective way has been put forward to complement the discontinuous marginal part of Newton rings. The transformational relation between unit pixel in image and actual physical distance has been conformed by one-dimensional methods of reading the transparent ruler put on plan convex lens and through cameral calibration methods. The curvature radius of Newton rings under stress and without have both been measured. By digital image processing experiments, the theoretical formula has been verified for measuring glass stress by Newton rings methods. It has been attested by comparison experiment that digital image processing methods can not only boost the precision of Newton rings technology and also improve the accuracy of measuring stress put on glass by the correspondent deformation of Newton rings.