Study On The Vision Measurement Method Based On Non-diffracting Imaging System

In visual measurement, ordinary imaging system can not achieve the purpose ofmeasurement for a large depth of field space objects by a single image because of thelimited depth of field. In this paper, a large depth of field vision measurement methodhas been studied by using the characteristics of center spot of non-diffracting beam,which with high strength and concentration, long transmission distance, etc. For thismeasurement system we analyzed the relevant theoretical analysis of non-diffractingimaging system and studied an efficiency of image restoration method. Moreover, the2D planar target method is used in calibration experiment to obtain camera internalparameters. The main contents are as follows:Firstly,based on the presentation of the research status and development trend ofvisual measurements and methods of non-diffracting beam generation, a nondiffractingimaging system has been designed through an axicon which can produce non-diffractingbeam. According to Fourier optics theory, the point spread function (PSF) of opticalsystem after adding an axicon and optical transfer function (OTF) and the calculationmethod of depth of field has been deduced theoretically by treating the penetrationfunctionof axicon as a part of the generalized pupil function. Analyzed the influence ofdefocus and axicon angle to point spread function combined with Matlab simulation andexperiment. Simulated MTF curves with different defocus of lens by ZEMAX software,further validated the axicon can extend the depth of field of vision measurement system.Secondly,completed imaging experiments with inclined plane filled with charactersby use of non-diffracting imaging system to analyze its imaging characteristics. Basedon the introduction of principle of several common algorithms such as Wiener Filter,Regularization Filter, Lucy-Richardson algorithm and Blind Deconvolution, restoredimages of large depth of field with these methods, and compared their advantages anddisadvantages. A restoration approach of multiple images fusion is proposed to get clearimages for non-diffraction imaging characteristics that with weak details and strongbackground. And then, the use of appropriate edge operator helps obtain the coordinatesof the image edge.Thirdly, Elaborated described spatial coordinates conversion relationship andpinhole imaging model of camera calibration and the actual internal reference model,utilized Zhang Zhengyou calibration method and deduced the solving process ofcamera internal parameters.Experiment with MATLAB Calibration Toolbox, analyzedthe actual physical dimensions error of adjacent corners of Checkerboard. According tothe parameter of calibration experiments, measured the "E" character size at same plane, and then analyzed experimental error sources.Finally, the summary and outlook for this paper indicated that depth of field ofimaging system has been extended with an axicon,which has a reference significancefor the visual measurement of large depth of space object.