Study On Measurement System Of Centering Errors Based On Digital Image Processing

In all kinds of optical systems, a consistent optical axis is the basic requirementof high-quality imaging. However, in the process of lens manufacture, the centeringerrors will be produced because of the influence of circumstances, machines,techniques etc. The presence of centering errors destroys the coaxal theory of theoptical system. So the centering error is one of indexes in optical system evaluating.The instruments of centering errors measurement play an absolutely necessary role inthe surveying optical system, especially in surveying precision optical system.Conventional optical measuring instruments get data by eye reading, whichmeans that the measurement is with low efficiency and an intense work. It can notmeet the requirement of modern application. On the basis of the working theory andthe structure of the optical measuring instruments, the main task of the project isresearching and designing a novel multi-purpose system for measurement of lens,especially for the centering errors.Combined with modern measuring technology and modern digital image processtechnology, a kind of measurement system is designed based on digital image, whichis formed by transmitted light. This paper introduces the structure and the modules ofthe measurement system. Through researching the principle theory and the methodused in the measurement of centering errors and other parameters of lens, the opticalpath of the system is designed. The modules of the measurement system include theauto collimations, the lens holder, the matrix CCD camera and the computer. After theacquisition and digitization of the video signal, MATLAB is used for processing thedigital image and error analysis. The numeric result of the experiment shows theprecision of the measurement system.At the end of the paper, the accuracy of the multi-purpose system is estimated bythe result of experiment. The standard deviation of eccentricity measurement is0.0038mm without displacement of high precision hardware. The measuring error ofthe system is analyzed and technique for improvement is discussed.It is proved through experiments that the optical measuring system is correct andfeasible. It can improve measuring efficiency and the instrument is integrative andminiaturization. Furthermore, this kind of measuring system is one of the approachesof precision improvement.