Research On Measurement Of Centering Errors Based On Digital Image Processing

About most optical theories, the co-axis theory of the optical system is the premiseand foundation of other basic theories. However because of the limitation of the actuallens production conditions, the lenses are made with some quality defects. And theco-axis factor is destroyed with defects. As a result, centering errors are appeared. Thecentering errors destroy the base of ideal optical theory, so that the quality of pictures ofoptical system is reduced. Moreover, to a certain extent, it affected measurement ofother optical parameters of the lens measuring equipment. Consequently, it is importantfor lens production and testing to research the theory of centering errors, and to developreasonable and efficient methods of measurement.According to ISO definition of centering errors, centering errors of lens are mainlydivided into translational displacement of light axis and surface tilt error. On the basis ofdifference of measurement principles, measurement methods of centering errors can bedivided into interference and autocollimator mode. The optical path of interferencemode is complex and its efficiency is low. This project uses common optical path calledcollimator-autocollimator mode, compared with measurement principles and opticalpath of other Lens parameters, like EFL, BFL, R.etc. Through studying of measurementmethod of centering errors, appropriate measurement algorithm is made. Firstly thecorners of cross are found through their intersection of the lines. And then the center ofcross is determined. Finally the error circle of a lens is found. The measurement systemis mainly suitable for transmission mode, taking into account the reflection mode.The precision measurement of centering errors proposes new requirements ondesign and debugging new measurement platform. Firstly, mechanical parts ofmeasurement platform are made. The design of column with ball screw and wide rail isa key part. And it is convenient for adjusting optical path to design Fine-tuning fixtureof autocollimator. Second, control system uses a stepper motor with an encoder forfeedback. As a result, the coordinates calculated values need to be compensated. Finally,and the most importantly, in order to ensure the accuracy of the rotating machinery shaft,a set of high-precision air flotation rotating platform should be designed.Based on actual situation and requirements of the measurement process, themethod of amending luminous flux, the modified algorithm of image subdivision, theway of corner detection and the optimum algorithm of center approximation isintroduced. Finally through testing those methods, this paper analyzes the main reasonof error, and suggests ways to improve the measurement accuracy of the program.