The Autofocusing Technique Based On Measuring Micro-parts

Computer vision-based precision measurement technology with easy operation, strong anti-jamming, high precision, has been widely used in the engineering fields, applicable to micro-parts assembly process of high-precision measurement. the ability of imaging systems for optical images to distinguish details that affect the accuracy of digital image optical measurement: When the image is in focus, it is most clear with more detail, the precise measurement is easier; and when the image deviate from the focus, the image blur, detail is lost, detect the shape or location of micro-parts becoming more difficult. So how to get the focus area exactly has become a urgent problem to solve.This paper studies the historical development of auto-focus, analyzed the specific reasons of out-of-focus image, described the various traditional methods of auto-focus in detail, and in-depth studied image-based autofocus technology, which including the image preprocessing technology ,focus area designing, autofocusing function and the focal point of the search algorithm technology.1) Verified several image filtering denoising method through experiments , analyzed their impact on AF function curve, considering the filtering results and algorithms speed, finally chose median filtering as the subject filtering method;2) Verified several focus area designing algorithms, combined with the issue, designed the algorithm with manual focus area for the column cavity, designed the algorithm with circular focus area for the micro-ball under low contrast;3) Studied a variety of focal point searching algorithms, through simulation experiments, analyzed two new search algorithms’advantages and disadvantages, and designed a new focal point searching algorithm with parabolic method based on based on optimization theory, compared with several common searching algorithms, demonstrated its advantages of less time-consuming, focusing accurately;4) Studied a variety of commonly used AF function, compared the advantages and disadvantages of various functions through analysis, and for the problem that the most AF functions losing their ideal characteristics under low-contrast environment , proposed an AF function based on Zernike orthogonal moments, by adjusting the weight coefficients of order moments, can adapt to the autofocus under different contrast;5) Built an auto-focus experimental platform, achieved the AF algorithm of the paper studied through the system.