Research On Autofocusing Of CCD Image Detection System

This thesis describes the design of autofocusing implementation for CCD measuring microscope system.It's essential to find the best distance between the specimen and the microscope objective in CCD measuring microscope system. The boomed technique of CCD application and personal computer bring us high repeatability by means of autofocusing. So it is important how to realize auto-focusing quickly and effectively in microscope system.Firstly, the article summarizes much work that has been done in autofocusing and structure principle of autofocusing measuring system. The paper mainly works on autofocusing method of digital image processing. The common autofocusing methods or criterion functions are classified as frequency domain function, gradient functions, power functions, information content functions and statistic functions. Many experiments have been done to analysis performance of the classified criterion functions. Variance function, entropy function and Brenner function were used as criterion function in this focusing function. In addition, auto-searching in focusing field is also developed, and successive approximation approach was adopted as a method of auto-searching in this focusing system.The thesis have also implemented the control system and the driver circle for stepping motor. Based previous tasks, work out the software of autofocusing system implement.The analysis of experiments testified that the focus accuracy of this system is±16μm in the focus range of±1000μm and in this accuracy range, its repeatability is±0.1μm. So the scheme of auto-focusing and auto-location given in this paper can fulfill the requirement of measurement.