Research On Optical Auto-focus System With Multiple Objectives

As a type of liquid-crystal displays, TFT-LCD rapidly becomes the main product in new age because of its advantages on brightness, contrast, power consumption, lifespan and volume, and will be a highlight of global economic growth. In order to get clear detecting images of TFT-LCD, optical auto-focus is the key technology based on machine vision defects detection during the process of production of TFT-LCD. Since the dimension of TFT-LCD glass panel increases with production lines of new generation, the increasing size of glass panel demands more on efficiency and reliability, which traditional autofocus technical solutions can't meet. For the vibrated influence to TFT-LCD glass surface caused by the air floating stage, and for the special requirement on auto-focus of multiple-zoomed objectives, wide in range and high in accuracy, when DOF changing the lens from 0.5um to 91um, this article proposes a instant multiple auto-focus system used in TFT-LCD glass surface detection.The main work of this research:(1)Based on the principle of laser triangulation, a improved system designing program on microscope multiples auto-focusing was proposed, and with the design of special optical results, the linear relationship between the focal quantity and the detecting quantity was established, and overcame limitations of methods in nonlinear, defocus direction discrimination, defocus detection range in traditional astigmatic method and pinhole focal direction.(2)With the further study of focus spot image data processing, the research focused on three applied algorithm, including qualitative method, energy method, Gaussian curve fitting and Kalman filter, and analyzed the functions of Gaussian curve, including eliminating spot ghost, solving reflective metal circuit emergency situation and performance characteristics of energy saturated condition when the light reflex are too strong.(3)In order to resolve the the problems multiple objectives, whose depth of fields are range 0.5um to 91um, and vibration of detected objects brought in detecting process, double drive micro-macro structure wans firstly applied in to the optical auto-focus which described in this article, and the motion control of macro micro double drive structure, consists of piezoelectric ceramics (whose itinerary is 100um) and DC (whose itinerary is 25mm) were also studied,including Z to focus movement macro micro double drive structure mathematic model and control algorithm, and XY platform dc motor PID control algorithm.(4)At last, according to the requires of TFT-LCD detection experimental verification and results analysis including the system on scope, speed, accuracy, and function,were taken on the actual project hardware platform,we took of and compared to performance of the current international advanced automatic focusing technology products.Compared with the traditional method of microscope focusing, the optical auto-focus system with multiple objectives has the advantages of high accuracy, good linearity and fast focus speed to meet the practical needs of industrial inspection a wide range requirements and improved TFT-LCD detection efficiency. Based on the structure and laser triangulation, multiple objectives defocus amount and direction is the rapidly detected, have theoretical significance and high practical value. It can also be applied in many other fields, such as laser direct writing, confocal scanning, microdevices distance fast measuring and so on.