激光三角法改进的显微镜快速自动对焦方法

为了满足TFT-LCD显微镜光学检测系统在工业上的需求,基于激光三角测距法提出一种改进的显微镜快速自动对焦方式,并建立了光路数学模型。该方法在可见光光路中加入一路808 nm波长的激光,激光光束在被检测物体表面反射后经过一系列光学器件投射在CCD相机上形成一个半圆光斑。以对焦完成时CCD上的光斑半径最小为基准,给出了离焦量与光斑信息探测量之间的数学模型关系,实时控制PZT进行自动调焦。根据给定的数学模型,利用高斯曲线拟合对光斑中心进行定位并计算离焦量,实现对实时控制压电陶瓷的自动对焦。在50倍物镜下的实验结果表明:实际测量值与理论值有很好的线性度,在±30μm的对焦平面上对焦重复定位精度可达到0.2μm,对焦时间在0.26 s。与传统的显微镜对焦方法相比,该方法有较高的精度、较好的线性度和更高速等优点,可满足工业光学检测的需求。

Improvement for fast auto-focus system using laser triangulation

To satisfy the requirements of industrial TFT-LCD inspection system in active auto-focus,a distance measurement approach based on the laser triangulation theory was proposed with the corresponding mathematical model.Experimental data analysis proves the feasibility in the paper.The approach was to select a shaft of laser with the wavelength of 808 nm into the optical light,then the light would be reflected from the surface of the tested object to the CCD camera and form a spot on the CCD via a series of optical devices.In order to control PZT to obtain real-time auto-focus,Gaussian curve fitting method was used to analyze spot information by a mathematical model.Experiments with 50 X objective lens show that the measured values are consistent with the theoretical values with good linearity,and the focusing accuracy reaches 0.2 μm in the focal plane.Compared with the traditional method of microscope focusing,this method has the advantages of high accuracy,good linearity and fast focus speed It can satisfy the practical requests of industrial inspection.