TFT-LCD面板光学检测自动对焦系统设计

Design of TFT-LCD panels optical detection auto-focus system

针对TFT-LCD面板尺寸大、厚度薄、光透过率高的特性,建立了基于激光三角测距法的自动对焦系统。采用光学回路和机械结构设计,对激光光斑中心位置准确求取以及自动对焦原理等算法进行了研究。首先,根据激光三角法测距原理进行了光学回路设计,并以纳米定位平台作为微小行程对焦驱动轴。其次,通过分析光斑图像特性,调节相机快门调整曝光量从而对图像进行噪声消除。另外,采用质心法快速提取光斑中心,在分析激光光斑中心位置与离焦关系的基础上,说明了自动对焦算法。最后,介绍了系统自动对焦时间的设定方法。实验结果表明:在行程为100μm的自动对焦范围内,5X物镜下,自动对焦时间为0.36 s,重复定位精度为±1.98μm。50X物镜下,自动对焦时间为0.41 s,重复定位精度为±0.26μm。该系统稳定性好、对焦精度高、抗干扰能力强,基本满足大尺寸玻璃基板光学检测的需要。

In connection with the characteristics of TFT-LCD panel large size, thin thickness and high light transmittance, an auto-focusing system based on the distance measuring of laser triangulation sensor was established. Moreover, with the design of optical circuit and mechanical structure, the laser spot center was accurately calculated and the theory of auto-focusing was studied in this paper. Firstly, according to the principle of laser-triangulation, the optical system was design and the driveshaft was auto-focused using the nano-positioning stage as the minor stroke. Secondly, by analyzing the characteristics of spot images, using the camera shutter to adjust the image exposure, the noise of the image was eliminated. Thirdly, employing the center of gravity theory to pick up the spot center quickly, the algorithm of auto-focusing was explained on the basis of analyzing the relationship between the laser spot center and the out-focusing. Finally, the setting methods of auto-focusing was introduced. Experimental results indicate that with less than the 100 μm of auto-focusing and the 5 times objective lens the auto-focusing time is 0.36 s, the repetitive positioning accuracy is±1.98 μm. Under the conditions of 50 times objective lens, the auto-focusing time is 0.41 s, the repetitive positioning accuracy is ±0.26 μm. It can satisfy the system requirements of non-contact, online, real time, higher precision and rapid speed, as well as strong anti-jamming and stabilization.