基于CCD的透镜焦距测量实验系统的设计

Design of Experiment System for Focal Length Measurement of Lens Based on CCD

针对传统测量焦距读数所引起误差较大的问题,实验系统在传统放大率法测焦距的基础上用CCD代替人眼实现数字化测量,并用电控平移台控制步进精度,显著提高了其测量精度和自动化程度。图像清晰度评价是焦距测量的一个关键步骤,在对CCD工业相机获取的图片的清晰度评价中,提出了一种改进的灰度差分评价函数,提高了图片清晰度评价精度和速度,从而提高了系统的测量速度。实验进行了光学成像系统的搭建,以Matlab为开发平台进行软件开发,实验系统搭建方便,操作简单,测量精度和自动化程度高。实验结果表明,该系统能够对透镜焦距(以正透镜为例)进行准确测量,改进的清晰度评价函数聚焦速度比传统的清晰度评价函数快3倍,测量焦距重复精度高于1%。

The CCD-based experiment system is based on the traditional magnification method to measure the focal length and it uses CCD instead of the human eyes to achieve digital measurement. Meanwhile, the motor control console is used for stepper precision which significantly improves the accuracy and automation. The key to focal length measuring system is whether it can meet the real-time and fo- cus accuracy in image clarity evaluation function. An improved definition evaluation algorithm called improved gray-difference evaluation has been proposed to improve the speed and accuracy of evaluation algorithm. And the quality of system has also been improved. Optical imaging system has been built in experiment and Matlab is used as a software development platform. It is convenient to set up the experi- ment system with high degree of automation and easy operation. Experimental results show that the system is accurate to measure the focal length of positive lens and the requirements of experiments have been met which the focus time of improved evaluation function is 3 times faster than traditional definition evaluation and that repeatability of measurement accuracy is better than 1%.