A Hardware-Based Image Acquisition Scheme for Low-cost Machine Vision Systems

• Main Authors: Yu-Chieh Chen, 陳佑杰
• Other Authors: Yin-Tien Wang
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/67971319281333903798

碩士 === 淡江大學 === 機械與機電工程學系碩士班 === 93 === In this research, a Machine Vision System (MVS) is developed based on a low-cost CMOS vision module. Many limitations on image processing for the CMOS vision are investigated and improved in order to design an applicable MVS for industry applications. These problems include the environment setting during the process of image acquisition, the image encoded format, and the image processing after the image is acquired. First, in image acquisition setting, the working frequencies of the vision module are varied to perform different exposure time and obtain different quality of image. After that, an image quality selection procedure is executed by analyzing the sub-images. Sub-images with best quality are collected to reform a full image. Second, the original image encoded format of the CMOS module is utilized for image transmission. Therefore, the transmitted image will preserve complete but small-in-volume information. Finally, utilize the technique of image segmentation to separate the image pixel of the tracked object from those of the environment. Then the information about the tracked object can be abstracted and fed back to the mechanism control system. In hand-on practice, all of the mathematical algorithms for image acquisition and processing are programmed in an Altera FPGA chip using SOPC design tools. Four functional modules, namely working frequency selection, image acquisition, signal hand-shaking, and UART transmission, are designed based on VHDL. Furthermore, a Nios CPU is designed to perform the procedures for image selection and processing. The developed MVS is utilized in the automatic sensing and inspection processes of a CD/DVD duplicator. Three experiments are implemented, including logic detection of the existence of a compact disc, one-dimensional measurement of stretch length of a CD tray, and two-dimensional measurement of the center position of a compact disc. In the near future, an attempt will be made to apply this vision system to a dynamic environment, for example, the sensing device for a mobile robot.