The Development Of A Portable On-line Crack Width Measuring System

Presently available crack survey instruments are usually huge when used to cover a wide range, and they are not portable and need human aid in reading. To overcome these shortcomings, a portable on-line crack width measuring system is designed based on ARM, by combining the photoelectric detecting technology, embedded system and image processing technology. The focus of this paper is the accomplishment of hardware and software design and implementation of the system. Following are the main contents in this paper:(1) Hardware design includes optical imaging system, image acquisition and display system, infrared ranging system, lighting system and mechanical structure. The optical imaging system uses the two imaging systems that can be switched to meet the measurement requirements of both the short-range and long-distance detection. According to detection demands, the1/3" CMOS image sensor with1.3million pixels was used after comparison of the advantages and disadvantages of CMOS image sensor and CCD image sensor. Considering the portable demands of the measuring system, ARM was used to process images. The lighting scheme was realized using LED instead of incandescent lamp. The infrared ranging system of Leica was renovated as the infrared ranging system of the measuring system.(2) According to detection principle and demands, assembly language and C++language were combined to develop the image measurement software. The C++language was used to write the whole framework, and the assembly language was used to write each sub-module. The image measurement software has mainly three functions:image acquisition, image preprocessing and image measurement.(3) Experiments was carried out to analyze the measurement range and the measurement accuracy of the system The results show that the measurement distance is between Om and100m, and the measuring system can measure cracks whose width is between Omm and10mm, and the measurement accuracy is better than0.02mm when the measurement distance is less than2m, while the measurement accuracy is better than0.5mm when the measurement distance is between2m and100m.