Metallic Materials Should Be Variable Based On Computer Vision Real-time Measurement System

Real-time online measurement of strain is a basic process in tensile testing of metal material. Its precision is one of the factor to determine many other parameters'precision. Aimed at the requirements of strain measurement in tensile testing, the paper researches the appliance of non-contact measurement based on computer vision in strain measurement of tensile testing, and the author has developed a set of vision measurement system, which including the design of its hardware and the development of its software.At first, the article introduces the research condition of non-contact measurement techniques and strain measurement techniques. We decide to adopt computer monocular vision principle. Key techniques are discussed in this paper, including the obtainment of digital image, image processing, image recognition, system calibration and subpixel location etc. It's the foundation of vision measurement to obtain a series of digital images of measured object steadily and fastly, which keep its features in focus. After image preprocessing such as smoothing filtering and threshold, the binary image can be obtained. And then, by edge detection and pattern recognition, the contour of the measured object is separated and the line edge could be picked up. At this time, the edge has reached pixel precision. In order to improving the measuring precision at the condition of not increasing the hardware's cost, the paper adopt the technique of subpixel location which is proved effective by subsequent experiments. Guide to the expression the Uncertainty of strain measurement value of the system.The paper lays emphasis on edge detection and subpixel location and the expression the Uncertainty of strain measurement value of the system. Researches their related algorithms and puts forwards the best methods after experimental verification.The measurement system software is developed with Borland Delphi on Windows XP operation system. It has almost realized the function of real-time non-contact measurement of strain in tensile testing.