Research On Precision Measurement Of Fragment Parameter Based On Computer Vision

The measurement of fragment parameter is indispensable during the development and confirmation of bomb. The workload of measurement is very heavy, because the number of fragment is very big after explosion and there are too many parameters to measure. Manual method and photoelectric method have some shortcomings, such as inefficiency, big man-made error and low-level automatization, so conventional methods do not meet the requirement in measurement of fragment parameters. Computer vision inspection is a new technology based on modern optics, which syncretizes optical electronics, computer image, information processing, and computer vision. It has many advantages, such as non-contact, big field, high efficiency and high precision. It also has the ability of on-line inspection, real-time analysis and control. It is widely used in military industry, mechanism, electronics, agriculture, medicine and so on. Some principles and algorithms of computer vision inspection can be used to improve the efficiency and accuracy in measure system of fragment parameters.The dissertation is based on the project of the study of fragment parameter measuring system, which is supported by mechanics institute of Nanjin Science & Technology University to develop a fragment parameter measuring system. Some principles and algorithms of computer vision inspection are adopted to improve the efficiency and accuracy of this measuring system.Many papers have been referred in this study. The situation on the research of fragment parameter measurement has been inquired, and the difficulties to realize the project have been analyzed. The idea is put forward that the principles and algorithms used in computer vision inspection will be adopted in fragment parameter measuring system. The history, situation and trend in development of computer vision inspection have been summarized. As critical factors of computer vision inspection, accuracy and efficiency have been discussed. The content of this dissertation is related to measuring model, measuring method, system composition, image processing, camera calibration and accuracy analysis.The measuring model, regular icosahedra, has been established. The system simulates the direction of fragment's windward using the 16 special orientations of regular icosahedra, and measures the fragments' projected area in 16 different directions. According to the measuring model, a fragment parameter measuring system based on computer vision inspection has been designed. The system is composed of illumination unit, object stage, mechanical unit, optical unit, electric unit, and software. Image of projected area can be obtained by camera in projected direction, and image area can be calculated throught image processing. According to the equivalent of pixel, the fragment's windward area can be gotten. The system qualifications require that the time consumption is less than 35s for one fragment measurement. This system uses four cameras to capture image at the same time, so the time consumed in moving the cameras is decreased greatly. Multi-thread technique has been adopted in this system's software, and the system efficiency has been improved greatly, when main thread and image processing thread works parallel.Image processing is the kernel of computer vision inspection, and has great effect on accuracy and efficiency. In this paper, the basic concept of digital image is introduced, and some methods of image processing, such as image filter, image segmentation and edge detection, are discussed in detail. Based on basic image processing methods, the special image processing method is designed in this measure system. When outside the depth of field, images obtained are usually obscure, so there is big error in the results of area measurement. Two image processing arithmetic's are developed to amend area error from defocus. The two methods, one based on image gradient and the other based on edge detection, can amend the results to meet the system's requirements.Camera calibration is a very important step in computer vision inspection. In practice, the camera cannot obey exactly the principle of pinhole imaging, so there is aberration in images. In high accuracy measurement, the aberration should be eliminated. The cause of image aberration is analyzed and the method to correct aberration using grid is introduced. For the requirement of real-time, conventional method of camera calibration is very difficult to realize in practical system. According to the character of images, a new calibration method based on special contrastive object is put forward. In this method, the 13 camera parameters are not need to calculate, and only the area equivalent of pixel is calibrated. The test results indicated that the calibration method is perfect and does not increase image-processing time.Accuracy is the most important technical parameter in this system. The accuracy of this measuring system is analyzed using the theory of uncertainty. In this system, the random errors include noise, principle error of measure model, position error of rotating stage, area error caused by defocus image, and image segmentation error. All errors mentioned above are analyzed thoroughly, and uncertainty of errors is calculated. At last, the whole uncertainty of the system is gotten by synthesis.The accuracy and repeatability of this system are verified. According to the slenderness ratio and the maximum windward area, four experiments are designed. The result shows that the error of average windward area is less than 1.38%, and the maximum deviation of repeatability is less than 0.03%. The accuracy of this system meets the requirement. According to the result, the more slender the fragment is, the less accurate the result is.At the end of the dissertation, the research results and original discoveries are presented, and the succeeding research is suggested.