Study On The Fast And Precise Machine Vision System For The Hole-positions On Sphere Surface

In space the development of computer technology, communication technology and large-scale integrated circuit technology, various new technologies and products of measuring instrumentations in the worldwide develop towards digitized and information.The digital measurement is the key technology for the modern manufacturing technology. The digital measuring technology of the high speed, high efficiency, high precision, high dependability, and multi-purpose promotes the development of the digital manufacturing technology .The reliance on the relationship between them decides the essentiality and urgency of the development of precise measurement technology. Therefore, to research the basic theories of precise measurement and to adopt the digital technology are important to the development of manufacturing level.The precise measurement in the worksite is difficult. With the development of the aviation, space and defense industries, such measurements are growing. The accuracy and efficiency of them are increasing. The 3D coordinate measuring machine can achieve the precise measurements of the sphere or other complex surfaces, but the efficiency is very low and difficult to meet the requirements of automatic measurement. Advanced 3D coordinate measuring machine can simultaneously meet the requirements about speed and accuracy, but it is at the price of million dollars that is difficult to accept for the normal users. Although the almighty tools microscopes can realize similar measuring, it requires manual operation to complete and it is difficult to achieve the automatic measuring. If the measured material has a particularity (such as radioactivity, etc.), the measuring is more difficult to be achieved by the operating force. Thus the research of the testing technology based on the machine vision and achieving the sphere micro/small hole location measuring using the non-contact way have significant sense.This paper is based on a defense industry suitable project, undertaken by the Applied of Lasers Research Institute, Sichuan University. It is also associated with the subject of "Research on machine vision system and image processing" of the applied basic research projects in Sichuan Province. The technical projblem and the relative theory of the measurement have been solved.The research of this subject has made good for the scarcity on the measurement of the hole-positions on sphere or similar sphere surfaces using the existing measurement methods. And the test results are achieved on the technical requirements of the project. The testing time should less than 40s/ per holes position and the measurement inaccuracy is not larger than 30". The project has been identified by the Science Department of Sichuan Province, and the technical level is in lead in China.The main research work and innovation points in this paper include:1. The research and application of the machine vision system were comprehensively introduced. The advantages and disadvantages of various methods and applications were analyzed. The mathematical model of the hole-coordinates on sphere surface was set up. Moreover, an system of image signal acquisition and processing based on DSP+FPGA architecture and CCD camera with high pixels was proposed. The system provided higher speed and precision.2. A innovation idea which identifies hole type automatically ( through hole and blind hole) according to gray-level histogram was given .The method improved the intelligence level of the system and the wide adaptability of measurement. 3. By analyzing the structure characteristics of system and measurement requirements, a pinpoint method using a reflection type of collimating laser beam -guided positioning system based on machine vision was proposed. And the calibration experiment proved that the method provided higher speed and precision.4. According to the requirement of the pinpoint method, a fiber semiconductor laser collimating system was designed, which divergence angle of the laser beam is less than 0. 5°. It can meet the demands of the position system based on machine vision.5. Based on the traditional Hough transform method, a adaptive searching method in target area was proposed. In this way, the accumulation range of the circle center can be restricted near the center point(x₀,y₀), and non-effective accumulation can be greatly reduced. The testing error and the time are respectively less than 1 pixel and 50 ms.6. The master-slave operation mode constituted by the PC and DSP+FPGA digital circuits was adopted. The PC completed the controlling of DSP and display of the data processing results and man-machine interaction. And a great deal of data processing calculation completed by the DSP. Especially the advanced digital circuit design of the DSP +FPGA was integrated the CCD image acquirement and processing and the movement controlling of the sphere-shifting device as a whole, and in this way, high precision and high efficiency of the measuring can reality.7. The research on the control algorithm of the stepping motor based on the fuzzy control theory was proposed. A advanced feedback controlling system was developed . Its practical and applications proved that it can meet demands.Based on image processing, recognition algorithm and controlling mode converts 3D measurement into 2D image recognition only changes the locomotion or movement mode, the non-contacted measurement for other surface type is realized. The research on this paper can be applied widely, provides a resolution for the completely digital, intelligent and miniaturization of the machine vision system. It is important consulting value and theory sense to the development of non-contacted precision measuring technology.