The Study Of Active On-line Measurement Method For Diameter Of Steel Pipe

With the rapid developm ent of som e industries such as ener gy, architecture, chemical engineering, petroleum and communication, the demand of cylindrical steel increases dramatically. As one of the most important indicators for the quality of steel pipe, how to perform the online and real-time measurement to the diameters of steel pipe has becom e the prim ary issue of many m anufacturers. At present, the measurement system of steel pipe diam eters is not only expensive, but having some weaknesses, such as failure of m easuring large-caliber steel pipe, incompetence for dynamic measurement, and so on. Aiming at the deficiency of the previous steel pipe measurement system, this paper proposes a new online diameter measurement method for the large-diameter pipe. The m ethod uses the principles of binocular vision, and determines the relative positions of cameras and other devices via camera calibration. The system calculates the four tangential equations of the pi pe’s cross-section by the edge information extracted from the im age ca ptured by the two ca meras. And it calculates the inscrib ed circle’s diameter of the quadrilateral form ed by these four tangents, and determines the diameter of steel pipe. The system has the merits of high accuracy, stable anti-vibration performance, and can display images and measurement results in real-time, especially for the online diameter measurement of large-diameter steel pipe.The major innovations achieved in this dissertation are as follows:1. Camera synchronization system is designed, in order to overcom e the impact of pipe vibration, by internal and external synchronization of the measurement. In the external mode, the signal generator cont rolled by the computer transmits the TTL signal to trigger the ca mera to capture im ages. In th e in ternal m ode the sys tem achieves synchronization by the wa iting thread. The system succeeds in overcoming the impact of vibration.2. A new adaptive method of checkerboard corner detection is designed, and its error rate is low and measurement accuracy is high. The method highlights the corner areas by the m orphological method. And it perform s the multi-threshold selection to the corner areas by the symmetric operator. It locates the sub-pixel edge by the Taylor series, and accelerates the speed with the help of operators. 3. A new method of edge detection is designed, transforming the edge detection problem into its one-dim ensional form, so as to determ ine the rough edge regions. Then it locates the sub-pixel edges by Legendre orthogonal moments.4. Experiments such as calibration e xperiment, pipe diam eter precision experiment are designed. And they can pr ovide the necessary conditions for the implementation and verification of the measurement system.5. The overall framework of the measurement system is designed and based upon the Visual C + + platform. The structure p rocesses the image data simultaneously by the main thread opening up four sub-thread s so that th e speed of the m easurement improves and the impact of vibration on the results decreases.