Study On Flatness Measurement Method And Equipment Based On CCD For Hot-rolled Strips

Strip steel is one of the most important steel products and is also an essential part in the national economy. Strip steel products can be divided into two types, namely hot-rolled strips and cold-rolled strips. Currently, the hot-rolled strips are more popular in the market. As an important indicator in shape control, flatness measurement has been researched for its difficulty to achieve in factory. In order to obtain high-precision flatness in a fast way, the flatness measurement is turned into height inspection firstly; then the laser triangulation is used to detect the height of the steel; finally, a detection system is designed to apply in the steel mills. The main contributions of this paper can be summarized as follow:The calibration algorithm of camera is investigated. Firstly, the lens distortion model is established and the imaging system is analyzed to solve the distortion coefficient, which can be used to correct the lens distortion. Then a fast camera calibration method is proposed based on the undistorted image. The method combining with the trapezoid distortion correction can obtain high precision. In addition, the calculation process is simplified and an integrative device is designed. Experiments have been done to compare this method with general method at last.The extraction of the laser strip is investigated. In order to get clear laser strip images, the green channel gray image is split from the color image and a laser stripe definition evaluation function is proposed to control the exposure time. Then the laser edge scanning method that is based on the Otsu algorithm is applied to detect the integral edge of the laser. Finally, the subpixel edge is extracted by using the gray weighted centroid location algorithm.The influences of external factors on the detection accuracy are investigated. Four factors including the pitch angle of camera, the size and number of chessboard squares, the light condition and the parameters of hardware is taken into consideration. The optimization methods for the factors are also proposed in the paper.The whole detection system including the hardware and software is applied in the steel mills. Flatness is detected in real time online.