Study On Theory And Application Of3D Surface Defect On-line Detecting Based On Line-structured Laser Scanning

With the increasingly high demand for product quality, and the detection means getting rich, product surface defects detecting is becoming more and more stringent. At current moment, in addition to obtain the2D (two-dimensional) information of the surface defects, but also the depth or hight of the defects should be known by the3D (three-dimensional) detection method. The main method for extracting the3D surface point-cloud data is3D vision measurement. By using3D detecting method, some defects, which are not obvious or cannot be recognized by2D detecting method, can be recognized more reliably. Moreover, more advising information for adjusting production produce can be obtained through3D vision measurement. So3D surface defects detecting based on3D vision measuring is getting more and more attention by enterprises. In this paper, the theory and application of3D surface defect on-line detecting based on line-structured laser scanning are put forward and studied.The main research work and creative items are discussed in the following.Firstly, the mathematic model for the3D scanning system based on line-structured laser vision sensor is built up. A universal mathematic model for line-structured laser vision sensor is built up first of all. But this model is difficult to be realized and should be simplified. So, the measurement coordinate system is moved and rotated to the line-structured plane coordinate system, and the Y axis of the measurement coordination system is alone with the scanning direction forward. Thus, the relationship among the measurement coordination system, the line-structured plane coordination system and the camera coordination system is easy to be transformed. Finally, using line-structured laser vision sensor in the case of the camera radial distortion, the simplified mathematic model for the3D scanning system is built up. This model is easy to be realized for on-line scanning surface defects.Secondly, a feature extracting algorithm for the existing calibration method based on3D sawtooth target is improved and used to directly calibrate the line-structured laser vision sensor. Against the disadvantages of3D target calibration methods, a new calibration method based on a2D plane target is proposed. On the2D plane target, there are three sizes of circle points which are arranged according to a certain position order. The calibration model is built up, and the feature points mapping method between target coordination system and camera coordination system is designed. The position and pose relationship between the line-structured plane and camera coordination system can be calculated conveniently on field.Thridly, the automatic line-structured laser stripe center extracting method based on weighted gravity formula alone with direction field is put forward. Compared with an improved Steger extracting method the efficiency of this method is higher, more suitable for all kinds of surface with different color and material.Fourthly, the3D surface defects online detecting method based on a mapping policy between the Z level and color value is proposed. According to the mapping policy, the3D point-cloud is projected to a color image, and then the color image is transformed and rotated to registrating with a standard color image, which is mapped from a standard product, using a2D interative closest-point algorithm. Thus, the color difference between the projected color image and the standard color image can be calculated. Through color difference threshold, the defect can be recognized. Compared with a common directly3D point-cloud registrating and difference calculating method, the efficiency of this method is higher, and can be used to online detect the3D surface defects.Finally, the3D surface scanning and defects detecting hardware system is built up, and a detecting software system is programmed in Visual C++2010platform. By using this device, edge-breaking defects of the magnetic tile surfaces are recognized, label pasting bubbles defects are detected, and position locating of the steel wire in a model is realized. All experiments show that the3D surface defect online detecting method based on line-structrued laser vision sensor is feasible and can be used in all kinds of fields.