Discrete Rotational Symmetric Triangulation And Its Application In Depth Measurement

With the rapid development of modern manufacturing, advanced detection technology is essential to ensure the manufacturing quality of products, improve the rate of qualified products, lower energy and raw material consumption, improve labor productivity and economic eciency. Compared with manual testing and oine testing, the online detection reduces the handling and installing time of products, shortens the inspecting time of products, increases the eciency of testing process and provides greater accuracy of test results.Therefore, it is important for online detection system to study discrete rotational symmetric triangulation system. Rotational symmetric triangulation measurement is an important development direction of the laser triangulation measurement system. It can solve the problem of directional dependence which exists in the traditional laser triangulation measurement.Based on the background in the development of online detection system, combined with the existing non-contact optical measurement technology and current development, this paper researches and designs a discrete rotational symmetric triangulation system.Firstly, this paper summarizes the current research of online detection system and optical non-contact measurement at home and abroad, describes the development of the rotational symmetric triangulation.Secondly, the principle and optical structure of discrete rotational symmetric triangulation are showed. According to optical structure, the system should match Scheimpflug condition to ensure that the object point always have a good focus in the whole range. The parametric modeling of optical system is designed and the constraint equations is derived.And the imaging system is designed, such as lens,mirrors,camera and so on.After then, this paper decribes the mechanical structure design of a prototype system. Using 3D model, the system’s imaging condition which is under the condition of dierent surface characteristics or dierent angles is simulated with Zemax.Thirdly, this paper analyses the image processing algorithms which can inspect the center of each laser imaging spot.The thesis describes the pre-processing process of original images which includes binarization, open operation, connected components labeling and Gaussian filter. And the two algorithms about gravity and peak subpixel detection are described.Through compared the detecting accuracy of laser spot, one suitable algorithm for the system is chosed in the two algorithms. Point repeatability experiments of a single laser spot are done under the condition of dierent surface characteristics and dierent angles, so that the total repeat accuracy 0.7μm of the system is acquired.Finally, the measurement system is calibrated. In order to make sure the relationship between the depth of object point and the relative moving distance of laser imaging spot,this paper calibrates the measurement system and establishes the calibration model. Calibration experiments should be done to obtain the system internal parameters. Calibration experiments include measuring the paper surface, metal surface and the surface with different angles of inclination. After then the system measurement error can be calculated.Compared with touch probe and this system, the step plane is measured. The experimental results show that the system reduces the impact which comes from the dierent characteristic surfaces.