The Measurement System Of Objects’ Three-dimension Figure Based On The Laser Triangulation

In recent years, with the development of image processing technique and computer technique, the measurement technique of objects’ three-dimension profile has developed rapidly, and it has been applied widely to product design, quality control, volume measurement, machine vision, reverse reverse engineering, etc. In most cases, we have the product samples or mock-up without the product document. In order to better meet the needs of advanced manufacturing technology development, we need to measure the three-dimension profile of the product samples and mock-up to establish the digital 3D model. Now a vatiety of objects’ three-dimension profile measurement technique has been developed, and laser triangulation is one of the non-contact measurment applied broadly.Discussed on the current measurement technique, the measurement system of objects’ three-dimension profile based on the theory of laser triangulation is designed. The main conten in thesis includes:(1) Analyzing the principle of laser triangulation, the system uses the direct laser triangulation measurement as the measuring method, and designs the optical structure of measurement system. LD is used as the light source, and linear array CCD is used as the photoelectric detector. The laser triangulation measuterment system is builded and fixed on the three-dimensional displacement platform.(2) The hardware of linear array CCD image acquisition system based on FPGA is completed. In Altium software platform, the CCD output signal processing module with AD9826 and data transmission module with the USB 2.0 interface chip CY7C68013 are designed. The complexity of system hardware design is reduced.(3) The software of linear array CCD image acquisition system based on FPGA is completed. The FPGA logic program is generated in Quartus II software platform, and verified through functional simulation. In Visual Studio 2008, the upper machine software is designed to realize the communication with USB chip, and it could acquire image output from linear array CCD in a continuous or single-frame manner. Cooperation of each module realizes the acquisition, transmission, display and storage of CCD output signal.(4) The measurement system acquires the digital image information of spot with noise. According to the noise characteristics, digital signal would be transformed into the smooth and steady spot image by low-pass filter and mean filter. In this paper, a variety of spot positioning algorithms are compared, and a improved algorithm based on square weighted gray centroid algorithm is proposed, and proved to be better than other algorithms through experiments. By measuring the non-linear relationship between displacement in the measured surface and changes of linear CCD image point, the measurement system is calibrated, then results are analyzed.