Research On Optical Precision Measurement System For Straight Edge

With the growth of precision machining and the demand for high quality production, the requirement for quality control is increasing. Contrasted to traditional contact measurement methods, optical measurement methods have advantages such as non-contact, non-abrasion, high response speed and good flexibility, and are widely applied in the quality control. So the requirement for the precision of the optical measurement methods is increasing too. But the precision of the traditional measurement methods depend mainly on the size of the image sensor's cells. To break the limitation of the size of the image sensor'cells, subpixel edge detection technology are proposed that improves the precision by image processing methods. The straight edge is the profile of parts which generator is line and vertical cross the section. In this dissertation, the scheme of linear CCD measurement is established, and the subpixel edge measurement system on a chip based on FPGA is developed to resolve the conflict between the precision and speed of image processing methods for the straight edge. The work including in the dissertation is shown as follows:1. Design of entire scheme of edge measurement of the.At first, three kinds of optical measuring principle is described. Based on the analysis of their advantages and disadvantages, the edge of the measurement system sheme which is based on the parallel light projection method is established. The illumination match between CCD image sensors and the light source is analyzed, and optical system of the edge measurement is built based on this.2. Principle of sub-pixel edge detection algorithm.The origin and principle of subpixel edge detection are introduced, and introduced the sub-pixel edge detection technique prerequisite. Then the common subpixel edge detection algorithms are reviewed. Finally, an improved sub-pixel edge detection algorithm based on Canny-Legendre moment operator is proposed. And a simulation experiments that measure the ideal edge with the algorithm is designed.3. The design of subpixel edge measurement system on a chip based on FPGA. Firstly, the hardware system architecture of the edge measurement system is designed. Then the hardware circuit of the noise processing of CCD signal and AD conversion is introduced. The edge measuring system is established in a single FPGA chip with the Verilog HDL language. Finally a simulation experiments is designed to test the system.4. The straight edge measurement system experimental and the analysis of its data. A set of straight edge image acquisition system is designed to analyze the difference of the actual edge shape between the cylindrical parts and the rectangular parts. Two experiment models are built for the diametaer measue and deflection measure.The experiment datas show the mean error of subpixel edge measurement system on a chip based on FPGA can reach 0.5μm, and repetitive error(2σ) is less than 1μm. Finally, the factors which affect the measurement precision are analyzed.