Study On Semi-automatic Steel Tape Verification System Based On Visual Detection

The line scale is a kind of standard or etalon which can measure the length of the target object referring to the vertical distance between any two of the scribed lines. It's mainly used for measuring the geometry size of the workpiece and the quality inspection of the final products. The accuracy of the quantity value can directly affect the machining accuracy and the quality of the products. Therefore, to ensure the accuracy, periodic verification of the line scale is very important. Among the various verification operation, the verification of steel tape is one of the most important research content of the verification institutions, because of its wide range and the large labor intensity and low efficiency of the existing mannual testing mode.In order to liberate the workforce, using visual inspection technology to improve the manual verification platform is proposed in this paper. An idea of measuring by an automatic walking trolley carried with industrial camera is first proposed and the deviation between the standard and the measurand tape is calculated by identifying the scribed lines intelligently. Except for the tape reeling and the loading(unloading) mechanism, the system has realized the automation of the steel tape verification and can conduct the semi-automatic verification of typical tapes. The main work of this paper is as follows:1. Discuss the scheme of steel tape visual verification, including selection of the industrial camera, lens and the light source and the determination of the trolley'e moving way. Finally a high resolution CMOS camera and a coaxial light source are choosed and the walking mode of the trolley is to pause and capture an image at every checkpoint.2. Directing at the phenomenon of uneven illuminaton in the images, this paper proposes an equalization algorithm based on background extration. Combined with some other threshold segmentation algorithms, clear and effective binary image is achieved after the image preprocessing.3. Design the positioning algorithm of the tape lines and the dynamic calibration algorithm of the pixel equivalent. Realize the high-precision calculation of the deviation between the standard and measurand tape.4. Design the user interface to make the operation of parameter inputing, measurement process controlling and the final report exporting more convenient.5. Realize automatic measurement of the trolley based on serial communicaiton. Complete the high-precision and high-efficiency verification of the common types of steel tape. Analyze the repeatability and the possible influencing factors of the actual measurement results and make an improvement scheme of the verification system.