| In the process of manufacturing production, the measurement for position degree of holegroup is needed to be carried out in many working procedure. This is because the errors ofprocessing and manufacturing, the size and location of hole will all exist some errors, whichhave an impact on the assembly of parts that cooperated with the hole and operation ofmachinery, and result in a positioning error for hole used to locate. The traditionalmeasurement methods for position degree of hole group can neither meet the requirements ofrapid mass production, nor achieve on-line measurement. By Applying visual techniques,measuring the position of the spatial circle will be affected by the perspective projectiondistortion, making it easy to detect error of the spatial circle center. At present, the mainmethods are binocular stereo vision and structured light scanning. However the equipmentsneeded for both methods are complex, and have their own limitations. Therefore, this paperputs forward the vision measuring technology for position degree of hole group based onstructured light. This method uses structured light to calibrate the measured plane, and makescoordinate transformation for edge point of the hole in order to avoid perspective projectiondistortion. In this paper, the main research works are as follows:This paper analyzes the detection method of circular hole image center and the distortiongenerated in the perspective projection process when CCD cameras capture the image of hole.Determining the method of circular hole image center based on circle fitting. Sub-pixel edgedetection algorithm is used to get the edge points pixel coordinates to find the spatial three-dimensional coordinate, and then get the position of the circle center by means of spatial circlefitting. This paper selects the Zernike moment method for edge detection. The principles ofthe Zernike moments algorithm is analyzed. Template effect is considered when calculatingthe edge position. Through the experiment this paper analyzes the selection of thresholdparameter in the algorithm. This paper establishes the mathematical model of gray level distribution of the light fromimage and analyses sub-pixel detection algorithms of the light central point. Through theexperiment comparing the precision and stability of algorithm to select the algorithm. Planetargets used for calibration of structure light plane is fabricated, meanwhile calibration modelof structured light is established. According to the characteristics of the structure lightmeasurement system need two beams structured light are needed to calibrate the plane, thispaper improved the optimization method of structured light plane.The vision measurement model for the position degree of hole group based on structuredlight is established. Calibrating the plane of the hole group through structured light to obtainthe three-dimensional coordinates of the hole edge points in the camera coordinates. The localcoordinate system is established on the plane of the measured hole group. Camera coordinateof the edge points are transformed to the local coordinate system, so that the three-dimensionallocation problem of circle hole is converted into a two-dimensional problem. Obtaining thecoordinates of the circle center through fitting circle in the two-dimensional coordinate systemto calculate the position of the hole group.Experiment platform for vision measurement of the position of the hole group based online structured light is set up to measure errors of the flange position degree. The experimentresults is compared with the measurement results of CMM. According to the comparison, theaverage error is0.0739mm. Through the experiment this paper analyzes the impact of differentbacklight brightness on vision measurement results. The experiment indicates that althoughthe brightness of the backlight has great influence on the measurement error of circle holediameter, standard deviation of center coordinate values is relatively small, that is to say, it haslittle influence on the measured value of the position degree.The work and research on vision measuring technology for position degree of hole groupin this paper has certain significance for applications in engineering. |
