Research On Normal Vector Vision Measurement Method For Riveting Hole Of Aircraft Skin

Riveting is one of the main assembly processes of the aircraft.Because of the low efficiency and poor quality consistency of manual riveting,it is difficult to meet the requirements of aerodynamic shape performance of aircraft.Automatic riveting can improve the quality of riveting and increase efficiency,which is a hot spot in aviation industry research.This research is aimed at the positioning problem of riveting hole in the automatic riveting process,binocular vision is used to measure the normal vector of the riveting hole,and the feasibility verification is carried out through experiments.The camera imaging process and Zhang Zhengyou calibration method are introduced.Riveting hole pretreatment is performed using hybrid filtering.The characteristics of riveting hole feature extraction based on Otsu threshold segmentation,Canny edge detection,region growing method and regional active contour model are discussed.A local active contour model is proposed to complete the feature extraction of riveting hole.By comparing the positioning accuracy of these methods,the results show that the local active contour model has higher accuracy.The normal vector measurement of the riveting hole is performed using binocular vision.Firstly,the ideal binocular vision model and triangulation principle are introduced.The remapping relationship from plane to space is analyzed.The stereo calibration and Bouguet stereo rectify are studied.Then the discrete points of the riveting hole in the image coordinate system are solved,and the three-dimensional point cloud of the riveting hole is extracted by the parallax method.Finally,the plane fitting of riveting hole is carried out,and the normal vector is obtained.The experimental platform is built to carry out the binocular vision riveting hole normal vector detection experiment.Firstly,the measured angle between normal vector of riveting hole and normal vector of calibration plate is obtained by binocular vision.Then the coordinates of the plane points are measured by the three-coordinate measuring machine,and the reference angle of the normal vector is obtained by fitting.Finally,the measured angle is compared with the reference angle to obtain the measurement error of binocular vision.Through the experiment of 6 riveting hole and transforming 10 kinds of gestures of each riveting hole,the maximum error is 2.71°,the average error is 1.69°,which is less than the maximum error of riveting angle of 5.74.The results verify the feasibility of the method.