Study On Key Techniques Of Visual Positioning And Its Application In Aircraft Assembly

Digital measurement technology is a key technology in aircraft digital assembly,which can provide reliable assurance for assembly tasks such as:aircraft structures positioning,pose alignment,and fine machining.Measurement equipment such as laser tracker,indoor GPS can provide high precision three-dimensional measurement,but they're expensive and inflexible.In contrast,vision sensor is low-cost,highly reliable,combined with computer vision technology,non-contact online dynamic measurement system with high precision,high efficiency,and strong environment adaptability can be established,which can provide rich features and position information.Therefore,in this dissertation,the key technologies of visual positioning are deeply studied to solve the problems of aircraft structures transshipment,rivet-in-hole insertion,and adaptive ball-head positioning in aircraft digital assembly,and the corresponding positioning control strategies are proposed to improve the positioning accuracy and environment perception of digital equipment,which provides a new technical approach for aircraft assembly.The main work and innovation points are as follows:The key technologies of aircraft digital assembly at home and abroad are introduced,the research status of visual positioning and its application in aircraft digital assembly are reviewed.The basic theory needed to construct a visual positioning system is systematically discussed.The maim visual servoing models have been reviewed,the advantages and disadvantages of various servoing models are analyzed.A precise transshipment system is developed for automatic transporting material between an automated guided vehicle(AGV)and a load transfer station,which consists of on-board multi-sensor pose measurement system and pose alignment system.The pose estimation algorithm integrating 1D distance errors and 2D position errors is proposed and the calibration method of the pose measurement system is elaborately stated.A 5th order polynomial function is applied to fit the trajectory,then the pose deviations are iteratively corrected to implement alignment of the frame fixture on board the AGV with that of the station.The developed automatic transshipment system can meet the accuracy,repeatability and efficiency required in industrial applicationConcerning the rivet-in-hole insertion task in the complementary riveting,a hybrid visual servoing based rivet-in-hole insertion method is proposed,which implements pose alignment of the end-effector.Based on combination of the position of hole center in image space and the discrepancies between the displacement sensors.feature vector is defined to represent the relative pose errors of the rivet hole in camera frame.and the corresponding Jacobian matrix is derived in detail.For five DOFs motion control,the Jacobian matrix is full rank,and there is no singularity and local minima,decoupled control effect can be gained.An adaptive sliding mode controller is designed to provide continuous control inputs.Finally,the experimental results of rivet-in-hole insertion verify the effectiveness of the proposed control approachAiming at gaining accurate support for large aircraft structures by ball joints,a novel approach based on uncalibrated visual servoing is proposed such that the positioner's ball-socket can adaptively approach the ball-head fixed on the aircraft structures.With typical "Eye-in-hand" camera configuration,image moments of circular marker labelled on the ball-head are selected as visual features to control the three translational degrees of freedom of the positioner.Kalman Bucy filter is adopted for online estimation of the Jacobian matrix,which avoids the complicated system calibration.A combination of proportional control with sliding mode control is proposed to improve the system stability and compensate the system uncertaintiesFinally,the research work of the full text is summarized,and future work is discussed.