Research On The Flush And Gap Measurement For Aircraft Skin Based On Dual Linear Structured Light

A large number of flush and gap exists on the aircraft surface,which is the main index to evaluate the smoothness of aircraft surface.The measurement of flush and gap is one of the work of the inspection of aircraft aerodynamic outer edge deviation.With the improvement of aerodynamic performance and stealth performance of aircraft,the traditional methods of checking aerodynamic outer edge deviation are difficult to meet the requirements.The linear structured light measurement method has the advantages of non-contact,high precision and real-time.It can overcome the problems of the traditional plug method and capacitance method,such as large measurement error and limited application range.The linear structured light measurement method is the development direction of the field of the seam measurement of aircraft skin.This paper focuses on the subject of the flush and gap measurement of aircraft skin.The dual linear structured light measurement method is adopted to construct the flush and gap with two light stripes,so as to solve the problems existing in the measurement using single linear structured light,such as the inability to ensure that the laser stripe is perpendicular to the skin seam,the large measurement result error.This paper studies the characteristics of structured light in the measurement of skin seam,the calibration method of dual line structured light measurement system,the image processing method,the feature expression of the stripe of the seam and the solution of flush and gap to improve the accuracy and stability of the seam measurement of aircraft skin.The research results of this paper include:(1)The characteristics of structured light the skin surface are studied,the optical model of the line structured light is analyzed,and the laser optical model of the common line laser emitter is determined.The mathematical model of the skin structured light strip is studied,and the section model of the light strip when the structured light interferes with the aircraft skin emission is given,and the influence of the skin material,the seam structure and other factors on the structured light are summarized.(2)In view of the problems of large fluctuation of camera calibration results and low calibration accuracy of structured light plane parameters in the calibration of structured light measurement system,a new fast calibration method of linear structured light measurement system is proposed.Compared with the existing calibration methods of structured light measurement system,the new proposed calibration method can obtain the calibration results of camera and structured light plane with higher accuracy.A new calibration method based on circular points and RANSAC method for a camera’s intrinsic parameters and double line structured light is proposed,and the model of camera intrinsic parameters calculation based on circular points is derived.The calibration process of structured light plane parameters is obtained with camera calibration process,which simplifies the calibration process of structured light measurement system.The calibration results are further optimized based on Sampson error estimation.The accuracy of camera calibration results is verified by simulation and real experiments.(3)In the process of preprocessing the image of seam measurement,there are many noises around the light strip and big errors in the extraction results of light strip features.The denoising methods of skin structured light image and the extraction methods of structured light strip center are studied respectively.A mixed noises denoising model based on adaptive total variation is proposed,which is proved by convex optimization model.The noise model is solvable and unique.The Bregman distance is introduced to solve the variational denoising model,and the anti-noise and fidelity of the model are verified by simulation experiments.The fuzzy C-means(FCM)algorithm is introduced into the extraction process of light strip center,and the anti-noise ability is improved by improving the fuzzy membership function and the objective function of the traditional FCM algorithm.Based on multi template and region gray center of gravity,this paper proposes a method to extract the center of light strip with the result of light strip image segmentation.(4)The feature extraction of skin seam and the solution method of flush and gap are studied.The template of structured light strip for flush and gap measurement is constructed.Based on the full analysis of various seam structures,the recognition algorithm of skin seam area is designed,which improves the accuracy of recognition of specific area of structured light strip.The solution of butt joint step and gap based on line structural light is improved.According to the different measurement conditions,the corresponding light strip template is used to solve the skin flush and gap.(5)On the basis of the research content above,the flush and gap measurement system is designed for PC and hand-held respectively,and the measurement softwares are developed based on VS2010 and Qt5.2.2 respectively.The accuracy of the measurement system is verified by the verification parts,and the results show that the measurement accuracy can reach 17μm and 38μm for flush and gap measurement.The research results of this paper provide theoretical and application support for the domestic aircraft manufacturers in flush and gap measurement.