| Flexible structures in spacecraft are prone to large-value,low-frequency vibrations,which may even affect the normal operation of spacecraft in severe cases.When the spacecraft is working,it will be periodically in the shadow area and the light area of the earth.The working temperature is-180°C～150°C.The temperature change will change the physical properties of the material,and the uneven heating of the structure will produce thermal stress.Changes in material properties and thermal stress will change the dynamic characteristics of the structure.Therefore,studying the dynamic characteristics of the structure under thermal environment is of great significance to the design of large-scale flexible structures,vibration control and attitude control in spacecraft.Aiming at the problem of measuring the vibration response of flexible structures under thermal environment,this thesis studies the measurement method based on binocular vision.Firstly,the binocular vision imaging model and the dual camera calibration method are studied.The dual camera calibration is completed by using Radon transform-based checkerboard corner detection and Zhang Zhengyou camera calibration method.Secondly,a vibration displacement measurement method based on binocular vision is proposed based on the connected domain detection and digital image correlation method,and the accuracy and effectiveness are verified through experiments.Finally,the influence of the thermal environment on the image quality is studied.A binocular vision measurement system under the thermal environment is built using blue band-pass filters and blue light sources.The vibration response of the structure under the thermal environment is successfully measured using this system.The main contents of this thesis are as follow:1.The calibration method of binocular vision imaging model and dual camera system is studied.Aiming at the problem of detecting the corners of the checkerboard calibration board in the process of camera calibration,a checkerboard corner detection algorithm based on Radon transform is studied.The Radon transform is used to detect the edge of the straight line in the checkerboard calibration board,and the intersection of the straight lines is solved to determine the position of the corner.The simulation accuracy and robustness of the method are analyzed by simulating checkerboard pictures and experiments.The results show that the corner detection accuracy of the method can reach 0.2pixels,and it has good robustness to light intensity and complex background.According to the detection results of the checkerboard calibration board corners,the calibration of the dual camera system was completed using the Zhang Zhengyou calibration method,and the average re-projection error of the two cameras was 0.13 pixel.2.Combining connected domain detection and digital image correlation method,a vibration displacement measurement method based on binocular vision is proposed.In this method,feature signs are arranged at the measuring points,two cameras are used to simultaneously take photos of structural vibrations,and the connected domains are detected to determine the connected domains and their center of gravity.Accurate positioning,and finally obtain the vibration displacement of the structure through three-dimensional reconstruction.Through static displacement measurement test,cantilever beam vibration displacement measurement test and windsurfing model vibration displacement measurement test,the measurement accuracy,calculation speed and effectiveness of this method are analyzed and verified.The measurement error of vibration displacement is 0.07 mm.3.The influence of the thermal environment on the imaging quality of the camera is analyzed,and a binocular vision measurement system under the thermal environment is built.Adopt blue bandpass filter and blue light source to assist imaging,reduce the impact of thermal environment on the imaging quality of the camera.Combined with the image acquisition system and quartz lamp array heating system,a binocular vision measurement system under thermal environment was built,and the The rigid body translation test and the windsurfing model vibration displacement measurement test verify the measurement accuracy and effectiveness of the measurement method based on binocular vision under thermal environment.The results show that the static displacement measurement error under thermal environment is 0.04 mm,which can be used Measure the vibration displacement of the structure. |
