| To meet the requirements of the rapid development of China’s aerospace industry, in particular, with the emerging of the high-performance and technical requirements of the satellite antenna new products, such as large, deployable, flexible, etc., the performance and quality of the antenna should be grasped before launch in order to ensure the using performance and reliability and safety of the satellite in the space environment. It requires the selection of high-precision measurement technique or tool in the space environment to measure its shaped reflective surface. Traditional measuring apparatuses and methods which have some limitations because of low accuracy, short distance, low speed, low degree of automation, high labor intensity and high attitude, so it is difficult to meet the fast and efficient, high precision special measurement needs of the new type of satellite antenna which is facing the special space environment. So, to explore and research the satellite antenna shape-surface measurement technology with high precision, high efficiency, automation, intelligent features in the special environmental conditions has important practical significance and value.Through the comparison and analysis of various measurement techniques, it is found that the close-range photogrammetry technology has the characteristics of high accuracy, non-contact, portability, etc., and it has some incomparable advantages compared with other measurement techniques: intelligence, automation, fast and efficient, high reliability(a large number of redundant observations), adapt to the environment(such as high-low temperature, high-low pressure, toxic and harmful to human body and other environment), and dynamic objects can be measured and so on. In view of the high-low temperature test environmental conditions and test target object for flexible ribbed expanded mesh type satellite antenna, the advanced new type of close-range photogrammetry technology with the higher accuracy, non-contact, fast and efficient, can give full play to its advantages and can well satisfy the demand of this very special measurement.Based on the background of research and production projects in aerospace engineering, the methods of combining theoretical analysis and experimental research were used to study from the four aspects: the theoretical basis, precision estimation, influence factor analysis and test and measurement data post processing techniques. The satellite antenna high-low temperature test for shape-surface deformation photogrammetry technology and its after-treatment was researched more systematically and in-depth, in order to provide a guarantee for improving the photogrammetry measurement accuracy and reliability in high-low temperature environment. It also provides a theoretical support for smarter decisions on other industrial products detect and install and its shape-surface deformation measurements. The main research work and achievements of this paper are as follows:(1) The measuring principle of a single camera, double(multi) camera are individually described from the perspective of projective geometry in the paper. The main methods of precision estimation for the photogrammetry system: the internal compliance with covariance propagation law and repeatability accuracy law, the external compliance with the reference length method and coordinate comparison method, and Fraser precision estimation method were described respectively. The measured performance of the single camera photogrammetry system was key researched from inside and outside accuracy index, respectively, through detailed analysis and experimental testing, and ideal measurement accuracy results for measurement system were inspected by combining measuring methods of the satellite antenna shape-surface deformation under high-low temperature environments.(2) A digital camera and its calibration methods were researched and analyzed in high-low temperature environment respectively. In view of the special characteristics of high-low temperature test environment, a guard of convenient and flexible use and capable of efficient protective camera is designed. The structural stability and the relationship between resolution and imaging quality of the camera were studied and analyzed. The 10-parameter distortion model of the camera is given, combined with the special characteristics of the test environment. In order to ensure the effectiveness of the camera calibration, the 10-parameter model of camera for the bundle self-calibration method is proposed. The influence of temperature variation on the camera and imaging quality is analyzed. The pilot test of camera calibration and camera guards in special environment shows better performance and convenience of engineering service.(3) The close-range photogrammetric target and characteristics of its reflective material and its type and size were analyzed. The gray-scale distribution law and center location algorithm of image targets were summarized, a variable exponential gray-scale threshold weighted centroid location algorithm was proposed. The simulation and real images are used to verify the algorithm and the results are analyzed. The results show that the algorithm has a higher positioning accuracy than other algorithms, which is compared with the V-STARS obtained coordinates of measured image and obtain its comprehensive positioning accuracy RMS is 0.0122 pixels.(4) Based on a large number of experiments for the influence of flash intensity on close-range photogrammetry imaging quality and measurement accuracy, the discrimination method of the maximum gray value of the pixels of image quality screening is proposed. The correlativity of the photogrammetry precision and the shooting distance and flash intensity were obtained. Research shows the photogrammetry precision with a shooting distance has an approximately inversely proportional relationship while ensuring image quality under the same light intensity. The effects of temperature changes on the photography auxiliary light source were analyzed. Take MF18 Nissin flash as an example, the results showed that the RMS values of the bundle adjustment precision were 0.028 mm, 0.039 mm, and 0.085 mm, and the RMS value of the measuring precision of the coordinate repeatability were correspondingly 0.038 mm, 0.053 mm, and 0.118 mm, while the best imaging quality was achieved with photographic distances of 3m, 5m, and 7m, with a corresponding output light intensity of 1/64, 1/32, and 1/16, respectively. At this point, the optimal measurement accuracy is obtained.(5) The calibration methods of length for the photogrammetric scale bar were experimentally researched and analyzed by using the method of photogrammetry, image processing, microscope and the three coordinate measuring machine, respectively. Repeated tests in different periods showed that better consistency of the calibration results of the scale bar on the four methods when the shape quality of targets is the better. But the three coordinate measuring machine due to its high accuracy, good measurement environmental conditions, the repeatability accuracy is very high, and also as a kind of traceable measurement methods. Therefore, it can be used by priority consideration selecting the three coordinate measuring machine method, which provides a data basis and valuable reference for the development of calibration norms of the photogrammetry scale bar, and has guiding significance.(6) The impact of photogrammetry net-shaped space geometry on measurement accuracy was analyzed in detail. By the test analyzing one of the key factors affecting the accuracy of the measurement, it showed great influence on measurement accuracy with different forms of photogrammetry net-shaped space geometry. This paper presents the principles for the design of the space network geometric structure in the actual photogrammetry engineering, which provided a basis for decision making optimization of measuring net-shaped design in engineering practice.(7) The precision assessment indicators of shape-surface deformation of satellite antenna measurement accuracy were summarized comprehensively and systematically, and the concept of the measurement accuracy of the shape-surface is presented. The postprocessing methods of the shape-surface deformation measurement data were analyzed emphatically. Based on the existing information of the research object, a fast iterative closest point(FICP) registration algorithm based on the design coordinates is proposed, and the experimental verification is carried out, and the algorithm is fast, precise and accurate.(8) Based on the comprehensive study of the theory, technology and method of photogrammetry, this paper designs and presents a test scheme for the high-low temperature photography measurement about an antenna of 4m diameter flexible rib deployable mesh, and shape-surface deformation measurement test of satellite antenna in the high-low temperature environment was carried out successfully. Test results show that the repetitive accuracy of the three dimensional coordinates of the target points on the reflective surface varies with the temperature change. To obtain the best accuracy at 20℃, the corresponding RMS mean is 0.027 mm, and the worst accuracy at-60℃, the corresponding RMS mean is 0.048 mm. The repetitive measurement accuracy of the shape-surface of antenna is generally better, and the maximum value of RMS is not more than 0.04 mm. The measurement error of scale bar length of precision test with the temperature variation is not obvious, but its maximum measurement error mean of the length is 0.039 mm, and the minimum measurement error mean is 0.014 mm, and the measurement results generally are more consistent with the accuracy of repeated measurement results of antenna shape-surface. The photogrammetry system has better measurement accuracy.The accuracy of antenna shape-surface(ribs) varies significantly with the temperature change, and it is worst at the temperature node of-60℃, and its RMS maximum value reached 0.878mm(0.761mm). Because of the shape-surface error is comprised of photographic measurement error, shape-surface registration error, antenna deformation error, etc., the overall comprehensive analysis shows the deformation error caused by temperature is relatively large, but it also meets the requirements of the design specifications for the accuracy of the shape-surface. At the same time, the amount of shape-surface deformation can be further obtained by shape-surface error of the other nodes with respect to intermediate node temperature(+20℃) in the temperature cycle about each measurement cycle. In this paper, the deformation distribution trend chart of the shape-surface is given. The results show the amount of shape-surface deformation is less than 0.3mm(RMS) at the difference of every 40℃, and the technical design index of the amount of shape-surface deformation is achieved. |
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