Research And Application Of Close-range Photogrammetry In Measurement Of Mesh Antenna Profile Accuracy

The excellent characteristics of the mesh-shaped deployable antenna in terms of surface accuracy,storage rate and surface density make it a research hotspot of spaceborne antennas.However,due to the multiple errors during the work process,the actual curved surface of the antenna cannot fit perfectly with the ideal parabolic surface,so it is necessary to continuously adjust the reflecting surface.In order to obtain the required adjustment amount accurately,the coordinates of the nodes on the antenna surface need to be measured.Combining with the current situation of antenna profile accuracy measurement,this paper proposes to use close-range photogrammetry to detect the profile accuracy of mesh antennas based on the in-depth study of the advantages and feasibility of the application of closerange photogrammetry technology.The thesis mainly focuses on the following research has been conducted on:(1)The design and coding principles of coding points and marking points used in closerange photogrammetry are introduced and analyzed.The recognition process of 15-bit Schneider type coding points and circular marking points is described in detail.Finally,the C++ programming language is adopted to realize the recognition process combined with the Open CV function library,which gets a accurate result.(2)Combining the ground experiment scene of the mesh antenna and the space work scene,a method for measuring the accuracy of the antenna profile using a fixed binocular camera is proposed.First of all,the background of binocular photogrammetry is introduced,and the front intersection of the two-image in close-range photogrammetry is introduced in detail.Through this method,31 nodes on the surface of a 2-meter-aperture antenna are measured,and the results are obtained.The coordinates of 31 nodes of the antenna are fitted with a parabola and the profile accuracy error of the antenna is calculated.Finally,the calculation accuracy of the method is given by a scale whose length is strictly calibrated.(3)The principle of multi-camera measurement in close-range photogrammetry is described in detail,and two major condition equations are emphasized.Because the core algorithm of photogrammetry(bundle adjustment)requires high initial value of iteration,a method of adding relative length control under relative orientation is proposed to find the initial value of beam adjustment,and then the bundle adjustment method is performed.Similarly,a 2-meter-caliber deployable mesh antenna prototype is measured using multi-camera photogrammetry.The corresponding results are displayed and the surface accuracy error is calculated.Finally,based on the scale used in the multi-camera measurement,the calculation accuracy of the method is given.