基于视场一致性的多波段共口径成像系统结构研究

发布时间：2018-11-17 09:19

【摘要】：由于目标在不同光谱波段表现的光学特征有较大差异,因而可以利用多波段来获得更加精确全面的信息,实现全天候、宽覆盖、高分辨率的目标侦察。多波段成像系统的宗旨是融合各波段图像的特征信息,以便对目标进行综合分析。这就要求各波段的探测器在同一时刻对同一目标成像,即各波段图像的像素之间需要在空间上严格的对准,或者说各波段视场应一致。在一定程度上,视场之间的偏差越大,图像配准过程中搜索范围就越大,也就是说配准的运算量就越大。为了增强系统的实时性,降低图像融合的计算量,在结构设计阶段考虑多种因素以提高视场的一致性是非常必要的。论文将视场一致性作为评价标准,综合考虑装校误差、结构变形、温度变化等因素的影响,运用有限元分析、拓扑优化、无热化和热补偿等技术手段,完成了多波段共口径成像系统的样机研制与结构改进。具体研究内容如下:(1)概述多波段成像系统的使用环境和技术指标;介绍光学系统总体结构及三路光学子系统的设计方案;分析各个光学子系统的成像质量;设计出成像系统的总体机械结构,包括三路凸轮调焦机构、反射镜支撑结构和棱镜固定结构;在此基础上,研制出多波段成像系统的原理样机;完成样机的常温稳定性实验、高低温储存实验和高温工作实验,实验表明:样机的三路光学子系统之间存在视场偏移,超出了技术指标要求,需要进行结构改进。(2)分析成像系统中主要光学元件的位置误差对视场一致性的影响,包括棱镜、反射镜、透镜组及CCD相机等;简要说明装校时调整反射镜以实现视场偏移的误差补偿原理;进行调焦结构、反射镜结构、棱镜结构和总体结构的静力分析,结果表明:支撑架的静力变形是影响视场一致性的主要因素,因此需要提高支撑架的结构刚度;完成调焦结构、反射镜结构、棱镜结构和总体结构的热变形分析,得出结论:反射镜结构的热变形引起的视场偏移最为显著,拟采用无热化、热补偿等技术手段加以改善。(3)提出一种以视场一致性为目标函数的拓扑优化方法,具体步骤包括:首先,确定目标函数、优化约束以及设计空间;其次,分别建立光轴和反射镜的偏转角方程,依据平方和加权法,构造出视场偏移的总目标函数;最后,实施拓扑优化,并根据优化结果,提取适合加工的支撑结构拓扑优化模型,迭代曲线表明整个拓扑优化过程是收敛的;对拓扑优化模型进行尺寸优化,以进一步提高支撑结构的性能,仿真表明:尺寸优化后的支撑结构的变形所引起的视场偏移量约为0.5和0.7个像素;与原始结构进行对比分析,可知优化结构的视场偏移减小了约50%~60%;分析云台的俯仰运动对视场一致性的影响,得出俯仰运动会恶化视场一致性的结论。(4)对原始结构进行热力耦合分析,获得+35°C均匀温升下可见和紫外反射镜的面型精度RMS值分别为599.5nm和366.7nm,超出了技术指标要求;为了提高反射镜面型精度,决定采用粘接的方式固定反射镜,并通过调节胶层厚度实现反射镜结构的无热化;改进反射镜结构的材料和连接方式,以进一步提高反射镜得面型精度,同时也利于实现视场偏移的热补偿,分析表明:RMS值约为107.2nm和64.34nm,基本满足要求;阐述反射镜结构的热补偿原理;进行不同温度下光机结构的热变形分析,获得光轴和反射镜的偏转角数据,拟合出偏转角与温度的关系曲线;估算出能够实现热补偿的反射镜结构中垫片的热膨胀系数,并通过仿真对比,最终确定垫片的材料组合;改造样机,完成热补偿实验,结果表明:经历多次高低温后,可见视场的偏移量约稳定在(-2,2)像素,高温工作过程中的偏移量约为(-4,3)像素,低温工作时的偏移量约为(-2,5)像素,均满足技术要求,达到了预期目的。
[Abstract]:Due to the large difference of the optical characteristics of the target in different spectral bands, the multi-band can be utilized to obtain more accurate and comprehensive information, and the target reconnaissance of all-weather, wide coverage and high resolution can be realized. The purpose of the multi-band imaging system is to fuse the characteristic information of each wave band image so as to make a comprehensive analysis of the target. this requires the detectors of the respective bands to image the same target at the same time, i. e., there is a need for strict alignment between the pixels of each band image, or the field of view of each band should be consistent. To some extent, the greater the deviation between the field of view, the greater the search range in the image alignment process, that is, the greater the computation of the alignment. In order to enhance the real-time performance of the system, it is necessary to consider various factors to improve the consistency of the field of view in the design stage of the structure. In this paper, the field-of-view consistency is used as the evaluation criterion, and the influence of the correction error, the structure deformation and the temperature change is comprehensively considered, and the development and the structure improvement of the multi-band co-aperture imaging system are completed by means of the technical means such as finite element analysis, topology optimization, non-thermalization and thermal compensation. The specific research contents are as follows: (1) The use environment and technical index of the multi-band imaging system are summarized; the overall structure of the optical system and the design scheme of the three-way optical subsystem are introduced; the imaging quality of each optical subsystem is analyzed; the overall mechanical structure of the imaging system is designed, comprises a three-way cam focusing mechanism, a reflecting mirror supporting structure and a prism fixing structure, on the basis of which, a principle prototype of a multi-band imaging system is developed, and the normal temperature stability experiment, the high and low temperature storage experiment and the high-temperature working experiment of the prototype are finished, and the experiments show that: There is a field-of-view offset between the three-way optical sub-system of the prototype, which exceeds the technical index requirement and needs to be improved. (2) analyzing the influence of the position error of the main optical element in the imaging system on the consistency of the field of view, The static analysis of the prism structure and the overall structure shows that the static deformation of the support frame is the main factor which influences the field of view, and therefore it is necessary to improve the structural rigidity of the support frame; to complete the thermal deformation analysis of the focusing structure, the mirror structure, the prism structure and the overall structure, It is concluded that the offset of the field of view caused by the thermal deformation of the mirror structure is the most significant, and it is proposed to adopt the technical means of non-thermalization, thermal compensation and so on. (3) a topological optimization method based on the field-of-view consistency as a target function is proposed, which comprises the following steps of: firstly, determining a target function, an optimization constraint and a design space; secondly, respectively establishing a deflection angle equation of an optical axis and a reflector, and finally, carrying out topology optimization, and extracting a support structure topology optimization model suitable for processing according to the optimization result, wherein the iteration curve shows that the whole topology optimization process is convergent; and the topological optimization model is subjected to size optimization, In order to further improve the performance of the support structure, the simulation shows that the field-of-view offset caused by the deformation of the support structure after the size optimization is about 0.5 and 0.7 pixels, and compared with the original structure, it can be seen that the field-of-view offset of the support structure is reduced by about 50% to 60%; The effect of the pitching motion on the consistency of the field of view is analyzed, and the conclusion that the pitching motion has deteriorated the field of view is obtained. and (4) carrying out thermal coupling analysis on the original structure, obtaining the surface-type precision RMS value of the visible and the ultraviolet reflecting mirror at the temperature of + 35 DEG C and the surface-type precision RMS value of 595.5nm and 366.7nm, respectively, and exceeding the technical index requirement; in order to improve the surface-type precision of the reflecting mirror, and the material and the connection mode of the reflector structure are improved, so that the surface-type precision of the reflector is further improved, and the thermal compensation of the field-of-view offset is also facilitated, and the analysis shows that the RMS value is about 107.2nm and 643.34nm, which basically meets the requirements; the thermal compensation principle of the reflecting mirror structure is described, the thermal deformation analysis of the optical machine structure at different temperatures is carried out, the deflection angle data of the optical axis and the reflecting mirror are obtained, the relation curve of the deflection angle and the temperature is fitted, the thermal expansion coefficient of the gasket in the mirror structure capable of realizing heat compensation can be estimated, and through simulation comparison, the material combination of the gasket is finally determined; the prototype is modified, and the thermal compensation experiment is finished; and the result shows that the offset of the visible field of view is about (-2, 2) pixels after a plurality of high and low temperature, and the offset in the high-temperature working process is about (-4, 3) pixels, The offset of the low-temperature operation is about (-2,5) pixels, all of which meet the technical requirements and achieve the intended purpose.
【学位授予单位】：中国科学院研究生院(长春光学精密机械与物理研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TP391.41

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