| Along with the progress of aerospace technology,the testing function of collimator system becomes more and more important.At present,the requirements for collimator system are generally long focal length,large aperture,wide spectrum,strong environmental adaptability and compact structure.In addition,off-axis reflective optical system is widely used in large aperture,multi band and high optical efficiency systems because of its small size,light weight and no chromatic aberration.Because collimator needs to be used with detection instrument,in order to reduce the background noise of detection instrument and improve the detection sensitivity of detection instrument,the most commonly used method is to use low-temperature optical system to put detection instrument and collimator in the low-temperature environment created by vacuum tank.The use environment of collimating system is lower than 150k,the internal stress of each part will be generated due to the difference of thermal expansion coefficient of materials,which will affect the surface shape accuracy of the mirror.In addition,with the change of temperature,the relative position of each mirror will also change,which will affect the overall performance of the system.Therefore,in order to make the whole collimator system maintain good performance and meet the needs of field use,this paper designs and analyzes the components of the low-temperature off-axis reflective collimator system(such as mirror components,support structure,temperature compensation mechanism),and investigates the deformation of all mirrors and main support structure at low temperature.This paper is mainly divided into the following parts1.Design and analyze the mirror assembly.Firstly,the material and support mode of each mirror assembly are determined;According to the selected support mode,the structure design of each mirror assembly is completed,and then the temperature compensation design of the mirror is completed;Finally,the finite element analysis of the mirror assembly is carried out to investigate the deformation of the mirror,and the mirror type is fitted at room temperature.The final analysis results show that the mirror surface shape accuracy RMS value of each mirror at room temperature meets 1/50λ.2.Complete the design and analysis of the main support structure of the system.The design and analysis of the main support structure are completed from the perspective of performance and economy.Under the temperature of 150K,the maximum deformation of the base is 4.816mm,and the maximum deformation of the mounting surface of the base is 3.632mm;The overall stress of the support base is 0.2MPa;The first-order frequency of the support base is 115.21Hz,and the modal distribution is reasonable.The simulation results show that the main support structure can meet the field requirements.Passive compensation is used to complete the design of temperature compensation mechanism.After using this compensation method,the RMS of wavefront aberration is 1/24λ,The results show that this platform can effectively reduce the influence of temperature change on the imaging quality of the system.3.The design and Simulation of low temperature thermal control scheme of the system are completed.A liquid nitrogen heat sink is arranged at the back of the frame to reduce the temperature of the mirror body,and a flexible heat pipe with low temperature and high efficiency heat transfer is used between the frame and the liquid nitrogen heat sink to realize the efficient transmission of cold energy,so as to avoid hard connection.Then,the thermal control scheme is simulated and analyzed.The results show that when the ambient temperature is 150K,the temperature of all mirrors is stable below 150K.Combined with the simulation results of thermal control system,the surface shape changes of all mirrors at low temperature are further simulated and analyzed.The results show that the RMS values of all mirrors meet the tolerance given by the optical designer,RMS≤1/50λ,under the low temperature environment of 150K,It shows that the structure design is reasonable and can meet the needs of practical use. |
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