| Low light level multispectral imager has the ability of imaging in low illumination environment,and has great economic and scientific value in the application fields of observing urban night light,detecting particulate pollution,studying glaciers in the north and south poles,detecting marine environment and so on.In the process of satellite launching and in orbit operation,the focal plane of the optical load will shift due to shock oscillation,temperature change,atmospheric pressure,satellite attitude and other factors,which is defocusing phenomenon.If no measures are taken to compensate the defocusing amount,the imaging quality will be seriously affected.Therefore,high-precision space telescope will be equipped with a focusing mechanism to ensure the coincidence of the photo detector and the image plane.In view of the low light level multispectral imager needs to work in low illumination environment,the optical payload needs to have the function of image motion compensation to achieve the effect of staring imaging.In this paper,a focusing and image motion compensation mechanism is designed,analyzed and verified.The biggest advantage of the device is that it combines the two functions together.On the premise of ensuring the required technical indicators,it minimizes the space required by the whole,simplifies the structure,and has a dynamic and static two-stage locking device,which significantly improves the reliability and impact resistance of the mechanism High.The specific research contents are as follows.(1)This paper investigates the historical development background of low light level space remote sensing imager,combined with a large number of practical application experience of focusing mechanism at home and abroad,analyzes the main factors of defocusing phenomenon caused by imager in satellite launching and in orbit working environment,and determines the corresponding technical indicators such as maximum image motion compensation,maximum focusing amount,positioning accuracy better than and first-order natural frequency.(2)According to the structural characteristics and working conditions of the low light level multispectral imager,the focusing mode and transmission scheme are determined.The self-locking property of the screw nut is analyzed.The mechanical structure of focusing and image motion compensation mechanism is designed,including image motion compensation transmission mode,dynamic and static locking mechanism.The reasons for selecting materials,driving elements,encoder and lubrication mode are explained in detail.The overall dimension of the structure is 349 mm × 192 mm × 174 mm,and the total mass is 9.8 kg(excluding the dynamic locking mechanism on both sides).(3)Focusing and image motion compensation are analyzed theoretically.Based on its motion characteristics,the accuracy of focusing function is analyzed by using Monte Carlo algorithm.The results show that the positioning accuracy is better than ±10 μ m under the current processing conditions.The dynamic performance of focusing and image motion compensation mechanism is analyzed by finite element simulation.(4)The focus and image motion compensation mechanism are verified by experiments: the restoring force test and compression test of the memory alloy ring in the dynamic unlocking device are carried out.The open-loop and closed-loop control curves are fitted,and the positioning accuracy of the focusing mechanism is tested by closed-loop control.The results show that the positioning accuracy is better than ± 5.7μm.The vibration test of the mechanism is carried out.The first order natural frequency in three directions of XYZ are 243.24 Hz,240.11 Hz and 388.6 Hz respectively.The sine vibration test curve follows well.The maximum magnification of random vibration test is 3.39 times.The self-locking ability of the mechanism is good after vibration test.All the test results are in accordance with the technical specifications and the theoretical analysis results.It shows that the stiffness and strength of the structure are good,and the impact vibration in the process of satellite launching has little influence on it. |
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