一种空间相机热控调焦机构的设计与分析

Design and Analysis of a Thermally Driven Focusing Structure for Space Camera

为满足空间相机成像质量的要求,设计了一种热控调焦机构来修正离焦量.首先,根据光学系统确定调焦方式,并通过驱动次镜沿光轴方向移动的方式设计了调焦机构,该结构占用空间小且质量较轻.然后,根据调焦需求,选取热膨胀系数较高的铝作为主要材料,采用在镜座背面贴加热片等措施保证次镜在恒温下工作,并通过有限元方法对调焦机构性能进行了建模分析.最后,对调焦机构工作状态进行分析验证,利用Zernike多项式对其工作时所产生温度变化引起的镜面变形进行拟合,把变形后的面形输入到Zemax软件中,以调制传递函数作为光学系统成像质量评价指标,分析了调焦机构在正常工作时次镜面形变化对相机成像质量的影响.结果表明,调焦机构符合设计指标,且工作时次镜面形的变化对光学系统成像质量的影响可以忽略,与传统调焦机构相比,具有质量轻、结构简单等优点.

In order to improve imaging quality of the space camera,a thermally driven focusing structure is designed to compensate the offset.Firstly,the focusing method is chosen according to the optical system,and the focusing structure is designed by driving the secondary mirror to move along the direction of the optical axis which occupies small space and is light in quality.Then,according to the demand of focusing,the aluminum with higher thermal expansion coefficient is selected as the main material.To ensure the secondary mirror works at constant temperature,some heating films are attached to the back of the mirror seat.And the performance of the focusing structure is simulated by the finite element method.Finally,the working state of the focusing structure is analyzed,and the deformation of the mirror caused by the temperature change is fitted by Zernike polynomial,and the fitting coefficients are input into the Zemax.As the measurement of imaging quality,the modulation transfer function is used to reflect the impact of the deformation of the sub-mirror on the optical performance of the space camera.The result shows that the focusing structure meets the design specifications and the impact of deformation belonging to the sub-mirror on the imaging quality of optical system can be neglected when the focusing structure is working.Compared with traditional focusing structures,the thermally driven focusing structure has the advantages of light weight and simple structure.