Design and testing of a two-dimensional adjustment mechanism for the wide-field space camera focusing mirror

To better meet the requirements of space wide-field optical cameras for the precision and freedom of the focusing mechanism, this paper designs a 2-dimensional adjustment mechanism based on a focusing mirror assembly (FMA) that can adjust defocus and tilt, according to the characteristics of and the long focal plane assembly (FPA) of the wide-field camera. To meet the requirements of space cameras for the surface accuracy and structural rigidity of mirror assemblies, this paper proposes a flexible connection structure and optimizes the geometric parameters of the flexible structure using design of experiments(DOE) methods. Through finite element simulation, the surface accuracy of the focusing mirror under different conditions was analyzed; the structural fundamental frequency after adding the adjustment mechanism was also analyzed. The control system for the adjustment mechanism was implemented using ZYNQ, and a kinematic test platform for the adjustment mechanism was constructed using a mechanical prototype of the FMA. The surface figure of the sub-aperture of the mirror was measured in an actual test environment. Under conditions of gravity, temperature rise, and maximum tilt, the root mean square (RMS) of the sub-aperture surface figure of the mirror is a maximum of 6.393nm, better than 1/80λ(λ = 0.632 μm). The fundamental frequency of the FMA and adjustment mechanism is 216Hz, the amplification factor of the response of the mirror assembly and the adjustment mechanism to sinusoidal and random vibration acceleration is less than 5 times. When adjusting the defocus, the translation positioning accuracy of the mechanism and the synchronization accuracy at ±1 field of view of the mirror are both 5 μm, better than 1/8 half focal depth. When adjusting the tilt, the angular positioning accuracy is 1.5^''. In actual testing conditions, the RMS of the sub-aperture surface figure of the focusing mirror is a maximum of 4.889nm, which is better than 1/80λ. After defocus and tilt occur in the optical system, the adjustment mechanism can compensate and make the MTF of each field of view better than 0.5, and the service life of the adjustment mechanism is greater than 1500 times. The results show that the flexible connection structure of the adjustment mechanism can meet the requirements of the surface figure accuracy of the mirror surface when adjusting the tilt; the structural rigidity of the mirror assembly and the adjustment mechanism can meet the requirements of the space camera, and the translation adjustment range, angle adjustment range, translation positioning accuracy, synchronization accuracy, and angle positioning accuracy of the adjustment mechanism and its control system can meet the range and accuracy requirements of the space wide-field camera for the focusing mechanism. The adjustment mechanism can compensate for defocus and tilt caused by the optical system, and its lifespan meets the usage requirements of wide-field cameras.