针对4 m光电望远镜中SiC轻量化主镜比刚度大, 面形精度要求高的特点, 提出采用液压whiffletree被动支撑并联力促动器主动支撑的轴向液压主动支撑方案。液压被动支撑承担镜重, 主动支撑仅输出校正主镜面形误差所需的主动校正力, 从而减小主动支撑元件力促动器的作用力范围, 提高主动校正力精度。借助于有限元法完成了轴向和侧向支撑系统的优化, 确定了轴向54点和侧向24点等间距等力(β=0.5)支撑系统设计。当仅有被动支撑作用时, 主镜水平和竖直状态下重力引起的镜面变形误差RMS值分别为37.8 nm和82.9 nm。采用主动校正后, 主镜水平和竖直状态下的镜面变形误差RMS分别减小到12.0 nm和9.8 nm。不同俯仰角下主镜的镜面变形均能满足面形误差RMS不大于λ/30(λ=632.8 nm)的指标要求。

As the SiC lightweight primary mirror in a 4 m photoelectric telescope has high specific stiffness and needs strict surface precision, this paper proposes an axial active support system based on the hydraulic whiffletree passive support for the primary mirror. The hydraulic whiffletree support system was used to support the mirror weight, and the active support was just output active forces to correct mirror surface errors, reduce the active force range and to increase the precision of active force. A 54-point axial support system and a 24-point lateral support system were optimized by the Finite Element Method(FEM), and the parameter of lateral force β was 0.5. With the hydraulic passive support system, the mirror surface deformation Root Mean Square(RMS) values from the gravity of the primary mirror are 37.8 nm and 82.9 nm respectively under horizontal and vertical states. After active correction, the mirror surface error RMS values are reduced to 12.0 nm and 9.8 nm accordingly. Analysis indicates that the mirror surface deformation of 4 m SiC lightweight primary mirror at different pitch angles is less than λ/30(λ=632.8 nm) and meets the requirements of surface errors.