| Large-aperture standard spherical mirrors are essential for large-aperture optical systems.The commonly used interferometers are unable to meet the direct detection requirements for large-aperture flat mirrors.The Ritchey-Common test can indirectly detect large-aperture flat mirrors by using a standard spherical mirror with a diameter approximately 1.5 times that of the flat mirror as the reference mirror.Under traditional support,the surface shape of a 1-meter standard spherical mirror is subject to errors caused by factors such as gravity and temperature,which can be corrected using active optics technology.Active optics technology detects the wavefront of the mirror surface and uploads it to the host computer for calculation of the correction force to be applied to the mirror surface.This can compensate for some of the low-frequency errors in the mirror surface shape,enabling the mirror to achieve better surface shape and improve the optical performance of the telescope.This paper presents the design.and experimental verification of a 1-meter standard spherical mirror active optics test prototype for correcting the surface shape of the mirror in various orientations.First,a model of the active support system for the 1-meter standard spherical mirror is established.Finite element analysis software is used to apply a unit force to the active support points of the simulation model,and MATLAB was is to calculate the correction force.After correction,the mirror surface,which is only subjected to its own gravity and lateral support force at the bottom,decreases from an initial surface error of RMS=23.7nm to RMS=4.32nm in the horizontal axis,verifying the rationality of the correction algorithm and providing a simulation basis for subsequent experimental prototypes.Based on the simulation results,the active support system is designed with three positioning points evenly distributed on a circle with a radius of 234mm and 18 active support points evenly arranged in a triangular layout on three concentric circles.Additionally,finite element analysis is conducted on the overall structure of the mirror frame,and it is found that the maximum deformation under self-gravity load is 0.05mm,and the maximum stress is 6.2MPa,which is lower than the material strength limit and met the design requirements.Secondly,the key components of the active support system are designed,and after comparing and studying three designs for the actuator,a high-precision and highlinearity force actuator suitable for the active support system is selected.The force actuator converts the linear displacement of the stepper motor driving the screw nut into the pressure of the composite spring group connected in series by dual springs.The output tensile and compressive force is realized through preloading the spring group and avoids the problem of spring zero-crossing hysteresis.The force actuator has high linearity,with a maximum tensile and compressive force of 200N,a repeatability accuracy within 0.1N,and an output stroke within 2mm,achieving the design target.Finally,this article conducted correction experiments on the prototype under multiple attitudes based on the simulation results.After three iterations in the horizontal axis attitude,the mirror surface error decreased from an initial RMS=1.25λ to RMS=0.14λ.After two iterations in the 22° elevation angle attitude,the mirror surface error decreased from an initial RMS=0.95λto 0.14λ,with a fast convergence rate,achieving the experimental target of the prototype. |
PDF Full Text Request