Study On Structural Characteristics Of Small Light Catadioptric Optical System

With the technical development of the modern optical engineering, the small lightcatadioptric optical system was widely applied because it had compact structure, lightweight, relative large field of view, small aberration, etc. The miniaturization andlightweight limited the structural stiffness and stabilization. To assure the image qualityand of light-of-sight stability, this paper synthetically studied on structuralcharacteristics of the small light catadioptric optical system.For super compact optical layout such as the ratio of system length to focal lengthwas less than0.5and the distance between the optical vertex of primary mirror to theimage interface was limited, the support bracket of secondary mirror was designed asthe mounting base plate, thus the primary mirror and corrective lens tube werecrisscross mounted on it frontward in the same circumferential ring. This methodsuccessfully implemented total structural layout in thin spatial range. To evaluate thesurface figure of primary mirror under the mounting state, FEM analysis model of boltpretension was built. On the basis of analysis, flexural annular plate parameters andintensified supporting structural schemes were chosen and confirmed. Moreover,stability measures to keep reflective mirrors’ surface figure were discussed. Mountingway consistent with the actual assembling state gave the demonstration that it couldweaken mounting stress influence of bolts.To improve the adaptability of the corrective lens assembly under assembling forceof clamping ring and thermal environments, contact surface shape of drawtubestructures was optimized. On the other hand, considering the temperature influence,clearances of optomechanical structures in the radial direction were checked. In theaxial direction, pretension force of clamping ring was computed to match the hightemperature point and the lens’ stress and deformation at the low temperature point wasanalyzed.The system had an integrated support bracket of secondary mirror which wasrestricted by volume, weight and obscuration area. According to optimization theoryand flow of ANSYS, parametric model was built and optimized consideringfundamental frequency as the objective function. Moreover, new type of support bracket of secondary mirror with the truss of spiral surrounded supporting ribs which hadexcellent structure stiffness performance and bending resisting ability was designed andapplied in the system. Finally, line-of-sight drift of the system was tested on the shockcondition by established test-bed.Base on the wavefront match method that secondary mirror revolved about its axisrelative to primary mirror, a new type of adjustment and assembling structure ofsecondary mirror was created to achieve the effect, and it could improve system imagequality at the actual known figure state. Also the new structure could consecutivelyadjust tilt degree of secondary mirror monotonically to adapt to the need of optical fineassembling and mechanics environments. To associate with the structural character,single point diamond turning technology was adopted to machine datum to transferassembling reference, and the method of interference measure was combined to assistthe location adjustment of secondary mirror relative to primary mirror to simplify theassembling process. The actual system test of image quality and line-of-sight showedthat research work in this paper had acquired better application effect.