Research On The Active Support Of620mm Thin Meniscus Mirror

The aperture of astronomical telescope was getting larger and larger,and highercollecting and resolution power were required to detect the mystery of the remoteastrospace. If building the telescope in a traditional way, that is, increasing theaperture of the telescope would make the mass and cost increase by the cube of thediameter of the primary mirror that could be a great difficulty for the manufacturingof modern astronomical telescope. New method was explored in order to face up tothe challenge, and active optics was one of the most inspiring achievements duringthe investigating progress.The principle of active optics was to adjust the position or figure of the opticalelements in real time to compensate for the effects of gravity direction andtemperature gradient. Thin monolithic mirror active optical technology andsegmented mirror active optical technology were two different types of active opticsaccording to the structure of the mirror. Wavefront aberration was compensated bydeforming the primary mirror in thin monolithic active optics, while for segmentedmirrors; this was achieved by rigid displacement of each sub-mirror. Active opticsmakes the possibility of using lighter and thinner mirrors, relaxing its polishingtolerances, alleviating the rigorous requirements of telescope structure andmechanical system enormously, engendering a significant reduction in mass and cost.This initiative mounting mechanism was described as active support compared to thetraditional passive way.Design of the620mm thin meniscus mirror active support system and active correction of its surface deformation was the subject of the thesis. The calibration ofthe free modal vibration of the primary mirror was dealt, and active correctionprocedure was also simulated by means of finite element method, some analysis andoptimization were done during the supporting structure design.This thesis covers four major sections:Theoretical reasoning was the main contents of the first section. The dynamicequation of a mirror was established in the first place, fitting mirror deformation wasrealized using its modal shape, and the relation between the number of supportingrings&points and the radial function&azimuth frequency were discussed in detail.The first N items of the modal shape were adopted to fit the mirror deformation, andactive correction course was described, the errors were also calculated in a matrixform during the correction procedure.Optimization of the supporting structure was accomplished in the secondsection. The axial supporting position was optimized and force actuator wasdesigned according to the structure of thin meniscus mirror, the characteristic andworking principled of the radial supporting structure were dealt in the followingsession, the stiffness was analyzed after establishing the finite element model.Supporting structure of the main optical system such as the square base, the primarymirror cell, the secondary mirror cell, and the corrective mirror cell weresummarized at the last session.Finite element simulation of active control was carried out in the third section.Finite element model for active correction was established based on the supportingstructure of the mirror, the first10items of free vibration mode of the mirror wereadopted as the base vector, its displacement were unified and calibrated for activecorrection, mirror deformation on different gravity orientations were analyzed and itsdeformation were the source for active correction, error items caused by correctionwere also described.Active optics experiments were implemented in the fourth section. Theexperiment platform was built according to the supporting structure, and only thefirst eight items of mode shape were calibrated. And its deformations were corrected when the mirror was zenith oriented and low frequency disturbance exists.Correction efficiency and errors were analyzed, and some improvements were alsobrought out.Theoretical reasoning, mechanical embodiment, FEM simulation andexperiment verification were the skeleton of the thesis. Theoretical reasoning wasthe soul of active optics, and the rests were the verification of this principle, thesecond section was the mechanical embodiment, the third part was the simulation,and the last part was the validation of this principle. The author would be verygrateful if this thesis could be of little value to the development of astronomicaltelescope.