Research On Design And Test Of The Multi-point Hybrid Support Structures For In-situ Optical Fabrication And Test Of Large Optics

People are working on many large telescope projects,the maximum size/precision ratio whose primary mirror has exceeded 10 million order.There is a large gap between the limited fabrication ability and the strict requirements on the production precision and efficiency.Due to the embargo and blockade imposed by the developed countries,many core elements,instruments and equipments should be developed independently.In detail,for the optical testing,large interferometers and reference flats are limiting these projects to success.Furthermore,traditional off-line fabricating-testing is ineffective,dangerous and rough when facing large/heavy optics.It is urgent to develop an in-situ fabricating-testing mode for large optics.As the fabrication and testing technologies have almost achieved their limit level,the performance of mirror support system has become the bottleneck of fabrication quality of large optics.To overcome the shortcomings of the current in-situ mirror support systems,such as of low precision,high difficulty and risk,this paper focuses on designing several types of hybrid support systems for in-situ optical fabrication-test of the large optics based on full analysis of the figure error sources.Specifically,the hybrid support system of the Off-Axis Parabola(OAP),the counterweight type support system for the transmitting flat(TF),and the new hydrostatic support system for mirrors up to 4m to be fabricated are studied.Common key technologies such as optics-metal interface technology and opto-mechanical integrated optimization are discussed.Finally,the design,analysis,testing,integration and application verification of these support systems are completed.The application results show that the in-situ testing support system can greatly improve the on-line measurement accuracy and significantly improve the full-cycle fabricating efficiency.The main research contents of the full text are as follows.(1)The general opto-mechanical interface epoxy bonding technique is sought,which lays a foundation for the designing different in-situ support systems for various large optics.A precise positioning and bonding method suitable for large optical components of arbitrary shape is proposed,and the reliability-based safety of the bonding process in massive use is evaluated through limited samples.Through the novel combination of laser tracker and positioning facility,the positioning accuracy of ±0.2 mm could be achieved.Based on the probabilistic prediction model,the test data of sample strength is statistically analyzed and the lower limit of strength under different confidence levels is predicted,after which the process safety is evaluated.The strength limits are also corrected according to the finite element analysis of actual working conditions.Finally,the process stability is verified by the bonding and serving of OAP and TF.(2)The hybrid support systems for gravity off-loading of OAP and TF,which are designed for the ?1.5 m aperture interferometer,have been designed and verified.For OAP facing down,the combination of Whiffletree and counterweight is adopted;for the TF,the design concept of “counterweight + mechanical limit” is chosen.Success job on epoxy bonding process,conceptual design,FE analysis,manufacturing,adjustment and long-term serving of the support systems are all finished.(3)Ultra-large optics' in-situ hydrostatic support system(HISS),for polishing-testing iterations,has been designed and verified.From the unit level,the design scheme of single-cylinder static pressure(hydraulic)support unit is proposed,and the output force precision and support stiffness are theoretically derived.At the group level,the stiffness uniformity and long-term serving stability are tested.Finally,at the system level,the testing,integration,control and performance verification of the entire hydrostatic pressure system was completed.(4)Application of the above HISS to two typical mirror structure,lightweight Si C and bulk glass,has been investigated.The 54-point support system for Si C mirror could provide a relative precision of 0.019 ? RMS and an absolute precision of 0.004 ? RMS.It also achieved a precision of 0.97 ?rad Slope RMS on the 1/4 prototype of the tertiary mirror of Thirty Meter Telescope.Through engineering applications and careful verification,the in-situ support systems have produced very positive effects,and it is believed that in-situ support system will continue playing an important role in the future fabricating and testing of ultra-large optics.