| Diffraction grating is an extremely important optics dispersive element. The large area and high-precision plane diffraction grating is widely used in the military, astronomy, nuclear, aerospace and civilian areas. There are two main manufacturing methods of diffraction grating: mechanical ruling method and holographic etching method. Some certain gratings such as low groove-density grating for infrared laser and all echlle gratings must be manufactured by mechanical ruling, as their grooves are deep and the shape of grooves are strictly restricted. The grating ruling is an extremely sophisticated technology, and the grating ruling engine is so called "the king of the fine mechanics". This paper, which is funded by the National Key Technologies R&D Program for the 11 th Five-year Plan and National R&D Projects for Key Scientific Instruments, is mainly focused on the structure design of the ruling system of the large-scale high-precision diffraction grating ruling engine(hereinafter referred to as the large grating ruling engine), with the discipline of reducing the mechanical ruling error of gratings and thus to improve the quality of large-scale machinery ruled gratings. This paper analyses the mechanical error of each part of the ruling system and improve the structure according to the results of experimental verification. A large area echelle grating was manufactured through the improved structure. Firstly, the basic structure, working principle and the error sources of grating ruling engine were introduced. The detection method of grating-line curve error was described and the error distribution of large grating ruling engine was made. Secondly, the quartz rail scheme ruling system was designed. The structure of quartz rail and ruling tools system was determined and its deformation was calculated by static analysis. The adjustable diamond turret was designed and its error was analyzed. The driving mechanism was designed as two equal and opposite velocity constant speed cam operating synchronously, in order to offset the impact of inertia force on the ruling process. This part also optimized the profile curve of cam and conducted a stress analysis of the drive mechanism. Thirdly, the factors causing grating-line curve error was segmented analyzed and detected, with mechanical correction methods proposed. In order to reduce the impact of commutation on the grating ruling, non-constant speed cam and crank link was applied instead of the former constant speed cam. It was found that the ruling tools system creeping during the simulation grating ruling experiment, affected by friction, which lead to increasing vibration spectral density, is not conducive to closed-loop control. Fourthly, using aerostatic guide to replace the original quartz guide to eliminate the creeping phenomenon.The aerostatic guide’s basic operating principle was presented and its structure was determined according to the request of grating ruling and the restrict of overall grating ruling engine. A double aerostatic guidein parallel form was adopted for better stiffness and its support structure taking the stability and adjustability into account. The structure and capability parameters was also optimized. Fifthly, control the various error during the assembly of the aerostatic guide strictly in order to improve its accuracy. Analyzed and detected the errors that affect the grating ruling such as the roll of slider, the vibration of aerostatic guide and the air turbulence,with the solutions proposed. Sixthly, the grating-line curve error was compensated to meet the requirements of error distribution. A 400mm×500mm echelle grating was manufactured by this system. The real-time monitoring data shows that the RMS of the grating-line curve error repeatability is no more than 2.9nm. The testing results showed that the overall echelle grating’s stray light intensity meets the target requierments, especially the initial part could reach 0.02%. |
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