Opto-mechanical Structure Design And Analysis Of The Spectrometer System For The Carbon Dioxide Detector

The carbon dioxide detector is the high precision optical instrument used tomeasure the concentration and distribution of the carbon dioxide in the atmosphere.The greenhouse effect has been intensified by the increasing emissions of thegreenhouse gases such as carbon dioxide. The consequences are that extreme climatechange already seriously affected the human life activities and the survival of humanis threatened. So accurate monitoring the global greenhouse emissions has becomeone of the important directions in the climate research. The current foundation gasmeasurement methods can’t satisfy the requirements of the coverage and highresolution of the greenhouse gases, so in order to realize the accurate measurementof the carbon dioxide content and fully understand the global carbon cycle and itsinfluence on the climate, to develop the high resolution carbon dioxide detector hasimportant scientific research and economic value. In this paper, it has done a verydetailed research in Opto-mechanical structure design and analysis for one of thespectrometer systems of the carbon dioxide detector, the main research work is asfollows:(1) The design of lens assembly. According to the optical aperture of each lensand surface figure, the mounting methods and the size of the contour structure weredetermined. The support structure adopted the modular design, in which each lens has independent cell, then it was very convenient to assembly and adjust. Becausethe working temperature changed greatly, the tolerance for tilt, decentration and lenssurface shape error were very high, so a radial support structure was designed.Compared with general support structure, under the thermal load, the radial supportstructure cane keep lens centration well and reduce the surface shape error. Theanalysis results validate the rationality of the structure and satisfy the designreauirments.(2) The design the grating assembly. According to the specifications, theprinciples of grating material selecting, the shape of the grating and the support formfor grating were investigated. A flexible structure for the grating was designed andanalyzed, the results show that it satisfies the requirements.(3) Multi-objective optimization design of lens barrel. Lens barrel is one of theimportant parts of carbon dioxide detector. It is the supporter of various opticalelements and determines their axial and radial position. The features of high stiffness,lightweight and dimensional stability have been significant task for lens barreldesign. Using the continuum structure topology optimization, the lens barrel wasoptimized with the multi-objective function. Based on the SIMP method, weight summethod and Target-vector approach were adopted to define the multi-objectivefunction. With this multi-objective function, a creative frame layout with the firstnatural frequency and stiffness both maximum was got. After the topologyoptimization, the thickness optimization was adopted to minimum the barrel’s mass.Compared with the original model, the optimization results show that it has a greatimprovement in many aspects.(4) Dynamic analysis of the general assembly. During the transportation, launchphase, the detector would be subjected to many dynamic loads like the vibration,impact load, the acceleration load and so on. It was very necessary to do dynamicanalysis to verify the rationality of the structure. Firstly, The modal analysis. Thefirst three order natural frequencies were obtained. Then, The harmonic analysis. Theresponse curve and the maximum response value were got. Finally, The random response analysis. The response curve and the maximum response value were alsogot.(5) The optical-structure-thermal analysis. Thermal load was one of the mainloads for spece instruments. When temperature changed, the surface radius of theoptical components, the air gap and the refractive index of the optical materialswould change, this would cause the optical system defocus. So it was necessary tocheck the influences on the image quality under the thermal load. The deformationof the optical elements was got by the thermal analysis of the general assembly. Byusing the Zernike polynomial to fit the deformation surface, the Zernike coefficient,and rigid body displacement were got. Taking them into the optical design softwareand considering the temperature’s influence on the refractive index of the opticalmaterials, the defocus distance under different temperature was got, which can be areference for designing the focusing mechanism.