The concepts of atmospheric refraction and atmospheric dispersion are introduced and the method of how to eliminate atmospheric dispersion. This article introduces the structure of Atmospheric Dispersion Correction , the installation position of ADC in TMT telescope and the introduction to the principle of ADC in detail. Using the finite element analysis software Ansys Workbench to analyze the rationality of the ADC structure. Static analysis The ADC structure is loaded with two tape lens, which is more 400kg in weight, as well as itself weight, will deform in x, y, z directions. Dynamic analysis The dynamic performances of ADC structure are very important for the construction of the instrument, for the environmental vibration need to be tested. That is the effect of ADC dynamic deformation on optical accuracy is crucial for imaging quality. Here three order modes of dynamic performance are presented for the references of ADC design. They are 1st order mode , 2nd order mode and 3rd order mode. Thermal deformation according to the ADC working environment temperature change, the instrument temperature would be from -5 to 9 degree. So the thermal deformation of ADC is performed in this temperature fluctuation. ADC structure FEA conclusions: The ADC tapered lens are assumed as a rigid body and the mechanical analysis results are: Static analysis, Kinetics analysis and Thermodynamic analysis. Based on the FEA results, we get the image motion information in the telescope plane. Then, we draw a conclusion that: image motions induced by current structure design are very small and meet the requirements of ADC.
The performance of The Grating Exchange System can satisfy the Thirty Meter Telescope - TMT for astronomical observation WFOS index requirements and satisfy the requirement of accuracy in the grating exchange. It is used to install in the MOBIE and a key device of MOBIE. The Wide Field Optical Spectrograph (WFOS) is one of the three first-light observing capabilities selected by the TMT Science Advisory Committee. The Multi-Object Broadband Imaging Echellette (MOBIE) instrument design concept has been developed to address the WFOS requirements as described in the TMT Science-Based Requirements Document (SRD). The Grating Exchange System uses a new type of separate movement way of three grating devices and a mirror device. Three grating devices with a mirror are able to achieve independence movement. This kind of grating exchange system can effectively solve the problem that the volume of the grating change system is too large and that the installed space of MOBIE instruments is too limit. This system adopts the good stability, high precision of rotary stage – a kind of using air bearing (Air bearing is famous for its ultra-high precision, and can meet the optical accuracy requirement) and rotation positioning feedback gauge turntable to support grating device. And with a kind of device which can carry greater weight bracket fixed on the MOBIE instrument, with two sets of servo motor control rotary stage and the mirror device respectively. And we use the control program to realize the need of exercising of the grating device and the mirror device. Using the stress strain analysis software--SolidWorks for stress and strain analysis of this structure. And then checking the structure of the rationality and feasibility. And prove that this system can realize the positioning precision under different working conditions can meet the requirements of imaging optical grating diffraction efficiency and error by the calculation and optical performance analysis.