The Global Model of the Gran Telescopio Canarias

摘要

During the conceptual design of the GTC (Gran Telescopio Canarias) it was suggested to develop a Global Model of the behaviour of the GTC system to be used as a tool for the system engineering. This Global Model should be a dynamical simulation capable to predict the pointing, tracking, guiding and image quality of the GTC system in several simulation scenarios depending of the behavior of each subsystem. It was decided to develop the simulation in the Matlab/ Simulink~(~R) enviroment. The kernel of the Global Model was a Simulink~(~R) model of the telescope mechanics. The model included the structural dynamics, control loops of the main axis (azimuth, elevation and rotators), and load models (wind, gravity, seism). Each component included error sources inherent to it (cogging and ripple on motors, encoding errors, bearing run-out, etc). The model permitted large rotations in elevation axis, which was necessary to test pointing performances. A specific simulation was developed within the project office for the analysis of the image quality of the optical system. It includes polishing defects of the optical surfaces (Ml segments, M2 and M3), low spatial frequency distortions of the optical surfaces (due to fabrication, gravity of instability) and misalignment between the primary mirror segments.