Several approaches for design optimization in control-structure interaction problems for precision reflectors and structure are discussed. Applications for shape control and active vibration damping show the need to treat this interaction simultaneously or to use properly defined iterative decomposition.
The "phase A" of the opto-mechanical design, which started in 1997, is now basically completed. It provides a clean, symmetrical geometry of the pupil, with a near-circular outer edge. The modular design of the mechanical structure is built on the size of the hexagonal segments, provides a perfect match with the optical elements and allows production at reasonable costs. This paper is a summary of the various design iterations. A discussion is devoted to the evaluation of the design assumptions and principles which have been set at the beginning of the study, and to their validity after the completion of this first phase. This includes a discussion about specific aspects whose criticality had been under- or overestimated, and the methodology applied to define system and sub-system requirements. Finally, we present a summary of the present and future activities, which are mainly devoted to sub-systems definition.
In a joint effort, the European Southern Observatory (ESO), the Institute for Lightweight Structures, Technical University of Munich, and EADS Astrium, Germany, have developed a set of software tools for integrated modeling of astronomical telescopes and interferometers. Integrated modeling aims at time-dependent system analysis combining different technical disciplines (optics, mechanical structure, control system with sensors and actuators, environmental disturbances). As example for the application of this modeling technique, we present an integrated model of the Very Large Telescope Interferometer (VLTI). It can be regarded as a "precursor" model for future telescope or interferometer projects. Besides its demonstrator role, it also serves for practical applications. An example is prediction of the dynamic VLTI output performance at interface-level to future scientific instruments, such as GENIE. The basic output of the integrated model is a complete description of the time-dependent electromagnetic field within a broad spectral range and for each interferometer arm.
Alternatively, a more elaborated output can be created, such as a fringe pattern resulting from a superposition of several beams after modal filtering by single-mode fibers. The paper shows the architecture of the integrated model with its components such as telescope structures, optics, control loops and disturbance models for wind load, seismic ground acceleration and atmospheric turbulence.
Results illustrating the capability of the model approach are presented.
Within the scope of the Very Large Telescope Interferometer (VLTI) project, ESO has developed a software package for integrated modeling of single- and multi-aperture optical telescopes. Integrated modeling is aiming at time-dependent system analysis combining different technical disciplines (optics, mechanical structure, control system with sensors and actuators, environmental disturbances). This allows multi-disciplinary analysis and gives information about cross-coupling effects for system engineering of complex stellar interferometers and telescopes. At the moment the main components of the Integrated Modeling Toolbox are BeamWarrior, a numerical tool for optical analysis of single- and multi-aperture telescopes, and the Structural Modeling Interface, which allows to generate Simulink blocks with reduced size from Finite Element Models of a telescope structure. Based on these tools, models of the various subsystems (e.g. telescope, delay line, beam combiner, atmosphere) can be created in the appropriate disciplines (e.g. optics, structure, disturbance). All subsystem models are integrated into the Matlab/Simulink environment for dynamic control system simulations. The basic output of the model is a complete description of the time-dependent electromagnetic field in each interferometer arm. Alternatively, a more elaborated output can be created, such as an interference fringe pattern at the focus of a beam combining instrument. The concern of this paper is the application of the modeling concept to large complex telescope systems. The concept of the Simulink-based integrated model with the main components telescope structure, optics and control loops is presented. The models for wind loads and atmospheric turbulence are explained. Especially the extension of the modeling approach to a 50 - 100 m class telescope is discussed.
Within the scope of the Very Large Telescope Interferometer (VLTI) project, a set of software tools for integrated modeling of ground- and space-based stellar interferometers has been developed. Integrated modeling aims at time-dependent system analysis combining different technical disciplines (optics, mechanical structure, control system with sensors and actuators, environmental disturbances). The main components of the software are
BeamWarrior, a tool for creation of dynamic optical models, and SMI (Structural Modeling Interface), which generates linear state-space models from finite element models of a mechanical structure. Based on these tools, models of the various subsystems (e.g. telescope, delay line, beam combiner) can be created in the relevant technical disciplines (e.g. optics, structure). All subsystem models are integrated into the Matlab/Simulink
environment for dynamic control system simulations. The output of the dynamic model is a complete description of the time-dependent electromagnetic field in each interferometer arm. This output serves as input to an instrument model simulating the creation of interference fringes.
This paper shows the application of the integrated modeling concept to the VLTI. The architecture of a Simulink-based integrated model with its main components, telescope structures, optics and control loops, is presented. Disturbance models for wind load, seismic ground excitation and atmospheric turbulence are included. Beam combination is performed using a simplified model of the VINCI instrument. Results of closed-loop dynamic simulations are presented.
This article presents a software package for “integrated modeling” of single- and multi-aperture optical telescopes. Integrated modeling is aiming at time-dependent system analysis combining different technical disciplines such as optics, mechanical structure, control system with sensors and actuators. Various, environmental and internal disturbances can be taken into account. Software design and development is done in a joint effort by the European Southern Observatory (ESO), Astrium GmbH and the Institute of Lightweight Structures (LLB), Technical University of Munich. The architectures of the two most advanced modules generating dynamic models of the mechanical structure and the optical system are described. A “real-life” example related to the Very Large Telescope Interferometer (VLTI) illustrates the application in practice.
In cooperation with the European Southern Observatory (ESO), the Institute of Lightweight Structures (LLB), Technische Universtitaet Muenchen, has developed the Structural Modeling Interface Toolbox (SMI), a Matlab based software package for creation of a dynamical model of a telescope structure. It is called Interface, since it uses the modal data of a finite element (FE) analysis and creates a dynamic model to be used within a time-dependent control loop simulation in the Matlab/Simulink environment. SMI is part of the Integrated Modeling Toolbox (IMT) developed in a joint effort by ESO, Astrium GmbH and LLB.
Since SMI can read modal data in a general format, it is not depending on the FE-software. In addition to that, an interface to the FE-package ANSYS has been developed. It allows the variation of parameters and some settings for the FE-analysis directly within SMI.
Both, force excitation like windloads and base excitation like micro seismic perturbations can be included. Several tools for model reduction are provided. Some of them are modal based, like effective modal masses, others are general model reduction procedures from control engineering like balanced truncation.
For the evaluation of the reduced models, transfer functions of different models can be displayed in a Bode-plot. Time characteristics like step response or impulse response are also available. Moreover, for a typical excitation PSD the response PSD can be computed. This response can either be compared to the response of an exact model or to measured data and the rms-error can be calculated.
The final result is a linear statespace model of the structure and a Simulink block, which can be included into a Simulink model.
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