1,721,194 research outputs found
Ground-based telescope pointing and tracking optimization using a neural controller
Full text linkNeural network models (NN) have emerged as important components for applications of adaptive control theories. Their basic generalization capability, based on acquired knowledge, together with execution rapidity and correlation ability between input stimula, are basic attributes to consider NN as an extremely powerful tool for on-line control of complex systems. By a control system point of view, not only accuracy and speed, but also, in some cases, a high level of adaptation capability is required in order to match all working phases of the whole system during its lifetime. This is particularly remarkable for a new generation ground-based telescope control system. Infact, strong changes in terms of system speed and instantaneous position error tolerance are necessary, especially in case of trajectory disturb induced by wind shake. The classical control scheme adopted in such a system is based on the proportional integral (PI) filter, already applied and implemented on a large amount of new generation telescopes, considered as a standard in this technological environment. In this paper we introduce the concept of a new approach, the neural variable structure proportional integral, (NVSPI), related to the implementation of a standard multi layer perceptron network in new generation ground-based Alt-Az telescope control systems. Its main purpose is to improve adaptive capability of the Variable structure proportional integral model, an already innovative control scheme recently introduced by authors [Proc SPIE (1997)], based on a modified version of classical PI control model, in terms of flexibility and accuracy of the dynamic response range also in presence of wind noise effects. The realization of a powerful well tested and validated telescope model simulation system allowed the possibility to directly compare performances of the two control schemes on simulated tracking trajectories, revealing extremely encouraging results in terms of NVSPI control robustness and reliability. © 2003 Elsevier Science Ltd. All rights reserved
A Neural Tool for Ground-Based Telescope Tracking control
Full text linkNeural Network models (NN) have emerged as important components for applications of adaptive control theories. Their basic generalization capability, based on acquired knowledge, together with execution rapidity and correlation ability between input stimula, are basic attributes to consider NN as an extremely powerful tool for on-line control of complex systems. By a control system point of view, not only accuracy and speed, but also, in some cases, a high level of adaptation capability is required in order to match all working phases of the whole system during its lifetime. This is particularly remarkable for a new generation ground-based telescope control system. Infact, strong changes in terms of system speed and instantaneous position error tolerance are necessary, especially in case of trajectory disturb induced by wind shake. The classical control scheme adopted in such a system is based on the Proportional Integral (PI) filter, already applied and implemented on a large amount of new generation telescopes, considered as a standard in this technological environment. In this paper we introduce the concept of a new approach, the Neural Variable Structure Proportional Integral, (NVSPI), related to the implementation of a standard Multi Layer Perceptron (MLP) network in new generation ground-based Alt-Az telescope control systems. Its main purpose is to improve adaptive capability of the Variable Structure Proportional Integral model, (VSPI), an already innovative control scheme recently introduced by authors [1], based on a modified version of classical PI control model, in terms of flexibility and accuracy of the dynamic response range also in presence of wind noise effects. The realization of a powerful well tested and validated telescope model simulation system allowed the possibility to directly compare performances of the two control schemes on simulated tracking trajectories, revealing extremely encouraging results in terms of NVSPI control robustness and reliability
The VST axes control software
No full textOne of the tightest requirements to be respected for a telescope as the VST, hosted in a one of the best astronomical sites as the ESO Paranal Observatory, is an excellent axes control, to obtain the best overall performance of the telescope that, otherwise, can be dramatically affected. The software strategy to control the VST axes (azimuth, altitude, rotator) is here described
The active optics control software for the VST telescope
No full textThe VST active optics software must basically provide the analysis of the image coming from the wavefront sensor (a 10×10 subpupils Shack Hartmann device) and the calculation of primary mirror forces and secondary mirror displacements to correct the intrinsic aberrations of the optical system and the ones originated for thermal or gravity reasons. The software architecture, the simulation code to validate the results and the status of work are here described
Software Design Aspects and First Test Results of VLT Survey Telescope Control System
No full textThe 2.6 m VLT Survey Telescope (VST) is going to be installed at Cerro Paranal (Chile) as a powerful survey instrument for the ESO VLT. The tightest requirements to be respected for such a telescope, (large field of view of 1°x1°, pixel scale of 0.21 arcsec/pixel, and hosted in a one of the best worldwide astronomical sites), are basically very high performances of active optics and autoguiding systems and an excellent axes control, in order to obtain the best overall image quality of the telescope. The VST active optics software must basically provide the analysis of the image coming from the 10x10 subpupils Shack Hartmann wavefront sensor and the calculation of primary mirror forces and secondary mirror displacements to correct the intrinsic aberrations of the optical system and the ones originated for thermal or gravity reasons. The algorithm to select the guide star depends on the specific geometry of the adapter system. The adapter of the VST hosts many devices handled by the overall telescope control software: a probe system to select the guide star realized with motions in polar coordinates, a pickup mirror to fold the light to the image analysis and guiding cameras, a selectable reference light system and a focusing device. All these devices deeply interface with autoguiding, active optics and field rotation compensation systems. A reverse engineering approach mixed to the integration of new specific solutions has been fundamental to match the ESO commitments in terms of software re-use, in order to smoothen the integration of a new telescope designed and built by an external institute in the ESO environment. The control software architecture, the simulation code to validate the results and the status of work are here described. This paper includes also first results of preliminary tracking tests performed at the VST integration site for azimuth, altitude and rotator axes, that already match system quality requirements
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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