WEAVE is a new wide-field multi-object spectroscopy (MOS) facility proposed for the prime focus of the 4.2m William Herschel Telescope. The facility comprises a new 2-degree field-of-view Prime Focus Corrector (PFC) with a 1000-multiplex fibre positioner, a small number of individually deployable integral field units, and a large single integral field unit (IFU). The IFUs and the MOS fibres can be used to feed a dual-beam spectrograph that will provide full coverage of the majority of the visible spectrum in a single exposure at a spectral resolution of ~5000 or modest wavelength coverage in both arms at a resolution ~20000. In order to compensate the field rotation, the Prime Focus Rotator (PFR) is assembled in between the WEAVE Fiber Positioner (system that positions the fibers in the focal plane) and with the Central Can (contains the Prime Focus corrector optics) on the William Herschel Telescope (WHT). The Prime Focus Rotator must provide a rotation degree of freedom for the Fibre Positioner with a high bending stiffness (causing a deflection smaller than 0.008° between interface flanges) adding the minimum mass possible to the system (less than 700kg). This is easily identified as the main design driver to be considered. The Prime Focus Rotator positions the Fibre Positioner to an accuracy of 5 arcsec when tracking and guides all the fibres and other power and control lines through a cable wrap, for which the available space is limited. IDOM proposal to comply with these coupled requirements consists of an optimized structural system with a slightly preloaded cross roller bearing providing the highest possible stiffness to weight ratio. The rotation is driven by means of a direct drive motor powered by a servo drive. For the Cable Wrap, a compact design based on a concept previously developed by IDOM for the Folded Cassegrain Sets the GTC was proposed.
KEYWORDS: Mechanics, Camera shutters, Telescopes, Control systems, Safety, Design for manufacturability, Manufacturing, Chemical elements, Mechanical engineering, Silver
The Gran Telescopio Canarias (GTC) has been recently equipped with the Main Cassegrain Focal Station (CG-Set), composed of an Instrument Rotator (IR) and the corresponding Acquisition, Guiding and Wavefront Sensing (AGWS) system. A shutter protects the Science Instrument during maintenance operations. IDOM was awarded in November 2017 the supply of this equipment, covering its design, manufacturing, assembly and commissioning of the CG-Set. The equipment was transported to the Observatorio del Roque de los Muchachos (ORM) in December 2019. The Site Acceptance Tests were successfully completed in January 2020. The final installation on the telescope has been carried out at the end of November 2020. The Cassegrain Station features a compact and lightweight design with an innovative cable wrap solution. This design results in a smooth and precise movement, whilst guarantees good access to relevant components, simplifying the maintainability. The CG-Set permits a range of movement of the Instrument Rotator of ±270º, providing a tracking accuracy better than 7 arcsec. The AGWS Mechanics provides the required pointing and focusing capabilities, using a reference star to accurately correct the telescope drives and optics. The Cassegrain Focal Station is remotely commanded from the Telescope Control System (GCS) during normal operation and from the Local Control System (LCS) supplied by IDOM for maintenance. For this purpose, two mobile HMIs can be connected at different locations. The Local Interlock and Safety System (LISS) communicates with the Telescope Interlock and Safety System (ISS) to guarantee safe operation of the CG-Set on both local and remote operation. This system is accommodated in an active thermally controlled electronic cabinet The project has been financed by both Spanish and Canary Governments (European Regional Development Funds).
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