Hexapods are general solutions that provide movement with six degrees of freedom for instrument positioning, alignment, and support. In the case of the METIS instrument, the hexapod must satisfy the following stringent requirements: a) support the 11-ton weight of an instrument; b) allow alignment and provide position stability to the instrument to within a tenth of a millimeter; c) provide an adjustment range of about 20 cm; d) support the instrument allowing for accelerations of over 3 g in all directions; e) have the lowest mass possible.
Commercial linear actuators that are generally used in such cases are designed for extended movement, include a complete set of bearings that constrain each actuator lateral displacements and a sophisticated central screw that defines only the longitudinal movement. These solutions tend to be heavy and costly if roller screws are used to avoid backslash. They encompass ranges that are a major fraction of the total length and are designed for fast movement. Both these characteristics exceed the requirements of the METIS application.
We present an optimized design for the hexapod which includes a different, lightweight, sturdy, small-range, highprecision, no backslash, earthquake-proof actuator. The design of the hexapod is such that it can be used, in general, as a mass and vibration optimized solution for precision heavy instrument alignment.
This article presents the final design of the METIS/ELT warm support structure subsystem. The warm support structure provides the mechanical interface between the cryostat and the Nasmyth platform. It consists of three substructures: the elevation platform, the cryostat alignment structure (CAS), and the instrument access platform. The elevation platform is connected to the Nasmyth platform and holds the CAS. It consists of seven legs connected to three notes. The CAS is a hexapod holding the cryostat, allowing maintenance, alignment, and positioning. The instrument access platform allows human access to the cryostat, it holds the cable support system and is prepared to support the future Single Laser Adaptive Optics system. The subsystem requirements, design trade-offs, interface considerations, final design and simulation results of the substructures will be detailed as presented to the METIS Final Design Review, in 2022.
Portugal will build the warm support and access structure (WSS) to the mid-infrared, first generation ELT instrument - METIS. The particular characteristics of METIS and the ELT pose several challenges to designing the WSS according to requirements, as well challenges to the assembly and integration of the WSS. We here provide you an overview of those challenges, as well as strategies to overcome and mitigate issues related to the mass and dimensions of the WSS.
The METIS consortium in Portugal will build the support and access structure (WSS) for the mid-infrared, first generation ELT instrument - METIS. The specific characteristics of the METIS instrument and the ELT pose several challenges to building the WSS according to functional requirements. In addition, the assembly of the WSS and integrating the WSS with METIS poses its own particular challenges due to the singular loads and dimensions. Transversal to all phases of assembly and integration of the WSS and METIS is the concern for the safety of the instruments and personnel involved. We here present these requirements, challenges and mitigation measures in light of the assembly and integration of the WSS, and the WSS with METIS.
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