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METIS is one of the first-generation instruments currently in development for the Extremely Large Telescope (ELT). As one of the partners in the project consortium, the team at University of Cologne is responsible for the development of the Warm Calibration Unit (WCU) subsystem. This subsystem is designed to deliver a selection of broadband and single wavelength sources for the calibration of the METIS instrument along with pupil/focal plane imaging optics serving as feedback for the internal alignment of the subsystems of METIS during the integration phase foreseen in Leiden. After the satisfactory Final Design Review (FDR) towards the end of 2022, the development of the WCU subsystem is currently in the manufacturing/procurement phase along with the integration of sub-assemblies. We provide an overview of the development of the WCU subsystem at this phase of the project including the progress on the manufacturing of custom components and the details on the compliance with the design principles with a primary focus on the mechanical aspects. These components include as an example: (1) a lightweight optical bench made of carbon-fiber reinforced polymer (CFRP) and with dimensions of roughly 2.5mx3m and a thickness of 20cm, satisfying compliancy both with high loads and tight tolerances (on the level of several tens of microns), (2) custom-designed six adjustable supporting links responsible for carrying the subsystem (roughly 1 tons) and its alignment to METIS focal/pupil planes within desired accuracies 50 microns with the help of laser sensors, (3) kinematic optical Aluminum mounts with a thermal invariant design (i.e. positioning of the optics are not affected by temperature). In the light of the progress, we discuss further the perspectives and the planning towards the full integration and testing of the full subsystem, foreseen to start within the second quarter of 2025.
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