The MICADO first light imager for the ELT: design and performance of the Focal Plane Mechanism prototype

MICADO is a first-generation instruments for the ELT, which will provide diffraction limited imaging in standard, astrometric, and coronagraphic modes, and long-slit spectroscopy at near-IR wavelengths. The core of the MICADO instrument is its cryostat. Following a light ray entering the cryostat through the entrance window, the first mechanism it encounters is the Focal Plane Mechanism (FPM). It consist of two independent movable devices mounted together in one assembly: the aperture wheel (AW) and the focal plane wheel (FPW). The FPW holds field stops, calibration masks, slits and coronagraphs, which require better than 15 µm RMS repeatability of the mechanism. To fulfill this specifications and avoid mechanical wear in the drive a novel magnetically coupled gear system was developed at our institute. This contribution will describe the design and performance of the magnetic drive as well as the first results of the FPW prototype tests.