Automated metrology simulator for multi-objects instruments

The most challenging of the metrology needs of multi-objects instruments is the registration of the pupil on the deformable mirror which corrects the wavefront errors. Pick-off mirrors in multi-objects instruments and specially spectrographs (MOS) require accurate positioning and simultaneous viewing of the pupil on the deformable mirror (DM) and the focal plane image on the image slicer at the sub-micron level. A laboratory test prototype simulating the telescope (E-ELT), the beam steering mirror (BSM) and the pupil imaging mirror (PIM), is presented to confirm the correct positioning of the pupil on the DM and to provide the movements of the moveable optical elements to achieve it. The opto-mechanical design and testing of this prototype is shown. The BSM stages (Goniometric cradle, Rotation, & Linear) provide the key mechanical system elements, with precision alignment, resolution, and repeatability. The design and behaviour of the control system is discussed; the ultimate aim of which is to adjust the BSM and PIM to correct for any slight mis-positioning of the pick-off mirror and any temporal drift of all the components to achieve the required alignment. The control system can also cope with flexure effects when required.