A Configurable Slit Unit (CSU) has been developed for the Multi-Object Spectrometer for Infra-Red Exploration
(MOSFIRE) instrument to be installed on the Keck 1 Telescope on Mauna Kea, Hawaii. MOSFIRE will provide NIR
multi-object spectroscopy over a field of view of 6.1' x 6.1'. The reconfigurable mask allows the formation of 46 optical
slits in a 267 x 267 mm2 field of view. The mechanism is an evolution of a former prototype designed by CSEM and
qualified for the European Space Agency (ESA) as a candidate for the slit mask on NIRSpec for the James Webb Space
Telescope (JWST). The CSU is designed to simultaneously displace masking bars across the field-of-view (FOV) to
mask unwanted light. A set of 46 bar pairs are used to form the MOSFIRE focal plane mask. The sides of the bars are
convoluted so that light is prevented from passing between adjacent bars. The slit length is fixed (5.1 mm) but the width
is variable down to 200 μm with a slit positioning accuracy of ± 18 μm. A two-bar prototype mechanism was designed,
manufactured and cryogenically tested to validate the modifications from the JWST prototype. The working principle of
the mechanism is based on an improved "inch-worm" stepping motion of 92 masking bars forming the optical mask.
Original voice coil actuators are used to drive the various clutches. The design makes significant use of flexure
structures.
M. Stampanoni, A. Groso, A. Isenegger, G. Mikuljan, Q. Chen, A. Bertrand, S. Henein, R. Betemps, U. Frommherz, P. Böhler, D. Meister, M. Lange, R. Abela
Synchrotron-based X-ray Tomographic Microscopy (SRXTM) is nowadays a powerful technique for non-destructive,
high-resolution investigations of a broad kind of materials. High-brilliance and high-coherence third generation
synchrotron radiation facilities allow micrometer and sub-micrometer, quantitative, three-dimensional
imaging within very short time and extend the traditional absorption imaging technique to edge-enhanced
and phase-sensitive measurements. At the Swiss Light Source TOMCAT, a new beamline for TOmographic Microscopy and Coherent rAdiology experimenTs, has been recently built and started regular user operation in
June 2006. The new beamline get photons from a 2.9 T superbend with a critical energy of 11.1 keV. This makes
energies above 20 keV easily accessible. To guarantee the best beam quality (stability and homogeneity), the
number of optical elements has been kept to a minimum. A Double Crystal Multilayer Monochromator (DCMM)
covers an energy range between 8 and 45 keV with a bandwidth of a few percent down to 10-4. The beamline
can also be operated in white-beam mode, providing the ideal conditions for real-time coherent radiology. This
article presents the beamline design, its optical components and the endstation. It further illustrates two recently
developed phase contrast techniques and finally gives an overview of recent research topics which make intense
use of SRXTM.
A mechanical slit mask mechanism has been designed for the Near Infrared Spectrograph of the James Webb Space Telescope. This mechanism was successfully tested at a cryogenic temperature of 30K, in vacuum. The reconfigurable mask allows to form 24 optical slits in a 137 x 137 mm2 field of view. The slit length is fixed (4.8 mm) and their width can range from 50 μm to 137 mm. The slit positioning accuracy is ± 5 μm and the slit width accuracy is ± 8 μm. The working principle of the mechanism is based on an improved "inch-worm" stepping motion of 48 masking bars forming the optical curtain. Voice coil actuators are used to drive the various clutches and the principal mobile stage. Ratchets which engage in the teeth of a rack machined on the bars allow to cancel the accumulation of motion errors as steps succeed one another. The design makes significant use flexure structures. Cryogenic performance, life and vibration tests have been performed successfully on subassemblies of the mechanism and a full-scale prototype.
This paper inquires into the exportability of the fatigue measurements made on standard test-specimen to wire electro- discharge machined flexures with thin cross sections (50 micrometers ). It describes the results of a set of fatigue measurements made on 66 circular flexible hinges machined in steel and bronze by wire electro-discharge machining. After reminding the fatigue theory and describing the theoretical model used to calculate the stresses inside the bent hinges, the paper describes the experimental setup and the measured results. The main conclusions drawn out of this work is that the admissible stresses for the tested flexures having a low surface roughness (Ra equals 0.2 micrometers ) are at least as high as the admissible stresses for standard test specimens. This indicates that fatigue data found in literature can be used to calculate the dimensions of this kind of flexures without any reduction of the safety factor.
This paper describes a detailed study of the behavior of the parallel spring stage having four circular flexure hinges of very thin cross-sections manufactured by wire electro- discharge machining. The state of the art recalls the abundant literature published on the parallel leaf spring stage, and presents the few articles found dealing with the parallel spring stages. The theoretical modeling for the calculation of the linear stiffness of the parallel spring stage is described. The starting point of the discussion is the observation that the theoretical model which is valid when applied to stages of large dimensions produces large errors when applied to wire-EDM machined flexures of very thin cross-sections. As an explanation of this observation, a hypothesis is put forward: on the surface of each neck a thin layer affected by the EDM process is not playing any mechanical role in the bending of the flexure and the thickness of this layer is related to the roughness of the surface. The experimental results show that the hypothesis is true to a large extent but that roughness is probably not the only factor affecting the neutral zone. The 'white layer' and the microstructural homogeneity of the material used could also be determinant.
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