Dr. Ivar Kjelberg Profile

Dr. Ivar Kjelberg

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Publications (5)

Proceedings Article | 27 July 2016 Paper

SOFIA secondary mirror mechanism heavy maintenance and improvements

Yannick Lammen, Andreas Reinacher, Ivar Kjelberg, Serge Droz, Holger Jakob, Friederike Graf, Michael Lachenmann, Alfred Krabbe

Proceedings Volume 9906, 99061R (2016) https://doi.org/10.1117/12.2231352

KEYWORDS: Mirrors, Calibration, Temperature metrology, Observatories, Autocollimators, Telescopes, Sensors, Shape memory alloys, Sensor calibration, Position sensors

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The Stratospheric Observatory For Infrared Astronomy (SOFIA) reached its full operational capability in 2014 and completed hundreds of observation flights. Since its installation in 2002, the Secondary Mirror Mechanism was subject to thousands of operating hours equivalent to millions of load cycles. During the aircraft heavy maintenance in fall 2014, a four month time window enabled the removal of the mechanism from the telescope structure for service and improvements. Next to visual corrosion- and crack-inspection of the flexures, critical electronic components (in particular the set of three eddy current position sensors that determine the mirror tilt) were replaced. Moreover, a detailed temperature dependent position calibration of the system was performed in a cold chamber to improve the pointing accuracy. Until then, a simple temperature independent linear gain was used to translate the sensor output voltage into a position. For accurate positioning across the whole temperature range, a temperature dependent correction function had to be developed. This calibration would have cost hours of observing time when performed in flight which made it an essential goal for completion during the maintenance period. An autocollimator was used as optical reference camera to measure the tip-tilt position of the secondary mirror in the cold chamber. Using this calibration setup, a pattern of many mirror positions in the tip-tilt domain was approached at several temperature points to provide a high resolution data set for the new multidimensional calibration function. Follow-up in-flight verification measurements confirmed a large improvement in pointing accuracy as soon as the temperature measurements were included into the position correction. Improvements of up to a factor of 10 were especially noticed in the lower temperature range. This contribution provides an insight into the work performed during the SOFIA - Secondary Mirror Mechanism maintenance with the focus on the temperature dependent position calibration.

Proceedings Article | 28 July 2010 Paper

E-ELT M5 field stabilisation unit scale 1 demonstrator design and performances evaluation

J. Casalta, J. Barriga, J. Ariño, J. Mercader, M. San Andrés, J. Serra, I. Kjelberg, N. Hubin, L. Jochum, E. Vernet, M. Dimmler, M. Müller

Proceedings Volume 7736, 77360M (2010) https://doi.org/10.1117/12.857078

KEYWORDS: Mirrors, Actuators, Control systems, Telescopes, Sensors, Atmospheric optics, Silicon carbide, Manufacturing, Interfaces, Electronics

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Proceedings Article | 10 July 2008 Paper

The field stabilization and adaptive optics mirrors for the European Extremely Large Telescope

Elise Vernet, Lieselotte Jochum, Paolo La Penna, Norbert Hubin, Riccardo Muradore, Joan Manel Casalta, Ivar Kjelberg, Jean-Christophe Sinquin, Frédéric Locre, Pierre Morin, Raphaël Cousty, Jean-Marie Lurçon, Jean-Jacques Roland, Bruno Crepy, Eric Gabriel, Roberto Biasi, Mario Andrighettoni, Gerald Angerer, Daniele Gallieni, Marco Mantegazza, Matteo Tintori, Emilio Molinari, Daniela Tresoldi, Giorgio Toso, Paolo Spanó, Marco Riva, Giuseppe Crimi, Armando Riccardi, Gilles Marque, Jean-Louis Carel, Eric Ruch

Proceedings Volume 7015, 70150S (2008) https://doi.org/10.1117/12.787855

KEYWORDS: Mirrors, Actuators, Telescopes, Control systems, Electronics, Prototyping, Adaptive optics, Sensors, Large telescopes, Optics manufacturing

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Proceedings Article | 16 June 1998 Paper

Resistor-damped electromechanical lever blocks

Lorenzo Zago, Pierre Genequand, Ivar Kjelberg

Proceedings Volume 3327, (1998) https://doi.org/10.1117/12.310699

KEYWORDS: Actuators, Interfaces, Electromagnetism, Signal attenuation, Control systems, Optical isolators, Vibration control, Chemical elements, Resistance, Ranging

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The paper presents an innovative technical solution which provides a combined damping and isolation interface with the appropriate transmissibility characteristics between a vibrating base and a sensitive payload, typically an optical terminal/telescope. The novelty of the solution is primarily found in the implementation of uncoupling and magnification of the incurred vibrations by means of flexures combined with the implementation of energy dissipation by means of a linear electro-magnetic actuator to constitute a passive integrated resistor-damped electromechanic lever block. By means of frictionless flexible lever systems, the amplitude of the payload vibrations is adapted to the optimal range of the actuator with a magnification by a factor ranging typically between 10 and 30. Passive viscous damping is obtained by simply short-circuiting the electro-magnetic motor and can be adapted by setting the impedance of the shorting connection. The desired stiffness is provided by the passive springs of the elastic motor suspension and by the stiffness of the lever flexure blades. The mobile mass of the motors also provide a reaction mass which, like damping and stiffness, is amplified by the square of the lever factor. A theoretical model of resistor-damped electromechanical lever blocks has been established. A particular property is it the good attenuation of excited vibrations only over a set frequency range. Above this range the interface properties rejoin the ones of a rigid connection. This performance makes this type of isolators particularly suitable for integration into multi-layer vibration control systems where sensitive equipment is protected by a mix of passive and active damping/isolation devices acting optimally at different frequency ranges. Experiments performed with a dummy load (80 Kg) representative of a satellite based optical terminal demonstrated the efficiency of the system in protecting the payload by passive damping for vibration excitations of amplitude up to 0.15 mm and frequency up to about 120 Hz achieving an attenuation of the eigenmodes of the load structure by more than 20 dB.

Proceedings Article | 21 March 1997 Paper

Application of flexure structures to active and adaptive opto-mechanical mechanisms

Lorenzo Zago, Pierre Genequand, Ivar Kjelberg, Joseph Morschel

Proceedings Volume 2871, (1997) https://doi.org/10.1117/12.269023

KEYWORDS: Actuators, Mirrors, Interfaces, Kinematics, Control systems, Space operations, Manufacturing, Chemical elements, Sensors, Space telescopes

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