The Configurable Slit Unit (CSU) for EMIR shall enable the possibility to generate a multi-slit configuration, a long slit,
or an imaging aperture at the entrance focal plane of the GTC-EMIR instrument. The CSU is therefore a cryogenic
reconfigurable slit mechanism. It contains 110 sliding bars which can be positioned within the 340x340mm wide
aperture of EMIR's instrument field of view.
Based on the results which haven been obtained in the previously performed demonstration programme, the current
developments have focused on the optimization of the performance and up scaling of the construction. Major progress
and improvement have been made on the position measurement of the slits, as a result of conceptual improvements in the
measurement system but also as a result of fundamental hardware changes. Furthermore an improvement of the thermal
household of the instrument will contribute to the position stability performance. Main development advances on several
aspects of the instrument design are presented. This work is performed under contract of the Instituto de Astrofisica de
Canarias as part of the development of the EMIR instrument to be installed at the GTC telescope.
Currently, a number of astrophysical institutes all over the world are working on the design of Extremely Large
Telescopes (ELT). Due to the enormous size of the primary mirror these telescopes make use of segmented mirrors.
These segments have to be positioned with respect to each other with nanometer accuracy in spite of all kind of external
disturbances such as wind loads, thermal loads, deformation of the base frame, varying orientation with respect to the
field of gravity, etc.
Janssen Precision Engineering (JPE) developed a revolutionary position actuator called the HiPAC which is able to
fulfill the demanding requirements for this kind of actuators.
The actuator is based on an integrated system of a pneumatic actuator, an electric voice coil and smart control strategy
and has the following features:
high positioning accuracy performance due to play-free and frictionless actuation;
high reliability and maintenance free operation due to flexure-based frictionless guiding;
system behavior is constant in time, because no parts affected by wear are used in the actuator;
low cost, because no highly accurate machined parts required to reach high end performance;
the position actuator acts as an integrated vibration isolator which isolates the segmented mirrors from
external vibrations induced in the telescope frame;
In this paper the design, simulation and measurements of the HiPAC actuator will be presented.
The Configurable Slit Unit (CSU) for EMIR shall enable the possibility to generate a multi-slit configuration, a long slit, or an imaging aperture at the entrance focal plane of the GTC-EMIR instrument. The CSU is therefore a cryogenic reconfigurable slit mechanism. It contains 100 sliding bars which can be positioned within the 307x307mm wide aperture of EMIR's instrument field of view. The development of the CSU has been a challenging task for several reasons: the high number of elements to control to configure a single observing pattern; the nominal working temperature of 77 K at which all the functionalities have to be accomplished, the stringent requirements in both accuracy and repeatability for most of the functionalities and the rotating nature of the EMIR instrument. The combination of these requirements urged the need to develop new pioneering concepts for actuation and position measurement. An actuation mechanism has been developed based on a piezo drive concept. A dedicated incremental, endless capacitive measurement system has been developed to measure the position of each separate bar. Both technologies are successfully realized in the demonstration programme that has been launched to prove the feasibility of the CSU concept. Besides actuation and position control of the bars, also thermal behavior of the CSU concept have been evaluated within the demonstration programme.
Currently, a number of astrophysical institutes all over the world are working on the design of Extremely Large
Telescopes (ELT). Due to the enormous size of the primary mirror these telescopes make use of segmented mirrors.
These segments have to be positioned with respect to each other with nanometer accuracy in spite of all kind of external
disturbances such as wind loads, thermal loads, deformation of the base frame, varying orientation with respect to the
field of gravity, etc.
Janssen Precision Engineering (JPE) developed a revolutionary position actuator called the HiPAC which is able to
fulfill the demanding requirements for this kind of actuators.
The actuator is based on an integrated system of a pneumatic actuator, an electric voice coil and smart control strategy
and has the following features: high positioning accuracy performance due to play-free and frictionless actuation; high reliability and maintenance free operation due to flexure-based frictionless guiding; system behavior is constant in time, because no parts affected by wear are used in the actuator; low cost, because no highly accurate machined parts required to reach high end performance; the position actuator acts as an integrated vibration isolator which isolates the segmented mirrors from external vibrations induced in the telescope frame; In this paper the design, simulation and measurements of the HiPAC actuator will be presented.
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