This paper discusses the development, realization, and qualification of a positioning actuator concept specifically for
cryogenic environments. Originally developed for quantum physics research, the actuator also has many applications in
astronomic cryogenic instruments to position optical elements with nanometer level accuracy and stability. Typical
applications include the correction of thermally induced position errors of optical components after cooling down from
ambient to cryogenic temperatures or sample positioning in microscopes.
The actuator is nicknamed the ‘PiezoKnob’ because it is piezo based and it is compatible with the typical manipulator
knob often found in standard systems for optical benches, such as linear stages or tip/tilt lens holders. Actuation with
high stiffness piezo elements enables the Piezoknob to deliver forces up to 50 Newton which allows relatively stiff
guiding mechanisms or large pre-loads. The PiezoKnob has been qualified at 77 Kelvin and was shown to work down to
2 Kelvin. As part of the qualification program, the custom developed driving electronics and set point profile have been
fine-tuned, by combing measurements with predictions from a dynamic model, thus maximizing efficiency and
minimizing power dissipation. Furthermore, the actuator holds its position without power and thanks to its mechanical
layout it is absolutely insensitive to drift of the piezo elements or the driving electronics.
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.
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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