08-Optical Tables.pdf - Qioptiq Q-Shop

Optical Tables
Vibrational isolation is provided by a
gimbal-piston assem bly, free to move in
an upper air chamber, or com pres sion
chamber, sealed by a 0.5 mm thick,
Dacron -reinforced, bellows that excludes
ambient air. A suppor ting rod welded
onto the underside of the unit‘s moun ting
plate is bolted to the piston‘s flexible
base plate. The compression chamber is
pneumatically inter connected to a second
chamber, a so-called „damping“ chamber,
via a calibrated orifice. When these units
are used, Table Tops are supported on air
cushions consti tu ting extrem ely „weak“
springs of a spring-mass system.
These types of table systems have
extremely low reso nant frequencies, due
to the low restoring forces of their
supports and the high weights of their
tops. The bellows used for sealing add no
stiffness to support units, since they are
rather thin, and thus highly flexible.
Horizontal displacements of Table Tops
are transmitted via supporting rods,
producing lateral motions of flexible
piston baseplates. This causes pistons to
execute vertical tilting motions about
points lying roughly in the planes of their
sealing bellows. The lengths of pistons
and supporting rods have been chosen to
optimize the resonant frequencies of
these motions. Horizontal dis place ments
of Table Tops thus also cause air to flow
back and forth between compression and
damping chambers, thereby damping any
lateral motions of Table Tops.
The lowest resonant frequencies achievable
with these vibration isolators range
from 1.5 Hz to 1.7 Hz in both vertical and
horizontal planes, and vary with the loads
supported. The following graphs present
typical vibra tion -transmission and
transmissibility curves for our Gimbal
Piston vibration-isolators.
Gimbal Piston systems effectively damp
vibrational motions in both vertical and
horizontal planes over the entire critical
range, which extends from 2 Hz to 50 Hz.
This superior performance makes these
systems suitable for supporting experimental
setups, such as those used in
interferometry and holography, that are
highly sensitive to vibrations.
The excellent vibrational isolation they
provide in both vertical and horizontal
planes isolate experimental setups even
from the large-amplitude floor vibrations
typcially encountered on the upper floors
of tall buil dings. They should thus be used
in all applications ad versely affected by
floor vibrations and/or subject to critical
constraints on their ambient acoustic
environ ments.
If a Table Top supported on these units is
vertically displaced, the resulting motions
of their pistons will alter the volumes of
their compression chambers, thereby
altering chamber pressures. This is what
provides the desired cushioning effect.
Since air may enter or exit compression
chambers through calibrated orifices in
the walls separating them from damping
chambers, air will flow back and forth
through these orifices as com pres sion
chamber volumes vary, damping the
motions of the mounting plates on which
the Table Top rests.
Amplitude (nm)
200
20
Floor
2
0.2
Vibration Isolator
0.02
0 5 10 15 20 25 30 35 40 45 50
Frequency (Hz)
Vertical vibration isolation
Amplitude (nm)
200
20
2
0.2
Vibration
Isolator
Floor
0.02
0 5 10 15 20 25 30 35 40 45 50
Frequency (Hz)
Horizontal vibration isolation
High Quality
Mounting plate
Bellows
Compression chamber
Support rod
Piston
Stiffener plate
Stop
Flexible base plate
Calibration orifice
Damping chamber
With high-precision valves, the resetting
accuracy can be increased
to ±0.1 mm. The quick response of
the valves prevents build-up in
structures with a center of gravity
far above the work surface.
Optical Tables
Cutaway view of a Gimbal Piston TM vibration
isolation unit
Phone numbers: Germany +49 551 69 350
France +33 47 25 20 420
303