Transmissibility Curves for Vibration Isolation
Tables, Platforms, Isolators & Systems
Performance:
Based on field testing and user evaluations, the Minus K
1/2-Hz vibration isolation platforms and workstations perform
about 10 to 100 times better than high-performance air tables
depending on the vibration isolation frequencies. They also
perform better than active or electronic-cancellation systems.
The transmissibility curves, which compare top-performing
air tables with the typical Minus K 1/2-Hz performance, are
shown below. Minus K isolators (adjusted to 1/2 Hz) achieve
93% isolation efficiency at 2 Hz, 99% at 5 Hz, and 99.7% at
10 Hz. Isolation performance closely follows that of an ideal
undamped single DOF system up to about 10 Hz and reaches a
floor in the transmissibility curve with some resonances at
the higher frequencies.
The Minus K curve below is typical for any Minus K 1/2-Hz
system, horizontal or vertical. Measured transmissibility
curves for some Minus K bench top products are also shown
below.
Transmissibility test procedure:
The transmissibility curves provided by Minus K Technology
are generated using a Stanford Research Instruments SR785
Dynamic Signal Analyzer. The output source of the SR785 is
set to generate a swept sine signal. This signal is fed into
a Labworks PA-138 power amplifier. The amplifier drives a
Labworks ET-126 electrodynamic shaker. The shaker is mounted
in a heavily reinforced frame that also supports a 650BM-1
isolator. This support isolator has been adjusted to about
2.75 Hz. It has also been modified to work only in the vertical
direction. This isolator supports a heavy top plate and whatever
ballast weight is needed to bring the total payload including
the test isolator up to around 650 pounds.
Transmissibility as it applies to our isolators is a ratio
of the output signal on the top plate divided by the input
signal that the base of the isolator sees. One can also think
of it as the ratio of what gets through the isolator divided
by what is present on the isolator support. Two similar accelerometers
are used to acquire the input and output signals. The input
accelerometer is attached to the heavy top plate on the 650BM-1
support isolator. The test isolator rests on the heavy top
plate as well. This way the accelerometer measures the vibrations
that are fed to the isolator. The output accelerometer is
placed on top of the properly loaded test isolator top plate.
Both accelerometers are held in place with a thin layer of
seismic wax. This works quite well, providing a secure, yet
easy to undo bond for measurement.
The SR785 acquires both sets of data, calculates their ratio
and displays the ratio as transmissibility..
The horizontal transmissibility was acquired in much the same
way. The differences were that the support isolator was
allowed to move horizontally. The electrodynamic shaker was
mounted horizontally. The accelerometers were mounted on their
sides, which allowed the ratio of horizontal data to be calculated
and displayed as horizontal transmissibility.
The curve below shows the typical vertical 1/2 Hz performance
of the BM-1. It offers 10-100 times better performance
than typical high-performance air tables.
The curve below shows the typical vertical 1/2 Hz performance
of the BM-4. It offers 10-100 times better performance than
typical high-performance air tables.
The curves below demonstrate the better-than-air performance
that the BM-6 delivers. Vertically, the BM-6 offers a resonant
frequency that is comparable to or better than most air tables.
Horizontally, the BM-6 offers much better performance than
typical air tables, which can have horizontal frequencies
as high as 4-5 Hz.
The curve below demonstrates the vertical 1/2 Hz performance
of the BM-8. The BM-8 delivers the high performance of our
larger isolators in a package only 4.6 inches tall. The horizontal
performance of the BM-8 is the same as that of the BM-6.
The curve below shows the vertical 1/2 Hz performance
of the BM-10. It offers 10-100 times better performance than
an air table in a package many times smaller. The horizontal
isolation performance of the BM-10 is the same as that of
the BM-6.
Transmissibility curves for vibration isolation isolators and isolator table systems. See
overall performance data and procedure above with test
ratios, testing and equation calculating procedures, use of accelerometers
and reference to passive, air, active, negative and efficiency factors. Minus K builds
passive vibration isolation tables, platforms, bench tops and custom systems.
Our antivibration control products offer the best devices and instruments among companies and
manufacturers of equipment used for micro and nano technology applications including microscope-microscopy (sem, afm, stm, tem, spm)
research.
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