TMC’s constant development
and refining process has yielded a new level in performance for
optical tops.
TMC has long adhered to the philosophy
that dry damping of an optical top is preferable to oil-based
dampers. Oil’s characteristics can change over time and
hidden oil reservoirs are always in danger of being pierced by
an end-user customizing his system.
Our approach to damping of structural resonances
has consistently been based on a “broadband damping” approach. “Tuned
damping,” or using a tuned-mass-damper to resonate out-of-phase
with a top’s bending mode, is a risky approach. First, it
assumes the damper can be set to exactly coincide with the resonant
frequency of the top. An optical top’s resonant frequency
will vary based on load, distribution of load, temperature, and
even the presence of the dampers themselves. Therefore, in practice,
it is difficult to tune the dampers to the top’s resonance.
Furthermore, it assumes that only the lowest resonant frequency
requires damping when many secondary bending and twisting modes
require attention.
More importantly, the notion of incorporating
a tuned-mass-damper to suppress a structural resonance is a flawed
one. Tuned damping is only effective in damping discrete resonances
and is misapplied when used to damp a broadband structural resonance.
In simple terms, a tuned damper “splits” a structural
resonance into two resonances by creating a coupled mass system.
TMC’s proprietary broadband damping
techniques are the most effective way to damp an optical top. This
approach works over the entire frequency range of interest, dissipating
energy at the top’s primary, secondary, and higher resonant
frequencies. In addition, performance will not be compromised by
adding weight to the top. Our new, improved damping incorporates
our broadband approach along with the latest improvements in materials
and new proprietary techniques from TMC.
TMC optical tops have guaranteed performance
levels which are unsurpassed. In addition, with three levels of
broadband damping, two skin thicknesses, and three environmental
choices, TMC offers the most flexibility in choosing a performance
level.
Guaranteed
maximum compliancelevels for the maximum damping level are
tabulated in the chart below. The standard
damping level offers compliance levels a factor of four times
higher than those tabulated. The minimum
damping level is only recommended for non-sensitive applications. The
charts summarize the guaranteed performance levels of TMC optical
tops. In addition, table top corner compliance data are presented
for the three damping levels available. Data were acquired by
impact testing, using a one-pound calibrated hammer, accelerometer,
and dual-channel spectrum analyzer. As these examples demonstrate,
actual, measured performance is often considerably better than
our guaranteed performance. For a more complete discussion
of optical top performance, see TMC's
Technical Background Section
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Guaranteed Maximum Compliance Levels –
Tops with Maximum Fixed Damping
Level (micro-in./lb force input)
|
Top Thickness
|
Top Length |
| |
6' (1.8 m) |
8' (2.4 m) |
10' (3.0 m) |
12' (3.6 m) |
14' (4.2 m) |
16' (4.8 m) |
8 in.
(200 mm) |
3.0 |
5.5 |
10.0 |
15.0 |
20.0 |
30.0 |
12 in. (300 mm) |
1.5 |
2.5 |
4.5 |
6.5 |
10.0 |
13.0 |
18 in. (450 mm) |
0.7 |
1.5 |
2.5 |
3.5 |
5.0 |
7.0 |
24 in. (600 mm) |
0.3 |
1.5 |
0.7 |
2.0 |
2.5 |
3.5 |
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Guaranteed Minimum
Resonant Frequency (Hz)
All series of TMC Tops |
Top Thickness
|
Top Length |
| |
6' (1.8 m) |
8' (2.4 m) |
10' (3.0 m) |
12' (3.6 m) |
14' (4.2 m) |
16' (4.8 m) |
8 in.
(200 mm) |
160 |
135 |
110 |
85 |
65 |
55 |
12 in. (300 mm) |
200 |
170 |
135 |
110 |
85 |
70 |
18 in. (450 mm) |
230 |
200 |
165 |
130 |
100 |
80 |
24 in. (600 mm) |
250 |
230 |
185 |
150 |
120 |
90 |
|