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Laboratory Tables & TableTop ™ Platforms 2 Technical Manufacturing Corporation • 978-532-6330 • 800-542-9725 (Toll Free) • Fax: 978-531-8682 • sales@techmfg.com • www.techmfg.com Vibration Isolation vs. Pneumatic Damping Isolation Amplification Transmissibility ( Acceleration Transmitted ) 1000% 90% 123451020305010 99% Frequency, Hz a73 Theoretical 1.5 Hz isolator with no damping a73 Theoretical 1.5 Hz isolator with 0.2 damping coefficient a73 Measured 63-500 Series Table with 40-microinch floor inputs (vertical) (source for theoretical curves: Harris & Crede, Shock and Vibration Handbook) 10 1 0.1 0.01 Acceleration Input Low-Amplitude Input Response Isolation Amplification Transmissibility ( Acceleration Transmitted ) 10 1 0.1 0.01 1000% 90% 123451020305010 99% Frequency, Hz a73 Measured 63-500 Series Table with 40-microinch floor inputs (vertical) a73 Measured 63-500 Series Table with 4-microinch floor inputs (vertical) a73 Measured 63-500 Series Table with 0.1-microinch floor inputs (vertical) Acceleration Input The key element in all TMC vibration isolation tables is our Gimbal Piston ™ Air Isolator. These assemblies have repeat- edly proven, in independent tests, to provide outstanding isolation in all direc- tions for even the lowest input levels. The Gimbal Piston utilizes proprietary pneumatic damping techniques, which include air flow restrictors and a unique geometry. It is lightly damped and highly responsive to typical, low-amplitude ambient floor vibrations, yet achieves very high damping for gross transient disturbances, such as sudden load changes or bumping the top plate. The result is that Gimbal Piston Isolators provide superior isolation yet will virtu- ally eliminate any gross disturbance within a few seconds. The Gimbal Piston can also stabilize isolated systems with relatively high cen- ters of gravity without compromising isolation. Low-Amplitude Input Response The greatest challenge in designing an effective isolator is to maintain good per- formance at the low vibration amplitude inputs typical of ambient building floor vibration. Isolator specifications are often based on measurements done with the isolator placed on a “shaker table” with very high amplitude input levels. Such testing, with input amplitudes on the order of millimeters, yields unreal- istic performance expectations and is misleading as results will not reflect the actual performance in use. The Gimbal Piston Isolator design is unique in its ability to maintain its stated resonant frequency and high level of attenuation in even the most quiet, real, floor environments. The performance is linear to such low amplitudes because the design is virtually free of friction and therefore able to avoid rolling friction to static friction transitions. Every other system that we have tested at levels typical for floor vibration ex- hibits either a higher resonant frequency than claimed or a substantial increase in transmission through the isolator mount. We stress the importance of performance specifications at low levels because we have repeatedly observed, in our own testing and in many as-used installations, that better performance is much easier to achieve at greater amplitudes and higher frequencies. Horizontal vs. Vertical Inputs Our innovative Isolator allows a thin-wall, rolling diaphragm seal to accommodate horizontal displacement by acting as a gimbal. Instead of using a cable-type pendulum suspension, the Gimbal Piston Isolator carries the load on a separate top plate that has a rigid rod extending down into a well in the main piston. The bottom of the rod has a ball-end that bears on a hard, flat seat. The result is an inherently flexible cou- pling which allows horizontal flexure in the isolator as the ball simply rocks (without sliding or rolling) very slightly on the seat. The approach works extremely well, even with sub-microinch levels of input displacement, because the static friction is virtually the same as the rolling friction. Horizontal motion is simply con- verted to the usual vertical diaphragm flexure but out of phase: one side of the piston up, the other down, in a gimbal- like motion. Gimbal Piston ™ Isolators

1 3Technical Manufacturing Corporation • 978-532-6330 • 800-542-9725 (Toll Free) • Fax: 978-531-8682 • sales@techmfg.com • www.techmfg.com Photo courtesy of Argonne National Laboratory Limitations of Other Types of Isolators Thick-Wall Rubber Diaphragms. Most commercial isolators employ an inexpensive, thick-walled rubber diaphragm in the piston to achieve vertical isolation. Because of the rela- tive inflexibility of these elements, low amplitude vibration isolation per- formance is compromised. Though such a system feels “soft” to gross hand pressure, typical low-level floor vibration causes the rubber to act more like a rigid coupling than a flexible isolator. Sealed Pneumatic Isolators (Passive). Sealed air isolators do not automatically adjust to load changes. The primary limitation of such systems is that they must be made too stiff to be effective isolators. For example, a passive isolator with a true 1.5 Hz resonant frequency would drift several inches vertically in response to small changes in load, temperature, or pressure and require constant man- ual adjustment. Thus, no practical sealed isolators are designed with such low resonant frequencies. Bearing Slip Plates. In theory, bearing slip plates should allow horizontal iso- lation by their decoupling effect. In practice, for such a design to work at low amplitudes, it would require preci- sion ground, hardened bearings with impossibly small tolerances. The com- mercially available versions cannot overcome the static frictional forces at low amplitudes to get the bearings rolling at all. In addition, all such systems are difficult to align initially and easily drift out of calibration. Homemade Assemblies. Home- made isolation systems - often a steel or granite slab placed on rubber pads, tennis balls, or air bladders - will work only if the disturbing vibrations are high frequency and minimal isolation is required. While all isolators use the principle of placing a mass on a damped spring, their performance is differentiated primarily by spring stiff- ness: the stiffer the spring, the higher the resonant frequency. Thus, home- made solutions are limited by their high resonant frequency. A Gimbal Piston ™ Isolator with a 1.5 Hz vertical resonant frequency begins to isolate at 2 Hz and can reduce vibration by over 95% at 10 Hz. A tennis ball under a steel plate with a 7 Hz resonant frequency begins to isolate above 10 Hz and reduces vibrations by 90% at 30 Hz. But most building floors exhibit their highest vibrational displacements between 5 and 30 Hz, so that a tennis ball or rubber pad actually makes the problem worse by amplifying ambient frequencies between 5 and 10 Hz. Horizontal vs. Vertical Isolation Isolation Amplification Transmissibility ( Acceleration Transmitted ) 10 1 0.1 0.01 1000% 90% 123451020305010 99% Frequency, Hz a73 Measured 63-500 Series Table with 40-microinch floor inputs (vertical) a73 Measured 63-500 Series Table with 4-microinch floor inputs (horizontal) Comparative Performance Curves Isolation Amplification Transmissibility ( Acceleration Transmitted ) 10 1 0.1 0.01 1000% 90% 123451020305010 99% Frequency, Hz a73 Measured 63-500 Series Table with 40-microinch floor inputs (vertical) a73 Measured steel plate on tennis balls (vertical) a73 Measured steel plate on rubber pads (vertical) a73 Measured steel plate on commercial passive isolator claiming 5Hz resonance Acceleration Input Acceleration Input Gimbal Piston ™ Isolators are routinely used for the most demanding electron microscope installations.

978-532-6330800-542-9725TollFreewww.techmfg.com, in.mmin.mm, in.mmin.mm, thenpositionedtowithinH110070.001in.in, in.mmin.mm, in.mmin.mm, 978-532-6330800-542-9725TollFreewww.techmfg.com,
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