The Gimbal Piston™ Air Isolator provides outstanding isolation in all directions for even the lowest input levels. 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 virtually eliminate any gross disturbance within a few seconds. It can also stabilize isolated systems with relatively high centers of gravity without compromising isolation.
Low-Amplitude Input Response
The greatest challenge in designing an effective isolator is to maintain good performance 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 unrealistic 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 exhibits either a higher resonant frequency
than claimed or a substantial increase in transmission through the
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 coupling 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 converted to the usual vertical diaphragm flexure but out of phase: one side of the piston up, the other down, in a gimbal-like motion.
Thick- Wall Rubber Diaphragms. Most commercial isolators employ an inexpensive, thick-walled rubber diaphragm in the piston to achieve vertical isolation. Because of the relative inflexibility of these elements, low amplitude vibration isolation performance 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 manual adjustment. Thus, no practical sealed isolators are designed with such low resonant frequencies.
Bearing Slip Plates. In theory, bearing slip plates should allow horizontal isolation by their decoupling effect. In practice, for such a design to work at low amplitudes, it would require precision ground, hardened bearings with impossibly small tolerances. The commercially 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. Homemade 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 stiffness: the stiffer the spring, the higher the resonant frequency. Thus, homemade 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.
Gimbal PIston™ Isolators
are routinely used for the
Gimbal Piston Isolators
Our Patented Gimbal Piston™ Isolator has been proven by independent tests to consistently outperform the competition. It achieves both horizontal and vertical isolation down to very low input levels.
Thin-Wall Rolling Diaphragms
An integral part of the Gimbal Piston, the thin-wall, dacron-reinforced, rolling diaphragm air seals are only 0.020 in. (0.5 mm) thick and extremely flexible. They do not stiffen the spring as thicker rubber diaphragms do.
Aluminum Height Control Valves
All systems are equipped with rugged aluminum height control valves. Virtually unbreakable, they are finger adjustable with no need for tools. The standard model maintains height to ± 0.050 in. (± 1 mm); the precision model, to ± 0.005 in. (± 0.1 mm).
Internal Piston Travel Restraint
Unique in the industry, TMC provides husky, tamper-proof, built-in piston travel restraints. The restraints are completely independent of the table valves and have been ram-tested at forces above those produced by the pistons operating at full pressure. They cannot be decoupled accidentally and do not interfere with setting up and using the table, but simply protect against overtravel without the use of external bars that create hazardous pinch points. Heavy loads, including the top plate, can be safely removed from a table in full operation.
Exclusive TMC tiebar gussets increase table frame rigidity. They compensate for the elimination of the front tiebar in order to provide kneewell space.
Rugged Built-in Leveling Feet
Table legs include built-in fine-thread 3 in. (75 mm) diameter screw jack levelers with 1/2 in. (13 mm) travel, provision for external adjustment, and a handy adjustment wrench. The base is a solid, slightly domed shape to assure solid, wobble-free contact with sloping or irregular floors.
CleanTop® II features TMC's proprietary spill-proof, drilled and tapped mounting hole array (shown below). Tops are 4 in. (100 mm) thick and have 1/4–20 holes on 1 in. spacing or M6 holes on 25 mm spacing. The small cell-size steel honeycomb design provides even stiffer and better damping than our stainless steel laminate. Guaranteed flat to ± 0.005 in. (± 0.13 mm).
Steel Laminate, our least expensive 63-500 Series top, is recommended for applications that require a strong magnetic attachment and will not involve repeated exposure of the top to corrosive liquids. However, stains from such liquids can be removed with an industrial strength stainless steel cleaner. This top does not have the precision flatness of our CleanTop® honeycomb top. Flatness is ± 0.030 in. (± 0.8 mm).
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