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High-Capacity CleanBench™
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Overview
For table applications that require isolating over 350 lbs (160 kg) of net load, we recommend our High Capacity CleanBench 68-500 Series tables. They are similar in design to our 63-500 Series tables, with higher capacity isolators and a more massive stainless steel top plate.

In addition to high load applications, the High Capacity CleanBench is also recommended for payloads with unusually high centers of gravity and equipment with moving stages. These applications should benefit from the increased stability.

With a stiffer, more massive top plate, a lower natural frequency isolator, and stiffer, heavier leg frames, High Capacity CleanBenches provide performance that is markedly superior to any other passive table in the industry.




Specifications




Gimbal Piston
All CleanBench tables incorporate TMC’s Gimbal Piston Air Isolators as a standard feature. The Gimbal Piston has consistently shown to out-perform other air isolators in side-by-side testing. It offers outstanding low frequency vibration isolation in all axes and maintains its performance specifications even when subjected to extremely low input levels of excitation. Proprietary damping techniques allow the Gimbal Piston to stabilize relatively top-heavy payloads and quickly dissipate disturbances of the isolated table top.

Benefits

  • Vertical and horizontal vibration isolation starting at 2 Hz
  • Reduces vibration by more than 95% at 10Hz
  • Virtually free of friction, avoiding rolling friction to static friction transitions
  • Accommodates horizontal displacement by acting as a gimbal
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

Chart 1

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 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.

Gimbal Piston Chart 3

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.

Horizontal vs Vertical
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 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.

Comparative Performance

ArgonneArgonne
Photo courtesy of Argonne National Laboratory

Gimbal PIston™ Isolators are routinely used for the
most demanding electron microscope installations.





Accessories
Adjustable Steel Front Support Bar  mounts on the table’s front legs.It has a slot in which the shelves mount and is normally ordered with the armrest pads. The bar may be centered along the length of the table or cantilevered to either side, allowing for a wider sliding shelf to suit your application.

Adjustable Steel Rear Support Bar mounts on the rear table legs and supports the rear end of the sliding shelves. It may also be cantilevered to either side, allowing for a wider sliding shelf.

Both front and rear support bars can be retrofitted but cannot be used with the Full Perimeter Enclosure or Faraday Cage.


Retractable Casters have a total weight capacity of 1,000 lb (450 kg) and can be mounted to the base of the table legs. Casters are required when using the OnTrak™ feature.



Adjustable Armrest Pads fasten to the front support bar. TMC also offers an armrest pad that attaches to the Full Perimeter Enclosure.




White Laminate Sliding Shelves slide freely from side to side and are easily lifted off the support bars. Built-in stops prevent shelves from sliding out of slots. When ordering sliding shelves, you must order front and rear support bars.

Subshelf offers additional storage space. It can be mounted beneath the isolated table top and may be retrofitted.

Fixed Full-Perimeter Enclosure A welded-steel structure that completely surrounds the table top to provide nonisolated support for Faraday cages or other special fixtures. It cannot be used with sliding shelves or support bars. There is an 8 in. wide sliding shelf specifically for the Full Perimeter Enclosure and it is required for use with a Faraday Cage.

Precision Height Control Valves minimize bottled air supply usage, standard TMC height control valves have a small “dead band,” resulting in a height return accuracy of +/- 0.05 in. (+/- 1.3 mm). Precision valves control height to within +/- 0.005 in. but exhaust continuously.

To specify precision height control valves with a table, add the letter “P” after the basic table model number. (ie.: 63P-733) Precision valves may also be retrofitted to installed tables.

CleanBench Faraday Cage offers improved access and simplified assembly. It’s designed for shielding in electro-physiology type applications (60 Hz and harmonics). The “window-shade” retracting front panel is easy to operate and causes less disturbance when adjusted. The front panel may be positioned anywhere between fully opened and closed and stays in position without a fastener. This cage incorporates a steel frame and bronze-mesh material and mounts to a required full-perimeter enclosure. Our 40 in.(1 m) tall Faraday Cage includes a 2 in.(50 mm) diameter hole in the base of the side and rear panels. This feature eases cable interface to the interior of the cage. A new version of our armrest pads are compatible with our cages. They are identical to our non-Faraday Cage pads but adhere with Velcro





Order Chart




See Also
See Also CleanBench

           
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