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Micro-g® Lab Table with Gimbal Piston Isolators




Overview
TMC’s Micro-g® laboratory tables provide superior vibration control for loads up to 350 pounds (160 kg). With a ferromagnetic stainless steel working surface, this modular vibration isolation table system is recommended for use in such diverse applications as electrophysiology, cell injection, ultramicrotomy, photomicroscopy, scanning probe microscopy, and confocal laser scanning microscopy.

The key element in our 63-500 Series Micro-g lab table and many other TMC vibration isolation tables is our Gimbal Piston™ Air Isolator. These passive pneumatic air isolators achieve outstanding vertical and horizontal vibration isolation down to very low frequencies and input levels. The Gimbal Piston can also stabilize isolated systems with relatively high centers of mass without compromising vibration isolation.

NOTE: CleanBench™ has replaced the 63-500 Series Lab Tables, however, they are still available for a limited time.
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.




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.

A Subshelf offers additional storage space. It can be mounted beneath the isolated table top and may be retrofitted.
TMC's Precision Height Control Valves. To 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
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.
The Type II 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.

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.





Specifications




 

 

 

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.

Tiebar Gussets
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.

 

Superior Table Tops
Our standard laminated tops provide an attractive stainless steel ferromagnetic working surface with highly damped, high stiffness construction at low cost. For applications requiring the ultimate stiffness and damping or mounting holes, specify our patented CleanTop® II honeycomb top.




Which top is best for you?

CleanTop

 

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).

 

Stainless Steel laminateStainless 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).







Features




Performance
Micro-g ordering chart




Gimbal Piston




Ordering Chart