Structural Damping –
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.
TMC's CleanTops are engineered using the most advanced methods for structural analysis and design. The Operational Deflection Shape shown above was measured using a technique called Laser Scanning Vibrometry (LSV). LSV is among the most sensitive and most accurate non-contact vibration measurement techniques commercially available. It uses the laser doppler effect to measure the behavior of the entire table rather than the behavior one discrete point.
Structural Damping Performance Summary – TMC optical tops have guaranteed performance levels which are unsurpassed. In addition, with three levels of broadband damping and three environmental choices, TMC offers the most flexibility in choosing a performance level. Guaranteed maximum compliance levels for the maximum damping level are tabulated in the plots 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 curves 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.
TMC's CleanTop Optical Top is the best method yet for providing a spill-proof, clean, precise, and corrosion resistant optical top with unmatched structural performance. CleanTop is now a standard feature of all TMC optical tops.
Individual CleanTop cups are epoxy-bonded under each tapped hole after it is tapped and cleaned. Cups are made from chemically resistant nylon 6, and stainless steel (304 alloy) cups are available. Holes are now tapped and countersunk prior to adding the cups to allow the machined top sheet to be thoroughly cleaned with open, rather than blind, holes prior to bonding. The top plate is processed through a custom TMC industrial cleaning center where a high pressure, high temperature cleaning solution is forced through each threaded hole, completely clearing any machining or tapping debris. Several rinse and dry cycles ensure an essentially "sterilized" top surface prior to bonding the cups.
CleanTop represents another innovation
in TMC's long optical top tradition of
industry "firsts" including:
• First spill-proof optical top (CleanTop).
• First all-steel optical top.
• First oil-free optical top.
• First honeycomb core registered
to the tapped hole array.
• First lightweight breadboard with formed
rather than drilled holes.
• First vacuum compatible optical top.
• Liquid spills on the surface are contained and
cannot reach the top's honeycomb core.
• The core is completely clean and dry with no
residual thread-cutting oils to out-gas.
• Extremely clean tapped holes make screw
insertion smooth and simple.
• Easy retrieval of small parts dropped into the
holes is assured.
• Since no penetration of the core is possible
when dangerous chemicals
are used on the top's surface, health hazards
will not occur by chemicals reaching the
Choose from Gimbal Piston Isolators or Rigid Supports –
Micro-g® gives you superior convenience and economy in acquiring precisely the equipment you need for supporting optical tables or other large work surfaces. The unique Micro-g design lets you customize basic features and still have off-the-shelf prices and speedy delivery. There are six categories of options, and the convenient selection charts help you construct a part number for ordering. Systems can also be easily upgraded – whether to convert from a leveling stand to an isolator or add casters – whenever required.
Isolators/Leveling Posts – If you need vibration isolation now, the choice is our Gimbal Piston™ isolators, which are unsurpassed in the industry for passive vertical and horizontal vibration attenuation – especially as demonstrated at realistic, low levels of input.
If a rigid stand will suffice for the present, Micro-g offers an economical leveling mount option with rugged, adjustable jack screws that provide +2 1/2 and - 0 in. (+62 and - 0 mm) of travel. Later, you can upgrade the system to full vibration isolation performance, with a total cost only slightly more than if you had opted for this feature originally.
Load Capacities – Depending on the weight of your table and onboard equipment, you can select support systems with capacities of 1,400, 4,000, 6,000, 10,000, or 15,000 lb (600, 2,000, 3,000, 4,500, or 7,000 kg, respectively). Customized systems can be configured from standard components to support virtually any structure.
Height – Seven post heights are available as standard: 12, 16, 18, 22, 24, 28, and 32 in. (300, 400, 450, 550, 600, 700, and 800 mm, respectively) – though not all sizes are available in all capacities. Taking into account the table thickness and height of equipment components, select the post size that provides the working height you need. Ergonomic convention would dictate 36 in. (900 mm) from floor to table top surface.
Tiebars – For safety reasons, tiebars are recommended. They are mandatory when you choose casters or anticipate upgrading to them. If you require constant access to the area under the table, free-standing support bases will provide more than adequate stability.
Casters – Micro-g's optional casters are of a rugged, heavy-duty design making an installed table easily movable when they are engaged. Once the table is positioned, the casters retract to establish solid floor contact during equipment operation. Like other Micro-g features, they can be integrated at the outset or purchased later if you choose to upgrade. Casters retract externally on the smallest capacity posts, internally on the intermediate, and are not available for the highest capacity. They are not available on posts less than 18 in. tall.
Configurations – A simple four-post frame configuration is the most common; however, depending on the size and shape of the supported structure and on the weight and position of onboard equipment, another multiple support system may be preferred. For unusual size tops or if you have any doubt as to your approach, please call us.
STACIS iX LaserTable-Base
Hybrid Piezoelectric/Air Active Vibration Cancellation System (more information about the STACIS iX LaserTable Base)