- Smallest core cell size, highest core density. The CleanTop design does not require enlarging the steel honeycomb core cell size because CleanTop cups are cylindrical, not conical as found in plastic layer designs. CleanTop's average cell size of 0.5 in.(2) is at least 50% smaller than that achieved with plastic layer designs assuring the highest stiffness and greatest core-to-skin bonding contact area
- Steel to steel to steel. CleanTop achieves a spill-proof core with only two bonding layers: top skin to core and core to bottom skin. Imitations must add a third bonding layer which weakens the structure: top skin to plastic layer, plastic layer to core, and core to bottom skin.
- Thermal stability. The CleanTop all steel construction assures materials of identical coefficient of thermal expansion ensuring optimal thermal stability.
TMC's CleanTop Optical Top, available in a non-magnetic construction, is recommended for applications requiring the support of a high-strength magnet or the maintenance of a homogenous magnetic field.
Though no alloy of stainless steel can be 100% non-magnetic, the 316 alloy top and bottom layers offer a dramatic reduction in ferromagnetic properties. At the same time the sidewalls and cups are completely non-ferrous.
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 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. Holes are 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 core unnoticed.
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.
Support (Leg) Options:
TMC offers a wide variety of leg systems for CleanTop optical tables. Traditionally TMC optical tables are a great match with our Micro-g pneumatic vibration isolation systems, which provide the best balance between cost and performance.
For less vibration-sensitive applications we have rigid non-isolating legs, while ultra-sensitive equipment will benefit from our STACIS piezoelectric vibration cancellation technology solutions, such as LaserTable-Base.
Core: 304 steel alloy honeycomb, closed cell, 0.01 in. (0.2 mm) thick foil
Core shear modulus: 275,000 PSI (19300 kg/cm2)
Core cell size: < 0.5 in.2 (3 cm2)
Core density: 13.3 lb/ft3 (230 kg/m3)
Flatness: +/-0.005 in. (0.13 mm) within entire tapped hole pattern, regardless of table size | +/- 0.004 in. (0.1 mm) over a 2 x 2 ft (60 x 60 cm) area
Top and bottom skin: 316 alloy stainless steel - 3/16 in. (5 mm) thick
Sidewalls: Vinyl covered composite side with damped interior surface
Tapped holes: Backed by 1 in. (25 mm) long CleanTop nylon cups
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