|Optical Table Support Legstand Basics
Choose The Support System That’s Best For Your Application
To complement our optical tabletops and breadboards, we offer two series of table supports to meet your vibration isolation needs and your budget. Our Model 505 Active-Air™ systems provide the best state-of-the-art vibration isolation for most critical applications. Our Model 500 series is a modular multi-modal support system that is initially supplied as a rigid system and can be upgraded with braces, casters, and passive, active-air or pendulum active-air vibration isolators.
For both series you can choose from five standard heights, 18" (457mm), 22" (559mm), 24" (610mm), 28" (711mm), and 32" (813mm), to accommodate standard tabletop or breadboard thickness and give you a variety of convenient working heights for your system.
Choose From Three Load Ranges
Experience shows that an isolator with a single load range will not perform efficiently for all applications. Unlike many manufacturers that offer only one load range, we provide isolators with three load ranges from which to choose: 500 lbs (227kg), 1000 lbs (454kg), and 2000 lbs (907kg) per leg. For best efficiency make your isolator selection based on operating at no more than 80% of maximum rated load. This provides the best possible isolator selection for your application. Our multiple load ranges enable you to obtain high vibration efficiency for your equipment, regardless of weight.
Active-Air™ Vibration Isolation
For superior vibration isolation at low frequency disturbances typical of buildings, choose from Model 505 Active-Air vibration isolation legs, 500A Active-Air “drop-in” isolator modules, or 500AP Active-Air pendulum “drop-in” isolator modules (see Figure 29.1). All our active-air legs and drop-in modules utilize the ideal low stiffness properties of air in a proprietary dual air chamber and damping orifice design (see Figure 29.2). In the 505, the entire leg is an air chamber to maximize air volume, and thereby provide the lowest physically possible vertical natural frequency to achieve the highest possible vertical isolation efficiency. Complementing our vertical performance, high efficiency horizontal isolation in the 505 and 500A is provided by our patented Kinematic Mod II horizontal isolation pistons, shown in Figure 29.2. In our 500AP active-air
pendulum drop-in module, horizontal isolation efficiency is further enhanced because the pendulum length is maximized to achieve the lowest possible horizontal natural frequency (below 1 Hz). In addition, the piston chamber’s thin wall, low hysteresis rolling diaphragm with negligible air permeability, insures frictionless motion. Eliminating friction assures isolation of micro-inch vibration disturbances which usually cause “jitter” in optical systems. Low air permeability is, of course, beneficial for operation with a bottled air source. Consult our engineering department when planning to use a bottled air supply. For automatic system leveling and height control, connection to a pressurized air source is required. KSI’s VIBRALEVEL™ servo valves in each table system then feed air from the pressurized air source, or bleed air from the legs, so the isolated tabletop is conveniently maintained at a preset zero-deflection level independent of load addition or removal. KSI’s zero-deflection active-air system conveniently provides the same isolation performance that would require over 10" deflection between zero and maximum rated load, in a conventional metal coil spring passive isolator design. VIBRALEVEL valves provide returnability of ±0.015". A precision option is available with ±0.0025" returnability.
Understanding Horizontal Vibration
In ideal terms, the vertical vibration response of an optical table on isolators is defined as a single degree-of-freedom system. The system is symmetrical about the vertical (gravity) axis, and a vertical force through the c.g. of the table produces only translation motion. Only one linear deflection parameter is required to define the position of the table in space. For horizontal forces and motion, since the isolators are beneath the table there is no symmetry with respect to the c.g., and a horizontal force through the table’s c.g. will simultaneously cause rotation (tilt) plus translation. Two deflection parameters are required, therefore the horizontal system (in one plane) has two degrees-of-freedom and two resonant frequencies. The rotation and translation occur simultaneously, therefore it can be shown that these are “coupled” to the vertical resonance with one slightly higher (upper rocking mode) and one slightly lower (lower rocking mode). These coupled resonances are a function of the inertia properties of the table and its load. There are an infinite variety of possible loads in service, therefore horizontal isolation test data can vary slightly from one application to the next. KSI horizontal data reflect typical service conditions and are presented without editing.We make our vertical natural frequency as low as practical so that the inherent horizontal coupling has negligible effect on high frequency isolation.
Passive-Air™ Vibration Isolation
For less critical applications, and where low frequency vibration below 10 Hz is not expected, our Model 500P Passive-Air™ module offers excellent high frequency vibration isolation. This is a simple unconstrained balloon-type omnidirectional airspring designed for our Model 500 modular Legstand. A “tire valve” permits inflation with a bicycle hand air pump. There is no need for a pressure gauge. Proper inflation is automatically indicated when the table floats freely.
Rigid-Passive-Active Modular Support System
For those with modest budgets or changing needs,we offer our Model 500 modular support system which starts as Model 500R rigid leg units with 3" (76mm) adjustable height screw jacks and a maximum load of 2000 lbs per leg. This unit is “upgradeable” at time of initial order or any time thereafter as a retrofit, with leg braces, 500RC retractable casters, 500P “add-on” passive-air mounts, 500A “drop-in” activeair vibration isolation, or 500AP active-air pendulum isolators as shown in Figure 29.1. Maximum load for passive-air add-on isolators is 1600 lbs (726kg) per leg; for active-air drop-in isolators there are two load ranges: 500 lbs (227kg) and 1000 lbs (454kg) per leg. Maximum load for the Model 500AP active-air pendulum is 1000 lbs (454kg) per leg.
4 Himmelblau, H. and S. Rubin, “Vibration of a Resiliently Supported Rigid Body”, Chap. 3,Vol. 1, Shock and Vibration Handbook, edited by C.M. Harris and C.E. Crede, pub. McGraw Hill, 1961.