Foot traffic, highway traffic, air conditioner blowers, and furnaces are just a few of the sources that can interfere with vibration-sensitive equipment and experiments. Conversely, shakers can create unwanted vibration. Using a sprung platform could mitigate the problems.
When an engineer’s efforts are thwarted by vibration, when vibration interferes with a project, the response is to reduce (attenuate, lessen) the troublesome vibration. Alternate
ly, you can isolate or protect or cushion activities from the troublesome vibration.
“Control” is wrong verb. I don’t like to say that you control the unwanted vibration, even though some engineers use that phrase. Do we ever control vibration? Yes, indeed. When we’re performing vibration tests, using a shaker, we control the shaker’s vibratory force and frequency. I want to save the word “control” for that application. It’s not appropriate for this discussion.
A cleanroom can be damaged by building vibration and protecting it is feasible in a to-be-constructed building. Just erect your cleanroom upon a very expensive isolate
d platform similar to Figure 1. That platform is supported on numerous isolators, pistons inside the air-filled cylinders of Figure 2. It’s a pricey option and such a cleanroom support would be even more expensive when placed into an existing building.
This is an impractical and “not in the budget” solution to protecting a delicate apparatus that can’t be floor-mounted because of building vibrations.
Cushion your experiment
So you want to isolate, to protect, your delicate assembly or delicate experiment from building vibrations that are caused by nearby foot traffic, by air conditioner pumps and blowers, by a furnace, by production machinery, by office printers, etc.? Also by aircraft flyovers, by nearby railroad and highway traffic? Rather than “hard mount” your delicate assembly or delicate experiment onto an ordinary lab floor, cushion it. Mount it on the “sprung platform” I’m going to describe. (The idea is oversimplified by Figure 3). 
Sprung platform
Build a rather heavy “sprung” platform (not as massive as the Figures 1 and 2 platform, but dimensionally appropriate for attaching your apparatus). Position the platform on four or six compression springs. Much heavier springs, of appropriate total stiffness K, but shaped like those of Figure 4 (flat ends).
How stiff is Figure 3’s K in pounds/inch? That depends upon the total load W on the springs, in pounds, divided by the number of springs. It also depends on the natural frequency fn you want, about half the lowest frequency ff that’s disturbing you. Here’s a useful equation:
fn = 3.13/√δ
δ is the static deflection (change in length) of each spring, assuming they’re equally loaded. From δ = W/K, calculate the total K. Go purchase 4 or 6 appropriate stiffness springs. You probably need not worry about Figure 3’s damper C; your compression springs probably have adequate friction.
Some of my students direct environmental test labs, some run “shakers,” more formally called vibration exciters, some design fixtures for attaching specimens to shakers, etc. Collectively, they perform dynamic environmental tests, making sure that electronic and other hardware will function in locations and on vehicles (rockets, for instance) where vibrations are very severe. Relating to this article, shakers are often isolated to protect the buildings in which they function.
Wayne Tustin is President Equipment Reliability Institute, Santa Barbara, Calif., www.equipment-reliability.com. Upcoming seminars are February 18-20 in Santa Barbara, April 7-11 in Detroit, Mich., and June 3-5 at Boxborough, Mass. His vibration and shock test iBooks are offered by Apple Bookstore; ttp://goo.gl/xNWC49. iBook 5 expands upon this article.
