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Ultra-Low Frequency Vibration Isolation.... Continued from page 56
unit to test, as well as a negative- stiffness system, explains McMillan. “We compared the two systems, and the negative-stiffness system per- formed better with the frequencies of our concern, which were the lower frequencies caused by the move- ments of the building, between 10 and 24 Hertz.” McMillan was originally inter-
without affecting the static load-sup- porting capability of the spring. Beam-columns connected in series with the vertical-motion isolator pro- vide horizontal-motion isolation. A beam-column behaves as a
spring combined with a negative-stiff- ness mechanism. The result is a com- pact passive isolator capable of very low vertical and horizontal natural frequencies and very high internal
tions with frequencies above 0.7 Hz are rapidly attenuated with increase in frequency. Air tables, as vibration isolation systems, deliver limited iso- lation vertically and less isolation horizontally. They can make vibra- tion isolation problems worse, since they have a resonant frequency that can match that of floor vibrations. Air tables will actually amplify, instead of reduce, vibrations in a typ- ical range of 2 to 7 Hz, because of the natural frequencies at which the tables resonate. All isolators will amplify at their resonant frequency, and then they will start isolating. With air tables, any vibrations in that resonant frequency range could not only fail to be attenuated, they could be amplified. Also, transmissibility with neg-
Schematic of a negative-stiffness isolator.
ested in the negative-stiffness isolator because of reports that promised very good low-frequency vibration isolation in a small footprint, making it much easier to place in a compact box for thermal stability. “I put it on a cyclic accelerometer and it performed out- standingly,” continues McMillan. “Much better than any other vibration isolation we had used before.” In negative-stiffness vibration
isolation, vertical-motion isolation is provided by a stiff spring that sup- ports weight, combined with a nega- tive-stiffness mechanism. The net vertical stiffness is made very low
structural frequencies. The isolator provides 0.5 Hz vertical isolation, and 0.5 Hz horizontal isolation, using a totally passive mechanical system — no air or electricity required. For an isolation system with a 0.5 Hz natural frequency, isolation begins at about 0.7 Hz and im proves with increase in the vibration frequency. The natural frequency is more commonly used to describe the system performance. Negative-stiffness isolators res-
onate at 0.5 Hz. At this frequency there is almost no energy present. It would be very unusual to find a sig- nificant vibration at 0.5 Hz. Vibra -
ative-stiffness isolators is substan- tially improved over air systems. Transmissibility is a measure of the vibrations that are transmitted through the isolator relative to the input vibrations. The negative-stiff- ness isolators, when adjusted to 0.5 Hz, achieve 93 percent isolation effi- ciency at 2 Hz, 99 percent at 5 Hz and 99.7 percent at 10 Hz. “Over the past four years, we
have put six negative-stiffness isola- tion systems into the lab,” explains McMillan. “And since, we have relo- cated into quarters with less move- ment. Although we do still have some air tables in use, our staff and gradu- ate students prefer the negative-stiff- ness isolators.” Contact: Minus K Technology,
Inc., 460 Hindry Avenue, Unit C, Inglewood, CA 90301 % 310-348-9656 fax: 310-348-9638 E-mail:
sales@minusk.com Web:
www.minusk.com r
December, 2017
Machine Optimization: Is it Artificial Intelligence?
Continued from page 54
nicate machine-to-machine for auto- matic decisions or adjustments within process criteria. The above-referenced technology, which may seem impres- sive to some and child’s play to others, actually was developed and launched last century. It does, however, give a hint of the power and benefits to man- ufacturers that can be created this century. As an example, Vitronics Soltec,
a reflow oven manufacturer, has been shipping their ovens with a sim- ilar oven setup software that goes one step further. The reflow oven software includes an intelligent data- base that contains a rich library of these “cause and effect” observations. A user can simply enter the length, width and weight on the new PCB and the software will suggest the optimum oven setup without the need to run a single profile. With Industry 4.0 and the smart
factory trend ramping up, we are entering an exciting new world of run- ning machines and factories vastly more effectively, with lower cost and consistent quality. This is done while adding process transparency and traceability, machine learning, system interconnections, and much more. Contact: KIC, 16120 Bernardo
Center Drive, San Diego, CA 92127 % 858-673-6050 E-mail:
bjorn@kicmail.com Web:
www.kicthermal.com r
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