Fabr Pneumatic 033009

Low Frequency

Pneumatic Isolation Solutions

Low FrequencyPneumatic Isolation Solutions

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GlobalThinking

�� Fabreeka® International, Inc.Corporate Headquarters - Stoughton, MA, USA

�� Fabreeka-Canada Ltd.

�� Fabreeka United Kingdom

�� Fabreeka GmbH Deutschland

�� Fabreeka Taiwan

Fabreeka® International has been a leader

in the field of shock and vibration control

since 1936. Our company provides vibration

isolation and shock control solutions for

industries worldwide.

Sound engineering principles and tested

performance support all of our isolation

systems. Fabreeka® is more than a

manufacturer of isolators. We engineer

solutions for your vibration and shock

problems.

� Service

� Solutions

� Products

Contact us at any one of our worldwide

facilities, listed on the back page, for

assistance.

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IntroductionThe purpose of isolation is to control unwanted vibration so itsadverse effects are kept within acceptable limits.

Technical Discussion - Pneumatic IsolatorsThe basics of pneumatic isolator design - natural frequency, dampingand transmissibility.

Design ServicesOur engineering team can provide vibration measurement & analysis,as well as dynamic, structural and finite element (FE) analysis as partof the total isolation solution.

ProductsPrecision-AireTM Leveling Isolators (PAL)Low frequency, self-leveling, pneumatic isolators that support loadsup to 120,000 lbs each.

Delta-KTM Pneumatic Isolation System ModuleProvides an increase in machine throughput by allowing fast measuring/positioning to occur at the machine’s designed accuracy.

Precision-AireTM Digital Electronic LevelingThe PA-DEL controller is used where higher leveling accuracyand an increase in isolator settling time is required.

RDS (Rapid Deflate System) and SSTTAATTUUSSThe RDS module allows for rapid system deflating for partloading/unloading. STATUS is position feedback indicating theheight of a floating system.

Precision-AireTM Pneumatic Leveling Mounts (PLM)Rugged, low frequency, pneumatic/elastomeric vibration and shockisolators.

ApplicationsPrecision Machine ToolsDiamond turning and high accuracy machine tools.

Metrology/InspectionCoordinate measuring, wafer inspection and sensitive inspectionequipment.

Automotive TestingApplications including engine test rigs, road simulators, shakers.

Aerospace TestingVacuum compatible isolators and vacuum chamber isolation.

Aircraft Ground Vibration TestingSoft support systems for aircraft ground vibration testing.

MRI/NMRVibration isolation solutions for MRI and NMR equipment.

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Introduction

Mechanical vibration and shock exist in allenvironments. Depending on how severe thedisturbance and how sensitive the equipment, theproblems caused by the vibration or shock can benegligible or destructive.

A vibration environment consisting of low levelseismic disturbances, present everywhere on earth,may be imperceptible to humans but can causeoperating problems for sensitive equipment. Add tothis everyday vibration created by vehicles, foottraffic, fork lifts, machinery and HVAC systems, andan even greater range of equipment is affected.

Vibrations originating from machines or othersources (acoustically) are transmitted to a supportstructure such as a facility floor, and can cause adetrimental environment and unwanted levels ofvibration.

Some of the equipment and processes affected byvibration include precision machine tools, coordinatemeasuring machines, magnetic resonance imaging(MRI/NMR) equipment, laboratory andsemiconductor processing equipment.

The purpose of vibration isolation is to controlunwanted vibration so that its adverse effects arekept within acceptable limits. Isolators are designedto provide vibration and shock protection to theseand other types of equipment.

If the equipment requiring isolation is the source ofunwanted vibration (i.e. shock and vibration testequipment), the purpose of isolation is to reduce thevibration transmitted from the source to the supportstructure. (Fig 1)

Conversely, if the equipment requiring isolation is arecipient of unwanted vibration (i.e. electronmicroscope, coordinate measuring machines), thepurpose of isolation is to reduce the vibrationtransmitted from the support structure to therecipient. (Fig 2)

An isolator is a resilient support that decouples anobject from steady state or forced vibration. Theprimary advantage to pneumatic isolators is thatthey can be designed to have vertical and horizontalnatural frequencies as low as 0.4 Hz to 5.0 Hz.Therefore, vibration isolation can be achieved atfrequencies as low as 0.7 Hz.

Low frequency vibration and shock can affect the accuracy, repeatability and throughput of precision measuring, positioning and manufacturing equipment. Since finer resolution of a finished product is required,manufacturing, metrology, engineering and research facilities require increased dynamic stability. Low frequency and ultra-low frequency vibration isolation is a method of improving the current vibration environment to achieve a significant increase in precision manufacturing accuracy or to offer a solution whichapproaches the “vibration free” domain.

Due to the accuracy of the machine’s measurements, acoordinate measuring machine is sensitive to certain amplitudesof vibration and shock. Pneumatic isolators provide lowfrequency vibration isolation to reduce environmental vibration.

A four-post road simulator test rig creates high amplitudevibration and shock at low frequencies to test vehicles for“squeak, rattle and roll” conditions. Pneumatic isolators reducethe vibration and shock transmitted to the environment.

Fig 1

Fig 2

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Technical Discussion

Pneumatic isolators consist of a volume of air (air chamber)that is sealed with a reinforced, flexible diaphragm. Whenpressurized, the isolator supports its payload using a piston,which is located on top of the diaphragm. (Fig 3)

The effective area of the diaphragm and the pressure on thediaphragm define the load capacity of the isolator. Thepressure in the isolator is controlled by a leveling valve thatcontrols both the internal pressure and “float” height of theisolator.

The typical pneumatic isolator design incorporates dual airchambers, a spring chamber and a damping chamber. In theFabreeka design, the damping chamber is separated from thespring chamber and connected by pneumatic tubing (seeDamping). This design concept can take different shapes,since only the total or “effective” volume is critical to thenatural frequency of the isolator (Eq 1). Note that thepressure (P) is proportional to the load (W), thus maintaininga constant natural frequency even when the load changes.

Where: Fn = natural frequency (Hz)g = gravity (in/sec2)

n = rate of specific heat of gasat constant pressure andvolume (1.4 for air)

W = weight of supported load(lbs)

Aeff = effective area of diaphragm

(in2)V = air volumePabs = absolute pressure (psig)

The stiffness of pneumatic isolators comesprimarily from the pressure and volume of agiven air column. The stiffness of apneumatic spring can be derived from thepressure-volume relationship of gas laws,assuming:

(a) Adiabatic compression(b) Any change in volume is small

relative to the initial volume

Yields:

Where:K = stiffness (lbs/in)n = ratio of specific heat for the gas(n = 1.0 for air at low frequencies

less than 1 Hz.)Pabs = absolute gas pressure of air

column (psi)Aeff = area of air column (in2)

From this expression it can be seen that theresponse of a mass supported by anundamped air spring is determined by thevolume of air.

Note that even when using a thin, flexiblediaphragm, the elastomeric material willexhibit an added stiffness at very lowpressures. This added stiffness affects thepneumatic contribution of the isolator. Toreduce this stiffness contribution, operatingpressures should be higher than 3 bar. Valvestiffness can also have an effect on theoverall stiffness of a pneumatic isolator.

Natural Frequency

Fig 3

Eq 1*

Eq 2

Damping ChamberVD

Piston

Spring Chamber

VS

Diaphragm

LevelingValve

*For operating pressures greater than 40 psi (3 bar).

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The purpose of damping in an isolator is to reduceor dissipate energy as rapidly as possible. Damping isalso beneficial in reducing vibration amplitudes atresonance. Resonance occurs when the naturalfrequency of the isolator coincides with thefrequency of the source vibration.

The ideal isolator would have as little damping aspossible in its isolation region and as much aspossible at the isolator's natural frequency to reduceamplification at resonance. Damping however canalso lead to a loss of isolation efficiency. (Fig 5)

To provide vertical damping for a system, a dampingchamber is connected to the spring chamber usingpneumatic tubing. (Fig 4) An expression for thedamping can be obtained by analyzing the rate ofchange of energy, which occurs when the air flowsbetween chambers. This expression is a function ofthe tubing and the volume ratio between the springand damping chambers.

The natural frequency (dynamic stiffness) anddamping properties of an isolator determine theisolator’s transmissibility.

The ratio of vibration transmitted after isolation tothe disturbing vibration is described as"transmissibility" and is expressed in its basic formin Equation 3, where Fd is the disturbing frequency

of vibration and fn is the natural frequency of the

isolator.

When considering damping, the equation isrewritten (Eq 4), where ξ represents the damping ofthe isolator.

Maximum transmissibility of an isolator occurs atresonance when the ratio of the disturbingfrequency to the natural frequency is equal to 1 (Fd / Fn = 1). At resonance the transmissibility is

given by equation 5. Note that the magnitude of anisolator's amplification at resonance is a function ofthat isolator’s damping.

Fig 5 graphically shows the transmissibility of anisolator as a function of the frequency ratio. Severalpercentages of critical damping are displayed toshow the effect of damping in the isolation region

Damping

Transmissibility

Eq 3

Eq 5

Eq 4

Damping is looked at carefully to give the besteffective isolation that can be achieved. For airspring-mass systems, damping is essential to stoptransient vibrations following a disturbance such asa stage or bridge moving and to limit the amplitudeof forced vibration at the isolator’s naturalfrequency. The length and diameter of the tubingare chosen for a given volume ratio to createlaminar flow in the damper. This design concept

AdjustableDamping

allows for a wide range of damping values to beused depending on the application. Damping isoptimum when the air flow in the tubing is laminarfor both large and small disturbances.

Fig 4

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and the amplification region, including the maximumamplification at resonance.

At frequencies greater than the square root of 2 (1.41) timesthe isolator’s natural frequency, isolation (reduction intransmissibility) begins. Isolation improves as a function of thefrequency ratio. The primary benefit of a pneumatic isolator isits low natural frequency and corresponding transmissibility atlow frequencies. 80% to 90% reduction can be achievedbelow 10 Hz even with high damping.

Note that as damping is increased, the curve oftransmissibility is flattened, so that in the region near toresonance (ratio = 1.0) the curve is reduced, but in the regionwhere isolation is required, the curve is increased. The curvesshow that if there is a significant amount of damping in anisolator, its natural frequency has to be reduced to retain thedesired degree of isolation at the frequency ratio of concern.

Fig 5

Theoretical (calculated) transmissibility curves do not indicate the vibrationamplitude input of the disturbing frequencies (Fd). All isolators, including

pneumatic isolators, can exhibit different dynamic natural frequencies as afunction of amplitude input. At low vibration amplitudes, isolators canbehave “stiffer” therefore having a slightly higher natural frequency. Thebehavior of isolators closely follows their theoretical transmissibility curvesfor larger vibration inputs.

Before a pneumatic isolation system isselected by analysis or test, the payload andits support base should also be evaluateddynamically for proper implementation. Poorstructural stiffness can compromise theisolation efficiency of a system. The supportbase or structure of a payload can beconsidered a spring, since its stiffness can becalculated or determined by test. If thepayload support structure is too “soft” andbends or deflects at low frequencies near thenatural frequency of the isolation system, theisolation effectiveness of the system isreduced.

To ensure that an isolator will perform asintended, it is good design practice to havethe support structure dynamic stiffness atleast 10 - 20 times higher than the isolator,depending on the application. Everystructure (frame, base, inertia mass) hasmass and stiffness. Structures also havemany frequencies at which they vibrate orresonate. These frequencies are calledstructural resonances and are a function ofthe shape, method of support and materialof the structure.

Recall from a transmissibility curve that whenusing pneumatic isolators, it is possible toachieve 80-90% isolation at frequenciesgreater than 10 Hz. Therefore, if the supportstructure stiffness is at least ten timesgreater than the isolator natural frequency,any vibration inputs at a structural resonancewill be significantly reduced. This is especiallyimportant when support structures arefabricated steel or aluminum. Since thesemetals have very little damping when excitedat their structural natural frequencies, theamplification at resonance is large. (Fig 6)

Application

IsolationRegion

AmplificationRegion

Measured transmissibility curves shouldindicate the input amplitude of the vibrationused during the measurement.

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When structural resonances are objectionable, aneffective solution could be to add damping to thestructure, which reduces amplification at thestructural resonance. Stiffening the structure mayalso help, since a structural resonance at a higherfrequency may not affect the total systemperformance.

A second criteria for proper implementation of apneumatic isolation system is the location/placementof the isolators. During design, the elastic plane ofthe isolators ideally should be in the same plane asthe composite center of gravity (CG) of the payloadand its support structure. In this manner, onlytranslational modes (horizontal and vertical) of theisolator are observed. Since all isolators are free tomove in all six axes (translational and rotational),rotational modes are also observed when theisolators are located below the center of gravity. (Fig 6)

When a payload vibrates purely in the verticaldirection, a transmissibility curve that is very similarto the theoretical curve in Fig 5 is created. However,in addition to structural modes, rocking modes arecreated when a payload vibrates in the horizontaldirection and the center of gravity is above theelastic plane of the isolators. Objectionable rocking

modes can be addressed by changing thelocation of the isolators, so that the rotationalmodes are “coupled” with the translationalmodes.

If the center of gravity is too high above theisolator’s elastic plane, instability can occur.Pneumatic isolator locations must satisfy therequirements for a stable system. Thisrequirement is met by positioning the isolatorswithin the limits of design guidelines for astable system. (Fig 7)

An industry standard is to consider a lineconnecting the center line of the isolators.Using this line as a base, construct a trianglewhose vertical height is 1/3 the length of thebase. If the projection of the center of massonto this plane lies within the triangle, thesystem will likely be stable and exhibitoptimum isolation and dampingcharacteristics.

Note: The relative position or distance of theisolators to each other in all axes of rotation isthe primary design factor for a stable system.Another important factor for stability is thedesign of the isolators. The damping rate,effective volume and valve flow are allvariables. Fabreeka® Engineers can provideproper recommendations for your application.

Fig 7

Fig 6

Transmissibility curve showing isolator translational and rotational frequencies, as well as support/machine base structural modes (resonances)above 80 Hz.

If the center of gravity is outside the triangle, the system is likelyto have stability problems. If this is the case, it is sometimespossible to modify the isolators in the field with additive dampingand/or a variable gain leveling valve to achieve stability. Additivedamping however, will slightly increase the stiffness of the systemand hence the vertical natural frequency of each isolator.

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Low frequency vibrations and large shock inputs canaffect the accuracy, repeatability and throughput ofprecision machines and equipment. Most precisionmachine tool and measuring machine manufacturershave established allowable vibration specificationsfor their machines. Fabreeka® utilizes highlyaccurate instrumentation to quantify the amplitudeand frequency of vibration to make proper vibrationcontrol recommendations.

Measurements with unique data analysisrequirements are performed regularly by ourEngineering staff for vibration isolation projectsworldwide.

Design Services

Fig 9 (middle right) Comparing site vibration levels to themanufacturer's specifications will determine the isolationefficiency required at the frequencies where themeasured vibration amplitudes exceed the machineallowable vibration criteria.

Vibration Measurement & Analysis Services

Fig 8 (above right) Vibration measurement softwarerecords amplitude and frequency data for analysis.Fabreeka® can provide vibration measurement servicesfrom any of our worldwide facilities.

Fig 8

Fig 9

Fig 10

Fig 10 (lower right) Fabreeka® Engineers also conductacceptance test measurements after isolation systeminstallation. Acceptance test measurements provide theresultant vibration amplitudes after isolation is installed.

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Dynamic and Finite Element Analysis

As mentioned in the technical discussion(page 7), the dynamic response of a supportstructure is part of the total system vibrationsolution.

Examining mode shapes in a vibratingstructure is a valuable step in adjustingvibration amplitudes at critical points byvarying the stiffness, mass and damping.

A finite element analysis will define andmodel the mode shapes and responsefrequencies of a structure, as well as theresponse of the isolation system to machine-induced inputs and/or environmental inputs.

Mode shapes (stiffness in each axis) identifythe physical direction of each frequencymode and any deformations, such asbending or twisting. In general, a structure'smodes indicate the relative degree ofstructural stiffness among various points onthat structure. (Fig 11)

To be acceptable, the proposed design of afoundation or any support structure mustprovide a reliable structural configurationthat also meets the static and dynamiccriteria for the structure. Deflections causedby static loads or by dynamic forces/inputsshould be within acceptable limits. This

design approach requires modeling so that the real structurebehavior is predetermined and errors are minimized.

The calculations for the stiffness of a support structure yieldthe static and dynamic behavior and stress concentrationpoints that occur. Stresses are related to the geometry of thestructure and the distribution of loads and forces acting uponit. A stress analysis will indicate the magnitude of stressimposed by static and dynamic loading. (Fig 12)

Fig 11First three structural modes of a concrete support foundation for an MRI unit.

Fig 12Stress analysis of a steel support frame for an electron microscope. Theframe will also be analyzed dynamically for structural modes (resonances).

Mode 7: 69.58533 Hz. Mode 9: 99.11916 Hz.Mode 8: 73.43653 Hz.

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Precision-AireTM Leveling Isolators (PAL)

Fabreeka’s® Precision-AireTM Leveling (PAL) modelpneumatic vibration isolation systems use servocontrolled air springs. These isolators are ideallysuited for conditions where height control andvibration control must co-exist. Fabreeka PALisolators meet the critical needs of metrologyinstruments, electron microscopes, inspectionstations and precision manufacturing equipment.

PAL Isolators Description

The standard Fabreeka® PAL isolators have a naturalfrequency as low as 1.7 Hz, however, lower naturalfrequencies (0.5 Hz) can be obtained from customdesigned isolators.

A complete Fabreeka® PAL system consists of aminimum of three master isolators for 3-pointdeterminate leveling. Each isolator incorporates aleveling valve which is the load sensing and heightcontrolling element. Any number of support isolatorsmay be added to support the total weight of theequipment.

Systems are supplied with a control panel, automaticheight control valves, tubing and all other pneumaticaccessories necessary for complete systeminstallation.

PAL Isolator Performance

PAL isolators react quickly to changes in thesupported load and to center of gravity shifts byautomatically releveling to a preset position.

A pneumatic isolation system’s performance is acompromise between natural frequency (isolation),valve leveling accuracy and settling time.

Settling time can be defined as the time it takes foran isolation system’s motion to return to apredetermined reference with respect to a definedinput disturbance. The disturbance can be anenvironmental input or machine induced, such as agantry or stage movement.

Settling time is minimal with optimum damping andcorresponding valve flow. Long settling times usingpneumatic isolators are unacceptable becauseprecision measuring and positioning machines cansuffer repeatability errors and throughput losses.

Fabreeka offers many leveling valve optionsdepending on the application. Valve flow rate,stiffness and accuracy characteristics are keyvariables in the design of an acceptable solution.Leveling accuracies of +/- 0.006” (0.15 mm) or +/-0.001” (0.025 mm) are available. The flow rate andstiffness of a valve are chosen based on the isolatordesign and damping.

PAL isolators integrated into a coordinate measuring machinesupport frame.

Products

PAL-type pneumatic isolators provide superior lowfrequency isolation for metrology instruments,electron microscopes, MRI units, coordinatemeasuring machines and precision manufacturingequipment.

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Isolation Characteristics/Specifications Isolator Dimensions*

H H Max Lifting Capacity1

Type D1 D2 Deflated Max. Lift L lbs Kg

PAL 18-66.50 in

165 mm6.00 in

152 mm6.00 in

153 mm6.25 in

160 mm9.21 in

234 mm1,800 800

PAL 21-67.87 in

200 mm5.90 in

150 mm6.00 in

153 mm6.40 in

163 mm10.60 in270 mm

2,100 950

PAL 21-127.87 in

200 mm7.87 in

200 mm12.00 in305 mm

12.40 in315 mm

10.60 in270 mm

2,100 950

PAL 36-68.65 in

220 mm7.50 in

190 mm6.00 in

153 mm6.40 in

163 mm11.40 in290 mm

3,600 1,630

PAL 55-610.25 in260 mm

9.00 in230 mm

6.00 in153 mm

6.40 in163 mm

13.00 in330 mm

5,500 2,500

PAL 55-1210.25 in260 mm

10.25 in260 mm

12.00 in305 mm

12.40 in315 mm

13.00 in330 mm

5,500 2,500

PAL 75-611.80 in300 mm

10.45 in265 mm

6.00 in153 mm

6.40 in163 mm

14.55 in370 mm

7,500 3,400

PAL 133-615.00 in380 mm

13.78 in350 mm

6.00 in153 mm

6.40 in163 mm

17.70 in450 mm

13,300 6,030

PAL 133-1215.00 in380 mm

15.00 in380 mm

12.00 in305 mm

12.40 in315 mm

17.70 in450 mm

13,300 6,030

PAL 255-620.87 in530 mm

18.50 in470 mm

6.00 in153 mm

6.50 in165 mm

23.60 in600 mm

25,500 11,560

PAL 255-1220.87 in530 mm

18.10 in460 mm

12.00 in305 mm

12.50 in317 mm

23.60 in600 mm

25,500 11,560

PAL 416-825.20 in640 mm

23.00 in585mm

8.00 in203 mm

8.45 in215 mm

28.00 in710 mm

41,600 18,870

PAL 1000-637.40 in950 mm

35.80 in910 mm

6.00 in153 mm

7.00 in178 mm

40.15 in1020 mm

100,000 45,360

PAL 1000-1835.98 in914 mm

35.98 in914 mm

17.70 in450 mm

18.70 in475 mm

39.00 in990 mm

100,000 45,360

1At maximum working pressure of 100 psi (7 bar)

Natural Frequency (-6) (-12)Vertical 2.5 - 2.7 Hz 1.5 - 1.7 HzHorizontal 2.0 - 4.5 Hz 2.0 - 4.5 Hz

DampingVertical (Adjustable) 6% - 20% 6% - 20%Horizontal 5% - 6% 5% - 6%

*Verify actual dimensions with Fabreeka®. Dimensions subject to change.

1At maximum working pressure of 100 psi (7 bar)

Isolation Characteristics/SpecificationsPendulum Isolators

Isolator Dimensions*

H H Max Lifting Capacity1

Type D1 D2 Deflated Max. Lift D3 lbs Kg

PAL 21-15P7.87 in

200 mm11.00 in279 mm

15.00 in381 mm

15.40 in391 mm

N/A 2,100 950

PAL 55-15P10.25 in260 mm

18.50 in470 mm

15.00 in381 mm

15.40 in391 mm

23.75 in603 mm

5,500 2,500

PAL 55-52P10.25 in260 mm

18.50 in470 mm

52.00 in1321 mm

52.40 in1331mm

23.75 in603 mm

5,500 2,500

PAL 75-19P11.63 in295 mm

14.88 in378 mm

19.00 in483 mm

19.40 in493 mm

N/A 7,500 3,400

PAL 133-36P15.00 in380 mm

24.50 in622 mm

36.00 in914 mm

36.40 in924 mm

31.50 in800 mm

13,300 6,030

PAL 133-60P15.00 in380 mm

24.50 in622 mm

60.00 in1524 mm

60.40 in1534 mm

31.50 in800 mm

13,300 6,030

PAL 255-36P20.87 in530 mm

30.50 in775 mm

36.00 in914 mm

36.45 in926 mm

37.50 in953 mm

25,500 11,560

PAL 255-60P20.87 in530 mm

30.50 in775 mm

60.00 in1524 mm

60.45 in1536 mm

37.50 in953 mm

25,500 11,560

PAL 416-36P25.20 in640 mm

36.50 in927 mm

36.00 in914 mm

36.45 in926 mm

45.00 in1143 mm

41,600 18,870

PAL 416-60P25.20 in640 mm

36.50 in927 mm

60.00 in1524 mm

60.45 in1536 mm

45.00 in1143 mm

41,600 18,870

Natural Frequency (-15/-19) (-36) (-52/-60)Vertical 1.3 - 1.5 Hz 0.9 - 1.0 Hz 0.7 - 0.9 HzHorizontal 1.3 - 1.5 Hz 0.6 - 0.7 Hz 0.4 - 0.5 Hz

DampingVertical (Adj) 6% - 20% 6% - 20% 6% - 20%Horizontal (Adj) 3% - 6% 3% - 6% 3% - 6%

*Verify actual dimensions with Fabreeka®. Dimensions subject to change.

Pendulum Isolators

Specially designed diaphragms may be used to lowerthe horizontal natural frequency of an isolator toapproach 1.5 Hz. Alternatively, natural frequenciesas low as 0.4 Hz can be achieved using pendulums.The pendulum natural frequency is given by Eq 6,where L is equal to the length of the pendulum.

Eq 6

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At right, PAL 133-36P pneumatic isolators support a 80,000 lbreaction mass for a large NMR magnet. The vertical andhorizontal natural frequencies are 1.0 Hz and 0.7 Hz.

Custom/OEM Isolators

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Leveling Valves

*Lever arm will change accuracy; however will increase stroke.

A wide range of leveling valves are available. Leveling valves haveaccuracies from +/- 0.006” (0.15 mm) to +/- 0.001” (0.025 mm)*with adjustable flow rates to accommodate applicationrequirements. Valve stiffness, flow rate and accuracy are importantvariables to optimum isolator settling time and isolation efficiency.

H H Max Lifting Capacity1

Type D1 D2 Deflated Max. Lift L lbs Kg

PAL 3-2.53.20 in80 mm

3.20 in80 mm

2.50 in64 mm

2.75 in70 mm

6.20 in157 mm

260 115

PAL 4-3.56.00 in

152 mm4.00 in

102 mm3.50 in89 mm

3.75 in95 mm

8.00 in203 mm

295 130

PAL 5.5-2.53.95 in

100 mm3.95 in

100 mm2.50 in64 mm

2.75 in70 mm

6.95 in177 mm

480 210

PAL 9-45.10 in

130 mm5.10 in

130 mm3.65 in94 mm

3.95 in100 mm

8.15 in207 mm

735 330

PAL 9-65.10 in

130 mm5.10 in

130 mm6.00 in

153 mm6.25 in

159 mm8.71 in

221 mm735 330

1At maximum working pressure of 100 psi (7 bar)

Isolators for OEM applications or having custom requirements areavailable for easy integration into machine designs. For cleanroomapplications, the exhaust air from the leveling valves is vented andthe isolators are made using cleanroom compatible materials,cleaned and packaged. Isolators can also be made using non-magnetic materials.

Class 100,000 cleanroomcompatible isolator.

Cradle Platforms and Machine Frames

An important criteria for proper implementation ofpneumatic isolators is their location/placement underthe equipment or machine being isolated. In thesystem design, the elastic plane of the isolatorsshould be as close to the center of gravity of thepayload and its support structure as possible.

Rocking modes are created when a payload vibratesin the horizontal direction and the center of gravityis above the elastic plane of the isolators. If thecenter of gravity is too high above the isolator’selastic plane, instability can occur. Pneumatic isolatorlocations must satisfy the requirements for a stablesystem. (Fig 7, page 8)

A cradle support frame is used to position theisolators closer to the center of gravity to reducerocking. (Illustration, upper right) A cradle is alsoused when a machine’s base cannot be modified toaccept isolators and a rigid support frame isrequired.

The structural and dynamic design of the cradle iscritical. (Fig 12, page 10) Stresses and deflections(bending) due to machine/equipment weight andthe dynamic stiffness (structural resonances) are partof a successful solution using PAL or PLM pneumaticisolators.

Cradles and custom designed frames increase thestability of self-leveling pneumatic isolation systemsby lowering the center of gravity.

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Air bag type isolators can have vertical andhorizontal natural frequencies from 1.2 to 4.0 Hz,depending on the floatation height and style of airbag (single, double or rolling convolution). Thehorizontal spring rate (stiffness) and air bag stabilityare also a function of the flotation height. Each typeof air bag has an optimal flotation height for thesereasons. Lower vertical natural frequencies can beobtained by adding additional air volume, such asan auxiliary tank.

One of the features of an air bag type isolator isthat they provide a large stroke when inflated. Liftor float heights can be 2” - 3”, depending on thestyle of convolution. Therefore, air bag isolators areable to be designed into applications where largedynamic displacements are a factor.

Air bags and diaphragm-type pneumatic isolatorshave very little damping (3% - 4%) unless adamping volume is connected to the isolatorvolume. Most designs will require 10% - 15%damping, depending on the application and thespecifications for isolation and settling time.

A complete isolation system consists of a minimumof three master isolators for 3-point determinate leveling. Each isolator incorporates a leveling valvewhich is the load sensing and height controlling element. Any number of support isolators may beadded to support the total weight of theequipment.

Systems are supplied with a control panel,automatic height control valves, tubing and all otherpneumatic accessories necessary for completesystem installation.

Air Bag Isolators

Air bag isolators provide a low natural frequency and largedynamic stroke where dynamic deflection is acceptable.

Single convolution air bag isolator with damping chamberand leveling valve supporting a reaction mass forelectrodynamic shaker.

Double convolution air bags designed with additional airvolume (auxiliary tanks), damping chambers and levelingvalves. This isolation system supports a reaction mass witha bedplate for an engine/dynamometer test rig.

Air bag type pneumatic isolators provide lowfrequency isolation for test rigs, large reactionmasses and applications where large dynamicdisplacements and lift height are required.

The Fabreeka® Delta KTM (DKTM) controller works withlow frequency, pneumatic isolation systems toprovide both vibration isolation and an increase inrepeatability and throughput by allowing themeasuring machine to operate at its designedacceleration in harsh environments.

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Delta KTM Pneumatic Isolation System Module

DK should be considered for any precisionmeasurement machine that requires pneumaticisolation combined with rapid measurements. Thevibration isolation system with DK controller isspecifically designed to have a very high (stiff) springrate when the machine is moving and a very low(soft) spring rate when the machine is measuring.

As the moving portion of the machine acceleratesand decelerates to the point of measure, the stiffisolators with high damping prevent excess machinemotion, reducing settling time prior tomeasurement. At the time of measuring, the DKcontroller receives a signal from the stylus/probe ormachine controller and changes the stiffness anddamping of the isolation system, converting it to asofter isolation system. In effect, the isolatorsundergo a change in stiffness (DK). (Fig 13)

Benefits of using a Fabreeka® DDKTM

controller:

�� Improvement in machine repeatability whenmachine requires isolators

�� Rapid settling time

�� Allows machine to operate at 100% accelerationwithout degradation to accuracy or repeatability

�� DDK can be used on existing pneumatic isolationsystem installations to improve machine/isolationperformance

�� DDK controller works with both "touch trigger" and"strain gauge" type probes

Fig 13

Delta K pneumatic isolation system module allows the Brown &Sharpe Global 7.10.7 CMM to operate at its designed speedand accuracy when supported on pneumatic isolators.

Working Principle

Low frequency and large amplitude vibrations canaffect the accuracy, repeatability and throughput ofprecision measuring machines. A pneumaticisolation system must provide isolation ofenvironmental vibration and shock while minimizingrelative motion between the workpiece andstylus/probe.

Precision-AireTM Digital Electro-Pneumatic Level Control (PA-DEL®)

18

�� Fully digital control circuit (controller, amplifier,valves) allows for feed forward or feedbacksignal processing

�� Digital control algorithm allows for optimumcontrol parameters with combined pulsewidth/pulse frequency modulation

�� “Docking” or deflating to a preset position forpart loading/unloading

�� Programming of the controller and setting of thecontrol panel parameters are done via serial port

�� Connection of the PA-DEL controller to existingSPS machine controllers is possible forimplementation into process automation

�� Optionally equipped with remote control, soleveling of very large applications can beexecuted by one person

�� Rack mountable via standard 19-inch mountingor standalone chassis

The PA-DEL utilizes a digital controller, non-contactposition sensors and high-flow electronic valves toenhance the performance of self-leveling pneumaticisolation systems. The electronic valves and positionsensors allow the isolators to re-level three timesfaster than traditional mechanical leveling valves.The leveling accuracy of the PA-DEL controller is +/-20 µm (microns), and the electronic valve flow ratecan be adjusted for isolators of all sizes. The PA-DELcan be installed on existing pneumatic isolationsystems where an increase in throughput is desiredwithout sacrificing vibration isolation.

The PA-DEL digital electro-pneumatic levelingcontroller is for use with pneumatic isolation systemswhere a higher leveling accuracy and increase inisolator settling time is required.

�� Non-contact position sensing, therefore no“vibration shortcut” possible between theisolated machine and the environment

�� Measuring range of the sensors up to 45 mm

�� Optional customized sensors may be used(voltage or current types)

�� Accuracy of the position control can be adjusteddepending on the application to +/- 20 µm

Position ControlOperating Features

19

SSTTAATTUUSS

RDS Rapid Deflate SystemRDS is ideal for applications where the isolatedmachine must be positioned at a reference datumprior to loading/unloading parts for measure.

The RDS components can be added to anypneumatic control panel to enable the operator toquickly lower or raise a machine supported by apneumatic isolation system. This is especiallyimportant for large measuring machines requiringfoundations and many isolators.

RDS deflates and inflates five to ten times fasterthan allowing the air pressure to exhaust backthrough the leveling valves. Only 10 psi (0.7 bar) ofpressure is used, so that the isolators remainpressurized until re-inflated. Connection of the RDSto existing machine controllers is possible forimplementation into process automation.

The STATUS controller uses proximity sensors tomonitor the floating or inflated position of apneumatic isolation system. The sensors are installedon the three master isolators of any pneumaticisolation system.

If a master isolator or any isolator in its groupdeflates or is lowered out of an acceptable inflatedposition, the STATUS controller will indicate thatthere is a problem via a red LED. An audible alarmcan be added as an option.

Often it is not possible to visually verify that isolatorsare in their proper inflated position, especially wheninstalled under large foundations. Isolators candeflate or lower when leveling valves are subjectedto moisture or oils in the air supply.

Existing systems can be easily upgraded in the field withRDS.

STATUS can be installed on any existing pneumaticisolation system or isolation table.

Precision-AireTM Pneumatic Leveling Mounts (PLM)

20

At left, an electro-dynamic shaker that produces a force rangeof 18,000 lbf (80 kN) to 50,000 lbf (222 kN). This testequipment is installed on PLM mounts to reduce the vibrationcreated during testing.

PLM mounts provide low frequency vibration andshock control for surface plates, coordinatemeasuring machines, fans, air compressors,motor/generator sets, high-speed punch pressesand more.

PLM Mount Specifications

3.00 in76 mm

4.19 in106 mm

5.12 in130 mm

6.88 in175 mm

10.0 in254 mm

13.50 in343 mm

18.50 in470 mm

24.00 in610 mm

2.38 in60.5 mm

3.50 in89 mm

4.25 in108 mm

6.00 in152 mm

8.50 in216 mm

12.00 in305 mm

16.00 in406 mm

20.00 in508 mm

0.28 in6.9 mm

0.28 in6.9 mm

0.29 in7.4 mm

0.29 in7.4 mm

0.56 in14.2 mm

0.56 in14.2 mm

0.81 in20.6 mm

0.81 in20.6 mm

0.375-16M10

0.500-13M12

0.500-13M12

0.500-13M12

0.625-11M16

0.625-11M16

1.000-14M24

1.000-14M24

0.47 in12.0 mm

0.53 in13.5 mm

0.53 in13.5 mm

0.53 in13.5 mm

0.75 in19.0 mm

0.75 in19.0 mm

0.88 in22.4 mm

0.88 in22.4 mm

2.88 in73 mm

4.14 in105 mm

4.99 in127 mm

6.74 in171 mm

9.66 in245 mm

13.31 in338 mm

18.44 in468 mm

24.00 in610 mm

1.00 in25 mm

1.75 in44 mm

2.13 in54 mm

3.00 in76 mm

4.75 in138 mm

7.50 in190 mm

10.50 in267 mm

15.75 in400 mm

2.50 in65 mm

2.45 in65 mm

3.50 in90 mm

3.50 in90 mm

3.50 in90 mm

3.50 in90 mm

3.50 in90 mm

3.50 in90 mm

0.125 in3.2 mm

0.125 in3.2 mm

0.125 in3.2 mm

0.125 in3.2 mm

0.188 in4.8 mm

0.188 in4.8 mm

0.250 in6.4 mm

0.250 in6.4 mm

100 lbs45 Kg

300 lbs136 Kg

600 lbs272 Kg

1200 lbs544.3 Kg

2400 lbs1089 Kg

4800 lbs2177 Kg

9600 lbs4354 Kg

19200 lbs8709 Kg

ModelDimensions

A B C D* E F G H I

PLM 192

PLM 96

PLM 48

PLM 24

PLM 12

PLM 6

PLM 3

PLM 1

Max Load

*Metric threads available upon request. Verify actual dimensions with Fabreeka.

The Fabreeka PLM series pneumatic isolation mountsare low frequency vibration and shock isolators that provide both attenuation of disturbingvibration and equipment leveling.

For vibration control applications, the pneumatic(pressurized) portion of these mounts providessignificant reduction of vibration amplitudes occurringat frequencies above 5 Hz, having a natural frequency as low as 3 Hz.

PLM isolation mounts will also continue to isolatewith no pressure having a vertical natural frequencyof approximately 10 Hz, isolating frequencies above14 Hz.

The vertical to horizontal natural frequency ratio isapproximately 1:1 with a high degree of horizontalstability.

For shock or impact applications, the outerelastomeric wall construction provides a highdeflection shock mount. A low natural frequency (3 Hz) can be maintained by utilizing an externalspacer to prevent a “bottom out” condition.

21

Low profile, leveling valves can be used with the PLMisolation mounts when automatic height control isrequired.

PLM-3 mounts are integrated into the frame of Carl ZeissEVO series SEM microscopes. The chamber and columnare isolated to provide greater than 300,000 times magnification for X-ray geometry and electron imaging.

Features

The Fabreeka® PLM design includes a moldedthreaded insert which allows the mounts to beinflated via either the standard tank valve or apneumatic fitting. No custom adapters are necessary.

Supplied with a tank valve, the isolators are inflatedand leveled manually using a hand pump or air chuckconnected to an air supply. When supplied with a fitting, the mounts can be plumbed to a dedicated,regulated air supply making pressurizing and levelingeasier. A regulator control panel (right) can be supplied to regulate the pressure and height of theinterconnected mounts when leveling valves are notused.

The PLM mounts can also be supplied with automaticleveling valves for height control. Each master isolator incorporates a leveling valve, which is theload sensing and height controlling element. Anynumber of support isolators may be added tosupport the total weight of the equipment.

Systems can be supplied with a control panel, automatic height control valves, tubing and all otherpneumatic accessories necessary for complete systeminstallation.

Precision Machine Tools

Applications

22

(Photo courtesy of Precitech)

(Photo courtesy of X-TEK)

(Photo courtesy of Motion X)

(Photo courtesy of Precitech)

The degree of precision required for precisionmachine tools is ever-increasing. Equipment thatcuts, turns, polishes and positions withnanotechnology can provide finishes andmeasurements within microns and even angstroms.

Ultra-precision equipment is used in many industriesincluding semiconductor wafer processing,optics/lens manufacturing and non-standardmaterial machining processes.

High accuracy positioning equipment includingdiamond turning lathes, X-Y stages and CDmetrology machines typically utilize laserinterferometry (position feedback) to positionmaterials to be inspected with nanometerspecifications. Additionally, equipment such asprofilometers, form/contour androughness/roundness machines are required toprovide sub-micron measurements.

Machine capabilities include ultra-precision turningand microgrinding of materials such as optical glass,crystals, non-ferrous metals, polymers and ceramics.The surfaces of these materials are machined suchthat the results typically require little or no polishingwith surfaces having sub-micron finishes. Productsmade via this process include CD's, contact lenstooling, optical lens components and mirrors forlaser applications.

Fabreeka® provides precision equipmentmanufacturers and end users with low frequencyvibration and shock isolation systems to maintainthe designed accuracy of this equipment. Someapplications require custom systems and structuralanalysis and design of the support structures andframes used in conjunction with the isolation systemand integrated in the machine design.

Metrology/Inspection Equipment

The measuring speed and accuracy of CoordinateMeasuring Machines (CMM's) are improving everyyear. Newer CMM's are being designed and built tobe shop floor "hardened" so they can function withrepeatability right on the production floor. Vibrationis one environmental factor which can compromise aCMM's accuracy and repeatability.

Ideally, if all components of a CMM, including thepart to be measured, were to vibrate in unison at aspecific frequency, amplitude, phase and orientation,no degradation in measured performance wouldresult. To the CMM, this situation would representthe same condition as no vibration excitationwhatsoever, since all parts of the CMM would besynchronized relative to one another. Whencomponents begin to move out-of-phase with eachother or a structural resonance is excited, accuracyproblems can occur.

Without compromising accuracy, CMMmanufacturers provide their users with the maximumlevels of vibration which their machines are capableof withstanding. This allowable vibration criteria is animportant factor when considering if a machinerequires vibration isolation or not.

23

Fabreeka® International has a leading role in providingvibration isolation systems and design techniques tomeet the increasing demands of vehicle testing in simulated environments. Fabreeka® regularly providesisolation solutions for many applications includingdynamometers, engine test rigs, road simulators andmulti-axis shaker tables. Fabreeka’s® technicalexpertise includes the structural design of supportstructures and reaction masses; static and dynamicanalysis and acceptance testing.

Automotive Testing

24

Engine/dynamometer testing on bedplate and supportfoundation.

Multi-axis shaker table vibration/dynamic analysis

Rolling road test equipment on isolated support foundation

(Photo courtesy of Schenck)

Four-post actuator/road simulator

Aerospace Testing

25

Fabreeka® provides low frequency vibration isolationsystems for critical testing applications in theaerospace/defense industry, which require ultra-lowfrequency isolation. Applications often include nano-type measurements and can have error budgetswithin microns or tenths of arc seconds.

When performing testing of large spacecraft orhardware that will be launched into orbit, it isnecessary to conduct testing in a space-simulatedenvironment. To achieve this, a vacuum chamber orthermal vacuum chamber is used, which creates anenvironment to simulate the pressure and thermaleffects of launch or space travel.

In cases where the size of the chamber, or theexisting chamber, does not allow for "external"isolators, the test payload must be isolated inside thechamber. To achieve this, a vacuum compatibleisolation system is used. When isolators are usedinside a vacuum chamber, they must meet strictmaterial specifications to limit outgassing and beconstructed to meet particulate and molecularcleanliness requirements as well. Additionally, inthermo-vacuum applications, the isolators may berequired to operate in temperature extremes whereheater blankets are necessary to keep the isolatorsat an operable temperature.

Vacuum compatible, pneumatic isolator materialshave a total mass loss (TML) of 0.85% and a collected volatile consumable material (CVCM) limitof 0.09%. Fabreeka’s® design can operate in a 1 x 10-6 Torr environment and have a maximumleak rate of 1 x 10-7 cc/sec.

(Photo courtesy of B.F. Goodrich)

(Photos courtesy of NASA)

Fabreeka® has designed a number of "soft supportsystems" (SSS) using standard and custompneumatic isolators for ground vibration testing(GVT) of aircraft. To obtain accurate results duringGVT, the modal testing of the aircraft requiressimulation of a “free-free” condition. To achievethis condition, Fabreeka® works with the structuraland dynamics testing groups of aircraftmanufacturers to design the required SSS for theGVT.

The pneumatic isolators support and decouple theaircraft from the ground when the aircraft isundergoing dynamic testing and modal/flutteranalysis. The role of the system is especiallyimportant in identifying structural resonances andvalidating flutter models. The SSS can also include ajacking system to lift the aircraft off of its landinggear.

Soft Support Systems for Ground Vibration Testing

26

(Photo courtesy of EADS)

Embraer 190 aircraft (Photo courtesy of Embraer)

F-35 joint strike fighter (Photo courtesy of Lockheed Martin)

Isolators used for GVT have vertical and horizontal naturalfrequencies as low as 0.5 Hz.

MRI / NMR Spectrometer Equipment(Magnetic Resonance Imaging / Nuclear Magnetic Resonance)

27

Fabreeka’s® commitment to the science of vibrationcontrol is shown by the technical expertise, productknowledge and design solutions offered to ourcustomers. Fabreeka® has provided vibrationisolation solutions for all types of high resolutionMRI, NMR and Cryostat equipment ranging in sizefrom 300 MHz to 900 MHz.

All isolator hardware for NMR applications is madenon-magnetic using stainless, aluminum or brass andis designed to interface with the existing magnetsupport brackets at the desired height.

Vibration isolation solutions include vibrationmeasurements and the design of the supportstructures, including structural and dynamic analysis.

Varian horizontal cryostat (Photo courtesy of Astra-Zeneca)

Above left, 800 MHz magnet supported on threePAL133-72P isolators (Photo courtesy of Magnex Scientific)

Above right, isolators for NMR magnets can be 42” to72” in height and have vertical and horizontal naturalfrequencies as low as 0.8 Hz.

(Photo courtesy of the Cleveland Clinic)

MRI equipment is typically supported by arecessed platform or inertia mass, which issupported on pneumatic isolators below theexamination room floor.

www.fabreeka.com

United States

PO Box 2101023 Turnpike StreetStoughton, MA 02072Tel: (781) 341-3655or: 1-800-322-7352

Fax: (781) [email protected]

Canada

Tel: 1-800-322-7352Fax: (781) [email protected]

United Kingdom

8 to 12 Jubilee WayThackley Old RoadShipley, West YorkshireBD18 1QGTel: 44-1274-531333Fax: [email protected]

Germany

Hessenring 13D-64572 , ButtelbornTel: 49-6152-9597-0Fax: [email protected]

Taiwan

14F, No. 230 HuanjungEast RoadJung-Li City320 TaiwanTel: 886-3-451-7989Fax: [email protected]

©2009 Fabreeka International, Inc. FAB 3000-310 03/09

*Fabreeka is a registered trademark of Fabreeka International, Inc.