IEST RP-DTE009 1-1999 VIBRATION SHAKER SYSTEM SELECTION.pdf

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1、 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY Design, Test and Evaluation Division Recomended Practice 09.1 IEST-RP-DTE09.1 Vibration Shaker System Selection INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY Arlington Place One 2340 S. Arlington Heights Road, Suite 10 Arlington Heights, IL 60

2、05-4516 Phone: (847) 981-010 Fax: (847) 981-4130 E-mail: iestiest.org Web: ww.iest.org IEST-RP-DTE009.1 InstItute of envIronmental scIences and technology Copyrighted materialCOPYING IS ILLEGALIEST-RP-DTE009.1 InstItute of envIronmental scIences and technologyCopyrighted material COPYING IS ILLEGALT

3、his Recommended Practice is published by the InstItute of envIronmental scIences and technology to advance design, test, and evaluation technology and the technical and engineering sciences. Its use is entirely voluntary, and determination of its applicability and suitability for any particular use

4、is solely the responsibility of the user.This Recommended Practice was prepared by and is under the jurisdiction of Working Group 009 of the Institutes Design, Test, and Evaluation Division.Copyright 1997 by the Institute of Environmental Sciences and TechnologySecond printing, October 1999ISBN 978-

5、1-87786-58-8InstItute of envIronmental scIences and technologyArlington Place One40 S. Arlington Heights Rd., Suite 100Arlington Heights, IL 60005-4516Phone: (847) 981-0100 Fax (847) 981-410E-mail: iest iest.org Web: www.iest.orgIEST-RP-DTE009.1 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY4 Co

6、pyrighted materialCOPYING IS ILLEGALIEST-RP-DTE009.1 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY Copyrighted material 5COPYING IS ILLEGALCONTENTS1SCOPE AND LIMITATIONS 62 REFERENCES AND APPLICABLE DOCUMENTS 63 TERMS AND DEFINITIONS 64BACKGROUND AND PURPOSE 75SHAKER SELECTION FOR VIBRATION AND

7、 SHOCK 76 NONRECOMMENDED PRACTICES . 14Table 1Frequency range and waveforms 8Table 2Displacement and velocity . 10Table 3Worksheet for determining target tests 15PROPOSAL FOR IMPROVEMENT . 17VIBRATION SHAKER SYSTEMSELECTIONIEST-RP-DTE009.1IEST-RP-DTE009.1 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECH

8、NOLOGY6 Copyrighted materialCOPYING IS ILLEGALVIBRATION SHAKER SYSTEMSELECTIONIEST-RP-DTE009.1INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGYDesign, Test, and Evaluation DivisionRecommended Practice 009.11 SCOPE AND LIMITATIONS1.1 ScopeThe purpose of this Recommended Practice (RP) isto define an

9、orderly approach that addresses themajor issues involved in selecting a shaker for dy-namic testing. In some cases, this selection processis associated with deciding which shaker system toprocure. In other cases, the user will already haveshaker systems available (in-house or at commer-cial test lab

10、oratories) and must decide which one isbest suited for the task at hand. The process is thesame in either case.Shakers are generally used for sine vibration, ran-dom vibration, and many types of shock tests.It is the intent of this document to cover the follow-ing applications for shakers: simulatio

11、n of operat-ing conditions, design qualification tests, transpor-tation simulation, and vibration for environmentalstress screening (ESS).All major types of shaker systems will be includedin the discussions, namely: electrodynamic (E-D),servo-hydraulic (hydraulic), mechanical, and pneu-matic impacto

12、r. In the context of this RecommendedPractice, a shaker system includes the power supply(electronic, hydraulic, or pneumatic) as well as thecooling system required for the shaker system.Closed-loop control systems (required to run testson E-D and hydraulic shakers) are addressed in adifferent RP.1.2

13、 LimitationsThis document addresses technical matters and doesnot present any issues relating to specific commer-cial applications. This document also does not ad-dress any specific financial considerations, whichcertainly must be considered when selecting a vi-bration shaker system.2 REFERENCES AND

14、APPLICABLE DOCUMENTSNone.3 TERMS AND DEFINITIONSarmatureThat part of an electrodynamic shaker that moveswith the payload.The armature consists of a mounting table, a drivercoil, and the structure that connects the mountingtable to the driver coil.axial resonanceThe first mode of vibration of an arma

15、ture that hasthe mounting table moving out-of-phase with thedriver coil.diaphragm modeThe first mode of vibration of an armature that hassignificant variations in vibration amplitude acrossthe surface of the mounting table.driver coilThe part of an armature that converts electricalenergy to mechanic

16、al motion.E-DAn abbreviation for electrodynamic (which see).electrodynamicA type of shaker that uses electrical energy to createdynamic motion. In physics, the technology used iscalled the voice coil principal.exciterAnother word for shaker.hydraulicA shortened form of the phrase servo-hydraulic.IES

17、T-RP-DTE009.1 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY Copyrighted material 7COPYING IS ILLEGALmounting tableThe part of an E-D shakers armature to which thepayload is attached.moving elementAnother word for armature.payloadEverything that is attached to the mounting table ofa shaker.pisto

18、nThat part of a servo-hydraulic shaker that moveswith the payload.pneumatic impactorA type of shaker that uses compressed air to createmotion.servo-hydraulicA type of shaker that uses high pressure oil (i.e.hydraulics) and a servo valve to create motion.shakerA device that creates the motion that sh

19、akes pay-loads (some shakers can also shock payloads).shaker tableAnother word for shaker.test articleAnother word for unit under test.unit under test (UUT)That which is being tested.vibration tableAnother word for shaker.4 BACKGROUND ANDPURPOSEThose charged with the responsibility of selecting asha

20、ker are faced with an opportunity that is chal-lenging and concerning. The challenge results fromthe fact that selecting a shaker is not a straightforward or mundane task. The concern, be it mild orsevere, centers around the nagging question: “Whatif I make the wrong selection?”It is sometimes said

21、that a shaker cannot be toopowerfuland this is true as long as there is aninexhaustible supply of money! Its not uncom-mon, however, for an in-house test system to bestillborn (and the test work farmed out) because thetechnical people involved in defining what wasrequired either over-specified a sys

22、tem that ex-ceeded the available budget and therefore couldntbuy anything, or bought one that was undersized.This Recommended Practice presents a structuredapproach to selecting a shaker that involves sevencategories. If these factors are addressed properly,then the selection will have been made usi

23、ng thebest available information. These seven categoriesare:1) Frequency range and waveforms,2) Displacement and velocity,3) Number of axes to be tested,4) Payloads and vibration and shock levels,5) Force rating,6) Dynamics of the shaker system,7) Defining target tests.Fixturing is usually extremely

24、 important in theshaker selection process. Sometimes it is a criticalfactor. Note that in this context, everything (exceptthe unit under test and armature) is defined asfixturing.Fixturing can be divided into two categories: a)special purpose fixturing used to attach the UUT tothe shaker system, and

25、 b) general purpose fixturingsuch as slip tables, head expanders, cubes, T-plates,and so forth. In many cases, the actual test article isonly a small part of the total weight that has to bevibrated or shocked. This is especially true in situa-tions where a slip table or head expander is in-volved. I

26、n such cases, poor assumptions made aboutthe fixturing will badly taint the shaker selectionprocess.If the fixturing ends up being a lot heavier than wasassumed, the shaker may not be able to achieve thedesired vibration levels. If, on the other hand, toomuch safety factor is built into the assumpti

27、ons offixturing weight, the shaker specified will be unnec-essarily large. Lastly, if the fixturing has powerful,lightly damped resonances and anti-resonances inthe test bandwidth, then it is entirely possible thateven a drastically oversized shaker will not be ableto run a desired test.5 SHAKER SEL

28、ECTION FORVIBRATION AND SHOCK5.1 Frequency range and waveformsVarious technologies are being used as energysources for shakers and each has a different fre-quency range, although there is considerable over-lap. Furthermore, each technology can produce cer-tain waveforms, i.e., some can only do sine

29、tests,whereas others can produce many types of wave-IEST-RP-DTE009.1 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY8 Copyrighted materialCOPYING IS ILLEGALforms. Table 1 defines frequency ranges and wave-forms.Current and future test needs in terms of frequencyrange and waveforms should be evalu

30、ated. Oftenthe available technologies will be reduced consid-erably for a certain application, since several willnot handle the needed frequency range or wave-forms.(1) E-D shakers are usually transformer coupled which enhances their velocity andrandom capabilities but limits their low-frequency cap

31、ability due to transformermagnetics. E-D shakers can be direct coupled but in some designs the velocity orrandom ratings may be compromised. If good low-frequency response is desired,ask the supplier for specifications applicable in the direct coupled mode.(2) It is uncommon for medium- to large-siz

32、ed E-D shakers to provide full force above3 kHz, but small ones (100 lbf-500 lbf) can produce energy out to 5,000 Hz, and verysmall ones ( 75 lbf) can exceed 10 kHz.(3) Some suppliers have recently begun promoting higher frequency hydraulics.Details are not yet available.(4) Hydraulic shakers are in

33、herently nonlinear, causing problems for some control-lers. Ask the controller supplier if they have experience with hydraulic shakers.(5) Some mechanical tables can be outfitted to produce a swept sine at fixed displace-ment. If sine wave purity is a concern, then care must be taken in specifying a

34、mechanical table. The upper half of a particular machines frequency range can beplagued by gaps in the mechanism that cause harmonically related glitches (i.e.,once/cycle, twice/cycle, etc.). Such glitches cause spurious inputs that can bequite large when an accelerometer output is viewed on a scope

35、.(6) Quasi-random is created by a continuous series of impacts which, when viewed onan FFT analyzer with a long sample time, happens to have a broadband frequencycontent.(7) There is no cutoff at 2 kHz with impactors, so be sure to confirm the actualfrequency content.Type of energy sourceTypical low

36、-frequency limitExtreme case lowest frequencyTypical high-efficiency limitExtreme case highest frequencyWaveformelectrodynamic (E-D)5 Hz20 Hz 2 Hz( 1 )2 kHz3 kHz( 2 )5 kHz10kHz( 2 )anyservo-hydraulic(hydraulic)DC DC 100 Hz250 H 500 Hz( 3 )usually sine but any waveform is possible( 4 )mechanical 15 H

37、z 5 Hz 60 Hz 80 Hz120 H sine only (usually fixedfrequency)( 5 )modulated pneumatic impactor20 Hz 10 Hz approx 23 Hz( 7 )( 7 ) quasi- random only( 6 )Table 1Frequency range and waveformsIEST-RP-DTE009.1 INSTITUTE OF ENVIRONMENTAL SCIENCES AND TECHNOLOGY Copyrighted material 9COPYING IS ILLEGAL5.2 Dis

38、placement and velocityAcceleration, velocity, and displacement are simplythree ways of quantifying vibration levels. There isa frequency-based conversion factor between thethree quantities.When dealing with sinusoidal motion, the follow-ing formulae define the relationship between D (i.e.,displaceme

39、nt in inches pk-pk), V (i.e., velocity ininches per second peak), g (i.e., g units, gpk, asderived in section 5.4), and f (i.e., frequency in Hz).D = 19.57g/f2D = 0.3183V/fV = 61.44g/f V = 3.142Dfg =0.0511Df2g = 0.0162VfIts worth noting that many organizations makeslide rules that are very handy for

40、 approximateconversion between D, V, and g for sinusoidal mo-tion. Furthermore a PC-based program (for eitherWindows or DOS) is available at no charge.*Shakers have definite limits on the vibration levelsthey can produce, and it is convenient to quantifythese limits in terms of acceleration, velocit

41、y, anddisplacement. Acceleration is related to the forcerating of the shaker and the mass that must bevibrated using Newtons Law; namely, F = ma. (Seesection 5.4.)When a test specification clearly defines the dis-placement and velocity limits, it is a relatively simplematter to compare the requireme

42、nts to the capabil-ity of the shaker system. A disastrous situation canarise, however, when large displacement or largevelocity requirements are hidden by the way thetest specification is presented. For instance, at firstglance the following requirement appears ratherbenign:Perform a sine sweep at 1

43、“ (pk-pk) from 10 Hz to17 Hz,then hold 15 g(pk) from 17 Hz to 2,000 HzWhat is not stated in the above specification can bejust as important as what is stated. Namely, at 17 Hzthe 1 inch (pk-pk) of displacement equates to avelocity of approximately 53 IPS (pk). If you selecta shaker with a 40 IPS vel

44、ocity limit, it will trip off-line at 13 Hz regardless of how big its force rating is (inwhich case 13 Hz would indeed be a very unluckynumber)!Another way that requirements can be obscured isas follows:Perform a sine sweep in the 5 Hz to 2,000 Hzrange at 4 g(pk)At first glance, this requirement see

45、ms innocentuntil you discover that 4 g(pk) at 5 Hz equates to adisplacement of over 3 inches (pk-pk)! This testcannot be run on many conventional E-D shakers(which typically have 1 or 2 inches of stroke).Historically, “canned” specifications were exten-sively used. Such specifications were specifica

46、llydesigned to be run on a particular type of shaker.Therefore, users seldom ran into specifications thathad nasty surprises. Now that more tests are beingbased on actual field and end-use measurements,users can no longer rely on other people havingalready run a particular test. Some operating envi-

47、ronments can easily exceed the velocity limits of anexisting shaker or a low-cost shaker system with alarge force-rating but low velocity limit.Exceeding the velocity limits has very unpleasantconsequences. In the case of an E-D shaker system,the output of the power amplifier will be “clipped,”produ

48、cing out of band energy that is not control-lable and not readily apparent unless the high-frequency energy is being monitored. For hydraulicsystems, pump flow is at a maximum of the velocitylimit, and compensator recovery compromises per-formance as the system comes out of the overdrivencondition.I

49、t is worth noting that displacement and velocitylimits apply to random vibration and shock tests, aswell as for sine tests. Velocity limits in particular aresometimes not understood, even by seasoned veter-ans. Many test people come face-to-face with thisreality when they try to use their traditional electro-dynamic shaker for the so-called transportationrandom tests that originally came out in MIL-STD810-D. They find that the required displacementsexceed the capabili