cliffcrag 发表于 2007-6-6 12:59:51

Reliability Growth

ObservingandPredictingTrendsinReliability

Today'scomplexproductsrequirethatcompaniesfocusonestablishingdetailedplansandproceduresfordevelopingandmanufacturingproductsthatmeetspecifiedreliability,maintainability,andotherperformancerequirements.Reliabilitygrowthreferstoawell-definedprocessforidentifyingandcorrectingreliabilityproblemsearlyinthedesignprocesssothatthereliabilityofaproductincreasesor"grows"astheproductgoesthroughsuccessivedevelopmentstages.Reliabilitygrowthprogramsshouldbeestablishedforallnewproductsandforallexistingproductsundergoingmajorredesignssothattheimprovementduetochangesindesignandmanufacturingprocessescanbeeasilytracked.
Duringtheearlydesignstage,areliabilitygoalissetforaproduct.Becausefailuredatafromprototypetestingisnotyetavailable,theinitialreliabilitygoalisoftenbasedoneitherthefailuredataforsimilarproductsorthefailuredataforthesubcomponentsoftheproduct.Duringthedevelopmentstage,productprototypesgenerallyundergoextensivetestingsothatdeficienciesinrespecttodesign,engineering,andmanufacturingcanbeidentifiedandcorrected.
Atypicalreliabilityimprovementtestconsistsofoperatingproductprototypesforseveralweeksinthesametypesofenvironmentsinwhichcustomerswilleventuallyoperatetheproduct.Ateamofprojectengineersandtechniciansanalyzeeveryfailurethatoccurs,determiningrootcausesforfailuresanddevelopingdesignandmanufacturingimprovementsthataretoeithereliminateorreducetherecurrencesofthesefailures.Asthetestingcontinues,theimprovementsdevelopedbytheteamareincorporatedintotheprototypesothatproductreliabilitycontinuestoimprovethroughoutthetestingperiod.

AchievingReliabilityGrowth
Thethreemostimportantstepsintheiterativeprocessforachievingreliabilitygrowtharedepictedinthefeedbackloopthatfollows:

Mostoftheproblemsencounteredduringtestingarelikelytobecomponentfailuresandmanufacturingdeficienciesthatcouldnotbeforeseenintheearlydesignphase.Becausevariousperformancerequirementscanconflict,optimizingadesigntomeetonerequirementcancausethedesigntofailtomeetanotherrequirement.Thus,iterationsofdesignsareoftenneededtocorrectallofthecomponentselectionandmanufacturingdeficienciesthatarefoundduringprototypetesting.
Inadditiontoimprovingreliability,earlyimplementationofareliabilitygrowthprogramminimizestheimpactonproductionschedulingandtotalproductcost,especiallysincethecostsassociatedwitheitherredesigningaproductlateinthedevelopmentcycleorretrofittingproductsalreadyinthefieldareextremelyhigh.Developingaproductthatmeetsreliabilityrequirementsalsoensuresthattheproductultimatelymeetsuserneedsandhasanacceptabletotallifecyclecost.Settinginterimreliabilitygoalsthataretobeachievedduringtestingensuresthatresourcesareallocatedefficiently.

ReliabilityGrowthData
Thebasicprincipleofanyreliabilitygrowthmodelistoapplythetestingresultsanddatapointstodetermineifthereliabilityoftheproductisgrowingsufficientlytomeetthereliabilityrequirementsfortheproduct.Thetypesofdatausedforpredictingreliabilitygrowthare:
•ReliabilityData.Thereliabilityoftheproductisrecordedatdifferentpointsintime.Thereliabilityisaratioofthenumberofunitsstillfunctioningandthenumberofunitsthatenteredthestage.
•Success/FailureData.Theitemistestedandcaneithersucceedorfail.Successdatacanconsistofacodeindicatingtheoutcome,suchasSforSuccessorFforFailure;or,itcanconsistofacodeindicatingthefailuremodeforeachfailure.Success/failuredatamightalsoindicatethenumberoffailuresthatoccurredwhenseveralunitsaretestedtogether.
•FailureTimeData.Thetimetofailureforanitemistrackedusingeithercumulativeornon-cumulativeoperatingtimes.Failuretimedataisthemostcommonlyusedtypeofdatainreliabilitygrowth.Thisdatacanbeforonefailureorsystem,oritcanbeformultiplefailuresormultiplesystems,whichiscommonlycalledintervalorgroupeddata.
Thefailuredatacollectedduringprototypetestingisusedtodeterminewhetherthereliabilitygoalfortheproductislikelytobemetorexceededbythetimetheproductisscheduledtobeputintofull-scaleproduction.Althoughmanymethodsexistformodelingthereliabilitygrowthprocess,theDuane/Crow-AMSAAmodelisconsideredthebestpractice.In1964,J.T.Duane,anengineerattheAerospaceElectronicsDepartmentofGeneralElectronicCompany,publishedapaperdemonstratinghowalearningcurveapproachcouldbeusedtomonitorthecontinuingreliabilityimprovementsintheearlystagesofdevelopingcomplexelectromechanicalandmechanicalsystems.Duaneexplainedhowthiswasbecausethelessonslearnedfromfailureswereusedtorefinedesigns.
AccordingtoDuane,agraphofthecumulativeMTBFversusthecumulativeoperatingtimeplottedonlog-logpaperfellclosetoastraightline.Graphingthislearningcurveprovidesameansofmeasuringandpredictingreliabilityduringaperiodofproductchange.Dr.LarryCrowlateraddedpowerfulstatisticalcapabilitiestoDuane'spostulateforlearningcurvemodelingtocreatethemodelsowidelyrespectedandimplementedtoday.AnexampleofareliabilitygrowthchartgeneratedbytheDuane/Crow-AMSAAmodelfollows:

Reliabilitygrowthisgenerallyquantifiedbygraphinganyofthefollowingthreemeasuresovertime:
•Theincreaseinthemissionsuccessprobability(reliability).
•TheincreaseinMTBF.
•Thedecreaseinfailurerateasafunctionoftime.
Reliabilitygrowthchartsdepicttrendsthatareusedtoforecastfailuresasafunctionofadditionaltesttimeorcalendartime,therebymakingplanningforredesignandtestresourceseasier.Inadditiontoallowingyoutodeterminewhetherreliabilityrequirementswillbeachieved,reliabilitygrowthchartscanhelpyoutodeterminethetimeneededtomeettheserequirementsandtheassociatedcosts.Extrapolatingagrowthcurvebeyondthecurrentlyavailabledatashowswhatreliabilityaprogramcanbeexpectedtoachieveprovidingthattheconditionsofthetestandtheengineeringefforttoimprovereliabilityaremaintainedattheirpresentlevels.
Ifthereliabilitygrowthgraphindicatesthatthereliabilitygoalisnotgoingtobemetorexceeded,thentheproductdesignmustbeimproved.Thismightrequiretheuseofmorereliablecomponentsorredundancy.Additionalresourcesmightalsohavetobedevotedtodesigningandmanufacturingamorereliableproducttomeettherequireddeliverydate.

OtherUsesforReliabilityGrowthCharts

Inadditiontoanalyzingtheresultsfromtestingnewlydevelopedorredesignedproducts,theDuane/Crow-AMSAAmodelcanbeusedto:
•Predictfuturefailures.
•Trackfleetsofrepairablesystems.
•Provideaccuratetrendingofsignificanteventsformanagement.
•Forecastsafetyincidentsthatcanbecontrolled.

bluryy 发表于 2007-7-16 10:30:39

很有参考学习的价值谢谢

basetwins 发表于 2010-4-16 10:55:11

goodinformation

deadxiaoh 发表于 2010-6-21 17:34:15

不是可靠性增长测试？？、、、、

whxuzhi 发表于 2010-7-5 23:29:43

看了以后再评论

forest_sheep 发表于 2016-5-11 13:39:25

goodinformation
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