00基于故障树分析法构建专家系统知识库模型

基于故障树分析法构建专家系统知识库模型摘要：本文在广泛搜集往复式压缩机故障类型的基础上，探析故障机理。运用故障分析法，建立故障树模型，并用二维表格将其表示出来。然后并运用access数据库和vb语言构建知识库链表。最后，给出故障诊断专家系统知识库维护方法。关键词：往复式压缩机知识库故障树引言：往复式压缩机由于其自身的特点广泛应用于石油石化企业。但由于机构复杂、零件繁多，现场维修人员在诊断故障问题时困难重重。在维护和维修往复式压缩机时，故障诊断专家系统可以给现场维修人员提出宝贵建议的。在往复式压缩机故障诊断专家系统中，知识库的优劣直接影响到诊断的准确性和真实性。在构建知识库过程中，故障树分析法直接简明、逻辑性强等特点，所以本文采用故障树模型建立往复式压缩机故障诊断系统的知识库，保证诊断的准确性和真实性。Buildingaknowledgebaseofexpertsystemmodelbasedonthefaulttreeanalysis1，故障树分析法基本知识1.1定义：故障树分析法就是把所研究系统的最不希望发生的故障状态作为故障分析的目标，然后寻找直接导致这一故障发生的全部因素，再找出造成下一级事件发生的全部直接因素，一直追查到那些原始的、其故障机理或概率分布都是已知的，毋需再深究的因素为止。通常，把最不希望发生的事件称为顶事件，毋需在深究的事件称为底事件，介于顶事件和底事件之间的一切事件为中间事件，用相应的符号代表这些事件，再用适当的逻辑门把顶事件、中间事件和底事件联结成树形图。这样的树形图称为故障树，用以表示系统或各个部件故障事件之间的逻辑结构关系。以故障树为工具，分析系统发生故障的各种途径，计算各个可靠性特征量，对系统的安全性或可靠性进行评价的方法称为故障树分析法。1．Thefailureanalysis1.1BasicknowledgeoffaulttreeanalysisFaulttreeanalysisisthatthemostreluctantfaultconditionoccurredinthestudiedsystemwillbeasafailureanalysisoftarget;thenlookforallthefactorsleadingtothemostreluctantfaultcondition;nextseekforallthedirectfactorscausingthenextlevelfaultstilloriginalfaultfactors、wellknownfailuremechanismsoropenProbabilitydistributionoffaultfactorswouldbefondout;finally,youcanobtainalltheoriginalfaultfactorsthatcan’tbedivided.Usually,themostreluctantfaultcasewouldbeconsideredasthetopincindents;thefaultfactorsthatcouldn’tbesearchedwouldbeactedasthebottomincindents;thefaultcaseinthemiddleofthetopincindentsandthebottomincindentswouldbethoughasintermediateincindents.Byappropriatesymbolsoffaulttreeanalysisexpressingthethreetypleofmentionedincindentsandcombiningthetopincindents、intermediateincindentsandthebottomincindentsinlogicrelationship,wecanmakeoutthemodelofthefaulttreeanalysis-thegraphoffaulttreeanalysisthatitwouldindicatethelogicstructureforeachfaultincidentsorfaulttreeanalysis.Faulttreeanalysisisthemethodthatitcanevaluatesecurityandreliabilityofthestudiedsystemsaccuratellythatbythewayofthemodeloffaulttree,analyzingallkindsoffaultsincindent,caculatingvaviouscharacteristicquantitiesofreliability.1.2故障树分析法步骤故障树分析步骤具体如下：1.对所选定的系统作必要分析，了解系统的组成及各项操作的内容。2.对系统的故障进行定义，对预计可能发生的故障、过去发生的故障事例及故障统计，作广泛调研。3.仔细分析各种故障的形成原因并收集各故障发生概率数据。4.选定系统可能发生的最不希望发生的故障状态为顶事件，作出故障树逻辑图。5.对故障树结构作定量分析。如故障树各底事件的故障概率数据为已知，就可以根据故障树逻辑，对系统的故障作定量分析；若底事件概率值系未知数，可假设某个合理值，以便对系统进行可靠性方案的比较。下图是故障树分析法框图：1.2theprocedureoffaulttreeanalysisTheconcretestepsoffaulttreeanalysisasfollows:1.Dothenecessaryanalysisforselectedfaultsystems,obtainallthecompositonsandoperationcontentsforselectedsystems.2.Definethetypeofincidentsforthefaultsystems,takeseriousresearchandwildstatisicsforforcastpossiblefaultcase、alreadyhappenedfaultsamples.3.analyazeallbecomingacuasesforvaviousfaultscarefully,andtaketogethertheprobabilitydatasforallkindshappenedfaultsamples.4.Takethemostrelutantfaultcasesasthetopincindents;taketheoriginalcasesorcausesasthebottomincindentsandsoon,thenfigeroutthemodeloffaulttree.5.Makethequantitativeanalysisforelementsofthefaultsystem.Forexample,ifthedatasoftheprobabilitiesforthehappenedcasescouldbeobtained,wecouldmakethequantitativeanalysisforelementsofthefaultsystemonthebasisoflogicconectionsinthefaultsystems;ifthedatasoftheprobabilitiesforthehappenedcasescouldnotbeobtained,wecansupposereliabledatas,thenanalyzethefaultsystemsinorderthatwecancomparetheresultswiththereliabilitymethod.图1故障树分析法的顺序调研资料初步分析建立故障树布尔代数应用事故分析与防止故障率故障的发生概率Figure1thesequenceoffaulttreeanalysis2故障机理分析12.故障表示由于往复压缩机故障诊断专家系统的知识通常是描述过程性的知识。很多情况下，知识是松散杂乱的，因此非常适合采用产生式规则来组织知识库。但是往复压缩机故障知识数量很多，为了提高推理速度,需要将其分门别类地存储,因此推荐采用“框架+产生式”规则。以“往复压缩机二级排气温度高”故障为例，下图中每个故障事件结点就是一个诊断对象,每个诊断对象对应于一个描述框架。2.faultrepresentationBecausetherewerealotofdiscriptionprocedureinformationinexpertfaultdiagnosissystemforreciprocatingcompressorusually.Aswellas,theinformationabortfaultdiagnosiswerelooseandmessinmostcases.Soitisverysuitabletoestablishknowledgebasebyproductionregulation.Buttheinformationofthefaultcasesweremuchhuge.Inordertoimprovethespeedofcaculation,weshouldstorethedatasregulatelyandapply“frame+produce”rulepropably.Take“hightemperatureinsecondgradeexhaustofreciprocatingcompressor”forexample,inthefollowingfigure,everyfaultcasenodeisatargetoffaultdiagnosis,andeachtargetoffaultdiagnosiscorrespondwitheachdiscriptingframe.StudymeterialPreliminaryanalysisEstablishfaulttreeBooleanalgebraapplicantionsPreventionandanalysisofincindentFailureprobabilityProbabilityofoccurence冷却水节温器失效二级排气压力过二级缸排气温度高压缩缸故障冷却系统故障机组负荷大排气阀损坏漏气压缩缸积碳严重进气处理量过多空冷器电机损坏二级压缩缸排气温度高故障树模型Thefaulttreemodelofhightemporatueinsecondexhaust在构建诊断系统知识库时，本文使用Mirconsoftaccess数据库软件和SQL（结构查询语言）。首先，建立access数据库中表格字段，包括序号、故障名、故障现象、处理意见。接着，对每个字段填入相应记录，如1号故障名填写压缩缸故障。然后，录入诊断条件即诊断规则。最后，使用vb语言建立if—then条件语句和链接。下面是将“二级压缩缸排气温度高”故障树模型转化为二维表格，如下表所示：Intheproccedureofestablishingknowledgebaseofdiagnosissystem,wemakeuseofmirconsoftaccessandSQL.Firstly,establishnumericfieldinthelist,including:numble、faultname、apperanceoffault、treatmentadvice.Then,writeappropriatedatasinfitablenumericfield.Forexample,1#faultnameiscompressorcylinderfailure.Next,typetherequirementoffaultdiagenosisthattheruleofdiagenosis.Finally,establ