00基于故障树分析法构建专家系统知识库模型.doc

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。 Building a knowledge base of expert system model based on the fault tree analysis1，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。1The failure analysis1.1 Basic knowledge of fault tree analysis Fault tree analysis is that the most reluctant fault condition occurred in the studied system will be as a failure analysis of target; then look for all the factors leading to the most reluctant fault condition; next seek for all the direct factors causing the next level faults till original fault factors、well known failure mechanisms or open Probability distribution of fault factors would be fond out; finally, you can obtain all the original fault factors that cant be divided. Usually, the most reluctant fault case would be considered as the top incindents; the fault factors that couldnt be searched would be acted as the bottom incindents; the fault case in the middle of the top incindents and the bottom incindents would be though as intermediate incindents. By appropriate symbols of fault tree analysis expressing the three typle of mentioned incindents and combining the top incindents、intermediate incindents and the bottom incindents in logic relationship, we can make out the model of the fault tree analysis-the graph of fault tree analysis that it would indicate the logic structure for each fault incidents or fault tree analysis. Fault tree analysis is the method that it can evaluate security and reliability of the studied systems accuratelly that by the way of the model of fault tree, analyzing all kinds of faults incindent, caculating vavious characteristic quantities of reliability.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：1.2 the procedure of fault tree analysis The concrete steps of fault tree analysis as follows: 1.Do the necessary analysis for selected fault systems, obtain all the compositons and operation contents for selected systems. 2.Define the type of incidents for the fault systems, take serious research and wild statisics for forcast possible fault case、already happened fault samples. 3.analyaze all becoming acuases for vavious faults carefully, and take together the probability datas for all kinds happened fault samples. 4.Take the most relutant fault cases as the top incindents; take the original cases or causes as the bottom incindents and so on, then figer out the model of fault tree. 5.Make the quantitative analysis for elements of the fault system. For example, if the datas of the probabilities for the happened cases could be obtained, we could make the quantitative analysis for elements of the fault system on the basis of logic conections in the fault systems; if the datas of the probabilities for the happened cases could not be obtained, we can suppose reliable datas, then analyze the fault systems in order that we can compare the results with the reliability method. 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 图 1 故障树分析法的顺序Study meterialPreliminary analysisEstablish fault treeBoolean algebra applicantionsPrevention and analysis of incindentFailure probabilityProbability of occurenceFigure 1 the sequence of fault tree analysis2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.fault representation Because there were a lot of discription procedure information in expert fault diagnosis system for reciprocating compressor usually. As well as, the information abort fault diagnosis were loose and mess in most cases. So it is very suitable to establish knowledge base by production regulation. But the information of the fault cases were much huge. In order to improve the speed of caculation, we should store the datas regulately and apply “frame +produce” rule propably. Take “high temperature in second grade exhaust of reciprocating compressor” for example, in the following figure, every fault case node is a target of fault diagnosis, and each target of fault diagnosis correspond with each discripting frame. 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Coling water thermostat failureHigh pressure in second exhaustHigh temperatue in second exhaustCompression cylinder failureCooling system failureHuge load on mechineExhaust valve leakCoke in compression cylinder seriousToo much suck productionAir cooler motor damege The fault tree model of high temporatue in second exhaust在构建诊断系统知识库时，本文使用Mirconsoft access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ifthen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：In the proccedure of establishing knowledge base of diagnosis system, we make use of mirconsoft access and SQL. Firstly, establish numeric field in the list, including: numble、fault name、apperance of fault、treatment advice. Then, write appropriate datas in fitable numeric field. For example, 1#fault name is compressor cylinder failure. Next, type the requirement of fault diagenosis that the rule of diagenosis. Finally, establish the connection that list tolist by VB and if-then sentense. There was two-dimensional table that fault tree daigenosis model of high temperature in second exhaust for reciprocating compressor was transformed.序号故障名 故障现象处理意见1压缩缸故障进气阀损坏漏气更换新的新进气阀压缩缸余隙过大参考手册调整活塞余隙2冷却系统故障空冷器电机损坏维修空冷器电机冷却水节温器损坏更换节温器3机组负荷大入口压力过高调节入口压力阀门二级排气压力过高调整工艺运行参数二级压缩缸排气温度高故障的二维表示NO.Fault name Appreance Treatment advice1Compression cylinder failureExhaust valve leakInstall new exhaustCoke in compression cylinder seriousRemove coke2Cooling system failureAir cooler motor damegeMending air cooler motorColing water thermostat failureInstall new thermostat3Huge load on mechineToo much suck productionAdjust pressure vavel of suctionHigh pressure in second exhaustRegulate precess parameterTwo-dimensional table for high temperatue of second exhaust3, 知识库的构建 在面向对象知识库中, 知识类型包括事实、规则和过程三种。本专家系统主要采用规则知识表达。知识库中单条规则主体由ifthen两个部分组成。规则的表示形式为rule（规则标号）（规则名）（规则说明）。但由于采用的是vb中的可视化数据管理器,因此在编写数据库时比较简单, 它不需要用代码和Ifthen语句来建立压缩机故障现象与故障原因、排出方法一一对应的关系, 因为vb中的microsoft access数据库本身就具有一一对应的关系,只需要建立序号、故障名、故障现象、排出方法四个字段。这样只需要搜索故障知识库中的故障现象所对应的序号就能找到故障名和排除方法, 只需要一个循环语句和一个ifthen语句就能把整个知识库中的故障知识对应起来。以“二级压缩缸排气温度高故障”为例，把它的每一字段使用SQL查询语言写成如下形式:3, establish knowledge base In the knowledge base vision object, the type of knowledge include: fact、rule、and process. This fault diagenosis expert system mainly adopt expression in rules. In the procession of building knowledge base, there is only if-then selected sentense in single rule. The expression is rule(numble)(name of rule)(explanation). we adopt vision data management in microsoft access in which one-to-one corresponding conection. So it is very easy to program data base which we neednt use codes and if-then selected sentenses to combine appreance of fault with the reason of fault and treatment. We only look for the numble corresponding the appreance of the fault in knowledge base. We can get the name and treatment by single loop sentense and if-then selected sentense in entire knowledge base. Taking “high temperature of second exhaust in compressor cylinder” for example, we can program each row by SQL. As follows: Create table 故障树知识库（序号 数字primary，故障名 text，故障现象 text，处理意见 备注）。然后，每个记录导入到数据库中，建立起知识库模型如下： Creat table knowledge base of fault tree analysis(NO. numlbe primary, name of fault text, appreance of fault text, treatment remark). Then,