>> P.531
QualityControlGeneralTerminMeasurement:QualityControlX-RControlChartAcontrolchartusedforprocesscontrolthatprovidesthemostinformationontheprocess.AnX-Rcontrolchartconsistsofthefollowing:•Acontrolchartthatusesthemeanofeachsubgroupforcontroltomonitorabnormalbiasoftheprocessmean,•AnRcontrolchartthatusestherangeforcontroltomonitorabnormalvariation.Usually,bothchartsareusedtogether.inthechartcontroltrendsofsuccessivepointpositionHowtoReadtheControlChartTypicalthatareconsideredundesirableareshownbelow.Thesedeterminationrulesonlyprovideaguideline.Taketheprocess-specicvariationintoconsiderationwhenmakingdeterminationrules.Assumingthattheupperandthelowercontrollimitsare3awayfromthecenterline,dividethecontrolchartintosixregionsatintervalsof1toapplythefollowingrules.TheserulesareapplicabletotheXcontrolchartandtheXcontrolchart.Notethatthese'trendrulesforaction'wereformulatedassuminganormaldistribution.UCLXLCLX+3σX+2σX+1σX-1σX-2σX-3σUCLXLCL(1)Thereisapointbeyondeitherofcontrollimitlines(±3).the(2)Nineconsecutivepointsaresideofthecenterline.UCLXLCLX+3σX+2σX+1σX-1σX-2σX-3σUCLXLCLX+3σX+2σX+1σX-1σX-2σX-3σtooneX+3σX+2σX+1σX-1σX-2σX-3σ(3)Sixpointsconsecutivelyincreaseordecrease.(4)points14decrease.alternatelyincreaseandUCLXLCLX+3σX+2σX+1σX-1σX-2σX-3σUCLXLCLX+3σX+2σX+1σX-1σX-2σX-3σ(5)Twoofthreeconsecutivepointsareover±2fromthecenterlineoneitherside.(6)Fourofveconsecutivepointsareover±1fromthecenterlineoneitherside.UCLXLCLX+3σX+2σX+1σX-1σX-2σX-3σUCLXLCLX+3σX+2σX+1σX-1σX-2σX-3σ(7)Thereare15consecutivepointswithin±1fromthecenterline.(8)Thereareeightconsecutivepointsover±1fromthecenterline.Theprocesscapabilityistheminimumvaluethatcanbegenerallyacceptedasitisnocloserthan1sigmatothetolerancelimits.Theprocesscapabilityissufficientasitisnocloserthan2sigmatothetolerancelimits.USLUSLUSLUSLUSLUSL66688661010LSLLSLLSLLSLLSLLSLCp=1.33Cp=1.67NotethatCponlyrepresentstherelationshipbetweenthetolerancelimitsandtheprocessdispersionanddoesnotconsiderthepositionoftheprocessmean.thattakesindexcapabilityNote:AprocessthedeviationbetweenthespecicationcenterandtheprocessmeanisgenerallycalledCpk.Itistheuppertolerance(USLminusthemean)dividedby3(halfofprocesscapability)orthelowertolerance(themeanvalueminusLSL)dividedby3,whicheverissmaller.accountintointocontrolvariationsseparatingthoseduetheprocessbyControlChartUsedtochancecausesintheprocessandthoseduetoamalfunction.Itconsistsofonecenterline(CL)andthecontrollimitlinesrationallydeterminedaboveandbelowit(UCLandLCL).Itcanbesaidthattheprocessisinastateofstatisticalcontrolifallpointsarewithintheupperandlowercontrollimitlineswithoutnotabletrendswhenthecharacteristicvaluesthatrepresenttheforcontrollingprocessoutput,andthereforequality.plotted.processcontroloutputusefulcharttoolisatoareTheUppercontrollimit(UCL)Lowercontrollimit(LCL)1234567SubgroupnumberCenterline(CL)ChanceCausesThesecausesofvariationareofrelativelylowimportance.Chancecausesaretechnologicallyoreconomicallyimpossibletoeliminateeveniftheycanbeidentied.Note:Thispartof'QuickGuidetoPrecisionMeasuringInstruments'(pages13-3and13-4)hasbeenwrittenbyMitutoyobasedonitsowninterpretationoftheJISQualityControlHandbookpublishedbytheJapaneseStandardsAssociation.References•JISQualityControlHandbook(JapaneseStandardsAssociation)Z8101:1981Z8101-1:1999Z8101-2:1999Z9020:1999Z9021:199813-4
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