摩托罗拉六西格玛企业培训 2.4 Evaluate Measurement Systems

1、Additional Department InfoCopyright 2002 Motorola. All rights reserved.Six Sigma Black Belt Program 2.4 Evaluate Measurement Systems2.4 - 1Six SigmaBlack Belt Program2.4 - EvaluateMeasurement SystemsThese materials, including all attachments, are protected under the copyright laws of the United Stat

2、es and other countries asan unpublished work. These materials contain information that is proprietary and confidential to Motorola University and are thesubject of a License and Nondisclosure Agreement. Under the terms of the License and Nondisclosure Agreement, thesematerials shall not be disclosed

3、 outsider the recipients company or duplicated, used or disclosed in whole or in part by therecipient for any purpose other than for the uses described in the License and Nondisclosure Agreement. Any other use ordisclosure of this information, in whole or in part, without the express written permiss

4、ion of Motorola University is prohibited.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 22.4 Evaluate Measurement SystemsObjectiveTo identify why measurement system evaluation should be performed,perform an evaluation.Key TopicsBiasPrecisionRepeatabilityReproducib

5、ility2.1DetermineWhat toMeasure2.2ManageMeasurement2.4EvaluateMeasurementSystems2.3EvaluateVariation2.5DetermineProcessPerformanceCopyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 3Importance of Measurement SystemsAnalysis (MSA) Measurement systems analysis - a proce

6、ss to evaluate thefactors (e.g., measuring tools, operators, measurementprocedures, etc.) that effect the quality ofmeasurements. Output is the recorded measurement. Evaluating the Measurement System is really no differentthan evaluating any process. Quality of the measurement system is related to t

7、hestatistical properties of multiple measurements obtainedfrom a measurement system operating under stableconditions.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 4Importance of Measurement SystemsAnalysis (MSA) Two properties used to characterize themeasurement

8、system. Bias refers to the location of the distribution ofmeasurements relative to a “true” or reference value. Precision refers to the variability of the measurementsystem distribution.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 5For each bucket: Identify sour

9、ces of variation Quantify the variation Remove or Control the variationSources of Variation in aMeasurement SystemMeasurementSystemVariabilityProcessVariabilityTotalVariabilityM1M2M3=+Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 6Impact of Measurement Variabilit

10、yInitial ProcessingProcess Under DevelopmentMeasurement SystemMetrologyToolOutputSome incorrect assumptions Metrology tools are perfect. No day to day variation exists.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 7Standard Terms Related to MSA Measurement - “Ass

11、ignment of numbers to materialthings to represent the relations among them withrespect to particular properties.” Gauge (Metrology Tool) - device used to obtainmeasurements.This includes go/no-go devices. Measurement system - collection of operations,procedures, gauges and other equipment, software,

12、materials, facilities, and personnel used to assign anumber to the characteristic being measured.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 8Why Do Measurements Vary? Tool Instability Work Methods EnvironmentCopyright 2002 Motorola. All rights reserved.2.4 Eva

13、luate Measurement Systems2.4 - 9When Should a MeasurementSystems Analysis be Performed? An MSA study should be performed before using anymeasurement in analyses and decision-making, unlessdocumentation exists to show that the measurementsystem is still performing acceptably. An MSA may be appropriat

14、e when: A gauge is found to be out of calibration during regular gaugemaintenance. A change has been done on the gauge, such as a componentreplaced that might affect the performance of the gauge. A major repair has been performed on the gauge.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate

15、 Measurement Systems2.4 - 10When Should a MeasurementSystems Analysis be Performed? A gauge will be used as part of the machine/processcapability study. Recommended as part of a regularly scheduled review ofyour measurement system. The measurement system is statistically unstable over time. The meas

16、urement variation has significantly increased ordecreased. Providing a criterion to accept new measuring equipment(e.g. in an Equipment Purchase Agreement (EPA). Providing a comparison of one measuring device againstanother. The requirements for the measurement system have changed(e.g. due to proces

17、s development or technology transfer). There is significantly reduced process variation. This couldnow stretch the limits of the gauge.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 11When Should a MeasurementSystems Analysis be Performed? An MSA is appropriate be

18、fore: Statistical Process Control implementation on aprocess. Running any Design of Experiment (DOE). Doing a process SOV study. Doing a process capability study.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 12In Class Exercise Objective Identify potential source

19、s of measurement variation in yourworkplace. Timing Participants will have 10 minutes to complete this exercise. Instructions For a measurement process youre familiar with: What is the parameter of interest? (That is, the specificcharacteristic of the object being measured, such as length,width, ela

20、psed time, resistivity, impurity level, etc.). What is the measurement tool? What are the potential sources of variability in the overallmeasurement system.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 13Management Responsibility Ensuring that the statistical pro

21、perties ofmeasurement systems are identified. Ensuring that those properties are used as thebasis for selecting a measurement system. Continuously improving the measurementsystem. Making the decision to replace the system whennecessary.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measur

22、ement Systems2.4 - 14Measurement Systems Analysis:Knowledge Obtained How big is the measurement system variability? What are the sources of measurement systemvariability? Is the measurement system stable over time? Is the measurement system capable of making therequired measurements for this project

23、 orprocess? What needs to be done to improve themeasurement process?Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 15Statistical Properties of aMeasurement System Should have increments of measure which aresmall relative to either the process variability orthe spe

24、cification limits (discrimination orresolution). Should be in Statistical Control. Should have acceptable bias and precision. Should have acceptable linearity.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 16Measurement Discrimination Discrimination Capability of

25、a measurement tool to detect andadequately indicate small changes in a measuredcharacteristic. The higher the discrimination, the smaller thechanges that can be detected by the measurementtool. Measurement unit Smallest value of the measurement scale that candiscriminate effectively without grouping

26、 orrounding the measurements.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 17Stability - Measurement System While there are many definitions of stability,we prefer to use one that directly reflects theproperties of statistical control. The distribution of the mea

27、surements remainsconstant over time average. standard deviation. No drifts, sudden shifts, cycles, etc. Stability is evaluated using a trend chart or acontrol chart.PolyThickness(Angstroms)Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 185040302010042404230Reading

28、 No.6/22/xxStability - Example Trend chart for poly thickness measurements in a CVDarea. Something occurred on 6/22 to apparently change theprocess. The “change” was due to a faulty measurement tool.42507/11/xx6/9/xxCopyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 1

29、9The Measurement System Distribution:Location and Spread Location refers to where the measurement systemdistribution is “centered”. Bias (accuracy) is the difference between the observedaverage and the reference value. We will define precision as the standard deviation ofthe measurement error or act

30、ual measurementdistribution. We will denote it as Measurement Systemor MS.XXCopyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 20XXXXXXThe Measurement System Distribution:Location and Spread Which target, upper orlower, exhibits thesmaller bias? Which target exhibitsm

31、ore “precise” results?Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 21Calibration Procedure to compare readings from a tool witha standard reference. Centering the mean of the distribution ofreadings on the “true” or reference value. Requires the use of a traceab

32、le standard.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 22Precision Spread refers to the standard deviation of adistribution. The standard deviation of the measurement systemdistribution is called the precision, MS. Precision is made up of two sources of variat

33、ion orcomponents, one called repeatability and one calledreproducibility.Precision2 MS=+Reproducibility2 rpdRepeatability2 rptCopyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 23Repeatability The inherent variability of the measurement system. The variation that resu

34、lts when repeatedmeasurements are made of the same parameter underas absolutely identical conditions as possible:same operator.same set up procedure.same test unit.same environmental conditions.during a short interval of time.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Syst

35、ems2.4 - 24Repeatability Measured by RPT, the standard deviation of thedistribution of repeated measurements. Repeatability is usually much smaller (better)than the precision of the system.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2Measurement System = 2RPT2.4 - 25

36、+2RPDReproducibility The variation that results when different conditions areused to make the measurement:different operators.different set up procedures, maintenance procedures, etc.different parts.different environmental conditions. During a longer period of time. Measured by RPD.Copyright 2002 Mo

37、torola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 26BCAA2 + B2 = C22MS = 2RPT + 2RPDRelationship of Precision, Sigma RPT,Sigma RPDCopyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 27100 MS Total100 =6 MS6 Total%R & R =Metrics for Statistical Propertie

38、s% R&R% R&R (Percent Repeatability andReproducibility) is the width of themeasurement distribution as a fraction of thetotal distribution, expressed as a percentage.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems1006 MSUSL LSL2.4 - 28%P / T =Metrics for Statistical Prop

39、erties% P/T% P/T (Percent Precision to Tolerance Ratio) is thewidth of the measurement distribution as a fractionof tolerance window, expressed as a percentage.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 29Metrics for Statistical Properties%R&R Important for pr

40、ocess improvement studiesincluding the design of experiments. Focus is on the process variation and not onprocess specifications.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 30Metrics for Statistical Properties%P/T Important for Cp, Cpk studies. Ratios are defin

41、ed using specification limits. Important for discriminating between good andbad products.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement Systems2.4 - 31Requirements for MSA Metrics There are several factors to be considered when determiningthe acceptance of gauge repeatability

42、and reproducibilityvalues. The %R&R and %P/T values must be judged againstthe criticality of the measurement being made, the cost ofretraining people in using the gauge, the available resources,customers requirements, etc. In most cases, the gauge%R&R and %P/T results should be compared with thefoll

43、owing guidelines: Under 10% - Present gauge is acceptable. 10% to 30% - May be acceptable depending on the importanceof the application and various economic factors. Efforts shouldbe made to improve the gauge capability. Gauge should beconsidered unacceptable for critical measurements. Over 30% - Gauge is not suitable for use. Efforts must bemade to reduce the measurement variation.Copyright 2002 Motorola. All rights reserved.2.4 Evaluate Measurement