1. Schilling Robotics
How to: Gauge Repeatability and Reproducability
August, 2012
This is an interactive Presentation: Click on the start button to begin!
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What is GR&R
• Gauge Repeatability and Reproducibility
• Repeatable – One operator can achieve the same
measurement multiple times
• Reproducible – Multiple operators can achieve the
same measurement.
• Gauge – is an estimate
• Gage - is an instrument used to measure a magnitude
or position
If at any time you need a definition click the info button and see if it is on the definition page
4. Why do we Care?
GR&R provides a quantitative way
for the IQC department to validate
our mechanical measuring systems
and operators.
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6. Starting Your GR&R Test
It is important to understand what you are trying to accomplish before
running a study.
CLICK ON THE ICON NEXT TO A TEST TO UNDERSTAND WHAT
THAT PARTICULAR TEST ACCOMPLISHES
Testing the Capability of an Operator
Testing the Accuracy & Precision of a Measuring Device
Testing the Quality of Incoming Parts
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7. Testing the Capability of an Operator
Purpose: This test is designed to show how well
operators are using measuring devices.
End Result: It can reveal if operators need training
or are sufficient on that particular
measuring device.
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8. How to Set up a GR&R to Determine:
The Capability of an Operator
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9. The Capability of an Operator:
Selecting Operators
Select the desired operators to be evaluated. Good
choices include but are not limited to the following
–New hires
–All employees on new machinery
–Trainers to ensure they are competent
–Inspectors who differ from the average “accept/reject”
rate
–Must have at least 2 operators per study.
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10. The Capability of an Operator:
Selecting a Measuring Device
When selecting a measuring
device make sure…
– To select a device commonly used
by the operators involved
– The device is calibrated
– Each operator uses the exact same
device
– The devices operational functions
are not compromised before or
during the testing period.
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11. The Capability of an Operator:
Selecting Parts
When picking parts make sure
you
– Use parts that have tolerance
ranges that match the measuring
device you selected
– Use “Bad Parts”
– Use completely different parts
– Use both parts that the operators
have and haven't seen
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Back to Tests
12. How to Set up a GR&R to Determine:
The Accuracy & Precision of a Measuring
Device
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13. Testing the Accuracy & Precision of a
Measuring Device
Purpose: This test is designed to validate that a
measuring device is accurate & precise for a
particular tolerance range.
End Result: Lead to re-calibration of a device or change
in the tolerance range that the measuring
device is allowed to inspect. Can also help
discover machines that are not worth their
cost.
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14. The Accuracy & Precision of a Measuring Device
Selecting Operators
Select operators who are competent on the selected
measuring device.
–Can use another GR&R to verify competency of the
operators
–Must have at least 2 operators per study
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15. The Accuracy & Precision of a Measuring Device:
Selecting a Measuring Device
Select the measuring device of
your choice.
– Should be a device that has reason
to be tested
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16. The Accuracy & Precision of a Measuring Device:
Selecting Parts
When picking parts make sure you
– Use parts that have tolerance ranges that match the
measuring device you selected
– Use “Bad Parts”
– Use parts that cover a certain tolerance range
– Use both parts that the operators have and haven't
seen
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Back to Tests
18. Guide Lines for an Effective Study
• The Manager of the study should be present during every trial
in the study
• Each trail must be conducted in similar environments
• Study should be conducted in a RANDOMIZED order
• Conduct Studies in a Non-bias fashion
• Minimize error by defining the measuring objective
completely.
• Do not reveal operators names when presenting you findings
• Every study should have…
– At least 2 operators (3)
– At least 5 parts (10)
– At least 2 trails (3)
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19. How to Set up a GR&R to Determine:
The Quality of Incoming Parts
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20. Testing the Quality of Incoming Parts
• Purpose: This test is equivalent to IQC inspection.
• End Result: Will determine if a part or group of parts is
in or out of spec.
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21. The Quality of Incoming Parts:
Selecting Operators
Select the top operators on the selected measuring
device.
–Must have at least 3 operators per study
–The more GOOD operators used the better the
results
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22. The Quality of Incoming Parts:
Selecting a Measuring Device
When selecting a measuring
device…
– Select a measuring device that is in
scope of the parts tolerance range
– Should be a device that has been
proven accurate and precise
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23. The Quality of Incoming Parts:
Selecting Parts
Use the incoming parts in question
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Back to Tests
26. Open a GR&R Study Worksheet
1. Open the program
2. Stat menu → quality tools → Gauge Study → Gauge R&R
Study Worksheet
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27. Open a GR&R Study Worksheet
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• Now complete the pop up box with the following information.
− Enter your number of parts (minimum of 5, typically 10+)
− Enter your number of Operators (minimum of 2, typically 3)
− Enter the number of replicates (minimum of 2, typically 3+)
− Now Click Options
− Ensure that “randomize runs within operator” is checked and click “OK”
− Click “Ok” to create the study
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NOTE: There is no optimum number of
parts, operators or replications to use. The
more the study has of each, the more
variation you can reveal but the more
variation you introduce. It all depends on the
system you are attempting to analyze
29. Editing GR&R Study Worksheet
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Add a measurement column to the worksheet and print out individual
copies for each operator for each trial.
NOW RUN YOUR STUDY & IPUT ALL THE DATA INTO MINITAB
32. Two Types of Data are Generated
Hard Data Graphical Data
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Generating Your Own Data
33. Take Away
• P/T or %Tolerance: Is the measurement system good
enough(precise) to measure against customer requirements.
• %R&R or %study variation: Is the measurement system good
enough to detect changes in the process.
• %Contribution: How much variation each component of the
study is providing
• P-T-P: Want to be as close to 100% as possible to show that
the variation is coming from the parts not the measuring
system.
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34. Hard Data
• The Numerical data that is generated
from the study
• What you're looking for
– % Contribution
• x≤1%= Acceptable
• 1%≤x≤9% = Rework considered but acceptable
• x≥9% = Fail
– % Study Variation
• x≤10%= Acceptable
• 10%≤x≤30% = Rework considered but acceptable
• x≥30%= Fail
– Number of Distinct categories (NDC)
• NDC >5
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Back to Analyzing Data
36. Components of Variation
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GOOD
BAD
The ideal graph has a low Gage R&R percentage, a
larger Part-to-Part percentage and Repeat & Reprod
percentages under 30%
37. R Chart By Operator
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The ideal graph should have all points inside the UCL
and LCL to be under control, If there are multiple points
lying outside these limits it depicts that there is not
enough consistency in the current measurement system
GOOD
BAD
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GOOD
BAD
Xbar Chart by Operator
There should be a lot of part variation and all data
on this plot should be outside the UCL and LCL,
demonstrating part variation is easy to detect.
39. Variation by Part Sample
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GOOD
BAD
The ideal chart should have a large variation
between parts showing that the measurement
system can detect different parts easily.
40. Measurement by Operators
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GOOD
BAD
The ideal chart will have little variation within each operator
[i.e. smaller gray box] and between all operators [i.e.
horizontal straight line connecting the grey boxes]. This
proves that the average is not effecting the final calculations.
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Parts * Operator Interaction
GOOD
BAD
The ideal chart would have parallel lines meaning that
there was no conflicting interactions proving the
measurement system is good.
Back to Analyzing Data
42. Generating Your Own Data
• One option is
Histograms
• To generate:
Graph Histogram
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From here a pop
up box will appear
asking you to
select the data you
wish to graph.
This training will cover an ANOVA Crossed GR&R study
MSA Pythagorean relation
Disclaimer that all number in this presentation are recommendations and vary depending on the source.
Also great for testing and maintaining quality work
This ensures that the operators are measuring according to the guidelines of the study
No significant temperature differences
Normal working environment for the inspector
If you testing operators, don’t tell them everything
Like where to measure thickness of a part
Provide them with parts that should not be measured using the devices at hand
Run GR&R First trial (2 teams of 3)
- pin gauges; 1 set per group
- calipers; 1 set per group
1 manager per team, 2 operators
Each operator measure once….
Ask them what they have learned from the study, where bias data can be introduced
Then Introduce mini tab
----- Meeting Notes (8/26/12 17:59) -----
Appears in the sessions tab
Also want to look at %Tolerance
Natural Variation is the variation that will always be present in a system due to the impracticality of eliminating all variation from anything.
