TUESDAY, Session 5B, 2:30 PM - NCSL International · PDF fileTUESDAY, Session 5B, 2:30 PM ... - the calibration of calipers is performed a few ... vernier-calipers 38 % of tolerance)

Metrologie Service-Basis GmbH
TUESDAY, Session 5B, 2:30 PM
SIMULTANOUS IMPROVEMENT OF ACCURACY AND EFFICIENCY OF THE CALIPER CALIBRATION CAUSED BY
AUTOMATION

Content of this presentation The Business End of Metrology
Manual Calibration of Calipers (state of the art) - the calibration of calipers is performed a few million times a year worldwide - but it has problems and limitations - So we will formulate a task list for a method update
Automated calibration of Calipers - Technical realization of the project - Additional testing procedures
Benefits of a new Calibration Method - Efficiency improvement in a calibration lab - Accuracy improvement for the instrument user - Economic advantages
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Manual Calibration of Calipers State of the Art?
Part 1: PROBLEMS of the traditional calibration method
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Manual Calibration of Calipers What is the resolution of an human eye?
Light Gap testing - Human can only see linear gaps that are wider then 19,2 m (0.76 mil) - all problems of flatness and non-parallelism do influence the accuracy of the instrument directly
e.g. Tolerances DIN 862 20 m (0.79 mil) for digital (96 % of tolerance) 50 m (1.97 mil) for vernier-calipers 38 % of tolerance) 8/10/2012 4

Calibration procedure using block and ring gauges
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Influence of operating power If you are pushing to hard
What happens, if the operating force brought to a caliper will change? Youtube-Video Influence of force
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http://www.youtube.com/watch?v=kI_uAgguJ2E&list=FLpi2tScpkXUiCkIk04H1oNQ&index=3&feature=plcphttp://www.youtube.com/watch?v=kI_uAgguJ2E&list=FLpi2tScpkXUiCkIk04H1oNQ&index=3&feature=plcphttp://www.youtube.com/watch?v=kI_uAgguJ2E&list=FLpi2tScpkXUiCkIk04H1oNQ&index=3&feature=plcp

Force does influence the accuracy! Force, deviation, uncertainty
8/10/2012 7 Optimum Force for an individual caliper

Stability of the tool How strong are your hands?
Analyzing the average force vs. deviation curve - Using linear regression leads to a new quality factor Change of the displayed value in m The Stability = ------------------------------------------ Operating force in N
So far, we found a huge range - #1) min. - 1 m / N (very stable) #2) max. - 6 m /N (weak)
Imagine the operating force changes by 5 N - This leads to a ERROR of 30 m - out of tolerance (digital caliper)! - average force influence = 5 N x 3 m/N = 15 m (0.59 mil)
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Psychological Influence You cant stop thinking
During a normal calibration (without force control) - there are ridges or dirt on the jaws - some calipers indicate a little to much.
But how does the technician reacts? - almost everybody will increase the force he puts on the caliper automatically until he sees the right expected value - Bad instruments will be calibrated good
This leads to measuring ERRORS in the field - because there is no expectation, the force will not be varied in the same way - the technicians puts on the force, what feels good for him
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Psychological Influence graphic comparision
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Man adapts the force
to see the expected value
to hard pushing
to soft pushing

Manual Calibration It cant be better than .
Uncertainty calculation for a manual calibration - If you consider the discoveries mentioned before - If you include them into the uncertainty calculation model : (n) = normal, (r) = rectangular distribution
Manual calibration cant be more accurate than (k=2) 28,36 m (1.11 mil) -> 150 % of the tolerance of a digital caliper (DIN 862) 8/10/2012 11
Uncertainty Variance calc. value
Light gap testing 19,2 m (r) 11,1 m
Average force influence 15,0 m (n) 7,5 m
Digital resolution 2 x 5 (r) 2 x 2,9 m
Temperature, gauges, other (n) 2,7 m

Some Space for Improvements What there is to do
Task List for a new calibration method - Measures and compensates the influence of the operating force. - Is not effected by the psychological influence of an expected value. - Identifies ridges on the measuring jaws - Follows the rules of accredited calibration - Creates a conformance statement acc. to EN ISO 14253-1.
Provides adequate costs of calibration in relation to the purchasing price of the instruments.
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Automatic calibration Let a robot do that
Part 2: REALIZATION
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Realization Its not a laboratory, its a factory!
Calibration 2.0
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air-conditioned automated warehouse
Conveyor belts
Calibration robots for calipers capacity 500/day
Calibration robots for micrometers capacity 350
/day
Calibration robots for dial gauges capacity 350 /day

Automatic Calibration A fixed mounted camera is superior to the eye
Light Gap testing - the digital image recognition system is able to measure damages of the jaws if they are larger than > 3,5 m (0.14 mil)
Reminder: all problems of flatness and non-parallelism do influence the accuracy of the instrument directly
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Total Control curve force vs. time, duration = 63 sec
Recording of the force curve during the complete calibration
10.08.2012 16 Time [sec]
F
orc
e [N
]
Smooth run testing (1)
Force deviation curve (3)
Calibration with a constant force - (4-11) block gauges - (12- 13) ring gauges - (14) depth measurement - (15 ) step measurement

Automatic calibration one detailled view into the robot
Automatic calibration of calipers
objective
6-times faster
3-times less uncertain
cost saving
Youtube, view to our factory
more videos: http://www.youtube.com/user/msbasis2
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http://www.youtube.com/watch?v=PgtPNY0M0nc&list=FLpi2tScpkXUiCkIk04H1oNQ&index=1&feature=plcphttp://www.youtube.com/watch?v=PgtPNY0M0nc&list=FLpi2tScpkXUiCkIk04H1oNQ&index=1&feature=plcphttp://www.youtube.com/watch?v=PgtPNY0M0nc&list=FLpi2tScpkXUiCkIk04H1oNQ&index=1&feature=plcphttp://www.youtube.com/watch?v=PgtPNY0M0nc&list=FLpi2tScpkXUiCkIk04H1oNQ&index=1&feature=plcphttp://www.youtube.com/user/msbasis2http://www.youtube.com/user/msbasis2

Part 3: APPLICATION
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Automatic Calibration But, what for?
Accuracy is not a reason on its own
Which advantages result from a modernization of the calipers calibration procedure?
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Manufacturers
Advantages for manufacturers of measuring instruments
systematic and 100% reproducible testing *
Accuracy / repeatability * - approx. 3-times better than a manual calibration
determination of wear by performing a few hundred calibration with the same instrument - approx. 6-times faster than a manual calibration
* testing of new models
*testing of the correct torque to fix the slider
* testing design changes
* testing competitors instruments
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Advantages of Automatic Calibration

Design tests
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Competition analyses
Example: Test at Block gauge (41.30 mm outside) with a the same pressure force (14 N)
Product 1 reacts 3-times stronger on the force than the reference instrument
Springs, material and dimensions are designed less strong
Design change, change of supplier
Product 1,
under test:
average devation
= 41 m (1.61 mil)
Product 2 (> 200 tests)
average devation
= 14 m (0.55 mil)
repeat. 1 digit

Advantages of Automatic Calibration for the end-user
Advantages for the user of the instrument - Comparing the calibration record and diagrams for free-run, light-gap, deviation allows a determination of wear inside this single application - Sorting out problematic devices before they produce wrong results
The values for Stability and optimal force allow to - select the adequate instruments for
the application (sledge or building watches)
the user (body builder)
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Part 4: The Business End of Metrology
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Metrologi

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TUESDAY, Session 5B, 2:30 PM - NCSL International · PDF fileTUESDAY, Session 5B, 2:30 PM ... - the calibration of calipers is performed a few ... vernier-calipers 38 % of tolerance)