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Table B.1 Gage linearity and bias report for force measurements.
Force platform 1
Forcec platform 2
Predictor
Constant
Slope
Gage linearity
Coef
SE Coef
-1.14
0.30
-0.007 0.001
P
0.000
0.000
Predictor
Constant
Slope
Gage linearity
Coef
SE Coef
-0.70 0.22
-0.02 0.0008
P
0.000
0.000
S
Linearity
1.74
0.10
17.5%
0.7
S
Linearity
1.25
0.26
76%
2.0
Reference
Average
98
196
294
392
Gage bias
Bias
%Bias
-2.92
22.5
-3.33
25.6
-0.24
1.8
-4.45
34.2
-4.14
31.9
P
0.000
0.000
0.001
0.000
0.000
Reference
Average
98
196
294
392
Gage bias
Bias
%Bias
-5.62 43.2
-3.66 28.1
-2.68 20.6
-7.53 57.9
-8.61 66.2
R-Sq
%Linearity
R-Sq
%Linearity
P
0.000
0.000
0.000
0.000
0.000
and of the force platform 2 was −5.62 N. They represent the 22.5% and 43.2% of the process
variation, respectively, which was specified to be 13.015 N for both force platforms. The linearity
(change in bias across the range of product variation) represents 0.7% and 2% of that range for
force platform 1 and force platform 2, respectively. These are statistically significant changes in
the bias over the range of the reference values at the 5% significance level.
B.2.
Gage Repeatability and Reproducibility Study for Force
Measurements
B.2.1.
Background
A R&R study is a designed experiment to study the variation (Repeatability & Reproducibility) in the
measurements results. The Repeatability is an estimation of the variation between measurements
made by the same operator on the same part, usually attributed to the gage. The reproducibility is
an estimation of the variation between measurements made by different operators on the same
part, usually attributed to the operator. Since two force platforms were used in the study, an
expanded R&R analysis carried on with additional factor the force platforms (operators and parts
are the typical factors). Therefore, the variation between the measurements made by the two force
platforms can be added to the total Gage R&R variation. The objective of the current experiment
design was to estimate the repeatability and reproducibility of the force measurement system, and
to determine if the two force platforms are equally capable for measuring the different parts. The
response variable was the Fz of the ground reaction force.
B.2.2.
Design of Gage RR Experiment
A full factorial design of experiment (DOE) with 3 factors (Operators: 2-levels, Force platforms:
2-levels, Parts: 4-levels) and 16 treatment combinations that replicated 50 times in randomized
order was run to chart the response of the measurement process (expanded R&R design). The
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