Master Thesis - Fachbereich Informatik

5.3. EXPERIMENTAL RESULTS 123
Length [mm]
50.4
50.2
50
49.8
49.6
Measurements
Mean
0 20 40 60 80 100
N
(a)
1
0.8
0.6
0.4
0.2
Measurement distribution
0
49.4 49.6 49.8 50
Length [mm]
50.2 50.4 50.6
Figure 5.19: Repeatability results of a metallic cylinder simulating a tube of 49.99mm ground
truth length. (a) 100 measurements of the gage at 30m/min. (b) Gaussian distribution of the
results with µ =49.94 and σ =0.033.
is also influenced by other parameters such as the tube orientation within the guide bars
and the limits of the discrete input image (although subpixel techniques are applied).
This experiment shows how accurate the vision-based system is able to measure even
transparent tubes if the tube edge detection is successful.
The experiment has been repeated with a metallic cylinder of 49.99mm length simulating
an ideal tube (gage). The cross-section of this gage is circular and not deformable manually.
The results of this experiment are shown in Figure 5.19(a) and (b). The mean over all
100 measurements is 49.94 with a standard deviation of 0.0331. This deviation is close to
the error that has been estimated in Section 4.2.6 with respect to the maximum possible
tube orientation within the guide bars.
One can conclude, as long as the orientation within the guide bars is neglected, the
maximum precision of the system is about 0.03mm for tubes that are ideally round and
not bent. This is much more than twice as precise as human measurements. It is assumed
that this precision could be even increased, if the tubes are not only approximately but
ideally horizontally oriented.
5.3.6. Outlier
The system is evaluated with respect to outliers in two steps. First more than 150 tubes
(about 50mm, ∅8mm) are measured by the system at 30m/min. Approximately 1/3 of
thetubesmeetthetoleranceswhiletheother2/3 have a manipulated length. The ground
truth length of the tubes is known as well as the measuring order, i.e. each measurement
can be assigned to a corresponding ground truth length. With the results of the previous
experiments one can assume that the results of the black tubes will be better or equal to
the transparent tube results.
The results of this experiment are visualized in Figure 5.20. All of the 150 tubes are
classified correctly. There is not a single false positive or false negative in the data.
In the second stage of this experiment 30 manipulated and 22 good tubes are randomly
mixed. All tubes are measured online at 30m/min while the blow out mechanism is
(b)