Master Thesis - Fachbereich Informatik

1.4. RELATED WORK 5
Length [mm] Tolerance [mm]
20 − 30 ±0.5
31 − 50 ±0.7
51 − 100 ±1.0
Table 1.2: Tolerance specifications of different tube lengths
lengths, the position of the printing is not consistent among the tubes and must not affect
the measuring results.
The tube length ranges from 20mm to 100mm. In this thesis, however, the focus will
be on 50mm tubes since this is the dominant length in production. The outer diameter
varies between 6mm and 12mm.
The tolerances differ between 0.5 and1.0mm depending on the tube length as can be
seen in Table 1.2. This table includes the tolerable deviations from a given target length
in mm.
Themeasurementshavetobeaccomplishedatlineproductiononaconveyorinrealtime.
The system is intended to reach a 100% control without reducing production velocity.
Currently the conveyor runs at approximately 20m/min, i.e. 3-17 tubes per second are
cut depending on the segment size. Theoretically the cutting machine is able to run at
up to 40m/min. A faster velocity results in less processing time per tube segment. The
system design must be robust with respect to industrial use. Theoretically, it must be
able to run stable 24 hours/day, 7 days/week and 365 days/year.
Although there are many different tube types, only one kind of tube is processed at
one production line over a certain period of time. This means, the tube segments to be
inspected on the conveyor are all of the same kind. However, to be flexible to customer
demands, a production line must be able to be rearranged to a different kind of tube
several times a day. This emphasizes the importance of an easy to operate calibration and
teach-in step of the inspection system for practical application.
The goal of the visual inspection is a reliable good/bad decision for each tube segment
whether it has to be sorted out or not. In the following, tube segments wrongly classified
as proper, but nevertheless deviating from the given target length above the allowed
tolerances (see Table 1.2), are denoted as false positives. On the other hand, false negatives
are tube segments that are classified for sorting out, although the actual length meets the
tolerances. To reach optimal product quality, the number of false positives must be reduced
to zero. Large numbers of false negatives indicate that the system is not adjusted properly
and has to be reconfigured.
1.4. Related Work
In Section 1.1 several examples of vision-based measuring systems in industrial applications
have been presented. Much more work in this area has been done over the past 20 years
[4]. However, MV related publications of academic interest often consider only specific
subproblems, but do not present a detailed insight of the whole system. On the other
hand, commercial manufacturers of MV systems hide the technical details in order to keep
the competitive advantage [18].