Master Thesis - Fachbereich Informatik

3. Hardware Configuration
This chapter introduces the physical design of the visual inspection prototype. This includes
the conveyor, the camera setup, the choice of illumination as well as the blow out
mechanism. Figure 3.1 gives an overview on the hardware setup of the prototype.
3.1. Conveyor
For the prototype, a 200cm long and 10cm wide conveyor is used to simulate a production
line. It can be manually fit with several tube segments where the exact number depends
on the target length and the distance between two consecutive segments. The measuring
is performed at a certain area of the conveyor denoted as measuring area in the following.
The field of view of the camera is adjusted to this area, as well as the illumination as will
be introduced in Section 3.2 and 3.3 respectively.
The dimension of the measuring area depends on the size of the tubes to be measured.
Therefore, with respect to the range of tube sizes, the measuring area is designed to cover
the maximum tube size of 100mm in length and about 12mm in diameter. It must be
even larger to be able to capture several images of each tube while passing the visual field
of the camera.
Since in production the tubes are cut to lengths from a continuous tube using a rotating
knife (flying knife), there would not be a notable spacing between two consecutive tube
segments if transfered to the measuring area with the same speed as entering the knife.
Thus, it can be difficult to determine where one tube starts and ends in the continuous
line by looking both for humans and artificial vision sensors. To overcome this problem,
after cutting, the tube segments have to fall onto another conveyor with a faster velocity
to separate them. The faster the second conveyor is compared to the first one, the larger
the gap.
Since processing time is expensive, the goal is to simplify the measuring conditions as
much as possible using an elaborated hardware setup. One easy but effective simplification
is to mount two guide bars to the conveyor that guarantee almost horizontal oriented tube
segments. The guide bars are arranged like a narrow ‘V’ (see Figure 3.1(b)). The tubes
enter the guide bars at the wider end and are adjusted into horizontal position while
moving. At the measuring area the guide bars are almost parallel and just slightly wider
than the diameter of the tubes. The distance of the guide bars can be easily changed using
adjusting screws if the tube type changes.
The color and structure of the conveyor belt is crucial to maximize the contrast between
objects and background for the inspection task. Therefore, a white-colored belt is used.
The advantage of this choice with respect to the range of tube types to be inspected in
combination with the illumination setup will be discussed in more detail in Section 3.3.
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