Master Thesis - Hochschule Bonn-Rhein-Sieg

2. Overview on human-robot Master Thesis Björn Ostermann page 17 of 126
but stopping and waiting in a safe distance from the intrusion. Its advantage is its simpler realisation,
which can be easier verified for freedom from errors.
Both approaches can be combined. In this case, only the distance measurement needs to be approved
for safety related work. The robot can not collide with any object due to path planning, if its approach
on those objects is monitored. The functionality of the path planning algorithm is then only relevant
for the performance of the process.
2.3.2 Necessary algorithms and features
To complete the given task several sub-goals had to be reached. The developed and applied solutions
are described in chapter 4 and 5.
There is no interface available from the manufacturer that allows the control of the chosen industrial
robot with a C++ program. To remotely control the robot, only a set of XML (extended markup
language) commands are available (see chapter 3.5 and chapter Fehler! Verweisquelle konnte nicht
gefunden werden.) that have to be sent to the robot via TCP/IP. From those XML commands an own
C++ interpreter had to be created. The XML commands are limited in their amount and can not be
extended by the user. The robot needed to be controlled with relative and absolute positioning
commands, but the relative positioning commands are not supported by the given XML commands.
The solution to the relative control was achieved in the R&D 2 project [78]. In this master thesis the
C++ library of the commands implemented in the R&D 2 was created (see source code on CD).
The chosen 3D camera delivers a set of image data, containing the distance of objects and their
reflectivity in the used near infrared spectrum. The image data delivered by the 3D camera can not be
interpreted by a human observer. The values of reflectivity are usually very close to each other,
resulting in a mostly black image when depicted in greyscale, and thus have to be enhanced, in order
to depict an understandable image. The distance data need to be interpreted by the program as well, to
show an understandable image.
The optical analysis by a human observer is not only necessary for the development process of the
final program. The illustration of the correctly working algorithm next to the robot can, especially at
the introduction of this new technology, also enhance the operators trust in the developed concept.
Algorithms for the reflection image as well as the distance image have been developed in previous
work [78] and combined in this thesis with highlighting algorithms that show the robot, dynamic
objects and the flexible border or the distance between robot and object, depending on the chosen
algorithm.
From the distance data, delivered by the 3D camera, the background of the empty workspace has to be
acquired as a reference image, in order to be able to find intrusions later. Those intrusions have to be
distinguished into robot and other objects. Problems in this area are mainly induced by the fluctuation
noise, present in the acquired distance data. In order to achieve the desired goal, filters had to be tested
and implemented, which reduce the fluctuation noise as much as possible.