Table Of ContentStraBer • Wahl
Graphics and Robotics
Wolfgang StrafSer
Friedrich Wahl
Editors
Graphics
and Robotics
With 128 Figures,
some in Colour
, Springer
Prof. Dr.-lng. Wolfgang StraBer
Wilhelm-Schickard-lnstitut fUr lnformatik
Graphisch-lnteraktive Systeme
Universitat Tiibingen
Auf der Morgenstelle 10, C9
D-72076 Tiibingen, Germany
Prof. Dr.-lng. Friedrich Wahl
lnstitut fUr Robotik und ProzeBinformatik
Technische Universitat Braunschweig
Hamburger StraBe 267
D-3S114 Braunschweig, Germany
Library of Congress Cataloging-in-Publication Data
Graphics and robotics/Wolfgang Strasser, Friedrich Wahl. p. cm.
Includes bibliographical references and index.
ISBN-13: 978-3-540-58358-5 e-ISBN-13: 978-3-642-79210-6
DOl: 10.1007/978-3-642-79210-6
1. Robotics. 2. Computer graphics. I. Strasser, Wolfgang, 1941- .
II. Wahl, Friedrich. TJ211.G72 1995 629.8' 9266-dc20-95-36099 CIP
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Preface
This book is a result of the lectures and discussions held during the international
workshop on "Graphics & Robotics", which took place at SchloB Dagstuhl, FRG,
April 19-22, 1993. The event brought together leading experts from both disciplines
to identify common scientific problems, to present new solutions and to discuss
future research directions in graphics and robotics.
The papers included in this book were written after the workshop and reflect
the exchange of ideas and experiences during the workshop. The final selection was
made after a careful reviewing process.
The organisation of the papers:
Since the availability of reasonably priced graphical workstations, robot designers
and researchers have used these devices to anticipate the kinematic/dynamic be
havior of robots before actual construction and application. Nowadays, simulation
and offline programming constitute indispensable tools in modern production engi
neering. Nevertheless, there are still many efforts needed to further the knowledge
of efficient graphical representations and computer graphics algorithms to build
artificial robot worlds. A state-of-the-art introduction to the principles of robot
simulation is given in the first paper by Laloni et al. The contribution by Brunner
et al. outlines new simulation concepts in the framework of teleoperation such as
space applications. The papers of Miiller and Purgathofer et al. deal respectively
with path planning strategies and collision detection techniques for environments
with obstacles.
To extend the possibilities of virtual experimentation and artificial imagina
tion, worldwide investigations towards virtual reality are in progress. The paper
by Wachsmuth et al. outlines research in this direction and presents first results.
There are many international efforts to achieve task-level programming and/or
automated programming of robots/ assembly stations on the basis of product descrip
tions like CAD data for assemblies. These tasks need powerful modeling techniques
and geometric representation schemes and thus again are a common research area
for graphics and robotics people. The papers by Gutsche et al., Caracciolo et al., and
van Holland et al. stress this interesting field of active research. Advanced modeling
techniques for objects with curved surfaces are treated in the papers by Seidel and
Greiner. The paper by Klein shows how to integrate various surface representations
into one object-oriented programming environment and demonstrates the elegance
and power of object-oriented implementations.
VI
Certainly one further area of close interrelations between graphics and robotics
is the field of robot vision. It would have been beyond the scope of this workshop
to host this subject extensively - there are many events especially devoted to this
topic. In these proceedings there are four papers touching the area. The paper by
Kroll et al. outlines an interesting new approach for depth or range data acquisition,
which may be used for automated model-generation as described in the paper by
Winzen et al. The paper by Ehricke deals with the visualization of 3-dimensional
data and presents new and intuitive mechanisms for their quick interpretation.
The last paper of the book, by Gagalowicz, can be considered as the quintessence
of the workshop: his vision system for a domestic robot makes use of advanced theo
ries and techniques from both disciplines and defines the most challenging research
t.ask, which will be solved by joined efrorts of both scientific communities to free us
from housework and to leave - finally - housecleaning to the robot.
Wolfgang Strailer, Tiibingen Fritz Wahl, Braunschweig
June 1994
Table of Contents
Principles of Robot Simulation and their Application in a PC-based Robot
Simulation System ............................................................ 1
C. Laloni and F.M. Wahl
Graphical Robot Simulatjon within the Framework of an intelligent
TeleSensorProgramming System ............................................. 31
BcmhU1·d BrU1t1!Cl·, [(laus Arbtcr and Gc1"1tard Ilirzingcr
Using Graphics Algorithms as Subroutines in Collision Detection ............. 45
Heinrich Mullcr
CSG Based Collison Detection ............................................... 59
W. Purgathofer and M. Zeitler
Interactive Graphics Design with Situated Agents ............................ 73
/pke Wachsmuth and Yong Tao
Assembly Planning Using Symbolic Spatial Relationships ..................... 87
R. Gutsche, F. Riihrdanz and F.M. Wahl
From CAD Models to Assembly Planning ................................... 115
R. Caracciolo, E. Ceresole, T. De Martino and F. Giannini
Feature Modelling for Assembly ............................................. 131
Winfried van Holland, Willem F. Bronsvoort and Fredcrik W. Jansen
Triangular B-SplinesVor Modeling in Graphics and Robotics 149
Hans-Peter Seidel
Blending Surfaces with Minimal Curvature .................................. 163
Gunther Greiner
Surfaces in an object-oriented geometric framework ......................... 175
Reinhard [([ein
VIII
An Active Stereometric Triangulation Technique Using a Continuous
Pattern .................................................................... 191
A. Knoll and R. Sasse
Automatic Model-Generation for Image Analysis ............................ 207
A. Winzen and H. Niemann
Navigation Through Volume Data by Active Vision Methods ................ 221
Hans-Heino Ehricke
Towards a Vision System for a Domestic Robot ............................. 229
A. Gagalowicz
Principles of Robot Simulation and their
Application in a PC-based Robot Simula
tion System
C. Laloni and F. M. Wahl
Institute for Robotics and Computer Control, Technical University of Braunschweig
Hamburger Str. 267, D-38114 Braunschweig, Germany
Abstract
This paper addresses some fundamental topics which have to be regarded
during the design, implementation and usage of graphical robot simulation
systems.
After a short summary of robot simulation system purposes, we derive the
basic requirements, which have to be satisfied, in order to obtain a useful sim
ulation system. We show, that different modeling steps are necessary to build
up an internal representation of a robot arm and the robot work cell, which
can be used to simulate and visualize the execution of robot tasks. The main
parts of such a model are the geometrical and the kinematical representa
tion. Different geometrical representations and possible modeling techniques
are presented. In addition, general considerations about the computation of
the robot kinematics and its inverse, which plays an important role in off-line
robot program development, are made. An affixment technique which is used
to combine the kinematical and the geometrical model is introduced and the
working principle is demonstrated with the help of a modeled example world.
Finally we focus on some special aspects of robot simulation such as the
graphical visualization and the different interpretations of time within a sim
ulation system; in addition, we outline the main software modules, which are
more or less incorporated in each graphical robot simulation system.
2
Many of the discussed principles of graphical robot simulation are illus
trated by means of a PC-based graphical robot simulation system. This
system was designed and implemented at our institute and is currently used
to teach students some principles of robotics within practical courses.
1 Introduction
The simulation of robots and robot work cells is one of the main aspects in the
field of robotics research. To understand the importance of graphical robot
simulation, it is helpful to consider the various aspects why and where graphic
robot simulations are used. During the design of new robot arm structures
and work cell layouts the functionality of the robot and the work cell can
be tested without building expensive prototypes. In addition, existing robot
work cell layouts can be optimized easily; thus, e.g., the optimal position of
the robot arm, tools or workpieces can be determined within the simulated
work cell.
A fundamental advantage in industrial applications is the usage of simula
tion systems for off-line program development; due to this, it is not necessary
to interrupt the work of the real world robots which usually are integrated
in a complex production line. This saves money, because the factory pro
duction need not to be hindered. The verification of robot trajectories and
the possibilities of early object collision detection within simulation systems
provide a higher security and prevent serious damages. Even the coordina
tion of multiple robots, which usually requires more careful planning can be
tested without any danger to man and machine. Finally, the use of robot
simulation systems should not be underestimated in the fields of research
and education. New control algorithms, e.g., can be tested long before the
corresponding hardware is available and students can be taught the principles
of robotics on simulation systems inexpensively and safely.
To obtain this wide range of functionalities, it is clear that a robot simula
tion system has to satisfy a variety of requirements. In the following, some
of the basic requirements are discussed and the associated techniques which
are used to fulfill these requirements are presented.
First of all, the robot arm and each component of the robot work cell has to
be modeled. As we will show in section 2, this modeling consists of various
steps, depending on the type of objects which have to be modeled, or the
purpose of the simulation. The main modeling steps, which are discussed in
more details in this paper are the geometrical modeling (section 2.1) and the
kinematical modeling steps (section 2.2).
To achieve a 3d graphical animation capability, the previously defined
graphical model of the objects or object parts and the kinematic model have
to be combined. This is done in robot simulation systems by using the so
called aflixment data-structures, which are presented in section 3. As we will
show, with these affixments a simulated world can be completely modeled
3
and even object relationships such as 'object A is mounted to object B', or
'object C is gripped by the robot's hand' can be expressed.
Subsequently, the main software modules, constituting a typical robot simu
lation system and their organization is described in section 4. Simultaneously
we consider some additional aspects which have to be regarded during the
simulation. Thus, a variety of tools like a robot program editor and inter
preter are necessary to achieve a comfortable simulation environment with
off-line robot programming capabilities. In addition we show, how virtual
cameras can be used (see also section 4), to enhance the visual output and to
give the user an optimal visual feedback during fine positioning tasks. Fur
ther, we explain the importance of the term time within a graphical robot
simulation system. Especially, if the simulation computation only can be
done off-line and the simulation time is not identically with the simulated
time, it is necessary to get correct information about elapsed times, if the
simulated actions should be executed in a real world environment.
Finally we summarize the main topics of this paper and give a a short
conclusion.
2 Modeling of Robots and Components
If we consider a typical robot work cell or robot environment, we basically
can distinguish different components which have to be modeled within the
robot simulation system. Usually, the main component is the robot arm
itself. In addition to this, there are grippers and tools, such as welding
guns or screw drivers, which are used by the robot. In contrast to these
components, belonging directly to the robot, there are the components of
the robot environment. These components can be divided into two main
classes - dynamic and static environment components. The class of dynamic
environment components consists of all objects, which are able to perform
autonomous actions or which can be activated by external applied forces.
Typically, part suppliers, feeders or conveyer belts belong to this class. The
remaining environment objects, such as walls, desks, control units etc. are
constituting the class of the static environment components.
Each of these components has to be modeled; depending on the type of
object, different modeling steps have to be performed.
Usually the first modeling step is the definition of a geometrical model. This
model is necessary for the visualization of the simulated work cell during the
simulation period. The various representation forms, which can be used are
outlined in section 2.1. To build up such a graphical representation, special
graphical editors (e.g. CAD systems) can be used. Some basic and simple
object construction methods, which were implemented within our PC-based
simulation system [Schlorff88, Laloni+91] are explained in section 2.
In addition to this, a kinematic description (section 2.2) is necessary for
all mechanical parts, which are able to perform any kind of motion; typical
