Graphics and Robotics PDF
Preview Graphics and Robotics
StraBer • 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 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on micro-film or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution under the German Copyright Law. © Springer-Verlag Berlin Heidelberg 1995 Softcover reprint of the hardcover 1s t edition 1995 The use of general descriptive names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Cover Design: Konzept & Design, nvesheim Typesetting: Camera-ready by authors Printed on acid-free paper SPIN 10057326 33/3140 - 5 4 3 2 10 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
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