Applied Dynamics of Manipulation Robots

Transcription

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2 Miomir Vukobratovic Applied Dynamics of Manipulation Robots Modelling, Analysis and Examples With 176 Figures Springer-Verlag Berlin Heidelberg New York London Paris Tokyo Hong Kong

3 Professor Miomir Vukobratovic, Ph. D., D. Sc. Corr. member of Serbian Academy of Sciences and Arts Foreign member of Soviet Academy of Sciences Institute Mihailo Pupin Volgina 15 P.O. Box Beograd Yugoslavia Based on the original Primenjena Dinamika Manipulacionih Robota published by NIRO"Tehnicka Knjiga", Beograd, Yugoslavia ISBN-13: e-isbn-13: : / This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specificaily the rights of translation, reprinting, re-use of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and stordge in data banks. Duplication of this publication or parts thereof is only permitted under the provision of the German Copyright Law of September9, 1965, in its version of June 24, 1985,and a copyright fee must always be paid. Violations fall under the prosecution act of the German Copyright Law. Springer-Verlag Berlin Heidelberg 1989 Softcover reprint of the hardcover 1st edition 1989 The use of registered names,trddemarks,etc. in this publication does not imply,even in the absence ofa specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use Printed on acid-free paper

4 Preface During the period , six books of the series: Scientific Fundamentals of Robotics were published by Springer-Verlag. In chronological order these were: Dynamics of Manipulation Robots: Theory and Application, by M. Vukobratovic and V. Potkonjak, Control of Manipulation Robots: Theory and Application, by M. vukobratovic and D. Stokic, Kinematics and Trajectory Synthesis of Manipulation Robots, by M. Vukobratovic and H. Kircanski, Real-Time Dynamics of Hanipulation Robots by M. Vukobratovic and N. Kircanski, Non-Adaptive and Adaptive Control of Manipulation Robots, by M. Vukobratovic, D. Stokic and N. Kircanski and Computer-Aided Design and Applied Dynamics of Manipulation Robots, by M. Vukobratovic and V. Potkonjak. Within the series, during 1989, two monographs dealing with new subjects will be published. So far, amongst the published monographs, Vol. 1 has been translated into Japanese, Volumes 2 and 5 into Russian, and Volumes 1-6 will appear in Chinese and Hungarian. In the author's opinion, the afore mentioned monographs, in principle, cover with sufficient breadth, the topics devoted to the design of robots and their control systems, at the level of post-graduate study in robotics. However, if this material was also to apply to the study of robotics at under-graduate level, it would have to be modified so as to obtain the character of a textbook. With this in mind, it must be noted that the subject matter contained in the text cannot be simplified but can only be elaborated in more detail. This reasoning is derived from the fact that contemporary design of robots and their control systems do not allow for different levels of approach, that is, one applicable to postgraduate and the other to undergraduate study. Thus, this textbook series will in essence contain no simplifications in comparison with the preceding series of research monographs.

5 VI This series was envisaged as bearing the contents of a course in robotics involving the study of modern techniques in the design of robots and their control systems. This would encompass the treatment of controlling robots at the lowest execution level as well as cooperative robot perfornance and robot control at higher levels, such as is encountered in controlling flexible manufacturing cells and lines. The minimal, yet sufficiently autonomous part of the series, consists of two books of the following content. The first is devoted to the study of manipulation robot dynamics and its applications. It embodies a computational procedure for the automatic generation of mathematical models of robot dynamics, comprising the linearized models of robot dynamics and the parameter sensitivity models together with a selection of problems of practical significance involving the complete models of robot dynamics operating under conditions of constrained and unconstrained work space. The second book treats the problem of controlling manipulation robots with the use of mathematical models of their dynamics which were studied in the first book. It further presents the problems associated with the numerical complexity involved in the executi?n of various control tasks and in their microcomputer implementation. Special attention was focussed on the programming support to the synthesis of - \ control laws which are based on the complete mathematical models of robotic manipulator dynamics. It is possible to extend the scope of the books in this series to include: the study of robot kinematics involving the non-redundant and redundant mechanical configurations, synthesis of trajectories in space with and without constraints and obstacles, material relating to computer-aided design of robots, programming and robot teaching, synthesis of the multilevel control of flexible manufacturing cells, the study of dynamics and control synthesis of elastic robotic mechanisms, expert systems for robot control synthesis of adaptive algorithms etc. As previously mentioned, this book is devoted to the study of manipulation robot dynamics and its application. It is organized into three chapters and nine appendices. The first chapter presents definitions and systematization of robotic systems as well their features and specification.

6 VII The second chapter constitutes the central part of the book. It includes the computer-aided procedure for automatic generation of mathematical models of rigid body manipulation robots dynamics having an open kinematic chain structure and cooperative manipulation. Dynamic models of robotic manipulators with elastic links are also presented. Theprocedure presented is founded upon the general theorems of mechanics and describes, in chronological order, the first method for computer-aided generation of mathematical models of rigid body robotic mechanisms. This procedure was selected, among other practical and educational resons, because it adheres to the physical essence of the problem in practically all stages of mathematical model generation. Furthermore, Chapter 2 considers mechanical vibrations of fundament and their influence on the overall accuracy of the robot, and also regards the problems involving constraints on robot gripper motion. Dynamic model of such constrained gripper motion is presented. Chapter 3 deals with automatic procedures for forming the linearized and parameter sensitivity models. These procedures naturally belong to Book 1 since both, the linearized models and models of parameter sensitivity will be used in the forthcoming books of the series dealing with non-adaptive and adaptive dynamic control synthesis of robotic manipulators. The distinctiveness of this book is highlighted by the relatively large number of appendices. Appendix 1 contains the coordinate transformations between two orthogonal coordinate systems which provide for better understanding of the relationships between the local and the fixed coordinate systems. Denavit-Hartenberg coordinates, which are thought to be best suited to the forming of kinematic models of robotic mechanisms, as well the correlation between them and Rodrigue's formula, are presented in Appendix 2. The fundamental relations between kinematic variables of a rigid body or more precisely of a robotic mechanism's kinematic pair, are given in Appendix 3, and moment of momentum, as well as Euler's dynamic equations of a rigid body are presented in Appendix 4. In Appendix 5, the conditions under which a link of a robotic mechanism

7 VIII can be approximated as a cane are derived. This leads to significant simplifications in the formation of dynamic equations of robot motion. Mathematical models of actuator units of different types and varying complexity are given in Appendix 6. On the basis of the formed mathematical models of actuator dynamics, the complete mathematical model including the dynamics of the robotic mechanism can be formed. The most characteristic examples of "STANFORD" robot and UMS-2 cylindrical manipulator configuration are given in Appendix 7. The dynamic equations of motion of these examples were derived "by hand" in compliance with the algorithm for automatic generation of mathematical models given in Chapter 2. In this manner, the computational procedure is systematically presented using the basic (3 d.o.f.) configuration of characteristic manipulation robot types. In Appendix 8, dynamic equations of the "ASEA" mechanism basic configuration are derived. In order to provide full autonomy of the computer-aided generation of dynamic equations of an open, arbitrarily complex, kinematic configuration of the manipulation mechanism, Appendix 9 contains the programme for nominal dynamics calculation of manipulation robots based on Newton-Euler's equations, described in Paragraph 2.1. This programme is written in programming language FORTRAN-77 and it can be used on arbitrary computer system with FORTRAN compiler. In Appendix 9, the programme for automatic linearization of the dynamic model of a manipulation mechanism having an open chain configuration is presented, too. Appendix 9 presents the programme VIBRO, on the basis of which and in conjunction with the main programme, the problem of mechanical vibrations at the robot fundament or vibrations in mechanisms with a mobile first link,issolved. Appendix 9 also presents the programming support for solving the robot dynamics in cases where dynamic constraints are imposed on the manipulator gripper motion. This book is primarily dedicated to students of undergraduate courses in robotics as well as to the engineers whose research interests lie in the field of mathematical modelling of robotic mechanism dynamics. However, it is also of importance to post-graduate students and speciaily to those concerned with non-adaptive and adaptive control based on complete dynamic models of robotic mechanisms. In this age of torrential development in robotics, it would be, of course, pointless and rather conservative to approach the problem of dynamic model generation, which is the crucial information in contemporary design of robotic

8 IX mechanisms, in the classical manner of constructing it "by hand". On the other hand, there should be no significant difference in the level at which research is undertaken, at undergraduate or post graduate study, especially not in as far as mathematical modelling of robotic mechanisms is concerned. It should be underlined, too, that besides its basic textbook character, this book has also some characteristics of a monograph, concerning results on modelling of elastic robots and cooperative manipulation, presented here for the first time. It has to be pointed out that this book was meant as lecture material at technical faculties and for engineers to whom robot dynamics will be not the aim, but the means towards the solution of problems in robot control. For this reason, it was the opinion of the author, that this book should be free of extensive presentation of alternative techniques for generating mathematical models of robot mechanism dynamics. Hence, in this book robot dynamics is presented only as direct function of the concrete application of the modelling task. The presented mathematical models of robot dynamics do not include the effects of dry friction which appear in conventional realizations of mechanical transmission. Due to the evident trend towards direct drive motor application, the exclusion of friction forces becomes justifiable and in view of the delicacy involved in calculating these effects, provides the means for considerably simplifying the mechanism model. Furthermore, in these situations where the exclusion of dry friction effects is justified, and at the same time the model retains its fidelity, its significance in the control law synthesis of robotic systems becomes evident It is also clear that tasks involving adaptive control introduce the requirement for exceptionally effective computational procedures for generating mathematical models of robot dynamics which are to be implemented on modern micro-computer systems. Such procedures, which are based on symbolic modelling concept will for obvious reasons not be dealt with in this book. Instead, it will be the subject studied in one of the forthcoming books of this series which will consider the problems associated with the numerical complexity in the derivation of control laws and their subsequent microcomputer implementation, as well as the synthesis of the general purpose digital controller. The fact remains that the programme support to the modelling of robot dynamics which was given in Appendix 9 is of general interest, since the algorithm upon which it is founded is a general one, and as such, includes

9 x all phases of the model generation process, from mechanism assembly to the problem of solving the direct and inverse dynamics. As previously mentioned, this version of the application software is suitable for modular extension as well as for specific purpose applications and as such, the author believes it, to be the very procedure naturally belonging to this type of book. f.1ore detailed involvement in the dynamics of robotic mechanisms which can be of interest to mechanical engineers and applied mathematicians whose research interests lie within this domain of technical science, can be found in the bibliography at the end of Chapter 2. I think that this textbook will enable the reader to gain a sufficient knowledge for his further work on the problems of dynamics and dynamic analysis of robotic systems and for implementation of theoretical approaches into-practice. We want the reader to develop an engineer'sapproach to the subject and to direct him to use computer approach to learn robot dynamics, as this approach enables efficient linking of mathematical models and the practical requirements to be realized by current robots. How well we have succeeded it remains to be judged on the basis of the use of this book as a textbook in teaching practice, as well as in the research and development units for applied robotics. In relation to this book, and bearing in mind the contributions which have been made towards the development of computer oriented methods based on general theorems of mechanics, I wish to give some comments. In this book chronologically the first method of a numerical-iterative type was presented. I profit of this opportunity to mention Vesna Zivkovic, Ph.D., a senior researcher at "Mihailo Pupin" Institute for her efforts in further operationalization and realizing the basic version of the computer programme (1977), based on the algorithm presented in this book, which was provided foremostly by Y. Stepanenko (1971, 1974) and extended by the author of this book and Y. Stepanenko (1972, 1973, 1976) on the class of anthropomorphic mechanisms. Subsequent computer -oriented methods presented in several joint papers and the monograph with V. Potkonjak, Ph.D. used the same principle for mathematical models generation of robot dynamics but were based either on 2nd order Lagrange's equations or else Appel's equations and Gibb's acceleration functions. I would also like to emphasize the activity of Nenad Kircanski, Ph.D.,

10 XI senior researcher at the Robotics Laboratory of the "Mihailo Pupin" Institute, who, on the basis of the same method of general theorems, together with the author of this book developed new efficient numerical-symbolic procedure which was presented in Volume 4 of the aforementioned Springer-Verlag monographic series. The latest results in the field of modelling the dynamics of manipulation robots are the symbolic models which belong to the efficient single-step and multi -step customized algorithms, in the creation of which substantial contribution was done by A. Timcenko, junior researcher, as well. The author wishes to express his gratitude to associates in the Laboratory for Robotics and Flexible Automation of the "r1ihailo Pupin" Institute, B. Karan senior researcher, D. Katie, Miss N. Djurovic, Lj. Zaric, N. Djuric, junior researchers, for elaborating the mathematical models of typical robotic mechanisms and driving units, as well as to M. Djurovic for derivation of the dynamic model of "ASEA" mechanism based on adopted computer-aided procedure for the mathematical modelling of robotic mechanisms. The author is also grateful to D. Vujic Ph.D. for his extension of programme support for manipulation robotdynamics with constrained gripper motion and vibrations of fundament, as well as to junior researcher A. Rodic for his participating in testing of the mentioned software. The author expresses his thanks to D. i!lurdilovic, M. Sc. for his essential contribution in conceiving the text dedicated to flexible manipulation robots, as well as to Miss M. Kolarski and M. Kostic research assistants for their programming and testing of the "ASEA" dynamic model. I further extend my gratitude to D. Hristic, Ph.D. for his high professional reading of the text and useful remarks, as well as to Professor M. Micunovic who reviewed the Serbo-Croation edition of this book. Finally, my appreciation goes to Miss V. Cosic for her excellent typing of the entire book. December 1988, Beograd, Yugoslavia Aut h 0 r

11 Contents Chapter! GenemlAboutRobou 1.1. Dedication and classification of robotic systems General features of robotic mechanisms and its classification Specifities of manipulation robots Definition of position of an object in space Structure of an industrial manipulation robot Disposition of segments and their connections Simple chain structure types Mobility index and degrees of freedom of a manipulation robot Redundancy and singularity Degrees of freedom of a task: (d.o.f.t.) Compatibility Oecoupling the orientation and the position of the terminal device Different minimal configurations Workspace Compari'son of the workspaces of different minimal configurations References Chapter 2 Computer Forming of Mathematical Model of Manipulation Robou Dynamics General about computer-oriented procedures for forming of mathematical models of robot dynamics

12 XIII 2.2. Complete mathematical models of manipulation robots Influence of mechanical vibrations on dynamic behaviour of manipulation robots Example Dynamics of manipulation robots with gripper constrained motion Example : Dynamic analysis of manipulation robots Example Dynamics of flexible manipulation robots Approximate method for dynamic analysis of flexible manipulation robots Dynamics of cooperative manipulation References Chapter 3 Computer Method for Linearization and Parameter Sensitivity of Manipulation Robots Dynamic Models Introduction Method of computer linearization of dynamic models based on general theorems of mechanics Sensitivity analysis of manipulation robots dynamic models. 172 References Appendix 1 Connection Between the Moving and Fixed System 187 References Appendix 2 Manipulator Kinematical Model Examples References 214 Appendix 3 Determining Velocities and Accelerations References

13 XIV Appendix 4 Momentum of Rigid Body with Respect to a Fixed Pole References 220 Appendix 5 Specifities of Lever-Mechanisms Dynamics 221 Appendix 6 Mathematical Models of Driving Units Introduction Permanent-magnet DC servomotor AC servomotor Synchronous motors with permanent magnet rotor (SM) Direct-drive motor 240 Brushless DC servomotors Electrohydraulic actuators 253 Electropneumatic actuators 273 References 283 Appendix 7 Automatic Forming of Dynamic Models 284 Example 1: "Cylindrical" Mechanism (Basic Configuration) Introduction Example 2: "Stanford" Manipulator (Basic Configuration) Introduction 300 Appendix 8 Dynamics of "A SEA" Mechanism (Basic Configuration) 334 Kinematics Dynamics Source file for the computation of "ASEA" mechanism driving torques Appendix 9 Programme Support for Dynamics Modelling of Manipulation Robots Subject Index