Lecture Notes in Control and Information Sciences

Transcription

1 Lecture Notes in Control and Information Sciences Edited by A.V. Balakrishnan and M.Thoma 33 Peter Dransfield Hydraulic Control Systems - Design and Analysis of Their Dynamics Springer-Verlag Berlin Heidelberg New York 1981

2 Series Editors h~ V. Balakrishnan - M. Thoma Advisory Board I D. Davisson A. G. J. MacFarlane. H. Kwakernaak J. I Massey Ya. 7_ Tsypkin A. J. Viterbi Author Peter Dransfield, Ph.D., Department of Mechanical Engineering Monash University, Australia ISBN Springer-Vertag Berlin Heidelberg NewYork ISBN Springer-Verlag NewYork Heidelberg Berlin This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under 54 of the German Copyright Law where copies are made for other than private use a fee is payable to 'Verwertungsgesellschaft Wort', Munich. Springer-Verlag Berlin Heidelberg 1981 Printed in Germany Printing and binding: Beltz Offsetdruck, Hemsbach/Bergstr

3 PREFACE The Text centres around the ideas that for hydraulic control systems the quality of their dynamic response is important to their proper operation, prediction of dynamic response capability is best obtained via the development of dynamic models, the inability of many designers to efficiently effect predictive dynamic analysis has its roots in a lack of confidence in the forming of models, the use of po~ bon~ ~aphs is a natural and superior approach to the development of reliable dynamic models, digital simulation provides the most appropriate method for extracting response information from dynamic models. Among these, the use of bond graphs (abbreviation for power bond graphs) is paramount to the Text. Therefore, bond graphs are introduced, explained, demonstrated, and utilized in substantial detail. The features of bond graphs which make them desirable in the hydraulic control system design situation include their structural affinity with the real system and its components, the formality in the assembly of a bond graph structure, their modular and re-usable nature, and the provision of a structure from which the set of equations which become the model can be formally prepared. It is assumed that the reader has a general appreciation of the nature and operation of hydraulic control systems and their major components. The Text is written mainly for those mechanical and control engineers who would like to be able to include predictive dynamic analysis among their techniques for the design of hydraulic control systems but who find existing approaches unsatisfying or inappropriate. The Text should be suitable also for up to twenty hours in appropriate graduate or senior undergraduate courses, and for specialized extensiontype courses. For full appreciation of the Text, the reader will need to make a "break through" by thoroughly understanding and using the symbols and structures of bond graphs. Such a break through was literally forced on me by a graduate student whom I was supervising for a research Master degree. I gladly acknowledge my debt to Bevis Barnard, Senior Lecturer at Caulfield Institute of Technology, for the gentle persuasion emanating from his own discovery and conviction that bond graphs offered something unique to the modelling, simulation and design of powered control systems. I acknowledge also the conceptions of Henry Paynter, the original and sustained developmental work of Dean Karnopp and Ron Rosenburg, the work of bond graph entrepreneur Jean Thoma, the assistance of colleague Jacek Stecki, and the contributing work of a small but steady stream of undergraduate and graduate students including Rob Winton, M.K. Teo, Roger LaBrooy, Kevin Duke, S. Ramachandran, V.K.L. Mai, and Merren Cliff. Many people contribute to the production of a text. I single out two for special thanks and appreciation; Lorry Ryan and John Millar, both of Monash University, for their excellent work in typing and drafting respectively. And there is an individual without whose encouragement this Text would not have been completed my wife Nevillie whose support was sustained, inspirational, and essential. To those willing to learn, and to those willing to try a new way, welcome aboard. P.D. March 1981

4 CONTENTS PREFACE CHAPTER 1 INTRODUCTION 1.1 Introduction 1.2 A Design Philosophy 1.3 Dynamic Modelling 1.4 A Desirable Background 1.5 Arrangement of Text 1.6 Conclusion C~PTER NOTATION AND UNITS Introduction Notation Symbols Examples of Symbol Use Operations Equations Comments 2.3 Units 2.3.i Comments 2.4 References CHAPTER 3 CONVENTIONAL MODELLING PROCEDURES 3.I Introduction 3.2 Conventional Model Forms Informal Equation Set Transfer Function Vector-Matrix Models Block Diagrams and Signal Flow Graphs 3.3 Deriving the Model 3.4 Selection of Relationships 3.5 Selection of Parameter Values 3.6 Another Example 3.7 Conclusion 3.8 References CHAPTER 4 POWER FLOW MODELLING 4.1 Introduction 4.2 Power Ports 4.3 Describing Power Flow 4.4 Getting Equations 4.5 An Example 4.6 Summary 4.7 References CHAPTER 5 POWER BOND GRAPHS 5.1 In troduction 5.2 Bond Graph Terms and Symbols Effort and Flow Variables Sources Power Bonds Power Transformers Dynamic Effects Resistive Power Dissipation Capacitive Power Storage Inertive Power Storage Summing Junctions Summary of Basic Terms and Symbols ii ii

5 CHAPTER 5 (contd.} 5.3 Forming Power Bond Graph Structures Inertia Load with Friction Hydraulic Cylinder Induction Electric Motor A Simple System 5.4 Power Flow Directions, and Causality Introduction Directions of Power Flow Causality Exa/m~le: Hydraulic Cylinder Example : Induction Electric Motor Example: Simple cylinder-load System Summary 5.5 Preparing Equation Set In troduction Example: A Simple Component An Elementary System Example A More Cc~plete System Summary 5.6 Some Further Aspects of Bond Graphs Modulation of Effects Modulated Transformers Fields and Junction Structures Simplifications 5.7 Conclusion 5.8 References CHAPTER 6 SOLUTION OF POWER FLOW MODELS 6.i Introduction 6.2 Digital Simulation 6.3 Expression-Orientated CSSL' s 6.4 Conclusion 6.5 References CHAPTER 7 SELECTING EQUATIONS AND COEFFICIENTS 7.1 Introduction 7.2 Compliance Introduction Oil Compliance Values for Bulk Modulus Mechanical Compliance 7.3 Friction 7.4 Modelling Driven Loads Inherent Load s External Load Forces 7.5 Leakage Flowrate Re laticn shlps Coefficients 7.6 Relief Valve Flowrates Relationships Coefficients 7.7 Electric Induction Motor Re lation ships Model Coefficients Conclusion 7.8 Hydraulic Pumps Relationships Coefficients O O 9O i ii

6 VI CHAPTER 7 (contd.) Way Control Valves Introduction The Basic Relationship Valve Flow Nomenclature The Closed-Centre Control Valve The Open-Centre Control Valve The Tandem-Centre Control Valve Summary Actuators Introduction Linear Actuator Rotary Actuator (Hydraulic Motor) Equations and Coefficients Some Other Common Components Hydraulic Lines Filters Accumulators Some Other Valves (Check Valve, 148 Counterbalance Valve) 7.12 Conclusion References 152 CHAPTER 8 APPLICATIONS OF BOND GRAPHS Introduction Closed-Centre Valve-Controlled Inertia Load 153 with Friction 8.3 Loaded Hydraulic Servosystem Pump Sub-System Pump-Controlled Hydrostatic Drive Valve-Controlled Hydrostatic Drive A Lifting System Introduction Development of Bond Graph The Equations and Coefficients Simulation Conclusion A Highly Dynamic Electrohydraulic Control System Introduction The Bond Graph Conclusion Conclusion References 182 CHAPTER 9 OPTIMIZING DYNAMIC RESPONSE Introduction The Requirements Error Criteria Search Procedure Introduction Single-Parameter Optimization Multi-Par~eter Optimization Complex Example Conclusion References 194 CHAPTER i0 PHENOMENA WHICH CAN AFFECT RESPONSE Introduction 196

7 Vil CHAPTER i0 (contd.) 10.2 cavitation i0.2.1 General Discussion Cavitation in Modelling and Simulation 10.3 Hydraulic Backlash 10.4 Flow Forces in Valves i0.5 Hydraulic Lock i0.6 Contaminated Fluid i0.7 Conclusion 10.8 References CHAPTER ii APPENDIX 1 APPENDIX 2 CONCLUSION STATIC DESIGN APPROACHES SI CONVERSION FACTORS APPENDIX 3 DYNAMIC RESPONSE --A BIBLIOGRAPHY INDEX