ABSTRACT Title of Thesis: SWARM INTELLIGENCE AND STIGMERGY: ROBOTIC IMPLEMENTATION OF FORAGING BEHAVIO R Mark Russell Edelen, Master of Science, 2003 Thesis directed by: Professor Jaime F. Cárdenas -García Professor Amr M. Baz Dep artment of Mechanical Engineering Swarm intelligence in multi -robot systems has become an important area of research within collective robotics. Researchers have gained inspiration from biological systems and proposed a variety of industrial , commercial , and military robotics applications. In order to bridge the gap between theory and application, a strong focus is required on robotic implementation of swarm intelligence. To date, theoretical research and computer simulations in the field have dominate d, with few successful demonstrations of swarm -intelligent robotic systems. In this thesis , a study of intelligent foraging behavior via indirect communication between simple individual agents is presented . Models of foraging are reviewed and analyzed with respect to the system dynamics and dependence on important parameters . Computer simulations are also conducted to gain an understanding of foraging behavior in systems with large populations. Finally, a novel robotic implementation is presented. The experiment successfully demonstrates cooperative group foraging behavior without direct communication. Trail -laying and trail -following are employed to produce the required stigmergic cooperation. Real robots are shown to achieve increased task efficien cy, as a group, resulting from indirect interactions. Experimental results also confirm that trail -based group foraging systems can adapt to dynamic environments. SWARM INTELLIGENCE AND STIGMERGY: ROBOTIC IMPLEMENTATION OF FORAGING BEHAVIO R by Mark Russell Edelen Thesis submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of Master of Science 2003 Advisory Committee: Professor Jaime F. Cárdenas-García, Co -chair Professor Amr M. Baz, Co -ch air Professor Balakumar Balachandran ©Copyright by Mark Russell Edelen 2003 Acknowledgements First and foremost, I would like to thank my heavenly Father and the Lord Jesus Christ, for making this possible. Without God’s supernatural intervention, I would never have persevered. All credit and praise belong to my God. I would like to thank Professors Amr Baz and Balakumar Balachandran for their assistance and support. A special thanks goes to Professor Jaime Cárdenas -García for all of his valuable advice and patience. I appreciate the freedom that he allowed me in pursuing a topic of my interest. That is a rare luxury, but he made it a reality. Lastly, thank you to everyone who played a role in proofreading this text, donating supplies, or simply supporting me while I labored. I want to thank you all for your understanding and selfless desire to help. ii Dedication You are my God, and I will give you thanks; You are my God, and I will exalt you. - Psalms 118:28 Whatever you do, work at it with all your heart, as working for the Lord, not for men, since you know that you will receive an inheritance from the Lord as a reward. It is the Lord Christ you are serving. - Colossians 3:23-24 Go to the ant, you sluggard! Consider her ways and be wise. - Proverbs 6:6 iii TABLE OF CONTENTS LIST OF TABLES ............................................................................................................ vii LIST OF FIGURES .........................................................................................................viii Chapter 1: Introduction....................................................................................................... 1 Chapter 2: Background – Swarm Robotics ......................................................................... 5 Section 2.1: Cooperative Mobile Robotics ............................................................. 5 Section 2.2: Ori gins of Swarm -Based Robotics ..................................................... 6 Section 2.3: Swarm Control Arc hitectures ............................................................. 8 Section 2.4: Communication................................................................................. 14 Section 2.5: Learning ............................................................................................ 16 Section 2.6: Morphologies .................................................................................... 17 Section 2.7: Cooperative Tasks in Mobile Ro botics ............................................. 23 Section 2.8: Conclu sion ........................................................................................ 34 Chapter 3: Biological Inspirations .................................................................................... 36 Section 3.1: Se lf -Organization in Biological Systems .......................................... 36 Section 3.2: Microscopic Organisms .................................................................... 43 Section 3.3: Social Insects .................................................................................... 44 Section 3.4: Birds, Fish, Mammals ....................................................................... 65 Section 3.5: Misconceptions of Self -Organization ............................................... 67 Chapter 4: Foraging Theory and System Modelling......................................................... 69 Section 4.1: Individ ual Agent Dynamics .............................................................. 69 Section 4.2: Foraging Theory and Task Efficiency .............................................. 71 iv Section 4.3: Mo deling Self -Organization ............................................................. 74 Section 4.4: Foraging Models ............................................................................... 78 Section 4.5: Model -Ba sed Predictions................................................................ 100 Chapter 5: Simulation ..................................................................................................... 102 Section 5.1: Why Simulate? ................................................................................ 102 Section 5.2: Introduction to StarLogo ................................................................. 103 Section 5.3: Program Description....................................................................... 104 Section 5.4: Simulated Scenarios........................................................................ 107 Sectio n 5.5: Results ............................................................................................. 110 Chapter 6: Experimental Design ..................................................................................... 150 Section 6.1: Experi mental Motivations and Goals ............................................. 150 Section 6.2: LEGO ® Mindstorms™ ................................................................... 153 Section 6.3: Disappearing Ink............................................................................. 158 Section 6.4: Mechanical Design ......................................................................... 161 Section 6.5: Behavior-based Programming ........................................................ 182 Section 6.6: Experimental Setup......................................................................... 190 Section 6.7: Experimental Cases ......................................................................... 195 Section 6.8: Results ............................................................................................. 197 Chapter 7: Analysis and Discussion ............................................................................... 211 Section 7.1: Disc ussion of Simulation Results ................................................... 211 Section 7.2: Discussion of Experimental Results ............................................... 218 Section 7.3: Compariso n of Results to Theoretical Predictions ......................... 224 Chapter 8: Conclusions................................................................................................... 228 v APPENDIX A – StarLogo Documentation .................................................................... 231 APPENDIX B – StarLogo Simulation Code .................................................................. 235 APPENDIX C – Bricx Command Center Documentation ............................................. 238 APPENDIX D – Not Quite C (NQC) Documentation.................................................... 239 APPENDIX E – NQC Program Code............................................................................. 247 APPENDIX F – LEGO Robot Assembly Instructions ................................................... 252 REFERENCES ............................................................................................................... 271 vi LIST OF TABLES Table 1. Robotic Locomotion Configurations ................................................................. 20 Table 2. Commercial Robot Platforms ............................................................................. 22 Table 3. Foraging Methods Used by Ants (adapted from [93], pp. 248-251) .................. 45 Table 4. Examples of self -organization in nature (adapted from [69], pp. 170 -171) ....... 66 Table 5. StarLogo Observer Procedures ......................................................................... 106 Table 6. Technical Specific ations for LEGO RCX [110]..............................................