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From Ants to Service Robots: an Exploration in Stigmergy-Based Navigation Algorithms عمر بهر تيری محبت ميری خدمت گر رہی ميں تری خدمت کےقابل جب هوا توچل بسی )اقبال( To my late parents with love and eternal appreciation, whom I lost during my PhD studies Örebro Studies in Technology 79 ALI ABDUL KHALIQ From Ants to Service Robots: an Exploration in Stigmergy-Based Navigation Algorithms © Ali Abdul Khaliq, 2018 Title: From Ants to Service Robots: an Exploration in Stigmergy-Based Navigation Algorithms Publisher: Örebro University 2018 www.publications.oru.se Print: Örebro University, Repro 05/2018 ISSN 1650-8580 ISBN 978-91-7529-253-3 Abstract Ali Abdul Khaliq (2018): From Ants to Service Robots: an Exploration in Stigmergy-Based Navigation Algorithms. Örebro Studies in Technology 79. Navigation is a core functionality of mobile robots. To navigate autonomously, a mobile robot typically relies on internal maps, self-localization, and path plan- ning. Reliable navigation usually comes at the cost of expensive sensors and often requires significant computational overhead. Many insects in nature perform robust, close-to-optimal goal directed naviga- tion without having the luxury of sophisticated sensors, powerful computational resources, or even an internally stored map. They do so by exploiting a simple but powerful principle called stigmergy: they use their environment as an external memory to store, read and share information. In this thesis, we explore the use of stigmergy as an alternative route to realize autonomous navigation in practical robotic systems. In our approach, we realize a stigmergic medium using RFID (Radio Frequency Identification) technology by embedding a grid of read-write RFID tags in the floor. A set of mobile robots, then, build and store maps used for navigation in the stigmergic medium itself. These maps are of three types: (1) goal maps which guide robots to known locations; (2) clearance maps which help robots avoid obstacles; (3) feature maps which can be used to store observable properties, such as light intensity or gas concentration. We show how these maps can be built both in static and in dynamic environments and used for navigation of heterogeneous robots. We also show that goal maps can be used for navigation to previously unknown and/or dynamic locations, and that feature maps can be used to navi- gate towards specific features, e.g., places with high gas concentration that are beyond the sensor’s range. We address the issue of perceptual errors (e.g., broken tags) during navigation. We further study the use of the built navigation maps to enable different types of human-aware robot navigation on the RFID floor. We define several stigmergic algorithms for building maps and navigating on these maps. We formally analyse the properties of the main algorithms, and em- pirically evaluate all the algorithms both in simulation and with multiple physical robots. Results collected from tens of hours of real experiments and thousands of simulated runs demonstrate the effectiveness of our approach. Keywords: Stigmergy, Minimalistic Robots, Mobile robot navigation, RFID technology, Multi-robot system, Path planning, Localization, Map building. Ali Abdul Khaliq, School of Science and Technology Örebro University, SE-70182 Örebro, Sweden, [email protected] Acknowledgement Writing this part of the thesis has refreshen the memories of my PhD years, starting all the way back to my initial days in the lab when Ales- sandro gave me tiny robots to play with (of course I was given larger sized robots to play with later as I progressed). And the journey began: reading a lot of research articles, conducting exciting experiments, late night dead- lines, early morning teaching assistance, and finally thesis writing. The completion of this journey would not have been possible without some wonderful people, hence, I would like to take this opportunity to express my gratitude to all these wonderful people. First and foremost, I would like to express my deepest gratitude to my main supervisor Prof. Alessandro Saffiotti for believing in me and giving me the opportunity to work under his guidance. His knowledge, expertise, through feedback and support during the stressful moments have been invaluable throughout my PhD studies. I would like to express my heart- felt gratitude to my co-supervisor, Federico Pecora for detailed discus- sions, constructive comments, and encouragement. Working with both of my supervisors has not only helped producing this thesis, but also boosted my self-confidence in dealing with scientific issues and shaped my way of looking into problems. More supportive and considerate supervisors I could not have asked for. Thank you, Alessandro and Federico. Many thanks to Dr. Maurizio Di Rocco, who was my co-supervisor in the first year of my PhD, for inspiring discussions and advises that helped a lot in creating a better start for my PhD. I would like to thank my re- viewer, opponent, and committee members that took the time to review my work. I would like to thank all AASS people for providing a friendly and great working environment. Among the AASS people, special thanks go to Marco Trincavelli, Sepideh Pashami and Victor Hernandez Bennetts for their guidance before starting and in the initial phase of my PhD studies. Thanks also go to our lab engineers Per Sporrong and Bo-Lennart Silfverdal for providing technical support and customized building of the RFID antennas. Many thanks to Chittaranjan, Hadi, Iran, Marjan, Ravi, Sai, and Stevan with whom I not only had constructive discussions in the lab but also a good time outside the lab. Thank you, Alberto, André, and Neziha for nice chitchats during the coffee breaks. I would like to extend my thanks to wonderful Pakistani circle of friends (mini Pakistan in Örebro) for their moral support and making my stay pleasant in Örebro during my PhD studies (in alphabetical order): Abdullah, Ali, Idrees, Muneeb, M. Abdullah, Qasim, Shoaib, Taimur, Umer, and Zulqarnain. Thank you, wonderful families, for making Öre- bro feel like home and for the delicious food! (in alphabetical order): Amin, Asif, Faisal, Farrukh, Humanyun, Mubashar, Naeem, and Naveed. Last but not the least, my gratitude goes to those without whom none of this would be possible in the first place: my wonderful family. I would like to thank my sisters: Zaib, for being most encouraging and caring; Sajeela, for being my strength and my best friend; Romana, for being most supportive and loving; Uzma, for being caring and the heart of the family; my brother Khuram, for being my childhood mentor. Despite being far away, I can always count on them. I wish I could thank my late mother Jamila and my late father Abdul khaliq for their unconditional support, endless sacrifices, countless prayers, immense love throughout my life and, believing in me. The void they left will never be filled again. People go, but memories remain. Contents 1 Introduction 1 1.1 Stigmergy in nature ......................... 1 1.1.1 Stigmergic medium ..................... 2 1.1.2 Stigmergic agents ...................... 3 1.1.3 Stigmergic algorithms ................... 3 1.1.4 Stigmergic tasks ....................... 3 1.1.5 Stigmergic maps ...................... 4 1.2 Realization of stigmergy in robots ................. 4 1.2.1 The stigmergic medium: RFID floor ............ 4 1.2.2 Robotic agents ....................... 5 1.2.3 Human agents ....................... 5 1.3 Objectives of this thesis ....................... 6 1.3.1 Research questions ..................... 7 1.3.2 Contributions ........................ 8 1.3.3 Outline ........................... 9 1.4 Publications ............................. 9 2 Method Overview 13 2.1 Introduction ............................. 13 2.2 Scope of the thesis ......................... 13 2.3 System overview .......................... 14 2.4 System components ......................... 16 2.4.1 The RFID technology .................... 16 2.4.2 The environments ...................... 16 2.4.3 The robots ......................... 17 2.4.4 RFID slipper ........................ 19 2.4.5 The simulator ........................ 20 2.5 Notation used in the thesis ..................... 21 2.6 Performance metrics ........................ 21 2.7 Conclusions ............................. 23 v vi CONTENTS 3 Related Work 25 3.1 Introduction ............................. 25 3.2 Stigmergy in computer science ................... 25 3.3 Stigmergy in robotics ........................ 26 3.3.1 Stigmergy in robotics using physical markers ....... 27 3.3.2 Stigmergy in robotics without physical markers ..... 28 3.3.3 Stigmergy in robotics using RFID technology ....... 31 3.4 Other uses of RFID technology in robotics ............ 32 3.5 A landscape of stigmergy in robotics ............... 33 3.6 Human robot interaction ...................... 34 3.6.1 Navigation in the presence of humans ........... 35 3.6.2 Human following ...................... 35 3.6.3 Interaction with children .................. 36 3.6.4 Comparison with the work in this thesis ......... 36 3.7 Conclusions ............................. 36 4 Building Navigation Maps 39 4.1 Introduction ............................. 39 4.2 Map building system ........................ 39 4.3 Building goal maps ......................... 41 4.3.1 On the use of multiple seeds ................ 43 4.4 Goal map building in dynamic environments ........... 44 4.5 Building a clearance Map ..................... 46 4.6 Experiments and results .....................
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