A Novel Behavior Based Mobile Robotic Platform for Landmine Detection By: AMPIKATHASAN ARAVINTHAN This thesis was submitted to the department of Electrical Engineering of University of Moratuwa in partial fulfillment of the requirements for the Degree of Master in Science Department of Electrical Engineering University of Moratuwa Sri Lanka December 2004 Supervisor: Thrishantha Nanayakkara PhD Co-Supervisor: Chatura De Silva PhD Universityof Moratuwa 83812 83812 Abstract Humanitarian demining is an urgent and necessary activity to be carried out to resettle in places where the civilians were used to live before the war. Humanitarian mine clearance technology currently used in various parts of the world is based on the use of very basic equipment, techniques, and procedures developed in early years. Robotics has come into all aspects of life today. It has come into the industrial aspect, the biological and practical sciences aspect, everyday life, and especially in the rescue aspect. Humanitarian Demining is one of the areas where the robots can be used to reduce risk and speed up the process. A novel behavior based mobile robotic platform for landmine detection is proposed in this thesis. A fully autonomous wheeled mobile robot called Autonomous Mine Detecting Robot(AMDR) was designed and developed for this purpose. A microcontroller based system was developed for processing sensor signals and driving actuators. Networks of microcontrollers were used to implement the whole system while reducing complexity of algorithm. Bumper switches,photoreflectors and sonar sensor were used in the robot to sense the world and two DC motors were used for locomotion. A Subsumption based behavior based controller was implemented to enable the robot to do simple search operation to detect landmines. Six behaviors were arranged according to its priority level. Behaviors were tuned to give better performance. This thesis explains about Humanitarian Demining in the first chapter. The design of the robot and design of the proposed controller are explained in consecutive chapters. In the final chapter the results of experiments are summarized. 111 (])ecfaration The work submitted in this thesis is the result of my own investigations, except where stated. It has not already been accepted in substance for any degree, and also not being concurrently submitted for c:..iy other degrees. ·-f~rA ~ :=!\ A. Aravinthan Candidate 171~ Dr. D P T Nanayakkara Supervisor Co Supervisor --~ "' .f :- .... .., , .~ . ~ · ,~ ~ Jlck,nowfedgement The first person I would like to thank is my supervisor Dr Thrishantha Nanayakara .. During the last two years I have known Dr. Thrishantha as a determined and principle- centered person. His overly enthusiasm and integral view on research and his mission for providing 'only high-quality work and not less', has made a deep impression on me. 1 owe him lots of gratitude for having me shown this way of research. He could not even realize I how much I have learned from him I would like to thank my co supervisor Dr. Chathura De Silva who kept an eye on the progress of my work and always was available when I needed his advises. I would also like to thank the other members of my review committee who monitored my work and took effort in reading and providing me with valuable comments, Prof H. Sriyananatha, Dr. HYR Perera and Dr L Udawatta. This research has been supported and funded by ADB and NSF. I thank them for their confidence in me. I take this oppo'1Urity to Prof (Mrs) N. Ratnayake for the extra effort taken on behalf of me in awarding the scholarship. I also thank director post graduate studies Dr. N. Munasinghe and his staff for the guidance ... apd support given to me. "' I am grateful for Prof JR Lucas, former head of the department and Dr. Ranjith Perera, head of the department for their valuable guidance and the support given to . ..ro"e during difficulties. I also thank the technical officers from the department for their support given to me. My sincere thanks to technical staff from Mechanical Engineering ?ep~ent who ... .. gave their hands in fabricating the AMDR. .., ~ / lV My colleagues of the demining project, Kumarathasan and Aravinthan, both gave me the feeling of being at home, many thanks for being my colleague. Last but not least I thank my mother for her unconditional support to lift me whenever I underwent difficulties and for her love A. Aravinthan 1st October 2004 I A~ "' ..,~' . ' ' ~ - .... v / ., v Declaration Dedication Abstract Acknowledgement List of Figures Chapter 1. Introduction 1. 1 Humanitarian Demining 1.2 Humanitarian Demining Technologies 1.3 Demining Robots 1.4 Problems in Humanitarian Demining ! .5 Goal of the Thesis 1.6 Outline of the Thesis 2. Behavior Based Control 2.1 Hierarchical Control 2.1.1 Hierarchical Control Architecture 2.2 Behavior Based Control 2.2.1 Characteristics of Behavior based Control 2.2.2 Behavior selection 2.2.3 Behavior expression and encoding 2.2.4 Behavior Coordination 2.3 Behavior-Based Control Architectures 2.3.1 Subsumption Architecture 2.3.2 Schema-Based Approach .. ~ " 3. Design of Autonomous Mine Detecti~g Robot- I 3.1 Physical Characteristics 3.2 The Mother Board 3.2.1 PIC 18F452 Microcontroller 3.3 Sensors 3.3.1 Sonar Sensor 3.3.2 Photo-Reflector 3.3.3 Bumper switches j Contents ~--.., ·"""· Page ,. II Ill IV VIII 1 I 2 4 7 9 10 11 II 12 14 15 16 17 19 19 20 21 23 ~ · 24 25 / 25 27 28 30 32 VI 4. Design of Autonomous Mine Detecting Robot - II 4.1 Alphanumeric Liquid-Crystal Display 4.2 Microcontroller Network - Serial Peripheral Interface 4.3 DC Motors 4.3.1 Motor Control 4.3.2 Motor Driver 5. The Proposed Controller 5.1 The Behavior Based Controller 5.2 Behavior Implementation 6. Results and Discussion 6.1 Autonomous Mine Detecting Robot 6.2 Experiments results with Rug Warrior PRO 6.3 Simulation Results of the Controller 6.4 Future Extension 7. Conclusions .. ~ .,; j .... v ·""'·, .._ . 34 34 36 37 39 41 42 42 45 52 52 53 58 65 66 / ., vii List ofPigures ~ 'l'a6fes Figure(l.l) Metal Detectors for Demining Figure(l.2) Dogs in Demining Figure(1.3) High tech machines are used for Demining Figure(l.4) The ARJEL, a hexapod crablike robot Figure(l.S) The STAR robot Figure(1.6) The MR1 robot Figure(1.7) The MR-2 robot Figure(1.8) The DERVISH robot Figure(2.1) Hierarchical Control structure Figurc(2.2) Structure of Behavior Based Controller Figure(2.4) FSA for a simple behavior I Figure(2.5) Augmented Finite State Machine used in Subsumption Architecture Figure(2.6): Simple Subsumption based Control architecture Figure(2.7) Simple Schema based Control architecture Figure(3.1) The front and top views of AMDR Figure(3.2) The PCB drawings of AMDR mother board Figure(3.3) Hardware Architecture of AMDR motherboard Figure(3.4) The Devantech SRF04 sonar sensor # .. , Figun~(3.5) Timing Diagram for gl"nerating T1igger to Sonar Sensor Figure(3.6) Sonar sensor driver Flowchart Figure(3. 7) The Hamatsu P30620 1 photoreflector Figure(3.8) Pulse Accumulator Driver Flowchart Figure(3.9) The Bumper Switch Figure(3.10) Bumper switch collision detector Algorithm Figure(4.1) The 16X1 Liquid-Crystal Display Figure(4.2) LCD Driver Flowchart Figure(4.3) SPI Driver Flowchart -=-~- v . .... -. ~ · ~ / 2 3 4 5 5 6 6 7 12 15 18 20 21 22 23 24 26 28 29 30 30 31 32 33 34 35 37 Vl!l Figure(4.4) Simple DC Motor model Figure(4.5) PWM singles for duty cycle 50% and 25% Figure(4.6) Registers and functions- PWM module PIC18F452 Figure(4.7) H Bridge Figure(S.l) Proposed Behavior Based Controller Figure(5.2) Detail Diagram of the Behavior Based Controller Figure(5.3) State Transition Diagram for each Behavior Figure(5.4) The Coordinator Algorithm Figure(6.1) AMDR Figure(6.2) The Simulated Environment Figure(6.3) The robot path with open loop controller I 38 39 40 41 43 44 47 48 53 54 54 Figure(6.4) The Robot Positions - Avoid Obstacle Behavior 55 Figure(6.5) Robot Path - Avoid Obstacle Behavior 55 Figure(6.6) Robot Positions(Large Obstacle) - Avoid Obstacle Behavior 56 Figure(6.7) Robot Path(Large Obstacle) - Before Tuning 57 Figure(6.8) Robot Path(Large Obstacle) - After Tuning 57 Figurc(6.9) Simulated Environment Terrain Conditions 58 Figure(6.10) Schematic Diagram of a Robot 59 Figure(6.11) Robot path with Search Mine Behavior 60 Figure(6.12) Robots Torque, Rotational Velocity during Search Mine Behavior 60 Figure(6.13) Robot path with Excess Torque Behavior 61 Figure(6.14) Robots Torque, Rotational Velocity during Excess Torque Behavior 62 1 . Figure(6.15) Robot path with A void Obstacle Behavior"".!"' 62 Figure(6.16) Robots Torque, Rotational Velocity during Avoid Obstacle Behavior 63 Figure(6.17) Robot path with all behaviors are active at different positions ,. 64 ;'. Figure(6.18) Robots Torque, Rotational Velocity when all behaviors are acti"ve 64 ... --·- .., ,~ Table(6.1) AMDR Specifications 53 IX