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Tesi Dottorato UNIVERSITÀ DEGLI STUDI DI ROMA "TOR VERGATA" FACOLTA' DI INGEGNERIA DOTTORATO DI RICERCA IN INGEGNERIA DEI MICROSISTEMI CICLO DEL CORSO DI DOTTORATO XXI Plantoid: Plant inspired robot for subsoil exploration and environmental monitoring Alessio Mondini A.A. 2008/2009 Docente Guida/Tutor: Dott. Barbara Mazzolai Dott. Virgilio Mattoli Prof. Cecilia Laschi Prof. Paolo Dario Coordinatore: Prof. Aldo Tucciarone Abstract Biorobotics is a novel approach in the realization of robot that merges different disciplines as Robotic and Natural Science. The concept of biorobotics has been identified for many years as inspiration from the animal world. In this thesis this paradigm has been extended for the first time to the plant world. Plants are an amazing organism with unexpected capabilities. They are dynamic and highly sensitive organisms, actively and competitively foraging for limited resources both above and below ground, and they are also organisms which accurately compute their circumstances, use sophisticated cost–benefit analysis, and take defined actions to mitigate and control diverse environmental insults. The objective of this thesis is to contribute to the realization of a robot inspired to plants, a plantoid. The plantoid robot includes root and shoot systems and should be able to explore and monitoring the environment both in the air and underground. These plant-inspired robots will be used for specific applications, such as in situ monitoring analysis and chemical detections, water searching in agriculture, anchoring capabilities and for scientific understanding of the plant capabilities/behaviours themselves by building a physical models. The scientific work performed in this thesis addressed different aspects of this innovative robotic platform development: first of all, the study of the plants‟ characteristics and the enabling technologies in order to design and to develop the overall plantoid system. The proposed system can be easily sub- divided in two major sections, the aerial part and the subsoil part. About the subsoil part, the activity focused on the realization of a miniaturized mechatronic system that imitates the behaviour of the plant radical apex. Plants show a peculiar directional growth in response to external stimulations, such as light (phototropism), gravity (gravitropism), touch (thigmotropism) or water/humidity gradient (hydrotropism). Tropisms frequently interact between and among each other, and the final grown form of the plant is influenced by such interactions. In order to imitate the powerful performances of the plant root system, a novel actuator has been proposed. This actuator is based on the osmotic principle (osmotic actuator) and, differently by the state-of-the-art actuators based on the osmotic principle, it has been designed in order to have a reversible reaction. This actuator permits to perform the elongation and the typical steering capabilities of the root apex, generating high forces with low power consumption (in the time scale of the plant). Theoretical studies on this actuator show interesting performances in terms of actuation pressure (more than 20 atm) with power in the order of some mW and with actuation in the hours scale time. The robotic root apex was designed to be equipped with sensors (gravity and moisture) to imitate the plants sensing characteristics, and with the novel osmotic actuator to drive the growth in the correct direction. An embedded microcontroller implements the basic root behaviour on the basis of the information coming from the sensors. About the aerial part the activity in this thesis was focused on the realization of a sort of environmental monitoring module in order to imitate the high sensing capabilities of the plants. This part has been designed and realized in a more traditional way, without attempt to imitate completely the plant behaviour but taking inspiration from the fundamental characteristics (energy scavenging, wide sensing capabilities and communication). In order to integrate a wide amount of sensors an innovative interface board that guarantees the conditioning of the sensor, with plug-and-play capabilities and low power consumption, was developed. Several aspects of the plantoid system are not faced yet and they will be part of the future works. In particular, the growing mechanism of the roots (some possible solutions are proposed and explained in this thesis) and the integration of chemical sensors in the root apex. Foreword The work performed in this thesis has been produced during the period of my PhD as student in Microsystems Engineering at the CRIM lab of Scuola Superiore Sant‟Anna of Pisa from 2005 to 2009. During these years I was part of Prof. Paolo Dario team and in particular of the Dr. Barbara Mazzolai group, that is focused on technologies and robotic systems for environmental monitoring. In these years I had the chance to collaborate with several people both internal to the CRIM Laboratory than from other international groups. Two special persons for beginning the acknowledgments: Barbara Mazzolai and Virgilio Mattoli. They have accepted me at the beginning of this adventure; I have shared with them the greater amount of these last years. They are not only tutors but masters, partners and above all friends. I am thankful to Prof. Paolo Dario and Prof. Cecilia Laschi for supporting and tutoring me during the PhD studies. I am thankful to Paolo Corradi that has collaborated with me during these years and in particular he has helped me in this final important phase as an added tutor. Then a special thanks to: Gabriele Ferri the odour expert (even if less than his doggie), the demo man, the first price avoidance, he has been a reference in these years; Silvia Taccola for her collaboration and “practical” help; Carlo Filippeschi the “Mayor of Luciana” for sponsoring me and for all the fruitful conversations; Stefano Zampolli and Simona Raffa that have supplied me most of the knowledge necessary to pass the first difficult phases of the PhD; The Porf. Stefano Mancuso group for the collaboration in this amazing project. Finally, I wish to express my thanks to my family and Mary that are all for me and that have supported me along these years. Luciana, May 2009 Alessio Mondini Table of Contents Abstract ....................................................................................................................................................................... 3 Foreword ..................................................................................................................................................................... 5 1 Objectives and Motivations ................................................................................................................................ 9 2 Introduction ....................................................................................................................................................... 11 2.1 Biorobotics ............................................................................................................................................. 11 2.1.1 Robotics evolution ........................................................................................................................... 11 2.1.2Definition of Biorobotics ......................................................................................................................... 12 2.1.3 Biomimetic Robotics ....................................................................................................................... 13 2.1.4 Bioinspired Robotics ........................................................................................................................ 16 2.2 Microsystems ......................................................................................................................................... 17 2.2.1 Microsensors .................................................................................................................................... 18 2.2.2 Microactuators ................................................................................................................................. 20 2.3 Plants: a new source of bioinspiration and biomimicking ..................................................................... 21 2.3.1 Structure of the whole plant ............................................................................................................. 22 2.3.2 Root system and its architecture ...................................................................................................... 24 2.3.3 The transition zone: a „command centre‟ for the environment exploration ..................................... 25 2.3.4 The root cap and the soil penetration ............................................................................................... 26 2.3.5 Root growth ..................................................................................................................................... 27 2.3.6 Hormones and growth. The role of auxin ........................................................................................ 29 2.3.7 Tropism in plants ............................................................................................................................. 29 3 Plantoid biomechatronic design ........................................................................................................................ 34 3.1 System functionalities and application scenarios ..................................................................................
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