Smart materials for microrobotics. Motion Control and Power Harvesting Programa de Doctorat: Enginyeria i Tecnologies Electròniques Bienni: 2003-2005 Departament d’Electrònica Facultat de Física Universitat de Barcelona Autor: Jordi Brufau Penella Director: Manel Puig i Vidal Agraïments: Primer de tot vull agrair al Dr. Manel Puig i Vidal la oportunitat que m’ha donat per començar a treballar en el camp dels materials per a la micirorobòtica. Gràcies a ell he pogut realitzar aquesta tesi i formar-me com a investigador. Vull agrair també la paciència tinguda envers meu durant tots el anys que ha durat la execució del meu doctorat. També agrair al cap del departament Dr. Albert Cornet i a en Dr. Josep Samitier per permetrem treballar en el Departament d’Electrònica i en el SIC. A un gran nombre de persones vinculades al departament agrair l’ajuda, tant professional com personal, que m’han donat durant tot aquest temps. En especial al Dr. Pere Miribel Català i al Dr. Ángel Diéguez Barrientos per la possibilitat que m’han ofert de treballar juntament amb els seus grups de recera. També al Dr. Javier Sieiro Córdoba per tot el que m’ha ensenyat i ajudat durant aquest temps. A tota la gent amb qui he compartit passadís, laboratori i dinars, Mariano, Youcef, Josep, Romén, Gonzalo, Otero, Andreu, Oscar, Dani, etc. Un especial menció se la dedico a una de les persones mes entranyables i que mes m’ha ajudat en temes técnics i demés, Francisco Palacio. A la meva família, la meva mare, el meu pare, els meus germans, cunyats, etc, per el suport que incondicionalment han mostrat durant tot aquest llarg camí. Un caluros agraïment per a la meva companya la Mireia que ha aguantat aquest últims mesos al meu costat. Als meus amics Juan, Diana, Marcelo, Laia, Alberto, Bàrbara i Coco. I would like to give tanks to the people from the “Dipartimento di Ingegneria Elettrica, Elettronica e dei Sistemi, Università degli Studi di Catania” in Sicily (Italy)”. Specially to Dr. Salvatore Graziani for accepting me in his lab and give me the opportunity to work with the IPMC, and to Pietro Giannone and Salvatore Stratzzeri for helping me in the research and for introducing me to the Sicily type of live. Finally I want to give thanks to the people from the Aristotle University of Thessaloniky in Greece. To Dr Theodore Laopoulos and Kiriakos Tsiatmaikis for the great pleasure that has been working together. Moltes gràcies a tots i totes!!! Prologue This thesis focuses on the use of smart materials in microrobotic applications. The development of materials with the capabilities to mechanically respond to electrical stimuli or, at the same time, to electrically respond to mechanical stimuli, has entailed the microrobotics rapid evolution. Along this thesis the use of three smart materials families in the filed of microrobotics is studied. The materials used are the piezoelectric ceramics, the piezoelectric polymers and the ionic polymers metal composites IPMC. The similitude in the way they respond to external stimuli has motivated this study. The three materials respond with an induced mechanical strain under the application of an electric field and respond with an induced electrical charge variation when a mechanical pressure is applied. Although these materials respond similarly, their application in microrobotic systems entails different problems. In this thesis their use in different applications is studied and the problems enclosed with their use are treated. First of all in this thesis the use of piezoelectric polymers and ionic polymers as materials for motion control of microrobots is studied. Their flexibility opens the door to new applications for microrobot systems as is the case of biomimetics. The first application regards the use of piezoelectric polymers in insect-like mm3 microrobot. The microrobot is composed with three legs and one antenna or tool for object collision based on piezoelectric polymers. The object collision tool is used as a sensor for motion control to avoid collisions with other objects. The work presented consists on the development of theoretical models to predict the motion of the leg and the tool of the microrobot. The second application regards the development of a control system for controlling the motion of an ionic polymer IPMC underwater. It is difficult to obtain physical models that describe the motion of these materials, thus it is important to design control strategy to work with IPMCs. Furthermore in this thesis, the problem of manufacturing electrodes for IPMC is also treated. In the second part of the thesis the use of piezoelectric ceramics to harvest power from mechanical vibrations is studied. Piezoelectric ceramics have higher energy densities compared with other methods for power harvesting from vibrations. In comparison with the piezoelectric polymers, the piezoelectric ceramics produce voltages and current levels more acceptable. From the study performed in this thesis the conditions for a maximum power generation are obtained and an optimum electronic circuit for energy storage and management is designed. At the end of the thesis the capabilities to harvest power using ionic polymers are studied. Table of contents TABLE OF CONTENTS 1. INTRODUCTION ............................................................................................ 1-1 1.1. Smart systems and materials..................................................................... 1-2 1.1.1. Classification .................................................................................... 1-4 1.1.2. Piezoelectrics .................................................................................... 1-9 1.1.2.1. Piezoelectric ceramics............................................................. 1-11 1.1.2.2. Piezoelectric polymers............................................................ 1-12 1.1.2.3. Modeling piezoelectrics.......................................................... 1-14 1.1.3. Ionic Polymer Metal Composites (IPMCs) .................................... 1-16 1.1.3.1. Modeling IPMC...................................................................... 1-19 1.2. MST and Microrobotics.......................................................................... 1-22 1.2.1. Motion control................................................................................ 1-25 1.2.1.1. Micromanipulation and microassembling with microrobots .. 1-27 1.2.1.2. Insect-like microrobots ........................................................... 1-30 1.2.1.3. Fish-like microrobot ............................................................... 1-32 1.3. Power harvesting..................................................................................... 1-34 1.3.1. Power from mechanical vibration................................................... 1-35 1.3.1.1. Magnetic induction converters................................................ 1-36 1.3.1.2. Electrostatic converters........................................................... 1-37 1.3.1.3. Piezoelectric converters.......................................................... 1-37 1.3.1.4. Converters performances comparison .................................... 1-38 1.3.2. Alternative power sources.............................................................. 1-40 1.3.2.1. Solar energy ............................................................................ 1-40 1.3.2.2. Heat converters ....................................................................... 1-40 1.3.3. Autonomous power sources for microrobots.................................. 1-43 1.4. Thesis objectives..................................................................................... 1-46 1.5. Overview................................................................................................. 1-49 1.6. References............................................................................................... 1-50 i Table of contents 2. MOTION CONTROL IN MICROROBOTICS ............................................... 2-1 2.1. Piezoelectric polymer based microrobotic actuator.................................. 2-3 2.1.1. The I-Swarm microrobot structure: .................................................. 2-4 2.1.2. Actuator motion:............................................................................... 2-6 2.1.2.1. Design and manufacturing:....................................................... 2-6 2.1.2.2. Physical model.......................................................................... 2-7 2.1.2.3. Experimental test:................................................................... 2-11 2.1.3. Contact sensing tool: ...................................................................... 2-17 2.1.3.1. Design and manufacturing:..................................................... 2-17 2.1.3.2. Physical model: ...................................................................... 2-17 2.1.3.3. Experimental test.................................................................... 2-21 2.1.3.4. Control system........................................................................ 2-23 2.1.4. Conclusions: ................................................................................... 2-24 2.2. Ionic polymer based microrobotic actuator............................................ 2-27 2.2.1. The underwater microrobotic structure: ......................................... 2-28 2.2.2. Actuator motion.............................................................................. 2-31 2.2.2.1. Design and manufacturing:....................................................