Zurich Open Repository and Archive University of Zurich Main Library Strickhofstrasse 39 CH-8057 Zurich www.zora.uzh.ch Year: 2013 Learning from the octopus: sensorimotor control of octopus-inspired soft robots Li, Tao Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-91630 Dissertation Published Version Originally published at: Li, Tao. Learning from the octopus: sensorimotor control of octopus-inspired soft robots. 2013, University of Zurich, Faculty of Economics. Department of Informatics Learning from the Octopus: Sensorimotor Control of Octopus-Inspired Soft Robots A dissertation submitted to the Faculty of Economics, Business Administration and Information Technology of the University of Zurich for the degree of Doctor of Science (Ph.D.) by Tao Li from China Accepted on the recommendation of Prof. Dr. Rolf Pfeifer Prof. Akio Ishiguro, Ph.D. 2013 The Faculty of Economics, Business Administration and Information Technol- ogy of the University of Zurich herewith permits the publication of the afore- mentioned dissertation without expressing any opinion on the views contained therein. Zurich, October 23, 2013 Head of the Ph.D. committee for informatics: Prof. Abraham Bernstein, Ph.D Abstract Soft robotics is one of the most promising, yet challenging, research topics in bio-inspired robotics. In terms of morphological and behavioral flexibility as well as interaction safety, soft robots have significant advantages over traditional articulated rigid robots. However, it is difficult to achieve autonomous sensorimotor control of a soft robot by conventional engineering approaches primar- ily because of its complex nonlinear soft body dynamics. Most soft robots are currently controlled only in an open-loop scheme. The octopus exhibits various sophisticated behaviors with muscular-hydrostats and appar- ently has solved the challenges to harness a completely soft body. Studying the control strategy of the octopus, by constructing robots inspired by the octopus’ morphology and implementing octopus-like behaviors, can provide insights into understanding its biological control scheme and designing novel control methods for soft robots. Many researchers have used global parameters to reduce the control dimensions of soft robots, but that is not sufficient for autonomous sensorimotor control. In this thesis, we investigate the sensorimotor control strategies of octopus-inspired soft robots for both single-arm manipulation and multi-arm coordination tasks. By reviewing and interpreting biological studies on the octo- pus, we propose a control scheme to implement autonomous behaviors on soft robots. Several octopus arm simulators and octopus-inspired soft robotic platforms are built to evaluate the con- trol scheme. We evaluated the control scheme by: (1) controlling a simulated octopus arm for a reaching task; (2) embedding and switching among multiple behaviors for a single soft robotic arm; and (3) achieving autonomous direction and speed control of a multi-arm soft robot with the coordination of all arms. We found that initiating these global parameters at the proper time is a key factor to achieving autonomous sensorimotor control in soft robots. Finally, we show the potential to exploit complex soft body dynamics as a computational resource. With this work, we present a promising approach both for the control of soft robots and for morphological computation. Zusammenfassung Soft-Robotik ist eine der vielversprechendsten, jedoch auch herausforderndsten Forschungsge- biete innerhalb der biologisch inspirierten Robotik. Im Gegensatz zu traditionellen Robotern, welche starre Strukturen aufweisen und aus harten Materialien aufgebaut sind, haben Soft-Roboter hinsichtlich der Flexibilität der Morphologie und der Bewegungen einen erheblichen Vorteil. Dazu kommt die erhöhte Interaktionssicherheit, die Soft-Roboter aufgrund ihrer elastischen Ma- terialeigenschaften mit sich bringen. Es ist jedoch sehr schwierig, mit den gängigen Methoden ein autonomes, sensomotorisches Regelsystem für diese Roboter zu entwickeln. Grund dafür ist das komplexe, nichtlineare Verhalten elastischer Körper. Demzufolge werden die meisten Soft- Roboter heutzutage nur mittels eines einfachen offenen Regelkreises gesteuert. Der Oktopus zeigt mit seiner speziellen muskulären Struktur (muscular hydrostat) hoch kom- plexe Verhaltensweisen und schafft es offensichtlich, seinen vollständig elastischen Körper ohne Probleme zu kontrollieren. Durch das Entwickeln von Oktopus-inspirierten Robotern, welche ähnliche Körpereigenschaften und Verhaltensweisen aufweisen, versuchen wir besser zu verste- hen, wie das Tier seine Bewegungen steuert. Die Erkenntnisse dieser Forschung können dann in Folge zur Entwicklung neuer Steuerungssysteme für Soft-Roboter beitragen. Viele Forscher haben versucht, die Dimensionen der Steuerungssysteme von Soft-Robotern mit globalen Parametern zu reduzieren. Dies ist jedoch bei autonomen, sensomotorischen Regel- systemen nicht ausreichend. In dieser Dissertation untersuchen wir die sensomotorischen Steue- rungssysteme von Oktopus-inspirierten Soft-Robotern, insbesondere bei der Manipulation mit einem Arm sowie bei der Koordination von mehreren Armen. Basierend auf biologischen Studien des Oktopus entwickelten wir ein Regelsystem für die Implementierung von autonomen Ver- haltensweisen bei Soft-Robotern. Um das Regelsystem zu evaluieren, entwickelten wir sowohl mehrere Simulationen von Oktopusarmen als auch mehrere Oktopus-inspirierte Soft-Roboter- Plattformen. Folgende Experimente dienten der Evaluation: (1) Die Steuerung einer Greifbewe- gung mit einem simulierten Oktopusarm, (2) das Einbinden und Wechseln von Bewegungsabläufen in einem echten, einarmigen Soft-Roboter und (3) das Erzielen einer autonomen Richtungss- teuerung und Kraftregelung in einem mehrarmigen Soft-Roboter unter Berücksichtung der Ko- ordination aller Arme. Wir beobachteten, dass bei der Initiierung der globalen Parameter der richtigen Zeitpunkt ausschlaggebend ist, um eine autonome, sensomotorische Steuerung bei Soft- vi Robotern zu erzielen. Schliesslich zeigten wir das Potential, das in der Verwendung der kom- plexen Dynamik von Soft-Robotern als Rechenressource (computational resource) liegt. Mit dieser Arbeit präsentieren wir einen vielversprechenden Ansatz für die Steuerung von Soft-Robotern und leisten einen Beitrag im Gebiet der Morphological Computation. Acknowledgements First of all, I would like to thank my thesis supervisor Rolf Pfeifer to provide the valuable oppor- tunity to carry out my research at the legend Artificial Intelligence Laboratory (AI Lab). I wish to thank my thesis co-supervisor Akio Ishiguro for giving thoughtful and constructive feedbacks. During the expedition of my Ph.D. study, I have received enormous help and continuous encour- agement from Kohei Nakajima. I sincerely appreciate all the inspiring discussions and sharing of research experiences. Without his help, the journey would be much more difficult. Many thanks to Nathan Labhart and Qian Zhao for kindly spending time to proofread my thesis draft. The thesis abstract was translated into German by Dorit Assaf, Helmut Hauser, and Nathan Labhart. Thanks all for your help. I would like to acknowledge all my colleagues at the AI Lab for fruitful discussions and shared time. This research was mainly funded by the European Commission under the Seventh Framework Programme for Research and Technological Development (FP7) in the theme of the Future and Emerging Technologies (FET). It was conducted as part of the ICT-FET OCTOPUS Integrating project (EU project FP7-231608). I am very appreciated for the four and half years support. I wish to express my gratitude for my project collaborators who have contributed to the studies included in this thesis. Living and studying in a foreign country is both exciting and challenging. Thanks Nathan Labhart, Dorit Assaf, Lijin Aryananda, Alejandro Hernandez Arieta, and many others who have helped me to deal with lots of complicated situations and to settle down in Switzerland. Thanks all my friends to make life more enjoyable and to assist me in various occasions. I own a lot to my family: my parents, Zhenlan Niu and Yuchun Li, are always my firm sup- porters and have provided all the resources they own for my development and education; my older sister and her family (Juan Li, Mingwei Li, Jiaqi Li, and Jiaze Li) have always given me the sincere love and thoughtful care; my wife, Ni Jiang, has accompanied and supported me all the way from China, Singapore to Switzerland; My son, Ruisheng Li, brings me lots of fun and smile. Thank you all! Contents 1 Introduction and Motivation 1 1.1 Emergence of Soft Robotics . 1 1.1.1 Softness and Soft Robotics . 2 1.1.2 Soft Robot Designs . 4 1.1.3 Differences between Soft and Hyper-Redundant Robots . 4 1.2 Challenges to Achieve Sensorimotor Control of Soft Robots . 6 1.3 Previous Attempts to Control Soft Robots . 7 1.4 Learn from the Octopus . 9 1.4.1 Octopus Sensorimotor Control Capabilities . 9 1.4.2 Octopus Sensorimotor Control Strategy . 9 1.5 Research Methodologies . 12 1.5.1 Synthetic Approach . 12 1.5.2 Distributed Control . 12 1.5.3 Dynamical Systems and Implementation in Recurrent Neural Networks . 14 1.5.4 Morphological Computation . 16 1.6 The OCTOPUS Integrating Project . 17 1.7 Research Questions and Hypotheses . 17 1.8 Overview . 19 2 Octopus-Inspired Sensorimotor Control Architecture for Soft Robots 21 2.1 Results . 21 2.2 Contributions . 22 3 Control a Simulated