UNIVERSITY OF BELGRADE SCHOOL OF ELECTRICAL ENGINEERING Kosta M. Jovanović MODELING AND CONTROL OF THE ANTHROPOMIMETIC ROBOT WITH ANTAGONISTIC JOINTS IN CONTACT AND NON-CONTACT TASKS Doctoral Dissertation Belgrade, 2015 УНИВЕРЗИТЕТ У БЕОГРАДУ ЕЛЕКТРОТЕХНИЧКИ ФАКУЛТЕТ Коста М. Јовановић MОДЕЛИРАЊE И УПРАВЉАЊE АНТРОПОМИМЕТИЧКОГ РОБОТА СА АНТАГОНИСТИЧКИМ ПОГОНИМА У КОНТАКТНИМ И БЕСКОНТАКТНИМ ЗАДАЦИМА докторска дисертација Београд, 2015 Thesis Committee Dr. Veljko Potkonjak, Thesis Supervisor Full Professor School of Electrical Engineering, University of Belgrade, Serbia Dr. Mirjana Popović Full Professor School of Electrical Engineering, University of Belgrade, Serbia Dr. Aleksandar Rodić Scientific Advisor Mihailo Pupin Institute, University of Belgrade, Serbia Dr. Alin Albu-Schäffer Full Professor Technical University Munich, Germany; and Director of the Institute of Robotics and Mechatronics, German Aerospace Center-DLR Željko Đurović, PhD Full Professor School of Electrical Engineering, University of Belgrade, Serbia Acknowledgments A number of people have helped pave the way to my PhD. My special gratitude goes to: My wife Marija, for all the love and support, and because she learned what ZMP was when that was really important; My parents Dušica and Miloš, for their unconditional support and for making it possible for me to become professionally involved in what I love; My mentor Prof. Veljko Potkonjak, for all the opportunities he has given me, for his enormous support, and for teaching me how to become a better person and a better professional; My colleagues Bratislav, Predrag and Nenad, because our team work was extremely enjoyable; Prof. Alin Albu-Schäffer, for giving me a chance and for being my supervisor during my research stay at the DLR Institute of Robotics and Mechatronics; Prof. Owen Holland, for a number of ideas, discussions, and consultations; and My colleagues from the Signals & Systems Department and my office mates Branko, Zaviša and Vladimir, for making my job personally rewarding; The research leading to this PhD thesis has received funding from the European Community’s Seventh Framework Programme FP7/2007-2013, Challenge 2 (Cognitive Systems, Interaction, Robotics), under Grant Agreement no. 231864-ECCEROBOT, and from the Serbian Ministry of Education, Science and Technological Development under Agreement no. TR35003. Kosta M. Jovanović Belgrade, December 28th, 2015. i Dissertation title: Modeling and control of the anthropomimetic robot with antagonistic joints in contact and non-contact tasks Abstract. The thesis considers a very popular and rapidly growing topic in robotics – modeling and control of anthropomimetic robots, in particular robots that feature compliant antagonistic actuation. The term ‘anthropomimetic’ refers to a robot of fully human-like appearance, but also human-like inner structure and functionality. The motivation for the thesis came from the involvement of the author and the School of Electrical Engineering, University of Belgrade in the project Eccerobot (Embodied Cognition in a Compliantly Engineered Robot), funded by European 7th Framework Programme, and the project Ambient Intelligent Service Robots of Anthropomorphic Characteristics funded by Serbian Ministry of Education, Science and Technological Development. Since conventional rigid actuators have become obsolete for inherently-safe future robotic applications, the design and control of novel compliant actuators have recently been under intensive investigation. In particular, variable stiffness (impedance) actuators (VSAs), which can trade-off between robot trajectory tracking and overall safety, are the focus of robotics research. We focus on antagonistically-driven joints, as a subgroup of bio-inspired VSAs. The thesis is organized in six sections and bibliography. The first section outlines the main ideas and motivation for the work. It presents research directions, points of view and initiatives in the design and control of compliant robots, with special emphasis on antagonistic drives. It also addresses safety issues of future service robots, and lists technologies, trends, and approaches towards achieving that goal: moving from stiff to compliant actuators, the benefits introduced by passive and active compliance, VSA, etc. As a special group of bio-inspired VSAs in robotics, antagonistic actuators are reviewed comprehensively. Such a detailed review of antagonistic actuator design aims to highlight the importance of the subject, on the one hand, while on the other hand it presents the technology that will be intensively exploited in future anthropomimetic robots. ii The second section presents a development of the simulation-based model of the robot driven by antagonistically-actuated compliant drives. To that end, Stepanjenko’s method to robot modeling is exploited since it has demonstrated superior performance in simulating robot dynamics. To begin with, basic models of antagonistically-actuated joints that resemble typical human-like antagonistic structures are introduced. These models are incorporated into the upper-body anthropomimetic robot model, which is a close approximation of the Eccerobot prototype. Since such a robot is intended to work in proximity to humans and directly interact with its surroundings, modeling of contacts is introduced. This section as a whole represents an efficient and accurate tool for simulating the anthropomimetic robot dynamic, which is then implemented in Matlab and C++. Two simulation case studies are presented. The first emulates an anthropomimetic robot on a wheeled-base, working in an unstructured environment and therefore exposed to impulse and long-term external disturbances. Here the model is used to observe the robot’s zero-moment-point and thus its balance. The second case study emulates intentional contact – grasping of an object. Models of all contact stages are demonstrated: approach, impact and in-contact-motion phases. Although some applications to the physical robot Cassius [1] and the simulation-base study [2] have already been implemented, there are numerous possibilities for prospective model utilization: simulation and analysis of biomechanical systems/subsystems, study of potential transfer from biological concepts to bio-inspired robotics, anthropomimetic robot system design and analysis, simulation of anthropomimetic robots in interaction tasks, development of model-based advanced control techniques for anthropomimetic robots, testing of anthropomimetic control approaches with additional possibilities of control in interaction tasks, etc. The main outcomes of this section, relating to anthropomimetic model development and extension to include analysis of contact dynamics, have already been published in [3]. At the same time, the simulation model served as a platform for the development of control algorithms elaborated in the following sections. The third section presents the contribution of this thesis to the control of antagonistically actuated, linear/non-linear, cable driven, compliant robot joints, using iii control methods that rely on the conventional control theory. After an overview of the background work on antagonistic actuator control and feedback linearization in robot control, an upgraded puller-follower approach, outlined in the Master’s thesis of Svetozarevic [4], is presented. This biologically-inspired and energy efficient approach simultaneously controls joint position and force in one of the antagonistic tendons. In the present thesis, the puller-follower approach extends to control joint position and joint stiffness. An initially demonstrated single-joint control algorithm, based on feedback linearization, is optimized to compensate for gravity load, changeable effective joint inertia and dynamic coupling in multi-joint systems, by introducing the robust control theory. In addition to loop-shaping robust control, methods based on the non-linear and multivariable control theories were exploited in the puller-follower control scheme. This section ends with limitations and issues that remain open and will be the topic of future research. In addition to control methods that rely on conventional engineering techniques, several cognitive approaches to the control of antagonistically coupled compliant drives in robotics were developed. In accordance with a bio-inspired background and fully human-like design of the anthropomimetic robot, the focus was on human-like control as well – control based on experience, learning and heuristics. To that end, nearest- neighbor algorithms for feedforward and feedback control of the anthropomimetic robot, an algorithm for neural network feedforward control using radial-basis networks, and an algorithm for feedback control based on on-line estimation of kinematic coefficients and fuzzy rules were developed. Although cognitive algorithms were not of primary importance in this thesis, they present a step forward in the control of a fully anthropomimetic robot since engineering-based control algorithms reach their limits if multi-articular muscles or multi-axes joints are considered. On the other hand, cognitive methods outlined in the thesis can be applied to such systems without restrictions. Finally, a comparative simulation study in Matlab was carried out to highlight the main features of the developed cognitive-based control schemes. The scientific contributions regarding cognitive-based control algorithms are presented in the fourth section of the thesis, while all contributions to control anthropomimetic