Abstract
In this paper, a tracking controller for robots is analyzed, which allows both the specification of the convergence rate of the tracking errors and the parameterization of a desired contact stiffness and damping. It is shown that the control approach can be interpreted as a generalization of the well-known PD+ and Slotine-Li controllers, combining the benefits of both approaches. Although mentioned in the literature before, no thorough theoretical and practical analysis of the aforementioned passivity-based control concept has been performed so far. In this work, the implications of the gains are discussed w.r.t. convergence and interaction properties, addressing possible tuning strategies. Finally, the performance of the controller is evaluated in terms of tracking and interaction experiments on a KUKA LWR IV+.
Zusammenfassung
In dieser Arbeit wird ein Trajektorienfolgeregler für Roboterarme analysiert. Dieser erlaubt sowohl die Spezifikation einer Konvergenzrate für die Regelfehler als auch die Parametrisierung einer gewünschten Kontaktsteifigkeit und Dämpfung. Es wird gezeigt, dass der Regler als eine Verallgemeinerung der bekannten PD+ und Slotine-Li-Regler interpretiert werden kann und dabei die Vorteile beider Ansätze vereint. Obwohl das besagte passivitätsbasierte Regelgesetz in der Literatur bereits bekannt ist, wurde bisher noch keine umfassende Analyse der theoretischen und praktischen Eigenschaften veröffentlicht. In dieser Arbeit wird daher insbesondere die Bedeutung der Verstärkungsfaktoren hinsichtlich der Konvergenz- und Interaktionseigenschaften diskutiert. Dabei werden verschiedene Gain-Tuning-Strategien aufgezeigt. Die Performanz des Reglers wird schließlich anhand von Trajektorienfolge und Mensch-Roboter-Interaktions-Experimenten an einem KUKA LWR IV+ Roboterarm evaluiert.
About the authors
Kristin Lakatos received her M.Sc. degree in mechanical engineering with focus on control theory and information technology from the Technical University of Munich (TUM) in 2014. In the same year, she joined the German Aerospace Center (DLR), Institute of Robotics and Mechatronics, as a research assistant. Her current research interests include passivity-based control concepts, the control of nonholonomic systems and mobile manipulation.
Dominic Lakatos received the Dipl.-Ing. degree in mechanical engineering from the University of Applied Sciences Munich, Germany, in 2011, and the PhD in theoretical mechanics, robotics and control theory from the Technical University of Munich, Germany, in 2018. From 2011 to 2019, he has been with the Institute of Robotics and Mechatronics, German Aerospace Center, Wessling, Germany, as a research associate. From 2017 to 2023, he has been with the lidar company Blickfeld GmbH, Munich, Germany, heading and developing MEMS scanner control, and since 2023 he is with Carl Zeiss SMT, Oberkochen, Germany, as Cluster Architect for System Control of EUV Lithography Optics. His main research interests include control of nonlinear systems, underactuated systems, human and robotic dynamics, nonlinear oscillations, limit cycles, robot design, bioinspired and legged robots, control systems, MEMS design and control, optics, and EUV lithography optics.
Xuwei Wu received the B.E. degree in vehicle engineering from the Tongji University, Shanghai, China, in 2013, and the M.Sc. degree in mechanical engineering from the Technical University of Munich (TUM), Germany, in 2016. In 2019, he joined the German Aerospace Center (DLR), Institute of Robotics and Mechatronics, as a research assistant. His current research interests include nonlinear stability theory, whole-body control of humanoid robots, and safe physical human-robot interaction.
Paul Kotyczka received the Dipl.-Ing. degree in Electrical Engineering and the Dr.-Ing. degree in Automatic Control from Technical University of Munich (TUM) in 2005 and 2010, respectively. From 2015 to 2017 he was a Marie Skłodowska-Curie Fellow at the Laboratory of Automatic Control, Chemical and Pharmaceutical Engineering (LAGEPP), University Claude Bernard Lyon 1. After his habilitation in 2019 he became Privatdozent (adjunct teaching professor). He leads the Energy-based Modeling and Control Group at the Chair of Automatic Control, TUM. He works on structured modeling, geometric numerical methods and nonlinear control design for multi-domain physical systems, with applications to mechatronic, robotic and process systems. He is program coordinator of the French-Dutch-German Doctoral College Port-Hamiltonian Systems: Modeling, Numerics and Control.
Alexander Dietrich received the Dr.-Ing. degree from the Technical University of Munich (TUM) in 2015. In 2010, he joined the German Aerospace Center (DLR), Institute of Robotics and Mechatronics, as a research scientist. Among others, he received the Georges Giralt PhD Award 2016 for the best European thesis in robotics, the DLR Science Award in 2020, and the Distinguished Service Award for Outstanding Associate Editors of the IEEE Robotics and Automation Letters in 2020. He published more than 60 peer-reviewed papers in international journals, books and on conferences, and he is holding 13 patents. He is IEEE Senior Member, Editor of the IEEE ICRA (2020–2022), Associate Editor for IEEE T-RO (since 2021), IEEE RA-M (2018–2020), IEEE RA-L (2017–2021), and he was co-chair of the IEEE RAS Technical Committee on Whole-Body Control (2018–2021). Since 2017 he is head of the whole-body control group at the Institute of Robotics and Mechatronics of the DLR, and since 2019 he is lecturer at TUM on the control of modern lightweight robots. His current research interests include whole-body mobile manipulation, impedance and force control, hierarchical control for kinematically redundant robots, safe physical human–robot interaction, and the stability analysis of the corresponding control approaches.
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Research ethics: Not applicable.
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Author contributions: The authors have accepted responsibility for the entire content of this manuscript and approved its submission. Individual contributions: Kristin Lakatos did the theoretical analyses as well as the experiments and the data analysis and processing, as well as the main part of the writing of the manuscript; Dominic Lakatos, Alexander Dietrich and Paul Kotyczka provided parts of the theoretical contributions, and helped with writing and reviewing the manuscript; Xuwei Wu gave valuable comments on the theoretical contributions and the related literature. Additionally, he set up and operated the experiments.
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Competing interests: The authors state no conflict of interest.
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Research funding: None declared.
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Data availability: The raw data can be obtained on request from the corresponding author.
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