@TECHREPORT{2008:RoboCup-TDP-GermanTeam,
  author = {David Becker and Jörg Brose and Daniel Göhring and Matthias Jüngel and Max Risler and Thomas Röfer},
  title = {GermanTeam 2008 - The German National RoboCup Team},
  year = {2008},
  institution = {DFKI Bremen, TU Darmstadt, HU Berlin},
}

@INPROCEEDINGS{cirpicme:2008,
  author = {E. Abele and J. Bauer and C. Bertsch and R. Laurischkat and H. Meier and S. Reese and M. Stelzer and O. von Stryk},
  title = {Comparison of Implementations of a Flexible Joint Multibody Dynamic System Model for an Industrial Robot},
  year = {2008},
  pages = {to appear},
  booktitle = {6th CIRP International Conference on Intelligent Computation in Manufacturing Engineering},
}

@INPROCEEDINGS{pmi:2008,
  author = {E. Abele and J. Bauer and S. Rothenbücher and M. Stelzer and O. von Stryk},
  title = {Prediction of the Tool Displacement by Coupled Models of the Compliant Industrial Robot and the Milling Process},
  year = {2008},
  pages = {to appear},
  booktitle = {International Conference on Process Machine Interactions, Hannover, Germany},
}

@ARTICLE{wtonline2008,
  author = {E. Abele and J. Bauer and M. Stelzer and O. von Stryk},
  title = {Wechselwirkungen von Fräsprozess und Maschinenstruktur am Beispiel des Industrieroboters},
  journal = {WT online},
  year = {2008},
  pages = {submitted},
}

@INPROCEEDINGS{2008-Kropf-etal-MMULATOR,
  author = {Matthias Kropff and Christian Reinl and Kim Listmann and Karen Petersen and Katayon Radkhah and Faisal Karim Shaikh and Arthur Herzog and Armin Strobel and Daniel Jacobi and Oskar von Stryk},
  title = {MM-ulator: Towards a Common Evaluation Platform for Mixed Mode Environments},
  year = {2008},
  publisher = {Springer (ACCEPTED FOR PUBLICATION)},
  booktitle = {Proceedings of Int. Conference on Simulation, Modeling, and Programming (SIMPAR)},
  abstract = {We investigate the interaction of mobile robots, relying on information provided by heterogeneous sensor nodes, to accomplish a mission. Cooperative, adaptive and responsive monitoring in Mixed-Mode Environments (MMEs) raises the need for multi-disciplinary research initiatives. To date, such research initiatives are limited since each discipline focusses on its domain specific simulation or testbed environment. Existing evaluation environments do not respect the interdependencies occurring in MMEs. As a consequence, holistic validation for development, debugging, and performance analysis requires an evaluation tool incorporating multi-disciplinary demands. In the context of MMEs, we discuss existing solutions and highlight the synergetic benefits of a common evaluation tool. Based on this analysis we present the \emph{MM-ulator}: a novel architecture for an evaluation tool incorporating the necessary diversity for multi-agent hard-/software-in-the-loop simulation in a modular and scalable way.},
}

@INPROCEEDINGS{2008:RCS-BeckerRisler,
  author = {D. Becker and M. Risler},
  title = {Mutual localization in a team of autonomous robots using acoustic robot detection},
  year = {2008},
  month = {July 15-18},
  address = {Suzhou, China},
  booktitle = {RoboCup International Symposium},
  abstract = {In order to improve self-localization accuracy we are exploring ways of mutual localization in a team of autonomous robots. Detecting team mates visually usually leads to inaccurate bearings and only rough distance estimates. Also, visually identifying teammates is not possible. Therefore we are investigating methods of gaining relative position information acoustically in a team of robots. The technique introduced in this paper is a variant of code-multiplexed communication (CDMA, code division multiple access). In a CDMA system, several receivers and senders can communicate at the same time, using the same carrier frequency. Well-known examples of CDMA systems include wireless computer networks and the Global Positioning System, GPS. While these systems use electro-magnetic waves, we will try to adopt the CDMA principle towards using acoustic pattern recognition, enabling robots to calculate distances and bearings to each other. First, we explain the general idea of cross-correlation functions and appropriate signal pattern generation. We will further explain the importance of synchronized clocks and discuss the problems arising from clock drifts. Finally, we describe an implementation using the Aibo ERS-7 as platform and briefly state basic results, including measurement accuracy and a runtime estimate. We will briefly discuss acoustic localization in the specific scenario of a RoboCup soccer game.},
}

@INPROCEEDINGS{2008:Robotik2008-Klugetal,
  author = {Sebastian Klug and Thomas Lens and Oskar von Stryk and Bernhard Möhl and Andreas Karguth},
  title = {Biologically Inspired Robot Manipulator for New Applications in Automation Engineering},
  year = {2008},
  number = {2012},
  month = {June 11-12},
  publisher = {VDI Wissensforum GmbH},
  series = {VDI-Berichte},
  address = {Munich, Germany},
  booktitle = {Proceedings of Robotik 2008},
  owner = {FG SIM, TUD},
  abstract = {The fast growing interest in flexible, versatile and mobile robotic manipulators demands for robots with inherent high passive safety suited for direct human-robot interaction. To gain access to these new applications in the field of automation engineering where close vicinity and direct cooperating with humans are required, the ""BioRob"" project demonstrates the applicability of a new biologically inspired, lightweight and elastic ""bionic"" robot manipulator specifically designed for safe human-robot interaction. This paper presents the mechanical design and controller structure used for the new demonstrators with up to four compliant joints. The advantages of the design and potential application areas for the manipulator are discussed.},
}

@INPROCEEDINGS{robotik2008_ptw_sim,
  author = {M. Stelzer and O. von Stryk and E. Abele and J. Bauer and M. Weigold},
  title = {High speed cutting with industrial robots: Towards model based compensation of deviations},
  year = {2008},
  booktitle = {Proceedings of Robotik 2008, Munich, Germany},
}

@INPROCEEDINGS{2008:RislervonStryk,
  author = {M. Risler and O. von Stryk},
  title = {Formal behavior specification of multi-robot systems using hierarchical state machines in XABSL},
  year = {2008},
  month = {May 12-16},
  address = {Estoril, Portugal},
  booktitle = {AAMAS08-Workshop on Formal Models and Methods for Multi-Robot Systems},
  abstract = {This paper presents the latest developments of the Extensible Agent Behavior Specication Language (XABSL), a modular and scalable tool for engineering complex multiagent behavior. It is based on hierarchical finite state machines. By the new extensions the development of cooperative multi agent behavior is supported through language elements which allow to conveniently specify how the state machines of multiple agents interact. Basic properties of XABSL are illustrated in direct comparison with Petri Net Plans and the COLBERT language using examples of basic robot behavior. More complex examples from robot soccer are used to illustrate the new extensions of XABSL. The complete system is available online on the XABSL website (http://www.xabsl.de).},
}

@INPROCEEDINGS{2008:ReinlRuhStolzenburgStryk,
  author = {C. Reinl and F. Ruh and F. Stolzenburg and O. von Stryk},
  title = {Multi-Robot Systems Optimization and Analysis Using MILP and CLP },
  year = {2008},
  month = {May 12-16},
  address = {Estoril, Portugal},
  booktitle = {AAMAS08-Workshop on Formal Models and Methods for Multi-Robot Systems},
  abstract = {Formal methods for multi-robot system analysis, specially logic-based methods, operate on discrete models. Optimization methods for simultaneous trajectory and task allocation, namely mixed integer dynamic optimization, operate on hybrid dynamical models which take into account a model of the motion dynamics of the physical robot. In this paper, ongoing work towards a coherent treatment of both approaches is described. A benchmark problem from robot soccer is introduced and used as an illustrative example.},
}

@INCOLLECTION{2007:InsectMimetics-Moehl-etal,
  author = {B. Möhl and S. Klug and T. Lens and O. von Stryk},
  title = {Elasticity in insect wings: applications to compliant robot joints (in Japanese)},
  year = {2008},
  pages = {submitted},
  publisher = {tba},
  editor = {M. Matsukaze},
  booktitle = {Insect Mimetics (in Japanese)},
}

@INCOLLECTION{2008:StelzervonStryk,
  author = {M. Stelzer and O. von Stryk},
  title = {Walking, running and kicking of humanoid robots and humans},
  year = {2008},
  pages = {175-192 and 337},
  publisher = {Springer Verlag},
  editor = {M.H. Breitner and G. Denk and P. Rentrop},
  booktitle = {From Nano to Space - Applied Mathematics Inspired by Roland Bulirsch},
  abstract = {In this paper key aspects and several methods for modeling, simulation, optimization and control of the locomotion of humanoid robots and humans are discussed. Similarities and differences between walking and running of humanoid robots and humans are outlined. The presented methods are different steps towards the ultimate goals of understanding and predicting human motion by validated simulation models and of developing humanoid robots with human like performance in walking and running. Numerical and experimental results are presented for model-based optimal control as well as for hardware-in-the-loop optimization of humanoid robot walking and for forward dynamics simulation and optimization of a human kicking motion.},
}

@ARTICLE{2008:IJHR-Friedmann-etal,
  author = {M. Friedmann and J. Kiener and S. Petters and H. Sakamoto and D. Thomas and O. von Stryk},
  title = {Versatile, high-quality motions and behavior control of humanoid robots},
  journal = {International Journal of Humanoid Robotics},
  year = {2008},
  pages = {submitted, under review},
}

@ARTICLE{2007:OptEng-HemkerFowlervonStryk,
  author = {T. Hemker and K.R. Fowler and M.W. Farthing and O. von Stryk},
  title = {A mixed-integer simulation-based optimization approach with surrogate functions in water resources management},
  journal = {Optimization and Engineering},
  year = {2008},
  pages = {to appear},
  doi = {10.1007/s11081-008-9048-0},
}

@ARTICLE{2008:IJRR-Hemkeretal,
  author = {T. Hemker and H. Sakamoto and M. Stelzer and O. von Stryk},
  title = {Efficient walking speed optimization of a humanoid robot},
  journal = {International Journal of Robotics Research},
  year = {2008},
  pages = {accepted for publication},
  abstract = {The development of optimized motions of humanoid robots that guarantee a fast and also stable walking is an important task especially in the context of autonomous soccer playing robots in RoboCup. We present a walking motion optimization approach for the humanoid robot prototype HR18 which is equipped with a low dimensional parameterized walking trajectory generator, joint motor controller and an internal stabilization. The robot is included as hardware-in-the-loop to define a low dimensional black-box optimization problem. In contrast to previously performed walking optimization approaches we apply a sequential surrogate optimization approach using stochastic approximation of the underlying objective function and sequential quadratic programming to search for a fast and stable walking motion. This is done under the conditions that only a small number of physical walking experiments should have to be carried out during the online optimization process. For the identified walking motion for the considered 55 cm tall humanoid robot we measured a forward walking speed of more than 30 cm/sec. With a modified version of the robot even more than 40 cm/sec could be achieved in permanent operation.},
}

@ARTICLE{2008:IJRR-Seyfarthetal,
  author = {A. Seyfarth and R. Tausch and M. Stelzer and F. Iida and A. Karguth and O. von Stryk},
  title = {Towards bipedal jogging as a natural result for optimizing walking speed for passively compliant three-segmented legs},
  journal = {International Journal of Robotics Research},
  year = {2008},
  pages = {accepted for publication; see also the video},
  abstract = {Elasticity in conventionally built walking robots is an undesired side effect that is suppressed as much as possible because it makes control very hard and thus complex control algorithms must be used. The human motion apparatus, in contrast, shows a very high degree of flexibility with sufficient stability. In this research we investigate how compliance and damping can deliberately be used in humanoid robots to improve walking capabilities. A modular robot system consisting of rigid segments, joint modules and adjustable compliant cables spanning one or more joints is used to configure a human-like biped. In parallel, a complex simulation model of the robot has been established. Walking motion is gained by oscillatory out-of-phase excitations of the hip joints. An optimization of the walking speed has been performed by improving the viscoelastic properties of the leg and identifying the appropriate hip control parameters. A good match was found between real robot experiments and numerical simulations. At higher speeds, transitions from walking to running are found in both the simulation as well as in the robot.},
}

@INPROCEEDINGS{2007:RCS-FriedmannPetersenvonStryk,
  author = {M. Friedmann and K. Petersen and O. von Stryk},
  title = {Tailored real-time simulation for teams of humanoid robots},
  year = {2008},
  volume = {5001},
  pages = {425-432},
  publisher = {Springer-Verlag},
  editor = {U. Visser and F. Ribeiro and T. Ohashi and F. Dellaert},
  series = {Lecture Notes in Computer Science/Artificial Intelligence},
  address = {Berlin/Heidelberg},
  booktitle = {RoboCup 2007: Robot Soccer World Cup XI},
  doi = {http://www.springerlink.com/content/41251kv140217484/},
  url = {http://www.springer.com/computer/artificial/book/978-3-540-68846-4},
  abstract = {Developing and testing the key modules of autonomous humanoid soccer robots (e.g., for vision, localization, and behavior control) in software-in-the-loop (SIL) experiments, requires real-time simulation of the main motion and sensing properties. These include humanoid robot kinematics and dynamics, the interaction with the environment, and sensor simulation, especially the camera properties. To deal with an increasing number of humanoid robots per team the simulation algorithms must be very efficient. In this paper, the simulator framework MuRoSimF (Multi-Robot-Simulation-Framework) is presented which allows the flexible and transparent integration of different simulation algorithms with the same robot model. These include several algorithms for simulation of humanoid robot motion kinematics and dynamics (with O(n) runtime complexity), collision handling, and camera simulation including lens distortion. A simulator for teams of humanoid robots based on MuRoSimF is presented. A unique feature of this simulator is the scalability of the level of detail and complexity which can be chosen individually for each simulated robot and tailored to the requirements of a specific SIL test. Performance measurements are given for real-time simulation on a moderate laptop computer of up to six humanoid robots with 21 degrees of freedom, each equipped with an articulated camera.},
}

@INPROCEEDINGS{2007:RCS-JuengelRisler,
  author = {Matthias Jüngel and Max Risler},
  title = {Self-Localization Using Odometry and Horizontal Bearings to Landmarks},
  year = {2007},
  note = {to appear},
  publisher = {Springer},
  editor = {U. Visser and F. Ribeiro and T. Ohashi and F. Dellaert},
  series = {Lecture Notes in Artificial Intelligence},
  booktitle = {RoboCup 2007: Robot Soccer World Cup XI},
}

@INPROCEEDINGS{2007:FriedmannPetersenVonStryk_WsHumSoc,
  author = {M. Friedmann and K. Petersen and O. v. Stryk},
  title = {Adequate Motion Simulation and Collision Detection for Soccer Playing Humanoid Robots},
  year = {2007},
  month = {Nov. 29 - Dec. 1},
  address = {Pittsburgh, PA, USA},
  booktitle = {Proc. 2nd Workshop on Humanoid Soccer Robots at the 2007 IEEE-RAS Int. Conf. on Humanoid Robots},
  url = {http://www.humanoidsoccer.org/ws07/program.html},
  abstract = {In this paper a humanoid robot simulator built with the Multi-Robot-Simulation-Framework (MuRoSimF) is presented. Among the unique features of the this simulator is the scalability in the level of physical detail in both the robot’s motion and sensing systems. It facilitates the development of control software for humanoid robots which is demonstrated for several scenarios from the RoboCup Humanoid Robot League. Different requirements exist for a humanoid robot simulator. E.g., testing of algorithms for motion control and postural stability require high fidelity of physical motion properties where as testing of behavior control and role distribution for a robot team requires only a moderate level of detail for real-time simulation of multiple robots. To meet such very different requirements often different simulators are used which makes it neccessary to model a robot multiple times and to integrate different simulations with high-level robot control software. MuRoSimF provides the capability of exchanging the simulation algorithms used for each robot transparently, thus allowing a trade-off between computational performance and fidelity of the simulation. It is therefore possible to choose different simulation algorithms which are adequate for the needs of a given simulation experiment, for example, motion simulation of humanoid robots based on kinematical, simplified dynamics or full multibody system dynamics algorithms. In this paper the sensor simulation capabilities of MuRoSimF are revised and the algorithms for motion simulation and collision detection and handling are presented in detail. An algorithm is presented which allows the real time simulation of the full dynamics of a 21 DOF humanoid robot. Special consideration is given to the merits and drawbacks of the different algorithms depending on the scenario. The simulation’s performance is measured and comparisons with the experimental performance of the humanoid robots are given.},
}

@TECHREPORT{2007:RoboCup-TDP-GermanTeam,
  author = {T. Röfer and J. Brose and D. Göhring and M. Jüngel and T. Laue and M. Risler},
  title = {GermanTeam 2007 - The German National RoboCup Team},
  year = {2007},
  institution = {DFKI Bremen, TU Darmstadt, HU Berlin, Universität Bremen},
}

@ARTICLE{hemker_et_al_2008,
  author = {T. Hemker and H. De Gersem and O. von Stryk and T. Weiland},
  title = {Mixed-Integer Nonlinear Design Optimization of a Superconductive Magnet},
  journal = {IEEE Transactions on Magnetics},
  year = {2007},
  volume = {44},
  number = {6},
  pages = {1110-1113},
  month = {June},
  abstract = {The numerical optimization of continuous parameters in electrotechnical design using electromagnetic field simulation is already standard. When integer-valued variables are involved, the complexity of the optimization problem rises drastically. In this paper, we describe a new sequential surrogate optimization approach for simulation-based mixed-integer nonlinear programming problems. We apply the method for the optimization of combined integer- and real-valued geometrical parameters of the coils of a superconductive magnet.},
}

@INPROCEEDINGS{2007:IROS-WS-Architectures-PettersThomasvonStryk,
  author = {S. Petters and D. Thomas and O. von Stryk},
  title = {RoboFrame - A Modular Software Framework for Lightweight Autonomous Robots},
  year = {2007},
  month = {Oct. 29},
  address = {San Diego, CA, USA},
  booktitle = {Proc. Workshop on Measures and Procedures for the Evaluation of Robot Architectures and Middleware of the 2007 IEEE/RSJ Int. Conf. on Intelligent Robots and Systems},
  url = {http://wiki.robot-standards.org/index.php/IROS_2007_WS},
  abstract = {The complexity of autonomous robot systems has increased dramatically in recent years. Besides an increased variety of robots, sensors, actuators, onboard computers and intelligent algorithms, the architecture of the software has gained crucial relevance with respect to the efficiency for adopting a robotic system to new hardware, new software or new tasks. For evaluation of different robot architectures and middleware not only a set of set of evaluation criterias is required. At least equally important for an evaluation is to define a representative set of the boundary conditions, i.e., different types of robots, tasks and scenarios as well as robot programmers. How the different criteria of an evaluation will be weighted also depends on these boundary conditions. To address the special needs of heterogeneous teams of autonomous lightweight robots, the software framework RoboFrame has been developed. Its main characteristics are platform independency, modularity and high efficiency. It is also bundled with a library of common components for robot control software, which provides much more support to the robot programmer than a robot middleware system alone. },
}

@INPROCEEDINGS{2007:ReinlVonStryk_RoboMat,
  author = {C. Reinl and O. von Stryk},
  title = {Optimal Control of Cooperative Multi-Robot Systems Using Mixed-Integer Linear Programming},
  year = {2007},
  pages = {145 - 151},
  month = {Sept. 17-19},
  editor = {Centro Internacional de Mathematica},
  address = {Coimbra, Portugal},
  booktitle = {Proc. RoboMat 2007},
  url = {http://labvis.isr.uc.pt/robomat/},
  abstract = {A new planning method for optimal control of multi-robot systems is discussed which accounts for the (continuous) physical locomotion dynamics of the robots and its tight coupling to the distribution and allocation of (discrete) subtasks to the robots to fulfill a joint mission. The point of departure is a nonlinear and nonconvex hybrid optimal control problem (HOCP) formulation which incorporates a detailed hybrid automaton model. Because of the many difficulties involved in solving this problem like large computational times and the lack of good or global convergence properties it is transcribed into a mixed- integer linear program (MILP). This can be solved much more efficiently using existing algorithms. The proposed approach is outlined for an example problem of cooperative soccer robots. The MILP solution itself may serve either as a good initial solution estimate for a method addressing the nonlinear HOCP or may later become the kernel of a model predictive control method for cooperative multi-robot systems. Despite the promising results obtained so far a variety of open questions yet remains to be answered including the ”best” way of transcribing HOCP to MILP with respect to both computational efficiency and good HOCP solution approximation. },
}

@INPROCEEDINGS{2007:AMS-Friedmannetal,
  author = {M. Friedmann and S. Petters and M. Risler and H. Sakamoto and D. Thomas and O. von Stryk},
  title = {A new, open and modular platform for research in autonomous four-legged robots},
  year = {2007},
  pages = {254 - 260},
  month = {18 - 19 Oct.},
  publisher = {Springer Verlag},
  editor = {K. Berns and T. Luksch},
  series = {Informatik aktuell},
  address = {Kaiserslautern},
  booktitle = {Autonome Mobile Systeme 2007},
  abstract = {In this paper the design goals for a new, open and modular, four-legged robot platform are described that was developed in reaction to the open call for a standard platform issued by the RoboCup Federation in 2006. The new robot should have similar motion and sensing capabilities like the previously used Sony AIBO plus several new ones. The hardware and software should be open, modular and reconfigurable. The robot should be resonably priced and allow annually upgrades.},
}

@INPROCEEDINGS{2007:IROS-Kiener-vonStryk,
  author = {J. Kiener and O. von Stryk},
  title = {Cooperation of heterogeneous, autonomous robots: A case study of humanoid and wheeled robots},
  year = {2007},
  pages = {959-964},
  month = {Oct. 29 - Nov. 2},
  address = {San Diego, CA, USA},
  booktitle = {Proc. IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)},
  abstract = {In this paper we present a case study of cooperation of a strongly heterogeneous robot team, composed of a highly articulated humanoid robot and a wheeled robot with largely complementing and some competing capabilities. By combining two strongly heterogeneous robots the diversity of accomplishable tasks increases as the variety of sensors and actuators in the robot systems is extended compared with a team consisting of homogeneous robots. The scenario describes a tightly cooperative task, where the humanoid robot and the wheeled robot follow for a long distance a ball, which is kicked finally by the humanoid robot into a goal. The task can be fulfilled successfully by combining the abilities of both robots. For task distribution and allocation, a newly developed objective function is presented which is based on a proper modeling of the sensing, perception, motion and onboard computing capabilities of the cooperating robots. Aspects of reliability and fault tolerance are considered.},
}

@INPROCEEDINGS{2007:ReinlVonStryk_ROBOCOMM,
  author = {Christian Reinl and Oskar von Stryk},
  title = {Optimal Control of Multi-Vehicle Systems Under Communication Constraints Using Mixed-Integer Linear Programming},
  year = {2007},
  month = {Oct. 15-17},
  address = {Athens, Greece},
  booktitle = {Proceedings of the. First International Conference on Robot Communication and Coordination (RoboComm)},
  organization = {ICST},
  keywords = {connectivity network, mobile communication network, linearized optimal control, mixed-integer linear optimal control, cooperative multi-vehicle system},
  abstract = {A new planning method for optimal cooperative control of heterogeneous multi-vehicle systems is investigated which enables to account for each vehicle’s nonlinear physical motion dynamics in a structured environment as well as for connectivity constraints of wireless communication. A general formulation as nonlinear hybrid optimal control problem (HOCP) is presented. A transformation technique is proposed to reduce the large computational efforts for solving HOCPs towards a future online application of this approach. Hereby the general problem is transcribed to a linearized mixed-integer linear programming problem (MILP) which can be solved much more efficiently. The proposed approach is successfully applied to the numerical solution of a representative, cooperative monitoring problem involving heterogeneous vehicles and conditions.},
}

@TECHREPORT{2007:RoboCup-TDP-Dribblers,
  author = {M. Friedmann and J. Kiener and S. Petters and D. Thomas and O. von Stryk},
  title = {Darmstadt Dribblers: Team Description for Humanoid KidSize League of RoboCup 2007},
  year = {2007},
  note = {11 pages},
  institution = {Technisch Universität Darmstadt},
  abstract = {This paper describes the hardware and software design of the kidsize humanoid robot systems of the Darmstadt Dribblers in 2007. The robots are used as a vehicle for research in control of locomotion and behavior of autonomous humanoid robots and robot teams with many degrees of freedom and many actuated joints. The Humanoid League of RoboCup provides an ideal testbed for such aspects of dynamics in motion and autonomous behavior as the problem of generating and maintaining statically or dynamically stable bipedal locomotion is predominant for all types of vision guided motions during a soccer game. A modular software architecture as well as further technologies have been developed for efficient and effective implementation and test of modules for sensing, planning, behavior, and actions of humanoid robots.},
}

@INPROCEEDINGS{2007:Compumag-Hemkeretal,
  author = {T. Hemker and O. von Stryk and H. De Gersem and T. Weiland},
  title = {Simulation-based design improvement of a superconductive magnet by mixed-integer nonlinear surrogate optimization},
  year = {2007},
  pages = {449-450},
  month = {June 24-28},
  address = {Aachen, Germany},
  booktitle = {16th Intl. Conf. on the Computation of Electromagnetic Fields - Compumag 2007},
}

@INPROCEEDINGS{2007:AIM-Kratzetal,
  author = {R. Kratz and M. Stelzer and M. Friedmann and O. von Stryk},
  title = {Control approach for a novel high power-to-weight ratio SMA muscle scalable in force and length},
  year = {2007},
  pages = {to appear},
  month = {September 4-7},
  address = {Zürich, CH},
  booktitle = {IEEE/ASME Intl. Conf. on Advanced Intelligent Mechatronics (AIM)},
  abstract = {The development of a control approach for a novel, soundless, lightweight and multifunctional shape memory alloy (SMA) actuator scalable in force and length for personal assistance or home-help robots is presented in this paper. The SMA actuator is based on lightweight bundles of thin wires of prestrained shape memory alloy that change their length when heated above their transformation temperature. The design approach of the actuator allows arranging the point of actuation in any direction and ensures a short cool down time to guarantee a frequency of contraction/stress cycles that is high enough to allow fast joint motions. This is needed for the generation of fast joint motions. For the use of the actuator the novel control approach has been experimentally validated. The approach uses the resistance of the actuator as a linear position encoder and there are no additional external sensors needed. The application of the new actuator to a novel lightweight humanoid robot is outlined. One advantage of the actuator over electric motors lies in the large variety of user-defined points of actuation of the in pull-force and length free scalable actuators and the high power-to-weight ratio. The results demonstrate that it is possible to build a large humanoid robot actuated with SMA actuator in a new way.},
}

@INPROCEEDINGS{biomed:2006,
  author = {M. Stelzer and O. von Stryk},
  title = {Human Kicking Motion Using Efficient Forward Dynamics Simulation and Optimization},
  year = {2007},
  volume = {15},
  pages = {192--196},
  publisher = {Springer, Berlin},
  editor = {F. Ibrahim and N. A. Abu Osman and J. Usman and N. A. Kadri},
  booktitle = {3rd Kuala Lumpur International Conference on Biomedical Engineering 2006: Biomed 2006, 11-14 December 2006, Kuala Lumpur, Malaysia},
  doi = {10.1007/978-3-540-68017-8},
}

@INPROCEEDINGS{icmmb:2006,
  author = {M. Stelzer and O. von Stryk},
  title = {Applications of Efficient Forward Dynamics Simulation in Biomechanics},
  year = {2006},
  booktitle = {Proceedings of the XVth International Conference on Mechanics in Medicine and Biology, Singapore},
}

@INPROCEEDINGS{2006:HumanoidsSoccerWS-DarmstadtDribblersandHajimeTeam,
  author = {M. Friedmann and J. Kiener and S. Petters and H. Sakamoto and D. Thomas and O. von Stryk},
  title = {Versatile, high-quality motions and behavior control of humanoid soccer robots},
  year = {2006},
  pages = {9-16},
  month = {Dec. 4-6},
  address = {Genoa, Italy},
  booktitle = {Proc. Workshop on Humanoid Soccer Robots of the 2006 IEEE-RAS Int. Conf. on Humanoid Robots},
  url = {http://www.dei.unipd.it/~emg/whs2006/schedule.html},
  abstract = {Many different and high-quality humanoid otions have been developed based on a tailored, 55cm tall humanoid robot kinematics and design using 21 servo motors and inertial sensors for stabilization. These include fast forward walking of about 1.5 km/h in permanent operation, multidirectional walking capabilities, a variety of standard and spectacular kicks, standing up motions as well as motions displaying an emotional state of the robot. While all robot motions are executed in real-time on a controller board an adaptive selection of different motions and autonomous robot behavior are controlled by hierarchical state machine executed on an onboard Pocket PC. Information about the current state of the dynamic environment in a soccer game is obtained from two directed cameras with wide and narrow angles. During RoboCup 2006 the robot demonstrated the fastest walking of all kid- and teen-size humanoid robots on regular terrain as well as in the rough terrain challenge. Also a large variety of different motions as well as individual and team behaviors during successful autonomous soccer games have been demonstrated including the scoring of a goal with the first autonomously performed backheel kick of a humanoid robot.},
}

@INPROCEEDINGS{2006:ROBIO-Friedmannetal,
  author = {M. Friedmann and J. Kiener and S. Petters and D. Thomas and O. von Stryk},
  title = {Modular software architecture for teams of cooperating, heterogeneous robots},
  year = {2006},
  pages = {613-618},
  month = {December 17-20},
  address = {Kunming, China},
  booktitle = {Proc. IEEE International Conference on Robotics and Biomimetics (ROBIO)},
  abstract = {For teams of cooperating autonomous lightweight robots with challenging dynamical locomotion properties a platform independent modular software architecture and platform independent modules for sensor data processing, planning and motion control have been developed. The software architecture allows high level communication between modules on different abstraction levels of the control architecture within one robot system as well as communication between different and heterogeneous robots and computers using wireless network. Very different behavior control paradigms may be realized on the basis of the developed architecture. The application to teams of cooperating small and medium size humanoid robots is investigated in this paper. Scenarios for inter robot communication and cooperative task accomplishment are described.},
}

@INPROCEEDINGS{2006:ROBIO-Kratzetal,
  author = {R. Kratz and S. Klug and M. Stelzer and O. von Stryk},
  title = {Biologically inspired reflex based stabilization control of a humanoid robot with artificial {SMA} muscles},
  year = {2006},
  pages = {1089-1094},
  month = {December 17-20},
  address = {Kunming, China},
  booktitle = {Proc. IEEE International Conference on Robotics and Biomimetics (ROBIO)},
  abstract = {Suddenly occurring collisions or unintentional motions represent a high safety risk in robotics and must be prevented. Especially for humanoid robots, the influence of disturbances that occur unexpectedly during bipedal locomotion are difficult to compensate. A model based online control approach for stabilization of a humanoid robot with many degrees of freedom may require too much time for computing and implementing an adequate compensating motion. In addition, such a control approach usually requires accurate sensor information about the type and magnitude of the disturbance. The goal of the present paper is a reflex based online stabilization control of a humanoid robot actuator based on artificial SMA muscles. The design of a humanoid robot actuated with SMA muscles allows a lightweight robot design and simplifies the direct implementation of reflexes. The reflex that is integrated into the robot depends on an evaluation of the pressure distribution of the feet. An instable position of the center of mass of the robot leads to a known specific pressure disturbance that should be avoided. The experiments show that the implementation of a reflex for the actuators in the calf leads to a stabilization of the entire robot. Additional reflexes are required when the strength or speed of disturbances are increased, such as in the upper leg or arms.},
}

@ARTICLE{2006:ZAMM_Stelzer_vonStryk,
  author = {Maximilian Stelzer and Oskar von Stryk},
  title = {Efficient Forward Dynamics Simulation and Optimization of Human Body Dynamics},
  journal = {ZAMM, Zeitschrift für Angewandte Mathematik und Mechanik, Journal of Applied Mathematics and Mechanics},
  year = {2006},
  volume = {86},
  number = {10},
  pages = {828-840},
  keywords = {Forward dynamics simulation, forward dynamics optimization, multibody systems, optimal control, biomechanics, human motion},
}

@INCOLLECTION{2006:BionikGothavonStryk,
  author = {O. von Stryk},
  title = {Ihr intelligenter "Personal Robot" im Jahr 2050: Haushaltshilfe, Terminator oder Fußballspieler?},
  year = {2006},
  pages = {48-50},
  publisher = {Stiftung Schloss Friedenstein Gotha},
  editor = {Museum der Natur Gotha},
  address = {Gotha, Germany},
  booktitle = {Bionik - Vom Ursaurier zum laufenden Roboter},
}

@INPROCEEDINGS{2006:IROSLoetzschRislerJuengel,
  author = {M. Lötzsch and M. Risler and M. Jüngel},
  title = {XABSL - A Pragmatic Approach to Behavior Engineering},
  year = {2006},
  pages = {5124-5129},
  month = {October 9-15},
  address = {Beijing, China},
  booktitle = {Proceedings of IEEE/RSJ International Conference of Intelligent Robots and Systems (IROS)},
  abstract = {This paper introduces the Extensible Agent Behavior Specification Language (XABSL) as a pragmatic tool for engineering the behavior of autonomous agents in complex and dynamic environments. It is based on hierarchies of finite state machines (FSM) for action selection and supports the design of longterm and deliberative decision processes as well as of short-term and reactive behaviors. A platform-independent execution engine makes the language applicable on any robotic platform and together with a variety of visualization, editing and debugging tools, XABSL is a convenient and powerful system for the development of complex behaviors. The complete source code can be freely downloaded from the XABSL website (http://www.informatik.huberlin.de/ki/XABSL/). The language has been successfully applied on many robotic platforms, mainly in the domain of RoboCup robot soccer. It gave the GermanTeam the crucial advantage over other teams to become the 2004 and 2005 world champion in the Four-Legged League and helped the team CoPS Stuttgart to become third in the Middle Size League in 2004.},
}

@INPROCEEDINGS{2006:IFAC-MVS-Friedmann-etal,
  author = {M. Friedmann and J. Kiener and S. Petters and D. Thomas and O. von Stryk },
  title = {Reusable architecture and tools for teams of lightweight heterogeneous robots},
  year = {2006},
  pages = {51-56},
  month = {October 2-3},
  address = {Salvador, Brazil},
  booktitle = {Proc. 1st IFAC Workshop on Multivehicle Systems},
  abstract = {The software framework RoboFrame has been designed to meet the special requirements for teams of lightweight autonomous heterogeneous robot systems. Due to platform abstraction and modern object oriented design, it allows the reuse of components of common robot control software. It can also efficiently be implemented on new platforms and enables different control architectures for different tasks. For the exemplary application in autonomous robot soccer teams configurable and portable algorithms for vision, world modeling, behavior and motion control have been developed on top of the framework. For debugging, controlling and monitoring, an extendable graphical user interface and a generic simulator package have been implemented around the framework. Based on these instruments, different applications for homogeneous and heterogeneous robot teams can be realized in short time.},
}

@INPROCEEDINGS{2006:IFAC-MVS-GlockerReinlvonStryk,
  author = {M.Glocker and C. Reinl and O. von Stryk},
  title = {Optimal task allocation and dynamic trajectory planning for multi-vehicle systems using nonlinear hybrid optimal control},
  year = {2006},
  pages = {38-43},
  month = {October 2-3},
  address = {Salvador, Brazil},
  booktitle = {Proc. 1st IFAC-Symposium on Multivehicle Systems},
  abstract = {Based on a nonlinear hybrid dynamical systems model a new planning method for optimal coordination and control of multiple unmanned vehicles is investigated. The time dependent hybrid state of the overall system consists of discrete (roles, actions) and continuous (e.g. position, orientation, velocity) state variables of the vehicles involved. The evolution in time of the system’s hybrid state is described by a hybrid state automaton. The presented approach enables a tight and formal coupling of discrete and continuous state dynamics, i.e. of dynamic role and action assignment and sequencing as well as of the physical motion dynamics of a single vehicle modeled by nonlinear differential equations. The planning problem of determining optimal hybrid state trajectories that minimize a cost function as time or energy for optimal multi-vehicle cooperation subject to constraints including the vehicle’s motion dynamics is transformed to a mixed-binary dynamic optimization problem being solved numerically. The numerical method consists of an inner iteration where multiphase optimal control problems are solved using a direct collocation method and an outer iteration based on a branch-and-bound search of the discrete solution space. The approach presented in this paper is applied to the scenarios of optimal simultaneous waypoint or target sequencing and dynamic trajectory planning for a team of unmanned aerial vehicles in a plane and to optimal role assignment and physics-based trajectories in robot soccer.},
}

@INPROCEEDINGS{2006:CLAWARHemkeretal,
  author = {Th. Hemker and H. Sakamoto and M. Stelzer and O. von Stryk},
  title = {Hardware-in-the-loop optimization of the walking speed of a humanoid robot},
  year = {2006},
  pages = {614-623},
  month = {September 11-14},
  address = {Brussels, Belgium},
  booktitle = {CLAWAR 2006: 9th International Conference on Climbing and Walking Robots},
  abstract = {The development of optimized motions of humanoid robots that guarantee a fast and also stable walking is an important task especially in the context of autonomous soccer playing robots in RoboCup. We present a walking motion optimization approach for the humanoid robot prototype HR18 which is equipped with a low dimensional parameterized walking trajectory generator, joint motor controller and an internal stabilization. The robot is included as hardware-in-the-loop to define a low dimensional black-box optimization problem. In contrast to previously performed walking optimization approaches we apply a sequential surrogate optimization approach using stochastic approximation of the underlying objective function and sequential quadratic programming to search for a fast and stable walking motion. This is done under the conditions that only a small number of physical walking experiments should have to be carried out during the online optimization process. For the identified walking motion for the considered $55$ cm tall humanoid robot we measured a forward walking speed of more than $30$ cm/sec. With a modified version of the robot even more than $40$ cm/sec could be achieved in permanent operation.},
}

@INPROCEEDINGS{2006:CLAWARSeyfarthetal,
  author = {A. Seyfarth and R. Tausch and M. Stelzer and F. Iida and A. Karguth and O. von Stryk},
  title = {Towards bipedal running as a natural result of optimizing walking speed for passively compliant three-segmented legs},
  year = {2006},
  pages = {396-401},
  month = {September 12-14},
  address = {Brussels, Belgium},
  booktitle = {CLAWAR 2006: 9th International Conference on Climbing and Walking Robots},
  abstract = {Elasticity in conventionally built walking robots is an undesired side-effect that is oppressed as much as possible because it makes control very hard, and thus complex control algorithms must be used. The human motion apparatus, in contrast, shows a very high degree of flexibility with suffcient stability. In this research we investigate how elasticities and damping can sensibly be used in humanoid robots to improve walking capabilities. A modular robot system consisting of rigid segments, joint modules and adjustable elastic strings spanning one or more joints is used to configure a human-like biped. In parallel, a complex simulation model of the robot has been established. Walking motion is gained by oscillatory out-of-phase excitations of the hip joints. An optimization of the walking speed has been performed by improving the viscoelastic properties of the leg and identifying the appropriate hip control parameters. Experiments on the real robot very well matched the numerical results. At higher speeds, transitions from walking to running are found in both the simulation as well as in the robot.},
}

@INPROCEEDINGS{2006:IFACKratzStelzervStryk,
  author = {R. Kratz and M. Stelzer and O. von Stryk},
  title = {Macroscopic SMA wire bundle actuator/sensor system: design, measurement, control approach},
  year = {2006},
  month = {September 12-14},
  address = {Heidelberg},
  booktitle = {Proc. 4th IFAC-Symposium on Mechatronic Systems},
}

@INCOLLECTION{2006:MoehlvonStryk-Bionikbuch,
  author = {Bernhard Möhl and Oskar von Stryk},
  title = {Menschen aus Stahl},
  year = {2006},
  pages = {174-180},
  publisher = {Bionik Media},
  editor = {K.G. Blüchel and F. Malik},
  booktitle = {Faszination Bionik - Die Intelligenz der Schöpfung},
}

@INPROCEEDINGS{2006_hemker_CMWR,
  author = {Th. Hemker and K.R. Fowler and O. von Stryk},
  title = {Derivative-Free Optimization Methods for Handling Fixed Costs in Optimal Groundwater Remediation Design},
  year = {2006},
  month = {19-22 June},
  booktitle = {Proc. of the CMWR XVI - Computational Methods in Water Resources},
  abstract = {Groundwater remediation design problems are routine in water resource management. The starting point for such a design problem is to formulate an objective function that represents a measure of the manager´s goal. For example, in plume migration control, we need to determine the cost to design a well field to alter the direction of groundwater flow and thereby control the destination of a contaminant. Constraints must be specified to ensure that the plume is captured, the physical domain is protected, and the wells operate under realistic conditions. Optimization algorithms must work in conjunction with groundwater flow and possibly contaminant transport simulators to determine the minimal cost well design subject to the constraints, but typically these numerical simulation codes have been developed for many years and have usually not been designed to meet the specific needs of optimization methods as, e.g., providing gradient information. Decision variables can be real-valued, in the case of pumping rates and well locations, or integer valued in the case of the number of wells in the design. In this work we focus on formulations that include a fixed installation cost as well as an operating cost, resulting in a simulation-based nonlinear mixed-integer optimization problem. The motivation is that our preliminary studies have shown that convergence to an unsatisfactory, local minimum with many wells operating at low pumping rates is common when the fixed cost is ignored. The challenge in the fixed cost formulation is the integer variable for the number of wells in the design. Removing a well from the design space leads to a large decrease in cost meaning optimizers must be equipped to either handle a mixed-integer or approximate mixed integer, black-box problem and discontinuities in the objective function. Moreover since evaluation of the objective function requires numerical results from a simulation, derivative information is unavailable. Gradient based optimization methods are not appropriate for these applications, hence methods that rely only on function values are more appealing. We compare three methods for handling the installation cost on a hydraulic capture benchmarking problem proposed in the literature. All the approaches described below do not use the gradient of the objective function, only function values for minimization. In one approach, we use penalty coefficients proposed in the literature for the installation term to transform the discontinuous problem into a continuous one. In another approach, we bypass including the number of wells as a decision variable by defining an inactive-well threshold. In the course of the optimization, if a well rate falls in this threshold, the well is removed from the design space, leading to large discontinuities in the objective function. For the two above formulations, we use the implicit filtering algorithm, a method which uses a sequence of finite difference gradients, for minimization. In the third approach, we use sequential stochastic modeling to build surrogate functions to approximate the original objective function. With this procedure the use of a branch and bound technique becomes possible to solve the mixed integer problem in contrast to methods working directly on the simulation results, which impedes relaxation of integer variables. We present promising preliminary numerical results on the benchmarking problem and point the way towards improvement and future work. },
}

@INPROCEEDINGS{2006:ACTUATORKratzStelzervonStryk,
  author = {R. Kratz and M. Stelzer and O. von Stryk},
  title = {Design, measurement experiments and application of a macroscopic shape memory alloy actuator system},
  year = {2006},
  month = {June 14-15},
  address = {Bremen, Germany},
  booktitle = {ACTUATOR 2006 - 10th International Conference on New Actuators},
  abstract = {Prestrainend shape memory alloys (SMA) change their length when heated above their transformation temperature. Based on this property various micro-technical actuators have been developed in the past. This paper presents the design of novel macroscopic SMA actuators scalable in force and length. Our design approach allows arranging the point of actuation in any direction and ensures a short cool down time to guarantee a high frequency of contraction/stress cycles. The use of the new actuator also necessitates a novel control approach. A model to describe the actuators behavior has been developed and experimentally validated. It offers the possibility of using the resistance of the actuator as a linear position encoder and provides a basis for the control approach of the actuator. The application to a new bipedal walking robot demonstrates one envisioned future use of the actuators. One advantage over electric motors lies in the large variety of user-defined points of actuation of the scalable actuators on a mechanical structure. This allows generating joint movements without the common restrictions holding for electric motors on the possible point of actuation. },
}

@INPROCEEDINGS{2006BioRob:KlugvonStrykMoehl,
  author = {S. Klug and O. von Stryk and B. Möhl},
  title = {Design and Control Mechanisms for a 3 DOF Bionic Manipulator},
  year = {2006},
  number = {210},
  month = {February 20-22},
  address = {Pisa, Italy},
  booktitle = {Proc. 1st IEEE / RAS-EMBS Intl. Conf. on Biomedical Robotics and Biomechatronics (BioRob)},
  url = {http://www.biorob.de},
  abstract = {Functionality and design of a bionic robot arm consisting of three joints driven by elastic and compliant actuators derived from biologically inspired principles are presented. In the first design standard springs with linear characteristics are utilized in combination with electrical drives. Different control approaches for the bionic robot arm are presented, discussed and evaluation in numerical simulations and experiments with regards to the long-term goal of a natural-like control perfomance.},
}