Franziska Zacharias

German Aerospace Center (DLR), Köln, North Rhine-Westphalia, Germany

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Publications (18)0.37 Total impact

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    ABSTRACT: More and more systems are developed that include several robot arms, like humanoid robots or industrial robot systems. These systems are designed for complex tasks to be solved in cooperation by the robot arms. However, the capabilities of the individual robot arms to perform given tasks or the suitability of a multi-robot system for cooperative tasks cannot be intuitively comprehended. For planning complex tasks or designing robot systems, a representation of a robot arm's workspace is needed that allows to determine from which directions objects in the workspace can be reached. In this paper, the capability map is presented. It is a representation of a robot arm's kinematic capabilities in its workspace. The capability map is used to compare existing robot arms, to support the design phase of an anthropomorphic robot arm and to enable robot workcell planning.
    International Journal of Humanoid Robotics 12/2013; 10(4):1350031. · 0.37 Impact Factor
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    ABSTRACT: Assistive robotic systems in household or industrial production environments get more and more capable of performing also complex tasks which previously only humans were able to do. As robots are often equipped with two arms and hands, similar manipulations can be executed. The robust programming of such devices with a very large number of degrees of freedom (DOFs) compared with single industrial robot arms however is laborious if done joint-wise. Two major directions to overcome this problem have been previously proposed. The programming by demonstration (PbD) approach, where human arm and recently also hand motions are tracked, segmented and re-executed in an adaptive way on the robotic system and the high-level planning approach which tries to generate a task sequence on a logical level and attributes geometric information as necessary to generate artificial trajectories to solve the task. Here we propose to combine the best of both worlds. For the very complex motion generation for a robotic hand, a rather direct approach to assign manipulation actions from human demonstration to a human hand is taken. For the combination of different basic manipulation actions the task constraints are segmented from the demonstration action and used to generate a task oriented plan. This plan is validated against the robot kinematic and geometric constraints and then a geometric motion planner can generate the necessary robot motions to fulfill the task execution on the system.
    01/2012: pages 59-122; , ISBN: 978-3-642-29040-4
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    ABSTRACT: Abstract-This article accompanies a video that presents a bimanual haptic device composed of two DLR/KUKA Light weight Robot (LWR) arms. The LWRs have similar dimensions to human arms, and can be operated in torque and position control mode at an update rate of 1kHz. The two robots are mounted behind the user, such that the intersecting workspace of the robots and the human arms becomes maximal. In order to enhance user interaction, various hand interfaces and additional tactile feedback devices can be used together with the robots. The presented system is equipped with a thorough safety architecture that assures safe operation for human and robot. Additionally, sophisticated control strategies improve performance and guarantee stability. The introduced haptic system is well suited for versatile applications in remote and virtual environments, especially for large unsealed movements.
    IEEE International Conference on Robotics and Automation, ICRA 2011, Shanghai, China, 9-13 May 2011; 01/2011
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    ABSTRACT: This paper presents the graspability map, a novel approach to represent for a particular object the positions and orientations that a given mechanical hand can adopt to achieve a force closure precision grasp. The algorithm is based on the intersection between the fingertip workspaces and the object, plus the verification of a necessary condition for force closure grasps. The maps are computed offline and can be used for comparing the grasp capabilities of different mechanical hands with respect to some benchmark objects. The maps have also potential applications in online grasp and manipulation planning.
    IEEE/RSJ Int. Conf. Intelligent Robots and Systems - IROS; 01/2011
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    ABSTRACT: It contradicts the human's expectations when humanoid robots move awkwardly during manipulation tasks. The unnatural motion may be caused by awkward start or goal configurations or by probabilistic path planning processes that are often used. This paper shows that the choice of an arm's target configuration strongly effects planning time and how human-like a planned path appears. Human-like goal configurations are found using a criterion from ergonomics research. The knowledge which pose of the Tool Center Point (TCP) can be reached in a natural manner is encapsulated in a restricted reachability map for the robot arm. I. INTRODUCTION People have strong expectations of how other persons will act and move in a given situation. This may be a source of confusion in a human's interaction with humanoid robots, if the robot does not move in a predictable or expected manner. If a humanoid robot like Rollin' Justin (Fig. 1) uses awkward arm configurations, or trajectories to perform tasks, the human may feel uncertain and insecure. The principles of path planning, especially probabilistic path planning, have been extensively examined in the last decade. However, the paths that the planner computes are unpredictable and may seem awkward. While the problem of how to get to an object is solved, the solution may not be comprehensible for the human observer or coworker. This paper shows that the choice of an arm's target configuration strongly effects planning time and how human-like a planned path appears. Human-like configurations are found using a criterion from ergonomics research, the rapid upper limb assessment (RULA) (1). By restricting the planning process to the regions of the robot arm workspace where human- like manipulation is possible, planning times and motion quality are enhanced. The knowledge which pose of the Tool Center Point (TCP) can be reached in a natural manner, is encapsulated in a restricted capability map for the robot arm. This map is used to determine which grasps from a given grasp set are usable for human-like manipulation. The proposed concepts are evaluated using the humanoid robot Justin.
    IEEE International Conference on Robotics and Automation (ICRA) 2011; 01/2011
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    ABSTRACT: In virtual assembly verification or remote maintenance tasks, bimanual haptic interfaces play a crucial role in successful task completion. This paper proposes a method for objectively comparing how well a haptic interface covers the reachable workspace of human arms. Two system configurations are analyzed for a recently introduced haptic device that is based on two DLR-KUKA light weight robots: the standard configuration, where the device is opposite the human operator, and the ergonomic configuration, where the haptic device is mounted behind the human operator. The human operator directly controls the robotic arms using handles. The analysis is performed using a representation of the robot arm workspace. The merits of restricting the comparisons to the most significant regions of the human workspace are discussed. Using this method, a greater workspace correspondence for the ergonomic configuration was shown.
    Intelligent Robots and Systems (IROS), 2010 IEEE/RSJ International Conference on; 11/2010
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    ABSTRACT: In autonomous bimanual operation of a robot, parallelized planning and execution of a task is essential. Elements of a task have different functional and spatial relationships. They may depend on each other and have to be executed in a specific order or they may be independent and their order can be determined freely. Consequently, individual actions can be planned and executed in parallel or not. In a proof of concept, this paper shows that the structure of a task and its mapping onto subordinate planners can significantly influence planning speed and task execution. Independent tasks are planned using two parallel path planners. Dependent tasks are planned using one path planner for both arms. Using a simple, yet expandable experimentation scenario, the resulting recommendations for parameterizing path planners are verified on a humanoid robot. For execution on the real robot a violation of the rigid body model used in path planners had to be addressed.
    Intelligent Robots and Systems (IROS), 2010 IEEE/RSJ International Conference on; 11/2010
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    F. Zacharias, W. Sepp, C. Borst, G. Hirzinger
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    ABSTRACT: Humanoid robots are envisioned in general household tasks. To be able to fulfill a given task the robot needs to be equipped with knowledge concerning the manipulation and interaction in the environment and with knowledge about its own capabilities. When performing actions, e.g. opening doors or imitating human reach to grasp movements special 3-d trajectories are followed with the robot's end-effector. These trajectories can not be executed in every part of the robot's arm workspace. Therefore a task planner has to determine if and how additional degrees of freedom such as the robot's upper body or the robot's base can be moved in order to execute the task-specific trajectory. An approach is presented that computes placements for a mobile manipulator online given a task-related 3-d trajectory. A discrete representation of the robot arm's reachable workspace is used. Task-specific trajectories are interpreted as patterns and searched in the reachability model using multi-dimensional correlation. The relevance of the presented approach is demonstrated in simulated positioning tasks.
    Humanoid Robots, 2009. Humanoids 2009. 9th IEEE-RAS International Conference on; 01/2010
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    F. Zacharias, C. Borst, G. Hirzinger
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    ABSTRACT: In service robotic tasks, the ability to grasp and handle objects is mandatory. Short response times with respect to execution of commanded tasks are necessary. Planning in general and grasp planning in particular should happen online. We extend the online grasp planner by Borst et al. to generate reachable grasps while preserving the integrity and modularity of the grasp planner. To achieve this a representation of the reachable space of a robot arm is used to determine a grasp's reachability. Furthermore we show the influence of obstacles on the reachability throughout the workspace. A method to include obstacles into the representation of reachability is sketched. The resulting representation is used by the grasp planner. The performance of the algorithms is evaluated by measuring their computation times. Even in the worst case our grasp planner outperforms comparable state of the art approaches.
    Advanced Robotics, 2009. ICAR 2009. International Conference on; 07/2009
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    ABSTRACT: Research on humanoid robots for use in servicing tasks, e.g. fetching and delivery, attracts steadily more interest. With “Rollin' Justin” a mobile robotic system and research platform is presented that allows sophisticated control algorithms and dexterous manipulation. This video gives an overview of the mobile humanoid robotic system “Rollin' Justin” with special emphasis on mechanical design features, control issues and high-level system capabilities such as human robot interaction.
    ICRA2009, International Conference on Robotics and Automation; 06/2009
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    ABSTRACT: Research on humanoid robots for use in servicing tasks, e.g. fetching and delivery, attracts steadily more interest. With "Rollin' Justin" a mobile robotic system and research platform is presented that allows sophisticated control algorithms and dexterous manipulation. This video gives an overview of the mobile humanoid robotic system "Rollin' Justin" with special emphasis on mechanical design features, control issues and high-level system capabilities such as human robot interaction.
    Proceedings of the 2009 IEEE international conference on Robotics and Automation; 05/2009
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    ABSTRACT: Analytic modeling, imitation, and experiencebased learning are three approaches that enable robots to acquire models of their morphology and skills. In this paper, we combine these three approaches to efficiently gather training data to learn a model of reachability for a typical mobile manipulation task: approaching a worksurface in order to grasp an object. The core of the approach is experience-based learning. For more effective exploration, we use capability maps as analytic models of the robot’s dexterity to constrain the area in which the robot gathers training data. Furthermore, we acquire a human model of reachability from human motion data and use it to bias exploration. The acquired training data is used to learn Action-Related Places. In an empirical evaluation we demonstrate that combining the three approaches enables the robot to acquire accurate models with far less data than with our previous exploration strategy.
    International Conference on Humanoid Robots (Humanoids); 01/2009
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    Franziska Zacharias, Christoph Borst, Gerd Hirzinger
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    ABSTRACT: Humans use learned knowledge to solve reaching tasks and to manipulate objects and tools.We believe that representations of manipulation characteristics of an object and of the reaching capabilities of a robotic arm can speed up low-level planners, like grasp planners. They also enable sophisticated scene analysis and reasoning for high-level planners, like task planners. We present object-specific grasp maps to encapsulate an object’s manipulation characteristics. A grasp planner is shown to use the grasps maps and a representation of the reachable workspace. The exploitation of the provided knowledge focuses the planning on regions of the object that are promising to yield high quality grasps. Speed ups of factor 2-12 are reported.
    German Workshop on Robotics. 01/2009;
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    F. Zacharias, C. Borst, M. Beetz, G. Hirzinger
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    ABSTRACT: For mobile manipulators envisioned in home environments a kitchen scenario provides a challenging testbed for numerous skills. Diverse manipulation actions are required, e.g. simple pick and place for moving objects and constrained motions for opening doors and drawers. The robot kinematics and link limits however are restrictive. Therefore especially a constrained trajectory will not be executable from arbitrary placements of the mobile manipulator. A two stage approach is presented to position a mobile manipulator to execute constrained linear trajectories as needed for opening drawers. In a first stage, a representation of a robot armpsilas reachable workspace is computed. Pattern recognition techniques are used to find regions in the workspace representation where these trajectories are possible. A set of trajectories results. In the second stage mobile manipulator placements are computed and the corresponding trajectories are checked for collisions. Compared to a brute force search through the workspace, the success rate of finding a mobile manipulator placement can be increased from 2% to 70%.
    Intelligent Robots and Systems, 2008. IROS 2008. IEEE/RSJ International Conference on; 10/2008
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    F. Zacharias, C. Borst, G. Hirzinger
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    ABSTRACT: Humans have at some point learned an abstraction of the capabilities of their arms. By just looking at the scene they can decide which places or objects they can easily reach and which are difficult to approach. Possessing a similar abstraction of a robot arm's capabilities in its workspace is important for grasp planners, path planners and task planners. In this paper, we show that robot arm capabilities manifest themselves as directional structures specific to workspace regions. We introduce a representation scheme that enables to visualize and inspect the directional structures. The directional structures are then captured in the form of a map, which we name the capability map. Using this capability map, a manipulator is able to deduce places that are easy to reach. Furthermore, a manipulator can either transport an object to a place where versatile manipulation is possible or a mobile manipulator or humanoid torso can position itself to enable optimal manipulation of an object.
    Intelligent Robots and Systems, 2007. IROS 2007. IEEE/RSJ International Conference on; 12/2007
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    ABSTRACT: This video presents a humanoid two-arm system developed as a research platform for studying dexterous two-handed manipulation. The system is based on the modular DLR-Lightweight-Robot-III and the DLR-Hand-II. Two arms and hands are combined with a three degrees-of-freedom movable torso and a visual system to form a complete humanoid upper body. The diversity of the system is demonstrated by showing the mechanical design, several control concepts, the application of rapid prototyping and hardware-in-the-loop (HIL) development as well as two-handed manipulation experiments and the integration of path planning capabilities.
    Robotics and Automation, 2007 IEEE International Conference on; 05/2007
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    IEEE-RAS; 01/2007
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    F. Zacharias, C. Borst, G. Hirzinger
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    ABSTRACT: Autonomous service robots have to recognize and interpret their environment to be able to interact with it. This paper focuses on service tasks such as serving a glass of water where a humanoid two-arm-system has to acquire an object from the scene. A task planner should be able to autonomously discern the necessary actions to solve the task. In the process, a path planner can be used to compute motion sequences to execute these actions. To plan trajectories, the path planner requires a pair of configurations, the start and the goal configuration of the robot, to be provided e.g. by a task planner. This paper proposes a method to autonomously find the goal configurations necessary to acquire objects from the scene and thus makes an attempt to bridge the gap between task planning and path planning. The method determines where to grasp an object by analyzing the scene and the influence of obstacles on the intended grasp location. For the case where the goal object can not be grasped due to obstructing obstacles, a solution is proposed
    Intelligent Robots and Systems, 2006 IEEE/RSJ International Conference on; 11/2006