Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    What dynamics should impedance-controlled robots render?
    ( 2019)
    Haninger, Kevin
    ;
    Surdilovic, Dragoljub
    ;
    Bastidas Cruz, Arturo
    While impedance control is the standard framework for physically interactive robots, the design choice of what dynamics should be rendered requires additional information (assumptions on environment, in-situ data). The range of dynamics which can be rendered by a robot is informed by its mechatronic design (actuators, physical compliance, innerloop control), and these mechanical design decisions must be made in advance. How can a mechatronic design be evaluated when the system objectives and environment dynamics are not quantified? This paper presents performance metrics proposed for pHRI in literature, and seeks to move towards a unified methodology for mechatronic design on interactive robots: supporting potential performance and safety over a set of environments.
  • Publication
    Bounded Collision Force by the Sobolev Norm: Compliance and Control for Interactive Robots
    ( 2019)
    Haninger, Kevin
    ;
    Surdilovic, Dragoljub
    A robot making contact with an environment or human presents potential safety risks, including excessive collision force. While experiments on the effect of robot inertia, relative velocity, and interface stiffness on collision are in literature, analytical models for maximum collision force are limited to a simplified mass-spring robot model. This simplified model limits the analysis of control (force/torque, impedance, or admittance) or compliant robots (joint and end-effector compliance). Here, the Sobolev norm is adapted to be a system norm, giving rigorous bounds on the maximum force on a stiffness element in a general dynamic system, allowing the study of collision with more accurate models and feedback control. The Sobolev norm can be found through the H 2 norm of a transformed system, allowing efficient computation, connection with existing control theory, and controller synthesis to minimize collision force. The Sobolev norm is validated, first experimentally with an admittance-controlled robot, then in simulation with a linear flexible-joint robot. It is then used to investigate the impact of control, joint flexibility and end-effector compliance on collision, and a trade-off between collision performance and environmental estimation uncertainty is shown.
  • Publication
    Identification of Human Dynamics in User-Led Physical Human Robot Environment Interaction
    ( 2018)
    Haninger, Kevin
    ;
    Surdilovic, Dragoljub
    Human dynamic models are useful in design of physical human-robot and human-robot-environment interaction: informing choice of robot impedance, motivating relaxations to passivity-based safety constraints, and allowing online inference to user intent. Designing for performance objectives such as stable well-damped contact transitions also requires nominal models, but the use of human models in controller design is limited. Established approaches to identify human dynamics apply position or force perturbation and measure the corresponding response, mostly to validate neuromuscular hypotheses on motor control, which raises questions about their transferability to human-led collaboration. Here, human dynamics are identified in a task which closely resembles the final application, where the human leads the robot into contact with a (virtual) wall. This paper investigates the impact of human dynamics on coupled system behavior, and establishes a general framework for identification in human-led scenarios, making consideration of unmeasured human input. Experiments with different stiffness environments allow inference to human dynamics, and characterize the range of human dynamics which can be modulated by the user.
  • Publication
    Multimodal Environment Dynamics for Interactive Robots
    ( 2018)
    Haninger, Kevin
    ;
    Surdilovic, Dragoljub
    Interactive robots offer improved performance in tasks with environmental uncertainty, but accommodating environment input weakens predictions of contact force or position trajectories, making the identification of subtask completion or faults difficult. This paper develops a task monitoring approach for complex assembly tasks that involve transitions between discrete environment dynamic modes. In semi-structured environments, these dynamic modes and their transitions are approximately known a priori, allowing task monitoring through estimation of the current mode and fault detection as a deviation from expected, desired dynamic mode transitions. This allows a more natural description of many interactive tasks, improving robustness to variations in force or position trajectories that impedance control seeks to address. The ability of impedance and admittance controlled robots to identify their environment is investigated, making consideration of joint and end-effector physical compliance. Prior information on environment dynamics and mode transitions allow recursive estimates of dynamic mode suitable for online use, under both full state knowledge and only force/position measurements. Experiments with an admittance controlled robot in a gear assembly task validate the approach.