TechTalks from event: Technical session talks from ICRA 2012

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Redundant robots

  • Motion Control of Redundant Robots under Joint Constraints: Saturation in the Null Space Authors: Flacco, Fabrizio; De Luca, Alessandro; Khatib, Oussama
    We present a novel efficient method addressing the inverse differential kinematics problem for redundant manipulators in the presence of different hard bounds (joint range, velocity, and acceleration limits) on the joint space motion. The proposed SNS (Saturation in the Null Space) iterative algorithm proceeds by successively discarding the use of joints that would exceed their motion bounds when using the minimum norm solution and reintroducing them at a saturated level by means of a projection in a suitable null space. The method is first defined at the velocity level and then moved to the acceleration level, so as to avoid joint velocity discontinuities due to the switching of saturated joints. Moreover, the algorithm includes an optimal task scaling in case the desired task trajectory is unfeasible under the given joint bounds. We also propose the integration of obstacle avoidance in the Cartesian space by properly modifying on line the joint bounds. Simulation and experimental results reported for the 7-dof lightweight KUKA LWR IV robot illustrate the properties and computational efficiency of the method.
  • Priority Oriented Adaptive Control of Kinematically Redundant Manipulators Authors: Sadeghian, Hamid; Keshmiri, Mehdi; Villani, Luigi; Siciliano, Bruno
    In this paper an adaptive multi-priority nonlinear control algorithm for a redundant manipulator system is developed based on the Lyapunov like approach. The method considers the parametric uncertainties in the system and defines a proper filtered error signal to achieve asymptotic stability and convergence in tracking error both for the main task and sub-tasks according to the allocated priority. The performance of the proposed method is studied by some numerical simulations.
  • Resolving the Redundancy of a Seven DOF Wearable Robotic System Based on Kinematic and Dynamic Constraint Authors: Kim, Hyunchul; Li, Zhi; Milutinovic, Dejan; Rosen, Jacob
    According to the seven degrees of freedom (DOFs) human arm model composed of the shoulder, elbow, and wrist joints, positioning of the wrist in space and orientating the palm is a task requiring only six DOFs. Due to this redundancy, a given task can be completed by multiple arm configurations, and there is no unique mathematical solution to the inverse kinematics. The redundancy of a wearable robotic system (exoskeleton) that interacts with the human is expected to be resolved in the same way as that of the human arm. A unique solution to the system's redundancy was introduced by combining both kinematic and dynamic criteria. The redundancy of the arm is expressed mathematically by defining the swivel angle: the rotation angle of the plane including the upper and lower arm around a virtual axis connecting the shoulder and wrist joints which are fixed in space. Two different swivel angles were generated based on kinematic and dynamic constraints. The kinematic criterion is to maximize the projection of the longest principle axis of the manipulability ellipsoid for the human arm on the vector connecting the wrist and the virtual target on the head region. The dynamic criterion is to minimize the mechanical work done in the joint space for each two consecutive points along the task space trajectory. These two criteria were then combined linearly with different weight factors for estimating the swivel angle. Post processing of experimental data collected with a motion capturing
  • Dual-Arm Redundancy Resolution Based on Null-Space Dynamically-Scaled Posture Optimization Authors: Zanchettin, Andrea Maria; Rocco, Paolo
    Dual-arm robotic systems have been intensively studied in the literature. However, in industrial robotics, the resolution of the kinematic redundancy allowed by the coordinated manipulation task is still an open issue. In fact, typical proprietary industrial robotic controllers do not allow the programmer to modify the inverse kinematics algorithm, and thus to solve redundancy following any specified criterion. In this paper a method to enforce an arbitrary redundancy resolution criterion on top of an industrial robot controller is discussed and applied to the execution of a coordinated manipulation task. The extra degrees of freedom are used to maximize the dynamic manipulability measure in order to reduce the needed torque. Simulations and experimental results achieved on an ABB IRC 5 industrial robot controller are presented.
  • Optimal Decentralized Gait Transitions for Snake Robots Authors: Droge, Greg; Egerstedt, Magnus
    Snake robots are controlled by implementing gaits inspired from their biological counterparts. However, transitioning between these gaits often produces undesired oscillations which cause net movements that are difficult to predict. In this paper we present a framework for implementing gaits which will allow for smooth transitions. We also present a method to determine the optimal time for each module of the snake to switch between gaits in a decentralized fashion. This will allow for each module to participate in minimizing a cost by communicating with a set of modules in a local neighborhood. Both of these developments will help to maintain desired properties of the gaits during transition.