The Experts below are selected from a list of 6867 Experts worldwide ranked by ideXlab platform

M Jagersand - One of the best experts on this subject based on the ideXlab platform.

  • uncalibrated visual servoing using a biased newton method for on Line Singularity detection and avoidance
    Intelligent Robots and Systems, 2005
    Co-Authors: Masoud Shahamiri, M Jagersand
    Abstract:

    While in calibrated settings trajectories can be planned so to avoid singular or poorly observable configurations, in uncalibrated visual servoing in general a priori information about singularities (visual or robotic) may be unavailable. Instead we propose a method where trajectories are corrected onLine to avoid singular and near singular regions. Mathematically this is achieved using a so called nullspace-biased Newton step in a visual servoing with a Broyden type Jacobian estimation. The bias is applied so to first hand use (any) robot redundancy and thus not compromise the visually specified aspects of the trajectory. The closeness to a singular region is measured onLine from the estimated visual motor Jacobian. We also illustrate how to apply the bias method for simple visual obstacle avoidance. To show the practical applicability of our method we have applied it to Barrett WAM and PUMA560 manipulators and tested both numerous real trajectories, as well as run exhaustive simulations around critical configurations using a simulation model to confirm empirically that both safe and efficient trajectories are chosen around singular regions.

  • IROS - Uncalibrated visual servoing using a biased Newton method for on-Line Singularity detection and avoidance
    2005 IEEE RSJ International Conference on Intelligent Robots and Systems, 2005
    Co-Authors: Masoud Shahamiri, M Jagersand
    Abstract:

    While in calibrated settings trajectories can be planned so to avoid singular or poorly observable configurations, in uncalibrated visual servoing in general a priori information about singularities (visual or robotic) may be unavailable. Instead we propose a method where trajectories are corrected onLine to avoid singular and near singular regions. Mathematically this is achieved using a so called nullspace-biased Newton step in a visual servoing with a Broyden type Jacobian estimation. The bias is applied so to first hand use (any) robot redundancy and thus not compromise the visually specified aspects of the trajectory. The closeness to a singular region is measured onLine from the estimated visual motor Jacobian. We also illustrate how to apply the bias method for simple visual obstacle avoidance. To show the practical applicability of our method we have applied it to Barrett WAM and PUMA560 manipulators and tested both numerous real trajectories, as well as run exhaustive simulations around critical configurations using a simulation model to confirm empirically that both safe and efficient trajectories are chosen around singular regions.

Reaz A Chaudhuri - One of the best experts on this subject based on the ideXlab platform.

  • interlaminar shear stresses around an internal part through hole in a laminated composite plate
    Composite Structures, 2010
    Co-Authors: Reaz A Chaudhuri, Paul Seide
    Abstract:

    Abstract The equilibrium/compatibility method, which is a semi-analytical post-processing method, is employed for computation of hitherto unavailable through-thickness variation of interlaminar (transverse) shear stresses in the vicinity of the bi-layer interface circumferential re-entrant corner Line of an internal part-through circular cylindrical hole weakening an edge-loaded laminated composite plate. A C o -type triangular composite plate element, based on the assumptions of transverse inextensibility and layer-wise constant shear-angle theory (LCST), is utilized to first compute the in-plane stresses and layer-wise through-thickness average interlaminar shear stresses, which serve as the starting point for computation of through-thickness distribution of interlaminar shear stresses in the vicinity of the bi-layer interface circumferential re-entrant corner Line of the part-through hole. The same stresses computed by the conventional equilibrium method (EM) are, in contrast, in serious error in the presence of the bi-layer interface circumferential re-entrant corner Line Singularity arising out of the internal part-through hole, and are found to violate the interfacial compatibility condition. The computed interlaminar shear stress can vary from negative to positive through the thickness of a cross-ply plate in the neighborhood of this kind of stress Singularity.

  • transverse shear stress distribution through thickness near an internal part through elliptical hole in a stretched plate
    Composite Structures, 2010
    Co-Authors: Reaz A Chaudhuri
    Abstract:

    Abstract A semi-analytical post-processing method, termed the equilibrium/compatibility method here, is used for computation of hitherto unavailable through-thickness variation of transverse shear stresses in the vicinity of the circumferential re-entrant corner Line of an internal part-through elliptical cylindrical hole weakening an edge-loaded rectangular plate. A C0-type triangular “composite” plate element, based on the assumptions of transverse inextensibility and piece (“layer”)-wise constant shear-angle theory (LCST), is employed to first compute the inplane stresses and “layer”-wise through-thickness average transverse shear stresses. These serve as the starting point for computation of through-thickness distribution of transverse shear stresses in the vicinity of the circumferential re-entrant corner Line of the internal part-through elliptical hole. As in the case of its circular counterpart, the transverse shear stresses computed by the conventional equilibrium method (EM) are, in contrast, in serious error in the presence of the circumferential re-entrant corner Line Singularity arising out of the internal part-through elliptical hole, and are found to violate the compatibility condition. The computed maximum transverse shear stress can be high enough to cause catastrophic transverse shear fracture in the shape of a cone, of elliptical cross-section starting from the circumferential re-entrant corner Line of the internal part-through hole. The results computed by the present analysis are in Line with a three-dimensional asymptotic analysis.

Masoud Shahamiri - One of the best experts on this subject based on the ideXlab platform.

  • uncalibrated visual servoing using a biased newton method for on Line Singularity detection and avoidance
    Intelligent Robots and Systems, 2005
    Co-Authors: Masoud Shahamiri, M Jagersand
    Abstract:

    While in calibrated settings trajectories can be planned so to avoid singular or poorly observable configurations, in uncalibrated visual servoing in general a priori information about singularities (visual or robotic) may be unavailable. Instead we propose a method where trajectories are corrected onLine to avoid singular and near singular regions. Mathematically this is achieved using a so called nullspace-biased Newton step in a visual servoing with a Broyden type Jacobian estimation. The bias is applied so to first hand use (any) robot redundancy and thus not compromise the visually specified aspects of the trajectory. The closeness to a singular region is measured onLine from the estimated visual motor Jacobian. We also illustrate how to apply the bias method for simple visual obstacle avoidance. To show the practical applicability of our method we have applied it to Barrett WAM and PUMA560 manipulators and tested both numerous real trajectories, as well as run exhaustive simulations around critical configurations using a simulation model to confirm empirically that both safe and efficient trajectories are chosen around singular regions.

  • IROS - Uncalibrated visual servoing using a biased Newton method for on-Line Singularity detection and avoidance
    2005 IEEE RSJ International Conference on Intelligent Robots and Systems, 2005
    Co-Authors: Masoud Shahamiri, M Jagersand
    Abstract:

    While in calibrated settings trajectories can be planned so to avoid singular or poorly observable configurations, in uncalibrated visual servoing in general a priori information about singularities (visual or robotic) may be unavailable. Instead we propose a method where trajectories are corrected onLine to avoid singular and near singular regions. Mathematically this is achieved using a so called nullspace-biased Newton step in a visual servoing with a Broyden type Jacobian estimation. The bias is applied so to first hand use (any) robot redundancy and thus not compromise the visually specified aspects of the trajectory. The closeness to a singular region is measured onLine from the estimated visual motor Jacobian. We also illustrate how to apply the bias method for simple visual obstacle avoidance. To show the practical applicability of our method we have applied it to Barrett WAM and PUMA560 manipulators and tested both numerous real trajectories, as well as run exhaustive simulations around critical configurations using a simulation model to confirm empirically that both safe and efficient trajectories are chosen around singular regions.

Arezki Boudaoud - One of the best experts on this subject based on the ideXlab platform.

  • Spreading of non-Newtonian fluids on hydrophilic surfaces
    Journal of Fluid Mechanics, 2004
    Co-Authors: Salima Rafaï, Daniel Bonn, Arezki Boudaoud
    Abstract:

    The spreading of Newtonian fluids on smooth solid substrates is well understood; the speed of the contact Line is given by a competition between capillary driving forces and viscous dissipation, yielding Tanner's law R ~ t(1/10) . Here we study the spreading of non-Newtonian liquids, focusing on the two most common non-Newtonian flow properties, a shear-rate dependence of the viscosity and the existence of normal stresses. For the former, the spreading behaviour is found not to deviate strongly from Tanner's law. This is quite surprising given that, within the lubrication approximation, it can be shown that the contact Line Singularity disappears due to the shear-dependent viscosity. The experiments are compared with the predictions of the lubrication theory of power-law fluids. If normal stresses are present, again only small deviations from Tanner's law are found in the experiment. This can be understood by comparing viscous and normal stress contributions to the spreading; it turns out that only logarithmic corrections to Tanner's law survive, which are nonetheless visible in the experiment.

Jerry B. Griffiths - One of the best experts on this subject based on the ideXlab platform.

  • Exact solutions for gravitational waves with cylindrical, spherical and toroidal wavefronts
    Classical and Quantum Gravity, 1996
    Co-Authors: G A Alekseev, Jerry B. Griffiths
    Abstract:

    Three families of exact vacuum solutions of Einstein's equations are presented which, when considered locally or in some finite spacetime region, describe gravitational waves with distinct nonplane wavefronts propagating into a Minkowski background. The wavefronts may be cylindrical, spherical or toroidal and may include impulsive or shock components or be characterized by arbitrarily weak discontinuities. Considered globally, without matching to any material sources but extending maximally as vacuum solutions, particular curvature singularities arise in the outer regions as the sources of these waves. Specifically, we find waves with a half-cylindrical wavefront driven by two singular parallel half-planes moving apart at the speed of light, waves with a complete exact spherical wavefront created by an expanding Line Singularity joining opposite poles of the wavefront, and waves with toroidal fronts produced by two parallel coaxial disc-like singularities and an additional Line Singularity joining their centres. In each case, the character of the gravitational wave on the wavefront is analysed and the collision and subsequent interaction of these waves is considered.

  • Gravitational waves with spherical wavefronts
    Classical and Quantum Gravity, 1996
    Co-Authors: G A Alekseev, Jerry B. Griffiths
    Abstract:

    We present a large family of exact vacuum solutions of Einstein's equations which describe gravitational waves with a distinct spherical wavefront and which propagate into a Minkowski background. The gravitational waves may have either shock wavefronts or fronts on which the metric and the Weyl tensor components possess n continuous derivatives for any . The wave region behind the spherical wavefront contains a Line Singularity.