1,007 research outputs found
Deep Haptic Model Predictive Control for Robot-Assisted Dressing
Robot-assisted dressing offers an opportunity to benefit the lives of many
people with disabilities, such as some older adults. However, robots currently
lack common sense about the physical implications of their actions on people.
The physical implications of dressing are complicated by non-rigid garments,
which can result in a robot indirectly applying high forces to a person's body.
We present a deep recurrent model that, when given a proposed action by the
robot, predicts the forces a garment will apply to a person's body. We also
show that a robot can provide better dressing assistance by using this model
with model predictive control. The predictions made by our model only use
haptic and kinematic observations from the robot's end effector, which are
readily attainable. Collecting training data from real world physical
human-robot interaction can be time consuming, costly, and put people at risk.
Instead, we train our predictive model using data collected in an entirely
self-supervised fashion from a physics-based simulation. We evaluated our
approach with a PR2 robot that attempted to pull a hospital gown onto the arms
of 10 human participants. With a 0.2s prediction horizon, our controller
succeeded at high rates and lowered applied force while navigating the garment
around a persons fist and elbow without getting caught. Shorter prediction
horizons resulted in significantly reduced performance with the sleeve catching
on the participants' fists and elbows, demonstrating the value of our model's
predictions. These behaviors of mitigating catches emerged from our deep
predictive model and the controller objective function, which primarily
penalizes high forces.Comment: 8 pages, 12 figures, 1 table, 2018 IEEE International Conference on
Robotics and Automation (ICRA
Multidimensional Capacitive Sensing for Robot-Assisted Dressing and Bathing
Robotic assistance presents an opportunity to benefit the lives of many
people with physical disabilities, yet accurately sensing the human body and
tracking human motion remain difficult for robots. We present a
multidimensional capacitive sensing technique that estimates the local pose of
a human limb in real time. A key benefit of this sensing method is that it can
sense the limb through opaque materials, including fabrics and wet cloth. Our
method uses a multielectrode capacitive sensor mounted to a robot's end
effector. A neural network model estimates the position of the closest point on
a person's limb and the orientation of the limb's central axis relative to the
sensor's frame of reference. These pose estimates enable the robot to move its
end effector with respect to the limb using feedback control. We demonstrate
that a PR2 robot can use this approach with a custom six electrode capacitive
sensor to assist with two activities of daily living-dressing and bathing. The
robot pulled the sleeve of a hospital gown onto able-bodied participants' right
arms, while tracking human motion. When assisting with bathing, the robot moved
a soft wet washcloth to follow the contours of able-bodied participants' limbs,
cleaning their surfaces. Overall, we found that multidimensional capacitive
sensing presents a promising approach for robots to sense and track the human
body during assistive tasks that require physical human-robot interaction.Comment: 8 pages, 16 figures, International Conference on Rehabilitation
Robotics 201
Defect turbulence in inclined layer convection
We report experimental results on the defect turbulent state of undulation
chaos in inclined layer convection of a fluid withPrandtl number .
By measuring defect density and undulation wavenumber, we find that the onset
of undulation chaos coincides with the theoretically predicted onset for
stable, stationary undulations. At stronger driving, we observe a competition
between ordered undulations and undulation chaos, suggesting bistability
between a fixed-point attractor and spatiotemporal chaos. In the defect
turbulent regime, we measured the defect creation, annihilation, entering,
leaving, and rates. We show that entering and leaving rates through boundaries
must be considered in order to describe the observed statistics. We derive a
universal probability distribution function which agrees with the experimental
findings.Comment: 4 pages, 5 figure
Ultrafast IR spectroscopy of photo-induced electron transfer in self-assembled donor-acceptor coordination cages.
Photo-induced processes in self-assembled coordination cages were studied by femtosecond infrared pump-probe spectroscopy. Densely packed, interpenetrated double cages were constructed from eight bis-monodentate redoxactive ligands bound to four Pd(ii) nodes. Two types of ligands consisting of electron rich phenothiazine (PTZ) or electron deficient anthraquinone (ANQ) chromophores were used to assemble either homo-octameric or mixed-ligand cages. Upon photoexcitation the homo-octameric acceptor cage undergoes intersystem crossing to a long-lived triplet state, similar to the free acceptor ligand. Excitation of the free donor ligand leads to a fluorescent state with intramolecular charge transfer character. This fluorescence is completely quenched in the homo-octameric donor double cage due to a ligand-to-metal charge transfer followed by back electron transfer on a ps timescale. Only for the mixed-ligand cage irradiation produces a charge separated state with an oxidized PTZ radical cation and a reduced ANQ radical anion as proven by their vibrational fingerprints in the transient IR spectra. In dichloromethane the lifetime of this charge separated state extends from tens of ps to >1.5 ns which is attributed to the broad distribution of mixed-ligand cages with different stoichiometry and/or stereo configurations
Fractal Stability Border in Plane Couette Flow
We study the dynamics of localised perturbations in plane Couette flow with
periodic lateral boundary conditions. For small Reynolds number and small
amplitude of the initial state the perturbation decays on a viscous time scale
. For Reynolds number larger than about 200, chaotic transients
appear with life times longer than the viscous one. Depending on the type of
the perturbation isolated initial conditions with infinite life time appear for
Reynolds numbers larger than about 270--320. In this third regime, the life
time as a function of Reynolds number and amplitude is fractal. These results
suggest that in the transition region the turbulent dynamics is characterised
by a chaotic repeller rather than an attractor.Comment: 4 pages, Latex, 4 eps-figures, submitted to Phys. Rev. Le
Localized transverse bursts in inclined layer convection
We investigate a novel bursting state in inclined layer thermal convection in
which convection rolls exhibit intermittent, localized, transverse bursts. With
increasing temperature difference, the bursts increase in duration and number
while exhibiting a characteristic wavenumber, magnitude, and size. We propose a
mechanism which describes the duration of the observed bursting intervals and
compare our results to bursting processes in other systems.Comment: 4 pages, 8 figure
Asymmetric Squares as Standing Waves in Rayleigh-Benard Convection
Possibility of asymmetric square convection is investigated numerically using
a few mode Lorenz-like model for thermal convection in Boussinesq fluids
confined between two stress free and conducting flat boundaries. For relatively
large value of Rayleigh number, the stationary rolls become unstable and
asymmetric squares appear as standing waves at the onset of secondary
instability. Asymmetric squares, two dimensional rolls and again asymmetric
squares with their corners shifted by half a wavelength form a stable limit
cycle.Comment: 8 pages, 7 figure
Wavy stripes and squares in zero P number convection
A simple model to explain numerically observed behaviour of chaotically
varying stripes and square patterns in zero Prandtl number convection in
Boussinesq fluid is presented. The nonlinear interaction of mutually
perpendicular sets of wavy rolls, via higher mode, may lead to a competition
between the two sets of wavy rolls. The appearance of square patterns is due to
the secondary forward Hopf bifurcation of a set of wavy rolls.Comment: 8 pages and 3 figures, late
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