715 research outputs found
Goal Set Inverse Optimal Control and Iterative Re-planning for Predicting Human Reaching Motions in Shared Workspaces
To enable safe and efficient human-robot collaboration in shared workspaces
it is important for the robot to predict how a human will move when performing
a task. While predicting human motion for tasks not known a priori is very
challenging, we argue that single-arm reaching motions for known tasks in
collaborative settings (which are especially relevant for manufacturing) are
indeed predictable. Two hypotheses underlie our approach for predicting such
motions: First, that the trajectory the human performs is optimal with respect
to an unknown cost function, and second, that human adaptation to their
partner's motion can be captured well through iterative re-planning with the
above cost function. The key to our approach is thus to learn a cost function
which "explains" the motion of the human. To do this, we gather example
trajectories from pairs of participants performing a collaborative assembly
task using motion capture. We then use Inverse Optimal Control to learn a cost
function from these trajectories. Finally, we predict reaching motions from the
human's current configuration to a task-space goal region by iteratively
re-planning a trajectory using the learned cost function. Our planning
algorithm is based on the trajectory optimizer STOMP, it plans for a 23 DoF
human kinematic model and accounts for the presence of a moving collaborator
and obstacles in the environment. Our results suggest that in most cases, our
method outperforms baseline methods when predicting motions. We also show that
our method outperforms baselines for predicting human motion when a human and a
robot share the workspace.Comment: 12 pages, Accepted for publication IEEE Transaction on Robotics 201
The Kaapvaal craton seismic anisotropy: Petrophysical analyses of upper mantle kimberlite nodules
International audienceA dense network of seismic stations has been deployed on the Kaapvaal craton (South Africa) to investigate the upper mantle seismic structures. In order to bring independent petrophysical constraints, we analyze a direct sampling of the cratonic upper mantle and determine the seismic properties of 48 mantle nodules brought up to the Earth's surface by kimberlite eruptions. Seismic properties of these nodules are calculated from the olivine and pyroxene crystal preferred orientations and the single crystal elastic constants. Despite variations in the nodules compositions, microstructures and crystallographic preferred orientations, seismic anisotropy is rather homogeneous throughout the craton. Mean S-wave anisotropy is weak (2.64 %), which is compatible with the small measured SKS wave splitting (mean delay time of 0.62 s)
Prediction of Human Full-Body Movements with Motion Optimization and Recurrent Neural Networks
Human movement prediction is difficult as humans naturally exhibit complex
behaviors that can change drastically from one environment to the next. In
order to alleviate this issue, we propose a prediction framework that decouples
short-term prediction, linked to internal body dynamics, and long-term
prediction, linked to the environment and task constraints. In this work we
investigate encoding short-term dynamics in a recurrent neural network, while
we account for environmental constraints, such as obstacle avoidance, using
gradient-based trajectory optimization. Experiments on real motion data
demonstrate that our framework improves the prediction with respect to
state-of-the-art motion prediction methods, as it accounts to beforehand unseen
environmental structures. Moreover we demonstrate on an example, how this
framework can be used to plan robot trajectories that are optimized to
coordinate with a human partner.Comment: International Conference on Robotics and Automation (ICRA) 202
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