5,823 research outputs found
NEPTUNE: Non-Entangling Planning for Multiple Tethered Unmanned Vehicles
Despite recent progress on trajectory planning of multiple robots and path
planning of a single tethered robot, planning of multiple tethered robots to
reach their individual targets without entanglements remains a challenging
problem. In this paper, we present a complete approach to address this problem.
Firstly, we propose a multi-robot tether-aware representation of homotopy,
using which we can efficiently evaluate the feasibility and safety of a
potential path in terms of (1) the cable length required to reach a target
following the path, and (2) the risk of entanglements with the cables of other
robots. Then, the proposed representation is applied in a decentralized and
online planning framework that includes a graph-based kinodynamic trajectory
finder and an optimization-based trajectory refinement, to generate
entanglement-free, collision-free and dynamically feasible trajectories. The
efficiency of the proposed homotopy representation is compared against existing
single and multiple tethered robot planning approaches. Simulations with up to
8 UAVs show the effectiveness of the approach in entanglement prevention and
its real-time capabilities. Flight experiments using 3 tethered UAVs verify the
practicality of the presented approach.Comment: Accepted for publication in IEEE Transaction on Robotic
Axel: A Minimalist Tethered Rover for Exploration of Extreme Planetary Terrains
Recent scientific findings suggest that some of the most interesting sites for future exploration of planetary surfaces lie in terrains that are currently inaccessible to conventional robotic rovers. To provide robust and flexible access to these terrains, we have been developing Axel, the robotic rover. Axel is a lightweight two-wheeled vehicle that can access steep terrains and negotiate relatively large obstacles because of its actively managed tether and novel wheel design. This article reviews the Axel system and focuses on those system components that affect Axel's steep terrain mobility. Experimental demonstrations of Axel on sloped and rocky terrains are presented
Entanglement Definitions for Tethered Robots: Exploration and Analysis
In this article we consider the problem of tether entanglement for tethered
robots. In many applications, such as maintenance of underwater structures,
aerial inspection, and underground exploration, tethered robots are often used
in place of standalone (i.e., untethered) ones. However, the presence of a
tether also introduces the risk for it to get entangled with obstacles present
in the environment or with itself. To avoid these situations, a
non-entanglement constraint can be considered in the motion planning problem
for tethered robots. This constraint can be expressed either as a set of
specific tether configurations that must be avoided, or as a quantitative
measure of a `level of entanglement' that can be minimized. However, the
literature lacks a generally accepted definition of entanglement, with existing
definitions being limited and partial. Namely, the existing entanglement
definitions either require a taut tether to come into contact with an obstacle
or with another tether, or they require for the tether to do a full loop around
an obstacle. In practice, this means that the existing definitions do not
effectively cover all instances of tether entanglement. Our goal in this
article is to bridge this gap and provide new definitions of entanglement,
which, together with the existing ones, can be effectively used to qualify the
entanglement state of a tethered robot in diverse situations. The new
definitions find application mainly in motion planning for tethered robot
systems, where they can be used to obtain more safe and robust
entanglement-free trajectories. The present article focuses exclusively on the
presentation and analysis of the entanglement definitions. The application of
the definitions to the motion planning problem is left for future work.Comment: 30 pages, 19 figure
UAV/UGV Autonomous Cooperation: UAV Assists UGV to Climb a Cliff by Attaching a Tether
This paper proposes a novel cooperative system for an Unmanned Aerial Vehicle
(UAV) and an Unmanned Ground Vehicle (UGV) which utilizes the UAV not only as a
flying sensor but also as a tether attachment device. Two robots are connected
with a tether, allowing the UAV to anchor the tether to a structure located at
the top of a steep terrain, impossible to reach for UGVs. Thus, enhancing the
poor traversability of the UGV by not only providing a wider range of scanning
and mapping from the air, but also by allowing the UGV to climb steep terrains
with the winding of the tether. In addition, we present an autonomous framework
for the collaborative navigation and tether attachment in an unknown
environment. The UAV employs visual inertial navigation with 3D voxel mapping
and obstacle avoidance planning. The UGV makes use of the voxel map and
generates an elevation map to execute path planning based on a traversability
analysis. Furthermore, we compared the pros and cons of possible methods for
the tether anchoring from multiple points of view. To increase the probability
of successful anchoring, we evaluated the anchoring strategy with an
experiment. Finally, the feasibility and capability of our proposed system were
demonstrated by an autonomous mission experiment in the field with an obstacle
and a cliff.Comment: 7 pages, 8 figures, accepted to 2019 International Conference on
Robotics & Automation. Video: https://youtu.be/UzTT8Ckjz1
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