17,053 research outputs found
Safety Barrier Certificates for Heterogeneous Multi-Robot Systems
This paper presents a formal framework for collision avoidance in multi-robot
systems, wherein an existing controller is modified in a minimally invasive
fashion to ensure safety. We build this framework through the use of control
barrier functions (CBFs) which guarantee forward invariance of a safe set;
these yield safety barrier certificates in the context of heterogeneous robot
dynamics subject to acceleration bounds. Moreover, safety barrier certificates
are extended to a distributed control framework, wherein neighboring agent
dynamics are unknown, through local parameter identification. The end result is
an optimization-based controller that formally guarantees collision free
behavior in heterogeneous multi-agent systems by minimally modifying the
desired controller via safety barrier constraints. This formal result is
verified in simulation on a multi-robot system consisting of both cumbersome
and agile robots, is demonstrated experimentally on a system with a Magellan
Pro robot and three Khepera III robots.Comment: 8 pages version of 2016ACC conference paper, experimental results
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Safe Learning of Quadrotor Dynamics Using Barrier Certificates
To effectively control complex dynamical systems, accurate nonlinear models
are typically needed. However, these models are not always known. In this
paper, we present a data-driven approach based on Gaussian processes that
learns models of quadrotors operating in partially unknown environments. What
makes this challenging is that if the learning process is not carefully
controlled, the system will go unstable, i.e., the quadcopter will crash. To
this end, barrier certificates are employed for safe learning. The barrier
certificates establish a non-conservative forward invariant safe region, in
which high probability safety guarantees are provided based on the statistics
of the Gaussian Process. A learning controller is designed to efficiently
explore those uncertain states and expand the barrier certified safe region
based on an adaptive sampling scheme. In addition, a recursive Gaussian Process
prediction method is developed to learn the complex quadrotor dynamics in
real-time. Simulation results are provided to demonstrate the effectiveness of
the proposed approach.Comment: Submitted to ICRA 2018, 8 page
Multi-objective Compositions for Collision-Free Connectivity Maintenance in Teams of Mobile Robots
Compositional barrier functions are proposed in this paper to systematically
compose multiple objectives for teams of mobile robots. The objectives are
first encoded as barrier functions, and then composed using AND and OR logical
operators. The advantage of this approach is that compositional barrier
functions can provably guarantee the simultaneous satisfaction of all composed
objectives. The compositional barrier functions are applied to the example of
ensuring collision avoidance and static/dynamical graph connectivity of teams
of mobile robots. The resulting composite safety and connectivity barrier
certificates are verified experimentally on a team of four mobile robots.Comment: To appear in 55th IEEE Conference on Decision and Control, December
12-14, 2016, Las Vegas, NV, US
Control Barrier Function Based Quadratic Programs for Safety Critical Systems
Safety critical systems involve the tight coupling between potentially
conflicting control objectives and safety constraints. As a means of creating a
formal framework for controlling systems of this form, and with a view toward
automotive applications, this paper develops a methodology that allows safety
conditions -- expressed as control barrier functions -- to be unified with
performance objectives -- expressed as control Lyapunov functions -- in the
context of real-time optimization-based controllers. Safety conditions are
specified in terms of forward invariance of a set, and are verified via two
novel generalizations of barrier functions; in each case, the existence of a
barrier function satisfying Lyapunov-like conditions implies forward invariance
of the set, and the relationship between these two classes of barrier functions
is characterized. In addition, each of these formulations yields a notion of
control barrier function (CBF), providing inequality constraints in the control
input that, when satisfied, again imply forward invariance of the set. Through
these constructions, CBFs can naturally be unified with control Lyapunov
functions (CLFs) in the context of a quadratic program (QP); this allows for
the achievement of control objectives (represented by CLFs) subject to
conditions on the admissible states of the system (represented by CBFs). The
mediation of safety and performance through a QP is demonstrated on adaptive
cruise control and lane keeping, two automotive control problems that present
both safety and performance considerations coupled with actuator bounds
NON-TARIFF TRADE BARRIERS IN AGRICULTURE
As trade agreements lower tariff rates throughout the world, other barriers to trade emerge. These non-tariff barriers can be just as troublesome for exporting companies. Non-tariff barriers include technical measures, customs rules and procedures, transport regulations or costs, lack of knowledge of regional markets, and import policies. The objective of this study is to identify non-tariff barriers faced by U.S., and more specifically North Dakota, exporting businesses, especially those involved in agriculture, and to identify difficulties involved in exporting products. A survey of North Dakota businesses is conducted to identify important trade barriers. Phytosanitary regulations and railroad problems are two frustrating issues that create barriers to export for North Dakota agribusinesses. Other non-tariff barriers mentioned in the survey include labeling, paperwork, registration, and language differences. When entering new markets, the biggest problems exporters have are making contacts, resolving credit issues, and competing with low-cost competitors from foreign countries.non-tariff barriers, trade, survey, North Dakota exporters, International Relations/Trade,
Safe certificate-based maneuvers for teams of quadrotors using differential flatness
Safety Barrier Certificates that ensure collision-free maneuvers for teams of differential flatness-based quadrotors are presented in this paper. Synthesized with control barrier functions, the certificates are used to modify the nominal trajectory in a minimally invasive way to avoid collisions. The proposed collision avoidance strategy complements existing flight control and planning algorithms by providing trajectory modifications with provable safety guarantees. The effectiveness of this strategy is supported both by the theoretical results and experimental validation on a team of five quadrotors
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