| 1. |
- Doeser, Ludvig, et al.
(författare)
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Invariant Sets for Integrators and Quadrotor Obstacle Avoidance
- 2020
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Ingår i: Proceedings of the American Control Conference, ACC 2020. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 3814-3821
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Konferensbidrag (refereegranskat)abstract
- Ensuring safety through set invariance has proven a useful method in a variety of applications in robotics and control. However, finding analytical expressions for maximal invariant sets, so as to maximize the operational freedom of the system without compromising safety, is notoriously difficult for high-dimensional systems with input constraints. Here we present a generic method for characterizing invariant sets of nth-order integrator systems, based on analyzing roots of univariate polynomials. Additionally, we obtain analytical expressions for the orders n <= 4. Using differential flatness we subsequently leverage the results for the n = 4 case to the problem of obstacle avoidance for quadrotor UAVs. The resulting controller has a light computational footprint that showcases the power of finding analytical expressions for control-invariant sets.
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| 2. |
- Bulancea Lindvall, Oscar, et al.
(författare)
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Nonuniform abstractions, refinement and controller synthesis with novel BDD encodings
- 2018
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Ingår i: IFAC PAPERSONLINE. - : Elsevier. - 2405-8963. ; , s. 19-24
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Konferensbidrag (refereegranskat)abstract
- This paper presents a control synthesis algorithm for dynamical systems to satisfy specifications given in a fragment of linear temporal logic. It is based on an abstraction-refinement scheme with nonuniform partitions of the state space. A novel encoding of the resulting transition system is proposed that uses binary decision diagrams for efficiency. We discuss several factors affecting scalability and present some benchmark results demonstrating the effectiveness of the new encodings. These ideas are also being implemented on a publicly available prototype tool, ARCS, that we briefly introduce in the paper.
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| 3. |
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| 4. |
- Nilsson, Petter, et al.
(författare)
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Invariant sets of defocused switched systems
- 2013
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Ingår i: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC). - : IEEE conference proceedings. - 9781467357142 ; , s. 5987-5992
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Konferensbidrag (refereegranskat)abstract
- We consider affine switched systems as perturbations of linear ones, the equilibria playing the role of perturbation parameters. We study the stability properties of an affine switched system under arbitrary switching, assuming that the corresponding linear system is uniformly exponentially stable. It turns out that the affine system admits a minimal invariant set , whose properties we investigate. In the two dimensional bi-switched case when both subsystems have nonreal eigenvalues we are able to characterize completely and to prove that all trajectories of the system converge to . We also explore the behavior of minimal-time trajectories in by constructing optimal syntheses.
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| 5. |
- Nilsson, Petter, et al.
(författare)
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Temporal logic control of switched affine systems with an application in fuel balancing
- 2012
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Ingår i: 2012 American Control Conference (ACC). - : IEEE Computer Society. - 9781457710957 ; , s. 5302-5309
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Konferensbidrag (refereegranskat)abstract
- We consider the problem of synthesizing hierarchical controllers for discrete-time switched affine systems subject to exogenous disturbances that guarantee that the trajectories of the system satisfy a high-level specification expressed as a linear temporal logic formula. Our method builds upon recent results on temporal logic planning and embedded controller synthesis. First, the control problem is lifted to a discrete level by constructing a finite transition system that abstracts the behavior of the underlying switched system. At the discrete level, we recast the problem as a two player temporal logic game by treating the environment driven switches as adversaries. The solution strategy for the game (i.e. the discrete plan) is then implemented at the continuous level by solving finite-horizon optimal control problems that establish reachability between discrete states and that compensate the effects of continuous disturbances. We also extend the earlier work by making efficient use of propositions in the temporal logic formula to drive the abstraction procedure and to facilitate the computation of continuous input at implementation time. An aircraft fuel system example is formulated; and solved using the proposed method. This sample problem demonstrates the applicability of the abstraction procedure and correct-by-construction controllers to regulate the fuel levels in multiple tanks during interesting operations like aerial refueling.
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| 6. |
- Persson, Bertil, et al.
(författare)
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Betonguttorkning med byggcement
- 2000
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Ingår i: Bygg & teknik. - 0281-658X. ; , s. 30-32
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- I denna artikel redogörs för uttorkning hos betong med Byggcement jämfört med andra cementsorter: Slite Std-cement samt anläggningscement. Inverkan av silikastoft på uttorkningen hos Slite Std-cement redovisas. För ändamålet studerades 14 betonger upp till ett halvt år. Inverkan av självuttorkning, lufthärdning och vattenlagring fanns med i programmet. Resultaten visar att uttorkningen i huvudsak följer vattencementtalet, dvs eftersom Byggcement innehåller cirka åtta procent mindre rent cement än vad Slite Std-cement gör, får man räkna med något sämre självuttorkning vid användning av Byggcement jämfört med självuttorkningen i betong med Slite Std-cement.
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