| 1. |
- Feng, Lei, et al.
(författare)
-
On the Computation of Natural Observers in Discrete-Event Systems
- 2010
-
Ingår i: Discrete event dynamic systems. - : Springer Science and Business Media LLC. - 0924-6703 .- 1573-7594. ; 20:1, s. 63-102
-
Tidskriftsartikel (refereegranskat)abstract
- Natural projections with the observer property have proved effective in reducing the computational complexity of nonblocking supervisory control design, and the state sizes of the resulting controllers. In this paper we present an algorithm to verify this property, or if necessary to achieve it. A natural projection is a special type of general causal reporter map; for the latter an algorithm is already known for verification and modification. This algorithm could be used to verify the observer property of a natural projection, but if the natural projection is not an observer the algorithm is not applicable to modify it to an observer. Also, while a general reporter map always admits a unique smallest refinement with the observer property, a natural projection does not. Indeed there may exist several minimal extensions to the original observable event set of a natural projection. We show that the problem of finding a minimal extension is NP-hard, but propose a polynomial-time algorithm that always finds an acceptable extension. While not guaranteed to be minimal, it is in practice often reasonably small.
|
|
| 2. |
- Flordal, Hugo, 1977, et al.
(författare)
-
Compositional Synthesis of Maximally Permissive Supervisors Using Supervision Equivalence
- 2007
-
Ingår i: Discrete Event Dynamic Systems: Theory and Applications. - : Springer Science and Business Media LLC. - 0924-6703 .- 1573-7594. ; 17:4, s. 475-504
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a general framework for efficient synthesis of supervisors for discrete event systems. The approach is based on compositional minimisation, using concepts of process equivalence. In this context, a large number of ways are suggested how a finite-state automaton can be simplified such that the results of supervisor synthesis are preserved. The proposed approach yields a compact representation of a least restrictive supervisor that ensures controllability and nonblocking. The method is demonstrated on a simple manufacturing example to significantly reduce the number of states constructed for supervisor synthesis. © 2007 Springer Science+Business Media, LLC.
|
|
| 3. |
- Goorden, Martijn, et al.
(författare)
-
Compositional coordinator synthesis of extended finite automata
- 2021
-
Ingår i: Discrete Event Dynamic Systems: Theory and Applications. - : Springer Science and Business Media LLC. - 0924-6703 .- 1573-7594. ; 31:3, s. 317-348
-
Tidskriftsartikel (refereegranskat)abstract
- To avoid the state-space explosion problem, a set of supervisors may be synthesized using divide and conquer strategies, like modular or multilevel synthesis. Unfortunately, these supervisors may be conflicting, meaning that even though they are individually non-blocking, they are together blocking. Abstraction-based compositional nonblocking verification of extended finite automata provides means to verify whether a set of models is nonblocking. In case of a blocking system, a coordinator can be synthesized to resolve the blocking. This paper presents a framework for compositional coordinator synthesis for discrete-event systems modeled as extended finite automata. The framework allows for synthesis of a coordinator on the abstracted system in case compositional verification identifies the system to be blocking. As the abstracted system may use notions not present in the original model, like renamed events, the synthesized coordinator is refined such that it will be nonblocking, controllable, and maximally permissive for the original system. For each abstraction, it is shown how this refinement can be performed. It turns out that for the presented set of abstractions the coordinator refinement is straightforward.
|
|
| 4. |
- Hagebring, Fredrik, 1985, et al.
(författare)
-
Time-optimal control of large-scale systems of systems using compositional optimization
- 2019
-
Ingår i: Discrete Event Dynamic Systems: Theory and Applications. - : Springer Science and Business Media LLC. - 0924-6703 .- 1573-7594. ; 29:3, s. 411-443
-
Tidskriftsartikel (refereegranskat)abstract
- Optimization of industrial processes such as manufacturing cells can have great impact on their performance. Finding optimal solutions to these large-scale systems is, however, a complex problem. They typically include multiple subsystems, and the search space generally grows exponentially with each subsystem. In previous work we proposed Compositional Optimization as a method to solve these type of problems. This integrates optimization with techniques from compositional supervisory control, dividing the optimization into separate sub-problems. The main purpose is to mitigate the state explosion problem, but a bonus is that the individual sub-problems can be solved using parallel computation, making the method even more scalable. This paper further improves on compositional optimization with a novel synchronization method, called partial time-weighted synchronization (PTWS), that is specifically designed for time-optimal control of asynchronous systems. The benefit is its ability to combine the behaviour of asynchronous subsystems without introducing additional states or transitions. The method also reduces the search space further by integrating an optimization heuristic that removes many non-optimal or redundant solutions already during synchronization. Results in this paper show that compositional optimization efficiently generates global optimal solutions to large-scale realistic optimization problems, too big to solve when based on traditional monolithic models. It is also shown that the introduction of PTWS drastically decreases the total search space of the optimization compared to previous work.
|
|
| 5. |
- Hashimoto, K., et al.
(författare)
-
Resource-aware networked control systems under temporal logic specifications
- 2019
-
Ingår i: Discrete event dynamic systems. - : Springer. - 0924-6703 .- 1573-7594. ; 29:4, s. 473-499
-
Tidskriftsartikel (refereegranskat)abstract
- Temporal logics for control of dynamical systems have the potential to automatically synthesize controllers under complex goals expressed by temporal logic formulas. In this paper, we are interested in the situation, where a controller system that implements high and low level controllers is connected to a plant over a communication network. In such control architecture, it is known that the limited nature of computation and communication resources should be explicitly taken into account. In view of this, we jointly provide control and communication strategies, such that the resulting state trajectories satisfy the desired temporal logic formula, while at the same time the average communication rate is below a certain threshold. The proposed strategies are illustrated through numerical simulation examples.
|
|
| 6. |
|
|
| 7. |
- Kiener, Georg Alexander, et al.
(författare)
-
Actuator saturation and anti-windup compensation in event-triggered control
- 2014
-
Ingår i: Discrete event dynamic systems. - : Springer Science+Business Media B.V.. - 0924-6703 .- 1573-7594. ; 24:2, s. 173-197
-
Tidskriftsartikel (refereegranskat)abstract
- Event-triggered control aims at reducing the communication load over the feedback link in networked control systems by sending information only if certain event conditions, which guarantee a desired control performance, are satisfied. This article investigates the consequences of actuator saturation on the behavior of the event-triggered control loop in terms of its stability and information exchange. Stability properties are derived using linear matrix inequalities (LMIs) which show how the stability of the event-triggered control loop depends on the selection of the event threshold. Moreover, it is shown that a lower bound on the minimum inter-event time exists being likewise affected by the event threshold. As actuator saturation might severely degrade the performance of the event-triggered closed-loop system, the scheme is extended by incorporating an anti-windup mechanism in order to overcome this problem. The results are illustrated by simulations and experiments.
|
|
| 8. |
- Kobetski, Avenir, 1977, et al.
(författare)
-
Time-Optimal Coordination of Flexible Manufacturing Systems Using Deterministic Finite Automata and Mixed Integer Linear Programming
- 2009
-
Ingår i: Discrete Event Dynamic Systems: Theory and Applications. - : Springer Science and Business Media LLC. - 0924-6703 .- 1573-7594. ; 19:3, s. 287-315
-
Tidskriftsartikel (refereegranskat)abstract
- Automation and flexibility are often mentioned as key concepts in modern production industry. To increase the level of flexibility, deterministic finite automata (DFA) can be used to model, specify and verify the production systems. Often, it is also desirable to optimize some production criteria, such as for example the cycle time of a manufacturing cell. In this paper, a method for automatic conversion from DFA to a mixed integer linear programming (MILP) formulation is first presented. This conversion is developed for a number of DFA structures that have shown to be useful in practical applications. Special attention is paid to reducing the search region explored by the MILP solver. Second, a conversion from the MILP solution to a DFA supervisor is described. This allows to combine the advantages of DFA modeling with the efficiency of MILP and supervisory control theory to automatically generate time-optimal, collision-free and non-blocking working schedules for flexible manufacturing systems.
|
|
| 9. |
- Lennartson, Bengt, 1956, et al.
(författare)
-
Special Issue on WODES'08
- 2009
-
Ingår i: Discrete Event Dynamic Systems: Theory and Applications. - : Springer Science and Business Media LLC. - 0924-6703 .- 1573-7594. ; 19:4, s. 449-50
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 10. |
- Lindström Claessen, Koen, 1975, et al.
(författare)
-
SAT-Solving in Practice, with a Tutorial Example from Supervisory Control
- 2009
-
Ingår i: Discrete Event Dynamic Systems. - : Springer Science and Business Media LLC. - 0924-6703 .- 1573-7594. ; 19:4, s. 495-524
-
Tidskriftsartikel (refereegranskat)abstract
- Satisfiability solving, the problem of deciding whether the variables of a propositional formula can be assigned in such a way that the formula evaluates to true, is one of the classic problems in computer science. It is of theoretical interest because it is the canonical NP-complete problem. It is of practical interest because modern SAT-solvers can be used to solve many important and practical problems. In this tutorial paper, we show briefly how such SAT-solvers are implemented, and point to some typical applications of them. Our aim is to provide sufficient information (much of it through the reference list) to kick-start researchers from new fields wishing to apply SAT-solvers to their problems. Supervisory control theory originated within the control community and is a framework for reasoning about a plant to be controlled and a specification that the closed-loop system must fulfil. This paper aims to bridge the gap between the computer science community and the control community by illustrating how SAT-based techniques can be used to solve some supervisory control related problems.
|
|
