| 1. |
- Feng, Lei, et al.
(författare)
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A structural approach to the non-blocking supervisory control of discrete-event systems
- 2009
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 41:11-12, s. 1152-1168
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Tidskriftsartikel (refereegranskat)abstract
- Many practical and important systemic properties of manufacturing systems, like deadlock freeness, liveness, and reversibility, can be formulated as the non-blocking property of discrete-event systems. It can be difficult, however, to verify non-blocking or design a supervisor to guarantee non-blocking control because of state size explosion in the concurrency model. In this paper, we present sufficient conditions for the computation of (small) model abstractions that preserve the non-blocking property. As a consequence, hierarchical and decentralized control structures can be flexibly integrated, and the proposed approach can synthesize maximally permissive and non-blocking control with reduced computational effort. The solution is a group of decentralized supervisors that transparently displays control logic and admits relatively simple implementation.
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| 2. |
- Feng, Lei, et al.
(författare)
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Designing communicating transaction processes by supervisory control theory
- 2007
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Ingår i: Formal methods in system design. - : Springer Science and Business Media LLC. - 0925-9856 .- 1572-8102. ; 30:2, s. 117-141
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Tidskriftsartikel (refereegranskat)abstract
- A Communicating Transaction Process (CTP) is a computational model that serves as a high level specification language for reactive embedded system components and their interactions. It consists of a network of communicating processes coordinating their behaviors via common actions and the common actions are refined as a set of guarded Message Sequence Charts (MSCs). There has been little work devoted to developing CTP models systematically. This paper takes the first step towards bridging this gap. In our work, communicating processes of embedded components are modeled and controlled as Discrete-Event Systems (DES). The control logic among communicating components is derived by Supervisory Control Theory (SCT), so as to guarantee that the communicating processes meet all predefined constraints and possess other desirable system behavioral properties. The control logic is then translated into propositional formulas for guarded MSCs which then results in a CTP model with guaranteed behavioral properties.
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| 3. |
- Feng, Lei, et al.
(författare)
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On the Computation of Natural Observers in Discrete-Event Systems
- 2010
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Ingår i: Discrete event dynamic systems. - : Springer Science and Business Media LLC. - 0924-6703 .- 1573-7594. ; 20:1, s. 63-102
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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.
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| 4. |
- Feng, Lei, et al.
(författare)
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Supervisory control architecture for discrete-event systems
- 2008
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Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 53:6, s. 1449-1461
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Tidskriftsartikel (refereegranskat)abstract
- A flexible decentralized and hierarchical architecture is presented to reduce computational effort in designing optimal nonblocking supervisors for discrete-event systems (DES). We organize a DES into modular subsystems that embody internal interacting dependencies. Verification of, and coordination among modular subsystems are achieved through their model abstractions. Sufficient conditions are presented to guarantee that coordinators and modular supervisors result in maximally permissive and nonblocking control. A medium-sized example demonstrates the computational effectiveness of our approach.
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