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Now showing 1 - 8 of 8
  • Conference Object
    Citation - Scopus: 12
    Computation of Supervisors for Fault-Recovery and Repair for Discrete Event Systems
    (IFAC Secretariat, 2014) Sülek, A.N.; Schmidt, K.W.
    In this paper, we study the fault-recovery and repair of discrete event systems (DES). To this end, we first develop a new method for the fault-recovery of DES. In particular, we compute a fault-recovery supervisor that follows the specified nominal system behavior until a fault-occurrence, that continues its operation according to a degraded specification after a fault and that finally converges to a desired behavior after fault. We next show that our method is also applicable to system repair and we propose an iterative procedure that determines a supervisor for an arbitrary number of fault occurrences and system repairs. We demonstrate our method with a manufacturing system example. © 2021 Elsevier B.V., All rights reserved.
  • Conference Object
    Citation - Scopus: 11
    Computation of Supervisors for Reconfigurable Machine Tools
    (IFAC Secretariat, 2012) Schmidt, K.W.
    The rapid reconfiguration of manufacturing systems is an important issue in today's manufacturing technology in order to adjust the production to varying product demands and types. In this paper, we study the control of reconfigurable machine tools (RMTs) with the aim of fast reconfiguration and an easy controller implementation. We first formulate a particular reconfiguration problem for RMTs in a discrete event system setting, and then provide necessary and sufficient conditions for its solution. Moreover, we propose an algorithm for the construction of a reconfiguration supervisor as the composition of one supervisor for each separate RMT configuration and one supervisor that performs the transition between configurations. The reconfiguration supervisor can be computed in polynomial time, and allows configuration changes within a bounded delay. In addition, our method facilitates the addition of a new configuration during system operation.
  • Article
    Citation - WoS: 2
    Citation - Scopus: 2
    Order-Preserving Languages for the Supervisory Control of Automated Manufacturing Systems
    (Ieee-inst Electrical Electronics Engineers inc, 2020) Nooruldeen, Anas; Schmidt, Klaus Werner
    Automated manufacturing systems (AMSs) consist of computer-controlled interconnected manufacturing components (MCs) that are used to transport and process different product types. Each product type requires a certain sequence of processing steps in different MCs. Hereby, multiple product types can share processing steps on the same MC and the paths of different products types can overlap. In this paper we consider the modeling of AMSs in the scope of supervisory control for discrete event systems (DES). On the one hand, a suitable AMS model must allow the representation of sequential and concurrent processing steps in MCs. On the other hand, such model must be able to track different product types traveling through the AMS so as to process the products correctly. While previous work is commonly concerned with the first requirement, this paper identifies that the existing literature lacks a general treatment of the second requirement. Accordingly, we first introduce order-preserving (OP) languages that preserve the order of different product types in MCs and we propose a suitable finite state automaton model for OP languages. Then, we show that the composition of OP languages again leads to an OP language. That is, modeling MCs by OP languages, an OP model of a complete AMS that is suitable for supervisory control is obtained. In addition, it is possible to use both OP models and non-OP models for general AMSs, where MCs have different properties. We demonstrate the applicability of the proposed modeling technique by a flexible manufacturing system example.
  • Conference Object
    Citation - WoS: 5
    Citation - Scopus: 6
    Fault-Tolerant Control of Discrete-Event Systems With Lower-Bound Specifications
    (Elsevier, 2015) Moor, Thomas; Schmidt, Klaus Werner
    Fault-tolerant control addresses the control of dynamical systems such that they remain functional after the occurrence of a fault. To allow the controller to compensate for a fault, the system must exhibit certain redundancies. Alternatively, one may relax performance requirements for the closed loop behaviour after the occurrence of a fault. To achieve fault tolerance for a hierarchical control architecture, a combination of both options appears to be advisable: on each individual level of the hierarchy, the controller may compensate the fault as far as possible, and then pass on responsibility to the next upper level. This approach, when further elaborated for discrete-event systems represented by formal languages, turns out to impose a hard lower-bound inclusion specification on the closed-loop behaviour. The present paper discusses the corresponding synthesis problem and presents a solution. (C) 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.
  • Conference Object
    Citation - Scopus: 8
    Computation of Fault-Tolerant Supervisors for Discrete Event Systems
    (IFAC Secretariat, 2013) Sülek, A.N.; Schmidt, K.W.
    Fault-tolerance addresses the problem of operating a system even in case of faults. In this paper, we study fault-tolerance in the supervisory control framework for discrete event systems (DES). We consider DES, where certain events might no longer be possible in case a fault happens. In this setting, we first identify necessary and suficient conditions for the existence of a supervisor that realizes a given behavioral specification both in the non-faulty and in the faulty case. We further show that it is possible to determine a supremal fault-tolerant sublanguage in case the existence condition is violated. Finally, we propose an algorithm for the computation of this sublanguage and prove its correctness. Different from existing work, our fault-tolerant supervisor allows fault occurrences and system repairs at any time. The concepts and results developed in this paper are illustrated by a manufacturing system example. © 2013 IFAC.
  • Conference Object
    Citation - Scopus: 5
    Abstraction-Based Supervisory Control for Recon-Gurable Manufacturing Systems
    (IFAC Secretariat, 2013) Khalid, H.M.; Kirik, M.S.; Schmidt, K.W.
    Reconfiguration control for discrete event systems (DES) is concerned with the realization of different system configurations by modification of the supervisory control loop. In this paper, we study the reconfiguration supervisor design for reconfigurable manufacturing systems (RMS) that comprise multiple components. We construct a modular supervisor for each configuration and system component in order to realize each active configuration and to quickly change between configurations. Different from the existing literature that is focused on monolithic design, our method is abstraction-based, and, hence applicable to large-scale DES. © 2013 IFAC.
  • Conference Object
    Citation - Scopus: 7
    Abstraction-Based Control for Not Necessarily Closed Behaviours
    (IFAC Secretariat, 2011) Moor, T.; Schmidt, K.; Wittmann, T.
    This paper addresses abstraction-based supervisory control for plant and specification behaviours that are not necessarily ω-closed, i.e. plant behaviours that exhibit eventuality properties and specifications that impose eventuality properties on the closed loop. Technically, the core idea is to combine results from previous work on abstraction-based supervision of input-output behaviours with results on supervisory control of ω-languages. As our main result, we identify a controllability condition for the plant, that ensures a nonblocking closed-loop behaviour with a controller that has been obtained for a plant abstraction. © 2011 IFAC.
  • Conference Object
    The Controllability Prefix for Supervisory Control Under Partial Observation With an Application To Fault-Tolerant Control
    (Elsevier, 2017) Moor, Thomas; Schmidt, Klaus Werner
    The controllability prefix is known as a useful concept for the discussion and solution of synthesis problems in supervisory control of cp-languages, i.e., formal languages of infinite-length words. There, the controllability prefix is defined as the set of all finite-length prefixes that can be controlled to satisfy prescribed liveness and safety properties. In this paper, we discuss a variation of the controllability prefix to address supervisory control under partial observation for regular *-languages, i.e., formal languages of finite-length words. We derive algebraic properties that are useful for a quantitative analysis on how an upper-bound language-inclusion specification affects achievable lower-bound specifications. Our study is motivated by the synthesis of fault-tolerant supervisory controllers, where the possible occurrence of a fault may restrict the achievable pre-fault behaviour so severe, that a relaxation of the upper-bound specification becomes a practical option. As our study shows, such a relaxation can be systematically constructed in terms of the controllability prefix. (C) 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.