A hybrid approach to supervisory control of discrete event systems coupling RW supervisors to Petri nets


UZAM M. , Wonham W.

INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, vol.28, pp.747-760, 2006 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 28
  • Publication Date: 2006
  • Doi Number: 10.1007/s00170-004-2426-7
  • Title of Journal : INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY
  • Page Numbers: pp.747-760

Abstract

In this paper a hybrid approach is proposed for supervisory control of discrete event systems (DES) subject to forbidden states. Assuming that an uncontrolled bounded Petri net (PN) model of a (plant) DES and a set of forbidden state specifications are given, the proposed approach computes a maximally permissive and nonblocking closed-loop hybrid model. The first step is to simplify the given PN model by means of PN reduction rules. The simplified model and the specifications are then represented as buffers, and supervisory control theory (SCT) is applied to obtain a Ramadge-Wonham (RW) supervisor in the form of an automaton. After reduction of the latter's state size by a 'control congruence', the simplified RW supervisor is represented by a so-called auto-net and coupled to the given uncontrolled PN plant model by means of inhibitor arcs to represent the disabling actions. The plant model and supervisor auto-net run concurrently, synchronizing on shared events. This procedure provides a maximally permissive and nonblocking 'hybrid' (mixed PN/automaton) closed-loop controlled system. The method is straightforward logically, graphically, and technologically. Its applicability is shown by two examples, one of them a workcell from the PN control literature.