Shinzo Kodama

Maximally permissive controllers for controlled time Petri nets

Studies concurrent discrete event systems modeled by controlled time Petri nets. The authors derive a necessary and sufficient condition for the unique existence of the maximally permissive controller (MPC). Then the authors derive a closed form expression of the unique MPC if it exists.<<ETX>>

A note on static state feedback control of discrete event systems under partial observation

Studies static state feedback control of discrete event systems under partial observation. The authors first show a necessary and sufficient condition for the existence of a balanced state feedback in the Golaszewski-Ramadge model. Next, in the Ramadge-Wonham model, the authors present a necessary and sufficient condition for the existence of a state feedback which is not necessarily balanced. This condition is a special case of the condition for the existence of a dynamic controller obtained by Kumar et al. (1993). However, the condition obtained in this paper has computational advantage in contrast with that obtained by Kumar et al.<<ETX>>

Petri net based qualitative simulation with quantitative information

This paper deals with qualitative modeling and simulation of continuous-time systems based on Petri nets. Qualitative simulation faces an intrinsic problem of scale. As the number of variables increases, the number of possible qualitative behaviors may grow exponentially in the worst case. We extend conventional Petri net and propose a method for qualitative simulation with time and quantity, and show that the proposed method can predict system behaviors precisely.

A Note on Realizable Sequences in Supervisory Control of Timed Event Graphs

Abstract This paper studies realizable sequences in the max-algebra model of timed event graphs. First, a specification given as a sequence of firing times of all transitions is considered. A necessary and sufficient condition for the existence of a realizable sequence less than (greater than) a given specification sequence is derived. Then, a formula for the supremal realizable sequence less than a given sequence is presented. A formula for the infimal realizable sequence greater than a given sequence is also obtained under some assumption. Moreover, these results are extended to the case where a specification is defined on firing times of a specified subset of transitions.

Decentralized Supervisory Control Based on Partial Observations of Events and States

In our previous work on supervisory control of discrete event systems, we proposed a novel supervisor which assigns a control pattern based on partial observations of both events and states, and showed necessary and sufficient conditions for its existence. This paper extends the result to decentralized supervisory control of large-scale discrete event systems consisting of several subsystems which operate concurrently. We address two types of decentralized control problems. One requires that the behavior of the closed-loop system equals a given legal language. The other requires that the behavior of the closed-loop system lies in a given admissible range. For each problem, we derive a necessary and sufficient condition for the existence of a decentralized supervisor.

Concurrency and State Feedbacks in Petri Nets with External Input Places

Concurrency is a very important problem in real-time discrete-event systems, and has a crucial effect on control. In this paper, we consider concurrent discrete-event systems modeled by Petri nets with external input places, with a control specification given in terms of a predicate on the set of all reachable markings. First, we derive a simpler condition for the unique existence of the maximally permissive feedback which can be checked without constructing the set of permissive feedbacks. Next, we obtain a necessary and sufficient condition for concurrency to have no effect on the set of permissive feedbacks. And we study the relationship between these two properties. Moreover, we demonstrate synthesis of the unique maximally permissive feedback for a simple manufacturing system.