Pascal Yim

State Observer for DES Under Partial Observation with Time Petri Nets

This paper deals with a state observation approach for Discrete Event Systems with a known behavior. The system behavior is modeled using a Time Petri Net model. The proposed approach exploits temporal constraints to assess the system state and therefore detect and determine faults given partial observability of events. The goal here is to track the system state and to identify the event scenarios which occur on the system. Our approach uses the class graph of the Time Petri Net which models the complete system behavior to develop a state observer which is a base to perform online fault detection and diagnosing.

Mathematical programming approach to the Petri nets reachability problem

This paper focuses on the resolution of the reachability problem in Petri nets, using the mathematical programming paradigm. The proposed approach is based on an implicit traversal of the Petri net reachability graph. This is done by constructing a unique sequence of Steps that represents exactly the total behaviour of the net. We propose several formulations based on integer and/or binary linear programming, and the corresponding sets of adjustments to the particular class of problem considered. Our models are validated on a set of benchmarks and compared with standard approaches from IA and Petri nets community.

Container handling using multi-agent architecture

Container terminals are essential intermodal interfaces in the global transportation network. Efficient container handling at terminals is important in reducing transportation costs and keeping shipping schedules. This paper discusses a multi-agent model to simulate, solve and optimise the amount of storage space for handling container departures within a fluvial or maritime port. The multi-agent model is developed to minimise the expected total number of shifts or relocations while respecting spatio-temporal constraints. Experimental and numerical runs are given and illustrated. These runs carry out the proposed multi-agent model with comparison to the associated centralised version, basing on non-informed search algorithm and informed search algorithm. They show that the multi-agent model reduces rather the number of expected relocation movements especially when basing on informed search algorithm. We have also compare performances of our model with those of the B&B method and the heuristic-based method proposed in related works.

Reachability search in timed Petri nets using constraint programming

This paper presents a logical abstraction of the reachability graph of a timed Petri net using constraint programming. We apply it to the scheduling of transient inter-production states for cyclic productions in flexible manufacturing system. So, we propose to adapt the approach of Benasser and Yim (1999) based on the search of the accessibility by means of constraints using concepts of partial marking and partial step which allow a logical abstraction of the reachability graph of a Petri net. Having the timed Petri net (where a duration is associated to each transition), we propagate time to the obtained steps. In fact, we associate, to each marking extracted from a step, a timestamp vector: each timestamp corresponds to the date of the last token produced in a place at a step. Then, under temporal constraints, we solve scheduling problems, using constraint programming

Efficient reachability analysis of bounded Petri nets using constraint programming

In this paper, we consider the Petri net (PNs) reachability problem, which consists of finding transition firing sequences leading to a given target marking. We focus on bounded Petri nets for which we develop a correct and complete algorithm using the logical abstraction technique proposed by Benasser and Yim. We define for that the PN sequential depth parameter, which corresponds to the maximal number of transitions to fire in order to reach any marking of the reachability graph.

Solving the Petri Nets Reachability Problem Using the Logical Abstraction Technique and Mathematical Programming

This paper focuses on the resolution of the reachability problem in Petri nets, using the logical abstraction technique and the mathematical programming paradigm. The proposed approach is based on an implicit exploration of the Petri net reachability graph. This is done by constructing a unique sequence of partial steps. This sequence represents exactly the total behavior of the net. The logical abstraction technique leads us to solve a constraint satisfaction problem. We also propose different new formulations based on integer and/or binary linear programming. Our models are validated and compared on large data sets, using Prolog IV and Cplex solvers.

Solving Transient Scheduling Problems with Constraint Programming

We are interested in Discrete Event Dynamic Systems and especially in Flexible Manufacturing Systems (FMS) and their production management. In order to master the combinatorial complexity, we adopt steady, repetitive and deterministic schedule. We have already determined an approach to compute this cyclic schedule (which corresponds to the steady state) while optimizing quantitative and qualitative performance criteria: cycle time (throughput), Work In Process, simplicity of the schedule. In order to apply this schedule we consider and compute the transient periods to start and end the production. In a previous paper [9], we gave a preliminary study ofthe transient states. We computed upper and lower bounds for the transient state, the steady state and the makespan then we established a method to optimize the makespan. In this paper, we recall some necessary assumptions and definitions for the study of the transient states then we give a heuristic for the computation and optimization of the makespan.

Container assignment to stock in a fluvial port

Fluvial transport is getting a strong position as a good way of transport in certain Europeans countries as Belgium, Holland, France, etc. Therefore, fluvial ports are very interested in getting better structures and operational methods in order to improve their service to companies. In these days, of increasing fluvial traffic, a fast berthing time would be crucial in terms of a good service quality. Berthing time consists on the time to load and unload a ship. In this process, a minimum of container relocation movements would be needed to achieve this objective. This study aims to design a real time tool to store containers in the storage yard with the minimum expected relocation movements.

Transient inter-production scheduling based on Petri nets and constraint programming

In this article, we focus on the transient inter-production scheduling problem between two cyclic productions in the framework of flexible manufacturing systems. This problem is first formulated as a reachability problem in timed Petri nets (TPN), then solved using a methodology based on constraint programming. Our work is based on the controlled executions proposed by Chretienne to model the sequence of transition firing dates. Our methodology is based on a preliminary resolution of the state equation between initial and final states in the underlying non-TPN. Then, we choose a duration T max corresponding to the maximal duration time of the scheduling. For each solution S of the state equation, we build a controlled execution from the sequence of firings in S. After the propagation of firing date constraints and reachability constraints in the TPN, we use constraint programming to enumerate the set of feasible controlled executions.

Incremental Integer Linear Programming Models for Petri Nets Reachability Problems

The operational management of complex systems is characterized, in general, by the existence of a huge number of solutions. Decision-making processes must be implemented in order to find the best results. These processes need suitable modeling tools offering true practical resolution perspectives. Among them, Petri nets (PNs) provide a simple graphical model taking into account, in the same formalism, concurrency, parallelism and synchronization. Their graphical and precise nature, their firm mathematical foundation and the aboundance of analysis methods have made them become a classical modeling tool for the study of discrete event systems, ranging from operating systems to logistic ones. However, their interest in the field of problem solving is still badly known. In this paper, we consider some PN reachability problems. Since PNs can model flows in a natural and efficient way, many operations research problems can be defined using reachability between states, e.g. scheduling (Lee and DiCesare, 1994; Van Der AAlst, 1995), planning (Silva et al., 2000), car-sequencing problems (Briand, 1999). Moreover, research on Petri nets addresses the issue of flexibility: many extensions have been proposed to facilitate the modeling of complex systems, by addition of ``color’’, ``time’’ and ``hierarchy’’ (Jensen, 1992; Wang,1998). For example, it is relatively easy to map scheduling problems onto timed PNs. Their graphical nature reinforce obviously this strength, by allowing a kind of interactivity with the system. At last, a large number of difficult PN analysis problems are equivalent to the reachability problem, or to some of its variants or sub-problems (Keller, 1976). Particularly, model-checking (Latvala, 2001) which represents a key point when dealing with systems analysis is directly linked to an exhaustive traversal of the corresponding PN reachability graph. Various methods have been suggested to handle the PNs reachability problem. In this paper, we propose to use the mathematical programming paradigm. Some PN analysis problems have already been handled using such techniques (Melzer and Esparza, 1996;Silva et al., 1998; Khomenko and Koutny, 2000), but none has considered the general PNs reachability problem. The proposed approach is based on an implicit traversal of the Petri net reachability graph, which does not need its construction. This is done by considering a unique sequence of steps growing incrementally to represent exactly the total behavior of the net. We follow here a