Yi-Sheng Huang

Computationally Improved Optimal Deadlock Control Policy for Flexible Manufacturing Systems

Deadlock prevention, deadlock detection, and deadlock avoidance strategies are used to solve the deadlock problems of flexible manufacturing systems. The theory of regions is recognized as the unique method for obtaining maximally permissive (i.e., optimal) controllers in the existing literature. All legal and live maximal behavior of a Petri net model can be preserved by using a marking/transition-separation instance (MTSI). However, obtaining them is an extremely time consuming problem. This work proposes crucial MTSIs that allow designers to employ much fewer MTSIs to deal with deadlocks. The advantage of the proposed policy is that an optimal deadlock controller can be obtained with drastically reduced computation. Experimental results, by varying the markings of given net structures, indicate that it is the most efficient policy to obtain such controllers.

Critical Scenarios and Their Identification in Parallel Railroad Level Crossing Traffic Control Systems

Deterministic and stochastic Petri nets (DSPNs) are well utilized as a visual and mathematical formalism to model discrete event systems. This paper proposes to use them to model parallel railroad level crossing (LC) control systems. Their applications to both single- and double-track railroad lines are illustrated. The resulting models allow one to identify and thus avoid critical scenarios in such systems by conditions and events of the model that control the phase of traffic light alternations. Their analysis is performed to demonstrate how the models enforce the phase of traffic transitions by a reachability graph method. Their important properties are verified. To our knowledge, this is the first work that employs DSPNs to model a parallel railroad LC system and identify its critical scenarios for the purpose of their complete avoidance. This helps advance the state of the art in traffic safety related to the intersection of railroads and roadways.

Modular Design of Urban Traffic-Light Control Systems Based on Synchronized Timed Petri Nets

Timed Petri nets (TPNs) have been utilized as visual formalism for the modeling of complex discrete-event dynamic systems. They illuminate the features in describing the properties of causality and concurrency. Moreover, it is well known that a synchronized TPN (STPN) allows us to present all of the concurrent states in a complex TPN. In this paper, we propose a new methodology to design and analyze an urban traffic network control system by using the STPN. In addition, the applications of the STPN to eight-phase, six-phase, and two-phase traffic-light control systems are modularized. The advantage of the proposed approach is the clear presentation of the behaviors of traffic lights in terms of the conditions and events that cause phase alternations. Moreover, the size of the urban traffic network control system can be easily extended with our proposed modular technique. An analysis of the control models is performed via a reachability graph method to demonstrate how the models enforce the transitions of the traffic lights.

Design of Traffic Safety Control Systems for Emergency Vehicle Preemption Using Timed Petri Nets

Timed Petri nets (TPNs) are useful for performance evaluation of discrete event systems due to their mathematical formalism. This paper focuses on their use to model the preemption of emergency vehicle systems. The advantage of the proposed approach is the clear presentation of traffic light behaviors in terms of conditions and events that cause the preemption of phases being changed. The resulting models allow one to identify and thus avoid urgent spectacles in such systems by conditions and events of the model that control the phase of traffic light alternations. Moreover, this work proposes a new emergency vehicle preemption policy to ensure that emergency vehicles can pass through intersections with no or less delay. The analysis is performed to demonstrate how the models enforce the phase of traffic transitions by a reachability graph with time information. The liveness and reversibility of the proposed model are verified. To our knowledge, this is the first work that employs TPNs to model an emergency vehicle preemption system and identify its urgent spectacles for the purpose of their complete avoidance. This helps advance the state-of-the-art in traffic safety related to the intersection of roadways.

A green wave band based method for urban arterial signal control

Optimal signal timing is an efficient and effective method to mitigate traffic congestion in urban road traffic networks. In this paper, we propose a new method for signal-timing optimization of urban arterial roads. The main idea to the method is to design a bi-direction green wave band for arterial roads. In order to reduce delay and stops, an arterial road signal coordination approach is developed. In addition, the arterial signal coordination approach has been expanded to deal with the problem of coordination for urban traffic networks coordination control. Finally, simulation experiments are given to illustrate the effectiveness of the proposed method.

Modelling of traffic safety control systems using timed Petri nets

Timed Petri nets (TPNs) are well utilized as a visual and mathematical formalism to model discrete event systems. This paper proposes to use them to model parallel railroad level crossing control systems. Their applications to both single and double-track railroad lines are illustrated. The resulting models allow one to identify and thus avoid critical scenarios in such systems by conditions and events of the model that control the phase of traffic light alternations. Their analysis is performed to demonstrate how the models enforce the phase of traffic transitions by a reachability graph method. Their important properties are verified. This helps advance the state-of-the-art in traffic safety related to the intersection of railroads and roadways.

Design of elevator control systems using statecharts

Statechart has been utilized as a visual formalism for the modeling of complex and interactive systems for its illuminating features on describing properties of causality, concurrency, and synchronization. This paper employs the application of statechart to design an elevator control system, whose system behavior involves aggregating complexity of state descriptions, and imposition of underlying control policy. Based on the rules of an elevator, we derive the associated statechart model by looking into the inherent hierarchical structure of the elevator.

Using theory of regions with selective siphon control for deadlock prevention policy in Petri nets

Deadlock prevention policies are used to solve the deadlock problems of FMSs. The theory of regions is recognized as the unique method for obtaining maximally permissive (i.e., optimal) controllers in the existing literature. In this paper, the selective siphons and critical markings method [17] is merged in the new deadlock prevention policy. First of all, reachability graph is still needed. Second, CMTSIs are identified. Further, selective siphons and critical markings method is used to check if all dead/quasi-dead markings of CMTSIs are covered by these selective siphons. Furthermore, choose anyone CMTSI that belongs to a same selective siphon to be processed. Finally, controllers are therefore obtained. Experimental results indicate that the computational cost can be reduced again. Besides, it is the most efficient policy to obtain maximal permissive behavior of Petri net models.

An efficient deadlock prevention policy for FMSs using reduction method and theory of regions

Petri nets have been recognized as one of the most powerful tools for modeling FMSs. The reason is that PNs are suited well to represent FMS characteristics such as present relations, concurrence, conflict and synchronization. On the other hand, it is well known that the marking/transition-separation instances (MTSIs) method with the theory of regions has been recognized as the best (i.e. maximally permissive) policy in deadlock problems. However, its major shortcoming is the state explosion and redundant inequalities problem since the reachability graph of a plant model has to be generated when one wants to find all MTSIs. For improving these drawbacks, this paper uses the reduction method and proposes a novel concept of the crucial marking/transition-separation instances (CMTSI) which is the key of MTSIs based on Petri nets and the theory of regions. According to our experimental results, our deadlock prevention policy is more efficient in existing literatures based on the theory of regions.

Traffic Light Controller for Parallel Railroad Level Crossing Traffic Control Systems Using Deterministic and Stochastic Petri nets

Abstract Deterministic and stochastic Petri nets (DSPNs) are well utilized as a visual and mathematical formalism to model discrete event systems. This paper proposes to use them to model parallel railroad level crossing control systems. Their applications to both single and double-track railroad lines are illustrated. The resulting models allow one to identify and thus avoid critical scenarios in such systems by conditions and events of the model that control the phase of traffic light alternations. Their analysis is performed to demonstrate how the models enforce the phase of traffic transitions by a reachability graph method. Their important properties are verified. In this paper, we employ DSPNs to model a parallel railroad level crossing system and identify its critical scenarios for the purpose of their complete avoidance. This helps advance the state-of-the-art in traffic safety related to the intersection of railroads and roadways.