Libin Han

Deadlock-Free Genetic Scheduling Algorithm for Automated Manufacturing Systems Based on Deadlock Control Policy

Deadlock-free control and scheduling are vital for optimizing the performance of automated manufacturing systems (AMSs) with shared resources and route flexibility. Based on the Petri net models of AMSs, this paper embeds the optimal deadlock avoidance policy into the genetic algorithm and develops a novel deadlock-free genetic scheduling algorithm for AMSs. A possible solution of the scheduling problem is coded as a chromosome representation that is a permutation with repetition of parts. By using the one-step look-ahead method in the optimal deadlock control policy, the feasibility of a chromosome is checked, and infeasible chromosomes are amended into feasible ones, which can be easily decoded into a feasible deadlock-free schedule. The chromosome representation and polynomial complexity of checking and amending procedures together support the cooperative aspect of genetic search for scheduling problems strongly.

Transition Cover-Based Design of Petri Net Controllers for Automated Manufacturing Systems

In automated manufacturing systems (AMSs), deadlock problems must be well solved. Many deadlock control policies, which are based on siphons or Resource-Transition Circuits (RTCs) of Petri net models of AMSs, have been proposed. To obtain a live Petri net controller of small size, this paper proposes for the first time the concept of transition covers in Petri net models. A transition cover is a set of Maximal Perfect RTCs (MPCs), and the transition set of its MPCs can cover the set of transitions of all MPCs. By adding a control place with the proper control variable to each MPC in an effective transition cover to make sure that it is not saturated, it is proved that deadlocks can be prevented, whereas the control variables can be obtained by linear integer programming. Since the number of MPCs in an effective transition cover is less than twice that of transition vertices, the obtained controller is of small size. The effectiveness of a transition cover is checked, and ineffective transition covers can be transformed into effective ones. Some examples are used to illustrate the proposed methods and show the advantage over the previous ones.

Deadlock-free genetic scheduling for flexible manufacturing systems using Petri nets and deadlock controllers

In this paper, a new deadlock-free scheduling method based on genetic algorithm and Petri net models of flexible manufacturing systems is proposed. The optimisation criterion is to minimise the makespan. In the proposed genetic scheduling algorithm, a candidate schedule is represented by a chromosome that consists of two sections: route selection and operation sequence. With the support of a deadlock controller, a repairing algorithm is proposed to check the feasibility of each chromosome and fix infeasible chromosomes to feasible ones. A feasible chromosome can be easily decoded to a deadlock-free schedule, which is a sequence of transitions without deadlocks. Different kinds of crossover and mutation operations are performed on two sections of the chromosome, respectively, to improve the performance of the presented algorithm. Computational results show that the proposed algorithm can get better schedules. Furthermore, the proposed scheduling method provides a new approach to evaluate the performance of different deadlock controllers.

Minimizing the total completion time in a distributed two stage assembly system with setup times

In this paper, a novel distributed two stage assembly flowshop scheduling problem (DTSAFSP) is addressed. The objective is to assign jobs to several factories and schedule the jobs in each factory with the minimum total completion time (TCT). In view of the NP-hardness of the DTSAFSP, we develop heuristics method to deal with the problem and propose three hybrid meta-heuristics (HVNS, HGA-RVNS, and HDDE-RVNS). The parameters of HGA-RVNS and HDDE-RVNS are tuned by using the Taguchi method and that of HVNS is done by using the single factor ANOVA method. Computational experiments have been conducted to compare the performances of the proposed algorithms. The analyses of computational results show that, for the instances with small numbers of jobs, HDDE-RVNS obtains better performances than HGA-RVNS and HVNS; whereas for the instances with large numbers of jobs, HGA-RVNS is the best one in all the proposed algorithms. Computational results indicate that the performances of the HDDE-RVNS and HGA-RVNS are not much affected by the number of machines at the first stage and factories. The experimental results also show that the RVNS-based local search steps in both HGA-RVNS and HDDE-RVNS are efficient and effective.

A robust deadlock prevention control for automated manufacturing systems with unreliable resources

For a deadlock problem in automated manufacturing systems (AMSs) with unreliable resources, the existing control methods mostly belong to the class of deadlock avoidance. This paper focuses on deadlock prevention for AMSs with an unreliable resource. We use Petri nets to model such AMSs and develop their robust deadlock prevention controller. The controller is designed in three layers. In the first layer, the optimal controller is used to ensure that the system can process all types of parts in the absence of resource failures. The function of the second layer controller is to ensure that, when a fault of the unreliable resource occurs at any reachable state, all parts not requiring the faulty resource can be processed and all resources, that they need, but are held by parts requiring the faulty resource for further processing, can be released in order to maximize the resource utilization. The so-called second-level deadlocks caused by the controllers are prevented by the third layer controller. These three controllers together are shown to satisfy the desired properties and hence, able to ensure the robust deadlock-free operation of AMSs with an unreliable resource.

A Petri net-based particle swarm optimization approach for scheduling deadlock-prone flexible manufacturing systems

This paper proposes an effective hybrid particle swarm optimization (HPSO) algorithm to solve the deadlock-free scheduling problem of flexible manufacturing systems (FMSs) that are characterized with lot sizes, resource capacities, and routing flexibility. Based on the timed Petri net model of FMS, a random-key based solution representation is designed to encode the routing and sequencing information of a schedule into one particle. For the existence of deadlocks, most of the particles cannot be directly decoded to a feasible schedule. Therefore, a deadlock controller is applied in the decoding scheme to amend deadlock-prone schedules into feasible ones. Moreover, two improvement strategies, the particle normalization and the simulated annealing based local search, are designed and incorporated into particle swarm optimization algorithm to enhance the searching ability. The proposed HPSO is tested on a set of FMS examples, showing its superiority over existing algorithms in terms of both solution quality and robustness.

Two-stage deadlock prevention policy based on resource-transition circuits

This paper presents a suboptimal deadlock controller for a class of manufacturing systems of sequential processes with resources, where deadlocks are characterized by saturated maximal perfect resource-transition circuits (MPRT-circuits), and the controller consists of two parts. In the maximally permissive Petri net controller, which avoids all MPRT-circuits being saturated, some control places are redundant. By deleting all redundant control places and their related arcs, the first part of our controller, non-redundant controller, is obtained. In the controlled system with the non-redundant controller, deadlocks may occur if the system contains crucial resources. Then we propose for the first time the concept of the maximal perfect control-transition circuits (MPCT-circuits), which is used to characterize the deadlock in the controlled system with the non-redundant controller. When deadlock occurs under a reachable marking, some MPCT-circuits in the controlled system become empty. The Petri net controller to prevent all MPCT-circuits from being empty is the second part of our controller. It is proved that the controller consisting of two parts can guarantee the liveness of the controlled system.

Hybrid heuristic search approach for deadlock-free scheduling of flexible manufacturing systems using Petri nets

Display OmittedBased on the Petri net models of flexible manufacturing systems, this paper focuses on deadlock-free scheduling problem with the objective of minimizing the makespan. To avoid deadlocks, the deadlock control policy is embedded into heuristic search strategies, and two hybrid heuristic search algorithms for deadlock-free scheduling of FMSs are proposed. Deadlock control and scheduling for flexible manufacturing system is integrated.Deadlock control policy is embedded into the heuristic search algorithm.Two hybrid deadlock-free scheduling algorithms for flexible manufacturing system are proposed. Based on the Petri net models of flexible manufacturing systems (FMSs), this paper focuses on deadlock-free scheduling problem with the objective of minimizing the makespan. Two hybrid heuristic search algorithms for solving such scheduling problems of FMSs are proposed. To avoid deadlocks, the deadlock control policy is embedded into heuristic search strategies. The proposed algorithms combine the heuristic best-first strategy with the controlled backtracking strategy based on the execution of the Petri nets. The scheduling problem is transformed into a heuristic search problem in the reachability graph of the Petri net, and a schedule is a transition sequence from the initial marking to the final marking in the reachability graph. By using the one-step look-ahead method in the deadlock control policy, the safety of a state in the reachability graph is checked, and hence, deadlock is avoided. Experimental results are provided and indicate the effectiveness of the proposed hybrid heuristic search algorithms in solving deadlock-free scheduling problems of FMSs. Especially, the comparison against previous work shows that both new algorithms are promising in terms of solution quality and computing times.

Research on Finding Elementary Siphon in a Class of Petri Nets

This paper develops an algorithm to find a set of elementary siphons for a linear simple sequential process with resources. A graph-based technique is used to achieve elementary resource transition circuits (RTCs) initially. Then, some maximal perfect resource-transition circuits (MPCs) can be derived from elementary RTCs. Next, MPCs are used to developed T-characteristic vectors according to their correspondence relation. Finally, the set of elementary siphons can be established through computing a maximal set of linear indepen- dent rows of the characteristic T-vector matrix using the Gauss elimination. An example is included to validate the effectiveness of the proposed method.