Resource-oriented Petri Net Research Articles

Scheduling of time-constrained single-arm cluster tools with purge operations in wafer fabrications

Purge operations are widely used to remove residual chemicals and impurities in chambers of wafer fabrication systems to ensure wafer quality. However, such operations lead to more start-up transient processes and wafer delays. In addition, wafer residency time constraints must be met to ensure the wafer quality. Thus, the system scheduling problem with such considerations will become more complicated. This work aims to optimize the start-up transient process of a single-arm cluster tool with purge operations and wafer residency time constraints by using resource-oriented Petri net (ROPN) models. Based on the models, we dynamically depict the behavior of the steady state and start-up transient processes of a single-arm cluster tool with purge operations. Then, a scheduling method that dynamically adjusts the robot waiting time is proposed to find an optimal schedule for such systems with purge operations and wafer residency time constraints. Finally, some examples are tested to illustrate the effectiveness of our method.

Liveness of Disjunctive and Strict Single-Type Automated Manufacturing System: An ROPN Approach

The resource-oriented Petri net (ROPN) modeling method is applied in this paper to model a class of automated manufacturing systems (AMS) named disjunctive and strict single-type AMSs (DS-AMS), where multiple units of a single resource type are required to support a processing stage. This modeling method is more compact and intuitive than the existing ones in the contemporary literature, named weighted systems of simple sequential processes with resources. Based on the ROPN model, a significant result is re-proved in a different way, which is more succinct and understandable. Such a result presents a sufficient and necessary condition on the liveness of an ROPN. Furthermore, based on this result, we develop efficient strategies to ensure the liveness of an ROPN modeling a DS-AMS. To enforce the liveness of such an ROPN, only some specific transitions need to be controlled by taking advantage of its structural properties. Also, an efficient approach is developed to implement the proposed policy by identifying and controlling such transitions. Two examples are employed to demonstrate the efficiency of the developed method. Some limitations of the method are pointed out in the end, which will be studied in the future.

On a maximally permissive deadlock prevention policy for automated manufacturing systems by using resource-oriented Petri nets

It is theoretically and practically significant to synthesize a maximally permissive (optimal) controller to prevent deadlocks in an automated manufacturing system (AMS). With an AMS being modeled with Petri nets, by the existing methods, integer linear programming (ILP) problems are usually formulated and solved to obtain optimal policies by forbidding illegal markings at the same time no legal marking is excluded. Without an efficient technique for solving an ILP, such a method is usually computationally prohibitive. A resource-oriented Petri net (ROPN) is employed to model a class of AMS for resolving the deadlock control problem with maximal permissiveness in this paper. Efficient methods are developed to figure out the key structures in an ROPN model for deadlock prevention. Based on the structural properties of ROPN models, this work explores several types of illegal markings that can be prohibited optimally by structural analysis. For these markings, a deadlock prevention policy can be derived in an algebraic way without solving a notorious ILP problem. For the other markings, linear programming (LP), instead of ILP, approaches are developed to forbid them optimally. Thus, a maximally permissive controller can be developed while the computational cost is reduced greatly. The proposed methods are verified by typical examples in the literature.

A novel method for deadlock prevention of AMS by using resource-oriented Petri nets

Based on the systems of simple sequential processes with resources (S3PR) model, the existing methods involve prohibitive computation to synthesize a deadlock prevention controller for automated manufacturing systems (AMS). To reduce the computation, this work studies this problem by using a resource-oriented Petri net (ROPN) model. By revealing the relationship between the bad markings and structural properties of an ROPN, it presents a method such that a deadlock prevention controller can be obtained by simple calculation. By such a controller, for each strongly connected subnet in an ROPN, only one control place is needed such that it is structurally very simple. Furthermore, a condition is given under which a maximally permissive controller can be efficiently obtained, which was never seen before. Examples are used to show the application and performance of the proposed method.

Adaptive Scheduling Model in Hybrid Flowshop Production Control using Petri Net

Flowshop scheduling problems with a work shop or group shop in which the flow control shall enable an appropriate sequencing for each job and for processing on a set of machines are very significant for production control. HFS (Hybrid Flowshops) is a typical mass-customization with large product series which is widely used in the current production companies. However, as the increasing customization requirements from large number of customers, the control of HFS is really difficult. This paper introduces a Petri net-based adaptive scheduling model for easing the qualitative analysis of the production system and reducing the complexity. Resource-oriented Petri Net (ROPN) is used to establish the relation in terms of logics and behaviors of various resources, converting the dynamics control of manufacturing system into resources aspects. After the model analysis and a real-life case illustration, this model can perform good interpretation of various objective functions and real case considerations. That could be used for guiding production schedules control and automation.

One-Step Look-Ahead Maximally Permissive Deadlock Control of AMS by Using Petri Nets

It is desired that a deadlock control policy for automated manufacturing systems (AMS) is maximally permissive. However, its tractability issue remains open, and this work addresses this important issue. It models AMS with a resource-oriented Petri net (ROPN) and presents a necessary and sufficient condition under which there exists a one-step look-ahead maximally permissive control policy for deadlock avoidance in AMS. It further identifies some conditions under which a one-step look-ahead maximally permissive deadlock control policy exists for a single-capacity system. The conditions can be conveniently examined by using the developed ROPN model.

Resource-Oriented Petri Net for Deadlock Avoidance in Flexible Assembly Systems

In many flexible assembly systems, base components are transported with pallets; parts to be mounted onto the base ones are transported by trays with no pallets. When an assembly operation is performed by using some parts in a tray but not all, the tray with the remaining parts still occupies a buffer space. In this way, an assembly/disassembly material flow is formed. In such a material flow, deadlock can occur both in the base component and part flow. Furthermore, the assembly operations can also result in a deadlock. Thus, it is a great challenge to tackle deadlocks in such processes. This paper models them using resource-oriented Petri nets. Based on the models, a deadlock control policy is proposed and proved to be computationally efficient and less conservative than the existing policies in the literature. An industrial case study is used to show the results.

Deadlock modeling and control of semiconductor track systems using resource-oriented Petri nets

This paper addresses the deadlock avoidance problem in track systems in semiconductor fabrication. For the system without buffer space in it, the existing deadlock avoidance policies tend to be too conservative. Routing flexibility provides a chance to develop better ones, but makes their computation more complex. This paper models a track system using coloured resource-oriented Petri net (CROPN). Based on the model, a sufficient condition for deadlock-free operation and the corresponding control law are presented. This proposed policy is shown computationally efficient and less conservative than existing methods. An example is presented to demonstrate its application.