Resource-oriented Petri Net Model Research Articles

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.

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.