نسبت زنده بودن پارامتر-اجرای سرپرست برای یک کلاس از شبکه های عمومی پتری

The work proposes a synthesis method of supervisors for flexible manufacturing systems modeled by a class of generalized Petri nets. A concept of resource usage ratios (RU-ratios) is first presented to describe the occupation degree of a resource by an operation. Next, an intrinsically live structure characterized by a special numerical relationship between arc-weights and initial markings is investigated from a perspective of RU-ratios. Then, a new kind of supervisors is synthesized on the ground of the generic nature of the intrinsically live structure. Such a supervisor can achieve the purposes of both liveness-enforcement and resource usage ratio-enforcement of the system under consideration. Given a plant, it is easy to determine the topological structure of such a supervisor and the number of monitors is bounded by that of resources used in the plant. In addition, when the configuration of the plant model changes, the supervisor can be reusable through adjusting control parameters only without rearrangement of connections. This makes it easy enough and intuitive to be used by industrial practitioners. Instead of maximal behavioral permissiveness, it pursues a precise usage of shared resources that are limited and valuable. Several examples are used to illustrate the proposed methods.

In this new millennium, the global economy becomes increasingly inseparable. As a paramount foundation of our society’s economy system, manufacturing encounters more and more intense global market competition. A new strategy for manufacturing called customizability becomes a popular trend and is extensively adopted by an increasing number of companies, especially those manufacturing high value-added and technology-intensive products. In these fields, the mass production is replaced by a high-mix–low-volume production mode (Mahoney, 1997). It is the very reason that flexible manufacturing systems (FMSs) are built to realize a rapid and mixed production. Moreover, flexibility and agility processed by an FMS make it completely different from the traditional manufacturing systems (Zhou, 1995).

A new liveness and resource usage ratio-enforcing supervisor is proposed in this work. By the concept of resource usage ratios, the essence of an intrinsically live structure is analyzed and adopted to design an LRS, which makes a WS3PR model live through controlling the maximal RU-ratios of upstream activity places with respect to corresponding resource places. An appropriate scheme of quotas on resource capacities is implemented for the competitive operations by this supervisor. The connection of monitors is exactly the same as that of the corresponding resource places. The number of monitors is bounded by that of resource places of a plant model. Moreover, an LRS is highly reusable by adjusting control parameters. All the above features make it easy to be used by designers, researchers, and engineers. The future work includes choosing an optimal set of competition paths to be controlled, which yields as more as reachable states of the controlled system. In order to avoid the NP-hard problem in mathematical programming, another way to compute control parameters also needs to be considered by exploring the characteristic structure of WS3PR. Extension to LRS applied to a more general class of Petri nets modeling more complex resource allocation systems remains open.