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Development and Implementation of Hierarchical Control Structures of Flexible Production Systems Using High-Level Petri Nets.

Colombo, Armando Walter

University Erlangen-Nürnberg: Dissertation. Fertigungstechnik, pages 1-216. Bamberg: Meisenbach Verlag, August 1998. ISBN 3-87525-109-1.

Abstract: This work describes an H-L-PN-based approach for development of Flexible Production Systems (FPS) that comprises a new control- and monitoring-concept. Opposite to other solutions, a designed, modelled and validated FPS can be controlled directly through data exchange between H-L-PN-based model and production system, and through information exchange between H-L-PN-based model and overlapped control levels (real-time decisions and/or planning level). The usage of such complete platform-independent and -configurable models of the systems and their control structures makes possible important saves of time and costs.

Two new engineering methods are presented. The first method supports the user in the design and implementation tasks of the H-L-PN- and PC-based control- and monitoring-system of FPS. The second one allows automatic creation of IEC 1131-conform PLC-code out of validated and optimized H-L-PN-based models of FPS. In this case, the resulted control code can be loaded directly in a PLC or an off-line simulator.

The complete FPS development process, i.e., design, programming and implementation, can be entirely supported through the engineering-tool - based on the H-L-PN theory - developed within this work.

The both above named methods used H-L-PN-based models. For this reason, they are suitable, not only for the development and control of a FPS, but also, because of their graphical and mathematical character, for the visualization of the internal events of the system, and through this for the monitoring/control of the production processes. An extension of the new FPS control concept using an industrial control- and monitoring-component was also developed. This component offers, not only the possibility to show the evolution of H-L-PN-based control model, but allows also the preparation of user-friendly graphic representation of the controlled process. Herewith is achieved the integration of the human operator into the development concept (human-machine system).

Because of their extension abilities and their modular construction, the control structures developed and implemented in this work can be used as an excellent base for further ones. Especially, the engineering-tool can be seen as a new FPS component: a virtual representation of the real flexible production environment. It is able to run synchronous with the FPS and both can be seen as a unique production entity. Compared with other approaches, the proposed engineering-tool does offer a number of advantages, for instance: specifications can be verified, implementation can be automated, test cases can be generated, labour costs can be saved by reducing working-time of designing a test suite. However, the most important aspect is the possibility to develop and implement more reliable FPS/DECS.

Keywords: High-Level Petri Nets, Flexible Production Systems, Discrete-Event Control, Monitoring, Programmable Logic Controllers.

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