Hybrid Supervisory Control And Self-adaptive Scheduling Of Virtual Production Systems Based On Automata

With the development of technology and economic globalization, today's manufacturing environment has changed quite a lot. Besides providing high-quality and high-performance products, manufacturing enterprises should be able to react quickly to the dynamic and changing market environment in a cost-effective manner and satisfy customers'demands with diverse variety and small batch size production or even mass customization. Customer-oriented Agile Manufacturing has been the main pattern for the 21-century enterprises, which aims at realizing flexibility and response to the changing market requirements as quick as possible. In the researches on agile manufacturing, how to make the resources structure (organization pattern of resources) and the control structure (scheduling method of resources) of enterprise's production system adapt to the market requirements quickly, high-efficiently and economically is the core to realize agile ideas. To Chinese manufacturing enterprises, most of them have had the hardware conditions to implement agile manufacturing. However, they still lack effective and proper solftware technologies to support resources organization, scheduling, control and etc. Therefore, to research resources structure and control structure in the level of enterprises'plants and their complex optimization problems from agile manufacturing viewpoint will be a powerful guaidunce and propulsion for Chinese manufacturing enterprises to further develop agile manufacturing and increase therir competitive abilities.On the basis of comparisons of the existing researches, the development trends of resources structure and control structure of production systems are analyzed and summarized. Furthermore, Virtul Production Systems (VPSs), which is proposed through combing the theories of new resources structures, are anticipated to have the potential research and application values. In order to increase control efficiency, real-time ability and stability of dynmic scheduling, and reduce changeover cost, on the basis of analysis on the existing researches about VPSs, an integrated system for supervisory control and scheduling of VPSs is proposed to establish on virtual space. It is charazterized by reconfiguration, robustness, self-adaption and cost-effectivity, and suitable for the environment of diverse variety and small batch size production.First, in order to improve the control efficiency of VPSs modeled by Petri Nets, a supervisory control and scheduling system based on autonomy and coordination is built for both controlling and scheduling VPSs and realized on the software platform of UPPAAL. The system mainly consists of the following parts: the reconfiguable DEDS model of VPSs which is built by using Automata and Formal Language method in combination with object-oriented technology and hierarchical ideas; the hybrid supervisory control framework which is then designed based on autonomy and coordination according to the logical (virtual) and physical characteristics of VPSs; and furthermore, the two-layer hybrid supervisory control structure which is established for VPSs based on autonomy and coordination by applying the feed-back supervisory control theory of automata and the network technology. On UPPAAL, the supervisory control and scheduling system based on autonomy and coordination is eventually implemented for VPSs by jointly using the timed automata (networks) theory and the designed close-loop control system of VPSs. In addition, deadlock-free analysis, and simulation of schedule optimization are made.Second, in order to overcome the limitation of the whole rescheduling in real-time ability, stablility and cost-effectivity of VPSs'dynamic scheduling, a self-adaptive dynamic scheduling expert system is proposed for VPSs by using local rescheduling method and developed on the software platform of CLIPS, an expert system platform. It is mainly composed of following parts. The basic framework of self-adaptive dynamic scheduling based on event-driven is built for VPSs according to its own characteristics. Furthermore, the contents of self-adaptive dynamic scheduling mechanism are systemically specified for VPSs. The modified heuristic rescheduling algorithm for affected operations is developed to act as the self-adaptive dynamic scheduling algorithm of VPSs. The self-adaptive dynamic scheduling expert system of VPSs is eventually built on CLIPS.Finally, an integrated system for supervisory control and scheduling of VPSs is established, which consists of the above two systems. A case study is made in a typical and complex FMS. In the case study, real-time supervisory control in normal situations and dynamic adjustment to schedule in unexpected situations are respectively made. The results show that the proposed approaches and developed system are feasibile and efficient.