Compositional Methods for the Control of Concurrent Timed Discrete-Event Systems

• Applicants: Professor Dr.-Ing. Thomas Moor; Professor Dr.-Ing. Jörg Raisch
• Subject Area: Automation, Mechatronics, Control Systems, Intelligent Technical Systems, Robotics
• Term: from 2019 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 412108828

The emergence of technological systems with more and more autonomous modes of operation and several communicating components brought the necessity of new approaches to their modeling and control in order to guarantee their correct behavior. Discrete-Event Systems are dynamical systems governed by asynchronous occurrences of events. Such systems are typically encountered in technological man made systems, such as automated transport systems, automated manufacturing, and logistics in general. These application areas have stimulated the development of supervisory control of DES. The term "supervisory Control" points to a control paradigm where the controller to be synthesized will disable certain events that may eventually lead to an unacceptable closed loop behavior, but will allow all other events. Referring to the multi-component structure of the typical target application, the main challenge in the synthesis of a supervisorycontroller is the exponential growth of the overall state set in terms of the number of components. This is addressed by compositional methods which avoid the explicit construction of an overall model. In their basic form, DES model the order of events and this is adequate to synthesise supervisor that guarantees safe operation of the system; e.g. for automated transport, a segment of a track shall only be used by one train at a time to be safe. However, for many applications performance explicitly relates to physical time; e.g. for automated transport, we are concerned about the overall throughput realised with all available trains and tracks. Here, the literature provides multiple modelling frameworks which differ in expressiveness. On the one end of the range, there are the Brandin-Wonham framework, which uses a global tick-event to represent the elapse of time, and there are timed events graphs (TEG), which are a specific type of Petri nets that translate to linear (max, +)-equations. For both frameworks, controller synthesis is well understood. However, being on the low end regarding expressiveness, both frameworks have severe limitations.With Brandin-Wonham, one cannot model concurrent system with multiple real-time clocks, and TEG cannot address logical decision making. In this research project, we will establish efficient methods for the control of timed DES that are more expressive than the Brandin-Wonham framework and TEG. Technically, we will consider so called (max, +)-automata and specific classes of timed Petri nets as base models, in order to develop modular and hierarchical approaches to supervisory control, including the respective synthesis algorithms. Our results will considerably enlarge the scope for model based controller synthesis of DES.

• DFG Programme: Research Grants
• International Connection: Czech Republic
• Partner Organisation: Czech Science Foundation
• Cooperation Partners: Dr. Jan Komenda; Dr. Tomas Masopust