چارچوب شبیه سازی شی گرا برای کنترل زمان واقعی سیستم های تولید انعطاف پذیر خودکار

This paper describes an object-oriented simulation approach for the design of a flexible manufacturing system that allows the implementation of control logic during the system design phase. The object-oriented design approach is built around the formal theory of supervisory control based on Finite Automata. The formalism is used to capture inter-object relationships that are difficult to identify in the object-oriented design approach. The system resources are modeled as object classes based on the events that have to be monitored for real-time control. Real-time control issues including deadlock resolution, resource failures in various modes of operation and recovery from failures while sustaining desirable logical system properties are integrated into the logical design for simulating the supervisory controller.

Performance evaluation of discrete parts manufacturing plant design is quite difficult and has to date been tractable mostly through simulation models. Current commercial software for the simulation of manufacturing system designs does not incorporate models of the sensory data collection and electronic control systems that will eventually drive the operation of the factory that the simulation is modeling. This leaves the control system design architecture as a separate design task to be performed later. Consequently, the impact of the control system on system performance is evaluated after the construction of the plant. Integration of control system design into plant simulation models requires modeling the plant in terms of events that will have to be monitored, recorded, and used for control. In principle, the software used to control the simulated factory operations could also be used to drive the operations of the actual factory after it is constructed. The traditional hierarchical decomposition approach to the design and control of manufacturing systems includes the strategic level (initial design) at the top, followed by the tactical (system configuration) and operational levels (part dispatching) towards the bottom. The control systems as they are referred to in this paper, reside below the operational decisions layer and deal with real-time control of the manufacturing system, which includes deadlock resolution and recovery from resource failures.

Integration of control requirements into plant simulation models requires modeling the plant in terms of events that have to be monitored, recorded, and used for control. In this paper we describe an object-oriented approach to the design of flexible manufacturing system simulation that allow the implementation of control logic during the system design phase. The object-oriented design approach is structured around formal supervisory control theory. While object-oriented design approaches have several advantages for software development, especially in specifying intra-object relationships, the interactions between objects in a complex system are difficult to capture. The formalisms in supervisory control theory are utilized to capture and implement these inter-object interactions. We have described a design platform that allows a design engineer to design and evaluate the impact of different control programs on factory performance. Important contributions of this work are: (1) the development of an extendable object-oriented manufacturing system simulation framework, (2) the design of simulation objects that properly communicate state information and service requests to a supervisory controller, (3) the design of a supervisory control object model based on formal methods that can service a range of flexible manufacturing systems, and (4) addresses subtle implementation issues such as dynamic routing flexibility, deadlock resolution, use of PLCs and diagnostic procedures in repairs allowing the simulated control code to be used as a real-time supervisory controller for the actual system. Complementary to and different from other proposed object-oriented manufacturing system simulations in the literature, the implementation of simulation logic that incorporates a range of realistic resource failures and failure recovery procedures while sustaining desirable logical properties of the system such as deadlock-freeness and proper termination is a novel contribution