Hierarchical interface-based supervisory control of a flexible manufacturing system

Flexible manufacturing systems have long been touted as an application area for supervisory control theory. Unfortunately, due to the typical exponential growth of state space with the number of interacting subsystems, concurrent systems such as manufacturing applications have, for the most part, remained beyond the reach of existing supervisory control theory tools. This paper demonstrates how, by imposing a hierarchical, modular, interface-based architecture on the system, significant gains can be made in the size of applications that can be handled by supervisory control theory. We first review hierarchical interface-based supervisory control, providing the theory necessary to motivate the creation of well-defined automata-based interfaces between components. This architecture permits the verification of global safety (controllability) and nonblocking properties to be decomposed into a set of local checks, each of which only involves an individual component subsystem and its interface automata. The paper then provides a detailed description of how the theory can be applied to the design and verification of a flexible manufacturing system work cell. The work cell model is based on the Atelier Intere´tablissement de Productique flexible manufacturing workcell, a system that has been previously studied in the literature with limited success.