New results on the nonconflict test of modular supervisors

This paper presents new contributions on the use of abstractions in modular control of discrete event systems. First, a new strategy, named WoT, is proposed for the construction of abstractions for the nonconflict test of local modular supervisors. Second, an efficient computational tool is presented for the problem of verifying if given abstractions of modular supervisors satisfy the so-called observer property (OP); the OP property plays an important role in the validity of the nonconflict test over abstractions. Third, this new computational tool is used to validate the WoT strategy in the context of a case study of a comprehensive manufacturing example. It is shown that the conflict is efficiently detected when solving a supervisory control problem for the manufacturing cell using local modular control. Then, a conflict resolution scheme is proposed and a nonconflicting solution is efficiently found.