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We introduce the notion of directed control, where a directed controller is one that selects at most one controllable event to be enabled at any instant. This is in contrast to supervisory control, where a supervisory controller enables a maximum allowable set of controllable events at any instant, i.e., no specific selection for executing an enabled event is made. While the design of a supervisory controller is meaningful for plants that are generator of controllable events, a directed controller design makes more sense for plants that are executor of controllable events. The control goal is the same as that in a supervisory control setting, namely, safety and nonblockingness. A safe and nonblocking directed controller exists if and only if a safe and nonblocking supervisory controller exists, thereby proving the polynomiality of verifying existence. We also develop a set of algorithms of polynomial complexity to compute a safe and nonblocking directed controller (whenever one exists).
Automation Science and Engineering, IEEE Transactions on (Volume:5 , Issue: 4 )
Date of Publication: Oct. 2008