A deadlock avoidance supervisory controller for Discrete Event (DE) Systems is implemented. The DE controller uses a novel rule-based matrix dispatching formulation (US patent received). This matrix formulation makes it direct to write down the DE controller from standard manufacturing tools such as the bill of materials or the assembly tree. It is shown that the DE controller’s matrix form equations plus the Petri Net marking transition equation together provide a complete dynamical description of DE systems. Deadlock-free dispatching rules are derived by performing circular wait analysis (CW) for possible deadlock situations. We analyze the so-called critical siphons, certain critical subsystems and resources to develop a DE controller that guaranties deadlock-free dispatching by limiting the work-in-progress in the critical subsystems associated with each CW. This is the least-restrictive dispatching policy that avoids deadlock. The deadlock-free dispatching rules are implemented by the DE controller on a three-robot, two machine reentrant flow line, the Intelligent Material Handling cell at the Automation and Robotics Research Institute of UTA. Technical information given includes the development of the deadlock-free controller in LabVIEW®.
A supervisory controller for discrete-event (DE) systems is presented that uses a novel matrix formulation. This matrix formulation makes it direct to write down the DE controller from standard manufacturing tools such as the bill of materials or the assembly tree. The matrices also make it straightforward to actually implement the DE controller on a manufacturing workcell for sequencing the jobs and assigning the resources. It is shown that the DE controller equations plus the Petri net marking transition equation together provide a complete dynamical description of a DE system. This means that a computer simulation can be performed to check the DE performance of the controller before it is implemented. In this paper, we implement the DE controller on an actual three-robot intelligent material handling cell at the Automation and Robotics Research Institute, University of Texas at Arlington. Then, we show that the actual implementation and the simulated system give commensurate results. The versatility of the system developed with this DE controller permits implementing different methodologies for conflict resolution, as well as optimization of the resource assignment and part throughput. Technical information given includes the development of the controller in Lab-VIEW and its simulation using MATLAB.
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