Intelligent material handling: development and implementation of amatrix-based discrete-event controller

A supervisory controller for discrete-event (DE) systems is presented that uses a novel matrix formulation. This matrix formulation makes it possible to directly 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, the authors 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, USA. Then, they 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 LabVIEW and its simulation using MATLAB.