Model-Based Diagnostics for the Supervisory Control of Manufacturing Systems

R. A. Williams, B. Benhabib, and K. C. Smith

Because of their nondeterministic nature of behaviour, the supervisory control of manufacturing systems must be carried out in closed loop. This trait greatly increases the size and complexity of the Discrete-Event System (DES)-based supervisorycontrollers of manufacturing systems. Attempting to cope with this complexity, a Hybrid Supervisory Controller (HSC), that distributes operations between a DES-based supervisory controller, an alternate mechanism, and a diagnostic system, was developed. The implemented diagnostic system had to be able to detect multiple faults, be robust, as well as integrate well with the other elements of the HSC. A model-based method derived from the General Diagnostic Engine [de Kleer and Williams, 1989] utilizing set of models was developed and found to be suitable. Models are chosen and expectations of their predictions are adjusted according to the state of the equipment, the operations they are performing, and the location of parts.

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