Fuzzy logic in a blackboard system for controlling plasma deposition processes

A blackboard system, ARBS, has been used to control a plasma processing unit, which is used for depositing coatings on the surface of electronic or mechanical components. Previous applications of ARBS have been based on crisp logic, but fuzzy logic was added in this study for plasma deposition control. Fuzzy rules have been introduced into ARBS without changing either the rule syntax or the existing inference engines, thereby demonstrating the flexibility of the software. Consequently crisp and fuzzy rules can coexist within a single knowledge source (i.e. module). An efficient technique for defuzzification has been employed in which the membership functions are replaced by Dirac delta functions. The technique is equivalent to standard methods of defuzzification, without loss of precision or accuracy, but with a reduced number of calculations. Multi-variable control of DC-bias (an electrical parameter) by automatic adjustment of pressure and RF (radio frequency) electrical power is demonstrated.