FUZZY-LOGIC IN A BLACKBOARD SYSTEM FOR CONTROLLING PLASMA DEPOSITION PROCESSES

A blackboard system, ARBS, has been used to control a plasma processin g unit, which is used for depositing coatings on the surface of electr onic or mechanical components. Previous applications of ARBS have been based on crisp logic, but fuzzy logic was added in this study for pla sma deposition control. Fuzzy rules have been introduced into ARBS wit hout 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 employ ed in which the membership functions are replaced by Dirac delta funct ions. The technique is equivalent to standard methods of defuzzificati on, without loss of precision or accuracy, but with a reduced number o f calculations. Multi-variable control of DC-bias (an electrical param eter) by automatic adjustment of pressure and RF (radio frequency) ele ctrical power is demonstrated. (C) 1998 Elsevier Science Limited. All rights reserved.