Closed-loop disturbance identification and controller tuning for discrete manufacturing processes

A closed-loop identification procedure for pure gain-plus noise processes is presented for a family of disturbances that model drift in a discrete-part manufacturing system. Tuning techniques for the identified disturbance are provided for proportional integral (PI) controllers. These include the particular case of exponentially weighted moving average controllers, popular in semiconductor manufacturing. Expressions are derived for the mean squared deviation of the quality characteristic and for the variance of the adjustments. An optimization model is presented that balances adjustment variance with output variance. The optimal trade-off solution for a constrained PI controller is shown to depend on the assumption of no drift.