Integrated identification and control for diffusion/CVD furnaces

Abstract

The paper describes an integrated approach for modeling and robust multivariable controller design, with application to temperature control of diffusion and CVD furnaces. The modeling relies on input-output data, collected in a preliminary identification experiment at the desired operating conditions. An important component of the identification is the computation of uncertainty bounds that describe the confidence limits of the model, in a manner consistent with robust control theory. The results of the identification are then used to design an H-infinity controller with a cascade, hierarchical structure. The final implementation of the controller also includes mechanisms to prevent integrator wind-up. Special emphasis is placed on automating the procedure-for classes of furnaces-so that, potentially, it can be used by nonexperts in the field. Implementations include several industrial furnaces. Experimental results demonstrate the success of the approach as well as a good agreement between predicted and actual closed-loop behavior.