CONTROL OF ALUMINUM ROLLING MILLS

Abstract

The aluminum rolling mills suffer from the presence of large time-delay-to-time-constant ratios. Conventional proportional–integral–derivative (PID) controllers and their variants do not provide adequate performance when used to control these types of processes. Advanced control strategies are needed. The Smith predictor (SP) is a relatively simple control scheme that is used for time delay compensation. In this paper, the SP has been used to control a rolling mill, and its performance has been compared with that obtained from a conventional proportional plus integral (PI) controller. In addition, the sensitivity of the SP to modeling errors and changing plant conditions was investigated. As expected, it was found that, for the perfect model case, the SP provides superior performance as compared to the classical PI. The superiority of the SP is maintained as long as the modeling errors are not too large. The PI algorithm is much more robust than the SP control scheme.

Keywords:

• Aluminum processing
• Control of thickness
• PID control
• Rolling mill
• Smith predictor
• Time delay

Acknowledgments