Servomechanism controller design of web handling systems

In traditional web handling processes, web tension and speed are typically controlled assuming that the web system consists of a number of single-input-single-output systems. This assumption often results in large interactions occurring in the closed-loop system between the control loops and, hence, results in high-quality control being difficult to achieve. In this paper, the control of the web handling processes is treated as a multivariable servomechanism problem. Two types of controller design, the "perfect control servomechanism controller" and the "tuning regulator", are studied and implemented on an industrial web machine. The experimental results obtained show that these controllers provide excellent tension and speed response compared with conventional controllers used in web systems. In particular, it is shown that the "tuning regulator" approach is only marginally worse than the "perfect control servomechanism controller" approach, despite the fact that it does not require a mathematical model of the web process, and is simpler to implement.