Web tension regulators - control heuristics

Abstract

Classical Control Theory using closed-loop controllers has been applied to drives for web handling beginning in the 1940's. Back then the mathematics was ahead of the tools for analysis as well as the modeling and the drive control equipment available. Nevertheless, using frequency domain analysis such as Bode Plots, and well thought out heuristics, strategies were developed for web tension control that were successful in developing the web handling drive systems at that time and continuing to the present. The control strategy heuristics developed in the 1940's are still in widespread use today although with newer equipment. It may be that these heuristics are so ingrained, that first principles are being forgotten or ignored.

Newer drives, controllers and tension measurement have resulted in drive systems with better specifications, but improvements in tension control may not be evident. Modern Control Theory state-space controllers are now available, but must be implemented in ways that do not ignore the web tension control strategies developed over the past 60 years. At a minimum, we expect new controllers will provide improved performance over classical controllers. This paper documents the classical heuristics developed for and used in drive systems for web handling machinery. It will discuss some practical concerns of implementing modern tension control algorithms in the web handling industry. These concerns include engineering and commissioning of the web tension control.