Disturbance Rejection in Parameter-Varying Web-Winding Systems

We propose a control scheme to reject disturbances in web tension that are caused by reel eccentricities in parameter-varying web-winding systems. When the web winds from one reel to the other, the nominal reel radii vary. In addition to this, the reels are not perfectly circular and the eccentricities introduce disturbances to the tension output. If the web is thin enough, in a certain time span, the nominal reel radii can be considered as constants and the reel eccentricities are periodic. In our design, the entire web winding process in which the whole pack of web winds from a full source reel to an empty take-up reel is investigated at a certain number of operating points. At each operating point, an adaptive controller that synthesizes the inverse input whose system response cancels the disturbances is developed. Gain-scheduling control is then used between different operating points. The scheme is simulated on a decoupled tension loop of an example reel-to-reel web-winding system that represents a digital tape system.