Experimental study of winding zone dynamics

The elastic nature of plastic films and the rotational inertia of rolls, spindles and drives cause a film handling line to exhibit the characteristics of a dynamic system. This dynamic response can be observed by measuring on-line variables such as tension, roll velocity or dancer motion. Because of the dynamic behavior, a variety of control systems are employed to keep tensions and velocities in bounds. For purpose of control and isolation, a film line is divided into separate zones. One of the most difficult zones to control is the winding zone.This paper describes an experimental study conducted on an existing film line where the winding zone was experiencing large tension variations at certain speeds. An experimental technique was developed to measure the natural frequency of the zone. The natural frequency was found to vary with package diameter and film thickness. Using FFT analysis on the winding tension signal, the resonant excitation was identified as the winding spindle frequency. A computer model was used to predict the transfer functions and natural frequencies for the zone. Very good agreement was obtained between the predicted and measured natural frequencies.In addition to explaining the source of the large tension variations during winding, this study also provided a better understanding of the dynamics of a winding zone and the possibilities for resonant conditions. With these tools, alternate solutions to the problem could be evaluated