Theoretical comparison of winding tension control methods

Several methods are used to control tension in the winding zone. The two most common methods use either a tension signal from a loadcell or a position signal from a dancer system. Both techniques control tension, however, the insertion of a dancer roll also affects the dynamics of the web transport line. The moving mass of the dancer roll and the fact that it can move add another degree of freedom to the system.The method used in this analysis to compare the two control techniques was the closed loop transfer function. Differences between the two systems can be clearly seen in the frequency domain. Two excitations were considered. The first was an upstream disturbance from the in-feed roll velocity. The second was a torque disturbance on the winding spindle. The output variables of interest were the winding tension and the package velocity. Two identical zones were analyzed.The closed loop transfer functions were obtained using an in-house, software program. Results showed that the loadcell system was better for low frequency disturbances because of the additional natural frequency created by the dancer roll. The dancer system provided better control in the mid-frequency range. Both systems were identical in the high frequency range because the dancer roll could not respond fast enough. The conclusion was that the successful use of a dancer system requires knowledge of the excitation frequencies and a good design for the dancer system