Regulating web tension in tape systems with time-varying radii

A tape system is time-varying as tape winds from one reel to the other. The variations in reel radii consist of two components: the nominal reel radii change due to tape winding and the reel eccentricities as a result of non-circular reels. These variations introduce disturbances in the tape tension. This paper presents a feedforward control that addresses the time-varying reel radius to regulate the tension. The algorithm is based on the fact that the change of the nominal radius is slow and hence the nominal plant in two consecutive revolutions can be considered as the same. The reel eccentricity disturbance is then repetitive in these two revolutions. We investigate the tension error in the previous revolution and calculate the compensation input that should have cancelled it. The compensation input is interpolated properly and then fed forward to the system in the current revolution. A new compensation input sequence is computed for the immediately following revolution. This computation pattern continues until the end of the tape winding process. Simulation results demonstrate and compare the performance of the proposed algorithm with other recently developed methods.