Dynamics of Web Tension Control with Velocity or Torque Control

Because of the transport of strain across rollers in a tension control system, the output from one tension control station is a disturbance to the next station. Tension disturbances are also transmitted upstream if frictional engagement between the web and the roller is inadequate or if velocity control of a driven roller between the spans is imperfect. Differential equations for process tension control are derived, simplified, and linearized. Tension control by means of torque control as well as velocity control of a roller or rewinding roll of material is examined, and the two methods are compared.