Web tension control in an industrial accumulator

Abstract

This paper presents the study of an industrial accumulator used in a web transport system. In order to understand the main characteristics of the accumulator and the causes of problems appearing during transient phases, different models based on physical laws have been built.

Different approaches are tested to calculate the web tension between two rolls. The selected approach uses an empirical law to express the web tension as a function of the downstream span tension and the difference of velocities between consecutive rolls. The empirical law aims to respect the mechanical behavior and the tension and velocity conditions imposed at the entry and the exit of the accumulator, which is not realized in classical web transport modeling.

One actuator is available to maintain the web tension approximately constant in the whole accumulator during the accumulator descent. Experiments and simulations have permitted to show that the existing industrial PI control of the web tension is not very satisfactory. The comparison of the PI control with a multivariable control (H(infinity) robust control) is presented. To improve the accumulator operation, new approaches are suggested, such as modifying the input parameter or introducing a mechanical tension regulator.