Modeling and control of an industrial accumulator in a web transport system

This paper presents the study of an industrial accumulator (see figure 1) used in a web transport system. Different models based on physical laws have been built in order to understand the main characteristics of the accumulator and its behavior during transient phases. A mechanical equation is used for the calculation of the velocity of a roll and different approaches are tested to calculate the web tension due to roll traction. The selected approach uses an empirical law to express the web tension. This law is defined using the inverse transmissibility of the tension and the difference of velocities between consecutive rolls. This empirical law aims to respect the mechanical behavior of the accumulator, which is not realized in classical web transport modeling. The model obtained is non-linear and of high order. Moreover, in practice only one actuator is available to maintain the web tension approximately constant in the whole accumulator. Experiments and simulations show that the existing industrial PI control of the web tension is not satisfactory. The comparison of the PI control with a modern control strategy (H_∞ robust control) is presented. To improve the accumulator operation, new approaches are also suggested, such as modifying the input parameter or introducing a mechanical tension regulator.