Model-based control of lateral web behavior - An interconnection of two web guiding systems within packaging machinery

Abstract

Within packaging industry mostly web materials are used to form bags or similar shaped packages. In order to professionally convert these materials and achieving increasing quality requirements of bags, detailed knowledge of lateral web dynamics is mandatory. One major problem of vertical form fill and seal machines is accuracy of the lateral web positioning process of multi-layer webs. To obtain a high quality bag with minor visibility of inner web layer, positioning accuracy has to be ±0.5 mm. Due to different converting steps within a vertical form fill and seal machine and necessity of positioning for each step, more than one web guiding system is required. This leads to the major problem, which is solved within this paper: the combination of two web guiding systems within a vertical form fill and seal machine.

First of all, this paper shows some of the most important milestones within research work of lateral web dynamics presenting the current state of the art. A special approach of hybrid modeling the lateral web behavior is established as well. Thus, a hybrid model of a rotating frame system can be introduced. Direct use of the model within a machine control leads to the hybrid modeling approach. Measurements and simulation results are matching with less than ±0.5 mm difference.

After introducing the hybrid modeling approach of a rotating frame system, interconnection strategies of a lateral moveable web roll system and the mentioned rotating frame system are given. To reach the target of combining these systems with the mentioned positioning accuracy and usability of a certain controller directly on a machine control unit, different types of controllers are developed and evaluated. A PID-controller analyzed firstly in this paper shows good results but doesn't achieve the target accuracy. The next investigated controller is a model-based control algorithm. This uses the simulated lateral web behavior, induced by the lateral movable web role, to predict and calculate the needed movement of rotating frame system in order to e.g. compensate the movement. With this method, results in the needed accuracy range are achieved and assured by measurements. However, the issue of exceeding the accuracy level due to differences between simulated and real web behavior still exists.

A controller containing a tuned PID-controller and a model-based control algorithm is investigated at the end of this paper via a simulation and achieves the accuracy range of ±0.5 mm despite of high position differences between simulated and real web behavior. Summarized, the paper presents simulation and control methods of lateral web behavior, which can be directly computed and used on a machine control unit with very good results.