modeling

In roll-to-roll processes the presence of non-ideal elements, such us out-of-round or eccentric rollers is fairly common. Periodic oscillations in web tension and web velocity are observed because of the presence of such non-ideal elements. Models of web transport on rollers based on the ideal behavior of various machine elements are not able to reproduce these oscillations in model simulations but can only follow the average of the measured tension and velocity signals. In order to reproduce the tension oscillations the models have to be modified to include the mechanism that creates the oscillations.

Periodic oscillations in the tension signal are frequently observed in roll-to-roll manufacturing due to the presence of many rotating elements which are often non-ideal, such as out-of-round material or eccentric rolls. In certain situations the amplitude of the oscillations is large enough to affect normal operation of the web line. The proportional-integral-derivative (PID) feedback control algorithms that are commonly used for tension regulation do not have the dynamic complexity to compensate for such periodic disturbances. In this paper we investigate a two-degree-of-freedom controller which has two control actions, feedback and feedforward. The feedforward part is adaptive and is designed to provide control actions to compensate for periodic oscillations. Several issues must be considered when designing a control algorithm for the attenuation of periodic oscillations. First, since the control algorithm is executed in real-time using a real-time system which may have restrictions on the sampling period, the complexity of the algorithm must be such that the control action can be computed in a time period that is less than the sampling period, and the sampling period for most systems is typically in the range of tens of milliseconds. Second, it is desirable to have a feedforward algorithm that can be implemented in parallel with an existing feedback control scheme for tension and speed regulation without the need to retune and redesign the existing scheme. Further, it is desirable to have an algorithm that is understandable to practicing engineers who may have limited or no advanced controls background other than an undergraduate course in control systems. Considering the aforementioned issues, an adaptive feedforward (AFF) algorithm that can work in parallel to an existing feedback control systems is developed for control of web tension and to attenuate periodic oscillations. The essential ingredient of the AFF algorithm is the estimation of amplitude and phase of the periodic oscillations based on which a feedforward compensating control action is generated. The action of the AFF algorithm is such that retuning or redesign of the existing feedback controller is not required. Several different configurations of the AFF for different scenarios in terms of where to apply the feedforward action in the control system are investigated. Extensive experiments are conducted on a large web platform with different scenarios and by transporting two different web materials at various speeds. Results from these experiments are presented and discussed. Experimental results show the effectiveness of the proposed AFF algorithm to attenuate tension oscillations.

The process of manufacturing products using roll-to-roll (R2R) methods involves unwinding of thin, flexible material in rolled form into machinery for processing and winding of the processed material into a roll. This paper describes modeling and control of a rotating turret winder in the rewind section of a R2R printing press. Governing equations for web speed and web tension within the rewind section are described by taking into consideration the motion of the rotating turret winder. Data from production runs of an industrial R2R printing press are analyzed to determine web behavior during a wound roll change sequence accomplished by the rotating turret. Model simulations are conducted and data from these simulations are compared with typical data from production runs. The key challenges associated with controlling web speed and web tension in a rewind section containing a rotating turret winder are discussed along with recommendations for machine and control design to achieve improved regulation of process parameters.

In this paper, winding issues in an industrial R2R printing press using a rotating turret winder are investigated by utilizing a new mathematical model and data are collected during production runs. Production data and simulation results from the developed model are analyzed to identify the causes for tension disturbances that affect winding quality. Model simulations are conducted by incorporating production data as inputs to the model to gather insights into the effect of dynamic behavior of the rotating turret winder on winding web tension. The developed model captures the various dynamic events associated with the roll change operation with a rotating turret winder. Measured data are provided to support the results of this work in improving winding tension regulation during the roll change operation. The new model together with the analysis and recommendations provides a good framework for the development of model-based tension control schemes that can further improve winding tension regulation performance, and thereby improves wound roll quality.