registration

Control of print quality (registration) in roll-to-roll (R2R) printing is challenging because of the presence of transport delays involved in the printing process. In this work we present a delay-independent state feedback control design to stabilize a R2R printing press by considering all the significant dynamics involved in the printing process. State feedback control design using past state measurements (controllers with memory) are discussed first. Since controllers with memory are less desirable in industrial applications, we investigate and discuss the feasibility of designing a simple, memoryless, delay-independent state feedback controller for printing applications. The feasibility is shown by the use of a control design procedure that exploits the structure information in the system matrix to find a stabilizing controller. The design procedure is also extended to other common industrial R2R control strategies, such as decentralized control and state feedback with integral action for R2R printing applications.

Roll-to-roll (R2R) machines have been extensively used to manufacture a wide variety of consumer products, such as paper, plastics, textile, etc. R2R machines facilitate continuous processing of materials with minimal stoppage time and provide significant improvement in productivity over batch manufacturing. With recent advances in technology it is now possible to manufacture flexible electronics, flexible digital displays, solar films, etc., using R2R processing. R2R processing of flexible electronics requires better understanding of machine and process dynamics to achieve tight tolerances required in their manufacturing. One of the conventional R2R processes that is critical to enable R2R processing of flexible electronics is printing. In this paper, machine and process dynamics for R2R printing are studied in detail. Specifically two control configurations, depending on the type of control input, are analyzed; a compensator based registration control strategy (CRC) typically used with mechanical line shafts (MLS) and a print cylinder angular position based registration control (PARC) strategy used typically with electronic line shafts (ELS), are compared. A comparison of these strategies is given based on a dynamic model for the print section, which includes governing equations for strain in the material, print cylinder velocities, and registration error (a metric that quantifies print quality). An interaction metric is used to analyze interaction of key process variables between print units. Model simulations are conducted for different scenarios to evaluate the strategies. Results of the model simulations are presented and discussed.

Roll-to-roll (R2R) printing is a continuous process in which thin flexible materials such as paper are passed through a printing press to print the required pattern onto the material. Each printing press may have several printing units depending on the number of colors to be printed and the complexity of the pattern. The flexible material, often referred to as a “web,” is passed successively through each print unit to create a multicolor pattern. Print registration is the process of overlapping successive printed patterns to form a complex multicolor pattern and the registration error is the position misalignment in the overlapped patterns. This paper develops a machine direction print registration model in a printing press with multiple print units whose print cylinders are driven using mechanical line shafts. The registration model considers the effects of interaction between adjacent print units due to variations in material strain and machine dynamics, including various dynamic elements, such as the print cylinder, doctor blade assembly, print unit compensator roller, print unit motor, friction at various locations, etc. Measured data from typical production runs on an industrial printing press are used to corroborate the developed print registration model. Mechanical design and control design recommendations to reduce registration error in print units are also provided. The developed registration model is applicable to many R2R printing technologies, such as offset, flexo, and rotogravure printing.