Modeling and Register Control of the Speed-Up Phase in Roll-to-Roll Printing Systems

High precision register controls are indispensable in roll-to-roll (R2R) printing systems for mass manufacturing. In R2R printing systems, each gravure cylinder is driven by an individual motor and guiding rolls distributed between two adjacent gravure cylinders are driven by the tension of their wrapped web. In the speed-up phase, tension fluctuations caused by torque balance of guiding rolls generate register errors in each printing unit. Therefore, it is a challenging issue to design a control method to reduce the register errors. In this paper, a mechanical model of R2R printing systems in the speed-up phase is developed based on the principle of mass conservation and torque balance. A model-based feed-forward proportion-derivative controller is designed to reduce the register errors caused by the tension fluctuations. The validity of the proposed method is demonstrated by simulation and experiments carried out on an industrial rotogravure printing press. A comparison with other control methods especially a well-tuned proportion differential control which is widely adopted by printing presses shows that the absolute maximum register error is drastically reduced and the average register error is greatly decreased by the proposed method. The results verify the effectiveness and feasibility of the proposed control method. Note to Practitioners-This paper presents control strategy for the speed-up phase in R2R printing system, particularly for printing systems with electronic line shafts. Few existing systematic research is relevant with the speed-up phase in the R2R printing system. This paper analyses the relationship of the register error and the web tension fluctuations between two adjacent gravure cylinders which are driven by the guiding rolls, then proposes the control strategy based on the identification of the acceleration of guiding rolls. The proposed method can be extended to other similar R2R systems. Simulation and industrial experiments suggest that the control method is feasible and has superior performance compared with the existing methods. In the future research, we will study the adaptive model representing the acceleration of guiding rolls in different R2R web systems.