A backstepping-based control algorithm for multi-span roll-to-roll web system

Multi-layer printing technology is used wisely in printed electronics industry. The small variation of web tension will reduce the quality of production. Thus, web velocity and tension control algorithm play an important role in improving the quality of product in roll-to-roll manufacturing technology. Most algorithms of linearized systems proposed in recent years use PI or PID controllers. Due to the increasing demand of high accuracy in printed electronics industry at micrometer-level, it is necessary to have a precise control scheme of web velocity and tension in the presence of disturbance. In this paper, a mathematical model of modified strict form model is proposed, and a systematic design method of backstepping controller is formulating for this model by using the backstepping based design. By using the proposed theory, a precise control algorithm is proposed for three-span roll-to-roll web control system. The design parameters are chosen optimally by using the modified genetic algorithm. The outcomes of proposed algorithm prove the reliability throughout simulation results in Matlab/Simulink and experimental results.     

Fuzzy decoupling to reduce propagation of tension disturbances in roll-to-roll system

Control of web tension is crucial for maintaining quality of products processed on roll-to-roll (R2R) system. An R2R system can be divided into different tension spans which interact with each other. But converting industries tend to neglect these interactions and use decentralized single-input–single-output (SISO) control approaches to deal with tension control. Multi-input–multi-output approaches have been reported in literatures but are practically not in use. Interaction between the various tension spans is unavoidable as they are all connected by a single web. Disturbances produced in a span tend to travel further downstream along the direction of web travel. When the number of spans is less or the disturbance amplitudes are small, this does not present a big challenge and simple SISO control is sufficient. But when the amplitudes of disturbances produced in processing is large—as is the case with printed electronics—or the number of spans is large or both, then the interactions cannot be neglected. R2R-based offset printers have the potential for mass production of precision-printed electronics. In this paper, a fuzzy logic-based hybrid approach has been followed that specifically targets the printed electronics industry and this method considerably reduces the interactions. The algorithm has been designed such that it takes information from previous span to reduce the propagation of tension disturbances to the given span. This has been achieved through online computation of correlation coefficient and reducing the interaction through fuzzy feedback control.     

Steering guide-based lateral control for roll-to-roll printed electronics

This paper presents the lateral displacement control of a moving web using a steering guide system which can be an important part in roll-to-roll (R2R) printed electronics. In general, R2R systems in printed electronics need a long drying section for the reduction of time and cost by reducing the delay of drying time. However, the lateral web displacement can be a worse problem because the web should be affected by the air blow from the dryer. Therefore, the lateral position control of long span will play a significant role in the R2R production process for better product quality. In our work, PID control method is designed to control the lateral displacement of a moving web by using a steering guide system, and simulations and experiments were performed to test the method.     

Design of roll-to-roll printing equipment with multiple printing methods for multi-layer printing

In this paper, a novel design concept for roll-to-roll printing equipment used for manufacturing printed electronic devices by multi-layer printing is presented. The roll-to-roll printing system mainly consists of printing units for patterning the circuits, tension control components such as feeders, dancers, load cells, register measurement and control units, and the drying units. It has three printing units which allow switching among the gravure, gravure-offset, and flexo printing methods by changing the web path and the placements of the cylinders. Therefore, depending on the application devices and the corresponding inks used, each printing unit can be easily adjusted to the required printing method. The appropriate printing method can be chosen depending on the desired printing properties such as thickness, roughness, and printing quality. To provide an example of the application of the designed printing equipment, we present the results of printing tests showing the variations in the printing properties of the ink for different printing methods.     

Precision design and control of a flexure-based roll-to-roll printing system

This paper presents the design, characterization, and control of a flexure-based roll-to-roll (R2R) printing system that achieves nanometer level precision and repeatability. The R2R system includes an unwinding/rewinding module, a web guide mechanism, and a core positioning stage consisting of two monolithic compliant X–Y stages that control the position/force of the print roller. During the printing process, capacitance probes, eddy current sensors and load cells are used to monitor the displacements of the flexure stage and contact force in real time. Control strategies, including decoupling, PID, and cascade control, have been implemented to decouple the cross-axis and cross-stage motion coupling effect and improve the overall precision and dynamic performance. In actual printing processes, the contact force and roller position can be uniformly controlled within ±0.05 N and ±200 nm respectively across a 4 in. wide PET web. To demonstrate the performance, a positive microcontact printing (MCP) process is adapted to the R2R system, printing various fine metal patterns, e.g., optical gratings and electrodes, in a continuous fashion.     

Study on the web deformation in ink transfer process for R2R printing application

Web deformation occurring in the ink transfer process from the printing roller to the flexible web was investigated using a CFD technique for the application in roll-to-roll printed electronics. Analysis for the flow-structure interaction was conducted to assess the deflection and stress distributions of the web. To make the present analysis more relevant to the real printing system, both realistic geometric configuration and ink properties were set up using the information obtained from the typical roll-to-roll system. Fluid properties were found to influence to the shape of the transferred ink and the web deformation. As the line width becomes smaller than 100 microns, the appreciable distortion in the shape of the transferred ink occurred due to a relative importance of surface tension. Non-negligible web deflection occurs in all the cavity geometries considered in the present work but the ratio of the web deflection to the line width gets smaller as the printing pattern width becomes smaller. Thus, the surface and deflection will be important factors for the better printing quality under the 100 micron range.     

Cross direction register modeling and control in a multi-layer gravure printing

For the adaptation of the roll-to-roll printing method to printed electronics, it is mandatory to increase the resolution of the register control. Therefore, it is desired to derive a mathematical model for the register and to develop a controller to reduce register error. The mathematical model of cross direction register was derived considering both a lateral motion of a moving web and a transverse position of a printing roll. The proposed mathematical model could be used to improve the performance of the cross direction (CD) register controller in a large area, roll-to-roll printing machine. The mathematical model was validated by numerical simulations and experimental verifications in various operating conditions using a multi-layer direct gravure printing machine. The results showed that the proposed model was effective in predicting the CD register in multi-layer printing.     

Quality control with matching technology in roll to roll printed electronics

R2R (Roll to roll) printed electronics has been an attractive technology for the mass production. Therefore, many research works have been focused on an optimal flexible substrate, ink formulation, printing process, curing method for a conductive ink in printed electronics applications. However, they did not relate their analysis with the system parameters of R2R continuous printing systems. In this paper, it is found that a printed pattern geometric quality which affects functional quality of printed electronic device could be changed with respect to operating tension of bare substrate even if local optimized ink, substrate, and printing process were applied. Additionally, ink transfer mechanism for R2R printed electronics is analyzed regarding a dynamic surface energy of a bare substrate under a tension in R2R printing systems. With the aim of an efficient prediction of the thickness of R2R printed patterns for given operating conditions, a simple meta-model is developed by using the design of experiment (DOE) method. Also, the proposed meta-model has been verified by several experiments. Through the results, it is presented that how to find an optimal operating tension in R2R printed electronics for guaranteeing a required thickness of R2R printed patterns.     

Analysis on the ink transfer mechanism in R2R application

Ink transfer process from the printing roll to the web was investigated using a Computational Fluid Dynamics (CFD) technique for the roll-to-roll (R2R) printing application. A parametric study was conducted to identify the effects of fluid parameters such as viscosity, surface tension and contact angle. To make the present analysis more relevant to the real printing system, a three-dimensional computational configuration for the commercial software was set up using the information obtained from the typical R2R system. Simplified one-dimensional semi-analytic model based on Reynolds equation was compared with the CFD results to assess the validity of the results. Pressure distribution states that 1-D analysis is reasonably good in capturing the flow physics. The 3-D simulation with VOF (Volume of Fluid) shows that viscosity is the most important parameter. Moreover, the larger surface tension resulted in smaller amount of ink transfer.     

A study on the tension estimator by using register error in a printing section of roll to roll e-printing systems

The focus of this study is on the development of a mathematical model for estimating tension of a printing section by using the register error in R2R (Roll to Roll) e-Printing systems. In a printing section of conventional R2R printing systems, the tension is generally measured not for controlling but for monitoring, because the tension control may cause the occurrence of a register error. But, for high precision control, the tension in the R2R e-Printing system must be controlled as well as measured for more precise control of the register error. The tension can be measured by the loadcell in the conventional R2R systems. However, installing a loadcell on the R2R systems causes extra economic burden. In addition, the space for adding a loadcell on R2R systems is limited due to many components including dryers, lateral guider, doctor blade, ink supply unit and cooling unit. Therefore, a tension estimator can be another possibility for predicting the tension in a printing section. In this study, a new tension estimation model is proposed. The proposed model is based on the register error model, the equivalent torque equation, and the tension model considering tension transfer. Numerical simulations and experimental results showed that the proposed model was effective in estimating the tension in a printing section. This paper was recommended for publication in revised form by Associate Editor Hong Hee Yoo Chang-Woo Lee received a B.S. degree in Mechanical Engineering from Konkuk University in 2001. He received his M.S. and Ph.D. degrees from Konkuk university in 2003 and 2008, respectively. Dr. Lee is currently a researcher at the Flexible Display Roll to Roll Research Center at Konkuk University in Seoul, Korea. Dr. Lee’s research interests are in the area of fault tolerant control, R2R e-Printing line design, and tension-register control. He is the holder of several patents related to R2R e-Printing system. Jang-Won Lee received the B.S. and M.S.degrees in mechanical engineering from Konkuk University, Seoul, Korea. He studied continuous flexible process at the FDRC (Flexible Display R2R Research Center, Project Director: Kee-Hyun Shin), as a reseacher from the concentment to 2008. Since 2008, he has been a Research Engineer with the SKC Films R&D, Suwon, Gyeonggi-do, Korea. Now he is great on the plastic flim mechanics such as a scratch on the film surface, film extruding, winding/slitting mecha-nism and coating processes. Hyunkyoo Kang received the B.S. and M.S degree in 2000 and 2003 res-pectively from Konkuk Uni-versity, Seoul, Korea, where he is currently working toward the Ph. D. degree in mechanical design. He took part in the development of an autoalign guiding system for high-speed winding in a cable winding system, a 3-D roll-shape diagnosis method in a steel rolling system, a design of register controller for high-speed converting machine and real-time control design of electronic printing machine. His research topics include register modeling and control for printed electronics and distributed real-time control. Kee-Hyun Shin received the B.S. degree from Seoul National University, Seoul, Korea, and the M.S. and Ph.D. degrees in mechanical engineering from Oklahoma State University (OSU), Stillwater. Since 1992, he has been a Professor with the Department of Mechanical and Aerospace Engineering, Konkuk University, Seoul, Korea. For more than 18 years, he has covered several research topics in the area of web handling, including tension control, lateral dynamics, diagnosis of defect rolls/rollers, and fault-tolerant realtime control in the Flexible Display Roll-to-Roll Research Center, Konkuk University, of which he has also been a Director. He is the author of Tension Control (TAPPI Press, 2000) and is the holder of several patents related to R2R e-Printing system.     

Advanced technique for achieving 10-μm-width fine lines in roll-to-roll continuous gravure printing

In roll-to-roll continuous printing, given the limitations in the pattern engraving technique and the need for accurate contact angle control between the ink and substrate, printing fine lines in the 10-μm scale is a major hurdle that needs to be addressed to achieve mass production of printed electronic devices. To address this issue, we propose a novel printing method based on gradation engraving; this method allows for both greater control over the width decrement of printed patterns as well as narrower fine lines than those achieved using an engraved pattern in the printing roll. Our experimental results show that, using the proposed method, printed line widths could be decreased according to the curvature of the sidewall of the engraved cell, even in the same aspect ratio. Furthermore, the width of the printed pattern was decreased by up to 62%, as compared to that achieved via the engraved cell, and a fine printed line narrower than 10-μm could be achieved. The proposed method represents a suitable alternative for the fabrication of 10-μm, or even thinner, fine conductive lines via the roll-to-roll continuous printing process.     

Effect of roll patterns on the Ink transfer in R2R printing process

Ink transfer process from the printing roller to the web was investigated using a CFD technique for the roll-to-roll printing applications. A parametric study was conducted to identify the effects of roll pattern geometry on the ink transfer process. In order to make the present analysis more relevant to the real printing system, 3-D computational configuration was set up using the information obtained from the typical roll-to-roll system. Simplified one-dimensional semi-analytic analysis based on Reynolds equation was also conducted in order to assess the validity of the 3-D CFD results. Pressure information suggests that even a simplified 1-D analysis is reasonably good in capturing the relevant flow physics. 3-D simulation shows that the quality of the ink transfer process is very sensitive to the width of the roll patterns. This sensitivity is believed to be due to the relative importance of surface tension over any other force modes under the 100 micrometer range.     

Design of a precision multi-layer roll-to-roll printing system

Roll-to-roll (R2R) printing technologies have been widely adopted in a variety of engineering fields, e.g., organic photovoltaics and flexible electronics, owing to the advantages of cost and throughput. Although a minimum feature size of 100 nm has been demonstrated on R2R systems, the layer to layer registration accuracy (i.e., overlay accuracy) still remains as low as tens of microns, which prevents the fabrication of common electronic and functional devices, such as transistors. To realize the full potential of R2R technologies, the registration accuracy must be improved to match the printing resolution, i.e., 100s nm. To address the issue, we have developed a multi-layer R2R system with multiple-input multiple-output (MIMO) closed-loop control that achieves submicron level alignment precision for large-scale continuous printing processes. The enabling elements in the multi-layer R2R system include: (1) new vision-based alignment algorithm/method, which provides 100s nm position detection capability based on low-cost cameras; and (2) custom-built five-axis compliant roller positioner. Experimental results show that the compliant roller positioner has a ±1 mm range with 100s nm precision in X, Y, and Z axes respectively. For correcting in-plane web errors, the roller positioner can achieve a range of 1 mm with < 1 μm precision, realizing multi-layer R2R printing with submicron overlay accuracy. Based on the new methods, a gate/source-drain multi-layer electrode structure for field-effect transistors (FETs) has been designed and fabricated on a 4-inch PET web, demonstrating better than 1 μm overlay precision in fabricating flexible electronics on a R2R platform for the first time.     

A study on tension behavior considering thermal effects in roll-to-roll E-printing

The mathematical model for tension in a moving web by Shin [1] was extended by considering thermal strain due to temperature fluctuations in the drying of a roll-to-roll system. The extended model describes variations in tension and includes terms that represent the change of the Young’s Modulus, the thermal coefficient, and the thermal strain. In this paper, a new control scheme based on the extended model is proposed for mitigation of tension disturbances due to thermal strain in the drying process. Tension feedback control logic generally is not be applied due to the fact that register errors can be induced by speed alterations that help to compensate for tension disturbances. But in our approach, the thermal strain in the web is compensated for by means of velocity adjustments without adding extra register errors in the steady state. A computer simulation followed by an experimental validation was carried out to confirm the performance of the proposed method. The results show that the proposed model is useful for describing tension behavior and suggest that tension control logic improves control precision for the drying module of a roll-to-roll e-printing system.     

A precision desktop plate-to-roll apparatus for development of advanced flexographic printing processes

Flexographic printing, which involves high-speed contact of an inked stamp against a substrate, is of increasing interest for scalable manufacturing of electronics in new formats. However, the adaptation of flexography to thinner, finer features which are generally required for printed electronics requires improved understanding of stamp-substrate contact mechanics. Here, we present a desktop plate-to-roll (P2R) printing apparatus which enables the study of flexographic printing in a semi-continuous format that mimics industrial printing. In particular, we tailor the specifications of the machine to use nanoporous stamps which have been shown to enable flexographic printing of ultrathin ink features with micron-scale linewidth. Printing with nanoporous stamps requires precise control of stamp-substrate contact force (2–250 mN) and elimination of shear force at the interface among others; these are accomplished using a flexure-supported substrate, and by coordinated rotary-linear motion of the system. We detail the design and evaluation of the P2R machine and demonstrate printing of high-resolution features (<3 μm line width) with nanoporous stamps at speeds of up to 0.2 m/s.     

三相三线制有源滤波器的运行特性研究

随着电力电子技术、控制理论、数字信号处理（DSP）技术的发展,有源电力滤波器（APF）逐渐取代传统的无源滤波器。成为低压配电系统的电能质量治理的首选方案。本文研究了三相三线制有源滤波器在三相三线、三相四线系统中的运行特性。以及对平衡负荷、不平衡负荷的补偿性能。动态模拟实验结果表明,三相三线制有源滤波器对三相三线负荷的谐波电流具有很好的补偿效果。而对于三相四线平衡负荷、三相四线不平衡负荷的补偿能力较差。甚至对电网还会产生额外的谐波注入。使公共点电能质量进一步恶化。     

卷到卷制造中基板横向振动研究进展

运动基板的横向振动问题已经成为严重限制卷到卷制造效率和质量的关键。详细介绍了卷到卷制造中运动基板横向振动问题的研究概况。讨论了运动基板横向振动的建模方法,以Hamilton原则为例,推导了基板横向振动的控制方程,结合解析求解和数值求解方法,计算横向振动的频率和模态。分析了基板张力、速度、材料特性、中间支撑和外界环境等因素对基板自由振动特性及动态稳定性的影响。研究了基板参数振动特性,考虑基板张力和速度两个主要参数的波动,阐述了基板横向振动被动控制和主动控制方法。联合基板纵向张力控制和侧向纠偏控制,讨论了横向振动控制在卷到卷制造中的工程应用。最后,展望卷到卷制造工程应用中基板横向振动研究的关键问题。     

Decentralized coordinated control of elastic web winding systems without tension sensor

In elastic web winding systems, precise regulation of web tension in each span is critical to ensure final product quality, and to achieve low cost by reducing the occurrence of web break or fold. Generally, web winding systems use load cells or swing rolls as tension sensors, which add cost, reduce system reliability and increase the difficulty of control. In this paper, a decentralized coordinated control scheme with tension observers is designed for a three-motor web-winding system. First, two tension observers are proposed to estimate the unwinding and winding tension. The designed observers consider the essential dynamic, radius, and inertial variation effects and only require the modest computational effort. Then, using the estimated tensions as feedback signals, a robust decentralized coordinated controller is adopted to reduce the interaction between subsystems. Asymptotic stabilities of the observer error dynamics and the closed-loop winding systems are demonstrated via Lyapunov stability theory. The observer gains and the controller gains can be obtained by solving matrix inequalities. Finally, some simulations and experiments are performed on a paper winding setup to test the performance of the designed observers and the observer-base DCC method, respectively.     

Design and implementation of adaptive PI control schemes for web tension control in roll-to-roll (R2R) manufacturing

In this paper, two adaptive Proportional-Integral (PI) control schemes are designed and discussed for control of web tension in Roll-to-Roll (R2R) manufacturing systems. R2R systems are used to transport continuous materials (called webs) on rollers from the unwind roll to the rewind roll. Maintaining web tension at the desired value is critical to many R2R processes such as printing, coating, lamination, etc. Existing fixed gain PI tension control schemes currently used in industrial practice require extensive tuning and do not provide the desired performance for changing operating conditions and material properties. The first adaptive PI scheme utilizes the model reference approach where the controller gains are estimated based on matching of the actual closed-loop tension control systems with an appropriately chosen reference model. The second adaptive PI scheme utilizes the indirect adaptive control approach together with relay feedback technique to automatically initialize the adaptive PI gains. These adaptive tension control schemes can be implemented on any R2R manufacturing system. The key features of the two adaptive schemes is that their designs are simple for practicing engineers, easy to implement in real-time, and automate the tuning process. Extensive experiments are conducted on a large experimental R2R machine which mimics many features of an industrial R2R machine. These experiments include trials with two different polymer webs and a variety of operating conditions. Implementation guidelines are provided for both adaptive schemes. Experimental results comparing the two adaptive schemes and a fixed gain PI tension control scheme used in industrial practice are provided and discussed.     

周期性扰动下卷绕基板的横向位移控制

柔性基板的横向位移控制是卷到卷（roll-to-roll）系统中的关键技术之一,横向偏移会导致定位误差、收卷不齐,直接影响成品的质量。针对卷绕过程中辊筒的旋转偏心造成的基板横向位置上的周期性干扰,提出将插入式重复控制器应用于柔性基板的横向位移控制。该方法不需要改变原有控制器的结构,只需在其之前增加一个重复控制器环节,即能实现对任意周期信号或干扰的高精度跟踪或抑制。仿真实验结果表明,插入式重复控制算法相比单纯PID控制能显著提高系统对辊筒偏心引起的横向周期性干扰的抑制能力,提高系统的稳态精度,具有良好的鲁棒性。