Design and implementation of adaptive PI control schemes for web tension control in roll-to-roll (R2R) manufacturing Pramod R. Raul, Prabhakar R. Pagilla n Mechanical & Aerospace Engineering, Oklahoma State University, Stillwater, OK 74078, United States article info Article history: Received 4 April 2014 Received in revised form 28 October 2014 Accepted 30 November 2014 This paper was recommended for publica- tion by Dr. Didier Theilliol Keywords: Adaptive control Roll-to-roll manufacturing PI control Web tension Relay feedback technique Web handling systems abstract 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. & 2014 ISA. Published by Elsevier Ltd. All rights reserved. 1. Introduction In Roll-to-Roll (R2R) manufacturing of continuous materials, control of web tension is critical during transport of the materials through many processes such as printing, coating, and lamination. It plays an important role in ensuring the quality of the finished web products. During transport, many processes may require transport under different operating speeds and heating/cooling of the webs. Further, there are many process and machine induced disturbances which the tension control systems must compensate to achieve a good tension regulation performance. Tension varia- tions cause a variety of product defects. For example, high web tension may result in wrinkles and tears while low tension may cause web slack, loss of traction on rollers during transport, and difficulty in guiding the webs on rollers. The consolidated effect of large web tension variations may result in disruption in produc- tion, diminishing product quality, and machine hardware damage. Industrial web tension control systems typically employ a fixed gain PI controller. The PI controller gains are tuned to give a stable response for a given operating condition and material. This is typically done empirically on the machine because analytical tuning of PI controllers is a challenging task due to changing operating conditions and uncertainty in the knowledge of web material parameters and machine parameters. In practice, the PI tension controllers are tuned on-site based on real-time observation of the tension response performance. When operating conditions or material properties change, the fixed gain PI tension controllers do not provide adequate performance or in some cases render the closed-loop tension control system unstable. The better approach is to use an adaptive control scheme that facilitates the adjustment of controller parameters for such changing conditions. An adaptive controller can modify closed-loop system behavior by compensat- ing for the changes in system parameters. There are many approaches to design adaptive control schemes, such as gain scheduling, self-tuning regulators, and model reference adaptive control [1,2,8,13]. The direct and indirect adaptive schemes are promising but the design and implementation of those controllers are cumbersome and provide many difficulties for practicing engi- neers. For example, since many of these schemes are model based and Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/isatrans ISA Transactions http://dx.doi.org/10.1016/j.isatra.2014.11.020 0019-0578/& 2014 ISA. Published by Elsevier Ltd. All rights reserved. n Corresponding author. Tel.: þ1 405 744 6579; fax: þ1 405 744 7873. E-mail addresses: pramod.raul@okstate.edu (P.R. Raul), pagilla@okstate.edu (P.R. Pagilla). Please cite this article as: Raul PR, Pagilla PR. Design and implementation of adaptive PI control schemes for web tension control in roll- to-roll (R2R) manufacturing. ISA Transactions (2014), http://dx.doi.org/10.1016/j.isatra.2014.11.020i ISA Transactions ∎ (∎∎∎∎) ∎∎∎–∎∎∎