Vincent Gassmann

Fixed-Order

Flexible materials such as textiles, papers, polymers, and metals are transported on rollers during their processing. Maintaining web tension in the entire processing line under changing web speed is a key factor in achieving good final product quality. Many industrial applications use dancer position feedback to indirectly regulate tension. Although widely used in the industry, pendulum dancers (rotational motion of the dancer roller) have received very little attention in the literature compared to linear ones (translational motion). The lack of clearly identified controllers synthesis methods can thus be noticed, as industry typically uses hand-tuned decentralized PI controllers. An improved alternative based on H∞ methods is proposed in this paper to provide a systematic framework. The focus in this study is the unwind section of a processing line that contains a pendulum dancer (PD). The nonlinear and linear phenomenological models of the unwind section containing the PD are discussed first. The position controller based on dancer position feedback is synthesized using the standard H∞ approach with mixed sensitivity. Because of the high order of the controllers synthesized with this approach, techniques to generate reduced-order controllers are used to calculate a fixed-order controller resembling standard industrial practice. The performance of the proposed controllers is demonstrated by carrying out experiments on a large experimental web handling platform containing four driven rollers, many idle rollers, and a PD in the unwind section. To the best of our knowledge, these are the first published results of successful application of an H∞ controller to a real plant containing a PD.

H_{\infty}

The tension measurement is a key point in the operation of web systems handling thin materials such as textile, paper, polymer or metal. An experimental procedure is proposed to compute the web tension using a contactless sensor, which can be implemented on existing industrial web handling machines. A laser sensor measures the position of the web during the process and identifies out of plane vibrations. Using a sliding FFT, those vibrations can be separated into forced vibrations created by the process and machines, and free vibrations. It is then possible to compute the web tension as the frequencies of free vibrations are directly related to web tension. A test bench has been set up to represent a classical web handling systems and measurements have been made to identify free and forced vibrations. The procedure to compute web tension from measurements is then detailed.

Tension Control in the Unwinding Section of a Web Handling System Using a Pendulum Dancer

Abstract Flexible materials such as textiles, papers, polymers and metals are transported on rollers during their processing. Maintaining web tension in the entire processing line under an expected web speed is a key factor in achieving good final product quality. It is common practice in industrial web transport systems to use decentralized PI–type controllers. The performances of such control strategies highly depend on web speed and elasticity because of the strong coupling between these two variables. Moreover web speed and elasticity are subject to large variations during a same processing. The emphasis of this paper is on the design of linear parameter varying PI controllers with quadratic H ∞ performance to increase closed–loop system robustness regarding these parameters variations. First a polytopic model of the experimental plant is derived from web speed and tension dynamics. A design methodology of the PI–LPV controllers, that guarantees closed–loop quadratic stability and H ∞ performance, is then presented. The method uses an optimization software with genetic algorithms to determine the controllers parameters while minimizing the H ∞ norm. Moreover, as it is difficult to measure web elasticity online, an observer is synthesized to estimate the Youngs modulus. The effectiveness of the proposed control strategy is illustrated with simulations.

Moving Web Tension Determination by Out of Plane Vibrations Measurements Using a Laser

All flexible materials such as textiles, papers, polymers or metals are handled on rollers during their processing. Maintaining web tension in the entire processing line under changing web speed is a key factor for achieving good final product quality. Two approaches are mostly used for tension control: load cells which provide direct web tension measurement or dancers which indirectly regulate web tension via regulation of dancer position. Dancers are mobile mechanisms located in specific area of the processing line to regulate web tension. The focus of this paper is to propose an improved alternative to web processing industry practice (PI controllers) based on H∞ synthesis for pendulum dancers. Even though pendulum dancers are widely used on industrial plants, they have been studied very rarely. The nonlinear and linearized phenomenological models of the subsystem containing the dancer are first proposed. The position controller of the dancer is then synthesized using the standard H∞ framework and the mixed sensitivity approach. The performance of the proposed approach is illustrated by experimental results carried out on a large experimental web handling platform containing four driven rollers and the pendulum dancer in the unwind section. These are the first published results of successful application of an H∞ controller to a real plant containing a pendulum dancer.

Robust PI–LPV Tension Control with Elasticity Observer for Roll–to–Roll Systems

All thin materials such as textiles, paper, polymers or metals are handled on rollers during their processing inside a plant or from a plant to another. This requires unwinding and winding the web a number of lines. Maintaining web tension in the entire processing line is key for achieving good final product quality. Estimators or observers, developed based on a system model, represent a cost-effective method in order to limit the number of load cells or dancers. After a summary of the fundamental laws used for system modeling, two different approaches to design tension observers are presented and discussed. The first approach is based on a linearized system model using a Kalman filter and the second one is based on the nonlinear model and uses the extended Kalman filter theory. Both approaches are analyzed and discussed with variations in friction torques and nominal set points of the web velocity and tension. The limitation of assuming negligible friction and inertia in the idler rolls are also discussed. Simulation results for different situations with the two approaches are shown and discussed.Copyright

H ∞ unwinding web tension control of a strip processing plant using a pendulum dancer

Abstract The system under study is a web handling machine composed of an unwinder, several traction motors, several idlers with or without load cells and a winder. All flexible materials such as textiles, papers, polymers or metals are handled on rollers during their processing. Maintaining strip tension in the entire processing line while increasing web speed is a key factor for achieving good final product quality. Due to sources of disturbance and the high coupling introduced by elastic webs, robust multivariable control strategies such H∞-controllers require the knowledge of web tension in each span of the process. Estimators or observers represent a cost-effective method in order to limit the number of load cells or dancers. After a summary of the main laws used for system modeling, two different approaches to design tension observers in a section of a process line are presented and discussed. The first approach is based on a PI-observer calculated in a H∞ sense thanks to optimization techniques. The second approach uses Kalman filtering theory. Both approaches underline the importance of friction in estimation accuracy and propose alternatives to face this issue. This friction on rollers are generally neglected or assumed to be well-modeled in the literature. The proposed observers are also analyzed and discussed with variations in friction torques and nominal set points of the web velocity and tension. Both observers have the major advantage of being easily understandable for industrial applications and can be rapidly programmable in industrial plant controllers.

Tension Observers in Elastic Web Unwinder-Winder Systems

Abstract The focus of this paper is on the presentation of a hybrid projectile/MAV concept, namely the Gun-Launched Micro Air Vehicle (GLMAV), with a particular attention on the control strategy used for the hovering flight. The main objective of this concept is the remote observation of hazardous or inaccessible environments, especially for the protection of citizens and vital infrastructures and networks. Prior to its principal use as a standard MAV with two bladed coaxial counter-rotating rotors, the MAV is packaged as a projectile that is launched with the energy delivered by a portable weapon. The first part of the paper gives a description of the GLMAV concept as well as a complete nonlinear mathematical model for hover and near-hover flight. The second part of the paper emphases on nonlinear control strategies for the hover and near-hover flight, particularly backstepping control. The effectiveness of the proposed approaches is illustrated and discussed with some simulations and experimental results.

H∞-based PI-observers for web tension estimations in industrial unwinding-winding systems

Robustness and autonomy enhancement is a topic of high interest in the UAV community. To this end, most of the modern control techniques require a model of the system dynamics. Besides the structure of the model, accuracy of parameter identification has a direct impact on the models quality. This is usually a tedious task that requires a number of experiments based on different test-benches. In an attempt to simplify this process, we study the question of identifying the parameters from data collected during a short near-hover flight. With a structural identifiability analysis, we first highlight the parameters that can, or cannot, be identified with this method, depending on the sensors available on the UAV. Based on practical identifiability analysis, the parameter uncertainties are estimated and we evaluate the quality of a given flight dataset. Simple experiments are proposed to estimate the unidentifiable parameters beforehand. The study is applied on a miniature “flybarless” coaxial helicopter, for which a mathematical model is provided. This model lies on the standard 6 degrees-of-freedom rigid-body dynamics and includes models of the actuators and of the swashplate, aerodynamic effects caused by the two rotors, and coupling effects. The identification procedure is applied on a manual indoor flight and leads to a good agreement when comparing the model outputs with a validation dataset.