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Sensorless tension control of webs

Wolfermann, W.
Production plants with continuous moving webs have a complex structure where mechanical, electrical and control problems are involved. To solve the problems of these systems, it is necessary to take the entire system into account.
In many processing machines in the plastic-, textile- and paper industry only the speed of the roller is controlled. The web tension is a function of the speed relation. The disadvantage of only controlling the speed is that the changes in the tension of the web during the technological process cannot be controlled. Therefore some nip sections are equipped with a sensor to measure the tension so that a closed loop control of the web tension can be used.
The sensor is a roller which is able to measure the web tension by transforming the mechanical signal to an electrical signal. But each roller in the plant is able to cause problems in the lateral control of the web or generate web wrinkling. Therefore it would be better to get the web tension sensorless. This would save problems and money.
In this paper observers to estimate the web tension are discussed. But there are some problems to realize observers in plants with continuous moving webs. The first problem is that all rollers and drives are coupled in the plant. Therefore, we have to design decentralized observers. The second problem are unknown and sometimes nonlinear parameters in the plant or not measurable inputs, for example disturbances that change while the process is running. Therefore observers have to be designed to estimate the tensions without a steady-state error.