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

Tension measurement is a key point in the operation of web systems that handle thin materials such as textiles, paper, polymers, or metal. An experimental procedure is proposed to compute web tension using a contactless sensor, which can be implemented on existing industrial web-handling machines. A laser sensor measures the out-of-plane position of the moving web during the process and identifies out-of-plane vibrations. Using a sliding fast Fourier transform (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 system, and measurements have been made to identify free and forced vibrations. The procedure to compute web tension from measurements is detailed and implemented. The web tension is calculated from measured web vibrations for different velocity and tension references. The validity and accuracy of the method are then discussed.