Interferometric Instrument for Thickness Measurement on Blown Films

Abstract

Real-time measurement of plastic film thickness during production is extremely important to guarantee planarity of the final film. Standard techniques are based on capacitive measurements, in close contact with the film. These techniques require continuous calibration and temperature compensation, while their contact can damage the film. Different optical contactless techniques are described in literature, but none has found application to real production, due to the strong vibration of the films. We propose a new structure of low-coherence fiber interferometer able to measure blown film thickness during productions. The novel fiber-optic setup is a cross between an autocorrelator and a white light interferometer, taking the advantages of both approaches.

Special Issue “Optical Fiber Interferometric Sensors: New Production Methodologies and Novel Applications”

“…The authors of [3] report on the development and implementation of an optical contactless technique to monitor the production of plastic films which thicken in real time. The developed apparatus is a low-coherence fiber interferometer, based on a cross between an auto-correlator and a white light interferometer, which is able to measure blown film thickness during production [3].…”

Experimental Investigations and Modeling of Interference Fringe Geometry in Line-Shaped Gaussian Beam Intersections for Laser Doppler Sensors

“…For this purpose, a novel laser Doppler distance sensor is developed [1][2][3]. Compared to conventional optical distance measurement techniques [4][5][6][7][8][9][10][11], it offers the advantage of simultaneous axial distance and lateral velocity measurement based on two interference fringe systems by superimposing dual-wavelength Gaussian beams. In this sensor, the velocity and distance are respectively determined from the Doppler frequency and phase difference of the speckle signals generated by optically rough surfaces or particles passing through the fringe systems.…”