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US 5,047,640 AGranted
Web inspecting method
OwnerDavid Brunnschweiler, Neil R. Henderson +1inventors
InventorsDavid Brunnschweiler, Neil R. Henderson, David W. Swift
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Abstract
A web e.g. a fibre web as used in the manufacture of textiles is inspected e.g. for thickness uniformity or the like by transillumination, where the web is subject to ambient illumination, the transillumination being effected in modulated fashion whereby to distinguish measuring illumination from ambient illumination. Modulation may be effected by time-chopping a beam or by a narrow spectral band filter to improve signal-to-noise ratio.
Claims6
A method of inspecting travelling web material subject to ambient light which comprises
- a) emitting light from a light source,
- b) modulating the emitted light into alternating on and off pulses,
- c) traversing the modulated light back and forth from edge to edge across the web transverse to its direction of travel, so that it travels along a first path which passes through the web to emerge therefrom with a reduced intensity,
- d) measuring the intensity of the sum of the emitted light beam passing through the web plus ambient light during the on pulses and measuring the intensity of ambient light alone during the off pulses to yield a measurement of the intensity of the emitted light alone passing through the web during the on pulses independent of ambient light, and
- e) measuring the intensity and variations thereof of the emitted light travelling along a second path the same length and through the same atmosphere as the first path, but not passing through the web during some of the on pulses and comparing the same to said yielded measurements of the intensity and variations thereof of the emitted light alone passing through the web during the on pulses in order to monitor web properties irrespective of variations in intensity of light emitted from the light source.
2 more elements
Dependencies are inferred from the claim text.