Optical monitor for measuring a gap between two rollers

A method of measuring a gap between a first roller and a second roller, said gap varying due to thermal dimensional changes of at least one of said first roller and said second roller, comprising the steps of:

• (a) reflecting light off of said first roller and generating an optical first-distance signal indicative of a first distance to said first roller based on the intensity of light reflected off of said first roller;
• (b) reflecting light off of said second roller and generating an optical second-distance signal indicative of a second distance to said second roller based on the intensity of light reflected off of said second roller;
• and
• (c) generating a thermal expansion/contraction signal indicative of said thermal dimensional changes based on said first-distance signal and said second-distance signal.

A film subbing station, comprising:

• a first roller and a second roller, said first roller and said second roller defining a gap therebetween which determines a subbing layer thickness, said gap varying due to thermal dimensional changes of at least one of said first roller and said second roller;
• a first optical probe to measure a first distance to said first roller and to generate a first-distance signal indicative of said first distance;
• a second optical probe to measure a second distance to said second roller and to generate a second-distance signal indicative of said second distance;
• and
• an electronics module, coupled to said first optical probe and to said second optical probe, to generate a gap-width signal in real time which is indicative of said gap based on said first-distance signal and said second-distance signal.