Real-time web inspection method and apparatus using combined reflected and transmitted light images

A web inspection method comprising:

• projecting light from a source to be incident on a select portion of a web that is moving in a down-web direction and that extends laterally to define a width in a cross-web direction, wherein said select portion of said web comprises an unsupported free-span portion of said web that extends and is moving between first and second spaced-apart idler rolls, wherein said web moves in said down-web direction while being maintained under a select tension of at least one pound of tension for each inch of said width of said web;
• using a reflected light image capturing camera system to capture reflected light from said source that is reflected by said select web portion and deriving a digital image of said reflected light;
• simultaneously with said step of capturing reflected light, using a transmitted light image capturing camera system to capture transmitted light from said source that is transmitted through said select web portion and deriving a digital image of said transmitted light;
• wherein said light source and said reflected light image capturing system are located on a first side of said web and wherein said transmitted light image capturing system is located on a second side of said web that is opposite said first side so that said web passes between said light source and said transmitted light image capturing system;
• wherein said light projected from said source is incident on said web at an angle of x degrees relative to a vertical plane, said reflected light image capturing system is located at an angle y relative to said vertical plane, and wherein said transmitted light image capturing system is directly aligned with said projected light;
• wherein said reflected light image capturing system comprises a plurality of reflected light imaging cameras with overlapping reflected light imaging fields in said cross-web direction that are registered with each other in said down-web direction, and wherein said transmitted light image capturing system comprises a plurality of transmitted light imaging cameras with overlapping transmitted light imaging fields in said cross-web direction that are registered with each other in said down-web direction, and wherein each of said reflected light imaging cameras corresponds to and is registered with one of said transmitted light imaging cameras so as to define a corresponding pair of imaging cameras located on opposite sides of said web;
• digitally merging said reflected light digital image and said transmitted light digital image to derive merged image data that represent both said reflected light and said transmitted light;
• using all of:
• (i) said reflected light digital image;
• (ii) said transmitted light digital image;
• and, (iii) said merged image data to identify defects in said web;
• without interrupting movement of said web in said down-web direction, physically marking said web at or near all identified defects to define marked defects;
• culling said marked defects from said web.