Self-calibrating seam detector

Claim 1

A self-calibrating seam detector for a running web, comprising a. a first web-engaging roller mounted in fixed position along one side of the path of travel of said web, b. a second web-engaging roller movably mounted along the other side of the path of travel of said web opposite said first roller to form a web thickness gauge therewith, c. resilient means operatively connected to said second roller for urging said second roller towards said first roller with said web therebetween, d. a third web-engaging roller movably mOunted along said one side of the path of travel of said web, e. movable mounting means supporting said second and third rollers for simultaneous cooperating movement to and away from the plane of said web, and, f. seam sensing means mounted along the other side of the path of travel of said web opposite said second roller adapted to be actuated by a seam in said web passing between said third roller and said sensing means, g. the spacing between said sensing means and said third roller controlled by the thickness of said web as said web first passes between said first and second rollers, said second roller moving to and away from said first roller according to changes in the thickness of said web and thereby simultaneously moving said third roller and said sensing means, h. the axes of said rollers being parallel and extending transversely of said web, i. said mounting means including a rigid bracket carrying said rollers in spaced parallel relation and mounted for pivotal movement about an axis parallel to said rollers and substantially mid way between said second and third rollers, j. said seam sensing means including a resiliently mounted webengaging roll bearing against said web and a switch operatively connected to said roll whereby said switch will be actuated by a seam engaging said roll.