Web edge control for strip processing lines

Claim 1

In apparatus for cutting moving webs of the type wherein at least one cutting tool is carried on a first movable carriage which can move transverse to the direction of movement of the web to maintain a fixed distance between the tool and the web edge; tHe combination of a pair of photocell devices positioned ahead of said cutting tool in the direction of movement of the web and at one side of the web, one of said photocells being sighted on said web and the other being sighted on a lighter background adjacent the web, a second carriage movable transverse to the forward direction of movement of the web and on which said photocell devices are mounted, means for moving said second carriage in one direction transverse to the direction of movement of the web when the web moves transversely in said one direction to a position where both photocell devices sight on the web and for reversing movement of the second carriage when the web moves in the opposite transverse direction to a position where both photocells sight on said lighter background, means for causing said first carriage to move in unison with the second carriage to maintain an essentially fixed distance between said cutting tool and the edge of the web, potentiometer means connected to said first and second carriages for producing output signals indicative of the reflective positions of said carriages in regard to the web, and means for comparing said output signals to derive an error signal for moving said cutting tool in the same direction as movement of the sensing head.