| 摘要 |
A method and apparatus for monitoring the passage of a mark (13-16) on a web (5). The web (5) is caused to move through a detection station (7) at which at least that portion of the web carrying the mark is illuminated. An image of the mark (13-16) is projected onto a quadrant array (20) of photodetector elements at the detection station (7). The axes (25,26) defined between the elements (21-24) are tranverse to the direction of movement of the web. The time t1, t2 at which substantially equal areas of a mark are projected on either side of the axes is determined which provide an indication of registration of the web. |
