Automatic registration control method and apparatus

A method of registration control in a multi-station processing system comprising successively applying to a running web groups of marks, the marks being spaced along the length of the web, each group comprising a plurality of reference marks applied in accordance with the location on the web of a first processing operation performed by a first station and a plurality of control marks respectively corresponding to the locations of other processing operations performed on the web by a plurality of other stations;

• measuring quantities dependent upon separations between pairs of said reference marks;
• and measuring quantities dependent upon separations between each control mark and one of said reference marks;
• storing the measured quantities;
• and analyzing the stored quantities to detect misregistration.

A method of registration control in multi-color printing wherein each of a plurality of printing stations prints a different color registration mark on a running web and positions of the marks are detected to determine registration, comprising imaging a light beam onto the web so as to be intercepted by the marks;

• detecting light reflected from the web;
• measuring and storing a first quantity representative of a time, as each mark enters the beam, that the amount of light reflected changes to a predetermined level;
• measuring and storing a second quantity representative of a time, as said mark leaves the beam, that the amount of light reflected changes beyond said predetermined level;
• and determining from said first and second quantities a midpoint of said mark.

An apparatus for registration control in a multi-color printing system, wherein each of a plurality of printing stations prints a different color registration mark on a running web and the positions of the marks on the web are detected for registration, the apparatus comprising means for imaging a light beam onto the web so as to be intercepted by the marks;

• means for detecting light reflected from the web;
• means for measuring a first quantity dependent upon a time, as a mark enters the beam, that the amount of reflected light changes to a predetermined level and for measuring a second quantity dependent upon a time, as said mark leaves the beam, that the amount of reflected light changes beyond said predetermined level;
• means for storing said quantities;
• and means for determining from said first and second quantitites a third quantity corresponding to a midpoint of the mark.