IMPROVEMENTS IN ROTARY OFFSET PRINTING PRESSES

1,217,740. Printing apparatus. VANDERCOOK & SONS Inc. 11 June, 1968 [11 July, 1967], No. 27691/68. Heading B6C. A multi-colour rotary offset printing press comprises a plate cylinder 56, divided into a plurality of segments each of which may bear a printing plate, a blanket cylinder 57 of the same diameter as the plate cylinder 56 and a papercarrying impression cylinder 58 which during a single revolution of cylinders 56 and 57 revolves as many times as there are segments on cylinder 56. Each segment on plate cylinder 56 has its own inking system and dampening system. Cam-operated trips are provided whereby the inking and dampening systems 69-72 and 76- 79 contact only their own segments of plate cylinder 56. Blanket cylinder 57 may be tripped and held out of engagement with plate cylinder 56 as a segment of cylinder 56 from which it is not desired to print passes through what would otherwise be the nip of cylinders 56 and 57, and impression cylinder 58 may correspondingly be tripped out of engagement with blanket cylinder 57. Both these actions are actuated by cams on blanket cylinder 57, and in normal operation the cylinders are tripped and returned as each segment of cylinder 56, or corresponding portion of cylinder 57, nears the relevant nip. When it is desired to hold the cylinders in their trip positions electromechanical latches are operated. Electromechanical latches are also employed to hold inking and dampening apparatus out of engagement with their respective segments of plate cylinder 56 if a segment is not to be printed from. Gears and chains synchronize the various cylinders and trips. Preferably plate cylinder 56 has four segments, each of which prints a different colour when all are in use. Each inking system 69-72 incorporates a fountain roller 91, wiped by a blade, a messenger roller 92 and axially reciprocated rollers 84 and 86, together with frame rollers 80-83 and other, fixedaxis, rollers. Means are provided for varying period during which messenger roller 92 contacts fountain roller 91, and for locking messenger roller 92 out of contact with fountain roller 91. The rollers 84, 86 are reciprocated by engagement of a follower with a grooved shaft. Similarly each dampening system 76-79 comprises a fountain roller 97, a messenger roller 98 an axially oscillated roller 98 and frame rollers 93, 94. The fountain rollers 97 are rotated by individual variable speed electric motors and the rollers 98 are oscillated by engagement of grooved col