Abstract: An auxiliary printing unit assembly including an auxiliary press unit dimensioned to fit between the frame members of a press main frame. Stops on the main frame define a working position adjacent the press impression cylinder. A coupling assembly is journaled in the press main frame for interconnecting the press drive and the shaft of the press unit. The coupling assembly has an internally splined hollow drive shaft and an externally splined mandrel slidable in the drive shaft between inwardly extended and retracted positions. The mandrel has an expandible hub at its inner end dimensioned to mate with a recess in the press unit shaft when the mandrel is inwardly extended. The mandrel and press unit shaft have respective off-center registering elements which are also axially engaged when the mandrel is inwardly extended. Register indicia on the mandrel and the press unit shaft are so positioned that upon alignment thereof the registering elements are aligned with one another in readiness for axial engagement.

Abstract: A device for interrupting the feeding of sheets to a sheet-fed printing press. A feed table is provided having stops to define the registered position of successively fed sheets. After a register interval during which the sheet settles against the stops the sheet is picked up by a gripper cylinder. Photocells are provided for detecting failure of a sheet to register during the register interval. The photocells energize a retaining device on the feed table having a retaining foot which presses downwardly against the non-registered sheet to prevent such sheet from being picked up by the gripper cylinder. A device providing a time delay is interposed ahead of the retaining device to delay operation of the retaining device for a brief time interval to insure that the preceding sheet picked up by the gripper cylinder is clear of the feed table. A latch is provided to maintain the foot in pressing engagement with the sheet, but the foot is resiliently mounted so that an offending sheet may be manually removed.