Abstract

A vacuum shingler for a plurality of sheets (9) traveling in succession through an upstream infeed nip (13) is provided with a vacuum modulating control which applies sheet slow-down forces primarily to only the tail ends of the sheets. In one embodiment, the control provides a substantially "on-off" vacuum operation, with the vacuum "off" when the leading end portion of the sheet is adjacent the vacuum plenum opening(s) (39), and with the vacuum "on" when the tail end portion of the sheet is adjacent the opening(s). In another embodiment, the control modulates the vacuum so that it is at a basically unshingling low or reduced level when the leading end portion of the sheet is adjacent the opening(s), and is at a substantially increased high level when the tail end portion of the sheet is adjacent the opening(s) so that basic shingling occurs. The vacuum modulating control includes devices (12, 63) for sensing the position, speed and length of the traveling sheets, with this information being processed to provide an output signal which controls the speed of a shaft (52) with which a rotary valve is associated. The valve is disposed within the vacuum shingler plenum (34) and modulates the flow of air through the plenum opening(s) in correlation with the determined information. The vacuum shingler assembly is disposed so that its sheet input is substantially horizontally aligned with the discharge of the infeed nip (13). Furthermore, the assembly is disposed with its conveyor portions (28) generally horizontal, rather than inclined, so that even the middle of a sheet is supported thereby as the sheet spans the conveyor.