Apparatus for conveying a sheet through a printing machine with radially moving suction grippers
Sheets are conveyed through a printing machine with improved reliability of the suction grippers. The apparatus for conveying a sheet through a printing machine has a cylinder with grippers in a channel for holding the sheet at its leading edge, circulating grippers for holding and for transferring the sheet from the cylinder at its leading edge, and circulating, radially positionable suction grippers for holding the sheet at its trailing edge. An actuating apparatus opens and closes the grippers and controls vacuum for the suction grippers. A drive for the cylinder and circulating grippers and suction grippers. A control device switches on and off the sheet feed to the cylinder. The suction grippers can be moved in the radial direction into a rest position when the sheet feed is switched off.
1. An apparatus for conveying a sheet through a printing machine, comprising:
a cylinder formed with a channel therein;
grippers disposed in said channel for holding the sheet at a leading edge thereof;
a delivery for forwarding the sheets, the delivery including:
circulating leading-edge grippers for holding and for transferring the sheet from said cylinder at the leading edge, and circulating, radially positionable, trailing edge suction grippers for holding the sheet at a trailing edge thereof;
an actuating apparatus for opening and closing said leading edge grippers and for controlling a vacuum for said trailing edge suction grippers;
a drive for said cylinder and said circulating leading-edge grippers and said trailing edge suction grippers;
a control device for selectively switching on and off a sheet feed to said cylinder;
a chain conveyor with endless chains having fixed thereto said leading-edge grippers;
rotating chain wheels carrying said endless chains;
coaxially circulating supporting elements for the sheet disposed between said chain wheels assigned to said cylinder, said supporting elements being in rolling contact with a peripheral surface of said cylinder and being movably mounted in a direction of an axis of rotation of said chain wheels in dependence on a sheet transverse format; and
at least one valve spool connected to said supporting elements via a pull cable, for switching off respective said trailing edge suction grippers disposed laterally outside a given sheet width;
wherein said trailing edge suction grippers are mounted to be moved in a radial direction into a rest position when the sheet feed is switched off, said trailing edge suction grippers are moveable in the radial direction into a rest position in dependence on a sheet width of the sheet when the sheet feed is switched on, and said trailing edge suction grippers are movably disposed in the radial direction into the rest position as a result of an actuation of positioning elements for the axial displacement of said supporting elements.
2. The apparatus according to claim 1 , wherein each respective said trailing edge suction gripper includes a valve nozzle, and said valve nozzle rests against a sealing surface in the rest position of said trailing edge suction gripper, to suppress a vacuum feed to said trailing edge suction gripper.
3. The apparatus according to claim 2 , which comprises a bellows carrying the vacuum.
4. The apparatus according to claim 1 , which comprises a cam shaft and plungers connected to said trailing edge suction grippers for moving said trailing edge suction grippers.