Patent ID: 6499395
Filing Date: 2002-12-31
Classification: B41F

Abstract:
An offset printing machine for forming an image on a sheet comprising:a plate cylinder rotatable about its axis and having an outer peripheral surface equally divided in a circumferential direction into at least two color regions, an ink image being formed on each color region, each color region having an equal circumferential length; a blanket cylinder rotatable about its axis and having an outer peripheral surface in contact with the color regions and equally divided in a circumferential direction into at least two color sections, each ink image on each color region being transferred to each color section, and each color section having an equal circumferential length; an impression cylinder rotatable about its axis and having an outer peripheral surface for holding and transferring a sheet, each color section being in contact with the outer peripheral surface of the impression cylinder so as to be capable of transferring each ink image on each color section onto the sheet, the outer peripheral surface of the impression cylinder being equally divided into a plurality of segments each having a peripheral length equal to the circumferential length of the color region and the color section; impression cylinder grippers provided at the outer peripheral surface of the impression cylinder and movable along with the rotation of the impression cylinder, each impression cylinder gripper being positioned at each leading end portion of each segment, and each impression cylinder gripper being movable between an open position and a closed position; a sheet feed cylinder rotatable about its axis and having an outer peripheral surface on which a sheet is capable of being held and transferred and in contact with the outer peripheral surface of the impression cylinder at a contact position for transferring the sheet to the impression cylinder, the outer peripheral surface of the sheet feed cylinder having a peripheral length equal to a peripheral length of each of the segments; a sheet feed cylinder gripper provided at the outer peripheral surface of the sheet feed cylinder and movable along with the rotation of the sheet feed cylinder, the sheet feed cylinder gripper and one of the impression cylinder grippers being so positioned to simultaneously reach the contact position, the sheet feed cylinder gripper being movable between an open position and a closed position; a sheet feed side impression cylinder gripper drive mechanism for moving the impression cylinder gripper to either its open position or closed position at the contact position; and a sheet feed cylinder gripper drive mechanism for moving the sheet feed cylinder gripper to either its open position or closed position, wherein a combination of the sheet feed side impression cylinder gripper drive mechanism and the sheet feed cylinder gripper drive mechanism comprise means for providing a sheet transfer timing, when the sheet feed cylinder gripper holds a sheet to be transferred, by switching the impression cylinder gripper from its open position to its closed position and by switching the sheet feed cylinder gripper from its closed position to its open position at a predetermined timing of confrontation between the impression cylinder gripper and the sheet feed cylinder gripper at the contact position, the predetermined confronting timing occurring when the confronting times per sheet printed is equal to the number of the color sections of the blanket cylinder, and wherein, when the sheet feed cylinder gripper does not hold a sheet to be transferred, the sheet feed side impression cylinder gripper drive mechanism comprises means for maintaining the closed position of the impression cylinder gripper when the impression cylinder gripper passes by the contact position, and the sheet feed cylinder gripper drive mechanism comprises means for maintaining the open position of the sheet feed cylinder gripper when the sheet feed cylinder gripper passes by the contact portion, a combination of the maintaining means of the sheet feed side impression cylinder gripper drive mechanism and the maintaining means of the sheet feed cylinder gripper drive mechanism constituting the providing means.