A similar press is disclosed in DE-PS No. 1 107 246. When this press is set up for perfecting, grippers on the turning cylinder periphery and operative in perfecting, engage the trailing edge of the sheet and disengage it from the previous double-size transfer cylinder. Thereafter the grippers pivot inwards around their own axis until they engage an inner abutment element. Grippers for two-color printing, present on the turning cylinder periphery, also pivot inwards around their own axis until they abut another inner abutment element. The trailing edge of the sheet is then transferred from the pivoted-in perfecting grippers to the two-color grippers turning the sheet and maintaining registration so that the trailing edge of the sheet is now the leading edge. The entirely mechanical gripper transfers of this known press ensure that the engagement, transfer and delivery of each sheet is always exactly uniform, thus ensuring the necessary maintenance of registration.
The known machine also has suction devices on the turning cylinder periphery located behind the grippers relative to the direction of rotation of the turning cylinder. These suction devices provide additional retention of the trailing sheet edge. The disadvantage of this patented press is that the sheet moves jerkily and creates registration problems in multi-color printing on one side when operating at increased speeds. Another disadvantage arises when the press is required to print rigid substrates such as paper board or card stock. Also, the considerable curvature of the sheet on the single-size transfer cylinders, the many changes of curvature, and of the large number of gripper transfers hamper the printing process when applying multiple colors. The greatest speeds at which multi-color printing can be carried out using this press are merely the lowest speeds of conventional perfecting.
Another patent, DE-AS No. 2 350 132, teaches a series-produced rotary press in which the sheets are conveyed entirely by means of mechanical gripper transfers from a first double-size impression cylinder. The sheets run smoothly in multi-color printing on one side in this press. However, the disadvantage arises in perfecting where blowing and suction boxes are additionally needed in the transfer zone of the double-size transfer drum to obviate set-off of the sheet on the drum, more particularly, set-off of the sheet end after turning.
USPTO Backgrounds
USPTO Backgrounds