Sheet-fed rotary printing press for printing on both sides of a sheet

Claim 1

In a sheet-fed rotary printing press for printing on both sides of a sheet, an assembly of a transfer drum, a storage drum and a sheet turn-over drum mounted in succession and located between two printing units, clamping grippers on said storage drum for gripping the leading edge of a sheet being fed from the transfer drum to the storage drum, means for exerting a clamping force by said clamping grippers, tong grippers on said turn-over drum for gripping the trailing edge of the sheet at an imaginary straight line connecting the rotary centers of the storage drum and the turn-over drum as the sheet is being transferred from the storage drum to the turn-over drum and as the clamping grippers of the storage drum release the leading edge of the sheet, means for exerting a clamping force by said tong grippers that is weaker than the clamping force exerted by the clamping grippers yet strong enough to overcome the tension forces in the sheet tending to produce waves therein, means for rotating said turn-over drum and said storage drum in opposite directions and moving said tong grippers gripping the trailing edge of said sheet away from said clamping grippers gripping said leading edge of said sheet thereby tensioning said sheet between said tong grippers on said turn-over drum and said clamping grippers on said storage drum so as to smooth out any waves produced in the sheet, to and permitting said sheet to undergo a predetermined amount of sliding movement relative to said tong grippers while gripped thereby.