Patent ID: 8503922

Claim:
A duplex printing apparatus provided with a circulating transfer route including a sheet reversing path, and configured to transfer a sheet printed on a front side thereof in a circulating manner along the circulating transfer route, reversing front to rear, to make a print on a rear side thereof in an interleaf control method, the duplex printing apparatus comprising: a printer adapted for image formation onto a sheet of a sheet width Lp in a transfer direction, with a sheet spacing Lg and a printing transfer speed Vg; a constant speed transferrer adapted for constant speed transfer of sheet at the printing transfer speed Vg from a register for sheet registration via the printer to a prescribed speed change position in the circulating transfer route; a variable speed transferrer adapted for transfer of sheet from the speed change position via the sheet reversing path to the register, and a transfer controller configured to control transfer speeds of sheet in the variable speed transferrer, the variable speed transferrer comprising sections configured for sheet transfer, including a combination of a deceleration section and an acceleration section adapted for sheet reversal at the sheet reversing path, and a constant speed section adapted for transfer at a transfer speed Vr, the transfer controller being adapted to, in the case of two or more sheets: determine a circulating sheet number N employing a combination of sheet width Lp, spacing between sheets Lg and a total circulating transfer distance, execute a calculation of transfer speed Vr employing a combination of the circulating sheet number N, sheet width Lp, sheet spacing Lg, printing transfer speed Vg, and accelerations to be applied at the deceleration section and the acceleration section, to transfer a sheet from the register in the circulating manner to the register within a time interval of N×(Lp+Lg)/Vg, and compare the calculated transfer speed Vr and the printing transfer speed Vg, and to set the transfer speed Vr to be the printing transfer speed Vg or more by reducing the circulation sheet number N and recalculating the transfer speed Vr, if the transfer speed Vr is less than the printing transfer speed.