Hewlett-packard Development Company, L.P.

Ching Keong Tham

Xiaoxi Huang

An apparatus and a method for duplex printing are disclosed. The apparatus includes a print zone where printing is performed and a duplex module configured to change the orientation of the media sheet. The duplex module is positioned so as to receive the media sheet from the print zone, trailing edge first. The method includes feeding a media sheet to the print zone and printing swaths of ink dots on a first side of the media sheet. Black ink density is calculated for each swath containing black ink dots. The highest black ink density is then determined. The media sheet is stopped from advancing after the last swath has been printed on the first side. The first side is allowed to dry for a drying period, which is based on the highest black ink density. After the drying period has elapsed, the media sheet is moved in the reverse direction from the print zone to the duplex module to change the orientation of the media sheet to an orientation suitable for printing on a second side. If the trailing edge of the media sheet is at a position that cannot enter the duplex module after the last swath has been printed on the first side, the media sheet is moved in the forward direction for a minimum distance to enable the trailing edge to enter the duplex module. The media sheet is then re-introduced into the print zone for printing on the second side.

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Singapore, Singapore

Ching Keong Tham