This invention relates generally to a method and a system for handling media in a printer system, and more particularly, to deposition of media in an output tray without disrupting a stack of media sheets previously deposited in the tray.
Printers generally operate by serially drawing media sheets from a media supply, moving each sheet along a media path during which an image is formed on the sheet, and depositing the sheet on an output stack in an output tray. As printing proceeds, the supply is diminished, and the output stack increases. It is desirable to maintain a neat output stack that remains in the tray for ready removal by a user, and which preserves the order of printing. However, printers are susceptible to disruptions in the output stack caused by interaction of ejected sheets with those sheets already on the stack.
Typically, with a generally horizontal output tray, the printer's media exit is positioned a moderate height above the bottom of the tray to allow it to remain at a level adequately above a growing stack of media in the tray. However, this height causes an exit sheet ejected into an empty or nearly empty tray to curl downward under its own weight as it is ejected from the printer exit. Consequently, the leading edge of the exiting sheet strikes a middle portion of the prior sheet, and is scraped across the prior sheet as the exiting sheet is further ejected. This often causes the prior sheet to be slightly or moderately displaced from the stack, and the accumulation of such displacements during a long print job may lead to some sheets being spilled from the output tray. In addition, the scraping action of the exiting sheet's leading edge may damage a printed image, either when the image is formed of a malleable, ductile solid ink, or formed of a still-wet liquid ink.
Printers have addressed this issue by providing paper stops at the far edge of the media output tray away from the printer media exit. However, these add to complexity and cost, have undesirable aesthetics, and require adjustment for different media sizes. Other printers have employed media-stiffening mechanisms at the media exit that bend or crimp the media upon exit to cause it to eject without substantial downward curvature. However, these have proven unsuitable for printing solid ink images and for duplex (double-sided) printing, because they aggressively contact the sheet, and would damage such printed images. Accordingly, there is a need for a printer that overcomes these disadvantages.
The present invention overcomes these disadvantages by providing a printer for generating an image on a media sheet which has a printer body with a media path extending from a media supply in a downstream direction to a media exit. An output tray and a media ejection mechanism are connected to the printer body adjacent the media exit. The ejection mechanism has a number of drive roller pairs, each of which includes a first roller and a second roller contacting each other at a nip defining a nip plane. The first rollers of the respective roller pairs are coaxial with each other, and the second rollers of the respective roller pairs are coaxial with each other. The nips of the drive roller pairs occupy a common plane, and the drive roller pairs are spaced apart from each other to define a gap. The ejection mechanism includes at least one corrugation roller positioned in the gap, rotatable on a corrugation roller axis, and having a curved surface portion displaced from the nip plane.