Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are placed in a feed chute and a feed mechanism delivers the solid ink to a heater assembly. Solid ink sticks are either gravity fed or urged by a spring through the feed chute toward a heater plate in the heater assembly. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto a recording medium. U.S. Pat. No. 5,734,402 for a Solid Ink Feed System, issued Mar. 31, 1998 to Rousseau et al. and U.S. Pat. No. 5,861,903 for an Ink Feed System, issued Jan. 19, 1999 to Crawford et al. describe exemplary systems for delivering solid ink sticks into a phase change ink printer.
In known printing systems having an intermediate imaging member, such as ink printing systems, the print process includes an imaging phase, a transfer phase, and an overhead phase. In ink printing systems, the imaging phase is the portion of the print process in which the ink is expelled through the piezoelectric elements comprising the print head in an image pattern onto the image drum or other intermediate imaging member. The transfer or transfix phase is the portion of the print process in which the ink image on the image drum is transferred to the recording medium. The overhead phase is the portion of the print process in which the operation of the intermediate imaging member and the transfer roller are synchronized for transfer of the image from the image drum or intermediate imaging member.
In currently known print processes for ink printing machines, bi-directional rotation of the intermediate imaging member is used for formation of the image on the intermediate imaging member. After the image is formed, the intermediate imaging member is stopped and its direction of rotation is reversed for transfer of the image from the drum. As the leading edge of the image approaches the transfer roller, the transfer roller is engaged to press the recording medium against the intermediate imaging member for transfer of the image from the intermediate imaging member to the recording medium. The intermediate imaging member is rotated more slowly during the transfer phase to transfer the image to the recording medium more efficiently. After the image is transferred and while the recording medium which bears the image is being transported into the output tray, the transfer roller is disengaged and the intermediate imaging member rotation is reversed for a new imaging operation.
In an improvement for such a printer, the intermediate imaging member is rotated in the same direction for both generating an image on the imaging member and transferring the generated image to a sheet of media. Such a printer is described in co-pending patent application Ser. No. 11/xxx,xxx entitled “Ink Printer Using Forward Direction Printing Process” that was filed on Nov. 14, 2005 and is commonly owned by the-assignee of this application. In this type of printer, the intermediate imaging member is slowed and the sheet of media is registered with the transferring roller as the image rotates into position for the transfer. Timing the registration of the media sheet with the generated image on the imaging member is complicated by the delivery of release agent layer on the imaging member with known drum maintenance systems. The release agent layer is applied by a drum maintenance roller that also moves into and out of engagement with the imaging member. If the transferring roller engages the imaging member before the media sheet reaches the nip between the imaging member and the transferring roller, then release agent is transferred to the transferring roller. This release agent may then be transferred to the back side of the media sheet as an image is transferred from the imaging member to the front side of the media sheet.
The presence of release agent on the transferring roller typically does not affect printing for one-sided images as the release agent is only on the side of the media sheet to which no image was transferred. In duplex or two-sided printing, the presence of release agent may degrade the quality of the image. This degrading occurs because the release agent on the back side of the media sheet affects the transfer of ink from the imaging member to the media sheet. Consequently, the coordination of the arrival of the image on the imaging member and the registration of the media sheet at the transferring roller is important for good image transfer, particularly in duplex printing operations.
Another issue arising from the use of known drum maintenance systems is the occurrence of streaks at the beginning of a transferred image. These streaks may be caused by too little release agent being delivered to the imaging agent near the leading edge of area on the imaging member in which the image is generated. These streaks typically occur near the end of life of the drum maintenance roller. Additionally, near the end of the drum maintenance roller life, the volume of release agent applied to the imaging member may be low as the drum is disengaged from the imaging member. Thus, a drier zone may occur near the end of the area in which an image is generated and streaks may result.