Sheet feeding or delivering – Delivering – By pneumatic conveyor
Reexamination Certificate
1999-01-19
2001-01-30
Walsh, Donald P. (Department: 3653)
Sheet feeding or delivering
Delivering
By pneumatic conveyor
C271S266000, C346S134000, C346S104000
Reexamination Certificate
active
06179285
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to marking devices and, in particular, to a media transport assembly and method in which a media sheet is pushed and/or pulled by step advancing drive assemblies in a highly repeatable manner against the action of a vacuum force applied to hold the media sheet flat for accurate scanned marking.
2. Description of Related Art
Consumers continue to demand marking devices with increased capabilities. For example, consumers now desire a low cost alternative to conventional laser color printers. Marking devices using other technologies (e.g., ink jet printing) potentially provide such a low-cost alternative, but must be configured to operate at speeds comparable to the competing laser printers.
In marking devices with one or more moving print elements that reciprocate across the width of a media sheet (i.e., from left to right or from right to left) in passes, the media sheet is marked in swaths equal to the length of the print element(s). The operating speed of such a marking device can be increased by increasing the size to the swath marked in each pass. With a larger swath size, fewer passes are required to mark each media sheet.
As the print swath area increases, the area of the marking zone must be increased. The marking zone is defined as the area of the media sheet available for marking in the current swath. The marking zone extends between the entrance drive assembly immediately upstream of the print element(s) to the exit drive assembly immediately downstream of the print element(s). With an increased marking zone area, maintaining the flatness of the media sheet and providing a highly accurate incremental media advance without increasing lead and/or trail edge borders to ensure accurate marking, becomes more difficult. Because the gap between the print element(s) and the media sheet is small (on the order of 1.1 mm), it is not possible to secure the media sheet from the reverse side. In typical marking devices with moving print elements, sufficient flatness and advance accuracy of the media sheet is a concern in leading edge or trailing edge marking situations.
In leading edge or trailing edge marking situations, only one edge of the media sheet is secured and driven by the entrance drive assembly or the exit drive assembly. In contrast, when middle portions of the media sheet are being marked, the leading portion is secured by the exit drive assembly and the trailing portion is secured by the entrance drive assembly. Thus, the flatness of the media sheet and the advance accuracy must be ensured by appropriate tensioning between the entrance drive assembly and the exit drive assembly.
Accordingly, it would be desirable to provide a media transport system capable of advancing at a sufficient speed and accuracy, while ensuring that the media sheet is sufficiently flat.
SUMMARY OF THE INVENTION
According to the invention, a media transport system and method are provided by which a media sheet is transported through the marking device by an entrance drive assembly and/or an exit drive assembly, and a portion of the media sheet between the entrance drive assembly and the exit drive assembly is subjected to a vacuum force.
According to a preferred embodiment, the media transport system includes an entrance drive assembly and an exit drive assembly. The entrance drive assembly receives and transports the media sheet in a process direction by contacting top and bottom surfaces of the media sheet. The entrance drive assembly exerts an entrance drive force on the media sheet. The exit drive assembly receives and transports the media sheet by contacting the top and bottom surfaces of the media sheet. The exit drive assembly is spaced from the entrance drive assembly and exerts an exit drive force on the media sheet.
A vacuum generator applies a vacuum force to the media sheet in the area of the media sheet between the entrance drive assembly and the exit drive assembly. The vacuum force acts on the media sheet in a vacuum force direction substantially normal to the process direction. The vacuum force is set such that the entrance drive force and the exit drive force acting in the process direction are each greater than the vacuum force acting in the vacuum force direction. Preferably, the vacuum force is also set to maintain the media sheet within a desired flatness range.
Preferably, the entrance drive assembly and the exit drive assembly each include a pair of drive elements that contact each other to form, respectively, an entrance nip and an exit nip. Preferably, each pair of drive elements includes a driven element and an idler element with sufficient pressure between them to prevent slip during the media advance. Preferably, each pair of drive elements includes a dual grit coated roll. Further, each pair of drive elements preferably includes an elastomer roll.
The media transport system preferably includes a platen positioned in the area between the entrance drive assembly and the exit drive assembly. The platen has a media sheet side, a vacuum force side opposite the media sheet side and vacuum holes extending through the media sheet side to the vacuum force side. The vacuum force is generated on the vacuum force side of the platen and applied to the media sheet through the vacuum holes to draw the media sheet against the media sheet side.
The media sheet side of the platen preferably includes vacuum grooves that communicate with the vacuum holes. Preferably, the vacuum grooves extend in the process direction. Preferably, the vacuum force applied to the media sheet is substantially constant. Preferably, the length of the grooves is set to allow acquisition or release of the media in a controlled manner to prevent a sudden retard action in the drive system that would cause image distortion.
The vacuum grooves are preferably arranged in rows extending perpendicular to the process direction. The vacuum grooves within each row are preferably spaced apart from each other, and the vacuum grooves in a first row are staggered with respect to the vacuum grooves in a second row.
Preferably, the vacuum generator includes an entrance fan having an entrance plenum positioned near a media sheet entrance area of the platen and an exit fan having an exit plenum positioned near a media sheet exit area of the platen.
The media transport system preferably includes edge guides extending along the platen in the process direction. The edge guides receive, guide and hold the edges of the media sheet flat.
The media transport system preferably includes a drive motor coupled to the entrance drive assembly and to the exit drive assembly by respective helical gears with associated anti-backlash springs. The media transport system preferably includes a spring plate positioned across the entrance area of the platen that guides the media sheet into contact with the vacuum force.
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patent: 3288037 (1966-11-01), Burnett
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Burger William R.
DeHond Paul S.
Gilliland W. Keith
Merz Eric A.
Teumer Roger G.
Oliff & Berridg,e PLC
Schlak Daniel K
Walsh Donald P.
Xerox Corporation
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