Patent Application
20100133744
None.
1. Field of the Invention
The present invention relates generally to electrophotographic (EP) image forming machines and, more particularly, to a media sheet guide device and method for maintaining proper sheet alignment in the EP image forming machine.
2. Description of the Related Art
In an EP image forming machine, such as a laser printer, having a duplexer, each sheet of media has to be repositioned relative to a desired location in the media return path of the duplexer prior to the sheet being returned into the media input path of the printer. Repositioning of the sheet is required due to the possibly of it becoming misaligned during its initial advancement through the printer when printing occurs on its first side. Misalignment may be to the left or right of the desired location of the sheet. The sheet also may be angled or skewed relative to its desired location. To have accurate positioning of each sheet during its return to the printing area of the printer so that printing on its second side is accurate, the sheet must be accurately repositioned relative to a known location or surface, such as defined by a reference edge extending generally parallel to the paper path. See U.S. Pat. No. 6,840,514 assigned to the assignee of the present invention for a discussion of these issues and for disclosure of a media alignment mechanism as one approach for their resolution.
In various prior art arrangements to align a sheet of media with a reference edge to its correct position and orientation, alignment rollers have been employed. These alignment rollers are skewed so that they apply both a force perpendicular to the reference edge and a force parallel to the reference edge to advance the sheet in a desired alignment. In printers that utilize reference edge alignment, successively positioned upstream and downstream media alignment mechanisms made up of skew rollers and reference edges can be found at various areas in the printers, one such area being between the image formation path of the base printer and the duplex path. It is desired that the reference edges in these successively positioned media alignment mechanisms be placed together as close as possible (i.e. lie in the same theoretical plane) to eliminate sheet skew as the sheet passes from one mechanism to the next.
One problem with this arrangement is that if the reference edges of the successive media alignment mechanisms are located far apart, such as at a distance D>50 mm, in the downstream sheet path, when the leading edge of the sheet enters the entrance to the next reference edge, it could engage the entry end of the reference edge and create a paper jam if there is not enough offset distance between the two reference edges involved in the hand-off. This is because a very large offset may be required to account for physical tolerances between the successive sheet alignment mechanisms and any walking or steering imparted into the sheet by the feed system. Also, in the case of the duplex path, the position and orientation of the sheet is not known when the leading edge of the sheet enters the entrance to the reference edge in its duplex operation. Thus, it is necessary to ensure that the sheet does not engage the entry end of the reference edge when the sheet is to be printed on its second side.
Thus, there is a need for an innovation that will address and satisfactorily solve the aforementioned problems.
The present invention meets this need by providing an innovation for maintaining proper alignment of media sheets in an image forming machine through introducing or applying differential drag across each of the media sheets to bring about its proper alignment between successive media alignment mechanisms. In such manner, the present invention solves the design paradox by providing a way of minimizing offset between reference edges of upstream and downstream media alignment mechanisms of an image forming machine for good skew performance, while allowing sheets to pass between the mechanisms without jamming into the reference edge downstream.
Accordingly, in an aspect of the present invention, a media sheet guide device for maintaining proper sheet alignment in an image forming machine includes a body extending between spaced apart reference edges of respective upstream and downstream media alignment mechanisms in the machine, and a face on the body defining a path along which a sheet moves lengthwise from the reference edge of the upstream media alignment mechanism to the reference edge of the downstream media alignment mechanism. The face has a widthwise section defining a portion of the path and about which the sheet bends widthwise as the sheet moves lengthwise along the portion of the path. The section of the face has first and second segments differing in curvature for applying a differential drag widthwise across the sheet as the sheet bends widthwise about the section of the face and moves lengthwise along the portion of the path. The application of the differential drag across the sheet causes a rotation of the sheet sufficiently to displace a leading end of the sheet away from the reference edge of the downstream media alignment mechanism, thereby ensuring that a leading corner of the sheet can enter into the reference edge of the downstream media alignment mechanism without jamming against an entry end of the downstream reference edge.
In another aspect of the present invention, a method for maintaining proper sheet alignment in an image forming machine includes defining a path along which a sheet moves lengthwise from an upstream reference edge of an upstream media alignment mechanism to a downstream reference edge of a downstream media alignment mechanism and applying a differential drag widthwise across the sheet causing a rotation of the sheet sufficiently to displace a leading end of the sheet away from the downstream reference edge to thereby ensure that a leading corner of the sheet can enter into the downstream reference edge without jamming against an entry end thereof.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numerals refer to like elements throughout the views. Furthermore, terms such as “lengthwise” and “widthwise” are used for the purpose of facilitating an understanding of the various aspects of the invention and do not to imply relative sizes of such aspects; terms such as “fore-and-aft” and side-to-side? could just as readily be used in place of “lengthwise” and “widthwise”.
Referring now to
A multi-purpose feeder 30 may also be included in the housing 12 of the printer 10 to move additional sheets toward the entrance end 24a of the image formation path 24. The multi-purpose feeder 30 includes a support floor 32 adjacent to another ramp 34. An additional sheet pick mechanism 36 is provided, having a pivoting arm 38 and a roller 40 thereon. Rotation of the roller 40 moves the sheet from the support floor 32 up the ramp 34 toward the entrance end 24a of the image formation path 24. The additional sheet pick mechanism 36 within the multi-purpose feeder 30 may be the same or different from the sheet pick mechanism 20 associated with the media input tray 14.
The operation of the printer 10 is conventionally well-known. After a media sheet is introduced through the input tray 14 or the multi-purpose feeder 30, the sheet is presented at the entrance end 24a of the image formation path 24 as defined by a nip 42 of a media alignment mechanism 44 formed between its set of drive roller 46. The media alignment mechanism 44 removes lateral skew from the sheet and precisely times its passage on to the image forming stations 48 located downstream along the image formation path 24.
After the sheet passes the media alignment mechanism 44 it contacts a transport belt 50, which carries the sheet along the image formation path 24 past successive photoconductor units 52 of the image forming stations 48. At each successive photoconductor unit 52, a latent image is formed by an imaging device 54 and optically projected onto a photoconductive member. The latent image is developed by applying toner to the photoconductive member from a toner reservoir. The toner is subsequently deposited on the sheet as it is conveyed past each of the photoconductor units 52 by the transport belt 50.
The toner is then thermally fused to the sheet by a fuser 56 and the sheet then passes through an exit end 24b of the image formation path 24 to a media sheet directing mechanism in the form of a pair of reversible exit rollers 58 which feed the media sheet face down onto a media sheets collection site 60 on a top exterior portion 62 of the printer housing 12. Alternatively, the exit rollers 58 may reverse motion after the trailing edge of the sheet has passes an inlet end 64a to a duplex path 64. The reversible exit rollers 58 then direct the sheet through the inlet end 64a of the vertically-oriented duplex path 64 to where the sheet falls by gravity through an internal structure 66 defining the duplex path 64 to an outlet end 64b of the duplex path 64. From there, the sheet then travels along a return path 68 defined between a pair of upper and lower sheet turn-around guides 70, 72 mounted on the tray 14. The guides 70, 72 interconnect the outlet end 64b of the duplex path 64 with the nip 42 at the entrance end 24a of the image formation path 24. The sheet is transported by the transport belt 50 through the image formation path 24 where it is processed for the printing of another image on the back side of the sheet. The double-sided media sheet is then delivered face down to the collection site 60 on the printer housing 12.
Turning now to
As can be understood in
The addition of differential drag can be customized based on the media set supported by the printer 10. For the example shown in
Referring now to
More particularly, the media sheet guide device body 88 includes a base 96 and a plurality of guide elements in the form of guide ribs 98 formed on an underside 96a of the base 96 and arranged to extend lengthwise of the base 96 and generally parallel to one another in the direction of sheet movement. The guide ribs 98 are spaced apart laterally from one another across the width or widthwise of the base 96 and have respective thicknesses less than the distance between adjacent ones of the guide ribs 98. The outer edge surfaces 98a of the guide ribs 98 collectively define the face 90 of the body 88. Particularly, downstream end portions 98b of the guide ribs 98 on the downstream end portion 88a of the body 88 having curvatures that cause the sheet 80 to turn nearly 90° before reaching the downstream nip 42 and downstream reference edge 76 of the downstream media alignment mechanism 44. Thus, each sheet 80 will bend about or around the lengthwise curved guide rib end portions 98b as the leading end 80d of the sheet 80 approaches and moves into the nip 42. The guide ribs 98 may be spaced apart laterally from one another by substantially the same amount of distance and have the same heights to which they extend outwardly from the base 90.
However, for applying the desired differential drag on the sheet 80 as the sheet 80 passes and bends around the downstream end portion 88a of the body 88, between selected ones of the guide ribs 98 at the downstream end portions 98a thereof one or more fillers are installed to provide, in effect, rib extensions 100 which modify or change the lengthwise curvatures of the downstream end portions 98a of the selected guide ribs 98. The locations of and additional increments of height added by these rib extensions 100 are calculated to introduce or apply the desired differential drag to the media sheet 80 such as will bring about rotation of the leading end 80d of the sheet 80 sufficiently away from the downstream reference edge 76 of the downstream media alignment mechanism 44 so as to avoid jamming of the leading corner 80e of the sheet with the entry end 76a of the downstream reference edge 76 as the sheet 80 approaches the downstream nip 42 of the mechanism 44 and the entrance end 24a of the image formation path 24. Thus, the desired differential drag is physically introduced into the downstream portion 68a of the sheet return path 68 by altering or modifying the rib geometry at a location just prior to the downstream reference edge 76 of the downstream media alignment mechanism 44. In the portion of the duplex re-entry or return path 68 at the location of the downstream end 88a of the guide device body 88 defined by the curvature of the guide ribs 98, the sheet 80 is nominally fed through a 45 mm turn radius defined thereon. The sheet 80 is guided and supported through this area by the downstream end portions 98b of the ribs 98 (located within the first segment 92 of the face 90) that allow the sheet to take or bent through this radius (see the long dash/short dash line in
To recap, the above-described method of reliably handing off media sheets applies to any two reference edges in the printer where the offset between the edges is minimal. The rib extensions 100 on the ribs 98 at the downstream end portions 98b of selected one of the ribs 98 provide the differential bend radii across the width or widthwise of the sheet 80. Also, the rib geometry provides differential drag widthwise across the sheet and acting in a direction parallel to sheet feed direction of movement, while minimizing additional drag lengthwise of the sheet and acting in a direction perpendicular to the feed direction, so that downstream media alignment can be performed more reliably.
The foregoing description of several embodiments of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.
