Cassette tray sheet feeding assembly

Abstract: Described herein is a high capacity, high reliability cassette tray sheet feeding assembly (70) for supporting a high capacity stack of sheets, and for feeding such sheets with a high degree of reliability, one at a time, in a sheet using machine. The assembly (70) includes a cassette frame (74) for removing and reinstalling into a sheet supply station of the sheet using machine. The cassette frame (74) includes a fixed position stationary base plate (96) for supporting a high capacity stack (94) of sheets. The high capacity, high reliability cassette tray sheet feeding assembly further includes a variable position sheet receiving path (104), and a pivotable feed wheel assembly (100) for reliably feeding topmost sheets seriatim from the stack (94) into the variable position sheet path (104). The pivotable feed wheel assembly (100) provides a constant sheet feeding angle (F3°), and a constant sheet feeding normal force (P3), thereby enabling continuous high reliability feeding of sheets.

Description: This invention relates to a cassette tray sheet feeding assembly, and is more particularly concerned with document production or reproduction machines having such a cassette tray sheet feeding assembly for holding a high capacity stack of sheets, and for feeding such sheets with a high degree of reliability within the machine. Document productions machines include all types of printers, as well as electrostatographic process reproduction machines. Generally, the process of electrostatographic reproduction machines includes uniformly charging an image frame of a moving photoconductive member, or photoreceptor, to a substantially uniform potential, and imagewise discharging it or imagewise exposing it to light reflected from an original image being reproduced. The result is an electrostatically formed latent image on the image frame of the photoconductive member. For multiple original images, several such frames are similarly imaged. The latent image so formed on each frame is developed by bringing a charged developer material into contact therewith. Two-component and single-component developer materials are commonly used. A typical two-component developer material comprises magnetic carrier particles, also known as "carrier beads," having fusable charged toner particles adhering triboelectrically thereto. A single component developer material typically comprises charged toner particles only. In either case, the fusable charged toner particles when brought into contact with each latent image, are attracted to such image, thus forming a toner image on the photoconductive member. The toner image is subsequently transferred at a transfer station to an image receiver or copy sheet. The copy sheet is then passed through a fuser apparatus where the toner image is heated and permanently fixed to the copy sheet, thus forming a hard copy of the original image. The copy sheets typically are held and positioned (for feeding to the transfer station) in a motorized elevator sheet supply assembly within the machine, or in a non-motorized portable or removable spring and pivot cassette tray assembly cooperating with a fixed position feed wheel assembly. Conventional non-motorized spring loaded and pivoting type cassette trays or tray assemblies of the sort are well known. Typically, forward feed corner snubber type cassette tray cooperating with a fixed position feed wheel assembly can effectively hold and reliably feed only up to a maximum of 250 sheets per full tray in image reproduction machines. Examples of such cassette trays are described in US-A-4 591 141, US-A-4 358 102, US-A-3 599 972, US-A-3 408 064 and Japanese Utility Model JP 47-146600. US-A-4 591 141 discloses a sheet feeder that is pivotably mounted so that the paper supply is maintained in contact with a fixed position feed roller. The sheet feeder's pivot point is selected to provide constant feed pressure to the paper supply regardless of the size of the remaining paper supply. US-A-4 358 102 discloses a cassette that has a cut out or gate centrally defined in each wall of the cassette. The cassette also has a reinforcing plate pivotally mounted at a forward portion of each side wall. Upon mounting in a machine, the reinforcing plates bridge the cut outs or gate and cooperate with machine members to prevent skewed feeding of a topmost sheet. US-A-3 599 972 discloses a floating feed tray including a pair of feed rollers positioned above the forward end of the tray and mounted on a fixed axis. The rearward end of the tray is biased downwardly to pivot the tray about a pivot point so as to raise the forward end to bring the topmost sheet into feeding engagement with the feed rollers. Japanese Utility Model JP 47-146600 discloses a paper feeding cassette including a sheet separating pivot or snubber that shifts from the paper feeding positions when sheets are being loaded. US-A-3 408 064 discloses a paper tray that has lateral and end guides or walls that are fixedly attached to the bottom plate of the tray to accommodate a stack of sheets. As illustrated in FIGS. 1 and 2 of the drawings, such non-motorized, removable conventional cassette tray assemblies, for example, those that have forward feed corner snubbers cooperating with a fixed position feed roller, are very sensitive to a stack-height dependent sheet feeding angle. The sheet feeding angle being defined by the top of a stack of sheets relative to a horizontal plane through the corner snubber. They are also very sensitive to variations in a normal force acting through the sheet feeding nip. Variations in the sheet feeding angle also detrimentally affects the length FL1, FL2 or amount of each sheet fed per feed stroke or feed cycle of the feed wheelsat full and at near empty states of the cassette tray. Referring still to FIGS.1 and 2, a conventional cassette tray assembly 200 is illustrated in the full position (FIG. 1) and in the near empty position (FIG. 2). The conventional cassette tray assembly 200 has a single piece base plate 202 that is mounted pivotably to a cassette frame (not shown). The base plate 202 is supported by a compression spring 226 towards its front end, below a fixed position rotatable feed wheel or roller 33. As shown, the topmost sheet in the stack has a plane 212 when the springs 226 are compressed by the feed wheel 33 during a feeding stroke. The compressed spring pushes up on the pivotably movable base plate, applying an upward net normal force P1 at the sheet feeding nip when the base plate has a full stack of sheets thereon. The net force P1 is the difference between the maximum force of the spring 226 and the weight of the stack of sheets on the base plate 202. Accordingly, when the base plate is near empty with almost no weight of a stack of sheets acting down on the spring, a greater net normal force P2 will act and push upwardly on the sheet feeding nip. This variation in the normal force contributes to unreliability of a conventional cassette tray assembly in sheet feeding. Additionally as shown, the sheet feeding angle F1° measured as the angle between the top of a stack of sheets and a horizontal plane through the corner snubber is approximately 2° when the cassette tray is full. Full conventional cassette trays (FIG.1) with a small sheet feeding angle F1° of about 2° therefore work more reliably and effectively than partially full or near-empty ones (FIG. 2) where a larger sheet feeding angle F2° undesirably has increased substantially by more than 9° to approximately 11.3°. Such variability in both the sheet feeding angle, and the normal force at the sheet feeding nip are significant factors that undesirably limit sheet holding capacity, and sheet feeding reliability in conventional, non-motorized snubber type cassette trays. There has therefore been a need for a relatively low cost, and highly reliable snubber type cassette tray assembly that can hold and position as well as reliably feed from stacks of sheets greater than the ordinarily limited 250 sheet maximum. US-A-3588106 and US-A-4928951 also disclose cassette tray assemblies although in these cases the feed angle between the sheets and the feed rollers is maintained substantially constant with the height of the stack. In accordance with the present invention, a high capacity cassette tray sheet feeding assembly for supporting a high capacity stack of sheets and for feeding such sheets with a high degree of reliability, the cassette tray sheet feeding assembly comprises: a cassette for the stack of sheets, the cassette having a frame including a front end over which sheets are fed and a fixed position stationary base plate for supporting the stack of sheets; a forward feed corner snubber mounted to one corner of said front end of said cassette frame for preventing the feeding of multiple sheets at a time and for movement with the height of the stack; a pivotable feed wheel assembly including feed wheels positioned relative to the snubber for feeding topmost sheets seriatim from said fixed position stationary base plate, wherein said pivotable feed wheel assembly has a first position defined by a top of a full stack of sheets on said fixed position base plate, and a second position defined by said fixed position base plate, and wherein said pivotable feed wheel assembly has a constant sheet feeding angle, and a constant sheet feeding normal force, for enabling continuous high reliability feeding of sheets as the assembly moves from its first position through to its second position, and is characterised in that the pivotable feed wheel assembly further comprises a lifting mechanism for moving said feed wheels pivotably back and forth between said first and second positions, said lifting mechanism including pivotable lifting bars having a pivot point spaced a desired distance from said front end of said cassette frame so as to maintain said constant sheet feeding angle of said feed wheels, a drive assembly coupled to said lifting bars for moving them about said pivot point, and a wrap spring clutch for selectively controlling drive motion of said drive assembly to a shaft on which said feed wheels are mounted. In accordance with a second aspect of the present invention, there is provided a document production machine using sheets for producing hard copies of images, the document production machine comprising: a machine frame; image forming means mounted to said machine frame and including marking material for forming a visible image on a sheet; a cassette receiving aperture defined within a portion of said machine frame for removably receiving a cassette tray assembly supporting a high capacity stack of sheets; and a high capacity cassette tray sheet feeding assembly as described above mounted in said cassette receiving aperture. In the detailed description of the invention presented below, reference is made, by way of example only, to the accompanying drawings, in which: FIGS. 1 and 2 are schematics of conventional (fixed position feed wheels and pivoting base plate) type cassette trays showing variable sheet feeding angles and variable sheet feeding normal forces at the full and near empty states respectively; FIG. 3 is schematic illustration of the high capacity, high reliability cassette tray sheet feeding assembly of the present invention showing a constant sheet feeding angle and a constant normal force at the sheet feeding nip, both at the full and at the empty states of the cassette tray; FIG. 4 is a schematic plan view of the high capacity, high reliability cassette tray sheet feeding assembly of the present invention; FIG. 5 is a schematic vertical view of the cassette tray sheet feeding assembly of FIG. 1 along the view plane 5 - 5 showing the fixed position stationary base plate and pivoting feed wheel subassemblies of FIG. 4; FIG. 6 is a schematic vertical view of the cassette tray sheet feeding assembly of FIG. 1 along the view plane 6 - 6 showing the fixed position stationary base plate and pivoting feed wheel assembly of FIG. 4; FIG. 7 is a schematic vertical view of the cassette tray sheet feeding assembly of FIG. 4 along the view plane 7 - 7 showing the fixed position stationary base plate and pivoting feed wheel assembly of FIG. 4; and FIG. 8 is a vertical schematic of an exemplary electrostatographic reproduction machine including the high capacity, high reliability cassette tray sheet feeding assembly in accordance with the present invention. Referring first to FIG. 8, a document production machine in the form for example of an exemplary electrostatographic reproduction machine 8 according to the present invention is illustrated. As shown, the machine 8 has conventional imaging processing stations associated therewith, including a charging station AA, an imaginglexposing station BB, a development station CC, a transfer station DD, a fusing station EE, and a cleaning station FF. Importantly, the machine 8 includes a sheet supply station shown generally as GG, that includes the non-motorized high capacity high reliability cassette tray sheet feeding assembly of the present invention (to be described in detail below). The sheet supply station GG advantageously may also include a conventional snubber type cassette tray assembly shown as 200. As shown, the machine 8 has a photoconductive belt 10 with a photoconductive layer 12 which is supported by a drive roller 14 and a tension roller 15. The drive roller 14 functions to drive the belt in the direction indicated by arrow 18. The drive roller 14 is itself driven by a motor (not shown) by suitable means, such as a belt drive. The operation of the machine 8 can be briefly described as follows. Initially, the photoconductive belt 10 is charged at the charging station AA by a corona generating device 20. The charged portion of the belt is then transported by action of the drive roller 14 to the imaging/exposing station BB where a latent image is formed on the belt 10 corresponding to the image on a document positioned on a platen 24 via the light lens imaging system 28 of the imaging/exposing station BB. It will also be understood that the light lens imaging system can easily be changed to an input/output scanning terminal or an output scanning terminal driven by a data input signal to likewise image the belt 10. As is also well known, the document on the platen 24 can be placed there manually, or it can be fed there automatically by an automatic document handler device 25 that includes a multiple document sheet holding tray 27. The portion of the belt 10 bearing the latent image is then transported to the development station CC where the latent image is developed by electrically charged toner material from a magnetic developer roller 30 of the developer station CC. The developed image on the belt is then transported to the transfer station DD where the toner image is transferred to a copy sheet fed from a sheet cassette tray, for example, from the high capacity, high reliabilty cassette tray sheet feeding assembly 70, 72 of the present invention (to be described in detail below). As shown, the sheets so fed are taken away by a copy sheet handling system 31 for transport to the transfer station DD. At the transfer station DD, a corona generating device 32 is provided for charging the copy sheet so as to attract the charged toner image from the photoconductive belt 10 to the copy sheet. The copy sheet with the transferred image thereon is then directed to the fuser station EE. The fuser apparatus at station EE includes a heated fuser roll 34 and backup pressure roll 36. The heated fuser roll 34 and pressure roll 36 rotatably cooperate to fuse and fix the toner image onto the copy sheet. The copy sheet then, as is well known, may be selectively transported to the finishing area, or to a duplex tray 40 along a selectable duplex path 42 for duplexing. The portion of the belt 10 from which the developed image was transferred is then advanced to the cleaning station FF where residual toner and charge on the belt are removed by a cleaning device such as a blade 44, and a discharge lamp (not shown) in order to prepare the portion for a subsequent imaging cycle. When not doing duplex imaging, or at the end of such duplex imaging, the copy sheets upon finally leaving the fusing rolls 34, 36, are passed to finishing area input rolls 46 and 48. From the input rolls 46, 48, the copy sheets are fed, for example, individually to an output tray (not shown) or to a bin sorter apparatus 50 where the sheets can be arranged in a collated unstapled set within the tray or within each bin 52 of the bin sorter apparatus. The bin sorter apparatus 50 can comprise any number of bins 52. A machine user making such set of copy sheets on the reproduction machine 8 can thus manually remove each such set at a time, and insert a corner or edge of the set into a convenience stapler assembly 60 that is built into a portion 62 of the frame of the machine 8. Referring now to FIGS. 3 to 7, the high capacity, high reliability cassette tray sheet feeding assembly 70, 72 of the present invention is illustrated in detail. Cassette tray sheet feeding assemblies 70 and 72 are generally and conceptually identical in design and operation except that the assembly 70 is adapted to feed sheets short edge first, and the assembly 72 is adapted to feed sheets long edge first. Therefore, a detail description of the assembly 70 will suffice for the assembly 72. As shown in FIGS. 3 and 4, the cassette tray sheet feeding assembly 70 of the present invention includes a cassette 73 having a frame 74 that can be removed and reinstalled into the sheet supply station GG of the machine 8. The cassette frame 74, as is well known, can be a portable frame member that contains a single cassette tray and that can be completely removed from the sheet supply station, placed on a platform to be reloaded with sheets, and then reinstalled into the supply station. Alternatively, the cassette frame 74 can be part of a multiple tray drawer frame usually holding more than one non-motorized, removable cassette tray. The drawer frame is retractable from the sheet supply station for sheet reloading, and is reinstallable into a sheet feeding position within the sheet supply station of the machine. The cassette frame 74 in either case has a front or feeding end 76 (for short edge fed sheets) over which sheets are fed, one at a time, to the sheet handling apparatus 31, and then to the image transfer station DD of the machine 8. The front end 76 has a forward feed corner snubber 80 mounted to a corner of such front end 76 so that it is movable up and down, and more importantly, it is automatically movable downwards with the top of a stack of sheets in the cassette tray 73, for preventing the feeding of multiple sheets at a time. The front end 76 also includes a first sheet guiding wall 84 for supporting the lead edges of a stack of sheets advantageously relative to the corner snubbers 80. In accordance with the present invention, the front wall 84 is made movable up and down with the corner snubber 80. The movable corner snubber 80 is mounted, for example, to a side wall of the cassette frame (FIG. 5) so as to be movable up and down, in a constant downward, relative position to a height of a stack 94 of sheets in the tray 73. The cassette frame 74 also includes a rear end 88 that has a second sheet guiding wall 90. The second sheet guiding wall 90 is adjustable backwards and forwards, so as to enable handling of a stack 94 of sheets, of various lengths, such as letter size and legal size length sheets. Importantly however, the first and second walls 84, 90 thus cooperate in each cassette tray 73 to place the leading edge of each sheet of the stack 94, at a constant position relative to the forward feed corner snubber 80. Additionally, in accordance with the present invention, the cassette frame 74 includes a stationary, fixed position base plate 96 for supporting a high capacity stack 94, of more than 250 sheets. More importantly, the high capacity, high reliability cassette tray sheet feeding assembly 70 of the present invention further includes a pivotably movable feed wheel assembly 100 that has at least a pair of feed wheels 102 positioned relative to the movable corner snubber 80 for feeding, with a high degree of reliability into the machine, a top sheet SS of a stack of sheets being supported on the fixed position base plate 96. For cooperating with the pivotable feed wheel assembly 100, the high capacity, high reliability cassette tray sheet feeding assembly 70 advantageously includes path means 104 defining a variable position sheet path leading from the feed wheels 102 into the machine 8. The path means 104 as shown (FIG. 3) include nip forming, sheet take away upper rollers 108, and lower rollers 110. It also includes upper and lower sheet guides 112, 114 respectively, that are mounted pivotably about the sheet take away lower rollers 110. The pivotably movable feed wheel assembly 100 is mounted to frame 116 of the machine has a pivot point PY, and a first position PL1 defined by a top of a full stack 94 of sheets (FIGS. 3, 5, and 7). It also has a second position PL2 defined by the fixed position base plate 96. A drive assembly 120 mounted to the frame 116 of the machine for driving and moving the feed wheel assembly between the first and second positions PL1, PL2 respectively. The feed wheels 102 of the feed wheel assembly 100, in being moved from the first position PL1 to the second position PL2, have a constant sheet feeding angle F3° defined by a top sheet to be fed, and a horizontal plane through the movable corner snubber 80, so as to enable continuous high reliability feeding of sheets into the machine. The feed wheels 102, in being moved as such, also have a constant sheet feeding normal force P3 acting on a stack of sheets on the base plate 96, so as to further enable continuous high reliability feeding of sheets into the machine. In accordance with an aspect of the present invention, a weight supporting means 122 is connected to the shaft 124 of the feed wheels 102 for supporting selectable weights. Accordingly, a selectable weight (not shown) may advantageously be added to the supporting means 122 for changing a value of the constant normal force P3 acting on the stack of sheets. The feed wheel assembly 100 as illustrated includes a lifting mechanism 130 that is mounted to the machine frame 116, and that is coupled to the feed wheel shaft 124 for moving the feed wheels 102 pivotably back and forth between the first and the second positions PL1 and PL2 respectively. The lifting mechanism 130 includes pivotable lifting bars 132 which advantageously have a pivot point PV (FIG. 5) that is spaced a desired distance from the front end 76 of the cassette frame 74 so as to maintain the constant sheet feeding angle F3° of the present invention. Additionally, the lifting mechanism 130 includes a drive assembly 140 (FIG. 5) that is also mounted to the machine frame 116, as well as, coupled to the lifting bars 132 for moving the lifting bars pivotally about the pivot point PV. The drive assembly 140 includes a drive belt 142 for driving the feed wheel shaft 124, and a wrap spring clutch 144 that enables engagement and disengagement of drive motion to the shaft 124. A control collar 146 mounted over the wrap spring clutch 144 is engageable and disengageable by a pawl 148 that is actuatable by a solenoid switch 150 for enabling and disenabling rotation of the shaft 124. The feed wheels 102 are each a segmented roll, and are selectively driven through the wrap spring and solenoid controls as above, through a feed stroke or feed cyle so that the uncut length of the circumference of each wheel is in contact with a sheet SS being fed. The feed wheels 102 are mounted pivotably as such so as to have changing path 152 (FIG. 3) of movement relative to the front end 76 of the cassette frame 74. The document production machine which includes the pivotably movable feed wheel assembly of the present invention provides for feeding with a high degree of reliability from a fixed position base plate cassette tray that is removably insertable into the cassette receiving aperture. The cassette tray having the fixed position base plate, and the pivotably movable feed wheel assembly comprise the high capacity, high reliability cassette tray sheet feeding assembly of the present invention that fully satisfies the aims and advantages hereinbefore set forth.

Claims: A high capacity cassette tray sheet feeding assembly (70,72) for supporting a high capacity stack (94) of sheets and for feeding such sheets with a high degree of reliability, the cassette tray sheet feeding assembly (70,72) comprising: a cassette (73) for the stack (94) of sheets, the cassette (73) having a frame (74) including a front end (76) over which sheets are fed and a fixed position stationary base plate (96) for supporting the stack (94) of sheets; a forward feed corner snubber (80) mounted to one corner of said front end (76) of said cassette frame (74) for preventing the feeding of multiple sheets at a time and for movement with the height of the stack; a pivotable feed wheel assembly (100) including feed wheels (102) positioned relative to the snubber (80) for feeding topmost sheets seriatim from said fixed position stationary base plate (96), wherein said pivotable feed wheel assembly (100) has a first position defined by a top of a full stack (94) of sheets on said fixed position base plate (96), and a second position defined by said fixed position base plate (96), and wherein said pivotable feed wheel assembly (100) has a constant sheet feeding angle (F3°), and a constant sheet feeding normal force (P3), for enabling continuous high reliability feeding of sheets as the assembly (100) moves from its first position through to its second position, characterised in that the pivotable feed wheel assembly further comprises a lifting mechanism (130) for moving said feed wheels (102) pivotably back and forth between said first and second positions, said lifting mechanism (130) including pivotable lifting bars (132) having a pivot point (PV) spaced a desired distance from said front end (76) of said cassette frame (74) so as to maintain said constant sheet feeding angle (F3°) of said feed wheels (102), a drive assembly (140) coupled to said lifting bars (132) for moving them about said pivot point (PV), and a wrap spring clutch (144) for selectively controlling drive motion of said drive assembly (140) to a shaft (124) on which said feed wheels (102) are mounted. An assembly according to claim 1, further including feed wheels (102) positioned relative to the corner snubber (80) on the stack (94) of sheets for feeding sheets from the stack (94), the feed wheels (102) being movable between said first and second positions to maintain the constant sheet feeding angle (F3°). An assembly according to claim 2, wherein the feed wheels (102) are mounted on the shaft (124) which has weight supporting means (122) connected thereto for supporting a selectable weight for charging the constant sheet feeding normal force (P3). An assembly according to claim 2 or claim 3, further including path means (104) defining a variable position sheet path from said feed wheels (102). An assembly according to claim 4, wherein said path means (104) include nip forming sheet take away upper rollers (108) and lower rollers (110), and upper and lower sheet guides (112,114) mounted pivotably about said sheet take away lower rollers (110). A document production machine (8) using sheets for producing hard copies of images, the document production machine comprising: a machine frame (116); image forming means (BB) mounted to said machine frame (116) and including marking material (CC) for forming a visible image on a sheet; a cassette receiving aperture defined within a portion of said machine frame (116) for removably receiving a cassette tray assembly supporting a high capacity stack of sheets; and a high capacity cassette tray sheet feeding assembly (70,72) according to any one of the preceding claims mounted in said cassette receiving aperture.

Inventors: HOLLAND CARL W, MILLER GREGORY P, HOLLAND, CARL W., MILLER, GREGORY P.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1997
Main classification: G03G15
IPC codes: B65H1, G03G15, B65H3