Bottom scuff sheet feeder

Sheet feed apparatus including a scuff feeder for reliably transporting sheets from the bottom of a stack of sheets without marking of the sheets. The sheet transport apparatus comprises a retard device, located in contact with the lead edge, in the direction of sheet feed, of a sheet stack for preventing double feeding of sheets from the sheet stack. A scuff feed belt is located to have a run extending in the direction of sheet feed substantially above the surface of the tray and below the retard device to form a sheet separation nip with the retard device. The run of the scuff feed belt presents an area of contact with the sheet stack to carry about 50% of the weight of the sheet stack. Additionally, the scuff feed belt of the scuff feeder and the retard device respectively have a plurality of grooves oriented in the direction of sheet feed. The grooves assure adequate sheet feeding contact by the scuff feed belt and the retard device in that the lands of the grooves are far enough apart to penetrate any oil on the sheets and collect the oil in the valleys away from the traction area, yet close enough together to prevent localized high pressure points which would result in toner ruboff.

BACKGROUND OF THE INVENTION 
The present invention relates in general to feeders for transporting sheets 
from a sheet stack, and more particularly, to a scuff feeder for reliabily 
transporting sheets from the bottom of a stack of sheets without marking 
of the sheets. 
In modern reproduction apparatus, such as electrostatographic copiers or 
printers, for example, a latent image of information to be reproduced is 
formed on a uniformly charged dielectric member to altering the charge in 
an image-wise pattern. The latent image charge pattern is then developed 
with pigmented marking particles. Thereafter, the developed image is 
transferred to a receiver member and fixed to the receiver member by 
application of heat and/or pressure to form the desired reproduction. 
In order to improve productivity of reproduction apparatus, certain 
reproduction apparatus provide sheet feed paths capable of enabling the 
apparatus to reproduce information on both sides of receiver sheets. This 
is commonly referred to as duplex copying. Duplex copying may be 
accomplished in a single pass through the reproduction cycle of a 
reproduction apparatus (single pass duplexing), or in two passes through 
the reproduction cycle (double pass duplexing). For single pass duplexing, 
developed images of appropriate information are transferred respectively 
to each side of a receiver sheet and then fixed simultaneously to the 
receiver sheet. On the other than, for double pass duplexing, a sheet feed 
path is provided having an intermediate tray in which sheets, after having 
developed images transferred and fixed respectively on one side thereof, 
are stored and then at a subsequent time fed seriatim from the 
intermediate tray to have developed images transferred and fixed 
respectively on the opposite side thereof. 
While double pass duplex copying is typically somewhat slower in overall 
reproduction productivity than single pass duplex copying, double pass 
duplex copying does simplify handling of receiver sheets during transport 
to the fixing device. This is due to the fact that only one side of the 
respective receiver sheets bears an unfixed toner image. However, the use 
of an intermediate tray in reproduction apparatus for enabling the 
production of duplex copies does expose the reproduction apparatus to the 
possibility of encountering several operational problems. Specifically, 
after the first side reproduction is formed on a sheet, the toned image on 
the first side may be soft due to insufficient time for the marking 
particles comprising the toned image to completely cool for fixing of the 
image to the sheet. This may result in fresh toner rubbing off one sheet 
onto the next sheet, as the sheets are fed from the intermediate tray, 
forming undesirable marks on such next sheet. Additionally, it is common 
practice to use an offset preventing oil (for example, a silicone oil) in 
the reproduction apparatus fusing mechanism. Some quantity of this offset 
preventing oil from the fusing mechanism may be deposited on the surfaces 
of the sheets when the fusing mechanism is used to fix the first side 
reproductions to the sheets respectively. As a result, the oil may 
materially alter the coefficient of friction in the mechanism for feeding 
sheets from the intermediate tray, thereby interfering with reliable 
feeding of the sheets from the intermediate tray (may result in misfeeds 
or multifeeds). 
SUMMARY OF THE INVENTION 
This invention is directed to a sheet feed apparatus including a scuff 
feeder for reliably transporting sheets from the bottom of a stack of 
sheets without marking of the sheets. The sheet transport apparatus 
comprises a retard device, located in contact with the lead edge, in the 
direction of sheet feed, of a sheet stack for preventing double feeding of 
sheets from the sheet stack. A scuff feed belt is located to have a run 
extending in the direction of sheet feed substantially above the surface 
of the tray and below the retard device to form a sheet separation nip 
with the retard device. The run of the scuff feed belt presents an area of 
contact with the sheet stack to carry about 50% of the weight of the sheet 
stack. 
As an additional aspect of this invention, the scuff feed belt of the scuff 
feeder and the retard device respectively have a plurality of grooves 
oriented in the direction of sheet feed. The grooves assure adequate sheet 
feeding contact by the scuff feed belt and the retard device in that the 
lands of the grooves are far enough apart to penetrate any oil on the 
sheets and collect the oil in the valleys away from the traction area, yet 
close enough together to prevent localized high pressure points which 
would result in toner ruboff. The grooves have a substantially square 
cross-section such that as wearing occurs, the contact relationship 
remains relatively constant. 
The invention, and its objects and advantages, will become more apparent in 
the detailed description of the preferred embodiment presented below.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the accompanying drawings, the bottom scuff sheet feeder, 
according to this invention, is designated generally by the numeral 10. 
The bottom scuff sheet feeder 10 includes a tray 12 and a scuff feed 
mechanism 20 associated with the tray for feeding sheets seriatim from the 
tray in the direction of arrow A. The tray 12 has a substantially planer 
surface 12a upon which a stack of sheets S (shown in phantom lines in 
FIGS. 1 and 2) may be located. In the instance where the tray 12 serves as 
an intermediate tray for a reproduction apparatus capable of double pass 
duplex copying, sheets are fed seriatim to the tray 12 and collected on 
the surface 12a to form the stack S. Of course this invention is also 
suitable for use where a stack of sheets is manually or automatically 
loaded onto the surface 12a. 
The opposed marginal edges of the sheet stack S, in the crosstrack 
direction relative to the sheet feed direction, are bounded by side guides 
16, and 18. The rear marginal edge of the sheet stack is bounded by an end 
guide 14. The side guides 16, 18 and the end guide 14 are adjustable, in 
any well known manner, in order to accommodate sheet stacks of various 
dimensions. Adjustably setting the location of the side guides and end 
guide maintains the respective loaded sheet stacks in a desired position 
on the surface 12a of the tray 12 relative to the scuff feed mechanism 20. 
The scuff feed mechanism 20 is generally of the type described in U.S. Pat. 
No. 5,007,627, issued Apr. 16, 1991, in the names of Giannetti et al. The 
Giannetti et al patent can be referred to for a detailed description of 
the basic scuff feed mechanism and its operation. Such scuff feed 
mechanism is discussed hereinbelow in sufficient detail for a full 
understanding of the advantageous modifications to the basic scuff feed 
mechanism provided by this invention. 
Specifically, the scuff feed mechanism 20 includes a scuff feed belt 22 and 
a retard device 24. The scuff feed belt 22 is drivingly entrained about 
rollers 26, 28 located to establish a run for the scuff feed belt 
positioned above the level of the surface 12a of the tray 12 (see FIGS. 2 
and 3) to substantially support the sheet stack S in a manner discussed 
below. Roller 28 is mounted on a shaft 30 coupled through a clutch 32 (and 
a pulley and belt arrangement G) to a motor M for selective rotation of 
the shaft. When it is desired to feed a sheet from the stack S, the scuff 
feed belt 22 is driven in the direction of arrow B, about the closed loop 
path defined by the rollers 26 and 28, by energizing the clutch 32 to 
connect the shaft 30 to the motor M. 
The retard device 24, for preventing multisheet feeds, includes a retard 
roller 34 supported by arms 36. The arms 36 are, in turn, supported for 
pivotable movement about a shaft 38 located downstream, in the direction 
of sheet travel, of the retard roller 34 and above the plane of the 
surface 12a of the tray 12. The retard roller 34, which normally rests on 
the scuff feed belt 22, engages the lead marginal edge of the sheet stack 
S and forms a separation nip with the scuff feed belt. An internal brake 
40, associated with the retard roller 34, prevents rotation of the retard 
roller when one or more sheets enter the nip between the retard roller and 
the scuff feed belt 22, but permits rotation of the retard roller when no 
sheets are in such nip. This keeps the main body of the sheet stack out of 
the nip itself. As a result, sheet-to-sheet contact in the nip and under 
the pressure exhibited therein is avoided. Pressure between the sheets, as 
further discussed below, is a prime contributor to toner ruboff. 
As a more detailed explanation of how the internal brake functions to aid 
the retard roller 34 in preventing multisheet feeds, it is noted that the 
coefficients of friction of both the scuff feed belt 22 and the retard 
roller 34 are selected to be quite high when compared to the coefficients 
of friction of sheets being fed. The braking force of the internal brake 
40 on the retard roller 34 is selected to be sufficiently high enough to 
keep the retard roller from rotating when the bottom sheet, under the 
urging of the scuff feed belt 22, slides on the next adjacent sheet 
through the separation nip between the retard roller and the scuff feed 
belt. Accordingly, such next adjacent sheet remains stationary in the 
entrance to the separation nip as the bottom sheet is separated from the 
sheet stack S (see FIG. 4). That is, such next adjacent sheet is held 
further back in relation to the sheet stack and less under the retard 
roller 34 than with previously known scuff feeders. At the time between 
sheet feeds when the bottom sheet has left the separation nip or when the 
last sheet in the stack has been fed, the friction urging force on the 
retard roller 34 by the scuff feed belt 22 is substantially increased over 
that exerted with a sheet between the scuff feed belt and the retard 
roller. Under such condition, the internal brake 40 has insufficient 
braking force to prevent the retard roller from rotating, and thus the 
retard roller will be rotated by the frictional engagement with the scuff 
feed belt. This has the effect of bringing the next sheet to be fed from 
the stack into the separation nip. Such frictionally induced rotation has 
a further benefit in that it prevents undue wear and tear on the scuff 
feed belt and retard roller that would otherwise occur due to relative 
movement between the retard roller and the scuff feed belt when no sheet 
is present in the separation nip therebetween. 
A sheet transport device 42 is located immediately downstream, in the 
direction of sheet feed, from the separation nip formed by the scuff feed 
belt 22 and the retard roller 34. The sheet transport device 42 includes a 
drive roller 44 mounted on a shaft 46. The shaft 46 is coupled through a 
clutch 48, and the pulley and belt arrangement G, to a motor (for example, 
motor M). Selective activation of the clutch 48 provides for rotation of 
the shaft, and thus selective rotation of the drive roller 44. A roller 50 
is supported by arms 52, which are in turn supported for pivotable 
movement about the shaft 38. Spring members 54 urge the arms 52 in a 
direction (clockwise in FIG. 1) such that the roller 50 forms a feed nip 
with the roller 44. 
The purpose of the feed nip between the roller 50 and the drive roller 44 
is to effect transport of a sheet removed from the sheet stack S by the 
scuff feed belt 22 away from the tray 12 in the direction of arrow A. That 
is, when a sheet is removed from the stack S by the scuff feed belt 22 and 
forwarded to the feed nip, the clutch 48 is activated to cause the drive 
roller 44 to rotate and transport the sheet away from the tray 12. The 
surface velocity of the drive roller 44 is selected to be slightly greater 
than the surface velocity of the scuff feed belt 22. As such, a separated 
sheet is sped up on entering the nip between the drive roller 44 and the 
roller 50. This assures removal of the sheet from the separation nip 
between the scuff feed belt 22 and the retard roller 34, thereby further 
preventing any misfeeds (multifeeds) of sheets from the stack S in the 
tray 12. 
As noted above, previous scuff sheet feeders have suffered from two major 
problems: misfeeds (multifeeds) due to, for example, fuser oil on the 
individual sheets; and marking of adjacent sheets due to toner ruboff. As 
will be readily appreciated, when considering remedies to these problems, 
one is led to opposite suggestions for each of the respective problems. 
That is to say, to prevent misfeeds (multifeeds) due to the reduction in 
friction caused by oil on the sheets, technology would suggest that the 
pressure in the sheet separation nip should be increased. However, an 
increase in the sheet separation nip pressure would increase the 
possibility that soft toner will be rubbed off, thus accentuating the 
marking problem. Of course, reducing the sheet separation nip pressure to 
relieve the toner ruboff marking problem would increase the potential for 
misfeeds (multifeeds). 
The sheet feeder 10 according to this invention solves both the misfeeding 
and toner ruboff marking problems by markedly reducing the pressure in the 
sheet separation nip while substantially extending the area over which the 
sheet separation nip pressure is applied. Specifically, the scuff feed 
belt 22 is arranged such that the upper run thereof supports about 50% of 
the weight of the sheet stack S in the tray 12. As shown in FIG. 3, the 
scuff feed belt 22, which is much wider than those of prior known scuff 
feed belts, extends in the direction cross-track to the sheet feed 
direction A over a distance to support the major portion of the sheet (at 
least 30% of the cross-track sheet dimension). Further, the portions 16a, 
18a of the side guides 16, 18 have upstanding louver-like segments 16b, 
18b respectively to present less surface area contact with that portion of 
the sheet stack supported on such portions of the side guides. Since any 
oil on the sheets would tend to cause the sheets to stick to a flat 
supporting surface, the louver-like arrangement reduces the frictional 
engagement area between the side guide portions 16a, 18a and the sheets, 
and thus reduces the friction forces acting in opposition to feeding of 
the sheets from the stack. 
This described arrangement substantially increases the effective traction 
surface area for scuff feeding of the sheets from the sheet stack by the 
scuff feed belt 22 and decreases the contact area supporting the sheet 
stack in the tray 12. Accordingly, the forces effecting sheet separation 
are distributed over a substantially increased area, reducing the force 
per unit area on any sheet; and the friction force exerted on the sheet by 
the tray surface 12a, retarding sheet separation, is reduced. While the 
total force to effect separation is at least as great as heretofore 
provided, the actual pressure at any point is substantially reduced (such 
pressure reduction is on the order of a factor of 50 from previously known 
scuff feeders). This substantially reduces any potential to rub off toner 
from one sheet to an adjacent sheet. 
It should also be noted that the sheet engaging outer surface of the scuff 
feed belt 22 is formed of a material having a high coefficient of 
friction, and is grooved to maintain effective traction contact with the 
sheet being fed in the sheet separation nip. The grooved configuration of 
the scuff feed belt provides small lands 22a, which are effective in 
penetrating any oil on the sheet, and valleys 22b, which establish a 
reservoir in which the oil may collect (see FIG. 5). The lands, oriented 
in the intrack direction, optimally make up approximately 30% of the scuff 
feed belt area. The grooves are of a generally square cross-section 
configuration. This is important in that, with such configuration, wearing 
of the scuff feed belt over time does not appreciably alter the optimum 
surface area contact between the scuff feed belt and the sheets being fed. 
The grooves are spaced far enough apart such that the lands 22a penetrate 
any oil on the sheets and the oil collects in the valleys 22b away from 
the traction area, yet close enough together to prevent localized high 
pressure points which would result in toner ruboff. With such grooved 
configuration for the scuff feed belt 22, the potentially adverse feeding 
effect of oil on the sheets to be fed by the scuff feed belt is 
substantially overcome. 
Another way in which the sheet separation nip pressure is substantially 
reduced, involves the arrangement of the retard roller 34. The retard 
roller 34 is of a larger diameter and an increased longitudinal dimension 
when compared to retard rollers heretofore utilized (such as, for example, 
in the aforementioned U.S. Pat. No. 5,007,627). Additionally, the retard 
roller is formed of a substantially rigid hollow core 34a with a high 
coefficient of friction overcoat of soft foam 34b sufficient to yield 
about a 20% radial deflection for the retard roller (see FIG. 4). The core 
34a has a relationship to the retard roller such that its diameter is 
approximately 50% of the overall retard roller diameter. As a result of 
the radial deflection of the retard roller, the sheet separation nip area 
established by engagement of the retard roller 34 with the scuff feed belt 
22 is about 50 times greater than previously provided. At the same time, 
the rigid hollow core 34a prevents any substantial tangential deflection 
of the retard roller which might allow a subsequent sheet to be 
prematurely fed into the separation nip between the retard roller and the 
scuff feed belt. 
As with the scuff feed belt 22, the retard roller 34 has a groove pattern 
to provide adequate sheet contact (i.e., penetrate any oil on the sheet 
and collect the oil away from the traction area, and prevent localized 
high pressure points, as described above). It is important to realize that 
the groves in the retard roller 34 should not interlock with the grooves 
in the scuff feed belt 22 (see FIG. 5). This is because, as previously 
described, the scuff feed belt is used to rotate the retard roller between 
sheet feeds (i.e., overcome the action of the internal brake 40) to 
prevent wear therebetween. Therefore, there must be sufficient contact 
between the lands of the grooves of the scuff feed belt 22 and the lands 
of the grooves of the retard roller 34 for the belt to rotate the roller 
to pull the next sheet into the separation nip. 
The material forming the retard roller 34 must also exhibit a high tear 
strength and a high elasticity rating to overcome the fact that the retard 
roller is continually being rubbed by sharp edges of the sheets being fed. 
Further, the retard roller material must be stable in the harsh 
environment of the reproduction apparatus, such as elevated temperatures 
and the presence of fuser (silicone) oil and ozone. 
The pivot angle of the arms 36 supporting the retard roller 34 are set to 
approximately 28.degree..+-.5.degree. from the horizontal. The increased 
pivot angle, over prior scuff feeders, results in an increased normal 
force in the sheet separation nip at the start of sheet separation, and a 
reduced normal force in the nip as the separated sheet moves out of the 
sheet stack. This reduces the average sheet-to-sheet pressure and thus the 
tendency for marking (toner rub off between adjacent sheets). 
Additionally, as discussed above, the retard roller internal brake 40 has 
a relatively high braking force. This holds a second sheet further back in 
relation to the sheet stack and less under the retard roller 34. This 
further assures a reduced sheet-to-sheet pressure, and likewise reduced 
tendency for marking due to toner ruboff. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention as set forth in the claims.