Apparatus for feeding sheets one by one

An apparatus for feeding sheets one by one from a group of at least partially overlapping sheets, in which a conveyor belt in contact with the lowermost sheet is driven to feed that sheet in the desired transport direction while a sheet separating roller forming a nip with the belt is driven so as to move the surface of the roller through the nip in the opposite direction, thus holding back of the nip sheets lying on the lowermost sheet, is provided with a displaceable member, for example a flat end portion of a leaf spring wound into a spiral, which has a smooth underside to receive under this member and press on the sheets approaching the nip and has a forward end edge slidably engaged with the surface of the roller immediately adjacent to the location where the sheets contact the roller. The displaceable member prevents the sheets from curling up or buckling in the vicinity of the roller, irrespective of the number of sheets and irrespective of variations of the position of the separating roller.

This invention relates to an apparatus for feeding sheets one by one from a 
group of at least partially overlapping sheets, so as to make sure that 
only one sheet at a time is delivered into a processing path such, for 
example, as a sheet transport path of a copying machine. 
German Offenlegungsschrift No. 2 334 551 discloses an apparatus for this 
purpose which comprises a drivable conveyor system for advancing at least 
the outermost sheet from a stack of sheets and a separator roller that 
forms a nip with a member of the conveyor system and is driven in 
direction opposite to the direction of the advance of the sheets in order 
to retain or push backward the leading edges of sheets fed to the roller 
with the outermost sheet. 
In that known apparatus, a plate is provided between the stack and the 
sheet separating roller, with part of the plate extending at some distance 
from and approximately concentric to the surface of the roller. The plate 
insures that only a limited number of sheets can be fed simultaneously 
from the stack toward the roller. This plate device, however, is 
disadvantageous in that the leading edges of sheets coming into contact 
with the separating roller may curl up and then reach the space between 
the roller and the plate, thus damaging the sheets. The sheets may also be 
damaged by being buckled in the space between the stack and the plate as a 
result of the counteracting forces exerted on the sheets by the roller and 
the conveyor member. 
These disadvantages will occur particularly when thin and/or limp sheets 
are processed, or sheets which already exhibit a tendency to curl or 
buckle, for example, because of having been folded previously. 
The object of the present invention is to provide an apparatus for feeding 
sheets one by one from a group of at least partially overlapping sheets 
advanced by a conveyor, whereby the above-noted disadvantages can be 
overcome. Thus, with this apparatus the position of the sheets advanced by 
a conveyor to a sheet separating roller is controlled so that only one 
sheet at a time will be fed through the nip of the roller and the sheets 
will neither be curled up at the roller nor buckled as they are advanced 
to the nip. 
According to the present invention, in an apparatus including conveyor 
means for engaging with and drivable to advance at least the outermost 
sheet of a group of at least partially overlapping sheets, a sheet 
separating roller positioned adjacent to the conveyor means so as to form 
a nip with it and means for driving the roller to move its surface through 
the nip in a direction opposite to the direction of advance of sheets by 
the conveyor means, a sheet position controlling means is provided which 
comprises a displaceable member that is disposed behind the nip, is 
continually pressed toward the conveyor means, has an underside that bears 
under pressure slidably against a leading portion of a sheet or sheets in 
the vicinity of the nip, and has a forward end edge of the member disposed 
in slidable contact with the surface of the separating roller behind the 
nip. As a result of this position controlling means, the sheets 
approaching the nip are kept completely flat over an appreciable leading 
portion thereof until they reach the roller surface, so that they are 
prevented from curling and buckling notwithstanding the forces exerted on 
their leading edges by the counter-moving surface of the roller. 
As another feature of this arrangement, the displaceable member can remain 
in contact with the surface of the separating roller even upon variations 
of the location of the roller relative to the conveyor means at the nip, 
which variations may occur, for example, as a result of wear of the roller 
surface; and the displaceable member can also adapt automatically to the 
number of sheets present near the nip.

The apparatus as shown schematically in FIGS. 1 and 2 comprises an endless 
conveyor belt 1 running about a driving roller 2 and a freely rotatable 
roller 3. Roller 2 can be driven in the direction indicated by the arrow. 
A stack 4 of sheets is supported partially on the upper flight 1A of the 
conveyor belt and partially on a fixed plate 5. The belt flight 1A extends 
away from the stack 4 in the direction of conveyance of the sheet. An 
abutment strip 6 disposed above and across the belt flight 1A limits the 
position of sheets at the front side of the stack and forms a slit-like 
passage 7 through which a number of at least partially overlapping sheets 
can pass simultaneously between the lower edge of the abutment strip 6 and 
the conveyor belt. 
A sheet separating roller 8 is positioned adjacent to the belt flight 1A so 
as to form with the belt a nip located in the path of movement of the 
sheets, though at some distance from the passage 7. The shaft of the 
roller 8 is mounted in bearings in at least one arm 9 which is swingable 
about the axis of a drivable shaft 10. The roller shaft is connected via a 
belt 11 with the shaft 10 so that by rotation of the shaft 10 the roller 8 
can be rotated to move its surface through the nip in the direction 
opposite to the direction of movement belt flight 1A. 
By appropriate choice of materials the conveyor belt 1 and the surface of 
the sheet separating roller 8 are readily made so that the friction 
between a sheet and the conveyor belt is greater than the friction between 
a sheet and the roller surface and the friction between the roller surface 
and a sheet is greater than the friction between two sheets. Thus, while 
the lowermost sheet of the group being advanced to the roller is being 
delivered by the belt through the nip between the roller and the belt, 
each other sheet of the group or pile will be retained or pushed backward 
by the roller surface moving counter to the belt at the nip. 
In the apparatus according to FIG. 1, a position controlling means in the 
form of a smooth leaf spring 12 wound into a spiral is disposed in the 
space between the passage 7 and the sheet separating roller 8. The leaf 
spring 12 has a substantially flat, displaceable end portion 12A which is 
pressed yieldably toward the conveyor belt 1 or against a leading portion, 
in the vicinity of roller 8, of the sheet or sheets lying on the belt. The 
flat end portion 12A extends to a free end thereof which is held 
resiliently in slidable contact with the surface of the separator roller. 
When the roller 2 is driven, the conveyor belt 1 feeds sheets from the 
stack 4 via the passage 7. The number of sheets entrained is restricted by 
the height of the passage 7. The sheets can readily slide along the smooth 
underside of the leaf spring 12 and come into contact with the separator 
roller 8. The underside of the spring 12 along and leading into its 
displaceable end portion 12A is made smooth so as to keep the friction of 
that portion relative to the sheets as low as practicable, e.g., by making 
the surface of the spring therealong of well-polished metal or of a 
plastic having a low coefficient of friction, such as e.g., 
polytetrafluoroethylene. 
The sheet separating roller 8 exerts a retaining or backward pushing 
frictional force on the leading edges of the entrained sheets and on the 
free end of the leaf spring 12, while the displaceable end portion 12A 
presses down flatly on these sheets. Only the bottom sheet is fed through 
the nip, as the conveyor belt 1 exerts a frictional force on the sheet far 
greater than the frictional force of the roller surface on the leading 
edge of the sheet. 
The flat end portion 12A of the leaf spring rests on the top one of the 
entrained sheets. The leading edges of these sheets bear against the 
roller 8 in such a way that, while abutting the roller, these sheets rest 
on one another with their edges offset, somewhat like roof tiles. The 
displaceable flat end portion 12A of the leaf spring prevents the sheets 
from buckling in the space between the passage 7 and the roller 8, and 
since the free end of the displaceable portion 12A is held resiliently in 
sliding contact with the surface of roller 8 rotating thereagainst, the 
leading edges of the sheets are prevented from curling up behind the 
roller. 
Depending upon the number of sheets coming between the conveyor belt and 
the leaf spring, and the thickness thereof, the leaf spring will be 
displaced upward to a varying degree with consequent variation of the 
location of its point of contact with the surface of the roller 8. The 
accompanying horizontal movement of the free end and flat portion 12A of 
the spring is accommodated by the spiral portion of the leaf spring 12. As 
another result of the horizontal mobility of the flat end portion of the 
leaf spring, its free end will be kept in contact with the roller surface 
when a change occurs in the location of the nip between the roller 8 and 
the belt flight 1A. Such a change will occur, for example, upon a decrease 
of the diameter of the roller 8 due to wear, when the roller position will 
be shifted in the direction toward the leaf spring by the action of a 
spring 17 that pulls on the swingable arm 9 of the roller. 
The force with which the flat end portion of the leaf spring presses on the 
conveyor belt or on the sheets thereon can be adjusted by turning the 
pivot element 13 to which the fixed end of the leaf spring is secured. 
Such an adjustment can also ensure that when sheets are not present the 
free end of the leaf spring will not be pulled past the nip of the roller 
by friction of the belt. 
In another embodiment of the invention, as illustrated in FIG. 2, the 
position controlling means comprises a leaf spring 14 having a 
displaceable flat end portion thereof held in contact with the conveyor 
belt or the sheets thereon, and having its free end held in slidable 
contact with the surface of the sheet separating roller 8, in 
substantially the same way as described hereinbefore with reference to 
FIG. 1. In this embodiment, however, the other end of the leaf spring 14 
is secured to a turnable element 15 which is fixed pivotally to a 
projection 16 of a swingable arm 9a on which the roller 8 is mounted. A 
compression spring 17a presses arm 9a toward belt flight 1A. 
It results in the embodiment of FIG. 2, since the leaf spring 14 is fixed 
to the arm 9a, that the leaf spring will follow any movement of the arm 9a 
and hence any displacement of the sheet separating roller 8. Consequently 
the leaf spring to be used in this embodiment can have less curvature than 
the leaf spring 12 of the apparatus according to FIG. 1, although it still 
is to keep its displaceable flat end portion sufficiently mobile relative 
to the point where the spring 14 is fixed to the turnable element 15 so 
that the free end of the spring can continue to be in contact with a part 
of the surface of the roller 8 behind the nip in the presence of the 
maximum number of sheets that will be fed to the separating roller. 
It will be apparent that a displaceable member continually pressed toward 
the conveyor means and contacting a sheet separating roller so as to serve 
functions of the spring pressed end portion of element 12 or element 14 
may also be provided by devices of other forms. For instance, a suitably 
formed block may be provided for pressing by its own weight on the sheets 
in the space leading to the sheet separating roller, this block being 
provided with a smooth flat underside having a tapering entry portion to 
admit sheets beneath the block and with a forward end edge that can stay 
in sliding contact with the roller surface. 
In still another form of a device embodying the invention, the displaceable 
member may also extend laterally to either side of the nip of the sheet 
separating means so as to hold a sheet or sheets pressed flat on the 
conveyor belt in these regions as well.