U.S. patent application number 13/120439 was filed with the patent office on 2011-09-29 for sheet containing device.
Invention is credited to Dimitrios Kostudis, Stefan Schluenss.
Application Number | 20110233848 13/120439 |
Document ID | / |
Family ID | 41278236 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110233848 |
Kind Code |
A1 |
Kostudis; Dimitrios ; et
al. |
September 29, 2011 |
SHEET CONTAINING DEVICE
Abstract
In a sheet conveying device comprising at least one conveying
arrangement with a porous conveyor belt that can be moved in a
circulating manner, at least one vacuum source and at least one air
line whose one end is connected to the vacuum source and whose
other end abuts against the porous conveyor belt, a simple and
automatic control of the suction pressure for different sheets is
achieved by at least one constant pressure controller in the air
line in order to essentially maintain constant a pressure
differential between the interior space of the air line and its
environment.
Inventors: |
Kostudis; Dimitrios; (Wedel,
DE) ; Schluenss; Stefan; (Schacht-Audorf,
DE) |
Family ID: |
41278236 |
Appl. No.: |
13/120439 |
Filed: |
July 24, 2009 |
PCT Filed: |
July 24, 2009 |
PCT NO: |
PCT/EP2009/059582 |
371 Date: |
May 10, 2011 |
Current U.S.
Class: |
271/12 ;
271/90 |
Current CPC
Class: |
B65H 2515/342 20130101;
B65H 3/124 20130101; B65H 2515/342 20130101; B65H 2511/22 20130101;
B65H 7/16 20130101; B65H 2406/36 20130101; B65H 2220/01 20130101;
B65H 2220/02 20130101 |
Class at
Publication: |
271/12 ;
271/90 |
International
Class: |
B65H 5/22 20060101
B65H005/22; B65H 3/12 20060101 B65H003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2008 |
DE |
10 2008 049 809.2 |
Sep 30, 2008 |
DE |
10 2008 049 810.6 |
Claims
1. Sheet conveying device comprising: at least one conveying
arrangement with a porous conveyor belt that can be moved in a
circulating manner; at least one vacuum source; at least one air
line whose one end is connected with the vacuum source and whose
other end abuts against the porous conveyor belt; at least one
constant pressure controller provided in the air line in order
maintain a substantially constant pressure differential between the
interior space of the air line and its environment, wherein the air
line comprises a main line that is connected, at its one end, to
the vacuum source and comprising a plurality of branch lines, each
of the plurality of branch lines leading to the conveying
arrangement.
2. Sheet conveying device as in claim 1, with the conveyor belt
being arranged so as to circulate around at least two rollers.
3. Sheet conveying device as in claim 1, with the air line
containing downstream of the constant pressure controller a main
flap in order to partially or completely seal the air line with
respect to the vacuum source.
4. (canceled)
5. (canceled)
6. Sheet conveying device as in Claim 4, with one constant pressure
controller being arranged in the region of each branch line.
7. Sheet conveying device as in claim 4, with the main flap being
arranged so as to shut off the branch line with respect to the main
line.
8. Sheet conveying device as in claim 7, with the constant pressure
controller being arranged between the main flap and the free end of
the branch line.
9. Sheet conveying device claim 1, with the constant pressure
controller being in an open position when a pressure differential
between the interior space of the air line and its environment is
greater than a threshold value.
10. Sheet conveying device claim 1, with the constant pressure
controller comprising a valve element and a spring that holds the
valve element in a closed position.
11. Sheet conveying device as in claim 10, with the spring
displaying a spring characteristic that is variable along the
spring path.
12. Sheet conveying device as in claim 10, with the spring bias
being adjustable.
13. Sheet conveying device as in claim 1, said device further
comprising a pressure sensor.
14. Sheet conveying device as in claim 4, said device comprising at
least one pressure sensor that is arranged in a branch line,
respectively.
15. Sheet conveying device as in claim 13, said device further
comprising a controllably driven pressure control valve and a
control device that communicates with the pressure sensor and the
pressure control valve in order to control the actuation of the
pressure control valve.
16. Sheet conveying device as in claim 1, with the constant
pressure controller comprising a flap valve.
17. Sheet conveying device as in claim 1, with the constant
pressure controller comprising a sliding valve.
18. Sheet conveying device as in claim 15, with the opening
cross-section of the sliding valve not increasing proportionally
along its opening path.
19. Sheet conveying device as in claim 1, said device being
arranged in a sheet separating device.
20. Sheet conveying device as in claim 1, said device being
arranged in a feeder of a printing machine.
21. The sheet conveying device claim 1 further comprising a sheet
support for the accommodation of a stack of sheets, with at least
one part of the sheet conveying device being movable toward the
sheet support and away therefrom in order to be able to lift a
sheet off the stack of sheets on the sheet support.
22. Sheet conveying device as in claim 21, with the sheet support
being height-adjustable.
23. Sheet conveying device as in claim 21, with the part of the
sheet conveying device being the at least one conveyor belt.
24. Sheet conveving device as in claim 23, with the part of the
sheet conveying device being at least one of the rollers.
25. Sheet conveying device as in claim 21, with the part of the
conveying arrangement being at least one suction finger connected
to the vacuum source.
26. Sheet conveying device as in claim 25, with the suction finger
being preferably separated from the vacuum source when said suction
finger is in a position away from the sheet support.
27. Sheet conveying device as in claim 26, with the connection of
the suction finger with the vacuum source being preferably open
toward the environment when said suction finger is in its position
away from the sheet support.
28. Sheet conveying in device as in claim 21, with the sheet
conveying device being movable, as a whole, toward the sheet
support and away therefrom.
29. Sheet conveying device as in claim 21, with the part of the
conveying arrangement being moved in linear direction.
30. Sheet conveying device as in claim 21, with the part of the
conveying arrangement being pivotable.
31. Method for separating sheets in a sheet conveying device,
comprising the following steps: providing a stack of sheets below a
sheet conveying device operating with a vacuum; attracting the
uppermost sheet of the stack of sheets by means of a vacuum;
limiting the level of the vacuum with which the sheet is being
attracted to a prespecified value following the attraction of the
sheet, that is, via a constant pressure control valve inside the
sheet separating device.
32. Method as in claim 31, wherein at least one part of the sheet
conveying device is moved into the vicinity of the uppermost sheet
of the stack of sheets before attracting the uppermost sheet by
vacuum, and moving the at least one part of the sheet conveying
device away from the stack of sheets after attracting the uppermost
sheet.
33. Method as in claim 32, wherein the step of moving at least one
part of the sheet conveying device comprises the step of moving at
least one suction finger to which a vacuum is being applied.
34. Method as in claim 32, wherein, following the step of moving
the part of the sheet conveying device away from the stack of
sheets, the vacuum on the suction finger is shut off.
35. Method as in claim 32, wherein the step of moving at least one
part of the sheet conveying device comprises the step of moving at
least one porous conveyor belt.
36. Method as in claim 32, wherein the step of moving at least one
part of the sheet conveying device comprises the step of moving the
entire sheet conveying device.
37. Method as in claim 32, wherein the steps of moving the part of
the sheet conveying device away from the stack of sheets and of
transporting away the sheet occur at the same time.
38. Method as in claim 32, wherein the step of moving at least one
part of the sheet conveying device comprises a linear movement.
39. Method as in claim 32, wherein the step of moving at least one
part of the sheet conveying device comprises a pivoting movement.
Description
TECHNICAL FIELD
[0001] The present invention relates to a sheet conveying device,
said device operating with a vacuum.
[0002] Such sheet conveying devices are used at various locations
in machines for printing and other processing of individual sheets.
For example, a vacuum is used in such a sheet conveying device in
order to attract individual sheets by suction off a stack and to
then feed the individually attracted sheets to the subsequent
processing operation.
BACKGROUND OF THE INVENTION
[0003] Usually, such a sheet conveying device comprises a porous
conveyor belt for transporting a sheet. An air line with a
prevailing internal vacuum is arranged adjacent to the conveyor
belt in such a manner that air is drawn by suction through the
conveyor belt. The vacuum in the air line is generated, for
example, by a blower. By sucking air though the conveyor belt, a
sheet may be sucked against the conveyor belt and then be
transported away by said conveyor belt. If there is no sheet
abutting against the conveyor belt, air is continuously sucked
through the conveyor belt, so that, as a rule, there is only a
minimal vacuum in the air line. This initial vacuum, i.e., the
pressure differential with respect to the environment, thus
substantially depends on the suction power of the blower and the
flow resistance of the porous conveyor belt. If a sheet reaches a
specific distance from the porous conveyor belt, it is attracted in
dependence of the vacuum level and the properties (of the material)
of said sheet. This combination of the distance from the conveyor
belt, the level of the vacuum and the properties of the sheet at
the time when said sheet is being attracted by suction is also
referred to as the dynamic work point of the sheet conveying
device. When the sheet has been sucked against the porous conveyor
belt, said belt is covered by the attracted sheet, which causes the
flow resistance of the conveyor belt to be significantly increased.
Now, the air line can hardly attract any air through the conveyor
belt. As a result of this, the pressure in the air line drops
because the blower continues to draw air through the air line.
[0004] The dynamic work point of the sheet conveying device, as
stated, depends on the sheet and its properties, among other
things. For example, as a rule, using the same vacuum, a
light-weight flexible sheet may be attracted over a greater
distance than a heavy inflexible sheet. But also the normal forces
that are necessary for separating superimposed sheets of a stack
may vary for different sheets. Even sheets of the same
material--e.g., with different fiber orientation that affects the
stiffness of the sheet--may result in different dynamic work
points. Inasmuch as the sheet properties are prespecified by the
sheet, the dynamic work point must now be adjusted by way of the
distance and/or the vacuum in such a manner that a reliable
attraction of the sheets takes place. As a rule, an exact
adjustment of the distance is difficult to achieve and, usually, a
distance range is provided within which the sheets must be
attracted by suction. To ensure that this is the case for all
sheets, one possibility would be to simply increase the vacuum to a
level sufficient to ensure the attraction of the sheet. However,
this may result in the problem that, in particular, light-weight
flexible sheets are damaged because the pressure in the air line
drops as soon as the sheet has been drawn against the conveyor
belt. As a result of this, also the forces acting on the sheet are
increased, thus potentially damaging the sheet. Consequently, only
a limited adjustment of the dynamic work point is possible by
adjusting the level of the vacuum. Frequently, it is possible to
only use sheets satisfying specific specifications in known sheet
conveying devices in a machine, i.e., the sheets must maintain a
prespecified undulation, stiffness, density, thickness and fiber
orientation in order to be able to be processed by a machine.
SUMMARY OF THE INVENTION
[0005] Therefore, it is the object of the present invention to
provide a sheet conveying device that can be used for a broad
spectrum of sheets.
[0006] This object is achieved by a sheet conveying device in
accordance with claim 1, as well as by a method for separating
sheets in accordance with claim 32. Additional embodiments of the
invention are obvious from the subclaims.
[0007] In particular, the sheet conveying device comprises a
conveying arrangement with a porous conveyor belt that can be moved
in a circulating manner, at least one vacuum source, and at least
one air line, the one end of said air line being connected to the
vacuum source and the other end of said air line abutting against
the porous conveyor belt. Furthermore, at least one constant
pressure controller is provided in the air line in order maintain a
substantially constant pressure differential between the interior
space of the air line and its environment. This way, a broad
spectrum of sheets may be transported because any excessive rise in
the vacuum in the air line following the attraction of a sheet is
avoided. Thus, the vacuum that originally prevails in the air line
when no sheet is attracted may be selected to be relatively
high.
[0008] Advantageously, the conveyor belt is arranged so as to
circulate around at least two rollers in order to achieve a simple
design.
[0009] Preferably, the air line contains--downstream of the
constant pressure controller--a main flap in order to partially or
completely seal the air line with respect to the vacuum source.
Consequently, a vacuum may be preset and a pressure loss
avoided.
[0010] Preferably, the air line comprises a main line that is
connected, at its one end, to the vacuum source, and comprises a
plurality of branch lines. Due to this branching, one vacuum source
is sufficient for several purposes of use. Advantageously, each of
the plurality of branch lines leads to a conveying arrangement in
order to be able to supply several conveying devices with one
vacuum source. One constant pressure controller is advantageously
arranged in the region of each branch line in order to permit an
individual adjustment of the vacuum. Preferably, the main flap is
arranged so as to close the branch line with respect to the main
line in order to avoid pressure losses via a sheet conveying
arrangement that is not in use. In this case, the constant pressure
controller is advantageously arranged between the main flap and the
free end of the branch line.
[0011] Preferably, the constant pressure controller is in an open
position when a pressure differential between the interior space of
the air line and its environment is greater than a threshold value,
thus limiting the pressure differential to a prespecified
value.
[0012] Preferably, the constant pressure controller comprises a
valve element and a spring that holds the valve element in a closed
position in order to achieve a design that is as simple as
possible. The spring displays--as one option--a spring
characteristic that is variable over the spring path in order to
generate a changed response behavior. Furthermore, the spring bias
can advantageously be adjusted to provide adjustability at the
location of use.
[0013] Alternatively, the sheet conveying device may comprise a
pressure sensor in order to be able to detect the internal pressure
in the air line. At least one pressure sensor may be arranged in
each branch line in order to be able to determine the internal
pressure in the branch line. In this case, the sheet conveying
device may further comprise a controllably driven pressure control
valve and a control device that communicates with the pressure
sensor and the pressure control valve in order to control an
actuation of the pressure control valve. In this way, it is
possible to control the opening behavior as desired.
[0014] Advantageously, the constant pressure controller comprises
either a flap valve or a sliding valve in order to achieve a simple
design. In particular for the sliding valve, the opening
cross-section of the sliding valve preferably does not increase
proportionally along its opening path.
[0015] Preferably, the sheet conveying device is arranged in a
sheet separating device and/or in a feeder of a printing machine.
As a result of this, a broad spectrum of sheets may be fed to the
printing machine.
[0016] At least a part of the conveying device can be
advantageously moved toward the sheet support and away therefrom in
order to be able to lift a sheet off the stack of sheets on the
sheet support.
[0017] The sheet support of the sheet separating device is
advantageously adjustable as to height in order to be able to
accommodate various sheet stacks and sheets and to advance them
during continuous use.
[0018] Preferably, the movable part of the conveying arrangement is
the at least one conveyor belt. Consequently, the sheet in direct
contact with the conveyor belt is transported away. Alternatively,
the part of the conveying device is at least one suction finger
connected to the vacuum source, thus requiring less mass to be
moved. Alternatively, the part of the conveying device may be at
least one of the rollers, thus requiring less mass to be moved.
Alternatively, the sheet separating device can be moved, as a
whole, toward the sheet support and away therefrom in order to be
able to lift a sheet off the stack of sheets on the sheet
support.
[0019] If it exists, the suction finger--in its position away from
the sheet support--is preferably separated from the vacuum source
in order to avoid damaging the sheet as it is being transported
away by the conveyor belt. The connection of the suction finger
with the vacuum source is preferably open toward the environment
when said suction finger is in its position remote from the sheet
support, thus providing a simple and fast pressure shut-off.
[0020] Advantageously, the part of the conveying arrangement can be
moved in a linear or pivotable manner in order to achieve a simple
design.
[0021] In accordance with the invention, a method for separating
sheets in a sheet separating device is also provided, wherein a
stack of sheets is located below a sheet feeding device operating
with a vacuum, wherein the uppermost sheet of the stack of sheets
is attracted by means of a vacuum, and wherein, following the
attraction of the sheet, the level of the vacuum with which the
sheet is being attracted is limited via a constant pressure control
valve inside the sheet separating device to a prespecified value.
With this method, the aforementioned advantages can be achieved; in
particular, this method permits the use of an additional format
range of the sheets to be conveyed.
[0022] Preferably, the method additionally comprises the step of
moving at least a part of the sheet separating device into the
vicinity of the uppermost sheet of the stack of sheets before
attracting the uppermost sheet by vacuum, and the step of moving
said part of the sheet separating device away from the stack of
sheets after attracting the uppermost sheet, followed by the step
of transporting the sheet away. This makes it possible to reduce
the distance range over which the sheets must be attracted by
suction, as a result of which the spectrum of sheets that can be
conveyed is additionally increased.
[0023] The step of moving at least a part of the sheet separating
device preferably comprises the step of moving at least one suction
finger operating with a vacuum in order to permit a rapid motion.
In so doing, the vacuum at the suction finger is shut off,
preferably after the step of moving the sheet away from the stack
of sheets, in order to avoid damage to the sheet.
[0024] The step of moving at least a part of the sheet separating
device alternatively comprises the step of moving at least one
porous conveyor belt in order to bring the sheet into direct
contact with the conveyor belt.
[0025] Alternatively, the step of moving at least a part of the
sheet separating device comprises the step of moving the entire
sheet separating device in order to avoid any mutual displacement
of the individual components. The steps of moving the part of the
sheet separating device away from the stack of sheets and of
transporting away the sheet preferably occur at the same time in
order to permit rapid processing of the sheets.
[0026] The step of moving at least a part of the sheet separating
device comprises either a linear movement or a pivoting
movement.
[0027] Hereinafter, the invention, as well as additional details
and advantages thereof, will be described in greater detail with
the use of preferred embodiments and with reference to the
drawings.
[0028] They show in
[0029] FIG. 1 a schematic side view of a sheet conveying device in
accordance with a first embodiment;
[0030] FIG. 2 a schematic side view of a sheet conveying device in
accordance with a second embodiment;
[0031] FIG. 3 a schematic side view of a sheet conveying device in
accordance with a third embodiment.
[0032] In the description hereinafter, the terms right, left, up,
down, as well as corresponding expressions are used with reference
to the figures; however, they should not be understood to have a
restrictive meaning. Furthermore, the same reference signs are used
in the drawings and in the description to describe the same or
corresponding parts and features in different embodiments. It
should be noted that the features of different embodiments may be
freely combined, provided they are compatible.
[0033] FIG. 1 shows a first embodiment of a sheet conveying device
1 that comprises a conveying arrangement 3, a blower 5, an air line
7 and a constant pressure controller 9.
[0034] Located under the sheet conveying device 1 is a sheet
support 11 on which a sheet stack 12 of individual sheets 13 is
arranged. The sheet conveying device 1 is provided to convey
individual sheets 13 away from the sheet stack 12. The sheet
conveying device 1 operates as a sheet separating device for
removing and trans-porting individual sheets 13 away from the sheet
stack 12. The sheet conveying device 1 is arranged in a
not-illustrated feeder of an also not-illustrated printing machine,
said feeder being disposed to introduce sheets into a printing
process. However, the sheet conveying device 1 may also be arranged
at a suitable location of another sheet processing device. As will
be explained in greater detail hereinafter, it is possible to move
at least a part of the sheet separating device 1 toward the sheet
support 11 and away therefrom. As a result of this, a distance
between the conveying arrangement 3 and the uppermost sheet 13 of
the sheet stack 12 on the sheet support 11 can be bridged quickly.
For this, a pivoting movement as well as a linear movement are
used.
[0035] The sheet support 11 is height-adjustable and lifts the
sheet stack 12 in the vicinity of the conveying arrangement 3.
Usually, air is blown (from the right, in the figures) laterally at
the sheet stack 12 in the upper region of a not-illustrated
pressurized air nozzle that is also referred to as an "air knife"
in order to slightly fan out the sheets 12 before they are being
received by the sheet conveying device 1.
[0036] The conveying arrangement 3 comprises a porous conveyor belt
15 that is passed around two rollers 17; 18. At least one of the
rollers is connected with a not-illustrated motor. The motor is
provided so as to intermittingly drive the roller in a controlled
manner. As an alternative, the porous conveyor belt 15 may consist
of a plurality of porous conveyor belts arranged next to each other
(perpendicular to the sheet plane of the figures), said conveyor
belts being movable so as to circulate around the rollers 17, 18.
Depending on the format range of the sheets 13 to be conveyed, the
width of the conveyor belt 15 varies, or more or fewer conveyor
belts are arranged next to each other. It should be noted that in
the description hereinafter, only one conveyor belt 15 is being
considered, even though, at this point, several conveyor belts
could be used. Likewise, instead of the two rollers 17, 18, it is
possible to use more rollers, for example three or four rollers,
should this be advantageous for guiding the conveyor belt 15. Also,
instead of the rollers, the use of different guiding or driving
elements is also possible such as, for example, wheels, in order to
move the conveyor belt 15 in a circulating manner.
[0037] Optionally, it is also possible to move the roller 18 up and
down, as shown by the double arrow A in FIG. 1, in order to be able
to quickly bridge the distance between the conveyor belt 15 and the
sheet stack 12 for the accommodation of a sheet 13. During a
corresponding movement of the roller 18, a lower side of the
conveyor belt 15 performs a pivoting movement in the direction of
the stack of sheets and away therefrom. If several conveyor belts
are provided next to each other, it may be sufficient to move only
one of them over a corresponding roller. Of course, it is also
possible to move both rollers 17 and 18 up and down as in FIG. 1,
this causing the lower side of the conveyor belt 15 to perform a
linear movement toward the sheet stack 12 and away therefrom. The
function of the movement will be explained in greater detail
hereinafter.
[0038] In the figures, the vacuum source 5 is shown as a radial
blower 5; however, it should be noted that the vacuum source itself
may also be configured as any suction blower of any suitable
design. In particular, the vacuum source 5 may be a central
negative pressure/positive pressure source that comprises a blower
or a compressor, whereby, on the one side of the negative pressure
source/positive pressure source, a vacuum is generated for use at
various locations of a machine or production line, and whereby, on
the other side thereof, a positive pressure is generated for use at
another suitable location of the machine or production line, as,
for example, considering the aforementioned air knife. The arrows
in FIG. 1 show the air current generated by the vacuum source
5.
[0039] In accordance with FIG. 1, the conveying arrangement 3 and
the vacuum source 5 communicate with each other via an air line 7.
On its one end or on the blower end 20, the air line 7 is connected
to the vacuum source 5. The other end or suction end 22 is located
adjacent to the porous conveyor belt 15. The shape and size of the
suction cross-section of the suction end 22 are adapted to the size
of the porous conveyor belt 15. Inasmuch as the conveyor belt 15 is
porous, the air may enter through the conveyor belt 15 into the
suction end 22 of the air line 7 and exit at the blower end 20. A
main flap 24 and a constant pressure controller 9 are provided in
the air line 7. The main flap 24 is located downstream of the
constant pressure controller 9. The main flap 24 is suitable to
completely separate the air line 7 from the vacuum source 15 or to
provide a rough control of the flow through the air line 7.
[0040] A passage opening 27 is provided in one exterior wall of the
air line 7, said passage opening creating a connection between the
interior of the air line 7 and the environment. The constant
pressure controller 9 comprises a valve element 32 in the form of a
valve flap and a spring 34. The valve element 32 is arranged in
such a manner that it can be moved between a sealing position and a
position clearing the passage opening 27. The spring is arranged in
such a manner that it biases the valve element in the position
sealing the passage opening 27. Spring 34 may be a pressure spring
or a tension spring. Furthermore, spring 34 may display a spring
characteristic that is variable along the spring path. Thus, the
constant pressure controller 9 establishes a connection between the
interior of the air line 7 and its environment as soon as a
pressure differential between the vacuum in the air line 7 and the
atmospheric pressure of the environment reaches a specific
threshold value. This threshold value may be adjusted by the
operator to match different sheet stacks 12.
[0041] The constant pressure controller 9 shown in the figures is
of the type that comprises a valve flap. However, it should be
noted that the constant pressure controller 9 may also comprise a
sliding valve having an opening cross-section that may increase
along its opening path, either proportionally or not
proportionally. Furthermore, other suitable valves may be taken
into consideration for the constant pressure controller 9 such as,
for example, diaphragm valves or ball check valves.
[0042] FIG. 2 shows an alternative embodiment of a sheet conveying
device 1 that is different from the above-described device in view
of the design of the air line 7. In this embodiment, the air line 7
comprises a main line 28 and a plurality of branch lines 30. The
main line 28 is connected to the vacuum source 5, on the one side,
and to the branch lines 30, on the other side. Each of the branch
lines 30 leads to a separate conveying arrangement 3, each of said
arrangements being allocated a sheet stack 12, for example. Each
branch line 30 contains a main flap 24 that can completely separate
the associate branch line 30 from the main line 28 or can roughly
control a flow. Upstream of each main flap 24, a passage opening 27
is provided in each branch line 30, each of said branch lines being
associated with a constant pressure controller 9 as described
above. In this embodiment, it is optionally possible to move
respectively one of the branch lines 30 together with the
respective conveying arrangement 3 toward the sheet support 11 and
away therefrom, as is shown by the double arrow B in FIG. 2. The
connection to the main line 28 is maintained by suitable means. The
joint movement of the branch line 30 with the conveying arrangement
3 ensures that the suction conditions in the region of the conveyor
belt 15 are not changed by the movement.
[0043] The second embodiment is used to operate several conveying
arrangements 3 on a vacuum source 5. This means that the individual
conveying arrangements 3 can be operated with different flow rates
and negative pressures, respectively.
[0044] FIG. 3 shows another embodiment of a sheet conveying device
1 that has essentially the same basic design as the sheet conveying
device 1 in accordance with FIG. 1. However, this device is
different in view of the constant pressure controller 9, on the one
hand, and in view of the provision of at least one optional suction
finger 42 as part of the conveying arrangement 3 that can be moved
toward the sheet support 11 and away therefrom, on the other hand,
as is shown by the double arrow C. For example, a sheet 13 can be
lifted off the sheet stack 12 on the sheet support 11 and be
transported to the conveyor belt 15 by the suction fingers 42, as
will be explained in greater detail hereinafter. The other features
and parts of the sheet conveying device 1 of the embodiment in
accordance with FIG. 3 are configured as those in FIG. 1.
Therefore, no description is provided in order to avoid
repetitions.
[0045] As an alternative to the at least one suction finger 42 or,
also in addition thereto, it is possible to configure the conveying
arrangement 3 or parts thereof so as to be movable toward the sheet
support 11 or away therefrom. This is indicated by the box 60 in
FIG. 3 and by the double arrows D and E, with the double arrow D
indicating a linear movement and the double arrow E indicating a
pivoting movement. For example, the part of the conveying device 3
that is moved toward the sheet stack 12 may be the porous conveyor
belt 15. To do so, it is possible, for example, to move at least
one of the rollers 17, 18 toward the sheet stack 12 and away
therefrom. Alternatively, it is also possible for an actuating
element extending across the conveyor belt 15 to push said conveyor
belt 15 in the direction of the sheet stack 12. Another possibility
of providing a movement of the conveyor belt 15 is that the suction
end 22 of the air line 7 abutting against the conveyor belt 15 is
configured so as to be movable in the direction of the sheet stack
12. As a result of such a movement, the conveyor belt 15 is pushed,
together with the suction end 22, in the direction of the sheet
stack 12.
[0046] In accordance with FIG. 3, the constant pressure controller
9 comprises a pressure sensor 36, a control device 38 and a
controllably driven pressure control valve 40. In FIG. 3, the
pressure control valve 40 is shown as a flap valve; however, it may
also be a sliding valve or have another valve design. The pressure,
control valve 40 may be driven, for example, by piezo-electric or
electromagnetic means. The pressure sensor 36 is suitable to sense
the air pressure inside the air line 7 and to output a
corresponding signal to the control device 38. The control device
38 is suitable to process the signal output by the pressure sensor
36 and to activate the controllably driven pressure control valve
40 in response to this signal, i.e., to more or less open said
valve in order to adjust a substantially constant pressure in the
air line 7.
[0047] The at least one optional suction finger 42 is arranged
adjacent to the conveyor belt and connected with the vacuum source
5 or another suitable vacuum source. The at least one optional
suction finger 42 can be moved toward the sheet support 11 and away
therefrom. Preferably, suction fingers 42 are arranged to the right
and to the left of the conveyor belt 15. Whenever a plurality of
conveyor belts are arranged adjacent to each other, the suction
fingers 42 can be arranged not only to the right and to the left of
the conveying arrangement 3 but also between the individual
conveyor belts. However, it is also possible to provide only one
suction finger 42--in this instance, preferably between two
conveyor belts. In its position lowered relative to the sheet stack
12, the at least one suction finger 42 is connected to the vacuum
source 5. However, in its lifted-off position, said suction finger
is separated from the vacuum source. The at least one optional
suction finger 42 can thus first attract a sheet 13 by suction,
then lift said sheet to the conveying arrangement 3 and release
said sheet there.
[0048] It is also conceivable to move the entire sheet conveying
device 1 in the direction of the sheet support 11 and away
therefrom. The movable sheet conveying device 1 or its movable part
(e.g., conveyor belt 15, suction finger 42, . . . ) can either be
moved in linear direction or be pivoted. The distance over which
the sheet conveying device 1 or one of its parts can be moved in
the direction of the sheet support 11 ranges between 5 and 20
mm.
[0049] Hereinafter follows a description of the operation of
different sheet conveying devices 1. Arranged on the sheet support
11 is a sheet stack 12 of individual sheets 13, said stack being
ready for transport by the sheet conveying device 1. The vacuum
source 5. is in operation and generates a vacuum. The main flap 24
is opened, and thus a certain vacuum exists in the air line 7. This
initial vacuum, i.e., the pressure differential with respect to the
environment, is essentially a function of the suction power of the
blower and of the flow resistance of the porous conveyor belt. As a
rule, the initial vacuum is set so as to have the constant pressure
controller 9 close the passage opening 27.
[0050] When a sheet 13 comes close to the porous conveyor belt 15,
said sheet is drawn by suction--as of a certain distance--toward
the conveyor belt 15 depending on the vacuum in the air line 7 and
on the properties of the material of said sheet. By appropriately
lifting the sheet support 11 or also appropriately moving a part of
the sheet conveying device 1, the sheet can come close to the
conveyor belt, as mentioned above. For example, when the sheet 13
comes close to the porous conveyor belt 15 due to a movement of the
roller 18 toward the sheet stack 12, said sheet is attracted, and
then the roller 18 can again be moved away from the sheet stack
12.
[0051] When the sheet 13 has been sucked against the porous
conveyor belt 15, said belt is covered by the attracted sheet 13,
and the pressure in the air line 7 drops, meaning that the vacuum
becomes stronger. Now, there is the risk that the sheet 3 is sucked
too strongly against the porous conveyor belt 15 because the vacuum
source 5 continues to draw in air through the air line 7.
[0052] When a preset pressure threshold value is reached, however,
the constant pressure controller 9 opens and establishes the
connection between the interior of the air line 7 and the
environment, so that the vacuum source 5 will now also suck air in
from the environment. This prevents the sheet 13 from being sucked
too strongly against the conveyor belt 15. As the vacuum becomes
stronger, the constant pressure controller 9 opens wider. If the
vacuum becomes weaker, the constant pressure controller 9 opens
less widely. Consequently, the vacuum in the air line 7 is
maintained essentially constant. Essentially, in so doing, a
pressure deviation from the set vacuum of 10%, and preferably of
5%, is to be possible. The movement of a part of the sheet
conveying device 1 such as, for example, a roller 17, 18 may be
coupled with the opening of the constant pressure control valve,
because said control valve signals a safe attraction by suction of
a sheet from the stack.
[0053] When the sheet 13 has been attracted by suction, the
movement of the conveyor belt 15 is started in order to transport
the sheet away. When this happens, the suction end 22 of the air
line 7 that is being blocked by the sheet 13 is gradually cleared
again. Thus, the vacuum source 5 can again suck in more air through
the porous conveyor belt 15; and, consequently the vacuum in the
air line 7 is reduced. This has the effect that the constant
pressure controller 9 again closes gradually until said controller
is completely closed when the pressure threshold value is not
reached.
[0054] As will be obvious to the person skilled in the art, the use
of the constant pressure controller 9 permits the adjustment of a
relatively high initial vacuum, because damage to a sheet 13 due to
an excessive pressure drop in the air line 7 after the attraction
of the sheet 13 by suction is prevented. Consequently, the spectrum
of sheets that can be attracted without being damaged can be
expanded considerably.
[0055] In the embodiment of FIG. 2, a vacuum source 5 is used to
provide a vacuum for several conveying arrangements 3. Other than
that, the operation is substantially the same as has just been
described in the case of the embodiment of FIG. 1. However,
different branch lines 30 can be shut off completely or activated
only partially by their associate main flap. As a result of this,
for example, a negative pressure loss is prevented when a conveying
arrangement 3 is stopped. The respective constant pressure
controller 9 in a branch line 30 controls the suction pressure that
is ideal for the sheets 13 that are to be conveyed by the
corresponding conveying arrangement 3. For an initial pickup of a
sheet, the branch line 30, together with the sheet conveying
arrangement 3, can be moved toward the sheet stack 12 and away from
said stack. After, or also during, a movement of the branch line 30
and the sheet conveying arrangement 3, the conveyor belt 15 is
operated in a circulating manner in order to transport away an
attracted sheet. If the porous conveyor belt 15 or a part thereof
is lowered in the direction of the sheet stack 12 in order to lift
off the uppermost sheet 13, the suction, lifting and transporting
steps of the sheet 13 off the sheet stack 12 may essentially take
place at the same time. To do so, the conveyor belt 15 is usually
driven intermittently.
[0056] Hereinafter, the operation of the embodiment of the sheet
conveying device 1 shown in FIG. 3 will be described, said device
comprising at least one suction finger 42 as a part of the
conveying arrangement that can be moved toward the sheet support
and away therefrom.
[0057] As is the case in the other embodiments, a sheet stack 12 is
provided under the conveying arrangement 3. The conveyor belt 15 is
initially stopped. For an initial pickup of an uppermost sheet 13
of the stack of sheets, the suction fingers 42 are moved in the
direction of the sheet stack 12, and the uppermost sheet 13 is
attracted by suction by the suction fingers 42. Subsequently, the
suction fingers 42 are again moved away from the sheet stack 12, as
a result of which the uppermost sheet enters the region of the
conveyor belt 15 and is attracted by suction by said conveyor belt.
Then, the suction fingers 42 release the sheet, and the conveyor
belt 15 is moved in a circulating manner in order to transport away
the sheet 13.
[0058] While the suction fingers 42 are lowered near the uppermost
sheet 13, they are automatically connected to the vacuum source 5,
and the conveyor belt 15 is stopped. While the suction fingers 42
are being lifted and before the conveyor belt is being moved in a
circulating manner, the suction fingers are again automatically
separated from the vacuum source 5.
[0059] Alternatively or also additionally, it is also possible for
at least a movable part of the conveying arrangement 3 to be
lowered by means of a linear or pivoting movement into the vicinity
of the uppermost sheet 13 of the sheet stack 12. As described
above, this part may be, for example, the conveyor belt 15 or also
the entire sheet conveying device 1. After drawing the uppermost
sheet 13 against the conveyor belt 15 by means of a vacuum, the
movable part is moved with the sheet 13 away from the sheet stack
12 in upward direction and transported away with the aid of the
conveyor belt 15.
[0060] In so far as the porous conveyor belt 15 (optionally by
itself or also in combination with other elements) is lowered in
the direction of the sheet stack 12 in order to lift off the
uppermost sheet 13, the attraction by suction and the lifting of
the sheet 13 off the sheet stack 12 takes place essentially at the
same time. In so doing, the conveyor belt 15 is usually
intermittently driven in such a manner that it is not driven in the
lowered position.
[0061] The invention has been described with reference to preferred
embodiments, whereby the individual features of the described
embodiments can be freely combined with each other and/or
interchanged, provided that they are compatible. Numerous
modifications and designs are possible and obvious to the person
skilled in the art, without departing from the idea of the
invention.
[0062] In particular, optional elements of the sheet separating
device 1 have been discussed, said elements being movable toward
the sheet stack 12 and away therefrom. However, elements other than
those that have been mentioned can be provided for a movement
toward the sheet stack 12 and away therefrom. For example, the
conveyor belt 15 could display a certain elasticity, and an
actuation element extending in a direction transverse to the
conveyor belt 15 could be provided, said actuation element moving
the lower part of the conveyor belt 15 (between the rollers 17, 18)
in the direction of the sheet stack 12 and away therefrom. It is
also possible for the suction end 22 of the air line 7, said
suction end abutting against the conveyor belt 15, to be configured
so as to be movable in the direction of the sheet stack 12. With
such an embodiment, for example, it is possible to move the
conveyor belt 15, together with the suction end 22, in order to
maintain the suction geometry consistent in the region of the
conveyor belt. It is also possible for the entire sheet separating
device 1 to be movable in the direction of the sheet support 11 and
away therefrom. The movable sheet separating device 1 or its
movable parts (e.g., the conveyor belt 15, the suction fingers 42,
. . . ) can be moved either in linear direction or can be pivoted.
The distance along which the sheet separating device 1 or its part
can move in the direction of the sheet support 11 ranges between 5
and 20 mm, for example.
* * * * *