Sheet delivery device for continuously receiving sheets during stack removal

A sheet delivery device is provided that allows for high output and accurate operation during changing of the main stack. The device includes two secondary stack carriers which are normally disposed on opposite sides of the main stack in a first lateral waiting position. The secondary stack carriers are reciprocally moveable between the first lateral waiting position and an operative position. In the operative position, the secondary stack carriers accumulate a secondary stack while the main stack is being changed. This secondary stack is later deposited on the new main stack. Cooperating with the secondary stack carriers are separating elements normally disposed above the secondary stack carriers in a second lateral waiting position. The separating elements are reciprocally moveable between the second lateral waiting position and a separating position. In the separating position, the elements accumulate a temporary stack to form an entry gap above the main stack. The secondary stack carriers, which are plate-like enter this entry gap to arrive at the operating position. The separating elements thereafter deposit the temporary stack on the secondary stack carriers to form the secondary stack.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a sheet delivery device for 
sheet-fed machines, and more particularly concerns a sheet stacking device 
for use in printing presses. 
2. Description of the Prior Art 
Various types of sheet delivery devices are known in the art. Generally, 
these include a stack-receiving tray or pallet for receiving a stack of 
sheets. The stack-receiving pallet is lowered until the stack reaches a 
predetermined height. The stack-receiving pallet is then removed, and an 
empty one substituted. To avoid having to stop sheet-feeding during this 
change, a secondary stack-receiving device is generally provided. This 
secondary stack-receiving device accumulates sheets until the new 
stack-receiving pallet is in place, whereupon these sheets are deposited 
on the stack and normal operation continues. An arrangement of this kind 
is known from DE-PS 1 231721 wherein the secondary stack-receiving device 
is in the form of a roller shutter which is unwindable from a winding 
shaft disposed near the back of the delivery mechanism and whose side 
edges run in stationary horizontal guides. The roller shutter has a 
relatively large mass and, therefore, can move only comparatively slowly. 
Consequently, the output rate of the sheet-fed machine has to be reduced 
upon activation of the secondary stack-receiving device. However, it is 
inevitable that a number of sheets arrive before termination of the entry 
operation of the roller shutter so that there are bound to be relative 
movements between the shutter and the bottom sheet and, therefore, 
relative movement between the sheets above the bottom sheet, with the risk 
of damage to the sheets and the freshly printed image. This disadvantage 
is further heightened in the known arrangement because the roller shutter 
is required to bridge substantially the whole length of the stack, so that 
the required entry time is quite long. Another disadvantage of the known 
arrangement is that when the shutter withdraws, the secondary stack 
thereon may be skewed because of friction. Also, the shutter is in the 
form of a bulky coil when wound and may hinder access to the delivery 
mechanism from the front thereof. 
Objects and Summary of the Invention 
It is therefore the primary aim of the present invention to provide a sheet 
delivery device which can provide a high output during stack changing 
while still ensuring accurate and troublefree operation. 
According to the invention, the sheet delivery device includes means for 
receiving the main stack that is removed and replaced along with the main 
stack. Also included is a main stack elevator that controls the position 
of the main stack receiving means according to timing signals, the timing 
signals being provided by a level switch. The sheet delivery device 
further includes a non-stop means for allowing continuous feeding of 
sheets when the main stack is being changed. The non-stop means accumulate 
a secondary stack during stack changing, and this secondary stack is 
thereafter deposited on the main stack-receiving means containing the new 
main stack. 
Pursuant to one aspect of the invention, the nonstop means includes two 
secondary stack carriers which are each normally disposed on opposite 
sides of the main stack in a first lateral waiting position. The secondary 
stack carriers are reciprocally moveable between the first lateral waiting 
position and an operative position over the main stack-receiving means. 
When the secondary stack carriers are in the operative position, sheets 
are accumulated to form the secondary stack on the secondary stack 
carriers. The non-stop means further includes separating elements normally 
disposed above each of the secondary stack carriers in a second lateral 
waiting position. The separating elements are reciprocally moveable 
between the second lateral waiting position and a separating position in 
which they accumulate a temporary stack to create an entry gap between the 
temporary stack and the main stack. This entry gap allows for movement of 
the secondary stack carriers to the operative position. The separating 
elements are adapted to thereafter deposit the temporary stack on the 
secondary stack carriers which are in the operative position. Thus, the 
secondary stack is formed on the secondary stack carriers when the 
separating elements are moved to the second lateral waiting position. 
In a preferred embodiment, the separating elements take the form of 
relatively light pins or the like and can move rapidly because of their 
reduced weight. The separating elements can therefore be "shot in" at high 
speed during the passage of a gap between two sheets. Relative movement 
between the entering separating elements and the sheet material to be 
received thereon is, therefore, precluded. As a result, there is no need 
to reduce output. Consequently, the secondary stack carriers introducible 
into the entry gap, kept open by the separating elements, can move 
relatively slowly, with the further advantage that stressing of the 
associated motion equipment and noise are reduced. Because each of the two 
reciprocally movable secondary stack carriers has to travel only half the 
distance under the stack, movement times are comparatively short. Also, 
because the secondary stack carriers move in opposite directions, the 
thrust forces they produce cancel one another out in an advantageous 
manner so that there is essentially no risk of the secondary stack 
shifting. Furthermore, because the secondary stack carriers are disposed 
laterally of the main stack there is an appreciable saving of space. 
In the preferred embodiment, the secondary stack carriers are disposed for 
displacement on a lifting frame guided vertically by means of a vertical 
guide and suspended on a secondary stack elevator which, with the 
secondary stack carriers in the inserted position, is lowerable in timed 
fashion by means of the level switch. This feature ensures that the 
increase in secondary stack height can be compensated for by timed 
lowering, so that the arriving sheets are always presented with the same 
deposition level, resulting in greater stacking accuracy and freedom from 
malfunctioning. 
According to another aspect of the preferred embodiment, the lifting frame 
has longitudinal guides for a slide receiving a secondary stack carrier, 
the slides being synchronized by synchronizing means preferably in the 
form of a cable control. Synchronizing the two oppositely movable 
secondary stack carriers ensures that forces tending to displace the 
secondary stack on the carriers cancel one another out right from the 
start, thereby increasing the level of accuracy obtainable. 
Preferably, the secondary stack carriers are in the form of plate-like 
swords, tapered panels or the like. The swords or panels are arcuately 
contoured and have tapered wedge-like shapes in their facing edge zones. 
These features not only facilitate reliable reception of the secondary 
stack but also and advantageously ensure that when they enter the 
associated gap, the secondary stack carriers can open up a path without 
causing damage, so that even if the entry gap is not ideal, a high level 
of operating reliability and careful handling of the sheets are ensured. 
Also, the features have the advantage of providing, in a simple manner, 
the production of an air cushion, which further helps to ensure operation 
which avoids damage to the sheets. 
In a particularly preferred embodiment, the secondary stack carrier swords 
or panels can take the form of sandwich panels, whose interior is 
subdivided by webs and is connected to a source of compressed air which 
exits from the top panel through blowing nozzles, preferably in the form 
of ball valves. 
In a further development according to the preferred embodiment, the 
separating elements on each side can be received in a slide adjustably 
received on a horizontal guide rigidly secured to the frame. Consequently, 
the separating elements are not lowered together with the lifting frame, a 
feature which helps to simplify construction. Additionally, the separating 
elements are pivotable and can be lowered at their front end from a 
horizontal insertion position by associated pivoting means. The separating 
elements, when thus lowered, extend in a manner adapted to the sheets, 
whose side edges are received on such elements such that the sheets sag in 
the center as far as the main stack. This ensures that a reliable entry 
gap for the sword-like or plate-like secondary stack carriers is created. 
According to another feature of the preferred embodiment, the displacing 
means associated with the separating elements are actuated by means of a 
sensor providing direct or indirect sensing of each arriving sheet, thus 
reliably obviating collisions. Desirably, vibratable side joggers are also 
provided near the vertically stationary separating elements. This further 
helps to improve stacking accuracy. 
These and other features and advantages of the invention will be more 
readily apparent upon reading the following description of a preferred 
exemplified embodiment of the invention and upon reference to the 
accompanying drawings wherein:

Detailed Description of the Preferred Embodiment 
FIG. 1 shows the sheet delivery device according to the present invention. 
Sheets printed in a sheet printing press are delivered in the form of a 
stack by means of a delivery device disposed after the press. The delivery 
device shown in FIGS. 1 and 2 comprises a gantry frame 1 into which a 
sheet transport device enters, the sheet transport device having gripper 
bars 3 disposed on side chains 2. The sheet transport device discharges 
the sheets retained by the gripper bar grippers 3 on to stack-receiving 
means disposed in the frame 1. In the present case, main stack receiving 
means and secondary stack receiving means which are used alternately are 
provided, in order to achieve non-stop operation. 
The main stack receiving means comprises a vertically movable platform 4 
movable by means of an associated main stack elevator indicated here by 
its chains 5 driven by a motor not shown in greater detail. The platform 4 
is adapted to be loaded with a pallet 6 for receiving a stack of sheets. 
The main stack elevator motor (not shown) can be controlled by a level 
switch 7 in the form, for example, of a capacitative sensing head, so that 
the top edge of the stack received on the pallet 6 is always at a constant 
level. The platform 4 is lowered to floor level for loading and unloading. 
For the lateral exit of a pallet with a stack or for the lateral 
introduction of a new empty pallet, a conveyor in the form of a roller 
train 8 extending transversely of the sheet delivery direction is provided 
and the conveyor drive elements can be controlled by sensors in the form 
of light barriers 9. The conveyor 8 comprises a central part 8a mounted on 
platform 4 and flanked by preceding and subsequent parts for supplying a 
new pallet or removing a loaded pallet, respectively. Drive means 10 in 
the form of a piston and cylinder unit are provided to shift a pallet 
which has entered the central conveyor part 8a, the same being rigidly 
secured to the sheet delivery device. 
As previously stated, the function of the non-stop means, particularly the 
secondary stack receiving means is to facilitate non-stop operation during 
stack changing --i.e., during the removal of a pallet loaded with a 
complete stack and the supply of the next empty pallet. The sheets 
arriving during stack changing are received on the secondary stack 
receiving means in the form of a secondary stack which can subsequently be 
deposited on the empty pallet which has in the meantime been moved into 
position on the main stack receiving means. Here the secondary stack 
receiving means comprises two secondary stack carriers 11 which can enter 
and exit laterally to opposite sides of the sheet delivery device and 
which can be moved from a first lateral waiting position, shown in FIGS. 1 
and 2 on opposite sides of the base area of the stack, into an operative 
position which is shown in FIG. 4 and in which the secondary stack 
carriers 11 engage over the base area of the stack. 
To ensure that the top edge of the secondary stack remains at a constant 
level the two carriers 11 and the platform 4 are lowerable in timed 
fashion. To this end, a lifting frame 12 is provided which receives the 
two carriers 11 and is guided in the lifting direction by a vertical guide 
and which is activatable by means of an associated secondary stack 
elevator 13. In the case shown here the secondary stack elevator 13 
comprises a shaft 14 which bridges the delivery device, is drivable by 
means of an associated geared motor 15 and can be elongated or shortened 
by means of lifting elements 16 receiving the lifting frame 12. The timing 
of the motor 15 when the carriers are entered can be controlled in the 
same way as the timing of the motor of the main stack receiving platform 
by means of the level switch 7. 
As will be most clearly apparent from FIG. 2, the lifting frame 12 is a 
closed rectangular frame providing good stability and torsional rigidity. 
Adjacent the frame members which extend transversely to the direction of 
sheet conveyance, the lifting frame 12 has longitudinal guides 17 on each 
of which a slide 18 receiving a secondary stack carrier 11 is guided for 
horizontal movement. (See FIG. 1) The internal width of the lifting frame 
12 in the direction of sheet conveyance is greater than the maximum format 
length of the sheets to be dealt with. The internal width transversely 
thereof corresponds at least to the maximum format width of the sheets 
plus a distance sufficient to allow passage of sheets having the maximum 
format width past the secondary stack carriers 11 when they are in the 
first lateral waiting position. That is, this internal transverse width 
corresponds to the maximum format width plus the maximum depth of entry of 
the secondary stack carriers 11 in the operative position. Consequently, a 
free space corresponding to at least the maximum base area of the stack is 
present and so collisions are reliably avoided. 
The slides 18 are movable synchronously in opposite directions, 
synchronization being provided by synchronizing means which in the present 
case take the form of a cable control 19. The synchronizing means can be 
connected to a common drive. In the embodiment shown, separate drives 
associated with the two slides 18 are provided in the form of piston and 
cylinder units 20. To terminate the entry or exit movement of the 
secondary stack carriers 11 an inner limit switch 21 and an outer limit 
switch 21 are provided and co-operate with a cam 22 on one of the slides 
18. (See FIG. 1) The limit switches 21 control the drives associated with 
the two synchronously moving slides 18. The inner end switch 21 can be 
stationary since the two secondary stack carriers 11 always enter so far 
that, as FIG. 4 shows, their adjacent edges are disposed near and opposite 
one another. The outer limit switch 21 can be adjustable so that the exit 
end position can be adapted to the particular format width being dealt 
with. 
As can best be appreciated from FIG. 3, separating elements 23 associated 
with the secondary stack carriers 11 are disposed thereabove and, at the 
start of stack changing, are effective to keep open an entry gap 24 for 
the associated secondary stack carrier 11--i.e., they are effective to 
serve as separating aids. The separating elements 23 can be simple pins 
which in this case have at their front end a generally rounded or 
drop-like part 25. The separating elements 23 are movable axially by means 
of an associated displacing means which in the case shown takes the form 
of piston and cylinder units 26. The separating elements 23 can simply be 
prolonged extensions of the piston rod. Since they are of reduced weight 
the separating elements 23 can be moved in and out rapidly by means of the 
associated units 26. In the preferred embodiment, an as shown in FIG. 2, 
two separating elements 23 are provided near each side of the stack and 
are arranged in a V-fashion, such that they forwardly diverge relatively 
to one another. The separating elements 23 of each side are received on an 
associated slide 27 guided on an associated horizontal guide 28 to the 
press frame 1. The slides 27 can be moved manually or by motor means. 
Desirably, the slides 27 are so adjusted that the separating elements 23, 
when in their withdrawn waiting position shown in FIGS. 1 and 2, have 
their front end outside the base plan of the stack and, when in their 
introduced operative position shown in FIG. 3, have their front end 
extending over the associated side edge of the stack. 
As FIG. 1 shows, the separating elements 23 extend substantially 
horizontally when in the second lateral waiting position. In the operative 
position shown in FIG. 3 the separating elements 23 have their front end 
inclined downwardly and thus extend substantially in a manner adapted to 
the passage of the sheets 29 whose edges they support. To this end, the 
separating elements 23 are mounted pivotally on the associated slide 27. 
In the illustrated embodiment, each slide has a pivoting means in the form 
of a pivoting frame 31 which is pivotable by means of an associated 
pivoting drive 30, the same also being a piston and cylinder unit, and on 
which the associated separating elements 23 and the drive elements 
associated with the separating elements 23 are received. If desired, the 
pivoting movement of the frames 31 can be limited by abutments. 
In response to an instruction to change the stack, given when the stack 32 
on the main stack receiving means has reached a predetermined height 
detectable by means of an appropriate sensor, the separating elements 23 
first move from the second lateral waiting position of FIGS. 1 and 2 into 
the separating position of FIG. 3. This step can proceed rapidly since the 
elements 23 are of reduced weight so that it is possible to effect rapid 
insertion or "shoot-in" of the separating elements 23. To ensure that 
entering elements 23 do not collide with an arriving sheet, the insertion 
or shoot-in movement is placed laterally so that the separating elements 
23 shoot in during the passage of a gap between two consecutive sheets. 
The necessary instruction is derived from the arriving sheet itself. To 
this end, in the preferred embodiment and as FIG. 1 shows, a means for 
sending in the form of a sensor 33 is provided which co-operates with the 
sheet transfer device, senses the gripper bar 3 pulling the arriving sheet 
and operates the piston and cylinder units 26 associated with the 
separating elements 23 in the correct timing. Further, operation of the 
piston and cylinder units 30 associated with the pivoting frames 31 can be 
based on sequential switching. The separating elements 23 are inserted in 
a horizontal alignment, then lowered. The pins serving as the separating 
elements 23 can initially still rest on the surface of the stack 32 
received on the main stack receiving means. Upon initiation of the 
shoot-in of the separating elements 23 the main stack receiving means 
descend at high speed so that the separating elements 23 rapidly disengage 
from the top of the stack 32 and the stack moves by way of its top edge 
below the level of the secondary stack carriers 11 which have moved into 
their top position and which are in the waiting position. 
As FIG. 3 clearly shows, the temporary stack 29 arriving after the shoot-in 
of the separating elements 23 have their edge raised. The central zone of 
the temporary stack 29 can still rest on the top of the stack 32. This 
leads to the formation of the wedge-shaped entry gap 24 which has 
previously been referred to and which the secondary stack carriers 11 can 
enter without colliding, as indicated by chain lines in FIG. 3. The entry 
movement can be comparatively slow since the temporary stack 29 accruing 
during the entry step are kept raised by the separating elements 23 at 
least at their edges. Since the secondary stack carriers 11 move 
synchronously and in opposite directions, the displacing forces they exert 
cancel one another out and so there is no shifting of the temporary stack 
29. 
In a particularly preferred embodiment and as shown in FIG. 2, the 
secondary stack carriers 11 are panel-like swords which have arcuate 
contouring near their front edge and which narrow wedge-fashion near such 
contouring. To simplify production, moldings 34 can be used which contain 
the arcuate contouring and wedge-shaped narrowing and which are simply 
attached to the rear zone of the associated secondary stack carrier 11. 
The contouring of the front ends of the secondary stack carriers 11 
ensures that the same can contrive a passage even if the entry gap 24 is 
not ideal without any risk of damage to the bottom sheet 29 of the group 
of sheets below which the secondary stack carriers 11 have moved and which 
are received on the separating elements 23. As FIG. 4 shows, in the 
entered position the adjacent ends of the two secondary stack carriers 11 
are disposed opposite and near one another, thus providing reliable 
support over a large area of the secondary stack 38 to be placed on them. 
As will also be apparent from FIG. 4, after the entry of the secondary 
stack carriers 11, the separating elements 23 return to the second lateral 
waiting position. The temporary stack 29 previously kept raised by 
separating elements 23 is deposited on the entered secondary stack carrier 
11, as are also the subsequent sheets. There therefore arises a secondary 
stack 38 whose top edge, as previously stated, is maintained at a constant 
level by lowering of the lifting frame 12 in which the secondary stack 
carriers 11 are received. 
In this embodiment stacking accuracy is enhanced by the slides 27 which 
receive the elements 23 having side joggers 35 adjustable by means of the 
slides 27 to the associated stack side edge. The joggers 35 can be driven 
so as to vibrate the secondary stack both in response to delivery of the 
sheets on the main stacking means and to delivery of the sheets to the 
secondary stacking carriers. As the embodiment of FIG. 2 also shows, the 
side joggers 35 are formed with through passages 36 through which the 
separating elements 23 can engage when in the operative position. 
Consequently the separating elements 23 do not need to participate in the 
vibratory motion of the side joggers 35. 
After the entry of the secondary stack carriers 11, the main stack 32, 
which was initially lowered into the position of FIG. 3 in which the 
sheets 29 raised at their edges by the elements 23 can bear in their 
central zone on the top of the stack, is further lowered until the 
platform 4 is in its bottom position in which the various parts of the 
conveyor 8 register with one another so that the pallet carrying the main 
stack 32 can be removed from the feeder and a new empty pallet introduced 
thereinto. The introduced empty pallet is raised by the platform 4 to 
closely below the secondary stack carriers 11. As can be seen in FIGS. 1 
and 3, this position is sensed by means of a sensor 37 which is disposed 
on the frame 12 and which in this case is in the form of a light barrier. 
When the empty pallet has reached the height of the sensor 37 the same 
switches off the lifting means associated with the platform 4, whereafter 
the secondary stack carriers 11 move out. This step can also be triggered 
by the sensor 37 through the agency of a sequential circuit arrangement, 
the secondary stack 38 on the secondary stack carriers 11 being deposited 
on the empty pallet which has been positioned below the secondary stack 
carriers 11. Since the secondary stack carriers 11 move synchronously in 
their outward movement, the resulting displacement forces cancel one 
another out in the outward movement. 
In accordance with another detailed aspect of the invention, an air cushion 
or buffer is produced to ensure very reduced friction between the 
secondary stack carriers 11 and the secondary stack 38 in the inward and 
outward movements. To this end, and as FIG. 5 shows, the secondary stack 
carriers 11 have near their top air-energized blowing nozzles 39. In this 
embodiment the nozzles take the form of ball valves which close 
automatically and open only when the associated ball is depressed. To 
simplify the supply of air to the nozzles 39 the secondary stack carriers 
11 are, as will also be apparent from FIG. 5, simply in the form of 
sandwich panels having top and bottom cover plates 40, 41 secured to 
spacing webs 42. The same are disposed so that the interior 43 consists of 
a plurality of intercommunicating inner chambers. The interior 43 
communicates by way of a line 44 with a source of compressed air and so 
can act as an air distributor for all the nozzles 39. The nozzles 39 can 
start to be supplied with air upon entry of the secondary stack carriers 
11 and the supply can continue until termination of the exit step. 
Preferably, however, the secondary stack carriers 11 are supplied with air 
only during their entry or exit movement--i.e., the supply of air is 
activated at the start of the entry or exit operation and is stopped upon 
an appropriate termination. This step minimizes air consumption and also 
ensures that the secondary stack does not float during normal secondary 
stack operation.