Sheet stacking apparatus

A stack (S) of sheets is formed on a downwardly moving platform (4), the stack being divided into portions (P) each consisting of a predetermined number of sheets. As each alternate portion is completed, that portion is gripped between two plates (5, 20) and moved horizontally so that it is offset relative to the portion next below it. A completed stack containing the required number of portions is separated from the rest of the stack by inserting a divider (40) at the desired position. The platform (4) is then moved to remove those portions below the divider and, at the same time, an auxiliary support (41) moves beneath the divider (40) to support the stack above. The completed stack is removed from the platform (4) which is then raised level with the support (41). The divider (40), support (41) and platform (4) move together so that the stack is again supported on the platform (4).

This invention concerns improvements in or relating to apparatus for 
forming a stack from a succession of sheets of, for example, paper. 
It is usual for sheets to be formed into large stacks either by a delivery 
unit which is raised in unison with the growing stack or more usually the 
sheets are collected on a platform or table which descends at the growing 
rate of the stack. These stacks are often required to be separated into 
smaller batches or portions (e.g. a ream of 500 sheets) for feeding to 
machines for carrying out further operations such as wrapping the reams in 
an outer wrapper. 
The individual batches contained in a stack are commonly marked by 
inserting paper tabs at appropriate positions. These stacks are then 
separated into the required batches manually, which is rather time 
consuming. A disadvantage of the tab system is that the tabs can become 
disturbed and the benefit of marking the batches is lost. Where other more 
substantial devices are used to mark the stack, e.g. angle strips, then 
these must be moved around the factory either manually or automatically. 
It is also known to divide a stack as it is being formed into batches and 
remove the lowermost batch, whilst the rest of the stack is being 
supported by an auxiliary support, for feeding to apparatus for carrying 
out further operations on each batch. 
According to the invention there is provided apparatus for forming a stack 
from a succession of sheets, including support means on which said stack 
is formed, means for feeding said sheets in succession onto said support 
means, stop means for arresting lengthwise motion of said sheets whilst 
being fed onto said support means, characterised by gripping means for 
gripping a portion of said stack, and first means for moving said grippng 
means to offset the gripped portion relative to the next adjacent portion 
of the stack. 
Preferably the apparatus may include second means for moving said support 
means downwards as the stack grows, to keep the top of the stack at a 
constant level. 
In a preferred form the gripping means may comprise first and second 
gripper plate means, third moving means for moving said gripper plate 
means vertically, said first and third moving means being operable to move 
each gripper plate means independently along similar closed paths in a 
vertical plane so that each gripper plate means moves in succession into 
said stack, downwards with said stack, out of said stack and upwards, the 
motions of the gripper plate means being out of phase so that in 
alternation each gripper plate means changes its vertical position 
relative to the other gripper plate means, each gripper plate means 
alternately becoming the upper and lower one. 
A required number of portions may be removed from beneath the rest of the 
stack by moving the support means horizontally and supportng the rest of 
the stack on auxiliary support means. 
A microprocessor may be used for controlling the operation of the moving 
means in a predetermined timed sequence.

Referring to FIGS. 1, 2A, 2B and 14, a stream of overlapped sheets is fed 
to the right by a pair of cooperating rollers 1 and on leaving the nip of 
these rollers each sheet travels further to the right above a stack S, in 
the course of formation, until it strikes a stop means in the form of a 
backboard 2, whereupon the sheet falls on top of the stack. The left hand 
edge of the stack is kept in alignment by known vibrating plates 3. 
The stack is formed on a support platform 4 comprising a table 85 (to be 
described in more detail later) which extends across the width of the 
machine and is carried on a pair of cross members 86 supported at each end 
on beams 87, one such beam being provided on each side of the machine. The 
beams 87 are supported on further cross members 88 which support plates 
89, 89a on each side of the machine. The plates 89, 89a are provided 
respectively with wheels 90, 91 which run on rails 92 fixed to carrier 
beams 93. The latter each have a chain 60 attached to each end thereof, 
which thus supports the platform 4. The platform 4 is raised and lowered 
by the chains 60 (FIG. 2B), which are driven in known manner by a motor 
61, the table being constrained to move in a vertical path by guides 60a. 
During stack formation the platform is lowered a short distance at a time, 
under the control of a photoelectric stack height sensor 62 (FIG. 1), of 
any suitable type, so that the top of the stack S is maintained at optimum 
spacing below the path of sheets from rollers 1 to the backboard 2. 
Vertical movement of the platform 4 is detected by a positional transducer 
94 (FIG. 2B), of any convenient type, which is fixed on the rail 93. A 
pinion 95, engaging a rack 96 fixed to one of the guides 60a, rotates as 
the platform 4 moves, and the transducer 94 emits pulses, as the pinion 
rotates, indicative of the vertical position of the platform, which pulses 
are fed to a central microprocessor control unit 97 (FIG. 14) referred to 
later; the motor 61 also being connected thereto. Tapes 63, which pass 
round pulleys 64, 64a, extend across the top of the stack, in known 
manner, to ensure that the sheets are fed correctly to the top of the 
stack. In order that the tapes 63 can be correctly positioned for 
different length sheets, which require the backboard 2 to be in a 
different position to that shown, the pulley 64 is mounted on a toothed 
quadrant 65, pivoted at 66, and meshing with a gear 67. The latter is 
rotated to move the quadrant about its pivot, and thus move the pulley 64 
up or down depending on the required position of the tapes 63. 
Although only one stack S is shown, it should be noted that a number of 
stacks may be formed simultaneously across the width of the machine, the 
sides of adjacent stacks being kept in alignment by vibrating plates 68 of 
known type. 
As the sheets are fed on to the stack their leading edges are detected by a 
photoelectric detector 81 which, for each sheet, emits a pulse which is 
fed to a counter 82 and moves the count up by one. The counter emits 
pulses, indicative of the count, which are fed to the unit 97. It is 
common, in machines of this type, to feed the sheets as "spurs" (i.e. a 
number of superimposed sheets). In this case the counter 82 would be 
arranged to move up by the number of sheets in the "spur" each time a 
pulse is emitted from detector 81. 
As the stack is formed it is divided into portions P, alternate portions 
being offset to the right from the portion next below in the stack. The 
formation and offsetting of alternate portions of the stack will now be 
described with additional reference to FIGS. 3 to 7. 
The portion P1 is separated, at the right hand end thereof, from the 
portion P below it by a number of gripper plates 5 spaced across the 
stack, only one being visible. Each gripper 5 is carried by an arm 6 which 
is moved, at predetermined times, backwards and forwards horizontally by 
means of a lever 7 fixed on a rotatable shaft 8. The lever 7 carries a 
roller which runs in a vertical channel 9 formed in an extension 10 of the 
arm 6. An arm 7a, also fixed on the shaft 8, carries a cam follower 69 
which engages with a cam 70 fixed to a shaft 71 driven from the output 
side of a single-revolution clutch 72 through a reduction gearbox 72a, so 
that the shaft 71 rotates through 90.degree. for each revolution of the 
output side of the clutch 72. The input side of the clutch is driven 
continuously by a motor 73. For clarity, the shaft 71, gearbox 72a, clutch 
72 and motor 73 are shown in perspective in this figure. The clutch 72 is 
operated, under the control of unit 97, to drive the end of shaft 71 
carrying the cam 70 at certain times, to move the gripper plate 5 into and 
out of the stack S, as will be described later. The arm 6 is constrained 
to move in a horizontal plane by rollers 11 mounted on a vertical support 
12 which itself is movable in a vertical plane on rollers 13 which run on 
rails 14 carried on a fixed support 15. The support 12, and thus also the 
gripper 5, are raised by a lever 16, which is fixed, at one end, on a 
rotatable shaft 17. The other end of lever 16 contacts the bottom surface 
of a block 18 fixed to the support 12. A lever 16a, also fixed to shaft 
17, is attached to the piston of a pneumatic cylinder 74, air being fed to 
the cylinder at appropriate times via an electromagnetic valve 75, which 
is connected to, and operated under the control of unit 97. The support 12 
lowers by reason of its own weight as will be described later. 
Above each gripper plate 5 is a second gripper plate 20 which is movable 
horizontally and vertically, independently of the gripper plate 5, in a 
similar manner to the plate 5. Each gripper 20 is moved horizontally by a 
lever 21, vertical channel 22 and arm 23 which correspond respectively to 
the lever 7, vertical channel 9 and arm 6, the lever 21 being fixed to a 
rotatable shaft 8a. A lever 21a, also fixed to a shaft 8a, carries a cam 
follower 78 which engages with a cam 79, similar to the cam 70, and also 
fixed to the shaft 71, so that the cams 70, 79 rotate stepwise in unison 
but out of phase. The upward movement of plate 20 is obtained from a lever 
24 which, at one end thereof, contacts a block 25 fixed to a support (not 
shown) similar to support 12, the other end being fixed to a rotatable 
shaft 17a. The plate 20 moves downwards by reason of its own weight. A 
lever 24a, also fixed to shaft 17a, is attached to the piston of a 
pneumatic cylinder 76. The lever 24, as with the lever 16, is operated at 
appropriate times by the pneumatic cylinder 76, air being fed thereto via 
a electromagnetic valve 77, which is also connected to, and operated under 
the control of, unit 97. 
The support 12 also carries a pair of further blocks 26, 27 and, similarly, 
the support plate associated with the gripper 20 also carries a pair of 
further blocks 28, 29. 
The grippers 5, 20 are chamfered at their left hand edges and are so 
constructed that air under pressure may be fed out through apertures in 
their left hand edges to provide a layer of air between the surfaces of 
the sheets between which they are moved, as will be described later. 
A pneumatic cylinder 30, to which air is fed via an electromagnetic valve 
80, extends between two levers 31, 32 mounted on fixed pivots 33, 34 
respectively. The free ends of the levers 31, 32 are arranged to contact 
respectively the blocks 26 and 29 or 28 and 27, depending on the relative 
positions of the blocks, 18, 25, so as to urge the grippers 5, 20 towards 
each other, as will be described later. 
The control unit 97 is a microprocessor which, in known manner, controls 
the motors 61, 73, clutch 72 and valves 75, 77 and 80 according to a 
pre-set program so that the various operations take place in the correct 
sequence and at the correct time, as will now be described. 
A number of pairs of gripper plates 5, 20 are provided, spaced apart across 
the width of each stack being formed. Each pair is operated by separate 
levers, corresponding to levers 7, 21, 16, 24 which are fixed to 
respective shafts 8, 8a, 17, 17a. However, a separate cylinder, 
corresponding to cylinder 30 is provided for each pair of grippers 5, 20. 
When the count in counter 82 reaches the required number of sheets to form 
the portion P1, the gripper plate 20 is lowered on to the top of the 
portion P1, by the valve 77 being operated so that the cyinder 76 moves 
the lever 24 clockwise about its pivot. When the gripper 20 contacts the 
top of portion P1 the lever 24 continues its clockwise movement and moves 
away from the block 25. Also, at this time, the lever 16 is away from the 
block 18. The grippers 5, 20 are now supported only by the stack and will 
thus move downwards, under their own weight, in unison with the stack. 
The leading edge of the next succeeding sheet will thus now rest on top of 
the gripper plate 20 (FIG. 3). When several sheets have been delivered on 
top of the gripper 20, the clutch 72 is energised to rotate the cams 70, 
79, so that the lever 21 is operated to move the gripper 20 to the left to 
insert it further into the stack to a position similar to the gripper 
5(FIG. 4), the clutch then being de-energised. Depending on the material 
of the sheets and to ensure that the sheets, which will form a portion on 
top of the portion P1, do not foul the edge of the gripper 20, air may be 
blown out of its leading edge. 
The valve 80 is now operated so that cylinder 30 moves the levers 31, 32 
about their pivots so as to apply pressure to the blocks 26, 29 
respectively which urge the support plate 12 upwards, and the support 
plate associated with the divider plate 20, downwards, thus urging the 
grippers 5 and 20 together so that they firmly grip the portion P1 between 
them. 
When sufficient sheets have been delivered on top of the stack S so that 
the gripper 20 has been lowered to a position in which it is clear of the 
bottom of the backboard 2, the clutch 72 is energised to rotate the cams 
70, 79 so that the levers 7, 21 are operated to move the grippers 5 and 
20, and therefore also the portion P1, to the right a predetermined 
distance, thus producing a step in the stack (FIG. 5). The clutch 72 is 
then de-energised. At the same time air is blown from the front of both 
grippers 5 and 20 to lubricate the sheets above and below the portion P1 
to ensure easy movement. The valve 80 is now operated so that cylinder 30 
moves the levers 31, 32 to release the grip of the grippers 5, 20. The 
clutch 72 is energised so as to rotate the cams 70, 79 to move the gripper 
20 to the left so that it again extends fully into the stack (FIG. 6). 
The gripper 5 is now fully withdrawn from the stack (FIG. 6) by operation 
of the lever 7 by cam 70, and the clutch 72 is de-energised. The gripper 5 
is raised to a position above the level of the top of the stack S (FIG. 
7), by operation of the lever 16, which is caused to move anticlockwise 
about its pivot by cylinder 74 on operation of the valve 75. The clutch 72 
is then again energised to cause operation of the lever 7 so that the 
gripper 5 is moved to the left to the position occupied by the gripper 20 
in FIG. 1. 
The formation of the next portion P in the stack S is the same as just 
described in relation to the portion P1 with the exception that the 
positions of the grippers 5 and 20 are reversed and the valve 80 is not 
operated to cause the cylinders 30 to urge them together and they thus do 
not grip the portion between them. Thus this portion is not offset to the 
right as was the portion P1. 
It will be understood that the gripper plates need not always grip and 
offset every alternate portion. A number of successive alternate portions 
may be offset or not, depending on the arrangement required in the stack, 
the operations required to produce the stack being controlled from a 
suitable program in the unit 97. 
When a required number of portions P have been formed as described above to 
give a completed stack, the stack is removed from the apparatus as will 
now be described with reference to FIGS. 1, 2A, 2B, 8, 9, 14. The 
separation is effected by a divider 40, formed from a thin hollow member 
having an angled front portion 40a (FIG. 2B), and provided with apertures 
(not shown) through which pressure air is fed to form a layer of air on 
its surfaces. 
The divider 40 comprises a number of hollow members spaced apart across the 
machine, only one being visible. It is supported on an auxiliary support 
in the form of a movable support tale 41, the divider 40 and table 41 
being movable both horizontally and vertically as will be described later. 
A layer 98 of low friction material is provided between them to allow 
relative lengthwise movement therebetween. The table 41, which also 
consists of a number of spaced members, is supported, at each side of the 
machine, by a beam 99. The latter are supported on cross members 100, 100a 
to which plates 101, 101a are respectively fixed, on each side of the 
machine, the plates being provided respectively with wheels 102, 103 which 
run on rails 104 fixed to long carrier beams 105. Fixed to each of the 
beams 105 is a toothed rack 108 which are engaged by gear wheels 109 
carried on a cross shaft 109a journalled in the plates 101. Carried on the 
cross members 100 is a motor 110 drivingly connected to the shaft 109a by 
a chain 111. The motor 110 is controlled by the unit 97, so that at the 
appropriate times the motor is operated to rotate the gear 109 and thus 
move the table 41 towards and away from the stack, as will be described. 
Movement of the table is detected by a positional transducer 112 which is 
fixed to the plate 101 and emits pulses, indicative of the horizontal 
position of the table 41, which are fed to the unit 97. 
The divider 40 is fixed at each side of the machine to a plate 113, the 
latter being joined also by cross members 114. Each plate 113 is provided 
with wheels 115 which run on the rails 104. The divider 40 is moved, at 
appropriate times, into and out of the stack by a gear 116 which engages 
the rack 108 and is driven by a chain 114 from a motor 118. The latter is 
controlled from the unit 97 and the horizontal position of the divider is 
detected by a positional transducer 119, similar to the transducer 112, 
fixed to the plate 113. 
At certain times the divider 40 and table 41 are moved vertically, and for 
this movement the carrier beams 105 are each supported, at the left hand 
end, by a connecting rod 120, and about halfway along their lengths by a 
support rod 121. The upper end of rod 120 is loosely connected, at 122 to 
the beam 105 and the lower end is pivotally connected to one arm of a 
bell-crank lever 123, mounted on a fixed pivot 124. The other arm of the 
lever 123 is fixed at its free end to a chain 125 which engages a sprocket 
126 fixed on the shaft of a motor 127, controlled by unit 97. 
The beam 105 rests on top of the rod 121, the lower end of which contacts a 
roller 128 carried on one arm of a further bell-crank lever 129 mounted on 
a fixed pivot 130. The rod 121 is constrained to move vertically by guides 
131. The other arm of lever 129 is connected to one end of a bar 132, the 
other end of which is connected to the other arm of the lever 123. The 
left hand end of the beam 105 carries a roller 133 which runs in a fixed 
track 134, to guide the beam in a vertical path. The arrangement is such 
that when the motor 127 is operated, the levers 123, 129 rotate on their 
respective pivots to move the divider 40 and table 41 vertically. This 
movement is detected by a positional transducer 135 mounted on a fixed 
part of the machine, and having a pinion 136 which engages a rack 137 on 
the rod 121. Movement of the latter rotates the pinion and the transducer 
emits pulses, indicative of the vertical position of the divider 40 and 
table 41, which are fed to the unit 97. 
Fixed to each of the beams 93 (FIG. 2B) is a rack 138 which are engaged by 
gear wheels 139 rotatably carried on a cross-shaft 140 journalled in the 
plates 89. The gears 139 are driven from a motor 141 by a chain 142 so as 
to move the platform 4 horizontally, as will be described later, such 
movement being detected by a positional transducer 143 which is operated 
to send pulses, indicative of the horizontal position of the platform 4, 
to the unit 97. 
To enable the completed stack to be removed from the platform 4, the table 
85 comprises a number of slats 144 (FIGS. 8, 9) spaced apart across the 
width of the table, each slat being provided with a row of apertures 145 
in its upper surface. The apertures in each slat communicate with a hollow 
chamber 146, one such chamber being provided for each slat. Air under 
pressure is supplied at appropriate times, from a pump (not shown), to the 
chambers 146 and out through the apertures 145. 
An endless chain conveyor 147 is provided in each of the spaces between 
adjacent slats 144. Each chain 146 carries a single pusher 148 positioned 
so that all the pushers are in alignment across the table 85. Each 
conveyor 147 passes over sprockets 149, 150, 151 and 152, all the 
sprockets 151 being mounted on a common shaft 153. The latter is driven by 
a chain 155 from a motor 154, fixed on one of the cross members 88. 
Whilst a stack is being formed on the table 85 the pushers 148 are 
stationary in the position shown in FIG. 8. The motor 154 is operated at 
certain times, by the unit 97, to drive the conveyors 147 in a clockwise 
direction and the pushers 148 push the completed stack off the table 85, 
the position of the pushers 148 being indicated to the unit 97 by pulses 
emitted by a positional transducer 156 mounted on the shaft 153. 
To prevent undesirable movement of the portion P above the portion forming 
the top of a completed stack, as the divider 40 is inserted into the 
stack, and the completed stack removed, blocking means, in the form of a 
pad 157 (FIG. 1) is provided. The pad is fixed to a cross member 158 
having a plate 159 attached to each end thereof, only one plate being 
visible, and being slideable between horizontal guide rails 160 carried on 
a side plate 160a. The plates 159 and thus also the pad 157, are moved by 
an arm 161 connected to one arm of a bell-crank lever 162, pivoted at 163, 
the other arm of which is connected to the piston rod of a pneumatic 
cylinder 165. The latter is supplied with air via a valve 166 under the 
control of the unit 97. Whilst the pad 157 is in contact with the stack it 
is moved downwards in unison therewith. For this movement the plate 160a 
runs between wheels 167, 168 carried on a fixed part of the machine, and 
the movement is derived from the carrier beam 105, on which runs a wheel 
169 mounted on an extension of the plate 160a. Thus the pad 157 is moved 
upwards by the beam 105 and downwards under the weight of the plate 160a 
and the attached parts, as the beam 105 so moves. 
The operation of the apparatus for removing a completed stack from the 
machine will now be described with added reference to FIGS. 10 to 13. 
When the portion P forming the top of the stack reaches a position level 
with the divider plate 40, motor 118 is operated, so as to move divider 40 
horizontally to the right between the facing surfaces of the top portion 
of the required completed stack and the next portion above (FIG. 10). 
Separation of the completed stack takes place between the top of a portion 
which has been offset and the bottom of a portion not so offset. 
On the divider 40 being inserted into the stack, the pad 157 is moved to 
the left against the edge of the portion P immediately above the divider 
40, by valve 166 being operated so that cylinder 165 moves lever 162 
clockwise on its pivot. 
As sheets are still being fed on to the top of the stack, the divider 40 
and table 41 are moved downwards, with the platform 4, as soon as the 
divider 40 starts to enter the stack. For this, the motor 127 is operated 
to rotate sprocket 126 anticlockwise to pay out chain 125, which is kept 
taut by the combined weights of divider 40, table 41, beams 104 and 
associated parts, acting to rotate levers 123, 129 on their pivots. The 
signals from sensor 62 are now also fed, by unit 97 to the motor 127 which 
thus operates to lower plate 40 and table 41 in unison with platform 4. 
The pad 157 also moves down with table 41 due to it being supported by the 
beam 105. 
When divider 40 reaches the position shown in FIG. 11, motor 141 is 
operated to move the table 85, and thus also the completed stack, 
horizontally to the right. At the same time motor 110 is operated to move 
the support table 41 also to the right so that the portions P above the 
stack being removed are supported by table 41 by the time this movement is 
completed (FIG. 11). The pad 157 prevents the portion P next above divider 
40 from also moving to the right during this movement. 
When the various parts reach the positions shown in FIG. 12, valve 166 is 
operated so that cylinder 165 withdraws pad 157 to the right, pressure air 
is supplied to chambers 146 (FIG. 8) and out through apertures 145 to 
provide a layer of air on the upper surface of table 85 and the motor 61 
is stopped. Also, motor 14 (FIG. 2B) is operated to drive the conveyor 147 
in a clockwise direction so that pushers 148 push the completed stack to 
the right, off the table 85, after which the motor 154 is stopped and the 
air supply to chambers 146 is turned off. The stack then has further 
operations carried out on it as will be described later. 
The motor 141 is now operated to move the empty platform 4 to the left to a 
position to the right of the position it is shown occupying in FIG. 10. 
Whilst this movement is taking place the motor 154 is operated to drive 
the conveyors 147 in an anti-clockwise direction to move the pushers 148 
back to their starting position shown in FIG. 8. 
Motor 61 is now operated to raise the platform 4 such that the upper 
surface of table 85 is level with the upper surface of the table 41. 
Motors 141, 110 and 118 are then operated to move divider 40, table 41 and 
platform 4 together to the left until they occupy the positions shown in 
FIG. 13, at which time the motor 127 is stopped and the stack being formed 
is again supported by the platform 4. During this latter movement motor 61 
is operated to move the platform 4 downwards again, under the control of 
sensor 62. 
Motor 127 is now operated to rotate sprocket 126 anticlockwise to raise 
plate 40, table 41 and pad 157 back to the positions shown in FIG. 1. 
The above operations for removing a completed stack are repeated after a 
further stack has been formed as described above with reference to FIGS. 1 
to 7. 
With reference now to FIG. 15 the completed stacks, after being removed 
from the table 4, are fed along a conveyor 170 to a transverse conveyor 
171 from which the stacks are fed to a machine 172 of any known type which 
separates each individual portion from the stacks. 
Successive portions in each stack are removed therefrom in opposite 
directions, thus forming two rows 173, 174 of individual portions. Each 
row of portions is fed respectively to machines 175, 176 which enclose 
each portion in a carton having a lower body half and an upper lid half. 
The filled cartons are then shrink-wrapped at 177 and formed into large 
batches in a palletising unit 178.