Method and apparatus for the production of numerically correct stacks

A method and apparatus for producing numerically correct partial stacks from individual leaves or sheets interfolded in a U-shaped or zigzag form on an interfolder. A double stream is formed from one or more streams of sheets by staggering or guiding together. This double stream is then continuously folded into zigzag form and piled up in a continuously growing stack, from which partial stacks of a specific size are separated. Gaps are formed in the streams of sheets which simplify the introduction of separating elements into the stack. For this purpose, sheets are removed from the streams of sheets and optionally placed accurately in position on successive sheets.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method and apparatus for producing 
numerically correct partial stacks from individual leaves or sheets 
interfolded in a U-shape or a zigzag form on an interfolder. A double 
stream is formed from one or more streams of sheets by staggering or 
guiding together the streams. This double stream is then continuously 
folded in a zigzag form and is piled up in a continuously growing stack, 
from which partial stacks of a specific size are separated. Gaps are 
formed in the streams of sheets which simplify the introduction of 
separating elements into the stack. For this purpose, sheets are removed 
from the streams of sheets and optionally placed accurately in position on 
successive sheets. 
2. The Prior Art 
An apparatus of this type is known to those skilled in the art as an 
interfolder and have been known for a long time. They function by folding 
material into U-shaped or zigzag-shaped folds, and for producing stacks of 
folded sheet material. During this method of operation, one common stream 
of sheet material is formed from one or more, preferably two, prepared 
lengths of material which each consists of an uninterrupted series of 
sheets of equal length which are separated from one another or are 
attached to one another by a perforation. The single stream of sheet thus 
produced is then folded in a zigzag format and is then piled up in a 
stack. 
Depending upon the number of folds per sheet, the common stream of sheet 
material is produced either by staggering the prepared lengths of material 
or by guiding them together in an offset manner. Most common are 
interfolders which process two lengths and produce sheets which have only 
one fold and are placed on one another in a U shape. In this type, the 
sheets of the two lengths of material are placed one on top of the other 
in such a way that they are staggered with respect to one another by half 
a sheet in length. 
In order to make full use of the productivity of the interfolders of the 
prior art type, it is necessary for them to be followed by a 
semi-automatic or fully-automatic packaging arrangement. This gave rise to 
the requirement for the sheet stacks which are continuously produced by 
the zigzag folding to be divided into numerically correct partial stacks 
which are then packaged. For this purpose, depending upon the machine 
cycle and the predetermined lot size of the partial stacks, separating or 
supporting elements are introduced from the side into the sheet stack and 
a partial stack is separated from the sheet stack. In order to achieve the 
most accurately possible division of the sheet stack into numerically 
correct partial stacks, it is advisable to carry out separation directly 
upon formation of the stack; that is, immediately downstream from the 
folding rollers. Separations of this type generally operate 
satisfactorily. However, problems occur at the moment when the downstream 
front sheet of the sheet stack and the upstream rear sheet of the partial 
stack, which are interfolded, are to be separated without disruption. This 
then leads to difficulties and disruptions, particularly when partial 
stacks with small lot sizes have to be formed at high production 
capacities by the interfolder. 
In order to solve problems of this type, there have already been proposals, 
such as in U.S. Pat. No. 4,717,135 and in EP-O 291,211 A 2, in which small 
gaps are created by folding back advancing sheet parts onto the sheet 
itself in the individual sheet streams. In this way, interfolding of the 
sheets corresponds to a plane of separation, so that the actual separating 
operation is simplified. 
However, it has been found in practice with modern high-capacity 
interfolders that this small gap is not sufficient for a simple separating 
operation. Even a high expenditure on control technology and machinery 
which is urgently required as a result does not guarantee reliable 
separation of numerically correct partial stacks. Folding back, or round 
folding, of several sheets, which might be proposed as a possible 
solution, cannot be carried out. The material thickness produced in these 
operations with the combined lengths of material is limited by the width 
of the folding gap between the folding rollers, since this needs to be as 
narrow as possible in order to achieve a good quality fold. In addition, 
this possible solution has the inherent danger that when several sheets 
are folded back, or folded round, they are shifted out of register with 
respect to one another and to the rest of the series of sheets. This would 
inevitably lead to disruptions in the taking up, the transporting, and the 
zigzag folding. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a method and an interfolder 
apparatus for carrying out the method which permits a problem-free and 
reliable division of a stack of sheet material which is continuously 
produced by zigzag folding into numerically correct partial stacks. These 
desired results are provided even with high production capacities in 
combination with partial stacks of small lot sizes. In addition, the 
expenditure on control technology and machinery is to be kept as low as 
possible. 
The above objects are accomplished in accordance with the present invention 
by providing a method of producing numerically correct partial stacks of 
individual sheets which are of U-shape or zigzag-shape and which are 
interfolded so as to overlap, comprising providing at least one 
continuously moving length of material; producing at least one 
continuously produced stream of neighboring sheets of equal length from 
the at least one continuously moving length of material by 
cross-separation or cross-perforation; providing a double stream of these 
sheets; the double stream being guided together and staggered, so that 
neighboring sheets lying opposite to one another are offset with respect 
to one another; forming a gap in the stream by removing at least one 
removable sheet; continuously folding the double stream in U-shape or 
zigzag shape; piling up the double stream in the form of a stack; dividing 
the stack which is continuously being formed into numerically correct 
partial stacks; and separating off the partial stacks from the stack by 
the introduction of separating elements in a separating zone of the stack. 
In addition, the present invention provides an apparatus for producing 
numerically correct partial stacks comprising a pair of feed rollers for 
supplying a double stream length of material; a cross-separating or 
cross-perforating means for defining a cutting gap; a pair of folding 
rollers running in the opposite direction and defining a folding gap for 
zigzag folding of the double stream to form a stack; a shaft arranged 
after the double stream and receiving the stack; distributors which are 
coordinated with the pair of folding rollers and which are arranged on 
both sides of the shaft; a separating means which is arranged downstream 
of the pair of folding rollers and which can be introduced into the stack 
from the side; a storage table which goes into the shaft; and at least one 
removing means arranged between the cutting gap and the folding gap and 
tangent to the double stream. 
The advantages achieved reside, in particular, in that before the zigzag 
folding using relatively simple means, the formation of sufficiently large 
gaps in the sheet streams is possible. This substantially simplifies the 
subsequent separating operation. In this way, an absolutely reliable 
separation of the continuously formed partial stacks of the sheet material 
into numerically correct partial stacks is possible. The formation of a 
sufficiently large gap not only prevents interfolding of the sheets which 
are adjacent in the plane of separation provided, but it also ensures 
that, even with high production capacities of the interfolder combined 
with the formation of partial stacks of small lot sizes, there is 
sufficient time available for the introduction of separating and 
supporting means into the sheet stack. This measure also reduces the 
expenditure on control technology and machinery for the separating and 
supporting means. This is not difficult to recognize in comparison with 
other interfolders, e.g., that described in U.S. Pat. No. 4,770,402. It 
has also proved advantageous that the sheets removed in order to form a 
gap are stored for a time. Then these are delivered back to the sheet 
stream individually one after the other in such a way that they come to 
lie congruently on corresponding sheets and the alternative exists of 
placing them at the end of the beginning region of a partial stack.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A machine for producing sheets which are interleaved in a U-shape or are 
interfolded in a zigzag form, comprises essentially an unrolling station, 
processing apparatus with a storage area, designated hereafter as an 
interfolder, and a packaging station arranged after it. In the drawing 
only the interfolder 1, which is of interest for the invention, is 
illustrated. 
In order to produce the interfolded sheets T1, T2, the interfolder 1 shown 
in FIG. 1 processes two lengths of material W1, W2. The length of material 
W1 is drawn from a left-hand pair of feed rollers 3, 4 to a left-hand 
cross-separating arrangement 5. This includes a blade roller 6 bearing 
cross-separating blades 7 and a cutter roller 8 equipped with 
counterblades 9 which cooperate with the cross-separating blades 7. The 
blade roller 6 and the cutter roller 8 form a common roller gap 10, in 
which the length of material W1 is divided into sheets T1 of equal length, 
which are then delivered as a continuous stream W1' to a left-hand folding 
roller 12 of a pair 11 of folding rollers. In order to grip and transport 
the sheets T1, the cutter roller 8 and the folding roller 12 are equipped 
with radially arranged suction air openings 14 and 15 respectively. The 
suction air opening 14 is in air-duct communication with a suction air 
control channel 17 via a cross-bore 16, while the suction air opening 15 
is connected by a cross-bore 19 to suction air control channels 20 or 21. 
The rollers 3, 4, 6, 8 and 12 are rotatably mounted in common sliding 
walls 22, 22', which are movably mounted on a lower frame of the machine 
23. They are driven in rotation by a miter gear 24, a roller drive chain 
25 and wheel arrangements which are not shown. The particular direction of 
rotation of each one is shown by the arrows in FIG. 1. 
The length of material W2 is delivered at the same speed to the interfolder 
1 and is further processed there like the length of material W1. In this 
case, it is drawn from a right-hand pair of feed rollers 26, 27 to a 
right-hand cross-separating arrangement 28. This comprises a blade roller 
29 bearing cross-separating blades 7 and a cutter roller 30 equipped with 
counterblades 9, which cooperate with the cross-separating blades 7. The 
blade roller 29 and the cutter roller 30 form a common roller gap 31, in 
which the length of material W2 is divided into sheets T2 of equal length. 
Sheets T2 are then delivered as a continuous stream W2' to a right-hand 
folding roller 13 of the pair 11 of folding rollers. In order to grip and 
transport the sheets T2, the cutter roller 30 and the folding roller 13 
are equipped with radially arranged suction air openings 32 and 33 
respectively. The suction air opening 32 is in air-duct communication with 
a suction air control channel 35 via a cross-bore 34, while the suction 
air opening 33 can be supplied with suction air via a cross-bore 36 from 
the suction air control channels 37 or 38. The rollers 26, 27, 29, 30 and 
13 are rotatably mounted in common sliding walls 39, 39', which are 
movably mounted on a lower frame of the machine 23. They are driven in 
rotation by a miter gear 40, a roller drive chain 25 and wheel 
arrangements which are not shown. The particular direction of rotation of 
each one is shown by the arrows in FIG. 1. 
The folding rollers 12, 13 of the pair of folding rollers 11 form a common 
folding gap 41, which can be varied in width by displacing the sliding 
walls 22, 22' and 39, 39'. The streams W1' and W2' are guided together in 
the folding gap 41, forming a double stream W3, so that the sheets T1 of 
the stream W1' are staggered by half a sheet length with respect to the 
sheets T2 of the stream W2'. The double stream W3 is then folded in zigzag 
form and piled up into a continuously growing stack S. The sheets T1, T2, 
which have been given a central fold 101 or 102, respectively, by the 
folding operation, are interleaved in such a way that the folds 101 always 
face towards the left and the folds 102 always face towards the right. The 
beginning and end of each of the sheets T1 or T2, which are adjacent in a 
stream W1' or W2', respectively, come to rest, in each case, in the 
central fold 102 or 101 of the sheets T2 or T1, respectively of the 
opposing steam W2' or W1'. For the formation of the folds, the folding 
rollers 12, 13 are provided with additional air intake gripping 
arrangements which are not essential to the invention and, for the sake of 
clarity, are not included in the drawings, although they are mentioned 
briefly here for the sake of completeness. 
A shaft 42, in which a stack table 43 which is vertically movable upwardly 
and downwardly is located, is arranged centrally with respect to the 
folding gap 41 underneath the pair 11 of folding rollers. A left-hand 
distributor 44 and a right-hand distributor 45 are arranged laterally 
adjacent to the shaft 42 and below the folding rollers 12, 13. The 
distributors 44, 45 are of comb-like construction and in the machine cycle 
they carry out working movements in which they engage with their front 
ends 44' and 45', respectively, both in the folding rollers 12 and 13 and 
also in the shaft 42. For this purpose, the folding rollers 12, 13 have 
annular grooves 12', 13' and the shaft 42 has vertical slots. The 
distributors 44', 45 are controlled as regards time in the course of their 
movement in such a way that they work offset from one another. In this 
way, the folds 101 of the sheets T1 and the folds 102 of the sheets T2, 
which are formed alternately in the zigzag folding are taken off of the 
folding rollers 12 or 13 by the distributors 44 or 45 in the correct 
sequence and are pushed downwards with the sheets T1, T2 into the shaft 
42. In the shaft 42, the sheets T1, T2 are then piled up by means of the 
stack table 43 into a stack S, the stack table 43 being moved downwards 
depending upon the number of interfolded sheets T1, T2. After a 
predetermined number of sheets T1, T2, a separating arrangement 46 is 
introduced into the stack S from the side. By means of this separating 
arrangement, a partial stack S1 of predetermined size can be separated 
from the stack S. 
In a simple construction, the separating arrangement 46 has two 
horizontally movable forks 47, 48, which are mounted on displacement 
devices 49, 50, which are arranged so as to be vertically movable on guide 
elements which are not shown. In order to separate off one partial stack 
S1, the forks 47, 48 travel from one common starting position into the 
stack S in the same horizontal plane. After this, the fork 47 briefly 
assumes the function of the stack table 53 and supports the stack S which 
is continuously being built up, and, at the same time, the fork is moved 
downwards. The partial stack S1, which has been separated off, is moved 
rapidly downwards jointly with the stack table 43 and the fork 48, and 
from there, the partial stack S1 is taken over by a conveyor arrangement 
which is not shown. The fork 48 is then withdrawn from the shaft 42, and 
the stack table 43 is moved upwards below the fork 47. The latter is also 
withdrawn from the shaft 42 and afterwards travels back with the fork 48 
upwards into their common starting position. 
In order for a partial stack S1 to be separated off without problems, it is 
desirable if, according to the desired number of sheets T1, T2 in the 
stack S1, a gap 2 is arranged between the partial stack S1 and the 
remaining stack S. The result of this is that the sheets T1, T2 in the 
plane of separation are not interfolded, so that the forks 47, 48 of the 
separating arrangement 46 can pass through the stack S from the side. An 
arrangement for forming gaps 2 is shown in FIG. 1. It is a removal 
arrangement 51 which is constructed as a storage arrangement 2. In the 
embodiment which is illustrated in FIGS. 1 and 4, this storage arrangement 
52 is constructed as a storage roller 53. The storage roller 53 is 
arranged on the folding roller 12 upstream of the folding gap 41, tangent 
to the stream W1', these two rollers forming a common removing and 
returning gap 54. As FIG. 4 shows, the storage roller 53 has a cylindrical 
main body 55, the rolling circumference of which corresponds to the 
distance between corresponding edges of neighboring sheets T1. The main 
body 55 is mounted coaxially and so as to be fixed against rotation on a 
shaft 56 which is rotatably mounted in the sliding walls 22, 22' by means 
of ball bearings 57 and securing elements which are not shown. A toothed 
wheel 58, which is arranged so as to be fixed against rotation on one end 
of the shaft 56', engages in a toothed wheel 59, which is arranged so as 
to be fixed against rotation on the folding roller 12. 
The folding roller 12 also has a cylindrical main body 60, and in its 
casing 60' are arranged the annular grooves 12' in which the distributor 
44 engages. The main body 60 is mounted coaxially and so as to be fixed 
against rotation on a shaft 61 which is rotatably mounted in the sliding 
walls 22, 22' by means of ball bearings 62 and securing elements which are 
not shown. The toothed wheel 59 is mounted so as to be fixed against 
rotation on one end of the shaft 61'. 
The number of teeth on the toothed wheels 58 and 59 are chosen so that the 
storage roller 53 is driven in the machine cycle, that is to say that it 
rotates once per sheet T1. In order to grip sheets T1, the storage roller 
53 has in the casing 55' of its main body 55 suction air openings 63 which 
open into a cross-bore 64 which is moved with its end opening 64' past 
control channels 65 and 66 during the rotary movement of the storage 
roller 53. While the control channel 65 can be supplied with suction air, 
the channel 66 is continuously connected to atmospheric air pressure. The 
control channels 65, 66 are arranged in a control valve which is rotatably 
mounted on the shaft 56, but is fixed to the sliding wall 22' by means of 
a holder 68 and a bolt 69, so as to be fixed against rotation. The suction 
air control channels 20, 21, which are described above for the folding 
roller 12, are arranged in a control value 70 which is rotatably mounted 
on the shaft 61, but is fixed by means of a holder 71 and a bolt 72 to the 
sliding wall 22', so as to be fixed against rotation. 
In normal transport operation, the folding roller 12 with its air intake 
openings 15 picks up the downstream edges of the sheets T1 and moves the 
sheets T1 to the folding gap 41. For this, the suction air openings 15 are 
supplied with suction air via the cross-bore 19 of the suction air control 
channels 20, 21. 
In order to form a gap 2 in the stream W1', the suction air control channel 
21 is connected to atmospheric air pressure for one machine cycle, while 
simultaneously, the control channel 65 of the storage roller 53 is 
supplied with suction air for one machine cycle. In this way, a specific 
sheet T1' is gripped in the removing and returning gap 54 by the storage 
roller 53 by means of its suction air openings 63, and a gap 2 is formed 
in the stream W1'. After one rotation of the storage roller 53, the 
control channel 65 thereof is connected to atmospheric air pressure, and 
the control channel 21 of the folding roller 12 is again supplied with 
suction air. The sheet T1' is thereby placed accurately in position on the 
sheet T1 which follows it. Both are then delivered together to the folding 
gap 41. 
The accurate supply of suction air and aerating of the control channels 21 
and 65 which is necessary for the formation of a gap 2 takes place in the 
machine cycle and depends upon the desired number of sheets T1, T2 in the 
partial stacks S1. 
This control function is advantageously assumed by a control valve which is 
arranged before the control valves 67, 70 and carries out a switch 
function. Valves of this type are known, and U.S. Pat. No. 4,714,394 
discloses such an example in the prior art. 
A storage roller 53' which is arranged on the folding roller 13 and the 
stream W2' is shown in dash-dot lines in FIG. 1. The storage roller 53' 
can replace the storage roller 53 or can cooperate therewith. 
In FIG. 6, the double stream W3 is shown before and after the zigzag 
folding. A gap 2 is formed in the stream W1' of the double stream W3 by 
means of the storage roller 53 described above. The arrow 73 indicates 
that the sheet T1', which is stored for a brief time, has been placed on 
the following sheet T1, so that a gap 2 is produced. After the 
zigzag-shaped folding, the sheets T1, T2 are interleaved, except in the 
region of the gap 2 in which the separating device 46 engages during the 
separating operation. 
It is advantageous if for the formation of a gap 2, one more sheet T1 is 
removed in the stream W1' opposite the separating arrangement 46 than in 
the stream W2' facing the separating arrangement 46. This ensures that the 
separating arrangement 46 moves into the stack S from the side on which 
two fold edges 102 (101) define the gap 2. 
A second embodiment of an interfolder 1, which includes the structure and 
features set out in the aforementioned description, is shown in FIG. 2. 
Upstream of the folding gap 41, a storage roller 153 is arranged on the 
folding roller 12, so as to be tangent upon the stream W1'. Its diameter 
is twice as great as that of the storage roller 53', which is arranged 
upstream of the folding gap 41 on the folding roller 13, so as to be 
tangent to the stream W2'. The storage rollers 153 and 536 function and 
are constructed in a similar manner to the storage roller 53. In order to 
form a gap 2, one sheet T2' is removed from the stream W2' by the storage 
roller 53' and is placed accurately in position on the following sheet T2. 
In order to form a gap 202, on the other hand, two adjacent sheets T1' are 
removed from the stream W1' by the storage roller 153 and are placed 
accurately in position on the two sheets T1 which immediately follow the 
gap 202. Larger gaps 202, 2 formed in this way are shown in FIG. 7. The 
arrows 86 or 87, 88 indicate the direction in which the sheet T2' or the 
sheets T1' have been moved in order to form a gap 2 or 202. The larger 
gaps 202, 2 which are present after the zigzag folding of the double 
stream W3 make it possible to insert the separating arrangement 46 into 
the stack S, even with the highest production capacities of the 
interfolder 1. 
A third embodiment showing storage arrangements 52, 52' is illustrated in 
FIG. 3. A modified cutter roller 8 or a modified blade roller 29 is 
constructed at the same time as storage rollers 8' or 29'. 
The cutter roller 8 requires an additional suction air control channel 76. 
In order to form a gap 2 in the stream W1', the control channel 76 is 
supplied with suction air, and the suction air control channel 20 of the 
folding roller 12 is simultaneously connected to the atmospheric air 
pressure. Thus, specific sheets T1 remain fixed on the cutter roller 8', 
are guided in a circular movement below the length of material W1 and 
there come to rest accurately in position below a sheet T1 which is still 
to be separated off. While this sheet T1 is being separated from the 
length of material W1, the suction air control channel 76 is connected to 
the atmospheric air pressure, and the suction air control channel 20 is 
again supplied with suction air. The sheets T1, T1', which lie doubled, 
are then picked up together by the folding cylinder 12 and delivered to 
the folding gap 41. 
By means of additional suction air elements, the blade roller 29 can also 
assume the function of a storage roller 29'. For this purpose, it is 
equipped behind the blades 7 (when viewed in the direction of rotation) 
with suction air openings 78 which ca be brought into airduct 
communication with suction air control channels 80, 81 via a cross-bore 
79. In addition, the suction air control channel 35 of the cutter roller 
30 is divided into two suction air control channels 35' and 35". In order 
to form a gap 2 in the stream W2', the suction air control channels 80, 81 
are supplied with suction air, while, at the same time, the suction air 
control channel 35' is connected to atmospheric air pressure. Thus, before 
being separated, sheets T2' are picked up by means of the suction air 
openings 78 and fixed on the blade roller 29'. The separated sheets T2' 
are then guided onto the length of material W2 and there placed accurately 
in position on the next sheets T2 to be cut off. For this purpose, the 
suction air control channels 80, 81 are connected to atmospheric air 
pressure, and the suction air control channel 35' is again supplied with 
suction air. The sheets T2, T2', which lie double, are then delivered to 
the folding gap 41 by means of the cutter roller 30 and the folding roller 
13. 
Storage belts 74 and 75 are shown in greatly simplified representation in 
FIG. 5. The storage belt 74 runs around guide rollers 82 and 83 and forms 
with the folding roller 12 a common removing and returning gap 54. The 
storage belt 75 runs around guide rollers 84 and 85 and forms with the 
folding roller 13 a common removing and returning gap 54'. The storage 
belts 74, 75 are preferably equipped with intake air gripping elements 
(not shown). Their function, in principal, is similar to that of the 
storage roller 53. 
The present invention is not limited to the embodiments illustrated in the 
drawings, since many other alterations and additions could be made, 
without deviating from the fundamental idea of the invention. Thus, for 
example, in one embodiment, there can be only one belt or roller storage 
arrangement which is tangent to the stream W1' and the stream W2' and 
which can receive, store and return both sheets T1' and sheets T2'. A 
further embodiment is to provide two storage arrangements 52, 52' on a 
folding roller 12 or 13. Thus, it is possible to place several sheets T1' 
or T2' accurately in position on a cloth T1 or T2 in order, thus, to form 
a larger gap 2. 
While only a few embodiments of the present invention have been shown and 
described, it is to be understood that many changes and modifications may 
be made thereunto, without departing from the spirit and scope of the 
invention as defined in the appended claims.