EP0453790A1 - Device for conveying sheets - Google Patents

Abstract

Conveying tables for overlapping sheet transport between a feeding device and a printing machine are known, which work with suction air acting through suction bands. The underpressure created in a suction chamber must not, however, fasten, by suction, the printed sheet on the conveying table via spurious air flowing through side regions. <??>The suction bands 6 are let into the conveying table 3. At the side of the guide grooves 10, ventilation openings 11, 12 are provided, which are connected to the environment separately from the suction chamber. To this end, ventilation ducts are provided, which unite the ventilation openings 11, 12. The perforation in the suction band 6 can be made in the form of slots 14 which are arranged in a mutually offset manner and leave free support regions on the edge and in the centre 16 of the band. <??>Spurious air caused by band expansion is avoided. The printed sheets are held uniformly on both sides and guided across the conveying table without distortion. <IMAGE>

Description

The invention relates to a device for conveying printed sheets to a printing press according to the preamble of claim 1. Such a device is known from DE-OS 3 838 078.

So-called belt tables or conveyor tables are used to feed printed sheets to a printing press. On these conveyor tables, the printed sheets are usually transported under scales by conveyor belts in order to achieve a tight sheet sequence at high speeds. It has been shown to be particularly advantageous to operate the conveyor table with suction air. The possible solutions described for this in the past have many deficiencies.

For example, DE-OS 3 838 078 describes a device for conveying an in particular scaled stream of sheets. The conveyor table is designed as a box to which an axial fan is connected. Perforated suction belts are guided over the conveyor table, which correspond to openings in the conveyor table. When the axial fan is operating, the interior of the conveyor table is evacuated and sheets of paper running over the conveyor table are sucked in by the suction belts and transported forward with them. Special features include the arrangement of an additional suction space on the discharge side of the conveyor table, its separate controllability and the arrangement of the suction belts in guide troughs below the table level, so that the surface of the suction belts lies approximately at the table level.

The device is readily functional for normal papers and is also reliable. However, problems arise for special papers, in particular thinner substrates. On the one hand, the suction belts lengthen under the operating stress over time. This creates an undefined slip behavior between the suction belts and the drive rollers. This can be countered by re-tensioning devices, but the drive conditions are no longer the same on both sides of the conveyor table and are constant over time. On the other hand, the suction belts are not always perfectly smooth on the conveyor table or in the guide troughs, which creates a more or less large air gap. This is partly unavoidable due to an arching of the suction belts, partly due to the surface conditions. This causes air to be drawn in laterally through the suction belt support and the negative pressure to spread over large areas of the conveyor table. Here, the printing material is sucked around the edges of the suction belts and then rubs heavily on the conveyor table, which often leads to late or oblique sheets in the sheet feeder. In addition, the sheets no longer lie smoothly when they arrive in the sheet feeder.

Further problems arise when discontinuous drive conditions are present, as is the case, for example, with cyclical braking of the printed sheets entering the sheet feeder. This can be achieved, for example, by a drive of the conveyor belts or suction belts which changes the speed periodically every bend. Since the printed sheets are only held on the suction belts with a reduced suction area in the transition area between the conveyor table and sheet system, the sheet position can no longer be adequately controlled at the time of maximum delays. In this case, the solution according to the prior art offers the possibility of a higher vacuum level in the front area of the conveyor table via the additional suction space to have an effect on the printed sheets than in the rear area. However, this requires a clocking of the air intake. The suction belt table becomes more complicated again, since it has been shown in practice that a separate fan may be necessary to supply the additional suction space with suction air. Especially with thinner papers, the higher level of negative pressure has a very negative effect due to the risk of suction and the consequent hindrance to sheet alignment. For thinner papers and thick cardboard boxes, a whole range of aids such as pressure rollers, brake brushes, ball riders, elaborate suction air regulators and the like are often used in contrast to the actual construction principle of a simple construction of the generic conveyor table. used to achieve a reasonably safe sheet guidance on the conveyor table.

It is therefore an object of the invention to ensure that the printed sheets are transported as smoothly as possible and under uniform conveying conditions seen over both the width and the entire length, and can be kept under constant conditions over a longer operating period. In addition, taking into account all expansion, slip and suction conditions, it should be possible to propel the printed sheets to the printing press in a suitable manner. In addition, the function of sheet transport for all formats and qualities of substrates should be ensured without additional aids.

The solution to this problem results from the characterizing part of patent claim 1. It is particularly important here that incorrect air, which led to the lateral suction of the sheet to be conveyed, is compensated for by the ventilation openings now provided on the side of the conveyor belts can be. The printed sheets are therefore kept even and can be continuously guided over the conveyor table without tension. It is ensured by further means that the conveyor belts cannot become excessively long, so that defined slip ratios for driving them are achieved. In addition, the effective suction surface is kept constant in all phases of the drive and so large in the front edge area of the conveyor table with reduced sheet support that the printed sheets are always subjected to the same and sufficiently large holding forces. To this end, the hole arrangement is advantageously chosen such that load-bearing areas in the perforated band remain hole-free at least at the edge and in the middle of the band. This prevents uncontrolled expansion slippage between drive rollers and suction belts caused by excessive stretching of the suction belts. In addition, the suction openings in the conveyor table are adapted to the required force in the sheet transport direction. For this purpose, larger suction openings are provided especially at the front edge of the conveyor table. In this way, the printed sheet can still be held securely in the front table area.
A further fundamental improvement is the arrangement of ventilation openings within the suction belt guide, but apart and separate from the suction openings. This reduces wear on the suction belt, furthermore the tensile forces on the suction belts are reduced, and in connection with this the belt stretch can be minimized and, above all, evened out.
The control of the printed sheets can be improved by arranging two suction spaces one behind the other in the sheet running direction. An additional suction belt can be provided on the discharge side in order to increase the holding forces there. Alternatively, the suction belts can also be designed as toothed belts. In this way, better holding forces and absolutely defined expansion / slip ratios are achieved.

The invention is explained in more detail below with reference to drawings.

Figur 1

die Anordnung eines Fördertisches zwischen Anleger und Druckmaschine,

Figur 2

eine Draufsicht des beanspruchten Fördertisches,

Figur 3

einen Querschnitt durch einen Teil des beanspruchten Fördertisches,

Figur 4

die Anordnung eines Fördertisches mit zwei Saugkästen in Längsrichtung des Fördertisches und

Figur 5

einen Querschnitt durch einen Saugband in Form eines Zahnriemens.

In detail shows

Figure 1

the arrangement of a conveyor table between feeder and printing machine,

Figure 2

a plan view of the claimed conveyor table,

Figure 3

a cross section through part of the claimed conveyor table,

Figure 4

the arrangement of a conveyor table with two suction boxes in the longitudinal direction of the conveyor table and

Figure 5

a cross section through a suction belt in the form of a toothed belt.

In Figure 1, a conveyor table 3 is arranged between a printing press 1 and a feeder 2. It has a suction chamber 4, to which an axial fan 5 is connected on the underside. Suction chamber 4 and axial fan 5 result in a common storage space in which a negative pressure is built up. Perforated suction belts 6 are guided over the conveyor table 3. The suction belts 6 are guided on the underside of the conveyor table 3 via tensioning rollers 7 and on the end faces via drive or guide shafts 8. The conveyor table 3 is continuously broken through in the area of the guide for the suction belts 6, so that the entire length of the conveyor table 3, an air flow from the top of the conveyor table 3 through the suction chamber 4 and the axial fan 5 can arise.

The printed sheets are removed by the feeder 2 in shingled form, i.e. the rear end of a printing sheet, seen in the direction of sheet travel, lies above the front end of the following printing sheet. The part of a printing sheet lying at the bottom is held by the suction belts 6 on the conveyor table 3 and transported in the direction of the printing press. There, each printing sheet is aligned in an alignment unit 9, after it has been released from the conveyor table 3, at its front and side edges and transferred to the printing press 1.

In Figure 2, the conveyor table 3 is shown from its top. The suction belts 6 are embedded in guide grooves 10 and have evenly distributed suction openings 14 which are effective over the entire length. Ventilation openings 11 are provided on the side of the guide grooves 10 in the conveying table 3 and are connected to the ambient air, as a result of which the negative pressure of the axial fan 5 cannot come into effect in their area. If so-called defective air occurs, which arises, for example, from suction belts 6 that are not smoothly lying on, relief of the printing sheet to be conveyed is to be achieved in the area of these ventilation openings 11. Furthermore, to protect the suction belts 6, a number of ventilation openings 12 can also be provided in the guide grooves 10 in the edge region of the suction belts 6. This ensures that the suction belts 6 are no longer sucked so strongly against their support on the bottom of the guide grooves 10. Then the ventilation openings 11 next to the suction belts 6 may no longer be required.

FIG. 3 shows a cross section through the conveyor table 3 in the area of one of the suction belts 6. The suction belt 6 lies in the guide groove 10 so that it protrudes about 0.2 mm above the surface of the conveyor table 3. The guide groove 10 is connected to the suction chamber 4 by means of suction openings 13, the suction openings 13 each corresponding to the suction openings 14. The conveyor table 3 is broken through by the ventilation openings 11 to the side of the guide groove 10. The ventilation openings 11 are combined on the underside of the conveyor table 3 within the suction chamber 4 with ventilation channels 15 and thus closed off from the suction chamber 4. These ventilation channels 15 are connected to the environment i.e. they are not pressurized. If suction is created by a suction belt 6 that does not terminate laterally, the negative pressure in the side region is compensated for by the ventilation openings 11. The effect is supported by the suction belt 6 protruding slightly above the table surface, as a result of which the connection of the guide groove 10 to the ventilation openings 11 is kept open. As an alternative or in addition, further ventilation openings 12 can also be present within the guide groove 10. These are then arranged below the unperforated lateral areas of the suction belts 6 and are also connected to the ventilation channels 15, so that there is no impairment of the function of the conveyor table 3.

By both measures, incorrect air, which arises on the one hand under the edge of the suction belt 6 but also through a wavy surface of the suction belt 6 and in both cases leads to the suction of the printed sheets on the conveyor table, is eliminated.

However, the problem of the uneven deformation of the suction belts 6 due to the operating stress has not yet been completely eliminated. As a further measure to compensate for problems with sheet conveyance by different deformations of the suction belts 6, the change in arrangement and / or shape of the suction openings 14 is therefore proposed. It is important not to provide the perforation continuously over the full width of the suction belts 6, but to provide a strip without perforation at least in the middle of the belt 16, so that the strength of the belt is increased in this area. The suction belt 6 is then divided into supporting areas at the edge and in the middle 16 of the belt and suction areas with the suction openings 14 symmetrically thereto. This avoids that the suction belt 6 is longer in this area and thus bulges after a long period of operation, or disproportionately stretches at all, so that the drive forces can only be imperfectly transmitted by the guide and drive shafts 8. In addition, instead of circular suction openings 14, elongated holes can also be provided, which ensure a continuous air passage or suction cross section when the suction openings 13 overflow in the conveying table 3. This avoids that, depending on the operating state, unequal suction surfaces per suction belt 6 are available. The elongated suction openings 14 are then arranged on both sides of the belt center 16 in two or more rows and offset from one another. There is a hole-free strip between the rows of holes, which ensures the tensile strength of each suction belt 6.

In the described combination of features with the arrangement of ventilation openings 11, 12, it could be advantageous to arrange suction channels under the belt guides instead of designing the entire conveyor table 3 as a suction box. Here, however, the storage volume of the suction space 4 is greatly reduced. Such an arrangement is conceivable as a special design for special applications, such as in small-format machines or for cardboard printing. To simplify this, the fact that the ventilation openings 11, 12 no longer have to be combined in ventilation channels, since they then directly in the surroundings flow.

The problem of the different suction cross-sections when transporting the printed sheets over the conveying table 3 plays a special role for cyclical speed changes in the drive of the suction belts 5. Such drive conditions are e.g. needed to brake the printed sheets before the front and side edge alignment.

In FIG. 2, four printed sheets A, B, C and D are shown in broken lines as a shingled sheet stream which is moved forwards over the conveying table 3 in accordance with the directional arrows. The first printed sheet A extends into the alignment area. In the area of the suction belts 6, the suction openings 13 are also shown in broken lines. The respective leading printing sheet A or B or C is only held on the suction belts 6 in the region of its front edge to the front edge of the next following printing sheet B or C or D. After the first printing sheet A has already partially run off the feed table 3 on its delivery side 17 facing the printing press 1, it is also only held in the relatively short area between the delivery side 17 and the following printing sheet B. The printed sheet B already covers part of the suction openings 18, 19 located on the discharge side 17 and thus reduces the holding forces available for the first printed sheet A. In order to maintain the holding forces at a sufficient level, for example for braking the printed sheet A using the suction tapes 6, the suction openings 18, 19 are enlarged compared to the normal suction openings 13. Depending on the force required, the cross-sectional shape can also be varied. A circular cross section is provided at the suction opening 18, which leads to a gain of 30% suction area. The suction opening 19 is designed as a semicircle with an attached rectangle, so that an area gain of 50% compared to the normal suction opening 13 is achieved here becomes. A further variation is possible by designing the rectangular area portion of the suction opening 19 as a trapezoid, so that there is an additional area gain in the direction of sheet travel. As a result, the holding forces between the suction belt 6 and the printed sheet decrease much more slowly than with suction openings of the same size, although the contact surface is reduced when the printed sheets run off. On the other hand, the printed sheets are held further up on the conveyor table 3 only with the force that is just required, which largely eliminates the risk of tension and uneven conveying. Incidentally, the suction openings 18, 19 are of course optionally used in reality and carried out identically for all suction belts 6.

With the means mentioned, tension and uneven propulsion can be kept away from the printed sheets. However, further measures may be necessary, especially for higher speeds. FIG. 4 shows a conveyor table 3 on which two suction spaces 20, 21 are provided. These are arranged one behind the other in the direction of sheet travel. An axial fan 22, 23 is arranged on each of the suction spaces 20, 21. Both can be controlled separately to influence the suction air. Suction belts 24 are guided around both suction spaces 20, 21 and guided over guide or drive shafts 28 and tensioning rollers 27. The necessary suction openings are again present in the conveyor table 3. With this arrangement, different holding forces can be achieved over the length of the conveyor table 3 by different levels of negative pressure. In addition, further suction belts 25 can be guided around the suction box 21 on the conveyor table 3 on the delivery side 26 facing the printing press 1. These are then to be guided via additional tensioning rollers 29 and guide shafts 30. This arrangement can look such that an additional suction belt 25 is arranged centrally between two suction belts 24. Of course, the necessary suction openings in the conveyor table 3 are also assigned to the suction belt 25. in the In the area of the suction chamber 21, higher holding forces can thus be achieved, since the holding surface is increased by 50% over the entire length of the suction chamber 21. The guidance of the printed sheets is therefore no longer so heavily dependent on the expansion ratios of the individual suction belts 24, 25. Of course, enlarged suction openings can also be provided here on the discharge side 26 of the conveyor table 3.

The problem of belt stretching and the resulting slippage in the belt drive can be further reduced with a little additional effort. FIG. 5 shows a section through a special suction belt. It is designed as a toothed belt 31 acting on both sides. Appropriately designed guide and drive shafts 28 are also required for a suction belt of this shape, for example as toothed shafts. In this case, no slip can occur between drive shaft 28 and toothed belt 31. The elongation of the toothed belt 31 as a result of the driving forces is retained, but cannot lead to relative movement and thus inaccuracies when transporting the printed sheets. To guide the air through the toothed belt 31, a deeper guide groove 35 is required than in the case of the flat suction belts 6, 24, 25, since the tooth gaps must be sealed as well as possible from the side. In each tooth base 32 between teeth 33 of the toothed belt 31, a suction opening 34 is provided which communicates with the suction openings 36 in the conveyor table 3. The negative pressure spreads through the suction openings 34 into the gaps of the toothed belt 31 and holds the printed sheet flat against the teeth 33 there. Here, however, relief measures against the spreading of the negative pressure via the conveyor table 3 are necessary. For this purpose, the ventilation openings 11 on the side of the suction belt guide in the surface of the conveyor table 3 can be used particularly advantageously. The negative pressure that is inevitably spreading due to the poorly sealed tooth gaps is thus reduced again in the shortest possible way underneath the printed sheet. Ventilation openings within the guide groove 35 could not be provided here, since otherwise a short circuit in the suction system would otherwise be caused. However, a higher negative pressure is required for the system with the toothed belt 31, since the passage cross-sections are not so large for the air extraction. This system should therefore be reserved for high-performance applications in which high accelerations and speeds are to be achieved.

Reference symbol list

1

Printing press

2nd

Investors

3rd

Promotion table

4th

Suction chamber

5

Axial fan

6

Suction belt

7

Idler pulley

8th

drive shaft

9

Alignment unit

10th

Guide groove

11

Ventilation opening

12

Ventilation opening

13

Suction opening

14

Suction opening

15

Ventilation duct

16

Band

17th

Delivery side

18th

Suction opening

19th

Suction opening

20th

Suction chamber

21

Suction chamber

22

Axial fan

23

Axial fan

24th

Suction belt

25th

Suction belt

26

Delivery side

27th

Idler pulley

28

Guide shaft, drive shaft

29

Idler pulley

31

Timing belt

32

Tooth base

33

tooth

34

Suction opening

35

Guide groove

36

Suction opening

A

Printed sheet

B

Printed sheet

C.

Printed sheet

D

Printed sheet

Claims (15)

Conveying table for guiding printed sheets to a printing press with at least one suction space and an axial fan attached to it, as well as around perforated suction belts running around it via suction openings in the conveying table,
characterized by
that openings (11, 12) are provided in the conveyor table (3) parallel to the suction belts (6, 24, 25, 31) and are connected to the environment separately from the suction chamber (4). Conveying table according to claim 1,
characterized by
that the openings are arranged in a single row and evenly distributed as ventilation openings (11, 12) over the entire conveyor table (3) along the suction belts (6, 24, 25, 31) and on the underside of the table within the suction space (4) with ventilation channels (15 ) are summarized. Conveying table according to claim 2,
characterized by
that ventilation openings (11, 12) are provided on the side and / or below the edges of the suction belts (6, 24, 25, 31). Conveying table according to claim 3,
characterized by
that the suction belts (6, 24, 25, 31) are guided in guide grooves (10, 35) which are slightly flatter than the thickness of the suction belts (6, 24, 25, 31). Conveying table according to claim 4,
characterized by
that the ventilation openings (12) are arranged in the guide grooves (10, 35) in the region of the non-perforated edges of the suction belts (6, 24, 25, 31). Conveying table according to claims 1 to 5,
characterized by
that the suction openings (13) are combined by large suction channels and the ventilation openings (11, 12) open directly outdoors. Conveying table according to claim 3,
characterized by
that the ventilation openings (11) are provided outside of guide grooves (35) and the edge of the suction belts and as suction belts toothed belts (31) with teeth (33) arranged on both sides and suction openings (34) arranged in the tooth base (32). Conveying table according to claim 1,
characterized by
that in the suction belts (6, 24, 25) suction openings (14) are distributed in such a way that at least in the belt center (16) and at the edges there is a comparatively wide hole-free space. Conveying table according to claim 8,
characterized by
that the suction openings (14) in the suction belts (6, 24, 25, 31) are designed as rows of elongated holes offset in the longitudinal direction. Conveying table according to one of claims 1 to 5, 7 and 8,
characterized by
that the suction openings (13) in the conveyor table (3) up to its discharge side (17, 26) facing the printing press (1) have a cross section which increases in the direction of the sheet travel. Conveying table according to claim 9,
characterized by
that on the discharge side (17, 26) the cross section of the last suction openings (13) with respect to the cross section of the guide groove (10) is maximum and can optionally also be carried out increasingly in the direction of sheet travel. Conveying table according to claim 10,
characterized by
that suction openings (18, 19) are provided on the discharge side (17, 26) with an intake cross section enlarged by at least 30% compared to the normal cross section of the suction openings (13), with a circle, a semicircle, a square or a semicircle with an attached cross-section Rectangle or trapezoid is used. Conveying table according to one of the preceding claims,
characterized by
that under the conveyor table (3) two suction spaces (20, 21) with axial fans (22, 23) are arranged one behind the other in the sheet travel direction and can be controlled separately, suction belts (24) around both suction spaces (20, 21) simultaneously and via suction openings to be provided accordingly be guided in the conveyor table (3). Conveying table according to claim 13,
characterized by
that at least one additional suction belt (25) is guided symmetrically to the suction belts (24) around the suction space (21) arranged on the discharge side (26) and via suction openings to be provided accordingly in the conveyor table (3). Conveying table according to one of claims 1 to 13,
characterized by
that only a single wide suction belt is provided.

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