EP0778128B1 - Drive for several transfer cylinders of a printing machine - Google Patents

Description

The invention relates to a device for driving several Transfer cylinder of a digital printing machine.

In conventional offset presses, they are Transfer cylinders, such as plate and blanket cylinders, over Gears linked together to synchronize together to be driven. The absolute forced synchronization of the Transfer cylinder through gears is required so their relative phase position even after any number of revolutions remains exactly the same.

In addition, you have on both sides of the plate and Rubber cylinders provided so-called bearer rings, hardened and ground steel rings, the outside diameter of which is usually equal to the diameter of the pitch circle of the Gear of the corresponding cylinder. The bearer rings roll together with the cylinders under a preload against each other, which makes the machine run smoothly Drive protects and the life of the pressure plate extended.

The invention is based, for Transfer cylinder of a digital printing press to create a particularly simple drive.

This object is achieved according to the invention by the Claim 1 specified device solved. Beneficial Embodiments of the invention are in the subclaims specified.

A digital press, for example, works so that a Print image applied to a first transfer cylinder becomes a hard surface for printing reasons has, from this to a second transfer cylinder is transferred from a jacket made of an elastic Has material, and from the second transfer cylinder is transferred to a substrate, the elastic Material for an even color transfer to one Substrate such as B. can nestle paper. This corresponds to the first transfer cylinder the plate cylinder one Offset printing machine and corresponds to the second Transfer cylinder the rubber cylinder one Offset printing machine.

According to the invention, any Gear elements between the transfer cylinders of the digital printing machine and the Transfer cylinders are only on bearer rings coupled to each other, usually at the ends of the Transfer cylinders are arranged. One of Transfer cylinder is powered by a printing press engine driven and takes the other transfer cylinder using the bearer rings. The driven one Transfer cylinder is preferably the one that the Transfer ink to the substrate because of the multiple Torque requirement on this transfer cylinder.

The invention takes advantage of the fact that in a digital Printing machine on an absolute synchronization between the Transfer cylinders can be dispensed with. One is enough relative synchronization, such that the phase shift along the transfer path of the ink due to the at least not inevitable slip of the bearer rings is larger than the desired print resolution. Because with one digital printing machine no printing plate with the structure of the printed image is required, but every machine cycle a complete print image is produced, it has none Influence the print result if the minor ones Add up phase shifts over time. This also applies in the event that the transfer cylinder is not only one printing unit, but several printing units on the are driven according to the invention.

A prerequisite for such a relative synchronization is however, that the preload between the bearer rings two transfer cylinders rolling against each other large is enough that the deadweight effect through the Bearings friction and not due to friction between the Transfer cylinders comes about. Leave the bearer rings namely with a precisely defined diameter establish, while the settlement relationships to the Transfer cylinders are usually complicated especially when one of the transfer cylinders is on Cylinder with a jacket made of an elastic material, e.g. B. rubber.

A rubber blanket jams in front of one during operation Transfer point at which it is e.g. B. against another Transfer cylinder is pressed. This enlarges the effective scope of the rubber blanket and its Circumferential speed by about 2 to 3 percent. In case that Transfer cylinders, one of which is a rubber cylinder, are driven according to the invention via bearer rings, can, however, by suitable choice of the diameter ratio the bearer rings ensure that the Circumferential speeds of the transfer cylinders approximately are the same, so that as little as possible at the transfer point Slip occurs.

Note also that the coefficient of static friction of rubber on steel about five times larger than that on steel Steel is. In the event that one of the transfer cylinders Rubber cylinder is, must therefore in an inventive Drive be ensured that the contact pressure between the bearer rings at least about five times as large as that Force is with which the transfer cylinder against each other are pressed, usually much larger to Safety reserves for changing operating conditions too create. In addition, the bearings of the transfer cylinders be set up to absorb these forces.

On the other hand, none according to the invention Gear elements between the individual transmission cylinders required so that the drive much easier than at conventional printing machines built and essential is more maintenance free. The bearer rings make you extremely uniform, by no infeed between any gear elements affected the run of the Transfer cylinder.

The invention is not only for systems with two Transfer cylinders suitable, as described above, but also for a common drive of three or more Transfer cylinders. For example, from three cascaded transmission cylinders one Printing unit of the middle are driven during the the other two can be taken away via bearer rings. Even the transfer cylinders in a row arranged printing units can with each other by bearer rings be coupled, with only one of the transfer cylinders is driven. Even with a series connection The slip can be caused by several bearer ring couplings make the bearer rings small enough that the accuracy of the Synchronization is within the tolerable range.

Further features and advantages of the invention result from the following description of several exemplary embodiments and from the drawing to which reference is made.

Fig. 1

eine teilweise schematische Seitenansicht eines digitalen Druckwerks mit zwei Übertragungszylindern;

Fig. 2

eine Schnittansicht längs einer Linie II - II des Druckwerks von Fig. 1;
und

Fig. 3

eine teilweise schematische Seitenansicht einer digitalen Druckmaschine mit über Schmitzringe gekoppelten Übertragungszylindern mehrerer Druckwerke.

In it show:

Fig. 1

a partially schematic side view of a digital printing unit with two transfer cylinders;

Fig. 2

a sectional view taken along a line II - II of the printing unit of Fig. 1;
and

Fig. 3

a partially schematic side view of a digital printing machine with transfer rings coupled via bearer cylinders of several printing units.

The digital printing unit shown in FIGS. 1 and 2 contains one first transfer cylinder 1 and a second Transfer cylinder 2 arranged parallel to each other are and touch each other on the circumference. The Transfer cylinders 1, 2 are rotatable on not shown Side walls of a printing press stored. At the extent of first transfer cylinder 1 are a write head 3 and a Inking unit 4 arranged, each over the entire Extend printing width. The second transfer cylinder 2 has a drive shaft 5 which is connected to a motor 6 connected is. The motor 6 is in the figures as on the Axis of the second transfer cylinder 2 lying shown, but can of course also on any be located elsewhere in the printing press and over Power transmission elements, e.g. B. a gear with Drive shaft 5 may be connected. The second Transfer cylinder 2 also has one not separately drawn in jacket made of an elastic material like Rubber on. Adjacent to the second transfer cylinder 2 runs a conveyor belt 7 which is only partially drawn in, rest on the substrates 8 to be printed.

As shown in Fig. 2, there are at each Transfer cylinder 1, 2 laterally two axial Bearings 9, 10 flanged from case-hardened steel, which are each essentially the same diameter as the have corresponding transfer cylinders 1, 2. The exact diameter of the transfer cylinder 1, 2 and Bearings 9, 10 are in accordance with the respective Material properties chosen so that between the Bearings 9 and 10 have a defined contact pressure is maintained while the transfer cylinders 1, 2 pressed against each other with a much lower force as will be explained in more detail later.

The transfer cylinders 1, 2 are in Fig. 1 and 2 with same diameters, but can also have different diameters. For example, the Transfer cylinder 1 and the bearer rings 9 larger Diameter than the transfer cylinder 2 and the Bearings 10 have. The exact diameter ratio The bearer rings 9, 10 are on the special Settlement conditions on the transfer cylinders 1, 2 adjusted as will be described.

In operation, the conveyor belt 7 conveys the substrates 8 rectilinear in the direction of the arrow, the Substrates 8 along a straight contact point against the second transfer cylinder 2 are pressed. The Motor 6 rotates the second transfer cylinder 2 so that its peripheral speed is equal to the conveying speed of the conveyor belt 7. The second transfer cylinder 2 takes the first transfer cylinder 1 over the Bearings 9, 10 with, so that the transfer cylinder 1, 2nd against each other in the indicated arrow directions unroll. The write head 3 describes the past rotating first transfer cylinder 1 with a latent Image that is developed on the inking unit 4. That developed Print image is on the second transfer cylinder 2nd transferred from it then transferred to a substrate 8 becomes. If necessary, you can contact the Transfer cylinders 1 or 2 cleaning devices for leftover, non-transferred color may be provided.

The bearer rings 9, 10 bring about a very precise Synchronization of the rotation of the transfer cylinders 1, 2. On the way from the print head 3 to the transfer point on the second transfer cylinder 2 is a slip of the first Transfer cylinder 1 compared to the second Transfer cylinder 2 of only a few micrometers or less accessible, which is easily tolerable.

The prerequisite for this, however, is that the Stiction of friction between the bearer rings 9, 10 larger than that between the transfer cylinders 1, 2 is. The bearer rings 9, 10 then roll - except for one small slip - almost ideally on each other. That changes also not that between the surfaces of the Transfer cylinder 1, 2 an inevitable in practice Relative movement occurs. The sliding friction resistance at Such a relative movement is always smaller than the static friction resistance. In addition, such Relative movements as small as possible from the start kept by the diameter ratio of the Bearings 9, 10 equal to the circumferential ratio of the Transfer cylinder 1, 2 taking into account the elongation of the rubber jacket of the second transfer cylinder 2 in Operation is selected. This elongation is caused by a Deformation of the rubber jacket of the second Transfer cylinder 2 in the area of the transfer point from first transfer cylinder 1.

It is now an estimate of the contact forces between the Bearings 9, 10 made that are required the first transfer cylinder 1 largely in sync with that second transfer cylinder 2 is taken.

It is assumed that the two transfer cylinders 1, 2 are pressed against each other with a force F _Z , which is required for the transfer process. There is a material-dependent coefficient of static friction µ _Z between the transfer cylinders 1, 2. The corresponding static friction resistance is R _Z = µ _Z * F _Z. The maximum of these static friction resistance R _Z must by a static friction resistance R _S between the bearer rings 9, are overcome 10, the _S equal μ to the product of a contact force F _S between the bearing rings 9, 10 and a corresponding material-dependent friction coefficient. Therefore: R S = µ S * F S ≥ µ Z. * F Z. = R Z.

In the event that one of the transfer cylinders is made of steel and the other has a jacket made of rubber, while the bearer rings are made of steel, µ _{Z is} approximately five times as large as µ _S. Therefore, the contact pressure F _S between the bearer rings must be at least five times the contact pressure F _Z between the transfer cylinders, so that the friction between the bearer rings predominates and - apart from the slight slip - there is no relative movement between them.

In particular in a transfer cylinder with a rubber jacket, the frictional resistance can, however, be subject to fluctuations in time during operation, e.g. B. because of uneven material properties or due to the material jam mentioned in front of the transfer point. For this reason, a much higher contact pressure F _S between the bearer rings should be selected in practice than would be arithmetically calculated, for example ten or twenty times the force F _Z with which the transfer cylinders are pressed against each other.

Cylinder bearings that can absorb these forces can be realize with reasonable effort, especially since the Ink transfer techniques used in digital presses come into consideration, often only relatively small Demand contact forces. There are also digital Printing press transmission techniques that practically no ins Require weight falling contact forces and with which the invention can thus be implemented particularly easily.

In the case of an alternative not shown in the drawing, that the first transfer cylinder 1 and not the second Transfer cylinder 2 driven by a motor would be in an estimate of the contact pressure, the Torque requirement at the transfer point to the substrate 8 to consider. The same applies to cases in which not just a transfer cylinder, but more Transfer cylinders are to be driven via bearer rings. The Transfer cylinders can drive be connected in series, or it can be from the Bearings of a transfer cylinder several more Transmission cylinders are driven, if necessary under Interposition of further bearer rings to cover distances to bridge between the transfer cylinders. On such a case is shown in FIG. 3.

The printing machine shown in Fig. 3 contains three Transfer cylinder 11, 12, 13, one behind the other a conveyor belt 14 are arranged, the substrates 15 in Arrow direction conveyed. A motor 16 is with the middle one Transfer cylinder 12 connected, possibly via a not shown gearbox, and turns this in Arrow direction. The transfer cylinders 11, 12 and 13 have as well as in the embodiment of FIGS. 1 and 2 side bearer rings on, with the interposition of two other bearers 17 in a row against each other be pressed.

When the motor 16 rotates, the bearer rings rotate the transfer cylinder 11, 12, 13 and the others Bearings 17 in the directions of the arrows shown, and the transfer cylinders 11, 12, 13 rotate accordingly on print heads 18 and not shown here Ink units over to print images on the substrates 15 transfer.

The principle shown in Fig. 3 is in many ways changeable and expandable. For one, instead of shown three printing units z. B. four or five printing units are driven. Furthermore, each of the printing units cannot have only one transfer cylinder 11, 12 and 13, respectively shown in Fig. 3, but each a system with two Transfer cylinders, as shown in Figs. 1 and 2, or still be more transfer cylinders. Even with such a chain of transfer cylinders connected with bearer rings the total slip remains between the bearer rings tolerable as it is still in the Order of magnitude of micrometers and therefore not noticeable on the raster accuracy of the printed images affects.

REFERENCE SIGN LIST

1

Transfer cylinder

2nd

Transfer cylinder

3rd

Printhead

4th

Inking unit

6

engine

7

Conveyor belt

8th

Substrate

9

Bearer ring

10th

Bearer ring

11

Transfer cylinder

12th

Transfer cylinder

13

Transfer cylinder

14

Conveyor belt

15

Substrate

16

engine

17th

Bearer ring

18th

Printhead

Claims (6)

1. Device for driving a plurality of transfer cylinders in a digital printing machine,
   characterized in
   that only one transfer cylinder (2; 12) of the plurality of transfer cylinders (1, 2; 11, 12, 13) is connected to a motor (6; 16), and that the plurality of transfer cylinders is connected to each other via bearer rings (9, 10; 17) rolling off against each other under a pre-load.
2. Device according to Claim 1,
   characterized in
   that a bearer ring (9, 10) is axially fastened to each axial end of each transfer cylinder (1, 2) of said plurality of transfer cylinders (1, 2), that two respective transfer cylinders and the corresponding bearer rings roll off against each other, and that the pre-load (F_S) between the bearer rings of two transfer cylinders rolling off against each other is essentially higher than a contact force (F_Z) existing between said transfer cylinders multiplied by the ratio of the static friction coefficient (µ_Z) of the contacting surfaces of the transfer cylinders to the static friction coefficient (µ_S) of the contacting surfaces of the bearer rings.
3. Device according to Claim 2,
   characterized in
   that the ratio of the diameters of the bearer rings (9, 10) of two transfer cylinders (1, 2) rolling off against each other approximates the ratio of the circumferences of the transfer cylinders being effective when in operation.
4. Device according to Claim 2 or Claim 3,
   characterized in
   that one transfer cylinder (2) of two transfer cylinders (1, 2) rolling off against each other features an outer cylindrical surface made of an elastic material for transferring printing ink onto a substratum (8).
5. Device according to Claim 4,
   characterized in
   that the motor (6) is connected to the transfer cylinder (2) featuring an outer cylindrical surface made of an elastic material.
6. Device according to anyone of the preceding claims,
   characterized in
   that transfer cylinder (11, 12, 13) of several printing units of the printing machine are connected to each other via bearer rings (17), with only one transfer cylinder (12) of said transfer cylinders being connected to the motor (6).

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