EP0778128A1 - Drive for several transfer cylinders of a printing machine - Google Patents

Abstract

The drive is for a digital printing press. Only one (2) of its several transfer cylinder (1, 2) is connected to a motor (6). The transfer cylinders are connected to each other by lashing rings (9, 10), which roll back against each other under initial tension The initial tension is set to provide sufficient synchronisation between the transfer cylinders. The cylinders may each have a lashing ring at each axial end. The initial tension of two cylinders rolling against each other is considerably greater than the pressing force between them multiplied by the grip friction coefficient.

Description

The invention relates to a device for driving a plurality of transfer cylinders of a digital printing press.

In conventional offset printing machines, the transfer cylinders, such as plate and blanket cylinders, are connected to one another via gearwheels in order to be driven synchronously together. The absolute forced synchronization of the transfer cylinders by gears is necessary so that their relative phase position remains exactly the same even after any number of revolutions.

In addition, so-called bearer rings have been provided on both sides of the plate and rubber cylinder, hardened and ground rings made of steel, the outer diameter of which is generally equal to the diameter of the pitch circle of the gear wheel of the corresponding cylinder. The bearer rings roll together with the cylinders under pre-tension, which makes the machine run smoothly, protects the drive and extends the service life of the pressure plate.

The invention has for its object to provide a particularly simple drive for the transfer cylinder of a digital printing press.

This object is achieved according to the invention by the device specified in claim 1. Advantageous embodiments of the invention are specified in the subclaims.

A digital printing machine works, for example, in such a way that a print image is applied to a first transfer cylinder which has a hard surface for printing reasons has, is transferred from this to a second transfer cylinder having a jacket made of an elastic material, and is transferred from the second transfer cylinder to a substrate, wherein the elastic material for a uniform color transfer to a substrate such. B. can nestle paper. The first transfer cylinder corresponds to the plate cylinder of an offset printing press and the second transfer cylinder corresponds to the blanket cylinder of an offset printing press.

According to the invention, any transmission elements between the transfer cylinders of the digital printing machine are now dispensed with and the transfer cylinders are only coupled to one another via bearer rings, which are normally arranged at the ends of the transfer cylinders. One of the transfer cylinders is driven by a motor of the printing press and takes the other transfer cylinder with it by means of the bearer rings. The driven transfer cylinder is preferably the one that transfers the ink to the substrate because of the multiple torque requirements on this transfer cylinder.

The invention takes advantage of the fact that an absolute synchronization between the transfer cylinders can be dispensed with in a digital printing press. A relative synchronization is sufficient, such that the phase shift along the transfer path of the printing ink is at least not greater than the desired print resolution due to the inevitable slippage of the bearer rings. Since a printing plate with the structure of the printed image is not required in a digital printing machine, but a complete printed image is produced in each machine cycle, it has no influence on the printing result if the slight phase shifts add up over time. This also applies in the event that the transfer cylinders are driven not only one printing unit, but several printing units in the manner according to the invention.

A prerequisite for such a relative synchronization is, however, that the pretension between the bearer rings of two transfer cylinders rolling against each other is large enough that the entrainment effect is caused by the bearer ring friction and not by friction between the transfer cylinders. The bearer rings can namely be made with a precisely defined diameter, while the processing conditions on the transfer cylinders are generally complicated, especially when one of the transfer cylinders is a cylinder with a jacket made of an elastic material, e.g. B. rubber.

A rubber blanket builds up in operation in front of a transfer point where it is e.g. B. is pressed against another transfer cylinder. This increases the effective size of the rubber blanket and its peripheral speed by approximately 2 to 3 percent. In the event that transfer cylinders, one of which is a rubber cylinder, are driven according to the invention via bearer rings, it can, however, be ensured by a suitable choice of the diameter ratio of the bearer rings that the peripheral speeds of the transfer cylinders are approximately 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 is approximately five times that of steel on steel. In the event that one of the transfer cylinders is a rubber cylinder, it must therefore be ensured in a drive according to the invention that the contact pressure between the bearer rings is at least about five times as large as that The force with which the transfer cylinders are pressed against each other is usually much greater in order to create safety reserves for changing operating conditions. In addition, the bearings of the transfer cylinders must be set up to absorb these forces.

On the other hand, according to the invention, no gear elements are required between the individual transfer cylinders, so that the drive is much simpler than in conventional printing presses and is considerably less maintenance. The bearer rings result in an extremely uniform running of the transfer cylinders, which is not influenced by any running-in impacts between any gear elements.

The invention is not only suitable for systems with two transfer cylinders, as described above, but also for a common drive of three or more transfer cylinders. For example, three series-connected transfer cylinders of a printing unit can drive the middle one, while the other two are carried away by bearer rings. The transfer cylinders of a plurality of printing units arranged one behind the other can also be coupled to one another by bearer rings, only one of the transfer cylinders being driven. Even if several bearer ring couplings are connected in series, the slip at the bearer rings can be made 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 a first transfer cylinder 1 and a second transfer cylinder 2, which are arranged parallel to one another and touch one another on the circumference. The transfer cylinders 1, 2 are rotatably mounted on side walls of a printing press, not shown. A write head 3 and an inking unit 4 are arranged on the circumference of the first transfer cylinder 1 and each extend over the entire printing width. The second transfer cylinder 2 has a drive shaft 5 which is connected to a motor 6. The motor 6 is shown in the figures as lying on the axis of the second transfer cylinder 2, but can of course also be arranged at any other point in the printing press and via power transmission elements, for. B. a gear, be connected to the drive shaft 5. The second transfer cylinder 2 also has a jacket (not shown separately) made of an elastic material such as rubber. Adjacent to the second transfer cylinder 2 is a conveyor belt 7, only partially drawn, on which substrates 8 to be printed lie.

As shown in FIG. 2, two axial bearer rings 9, 10 made of case-hardened steel are flanged to the side of each transfer cylinder 1, 2, each having essentially the same diameter as the corresponding transfer cylinder 1, 2. The exact diameters of the transfer cylinders 1, 2 and the bearer rings 9, 10 are chosen in accordance with the respective material properties so that a defined contact pressure is maintained between the bearer rings 9 and 10, while the transfer cylinders 1, 2 are pressed against each other with a much lower force as will be explained in more detail later.

The transfer cylinders 1, 2 are shown in FIGS. 1 and 2 with the same diameters, but can also have different diameters. For example, the transfer cylinder 1 and the bearer rings 9 can have larger diameters than the transfer cylinder 2 and the bearer rings 10. The exact diameter ratio of the bearer rings 9, 10 is adapted to the special processing conditions on the transfer cylinders 1, 2, as will be described.

In operation, the conveyor belt 7 conveys the substrates 8 in a straight line in the direction of the arrow, the substrates 8 being pressed against the second transfer cylinder 2 along a straight contact point. 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 along with the bearer rings 9, 10, so that the transfer cylinders 1, 2 roll against each other in the directions of the arrows shown. The write head 3 describes the first transfer cylinder 1 rotating past it with a latent one Image that is developed on the inking unit 4. The developed print image is transferred to the second transfer cylinder 2, from which it is then transferred to a substrate 8. If necessary, 1 or 2 cleaning devices for leftover, non-transferred ink can be provided on the transfer cylinders.

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 write head 3 to the transfer point on the second transfer cylinder 2, a slip of the first transfer cylinder 1 with respect to the second transfer cylinder 2 of only a few micrometers or less can be achieved which is easily tolerable.

The prerequisite for this, however, is that the static friction resistance between the bearer rings 9, 10 is greater than that between the transfer cylinders 1, 2. The bearer rings 9, 10 then roll - except for a very small slip - almost ideally on top of each other. This does not change the fact that an inevitable relative movement occurs between the surfaces of the transfer cylinders 1, 2. The sliding friction resistance with such a relative movement is always smaller than the static friction resistance. In addition, such relative movements are kept as small as possible from the outset by selecting the diameter ratio of the bearer rings 9, 10 to be equal to the circumferential ratio of the transfer cylinders 1, 2, taking into account the elongation of the rubber jacket of the second transfer cylinder 2 during operation. This elongation results from a deformation of the rubber jacket of the second transfer cylinder 2 in the area of the transfer point from the first transfer cylinder 1.

The contact forces between the bearer rings 9, 10 are now estimated, which are necessary so that the first transfer cylinder 1 is carried largely synchronously by the second transfer cylinder 2.

. Im Maximum muß dieser Haftreibungswiderstand R_Z durch einen Haftreibungswiderstand R_S zwischen den Schmitzringen 9, 10 überwunden werden, der gleich dem Produkt aus einer Anpreßkraft F_S zwischen den Schmitzringen 9, 10 und einem entsprechenden materialabhängigen Haftreibungskoeffizienten µ_S ist. Somit gilt: $${\text{R}}_{\text{S}}{\text{= µ}}_{\text{S}}{\text{* F}}_{\text{S}}{\text{≥ µ}}_{\text{Z}}{\text{* F}}_{\text{Z}}{\text{= R}}_{\text{Z}}$$

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. Between the transfer cylinders 1, 2 there is a material-dependent coefficient of static friction µ _Z. The corresponding static friction resistance is ${\text{R}}_{\text{Z.}}{\text{= µ}}_{\text{Z.}}{\text{* F}}_{\text{Z.}}$

. 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: $${\text{R}}_{\text{S}}{\text{= µ}}_{\text{S}}{\text{* F}}_{\text{S}}{\text{≥ µ}}_{\text{Z.}}{\text{* F}}_{\text{Z.}}{\text{= R}}_{\text{Z.}}$$

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.

Especially in a transfer cylinder with a rubber jacket, the frictional resistance can, however, be subject to temporal fluctuations in 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, in practice a much higher one To choose contact force F _S between the bearer rings than would be 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 realized with reasonable effort, especially since the ink transfer technologies that come into consideration in digital printing presses often only require relatively low contact forces. In addition, there are transmission technologies in digital printing presses which require practically no significant contact forces and in 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 are driven by a motor, the torque requirements at the transfer point on the substrate 8 would also have to be taken into account in an estimation of the contact forces. The same applies to cases in which not only one transfer cylinder but also other transfer cylinders are to be driven via bearer rings. The transfer cylinders can be connected in series in terms of drive, or several other transfer cylinders can be driven by the bearer rings of a transfer cylinder, possibly with the addition of further bearer rings, in order to bridge distances between the transfer cylinders. Such a case is shown in FIG. 3.

The printing machine shown in Fig. 3 contains three transfer cylinders 11, 12, 13, which are arranged one behind the other on a conveyor belt 14 which conveys substrates 15 in the direction of the arrow. A motor 16 is connected to the central transfer cylinder 12, possibly via a gear (not shown), and turns it into Arrow direction. As in the exemplary embodiment of FIGS. 1 and 2, the transfer cylinders 11, 12 and 13 have side bearer rings which are pressed against one another in a row with the interposition of two further bearer rings 17.

When the motor 16 rotates, the bearer rings of the transfer cylinders 11, 12, 13 and the other bearer rings 17 rotate in the direction of the arrows shown, and the transfer cylinders 11, 12, 13 accordingly rotate past write heads 18 and inking units not shown here, to transfer printed images to the substrates 15.

The principle shown in FIG. 3 can be modified and expanded in a variety of ways. For one, instead of the three printing units shown, for. B. four or five printing units are driven. Furthermore, each of the printing units may not only have one transfer cylinder 11, 12 or 13, as shown in FIG. 3, but may also be a system with two transfer cylinders, as shown in FIGS. 1 and 2, or even more transfer cylinders. Even with such a chain of transfer cylinders, which are connected to one another via bearer rings, the total slip between the bearer rings remains tolerable, since it is still of the order of micrometers and therefore has no noticeable effect on the raster accuracy of the printed images.

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)

Device for driving several transfer cylinders of a digital printing machine,
characterized by
that only one (2; 12) of the plurality of transmission cylinders (1, 2; 11, 12, 13) is connected to a motor (6; 16) and that the plurality of transmission cylinders are connected to one another by bearer rings (9, 10; 17), that roll against each other under a preload. Device according to claim 1,
characterized by
that a bearer ring (9, 10) is axially attached to each axial end of each of the plurality of transfer cylinders (1, 2), that two transfer cylinders and the associated bearer rings roll against each other, and that the preload (F _S ) between the bearer rings of two transfer cylinders rolling against each other is significantly greater than a contact pressure (F _Z ) between these transfer cylinders multiplied by the ratio of the coefficient of static friction (µ _Z ) of the contacting surfaces of the transfer cylinder to the coefficient of static friction (µ _S ) of the contacting surfaces of the bearer rings. Device according to claim 2,
characterized by
that the ratio of the diameters of the bearer rings (9, 10) of two transfer cylinders (1, 2) rolling against one another is approximated to the ratio of the effective sizes of the transfer cylinders during operation to one another. Device according to claim 2 or claim 3,
characterized by
that one (2) of two mutually rolling transfer cylinders (1, 2) has a jacket made of an elastic material for transferring printing ink to a substrate (8). Device according to claim 4,
characterized by
that the motor (6) is connected to the transfer cylinder (2), which has a jacket made of an elastic material. Device according to one of the preceding claims,
characterized by
that transfer cylinders (11, 12, 13) of a plurality of printing units of the printing press are connected to one another by bearer rings (17), only one of the transfer cylinders (12) being connected to the motor (16).

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