HK1215009B - Printing unit for variable-format offset printing presses - Google Patents

Description

Printing unit for variable format offset press

Technical Field

The present invention relates to a printing unit for a so-called offset printing press, and more particularly, to a printing unit for a variable format offset printing press.

Background

As is known, a variable format offset printing apparatus comprises three rotating cylinders, the axes of which are oriented horizontally. The first cylinder, commonly referred to as the plate cylinder, carries a printing plate around the plate cylinder, which is designed to transfer ink received by a number of ink rollers across the image area. The second cylinder, commonly referred to as the intermediate or transfer cylinder, is covered with an elastic material, such as natural rubber, and is in contact with the plate cylinder. A third cylinder (often referred to as an impression cylinder) is in contact with the intermediate cylinder. A web of paper or other material to be printed is fed between the intermediate cylinder and the impression cylinder. In use, the intermediate cylinder receives ink from the plate cylinder through an image area consisting of the printed image and transfers ink on the web fed between the intermediate cylinder and the impression cylinder.

A pair of cylinders consisting of a plate cylinder and an intermediate cylinder having the same diameter is called a printing format. To change the printing length, it is necessary to change the diameters of the plate cylinder and the intermediate cylinder and thus the distance between the axes of these three cylinders. The variable format offset printing apparatus is therefore provided, in a known way, with mechanical means for adjusting the distance between the cylinders, which allow the distance between the cylinders to be suitably varied in the event of a variation in the diameter of the cylinders, in particular in the event of a variation in the diameter of the plate cylinder and of the intermediate cylinder (which determines the printing format and affects the printing length), so as to ensure, on the one hand, the contact between the intermediate cylinder and the plate cylinder and, on the other hand, the contact between the intermediate cylinder and the impression cylinder. In addition, in order to ensure that the printing process is carried out correctly, a given contact pressure must be maintained between the cylinders of the printing units in contact with each other, that is to say between the intermediate cylinder and the plate cylinder and between the intermediate cylinder and the impression cylinder.

Document EP- ｃA-2388140 discloses ｃA variable offset printing apparatus and proposes to support the plate cylinder in ｃA fixed position for this purpose, to support each of the axially opposite ends of the intermediate cylinder (or impression cylinder) at the end of ｃA respective tilting arm, which is hinged at the opposite end, so as to be tiltable about ｃA fixed tilting axis, and to support each of the axially opposite ends of the impression cylinder (or intermediate cylinder) along ｃA respective linear guide. In this way, when the axis of the plate cylinder is fixed, the axis of the intermediate cylinder (or impression cylinder) can move along a circular path, the centre of which lies on the fixed tilt axis of the tilt arm articulation, while the axis of the impression cylinder (or intermediate cylinder) moves along a linear path defined by the linear guide. The tilting movement of the tilting arm of the support member carrying the intermediate cylinder (or impression cylinder) and the horizontal movement of the carriage(s) carrying the support member of the impression cylinder (or intermediate cylinder) are driven by respective actuators. In the event of a change in printing format, and thus in the event of a resulting movement of the plate cylinder and the intermediate cylinder, the tilting arm and the support member must be moved appropriately by respective actuating means in order to bring the intermediate cylinder into contact with the plate cylinder at the desired contact pressure and the impression cylinder into contact with the intermediate cylinder at the desired contact pressure. A drawback of this known solution is that any variation of the position of the axis of the intermediate cylinder, for example due to the need to adjust the pressure against the plate cylinder, inevitably causes a contact pressure between the intermediate cylinder and the impression cylinder, thus forcing the operator to intervene by suitably controlling the actuating means associated with the impression cylinder to restore the correct pressure between the intermediate cylinder and the impression cylinder.

Disclosure of Invention

It is therefore an object of the present invention to provide a variable format offset printing apparatus which is not affected by the prior art discussed above and which therefore allows maintaining the correct contact pressure between the intermediate cylinder and the impression cylinder, even if the position of the intermediate cylinder is changed.

This and other objects of the invention are achieved according to the invention by means of a variable format offset printing apparatus. The printing unit includes: a support structure; a plate cylinder supported by the support structure for rotation about a first axis; an intermediate drum supported for rotation about a second axis, the second axis being parallel to the first axis; an impression cylinder supported for rotation about a third axis, the third axis being parallel to the first and second axes, wherein the intermediate cylinder or the impression cylinder is supported at axially opposite ends of the intermediate cylinder or the impression cylinder by respective support members carried by respective tilting rods supported by the support structure so as to be tilted about a fixed tilting axis parallel to the first, second and third axes, whereby the second or third axis, respectively, is movable along a circular path with a fixed centre on the tilting axis, wherein the impression cylinder or the intermediate cylinder is supported at axially opposite ends of the impression cylinder or the intermediate cylinder, respectively, by respective support members, said support members being slidable along respective linear guides carried by said support structure, whereby said third axis or said second axis is respectively movable along a linear path, wherein each of said support members of said intermediate cylinder is connected to a respective support member of said impression cylinder by respective linear actuation means comprising a first element and a second element movable with respect to each other along a relative movement direction, said first element being articulated to a respective support member of said intermediate cylinder and said second element being articulated to a respective support member of said impression cylinder.

Briefly, the present invention provides a variable format offset printing apparatus, wherein each of the two support members of the intermediate cylinder is connected to the respective support member of the impression cylinder by a respective linear actuator device comprising a first element and a second element movable relative to each other in a direction of relative movement, wherein the first element of each linear actuator device is hinged to the respective support member of the intermediate cylinder, and wherein the second member of each linear actuator device is hinged to the respective support member of the impression cylinder. These devices allow to vary the distance between the axis of the intermediate cylinder and the impression cylinder, by means of linear actuation means coupled on the one hand to the axis of the intermediate cylinder and on the other hand to the axis of the impression cylinder, thus making it possible to adjust the contact pressure between these cylinders. Once a given distance, and therefore a given contact pressure, between the intermediate cylinder and the impression cylinder has been set, this distance (and therefore the contact pressure) remains unchanged, without requiring readjustment by the operator, even if the position of the axis of the intermediate cylinder and/or of the axis of the impression cylinder changes.

Drawings

Further characteristics and advantages of the invention will become clearer from the following description, given purely by way of non-limiting example, with reference to the attached drawings, in which:

fig. 1 shows a perspective view of the cylinders (plate cylinder, intermediate cylinder and impression cylinder) of a printing unit for a variable offset printing press, and their respective adjustment devices, according to an embodiment of the invention;

FIG. 2 shows a perspective view of one of the two sides of the printing unit of FIG. 1 on an enlarged scale;

FIG. 3 shows a side view of the printing unit of FIG. 1;

FIG. 4 shows a cross-sectional view of the printing unit of FIG. 1 through section line IV-IV;

FIGS. 5A and 5B show side views of the printing unit of FIG. 1 in operating conditions for a large print format and in operating conditions for a small print format;

fig. 6 shows a side view of a cylinder of a variable offset printing press device and its respective adjusting means according to another embodiment of the invention.

Detailed Description

Referring to the drawings, reference numeral 10 generally designates a printing unit (hereinafter simply referred to as a printing unit) to be used in a variable format offset printing machine, and shows only components important to the present invention.

Printing unit 10 first includes three rotating cylinders, plate cylinder 12, intermediate cylinder 14, and impression cylinder 16, with their axes designated x1, x2, and x3, respectively, and oriented horizontally. In the proposed embodiment, the plate cylinder 12 and the intermediate cylinder 14, which are configured as sleeves (i.e. hollow cylinders) and fitted on the intermediate support shafts 12a and 14a, respectively, form a printing format and can therefore be replaced with cylinders of different diameters. In this way, when a printing format is to be changed, a plate cylinder having a desired diameter and a new intermediate cylinder can be mounted on the respective intermediate support shafts by simply removing the plate cylinder and the intermediate cylinder from those shafts. The plate cylinder and the intermediate cylinder may be of different types, for example with the intermediate support shaft removed and the end support hubs provided.

Plate cylinder 12 (with respective central support shafts, if any) is supported for rotation about plate cylinder axis x1 by support members (not shown) mounted on a pair of side vertical walls or shoulders 18 of support structure 20 of printing unit 10. The support members of plate cylinder 12 are preferably made as eccentric support members to allow the cylinder to be removed from intermediate cylinder 14 if necessary.

Intermediate cylinder 14 (with respective intermediate support shafts 14a, if any) and impression cylinder 16 are supported at axially opposite ends by respective support members, the positions of which are adjustable by respective adjustment means, further elaborating to be able to vary the distance between axis x1 of plate cylinder 12 and axis x2 of intermediate cylinder 14, and between axis x2 of intermediate cylinder 14 and axis x3 of impression cylinder 16, when plate cylinder 12 and intermediate cylinder 14 have to be replaced by cylinders of different diameters to change the printing format. The support members of the intermediate cylinder 14 and the impression cylinder 16 and their adjustment devices on both sides of the printing unit 10 are substantially identical to each other. The following description therefore refers to only one of the two sides of the printing unit, and the description relating to this side will of course equally apply to the other side of the printing unit.

More specifically, according to the invention, the intermediate cylinder 14 and the impression cylinder 16 are supported in such a way that: the axis of one of these two cylinders (axis x2 of intermediate cylinder 14 in the embodiment shown in fig. 1 to 5B, and axis x3 of impression cylinder 16 in the embodiment shown in fig. 6) moves along a circular path with a fixed center (the term "fixed" here in relation to support structure 20 of printing unit 10), while the axis of the other cylinder (axis x3 of impression cylinder 16 in the embodiment shown in fig. 1 to 5B, and axis x2 of intermediate cylinder 14 in the embodiment shown in fig. 6) moves along a linear path.

With reference to the embodiment shown in fig. 1 to 5B, the intermediate drum is supported on a tilting bar 22, which is hinged to the support structure 20 so as to be able to tilt in either direction about a fixed tilting axis x4, as indicated by the double arrow R in fig. 1 and 3. The axis x2 of the intermediate cylinder 14 can thus move along a circular path centred on the tilt axis x 4. Such movement allows the distance between the axes of plate cylinder 12 and intermediate cylinder 14 to be adjusted.

According to the embodiment shown in fig. 1 to 5B, the tilting lever 22 is a bell-hammer lever in which a first arm 22a and a second arm 22B form a given angle, for example about 90 degrees, and which is hinged in the region where the two arms 22a and 22B are joined together. According to this embodiment, the intermediate cylinder 14 is supported at the free end of the arm 22a of the tilting lever 22, while the end of one linear actuator (not shown), for example an electrically, hydraulically or pneumatically operated linear actuator causing the tilting lever 22 to tilt about the tilting axis x4, is designed to be hinged at the free end of the other arm 22 b.

According to the embodiment shown in fig. 1 to 5B, the free end of the arm 22a of the tilting lever 22 is forked and has a pair of coaxial through holes 24 (fig. 2 and 4), in which a support sleeve 26 is mounted coaxially. Respective end support shafts 28 and 28' extend coaxially inside the support sleeve 26 on both sides of the printing unit 10, through which the intermediate support shaft 14a is supported by the sleeve 26 at the opposite end. More specifically, in the illustrated embodiment, the end support shaft 28 (the axis on the left-hand side from the perspective of viewing fig. 4) is integrally formed with the intermediate support shaft 14a, and has a smaller diameter than, or is at least drivingly connected for rotation with, the intermediate support shaft, while the end support shaft 28' (the axis on the right-hand side from the perspective of viewing fig. 4) is made as a separate component from the intermediate support shaft 14a and engages with an axis cavity provided in the latter. The end support shafts 28 and 28' and the support sleeve 26 are all arranged coaxially with the intermediate support shaft 14a, so that their axes are coincident with the axis x2 of the intermediate drum 14. In this way, when the tilting lever 22 is tilted about the tilting axis x4, the axis x2 of the intermediate drum 14 moves along a circular path centered on the tilting axis x 4.

The intermediate drum 14 is rotated by a motor (not shown) about its axis x 2. According to one embodiment, the motor is fixed to the free end of the arm 22a of the tilting lever 22 and is torsionally coupled to one of the two end support shafts, that is to say to the end support shaft 28, which is integrally formed by the intermediate support shaft 14a or at least drivingly connected thereto for rotation.

Referring again to the embodiment illustrated in fig. 1-5B, the impression cylinder 16 is supported at opposite ends of the impression cylinder 16 by a pair of support members 32 secured to a carriage 34. Carriage 34 is movably mounted in a linear direction (indicated by double arrow T in fig. 1 and 3) by a pair of linear guides 36 secured to support structure 20. The axis x3 of the impression cylinder 16 is therefore movable along a rectilinear path, which in the embodiment shown is inclined at a given angle to the vertical, in particular less than 45 degrees. Although the two support members 32 in the illustrated embodiment are secured to a common element (i.e., the carriage 34), they are completely independent of each other.

In order to allow adjustment of the distance between the axis of the intermediate cylinder 14 and the axis of the impression cylinder 16, the printing unit 10 comprises, on each of its two sides, a respective linear actuator 38 comprising a first element 40 and a second element 42 movable with respect to each other along a relative movement direction y, wherein the first element (preferably, though not necessarily, about the axis x2 of the cylinder) is hinged to a respective support member of the intermediate cylinder 14; the second element 42 is hinged (preferably, although not necessarily, about the axis x3 of the cylinder) to the opposite support member of the impression cylinder 16. Thus, the linear actuation device 38 is coupled on the one hand to the intermediate cylinder 14 and therefore to the axis x2 of the intermediate cylinder, and on the other hand to the impression cylinder 16 and therefore to the axis x3 of the impression cylinder. Thus, the linear actuation device 38 allows to vary the distance between the axes x2 and x3 and thus to adjust the distance between the intermediate cylinder 14 and the impression cylinder 16. In addition, once a given distance has been set, and thus a given contact pressure between intermediate cylinder 14 and impression cylinder 16 has been established, linear actuator 38 ensures that this distance (and thus the contact pressure) remains unchanged even in the event of a change in the position of axis x2 of intermediate cylinder 14 and/or axis x3 of impression cylinder 16, without readjustment by the operator.

The linear actuator 38 may be of various types, for example in the embodiment shown in fig. 1-5B, the linear actuator 38 is a screw and nut arrangement driven by a motor 44. The first element 40 is in this case present in a screw supported by the body 46 for rotation about its own axis (coinciding with the direction y). The axis of the screw 40 extends perpendicularly to the axis x2 of the intermediate cylinder 14 and the axis x3 of the impression cylinder 16, and intersects both axes. The body 46 is hinged to the free end of the arm 22a of the tilting lever 22 so as to rotate with respect to the tilting lever about the axis x2 of the intermediate drum 14. In the embodiment shown, the main body 46 is received between two prongs of the forked free end of the arm 22a of the tilting lever 22 and has a through hole through which the support sleeve 26 extends, whereby the main body 46 can rotate relative to the support sleeve 26 about the axis x 2. As for the second element 42, this latter in this case consists in a nut hinged to the support member 32 so as to rotate with respect to the latter about the axis x3 of the impression cylinder 16. The arrangement of the screw and nut may also be reversed, wherein the screw 40 may be associated with the impression cylinder 16 and the nut associated with the intermediate cylinder 14. In the illustrated embodiment, the motor 44 is carried by a body 46, and the axis of the body is parallel to the axis of the screw 40, the motor controlling the rotation of the screw through a transmission generally indicated at 48.

Fig. 5A and 5B show the printing unit 10 in two different operating conditions, that is, an operating condition of a large-size printing format and an operating condition of a small-size printing format, respectively. A reduction in the distance between the axis of the plate cylinder 12 and the axis of the intermediate cylinder 14 when changing from the large to the small printing format can be obtained by causing the tilting bar 22 to tilt about its axis x4 (clockwise in the view of a person viewing the figures), whilst a reduction in the distance between the axis of the intermediate cylinder 14 and the axis of the impression cylinder 16 when changing from the large to the small printing format can be obtained by causing the carriage 34 (and thus the support member 32) to slide upwards along the linear guide 36 by the linear actuator 38. Once the desired distance between the axis of the intermediate cylinder 14 and the axis of the impression cylinder, and therefore the desired contact pressure between these cylinders, has been set, that is to say once the relative position of the two elements 40 and 42 of each of the two linear actuators 38 has been set, the contact pressure between these cylinders remains constant until the relative position of the two elements 40 and 42 of each of the two linear actuators 38 has been changed.

Finally, fig. 6 (in which parts and elements identical or corresponding to those of the previous figures are given the same reference numerals) shows a variant embodiment of the printing unit 10, which differs from the one described above with reference to fig. 1 to 5B, essentially in contrast to the adjustment means associated with the intermediate cylinder 14 and the impression cylinder 16. In this case, in fact, the intermediate cylinder 14 is supported (by the support member 32 which can slide along the linear guide 36) in such a way that its axis x2 can move along a linear path, while the impression cylinder 16 is supported (by the inclined bar 22) in such a way that its axis x3 can move along a circular path. In addition, in the embodiment of fig. 6, other motors or actuators are provided to control the tilting movement of the support member 32 along the linear guide 36, while the tilting lever 22 will tilt freely about the respective tilting axis x 4.

Naturally, the principle of the invention remaining the same, the construction details and embodiments may vary widely from those described and illustrated purely by way of non-limiting example.

Claims (7)

1. Printing unit (10) for a variable format offset printing press, comprising

A support structure (20) for supporting the support structure,

a plate cylinder (12, 12a) supported by the support structure (20) for rotation about a first axis (x1),

an intermediate roller (14, 14a) supported for rotation about a second axis (x2) parallel to the first axis (x1),

an impression cylinder (16) supported for rotation about a third axis (x3) parallel to the first axis (x1) and the second axis (x2),

wherein the intermediate cylinder (14, 14a) or the impression cylinder (16) is supported at axially opposite ends thereof by respective support members (26, 28, 28 '), the respective support members (26, 28, 28') each being carried by a respective tilting rod (22) supported by the support structure (20) so as to be tilted about a fixed tilting axis (x4) parallel to the first (x1), second (x2) and third (x3) axes, whereby the second (x2) or third (x3) axis, respectively, is movable along a circular path with a fixed centre on the tilting axis (x4),

wherein the impression cylinder (16) or the intermediate cylinder (14, 14a) is respectively supported at axially opposite ends thereof by respective support members (32) slidable along respective linear guides (36) carried by the support structure (20), whereby the third axis (x3) or the second axis (x2) is respectively movable along a linear path,

characterized in that each support member (26, 28, 28 '; 32) of the intermediate cylinder (14, 14a) is connected to a respective support member (32; 26, 28, 28') of the impression cylinder (16) by a respective linear actuation device (38) comprising a first element (40) and a second element (42) movable with respect to each other along a relative movement direction (y), the first element (40) being hinged to the respective support member (26, 28, 28 '; 32) of the intermediate cylinder (14, 14a) about the second axis (x2), and the second element (42) being hinged to the respective support member (32; 26, 28, 28') of the impression cylinder (16) about the third axis (x 3).

2. Printing unit according to claim 1, wherein the relative movement direction (y) of the first element (40) and the second element (42) of each linear actuation device (38) extends perpendicularly to the second axis (x2) and the third axis (x3), and intersects them.

3. Printing unit according to claim 1 or 2, wherein each linear actuation device (38) is a screw and nut device.

4. A printing unit according to claim 3, wherein the screw and the nut of said screw and nut means constitute a first element (40) and a second element (42), respectively, of each linear actuation means (38).

5. Printing unit according to claim 4, wherein each inclined bar (22) comprises a fork-shaped free end having a pair of coaxial through holes (24) in which end support shafts (28) connected for rotation with the intermediate cylinders (14, 14a) or with the impression cylinder (16) are rotatably supported.

6. Printing unit according to claim 5, wherein the screw (40) of each linear actuator (38) is supported for rotation about its own axis by a body (46), said body (46) being received between two of said free ends of the fork of the respective tilting lever (22), and having a through hole through which the respective end support shaft (28) extends.

7. Printing unit according to claim 6, wherein each linear actuation device (38) further comprises motor means (44) carried by the main body (46) and adapted to generate a rotary motion, and motion transmission means (48) adapted to transmit the rotary motion generated by the motor means (44) to the screw (40).