EP0056532B1 - Method and means for diagonal adjustment in an offset-printing machine, and printing machine produced with said means - Google Patents

Description

The present invention relates to a "crooked" correction method in an offset printing machine; it also relates to the device used for this purpose, and to a printing machine comprising such a device.

In an offset printing machine, the plate or plate is fixed on a cylinder called plate cylinder, where it is wet and inked by contact with rollers themselves in contact with distribution rollers. The ink selectively deposited on the plate is distributed over an intermediate cylinder called the blanket cylinder, and from there is deposited on the sheet of paper which passes in contact with the blanket cylinder. Of course the axes of the blanket cylinder and the plate cylinder are normally strictly parallel. If printing takes place on only one side of the paper, the sheet is applied in contact with the blanket by a pressure counter-cylinder; very frequently for two-sided printing machines, another inking assembly with plate cylinder and blanket is disposed approximately symmetrically with respect to the first, and the sheet circulates between the two blanket cylinders, each providing back pressure for the other. The plate plate is fixed and tensioned by a usual device arranged according to a generator of the plate cylinder. In a usual manner also, the machines comprise a device for adjusting the circumferential and lateral register, allowing an angular and axial relative offset of the plate cylinder with respect to the general drive kinematic chain of the machine, so as to allow in particular the location colors on machines with several printing stations.

Whatever care is taken in making the plates, quite often a so-called "skew" defect occurs when the image on the plate is not formed strictly along the axis of the plate. It is possible to compensate for this defect during the positioning of the plate on the plate cylinder, by placing it slightly at an angle so that it is then wound slightly helically on the cylinder. But this adjustment is obviously not possible when running, while very often the defect in the skew is not detected until after the installation of the plate, when we check the first impressions.

A correction is sometimes made by acting on the plate cylinder to put it slightly at an angle to the blanket cylinder, so as to thus restore the correct position of the image formed on the plate relative to the blanket. This means of correcting the "cross" obviously makes it possible to act in operation, if care has been taken to mount at least one of the bearings of the plate cylinder on an eccentric housing. But the bearings of the plate cylinders generally comprising the mechanisms for adjusting the circumferential and lateral markings, already bulky mechanisms, so that it proves difficult and complex, and consequently expensive to add an additional device for biasing by independent movement of one of the bearings. In addition, the skew movement of the plate cylinder leads to an adjustment of the contact of the inking and wetting rollers, and to remedy this new drawback it would be necessary to introduce other devices, again bulky and expensive.

Furthermore, it can be easily established that if a "skew" defect results, for a point in the picture, by a linear offset a at one of the ends of the plate cylinder, for example in advance of its theoretical position, the transfer to the blanket so that we find on the printed sheet a linear offset has the same value. For correction, the linear offset of the end of the plate cylinder must also be a, and the sine of the angle of the angular offset will be a / L, L being the length of the cylinder table. The values of a and L result in imposing spherical bearings for the bearings of the cylinder in order to be able to absorb such angular offsets. In addition, an excessive angular offset may reduce the backlash of the drive sprockets, and lead to abnormal and premature wear of the latter.

The present invention provides a new solution for the correction on the fly of the consequences of a "skewed" defect in photographs.

The invention relates to a "crooked" correction method in a rotary offset printing machine comprising at least one assembly of a plate plate plate cylinder and a blanket cylinder in contact with the sheet to be printed, method intended to compensate a slight misalignment of the plate formed on the plate. According to the invention, action is taken by angularly displacing the axis of the blanket cylinder with respect to the axis of the plate cylinder, this displacement being effected substantially in a plane perpendicular to the plane containing the two parallel axes in their normal mean position.

The invention also relates to a device for implementing this correction method, applied to a machine where the journals of the blanket cylinders are carried by eccentric bearings associated with a device for controlling the rotation of these eccentric bearings, to separate or bring the blanket closer to the sheet to be printed.

According to the invention the eccentric bearings of the blanket cylinders are themselves each carried by an eccentric sleeve engaged in a bore of the frame; for each blanket cylinder, the eccentric sleeve relative to one of the pins is kept fixed in the frame, while the other is associated with a controlled rotation mechanism, the relative positions of the centers of the eccentric elements of the sleeve being determined so that in the normal range of movement, the movement of the axis of the blanket cylinder can remain comparable to a movement in a plane perpendicular to the plane defined by the parallel axes of the blanket cylinder and of the plate cylinder in the normal normal position.

The invention will be better understood by referring to a particular embodiment given by way of example and represented by the accompanying drawings.

Figure 1 gives the detail of the mounting of the two blanket cylinders in the frames of a double-sided printing machine comprising the "skew" correction device according to the invention.

Figures 2 and 3 show the actuators of the correction device. Figure 2 is a partial front view of the frame; FIG. 3 is a view along III-III of FIG. 2.

In Figure 1, where to simplify the drawing we have omitted various usual details such as the lubrication devices of the different bearings, we will see in particular the two frames 1 and 2, respectively on the drive side and the pipe side, which support the two blanket cylinders 3 and 4 each associated with the corresponding plate cylinders 5 and 6. The blanket and double-sided plate cylinders are driven here as in French patent application FR - A - 2,458,395 by the same applicant. Thus the lower blanket cylinder 4 is directly driven from the plate cylinder 6 by the pair of pinions 8-9, while the upper blanket cylinder 3 is directly driven from the plate cylinder 5 by the pinions 10-11 , without the meshing of the pinions 9 and 11. The transmission of the movement of the plate cylinder 6 to the plate cylinder 5 is obtained by the intermediate pinions 13 and 14 simply centered on the trunnions of the blanket cylinders 3 and 4, without positive link in rotation.

The blanket cylinder 4 is carried by the bearings 16 and 17, each engaged in an eccentric housing 18 and 19. Similarly, the blanket support bearings 3 are held in the eccentric housings 20 and 21. This mounting on the eccentric housing constitutes a usual arrangement on such machines, and is used to be able to pressurize the blanket cylinders for example when the machine stops. For this, a control device (not shown) simultaneously rotates the two housings of each of the pins to produce a movement of separation or of parallel approaching of the cylinders with respect to one another. The device can also be used to adjust the pressure of the blanket cylinders against each other according to the characteristics of the printed sheet.

According to the present invention each of the eccentric housings 18, 19, 20 and 21 of the blanket cylinder bearings is itself included in another eccentric sleeve respectively 24, 25, 26 and 27, each engaged in a bore of the frames 1 or 2. On the side of the drive mechanisms, the sockets 24 and 26 are locked in rotation in the frame 1 by screws between leather and flesh 29 and 30. On the pipe side, on the contrary, the eccentric sockets 25 and 27 can be rotated by a device more visible in Figures 2 and 3. There is shown in these two figures that the device for the cylinder 4, but of course, the other blanket cylinder 3 is provided with a control device identical in all respects.

A part 32 in the form of an annular sector is fixed by screws 33 to the external flange 34 of the sleeve 25. At one end the part 32 has a countersink which forms a yoke with the flange 34, and a threaded nut 36 is held captive in the yoke while remaining freely articulated on pins engaged in corresponding bores of the part 32 and the flange 34. The threaded end 37 of a control rod 38 is engaged in the nut 36; the rod 38, which can rotate freely in the bore of a support 39 fixed to the frame, is blocked in axial movement by two rings 40 which respectively come into abutment on one or the other face of the support 39. We see that by rotating the rod 38, by means of a key engaged on its tip 41, it causes the displacement of the nut 36 on the threaded rod 37, which causes the rotation of the sleeve 25-34 relative to the frame . A spring 44, supported on an extension 45 of the part 32 and on a stop 46 secured to the frame, allows a catch up of all the games of the device.

The relative position of the centers of the eccentric elements of the sleeve is determined so that in the normal range of movement the movement of the cylinder axis can be assimilated to a movement in a plane perpendicular to the plane defined by the axes of the blanket cylinder and the plate cylinder in the normal position.

Thus, the angular displacement of the blanket cylinder resulting from the rotation of the sleeve 25 is such that the distances between cylinders are preserved, so that the pressure adjustment of the plate cylinder on the blanket or of the blanket on the sheet are not affected. In addition, the plate cylinder having remained stationary, all the setting of wetting and inking is fully preserved.

We can also establish that, taking the example cited above of a flaw in the cliché resulting in a linear offset a at the end of the plate cylinder, it suffices now, when acting on the blanket cylinder at instead of acting on the plate cylinder, a linear offset from the end by a value of a / 2 to bring the print back to its correct place on the sheet. This is very important because for the usual values of the defect a and of the length of the cylinder tables, the angular offset of correction being no more than the half of what would have been necessary by acting on the plate cylinder, we can generally be satisfied with normal bearings for the bearings of the blanket cylinders. It will also be noted that the harmful consequences of such an angular offset on the backlash are also halved.

Of course, the invention is not strictly limited to the embodiment which has been described by way of example, but it also covers the embodiments which would differ from it only in details, in variant embodiments or in the use of equivalent means. In particular, the invention applies in the same way whether it is a double-sided or single-sided offset printing machine, the devices used being identical for each blanket cylinder in the case of a machine both sides.

Claims (3)

1. A process for correcting known as "skew", in an offset rotary printing machine, comprising at least one plate cylinder unit (5, 6) supporting a printing plate and a blanket cylinder (3, 4) in contact with the sheet to be printed, a process intended to compensate a slight fault in alignment of the printing form made on the plate, characterised by performing an angular movement of the axis of the blanket cylinder (3, 4) relative to the axis of the plate cylinder (5, 6), this movement being carried out substantially in a plane perpendicular to the plane containing both parallel axes in their normal position.

2. A device for carrying out the process according to Claim 1, applied to a machine where the journals of the blanket cylinder (3, 4) are carried by eccentric bearings (18, 19, 20, 21) associated with a device for controlling the rotation of the eccentric bearings for separating or closing up the blanket in relation to the sheet to be printed, characterised by the fact that the eccentric bearings (18, 19, 20, 21) of the blanket cylinders are themselves each carried by an eccentric socket (24, 25, 26, 27) engaged in a bore in the frame (1, 2), and by the fact that, for each blanket cylinder (3, 4), the eccentric socket (24, 26) relative to one of the journals is held fixed in the frame (1) whilst the other (25, 27) is associated with a mechanism (32, 36, 38, 39) for producing a controlled rotation, the relative positions of the centres of the eccentric components of the socket being determined so that in the normal range of movement, the motion of the axis of the cylinder can remain comparable to a movement in a plane perpendicular to the plane defined by the parallel axes of the blanket cylinder and of the plate cylinder in a normal mean position.

3. An offset rotary printing machine com- .prising at least one plate cylinder unit (5, 6) supporting a printing plate and a blanket cylinder (3, 4) in contact with the sheet to be printed, characterised by the fact that each blanket cylinder is equipped with a device for angular shifting according to Claim 2.

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