WO2012119704A1

WO2012119704A1 - Process and device for machining a cylinder, in particular an impression or embossing cylinder

Info

Publication number: WO2012119704A1
Application number: PCT/EP2012/000740
Authority: WO
Inventors: Jörg POHÉ
Original assignee: Hell Gravure Systems Gmbh & Co. Kg
Priority date: 2011-03-09
Filing date: 2012-02-21
Publication date: 2012-09-13
Also published as: EP2683553A1; EP2683553B1

Abstract

The invention relates to a process and a device (10) for machining a cylinder (12) with at least one laser beam (16), wherein recesses (22, 50) are made in a surface (20) of the cylinder using the laser beam (16) in order to produce a structure on the cylinder surface (20), wherein individual structure elements (50, 56, 62) of the structure produced are measured on at least part of the cylinder surface (20), wherein at least one geometrical measured value for each measured structure element (50, 56, 62) is compared with a corresponding geometrical desired value for the same structure element (50, 56, 62) in order to determine a difference between the measured value and the desired value, and wherein a correction is made on the basis of the differences determined. In order to make it possible to also correct irregularly occurring differences, it is proposed that, in the correction, the laser beam (16) is used to rework those structure elements (50, 56, 62) in the case of which the difference between the measured value and the desired value exceeds a predetermined extent in one direction.

Description

description

Method and device for processing a cylinder, in particular a printing or embossing cylinder.

When printing cylinders or embossing cylinders are processed by direct engraving by means of a laser beam in order to produce on the cylinder surface an uneven surface structure required for printing or embossing, at the point of impact of the laser beam by its thermal energy, a part of the material of the cylinder adjoining the cylinder surface evaporates. This makes it possible to excavate crater-shaped depressions in the cylinder surface, which can be extended to groove-shaped depressions, when the laser beam along a track on the

Cylinder surface is moved. Larger depressions can be excavated by moving the laser beam across multiple cylinder surfaces along multiple parallel tracks. For this purpose, the cylinder is rotated at a high speed while the laser beam is directed onto the cylinder from a laser processing member, which is also referred to as a laser processing head, in the axial direction of the cylinder, so that the laser beam travels along adjacent helical tracks the cylinder surface impinges.

In gravure engraving of gravure cylinders, where the material adjacent to the cylinder surface is copper, wells are engraved into the cylinder surface, the lateral dimensions depending on the printing density between 20 and 240 pm, while their depth is up to about 35 pm. In order to improve the image sharpness of the image to be printed and to reproduce halftone progressions better, the applicant has already proposed in EP 1 568 490 B1 to build up the wells from a predetermined number of individually engraved pixels. For engraving these pixels, the laser beam is moved along adjacent tracks having a width of about 20 to 30 pm over the cylinder surface and thereby modulating its intensity with a modulator located in the beam path so as to increase the depth and the length of the tracks control that theoretically results in the desired well shape and the desired well volume.

However, especially in the laser engraving of copper or other metals on the surface of gravure cylinders, the problem arises that the metal does not always evaporate completely, but partly only melts, with the resulting

Melt is ejected by the volume expansion of the evaporating metal in the form of small metal droplets from the wells. Although this melt ejection is sucked off, but usually succeeds not completely, so that a part of the liquid metal together with other impurities, such as

Smoke from metal oxides, as overburden within a just excavated cup, precipitated on the edge of this cup or in a previously excavated adjacent wells or deposits. While the overburden in the interior of wells results in geometrical cup parameters, in particular the well depth but also cross-sectional dimensions within the wells, not meeting the desired target value, the overburden on the edge of the wells results in an uneven surface during printing Cylinder surface rests and excess ink can not be stripped clean.

However, similar problems can also occur when engraving metallic embossing cylinders or printing cylinders for flexographic printing.

From US Pat. No. 5,652,804 a method and a device for processing gravure cylinders are already known, where wells are dug in the surface of the gravure cylinder with an engraving stylus or with a laser beam. In order to determine defective cells, an image processing device is provided there which takes and evaluates an image of the previously engraved wells, in order to calculate its depth from the outline of the wells. The calculated well depth is then compared with a nominal depth of well depth derived from the image or engraving data. In the event of a deviation, for example if the well depth is shallower than it should be, correction information may be fed back to an engraving stylus or laser head controller for subsequent engraving Dump wells with a corrected well depth. However, this means that, at least in the case of the wells engraved immediately before the correction, the well depth does not correspond to the desired value, so that these wells may not later deliver the desired print image. Moreover, the method known from US Pat. No. 5,652,804 works only if the error is an error that occurs identically in the surveyed wells and in the subsequently engraved wells, such as one caused by wear of an engraving stylus Error. However, the method does not work if the errors in different wells are different, such as errors caused by melt ejection from adjacent wells, since the amount or distribution thereof depends, inter alia, on the number, depth and / or dimensions of the well cups depends on the distance to the neighborsäpfchen. Proceeding from this, the object of the invention is to improve known methods and devices in such a way that it is also possible to correct irregular deviations.

This object is achieved in the method according to the invention in that in the correction those structural elements are reworked with the laser beam, in which the deviation of the measured value from the desired value in one direction exceeds a predetermined level. By contrast, the device according to the invention is characterized in that the control device controls the carriage and the laser in order to rework structural elements, in which the measured value deviates from the nominal value, with the laser beam, if the deviation exceeds a predetermined amount.

The invention is based on the idea that the correction of each structural element to be corrected is based on the extent to which the measured value of this structural element deviates from the nominal value of this structural element. In other words, a measurement is used to determine quantitatively in which structural elements the measured value deviates from the nominal value and how large the deviation is. Subsequently, the degree of deviation is compared with a predetermined threshold value, to then correct only those structural elements by post-processing with the laser beam, in which the deviation exceeds the predetermined level or the predetermined threshold. The term post-processing also makes it clear that processing of this part with the laser beam has already taken place before the measurement of a part of the cylinder. Since in the course of a post-processing with the laser beam as well as during the processing with the laser beam only a material removal is possible, but no material can be added, can be corrected by the post only deviations in which the deviation of the measured value of the target value too much of material equivalent. Structural elements of the structure in which no deviation or only a small deviation of the measured value from the desired value lying below the predetermined dimension or threshold value are not corrected.

In the following, when the term measured value is used, this need not be a directly measured value, but may also be a value derived from a directly measured value. However, the measured value is a quantitative measured value which allows a statement about the degree of deviation from the nominal value. The term cylinder or cylinder surface also includes a material spanned on the cylinder or its surface.

A preferred embodiment of the method according to the invention provides that not only individual structural elements of the structure produced are measured, as in the prior art, but all structural elements in which, as a result of deposition of overburden, such as melt ejection or the like, deviations of the measured value from the nominal value can occur. which show too much material. The measured value of all the measured structural elements is compared with the corresponding nominal value of each structural element and then all the structural elements in which the deviation exceeds the predetermined level or the predetermined threshold value are reworked.

In the post-processing of a structural element material is removed with the laser beam, wherein the removal is controlled by a corresponding modulation of the laser beam so that the degree of erosion about the extent of the Ab- deviation of the measured value from the setpoint. Due to the individual

Adjustment of the material removal to the deviation will usually correspond to the measured value after finishing pretty much the setpoint, especially since it will come to a deposition of melt discharge or other overburden much less often than during the first processing, since the mutual distances of the reworked wells are larger and less material is removed in total, whereby a better evaporation of the material is ensured by the laser beam.

In order to keep the total time required for machining the cylinder as low as possible, another preferred embodiment of the invention provides that the machining of the cylinder with the laser beam and the measurement of the structures produced thereby take place simultaneously. If the processing and the measurement can be carried out at the same speed, are used for emitting the laser beam laser processing element and a for

Measuring the structures or the individual structural elements serving sensor expedient mounted on a common carriage or carriage, which can be during the rotation of the cylinder in the axial direction along this move, so that a constant distance between the laser processing member and the sensor is maintained. If a processing and measurement at the same speed is not possible, the serving for measuring sensor is preferably arranged separately from the laser processing organ on a separate carriage or carriage, which has its own drive and the carriage or carriage with the laser processing organ expediently follows in a variable axial distance ,

To ensure that the shape of the structural elements is no longer changed after their measurement by a subsequent deposition of overburden, the measurement of the structures is advantageously carried out in the circumferential direction and / or in the axial direction

Direction of the cylinder at a sufficient distance from the machining with the laser beam. Basically, a distance of only a few tracks in the axial direction of the cylinder or a distance of about 10 degrees in the circumferential direction of the cylinder is sufficient, but the distance is preferably selected to be slightly larger. For example, the sensor may be positioned on the opposite side of the cylinder from the laser processing member, ie circumferentially at an angular distance of about 180 degrees from the laser processing member, because at this point, the influence of melt ejection from the laser processing is practical

is excluded.

Since the structure produced on the cylinder surface includes not only the wells excavated with the laser beam but also areas between or adjacent to the wells in which deposition of melt discharge or other overburden may also occur during processing with the laser beam, preferably not only Measured structural elements within the wells and post-processed with the laser beam when the deviation of the measured value from the desired value exceeds the predetermined level, but also at least a portion of the previously un-laser-processed areas of the cylinder surface, said areas at least adjacent to the edges of the wells surfaces and in particular the surfaces of narrow webs between adjacent recesses, on which there is also often a deposit of overburden. Such webs are mainly webs between adjacent wells of gravure cylinders, which serve as a support for a squeegee during printing and therefore should not have any overburden caused by overburden.

The geometric measured value determined during the measurement is advantageously the radial distance between the unprocessed cylinder surface and the surface of the structural elements, the information relating radially to the cylinder. In this way, overburden deposited within the depressions can be detected, since there the measured distance from the unprocessed cylinder surface is smaller than the nominal value, as well as overburden deposited on the edges of depressions, since there the measured distance from the untreated cylinder surface becomes greater is the setpoint that is zero in these ranges. The quantitative determination of the aforementioned radial distance between the unprocessed cylinder surface and the surface of the structural elements is preferably carried out by a non-contact measuring method, for example by

Laser scanning or by a confocal or chromatic-confocal

Measuring method with which the structural elements can be detected with an accuracy of less than 3 μm, and preferably less than 1 μm. In the

Laser scanning, for example, the distance between a sensor and the surface of the structural elements is measured and after a subtraction of the

Distance between the sensor and the unprocessed cylinder surface compared with the setpoint of the structural elements, i. for example, the desired depth of a pixel within a well.

By the quantitative measurement of the structural elements and the following

Post-processing with the laser beam can not only be deposited by

Eliminate melt discharge or other overburden, but also all other deviations, in which at individual or possibly also at all

Structural elements an excess of material is present. Such deviations may be caused, for example, by a decrease in the intensity of the laser beam during processing due to the evaporation of material, as the laser beam may be partially scattered by the vaporized material and thus weakened in intensity.

In order to ensure after a post-processing of structural elements to ensure that the setpoint is maintained in the post-processed structural elements, it may be advantageous to re-measure the post-processing structural elements to rework if necessary again, if the deviation of the determined during the re-measurement Measured value from the setpoint value still exceeds the specified value. Even a multiple measurement and post-processing is conceivable depending on the quality requirement.

In the following the invention with reference to a shown in the drawing

Embodiment explained in more detail. Show it: 1 is a perspective view of an engraving machine,

Fig. 2 is a schematic cross-sectional view of the engraving machine;

3 shows a top view of a groove-shaped depression engraved in the cylinder surface;

Fig. 4 is a cross-sectional view of the recess;

Fig. 5 is a schematic top view of a plurality of wells engraved in the surface of the gravure cylinder;

Fig. 6 is an enlarged top view of some in the surface of the

Gravure cylinder engraved wells before post-processing with the

Laser beam;

7 is a top view of the cups engraved in the surface of the gravure cylinder after post-processing with the laser beam;

Fig. 8 is an enlarged sectional view taken along a part of the cylinder surface by two wells.

9 is an enlarged sectional view corresponding to FIG. 8 after a

Post-processing with the laser beam;

Fig. 10 is a schematic cross-sectional view of parts of a modified

Engraving machine.

The engraving machine 10 shown schematically in the drawing is used for

Example for engraving gravure cylinders 12, which can be clamped individually in the engraving machine 10 and rotated by a rotary drive (not shown) at high rotational speed about its longitudinal central axis 14. The engraving of a rotogravure cylinder clamped in the machine 10 and rotated Linders 12 takes place with the aid of a laser beam 16, which is directed by a laser processing member 18 on the surface 20 of the gravure cylinder 12 to excavate in the cylinder surface 20 at the desired locations depressions in the form of wells 22, which later serve to receive ink.

The engraving machine 10 comprises, in addition to the rotary drive, two holders 24 for clamping the gravure cylinder 12, an engraving carriage 26 which can be moved by an engraving carriage drive (not shown) in the axial direction of the impression cylinder 12 by means of a spindle 28 and the laser processing member 18 carries, as well as a control panel 30 which is movable on guides 32 in the axial direction along the cylinder 12.

As shown in Fig. 2, the laser processing member 18 is connected by an optical fiber 32 with a fiber laser 34, which together with his

Pump source 36 and a heat sink 38 for cooling the pump source 36 is located in a stationary lower part 40 of the engraving machine 10, which further includes a cooling system 39 for cooling the heat sink 38, a machine control unit 42 for controlling the rotary drive and the engraving car drive and a laser control unit 44. The laser beam generated by the fiber laser 34 is fed through the optical fiber 32 in the gas-tight closed tubular laser processing device 18, inter alia, a controlled by the laser control unit 44 acousto-optic modulator (not shown) for deflection and intensity modulation of the laser beam and optical elements (not illustrated) for focusing the laser beam in a processing spot 46 on the cylinder surface 20 comprises. Such an engraving machine 10 is described in detail in the applicant's WO 00/13839.

Unlike the engraving machine 10 from WO 00/13839, in the case of the engraving machine 10 in FIG. 1, a measuring head 48 is still mounted on the engraving carriage 26. In the measuring head 48, a non-contact laser path sensor or laser distance meter (not shown) is mounted, with which the distance between the sensor and a sensor opposite point on the cylinder surface 20 can be measured with an accuracy of about 1 μηι. In operation of the engraving machine 10, when the laser beam 16 from the laser processing member 18 impinges on the surface 20 of the gravure cylinder 12 while the gravure cylinder 12 is rotated about its longitudinal center axis 14 relative to the laser processing member 18, a portion of the cylinder surface 20 becomes in gravure cylinders 12, usually made of copper adjacent to the cylinder surface 20 vaporized. In this case, along the path of movement of the processing spot 46 on the surface 20, a groove-shaped recess 50 is formed, which has a generally V-shaped cross-section, as best shown in Fig. 5.

As can be seen from FIG. 5, the depression 50 has oblique lateral boundary walls 52 which, however, do not have a smooth surface, but like the regions of the cylinder surface 20 adjoining the upper edges 54 of the boundary walls 52 are very uneven. These bumps consist to a large extent of overburden 56, which has deposited along the edges 54 of the recess 50 on the cylinder surface 20 and within the recess 50 on the boundary walls 52. The deposition of the spoil 56 is mainly caused by the fact that the cylinder material is not completely evaporated along the path of movement of the processing spot 46, but only partially melted. Due to the volumetric expansion of the evaporating material, a portion of the melt is ejected from the well 50 in the form of small droplets and settles along their edges 54 on the cylinder surface 20 where the droplets cool and cake. Another part of the molten material is either not even ejected from the recess 50 or comes after the ejection back into the recess 50, where the overburden 56 settles or precipitates mainly on the boundary walls 52. The deposited overburden 56 may contain other contaminants, such as combustion products or the like, in addition to the melt discharge.

Although the engraving machine 10 has a suction device (not shown) in order to suck off the melt ejection before it can settle on the cylinder surface 20, however, this succeeds only incompletely. As best shown in Fig. 5, in the surface 20 of the gravure cylinder 12 engraved wells 22 have a generally diamond-shaped outline, depending on the print density of a master copy lateral dimensions between 20 and 100 pm, while their depth is up to about 35 pm , In engraving machines 10 with a fiber laser 34, the laser beam 16 emerging from the laser processing element 18 and focused on the cylinder surface 20 has a beam diameter of approximately 10 μm. The laser beam 16 has an intensity of about 600 MW / cm ² , which is sufficient for an exposure time of about 1 ps to be within the

Processing spot 46 of about 20 pm diameter evaporate so much copper that in the cylinder surface 20 a crater-shaped depression can be excavated with a depth of up to 35 pm. Since the diameter of the laser beam 16 and the spot diameter of the processing spot 46 are considerably smaller than the dimensions of the wells 22, the latter can each be formed or assembled from a plurality of individually engraved pixels with variable depth, as described in EP 1 568 490 A1 of the applicant is described.

As best shown in FIG. 5, wells 22 formed from a plurality of pixels are each engraved by excavating along parallel tracks 60 a plurality of parallel groove-shaped depressions 50 slightly overlapping with adjacent depressions 50 such that between these only low burrs at the bottom of the wells 22 remain standing. Each of the groove-shaped depressions 55 is formed by a plurality of crater-shaped depressions, each corresponding to a pixel. The crater-shaped depressions arranged along each track 60 overlap in the longitudinal direction of the track 60, so that together they form a continuous recess 60 in which only small burrs remain at the bottom of the cells 22 between adjacent pixels. The individual pixels can be engraved with different depths by the intensity of the laser beam by an intensity modulation by means of the acousto-optical modulator of the laser processing member 18 is changed from pixel to pixel, so that each

Pixel can impart a desired depth regardless of the depth of adjacent pixels. The length of the recesses 50 can be controlled by the Laser beam is directed by the serving as a deflector acousto-optic modulator on the cylinder surface 20 or deflected away from this, depending on whether there is a well to be engraved or not. By a stepped length of the adjacent depressions 50, the wells 22 receive the desired generally diamond-shaped outline.

For engraving the gravure cylinder 12, a master copy is divided by screens into individual raster meshes, in each of which one of the wells 22nd

is arranged. In a computer, each well 22 is predetermined

Assigned dimensions that correspond to the tone value of the artwork at the location of the grid with the well 22. Furthermore, depending on the size of the cup 22, the depth of the individual pixels is determined, from which the

Well 22 is formed. To engrave each of the pixels within the well 22 with the desired depth, the acousto-optic modulator included in the laser processing member 16 is controlled by the laser controller 44 based on the engraving data derived from the master so that the intensity of the laser beam 16 varies according to the desired engraving depth becomes.

The engraving of the wells 22 with the laser beam 16 also leads to deposition of overburden 56, as described above with reference to FIGS. 3 and 4. The overburden 56 found in part within the wells 22 and partly on the webs 62 between adjacent wells 22, as best shown in FIGS. 6 and 8. A portion of the overburden 56 within the wells 22 is formed here by melt ejection, the same when digging adjacent wells 22 and when digging an adjacent groove-shaped recess 50 within the same

Well 22 is produced. Depending on the size and spacing of the adjacent wells 22, therefore, not only the amount of deposited overburden 56 from wells 22 to well 22 can change greatly, but also the distribution of the overburden 56 within the well 22 or on the webs 62nd

While larger amounts of overburden 56 in the interior of wells 22 lead to geometrical cell parameters, in particular the depth but also the cross-sectional dimensions of the wells 22, not being at the desired value. speak, have larger amounts of overburden 56 on the webs 62 between the wells 22 result in that there during printing, the doctor rests on an uneven surface and therefore excess ink can not be stripped clean. Therefore, larger deposits of overburden 56 both inside and outside the wells 22 are undesirable. In the case of a processed with a laser beam 16 rotogravure cylinder 12 with a surface 20 made of copper measurements have shown that especially the spoil 56 has a disturbing effect, the largest dimensions are more than about 8 to 10 pm. However, under

unfavorable circumstances already cause overburden deposits with a size of about 5 pm disturbances.

In order to find and then eliminate such larger deposits of overburden 56, first the three-dimensional geometric structure of the cylinder surface 20 generated by the laser beam 16 during laser engraving becomes quantitative

measured, consisting of wells 20 and unprocessed surface areas, such as webs 62, between the wells 20. To measure the surface 20 of the gravure cylinder 12 of the laser path sensor in the measuring head 48 in

Direction of movement behind the laser processing member 18 is scanned with a laser beam which is directed in the radial direction on the surface 20 of the gravure cylinder 12 and reflected from the machined or unprocessed surface 20 partially in the direction of the sensor. The distance between the surface 20 and the laser path sensor can then be measured, for example, by evaluating the phase shift between the scanning beam and the reflected beam with an accuracy of about 1 pm. The measurement of the distance is made along the previously engraved tracks 60, with surface profiles

are recorded, as shown in Fig. 8 and 9.

In the engraving machine 10 in Fig. 1, in which the measuring head 48 is mounted together with the laser processing member 18 on the engraving 26, the processing of the cylinder surface 20 with the laser beam 16 and the measurement is carried out simultaneously, the measuring head 48 at the same feed rate as the Laser processing member 18 is moved along the cylinder 12 along. The Post-processing, if necessary, takes place there after the evaluation of the measured values by the laser processing device 18 on the engraving carriage 26.

However, it is also possible, in addition to the measuring head 48 and the laser processing organ 18, a further laser processing member (not shown) on the

Engraving carriage 26 so that the machining, the measurement and the post-processing can be made simultaneously, but on different areas of the cylinder surface 20. If the measurement is performed at the same speed as the processing of the gravure cylinder 12 with the laser beam 16, as in Fig. 1 shown. If the measurement and the processing are carried out at different speeds, the measuring head is mounted on a separate measuring carriage

The measurement is carried out at a speed or sampler rate that is matched to the rotational speed of the gravure cylinder 12 and the size of the disturbing Abraumablagerungen. As noted above, when the dimensions of the spurious overburden are about 10 m, as the cylinder surface 20 is scanned with the laser beam of the laser path sensor, at least four to five readings are taken at each pixel to detect all such overburden. In order to record a more accurate surface profile, however, preferably more than ten and, preferably, approximately 20 measured values per pixel can be recorded, from which an average value is then formed. At a peripheral speed of the gravure cylinder of about 10 m / s and five to twenty measurements per pixel results in a sampler rate of about 250 kHz to 1 MHz.

From the measured values recorded for each pixel, ie the corresponding distances between the sensor and the unprocessed cylinder surface 20, a mean actual depth of each pixel can be calculated quantitatively by determining the distance between the laser displacement sensor and the average of the measured distances the unprocessed cylinder surface 20 is subtracted. If the result of the subtraction is positive, the measured pixel lies within a well 22. In this case, the measured value, ie the engraving depth of the pixel determined from the distance measurement, is compared with the target value of the engraving depth of the same pixel which previously accompanied the engraving the laser beam 16 has been used. If a deviation is found in the comparison and this deviation exceeds a predetermined threshold, which corresponds for example to 5 to 10 pm to the dimensions of interfering overburden 56, the pixel is subsequently reworked with the laser beam 16. In the post-processing, the intensity of the laser beam 16 is controlled by means of the acousto-optic modulator in the laser processing member 18 so that the removed in the post-processing amount of material corresponds approximately to the measured deviation from the target value. If no deviation is detected in the comparison, or if a detected deviation does not exceed the predetermined threshold, the pixel is not post-processed.

If the result of the subtraction is zero or negative, the measured pixel lies on the unprocessed surface 20 of the gravure cylinder 12. In this case, the measured value, ie the average projection of the pixel determined from the distance measurement over the unprocessed smooth cylinder surface 20, directly a predetermined threshold corresponding to the maximum allowable supernatant. If the measured value is greater than the threshold value and, for example, more than 5 to 10 μm, the pixel is subsequently finished with the laser beam 18. In this case as well, the intensity of the laser beam 16 during the post-processing is controlled in accordance with the measured deviation of the measured value from the threshold value in order to substantially completely remove the overburden 56 from the surface 20. If the reading is less than the threshold, the pixel is not post-processed. As a result, only the overburden deposits which have disturbing dimensions, ie the larger overburden deposits, are thus removed during the post-processing, as can be seen in a comparison of FIGS. 6 and 7 or 8 and 9. The measurement of the three-dimensional structure of the machined cylinder surface 20 can be made during the engraving by measuring an already finished engraved part of the surface 20. However, the distance between the already finished engraved part, which is to be measured, of the part still being processed, in which is being engraved with the laser beam 16, must be sufficiently large to rule out that melt ejection from the part being processed deposited after the measurement on the measured part. In experiments, it has been shown that such a subsequent deposition of melt ejection after the measurement can already be ruled out if the measurement in the circumferential direction at an angular distance of a few degrees or in the axial direction at a distance of more than 5 to 6

Traces 60 takes place. However, in order to ensure that the material ejected during the engraving does not falsify the measurement of the sensor, this is expediently carried out at a greater distance from the laser beam 16 serving for processing.

This is shown schematically in the engraving machine 10 in FIG. 10, where the measuring head 48 is mounted on a separate measuring carriage 64, which faces the

Measuring the cylinder surface 20 by means of its own feed or

Spindle drive 66 can move on the side facing away from the engraving 26 side of the cylinder 12 along. Instead of using a laser path sensor, the measuring head 48 is equipped there with a non-contact confocal or chromatic-confocal sensor 70, which also measures the radial distance between the sensor 70 and the opposite cylindrical surface 20.

Claims

claims

A method of processing a cylinder with at least one laser beam, wherein the laser beam in a surface of the cylinder recesses are excavated to produce a structure on the cylinder surface, wherein at least a portion of the cylinder surface, individual structural elements of the structure produced are measured at least one geometric measured value of each measured structural element is compared with a corresponding geometric nominal value of the same structural element in order to determine a deviation of the measured value from the nominal value, and wherein a correction is made on the basis of the determined deviations, characterized in that in the correction those structural elements ( 50, 56, 62) are post-processed with the laser beam (16), in which the deviation of the measured value from the desired value in one direction exceeds a predetermined level.

2. The method according to claim 1, characterized in that all structural elements (50, 56, 62) of the generated structure are measured, that for all measured structural elements (50, 56, 62) a quantitative comparison of the measured value with the desired value is made, and that all

Structure elements (50, 56, 62) are post-processed, in which the deviation of the measured value from the desired value exceeds the predetermined level.

3. The method according to claim 1 or 2, characterized in that in the

Post-processing of a structural element (50, 56, 62) material with the laser beam (16) is removed, wherein the degree of material removal corresponds approximately to the extent of the deviation of the measured value from the desired value.

4. The method according to any one of the preceding claims, characterized in that the measurement of the structures during the processing of the cylinder (12) with the laser beam (16). Method according to one of the preceding claims, characterized in that the geometric measured value determined during the measurement is the radial distance between the unprocessed cylinder surface (20) and the surface of the structural element (50, 56, 62).

Method according to one of the preceding claims, characterized in that the measurement of the structural elements (50, 56, 62) by a distance measurement, wherein the distance between a sensor (70) and the surface of the structural element (50, 56, 62) is measured ,

Method according to one of the preceding claims, characterized in that the post-processed structural elements (50, 56, 62) are measured and reworked at least once more when the

Deviation of the measured value determined during the further measurement from

Setpoint exceeds the specified amount.

Method according to one of the preceding claims, characterized in that the processing of the cylinder surface (20) and the measurement of the structural elements (50, 56, 62) as well as the post-processing of the structural elements (50, 56, 62) is track by track.

Apparatus for excavating indentations (22, 50) on the surface (20) of a cylinder (12), comprising a drive for rotating the cylinder (12), at least one laser (34), a laser processing member movable relative to the cylinder (12) (18) for irradiating the cylindrical surface (20) with a laser beam (16) generated by the laser (34), control means (42, 44) for controlling the movement of the laser processing member (18) and / or the laser beam (16) relative to the cylinder (12) as well as for the control of

Modulation devices for modulating the laser (34) or laser beam (16), at least one sensor (70) movable relative to the cylinder (12) for measuring a structure generated by the laser beam (16) on the cylinder surface (20), with the sensor (70 ) connected to determine at least one geometric measurement of individual structural elements (50, 56, 62) of the structure and for comparing the measured values with corresponding geometric nominal values of the structural elements, wherein the control means (42, 44) the movement of the laser processing member (18) and / or the laser beam (16) and the modulation means in dependence 5 from the geometric measured values in order to reprocess structural elements (50, 56, 62), with which the measured value deviates from the nominal value, with the laser beam (16) if the deviation exceeds a predefined dimension.

10. The device according to claim 9, characterized in that the sensor (70) is a non-contact sensor.

11. The device according to claim 9 or 10, characterized in that the sensor is a laser-path sensor. 12. Device according to claim 9 or 10, characterized in that the sensor

(70) is a confocal sensor or a chromatic confocal sensor.

13. Device according to one of claims 9 to 12, characterized in that the sensor (70) in a feed direction of the laser processing member (18) 0 and / or in the direction of rotation of the cylinder (12) at a distance behind the

Laser processing element (18) is arranged.

14. Device according to one of claims 8 to 12, characterized in that the laser processing member (18) and the sensor are movable together in the axial direction5 of the cylinder (12).

15. Device according to one of claims 8 to 12, characterized in that the control means (42, 44) in the post-processing a material removal by the laser beam (16) so control that the degree of material removal about o the degree of deviation of the measured value from Setpoint corresponds.