Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C1/00—Forme preparation
  • B41C1/02—Engraving; Heads therefor

Definitions

• the invention relates to a method for producing engraved printing plates, a device for producing these plates and the printing plate itself.
• Printing plates within the meaning of the invention are not only to be understood as printing plates, in particular intaglio printing plates for ink-carrying printing, but also for blind printing, so-called embossing plates.
• Printing forms used for gravure printing are produced, for example, by means of chemical or mechanical processes.
• cup-like depressions typical of gravure printing are produced using a photochemical etching process in which acid acts on the printing form surface.
• the grid bars between the wells are relatively sensitive to pressure, so that they are affected or even destroyed during the printing process and so a long print run is not guaranteed (Bruckmann's Handbuch der Drucktechnik, p 171ff). It is also not possible to repeat absolutely identical etchings.
• image motifs are traditionally engraved into a metal plate, such as steel or copper, using a stylus in a time-consuming process.
• the gray levels are of the image motif with different widths and / or deep lines and a different number of lines per area.
• the engraving of a printing cylinder can also be done mechanically.
• Intaglio printing is characterized by the fact that a continuous line print pattern, which can be felt with the application of ink, is transferred to the print carrier, which is characterized in particular by its filigree lines.
• WO 97/48555 therefore proposes a method for producing a steel intaglio printing plate, in which the plate is machine-engraved and the image motif is not converted into a well grid, but rather surface elements determined from a line drawing are engraved.
• EP 0 652075 A describes a device for machining workpieces.
• the device has a tool stand made of natural stone designed as a portal, which is mounted on a work table made of the same material by means of an air bearing device in order to displace the tool stand, the bearing device A vacuum clamping device is formed in the work table in order to hold the workpiece to be machined on the surface of the work table.
• material with three-dimensional contours or free-form surfaces or thin-walled parts can be machined with high accuracy and high feed rates.
• the object of the invention is therefore to provide a method for producing printing plates, the printing or embossing contours of the plate having an accuracy of preferably approximately at least 1 ⁇ m.
• intaglio printing plates in the mechanical engraving of intaglio printing plates, all the essential parameters influencing the engraving process are monitored and, if necessary, regulated, so that they are sufficiently stabilized over the entire processing period of a printing plate.
• intaglio printing plates can be produced whose contours have an accuracy of preferably approximately at least 1 ⁇ m.
• a device with at least three free axes that work independently of one another and are preferably each driven by linear motors and moved on hydrostatic bearings is suitable for processing the printing plates.
• Several components of the device are thermally stabilized.
• several correction values can be determined and taken into account when controlling the immersion depth of the engraving tool.
• “accuracy” of a contour is understood to mean the accuracy of the dimensions in the engraved motif, such as the depth of the contour, the width of the contour, the position of the contours relative to one another and the shape of the contour.
• the complete machining device is advantageous for the complete machining device to be as vibration-free as possible or at least to set it up with vibration damping. Additional advantages result from the use of hydrostatic bearings for the components to be moved, which enable a high degree of rigidity and at the same time very low-friction movement. While plain or roller bearings produce uncontrolled jerky movements (so-called stick-slip effect) caused by adhesive forces when starting to move, or when the direction of movement is reversed (so-called stick-slip effect), hydrostatic bearings enable a very smooth and jerk-free movement and thus also one more precise positioning. Hydrostatic bearings can, for example, be integrated in longitudinal grooves that correspond to the directions of movement or axes of the machining device. Individual components of the processing device can thus be floating, moved and positioned on an oil film.
• the actual temperature can be measured in intervals of 1 s to 5 min, measuring intervals of approximately 10 s are typical.
• the control accuracy is preferably ⁇ 1 °, particularly preferably ⁇ 0.5 °, extremely preferably ⁇ 0.1 ° C.
• a high degree of control accuracy and constancy of the controlled temperatures is required because it has been shown that with the given dimensions and materials, a temperature fluctuation of approx. 5 ° C on one axis can lead to a deviation of up to 6 ⁇ m.
• Separate electronic data processing for example a personal computer (PC), is preferably used for the recording, storage and visual representation of the time profile of the logged parameters.
• PC personal computer
• the long-term logging of critical parameters has the advantage that the causes can be determined retrospectively if errors occur. This is particularly the case with printing and embossing plates that are particularly large and / or one have particularly complex or filigree patterns, a great advantage because their processing times can take several days.
• Highest precision and reproducibility in printing plate processing requires an independent and mechanically decoupled movement along the individual spatial axes.
• a separate, independently operating drive is used for each of the three spatial axes.
• the machining device is preferably designed such that the workpiece, including the workpiece holder, can be moved horizontally along the x and z axes by two mutually independent drives.
• a predetermined y-coordinate is set by a vertical movement of the tool or the machining module. The movement of the tool along the y-axis takes place along a separate, column-shaped holder and is therefore completely mechanically decoupled from the movement along the x and z coordinates.
• the drives for the movement along the individual axes are of particular importance for the accuracy and reproducibility of the machined workpieces. Since the errors resulting from the machining of the workpieces on the individual axes add up, conventionally operating mechanical drives, for example gearwheels and threaded rods, are dispensed with according to the invention. A particularly high positioning accuracy is achieved through the use of linear motor drives, since they have no mechanical play. A separate drive is preferably used for each axis. A linear motor is particularly preferred as a drive for movements along the y axis, as a result of which the tool is positioned vertically.
• the workpieces to be machined are preferably fixed via a flat suction plate, which fixes the workpiece in a force-fitting manner by means of a vacuum acting on one side.
• the interior of the suction plate is traversed by largely parallel, for example vertically arranged channels.
• the channels are connected to a device for generating a negative pressure, for example a vacuum pump.
• Openings are arranged along the channels, which connect the vacuum channels to the workpiece-side surface of the suction plate.
• These suction openings are preferably arranged so that they are evenly spaced apart.
• the distance between two adjacent suction openings can be, for example, approximately 1 cm.
• the suction openings have a diameter which is preferably not significantly larger than approximately 1 mm.
• at least two adjacent rows of suction openings are preferably connected to the same channel.
• Intake plates known from the prior art are made from metal, predominantly aluminum plates. Due to the high thermal conductivity and the comparatively large thermal expansion coefficient of metals, and in particular of aluminum, large temperature fluctuations and changes in length can be introduced into the workpiece, which leads to non-negligible errors in precision engraving.
• a suction plate is preferably used, which is made of natural stone, preferably granite. Slabs of natural stone, and especially of granite, also have a vibration-damping effect and are characterized by a particularly high mechanical rigidity. Their surface can be made extremely flat and they have a high heat capacity with low thermal conductivity. This also leads to lower temperature fluctuations on the workpiece.
• suction ducts with a very small diameter of, for example, 1 mm can be drilled, the holes can also be made larger and retrofitted with e.g. glued or pressed in sleeve.
• the sleeves, which are easier to machine, are then to be provided with a channel of the desired diameter (for example 1 mm) along their longitudinal axis.
• the workpieces to be machined such as plates and sheets, deviate from their ideal target geometry and have fluctuations in the thickness and flatness of their surface.
• these irregularities and deviations of the workpiece surface are preferably taken into account when calculating the immersion depth of the engraving tool. Theoretically, any unevenness in the workpiece can be compensated for. In practice, deviations of up to ⁇ 100 ⁇ m can be expected, with values around ⁇ 60 ⁇ m being common.
• the three-dimensional height profile of the workpiece surface is determined before the start of engraving.
• the coordinates of individual support points are known from a large number of individual measuring points, which preferably form a grid that extends regularly over the workpiece surface, while the position of the workpiece surface can be mathematically interpolated for points lying between the measuring points.
• the number of measuring points can be 40,000.
• 20,000 measuring points are usually determined for common printing plate formats.
• the surface scanning of the workpiece thus provides a correction value WO for the calculation and control of the immersion depth of the graph. four tool. This movement of the tool relative to the workpiece takes place in the direction of the z axis.
• a further correction value for the z coordinate is obtained if the axial change in position of the machining spindle is also taken into account.
• the axial changes in position of the spindle during operation have two main causes. On the one hand, the position of the spindle in its axial bearing changes depending on the speed of the spindle drive, and on the other hand, heating the spindle due to the heat loss of the drive leads to an axial linear expansion.
• the engraving tool is e.g. B. attached with a collet. The two influences mentioned lead to an axial change in position of the machining spindle at the front, tool-side end, which change the immersion depth (i.e. the actual z-coordinate) of the tip of the engraving tool.
• the axial position of the spindle in the z direction is continuously determined during operation at a point as close as possible to the tool, these influences can be eliminated by a corresponding correction value SO for the z coordinate. As a result, long and disruptive warm-up phases can be avoided to achieve constant conditions.
• the position measurement is preferably carried out directly on the tool tip.
• the two correction values WO and SO for the z-coordinate enable highly precise and reproducible machining of the workpiece surfaces, the target depth of the machined areas, which is very important for gravure plate production, in particular being precisely maintained.
• the tip of the engraving tool is moved against a measuring system and the position of the tool tip in the z direction is recorded with the greatest precision.
• Mechanical measurement systems with a flat stop surface against which the tool tip is moved are preferably used for the measurement.
• the measuring force should not exceed 0.1 N and is preferably ⁇ 0.01 N. Such values are achieved, for example, by air-bearing probes.
• Non-contact optical measuring systems in which the position of the tool tip is recognized and measured using suitable optics and means and methods of image processing, can also be used.
• Embossing plates are preferably used with engraving tools with different cutting edge geometries.
• a suitable tool is selected for engraving the relevant area of the plate.
• tools with a larger tip radius and a larger tip angle are preferred for the mere clearing of larger surface areas.
• the machine is preferably equipped with a magazine for holding a large number of tools and a device for an automatic tool change.
• the tool magazine in connection with the changing device not only enables the quick and uncomplicated exchange of tools of different geometries, but also the exchange of damaged or worn tools. For example, a dozen different and / or identical engraving styluses can be kept in a magazine.
• the tool magazine is preferably made rigid and immovable. This means that when the tool is changed, the magazine is not moved so that the new tool is brought up to the tool holder, but rather the tool holder, for example one
• the collet moves to the tool in the intended change position.
• the tools In order not to damage the sensitive cutting edges of the engraving tools, the tools must be guided when changing and fixed in the magazine so that the cutting edges are not touched.
• the engraving tools are preferably made of wear-resistant material.
• wear-resistant material for example, sintered hard metals are possible, but also ceramic cutting tools or those made of high-alloy tool steels with a diamond-coated cutting edge or one Cutting edge made entirely of diamond material.
• the hardness of the engraving tool is preferably about 10 to 20 times higher than the hardness of the machined workpiece (based on the Vickers hardness).
• the unit consisting of tool, tool holder and tool drive is also referred to as a machining spindle.
• the machining spindle, the spindle holder and other components are combined in the machining module.
• the complete processing module can in the device according to the invention in the vertical direction, i.e. can be moved along the y axis. This movement is completely independent of the movements along the other axes. To ensure trouble-free operation and its control, the processing module is preferably equipped with various additional devices, which are described below.
• the required coolant is not supplied as a liquid jet, but is sprayed into the working area of the tool cutting edge as a spray from one or more spray devices under controllable, high pressure.
• a suction device is preferably mounted on the side of the tool opposite the spray devices, as a result of which the undesired spreading of spray mists is prevented.
• Fatty alcohols are preferably used as the cooling medium.
• the processing module is preferably equipped with an observation device.
• This can consist, for example, of a video microscope, which is aimed at the processing area via an angle mirror. Order for adequate and To ensure constant lighting conditions, the processing area can be illuminated by additional lighting means that are also attached to the processing module. Flexible light guides are suitable for this, for example.
• the device according to the invention is preferably equipped with a second observation device, which can also be mounted on the processing module.
• This second device is designed so that it can be used with the required accuracy for measuring the machined workpiece surface or the engravings generated.
• This second optical device can also be designed as a video microscope.
• the viewing direction of the optical measurement unit is preferably perpendicular to the workpiece surface.
• the processing spindle can be held at a constant temperature by a control circuit and / or can be made of a material with a low coefficient of thermal expansion.
• natural stone such as granite, or iron nickel alloys, such as Invar, come into consideration.
• thermoforming inks are used, high-precision engraved printing or embossing plates can be used advantageously to control the color tone in the printed image.
• the deeper the engraving in the printing plate the more color it can absorb and the more color is transferred to the substrate to be printed, usually paper.
• the more color that is transferred the darker the color on the substrate and vice versa.
• even slight fluctuations in the engraving depth can lead to fluctuations in the color tone. It is therefore all the more important to be able to produce an exactly determinable engraving depth in the printing plate, as it has the printing plate according to the invention.
• FIG. 1 is a perspective view of an engraving machine according to the invention
• FIG. 2 shows the engraving machine according to FIG. 1 from a different view
• FIG. 3 is a suction plate as a vacuum clamping device for the workpieces in supervision, 4 shows a cross section through a suction plate according to FIG. 3,
• FIG. 5 shows a processing module of an engraving machine according to the invention with additional devices in supervision
• Fig. 6 shows a detail of the tool magazine in cross section.
• FIG. 1 and 2 show in a different perspective view and in a schematic manner the basic structure of a microprocessing machine 1 with a three-axis system (x, y, z) for the precision engraving of intaglio originals.
• a straight groove 3 is machined into the machine bed 2.
• the orientation of this groove 3 corresponds to the x axis.
• the cross table 4 is guided in the groove 3 of the machine bed 2 and thereby moved along the x-axis.
• the cross table 4 also has a groove 5, the orientation of which corresponds to the z-axis and which is positioned exactly perpendicular to the groove 3 and thus to the x-axis.
• a holder 6 is guided, which receives the suction plate 7.
• the suction plate 7 serves as the actual workpiece holder on which the plates to be machined are clamped by means of negative pressure. It is perpendicular to the plane formed by the x and z axes.
• the tool magazine 8 can also be attached to the holder 6 and is used to hold a large number of engraving tools.
• a column-shaped vertical support 9 is also arranged on the machine bed 2 and has a vertically running groove 10 which extends along the y-axis.
• the processing module 11, which also includes the engraving tool, is guided in this groove 10.
• a guide column with a cage rotor, parallel to the vertical support 9, can be used to form the y-axis. Then in the groove of the vertical support the linear motor housed.
• the advantage of this arrangement is the light squirrel-cage rotor with optimal power distribution.
• the machine bed 2, the cross table 4, the holder 6, the suction plate 7 and the vertical support 9 are preferably made of natural hard stone, such as granite. At least in the areas where other machine components are moved, their surfaces are extremely flat, preferably ground and lapped.
• the grooves 3, 5 and 10 arranged perpendicular to each other accommodate the linear motors (not shown in FIGS. 1 and 2) and the hydrostatic bearings. With a repeat accuracy of approx. ⁇ 0.5 ⁇ m and better, these bearings and drives allow an absolute positioning accuracy in the range of ⁇ 5 ⁇ m and better. In addition, such a combination avoids the so-called “stick-slip effect” and enables free and very even starting and moving along the three axes.
• each axis is equipped with its own drive, the movements can be independent of one another
• the arrangement described ensures in particular that a vertical movement of the tool along the y axis is completely independent and unaffected by a horizontal movement of the workpiece in the xz plane.
• damping elements for example air spring elements 12.
• the suction plate 7 is shown in supervision.
• a surface of the suction plate 7 is provided at a distance a, which can be, for example, approximately 10 mm, with suction openings 20 through which a workpiece is fixed on the plate surface.
• the suction openings extend across the entire surface, but are only shown in the drawing in the upper left corner of the suction plate 7.
• the suction plate 7 is preferably dimensioned in such a way that the clamping surface covered by the suction openings 20 has a dimension of 500 ⁇ 600 mm and thereby also enables the processing of relatively large printing plate originals.
• the clamping surface is preferably divided into individual quadrants, which are designated I to IV in FIG. 3.
• the individual quadrants can have a different size and they can be controlled individually and independently of one another. This makes it possible to clamp plates or workpieces of different dimensions without having to cover the individual suction openings 20 that are not required.
• the division into the individual quadrants is preferably carried out in such a way that even small plates with a standard dimension of 250 ⁇ 250 mm can be clamped in a quadrant, for example I, without additional cover.
• FIG. 4 shows a section of a cross section through the suction plate 7.
• the suction openings 20 are connected via bores 22 to vacuum channels 23, which can run in rows or columns through the suction plate 7.
• the vacuum channels 23 are preferably arranged offset, so that they run in different depths.
• the suction openings 20 are therefore made as small as possible and have a diameter of approximately 1 mm, for example.
• the clamping surface is first connected to the vacuum channels 23 by bores 22 which have a larger diameter and are therefore easier to manufacture. At least two rows of bores 22 are preferably connected to a vacuum channel 23. This prevents the suction plate from being mechanically weakened too much by an excessive number of channels 23.
• the outlet openings of the bores 22 on the clamping surface are provided with additional pressed-in or glued-in sleeves, preferably made of brass, which reduce the effective outlet opening.
• the inner sleeve diameter forms the actual suction opening 20.
• the clamping surface of the suction plate 7 can be lapped after the sleeves 21 have been introduced, which also ensures exact flatness of the clamping surface in this preferred embodiment.
• FIG. 5 shows a top view of the processing module 11, which takes place in the illustration of FIG. 2 in the direction of the z-axis.
• the machining module 11 includes, among other things, the machining spindle 30 on which a collet with the engraving tool 31 is located.
• the following are preferably provided as additional devices: spray nozzles 32 for supplying a cooling and / or lubricating medium, which are aligned with the tip of the engraving tool 31, and a suction device 33 for removing spray mist of the coolant or lubricant and chips.
• a non-contacting distance sensor 34 is preferably arranged at a short distance in front of the tool-side end face of the machining spindle 30.
• Suitable distance sensors are, for example, eddy current sensors, capacitive distance sensors or light sensors. These measure the growth in length, that is to say the axial change in position of the machining spindle in the direction of the z axis, and provide the correction value SO for the z coordinate.
• the dissolving The capacity of such distance sensors for measuring the change in length of the machining spindle is approximately 0.1 ⁇ m.
• the processing module 11 is equipped with observation devices 35, 36 for observing the probing of the engraving tool tip on the workpiece surface, the actual machining process, and for precise measurement of the engravings produced without having to clamp the workpiece.
• observation devices 35, 36 for observing the probing of the engraving tool tip on the workpiece surface, the actual machining process, and for precise measurement of the engravings produced without having to clamp the workpiece.
• a video microscope 35 is aligned with the tool tip and the machining area via an angle mirror.
• a sufficient light guide for example, ensures that the observed area is adequately illuminated.
• the image signal of the video microscope 35 is forwarded to a monitor and enables reproduction with a preferably 50 to 100 times total magnification.
• Another video microscope 36 can be engraved on the workpiece surface in the direction of the z-axis.
• This measurement system is preferably equipped with a further illuminating means 38 and with a rotatable cover for protecting the objective.
• the cover can be rotated so that the opening 39 exposes the lens.
• the measurement system enables, for example, a connected monitor, preferably a computer with a frame grabber and image processing software, to precisely measure even the finest engravings with a magnification of approximately 400 to 600 times.
• the entire processing module 11 is guided on the vertical support 9 in the groove 10 or on the guide column and is moved by a linear motor in the direction of the y-axis on the vertical support.
• 6 shows the automatic tool change in the tool magazine 8 in a schematic manner. A section from a cross section through the tool magazine 8 is reproduced, by means of which the storage and positioning of the engraving tool 31 is illustrated.
• the engraving tool For precision machining, the engraving tool must be clamped into the tool holder with a specified, protruding length. To do this, it is necessary to store the tools in such a way that the machining tip assumes a defined position. On the other hand, it must be ensured that the sensitive tool cutting edge is undamaged and is therefore stored without contact.
• the engraving tool 31 can be inserted with the machining tip into a cavity of the tool magazine 8 through an opening 40, which is made slightly larger than the tool diameter. After passing through the opening 40, the tool 31 is guided through a clamping element 42 and fixed by this by frictional engagement.
• the clamping element 42 is preferably designed as a rubber O-ring.
• a sliding sleeve 44 for example designed as a brass bush, is movably mounted in the cavity in the direction in which the tool removal and supply takes place by a spring element 45. Sideways movements of the sliding sleeve 44 are not possible due to the supporting walls of the cavity.
• the sliding sleeve 44 forms a stop for the cutting end of the engraving tool 31 and positions the inserted tool in a defined, predetermined position.
• a central bore in the sliding sleeve 44 ensures that the cutting edge is mounted on the tip of the engraving tool 31 without contact.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Manufacture Or Reproduction Of Printing Formes (AREA)
• Laminated Bodies (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Shaping Of Tube Ends By Bending Or Straightening (AREA)

Priority Applications (4)

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Citations (7)

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• 2002
  • 2002-12-20 DE DE10260253A patent/DE10260253A1/de not_active Withdrawn
• 2003
  • 2003-12-19 DE DE50313570T patent/DE50313570D1/de not_active Expired - Lifetime
  • 2003-12-19 AU AU2003290099A patent/AU2003290099A1/en not_active Abandoned
  • 2003-12-19 RU RU2005122907/11A patent/RU2348533C2/ru not_active IP Right Cessation
  • 2003-12-19 WO PCT/EP2003/014610 patent/WO2004056568A2/de not_active Application Discontinuation
  • 2003-12-19 EP EP03782459.6A patent/EP1578604B2/de not_active Expired - Lifetime
  • 2003-12-19 AT AT03782459T patent/ATE502775T1/de active

Patent Citations (7)

Non-Patent Citations (1)

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