DE2354732A1 - PREPARATION OF PRINT SURFACES - Google Patents

Description

PATENT LAWYERS

ing. H. NEGENDANK · dipl.in &. H, HAlJCK · bipl.-phys. W. SCHMITZ PIPL.-ING. E. GRAALFS · bipi ^ -ing. W. WEHNERT

HAMBURG-MUNICH 2 35 4 73

HAMBURG 36 -NKUER WALL 41

TEI ,. 86 74 88 AND 3Θ 41 18

TET-EGH. NEGEDAPATENT HAMBtTHG MUNICH 15 MOZARTSTR. 23

TEIi. 5 38 03 88

TKLEGH. NEQEDAPATENT MUNICH

Hamburg, Oct. 29, 1973

CROSFIELD ELECTRONICS LIMITED
766 Holloway Road,
London, NT9 3JG / England

Preparation of printing surfaces

The invention relates to an engraving device an engraving pressure body, in the up to the required maximum pressure depth Engraving cells have been etched and filled with a material that is more susceptible to engraving is considered the actual pressure hull materialο such a process is for example in British Patent No. 1,229 described. In the latter description, engraving is used The laser beam is used, but it could also be used as an option an electron beam can be used.

With such an engraving, there is a possibility of formation an unwanted interference pattern. This pattern, known as "moire", is created when the effect of a number adjacent lines of the imaging beam is not uniform for a given intensity. It can "for example as a result of errors in the profile of the effective Intensity of the beam or at a distance of a tactile

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line to the next the effect of the beam in the middle

every single touch line be more intense than at the edge, where it overlaps the next, or vice versa. In some areas of the picture the more intense effect of the Ray mainly lie along the cell walls, where they have little effect, while they are in others Basichen lies predominantly across the cells, where it leads to an increase in the print density.

A device according to the invention contains a beam- generation engraving device for removing the filler material from a cell on which the engraving beam is directed a cell detector including a scanning device for scanning the surface of the pressure hull, as well as peeling devices for determining the presence of a filled cell on a scanned one Point on the surface, devices that respond to the output of the sensing devices to electrical Generate signals corresponding to the position of the sampling point at which a cell was detected, as well as a beam guiding device, which is controlled by the electrical signals of the cell detector, to the Adjust the engraving beam so that it falls on the cell to be engraved as determined by the detector.

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In the preferred embodiment of the invention, the Pressure body has a cylindrical shape and is used for circulation driven around its own axis; finds at the same time between the engraving device and the cylinder a relative longitudinal movement instead, so that the engraving beam, if he for the duration of such a turn and relative Longitudinal displacement is switched on, describing a spiral path on the surface of the cylinder would. The direction of movement of the probe beam relative to the cylinder is such that it is on the cylinder surface describes a path parallel to the axis of rotation of the cylinder. This tactile path is in front of the position of the engraving beam relative to the circumferential cylinder surface, and the signals obtained when the probe beam reaches a cell, and which is the position of the Representing the scanning beam at the specific moment are stored before they are used to guide the engraving beam to be used. In the preferred embodiment, the signals are stored in buffers, on which they can then be pushed by suitable slide impulses; the buffers each contain a number of storage elements, with corresponding Storage elements in the various buffers each successive points along a scanned line on the surface of the pressure body put there. When the cylinder revolves and when it approaches

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A detected cell at the point of impact of the engraving beam on the cylinder are signals from a converter actuated by the rotary movement of the cylinder is used to convert the cell position signals to move to the buffers. These signals, as well as the detected cell, become the work surface of the beam reached, pushed out of the storage and used to deflect the engraving beam, so that it hits the center of the filled cell. The engraving beam can be an electron beam or a laser beam.

For a better understanding of the invention, reference is now made to an example of the device according to the invention on the accompanying drawings. Show it:

Fig. 1 is a diagram of the device for engraving a Cylinder by means of an electron beam engraving device,

FIG. 2 is an enlargement of part of the surface of the cylinder shown in FIG. 1 when shown the area, the content of which is shown in the buffer memory according to FIG. 1,

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Fig. 3 shows in greater detail the connections for certain of the lattice circles shown in Fig. 1,

Fig. 4 shows an arrangement for determining a filled Cell and

FIGS. 5 and 6 are waveforms taken from portions of FIG Device according to FIG. 4.

The drawings show a cylinder 8 with yorge etched and filled cells on its cylindrical outside, which by means of an electron beam engraving device 4 is engraved (the position of which is shown schematically in the drawing); the beam 5 of the engraving device falls on the working surface 10 of the cylinder. The beam 5 can be deflected in the directions χ and y, and although with the help of diversion control circuits that are still too describe are. During the engraving, the cylinder 8 is continuously driven to rotate by a motor 11; In addition, there is a slow relative between the cylinder 8 and the jet engraving device 4 Longitudinal movement takes place parallel to the axis of rotation of the cylinder, so that the engraving beam on the cylindrical Surface draws a spiral path. This longitudinal movement can be achieved, for example, by arranging the engraving device be effected on a lead screw that

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is driven to rotate by the motor 11 via a reduction gear.

The cell detector in the apparatus shown includes a cathode ray tube 12 which is a light point scanner, together with a photoelectric cell and associated circuits for generating signals representative of the location of a detected gravure cell. The cathode ray tube 12 projects a single tactile line 14 parallel to the axis of the cylinder onto the part of the cylinder which approaches the engraving beam working area 10. A time base for the control of the line scanning äs: tube 12 contains a pulse-generating oscillator 16, a counter 18 which counts the pulses from the oscillator 16 and has a capacity adapted to the required length of the scanning line 14, a digital-to-analog converter 20 which receives the counter output and a deflection amplifier 22 which transmits the analog signal from converter 20 to the deflection electrodes in tube 12. In the example shown, the counter returns to zero after each maximum count and a sawtooth waveform is consequently transmitted to the deflection electrodes. If necessary, the counter could also count alternately in opposite directions; in that case a triangular waveform would be transmitted to the deflection electrodes. The key repeat

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fetch speed is such that every filled cell on a cylindrical surface as it passes through the working area of the tube 12 at least once is scanned.

The photoelectric device 24 (which may contain a number of photocells) establishes the presence a filled gravure cell when the cell is scanned through the light spot from the tube 12 due to the difference in the reflectivity of the cell walls and the filler material fixed. "-.-..- ·

The pulses from the photoelectric unit 24 are transferred to AND gate 28 through pulse shaping circuits 26. The other inputs for these AND gates are derived from the decoder 30 which is connected to the output of the Counter 18 is fed. The effect of this is that the AND gates 28 are enabled. Impulses to pass through the photoelectric unit one at a time, wherein the control pulse from the decoder is synchronous with the movement of the scanning light spot from tube 12 on path 14 of the cylindrical surface going along the entire row of AND gates from one AND gate 28 to the next. Thus become the successive states of the photocells »the with successive counts in the counting device coincide, as logical values zero or 1 in one

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consecutive one of a number of parallel buffers 32 registered. The number of buffers (and therefore the capacity of the counter 18) is the number that is required is to follow the steps of cell positioning Direction χ to resolve on the surface of the cylinder 8. .

Each of the buffer memories 32 is of the type "first in, first out" (¥ irs.t in, first out "kind) and is constructed in a manner similar to a shift register Set of points on the scanned line 14 in the direction χ of the cylindrical surface, the contents of these storage locations in the form of the stored logic values 0 and 1 indicating the absence or presence of a cell at each scanned point along the line 14. These sets of values are shifted to the buffers by pulses on the line 33 taken from a transducer 34 mounted on the cylinder shaft, each such shift pulse representing an increase in the angular movement of the cylinder Memory 32 each the presence or absence of engraving cells on successive Points on a circumferential line of the cylinder 8 determined, ie. on a line in the direction y on 'the cylindrical surface. 409819 / 092S _ _g

The length of the buffer in the form of the number of digits and the distance between the work area 10 and the The scanned line 14 on the cylindrical surface is such that a set of values in the x-direction of the memory 32 reaches the output ends of the memory exactly when the jet engraving device is ready, each filled cell, when the cylindrical surface is scanned by the tube 12 on this section the cylindrical surface was found to be graze. The contents of all buffers thus form Cell storage locations in an area · the cylindrical Surface (shown hatched in Fig. 2); one side of which is delimited by the tactile line 14, and the other side includes the point 10 a, at which the undeflected electron beam hits the cylinder. It should be noted; that in the Figures 1 and 2 show the length of line 14 and its separation from the point of incidence of the electron beam in the interest of Clarity are shown exaggerated »

The position of each in the x-direction of the tactile line determined cell is represented by the set of values, from the output of the buffer memory to a Encoder and digital-to-analog converter 36 is transmitted.

This circle forms an analog signal to represent any deviation of the detected cell in the x-direction from the center of the engraving beam working

. area. The signal is sent to the x deviation control section

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the Strahlgraviereinriclitung 4 and transferred to the deflection of the beam 5 in the x-direction is used to the extent necessary to keep the beam in the center of the to fold in the filled cell. If this cell has been engraved, then a new set of values is fetched from the buffers to store the x-position of the engraving beam to control for the next cell, and so on. The value sets are made from taken from the buffers 32 with the aid of "off" pulses which are sent via a line 37 to all buffers be transmitted. These pulses, similar to the "on" pulses on line 33 from the Transformer 34 removed, but in this case go through a buffer counter 38. Once a cell has been detected, then IMPULSES accumulate in the buffer counter 38, so that another output of the buffers 32 is delayed. .

Since the cylinder continues to rotate during the engraving, the engraving beam is forced to to follow the moving engraving cell in the y-direction while engraving this cell. This is achieved by.Using the count in the buffer counter 38, which shows the delay since the start of the engraving of the cell to control the engraving beam position in the y-direction. To do this, will

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the counter output through a digital-to-analog converter \. 40 is transferred to the y deviation control part of the electron beam engraver 4.

Since the scan is helical, during the Engraving also gives a movement of the cell in x-direction, but this is so small that it is neglected can be. As already described above, the buffer counter 38 is used to measure the output of signals from the buffers 32 during the engraving of a cell to prevent, and thus prevents a movement of the engraving beam in the x-direction until the engraving this cell is completed.

The Bärieb of the buffer counter 38 is through a fixed monostable circuit 42 regulated by an OR gate 44 is controlled which of each of the buffer memories 32 receives signals. So if any of the buffers 32 has a signal with the logic value 1 at its output, then the gate 44 transmits to the monostable circuit 42 a signal indicating that a cell has been detected. This signal brings the buffer counter 32 into operation, and the stored count becomes one of the one-shot circuit after the expiry of the count 42 set period triggered; this period is greater than the longitudinal / possible engraving time. '

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In the device described here, the depth of the engraving determined by the period during which the beam of the beam generator 4 at constant Power is on. The period for which the beam is on is determined by the image display signal set by an input scanner 46 or a source of stored image information. The image display signal is used as a control signal transmitted to a voltage-controlled monostable circuit 48, which upon receipt of the signal "cell determined "(cell located) generated by the OR gate 44 a beam switching pulse, the duration of which by. the image display signal is controlled from the input scanner. Signals are obtained from the input scanner decreased at a rate controlled by the synchronization signal from the transducer 34 will ,

Pig. 1 shows the connections for the gate circles 48 in FIG simplified form. In the Prais it is desirable to see a cell by more than one Place the buffer memory 32 (either in the x or y direction) to prevent the gates 28 from being connected to one another as shown in FIG. Here the gates receive signals from the decoder 30 and from the photocell 24 via the amplifier and pulse shaper 26 (Fig. 1) and a gate 54 which is triggered by an "on" pulse on line 33a. aside from that

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235A732

However, each gate has a number of further input connections and its output is connected to a monostable circuit 52. Whenever a gate generates a signal "t" at its output, it releases its monostable circuit 52 and the feeding of the signal "1" into the corresponding buffer storage. ' The output of the monostable circuit 52 is connected back to the input of its AND gate, as well as: also to the inputs of the various adjacent gates in each direction (with the two gates in each direction in the arrangement in FIG. 3) Operation of these gates for a period determined by the one-shot circuit. It. will-therefore? once a cell has been detected, a certain bex & ch is dimmed so that the same cell cannot be detected again. "The covered area extends evenly on each side of the cell in the x-direction and follows it in the y-direction. The gate interconnections are cyclical so that the determination is made: cell at one end of the scan line in the x-direction covers certain sections at both ends of the scan line The line scanned in the x-direction is of course slightly larger than the cell spacing to ensure that a cell is not completely skipped; as a result, it would be without the one described above

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Arrangement, there is a risk that occasionally two Cells could be detected when scanning the same line.

In order to prevent a cell that is already in a previous cylinder rotation was engraved again is engraved, the photocell and the optical system are arranged so that they are on engraved cells do not address. This is achieved by the arrangement shown in Fig. 4, which is based on the fact that, if the cylindrical surface is polished copper, a filled cell shows a slight decrease in specular reflectance ± degree R, and only compared to the surface between the cells has a low scatter S, while an engraved cell has a strong ÄMall in the specular Reflectance R and a greater increase in scattering S has. The cathode ray tube 20 illuminates the surface of the cylinder 8. A photocell 6.2 receives light through the specular reflectance and transmits a signal R. to a well detector and pulse shaping circuit 64? a photocell 66 receives scattered Light and transmits a signal S to a threshold detector 68. The photocell outputs for filled and engraved cells are shown in FIG. The signals from the circles 64 and 68 are transferred to a grid circle 7O in which the increase in the signal S for

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Blocking the pulse from circuit 64 is used. If thus an output from the circle 70 "(Fig. 6) before - * - is present / then the engraver operates normally, but if there is no output from the circuit 70 then the detection of a cell is passed the device of Fig. 1 prevents.

The well detector and pulse shaping circuit can be used by the Be kind in which the input signal is compared with a slightly delayed ^ form of the same signal and a monostable circuit is switched when the Difference between the two compared signals changed the sign in the required direction

It can be seen from Fig. 1 that the jet engraving part the device is housed in a vacuum enclosure. This is in the drawing in the interest omitted for clarity.

It may be desirable in individual cases to choose between the point on the cylinder at which the engraving beam works, and the scanned by the cathode ray tube To assign a barrier to the line. Such a barrier would contaminate the optical equipment of the ' Scanning system through the decomposition products of the cell filling material help prevent. The buffer memory 32

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must of course be so long that the barrier between the scan line and the beam operating point can be accommodated.

In a slightly modified form, it becomes a memory data source loaded with computer equipment with the current beam deflection values (i.e. with the output, of circles 36 and 38 at the beginning of a cell), and these are used to determine the correct image signal for the to form the exact location of each engraved cell. This prevents the slight distortion that occurs with Device according to FIG. 4 arises in that the of the Transformer 34 on the input scanner 46 transmitted information not clearly the current position of each engraved cell due to the deflection of the engraving stralis.

It can be seen that various modifications can be made to the scanning system and also to the memory and control circuits. It can for example Instead of the cathode ray tube 12, a laser beam with electro-optical deflection can be used. WahVeise can instead of the combination of the cathode ray tube and the Photocell according to the drawing a television picture tube or a picture decomposition tube can be used.

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In addition, some or all of the digital parts of the Systems shown in the scheme by a General purpose digital computer equipped with program and boundary layer to be replaced by Calculate to perform the functions of some or all of the digital blocks in the scheme. .

Although the device described here uses an electron beam generator is used as an engraving device but advised that optional a laser with electro-optic deflection can be used. aside from that particle beams other than electron beams are possible, for example ion beams.

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Claims (1)

Patent claims: Device for engraving a gravure pressure body, in which gravure cells have been etched to the required maximum pressure depth and filled with a material that is more susceptible to engraving than the material of the actual pressure body, with jet-generating engraving devices for removing the filling material from a cell , to which the engraving beam is directed, indicated by a. Cell detector with a scanning device (12) for scanning the surface of the pressure body, sensing devices (24) for determining the presence of a filled cell at a scanned point on the surface, and devices (28, 32, 36) which respond to the output of the sensing device Responding generation of electrical signals representative of the position of the scanned Purifces at which a cell was detected, and beam guiding devices, which by the electrical signals from the. Cell detector are controlled to adjust the Gravjar-beam so that it falls on the _t determined to be engraved cell. . "- ■ '- -' · ■ '- ■; _ ■■ ' ■■ - ^;:; ■ '; ■■: ■" ■■ - ·. - 19 - 409819/0925 2. Device according to claim 1, characterized by a signal storage device (32) which is controlled by the position of the scanned point at the moment of the detection of a full cell for storing signals which are representative of the position of the full cell on the upper, surface, of the pressure hull, as well as directions for the subsequent removal of the stored signals from the memory and for transferring them to the _r . Beam guiding devices. ,., ..;:, 3. Device according to claim 2, characterized in that that the storage devices contain a number of buffer memories (32), each in a sequence Include stored locations on which digital data can be moved, as well as corresponding memory shares in the various buffer memories, which are representative of the successive ones Points on a scanned line on the surface of the pressure hull .. " 4.Vorrichtung according to claim V, 2 or 3, characterized ^. draws _f that the pressure body has the shape of a cylinder - and the device further includes devices for driving the cylinder to rotate around its own axis, as well as devices through which during a 4098) 9/0925 such rotation a longitudinal movement take place between the engraving device and the cylinder can, whereby the engraving device during a s & chen turn a spiral path on the Cylinder follows, and further characterized / by scanning the direction of the surface for detection a cell is parallel to the axis of rotation of the cylinder. 5. Apparatus according to claim 3 and 4, characterized through a converter (34) which increases in the orbital motion of the cylinder provides electrical impulses that are used to shift data signals on and out of the buffers (32). 6. Apparatus according to claim 5, characterized by ei'nen counter (38) ,, which is arranged so that it Pulses from the transducer are counted as well as a cell is detected and the engraving process has started is, the output of the counting device (38) on the beam training device is transmitted in order to achieve a compensating deflection on the engraving beam and transfer it regardless of the revolution of the cylinder to hold on to the cell to be engraved while the cell is being engraved. - 21 - 409819/0925 7. Apparatus according to claim 5 or 6, characterized by means (42, 38) for modifying a shift out of data from the buffer memories (32) by pulses from the transducer in the period from the start of engraving a detected cell until the completion of the engraving of this cell. 8. Apparatus according to claim 3, characterized by. Bodies (44, 48) on the content of all Address the buffer memory to start an engraving process to be initiated when any of the memories has an output indicating a fixed cell » 9. Apparatus according to claim 3 or any of claims ~ 5 to 8, characterized * that the sensing device is a cathode ray tube (12) with devices (18, 20) for controlling the beam deflection of the same in order to scan the surface of the pressure body (8) -to allow, and wherein the deflection control means; (18, 20) for the cathode ray tube for Control of the buffer memory (32) is connected in such a way that the output of a photoelectric device (24), which ©: the LMe scanned on the surface of the pusher sifts, in such a way into the buffer memory (32> fed into the A0 981 970 925 - is characteristic of the deflection of the beam at the moment of entry. 10. The device according to claim 9, characterized in that that the deflection control means (18, 20) for the Cathode ray tube for the transmission of a control signal connected to each buffer memory (32) is to receive the controlled buffer memory of the output of the photoelectric device (24) to allow the scanned line on the surface sifts through the pressure hull .. 11. The device according to claim 3, characterized by Means responsive to a signal indicating the detection of a cell to stop storage of the signals indicating the cells in memory positions corresponding to the points next to the point at which the cell has been found to prevent. 12. The device according to claim 1-1, characterized by means (52) which store signals for displaying a second detected cell on the same scan line of the cell detector impede. ' 13. Device according to each of the preceding »claims, characterized by devices (62, 66) which respond to the detection of an already engraved cell, to avoid having to engrave this cell again 409819/0925 _ ₂₃ _ WHERE- prevent / with these facilities on the reflectance and address the light scattering properties of the cell. - ' 14. Device according to any of the preceding claims, characterized in that the engraving device is a Electron beam generator is. " 15. Device according to any one of claims 1 to 12, characterized in that the engraving device is a laser . - - ^; . "■ - ■ - -" - - '" ■; - ■; ■"' ^: 4098 19/092 5 Blank page