US3506779A - Laser beam typesetter - Google Patents

Description

April 14, 1970 Filed April 3, 19 67 E. F. BROWN ET AL LASER BEAM TYPESBTTER FIG. 3

| l 1 l I I 4 Sheets-Sheet 3 3,506,779 LASER BEAM TYPESETTER Earl F. Brown, Piscataway, and Charles F. Hempstead,

Holmdel, N.J assignors to Bell Telephone Laboratories, Incorporated, Murray Hill and Berkeley Heights,

N.J., a corporation of New York Filed Apr. 3, 1967, Ser. No. 628,042

Int. Cl. H04n 1/10, 1/24 US. Cl. 1786.6 '2 Claims ABSTRACT OF THE DISCLOSURE A printing plate, used for printing text and illustrations, is formed bya controlled laser beam writing directly upon a plate blank. A very high intensity :beam of small cross section from a C laser removes material from the plate surface by vaporizing to form relief type plates for letter- BACKGROUND OF THE INVENTION This invention relates to printing and the graphic arts, particularly to the preparation of plates for reproducing the same.

Typically in the printing art, the plates which transfer the ink to the paper are either of the relief type, such as letter press and intaglio, or of the planographic type, such as lithograph and offset. Relief type platesare used for high quality reproduction of large volume, and are made of a relatively hard and durable material, usually metal. Text may be composed with individual letters set up by hand or whole lines cast as a unit by the lintoype process. In both cases, the spacing between words should be adjusted to completely fill each. column with proper hyphenation, a process calledjustification. For the purpose of editing, a whole page of type must be assembled and a proof sheet printed; then the page is disassembled and reset to make any changes.

Relief type plates to reproduce pictorial matter are normally produced by the more complicated process of photoengraving. This process entails photographing the pictorial matter, transferring the photograph to a sensitized metal surface, removing non-printing areas of the surface by etching, and perfecting the plate by hand engraving.

Planographic plates, on the other hand, are smooth surfaced, and, due to the immiscibility of grease and water, ink adheres only to the printing areas. Because the printing areas which form the image'spread with use, the planographic printing processes are basically lower volume, but they are also lower cost. The ima-gecarrying plates may be plastic coated paper and are usually produced photographically or electrostatically. These processes, therefore, initially require a perfected original display to be photographically copied onto a plate.

According to a recent development shownin United States Patent No. 3,422,419, issued Jan. 14, 19 69 to M. V. Mathews and H. S. McDonald, graphic images such as letters, numbers and symbols may be rapidly assembled from basic common segments and displayed on the face of a cathode ray tube. Information for generating letters and symbols to form text is stored in a memory and as sembled by a computer which directs the deflection and modulation of the cathode ray beam. With this system,

Uhited States Patent 0 text can be edited and printed out on the cathode ray tube in ustified columns at the rate of hundreds of letters per second. To turn this cathode ray tube display into prmtmg plates for graphic reproduction, conventional photoengraving and photographic methods are used. This I latter step of transferring the information from the cathode ray tube to produce plates is, however, subject to two serious limitations: (1) the resolution attainable is limited because of the electron beam size and focus, the characteristics of the phosphor and the distortion of the glass face plate, and (2) the speed of photoengraving is limited because of the small amount of light generated by the tube phosphor.

An object of this invention is, therefore, to provide a new, fast and eflicient technique for forming printing plates.

Another object is to produce printing plates from stored digital information with improved resolution and speed.

Another object is to produce relief type printing plates, properly edited, without proof printing.

Still another object is to produce relief type pictorial printing plates without chemical processing.

SUMMARY OF THE INVENTION A laser beam is intensity modulated and deflected in accordance with control signals to strike areas on the surface of a printing plate blank in a pattern of information to be reproduced. The areas so struck are permanently altered to affect their ability to transfer ink; they may be vaporized, forming ink transferring recesses for intaglio printing or leaving raised ink transferring surfaces for letter press printing; or they may be chemically altered for further processing.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION -In the embodiment of the invention illustrated in block form in FIG. 1 a laser 11 produces a beam of intense coherent radiation 12. The beam is passed through a modulator 13 which varies its intensity in accordance with a control signal from a character generator 23. The modulated beam is then directed to a small angle stecrer '16, which, as discussed hereinafter, may employ conventional front surface mirror techniques to steer the beam through small angles so that it traces letters or symbols, again under the control of a signal from character generator 23. The modulated and steered beam is now positioned or stepped either horizontally for letter spacing or vertically for line spacing by a spacing deflector 17. As also discussed hereinafter, spacing defiector 17, which may be a simple mirror system, is controlled by a word, column and page layout control 26. The modulated, steered, and deflected laser beam then strikes and etches a plate blank 18 with the desired text as determined by the control signals from the character generator 23 and the word, column and page layout control 26. It should be noted at this point that the plate blank 18 is prepared directly in accordance with the desired text thus eliminating the disadvantages of the prior art photographic and photoengraving methods discussed heretofore.

Patented Apr. 14, 197i) Also stored in memory 21 are instructions for deflecting a laser beam to trace characters and to space letters, words, lines and columns. Upon command, computer 22 assembles spacing instructions as well as character instructions in accordance with the temporarily stored data. An editing control 29 may also be connected to computer 22 along with a display device 28 to allow editing of the temporarily stored text. With this feature, the text may be displayed, read, corrected, and justified before any work is done on actual plates. Furthermore, since the editing is done electronically rather than by hand,

the time saving can be immense. The outputs of the computer are fed to character generator 23 and word, column and page layout control 26, both of which convert the computer instructions into analog voltage and current signals that control the intensitymodulator 13, the small angle steerer 16 and the spacing deflector 17.

One such control system 25 is disclosed in the aforementioned Patent No. 3,422,419 by M. V. Mathews and H. S. McDonald. In that system, a digital memory unit such as unit 21 permanently stores instructions for defleeting a cathode ray tube beam to trace several individual elementary patterns and for varying their orientation. A computer upon command assembles and gates out of storage the correct sequence of such instructions to trace each character, and circuits similar to those which may be employed for character generator 23 transform the instructions into signals to drive a cathode ray tube display.

Since the laser beam does considerable work in etching away plate material, a high energy continuous wave laser operating in the infra-red region is most advantageous. The higher the beam energy, the faster the material can be vaporized and the faster the writing. One such laser which might be employed as the laser 11 of FIG. 1 is disclosed by C. K. N. Patel in copending application Ser. No. 495,884 filed Oct. 14, 1965. Patels laser uses a mixture of gases including typically carbon dioxide, nitrogen and helium and has put out over 100 watts continuous at 10.6 microns wavelength.

With laser 11 operating at 10.6 microns wavelength, a gallium arsenide ,electro-optic modulator whose transmittance varies with applied voltage may be used as modulator 13. The laser beam is directed through the modulator so that the intensity of the emerging beam varies in accordance with an intensity signal from character generator 23. The beam may thereby. be effectively shut off to prevent it from striking unwanted areas of the plate blank. A suitable modulator is described in the RCA Review, September 1966, volume XXVII, No. 3 at pages 323-335. According to author, T. E. Walsh, 70% modulation has been obtained wavelength.

At the present time, the function of small angle steerer 16 of deflecting the beam to trace out each character can be fulfilled using front surface mirror techniques which are old in the art. One mirror, with high reflectivity at the laser wavelength may be mounted on a vertical pivot and driven by a dArsonval meter movement which is in turn responsive to a horizontal deflection signal from character generator 23 to provide horizontal deflection. A similar mirror, mounted on a horizontal pivot and driven by a dArsonval movement responsive to a vertical deflection signal from character generator 23 will provide vertical deflection.

Spacing deflector 17, since it performs a very similar function, may be a mirror device similar to small angle steerer 16. Alternatively, however, since the stepping speeds required for thermal writing are relatively slow the spacing deflector may operate on the plate blank 18 at 10.6 microns rather than the laser beam. Any electro-mechanical systemfor stepping the plate blank horizontally for letter spacing and vertically for line spacing will suffice. Such systems are conventional in the electrical typewriter art to move the carriage and to advance the roll.

Plate blank 18 may be made in any shape or form convenient to the printing press in which it is to be used. Its surface, however, should be smooth and made of some material that is hard enough to stand the wear of printing, yet is easily vaporized locally. A fusible metal or thermoplastic high in infra-red absorption is particularly useful. If the surface material is of the thickness desired for type depth, and it is backed up with harder material of higher melting point, the laser beam can quickly etch away the areas of surface material it strikes right down to the backing material. The beam may be directed to etch away the areas which transfer ink, thereby recessing the letters into the plate for intaglio printing; alternatively, the beam may be directed to etch away the areas which do not transfer ink, thereby leaving I the text raised for letter press printing.

The present invention may also be practiced to advantage making use'of the photographic processes conventionally employed in making plates. The high energy of the laser beam allows extremely high Writing rates and the ability to focus the beam to a small spot provides excellent resolution. In such a photographic process, the surface of plate blank 18 is treated by any of the well known conventional methods to be sensitive to light. Wherever laser beam 12 strikes, the surface is exposed. A physical or chemical change occurs which differentiates between exposed and unexposed areas and further processing causes the exposed areas alone to print. Such finish processing could include any ofthe known methods from photoengraving of metal plates to the electrostatic process of Xerox. In a particularly useful process, the plate blank 18 may be coated with a substantial thickness of a photo-polymer. Upon exposure to light, the coating polymerizes into a hard plastic. After laser beam 12 has written on the plate blank, therefore, the unexposed photo-polymer may be washed away, leaving the exposed areas in relief as letter press print. One such photo-polymer is Dycril, a'registered trademark of the E. I. du Pont de Nemours Co.

Very little power is required to expose light sensitized surfaces for wavelengths below a threshold of about 1 micron. Consequently, almost any known continuous wave laser operative at a Wavelength below 1 micron can be used to practice the'invention by a photographic process, with wavelengths below .6 micron being most useful.

The use of such a shorter wavelength, furthermore, can be' very helpful in allowing alternative deflection and modulating techniques. In US. Patent No. 3,413,568 issued Nov. 26, 1968 to E. I. Gordon, E. F. Labuda and R. C. Miller, a technique is shown for providing high output from a typical argon ion laser which would be quite satisfactory.

For modulating and steering laser beams of wavelengths in the visible range, such as that produced by the aforenoted argon ion laser, devices employing electro-optic crystals may be used. These are, of course, controllable much faster than the mirror devices. In US. Patent No. 3,413,476 issued Nov. 26, 1968, E. I. Gordon teaches a technique for building intensity modulator 13 and small angle steerer 16. According to Gordons invention, a microwave modulating signal is propagated along a waveguide filled with an electro-optic material such as KTN ('potassium-tantalate-niobate). The laser beam is formed by lenses or prisms into an elliptical cross section, the major axis of which lies parallel to the Waveguide axis. The beam is then directed through the electro-optic material via elongated ports in the narrow faces of the waveguide. A portion of the beam energy is thereby deflected by an angle dependent upon the frequency of the modulating signal and the portion of energy so deflected depends upon the amplitude of the modulating signal. The emerging energy is therefore split into two beams, one deflected and one not.

For our small angle steerer two such waveguides may be used. After the beam has been deflected by one waveguide, it is reformed by lenses into a circular cross section, and then into an ellipse whose major axis is at right 'angles to that of the original ellipse and waveguide. The

beam then passes'through a second waveguide similar and at right angles tothe first and the deflected portion is reformed to circular cross section. The microwave signal propagated along the first waveguide may be frequency modulated with a horizontal steering signal and its amplitude adjusted for maximum energy in the deflected beam. The microwave signal propagated along the second waveguide may be frequency modulated with a vertical steering signal and amplitude modulated with a beam intensity signal; The emerging deflected beam will then be deflected to accomplish both horizontal and vertical small angle steering and modulated in intensity.

beam is deflected linearly along line 47 the width of the As discussed'heretofore, coil driven mirrors may be.

employed to accomplish spacing between letters, words, columns and lines, or plate blank 18 may be shifted as in the thermal systems.

The principles of the invention can also be used in making plates for reproducing pictorial matter or for copyingpreviously printed matter according to the system diagrammed in FIG. 2. As in the previous embodiment, a laser 11 produces a beam of energy 12 which is varied in intensity by a modulator 13, deflected both horizontally and vertically by a pair of cell deflectors and 56 as discussed hereinafter, stepped through larger deflections by a pair of step deflectors 57 and 58, and focused to write upon a plate blank 18. Also as in the previous embodiment, either a high intensity thermal etching system or a photographic system may be employed.

In the embodiment of FIG. 2 a conventional television camera 31 scans'a display to becopied 32 and produces a signal 33, which corresponds to the brightness of the original 32 at the instantaneous scan point. Signal 33, with any necessary amplification, is used to drive intensity modulator 13. Of course, as in all television systerns, the scan of the camera must be exactly synchronized with that of the display. Consequently, a sync gen- .erator 34 provides synchronizing signals for both the camera deflecting circuits and the laser beam deflecting circuits. While the invention may be practiced with single horizontal and vertical deflection circuits for both camera and laser beam, a dual deflection system, that is, one in which there are two horizontal deflectors and two vertical deflectors for the laser beam and a like number for the camera, can be advantageous; Mirror deflectors are relatively slow; electro-optic deflectors are very fast, but the angle through which they can deflect a laser beam is limited. The longer the path through the electro-optic crystal, the larger the deflection angle, but the greater the attenuation of the laser beam. A system, therefore, in which the beam is quickly deflected through small angles to cover an'area, and then stepped more slowly to a new area can be fast and have lower losses. Thus, horizontal and vertical cell deflectors 55 and 56 respectively are driven by a pair of continuous cell deflection circuits 37 which quickly deflect the beam through small angles, and horizontal and vertical step deflectors 57 and 58 are driven by a pair of step deflection circuits 39 and 41 respectively, which step the beam through larger angles. Of course, the camera must have a pair of similar continuous deflection circuits 36 and a pair of step deflection circuits 38. Sync generator 34 provides sync pulses which are fed simultaneously to camera continuous deflection circuits 36 and laser beam continuous deflection circuits 37 and additional sync pulses fed simultaneously to camera step deflection circuits 38 and beam step deflection circuits 39 and 41.

single cell block to point 48. The beam is then quickly retraced to point 49 to linearly scan line 51. The process continues until the whole cell has been covered. When the beam reaches the bottom of the cell at. point 52, it is quickly deflected to start scanning an adjacent cell at point 53. When one line of cells has been scanned in this manner, the beam is quickly deflected to start another. With available deflection systems each cell could easily contain scan lines and a matrix of 100 x 100 Cells is not unreasonable.

Horizontal cell deflector 55 and vertical cell deflector 56 may therefore be either electro-optical crystals or driven mirrors, and their driving signals, derived from the continuous deflection circuits 37 are of a sawtooth shape just as in a television set. Step deflectors 57 and 58, on the other hand may be driven by staircase type signals from deflection circuits 39 and 40 and may -deflect the beam by mirrors or move the plate blank 18.

Plates may be made using this facsimile embodiment with either a thermal or a photographic process. The thermal process is particularly suited to making intaglio plates, where the printing areas are recessed into the plates. The amount of ink available for any given spot is determined by the depth of the recess. Hence the blackness of a printed spot depends upon the intensity of the laser beam when it traced that spot in making the plate.

Letter press types of plates can also be readily made by this facsimile embodiment with a thermal process. The signal into intensity modulator 13 is merely inverted by a single stage of amplification; the laser beam in 'scanning the plate blank removes surface material by vaporization from all areas except those which are to transfer ink. If the intensity signal is amplified and clipped so that it has only two levels, the resulting printing areas will be raised a uniform amount above the etched out areas.

Finally, the control portion of the facsimile system of FIG. 2 may be added to the embodiment of FIG. 1 as shown in the block diagram of FIG. 4 to allow production of plates for printing illustrated text. The functions of each of the elements is as previously explained in con nection with FIG. 1. In addition, character generator 23 performs the added duty of generating cell scanning signals, and word, column and page layout control 26 provides inter-cell stepping signals'upon appropriate instructions from computer 22. The camera deflection circuits, not separately shown, are included within the camera, and synchronizing signals are generated by computer 22. Entire sheets of illustrated text may therefore be assembled by computer 22, displayed on display 28 andeditedand arranged by editing control 29. Laser 11 may then be energized to quickly produce a plate capable of printing the sheet.

The above-described arrangement is illustrative of the principles of the invention. Other embodiments may be devised by those skilled in the art without departing from the spirit and scope of the invention.

We claim: 1. Apparatus for forming plates having an inking surface which reproduces print' and the graphic arts by the transfer of ink from selected areas comprising a laser that tween said continuous deflection means and said plate blank surface-for deflecting said raster in steps equal in length to the dimensions of said raster to provide laser beam tracing over said plate blank surface, and modulating means positioned between said laser and sa'id continuous deflection means for varying the intensity of said beam to permanently alter predetermined areas of said plate blank surface corresponding to the information which it is desired to reproduce.

2. Apparatus as in claim 1 wherein said continuous deflection means comprises an electro optic beam steerer and said step deflection means comprises coil driven mirrors.

References Cited UNITED STATES PATENTS ROBERT L. GRIFFIN, Primary Examiner 10 H. W. BRITTON, Assistant Examiner US. Cl. X.R.

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