US 3736459 A
A character generator which is capable of producing a large and arbitrary character set. The character set is stored as a set of holograms on a hologram plate. The character that is desired to be generated is selected by the hologram selector which produces a beam of energy which illuminates the hologram of the desired character producing a reconstructed image of the desired character. The reconstructed image illuminates a photocathode internal to a vacuum envelope. The photocathode produces an electron image within the vacuum envelope which is then amplified, focused and positioned in the appropriate display position on a phosphor screen thus allowing an externally stored character to be reconstructed and displayed within the vacuum envelope. The provision is also made for changing the size of said character on display.
Description (OCR text may contain errors)
United States Patent  Harris 51 May 29, 1973  Inventor: Thomas J. Harris, Poughkeepsie,
 Assignee: International Business Machines Corporation, Armonk, N.Y.
22 Filed: Apr. 19,1971
211 Appl. No.: 134,943
 US. Cl. ..3l5/1l, 315/12, 315/31 R,
340/l5.5 VD  Int. Cl ..H0lj 31/48  Field of Search ..315/l0,11, 12,15,
315/17, 31 R; 350/35; 340/155 VD  References Cited UNITED STATES PATENTS 3,278,683 10/1966 3,417,242 12/1968 3,504,609 4/1970 3,109,957 1l/l963 3,128,406 4/1964 3,501,673 3/1970 3,617,801 1l/l97l OTHER PUBLICATIONS Hologram Replication, McDonnell, IBM Tech. Disc. Bull., Vol. 11, No. 1,June 1968, p. 15.
Cable TV Data Service, Leonard et al., IBM Tech. Disc. Bulletin, V01. 12, No. 7, Dec. 1969, pp. 1064-1066.
Primary Examiner-Carl D. Quarforth Assistant Examiner -P. A. Nelson Attorney-Hamlin and Jancin and M. H. Klitzman  ABSTRACT A character generator which is capable of producing a large and arbitrary character set. The character set is stored as a set of holograms on a hologram plate. The character that is desired to be generated is selected by the hologram selector which produces a beam of energy which illuminates the hologram of the desired character producing a reconstructed image of the desired character. The reconstructed image illuminates a photocathode internal to a vacuum envelope. The photocathode produces an electron image within the vacuum envelope which is then amplified, focused and positioned in the appropriate display position on a phosphor screen thus allowing an externally stored character to be reconstructed and displayed within the vacuum envelope. The provision is also made for changing the size of said character on display.
4 Claims, 2 Drawing Figures CONTROL t 26 DEFLECTION comm] Patented May 29, 1973 2 Sheets-Sheet 1 2a /'DEFLECTION CONTROL POWER SUPPLY CONTROL FIG. 1
INVENTOR THOMAS J. HARRIS ATTORNEY LASER ACTIVATED HOLOGRAPHIC DATA SELECTION AND DISPLAY APPARATUS BACKGROUND OF THE INVENTION The present invention relates generally to character generation systems and more particularly to character generation systems for use in display and printing applications.
The present invention has particular application to character generating systems of the kind in which a symbol or character is presented at a selected location on the face of a vacuum tube for printing or display purposes. Many techniques have been devised in these systems to form the required symbols or characters. Some systems have created the characters by establishing a matrix of dots and forming the characters from the dots of the matrix while other systems have used a beam of energy to illuminate an existing copy of the character to create the desired display character. This latter form of character generation is the type to which the present invention is drawn.
Prior art systems have provided a set of characters or symbols by cutting openings in a metal plate in the form of the characters or symbols. The plate was then inserted into a vacuum tube between the source of a beam of energy and the face of the tube. The beam of energy was then selectively passed through the desired opening in the metal plate thus, forming a shaped energy beam which was then directed to the desired location on the face of the tube. Although this system worked, it possessed several inherent shortcomings. For example, since the metal plate was installed within the vacuum chamber it was a permanent installation. The user of the system was, therefore, restricted to the use of the characters contained on the metal plate. Additionally, the installation of the metal plate within the vacuumtube limited the size of the metal plate, and therefore, the number of characters that could be represented on the metal plate, to the physical dimensions of the tube. Since increasing the diameter of the vacuum envelope neck is expensive and impractical, character systems which required a large number of characters were, therefore, impractical to represent. Additionally, the technique of forming the characters by cutting an opening in the metal plate did not provide characters of very high resolution. Also since the metal plate was located between the beam source and the vacuum tube face, in order to cause the electron beam to pass through a desired character on the metal plate it was normally necessary to deflect the beam off its primary axes in order to pass the beam through the character. A second deflection of the beam was necessary after it had been passed through the desired character in order to place it at the desired character XY position on the target. This second deflection was complicated since in addition to placing the shaped beam at the desired XY position on the target it additionally was required to correct for the off axes position of the selected character caused by passing it through the selected character on the metal plate. The second deflection caused by the beam off axes position greatly increased the control circuitry required utilizing this prior art technique. A final shortcoming of this prior art system was that in order to have different sized characters, different sized characters had to be cut out of the metal plate. No provision was made for varying the size of an existing character or symbol.
It is, therefore, an object of this invention to provide improved character generation.
It is another object of the present invention to provide character generation which allows the use of a large and arbitrary character set.
A further object of the present invention is to provide character generation which provides for generation of a shaped electron beam which is transmitted on axes within the vacuum tube.
A still further object of the present invention is to provide improved character generation which allows for electronic changing of the character or symbol size.
SUMMARY The present invention accomplishes the above objects by providing a character set that is stored as a set of holograms on a hologram plate. The character that is desired to be generated is selected by a hologram selector which produces a beam of energy that illuminates the desired hologram on the hologram plate. The reconstructed image from the hologram generates a character on a photocathode located in a vacuum tube. The photocathode produces an electron image within the vacuum tube which is in the shape of the desired character. This reconstructed shaped beam is then amplified and focused, on-axes, within the vacuum tube and positioned by standard deflection control circuitry to the appropriate desired display position on the face of the tube.
A feature then of the present invention resides in the use of an external set of characters which is easily changeable and the on-axes operation of the electron beam within the vacuum tube.
These and other objects, advantages and features of the present invention will become more readily apparent from the following specification when taken in conjunction with the drawings.
FIG. 1 shows a system embodying the present invention in its broadest form.
FIG. 2 shows an improved version of the system in FIG. 1 which allows the electronic changing of the character size and intensity on the target.
DESCRIPTION Referring to FIG. 1, hologram plate 14 stores the character set which consists of a plurality of holograms 13. The shape of the individual characters in each hologram 13 can be arbitrary, since the hologram is similar to a photograph of the actual character. Utilizing the technique of the present invention very large character sets can be stored, since the hologram plate 14 is located external to the vacuum envelope 16 and may be readily changed. For example, it is possible to have 128 X 128 l millimeter holograms on a 1% millimeter centers on a 6.4 X 6.4 inch hologram plate. In this case the hologram plate stores over 16,000 different characters. It is, therefore, obvious that with this large of a character set the character generator is attractive for use with languages such as Japanese which require a very large character set.
Selection of the desired hologram 13 is accomplished by hologram selector 10 which is controlled by control 12. Control 12 functions to cause the hologram selector 10 to select the appropriate character or hologram 13 on hologram plate 14. The hologram selector 10 can use any of a number of techniques such as X-Y galvanometers; rotating mirrors, array of lasers; digital and- /or analog electro optic light deflectors. In order to achieve maximum clarity of characters, a laser would probably be best suited. The reconstructed image produced by the selected hologram 13 illuminates photocathode 20. Photocathode 20 which is mounted within vacuum envelope 16 is a photo emissive surface which emits electrons with a pattern identical to that which is displayed upon it by the reconstructed hologram image. Therefore, photocathode 20 emits electrons within vacuum envelope 16 with a pattern identical to the character pattern reconstructed from the selected hologram 13. Since the reconstructed image from the selected hologram is directed to the center of photocathode 20 independent of position on hologram plate 14, it is formed centered on the photocathode 20 surface inside the vacuum envelope l6.
Coaxial cylinder 22, coaxial cylinder 24 and coaxial cylinder 26, are provided in the neck of vacuum envelope 16 to accelerate and focus the reconstructed shaped beam that is emitted from photocathode 20 within vacuum envelope 16. Power supply 18 provides the necessary power to activate coaxial cylinders 22, 24 and 26 as well as anode 34 of the vacuum envelope 16. Coaxial cylinders 22 and 24 form a first electrostatic lens. This lens provides acceleration to the electrons leaving photocathode 20 which have essentially zero velocity. The photocathode 20 surface is conducting and is electrically connected to the coaxial cylinder 22. The potential applied by power supply 18 to coaxial cylinder 24 is higher than the potential applied to coaxial cylinder 22 and the electrons emitted from photocathode 20 in response to the reconstructed hologram image are accelerated away from photocathode 20 so as to form an electron image of the photocathode image within coaxial cylinder 24. Coaxial cylinders 24 and 26 form a second electrostatic lens which is provided to further accelerate the energy beam. The potential on coaxial cylinder 26 is adjusted so that the electron image in coaxial cylinder 24 is imaged on the target at the front of the vacuum envelope 16 or the target 36. The target 36 can be a phosphorus coating, a matrix of conducting pins in a glass substrate, or any material which can be inserted into the vacuum envelope. The type of target 36 utilized will, of course, depend upon the application of the character generator. That is, whether the device is being utilized as a visual display device or as an electrostatic printer. The image within coaxial cylinder 24 will be smaller than the image on the photocathode 20, and the final image on the target will be smaller than the image within coaxial cylinder 24. The brightness of the image on the target will be several orders of magnitude brighter than the image on the photocathode 20 due to the reduction in image size and the acceleration of electrons through the two electrostatic lens. Vertical deflection plates 30 and horizontal deflection plates 32 provide a means to deflect the reconstructed shape beam to the desired X-Y position on target 36 in the vertical and horizontal plane, respectively. Deflection might be accomplished by electrostatic or magnetic deflection means in the normal manner well known to those skilled in the art. Control 12 which controls the selection of hologram 13 by hologram selector also controls the operation of the vertical deflection plate 30 and horizontal deflection plate 32.
The present invention makes possible the electronic changing of the size of the character on the target utilizing the embodiment shown in FIG. 2. FIG. 2 shows an embodiment of this invention which provides for the electronic changing of the character size on the target and a means for current amplification. In this embodiment the hologram selector 10, control 12, hologram l3, hologram plate 14, vacuum envelope 16, power supply 18, photocathode 20, coaxial cylinders 22, 24 and 26, deflection control 28, vertical deflection plate 30, horizontal deflection plate 32, anode 34, and target 36 perform essentially the same functions as that described above for the embodiment shown in FIG. 1. Additionally, this embodiment provides a zoom lens 37 which provides a means for varying and imaging the electron image from the photocathode 20 on the first dynode 40 of the current amplification structure independent of magnification. The zoom lens 37 controls the size of the image on the first dynode 40 by varying the potential on the various electrodes 39 (cylinders) in the zoom lens 37. Variable field control unit 38 which is controlled by control 12 provides the means to vary the potential on the various zoom lens electrodes 39. Image current amplification or intensification in order to improve the brightness of the character on the target, is performed by dynodes 40, 41, 43, 44 and 45. This is accomplished by imaging the electrons from the photocathode 20 onto the first dynode 40. The dynodes are thin screens which have the property of releasing secondary electrons from one side when bombarded by high energy electrons from the other. The screen consists of an aluminum oxide supporting film coated on the emitter side with a thin metal film on which is deposited a relatively wideband gap semiconductor having a low-electron affinity, which serves as the secondary emitter. Both potassium chloride and barium fluoride have been successfully used as the semiconductor. The primary electrons penetrate the aluminum oxide and the conducting film with small loss of energy, and their energy is absorbed in the semiconductor. This excites electrons in the material, some of which have sufficient energy to escape into the vacuum as secondary electrons. Magnetic focusing coil 42 provides a field which images the secondary electrons from one dynode to the next. In this manner the secondary image from first dynode 40 is imaged on the second dynode 41, which in turn is imaged on the third dynode 43, which in turn is imaged on fourth dynode 44, which in turn is imaged on last dynode 45. Using five cascaded dynodes, each with a current gain of 4 at 4,000 volts per dynode allows a current gain of close to 1,000 to be achieved. At 5,000 volts per stage the current gain per dynode stage is 7 and a cascaded five stage system would have a current gain of close to 20,000.
For the character generator shown in FIG. 2, the reconstructed holograph image can be large, for example, 3 inches in diameter. The subsequent reduction by the zoom lens 37 increases the current density in the shaped electron beam. The image on the dynodes 40, 41, 43, 44 and 45 in the current amplification section can be the full diameter of the dynodes, for example, 1 inch. This allows heat generated by the secondary emission to be distributed over a larger area of the dynodes. This is made possible since the characters are large and are all generated on-axes.
As in FIG. I, the electron image from the last dynode 45 in the current amplification or intensifier stage is imaged onto the target by the electrostatic lens formed by coaxial cylinders 22, 24 and 26. The image on the screen can be smaller than the image from the last dynode 45, providing additional current density gain. In addition, the increased electron velocities increase the effective image brightness.
OPERATION Referring now to FIG. 2, the operation of the character beam generator will be described. Control 12 pro vides the required signal to hologram selector to initiate the selection of the required character shown in hologram 13 on hologram plate 14. The character stored in hologram 13 is reconstructed on photocathode 20 in vacuum envelope 16. Photocathode 20 internally emits an electron pattern of the character stored by hologram 13 within the vacuum envelope 16. This shaped electron beam is reduced to the desired size by zoom lens 37 under the control of variable field control unit 38 which is in turn controlled by control 12. The zoom lens 37 directs the shaped electron beam onto first dynode 40 which emits secondary electrons based upon the image produced on it by zoom lens 37. The secondary electrons emitted from one dynode are imaged onto the next dynode by the field of the focusing coil 42. In this manner image intensification or amplification is accomplished. The shaped beam from the last dynode 45 is then accelerated and focused by coaxial cylinder 22, 24 and 26. The beam is then deflected in a vertical plane by vertical deflection plates 30 and in a horizontal deflection plane by horizontal deflection plates 32 to the desired X-Y position on target 36. Control of the deflection is accomplished by deflection control 28 under the control of control 12.
It should be noted that the zoom lens feature allows flexibility in the size of characters imaged on the target 36. For example, the storing of a single dot on a hologram 13 when used in the embodiment of the present invention shown in FIG. 2 allows the production of various size dots and widths of lines on the target 36 by controlling the size of the dot produced in the zoom lens 37 stage of the system.
While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those of skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
means external to said device, including a hologram matrix containing many individual characterrepresenting holograms in equal area sections thereof and laser projection apparatus selectively operable to illuminate individual said holograms at different discrete angles causing corresponding different character image illumination to impinge on said photocathode and be entirely imaged on the predetermined area of said photocathode; and by successive operation permit the formation of a composite image of multiple characters on said screen means external to said device for electrically controlling said beam-controlling means in coordination with the operation of said laser projection apparatus to form said composite image of multiple characters on said device viewing screen, said displays subject to comprising legible page information including character components of variable size and intensification.
2. Apparatus according to claim 1, wherein said hologram matrix is configured to be replaceable as a module.
3. Apparatus according to claim 2 wherein said laser projection apparatus is configured to interact with hologram matrices of variable area dimensions containing variable numbers of individual character holograms.
4. Apparatus according to claim 1 wherein said device comprises an evacuated envelope containing said path and the deflection space intercepted by said