US 3626084 A
Description (OCR text may contain errors)
United States Patent lnventors Robert J. Wohl San Jose; Frank A. Hawn, Los Gatos; Harold C. Medley, Los Gatos, all of Calif.
Appl. No. 48,862
Filed June 12, 1970 Patented Dec. 7, 1971 Assignee International Business Machines Corporation Annonk, N.Y.
Continuation of application Ser. No. 683,292, Nov. 15, 1967, now abandoned. This application June 12, 1970, Ser. No. 48,862
DEFORMOGRAPHIC STORAGE DISPLAY TUBE 17 Claims, 5 Drawing Figs.
US. Cl l78/7.5 D, 350/161 Int. Cl H04n 5/74 Field of Search 178/7.5 D, 7.3 D, 7.5 E; 350/161 DEFORIOGRAPHIC DIELECTRIC  Reierences Cited UNITED STATES PATENTS 2,896,507 7/1959 Mast et al. 350/161 R 2,943,147 6/1960 Glenn,Jr. 350/161 R 2,985,866 5/1961 Norton 350/161 R 2,335,659 ll/l943 Fraenckel et a1. 178/7.5 2,391,451 12/1945 Fischer 178/7.87 2,605,353 7/1952 Fischer..... 178/1 7.5 2,957,942 10/1960 Glenn, Jr. 178/7.5 3,016,417 l/l962 Mast et al. l78/7.5 3,538,251 11/1970 Gear l78/7.87 FOREIGN PATENTS 1,084,624 9/1967 Great Britain l78/7.5 D
Primary E.raminerRichard Murray Assistant Examiner-Alfred H. Eddleman Att0rneyFraser and Bogucki ABSTRACT: A display tube is provided in which a dielectric target is charged by an information modulated electron beam, and the resulting electrostatic field between the target and a conductive ground plane deforms a dielectric film. The film is located in a separate chamber of the tube at the side of the target opposite the electron beam generating equipment. The film deformations behave as point light valves, and a visible image of the information contained therein is provided by transmissive or reflective optical systems.
SWEEP VOLTAGE GENERATOR lllFORIATlOA SIGNAL CIRCUITS CIRCUITS PATENTED DEC 7197:
SHEET 2 DE 2 TUBE FACEPLATE I2 CDNDUCTIVE CR PLANE 38 DUND DEFORI IDCRAPHIC FIL II 36 DIELECTRIC IIIRRDR 94 DIELECTRIC TARGET 22 DEFORIMTOCRAPHIC FILM 36 MIRROR 94 DIELECTRIC TARGET 22 INVENTURS BY HAROLD c. MEDLEY ATT RNEYS ,1 DIELECTRIC DEFORMOGRAPIIIC STORAGE DISPLAY TUBE CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation of Ser. No. 683,292, Robert J. Wohl et al. Deformographic Storage Display Tube, filed Nov. 15, 1967 and now abandoned.
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention pertains to arrangements for converting an electrical information bearing signal into a visible image, and more particularly to display tubes in which an image is formed in accordance with charges imparted by an information modulated electron beam.
2. Description of the Prior Art Display tubes as known today developed from experimentation with cathode-ray tubes. In the cathode-ray tube, an image corresponding to an information modulated electron beam is typically provided by directing the electron beam onto a fluorescent screen or coating on the inside of the face plate of the tube. The persistence of the image for a given application of the electron beam is relatively short, and maintenance of a particular image for long periods of time is normally possible only by the continuous scanning of the fluorescent screen or coating by the electron beam. Where the fluorescent screen or coating is confined with the tube, the size of the image which may be provided is directly dependent upon tube dimensions. Projection-type tubes and other projection systems are known, but these suffer from insufficient light output or inability to modify the image by high speed electronic means.
It has been found that the persistence of an image for a given application of the electron beam may be improved by replacing the fluorescent screen or coating within a cathoderay tube by a nonconductive or dielectric material, the surface of which is exposed to the electron beam. A charge pattern is produced upon the dielectric material, and a temporary or permanent image is then provided directly from the charge itself, such as by depositing certain powders or colored toner particles on the dielectric material, as shown for example in U.S. Pat. No. 3,109,062. Such an arrangement, which is commonly referred to as the electrostatic storage display tube, has been found to provide an image of reasonably good resolution, contrast and brightness, which image persists indefinitely without the need for continuous scanning of the dielectric material by the electron beam. Due to rather lengthy develop and erase times involved in such tubes, their use has been confined primarily to long-term storage applications. Although projection-type systems have been devised, improvement is desirable with respect to reliability and tube life where such tubes are to be used for general applications. In particular it would be advantageous for many situations to substantially increase the rates at which images may be changed or modified, which rates are now substantially limited by the mechanical systems that are used.
Efforts to provide large visible images independent of tube size led to the discovery that certain liquid and solid materials may be deformed in accordance with a modulated electron beam, the resulting deformations behaving as point-by-point light valves to control the passage of light from an external source to a large external projection screen using an appropriate optical system such as that of the schlieren type. The deformations of the liquid or solid materials may be provided by electrostatic, temperature, photoconductive or other means in accordance with the electron beam. Typical examples of photoconductive deformation media are provided by U.S. Pat. Nos. 2,892,380 and 3,274,565. Typical examples of thermal or temperature deformation media are provided by U.S. Pat. Nos. 3,072,742 and 3,196,009. While such arrangements permit projection of relatively large visible images, they are of limited versatility, particularly because their speeds of operation are confined within a limited range. Because of the relatively long develop and erase times involved in systems such as those of the photoconductive or temperature type,
such arrangements are generally suitable only for low speed and long-term storage operations. In the well-known thermoplastic recording, for example, a charged member is developed by exposure to heat followed by freezing, a process which requires considerable time. Erasure is equally involved and time consuming. Relatively high speeds of operation in combination with relatively large visible images are provided by arrangements which electrostatically charge a nonconductive or dielectric liquid or solid material, such as in the wellknown Eidophor tubes. Typical examples of such arrangements are shown in U.S. Pat. Nos. 2,391,450, 2,510,846, 2,919,302, 3,l64,67l. Such tubes have very fast develop and erase times but are not generally practical for long-term storage.
All of the prior art tubes thus far discussed suffer from one or more of a number of distinct disadvantages aside from those already mentioned. In such tubes, the liquid or solid member which is responsible for providing the image is itself directly exposed to the electron beam. As the beam strikes the exposed member, a molecular breakdown occurs and gases are produced which pose a serious contamination problem within the tube. A continuously operating vacuum pump coupled to the tube aids in the removal of a portion of the gases. Some gases are, however, deposited on the various internal tube components, necessitating that the tube periodically dismantled and cleaned. Because of such vapor deposition, a tungsten or filament type cathode must be used instead of the more desirable oxide coated cathode, and such cathode must be periodically replaced. The chargeable member experiences a change in its properties during prolonged use of the tube, and some materials eventually undergo disassociation or polymerization. During such deterioration, the member typically loses some or all of its transparency, thereby decreasing image brightness. Its viscosity is also usually increased, requiring increasingly longer developing times. Residual electrostatic charges on the member degrade the image and may require separate apparatus to minimize their effects. In the Eidophor tube, for example, a blade is one expedient used to smooth the surface of the generally liquid chargeable member and to remove residual electrostatic charges therefrom.
Ideally, then, it is preferred that display tubes be sufficiently versatile to provide a superior image throughout a wide range of operating speeds including substantially indefinite storage at one extreme and relatively high speeds such as those on the order of television speeds or greater at the other extreme. Relatively high resolution, brightness and contrast should be provided at substantially all speeds of operation, and the tube and image provided thereby should not be subject to deterioration due to factors such as contamination, beam irradiation, vapor deposition, and residual electrostatic charges.
BRIEF DESCRIPTION OF THE INVENTION In brief, the present invention provides a deformographic storage display tube in which a target of electrically nonconductive material mounted within a sealed envelope divides the envelope interior into two separate and isolated chambers hermetically sealed from one another. Conventional electron beam generating apparatus is located within one of the chambers of the tube to direct an electron beam onto an extended surface of the target, such beam being modulated in accordance with an electrical information bearing signal. The electrostatic charge deposited on the target by the electron beam results in an electrostatic field between the target and a conductive ground plane spaced apart from the side of the target opposite the electron beam generating apparatus. A deformable medium or deformographic film located between the target and the conductive ground plane and which is preferably generally coextensive with the target deforms under the forces of the electrostatic field to provide an image corresponding to he infonnation within the electrical information bearing signal. The image may be projected as a visible image of any desirable size by an appropriate optical system such as a schlieren type system.
In accordance with one particular aspect of the invention, storage times ranging from the long times necessary for substantially indefinite persistence to the relatively short times necessary for high speed operation, such as at television speeds or greater, are provided by a single tube arrangement. High speed operation is enhanced by the elimination of timeconsuming image development normally required in conventional electrostatic storage display tubes, photoconductive tubes and thermoplastic tubes. The writing, development and display times are relatively small and are limited only by the latency period during which the deformographic film undergoes deformation. The latency period is determined in part by the viscosity of the material used as the film. Erase times are equally short, and are determined primarily by the time required for the film to relax to a substantially plane state. The relaxation time is determined in part by the elastic modulus of .the material used as the film. The long-term storage capability of the tube is limited only by the eventual relaxation of the deformations within the film, which relaxations are substantially deterred by isolating the film from the electron beam equipment.
In accordance with further particular aspects of the invention, isolation of the deformographic film from the electron beam equipment minimizes or substantially eliminates problems with respect to contamination, vapor deposition, beam irradiation, and deterioration and eventual failure of the deforming material. Tube life is substantially lengthened.
In accordance with further aspects of the invention, the deformographic film comprises a deformable member of dielectric material, the particular material used and the thickness thereof being chosen in accordance with known properties of the material, such as its viscosity and elastic modulus, to provide rapid deformations which will persist for any desired period of time. The dielectric target may comprise a single thickness of material so long as the material is sufficiently nonconductive. Where it is desired to use a material of relatively high conductivity in the target for reasons such as superior optical properties, a layer of lower conductivity material deposited or otherwise formed on the electron beam side of the target compensates for such high conductivity to provide effective charge storage and deformation.
In accordance with further aspects of the invention, the deformations within the deformographic film may be converted into a visible image, using either transmissive or reflective optics. Where transmissive optics are used, the conductive ground plane, deformographic film and target are made of highly translucent or substantially transparent materials, and light from a source is directed through such materials for projection of the desired image on an external screen. Where reflective optics are used, a dielectric mirror is disposed between the target and deformographic film, and light directed from a source onto the deformographic film is reflected by the mirror.
BRIEF DESCRIPTION OF THE DRAWINGS Objects and advantages other than those indicated above will be apparent from the following description, when read in connection with the accompanying drawings, in which:
FIG. 1 is a perspective view, partly broken away, illustrating a deformographic storage display tube in accordance with the present invention;
FIG. 2 is a sectional enlarged view of one particular target and film arrangement in accordance with the invention;
FIG. 3 is a sectional enlarged view of an alternative target and film arrangement in accordance with the invention;
FIG. 4 is a perspective view, partly broken away, of a different arrangement of a deformographic storage display tube in accordance with the invention; and
FIG. 5 is a sectional enlarged view of the target and film arrangement used in the tube arrangement of FIG. 4.
DETAILED DESCRIPTION FIG. 1 illustrates one particular arrangement of a deformographic storage display tube in accordance with the present invention. It should be understood, however, that the particular tube arrangement of FIG. 1 is provided by way of example only, and other appropriate electrostatic display tube configurations may be used within the scope of the invention.
The display tube of FIG. 1 includes an evacuated envelope 10 of a suitable material, such as glass or metal, and of any suitable shape, such as that of a conventional cathode-ray tube having an electron gun and focusing system at one end and an enlarged transparent face plate 12 at the other end. In the arrangement of FIG. 1, individual write and erase guns are disposed in separate necks extending from the envelope 10. The write gun 14 includes a cathode 16 and a control grid 18 to which signals are applied to modulate the electron beam intensity in conventional fashion. The modulating input signals may be derived from any suitable source, such as from video information signal circuits 20. The modulated electron beam is scanned in raster fashion across the surface of a dielectric target 22 by deflection means, such as a deflection yoke 24 disposed around the neck of the envelope 10, and controlled by sweep voltage generator 26. Although a video-type scanning system is shown, selective scanning or other displays may alternatively be generated by digital-type circuits, by character beam-type tubes or by any other circuits appropriate for a particular application.
An erase gun 28 operated by erase control circuits 30 is utilized for erasure of the electrostatic charge distribution pattern on the writing side of the target 22. As shown in FIG. 1, the erase gun 28 is mounted in a separate neck of the envelope l0 and directs a dispersed high intensity beam toward the target surface. Details of the beam focusing and accelerating system have not been shown because they may assume any of a number of conventional forms. The erase gun 28 is operated at sufficient energy levels to provide the accelerating voltages needed to establish a secondary emission ratio greater than unity at the dielectric target 22. As is well known, the secondary emission ratio of many insulating materials becomes greater than unity when bombarded by an electron beam having an accelerating potential in a given range. Within this accelerating potential range, every electron striking the target 22 causes more than one electron to be emitted by a secondary emission from the target, thereby driving the target potential less negative until equilibrium is reached.
As shown in FIG. 1, the dielectric target 22 is an extended surface member that is a generally planar or sheetlike member, although it will be recognized that the target may be flat, a portion of a sphere, or a more complex concave shape. The outer periphery of the target 22 is mounted to the inner wall of the envelope 10 in appropriate sealed fashion, as by peripheral seals and joinders (not shown in detail) to define two separate and independent chambers 32 and 34 within the envelope 10. The sealed chamber 32 on the one side of the dielectric target 22 may be referred to as the electron beam chamber, because it contains the write gun l4 and the erase gun 28 and associated components. The sealed chamber 34 on the other side of the dielectric target 22 from the chamber 32 extends between the target and the tube face plate 12, and may be termed a deformographic film chamber, since it contains a deformographic film 36. The film 36 is another generally planar or otherwise extended surface member of dielectric material disposed between the target 22 and the face plate 12.
In the arrangement of FIG. 1, the film 36 is illustrated as being mounted directly on the side of the target 22 opposite the electron beam chamber 32. A conductive reference potential plane is disposed adjacent the tube face plate 12 within the film chamber 34 to define appropriate means for establishing a reference potential within an extended surface area spaced apart from and substantially coextensive with the target 22. The reference potential plane here comprises a conductive ground plane 38, specifically a coating of transparent conductive material on the inner surface of the face plate 12. It has been found that a suitable ground plane 38 is provided by coating the inner surface of the tube face plate 12 with an electrically conductive film sold under the designation NESA by the Pittsburgh Plate Glass Company.
Referring to FIG. 2, which is an idealized representation of the target 22 and deformographic film 36 for the sake of simplicity, the charges imparted to the target by the electron beam establish an electrostatic field between the target and the conductive ground plane 38. It can be shown from published analyses that, with charges on the target 22, the presence of a field gradient (or a diverging field) causes localized deformations in the deformographic film, which deformations are approximately proportional to the square of the electrostatic field strength. The localized field strengths are, in turn, determined by the magnitudes of the localized charges placed upon the target 22. The charges on the target 22 are only symbolically depicted in FIG. 2, in order to aid in visualizing the manner in which electrons are accumulated on the beam side of the target. A large charge 50 placed upon the target 22 results in a relatively great deformation 52 of the film 36, while a small charge 54 on the target results in a relatively small deformation 56 of the film.
The deformations of the deformographic film 36 are translated into a visible image of desired size by a deformationresponsive optical system. Such optical system may be of the transmissive type wherein the light is caused to pass directly through the tube face plate 12, the conductive ground plane 34, the deformographic film 36 and the dielectric target 22. In transmissive-type systems, the dielectric target should comprise a material which is highly translucent or substantially transparent. Alternatively, reflective-type systems can be used, in which event light directed onto the deformographic film 36 is reflected by a dielectric mirror disposed between the film and the target 22. It should be noted that, depending upon particular needs for a given application the positions of the op tical and electron beam components may be interchanged without affecting the basic aspects ofthe system.
A transmissive optical system of the schlieren type is illustrated in FIG. 1. Light from a source 60, which in this instance comprises a projection lamp, is focused along an optical axis 62 by a condenser comprising a pair of lenses 64. The focused light passes through a schlieren aperture 66 which is shown as comprising a perforated metal screen and through the tube face plate 12 and conductive ground plane 38 to the deformographic film 36 where it is refracted and diffracted by the deformations therein. Light passing through the film 36, the target 22 and an optically clear window 68 in the envelope reaches a projection lens 70. The projection lens 70, which is preferably wide angle to compensate for the substantial inclination of the optical axis 62 relative to the central axis of the tube, directs the light through a schlieren stop 72 comprising a glass plate bearing the negative of the pattern on the schlieren aperture 66 to a screen 74, upon which is projected a visible image corresponding to the deformations within the film 36: Because the lens 70, the stop plate 72 and the screen 74 must be positioned so as not to interfere with the electron beam generating equipment within the chamber 32, the optical axis 62 must be inclined to the central axis of the tube, a typical angle of inclination being about 23. The deformations within the film 36 behave as point-by-point light valves, selectively controlling the passage of light between the aperture plate 66 and the projection lens 70. Further details of the schlieren system are well known to those skilled in the art and have been omitted here for brevity.
The tube may be of the permanently sealed type, or it may be of the demountable type. Tubes of the permanently sealed type are advantageous in some situations because of their superior ability to maintain a very high vacuum. Where it is necessary to change, adjust or replace the materials or components within the tube, however, it is usually advantageous to use a tube of the demountable type, and then to evacuate the interior. For simplicity of representation, and because such tubes are most used in practice, sealed constructions have been illustrated in the drawings.
Any appropriate well-known dielectric material can be used as the dielectric target 22 in both the sealed tube and the demountable tube. However, because of its strength, availability, ease of handling, low cost, and high resistivity, polyethylene terephthalate sold under the designation Mylar" is the preferred dielectric material used for the target 22 in demountable tubes. A Mylar membrane of approximately one-half to 1 mil thickness has proven to be satisfactory for use in such tubes. In sealed tubes, the dielectric target 22 is preferably made of an approximately one-fourth mil thick layer of mica because of its excellent thermal and optical properties. Since optical grade mica is relatively conductive, the charge pattern thereon dissipates too rapidly for some applications, necessitating that a thin insulating layer be placed on the side of the mica facing the electron gun. The insulating layer 80 comprises a thin layer of very highly resistive material such as silicon monoxide, silicon dioxide, magnesium oxide or magnesium fluoride, magnesium fluoride being preferred for most applications. The insulating layer 80 is evaporated or otherwise appropriately placed on the target surface. Such an arrangement is illustrated in FIG. 3.
The dielectric target 22 in either the sealed or the demountable tube may alternatively comprise a material sold under the designation Kapton or H Film" by E. I. Dupont de Nemours and Company. In the case of a sealed tube such film is bonded at its outer periphery using an appropriate adhesive such as that sold under the designation Plastilok 605 by B. F. Goodrich Company to provide a hermetic seal.
When generally planar members are used as the target 22, a certain amount of deflection defocusing may take place. For this reason, target materials having other than a planar configuration are sometimes desirable. One example of a target which substantially reduces or eliminates deflection defocusing comprises a glass film which is blown into a sphere such that a chordal section thereof is concave toward the electron beam.
In order to hermetically seal the deformographic film chamber 34 from the electron beam chamber 32, the dielectric target 22 which separates the two chambers is mounted to the inner wall of the envelope 10 in airtight fashion while also allowing for expansion and contraction.
Such a seal not only acts to isolate the deformographic film from the electron beam chamber, but also compensates for pressure differences. Whereas the electron beam chamber 32 is normally kept at a pressure of approximately 10 Torr. to provide a satisfactory environment for the electron beam generating and deflecting equipment, the deformographic film chamber 34 ordinarily need only be kept at a pressure of approximately 10 or 10' Torr. In one appropriate mounting arrangement for a sealed tube, the dielectric target 22 may be coupled at its outer periphery through a metal of intermediate expansion coefficient to a ring made of a metal which is sold under the designation Kovar." The Kovar ring is then heliarc welded or otherwise appropriately fastened and sealed to Kovar flanges on each side thereof. One Kovar flange may be sealed to the glass forming the electron beam chamber 32, while the second Kovar flange is sealed to the glass forming the deformographic film chamber 34.
The deformographic film 36 may generally comprise any highly translucent or substantially transparent dielectric material depending upon factors such as resolution, contrast and writing speed desired. The film should deform rapidly in response to stresses, the time of deformation being determined by the viscosity of the material used for the film. Upon removal of the charge, the film relaxes to a plane state principally due to surface tension forces and the elastic modules of the material. The writing, development and display are substantially simultaneous, the development and relaxation times being determined by the properties of the material used for the film. Materials which may be used for the deformographic film include oils, gels, plasticized resins, rubberlike films, and various thixotropic media. Oil is unsatisfactory for many applications, however, for various reasons. Thick films, for example cannot be used in other than a horizontal position, principally because gravity and surface tension variations result in a nonhomogenous layer. Polymeric media are generally preferred because of the longer storage times provided, faster erasure, high resolution, and no orientation limitation. Certain plasticized polymers, such as polyvinyl chloride-acetate, have proven to be generally unsatisfactory because of their relatively high conductivity. One film material which yields excellent results for practically all applications of the invention is silicone rubber. It has high optical transparency, high electrical resistivity, and high compliance. The imaginary or viscous component of the complex elastic modules of such material is reasonably low, providing good results.
An alternative arrangement of a deformographic storage display tube in which a reflective optical system is used is illustrated in FIG. 4. A front-surfaced parabolic mirror 90 is positioned in spaced-apart relation to the face plate 12 so as to illuminate the deformographic film 36 with parallel light derived from a source 92, imaged by relay lens 93 to a position approximately one focal length away from the mirror 90. The tube shown in FIG. 4 is a similar in construction to that of FIG. 1, except that a dielectric mirror 94 is interposed between the dielectric target 22 and the deformographic film 36 to reflect the light from one parabolic mirror 90 to a second similar parabolic mirror 96. The dielectric mirror 94 is an interference filter, and as best shown in FIG. 5 may comprise numerous alternating evaporated layers of two materials of differing dielectric constant. Appropriate materials for the alternating layers include magnesium oxide, magnesium fluoride, titanium dioxide, and calcium fluoride. The dielectric mirror, which is typically only a few microns thick, permits passage of the electrostatic field, but introduces constructive interference which results in reflectivity of about 99 percent of-all light over the entire visible spectrum.
In the absence of deformations in the film 36, the parallel light reaching the second parabolic mirror 96 is focused to an image of the light source 92 in the plane of a hole 98 in a planar front-surfaced mirror 100. In such case, all of the light passes through the hole 98 which serves as a schlieren stop, and no image appears on a screen 102. When deformations are present in the deformographic film 36, however, the light diffracted and refracted by the deformations is reflected onto the screen 102 as a focused image by the planar mirror 100, due to the lenslike action of the second parabolic mirror 96. Refracted light from the deformations which strikes the second parabolic mirror 96 is not a parallel beam, and it is therefore imaged at a point much further away than the focal point of the mirror. An alternative to the optical arrangement shown in FIG. 4 is to use a multiple aperture and a corresponding negative as the illuminating aperture and schlieren stop planes, respectively.
Although both transmissive optical systems such as that illustrated in FIG. 1 and reflective optic systems such as that illustrated in FIG. 4 provide good results, the reflective approach is generally preferred. In a reflective optical system, the optical axes are inclined at very small angles relative to the central axis of the tube. In most transmissive systems, however, the optical axis must be inclined at a substantial angle relative to the central axis of the tube, and a rear optical window within the tube is required, increasing the reflective losses of the system and the cost and difficulty of tube manufacture. In the reflective system, the simple folding of the optical path reduces the overall size of the system, and the light deflection sensitivity is substantially doubled by the double pass through the deformed film, although at some slight loss of resolution if the configuration is slightly off axis. The wide angle projection lens, which is required in order to maintain high resolution when operating at a substantial off-axis angle in the transmissive arrangement, is eliminated.
The isolation of the deformographic film 36 within a separate chamber apart from the electron beam chamber 32 indirectly provides for greatly enhanced resolution, brightness, contrast and writing speed by eliminating most, if not all, of the serious problems present in prior art devices. The persistence of the image may be varied between extremes to allow for optical large-screen television projection or longterm storage operations as desired. Since the dielectric target 22 and the deformographic film 36 comprise different materials, and particularly since the deformographic film is isolated from the electron beam equipment, substantially all of the problems present in most prior art arrangements are eliminated. Problems due to vapor deposition, beam irradiation and residual electrostatic charges are eliminated. Contamination of the various components and apparatus within the tube due to the deformographic material vapor is eliminated, obviating the necessity for periodically disman tling the tube to clean the components and the interior thereof. The deformographic film does not deteriorate due to contamination-type problems nor to beam bombardment.
a The isolation of the deformographic film also permits permanently sealed small-tube construction. Depending upon the type of material used for the deformographic film, such film will last indefinitely in most applications. A relatively long tube life is provided in contrast to many of the prior art deformographic display devices. Because there is no phosphor to fatigue and burn out, reliability and tube life are greater than in conventional cathode-ray projection tubes, and the cathode may be operated at very much lower voltage and current.
In operation, the write gun l4 deposits charges on the dielectric target 22 proportional to the brightness desired in the image. Writing may take place in a selective write mode or raster mode, as desired. The write gun is operated at a voltage far above the second crossover of the gun voltage versus secondary emission coefficient curve for the dielectric target, where secondary emission is negligible. The resulting 'defor mations which appear in the deformographic film 36 are es sentially proportional to the square of the field strength. Since the film deformations serve as point-by-point light vales, a bright display is obtained by means of an external light source, and high resultion is obtained along with high brightness. Contrast is enhanced because the schlieren optics are responsive to the slope of a deformation, rather than to its depth, and the present system provides sharp transitions between undeformed and deformed portions of the surfaces. The write gun electron beam power is of little consequence, and the voltage thereof need only be high enough to achieve the desired resolution. The beam current requirement may be expressed in terms of the charge deposition necessary to deform the film and is typically on the order of 10' to 10" coulombs per square centimeter of dielectric target surface area.
Write guns operating at voltage of approximately 10 to 15 kilovolts have been used successfully to provide a charge density on the order of l0 coulombs per square centimeter. Erase guns operated at approximately 1.6 kilovolts provide a beam current or approximately 1 milliampere, which is sufficient for flood-type erasure. Using such components, contrast ratios as great as 55 to l have been measured. Image brightness in excess of foot-lamberts has been provided, using a 1,000 -watt tungsten projection lamp as the light source, and image enlargement of several times its normal size. The total develop and erase times for an image have been measured at less than 100 milliseconds each, and storage times ranging from less than 100 milliseconds to 4 hours have been observed in a single tube. Some image deterioration will occur during prolonged storage, depending upon factors such as tube construction and the material used for the deformographic film. Such deterioration is due to a gradual decrease in the amplitude of the film deformations which results in decreased contrast or fading. The resolution, however, does not deteriorate, since there is no migration of the stored charges on the dielectric target.
The resolution which is obtainable is dependent, at least in part, on the write gun electron beam diameter and therefore the electron optics. Resolution has been observed equal to, and limited by, an electron beam measuring mils in diameter. This beam size was provided by a write gun comprising a simple triode having a hairpin-type tungsten filament approximately 5 mils in diameter. Greater resolution is of course possible by using a beam of smaller diameter. Using a silicone oil in earlier experiments, a 1,600 television line image was observed, indicating a spot size of 1.5 mils. It is thought, however, that the electrostatic field lines spread in a manner so as to establish an ultimate resolution limit at approximately 1 mil.
As previously pointed out, erasure may be performed by the separate erase gun 28 which directs a flood beam of electrons onto the surface of the dielectric target 22. Erasure may alternatively be performed by operating the write gun 14 at a lower potential than for writing. If the secondary emission ratio is greater than one, the charge on the dielectric target may be removed and collected by the Aquadag coating or a special collector ring within the tube. Selective erasure can be achieved in this way, providing the secondary emission ration exceeds one. Using the same deflection means employed for writing, but with different deflection constants, selected areas may be erased. The spot size is larger than during writing, so that an entire printed line, for example, may be erased with one sweep.
Variable persistence or variable storage time may be obtained by simultaneously operating the write gun l4 and the erase gun 28. The total beam current of the erase gun is much greater than that of the write gun. However, the current densi' ty of the write gun beam greatly exceeds that of the erase gun. The superior density prevails, and deformations occur in the deformographic film 36 even though the erase gun is simultaneously operated. However, such deformations disappear at a rate determined by the chosen erase beam current. For applications confined to one operation mode, such as television projection, a single short persistence is satisfactory, and for such applications a layer of intermediate resistivity material can be evaporated onto the write gun side of the dielectric target 22 (instead of the high resistivity layer shown in FIG. 3 which is appropriate where a long storage time is of prime importance). With the intermediate resistivity in effect, the image disappears in a time determined by the RC time constant. Thus, a single gun tube is feasible when only one screen persistence period is required.
While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope ofthe invention.
What is claimed is:
l. In an electron beam storage tube of the electrostatic charge, image projection type, a target system providing deformation patterns in accordance with an impinging electron beam comprising a nonconductive target having an extended surface disposed substantially normal to and in the path of the impinging electron beam, an electrostatically deformable solid member adjacent to and substantially coextensive with said target, and disposed on the opposite side of said target from the impinging electron beam, and means disposed adjacent said deformable solid member and on the opposite side thereof from said target for providing a reference potential therefor,
2. A target system in accordance with claim 1, further including a dielectric mirror disposed between said target and said deformable solid member, said dielectric mirror comprising at least two layers of material having different dielectric constants.
3. A target system in accordance with claim 1, wherein the outer periphery of said target is sealed to the tube providing a separate chamber isolated from the impinging electron beam and containing said deformable solid member and said reference potential means.
4. A target system in accordance with claim 1, wherein said target comprises a sheet of mica having an evaporated layer of magnesium fluoride on the side thereof adjacent the impinging electron beam.
5. A target system in accordance with claim 1, wherein said target is made of polyethylene terephthalate.
6. A target system in accordance with claim 1, wherein said deformable solid member is made of silicone rubber.
7. A deformographic storage display tube for forming an image from an electrical information bearing signal comprising an evacuated envelope, a target member of electrical insulating material mounted within the envelope, said target member dividing the interior of the envelope into separate electron beam and deformographic film chambers, a source of electrons within the electron beam chamber, means for controllable directing an electron beam from said source of electrons toward the target member to provide scanning of the target member, means disposed along the electron beam path for varying the beam intensity during scanning in accordance with the electrical information bear signal thereby to provide an electrostatic charge distribution pattern on the target surface, a conductive ground plane mounted within the deformographic film chamber and spaced apart relative to the target member, and a deformographic film disposed between the conductive ground plane and the target member within the deformographic film chamber and capable of deforming in accordance with the forces of an electrostatic field extending between the target member and the conductive ground plane.
8. A deformographic storage display tube in accordance with claim 7, wherein at least a portion of the envelope wall within the deformographic film chamber is transparent, the conductive ground plane includes a substantially transparent conductive coating on the inside surface of the transparent portion of the envelope wall, and the deformographic film is comprised ofan electrical insulating material.
9. A deformographic storage display tube in accordance with claim 8, wherein the target member and the deformographic film are made of substantially transparent material, and further including a source of light, means for focusing light from the source along an axis extending through the deformographic film and the target member, and means disposed on the opposite side of the deformographic film from the light source for focusing light passing through the deformographic film to form a visible image corresponding to deformations in the deformographic film.
10. A deformographic storage display tube in accordance with claim 9, wherein the means for focusing light from the source along an axis includes at least one lens and an aperture plate disposed between the at least one lens and the deformographic film, and wherein the means for focusing light passing through the deformographic film comprises a screen, at least one lens disposed between the screen and the deformographic film and a stop plate disposed between the at least one lens and the screen.
11, A deformographic storage display tube in accordance with claim 8, wherein the deformographic film is made of substantially transparent material, and further including a dielectric mirror disposed between the target member and the deformographic film, a source of light, means for focusing light from the source along an axis which extends through the deformographic film to the dielectric mirror, and means for focusing light reflected by the dielectric mirror to form a visible image corresponding to deformations in the deformographic film.
12. A deformographic storage display tube in accordance with claim 11, wherein the means for focusing light from the source along an axis includes a first parabolic mirror, and the means for focusing light reflected by the dielectric mirror comprises a screen, a second parabolic mirror disposed in an optical path between the dielectric mirror and the screen, and a planar mirror having an aperture therein and disposed in the optical path between the second parabolic mirror and the screen.
13. An arrangement for producing an image corresponding to an electrical information signal comprising means for generating an electron beam modulated in accordance with the electrical information signal, means defining a surface spaced apart from the generating means, means for maintaining a reference potential on the surface, a target member disposed between the surface and the generating means and electrostatically chargeable by the electron beam, and a deformable member disposed between the surface and the target member and capable of deformation according to electrostatic field forces therebetween.
14. An arrangement in accordance with claim 13, wherein the means defining a surface comprises an element of substantially transparent, conductive material.
15. A deformographic storage display tube comprising a sealed envelope, electron beam generating means located within the envelope, means extending inwardly from the inner wall of the envelope for dividing the interior of the envelope into first and second chambers sealed from one another, said means extending inwardly including a dielectric target of generally planar configuration, said electron beam generating means being located completely within the first chamber, a generally planar member being of solid dielectric material having a thickness less than 4 mils, said planar member being generally parallel to and disposed on the opposite side of the target from the electron beam generating means and in the second chamber, and means disposed adjacent said planar member on the opposite side thereof from said target and within the second chamber for providing a reference potential.
16. An electron beam storage tube of the electrostatic charge, image projection type, comprising a target assembly for providing deformation patterns in accordance with an impinging electron beam, including a nonconductive target member having an extended surface disposed substantially normal to and in the path of the impinging electron beam, means disposed adjacent to and substantially coextensive with said target member and on the opposite side thereof from said impinging electron beam for establishing a reference potential therefor, and an electrostatically deformable solid member disposed between said nonconductive target member and said reference potential establishing means.
17. An electron beam storage tube of the electrostatic charge, image projection type as defined in claim 16 and wherein said reference potential establishing means is spaced apart from said deformable solid member.