U.S. patent number 3,626,084 [Application Number 05/048,862] was granted by the patent office on 1971-12-07 for deformographic storage display tube.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Frank A. Hawn, Harold C. Medley, Robert J. Wohl.
United States Patent |
3,626,084 |
Wohl , et al. |
December 7, 1971 |
DEFORMOGRAPHIC STORAGE DISPLAY TUBE
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.
Inventors: |
Wohl; Robert J. (San Jose,
CA), Hawn; Frank A. (Los Gatos, CA), Medley; Harold
C. (Los Gatos, CA) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
21956851 |
Appl.
No.: |
05/048,862 |
Filed: |
June 12, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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683292 |
Nov 15, 1967 |
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Current U.S.
Class: |
348/772; 313/465;
359/293; 348/775; 348/E5.14 |
Current CPC
Class: |
H04N
5/7425 (20130101) |
Current International
Class: |
H04N
5/74 (20060101); H04n 005/74 () |
Field of
Search: |
;178/7.5D,7.3D,7.5E
;350/161 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Murray; Richard
Assistant Examiner: Eddleman; Alfred H.
Parent Case Text
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.
Claims
What is claimed is:
1. 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 controllably 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 of an 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.
Description
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 within 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 cathode-ray 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 well-known Eidophor tubes. Typical examples of such
arrangements are shown in U.S. Pat. Nos. 2,391,450, 2,510,846,
2,919,302, 3,164,671. 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 information 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 time-consuming 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 10 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 14 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 deformation-responsive 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 optical and electron beam components may be
interchanged without affecting the basic aspects of the 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 10 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.degree.. 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 1/2 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 80 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.sup..sup.-7 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.sup..sup.-3 or
10.sup..sup.-4 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 long-term 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 dismantling 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.
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 14 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 deformations which appear in
the deformographic film 36 are essentially 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.sup..sup.-7 to 10.sup..sup.-8 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 10.sup..sup.-7 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 1
have been measured. Image brightness in excess of 100 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 5 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 ratio 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 14 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 density 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 of the invention.
* * * * *