U.S. patent number 3,716,359 [Application Number 05/101,729] was granted by the patent office on 1973-02-13 for cyclic recording system by the use of an elastomer in an electric field.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Nicholas K. Sheridon.
United States Patent |
3,716,359 |
Sheridon |
February 13, 1973 |
CYCLIC RECORDING SYSTEM BY THE USE OF AN ELASTOMER IN AN ELECTRIC
FIELD
Abstract
The applications of elastomers to various imaging techniques are
described which may be used for the cyclic recording, storage and
subsequent erasure of optical information. Several embodiments of
the invention are described, all of which form images by the
elastic deformation of a thin elastomer layer. The pattern of the
surface deformation, in general, follows the light distribution of
the optical image being recorded. This image is formed on a
photoconductive layer which is adjacent to, or integral with, the
elastomer layer. An electric field is placed across the elastomer
and the photoconductor layers, the field being modulated by the
action of the image light on the conductivity of the photoconductor
and provides the mechanical force necessary to deform the
elastomer. Once the elastomer surface has deformed, it will in
general remain deformed as long as the field across it is
maintained; the image recorded, accordingly, being stored. Removing
the electric field allows the elastomer to relax and the image is
consequently erased. Reversing the field increases the rate at
which the image is erased. A new image may now be formed, and the
cycle started over again. Such an elastomer material is capable of
a great many recording/storage/erasure cycles.
Inventors: |
Sheridon; Nicholas K.
(Fairport, NY) |
Assignee: |
Xerox Corporation (Rochester,
NY)
|
Family
ID: |
22286094 |
Appl.
No.: |
05/101,729 |
Filed: |
December 28, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
23649 |
Mar 30, 1970 |
|
|
|
|
Current U.S.
Class: |
430/19; 386/326;
359/4; 365/126; 347/111; 347/264; 101/DIG.37; 346/77E; 359/291;
430/66; 348/40 |
Current CPC
Class: |
G03G
5/022 (20130101); G03G 16/00 (20130101); G03G
5/102 (20130101); C23C 14/20 (20130101); B21D
39/02 (20130101); Y10S 101/37 (20130101) |
Current International
Class: |
C23C
14/20 (20060101); B21D 39/02 (20060101); G03G
5/10 (20060101); G03G 5/02 (20060101); G03G
16/00 (20060101); G03G 5/022 (20060101); G03g
013/22 () |
Field of
Search: |
;96/1.1 ;340/173TP
;346/74TP,77E ;178/6.6TP |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cooper, III; John C.
Parent Case Text
CROSS REFERENCE
This application is a continuing application of my copending
application under the same title filed Mar. 30, 1970, Ser. No.
23,649, now abandoned.
Claims
What is claimed is:
1. An imaging method comprising the steps of:
providing an imaging member comprising a layer of photoconductive
material, an electric field deformable elastomer layer having a
volume resistivity above about 10.sup.4 ohm-cm. adjacent said
photoconductive material layer and a deformable layer of a
conductive gas adjacent said deformable elastomer layer, said
conductive gas layer including means for ionizing said conductive
gas;
subjecting said imaging member to an electric field; and exposing
said imaging member to information modulated electromagnetic
radiation to which the photoconductive material is responsive to
deform said elastomer layer corresponding to changes in the
electric field caused by the exposure.
2. The method as defined in claim 1 wherein said exposing includes
projecting a radiation image pattern onto said imaging member.
3. The method as defined in claim 1 wherein said imaging member
further includes a substrate for supporting the layers of said
imaging member.
4. The method as defined in claim 1 wherein said imaging member
includes a plurality of electric field deformable elastomer layers,
each said elastomer layer having different thickness and modulus of
elasticity from said other elastomer layers.
5. The method as defined in claim 1 further including the step of
erasing deformations created on said elastomer layer.
6. The method as defined in claim 5 wherein said step of erasing
includes removing the electric field to which said imaging member
is subjected.
7. The method as defined in claim 5 wherein said step of erasing
includes reversing the polarity of the field to which said imaging
member is subjected.
8. The method as defined in claim 1 further including illuminating
said imaging member with electromagnetic radiation to optically
construct an image of the surface deformation on said elastomer
layer.
9. The method as defined in claim 1 wherein said electric field to
which said imaging member is subjected is spatially modulated at a
frequency within the spatial frequency deformation capability of
the elastomer layer.
10. The method as defined in claim 1 wherein said radiation to
which said imaging member is exposed includes radiation generated
by a cathode ray tube.
11. The method as defined in claim 1 wherein said elastomer layer
has a predetermined elastic modulus such that a deformation created
therein by an electric field of sufficient strength can be locked
in and said electric field is of sufficient strength to lock in
said deformation, wherein said deformation remains while said
electric field is maintained and is not substantially affected by
subsequent exposure to illumination to which said photoconductive
material is responsive.
12. An imaging method comprising the steps of:
providing an imaging member comprising an electric field deformable
elastomer layer having a volume resistivity above about 10.sup.4
ohm-cm., said elastomer layer including photoconductive material,
and a deformable layer of a conductive gas adjacent said deformable
elastomer layer, said conductive gas layer including means for
ionizing said conductive gas;
subjecting said imaging member to an electric field; and
exposing said imaging member to information modulated
electromagnetic radiation to which the photoconductive material is
responsive to deform said elastomer layer corresponding to changes
in the electric field caused by the exposure.
13. The method as defined in claim 12 wherein said exposing
includes projecting a radiation image pattern onto said imaging
member.
14. The method as defined in claim 12 wherein said imaging member
further includes a substrate adjacent the side of the elastomer
layer opposite from that to which the deformable conductive gas
layer is adjacent.
15. The method as defined in claim 12 further including the step of
erasing deformations created on said elastomer layer.
16. The method as defined in claim 15 wherein said step of erasing
includes removing the electric field to which said imaging member
is subjected.
17. The method as defined in claim 15 wherein said step of erasing
includes reversing the polarity of the field to which said imaging
member is subjected.
18. The method as defined in claim 12 further including
illuminating said imaging member with electromagnetic radiation to
optically construct an image of the surface deformation on said
elastomer layer.
19. The method as defined in claim 12 wherein said electric field
to which said imaging member is subjected is spatially modulated at
a frequency within the spatial frequency deformation capability of
the elastomer layer.
20. The method as defined in claim 12 wherein said radiation to
which said imaging member is exposed includes radiation generated
by a cathode ray tube.
21. The method as defined in claim 12 wherein said elastomer layer
has a predetermined elastic modulus such that a deformation created
therein by an electric field of sufficient strength can be locked
in and said electric field is of sufficient strength to lock in
said deformation, wherein said deformation remains while said
electric field is maintained and is not substantially affected by
subsequent exposure to illumination to which said photoconductive
material is responsive.
22. An imaging member comprising a layer of photoconductive
material, an electric field deformable elastomer layer having a
volume resistivity above about 10.sup.4 ohm-cm. adjacent said
photoconductive material layer and a deformable layer of conductive
gas adjacent said deformable elastomer layer, said conductive gas
layer including means for ionizing said conductive gas, and said
elastomer layer being capable of deforming to correspond to an
electric field pattern created by altering an electrical field
across said elastomer layer by exposing the photoconductive
material to electromagnetic radiation to which it is
responsive.
23. The imaging member as defined in claim 22 further including a
substrate for supporting the layers of said imaging member.
24. The imaging member as defined in claim 23 wherein said
substrate is a transparent conductive member.
25. The imaging member as defined in claim 22 wherein said member
includes a plurality of said electric field deformable elastomer
layers, each said elastomer layer having different thickness and
elastic modulus from said other elastomer layers.
26. The imaging member as defined in claim 22 further including
means for spatially modulating an electric field across said
elastomer layer at a frequency within the spatial frequency
deformation capability of the elastomer layer.
27. The imaging member as defined in claim 26 wherein said means
for spatially modulating includes a line grating adjacent said
photoconductive material layer.
28. The imaging member as defined in claim 22 wherein said
elastomer layer has a predetermined elastic modulus wherein said
elastomer layer is capable of deforming and locking in said
deformation under the influence of an electric field of sufficient
strength and wherein said deformation remains while said electric
field is maintained and is not substantially affected by subsequent
exposure to illumination to which said photoconductive material is
responsive.
29. An imaging member comprising an electric field deformable
elastomer layer having a volume resistivity above about 10.sup.4
ohm-cm., said elastomer layer including photoconductive material,
and a deformable layer of a conductive gas adjacent said deformable
elastomer layer, said conductive gas layer including means for
ionizing said conductive gas, and said elastomer layer being
capable of deforming to correspond to an electric field pattern
created by altering an electrical field across said elastomer layer
by exposing said member to electromagnetic radiation to which said
photoconductive material is responsive.
30. The imaging member as defined in claim 29 further including a
substrate adjacent the side of the elastomer layer opposite from
that to which the deformable conductive gas layer is adjacent.
31. The imaging member as defined in claim 30 wherein said
substrate is a transparent conductive member.
32. The imaging member as defined in claim 29 further including
means for spatially modulating an electric field across said
elastomer layer at a frequency within the spatial frequency
deformation capability of the elastomer layer.
33. The imaging member as defined in claim 32 wherein said means
for spatially modulating includes a line grating adjacent said
elastomer layer.
34. The imaging member as defined in claim 29 wherein said
elastomer layer has a predetermined elastic modulus wherein said
elastomer layer is capable of deforming and locking in said
deformation under the influence of an electric field of sufficient
strength and wherein said deformation remains while said electric
field is maintained and is not substantially affected by subsequent
exposure to illumination to which said photoconductive material is
responsive.
35. An imaging method comprising the steps of:
providing an imaging member comprising a layer of photoconductive
material and a plurality of electric field deformable elastomer
layers overlying said photoconductive material layer, each said
elastomer layer having a volume resistivity above 10.sup.4 ohm-cm.
and each said elastomer layer having a different thickness and
elastic modulus from said other elastomer layers;
subjecting said imaging member to an electric field; and
exposing said imaging member to information modulated
electromagnetic radiation to which the photoconductive material is
responsive to deform said elastomer layers corresponding to changes
in the electric field caused by the exposure.
36. The method as defined in claim 35 wherein said exposing
includes projecting a radiation image pattern onto said imaging
member.
37. The method as defined in claim 35 wherein said imaging member
further includes a substrate for supporting the layers of said
imaging member.
38. The method as defined in claim 37 wherein said substrate is a
transparent conductive member.
39. The method as defined in claim 35 wherein said step of
subjecting said imaging member to an electric field includes
depositing electrostatic charge adjacent said elastomer layer.
40. The method as defined in claim 35 wherein said imaging member
further includes a deformable conductive layer adjacent the surface
of said elastomer layer remote from said photoconductive material
layer.
41. The method as defined in claim 40 wherein said deformable
conductive layer comprises a layer of conductive liquid.
42. The method as defined in claim 40 wherein said deformable
conductive layer comprises a layer of conductive gas, said
conductive gas layer including means for ionizing said conductive
gas.
43. The method as defined in claim 40 wherein said deformable
conductive layer comprises a flexible conductive metal layer.
44. The method as defined in claim 35 further including the step of
erasing deformations created on the elastomer layers.
45. The method as defined in claim 35 further including
illuminating said imaging member with electromagnetic radiation to
optically construct an image of the surface deformations on said
elastomer layer.
46. An imaging member comprising a layer of photoconductive
material and a plurality of electric field deformable elastomer
layers overlying said photoconductive material layer, each said
elastomer layer having a volume resistivity above about 10.sup.4
ohm-cm. and each said elastomer layer having a different thickness
and elastic modulus from said other elastomer layers, said
elastomer layers being capable of deforming to correspond to an
electric field pattern created by altering an electrical field
across said elastomer layer by exposing the photoconductive
material to electromagnetic radiation to which it is
responsive.
47. The imaging member as defined in claim 46 further including a
substrate for supporting the layers of said imaging member.
48. The imaging member as defined in claim 47 wherein said
substrate is a transparent conductive member.
49. The imaging member as defined in claim 46 further including a
deformable conductive layer adjacent the surface of said elastomer
layer remote from said photoconductive material layer.
50. The imaging member as defined in claim 49 wherein said
deformable conductive layer comprises a layer of conductive
liquid.
51. The imaging member as defined in claim 49 wherein said
deformable conductive layer comprises a layer of conductive gas,
said conductive gas layer including means for ionizing said
gas.
52. The imaging member as defined in claim 49 wherein said
deformable conductive layer comprises a flexible conductive metal
layer.
53. An imaging member comprising a plurality of electric field
deformable elastomer layers, each said elastomer layer having a
volume resistivity above about 10.sup.4 ohm-cm., each said
elastomer layer having a different thickness and elastic modulus
from said other elastomer layers, and at least one of said
elastomer layers including photoconductive material wherein said
elastomer layers are capable of deforming to correspond to an
electric field pattern created by altering an electrical field
across said elastomer layers by exposing the member to
electromagnetic radiation to which the photoconductive member is
responsive.
54. An imaging method comprising the steps of:
providing an imaging member comprising a layer of photoconductive
material, an electric field deformable elastomer layer having a
volume resistivity above about 10.sup.4 ohm-cm. adjacent said
photoconductive material layer and a deformable conductive layer
adjacent said elastomer layer, said deformable conductive layer
comprising gold and indium;
subjecting said imaging member to an electric field; and
exposing said imaging member to information modulated
electromagnetic radiation to which the photoconductive material is
responsive to deform said elastomer layer corresponding to changes
in the electric field caused by the exposure.
55. The method as defined in claim 54 wherein said exposing
includes projecting a radiation image pattern onto said imaging
member.
56. The method as defined in claim 54 wherein said imaging member
further includes a substrate for supporting the layers of said
imaging member.
57. The method as defined in claim 56 wherein said substrate is a
transparent conductive member.
58. The method as defined in claim 57 further including
illuminating said imaging member with readout electromagnetic
radiation to optically construct an image of the surface
deformation on said elastomer layer.
59. The method as defined in claim 58 wherein said information
modulated and readout radiation include radiation of different
wavelengths.
60. The method as defined in claim 58 wherein said readout
radiation is radiation to which the photoconductive layer is
substantially not responsive.
61. The method as defined in claim 58 wherein said readout
radiation includes radiation of substantially higher intensity than
said information modulated radiation for amplifying the image
represented by said modulated radiation.
62. The method as defined in claim 58 wherein one of said
information modulated and readout radiation includes coherent
radiation and the other non-coherent radiation.
63. The method as defined in claim 62 wherein said information
modulated radiation includes coherent radiation and said readout
radiation includes non-coherent radiation.
64. The method as defined in claim 62 wherein said information
modulated radiation includes non-coherent radiation and said
readout radiation includes coherent radiation.
65. The method as defined in claim 58 wherein said information
modulated radiation includes the interference pattern formed by
superpositioning of reference coherent radiation and object
modulated coherent radiation.
66. The method as defined in claim 54 wherein said imaging member
includes a plurality of electric field deformable elastomer layers,
each said elastomer layer having different thickness and elastic
modulus from said other elastomer layers.
67. The method as defined in claim 58 further including the step of
erasing deformations created on the elastomer layer.
68. The method as defined in claim 67 wherein said step of erasing
includes removing the electric field to which said imaging member
is subjected.
69. The method as defined in claim 67 wherein said step of erasing
includes reversing the polarity of the field to which said imaging
member is subjected.
70. The method as defined in claim 54 wherein said electric field
to which said imaging member is subjected is spatially modulated at
a frequency within the spatial frequency deformation capability of
the elastomer layer.
71. The method as defined in claim 54 wherein said radiation to
which said imaging member is exposed includes radiation generated
by a cathode ray tube.
72. The method as defined in claim 54 wherein said elastomer layer
has a predetermined elastic modulus such that a deformation created
therein by an electric field of sufficient strength can be locked
in and said electric field is of sufficient strength to lock in
said deformation, wherein said deformation remains while said
electric field is maintained and is not substantially affected by
subsequent exposure to illumination to which said photoconductive
material is responsive.
73. An imaging method comprising the steps of:
providing an imaging member comprising an electric field deformable
elastomer layer having a volume resistivity above about 10.sup.4
ohm-cm., said elastomer layer including photoconductive material,
and a deformable conductive layer adjacent said elastomer layer,
said deformable conductive layer comprising gold and indium;
subjecting said imaging member to an electric field; and
exposing said imaging member to information modulated
electromagnetic radiation to which the photoconductive material is
responsive to deform said elastomer layer corresponding to changes
in the electric field caused by the exposure.
74. The method as defined in claim 73 wherein said exposing
includes projecting a radiation image pattern onto said imaging
member.
75. The method as defined in claim 73 wherein said imaging member
further includes a substrate adjacent the side of the elastomer
layer opposite from that to which the deformable conductive layer
is adjacent.
76. The method as defined in claim 75 wherein said substrate is a
transparent conductive member.
77. The method as defined in claim 76 further including
illuminating said imaging member with readout electromagnetic
radiation to optically construct an image of the surface
deformation on said elastomer layer.
78. The method as defined in claim 77 further including the step of
erasing deformations created on the elastomer layer.
79. The method as defined in claim 78 wherein said step of erasing
includes removing the electric field to which said imaging member
is subjected.
80. The method as defined in claim 78 wherein said step of erasing
includes reversing the polarity of the field to which said imaging
member is subjected.
81. The method as defined in claim 73 wherein said electric field
to which said imaging member is subjected is spatially modulated at
a frequency within the spatial frequency deformation capability of
the elastomer layer.
82. The method as defined in claim 73 wherein said radiation to
which said imaging member is exposed includes radiation generated
by a cathode ray tube.
83. The method as defined in claim 73 wherein said elastomer layer
has a predetermined elastic modulus such that a deformation created
therein by an electric field of sufficient strength can be locked
in and said electric field is of sufficient strength to lock in
said deformation, wherein said deformation remains while said
electric field is maintained and is not substantially affected by
subsequent exposure to illumination to which said photoconductive
material is responsive.
84. An imaging member comprising a layer of photoconductive
material, an electric field deformable elastomer layer having a
volume resistivity above about 10.sup.4 ohm-cm. adjacent said
photoconductive material layer and a deformable conductive layer
adjacent said elastomer layer; said deformable conductive layer
comprising gold and indium, said elastomer layer being capable of
deforming to correspond to an electric field pattern created by
altering an electrical field across said elastomer layer by
exposing the photoconductive material to electromagnetic radiation
to which it is responsive.
85. The imaging member as defined in claim 84 further including a
substrate for supporting the layers of said imaging member.
86. The imaging member as defined in claim 85 wherein said
substrate is a transparent conductive member.
87. The imaging member as defined in claim 84 wherein said member
includes a plurality of said electric field deformable elastomer
layers, each said elastomer layer having different thickness and
elastic modulus from said other elastomer layers.
88. The imaging member as defined in claim 84 wherein said
elastomer layer comprises a dimethylpolysiloxane gel.
89. The imaging member as defined in claim 84 further including an
insulating liquid layer adjacent the side of the deformable
conductive layer opposite from that to which the elastomer layer is
adjacent.
90. The imaging member as defined in claim 84 wherein said
photoconductive material is chosen from the group consisting of
selenium, selenium alloys and mixtures of poly-n-vinyl carbazole
and a sensitizing dye.
91. The imaging member as defined in claim 84 further including
means for spatially modulating an electric field across said
elastomer layer at a frequency within the spatial frequency
deformation capability of the elastomer layer.
92. The imaging member as defined in claim 91 wherein said means
for spatially modulating includes a line grating adjacent said
photoconductive material layer.
93. The imaging member as defined in claim 84 wherein said
elastomer layer has a predetermined elastic modulus such that said
elastomer layer is capable of deforming and locking in said
deformation under the influence of an electric field of sufficient
strength and wherein said deformation remains while said electric
field is maintained and is not substantially affected by subsequent
exposure to illumination to which said photoconductive material is
responsive.
94. An imaging member comprising an electric field deformable
elastomer layer having a volume resistivity above about 10.sup.4
ohm-cm., said elastomer layer including photoconductive material,
and a deformable conductive layer adjacent said elastomer layer,
said deformable conductive layer comprising gold and indium, said
elastomer layer being capable of deforming to correspond to an
electric field pattern created by altering an electrical field
across said elastomer layer by exposing the photoconductive
material to electromagnetic radiation to which it is
responsive.
95. The imaging member as defined in claim 94 further including a
substrate for supporting said layers of said imaging member.
96. The imaging member as defined in claim 95 wherein said
substrate is a transparent conductive member.
97. The imaging member as defined in claim 94 further including an
insulating liquid layer adjacent the side of the deformable
conductive layer opposite from that to which the elastomer layer is
adjacent.
98. The imaging member as defined in claim 94 further including
means for spatially modulating an electric field across said
elastomer layer at a frequency within the spatial frequency
deformation capability of the elastomer layer.
99. The imaging member as defined in claim 98 wherein said means
for spatially modulating includes a line grating adjacent said
elastomer layer.
100. The imaging member as defined in claim 94 wherein said
elastomer layer has a predetermined elastic modulus such that said
elastomer layer is capable of deforming and locking in said
deformation under the influence of an electric field of sufficient
strength and wherein said deformation remains while said electric
field is maintained and is not substantially affected by subsequent
exposure to illumination to which said photoconductive material is
responsive.
101. An imaging member comprising a layer of photoconductive
material, an electric field deformable elastomer layer having a
volume resistivity above about 10.sup.4 ohm-cm. adjacent said
photoconductive material layer and a deformable conductive layer
adjacent said elastomer layer, said deformable conducting layer
comprising first and second metal materials, wherein said first
metal material is chosen from the group consisting of gold,
aluminum, silver, magnesium copper, cobalt, iron, chromium and
nickel, said second metal material is chosen from the group
consisting of indium, gallium, cadmium, mercury and lead, and said
elastomer layer being capable of deforming to correspond to an
electric field pattern created by altering an electrical field
across said elastomer layer by exposing the photoconductive
material to electromagnetic radiation to which it is
responsive.
102. An imaging member comprising an electric field deformable
elastomer layer having a volume resistivity above about 10.sup.4
ohm-cm., said elastomer layer including photoconductive material,
and a deformable conductive layer adjacent said elastomer layer,
said deformable conductive layer comprising first and second metal
materials, wherein said first metal material is chosen from the
group consisting of gold, aluminum, silver, magnesium, copper,
cobalt, iron, chromium and nickel, said second metal material is
chosen from the group consisting of indium, gallium, cadmium,
mercury and lead, and said elastomer layer being capable of
deforming to correspond to an electric field pattern created by
altering an electric field across said elastomer layer by exposing
the photoconductive material to electromagnetic radiation to which
it is responsive.
Description
BACKGROUND OF THE INVENTION
Prior art thermoplastic surface relief imaging taught the recording
of images by means of deformations in an otherwise smooth
thermoplastic surface. The image information is recorded as a hill
and valley structure on this surface. Light reflected or
transmitted through this surface may be used to make the recorded
image visible because such light will be scattered or diffracted by
this structure. Three basic types of thermoplastic surface relief
imaging may be distinguished.
Historically, the first of these is "frost imaging" which may be
seen in U.S. Pat. Nos. 3,196,009, 3,196,011, 3,258,336 and
3,196,008 as a few of many examples. Frost imaging has been
practiced in the past by creating a voltage pattern across a thin
layer of insulating thermoplastic. This voltage pattern is usually
established by means of an adjacent layer of photoconductor
material although the thermoplastic itself may be made
photoconductive. In use, the electric field is placed across the
thermoplastic/photoconductor sandwich or across the photoconductive
thermoplastic. The light intensity pattern of the image formed on
the photoconductor now creates a varying electrostatic field.
It has been observed by this inventor and others that a thin liquid
layer, across which a high electric field has been placed, will
preferentially deform in a pattern exactly matching the spatial
frequency variations in this field; provided these variations are
predominately composed of spatial frequencies in the neighborhood
of the characteristic or resonant frequency of the layer. For
moderate values of the electric field this resonant frequency
commonly has the value 1/2T, where T is the thickness of the liquid
layer. Where the field pattern varies much more slowly than this,
the surface will tend to wrinkle or randomly deform; such wrinkles
having characteristic spatial frequencies in the neighborhood of
1/2T and being referred to as frost. Hence, images having spatial
frequencies within the region of the resonant frequency of the
deformable surface will be faithfully reproduced by deformations of
this surface. Images, on the other hand, having spatial frequencies
much lower than this resonant frequency will tend to form frost in
the regions of greater illumination. In conjunction with a
Schlieren optical or other suitable system, good quality images may
be reconstructed from frost deformations. However, the inherent
noise structure of the frost image is objectionable for some
applications.
The second type of surface relief imaging was taught by Urbach and
is commonly called "screened frost." See U.S. Pat. Nos. 3,196,012
and 3,436,216. This imaging technique is capable of recording
surface deformation images of spatial frequency much lower than the
resonant frequency of the deformable layer. Urbach has shown that
by interposing an absorption type line grating of spatial frequency
close to the resonant spatial frequency of the deformable surface
between the image being projected on the photoconductor and the
photoconductor itself, the surface will deform without frost in
those regions where the photoconductor is eliminated. The solid
areas, i.e., low spatial frequency areas, of this screened frost
image are now filled, not with frost, but with remnants of the
screen. If these screen remnants are objectionable, they can be
removed by subsequent spatial filtering or by techniques further
taught by Urbach.
The third type of surface relief imaging is actually a variant of
the first two, but because of its importance deserves to be treated
separately. This relates to the recording of holograms on a
deformable surface structure and has been taught by Cathey, for
bleached gelatin emulsions and later by Urbach for
thermoplastic/photoconductor sandwich structures. Ser. U.S. Pat.
No. 3,560,205, Imaging System, Ser. No. 521,982, filed on Jan. 20,
1966. A hologram is a recording of the interference pattern between
two coherent light beams. One light beam usually contains
information about an object and the other is a reference beam,
generally of simple structure. The interference pattern generally
resembles a somewhat garbled image of a screen. If the spatial
frequency of the screen approximates the resonant frequency of the
thin liquid layer, the surface would deform along the structure of
the interference pattern and little noise would be generated.
All of the above imaging techniques involve the deformation of a
thin heat or solvent vapor softenable plastic layer to record image
deformation. They may, in principle, be recycled by applying heat
or solvent vapors to soften the plastic and allow the recorded
image to erase. Ordinarily, the surface would be allowed to
solidify again by cooling or vapor ventilation and another image
could be formed on it as before. However, these systems cannot be
cycled very rapidly or very conveniently. Moreover, cycling
requires the expenditure of solvents, or large amounts of power.
Further, it has been repeatedly observed that state of the art
plastics do not erase completely, due to chemical changes
associated with the development process; and, hence, only a limited
number of imaging cycles can be obtained with these materials.
Accordingly, there is a continuing need for surface deformation
imaging systems that will store information and can be repeatedly
cycled rapidly and conveniently, with low power consumption.
OBJECTS OF THE INVENTION
It is, therefore, an object of the present invention to provide an
optical imaging system which overcomes the above noted deficiencies
and satisfies the above-noted wants.
It is another object of the present invention to provide an optical
imaging system that will record optical information, store it,
erase it and do these things many times.
It is another object of this invention to provide an optical
imaging system capable of recording the high spatial frequency
optical interference patterns characteristic of holograms, as well
as the lower spatial frequency images commonly characteristic of
non-coherent light images.
It is another object of this invention to provide an optical
imaging system which records a surface relief image with light
incident from one side of the imaging member and to simultaneously
allow light of the same or different wave length or the same or
different intensity incident from the opposite side of the member
to form a similar optical image for purposes of wavelength change,
image projection, image intensification and other optical
transformations.
It is another object of this invention to provide an optical
imaging system which records a surface relief image on an
essentially transparent imaging member, such that images may be
recorded and reformed by transillumination.
It is another object of this invention to provide an optical
imaging system which will be capable of recording images most
efficiently within a narrow range of spatial frequencies, or within
several narrow ranges of spatial frequencies.
BRIEF SUMMARY OF THE INVENTION
In accomplishing the above and other desired aspects of the present
invention, Applicant has invented improved apparatus and methods
for a fully cyclycable imaging device on which images may be
recorded, stored for short periods of time and erased at will. The
inventor provides an imaging member which comprises a substrate
that is conductive or has a conductive surface. Coated on this
surface is a photoconductive layer whose conductivity is dependent
upon illumination, and coated above this is an elastomer layer. In
another embodiment a separate photoconductor layer is not used, but
rather the elastomer layer is photoconductive. A deformable
conductive layer including either a flexible conductive member, a
conductive liquid, a conductive gas or a layer of electrostatic
charge is placed contiguous to the surface of the elastomer. An
electric field established between the deformable conductive layer
and the conductive substrate increases in those regions where the
photoconductive layer is exposed to electromagnetic radiation
(hereafter referred to as light) causing the elastomer to deform in
those regions. Two types of imaging behavior have been observed. In
the case of very compliant elastomers and large electric fields the
elastomer remains deformed while the electric field is maintained.
This deformation is not substantially affected by subsequent
illumination of the photoconductor, and thus may be said to be
electrically locked. The recorded image information may now be read
out at leisure with any brightness illumination. The deformation is
removed by removing the field, allowing the elastomer to relax. By
reversing the field across the elastomer instead of removing the
field, the image may be erased much more quickly. A new image may
now be formed. It is to be noted, however, that the electrical
locking property of the elastomer exists only above a certain value
of the electric field. Below this field threshold value the image
erases slowly especially upon exposure of the photoconductor to
light. This constitutes the second type of imaging behavior. Here
again the image may be rapidly erased by removing or reversing the
field across the elastomer.
Because thin layers of elastomers behave in a manner similar to
thin layers of viscous liquids for small deformations, an elastomer
imaging device, much like a thermoplastic imaging device, is
capable of forming three types of image: frost images, screened
frost images and limited spatial frequency or holographic images.
However, because an elastomer is, in general, essentially an
incompressible material and because the extent of its possible
deformation is limited by internal elastic forces as well as
surface forces, a thin elastomer layer can exhibit an appreciable
response to surface force patterns lying only within a limited
spatial frequency bandwidth. The greatest response is in the
neighborhood of the resonant frequency, usually equal to
approximately 1/2T as in the case of thermoplastics. When an
elastomer is exposed to an image having the bulk of its information
within the spatial frequency response of the elastomer, the
elastomer will record that image very well. Such images are of
great interest primarily for holography and for recording printed,
written or numeric information of high contrast. When such an
elastomer layer is exposed to an image composed of spatial
frequencies lower than the recording band of the elastomer, the
brightly illuminated areas of the elastomer will deform into a
random deformation pattern similar to the frost of the
thermoplastic recording. The spatial frequency of the frost
deformation lies within the recording bandwidth of the elastomer,
and the frost will randomly scatter incident light. Less brightly
illuminated areas will not frost and hence will not scatter. Such
an image is called a frost image and, as in the thermoplastic case,
is sometimes objectionable for some applications because of its
inherently noisy structure.
The third type of surface relief image called screened frost is
suitable for recording images having spatial frequencies
substantially lower than the resonant deformation frequency of the
elastomer layer. This is formed by placing an absorption type line
grating between the projected image light and the photoconductor
upon which it is imaged. The elastomer will now deform along the
pattern of this high spatial frequency screen in those areas where
it is illuminated and, therefore, will not form frost. The screened
surface relief image will then consist of segments of the shadow of
the screen. The image obtained by illuminating the elastomer will,
thus, have a fine structure of lines superimposed upon the original
image that was recorded. If this line structure is objectionable,
it may be removed by suitable optical filtering techniques well
known in the art.
For the imaging structures described herein, the preferred location
of the screen, e.g., a line grating, is immediately adjacent to a
photoconductive layer in the imaging structure. Other types of
screens that may be similarly located are described in two
copending applications, both titled "Methods of Organized
Thermoplastic Xerography and Photoreceptor Structure Therefor," one
in the name of Lloyd F. Bean and the other in the name of John C.
Heurtley, filed Sept. 18, 1970, and Sept. 18, 1970, Ser. Nos.
73,406 and 73,317, respectively.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention as well as other
objects and further features thereof, reference is made to the
following detailed description taken in conjunction with the
accompanying drawings wherein:
FIG. 1 is a side sectional view of the elastomer imaging apparatus
of a first embodiment of the present invention;
FIG. 2 is a side sectional view of the elastomer imaging apparatus
of a second embodiment of the present invention;
FIG. 3 is a side sectional view of the elastomer imaging apparatus
of a third embodiment of the present invention;
FIG. 4 is a side sectional view of the elastomer imaging apparatus
of a fourth embodiment of the present invention;
FIG. 5 is a side sectional view of a multilayered elastomer in
accordance with the principles of the present invention;
FIGS. 6 to 10 are partly schematic, partly side sectional view of
various physical applications of the principles of the present
invention;
FIG. 11 is a schematic, perspective view of a computer print-out
systems using the imaging structures and methods of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The term "elastomer" in the various forms used herein is defined as
a usually amorphous material which exhibits a restoring force in
response to a deformation; that is, an amorphous material which
deforms under a force, and, because of volume and surface forces,
tends to return to the form it had before the force was
applied.
The first embodiment of the present application shown in FIG. 1 is
an elastomeric imaging device in which charges are placed on the
surface of the elastomer by means of a corona discharge. Modified
forms of a corona discharge device are well known in the art as
coratrons or scoratrons. With such a device, positive or negative
ions are produced by a high voltage field in a gas and deposited
upon the surface.
The apparatus of FIG. 1 includes a substrate 1 which is either
conductive or is conductive on one surface thereof. It will most
generally be a transparent substrate although, in those cases where
light is to be reflected from the elastomer to reconstruct an
image, it may be opaque. Substrate 1 may also have a highly
reflective mirror finish so that reconstruction light will pass
through the elastomer, reflect from it and pass through the
elastomer once again; thereby obtaining twice the modulation that a
transmissive device will impart. If the substrate is to be
transparent, commonly available NESA glass could be used. This is a
tin oxide coated glass conductive on the surface corresponding to
layer 2 in FIG. 1. Alternatively, it could be a piece of
transparent glass with a metallic conductive layer on the surface,
a layer thin enough to be transparent. If transparency of the
substrate is not important, a metallic substrate may be used. The
substrate could be a plastic material such as Mylar or acetate, if
flexibility were desired. If substrate 1 is not conductive, layer 2
which is a conductive layer must be added. This is normally a
transparent, or partially transparent layer.
The photoconductive layer 3 is a material which will allow the
passage of more electric charge in those regions which are exposed
to light. This definition of a photoconductor may be extended to
any materials in which the conductivity is inhibited by the
presence of light. Such a photoconductor is often a mixture of
poly-n-vinyl carbazole and a sensitizing dye. The thickness of the
photoconductor will probably range from 0.1 microns to 200 microns,
depending largely upon the spatial frequency of the information to
be recorded.
The elastomer layer 4 may be of a class of elastomeric soft solid
materials for use in this application including both natural, such
as natural rubbers and synthetic polymers which have rubber like
characteristics, i.e., are elastic and include materials such as
styrene-butadiene, poly-butadiene, neoprene, butyl, polyisoprene,
nitrile and ethylene propylene rubbers. Preferred elastomers for
use in this application include: water based gelatin gels and
dimethylpolysiloxane based silicone gels. These materials may be
coated on the photoconductor as monomers and polymerized in place
or they may be coated on the surface from solutions in volatile
solvents which will evaporate and leave a thin uniform layer. In
general, these materials should be reasonably good insulators,
having volume resistivities in excess of 10.sup.4
ohm-centimeters.
The preferred elastomer is a transparent composition comprising an
elastomeric dimethylpolysiloxane silicone gel made by steps
including combining about one part of Dow Corning No. 182, silicone
resin potting compound and anywhere from about zero to about 30
parts of Dow Corning No. 200 dimethylpolysiloxane silicone oil.
Suitable resins include transparent flexible organosilonane resins
of the type described in U.S. Pat. No. 3,284,406 in which a major
portion of the organic groups attached to silicon are methyl
radicals.
The thickness of the elastomer layer will range from approximately
0.1 microns to approximately 2,000 microns, depending upon the
spatial frequency of the information required. Various optical
properties of the device may be enhanced by a suitable selection of
the elastic modulus of the material used. For example, a stiffer
elastomer will recover more rapidly from an image when the electric
field is removed, that is, may be erased more quickly. On the other
hand, a material having a low elastic modulus will be capable of
greater deformations and hence greater optical modulation for a
given value of electric field.
The corona charging apparatus 5 may be a stationary charging unit
provided such a unit provides enough uniformity of charge
deposition, or it may be a scanning system. This device places
positive or negative charges on the surface of the elastomer. The
voltage drop across the elastomer photoconductive sandwich will lie
in the range of 1 to 25,000 volts depending on the modulus of
elasticity of the elastomer and its thickness, as well as certain
properties of the photoconductor. Particular types of scoratron
devices which have been found useful in corona charging are
disclosed in the Vyverberg U.S. Pat. No. 2,836,725 and the Walkup
U.S. Pat. No. 2,777,957 and assigned to the same assignee as
herein. The device should be placed in such a way that will cause
minimal interference with light reaching the photoconductor and
light used to reconstruct the image. It may be appreciated that
substrate 1 or layer 2 in FIG. 1 need not be conductive in the
corona charging mode since double sided corona charging may be used
to charge a surface of both layer 1 and the elastomer 4, the two
charging devices, one on each side of the imaging member, are
oppositely charged and are traversed more or less in register. In
other words, a second corona charging device may be used to obviate
the need for a conductive layer 2 or substrate 1.
In operation, the corona charging apparatus 5 lays charges down on
the elastomer layer 4. The sandwich in FIG. 1 is then exposed,
either simultaneously or subsequently to the charging step
depending upon the ability of the elastomer to hold charge on its
surface, to a light field which must come from the right if
substrate 1 is opaque. If substrate 1 is transparent, the light may
propagate from either the right or the left. Substrate 1, or the
alternate layer 2, are grounded thereby creating an electric field
across the photoconductor and elastomer combination. This electric
field induces a flow of charge in those regions of the
photoconductor which are exposed to light, varying the electric
field across the elastomer. The mechanical force of the electric
field across the elastomer causes it to deform. This deformation
will proceed until the forces of the electric field are balanced by
the surface tension and elastic forces of the elastomer. At this
point, the deformation stops and becomes stable as long as the
electric fields across the elastomer are maintained. This
deformation is different from that occurring in thermoplastic
materials in that the elastomer deformations are independent of any
developing step such as heat and/or solvent softening steps
employed with thermoplastic materials. Another difference between
elastomer and thermoplastics is that the elastomer deformations
assume a definite limit for a given electric field because elastic
forces oppose the deformation. The thermoplastic deformations do
not encounter such a definite limit for a given field as long as
the thermoplastic is maintained in a softened condition. To erase
this image, the field across the elastomer is removed; to erase
more quickly the field across the elastomer is reversed. Now the
device is ready to accept another image.
In FIG. 2 is a second embodiment wherein an electric field is
created across the elastomer 9 and photoconductor layer 8 by means
of a thin continuous conductive layer 10 on the surface of the
elastomer, which layer is flexible enough to follow the
deformations of the elastomer. In the case where this layer is
highly reflective, this apparaTus will utilize the readout light
with great efficiency. If the layer is opaque, light propagating
from the left may be used to form the surface deformation image,
while simultaneously light propagating from the right may be used
to reconstruct the image. The light sources used may be of
different wavelengths and/or intensities and/or one light source
may be coherent and the other noncoherent. Hence, this device may
be used to convert an image formed in one wavelength into an
equivalent image formed in a different wavelength. Also, if the
readout light incident from the right is very much more intense
than the imaging light incident from the left, the apparatus shown
in FIG. 2 will provide great amplification of an input image, such
amplified light being used, for example, for large panel displays.
Furthermore, the reconstruction light may be coherent, e.g., that
produced by a laser, so that image processing steps may be
performed on the surface deformation image which is formed with
non-coherent light propagating from the left. On the other hand,
the light giving rise to the surface deformation image may be
coherent light while the reconstruction light may be non-coherent.
This latter case is desirable because non-coherent light is more
pleasing to the human eye and current coherent light generators are
limited to production of light within narrow wavelength bands,
i.e., one color such as red. A reason for having coherent light for
forming the surface deformation image arises when it is the
reconstruction light for forming images with holograms. Therefore,
the present device may have a holographically reconstructed image
projected onto it forming a surface deformation image that is
viewed with non-coherent light of substantially greater intensity
as suited for large panel displays.
In FIG. 2, as it was for the embodiment shown in FIG. 1, substrate
6 may be transparent or opaque depending upon use. Conductive layer
7 is optional and is used if substrate 6 is not conductive. If
substrate 6 is transparent then the conductive layer 7 would
generally also be transparent. Over the conductive layer 7 is
coated the photoconductive layer 8. Over the photoconductive layer
8 is the elastomer layer 9. The thin conductive layer 10 must be
flexible enough to follow the deformations of the elastomer layer
9. If the conductive layer 10 is opaque, for example, a thin metal
film, the substrate 6 and conductive layer 7 must be transparent to
allow image information to reach the photoconductive layer 8. In
this case, image information can be read out continuously if the
readout light is incident from the right. If the conductive layer
10 is transparent, light may be reflected from its surface or the
device may be used in transillumination, provided substrate 6 and
layer 7 are transparent.
Conductive layer 10 may be a thin layer of gold, or a thin layer of
indium, or a combination of the two, or other suitable metal
layers. The thickness of the metallic layers would normally be
between approximately 50 angstroms to several thousand angstroms
thick, depending on the desired flexibility, and the necessary
conductivity. A transparent conductive layer 10 could also be used,
such as Dow Corning resin ECR 34 may be coated on the surface of
the elastomer 9. Other conductive layers, such as may occur to one
skilled in the art, may also be used within the principles of the
present invention. To form and lock the deformation image, the
values of voltage between substrate 6 and conductive layer 10 would
be approximately between 1 and 25,000 volts, depending on the
thickness, and other characteristics of elastomer 9.
The requirements for conductive layer 10 include: sufficient
conductivity to become an equipotental surface when connected to an
electrical energy source; sufficient flexibility to follow the
deformations of the elastomer; sufficient fatigue resistance to
withstand numerous and rapid formations and erasures of surface
deformations; and, in some cases, high opacity and reflectivity as
when being read out by a high intensity light source to which the
photoconductive layer is sensitive.
The preferred materials for conductive layer 10 include gold and
indium. The layer is formed by steps including vapor depositing the
materials onto the elastomer which involves heating a material to
or above its melting point and condensing the vapors on the desired
surface. This technique is well understood in the art and
conventional practices are followed in evaporating and condensing
the materials. However, a problem associated with shrinkage of a
condensed metal layer is overcome by novel techniques in order to
fabricate a conductive layer 10 meeting the above requirements.
Vapor deposited metals tend to shrink, i.e., contract, as they cool
and at some thermo-energy state the metal layer tends to break up
or crack making the layer discontinuous. This break up of a metal
layer is referred to herein as "mud-cracking" since mud cracks are
broadly descriptive of the appearance of the layer after shrinkage.
The instant novel technique includes vapor depositing a second
metal over the first before the first has mudcracked. The two
materials may be vapor deposited simultaneously. The second metal
is selected so as to have a lower melting point than the first
deposited metal. The final product is a continuous layer meeting
the above requirements which yet does not experience mud cracking
over a wide range of temperatures. The described layer may include
portions where the two metals (or other suitable materials) are
coated one over the other, portions where the two metals are
intermixed macroscopically as well as microscopically (e.g., to
form an alloy) and portions where they reside side by side.
Naturally, additional materials may be added to the layer to
enhance or suppress particular characteristics.
One theory, to which this invention is not limited, that explains
why mud cracking is suppressed in the above multiple component
layer, is connected with the relative mobility of atoms at the
surfaces of the different materials. The atoms of high melting
point materials normally exhibit low surface mobility which gives
rise to the mud cracking when the metals are coated over an
elastomer. The atoms of lower melting point materials exhibit by
comparison much greater surface mobility and their presence enables
the stresses developed in the high melting point material to be
relieved.
The preferred materials of gold and indium have high and low
melting points respectively. Mud cracking is usually observed in
vapor deposited gold layers within minutes after cooling to room
temperatures. This usually provides ample time to vapor deposit the
indium onto the gold layer. An example of a highly successful
coating is one formed by depositing from 50 to several thousand
angstroms of gold followed by depositing onto this gold layer from
50 to several thousand angstroms of indium. The resultant layer is
continuous and exhibits no mud cracking over a wide range of
temperatures. The indium is particularly advantageous because it
increases the opacity of the resultant layer and, because of its
silver appearance, enhances the reflectivity of the layer.
It is noted that indium by itself is not a highly efficient
material for layer 10 because of poor conductivity. The poor
conductivity is peculiar to low melting point materials because
they tend to form islands during condensation which do not join
together into a continuous layer of a reasonable thickness.
Accordingly, it is observed that vapor deposition of single
materials (or alloys thereof), whether high or low melting point
materials, yields layers that are less satisfactory than the layer
comprised of high and low melting point materials.
Other suitable high melting point materials besides gold include
aluminum, silver, magnesium, copper, cobalt, iron, chromium, nickel
and others. Aluminum has the further desirable property of being
highly corrosion resistant. Other suitable low melting point
materials besides indium include gallium, cadmium, mercury, lead
and others. Cadmium by itself exhibits a low tendency to mud
cracking.
Of course, the foregoing problems of mud cracking and island
forming may not arise if the conductive layer 10 is formed by
chemical reaction, precipitation out of a solution,
electrophoresis, electrolysis and/or other techniques.
Over the conductive layer 10 in FIG. 2 may also be an optional
transparent insulating layer of oil. Its purpose is to make less
stringent the fabrication requirements for this apparatus. The
presence of pin holes in the elastomer layer 9 may cause the
apparatus in FIG. 2 to short circuit, possibly destroying its
performance. The addition of the layer 12 prevents such short
circuits from disrupting the performance of the device by allowing
insulating oil to flow into such pin holes.
Layer 12 serves another important function when it has an index of
refraction different than air. The presence of oil 12 over the
conductive layer 10 means light propagating from the right will be
modulated more than it would be if only air was present. The reason
being is that for the same magnitude of surface deformation the
optical path changes are proportional to the refraction index of
the medium adjacent to the surface.
Power supply 11 of FIG. 2 provides DC voltage of one polarity to
form a deformation image on the surface of the elastomer. The
polarity required depends upon the nature of the photoconductor.
Power supply 11 must be capable of being turned off to erase the
image, or, undergo a shift in polarity to more rapidly erase the
image. For a television type of picture wherein approximately 30
images per second are formed, stored and erased, the power supply
must be capable of undergoing such cycles with appropriate speed.
The extent of the deformation and the rapidity with which
information may be erased is dependent upon the voltages supplied
by the power supply. The stability of the voltage output of the
power supply must be great enough to prevent unwanted erasure of
the image. An alternate scheme for erasing the surface deformation
image is to position a strobe light at the left in FIG. 2 to flood
the photoconductive layer 8 with light thereby erasing the
modulated field pattern across the structure set up by the
imagewise light. This operation is appropriate as long as the
fields across the elastomer layer 9 are below a level causing the
surface deformations to be locked.
The embodiment in FIG. 3 employs a very thick conductive liquid 16
in contact with elastomer 15 to provide the necessary electric
field across the elastomer/photoconductor sandwich. The other
components of the apparatus of FIG. 3 are similar to those in FIGS.
1 and 2. That is, substrate 12 may be transparent or opaque and in
turn may or may not be conductive. Conductive layer 13 must be
present if substrate layer 12 is not conductive. If substrate 12 is
transparent then conductive layer 13 will normally also be
transparent. Coated on the conductive layer 13 are the
photoconductor layer 14 and the elastomer layer 15.
The thick conductive liquid 16 in FIG. 3 may or may not be
transparent. Non-transparent conductive fluids include mercury,
room-temperature molten gallium-indium alloys, etc. Transparent
fluids include water to which conductive impurities have been
added. If transparent, the fluid 16 should have a substantially
different refractive index than the elastomer 15 in order that
deformations of the elastomer surface will phase modulate the
illuminating light. A transparent fluid may also be used for
reflection, which may be enhanced by placing a thin flexible
transparent layer on the elastomer 15 having a substantially
different refractive index than either the elastomer or the
transparent conducting fluid. Window layer 18 could be of normal
optical property glass which contains the conductive fluid against
the elastomer layer 15. Power supply 17 supplies the necessary
operating potential to the apparatus in FIG. 3. It is noted that
most conducting transparent fluids will undergo electrolysis in a
DC electric field. This is undesirable because it leads to a
deterioration of the operating components of the apparatus, as well
as the evolution of gas. Thus, operation with conductive
transparent fluids would normally require the use of an AC field
across the elastomer/photoconductor sandwich.
The fourth embodiment is illustrated in FIG. 4. This embodiment is
essentially identical to the embodiment illustrated in FIG. 3,
except that the thick conductive layer 16 in FIG. 3 is replaced by
a conductive gas 22 and requires an electrode 23 which may be a
transparent conducting window. The conductive gas in cavity 22 may
be obtained by means of a glow discharge through a low pressure gas
of a few millimeters of mercury pressure, or by means of a low
pressure arc discharge which commonly takes place at a few microns
of mercury pressure. The gas may also be ionized by means of
intense radioactivity in or near a low pressure gas 22 or radio
frequency excitation of the gas in cavity 22 or other techniques
for producing a conductive gaseous plasma well known in the art.
Charging of the elastomer surface 21 may also take place if gas 22
is at a sufficiently high vacuum and contains a source of thermally
excited electrons, such as a heated tungsten filament, which is
directed against the elastomer surface. This may be a scanned beam
as from an electron gun, or an unscanned beam, or from a
multiplicity of electron emitting sources. A reflective layer may
also be placed over layer 21 on the surface interface between
layers 21 and 22.
Apart from the conductive gas 22 in FIG. 4, the components thereof
are similar to that as shown in FIG. 3. That is, substrate 18 would
have a conducting layer 19 thereon with transparency or not as set
forth above. Photoconductive layer 20 and elastomer layer 21 are
placed over the conductive layer 19. Here, however, the conductive
gas 22 may be between 0.1 microns thick to an indefinite thickness.
As set forth above, electrode 23 may be a separate electrode or may
be coupled to a transparent conducting window to contain the
conductive gas against the elastomer layer 21. The container for
withholding the conductive gas 22 from escaping would, of course,
have to be airtight to contain the gas at the necessary level of
vacuum.
The embodiment of FIG. 4 is particularly suited for holographic
interferometry because the input light can be transmitted through
it to form a composite image with the output light. Therefore, a
holographically reconstructed image of an object may be
superimposed upon the actual image of the object to obtain
interference fringes as a result of dimensional changes.
Apart from comprising a novel imaging technique for imaging on an
elastomer layer, the embodiment in FIG. 4 teaches a novel technique
for charging a surface without the use of the prior art corona
discharging devices such as a corotron or a scorotron. The
limitations of the corotron and the scorotron are that the power
requirement is high in relation to the density of charge placed on
the receptive layer. Further, corotrons and scorotrons being corona
discharge devices must normally have a relative motion between the
corona discharge device and the receptive layer. In prior art
devices such as normally utilized in xerographic machines, an
electrophotographic drum such as an aluminum drum overcoated with
selenium, is rotated about a central axis past a corona discharge
device such as the corotron or scorotron hereinabove set forth.
Additionally, the corona discharge device could be advanced past a
receptive layer, for example, in a situation where the receptive
layer is flat with respect to the path of movement of the corona
discharge device. Further, the fact that the prior art corona
discharge devices operate in a normal room environment, that is,
with normal air of varying humidities, the charge laid upon a
receptive layer is not as accurate as could be desired. The
embodiment set forth in FIG. 4, however, overcomes these
disadvantages by utilizing the conductive gas in a predetermined
vacuum, the level of charge placed upon a receptive layer can be
precisely determined. If the conductive gas is coupled to a vacuum
pump, the evacuated pressure and/or the potential applied to the
electrode 23 may be controlled to specifically predetermine the
charge generated on the receiving layer.
A number of variations of the various elements may be substituted
for those used in the imaging devices set forth above in the
embodiments disclosed in FIGS. 1 to 4. Thus, any one of any
combination of the elements hereinafter described may be
substituted for a corresponding element hereinabove described.
With respect to the photoconductive layers hereinabove described,
in addition to the brilliant green dye produced by the J. T. Baker
Chemical Company which is added to the poly-n-vinyl carbazole
photoconductor to sensitize it for red light, other dyes may also
be used for sensitization, such as trinitro-9-fluorene for blue
light sensitivity. Finely ground pigments such as phthalocyanine
may also be added to the poly-n-vinyl carbazole to obtain visible
light sensitivity. Other organic photoconductors known in the art
may also be utilized effectively. In addition, non-organic
photoconductors, such as selenium and selenium alloys, may also be
used.
Adjacent photoconductor and elastomer layers may be replaced by a
single layer of a photoconductive elastomer under some
circumstances, in all embodiments hereinabove set forth. For
example, the elastomer made by combining sylgard 184 with
dimethylpolysiloxane oils may be made photoconductive for blue or
ultraviolet light by adding p-phenylenediamine, indoform and Calco
oil orange dye manufactured by the American Cyanamid Company prior
to the curing thereof.
With respect to the elastomer layers, a thin elastomer layer is
capable of undergoing appreciable elastic deformation for only a
limited bandwidth of spatial frequencies. Its response outside this
bandwidth is quite limited. The spatial frequency response of the
elastomer may be broadened or made multiply peaked by replacing the
single elastomer layer with a multiply layered apparatus as
illustrated in FIG. 5. Each of these layers 25, 26, 27 and 28 will
have a different limited spatial frequency response, but the
combination of layers will have a broad or multiply peaked spatial
frequency response. In general, it will be noted that the thickest
layer 25 will be placed closest to the photoconductor and the
thinnest layer 28 will have the deformable surface. Two or more of
such layers may be used as desired. As described previously, each
of these layers may also be photoconductive, eliminating the need
for a separate photoconductor and in some instances enhancing the
resolution of the device.
It should also be noted that in addition to controlling the
thickness of the elastomer layer to peak its spatial frequency
response for a given spatial frequency bandwidth, its elastic
modulus will also be controlled to obtain deformations commensurate
with that spatial frequency bandwidth. Materials of lower elastic
modulus are capable of greater elastic deformations. On the other
hand, materials of higher elastic modulus may be more quickly
erased. Such factors must be taken into account when designing the
apparatus for speed or greater deformation.
In several of the above embodiments, there is described the
reflection of light from the elastomer surface. Numerous methods
known in the art are available for enhancing such reflection. In
addition to these, the previously mentioned thin layers of gold or
indium, and/or other suitable metals, vacuum deposited on the
surface of the elastomer provide a highly reflective surface that
is sufficiently smooth to cause little optical noise. These metal
depositions do not appear to appreciably change the elastic
behavior or the electrical insulating properties of the elastomer
surface, but it greatly enhances the reflective power of such
surfaces.
It has hereinabove been set forth that the elastomer surfaces as
described herein may be used for the recording, storage and erasure
of image information over a great many cycles, provided that the
electric fields across the elastomer are not allowed to become
excessively great. When these fields do become great enough that
the deformations of the elastomer surface exceed the elastic limit
of the elastomer, it has been observed that the image is
permanently recorded on the elastomer. The upper limit on the
electric field applied to the previously mentioned
dimethylpolysiloxane silicone gel is observed to be about 100 volts
per micron. While for many systems this is regarded as undesirable,
there are those in which it is also desired to record a permanent
image. Thus, the cyclic properties of the elastomer may be used in
an attempt to obtain a satisfactory image, which is then
permanently recorded by an over voltage application.
FIGS. 6 through 10 show actual physical embodiments of imaging
systems which could utilize the inventive principles of the present
invention. FIG. 6a, for example, shows a frost or screened frost
imaging technique with the elastomer sandwich. A light source would
impinge upon an object, the reflected light from which would be
focused onto the imaging sandwich. The elastomer surface would
record the image as set forth in the embodiments of FIGS. 1 to 4.
Readout of the imaging sandwich is effected in FIG. 6b. The light
source would illuminate the elastomer surface of the sandwich, the
reflected light from which would be reflected away from the
elastomer surface in the unfrosted areas, while the light impinging
thereon would be scattered when reflected by the frosted area of
the image. Such scattered light from the frosted areas would enter
the lens and would form an image at the image plane. For this
image, frosted areas would appear bright, unfrosted areas dark,
yielding a positive image having bright and dark areas
corresponding to those of the original object.
If the light source were a coherent light source as from a laser,
the system set forth in FIG. 6 could be utilized to record a
hologram. That is, the light source in FIG. 6a would be extended to
impinge directly upon the imaging sandwich as a reference beam to
coact with the object modulated beam from the object to form a
holographic image at the imaging sandwich. Upon reconstruction, the
light source would be a similar light source which would impinge
upon the imaging sandwich as indicated in FIG. 6b. In FIG. 6b,
however, the lens would be unnecessary to form the reconstructed
image.
The apparatus in FIGS. 6a and 6b are pertinent to the embodiments
shown in FIGS. 1 to 4. With regard to the embodiment shown in FIG.
2, if conductor 10 is transparent, the readout light may be
incident from either the left or the right. If the layer 10 is
opaque, the readout light may be incident from the left. In this
latter case, the image may be readout at the same time the image is
being recorded. With regard to the embodiment shown in FIG. 3, if
fluid 16 is transparent, the readout light may be incident from
either the right or the left. If the fluid is opaque, the readout
light must be incident from the left.
FIG. 7 of the present application shows another structure which
utilizes the principles of the present invention. In a manner
similar to that for FIG. 6a, the light source impinges upon the
object, the reflection from which is imaged by the lens onto the
imaging device. With the technique utilized in FIGS. 1 to 4, the
elastomer in the presence of the electrical field records the image
impinged thereon. Upon reconstruction, in FIG. 7, the light source
now illuminates the recorded image on the elastomer layer. The
reflection from the elastomer layer is gathered by the lens which
images the reflected image onto a plane. Between the plane and the
lens is a focus point for the lens which, by the use of a spatial
filter, causes a positive or negative image to be generated at the
image plane. That is, a frost image reflects high frequency spatial
frequencies while the unfrosted areas reflect very low frequency
spatial frequencies. Thus, a solid spatial frequency filter placed
at the focal point for the lens filters the low frequency spatial
signals while allowing the high frequency spatial signals to be
passed and imaged on the image plane as a positive image. For a
negative image, an annular spatial filter is utilized which filters
the high frequency spatial signals while passing the low frequency
spatial frequency signals. The embodiments shown in FIG. 7 are
applicable to the embodiments set forth in FIGS. 1 to 4 and are
additionally applicable in the production of a hologram as set
forth above.
FIG. 8 shows an additional embodiment utilizing the principles of
the present invention, the image thereof being recorded in a manner
similar to that set forth in FIG. 6a. Upon reconstruction, however,
the light source would be transmitted through the elastomer layer
rather than reflecting from it as set forth in FIGS. 6 and 7.
Again, for either a positive or negative image, the particular
spatial filter is required. This embodiment is pertinent to FIGS. 1
through 4 as were the embodiments in FIGS. 6 and 7. With respect to
FIG. 2, the embodiment therein is to be utilized only if the
conductive layer 10 is transparent. With respect to the embodiment
in FIG. 3, the embodiment therein can be utilized only if the
conductive fluid 16 is transparent.
FIG. 9 shows apparatus utilizing the principles of the present
invention wherein the construction and reconstruction steps occur
simultaneously with similar or different light sources. That is,
light from an object illuminated with light of a given wavelength
and intensity is focused on the photoconductor of the imaging
sandwich. Simultaneously, light of a possibly different wavelength
and/or intensity is reflected from the coated surface of the
elastomer. This image is converted to an intensity image at the
image plane as was set forth above in conjunction with FIG. 6. The
apparatus of FIG. 9 can be extended as was the apparatus of FIGS. 6
and 7 for the construction of a hologram. That is, in FIG. 9 the
illumination light source would not only be impinged upon the
object to generate an object modulated wavefront, but would be
impinged upon the imaging sandwich as a reference beam. Then, at
the surface of the elastomer, a hologram would be constructed in
accordance with the object and reference wavefronts. Of course, the
illumination light source must now be coherent as from a laser
source, for example. Upon readout, a coherent light source would
impinge upon the other side of the imaging sandwich, the light
diffracted therefrom forming the reconstructed image. Here, of
course, the lens system would not be necessary. FIG. 9 is pertinent
to the embodiment set forth in FIG. 2 for simultaneous image
recording and readout primarily if a reasonably opaque metal is
used for layer 10, or if the readout wavelength is non-actinic for
the photoconductor. That is, the photoconductive layer of the
imaging sandwich cannot be sensitive to the readout light source or
else the readout light source will affect the generation of the
image on the elastomer surface. If these conditions do not hold,
FIG. 9 is pertinent to the embodiment set forth in FIG. 2 primarily
if the image is first formed and subsequently read out. That is,
readout light would not be present during image forming in
sufficient intensity to interfere with image forming. FIG. 9 is
also pertinent to the embodiments shown in FIGS. 1, 3 and 4 for
simultaneous image recording and readout. It is also pertinent to
the use of high and low pass spatial filters, depending upon the
generation of a positive or negative image.
FIG. 10 utilizes the imaging sandwich for holographic recording. In
FIG. 10a, a laser source would impinge upon the object by means of
reflection from a mirror, for example, while an unobstructed
reference beam would impinge upon the imaging sandwich. The
modulated beam from the object would coact with the reference beam
within the photoconductor layer forming a holographic image
therein. By deleting the mirror and the object itself, the laser
source can be used to reconstruct the image for an observer as
shown in FIG. 10b. Thus, FIG. 10 shows the use of the imaging
sandwich to record a holographic interference pattern instead of a
focused image. Those comments set forth above for FIG. 8 would
apply here except it is noted that for readout the impinging
wavefront must be coherent.
The system illustrated schematically in FIG. 11 employs a cyclic
imaging member 51 according to the present invention and preferably
the embodiment represented by FIG. 2. The portion 52 represents the
transparent substrate, conductive layer and photoconductor while
portion 53 represents an elastomer layer overcoated with an opaque,
reflective, electrically conductive layer which deforms with the
elastomer. The system utilizes the imaging member 51 as a buffer
storage device between devices such as a digital and/or analog
computer, the output of which is represented by the arrow 54, and
the xerographic reproduction apparatus 55. The buffer storage
device permits asynchronous operation of the computer and
xerographic apparatus.
Digital information is converted to analog information by the
analog to digital converter 57 which develops appropriate signals
for driving the cathode ray tube (CRT) 58. Conventionally, electron
beam position information is fed to the CRT through appropriate
vertical and horizontal deflection circuits 59 and 60,
respectively, and beam intensity information is fed to the CRT
through an appropriate brightness circuit 61. The CRT normally
includes a phosphor screen 62, or the like, which remains
illuminated sufficiently long after the scanning beam has passed to
form a full frame image over its face. Alternately, the screen may
be illuminated substantially only at areas at which the scanning
beam currently resides. In either case, the member 51 is able to
record the loci of the beam and retains the information for a
comparatively long period of time as long as an electric field is
applied across the elastomer. Consequently, a two dimensional image
may be formed on the surface of the CRT by any scanning or raster
pattern and be simultaneously or subsequently recorded as a surface
deformation image on member 51. Appropriate lens elements 63 are
interposed between the photoconductor on member 51 and the screen
62 to create the surface deformation image. The photoconductor in
the member 51 must be sufficiently sensitive to respond to the
relatively low levels of light available from CRT displays.
Selenium and selenium arsenic alloys are examples of
photoconductors having sensitivities in the order of 1 erg/cm.sup.2
which are capable of rapid response to the light levels associated
with CRT displays.
The surface deformation image created on portion 53 of member 51 is
simultaneously or subsequently read out by appropriate means such
as that including lamp 65 and lens 66. The lamp is a non-coherent
light source of high intensity. As explained earlier, the light is
diffracted by the surface deformation image, is collected by
appropriate lens elements 66 and focused onto a plane tangent to
drum 71. The image temporarily recorded on member 51 is permanently
recorded by the xerographic recording system 55. Lens element 66
scans an image on member 51 synchronously with rotation of the
xerographic drum 71. The temporary image is projected in a
line-by-line fashion through the slot in light shield 70 to a line
on drum 71 defined by point 72. The scanning arrangement shown is
representative and special consideration is given in an actual
machine to compensate for changing distances between lens 66 and
image point 72. For example, the focal length of lens 66 may be
that distance between the lens and point 72 when the lens is at the
midpoint in its scanning path as shown. The amount of out-of-focus
when the lens is at other points in the scan path indicated by the
phantom lines of a lens is minimized by techniques known in the
art.
The xerographic drum includes a photoreceptor coated onto a
grounded conductive drum. The photoreceptor is charged by a
corotron 73 and a latent electrostatic image is created on this
charged surface as the drum moves past the shield 70. The latent
image is developed by appropriate apparatus such as a cascade
developer 74 that pours microscopic toner particles onto the drum
that adhere in the image areas. The developed latent image, i.e.,
the toner image, is transferred to web 75 by electrostatics when
corotron 76 deposits charge of appropriate polarity on the back
side of the web. The toner image is permanently fixed to the web by
heating the toner as with fuser 77. The drum surface is cleaned by
means 78, e.g., a brush, flooded with light by lamp 79 and
recharged by corotron 73 to prepare for the formation of another
toner image.
When two or more imaging members 51 are arranged in parallel, one
can be used to record information generated on the CRT while other
imaging members are being read out by having their recorded
information projected onto a recording medium such as the
xerographic apparatus.
The above described systems are highly advantageous because analog
and digital computers often generate information in irregular time
intervals whereas xerographic and other recording apparatus operate
on highly organized information and employ fixed operating cycles.
The image device 51 bridges the gap because it is able to: record
irregularly generated information; hold the information in a highly
organized state for getting into phase with the reproduction cycle
of xerographic or other imaging device; rapidly erase the recorded
information; and immediately record new information.
The xerographic apparatus 55 may be replaced by other recording
materials and/or apparatus. For example, photographic type films
having sensitivities far too insensitive to respond to the light
levels generated by a CRT display may be used because the necessary
energy levels can be supplied by lamp 65. Vesicular duplicating
films available from the Kalvar Corp. of New Orleans, La. are
examples of such films.
In the foregoing there has been disclosed methods and apparatus
indicating the application of elastomers to various imaging
apparatus as described herein. By the use of an elastomer material,
there is obtained a fully cyclical imaging apparatus on which
images may be recorded, stored for short periods of time and erased
at will. In the specification herein, specific materials and
construction have been discussed with regard to the makeup of the
imaging sandwich, but it is obvious that other construction may be
available utilizing the elastomer material without deviating from
the principles of the present invention. Therefore, while the
invention has been described with reference to specific
embodiments, it will be understood by those skilled in the art that
various changes may be made and equivalents may be substituted for
elements thereof without departing from the true spirit and scope
of the invention. In addition, many modifications may be made to
adapt to a particular situation without departing from the
essential teachings of the invention.
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