U.S. patent number 3,655,371 [Application Number 02/822,097] was granted by the patent office on 1972-04-11 for method and apparatus for reproducing optical information.
This patent grant is currently assigned to General Electric Company. Invention is credited to George J. Chafaris.
United States Patent |
3,655,371 |
Chafaris |
April 11, 1972 |
METHOD AND APPARATUS FOR REPRODUCING OPTICAL INFORMATION
Abstract
The disclosure relates to a method and apparatus for storing and
reproducing information using a deformable material containing a
volumetrically homogeneous distribution of particles for scattering
light transmitted through said material. The information can be
introduced and read-out in optical form.
Inventors: |
Chafaris; George J. (East
Syracuse, NY) |
Assignee: |
General Electric Company
(N/A)
|
Family
ID: |
25235130 |
Appl.
No.: |
02/822,097 |
Filed: |
June 22, 1959 |
Current U.S.
Class: |
430/21; 386/314;
386/E5.057; 430/50; 348/772; 365/126; 430/104; 399/131;
347/113 |
Current CPC
Class: |
H04N
5/82 (20130101); G03G 16/00 (20130101); G03G
5/022 (20130101) |
Current International
Class: |
G03G
5/02 (20060101); G03G 16/00 (20060101); H04N
5/80 (20060101); H04N 5/82 (20060101); G03G
5/022 (20060101); B41m 005/20 () |
Field of
Search: |
;95/1,1.7
;346/1,74,76,107,74P,74ES,74TP ;41/17,24,46,10,18 ;96/1,1.1,1.5
;204/2 ;178/6.6,7.5,66TP ;355/9 ;340/173TP |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Van Horn; Charles E.
Claims
What I claim as new and desire to secure by Letters Patent of the
United States is:
1. A medium for storing information in distributed surface elements
for use in an optical reproducing system comprising a layer of
thermally softenable, transparent, nonconducting material,
deformable in thickness, supported by a base layer and a conducting
layer, the melting temperature of the deformable material being
lower than that of said base and conducting layers, said deformable
material having dispersed therein a volumetrically homogeneous
distribution of particles for scattering light transmitted through
said material, said layer containing a plurality of light
scattering particles for each element to cause a light scattering
effect as a function of the number of particles in said layer at
each said element which number is in turn a function of the
thickness of said layer at said element, whereby upon passage of
said light through each element of said material after deformation
thereof the light is scattered in each element, the extent of the
scattering being a function of the thickness of said each
element.
2. A storage medium as in claim 1 wherein said particles are of a
density to scatter said transmitted light without substantial
attenuation thereof.
3. A storage medium as in claim 2 wherein said particles have a
diameter in the range of from 1 to 5 microns.
4. A medium for storing information in distributed surface elements
for use in an optical reproducing system comprising a transparent
tape having a first and second outer layer and an intermediate
layer, said first outer layer serving as a supporting layer for the
other layers, said intermediate layer consisting of a transparent
conductive material, said second outer layer being deformable in
thickness and formed of a thermoplastic material having a melting
temperature below that of said other layers and having embedded
therein a volumetrically homogeneous distribution of light
scattering particles for scattering light transmitted through said
material, said particles having a diameter in the range of from 1
to 5 microns, said second outer layer containing a plurality of
light scattering particles for each element to cause a light
scattering effect as a function of the number of particles in said
layer at each said element which number is in turn a function of
the thickness of said layer at said element, whereby upon passage
of transmitted light through each element of said material after
deformation thereof said light is scattered in each element, the
extent of the scattering being a function of the thickness of said
each element.
5. A storage medium as in claim 4 wherein said light scattering
particles are of a density to scatter said transmitted light
without substantial attenuation thereof.
6. In a reproducing system wherein information is introduced in
distributed surface elements in the form of an optical image to a
recording device having as the storage medium a reusable
transparent tape having a layer of thermoplastic material in which
there is embedded a volumetrically homogeneous distribution of
light scattering particles, said thermoplastic layer containing a
plurality of light scattering particles for each element to cause a
light scattering effect as a function of the number of particles in
said layer at each said element which number is in turn a function
of the thickness of said layer at said element, said optical image
being applied to the surface of said transparent tape in the form
of a differential charge which is placed thereon by a
charge-discharge circuit including a layer of photoconductive
material, a method for the storing and processing of said
information comprising the steps of: moving a selected portion of
said thermoplastic layer and said photoconductive material into
electrical contact, uniformly charging each surface element of said
selected portion, variably discharging said each surface element by
the application of said optical image to said photoconductive
layer, there being retained by said surface an electrostatic image
which is a replica of said optical image, said electrostatic image
exerting electrostatic forces upon said surface, softening said
selected portion of said layer of thermoplastic material by
applying heat thereto whereby said electrostatic forces produce a
thickness modulation of said portion, said thickness modulation
causing the number of light scattering particles for said surface
elements of said selected portion to be varied.
7. In a reproducing system wherein information is introduced in
distributed surface elements in the form of an optical image to a
recording device having as the storage medium a reusable
transparent thermoplastic tape having a layer of thermoplastic
material in which is embedded a volumetrically homogeneous
distribution of light scattering particles, said thermoplastic
layer containing a plurality of light scattering particles for each
element to cause a light scattering effect as a function of the
number of particles in said layer of each said element which number
is in turn a function of the thickness of said element, said
optical image being stored in said tape by a charge-discharge
circuit which includes a layer of photoconductive material and
being read-out from said tape using a suitable projection system, a
method for the storing, processing and reading-out of said
information comprising the steps of: moving a selected portion of
said thermoplastic tape into a first position in electrical contact
with said photoconductive material, uniformly charging surface
elements in a variable manner through said photoconductive material
which material acts as a variable resistance in response to the
impinging optical image, there being retained on said surface an
electrostatic image which conforms to said optical image, said
electrostatic image exerting electrostatic forces upon said
surface, moving said selected portion into a second position out of
contact with said photoconductive material and adjacent to a
heating element, applying a short duration of heat to said selected
portion whereby the thermoplastic material of said selected portion
is heated to the melting point causing said electrostatic forces to
deform said selected portion thereby storing said information as a
thickness modulation, the number of said light scattering particles
for said surface elements being proportional to the elemental
thicknesses, cooling the thermoplastic material of said selected
portion, moving said selected portion to a third position within
said suitable projection system, and reading-out the stored
information by projecting a source of light through said selected
portion, whereby the projected light is scattered at said surface
elements as a function of said elemental thicknesses, the
information being determined by the extent of the scattering.
8. In combination in a recording system adapted to record
information introduced in distributed surface elements in the form
of an area display, a thermoplastic tape including a layer of
transparent non-conducting material having dispersed therein a
volumetrically homogeneous distribution of light scattering
particles, said layer containing a plurality of light scattering
particles for each element to cause a light scattering effect as a
function of the number of particles in said layer at each said
element which number is in turn a function of the thickness of said
layer at said element, a first means for simultaneously charging
each surface element of a selected portion of said tape in
conformance with said information, and second means for thermally
softening said electrically charged selected portion whereby the
electrostatic forces exerted by the surface charges produce a
variation in the thickness of said portion at said each surface
element, said thickness variations containing the recorded
information.
9. In combination in a recording system as in claim 8 wherein said
first means comprises a layer of photoconductive material.
10. A recording system as in claim 8 wherein said distribution of
light scattering particles is of a density to scatter light
transmitted through said tape without substantial attenuation of
said light.
11. In combination in a reproducing system adapted to store,
process and read-out information introduced in distributed surface
elements in the form of an optical image, a thermoplastic tape
including a layer of thermoplastic material having embedded therein
a volumetrically homogeneous distribution of light scattering
particles, said thermoplastic layer containing a plurality of light
scattering particles for each element to cause a light scattering
effect as a function of the number of particles in said layer at
each said element which number is in turn a function of the
thickness of said layer at said element, photoconductive means for
simultaneously charging each surface element of a selected portion
of said tape in conformance with the intensity of said optical
image, means for thermally softening said electrically charged
selected portion whereby the electrostatic forces exerted by the
surface charges produce a variation in the thickness at said each
surface element resulting in a thickness modulation of said
selected portion of said thermoplastic tape, and a phase
demodulation projection system responsive to scattered light for
reading out said information by projecting a source of light upon
the thickness modulated tape, whereby the passage of light through
said selected portion of said thickness modulated tape produces a
scattering of said light at each surface element, said scattering
being a function of the thickness at said each surface element and
the read-out information being determined by the extent of the
scattering.
12. In combination in a recording system adapted to record
information introduced in distributed surface elements in the form
of an optical image, a transparent thermoplastic tape having a
layer of thermoplastic material in which is embedded a
volumetrically homogeneous distribution of light scattering
particles, said thermoplastic layer containing a plurality of light
scattering particles for each element to cause a light scattering
effect as a function of the number of particles in said layer at
each said element which number is in turn a function of the
thickness of said layer at said element, a layer of photoconductive
material, first means for bringing a selected portion of said
thermoplastic material and said photoconductive material into
electrical contact, a charging circuit for placing a uniform charge
on the surface of said selected portion, second means for applying
said optical image to said photoconductive material, a discharging
circuit including said photoconductive layer for variably
discharging said surface in conformance with the intensity of said
optical image so as to retain thereon a variable charge in the form
of an electrostatic image, said electrostatic image being a replica
of said optical image and exerting electrostatic forces upon said
surface, and third means for heating said selected portion of the
thermoplastic material to the softening point whereby said
electrostatic forces produce a thickness modulation of said
selected portion, said thickness modulation causing the number of
light scattering particles for said surface elements of said
selected portion of the thermoplastic material to be varied.
13. A recording system as in claim 12 wherein said distribution of
light scattering particles is of a density to scatter light
transmitted through said tape without substantial attenuation of
said light.
14. In combination in a reproducing system adapted to store,
process and read-out information introduced in the form of an
optical image, a transparent thermoplastic tape having a layer of
thermoplastic material in which is embedded a homogeneous
distribution of light scattering particles, a layer of
photoconductive material, first means for bringing a selected
portion of said thermoplastic material and said photoconductive
material into electrical contact, a charging circuit for placing a
uniform charge on the surface of said selected portion, second
means for applying said optical image to said photoconductive
material, a discharging circuit including said photoconductive
layer for variably discharging said surface in conformance with the
intensity of said optical image so as to retain thereon a variable
charge in the form of an electrostatic image, said electrostatic
image being a replica of said optical image and exerting
electrostatic forces upon said surface, third means for heating
said selected portion of the thermoplastic material to the
softening point whereby said electrostatic forces produce a
thickness modulation of said selected portion, said thickness
modulation causing the number of light scattering particles for
elemental areas of said selected portion of the thermoplastic
material to be varied, a projection system comprising a source of
light that is projected to a screen through first and second bar
systems, each having alternating transparent and opaque portions,
said bar systems being placed between said light source and said
screen and serving to prevent direct rays of said projected light
from reaching said screen, said modulated portion of the
thermoplastic tape being placed between said first and second bar
systems to receive said projected light and to cause a scattering
thereof at said elemental areas which is in direct relation to the
number of scattering particles for said areas whereby the scattered
light reaching said screen forms thereon a replica of said
introduced optical image.
Description
The present invention relates to a method of and apparatus for
reproducing information, and to a novel medium for storing said
information, and relates more particularly to a reproducing system
wherein information is introduced and read-out in optical form,
said information being stored by a physically deformable
member.
Both military an commercial requirements for a long time have
existed for recording a replica of a phenomenon in such a manner
that it can be faithfully analyzed at a later time. The
requirements for recording duration, bandwidth, and number of
channels have become more demanding with the passage of time. Among
the techniques that have been used in satisfying these requirements
are those of photographic recording, magnetic tape recording,
dielectric recording, which is accomplished by placing a charge
distribution on the surface of a dielectric or by inducing a
polarization in the volume of a dielectric, and others. More
recently thermoplastic recording has been attempted and has been
shown to have certain advantages over other recording methods. A
complete disclosure of such a system may be found in an application
for U.S. Letters Patent Ser. No. 698,167 titled "Method and
Apparatus for Electronic Recording" filed Nov. 22, 1957 by William
Glenn and assigned to the present assignee now abandoned.
The above referred to reproducing systems lack the ability to
reproduce optical information in a simple and expedient manner. The
instant invention is intended to satisfy this need and provides a
system that is able to directly receive information in optical
form, similar to photographic recording, but which information is
processed, stored and readied for display within a fraction of a
second. The processing or developing operation is performed by an
electrical process. The system additionally utilizes a reusable
storage medium.
The earlier method of thermoplastic recording proposed by Glenn,
which present invention invention seeks to improve, utilizes as the
storage medium a deformable, clear thermoplastic tape. Generally,
this earlier method is an improvement over a known technique of
writing information on an oil film by the application of electrical
charges from a scanning modulated electron beam. In this technique,
the oil film is deformed to contain optical line gratings of
variable depth by the action of the electrostatic forces of
adjacent electrical surface charges deposited by the beam, but the
gratings are retained only so long as the electrical charges are
present. When these charges leak off, the oil film resumes its
normally even contour. A suitable optical system, similar to that
presently to be described with relation to FIG. 7, is utilized in
reading out the information from the deformed oil film. In this
manner theatre size projection of television signals has been
accomplished.
The use of thermoplastic tape in lieu of the oil film, as in the
above mentioned system, has the advantage of obtaining a permanent
record or recording of the input information. The thermoplastic
tape is effectively a very high resolution, reusable
photographic-like film that is developed almost instantaneously by
non-chemical means. In the Glenn method as in the oil film
technique, information to be stored is amplitude or velocity
modulated on a scanning electron beam. In explaining the operation
of this system, we will consider only amplitude modulation which is
commonly used for the recording of black and white television
pictures. The information is deposited on the surface of the
thermoplastic tape in the form of a geometrical distribution of
electrical charges. As a result of the surface scanning, which for
television pictures is at the conventional rate of 525 lines per
frame, these charges are laid down as a raster having many lines of
charges. Each elemental portion of each scanned line develops a
particular charge value corresponding to the beam intensity at that
element. By application of heat to the thermoplastic material which
softens the material, the lines of charges deform into optical
gratings, as will be explained below, which are in the shape of
ripples. This due to the action of the electrostatic forces of the
line charges. Upon cooling, the deformations become set and each
bit of information or picture element is stored in the
thermoplastic tape as an elemental optical grating. The optical
gratings are formed by the beam along parallel lines in the
direction of scanning. They consist of "troughs" and "crests,"
wherein the "troughs" are formed by the lines of charges deposited
by the electron beam causing rut-like depressions in the surface of
the tape and the "crests" by the spacings between scanned lines,
the elevation of which is substantially unaffected. A ripple effect
is thereby created wherein the instantaneous depth of the ripple
troughs is approximately proportional to the charge density as
determined by the amplitude of the signal applied to the electron
beam. For high intensity or bright signals the troughs are made
deeper, and for low intensity signals they are less deep. In this
manner the input information is stored in the surface deformations
of the thermoplastic medium, more specifically being stored in the
optical grating lines formed on said surface, from which the
information may be recovered as a result of the diffractive (or
refractive) properties of said gratings.
A special type of projection system, which is a form of optical
phase demodulation system, is utilized for recovering the
information stored in the diffraction (or refraction) gratings.
Briefly, the system responds to diffracted (or refracted) light
which is transmitted to a screen or other read-out medium, through
the modulated thermoplastic medium. As opposed to conventional
slide projection systems, this type of a system is non-responsive
to density variations. The diffraction (or refraction) of the light
occurs when light is incident upon the slope portions of the
gratings, and the extent thereof is a function of the slope.
Diffraction and refraction may be distinguished in that refraction
effects contemplate large incident surfaces relative to the
wavelength of light, and are explained by the simple rules of
geometrical optics. Diffraction effects contemplate small incident
surfaces relative to the light wavelength, and require explanation
by Huygens optical principles. Thus whether the projected light is
considered to be refracted or diffracted depends upon the
dimensioning of the gratings as related to the wavelength of light.
Both of these properties are referred to in accounting for the
dispersive phenomenon of the light contributed by the gratings.
With a modulated tape placed in this type of projection system, the
portions of the image formed on the tape, wherein the rippled
gratings are relatively deep, corresponding to bright picture
areas, will disperse a considerable amount of light. Hence the
light output transmitted to the screen, being determined by the
amount of dispersion, will also be considerable. The portions
corresponding to darkness, wherein the gratings are shallow, will
disperse and hence cause transmission of little light to the
screen. The information on the tape is thus recovered and may be
utilized directly by displaying on a screen, as indicated above, or
may be converted to an electrical signal by a photoelectric device
for further processing.
When the information to be handled in such prior art thermoplastic
reproducing systems as described above is of an optical nature,
such as a picture image, it is seen that it is necessary to first
scan the picture to convert the light energy to electrical energy
which is then used to modulate an electron beam. The writing
operation is thus required to be performed within a vacuum which
necessitates enclosing at least the tape and tape reels in a vacuum
chamber and providing effective vacuum seals and pumps. The present
invention avoids the necessity of obtaining a scanned intermediate
electrical signal by introducing the light information to the
thermoplastic tape directly as an optical signal rather than as an
electrical signal. This direct introduction of the light
information is accomplished by use of a two dimensioned charged
surface representative of the optical image.
It should be understood at this point that use of the grating
technique, above referred to, wherein the diffractive (or
refractive) properties of the slope portions of the grating are
utilized during read-out, is not possible when introducing light
information directly to the thermoplastic storage medium. This is
so because light thus introduced produces no grating lines on the
thermoplastic material. Rather surface deformations are formed on
the thermoplastic at each elemental area in accordance with the
intensity of the light input. The slope portions formed by these
surface deformations cannot be used in an optical projector to give
an accurate read-out. For example, both, extensive bright portions
and dark portions of a picture would appear similarly as a dark
output, since the surface contour for these portions would be flat
and have a zero slope. Only the boundaries between right and dark
portions would have a slope and appear bright.
Optical information has been introduced directly in recording
systems of the prior art, but these systems are of limited or
distinctly different application. In one such system, using a
xerographic process which employs a photoconducting plate,
electrical charges are formed on the surface of a uniformly charged
selenium plate by the selective discharging action of an applied
optical image. This process has been used in printing, etching, or
electroplating processes but has found no known application to
optical projection systems.
In another system an ultraviolet light when applied to an
ultraviolet-sensitive plastic emulsion, will release small
quantities of nitrogen gas which is held under pressure by the
plastic emulsion. Upon heating, the plastic is temporarily softened
allowing the gas to expand, forming tiny bubbles. Such system is
used for the production of projection positives from black and
white negatives or for the production of black and white negatives
from color transparencies. The negatives are placed in a printer
wherein a source of ultraviolet light is transmitted through the
negatives to the sensitive plastic. In development, bubbles are
formed in the plastic in accordance with the intensity of the
impinging ultraviolet light. The color transparencies are similarly
printed. Projection is performed in a conventional projector, the
bubbles scattering the transmitted light rays and having the same
effect as the opaque silver image in conventional films. This
system, although advantageous in producing positive and negative
transparencies without the need for chemicals and under normal
room-lighting conditions, cannot be used for taking pictures at
hand held shutter speeds because of the requirement of ultraviolet
light. Further, the special plastic is not subject to reuse.
It should be recognized that distinct limitations exist in prior
art recording techniques in the handling of optical information. In
most systems it has been necessary in the past to convert the
optical information to electrical energy which must be applied to
cumbersome electronic apparatus in the writing operation. In
devices where optical energy has been introduced directly, there
has been limited application. The instant invention is intended to
overcome these limitations and to be an improvement over the prior
art systems. Optical information in the form of ordinary light may
be introduced directly to a simple, portable recording equipment.
The recordings obtained are of a high resolution. No vacuum is
necessary in the writing operation. The recording medium may be
used recurrently. The recording and developing operations are
substantially instantaneous, requiring as little as a fraction of a
second. The recorded information is susceptible to being read-out
by optical means and may be projected on a screen or converted into
electrical energy for further processing by being applied to a
photoconductive device. The instant invention is flexible in its
application. It may be used to record purely optical images, such
as in conventional photography, or it may record electrical
information which has been converted into light energy, such as
information on a radar screen or a flying spot scanner. Moreover,
the rate of recording is sufficiently rapid for recording motion as
well as still subject matter.
It is accordingly a primary object of the present invention to
provide a novel method for the storage, processing and display of
information which is introduced optically.
It is a further object of the invention to provide a novel
reproducing apparatus for the storage, processing, and display of
information which is introduced optically.
A further object of the invention is the provision of a transparent
thermoplastic tape of novel composition for use in a reproducing
system wherein read-out is achieved in a suitable optical
projection system.
Another object of the invention is to provide a novel system for
the recording and displaying of an optical image by recording said
image upon a thermoplastic medium and displaying said image by use
of a suitable optical projection system which responds to scattered
light.
A further object of the invention is to provide an optical image
reproducing system in which information is applied by electrical
means upon a reusable storage medium without the requirement of a
vacuum.
Still a further object of the present invention is the provision of
a reproducing system in which read-out of a thermoplastic tape is
accomplished by means of a suitable projector responsive to
scattered light, wherein the novel composition of the thermoplastic
tape provides a scattering of the projected light.
These and other objects of the invention are achieved in a novel
reproducing system useful for the storage, processing, , and
display of information which is introduced as an optical image, or
other optical form, to a recording apparatus. A novel storage
medium is utilized which comprises a transparent thermoplastic tape
having embedded therein a homogeneous distribution of tiny light
scattering particles, In recording an optical image each elemental
area of the surface of a selected portion of the thermoplastic tape
is variably charged to form an electrostatic image which is in
conformance with the received optical image, by means of a
contiguous photoconductive material. The tape is then transformed
to a fluid state by heating and is then deformed by the action of
the electrostatic forces of the surface charges, resulting in a
thickness modulation of said tape. Read-out is accomplished by
placing the modulated tape in a suitable optical system responsive
to scattered light, one similar to the type used in the earlier
thermoplastic recording, in which the extent of the scattering of
projected light by the tape determines the information
obtained.
The recorded information in the present invention is contained in
the instantaneous thickness of elemental areas of the thermoplastic
material in which the particles are uniformly distributed. The
thickness of this material at any point is made to vary in
accordance with the light intensity of the applied image. The
thicker elemental portions thus contain a larger number of
scattering particles and create a brighter area in the output image
when displayed in the optical projector. The light intensity of
each elemental area of an image as it appears on the projection
screen is determined by and is a function of the number of
scattering particles contained at the corresponding elemental area
of the modulated tape. Thus the projected light is intensity
modulated by the scattering particles to form the desired image.
This read-out is seen to significantly differ from the earlier
method of thermoplastic recording using a grating technique with a
clear thermoplastic material, wherein the information is contained
in surface ripples and the projected light in the optical system is
diffracted or refracted by the variable slope surface portions of
the ripples.
The invention will be better understood from the following
description taken in connection with the accompanying drawings and
its scope will be pointed out in the appended claims.
In the drawings,
FIG. 1 is an isometric view of applicant's overall reproducing
system;
FIG. 2 is an isometric view of an alternative embodiment of
applicant's reproducing system;
FIG. 3 is a diagram of a composite recording and developing
apparatus used in the novel system illustrated in FIG. 1;
FIG. 3a is a cross sectional view of the thermoplastic tape
magnified many times actual size;
FIG. 3b is an illustration of a portion of FIG. 3 in an operational
sequence wherein the tape is out of contact with the pressure plate
and the photoconductive device;
FIG. 4 is a schematic diagram of the charge-discharge circuits of
FIG. 3;
FIG. 5 is a timing chart illustrating the timing relationship
between the shutter operation and the synchronized switching
circuitry;
FIGS. 6A, 6B, and 6C are diagrams illustrating the physical
principles involved in obtaining thickness modulation of the
thermoplastic material; and
FIG. 7 is an explanatory diagram of a suitable projection system
which may be used in the present invention.
Referring to FIG. 1 there is shown an isometric view of an
embodiment of applicant's thermoplastic tape reproducing system
consisting of a recording or encoding device 1 and a projection
system 2. Encoder 1, shown in detail in FIG. 3, takes the general
form of a camera and is adapted to receive optical information in
the form of an image I. The encoder is shown to comprise a lens
barrel 3, a shutter release button 4 and a shutter reset lever 5.
The encoder performs the function of thickness-modulating the tape
29 in accordance with the received optical image, the tape being
handled within the apparatus by a tape transport mechanism,
comprising a feed reel 37 and a take-up reel 38, guide sprockets 35
and 36, and a mechanical drive, not shown. Read-out of the
modulated tape is accomplished by a projector 8, whose lens system
is illustrated in FIG. 7, wherein a facsimile of the received image
is projected on screen 9. The projector includes a projection lamp
19, a tape transport mechanism for handling rolls of modulated
thermoplastic tape 29', comprising a feed reel 10 and take-up reel
11, and guide sprockets 17 and 18, shown in position with the lens
system. The lens system includes lenses 60, 62 and 64 and bar
systems 61 and 63 having concentric annular opaque and transparent
portions.
The illustrated system, comprising elements 1 and 8, is for the
taking and projecting of still pictures, or slides. It should be
understood, however, that the present invention is not limited to
processing stills since the rate of taking pictures may be set at
many times the rate necessary for motion picture projection, the
actual exposure and development time being within a fraction of a
second.
If desired, the projector and recorder units may be combined in a
single structure, such as unit 14 shown in FIG. 2, wherein the tape
transport mechanism comprising feed reel 15 and take-up reel 16
carries the developed tape directly to the projector. In this
manner the three sequences of operation, expose, develop, and
display, may be performed in uninterrupted fashion. The component
structural parts and the circuitry included in unit 14 are
essentially the same as contained in encoder 2 and projector 8.
Referring to the detailed illustration of the encoder in FIG. 3, an
optical image I is impressed on to a transparent thermoplastic tape
29 in the form of distributed electrical charges. In the
illustration shown, which is merely a schematic representation,
received light passes through an optical lens 21 which focuses the
image through an adjustable diaphragm 22, which controls the
exposure, through shutter 23 upon a layer of photoconductive
material 28. Button 4 operates the shutter and lever 5 performs the
reset. The lens, diaphragm, and shutter are standard photographic
components which may be found in a conventional still or motion
picture camera. 35MM camera parts are applicable but other size
camera components can be used. A suitable form of shutter is the
Kodak Flash Supermatic shutter manufactured by the Eastman Kodak
Company of Rochester, New York. A photoconductive device 24 is
provided which comprises a non-conducting mounting frame 25, a thin
optically flat glass plate 26, on which is deposited, in a known
manner, a thin layer of tin oxide 27 or a similar transparent
electrically conducting layer. The photoconductive material 28
abuts the conducting layer so that good electrical contact is made.
The photoconductive material may be cadmium sulfide, or a similar
material possessing photoconductive properties, and although shown
relatively thick with respect to the conducting layer may have
thickness dimensions comparable to said layer.
The thermoplastic tape 29, upon which an electrostatic image charge
is applied by means of the photoconductive material, is preferably
of three layer construction. This construction is seen more clearly
in FIG. 3a. The base layer 33 is a motion picture film stock of 1-3
mils thickness capable of withstanding the heat of development,
100.degree. to 150.degree. C. Lexan, a product of the General
Electric Company, Mylar or Cronar, both products of the E. I.
DuPont de Nemours & Company, are suitable. The intermediate
layer 32 is preferably of evaporated chromium which is a
transparent highly conductive material, usually deposited to about
1 micron in thickness. Other material such as a cuprous iodide may
be used. The third layer is a transparent thermoplastic material 31
in which are embedded a homogeneous distribution of tiny light
scattering particles 30, 1 to 5 microns in diameter. A polystyrene
preferably PS-2 hyperclean polystyrene, the number indicating the
molecular weight, in the order of 20 microns to 1 mil thickness, is
suitable for the material 31. The melting point of the polystyrene
is in the range of 100.degree. to 150.degree. C. This is
appreciably lower than the melting point of the plastic film stock.
The scattering particles 30 may be transparent, in the form of air
entrapped glass bubbles or finely ground glass particles, whose
index of refraction is different from that of the thermoplastic
material. Or they may be opaque, such as carbon black. They are
embedded by being mixed in a liquified form of thermoplastic
material, in a density to effectively scatter light transmitted
through the tape without substantial attenuation of the light as it
emerges from the tape.
The thermoplastic tape transport and positioning mechanism of FIG.
3 transports the tape in position for exposure in the encoder,
during exposure holds the thermoplastic layer in contact with the
photoconductive device, and after exposure transports the tape
through the developing position. This mechanism comprises a feed
reel 37 and take-up reel 38, driven either manually, or by a drive
motor 44, as shown. Sprockets 35 and 36 and idler wheels 52 and 53
serve to guide the tape into a position adjacent the
photoconductive device, but separated therefrom. The sprockets are
set back and exert a tension to maintain the tape displaced from
the photoconductive device when the tape is not being forced
against the photoconductor, as during its longitudinal movement.
This displaced position is shown in FIG. 3b. In the proper
operational sequence, as will be presently understood, metal
pressure plate 34 forces the tape against the photoconductor so
that good electrical contact is made between the thermoplastic
material 31 and the photoconductive material 28 and between the
pressure plate 34 and the Mylar base 33. The solenoid actuated rod
41 working against tension springs 42 and 43 actuate the pressure
plate 34 in a transverse direction into and out of contact with
material 31. The solenoid is energized by a circuit through switch
S2.
With plate 34 in contact with base 33 a charge circuit for the
thermoplastic tape is formed by the plate 34 being electrically
connected at its lower end through conductor 45 to a single pole
triple throw switch S1. Switch S1, as well as switch S2, are
mechanically linked to the shutter mechanism and shutter reset
mechanism contained in a housing 20 by means of shaft 50 coupled to
the shaft, not shown, which supports the shutter reset lever 5.
Operation of the shutter serves to synchronously move the switches
in the direction shown, as the shutter reset lever 5 moves.
Movement of the shutter reset lever 5 to reset the shutter
mechanism additionally serves to reset the switches S1 and S2 to
position 1. Contact 1 of switch S1 is connected to the positive
terminal of battery B1 having voltage in the range of 300 to 1,000
volts. When the recorder is not in use, S1 will normally be in this
charge position. It is seen that a closed circuit, including
conductor 46 and conducting layer 27, thereby connects the battery
in series with the thermoplastic tape 29 and the photoconductive
material 28 so that a charge of the total battery voltage is placed
across the thermoplastic tape 29. Contact 2 of switch S1 is
commonly connected to the negative terminal of battery B1 and to
the conducting layer 27 of the photoconductive device. When S1 is
connected to contact 2, which is the expose or discharge position,
a discharge path is formed for the charge previously developed
across the thermoplastic tape, from the surface of the
thermoplastic material 31 through the photoconductive material 28
to the transparent conducting layer 27, through conductor 46 to
contact 2, through the contact arm of S1 and through conductor 45
to the pressure plate 34. Movement of S1 to position 3 interrupts
the discharge circuit.
The discharge path as well as the charge path are illustrated in
schematic form in FIG. 4 wherein C.sub.b1- C.sub.bn are the
elemental capacitances across the Mylar base 33, C.sub.T1 -C.sub.tn
are the elemental capacitances across the thermoplastic material
31, and R.sub.p1 -R.sub.pn are the elemental variable resistances
of the photoconductive material 28. The components are represented
as forming N number of parallel paths. The sum of capacitances
C.sub.b1 -C.sub.bn is equal to the total capacitance of the base
layer 33, which is indicated as C.sub.B. The sum of capacitances
C.sub.t1 -C.sub.tn is equal to the total capacitance of the
thermoplastic layer 31, and is indicated as C.sub.T. The sum of the
resistances R.sub.p1 -R.sub.pn is equal to the total resistance of
the photoconductive layer 28, and is indicated as R.sub.P. In the
charge position with switch S1 engaging contact 1, battery B1 will
charge the base capacitance C.sub.B and the thermoplastic material
capacitance C.sub.T through the photoconductor resistance R.sub.P
which is in its high resistance state. After a finite period the
total battery voltage is distributed across capacitors C.sub.B and
C.sub.T. The component values of the circuit are selected So that
approximately half of the voltage appears across C.sub.T. This
provides for retaining a sufficient amount of charge across C.sub.T
after the discharge operation to readily deform the thermoplastic
material when heated to 100.degree.- 150.degree. C. A variable
discharge of C.sub.T occurs when S1 is moved to contact 2, R.sub.P
having been exposed to light, now being in a low resistance state
with the resistance in each path different as determined by the
light intensity at each point of the photoconductive material.
Movement of S1 to contact 3, which is unconnected, opens the
discharge circuit, and provides for retaining a variable charge on
the capacitance C.sub.T. The value of gamma may be controlled by
interrupting the discharge operation, the latter being related to
the exposure time and diaphragm setting, within a time determined
by the RC time constant of the circuit in elements of bright
exposure. If, for example, parallel branch 1 represents and element
of bright exposure, its RC time constant is low as compared to a
branch of dark exposure, and the duration of the discharge
operation is within said low time constant. As a result, the
variable charge that is retained on the surface of the
thermoplastic tape is in conformance with the received optical
image. The above method of charging and discharging the
thermoplastic tape using a photoconductive device is the preferred
form. However, it should be understood that alternative methods may
be used such as charging xerographic plate in accordance with a
light image and transferring the charge to the thermoplastic tape
by joining the charged surface of the xerographic plate and the
thermoplastic layer and connecting the tape conducting layer to the
backing electrode of the xerographic plate. Another method is to
maintain the thermoplastic capacitance C.sub.T in a normally
discharged condition, and upon exposure, to variably charge the
elemental capacitances C.sub.t1 -C.sub.tn. Gamma is then determined
by the time constant of the charge circuit.
Referring again to FIG. 3, the tape is developed when the switch S1
is in position 3. For this purpose a radiant heater circuit is
provided including battery B3 whose positive terminal is connected
through switch S3 to one side of heater element 47, which may, for
example, be a Nichrome wire, and the negative terminal is connected
to the other side of element 47. A coil form 48 supports the heater
element. The battery B3 provides a voltage sufficient to raise the
temperature of the thermoplastic material to
100.degree.-150.degree. C. In this temperature range the physical
property of the selectably softenable thermoplastic material is
changed from a solid to a fluid or softened state whereas the film
stock base remains in the solid state. An alternative form of
heater apparatus may be used of the induction type. Heat is
generated by inducing current in the conducting layer 32, the heat
being readily transmitted to the adjoining thermoplastic layer.
In the operation of the illustrated encoder, the shutter release
button 4 is mechanically coupled to the shutter operating mechanism
and through the shutter reset mechanism to the switches S1 and S2.
When button 4 is in the normal position, as shown, the shutter is
closed. Switch S1 engages contact 1 and switch S2 engages bar
contact 1, the forward edge of which corresponds to contact 1 of S1
which is indicated as position 1, and the rearward edge corresponds
to the rearward edge of bar contact 2 of S1. The bar contact of S1
is position 2. S2 in position 1 closes a circuit from battery B2
through S2, conductor 49, to the solenoid 40 back through conductor
51 through switch S4 to the other side of the battery. Solenoid 40
is thereby energized which forces plate 34 in good electrical
contact with Mylar base 33, so that a uniform charge is developed
across the thermoplastic tape through the photoconductive material
28 which is in its high resistance state. When button 4 is moved
inwards to operate the shutter mechanism, shutter 23 opens
admitting the optical image or energy. Simultaneously with the
opening, S1 engages bar contact 2, and S2 continues to engage its
bar contact 1. During the time interval that switch S1 is in
position 2 engaging bar contact 2, the length of which is
determined by the exposure time, the photoconductive material 28
becomes variably conductive in its elemental sections in accordance
with the light intensity applied to it. Accordingly, the charge on
the thermoplastic tape will leak off its elemental sections at
different rates through a myriad of parallel paths of differing
resistance. Simultaneously with the closing of shutter 23, switches
S1 and S2 disengage their respective bar contacts, and then travel
to position 3 where the contact of S1 is unconnected and the
contact of S2 is connected to the drive motor 44. With switch S1 in
position 3 the discharge circuit is interrupted which stops the
discharge process. The thermoplastic material retains a
differential surface charge representing a replica of the light
image received. Switch S2 in position 3 opens the circuit to
solenoid 40 de-energizing same, and causes the pressure plate to be
backed off from the thermoplastic tape by the action of tension
springs 42 and 43. Due to the tension exerted on the thermoplastic
tape by sprockets 35 and 36, the tape will accordingly take a
position clear of the photoconductive device and the pressure
plate. The position of the tape with respect to the pressure plate
and the photoconductive device in this sequence of operation is
shown clearly in FIG. 3b. Switch S2 in position 3 also closes a
circuit to single frame drive motor 44 which drives the tape
through one frame to a position adjacent heater element 47.
With the tape adjacent the heater in the development position, the
closing of switch S3 energizes the heater element which heats and
thereby liquefies the exposed portion of the thermoplastic material
causing it to deform by the action of the electrostatic forces
applied by the surface charges. This results in a thickness
modulation of the material wherein the number of particles in
elemental portions of the thermoplastic material is proportional to
the thickness of the material. Release of switch S3 opens the
heater circuit and allows the tape to cool in its deformed shape,
retaining the originally received light information in the form of
a thickness modulation. In the cooling process, the Mylar base acts
as a heat sink. The reset mechanism actuated by reset lever 5,
which is mechanically coupled to the shutter and to switches S1 and
S2, as previously mentioned, simultaneously acts to cock the
shutter and to reset the switches S1 and S2 to position 1. The
encoder is thus ready for the succeeding optical information. It is
noted that with switch S4 in the open position, a double exposure
may be obtained. This opens the circuit to the frame drive
mechanism and prevents the tape from being moved to the develop
position adjacent to the heater after a exposure sequence. When a
modulated tape is to be used again, in normal operation it need
only be put through the recording operation described above,
wherein erase and re-write can be carried out simultaneously. If
the tape is to be reused within 30 seconds to one minute,
electrical charges may remain trapped within the thermoplastic
material and it is desirable to erase the tape by reheating before
re-writing.
The timing sequence of the operation of switches S1 and S2 and the
shutter as they related to the above described operation can be
readily understood by referring to FIG. 5. Graph A shows the
shutter operation with respect to time. Graph B shows the charge
circuit operation with respect to time. Graph C shows the discharge
circuit operation with respect to time. Graph D shows the solenoid
energizing circuit operation with respect to time, and graph E
shows the drive mechanism energizing circuit operation with respect
to time. It is seen that the charge circuit, with switch S1
engaging contact 1, is closed for a time of n intervals during
which time the thermoplastic tape receives its even charge. This is
the normal position of S1. During this time the solenoid energizing
circuit is also closed maintaining the pressure plate in its
position in contact with the thermoplastic tape. At time tn, the
shutter operation commences and the charge circuit opens as S1
breaks engagement with contact 1. The shutter reaches the maximum
open position at time tn/ 1, at which time the discharge circuit
closes by S1 engaging bar contact 2. As shown, at predetermined
time tn/ 5, which time is determined by the exposure setting, the
shutter begins to close. A this point the discharge circuit and the
solenoid energizing circuit open, as switches S1 and S2
respectively disengage their bar contacts 1 and 2. At time tn/ 6
the drive mechanism energization circuit is energized to move the
tape a distance of one frame. This circuit remains energized until
the switches S1 and S2 are reset to position 1 by shutter reset
lever 5. The timing sequences indicated are exemplary and may be
modified in several respects without exceeding the scope of the
invention. For example, the charge circuit need not be opened at
the moment of the shutter operation but may be opened earlier, and
the drive energizing circuit need not be closed at the moment that
the shutter closes. It is advantageous that the discharge circuit
be closed during the time that the shutter is open for optical
efficiency.
It should be understood that the mechanical operation of the
switches, shutter and transport mechanism described herein is
merely exemplary and is not intended to form a part of this
invention. For example, if desired, the reset mechanism may be
automatic, operating at a finite time after the shutter is
actuated, or the develop switch S4 may be automatically actuated.
In a further alternative arrangement, the entire sequence of
operation may be made automatic so that a succession of pictures
are encoded and developed by operating a single lever, similar to a
motion picture camera.
FIGS. 6A, 6B, 6C illustrate the manner in which the electrical
charges, having been formed on the tape surface by the impinging
light, serve to deform the thermoplastic material. During the
expose operational sequence, shown in FIG. 6A, bright light is
applied to portion A of the photoconductor and absence of light to
adjacent portion B. This allows charge to run off from the surface
of portion A of uniformally charged thermoplastic through the
photoconductive material at a much greater rate than from portion
B. In a finite time period, corresponding to the exposure time that
switch S1 engages bar contact 2, no charge or a minimum charge is
retained at portion A while a maximum charge remains on the surface
at B, which creates induced charges on the surface opposite, as
shown in FIG. 6B. During the development sequence, after separation
of the thermoplastic tape from the photoconductor, when S1 is in
position 3, the thermoplastic material liquifies and the
electrostatic forces of repulsion between adjacent surface charges
and of attraction between surface and induced charges cause the
thermoplastic material to deform, as in FIG. 6C. Portion A is seen
to deform negligibly, if at all, whereas portion B deforms
appreciably. As illustrated in FIG. 6C, the number of scattering
particles per unit surface area in the deformed portion B is
considerably less than in the undeformed portion A. The number is
in proportion to the tape thickness since the density of the
particles in the material per unit volume remains approximately
constant. Another way of describing this is to say that the density
of the scattering particles per unit area of the tape surface
varies as the tape thickness varies. During projection, light will
be scattered to a greater degree by the portion A than by portion
B, and bright light will appear on the part of the screen
representative of portion A of the tape, whereas that part of the
screen representative of portion B will be dark.
The projection operation will be better understood by referring to
FIG. 7 of the drawing where read-out of the modulated tape is
accomplished using a suitable projection system responsive to
scattered light, which is a form of optical demodulation system
utilizing phase to amplitude conversion of the modulated projected
light energy. A detailed description of a comparable system may be
found in U.S. Pat. No. 2,813,146 by Wm. Glenn, issued Nov. 12,
1957. A projection light source at S emits rays of light which are
focused by lens 60 and passed through bar system 61, having
alternating transparent and opaque portions constructed in annular
or rectangular bar form. Light passed by the transparent portions
of bar system 61 are focused by lens 62 to normally form an image
on corresponding opaque portions of bar system 63. In the absence
of any scattering of the light waves traveling between bar systems
61 and 63, no light can reach the projection lens 64, for
projection on the screen 65. If the light waves are subjected to
scattering they are diverted from their normal path and some of the
light will pass around the opaque portions of bar system 63 and be
focused on projection screen 65. The amount of light passing
through system 63 and appearing on the screen is proportional to
the degree of scattering.
The source of light may take the form of a filament which is
represented as a line S composed of an infinite number of point
sources of light. Considering light from one such point source A, a
portion of this light is shown to be in the form of a beam B which
is focused by lens 60 to pass through the lower aperture 67 of bar
system 61 and through lens 62 which normally forms an image of the
aperture 67 on the center opaque portion 68 of bar system 63. By
placing the modulated thermoplastic tape to the right of imaging
lens 62 (as shown in FIG. 7), the light of beam B is scattered in
all directions by an elemental portion 69 of said tape and some
will pass around the opaque portions of bar system 63. A typical
bundle of scattered light is shown as beam C which is transmitted
to the screen and focused on the point X, which corresponds to said
tape elemental portion 69. Another portion of the light scattered
by the thermoplastic tape from beam B will pass through the lower
aperture of bar system 63 to point X on the screen. Each point in
the line S may be similarly treated as furnishing a source of
light, and as contributing to the final illumination of the point
X, the illumination of point X being a function of the area density
of scattering particles at the elemental portion 69. Similarly
beams are transmitted through each elemental portion of the tape so
that the brightness of the corresponding parts of the screen is
determined by the degree of scattering of the light transmitted
through the tape. Thus by placing the thickness modulated
thermoplastic tape 66 between bar systems 61 and 63, the recorded
information may be reproduced as a projected optical image. The
intensity at any point in the projected image depends on the
thickness of the thermoplastic material 31 representing that
picture element, since the thickness determines the number of
scattering particles in any portion of the thermoplastic material.
It is noted that the heating of the thermoplastic tape during
read-out is negligible since, unlike density projection of
photographic film, the majority of the light impinging on the
thermoplastic tape is passed through rather than absorbed.
It is to be understood that the specific embodiment described above
is merely illustrative of the general principles of the invention.
Various other arrangements can be devised without departing from
the spirit and scope of the invention. For example, the
intermediate conducting layer may be omitted from the thermoplastic
tape and the tape may consist of only the film stock base layer and
the thermoplastic layer. An external backing electrode may be
selectively positioned in contact with the base layer during the
development operation, much the same as pressure plate 34 is
positioned during the charge and discharge operations. The tape may
take a further alternative form wherein the conducting layer 32,
rather then being the intermediate layer, is an external layer
adjoining the film stock base layer. The mechanical linkages
including the tape transport mechanism and the synchronized
switching circuits may be of other construction. It should also be
appreciated that projection systems responsive to scattered light,
other than the type illustrated, may be utilized in applicant's
system without exceeding the scope of the present invention.
While certain embodiments of the invention have been shown and
described, it should be understood that the invention is not
limited thereto, and it is intended in the appended claims to claim
all modifications that fall in the true spirit of the present
invention.
* * * * *