Direct Image Transfer To Thermoplastic Tape

Abstract

A method and system for thermoplastic recording involves the transfer of an electrostatic charge pattern from a photoconductive member to a deformable thermoplastic storage medium. Upon softening, the thermoplastic medium deforms in accordance with the electrostatic charge pattern. The information can be permanently retained by cooling the deformed thermoplastic. The retrieval of the information may be accomplished by the use of a Schlieren optical readout system.

Description

The instant invention relates to a method and apparatus for storing information on a deformable storage medium in the form of permanent physical deformations, and more particularly, to a system wherein the information bearing deformations are formed directly in response to a light image.

The recording and storing of information, both analog and digital, in a permanent and easily reproducible form is a pressing technological problem. The demands on such systems in terms of speed, density of storage, resolution, etc. have become increasingly severe. Various techniques such as photographic recording, magnetic tape recording, dielectric recording, magnetic core recording, have been used in the past to satisfy these demands. While each of these may perform in a satisfactory manner in various environments and under diverse conditions, all have serious shortcomings which seriously limit their utility.

In the recent past, novel recording and storage technique has been developed which provides many advantages over the other recording and storage techniques. This novel scheme contemplates recording information on a deformable plastic medium in the form of minute light modifying deformations. The information bearing deformations are formed on the storage medium by depositing charges on the medium surface by an electron beam in a pattern representing the information to be stored. The deformable storage medium is then softened by the application of heat or the like and the electrostatic forces due to the charge pattern deform the softened material to produce physical deformations corresponding to the charge pattern. Upon cooling the medium, the deformations are frozen into the surface of the storage medium and are permanently stored unless deliberately erased by reheating. The information stored in the form of these deformations is retrieved by projecting a beam of light through the medium. The projected light is deflected or diffracted by the deformations, depending on their nature, to produce a spatial light image corresponding to the original image. The spatial light image may be viewed directly or may be converted to electrical signals by means of light-sensing devices such as photomultipliers or the like. A complete disclosure of such a system may be found in an application for U.S. Pat. No. 698,167 entitled "Method and Apparatus for Electronic Recording," filed Nov. 22, 1957 in the name of William E. Glenn and assigned to the assignee of the present invention and now abandoned.

While this recording and storage technique offers many advantages and operating efficiencies over heretofore known techniques, it is not at present capable of storing optical information directly. When light images such as photographs and television pictures, etc., are to be recorded in this manner it is first necessary to scan the picture and convert the light image into electrical signals representative of the light characteristics of the image. The electrical signals are caused to modulate an electron beam to deposit the desired charged pattern on the surface of the deformable medium. As a result, complex and expensive circuitry is required to convert the information from a light image to electrical form. In addition, the conversion from light image to electrical signals results in a considerable loss of resolution of the light image.

It is a primary object of this invention, therefore, to provide a method and apparatus for directly storing optical information in the form of light images on a deformable storage medium.

It is another object of this invention to provide a simplified, inexpensive apparatus and technique for storing optical information in the form of light images on a deformable storage medium.

It is yet another object of this invention to provide a high resolution optical information storage system.

The present invention contemplates producing a charge pattern on deformable storage medium directly from a light image without the intervention of a modulated electron beam. One resulting advantage is the elimination of the electron gun and the beam focusing and control assemblies. Furthermore, once the electron beam is eliminated it is no longer necessary that the recording and storage process take place in a vacuum thus greatly simplifying both the complexity of the equipment as well as the care required to establish and maintain the integrity of the vacuum system.

Hence, it is still another object of this invention to provide a method and apparatus for directly storing optical information wherein storage takes place under atmospheric conditions.

Other objects and advantages of this invention will become apparent as the description thereof proceeds.

The above objects and advantages are attained in one form of the invention by providing a photosensitive temporary storage element such as selenium, which is uniformly charged and then exposed to the light image to be stored. The impinging light image so modifies the electrical characteristics of the photosensitive element the charge leaks off selectively in accordance with the light characteristics of the image. This charge pattern is then transferred to a deformable storage medium, such as a thermoplastic film, by applying a polarizing transfer voltage between the photosensitive elements and the thermoplastic. The charge pattern on the deformable storage medium is then developed by softening the thermoplastic film so that the electrostatic forces due to the charge pattern deform the thermoplastic medium to form corresponding deformations.

The novel features which are believed to be characteristic of this invention are set forth with particularity in the appended claims.

The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 is an isometric perspective of one form of an apparatus for carrying out direct storage of optical information;

FIG. 2 is a plan view of the charge pattern on the photosensitive selenium element of FIG. 1;

FIG. 3 is an isometric perspective of a charge transfer assembly;

FIG. 4 is a schematic diagram of Schlieren optical system which may be used for retrieving stored information;

FIG. 5 is a schematic illustration of completely automatic system for storing information directly in response to a light image;

FIG. 6 is a sectional view of photosensitive selenium belt useful with the system of FIG. 5;

FIG. 7 is a sectional view of the mechanical details of an automatic storage system in accordance with the circuit of FIG. 5;

FIG. 8 is a sectional view taken along lines 8--8 of FIG. 7.

Referring now to FIG. 1 of the drawings, an information and recording storage system constructed in accordance with the principles of this invention is illustrated and comprises, broadly speaking, an assembly for storing and retrieving optical information by impressing an electrostatic charge pattern on a deformable thermoplastic storage medium directly in response to a light image and forming permanent deformations from the charge pattern. To this end, a transport mechanism is provided for positioning a photosensitive element and a deformable thermoplastic storage medium at a plurality of individual stations at which the various recording and retrieving operations take place. The transport mechanism comprises a track 10 along which a carriage 11 is constrained to move by means of a rope and pulley driving arrangement 12. The carriage driving arrangement 12 may either be manually operated or may be automatically controlled through a motor and servosystem to position the carriage at a plurality of stations 14, 15, 16 and 17. The carriage 11 which is made of a metallic conducting material, for a reason presently to be described, supports a photosensitive storage element 13 which changes its electrical characteristics in response to light and which may, for example, be fashioned of selenium or any material, such as cadmium sulfide, which has long term retention of radiation induced conductivity. The selenium plate 13 is characterized by the fact that it is photoconductive and hence, its conductivity varies with light intensity. By virtue of this characteristic, the selenium plate 13 is ideally suited for producing and temporarily storing a charge pattern directly in response to light image.

The selenium plate 13 on carriage 11 is first transported to charging station 14 where a uniform charge is impressed on its surface. The charging mechanism at station 14 consists of a corona generator 18 which includes a first set of corona forming wires 19 positioned above the plate 13 and energized from a source of unidirectional energizing voltage appearing at the input terminal 20. The DC energizing voltage appearing at the input terminal 20 and applied to the corona wires through a dropping resistance 21, is of the order of 7,500-8,000 volts and produces a voltage gradient between corona forming wires 19 and selenium plate high enough to produce a corona discharge. The ions from the corona discharge are accelerated by means of a set of wire electrodes 22 disposed between the corona forming wires 19 and the selenium plate 13. The wires 22 are energized from a source of unidirectional voltage supplied at a second input terminal 23 to produce an electrostatic field which accelerates the ions toward plate 13 charging it uniformly. The accelerating wires 22 and the corona forming wires 19 are staggered so that passage of the ions between the accelerating wires 22 to the selenium plate 13 is facilitated. The accelerating wire electrodes 21 also function as arc-over protective electrodes to guard against arc-over between the corona forming wires 19 and the selenium plate 13.

The uniformly charged selenium plate 13 is next transported to recording station 15 where it is exposed to the light image which is to be stored. The selenium plate 13, which is illustrated in its new position by means of dashed lines in, FIG. 1, is positioned at the image plane of a light projecting system 24 to intercept a light image projected from a negative 25. The light image impinging on the plate 13 changes its conductivity in accordance with the intensity of the impinging light so that the charge leaks off to form a charge pattern which corresponds to the impinging light image. That is, photoconductive elements such as selenium are characterized by the fact that they have a "dark resistivity;" i.e., resistivity when unexposed to light, of 10.sup.12 ohm centimeter or greater. When selenium is exposed to light, however, the resistivity value drops to 10.sup.10 ohm centimeter or less for maximum light intensity. The ease with which the deposited charge at any point on the surface of the selenium leaks off through the material to the metallic carriage 11 is, therefore, determined by the intensity of the impinging light at that point. Hence, a charge pattern is produced on the surface of the selenium 13 which has a point by point correspondence with the light intensity variations of the image. image, In storing the optical information by producing a charge pattern in response to a light image, it is desirable under many circumstances to dissect the light image and store it as an extremely fine line structure rather than in a continuous point by point fashion. That is, the image is dissected and stored in a manner analogous to that in which a television picture is produced by breaking the image into 525 or so individual segments or lines each of which is modulated in intensity. The charge pattern representing the light image is similarly fragmented into a plurality of spaced charge bearing strips separated by corresponding uncharged strips. Each charged selenium strip bears a charge distribution which corresponds to the light intensity variations of the corresponding image element.

The reason for dissecting the image and forming the charge pattern as a line structure of this type is determined in part by the characteristics of the mechanism for retrieving the information. Information retrieval takes place using a beam of light which is deflected or diffracted by the information bearing deformations. The light deflection or diffraction is produced by passage of the light through the sloping sides of the deformations. Therefore, if a large white area of an image is to be recorded on a point by point basis from a negative, the white area on the image would appear as a dark area on the negative and little or no light would pass through the negative. As a result, the charge density at this point on the pattern would be high since little or no charge would have leaked off. When this charge pattern is impressed on a deformable medium and the medium is heated, a large shallow groove having a flat bottom would be formed. The light in passing through the groove would not be bent in passing through the large flat portion but only at the sloping sides and, hence, would not be sensed. Consequently the large white area would not be reproduced as such during retrieval. By dissecting the image into a plurality of elements and producing a fine line charge pattern many small deformations rather than a single large groove, are produced so that the readout beam functions in the proper manner.

In addition, the problem of displacing a relatively large volume of the thermoplastic presents severe problems if it is necessary to produce a wide shallow groove. By dissecting the image before storage this problem is minimized. Before projecting the light image from negative 25, the selenium plate 13 is discharged selectively by a beam of unmodulated light projected through a bar or grid arrangement 26. The bar or grid 26 contains a grating structure of alternating transparent and opaque portions so that a plurality of individual parallel spaced light beams is projected onto the plate 13. The previous uniformly distributed charge on selenium plate 13 is converted to a uniform line pattern, as may be seen most clearly in FIG. 2. The line pattern consists of a plurality of charged strips 27, where the projected light was blocked by the opaque bars in the screen 26, separated by a plurality of uncharged portions 28 where the individual light beams from the grid arrangement 26 struck the selenium plate changing the conductivity sufficiently to cause the charge to leak off.

After the photosensitive selenium plate 13 has thus been conditioned to produce a uniform line charge structure, the screen 26 is removed and the light image to be recorded is projected from the negative 25 onto the selenium late 13. The light image then selectively discharges the charged strips 27 in accordance with the light intensity variations of the image to form a charge pattern corresponding to the intensity variations of the light image. Dissection of the light image may be achieved in other ways than that illustrated in FIG. 2. For example, it is equally feasible to utilize a mosaic of rectangular charged portions aligned in horizontal and vertical rows, in which case the screen 26 is constructed as a grid rather than as a plurality of parallel spaced bars. It is also possible to achieve the same result without using a screen by fabricating the plate 13 of a plurality of photoconductive strips separated by a material which is not photoconductive. Besides these specific alternatives it will, of course, be apparent to the man skilled in the art that other schemes for dissecting the picture prior to storage may be utilized without going outside of the scope of the instant invention.

The charge pattern on the temporary selenium storage plate 13 is transfered to the surface of a permanent deformable thermoplastic storage medium by bringing plate 13 into physical contact with a deformable storage element 30 illustrated in FIG. 3 and applying a polarizing voltage. The storage element 30 includes a thin thermoplastic film 31, a conductive substrate 32, shown partially broken away in FIG. 3, and a transparent base member 33. The composition and fabrication of such a thermoplastic storage medium will be described in detail later. The storage medium 30 and the plate 13 are brought in physical contact so that the charge pattern on the plate comes into contact with the thermoplastic film 31. Part of the thermoplastic film 31 is stripped away to expose conducting substrate 32 which is then grounded by a clip 34. A polarizing transfer voltage is applied between the selenium plate 13 and the substrate 32 by pressing an electrode 35 against the back of plate 13. The electrode 35 is connected to a source of unidirectional voltage of suitable magnitude to affect the transfer of the charge pattern from the selenium plate to the thermoplastic film 31. It has been found that the application of a unidirectional transfer voltage of the order of 1,600 volts is effective to transfer the charge pattern from the photosensitive element to the deformable thermoplastic medium.

If the unidirectional polarizing transfer voltage applied to the selenium plate is positive with respect to the conducting substrate 32, there is a direct charge transfer which corresponds to the charge pattern on the selenium element. If, on the other hand, the transfer voltage applied to the selenium plate 13 is negative with respect to the conducting substrate, electrons from the storage element 30 are drawn to the plate 13 producing a negative of the charge pattern.

After the charge pattern is transferred to the thermoplastic, deformations are developed by softening the thermoplastic so that the electrostatic forces due to the charge pattern deform film 31. The storage element 30 is, therefore, placed on the carriage 11 and moved to the developing station 16 and the hot air heating means 36. The hot air from heater 36 heats the thermoplastic film sufficiently to bring it to a softened condition so that deformations are formed by the action of the electrostatic forces.

The storage element is then removed from the heating station 16 to cool the deformed thermoplastic so that the deformations are "frozen" on the thermoplastic. Thus information is permanently retained in this form unless the medium is deliberately heated again to bring the thermoplastic film to a softened condition, at which time the surface tension of the viscous thermoplastic destroys the deformations and erases the information.

The information thus stored on the storage element 30 may be retrieved at the readout station 17 by projecting a beam of light through the storage element 30. The readout mechanism at station 17 includes an optical system 37 consisting of a light source 37a and a lens 37b which projects a beam of collimated light through opening 38 in the track 10 onto storage element 30. The beam passing through storage element 30 is intercepted by a blocking member 40 so that in the absence of deformations on storage medium 30 the collimated light is blocked. If deformations are present on storage medium 30 the light is so deflected that some of the light passes around the member 40 and is gathered by a field lens 41 and projected onto a viewing screen 42. The intensity distribution of the light on screen 42 is controlled by the amount the light is deflected and is thus a function of the depth and spacing of the deformations.

A system constructed in accordance with the principles of the invention need not be constructed so that the readout station 17 is adjacent to the developing station 15 whereby retrieval takes place immediately after storage. It is clear that the storage medium 30 may be removed and stored until the information stored thereon is needed. Under many circumstances, however, a system similar to that illustrated in FIG. 1 is preferred whereby the stored information may be retrieved immediately. The precise time at which the information is retrieved from the storage medium is determined by the end use to which the recording and storage system is to be put.

The retrieval of the information from the light modifying deformations on the storage medium 30 may best be understood by referring to FIG. 4 of the drawings where a detailed schematic illustration of a multiple bar Schlieren optical readout system is shown in place of the single blocking member of FIG. 1. A detailed description of a comparable system may be found in U.S. Pat. No. 2,813,146 --William E. Glenn, issued Nov. 12, 1957. A projection light source shown at 44 emits rays of light which are focused by lens 46 and pass through a bar system 47 having spaced light transmitting apertures. Light beams passing through the apertures of bar system 47 are normally focused by a lens 48 to form an image of the light beams on corresponding light blocking bars of a second bar system 49. In the absence of any deflection or diffraction of the light rays travelling between the bar systems 47 and 49, the light is completely blocked and no light reaches field lens 50 and screen 51. If, however, the light rays are deflected or diffracted in passing between the two, the light is no longer completely blocked by the bars, and a portion passes through the apertures and is focused on the projection screen 51. The amount of light passing through the bar system 49 is proportional to the amount of deflection or diffraction which is controlled by the spacing and the depth of the deformations on the thermoplastic storage medium 30.

The light source 44 is illustrated as a line source of light composed of an infinite number of point sources. Considering the light from one such point source A on line source 44, a portion of the light, shown in the form of a dappled beam B, is focused by the lens 46 to pass through aperture 52 of bar system 47 and thence to lens 48 which normally projects an image of the aperture 52 onto the light blocking bar 53 of the grating 49. By placing the thermoplastic storage medium 30, including light modifying deformations, between the lens 48 and the grating 49 light beam B in passing through a typical set of deformations, illustrated by the deformations 55, is deflected in all directions so that a portion thereof is deflected sufficiently so that it no longer strikes the light blocking bar 53, as shown by lines c--c, but passes through an aperture 56. A typical bundle of deflected light rays is shown as the deflected beam B' passing through the aperture 56 to the lens 50 to be focused thereby at the point X on screen 51. The light characteristics, such as the intensity at point X on screen 51 then correspond to the information stored on medium 30 as in the deformations 55. Another portion of the light, not shown, also deflected by the deformation 55 passes through the lower aperture member 57 also focused at point X on the screen 51. However, for simplicity of illustration, this latter beam of light as well as the light beams due to other deformations are not shown in FIG. 4.

Each point on the line light source 44, however, may be similarly considered as furnishing an independent source of light, and as contributing to the final illumination of the point X on the screen 51. The amount by which the elemental portion 55 deflects the light to control screen illumination is a function of the spacing between the deformations, since the angle of deflection or of diffraction depends on the spacing and the depth of the deformations, while the attenuation of the light intensity by the deformation is a function of the depth of the deformations so that the total intensity of the illumination at any point X on the screen 51 is a function both of the spacing as well as the depth deformations, illustrated at 55. Although in FIG. 4 only a single group of deformations is shown on storage medium 30, in order to simplify the description, the remaining portions of the thermoplastic storage medium 30 contain similar deformation patterns so that light may be transmitted through each of the elemental portions of the medium and the entire screen 51 is illuminated and the recorded information is reproduced as a spatial light image corresponding to the original image. The projection screen 51 illustrated in FIG. 4 may be replaced by a light sensitive electron-optic device such as a photomultiplier or the like which converts the projected spatial light image into electrical signals so that the information may be retrieved electrically rather than visually.

The deformable thermoplastic storage element 30 of FIG. 1 is constructed of a light transparent polyester film base material 33 such as that sold by the DuPont Company under their trade name "Mylar." The base material must be optically clear, smooth, and nonplastic at temperatures up to at least 150.degree. C. The thickness of the base material is not critical and excellent results have been obtained from a 4 mil strip. Another suitable material for the base 33 is an optical grade polyethylene terphthalate sold under the trade name "Kronar." The deformable thermoplastic film 31 on the base member 32 must be optically clear, resistant to radiation, have a substantially infinite room temperature viscosity and a relatively fluid viscosity at temperatures of 100.degree.-150.degree. C. In addition, the thermoplastic film 31 should have a high resistivity in ohms per centimeter. One thermoplastic material satisfying all of these requirements is a blend of polystyrene, m-terphenyl; and the copolymer of 95 weight percent of butadiene, and 5 weight percent of styrene. Specifically, the composition may be 70 percent polystyrene, 28 percent m-terphenyl, and 2 percent of the copolymer.

The thermoplastic film is prepared by forming a 10 percent solid solution of the blend in a toluene solvent and coating the base material with the solution. The toluene is evaporated by air drying and by pumping in a vacuum to produce the final deposited article. The film thickness of the thermoplastic film can vary from about 0.01 mils to several mils, with the preferred thickness being about equal to the minimum distance between deformations to be stored in the film.

In addition, a thin conducting substrate 32 of stannic oxide or cuprous iodide is deposited between the optically transparent base material 33 and the deformable thermoplastic film 31. The conducting substrate 32 is provided for two different reasons: first, to provide a ground or reference potential plane for applying the polarizing transfer voltage between the photosensitive selenium plate 13 and the storage element 30; and second, to provide, in a manner to be described in detail later, a mechanism for heating the thermoplastic film 31 to soften the thermoplastic so that the electrostatic forces due to the charge pattern form the light modifying deformations.

A conducting film of cuprous iodide, for example, may be prepared by vacuum depositing a thin film of metallic copper on the surface of the base material 33 and then immersing the copper coated base material in an iodine vapor to form the desired cuprous iodide film. For a more detailed description of the method and apparatus for producing such a cuprous iodide film, reference is hereby made to U.S. Pat. No. 2,756,165, entitled "Electrically Conducting Films and Process for Forming Same," D. A. Lyon, issued July 24, 1956. It will be apparent to those skilled in the art, however, that the conducting film 32 may be prepared by any one of many well-known processes and that the specific process referred to above is by way of illustration only and is not to be considered limiting.

Turning now to FIG. 5 of the drawings, another embodiment of the invention is shown in the form of a diagrammatic illustration of a continuous, automatic, direct image recording system. FIG. 5 illustrates a system in which the light image is projected onto a continuous photosensitive belt to produce the desired charge pattern representative of the image. An endless belt of photosensitive material such as selenium is supported on drive rolls 61 and 62 which are driven by a transport motor 63. Transport motor 63 is actuated intermittently to advance the belt 60 by a fixed amount during each movement so that one complete image or "frame" is stored on the belt. Selenium belt 60 may be constructed as shown in the sectional view of FIG. 6 and consists of a plurality of selenium photoconductor strips 64 separated by nonphotoconductive strips 65. The entire assembly is secured to a conducting backing strip 66 to which the charge leaks on exposure of the selenium by the light image. A corona generator 67 is positioned adjacent to the selenium belt 60 and sensitizes the selenium strips 64 by charging them uniformly.

A given portion or "frame" of sensitized belt 60 is advanced into recording position to store a light image when it passes over idler pulleys 68 at which time it is positioned at the image plane of an optical system illustrated generally at 69. The optical system 69 may be that of a camera so that operation of the camera shutter projects a light image onto belt 60. The impinging light, as explained previously, changes the conductivity of selenium strips in accordance with the light intensity of the impinging light, causing the charge on the strips to leak off selectively in accordance with the light intensity.

The exposed "frame" on belt 60 is advanced until the image representing charge pattern stored on the "frame" passes between drive roll 61 and a second roll 70, which form a set of transfer rolls for transferring the charge pattern to the thermoplastic. The upper transfer roll 61 has DC voltage supplied thereto periodically from a pair of input terminals 71 to apply a polarizing transfer voltage between the photosensitive selenium belt 60 and a thermoplastic tape 72 which is brought into physical contact with the belt in passing between the transfer rolls. Establishing an electric field between the thermoplastic and the belt transfers charge from belt 60 to thermoplastic film 72 so that a corresponding charge pattern is formed on the surface film of the thermoplastic tape 72.

The virgin thermoplastic film 72 is supplied from a supply reel 73 and is wound, after information is stored thereon, on a pickup reel 74. The reels 73 and 74 are driven intermittently by transport motors 75, only one of which is shown. The speed of tape transport motor 75 is controlled in such a manner that the thermoplastic tape 72 and the photosensitive selenium belt 60 are maintained in nonslip rolling contact to facilitate proper charge transfer. To this end, a transfer roll speed sensing arrangement 76, to be described in detail later with reference to FIG. 7, is provided. The sensing arrangement 76, broadly speaking, senses any difference in speed between the transfer rolls 61 and 70 and actuates a control potentiometer 77 to vary the input signal to motor control amplifier 78 to control the energization of transport motor 75. The speed of the two transfer rolls is thus always equalized to maintain continuous nonslip contact between the belt 60 and the thermoplastic tape 72.

After the tape 72 passes between transfer rolls 61 and 70 the tape is transported to heating station 80 where the transferred charge pattern is developed. Heating station 80 comprises a pair of spaced electrodes 81 and 82 which are periodically energized by an RF heating voltage. The RF voltage induces a circulating heating current in the conductive substrate of the tape to heat and soften the tape so that the electrostatic forces produced by the charge pattern deform the softened tape. The electrodes 81 and 82 are connected to a source of RF energy, such as an RF oscillator, not shown, which supplies the energizing voltage to an input terminal 83. The electrodes are energized through closure of a switch 84 connected between the terminal 83 and one of the electrodes.

The tape transport motors 63 and 75 are both intermittently operated so that both thermoplastic tape 72 and the selenium belt are advanced by a fixed amount during each actuation of the motors whereby individual stored images or frames are advanced to the various operating positions in the system. It will be obvious to those skilled in the art that the transport motors 63 and 75 may be energized simultaneously to synchronize their operation. In addition, manual switch 84 for energizing the RF heating electrodes 81 and 82 may be replaced by an automatic device which is also actuated in synchronism with the transport motors 63 and 75 so that the switch is closed and the heating energy supplied to the thermoplastic tape whenever these transport motors have positioned their respective tape members at the next succeeding position. However, for the sake of simplicity of illustration and explanation, a manually controlled switch 84 is shown for the purpose of periodically supplying RF heating energy to thermoplastic tape.

After heating, thermoplastic tape 72 is transported to a viewing microscope assembly 85 which is provided to permit the operator to observe the surface of the tape and determine the nature and characteristics of the deformations formed on its surface. The viewing microscope assembly 85 is preferably a phase contrast microscope which is particularly useful in observing minute physical differences. Microscope 85 includes a light source 86, a phase contrast condenser assembly 87 which introduces a fixed phase difference between the light ray components passing through the deformation peaks and valleys. This phase difference results in interference phenomena between the light components to produce a perceptible image in the microscope objective and eye piece assembly 88 though only very minute differences in thickness exist. Phase contrast microscope assemblies of this type are well known in the art and it is not believed that a further discussion thereof is necessary. For a detailed discussion of phase microscopes reference is made to the text "Phase Microscope" --Bennett, Jupnik, Osterberg, and Richards, John A. Wiley & Sons, New York (1951).

The thermoplastic tape is next transported to a readout station 89 where the information stored on the tape may be retrieved. At readout station 89 information stored on the thermoplastic tape is retrieved as a light image and then converted to electrical signals corresponding to the stored image. A scanning light source is provided in the form of a flying spot scanner cathode-ray device 90 energized from a suitable sweep circuit indicated at 91. The flying spot scanner 90 includes an electron beam which is deflected by the sweep signal from circuit 91 to scan the beam in a predetermined pattern across the face of cathode-ray device 90. The cathode-ray device 90 has a transparent phosphor deposited on its face so that the impinging beam produces a spot of light at the point of impact. By deflecting the beam both in the horizontal and vertical direction a continuously scanning spot of light is produced. The light beam from the flying spot scanner is projected through thermoplastic tape 72 onto a Schlieren optical system shown generally at 92. A photosensitive device 93 positioned behind the Schlieren arrangement 92 produces electrical signals in response to the light passing through the Schlieren system.

The Schlieren optical system 92, as described previously with reference to FIG. 4, transmits no light in the absence of deformations on the thermoplastic tape 72 since the light is normally blocked by the bars of the Schlieren system. Deformations on the thermoplastic tape 72 deflect or diffract the light so that a portion of the light passes through apertures in the Schlieren grating onto the photosensitive device 93. The magnitude of the light passing through the grating at any position on the thermoplastic tape is dependent on the spacing and depth of the deformations so that the magnitude of the electrical output signals from the photosensitive device 93 will vary correspondingly. As the scanning light spot sweeps across each elemental portion of tape 72 a varying electrical output is produced by photosensitive device 93 which may be stored again or which may be transmitted directly to an electrical utilization circuit. It will be understood, of course, that in order to be useful the output signal from the photosensitive device 93 must be synchronized with the sweep voltages supplied by the sweep circuit 91 in a manner similar to that used in television systems wherein the video signals must be provided with synchronizing impulses (i.e., sync signals) in order to correlate the light intensity information with the position on the video frame.

Again it must be pointed out that, although FIG. 5 shows the readout or retrieval station 89 in close physical proximity to the transfer and heating stations so that readout takes place immediately after storing the information, the invention is not limited to an immediate retrieval system. Under many circumstances, however, an immediate retrieval system is desired. For example, if for use with an aerial survey arrangement it is desirable to take a picture in the aircraft, store it on the thermoplastic tape, retrieve the information from the tape, and convert it to electrical form which may then be telemetered from the craft to ground. In such an environment immediate readout after storage is both useful and desirable.

Belt 98 in FIG. 7 is uniformly charged just before it is pulled into position for exposure through the medium of a corona charging device 99 located immediately above the mounting adapter 95. After exposure, belt 98 is transported by the drive rolls 100 and 101 until the store information "frame" is brought into contact with the thermoplastic storage element 102 supplied from a reel 103. The supply reel 103 and a corresponding pickup reel 104 on the other side of the housing are driven by the variable speed torque motor, not shown, to maintain nonslip rolling contact between thermoplastic belt 102 and the charge bearing selenium belt 98.

To insure that nonslip contact is maintained the thermoplastic tape 102 passes over a pair of idler pulleys 105 mounted on a rocker arm assembly 106. The idler pulleys and rocker arm assembly sense differences in speed between the tape 102 and the photosensitive belt 98 causing the rocker arm to rotate either in the clockwise or counter clockwise direction depending on which belt is moving at the higher speed. Rocker arm 106 is mounted for rotation on a potentiometer shaft 107 so that rotation of the rocker arm varies the output from the potentiometer to vary the energizing voltage to the variable speed drive motors for the supply and pickup reels 103 and 104. The rocker arm assembly and the potentiometer thus cooperate to provide feedback for a simple servosystem which controls the wheel drives and matches the thermoplastic film speed to the speed of the photosensitive selenium belt.

The transfer roll 101 is also supplied with a DC polarizing transfer voltage to effect the transfer of the charge pattern on the selenium belt 98 to the thermoplastic tape 102. To this end, the transfer roll 101 is supplied with a pair of brush elements, not shown, in sliding contact with its drive shaft. A source of DC energizing voltage is periodically applied to these brushes to supply the polarizing transfer voltage between the transfer roll 101 and the conducting film in the thermoplastic tape 102.

After passing over idler pulleys 107 the thermoplastic tape passes over a tape guide 108, one end of which supports RF heating electrodes 109 so that the thermoplastic tape is heated in passing between these electrodes. After passing through through RF heating electrodes 109 tape 102 passes through the viewing field of a phase contrast microscope 110 fastened to housing wall 111. The phase microscope includes the light source 112, phase contrast condenser assembly 113 supported in a mounting bracket 114 secured to the wall 111, a microscope objective 115 threaded into and secured by the tape guide 108, and an eyepiece 116 extending into the plane of the paper and through the wall 111 to the exterior of the housing. The microscope 110, as discussed previously, facilitates observation of the thermoplastic tape to ascertain whether the information has been properly stored.

The electrooptical readout system for retrieving the information stored on the thermoplastic tape in the form of electrical output signals may be seen most clearly in conjunction with FIG. 8 which is a sectional view taken along the lines 8--8 of FIG. 7. As can be seen in FIG. 8 the housing 94 is divided into two separate chambers by means of a dividing wall 111. Positioned in the right-hand chamber, and seen in dashed outline in FIG. 7, is a light source comprising a flying spot scanning device 117 secured in a suitable mounting bracket 118. The electron beam moving across the tube face 119 produces a moving spot of light which is reflected by the 45.degree. mirror 120 through an opening 121 in the wall 111. The light is intercepted by a second 45.degree. mirror 122 and projected downwardly through a lens 123 onto the thermoplastic tape 102.

The light passes through the thermoplastic tape 102 and is deflected by an amount controlled by the spacing and depth of the light modifying deformations on the tape. The deflected light is projected by field lens 124 secured to tape guide 108 onto a Schlieren bar system 125 mounted to an opening of a light integrating sphere 126. The scanning light beam is normally blocked by the bars 125 and passes through the apertures between the bars to the interior of the integrating sphere only if the tape bears the deformations. The light passing into integrating sphere 126 is gathered and focused on the photosensitive electrode of a photomultiplier 127 extending into the sphere. An amplifier 128 is electrically connected to the output of the photomultiplier 127 to amplify the output signals.

It can be seen that a direct image storage system has been described which stores optical information directly on a deformable thermoplastic medium at high speeds with high storage density, and without the need for an electron beam.

While particular embodiments of this invention have been shown and described it will, of course, be understood that it is not limited thereto since many modifications both in the circuit arrangement and in the instrumentalities employed may be made. It is contemplated by the appended claims to cover any such modifications as fall within the true spirit and scope of this invention.

Claims

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a method for storing information on a deformable thermoplastic medium directly in response to light images imaged on a photoconductive member, comprising the step of uniformly charging a photoconductive member to establish a uniform pattern on its surface, exposing the member to a light image to discharge said uniform pattern selectively in accordance with the light intensity variations of said image, transferring the resultant charge pattern from said member to a deformable thermoplastic storage medium, heating said medium after transfer of said resultant pattern to produce physical deformations thereon corresponding to the information to be stored.

2. The information storage method of claim 1 in which the step of transferring the resultant charge pattern includes the further steps of bringing the photoconductive member and saId deformable thermoplastic storage medium into physical contact and applying a polarizing transfer voltage therebetween to transfer said resultant pattern.

3. The method for storing information set forth in claim 1 further characterized by the step of retrieving the information recorded in the deformations formed on the deformable thermoplastic storage medium by imaging a light beam on the deformations to be read out, filtering out undeviated light rays emanating from the deformations, and converting the deviated light rays passing through the filtering operation into an output indication of the information recorded in the deformations.

4. A method of storing information in a layer of thermoplastic material in the form of a ripple pattern on one surface thereof that comprises: providing a layer of photoconductive material one surface of which defines a boundary for engagement with another surface of said thermoplastic layer, forming a substantially uniform electrostatic charge on one of said surfaces, light modulating said photoconductive layer in accordance with said information to form on said boundary an electrostatic charge pattern corresponding to said modulation, forming in said one surface of said thermoplastic layer an electrostatic force pattern corresponding to said charge pattern, and heating said thermoplastic layer to form in said one surface thereof a ripple pattern corresponding to said electrostatic force pattern.

5. The method defined in claim 4 wherein said uniform charge is placed on said one surface of said photoconductive layer.

6. The method as defined in claim 4 further comprising cooling said thermoplastic layer to fix said ripple pattern therein.

7. The method defined in claim 6 further comprising reheating said thermoplastic layer above the melting point thereof to erase said ripple pattern.

8. A method of storing information in a layer of thermoplastic material in the form of depressed discrete areas therein comprising placing a substantially uniform electrostatic charge on one surface of a layer of photoconductive material, exposing selected discrete areas of said photoconductive layer to light in accordance with said information to alter said charge in said selected areas thereby forming a light modulated charge pattern on said one surface of said photoconductive layer, transferring said charge pattern to one surface of said thermoplastic layer to produce a corresponding electrostatic force pattern therein, heating said thermoplastic layer to its melting point to form depressions in discrete areas thereof corresponding to said selected discrete areas of said photoconductive layer, and cooling said thermoplastic layer to fix said depressions therein.

9. The method defined in claim 8 further comprising reheating said thermoplastic layer above its melting point to erase said depressions and said electrostatic force pattern therefrom.

10. In a direct image recording system the combination comprising a solid deformable thermoplastic storage medium, photoconductive means for translating a light image directly into an electrostatic charge pattern, means for transferring the electrostatic charge pattern to the surface of said solid deformable storage medium, means positioned adjacent said solid deformable thermoplastic storage medium for transforming the charge pattern on said medium to corresponding physical deformations including means to soften said medium so that the electrostatic forces due to said charge patterns deform the medium to store the light image permanently in the form of the information bearing deformations.

11. The direct image recording system of claim 10 wherein said means for transferring the electrostatic charge pattern includes means for applying a voltage between the deformable thermoplastic storage medium and the photoconductive means of such magnitude that a charge is transferred therebetween.

12. The combination set forth in claim 10 further characterized by optical readout means positioned adjacent the deformable thermoplastic storage medium and including a light source for projecting a beam of light through the solid deformable thermoplastic medium, light filter means for passing only light rays deviated by the information bearing deformations, and means responsive to the deviated light rays passing through said filter means for producing an output indication of the information recorded in the deformations.

13. In direct light image recording system the combination comprising a solid deformable thermoplastic storage medium, positioned adjacent said thermoplastic storage medium and adapted to change its electrical characteristics in response to an impinging light image, means to generate a uniform electrostatic charge pattern on one of said media, means for exposing said photoconductive medium to a light image to selectively discharging said uniform pattern upon exposure to said light image to produce a modified charge pattern on said deformable medium corresponding to the light characteristics of said image, and means positioned in heat exchange relationship with said solid deformable medium for forming the information bearing deformations from the modified charge pattern including means to soften the deformable medium.

14. In a system for directly recording light images in the form of light modifying physical deformations, the combination comprising a solid deformable thermoplastic medium and photoconductive means positioned adjacent said deformable thermoplastic medium and capable of changing its electrical characteristics in response to an impinging light image, means for impressing an electrostatic charge pattern on the surface of said deformable medium including charging means for producing a uniform charge pattern on said photoconductive means, means for holding the deformable thermoplastic medium and said photosensitive means in charge transfer relation and exposing the photoconductive means to a light image to change its electrical characteristics in accordance with the light characteristics of said image so an electrostatic charge pattern is produced on said deformable medium which corresponds to the light image, and means for developing said charge pattern to form the information bearing deformations on said medium including heating means to soften said medium so that said charge pattern deforms said medium to store the light image as corresponding deformations.

15. In a direct image recording system the combination comprising a photoconductive temporary storage medium, means positioned adjacent said photoconductive medium for producing a charge pattern on said temporary storage medium in accordance with the light characteristics of an image, a permanent deformable thermoplastic storage medium in juxtaposition to said photosensitive storage medium, means to transfer said charge pattern from said temporary to said permanent storage medium, and means for treating said permanent storage medium to form deformations corresponding to said charge pattern.

16. The direct image recording system of claim 15 wherein said transfer means includes means for applying a voltage between said media of such magnitude that charge is transferred therebetween.

17. The combination set forth in claim 15 wherein said transfer means includes means for applying a voltage between said media of such magnitude that charge is transferred therebetween, and further characterized by optical readout means positioned adjacent the deformable thermoplastic storage medium and including a light source for projecting a beam of light through the solid deformable thermoplastic medium, light filter means for passing only light rays deviated by the information bearing deformations, and means responsive to the deviated light rays passing through said filter means for producing an output indication of the information recorded in the deformations.