US3426354A

US3426354A - Electrostatic charge image recorder

Info

Publication number: US3426354A
Application number: US371481A
Authority: US
Inventors: Robert W Gundlach
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1964-06-01
Filing date: 1964-06-01
Publication date: 1969-02-04
Anticipated expiration: 1986-02-04
Also published as: DE1280281B; DK115269B; GB1084494A; BE664729A; NL6506350A; SE338117B; FR1455131A; CH444906A

Abstract

1,084,494. Television and facsimile picture recording. RANK XEROX Ltd. May 14, 1965 [June 1, 1964], No. 20465/65. Heading H4F. Xerographic apparatus, Fig. 2, for recording television or facsimile pictures comprises a drum 17 bearing a photoconductive layer 56, Fig. 3, supported by a dielectric layer 50 on an earthed conductive member. 51 and, including electrically separate conductors 52, 53, 54 extending parallel to the drum axis. The ends of the conductors 15 engage a brush 13 whereby video signals to be recorded may be applied to successive conductors as, the drum rotates. A light source 31 is traversed back and forth adjacent the drum, the relative rate of traverse and, drum rotation being such the light makes one traverse as each conductor is brought into use. In response to the video signals and the change of conductivity produced in each elemental area by the light source a pattern of charges is created corresponding to the television or facsimile pictures. The charges are developed to a visual pattern by known apparatus 37 and the pattern is thereafter transferred to a record strip under the action of a high potential electrode 44 and fixed thereon by a heater 46. The charge pattern on the drum is then removed by exposure of the drum to an intense light source 25 whilst the electrodes are earthed by brush 20. The electrodes are also earthed by a brush 16 in the region following scanning by light source 31. Conductors 52, 54, 56 &c. may be embedded in dielectric 50 instead of being formed on the surface as shown in Fig. 3. In a modified construction, Fig. 5 (not shown), the earthed conductive member 51 is dispensed with and each of conductors 52, 54 &c. is replaced by two conductors, one of which is earthed. As an alternative to traversing light source 31 back and forth, a scanning light system based on a mirror drum, Fig. 6 (not shown), or rocking mirror may be used. Reference is made (without given details) to a drum system in which the photoconductive layer is removable and forms the base of the final picture. Reference is also made to the application of the invention to a flat bed scanning system.

Description

Feb. 4, 1969 w D H 3,426,354

ELECTROSTATIC CHARGE IMAGE RECORDER Filed June 1, 1964 Sheet of 2 LOCAL OSCILLATOR DEMODULATOR 4 50 AMPLIFIER 60 INPUT I AMPLIFIER FIG. 5

INVENTOR. ROBERT W. GUN DLACH BY M 9 9 ATTORNEYS Feb. 4, 1969 R. w. GUNDLACH 3,426,354

ELECTROSTATIC CHARGE IMAGE RECORDER Filed June 1, 1964 Sheet ,2 of 2 INPUT AMPLIFIER INVENTOR. ROBERT W. GUNDLACH ATTORNEYS United States Patent York Filed June 1, 1964, Ser. No. 371,481 US. Cl. 346-44 Int. Cl. Gtlld 15/06 11 Claims ABSTRACT OF THE DISCLOSURE A xerographic recorder having a drum coated with a photoconductive material and having beneath said photoconductive material a plurality of parallel signal conductors separated from a grounded base conductor by a dielectric material, wherein the signal conductors are closely spaced to each other and extend along the width of the drum and terminate at one end thereof at terminals to which an electrical video signal is applied through a brush positioned to contact each of the individual terminals as the drum rotates, wherein latent electrostatic images are formed on the photoconductive material by scanning the surface of the photoconductive material along lines corresponding to the lengths of the signal conductors with a scanning spot of constant intensity and by applying the video signal through the brush to a signal conductor in the vicinity of the scan, wherein development of the latent image is accomplished by cascading triboelectrically charged toner particles over the photoconductive material with the developed image thereafter being transferred and fused onto a copy sheet, and wherein in another embodiment of the drum structure a dielectric material is mounted beneath the photoconductive material having embedded therein a plurality of parallel con- This invention relates in general to the conversion of an electrical signal to a graphic image and, in particular, to a signal recsorder with electro-optical scanning.

Although there is a great demand today for recorders capable of producing graphic reproductions of high speed electrical signals containing large amounts of information for applications, such as video recorders in television or facsimile systems, this demand is still largely unsatisfied. This statement is epecially true with regard to relatively fast recording in high quality facsimile receivers. For example, in the field of facsimile recording, the receiver may be equipped with either one of the direct recorders now commonly employed in the art or a photo recorder of the type which now finds its greatest use in news-photo facsimile systems. The direct recording systems for the most part employ either an electrolytic or an electrosensitive recording paper. An image is formed on these specially fabricated recording papers by causing electrical discharges through very small surface areas of the recoding paper which discolor the papers according to the magnitude of the applied potential. Since these specially treated recording papers may not generally be reused to form a second image, materials cost with this type of recording system is relatively high and, in addition, the discrete nature of the electrical discharges leads to the formation of a rather crude image formed from a pluralit of small discete dots. Even when poor quality may be tolerated in the final image, these systems frequently may not be employed because of their extremely slow recording speed. Where higher quality or faster recording is required in facsimile systems, silver halide recording materials are generally utilized. However, there are certain disadvantages to the silver halide photo facsimile recorders which offset their advantages to a large extent. These include the high cost of the silver halide recording media and the fact that they may not be reused so as to amortize their relatively high cost over a large number of copies, the fact that they must be developed with messy liquid developers under controlled conditions and the fact that image access time is relatively high because the images formed are not visible until after development. Instead of using the input signal to cause an electrical discharge on the recording paper, most photo facsimile recorders employ glow lamp recording or a flying spot scan from a cathode ray tube output. With either the glow modulator tube or the cathode ray tube, the light output is focused on a spot of the recording medium and caused to scan across the recording medium while light intensity is varied according to the amplitude of the signal input.

It is possible to overcome many of the disadvantages of present day photo-recorders by substituting xerographic recording for the commonly utilized silver halide recording technique. Xeography as first described in US. Patent 2,297,691, and as amplified in many later related patents generally comprises uniformly charging a photoconductive insulating member, referred to in the art as a xerographic plate, to sensitize it, and then subjecting it to a light image or other pattern of activating electromagentic radiation which serves to dissipate charge in radiation-struck areas, thus leaving a charge pattern or latent electrostatic image on the photoconductor conforming to the electromagnetic radiation pattern. Of course, in a facsimile recording system, the whole of the light image would not be exposed to the xerographic plate simultaneously but rather the xerographic plate would be scanned with a light source, the intensity of which is varied according to the input signal amplitude. Following exposure, the image is developed by the deposition of electroscopic or electrostatically attractable, finely divided, colored material, referred to in the art as toner, on the exposed photoconductive insulator, which by virtue of its latent electrostatic image, forms a corresponding toner image on its surface. The toner image thus formed may then optionally be viewed in situ on the photoconductive insulating layer or transferred to a copy sheet such as paper or other material for later use. In the event that the xeographic plate employs amorphous selenium as its photoconductive insulating layer, as described more fully in US. Patent 2,970,906, to Bixby, the toner image may be transferred to a copy sheet and a xerographic plate may immediately be cleaned and reused in the process for many thousands of cycles. In view of the fact that the cost of the selenium xerographic plate may be amortized over the many thousands of copies which it is capable of producing, the cost of photosensitive materials per copy is extremely low as compared with silver halide materials and the process is still capable of producing photo-exact reproductions of the facsimile originals transmitted from the source. Although the above described xerographic photo-facsimile recorder has a number of advantages over ordinary silver halide recorders including low cost, ease of development, fast access time, etc., it is somewhat slower in photographic speed than the fastest silver halide recording materials.

Accordingly, it is an object of this invention to define a novel method for the xerographic recording of video signals.

It is a further objective of this invention to define a novel apparatus capabie of recording video signals at high speed and low cost.

It is yet another object of this invention to define novel methods and apparatus for the xerographic recording of video images with electro-optical mixing techniques.

Yet another object of the invention is to provide a xerographic photorecording method of greatly increased s eed.

The above and still further objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed disclosure of specific embodiments of the invention, especially when taken in conjunction With the accompanying drawings wherein:

FIGURE 1 is a partially diagrammatic isometric view of a facsimile receiver constructed according to this invention, with some of the major system components removed;

FIGURE 2 is a view of the right-hand end of the apparatus seen in FIGURE 1 including additional apparatus components not shown in FIGURE 1;

FIGURE 3 is a broken partially sectioned end view of the drum illustrated in FIGURES 1 and 2;

FIGURE 4 is a top sectional view taken along section lines 44 of FIGURE 3; and

FIGURE 5 is a broken partially sectioned end view of an alternate embodiment of the drum of FIGURE 3;

FIGURE 6 is an isometric view of an alternative high speed scanning mechanism.

Although this invention is broadly directed to an electrical signal-to-graphic image converter for the recording of images, a facsimile receiving system has been illustrated in isometric in FIGURE 1 as an exemplary illustration of the inventive concept. In this system, a facsimile signal received through a transmission line from a facsimile transmitter is fed through input lines 10 to a demodulator 11 where it is separated from its carrier frequency prior to being fed into an input amplifier 12. The input amplifier has its output connected to a small brush 13 which is mounted on a stationary support 14. The brush 13 is of such a size and is so positioned that it makes electrical contact with each successive contact 15 on the insulating end face of a cylindrical drum generally designated 17 as the drum is rotated about its longitudinal axis. Since, as is explained in more detail hereinafter, each of the contacts 15 is electrically connected to one of a great number of mutually parallel conductors which are also parallel to the longitudinal axis of rotation of the drum 17 and imibedded in the drum close to its outer peripheral face, rotation of the drum at a time when an input signal is being received by the system causes the input signal to be switched from one very small longitudinal segment near the face of the drum to the next. This is perhaps best seen by viewing the conductor 5254 in FIGURE 4. In other words, the system is constructed so as to cause the electrical input signal to scan around the drum surface, with this signal being applied to sequential line segments of the drum face which are taken along a line parallel to the drum axis.

The output signal of a very stable local oscillator 18 is fed into an amplifier 19 which in turn is employed to power a synchronous motor 21 that is used for mechanically driving the moving parts in the system. A pinion 22 is mounted on the shaft of the synchronous motor 21 and is in driving engagement with another gear 23. Gear 23 is mounted on the shaft 24 of drum 17 so that it directly rotates this drum in a direction indicated by the arrow in FIGURE 1. In addition, a large gear 26 is also mounted for rotation on shaft 24 and is in driving engagement with a small pinion 27. Pinion 27 is mounted on a shaft 28 in which there has been cut a reversing lead screw and on which there is mounted a carriage 29 for traversal back and forth in front of drum 17 as shaft 28 is rotated. Carriage 29 carries a light source 31 and a lens 32 positioned to image light from source 31 on a very small spot on the surface of drum 17. Light source 31 may consist of any high intensity, constant output light source such as a carbon arc lamp or the like. The ability to use a constant high intensity light source in this system as opposed to the modulated light sources of other photofacsimile systems is a great advantage, especially in xerographic systems which generally employ materials with rela ively slo P graphic speeds since this allows for a great increase in scanning speeds. Internal threading in carriage 29 and the extent of the thread cut on shaft 28 are designed so that the spot of light produced b light source 31 and lens 32 on the surface of the drum 17 will only traverse that portion of the drum 17 covered by a photoconductive insulating layer 33. Carriage 29 also contains a triangular hole which is utilized for mounting the carriage on a triangular guide bar 34 which in turn is mounted on a supporting stand 35. Although they are not illustrated in this figure so as to simplify the description of the invention, all shafts, the motor, and stand 35 are mounted on suitable rigid stationary supports. As described above, the electrical signal input to the system, after demodulation and amplification, is applied along whole line segments of the drum 17. Since, as will be explained more fully hereinafter, a latent electrostatic image is formed at the point Where a signal activated conductor intersects with the spot of light projected on the drum surface by light source 31 and lens 32, there is, in effect, a scanning across the drum by this light source and since the strength of the latent electrostatic image formed is dependent upon the magnitude of the input signal, the system is perhaps best understood by analogy to a cathode ra tube. In this analogy, light source 31, lens 32, their carriage and traversing mechanism are analogous to the horizontal deflection plates of a cathode ray tube While the conductors running through the drum are analogous to the electron gun in a cathode ray tube. This analogy holds because the scanning light determines where on the drum the latent electrostatic image will be formed and the signal on the conductor in the drum determines its strength or intensity. Vertical scanning of the drum is accomplished by its rotation.

It is to be understood, of course, that although the whole of the facsimile transmitter is not illustrated and described here, that the transmitter and recorder must be operated in very close synchronism so that an image which closely corresponds to the original is reproduced in the recorder. For example, in an exemplary system, the original is placed on a transmitting drum of the same size as recording drum 17 and driven with a local oscillator, amplifier, synchronous motor and gear train identical to that employed in the recorder. A light is placed on the original copy on the drum and a carriage carrying the light and a lens or lens system and p'hototube image the light reflected off a spot on the original copy onto the phototube. This carriage is carried by a reversing lead screw similar to, and driven in the same manner as, lead screw 28 in the recording head. The signal from the phototube is then fed to a modulator where it is mixed with a carrier frequency from a carrier signal generator, amplified and transmitted either on a transmission line or by radio propagation. If it is desired to keep costs at a minimum, local oscillators of the same frequency in the transmitter and the recorder may be dispensed with and the system may rely for synchronization on the frequency control of the local power lines. Other synchronization techniques Well known in the art such as employing the carrier for synchronization may also be employed. In addition, it is to be noted that the drive train in the illustrated recording system is continuous in nature. That is to say the local oscillator 18, amplifier 19, and synchronous motor 21, are in continuous operation except when manually switched on and off. However, in a detailed showing of a practical system, a phasing system to place the beginning of a received scanning line at the left-hand edge of the recording would also be included. In that type of a system, although the local oscillator, amplifier and synchronous motor are run continuously, a solenoid actuated clutch is included in the mechanical gear train and is actuated by a phase pulse amplifier operated by the system input,

Once the latent electrostatic image is formed on drum 17 by the combined action of light 31 and the electrical input signals, it is developed or made visible and transferrcd to a sheet of recording paper or other copy material. Apparatus for accomplishing these developing and transfer Steps have not been illustrated in FIG. 1 for simplicity of illustration of other system concepts; however, in addition to many of the system components illustrated in FIG. 1, the additional developing and transfer system components are illustrated in some detail in FIG. 2. Referring now to FIG. 2, it is seen that once the latent electrostatic image is formed by the combined action of light source 31 and the electrical signal applied to the drum through brush 13, it passes a grounded brush 16, the purpose of which is described hereinafter, and then the drum rotates around so as to move past a developing unit generally designated 37. This developing unit is of the cascade type which includes an outer container or cover 38 with a trough at its bottom containing a supply of developing material 39. The developing material is picked up from the bottom of container 38 and dumped or cascaded over the drum surface by number of buckets 41 on an endless driven conveyor belt 42. This development technique which is more fully described in US. Patent 2,618,552, to Wise and 2,618,551, to Walkup utilizes a two-clement developing mixture including finely divided, colored, marking particles, or toner, and grossly larger carrier beads. The carrier beads serve both to deagglomerate the toner and to charge it by virtue of the relative positions of the toner and carrier material in the triboelectric series. When the carrier beads with toner particles clinging to them are cascaded over the drum surface, the electrostatic fields from the charge pattern on the drum pull toner particles off the carrier beads serving to develop the image. The carrier beads along with any toner particles not used to develop the image then fall back into the bottom of container 38 and the developed image moves around until it comes into contact with a copy web 42 which is pressed up against the drum surface by two idle rollers 43 so that the web moves at the same speed as the periphery of the drum. A transfer unit 44 is placed behind the web and spaced slightly from it between rollers 43. The transfer unit illustrated contains one or more wire filaments which are connected to a source of high potential 45 and operate on the corona discharge technique as described in US. Patents 2,588,699, to Carlson, and 2,777,957 to Walkup. Essentially, this transfer technique which is described in US. Patent 2,576,047, to Schaffert, consists of spacing the filaments slightly from the surface to be charged, placing a grounded conductive base behind this surface and applying a high potential to the filament so that a corona discharge occurs between the filament and the surface, thus serving to deposit charged particles on the surface. The polarity of potential source 45 and consequently the polarity of the charge deposited on the surface is opposite to that of the charge on the toner particles employed to develop the drum so that the charge deposited on copy web 42 serves to attract the toner particles away from the surface of the drum. Obviously, this deposited charge must be sufiicient to overcome the force of attraction between the particles and the charge of the latent electrostatic image formed on the drum. It should be noted at this point that many other development and/or transfer techniques known in the xerographic art may be utilized with this invention. For example, development may be accomplished by magnetic brush development, as described in US. Patent 3,- 015,305, to Hall, or by powder cloud development, as described in US. Patent 2,918,900, to Carlson, and transfer may be accomplished by employing a roller connected to a high potential source opposite in polarity to the toner particles immediately behind the copy web or the copy web itself may be adhesive to the toner particles. In addition, transfer may be accomplished by placing a grounded conductive plate behind the copy web at the point of transfer and applying a pulse of the same polarity as the charge on the toner particles to the conductors in the drum. This transfer technique, which is more fully described in my above-referenced application, serves to repel the toner particles making up the developed image off the drum and onto the copy web. After transfer to the copy web, the web moves beneath a fixing unit 4 6 which serves to fuse or permanently fix the toner image to web 42. In this case, a resistance heating type fixer is illustrated; however, other fixing techniques known in the xerographic art may also be utilized including the subjection of the toner image to a solvent vapor or the spraying of the toner image with an overcoating. A-fter fixing, the web is rewound on a coil 47 for later use. Once past the transfer station, the drum continues around and moves into a position where it is exposed to a strong light source 25 while its conductors are grounded through a brush 20. This dissipates all charge remaining at the photoconductor dielectric interface. The drum then moves beneath a cleaning brush 48 which prepares it for a new cycle of operation.

In FIGURE 3, there is illustrated a fragmentary partially sectional end view of one embodiment of the drum structure which my be employed in this invention. This embodiment comprises a dielectric layer 50 on a grounded conductive backing member 51 which may also act as a rigid supporting structure for the drum. Over dielectric layer 50 there are a number of electrically separated

conductors

52, 53, 54, etc., which may desirably run in parallel lines in a direction parallel to the axis of rotation of the cylinder as seen in FIG. 1. These conductors are very slender and thin and are uniformly spaced ranging from about 75 to about 350 conductors per inch of drum circumference although less or more conductors per inch may be employed depending upon considerations of image quality to be reproduced, cost and the like. The conductors may cover on the order from about 30 to about 70% of the surface area of the underlying dielectric layer 50. These conductors may be placed on the supporting dielectric layer 50. These conductors may be placed on the supporting dielectric layer by means of photoresist and etch or engraving techniques which are well known in the printed circuit arts. It is also to be noted that if desired, the conductors may be embedded in the face of, or actually buried within dielectric layer 50; however, since the purpose of these conductors is to set up electrical fields through the uniform layer of photoconductive insulating material 56 overlying them, it is preferable that they be placed on the surface of the dielectric layer 50.

FIG. 4 is a partial section taken along section lines 4-4 of FIG. 3 which cuts through the drum along the top surface of

conductors

52, 53, and 54. This section also cuts through the photoconductive insulating layer 56 in those portions of the drum which are not covered by the conductors 5254. As shown in FIG. 4, the photoconductive insulating layer 56 does not extend the whole width of the drum but only covers a portion of the dielectric base 50. As also shown in this figure, after the conductors emerge from the photoconductive insulating film on the right-hand side as seen in the figure, they continue on above insulating layer 50 to an insulating end plate 57 which may be fabricated of the same material as layer 50 and are connected to a number of contacts on the right-hand surface of plate 57 for commutation with brush 13.

In FIG. 5, there is illustrated a fragmentary partially sectional view of an alternate embodiment of the drum, the illustration of which is similar in nature to that of FIG. 3. In this second embodiment, a number of electrioally separated

parallel conductors

59, 60, 61, 62 and 63, similar to conductors 52-54 of FIGURE 3, are embedded in a dielectric layer 64. This dielectric layer is overcoated with a photoconductive insulating layer 66. Preferably, the thickness of the dielectric material 64 between the conductors 59-63 and the photoconductive insulating layers 66 is kept quite thin so as to maximize the electrostatic field which will extend up to the photoconductive insulating layer from these conductors upon the application of an electrical potential to them. In this embodiment of the drum the electrical input signal from the amplifier is applied across two adjacent conductors to set up the electrical field necessary to form a latent electrostatic image on the drum. One method for accomplishing this result is to ground alternate conductors such as 59, 61, and 63, while connecting the conductors between these alternate conductors such as 60 and 62 to contacts such as 67 on the end face plate 68 of the drum. Then by grounding one output terminal of the input amplifier and connecting the other output terminal of this amplifier to brush 13, the output signal from the amplifier is applied across two adjacent conductors when brush 13 brushes against the contact 67 for one of those conductors.

The photoconductive insulating layer in either the FIG. 3 or FIG. 5 embodiment may, for example, consist of amorphous selenium, the xerographic use of which is more fully described in US. Patent 2,970,906, to Bixby. Amorphous selenium is, of course, the preferred material for the photoconductive insulating layer of the drum since it produces excellent copy and is reusable in the process for many thousands of cycles. It is to be noted, however, that any other suitable photoconductive insulator may also be employed even when they are photographically slower than amorphous selenium and not reusable shortly after light exposure. A prime example of this type of material is particulate French process zinc oxide in a film- -forming insulating binder such as a polystyrene or polyvinyl acetate resin. This type of photoconductive insulating layer may, for example, be deposited on a dielectric film backing and the recording drum may be provided with grippers and/ or rollers to hold a cut dielectric sheet with the zinc oxide coating against the drum in close proximity to the conductors during one cycle of operation. After completion of the cycle, a fresh photoconductive insulating layer may be placed in the system either manually or with an automatic feed system in which, for example, the grippers for the photoconductive insulating layer may be cyclically cam actuated. This type of system has the virtue that the transfer step may he eliminated from the overall process and the toner image may be fixed directly on the surface of the photoconductor.

Although a reversing lead screw scanning mechanism has been described in connection with FIGURE 1 so as to facilitate the description and understanding of the invention, it is to be noted that in actual practice, higher speed scanning mechanisms are employed to take advantage of the fact that the high unmodulated intensity light sources utilized with this invention will allow for much shorter scanning times. Such a high speed scanning device is shown in FIGURE 6, and this device includes a light source 74, a lens 76 and an aperture 77, designed to focus a spot of light on a rotating hexagonal mirror 78, mounted on a shaft 79 which is driven by a synchronous motor drive 80. After passing through aperture 77, the light is reflected oif whichever face of hexagonal minror 78 happens to be opposite the light source at that particular time, and is reflected through lens 81 to cylindrical recording drum 17 of the same type as described in connection with FIGURE 1 above. 60 of rotation of hexagonal mirror 78 causes each mirror then opposite the light source to cause the light reflected 01f its surface to scan from one end of cylindrical drum 17 to the other end as shown by the arrow moving across the drum. As the next mirror face comes opposite the light source, it causes the light to once again scan the drum so that for each rotation of hexagonal mirror 78, the drum is scanned 6 times from right to left as seen in FIGURE 6. The video signal is applied to the drum in the same manner as described above in connection with the FIGURE 1 embodiment of the invention and the rotational speed of cylindrical drum 17 is adjusted to coincide with the scanning rate of the light source.

In operation, an original copy is placed on the facsimile transmitter drum and the transmitter is switched on causing the drum to rotate at a speed determined by the frequency of its local oscillator and the characteristics of its synchronous motor. If the scanning head of the transmitter were tied in with this drum, turning on of the local oscillator at the transmitter would also initiate scanning by the scanning head. As described above, the transmitter scanning head includes a light source, a lens system, and a phototube pickup so positioned and arranged as to cause a spot of light from the light source to be reflected off the transmitting drum to the phototube pickup. Thus, when the scanning head light strikes a white or lightcolored portion of the original, it reflects a large amount of light back to the phototube, whereas when this light strikes a dark or black portion of the original, most of the light is absorbed and very little is reflected back to the phototube pickup. Consequently, the potential appearing at the phototube output is directly proportional to the lightness or darkness of the particular small elemental area of the original being scanned at any particular time. Since the rate of travel of the scanning head across the drum is high with respect to the speed of rotation of the drum, the whole surface area of the original on the transmitter drum is scanned one elemental area at a time in a line-by-line fashion. As explained above, the output signal of the phototube is mixed with a carrier frequency and transmitted either over a transmisison line or by radio propagation to the receiver which then demodulates and amplifies this signal prior to applying it to brush 13. This brush makes electrical contact with one of contacts 15 on the end face of the recording drum 17. The ratio between gear 26, which is mounted on the shaft of the drum 17, and gear 27, which is mounted on the shaft carrying the lead screw for carriage 29, is selected so that brush 13 makes electrical connection with one or several of the contacts 15 for a time interval equal to the time required for the scanning spot of light to make one traversal across the full width of the photoconductive insulating layer 33 on the drum surface. This means that the varying electrical input signal is continuously applied to one or several of the conductors in the drum as light source 31 on the carriage 29 scans across the photoconductive insulating layer 33 directly above the activated conductor or conductors.

Referring now to FIG. 3, it is seen that when an electrical signal is applied to one of the conductors such as 52, 53, or 54, an electrical field is set up between the conductor and the grounded conductive backing plate 51 of this drum embodiment. Although some of the field lines proceed directly from the bottom of the conductor to the conductive grounded plate 51, other field lines curve up from the top of these conductors through the photoconductive insulating layer 56 and then down through the photoconductive insulating layer between adjacent conductors through the dielectric layer 50 to the grounded conductive backing layer 51. Whether or not an electrical field is set up in the photoconductive insulating layer 56 is thus dependent upon whether or not a signal is applied to one of the conductors 52-54, and its instantaneous strength is dependent upon the instantaneous amplitude of the electrical signal being applied. If the photoconductive insulating layer 56 is not subjected to exposure by light or other Iactivating electromagnetic radiation, it will, of course, remain in its most insulating condition so that charge carriers within it will have little or no mobility. On the other hand, if any section of the photoconductive insulating layer is exposed to light, the illuminated areas will become relatively more conductive. As is well known, an electric field, when applied to a conductor, causes the charge carriers within it to move in such a way as to make the interior of the conductor a field-free, equi-potential volume. For example, if the area of the photoconductive insulating layer lying above condoctor 53 in FIGURE 3 were illuminated so as to render this area relatively conducting, while an electrical signal were being applied to this conductor from the input amplifier, the electric field resulting from the application of the signal between this conductor and the grounded conductive backing plate 51 would cause the free electrons in this conductive area of the photoconductive insulating layer 56 to move toward the grounded plate 51 (assuming that the applied signal had a negative polarity). It should be noted, however, that although the charge carriers can move through the illuminated photoconductive insulating layer that they would be stopped at the interface between the photoconductive insulating layer 56 and the dielectric layer 50 because the dielectric remains in an insulating condition regardless of illumination. In this instance, then, negative charge moving toward backing plate 51 would be stopped at the interface of the dielectric and photoconductive insulating layers between adjacent conductors such as 53 and 54, and when illumination is shut off, these charges would be trapped at this interface because the photoconductive insulating layer then reverts to its insulating condition, thereby limiting charge carrier mobility once more. This trapped charge then sets up its own field after the input is shut off and this field forms the image which is later developed. It is to be noted that the polarity of charge trapped at the interface is dependent upon the polarity of the applied signal so that if the signal is negative, negative charge will be trapped at the photoconductordielectric interface while if the signal is positive, positive charge will be trapped at the photoconductor-dielectric interface. Each of the small conductors 52-54 makes up an individual capacitor in conjunction with the dielectric layer 50 and a common second capacitor plate 51 so that some charge may be stored in each of these small capacitors. It is thus seen that the application of a signal across the capacitor plate for the purpose of trapping charge at the photoconductor-dielectric interface will also serve to store some charge in each of these small capacitors. In order to alleviate the problem of this additional stored charge, these capacitors are shorted so as to discharge them by connecting them through contacts 15 to a grounded brush 16 once the photoconductive insulating layer above them has passed out of the range of the light source 31 and the required charge has been stored at the photoconductor-dielectric interface by the signal input.

Since the instantaneous value of the signal received by the recorder is the electrical analog of the reflectivity of that portion or elemental area of the original document being scanned by the transmitter, and since the recorders scanning light source 31 is closely synchronized with the transmitters scanning pickup, an electrostatic latent image is formed on the recording drum which exactly corresponds to the image on the original. In effect, then, light source 31 is a traversing optical switch which allows the formation of a latent electrostatic image at the point where it has virtual intersection with one of the conductors in the recording drum providing that conductor is carrying an input signal at that particular time. The latent electrostatic image thus formed is then developed and transferred to a copy web, as described above.

The drum shown in the FIGURE embodiment of this invention operates in a manner similar to that of the FIGURE 3 drum, except that, instead of using a plurality of fine separated conductors in the selenium which are separated from a common grounded conductive backing plate by a dielectric layer, all conductors are imbedded in the dielectric layer so that they are mutually insulated from each other with alternate conductors being grounded so as to substitute for the conductive backing layer 51 of the FIGURE 3 embodiment. This alternate conductor grounding may also be used with the FIGURE 3 device. Operation of this drum is the same as the operation of the FIGURE 3 drum, the only difference being that the electric field produced is initiated completely from within the dielectric layer 64 and extends up into the photoconductive insulating layer 66 by virtue of the curved nature of the fringing fields produced. Additional detail on xerographic plates of somewhat similar construction to the FIGURES 3 and 5 drum may be had in the above-referenced copending application.

It should be recognized that many alternate materials, configurations, and modes of operation may be utilized in connection with the concept of this invention. For example, the drum components may be made substantially transparent and scanning light exposure may be made from within the drum. The drum itself may be made in the form of a fiat plate rather than a cylindrical drum and scanned by linear movement of this plate with respect to the scanning light source. Instead of scanning the drum with a light source carried on a carriage driven by a reversing lead screw, a rocking concave mirror may project light from a light source onto the drum surface or a rotating hexagonal mirror may be employed for the same purpose. Other methods of transmission, including sampling circuits and pulse and coding techniques, may be employed as well as many other Well-known synchronizing methods. In short, the list of alternatives is virtually endless.

What is claimed is:

1. A transducer for the conversion of an electrical signal to a latent electrostatic image comprising a photoconductive insulating layer,

a plurality of first electrically separated conductors contiguous to said photoconductive insulating layer,

at least one second conductor and a dielectric material,

said second conductor being closely spaced to said first conductors and separated therefrom by said dielectric material,

said first and second conductors being on a first side of said photoconductive insulating layer, a source of high intensity electromagnetic radiation to which said photoconductive layer is sensitive,

means to scan areas of said photoconductive insulating layer on a second side thereof opposite said successive first conductors with said source of electromagnetic radiation, and

means to apply an electrical signal representative of information to be recorded between successive first conductors and adjacent second conductors while areas of said photoconductive insulating layer adjacent said first conductors are being scanned with said electromagnetic radiation source.

2. A transducer according to claim 1 in which said first conductors are close to each other and mutually parallel.

3. A transducer according to claim 1 further including means to electrically connect said first and second conductors after they have been scanned by said electromagnetic radiation source.

4. A recorder for the conversion of electrical signals into visible images comprising a photoconductive insulating layer,

a plurality of first electrically separated conductors contiguous to said photoconductive insulating layer, said first conductors being separated from at least one closely spaced second conductor by a dielectric material, said first and second conductors being on a first side of said photoconductive insulating layer, means to scan areas of a second side of said photoconductive insulating layer opposite said first side, said scan covering portions corresponding to the length of successive first conductors, with a high intensity source of electromagnetic radiation to which said photoconductive insulating layer is sensitive,

means to apply an electrical signal representative of information to be recorded between successive first conductors and an adjacent second conductor while portions of said photoconductive insulator adjacent said first conductors are being scanned with said electromagnetic radiation source,

means to interconnect said first and second conductors after the completion of scanning, and

means to deposit finely divided electroscopic marking particles on said photoconductive insulating layer whereby the latent electrostatic image formed on said photoconductive insulating layer is made visible.

5. An image recorder according to claim 4 further including means to transfer the visible image made up of said deposited electroscopic marking particles from said photoconductive insulating layer to another surface.

6. An image recorder according to claim 5 further including means to discharge any residual electrostatic charge remaining on said photoconductive insulating layer after a particulate image has been transferred whereby said recorder is prepared for reuse.

7. An image recorder according to claim 6 in which said discharge means comprises means to ground said first and second conductors and means to simultaneously uniformly expose said photoconductive insulating layer to a source of electromagnetic radiation to which it is sensitive.

8. A transducer for the conversion of an electrical signal to a latent electrostatic image comprising a photoconductive insulating layer,

a plurality of first mutually parallel, electrically separated, conductors contiguous to said photoconductive insulating layer,

at least one second conductor and a dielectric material, said second conductor being closely spaced to said first conductors and separated from said first conductors by said dielectric material,

said first and second conductors being on a first side of said photoconductive insulating layer,

a source of high intensity electromagnetic radiation to which said photoconductive layer is sensitive,

means to scan the side of said photoconductive insulating layer opposite said first and second conductors with said electromagnetic radiation along a line which corresponds to one of said mutually parallel conductors,

means to advance the point of scanning radiation impingement a distance equal to the distance between adjacent first conductors each time the scanning line completes one traversal of said photoconductive insulating layer, and

means to apply an electrical signal corresponding to information to be recorded to a first conductor adjacent to the area of the photoconductive insulating layer being scanned.

9. A transducer according to claim 8 in which said photoconductive insulating layer is in the form of a cylinder, and said means to advance the point of scanning light impingment comprises means to rotate said cylinder about its longitudinal axis and said means to scan said photoconductive insulating layer in a direction parallel to said first conductors comprises means to cause traversal of scanning radiation impingement along the cylinder surface in a direction parallel to the longitudinal axis of said cylinder.

10. A transducer according to claim 9 in which said means to apply an electrical signal corresponding to information to be recorded to the conductor above Which the scanning radiation impinges comprises a plurality of electrical contacts on the end face of said cylinder, each of said electrical contacts being connected to only one of said first conductors, insulating means to maintain mutual electrical separation between all of said contacts and a stationary brush adapted to make contact with only one of said contacts during one traversal of said scanning light.

11. An electrical signal to latent electrostatic image transducer comprising a photoconductive insulating layer,

a plurality of first, electrically separated, elongated conductors contiguous to said photoconductive insulating layer,

at least one second conductor and a dielectric material, said second conductors being on the same side of said photoconductive layer as said first conductors and being slightly spaced from said first conductors by said dielectric material,

means to scan along the length of areas of said photo conductive insulating layer adjacent to successive first conductors on its side opposite said first and second conductors with said source of electromagnetic radiation, and

means to apply an electrical signal representative of information to be recorded between successive first conductors and an adjacent second conductor While areas of said photoconductive layer adjacent the length of said successive first conductors are 'being scanned with said electromagnetic radiation source.

References Cited UNITED STATES PATENTS 3,288,602 11/1966 Snelling 96-1 3,062,956 11/1962 Codichini 346-74 3,090,828 5/1963 Bain 346-74 3,199,086 8/1965 Kallmann 178-66 3,301,947 l/1967 Stone 346-74 3,308,233 3/1967 Button 178-66 3,308,234 3/1967 Bean 178-66 STANLEY M. URYNOWICZ, JR., Primary Examiner.

L. .T. SCHROEDER, Assistant Examiner.

US Cl. X.R. 178-66