US 3623122 A
Description (OCR text may contain errors)
United States Patent lnventor Appl. No. Filed Patented Assignee Richard A. Fotland Cleveland, Ohio June 4, 1970 Nov. 23, 1971 Horizons Incorporated, a division of Horizons Research Incorporated Cleveland, Ohio ELECTRIC RECORDING APPARATUS EMPLOYING LIQUID DEVELOPER 8 Claims, 11 Drawing Figs.
05. Cl. 346/74 E, 355/3, 355/8 lnt. CL G033 13/00 Field of Search 346/74 CH,
74 E, 74 P, 74 R, 74 ES; ass/3.4, s, 10;204/1s|, 30o
 References Cited UNITED STATES PATENTS 2,932,548 4/1960 Nau et al. 346/74 ES 3,270,637 9/1966 Clark 355/10 X 3,383,993 5/1968 Yeh 355/10 X Primary Examiner-Robert L. Richardson Allorney- Lawrence 1. Field PATENTEDmv 23 Ian SHEET 2 OF 2 L INVENTOR Richard A. For/0nd FIG. IO.
ATTORNEY ELECTRIC RECORDING APPARATUS EMPLOYING LIQUID DEVELOPER Methods and techniques for producing visible images from an electrical input have been known and practiced for many years. Facsimile recorders employing special papers are in wide use. The image is formed either through the electrolytic development of a color or through the use of an electrical discharge to vaporize (blast-off) an overlayer.
Another widely practiced technique involves a corona discharge from a fine stylus spaced a very short distance above an insulating surface-generally a paper whose surface is coated with an insulating thermoplastic film. This method of recording is well described in the patent literature, including the following US. Pats. Nos. 2,894,799, 3,064,259, 3,068,481, 3,131,256, 3,208,176, 3,217,330, 3,289,209, 3,383,697, 3,384,898, 3,409,899, 3,417,404, 3,434,157, 3,471,861.
Another method of generating an image is described in my U.S. Pat. No. 3,121,375 (Contrography).
A basic difference between these known techniques and the present invention is the presence of a liquid at the recording stylus in the process and apparatus of the present invention.
In the present description, a variety of apparatuses are described in which the use of a liquid medium disposed between the electrodes and the record medium, instead of air, produces several significant advantages including the following:
1. The realization of much higher resolution than obtained with an air electrical discharge technique;
2. A significant increase in recording speed due to the rapidity with which the stylus discharge forms the image (higher modulation rate of the potential applied to the stylus);
3. The recording and development step occur simultaneously or nearly simultaneously, thus simplifying the apparatus utilized for implementing this method of recording.
The present invention will be more fully understood from the description'which follows taken in conjunction with the drawings in which:
FIG. I is a schematic view of one kind of recorder which may be used;
FIG. 2 is a fragmentary view of a modified stylus which may be used;
FIG. 3 is a fragmentary view partly in section of a modification in which a plurality of styli are used;
FIG. 4 is a plan view of a record medium passing through the apparatus of FIG. 3;
FIG. 5 is a modification showing a computer output generated copying apparatus;
FIG. 6 is a further modification utilizing a line optical input;
FIGS. 7, 8 and 9 are views of a further embodiment of which FIG. 7 is a side elevation, FIG. 8 is a view of the embodiment of FIG. 7 looking toward the left side, and FIG. 9 is a schematic wiring diagram;
FIG. 10 is a further modification, shown schematically; and
FIG. 11 shows still further embodiment for high-speed recording of electrical inputs.
In the figures the use of primed and double-primed notation indicates that the structure equivalent to similar structure identified by the same numeral in an earlier figure (see trough 12 in FIG. 1, 12' in FIG. 10 and 12" in FIG. 11).
EXAMPLE 1 Example 1 is best understood with reference to FIG. 1. The recorder shown in FIG. 1 includes a medium 10 upon which the record is made. This recording sheet 10 may consist of a clear plastic film base or any type of paper. The recording medium 10 is guided through a trough 12 containing a liquid developer 14 by the use of rollers 16. Any conventional means (not shown) may be utilized for advancing the record medium 10 through the liquid developer 14 contained in trough 12. The web may be continuously drawn through the recording system or the drive may be intermittent; for example, if a single frame at a time is to be recorded. Excess developer is removed from the web by squeegee rollers 18. Residual developer solvent remaining on the web is removed by a warn air plenum 20. The recording stylus 22 includes a stylus tip 24 which may consist of a coarse wire sharpened to a tip width of 2 to 3 mils, or the tip 24 may be spherical with a radius of about 5 to 20 mils. The recording stylus is moved over the surface of the recording sheet, the stylus tip contacting the recording surface, by an electromechanical drive 26. A modulated source of electrical potential 30 establishes an electric field between the stylus 22 and a conducting counterelectrode 28.
The electromechanical drive which positions the stylus the recording medium may be any one of a variety of drives well known to the art, for example, an X-( recorder or servo drive to position the stylus in two directions or a high-speed recording pen motor or any other suitable known mechanism.
A developer was formulated by milling carbon black in a petroleum solvent (Isopar G manufactured by Humble Oil and Refining Company). This developer was diluted with the solvent until the solids concentration (by wt.) was 0.5 percent. Other liquid developers, such as those described in U.S. Pat. No. 3,259,581, were also effective in the examples which follow.
With the developer described above, dense thin lines were recorded at stylus potentials in excess of 200 volts; the recording stylus 22 being negative with respect to the counterelectrode 28. The line width could be varied from V4 to 10 mils, depending upon the geometry of the stylus point and to a lesser extend upon the applied potential. Dense lines were recorded at the highest velocity provided by the electromechanical drive or 200 inches/sec. The optical density of the line increased up to the maximum potential applied of 1 ,200 volts.
FIG. 2 is a fragmentary view showing a modified stylus which may be used in which a large tank of developer is not required. By employing the modification herein, means are provided for rapidly changing the developer so that, for example, different colored developers may be rapidly introduced near the recording stylus to change the image color. In this figure, the recording medium 10 is once again supported on a conducting counterelectrode 28. The recording stylus 22 is supported in a cylindrical tube 32 which is open on the bottom and closed on the top. The tube-stylus assembly is positioned by the electromechanical drive 26. Potential is once again supplied by the modulated voltage source 30. The interior space of the cylinder 32 contains the developer solution 14 which is recirculated through inlet tube 34 and removed at outlet tube 36. The liquid developer is continuously recirculated through a reservoir by a solenoid-operated valve and pump (not shown in the figure). By employing electrically operated solenoid valves, it is possible to switch from one color developer to a different color developer in a time period of less than 1 second. Thus, not only may'the density of the image be controlled by the voltage supply 30 but the color may also be selected at will.
EXAMPLE 2 The device sketched in FIG. 3'illustrates an apparatus for recording alphanumeric or other symbolic information. Here, rather than using a single stylus as shown in FIG. I, seven styli 22 are employed. By pulsing these styli at the appropriate time, alphanumeric characters (seven elements high) are formed. Referring to FIG. 4, which is a top schematic view of the recording system, showing the recording film 10 or paper and the styli 22 which are identified by the letters a through g. These styli are mounted in a recording head 40 which may or may not be mounted on an electromechanical transducer or rapidly revolving drum for the purpose of scanning across the film or paper. The styli pulse generators and logic are contained in an electronics package 42. The tips of the styli are, of course, submerged in the recording liquid (not shown).
The operation of this recorder may be best explained with reference to FIG. 4. In this drawing, the film or paper base is moving rapidly from left to right. The character A is shown formed here.
The styli may, if the character size is to be reasonably large (for example, of a size suitable for direct viewing), be arranged in a vertical array. In this case, the letter A would be formed by briefly pulsing electrodes C, D, E, F and G followed in sequence by pulses on BD, AD, BD, and then CDEF and G. The time interval between each pulse would be characteristic of the velocity of the web and the distance between the character elements in the direction of web travel. The styli shown in FIGS. 3 and 4 are staggered in such a manner that the distance between adjacent styli is increased over the distance which would be present if the styli were arranged in a vertical row. This minimizes crosstalk between styli, eliminates the possibility of voltage breakdown between styli, and simplifies the mounting and alignment of the styli. These advantages are important only if very small dimensions are realized; for example, when it is desirable to create alphanumeric characters mils or less in total height. In the case of staggered styli, appropriate electronic logic, well known in the art, must be employed so that the appropriate time delays are utilized to fonn desired characters.
It will be understood that, if desired, the styli may be continued, extending completely across the web in a direction either orthogonal or inclined to the direction of web travel. Proper commutation must be provided in order to select the printing styli out of the large number of styli present.
EXAMPLE 3 The apparatus of FIGS. 3 and 4 may be modified to generate, at a very high rate, alphanumeric characters from computer output. An example of a computer output generated microfilm apparatus is shown in the schematic of FIG. 5. This figure shows the transparent plastic base 10' in web form, the counterelectrode 28', and a scanning wheel 44. Embedded in the edge of the scanning wheel are four styli assemblies spaced 90 along the circumference. Each styli assembly consists of seven staggered styli of the type shown in FIGS. 3 and 4.
The modified apparatus is compatible with presently available computer output microfilm recorders of the type employing an optical intermediate such as a cathode-ray tube or laser diode matrix. Thus, the film I0 is 16 mm. and the recording is formed over a A inch width on this film. The characters on the film are reduced so that they are suitable for normal viewing at 26X magnification. On the film, the characters are 3 mils in height and 4 mils wide. The width of each incremental recorded area, corresponding to a single discharge from a single styli, is 0.4 mil. Since four styli assemblies record over a Vzto inch area along the circumference, the recording disc diameter is 0.64 inch. The recording rate is 10,000 lines of alphanumeric characters per minute or 166 lines per second. The peripheral velocity of the scanning wheel 44 is then 83 inches per second and the disc rotates at 2,500 rpm. The entire assembly is, of course, submerged in liquid developer of the type described in example I. In each line there is space for 132 characters corresponding to a packing density of 260 characters per inch. During operation, the device generates 22,000 characters per second Since the image element spacing is approximately 0.4 mil, the maximum pulsing rate at the styli is 220,000 pulses per second.
Since the recording is directly electronic, there is no need to utilize intermediate optics in forming the image. The image is recorded on a low-cost transparent base. The only complexity over more conventional COM recording techniques is the requirement for additional logic necessary for the proper formation of alphanumeric characters since the recording styli are staggered in the recording head.
In a further modification for generating computer output microfilm, the scanning wheel may be replaced by a highspeed pen motor drive. The recording stylus assembly is then mounted on the top of a pen connected to a high-speed pen motor. Many of these pen motors have mechanical linkages so that the scan is rectilinear rather than over an arc. Over a scanning distance of one-half, the required 166 scans per second are well within the state of the art.
EXAMPLE 4 This example describes a recording system employing an optical input. In some respects, examples 4 and 5 are similar to devices described in US. Pat. No. 3,121,375. The major difference is that the examples in the patent indicate the developer manifold placed on the side of the recording web opposite the control electrode (with the exception of the capillary manifold control). In the embodiment described in this example, the control electrode is immersed in the liquid developer and this electrode is in contact with the surface being recorded upon.
The apparatus shown schematically in FIG. 6 includes a line optical input to control the potential at styli, causing a visible image to appear on recording paper 10. In this figure, 28 is a counterelectrode. The liquid developer surrounding the tips of the styli is not shown in the figure. The recording head assembly consists of a glass plate 50 containing a cylindrical cavity 52 near the top surface. A photocathode layer 56 is deposited on the surface of the glass bore. The photocathode, which may be of the cesium-antimony type, is of sufficient thickness to be electrically conducting. An electrical connection 58 is made between the photocathode and a DC power supply 60. A number of styli 22" are embedded in the glass recording head 50. These styli consist of Kovar pins 5 mils in diameter spaced on l0-mil centers. The spacing determines the resolution in the direction across the paper; in this case equal to lines per inch.
In operation, an original document is moved past a l0-mil wide slit at a rate equal to which the copy paper 10 moves under the recording styli 22". Means, not shown in FIG. 6, are provided for imaging the illuminated original onto the photocathode. Optics effective for carrying out this imaging are shown in FIG. 1 ofU.S. Pat. No. 3,121,375.
The copy device shown in FIG. 6 is negative working. Thus, when illumination reflected from a white area of the original strikes the photocathode 56, electrons are emitted. These electrons are collected by the electrode connected to the stylus 22", causing the potential of the electrode to be driven negative with respect to the counterelectrode 28. The presence of a voltage at the paper results in the deposition of developer particles.
The effectiveness of this technique is illustrated by the following calculations. The capacity between a single styli and the counterelectrode is 10" picofarads, assuming a paper thickness of 3 mils. A total charge of 5 [Ly-COUIOI'IlbS per element is transported from the photocathode to the stylus to raise the pin potential 1,000 volts. Since there are approximately 10 discrete image elements per copy sheet, the total charge transported per copy (assuming the sheet was totally printed) would be 5 coulombs. At a copy sheet speed of 2 inches/sec., the copy is formed in 5 seconds and hence the total maximum recording current is 1 ampere.
The instantaneous potential of a recording styli is equal to 1/Cf idt,
where C is the capacity and i is the charging current. Since the charging current is independent of voltage, the charging time is merely equal to the product of the potential difference through which an electrode is charged and its capacity to the counterelectrode divided by the charging current per stylus. Since the charging current of a single styli during operation is near I nanoampere, the charging time is 5 msec. Thus, the maximum recording rate at the minimum current level required for operation is 200 elements per second. Since there are I00 recorded elements per inch, the maximum recording speed, at the lowest operational light level, is 2 inches/sec. At higher illumination levels, the recording speed may be propor- R. FotlanlifJ. Ap Phys, 3 i', U53? TEEDI per lumen.
tionally increased since the charging current is proportional to illumination.
The sensitivity of a typical cesium-antimony photocathode is 20 aa/lumen. In order to generate the required I a. charging current, 0.05 lumen is required at the photocathode. Since the efficiency of the optical system is near 5 percent, the total luminous flux from the scanned area on the original must be I lumen or greater. The area of the lO-mil scanning slit (8% inches wide) is 0.0006 ft. Thus, the illumination level at the slit must be 1,600 ft. candles or greater. This illumination level is easily obtained with simple condensing optics imaging a tungsten halogen lamp onto the slit.
EXAMPLE 5 FIGS. 7, 8 and 9 schematically illustrate another modification wherein the imaging concept described herein may be controlled via an optical input. In this embodiment, the potential at the styli is modulated by a photoconductor. In FIGS. 7 and 8, the copy paper or film 10, the counterelectrode 28, and he liquid developer 14 are disposed as shown. An array of conducting elements and photoconductors are deposited upon a recording head employing photoresist techniques well known to those skilled in the art.
The recording head 60 consists of a glass or ceramic substrate 62. Deposited directly upon this substrate are a series of conducting stripes 64. These stripes are 5 mils in width and spaced uniformly on lO-mil centers. A single broad stripe 66 of photoconductor material is deposited over stripes 64. The particular photoconductor chosen depends upon the specific application. If a high-sensitivity and relatively low-recordingspeed system is desired, cadmium sulfide or cadmium sulfoselenide may be deposited to form the photoconductor. In order to realize high recording speeds, a fast-response time photoconductor is required. Amorphous selenium falls into this category. The manner of preparing such a film and its characteristics are described in the literature. Two conducting electrodes electrodes, 68, 69 are deposited over the photoconductive film. One of these electrodes 69 must be semitransparent so that the incident illumination can irradiate the photoconductor, while the second electrode 68 may be semitransparent or opaque. Power supply 70 is connected between these two conducting stripes. As seen in the circuit diagram of FIG. 9, this arrangement provides a bridge, two arms of which are composed of the photoconductor. Upon illuminating one of the arms of the bridge, the potential at the recording electrode 64 rises, thus causing an image to forrn on the recording sheet.
This recording W252i; 7 when A fabricated employing amorphous selenium as a photoconductor, requires illumination levels similar to those required for example 4 since the sensitivity of an amorphous selenium layer is close to 20 a.
EXAMPLE 6 This example is an embodiment which provides for two significant advantages over previous examples. The imaging system is sketched in FIG. 10. Rather than develop the image directly on a paper or film 10 (as shown in previous examples), the image is formed on the insulating surface of a transfer roller 74. This roller is uniformly coated with an insulating film 76 having a thickness in the range of I to ID mils. A preferred coating material is a vitreous enamel because of its high strength, high abrasion resistance, and ease of cleaning. The image placed on this insulating surface 76 by the control recording head 72, which may consist of any of the previously shown types of recording head, is transferred to the copy paper 10 by a transfer roller 78. In order to effect efficient transfer, a high electrical potential may be connected between rollers 78 and 74 to aid in electrostatically transferring the image from the drum to the paper. Residual image is removed from insulating surface 76 by a cleaning brush 80.
One advantage of this approach is associated with a reduction in background levels on the copy sheet. It has been found that when the copy sheet is immersed directly in the liquid toner, small amounts of development liquid are carried out of the development bath by the sheet. As the developer solvent evaporates, developer particles are left on the sheet which results in a slight background level.
This background level may be reduced by predevelopment immersion of the copy paper into a bath of solvent not containing developer pigment particles.
The preimmersion serves to imbibe pure solvent into the paper, thus minimizing the pickup of pigment containing solvent during the development operation. In the device of FIG. 10, the paper background is extremely clean since there is very little solvent carryover by the hard insulating surface 76.
Another advantage of this embodiment is associated with registration in preparing full color copies. By employing color separation filters and three recording heads, the recording and imaging systems described herein may be readily adapted to form color images. An example of the color separation optics required is shown in FIG. 5 of US. Pat. No. 3,121,375. Any of the previous techniques may be employed in forming color images by mrely utilizing several heads and different colored developer pigments. In a three-color system, three separate recording heads are required. Although these heads may be positioned relatively lose to one another along the copy sheet, it is impossible to superimpose the heads since the liquid developers must be spatially separated along the web. If a color image is formed by recording directly upon a paper, the registry of the image in the direction of paper travel is dependent upon the accuracy of the optics, consistency of spacing in the recording heads, and uniformity of the paper geometry as the paper moves through the three recording stations. Since paper is subject to stretching and dimensional changes, an improvement in registration is observed if the colored recording is carried out by spacing three heads around the circumference of a transfer drum. Since the geometry of the drum is invariant, accurate registration is obtained. The full color image, in registry, may be subsequently transferred to a copy paper.
EXAMPLE 7 FIG. 11 shows a configuration of high-speed recording of electrical inputs. Shown here are copy sheet 10 which passes under a printing roller 82; this roller also serving as a counterelectrode. Development is carried out in a meniscus formed between the copy sheet 10 and a roller 84, the bottom half of which is immersed in a liquid developer reservoir 12". Roller 84 rotates with a surface, velocity higher than printing roller 82 to continuously replenish and supply liquid developer to the meniscus. Scanning across the paper i carried out with the aid of a high-tensile-strength wire 86, upon which are mounted conducting recording styli beads 88. Thirty-gauge stainless steel wire has been found satisfactory for this application; the beads being formed by cementing 30-mil diameter stainless steel balls onto the wire. The wire passes over pulleys 90, one of which is driven by a high-speed synchronous motor 92. A modulated recording signal is applied between conducting roller 82 and the recording wire 86 from the modulated power supply 94. The recording beads contact the surface of the paper and are mounted along the scanning wire at 8 VZ-inCh intervals. In one embodiment of this device, four balls are spaced equal distances along a 34 inch endless wire loop. The drive pulleys are 3 inches in diameter and the drive motor revolves at 12,000 r.p.m. At this rate, a given ball scans across the Bk-inch wide copy sheet at a velocity of 1,800 inches per second and generates 225 scans per second. The scans are on IO-mil centers and thus the time required to generate a single copy is 5 seconds. Since it is desired to have approximately 800 resolvable elements across the sheet, the recording bit rate is [80,000 bits per second. The modulator band width must then be approximately I00 kHz.
This high-speed facsimile Ewing technique has the advantage of compactness, high recording rate, and the capability of employing conventional papers.
In summary, this modification in which the recording stylus and developer are on the same side of the recording media and the stylus is submerged in developer appears to offer significant potential in a number of areas. The input may be either optical or electrical. The process is relatively simple. Line widths as narrow as one-fourth mil have been obtained, thus indicating a potential for forming microimagery. The writing speed, on film, is over 120 inches per second. The maximum modulation rate and writing speed observed have been limited by the apparatus presently available rather than the process itself.
1. A recording apparatus including at least one recording stylus, means to move a recording medium relative to said stylus and to maintain one end of said stylus in physical contact with said record, said end of said stylus being immersed in a liquid developer, a counterelectrode disposed on the face of said record medium opposite to the face which is maintained in contact with the stylus and means to feed a signal to said stylus indicative of the information to be recorded on said record medium.
2. The apparatus of claim 1 wherein means are provided for confining the liquid developer to an area surrounding said end of said stylus.
3. The apparatus of claim 1 wherein a source of potential is connected between said stylus and said counterelectrode.
4. The apparatus of claim 3 in which at least one electro-optical transducer is provided for controlling the potential between said stylus and said counterelectrode and optics for imaging an optical signal on said electro-optical transducers.
5. The apparatus of claim 1 wherein there are a plurality of styli disposed transversely of said record medium.
6. The apparatus of claim 5 wherein the styli are a plurality of fine wires embedded in an insulating support.
7. The apparatus of claim l wherein the record medium is a tape.
8. A recording apparatus including at least one recording stylus, means to move a rotary conducting drum having an insulating surface relative to said stylus and to maintain one end of said stylus in physical contact with said drum, said end of said stylus being maintained in a liquid developer, means to feed an electrical signal, indicative of the information to be recorded on said drum, between said drum and said stylus and means to contact a record medium to said drum to effect the transfer of information from drum to record media.
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