US 3778146 A
An apparatus in which light rays are generated for illuminating a transparent electrode adapted to electrostatically attract toner particles thereto. The intensity of light rays passing through the electrode indicates the density of toner particles adhering thereon. In this manner, the concentration of toner particles within a development system of an electrophotographic printing machine is determined.
Description (OCR text may contain errors)
United States Patent 1191 3,778,146 Knapp Dec. 11, 1973  LLUMINATWG APPARATUS FOREIGN PATENTS OR APPLICATIONS 1 lnvemorl Lowe" pp VICIOY, NY 1,223,741 3/1971 Great Britain 355/3  Assignee: Xerox Corporation, Stamford,
Conn. Primary ExaminerRobert P. Greiner [22} Filed 0c 2 1972 AttorneyJames J. Ralabate et al.
 Appl. No.: 294,064  ABSTRACT An apparatus in which light rays are generated for illu-  Cl minating a transparent electrode adapted to electro  Int Cl 6 15/00 statically attract toner particles thereto. The intensity [581 Fie'ld lag/637 of light rays passing through the electrode indicates I 18/7 250/218 the density of toner particles adhering thereon. In this manner, the concentration of toner particles within a development system of an electrophotographic print-  UNITE /:fr ;S rENTS ing machine is determined. 3,348,522 10/1967 Donohue 118/7 8 Claims, 6 Drawing Figures mmmnau 1 m5 SHEET 1 BF 2 FIG. I
PAIENIEDHEBI 1191s 3,778,146
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7 1 ILLUMINATING APPARATUS BACKGROUND OF THE INVENTION This invention relates generally to an apparatus for regulating the developability of amulti-color development system, and more particularly concerns an illumination apparatus for generating light rays which have the intensity thereof modulated to indicate the concentration of toner particles within a developer mix.
In the process of electrophotographic printing, a developer mix is used to form a powder image of an original document on sheet material. A developability regulating apparatus adjusts the characteristics of the developer mix to produce toner powder images having suitable density and color balance, i.e., developability. Developability is related to the concentration of toner in the developer mix, i.e. the percentage of toner particles relative to carrier granules therein. Environmental conditions such as temperature and humidity conditions effect developability. The physical parameters of the development system also effect developability, e.g., spacing, electrical bias, mass flow rate, and the magnetic field, amongst others. In addition, many other factors such as the state of compactation of the developer mix, and the electrical attraction between the toner particles and carrier granules influence developability. The developability regulating apparatus controlsthe toner particle concentration within the developer mix to maintain image density and color balance at an appropriate level.
Heretofore, the illuminating apparatus has been mounted external to the photoconductive drum of the electrophotographic ptinring machine. A system utilizing such an approach is described in copending patent application Ser. No. 213,056, filed on Dec. 28, 1971 and assigned to the assignee of the present invention. As described therein, a light source is mounted external to the photoconductive drum and a fiber optic light pipe transmits the light rays therefrom to the transparent electrode. The transparent electrode is mounted on the exterior circumferential surface of the photoconductive drum and is arranged to move, with the photoconductive drum, through all the processing stations. Thus, the transparent electrode has toner particles deposited thereon in the same manner as the electrostatic latent image recorded on the photoconductive drum. However, in order to illuminate the transparent electrode with light rays from the light source, it is necessary to transmit light rays from the light source to the transparent electrode. This increases the complexity of the apparatus inasmuch as the rotation of the drum relative to the light source must be considered to insure that the fiber optic light pipe does not twist about the shaft as the drum rotates. It is, therefore, apparent that it would be desirable to simplify the foregoing apparatus.
Accordingly, it is a primary object of the present invention to improve the illumination apparatus utilized in the developability regulating mechanism of an electrophotographie printing machine.
SUMMARY OF THE INVENTION Briefly stated, and in accordance with the present invention, there is provided an apparatus which illuminates an electrically biased transparent electrode of a development regulating mechanism. Light rays generated by an illuminating apparatus pass through the transparent electrode. The intensity of the light rays is modulated by toner particles adhering to the electrode. These modulated light rays are detected by a sensing member. Toner particle concentration is, thereby, indicated by the intensity of light rays transmitted through the electrode.
In accordance with the present invention, the apparatus includes a generally tubular support member mounted on a photoconductive member of a printing machine. The support member is positioned such that the bore thereof is substantially aligned with the transparent electrode mounted on the photoconductive member. A light source is located in the bore of the support member and arranged to produce light rays which are transmitted through the transparent electrode so as to be detected by the sensing member. In this manner, the intensity of the light rays passing through the transparent electrode indicates the density of toner particles adhering thereto. This, in turn, corresponds to the concentration of toner particles in the developer mix.
BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent upon reading and following detailed description and upon reference to the drawings in which:
FIG. 1 is a schematic perpsective view of an electrophotographic printing machine embodying the features of the present invention therein;
FIG. 2 is a sectional elevational view of a photoconductive drum used in the FIG. 1 printing machine, and showing, in detail, the illuminating apparatus of the present invention;
FIG. 3a schematically illustrates biasing electrically a transparent electrode of a development regulating mechanism to simulate an electrostatic latent image recorded on the photoconductive drum;
FIG. 3b schematically shows the deposition of toner particles on the transparent electrode;
FIG. 30 schematically depicts light rays being transmitted through the transparent electrode having toner particles deposited thereon and the intensity thereof being detected by a photosensor; and
FIG. 3d schematically portrays the transparent electrode being cleaned by a brush cleaner in preparation for the next machine cycle after the electrical biasing has been removed therefrom.
While the present invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to the embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended cliams.
DETAILED DESCRIPTION OF THE INVENTION With continued reference to the drawings wherein like reference numerals have been used throughout to designate like elements, FIG. 1 schematically illustrates an electrophotographic printing machine for producing multicolor copies from a colored original. The printing machine depicted in FIG. 1 employs a photoconductive member having a rotatably mounted drum 10 with a photoconductive surface 12 thereon. Drum 10 rotates in the direction indicated by arrow 14 to move photoconductive surface 12 sequentially through a series of processing stations. I
Photoconductive surface 12 initially passes through charging station A. A corona generating device, indicated generally by the reference numeral 16, is positioned at charging station A. Corona generating device 16 extends substantially transversely across photoconductive surface 12 to charge surface 12 to a relatively high uniform potential. A suitable corona generating device is described in US. Pat. No. 2,778,946 issued to Mayo in 1957.
Thereafter, charged photoconductive surface 12 is rotated to exposure station B. Exposure station B includes a moving lens system, designated generally at 18, and a color filter mechanism, shown generally at 20. Colored original document 22 is stationarily supported face down upon transparent viewing platen 24. In this way, successive incremental areas thereof are illuminated by means of a moving lamp assembly, indicated generally at 26. Lamp assembly 26 and lens system 18 are moved in a timed relation with drum to produce a flowing light image of original document 22 on photoconductive surface 12. During exposure, filter mechanism interposes selected color filters into the optical light path of lens 18. Filter mechanism 20 operates on the light passing through lens 18 to record an electrostatic latent image on photoconductive surface 12 corresponding to a preselected spectral region of the electromagnetic wave spectrum, i.e. a color separated latent image.
After recording the electrostatic latent image on photoconductive surface 12, drum 10 rotates to development station C, which has included thereat three individual development units generally indicated by the reference numerals 28, 30 and 32. The development units are all of a type generally referred to in the art as magnetic brush development units. Generally, in a magnetic brush development system, a magnetizable developer mix having carrier granules and toner particles is continually brought through a directional flux field to form a brush of developer mix. Development is achieved by bringing the brush of developer mix into contact with photoconductive surface 12. Each of the development units 28, 30 and 32, respectively, apply toner particles corresponding to the complement of the color separated latent image recorded on photoconductive surface 12. Thus, the toner particles contained in the respective development units 28, 30 and 32, ab-
sorb light within the preselected spectral region of the electromagnetic wave spectrum corresponding to the light transmitter through filter 20.
Additional toner particles are added to the respective developer mix when developability, as hereinbefore described, is reduced below an acceptable level. The regulating apparatus, indicated generally at 34, includes transparent electrode means 36 mounted on photoconductive surface 12 of drum 10. Illuminating means, or light source 38, is mounted on the interior circumferential surface of drum 10 and positioned such that the light rays therefrom are transmitted through transparent electrode 36. During development, toner particles are attracted electrostatically to transparent electrode 36 and the intensity of light rays passing therethrough is modulated indicating the density thereof. Sensing means, such as photosensor 40, is adapted to receive the modulated light rays passing through transparent electrode 36, and to develop, in response thereto, an
electrical output signal corresponding to the intensity of the light rays. Comparing means, i.e. suitable logic circuitry, compares the electrical output signal from photosensor 40 to a reference and generates a'control signal for dispensing selected toner particles into the appropriate development unit.
After development, the toner powder image electrostatically adheres to photoconductive surface 12 and moves therewith to transfer station D. At transfer station D, the powder image is transferred to a sheet of final support material 42 by means of a biased transfer roll, shown generally at 44. Support material 42 may be a sheet of paper or a transparent plastic amongst others. The surface of transfer roll 44 is biased electrically to a potential such that the magnitude and polarity thereof is sufficient to attract electrostatically the toner powder image from photoconductive surface 12 to support material 42. A single sheet of support material 42 is supported on transfer roll 44. Bias transfer roll 44 is arranged to recirculate support material 42 in synchronism with the rotation of drum 10 so that each of .the images developed on photoconductive surface 12 is transferred in superimposed registration thereto.
Bias transfer roll 44 has a recess therein torprevent contact with transparent electrode 36. In this way, toner particles deposited on transparent electrode 36 are not disturbed by the transfer process and represent a true indication of system developability.
After the last transfer operation, support material 42 is stripped from bias roll 44 and advanced to a fusing station (not shown) where the powder image is permanently fixed to support sheet 42. Thereafter, support material 42 is advanced to the catch tray (not shown) for subsequent removal by the machine operator.
The last processing station in the direction of rotation of drum 10, as indicated by arrow 14, is cleaning station E. A rotatably mounted fibrous brush 46 is positioned at cleaning station E, and engages photoconductive surface 12 and transparent electrode 36 to remove residual toner particles remaining thereon after the transfer operation.
Referring now to FIG. 2, there is shown the detailed configuration of development regulating mechanism 34. As depicted therein, development regulating mechanism 34 incorporates illuminating apparatus 38 of the present invention. Regulating mechanism 34 includes transparent electrode 36, light source 38, photosensor 40, and suitable logic circuitry (not shown) for processing the electrical output signal. In addition, each of the development units 38, 30 and 32, respectively, have associate toner containers for housing a supply of appropriately colored toner particles. For example, the toner container of development unit 28 houses cyan toner particles, development unit 30 magenta toner particles, and development unit 32 yellow toner particles. The toner container is adapted to meter out a specified quantity of selected toner particles to the appropriate development unit. Regulating mechanism 34 controls the dispensing of toner particles from the appropriate toner container to the respective development unit.
Transparent electrode 36 is mounted on photoconductive surface 12 of drum l0. Electrode 36 is located in a non-image portion of photoconductive surface 12.
Preferably, transparent electrode 36 is biased to about 200 volts above the developer bias, normal developer bias being about 500 volts. However, transparent electrode 36 may be biased from about 100 volts to about 600 volts above developer bias. The density of the image developed on transparent electrode 36 is detected by photosensor 40. The output signal from photosensor 40 is processed by logic circuitry, and, depending upon the density of the toner particles deposited on electrode 36, toner particles may or may not be added to the respective development unit; Photosensor 40 is mounted exterior to and spaced from photoconductive surface 12. It is positioned to sense the light rays passing through transparent electrode 36 just prior to the cleaning of photoconductive surface 12, i.e. before drum is rotated to cleaning station E. This is necessary since electrode 36 undergoes the same cleaning process as that of photoconductive surface 12.
Light source 38 is mounted on a generally tubular support member 48 which is in threaded engagement with a portion of the interior circumferential surface of drum 10. Support member 48 is positioned such that the bore thereof is substantially aligned with transparent electrode 36. As shown in FIG. 2, light source 38 is mounted slidably within the bore of support member 48. During assembly, light source 38 slides into the bore of support member 38 until depending flange 50 thereon engages undercut 52 of support member 48.
output which is utilized to excite lamp 38. Preferably,
the regulated current is transmitted through slip ring 58 along gauge tin stranded wire 60 having a polyalkieno and polyvinylide fluoride coating. Slip ring wires 60 extend to the light source wires 62 which are, preferably, silver plated copper having teflon shielding thereon. Preferably, light source or lamp 38 develops a spectral density ranging from 2% milliwatts per centimeter to 4% milliwatts per centimeter. I-Iowever, the spectral density of lamp 38 is adjusted to compensate for the distance between the transparent electrode 36 and face 63 of fiber optic light pipe 64.
As hereinbefore mentioned, transparent electrode 36 is electrically biased to a suitable voltage level in order to simulate the electrostatic latent image recorded on photoconductive surface 12. The application of the bias voltage to electrode 36 is controlled by slip ring assembly 58 which is segmented for approximately 60. In this way, no voltage is applied to transparent electrode 36 over an are extending from about fiber optic light pipe 64 to corona generating device 16. Hence, the bias voltageis removed from transparent electrode 36 during the cleaning process.
Transparent electrode 36 includes a glass window having a transparent tin oxide coating thereon. This type of transparent, electrically conductive glass is ,made by Pittsburgh Plate Glass under the trademark NESA, or is made by the Coming Glass Company under the trademark Electro-Conductive. The light rays passing through transparent electrode 36 are transmitted to photosensor 40 by fiber optic light pipe 64. Fiber optic light pipe 64 is mounted in plenum chamber 66 by suitable mounting means. Positive lamina air flow is directed into the chamber as indicated by arrow 68 to purge the system and reduce contamination. Fiber optic light pipe 64 extends into oven 70 and passes through a heat-tight aperture therein to conduct the modulated light rays transmitted through transparent electrode 36 to photosensor 40 mounted therein. Photosensor 40 and the associate circuit elements are all mounted within oven 70 and maintained at a temperature of 50 i 1 C. In this way, the temperature sensitivity of photosensor 40 does not influence the performance of regulating mechanism 34. Preferably, photosensor or photocell 40 is a commercially available silicon phototransistor, e.g., General Electric Company, Model No. LI4B.
Logic elements process the electrical output signal from photosensor 40. The logic elements, preferably include a discriminator circuit for comparing a reference with the electrical output signal from photosensor 40. The discriminating circuit may utilize a silicon control switch which turns on and effectively locks after an electrical output signal has been obtained having a magnitude greater than the reference (i.e., set point). The signal from the discriminating circuit changes the state of a flip-flop to develop an output signal therefrom. The output signal from the flip-flop, in conjunction with an output signal from the appropriate devel oped unit actuates an AND gate, which, in turn, transmits a control signal to the toner container for dispensing appropriate toner particles to the corresponding development unit.
While the present invention has been described in connection with on/off logic circuitry, one skilled in the art will appreciate that the invention is not necessarily so limited and that it is possible to utilize proportional circuitry which varies the quantity of toner particles metered to the respective development unit as a function of the magnitude of the control signal. This may be achieved bya suitable integrated circuit module for developing a stepped proportional dispensing rate.
Duplicate logic elements are utilized for each development unit. There are three separate, indpendent logic channels, each channel is associated with a respective development unit. The density of toner particles deposited on photoconductive surface 12 is a function of the concentration of toner particles within the developer mix. The concentration of toner particles is, in turn, a function of the magnitude of the reference. Thus, by adjusting the respective references, image density as well as color balance may be controlled.
Turning now to FIGS. 3a through 3d, inclusive, there is shown the sequence of events normally utilized in controlling the concentration of toner particles within the developer mix. In FIG. 3a, transparent electrode 36 is electrically biased to a suitable voltage level, e.g., approximately 200 volts above developer bias. This voltage, preferably, simulates the electrostatic latent image recorded on photoconductive surface 12. As drum 10 rotates into the development zone, as shown in FIG. 3b, the magnetic brush assembly of the respective development unit deposits toner particles on transparent electrode 36. Toner particles are attracted electrostatically to electrode 36 by the voltage differential between electrode 36 and the respective development unit. In FIG. 30, electrode 36 is aligned with fiber optic light pipe 64 to transmit the modulated light rays passing therethrough to photocell 40. This, in turn, produces an electrical output signal which is compared by the logic circuitry with the reference to develop a control signal for actuating, if required, the toner container of the appropriate development unit. When actuated, the toner container dispenses selected toner particles therefrom. As shown in FIG. 3d, the biasing voltage is removed from transparent electrode 36, i.e. slip ring 58 rotates to an open circuit position in which electrode 36 is not biased electrically, and, thereafter, brush 46, at cleaning station E, removes toner particles adhering thereto. The aforementioned procedure is repeated three successive times for each copy produced, i.e. it is repeated for each of the colored toner particles utilized in the printing machine (cyan, magenta, and yellow).
ln recapitulation, it is evident that the illuminating apparatus of the present invention improves the development regulating apparatus described heretofore. This is achieved by mounting the light source in a support member secured to the photoconductive member and aligned with the transparent electrode to transmit modulated light rays therethrough for indicating the density of toner particles attracted electrostatically thereto. In this manner, the concentration of toner particles within the developer mix is detected and adjusted accordingly.
It is, therefore, apparent that there has been provided, in accordance with this invention, an apparatus for illuminating the transparent electrode of a develop ment regulating mechanism that fully satisfies the objects, aims, and advantages set forth above. While this invention has been described in conjunction with the specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.
what is claimed is:
l. A development regulating apparatus for an electrophotographic printing machine of the type having a photoconductive member and a development system depositing toner particles on the photoconductive member in image configuration, including:
transparent electrode means mounted on the exterior surface of the photoconductive member spaced from the image region thereon, said electrode means being biased electrically to attract thereto toner particles being deposited thereon by the development system;
means for illuminating said electrode means substantially continuously, said illuminating means being mounted on the photoconductive member such that the light rays therefrom pass through said electrode means; and
means for sensing the intensity of the light rays passing through said electrode means to produce an electrical output signal indicative of the density of toner particles deposited thereon.
2. An apparatus as recited in claim 1, wherein said illuminating means includes:
a generally tubular support member having one end portion thereof secured to the photoconductive member; and
a light source mounted in the bore of said support member, said support member being located on the photoconductive member such that the light rays from said light source pass through said electrode means.
3. An apparatus as recited in claim 2, for an electrophotographic printing machine having a moving photoconductive member, wherein said illuminating means further includes:
a voltage source mounted substantially fixedly exterior to the moving photoconductive member; and
means for applying electrical current being generated by said voltage source to said light source mounted on the moving photoconductive member.
4. An apparatus as recited in claim 2, wherein said sensing means includes:
means for directing light rays passing through said electrode means; and
a photocell positioned in light receiving relation with said directing means to receive the light rays passing through said electrode means.
5. An illuminating apparatus for a development regulating mechanism having an electrically biased transparent electrode mounted on a photoconductive drum used in an electrophotographic printing machine, and a sensing member to detect the intensity of light rays passing through the transparent electrode, including:
a generally tubular support member mounted on the interior circumferential surface of the photoconductive drum extending radially inwardly therefrom; and
a light source mounted in the bore of said support member, said support member being located on the photoconductive drum such that the light rays from said light source pass through the transparent electrode.
6. An apparatus as recited in claim 5, for a rotatable photoconductive drum further including:
a voltage source mounted substantially fixedly exterior to the rotatable photoconductive drum; and
means for applying the electrical current being generated by said voltage source to said light source mounted on the rotatable photoconductive drum.
7. An apparatus as recited in claim 5, further including means for directing light rays passing through the transparent electrode to the sensing member.
8. An apparatus as recited in claim 7, wherein said directing means includes a fiber optic light pipe having one end portion thereof mounted exterior to the photoconductive drum and closely spaced to the transparent electrode secured thereto, said fiber optic light pipe having the other end portion thereof positioned such that the sensing member is in a light receiving relation therewith for guiding light rays passing through the transparent electrode to the sensing member.