US3557367A - Method and apparatus for increasing the efficiency of corona charging of a photoconductor - Google Patents

Method and apparatus for increasing the efficiency of corona charging of a photoconductor Download PDF

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Publication number
US3557367A
US3557367A US665049A US3557367DA US3557367A US 3557367 A US3557367 A US 3557367A US 665049 A US665049 A US 665049A US 3557367D A US3557367D A US 3557367DA US 3557367 A US3557367 A US 3557367A
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United States
Prior art keywords
corona
charging
photoconductor
insulating material
wire
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Expired - Lifetime
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US665049A
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English (en)
Inventor
Walter Roth
Charles F Gallo
Algrid G Leiga
John A Mcinally
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Xerox Corp
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Xerox Corp
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/02—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices
    • G03G15/0291—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices corona discharge devices, e.g. wires, pointed electrodes, means for cleaning the corona discharge device

Definitions

  • a method and apparatus for increasing the efficiency of corona charging of a photoconductive plate are disclosed in the present application.
  • the method comprises reducing the electromagnetic radiation received by the photoconductive plate by the use of an optical mask between the charging corona wires and the photoconductive plate
  • the ions produced by the corona wire are directed to the photoconductive plate by the use of a combination of electrostatic ion deflection techniques and/or the use of a gas flow to carry the ions around an optical mask.
  • the efficiency of corona charging is increased by charging an intermediate insulating material such as insulating beads or an insulating belt which may then be brought into contact with an optically shielded photoconductor or other material to be charged.
  • an intermediate insulating material such as insulating beads or an insulating belt which may then be brought into contact with an optically shielded photoconductor or other material to be charged.
  • the present invention relates to corona charging and more specifically to a method and apparatus for increasing the efficiency of corona charging.
  • Corona charging has become almost universally used as a method of sensitizing xerographic photoreceptors.
  • a large flux of ions is created by the corona discharge of a wire or wire array which is maintained at a high potential and supported near the photoconductor.
  • ions produced by the corona wire result in a deposition of charge'on the photoconductor or photoreceptor and sensitize its surface for later exposure or the like in the xerographic process.
  • the corona also generates electromagnetic radiation which can be observed visually. Although its intensity of the electromagnetic radiation from the corona appears weak to the human eye, the main emission is in the ultraviolet portion of the spectrum which is outside of the eye response. Since the sensitivity of xerographic selenium plates is relatively high in the ultraviolet region of the spectrum even ap-' parently weak radiation from the corona has a tendency to discharge the plate.
  • the electromagnetic radiation from charging coronas is not insignificant and that the radiation can be sufficiently intense to reduce the efficiency of the corona charging operation.
  • the charging efficiency with positive corona is adversely affected by approximately percent and may well be in excess of IO percent for specific photoreceptor combinations more sensitive than the selenium.
  • the electromagnetic radiation from a negative corona is approximately five times more intense than the radiation from position corona under similar conditions.
  • the adverse affect of electromagnetic radiation from negative corona on equally sensitive photocoriductors may be expected to, in general, ex ceed that of the positive corona.
  • the discharge problem resulting from corona radiation becomes more severe as more sensitive photoconductors are developed for use in higher speed operational configurations.
  • the present invention overcomes the deficiencies of the .prior art and achieves its objectives by providing an optical mask in the path of the electromagnetic radiation produced by the corona wire.
  • the ions produced by the corona charging are guided around the optical mask by a combination of ion I deflection techniques and/or a supplementary gas flow, or by charging an intermediate material such as a large number of small insulating beads or an insulatingbelt.
  • the intermediate material may then be cascaded or otherwise brought into contact with the photoconductor to achieve a charge transfer to the photoconductor.
  • FlG.l is a front view of a corona charging device according to the present invention. including a partial cross section of the photoconductive drum.
  • FIG. 2 is a cross-sectional representation of the present invention taken along line 22 of FIG. l.
  • FIG. 3 is a cross-sectional representation of an alternative embodiment of the present invention.
  • FIG. 4 is a cross-sectional representation of another embodiment of the present invention.
  • FIG. 5 is a cross-sectional representation of yet another embodiment of the present invention.
  • FIG. I A preferred embodiment of the present invention is shown in FIG. I in which corona charging unit 10 is positioned over and in close proximity to photoconductive drum 15 including a photoconductor 12 which overlays a grounded (2l) conductive backing l4.
  • the corona charging device l0 comprises a corona wire I6 enclosed by a shield 18.
  • At the orifice of the shield 18 is provided an electrostatic ion deflection element 20.
  • A- suitably high potential from DC power supply 22 is applied to the electrostatic ion deflection element 20 and is of the same relative polarity as the ions produced by corona wire l6.
  • a difference of potential suitable for producing the desired electrostatic ion deflection based upon the geometric configuration of the shield l8 and the ion deflection element 20 is provided, as illustrated, by a bias matrix 27 including, for example, an array of resistors 23, 24, 25, and 29 to provide a suitable potential difference between the electrostatic ion deflection element 20 and the corona wire 16.
  • the specific circuitry employed may, of course, as would be obvious to one of .ordinary skill in the art, involve many other circuit elements other than the resistors 23, 24, 25 and 29 which are representative of a suitable electrical circuit for producing the desired electrical potentials between corona wire l6 and a shield 18 and an electrostatic ion deflection element 20. It should be noticed that the electrostatic shield 18 may also be biased so as to repel additional ions through the orifice in electrostatic deflection shields l8.
  • electrostatic ion deflection element 20 By applying proper potential differences by means well known in the art of ion optics suitable potentials may be applied through the backing plate l4, the electrostatic ion deflection element 20, the shield l8, and corona wire l6 to cause a flow of ions to pass around electrostatic ion deflection element 20 and be directed to the photoconductive or photoreceptor layer l2. It should be noted that because of its con figuration and relative dimensions to the photoreceptor l2 and the corona charging unit 10, electrostatic ion deflection element 20 prevents any electromagnetic radiation, which travels in a straight line, from reaching the photoconductor directly.
  • electrostatic ion deflection element 20 While a specific configuration of electrostatic ion deflection element 20 is illustrated in FIG. 2 any suitable configuration for a specific dimension and configuration of the rest of the system which will produce the desired electrostatic deflection of the ion beam while inhibiting or preventing the passage of any electromagnetic radiation to the photoreceptor l2 may be employed.
  • the potentials applied may be altered both in polarity and in magnitude to provide the desired electrostatic deflection for the specific energies, configurations, and materials, being employed.
  • deflection element 20 need not be in the electrical circuit at all for some configurations and thus need not be a conductive metal but can be wood or other dielectric material. In the situation where the deflection element is a dielectric not in the circuit, element 20 merely builds up charges which serve to repel the ions produced by the corona discharge.
  • the structure and materials which make up the corona charging unit in this application may be of the type as taught in the numerous patents in this area, for example, 2,588,699, 2,777,957, 2,836,725. 2,885,556,;1nd 2,922,883.
  • the ions produced by the corona wire l6 are radiated in all directions uniformly.
  • the shield means l8 may be blackened with a conductive layer [9, such as colloidal graphite, platinum black, and the like so that large amounts of the normally reflected electromagnetic radiation will not be reflected so as to reach the photoconductor l2.
  • direct radiation from corona wire I6 is masked by means of the electrostatic ion deflection element 20 which serves both to act as an optical mask and to provide a means for deflecting the ion current produced by corona wire l6 onward to the photoconductive surface 12.
  • FIG. 3 An alternative configuration is illustrated in FIG. 3, in which in addition to the shielding means 18 and electrostatic deflection element 20, a flow of gas from compressed gas bottles 26 is provided.
  • the gas flow is a dual flow having dual entrance ports 28 to shield [8.
  • This flow of gas is produced by the pneumatic pressure of the compressed gas in bottles 26, and acts to carry the ion flow produced into the shield l8 in the area of corona wire l6 may beselected in one of several manners to ni minimize the problem of electromagnetic radiation as stated above for a v given set of conditions.
  • a gas may be selected with an optical spectrum outside the sensitivity range of the photoconductor.
  • oxygen or neon or a mixture of these gases may be utilized when a selenium plate is the material employed as photoconductor l2.
  • the gas flow may be utilized to direct the flow of ions around the optical mask element 20 by itself without any potential applied to optical mask element 20.
  • suitable potentials may be applied to the optical mask element 20 so that it continues to act as an electrostatic ion deflection element and in conjunction with the gas flow serves to direct the ions around itself as an optical mask and onto the photoconductive plate l2.
  • optical mask means combined with a gas flow in a wide variety of configurations and with the gas itself having a wide variety of flow rates and effects upon the optical radiation may be utilized to result in effectively blocking the optical radiation produced by corona wire 16 from reaching the photoreceptive plate 12 and yet insure that an adequate supply of ions from corona wire 16 is directed to the surface to be charged 12.
  • FIG. 4 represents a charging system which utilizes small insulating beads 48 as the intermediate material.
  • The'small insulating beads 48 are stored in a container 46 which feeds into the base of housing 52 for the corona unit 40.
  • a motor 60 drives a belt 45 which contains a number of buckets 44 around a pair of pulley wheels 42 and 58.
  • the configuration is such that the buckets 44 are caused to dip into the supply of small insulating beads 48 which lie in the base of unit 52.
  • These beads are carried upward in buckets 44 and at the top of pulley wheel 42 are dumped onto support means 62. While sliding and rolling down support means 62 the beads 48 are charged by the corona wires 64 in a corona shield 66.
  • the beads are not photoconductive and are therefore unaffected by the electromagnetic radiation produced by corona wires 64.- These beads proceede under the force ,of gravity or under mechanical conveyance to cascade over the photoreceptive surface 54 of, for example, a xerographic drum having a grounded conductive substrate 53.
  • drum is driven by motor means 56. In this way charge is transferred to the photoconductive layer 54 of the drum.
  • the optical radiation from the corona wires 64 does not reach the photoconductor 54. Further. it should be noted that by charging a large number of small insu' lating beads 48 it is no longer required that the corona wires 64 produce a uniform emission. Therefore. all of the corona current can be used to charge the beads 48 allowing selective steps taken in the prior art to becliminated, thus, simplifying the corona charging process. The above process produces a great increase in efficiency, since in conventional corona charging of the photoconductor, in order to achieve more uniform charging on the photoconductor, as much as 90 percent of the corona current is directed toward the shield means and thus is wasted.
  • the beads 48 have been referred throughout as small insulating beads, their dimensions andeomposition may vary over a relatively large range. For example, typical bead dimensions may be on the order of 40 to I000 microns. In general,- the smaller the bead size the more uniform the charging.
  • Typi-- cal materials suitable for use as the insulating beads include glass, and polystyrene. v 3
  • the cascade arrangement may be varied considerably from that shown in FIG.- 4 since it is only necessary to charge the insulating beads 48 in a way which prevents the electromagnetic radiation produced by the'corona from falling directly on the photoconductive mediato be charged and then cascading the small insulating beads 48 over the surface to be charged.
  • the arrangement shown in FIG. 4 is merely illustrative of the one possible embodiment of the present invention and many other variations both for drum and flat plate configurations will be obvious to those skilled in the art.
  • a layer of insulating beads may be deposited on a selenium or similar photoconductive plate to allow induction charging of the photoconductor through the charging of the layer of beads.
  • FIG. 5 Another embodiment is shown in FIG. 5.
  • the operating principle of the embodiment shown in FIG. 5 is essentially the same as that shown in FIG. 4 but in lieu of the small insulating beads 48 an insulating belt is employed.
  • This belt is driven by a driven pulley wheel 76 which is drivenby a motor 78.
  • Belt 80 is then corona charged by corona wire 74 which .is optically shielded from the photoconductive drum comprising photoconductive layer 86' overlying conductor 85.1
  • the drum is driven by motor means 88
  • the optical shielding of the photoconductor 86 from the light produced by the corona wire 74 may be achieved by the configuration of the insulating belt 80 shown in FIG. 5 and also by shields 72 and if necessary by additional baffles. and stops 70.
  • the insulating belt 80-then passes over pulley rolls 82 and 84 which bring the charges into intimate contact with the photoconductive drum 86 so as to transfer the charge from insulating belt 80 to the photoconductive layer 86.
  • the present invention is not limited to situations in which a photoconductor is to be charged but the present application is applicable to any situation in which it is desired to produce and utilize corona charging. It is also clear, however. that the problem solved by the present arrangement is most serious in the situations in which sensitive high speed photoconductors are being employed.
  • a method of increasing the efficiency of corona charging comprising: l. applying a potential to a corona charging wire;
  • a corona charging device comprising:
  • optical mask means for preventing the direct illumination of a photoconductor adjacent said corona wire from electromagnetic radiation produced by said corona wire;

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • General Physics & Mathematics (AREA)
  • Electrostatic Charge, Transfer And Separation In Electrography (AREA)
  • Photoreceptors In Electrophotography (AREA)
US665049A 1967-09-01 1967-09-01 Method and apparatus for increasing the efficiency of corona charging of a photoconductor Expired - Lifetime US3557367A (en)

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US66504967A 1967-09-01 1967-09-01

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US (1) US3557367A (xx)
BE (1) BE720017A (xx)
BR (1) BR6800368D0 (xx)
DE (1) DE1797213A1 (xx)
FR (1) FR1597512A (xx)
GB (1) GB1244378A (xx)
NL (1) NL6812170A (xx)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3660656A (en) * 1970-08-26 1972-05-02 Eastman Kodak Co Light lock for corona device
US3675096A (en) * 1971-04-02 1972-07-04 Rca Corp Non air-polluting corona discharge devices
US3739246A (en) * 1969-12-17 1973-06-12 Kalle Ag Process and apparatus for increasing the charge density of insulators
US3880514A (en) * 1973-09-14 1975-04-29 Coulter Information Systems Ion producing source for electrostatic recording apparatus
US3942079A (en) * 1970-10-29 1976-03-02 Brock Alan J Charging of electrophotographic surfaces

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2863063A (en) * 1955-11-21 1958-12-02 Bruning Charles Co Inc Charging of photo-conductive insulating material
US2934650A (en) * 1957-04-10 1960-04-26 Haloid Xerox Inc Charging apparatus
US3084061A (en) * 1953-09-23 1963-04-02 Xerox Corp Method for formation of electro-static image
US3409768A (en) * 1967-04-03 1968-11-05 Eastman Kodak Co Light lock for air ionizer to shield photosensitive material

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3084061A (en) * 1953-09-23 1963-04-02 Xerox Corp Method for formation of electro-static image
US2863063A (en) * 1955-11-21 1958-12-02 Bruning Charles Co Inc Charging of photo-conductive insulating material
US2934650A (en) * 1957-04-10 1960-04-26 Haloid Xerox Inc Charging apparatus
US3409768A (en) * 1967-04-03 1968-11-05 Eastman Kodak Co Light lock for air ionizer to shield photosensitive material

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3739246A (en) * 1969-12-17 1973-06-12 Kalle Ag Process and apparatus for increasing the charge density of insulators
US3660656A (en) * 1970-08-26 1972-05-02 Eastman Kodak Co Light lock for corona device
US3942079A (en) * 1970-10-29 1976-03-02 Brock Alan J Charging of electrophotographic surfaces
US3675096A (en) * 1971-04-02 1972-07-04 Rca Corp Non air-polluting corona discharge devices
US3880514A (en) * 1973-09-14 1975-04-29 Coulter Information Systems Ion producing source for electrostatic recording apparatus

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NL6812170A (xx) 1969-03-04
DE1797213A1 (de) 1971-07-29
FR1597512A (xx) 1970-06-29
GB1244378A (en) 1971-09-02
BR6800368D0 (pt) 1973-01-25
BE720017A (xx) 1969-02-27

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