US3760229A - Ac corotron - Google Patents

Ac corotron Download PDF

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Publication number
US3760229A
US3760229A US00214125A US3760229DA US3760229A US 3760229 A US3760229 A US 3760229A US 00214125 A US00214125 A US 00214125A US 3760229D A US3760229D A US 3760229DA US 3760229 A US3760229 A US 3760229A
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United States
Prior art keywords
electrode
shield
corotron
voltage
receiving surface
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US00214125A
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English (en)
Inventor
M Silverberg
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Xerox Corp
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Xerox Corp
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Publication date
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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

  • the a.c. corotron which includes an electrode and a shield partially surrounding the electrode is adapted to be driven by an a.c. source connectable between the electrode and the shield.
  • an impedance is connected intermediate the electrode and the a.c. source to tend to equalize the magnitude of the a.c. potential applied to the electrode during the intervals in the operation of the a.c. corotron in which positive and negative ion current flows. This reduces the magnitude of any offset voltage which may ultimately remain on the charge receiving surface.
  • This invention relates to an a.c. corotron utilizing an a.c. voltage for energizing an electrode to produce corona thereat to neutralize an electrostatic charge on a charge receiving surface disposed in proximity thereof, and more specifically to an impedance means embodied in such corotron for controlling the relative magnitudes of positive and negative peak values of the electrode energizing voltage to thereby reduce the magnitude of any offset voltage which may remain on the charge receiving surface.
  • Electrographic reproduction of the type disclosed in the U. S. Pat. No. 2,297,691, issued to Chester F. Carlson has heretofore been disclosed wherein a uniform layer of electrostatic charge is deposited on the surface of a suitable photoreceptor for selective dissipation in response to modulated radiation imaged thereon to form an electrostatic latent image of an original document. This image is thereafter developed and transferred to a support surface to form a final copy of the document.
  • various devices have been disclosed which deposit a uniform electrostatic charge on the surface of the photoreceptor such as the corona discharge devices disclosed in U.S. Pat. No. 2,777,957 issued to Walltup.
  • a corona discharge device of a type contemplated herein comprises an elongted corona discharge electrode and a conductive shield partially enveloping the electrode on a lengthwise axis thereof and connected to a reference potential, whereby a charge receiving surface is subject to an electrostatic charge.
  • An a.c. voltage is applied to the electrode for producing thereat a corona discharge which serves to neutralize an electrostatic charge on a surface. It is recognized that, when supplied with an a.c. voltage of sufficient magnitude, a negative corona discharge current is initiated at a lower threshold voltage than the positive corona discharge current. Consequently, more negative ions flow to a charge receiving surface during a given cycle than positive ions. Hence, after neutralization, a negative offset voltage. of finite magnitude may remain on the charge receiving surface. This offset voltage impairs the operation of the electrophotographic reproducing device in such manner that low quality images of the reproduced documents result.
  • the present invention contemplates an improved corotron for controlling the instantaneous relative magnitudes of positive and negative peak values of a.c. voltage energizing the corona discharge electrode on a reduce the magnitude of offset voltage remaining on a charge receiving surface.
  • Another object is to minimize the magnitude of an unwanted electrostatic charge occurring on a charge receiving surface by an a.c. a corotron.
  • a further object is to provide an improved corotron for enhancing the quality of images of documents reproduced in an electrophotographic reproducing device.
  • corona discharge device in combination with a prior-art type of corotron (corona discharge device) embodying an elongated wireform corona discharge electrode, and a conductive shield partially enveloping the electrode along a longitudinal axis thereof and referenced to a potential both the electrode and the shield being disposed in proximity an to a charge receiving surface to be neutralized, voltage wherein an a.c. is supplied to the electrode to produce a corona discharge thereat whereafter an unwanted finite magnitude of offset voltage remains, a specific embodiment of the present invention comprising a resistive impedance interposed between the electrode and a means for supplying an a.c. voltage to the electrode for controlling the instantaneous relative magnitudes of positive and negative peak values of the a.c. voltage whereby the magnitude of the offset voltage remaining on the charge receiving surface is reduced.
  • the positive peak value is made larger than the negative peak value.
  • a further embodiment concerns the use of a supply of do potential between the reference potential and a point common to the shield and a.c. source for charging the shield surface to a dc. potential of preassigned polarity and magnitude. Otherwise, the modification operates substantially in the manner of the specific embodiment as hereinbefore mentioned.
  • FIG. 1 is a side elevational view of a conventional corona discharge device energized with an a.c. voltage and including a specific embodiment of the invention
  • FIG. 2 is essentially a cross-sectional view of a mechanical portion taken along line 22 in FIG. 2;
  • FIGS. 3 and 4 are curves illustrating circuit action obtainable in FIGS. 1 and 2;
  • FIG. 5 is a modification of the circuit portion of FIGS. l and 2.
  • FIGS. 1 and 2 illustrate a conventional corotron (corona discharge device) embodying an elongated wiretype electrode 10 partially enveloped by a substantially half-round conductive shield ll and suitably supported at opposite ends thereof, not shown. This electrode is disposed on a center line which is close to and equidistant from both opposite lengthwise edges of the shield.
  • corotron corona discharge device
  • This shield is connected to a reference ground potential.
  • a supply of a.c. voltage 12 is connected between the electrode and the reference ground potential to produce corona discharge at the electrode.
  • a charge receiving surface 13 is spaced from an open end of the shield in proximity of the electrode to receive corona current therefrom.
  • the charge receiving surface 13 is assumed to be a suitable photoreceptor, and may have other applications depending on a particular use of the corona discharge device in given electrophotographic reproducing apparatus.
  • a conventional use of the apparatus schematicallyillustrated in FIGS. I and 2 is to neutralize an electrostatic charge effective on the photoreceptor surface. Since the major portion of ion current produced at the corona discharge of the electrode flows to the shield, the voltage effective on the electrode at any instant of time is substantially determined by the voltage-ion current relationship between the electrode and the shield. Referring to FIG. 3, it is seen therein that the voltageion current relationship between the electrode and shield is asymmetrical with respect to the polarity of the applied voltage at source 12. That is to say, the positive voltage threshold A is larger than the negative voltage threshold OB.
  • an impedance 14 positioned in series between the electrode and the ungrounded terminal of the a.c. in FIGS. 1 and 2 serves to reduce the magnitude of the above-noted offset voltage remaining on the photoreceptor in the following manner.
  • the impedance may be of a type which is preferably, but not necessarily, capable of transmitting direct current. It is seen, therefore, that the impedance may be a resistive type.
  • a high impedance presents a load to the corotron having an effect thereon which may be analyzed by superimposing a corresponding load line onto the graphical representation of FIG. 3.
  • the load line intersects the positive voltage-ion current curve at a positive current value that is substantially equal to the negative current value at which the negative voltage-ion current curve is intersected.
  • the positive voltage exceeds the negative voltage at the points of intersection.
  • the impedance cause the corona discharge to provide substantially equal magnitudes of positive and negative ion current flow to the photoreceptor, by increasing the positive peak voltages with respect to the negative peak voltages supplied by the a.c. supply to the electrode.
  • the amplitude of the negative ion current pulses delivered to both the shield and the photoreceptor surface are reduced to a value which is substantially equal to the magnitude of the positive ion current pulses delivered to both the shield and the photoreceptor surface. This substantially reduces the magnitude of the unwanted offset voltage remaining on the photoreceptor surface to a small or approximately zero value.
  • the magnitudes of the positive and negative ion current pulses effective between the electrode and shield are primarily a function of the voltage differences therebetween. This assumes that at least a small finite amount of ion current is flowing between the electrode and shield. If the potential of the photoreceptor surface admits of a given magnitude and polarity, one of the positive and negative ion current pulses is slightly increased in magnitude while the other is slightly decreased in magnitude. This enables the a.c. corotron to deliver a net value of direct current to the photoreceptor surface in response to a charge on said surface. That is to say, the voltage difference between the electrode and the surface permits the delivery of a net value of direct current to the photoreceptor surface as illustrated in FIG. 4.
  • FIG. 5 is a modification of FIGS. 1 and 2 in that a supply 15 of d.c. potential has a positive terminal connected to shield 11 and the other terminal of a.c. source 12 and a negative terminal to the reference potential.
  • This supply charges the shield surface to a voltage of preassigned polarity and magnitude, the latter being substantially equal to the terminal voltage of supply 15.
  • the aforedescribed offset voltage may be completely reduced to zero if the voltage provided by supply 15 is equal to the offset voltage.
  • the operation of FIG. 5 is identical with that of FIGS. 1 and 2 as hereinbefore described. It should be recognized that the photoreceptor surface may be charged to a desired value substantially equal to the magnitude and polarity of supply 15.
  • shield 11 having an internal diameter of inches
  • electrode 10 having a diameter of 3 mils and a length of 10 inches, which is approximately coextensive with the length of shield 11
  • an operating voltage of 7 kilovolts zero to peak, and a frequency of 60 HZ for source 12 for inducing a corona current of the order of 35 microamps per inch of the electrode
  • a series resistor on the order of 10 rnegohms
  • a voltage of 50 volts for supply 15 in FIG. 5 It has been experimentally ascertained that a net corona current of 5 microamps per inch is delivered to the photoreceptor surface if said surface exhibits a potential of +1000 volts.
  • impedance 14 may, therefore, be connected in series with source 12 in the primary circuit of the transformer.
  • the effective impedance thus connected in series with the electrode is a function of the turn ratio of the primary and secondary coils of the transformer. Accordingly, the turns ratio may be selected such that a higher impedance is reflected into the secondary circuit.
  • transformers may be advantageously exploited by utilizing a low impedance exhibiting preferable power dissipation characteristics in the primary circuit while achieving the desired results that may be obtained from using a high impedance connected in series with the electrode.
  • a precise commercially available low voltage variable impedance may be connected in the primary circuitto attain results not readily derived from impedances series connected to the electrode because precise, high voltage variable impedances are not readily found in the market place.
  • an elongated electrode a shield partially surrounding said electrode, said shield being maintained at a reference potential; impedance means coupled to said electrode for equalizing the relative magnitudes of positive and negative voltage applied to the coronode when ion current flows from the electrode; and means for supplying an a.c. voltage to said electrode to effect a corona discharge thereat, said last named means being connected intermediate said impedance means and a reference potential and said charge receiving surface being maintained in a fixed relationship with respect to said reference potential. 2; Corotron apparatus as defined in claim 1 wherein said reference potential is maintained at ground potential.
  • Corotron apparatus for charging a charge receiving surface comprising in combination;
  • impedance means coupled to said electrode for equalizing the relative magnitudes of positive and negative voltage applied to the electrode when ion current flows therefrom;
  • first means for supplying an a.c. voltage to said electrode to effect corona discharge thereat, said first means being connected intermediate said impedance means and a reference potential;

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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)
  • Elimination Of Static Electricity (AREA)
US00214125A 1971-12-30 1971-12-30 Ac corotron Expired - Lifetime US3760229A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US21412571A 1971-12-30 1971-12-30

Publications (1)

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US3760229A true US3760229A (en) 1973-09-18

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US00214125A Expired - Lifetime US3760229A (en) 1971-12-30 1971-12-30 Ac corotron

Country Status (5)

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US (1) US3760229A (de)
JP (1) JPS4878939A (de)
DE (1) DE2263120A1 (de)
GB (1) GB1410671A (de)
NL (1) NL7215756A (de)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3921042A (en) * 1974-11-25 1975-11-18 Xerox Corp Electrostatic reproduction machine with improved corona generating device
US3970381A (en) * 1973-02-26 1976-07-20 Xerox Corporation Method and apparatus for xerographic reproduction
US4156141A (en) * 1978-01-16 1979-05-22 Pitney-Bowes, Inc. Corona wire damage control resistor
US4415947A (en) * 1978-11-13 1983-11-15 Hoechst Aktiengesellschaft Method and apparatus for electrostatically charging a dielectric layer
US4526848A (en) * 1982-11-27 1985-07-02 Olympus Optical Company Ltd. Electrophotographic process with a.c. charger producing greater positive charge
US4672505A (en) * 1984-06-18 1987-06-09 Canon Kabushiki Kaisha Corona discharging device
US6313635B1 (en) 1999-12-03 2001-11-06 Illinois Tool Works Inc. High voltage sensor assembly
US8840241B2 (en) 2012-08-20 2014-09-23 Xerox Corporation System and method for adjusting an electrostatic field in an inkjet printer
US8947482B2 (en) 2013-03-15 2015-02-03 Xerox Corporation Active biased electrodes for reducing electrostatic fields underneath print heads in an electrostatic media transport
US9211736B2 (en) 2012-07-25 2015-12-15 Xerox Corporation System and method for reducing electrostatic fields underneath print heads in an electrostatic media transport
US9327526B2 (en) 2012-07-25 2016-05-03 Xerox Corporation Active biased electrodes for reducing electrostatic fields underneath print heads in an electrostatic media transport

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH621421A5 (en) * 1976-03-31 1981-01-30 Du Pont Magnetographic dry copying process and device for carrying it out
JPS5349988A (en) * 1976-10-18 1978-05-06 Canon Inc Electricity reduction method and its device
JPS5394931A (en) * 1977-01-28 1978-08-19 Ricoh Co Ltd Charging method
JPS57154261A (en) * 1981-03-18 1982-09-24 Ricoh Co Ltd Controlling method for electrostatic charging
JPS57205757A (en) * 1981-06-15 1982-12-16 Fuji Xerox Co Ltd Electrostatic charger

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2897395A (en) * 1955-08-18 1959-07-28 Westinghouse Electric Corp Grid electrodes for electric discharge devices
US3376208A (en) * 1964-05-19 1968-04-02 Canadian Ind Method of improving the adhesive properties of polyolefin film by passing a diffuse electrical discharge over the film's surface
US3396308A (en) * 1965-07-02 1968-08-06 Eastman Kodak Co Web treating device

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS439997Y1 (de) * 1965-09-20 1968-04-30
JPS446159Y1 (de) * 1965-09-20 1969-03-05

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2897395A (en) * 1955-08-18 1959-07-28 Westinghouse Electric Corp Grid electrodes for electric discharge devices
US3376208A (en) * 1964-05-19 1968-04-02 Canadian Ind Method of improving the adhesive properties of polyolefin film by passing a diffuse electrical discharge over the film's surface
US3396308A (en) * 1965-07-02 1968-08-06 Eastman Kodak Co Web treating device

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3970381A (en) * 1973-02-26 1976-07-20 Xerox Corporation Method and apparatus for xerographic reproduction
US3921042A (en) * 1974-11-25 1975-11-18 Xerox Corp Electrostatic reproduction machine with improved corona generating device
US4156141A (en) * 1978-01-16 1979-05-22 Pitney-Bowes, Inc. Corona wire damage control resistor
US4415947A (en) * 1978-11-13 1983-11-15 Hoechst Aktiengesellschaft Method and apparatus for electrostatically charging a dielectric layer
US4526848A (en) * 1982-11-27 1985-07-02 Olympus Optical Company Ltd. Electrophotographic process with a.c. charger producing greater positive charge
US4672505A (en) * 1984-06-18 1987-06-09 Canon Kabushiki Kaisha Corona discharging device
US6313635B1 (en) 1999-12-03 2001-11-06 Illinois Tool Works Inc. High voltage sensor assembly
US9211736B2 (en) 2012-07-25 2015-12-15 Xerox Corporation System and method for reducing electrostatic fields underneath print heads in an electrostatic media transport
US9327526B2 (en) 2012-07-25 2016-05-03 Xerox Corporation Active biased electrodes for reducing electrostatic fields underneath print heads in an electrostatic media transport
US8840241B2 (en) 2012-08-20 2014-09-23 Xerox Corporation System and method for adjusting an electrostatic field in an inkjet printer
US8947482B2 (en) 2013-03-15 2015-02-03 Xerox Corporation Active biased electrodes for reducing electrostatic fields underneath print heads in an electrostatic media transport

Also Published As

Publication number Publication date
GB1410671A (en) 1975-10-22
NL7215756A (de) 1973-02-26
DE2263120A1 (de) 1973-07-12
JPS4878939A (de) 1973-10-23

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