US3611074A - Corona discharge device - Google Patents

Corona discharge device Download PDF

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Publication number
US3611074A
US3611074A US879054A US3611074DA US3611074A US 3611074 A US3611074 A US 3611074A US 879054 A US879054 A US 879054A US 3611074D A US3611074D A US 3611074DA US 3611074 A US3611074 A US 3611074A
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United States
Prior art keywords
charge
rods
wire
corona discharge
potential
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Expired - Lifetime
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US879054A
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English (en)
Inventor
Heinz H Weichardt
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International Business Machines Corp
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International Business Machines 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

  • ABSTRACT A corona generator for providing a uniform and highly efficient corona discharge for use in such apparatus as eleeirophotographic printers.
  • This invention relates specifically to corona discharge devices for generating an ion flow particularly adapted to charge an electrophotographic plate used in electrophotography Xerography.
  • corona charging devices In electrophotographic copiers and other such printing devices, it is common to use corona charging devices to charge the electrophotographic plate surface.
  • the charge is eflected by imposing a high-voltage potential on a conductor spaced from the surface to impart a high-field intensity on the surrounding air.
  • the voltage potential causes the air to break down resulting in a migration of ions to the wire with ions of opposite potential migrating to the electrophotographic surface.
  • the migration of ions must be sufficient to deposit a predetermined charge on the electrophotographic plate for satisfactory operation of the electrophotography process. Additionally, the charge must be uniformly distributed across the plate.
  • the primary method of equalizing the charge distribution across the surface has been to position a ground shield on the opposite side of the charged conductors from the plate. It has also been common practice to drive the emitting conductors at a very high potential because, if not so driven, the phenomena occurs which is referred to as beading. The effect of such beading is a streaking of the charge pattern deposited on the electrophotographic surface.
  • the shield acts to raise the total ion flow along the corona wire length and thus at least partially prevents the beading.
  • the ground shield While solving some of the more immediate problems, the ground shield also presents disadvantages.
  • One disadvantage is that the shield is not transparent and therefore cannot be used where the charging and exposure of the electrophotographic plate must be concurrent. Additionally, the ground shield serves as a conductor for bleeding off ions which strike it and thereby limits the ion flow to the plate and decreases the efficiency of the corona unit. In the past, less than 10 percent of the ions actually reach the plate and more than 90 percent migrate to the ground shield thereby making the corona unit operate at a very low efficiency.
  • An additional object of the present invention is to provide a simple and relatively inexpensive corona charging unit.
  • the invention is embodied in a charging apparatus for use in electrophotographic devices to deposit increments ofcharge on a chargebearing surface and comprises a corona discharge wire held in spaced relationship to the surface to be charged, a bias rod positioned in spaced relationship on each side of said wire, and means to impress an electrical voltage potential on said wire and rods whereby said rods effect a virtual ground plane extending to the surface to be charged on either side of the wire to enhance the charge flow from the wire to the surface.
  • FIG. 1 illustrates a diagrammatic schematic view of an electrophotographic process in which the subject invention can be used
  • FIG. 2 illustrates the corona charging unit embodying the subject invention with the primary components disassembled
  • FIG. 3 is an enlarged cross-sectional view of the corona charging unit embodying the subject invention in assembled form
  • FIG. 4 is an enlarged schematic view of a corona wire plus bias rods showing the approximate path of the ions
  • FIG. 5 illustrates an alternate embodiment of the corona charging unit embodying the subject invention with primary components disassembled
  • FIG. 6 is an enlarged'cross-sectional view of the corona charging unit of FIG. Sembodying the subject invention in assembled form.
  • FIG. 1 One example of a particular apparatus in which the subject invention is adapted for use is the electrophotographic apparatus shown in FIG. 1.
  • a rotatable drum 1 carries around its periphery an electrophotographic photoconductive member 2 on which is directed an image which it is desired to reproduce on the paper sheets 3 stored in a hopper 4.
  • a document having the image to be copied is placed upon a transparent plate 5 mounted within a table 6 and the light sources 7 are energized which direct light onto the image for reflection back through a lens 8 onto the surface of the photoconductor 2.
  • the document is moved at a speed synchronized with the surface speed of drum I in a manner known in the art.
  • the surface of the photoconductor has been electrostatically charged in a manner to be described later and where illuminated by the image, is discharged leaving a charged pattern in a form of the image to be copied.
  • a drum passes a development station 10 at which atoner-carricr mixture 11 is cascaded across the elec trostatic image on the surface of the photoconductor 2.
  • the toner having a charge opposite from the polarity of the electrostatic image charge, is attracted to the drum surface to render the image visible.
  • An endless conveyor belt l2 carries the toner-carrier mixture to a position for gravity feeding across the surface of the photoconductive member.
  • a copy paper 3 is fed into contact with the developed electrostatic image by the rollers 14.
  • a corona unit I5 is disposed beneath the paper at the area of contact with a polarity opposite that of the toner thereby attracting the toner to the copy paper.
  • the paper 3 is separated from the drum and fed past a heating element 16 which serves to fuse and permanently fix the toner to the paper.
  • the drum continues to rotate past a cleaning brush 17 which wipes the surface of the photoconductor and removes any excess toner which drops into a receptacle 18. With the exception of the charging station, this describes the complete cycling of the drum for reproducing the image desired.
  • the corona unit 20 comprises at least one corona discharge wire held in spaced relationship to the photoconductor surface with a bias rod positioned to either side and approximately an equal distance from the photoconductor surface such that by impressing a high voltage on the wire and a lower voltage on the rod, the rods form a virtual ground plane extending normal to the photoconductor surface and through the rods so as to guide most of the resulting ions from the wire to the photoconductor surface for the charging of the photoconductor.
  • the wire support unit comprising a plurality of small diameter corona wires 21 mountedon a pair of insulator blocks 22 and 24 having extending fingers 25 contacting the wires.
  • the wires are supported in tension between a pair of spring fingers 26 made of a conductive metal and fixed to the end of a mounting block 27 by screws 28.
  • the rod support unit holds the bias rods 30 mounted to extend between a pair of insulator blocks 31 and 32 held in parallel spaced relationship by a pair of support rods 34 at each end.
  • the inner side of each of the mounting blocks includes a concave inset portion 35 sized to permit the entry of the wire support unit so that the corona wires 21 fit between and extend parallel to the bias rods 30.
  • Terminals 36 and 37 connect through the conductor plate to the bias rods for supplying a reference potential V. to the rods 30.
  • a terminal 38 extends through a slot 39 in the insulator block 31 when the support units are assembled for supplying a highvoltage potential V to the corona wires through the spring fingers 26.
  • the voltage to the corona unit 20 is provided by power supply 33.
  • the voltage is usually referenced to the support member for photoconductor 2 which is generally maintained at ground potential.
  • the voltage V applied to bias rods 30 may be selected at a value from ground potential to about 25 percent V and provide a substantial increase in efficiency over the type of corona unit which utilizes a ground shield.
  • the preferred potential for V is ground potential.
  • the magnitude of the potential V selected for the corona wires may vary over a fairly wide range dependent upon many design factors known to those in the art. However, the preferred range is a potential of 6 to 8 kilovolts and a polarity the same as that desired for the charge to be produced on the surface of photoconductor 2. 1
  • the support units are held together by a plurality of spring biased buttons 40 which snap between the support rods 34.
  • This construction facilitates the servicing of the unit since the parts can be easily disassembled by snapping the supports apart.
  • This construction also gives access to the individual parts for cleaning, adjusting or replacing any of the individual parts of the corona unit.
  • the corona unit is suitable for those applications in which charging and exposure of the photoconductor surface must be concurrent since the area where the wires run is substantially free of interfering material as shown in FIG. 1.
  • the embodiment shown in FIGS. 2 and 3 also possesses this advantage since support 27 can be constructed of a transparent material or alternatively support 27 can be constructed as a frameshaped member which is open in the area where the wires run.
  • FIG. 4 shows the approximate path of the ions from the corona wires 21 to the photoconductive member 2. It can be shown mathematically that the effect of the bias rods 30 on the electrostatic field is similar to that of two grounded shields whose planes are perpendicular to the surface of the photoconductive member 2 and parallel to rods 30, and this effect is essential to establish a high-corona current.
  • the ions tend to migrate to the ground planes but, inasmuch as the region from the rods 30 toward the photoconductor is essentially at ground potential and no conductor is present there, a large percentage of the ions continue on to the photoconductor surface thereby resulting in an efficient transfer of the high-corona current to charge on the photoconductor surface.
  • the bias rods 30 were constructed of metal rods having a diameter of 0.050 of an inch.
  • the corona wires were polished tungsten wires 0.002 of an inch in diameter.
  • the adjacent bias rods 30 as shown in FIG. 4 were approximately 1.5 centimeters apart.
  • the bias rods and the corona wires were in a plane substantially parallel to the photoconductive member and spaced approximately 0.65 centimeter from the photoconductor member in one operation.
  • This structure was energized with a potential V of 7 kilovolts applied to the corona wire and a reference potential V coupled to bias rods 30 of ground potential.
  • the voltage of the photoconductor support member was also ground potential.
  • This configuration provided a charge current approximately 10 times as high as conventional corona units having ground shields and supplying the same total current.
  • the plane including the bias rods and the corona wires was spaced from the photoconductive member by 0.5 centimeter, and this embodiment showed a further four-fold increase in the efficiency of transferring charge to the photoconductive surface as compared to a conventional corona unit having ground shields.
  • the disclosed construction provides greatly increased corona current as well as a higher efficiency in transfer of charge to the photoconductive surface.
  • This advantage results in a decreased high-voltage power supply capacity requirement for a given corona requirement, thereby resulting in a reduced cost for the system.
  • This construction has the added advantage of being an easily iterated structure. Additional individual units of corona wires and adjacent bias rods can be added without appreciably influencing the operation of ad- 5 jacent units.
  • the disclosed construction has the advantage of not only increased corona current and a higher efficiency in transfer of charge to the photoconductive member, but also the construction facilitates the servicing of the unit since the individual parts are easily accessible.
  • the high-current density provided by the corona charging device described above may cause damage to the photoconductor in places in which small pinholes or depressions exist in the photoconductive coating.
  • the irregularities in the photoconductive coating give rise to strong local fields in the area of the photoconductive member surrounding the pinhole. These strong local fields cause the onset of a glow discharge which eventually results in electrical breakdown and arc-over to the corona wire.
  • a suppressor screen is added between the corona wire and the photoconductive member and energized with a relatively low potential. The addition of the suppressor screen not only reduces the chance of arc-over, but also leads to a charge limiting effect so that the charge on the photoconductor is uniformly placed.
  • the corona wires can be operated at a higher voltage thereby operating at a greater efficiency due to the field gradient being greater between the corona wires and the photoconductive member.
  • FIGS. 5 and 6 The embodiment of the invention which includes the suppressor screen is shown in FIGS. 5 and 6.
  • components which are substantially the same as the embodiment shown in FIGS. 2 and 3 are assigned the same reference number followed by a prime Suppressor screen 42 is added in a plane parallel to the photoconductive member between the plane which includes corona wires 21' and the bias rods 30.
  • the suppressor screen comprises a plurality of spaced wires attached at the ends to mounting plates 43. Plates 43 are attached to insulator blocks 31 by screws 44, for example, to maintain screen 42 in a plane.
  • Suppressor screen 42 is energized by a suitable voltage V from power supply 45.
  • the photoconductive member 2' is maintained at a reference voltage V of ground potential and the suppressor screen is maintained at a voltage V of l kilovolts.
  • bias rods 30' are energized with a potential V of -2 kilovolts and corona wires 21 are energized with a potential V of 7 kilovolts.
  • This corona device produces a uniform charge on the photoconductive member without damaging the photoconductor surface and also produces an efficient utilization of current to produce charge on the photoconductive surface. This has the practical result of requiring a smaller size corona device for a specified charging current and a smaller capacity power supply to produce the required charge density.
  • said electrical voltage potential on said corona discharge wire comprises a potential in the range of 6 to 8 kilovolts and the electric voltage potential on said bias rods comprises a range from substantially ground potential to one quarter of the corona wire potential.
  • a charging apparatus for use in such apparatus as electrophotographic mechanisms for depositing increments of charge on a charge-bearing surface comprismg:
  • a charging apparatus for use in such apparatus as electrophotographic mechanisms for depositing increments of charge on a charge-bearing surface, said apparatus comprismg:
  • a plurality of corona discharge wires held in spaced relationship to said surface 1 a plurality of bias rods each positioned in substantially the same spaced relationship to said surface as said corona discharge wires; means for holding one of said bias rods in flanking relation on each side of each of said wires; and means to impress an electrical voltage potential on said wires and rods whereby said rods effect a virtual ground plane extending to the surface to enhance the charge flow from said wires to said surface.

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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)
US879054A 1969-11-24 1969-11-24 Corona discharge device Expired - Lifetime US3611074A (en)

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US87905469A 1969-11-24 1969-11-24

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US (1) US3611074A (de)
JP (1) JPS4828696B1 (de)
BE (1) BE756687A (de)
CA (1) CA928767A (de)
CH (1) CH519189A (de)
DE (1) DE2056423C3 (de)
FR (1) FR2071750A5 (de)
GB (1) GB1316469A (de)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3789222A (en) * 1971-08-13 1974-01-29 Fuji Photo Film Co Ltd Corona charge method
US3789223A (en) * 1970-08-11 1974-01-29 Fuji Photo Film Co Ltd Charging method for relatively movable electrophotographic means and corona means
US3843906A (en) * 1972-03-20 1974-10-22 Kalle Ag Method of reducing the generation of ozone
US3916269A (en) * 1973-02-09 1975-10-28 Turlabor Ag Charging device
US4038583A (en) * 1974-05-09 1977-07-26 Jacques Leon Georges Breton Apparatus for the generation of negative or positive atmospheric ions
US4174170A (en) * 1976-12-16 1979-11-13 Minolta Camera Kabushiki Kaisha Conductive toner transfer photocopying machine
US5268569A (en) * 1992-07-22 1993-12-07 Minnesota Mining And Manufacturing Company Imaging system having optimized electrode geometry and processing
US5332893A (en) * 1992-07-22 1994-07-26 Minnesota Mining And Manufacturing Company Imaging system and device having a simplified electrode design
US5774324A (en) * 1995-11-10 1998-06-30 Mita Industrial Co., Ltd. Scorotron charger for use in an image forming apparatus
US5812359A (en) * 1997-04-11 1998-09-22 Xerox Corporation Method and apparatus for lightweight corona device shield mounting
US20070108984A1 (en) * 2003-11-12 2007-05-17 International Business Machines Corporation Ionization test for electrical verification
US20070237546A1 (en) * 2006-04-06 2007-10-11 Xerox Corporation Direct charging device using nano-structures within a metal coated pore matrix

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3978380A (en) * 1975-03-26 1976-08-31 Coulter Information Systems, Inc. Reciprocating corona producing apparatus
DE3371712D1 (en) * 1982-10-30 1987-06-25 Fuji Photo Film Co Ltd Device for charging electrophotographic apparatus
DD237048A1 (de) * 1985-05-07 1986-06-25 Verpackungsmaschinenbau Dresde Einrichtung zur neutralisation elektrostatischer aufladungen auf verpackungsmitteloberflaechen

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2868989A (en) * 1956-01-03 1959-01-13 Haloid Xerox Inc Electrostatic charging method and device
US3382360A (en) * 1965-09-10 1968-05-07 Xerox Corp Xerographic charging system having means for providing an air cushion between the charging device and the xerographic drum

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2868989A (en) * 1956-01-03 1959-01-13 Haloid Xerox Inc Electrostatic charging method and device
US3382360A (en) * 1965-09-10 1968-05-07 Xerox Corp Xerographic charging system having means for providing an air cushion between the charging device and the xerographic drum

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3789223A (en) * 1970-08-11 1974-01-29 Fuji Photo Film Co Ltd Charging method for relatively movable electrophotographic means and corona means
US3789222A (en) * 1971-08-13 1974-01-29 Fuji Photo Film Co Ltd Corona charge method
US3843906A (en) * 1972-03-20 1974-10-22 Kalle Ag Method of reducing the generation of ozone
US3916269A (en) * 1973-02-09 1975-10-28 Turlabor Ag Charging device
US4038583A (en) * 1974-05-09 1977-07-26 Jacques Leon Georges Breton Apparatus for the generation of negative or positive atmospheric ions
US4174170A (en) * 1976-12-16 1979-11-13 Minolta Camera Kabushiki Kaisha Conductive toner transfer photocopying machine
US5268569A (en) * 1992-07-22 1993-12-07 Minnesota Mining And Manufacturing Company Imaging system having optimized electrode geometry and processing
US5332893A (en) * 1992-07-22 1994-07-26 Minnesota Mining And Manufacturing Company Imaging system and device having a simplified electrode design
US5774324A (en) * 1995-11-10 1998-06-30 Mita Industrial Co., Ltd. Scorotron charger for use in an image forming apparatus
US5812359A (en) * 1997-04-11 1998-09-22 Xerox Corporation Method and apparatus for lightweight corona device shield mounting
US20070108984A1 (en) * 2003-11-12 2007-05-17 International Business Machines Corporation Ionization test for electrical verification
US7808257B2 (en) 2003-11-12 2010-10-05 International Business Machines Corporation Ionization test for electrical verification
US20070237546A1 (en) * 2006-04-06 2007-10-11 Xerox Corporation Direct charging device using nano-structures within a metal coated pore matrix
US7466942B2 (en) * 2006-04-06 2008-12-16 Xerox Corporation Direct charging device using nano-structures within a metal coated pore matrix

Also Published As

Publication number Publication date
JPS4828696B1 (de) 1973-09-04
CH519189A (de) 1972-02-15
BE756687A (fr) 1971-03-01
GB1316469A (en) 1973-05-09
DE2056423C3 (de) 1975-01-02
DE2056423B2 (de) 1974-05-30
CA928767A (en) 1973-06-19
DE2056423A1 (de) 1971-06-09
FR2071750A5 (de) 1971-09-17

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