CA1176695A - Corona charging apparatus - Google Patents
Corona charging apparatusInfo
- Publication number
- CA1176695A CA1176695A CA000397002A CA397002A CA1176695A CA 1176695 A CA1176695 A CA 1176695A CA 000397002 A CA000397002 A CA 000397002A CA 397002 A CA397002 A CA 397002A CA 1176695 A CA1176695 A CA 1176695A
- Authority
- CA
- Canada
- Prior art keywords
- conductive
- control electrode
- elongate conductor
- dielectric
- conductor
- Prior art date
- 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
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
- H01T19/00—Devices providing for corona discharge
-
- 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
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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)
Abstract
CORONA CHARGING APPARATUS
ABSTRACT OF THE DISCLOSURE
A corona charging device includes a dielectric-coated elongate conductor contacting or closely spaced from a control electrode. In the first version of this device, the control electrode comprises a conductive grid, which is mounted against an insulating support and in a second version, the control electrode consists of a slotted conductor, with the dielectric-coated elongate conductor embedded in a slot. A high voltage varying potential between the elongate conductor and control electrode induces a glow discharge in an air region in proximity to the two conductors. The control electrode may act as a grounding member to provide a corona discharge device with respect to a proximate surface or alternatively, the control electrode may be maintained at a desired potential to provide a charging device with an automatically limited voltage. The corona charging devices of the invention are characterized by a linear relationship between output ion currents and a direct current extraction potential. In further versions of the second corona device, the slotted conductor and dielectric-coated conductor may be replaced with alternative structures which provide an equivalent enclosure.
ABSTRACT OF THE DISCLOSURE
A corona charging device includes a dielectric-coated elongate conductor contacting or closely spaced from a control electrode. In the first version of this device, the control electrode comprises a conductive grid, which is mounted against an insulating support and in a second version, the control electrode consists of a slotted conductor, with the dielectric-coated elongate conductor embedded in a slot. A high voltage varying potential between the elongate conductor and control electrode induces a glow discharge in an air region in proximity to the two conductors. The control electrode may act as a grounding member to provide a corona discharge device with respect to a proximate surface or alternatively, the control electrode may be maintained at a desired potential to provide a charging device with an automatically limited voltage. The corona charging devices of the invention are characterized by a linear relationship between output ion currents and a direct current extraction potential. In further versions of the second corona device, the slotted conductor and dielectric-coated conductor may be replaced with alternative structures which provide an equivalent enclosure.
Description
BACKGROUND OF THE INVENTION
The present invention relates to corona charging devices, particularly as used for discharging electrostatic images.
Corona charging devices in the form of -thin conducting wires or sharp points are well known in the prior art.
Illustrative U.S. Patent Nos. are Vyverberg 2,836,725; L.E.
Walkup 2,879,395, P. Lee 3,358,289; Lee F. Frank 3,611,414; A.E.
Jvriblis 3,623,123; P.J. McGill 3,715,762; H. Bresnik 3,765,027, and R.A. Fotland 3,961,564. Such devices are used almost exclusively in electrostatic copiers to charge photoconductors prior to exposure as well as for discharging. Standard corona discharges provide limited ion currents. Such devices as a rule achieve a maximum discharge current density on the order of 10 microamperes per square centimeter. ~dditionally, corona wires are small and fragile, and easily broken. Because of their high operating potentials they collect dirt and dust and must be frequently cleaned or replaced, in order to avoid fall-off of the emission current.
Corona discharges which enjoy certain advantages over standard corona apparatus are disclosed in Sarid et al. U.S.
Patent No. 4,057,723; Wheeler et al. 4,068,284; and Sarid 4,110,614~ These patents disclose various corona charging devices characterized by a conductive wire coated with a thick dielectric material, in contact with or closely spaced from a further conductive member. Various geometries are disclosed in these patents, all fitting within the above general 1 ~L7~g~
descrl~tlon. These devlces utllize an alternatlng potentlal ln order to generate a source of ions, and a ~C extraction potentlal. The patents dlsclose a prePerred blasing range Or 200~-6000 volts~ relatlvely high values which are requlred in order to obtain slgnlflcant extractlon currents and therefore higher charging rates. These current outputs are exponentlal in character, ln contrast to the fairly linear outputs of the present invention. In addltlon, these devlces are undeslrabl~
sensitlve to variations ln the gap width between the corona and the imaging member.
U.S; Patent No. 4,153,093 dlscloses lon generating apparatus which ma,y be used ~or charge neutrallzatlon as well as deposltlon of net charge. Thls apparatus ls superlor to ~tandard corona apparatus, but i3 dlrflcult to fabricateg and does not provide the hlgh charglng rates of the present lnventlon.
Accordlngly lt ls a prlnclpal ob,~ect of the lnventlon to provide charging and neutralizing devicee employlng corona dlscharges whlch h~ve superior performance as compared with prlor art corona devlces.
Another obJect of the invention ls to provide a corona charglng devlce which achieves high current densitles. A
related obJect is the achlevement of high charglng rates.
Another related obJect ls the avoldance of hlgh biasing potentials in providing such charglng rates.
A further obJect of the lnvention is to provide a charging devlce having a rugged and compact structure. A related obJect ~ ~7~6~
ls to provlde a device having a longer operatlonal life than ls customary in corona lon generators. A further related oh,~ect is the provislon of corona apparatus which does not re~uire ~reauent servicing.
Another ob~ect is to provide a corona chargin~ device capable Or charging or discharglng a remote dielectric or photoreceptor surface to potentlals withln a few volts of a preselected potential.
Stlll another ob~ect o~ the invention ls the avoidance of emlssion current ~all-of~ as the ion generator becomes sllghtly dirty. A related obJect is the achievement of uniform emission currents. Yet another obJect of the inventlon i~ the provlslon o~ a corona charglng devlce with a rellable output potentlal.
~ ~ 7~695 SUMrlARY OF THE INVENTIO~t ._ _ ____ ______ ____ In achleving the above and related ob~ect~, the inventlon provides a corona chargln~ device comprlslng an elon~ate conductor wlth a dlelec~ric sheath, and a control electrode ln pro~lmlty thereto. In a ~lrYt aspect o~ the lnventlon, the control electrode comprise~ a conductive grld overlylng the dielectrlc sheathed elongate conductor, wlth both mounted agaln~t an lnsulating ~ubstrate. In a second aspect o~ the lnventlon, the control electrode comprlse~ a conductive enclosure, which derlnes a slot ln whlch the ~heathed elongate conductor 1~ placed. The apparatus of the lnventlon may be used for corona charglng and dlscharglng by mean~ of a ~lme varylng potentlal applled between the elongate conductor and control electrode, whlch lnduces a glow dl~charge ln an air reglon adlacent the control electrode and dlelectrlc sheath.
The control electrode 18 malntalned at ground potentlal ~or char~e ne~trallzatlon, an~ at a limitlng blaslng potentlal ~or corona charglng. The corona charglng apparat~s 18 characterlzed by a llnear relatlonshlp between output ion current~ and a dlrect current lon extractlon potentlal.
In accordance wlth one a~pect o~ the ~lrst aspectl the grld electrode comprlses a one or ~wo dlmenslonal array o~ ~ine con~uctlYe members. In a pre~erred ver~ion the grid electrode compri~es a rine wire mesh ~creen. In an alternatlve version, the grld comprlses a parallel array o~ ~lne, clo8ely qpaced wlre~, tran~verse to the a~ls o~ the elongate conductorO
~ 1766~5 In a~cordance with a pre~erred ver~lon of the qecond aspect, the conductlve enclosure comprlses a unltary ~tructure havin~ a slot wlth the sheathed elongate conductor e~hedded ln the slot. ~hls unltary structure advanta~eously conslsts o~ a conductlve beam havlng an essentlally rectangular slot or channel. In an alternative verslon of thi~ aspect, the 310tted conductor 18 replaced by a palr of conductive rods, whlch are ~ounted on each slde o~ the dlelectrlc-coated conductor agalnst an ln~ulatlng ~upport.
In accordance wlth another aspect o~ the inventlon, the varlous dlmenslon~ may be altered to modiry the outp~t lon characterlstlc~ o~ the corona charglng and dl~char~in~ devlce.
In the rirst aspect, the mo~t lmportant parameter ls ~he proflle Or the grid electrode, and ln partlcular the wrap o~
the grld electrode over the dielectrlc sheathed elongate conductor. In the second aspect, lmportant parameters lnclude: the lateral separation, 1~ any, o~ the sheathed conductor ~rom the walls o~ the conductor; the extent of protruslon or lndentatlon Or the sheathed conductor with respect to oute~ qurraces Or the enclosure; and the width o~
the conductlve enclosure as compared wlth the diameter o~ the ~heathed conduc~or. In the pre~erred verslon o~ the second asp~ct the dlelectric sheathed conductor contacts the ~lde walls of ~he conductor and protru~es slightly thererrom~
advantageously, the conductive enclosure 1~ only sll~htly broader than the width of the slot. Another important parameter in either aspect ; ls the separatlon o~ the devlce from the sur~ace to be charged or dls~harged~
fi Another a~pect of the ~econd aspect relates to the ~se Or a rlller at the base of the 310t to prevent power 10~9 and dielectrlc hreakdown.
In accordance wlth a further aspect o~ the inventlon the elongate conductor may have a variety o~ cro~s ~ectlons. In the ~re~erred verslon o~ elther aspect the elon~ate conductor comprises a cyllndrlcal wlre. Alternatlvely, ln the rlrst prlnclpal aspect the electrode may con~lst o~ an etched roll. In accordance with a related aspect Or the lnventlon~ a varlety Or ln~ulated materlal~, prererably lnorganlc, may be utlllzed in the dlelectrlc 3heath ~or the elongate conductor.
In accordance wlth yet another aspect o~ the inventlon, the dielectrlc sheathed elongate conductor and control electrode are coextenslve ~tructures, prererably ~ormln~ a llnear composlte. In the rlr~ asp~ct, the grld may take a varlety o~ tran~ver~e cross sectlons wherein the grid contacts or 1B closely spaced ~rom the dielectrlc sheath at or near lts o~er sur~ace. In the second aspect~ the conductlve enclosure may have a varlety Or cros~ sectlons~ subJect to the llmltation that it must house the dlelectric-coated elongate conductor.
In an alternative ver~ion o~ the ~lrgt aspect, the corona charglng apparatus may lncl~de a thln dielectric separatlng khe conductlve grid from the elon~ate conductor, but not completely covering the latter memberO In a ~r~her alternatlve verslon Or thls ~irst aspect, the insulatlng sub~trate may lnclude a ~lot to ho~e the dielectric ~heathed conductor. In thl~ ver~ion the ~ielectrlc sheathed conductor ls embedded ln the slot alon~ lt~ length, and the conductlve grld ls mounted over thls member where it protrude~ rrom the 3 lot.
In an alternative ver~lon of thls second aspect a palr o~ dlelectrlc-3heathed conductors straddle a central conductlve rod, all mounted agalnst an ln~ulating board.
Prererably, in thls verslon the dlelectric-sheathed conductor Gomprlses a glass capillary llned wlth an lnner conductlve layer. In thls and all verslons Or the second aspect, the lnventlo~ ls prererably characterlzed by a d~scharge region at or near the ~pper portlon of a slot.
I~ accordance wlth yet another aspect o~ the lnventlon, the time varying potential 1~ advantageously a contlnuous wave alternating potentlal ln the range 600 to 1500 volts peak, ~lth a frequency in the range ~0 Hz to 10 MHz. Alternatlvely, the varying potentlal may comprlse a pulsed voltage. In ~he asp~ct ~or corona charglng, the extractlon potentlal prererably is on ~he order o~ tens or hun~reds of Yolts. aoth ln charglng and neutralizlng, th~ devlce provides lon output current~ whlch are approximately a llnear Punctlon Or the extraction potentlal.
In a prererred ~tillzatlon of the in~en~lon, the device is employed ror the erasure o~ electrostatlc lmages on a proxlmate dlelectric member. Alternatlvely, the devlce may be employed ror charglng such a dtelectrlc member to a prescrlbed volt~ge.
In the latter case the devlce~ Or the invention proYlde 6 9 ~
automatlc control o~ the charglng level. In either ~tllizatlon, the corona device is preferahly disposed at a distance in the range 5-20 mils ~rom the member to be charged or discharged.
7~695 ~RIF.F DESCRIPTION OF THE DRAWINGS
Other aspects Or the invention wlll become apparent after consldering the drawings and detalled desc~lptlon below.
Figure 1 ls a sectlonal vlew o~ a corona charglng devlce ln accordance wlth a pre~erred verslon of the flrst aspect:
Flgure 2 19 a plan vlew Orthe charglng devlce Or Fl~ure l;
Flgure 3 18 a sectlonal view o~ a charging devlce ln accordance with the flrst aspect, wlth an alternative grld electrod~ pro~lle;
Figure 4 i8 a sectlonal vlew o~ the charglng devlce Or Figure 1 deployed ror charglng or dl~charglng an ad~acent member-Figure 5 ls a sectional view o~ an alternatlve charglngdevlce desl~n in accordance wlth the ~lr~t aspect;
Flgure 6 1~ a sectlonal view o~ a ~urther charging device deslgn ln accordance wlth the ~irst aspect;
Flgure 7 18 a ~ectionai vlew Or a chargln~ head wlth an alternatlve corona constr~ction ln accordance wlth the rir~t aspect~; -~ igure R 18 a plan view o~ a charglng devlce accordlng to the rirst aspect, wlth an ~lternatlve grld electrode;
~ igure g is a perspectl~e view o~ a corona chargin~ devlce in accordance wl th a pre~erred veraion Or ~he seoond aspect;
.
., .
Flgure lO ls a ~ectional schematlc vlew o~ the corona device o~ Flgure 9 ln proxlmlty to an lma~ing surrace:
Figure 11 1~ a sectional view of the corona devlce o~
Flgure 9, lncludlng actuatlng electronlc~: -Flgures 12A, 12B, and 12C are partlal sectlonal vlews showlng various pro~iles Or the device o~ the aspect Or Flgure 9, and the a~oclated alr dlscharge reglons;
Figure 13 lq a ~ectlonal vlew o~ a corona device ln accordance with an alternative ver~lon Or the ~econd aspect;
Flgure 14 18 a sectlonal vlew Or a corona charging devlce ln accordance with a ~rther alternative verslon o~ the second aspect; and Flgure 15 is a ~ectional vlew Or a corona charglng device ln accordance wlth yet another ver~lon o~ the second aspect.
1 ~7669~
DFTAILED DESCRIPTIO~
Reference should now be had to Figure~ 1-15 ~or a detalled descrlption Or the corona charglng apparatus of the in~entlon.
Two prlnclpal aspects are lllu~trated ln Flgures 1 and ~-both Or the~e aspects are characterlzed by an elongate conductor wlth a dlelectrlc ~heath, and a control electrode ln proxlmlty thereto. In the ~irst aspect ~ the invention, ~hown generally ln Figures 1~, the control electrode takes the ~orm o~ a conductlve grid overlylng the dielectrlc sheathed cond~ctor, all mo~nted agaln~t an ln~ulatlng support. In the second a9pect, ~hown in varlo~ version~ in Flgure~ 9-15, the control electrode consl~t~ Or a conductlve enclosure, which define~ a ~lot ln whlch the dlelectrlc sheathed conductor i~
placed. A charac~erlstlc ~eature o~ bot~ corona devlce 10 (Fl~ure 2) and corona de~lce 90 (Flgure 9) lq that the corona electrode 11 and control electrode (respectively 179 99) ~orm a llnear ~tr~ctur~. The ~lrst And second aspectS o~ the inventlon are dl~cu~sed below sequentlally.
In both prlncipal aspects corona electrode 11 consl~t~
Or a conductive wire 12 (whlch m~y conslst Or any ~uitable conductor) encased in a thlck dielectrlc materlal 13. Althou~h a dieleckrlc-coated cyllndrical wlre is lllustrated in the pre~erred aspects, the electrode 11 1~ more generally descrlbe~ as an elongate cond~ctor o~ lndeterminate cross section "a" with dielectric sheath. Figure 7 illustrates an alternative corona eleetrode constructlon ln the rlr~t .....
6 ~ ~
prlnclpal aspect Corona electrode 72 comprlses a thln etched electrode with dlelectric encapsulatlon 73. The elongate conductor may rest dlrectly ln contact with the ln~ulatln~ support, as long as lt i8 separated rrom the mesh electrode by the dlelectric sheath at the surface 71.
In both prlnclp~l asp~cts, the dlelectrlc 13 sho~ld have sufrlclent dlelectrlc strength to wlthstand hlgh e~cltatlon potentlals wlthout dlelectrlc breakdown/ It 1B
deslrable to mlnlmlze the on~et voltage, l.e. the excltatlon voltage at whlch the dlelectric begins to charge. Thls voltage lncrea~e~ wlth thlcker dlelectric layers 13, and decrease~ wlth lower dielectrlc constants o~ that layer. Organlc dlelectrlc are generally unsultable ror thi~ applicatlon9 as most such materlals tend to degrade wlth time due to o~ldlzlng product~
formed ln atmospheric electrlcal dlscharges. In the pre~erred aspect, the dlelectrlc 13 comprlses a ~used glass layer whlch ls fabricated ln order to mlnlmize volds 9 havin~ a thlckness in the ran~e 1-3 mils. Other sultable materlals lnclude, ror example9 slntered ceramlc~ and mlca.
In the aspect Or Figures 1-4, corona electrode 11 1~
placed agalnst an ln~ulatlng substrate 15i Advantageously, the electrode 11 i8 constralned by me~h 01ectrode 179 but not bonded to the in~ulating substrate~ Thi8 arrangement permit~ i relatlve movement o~ these structures du~ to thermal e~panslon and contractlon. The sub~tr2te 15 consl3ts o~ lnsulating materlal Or ~ur~lcient rigldlty to ~upport the coated-wire electrode 11 and,mesh electrode 17.
~ 176695 Grld electrode 17 comprlses an array Or elongate conductors Or mlnute thickne~s a~ compared wlth the dlameter of dlelectrlc-coated electrode 11. In the prererred ver~lon Or thls ~lr3t aspect, thls electrode comprlses a rine wire mesh screen, advantageo~ly a screen wlth a mesh ln the range 30-1~0 aperture~/lnch, and a wire thicknes~ ln the ran~e 0.3-1.2 mll~. Prererably. the wlre meqh ~creen ls characterlzed by a hlgh percenta~e Or open area. The ~creen may conslst o~ ang well known metal or metal alloy, ~uch aq qteels, ~talnle~
steels, nlckel-chroml~m alloy~, copper alloys, and aluminwm alloy~. The u~e o~ a ~lne me~h provldes a desirably high density o~ lon generatlon ~ltes, and avoids overheatlng at cros~over polnts. In an alternatlve version, the grid electrode 18 ~abrlcated by photoetching a screen pattern on a metal ~oil. In a rurther alternative ver~lon lllustrated ln Figure ~, grld electrode ~7 eonslsts o~ a parallel array o~
~lne, closely spaced wire~ runnlng perpendlc~lar to corona electrode 11.
The grid electrode 13 wrapped over electrode 11, and 1~
anchored to lnsulating s~b~trate 15 at each side o~ electrode 11. The grid electrode 17 may descrlbe any o~ a wlde variety of prorlles as seen ~rom one end. In the pre~erred embodlment trated in Flgure 13 the grld electrode 17 1~ wrapped ~lghtly over the apex Or electrode 11, and 18 bonded to s~pport 15 ~o as to rorm R roughly V-~haped proflle~ An alternatlve arrangement 18 Yhown ln Figure 3, whereln the mesh 37 ~orm~ an arch over the corona eleotrode llo The rormer prorlle i8 ~ 17~6g~
prererre~, ln that the closeness Or the mesh 17 to the outer surface o~ dlelectric 1~ provldes a de~lrably low c~tor~
voltage. For thls reason, mesh 17 is advanta~eou~ly bonded or attached to support 15 ln such a manner a3 to tenslon the mesh to provlde rlrm contact wlth the electrode 11.
An alternative construction 50 for a corona device l~ in accordance wlth the flrst prlnclpal aspect ls ~hown in ~lgure 5. The lnsulatln~ substrate ~5 lnclu~es a ~lot Sfi ln whlch corona electrode 11 ls fltted. The grld electrode 57 i~
wrapped over substrate 55 ~nd electrode 11 as shown. Thls arrangement a~ords ease of posltionlng and supporting corona electrode 11.
As shown ln Figure 6, the conductlve core o~ the corona electrode need not be encased ln a dlelectrlc sheath ~or errectlve operatlon. In the alternatlve structure ~0, the dlele¢trlc sheath ls replaced by a thin, ~le~ible dlelectric strip 63. The elongate conductor 62 rests dlrectly against insulatlng support 65, and 18 separated from grid electrode ~7 by dielectrlc strlp 63. The dlelectric k3 may comprlse~ ~or example, mlca or a thin strip o~ gla3s.
In the prererred verslon of the second prlnclpal aspect, shown a~ 90 ln Flgure 9, ~he corona electrode ll 18 embedded ln a slot ~6 ln a conductive be~m 940 The dlmenslons Or the varlous structures are chosen to provlde desired operatlonal characterlstlcs o~ the devlce 90, as rurther de~cribed below. Slgnlrlcant ~eatures Or the ~evlce ln thls descriptlon lncl~de the slde walls 97 and ba~e 9~ Or 810t 9~, , . .
l~7~9~
as well as the outer surf~ces 99 adjacent the slot. Figure 10 shows the corona device of Figure 9 as seen in section, in proximity to an imaging surface 20. A number of dimenslons are important in describing these devices in structural termsO These include the total radius R of the corona electrode 11 and the thickness T of the dielectric layer 13; the separation G of the corona electrode from the side walls 97, if any; the width W of that portion of the beam 94 at each side of slot 96; the protrusion E~ of the corona electrode from slot 96 (the corona electrode 11 may be inset from the outer surface in which case H is negative); and the gap width Z between the corona device 90 and the imaging surface 20. In constructing a device 90 in accordance with the parameters, it is generally desirable that G=0~ that W be given a minimal value con-sistent with structural integxity and that H have a small positive value as compared with the magnitude of R. These preferred values provide superior performance characteristics as discussed in detail below.
A nomenclature listing of the reference numerals used in the figures is included at the end of this specification.
With reference to the partial sectional views of 12A-12C~ the relationship between the parameter H shown in Figure 10 and the configuration of the discharge region 100 is seen with respect to a variety of profiles of device 90. In all of these profiles G=0 and W is constantO If the electrode 11 protrudes prominently from slot 96 as shown in Figure 12A, the discharge region 100 will largely encompass the outer surface 99 of beam 94. The discharge xegion 100 is generally determined by the Paschen limits between elonga~e conductor and conductive beam ~7 lfi 94. ~lth the dl~charge reglon tO0 havln~ the characterl~tics shown ln Fl~ure 12A~ there wlll be con~lderahle lne~lclences ln the operatlon o~ the devlce 90 ~ue to the 1088 0~ lon~ to the outer ~ortion~ 9, whlch acts a~ a ground plane. This wlll lead to a dlmlnlshlng o~ the ion ou~,put current. In the conrlguratlon Or Flgure 12~, the corona electrode 11 protrude~
only ~ htly rrom the ~lot 9fi. In thl~ ca3el the dlscharge reglon 100 comprl~es a reglon at the outer portlon o~ the approximately V-shaped area derlned by the ~lde walls 97 and the dielectrlc 13. This area 1~ ~he optlmal locatlon ror the lon poolj ln that it provldes a readlly e~tractable source of lons wl~h mlnlmal lon current 1098 due to the dlversion of ions. Ir, on the other hand, the corona electrode 18 embedded considerably below the upper sur~ace 99, as ~hown ln Flgure 12C
the dlscharge region 100 wlll be inset from the surface o~ ~lot 96. Thls will incur the dlsadvantages that the lons wlll not be ea~lly extractable and that there wlll be inevltable lon current los~ due to dlverslon to the outer portlon o~ ~lde wall~ 970 In the pre~erred con~tructlon Or the corona devlce Or the ~econd principal aspect~ a rlller 18 lncluded in the inner regions Or slot ~. In ~igures 12A-12C an adheslve flller 95 18 contalned between dlelec~rlc rlller 19 and base 9~. ~he u~e of a ~lller prevent~ power 10~8e8 due to ~lr breakdown ln the~e region~ and reduces the rlsk o~ dlelectrlc breakdown due to the heatlng in these lower re~lons. Suoh air breakdown would be ~imilar ln ~orm to that depicted in FlgureA 12A-12C, but would ' _ . :
g 5 ~ 7 not ~rovlde a ~ser~l so~rce Or lons. It may be ~een with rererence to Flgure~ 12A-12C that a mlnl~ value for W wo~ld be de~lrable ln order to avold lon c~rrent los~, and that a s~all posltlve value Or H i8 preferred in order to provide a deslrable location for the dischar~e reglon 100.
It will be appreciated that while the slot 96 of the conductive beam 94 has been shown with a generally rectangular cross section, the slot 96 alternatively may be in the form of a U-shaped channel that cradles the dielec~ric coating 13 of the conductive wire 12. This would allow ~he coated wire 12 to sit on the base of the beam without any need for packaging.
It is advantageous to place the corona electrode in contact with the side walls 97 (i.e, G=O) in order to avoid erratic behavior in the operation of the device. This characteristic poses difficulties in the aspect of Figures 9-12 in keeping the dielectric-coated electrode in contact with the side walls throughout the length of the device. Figure 13 glves a sectional view of a corona device 110 in accordance with an alternative embodiment, wherein this difficulty is overcome. In the charging device 110, the slotted conductive beam 94 of Figures 12A-12C is replaced with a pair of conductive rods 116 and 117 illustratively with a rectangular cross section.
The conductive rods and dielec~ric-coated electrode are mounted 1~7~6 17a on an insulating support block 115. Rods 116 and 117 are flexible metallic structures which may be conformed to the dielectric-coated electrode 111 throughout its length, thereby ensuring that G will be negligible for the entire length of the device.
The mounting arrangement of Figure 13 may be further modified by altering the spacial arrangement of the various electrodes. In the sectional view of Figure 14, a pair of dielectric~coated elongate conductors straddle a central conductive rod~ Illustratively, the conductive rod comprises a thick cylindrical wire 121~ and each of the dielectric-coated 1 ~766g5 1~
electro~es 1~2 and 12h compri3e a glass capillar,~ of rectangular cross ~ectlon fllled with a metalllc core materlal.
Deslrably. the metalllc core material ls characterlzed by a low meltln~ polnt, an~ has a coerflclent o~ expansion whlch i8 compatlble with that o~ the caplllary material. As ln the case Or the device 110 Or Fl~ure 13, the charglng device 1~0 i~
fabricated by mountlng the electrodes 121, 122, and 12~ on an insulatln~ base 12~ 90 that these electrodes clo~ely conrorm to each other throughout the length Or the device. The corona devlce 12~ 1~ actuated by applylng tlme-varying potentials between each o~ the respective metallic cores 123 and 127 and the central electrode 121.
Flgure 1~ lllustrate~ a modl~ied version 130 of the devlce of 120 Or Figure 14. In corona devlce 130, the glas~
c~lllarie~ nre not completely ~llled ~ith a met~lllc core material, but are lined wlth an lnner metalllc layer o~
~ufrlclent thickness to conduct the energizlng current~
Suitable metal~ ~or the core structures o~ Figures 14 and 15 lnclude for example low meltlng alioy~ of bismuthg and lndium alloys.
The corona devlces o~ both prlnclpal aspects may be employed ~or the generatlon o~ ion~ both ~or charge neutrallzation and ~or charging a proxlmate dlelectric sur~ace to a predetermined potential. Thls ls illustrated ~or the respective principal aspects in Flgure~ 4 and 11, respectively. The ~ormer ~lgure wlll be dlscus~ed ror lllustrative purpo~es~ ~ut both device~ are e~sen~ially 1 17~6g5 ldentlcal ln operatlon and the di3cu~slon that ~ollows applles to the device 9~ Or Flgure 11 as well.
In the sectlonal view of Flgure ll, the devlce 10 i8 e~ploved ror the generatlcn o~ lon~ by appllcation o~ a tlme-varylng potentlal 23 between the elongate conductor 12 and grid electrode 17. Thls causes a pool Or posltlve and negatlve lon~
to be rormed in an alr space ln the vlcinlty Or that portlon Or grld 17 whlch 1~ ln contact wlth or close pro~lmity to dlelectrlc 13. Thls phenomenon i~ hereln termed "glow dl~charge". Wlth a perlo~ically varylng potentlal 23 alr gap breakdown occurs during each hal~ cycle lf the excltation potentlal exceeds approximately 1400 volt~ peak-to-peak, lf the dlelectrlc qheath thlckness i8 ln the range o~ two to three mll~. The dlelectric 13 will receive a net char~e, thereby e~tlngulshlng the dl~charge, and preventlng the direct rlow o~
an ln-phase current ~etween ~rld electrode 17 and elongate conductor 12.
Wlth the ~wltch in po~ltlon x, the lon generator 10 acts as a charge neutrallzing devlce with respect to an e1ectrostatlc lmage carrled on a proximate member. As seen in Fi~ure 4, the devlce 10 19 dlspoæed ad~acent a dlelectrlc ~urrace 20 havlng a conductlve backin~ 25, and the mesh electrode 17 18 ~rounded to counterelectrode 250 The elec~rical beharlor Or ~his devlce may be measured as a plot o~
output current, 1, a~ a ~unctlon of the voltaRe V between 8urrace 2n and electrode 17~ ~yplcally, the devlces o~ the lnventlon are characterized b~ roughly llnear l-V curve~
1 ~7~9~
~ o 1~ prererable to have a low orrset voltage V0 t l.e. voltage at whlch 12n.
Ir dielectrlc surface 2~ carrles any net poAitlve or negatlve charge, this charge wlll e~tabllsh an electrlcal fleld to grid electrode 17, causlng the extractlon o~ ion~ o~ ~he opposlte polarlty rrom the lon pool 1~ the ion generator 10 18 thus dlspo~ed for a su~lcient ~eriod of tlme, the surface 20 will be completely neutrallzed~ The surrace 20 bears llttle or no resld~al char~e under these clrc~mstances.
Another desirable ~eature ls that Or the typlcally high charging/discharge rates of thls devlce.
Advantageously, the corona devlce 10 i~ dlsposed at a dlstance ln the range 5-20 mils ~rom sur~ace 20, most pre~erably around 15 mils, as measured rrom the outer surrace of grid electrode 17~ A rurther advantageou~ ~eature o~ the lnventlon is that the of~set voltage o~ this devlce 19 relatlvely lnsensltlve to changes ln gap wldth wlthln thi~
range.
Wlth rurther rererence to Figure 4, the devlce lO may be ~tlllzed to deposit a net posltlve or negatlve char~e on sur~ace 20 when switch 21 lq at positlon y. Thl~ places a DC
blas potentlal 22 on grld electrode 17. Wlth a posltlve bla~ to electrode 17, ~or example, a positive charge of equal ma~nlt~de wlll be deposlted on ~ur~ace 20. When operated ln this mode, the corona device 10 provide3 automatic llmltlng o~ the charging potential.
-- , 1 ~7~g~
In a preferred utlllzatlon Or the corona devlce 10. a relAtlve ~otlon i~ provlded between the devlce 10 and s~r~ace 20. so that the devlce wlll be ad~acent to varlou~ surface areas over time. Layer 20 may comprlse, ~or example, the surrace of a rotatable drum with a dlelectric or photoconductlve sur~ace. It 13 generally deslrable to mlnlmlze variatlons o~ the ~ap wldth % between corona device lO and surface 20 during s~ch relatlve motlon. ~en operatlng in the corona charglng mode during such motion, the devlce wlll generally provlde a surface potentlal whlch 19 a ~ractlon o~
the blas potentlal; this rraction wlll lncrease wlth lower ~urrace ~peed~.
In the pre~erred embodlment7 tlme varying pot~ntial lq comprlse3 a high ~requency9 high voltage ~inusoidO Pre~erably9 excltatlon potentlal 23 has a magnitude in the ran~e 1700-2~00 volts peak-to-peak, mo~t advantageously around 2000 volts pea~-to-peak. E~cltatlon potentlal 23 may comprlse a continuou~
wave alternating potentlal, preferably of a rrequency in the range lOKHz to 1 r~z. Drivlng voltages at hlgher ~requencle~
have been observed to cau~e overheatlng o~ the corona devlce, whlle lower rrequency wave~orm~ may provl~e lnadequate outp~
c~rrent~. A contlnuo~ wave ~requency Or 100 KHz provide~
desirably hlgh emlsslon current~ wltho~t a serlous rlsk Or overheatlng deYlce 10. Alternatlvely, excitation potentlal 19 may comprlse a pulsed volta~e whlch may be 3pecl~1ed by the parameters o~ peak-to-peak voltage, repetltion perlod, pul3e 6 g 5 width, and base frequency. The devlce lO has been operated at frequencies as high as 1 rlHæ applled in short bursts havlng a duty c,ycle near 10 percent.
Both prlnclpal embodiments of the lnventlon are further lllustrated ln the following nonllmiting examples:
Example 1 A corona charging devlce of the type shown ln Flgure l was constructed as follows. The lnsulating support was fabrlcated of glass epoxy G-10 lamlnate. The corona electrode consisted of a 7 mll dlameter stainless steel wire having a 2 mll thlck glass coatlng. After laylng the coated wlre on the slipport block, a fine woven wire screen wa~ stretched over the glass coated wlre and bonded with a thermoset adhesive to the sides of the support. The screen was composed of a plain woven 1 mll stalnless steel wlre. havlng a mesh count of 100 and an open area of approximately 90 percent~ The coated wire electrode was not bonded to the support block, and was constralned only by the overlying screen.
A 100 KHz, 2000 volt continuous wave alternating potentlal was placed between the coated wlre and the mesh electrode~ me o~ter surface of the mesh electrode; was located 15 mlls from the s~rface of an lmaglng drum having a thln photoconductive s~rface layer, with a capacitance of 100 picofarads per cm2O
The photoconductive surface was charged to 500 volts wlth a charglng rate of 103 cm2/secO, by lmposing a 500 volt direct current potential between the mesh electrode and the 6 ~ 9 ~
drum's conductive core. Thls represented an average corona output current o~ 10 microamperes per cm. length o~ corona.
Example 2 The apparatus of Example 1 was employed as a corona dlscharge devlce by groundlng the mesh electrode to the photoreceDtor drum's conductlve core. In thls mode, the devlce ne~trallzed electrostatlc images at rates comparable to the charging rates of Example l, leaving virtually no resldual electrostatic lmage.
:`
Exam~le 3 The apparatu~ o~ Example 1 was modlfled as follows to provlde a corona charglng devlce o~ the type shown in Figure 7.
me corona electrode was fabricated by lamlnatlng a 1 mll stalnless steel foll to the support block uslng a pressure sensit1ve adheslve, and photoetching an electrode wlth a line width of 8 mils. The electrode was encapsulated with a 1.5 mll thick layer Or glas~ by sllk-~creenlng a glass frlt over the etched electrode, and sinterlng the glass at a high temperature ~to form a continuous glass coating.
This apparatus exhlblted equivalent performance to the structure Or ~xample 1, in both the charging and neutrallzing modes.
9 ~
Fxam~le 4 A corona charglng devlce 9~ o~ the type shown ln ~lgure 9 was constructed as ~ollows. me corona e7ectrode conslsted o~
a 7 mll dlameter stalnless steel wlre havlng a 2 mll thlck glass coatlng. The coated wire was embedded ln an ll mil wlde, lO mil deep rectangular slot in a stainless steel beam of total dlmenslons 50 mll wlde and 50 mll deep, after insertlng adheslve flller at the bottom of the slot, Thls provlded a beam wldth of 14.5 mil on each slde o~ the slotO
; A 100 KHz, 2000 volt peak-to-peak contlnuous wave alternating potential was placed between the coated wlre and the steel beam. The outer surface o~ the corona electrode was located 15 mils from the surface o~ an lmaglng drum havlng a thln photoconductlve sur~ace layer, wlth a capacitance Or 100 pico~arads per cm.2O m e lmagin~ drum wa~ rotated at a surface spee~ of 25 cm/second relatlve to the corona devlce 9 and wa~ charged to 500 volts by imposlng a 1000 volt direct current potential between the steel beam and the ~rum' 8 conductive core. This represented an average corona output current of 1.25 micro-ampere~ per centimeter length o~ corona~
, Rxam~le 5 __ ___ _ The apparatu~ o~ Example 4 was employed as a corona dlschar~e devlce by grounding the mesh electrode to the photoreceptor drwm's conductive core~ In thls modeg the ~evice neutralized electrostatic lmages at rates comparable to the charglng rates o~ Example 4, leavlng virtually no residual electrostatlc imageO
l 17G695
The present invention relates to corona charging devices, particularly as used for discharging electrostatic images.
Corona charging devices in the form of -thin conducting wires or sharp points are well known in the prior art.
Illustrative U.S. Patent Nos. are Vyverberg 2,836,725; L.E.
Walkup 2,879,395, P. Lee 3,358,289; Lee F. Frank 3,611,414; A.E.
Jvriblis 3,623,123; P.J. McGill 3,715,762; H. Bresnik 3,765,027, and R.A. Fotland 3,961,564. Such devices are used almost exclusively in electrostatic copiers to charge photoconductors prior to exposure as well as for discharging. Standard corona discharges provide limited ion currents. Such devices as a rule achieve a maximum discharge current density on the order of 10 microamperes per square centimeter. ~dditionally, corona wires are small and fragile, and easily broken. Because of their high operating potentials they collect dirt and dust and must be frequently cleaned or replaced, in order to avoid fall-off of the emission current.
Corona discharges which enjoy certain advantages over standard corona apparatus are disclosed in Sarid et al. U.S.
Patent No. 4,057,723; Wheeler et al. 4,068,284; and Sarid 4,110,614~ These patents disclose various corona charging devices characterized by a conductive wire coated with a thick dielectric material, in contact with or closely spaced from a further conductive member. Various geometries are disclosed in these patents, all fitting within the above general 1 ~L7~g~
descrl~tlon. These devlces utllize an alternatlng potentlal ln order to generate a source of ions, and a ~C extraction potentlal. The patents dlsclose a prePerred blasing range Or 200~-6000 volts~ relatlvely high values which are requlred in order to obtain slgnlflcant extractlon currents and therefore higher charging rates. These current outputs are exponentlal in character, ln contrast to the fairly linear outputs of the present invention. In addltlon, these devlces are undeslrabl~
sensitlve to variations ln the gap width between the corona and the imaging member.
U.S; Patent No. 4,153,093 dlscloses lon generating apparatus which ma,y be used ~or charge neutrallzatlon as well as deposltlon of net charge. Thls apparatus ls superlor to ~tandard corona apparatus, but i3 dlrflcult to fabricateg and does not provide the hlgh charglng rates of the present lnventlon.
Accordlngly lt ls a prlnclpal ob,~ect of the lnventlon to provide charging and neutralizing devicee employlng corona dlscharges whlch h~ve superior performance as compared with prlor art corona devlces.
Another obJect of the invention ls to provide a corona charglng devlce which achieves high current densitles. A
related obJect is the achlevement of high charglng rates.
Another related obJect ls the avoldance of hlgh biasing potentials in providing such charglng rates.
A further obJect of the lnvention is to provide a charging devlce having a rugged and compact structure. A related obJect ~ ~7~6~
ls to provlde a device having a longer operatlonal life than ls customary in corona lon generators. A further related oh,~ect is the provislon of corona apparatus which does not re~uire ~reauent servicing.
Another ob~ect is to provide a corona chargin~ device capable Or charging or discharglng a remote dielectric or photoreceptor surface to potentlals withln a few volts of a preselected potential.
Stlll another ob~ect o~ the invention ls the avoidance of emlssion current ~all-of~ as the ion generator becomes sllghtly dirty. A related obJect is the achievement of uniform emission currents. Yet another obJect of the inventlon i~ the provlslon o~ a corona charglng devlce with a rellable output potentlal.
~ ~ 7~695 SUMrlARY OF THE INVENTIO~t ._ _ ____ ______ ____ In achleving the above and related ob~ect~, the inventlon provides a corona chargln~ device comprlslng an elon~ate conductor wlth a dlelec~ric sheath, and a control electrode ln pro~lmlty thereto. In a ~lrYt aspect o~ the lnventlon, the control electrode comprise~ a conductive grld overlylng the dielectrlc sheathed elongate conductor, wlth both mounted agaln~t an lnsulating ~ubstrate. In a second aspect o~ the lnventlon, the control electrode comprlse~ a conductive enclosure, which derlnes a slot ln whlch the ~heathed elongate conductor 1~ placed. The apparatus of the lnventlon may be used for corona charglng and dlscharglng by mean~ of a ~lme varylng potentlal applled between the elongate conductor and control electrode, whlch lnduces a glow dl~charge ln an air reglon adlacent the control electrode and dlelectrlc sheath.
The control electrode 18 malntalned at ground potentlal ~or char~e ne~trallzatlon, an~ at a limitlng blaslng potentlal ~or corona charglng. The corona charglng apparat~s 18 characterlzed by a llnear relatlonshlp between output ion current~ and a dlrect current lon extractlon potentlal.
In accordance wlth one a~pect o~ the ~lrst aspectl the grld electrode comprlses a one or ~wo dlmenslonal array o~ ~ine con~uctlYe members. In a pre~erred ver~ion the grid electrode compri~es a rine wire mesh ~creen. In an alternatlve version, the grld comprlses a parallel array o~ ~lne, clo8ely qpaced wlre~, tran~verse to the a~ls o~ the elongate conductorO
~ 1766~5 In a~cordance with a pre~erred ver~lon of the qecond aspect, the conductlve enclosure comprlses a unltary ~tructure havin~ a slot wlth the sheathed elongate conductor e~hedded ln the slot. ~hls unltary structure advanta~eously conslsts o~ a conductlve beam havlng an essentlally rectangular slot or channel. In an alternative verslon of thi~ aspect, the 310tted conductor 18 replaced by a palr of conductive rods, whlch are ~ounted on each slde o~ the dlelectrlc-coated conductor agalnst an ln~ulatlng ~upport.
In accordance wlth another aspect o~ the inventlon, the varlous dlmenslon~ may be altered to modiry the outp~t lon characterlstlc~ o~ the corona charglng and dl~char~in~ devlce.
In the rirst aspect, the mo~t lmportant parameter ls ~he proflle Or the grid electrode, and ln partlcular the wrap o~
the grld electrode over the dielectrlc sheathed elongate conductor. In the second aspect, lmportant parameters lnclude: the lateral separation, 1~ any, o~ the sheathed conductor ~rom the walls o~ the conductor; the extent of protruslon or lndentatlon Or the sheathed conductor with respect to oute~ qurraces Or the enclosure; and the width o~
the conductlve enclosure as compared wlth the diameter o~ the ~heathed conduc~or. In the pre~erred verslon o~ the second asp~ct the dlelectric sheathed conductor contacts the ~lde walls of ~he conductor and protru~es slightly thererrom~
advantageously, the conductive enclosure 1~ only sll~htly broader than the width of the slot. Another important parameter in either aspect ; ls the separatlon o~ the devlce from the sur~ace to be charged or dls~harged~
fi Another a~pect of the ~econd aspect relates to the ~se Or a rlller at the base of the 310t to prevent power 10~9 and dielectrlc hreakdown.
In accordance wlth a further aspect o~ the inventlon the elongate conductor may have a variety o~ cro~s ~ectlons. In the ~re~erred verslon o~ elther aspect the elon~ate conductor comprises a cyllndrlcal wlre. Alternatlvely, ln the rlrst prlnclpal aspect the electrode may con~lst o~ an etched roll. In accordance with a related aspect Or the lnventlon~ a varlety Or ln~ulated materlal~, prererably lnorganlc, may be utlllzed in the dlelectrlc 3heath ~or the elongate conductor.
In accordance wlth yet another aspect o~ the inventlon, the dielectrlc sheathed elongate conductor and control electrode are coextenslve ~tructures, prererably ~ormln~ a llnear composlte. In the rlr~ asp~ct, the grld may take a varlety o~ tran~ver~e cross sectlons wherein the grid contacts or 1B closely spaced ~rom the dielectrlc sheath at or near lts o~er sur~ace. In the second aspect~ the conductlve enclosure may have a varlety Or cros~ sectlons~ subJect to the llmltation that it must house the dlelectric-coated elongate conductor.
In an alternative ver~ion o~ the ~lrgt aspect, the corona charglng apparatus may lncl~de a thln dielectric separatlng khe conductlve grid from the elon~ate conductor, but not completely covering the latter memberO In a ~r~her alternatlve verslon Or thls ~irst aspect, the insulatlng sub~trate may lnclude a ~lot to ho~e the dielectric ~heathed conductor. In thl~ ver~ion the ~ielectrlc sheathed conductor ls embedded ln the slot alon~ lt~ length, and the conductlve grld ls mounted over thls member where it protrude~ rrom the 3 lot.
In an alternative ver~lon of thls second aspect a palr o~ dlelectrlc-3heathed conductors straddle a central conductlve rod, all mounted agalnst an ln~ulating board.
Prererably, in thls verslon the dlelectric-sheathed conductor Gomprlses a glass capillary llned wlth an lnner conductlve layer. In thls and all verslons Or the second aspect, the lnventlo~ ls prererably characterlzed by a d~scharge region at or near the ~pper portlon of a slot.
I~ accordance wlth yet another aspect o~ the lnventlon, the time varying potential 1~ advantageously a contlnuous wave alternating potentlal ln the range 600 to 1500 volts peak, ~lth a frequency in the range ~0 Hz to 10 MHz. Alternatlvely, the varying potentlal may comprlse a pulsed voltage. In ~he asp~ct ~or corona charglng, the extractlon potentlal prererably is on ~he order o~ tens or hun~reds of Yolts. aoth ln charglng and neutralizlng, th~ devlce provides lon output current~ whlch are approximately a llnear Punctlon Or the extraction potentlal.
In a prererred ~tillzatlon of the in~en~lon, the device is employed ror the erasure o~ electrostatlc lmages on a proxlmate dlelectric member. Alternatlvely, the devlce may be employed ror charglng such a dtelectrlc member to a prescrlbed volt~ge.
In the latter case the devlce~ Or the invention proYlde 6 9 ~
automatlc control o~ the charglng level. In either ~tllizatlon, the corona device is preferahly disposed at a distance in the range 5-20 mils ~rom the member to be charged or discharged.
7~695 ~RIF.F DESCRIPTION OF THE DRAWINGS
Other aspects Or the invention wlll become apparent after consldering the drawings and detalled desc~lptlon below.
Figure 1 ls a sectlonal vlew o~ a corona charglng devlce ln accordance wlth a pre~erred verslon of the flrst aspect:
Flgure 2 19 a plan vlew Orthe charglng devlce Or Fl~ure l;
Flgure 3 18 a sectlonal view o~ a charging devlce ln accordance with the flrst aspect, wlth an alternative grld electrod~ pro~lle;
Figure 4 i8 a sectlonal vlew o~ the charglng devlce Or Figure 1 deployed ror charglng or dl~charglng an ad~acent member-Figure 5 ls a sectional view o~ an alternatlve charglngdevlce desl~n in accordance wlth the ~lr~t aspect;
Flgure 6 1~ a sectlonal view o~ a ~urther charging device deslgn ln accordance wlth the ~irst aspect;
Flgure 7 18 a ~ectionai vlew Or a chargln~ head wlth an alternatlve corona constr~ction ln accordance wlth the rir~t aspect~; -~ igure R 18 a plan view o~ a charglng devlce accordlng to the rirst aspect, wlth an ~lternatlve grld electrode;
~ igure g is a perspectl~e view o~ a corona chargin~ devlce in accordance wl th a pre~erred veraion Or ~he seoond aspect;
.
., .
Flgure lO ls a ~ectional schematlc vlew o~ the corona device o~ Flgure 9 ln proxlmlty to an lma~ing surrace:
Figure 11 1~ a sectional view of the corona devlce o~
Flgure 9, lncludlng actuatlng electronlc~: -Flgures 12A, 12B, and 12C are partlal sectlonal vlews showlng various pro~iles Or the device o~ the aspect Or Flgure 9, and the a~oclated alr dlscharge reglons;
Figure 13 lq a ~ectlonal vlew o~ a corona device ln accordance with an alternative ver~lon Or the ~econd aspect;
Flgure 14 18 a sectlonal vlew Or a corona charging devlce ln accordance with a ~rther alternative verslon o~ the second aspect; and Flgure 15 is a ~ectional vlew Or a corona charglng device ln accordance wlth yet another ver~lon o~ the second aspect.
1 ~7669~
DFTAILED DESCRIPTIO~
Reference should now be had to Figure~ 1-15 ~or a detalled descrlption Or the corona charglng apparatus of the in~entlon.
Two prlnclpal aspects are lllu~trated ln Flgures 1 and ~-both Or the~e aspects are characterlzed by an elongate conductor wlth a dlelectrlc ~heath, and a control electrode ln proxlmlty thereto. In the ~irst aspect ~ the invention, ~hown generally ln Figures 1~, the control electrode takes the ~orm o~ a conductlve grid overlylng the dielectrlc sheathed cond~ctor, all mo~nted agaln~t an ln~ulatlng support. In the second a9pect, ~hown in varlo~ version~ in Flgure~ 9-15, the control electrode consl~t~ Or a conductlve enclosure, which define~ a ~lot ln whlch the dlelectrlc sheathed conductor i~
placed. A charac~erlstlc ~eature o~ bot~ corona devlce 10 (Fl~ure 2) and corona de~lce 90 (Flgure 9) lq that the corona electrode 11 and control electrode (respectively 179 99) ~orm a llnear ~tr~ctur~. The ~lrst And second aspectS o~ the inventlon are dl~cu~sed below sequentlally.
In both prlncipal aspects corona electrode 11 consl~t~
Or a conductive wire 12 (whlch m~y conslst Or any ~uitable conductor) encased in a thlck dielectrlc materlal 13. Althou~h a dieleckrlc-coated cyllndrical wlre is lllustrated in the pre~erred aspects, the electrode 11 1~ more generally descrlbe~ as an elongate cond~ctor o~ lndeterminate cross section "a" with dielectric sheath. Figure 7 illustrates an alternative corona eleetrode constructlon ln the rlr~t .....
6 ~ ~
prlnclpal aspect Corona electrode 72 comprlses a thln etched electrode with dlelectric encapsulatlon 73. The elongate conductor may rest dlrectly ln contact with the ln~ulatln~ support, as long as lt i8 separated rrom the mesh electrode by the dlelectric sheath at the surface 71.
In both prlnclp~l asp~cts, the dlelectrlc 13 sho~ld have sufrlclent dlelectrlc strength to wlthstand hlgh e~cltatlon potentlals wlthout dlelectrlc breakdown/ It 1B
deslrable to mlnlmlze the on~et voltage, l.e. the excltatlon voltage at whlch the dlelectric begins to charge. Thls voltage lncrea~e~ wlth thlcker dlelectric layers 13, and decrease~ wlth lower dielectrlc constants o~ that layer. Organlc dlelectrlc are generally unsultable ror thi~ applicatlon9 as most such materlals tend to degrade wlth time due to o~ldlzlng product~
formed ln atmospheric electrlcal dlscharges. In the pre~erred aspect, the dlelectrlc 13 comprlses a ~used glass layer whlch ls fabricated ln order to mlnlmize volds 9 havin~ a thlckness in the ran~e 1-3 mils. Other sultable materlals lnclude, ror example9 slntered ceramlc~ and mlca.
In the aspect Or Figures 1-4, corona electrode 11 1~
placed agalnst an ln~ulatlng substrate 15i Advantageously, the electrode 11 i8 constralned by me~h 01ectrode 179 but not bonded to the in~ulating substrate~ Thi8 arrangement permit~ i relatlve movement o~ these structures du~ to thermal e~panslon and contractlon. The sub~tr2te 15 consl3ts o~ lnsulating materlal Or ~ur~lcient rigldlty to ~upport the coated-wire electrode 11 and,mesh electrode 17.
~ 176695 Grld electrode 17 comprlses an array Or elongate conductors Or mlnute thickne~s a~ compared wlth the dlameter of dlelectrlc-coated electrode 11. In the prererred ver~lon Or thls ~lr3t aspect, thls electrode comprlses a rine wire mesh screen, advantageo~ly a screen wlth a mesh ln the range 30-1~0 aperture~/lnch, and a wire thicknes~ ln the ran~e 0.3-1.2 mll~. Prererably. the wlre meqh ~creen ls characterlzed by a hlgh percenta~e Or open area. The ~creen may conslst o~ ang well known metal or metal alloy, ~uch aq qteels, ~talnle~
steels, nlckel-chroml~m alloy~, copper alloys, and aluminwm alloy~. The u~e o~ a ~lne me~h provldes a desirably high density o~ lon generatlon ~ltes, and avoids overheatlng at cros~over polnts. In an alternatlve version, the grid electrode 18 ~abrlcated by photoetching a screen pattern on a metal ~oil. In a rurther alternative ver~lon lllustrated ln Figure ~, grld electrode ~7 eonslsts o~ a parallel array o~
~lne, closely spaced wire~ runnlng perpendlc~lar to corona electrode 11.
The grid electrode 13 wrapped over electrode 11, and 1~
anchored to lnsulating s~b~trate 15 at each side o~ electrode 11. The grid electrode 17 may descrlbe any o~ a wlde variety of prorlles as seen ~rom one end. In the pre~erred embodlment trated in Flgure 13 the grld electrode 17 1~ wrapped ~lghtly over the apex Or electrode 11, and 18 bonded to s~pport 15 ~o as to rorm R roughly V-~haped proflle~ An alternatlve arrangement 18 Yhown ln Figure 3, whereln the mesh 37 ~orm~ an arch over the corona eleotrode llo The rormer prorlle i8 ~ 17~6g~
prererre~, ln that the closeness Or the mesh 17 to the outer surface o~ dlelectric 1~ provldes a de~lrably low c~tor~
voltage. For thls reason, mesh 17 is advanta~eou~ly bonded or attached to support 15 ln such a manner a3 to tenslon the mesh to provlde rlrm contact wlth the electrode 11.
An alternative construction 50 for a corona device l~ in accordance wlth the flrst prlnclpal aspect ls ~hown in ~lgure 5. The lnsulatln~ substrate ~5 lnclu~es a ~lot Sfi ln whlch corona electrode 11 ls fltted. The grld electrode 57 i~
wrapped over substrate 55 ~nd electrode 11 as shown. Thls arrangement a~ords ease of posltionlng and supporting corona electrode 11.
As shown ln Figure 6, the conductlve core o~ the corona electrode need not be encased ln a dlelectrlc sheath ~or errectlve operatlon. In the alternatlve structure ~0, the dlele¢trlc sheath ls replaced by a thin, ~le~ible dlelectric strip 63. The elongate conductor 62 rests dlrectly against insulatlng support 65, and 18 separated from grid electrode ~7 by dielectrlc strlp 63. The dlelectric k3 may comprlse~ ~or example, mlca or a thin strip o~ gla3s.
In the prererred verslon of the second prlnclpal aspect, shown a~ 90 ln Flgure 9, ~he corona electrode ll 18 embedded ln a slot ~6 ln a conductive be~m 940 The dlmenslons Or the varlous structures are chosen to provlde desired operatlonal characterlstlcs o~ the devlce 90, as rurther de~cribed below. Slgnlrlcant ~eatures Or the ~evlce ln thls descriptlon lncl~de the slde walls 97 and ba~e 9~ Or 810t 9~, , . .
l~7~9~
as well as the outer surf~ces 99 adjacent the slot. Figure 10 shows the corona device of Figure 9 as seen in section, in proximity to an imaging surface 20. A number of dimenslons are important in describing these devices in structural termsO These include the total radius R of the corona electrode 11 and the thickness T of the dielectric layer 13; the separation G of the corona electrode from the side walls 97, if any; the width W of that portion of the beam 94 at each side of slot 96; the protrusion E~ of the corona electrode from slot 96 (the corona electrode 11 may be inset from the outer surface in which case H is negative); and the gap width Z between the corona device 90 and the imaging surface 20. In constructing a device 90 in accordance with the parameters, it is generally desirable that G=0~ that W be given a minimal value con-sistent with structural integxity and that H have a small positive value as compared with the magnitude of R. These preferred values provide superior performance characteristics as discussed in detail below.
A nomenclature listing of the reference numerals used in the figures is included at the end of this specification.
With reference to the partial sectional views of 12A-12C~ the relationship between the parameter H shown in Figure 10 and the configuration of the discharge region 100 is seen with respect to a variety of profiles of device 90. In all of these profiles G=0 and W is constantO If the electrode 11 protrudes prominently from slot 96 as shown in Figure 12A, the discharge region 100 will largely encompass the outer surface 99 of beam 94. The discharge xegion 100 is generally determined by the Paschen limits between elonga~e conductor and conductive beam ~7 lfi 94. ~lth the dl~charge reglon tO0 havln~ the characterl~tics shown ln Fl~ure 12A~ there wlll be con~lderahle lne~lclences ln the operatlon o~ the devlce 90 ~ue to the 1088 0~ lon~ to the outer ~ortion~ 9, whlch acts a~ a ground plane. This wlll lead to a dlmlnlshlng o~ the ion ou~,put current. In the conrlguratlon Or Flgure 12~, the corona electrode 11 protrude~
only ~ htly rrom the ~lot 9fi. In thl~ ca3el the dlscharge reglon 100 comprl~es a reglon at the outer portlon o~ the approximately V-shaped area derlned by the ~lde walls 97 and the dielectrlc 13. This area 1~ ~he optlmal locatlon ror the lon poolj ln that it provldes a readlly e~tractable source of lons wl~h mlnlmal lon current 1098 due to the dlversion of ions. Ir, on the other hand, the corona electrode 18 embedded considerably below the upper sur~ace 99, as ~hown ln Flgure 12C
the dlscharge region 100 wlll be inset from the surface o~ ~lot 96. Thls will incur the dlsadvantages that the lons wlll not be ea~lly extractable and that there wlll be inevltable lon current los~ due to dlverslon to the outer portlon o~ ~lde wall~ 970 In the pre~erred con~tructlon Or the corona devlce Or the ~econd principal aspect~ a rlller 18 lncluded in the inner regions Or slot ~. In ~igures 12A-12C an adheslve flller 95 18 contalned between dlelec~rlc rlller 19 and base 9~. ~he u~e of a ~lller prevent~ power 10~8e8 due to ~lr breakdown ln the~e region~ and reduces the rlsk o~ dlelectrlc breakdown due to the heatlng in these lower re~lons. Suoh air breakdown would be ~imilar ln ~orm to that depicted in FlgureA 12A-12C, but would ' _ . :
g 5 ~ 7 not ~rovlde a ~ser~l so~rce Or lons. It may be ~een with rererence to Flgure~ 12A-12C that a mlnl~ value for W wo~ld be de~lrable ln order to avold lon c~rrent los~, and that a s~all posltlve value Or H i8 preferred in order to provide a deslrable location for the dischar~e reglon 100.
It will be appreciated that while the slot 96 of the conductive beam 94 has been shown with a generally rectangular cross section, the slot 96 alternatively may be in the form of a U-shaped channel that cradles the dielec~ric coating 13 of the conductive wire 12. This would allow ~he coated wire 12 to sit on the base of the beam without any need for packaging.
It is advantageous to place the corona electrode in contact with the side walls 97 (i.e, G=O) in order to avoid erratic behavior in the operation of the device. This characteristic poses difficulties in the aspect of Figures 9-12 in keeping the dielectric-coated electrode in contact with the side walls throughout the length of the device. Figure 13 glves a sectional view of a corona device 110 in accordance with an alternative embodiment, wherein this difficulty is overcome. In the charging device 110, the slotted conductive beam 94 of Figures 12A-12C is replaced with a pair of conductive rods 116 and 117 illustratively with a rectangular cross section.
The conductive rods and dielec~ric-coated electrode are mounted 1~7~6 17a on an insulating support block 115. Rods 116 and 117 are flexible metallic structures which may be conformed to the dielectric-coated electrode 111 throughout its length, thereby ensuring that G will be negligible for the entire length of the device.
The mounting arrangement of Figure 13 may be further modified by altering the spacial arrangement of the various electrodes. In the sectional view of Figure 14, a pair of dielectric~coated elongate conductors straddle a central conductive rod~ Illustratively, the conductive rod comprises a thick cylindrical wire 121~ and each of the dielectric-coated 1 ~766g5 1~
electro~es 1~2 and 12h compri3e a glass capillar,~ of rectangular cross ~ectlon fllled with a metalllc core materlal.
Deslrably. the metalllc core material ls characterlzed by a low meltln~ polnt, an~ has a coerflclent o~ expansion whlch i8 compatlble with that o~ the caplllary material. As ln the case Or the device 110 Or Fl~ure 13, the charglng device 1~0 i~
fabricated by mountlng the electrodes 121, 122, and 12~ on an insulatln~ base 12~ 90 that these electrodes clo~ely conrorm to each other throughout the length Or the device. The corona devlce 12~ 1~ actuated by applylng tlme-varying potentials between each o~ the respective metallic cores 123 and 127 and the central electrode 121.
Flgure 1~ lllustrate~ a modl~ied version 130 of the devlce of 120 Or Figure 14. In corona devlce 130, the glas~
c~lllarie~ nre not completely ~llled ~ith a met~lllc core material, but are lined wlth an lnner metalllc layer o~
~ufrlclent thickness to conduct the energizlng current~
Suitable metal~ ~or the core structures o~ Figures 14 and 15 lnclude for example low meltlng alioy~ of bismuthg and lndium alloys.
The corona devlces o~ both prlnclpal aspects may be employed ~or the generatlon o~ ion~ both ~or charge neutrallzation and ~or charging a proxlmate dlelectric sur~ace to a predetermined potential. Thls ls illustrated ~or the respective principal aspects in Flgure~ 4 and 11, respectively. The ~ormer ~lgure wlll be dlscus~ed ror lllustrative purpo~es~ ~ut both device~ are e~sen~ially 1 17~6g5 ldentlcal ln operatlon and the di3cu~slon that ~ollows applles to the device 9~ Or Flgure 11 as well.
In the sectlonal view of Flgure ll, the devlce 10 i8 e~ploved ror the generatlcn o~ lon~ by appllcation o~ a tlme-varylng potentlal 23 between the elongate conductor 12 and grid electrode 17. Thls causes a pool Or posltlve and negatlve lon~
to be rormed in an alr space ln the vlcinlty Or that portlon Or grld 17 whlch 1~ ln contact wlth or close pro~lmity to dlelectrlc 13. Thls phenomenon i~ hereln termed "glow dl~charge". Wlth a perlo~ically varylng potentlal 23 alr gap breakdown occurs during each hal~ cycle lf the excltation potentlal exceeds approximately 1400 volt~ peak-to-peak, lf the dlelectrlc qheath thlckness i8 ln the range o~ two to three mll~. The dlelectric 13 will receive a net char~e, thereby e~tlngulshlng the dl~charge, and preventlng the direct rlow o~
an ln-phase current ~etween ~rld electrode 17 and elongate conductor 12.
Wlth the ~wltch in po~ltlon x, the lon generator 10 acts as a charge neutrallzing devlce with respect to an e1ectrostatlc lmage carrled on a proximate member. As seen in Fi~ure 4, the devlce 10 19 dlspoæed ad~acent a dlelectrlc ~urrace 20 havlng a conductlve backin~ 25, and the mesh electrode 17 18 ~rounded to counterelectrode 250 The elec~rical beharlor Or ~his devlce may be measured as a plot o~
output current, 1, a~ a ~unctlon of the voltaRe V between 8urrace 2n and electrode 17~ ~yplcally, the devlces o~ the lnventlon are characterized b~ roughly llnear l-V curve~
1 ~7~9~
~ o 1~ prererable to have a low orrset voltage V0 t l.e. voltage at whlch 12n.
Ir dielectrlc surface 2~ carrles any net poAitlve or negatlve charge, this charge wlll e~tabllsh an electrlcal fleld to grid electrode 17, causlng the extractlon o~ ion~ o~ ~he opposlte polarlty rrom the lon pool 1~ the ion generator 10 18 thus dlspo~ed for a su~lcient ~eriod of tlme, the surface 20 will be completely neutrallzed~ The surrace 20 bears llttle or no resld~al char~e under these clrc~mstances.
Another desirable ~eature ls that Or the typlcally high charging/discharge rates of thls devlce.
Advantageously, the corona devlce 10 i~ dlsposed at a dlstance ln the range 5-20 mils ~rom sur~ace 20, most pre~erably around 15 mils, as measured rrom the outer surrace of grid electrode 17~ A rurther advantageou~ ~eature o~ the lnventlon is that the of~set voltage o~ this devlce 19 relatlvely lnsensltlve to changes ln gap wldth wlthln thi~
range.
Wlth rurther rererence to Figure 4, the devlce lO may be ~tlllzed to deposit a net posltlve or negatlve char~e on sur~ace 20 when switch 21 lq at positlon y. Thl~ places a DC
blas potentlal 22 on grld electrode 17. Wlth a posltlve bla~ to electrode 17, ~or example, a positive charge of equal ma~nlt~de wlll be deposlted on ~ur~ace 20. When operated ln this mode, the corona device 10 provide3 automatic llmltlng o~ the charging potential.
-- , 1 ~7~g~
In a preferred utlllzatlon Or the corona devlce 10. a relAtlve ~otlon i~ provlded between the devlce 10 and s~r~ace 20. so that the devlce wlll be ad~acent to varlou~ surface areas over time. Layer 20 may comprlse, ~or example, the surrace of a rotatable drum with a dlelectric or photoconductlve sur~ace. It 13 generally deslrable to mlnlmlze variatlons o~ the ~ap wldth % between corona device lO and surface 20 during s~ch relatlve motlon. ~en operatlng in the corona charglng mode during such motion, the devlce wlll generally provlde a surface potentlal whlch 19 a ~ractlon o~
the blas potentlal; this rraction wlll lncrease wlth lower ~urrace ~peed~.
In the pre~erred embodlment7 tlme varying pot~ntial lq comprlse3 a high ~requency9 high voltage ~inusoidO Pre~erably9 excltatlon potentlal 23 has a magnitude in the ran~e 1700-2~00 volts peak-to-peak, mo~t advantageously around 2000 volts pea~-to-peak. E~cltatlon potentlal 23 may comprlse a continuou~
wave alternating potentlal, preferably of a rrequency in the range lOKHz to 1 r~z. Drivlng voltages at hlgher ~requencle~
have been observed to cau~e overheatlng o~ the corona devlce, whlle lower rrequency wave~orm~ may provl~e lnadequate outp~
c~rrent~. A contlnuo~ wave ~requency Or 100 KHz provide~
desirably hlgh emlsslon current~ wltho~t a serlous rlsk Or overheatlng deYlce 10. Alternatlvely, excitation potentlal 19 may comprlse a pulsed volta~e whlch may be 3pecl~1ed by the parameters o~ peak-to-peak voltage, repetltion perlod, pul3e 6 g 5 width, and base frequency. The devlce lO has been operated at frequencies as high as 1 rlHæ applled in short bursts havlng a duty c,ycle near 10 percent.
Both prlnclpal embodiments of the lnventlon are further lllustrated ln the following nonllmiting examples:
Example 1 A corona charging devlce of the type shown ln Flgure l was constructed as follows. The lnsulating support was fabrlcated of glass epoxy G-10 lamlnate. The corona electrode consisted of a 7 mll dlameter stainless steel wire having a 2 mll thlck glass coatlng. After laylng the coated wlre on the slipport block, a fine woven wire screen wa~ stretched over the glass coated wlre and bonded with a thermoset adhesive to the sides of the support. The screen was composed of a plain woven 1 mll stalnless steel wlre. havlng a mesh count of 100 and an open area of approximately 90 percent~ The coated wire electrode was not bonded to the support block, and was constralned only by the overlying screen.
A 100 KHz, 2000 volt continuous wave alternating potentlal was placed between the coated wlre and the mesh electrode~ me o~ter surface of the mesh electrode; was located 15 mlls from the s~rface of an lmaglng drum having a thln photoconductive s~rface layer, with a capacitance of 100 picofarads per cm2O
The photoconductive surface was charged to 500 volts wlth a charglng rate of 103 cm2/secO, by lmposing a 500 volt direct current potential between the mesh electrode and the 6 ~ 9 ~
drum's conductive core. Thls represented an average corona output current o~ 10 microamperes per cm. length o~ corona.
Example 2 The apparatus of Example 1 was employed as a corona dlscharge devlce by groundlng the mesh electrode to the photoreceDtor drum's conductlve core. In thls mode, the devlce ne~trallzed electrostatlc images at rates comparable to the charging rates of Example l, leaving virtually no resldual electrostatic lmage.
:`
Exam~le 3 The apparatu~ o~ Example 1 was modlfled as follows to provlde a corona charglng devlce o~ the type shown in Figure 7.
me corona electrode was fabricated by lamlnatlng a 1 mll stalnless steel foll to the support block uslng a pressure sensit1ve adheslve, and photoetching an electrode wlth a line width of 8 mils. The electrode was encapsulated with a 1.5 mll thick layer Or glas~ by sllk-~creenlng a glass frlt over the etched electrode, and sinterlng the glass at a high temperature ~to form a continuous glass coating.
This apparatus exhlblted equivalent performance to the structure Or ~xample 1, in both the charging and neutrallzing modes.
9 ~
Fxam~le 4 A corona charglng devlce 9~ o~ the type shown ln ~lgure 9 was constructed as ~ollows. me corona e7ectrode conslsted o~
a 7 mll dlameter stalnless steel wlre havlng a 2 mll thlck glass coatlng. The coated wire was embedded ln an ll mil wlde, lO mil deep rectangular slot in a stainless steel beam of total dlmenslons 50 mll wlde and 50 mll deep, after insertlng adheslve flller at the bottom of the slot, Thls provlded a beam wldth of 14.5 mil on each slde o~ the slotO
; A 100 KHz, 2000 volt peak-to-peak contlnuous wave alternating potential was placed between the coated wlre and the steel beam. The outer surface o~ the corona electrode was located 15 mils from the surface o~ an lmaglng drum havlng a thln photoconductlve sur~ace layer, wlth a capacitance Or 100 pico~arads per cm.2O m e lmagin~ drum wa~ rotated at a surface spee~ of 25 cm/second relatlve to the corona devlce 9 and wa~ charged to 500 volts by imposlng a 1000 volt direct current potential between the steel beam and the ~rum' 8 conductive core. This represented an average corona output current of 1.25 micro-ampere~ per centimeter length o~ corona~
, Rxam~le 5 __ ___ _ The apparatu~ o~ Example 4 was employed as a corona dlschar~e devlce by grounding the mesh electrode to the photoreceptor drwm's conductive core~ In thls modeg the ~evice neutralized electrostatic lmages at rates comparable to the charglng rates o~ Example 4, leavlng virtually no residual electrostatlc imageO
l 17G695
2~
Exam~le 6 The apparatus of Example 4 was modified as follows to provlde a corona charging devlce o~ the type shown ln ~igure 13. A glass-coated tungsten wire as in Example ~ was bonded to an lns~latlng support conslstin~ of glass epoxy G-10 laminate~
Two tantalum wlres of 10 mll X 10 mll square cross-sections were bonded to the base on elther slde o~ the glass-coated wlre, contacting the dielectric sheath along its length.
This apparatus exhibited equivalent per~ormance to the structure o~ Example 4, ln both the charglng and neutrallzing modes.
Whlle various aspects of the invention have been set forth by the drawings and the speclficatlon, lt ls to be understood that the foregoing detailed descrlptlon ls ~or illustratlon only and that various changes ln parts, as well as the substltution of equivalent constltuents for those shown ana described, may be made without departlng ~rom the splrit and scope of the lnventlon as set forth ln the appended claims.
- 26 ~17~6~5 NOMENCLATURE
10. Corona device, first aspect. ~Fig.2) 11. Corona electrode 12. Conductive wire 13. Dielectric coating (eg. glass) 15. Insulatir,g substrate (eg. plastic) 17. Control electrode 19. Dielectric filler (Figs. 12A-12C) 20. Imaging surface (Figs. 4 and 10) ( eg. plastic) R Radius of corona electrode 11 T Thickness of dielectric layer 13 G Separation of corona electrode from side walls ~ W Width of beam 94 ; H Protrusion of corona electrode from slot Z Gap width between corona device and imaging surface 21. Switch x l'switch off" position y "switch on" position 22. DC biasing source 23. Excitation potential 25. Conductive backing (Fig. 4) 26. Excitation potential 27. DC biasing source 30. Corona device~ alternate arrangement (FigO 3) - 27 ~ 1~ 7 66g ~
37. Mesh 50. Corona device alternati~e structure (Fig. 53 55. Insulating substrate ~eg. plastic~
56. Slot 57. Grid electrode 60. Corona device, alternative structure ~Fig. 6 62. Elongate conduc~or 63. Dielectric strip 65. Insulating support (eg. plastic) 67. Grid electrode 71. Corona electrode surface (Fig. 7) 72. Conductive wire 73. Dielectric encapsulation (eg. plastic) 75. Insulating Support (eg. plastic~
80. Corona device, alternative structure (Fig~ 8) 85. Insulating support 87. Grid electrode (Fig. 8) 90. Corona device, alternative structure (Fig. 9) 94. Conductive beam 95. Adhesive Filler (FigO 12A3 96. Slot 97. Side ~all 98. Base 99. Control electrode (FigsO 9 and 12C) 100. Discharge region (Fig~ 12A)~
110. Corona device (Fig. 13 , ~7~69~
111. Dielectric coated elect~de 113. Dielectric coat~n~ (eg, gl~ss~
115. Suppoxt block teg. plastic) 116. Conductive rod 117. Conductive rod 120. Charging devlce ~Fig. 14) 121. Thick cylindrical wire (electrode) 122. Dielectric coated electrode 123. Metallic core 124. Dielectric coating (eg. glass) 125. Support block (eg. plastic) 126. Dielectric coated electxode 127. Metallic core 128. Dielectric coating (eg. glass) 130. Modification of device 120 IFig.15) 131. Cylindrical electrode 132. Dielectric coated electrode 133. Hollow metallic core 134. Dielectric coating (egO glass) 135. Support block (eg. plastic) 136. Dielectric coated electrode 1370 Dielectric coating (eg. glass)
Exam~le 6 The apparatus of Example 4 was modified as follows to provlde a corona charging devlce o~ the type shown ln ~igure 13. A glass-coated tungsten wire as in Example ~ was bonded to an lns~latlng support conslstin~ of glass epoxy G-10 laminate~
Two tantalum wlres of 10 mll X 10 mll square cross-sections were bonded to the base on elther slde o~ the glass-coated wlre, contacting the dielectric sheath along its length.
This apparatus exhibited equivalent per~ormance to the structure o~ Example 4, ln both the charglng and neutrallzing modes.
Whlle various aspects of the invention have been set forth by the drawings and the speclficatlon, lt ls to be understood that the foregoing detailed descrlptlon ls ~or illustratlon only and that various changes ln parts, as well as the substltution of equivalent constltuents for those shown ana described, may be made without departlng ~rom the splrit and scope of the lnventlon as set forth ln the appended claims.
- 26 ~17~6~5 NOMENCLATURE
10. Corona device, first aspect. ~Fig.2) 11. Corona electrode 12. Conductive wire 13. Dielectric coating (eg. glass) 15. Insulatir,g substrate (eg. plastic) 17. Control electrode 19. Dielectric filler (Figs. 12A-12C) 20. Imaging surface (Figs. 4 and 10) ( eg. plastic) R Radius of corona electrode 11 T Thickness of dielectric layer 13 G Separation of corona electrode from side walls ~ W Width of beam 94 ; H Protrusion of corona electrode from slot Z Gap width between corona device and imaging surface 21. Switch x l'switch off" position y "switch on" position 22. DC biasing source 23. Excitation potential 25. Conductive backing (Fig. 4) 26. Excitation potential 27. DC biasing source 30. Corona device~ alternate arrangement (FigO 3) - 27 ~ 1~ 7 66g ~
37. Mesh 50. Corona device alternati~e structure (Fig. 53 55. Insulating substrate ~eg. plastic~
56. Slot 57. Grid electrode 60. Corona device, alternative structure ~Fig. 6 62. Elongate conduc~or 63. Dielectric strip 65. Insulating support (eg. plastic) 67. Grid electrode 71. Corona electrode surface (Fig. 7) 72. Conductive wire 73. Dielectric encapsulation (eg. plastic) 75. Insulating Support (eg. plastic~
80. Corona device, alternative structure (Fig~ 8) 85. Insulating support 87. Grid electrode (Fig. 8) 90. Corona device, alternative structure (Fig. 9) 94. Conductive beam 95. Adhesive Filler (FigO 12A3 96. Slot 97. Side ~all 98. Base 99. Control electrode (FigsO 9 and 12C) 100. Discharge region (Fig~ 12A)~
110. Corona device (Fig. 13 , ~7~69~
111. Dielectric coated elect~de 113. Dielectric coat~n~ (eg, gl~ss~
115. Suppoxt block teg. plastic) 116. Conductive rod 117. Conductive rod 120. Charging devlce ~Fig. 14) 121. Thick cylindrical wire (electrode) 122. Dielectric coated electrode 123. Metallic core 124. Dielectric coating (eg. glass) 125. Support block (eg. plastic) 126. Dielectric coated electxode 127. Metallic core 128. Dielectric coating (eg. glass) 130. Modification of device 120 IFig.15) 131. Cylindrical electrode 132. Dielectric coated electrode 133. Hollow metallic core 134. Dielectric coating (egO glass) 135. Support block (eg. plastic) 136. Dielectric coated electrode 1370 Dielectric coating (eg. glass)
Claims (52)
1. Apparatus for generating ions, comprising:
an elongate conductor;
a dielectric sheath for said elongate conductor:
a control electrode in proximity to said dielectric sheath;
a time-varying potential applied between said elongate conductor and said control electrode in order to create a glow discharge; and an extraction potential for extracting ions from said glow discharge to produce an output ion current approximately proportional to said extraction potential.
an elongate conductor;
a dielectric sheath for said elongate conductor:
a control electrode in proximity to said dielectric sheath;
a time-varying potential applied between said elongate conductor and said control electrode in order to create a glow discharge; and an extraction potential for extracting ions from said glow discharge to produce an output ion current approximately proportional to said extraction potential.
2. Apparatus as defined in claim 1, wherein said control electrode comprises a conductive grid contacting said dielectric sheath, further comprising an insulating support for the elongate conductor and dielectric sheath.
3. Apparatus as defined in claim 2 wherein the conductive grid comprises a conductive mesh electrode.
4. Apparatus as defined in claim 3 wherein the conductive mesh electrode comprises a wire mesh screen.
5. Apparatus as defined in claim 4 wherein the wire mesh screen has a mesh in the range 30-150 apertures per inch.
6. Apparatus as defined in claim 4 wherein the wire mesh electrode has a high open ares ratio.
7. Apparatus as defined in claim 4 wherein the wire mesh screen comprises a lattice of wires having a thickness in the range 0.3-1.2 mils.
8. Apparatus as defined in claim 3 wherein the conductive mesh electrode comprises a metal foil etched in a mesh pattern.
9. Apparatus as defined in claim 2 wherein the conductive grid comprises an array of essentially parallel conductors.
10. Apparatus as defined in claim 2 wherein the conductive grid contacts the dielectric sheath along a line coextensive with the elongate conductor.
11. Apparatus as defined in claim 2 wherein the elongate conductor and dielectric sheath comprise a dielectric-coated wire.
12. Apparatus as defined in claim 11 wherein the dielectric sheath has a thickness in the range 1-3 mils.
13. Apparatus as defined in claim a wherein the elongate conductor and dielectric sheath comprise a conductive strip contacting the insulating support, with an encapsulating dielectric layer.
14. Apparatus as defined in claim 2 wherein the conductive grid is anchored against the insulating support on each side of the elongate conductor and dielectric sheath.
15. Apparatus as defined in claim 2 wherein the conductive grid has an approximately inverse V-shaped lateral cross section.
16. Apparatus as defined in claim 2 wherein the conductive grid has an arcuate lateral cross section.
17. Apparatus as defined in claim 2 wherein the elongate conductor and dielectric sheath are housed in a slot in said insulating support, with said conductive grid contacting the dielectric sheath above the slot.
18. Apparatus as defined in claim 1, wherein said control electrode comprises a conductive enclosure for the sheathed elongate conductor, including inner walls straddling the sheathed elongate conductor and further including an opening to expose said sheathed elongate conductor.
19. Apparatus as defined in claim 18 wherein said conductive enclosure comprises a conductive beam having a slot, and wherein the sheathed elongate conductor is embedded in said slot.
20. Apparatus as defined in claim 18 further including an insulating base, wherein the sheated elongate conductor is mounted against said insulating base, and wherein the conductive enclosure comprises a pair of conductive side members mounted against said insulating base.
21. Apparatus as defined in claim 20 wherein the conductive enclosure comprises conductive rods mounted against said insulating base and fitted against the sheathed elongate conductor along its length.
22. Apparatus as defined in claim 18 wherein the inner walls of the conductive enclosure contact opposite sides of the sheathed elongate conductor.
23. Apparatus as defined in claim 18 wherein the inner walls of the conductive enclosure straddle said dielectric sheath along lines coextensive with said elongate conductor.
24. Apparatus as defined in claim 18 wherein the conductive enclosure has outer surfaces which form corners with its inner walls.
25. Apparatus as defined in claim 24 wherein the sheathed elongate conductor protrudes beyond said outer surfaces for a small fraction of its thickness.
26. Apparatus as defined in claim 24 wherein the outer surfaces are narrow as compared with the thickness of the sheathed elongate conductor.
27. Apparatus as defined in claim 1, wherein the control electrode comprises a conductive rod, and the dielectric sheathed elongate conductor comprises a pair of elongate side members straddling said conductive rod, with the time varying alternating potential applied between each of said elongate side members and said conductive rod.
28. Apparatus as defined in claim 27 further comprising an insulating base for the conductive rod.
29. Apparatus as defined in claim 28 wherein the elongate side members are mounted against said insulating base and fitted to either side of said conductive rod.
30. Apparatus as defined in claim 27 wherein each of the elongate side members comprises a glass capillary tube with a conductive inner lining.
31. Apparatus as defined in claim 27 wherein each of the elongate side members comprises a glass capillary tube with a solid conductive core.
32. Apparatus as defined in claim 31 wherein the conductive core comprises a material chosen from the class consisting of low-melting alloys of bismuth, and indium alloys.
33. Apparatus as defined in claim 1 wherein the dielectric sheath comprises an inorganic dielectric material.
34. Apparatus as defined in claim 1 wherein the dielectric sheath comprises a material selected from the class consisting of glass, mica, and sintered ceramic materials.
35. Apparatus as defined in claim 1 wherein the extraction potential comprises a direct current potential between the control electrode and a counterelectrode.
36. Apparatus as defined in claim 35 wherein the direct current potential has a magnitude of from tens to hundreds of volts.
37. Apparatus as defined in claim 1, for corona discharging, wherein the apparatus is proximate to an imaging surface to be discharged, said imaging surface having a backing electrode, and wherein said control electrode is grounded to said backing electrode.
38. Apparatus as defined in claim 1 wherein the time varying potential comprises a high voltage alternating potential.
39. Apparatus as defined in claim 38 wherein the alternating potential has a frequency in the range 60 Hz - 4 MHz.
40. Apparatus as defined in claim 1 wherein the varying potential comprises a pulsed voltage.
41. Apparatus as defined in claim 1, wherein the control electrode is disposed at a distance in the range 5-20 mils from a member to be charged or discharged.
42. A method for electrostatic discharging comprising the steps of disposing a corona device near the member to be discharged, said corona device comprising an elongate conductor, a dielectric sheath for the elongate conductor, and a control electrode in proximity to the dielectric sheath, applying a time-varying potential between said elongate conductor and said control electrode to induce a glow discharge in an air region adjacent the control electrode and dielectric sheath; and grounding said control electrode to a counterelectrode for the member to be discharged.
43. The method of claim 42 wherein the control electrode comprises a conductive grid in contact with the dielectric sheath, and wherein the dielectric sheathed elongate conductor is mounted to an insulating support.
44. The discharging method of claim 42 wherein the control electrode comprises a conductive enclosure for the dielectric sheathed elongate conductor, including inner walls surrounding said dielectric sheathed elongate conductor and an opening to expose the dielectric sheath.
45. An electrostatic charging method, comprising the steps of:
disposing a corona device near the member to be discharged, said corona device comprising an elongate conductor, a dielectric sheath for the elongate conductor. and a control electrode in proximity to the dielectric sheath, applying a time-varying potential between said elongate conductor and said control electrode to induce a glow discharge in an air region adjacent the control electrode and dielectric sheath; and applying a bias potential between said control electrode and a counterelectrode for the member to be charged.
disposing a corona device near the member to be discharged, said corona device comprising an elongate conductor, a dielectric sheath for the elongate conductor. and a control electrode in proximity to the dielectric sheath, applying a time-varying potential between said elongate conductor and said control electrode to induce a glow discharge in an air region adjacent the control electrode and dielectric sheath; and applying a bias potential between said control electrode and a counterelectrode for the member to be charged.
46. The electrostatic charging method of claim 45 wherein the control electrode comprises a conductive grid in contact with the dielectric sheath, and wherein the dielectric sheathed elongate conductor is mounted to an insulating support.
47. The electrostatic charging method of claim 45 wherein the control electrode comprises a conductive enclosure for the dielectric sheathed elongate conductor, including inner walls surrounding said dielectric sheathed elongate conductor and an opening to expose the dielectric sheath.
48. Apparatus for generating free ions, comprising:
a control electrode;
an elongate conductor;
a dielectric member positioned between the elongate conductor and the control electrode in proximity with both the conductor and the control electrode;
a time varying potential applied between said elongate conductor and said control electrode in order to create a glow discharge; and an extraction potential for extracting ions from said glow discharge to produce an output ion current approximately proportional to said extraction potential.
a control electrode;
an elongate conductor;
a dielectric member positioned between the elongate conductor and the control electrode in proximity with both the conductor and the control electrode;
a time varying potential applied between said elongate conductor and said control electrode in order to create a glow discharge; and an extraction potential for extracting ions from said glow discharge to produce an output ion current approximately proportional to said extraction potential.
49. Apparatus as defined in claim 48, wherein said control electrode comprises a conductive grid and wherein the apparatus further comprises an insulating support for the elongate conductor.
50. Apparatus as defined in claim 49 wherein the conductive grid comprises a conductive mesh electrode.
51. Apparatus as defined in claim 49 wherein the conductive mesh electrode comprises a wire mesh screen.
52. Apparatus as defined in claim 51 wherein the wire mesh screen has a mesh in the range 30 - 150 apertures per inch.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US237,559 | 1981-02-24 | ||
| US06/237,559 US4379969A (en) | 1981-02-24 | 1981-02-24 | Corona charging apparatus |
| US24483381A | 1981-03-17 | 1981-03-17 | |
| US244,833 | 1981-03-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1176695A true CA1176695A (en) | 1984-10-23 |
Family
ID=26930809
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000397002A Expired CA1176695A (en) | 1981-02-24 | 1982-02-24 | Corona charging apparatus |
Country Status (11)
| Country | Link |
|---|---|
| EP (1) | EP0072862B1 (en) |
| AU (2) | AU8273282A (en) |
| CA (1) | CA1176695A (en) |
| DE (1) | DE3279781D1 (en) |
| ES (1) | ES510454A0 (en) |
| IL (1) | IL65099A0 (en) |
| IT (1) | IT1195781B (en) |
| MX (1) | MX151414A (en) |
| NZ (1) | NZ199827A (en) |
| PT (1) | PT74473B (en) |
| WO (1) | WO1982002983A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3279781D1 (en) * | 1981-02-24 | 1989-07-27 | Dennison Mfg Co | CORONA CHARGING APPARATUS |
| EP1928608A4 (en) * | 2005-09-29 | 2011-06-01 | Sarnoff Corp | Ballast circuit for electrostastic particle collection systems |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3370212A (en) * | 1965-08-19 | 1968-02-20 | Eastman Kodak Co | Corona charging apparatus |
| US3779882A (en) * | 1971-04-01 | 1973-12-18 | Union Carbide Corp | Electrode method for the surface treatment of thermoplastic materials |
| US3742301A (en) * | 1972-05-11 | 1973-06-26 | W Burris | Corona generator |
| US3875461A (en) * | 1973-09-18 | 1975-04-01 | Harris Intertype Corp | Static eliminator |
| US4068284A (en) * | 1973-09-28 | 1978-01-10 | Xerox Corporation | Corona discharge device |
| US4057723A (en) * | 1976-01-23 | 1977-11-08 | Xerox Corporation | Compact corona charging device |
| DE2849222A1 (en) * | 1978-11-13 | 1980-05-22 | Hoechst Ag | METHOD FOR ELECTROSTATICALLY CHARGING A DIELECTRIC LAYER AND DEVICE FOR CARRYING OUT THE METHOD |
| DE3279781D1 (en) * | 1981-02-24 | 1989-07-27 | Dennison Mfg Co | CORONA CHARGING APPARATUS |
-
1982
- 1982-02-23 DE DE8282901078T patent/DE3279781D1/en not_active Expired
- 1982-02-23 EP EP82901078A patent/EP0072862B1/en not_active Expired
- 1982-02-23 WO PCT/US1982/000222 patent/WO1982002983A1/en active IP Right Grant
- 1982-02-23 AU AU82732/82A patent/AU8273282A/en not_active Abandoned
- 1982-02-24 IL IL65099A patent/IL65099A0/en not_active IP Right Cessation
- 1982-02-24 MX MX191558A patent/MX151414A/en unknown
- 1982-02-24 NZ NZ199827A patent/NZ199827A/en unknown
- 1982-02-24 CA CA000397002A patent/CA1176695A/en not_active Expired
- 1982-02-24 PT PT74473A patent/PT74473B/en unknown
- 1982-02-24 ES ES510454A patent/ES510454A0/en active Granted
- 1982-02-24 IT IT19826/82A patent/IT1195781B/en active
-
1987
- 1987-01-22 AU AU67935/87A patent/AU586531B2/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| EP0072862A1 (en) | 1983-03-02 |
| IT8219826A0 (en) | 1982-02-24 |
| PT74473B (en) | 1984-11-19 |
| ES8306289A1 (en) | 1983-06-01 |
| DE3279781D1 (en) | 1989-07-27 |
| AU8273282A (en) | 1982-09-14 |
| WO1982002983A1 (en) | 1982-09-02 |
| ES510454A0 (en) | 1983-06-01 |
| EP0072862B1 (en) | 1989-06-21 |
| MX151414A (en) | 1984-11-14 |
| EP0072862A4 (en) | 1983-07-04 |
| AU586531B2 (en) | 1989-07-13 |
| PT74473A (en) | 1982-03-01 |
| NZ199827A (en) | 1985-12-13 |
| IL65099A0 (en) | 1982-04-30 |
| IT1195781B (en) | 1988-10-27 |
| AU6793587A (en) | 1987-05-07 |
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