Note: Descriptions are shown in the official language in which they were submitted.
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~
1 176695
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
1 176695
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~
14
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
19
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 ~
24
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~
- 28 -
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)
