Note: Descriptions are shown in the official language in which they were submitted.
14 Background and Summary of the Invention
This invention relates to the field of
;`.1- ,
, -16 electxophotography, and particularly to a xerographic
~', 17 copying machine wherein the various electrostatic
~' 18 charge sources are uniquely controlled to'facilitate
.
19 ~leaning of the photoconductor after the last copy
,
' 20 cycle, i.e. during the runout cycle.
21 In a typical electrophotographic process
22 a latent electrostatic image is formed on a photocon-
'23 ductor. The latent image,is then d,eveloped to a
24 ~isible image by subjecting the photoconductor to
~," ' 25 a ~low of two-component developer mix, i.e. carrier
.~ -~ .. . . .
, , 26 'and toner. Generally the carrier beads are much
: - .~ . . .
~ 27- larger than the toner particles. For example, toner
., . ,;
~ 28 particles'have an average diameter of bet~leen 1 and
~, ~. ... .. . .. . . . . ..
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.: -~. j .
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....
.
.
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1 30 microns, whereas carrier beads have an average
2 diameter bet~een 50 and 1000 microns.
3 Two methods of developing the photoconduc-
4 tor's latent image are known as charged area develop
ment and discharged area development, respectively.
6 In chaxged area development mixing of the carrier
7 an~ toner triboelectrically charges the carrier
8 to the same polarity as the latent image, and the
9 toner to the opposite polarity. In discharged area
development mixing of the carrier and toner tribo-
11 electrically charges the toner to the same polarity
. .
12 as the photoconductor's charged background area,
13 and ~he carrier to the opposite polarity. The carrier
14 beads ack as unsaturated vehicles to carry the toner
to the photoconductor. The carrier beads adjacent
16 the latent image gi~e hp toner to the latent image
17 to thereby form a visible image. The carrier beads -
- . :
18 adjacent the photoconductor's background area should
19 not give up toner to the photoconductorr and preferably
function to-pick up unwanted toner which may reside
~1 on the photoconductor from previous use. Toner
22 ~.hich ~desirably remains-on the photoconductor's
. . :
: 23 backgro~d area may later be transferred to the
24 backgxo~nd surface of the usually white copy paper,
t~lu~ c~ntributing to undesirable coloring of the
- . .
26 copy bac.kyround.
27 ~ After transfer of the toner ~rom the photo-
28 condu~tor ~o a ~heèt of copy paper, the photoconductor
,
~Eg7~009 -2-
1C~73L693
1 is sub~ected to a preclean electrostatic charge source which
2 floods the photoconductor with a charge of the opposite
3 polarity to which it was charged. As a result, the photo-
4 conductor's ~oltage is reduced and the electrostatic ~orce
holding residual toner thereon is reduced.
6 After transfer of the toner from the photocon-
7 ductor to a sheet of copy paper, the photoconductor is
8 cleaned. A well known cleaning station incorporates a
9 triboelec~rically charged brush whose fibers are tribo-
electrically charged as the fibers rotate past a stationary
11 knockoff bar. The charged brush fibers rotate counter to
12 photoconductor movement and physically sweep the photo-
13 conductor to remo~e foreign particles therefrom. This
14 particle xemoval is ef~ected both by mechanical scrubbing
action and by electrostatic attraction of particles which
16 are charged to a polarity opposite that of the brùsh fibers.
17 To assist in cleaning, a preclean electrostatic charge
18 source floods the photoconductor with a charge of this
19 opposite polarity before the photoconductor enters the brush
cleaning station. In addition, it is desirable to flood the
21 photoconductor with illumination prior to the cleaning
22 station, to thereby reduce the photoconductor charge.
23 In summary, two polarity relationships which must
24 exist are that the toner and carrier must be oppositely
charged, and the triboelectric
LE974009 -3-
.
1 sleanincJ brush and the preclean electrostatic charge
2 source ,nust be o~ opposite polarities. In a system
3 ~mploying charged area development, the toner is
4 charged opposite that of the photoconductor ! s latent
ima~e. If the system'employs discharged area develop-
6 ment, ~he toner is charged the same as the polarity
7 of the photoconductor's background area. In addition,
8 it is preferable with either -type of development
9 system that the charge of the triboelectric cleaning
brush be opposite that of the toner.
11 A specific example of such a brush material
12 and carrier bead is a polytetrafluoroethylene brush
13 and a magnetic bead coated with a thin layer of
14 polytetra~luoroethylene. In this and similar xero-
lS graphic systems particles which abrade off a carrier
16 bead are not easily cleaned from the photoconductor.
17 They thus tend -to remain thereon during subsequent
18 copy cycles to serve as residence sites for toner.
19 As a result the subsequent copies include unwanted
background color. In.addition, these unwanted parti-
21 cles tend to abrade and/or coat the photoconductor
22 so as to degrade its optical performance.
23 The present invention improves the cleaning
24 of such a photoconductor during the runout cyc]e
by turning off all electxostatic charge sources
26 whose polarity is the same as that of the cleaning
27 brush, and by subjecting the,se unwanted particles
28 to an electrostatic charye opposite that of the brush.
.
LE974009 ~4~
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~C)7~69~3
1 These particles are ~lereore charged opposite the
2 ~rush charge and electrostatically interact with
3 the triboelectric cleaning station. As a result,
4 they are more easily cleaned therefrom.
More speciically, and without limitation,
6 the present invention opera~es in a charged area
7 development system to turn off the charge and transfer
8 coronas during runout a~ter the last copy is trans-
9 ferred, and maintains the preclean corona operative
to flood the photoconductor carried particles with
11 a charse of the same polarity as the toner during
12 this runout. Thus, these particles interact with
13 the tri~oelectric cleaning station as if they were
14 t:c,ner and are cleaned ~rom the photoconductor.
15 Using toner charge-as a reference, it - - -
16 is cor~Jen~ional in a charged area development system
17 to proviae at least three charge sources along the
18- route of the photoconductor during a copy cycle.
19 The first of these is a photoconductor charge source
which charges the photoconductor to a polarity opposite
21 that of the toner. The next charge source is a
22 trans~er charge source which cooperates with transfer
23 material, such as paper, to cause the photoconductor-
24 carried toner to transfer to the paper. This charge
source is also of the opposite polarity.
26 The third charge source is a preclean
27 charge source, so named because its function is to
28 charge photoconductor-carried particles prior to the
J~97~003 -5-
~07~ 3
1 photoconduc~or cn~eriny the triboelectric cleaniny
2 station. Also a light source discharges the photocon-
3 ductor prior to the cleaning station and allows
4 residual toner to be more easily removed by the
cleaning station. It has been found that the results
6 achieved by the present invention, namely the cleaning
7 of-materials which exhibit essentially the same
8 triboelectric effect as the carrier, i.e. opposite
~ that of the toner, cannot be accomplished by the
expedience of increasing the magnitude of the preclean
11 charge source during the cleaning portions of each
12 copy cycle, since such operation overcharges the
13 residual toner in the photoconductor's image areas
~ and results in a greater electrostatic ~orce holding
the residual toner to the photoconductor, thus inhibit-
16 ing cleaning.
17 Thus, the present invention is limited
18 to the concept of maintaining charge sources opposite
19 the cleaning station polarity energized during the
.-,^unout cycle, and turning off charge sources of
21 the cleaning station's polarity during the runout
22 cycle. The present invention is particularly useful
23 in those machines employing a carrier which tends
24 to leave residual traces of the carrier on the drum,
which drum is then cleaned by a cleaning station
26 designed to triboelectrically interact with the
27 - toner, and not the carrier,
~8 A known prior xerographic cleaning system
29 teaches selective cleaning of carrier and toner
~E97~009 -6-
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.. . . ..
1 particl~s. Specif.ically, this prior cleaning system
2 charges the phol-oconductor in ~he usual manner ln
3 a first area t~ereof, and charges a secGnd area
4. to an o~posit~ polarity. The first area is used
for the latent electrostatic image and thus cooperates
6 primarily with the toner constltuent o the developer
7 mix. The second area, because of its reverse char~e,
:. B operates to clean foreign mater.ial, includ.ing fine
9 carrier chips, from t~e de~eloper's mix. Later
in the process, both photoconductor areas are cleaned
- ll by a cleaning brush.
12 - The foregoing and other features and advan-
13 tages of the invention will be apparent from the
14 following more particular description of a preferred
embodiment of the invention, as illustrated in the
:- 16 accompanying drawing.
- 17 : Brief Description of the Drawing
~ FIGURE 1 is a schematic view o~ the drum
19 photoconductor showing the processing stations which
20- . sequentially cooperate with the photoconductor.,
21 embodying the present invention
22 FIGURE 2 is a schematic side view of a
: 23 xerographic copying machine incorporating the apparatus
24 .of FIGURB l; and
FIGURE 3 is a simplified schematic showing
.6 t~le manner in which ~he preclean corona, transfer
. ~ c~r~na a~d charge corona o~ FIGU~ES 1 and 2 are
~8 controlled during the runout cycle~
.' ~ ~'
'
LE97400g 7 - .
. ~
.
~7~ 3
1 DescL~ption of ~le Pref xed Embodiment
2 The ollo~ing description of a preferred
3 embodiment of the p~esent invention will relate
4 to a charged ir,lage development system wherein the de-
veloper mix compri~es toner of a fixst polarity
6 ~positive) and carrier of an opposite polarity
7 (negative), wherein the photoconductor is charged
8 to the opposite polarity, whereln the toned image
9 is transferred to copy paper by a trans~er station
of the opposite polarity, and wherein the photoconduc-
11 tor is cleaned by a triboelectric brush of the opposite
12 polarity and a preclean charge source of the first
13 -polarity. ~owever! the present invention is not
14 to be limited thereto. In its broad generic sensel
the present invention relates to charging the photocon-
16 ductor carried particles to a polarity opposite
11 the cleaning station polarity during the machine's
18 runout cycle.
19 The runout cycle of an electrophotographic
copying apparatus is defined as that final portion
21 of the machine operation which is necessary to clean
22 the photoconductor, to restore the photoconductor
23 to an essentially neutral charge, to return the
24 photoconductor to what may be called a home posi.tion,
and to deposit the last copy sheet in an exit tray.
26 In the electrophotographic copying apparatus
27 of FIGURE 1, photoconductor 12 is stationary at
28 the home positi.on, and essentially at a neutral
I,E97400g 8-
.
. .
~7~693
1 electrostatic charg~ when a copy request is initiated,
2 for example by manual actuati.on of start switch
3 21, F r GURES 2 and 3. Immedia~ely ~ereafter the
4 photoconductor begins to move clockwise. The photocon-
~ tor is acc~lerated to a steady-state speed and
6 cl.larging station 18 is brouyht up to i.ts steady-
7 s-tat.~ operating condition by the time the leading
8 edge o the photoconductor's latent image area enters
.9.. charging scation 18. ~he photoconauctor is charged
as it mo~es past ~his charging s-tation. Thus the
11. leading edge of. an area which can accept image illumi-
12 nation, and thereby form an electrostatic latent
13 image, begins to move toward imaging station 11
14 which is located downstream of the charging station~
When thLs leading edge reaches the imaging
16 station, optical scanning mechanism 10 (FIGURE 2)
17 is activated to scan.an~riginal document in a moving
: 18 line or foo~print, as the charged photoconductor
19 passes the imaying station. At the imaging station,
-2~ the background area of the photoconductor, i.e.
21 background or white area of the original~document,
2~ is disch~rged, but not to a neutral potential, and
23 the image aréa retains substantially the original
24 charge applied thereto at the charging station.
The leading edge next-encounters developing .
26 station 1~ whereat the electrosta.tic latent image
Zl is toned by-a t.~o-component developer mix whose
28 toner constituent has an electrostatic affinity for
',
LE574009 -9- :
,, :.
7~3
1 the photocondllctorls l.atent irna~e, i.e. the portion
2 of the p}lotoconductor which has not been dischaxged
3 at tne imaging station.
4 Thc toned leading edge of a no~ visible
toned image next encountexs transer station 15
6 whereat the major portion o~ the photoconductor's
7 visual image is trans~erred to a support material
8, such as paper. The arrival of this leading edge
9 at the transfer skation is synchronized with the,
10. arrival of ~he leading edge of the sheet of paper.
ll-: A second charging source 15 is pos.itioned on the
12 opposite side of the paper from the toned image.
13 This transfer charging source, opera~es to charge
14 the adjacent side of the paper sheet so that the
toner is electrostatically attracted away from the
16 photoconductor's latent image and deposited on the
li paper~ As the paper,and photoconductor continue
18 to move through the transfer station a copy is formed
19 , and the photoconductor's leading edge separates
20 - rom the paper and moves toward a third charging
21 source, namely preclean charge source 16.
22 At about this time the trailing edge of
23 the photoconductor's area whlch can accept image
~4 illumination moves out of charging station 18. Control
o~ this trailing edge position can be achieved either
26 by turning charying station l8 off, or alternatively,
21 by leaving the charginy station continuously energized
28 and looding the photoconductor between the trailing
LE9,7~009 ~lO-
'
1~7~6~3
1 edge and the leading edge with illumination, either by
2 means of an interimage erase lamp located between imaging
3 station 11 and developing station 14, or by direct illumi-
4 nation of the photoconductor at the imaging station.
Returning now to the photoconductor's leading
6 edge, as it leaves the transfer station and moves toward
7 the preclean charging station, the photoconductor retains
8 its original electrostatic image charge. This charge has
9 been increased in potential in both the image and back-
ground areas by the electrostatic effect of the transfer
11 station. Some residual toner remains in the image area~
12 Much less residual toner remains in the background area;
13 and perhaps foreign particles such as, for example, small
14 particles of carrier remain on the photoconductor. As
this leading edge enters the influence of preclean
16 charging station 16, the photoconductor and the various
17 particles carried thereby are subjected to a charge of
18 a polarity opposite to the charge of cleaning station
19 17, and in this embodiment, opposite to the charge provided
at charging station 18 and transfer station 15. The
21 magnituae of this charge is substantially less than that -
22 of the charging station and the transfer station. This
23 magnitude relationship is necessary to insure that toner
24 particles, which are already of this polarity, are not
o~ercharged to the e~tent that the electrostatic
LE974009
-
6~3
1 force holc~i}~g the ton(r on the photoconduckor is
2 in fac~ inc.reased. It has been found that preclean
3 charginy station 16, which must be of a relatively
4 low magnitude, does not appreciably affect the opposite
S charge carried by the foreign par~.icles, such as
6 carrier particles.
7 Next the photoconductor's leading edge
8 - encounters preclean lamp 40 whereat the entire photo~
9 con~uctor is flooded with illumination. This illumina-
- 10 l::ion operates to discharge -the photoconductor so
11 as to reduce the electrostatic orce holding the
12 toner particles ~lereon.
13 The next and last processing station encoun~
- 14 tered by the photoconductor~s leading edge is triboe-
15 lectric cleaning station 17. One such reliable. ~ . -
16 cleaning station is one in which the photoconductor .~ ~
17 is engaged by a counter~rotating brush which is . ~ :
;18 t~iboelectrically charged to a polarity opposite
19 ~hat o the toner. Thus, toner i5 cleaned from
. 20 the photoconductor both by mechanical scrubbing ) .
21 actlon and by an electrical force of attraction.
- 22 It will be noted that electrically neutral foreign
23 material is cleaned only by the scrubbing action,
24 ` where`as particles having a similar charge, such
25 as carrier, are actually repelled by the brush bris~ . ~:
26 tles, making cleaning more difficult.
27 This cleaning operation may be aided by
28 an additional erase lamp which floods the photo-
. ' ' .
LE974009 -12~
' .
.
conductor with discharging illumi.natlon at the cleaning
2 station. In addition, the photocon~uctor may be .
3 subjected to discharging i.ll~i.nati~n at a stati.on
4 beyond the cleaning station, but before charge station
S 18.
6 The above description has traced the first
- 7 cycle of photoconductor 12. This cycle generates
8 one copy of an original document. If more than
9 one copy is desired, the cycle repeats, generating .
one copy for each cycle. The interimage area of
11 the photoconductor, i.e. the illumination-discharged
12 area bétween ~he trailing edge of one latent image
13 and the leading edge o the succeeding latent image,
14 is subjected to developer mi.x at developing station
14 as well as a charge a~ both transfer station
16 15 and preclean charge stations 16, and is cleaned
17 at cleaning station 17. ..
18 When the number of original docwnent scanning
: 19 operations equals the number of copies requested, ~ :
,
. 20 which number is contained in copy counter 22 ~FIGIJRE .~.
21 2), charging station 18 is deenergized when the .
22 trailing edge of this last latent image area passes
23 . therethrough. In turn, the passing of this same
.
24 latent image operates to render imaging station . : .
11, devel~ping station 14 and txansfer station 15
26 inoperative.
27 The passing o~ this last trailiny edge
28 through the transfer station initiates a unique
;
.
I,E974009 -13-
~t7~6~3
-
l r~mout cycle in ac~ordance ~ith the pre52nt invention.
~n ~eeordance with ~liS in~ention, the lea~ing edge
3 Gf what was the p~io oconducto~'s latent image area
~ during the ~revious copy run will now complete at
least one more c:ye:Le with charging station 18 and
6 transfer station 15 inopelative and wi-th preclean
7 charging st tion 16 operative. The results achieved
8 by the present in~rention can be appreeiated by consid-
9 ering a ~iven particle o o~eign material, such
~0 as a portioll of a carrier bead, which is carried
ll by the pho~oconductor. I such a particle is not
12 cleaned ~rom the photoconductor, i~ tends to serve
13 as a site for deposition of toner during subsequent
14 eopy runs and eontributes to unwanted toner coloration
in the background area o~ t-he copies.- In addition,
16 these particles tend to smear across the photoconduc-
17- tor, particular]y when they exist in large numbers,
18 and tend to degrade the optlcal per~ormance of the
l9 photoconductor.
In aecoxdance with the present invention,
21 the passing of the trailiny edye of the photoconduc-
22 tor's last latent image area through transfer station
23 15 results in deenergization of the transfer station.
24 It will be rememhered that charging station 18 was
2S deenergized at a prior point in time when this same
26 t~ailing edge let the eharging station. The home
27 position of the photoeonductor, which is now downstream
28 of the transfer station, now cycles through energized
.
LE97~009
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~C~7~3
i ~recle~t~ ch2rging station 16 at least twice prior
2 to stopping adjacent, ~or example, charging station
3 18. ~uriny this runout cycle, photoconductor 12
~ is subject to only the charging in~luence of preclean
charging station 16. As a result, the above mentioned
6 carrier particle, which is normally not easily removed
? by the cleaning station brush during a copy run,
8 is charged to the same polarity as the toner during
9 the runout cycle, i.e. a polarity opposite that
of the cleaning station, and is more easlly removed
11 from the photoconductor during this runout cycle.
12 It has been noted that the operation of
13 negative corona devices in a xerographic process tends
14 to generate hydroscopic salts which, if deposited on
the photoconductor, produce a thin conductive layer
whose lateral conductivity may undesirably result in
I7 partial discharge of the photoconductor's latent
18 image prior to developing. An additional benefit
19 realized by the present invention is that of minimiæing
exposure of the photoconductor to negative coro~a
21 emission during the runout cycle.
22 FIGURE 2 discloses, without limitation,
23 one form of a xerographic copying machine including~
24 the apparatus of FIGURE 1.
This particular machine employs a moving
26 original optical system 10 which is operable to
27 line-scan an original document and produce an image
28 thereo~ at imaging ~tation 11 adjacent photoconductor
7 7 ~, O O ~ 5 -
,
693
1 dr~. 12. This drum rotates in a clock~7ise direction,
2 driven by motor 13, and sequentially encounters
3 de~e]oping station 14, transfer station 15, preclean
~- cha~ge station 16, cleaning station 17 and charge
S station 18. In FIGURE 2, cleaning station 17 includes
6 a preclean lamp, not shown. A paper supply mechanism
7 supplies paper to sheet path 19, and a fuser control
8 network, not shown, cooperates to energize fuser
9 20 as toned paper passes therethrough.
The construction of the various above-
11 mentioned structures is not cri~ical to the present
12 invention. ~owever, cleaning station 17 is preferabIy
13 a triboelectric cIeaning station and may be of the
14 type described in U. S. Patent 3,682,689, issued
to R. L. Dueltgen et al. This patent describes
16 a triboelectric brush cieaner wherein the brush
li fibers are formed of materlal such as polytetrafluoro-
18 ethylene.
19 The developer station shown in FIGURE
2 is a cascade developer. However, the present
21 inven~ion is not limlted thereto and, for~example,
22 a magnetic brush developer such as shown in the
,
23 IB~ TF,CHNICAL DISCLOSVRE BULLETIN of September 1973,
24 ;~t pages 1251 and 1252, may be substituted therefor.
Charge corona 18 is preferably a grid
26 _on~ro11ed negative charge corona which is operated
27 to provide a negatively charged latent image area
2~ on dr~n photoconductor 12. Such a grid controlled
'.
LE974009 -16-
' :.
'
.. .. .
, . ' :. : : , : , . . . ,, ~
~L~7~3
1 charge corona is described in U. S. Pa-tent 3,736,424,
2 issued to T~ . Cecil et al.
3 The developer mix within developing sta~ion
4 14 is such that the carrier is triboelectrically
charged negative whereas the toner particles are
6 triboelectrically charged positive. A preferred
7 example of such a carrier is one carrying a coating
~ of polytetrafluoroethylene. If a magnetic brush
9 developer is employed, this coating covers a magnetic
carrier bead.
11 Transfer station 15 comprises a negative
12 ~transfer corona. The!-two negative coronas 18 and
13 15 may include emitting electrodes coated with a ~
14- thin inorganic dielectric, as described in U. S. ~`
Patent 3,789,278, issued to R. E. Blngham et al.
16 Preclean charge corona 16 provides positive charge
17 on the photoconductor. The charge sources 18, 15
.
18 and 16 function as above described~
19 Operation of the apparatus of FIGURE 2
is initiated by start button 21 after the copy counter
21 22 has been set to indicate the number of desired
22 copies. Sequencing control mechanism 23 is controlled
`23 -by the start signal and by the contents o the copy
24 counter, as well as by the output 24 of a drum position
2~ sensor 25 to se~uentially control the Yarious process-
26 ing stations of the apparatus, as above described.
27 For simplicity, the exact mechanism for controlling
28 these various devices is not disclosed. However,
:
I~E974009 17~
' ' '
': ' ' '~ ' . . ' ~
~7~3
1 it is usu~ t motor 13 provide the mechanical
2 power ~or scanning station 10, developing station
3 14, a paper movement rnechanism (not shown), and
4 cleaning station 17. This power is provided by
way of clutch and cam mechanisms, not shown. This
6 o~erative relationship is represented by control
7 lines emanating out of the sequencing control mechanism.
8 With reference to FIGURE 3, and considering
9 the runout cycle of the photoconductor, as above
described in greater detail, AND circuit 30 .operates
11 to sense the beginning of the runout cycle by the
12 coincidence o~ a signal on conductor 31 indicatin~
13 that copy counter 22 has reached a zero count (the
14 last copy is in the process of ~eing made) and a
signal on conductor 32 indicating that the trailing
16 edge of the last latent image is at transfer stati.on
17 15. Signal 32 is an.output of drum position sensox
18 25. When th~ beginning o~ the runout cycle is sensed,
19 conductor 33 is enabled to set latch 34. The output
of this latch, conductor 35, is operable to control
21 preclean corona 16 to maintaln this corona energized
22 and to deenergize transfer corona 15 and charge : .
23 corona 180 Photoconductor drum 12 continues to .
24 rotate for a given number.o~ rotations, as sensed
by axum position sensor 25. When this event is
26 sensed, conductor 36 is enabled to reset latch 34.
27 Drum 12 then conti.nues to rotate until it reaches
28 its home po~ition, as sensed by drum position sensor
LE974009 . ~18-
.
~ ~b'o'~ 3
1 25, whereupon sequenci.ng control mech~nism 23 is
2 contxo.lled to end the copy cycle of the apparatus
3 o~ FIG~ES 1 a.nd 2. As above described, t:his runout
~ cycle is operable to clean forei.gll material, such
as small particles of polytetrafluoroethylene which
may have been abraded o~f the carrier by the abrasive
7 operation of developer 14 and then deposited upon
8 photoconductor 12 as the photoconductor passes through
9 the developer.
Within the teachings of this invention,
11 the charge deposited on photoconductor~l2 by preclean
12 corona 16 may be increased as a result of the output
13 of latch 34, or alternatively, when the trailing
14 edge of the last latent imaye arrives at corona
16.
16 While the inve~tion haa been particularly
17 ~hown and described with reference to a preferred
18 embodiment thereof, it will be understood by those
19 skilled in the art that various changes in form
2p and details may be made therein without departing
21 from the spirit and scope of the invention.
22 What is ~la oed ~s:
', ' '
. ~
LEg74003 -19-
