CA1084770A - Image transfer unit for electrophotographic copying machines - Google Patents
Image transfer unit for electrophotographic copying machinesInfo
- Publication number
- CA1084770A CA1084770A CA262,851A CA262851A CA1084770A CA 1084770 A CA1084770 A CA 1084770A CA 262851 A CA262851 A CA 262851A CA 1084770 A CA1084770 A CA 1084770A
- Authority
- CA
- Canada
- Prior art keywords
- transfer
- toner
- cleaning
- transfer roller
- photosensitive member
- 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
Links
Classifications
-
- 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
- G03G15/14—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base
- G03G15/16—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer
- G03G15/1665—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer by introducing the second base in the nip formed by the recording member and at least one transfer member, e.g. in combination with bias or heat
- G03G15/167—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer by introducing the second base in the nip formed by the recording member and at least one transfer member, e.g. in combination with bias or heat at least one of the recording member or the transfer member being rotatable during the transfer
- G03G15/168—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer by introducing the second base in the nip formed by the recording member and at least one transfer member, e.g. in combination with bias or heat at least one of the recording member or the transfer member being rotatable during the transfer with means for conditioning the transfer element, e.g. cleaning
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G21/00—Arrangements not provided for by groups G03G13/00 - G03G19/00, e.g. cleaning, elimination of residual charge
- G03G21/0005—Arrangements not provided for by groups G03G13/00 - G03G19/00, e.g. cleaning, elimination of residual charge for removing solid developer or debris from the electrographic recording medium
- G03G21/0047—Arrangements not provided for by groups G03G13/00 - G03G19/00, e.g. cleaning, elimination of residual charge for removing solid developer or debris from the electrographic recording medium using electrostatic or magnetic means; Details thereof, e.g. magnetic pole arrangement of magnetic devices
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G2215/00—Apparatus for electrophotographic processes
- G03G2215/16—Transferring device, details
- G03G2215/1647—Cleaning of transfer member
- G03G2215/1652—Cleaning of transfer member of transfer roll
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Electrostatic Charge, Transfer And Separation In Electrography (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An image transfer unit provided with a cleaning device for use in an electrophotographic copying machine com-prises an electrically conductive transfer roller disposed in abutting relationship with a photosensitive member, an elec-trically conductive, rotatable cleaning device disposed in abutting relationship with the transfer roller, and electrical bias means connected with the cleaning device and having a switchable polarity. During a transfer step, a bias voltage of opposite polarity to that of the toner is applied to the trans-fer roller through the cleaning device. At this time, toner attaching to the transfer roller is electrostatically trans-ferred onto the cleaning device. During a cleaning step, a bias voltage of the same polarity as the toner is applied to the cleaning device, whereby the toner attaching thereto is transferred back to the photosensitive member through the transfer roller. The toner which is transferred back to the photosensitive member is removed by separate cleaner provided.
An image transfer unit provided with a cleaning device for use in an electrophotographic copying machine com-prises an electrically conductive transfer roller disposed in abutting relationship with a photosensitive member, an elec-trically conductive, rotatable cleaning device disposed in abutting relationship with the transfer roller, and electrical bias means connected with the cleaning device and having a switchable polarity. During a transfer step, a bias voltage of opposite polarity to that of the toner is applied to the trans-fer roller through the cleaning device. At this time, toner attaching to the transfer roller is electrostatically trans-ferred onto the cleaning device. During a cleaning step, a bias voltage of the same polarity as the toner is applied to the cleaning device, whereby the toner attaching thereto is transferred back to the photosensitive member through the transfer roller. The toner which is transferred back to the photosensitive member is removed by separate cleaner provided.
Description
BACKGROUND OF ~HE IN~NTION
The lnvention relates to an lmage transfer unit for use in an electrophotographic copying machine which incorporates a transfer roller to which a bias volt-age is applied.
An image transfer unit of the kind described ;
iB confronted with the problem of smearing of the back side of the transfer sheets that results from the deposi- ~ ;
tion on the surface o~ the transfer roller of a toner, - ;
which i~ floating in ~he internal space of the copying machine or which iB dri~en from non-image area~ on a photosensitive member. ~he deposlted toner contaminates th¢ back ~ur$ace of the transfer sheet which is held between the photosen-sitive member and the transfer roller during the image transfer step. Therefore, it 19 nece~sary to pro~ide some cleanlng unit for removln~ toner which 1B depo~ited on the tran~fer roller ~n order to pre~ent a ~mearing of the .
back side of the transfer sheet. ; `;
Conventional means for cleaning the trans-fer roller comprises a blade which i8 brought into abutting relatlon~hip therewith to ~crape any toner therefrom, or comprises a rotatable brush which i8 urged against the transfer roller to wipe off any toner thereon. These ~:
arrangements require some form of toner processing means which collects the separated toner or which prevents re~
deposition of the separated toner onto the transfer roller. ;~; ~
: , SUMM~RY OF THE IN~EN~ION ~ ~
.
In accordance with the invention, there 1s provided an image trans~er unit which comprises a~
The lnvention relates to an lmage transfer unit for use in an electrophotographic copying machine which incorporates a transfer roller to which a bias volt-age is applied.
An image transfer unit of the kind described ;
iB confronted with the problem of smearing of the back side of the transfer sheets that results from the deposi- ~ ;
tion on the surface o~ the transfer roller of a toner, - ;
which i~ floating in ~he internal space of the copying machine or which iB dri~en from non-image area~ on a photosensitive member. ~he deposlted toner contaminates th¢ back ~ur$ace of the transfer sheet which is held between the photosen-sitive member and the transfer roller during the image transfer step. Therefore, it 19 nece~sary to pro~ide some cleanlng unit for removln~ toner which 1B depo~ited on the tran~fer roller ~n order to pre~ent a ~mearing of the .
back side of the transfer sheet. ; `;
Conventional means for cleaning the trans-fer roller comprises a blade which i8 brought into abutting relatlon~hip therewith to ~crape any toner therefrom, or comprises a rotatable brush which i8 urged against the transfer roller to wipe off any toner thereon. These ~:
arrangements require some form of toner processing means which collects the separated toner or which prevents re~
deposition of the separated toner onto the transfer roller. ;~; ~
: , SUMM~RY OF THE IN~EN~ION ~ ~
.
In accordance with the invention, there 1s provided an image trans~er unit which comprises a~
- 2 - ; ;
.~ . . - -~.~, . .. . .
4~7 0 electrically conductive image transfer roller di~po~ed in abuttlng relationship with a photosen~itlve member~
an electrically conductlve, rotatable cleaning means dis-posed in abuttin~ relation~hip with the $mage transfer roller, and electrical bias means connected with the clean ing means and having a switchable polarity. Durlng an image transfer Btep~ a bias ~oltage i8 applied to the tran~-fer roller of the opposite polarity ~rom that of the toner which forms the visual image, causing the visual image to be trans~erred onto a copy ~heet. ~oner attachlng to the transfer roller i9 electrostatically transferred onto the cleaning meanR. During a cleanlng step 3 a bias ~oltage of the same polarity as the toner i8 applled to the cleaning means to transfer the toner which attaches to the cleanl~g means back to the photosensitive member through the trans-fer roller. Slnce the photo6ensitive member i8 chsrged to the o~posite polarity from the toner, lt reaaily attracts the toner. The toner which is transferred back to the photosensitive member is removed ~y a further cleaning unit which ls associated wlth the photosensitive member. In thls manner, the image transfer unlt according to the lnventlon represents simple mean~ which reliably removes any toner attaching to the transfer roller.
~here~ore, lt is an obJect of the inven-tion to provide an lmpro~ed image transfer unit having cleaning mean~ associated wlth an image transfer roller.
It i8 another ob~ect of the ln~ention to pro~ide an image trans~er unit of the kind described which iB eimple ln con~truction and capable of reliably removi~g a~y toner attaching to t~e transfer roller.
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More particularly, there is provided:
A transfer unit for use in an electrophotographic copying machine of the type having a photosensitive member on which a toner image is formed said unit comprising:
electrically conductive transfer roller means for pressing a transfer sheet against the photosensitive member for ~
transferring a toner image formed on the photosensitive member : ~:
onto said transfer sheet;
electrically conductive, rotatable cleaning means .
disposed in abutting relationship with the transfer roller means, for cleaning toner therefrom;
electrical bias means for producing a bias voltage of switcnable polarity; and switching means, connecting said bias means to sai~ ~:
cleaning means during the transfer of the toner image onto the transfer sheet, for applying a bias voltage of the opposite polarity from that of the toner to the transfer roller means `
through the cleaning means, such that the toner attaching to the transfer roller means is electrostatically transferred to the : 20 cleaning means to clean the transfer roller means, and after completion of an image transfer step, for switching the bias voltage applied to the cleaning means to the same polarity as that o~ the toner to transfer the toner attaching to the clean-ing means back to the photosensitive member through the transfer ~ -;
roller means, thus cleaning both the cleaning means and the tran- :
trans~er roller means. .. .
..' ,~. ' -~,:
. ~ . " ~ .
~ -3a-31L~B4~70 There is also provided: ~
A transfer unit for use in an electrophotographic copying machine of the type having a photosensitlve member on which a toner image is formed, said unit comprising:
electrically-conductive transfer roller means for pressing a transfer sheet against the photosensitive member ~o transfer a toner image formed on the photosensitive member onto said transfer sheet;
electrically-conductive rotatable cleaning means disposed in abutting relationship with the toner transfer rol-ler means, for cleaning toner therefrom;
first means for connecting a first bias voltage of switchable polarity to said transfer roller means;
second means for connecting a second bias voltage of switchable polarity to said cleaning means, said second bias voltage being greater than said first bias voltage; and switching means, connectea to said first and second connecting means, for applying said first and second bias vol-tages with a polari~y~opposite to that of the toner respectively to said transfer roller means and said cleaning means such that the toner attaching to the transfer roller means is electro-statically transferred to the cleaning means to clean the trans-fer roller means during the transfer of the toner image onto the transfer sheet, and after completion of an image transfer step, ~;
for applying said first and second bias voltages with the same polar.ity as that of the toner respectively to said transfer roller means and said cleaning means back to the photosensitive member th~ough the transfer roller means, thus cleaning both the .
cleaning means and the transfer roller me.~ns. :~
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The above and other ob jects of the invention will become apparent as the description proceeds with reference to the drawing~.
_RIEF DESCRIITION OF THE_DRAWINGS ~ , ~ig. 1 1B a schematic view of one embodi-ment of the invention;
Fig. 2 is a ~ragmentary perspective view of the embodiment shown in Fig. l;
Fig. 3 is a circuit diagram showing the electrical equivalent circuit of the embodiment shown in Figs. 1 and 2;
Fig. 4 is a ~chematic illustration, graph-ically showing the transfer of toner between the cleaning roller and the transfer roller;
Fig. 5 graphically shows the proportion of the transferred.toner as a function of the resistance of the cleanlng roller; ~ `
~igs. 6 and 7 are schematic views illustrat- ;i :;.
ing other embodiments of the invention; and Fig. 8 is a circuit diagram showing the equivalent clrcuit of the embodiment shown in Fig. 7.
.:' ` : ' DE~AI~ED DESCRIPTION 0~ PREFERRED EMBODIM~NTS
Referring to Fig. 1, there i~ shown a photosensitive member 2 in the form of a belt which carriee . : .
a developed toner image 1 thereon. ~he belt 2 i9 adapted ~ .
to be driven by a,grounded roller 3 to run along a path ~ :
indicated by appropriate arrows, which includes an image tranS~e roller 5. A blae ~oltage o~ the opposite polarlty from 4 ~ ~ ~
';`, ,~ ,.
8~
that of the toner ls applied to the transf~r roller 5, and as a portion of the belt whlch carrlea the toner image approaches the transfer roller 5, a transfer ~heet 4 is fed into superimposed and abutting relationshlp with the belt, whereby the toner image 1 is transferred onto the transfer sheet 4.
The lmage transfer roller 5 comprises a :;
metallic roller having lts surface coated with an ~lec-trically conduct.ive rubber material, and a bias voltage 0 lS applied thereto through a cleaning roller 6 having a similar surface coating of an electrically conductive rubber mate-rial which i8 disposed ln abutting relationship with the surface of the transfer roller 5. The cleanlng roller 6 ~ is connected to either of a pair of d-c. high voltage sources 7, 8 of oppoqite polaritie~ through a switch 9. The cleaning roller 6 has a diameter which i9 reduced as compared with the diameter of the transfer roller 5 so that contact ~ .
occurs therebetween at varying point~ during the rotation thereof. :
Fig~ 2 1~ a fragmentary perspective view showing a specific con~truetion. The trans~er roller 5 is mounted on a metal shaft 5a which 1R mounted ln a pair of insulating sideplates 12 of a transfer unit by means of bearings 13. ~he cleaning roller 6 has it~ support :
shaft also rotatably mounted in the sideplates 12 by means ~ ~:
of bearings 14, whlch however are dlsplaceably mounted.
An electrically conductive ~-shaped lever 15 is rockably mounted on one o~ the sideplates 12 by a ~crew 16, and a coiled tension spring 18 is disposed between an opening 15a formed in the end of one limb of the le~er 15 and a - 5 - :
~084770 Rcrew 17 fixed to the ~ideplate 12, thus urg1ng the lever 15 to rotate clockwise about the ~cr~w 16. The other limb of the lever 15 engages a groove 14a formed ln the bearing 14 and is thus biased by the spring 18 to urge the cleaning roller into abutting engagement with the transfer roller 5. One end of a lead wire 19 is secured to the le~er 15 by a set screw 20, and the other end of the lead wire 19 is connected with a power supply assembly 21. ~he ~ransfer unit also includes a cover 22 whlch also serves a~
a guide for the transfer sheets when separated from the transfer roller 5.
Fig. 3 shows the electrical equivalent c~rcuit of the above embodiment. A character R2 represent~
the resistance of the cleaning roller which i9 8ubgtan-tially equal to or greater than the resl~tance Rl of the transfer roller. As a consequence, when a bias voltage i~ applied from the cleaning roller to the transfer roller during an image transfer step, and a portion of the developer toner on the photosensiti~e member which lie8 out~ide the reg~on of a transfer cheet lnitially attaches to the trans-fer roller, the tonerwhich attaches to the transfer roller is then direct}y transferred, for the most part, to the cleaning roller because of the relative magnitudes of the resistances of the transfer roller and the cleaning ;
Z5 roller, and accordingly the greater attraction of the higher vol-tage on the cleaning roller than that on the transfer roller (it will be appreciated that the voltage on the cleaning roller will `
be still higher by an amount corresponding to the voltage drop when both are of the same resistance). As a result, the toner which remains attached to the transfer roller i8 ~;
~70 considerably reduced, thereby effectively preventing a smearing of the back 6urface of the transfer sheet by con-tact with the transfer roller.
After completion of an ~mage transfer step, the bias voltage is changed by switch 9 to the opposite polarity from the polarity utilized during the transfer step, that is to the same polarity as the toner. Thereupon, the toner attaching to the cleaning roller will be transferred to the lower ~oltage transfer roller and then to the photosensitive member which is charged to the same polarity as the toner, whereby the surface of both the transfer roller and the cleaning roller will revert to the clean condition which they assumed before the transfer step took place. The toner attaching to the photosen~itive member lc carried thereon to a cleaning station where it i6 removed ~rom the surface of the photosensitive member.
In the above embodiment, the cleanlng roller has a resistance which is greater than or substantially equal to the resistance of the transfer roller. However, thi8 is not essential~ and the cleaning roller may have a resi~tance which i9 less than that of the transfer ro~ler.
~he reason ~or this will be understood by reference to Fig. 4 where it will be noted that there exists a very thin air layer A ln the region of contaot between the tranRfer `
roller ~ and the cleaning roller 6, and a voltage drop VD
acro~s the resiBtance of the air layer A and the resistance Of the olean~ng roller 6 produce~ an attraction of the toner. Such an air layer will be eliminated when both rollers are urged agal~st each other with a pressure on the order of several ~ilograms per square centimeter7 but ~ ' ;- ,: . . - .:
.. . . .
~01~77~
remains or is maintained when a normal pressure of one kilo-gram per square centimeter is employed. As a consequence, lt can be said that the transfer of the toner from the transfer roller ~ to the cleaning roller 6 takes place independently from the resistance of the tran~fer roller 5 ana i9 ~olely determined by the resistance o~ the ~leaning roller 6. ;~
Referring to Fig. 5, it will be seen that when the resistance of the cleani~g roller i~ too low a~ ~
will be the oase with a metallic roller, the proportion i of transferred toner wlll be reduced. It fOllOWB therefore ~;
that a roller having a certain high value of resistance, such as a roller of an electrically conductive rubber, i8 preferred. However, an excesBively high resistance re~ults ln charging the roller surface, again reducing the propor- ;
tion of transferred toner.
Fig. 6 shows an arrangement for another embodiment of the invention. This embodiment differs `
from the ~irst mentioned embodiment ln that the cleaning roller is replaced by an a~sembly comprising a palr of electrically conduotive (metallic) roller~ 31 and 32, and a belt 33 formed of an electrically oonducti~e rubber which extend~ around these rollers 31, 32. The conductive roller 32 i8 connected with a pair of d.c. high blas ~olt-age sources 34, 35 of opposite polarities through a switch 36. The function of these elements is similar to those -mentio~ed above and therefore will not be repeated.
Fig. 7 shows an arrangement which represents a further embodiment of the inYention. In this embodiment9 a bias voltage 1~ applied to the transfer roller through a cleaning roller and al60 through a separate resistor R3 in order to prevent any significant change 1n the bia~
voltage applied to the transfer roller or a resulting degradation in the transfer efficiency i~ the event the resistance of the roller undergoe3 a conslderable change as re~ult of the deposition of the toner onto the tran~er roller and ~he cleaning roller. The electrical equi~alent circuit i~ shown ~n Fig. 8, where lt will be noted that the re~i~tance Rl of the transfer roller and the resistance R2 ~ the cleaning roller will vary as the to~er atta¢hes to the roller surface, with a corre~pond~ng cha~ge ln the bia~ ~oltage ~pplied. Since the lnitlal value of the bias ~oltage is cho~en 80 as to provide an optimum transfer efflclency, a change of the bia~ voltage from such value implieQ a reduction ln the image transfer e~ficlency. ~he connectlon of the re~istance R3 between the tran~fer roller and the blas source will compensate for any change ln the ~alue~ of the resistance Rl and the resistance R2 ~ as to malntain the bia~ ~oltage in a range which pre~ents a ~
reduction ln the lmage transfer efficiency. `
In the three embodiments described above, the photosensitive member u~ed is in the rOrm of a belt, but it should.be und~rstood that a drum-~haped photosen-sitive member may be used as well. The polarity of the bias voltage is determined by the characteris-tic o~ the photoconduative film on the photosensitive member used. Where a ~elenic photo3e~sltlve member i~
u6ed, lt is rharged to the positlve polarity when the mem-ber l~ unifor~ly charged, 80 that the bias voltage during ~0 the trans~er atep l~ al~o of the poslt~e polarity and i8 ,,.,.................... . ' ~
.
lOB4770 :, switched to the negatl~e polarity during the cleaning etep.
Conversely, when the photosensitive member compri~es a material such as 2inc oxide, it is charged to the negative polarity inltially, ~o that the bia~ voltage applied during the transfer ~tep will be of the negative polarity and 1R
switched to the poslti~e polarity duri~g the cleaning step.
In the above description, thP back transfer , ~ , .
of the toner which attaches to the cleaning means to the photosensitive member 1s performed ~ubseque~t to the com~
pletion o~ the image transfer, but may be performed after .i .
the termination of a copying cycle or cycles.
.:
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~ ~ ,. . . .. .. .
.~ . . - -~.~, . .. . .
4~7 0 electrically conductive image transfer roller di~po~ed in abuttlng relationship with a photosen~itlve member~
an electrically conductlve, rotatable cleaning means dis-posed in abuttin~ relation~hip with the $mage transfer roller, and electrical bias means connected with the clean ing means and having a switchable polarity. Durlng an image transfer Btep~ a bias ~oltage i8 applied to the tran~-fer roller of the opposite polarity ~rom that of the toner which forms the visual image, causing the visual image to be trans~erred onto a copy ~heet. ~oner attachlng to the transfer roller i9 electrostatically transferred onto the cleaning meanR. During a cleanlng step 3 a bias ~oltage of the same polarity as the toner i8 applled to the cleaning means to transfer the toner which attaches to the cleanl~g means back to the photosensitive member through the trans-fer roller. Slnce the photo6ensitive member i8 chsrged to the o~posite polarity from the toner, lt reaaily attracts the toner. The toner which is transferred back to the photosensitive member is removed ~y a further cleaning unit which ls associated wlth the photosensitive member. In thls manner, the image transfer unlt according to the lnventlon represents simple mean~ which reliably removes any toner attaching to the transfer roller.
~here~ore, lt is an obJect of the inven-tion to provide an lmpro~ed image transfer unit having cleaning mean~ associated wlth an image transfer roller.
It i8 another ob~ect of the ln~ention to pro~ide an image trans~er unit of the kind described which iB eimple ln con~truction and capable of reliably removi~g a~y toner attaching to t~e transfer roller.
~ - 3 - -~' ~
, ~ , . , ., 7~
More particularly, there is provided:
A transfer unit for use in an electrophotographic copying machine of the type having a photosensitive member on which a toner image is formed said unit comprising:
electrically conductive transfer roller means for pressing a transfer sheet against the photosensitive member for ~
transferring a toner image formed on the photosensitive member : ~:
onto said transfer sheet;
electrically conductive, rotatable cleaning means .
disposed in abutting relationship with the transfer roller means, for cleaning toner therefrom;
electrical bias means for producing a bias voltage of switcnable polarity; and switching means, connecting said bias means to sai~ ~:
cleaning means during the transfer of the toner image onto the transfer sheet, for applying a bias voltage of the opposite polarity from that of the toner to the transfer roller means `
through the cleaning means, such that the toner attaching to the transfer roller means is electrostatically transferred to the : 20 cleaning means to clean the transfer roller means, and after completion of an image transfer step, for switching the bias voltage applied to the cleaning means to the same polarity as that o~ the toner to transfer the toner attaching to the clean-ing means back to the photosensitive member through the transfer ~ -;
roller means, thus cleaning both the cleaning means and the tran- :
trans~er roller means. .. .
..' ,~. ' -~,:
. ~ . " ~ .
~ -3a-31L~B4~70 There is also provided: ~
A transfer unit for use in an electrophotographic copying machine of the type having a photosensitlve member on which a toner image is formed, said unit comprising:
electrically-conductive transfer roller means for pressing a transfer sheet against the photosensitive member ~o transfer a toner image formed on the photosensitive member onto said transfer sheet;
electrically-conductive rotatable cleaning means disposed in abutting relationship with the toner transfer rol-ler means, for cleaning toner therefrom;
first means for connecting a first bias voltage of switchable polarity to said transfer roller means;
second means for connecting a second bias voltage of switchable polarity to said cleaning means, said second bias voltage being greater than said first bias voltage; and switching means, connectea to said first and second connecting means, for applying said first and second bias vol-tages with a polari~y~opposite to that of the toner respectively to said transfer roller means and said cleaning means such that the toner attaching to the transfer roller means is electro-statically transferred to the cleaning means to clean the trans-fer roller means during the transfer of the toner image onto the transfer sheet, and after completion of an image transfer step, ~;
for applying said first and second bias voltages with the same polar.ity as that of the toner respectively to said transfer roller means and said cleaning means back to the photosensitive member th~ough the transfer roller means, thus cleaning both the .
cleaning means and the transfer roller me.~ns. :~
':
.''"':
... . ,. : . . ; ~ ~ - , . . .. .. .. . . . . .
~L~8~7~1~
The above and other ob jects of the invention will become apparent as the description proceeds with reference to the drawing~.
_RIEF DESCRIITION OF THE_DRAWINGS ~ , ~ig. 1 1B a schematic view of one embodi-ment of the invention;
Fig. 2 is a ~ragmentary perspective view of the embodiment shown in Fig. l;
Fig. 3 is a circuit diagram showing the electrical equivalent circuit of the embodiment shown in Figs. 1 and 2;
Fig. 4 is a ~chematic illustration, graph-ically showing the transfer of toner between the cleaning roller and the transfer roller;
Fig. 5 graphically shows the proportion of the transferred.toner as a function of the resistance of the cleanlng roller; ~ `
~igs. 6 and 7 are schematic views illustrat- ;i :;.
ing other embodiments of the invention; and Fig. 8 is a circuit diagram showing the equivalent clrcuit of the embodiment shown in Fig. 7.
.:' ` : ' DE~AI~ED DESCRIPTION 0~ PREFERRED EMBODIM~NTS
Referring to Fig. 1, there i~ shown a photosensitive member 2 in the form of a belt which carriee . : .
a developed toner image 1 thereon. ~he belt 2 i9 adapted ~ .
to be driven by a,grounded roller 3 to run along a path ~ :
indicated by appropriate arrows, which includes an image tranS~e roller 5. A blae ~oltage o~ the opposite polarlty from 4 ~ ~ ~
';`, ,~ ,.
8~
that of the toner ls applied to the transf~r roller 5, and as a portion of the belt whlch carrlea the toner image approaches the transfer roller 5, a transfer ~heet 4 is fed into superimposed and abutting relationshlp with the belt, whereby the toner image 1 is transferred onto the transfer sheet 4.
The lmage transfer roller 5 comprises a :;
metallic roller having lts surface coated with an ~lec-trically conduct.ive rubber material, and a bias voltage 0 lS applied thereto through a cleaning roller 6 having a similar surface coating of an electrically conductive rubber mate-rial which i8 disposed ln abutting relationship with the surface of the transfer roller 5. The cleanlng roller 6 ~ is connected to either of a pair of d-c. high voltage sources 7, 8 of oppoqite polaritie~ through a switch 9. The cleaning roller 6 has a diameter which i9 reduced as compared with the diameter of the transfer roller 5 so that contact ~ .
occurs therebetween at varying point~ during the rotation thereof. :
Fig~ 2 1~ a fragmentary perspective view showing a specific con~truetion. The trans~er roller 5 is mounted on a metal shaft 5a which 1R mounted ln a pair of insulating sideplates 12 of a transfer unit by means of bearings 13. ~he cleaning roller 6 has it~ support :
shaft also rotatably mounted in the sideplates 12 by means ~ ~:
of bearings 14, whlch however are dlsplaceably mounted.
An electrically conductive ~-shaped lever 15 is rockably mounted on one o~ the sideplates 12 by a ~crew 16, and a coiled tension spring 18 is disposed between an opening 15a formed in the end of one limb of the le~er 15 and a - 5 - :
~084770 Rcrew 17 fixed to the ~ideplate 12, thus urg1ng the lever 15 to rotate clockwise about the ~cr~w 16. The other limb of the lever 15 engages a groove 14a formed ln the bearing 14 and is thus biased by the spring 18 to urge the cleaning roller into abutting engagement with the transfer roller 5. One end of a lead wire 19 is secured to the le~er 15 by a set screw 20, and the other end of the lead wire 19 is connected with a power supply assembly 21. ~he ~ransfer unit also includes a cover 22 whlch also serves a~
a guide for the transfer sheets when separated from the transfer roller 5.
Fig. 3 shows the electrical equivalent c~rcuit of the above embodiment. A character R2 represent~
the resistance of the cleaning roller which i9 8ubgtan-tially equal to or greater than the resl~tance Rl of the transfer roller. As a consequence, when a bias voltage i~ applied from the cleaning roller to the transfer roller during an image transfer step, and a portion of the developer toner on the photosensiti~e member which lie8 out~ide the reg~on of a transfer cheet lnitially attaches to the trans-fer roller, the tonerwhich attaches to the transfer roller is then direct}y transferred, for the most part, to the cleaning roller because of the relative magnitudes of the resistances of the transfer roller and the cleaning ;
Z5 roller, and accordingly the greater attraction of the higher vol-tage on the cleaning roller than that on the transfer roller (it will be appreciated that the voltage on the cleaning roller will `
be still higher by an amount corresponding to the voltage drop when both are of the same resistance). As a result, the toner which remains attached to the transfer roller i8 ~;
~70 considerably reduced, thereby effectively preventing a smearing of the back 6urface of the transfer sheet by con-tact with the transfer roller.
After completion of an ~mage transfer step, the bias voltage is changed by switch 9 to the opposite polarity from the polarity utilized during the transfer step, that is to the same polarity as the toner. Thereupon, the toner attaching to the cleaning roller will be transferred to the lower ~oltage transfer roller and then to the photosensitive member which is charged to the same polarity as the toner, whereby the surface of both the transfer roller and the cleaning roller will revert to the clean condition which they assumed before the transfer step took place. The toner attaching to the photosen~itive member lc carried thereon to a cleaning station where it i6 removed ~rom the surface of the photosensitive member.
In the above embodiment, the cleanlng roller has a resistance which is greater than or substantially equal to the resistance of the transfer roller. However, thi8 is not essential~ and the cleaning roller may have a resi~tance which i9 less than that of the transfer ro~ler.
~he reason ~or this will be understood by reference to Fig. 4 where it will be noted that there exists a very thin air layer A ln the region of contaot between the tranRfer `
roller ~ and the cleaning roller 6, and a voltage drop VD
acro~s the resiBtance of the air layer A and the resistance Of the olean~ng roller 6 produce~ an attraction of the toner. Such an air layer will be eliminated when both rollers are urged agal~st each other with a pressure on the order of several ~ilograms per square centimeter7 but ~ ' ;- ,: . . - .:
.. . . .
~01~77~
remains or is maintained when a normal pressure of one kilo-gram per square centimeter is employed. As a consequence, lt can be said that the transfer of the toner from the transfer roller ~ to the cleaning roller 6 takes place independently from the resistance of the tran~fer roller 5 ana i9 ~olely determined by the resistance o~ the ~leaning roller 6. ;~
Referring to Fig. 5, it will be seen that when the resistance of the cleani~g roller i~ too low a~ ~
will be the oase with a metallic roller, the proportion i of transferred toner wlll be reduced. It fOllOWB therefore ~;
that a roller having a certain high value of resistance, such as a roller of an electrically conductive rubber, i8 preferred. However, an excesBively high resistance re~ults ln charging the roller surface, again reducing the propor- ;
tion of transferred toner.
Fig. 6 shows an arrangement for another embodiment of the invention. This embodiment differs `
from the ~irst mentioned embodiment ln that the cleaning roller is replaced by an a~sembly comprising a palr of electrically conduotive (metallic) roller~ 31 and 32, and a belt 33 formed of an electrically oonducti~e rubber which extend~ around these rollers 31, 32. The conductive roller 32 i8 connected with a pair of d.c. high blas ~olt-age sources 34, 35 of opposite polarities through a switch 36. The function of these elements is similar to those -mentio~ed above and therefore will not be repeated.
Fig. 7 shows an arrangement which represents a further embodiment of the inYention. In this embodiment9 a bias voltage 1~ applied to the transfer roller through a cleaning roller and al60 through a separate resistor R3 in order to prevent any significant change 1n the bia~
voltage applied to the transfer roller or a resulting degradation in the transfer efficiency i~ the event the resistance of the roller undergoe3 a conslderable change as re~ult of the deposition of the toner onto the tran~er roller and ~he cleaning roller. The electrical equi~alent circuit i~ shown ~n Fig. 8, where lt will be noted that the re~i~tance Rl of the transfer roller and the resistance R2 ~ the cleaning roller will vary as the to~er atta¢hes to the roller surface, with a corre~pond~ng cha~ge ln the bia~ ~oltage ~pplied. Since the lnitlal value of the bias ~oltage is cho~en 80 as to provide an optimum transfer efflclency, a change of the bia~ voltage from such value implieQ a reduction ln the image transfer e~ficlency. ~he connectlon of the re~istance R3 between the tran~fer roller and the blas source will compensate for any change ln the ~alue~ of the resistance Rl and the resistance R2 ~ as to malntain the bia~ ~oltage in a range which pre~ents a ~
reduction ln the lmage transfer efficiency. `
In the three embodiments described above, the photosensitive member u~ed is in the rOrm of a belt, but it should.be und~rstood that a drum-~haped photosen-sitive member may be used as well. The polarity of the bias voltage is determined by the characteris-tic o~ the photoconduative film on the photosensitive member used. Where a ~elenic photo3e~sltlve member i~
u6ed, lt is rharged to the positlve polarity when the mem-ber l~ unifor~ly charged, 80 that the bias voltage during ~0 the trans~er atep l~ al~o of the poslt~e polarity and i8 ,,.,.................... . ' ~
.
lOB4770 :, switched to the negatl~e polarity during the cleaning etep.
Conversely, when the photosensitive member compri~es a material such as 2inc oxide, it is charged to the negative polarity inltially, ~o that the bia~ voltage applied during the transfer ~tep will be of the negative polarity and 1R
switched to the poslti~e polarity duri~g the cleaning step.
In the above description, thP back transfer , ~ , .
of the toner which attaches to the cleaning means to the photosensitive member 1s performed ~ubseque~t to the com~
pletion o~ the image transfer, but may be performed after .i .
the termination of a copying cycle or cycles.
.:
~,. . .
' ' ' ,' .
'; .:'~
' ~ "
:.
- 10 ~
,~ :
~ ~ ,. . . .. .. .
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A transfer unit for use in an electrophotographic copying machine of the type having a photosensitive member on which a toner image is formed said unit comprising:
electrically conductive transfer roller means for pressing a transfer sheet against the photosensitive member for transferring a toner image formed on the photosensitive member onto said transfer sheet;
electrically conductive, rotatable cleaning means disposed in abutting relationship with the transfer roller means, for cleaning toner therefrom;
electrical bias means for producing a bias voltage of switchable polarity; and switching means, connecting said bias means to said cleaning means during the transfer of the toner image onto the transfer sheet, for applying a bias voltage of the opposite polarity from that of the toner to the transfer roller means through the cleaning means, such that the toner attaching to the transfer roller means is electrostatically transferred to the cleaning means to clean the transfer roller means, and after completion of an image transfer step, for switching the bias voltage applied to the cleaning means to the same polarity as that of the toner to transfer the toner attaching to the clean-ing means back to the photosensitive member through the transfer roller means, thus cleaning both the cleaning means and the tran-transfer roller means.
electrically conductive transfer roller means for pressing a transfer sheet against the photosensitive member for transferring a toner image formed on the photosensitive member onto said transfer sheet;
electrically conductive, rotatable cleaning means disposed in abutting relationship with the transfer roller means, for cleaning toner therefrom;
electrical bias means for producing a bias voltage of switchable polarity; and switching means, connecting said bias means to said cleaning means during the transfer of the toner image onto the transfer sheet, for applying a bias voltage of the opposite polarity from that of the toner to the transfer roller means through the cleaning means, such that the toner attaching to the transfer roller means is electrostatically transferred to the cleaning means to clean the transfer roller means, and after completion of an image transfer step, for switching the bias voltage applied to the cleaning means to the same polarity as that of the toner to transfer the toner attaching to the clean-ing means back to the photosensitive member through the transfer roller means, thus cleaning both the cleaning means and the tran-transfer roller means.
2. A transfer unit according to claim 1 in which the cleaning means has a peripheral length which is different from the peripheral length of the transfer roller means, thereby pre-venting the toner attaching to the transfer roller means from being concentratedly deposited on a particular location on the surface of the cleaning means.
3. A transfer unit according to claim 1 in which the bias means comprises a compensation resistor.
4. A transfer unit according to claim 1, 2, or 3 in which the cleaning means comprises a surface formed of an electrically conductive rubber.
5. A transfer unit according to claim 1, 2, or 3 in which the cleaning means comprises a roller.
6. A transfer unit according to claim 1, 2, or 3 in which the cleaning means comprises an endless belt extending around rollers.
7. A transfer unit for use in an electrophotographic copying machine of the type having a photosensitive member on which a toner image is formed, said unit comprising:
electrically-conductive transfer roller means for pressing a transfer sheet against the photosensitive member to transfer a toner image formed on the photosensitive member onto said transfer sheet;
electrically-conductive rotatable cleaning means disposed in abutting relationship with the toner transfer rol-ler means, for cleaning toner therefrom;
first means for connecting a first bias voltage of switchable polarity to said transfer roller means;
second means for connecting a second bias voltage of switchable polarity to said cleaning means, said second bias voltage being greater than said first bias voltage; and switching means, connected to said first and second connecting means, for applying said first and second bias vol-tages with a polarity opposite to that of the toner respectively to said transfer roller means and said cleaning means such that the toner attaching to the transfer roller means is electro-statically transferred to the cleaning means to clean the trans-fer roller means during the transfer of the toner image onto the transfer sheet, and after completion of an image transfer step, for applying said first and second bias voltages with the same polarity as that of the toner respectively to said transfer roller means and said cleaning means back to the photosensitive member through the transfer roller means, thus cleaning both the cleaning means and the transfer roller means.
electrically-conductive transfer roller means for pressing a transfer sheet against the photosensitive member to transfer a toner image formed on the photosensitive member onto said transfer sheet;
electrically-conductive rotatable cleaning means disposed in abutting relationship with the toner transfer rol-ler means, for cleaning toner therefrom;
first means for connecting a first bias voltage of switchable polarity to said transfer roller means;
second means for connecting a second bias voltage of switchable polarity to said cleaning means, said second bias voltage being greater than said first bias voltage; and switching means, connected to said first and second connecting means, for applying said first and second bias vol-tages with a polarity opposite to that of the toner respectively to said transfer roller means and said cleaning means such that the toner attaching to the transfer roller means is electro-statically transferred to the cleaning means to clean the trans-fer roller means during the transfer of the toner image onto the transfer sheet, and after completion of an image transfer step, for applying said first and second bias voltages with the same polarity as that of the toner respectively to said transfer roller means and said cleaning means back to the photosensitive member through the transfer roller means, thus cleaning both the cleaning means and the transfer roller means.
8. A transfer unit as in claim 7 wherein said clean-ing means has a peripheral length which is different from the peripheral length of the transfer roller means, thereby pre-venting the toner attaching to the transfer roller means from being concentratedly deposited on a particular location on the surface of the cleaning means.
9. A transfer unit as in claim 7 wherein said first bias means comprises a compensation resistor.
10. A transfer unit according to claim 7 wherein said cleaning means comprises a surface formed of an electrically-conductive rubber.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12095075A JPS5245344A (en) | 1975-10-07 | 1975-10-07 | Transfer device for electrophotographic copying machine |
| JP120950/75 | 1975-10-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1084770A true CA1084770A (en) | 1980-09-02 |
Family
ID=14798977
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA262,851A Expired CA1084770A (en) | 1975-10-07 | 1976-10-06 | Image transfer unit for electrophotographic copying machines |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5245344A (en) |
| CA (1) | CA1084770A (en) |
| DE (1) | DE2645379C3 (en) |
| FR (1) | FR2327581A1 (en) |
| GB (1) | GB1552483A (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57142673A (en) * | 1981-02-27 | 1982-09-03 | Sharp Corp | Cleaning method |
| JPS5834476A (en) * | 1981-08-24 | 1983-02-28 | Konishiroku Photo Ind Co Ltd | Method and device for cleaning of developer |
| US4490033A (en) * | 1983-04-28 | 1984-12-25 | Xerox Corporation | Reproducing apparatus with scrolled imaging web |
| US10372071B2 (en) | 2016-08-30 | 2019-08-06 | Canon Kabushiki Kaisha | Image forming apparatus |
| WO2018042893A1 (en) * | 2016-08-30 | 2018-03-08 | キヤノン株式会社 | Image forming device |
| JP7039193B2 (en) * | 2016-08-30 | 2022-03-22 | キヤノン株式会社 | Image forming device |
-
1975
- 1975-10-07 JP JP12095075A patent/JPS5245344A/en active Pending
-
1976
- 1976-09-29 GB GB4033276A patent/GB1552483A/en not_active Expired
- 1976-10-06 CA CA262,851A patent/CA1084770A/en not_active Expired
- 1976-10-06 FR FR7630077A patent/FR2327581A1/en active Granted
- 1976-10-07 DE DE19762645379 patent/DE2645379C3/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FR2327581A1 (en) | 1977-05-06 |
| FR2327581B1 (en) | 1982-09-10 |
| DE2645379A1 (en) | 1977-04-14 |
| DE2645379B2 (en) | 1978-11-16 |
| JPS5245344A (en) | 1977-04-09 |
| DE2645379C3 (en) | 1979-07-19 |
| GB1552483A (en) | 1979-09-12 |
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| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |