CA2105255C - Electrophotographic apparatus that prevents toner from attaching to a contact member of a transfer device - Google Patents

Abstract

At start of rotation of a photosensitive drum, rotation of a developing roller caused by a developing/
register rollers driver is kept stopped until a time required for a predetermined point on the photosensitive member, which was located at a charging position when charging thereof by a charging device was started, to reach a development position elapses, and thereafter the developing roller is rotated by the developing/register rollers driver. When the predetermined point on the photosensitive member, which was located at the developing position when at least rotation of the photosensitive member was started, passes the transfer position, a roller cleaning voltage having the same polarity as the charge polarity of toner is applied to a transfer roller.

Description

The present invention relates to an electropho-tographic apparatus for prtnting an image in accordance with an electrophotographic process.
In an electrophotographic apparatus, an electrostatlc latent image ls formed on the surface (photosensitive surface) of a photosensitive drum by charging the photosensitive surface of the photosen-sitive drum to a predetermlned potential (e.g., 600 V) by a charging device and exposing the photosensitive surface of the photosensitive drum by an exposure device in accordance with an image to be print~d. Toner is attached to the photosensitive surface of the photosen-sitive drum by a developing device in accordance with the formed electrostatic latent image, thereby deve-loping the image.
In the developing device, the toner ls carried bya developing roller and conveyed to be brought into con-tact with the surface of the photosensitive drum. While the toner carried by the developing roller is conveyed, it is regulated to a thin layer by a developing blade arranged to contact the developing roller, and ls charged by friction to have the same polarity as the charge potential of the photosensltive drum (i.e.~
negative polarity). A low-voltags developing bias (e.g., -200 V) having the same polarlty as that of the charge potential of the photosensitive drum is applied to the developing roller to cause the toner to ... . ...

. , .: . .: , . . . .
.. ,. ,: , . ..
:,,, , . . ... :. :. .. .
: . ~ : :, . . " "
: ..

21 0~255 selectively attach to the photosensltive drum by the electric field produced in accordance with the electrostatic latent image, the developing bias, and the charges of the toner. More speciflcally, since a non-exposed portion on the photosensitlve drum has a higherpotential than that of the toner, the toner does not attach to it. Slnce an exposed and discharged portion on the photosensltive drum has a lower potential than that of the toner, the toner attaches to lt. In this manner, a toner image corresponding to the electrostatic latent image is formed on the surface of the photosen-sitive drum. This toner image is transferred to a print1ng sheet by a transfer device.
In this electrophotographic apparatus, while the operation ls stopped, the surface potential of the pho-tosensitive drum is not stable. When the potential of the photosensitive drum. is not stable like this, at the start of printing, as the photosensitive drum passes a positlon (developing posltlon) where development ls per-formed by the developlng device, the toner undesirablyattaches to the photosensitive drum havlng a low potential.
Therefore, charglng by the charging device is startecl simultaneously when rotatlon of the 2~s photosensitive drum is started, thereby minimizing the non-stable surface potential range of the photosensltive drum to prevent the toner from undesirably attaching to .. . - . , , ~ : - .: ;.. .. , . . . . :

21~5255 the photosensitive drum.
However, a region of the surface of the photosen-sitive drum located between a position (charging posi-tion) where charging is performed by the charginy device and the developing position when the photosensitive drum is not rotated reaches the developlng position before it is charged when the photosensltlve drum ls rotated, and the toner cannot be prevented from attachlng to this reglon. When the toner attaches to the photosensitive drum in this manner, if the transfer device is of a con-tact type using a contact member, e.g., a roller or a brush, the toner attach1 ng to the photosensitive drum undesirably attaches to the contact member of the transfer device.
Sometimes a printing sheet jams on the convey path of the pr1nting sheet. Hence, ln the conventional electrophotographic apparatus, occurrence of a ~am is monitored, and when a ~am occurs, the printing operation is stopped.
For example, a ~am is detected in the following manner. A prlnting sheet sensor is provided mldway along the convey path of the prlntlng sheet and between a thermal fixing devlce and an sheet outlet. When the sensor ls OFF for a predetermlned time or more after the reglster sensor is turned on, a ~am is detected. Hence, occurrence of a jam cannot be recognlzed during a time period after the printlng sheet sensor is turned on and ,: . . . . :: .. , ~ .: , : . , , ;,.. . : . ., 210~2~

until the predetermined time elapses, and the apparatus undesirably continues operatlon even after a ~am occurs.
In this manner, toner attaches to a photosensltive drum after a ~am occurs and before the apparatus stops its operation. If the apparatus is of a contact type using a contact member, e.g., a roller or a brush, the toner attaching to the photosensltive drum as described above undesirably attaches to the contact member of the transfer device until the apparatus stops or resumes its operation.
When the toner is replenished or the developing device (integrally formed in a process unit together with, e.g., the photosensitive drum and the charging device) is replaced, the amount of toner reserved in the developing device is large ~mmedlately after replenish-ment or replac~msnt. The toner can easlly pass between the developing roller and the developing blade without friction due to the pressure of the larye amount of toner. Thus, the toner which is not sufficiently ~o charged contacts the photosensitive drum. Slnce deve-lopment is performed by the functlon of the electric field, as described above, if an amount of charge of the toner has not reached a rated value, the operation of the apparatus is not correctly performed. Even if the photosensitive drum is uniformly charged, the toner undesirably attaches to the photosensitive drum, and ~ then attaches to the contact member of the transfer '~' r 1'' ' i'' . ': ~; ' ' ; ' , . : . ,, :.: , : , ' ', ," ' ," ''' ' ' , ' :;:: "."'', - 210~2~

device.
When the toner attaches to the contact member of the transfer device, in this manner, the toner soils the rear surface of the printing sheet in subseguent printlng, or the transfer efficiency is decreased to cause transfer failure.
It is a first ob;ect of the present invention to provide an electrophotographic apparatus which prevents toner atta~hl ng to the contact member of a transfer device of a contact type from soiling the rear surface of a printing sheet when the printing operatlon is stopped.
It ts a second ob~ect of the present invention to provide an electrophotographic apparatus which prevents toner attaS-h1 ng to the contact member of a transfer device of a contact type from soiling the rear surface of a printlng sheet when the printing sheet is ~ammed.
It is a third ob~ect of the present inventlon to provide an electrophotographic apparatus which prevents toner attaching to the contact member of a transfer device of a contact type from solling the rear surface of a printing sheet when the toner is replenished or the developing device is replaced.
It is a fourth ob~ect of ths present invention to ;~
~ 25 provide an electrophotographic apparatus which prevents - toner attaching to the contact member of a transfer ' device of a contact type from decreasing a transfer , .
:., ;' !, . , ; ; , . : . ~ . ' .: ,, : .; ,. , ! , ' :
', , "; . . ".: '". ', ' ';
..

210~2~

efficiency when the printing operation is stopped.
It is a fifth ob~ect of the present invention to provide an electrophotographic apparatus which prevents toner attaching to the contact member of a transfer device of a contact type from decreaslng a transfer efficlency when the printing sheet ls ~ammed.
It is a sixth ob~ect of the present invention to provide an electrophotographic apparatus which prevents toner attaching to the contact member of a transfer device of a contact type from decreasing a transfer efficiency when the toner ls replenlshed or the deve-loping device is replaced.
According to the present invention, there is pro-vided an el~ctrophotographlc apparatus comprising charging means and developing means which are respec-tively arranged at a predeterm1ned charging position and a predeterm~ned developing position along a surface of a photosensitive member, the photosensitlve member having a predetermined point which is located at the charging position when charging of the photosensitive member by the charging means starts, the developing means includlng toner carrier means and carrier rotating means for rotatlng the toner carrler means, the apparatus further comprising:
development control means for keeping rotation of r the toner carrier means by the carrier rotatlng means stopped from start of rotation of the photosensitive . . - , . ~....... : .. ;,,....... ,... . , ., .,.: .
: ,. , ~ : ., . , . ........... ,.. ; .. ;
: . . , .. . :.. ;.. : : ~ , .;. ! : .. , ; . ,. . . ~: ' . . ' :, 2la~2~

member until the predeter~1rle~ point of the photosen-sitive member reaches the development position. -According to the present invention, there is pro-vided another electrophotographic apparatus comprising charging means which is arranged at a predetermined charging position along a surface of a photosensitive - member and developing means which is arra~ged at a pre-determined developlng position along the surface of the photosensitive member, the developing means including toner carrier means and carrier rotating means for rotating the toner carrier means, the toner being charged to have a predetermined polarity by rotation of the toner carrier means, the photosensitive member having a predetermined point whlch is located at the charging position when charging of the photosensitive member by the charging means starts, the apparatus further comprising:
first power supply means for generating a voltage having an opposite polarity to the predeter~tned polarity;
a contact member for applying the voltage gensrated by the flrst power supply means to a printing sheet ~ disposed at the photosensitive member;
:- second power supply means for generating a voltage ~~ 25 having the predetermlned polarity;
switching means having at least a first state, in which the voltage generated by the first power supply ,'~ .
-~: . . .
.. , ., ;. . :. . ; . ; ~ . . . . . ~ :

: ' ' ' :, ' ~' ' ' ' 'I' ' ' ' " ' ' '' i' ~.' ' '.' ', , ' ' "' ' ~ ' '' . . ' .'. ' . : , .

210~2~

means is applied to the contact member, and a second state, in which the voltage generated by the second power supply means is applied to the contact member;
and control means for sett:Lng the switching means to the second state when the predetermined point of the photosensitlve member passes the transfer position.
According to the present invention, there is provided a further electrophotographic apparatus comprising:
developing means, arranged at a predetermined deve-loping position, for forming a toner image on a photo-sensitive member;
transfer means, arranged at a predetermined transfer position, for transferring, to a printing sheet, the toner 1mage formed on the photosensitive member, and alignlng means for ad~usting a posture of the printing sheet to be convey~d to the transfer position to a predeterm1ned state, the aligning means being arranged at such a predeter~1ned position that a distance o~ a convey path of the printing sheet from the aligni.ng means to the transfer posltion is longer than a distance of a moving track of a surface of the .-~ 25 photosensi.tive member from the developing position to .~ the transfer position.
~ According to the present invention, there is :

: '. ': ' . .: ' ~ :

",. ..
., . :., , 21~52~5 g provided a still another electrophotographic apparatus whlch is shifted to a predeter~1ned standby mode from a normal mode if a printing instruction is not received for a predetermined period of time, the apparatus comprlsing:
developing means, arranged at a predeter~1ned developing position, for forming a toner lmage on a photosensitive member which is charged to have a predeter~lned polarity;
transfer means for transferring the toner image formed on the photosensitive member to a printing sheet, the transfer means including a contact member arranged to contact a printing sheet arranged to contact the photosensitlve member, first voltage generating means for generating a first voltage having an opposite -~
polarity to the predeter~1ned polarity, second voltage generating means for generating a predeterr1n~d second voltage having the predeterr1 ned polarity, and switching means having at least a first state, in which the first voltage is applied to the contact member, and a second state, in which the second voltage is applied to the : transfer roller; and ~ . control means for settlng the switching means to ~ the first state when the apparatus ls shifted from the 25 ' standby mode to the normal mode.
According to the present inventlon, there is pro-vided a still further electrophotographic apparatus - , ~ ; , . . :

"
'' ~ ' " " .;'" ' ' ' ~;' ' ". '' - ' ' ;'''' . ' '.'' ' ,"'' ' ' ' ~ ' "' . .
.1 ' 210~2~5 having an openable/closable apparatus cover, the appara-tus comprising:
developing means for fc~rming a toner image on a surface of a photosensitive member which is charged to have a predetermined polarity, the developlng means including toner carrier means, carrier rotating means for rotating the toner carrier means, developing blas pow~r supply means for generating a developing bias to be applied to the toner carrier means, and developlng switching means for turning on/off application of the developing bias to the toner carrier means;
transfer means for transferring the toner image ; formed on the surface of the photosensitive member to a printing sheet, the transfer means 1ncll~ding a contact member arranged to contact a printing sheet arranged to contact the photosensitlve member, first voltage generating means for generatlng a first voltage having an opposlte polarlty to the predeter~1ned polarity, :; .
~' second voltage generating means for generatlng a second ., voltage having the predetermined polarity, and switching .- means havlng at least a first state, in which the first voltage is applied to the contact member, and a second . state, in which the second voltage is applied to the contact member;
~ 25 detecting means for detecting that the apparatus ~ cover is closed from an open state; and ~. control means for setting, when the detecting ';

.-.. ,.... " , , .

., . . :
, . .. ~ ,:.. : . : , .. ~ ., .
.. ...

,~ 210~2~5 means detects that the apparatus cover is closed from the open state, the swltchlng means to the first and second states at least once in a state wherein the pho-tosensitive member is charged, the developing switching means is turned on to apply the developing bias to the toner carrier means, and rotatlon of the toner carrler means by the carrier rotating means is stopped.
According to the present lnvention, there is pro-vided a still another electrophotographic apparatus having a low-power mode ln which power supplles thereof, excluding predetermined ones thereof, are kept off, .
comprising:
developing means for forming a toner image on a photosensitive member, the developing means including : - 15 toner carrier means and carrier rotating means for rotating the toner carrier means; and control means for causing the carrier rotating means to r~tate the toner carrier means by a predeter-mined amount before performing printing in the low-power - 20 mode.
. .
-~. Accordlng to the present invention, there is pro-.. ~ .
vided a still further electrophotographic apparatus havlng a low power mode in whlch power supplies thereof, excluding predetermined ones thereof, are kept off, comprising:
developing means for forming a toner image on a photosensitive member, the developing means lncluding .. .. . .
- : , - . ,:- , :, ~ . ; . : , , :
,, , . : : , .. . . .

21052~5 toner carrier means and carrier rotating means for rotating the toner carrier means; and control means for causing the carrier rotating means to rotate the toner carrier by a predetermined amount immediately after the low-power mode is canceled.
According to the present invention, there is pro-vided a still another electrophotographlc apparatus comprising:
developing means for forming a toner image on a photosensitlve member, the developing means including toner carrier means and carrler rotatlng means for rotat~ng the toner carrier means;
measuring means for measuring a time in which rota- r - tion of the toner carrier means is stopped; and control means, respons1ve to the measuring means, ~; for, when the time exceeds a predeterrined time, causlng the carrier rotating means to rotate the toner carrier means by a predetermined amount before printing opera-tion is started.
This invention can be mor0 fully understood from the following detailed description when taken in con-~unction wlth the accompanying drawings, in which:
Fig. 1 is a sectlonal view showing the overall - arrangement of a facsimile apparatus incorporating an embodiment of an electrophotographic apparatus according to the present invention;
Fig. 2 is a sectional view showing a state wherein ;

., : . ,,.,. : . :,., , , ;:, ..

:: . : ., ,. , . , . : .: :
. . : : . :: ~ .
,: . .. ..

210~255 the upper body of the facsi,mlle apparatus shown in Fig. 1 iS flipped upward;
Fig. 3 ls a diagram showing the arrangement of a process unit, an exposure dsvice, and a developing device, and th~ function block arrangement of an electric system associated with them;
Fig. 4 is a flow chart showing the processing pro- ;~
cedure of a CPU in a normal mode;
Fig. 5 is a timing chart showlng a printing sequence;
Fig. 6 is a timlng chart showing in detail a change ~' in voltage applied to a transfer roller in the printing ~; sequence;
Fig. 7 is a timing chart showing a modification of the printing seguence;
Fig. 8 is a timing chart showing the actual state '~ of change in voltage applied to the transfer roller when a switch is switched;
Fig. 9 is a timing chart showing another mod~fica-tion of the printlng sequence;
Fig. 10 is a timlng showing still another modifica-tion of the printing sequence;
Fig. 11 is a timing chart showing a transfer roller cleaning ~equence;
Fig. 12 is a flow chart showing the processing pro-cedure of the CPU in a nlght mode; and Fig. 13 is a timing chart showing an lnitialize . , .. . , -. . .. ~. , .

. .
,'. 7 :.
, ': ' '' , :':: ', : .: '' ,' '. : :

. ' ', ~, ~ .' . , ' ' "'. ' .

21~25~

- sequence.
A preferred embodiment of an electrophotographlc device according to the present invention will now be described with reference to the accompanying drawings.
Hereinafter, a facsimile apparatus is explained as an example of the electrophotographic device.
Fig. 1 is a cross section, showing the overall - arrangement of a facsimile apparatus according to the embodiment of an electrophotographic device. A main body 1 is divided into a lower body 2 having an upper opening, and an upper body 3 having a lower opening.
he upper body 3 is mounted on the lower body 2 to be v~rtically plvotal about a shaft (not shown) and opensJcloses the upper surface portion of the lower body 2, as shown in Fiy. 2. The upper body 3 serves also as an apparatus cover to be capable of openlng/closing the apparatus, thereby allowlng maintPn~nce of the interior of the apparatus.
A process unlt 100, a trans~er device 102, a fixing device 103, a paper feed ~ech~n~ section or a paper feed device 104, register rollers 106, a registration sensor 107, and a cover open/close sensor 108 are pro-vided in the lower body 2. An exposure device 101 and a com~lnlcation device 105 are provided in the upper body 3.
The process unit 100 is an integral structure of a photosensitive drum 11, a charging device 12, ~ , ;. , ., ,:: . . . ::, ,: . . , . :: , , .,, , , , : , .. ..
.. , . :. : ., . :::.
. . . :

21052~

a developing device 13, and a cleaning device 14, and forms a toner image on the photosensltive drum 11 together with the exposure device 101 in accordance with the so-called Carlson process.
The exposure device 101 includes an hED array (not shown), obtained by arranging a plurality of LEDs in series in an elongated exposure device body 45, and a rod lens array (not shown). The exposure device 101 : guides light, emltted by the LED array in accordance with an image signal, to the photosensltive surface of the photosensltive drum 11 through the rod lens array.
The transfer device 102 transfers a toner image formed on the photosensltive drum 11 onto, of printlng sheets P stored in a printing sheet tray 109, one fed by the paper feed ~ech~n 1 sm sectlon 104.
The fixing device 103 fixes the toner image trans-ferred to the prlnting sheet.
The com~llnlcation devlce 105 optically reads an original to be transmltted and performs photoelectric conversion to gPnerate an image signal. The com-munication devlce 105 is connected to a c~ 1n1cation line (not shown).
A pair of register rollers 106 correct (allgn) any - skew of the printing sheet P conveyed by the paper feed 25 ~erh~--l sm section 104 and convey the printing sheet P to a position (transfer positlon) between the photosen-sitive drum 11 and the transfer devi.ce 102.

.
,. ~ .
,, ' ~' ~' ' ' '' ', ', .,,; " ' ' ; , ~ ' 21~2~5 The registration sensor 107 comprises, e.g., a microswitch, and is provided to face a printing sheet convey path between the paper feed me~h~n~ section 104 and the register rollers 106, to detect the presence/
absence of a printing sheet P on the printing sheet con-vey path.
The cover open/close sensor 108 is a swltch which is turned on/off by a pro~ection llO formed on the upper body 3, and detects whether or not thè upper body 3 closes the lower body 2.
Fig. 3 is a diagram showing the arrangement of the process unit lO0, the exposure device lOl, and the deve-loping device 102, and the ~unctlon block arrangement of an electrlc system associated with them. Note that the same reference numerals are used to denote the same por-tions as in Fig. l.
In the process unlt lO0, the charging device 12, the developing device 13, and the cle~n1n~ device 14 are arranged around the photosensltive drum ll. The photo-sensitive drum ll, the charging device 12, the deve-loping devlce 13, and the cleaning devlce 14 are-integrated as they are supported by unlt plates (not shown) located on the right and left sides of the pro-cess unit lO0.
The photosensitlve drum ll is obtained by forming a photosensitive layer made of a photosensitive conductor material on the outer surface of a conductor, e.g., c ': . : : : ' ' ' . ................ ': :, : .
.. ... . .. . ...... ...

210~2~

alllm1nl-m. The photosensitive drum 11 is a cylinder having a length larger than the m~xi~ width of the printing sheet on which an image is to be formed, and is supported by the unit plates.
The charglng device 12 uses, e.g., a Scorotron charging device having a known arrangement, and uni-formly charges the surface of the photosensitive drum 11 to a predeterr~ned potential.
Thè developing device 13 comprises a toner hopper 21, a toner pack 22, a feed roller 23, a developing roller 24, a developing blade 25, a support rod 26, a leaf spring or spring member 27, a support 28, a rein-forcing plate 29, a feed bias power supply 30, a deve-loping blas power supply 31, and switches 32 and 33.
The toner hopper 21 is a hollow container whose side surface and an upper surface are partially open, and stores toner (not shown) therein. The toner pack 22 is mounted on the upper open portion of the toner hopper ;;r ~'~ 21. The toner pack 22 is a container having an open surface. The toner pack 22 is fllled with toner, and its opening is sealed wlth a seal sheet (not shown).
i When the seal sheet is removed while the toner pack 22 is mounted on the toner hopper 21, as shown in Fig. 3, the toner filled in the toner pack 22 can be supplled to the toner hopper_21.
The feed roller 23 is arranged at the side opening portion of the toner hopper 21 such that it is partly , . .

.
:;

' '.' ' ~ ''',' '.'; ' ' ''' '" '~,''', ',' '.. ,':'', ;' ,"" ; "'~" ' 210~2~

located in the toner hopper 21. The feed rolle.r 23 con-tacts the developing roller 24 and carries the t~ner stored in the toner hopper 21. When the feed roller 23 is rotated, it conveys the toner to the developing roller 24. The developing roller 24 contacts the photo-sensitive drum ll and carries the toner supplled from the toner hopper 21. When the developing roller 24 ls rotated, it conveys the toner and brings it into contact with the surface of the photosensitivs drum ll.
The developing blade 25 is made of a silicone resin, urethane, or the like. The developing blade 25 maintains an amount of the toner (a thickness of the toner layer) carried and conveyed by the developing roller 24 and charges the toner by friction. The deve-loping blade 25 is provided to the columnar support rod 26 and contacts the developing roller 24. The support rod 26 is urged toward the developing roller 24 by the leaf spring 27, fix d to the support 28, with a prede-: termined force (e.g~ about 50 g~cm2 to 100 g/cm2).
~ 20 Thus, the developing blade 25 is urged against the deve-':: loping roller 24 with this force. The support 28 is :
fixed to the side wall of the toner hopper 21.
The reinforcing plate 29 is fixed to the support 28 and the unit plates ~not shown) of the process unit lO0 to increase the rigidity of the process unit 100 and to ,: prevent the toner carried by the developing roller 24 ' from scattering.

: :;~

,. .:: , ~ , .. - ., , - . ,1 .. . . ~. . .. .. . ..
:.

210~25~

The feed bias power supply 30 generates a feed bias having a predetermined voltage (e.g., -300 V). The feed bias power supply 30 is electrically cormected to the - feed roller 23 through the switch 32. The developing bias power supply 31 generates a low-voltage (e.g.~
-200 V) developing bias having the same polarity as that of the charge potential of the photosensitlve drum 11.
The developing bias power supply 31 ls electrlcally connected to the developing roller 24 through the switch 33.
The cleaning device 14 comprises a cle~n~ng blade 41, a waste toner storing tank 42, a convey roller 43, and an one-way vaive 44. The cleaning blade 41 scrapes off the toner which rem~n~ on the photosensitive drum 11 even after the transfer process by the transfer device 102. The waste toner storing tank 42 stores the waste toner scraped by the cleaning blade 41. The con-vey roller 43 conveys the waste toner scraped by the clean1ng blade 41 to the waste toner storing tank 42.
The one-way valve 4~ prevents the toner in the waste toner storing tank 42 from flowing back to the photosen-sltive drum 11.
The transfer device 102 comprlses a transfer roller 51, a transfer power supply 52, a roller clean~ng power supply 53, and a switch 54.
The transfer roller 51 contacts the photosensitive drum 11. The printing sheet P is inserted between the : ; , . ; . -, ~
. ~
. ~ ~ . ~ . . . ; , . .

., :

21~525~

transfer roller 51 and the photosensitive drum ll.
The transfer power supply 52 applies a predeter-mined transfer voltage (eOg., + 1,350 V) having an oppo-site polarity to that of the charge potential of the toner to the transfer roller 51. The roller cle~n1 ng power supply 53 applies a predeterr~ned roller cleanlng voltage having an opposlte polarlty to that of the transfer voltage (but the same polarity as that of the charge potential of the toner) to the transfer roller 51. One of the voltages generated by the transfer power supply 52 and the roller cleaning power supply 53 are selected by the switch 54 and applied to the transfer roller 51. The switch 54 can be controlled to select neither the transfer power supply 52 nor the roller cle~n1ng power supply 53 but turn off the voltage to be applied to the transfer roller 51.
~- A value Vl of the roller cle~n~ng voltage generated by the roller cleAn1ng power supply 53 is set to satisfy the following condltions:
¦V1 - V6 ¦ S discharge start voltage where Vs is the surface potentlal of the photosen-sitive drum 11.
he clischarge start voltage is a potential di~-ference between the transfer roller 51 and the photosen-~ :.
- 25 sltive drum 11 when dlscharge starts from the transfer roller 51 to the photosensitive drum 11, and is about, e.g., 500 to 600 V. The surface potentlal Vs of the .. ... .. . ...

. . . , :, .: :: . ..
~: : : , , : , , ;
: . : .: .. . : ..

-' 210~255 photosensitive drum 11 is almost equal to the charge potential (slightly lower t]han that ln fact due to dark current attenuation) and is e.g., -600 v. Hence, if the discharge start voltage is 500 v, the value Vl is lower than -1,100 V and is set to, e.g., -1,000 V.
Therefore, when the roller cleaning voltage ls applled to the transfer roller 51, discharge will not occur from the transfer roller 51 to the photosensitlve drum 11, and an electrlc field can be stably formed between the photo~ensitlve drum 11 and the transfer roller 51. Accordingly, the toner can be stably attrac*ed by the photosensitive drum 11 due to the func-tion of the electric field, reliably preventing the toner from attaching to the transfer roller 51.
The value Vl of the roller cleaning voltage and a value V2 of the transfer voltage satisfy a following relation:
.' lvll ~ IV2 :
: ~ AS other ma~or elements of the electric system associated with the above arrangement, a main driver 61, a developing/register rollers driver 62, a control cir-cuit 63, and a timer circuit 6~ are provided.
The main driver 61 comprises, e.g., a motor and a gear, and rotates the photosensitive drum 11 and the transfer xoller 51 in directions indicated by arrows in Fig. 3.
The developing/register rollers driver 62 .~
- . . . . .. . ... ,,, :

~ , . . .

21~52~

comprises, e.g., a motor and a gear, and rotates the feed roller 23, the developing roller 24, and the register rollers 106 in dir~ections indicated by arrows in Fig. 3.
The control circult 63 systematically controls the respective portions of the apparatus and includes a CPU
71, a ROM 72, a RAM 73, an I/O port 74, and a bus 75.
The CPU 71 operates in accordance with an operation program stored ln the ROM 72 and systematically controls the respective portions of the apparatus. The ROM 72 stores various types of data for use by the CPU 71 in addition to the operation program for the CPU 71. The .~! RAM 73 temporarily stores data required when the CPU 71 performs various types of processing operations. The I/O port 74 generates and outputs control signals and the like to the respective portions of the apparatus ~ under the control of the CPU 71. Also, the I/O port 74 - accepts a process start signal and a prlnt start signal ~ supplied from a facsimile main control circuit (not ; 20 shown) managing the entire facsimile apparatus, an out- -put signal from the cover open/close sensor 108, and time information output from the tlmer circuit 64, and supplies them to the CPU 71. The CPU 71, the ROM 72, the RAM 73, and the I~O port 74 are connected to each other through the bus 75.
The timer circuit 64 performs a time counting operation based on a slgnal oscillated by a reference ::,, , . . . :

.-., ' : '' ' . '' .'.:..... :. ' ' .~. ' .:
' ' ,. . .,'.. ' . . ~ ' , . . !, , :.: '. " ' , ' ~,' :'. :

21052~

oscillation source, e.g., a quartz oscillator, and out-puts time information.
he operatlon of the electrophotographic apparatus as part of the facsimile ap~paratus having the above arrangement will be describled in accordance with the -~
; control sequence of the CPU 71.
In the standby state, the CPU 71 stops the opera-tion of the main driver 61 (rotation of the photosen-sitive drum 11 and the transfer roller 51), the charging operation of the charging devlce 12, the exposing ~ operation of the exposure device 101, and the operation : of the developing/register rollers driver 62 (rotation of the feed roller 23, the developing roller 24, and the register rollers 106), and keeps the switches 33, 32, and 54 OFF.
: Also, in the standby state, as shown in Fig. 4, the CPU 71 repeats determination (step STl) as to whether or not a process start ~ignal is input, determination (step ST2) as to whether or not the upper body 3 is closed from the open state, and determinatlon (ST3) as to whether or not the present time is the start time of the night mode.
In this standby state, lf a process start slgnal is supplied from the facsimile main control circuit and accepted by the I/O port 74, the CPU 71 determines in step STl that a process start signal is input, and the flow advances to step ST4. In step ST4, the CPU 71 , : , ' ' ~' -' , .: , :. ' ' -- 21052~5 calculates the waiting time (standby time) of the standby mode. The waiting time is calculated from a time (stored in the RAM 73) when the apparatus is shifted from the operation state to the standby state and the present time indicated by the timer circuit 64.
Successlvely, the CPU 71 deterr1nes whether or not the waiting time is equal to a predeterm1ned time (e.g., several hours) or more tstep ST51. If NO in step ST5, the CPU 71 executes a printing sequence (step ST7).
The printing sequence will ~e described in detail with reference to the timing chart of Fig. 5.
The CPU 71 causes the main driver 61 to start its operation in synchronism wlth the process start signal in order to start rotation of the photosensitive drum 11 and the transfer roller 51, and to start the charging operation of the charging device 12 (a timing Tl in ~, Fiy. 5). ~t the timing Tl, the CPU 71 turns on the swltch 54 to be co~n~cted to the roller cleaning power supply 53. Then, a negative roller cle~nlng voltage generated by the roller cleaning power supply 53 is applied to the transfer roller 51.
Subsequently, a predetermined period of time TA
after the timiny Tl (a timing T2 in Fig. 5), the CPU 71 switches the switch 54 to be connected to the transfer _ 25 __power supply 52. The period of time TA is set to be equal to or longer than a period of time required for an arbitrary point on the surface of the photosensitive , ,, , ,; ,, ~

21~5255 drum 11 to move from the cellter (to be referred to as a ;~
developing position hereinà~Eter~ of the contact position of the photosensitive drum :Ll and the developing roller 24 to the center (to be referred to as a transfer posi-; 5 tion hereinafter) of the contact position of the photo-;; sensitive drum 11 and the transfer roller 51.
More speclfically, as shown in Fig. 6, the time ~2 is set to later than the end of a predeterr~ned period of time TC. The period of time TC has a predetermined period and a center whlch coincides wlth the end of .~ a period of time TB. The p~riod of time TB is a period of time required for an arbitrary point on the surface of the photosensltive drum 11 to move from the deve-loping posltion to the transfer position. The period of time TC is set to be Pqual to or longer than a period of time during which a portion of the photosensitive drum 11, which was in contact with the developing roller 24 while the rotation of the photosensitlve drum 11 was stopped, passes the contact portion with the transfer roller 51. Therefore, the start time of the period of time TC is the end of the perlod of time Tb required ~or the leading end of the portion of the photosensitive drum 11, which was in contact with the developlng roller 24 while the photosensitive drum 11 is stopped, to reach the transfer position.
~ssuming that the developing nip width and the transfer nip width are 2 mm, that the process speed (the 210~255 rotation speed of the outer surface of the photosen-sltive drum 11) is 32 mm/sec , and that the distance from the developing positlon to the transfer posit~on is ; 24 mm~ a period of time Tb :Ls about 0.688 sec. and a period of tlme TC is 0.125 sec.. Accordingly, in this case, the period of time TA is 0.813 sec. or more.
While the roller cleaning voltage generated by the roller cle~n1ng power supply 53 is applied to the transfer roller 51 in this manner, the swltch 33 for '- 10 applying the developing bias to the developing roller 24 is kept OFF, and the developing blas generated by the ; developing bias power supply 31 is not applied to the developing roller 24. The developing/reglster rollers drlver fi2 is kept stopped, and the developing roller 24 is not rotating. Therefore, the toner is not supplied to the surface of the photosensitlve drum 11, and almost - no toner attaches to a portion of the photosensitive drum 11, which was located between the charging posltion - of the charglng device 12 and the developing position while rotation of the photosensitive drum 11 was stopped, althouyh the potential of this portlon is non-stable. However, regardlng the toner which was loc~ted at the contact portion between the photosensitive drum 11 and the developing roller 24 while rotation of the _ ?.5 photosensitive drum 11 was stopped, it cannot be pre-vented from attaching to the photosensitive drum 11.
As described above, however, in a period during ::

: . : , . ;., . : . , , ,,; , 210525~

which the portion of the photosensitive drum 11, which ; was in contact with the developing roller 24 while rota-tion of the photosensitive drum 11 was stopped, passes the contact portion with the transfer roller 51, the roller cleaning voltage hav:Lng the same polarity as that - of the toner is supplied to the transfer roller 51.
Therefore, the toner attachl ny to the photosensltive drum 11 is electrically repulsed and does not attach to the transfer roller 51.
It suffices if the period of time during which the roller cleaning voltage generated by the roller cleaning power supply 53 is applied to the transfer roller 51 includes at least the period TC. Therefore, the : following modifications are possible.
More specifically, as shown in Fig. 7, the roller cleaning voltage may be applied to the transfer roller . 51 only during the period ~C. In this case~ however, a : delay of a period of tlme TD occurs after the swltch 54 is switched to be cnnnected to the roller cle~n 1 ng power supply 53 and until the potential of the transfer roller 51 reaches a predetermined value, as shown in Fig. 8.
; Therefore, it ls preferable to hast~n a tlming forswltching the switch 54 to the roller cleaning power supply 53 by a time corresponding to the period of time TD by considering this delay TD. , In periods before and after the period TD, the voltage to be applied to the transfer roller 51 may be ::
. :, : , ; ,: . ,;,', ,"~ ' :, ' ;, , ' , 210~2~5 ,, arbitrary. For example, as shown in Fig. 9, after the period TC, voltage supply to the transfer roller-51 may be temporarily turned off, and thereafter the positive transfer voltage generated lby the transfer power supply ~2 may be applied to the transfer roller 51.
Alternatively, as shown in :~lg. 10, the positlve transfer voltage generated by the transfer power supply : 52 may be supplied to the transfer rolIer 51 before a period TC.
~0 A predeter~1ned period of time TE after the timing Tl (a timing T3 ln Fig. 5), the CPU 71 turns on the .switches 32 and 33 to start application of the feed blas to the feed roller 23 and of the developing bias to the developing roller 24. The predetermined period of time TE is arbitrarily set, including a r~n~r of a period of time required for an arbltrary point on the surface of the photosensltive drum 11 to move from the charging position to the developing positlon. More specifically, the CPU 71 starts application of the feed bias to the ~eed roller 23 and the developing bias to the developing roller 24 when the region of the surface of the.photo-sensitive drum 11 charged by the charging device 12 reaches the developing positlon. In this embodiment, the periocl of time TE is set to a ~um (e.g., 4.81 sec) of a period of time requlred for the photosensitive drum 11 to rotate once and a perlod of time required for the arbitrary point on the surface of the photosensitive 210~25~

drum 11 to move from the charglng position to the deve-loping positlon. In th~s manner, the period of time TE
after start of charging and until start of application of the developing blas to the developing roller 24 is set be longer than the ~1 n ~ T~llm value by a perlod of time corresponding to one revolution of the photosensitlve drum 11, 50 that the developing device 13 ls operated after the entire surface of the photosensltlve drum 11 is stably charged. ~
A short period of time TF (e.g.~ 0.5 sec) after the timing T3, the CPU 71 starts the operation of the developing/register rollers drlver 62 to rotate the feed roller 23, the developing roller 24, and the reglster rollers 106 (a timlng T4 in Fig. 5). Then, the CPU 71 op~rates the developing/register rollers driver 62 for a predeterm~ned period of time TG to rotate the feed roller 23, the developing roller 24, and the reglster rollers 106. The predetermined period of time TG is set to an arbitrary value (e.g., 3 sec or more) lncluding a ; r~n~-m of a perlod of tlme required for the developing roller 24 to rotate once. The period of time TG ls a warm-up period of the developing device 13 and alms especlally at keeping the toner carried by the deve-loping roller 24 stably charged. When the period of time TG elapses a~ter the timing T4, the CPU 71 stops the operation of the developing/reglster rollers driver 62 to stop rotation of the feed roller 23, the " ,: , .. .. .. . .. . . .

21~2~
, developing roller 24, and the register rollers -106 (a timing T5 in Fig. 5).
The paper feed mechanism section 104 starts con-veyance of the printing sheet P at a predetermined timing based on the print start signal. The printing ~heet P conveyed by the paper feed mech~n1sr sectlon 104 is stopped whsn lts leadlng end ls abutted against the register rollers 106. At this time, any skew of the printing sheet P is corrected, and the posture of the printing sheet P is ad~usted.
Preparation of the respectlve portions is completed by the above operations, and an image printing operation is enabled.
While the printing sheet P is conveyed by the paper feed merh~n1 ~m section 104, when the printing sheet P
reach~s the registration sensor 107, the registration sensor 107 detects the printing sheet P. An output from the registration sensor 107 is supplied to the facsimile main control circuit. The facsimile main control cir-cuit outputs a pxint start signal when a predetermined time elapses after the registratlon sensor 107 detects the printing sheet P.
Upon reception of the print start signal from the facslmile main control circuit ~a timing T6 ln Fig. 5), the CPU 71 causes the exposure device 101 to start an exposure operation after a short time (a timing T7 in Fig. 5). Also, when a predetermined period of tlme TH

:' ,' ' ' :: '' ::' ' : ': '::', ,: :, : ......... , .. . ..

2~0~2~

elapses after the timing T6, the CPU 71 causes the developing/register rollers driver 62 to start opera-tion, thereby starting rotation of the feed roller 23, the developing roller 24, and the reglster rollers 106 (a timing T8 in Fig. 5). The predetermined perlod of time T~ is determined by an equation:
TH
- (a period of tlme re~uired for the printing sheet P
to move from the registratlon sensor 107 to the : 10 reglster rollers 106) ~ (a period of time required for registering a printing isheet by the reglster rollers 106) - (a time after the registration sensor 107 is turned on and until a print start signal is output) Note that the period of time required for registering a printing sheet by the register rollers 106 ls a period of time required after a printing sheet P is abutted against the reglster rollers 106 for the first time and until correction of its skew (allgning) is completed.
In this embodiment, the register rollers 106 are arranged such that the distance from the ragister rollers 106 to the transfer posltlon on the convey path of the printing sheet P ls longer than the dlstance from the developing posi~ion to the trani~fer ppsition on the moving track of the surface of the photosensitive drum 11 .

: ' . .

.. , ~ , ~ .. , ,.. , .. , ,,, ! . . . .

~ . ' , , , '~' ', ". ' . . ... . . .

210~2~

The reason for the above posit~onal relatlonship is as follows. At the transfer position, the leading end of the toner image on the photosensitive drum 11 and that of the printing sheet P must substantially coin-cide. In this embodiment, since the distance from theregister rollers 106 to the transfer position on the convey path of the printing sheet P is longer than the distance from the developing position to the transfer position on the moving track of the surface of the pho-tosensitlve drum 11, as described above, rotation of theregister rollers 106 is started before the leading end of the electrostatic latent image reaches the developing position in order to satisfy the above conditions.
Accordingly, when the electrostatic latent image reaches the developing position and the developing operation should be started by the develop~ng device 13, since ~ alignlng has alr~ady been completed, rotatlon of the - register rollers 106 need not be stopped by stopping the developing~register rollers driver 62. Therefore, rota-tion of the developing roller 24 which is caused by the developing/register rollers driver 62 is not stopped during the developing operation.
If rotation of the developing roller 24 is stopped durlng the developing operation, toner supply to the surface of the photosensitive drum 11 becomes non-stable to possibly degrade the image guality. Howaver, according to this embodiment, since rotation of the ,, ' " ;~ ; ';. ; ' ' ~ " ' :

,, ., . , .. : . ~ ., ,:.:.. . ........ .

-" 210~255 developing roller 24 is not stopped during the deve-loping operation, high-quality lmage printing can be performed.
Thereafter, a printing operation is performed in the following manner. The ~surface (photosensitive sur-face) of the photosensitive drum 11 is charged to a pre-determ1ned potential (e.g.~ -600 V) by the charging device 12, and exposed by the exposure devlce 101 ln accordance with an image to be printed, thereby forming an electrostatic latent image. The electrostatic latent lmage formed on the photosensitive surface of the photosensitive drum 11 is developed by the developing device 13.
In the developing device 13, the toner supplied from the toner hopper 21 mainly by the feed roller 23 is carried by the developing roller 24 and conveyed to be brought lnto contact with the surface of the photosen-sitive drum 11. when the toner carried by the deve-loping roller 24 is conveyed, it is regulated to a thin layer by the developing blade 25 and charged by frictlon to have the same polarity (negative) as that of the charge potential of the photosensitive drum 11.
Since a developing blas (e.g.~ -200 V) is applied from the developing bias power supply 31 to the deve-loping roller 24, the toner selectively attaches to thephotosensitive drum 11 by the functlon of the electric : field produced in accordan~e with the electrostatic :

,. : .............. :; .
::
.. . . .

latent image, the developing bias, and the char~e of the toner. More specifically, the toner do~s not attach to the non-exposed portion of the photosensitive drum 11 since the potential of the non-exposed portion of the photosensitive drum 11 ls higher, and the toner attaches to the exposed and discharged portion of the photosen-sitive drum 11 since the potential of the exposed and discharged portion of the photosensitlve drum 11 ls lower. In this manner, a toner image corresponding to the electrostatic latent image is formed on the surface of the photosensitlve drum 11. This toner image is transferred to the printing sheet P by the transfer device 102.
In the transfer device 102, a positlve transfer voltage (e.g., +1,350 V) is applied to the transfer roller 51 to in~ect charges to the rear surface of the pr1nting sheet P. Since the charges in~ected to the rear surface of the printlng sheet P are posltive, the negatively charged toner ls attracted by the printing sheet P. Then, the toner image formed on the surface of the photosensitive drum 11 is transferred to the printing sheet P.
Then, after the prlnting sheet P is separated from the photosensitive surface of the photosensitive drum 11, the toner which is not transferred and r~ma~ n~ on the surface of the photosensitive drum 11 is rel,loved by the clean:ing device 14.

; . . . : , . . . ,: .

.. .-. , ': , ., , ::.,.. '.::~.. :', '~ ',: . ;

2~0~2~5 A predetermined period of time TI after the timing T8, the CPU 71 stops the operation of the developing/
register rollers driver 62 to stop rotation of the feed roller 23, the developing roller 24, and the register rollers 106 (a timing T9 ln Fig. 5). The predeter~1ned period of time TI is deterr1ned in accordance with:
TI - (PS + f - L)/v ~ 1.0 where PS is the length of the prlntlng sheet, f is the distance from the register rollers 106 to the -- 10 transfer position on the convey path of the printing sheet P, L is the distance from the developing posltion : to the transfer positlon on the moving track of the pho-tosensitlve drum 11, and v ls the convey speed of the printing sheet P. More speclfically, lf the printing sheet size is A4, TI is, e.g., 11.73 sec; lf the printing sheet size is B~, TI is, e.g., 13.15 sec.
Thereafter, if the following page need be printed, the CPU 71 controls the respectlve portions of the appa-ratus at the same timings as those described above in ;~ 20 synchronism with a print start signal.
When printing of the last page in one printing : operation is completed, a predetermined period of time TJ after a timing (a timing T10 in Fig. 5) at which the exposure operation of a correspondlng image is _ 25 completed, the CPU 71 stops the operatlon of the _ : developing/register rollers driver 62 to stop rotation of the feed roller 23, the developing roller 24, and the :: :: . : ., ,,................ . .; :
:., . . ~ . ..... .. . .

- 21052~5 register rollers 106 (a timing Tll in Fig. 5). The pre-determined period of time TJ is set to an arbitrary value including a ~n~mllm of a time (e.g., 2.4 sec) re~uired for an arbitrary point on the surface of the photosensitive drum 11 to move from the developing posi-tion to the transfer position.
Furthermore, a pred~termined period of time TX
after the timing Tll, the CPU 71 switches the switch 54 to be connected to the roller cle~n1 ng power supply 53, thereby switchiny the voltage to be applied to the transfer roller 51 to a negative roller cle~n~ng voltage (a timing T12 in Fig. 5). The predetermined period of time ~X is set to be shorter than a period of time required for a portion of the photosensitive drum 11, 15 which was located at the developing position at the ~.
timing Tll at which rotation of the developing roller 24 was stopped, to reach the transfer posltion.
In this manner, when a portion of the developing roller 24, that has passed the developing position after rotation of the developlng roller 24 was stopped, passes the transfer position, the negatlve roller cleaning voltage is applied to the transfer roller 51. A portion of the surface of the photosensitive drum 11, that has passed the developing position after rotatlon of the ~ 25 developing roller 24 was stopped, rubs against the toner attaching to the developing roller 24. Therefore, the toner attaches to the photosensitive drum 11 due to "~

.. ,. , , ; .. :, . .

210~

- ~7 -a mechanical force. However, this toner is a normally charged toner; lt ls negatively charged. Therefore, when the toner passes the transfer position, it is repelled due to the negative roller cleaning voltage, and will not attach to khe t:ransfer roller 51.
Then, a predetermined period of time TL after the timing T12, the CPU 71 stops the operation of the main driver 61 to stop rotation of the photosensitlve drum 11 and the transfer roller 51 and the charging operation of the charglng device 12 (a period of time point T13 in Fig. 5). Simultaneously, the CPU 71 turns off the switches 33, 32, and 54 to respectively stop application of the feed bias to the feed roller 23, the developing bias to the developing roller 24, and the voltage to the transfer roller 51. Then, the apparatus returns to the standby state.
~ After the CPU 71 switches the swltch 54 to be con-; nected to the transfer power supply 52 at the timing T2, it fixes the switch 54 at the transfer power supply 52 side untll the timing T12, iOe., until all the pages in ; one printlng operatlon are printed.
After the toner is replenished, the pressure applied to the toner located between the developing roller 24 and the developing blade 25 is increased.
Then, the toner easily mov~s between the developing roller 24 and the developing blade 25, and part of the toner not sufficiently charged by friction with the , , , , " , ~, : , , ,, ~, ., . , . . : ; , .

210~255 developing blade 25 is brought into contact with the photosensitive drum 11. Such toner has a small amount of the negative charge and has a large amount of the positive charge inversely. Therefore, a large amount of positively charged toner attaches to the photosensitive drum 11 (fogging occurs).
In this embodiment, however, slnce a positive transfer voltage is always applied to the transfer roller 51 during the time T2 to T12, the positively charged toner attaching to the photosensitive drum 11, in the manner as described above, is repelled due to the positive transfer voltage and is prevented from attachi ng to the transfer roller 51.
The printing sequence has been described so far.
When the printiny sequence of step ST7 (Fig. 4) ends, the CPU 71 recognizes the time when the apparatus has shifted from the printing state to the standby state by referring to the time indicated by the timer circuit 64, and stores this time in the RAM 73 as the standby start tima. This standby start time is utilized ln calcula-tion (step ST4) of a waiting time required when a sub-sequent printing operation is started.
In the standby state~ when the upper body 3 is opened to allow maint~niRnce and then closed, the CPU 71 determ~nes that the upper body 3 is closed from the open state in step ST2 based on the output from the cover open/close sensor 108, and the flow advances to step 210~2~

ST9. In step ST9, the CPU 71 executes a transfer roller cleaning sequence.
The transfer roller cle~n 1 ng -sequence will be described ln detail with reference to the timing chart of Fig. 11.
The CPU 71 causes the main driver 61 to start operation to rotate the photosensitive drum 11 and the transfer roller 51 and causes the charging device 12 to start the charglng operation (a tlming T21 in Fig. 11).
Also, a period of time TE after the timing T21 (a timlng T22 in Fig. 11), the CPU 71 turns on the switches 32 and 33 to start application of the feed bias to the feed roller 23 and application of the developing bias to the developing roller 24.
Thereafter, until a predeterm1ned period of time TM
lapses (a timing T23 ln Fig. 11) after the timing T21, the CPV 71 continuously rotates the photosensitive drum 11 and the transfer roller 51 by the maln driver 61, causes the charging device 12 to perform the charging operation, and applies the feed bias to the feed roller 23 and the developlng bias to the d~veloplng roller 24.
In this period, the CPU 71 does not cause the developing/register rollers driver 62 to operate so that rotation of the feed roller 23, the developing roller 24, and the re~l~ster rollers 106 is kept stopped.
In the predetermined period of time TM in the state as described above, the CPU 71 repeatedly switches the .. . . . ..................... ....... . ............ ...............

- : . . , .. : :: ............. ;: . . : :, .
~, ,. , " ,. ~ , . ~: ::: . . :

21~255 switch 54 between the transfer power supply 52 slde and the roller cleaning power supply 53 side at a cyc~e of a predeter~1ned period of time TN. The predetermined period of ime TM is set to an arbitrary value including a ~tnlml of a time required for the transfer roller 51 to rotate once.
The upper body 3 is opened when elimination of a ~am of a printing sheet P is performed, the toner is replenished to the toner hopper 21 (a new toner pack 22 is mounted)~ the process unit lO0 is replaced, and so on. Before and after the occurrence of a ~am, toner replenishmen~, or replacement of the process unit 100, a large amount of toner attaches to the photosensitive drum ll, and the toner is thus attached to the transfer roller 51. The charge polarity of the toner attaching to the transfer roller 51 at this time is not fixed, but the toner is partly negatlvely charged and partly posi-tively charged in a mixed manner.
However, when the upper body 3 is closed, i.e., ~; 20 when each of the operations described above is ended, the transfer roller cleaning sequence as described above is executed. More specifically, while the surface of the photosensltive drum ll is unlformly charged, a posi-tive transfer voltage and a negatlve roller cleaning voltage are alternately applied to the transfer roller 51, as shown in Fig. 11. Accordingly, when the positive transfer voltage is applied to the transfer roller 51, :: . . .. . . . . . .. . . ...... . .

210~2~

it repels the positlvely charged toner which then returns to the surface of the photosensitive drum ll.
When the negative roller cle~n1 n~ voltage is applled to the transfer roller 51, it repels the negatively charged toner which returns to the surface of the photosensitive drum 11. The transfer roller 51 is cleaned in this manner. Thereafter, if a normal printing operatlon is to be performed, the rear surface of the prlntlng sheet P is prevented from being soiled.
In thls embodiment, since the cycle TN during which the transfer or roller cle~n1 ng voltage is applied ls set to be longer than the time required for the transfer roller 51 to rotate once, the toner can be reliably removed from throughouk the entire circumferentlal sur-face of the transfer roller 51. The period of time TM
during which the transfer roller cleaning sequence is executed is arbltrarily set to a time (e.g., about 30 to 60 sec) allowing sufficient cle~n1ng of the transfer roller 51.
The transfer roller cleaning sequence has been described so far. When the CPU 71 ends the transfer roller cleAnl n~ sequence of stap ST9, the apparatus is returned to the standby state.
In the standby state, when the CPU 71 recognizes in step ST3 that a predeterml ned night mode start time has reached based on a time indicated by the timer circuit 64, the apparatus is shifted to the night mode. In the : :' ' ' , ~ ', .'''' .' '.~,' ,, , , ::
. . , ~ . , . , ' . . ' ' ! i .~ , . ~ ;' -'' 210~2~5 night mode, the respective power supplies of the appara-tus excluding some (e.g., the control clrcuit 63 and the timer circuit 64) are kept OFF in a time zone having a less cnmmlln1cation frequency in order to decrease power consumption.
In the night mode, as shown in Fig. 12, the CPU 71 repeatedly performs in the standby state a determlnation ~step STll) as to whether or not a process start slgnal is input and a determinatlon ( tep ST12) as to whether or not the present time is the time to cAnrel the night mode.
- In this standby stat~, if a process start signal is supplied from the facsimile main control circuit and accepted by the I/O port 74, the CPU 71 determines in step STll that a process start signal has arrived, and the flow advances to step ST13. The CPU 71 executes an initialize sequence (step ST13) prior to the printi~g sequence (step ST14).
In the standby state, lf the CPU 71 recognizes that the predetermined night mode cancel time has reached in step ST12 based on the time indicated by the timer cir-cuit 64, the CPU 71 performs the initialize sequence (step ST15) prior to shiftlng to the normal mode.
Furthermore, in a shlft from the standby state to the operation state in the normal mode, if the CPU 71 determlnes in step ST5 of Fig. 4 that the waiting time ; is equal to a predetermined time or longer, it executes .

, .
~., , : ,, .. , , . , .. ::. ,: ; , . ,:

-- 2~0~2~5 the initialize sequence (stlep ST6 in Fig. 4) prior to the printing sequence of stlep ST7 ln Flg. ~.
The initialize sequencle will be descrlbed in detail with reference to the timing chart of Fig. 13.
The CPU 71 causes the main driver 61 to start operation to rotate the photosensitive drum 11 and the transfer roller 51, and causes the charging device 12 to start the charging operation (a timing T31 in Fig. 13).
At the timing T31, the CPU 71 switches the switch 54 to be conne~ted to the roller cle~n~ ng power supply 53.
Then, a negative roller cleaning voltage generated by the roller cleaning power supply 53 is applied to the transfer roller 51.
Subse~uently, a period of time TA after the timing T31 (a timlng T32 in Fig. 13), the CPU 71 switches the switch 54 to be connected to the transfer power supply 52. Furthermore, a period of time TE after the timing T31 ~a timlng T33 in Fig. 13), the CPU 71 turns on the switches 32 and 33 to start application of the feed bias to the feed roller 23 and of the developing bias to the developing roller 24. A short period of time TF after the timiny T33, the CPU 71 starts the developing~register rollers driver 62 to rotate the feed roller 23, the developing roller 24, and the register roller~ 106 (a timing T~ in Fig. 13).
' Thereafter, a predetermined period of time T0 after the timing T31 ~a timing T35 in Fig. 13), the CPV 71 '~
. , .~ ~
,, .,~ .

210~2~5 ~ 44 -ends the operation of the developing/register rollers driver 62 to stop rotatlon of the feed roller 23, deve-loping roller 24, and the register rollers 106. The predetermined period of time T0 is set to a time during which the developlng roller 24 can be rotated to a cer-tain degree at least once, which is, e.g., a time re~uired for the temperature of the heat roller incor-porated in the fixing device 103 to reach a predeter-mined temperature, or a time (e.g., 10 to 90 sec) arbitrarily set in the timer.
Upon a lapse of a predetermined period of time TK
after the timing T35, the CPU 71 switches the switch 54 to be ~-onnected to the roller cle~n~ng power supply 53, in order to switch the voltage to be applied to the transfer roller 51 to a negative roller cleaning voltage (a timing T36 in Fig. 13.) A predeterm1ned period of time ~L after the timing T36, the CPU 71 stops the operation of the main driver 61 to stop rotatlon of the photosensitive drum 11 and the transfer roller 51, and the charging operation of the charglng device 12 (a timlng T37 in Fig. 13).
~ Simultaneously, the CPU 71 turns off the switches 32, - 33, and 54 to stop application of the feed bias to the ; feed roller 23, the developlng blas to the developing roller 24, and the voltage to the transfer roller 51. 3 The initialize s~quence has been descrlbed so far.

.
' .

.. . : - , , .. , . ..... :: .,. ~ .~.

, . . , , ' ' ~
, ,. .' ' : ' ,, :, '. .: . ~ ' ''.'' , : :

- , 21~2~

After ~n~ng this initlalize sequence, the CPU 71 per-forms the printing sequence in step ST7 of Fig. 4 or step STl4 of Fig. 12, or shi.fts to the normal mode.
When the operation has been stopped for a long period of time, an amount of the charge of the toner is decreased in the developing device 13. When a deve-loping operation is started from this state, the toner having a low amount of charge is undeslrably brought into contact with the photosensitive drum ll, and a large amount of toner unnecessarily attaches to the pho-tosensitive drum 11.
In this embodiment, however, when the operatlon has been stopped for a long period of time, the initialize sequence is performed prior to the printing sequence or shifting to the normal mode, in order to rotate the developing roller 24 to a certaln degree. Hence, when a developing operation is to be successively performed, the toner carried by the developing roller 24 can be sufficiently charged. Accordingly, llnnecessary toner attachment to the photosensitive drum 11 is de~reased.
In this embodlment, since the printing frequency is : generally low in the night mode, the inltialize sequence ' is performed prior to starting the printing sequence in ~............... the night mode or shifting from the night mode to the : 25 normal mode regardless of the length of the waiting ~'. time.
When the operation has been stopped for a long ,.~' .' '' ,. ' ' ' ' '. . ' ' ' . ,., : ,:' ''' ,': ''' ;. '" ' "'. ' ' ' : ~ ':: ' . ~ ~' '. ' . . ::. . , 210~2~5 .

period of time, in the developing device 13, the deve-loplng blade 25 is constant:Ly ln contact wlth the same position of the developing roller 24. Since the deve-loping blade ~5 is urged by the leaf sprin~ 27 to compress the surface of the developing roller 24, a por-tion of the surface of the developlng roller 24 con-tacting the developing blade 25 is distorted. If a developing operation is performed in this state, a hori-zontal line is formed in a portion of an image as a result of development with the distorted developing roller ~4, thus degrading the image quality.
In thls embodiment, however, after the operation has been stopped for a long period of time, the ini-tialize sequence is performed prior to the prlnting sequence or shifting to the normal mode, so that the developing roller 24 is rotated to a certaln degree. As the developing roller 24 is mainly made of urethane or the like, when it is rotated, lt is restored to the ori-ginal state. Distortion is thus recovered by rotation in the initlalize sequence. Accordingly, when prlntlng is to be subseguently performed ln the printing sequence, a horizontal llne will not be formed ln the lmage.
Addltlonal advantages and modifications will readily occur to those skilled in the art. Therefore, - the present invention ln lts broader aspects is not limited to the specific details, representative devices, ''' ; ,, ~ : . . ~ , . - . .
.. .,' . . ~: . :, . .
, . ,: . . ~ ., ., , . ;
' ~', ' .;,. ' ' .: ! ' ' ' ' ' 210~2~

and illustrated examples shown and described herein.
Accordingly, various modlfications may be made without departing from the splrit or scope of the general inven-tlve concept as defined by the appended claims and their equivalents. For example, ln the above embodiments, the transfer roller 51 is used as a transfer contact member.
However, a component other than a roller, e.g., a brush may be used for transfer the toner image to the recording sheet. The present lnventlon ls not limlted to a facsimile apparatus, and may be applied to a copying ~ach1ne and a printer.

:
, . .
, .L

~.~

( , ~ . ' '' ~, ,' , " ' :"' . .' , ' . "

Claims (9)

1. An electrophotographic apparatus comprising charging means and developing means which are respectively arranged at a predetermined charging position and at a predetermined developing position along a surface of a rotatable photosensitive member, the photosensitive member having a predetermined point which is located at the charging position when charging of said photosensitive member by said charging means starts, and the developing means including toner carrier means and carrier rotating means for rotating the toner carrier means, the apparatus further comprising development control means for keeping rotation of said toner carrier means by said carrier rotating means stopped from start of rotation of said photosensitive member until said predetermined point of the photosensitive member reaches said predetermined developing position.

2. An electrophotographic apparatus according to claim 1, in which said development control means further includes means for causing said carrier rotating means to rotate said toner carrier means after said predetermined point of the photosensitive member reaches said predetermined developing position, and means for applying a developing bias to said toner carrier means after said predetermined point of the photosensitive member reaches said predetermined developing position.

3. An electrophotographic apparatus including charging means arranged at a predetermined charging position along a surface of a rotatable photosensitive member and developing means arranged at a predetermined developing position along the surface of the photosensitive member, the developing means including toner carrier means contacting the photosensitive member and carrier rotating means for rotating the toner carrier means, toner being charged to have a predetermined polarity by rotation of the toner carrier means, the photosensitive member having a predetermined point located at the developing position when the photosensitive member starts rotating, the apparatus further comprising:
first power supply means for generating a voltage having an opposite polarity to the predetermined polarity;
a contact member arranged at a predetermined transfer position for applying the voltage generated by said first power supply means to a printing sheet disposed at said photosensitive member;
second power supply means for generating a voltage having the predetermined polarity;
switching means having at least a first state, in which the voltage generated by said first power supply means is applied to said contact member, and a second state, in which the voltage generated by said second power supply means is applied to said contact member; and control means for setting said switching means to the second state upon start of rotation of the photosensitive member and maintaining the switching means in the second state until said predetermined point on said photosensitive member passes the transfer position.

4. An electrophotographic apparatus having a low-power mode, in which power supplied to some sections is decreased relative to power supplied thereto in modes other than the low-power mode, the apparatus comprising:
developing means for forming a toner image on a photosensitive member, the developing means including toner carrier means and carrier rotating means for rotating said toner carrier means; and control means for causing said carrier rotating means to rotate said toner carrier means by a predetermined amount before performing printing in the low-power mode.

5. An electrophotographic apparatus having a low-power mode, in which power supplied to some sections is decreased relative to power supplied thereto in modes other than the low-power mode, the apparatus comprising:
developing means for forming a toner image on a photosensitive member, the developing means including toner carrier means and carrier rotating means for rotating said toner carrier means; and control means for causing said carrier rotating means to rotate said toner carrier means by a predetermined amount immediately after the low-power mode is cancelled.

6. An apparatus according to claim 4 or 5, further comprising:
detecting means for detecting a present time; and determining means, responsive to the detecting means, for determining whether an operation mode is the low-power mode based on whether the present time falls within a predetermined period of time designated for the low-power mode.

7. An electrophotographic apparatus comprising:
a developing means for forming a toner image on a photosensitive member, the developing means including toner carrier means and carrier rotating means for rotating said toner carrier means;
measuring means for measuring a period of time between rotations of said toner carrier means; and control means for causing said carrier rotating means to rotate said toner carrier means by a predetermined amount before starting a printing operation when said period of time measured by the measuring means exceeds a predetermined length.

8. An electrophotographic apparatus comprising:
developing means for forming a toner image on a photosensitive member, the developing means including a toner carrier roller made of an elastic member for carrying a toner to said photosensitive member, a developing blade urged into contact with the toner carrier roller by a spring for maintaining an amount of toner carried to said photosensitive member, and rotating means for rotating said toner carrier roller to charge the toner by friction with the developing blade;
measuring means for measuring a period of time during which the rotation of said toner carrier roller is stopped; and control means for causing said rotating means to rotate said toner carrier roller by a predetermined amount before starting a printing operation when said period of time measured by the measuring means exceeds a predetermined length.

9. An electrophotographic apparatus comprising:
developing means for forming a toner image on a photosensitive member, the developing means including a toner carrier roller made of an elastic member for carrying a toner to said photosensitive member, a developing blade contacting the toner carrier roller for maintaining an amount of toner carried to said photosensitive member, and rotating means for rotating said toner carrier roller to charge the toner by friction with the developing blade;
measuring means for measuring a period of time during which the rotation of said toner carrier roller is stopped; and control means for causing said rotating means to rotate said toner carrier roller by a predetermined amount before starting a printing operation when said period of time measured by the measuring means exceeds a predetermined length;
wherein said developing means comprises a first motor for rotating said toner carrier roller, and a second motor for rotating said photosensitive member.