JP3486068B2 - Developing device in image forming apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention supplies toner to an electrostatic latent image formed on the surface of a photosensitive drum to develop the electrostatic latent image by toner, and at the same time, develops toner on the surface of the photosensitive drum. The developing device used in an image forming device such as a laser printer that transfers the formed image to a sheet to form an image. Especially, the deterioration of the surface of the developing roller and the increase of deteriorated toner remaining in the developing chamber due to aging. Even in this case, it is possible to effectively prevent the charging roller from being charged with poorly charged toner that occurs after the toner is replenished to the toner storage portion, and thus, it is possible to always form an image having a good image quality. In the developing device.

[0002]

2. Description of the Related Art Conventionally, various types of apparatuses have been proposed as a developing apparatus in an image forming apparatus such as a laser printer. Generally, a toner storage unit including a toner cartridge and toner from the toner storage unit are supplied to a developing chamber. The auger member to disperse the toner, the toner supply roller to supply the dispersed toner, and the developing roller to supply the toner supplied from the toner supply roller to the electrostatic latent image on the photoconductor to develop the toner. An example of such a toner supply device will be described with reference to FIG. FIG. 10 is an explanatory view schematically showing a side cross section of a main part of a developing device in a conventional image forming apparatus.

In FIG. 10, a toner supply device stores a toner and has a toner cartridge 100 in which a hole for a toner supply port is formed at a substantially central position in the width direction, and the toner cartridge 100 contains the toner. An agitator 103 that stirs and supplies toner from the toner supply port 101 to the developing chamber 102 side is provided. Further, a toner supply hole is formed in the frame F so as to correspond to the toner supply hole of the toner cartridge 100, and the toner supply port 101 is constituted by the two toner supply holes. Two auger members 109 and 110 are rotatably arranged at a position (right side in FIG. 10) near the toner supply port 101 in the developing chamber 102, which is closed by the upper frame F1 and the lower frame F2. Each auger member 109, 11
0 serves to uniformly disperse the toner discharged from the toner supply port 101. A toner supply roller 104 is rotatably arranged at a lower position in the developing chamber 102, and a developing roller 105 is rotatably arranged so as to face the toner supply roller 104. The toner supply roller 104 supplies the toner supplied from the toner supply port 101 to the developing roller 105. Here, the toner supply roller 104 includes a roller shaft body 104A made of metal (for example, formed of various steel materials) and a conductive sponge material 104B covering the periphery of the roller shaft body 104A. The developing roller 105 is a roller shaft body 105 made of metal (for example, made of various steel materials).
A and the circumference of the roller shaft body 105A are covered with a conductive rubber material 105B that is generally harder than the conductive sponge material 104B. Therefore, when the toner is supplied from the toner supply roller 104 to the developing roller 105, the conductive sponge material 104B of the toner supply roller 104 is compressed to a certain degree to the conductive rubber material 105B of the developing roller 105. Abutted. Further, the developing roller 105
A constant bias voltage is applied from the constant voltage DC power supply device 112 to the roller shaft body 105A. Further, the roller shaft 104A of the toner supply roller 104 is also applied with a constant bias voltage from the constant voltage DC power supply device 111 so that the charged toner goes from the toner supply roller 104 to the developing roller 105.

If a bias voltage is applied to the supply roller 104, the toner having good charging characteristics can be positively supplied to the developing roller 105.
When 0 is exchanged and a large amount of new insufficiently charged toner is supplied to the developing chamber 102, only the insufficiently charged toner is selectively collected to the developing roller 105.
It is possible to prevent fogging caused by supplying a large amount of poorly charged toner that is not sufficiently charged to the developing roller 105.

A blade 107 is fixed to the inner wall of the upper frame F1 above the developing roller 105 via a fixing member 106.
It acts to regulate the layer thickness of the toner layer supplied to the surface of the developing roller 105. Further, the developing roller 105 is arranged so as to be in contact with the photoconductor drum 108, and an electrostatic latent image is formed on the surface of the photoconductor drum by a laser emitting device (not shown) that scans laser light based on image data. Is formed. The developing roller 105 is the photosensitive drum 1.
The toner is supplied to the electrostatic latent image formed on the surface of the toner image 08 to develop the image, and the toner-developed image on the surface of the photoconductor drum 108 is fed from a paper feeding unit (not shown). The image is formed by being transferred onto the fed paper.

[0006]

However, in the developing device of the conventional image forming apparatus, since the bias voltage of the toner supply roller 104 is always applied, the amount of the sufficiently charged toner increases and the charging failure occurs. Even if there is no fear that a large amount of toner will be supplied, only the toner having a good charging property is supplied to the developing roller 105 and consumed, the toner having a bad charging property is not consumed, and the developing chamber 102 is not consumed.
There was a problem of being accumulated in. There is also a problem that the constant voltage DC power supply device 111 consumes a large amount of power.

Therefore, the present invention has been made to solve the above-mentioned problems, and it is possible to efficiently prevent a large amount of uncharged toner from adhering to the developing roller after toner supply. An object of the present invention is to provide a developing device in an image forming apparatus capable of preventing toner having poor chargeability from accumulating in the developing chamber and always forming an image having good image quality. And

[0008]

In order to achieve the above object, a developing device in an image forming apparatus according to claim 1 is a developing device in an image forming apparatus for forming an image by an electrophotographic process, wherein A developing roller, which is arranged oppositely, for developing the electrostatic latent image formed on the photosensitive member with toner, a developing bias applying means for applying a developing bias voltage to the developing roller, and a toner for the developing roller, which is arranged opposite to the developing roller. A supply roller for supplying, a supply bias applying means for applying a supply bias voltage such that the toner charged on the roller shaft of the supply roller is directed from the supply roller to the developing roller, and a toner storing portion for the toner supplied to the supply roller. And a toner replenishment detection unit that detects that toner has been replenished to the toner storage unit. A number of printed sheets detecting means for detecting the number of printed sheets of the photoconductor, the toner replenishing detecting means detects the toner replenishment, and until the number of printed sheets detected by the printed number detecting means reaches a predetermined number. A bias voltage is applied to the roller shaft of the supply roller via the supply bias applying means.

In the developing device of the image forming apparatus having such a feature, after the toner replenishment detecting means detects the toner replenishment to the toner storage portion, the printed sheet number detecting means counts the number of printed sheets to obtain the predetermined number of printed sheets. A bias voltage is applied to the roller shaft of the supply roller until it reaches.
As a result, when replenishing toner, it is possible to selectively supply a sufficiently charged toner to the developing roller and prevent a large amount of uncharged toner from being supplied to the developing roller, and always form an image with good image quality. It will be possible. Further, after the predetermined number of prints is reached, the amount of sufficiently charged toner is increased, so that even if the supply bias is not applied, a large amount of uncharged toner is not supplied to the developing roller. The bad toner is not properly consumed and accumulated. Further, it is possible to reduce the power consumption of the supply bias applying unit of the image forming apparatus.

According to a second aspect of the present invention, there is provided a developing device in the image forming apparatus according to the first aspect, wherein the developing device in the image forming apparatus according to the first aspect includes a cumulative printed sheet number storage means for detecting and storing the cumulative printed sheet number of the photoconductor. A print number information storage unit for storing number information, and after the toner replenishment detection unit detects the toner replenishment, the print number information storage unit stores the print number information based on the cumulative print number stored in the cumulative print number storage unit. The predetermined number of printed sheets corresponding to the cumulative number of printed sheets is read from the stored number of printed sheets, and the supply bias is supplied until the number of printed sheets is detected by the print number detecting means and the predetermined number of printed sheets is reached. It is characterized in that a bias voltage is applied to the roller shaft of the supply roller via the applying means.

In the developing device of the image forming apparatus having such a feature, after the toner replenishment detecting means detects the toner replenishment to the toner storage portion, it corresponds to the cumulative printed sheet number stored in the accumulated printed sheet number storing means. The printed sheet number information is read from the printed sheet number information storage means, and a bias voltage is applied to the roller shaft of the supply roller until the printed sheet number reaches the printed sheet number information. As a result, the operating time of the developing device becomes long, the toner charging failure is reduced due to surface deterioration of the developing roller due to aging, and the deterioration of the developing roller surface occurs even if the amount of deteriorated toner remaining in the developing chamber increases. The time to apply the bias voltage to the roller shaft of the supply roller can be optimized according to the state and the residual amount of deteriorated toner. It is possible to efficiently prevent the image sticking, and thus always form an image having good image quality.

Further, the developing device in the image forming apparatus according to claim 3 is the developing device in the image forming apparatus according to claim 1 or 2, wherein the printed sheet number detecting means is based on the movement amount of the photoconductor. The feature is that the number of printed sheets is detected.

In the developing device of the image forming apparatus having such characteristics, the number of printed sheets is detected based on the moving amount of the photosensitive member, and the detected number of printed sheets and the movement of the photosensitive member due to paper jam during printing. Even when the amounts do not match, it is possible to detect the actual operating time of the developing roller and the supply roller.

A developing device in the image forming apparatus according to a fourth aspect is the developing device in the image forming apparatus according to any one of the first to third aspects, wherein a constant current for controlling the supply bias applying means with a constant current. Equipped with control means,
A bias voltage having a predetermined current value is applied to the supply roller from the supply bias applying means by the constant current control means.

In the developing device of the image forming apparatus having such characteristics, the DC power supply device for applying the supply bias voltage to the roller shaft of the supply roller is controlled to a constant current so that the surfaces of the supply roller and the development roller are insulated. Even if a film or the like is formed, a current having a predetermined current value can be passed between the supply roller and the developing roller, and the toner held in the conductive sponge material of the supply roller can be surely charged to the developing roller. Therefore, it is possible to always form an image having good image quality.

The developing device in the image forming apparatus according to a fifth aspect is the developing device in the image forming apparatus according to the fourth aspect, in which a circuit connecting the supply bias applying means and the roller shaft of the supply roller is connected in series. A resistor provided and a diode connected in series from the supply bias applying means to the roller shaft of the supply roller in the circuit are provided, and a bias voltage having a predetermined current value is supplied from the supply bias applying means by the constant current control means. It is characterized in that it is applied to the roller shaft of the supply roller via a resistor and a diode.

In the developing device of the image forming apparatus having such a feature, the DC power supply device for applying the supply bias voltage to the roller shaft of the supply roller is subjected to constant current control, and the supply roller and the DC power supply device are connected. A resistor and a diode are connected in series with the circuit. As a result, even if an insulating film or the like is formed on the surfaces of the supply roller and the developing roller, a current having a predetermined current value can be passed between the supply roller and the developing roller, and the resistance value between the supply roller and the developing roller is reduced. Even if it decreases (for example, 2 MΩ or less), the voltage of the DC power supply device can be controlled, and among the toners held by the conductive sponge material of the supply roller, a sufficiently charged toner can be reliably supplied to the developing roller. Therefore, it is possible to always form an image having good image quality. Further, even if the DC power supply device is stopped, it is possible to prevent the backflow of current between the toner supply roller and the developing roller.

The developing device in the image forming apparatus according to claim 6 is the developing device in the image forming apparatus according to claim 4 or 5, wherein the current value controlled by the constant current control means is 2 μA or less. It is characterized by

In the developing device of the image forming apparatus having such a characteristic, a current having a predetermined current value of 2 .mu.A or less is passed between the supply roller and the developing roller to compensate for the black density and to obtain a high solid duty such as black solid. It is possible to suppress the occurrence of fog immediately after the printed part,
Therefore, it is possible to always form an image having good image quality.

Further, the developing device in the image forming apparatus according to a seventh aspect is the developing device in the image forming apparatus according to any one of the first to sixth aspects, in which the bias voltage is applied to the supply roller only during the rotation time of the supply roller. Is applied.

In the developing device of the image forming apparatus having such characteristics, the bias voltage is applied to the roller shaft of the supplying roller only during the rotation time of the supplying roller, whereby the power consumption of the image forming apparatus can be further reduced. It will be possible.

Further, the developing device in the image forming apparatus according to an eighth aspect is the developing device in the image forming apparatus according to any one of the first to sixth aspects, in which the time from the start of printing of each sheet to the end of printing is Is longer, and the bias voltage is applied to the supply roller only for a time shorter than the time from the start of printing of each sheet when printing a plurality of sheets to the start of printing of the next sheet.

In the developing device in the image forming apparatus having such characteristics, the time from the start of printing of each sheet to the end of printing is longer than the time from the start of printing of each sheet to the next start of printing. A bias voltage is applied to the supply roller for a period of time. As a result, a bias voltage can be applied to the toner held on the conductive sponge material of the supply roller even in an area wider than the image area.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, with respect to an image forming apparatus according to the present invention, first and second embodiments in which the present invention is embodied in a laser printer will be described in detail with reference to the drawings based on FIGS. 1 to 9. To do. First, a schematic configuration of the laser printer according to the first embodiment will be described with reference to FIG.
FIG. 1 is a side cross section of a laser printer. In FIG.
The laser printer 1 includes a main body case 2, a first paper feed tray 3 provided on an upper surface side of a rear portion of the main body case 2, a second paper feed tray 4, a paper transport mechanism 5 provided in the main body case 2,
A scanner unit 6, a process unit 7, a fixing unit 8, and other drive units for driving the first and second paper feed trays 3 and 4, the paper transport mechanism 5, and the like (not shown; accommodated in the left end portion of the main body case 2). Be done) etc. On the front upper surface side of the main body case 2, a top cover 10 that can open the upper surface side of the printing mechanism unit and a paper discharge tray 11 are provided. The paper discharge tray 11 can be switched between a closed position and an open position, and functions as a tray for receiving printed paper at the open position. Here, the scanner unit 6,
The process unit 7, the fixing unit 8 and the like correspond to the print mechanism section. The process unit 7 includes the casing 2
4, the photosensitive drum 25, the charger 26, the developing roller 27,
The cartridge structure is such that the transfer roller 28, the cleaning roller 29, etc. are accommodated and can be attached to and detached from a predetermined portion in the body case 2.

The first paper feed tray 3 is fixedly provided on the upper surface of the main body case 2 near the rear end thereof, and the second paper feed tray 4 is the first paper feed tray of the main body case 2. 3 is detachably provided on the upper surface of the front side. The paper transport mechanism 5 is for transporting the paper P selectively fed from the first paper feed tray 3 and the second paper feed tray 4 to the process unit 7. Of the pair of feed rollers 12a and 12b provided on the lower end side of the second sheet feeding tray 4 and the pair of registration rollers 1 provided on the lower end side of the second sheet feeding tray
3a and 13b. The feed roller 12a is a driving roller, and the feed roller 12b is a driven roller. The registration roller 13a is a driving roller, and the registration roller 13b is a driven roller. Further, a paper feed sensor 50 is arranged near the center of the registration roller 13a.
The sheet conveying path 14 from the first sheet feeding tray 3 to the registration rollers 13 a and 13 b includes a lower surface side conveying path 14 a extending along the lower surface of the second sheet feeding tray 4, and the second sheet feeding tray 4 is connected to the main body case 2. In the state of being removed from, the lower surface side transport path 14a is opened to the outside. Paper P fed from the first paper feed tray 3 via the pickup roller 36
Is driven by a pair of feed rollers 12a and 12b, passes through the lower surface side transport path 14a, and is registered to the registration rollers 13a and 1a.
When the sheet P reaches 3b, the sheet feed sensor 50 detects the passage of the sheet P, and after the registration, the sheet P is fed and driven to be conveyed to the process unit 7. The paper P fed from the second paper feed tray 4 via the pickup roller 36 reaches the registration rollers 13a and 13b, the paper feed sensor 50 detects the passage of the paper P fed, and the feed drive is performed after registration. It is then transported to the process unit 7.

The scanner unit 6 is arranged below the process unit 7, and has a laser emitting section (not shown),
The polygon mirror 20, the reflecting mirrors 21 and 23, the lens 22 and the like are provided, and the laser beam from the laser emitting section is indicated by a chain line in the polygon mirror 20, the reflecting mirror 21, and the lens 2.
2. An electrostatic latent image is formed on the surface of the photosensitive drum 25 by irradiating and exposing the outer peripheral portion of the charged and rotating photosensitive drum 25 of the process unit 7 through the reflecting mirror 23 at high speed scanning.

The process unit 7 includes a casing 2
4, photosensitive drum 25, scorotron charger 26, developing roller 27, transfer roller 28, cleaning roller 2
9, a toner box 30, a toner supply roller 31, etc. are built in. By inserting the toner cartridge 54 (see FIG. 2) into the toner box 30 with the process unit 7 removed from the main body case 2,
It is designed to replenish toner. The toner in the toner cartridge 54 is agitated by the agitator 32, discharged from the opening 30A of the toner box 30, and then supplied to the developing roller 27 via the toner supply roller 31, and the toner layer having a constant thickness is formed by the blade 33. Developing roller 2
It is carried by the photosensitive drum 7, and is supplied to the photosensitive drum 25. Two auger members 37 and 38 are rotatably arranged near the opening 30A of the toner box 30, and the auger members 37 and 38 store the toner discharged from the opening 30A in the casing 24. To evenly disperse.

The electrostatic latent image formed on the surface of the photosensitive drum 25 is visualized by adhering toner from the developing roller 27, and the paper is transferred between the photosensitive drum 25 and the transfer roller 28. Is transferred to the fixing unit 8
It is sent inside and fixed. The toner remaining on the surface of the photosensitive drum 25 is temporarily collected by the cleaning roller 29 and then collected by the developing roller 27 via the photosensitive drum 25 at a predetermined timing. Fixing unit 8
Is for thermally fixing the toner to the sheet, and includes the heating roller 34 and the pressing roller 3 pressed by the heating roller 34.
5. A pair of discharge rollers 1 provided on the downstream side of the rollers 34 and 35 for discharging the paper to the outside of the main body case 2.
It has 5a and 15b. Further, a paper discharge sensor 51 is arranged near the center of the discharge roller 15a.
The discharge sensor 51 detects discharge of the paper P to the outside.

In the above structure, the paper P is passed through the photosensitive drum 25 and the transfer roller 28 of the process unit 7.
The conveyance speed at which the fixing roller 8 is fed is the heating roller 34, the pressing roller 35, and the discharge rollers 15a and 15b of the fixing unit 8.
It is set so as to be equal to or higher than the transport speed at which the paper P is sent out via the.
This is because the conveyance speed at which the sheet P is sent out through the heating roller 34, the pressing roller 35, and the discharge rollers 15a and 15b is the sheet P via the photosensitive drum 25 and the transfer roller 28.
This is because there is a possibility that the image forming position may be displaced in the process unit 7 and the image may be disturbed if the conveying speed is higher than the conveying speed at which the sheet is conveyed.

Next, the detailed structure of the process unit 7 will be described with reference to FIG. FIG. 2 is a side sectional view showing the process unit 7 in an enlarged manner. In FIG. 2, the toner supply roller 31 is rotatably arranged at a lower position in the developing chamber 40, and the developing roller 27 is rotatably arranged so as to face the toner supply roller 31. The toner supply roller 31 supplies the toner supplied from the toner supply port 30A to the developing roller 27. Here, the toner supply roller 31 includes a roller shaft body 31A and a roller shaft body 31A made of metal (for example, formed of various steel materials).
And a conductive sponge material 31B that covers the periphery thereof. The developing roller 27 is made of metal (for example,
Roller shaft 27A made of various steel materials) and conductive rubber material 2 which is generally harder than conductive sponge material 31B
The periphery of the roller shaft body 27A is covered with 7B. Therefore, when toner is supplied from the toner supply roller 31 to the developing roller 27, the toner supply roller 31
The conductive sponge material 31B is in contact with the conductive rubber material 27B of the developing roller 27 while being compressed to some extent.

A toner sensor 52 for detecting the amount of toner in the toner cartridge 54 is soldered to the circuit board in the downward direction (lower left side in FIG. 2) of the toner box 30. It is screwed to 53. The toner sensor 52 is composed of an LED and a photo sensor, holds a part of the lower portion of the toner cartridge 54, and detects the presence or absence of toner by detecting the amount of light transmission.

Next, the process unit 7 of the first embodiment
The control configuration will be described with reference to FIG. Figure 3 is the first
Process unit 7 of laser printer 1 according to the embodiment
3 is a block diagram showing the control configuration of FIG. In FIG. 3, the laser printer 1 includes a CPU 61 that controls each device, a ROM 62 that stores a control program, a RAM 62 that stores processing data, a cumulative print number value, and a bias voltage of a toner supply roller corresponding to each cumulative print number value. EEP that stores the number of printed sheets applied and the counter value of the number of printed sheets
It is composed of ROM 64, ASIC, etc.
A sensor circuit such as a discharge sensor 51 and a toner sensor 52 is connected to the control circuit unit 66 for controlling the high-voltage power supply circuit unit 67, the photosensitive drum 25, the charger 26, the developing roller 27, the transfer roller 28, and cleaning. The roller 29 and the toner supply roller 31 have a high voltage power supply circuit section 67 for applying a high bias voltage.
Further, the CPU 61 controls the control circuit unit 66 based on each sensor value and the program stored in the ROM 62.
To control. Here, the roller shaft 27 of the developing roller 27
A is supplied with a bias voltage from the high-voltage power supply circuit section 67 via the control circuit section 66 (about DC in the case of the first embodiment).
700 V) is applied at a constant voltage. Further, a bias voltage (about DC800V in the case of the first embodiment) is applied as a constant voltage from the high voltage power supply circuit section 67 to the roller shaft body 31A of the toner supply roller 31 via the control circuit section 66. As a result, since the toner having the positive charging characteristic is used in this embodiment, the voltage for directing the toner to the developing roller 27 is applied to the toner supply roller 31.

Next, a process of applying a bias voltage to the toner supply roller 31 of the process unit 7 in the laser printer 1 according to the first embodiment having the above-mentioned structure will be described with reference to FIGS. 4 and 5. FIG. 4 is a flowchart of a process of applying a bias voltage to the toner supply roller 31 according to the first embodiment. FIG. 5 is a data table showing the number of printed sheets to which the bias voltage is applied, which corresponds to each cumulative number of printed sheets when the bias voltage is applied to the toner supply roller 31 after the toner cartridge 54 of the first embodiment is replaced. First, the laser printer 1 reads out whether or not the process unit 7 needs to be replaced, reads out the cumulative print number value stored in the EEPROM 64, and determines whether it is equal to or more than a predetermined value (S1). When it is not necessary to replace the process unit 7 (when the cumulative print number value is less than or equal to the default value) (S
1: NO), the toner sensor 52 detects the remaining amount of toner in the toner cartridge 54 (S4). When the process unit 7 needs to be replaced (when the cumulative print number value is larger than the predetermined value) (S1: YES), the process unit 7 is confirmed to be replaced (S2: YES), and the cumulative print number value is set to 0. And store it in the EEPROM 64 (S
3). Next, the toner sensor 52 detects the remaining amount of toner in the toner cartridge 54 (S4).

Next, the toner sensor 52 detects the toner remaining amount of the toner cartridge 54, and if the toner remains (S4: NO), the print count value is read from the EEPROM 64 (S5), and the print count value is 0 or not. It is judged (S6). If the print count value is 0 (S
6: YES), the voltage of the toner supply roller is turned off (S17), and printing is started (S7). Next, a timer (not shown) in the control circuit unit 66 detects whether the photosensitive drum 25 has rotated by one print, and printing is continued until one print is rotated (S8: N).
O), when the rotation of the photosensitive drum 25 for one print is detected (S8: YES), the cumulative print number stored in the EEPROM 64 is incremented by 1 and stored again in the EEPROM 64 (S9). Next, if printing is not completed (S10:
NO), the toner sensor 52 causes the toner cartridge 5 to
The remaining toner amount of No. 4 is detected (S4), and the printing operation is continued.
If the printing is finished (S10: YES), the printing work is finished.

Further, it is judged whether the print count value is 0, and if the print count value is not 0 (S6: NO),
A constant voltage bias voltage (about 8% in the case of the first embodiment) is applied by the high-voltage power supply circuit unit 67 via the control circuit unit 66.
00 VDC) to the roller shaft body 31 of the toner supply roller 31.
It is applied to A (S14). Next, printing is started (S1
5). Next, a timer (not shown) in the control circuit unit 66 detects whether or not the photosensitive drum 25 has rotated by one print, and printing is continued until one print is rotated (S16: NO), When a rotation (not shown) of the control circuit section 66 detects the rotation of the photosensitive drum 25 for one print (S16: YES), E
The print count value stored in the EPROM 64 is decremented by 1 and stored again in the EEPROM 64 (S18). Next, the cumulative print number value stored in the EEPROM 64 is incremented by 1 and stored again in the EEPROM 64 (S
9). Next, if the printing is not completed (S10: NO), the toner sensor 52 detects the toner remaining amount of the toner cartridge 54 (S4), and the printing operation is continued. If printing is completed (S10: YES), the high-voltage power supply circuit section 67 is stopped via the control circuit section 66 (S1).
9) The printing operation is completed.

When the toner sensor 52 detects the remaining amount of toner in the toner cartridge 54 and no toner remains (S4: YES), the printing operation is stopped and the toner cartridge 54 is replaced (S11: NO). ). Next, the toner sensor 52 detects the remaining amount of toner,
When it is detected that the remaining amount of toner is sufficient, it is determined that the toner cartridge 54 has been replaced (S11: YE
S) After replacing the toner cartridge 54 stored in the EEPROM 64, the print number value (see FIG. 5) corresponding to each cumulative print number of the print numbers for applying the bias voltage to the toner supply roller 31 is read from the EEPROM 64 (S12). The number of printed sheets is stored in the EEPROM 64 as a new print count value (S13). Next, the toner sensor 52 detects the remaining amount of toner in the toner cartridge 54 (S4), and the printing operation is continued.

Here, the print number value corresponding to each cumulative print number will be described with reference to FIG. When the cumulative number of prints obtained by converting the cumulative number of rotations of the photosensitive drum 25 into the cumulative number of prints (the amount of rotation of one print is converted to one print sheet) is 0, the toner supply roller 31 is biased after the toner cartridge 54 is replaced. When the number of prints to which the voltage is applied is 0 and the cumulative number of prints is 1 to 1000, the number of prints to which the bias voltage is applied to the toner supply roller 31 is 10, and when the cumulative number of prints is 100 to 2500, Toner supply roller 31
When the bias printing voltage is applied to 20 sheets, the cumulative printing sheet number is 2501 to 5000 sheets, when the bias voltage is applied to the toner supply roller 31, the printing sheet number is 30 sheets, and the cumulative printing sheet number is 5001 to 8000 sheets. Is 40 when the bias voltage is applied to the toner supply roller 31.
When the cumulative number of printed sheets is 8001 to 9000, the bias voltage is applied to the toner supply roller 31 for 50 sheets, and when the cumulative printed number is 9001 or more, the bias voltage is applied to the toner supply roller 31. The number of printed sheets is 60.

As described in detail above, in the process unit 7 according to the first embodiment, the toner sensor 52
After the replacement of the toner cartridge 54 is detected by the
After the toner cartridge 54 stored in the ROM 64 is replaced, the number of printed sheets corresponding to each cumulative number of printed sheets for applying the bias voltage to the toner supply roller 31 (see FIG. 5).
(Reference) is read from the EEPROM 64, and the number of printed sheets is stored in the EEPROM 64 as a new print count value. Next, while the photosensitive drum 25 is rotating until the photosensitive drum 25 rotates by the print count value,
A bias voltage is applied to the roller shaft body 31A of the toner supply roller 31. As a result, the operation time of the process unit 7 becomes long, and even if deterioration of the toner charging ability of the developing roller 27 due to aging and increase of deteriorated toner remaining in the developing chamber 40 occur, charging of the developing roller 27 is performed. The time for applying the bias voltage to the roller shaft body 31A of the toner supply roller 31 can be optimized in accordance with the deterioration of the performance and the residual amount of deteriorated toner, and the charging failure of the uncharged toner generated after the toner cartridge 54 is replaced. It is possible to efficiently prevent adherence to the developing roller 27, and thus always form an image having good image quality.

When the number of rotations of one print of the photosensitive drum 25 is converted into one of the prints, and the detected number of prints does not match the number of rotations of the photosensitive drum 25 due to a paper jam during printing. Also in this case, it is possible to detect the actual working time of the developing roller 27 and the toner supply roller 31.

Further, the bias voltage is applied to the roller shaft 31A of the toner supply roller 31 only while the photosensitive drum 25 is rotating until the number of print count values is counted, thereby consuming the laser printer 1. It becomes possible to reduce power consumption.

Next, the process unit of the laser printer according to the second embodiment will be described in detail. The schematic configuration of the laser printer according to the second embodiment is almost the same as the schematic configuration of the laser printer of the first embodiment (see FIGS. 1 and 2).

Next, the process unit 7 of the second embodiment
The control configuration of will be described with reference to FIG. FIG. 6 is the second
Process unit 7 of laser printer 1 according to the embodiment
3 is a block diagram showing the control configuration of FIG. 6, the laser printer 1 includes a CPU 61 that controls each device, a ROM 62 that stores a control program, a RAM 62 that stores processing data and the like, and an EE that stores a print number counter value and the like.
It is composed of PROM64, ASIC, etc.
0, a paper discharge sensor 51, a toner sensor 52, and other sensors, and a control circuit unit 66 for controlling the high-voltage power supply circuit unit 67, the constant current control unit 68, etc., the photosensitive drum 25, the charger 26, and the developing roller. 27, the transfer roller 28, and the cleaning roller 29 are subjected to constant current control of a high-voltage power supply circuit section 67 for applying a high-voltage bias voltage, a DC power supply circuit section 69 for applying a bias voltage to the toner supply roller 31, and a DC power supply circuit section 69. Constant current control unit 68,
A resistor 70 connected in series to a circuit connecting the DC power supply circuit unit 69 and the toner supply roller 31, and a diode 71 connected in the forward direction from the DC power supply circuit unit 69 to the toner supply roller 31 are connected to the circuit. Have

Further, the CPU 61 controls each sensor value and the ROM 6
The control circuit unit 66 is controlled on the basis of the program stored in FIG. Here, via the control circuit unit 66 to the roller shaft 27A of the developing roller 27,
A bias voltage (about 700 VDC in the case of the second embodiment) is applied as a constant voltage from the high-voltage power supply circuit section 67.
Further, the resistance value of the resistor 70 is large (about 300 MΩ in the case of the second embodiment), and when the resistance value between the DC power supply circuit unit 69 and the toner supply roller 31 becomes extremely small, the constant current control unit 68. Even if the current value controlled by
2 μA in the case of the embodiment), the output voltage of the DC power supply circuit unit 69 is several hundred V (600 V in the case of the second embodiment), which is a controllable voltage range of the DC power supply circuit unit 69.
Further, by connecting the diode 71 in the forward direction between the DC power supply circuit unit 69 and the toner supply roller 31,
Even if the DC power supply circuit unit 69 is stopped and the potential becomes 0V,
It is possible to prevent backflow of current from the developing roller 27. As a result, since the toner having the positive charging characteristic is used in this embodiment, the voltage for directing the toner to the developing roller 27 is applied to the toner supply roller 31.

Next, a process of applying a bias voltage to the toner supply roller 31 of the process unit 7 in the laser printer 1 according to the second embodiment having the above-mentioned structure will be described with reference to FIGS. 7 to 9. FIG. 7 is a flowchart of processing for applying a bias voltage to the toner supply roller 31 according to the second embodiment. FIG. 8 is a timing chart of applying a bias voltage to the toner supply roller 31 according to the second embodiment. FIG. 9 is a data table showing the number of printed sheets to which the bias voltage is applied, which corresponds to each cumulative number of printed sheets when the bias voltage is applied to the toner supply roller 31 after the toner cartridge 54 of the second embodiment is replaced.

First, the laser printer 1 reads out whether or not the process unit 7 needs to be replaced, and reads out the cumulative printed sheet number value stored in the EEPROM 64 to determine whether it is equal to or more than a predetermined value (S21). When the process unit 7 does not need to be replaced (when the cumulative print number value is less than or equal to the default value) (S21: NO), the toner sensor 52 detects the remaining amount of toner in the toner cartridge 54 (S2).
4). When the process unit 7 needs to be replaced (when the cumulative print number value is larger than the default value) (S21:
YES), confirm the replacement of the process unit 7 (S2
2: YES), the cumulative print number value is set to 0, and the EEPROM
It is stored in 64 (S23). Next, the toner sensor 52 detects the remaining amount of toner in the toner cartridge 54 (S24).

Next, the toner sensor 52 detects the remaining amount of toner in the toner cartridge 54, and if the toner remains (S24: NO), the print count value is read from the EEPROM 64 (S25), and whether the print count value is 0 or not. It is determined (S26). When the print count value is 0 (S26: YES), printing is started when the paper feed sensor 50 detects passage of the paper (S27). Next, a timer (not shown) in the control circuit unit 66
It is detected whether the photosensitive drum 25 has rotated by one sheet of printing by means of, and printing is continued until it rotates by one sheet of printing (S28:
When the rotation of the photosensitive drum 25 for one print is detected by the timer (not shown) in the control circuit unit 66 (S28: YES), the cumulative print number value stored in the EEPROM 64 is increased by 1, EEP again
It is stored in the ROM 64 (S29). Next, if the printing is not completed (S30: NO), the toner sensor 52 detects the remaining amount of toner in the toner cartridge 54 (S24),
Continue printing. If printing is completed (S30:
YES), and the printing operation is completed.

Further, it is judged whether or not the print count value is 0, and if the print count value is not 0 (S26: N
O), a constant voltage bias voltage (about 800 VDC in the second embodiment) is applied to the roller shaft body 31A of the toner supply roller 31 by the high-voltage power supply circuit section 67 via the control circuit section 66 (S34). Next, printing is started (S35). Next, as shown in FIG. 8, when the paper is conveyed to start printing and the paper feed sensor 50 detects the paper,
Time measurement is started by a time measuring unit (not shown), and after time T4, the time measurement is continued until the measurement time reaches T3, and printing is continued while applying a bias voltage to the toner supply roller 31 (S36: NO). ). Here, the measurement time T
3 is longer than the paper transport time T1 from the front end to the end of each paper, and is shorter than the time T2 from the start of printing of each paper to the start of printing of the next paper when a plurality of sheets are continuously printed. . Next, when the measurement time reaches T3 (S
36: YES), the high voltage power supply circuit section 67 is stopped via the control circuit section 66 (S37). Next, EEPR
Decrement the print count value stored in OM64 by 1,
It is again stored in the EEPROM 64 (S18). Then E
The cumulative number of printed sheets stored in the EPROM 64 is incremented by 1 and stored again in the EEPROM 64 (S29). Next, if the printing is not completed (S30: NO), the toner sensor 52 detects the toner remaining amount of the toner cartridge 54 (S24), and the printing operation is continued. If the printing is finished (S30: YES), the printing work is finished.

When the toner sensor 52 detects the amount of toner remaining in the toner cartridge 54 and no toner remains (S24: YES), the printing operation is stopped and the toner cartridge 54 is replaced (S31: NO). ).
Next, the remaining amount of toner is detected by the toner sensor 52, and when it is detected that the remaining amount of toner is sufficient, it is determined that the toner cartridge 54 has been replaced (S31: YE).
S) After replacing the toner cartridge 54 stored in the EEPROM 64, the print number value (see FIG. 9) corresponding to each cumulative print number of the print numbers for applying the bias voltage to the toner supply roller 31 is read from the EEPROM 64 (S32). The number of printed sheets is stored in the EEPROM 64 as a new print count value (S33). Next, the toner sensor 52 detects the amount of toner remaining in the toner cartridge 54 (S24), and the printing operation is continued.

Here, the print number value corresponding to each cumulative print number will be described with reference to FIG. When the cumulative number of printed sheets after replacement of the process unit 7 is 0, the number of printed sheets for applying the bias voltage to the toner supply roller 31 after replacement of the toner cartridge 54 is 0 sheet, and when the cumulative number of printed sheets is 1 to 1000, the toner is supplied. The number of prints for applying a bias voltage to the roller 31 is 10, and the cumulative number of prints is 1001 to 250.
When the number of sheets is 0, the number of printed sheets for applying the bias voltage to the toner supply roller 31 is 20, and the cumulative number of printed sheets is 2501 to 2501.
When the number of sheets is 5,000, the number of prints to which the bias voltage is applied to the toner supply roller 31 is 30, and the cumulative number of prints is 50.
When the number of printed sheets is 01 to 8000, the number of prints to which the bias voltage is applied to the toner supply roller 31 is 40, and when the cumulative number of prints is 8001 to 9000, the toner supply roller 3
When the bias voltage is applied to 1, the number of prints is 50, and when the cumulative number of prints is 9001 or more, the toner supply roller 3
The number of printed sheets for applying the bias voltage to 1 is 60 sheets.

As described in detail above, in the process unit 7 according to the second embodiment, the toner sensor 52 is used.
After the replacement of the toner cartridge 54 is detected by the
After the toner cartridge 54 stored in the ROM 64 is replaced, the number of printed sheets corresponding to each cumulative number of printed sheets for applying the bias voltage to the toner supply roller 31 (see FIG. 9).
(Reference) is read from the EEPROM 64, and the number of printed sheets is stored in the EEPROM 64 as a new print count value. Next, a sheet for starting printing is conveyed, and when the sheet feeding sensor 50 detects the sheet, time measurement is started by a time measuring unit (not shown), and after T4, until the measurement time reaches T3, Roller shaft 3 of toner supply roller 31
A bias voltage having a predetermined current value (2 μA in the case of the second embodiment) is applied to 1 A by constant current control via a resistor 70 and a diode 71. As a result, the process unit 7
Even if the charging ability of the developing roller 27 is deteriorated due to the change over time and the deteriorated toner having poor charging characteristics remaining in the developing chamber 40 is increased, the developing roller 2 is operated.
Corresponding to the deterioration of the charging ability of No. 7 and the residual amount of deteriorated toner,
The time for applying the bias voltage to the roller shaft body 31A of the toner supply roller 31 can be optimized, and the defective charging toner generated after the toner cartridge 54 is replaced in the toner box 30 can be efficiently attached to the developing roller 27. Therefore, it is possible to always form an image having good image quality.

Further, an insulating coating film or the like is formed on the surfaces of the toner supply roller 31 and the developing roller 27 by constant-current controlling the DC power supply device for applying the supply bias voltage to the roller shaft body 31A of the toner supply roller 31. The toner supply roller 31 and the developing roller 27.
In the case of the embodiment, a current of 2 μA) can be passed, and the charged toner held by the conductive sponge material 31B of the supply roller can be reliably supplied to the developing roller 27, so that an image having good image quality can be obtained. Can always be formed.

Even when the DC power supply device is stopped, it is possible to prevent the backflow of the current between the toner supply roller and the developing roller.

By passing a current having a predetermined current value of 2 μA between the toner supply roller 31 and the developing roller 27,
It is possible to compensate for the black density and suppress the fog under solid black, and thus always form an image having good image quality.

Further, by applying a supply bias voltage to the roller shaft body 31A of the toner supply roller 31 during the time T3 after the toner supply roller 31 starts rotating, the area is wider than the image area. Supply roller 31
A bias voltage can be applied to the toner held on the conductive sponge material 31B.

When the number of rotations of one print on the photosensitive drum 25 is converted into the amount of one print, the number of detected prints does not match the number of rotations of the photosensitive drum 25 due to a paper jam during printing. Also in this case, it is possible to detect the actual working time of the developing roller 27 and the toner supply roller 31.

Further, after replacing the toner cartridge 54,
Until the number of printed sheets of the print count value is counted, from the start of printing of each sheet of paper for a time T3, the toner supply roller 31
By applying a bias voltage to the roller shaft body 31A, the power consumption of the laser printer 1 can be reduced.

The present invention is not limited to the first and second embodiments described above, and it is needless to say that various improvements and modifications can be made without departing from the gist of the present invention. You may do like this. (A) Although the photosensitive drum 25 is used in the above-described embodiment, an endless belt type photosensitive member may be used instead of the photosensitive drum 25. (B) In the above-mentioned embodiment, the positive charging type toner is adopted, but the negative charging type toner may be adopted. In that case, a bias voltage for negatively charging the toner may be applied to the toner supply roller 31. Further, in this case, the diode 71 is connected in series in the opposite direction.

[0058]

As described above, in the developing device of the image forming apparatus according to the first aspect, after the toner replenishment detecting means detects the toner replenishment to the toner storage portion, the number of printed sheets is counted by the printed sheet number detecting means. A bias voltage is applied to the roller shaft of the supply roller until the predetermined number of prints is reached. As a result, when replenishing toner, it is possible to selectively supply a sufficiently charged toner to the developing roller and prevent a large amount of uncharged toner from being supplied to the developing roller, and always form an image with good image quality. A developing device in a possible image forming apparatus can be provided. Further, after the predetermined number of prints is reached, the amount of sufficiently charged toner is increased, so that even if the supply bias is not applied, a large amount of uncharged toner is not supplied to the developing roller. It is possible to provide a developing device in an image forming apparatus capable of appropriately consuming and accumulating bad toner, and reducing the power consumption of the supply bias applying means of the image forming apparatus.

Further, in the developing device of the image forming apparatus according to the second aspect, after the toner replenishment detecting means detects the toner replenishment to the toner storage portion, it corresponds to the cumulative printed sheet number stored in the accumulated printed sheet number storing means. The number of printed sheets information is read from the printed sheet number information storage means, and a bias voltage is applied to the roller shaft of the supply roller until the number of printed sheets reaches the printed sheet number information. As a result, the operating time of the developing device becomes long, the toner charging failure is reduced due to surface deterioration of the developing roller due to aging, and the deterioration of the developing roller surface occurs even if the amount of deteriorated toner remaining in the developing chamber increases. The time to apply the bias voltage to the roller shaft of the supply roller can be optimized according to the state and the residual amount of deteriorated toner. It is possible to provide a developing device in an image forming apparatus that can efficiently prevent the image sticking and can always form an image having good image quality.

Further, in the developing device of the image forming apparatus according to the third aspect, the number of printed sheets is detected based on the movement amount of the photoconductor, and the detected number of printed sheets and the photoconductor are detected due to paper jam during printing. It is possible to provide the developing device in the image forming apparatus capable of detecting the actual working time of the developing roller and the supply roller even when the moving amount does not match.

Further, in the developing device of the image forming apparatus according to the fourth aspect, the DC power supply device for applying the supply bias voltage to the roller shaft of the supply roller is controlled to a constant current so that the surface of the supply roller and the development roller is covered. Even if an insulating film is formed, a current of a predetermined current value can be passed between the supply roller and the developing roller, and it is possible to reliably develop a sufficiently charged toner out of the toner held on the conductive sponge material of the supply roller. It is possible to provide a developing device in an image forming apparatus capable of supplying an image to a roller and always forming an image having a good image quality.

Further, in the developing device of the image forming apparatus according to the fifth aspect, the direct current power supply device for applying the supply bias voltage to the roller shaft of the supply roller is subjected to constant current control,
A resistor and a diode are connected in series to a circuit connecting the supply roller and the DC power supply device. As a result, even if an insulating film or the like is formed on the surfaces of the supply roller and the developing roller,
A current of a predetermined current value can be passed between the supply roller and the developing roller, and even if the resistance value between the supply roller and the developing roller decreases (for example, 2 MΩ or less), the voltage control of the DC power supply device is possible. In addition, it is possible to reliably supply a sufficiently charged toner among the toners held by the conductive sponge material of the supply roller to the developing roller, and thus it is possible to always form an image having good image quality. The developing device can be provided. Further, it is possible to provide the developing device in the image forming apparatus capable of preventing the backflow of the current between the toner supply roller and the developing roller even when the DC power supply device is stopped.

Further, in the developing device in the image forming apparatus according to the sixth aspect of the invention, the distance between the supply roller and the developing roller is 2
By supplying a current of a predetermined current value of μA or less, it is possible to compensate for the black density and suppress the occurrence of fog immediately after a high-duty printed portion such as a black solid image, thus providing a good image quality. It is possible to provide a developing device in an image forming apparatus that can always form an image.

Further, in the developing device in the image forming apparatus according to the seventh aspect, the bias voltage is applied to the roller shaft of the supply roller only during the rotation time of the supply roller, thereby further reducing the power consumption of the image forming apparatus. It is possible to provide a developing device in an image forming apparatus capable of performing the above.

Further, in the developing device of the image forming apparatus according to the eighth aspect, the time from the start of printing of each sheet to the end of printing is longer than the time from the start of printing of each sheet to the next start of printing. A bias voltage is applied to the supply roller for a short time. Accordingly, it is possible to provide the developing device in the image forming apparatus capable of applying the bias voltage to the toner held by the conductive sponge material of the supply roller up to a region wider than the image region.

[Brief description of drawings]

FIG. 1 is a side sectional view of a laser printer according to first and second embodiments.

FIG. 2 is an enlarged side sectional view showing a process unit of the laser printer according to the first and second embodiments.

FIG. 3 is a block diagram showing a control configuration of a process unit of the laser printer according to the first embodiment.

FIG. 4 is a flowchart of a process of applying a bias voltage to a toner supply roller of the laser printer according to the first embodiment.

FIG. 5 is a data table showing a print number value to which a bias voltage is applied, which corresponds to each cumulative print number when a bias voltage is applied to the toner supply roller after the toner cartridge of the first embodiment is replaced.

FIG. 6 is a block diagram showing a control configuration of a process unit of a laser printer according to a second embodiment.

FIG. 7 is a flowchart of a process of applying a bias voltage to a toner supply roller of the laser printer according to the second embodiment.

FIG. 8 is a timing chart for applying a bias voltage to the toner supply roller according to the second embodiment.

FIG. 9 is a data table showing a print number value to which a bias voltage is applied, corresponding to each cumulative print number when a bias voltage is applied to the toner supply roller after the toner cartridge of the second embodiment is replaced.

FIG. 10 is an explanatory diagram schematically showing a side cross section of a main part of a developing device in a conventional image forming apparatus.

[Explanation of symbols]

1 laser printer 7 process unit 25 photosensitive drum 27 developing roller 31 Toner supply roller 27A, 31A roller shaft 50 Paper feed sensor 51 Paper ejection sensor 52 Toner sensor 54 toner cartridge 67 High-voltage power supply circuit section 68 Constant current controller 69 DC power supply circuit 70 resistance 71 diode

Continuation of front page (56) Reference JP-A-3-101772 (JP, A) JP-A-5-100563 (JP, A) JP-A-6-43742 (JP, A) JP-A-6-67501 (JP , A) JP-A-6-194944 (JP, A) JP-A-7-5765 (JP, A) JP-A-7-114261 (JP, A) JP-A-8-179602 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 13/06-13/095 G03G 15/00 303 G03G 15/06-15/095 G03G 21/00 370-502

Claims (8)

(57) [Claims] 1. A developing device in an image forming apparatus for forming an image by an electrophotographic process, comprising: a developing roller which is arranged to face a photoconductor and develops an electrostatic latent image formed on the photoconductor with toner. A developing bias applying means for applying a developing bias voltage to the developing roller, a supply roller arranged to face the developing roller to supply toner to the developing roller, and toner charged on the roller shaft of the supplying roller is supplied from the supplying roller to the developing roller. In a developing device having a supply bias applying unit that applies a supply bias voltage that is directed, and a toner storage unit for toner supplied to the supply roller, a toner replenishment detection that detects that toner has been replenished to the toner storage unit. Means and a printed sheet number detecting means for detecting the number of printed sheets of the photoconductor, After the toner replenishment is detected, a bias voltage is applied to the roller shaft of the supply roller via the supply bias applying means until the number of printed sheets detected by the printed sheet number detecting means reaches a predetermined number. Developing device in the image forming apparatus. 2. A cumulative print number storage means for detecting and storing the cumulative print number of the photoconductor, and a print number information storage means for storing the print number information, wherein the toner replenishment detecting means detects the toner replenishment. A predetermined print number corresponding to the cumulative print number is read from the print number information stored in the print number information storage unit based on the cumulative print number stored in the cumulative print number storage unit, and 2. The bias voltage is applied to the roller shaft of the supply roller through the supply bias applying means until the detection means starts to detect the number of printed sheets and reaches the predetermined number of printed sheets. Developing device in the image forming apparatus. 3. The developing device in the image forming apparatus according to claim 1, wherein the printed sheet number detecting means detects the printed sheet number based on the movement amount of the photoconductor. 4. A constant current control unit for controlling the supply bias applying unit with a constant current, wherein the constant current control unit applies a bias voltage having a predetermined current value from the supply bias applying unit to the supply roller. The developing device in the image forming apparatus according to claim 1. 5. A resistor arranged in series in a circuit connecting the supply bias applying means and the roller shaft of the supply roller, and a resistor connected in series in the circuit from the supply bias applying means to the roller shaft of the supply roller. 5. A diode according to claim 4, wherein the constant current control means applies a bias voltage having a predetermined current value from the supply bias applying means to the roller shaft of the supply roller via the resistor and the diode. A developing device in an image forming apparatus. 6. The developing device in an image forming apparatus according to claim 4, wherein a current value controlled by the constant current control means is 2 μA or less. 7. The bias voltage is applied to the supply roller only during the rotation time of the supply roller.
A developing device in the image forming apparatus according to claim 6. 8. The supply is performed only for a time longer than the time from the start of printing of each sheet to the end of printing and shorter than the time from the start of printing of each sheet when printing a plurality of sheets to the start of printing of the next sheet. The developing device in the image forming apparatus according to claim 1, wherein a bias voltage is applied to the roller.