JPH10239961A - Developing device in image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a countercurrent between a toner supplying roller and a developing roller by applying a bias voltage to the roller shaft of the supplying roller, with a resistor and a diode. SOLUTION: A CPU 61 controls a control circuit part 66, based on each sensor value, a program, etc. The bias voltage is applied to the shaft bodies of the developing roller 27 and a controller, with a constant voltage by a high- voltage power source circuit part 67 through the control circuit part 66. Further, the resistance value of the resistor 70 is high and when the resistance value between a DC power source circuit part 69 and the toner supplying roller 31 is very low, the output voltage of the DC power source circuit part 69 for a constant current circuit becomes hundreds of volts, to be within the range of a voltage which can be controlled by the DC power source circuit part 69. Further, the diode 71 is connected in a forward direction between the DC power source circuit part 69 and the toner supplying roller 31, so that even if the DC power source circuit part 69 is stopped and a potential becomes 0V, the countercurrent from the developing roller 27 is prevented and the transfer of the toner electrified to a reverse polarity to the developing roller 27 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic latent image formed on the surface of a photoreceptor drum and a method for developing the electrostatic latent image with toner. A developing device used in an image forming apparatus such as a laser printer that transfers an image formed on a sheet to form an image, and particularly, is connected to a supply roller even if a resistance value between a development roller surface and a supply roller surface fluctuates. It is possible to easily perform the constant current control of the DC power supply
The present invention relates to a developing device in an image forming apparatus that can prevent damage to the DC power supply device even when the DC power supply device is stopped, and thus can always form an image having good image quality.

[0002]

2. Description of the Related Art Conventionally, various types of developing devices in image forming apparatuses such as laser printers have been proposed. In general, a toner storing section including a toner cartridge and toner from the toner storing section are supplied to a developing chamber. An auger member for dispersion, a toner supply roller for supplying the dispersed toner, and a developing roller for supplying the toner supplied from the toner supply roller to the electrostatic latent image on the photoconductor and developing the toner. An example of such a toner supply device will be described with reference to FIG. FIG. 5 is an explanatory view schematically showing a side cross section of a main part of a developing device in a conventional image forming apparatus.

[0005] In FIG. 5, a toner supply device has a toner cartridge 100 having a toner supply opening formed substantially at the center in the width direction and containing toner. An agitator 103 is provided for stirring and supplying toner from the toner supply port 101 to the developing chamber 102 side. Further, a toner supply hole corresponding to the toner supply hole of the toner cartridge 100 is formed in the frame F, and the toner supply port 101 is formed by the two toner supply holes. Two auger members 109 and 110 are rotatably disposed at a position (the right side in FIG. 5) near the toner supply port 101 in the developing chamber 102 closed by the upper frame F1 and the lower frame F2. Each auger member 109, 110
Has the function of uniformly dispersing the toner discharged from the toner supply port 101. A toner supply roller 104 is rotatably disposed at a lower position in the developing chamber 102, and a development roller 105 is rotatably disposed facing 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 104A made of metal (for example, formed of various steel materials) and a conductive sponge material 104B covering the periphery of the roller shaft 104A. Further, the developing roller 105 is a roller shaft 105 made of metal (for example, formed of various steel materials).
A and a conductive rubber material 105B which is generally harder than the conductive sponge material 104B cover the periphery of the roller shaft 105A. 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 extent to the conductive rubber material 105B of the developing roller 105. Has been abutted. Further, the developing roller 105
A constant bias voltage is applied from the constant voltage DC power supply 112 to the roller shaft 105A. Further, a constant voltage bias voltage is applied to the roller shaft body 104A of the toner supply roller 104 from the constant voltage DC power supply 111 so that the toner charged in the toner cartridge 100 flows from the toner supply roller 104 to the developing roller 105. I have.

[0004] A blade 107 is fixed to the inner wall of the upper frame F1 above the developing roller 105 via a fixing member 106.
An operation of regulating the thickness of the toner layer supplied to the surface of the developing roller 105 is performed. Further, the developing roller 105 is disposed so as to be in contact with the photosensitive drum 108, and an electrostatic latent image is formed on the surface of the photosensitive drum by a laser light emitting device (not shown) that scans a laser beam based on image data. Is formed. The developing roller 105 is a photosensitive drum 1
A toner is supplied to the electrostatic latent image formed on the surface of the photoconductor drum 08 to develop the toner of the image, and the image developed on the surface of the photosensitive drum 108 is supplied from a paper feeding unit (not shown). The image is transferred onto the fed sheet to form an image.

[0005]

However, in the developing device of the conventional image forming apparatus, the operation time is long and the toner supply roller 10
An insulating material such as silica covering the surface of the toner particles adheres to the surfaces of the conductive sponge material 104B and the conductive rubber material 105B of the developing roller 105 to form an insulating film.
The bias voltages of the toner supply roller 104 and the developing roller 105 are respectively set to the constant voltage DC power supplies 111 and 112.
, The bias voltage difference between the toner supply roller 104 and the developing roller 105 is constant. Therefore, the current flowing between the toner supply roller 104 and the developing roller 105 due to the insulating film becomes a very small current (for example, 0.1 μA or less) or 0, and the normally charged toner from the toner supply roller 104 to the developing roller 105 due to the electric field. The problem that movement is impossible occurs.

When the conductive sponge material 104B does not hold a sufficient amount of toner, the resistance between the toner supply roller 104 and the developing roller 105 decreases (for example, 2 MΩ or less).
Current flowing between the conductive sponge material 104B and the developing roller 105 becomes excessive current (for example, 50 μA or more), and the toner held in the conductive sponge material 104B is excessively charged, and the local aggregation of the oppositely charged toner occurs. is there.

Even if the constant voltage DC power supply 111 for applying a bias voltage to the toner supply roller 104 is changed to a DC power supply with constant current control, the toner supply roller 1
When the resistance value between the DC power supply 04 and the developing roller 105 decreases (for example, 2 MΩ or less), there is a problem that the voltage may become lower than the controllable voltage of the DC power supply.

Further, when the DC power supply for applying the bias voltage to the toner supply roller 104 is stopped, the potential of the DC power supply becomes 0 V and the toner supply roller 10
4, a reverse current flows between the developing roller 105 and the developing roller 105, and a problem occurs in which the oppositely charged toner is transferred to the developing roller 105.

The bias voltage of the toner supply roller 104 is constantly applied, and the constant voltage DC power supply 111
Therefore, there is also a problem that power is constantly consumed.

In view of the above, the present invention has been made to solve the above-described problem, and the bias voltage applied to the roller shaft of the toner supply roller is controlled by a constant current so as to be held by the conductive sponge material. An object of the present invention is to provide a developing device in an image forming apparatus that can surely move a charged toner to a developing roller and can always form an image having good image quality. In addition, by connecting a resistor and a diode in series with a circuit connecting the supply roller and a DC power supply of constant current control that applies a bias voltage to the toner supply roller, the resistance value between the toner supply roller and the developing roller is reduced. Even when the DC power supply is stopped, the DC power supply can be controlled, and even if the DC power supply is stopped, the reverse flow of the current between the toner supply roller and the developing roller is prevented, and the toner charged to the opposite polarity is developed. An object of the present invention is to provide a developing device in an image forming apparatus capable of preventing transfer to a roller and capable of always forming an image having good image quality. Still another object of the present invention is to provide a developing device in an image forming apparatus capable of reducing power consumption of the image forming apparatus by applying a bias voltage to a toner supply roller until a predetermined number of sheets are printed after toner replenishment. And

[0011]

According to a first aspect of the present invention, there is provided a developing device for an image forming apparatus for forming an image by an electrophotographic process. A developing roller for developing the electrostatic latent image formed on the photoreceptor with toner disposed opposite to the developing roller; a developing bias applying unit for applying a developing bias voltage to the developing roller; A supply roller for supplying, a supply bias applying unit for applying a supply bias voltage such that the toner charged on the roller shaft of the supply roller goes from the supply roller to the developing roller, and a toner storage unit for the toner supplied to the supply roller A constant current control means for controlling the supply bias applying means with a constant current; The constant current control includes a resistor serially connected to a circuit connecting the assembling means and the roller shaft of the supply roller, and a diode serially connected to a roller shaft of the supply roller from a power supply device of the circuit. A bias voltage having a predetermined current value is applied from the supply bias applying means to the roller shaft of the supply roller via the resistor and the diode.

In the developing device of the image forming apparatus having such features, a DC power supply for applying a supply bias voltage to a roller shaft of a supply roller is controlled at a constant current, and connects the supply roller to the DC power supply. A resistor and a diode are connected in series with the circuit. As a result, even when 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 flow between the supply roller and the developing roller, and the resistance value between the supply roller and the developing roller can be reduced. Even if it decreases (for example, 2 MΩ or less), the voltage of the DC power supply can be controlled, and the charged toner held on the conductive sponge material of the supply roller can be reliably moved to the developing roller, which is favorable. An image having a high image quality can always be formed. Further, even if the DC power supply is stopped, it is possible to prevent the current from flowing backward between the toner supply roller and the developing roller.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the current value controlled by the constant current control means is 2 μA or less. I do.

In the developing device of the image forming apparatus having such features, a current having a predetermined current value of 2 μA or less is supplied between the supply roller and the developing roller to compensate for black density and to provide a high duty such as black solid. It is possible to suppress the occurrence of fogging under the printed portion, and thus it is possible to always form an image having good image quality.

According to a third aspect of the present invention, there is provided a developing device in the image forming apparatus according to the first or second aspect of the invention, wherein the toner supply detecting unit detects that toner has been supplied to the toner storage unit. Means, comprising a printed sheet number detecting means for detecting the printed sheet number of the photoconductor,
After detecting the toner replenishment by the toner replenishment detection means, the detection of the number of prints is started by the print number detection means, and a bias voltage is applied to the supply roller until the predetermined number of prints is reached. .

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 storing section, the number of printed sheets is counted by the printed sheet number detecting means, and the number of printed sheets is counted. Until the bias voltage is reached, a bias voltage is applied to the roller shaft of the supply roller.
As a result, it is possible to prevent the toner having poor charging during toner replenishment from being conveyed to the developing roller, and it is possible to always form an image having good image quality. Further, power consumption of the supply bias applying unit of the image forming apparatus can be reduced.

According to a fourth aspect of the present invention, there is provided a developing device in the image forming apparatus according to the first or second aspect, wherein the toner supply detecting unit detects that toner has been supplied to the toner storage unit. Means for detecting the number of printed sheets on the photoreceptor, and after detecting toner replenishment by the toner replenishment detecting means, starting detection of the number of printed sheets by the printed sheet number detecting means, and setting a predetermined number of printed sheets. , A bias voltage is applied to the supply roller only during the rotation time of the supply roller.

In the developing device of the image forming apparatus having such features, after the toner replenishment detecting means detects the toner replenishment to the toner storing section, the number of prints is counted by the print number detecting means, and the predetermined number of prints is obtained. Until it reaches, the bias voltage is applied to the roller shaft of the supply roller only during the rotation time of the supply roller. As a result, it is possible to prevent the poorly charged toner from being conveyed to the developing roller at the time of toner replenishment, to constantly form an image having good image quality, and to further reduce the power consumption of the image forming apparatus. Becomes possible.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in detail with reference to the drawings based on an embodiment in which the present invention is embodied for a laser printer. First, a schematic configuration of a laser printer according to the present embodiment will be described with reference to FIG. FIG. 1 is a side sectional view of a laser printer. In FIG. 1, a laser printer 1 includes a main body case 2 and a first
Paper feed tray 3, second paper feed tray 4, paper transport mechanism 5 provided in main body case 2, scanner unit 6, process unit 7, fixing unit 8, and other first and second paper feed trays 3, 4 And a drive unit (not shown, which is housed in the left end portion of the main body case 2) for driving the paper transport mechanism 5 and the like. On the front upper surface side of the main body case 2, a top cover 10 capable of opening the upper surface side of the print mechanism and a paper discharge tray 11 are provided. The paper discharge tray 11 is switchable between a closed position and an open position, and functions as a tray for receiving printed sheets at the open position. Here, the scanner unit 6, the process unit 7, the fixing unit 8, and the like correspond to a printing mechanism. The process unit 7 has a cartridge structure in which a photosensitive drum 25, a charger 26, a developing roller 27, a transfer roller 28, a cleaning roller 29, and the like are accommodated in a casing 24 and can be attached to and detached from a predetermined portion in the main body case 2. .

The first paper feed tray 3 is fixedly provided on the upper surface near the rear end of the main body case 2, and the second paper feed tray 4 is a first paper feed tray of the main body case 2. 3 is detachably provided on the upper surface part on the front side. The paper transport mechanism 5 is for transporting the paper P alternatively fed from the first paper feed tray 3 and the second paper feed tray 4 to the process unit 7. And a pair of registration rollers 1 provided at the lower end of the second paper feed tray 4.
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 provided near a substantially central portion of the registration roller 13a.
The paper transport path 14 extending from the first paper tray 3 to the registration rollers 13a and 13b includes a lower transport path 14a extending along the lower surface of the second paper tray 4, and the second paper tray 4 is connected to the main body case 2. In the state where it is detached from the lower side, the lower surface side transport path 14a is open 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 a lower-side transport path 14a, and passes through registration rollers 13a and 1b.
3b, the sheet P fed by the sheet feed sensor 50 is detected to be passed. After the registration, the sheet P is fed and driven to be transported 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, detects the passage of the paper P fed by the paper feed sensor 50, and drives the paper P after registration. And transported to the process unit 7.

The scanner unit 6 is disposed below the process unit 7 and includes a laser emitting unit (not shown),
It has a polygon mirror 20, reflection mirrors 21, 23, a lens 22 and the like, and a laser beam from a laser light emitting section is reflected by a polygon mirror 20, a reflection mirror 21, a lens 2 as shown by a chain line.
2. An outer peripheral portion of the charged and rotating photosensitive drum 25 of the process unit 7 is irradiated and exposed at high speed through the reflecting mirror 23 to form an electrostatic latent image on the surface of the photosensitive drum 25.

The process unit 7 includes a casing 2
4, a photosensitive drum 25, a scorotron charger 26, a developing roller 27, a transfer roller 28, and a cleaning roller 2.
9, a toner box 30, a toner supply roller 31, and the like. The process unit 7 is detached from the main body case 2 and a toner cartridge 54 (see FIG. 2) is inserted into the toner box 30.
It is designed to supply toner. The toner in the toner cartridge 54 is agitated by the agitator 32 and released from the opening 30 </ b> A of the toner box 30, and then supplied to the developing roller 27 via the toner supply roller 31. As developing roller 2
7 and supplied to the photosensitive drum 25. Incidentally, two auger members 37 and 38 are rotatably disposed in the vicinity of the opening 30A of the toner box 30. Each of the auger members 37 and 38 transfers the toner discharged from the opening 30A into the casing 24. Performs the function of uniformly dispersing.

The electrostatic latent image formed on the surface of the photosensitive drum 25 is visualized by adhering toner from a developing roller 27, and is formed while the paper passes between the photosensitive drum 25 and the transfer roller 28. Is transferred to the fixing unit 8
Sent inside and fixed. Note that 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. The fixing unit 8 heat-fixes the toner to the paper, and the heating roller 3
4. a pressing roller 35 pressed by the heating roller 34;
A pair of discharge rollers 15 provided downstream of these rollers 34 and 35 for discharging paper to the outside of the main body case 2.
a and 15b. A paper discharge sensor 51 is disposed at a position near the center of the discharge roller 15a, and the discharge sensor 51 detects discharge of the sheet P to the outside.

In the above configuration, the paper P is transferred via the photosensitive drum 25 and the transfer roller 28 of the process unit 7.
The conveying speed at which the sheet is fed is determined by the heating roller 34, the pressing roller 35, and the discharge rollers 15a, 15b of the fixing unit 8.
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 transport speed at which the sheet P is sent out via the heating roller 34, the pressing roller 35, and the respective discharge rollers 15a and 15b is changed via the photosensitive drum 25 and the transfer roller 28.
If the speed is higher than the transport speed at which the image is sent out, the process unit 7 may shift the formation position of the image formed on the sheet P, and the image may be disturbed.

Next, a detailed configuration 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, a toner supply roller 31 is rotatably disposed at a lower position in the developing chamber 40, and a developing roller 27 is rotatably disposed facing 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 31A made of metal (for example, formed of various steel materials) and a roller shaft 31A.
And a conductive sponge material 31 </ b> B that covers the periphery. The developing roller 27 is made of metal (for example,
And a conductive rubber material 2 which is generally harder than the conductive sponge material 31B.
The periphery of the roller shaft 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 a circuit board in a downward direction (lower left in FIG. 2) of a substantially central portion of the toner box 30. 53. The toner sensor 52 includes an LED and a photo sensor, and detects the presence or absence of toner by sandwiching a part below the toner cartridge 54 and detecting the amount of transmitted light.

Next, a control configuration of the process unit 7 of the present embodiment will be described with reference to FIG. FIG. 3 is a block diagram showing a control configuration of the process unit 7 of the laser printer 1. In FIG. 3, a laser printer 1 includes a CPU 61 for controlling each device, a ROM 62 for storing a control program, a RAM 62 for storing processing data and the like, an EEPROM 64 for storing a print sheet counter value and the like, an ASIC, and the like. 50, a paper discharge sensor 51, a toner sensor 52, and other sensors connected thereto, and a control circuit 66 for controlling a high-voltage power supply circuit 67, a constant current controller 68, and the like; a photosensitive drum 25;
A high-voltage power supply circuit section 67 for applying a high bias voltage to the developing roller 27, the transfer roller 28, and the cleaning roller 29; a DC power supply circuit section 69 for applying a bias voltage to the toner supply roller 31; A constant current control unit 68 for controlling the DC power supply circuit unit 69 and a resistor 70 connected in series to a circuit connecting the toner supply roller 31 to the toner supply roller 31; Diode 71 connected to
And

The CPU 61 stores the sensor values and the ROM 6
The control circuit 66 is controlled based on a program or the like stored in the control circuit 2. Here, the roller shaft 27A of the developing roller 27 is connected via a control circuit 66 to the roller shaft 27A.
A bias voltage (approximately DC 700 V in the case of the present embodiment) is applied at 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 present embodiment), and when the resistance value between the DC power supply circuit section 69 and the toner supply roller 31 becomes very small, a 2 μA constant current circuit is used. The output voltage of the DC power supply circuit section 69 is several hundred volts.
(600 V in the case of the present embodiment), which is a voltage range in which the DC power supply circuit section 69 can be controlled. Further, by connecting a diode 71 between the DC power supply circuit section 69 and the toner supply roller 31 in the forward direction, the DC power supply circuit section 6 is connected.
Even if the potential of the developing roller 9 is stopped and the potential becomes 0 V, the reverse flow of the current from the developing roller 27 can be prevented, and the transfer of the toner charged to the opposite polarity to the developing roller 27 can be prevented. Further, in this embodiment, since the toner having the positive charging characteristic is used, the voltage for directing the toner to the developing roller 27 is applied to the toner supply roller 31.
Will be applied.

Next, the process of applying a bias voltage to the toner supply roller 31 of the process unit 7 in the laser printer 1 having the above-described configuration will be described with reference to the flowchart of FIG. FIG. 4 shows the supply roller 31 according to the present embodiment.
9 is a flowchart of a process of applying a bias voltage to the power supply. First, when the laser printer 1 receives the print start command, it reads out the number-of-printed-sheets counter value stored in the EEPROM 64 and determines whether it is larger than a predetermined number of printed sheets (50 in this embodiment) (S1). If the printed sheet counter value is larger than 50 sheets (S1: YES),
The remaining amount of toner in the toner cartridge 54 is detected by the toner sensor 52, and if toner remains (S2: N
O), printing is started when the paper feed sensor 50 detects the passage of the paper (S11). Next, printing is continued until printing of one sheet is completed (S12: NO), printing of one sheet is completed, and when paper discharge is detected by the paper discharge sensor 51 (S12).
12: YES), the counter value of the number of printed sheets stored in the EEPROM 64 is incremented by 1, and stored again in the EEPROM 64 (S13). Next, if printing is not completed, the remaining amount of toner in the toner cartridge 54 is detected. If toner remains (S2: NO), printing of the next sheet is continued (S2).
14: NO), the printed sheet count value is set to 1 for each sheet printed.
Increase (S11 to S14: NO). If the printing is completed (S14: YES), the printing operation is completed.

Further, the laser printer 1 receives the print start command, reads the print number counter value stored in the EEPROM 64, and sets the print number counter value to 5
If the number of sheets is smaller than zero (S1: NO), a bias voltage of a predetermined current value (2 μA in the present embodiment) is supplied from the DC power supply circuit section 69 by the constant current control section 68 via the control circuit section 66 to supply toner. Roller shaft 3 of roller 31
1A (S5). Next, when the passage of the sheet is detected by the paper feed sensor 50, printing is started (S6), printing is continued until printing of one sheet is completed (S7: NO), printing of one sheet is completed, and discharge is performed. When the discharge of the sheet is detected by the sheet sensor 51 (S7: YES), the DC power supply circuit section 69 is stopped by the constant current control section 68 via the control circuit section 66 (S8). Next, the counter value of the number of printed sheets stored in the EEPROM 64 is incremented by one, and
64 (S9). Next, if printing is not completed (S10: NO), the counter value of the number of printed sheets is again set to EEPR.
Read from OM64 and determine if it is greater than 50 (S
1) Continue printing. When the printing is completed (S10: YES), the printing operation is completed.

The laser printer 1 receives the print start command, reads out the number-of-printed-sheets counter value stored in the EEPROM 64, and sets the number-of-printed-sheets counter value to five.
If the number is larger than zero (S1: YES), the remaining amount of toner in the toner cartridge 54 is detected by the toner sensor 52. If no toner remains (S2: YES), the printing operation is stopped and the toner cartridge 54 Wait for replacement (S3: NO). Next, the remaining toner amount is detected by the toner sensor 52, and when it is detected that the remaining toner amount is sufficient, it is determined that the toner cartridge 54 has been replaced (S3: YES), and the printing stored in the EEPROM 64 is performed. The number-of-sheets counter value is set to 0, and stored again in the EEPROM 64 (S4).

Next, the counter value of the number of printed sheets is stored in the EEPROM.
64, and determines whether the number is larger than 50 (S
1). If the number-of-printed-sheets counter value is smaller than 50 (S1: NO), the bias voltage of a predetermined current value (2 μA in the present embodiment) is applied by the constant current control unit 68 via the control circuit unit 66 to the DC power supply circuit. From the unit 69 to the roller shaft 31A of the toner supply roller 31 (S
5). Next, when the passage of the sheet is detected by the paper feed sensor 50, printing is started (S6), and printing is continued until printing of one sheet is completed (S7: NO), and printing of one sheet is completed.
When the discharge of the sheet is detected by the discharge sensor 51 (S7:
YES), the DC power supply circuit section 69 is stopped by the constant current control section 68 via the control circuit section 66 (S8).
Next, the value of the number-of-printed-sheets counter stored in the EEPROM 64 is incremented by 1 and stored again in the EEPROM 64 (S9). Next, if printing is not completed (S10: N
O) Then, the counter value of the number of printed sheets is read from the EEPROM 64 again, it is determined whether the number is greater than 50 (S1), and the printing operation is continued. When the printing is completed (S10: YE
S), the printing operation ends.

Therefore, in the process unit 7 of this embodiment, the roller shaft 3 of the toner supply roller 31
By controlling the DC power supply circuit 69 for applying a bias voltage to 1 A at a constant current of 2 μA, even if an insulating film or the like is formed on the surfaces of the toner supply roller 31 and the development roller 27, the toner supply roller 31 2 between rollers 27
A current of μA can flow, and the charged toner held on the conductive sponge material 31B of the toner supply roller 31 can be transferred to the developing roller 27 without fail. Further, it is possible to compensate for the black density and suppress the occurrence of fogging under a high-duty printing portion such as a solid black portion, so that an image having good image quality can be always formed.

After the replacement of the toner cartridge 54 is detected by the toner sensor 52, the discharge of the printed paper is detected by the discharge sensor 51, and the number of printed sheets is counted.
Until the number of printed sheets reaches 50, a bias voltage is applied to the roller shaft 31A of the toner supply roller 31 only during the rotation time of the toner supply roller 31. As a result, it is possible to prevent the toner having poor charging of the toner from being conveyed to the developing roller 27 when the toner cartridge 54 is replaced, so that an image having good image quality can be always formed, and the consumption of the image forming apparatus can be reduced. Power can be reduced.

Further, by connecting a resistor 70 having a large resistance value (about 300 MΩ in the present embodiment) between the DC power supply circuit section 69 and the toner supply roller 31 in series, the DC power supply circuit section 69 and the toner supply roller 31 are connected. When the resistance value between the rollers 31 becomes very small, the current value controlled by the constant current control unit 68 is a constant current of 2 μA.
The output voltage of No. 9 is several hundred volts (600 V or more in the case of the present embodiment), and can be in a controllable voltage range.

Further, by connecting a diode 71 in series in the forward direction from the DC power supply circuit section 69 to the toner supply roller 31 between the DC power supply circuit section 69 and the supply roller 31, the DC power supply circuit section 69 is stopped. Thus, even if the potential becomes 0 V, it is possible to prevent the reverse flow of the current from the developing roller 27 and prevent the toner charged to the opposite polarity from transferring to the developing roller 27.

It should be noted that the present invention is not limited to the above-described embodiment, and various improvements and modifications can be made without departing from the scope of the present invention. Good. (A) Although the photosensitive drum 25 is employed in the above embodiment, an endless belt-type photosensitive member may be employed instead of the photosensitive drum 25, for example. (B) In the above embodiment, a positively charged toner is used, but a negatively charged toner may be used. In that case, a bias voltage that negatively charges the toner may be applied to the toner supply roller 31. In this case, the diodes 71 are connected in series in the reverse direction.

[0038]

As described above, in the developing device in the image forming apparatus according to the first aspect, the DC power supply for applying the supply bias voltage to the roller shaft of the supply roller is controlled at a constant current, and the supply roller and the DC power supply are controlled. A resistor and a diode are connected in series with a circuit connecting the device. As a result, even when 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 flow between the supply roller and the developing roller, and the resistance value between the supply roller and the developing roller can be reduced. Even if it decreases (for example, 2 MΩ or less), the voltage of the DC power supply can be controlled, and the charged toner held on the conductive sponge material of the supply roller can be reliably moved to the developing roller, which is favorable. It is possible to provide a developing device in an image forming apparatus capable of always forming an image having an excellent image quality. Further, it is possible to provide a developing device in an image forming apparatus capable of preventing a backflow of current between the toner supply roller and the developing roller even when the DC power supply is stopped.

Further, in the developing device in the image forming apparatus according to the second aspect, the distance between the supply roller and the developing roller is two.
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 fogging under a high duty print portion such as a solid black, thereby having a good image quality. A developing device in an image forming apparatus that can always form an image can be provided.

Further, in the developing device in the image forming apparatus according to the third aspect, after the toner replenishment detecting means detects the toner replenishment to the toner storing section, the number of prints is counted by the print number detecting means, and the predetermined print number is determined. , A bias voltage is applied to the roller shaft of the supply roller.
As a result, it is possible to prevent the poorly charged toner from being conveyed to the developing roller at the time of toner replenishment, so that an image having good image quality can be always formed, and the power consumption of the supply bias applying unit of the image forming apparatus is reduced. It is possible to provide a developing device in an image forming apparatus capable of reducing the number of developing devices.

Further, in the developing device in the image forming apparatus according to the present invention, after the toner replenishment detecting means detects the toner replenishment to the toner storing section, the number of prints is counted by the print number detecting means, and the predetermined number of prints is obtained. , A bias voltage is applied to the roller shaft of the supply roller only for the rotation time of the supply roller. As a result, it is possible to prevent the poorly charged toner from being conveyed to the developing roller at the time of toner replenishment, to constantly form an image having good image quality, and to further reduce the power consumption of the image forming apparatus. And a developing device in the image forming apparatus capable of performing the above.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a laser printer according to an embodiment.

FIG. 2 is an enlarged side sectional view showing a process unit of the laser printer according to the embodiment.

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

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

FIG. 5 is an explanatory view schematically showing a side cross section of a main part of a developing device in a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser printer 7 Process unit 25 Photosensitive drum 27 Developing roller 31 Toner supply roller 27A, 31A Roller shaft body 50 Feed sensor 51 Discharge sensor 52 Toner sensor 54 Toner cartridge 67 High voltage power supply circuit section 68 Constant current control section 69 DC power supply circuit Part 70 Resistance 71 Diode

Claims (4)

[Claims] 1. A developing device in an image forming apparatus for forming an image by an electrophotographic process, wherein the developing roller is disposed to face a photosensitive member and develops an electrostatic latent image formed on the photosensitive member with toner. Developing bias applying means for applying a developing bias voltage to the developing roller, a supply roller disposed opposite to the developing roller to supply toner to the developing roller, and toner charged on the roller shaft of the supply roller from the supply roller to the developing roller. A developing device having a supply bias application unit for applying a supply bias voltage such that the supply bias voltage is applied to the supply roller, and a constant current control unit for controlling the supply bias application unit with a constant current; A resistor disposed in series with a circuit connecting the supply bias applying unit and a roller shaft of the supply roller;
A diode connected in series from a power supply device of the circuit to a roller shaft of a supply roller; and a bias voltage having a predetermined current value supplied by the constant current control unit. A developing device in the image forming apparatus, wherein the voltage is applied to a roller shaft. 2. The developing device according to claim 1, wherein a current value controlled by said constant current control means is 2 μA or less. 3. A toner replenishment detecting means for detecting that toner has been replenished to the toner storing portion, and a print number detecting means for detecting the number of prints on the photoconductor, wherein toner replenishment is detected by the toner replenishment detecting means. 3. The method according to claim 1, wherein after the detection, the detection of the number of printed sheets by the printed sheet number detecting means is started, and a bias voltage is applied to the supply roller until a predetermined number of printed sheets is reached. A developing device in the image forming apparatus. 4. A toner replenishment detecting means for detecting that toner has been replenished to the toner storage part, and a print number detecting means for detecting the number of printed sheets of the photoconductor, wherein toner replenishment is detected by the toner replenishment detecting means. 2. The method according to claim 1, wherein after the detection, the detection of the number of printed sheets by the printed sheet number detecting means is started, and a bias voltage is applied to the supply roller only during the rotation time of the supply roller until the predetermined number of print sheets is reached. A developing device in the image forming apparatus according to claim 2.