JP3449809B2 - Electrophotographic printer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus used in an electrophotographic printer, and more particularly to a charging device for charging a photosensitive member. 2. Description of the Related Art Conventionally, in an image forming apparatus used in an electrophotographic printer, an electrostatic latent image and a toner image are formed after the surface of a rotating photosensitive member is uniformly charged by a charging roller.
Some transfer a toner image to a print medium. Hereinafter, a charging roller used in such a conventional image forming apparatus will be described. The charging roller is formed by covering the periphery of a conductive shaft with semiconductive rubber, and is pressed against a photosensitive drum as an image carrier. When a negative charge is applied to the conductive shaft, the surface of the photosensitive drum is uniformly charged by discharge in a minute gap between the surface of the charging roller and the surface of the photosensitive drum. To apply voltage to the conductive shaft,
In order to reduce the size of the power supply and the apparatus itself of the electrophotographic printer at low cost, a DC method of applying a constant DC voltage is used. [0004] In the conventional image forming apparatus, the toner adheres to the surface of the charging roller as the printing operation is repeated. Thereafter, the attached toner settles down to a certain amount, and thereafter, stable charging is performed. When designing the charging device, a constant voltage applied to the conductive shaft is applied to the surface of the photosensitive drum in a state where the amount of toner attached on the charging roller is settled down at a constant level.
-130 so that an appropriate charging potential of 800 V is obtained.
It is set to 0V. [0005] In the conventional image forming apparatus, when the amount of toner adhered to the charging roller is settled down to a constant level, the surface of the photosensitive drum is kept at about -750V.
A constant voltage is applied to the conductive shaft so that an appropriate charging potential of -800 V is obtained. In particular, in the initial state, 50 sheets are required until the amount of toner adhered on the charging roller stabilizes to a constant level. In the previous printing, the toner has not yet sufficiently adhered to the charging roller, so the surface of the photosensitive drum cannot be sufficiently charged, and the image density is too high. In addition, during development, there is a problem in that toner adheres to portions other than the exposed portions and print quality deteriorates. [0006] By the way, although the detailed mechanism of the function of the toner on the charging roller to improve the charging ability is not yet known, the fine particles such as the toner enter the rough surface of the charging roller, and thus the charging is performed. It is expected that the charging ability will be improved because the surface of the roller becomes uniformly flat, the gap between the minute gaps between the charging roller and the photosensitive drum becomes more uniform, and the direction of electrolysis becomes more uniform. In order to solve the above-mentioned problems, an electrophotographic printer according to the present invention employs a charging roller.
Reset after a new charging roller is installed
It is, have a counter for counting the number of printed sheets of the print medium
The number of printed sheets counted by the counter after reset
Voltage applied to the charging roller when the number is less than the specified number
Is set higher than the voltage applied when the number of sheets reaches the specified value.
And apply it to the charging roller according to the number of printed sheets on the counter.
Voltage and apply a fixed voltage after the specified number of sheets.
A power supply control circuit for controlling the power supply is provided. The counter of the electrophotographic printer constructed as described above is reset after a new charging roller is mounted.
After that, every time the print medium is printed, the number of prints is counted, and the power supply control circuit resets the counter by the counter.
Charged when the counted number of printed sheets is less than the specified number
Apply the voltage applied to the roller when the number of sheets reaches the specified value.
Set the voltage higher than the
To reduce the voltage applied to the charging roller,
For falling, a constant voltage is applied . A first embodiment of the present invention will be described with reference to the drawings. FIG. 2 is an explanatory view showing the electrophotographic printer of the first embodiment. In FIG. 2, an electrophotographic printer 1
A photosensitive roller 2, a charging roller 3, a light emitting diode array head (LED head) 4, a developing device 5, a transfer device 12, a light source for static elimination 15, and a cleaning device 14 are provided in this order, and an image forming device 25 is configured. Have been. Further, a paper feed unit 9 and a fixing device 13 are provided on both sides thereof. The photosensitive drum 2 rotates at a constant speed in the direction of arrow B, and its surface is uniformly charged by the charging roller 3 to be charged. L on the charged photosensitive drum 2
The image light 4a is irradiated by the ED array head 4, and an electrostatic latent image is formed. The electrostatic latent image reaches a position facing the developing roller 6 in the developing device 5 by rotating the photosensitive drum 2 in the direction of arrow B. Here, the toner 7a is charged to the same polarity as the charging potential on the surface of the photosensitive drum 2, adheres to the electrostatic latent image, and is visualized (formation of a toner image). On the other hand, the recording paper 10 fed one by one from the paper supply unit 9 by the paper supply roller 8 is guided to the sheet guide 11 at the same timing as the photosensitive drum 2, and the medium is transferred by the transfer roller 12 a of the transfer device 12. Is transferred onto the recording paper 10 as a sheet. The recording paper 10 provided with the unfixed toner image is conveyed toward the fixing device 13 by conveyance means (not shown), and is heated and pressed by the fixing device 13 so that the toner image is fixed on the recording paper 10. To complete printing. Thereafter, the electrostatic latent image on the photosensitive drum 2 is erased by the irradiation of the light source for static elimination 15, and the toner remaining on the photosensitive drum 2 without being transferred to the recording paper 10 is removed by the cleaning device 14. It is removed and collected by the cleaning roller 16. The collected toner 7a is supplied to the developing device 5
It is returned to and reused. Then, in the next image forming process, the photosensitive drum 2 is charged again by the charging roller 3. The charging roller 3 is formed by covering the periphery of the conductive shaft 3a with a semiconductive member 3b. A voltage is applied to the conductive shaft 3a from a power source (not shown), and the voltage is applied to the semiconductive rubber 3b. Is applied to the surface of the photosensitive drum 2. The semiconductive member 3b is made of rubber or resin. The charging control of the image forming apparatus 25 as described above will be described. FIG. 1 is a block diagram showing the first embodiment of the present invention, FIG. 3 is a graph showing the relationship between the number of prints and the applied voltage, and FIG. 4 is a graph showing the relationship between the number of prints and the photosensitive drum charging potential. In FIG. 1, the charging device 22 includes:
A power supply 17, a power supply control circuit 18, an A / D converter 19, a page counter memory 20, and a reset switch 21 are connected to the charging roller 3 in this order. The page counter memory 20 counts and stores the number of printed sheets since an unused charging roller started to be used. The counted number data is sent to the power supply control circuit 18 via the A / D converter 19. The power supply control circuit 18 controls the power supply output of the power supply 17 to the charging roller 3 according to the number data received from the page count memory 20. Immediately after the manufacture of the electrophotographic printer 1 or immediately after the replacement of the image forming apparatus 25, since the charging roller 3 is in an unused state, the reset switch 21 sets the number of sheets in the page counter memory 20 to zero. . At the start of printing, since the number of printed sheets is 0, the page counter memory 20 outputs a page count signal a. Power supply control circuit 18 which receives page count signal a converted from a digital signal to an analog signal by A / D converter 19
Outputs a power control signal a ′ to the power supply 17. The power supply 17 receiving the power supply control signal a ', as shown in FIG.
A voltage of −1450 V is output to the charging roller 3. The page counter memory 20 outputs a signal a until the counted number of printed sheets reaches ten, and −1450 V is applied to the charging roller 3. After about 10 sheets have been printed, the toner 7a slightly adheres to the surface of the charging roller 3. When the counted number of printed pages is 10 to 20, the page counter memory 20 outputs a page count signal b, the power supply control circuit 18 outputs a power supply control signal b ', and as shown in FIG. -1400 V is applied. As the number of printed sheets increases, the toner 7a further adheres to the surface of the charging roller 3, and the minute gaps expand appropriately. Therefore, the page counter memory 20
Counted number of printed sheets output a page count signal c when 20-50 sheets, the power supply control circuit 18 outputs a power control signal c', -1 3 50 V to the charging roller 3, as shown in FIG. 3 is applied Is done. By the time 50 sheets are printed, sufficient toner adheres to the charging roller 3 , that is, the toner adhesion saturates and the charging becomes stable.
Thereafter, a page count signal d is output. As a result, the power supply control circuit 18 outputs a power supply control signal d ', and FIG.
As shown in (1), -1300 V is always applied to the charging roller 3. In any case, as shown in FIG. 4, the photosensitive drum 2 is almost charged to an appropriate value of -750 to -850V. In this way, by gradually lowering the voltage applied to the charging roller according to the number of prints, the photosensitive drum can always be charged at an appropriate charging potential even for a while after the unused charging roller is started to be used. Therefore, it is possible to prevent the image density from being too high or the toner from adhering to a portion other than the exposed portion during development, thereby deteriorating the print quality. Next, a modification of the first embodiment will be described with reference to the drawings. FIG. 5 is a block diagram showing a modification of the first embodiment, FIG. 6 is a graph showing the relationship between the number of prints and the applied voltage, and FIG. 7 is a graph showing the relationship between the number of prints and the charging potential of the photosensitive drum. In FIG. 5, an analog signal processing circuit 24 is connected to the charging device 23 between the power supply control circuit 18 and the page counter memory 20. The analog signal processing circuit 24 is a signal amplification circuit that changes a signal to be sent to the power supply control circuit 18 in an analog manner. Other components of the charging device 23 are the same as those of the charging device 22 of the first embodiment. Immediately after the manufacture of the electrophotographic printer 1 or immediately after the replacement of the image forming apparatus 25, since the charging roller 3 is not yet in use, the reset switch 21 sets the number of sheets in the page counter memory 20 to zero. . The page counter memory 20 outputs page count signals e of 0 to 50 pages to the analog signal processing circuit 24. The page count signal e processed by the analog signal processing circuit 24 is sent to the power control circuit 18. As shown in FIG. 5, the power supply control circuit 18 sends a power supply control signal to the power supply 17 to control the applied voltage from -1450 V to -1300 V in an analog manner according to the number of printed sheets. When the number of prints exceeds 50, the page counter memory 20 continues to send the page count signal f to the power control circuit 18 thereafter. As a result, the power supply control circuit 18 outputs a power supply control signal, and −1300 V is always applied to the charging roller 3 as shown in FIG. In any case, as shown in FIG. 7, the photosensitive drum 2 is almost charged to an appropriate value of -800V. As described above, by gradually lowering the voltage applied to the charging roller in an analog manner in accordance with the number of prints, a charging potential closer to an appropriate value can be obtained, so that print quality is improved. Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 8 is an external view showing the electrophotographic printer of the second embodiment. In FIG. 8, a sensor unit 32 is provided on an outer wall of the electrophotographic printer 31. In the sensor unit 32, a temperature sensor 33 such as a thermistor for detecting an environmental temperature outside the apparatus and a humidity sensor 34 for detecting an environmental humidity are arranged.
The other components of the electrophotographic printer 32 of the second embodiment and the image forming process are the same as those of the first embodiment, and a description thereof will be omitted. The charging control of the charging device in the electrophotographic printer 31 as described above will be described. FIG. 9 is a block diagram showing a second embodiment of the present invention, and FIG. 10 is a graph showing a relationship between an ambient temperature and an applied voltage. In FIG.
The charging device 35 is configured such that a power supply 17, a power supply control circuit 36, a power supply CPU 37, and a sensor driving power supply 38 are sequentially connected to the charging roller 3. A temperature sensor 33 and a humidity sensor 34 are connected to the sensor drive power supply 38. The sensor drive power supply 38 drives the temperature sensor 33 and the humidity sensor 34. The power supply CPU 37 processes the current flowing through the temperature sensor 33 and the humidity sensor 34 as temperature data and humidity data, and transmits the processed data to the power supply control circuit 36. The power supply control circuit 36 controls the power supply output of the power supply 17 to the charging roller 3 according to the temperature data and the humidity data received from the power supply CPU 37. When a power switch (not shown) of the electrophotographic printer 31 is turned on, a temperature sensor 33 and a humidity sensor 34 are turned on.
Detects the environmental temperature and the environmental humidity at that time, respectively. The power supply CPU 37 includes a temperature sensor 33, a humidity sensor 3
4 is processed into temperature data and humidity data and transmitted to the power control circuit 36. According to the temperature data and the humidity data received from the power supply CPU 37, the power supply control circuit 36, as shown in FIG.
7 sets the voltage applied to the charging roller 3 high. Curve g is humidity 20%, curve h is humidity 40%, curve i
Indicates the case where the humidity is 60%, and the curve j indicates the case where the humidity is 80%. The power supply 17 continues to apply the set voltage until the power switch of the electrophotographic printer 31 is turned off. As a result, the charged potential on the surface of the photosensitive drum 2 is always kept at an appropriate value of -750 V to -800 V. Since the temperature sensor 33 is provided on the outer wall of the electrophotographic printer, it is not affected by the heat of the heat roller of the fixing device. As described above, by setting the voltage to be applied to the charging roller 3 in accordance with the environmental temperature and the environmental humidity, the charging can always be performed at an appropriate voltage even when the temperature and the humidity are low. It is possible to prevent the image density from being changed due to the environment, and to prevent the print quality from deteriorating due to toner adhering to portions other than the exposed portions during development. In addition,
In the present embodiment, the temperature and humidity at the time when the power switch of the electrophotographic printer is turned on are detected. However, if the temperature and humidity are detected in real time and the applied voltage is controlled, the charging potential closer to the proper value can be obtained. Obtainable. Next, a third embodiment of the present invention will be described with reference to the drawings. The components of the electrophotographic printer according to the third embodiment and the image forming process are the same as those of the first and second embodiments, and thus the description thereof is omitted. FIG. 11 is a block circuit diagram showing a third embodiment of the present invention.
2 is a graph showing the relationship between the transfer voltage, the charging current, and the applied voltage. In FIG. 11, the image forming apparatus 41 of the third embodiment detects the potential of the photosensitive drum 2 immediately before charging from the transfer voltage and the charging current because the transfer voltage changes depending on the environment, and according to the value, This controls the applied voltage. The charging device 42 supplies the power supply 1 to the charging roller 3.
7. A power supply control circuit 43 and a power supply CPU 44 are connected in this order. A charging current detection circuit 45 is provided between the charging roller 3 and the power supply 17. Power supply CPU44
Is connected to a transfer voltage detection circuit 46 and a transfer voltage power supply control circuit 47 in addition to the charging current detection circuit 45.
The transfer voltage detection circuit 46 is provided between a power supply 48 and the transfer roller 12a connected to the power supply 48. A transfer voltage power supply control circuit 47 is connected to the power supply 48. First, detection of the transfer voltage applied to the transfer roller 12a will be described. The transfer voltage is applied in advance so that a constant current flows to the transfer roller 12a, and is obtained from the constant current at the moment when the recording paper 10 in FIG. 2 is inserted between the transfer roller 12a and the photosensitive drum 2. The transfer roller 12 is latched by a voltage
a. At this time, the transfer voltage that has become a constant voltage is divided by the voltage dividing resistors R1 and R2,
And stored in the capacitor 50 as electric charge. By comparing the electric charge stored in the capacitor 50 with the reference voltage 51 by the comparator 52, a transfer voltage value is obtained. The comparator 52 includes an A / D converter 53
The digital signal S1 is sent to the power supply CPU 44 via Next, detection of the charging current will be described.
A reference voltage is applied to the charging roller 3 by a signal S0 from the power supply CPU 44. At this time, the reference resistance RS
Is reduced by the step-down converters 54 and 55 and compared by the comparators 56 and 57 to obtain the reference resistance RS
The current value flowing through is detected. Comparators 56 and 57
Sends digital signals S2 and S3 to the power supply CPU 44 via A / D converters 58 and 59, respectively. The power supply CPU 44 includes a transfer voltage detection circuit 46
From the transfer voltage signal S1 sent from the printer and the charging current signals S2 and S3 sent from the charging current detection circuit 45, the charging roller resistance value, the pre-charging drum potential, and the like are calculated, and the signals S4 and S5 are calculated. To the power supply control circuit 43. The power supply control circuit 43 sets an applied voltage from these signals as shown in FIG. The curve k in FIG. 12 shows that the transfer voltage is +30.
00V, curve 1 is + 2000V, curve m is + 1000V
The case of is shown. In the third embodiment, the detection of the transfer voltage and the charging current and the setting of the applied voltage are performed in real time. As a result, the charged potential on the surface of the photosensitive drum 2 is always kept at an appropriate value of -800V. As described above, the transfer voltage and the charging current are detected, and the voltage applied to the charging roller 3 is set in accordance with these values. In any other environment, it is always possible to charge with the appropriate voltage,
It is possible to prevent variations in image density due to the environment and deterioration of print quality due to toner adhering to portions other than exposed portions during development. Since the present invention is configured as described above, it has the following effects. That is, a new charging roller is used as a charging roller.
The printer has a counter that counts the number of prints printed on the print medium, and is reset after the printer is installed.
If the number of prints counted by the
When the voltage applied to the charging roller
Higher than the voltage to be applied when
The voltage applied to the charging roller
By providing a power supply control circuit that controls to apply a constant voltage after the number of sheets , the charging roller to be used is newly installed.
Even if it is in the state of being worn, the charging ability will drop
Even when it arrives , the photosensitive drum is always charged with an appropriate charging potential, so that the image forming density becomes too high,
It is possible to prevent the toner from adhering to a portion other than the exposed portion during the development, thereby deteriorating the print quality.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 2 is an explanatory diagram illustrating the electrophotographic printer according to the first embodiment. FIG. 3 is a graph showing a relationship between the number of prints and an applied voltage. FIG. 4 is a graph showing the relationship between the number of prints and the charged potential of the photosensitive drum. FIG. 5 is a block diagram showing a modification of the first embodiment. FIG. 6 is a graph showing a relationship between the number of printed sheets and an applied voltage. FIG. 7 is a graph showing the relationship between the number of prints and the photosensitive drum charging potential. FIG. 8 is an external view illustrating an electrophotographic printer according to a second embodiment. FIG. 9 is a block diagram showing a second embodiment of the present invention. FIG. 10 is a graph showing a relationship between an environment and an applied voltage. FIG. 11 is a block circuit diagram showing a third embodiment of the present invention. FIG. 12 is a graph showing a relationship between a transfer voltage, a charging current, and an applied voltage. [Description of Signs] 2 Photosensitive drum 3 Charging roller 10 Recording paper 12, 41 Image forming device 18, 36, 43 Power control circuit 20 Page counter memory 24 Analog signal processing circuit 33 Temperature sensor 34 Humidity sensor 45 Charging current detection circuit 46 Transfer Voltage detection circuit

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Claims (1)

(57) and Patent Claims 1 image bearing member, is rotated in contact with said image bearing member, a charging <br/> roller to which a voltage is applied, a new charging as the charging roller After the rollers are installed
And a counter for counting the number of prints of the print medium, and the mark counted by the counter after the reset.
The voltage applied to the charging roller when the number of prints is less than a predetermined number is set higher than the voltage applied when the number of prints reaches the predetermined number, and the voltage applied to the charging roller according to the number of prints of the counter. And a power supply control circuit for controlling to apply a constant voltage after the predetermined number of sheets is provided .