JP2010250232A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that makes a supply roller and a developing roller equal in potential when image formation is unnecessary with a voltage applied to a charger, in the configuration in which a voltage is applied from the charger so that the voltage is divided in series to the supply roller and developing roller in that order. <P>SOLUTION: An electrostatic latent image is formed on the surface of a photoreceptor drum 12 charged by the charger 14, and toner supplied from the supply roller 16 to the developing roller 18 is supported by a photoreceptor drum 12, and thereby an electrostatic latent image is developed. A voltage applied to the charger 14 is applied so that the voltage is divided in series to the supply roller 16 and developing roller 18 in that order. A control section 40 performs the PWM control of a voltage applied to the developing roller 18. Based on the duty ratio of a PWM signal output in order that the control section 40 performs the PWM control of a voltage applied to the developing roller 18, an equalizing potential circuit 90 makes the supply roller 16 and developing roller 18 equal in potential. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that applies a voltage to a supply roller and a development roller, and develops the developer supplied from the supply roller to the development roller on an image carrier on which an electrostatic latent image is formed.

  2. Description of the Related Art Conventionally, in an image forming apparatus that supplies a developer from a supply roller to a developing roller and carries it on an image bearing member, a voltage applied from a high-voltage power source is divided and applied to the supply roller and the developing roller. (For example, refer to Patent Document 1).

  As a result, the voltages applied to the supply roller and the developing roller can be easily changed in synchronization. Further, by applying a voltage to the supply roller in addition to the developing roller, even when the remaining amount of the developer is reduced, the developer is attracted to the supply roller and the developer is transferred from the supply roller to the developing roller. Can supply.

  As the high-voltage power supply, a power supply common to a charger or the like can be considered. When an image is not printed on a recording medium such as paper, the power supply from the high-voltage power supply is cut off, so that no voltage is applied to the supply roller and the development roller. As a result, the supply roller and the development roller are at the same potential, so that the supply of the developer from the supply roller to the development roller is stopped.

  However, when a warming operation is performed to stir the developer in the developing unit with a stirring plate or the like when the image forming apparatus is turned on or released from the sleep state, an image is not printed on the paper, but from a high voltage power source. Power is supplied. Also, when printing is stopped between sheets (also referred to as between sheets) during continuous printing, power is supplied from a high voltage power source. As a result, a voltage is applied to the charger, the supply roller, and the developing roller.

Japanese Patent Laid-Open No. 6-301281

  As described above, even when it is not necessary to form an image on the recording medium, when power is supplied from a high-voltage power supply common to the charger and voltage is applied to the supply roller and the development roller, the supply roller and the development roller are developed. A potential difference is generated between the rollers. As a result, the developer is supplied from the supply roller to the developing roller, so that the developer adheres to the image carrier.

  In this case, for example, in an image forming apparatus that adjusts the amount of developer carried on the image carrier by controlling the voltage applied to the developing roller, the voltage applied to the developing roller is controlled to The applied voltage can be zero.

  However, in the configuration in which the voltage applied from the high voltage power supply to the charger is divided in series in the order of the supply roller and the development roller, even if the voltage applied to the development roller becomes 0, the voltage applied to the supply roller is 0. Instead, a voltage is applied to the supply roller. Then, since a potential difference is generated between the supply roller and the developing roller, the developer is supplied from the supply roller to the developing roller, and the developer adheres to the image carrier.

  As a result, the developer is unnecessarily consumed even though printing is unnecessary, so the number of printable sheets is reduced. Further, the developer attached to the image carrier and collected from the image carrier is deteriorated.

  The present invention has been made in order to solve the above-described problem. In the configuration in which voltage is applied by dividing the voltage in series from the charger to the supply roller and the developing roller, the voltage is applied to the charger. Therefore, an object of the present invention is to provide an image forming apparatus in which the supply roller and the developing roller have the same potential when image formation is unnecessary.

  The present invention made to achieve the above object includes a charger, an image carrier on which an electrostatic latent image is formed on the surface charged by the charger, and an electrostatic latent image formed on the surface of the image carrier. A developing roller for developing an electrostatic latent image by supporting the developer on the image, a supply roller for supplying the developer to the developing roller, and a voltage applied to the charger in series from the charger to the supply roller and the developing roller in this order. A voltage dividing circuit that divides the voltage into the developing roller, a voltage control unit that controls the voltage applied from the voltage dividing circuit to the developing roller based on the duty ratio of the PWM signal, and the supply roller and the developing roller based on the duty ratio of the PWM signal. And equipotential means.

  In the present invention configured as described above, it is not necessary to form an image on the recording medium, but when a voltage is applied to the charger, the duty ratio of the PWM signal that controls the voltage applied to the developing roller. Therefore, the supply roller and the developing roller are at the same potential.

  This prevents the developer from being supplied from the supply roller to the developing roller when the voltage is applied to the charger and prevents the developer from adhering to the image carrier. Can be prevented.

  Therefore, when image formation is unnecessary, unnecessary consumption of the developer can be prevented and the number of printable sheets can be increased. Further, since the developer adsorbed on the image carrier and collected from the image carrier is reduced, the deterioration of the developer can be suppressed.

  Here, it is not necessary to form an image on the recording medium, but the voltage applied to the charger is applied to the supply roller and the development roller. This represents a warming-up state in which the developer in the developing unit is stirred by a stirring plate or the like during the period of time or when the power is turned on or when returning from the sleep state.

In the present invention, the equipotential means is an equipotential circuit that makes the supply roller and the developing roller have the same potential based on the duty ratio of the PWM signal.
Accordingly, since the same potential circuit makes the supply roller and the developing roller have the same potential based on the PWM signal for controlling the voltage applied to the developing roller, the supply roller and the developing roller are based on the duty ratio of the PWM signal. And a new control signal for setting the same potential to each other is unnecessary. As a result, the control device for controlling the voltage can be downsized, the processing load of the control program can be reduced, the wiring can be reduced, and the manufacturing cost of the image forming apparatus can be reduced.

1 is a diagram showing a circuit configuration of a laser printer according to a first embodiment of the present invention. The characteristic view which shows the relationship between the duty ratio of PWM control, and an applied voltage. The flowchart which shows a voltage control routine. The flowchart which shows a warming mode routine. 6 is a flowchart showing a print mode routine. The flowchart which shows a paper interval mode routine. The figure which shows the circuit structure of the laser printer by 2nd Embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
(Configuration of image forming apparatus)
FIG. 1 is a diagram schematically illustrating a circuit configuration of a laser printer 2 as an example of an image forming apparatus to which the present invention is applied. The laser printer 2 according to the first embodiment includes an image forming unit 10 that forms an image on a sheet by an electrophotographic method as an example of a recording medium, and a power source unit 20 as an example of a PWM power supply device.

(Configuration of the image forming unit 10)
The image forming unit 10 forms a toner image on a sheet while the sheet is conveyed between a photosensitive drum 12 as an example of an image carrier and a transfer roller (not shown). The photosensitive drum 12 has a drum main body grounded and a positively chargeable photosensitive layer made of, for example, polycarbonate as an organic photosensitive material.

  On the outer periphery of the photosensitive drum 12, a charger (CHG) 14 and a developing roller (DEV) 18 are sequentially arranged along the rotation direction of the photosensitive drum 12 from a portion facing the transfer roller. The charger 14 is a positively charged scorotron charger that generates corona discharge from a charging wire 14A made of tungsten or the like, and uniformly charges the surface of the photosensitive drum 12 to a positive polarity.

  The surface of the photosensitive drum 12 is irradiated with laser light corresponding to image data from a light source that is a well-known technique (not shown). The image data is input from the outside of the laser printer 2 via, for example, a network. The voltage on the surface of the photosensitive drum 12 is lowered by laser light emitted from a light source (not shown), and an electrostatic latent image corresponding to image data is formed.

  A positively chargeable non-magnetic one-component toner housed in a developing unit including a supply roller (SR) 16 and a developing roller 18 has a positive voltage lower than the supply roller 16 from the supply roller 16 to which a positive voltage is applied. Is supplied to the developing roller 18 to which is applied. The toner supplied from the developing roller 18 to the photosensitive drum 12 is selectively attracted and carried by the electrostatic latent image formed on the surface of the photosensitive drum 12, whereby the toner image is developed.

  The toner image developed on the surface of the photosensitive drum 12 is transferred to the paper by a transfer bias applied to the transfer roller while the paper passes between the photosensitive drum 12 and the transfer roller. The toner image transferred onto the paper is conveyed to a fixing device (not shown) having a heating roller and a pressure roller, and is thermally fixed onto the paper.

(Configuration of power supply unit 20)
The power supply unit 20 of the laser printer 2 is provided with a boosting / smoothing rectifier circuit 22 including a transformer 24 and a smoothing rectifier circuit 26. A transformer drive circuit 30 is connected to the primary side of the transformer 24, and a known smoothing rectifier circuit 26 including a diode and a capacitor is connected to the secondary side of the transformer 24.

  The transformer drive circuit 30 is connected to the control unit 40 via the PWM signal control circuit 32. The control part 40 comprises a part of voltage control means as an example. The PWM signal output from the PWM port 52 of the control unit 40 is smoothed by the PWM signal control circuit 32, and a voltage corresponding to the duty ratio of the PWM signal is output from the PWM signal control circuit 32. The transformer drive circuit 30 energizes the primary side of the transformer 24 with a current corresponding to the output voltage of the PWM signal control circuit 32.

  On the secondary side of the transformer 24, a high voltage is generated in response to energization to the primary side. The generated high voltage is rectified and smoothed by the smoothing rectifier circuit 26 and applied to the charging wire 14A of the charger 14 as a CHG output. Further, the voltage applied to the charger 14 is divided and applied in series in this order to the supply roller 16 as the SR output and to the developing roller 18 as the DEV output via the resistor 28 and the Zener diode 60. .

A resistor 28 and a Zener diode 60 as an example of a voltage dividing circuit are connected in series in this order from the charger 14 side.
The voltage of the output of the grid 14B (GRID output) that generates a voltage by discharging the charging wire 14A of the charger 14 is divided into a predetermined ratio by the resistors 34 and 36 and is converted into an A / B of the control unit 40 as an FB-GRID signal. It is input to the D port 56. The control unit 40 controls the duty ratio of the PWM signal output from the PWM port 52 so that the GRID output input from the A / D port 56 becomes a predetermined voltage.

  The control unit 40 performs PWM control of the voltage applied to the image forming unit 10, and includes a CPU 42, a RAM 44, a ROM 46, a PWM generation unit 48, an A / D converter (A / D) 50, and the like. The control unit 40 is configured by a microcomputer including, for example, an ASIC (Application Specific Integrated Circuit).

  The PWM ports 52 and 54 provided in the control unit 40 output a PWM signal generated by the PWM generation unit 48 for PWM control of the CHG output and the DEV output, respectively. The A / D ports 56 and 58 are ports for inputting a DEV output and a GRID output, respectively, which are divided at a predetermined ratio. The DEV output and GRID output input from the A / D ports 56 and 58 are converted from analog signals to digital signals by the A / D 50.

  The zener diode 60 is used to set the SR output applied to the supply roller 16 to a predetermined voltage higher than the DEV output applied to the developing roller 18. In the present embodiment, for example, the Zener voltage of the Zener diode 60 is set so that the SR output voltage is 200 V higher than the DEV output voltage. The capacitor 62 suppresses fluctuations in the voltage applied to the supply roller 16.

  The PWM signal output from the PWM port 54 for PWM control of the DEV output is smoothed by the resistor 70 and the capacitor 72 and applied to the base of the transistor 74. The transistor 74 constitutes a part of voltage control means as an example.

  In this embodiment, when the duty ratio of the PWM signal output from the PWM port 54 increases as shown in FIG. 2 according to the voltage of the smoothed PWM signal applied to the base of the transistor 74, The voltage at the DEV output 300 decreases.

  When the toner deterioration progresses, the controller 40 increases the duty ratio of the PWM signal output from the PWM port 54 so that the supply roller 16 and the developing roller 18 attract the deteriorated toner, and the SR output and the DEV output. PWM control for lowering the voltage is performed. The degree of toner deterioration is determined based on, for example, the total number of printed sheets using the same developing unit. It is determined that deterioration is progressing as the number of printed sheets increases.

The capacitor 76 is provided to suppress fluctuations in the DEV output applied to the developing roller 18.
The DEV output voltage applied to the developing roller 18 is divided into a predetermined ratio by resistors 78 and 80 and input to the A / D port 58 as an FB-DEV signal. Thereby, the voltage of the DEV output applied to the developing roller 18 is detected.

  The equipotential circuit 90 as an example of the equipotential means includes a photocoupler 92, a Zener diode 98, and a transistor 100, and is connected in parallel with the Zener diode 60.

  When the duty ratio of the PWM signal output from the PWM port 54 increases, the voltage of the PWM signal smoothed by the resistor 70 and the capacitor 72 increases. When the difference between the smoothed voltage of the PWM signal and the Zener voltage of the Zener diode 98 exceeds the base voltage, the transistor 100 is turned on.

As a result, when a current flows through the light emitting diode 94 of the photocoupler 92 and the light emitting diode 94 emits light, the transistor 96 of the photocoupler 92 is turned on.
When the transistor 96 is turned on, the current flowing through the Zener diode 60 that sets the SR output to be higher than the DEV output by a predetermined voltage is bypassed to the photocoupler 92 side. As a result, when the duty ratio of the PWM signal output from the PWM port 54 exceeds a predetermined value, the SR output 302 and the DEV output 300 become the same potential as shown in FIG.

(Voltage control routine)
Next, a voltage control routine that is executed by the CPU 42 based on a program stored in the ROM 46 in the control unit 40 will be described. 3 to 6 are flowcharts showing a voltage control routine executed by the control unit 40. 3 to 6, “S” represents a step.

In S400 of FIG. 3, for example, it is determined whether or not the start of printing has been instructed by another routine (not shown) by data reception or the like to the laser printer 2 in the sleep state.
When printing start is instructed (S400: Yes), application of CHG output to the charger 14 is started, and a warming mode routine is executed in S402. In the warming mode routine, an image is not printed on the paper, but a warming operation of stirring the toner in the developing unit with a stirring plate or the like is performed. The warming operation of stirring the toner in the developing unit with a stirring plate or the like is executed when the sleep state is released and when the laser printer 2 is turned on.

(Warming mode routine)
In the warming mode routine, a PWM signal having a predetermined duty ratio is output from the PWM port 52 in order to apply a voltage to the charger 14 in S420 of FIG. The PWM port 54 outputs a PWM signal having a duty ratio of 100%.

  As a result, the CHG output is turned on, and a predetermined voltage is applied to the charger 14. Along with this, the stirring plate in the developing unit rotates to stir the toner. On the other hand, when a PWM signal having a duty ratio of 100% is output from the PWM port 54, the DEV output applied to the developing roller 18 becomes zero.

  Further, when a PWM signal having a duty ratio of 100% is output from the PWM port 54, the transistor 96 of the photocoupler 92 is turned on, and a current flows through the photocoupler 92 bypassing the Zener diode 60. As a result, the SR output voltage applied to the supply roller 16 is also zero, so that the supply roller 16 and the developing roller 18 have the same potential. Further, the voltage applied to the transfer roller is also controlled to 0 by a power supply unit different from the power supply unit 20 shown in FIG.

  If the duty ratio of the PWM signal output from the PWM port 54 is not limited to 100% but is equal to or greater than a predetermined value, the transistor 96 of the photocoupler 92 is turned on, bypassing the Zener diode 60, and a current flows through the photocoupler 92. . As a result, the supply roller 16 and the developing roller 18 have the same potential. In this embodiment, the predetermined value of the duty ratio is set to a value at which the voltage of the DEV output is about 200 V (see FIG. 2).

  When the warming of stirring the toner in the developing unit with a stirring plate or the like is completed (S422: Yes), a PWM signal having a duty ratio of 0% is output from the PWM port 52 (S424). As a result, the voltage of the CHG output applied to the charger 14 becomes zero. Further, since the duty ratio of the PWM signal output from the PWM port 54 does not change and remains 100%, the voltage applied to the supply roller 16 and the developing roller 18 is 0, and the supply roller 16 and the developing roller 18 Are the same potential.

When the warming mode routine ends, the printing mode routine is executed in S404 of FIG.
(Print mode routine)
In the print mode routine, a PWM signal having a predetermined duty ratio is output from the PWM port 52 in S430 of FIG. Further, the PWM port 54 outputs a PWM signal having a duty ratio smaller than the predetermined value so that the photocoupler 92 is turned on and the SR output and the DEV output do not have the same potential.

  As a result, the CHG output is turned on, and a predetermined voltage is applied to the charger 14. Further, a DEV output voltage corresponding to the duty ratio of the PWM signal output from the PWM port 54 is applied to the developing roller 18. The duty ratio of the PWM signal output from the PWM port 54 in the printing mode is such that the voltage applied to the developing roller 18 is in the range of 200V to 600V as shown in FIG. 2 according to the degree of toner deterioration. Set to

  If the voltage applied to the developing roller 18 is in the range of 200V to 600V, that is, if the duty ratio of the PWM signal output from the PWM port 54 is less than a predetermined value, the zener diode prevents the transistor 96 of the photocoupler 92 from turning on. A Zener voltage of 98 is set. Thereby, if the voltage applied to the developing roller 18 is in the range of 200V to 600V, an SR output that is 200V higher than the DEV output is applied to the supply roller 16.

  A predetermined voltage is also applied to the transfer roller. As a result, the electrostatic latent image formed on the photosensitive drum 12 is developed by the toner supplied from the supply roller 16 to the developing roller 18 and printed on the paper.

  When the print mode routine ends, it is determined in S406 in FIG. 3 whether or not all printing has been completed. When all printing is finished (S406: Yes), this routine is finished.

  If printing is not completed and printing continues (S406: No), printing on the paper set at the printing position is completed in S408, and the next paper to be fed is set at the printing position. It is determined whether or not the paper is in a paper-to-paper state until it is printed. If it is not between sheets (S408: No), the process proceeds to S406. If there is a paper interval (S408: Yes), a paper interval mode routine is executed in S410.

(Paper interval routine)
In the paper interval mode routine, a PWM signal having a predetermined duty ratio is output from the PWM port 52 in order to apply a voltage to the charger 14 in S440 of FIG. The PWM port 54 outputs a PWM signal having a duty ratio of 100%.

  As a result, the CHG output is turned on, and a predetermined voltage is applied to the charger 14. On the other hand, when a PWM signal having a duty ratio of 100% is output from the PWM port 54, the DEV output applied to the developing roller 18 becomes zero.

  Further, when a PWM signal having a duty ratio of 100% is output from the PWM port 54, the transistor 96 of the photocoupler 92 is turned on, bypassing the Zener diode 60, and a current flows through the photocoupler 92 as described above. As a result, the SR output voltage applied to the supply roller 16 is also zero, so that the supply roller 16 and the developing roller 18 have the same potential. A voltage having a predetermined value is applied to the transfer roller.

  In the voltage processing routine shown in FIGS. 3 to 6 described above, the voltage of the DEV output and the SR output is set to 0 in S420 and S424 of FIG. 4 and S440 of FIG. 4 corresponds to the function executed by the same potential means, and the voltage control means executes the function of controlling the voltage of the DEV output in S420 and S424 in FIG. 4, S430 in FIG. 5, and S440 in FIG. Corresponds to function.

  As described above, in the first embodiment, even when the CHG output is applied to the charger 14, when the image is not printed on the paper, for example, the warm-up operation of stirring the toner in the developing unit with a stirring plate or the like, and During the interval between sheets, control was performed so that the duty ratio of the PWM signal output from the PWM port 54 is equal to or greater than a predetermined value. As a result, the same potential circuit 90 operates based on the duty ratio of the PWM signal that controls the DEV output, and the SR output and the DEV output become the same potential.

  Even when the CHG output is applied to the charger 14, if the SR output and the DEV output are the same potential, no toner is supplied from the supply roller 16 to the developing roller 18, and no toner adheres to the photosensitive drum 12. .

  As a result, it is possible to reduce the amount of unnecessary toner adhering to the photosensitive drum 12 as much as possible when printing is not performed on a sheet in a state where the CHG output is applied to the charger 14. Thereby, the number of printed sheets increases. Further, it is possible to suppress deterioration of the toner that adheres to the photosensitive drum 12 and is collected from the photosensitive drum 12.

  In the first embodiment, when the duty ratio of the PWM signal output from the PWM port 54 exceeds a predetermined value, the same potential circuit 90 operates based on the PWM signal, bypassing the Zener diode 60, and the photocoupler 92. When the current flows through the supply roller 16, the supply roller 16 and the developing roller 18 have the same potential.

  As a result, the same potential circuit is generated based on the PWM signal output from the PWM port 54 without adding a control port for outputting a control signal for setting the supply roller 16 and the developing roller 18 to the same potential to the control unit 40. 90 enables the SR output and the DEV output to have the same potential. As a result, it is possible to reduce the size of the control unit 40, reduce the processing load of the control program, reduce the wiring of the power supply unit 20, and reduce the manufacturing cost of the power supply unit 20.

[Second Embodiment]
FIG. 7 shows a laser printer 4 according to the second embodiment of the present invention. Components that are substantially the same as those in the first embodiment are denoted by the same reference numerals.

  In the second embodiment, when the duty ratio for PWM control of the DEV output becomes a predetermined value or more, the transistor 96 of the photocoupler 92 is turned on so that the SR output and the DEV output have the same potential. Is provided with an ON / OFF port 122 for an SR output control signal. The control unit 120 and the photocoupler 92 constitute the same potential unit as an example.

  The controller 120 turns on the output of the ON / OFF port 122 when the duty ratio for PWM control of the DEV output becomes a predetermined value or more. As a result, the transistor 96 of the photocoupler 92 is turned on and a current flows through the photocoupler 92, so that the supply roller 16 and the developing roller 18 have the same potential.

  As a result, even when the CHG output is applied to the charger 14, when the image is not printed on the paper, the duty ratio of the PWM signal output from the PWM port 54 is controlled to a predetermined value or more. The same potential circuit 90 operates, and the SR output and the DEV output become the same potential.

[Other Embodiments]
In the above embodiment, a positively charged toner is used. On the other hand, negatively chargeable toner may be used. In this case, the photosensitive drum is negatively charged, and a negative voltage is applied to the supply roller and the developing roller.

  In the first embodiment, a comparator is used instead of the Zener diode 98 used in the voltage cut-off circuit 90, and the transistor 100 is turned on when the duty ratio of the PWM signal output from the PWM port 54 exceeds a predetermined value. A circuit configuration may be used.

  In the above embodiment, the circuit configuration is such that the voltage of the DEV output decreases as the duty ratio of the PWM signal output from the PWM port 54 increases. On the other hand, a circuit configuration in which the voltage of the DEV output increases as the duty ratio of the PWM signal output from the PWM port 54 increases may be adopted.

  The present invention can also be applied to various electrophotographic image forming apparatuses such as a copying machine, a facsimile machine, a color laser printer, and a multifunction machine including these. Further, the image carrier may be a photoreceptor belt or an image carrier other than the photoreceptor.

  As described above, the present invention is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

2, 4: Laser printer (image forming apparatus), 12: photosensitive drum (image carrier), 14: charger, 16: supply roller, 18: developing roller, 28: resistor (voltage dividing circuit), 60: Zener diode (voltage dividing circuit), 40: control unit (voltage control means), 74: transistor (voltage control means), 90: equipotential circuit (same potential means), 92: photocoupler (same potential means), 98: Zener diode (same potential means), 100: transistor (same potential means), 120: control unit (same potential means)

Claims (2)

A charger,
An image carrier on which an electrostatic latent image is formed on the surface charged by the charger;
A developing roller for developing the electrostatic latent image by supporting a developer on the electrostatic latent image formed on the surface of the image carrier;
A supply roller for supplying the developer to the developing roller;
A voltage dividing circuit for dividing the voltage applied to the charger in series from the charger to the supply roller and the developing roller;
Voltage control means for controlling a voltage applied from the voltage dividing circuit to the developing roller by a duty ratio of a PWM signal;
Equipotential means for making the supply roller and the developing roller have the same potential based on the duty ratio of the PWM signal;
An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, wherein the equipotential means is an equipotential circuit that makes the supply roller and the developing roller have the same potential based on a duty ratio of the PWM signal.

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