JP5067857B2 - Image forming apparatus and output control method - Google Patents

Description

  The present invention relates to an image forming apparatus including a charging unit that charges the surface of an image carrier, and an output control method for outputting a charging bias to the charging unit.

  2. Description of the Related Art Conventionally, an image forming apparatus employing an electrophotographic system is provided with a charging device (charging means) that uniformly charges the surface of a photosensitive drum provided as an image carrier. As such a charging device, a non-contact charging type corona charging is generally used in which a corona is generated by applying a high voltage to a thin corona discharge wire, and the generated corona is applied to the surface of the photosensitive drum for charging. Are known.

  On the other hand, in recent years, a contact charging method that is advantageous in terms of a low-pressure process, a low ozone generation amount, a low cost and the like is becoming mainstream. In this method, for example, a roller charging member (hereinafter referred to as a charging roller) is brought into contact with the surface of the photosensitive drum, and a charging bias is applied to the charging roller to charge the photosensitive drum.

  The charging bias applied to the charging roller may be only a DC bias. However, by applying an AC bias, discharge to the positive side and the negative side can be caused alternately to charge the surface of the photosensitive drum more uniformly. It becomes possible.

  For example, a charging roller is provided with an oscillating bias in which an AC bias having a peak-to-peak voltage equal to or greater than a threshold bias (charging start voltage) for starting discharge of a charged body when a DC bias is applied, and a DC bias (DC offset bias) Output to. By doing so, it is known that the surface of an object to be charged such as a charging roller is uniformly charged.

  When a vibration bias is applied to the charging roller, the charging roller includes a resistive load current that flows through a resistive load between the charging roller and the photosensitive drum, a capacitive load current that flows through a capacitive load between the charging roller and the photosensitive drum, and a charging roller. And a discharge current between the photosensitive drum and the photosensitive drum.

  At this time, in order to obtain stable charging, it has been empirically known that the discharge current amount should be a predetermined value or more. On the other hand, if the discharge current amount to the photosensitive drum increases, the photosensitive drum There is a problem that deterioration proceeds.

  This deterioration phenomenon is caused by the surface of the photosensitive drum being worn by energy due to discharge. Further, when the wear of the surface of the photosensitive drum progresses in this way, the charging performance of the photosensitive drum and the like are deteriorated, causing a problem that an abnormal image is generated.

  In other words, in order to stably charge the surface of the photosensitive drum and prevent deterioration of the photosensitive drum, charging that minimizes the discharge that occurs alternately between the positive side and the negative side by applying the minimum necessary voltage. Bias output control is required.

  Therefore, Patent Document 1 discloses a configuration in which the charging bias applied to the charging roller is subjected to constant current control as means for stably supplying the discharge current to the photosensitive drum. FIG. 5 shows a circuit configuration diagram of a conventional charging bias generation circuit that performs constant current control.

As shown in FIG. 5, the charging bias generation circuit that outputs the charging bias to the charging roller 1006 includes an AC bias generation circuit 1002, a DC bias generation circuit 1014, and a current detection circuit 1008 that detects the level of the AC bias current. Is provided.

  In addition, the AC bias generation circuit 1002 and the DC bias generation circuit 1014 are connected via a resistor 1013, and a capacitor 1012 is connected to the input portion of the current detection circuit 1008.

  The capacitance of the capacitor 1012 is set so that the impedance when an AC bias is applied is sufficiently smaller than that of the resistor 1013. By doing so, the AC bias current and the DC bias current that flow when the charging bias is applied flow separately to the current detection circuit 1008 and the DC bias generation circuit 1014. That is, only the AC bias current flows through the current detection circuit 1008 and only the DC bias current flows through the DC bias generation circuit 1014.

  By separating the current path in this way, it is possible to prevent the AC bias current from flowing into the DC bias generation circuit 1014, and the current detection circuit 1008 can detect the AC bias current with high accuracy.

  Further, as the impedance ratio between the capacitor 1012 and the resistor 1013 is increased, the AC bias current flowing through the DC bias generation circuit 1014 is decreased, and the AC bias current can be detected with higher accuracy.

  Further, the level of the DC bias is controlled by being divided by the resistors 1015 and 1024 and then compared with the reference value output from the controller 1001 by the comparator 1023, and the transformer 1008 is driven according to the result. The That is, the DC bias generation circuit 1014 is controlled with a constant voltage.

  The level of the AC bias is adjusted according to the result of the current detection circuit 1008, and is controlled so that the AC current becomes a predetermined level. During the printing operation, the AC bias generation circuit 1002 and the DC bias generation circuit 1014 are simultaneously driven, and the AC bias is controlled by a constant current and the DC bias is controlled by a constant voltage.

With the above circuit configuration, a bias in which a DC bias is superimposed on an AC bias is generated, and is output to the charging roller as a charging bias, whereby the surface of the photosensitive drum 1007 is charged.
Japanese Patent Laid-Open No. 2003-140446

  However, the image forming apparatus including the conventional charging bias generation circuit and the output control method of the charging bias generation circuit have the following problems.

  Conventionally, when the charging current output from the charging bias generation circuit fluctuates, the output level of the direct current bias fluctuates, causing a problem of image defects.

  Here, with reference to FIG. 6, a mechanism in which an image defect occurs due to a change in charging current will be described. FIG. 6A is a component arrangement diagram around the photosensitive drum 1101 in the electrophotographic image forming apparatus, and FIG. 6B shows the timing of applying the charging bias, developing bias, transfer bias, and drum potential voltage. FIG.

As shown in FIG. 6A, a charging roller 1102, a developing roller 1103, and a transfer roller 1104 are arranged around the photosensitive drum 1101. Further, the surface of the photosensitive drum 1101 is irradiated with laser light from the direction of arrow B and exposed.

  When the image forming operation is started, the photosensitive drum 1101 rotates in the direction of arrow A, and a charging bias is output at timing: t1 to start charging the photosensitive drum 1101.

  Thereafter, a developing bias is output at timing t3, and toner is selectively supplied to the surface of the photosensitive drum 1101. At this time, the electrostatic latent image formed on the surface of the photosensitive drum 1101 by the laser light is visualized as a toner image.

  Then, the transfer bias is output at timing t5. Further, at the timing t6, the sheet material 1105 is conveyed to the nip T between the transfer roller 1104 and the photosensitive drum 1101, and the toner image on the photosensitive drum 1101 is transferred to the sheet material 1105.

  The transition of the surface potential of the photosensitive drum 1101 due to the charging bias output at timing t1, the developing bias output at timing t3, and the transfer bias output at timing t5 will be described.

  FIG. 6B shows the potential transition at the nip portion C between the photosensitive drum 1101 and the charging roller 1102 and the potential transition at the nip portion T between the photosensitive drum 1101 and the transfer roller 1104.

  Timing: When a charging bias is applied at t1, the surface potential of the photosensitive drum 1101 at the nip C rises to the same level as the charging DC bias. At this time, a direct current flows from the charging high-voltage power supply. This is because a charge bias is applied to the uncharged photosensitive drum 1101 so that charges flow from the charged high-voltage power supply.

  The current flowing from the charging high-voltage power source flows in a section from timing: t1 to timing: t4 when the photosensitive drum 1101 rotates once.

  Thereafter, when the transfer bias is output at timing t5, the surface potential of the photosensitive drum 1101 at the nip T increases.

  Thereafter, when the photosensitive drum 1101 rotates and the region of the photosensitive drum 1101 whose potential has been increased by the transfer bias reaches the contact region with the charging roller 1102, the charging direct current greatly increases at timing t7.

  This is because a large amount of charge flows into the photosensitive drum 1101 due to an increase in the surface potential of the photosensitive drum 1101. At this time, the charging bias fluctuates due to an increase in the charging direct current, and the surface potential of the photosensitive drum 1101 also fluctuates, resulting in an image defect.

  This is because a voltage drop occurs in the resistor 1013 (see FIG. 5) connected to a DC bias generation circuit 1014 provided as a charging DC current generation circuit.

  That is, the resistance value of the resistor 1013 connected to the DC bias generation circuit 1014 may be reduced in order to reduce the fluctuation of the surface potential of the photosensitive drum 1101 due to a sudden change in the charging DC current.

  However, as described above, in order to detect the AC bias current with high accuracy in the current detection circuit 1008, it is not desirable to reduce the resistance value of the resistor 1013.

  The present invention has been made in view of the above situation, and an image capable of obtaining a stable charging bias output even when the charging output current fluctuates rapidly and performing constant current control of the charging AC bias with high accuracy. It is an object to provide a forming apparatus and an output control method.

  In order to achieve the above object, according to the present invention, in an image forming apparatus having a charging means for charging the surface of an image carrier, a charging bias generation circuit for outputting a charging bias to the charging means is provided in the apparatus body. And the charging bias generation circuit includes AC bias generation means, DC bias generation means, and current detection means for detecting AC current generated in the AC bias generation means, and the AC bias generation And the direct current bias generating means are directly connected, and the direct current bias generating means and the current detecting means are directly connected.

  The output control method of the present invention is an output control method of a charging bias generation circuit that outputs a charging bias to a charging unit that charges the surface of the image carrier. The charging bias generation circuit includes an AC bias generation unit and A DC bias generating means; and a current detecting means for detecting an AC current generated in the AC bias generating means, wherein the AC bias generating means and the DC bias generating means are directly connected to generate the DC bias. And the current detecting means are directly connected, and when the charging bias is output to the charging means, the DC bias generating means is stopped to drive the AC bias generating means, and the current After determining the output level of the AC bias generating means according to the detection result of the detecting means, the DC bias generating means Characterized in that it dynamic.

  According to the present invention, there is provided an image forming apparatus and an output control method capable of obtaining a stable charging bias output even when the charging output current fluctuates rapidly and performing constant current control of the charging AC bias with high accuracy. It becomes possible to do.

  The best mode for carrying out the present invention will be exemplarily described in detail below based on the embodiments with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

(First embodiment)
The image forming apparatus and output control method according to the first embodiment of the present invention will be described with reference to FIGS.

[Entire configuration of image forming apparatus]
FIG. 1 shows the overall configuration of the image forming apparatus according to the present embodiment. In this embodiment, a laser beam printer 100 that employs an electrophotographic system is used as the image forming apparatus.

  The apparatus body of the laser beam printer 100 is provided with a deck 101 that stores a plurality of sheet materials P. Further, around the deck 101, a sheet material presence sensor 102 that detects the presence or absence of the sheet material P in the deck 101 and a sheet material size detection sensor 103 that detects the size of the sheet material P in the deck 101 are provided.

A pickup roller 104 that feeds out the sheet material P is provided above the deck 101, and a feeding roller 10 that feeds the sheet material P fed out by the pickup roller 104.
5. A retard roller 106 for preventing double feeding of the sheet material P is provided. The feeding roller 105 and the retard roller 106 are provided as a pair.

  A feeding sensor 107 that detects the conveying state of the sheet material P is provided downstream of the feeding roller 105, and a conveying roller 108 for conveying the sheet material P and the sheet material P are synchronously conveyed further downstream. A registration roller pair 109 is provided. Further, a pre-registration sensor 110 that detects the conveyance state of the sheet material P is disposed between the conveyance roller 108 and the registration roller pair 109.

  Further, on the downstream side of the registration roller pair 109, a process cartridge 112 for transferring the toner image onto the sheet material P and a transfer roller 1104 are provided as a pair. The process cartridge 112 in this embodiment includes a photosensitive drum (image carrier) 1101 that is driven to rotate, a charging roller (charging unit) 1102 that charges the surface of the photosensitive drum 1101, and toner on the surface of the photosensitive drum 1101. A developing device 135 is provided.

  The developing device 135 includes a developing roller 1103 and is configured to be able to supply toner to the surface of the photosensitive drum 1101 when the developing roller 1103 comes into contact with the surface of the photosensitive drum 1101. The process cartridge 112 is configured to be detachable from the laser beam printer 100.

  Further, a laser scanner unit 111 that irradiates the surface of the photosensitive drum 1101 with laser light is provided in the vicinity of the process cartridge 112. The laser scanner unit 111 includes a laser unit 129 that emits a laser beam modulated based on an image signal transmitted from the external device 128, a polygon mirror 130 that scans the photosensitive drum 1101 with the laser beam, and a scanner motor 131. Is provided. Further, an imaging lens group 132 for imaging the laser beam on the surface of the photosensitive drum 1101 and a folding mirror 133 are provided.

  On the downstream side of the nip portion between the photosensitive drum 1101 and the transfer roller 1104, a static elimination needle 114 is provided to remove the electric charge stored in the sheet material P and to easily separate the sheet material P from the photosensitive drum 1101. Further, a conveyance guide 115 that guides conveyance of the sheet material P is provided on the downstream side of the static elimination needle 114.

  On the downstream side of the conveyance guide 115, a fixing roller 117 having a halogen heater 116 for heating inside in order to thermally fix the toner image transferred onto the sheet material P, and a pressure roller that is in pressure contact with the fixing roller 117. A fixing unit having 118 is provided. The toner image transferred onto the sheet material P is fixed on the sheet material P by being heated and pressed at the nip portion between the fixing roller 117 and the pressure roller 118.

  On the downstream side of the fixing unit, a fixing discharge sensor 119 for detecting a conveyance state from the fixing unit, and a double-sided flapper 120 for switching the destination of the sheet material P conveyed from the fixing unit to the discharging unit or the double-side reversing unit are provided. It is done.

  A discharge sensor 121 that detects a conveyance state of the sheet material to the discharge unit and a discharge roller pair 122 that discharges the sheet material are provided on the downstream side of the discharge unit.

  On the other hand, in order to print on both sides of the sheet material P, the sheet material P after the single-sided printing is turned upside down, and the sheet material P is fed again to the image forming unit on the double-sided reversing unit side by forward and reverse. A reverse roller pair 123 for switching back the material P is provided.

Further, a reversing sensor 124 for detecting the conveyance state of the sheet material P to the reversing roller pair 123,
A D-cut roller 125 for conveying the sheet material P is provided from a lateral direction registration portion (not shown) for aligning the lateral position of the sheet material P. Further, a double-sided sensor 126 for detecting the conveyance state of the sheet material P in the double-side reversing unit and a double-sided conveyance roller pair 127 for conveying the sheet material P from the double-side reversing unit to the feeding unit are provided.

  In addition, the laser beam printer 100 configured as described above includes a high-voltage power source 3 that supplies a desired voltage to a charging high-voltage power source, a developing roller 1103, a transfer roller 1104, and a charge eliminating needle 114, which will be described later. Further, each driving member constituting the laser beam printer 100 is supplied with a driving force by the main motor 136.

  In addition, the laser beam printer 100 is provided with a printer control unit 4 for controlling the driving of each driving member. The printer control unit 4 is provided with an MPU (microcomputer) 5 and various input / output control circuits (not shown).

  The MPU 5 includes a RAM 5a, ROM 5b, timer 5c, digital input / output port (hereinafter referred to as I / 0 port) 5d, analog-digital conversion input port 5e, and digital-analog output port (hereinafter referred to as D / A port) 5f. Provided. The printer control unit 4 is connected to an external device 128 such as a personal computer via an interface 138.

[Configuration of charging bias generation circuit]
With reference to FIG. 2, the configuration of the charging bias generation circuit provided in the charging high-voltage power supply in the present embodiment will be described. A charging bias generation circuit provided in the charging high-voltage power supply outputs a charging bias to uniformly charge the surface of the charging roller 1102, and is provided in the high-voltage power supply 3 of the laser beam printer 100.

  The charging bias generation circuit of the present embodiment includes an AC bias generation circuit (AC bias generation means) and a DC bias generation circuit (DC bias generation means). The charging bias obtained by superimposing the DC bias on the AC bias generated by these generating circuits is output from the output terminal to the charging roller. Hereinafter, the configurations of an AC bias generation circuit, a DC bias generation circuit, and a current detection circuit (current detection means) that detects current generated in the AC bias generation circuit will be described.

[Configuration of AC Bias Generation Circuit]
With reference to FIG. 2, the configuration of an AC bias generation circuit according to the present embodiment will be described. When the clock pulse (CLK1) is output from the I / O port of the CPU 245 to the AC bias generation circuit in this embodiment, the transistor 239 starts a switching operation via the pull-up resistor 260 and the base resistor 238. .

  When the transistor 239 starts a switching operation, the output pulse is amplified to a clock pulse having an amplitude corresponding to the output of the operational amplifier 280 connected to the pull-up resistor 237 and the diode 240. When the amplitude of the amplified clock pulse is large, the amplitude of the sine wave drive voltage input to the high voltage transformer 204 described later also increases, and as a result, the voltage level of the AC bias also increases.

  The output level of the operational amplifier 280 is determined by the analog output of the CPU 245 (CONT1 level). That is, the voltage level of the AC bias can be controlled by an analog output (CONT1 level).

The output clock pulse is input to a filter circuit 235 including resistors 216 to 226, capacitors 228 to 231 and operational amplifiers 233 and 234 via a capacitor 227.

  Thereafter, the filter circuit 235 outputs a sine wave centered on + 12V. The sinusoidal drive voltage output from the filter circuit 235 is input to the primary winding of the high-voltage transformer 204 via the push-pull high-voltage transformer drive circuit 205. The high-voltage transformer drive circuit 205 includes resistors 209 to 213, a diode 215, transistors 206 to 208, and the like.

  When a sine wave is input to the primary winding of the high-voltage transformer 204, an AC bias of a sine wave is generated on the secondary winding side provided opposite to the primary winding. Note that the pin terminal 3 of the secondary winding is connected to the output terminal 299. On the other hand, the pin terminal 4 is directly connected to a DC bias generation circuit 279 described later.

[Configuration of DC bias generator]
The configuration of DC bias generation circuit 279 in the present embodiment will be described. The pin terminal 4 of the secondary winding of the high-voltage transformer 204 described above is directly connected to the DC bias generation circuit 279.

Clock pulse (C from the I / O port of CPU 245 is applied to DC bias generating circuit 279.
When LK2) is output, the transistor 268 starts switching operation via the resistor 283 and drives the transformer 263.

  In the secondary winding of the transformer 263, an AC bias corresponding to the voltage at the pin 2 on the input side is generated, rectified by the diode 261 and the capacitor 262, and a negative DC bias is generated on the anode side of the diode 261.

  The DC bias generated in the secondary winding of the transformer 263 is divided by resistors 1015 and 1024 and input to the positive input terminal of the operational amplifier 269. On the other hand, the analog output signal (CONT2) of the CPU 245 is input to the negative input terminal of the operational amplifier 269.

  The output terminal of the operational amplifier 269 is connected to the base of the transistor 266 via the resistor 267 and adjusts the input voltage of the transformer 263. That is, the DC bias can be controlled at a constant voltage according to the level of the analog output (CONT2). The terminal pin 5 of the transformer 263 is directly connected to the current detection circuit 278.

[Configuration of current detection circuit]
The configuration of the current detection circuit 278 in this embodiment will be described. The current detection circuit 278 is a circuit that detects an AC current generated in the AC bias generation circuit described above.

  The alternating current generated by driving the high voltage transformer 204 described above passes through the capacitor 262 in the direct current bias generation circuit 279 and flows into the current detection circuit 278. The alternating current flowing into the current detection circuit 278 is separated into paths in the direction of arrow E and F in FIG.

The half-wave current in the direction of arrow E passes through the diode 270 and flows to the power source Vcc via the resistor 285 and to GND (ground potential) via the resistor 286. On the other hand, the half-wave current in the direction of arrow F passes through the diode 277 and is input to an integration circuit including the operational amplifier 274, the resistor 275, and the capacitor 276. Note that the values of the resistors 285 and 286 are set so that the K point becomes 0.6 V when the high-voltage transformer 204 is stopped and no alternating current is flowing.

In the integrating circuit, the half-wave current is integrated and converted into a DC voltage. The negative input terminal of the operational amplifier 274 is supplied with 0.6 V obtained by dividing the Vcc voltage by the resistors 272 and 273, and the voltage Vs at the output terminal of the operational amplifier 274 is expressed by the following equation.
Vs = 0.6 + R ₂₇₅ × Is

In the above equation, R ₂₇₅ is the resistance value of the resistor 275 provided in the integrating circuit, and Is is the average value of the half-wave current of the alternating current. The output terminal of the operational amplifier 274 is input to the analog input terminal of the CPU 245.

  In addition to the alternating current generated by the alternating current bias generation circuit, the direct current generated by the direct current bias generation circuit 279 and the ripple current generated by the direct current bias generation circuit 279 also flow into the current detection circuit 278.

  Since the direct current generated in the direct current bias generation circuit 279 has a negative polarity, the direct current flows in the direction of arrow E to GND (ground portion) via the diode 270. On the other hand, the ripple current flows in the directions of arrows E and F.

  That is, in this embodiment, when the AC bias generation circuit and the DC bias generation circuit are driven simultaneously, the current detection circuit 278 detects the total value of the AC current and the ripple current of the DC bias generation circuit. Therefore, in order to detect only the AC current with high accuracy, it is necessary to measure the charging AC bias at the timing when the DC bias generation circuit 279 is stopped.

[Output biasing circuit output control method]
With reference to FIGS. 3 and 7, the output control method of the charging bias generation circuit in the present embodiment will be described. FIG. 7 is a flowchart showing a series of processing of the charging bias. FIG. 3A is a layout diagram of components around the photosensitive drum 1101 in the present embodiment, and shows the layout of the charging roller 1102, the developing roller 1103, and the transfer roller 1104. An arrow B indicates the laser. The laser beam emitted from the scanner unit 111 is shown. FIG. 3B shows a driving sequence of the charging bias generation circuit in the present embodiment.

  When image formation on the sheet material starts, the photosensitive drum 1101 is rotated in the direction of arrow A, and at the timing t1, a clock pulse (CLK1) and an analog control signal (CONT1) are output to drive the AC bias generation circuit. (S702 of FIG. 7).

  Next, the output signal (SNS1) of the current detection circuit 278 is monitored (S703), the detection result of the current detection circuit 278 is compared with the predetermined value A (S704), and if it is smaller than the predetermined value, the CONT1 signal is output in S705. After the increase, the comparison with the predetermined value A is performed again in S704. On the other hand, if the predetermined value A is reached in S704, the CONT1 signal is determined in S706, and the level of the charging AC bias is fixed.

  During the printing operation, the analog control signal (CONT1 (0)) is fixed and the AC bias level is maintained. By controlling in this way, the output of the charging bias can be controlled with a constant current, and stable charging characteristics can be obtained.

Next, a DC bias is applied at timing: t2 (S707). As a result, the drum potential at the nip portion C of the photosensitive drum 1101 and the charging roller 1102 is charged to the negative electrode. When the drum 1101 further rotates in the direction of arrow A, the drum potential at the nip portion: T point of the transfer roller 1104 rises to the negative polarity at timing: t3. Next, a transfer bias is applied at timing t5, and the sheet material 1105 is conveyed to the nip portion T between the transfer roller 1104 and the photosensitive drum 1101 at timing t6, and the toner on the photosensitive drum 1101 is transferred to the sheet material 1105. The

  Next, the transition of the potential of the photosensitive drum 1101 that changes according to each high-voltage bias described above will be described. FIG. 3B shows the potential transition at the nip portion C between the photosensitive drum 1101 and the charging roller 1102 and the potential transition at the nip portion T between the photosensitive drum 1101 and the transfer roller 1104.

  When the DC bias is output, the potential C on the photosensitive drum 1101 rises to the same level as the DC bias (timing: t2). At this time, a direct current flows through the charging high-voltage power supply.

  This is because charges flow from the charged high-voltage power source into the photosensitive drum 1101 that is not charged by applying the charging bias. This current flows while the photosensitive drum 1101 makes one revolution from timing t2.

  When the transfer bias is applied at timing t5, the potential T on the photosensitive drum 1101 rises. When the photosensitive drum 1101 rotates and the photosensitive drum 1101 region whose potential is increased by the transfer bias reaches the charging roller 1102, the charging direct current greatly increases (timing: t7).

  This is because a large amount of charge flows into the photosensitive drum 1101 due to an increase in the potential of the photosensitive drum 1101. However, there is no charge bias level fluctuation at this time. This is because the charging bias generation circuit is not provided with a resistor that causes a voltage drop. That is, in the output control method of the charging bias generation circuit according to the present embodiment, no image defect occurs due to fluctuations in the output current.

  As described above, in the charging device according to the present embodiment, the AC bias generation circuit and the DC bias generation circuit are directly connected, and the DC bias generation circuit and the current detection circuit are further connected to each other by DC. The resistor is not connected to the current path.

  Further, the output level of the charging AC bias at which the charging AC current becomes a desired value is determined in a state where the DC bias generating circuit is stopped, and control is performed at the output level of the charging AC bias determined by the above method during printing.

  With such a configuration, even when the output current changes suddenly, the level of the charging bias does not occur, and it is possible to avoid the occurrence of image defects. Furthermore, the output of the charging bias can be controlled with constant current with high accuracy, and stable and uniform charging can be achieved.

(Second Embodiment)
With reference to FIG. 4, an output control method for an image forming apparatus and a charging bias generation circuit according to a second embodiment of the present invention will be described. FIG. 4 shows the configuration of the charging bias generation circuit in the present embodiment. Note that the overall configuration of the image forming apparatus, the configuration of the AC bias generation circuit, and the configuration of the DC bias generation circuit are not different from those of the first embodiment, and thus description thereof is omitted. Here, the configuration of the current detection circuit will be described.

[Configuration of current detection circuit]
FIG. 4 shows the configuration of the charging bias generation circuit according to the present embodiment. Compared with the charging bias generation circuit according to the first embodiment, a current detection circuit (current detection means) 4 is shown in FIG.
Only 78 configurations are different. Hereinafter, the configuration of the current detection circuit 478 will be described.

  The alternating current generated by driving the high voltage transformer 204 passes through the capacitor 262 in the direct current bias generation circuit 279 and flows to the current detection circuit 478.

  The alternating current flowing into the current detection circuit 478 is separated into the diode 401 and the diode 402 by polarity, and the half-wave current in the direction of arrow F passes through the diode 401 and flows to GND (grounding portion).

  On the other hand, the half-wave current in the direction of arrow E passes through the diode 402 and is input to an integrating circuit composed of an operational amplifier 407, a resistor 405, and a capacitor 406. In the integrating circuit, the half-wave current is integrated and converted into a DC voltage.

The negative input terminal of the operational amplifier 407 receives 3.0 V obtained by dividing the Vcc voltage by the resistors 403 and 404, and the voltage Vs at the output terminal of the operational amplifier 407 is expressed by the following equation.
Vs = 3.0−R ₄₀₅ × Is

In the above equation, R ₄₀₅ is the resistance value of the resistor 405, and Is is the average value of the half-wave current of the alternating current. The output terminal of the operational amplifier 407 is input to the analog input terminal of the CPU 245. In addition to the alternating current generated by the alternating current bias generation circuit, the direct current generated by the direct current bias generation circuit and the ripple current generated by the direct current bias generation circuit also flow into the current detection circuit 478.

  Since the direct current generated by the direct current bias generation circuit has a negative polarity, it flows in the direction of arrow E through the diode 402, the resistor 405, and the operational amplifier 407 to GND (grounding unit). On the other hand, the ripple current flows in the directions of arrows E and F.

  That is, when the AC bias generation circuit and the DC bias generation circuit are driven simultaneously, the total value of the AC current, the DC current, and the ripple current is detected by the current detection circuit 278.

  Therefore, in order to detect only the alternating current with high accuracy, it is necessary to measure the alternating current bias at the timing when the direct current bias generating circuit is stopped. The driving sequence of the charging bias generation circuit in the present embodiment is the same as that in the first embodiment.

  As described above, in the image forming apparatus according to the present embodiment, the AC bias generation circuit and the DC bias generation circuit are directly connected, and the DC bias generation circuit and the current detection circuit are directly connected.

  Thereby, the resistance connected to the current loop of the DC bias generation circuit is only the resistance inside the current detection circuit. Further, the AC bias level at which the charging AC current becomes a desired value is determined with the DC bias generation circuit stopped, and control is performed at the AC bias level determined by the above method during printing.

  With such a configuration, even when the output current changes suddenly, the level of the charging bias does not occur, and it is possible to avoid the occurrence of image defects. Furthermore, the output of the charging bias can be controlled with constant current with high accuracy, and stable and uniform charging can be achieved.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. The figure which shows the structure of the charging bias generation circuit in 1st Embodiment. The figure showing the drive sequence of the charge bias generation circuit in a 1st embodiment The figure which shows the structure of the charging bias generation circuit in 2nd Embodiment. The figure which shows the structure of the conventional charging bias generation circuit The figure showing the drive sequence of the conventional charging bias generation circuit The figure showing the processing flow of the charging bias generation circuit in 1st Embodiment

Explanation of symbols

205 High voltage transformer drive circuit 245 CPU
278 Current detection circuit 279 DC bias generation circuit 299 Output terminal

Claims (6)

In an image forming apparatus having a charging means for charging the surface of an image carrier,
In the device body,
A charging bias generating circuit for outputting a charging bias to the charging means is provided;
The charging bias generation circuit includes:
AC bias generating means,
DC bias generating means;
Current detecting means for detecting an alternating current generated in the AC bias generating means;
Have
Directly connecting the AC bias generating means and the DC bias generating means;
An image forming apparatus, wherein the DC bias generating means and the current detecting means are directly connected. The charging means is
The image forming apparatus according to claim 1, wherein the image forming apparatus is a charging roller in contact with a surface of the image carrier. The image carrier is
The image forming apparatus according to claim 1, wherein the image forming apparatus is a photosensitive drum that is rotationally driven. In the output control method of the charging bias generation circuit for outputting the charging bias to the charging means for charging the surface of the image carrier,
The charging bias generation circuit includes:
AC bias generating means,
DC bias generating means;
Current detecting means for detecting an alternating current generated in the AC bias generating means;
Have
The AC bias generating means and the DC bias generating means are directly connected,
The direct current bias generation means and the current detection means are directly connected,
When outputting the charging bias to the charging means,
Driving the AC bias generating means with the DC bias generating means stopped, and driving the DC bias generating means after determining the output level of the AC bias generating means according to the detection result of the current detecting means An output control method characterized by the above. The charging means is
The output control method according to claim 4, wherein the output roller is a charging roller that contacts the surface of the image carrier. The image carrier is
The output control method according to claim 4, wherein the output control method is a photosensitive drum that is rotationally driven.

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