JP3902974B2 - Charging bias voltage control method, charging bias power supply circuit, and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a charging bias voltage control method, a charging bias power supply circuit, and an image forming apparatus employing an electrophotographic method, an electrostatic recording method, and the like.TheUsing a charging bias voltage control method, orTheThe present invention relates to an image forming apparatus including a charging bias power supply circuit.
[0002]
[Prior art]
FIG. 13 shows a schematic configuration of an example of a general image forming apparatus. The image forming apparatus of this example is an electrophotographic copying machine or printer. Reference numeral 100 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as a latent image carrier, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed. The photosensitive drum 100 is subjected to a uniform charging process with a predetermined polarity and potential by the charging device 101 during the rotation process, and then subjected to image exposure by the exposure device 102. As a result, an electrostatic latent image is formed on the photosensitive drum surface. Next, the electrostatic latent image is developed by the developing device 103 to be visualized as a toner image. The toner image on the photosensitive drum surface is transferred by a transfer device 105 to a recording medium 104 such as paper fed from a paper supply unit (not shown). The recording medium 104 to which the toner image has been transferred is separated from the surface of the photosensitive drum, introduced into the fixing device 106, subjected to a toner image fixing process, and discharged as an image formed product. The photosensitive drum surface after separation of the recording medium is cleaned by scraping off the transfer residual toner by the cleaning device 107 and repeatedly used for image formation.
[0003]
The image forming apparatus forms an image by repeating the steps of charging, exposing, developing, transferring, fixing, and cleaning using the above-described means.
[0004]
As the charging device 101, a contact charging method is widely used in which a charging member such as a roller type or a blade type is brought into contact with the surface of the photosensitive drum, and a voltage is applied to the contact charging member to charge the surface of the photosensitive drum. In particular, the contact charging method using a roller-type charging member (charging roller) can perform stable charging over a long period of time.
[0005]
  A charging bias voltage is applied from a charging bias applying unit to a charging roller as a contact charging member. The charging bias voltage may be only a DC voltage, but when a DC voltage is applied to a DC voltage Vdc corresponding to a desired on-drum dark potential Vd as disclosed in JP-A-63-149669.ofA bias voltage is used in which an AC voltage having a peak-to-peak voltage (Vpp) that is twice or more the discharge start voltage is superimposed.
[0006]
This charging method is excellent for uniformly charging the photosensitive drum, and local potential unevenness on the photosensitive drum is eliminated by superimposing an alternating voltage on the direct current voltage. Vd converges uniformly on the DC applied voltage value Vdc.
[0007]
  However, this method increases the amount of discharge to the photosensitive drum as compared with the case where only the direct current component is applied as the charging bias voltage, and therefore surface deterioration such as scraping due to wear of the surface of the photosensitive drum with the cleaning device is easily promoted. To cope with this, the charging bias voltageAC peak-to-peak voltage (AC peak-to-peak voltage)It was necessary to keep Vpp as small as possible to prevent the charging roller from being excessively discharged to the photosensitive drum.
[0008]
The relationship between the AC peak-to-peak voltage (Vpp) and the discharge amount described above is not always constant because it varies depending on the film thickness of the photosensitive layer on the surface of the photosensitive drum, the usage environment, and the like. For example, even if the same peak-to-peak voltage is applied to the charging roller, the charging roller impedance increases in a low-temperature and low-humidity environment, so the amount of discharge is small. Conversely, in a high-temperature and high-humidity environment where the impedance decreases, the amount of discharge is large. Even when the usage environment is the same, if the surface of the photoconductor is scraped off due to wear, the impedance is reduced as compared with the initial use, and the amount of discharge increases.
[0009]
In order to avoid this problem, a method (Japanese Patent Publication No. 06-093150) for controlling the AC component with a constant current has been proposed. This is to detect the AC current Iac flowing through the photosensitive member and control it to be constant. When this method is used, the AC peak-to-peak is reduced with respect to impedance changes due to environmental fluctuations or photosensitive drum scraping. Since the voltage can be freely changed, the discharge amount can be kept almost constant regardless of environmental fluctuations, the film thickness of the photosensitive drum, and the like.
[0010]
Furthermore, Japanese Patent Laid-Open No. 2001-201920 detects an alternating current Iac flowing in a photoconductor when an AC peak-to-peak voltage Vpp in a discharge region and an undischarged region is applied to a charging device during non-image formation. There has also been proposed a method in which a discharge current amount is calculated from the above relationship, and an AC voltage that provides an appropriate discharge amount is applied as a charging bias during image formation. Since this method controls the discharge current more directly, it is possible to control the discharge current with higher accuracy than conventional constant current control.
[0011]
These methods have a great effect in extending the life of the drum and ensuring good chargeability.
[0012]
In addition, in Japanese Patent Laid-Open No. 09-190143, the process cartridge usage amount detection / storage means is mounted on the process cartridge, and two or more kinds of constant voltage outputs are provided for the AC peak-to-peak voltage, A method has been proposed in which the film thickness of the photosensitive drum is predicted according to the amount of process cartridge used, and the AC peak-to-peak voltage is lowered stepwise.
[0013]
  When the AC component is controlled at a constant voltage, the DC voltage isFIG.As shown in (a) of FIG. 1, by connecting a capacitor C for creating a DC voltage from a step-up transformer T-AC (voltage boosting means) for AC output via a diode D, the capacitor C is peak-charged. Since it can be created, it is possible to output a superimposed bias of alternating current and direct current with only one voltage booster T-AC.
[0014]
For this reason, there is no need to separate the DC power supply and the AC power supply, and the power supply circuit configuration can be greatly simplified as compared with the case of constant current control, which is advantageous in terms of cost and space saving of the power supply circuit.
[0015]
[Problems to be solved by the invention]
As described above, in order to control the discharge amount to be substantially constant regardless of the use situation, a constant current control method for alternating current components such as Japanese Patent Publication No. 06-093150, or Japanese Patent Application Laid-Open No. 2001-201920. What is necessary is just to employ | adopt the discharge amount calculation system like gazette. However, in these methods, as shown in FIG. 14 (a), when one voltage booster T-AC is used to output an alternating current and direct current superimposed voltage, the alternating current peak-to-peak voltage decreases, and the temperature and humidity are high. Under conditions such as the latter half, the capacitor cannot be fully charged, and a desired DC voltage cannot be obtained. As a result, the photosensitive drum is not charged satisfactorily, resulting in problems such as defective charging.
[0016]
  For this reason, when the above method is used, there is a limit in outputting a superimposed voltage of alternating current and direct current with one voltage boosting means, and in order to obtain a stable charging bias voltage,FIG.As shown in (b), the DC power supply T-DC and the AC power supply T-AC must be separated, and two voltage boosting means for DC and AC must be mounted.
[0017]
However, since the voltage boosting means is expensive and large in the charge generation circuit, in particular in a small-sized and low-cost image forming apparatus, one voltage boosting means is used from the viewpoint of space saving and cost reduction of the power supply circuit. It is desirable to output a stable charging bias voltage.
[0018]
In the method disclosed in Japanese Patent Application Laid-Open No. 09-190143, the charging bias generating circuit can be configured by a single voltage boosting unit, so that there are significant advantages in terms of space saving and cost of the power supply circuit. However, since this method performs voltage switching (AC peak-to-peak voltage down) when a predetermined timing (photoconductor usage amount) is reached, for example, AC peak-to-peak voltage output due to power supply tolerance of the charging bias generation circuit. When is the tolerance lower limit, the voltage may be switched even though the discharge amount is appropriate, resulting in insufficient discharge amount and charging failure.In addition, when the AC peak-to-peak voltage output is the tolerance upper limit, the discharge amount is In spite of the excessive state, voltage switching is not performed until a predetermined timing, and it is conceivable that wear abrasion of the photosensitive drum is promoted, which is inferior to the constant current control in terms of accuracy of discharge control. These are problems that can be solved by reducing the resistance value of the charging device and the power supply tolerance of the charging bias generation circuit, but it is not preferable to reduce the tolerance from the viewpoint of yield.
[0019]
Due to the above circumstances, in a small and low-cost image forming apparatus, even with a simple power supply configuration in which a single voltage boosting unit can output an AC and DC superimposed bias, charging failure does not occur and the photoconductor Therefore, there has been a demand for charge control that minimizes wear abrasion.
[0020]
Therefore, an object of the present invention is to perform good charging control even in a power supply system in which a superimposed bias of alternating current and direct current is used for the charging bias voltage and the direct current voltage is produced by the alternating voltage boosting means.
[0021]
The purpose is to achieve space saving, cost reduction and stable discharge control of the power circuit.
[0022]
[Means for Solving the Problems]
The present invention is a charging bias voltage control method, a charging bias power supply circuit, and an image forming apparatus characterized by the following configurations.
[0023]
  (1) At least a movable latent image carrier and contact with the latent image carrierCharge the latent image carrierAC with charging means and one voltage boosting means for the charging meansVoltageAnd DCVoltageSuperpositionChargedA charging bias voltage control method for an image forming apparatus having a charging bias power supply circuit that outputs a bias voltage, comprising:
  The charging bias power supply circuitPart of non-image formation,At least twoNo picVoltage betweenWhen the AC voltage is applied to the charging means, and the AC voltage is applied to the charging means,Flow to latent image carrierExchangeCurrentDetect
  Pre-set standard among detected AC currentsMore than current and smallestThe peak-to-peak voltage of the alternating voltage from which the alternating current was detected isDuring image formationDecided as peak-to-peak voltage of AC voltage used forAnd a charging bias voltage control method.
[0024]
  (2)SaidThe charging bias power supply circuitBetween AC voltage peaksThe voltage is Vpp-n, NonAC at least part of the image formationVoltageAn alternating current is detected by applying a voltage Vpp− (n + 1) that is one step lower than the peak-to-peak voltage.Alternating currentCurrentThe standardIf the current exceeds the value,Between AC voltage peaksThe charging bias voltage control method according to (1), wherein the voltage is switched to Vpp− (n + 1).
[0025]
  (3)Of the AC voltage applied to the charging means.minimumofThe peak-to-peak voltage Vpp-minApplied to the charging meansThe charging bias voltage control method according to (1) or (2), wherein the relationship with the DC voltage Vdc is Vpp−min / 2 ≧ | Vdc |.
[0026]
  (4)Of the AC voltagemaximumofThe peak-to-peak voltageFor the charging meansFlow when appliedExchangeCurrentIs the standardIt is more than current (1)To any of (3)The charging bias voltage control method described in 1.
[0027]
  (5)SaidThe charging means is characterized in that the ratio of the resistance R-low in a low temperature and low humidity environment to the resistance R-high in a high temperature and high humidity environment is 0.1 ≦ R-low / R-high ≦ 10 (1) To (4). The charging bias voltage control method according to any one of (4) to (4).
[0028]
  (6) At least a movable latent image carrier and contact with the latent image carrierCharge the latent image carrierAn image forming apparatus having a charging unit,The charging means is AC with one voltage boosting means.VoltageAnd DCVoltageSuperpositionChargedCharging bias power supply circuit that outputs bias voltageIn
  The charging bias power supply circuitPart of non-image formation,At least twoLikeThe peak-to-peak voltageWhen the AC voltage is applied to the charging means, and the AC voltage is applied to the charging means,AC current flowing through the latent image carrierDetect
  Pre-set standard among detected AC currentsMore than current and smallestThe peak-to-peak voltage of the alternating voltage from which the alternating current was detected isDuring image formationDecided as peak-to-peak voltage of AC voltage used forA charging bias power supply circuit.
[0029]
  (7)SaidThe charging bias power supply circuitAC peak-to-peak voltageAs Vpp-n, NonInterchange during image formation, at least partly during image formationVoltageAn alternating current is detected by applying a voltage Vpp− (n + 1) that is one step lower than the peak-to-peak voltage.Alternating currentCurrentIs the standardIf the current exceeds the value,Between AC voltage peaksThe charging bias power supply circuit according to claim 6, wherein the voltage is switched to Vpp− (n + 1).
[0030]
  (8)Of the AC voltage applied to the charging means.minimumofThe peak-to-peak voltage Vpp-minApplied to the charging meansThe charging bias power supply circuit according to (6) or (7), wherein the relationship between the DC voltage Vdc and the DC voltage Vdc is Vpp−min / 2 ≧ | Vdc |.
[0031]
  (9)Of the AC voltagemaximumofThe peak-to-peak voltageFor the charging meansFlow when appliedExchangeCurrentIs the standardIt is more than current (6)To any of (8)The charging bias power supply circuit according to 1.
[0032]
  (10)SaidThe charging means is characterized in that the ratio of the resistance R-low in the low temperature and low humidity environment to the resistance R-high in the high temperature and high humidity environment is 0.1 ≦ R-low / R-high ≦ 10 (6) To (9) The charging bias power supply circuit according to any one of (9) to (9).
[0033]
  (11)At least a movable latent image carrier, charging means for charging the latent image carrier in contact with the latent image carrier, and AC voltage and DC voltage are superimposed on the charging means by one voltage boosting means. In an image forming apparatus comprising: a charging bias power supply circuit that outputs a charging bias voltage;
  The charging bias power supply circuit applies an AC voltage having at least two types of peak-to-peak voltages to the charging unit in a part during non-image formation, and when the AC voltage is applied to the charging unit, Detects alternating current flowing in the latent image carrier,
  Among the detected AC currents, the peak-to-peak voltage of the AC voltage that is equal to or higher than a preset reference current and the smallest AC current is detected is determined as the peak-to-peak voltage of the AC voltage used during image formation. DoAn image forming apparatus.
  (12) The charging bias power supply circuit is at least partly at the time of non-image formation and is one step lower than the peak-to-peak voltage of the AC voltage at the time of image formation, with the voltage between the peaks of the AC voltage at the time of image formation being Vpp-n An alternating current is detected by applying a voltage Vpp− (n + 1), and when the detected alternating current becomes equal to or higher than the reference current, the peak-to-peak voltage of the alternating voltage at the time of image formation is switched to Vpp− (n + 1). The image forming apparatus as described in (11) above.
  (13) The relationship between the minimum peak-to-peak voltage Vpp-min of the AC voltage applied to the charging unit and the DC voltage Vdc applied to the charging unit is Vpp-min / 2 ≧ | Vdc | The image forming apparatus according to any one of (11) and (12), wherein
  (14) The alternating current that flows when the maximum peak-to-peak voltage of the alternating voltage is applied to the charging unit is equal to or greater than the reference current, according to any one of (11) to (13) Image forming apparatus.
[0034]
  (15)The charging means is characterized in that a ratio of a resistance R-low in a low temperature and low humidity environment to a resistance R-high in a high temperature and high humidity environment is 0.1 ≦ R-low / R-high ≦ 10 (11 )To any of (14)The image forming apparatus described in 1.
[0035]
  According to the present invention described above, it is possible to perform good charge control even in a power supply system in which a DC voltage is produced by an AC voltage booster using a bias in which an AC voltage and a DC voltage are superimposed on a charging bias voltage. In addition, it is possible to properly control the charging AC current, to save space and to reduce the cost of the charging power supply circuit.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
<First embodiment>
A feature of the present embodiment is that a charging bias generating circuit having an AC oscillation output capable of outputting an AC and DC superimposed voltage by at least one voltage boosting unit and outputting two or more types of AC peak-to-peak voltages, and charging In an image forming apparatus having an alternating current detecting means for detecting an alternating current Iac flowing through the photoconductor when a bias voltage is applied, the alternating current detecting means is at least two kinds of alternating current when the power is turned on or during non-image formation. An alternating current Iac flowing through the photosensitive drum is detected by applying the peak-to-peak voltage Vpp, and this is fed back to the engine controller to select a voltage level in an area where ideal discharge is performed as a charging bias voltage at the time of printing, It is in the place where it is applied during image formation.
[0039]
(1) Outline of configuration and operation of image forming apparatus
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present exemplary embodiment. The image forming apparatus according to the present exemplary embodiment is an electrophotographic type or process cartridge detachable type laser printer.
[0040]
Reference numeral 10 denotes a rotating drum type electrophotographic photosensitive member (photosensitive drum) as a latent image carrier. The photosensitive drum 10 of this example is a negatively charged organic photosensitive member, and is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed by a driving motor (not shown).
[0041]
The photosensitive drum 10 is uniformly charged to a predetermined negative potential by a charging device during its rotation. In this example, the charging device is a contact charging device using a charging roller 11 as a charging member.
[0042]
Both ends of the charging roller 11 are rotatably held by bearings 11-a, and are pressed toward the center of the photosensitive drum 10 by pressing means such as a pressure spring 11-b, and are driven by the photosensitive drum 10. Rotate. A bias voltage is applied to the charging roller 11 from the charging bias power source 1 through the pressure spring 11-b and the conductive bearing 11-a. As the charging bias voltage, a method is used in which a DC voltage Vdc corresponding to a desired on-drum potential Vd is superimposed on an AC voltage having a peak-to-peak voltage (Vpp) that is twice or more the discharge start voltage. This charging method aims to eliminate local potential unevenness on the photosensitive drum by applying an alternating voltage on the direct current voltage and uniformly charge the photosensitive drum to a potential Vd equal to the direct current applied voltage Vdc. Yes.
[0043]
  Next, image exposure is performed by the exposure device 12. The exposure device 12 forms an electrostatic latent image on the uniformly charged photosensitive drum 10, and in this example, a semiconductor laser scanner is used. The exposure apparatus 12 is an image forming apparatusOutsideA laser beam L modulated in response to an image signal sent from a host device (not shown) is output, and the uniformly charged surface of the photosensitive drum 1 is scanned and exposed through an exposure window portion a of a process cartridge C described later. (Image exposure). On the surface of the photosensitive drum, an electrostatic latent image corresponding to image information is sequentially formed as the absolute value of the potential of the exposed portion becomes lower than the absolute value of the charging potential.
[0044]
Next, the electrostatic latent image is developed by the reversal developing device 13 and visualized as a toner image. The developing device 13 visualizes the electrostatic latent image (reverse development) by developing the electrostatic latent image on the photosensitive drum 10 with the toner 13-a as a developer. In this example, a jumping development method is used. Was used. In this system, a developing bias voltage in which alternating current and direct current are superimposed is applied to a developing sleeve 13-c from a developing bias power source (not shown), whereby the developer layer thickness regulating member 13-b and the developing sleeve 13-c are applied. The toner 13-a that is negatively charged by frictional charging at the contact portion is reversely developed into an electrostatic latent image on the surface of the photosensitive drum.
[0045]
The toner image on the surface of the photosensitive drum is transferred by a transfer device to a recording medium (transfer material) 14 such as paper fed from a paper supply unit (not shown). In this example, a contact transfer device using a transfer roller 15 is used. The transfer roller 15 is pressed against the photosensitive drum 1 in the central direction of the photosensitive drum by an urging means such as a pressing spring (not shown). When the transfer material 14 is conveyed and the transfer process is started, a positive transfer bias voltage is applied to the transfer roller 15 from a transfer bias power source (not shown), and the photosensitive drum 10 is charged negatively. The toner is transferred onto the transfer material 14.
[0046]
  The transfer material that has received the transfer of the toner image is separated from the surface of the photosensitive drum, introduced into the fixing device 16, subjected to a fixing process of the toner image, and discharged outside the image forming apparatus main body. The fixing device 16 uses a means such as heat or pressure for the toner image transferred to the transfer material 14.FixedIt is what you wear.
[0047]
The photosensitive drum surface after separation of the transfer material is cleaned by scraping off the transfer residual toner by the cleaning device 17 and repeatedly used for image formation. The cleaning device 17 of this example uses a cleaning blade. The cleaning blade collects untransferred toner that has not been completely transferred from the photosensitive drum 10 to the transfer material 14 during the transfer process. The cleaning blade comes into contact with the photosensitive drum 10 at a constant pressure to collect the untransferred toner. Clean the surface. After completion of the cleaning process, the photosensitive drum surface again enters the charging process.
[0048]
The image forming apparatus forms an image by repeating the steps of charging, exposure, development, transfer, fixing, and cleaning using the above-described means.
[0049]
A process cartridge C is detachable and replaceable with respect to the image forming apparatus main body 20. The process cartridge C of this example includes four process devices including a photosensitive drum 10 as a latent image carrier, a charging roller 11 as a contact charging member for the photosensitive drum 10, a developing device 13, and a cleaning device 17. As a process cartridge.
[0050]
The process cartridge C is attached to and detached from the image forming apparatus main body 20 by opening and closing a cartridge door (main body door) 18 of the image forming apparatus main body 20. Mounting is performed by opening the cartridge door 18, inserting and mounting the process cartridge C into the image forming apparatus main body 20 in a predetermined manner, and closing the cartridge door 18. The process cartridge C is mechanically and electrically connected to the image forming apparatus main body 20 side by being mounted on the image forming apparatus main body 20 in a predetermined manner.
[0051]
The process cartridge C is removed from the image forming apparatus main body 20 by opening the cartridge door 18 and pulling out the process cartridge C in the image forming apparatus main body 20 to a predetermined extent. When the process cartridge C is removed, a drum cover (not shown) is moved to the closed position to conceal and protect the exposed lower surface of the photosensitive drum 10. The exposure window part a is also held closed by a shutter plate (not shown). When the process cartridge C is mounted in the image forming apparatus main body 20, the drum cover and the shutter plate are respectively moved to the open position and held.
[0052]
Here, the process cartridge is a cartridge in which a charging unit, a developing unit or a cleaning unit and an electrophotographic photosensitive member are integrally formed, and this cartridge can be attached to and detached from the image forming apparatus main body. In addition, at least one of the charging unit, the developing unit, and the cleaning unit and the electrophotographic photosensitive member are integrally formed into a cartridge that can be attached to and detached from the main body of the image forming apparatus. Further, it means that at least the developing means and the electrophotographic photosensitive member are integrated into a cartridge so that it can be attached to and detached from the apparatus main body.
[0053]
(2) Printer operation sequence
The outline of the printer operation sequence in this embodiment will be described with reference to FIG.
[0054]
First, when the power supply in the image forming apparatus is turned on, the pre-multi-rotation process starts. In this process, while the main motor rotates the photosensitive drum, the presence / absence of the process cartridge is detected and the transfer roller is cleaned.
[0055]
When the front multi-rotation is completed, the image forming apparatus enters a standby (standby) state. When image information is sent to the image forming apparatus from an output means such as a host computer (not shown), the main motor drives the image forming body and enters a pre-rotation process. In the pre-rotation process, printing preparation operations of various process devices are performed. Mainly, preliminary charging on the photosensitive drum, startup of the laser scanner, determination of the transfer print bias, temperature adjustment of the fixing device, and the like are performed.
[0056]
When the pre-rotation process is completed, the printing process is started. In the printing process, transfer material is fed, image exposure on a photosensitive drum, development, and the like are performed at a predetermined timing. When the printing process is completed, if there is a next print signal, the process enters the sheet interval process until the next transfer material arrives and waits for the next printing operation.
[0057]
If there is no next print signal after the printing operation is completed, the image forming apparatus enters a post-rotation process. In the post-rotation process, processes such as charge removal on the surface of the photosensitive drum and discharge of toner adhering to the transfer roller to the photosensitive drum (transfer roller cleaning) are performed.
[0058]
When the post-rotation process is completed, the image forming apparatus again enters a standby (standby) state and waits for the next print signal.
[0059]
(3) Charging bias creation method and determination of appropriate charging bias
3-1) Charging bias creation method (charging bias power supply circuit)
The charging bias power supply circuit 21 used in this example will be conceptually described with reference to FIG.
[0060]
In this example, the charging bias power supply circuit 21 has three different AC peak-to-peak voltages Vpp from the AC oscillation output 22: Vpp-1, Vpp-2, Vpp-3 (Vpp-1> Vpp-2> Vpp-3). ) Can be output. The outputs of the AC peak-to-peak voltages Vpp-1 to Vpp-3 from the AC oscillation output 22 are selectively made when the AC output selection means 30 is controlled by the engine controller 28.
[0061]
First, the output voltage output from the AC oscillation output 22 is amplified by the amplifier circuit 23, sine-converted by the sine voltage conversion circuit 24 including an operational amplifier, a resistor, a capacitor, and the like, and then the DC component is zeroed via the capacitor C1. And is inputted to a step-up transformer T1 as voltage step-up means. The voltage input to the step-up transformer T1 is boosted to a sine voltage corresponding to the number of turns of the transformer.
[0062]
On the other hand, the capacitor C2 is peak-charged after the boosted sine voltage is rectified by the rectifier circuit D1. As a result, a certain DC voltage Vdc1 is generated. Further, the DC oscillation output 25 outputs an output voltage determined depending on the print density, etc., rectified by the rectifier circuit 26, and then input to the negative input terminal of the operational amplifier IC1 as a constant voltage Va. At the same time, a voltage Vb obtained by dividing one terminal voltage of the step-up transformer T1 by a resistor and a resistor is input to the plus input terminal of the operational amplifier IC1, and the transistor Q1 is set so that both values (Va and Vb) are equal. To drive. As a result, a current flows through the resistors R1 and R2, causing a voltage drop, and a DC voltage Vdc2 is generated.
[0063]
A desired DC voltage can be obtained by adding the DC voltages Vdc1 and Vdc2 described above. This DC voltage is superimposed on the AC voltage described above on the secondary side of the AC voltage boosting means T1 and applied to the charging roller 11 in the process cartridge C.
[0064]
In this method, since the DC voltage is produced using the AC voltage booster T1, the DC voltage is dependent on the AC peak-to-peak voltage Vpp. That is, in order to obtain the desired DC voltage Vdc, it is necessary to charge the capacitor C2 with a certain level of charge by the AC voltage boosting means T1, and as shown in FIG. 4, in order to obtain the desired DC voltage Vdc ′. In this case, the AC peak-to-peak voltage Vpp must be 2 × | Vdc ′ | In a region where the AC peak-to-peak voltage Vpp is smaller than 2 × | Vdc ′ |, the capacitor C2 cannot be fully charged and the desired DC voltage Vdc ′ cannot be obtained. Therefore, the drum potential Vd is set to a desired value. It becomes impossible to charge and a good image cannot be obtained.
[0065]
On the other hand, if the capacitance of the capacitor C2 is increased, the amount of charge charge can be increased to increase Vdc. However, the time for charging the capacitor C2 becomes longer, and the time required for stabilizing the charging waveform is increased. Since it becomes longer, unevenness may occur in the photosensitive drum surface potential Vd.
[0066]
Therefore, in this example, the minimum value Vpp-min in the range in which the AC peak-to-peak voltage Vpp can be output is set so that the relationship of Vpp-min ≧ 2 × | Vdc | is established with respect to the desired DC voltage Vdc. Yes.
[0067]
3-2) Determination of proper charging bias voltage
Next, a method for determining a charging bias voltage during image formation will be described with reference to FIGS.
[0068]
In FIG. 3, when a charging bias voltage is applied to the charging roller 11, the alternating current Iac flows through the charging roller 11 and the photosensitive drum 10 to the high-voltage power supply circuit GND. At this time, the alternating current detecting means 27 extracts only the alternating current having a frequency equal to the charging frequency by a filter circuit (not shown) composed of a resistor, a capacitor, etc., and converts this alternating current into a voltage. The voltage value is input to the engine controller 28. The AC current detecting means 27 can be composed of a resistor, a capacitor, a diode, and the like, so that the influence of the cost increase of the power supply circuit and the space expansion is small.
[0069]
  The input voltage input to the engine controller 28 is compared with a necessary minimum voltage V0 whose input level is preset by the voltage comparison means 29. The required minimum voltage V0 is an output voltage with respect to the minimum AC peak-to-peak voltage at which charging unevenness does not occur, and the value is the minimum required current value at which uniform charging can be performed.(Reference current)It is determined based on Iac-0. Since the value of Iac-0 varies depending on the process speed and charging frequency of the device, the constituent material of the charging device 11 and the photosensitive drum 10, the necessary minimum voltage V0 is alsoFor each deviceA suitable setting is recommended.
[0070]
The AC output selection means 30 of the engine controller 28 selects the minimum AC output voltage that is equal to or higher than the necessary minimum voltage V0 and selects it as a charging bias at the time of image formation.
[0071]
  Next, the procedure for determining the charging bias from the AC current detection in this example will be described with reference to the flowchart of FIG. In this example, the charging bias power supply circuit having three types of output voltages Vpp-1, Vpp-2, and Vpp-3 (Vpp-1> Vpp-2> Vpp-3) in the AC oscillation output 22 is used.21Showed about.
[0072]
First, the lowest peak-to-peak voltage Vpp-3 is applied, and the alternating current detection means 27 converts the alternating current Iac-3 flowing through the photosensitive member into a detection voltage V3 and feeds it back to the engine controller 28 (step S1). At this time, if V3 ≧ V0, V3 is determined as a charging bias at the time of printing (hereinafter referred to as a print bias) (S2 and S6).
[0073]
When V3 <V0, the intermediate voltage Vpp-2 is applied, the detection voltage V2 is fed back, and compared with V0 (S2, S3, S4). If V2 ≧ V0, V2 is used as a print bias (S4 · S7), and if V2 <V0, Vpp-1 is used as a print bias (S4 · S5).
[0074]
At this time, the output voltage V1 when the maximum value Vpp-1 of the AC peak-to-peak voltage that can be applied is set to satisfy V1 ≧ V0 under any circumstances. As a result, charging failure does not occur under any circumstances.
[0075]
These processes may be performed in a pre-multi-rotation process immediately after the power is turned on, and more preferably at least once at any timing other than the printing process after entering the printing operation (during non-image formation). Good to be told. Further, the order of bias application is not necessarily as shown in FIG. As a result, the alternating current Iac flowing through the photosensitive member can be detected in a nearly sequential state, and better charging bias control is possible.
[0076]
(4) Effect
Then, the effect at the time of using this example is demonstrated below.
[0077]
a) Power circuit cost reduction and space saving effect
As described above, in this configuration, since the superimposed voltage of AC and DC is applied by a single voltage booster for AC output, space saving and cost reduction of the power supply circuit can be realized. . In addition, since the relationship between the minimum value Vpp-min of the AC peak-to-peak voltage that can be output and the desired DC voltage Vdc is set to Vpp-min ≧ | Vdc | × 2, a single voltage boosting means can be used for the DC and AC. Even if the superimposed voltage is output, it is possible to stably obtain a desired charging bias voltage.
[0078]
b) Effects on charge control
b-1) Effects on changes in usage environment
FIG. 6 shows the relationship of the detection voltage by the AC current detection means 27 when the charging Vpp-1 to 3 is applied using the same image forming apparatus in a low temperature and low humidity environment to a high temperature and high humidity environment. is there.
[0079]
Since the impedance of the charging device is large in a low temperature and low humidity environment and small in a high temperature and high humidity environment, the alternating current value Iac changes.
[0080]
The minimum peak-to-peak voltage for detecting the necessary minimum current value Iac-0 (detection voltage V0) or higher is Vpp-1 in low temperature and low humidity, normal temperature and normal humidity, and Vpp-2 in high temperature and high humidity environment. That's fine.
[0081]
As a result, even when the usage environment changes and the impedance of the charging device changes, an excessive alternating current does not flow through the photosensitive member, so that good charging control can be performed.
[0082]
b-2) Effects on fluctuations in the number of sheets used
In FIG. 7, the alternating current value Iac increases as the number of prints on the photosensitive drum 10 increases. This is due to the fact that the photosensitive layer on the surface of the photosensitive drum is scraped and impedance decreases.
[0083]
In the figure, for example, in the case of a low temperature and low humidity environment, the AC current value Iac− is obtained when Vpp-1 is used as a print bias at the initial stage of use and Vpp-2 is applied at the point of the photosensitive drum usage A. Since 2 exceeds the necessary minimum current value Iac-0, Vpp-2 is used as a print bias at the time of image formation after point A. Further, at the point where the photosensitive drum usage amount B is applied, the alternating current value Iac-3 when Vpp-3 is applied exceeds the necessary minimum current value Iac-0, so that Vpp-3 is printed at the time of image formation after point B. Use as a bias.
[0084]
The same control is performed even in a hot and humid environment. As a result, an increase in alternating current can be suppressed over the entire use, and good charging can be performed.
[0085]
b-3) Effect on output tolerance of AC peak-to-peak voltage
FIG. 8 shows the relationship between the number of sheets used and the AC current value Iac when the output value of the AC peak-to-peak voltage fluctuates at the upper and lower tolerances.
[0086]
When the power supply tolerance is at the upper limit, the output AC peak-to-peak voltage value increases as a whole. For this reason, in the drawing, Vpp-2 is used as a print bias in the initial stage of use, and after the point of the photosensitive drum usage D, the print bias is switched to Vpp-3. In the case of the power supply tolerance lower limit, Vpp-1 is set as the print bias in the initial stage of use, and the print bias is switched to Vpp-2 at the point of the photosensitive drum usage E, and to Vpp-3 after the point F. As a result, even when the tolerance of the charging bias power source is taken into consideration, it is possible to control while suppressing an increase in alternating current.
[0087]
As described above, the method of controlling the effect of the present embodiment using three types of AC peak-to-peak voltages has been described as an example, but other than this, as long as two or more types of AC peak-to-peak voltages can be output. The same applies to the scope of the present invention.
[0088]
As described above, according to the present invention, even in a system in which an AC and DC superimposed bias is applied by a single voltage booster, a plurality of pre-rotations or at any timing during non-image formation The AC current detecting means detects the current value flowing through the photoconductor and uses the optimum voltage level as a print bias, so that the AC current Iac flowing through the photoconductor is controlled to a value that is almost constant. Is done.
[0089]
As a result, it is possible to perform charging control that corrects the impedance change such as the usage environment, the film thickness of the photosensitive drum, and the tolerance of the charging bias power source. Therefore, the power supply circuit and the process cartridge, which are the objects of the present invention, can be realized at the same time as the cost reduction, the space saving, and the discharge control.
[0090]
<Second embodiment>
When the AC peak-to-peak voltage Vpp is controlled at a constant voltage, the current Iac flowing through the photosensitive member increases as the surface of the photosensitive drum is scraped with use, and the accompanying AC voltage is, for example, shown in FIG. Thus, Vpp-1 is applied from the initial use to point A, but from A, the bias is switched to Vpp-2 smaller than Vpp-1, so that the used print bias Vpp-n is at a certain stage. Always comes to a voltage value Vpp− (n + 1) that is one step lower.
[0091]
In this embodiment, the procedure from the detection of the current flowing through the photoconductor to the determination of the print bias at the time of image formation is simplified using this property. That is, in this embodiment, when the power is turned on, the alternating current detection shown in the first embodiment is performed to determine the print bias Vpp-n during image formation, and during printing, during non-image formation. A voltage Vpp- (n + 1) whose peak-to-peak voltage is one step lower than the print bias Vpp-n is applied to all or a part of the voltage Vn + 1 detected at this time exceeds the necessary minimum voltage value V0. In this case, the next print bias is lowered by one step.
[0092]
The procedure for determining the charging bias in this embodiment will be described with reference to the flowchart of FIG. First, when the process cartridge is mounted, the print bias Vpp-n at the time of image formation is determined by the same method as in the first embodiment.
[0093]
During printing, the voltage Vpp- (n + 1) that is one step lower is applied in all or part of the non-image formation. FIG. 9 shows a case where Vpp− (n + 1) is applied in the post-rotation process as an example. If the detected voltage Vn + 1 does not exceed the necessary minimum voltage V0 at this time, Vpp-n is continuously used for the print bias at the time of the next image formation. If Vn + 1 exceeds the necessary minimum voltage V0, the next Vpp− (n + 1) is used as a print bias at the time of image formation. Although FIG. 9 shows an example in which Vpp− (n + 1) is applied in the post-rotation process, this may be applied anywhere during non-image formation, for example, it is applied in the pre-rotation process. There is no problem.
[0094]
When this method is used, only one type of bias voltage (Vpp− (n + 1)) is applied in the current detection sequence at the time of printing, so that the time required from the AC current detection to the bias determination can be shortened. An image forming apparatus having a short time during non-image formation can also be handled.
[0095]
Furthermore, since a bias lower than the print bias is applied in part or all during non-image formation, the amount of discharge can be further reduced, and the effect of reducing wear abrasion of the photoconductor is also added.
[0096]
<Third embodiment>
As shown in FIG. 6, the alternating current value Iac that flows through the photosensitive member when the same charge Vpp is applied varies depending on the environment in which it is used even in the initial state of use. The main reason for this is considered that the resistance of the charging device is affected by humidity in particular, and is large in a low temperature and low humidity environment and small in a high temperature and high humidity environment.
[0097]
The feature of this embodiment is that the charging device used has a resistance value R-low in a low temperature and low humidity environment (temperature 10 ° C., relative humidity 10%) and a resistance value in a high temperature and high humidity environment (temperature 35 ° C., relative humidity 85%). The ratio with R-high has a relationship of 0.1 ≦ R-low / R-high ≦ 10. The “resistance” measurement method discussed here is as described in the next item (1).
[0098]
(1) Resistance measurement method
The resistance defined in this example refers to that measured by the following method. FIG. 10 is a conceptual diagram showing a resistance measurement method. The charging device is brought into pressure contact with a metal drum having a diameter of 30 mm at both ends of 500 gf. The metal drum is rotated at a speed of 30 rpm by a metal drum driving means (not shown). A voltage of 100 V is applied to the core of the charging device while the metal drum is rotating, and the value of the voltage E (V) applied to the fixed resistance r (Ω; fixed resistance of r = 1 to 100 kΩ) is read 10 seconds after the application. . The resistance R of the charging device is calculated by the following calculation formula.
[0099]
R (Ω) = 100 / (E / r)
The resistance of the charging device in a low-temperature and low-humidity environment means a value measured after leaving the charging device in an environment with an air temperature of 10 ° C. and a relative humidity of 10% for 8 hours. It means that measured after leaving the device in an environment of 35 ° C. temperature and 85% relative humidity for 8 hours.
[0100]
(2) Effects of this embodiment
FIG. 11A shows an AC current that flows through a photosensitive member in the initial stage of use using an image forming apparatus including a charging bias power source having five levels of switching voltage, and using a charging device having a large environmental variation in resistance of the charging device. (B) shows the current value transition in the case where durability is performed using this image forming apparatus.
[0101]
In (a), the charge Vpp in the low temperature and low humidity environment is larger than the necessary minimum current value, and Vpp-1 which is the smallest value is selected, and in the high temperature and high humidity environment, Vpp-4 is selected. Is done.
[0102]
When these are endured, as shown in (b), first, in a low-temperature and low-humidity environment, the charge Vpp is switched from Vpp-1 to Vpp-2 at the point of the endurance number L1, and hereinafter, L2, L3, L4 At this point, the charge Vpp is switched, and finally the photoconductor life LE is reached.
[0103]
In contrast, in a high-temperature and high-humidity environment, the charge Vpp is switched from Vpp-4 to Vpp-5 at the point H1, but since there is no charge Vpp smaller than Vpp-5, the lifetime of the photoreceptor HE is reached at an early stage. As a result, the photoconductor lifetime X that can be guaranteed to the user is shortened. In order to extend the life of the photoreceptor in a high-temperature and high-humidity environment, means such as adding an applied voltage (Vpp-6, Vpp-7...) Smaller than charging Vpp-5 to the charging bias power supply circuit. Although it is conceivable, it is desirable not to make such a change from the viewpoint of the cost and space of the power supply circuit.
[0104]
FIG. 12A shows an image forming apparatus including a charging bias power source having five levels of switching voltage, and a photosensitive device in an initial stage of use flows through a charging device in which the environmental fluctuation of the resistance of the charging device is relatively small. FIG. 6 schematically shows the environmental fluctuation of the alternating current, and FIG. 5B shows the transition of the current value when durability is performed using this image forming apparatus.
[0105]
In (a), the charge Vpp in the low temperature and low humidity environment is larger than the necessary minimum current value, and the smallest value Vpp-1 is selected. In the high temperature and high humidity environment, Vpp-2 is selected. Is done.
[0106]
When these are endured, as shown in (b), first, in a low-temperature and low-humidity environment, the charge Vpp is switched from Vpp-1 to Vpp-2 at the point of the endurance number L1 ′, and hereinafter, L2 ′, L3 The charging Vpp is switched at the point of “, L4”, and finally the photoconductor lifetime LE ′ is reached.
[0107]
On the other hand, in a high-temperature and high-humidity environment, the charged Vpp is switched from Vpp-2 to Vpp-3 at the point H1 ′, and thereafter, the charged Vpp is switched at the points H2 ′ and H3 ′ to reach the photoconductor life HE ′. When the environmental fluctuation of the charging device is small, the transition of the durable current value in the high temperature and high humidity environment can be made closer to the constant current control. Therefore, the life of the photoconductor in a high-temperature and high-humidity environment can be extended, so that the photoconductor life X that can be guaranteed to the user can be further extended.
[0108]
As discussed above, the smaller the environmental fluctuation of the resistance of the charging device, the better. However, according to the study by the authors, it was left in a low temperature and low humidity environment (temperature 10 ° C., relative humidity 10%) for 8 hours or more. The ratio R-low / R-high between the resistance R-low of the charging device and the resistance R-high of the charging device left in a high temperature and high humidity environment (temperature 35 ° C., relative humidity 85%) for 8 hours or more is 0. If 1 ≦ R-low / R-high ≦ 10, it is possible to control charging at a level where there is no problem in actual use. More preferably, if 0.5 ≦ R-low / R-high ≦ 2, It has been found that very good charge control can be performed.
[0109]
<Others>
1) The form of the contact charging member 11 is not limited to the roller body, and may be an endless belt body or the like. In addition to the charging roller, the contact charging member may be of a shape or material such as a fur brush, felt, or cloth. Moreover, these can be laminated | stacked and it can also obtain more suitable elasticity (flexibility) and electroconductivity. A charging blade or a magnetic brush charging member can also be used.
[0110]
2) The exposure means for forming the electrostatic latent image is not limited to the laser scanning exposure means 12 that forms a digital latent image as in the embodiment, but a normal analog image exposure or Other light emitting elements such as LEDs may be used, and any combination of a light emitting element such as a fluorescent lamp and a liquid crystal shutter may be used as long as it can form an electrostatic latent image corresponding to image information.
[0111]
3) The latent image carrier 10 may be an electrostatic recording dielectric or the like. In this case, the dielectric surface is uniformly primary-charged to a predetermined polarity and potential, and then selectively neutralized by a neutralizing means such as a static elimination needle head or an electron gun to write and form a target electrostatic latent image.
[0112]
4) Although the developing device 13 is a reversal developing device in the embodiment, the configuration of the developing device is not particularly limited. A regular developing device may be used.
[0113]
In general, the electrostatic latent image is developed by coating a non-magnetic toner on a developer carrying member such as a sleeve with a blade or the like, and magnetic toner on a developer carrying member. A method in which an electrostatic latent image is developed in a non-contact state with respect to an image carrier by coating and conveying by force (one-component non-contact development), and coating on a developer carrying member as described above A method for developing an electrostatic latent image by applying toner in contact with an image carrier (one-component contact development), and a developer obtained by mixing a magnetic carrier with toner particles (two-component developer) And a method of developing the electrostatic latent image by conveying it by magnetic force and applying it in contact with the image carrier (two-component contact development), and applying the above two-component developer to the image carrier. Apply electrostatic latent image in contact It is roughly divided into four types of methods (2-component non-contact development) to the image.
[0114]
5) The transfer means 15 is not limited to roller transfer, but may be belt transfer, corona transfer, or the like. The image forming apparatus may form not only a single color image but also a multicolor or full color image by multiple transfer or the like using an intermediate transfer member (intermediate transfer member) such as a transfer drum or a transfer belt.
[0115]
6) As a waveform of an alternating voltage component (AC component, voltage whose voltage value changes periodically) applied to the charging member 11 and the developer carrying member 13-c, a sine wave, a rectangular wave, a triangular wave, or the like is used as appropriate. Is possible. It may be a rectangular wave formed by periodically turning on / off a DC power supply.
[0116]
【The invention's effect】
As described above, according to the present invention, it is possible to perform good charge control even in a power supply system in which a DC bias is produced by an AC voltage booster using an AC and DC superimposed bias as a charging bias voltage. In addition, it was possible to properly control the charging AC current, save space and reduce the cost of the charging power supply circuit.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an image forming apparatus according to a first embodiment.
FIG. 2 is a schematic diagram of an image forming apparatus operation sequence.
FIG. 3 is a conceptual diagram illustrating a charging bias power supply circuit.
FIG. 4 is a diagram showing the relationship between AC peak-to-peak voltage and outputable DC voltage.
FIG. 5 is a flowchart showing a charging bias determination method.
FIG. 6 is a diagram for explaining the effect of the first embodiment (part 1);
FIG. 7 is a diagram for explaining the effect of the first embodiment (part 2);
FIG. 8 is a diagram for explaining the effect of the first embodiment (part 3);
FIG. 9 is a flowchart showing a charging bias determination method according to the second embodiment.
FIG. 10 is a diagram showing a resistance measuring method referred to in the third embodiment.
FIG. 11 is a diagram for explaining a case where the method of the present invention is applied to a charging device having a large resistance fluctuation in the environment.
FIG. 12 is a diagram for explaining a case where the charging device of the third embodiment is applied.
FIG. 13 is a diagram illustrating a configuration of a conventional image forming apparatus example.
FIG. 14 is a diagram conceptually illustrating a conventional charging bias power supply circuit.
[Explanation of symbols]
10. Photosensitive drum
11. Charging means
11-a ... Bearing
11-b ... Pressure spring
12 .... Exposure means
13. Development device
13-a Toner
13-b .. Developer layer thickness regulating member
13-c ... Developing sleeve
14. Transfer material
15. Transfer means
16 .. Fixing means
17. Cleaning means
18. Cartridge door

Claims (15)

At least a movable latent image carrier, charging means for charging the latent image carrier in contact with the latent image carrier, and AC voltage and DC voltage are superimposed on the charging means by one voltage boosting means . a charging bias voltage control method for an image forming apparatus having a charging bias power supply circuit for outputting a charging bias voltage,
The charging bias power supply circuit is part of the non-image-forming, applying an alternating voltage comprising at least two kinds of peak voltage to said charging means, when the AC voltage is applied to the charging unit the detected flow Ru ac current to the image bearing member,
Among the detected AC currents, the peak-to-peak voltage of the AC voltage that is equal to or higher than a preset reference current and has the smallest AC current detected is used as the peak-to-peak voltage of the AC voltage used during image formation. A charging bias voltage control method characterized by determining . The charging bias power supply circuit has a voltage Vpp− that is one step lower than the peak-to-peak voltage of the AC voltage at the time of image formation at least partly at the time of non- image formation , where the peak -to- peak voltage of the AC voltage at the time of image formation is Vpp−n. An alternating current is detected by applying (n + 1), and the peak-to-peak voltage of the alternating voltage during image formation is switched to Vpp− (n + 1) when the detected alternating current is equal to or greater than the reference current. The charging bias voltage control method according to claim 1. And the minimum of the peak-to-peak voltage Vpp-min of the AC voltage applied to the charging unit, the relationship between the DC voltage Vdc applied to the charging unit, Vpp-min / 2 ≧ | Vdc | is that The charging bias voltage control method according to claim 1 or 2. It said maximum flow Ru ac current when the peak-to-peak voltage applied to the charging means of the AC voltage, the charging bias voltage according to any one of claims 1 to 3, characterized in that said at reference current or Control method. The charging means is characterized in that a ratio of a resistance R-low in a low temperature and low humidity environment to a resistance R-high in a high temperature and high humidity environment is 0.1≤R-low / R-high≤10. 5. The charging bias voltage control method according to any one of 1 to 4. At least a movable image bearing member, an image forming apparatus having a charging unit that charges the latent image bearing member in contact with the latent image bearing member, the alternating voltage at one voltage step-up means to the charging means And a charging bias power supply circuit that outputs a charging bias voltage in which a DC voltage is superimposed ,
The charging bias power supply circuit is part of the non-image-forming, an AC voltage having a peak-to-peak voltage of at least two types is applied to the charging unit, when the AC voltage is applied to said charging means, detecting an alternating current flowing in the latent image carrier,
Among the detected AC currents, the peak-to-peak voltage of the AC voltage that is equal to or higher than a preset reference current and has the smallest AC current detected is used as the peak-to-peak voltage of the AC voltage used during image formation. A charging bias power supply circuit characterized by determining . The charging bias power supply circuit has a voltage Vpp− that is one step lower than the peak-to-peak voltage of the AC voltage at the time of image formation at least partly at the time of non- image formation , where the peak -to- peak voltage of the AC voltage at the time of image formation is Vpp−n. An alternating current is detected by applying (n + 1), and the peak-to-peak voltage of the alternating voltage during image formation is switched to Vpp− (n + 1) when the detected alternating current is equal to or greater than the reference current. The charging bias power supply circuit according to claim 6. And the minimum of the peak-to-peak voltage Vpp-min of the AC voltage applied to the charging unit, the relationship between the DC voltage Vdc applied to the charging unit, Vpp-min / 2 ≧ | Vdc | is that The charging bias power supply circuit according to claim 6 or 7, wherein: Maximum flow Ru ac current when the peak-to-peak voltage applied to the charging means of the AC voltage, the charging bias power supply according to any of claims 6 8, characterized in that the reference current or circuit. The charging means is characterized in that a ratio of a resistance R-low in a low temperature and low humidity environment to a resistance R-high in a high temperature and high humidity environment is 0.1≤R-low / R-high≤10. The charging bias power supply circuit according to any one of 6 to 9. At least a movable latent image carrier, charging means for charging the latent image carrier in contact with the latent image carrier, and AC voltage and DC voltage are superimposed on the charging means by one voltage boosting means. In an image forming apparatus comprising: a charging bias power supply circuit that outputs a charging bias voltage;
The charging bias power supply circuit applies an AC voltage having at least two types of peak-to-peak voltages to the charging unit in a part during non-image formation, and when the AC voltage is applied to the charging unit, Detects alternating current flowing in the latent image carrier,
Among the detected AC currents, the peak-to-peak voltage of the AC voltage that is equal to or higher than a preset reference current and the smallest AC current is detected is determined as the peak-to-peak voltage of the AC voltage used during image formation. An image forming apparatus. The charging bias power supply circuit has a voltage Vpp− that is one step lower than the peak-to-peak voltage of the AC voltage at the time of image formation at least partly at the time of non-image formation, where the peak-to-peak voltage of the AC voltage at the time of image formation is Vpp−n. An alternating current is detected by applying (n + 1), and the peak-to-peak voltage of the alternating voltage during image formation is switched to Vpp− (n + 1) when the detected alternating current is equal to or greater than the reference current. The image forming apparatus according to claim 11.   The relationship between the minimum peak-to-peak voltage Vpp-min of the AC voltage applied to the charging unit and the DC voltage Vdc applied to the charging unit is Vpp-min / 2 ≧ | Vdc | The image forming apparatus according to claim 11, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 11, wherein an alternating current that flows when a maximum peak-to-peak voltage of the alternating voltage is applied to the charging unit is equal to or greater than the reference current.   The charging means is characterized in that a ratio of a resistance R-low in a low temperature and low humidity environment to a resistance R-high in a high temperature and high humidity environment is 0.1≤R-low / R-high≤10. The image forming apparatus according to any one of 11 to 14.