JP3903019B2 - 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 in an image forming apparatus such as a printer or a copying machine.
[0002]
[Prior art]
At present, image forming apparatuses employing an electrophotographic system typified by a laser beam printer and a copying machine are widely used.
[0003]
FIG. 14 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 10 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 10 is subjected to a uniform charging process with a predetermined polarity and potential by the charging device 11 during its rotation, and then subjected to image exposure by the exposure device 12. 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 13 and visualized as a toner image. The toner image on the photosensitive drum surface is transferred by a transfer device 15 to a recording medium 14 such as paper fed from a paper supply unit (not shown). The recording medium to which the toner image has been transferred is separated from the surface of the photosensitive drum, introduced into the fixing device 16, 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 17 and repeatedly used for image formation.
[0004]
The image forming apparatus forms an image by repeating the steps of charging, exposing, developing, transferring, fixing, and cleaning using the above-described means.
[0005]
As the charging device 11, a contact charging method is widely employed 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.
[0006]
  A charging bias voltage is applied to a charging roller 11 as a contact charging member from a charging bias applying unit (not shown). The charging bias voltage may be only a DC voltage, but when a DC voltage is applied to a DC voltage Vdc corresponding to the desired dark potential Vd on the photosensitive drum as shown in Patent Document 1.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.
[0007]
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.
[0008]
  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.
[0009]
The relationship between the AC peak-to-peak voltage Vpp and the discharge amount 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.
[0010]
In order to avoid this problem, Patent Document 2 proposes a method of controlling an AC component with a constant current. 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.
[0011]
Further, Patent Document 3 discloses that the AC current Iac flowing in the photosensitive member when the AC peak-to-peak voltage Vpp in the discharge area and the non-discharge area is applied to the charging device during non-image formation is detected and the discharge is performed based on the relationship between the two. There has also been proposed a method in which the amount of current is calculated and an AC voltage that provides an appropriate amount of discharge 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.
[0012]
These methods have a great effect in extending the life of the drum and ensuring good chargeability.
[0013]
In addition, in Patent Document 4, a process cartridge usage amount detection / storage means is mounted on a process cartridge, and two or more types of constant voltage outputs are provided for the AC peak-to-peak voltage according to the process cartridge usage amount. A method for predicting the film thickness of the photosensitive drum and gradually reducing the AC peak-to-peak voltage has been proposed.
[0014]
When the AC component is controlled at a constant voltage, the charging bias power supply can output a superimposed bias of AC and DC with a single step-up transformer (voltage boosting means), greatly simplifying the power circuit configuration compared to constant current control This is advantageous from the viewpoint of cost and space saving of the power supply circuit.
[Patent Document 1]
JP-A 63-149669
[Patent Document 2]
Japanese Patent Publication No. 06-093150
[Patent Document 3]
JP 2001-201920 A
[Patent Document 4]
JP 09-190143 A
[0015]
[Problems to be solved by the invention]
When adopting a process cartridge system that includes at least a photosensitive drum and contact charging means and is detachable from the image forming apparatus, it is not uncommon to replace the image forming apparatus main body to be used. At this time, it is necessary to prevent charging failure from occurring in any combination of the process cartridge and the main body and not to apply a large bias.
[0016]
In response to this requirement, an AC component constant current control method as in Patent Document 2 or a discharge amount calculation method as in Patent Document 3 may be employed.
[0017]
However, in these methods, as shown in FIG. 15 (a), when one voltage booster T-AC outputs an AC and DC superimposed voltage, the AC peak-to-peak voltage decreases, resulting in high temperature and humidity and durability. 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.
[0018]
Here, the circuit of FIG. 15A will be explained a little. When the AC component is controlled at a constant voltage, the DC voltage is supplied from the AC output boost transformer T-AC (voltage booster) via the diode D to the DC voltage. Since it can be created by connecting the capacitor C for voltage creation and peaking the capacitor C, it is possible to output a superimposed bias of AC and DC with only one voltage booster T-AC. It is.
[0019]
When the above method is used, there is a limit in outputting the superimposed voltage of AC and DC with one voltage booster T-AC, and in order to obtain a stable charging bias voltage, the DC power source T-DC It is necessary to divide the AC power supply T-AC and mount two voltage boosting means for DC and AC as shown in FIG.
[0020]
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. Although it is desirable to output a stable charging bias voltage, there is a problem that it is easily affected by variations in the bias of the main body, impedance of the charging member, film thickness of the photosensitive drum, and the like.
[0021]
In the method described in Patent Document 4, since the charging bias generation circuit can be configured by one voltage boosting unit, 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.
[0022]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an appropriate charging bias that does not cause a charging failure and does not cause an excessively large discharge amount in any combination of a process cartridge and an image forming apparatus main body while suppressing cost increase and space expansion. Is to provide a charging bias voltage control method, a charging bias power supply circuit, and an image forming apparatus.
[0023]
[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.
[0024]
  (1) At leastMovePossible latent image carrier and contact with the latent image carrierCharge the latent image carrierCharging means;TheAC with one voltage booster for charging meansVoltageAnd DCVoltageSuperpositionChargedOutput bias voltageDoCharging bias power circuitA charging bias voltage control method for an image forming apparatus having:
  TheThe charging bias power supply circuitPart of non-image formation, at least2 typesLikePeak-to-peak voltageWhen an AC voltage comprising: is applied to the charging means, and the AC voltage is applied to the charging means,Flow to the latent image carrierExchangeCurrentdetectionAnd
  Of the detected AC current, a preset reference currentThat's all and the bestThe peak-to-peak voltage of the AC voltage in which a small AC current is detected,During image formationUsed between the peak of AC voltageDetermine the voltage,
Select the AC peak-to-peak voltage that is equal to or greater than the preset reference current and at which the smallest AC current is detected as the charging bias voltage used during image formation,
  The at least two types of AC peak-to-peak voltages applied in part during the non-image formation are:A charging bias voltage control method, wherein each is applied for a period of time during which the latent image carrier rotates once.
[0025]
  (2) During non-image formationofA part of the charging bias voltage control method according to (1), wherein the part is a part at the time of initial rotation when the image forming apparatus is turned on.
[0026]
  (3) At leastMovePossible latent image carrier and contact with the latent image carrierCharge the latent image carrierCharging means;TheAC with one voltage booster for charging meansVoltageAnd DCVoltageSuperpositionChargedOutput bias voltageDoCharging bias power circuitA charging bias voltage control method for an image forming apparatus having:
  TheThe charging bias power supply circuitPart of non-image formation, at least2 typesLikeThe peak-to-peak voltageAn AC voltage provided is applied to the charging unit, and when the AC voltage is applied to the charging unit, an AC current flowing through the latent image carrier is detected,
  Pre-set standard among detected AC currentsOver current andThe peak-to-peak voltage of the AC voltage at which the smallest AC current is detected,During image formationIs a voltage control method that determines the peak-to-peak voltage of the AC voltage used in
  Multiple AC appliedVoltageWhen the peak-to-peak voltage Vpp is Vpp-1, Vpp-2, ..., Vpp-n (Vpp-1> Vpp-2> ...> Vpp-n> ...), respectively.In addition,During image formationBetween AC voltage peaksWhen the voltage is Vpp-n, it is at least a part during non-image formation and one step lower than the charging bias voltage during image formationBetween AC voltage peaksA voltage Vpp− (n + 1) is applied to detect an alternating current, and the detected current isCurrent is the reference currentIf this is the case,AC peak-to-peak voltageIs switched to Vpp− (n + 1) and is one step lower than the image formation applied in a part of the non-image formation.Peak voltage of the AC voltageVpp− (n + 1) is applied for at least the time required for the latent image carrier to make one rotation.
[0028]
  (4) One step lower than the image formation applied in part during non-image formationBetween AC voltage peaksThe charging bias voltage control method according to (3), wherein the voltage Vpp− (n + 1) is applied in a part of a pre-rotation process immediately before image formation.
[0029]
  (5)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. An image forming apparatus having a charging bias power supply circuit for outputting 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. And
  Select the AC peak-to-peak voltage that is equal to or greater than the preset reference current and at which the smallest AC current is detected as the charging bias voltage used during image formation,
  The at least two types of AC peak-to-peak voltages applied in part during the non-image formation are each applied for a time during which the latent image carrier rotates once.Image forming apparatus.
  (6) The image forming apparatus according to (5), wherein the part during the non-image formation is a part during initial rotation when the image forming apparatus is turned on.
  (7) 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 by one voltage booster for the charging means. An image forming apparatus having a charging bias power supply circuit that outputs a charging bias voltage superimposed with
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. Voltage control method to
  Vpp-1, Vpp-2,..., Vpp-n (Vpp-1>Vpp-2>...>Vpp-n>...) When the peak-to-peak voltage of the AC voltage at the time of image formation is Vpp-n, the peak-to-peak voltage of the AC voltage is one step lower than the charging bias voltage at the time of image formation at least partly during non-image formation. An alternating current is detected by applying Vpp− (n + 1), and when the detected current becomes equal to or higher than the reference current, the peak-to-peak voltage of the alternating voltage is switched to Vpp− (n + 1), and The AC voltage peak-to-peak voltage Vpp− (n + 1), which is one step lower than the image formation applied in a part of the non-image formation, is applied for a period of one rotation of the latent image carrier. An image forming apparatus.
  (8) The peak-to-peak voltage Vpp− (n + 1) of the AC voltage that is one step lower than that during image formation applied in part during non-image formation is applied during part of the pre-rotation process immediately before image formation. The image forming apparatus as described in (7) above.
[0030]
  (9) Applied to the charging meansminimumOf AC voltagePeak-to-peak voltage Vpp-minAnd applied to the charging meansThe relationship between the DC voltage Vdc and Vpp−min / 2 ≧ | Vdc |(1) A charging bias power supply circuit using the charging bias voltage control method according to any one of 4).
[0031]
  (10) AC voltagemaximumofThe peak-to-peak voltage Vpp-maxFor the charging meansAC current value Iac-max detected when applied,Pre-set criteriaThe charging bias power supply circuit using the charging bias voltage control method according to any one of (1) to (4), wherein the relationship with the current Iac-0 is Iac-max ≧ Iac-0.
[0032]
  (11)Said(9) or (10)An image forming apparatus comprising the charging bias power supply circuit described in 1.
[0033]
<Operation>
When a plurality of constant voltage charging biases are switched and applied to the latent image carrier and the contact charging means, the charging bias AC voltage of the image forming apparatus main body and the latent image carrier are detected by detecting the charging AC current flowing through both. Even if the film thickness and the impedance of the charging means vary, an appropriate charging bias AC voltage can be determined, so that charging failure does not occur and damage to the latent image carrier can be reduced.
[0034]
In addition, since a plurality of charging AC peak-to-peak voltages applied stepwise are applied for a time that the latent image carrier rotates once, it is possible to perform charging AC current detection and charging bias voltage switching more accurately. is there.
[0035]
Furthermore, since only one voltage boosting unit is required in the power supply circuit of the image forming apparatus, the power supply circuit can be significantly increased in cost and space.
[0036]
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 An AC current detecting means for detecting an AC current Iac flowing in the latent image carrier when a bias voltage is applied, and the charging bias power supply circuit has an AC oscillation output capable of outputting two or more types of AC peak-to-peak voltages in stages. In an image forming apparatus that uses a bias voltage that is equal to or higher than an AC peak voltage selection control threshold current and that detects a minimum current value as a charging bias voltage,
During the initial rotation when the power is turned on, a plurality of AC peak-to-peak voltages are applied in a stepwise manner from the higher side, and the application time is that the latent image carrier is rotated once or more for each peak-to-peak voltage.
The alternating current detected by the charging alternating current detection means is subjected to an average value processing in the engine controller and then compared with a charging alternating peak-to-peak voltage selection control threshold,
It is characterized by.
[0037]
(1) Outline of configuration and operation of image forming apparatus
FIG. 5 is a schematic configuration diagram of the image forming apparatus of this embodiment. The image forming apparatus according to the present exemplary embodiment is an electrophotographic type or process cartridge detachable type laser printer.
[0038]
Reference numeral 2 denotes a rotating drum type electrophotographic photosensitive member (photosensitive drum) as a latent image carrier. The photosensitive drum 2 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).
[0039]
The photosensitive drum 2 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 3 as a charging member.
[0040]
The charging roller 3 is rotatably supported at both ends by a bearing 3-a, and is pressed toward the center of the photosensitive drum 2 by pressing means such as a pressure spring 3-b, and is driven by the photosensitive drum 2. Rotate. A bias voltage is applied to the charging roller 3 from the charging bias power source 1 through the pressure spring 3-b and the conductive bearing 3-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.
[0041]
  Next, image exposure by the exposure device 4 is performed. The exposure device 4 forms an electrostatic latent image on the uniformly charged photosensitive drum 2. In this example, a semiconductor laser scanner is used. The exposure apparatus 4 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 2 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.
[0042]
Next, the electrostatic latent image is developed by the reversal developing device 5 to be visualized as a toner image. The developing device 5 visualizes the electrostatic latent image (reverse development) by developing the electrostatic latent image on the photosensitive drum 2 with the toner 5-a that is a developer. Was used. In this method, a developing bias voltage in which alternating current and direct current are superimposed is applied to a developing sleeve 5-c from a developing bias power source (not shown), whereby the developer layer thickness regulating member 5-b and the developing sleeve 5-c are connected. The toner 5-a charged to the negative polarity by frictional charging at the contact portion is reversely developed into an electrostatic latent image on the surface of the photosensitive drum.
[0043]
The toner image on the photosensitive drum surface is transferred by the transfer device 6 to a recording medium (transfer material) 7 such as paper fed from a paper supply unit (not shown). In this example, a contact transfer device using a transfer roller 6 is used. The transfer roller 6 is pressed against the photosensitive drum 2 in the central direction of the photosensitive drum by a biasing means such as a pressing spring (not shown). When the transfer material 7 is conveyed and the transfer process is started, a positive transfer bias voltage is applied to the transfer roller 6 from a transfer bias power source (not shown), and the negatively charged photosensitive drum 2 is charged. The toner is transferred onto the transfer material 7.
[0044]
  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 8, undergoes a toner image fixing process, and is discharged out of the image forming apparatus main body. The fixing device 8 uses means such as heat and pressure for the toner image transferred to the transfer material 7.FixedIt is what you wear.
[0045]
The photosensitive drum surface after separation of the transfer material is cleaned by scraping off the transfer residual toner by the cleaning device 9 and repeatedly used for image formation. The cleaning device 9 of this example uses a cleaning blade. The cleaning blade collects transfer residual toner that has not been completely transferred from the photosensitive drum 2 to the transfer material 7 during the transfer process, and contacts the photosensitive drum 2 with a constant pressure to collect the transfer residual toner. Clean the surface. After completion of the cleaning process, the photosensitive drum surface again enters the charging process.
[0046]
The image forming apparatus forms an image by repeating the steps of charging, exposure, development, transfer, fixing, and cleaning using the above-described means.
[0047]
The process cartridge C of this example includes four process devices including a photosensitive drum 2 as a latent image carrier, a charging roller 3 as a contact charging member for the photosensitive drum 2, a developing device 5, and a cleaning device 9. As a process cartridge.
[0048]
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) 21 of the image forming apparatus main body 20. The cartridge door 21 is opened, the process cartridge C is inserted and mounted in the image forming apparatus main body 20 in a predetermined manner, and the cartridge door 21 is closed. 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.
[0049]
The process cartridge C is removed from the image forming apparatus main body 20 by opening the cartridge door 21 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.
[0050]
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.
[0051]
(2) Printer operation sequence
The outline of the printer operation sequence in this embodiment will be described with reference to FIG.
[0052]
First, when the detachable process cartridge C is mounted on the image forming apparatus main body 20 and the power supply in the image forming apparatus is turned on with the cartridge door 21 closed, 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. This embodiment is characterized in that a sequence for determining a charging bias is included in this process. Details thereof will be described later.
[0053]
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.
[0054]
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.
[0055]
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.
[0056]
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.
[0057]
When the post-rotation process is completed, the image forming apparatus again enters a standby (standby) state and waits for the next print signal.
[0058]
(3) Charging bias creation method and determination of appropriate charging bias
3-1) Charging bias power supply circuit
The charging bias power supply circuit 1 used in this example will be conceptually described with reference to FIG.
[0059]
In this example, the charging bias power supply circuit 1 can output Vpp-1, Vpp-2, Vpp-3, and Vpp-4, which are four different types of AC peak-to-peak voltages Vpp, from the AC oscillation output (Vpp-1> Vpp). -2> Vpp-3> Vpp-4). The outputs of AC peak-to-peak voltages Vpp-1 to Vpp-4 from the AC oscillation output are selectively made by being controlled by the engine controller.
[0060]
First, the output voltage output from the AC oscillation output is amplified by an amplifier circuit, sine-converted by a sine voltage conversion circuit comprising an operational amplifier, a resistor, a capacitor, etc., and then the DC component is cut to zero via the capacitor C1. Are input 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.
[0061]
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, an output voltage determined by the print density is output from the DC oscillation output, rectified by a rectifier circuit, 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 the resistors R1 and R2 is input to the plus input terminal of the operational amplifier IC1, and the transistors (Va and Vb) have the same value. Drive Q1. As a result, a current flows through the resistors R1 and R2, causing a voltage drop, and a DC voltage Vdc2 is generated.
[0062]
A desired DC voltage can be obtained by adding the DC voltages Vdc1 and Vdc2 described above. This DC voltage is superimposed on the above-described AC voltage on the secondary side of the AC voltage booster T1 and applied to the charging roller 3 in the process cartridge C.
[0063]
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. 8, 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, so that the drum potential Vd is charged to a desired value. Cannot be obtained, and a good image cannot be obtained.
[0064]
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.
[0065]
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.
[0066]
3-2) Method for determining appropriate charging bias voltage
The procedure for determining the charging bias from the AC current detection in this example will be described. In FIG. 7, when a charging bias voltage is applied to the charging roller 3, the alternating current Iac flows through the charging roller 3 and the photosensitive drum 2 to the high voltage power supply circuit GND. At this time, the alternating current detecting means 28 samples only the alternating current having a frequency equal to the charging frequency with a filter circuit (not shown) composed of a resistor, a capacitor and the like at a cycle of about 0.01 to 10 msec. The voltage is converted and input to the engine controller. The input voltage Vk sampled at a constant period is averaged in the engine controller. The average value processing is performed in order to more accurately detect the alternating current by the engine controller. For example, the input voltage that fluctuates with the rotation period of the photosensitive drum, which will be described later, or a pinhole on the photosensitive drum, for example. Even when there is an abnormality in the detected AC current value due to a defect such as the above, current detection closer to the true value can be performed by performing the averaging process.
[0067]
  The input voltage Vk-ave subjected to the average value processing is compared with a charging AC peak-to-peak voltage selection control threshold value V0 set in advance by a comparison unit in the engine controller. The charging AC peak-to-peak voltage selection control threshold V0 is an output voltage with respect to the minimum AC peak-to-peak voltage at which charging unevenness does not occur, and its value is the minimum necessary current value at which uniform charging can be performed.(Reference current)It is determined on the basis of Iac-0 (= charging AC peak-to-peak voltage selection control threshold current). Since the value of Iac-0 varies depending on the process speed and charging frequency of the device, the constituent materials of the charging roller 3 and the photosensitive drum 2, the charging AC peak-to-peak voltage selection control threshold V0 is alsoFor each deviceA suitable setting is recommended.
[0068]
In FIG. 2, when the door for opening and closing is closed when the cartridge is mounted on the image forming apparatus main body, and the power supply of the image forming main body is turned on, the main motor starts to rotate and the pre-multi-rotation process starts.
[0069]
The engine controller of the image forming apparatus main body applies the highest peak-to-peak voltage Vpp-1 that can be applied first, and detects the charging AC current detection voltage V1. This V1 is compared with the detection voltage Vx with respect to the reference AC current value Iac-x with and without the cartridge, and when V1 <Vx, the user is notified of “no cartridge”. In the case of “with cartridge (V1 ≧ Vx)”, the detected voltage value V1 when the maximum charge bias voltage Vpp-1 that can be applied is applied is set so that V1 ≧ V0 in any use situation. Keep it. As a result, charging failure does not occur under any circumstances.
[0070]
Subsequently, the second highest voltage Vpp-2 is applied to obtain the detection voltage V2. At this time, if V2 <V0 as shown in FIG. 1A, Vpp-1 is selected as the charging bias voltage. If V2 ≧ V0, the third highest voltage Vpp-3 is applied to obtain the detection voltage V3. As shown in FIG. 1B, if the value of V3 is V3 <V0, Vpp-2 is selected as the charging bias voltage. If V3 ≧ V0, the fourth highest voltage Vpp-4 is applied to obtain the detection voltage V4. As shown in FIG. 1C, if V4 <V0, Vpp-3 is selected as the charging bias at the time of image formation, and if V4 ≧ 0 as shown in FIG. -4 is selected as the charging bias voltage during image formation.
[0071]
At this time, it is desirable that the application time T of the applied bias voltage (Vpp-1, Vpp-2, Vpp-3, Vpp-4) is a time required for the latent image carrier to make one rotation or more. . In the photosensitive drum, the film thickness unevenness in the circumferential direction may occur due to uneven coating of the coating film of itself, shaving unevenness due to eccentric rotation, etc., and the impedance slightly changes in the circumferential direction. As a result, even when the same bias voltage is applied, as shown in FIG. 3, the flowing alternating current Iac changes with the rotation cycle of the photosensitive drum, so that the photosensitive drum rotates once or more for accurate current detection. Until then, a bias voltage is applied, and the flowing AC current Iac is sampled to improve accuracy.
[0072]
However, if the application time of the bias voltage is too long, problems such as an increase in the amount of scraping on the surface of the latent image carrier occur, so it should not be too long.
[0073]
The engine controller selects an AC output voltage that is equal to or higher than the charging AC peak-to-peak voltage selection control threshold V0 as an AC output voltage from the AC oscillation output, and selects it as a charging bias at the time of image formation.
[0074]
(4) Evaluation
In order to clarify the effect of the present invention, the following experiment was conducted.
[0075]
<Experiment 1>
In a room temperature and normal humidity environment (25 ° C., relative humidity 50%), a one-sheet intermittent durability test was performed using the charge control of the present invention, and the following items were examined.
[0076]
1. AC current flowing in the photosensitive drum
2. Photosensitive drum life
3. Image (solid white, 2 dots, 3 space horizontal line halftone)
* Images were taken every 500 sheets from the beginning and at the point where the voltage switching between charging AC peaks was performed.
[0077]
<Condition (Example 1)>
Environment: normal temperature and humidity environment (room temperature 25 ° C, relative humidity 50%)
Image forming process speed: 130 (mm / sec)
Image forming body resolution: 600 (dpi)
Charging bias voltage: 4 steps of constant voltage, 2000V, 1850V, 1700V, 1550V
Charging AC frequency f: 900 (Hz)
Charging AC peak-to-peak voltage threshold current Iac-0: 680 μA
Engine controller
・ Voltage sampling period from charging AC current detection means: 1msec
・ Sampling length: 0.68 sec (= one round of photosensitive drum)
・ Voltage sample calculation: Average value processing
Photosensitive drum diameter φ: 28 (mm)
Photosensitive drum surface layer average molecular weight M: 15000
Photosensitive drum initial surface layer film thickness: 25 (μm)
Contact pressure of cleaning blade against photosensitive drum: 40 (gf / cm)
Evaluation mode: 1 sheet intermittent durability.
[0078]
<Condition (Comparative Example 1: Detection time is less than one rotation of photosensitive drum)>
Engine controller
・ Voltage sampling period from charging AC current detection means: 1msec
・ Sampling length: 0.34 sec (= 0.5 photosensitive drum)
・ Voltage sample calculation: Average value processing
* Conditions other than the engine controller are the same as in Example 1.
[0079]
<Condition (Comparative Example 2: Use the maximum value in the sample without calculating the voltage sample)>
Engine controller
・ Voltage sampling period from charging AC current detection means: 1msec
・ Sampling length: 0.68 sec (= one round of photosensitive drum)
・ Voltage sample calculation processing: Without using voltage sample calculation processing, use the maximum value in all samples as the detection voltage.
* Conditions other than the engine controller are the same as in Example 1 and Comparative Example 1.
[0080]
<Condition (Comparative Example 3: Use the maximum value in the sample without calculating the voltage sample)>
Engine controller
・ Voltage sampling period from charging AC current detection means: 1msec
・ Sampling length: 0.68 sec (= one round of photosensitive drum)
・ Voltage sample calculation processing: Voltage sample calculation processing is not performed, and the minimum value in all samples is used as the detection voltage.
[0081]
* Conditions other than the engine controller are the same as in Example 1 and Comparative Examples 1 and 2.
[0082]
<Result (Example 1)>
FIG. 4 shows the experimental results when this example is used. FIG. 4A shows the durability transition of the charging AC current flowing through the photosensitive drum. In this figure, the charging AC current decreases when the number of sheets used is 3000 sheets and 5000 sheets, and this indicates that the voltage between the charging AC peaks is switched at this number of sheets. As shown in this figure, when the configuration of this example is used, the charging AC peak-to-peak voltage threshold value that does not cause charging failure throughout durability and the value as small as possible are almost constant, which is very good. It can be seen that proper charging control is performed. FIG. 4B shows the life of the photosensitive drum in Example 1 and the results of image collection (solid white, halftone image). As a result of the experiment, the life of the photosensitive drum was 7500 sheets, and the collected images were free from abnormalities such as defective charging, and very good control could be performed.
[0083]
<Result (Comparative Example 1: Detection time of alternating current sampling is less than one rotation of photosensitive drum)>
In FIG. 4A, in this configuration, the voltage switching of the charging AC peak-to-peak voltage is performed at the number of used sheets 2500 and 4300, and the durability transition of the charging AC current is more than the necessary minimum current. Looks like no problem. However, in this configuration, a black dot-shaped charging failure occurred in the white image that was printed at the 2500 and 4300 sheets where switching was performed. This is a problem caused by the timing of switching the voltage between the charging AC peaks too early.
[0084]
As the durability progresses, the photosensitive drum may be slightly eccentrically rotated. In such a case, the photosensitive drum is not evenly worn in the circumferential direction, and a portion with much shaving and a portion with little shaving appear. As a result, as shown in FIG. 3, since the charging alternating current flowing in the circumferential direction changes, the detection voltage also changes with the photosensitive drum cycle.
[0085]
The reason why such a charging failure has occurred in this example is a problem in the sampling length for current detection. This is because current detection is performed at a portion where a relatively large amount of charging AC current flows in the circumferential direction of the photosensitive drum, and the value exceeds the charging AC peak-to-peak voltage threshold. However, in actuality, current exceeding the charging AC peak voltage threshold does not flow over the entire circumference of the photosensitive drum, and it is considered that a charging failure occurred in a portion where the charging AC current hardly flows on the photosensitive drum.
[0086]
Therefore, from this comparative example, it became clear that it is necessary to perform current detection for one or more revolutions of the photosensitive drum.
[0087]
<Result (Comparative Example 2: Use the maximum value in the sample without calculating the voltage sample)>
In FIG. 4A, in this configuration, the voltage switching of the charging AC peak-to-peak voltage is performed at the point where the number of used sheets is 2000 and 3800, and the endurance transition of the charging AC current is more than the necessary minimum current. Looks like no problem. However, as shown in FIG. 4 (b), in this configuration, the white image and the halftone image that are solid at the 2000, 2500, 3800, and 4000 image points where the switching has been performed have black spots. A charging failure occurred. This is also a problem caused by the timing of switching the charging AC peak-to-peak voltage being too early, as in Comparative Example 1.
[0088]
The reason why such a charging failure occurred in this example is that the maximum value of the collected samples was used as the voltage sample in the current detection sampling. This means that the current detection is performed at the portion where the charging AC current flows most in the circumferential direction of the photosensitive drum, and even if the charging AC peak-to-peak voltage switching determination is performed based on the value, As in Comparative Example 1, in actuality, no current exceeding the charging AC peak voltage threshold value flows over the entire circumference of the photosensitive drum, and charging failure occurs in the portion where the charging AC current hardly flows on the photosensitive drum. it is conceivable that.
[0089]
<Result (Comparative Example 3: Use the minimum value in the sample without calculating the voltage sample)
In FIG. 4A, in this configuration, the voltage switching of the charging AC peak-to-peak voltage is performed at the point where the number of used sheets is 4000 and 5800, and the charging AC peak-to-peak voltage selection is also selected for the transition of the charging AC current durability. Since it is more than the control threshold current, it seems that there is no problem. Actually, in this comparative example, as shown in FIG. 4B, there is no problem with the image, but the life of the photosensitive drum has reached a relatively early stage of 6300 sheets.
[0090]
The reason why the life of the photosensitive drum is shortened in this example is that the minimum value of the collected samples is used as the voltage sample in the current detection sampling. Immediately after the charging AC peak-to-peak voltage application for current detection, the charging AC current may become unstable due to individual differences in the image forming apparatus main body. In addition, there is a possibility that various electrical noises may be added to the detection voltage. If the minimum value is held and the value is used, the switching timing of the charging AC peak-to-peak voltage is delayed or the charging AC peak is larger than necessary. Since the intermediate voltage is selected, an unnecessarily large discharge is applied to the photosensitive drum, so that the life of the photosensitive drum is shortened.
[0091]
From Comparative Examples 2 and 3, in order to perform this control with higher accuracy, it is necessary to average the collected voltage samples and then perform comparison with the charging AC peak-to-peak voltage selection control threshold V0. Became clear.
[0092]
From the above description, this is a feature of the present embodiment.
-During the initial rotation when the power is turned on, a plurality of alternating peak-to-peak voltages are applied stepwise from the higher side, and the application time is that the latent image carrier is rotated once or more for each peak-to-peak voltage. In addition, the AC current detected by the charging AC current detecting means is averaged in the engine controller and then compared with the required minimum voltage value, so that the charging control can be performed with higher accuracy. It became clear.
[0093]
<Second embodiment>
In the first embodiment, an example is shown in which a plurality of peak-to-peak voltages are applied from the higher side during the pre-multi-rotation process, and the charging bias voltage at the time of image formation is selected. During the rotation process, a plurality of AC peak-to-peak voltages are applied stepwise from the low side, and the application time is that the latent image carrier is rotated once or more for each peak-to-peak voltage.
[0094]
The second embodiment according to the present application will be described below. However, since the outline of the image forming apparatus, the printer operation sequence, and the charging bias power supply circuit are the same as those of the first embodiment, the description thereof will be omitted.
[0095]
(1) Determination method of appropriate charging bias voltage
The procedure for determining the charging bias from the AC current detection in this example will be described. In FIG. 9, when it is detected that the door that opens and closes when the cartridge is mounted on the image forming apparatus main body and the image forming apparatus main body is turned on, the engine controller of the image forming apparatus main body The lowest applicable peak-to-peak voltage Vpp-4 is applied. The alternating current detection means converts the current value Iac-4 flowing at this time into a detection voltage V4 and feeds it back to the engine controller. As shown in FIG. 10A, when V4 ≧ V0, Vpp-4 is determined as the charging bias voltage at the time of image formation, and the application of the charging bias voltage is completed. When V4 <V0, the second lowest Vpp-3 is applied to obtain the detection voltage V3. The comparison means in the engine controller compares V3 and V0. As shown in FIG. 10B, if V3 ≧ V0, Vpp-3 is used as the charging bias voltage and charging bias voltage application is terminated. To do. When V3 <V0, the third lowest Vpp-2 is applied to obtain the detection voltage V2, and when V2 ≧ V0 as shown in FIG. 10C, Vpp-2 is determined as the charging bias voltage. As shown in FIG. 10D, when V2 <V0, Vpp-1 is determined as the charging bias voltage.
[0096]
Thus, the application of the charging bias voltage for determining the bias voltage during image formation is completed.
[0097]
In this embodiment, bias voltage application for determining the charging bias at the time of image formation is performed from the side where the peak-to-peak voltage value is low, and the bias voltage is applied when a value equal to or higher than the necessary minimum voltage value V0 is detected. The application is stopped. These have the effect of making the photosensitive drum more difficult to scrape and prolonging the life of the photosensitive drum. By applying the charging bias voltage from the lower side, damage to the photosensitive drum can be reduced, so that the photosensitive drum is hardly scraped. In addition, the application of the charging bias voltage is stopped when there is a voltage exceeding the necessary minimum voltage value V0. Therefore, the amount of abrasion of the photosensitive drum is reduced without applying the charging bias voltage more than necessary, and the life of the photosensitive drum is increased. Can be expected.
[0098]
At this time, the application time T of the applied bias voltage (Vpp-1, Vpp-2, Vpp-3, Vpp-4) is the time for each latent image carrier to make one rotation or more. Is desirable. In the photosensitive drum, the film thickness unevenness in the circumferential direction may occur due to uneven coating of the coating film of itself, shaving unevenness due to eccentric rotation, etc., and the impedance slightly changes in the circumferential direction. As a result, even when the same bias voltage is applied, as shown in FIG. 3, the flowing alternating current Iac changes with the rotation period of the photosensitive drum, so that the photosensitive drum rotates once for accurate current detection. Until this is done, a bias voltage is applied and the flowing AC current Iac is sampled to improve accuracy.
[0099]
However, if the application time T of the bias voltage is too long, problems such as an increase in the amount of abrasion on the surface of the latent image carrier occur, so it should not be too long.
[0100]
<Third embodiment>
In this embodiment, when the charging bias voltage at the time of image formation is Vpp-n, the photosensitive drum rotates once at a voltage Vpp- (n + 1) that is one step lower than Vpp-n as part of the non-image formation. Apply current for more than time to detect current and select charging bias.
[0101]
This is because even when the image forming apparatus main body is not initially rotated when the power is turned on (the image forming apparatus main body power is left on), alternating current is sequentially detected to always select an appropriate bias voltage. The purpose is to do.
[0102]
When the AC peak-to-peak voltage Vpp is controlled at a constant voltage, the current Iac flowing through the photosensitive drum increases as the surface of the photosensitive drum is scraped with use, so that the accompanying AC voltage decreases stepwise. For example, as shown in FIG. 13, the highest voltage Vpp-1 is applied from the beginning of use to the number A of sheets used, but after A sheets, the voltage Vpp-2 is lower than Vpp-1. After switching to B sheets, the voltage is switched to Vpp-3, which is a voltage one step smaller than Vpp-2. As described above, the bias voltage Vpp-n used at the time of image formation is changed to Vpp- (n + 1) which is always smaller by one step when the photosensitive drum is scraped and reaches a certain number.
[0103]
Therefore, in this example, a bias voltage Vpp− (n + 1) which is a part lower than the image forming bias voltage Vpp−n determined by the method of the first embodiment at the time of power-on, which is part of the image forming time. ) And the detection voltage Vn + 1 detected at this time exceeds the charging AC peak-to-peak voltage selection control threshold V0, the bias voltage at the time of image formation is changed from Vpp-n to Vpp- (n + 1). ) Is a feature of this embodiment.
[0104]
The procedure for determining the charging bias voltage in this embodiment will be described with reference to FIGS. First, when the power is turned on, the charging print bias Vpp-n at the time of image formation is determined by the same method as in the first embodiment.
[0105]
During printing, the voltage Vpp− (n + 1), which is one step lower in all or part of the non-image formation, is applied. As described above, in order to accurately detect the current, The application time T is preferably equal to or longer than one rotation of the photosensitive drum, and the sampled detection voltage value is preferably subjected to an average value process.
[0106]
In addition, the timing at which Vpp− (n + 1), which is one step lower, may be applied basically at any time during non-image formation, but is preferably in the pre-rotation process. This is because the bias voltage switching timing can be determined with the highest accuracy if current can be detected by applying this voltage during the pre-rotation process immediately before image formation.
[0107]
When this method is used, a bias voltage smaller than the print bias at the time of image formation is applied in part during non-image formation, so the amount of discharge can be reduced and the wear of the photoconductor can be reduced. The effect that it can be reduced is also added.
[0108]
<Others>
1) The form of the contact charging member 3 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.
[0109]
2) The exposure means for forming the electrostatic latent image is not limited to the laser scanning exposure means 4 for forming 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 can be used as long as it can form an electrostatic latent image corresponding to image information.
[0110]
3) The latent image carrier 2 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.
[0111]
4) Although the developing device 5 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.
[0112]
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.
[0113]
5) The transfer means 6 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.
[0114]
6) As a waveform of a bias alternating voltage component (AC component, voltage whose voltage value changes periodically) applied to the charging member 3 or the developer carrying member 5-c, a sine wave, a rectangular wave, a triangular wave, or the like is appropriately used. Is possible. It may be a rectangular wave formed by periodically turning on / off a DC power supply.
[0115]
【The invention's effect】
As described above, in the present invention, a charging bias power supply circuit that outputs an AC and DC superimposed bias with a single voltage boosting means, the charging bias power supply circuit including at least two types of AC peak-to-peak voltages. AC charging output, and a charging AC current detecting means for detecting an AC current flowing through the photosensitive member when a charging bias is applied. The charging bias power supply circuit is provided when power is turned on or when a non-image is formed. At least in part, a plurality of AC peak-to-peak voltages are applied to detect the charging AC current flowing in the photosensitive drum, and this value is equal to or greater than the charging AC peak-to-peak voltage threshold current and the bias voltage at which the minimum current value is obtained. By using a charging bias voltage control method that is used as a charging bias voltage during image formation, the charging AC current can be controlled appropriately. Space saving the charging power supply circuit, can be realized cost reduction.
[Brief description of the drawings]
FIG. 1 is a flowchart for explaining a first embodiment;
FIG. 2 is a charge application sequence chart illustrating a first embodiment.
FIG. 3 is a diagram for explaining how the charging AC current fluctuates with the rotation cycle of the photosensitive drum.
FIG. 4 is a diagram showing evaluation results of the first example and comparative examples 1 to 3.
FIG. 5 is a diagram illustrating an image forming apparatus according to a first embodiment.
FIG. 6 is a diagram illustrating a printer operation sequence according to the first embodiment.
FIG. 7 is a diagram illustrating a charging bias power supply circuit according to the first embodiment.
FIG. 8 is a diagram showing the relationship between the value of the AC peak-to-peak voltage and the DC voltage that can be output in the charging AC constant voltage control system.
FIG. 9 is a flowchart for explaining a second embodiment.
FIG. 10 is a charge application sequence chart illustrating a second embodiment.
FIG. 11 is a flowchart illustrating a third embodiment.
FIG. 12 is a charge application sequence chart illustrating a third embodiment.
FIG. 13 is a diagram for explaining the relationship between the usage amount of a photosensitive drum and the alternating current flowing through the photosensitive drum in a charging AC constant voltage control system;
FIG. 14 illustrates a conventional image forming apparatus.
FIG. 15 is a diagram conceptually illustrating a conventional charging bias power supply circuit.
[Explanation of symbols]
1 .... Charging bias power supply circuit 2 .... Photosensitive drum (latent image carrier) 3 .... Contact charging means 4 .... Exposure means 5 .... Developing means 6 .... Transfer means 7 ... Recording medium (Transfer material), 8 ... fixing means, 9 ... cleaning means, C ... process cartridge

Claims (11)

At least a movable image bearing member, a charging unit for charging the latent image bearing member in contact with the latent image bearing member and an AC voltage superposed with a DC voltage at one voltage step-up means to the charging 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, 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 a flow Ru ac current to the latent image carrier,
Of the detected alternating current, the reference current or set in advance, and a peak-to-peak voltage of the AC voltage most small alternating current is detected, the peak voltage of the AC voltage used during image formation Decided on
Select the AC peak-to-peak voltage that is equal to or greater than the preset reference current and at which the smallest AC current is detected as the charging bias voltage used during image formation,
The charging bias voltage control characterized in that each of the at least two types of alternating peak-to-peak voltages applied in a part of the non-image formation is applied for a time during which the latent image carrier rotates once. Method. The charging bias voltage control method according to claim 1, wherein a part of the non-image formation is a part of an initial rotation when the image forming apparatus is turned on. At least a movable image bearing member, a charging unit for charging the latent image bearing member in contact with the latent image bearing member and an AC voltage superposed with a DC voltage at one voltage step-up means to the charging 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, 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. Voltage control method to determine,
A plurality of peak-to-peak voltage Vpp of the AC voltage, respectively Vpp-1, Vpp-2 applied thereto, ···, Vpp-n (Vpp -1>Vpp-2>···>Vpp-n> ···) and when, when the peak voltage of the AC voltage at the time of image formation of Vpp-n, at least part of the non-image-forming, the peak voltage of one step lower AC voltage than the charging bias voltage at the time of image formation Vpp- (n + 1) detecting an alternating current is applied to the case where the detected current becomes the reference current or performs switching the peak voltage of the AC voltage to Vpp- (n + 1), The AC voltage peak-to-peak voltage Vpp- (n + 1), which is lower by one step than the image formation applied in a part of the non-image formation, is applied for a period of one rotation of the latent image carrier. Charging bias voltage system Method. A peak-to-peak voltage Vpp− (n + 1) of an AC voltage that is one step lower than that at the time of image formation applied in part during non-image formation is applied in a part of the pre-rotation process immediately before image formation. The charging bias voltage control method according to claim 3. 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. An image forming apparatus having a charging bias power supply circuit for outputting 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. And
Select the AC peak-to-peak voltage that is equal to or greater than the preset reference current and at which the smallest AC current is detected as the charging bias voltage used during image formation,
2. The image forming apparatus according to claim 1, wherein each of the at least two types of AC peak-to-peak voltages applied in a part of the non-image formation is applied for a time required for one rotation of the latent image carrier.   6. The image forming apparatus according to claim 5, wherein the part at the time of non-image formation is a part at the time of initial rotation when the image forming apparatus is turned on. 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. An image forming apparatus having 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. Voltage control method to
Vpp-1, Vpp-2,..., Vpp-n (Vpp-1>Vpp-2>...>Vpp-n>...) When the peak-to-peak voltage of the AC voltage at the time of image formation is Vpp-n, the peak-to-peak voltage of the AC voltage is one step lower than the charging bias voltage at the time of image formation at least partly during non-image formation. An alternating current is detected by applying Vpp− (n + 1), and when the detected current becomes equal to or higher than the reference current, the peak-to-peak voltage of the alternating voltage is switched to Vpp− (n + 1), and The AC voltage peak-to-peak voltage Vpp− (n + 1), which is one step lower than the image formation applied in a part of the non-image formation, is applied for a period of one rotation of the latent image carrier. An image forming apparatus.   The AC voltage peak-to-peak voltage Vpp− (n + 1), which is one step lower than that at the time of image formation applied in part during non-image formation, is applied during a part of the pre-rotation process immediately before image formation. The image forming apparatus according to claim 7. The relationship between the peak-to-peak voltage Vpp-min of the minimum AC voltage applied to the charging unit and the DC voltage Vdc applied to the charging unit is Vpp-min / 2 ≧ | Vdc | charging bias power supply circuit using the charging bias voltage control method according to any one of 4 to 請 Motomeko no 1 shall be the features. An alternating current Iac-max, which is detected when the maximum peak-to-peak voltage Vpp-max of the AC voltage is applied to the charging unit, the relationship between the reference current Iac-0 which is set in advance, Iac-max ≧ Iac The charging bias power supply circuit using the charging bias voltage control method according to claim 1, wherein the charging bias power supply circuit is −0. An image forming apparatus comprising the charging bias power supply circuit according to claim 9 .

Images