JP3902973B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an image forming apparatus such as a process cartridge detachable printer and a copying machine.In placeIt is related.
[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. 8 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 14 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 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 adopted 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 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.
[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 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.
[0010]
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.
[0011]
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.
[0012]
These methods have a great effect in extending the life of the drum and ensuring good chargeability.
[0013]
In addition, in Japanese Patent Application Laid-Open No. 09-190143, a process cartridge usage amount detection / storage means is mounted on a process cartridge, and two or more 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 used, and the AC peak-to-peak voltage is lowered stepwise.
[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.
[0015]
In some cases, after the process cartridge is mounted, the presence or absence of the process cartridge is detected by applying a charging bias to the photosensitive drum and the contact charging member as described in JP-A-11-258957. This is to detect an alternating current value flowing through the photosensitive drum and the contact charging member when a charging bias is applied, and to notify the absence of a cartridge when the current value is below a certain value.
[0016]
[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.
[0017]
In response to this requirement, an AC component constant current control method such as Japanese Patent Publication No. 06-093150 or a discharge amount calculation method such as Japanese Patent Application Laid-Open No. 2001-201920 may be employed.
[0018]
However, in these methods, as shown in FIG. 9A, 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.
[0019]
Here, the circuit of FIG. 9A will be described a little. When the AC component is controlled at a constant voltage, the DC voltage is supplied from the AC output boosting transformer T-AC (voltage boosting means) 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.
[0020]
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. 9B.
[0021]
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.
[0022]
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.
[0023]
Accordingly, an object of the present invention is to prevent any charging failure and discharge amount from increasing immediately after the cartridge is mounted in any combination of the process cartridge and the image forming apparatus main body while suppressing an increase in cost and space. An object of the present invention is to provide an image forming apparatus of a process cartridge attachment / detachment type that can apply an appropriate charging bias.
[0024]
[Means for Solving the Problems]
  The present invention provides an image forming apparatus having the following configuration.In placeis there.
[0025]
  (1) At leastMovableA latent image carrier;TheContact the latent image carrierTo doLatent image carrierTo chargeCharging meansWhen,Process cartridge containingTheImage forming device bodyInDetachableAn image forming apparatus provided in
  SaidFor charging means of process cartridge1AC voltage boosting meansVoltageAnd DCVoltageSuperpositionChargedA charging bias power supply circuit for outputting a bias voltage;
  In a part of non-image formation before image formation after mounting the process cartridge to the image forming apparatus main body,The charging bias power supply circuit,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
  Of the detected AC current, a preset reference currentAbove, andMostAlso smallAC currentdetectionThe peak-to-peak voltage of the AC voltageDuring image formationUsed between the peak of AC voltageAn image forming apparatus that determines a voltage.
[0026]
  (2)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 higher than the reference current. The image forming apparatus according to (1).
  (3) of the AC voltage applied to the charging meansminimumNo picVoltage Vpp-minAnd applied to the charging meansThe relationship between the DC voltage Vdc and Vpp−min / 2 ≧ | Vdc | is characterized by (1)Or (2)The image forming apparatus described in 1.
[0028]
(Work)
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 when the process cartridge is mounted, so that charging failure does not occur and damage to the latent image carrier is reduced. be able to. On the other hand, since only one voltage booster is required in the power supply circuit of the image forming apparatus, the power supply circuit can be significantly increased in cost and space.
[0029]
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, In an image forming apparatus having an alternating current detecting means for detecting an alternating current Iac flowing in the photosensitive member when a bias voltage is applied, the alternating current detecting means is provided between at least two kinds of alternating current peaks at the time of multiple pre-rotations after mounting the cartridge. The AC current Iac flowing through the photosensitive drum is detected by applying the voltage Vpp, and this is fed back to the engine controller, and the voltage level in the region where no charging failure occurs is selected as the charging bias voltage at the time of printing. There is a place to apply.
[0030]
In this embodiment, it is shown that one image forming apparatus main body can apply an appropriate bias to each cartridge in two types of process cartridges having different film thicknesses of the photosensitive drum.
[0031]
(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.
[0032]
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).
[0033]
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.
[0034]
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.
[0035]
  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.
[0036]
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.
[0037]
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.
[0038]
  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.
[0039]
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.
[0040]
The image forming apparatus forms an image by repeating the steps of charging, exposure, development, transfer, fixing, and cleaning using the above-described means.
[0041]
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.
[0042]
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.
[0043]
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.
[0044]
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.
[0045]
(2) Printer operation sequence
The outline of the printer operation sequence in this embodiment will be described with reference to FIG.
[0046]
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 18 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.
[0047]
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.
[0048]
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.
[0049]
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.
[0050]
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.
[0051]
When the post-rotation process is completed, the image forming apparatus again enters a standby (standby) state and waits for the next print signal.
[0052]
(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.
[0053]
In this example, the charging bias power supply circuit 21 includes Vpp-1, Vpp-2, Vpp-3, Vpp-4 (Vpp-1> Vpp-2) which are four types of AC peak-to-peak voltages Vpp different from the AC oscillation output 22. > Vpp-3> Vpp-4). The outputs of the AC peak-to-peak voltages Vpp-1 to Vpp-4 from the AC oscillation output 22 are selectively made by being controlled by the engine controller 23.
[0054]
First, the output voltage output from the AC oscillation output 22 is amplified by the amplifier circuit 24, sine-converted by the sine voltage conversion circuit 25 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.
[0055]
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 26 outputs an output voltage determined by the print density and the like, rectified by the rectifier circuit 27, 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.
[0056]
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.
[0057]
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, so that the drum potential Vd is charged to a desired value. Cannot be obtained, and a good image cannot be obtained.
[0058]
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.
[0059]
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.
[0060]
3-2) Determination of proper charging bias voltage when cartridge is installed
Next, a method for determining an appropriate charging bias voltage will be described with reference to FIGS.
[0061]
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 28 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 23. Since the AC current detecting means 28 can be constituted by a resistor, a capacitor, a diode, and the like, the influence of the cost increase of the power supply circuit and the space expansion is small.
[0062]
  The input voltage input to the engine controller 28 compares the input level with a necessary minimum voltage V0 set in advance. 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.
[0063]
The engine controller 23 selects an AC output voltage that is equal to or higher than the necessary minimum voltage V0 as an AC output voltage from the AC oscillation output 22, and selects it as a charging bias at the time of image formation.
[0064]
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. The charging bias determination step is performed immediately after the process cartridge is mounted.
[0065]
First, when it is detected that the cartridge door 18 that opens and closes when the cartridge is attached to the image forming apparatus main body 20 (step S1), the engine controller 23 of the image forming apparatus main body 20 first applies the lowest applicable peak interval. A voltage Vpp-4 is applied.
[0066]
The alternating current detection means 28 converts the alternating current Iac-4 flowing through the photosensitive member at this time into a detection voltage V4 and feeds it back to the engine controller 23 (S2 and S3).
[0067]
Assuming that the reference alternating current value with and without the cartridge is Iac-x and the detected voltage at that time is Vx, if V4 <Vx, it is determined that the process cartridge is not installed, and the user is notified (S3 and S11). -S12).
[0068]
On the other hand, when V4 ≧ V0, Vpp-4 is determined as a charging bias at the time of printing (hereinafter referred to as a print bias) (S4, S13, S10).
[0069]
When V ′ <V4 <V0, the next highest voltage Vpp-3 is applied, the detection voltage V3 is fed back, and compared with V0 (S5).
[0070]
If V3 ≧ V0, Vpp-3 is used as the print bias (S6, S14, S10). If V3 <V0, the next higher voltage Vpp-2 is applied to obtain the detection voltage V2 (S7). ). If V2 ≧ V0, Vpp-2 is applied as a print bias (S8, S15, S10), and if V2 <V0, Vpp-1 is used as a print bias (S8, S9, S10).
[0071]
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.
[0072]
Further, the order of bias application is not necessarily as shown in FIG.
[0073]
(4) Effect
Next, the effect of the present embodiment will be described. Two types of process cartridge C_A, C_BWere prepared and mounted on the same image forming apparatus main body 20 and subjected to a pre-multi-rotation process. C_AIs new, C_BIs a process cartridge that has been used for about half of its service life.
[0074]
Process cartridge C_AThe photosensitive drum 10 is sufficiently thick so that the combined electrostatic capacity with the charging means 11 is small, so that an alternating current hardly flows._BSince the photosensitive drum 10 is scraped by use and the film thickness is reduced, the synthetic capacitance is increased and the value of the alternating current is also increased.
[0075]
The charging bias determination procedure is performed for each cartridge C._A, C_BThe result applied to is shown in FIG.
Process cartridge C_A, The AC current values Iac-4A, Iac-3A, and Iac-2A when Vpp-4 is applied, when Vpp-3 is applied, and when Vpp-2 is applied are less than the current value Iac-0 where no charging failure occurs. Since the alternating current value Iac-1A exceeds Iac-0 only when Vpp-1 is applied, the process cartridge C_AThe charging bias when mounting is set to Vpp-1.
[0076]
On the other hand, process cartridge C_BThe AC current values Iac-4B and Iac-3B when applying Vpp-4 and Ipp-3B are lower than Iac-0, but the AC current value Iac-2B when applying Vpp-2 is Iac-0 Is over. Therefore, process cartridge C_BIt can be seen that charging failure does not occur when Vpp-2 is applied. Therefore, process cartridge C_BThe charging bias at the time of mounting is set to Vpp-2.
[0077]
When Iac detection is not performed as described above, the cartridge C_BIn this case, Vpp-1 that does not cause a charging failure is necessarily applied, so that the amount of discharge becomes large and there is a concern about an increase in damage to the photosensitive drum 10.
[0078]
Although the case where the film thickness of the photosensitive drum 10 is different is shown here, the present invention can be similarly applied to the case where the impedance of the charging member 11 is different.
[0079]
As described above, a plurality of charging AC biases are switched and applied during the previous multi-rotation immediately after the process cartridge C is mounted, and the AC current values flowing through the photosensitive drum 10 and the charging unit 11 at that time are detected. The proper charging bias of the mounted process cartridge C can be determined. In this example, four types of charging AC bias can be applied. However, if two or more types of charging AC bias can be applied, it is within the scope of the present invention.
[0080]
(Second embodiment)
In the first embodiment, different process cartridges C_A, C_BHowever, in this embodiment, an example in which an appropriate charging bias is selected even when different image forming apparatus main bodies are used is shown.
[0081]
In the first embodiment, even when the same peak-to-peak voltage is applied, the detected alternating current value changes due to the difference in the film thickness of the photosensitive drum 10 and the difference in the impedance of the charging member 11.
[0082]
On the other hand, as is well known, the charging bias application circuit 21 of the image forming apparatus also has some variation. When the peak-to-peak voltage of the charging bias varies, even if the same photosensitive drum 10 and the same charging unit 11 are used, the AC current values flowing through both of them also differ as a result.
[0083]
Here, when the same process cartridge C is used, charging failure occurs in an image forming apparatus main body (hereinafter referred to as a main body D) having an upper limit of charging bias and an image forming apparatus main body (hereinafter referred to as a main body E) having the same lower limit. FIG. 7 shows a state in which the bias is selected in each main body so that it does not occur and the discharge amount can be suppressed. Note that the process cartridge C has a usage history.
[0084]
From the figure, in the main body D, the AC current value Iac-4D when Vpp-4 is applied is lower than Iac-0, but the AC current value Iac-3D when Vpp-3 is applied is already higher than Iac-0. Therefore, it can be seen that there is no problem if Vpp-3 is selected as the charging bias.
[0085]
On the other hand, in the main body E, the alternating current values Iac-4E and Iac-3E when Vpp-4 and Vpp-3 are applied are lower than Iac-0. For this reason, if Vpp-3 is selected as the charging bias as in the case of the main body of the upper limit of the charging bias, a charging failure occurs in the main body of the lower limit. Therefore, when a higher voltage Vpp-2 was applied and the alternating current value Iac-2E at that time was measured, it exceeded Iac-0. Therefore, it can be seen that it is necessary to apply Vpp-2 as the charging bias in the lower limit body.
[0086]
From the above, it has been shown that the smallest peak-to-peak voltage that does not cause charging failure in any of the main bodies D and E can be adopted as the charging bias, and it becomes possible to apply an appropriate charging bias regardless of variations in the main body. .
[0087]
(Other)
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.
[0088]
  2) As an exposure means for forming an electrostatic latent image, a laser that forms a digital latent image as in the embodiment is used.The runIt is not limited to the inspection exposure means 12, and other light emitting elements such as normal analog image exposure and LEDs may be used. A light emitting element such as a fluorescent lamp and a liquid crystal shutter may be used.Etc.As long as it can form an electrostatic latent image corresponding to image information, such as a combination of the above.
[0089]
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.
[0090]
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.
[0091]
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.
[0092]
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.
[0093]
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.
[0094]
【The invention's effect】
As described above, according to the present invention, a process cartridge detachable image forming apparatus can be used without a defective charging even when the process cartridge or the image forming apparatus main body is replaced, and the discharge amount is reduced. The damage to the latent image carrier can be reduced.
[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;
FIG. 7 is a diagram for explaining the effect of the second embodiment.
FIG. 8 is a diagram illustrating the configuration of an example of a conventional image forming apparatus.
FIG. 9 is a conceptual diagram 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 (3)

At least a movable image bearing member, an image forming apparatus provided detachably a charging unit that charges the image bearing member in contact with said image bearing member, a process cartridge including the image forming apparatus main body Because
Has a charging bias power supply circuit for outputting a charging bias voltage obtained by superposing an AC voltage and a DC voltage by one voltage step-up means to the charging means of the process cartridge,
Some of the non-image-formation of the previous image formation after mounting the process cartridge into the image forming apparatus main body, the charging bias power supply circuit, the charging AC voltage comprising at least two kinds of peak voltage is applied to the means, when the aC voltage is applied to said charging means, to detect the flow Ru ac current to the image bearing member,
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, between the peaks of the AC voltage to be used during image formation An image forming apparatus that determines a voltage. 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 higher than the reference current. The image forming apparatus according to claim 1. And minimum 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 | by the image forming apparatus according to claim 1 or 2, characterized in that.

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