JP2011133686A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out a stable image formation by satisfactorily maintaining applied voltage, even when a proper decision cannot be carried out for the applied voltage to a charging member for charging an image carrier in an image forming apparatus. <P>SOLUTION: An AC value measuring circuit 14 measures AC value flowing to the charging member when a plurality of known voltage values (voltage values between peaks) in AC voltage are applied to the charging member (charging roller 8). The voltage value of the AC voltage which should be applied to the charging member is calculated so that an amount of discharged current between the charging member and the image carrier 1 becomes a prescribed value based on the plurality of known voltage values and the AC value obtained by the measurement. When the voltage value is an abnormal value, the voltage value of the AC voltage is calculated again, by applying again the voltage which is different from a reference voltage to the charging member to measure the AC value. When the voltage value is not the abnormal value, charging is carried out by the applied voltage with the voltage value. Preferably, when the AC value is measured again, the measurement is carried out by stopping at least one of developing bias and transfer bias. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that charges an image carrier.

   Conventionally, in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, as a method of charging the surface of an image carrier as a charged body such as a photoreceptor or a dielectric, a high voltage is applied to a thin corona discharge wire. A corona charging system as a non-contact charging system in which charging is performed by causing the generated corona to act on the surface of the image carrier is generally used.

  In recent years, from the viewpoint of low-pressure process, low ozone generation, and low cost, a roller-type or blade-type charging member is brought into contact with the surface of the image carrier, and a voltage is applied to the charging member to Contact charging methods for charging are becoming mainstream.

  In particular, a roller-type charging member (that is, a charging roller) has an advantage that stable charging can be performed over a long period of time. The voltage applied to the charging member may be only a DC voltage, but charging can be performed uniformly by applying an oscillating voltage and alternately causing discharge to the plus side and minus side. For example, by applying an oscillating voltage in which an alternating voltage having a peak-to-peak voltage equal to or higher than a discharge start voltage (charge start voltage) of a charged object when a DC voltage is applied and a DC voltage (DC offset bias) are superimposed It is known that there is an effect of leveling the charge of the member to be charged and uniform charging is performed.

  As described above, a contact charging method in which an oscillating voltage is applied to the charging member for charging is hereinafter referred to as an “AC charging method”. A contact charging method in which only a DC voltage is applied for charging is referred to as a “DC charging method”. In the AC charging method, compared to the DC charging method, the total discharge current generated between the charging member and the image carrier is increased by applying a voltage, so that the deterioration of the image carrier such as scraping of the image carrier is promoted, and the discharge product An abnormal image such as image flow in a high temperature and high humidity environment may occur. Therefore, if discharge is performed more than necessary, discharge products that cause deterioration of the image carrier and image flow are excessively formed. On the other hand, if the discharge is not performed sufficiently, charging failure will occur. Therefore, it is necessary to minimize the discharge that causes the plus side and the minus side to occur alternately by applying the minimum necessary charging voltage so that charging failure does not occur.

  However, in practice, the relationship between the voltage and the amount of discharge current is not always constant, and varies depending on the film thickness of the photosensitive layer and dielectric layer of the image carrier, the environmental variation of the charging member and air, and the like. In a low-temperature and low-humidity environment (L / L), the material dries and the resistance value increases, making it difficult to discharge. Therefore, a peak-to-peak voltage of a certain value or more is required to obtain uniform charging. Even at the lowest voltage value at which charging uniformity can be obtained in this L / L environment, if the charging operation is performed in a high-temperature and high-humidity environment (H / H), the material absorbs moisture and the resistance value decreases. The member will discharge more than necessary. As a result, when the amount of discharge current increases, problems such as the occurrence of image defects such as image flow, the occurrence of toner fusion, and the wear of the image carrier due to the deterioration of the surface of the image carrier occur.

  In addition to the causes of environmental fluctuations described above, problems caused by changes in the amount of discharge current also occur due to fluctuations in charging member manufacturing and resistance values due to dirt, electrostatic capacity fluctuations of the image carrier due to durability, fluctuations in the main body high-voltage device, etc. I know you will.

  In order to suppress such a change in the amount of discharge current, there is a “discharge current control method” proposed in Patent Document 1. According to this method, the peak-to-peak voltage value of the image forming application voltage can be controlled so that the discharge current amount is constant in the pre-rotation process period, the printing process, and the inter-paper process.

JP 2004-157501 A

  However, the above-described “discharge amount control method” has the following problems.

  That is, when calculating the peak-to-peak voltage value of the image forming applied voltage in real time, the charging AC current value may be affected by noise due to a developing bias or the like. In such a case, the current waveform is distorted due to the influence of noise, and an error occurs in the required peak-to-peak voltage value of the applied image forming voltage.

  Therefore, the present invention is to maintain a good applied voltage and perform stable image formation even when the applied voltage for the charging member for charging the image carrier in the image forming apparatus cannot be properly determined. Objective.

  An image forming apparatus according to the present invention includes an image carrier, a charging member for charging the surface of the image carrier, and a developing bias for visualizing the electrostatic latent image formed on the charged surface of the image carrier. A developing means for converting the electrostatic latent image into a visible image by a voltage, a transfer means for transferring the visible image to a transfer material by a transfer bias voltage, a reference voltage is applied to the charging member, and the charging member A control unit that detects a current value flowing through the image carrier and calculates a voltage value of an AC voltage applied to the charging member based on the detected current value, and the control unit includes the calculated AC voltage. If the voltage value of the calculated AC voltage is an abnormal value, a voltage different from the reference voltage is reapplied to the charging member and recalculated. If the voltage value of the AC voltage is not abnormal If, the voltage value of the re-calculated AC voltage and performs charging of the image bearing member by said charging member.

  When the calculated voltage value of the AC voltage is an abnormal value, a voltage different from the reference voltage is re-applied to the charging member by the AC current value measuring means, and the AC current value flowing through the charging member It is possible to obtain a normal voltage value by re-measuring and recalculating the voltage value of the AC voltage.

  In particular, when the AC current value flowing through the charging member is remeasured by the AC current value measuring means, noise that affects the measurement of the AC current value is generated by stopping at least one of the development bias and the transfer bias. And the possibility of obtaining a normal voltage value can be increased.

  As a method for determining the abnormal value, for example, when the calculated voltage value of the AC voltage is not within a predetermined range, it can be determined as an abnormal value.

  The image forming apparatus includes a detecting unit that detects temperature and humidity, a storage unit that associates the voltage value of the AC voltage calculated by the calculating unit with the temperature and humidity detected by the detecting unit, and stores the history information as history information. When the abnormal value of the calculated voltage value of the alternating voltage is continuously detected a predetermined number of times, the history information is referred to and the AC voltage corresponding to the past temperature and humidity information approximated to the current temperature and humidity information Search means for searching for a voltage value, and applying the voltage value of the AC voltage to the charging member using the voltage value of the AC voltage approximated to the current temperature and humidity searched by the search means. And As a result, the image forming operation can be continued even when a normal value is not obtained as a voltage value even after predetermined remeasurement.

  According to the present invention, stable image formation can be achieved and deterioration of the image carrier can be prevented even when the obtained voltage value of an appropriate AC voltage for charge control cannot be obtained. .

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an operation sequence diagram of the printer shown in FIG. 1. FIG. 2 is a block circuit diagram illustrating a configuration example of a charging bias application system for a charging roller in an embodiment of the present invention. It is a graph which shows the relationship of the alternating current Iac with respect to the peak voltage Vpp in embodiment of this invention. It is explanatory drawing of the relationship between the peak-to-peak voltage (Vpp) and alternating current (Iac) measured in the peak-to-peak voltage calculation process in the embodiment of the present invention. It is an operation | movement conceptual diagram of the peak-to-peak voltage calculation in embodiment of this invention. It is the flowchart which showed the process which the control part in embodiment of this invention performs.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(1) Overview of Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus according to the present embodiment will be described using an electrophotographic laser printer as an example.

  The image carrier in the present embodiment is a rotating drum type electrophotographic photosensitive member (photosensitive drum) 1. The photosensitive drum 1 is a negatively charged organic photosensitive member, and is rotationally driven at a predetermined peripheral speed in a clockwise direction indicated by an arrow by a driving motor (not shown).

  The photosensitive drum 1 is uniformly charged to a predetermined negative potential by a charging device during its rotation. The charging device in this example employs a contact charging method using a charging roller 8 as a charging member. The charging roller 8 is driven to rotate with respect to the photosensitive drum 1. A bias voltage is applied to the charging roller 8 from a charging bias power source (not shown). As the charging bias voltage, a voltage obtained by superimposing a DC voltage corresponding to a desired on-drum potential on an AC voltage having a peak-to-peak voltage more than twice the discharge start voltage is used. This charging method aims to eliminate local potential unevenness on the photosensitive drum by applying an AC voltage superimposed on the DC voltage, and to uniformly charge the photosensitive drum to a potential equal to the DC applied voltage.

  Next, the photosensitive drum 1 is subjected to image exposure by an exposure device (not shown) as exposure means. The exposure apparatus forms an electrostatic latent image on the uniformly charged photosensitive drum 1. In this example, a semiconductor laser scanner is used. The exposure apparatus outputs a laser beam modulated in accordance with an image signal sent from a host apparatus in the image forming apparatus, and scans and exposes the uniformly charged surface of the photosensitive drum 1 through an exposure window (image). Exposure). An electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum by lowering the absolute value of the potential at the exposed portion as compared with the absolute value of the charged potential.

  The electrostatic latent image formed in this manner has toner attached thereto (developed) by the reversal developing device 10 and is visualized as a toner image on the photosensitive drum 1. In this example, a jumping development method is used. In this system, a developing bias voltage in which alternating current and direct current are superimposed is applied to the developing sleeve 9 from a developing bias power source (not shown), so that the developer layer thickness regulating member (not shown) and the developing sleeve 9 are in contact with each other. The toner charged negatively by frictional charging is applied to the electrostatic latent image on the surface of the photosensitive drum to reversely develop the electrostatic latent image.

  The toner image on the photosensitive drum surface is transferred by a transfer device (transfer means) to a recording medium P (transfer material) such as paper fed from the paper supply unit 3. The transfer device of this example is a contact transfer device using a transfer roller 2. The transfer roller 2 is pressed against the photosensitive drum 1 in the central direction of the photosensitive drum by a biasing means such as a pressing spring (not shown). When the transfer material P is conveyed and the transfer process is started, a positive transfer bias voltage is applied to the transfer roller 2 from a transfer bias power source (not shown), and the photosensitive drum 1 is charged negatively. The toner is transferred onto the transfer material P.

  The transfer material P that has received the transfer of the toner image is separated from the surface of the photosensitive drum, and is introduced into the fixing device 4 as a fixing unit, and undergoes a fixing process of the toner image. The fixing device 4 fixes the toner image transferred onto the transfer material to a permanent image using means such as heat or pressure. After the fixing, the transfer material P is discharged to a paper discharge portion by a paper discharge roller 6. The path 7 shown in the figure is a path for reversing the transfer material P for double-sided printing, and is not directly related to the present invention.

  The photosensitive drum surface after separation of the transfer material is cleaned by scraping off the transfer residual toner by a cleaning device (not shown), and is repeatedly used for image formation. After completion of the cleaning process, the photosensitive drum surface again enters the charging process.

  The image forming apparatus forms an image by repeating the steps of charging, exposing, developing, transferring, fixing, and cleaning using the above-described means.

(2) Printer Operation Sequence FIG. 2 is an operation sequence diagram of the printer shown in FIG. Hereinafter, each process will be described in the order of progress.

a. Initial rotation operation (front multiple rotation process)
This state is shifted from the stop state by turning on the main power switch. This period is a starting operation period (starting operation period, warming period) when the printer is started. First, the photosensitive drum is driven to rotate. In addition, a preparatory operation for a predetermined process device such as starting the fixing device to a predetermined temperature is executed.

  In the present embodiment, an appropriate voltage value of the applied AC voltage in the charging process of the printing process is calculated during this initial rotation operation period. In the present embodiment, an arithmetic program for calculating a peak-to-peak voltage value as this voltage value is executed. This specific process will be described later.

b. Print preparation rotation operation (pre-rotation process)
This period is a preparatory rotation operation period before image formation from the time when the print signal is turned on after the initial rotation operation is finished until the image formation (printing) process operation is actually performed. When a print signal is input during the initial rotation operation, it is executed following the initial rotation operation. When there is no print signal input, after the initial rotation operation is completed, the drive of the main motor is temporarily stopped to stop the rotation of the photosensitive drum, and the printer is kept in a standby (standby) state until a print signal is input. When the print signal is input, the print preparation rotation operation is executed.

  In the present embodiment, in the initial rotation operation a, it is checked whether or not the calculation result of the peak voltage value of the applied AC voltage in the charging process of the printing process is an abnormal value. In the rotation operation period b, the calculation program of the peak-to-peak voltage value of the applied AC voltage in the charging process of the printing process is re-executed (retry). At this time, in order to suppress the generation of noise, at least one of the development bias and the transfer bias, preferably both, are temporarily stopped.

c. Printing process (image forming process or image forming process)
When the predetermined print preparation rotation operation is completed, an image forming process for the rotating photosensitive drum is subsequently executed, and the toner image formed on the surface of the rotating photosensitive drum is transferred to a transfer material, and the toner image is fixed by the fixing device. The image formation is printed out. In the case of the continuous printing (continuous printing) mode, the above-described printing process c is repeatedly executed for a predetermined set number of prints n.

d. Inter-sheet process During this period, in the continuous printing mode, recording at the transfer position after the trailing edge of one transfer material passes the transfer position and before the leading edge of the next transfer material reaches the transfer position. This is a non-sheet passing state period of paper.

e. Post-rotation operation This period is a period during which a predetermined post-operation is executed by continuing to drive the main motor for a while even after the last transfer material printing process is completed to rotate the photosensitive drum.

f. Standby When the predetermined post-rotation operation is completed, the main motor is stopped and the photosensitive drum is stopped from rotating, and the printer is kept in a standby state until the next print start signal is inputted. In the case of printing only one sheet, after the printing is completed, the printer goes into a standby state through a post-rotation operation. When the print start signal is input in the standby state, the printer proceeds to the pre-rotation process.

  The printing process c is at the time of image formation, and the initial rotation operation a, the print preparation rotation operation b, the paper spacing process d, and the post-rotation operation e are at the time of non-image formation.

(3) Detailed Description of Charging Unit (A) Charging Bias Application System FIG. 3 is a block circuit diagram showing a configuration example of a charging bias application system for the charging roller 8 constituting the charging unit of the present invention.

  A power source 20 that is an AC voltage application unit for the charging roller 8 includes a direct current (DC) power source 11 and an alternating current (AC) power source 12. The power supply 20 generates a predetermined oscillating voltage (bias voltage Vdc + Vac) obtained by superimposing an AC voltage having a frequency f on a DC voltage. The generated vibration voltage is applied to the charging roller 8 through the cored bar 8a. Thereby, the peripheral surface of the rotating photosensitive drum 1 is charged to a predetermined potential. The waveform of the oscillating voltage is not limited to a sine wave, but may be a rectangular wave, a triangular wave, or a pulse wave. The “oscillating voltage” is the same as the voltage of a rectangular wave formed by periodically turning on / off the DC voltage or the superimposed voltage of the AC voltage and the DC voltage by periodically changing the value of the DC voltage. This includes output.

  The control unit 13 controls to turn on / off the DC power source 11 and the AC power source 12 of the power source 20 so as to apply a DC voltage, an AC voltage, or a superimposed voltage of both to the charging roller 8; And a function of controlling the DC voltage value applied to the charging roller 8 from the DC power source 11 and the peak-to-peak voltage value of the AC voltage applied from the AC power source 12 to the charging roller 8. That is, the control unit 13 is configured to calculate the peak-to-peak voltage value of the AC voltage to be applied to the charging roller 8. In the present embodiment, the control unit 13 includes a central processing unit (CPU) and a storage unit (memory) that stores a control program (including the arithmetic program) executed by the central processing unit in the present embodiment. The In the memory, as the past history information, a peak-to-peak voltage value corresponding to the environmental information described above, that is, information in which the calculated voltage value of the alternating voltage is associated with the detected temperature and humidity is stored. The control unit 13 also configures a search unit that refers to the history information and searches for a peak-to-peak voltage value corresponding to past environment information approximate to the current environment information.

  The alternating current value measuring circuit 14 is an alternating current value measuring unit that measures the alternating current value flowing through the charging roller 8 via the photosensitive drum 1. The AC current value information measured by the AC current value measuring circuit 14 is input to the control unit 13.

  The environment sensor 15 is a thermometer and a hygrometer as means for detecting the environment where the printer is installed. Environmental information detected by the environmental sensor 15 is input to the control unit 13.

  Based on the alternating current value information input from the alternating current value measurement circuit 14 and the environmental information input from the environmental sensor 15, the control unit 13 determines the interval between peaks of the alternating voltage applied to the charging roller 8 in the charging process of the printing process. It has a function of executing a calculation program for calculating and determining a voltage value. The storage unit 16 has a storage area (preferably a non-volatile memory) that is read and written by the control unit 13, and associates the environmental information detected when the voltage value is calculated with the peak-to-peak voltage value and records the history. Storage means for storing information is configured.

(B) Peak-to-peak voltage calculation (“discharge amount control method”)
Next, a method for calculating the peak-to-peak voltage of the AC voltage applied to the charging roller 8 during printing will be described.

  As shown in the graph of FIG. 4, the relationship of the alternating current Iac to the peak-to-peak voltage Vpp has a linear relationship at a predetermined ratio in a region lower than the charging start voltage Vs (V) (that is, an undischarged region). When entering the discharge region where the peak-to-peak voltage Vpp is equal to or higher than the charging start voltage Vs, the alternating current Iac increases at a rate larger than the predetermined ratio as the peak-to-peak voltage Vpp increases. In a similar experiment in a vacuum where no discharge occurs, the linearity is maintained, so that the region between the slopes of both ratios (the black portion shown in the figure) is the increment ΔIac of the current involved in the discharge. Conceivable.

Therefore, when the ratio of the current Iac to the peak-to-peak voltage Vpp less than the charging start voltage Vs (V) is α, the AC current such as the nip current other than the current due to the discharge is α · Vpp. The difference ΔIac can be obtained from the following equation (1) from Iac measured when a voltage equal to or higher than the charging start voltage Vs (V) is applied and this α · Vpp.
ΔIac = Iac−α · Vpp (1)

  This ΔIac is defined as a discharge current amount that indicates the amount of discharge instead.

  This amount of discharge current varies depending on the environment and aging. This is because the relationship between the peak-to-peak voltage and the amount of discharge current and the relationship between the alternating current value and the amount of discharge current vary.

  In the constant current control method in which the applied voltage is controlled so that the current flowing from the charging member to the member to be charged becomes a predetermined value when charging the charging member, the control is performed based on the total current flowing from the charging member to the member to be charged. Is called. As described above, this total current is the sum of the current flowing to the contact portion (hereinafter referred to as nip current: α · Vpp) and the current flowing due to the discharge at the contacted portion (hereinafter referred to as discharge current amount: ΔIac). It has become. Therefore, in the constant current control method, control is performed in a form that includes not only the discharge current, which is the current necessary for actually charging the member to be charged, but also the nip current.

  Next, a method for determining the peak-to-peak voltage at which the discharge current amount D is obtained when the target discharge current amount is D will be described.

  In the present embodiment, during the printing preparation rotation operation, the control unit 13 performs calculation / determination processing of the peak-to-peak voltage value of the AC voltage applied to the charging roller 8 in the charging process during the printing process. In the present embodiment, this process is realized by the execution of an arithmetic program by the control unit 13.

  Hereinafter, the operation of the present embodiment will be described more specifically with reference to the Vpp-Iac graph of FIG. 5 and the operation conceptual diagram of FIG.

  The control unit 13 controls the AC power source 12 to sequentially apply a plurality of known reference voltage values in the discharge region to the charging roller 8, in this example, three voltages Vα1, Vα2, Vα3, and a peak-to-peak voltage (Vpp), and A plurality of known reference voltage values in the undischarged region, in this example, three voltages Vβ1, Vβ2, and Vβ3 of the peak-to-peak voltage are applied. At this time, AC current values Iα1, Iα2, Iα3, Iβ1, Iβ2, and Iβ3 flowing to the charging roller 8 through the photosensitive drum 1 are measured by the AC current value measuring circuit 14 and input to the control unit 13. Further, during the re-measurement in the present embodiment, the voltages Vα1, Vα2, Vα3 and the voltages Vβ1, Vβ2, Vβ3 are applied with values different from the initial values to reduce the influence of noise.

  Next, the control unit 13 linearly approximates the relationship between the peak-to-peak voltage in the discharged and undischarged regions and the alternating current from the measured current values at the three points using the least square method, An approximate straight line represented by Equation 3 is obtained.

Approximate straight line of discharge area: Y = αX + A (2)
Approximate straight line of undischarged area: Y = βX + B (3)

  Based on the difference between the approximate straight line of the discharge region of Equation (2) and the approximate straight line of the undischarged region of Equation (3), the peak-to-peak voltage Vx that becomes the discharge current amount D is determined by the following equation. That is, if the Y value of equation (2) with respect to Vx is Yα, the Y value of equation (3) is Yβ, and these values are substituted into equations (2) and (3), the following equations (2) ′ (3) ′ Is obtained.

Yα = αVx + A (2) ′
Yβ = βVx + B (3) ′

From these equations (2) ′ (3) ′, Vx is obtained as in the following equation.
Vx = (D−A + B) / (α−β) (4)
(Here D = Yα−Yβ.)

  The peak-to-peak voltage Vpp applied to the charging roller 8 is switched to Vx obtained by the above equation (4), and the process proceeds to the above-described printing process.

  FIG. 7 is a flowchart illustrating processing executed by the control unit 13.

  In the pre-multi-rotation process, the control unit 13 executes a calculation program for obtaining the peak-to-peak voltage value of the applied AC voltage in the charging process (S101). Next, it is checked whether or not the calculation result is an abnormal value (S102). Whether or not it is an abnormal value can be determined by whether or not the obtained D value is within a predetermined range. That is, when it is not within a predetermined range, it is determined as an abnormal value. This predetermined range is a range of ± 3% from the voltage value of the peak-to-peak voltage and the value of the alternating current value calculated in advance by experiments. Within this range, the image is not affected. The predetermined range may be different depending on the temperature and humidity at that time (hereinafter referred to as environmental information). If there is no abnormal value in the calculation result (S102, No), the peak-to-peak voltage value is determined (S107).

  When an abnormal value is detected in the calculation result (S102, Yes), it is confirmed whether or not the detection of the abnormal value has occurred continuously for a predetermined number of times (S103).

  If the number of consecutive occurrences does not reach the predetermined number, in the pre-rotation process, the development bias and transfer bias are temporarily stopped in order to suppress noise generation, and the peak-to-peak voltage value calculation program for the applied AC voltage is re-executed. (Retry) (S104) and return to step S102.

  When abnormal value detection continues a predetermined number of times, the past history information is referred to (S105), and the peak-to-peak voltage value corresponding to the past environment information approximate to the current environment information is searched from the memory. If the peak-to-peak voltage value exists (S106, Yes), the peak-to-peak voltage value to be obtained is determined using it (S107). Also, the history information is updated (S108). The update may be performed only when the peak-to-peak voltage value corresponding to the current environment information is not stored in the memory. Further, even when stored, if the stored contents are updated to new contents, it is possible to cope with a change in charging characteristics over time. If the peak-to-peak voltage value does not exist (S106, No), the process ends in error. Instead of the error termination, a peak-to-peak voltage value corresponding to the closest stored environmental information among the past environmental information stored may be used.

  In this way, by calculating the peak-to-peak voltage Vx necessary for obtaining the predetermined discharge current amount D at the time of printing each time during the printing preparation rotation operation, and using the obtained peak-to-peak voltage Vx during printing, It is possible to absorb the fluctuation of the resistance value caused by the manufacturing variation of the charging roller 8 and the environmental variation of the material and the high voltage variation of the main body device, and to obtain a desired discharge current amount with certainty.

  As described above, according to the present embodiment, when the calculated peak-to-peak voltage of the applied AC voltage is abnormal due to the influence of noise, the abnormal value is detected and the peak-to-peak voltage calculation process is performed again. By performing this, stable charge control becomes possible. As a result, image defects such as image deterioration due to deterioration of wear due to acceleration of deterioration of the image carrier due to excessive discharge acting on the image carrier, shortening of the life, increase in generation of discharge products, and sufficient Uniform charging can be performed by eliminating problems such as charging failure due to the absence of charging. Thereby, stable image formation can be maintained over a long period of time.

  The preferred embodiments of the present invention have been described above, but various modifications and changes other than those mentioned above can be made. For example, although an electrophotographic laser printer has been described as the image forming apparatus, the image forming apparatus of the present invention is not limited to the laser system, and can be applied to any recording system that charges the image carrier. Further, the present invention is not limited to a printer, and can be applied to a copying machine, a facsimile, and the like. The charging member is not limited to a roller type.

2 Transfer roller 3 Paper feed unit 4 Fixing device 6 Paper discharge roller 7 Path 8 Charging roller 8a Metal core 9 Developing sleeve 10 Reverse development device 11 Power source 12 Power source 13 Control unit 14 AC current value measuring circuit 15 Environmental sensor 16 Storage unit 20 Power source

Claims (4)

An image carrier;
A charging member for charging the surface of the image carrier;
Developing means for making the electrostatic latent image visible by a developing bias voltage in order to visualize the electrostatic latent image formed on the surface of the charged image carrier;
Transfer means for transferring the visible image to a transfer material by a transfer bias voltage;
A control unit that applies a reference voltage to the charging member, detects a current value flowing from the charging member to the image carrier, and calculates a voltage value of an alternating voltage applied to the charging member based on the detected current value And comprising
The control unit determines whether or not the calculated voltage value of the alternating voltage is an abnormal value. If the calculated voltage value of the alternating voltage is an abnormal value, a voltage different from the reference voltage is set. Recharging the charging member, and if the recalculated AC voltage value is not an abnormal value, the charging member charges the image carrier with the recalculated AC voltage value. Image forming apparatus.   The image forming apparatus according to claim 1, wherein when the current flowing through the charging member is remeasured by the control unit, at least one of the developing bias and the transfer bias is stopped.   The image forming apparatus according to claim 1, wherein when the calculated voltage value of the AC voltage is not within a predetermined range, the image forming apparatus determines that the value is an abnormal value. Detection means for detecting temperature and humidity;
Storage means for associating the voltage value of the alternating voltage calculated by the calculation means with the temperature and humidity detected by the detection means, and storing it as history information;
When the abnormal value of the calculated voltage value of the alternating voltage is continuously detected a predetermined number of times, the history information is referred to and the AC voltage corresponding to the past temperature and humidity information approximated to the current temperature and humidity information A search means for searching for a voltage value,
4. The voltage value of the AC voltage is applied to the charging member using the voltage value of the AC voltage approximated to the current temperature and humidity searched by the search unit. 5. Image forming apparatus.