JP2010286767A - Image forming apparatus, and charging bias calibration method for the image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suitably suppressing a cleaning blade from being broken, and to provide a charging bias calibration method therefor. <P>SOLUTION: The image forming apparatus includes: an image carrier; a toner supplying section for supplying toner to the image carrier; a charging member to which charging bias is applied; the cleaning blade for removing the residual toner on a surface of the image carrier; a high voltage generation circuit for applying the charging bias by superposing DC voltage and AC voltage; a voltage control means for controlling the voltage between peaks in the AC voltage to a prescribed value; and a control means for carrying out a calibration control of the charging bias. The image forming apparatus is characterized in that a charged periphery surface is faced toward the cleaning blade in a state where at least a portion of the charged periphery surface of the image carrier charged by a charging member, is covered with the toner. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention makes the surface of an image carrier uniform without damaging a cleaning blade that removes residual toner on the image carrier of an image forming apparatus such as a printer, a copier, a facsimile machine, or a multifunction machine having these functions. The present invention relates to an image forming apparatus and a charging bias calibration method for performing charging bias calibration for determining a charging bias (vibration voltage) for charging.

  2. Description of the Related Art In recent years, many contact charging methods have been adopted as a method for charging the surface of an image carrier of an image forming apparatus such as a printer, a copier, a facsimile machine, or a multifunction machine having these functions. In the contact charging method, a charging member such as a roller type or a blade type is arranged in contact with or close to the surface of the image carrier, and a charging bias in which a DC voltage and an AC voltage are superimposed is applied to the charging member, and the surface of the image carrier This is a method of charging the battery uniformly. The contact charging method is a low-pressure process and has the advantage that it can reduce the generation amount of ozone and can be realized at low cost.

  Patent Document 1 discloses a relationship between an applied AC voltage and a charging potential. Japanese Patent Application Laid-Open No. 2004-133867 describes that when the peak-to-peak voltage value of the AC voltage constituting the charging bias is boosted, the charging bias of the image carrier increases in proportion to the increase of the AC voltage value, and the charging bias is configured. It is disclosed that when the peak-to-peak voltage value reaches a voltage approximately twice the charging start voltage due to the DC voltage, the charging potential is saturated and the charging potential does not change even if the peak-to-peak voltage is further increased. In Patent Document 1, in order to ensure the uniformity of charging, a charging bias having a peak-to-peak voltage more than twice the charging start voltage at the time of applying a DC voltage determined by various characteristics of the image carrier is applied. It is concluded that there is a need and mentions that the charging bias obtained by applying the charging bias depends on the DC component of the applied voltage.

  Based on the suggestion of Patent Document 1, the charging member used in the contact charging method has a peak-to-peak value that is equal to or greater than the inflection point (a value that does not change the charging potential even if the voltage between the peaks of the AC voltage is further increased). A charging bias having a voltage set is applied.

  The inflection point varies depending on various conditions such as a resistance value of the charging member, a use environment (temperature, etc.), and a change with time. When the peak-to-peak voltage exceeding the inflection point increases, the amount of discharge due to reverse discharge increases, and the amount of discharge products (NOx, etc.) adhering to the image carrier increases. As a result, the dynamic frictional resistance on the surface of the image carrier increases, causing problems such as toner slipping (cleaning failure) and blade curling. In order to prevent these problems, bias control called charging bias calibration is executed, and the peak-to-peak voltage is set to the minimum necessary voltage value (voltage value above the inflection point and near the inflection point). .

  Patent Document 2 discloses an example of charging bias calibration. The charging bias calibration disclosed in Patent Document 2 uses a current detection unit to detect a DC current value between the image carrier and the charging member, and between peaks until the detected DC current value becomes a predetermined value or less. Gradually increasing the voltage to determine a target voltage.

JP-A 63-149668 JP 2008-216753 A

  The charging bias calibration of Patent Document 2 includes a step of setting the peak-to-peak voltage to a value exceeding the inflection point in order to determine the target voltage. During this stage, excessive discharge is temporarily generated, and excessive discharge products adhere to a part of the peripheral surface of the image carrier. As a result, the coefficient of dynamic friction in the region where the excessive discharge product is attached increases, leading to a problem that the edge of the cleaning blade is damaged (for example, missing edge or blade sag).

  When the charging bias calibration of Patent Document 2 is executed in a low temperature environment, the resistance value of the charging member is higher than that at room temperature, and therefore the peak applied voltage used for the charging bias calibration is usually It is set higher than. For this reason, a temperature sensor is used for charging bias calibration, but when the temperature detected by the temperature sensor differs from the actual temperature of the charging member, and the actual temperature of the charging member is higher than the detected temperature, The problem of excessive application of the peak-to-peak voltage described above becomes even more remarkable.

  The present invention has been made in view of the above-described problems, and an image forming apparatus that suitably suppresses damage to a cleaning blade caused by application of an excessive peak-to-peak voltage during execution of charging bias calibration, and It is an object of the present invention to provide a charging bias calibration method.

  An image forming apparatus according to an aspect of the present invention that achieves this object includes: an image carrier; and a toner supply unit that supplies toner to the image carrier via a developing roller disposed in the vicinity of the image carrier. A charging member that is disposed in contact with or close to the image carrier and is applied with a charging bias; a cleaning blade that removes toner remaining on the surface of the image carrier; and a direct current voltage and an alternating voltage are superimposed. A high voltage generation circuit for applying a charging bias, voltage control means for controlling the peak-to-peak voltage of the AC voltage to a predetermined value, and control means for performing calibration control of the charging bias, the control means including the The voltage control means is configured to apply the charging bias to the charging member from the high-voltage generation circuit while changing the peak-to-peak voltage of the AC voltage. The image carrier is rotated, and the toner supply unit is started to supply toner to the image carrier, so that at least a part of the charged peripheral surface of the image carrier charged by the charging member is applied to the toner. In a covered state, the charged peripheral surface is directed to the cleaning blade (claim 1). In the above configuration, the developing roller includes a bias applying unit that applies a bias, and the bias applying unit applies a developing bias to the developing roller, whereby the toner is supplied to the image carrier. 2).

  According to the above configuration, the toner supplied to the image carrier covers the high dynamic friction coefficient region caused by the temporary excessive peak-to-peak voltage generated during the charging bias calibration. The frictional force between the bodies is reduced, and preferably, the cleaning blade can be prevented from being damaged.

  In the above configuration, the image forming apparatus further includes a current detection unit, and the current detection unit detects a direct current flowing between the image carrier and the charging member while the charging bias is applied (claim). Item 3). In this configuration, the voltage control means includes a memory, and a predetermined first peak-to-peak voltage value, second peak-to-peak voltage value, and third peak-to-peak voltage value are stored in the memory. The first peak-to-peak voltage value and the second peak-to-peak voltage value are lower than a predetermined reference peak-to-peak voltage value, and the third peak-to-peak voltage value is stored. Is a value higher than the reference peak-to-peak voltage. The predetermined reference peak-to-peak voltage can be, for example, a peak-to-peak voltage that saturates the charging potential of the image carrier. The memory of the voltage control means stores a plurality of values of the first peak-to-peak voltage, a value of the second peak-to-peak voltage, and a value of the third peak-to-peak voltage corresponding to a plurality of different temperatures. Store (claim 5).

  In the above configuration, the apparatus further includes a detection sensor that detects a temperature of the charging member and transmits a signal corresponding to the detected temperature to the voltage control unit, and the voltage control unit is based on a signal from the detection sensor. Reading the first peak-to-peak voltage value, the second peak-to-peak voltage value, and the third peak-to-peak voltage value corresponding to the temperature detected by the detection sensor; and The peak-to-peak voltage of the AC voltage, the read first peak-to-peak voltage value, the read second peak-to-peak voltage value, and the read third peak-to-peak voltage. And the current detection means applies a charging bias including an alternating voltage of the first peak-to-peak voltage and the second peak-to-peak value. Voltage exchange The value of the second direct current during application of the charging bias including the voltage and the value of the third direct current during application of the charging bias including the alternating voltage of the third peak-to-peak voltage It detects (Claim 6).

  In the above configuration, there are various methods for calculating a target charging bias, but in a specific configuration, the current detection unit sends a signal related to the value of the first DC current to the voltage control unit, and Transmitting a signal relating to the value of the second direct current and a signal relating to the value of the third direct current, wherein the voltage control means is configured to transmit the read first peak-to-peak voltage and the read first And calculating a regression line based on the peak-to-peak voltage of 2, the transmitted signal relating to the value of the first DC current and the signal relating to the value of the second DC current, and the value of the calculated regression line The step of calculating the value of the peak-to-peak voltage that is equal to the value of the third DC current is executed (Claim 7). In this specific configuration, the voltage control means adds a predetermined correction value to the value of the peak-to-peak voltage calculated based on the regression line, and the peak-to-peak obtained by adding the predetermined correction value A step of storing the value of the voltage in the memory as a charging bias is executed.

  In the charging bias calibration method according to another curved surface of the present invention, the first charging bias formed by superimposing a first alternating voltage and a direct current voltage having a peak-to-peak voltage lower than a predetermined reference peak-to-peak voltage, A voltage applied to a charging member disposed in contact with or close to the image carrier, and a peak-to-peak voltage different from the peak-to-peak voltage of the first alternating voltage and lower than the reference peak-to-peak voltage The charging member is applied with a second charging bias formed by superimposing the first AC voltage and the DC voltage, a third AC voltage having a peak-to-peak voltage higher than the reference peak-to-peak voltage, and the Applying a third charging bias formed by superimposing a DC voltage to the charging member; the first charging bias; the second charging bias; and the third charging bias. During application, a step of forming a toner layer on the surface of the image carrier charged by the charging member, and removing the image carrier and toner remaining on the surface of the image carrier on the toner layer It comprises the step of supplying between cleaning blades (claim 9). According to the above configuration, the toner supplied to the image carrier covers the high dynamic friction coefficient region caused by the temporary excessive peak-to-peak voltage generated during the charging bias calibration. The frictional force between the bodies is reduced, and preferably, the cleaning blade can be prevented from being damaged.

  As described above, the image forming apparatus and the charging bias calibration method according to the present invention can preferably prevent the cleaning blade from being damaged.

1 is an external view of a digital copying machine to which the present invention is applied. 1 is a schematic diagram showing an internal structure of a digital copying machine to which the present invention is applied. It is a block block diagram of the control means of a digital copying machine. It is a block block diagram of the charge control apparatus to which this invention is applied. It is a figure which shows an example of the alternating voltage waveform used for charging bias calibration. It is a flowchart which shows an example of charging bias calibration. FIG. 7 is a diagram schematically showing the image carrier after the charging bias calibration shown in FIG. 6 is executed. 5 is a flowchart for explaining an interruption operation by an initial voltage adjusting means 95. 5 is a flowchart for explaining an interruption operation by an initial voltage adjusting means 95. It is a figure which shows the calibration curve obtained by performing the charging bias calibration shown in FIG. It is a figure explaining the method of determining the target peak-to-peak voltage value using a charging bias calibration curve. It is a figure which shows the data structure built in the memory of the initial voltage adjustment means. 12 is a flowchart of charging bias calibration described with reference to FIG. 11. FIG. 14 is a diagram schematically showing an image carrier after performing a charging bias calibration described in relation to FIG. 13. It is a figure explaining the effect of a toner layer.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. In the following description, a digital copier is shown as an embodiment of the present invention. However, the present invention is not limited to this, and other devices such as a printer, a facsimile machine, and a multi-function machine having these functions can be used. The present invention can also be applied to other image forming apparatuses.

  FIG. 1 is a perspective view of a digital copying machine. FIG. 2 is a diagram schematically showing the internal structure of the digital copying machine. The digital copying machine 1 includes a document placing unit 2 for setting paper used as a document, an image reading unit 3 for converting data read from the document into electronic data, and an image converted into electronic data by the image reading unit 3. An image forming unit 4 that forms and outputs a toner image on paper based on data, a fixing unit 5 that heats and fixes the toner image output on the paper, and a transport unit 6 that transports the paper A plurality of paper feed cassettes 7 (7a to 7d) each containing different sizes or types of paper, a manual paper feed port (not shown) provided on the left side of the machine, and a plurality of various menus. And an operation unit 8 on which menu setting keys are arranged.

  The image forming unit 4 exposes the image carrier 41, the charging member 42 that is placed in contact with the image carrier 41 and executes a charging process, and the charged image carrier 41 to form an electrostatic latent image. A developing unit 44 (developing roller) that electrostatically attaches toner to the electrostatic latent image formed on the print head 43 and the image carrier 41 to visualize the toner image, and a toner that is filled inside the developing unit. A toner cartridge 45 to be supplied to 44, a transfer unit 46 for transferring the developed toner image to a sheet, a cleaner unit 47 (cleaning blade) for removing and collecting toner remaining on the image carrier 41 after the transfer, and an image. A static elimination lamp 48 is provided for lowering the residual potential on the surface of the carrier 41 and making it uniform. The image carrier 41 is composed of a photoreceptor drum having a photoreceptor in which an amorphous silicon layer, which is a positively chargeable photoconductor, is vapor-deposited on the surface of an aluminum cylinder, and a central support shaft by a driving device (not shown). Is driven around. The charging member 42 is a charging roller and includes a cored bar 421 and an epichlorohydrin rubber layer 422 that covers the cored bar 421. The epichlorohydrin rubber layer 422 is an elastic layer having conductivity. The toner cartridge 45 is an exchange unit, and is replaced with a new toner cartridge 45 when the toner is consumed. The image forming unit 4 further includes a charging control device 9. The charging control device 9 is connected to the charging member 42. The charging control device 9 plays a role of controlling charging of the image carrier 41 by applying a voltage to the charging member 42.

  FIG. 3 is a schematic block diagram showing the control means of the digital copying machine 1. The digital copying machine 1 supervises the image reading control means 100 that controls the reading operation of the original and data by the image reading unit 3 and the system of the digital copying machine 1, and includes the image forming unit 4, the fixing unit 5, and the transport unit 6. And an image output control means 200 for controlling the paper feed cassette 7 and an operation control means 300 for controlling input / output signals of the operation unit 8.

  Each of the control means 100, 200, and 300 includes a single or a plurality of control boards, a single or a plurality of CPUs fixed to the control board, a ROM that stores a control program executed by the CPU, and control data. And an input / output interface circuit that outputs signals to various loads to be controlled and inputs detection values from various sensors. The CPUs are connected to each other via a serial communication line 400 to construct a distributed control system. A predetermined function for causing the digital copying machine 1 to execute an image forming operation is realized by a control program executed by each CPU and related hardware.

  FIG. 4 is a schematic diagram showing the configuration of the charging control device 9. The charging control device 9 includes a high voltage generation circuit 91 that applies a charging bias in which a DC voltage and an AC voltage are superimposed on a charging member 42 disposed in contact with the image carrier 41, and between the image carrier 41 and the charging member 42. A current detection unit 92 that detects a DC current value and a voltage control unit 96 that controls the peak-to-peak voltage value Vpp of the AC voltage to a target voltage are provided.

  The voltage control unit 96 includes an initial voltage adjusting unit 95, an AC voltage unit 94, and a DC voltage control unit 93. The high voltage generation circuit 91 includes a DC voltage power supply 911 and an AC voltage power supply 912. The DC voltage power source 911 outputs an arbitrary DC voltage by a pulse transformer (not shown) under the control of the DC voltage control means 93. Further, the AC voltage power source 912 outputs an AC voltage by a pulse transformer (not shown) under the control of the AC voltage control means 94. The alternating voltage from the alternating voltage power supply 912 is a sine wave having a predetermined frequency and can have an arbitrary peak-to-peak voltage value Vpp.

  The current detection unit 92 detects a direct current value flowing between the image carrier 41 and the charging member 42 generated by the charging bias applied to the charging member 42 from the high voltage generation circuit 91.

  Voltage control means 96 controls the peak-to-peak voltage value Vpp of the AC voltage to the target voltage. As described above, the voltage control means 96 includes the DC voltage control means 93 that controls the DC voltage, the AC voltage control means 94 that controls the AC voltage, and the initial voltage adjustment means 95. The initial voltage adjusting unit 95 plays a role of obtaining the target voltage by gradually increasing the peak-to-peak voltage until the increase amount of the DC current value detected by the current detecting unit 92 becomes a predetermined value or less. The DC voltage control means 93 controls the DC voltage power supply 911 so that a DC voltage having a value designated by the initial voltage adjusting means 95 is applied to the charging member 42. The AC voltage control unit 94 controls the AC voltage power source 912 so that the AC voltage having the peak-to-peak voltage value Vpp indicated by the initial voltage adjusting unit 95 is applied to the charging member 42. The function of the voltage control unit 96 is realized by executing a control program in the image output control unit 200.

  Hereinafter, the initial voltage adjusting means 95 will be described in detail. The initial voltage adjusting means 95 operates when the digital copying machine 1 is turned on or returned from the power saving mode. When the initial voltage adjusting unit 95 receives a signal indicating that the power has been turned on or a signal indicating that the power saving mode has been restored from the operation control unit 300, the initial voltage adjusting unit 95 controls the DC voltage control unit 93 to generate a predetermined DC voltage as a high voltage generation circuit. 91 to output. Here, the predetermined DC voltage is a value when the charging potential of the image carrier 41 mounted on the digital copying machine 1 is adjusted to a predetermined value (for example, 300 V) when the digital copying machine 1 is assembled. It is a DC voltage value (for example, 400V).

  FIG. 5 is a diagram illustrating an example of an AC voltage output from the high voltage generation circuit 91 under the control of the initial voltage adjusting unit 95. When the initial voltage adjusting means 95 receives a signal indicating that the power has been turned on or a signal indicating that the power saving mode has been restored from the operation control means 300, the initial voltage adjusting means 95 controls the AC voltage control means 94 to generate a predetermined AC voltage as a high voltage generation circuit. 91 to output. Here, the predetermined AC voltage is an AC voltage in which the value of the peak-to-peak voltage value Vpp (the voltage value corresponding to the amplitude of the sine wave) increases with time as shown in FIG. For example, the predetermined AC voltage is an AC voltage in which the AC voltage of each peak-to-peak voltage value Vpp is output for 0.5 seconds while increasing the peak-to-peak voltage value Vpp by 100 V from 400 V to 1500 V.

  Initial voltage adjusting means 95 controls AC voltage control means 94 to gradually increase the peak-to-peak voltage value Vpp. Further, the DC current value when the peak-to-peak voltage value Vpp of each value is applied to the charging member 42 is received from the current detection means 92. Further, when the increase amount of the received DC current value becomes equal to or less than a predetermined value, the initial voltage adjusting means 95 determines the peak-to-peak voltage that caused the increase equal to or less than the predetermined value as the target voltage.

  The initial voltage adjusting unit 95 stores the detected direct current value in a RAM provided in the image output control unit 200. The difference between the latest direct current value sent from the current detection means 92 and the latest direct current value stored in the RAM is calculated. When the difference calculated by the initial voltage adjusting unit 95 becomes equal to or less than a predetermined value set in advance, the voltage control unit 96 sets the peak-to-peak voltage value Vpp when the latest DC current value is detected as a new peak-to-peak voltage. Set to the value Vpp. The newly determined peak-to-peak voltage Vpp becomes a target voltage value when the charging control device 9 applies a charging bias to the charging member 42 thereafter. This target voltage value is stored in the RAM. The initial voltage adjusting means 95 takes into account the calculation error and the like when storing the target voltage value, and sets the peak-to-peak voltage value Vpp larger than the above-described target voltage value by a predetermined ratio (for example, 5 to 10%). It can also be stored as a voltage value. On the other hand, when the difference calculated by the initial voltage adjusting unit 95 is larger than a preset value, the voltage control unit 96 determines that the calculated difference is equal to or less than the preset value or the peak-to-peak voltage value. The DC voltage control means 93 and the AC voltage control means 94 are controlled to continue application of the charging bias until Vpp becomes larger than the maximum value (in this embodiment, 1500 V which is the maximum value of the predetermined AC voltage described above). .

  When the digital copying machine 1 is powered on or returned from the power saving mode, the initial voltage adjusting means 95 operates as described above.

  As shown in FIG. 4, the digital copying machine 1 includes an environment sensor 10. In the example shown in FIG. 4, the environmental sensor 10 is disposed above the charging member 42, but the present embodiment is not limited to this, and the environmental temperature and environmental humidity of the charging member 42 can be detected. Arranged at any possible position (position near the charging member 42). When the environmental temperature and environmental humidity detected by the environmental sensor 10 are in a predetermined range and the target voltage obtained by the initial voltage adjusting means 95 is equal to or higher than the predetermined voltage, the image forming operation is performed. The initial voltage adjusting means 95 is interrupted.

  The interruption operation of the initial voltage adjusting means 95 is executed at a predetermined interval during the image forming operation. When the image forming operation continues for a predetermined time, the interruption operation of the initial voltage adjusting unit 95 is finished.

  When the interruption operation of the initial voltage adjusting unit 95 is executed, the initial voltage adjusting unit 95 performs the environmental sensor 10 during the process of obtaining the target voltage performed when the digital copying machine 1 is turned on or returned from the power saving mode. Whether the temperature detected by is in a preset range (15 degrees or less in this embodiment) and the humidity detected by the environmental sensor 10 is a preset range (60% RH or more in this embodiment). Judge whether or not.

  If the above condition is satisfied, the initial voltage adjusting means 95 sets a special mode reserve flag. The special mode reserve flag is set, for example, by changing a predetermined address assigned to the RAM of the image output control means 200 from 0 to 1. On the other hand, when the above condition is not satisfied, the initial voltage adjusting means 95 does not set the special mode reserve flag.

  A special mode reserve flag is set, and the target stored in the RAM provided in the image output control means 200 is obtained as a result of the process for obtaining the target voltage when the digital copying machine 1 is turned on or returned from the power saving mode. When the voltage value is equal to or higher than a preset value (for example, 1400 V in this embodiment), the initial voltage adjusting unit 95 sets a special mode flag. The special mode flag is set by changing a predetermined address (an address different from the special mode preliminary flag) assigned to the RAM of the image output control unit 200 from 0 to 1, like the special mode preliminary flag. The special mode reserve flag is lowered (returned from 1 to 0) by the initial voltage adjusting means 95 after the special mode flag is set. On the other hand, when the target voltage value is less than the preset value of 1400 V, or when the special mode reserve flag is not set, the initial voltage adjusting means 95 does not set the special mode flag.

  When the special mode flag is set, the initial voltage adjusting means 95 performs an interrupt operation during the image forming operation of the digital copying machine 1 to execute the special mode operation. On the other hand, when the special mode flag is not set, the initial voltage adjusting unit 95 does not execute the special mode operation, and the image output control unit 200 executes the normal image forming operation.

  When the image forming operation starts with the special mode flag set, the initial voltage adjusting unit 95 sends an interruption signal to the image output control unit 200 at regular intervals (60 seconds in this embodiment) to output an image. The image forming operation under the control of the control unit 200 is interrupted. Thereafter, in the same manner as when the digital copying machine 1 is turned on or returned from the power saving mode, the initial voltage adjusting means 95 executes a process for obtaining the target voltage.

  When the execution of the process for obtaining the target voltage is completed, the initial voltage adjusting unit 95 determines that the special mode flag is set when the newly obtained target voltage value is equal to or higher than a preset value (for example, 1400 V in the present embodiment). The image output operation is restarted by the image output control means 200. Since the image forming operation resumed by the image output control means 200 is in a state where the special mode flag is set, it is interrupted again by the initial voltage adjusting means 95 after 60 seconds. On the other hand, when the newly obtained target voltage value is less than a preset value (for example, 1400 V in this embodiment), the initial voltage adjusting means 95 lowers the special mode flag (returns from 1 to 0). Then, the image output control unit 200 restarts the image forming operation.

  When the above-described processing for obtaining the target voltage with interruption of the image forming operation is repeated a predetermined number of times (for example, 10 times in this embodiment), that is, for a total of 10 minutes, the initial voltage adjusting unit 95 sets the special mode flag. The image forming operation by the image output control means 200 is interrupted or resumed.

  FIG. 6 is a flowchart for explaining the process of executing the charging bias calibration and determining the charging bias. When the power of the digital copying machine 1 is turned on or when the digital copying machine 1 returns from the power saving mode (S100), the operation control means 300 transmits a trigger signal for starting the charging bias calibration to the image output control means 200. To do. The image output control means 200 operates the image forming unit 4 and the image carrier 41 rotates (S101). At the same time or thereafter, the image output control unit 200 transmits an operation signal to a bias power source provided in the developing unit 44, and the bias power source applies a development bias to the developing roller. As a result, the toner is adhered to the image carrier 41 from the developing unit 44 (S102). At this time, the image output control unit 200 transmits an operation signal to a bias power source provided in the transfer unit 46, and the bias power source of the transfer unit 46 applies a reverse polarity bias to the transfer unit during normal printing. . As a result, the toner adhered to the image carrier 41 reaches the cleaner unit 47. The initial voltage adjusting means 95 controls the DC voltage control means 93 and the AC voltage control means 94 to output a DC voltage from the DC voltage power supply 911 and to obtain a predetermined peak-to-peak voltage value Vpp (initial value) from the AC voltage power supply 912. An AC voltage is output, and a charging bias obtained by superimposing these DC voltage and AC voltage is applied to the charging member 42 (S103). As shown in FIG. 2, since the developing unit 44 is located downstream of the charging member 42 in the rotation direction of the image carrier 41, the charging bias is applied before the developing bias is applied. Also good. However, in this case, the developing bias is applied before the peripheral surface region of the image carrier 41 to which the charging bias is applied passes through the developing unit 44.

  The current detecting unit 92 detects the direct current value flowing through the charging member 42 by applying the charging bias, and sends the detected direct current value to the initial voltage adjusting unit 95 (S104). The initial voltage adjusting means 95 calculates the difference between the direct current value sent and the direct current value sent and stored previously (S105).

  When the difference calculated in the initial voltage adjusting unit 95 becomes a predetermined value (for example, approximately zero or less) set in advance (S106), the initial voltage adjusting unit 95 detects when the transmitted direct current value is detected. The peak-to-peak voltage value Vpp is stored as a target voltage value (S107). On the other hand, when the difference calculated in the initial voltage adjusting means 95 is larger than a predetermined value (S106), and the peak-to-peak voltage value Vpp when the transmitted DC current value is detected is less than the maximum value (for example, 1500 V). (S108), the initial voltage adjusting means 95 controls the AC voltage control means 94 to increase the peak-to-peak voltage value Vpp by a certain value (for example, 100V) (S109), and charge using the increased peak-to-peak voltage value Vpp. A charging bias is applied to the member 42 (S110). When the difference calculated in the initial voltage adjusting means 95 is larger than a predetermined value (S106), and the peak-to-peak voltage value Vpp when the transmitted direct current value is detected is larger than the maximum value (for example, 1500 V) (S108). For example, the initial voltage adjusting unit 95 controls the operation control unit 300 to display a warning message on a liquid crystal touch panel or the like provided in the operation unit 8 of the digital copying machine 1, and then ends the process (S111).

  FIG. 7 is a schematic diagram showing a state where the region on the image carrier 41 to which the charging bias is first applied has reached the cleaner unit 47 in the step of determining the target voltage value according to the flowchart shown in FIG. In FIG. 7, a region denoted by reference numeral 410 is a peripheral surface region of the image carrier 41 charged by the charging member 42. In FIG. 7, a layer denoted by reference numeral 411 is a toner layer in which the toner from the developing unit 44 is formed on the peripheral surface of the image carrier 41. As described above, the developing bias is applied before the leading region charged by the charging member 42 passes through the developing unit 44, and the toner layer 411 is formed on the circumferential surface of the image carrier 41. Therefore, the toner layer covers the area charged by the charging member 42. As a result, when the region charged by the charging member 42 passes through the cleaner unit 47, the toner layer 411 exists between the cleaner unit 47 and the image carrier 41. The toner layer 411 serves as a lubricating layer. Therefore, even if the dynamic friction coefficient on the peripheral surface of the image carrier 41 is locally increased due to the application of the charging bias, the toner layer covers a region where the dynamic friction coefficient is high, so that the cleaner 47 is prevented from being damaged. It will be.

  8 and 9 are flowcharts showing the interruption operation by the initial voltage adjusting means 95. FIG. When the power of the digital copying machine 1 is turned on or when the digital copying machine 1 returns from the power saving mode (S200), the initial voltage adjusting means 95 is within the range in which the temperature detected by the environment sensor 10 is set in advance and the environment sensor. It is determined whether or not the humidity detected by 10 is within a preset range (S201). When both the detected temperature and humidity are values within a preset range, the initial voltage adjusting means 95 sets a special mode preliminary flag (S202).

  Thereafter, the target voltage calculation process described using the flowchart shown in FIG. 6 is performed (S203), and the initial voltage adjusting means 95 determines whether or not the target voltage value obtained in step S203 is equal to or greater than a predetermined value. Judgment is made (S204). If the obtained target voltage value is equal to or higher than a preset value (for example, 1400 V) and the special mode preliminary flag is set in step S202, the initial voltage adjusting means 95 sets the special mode flag. Stand up (S205).

  When the digital copying machine 1 has not started the image forming operation (S206), when the power of the digital copying machine 1 is turned off or the digital copying machine 1 enters the power saving mode (S207), the power of the digital copying machine 1 is turned on. Or when the digital copying machine 1 returns from the power saving mode, the processing from step S200 is repeated.

  On the other hand, when the digital copying machine 1 has started the image forming operation (S206) and the special mode flag is not set (S208), the image output control means 200 performs normal image formation. The operation is executed (S213). When the digital copying machine 1 has started the image forming operation (S206) and the special mode flag is set (S208), the initial voltage adjusting means 95 interrupts the image forming operation. Then, the same target voltage calculation process as in step S203 is performed (S210).

  When the target voltage value obtained in the target voltage calculation process in step S210 is less than 1400 V (S211), the initial voltage adjusting unit 95 lowers the special mode flag (S212), and performs an image forming operation on the image output control unit 200. It is restarted (S213).

  On the other hand, if the target voltage value obtained by the target voltage calculation process in step S210 is 1400 V or more (S211), but the number of executions of the image forming operation for 60 seconds has not reached 10 times (S214), the initial voltage The adjustment unit 95 causes the image output control unit 200 to execute an image forming operation for 60 seconds (S209). Note that the initial voltage adjusting means 95 stores the number of executions increased by one count.

  When the target voltage value obtained in the target voltage calculation process in step S210 is 1400 V or more (S211) and the number of executions of the image forming operation for 60 seconds in step S209 has reached 10 (S214), The initial voltage adjusting unit 95 lowers the special mode flag (S215) and then controls the operation control unit 300 to display a warning message on the liquid crystal touch panel or the like provided in the operation unit 8 of the digital copying machine 1, for example. The process is terminated (S216).

  FIG. 10 is a graph showing a calibration curve obtained by changing the AC peak-to-peak voltage value Vpp as described above. The horizontal axis shows the AC peak-to-peak voltage Vpp, and the vertical axis shows the DC current detection value. Indicates. Of the curves shown in FIG. 10, the curve indicating the increase in the detected DC current value at the low AC peak-to-peak voltage Vpp is a curve obtained in a temperature environment of 23 ° C., and the DC at the high AC peak-to-peak voltage Vpp. A curve indicating an increase in the current detection value is a curve obtained in a temperature environment of 10 ° C. The calibration curve shown in FIG. 10 outputs, for example, the output signal of the AC voltage power supply 912, the output signal of the current detection unit 92, and the output signal of the environment sensor 10 to an appropriate storage medium such as a memory or a recording medium such as a plotter. Can be obtained. In the example shown in FIG. 10, in the environment of 23 ° C., the curve of the DC current detection value reaches an inflection point at an AC peak voltage of about 1000 V, and the AC peak voltage of about 1600 V in the environment of 10 ° C. It turns out that an inflection point is reached.

  FIG. 11 is a diagram illustrating a method for calculating the target voltage more simply than the target voltage calculation method described in detail with reference to FIG. When a calibration curve as shown in FIG. 10 is obtained or for each environmental temperature, an approximate value (that is, an inflection point) of the peak-to-peak voltage Vpp at which the decrease in the increase rate of the DC current detection value starts is experienced When it is known in principle (that is, when the value of the peak-to-peak voltage Vpp at which the charging potential of the image carrier 41 is saturated), the target peak-to-peak voltage Vpp can be easily determined. First, two voltage values V1 and V2 below the AC peak-to-peak voltage Vf corresponding to the inflection point and one voltage value V3 above the AC peak-to-peak voltage Vf are arbitrarily determined. In the example shown in FIG. 11, the two voltage values V1 lower than the AC peak-to-peak voltage Vf are AC peak-to-peak voltages lower than the voltage value V2. When the calibration curve is already obtained, it is preferable to determine the voltage values V1 and V2 from the range of the AC peak-to-peak voltage in which the increase rate of the DC current detection value is substantially constant.

  A developing bias is applied while rotating the image carrier 41 of the image forming unit 4 using the image output control means 200, and formation of a toner layer on the circumferential surface of the image carrier 41 is started. While forming the toner layer, a charging bias including an alternating voltage component having the selected peak-to-peak voltages V1, V2, V3 is further applied to the charging member 42 under the control of the initial voltage adjusting means 95. Thereafter, DC currents I1, I2, and I3 between the charging member 42 and the image carrier 41 generated by the selected peak-to-peak voltages V1, V2, and V3 are detected using the current detection unit 92, respectively. In the example shown in FIG. 11, the DC current I1 corresponds to the peak-to-peak voltage V1, the DC current I2 corresponds to the peak-to-peak voltage V2, and the DC current I3 corresponds to the peak-to-peak voltage V3. By this operation, points P1 (V1, I1) and P2 (V2, I2) can be determined in the two-dimensional coordinates. Here, a linear function F (Vpp) passing through the points P1 and P2 is calculated, and a peak-to-peak voltage Vg at which the value of the function F (Vpp) is I3 is calculated. Furthermore, considering an error between the calibration curve used and the actual relationship between the AC voltage Vpp and the DC current detection value, an arbitrary correction value ΔV (for example, 100 V) is added to the obtained peak-to-peak voltage Vg, This can be set as a target charging bias Vt.

  FIG. 12 shows a data structure stored in the memory of the initial voltage adjusting means 95. In the initial voltage adjusting means 95, three peak-to-peak voltage values V1, V2, and V3 corresponding to a plurality of temperatures are stored. In the example shown in FIG. 12, three peak-to-peak voltages determined based on a calibration curve corresponding to a temperature of 10 ° C. and three peak-to-peak voltages determined based on a calibration curve corresponding to a temperature of 23 ° C. It is shown. When the temperature of the charging member 42 is detected by the environmental sensor 10 and a signal corresponding to the detected temperature is sent to the initial voltage adjusting means 95, the initial voltage adjusting means 95 refers to the data structure in the memory, and The corresponding three temperatures are read from the data structure stored in. For example, when the environmental sensor 10 detects a temperature of 23 ° C., the initial voltage adjusting unit 95 reads out the peak-to-peak voltages V1 (500V), V2 (800V), and V3 (1400V) corresponding to the temperature of 23 ° C. The initial voltage adjusting means 95 sends a signal to the AC voltage control means 94 so as to sequentially apply these three read voltages. As a result, a charging bias having an AC voltage component of 500 V peak-to-peak voltage, a charging bias having an AC voltage component of 800 V peak-to-peak voltage, and a charging bias having an AC voltage component of 1400 V peak-to-peak voltage are sequentially added to the charging member. 42 is applied. Thereafter, the target voltage is determined based on the principle described with reference to FIG.

  FIG. 13 is a flowchart showing the operation of the digital copying machine 1 when the target voltage calculation method related to FIG. 11 is used. When the power of the digital copying machine 1 is turned on or when the digital copying machine 1 returns from the power saving mode (S300), the operation control unit 300 transmits a trigger signal for starting the charging bias calibration to the image output control unit 200. To do. The environmental sensor 10 detects the temperature of the charging member 42 and transmits a signal related to the detected temperature to the initial voltage adjusting means 95 (S301). As described with reference to FIG. 12, the initial voltage adjusting unit 95 refers to the data structure in the memory and determines the three peak-to-peak voltages V1, V2, and V3 to be applied (S302). Thereafter, the image output control unit 200 operates the image forming unit 4 and the image carrier 41 rotates (S303). At the same time or thereafter, the image output control unit 200 transmits an operation signal to a bias power source provided in the developing unit 44, and the bias power source applies a development bias to the developing roller. As a result, the toner is attached to the image carrier 41 from the developing unit 44 (S304). At this time, the image output control unit 200 transmits an operation signal to a bias power source provided in the transfer unit 46, and the bias power source of the transfer unit 46 applies a reverse polarity bias to the transfer unit during normal printing. . As a result, the toner adhered to the image carrier 41 reaches the cleaner unit 47. The initial voltage adjusting unit 95 controls the DC voltage control unit 93 and the AC voltage control unit 94 to output a DC voltage from the DC voltage power supply 911 and from the AC voltage power supply 912 to the three peak-to-peak voltages determined in Step 302. The AC voltage having the value Vpp is sequentially output, and a charging bias obtained by superimposing the DC voltage and the AC voltage is applied to the charging member 42 (S305). As shown in FIG. 2, since the developing unit 44 is located downstream of the charging member 42 in the rotation direction of the image carrier 41, the charging bias is applied before the developing bias is applied. Also good. However, in this case, the developing bias is applied before the peripheral surface region of the image carrier 41 to which the charging bias is applied passes through the developing unit 44.

  The current detecting unit 92 detects the direct current value flowing through the charging member 42 by applying the charging bias, and sends the detected direct current value to the initial voltage adjusting unit 95 (S306). The initial voltage adjusting means 95 determines a target peak-to-peak voltage value (target voltage value) using the technique related to FIG. 11 (S307).

  If the determined target voltage value is equal to or less than the maximum value (for example, 1500 V) assigned to the peak-to-peak voltage Vpp (S308), the determined target voltage value is stored in the memory of the initial voltage adjusting means 95. (S309). On the other hand, when the determined target voltage value exceeds the maximum value (for example, 1500 V) assigned to the peak-to-peak voltage Vpp (S 1500), the initial voltage adjusting unit 95 controls the operation control unit 300 to perform digital copying, for example. After displaying a warning message on a liquid crystal touch panel or the like provided in the operation unit 8 of the machine 1, the process is terminated (S310).

  FIG. 14 is a schematic diagram showing a state in which the step of determining the target voltage value is completed according to the flowchart shown in FIG. In the example shown in FIG. 14, three regions 410 on the image carrier 41 charged by the charging member 42 are shown. In FIG. 14, a layer denoted by reference numeral 411 is a toner layer in which the toner from the developing unit 44 is formed on the peripheral surface of the image carrier 41. As described above, the developing bias is applied before the leading region charged by the charging member 42 passes through the developing unit 44, and the toner layer 411 is formed on the circumferential surface of the image carrier 41. Therefore, the toner layer covers the area charged by the charging member 42. As a result, when the region to which the charging bias is applied passes through the cleaner unit 47, the toner layer 411 exists between the cleaner unit 47 and the image carrier 41. The toner layer 411 serves as a lubricating layer. Therefore, even if the dynamic friction coefficient on the peripheral surface of the image carrier 41 is locally increased due to the application of the charging bias, the toner layer covers a region where the dynamic friction coefficient is high, so that the cleaner 47 is prevented from being damaged. It will be. Further, as apparent from comparison with the example shown in FIG. 7, when the target voltage is determined according to the procedure shown in FIG. 13, there are only three regions charged using different peak-to-peak voltages, It is possible to significantly reduce the amount of toner covering these regions.

  In the embodiment described with reference to FIGS. 11 to 14, the peak-to-peak voltage Vpp as the target value is determined using the temperature of the charging member 42, but instead of the temperature of the charging member 42, the charging member 42 is used. A similar technique can be adopted based on the ambient humidity. Alternatively, the use of a three-dimensional calibration curve and a three-dimensional data structure using the temperature of the charging member 42 and the humidity around the charging member 42 are also included in the present embodiment.

(Test Example 1)
FIG. 15 is a diagram illustrating the effect of the toner layer 411. FIG. 15A shows fluctuations in rotational torque of the image carrier 41 when charging bias calibration is executed without applying the developing bias and without forming the toner layer 411 in the flowchart shown in FIG. FIG. 15A shows the fluctuation of the rotational torque of the image carrier 41 when the charging bias calibration is executed in accordance with the procedure shown in the flowchart of FIG. The rotational torque of the image carrier 41 was measured as the current value of the drive motor of the image carrier 41.

In this test example, the image carrier was rotated at a linear velocity of 300 mm / sec while performing the charging bias calibration. Further, the cleaning blade used in this test example was a new one, and had characteristics of a rebound resilience of 15%, a hardness of 73 degrees, a 300% modulus of 500 kgf / cm ² , and a tan δ peak temperature of 9 ° C. Furthermore, this test example was performed in a low temperature environment of 10 ° C. in order to make the environment easy to generate reverse discharge. The three peak-to-peak voltages V1, V2, and V3 were 800V, 1300V, and 2200V, respectively, and the charging bias application time using each peak-to-peak voltage was 400 msec.

The developing bias application time was set to 50 msec. Further, the toner consumption when forming the toner layer 411 was 0.20 mg / cm ² , and this consumption was about half of the toner consumption during normal printing. Therefore, the total consumption of toner used in the test example shown in FIG. 15B was 8.9 mg (0.20 mg / cm ² × 300 mm / sec × 50 msec × paper width (A3) 297 mm).

  Referring to FIG. 15A, when the toner layer 411 is not formed, the rotational torque of the image carrier 41 becomes noticeable when a charging bias including an AC voltage component having a peak-to-peak voltage exceeding the inflection point is applied. It can be seen that it increases. This means that the discharge product has adhered to the image carrier 41 as a result of the application of the charging bias including the AC voltage component of the peak-to-peak voltage exceeding the inflection point. It also means that the discharge product increases the dynamic friction coefficient of the peripheral surface of the image carrier 41 and increases the frictional resistance generated between the cleaning blade 47 and the image carrier 41. This means that a physical load (stress) is generated on the cleaning blade 47 at the same time. On the other hand, referring to FIG. 15B, an increase in the rotational torque of the image carrier 41 as observed in FIG. 15A is not observed. This means that the toner layer 411 suitably covers the peripheral surface region of the image carrier 41 charged by the charging member 42 and functions as a lubricating layer.

(Test Example 2)
In this test example, the occurrence of an image defect of the entire half-density image after performing the charging bias calibration a plurality of times without forming the toner layer 411 described with reference to FIG. 15A, and FIG. The toner layer 411 described in connection with the above was formed, and the occurrence of image defects in the entire half-density image after performing the charging bias calibration a plurality of times was compared. Table 1 shows the test results. Note that the image defect was determined by checking three images at each charging bias calibration.

  When the toner layer 411 was not formed, an image defect appeared when the charging bias calibration was executed five times or more. After the charge bias calibration was performed five times, when the image was confirmed, one vertical stripe image appeared from the middle of the second sheet. After the charging bias calibration was performed 10 times, two vertical stripe images could be confirmed, and after the charging bias calibration was performed 15 times, four vertical stripe images could be confirmed. . On the other hand, when the toner layer 411 was formed, no image defect related to the vertical stripe image was confirmed.

  In order to verify the cause of the image defect, the charging bias calibration was repeated five times, and after confirming one vertical stripe image, the edge of the cleaning blade was observed using a microscope. As a result, a chip having a length of about 100 μm and a depth of about 25 μm was confirmed. From this, it can be seen that the region of the high dynamic friction coefficient described above damages the cleaning blade 47. Further, it can be seen that the toner layer 411 suitably prevents the cleaning blade 47 from being damaged.

  In the above-described embodiment, a photoconductor drum having a photoconductor in which an amorphous silicon layer as a positively chargeable photoconductor is deposited on the surface of an aluminum cylinder is used as the image carrier 41. However, the photoconductor is an organic light. An OPC drum that is a conductor or another type of photoconductive semiconductor drum whose photoconductor is selenium or the like may be employed.

  Further, in the above-described embodiment, the charging member 42 is configured as a charging roller in which the core metal 421 is coated with the chlorohydrin rubber layer 422 which is a conductive elastic material. However, the fur brush, felt, cloth It may be configured with a shape or material such as. In the above-described embodiment, the configuration in which the charging member 42 is disposed in contact with the image carrier 41 has been described. However, the charging member 42 may be disposed in proximity to the image carrier 41. .

  In the above-described embodiment, the configuration in which the current detection unit 92 is provided outside the high-voltage generation circuit 91 has been described. However, the configuration may be provided in the high-voltage generation circuit 91.

  In the above-described embodiments, the waveform of the AC voltage of the charging bias is a sine wave, but it may be a rectangular wave, a triangular wave, a pulse wave, or the like.

  The above-described embodiments are merely examples of the present invention, and the scope of the present invention is not limited by the above description. The specific configuration of each part is within the scope of the effects of the present invention. Needless to say, it can be changed as appropriate.

  The present invention is applicable to various image forming apparatuses such as a printer, a copying machine, a facsimile machine, and a multifunction machine having these functions in addition to the digital copying machine described above.

1. Digital copier (image forming device)
10 .... Environmental sensor (detection sensor)
41... Image carrier 42... Charging member 44.
47... Cleaning blade 91... High voltage generation circuit 92... Current detection means 96.

Claims (9)

An image carrier;
A toner supply unit for supplying toner to the image carrier through a developing roller disposed in the vicinity of the image carrier;
A charging member that is disposed in contact with or close to the image carrier and is provided with a charging bias;
A cleaning blade for removing toner remaining on the surface of the image carrier;
A high voltage generating circuit for applying a charging bias formed by superimposing a DC voltage and an AC voltage;
Voltage control means for controlling the peak-to-peak voltage of the AC voltage to a predetermined value;
Control means for performing calibration control of the charging bias,
The control means causes the voltage control means to apply the charging bias to the charging member from the high-voltage generation circuit while changing the peak-to-peak voltage of the AC voltage, and further, the control means includes the image Rotating the carrier and causing the toner supply unit to start supplying toner to the image carrier;
2. An image forming apparatus according to claim 1, wherein at least a part of a charging peripheral surface of the image carrier charged by the charging member is covered with the toner, and the charging peripheral surface faces the cleaning blade. The developing roller comprises a bias applying means for applying a bias;
The image forming apparatus according to claim 1, wherein the bias applying unit applies a developing bias to the developing roller to supply the toner to the image carrier. The image output control means further comprises a current detection means,
3. The image forming apparatus according to claim 1, wherein the current detection unit detects a direct current flowing between the image carrier and the charging member while the charging bias is applied. The voltage control means comprises a memory;
A predetermined first peak-to-peak voltage value, second peak-to-peak voltage value, and third peak-to-peak voltage value are stored in the memory,
The first peak-to-peak voltage value and the second peak-to-peak voltage value are lower than a predetermined reference peak-to-peak voltage value,
The image forming apparatus according to claim 3, wherein a value of the third peak-to-peak voltage is higher than the reference peak-to-peak voltage.   The memory of the voltage control means stores a plurality of first peak-to-peak voltage values, a second peak-to-peak voltage value, and a third peak-to-peak voltage value corresponding to a plurality of different temperatures. The image forming apparatus according to claim 4. The image output control means further comprises a detection sensor for detecting a temperature of the charging member and transmitting a signal corresponding to the detected temperature to the voltage control means,
The voltage control means, based on the signal from the detection sensor, the first peak-to-peak voltage value, the second peak-to-peak voltage value, and the third peak corresponding to the temperature detected by the detection sensor. The step of reading the value of the inter-voltage,
During the charge calibration, the peak-to-peak voltage of the AC voltage is changed to the read first peak-to-peak voltage value, the read second peak-to-peak voltage value, and the read first peak-to-peak voltage value. Performing a step of changing to a peak-to-peak voltage of 3;
A value of the first direct current while the current detecting means is applying a charging bias including the alternating voltage of the first peak voltage and a charging bias including the alternating voltage of the second peak voltage And a third DC current value during application of a charging bias including an AC voltage of the third peak-to-peak voltage. The image forming apparatus according to claim 5. The current detection means transmits to the voltage control means a signal related to the value of the first DC current, a signal related to the value of the second DC current, and a signal related to the value of the third DC current;
The voltage control means includes the read first peak-to-peak voltage, the read second peak-to-peak voltage, the signal related to the value of the transmitted first DC current, and the second DC Calculating a regression line based on a signal relating to the value of the current;
7. The image forming apparatus according to claim 6, wherein a step of calculating a peak-to-peak voltage value at which the calculated regression line value is equal to the third DC current value is executed. The voltage control means adding a predetermined correction value to the value of the peak-to-peak voltage calculated based on the regression line;
8. The image forming apparatus according to claim 7, wherein the step of storing the value of the peak-to-peak voltage obtained by adding the predetermined correction value in the memory as the peak-to-peak voltage used for the charging bias is executed. A first charging bias formed by superimposing a first AC voltage and a DC voltage having a peak-to-peak voltage lower than a predetermined reference peak-to-peak voltage is applied to a charging member disposed in contact with or close to the image carrier. Applying, and
A second charge formed by superimposing the DC voltage and the first AC voltage having a peak-to-peak voltage different from the peak-to-peak voltage of the first AC voltage and lower than the reference peak-to-peak voltage. Applying a bias to the charging member;
Applying a third charging bias formed by superimposing the DC voltage and a third AC voltage having a peak-to-peak voltage higher than the reference peak-to-peak voltage to the charging member;
Forming a toner layer on the surface of the image carrier charged by the charging member while applying the first charging bias, the second charging bias, and the third charging bias;
A charging bias calibration method comprising: supplying the toner layer between the image carrier and a cleaning blade for removing toner remaining on the surface of the image carrier.

Images