JP2015148789A - Image forming apparatus and charging voltage control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control application of a charging voltage, by use of an appropriate charging voltage according to film thickness of a photoreceptor drum, regardless of changes in surrounding environment and secular change of the film thickness.SOLUTION: An image forming apparatus 1 includes: a film thickness detection section 102 which detects film thickness of a surface of a photoreceptor drum 21, on the basis of I-V characteristics indicated by a charging current in applying a plurality of different voltages; a temperature sensor 77 and a humidity sensor 78 for detecting ambient temperature and humidity of a charging device 22 and the photoreceptor drum 21; a film thickness correction section 104 which corrects the detected film thickness by use of a correction value determined according to the detected temperature and humidity; and a determination section 105 which determines a charging voltage corresponding to the corrected film thickness. An application bias control section 101 causes a charging-voltage application section 223 to apply the determined voltage as a charging voltage during image formation.

Description

  The present invention relates to an image forming apparatus and a charging voltage control method, and more particularly to a technique for controlling application of a charging voltage in accordance with a change in film thickness provided on a peripheral surface of an image carrier.

  In an image forming apparatus such as a printer or a multifunction peripheral, an electrostatic latent image is formed by charging and exposing a surface layer formed on the peripheral surface of an image carrier such as a photosensitive drum, and toner is supplied by a developing device. The toner image generated in this way is transferred onto the recording paper by the transfer unit, whereby the image is formed on the recording paper. In a mechanism for charging a photosensitive drum having a surface layer made of OPC (organic optical conductor) with a charging roller, a film as a photosensitive layer on the surface of the photosensitive drum is scraped by repeating this image formation. If the thickness of this film is reduced, the current that flows when a charging voltage is applied to the charging roller changes, so the surface potential of the photosensitive drum changes even when the same charging voltage is applied, and the target surface potential is changed. Cannot be obtained. Thus, charging voltage control is known in which the film scraping amount of the photosensitive drum is predicted from the driving time of the image forming apparatus, and the charging voltage is changed according to the driving time. However, this technology does not determine the charging voltage by detecting the actual film thickness, but the predicted amount of film scraping may differ from the actual film thickness. Even in this case, the target surface potential may not be obtained.

  For this reason, as shown in Patent Document 1 below, a technique for estimating the film thickness of the photoreceptor from the inclination of the relationship between the charging voltage and the detected charging current has been proposed. Patent Document 2 below proposes a technique for calculating and estimating the resistance value of the charging member and the film thickness of the photosensitive layer from the equation of Paschen's law, and determining the charging application voltage according to the estimated film thickness. Yes.

Japanese Patent No. 3064643 Japanese Patent Laid-Open No. 9-185220

  However, the technique disclosed in Patent Document 1 does not determine a charging voltage corresponding to the film thickness of the photosensitive drum. In addition, when the surrounding environment changes, the estimated film thickness may deviate from the actual film thickness. On the other hand, in the technique disclosed in Patent Document 2, the charging voltage is determined in accordance with the estimated film thickness of the photosensitive layer. As described above, this film thickness is an estimated value calculated from Paschen's law equation. Since the influence of the surrounding environment is not considered, if the surrounding environment changes, the surface potential obtained by applying the charging voltage may deviate from the target surface potential.

  The present invention has been made to solve the above problems, and uses an appropriate charging voltage according to the film thickness of an image carrier such as a photosensitive drum, regardless of changes in the surrounding environment and aging. Thus, it is an object to control charging voltage application.

An image forming apparatus according to an aspect of the present invention includes a voltage applying unit that applies a plurality of different voltages to a charging body that charges a peripheral surface of an image carrier,
A charging current detection unit that detects a charging current at the time of application of the plurality of voltages by the voltage application unit;
A film thickness detector that detects a film thickness provided on the peripheral surface of the image carrier based on an IV characteristic indicated by a charging current detected by the charging current detector when the different voltages are applied;
An ambient environment value detector that detects an ambient environment value composed of at least one of ambient temperature and ambient humidity of the charged body and the image carrier;
A film thickness correction unit that corrects the film thickness detected by the film thickness detection unit using a correction value determined according to the ambient environment value detected by the ambient environment value detection unit;
A determining unit that determines a charging voltage corresponding to the film thickness corrected by the film thickness correcting unit;
An application bias control unit that performs voltage application control that causes the voltage application unit to apply the voltage determined by the determination unit to the charged body as a charging voltage at the time of image formation is provided.

Further, the charging voltage control method according to another aspect of the present invention includes a voltage application step of applying a plurality of different voltages to a charging body that charges the peripheral surface of the image carrier,
A current detection step of detecting a charging current when applying the plurality of voltages;
A film thickness detecting step for detecting a film thickness provided on a peripheral surface of the image carrier based on an IV characteristic indicated by a charging current detected when a plurality of different voltages are applied;
An ambient environment value detecting step of detecting an ambient environment value comprising at least one of ambient temperature and ambient humidity of the charged body and the image carrier;
A film thickness correction step for correcting the detected film thickness using a correction value determined according to the detected ambient environment value;
A determining step for determining a charging voltage corresponding to the corrected film thickness;
An application bias control step of applying a charging voltage to the charged body by a voltage application unit using the determined voltage as a charging voltage at the time of image formation.

  According to the present invention, the film thickness of the image carrier is detected based on the IV characteristics, the detected film thickness is corrected according to the surrounding environment, and the charging voltage corresponding to the corrected film thickness is then obtained. Since the charging voltage application control is performed using the, an appropriate charging voltage can be applied to the charging body according to the film thickness of the image carrier that changes over time even when the surrounding environment changes. . For this reason, it is possible to realize charging voltage application control that maintains the surface potential of the image carrier at a target value regardless of changes in the surrounding environment and aging of the film thickness.

1 is a front sectional view showing a structure of an image forming apparatus according to a first embodiment of the present invention. It is front sectional drawing which shows the structure of an image formation part. FIG. 2 is a functional block diagram schematically showing a main internal configuration of the image forming apparatus according to the first embodiment. It is a figure which shows the IV characteristic for every film thickness of the photosensitive layer of the photoreceptor drum surface with a graph. It is a figure which shows the environmental dependence of IV characteristic about a charging current and a charging voltage. It is a figure which shows each correction value which a film thickness correction | amendment part uses for correction | amendment of a film thickness according to temperature and humidity. 3 is a flowchart illustrating charging voltage application control by the image forming apparatus according to the first embodiment of the present invention. It is a functional block diagram which shows roughly the main internal structures of the image forming apparatus which concerns on 2nd Embodiment of this invention. It is a figure which shows each charging current correction value used for correction | amendment of the charging current determined by the determination part according to temperature and humidity. 6 is a flowchart illustrating charging voltage application control by an image forming apparatus according to a second embodiment of the present invention.

  Hereinafter, an image forming apparatus and a charging voltage control method according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a front sectional view showing the structure of the image forming apparatus according to the first embodiment of the present invention.

  The image forming apparatus 1 according to the first embodiment of the present invention includes an image forming unit 2, a paper transport mechanism 3, a paper feeding unit 4, a fixing unit 5, and a discharge tray 6. In the present embodiment, a case where the image forming apparatus 1 is a printer will be described as an example.

  When the image forming apparatus 1 performs an image forming operation, the image forming unit 2 uses the paper transport mechanism 3 based on image data received from a network-connected computer or image data stored in a built-in HDD. A toner image is formed on a recording sheet P as a recording medium conveyed from the sheet feeding unit 4 through the conveyance path 31. Thereafter, the fixing unit 5 fixes the toner image on the recording paper P to the recording paper P by thermocompression bonding. The recording paper P on which image fixing has been completed is discharged to the discharge tray 6.

  The image forming unit 2 includes a photosensitive drum (image carrier) 21, a charging device 22, an exposure device 23, a developing device 24, a transfer roller 25, and a toner removing device 27. A detailed description of each component will be described later.

  The paper transport mechanism 3 includes a transport path 31, a transport roller 32, and a registration roller 33.

  The conveyance path 31 is a conveyance path through which the recording paper P is conveyed from the paper feeding unit 4 to the discharge tray 6 through the image forming unit 2 and the fixing unit 5. A conveyance roller 32 is provided at each position of the conveyance path 31, and the recording paper P is fed from the sheet feeding unit 4 to the image forming unit 2, the fixing unit 5, and the like in the conveyance path 31 by rotation of the conveyance roller 32. It is conveyed to the discharge tray 6.

  The registration roller 33 is provided on the upstream side in the transport direction of the recording paper P of the image forming unit 2 in the transport path 31, and the photosensitive drum 21 and the transfer roller 25 face the recording paper P transported in the transport path 31. The timing of conveying to the position (that is, the transfer position of the toner image by the image forming unit 2) is adjusted.

  The registration sensor 75 is provided in the conveyance path 31 on the upstream side of the registration roller 33 in the conveyance direction of the recording paper P. A control unit 100 (see FIG. 3), which will be described later, uses the timing at which the registration sensor 75 detects the arrival of the leading end of the recording paper P and uses the image forming unit 2 after a predetermined time has elapsed from the timing. The registration roller 33 is driven so that the recording paper P is conveyed to the transfer position of the toner image, and the timing at which the recording paper P arrives at the transfer position of the image forming unit 2 is adjusted.

  The fixing unit 5 is disposed downstream of the toner image transfer position to the recording paper P by the image forming unit 2 in the conveyance direction of the recording paper P, and is transferred to the recording paper P that has passed through the image forming unit 2. The toner image is heat-pressed by the heat roller 51 and the pressure roller 52 and fixed on the recording paper P.

  Next, each configuration of the image forming unit 2 will be described. FIG. 2 is a front sectional view showing the configuration of the image forming unit 2. This will be described with reference to FIGS.

  The photosensitive drum 21 is provided with a photosensitive layer on the surface thereof, and forms an electrostatic latent image and a toner image along the electrostatic latent image. In the present embodiment, as an example, a case where the photosensitive layer is made of OPC (organic optical conductor) will be described.

  The charging device 22 is provided at a position facing the surface of the photosensitive drum 21. The charging device 22 uniformly charges the peripheral surface of the photosensitive drum 21 rotating in the direction of the arrow shown in FIG. 2 with a predetermined charging capability. The predetermined charging capability of the charging device 22 is set to, for example, the capability of setting the surface of the photosensitive drum 21 to a predetermined potential. The charging device 22 includes a charging roller 222 (an example of a charging body in claims) having a rotation axis in the same direction as the rotation axis direction of the photosensitive drum 21. The charging roller 222 is applied with a charging voltage having the same polarity as the normal charging polarity (positive polarity in the present embodiment) of the toner by a charging voltage application unit (power supply device) 223. The charging voltage applied to the charging roller 222 is controlled by an application bias controller 101 (see FIG. 3) described later. When the charging roller 222 comes into contact with the surface of the photosensitive drum 21, the surface of the photosensitive drum 21 is charged. In addition, the charging device 22 includes a charging current detection unit 225 that detects a charging current flowing through the charging device 22 when a charging voltage is applied by the charging voltage application unit 223.

  The exposure device 23 is provided at a position facing the surface of the photosensitive drum 21 and on the downstream side of the charging device 22 in the rotational direction of the circumferential surface of the photosensitive drum 21. The exposure apparatus 23 applies laser light corresponding to image data received from a computer connected to the image forming apparatus 1 over a network, or image data stored in a built-in HDD, as shown by arrows in FIG. The photosensitive drum 21 is irradiated with a peripheral surface, and an electrostatic latent image corresponding to the image data is formed on the peripheral surface of the photosensitive drum 21. The exposure device 23 is a laser exposure unit, and includes a laser light source that outputs a laser beam, a polygon mirror that reflects the laser beam toward the surface of the photosensitive drum 21, and a laser beam reflected by the polygon mirror. 21 includes optical components such as a lens and a mirror for guiding the lens 21. The exposure device 23 may be of another method such as a method of irradiating the surface of the photosensitive drum 21 with an LED (Light Emitting Diode).

  The developing device 24 supplies toner to the electrostatic latent image formed on the surface of the photosensitive drum 21 by the exposure device 23. The developing device 24 includes a developing roller 241 having a rotation axis in the same direction as the rotation axis direction of the photoconductive drum 21 at a position facing the photoconductive drum 21, and the developing device 241 has a developing device on the surface of the photoconductive drum 21 by the developing roller 241. The toner stored in 24 is supplied. Then, the developing device 24 attaches toner to the electrostatic latent image on a portion exposed by the exposure device 23 on the surface of the photosensitive drum 21 to form a toner image corresponding to the electrostatic latent image. To the developing device 24, toner is supplied from a toner container (not shown).

  The transfer roller (transfer unit) 25 has a rotation axis in the same direction as the rotation axis direction of the photosensitive drum 21, is a position facing the photosensitive drum 21, and is a developing device 24 in the rotation direction of the photosensitive drum 21. It is provided in the downstream rather than. The transfer roller 25 is provided in a state of being pressed against the surface of the photosensitive drum 21. A transfer bias is applied to the transfer roller 25 by a transfer bias applying unit (power supply device) 252. A transfer bias applied to the transfer roller 25 is controlled by an applied bias control unit 101 described later. At the time of image formation, a transfer bias having a polarity different from the normal charging polarity of the toner is applied to the transfer roller 25, and the transfer roller 25 transfers the toner image formed on the surface of the photoconductor drum 21 to the photoconductor drum 21 and the photoconductor drum 21. Transfer is performed on the recording paper P conveyed to the nip N of the transfer roller 25.

  A toner removing device 27 is disposed on the downstream side of the transfer roller 25 in the rotation direction of the photosensitive drum 21. The toner removing device 27 removes toner remaining on the surface of the photosensitive drum 21.

  Next, the internal configuration of the image forming apparatus 1 according to the first embodiment will be described. FIG. 3 is a functional block diagram schematically showing the main internal configuration of the image forming apparatus 1 according to the first embodiment.

  The image memory 71 is an area for temporarily storing image data that is an object of image formation by the image forming unit 2.

  The HDD (hard disk drive) 72 is a large-capacity storage device that stores image data received from a computer connected to the image forming apparatus 1 via a network.

  The temperature sensor 77 includes a thermistor and detects the ambient temperature of the charging device 22 and the photosensitive drum 21 as an ambient environment value. The temperature sensor 77 outputs the detected temperature to a film thickness correction unit 104 (in the second embodiment, the film thickness correction unit 104 or the current correction unit 106) described later.

  The humidity sensor 78 detects the ambient humidity of the charging device 22 and the photosensitive drum 21 as an ambient environment value. The humidity sensor 78 outputs the detected humidity to a film thickness correction unit 104 (in the second embodiment, the film thickness correction unit 104 or the current correction unit 106) described later.

  The temperature sensor 77 and the humidity sensor 78 are an example of an ambient environment value detection unit in the claims. It should be noted that at least one of the temperature sensor 77 and the humidity sensor 78 is provided, and the film thickness correction unit 104 only needs to perform film thickness correction described later using the output value. In the present embodiment, the image forming apparatus 1 includes both a temperature sensor 77 and a humidity sensor 78, and the film thickness correcting unit 104 uses a temperature and humidity values output from both of them to be described later. An example of performing correction will be described.

  The image forming apparatus 1 includes a control unit 10. The control unit 10 includes a CPU (Central Processing Unit), a RAM, a ROM, a dedicated hardware circuit, and the like. The control unit 10 includes a control unit 100, an applied bias control unit 101, a film thickness detection unit 102, a film thickness correction unit 104, and a determination unit 105. In particular, the control unit 10 is configured such that the program stored in the ROM or the HDD 72 is executed by the CPU, whereby the applied bias control unit 101, the film thickness detection unit 102, the film thickness correction unit 104, and the determination unit 105. Function as.

  The control unit 100 governs overall operation control of the image forming apparatus 1. The control unit 100 includes an image forming unit 2, a fixing unit 5, a paper feeding unit 4, an image memory 71, an HDD 72, a charging device driving unit 221, a photosensitive drum driving unit 211 having a drum motor, a transfer roller driving unit 251, and a developing device. 24, the toner removing device 27, the registration sensor 75, and the like. The control unit 100 controls the operation of each connected mechanism and transmits / receives a signal or data to / from each mechanism.

  The charging device 22 includes a charging voltage application unit 223 and a charging current detection unit 225.

  The applied bias control unit 101 controls the voltage applied by the charging voltage applying unit 223 and the transfer bias applying unit 252 of the charging device 22.

  The application bias control unit 101 performs bias control to cause the charging voltage application unit 223 to apply a charging voltage having the same polarity as the normal charging polarity of the toner to the charging roller 222 during image formation, thereby performing photosensitivity on the surface of the photosensitive drum 21. The layer is charged to the same polarity as the normal charging polarity of the toner. Further, the applied bias control unit 101 performs bias control for causing the transfer bias applying unit 252 to apply a transfer bias having a polarity opposite to the normal charging polarity of the toner to the transfer roller 25, so that the recording paper is fed from the surface of the photosensitive drum 21. The toner image is transferred to P to form an image.

  Note that, as described above, the charging current detection unit 225 detects the charging current flowing through the charging device 22 when the charging voltage is applied by the charging voltage application unit 223. The charging current detection unit 225 outputs the detected charging current value to the film thickness detection unit 102 and the applied bias control unit 101.

  The film thickness detector 102 detects the film thickness of the photosensitive layer on the surface of the photosensitive drum 21. The application bias control unit 101 causes the charging voltage application unit 223 to apply a plurality of different charging voltages to the charging roller 222, for example, at regular time intervals as the charging voltage correction processing. The charging current detection unit 225 detects the respective charging currents when these charging voltages are applied.

  The film thickness detection unit 102 detects the film thickness of the photosensitive layer on the surface of the photosensitive drum 21 based on the IV characteristic indicated by the charging current detected by the charging current detection unit 225 when the different voltages are applied. .

  For example, the applied bias control unit 101 applies different charging voltages to the respective surface potentials so that the surface potentials of the photosensitive drums 21 are 350 (V) and 550 (V). The voltage value for setting the surface potential of the photosensitive drum 21 to 350 (V) and 550 (V) is determined in advance according to the value of the film thickness of the surface of the photosensitive drum 21, and is stored in the determination unit 105. ing. The determination unit 105 determines the value of the charging voltage applied by the applied bias control unit 101.

  When the application bias control unit 101 applies the plurality of different voltages by the charging voltage application unit 223, the charging current detection unit 225 detects the charging current at the time of applying each charging voltage. The film thickness detection unit 102 acquires the value of each voltage used for the application from the application bias control unit 101, and acquires the value of the charging current when the voltage is applied from the charging current detection unit 225. The film thickness detection unit 102 uses these voltage values and the values of the respective charging currents when each voltage is applied to calculate an IV characteristic indicating the relationship of the charging current change accompanying the change in the charging voltage.

  FIG. 4 is a graph showing IV characteristics for each film thickness of the photosensitive layer on the surface of the photosensitive drum 21. As shown in FIG. 4, the IV characteristics show different slopes depending on the film thickness of the surface of the photosensitive drum 21. Note that the IV characteristics of each film thickness determined in advance are collected in advance by experiments, and each film thickness and IV characteristics are stored in, for example, a memory built in the control unit 10 or the film thickness detector 102. Are stored in a data table indicating the relationship. The film thickness detection unit 102 detects the film thickness corresponding to the IV characteristic calculated when the different charging voltages are applied as the film thickness of the photosensitive drum 21.

  The film thickness correction unit 104 corrects the film thickness detected by the film thickness detection unit 102 according to the temperature and humidity detected by the temperature sensor 77 and the humidity sensor 78.

  Here, the environmental dependence of the IV characteristic will be described. FIG. 5 is a diagram showing the environmental dependence of the IV characteristic. As shown in FIG. 5, the IV characteristic changes depending on the ambient temperature and ambient humidity.

  For example, the IV characteristic in an environment of a temperature of 35 ° C. and a humidity of 15% (high temperature and low humidity state) has a slope indicated by a line HL in which each measurement point is marked with a circle. Further, in an environment where the temperature is 10 ° C. and the humidity is 15% (low temperature and low humidity state), the IV characteristic is indicated by a line LL marked with Δ. Furthermore, in an environment where the temperature is 10 ° C. and the humidity is 80% (low temperature and high humidity state), the IV characteristic is indicated by a line LH marked with □. In an environment where the temperature is 32.5 ° C. and the humidity is 80% (high temperature and high humidity state), the IV characteristic is indicated by a line HH marked with a cross. The IV characteristic in a standard environment at a temperature of 25 ° C. and a humidity of 50% (standard temperature and standard humidity) is indicated by a line RR marked with *.

  As described above, since the IV characteristic changes depending on the ambient temperature and the ambient humidity, the film thickness correcting unit 104 uses the correction value determined in advance according to the ambient environment to detect the detected film. Correct the thickness. This makes it possible to detect the film thickness with improved accuracy in consideration of the influence of the surrounding environment on the IV characteristics.

  FIG. 6 is a diagram showing the correction values used by the film thickness correcting unit 104 for correcting the film thickness according to temperature and humidity. The film thickness correction unit 104 stores an ambient environment indicated by a combination of each temperature and humidity shown in FIG. 6 and each film thickness correction value corresponding to each ambient environment in a data table. Based on this data table, the film thickness correction unit 104 reads out correction values determined for the temperature and humidity output from the temperature sensor 77 and the humidity sensor 78, and uses this correction value to read the film thickness detection unit. The film thickness detected by 102 is corrected. For example, when the temperature T = 26 ° C. and the humidity H = 70%, the film thickness correction unit 104 sets the correction value to −0.91, and adds the correction value to the detected film thickness value, thereby Correct the value.

  The determination unit 105 determines a voltage corresponding to the film thickness corrected by the film thickness correction unit 104. The determination unit 105 stores in advance a charging voltage corresponding to each film thickness value in a data table or the like, reads out the voltage corresponding to the corrected film thickness from the data table, and sets the image voltage at the time of image formation. Determined as charging voltage. Further, the charging voltage for the surface potential 350 (V) and the charging voltage for the surface potential 550 (V) for setting the surface potential of the photosensitive drum 21 to 350 (V) and 550 (V) are the photosensitive drum. Each value of the film thickness of 21 photosensitive layers is predetermined. The determination unit 105 stores each charging voltage for setting the surface potential to 350 (V) and 550 (V) by a data table or the like for each film thickness value, and is used for charging voltage correction processing described later. Determine as voltage.

  The applied bias control unit 101 causes the charging voltage applying unit 223 to apply the voltage determined by the determining unit 105 to the charging roller 222 as a charging voltage.

  The charging voltage application control by the image forming apparatus 1 according to the first embodiment of the present invention will be described. FIG. 7 is a flowchart showing charging voltage application control by the image forming apparatus 1 according to the first embodiment of the present invention.

  In the image forming apparatus 1, processing for correcting the charging voltage applied by the charging voltage application unit 223 at the time of image formation is performed at predetermined intervals (for example, every 24 hours or when the power is turned on). The applied bias control unit 101 measures the time or the passage of time with a timer built in the control unit 10, for example, and determines whether or not the fixed period has passed and the charging voltage correction time has come (S1).

  When the applied bias control unit 101 determines that the charging voltage correction timing has arrived (YES in S1), the charging voltage applying unit 223 sets the surface potential of the photosensitive drum 21 to 350 (V) and 550 (V). Therefore, a charging voltage for the surface potential 350 (V) and a charging voltage for the surface potential 550 (V) are applied. The determination unit 105 performs the charging for the surface potential 350 (V) and the charging for the surface potential 550 (V) corresponding to the film thickness value detected in S5, which will be described later in the previous correction process, during the execution of S2. The voltage is determined as the voltage used in S2.

  When the plurality of charging voltages are applied in S2, the charging current detector 225 detects the charging current when each charging voltage is applied (S3).

  Subsequently, the film thickness detection unit 102 increases the charging voltage based on each charging voltage applied in S2 and the charging current detected by the charging current detection unit 225 when each of these voltages is applied. The IV characteristic indicating the slope of increase / decrease of the accompanying charging current is calculated (S4).

  The film thickness detection unit 102 reads out the film thickness corresponding to the IV characteristic calculated in S4 from the data table showing the relationship between each IV characteristic and the corresponding film thickness, and uses the film thickness as the photoconductor. It is detected as the film thickness of the drum 21 (S5).

  Next, the film thickness correction unit 104 acquires the temperature and humidity at this time from the temperature sensor 77 and the humidity sensor 78 (S6). Then, the film thickness correction unit 104 reads out the correction values determined for the temperature and humidity acquired in S6 based on the above-described data table indicating the relationship between the combination of temperature and humidity and the correction value of the film thickness. The film thickness detected in S5 is corrected using this correction value (S7).

  Then, the determination unit 105 reads out the voltage corresponding to the film thickness corrected in S7 from the data table storing the respective charging voltages corresponding to the values of the respective film thicknesses as the charging voltage at the time of image formation. Determine (S8).

  The applied bias control unit 101 sets the charging voltage determined in S8 as the charging voltage at the time of image formation, and applies the charging voltage to the charging voltage application unit 223 using the set charging voltage at the time of image formation (S9). ).

  In S8, the determination unit 105 may determine a charging current corresponding to the corrected film thickness instead of determining the voltage with respect to the corrected film thickness. At this time, the determination unit 105 has a data table or the like that stores the charging current corresponding to each film thickness value, and reads the charging current corresponding to the film thickness corrected in S7 from the data table. Determine the charging current. In this case, the applied bias control unit 101 monitors the current detected by the charging current detection unit 225 during image formation, and changes the charging voltage so that the detected current becomes the determined charging current. The charging voltage application control is performed.

  As described above, in the image forming apparatus 1 according to the first embodiment, the film thickness of the photosensitive layer of the photosensitive drum 21 is detected based on the IV characteristic, and the detected film thickness is the ambient temperature and humidity. The correction is made according to the environment, and at the time of image formation, the application bias control unit 101 applies a charging voltage to the charging voltage application unit 223 using a charging voltage corresponding to the corrected film thickness. For this reason, even when the surrounding environment of the photosensitive drum 21 and the charging device 22 is changed and the film thickness of the photosensitive drum 21 is changed over time, appropriate charging is performed according to the changed surrounding environment and film thickness. A voltage can be applied to the charging roller 222. For this reason, it is possible to perform charging voltage application control that maintains the surface potential of the photosensitive drum 21 at a suitable target value regardless of changes in the surrounding environment and aging of the film thickness.

  Next, an image forming apparatus 1 according to the second embodiment of the present invention will be described. FIG. 8 is a functional block diagram schematically showing the main internal configuration of the image forming apparatus 1 according to the second embodiment. The description of the same configuration as that of the first embodiment shown in FIG. 3 is omitted.

  In the image forming apparatus 1 according to the second embodiment, the determination unit 105 determines a charging current corresponding to the corrected film thickness instead of determining the voltage with respect to the film thickness corrected by the film thickness correction unit 104. Similarly to the above, the determination unit 105 has a data table or the like that stores the charging current value for each film thickness value, and reads the charging current corresponding to the corrected film thickness from the data table. The charging current is determined.

  The image forming apparatus 1 according to the second embodiment further includes a current correction unit 106 in addition to the configuration shown in the first embodiment. The current correction unit 106 corrects the charging current determined by the determination unit 105 as described above according to the temperature and humidity detected by the temperature sensor 77 and the humidity sensor 78.

  The current correction unit 106 stores a charging current correction value for each combination of temperature and humidity detected by the temperature sensor 77 and the humidity sensor 78 in a data table or the like. FIG. 9 is a diagram showing each charging current correction value used for correcting the charging current determined by the determination unit 105 for each temperature and humidity. For example, the current correction unit 106 stores a data table having the contents shown in FIG. Then, when the charging current is determined by the determining unit 105, the current correcting unit 106 acquires the temperature and humidity from the temperature sensor 77 and the humidity sensor 78 at this time, and corrects the charging current corresponding to the combination of the temperature and humidity. Read the value. Then, the current correction unit 106 corrects the charging current according to the surrounding environment by adding the read charging current correction value to the determined charging current. For example, when the example temperature T = 26 ° C. and the humidity H = 70%, the current correction unit 106 sets the correction value to 0.75, and adds the correction value to the determined charging current value, thereby determining the charging Correct the current according to the surrounding environment.

  The applied bias control unit 101 monitors the current detected by the charging current detection unit 225, and performs charging that varies the charging voltage so that the detected current becomes the charging current corrected by the current correction unit 106. Voltage application control is performed.

  The charging voltage application control by the image forming apparatus 1 according to the second embodiment of the present invention will be described. FIG. 10 is a flowchart showing charging voltage application control by the image forming apparatus 1 according to the second embodiment of the present invention. The description of the same processing as that of the first embodiment described with reference to FIG. 7 is omitted.

  In the second embodiment, when the film thickness of the photosensitive layer on the surface of the photosensitive drum 21 is corrected by the film thickness correcting unit 104 (S17), the determining unit 105 displays the charging current for the corrected film thickness in the data table. (S18).

  At this time, the current correction unit 106 acquires the temperature and humidity from the temperature sensor 77 and the humidity sensor 78 (the temperature and humidity acquired in S16 may be used), and corresponds to the combination of the temperature and humidity. The charging current correction value is read from the data table held by the current correction unit 106. The current correction unit 106 corrects the set charging current using the read charging current correction value (S19).

  The applied bias control unit 101 varies the charging voltage so that the current detected by the charging current detection unit 225 becomes the charging current after being corrected in S19, that is, using the corrected charging current as a target value. The charging voltage application control is performed (S20).

  As described above, the film thickness of the photosensitive layer of the photosensitive drum 21 is detected based on the IV characteristics, and the detected film thickness is corrected according to the ambient environment including temperature and humidity. The applied bias control unit 101 performs control to vary the charging voltage applied to the charging voltage application unit 223 so that a charging current corresponding to the corrected film thickness is obtained. For this reason, even when the surrounding environment of the photosensitive drum 21 and the charging device 22 is changed and the film thickness of the photosensitive drum 21 is changed over time, appropriate charging is performed according to the changed surrounding environment and film thickness. A voltage can be applied to the charging roller 222. For this reason, it is possible to realize charging voltage application control that maintains the surface potential of the photosensitive drum 21 at a suitable target value regardless of changes in the surrounding environment and aging.

  The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, when only one of the temperature sensor 77 and the humidity sensor 78 is provided, and the film thickness correction unit 104 performs the film thickness correction using a value output from the one sensor, the film thickness correction unit 104 is One of the temperature and humidity output by the one sensor and the corresponding correction value are stored in a data table.

  Further, the configuration and processing shown in each of the above embodiments using FIGS. 1 to 10 are only one embodiment of the present invention, and the configuration and processing of the present invention are not limited to this.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Control unit 100 Control part 101 Applied bias control part 102 Film thickness detection part 104 Film thickness correction part 105 Determination part 106 Current correction part 2 Image formation part 21 Photosensitive drum 211 Photosensitive drum drive part 22 Charging device 221 Charging device driving unit 222 Charging roller 223 Charging voltage application unit 225 Charging current detection unit 77 Temperature sensor 78 Humidity sensor

Claims (5)

A voltage applying unit that applies a plurality of different voltages to a charging body that charges the peripheral surface of the image carrier;
A charging current detection unit that detects a charging current at the time of application of the plurality of voltages by the voltage application unit;
A film thickness detector that detects a film thickness provided on the peripheral surface of the image carrier based on an IV characteristic indicated by a charging current detected by the charging current detector when the different voltages are applied;
An ambient environment value detector that detects an ambient environment value composed of at least one of ambient temperature and ambient humidity of the charged body and the image carrier;
A film thickness correction unit that corrects the film thickness detected by the film thickness detection unit using a correction value determined according to the ambient environment value detected by the ambient environment value detection unit;
A determining unit that determines a charging voltage corresponding to the film thickness corrected by the film thickness correcting unit;
An image forming apparatus comprising: an application bias control unit that performs voltage application control in which the voltage application unit applies the voltage determined by the determination unit as a charging voltage at the time of image formation to the charged body. The determination unit determines a charging current corresponding to the corrected film thickness instead of determining a voltage with respect to the corrected film thickness,
The image according to claim 1, wherein the application bias control unit performs control to vary the charging voltage as the voltage application control so that the current detected by the charging current detection unit is the determined charging current. Forming equipment. A current correction unit that corrects the charging current determined by the determination unit using a current correction value determined according to the ambient environment value detected by the ambient environment value detection unit;
The application bias control unit performs, as the voltage application control, control for varying the charging voltage so that the current detected by the charging current detection unit becomes the charging current after the correction by the current correction unit. Item 3. The image forming apparatus according to Item 2.   The voltage application unit applies the plurality of different voltages to the charged body using each voltage corresponding to the film thickness corrected last time from among the values determined for each film thickness as the plurality of different voltages. The image forming apparatus according to claim 1, wherein: A voltage applying step of applying a plurality of different voltages to the charging body for charging the peripheral surface of the image carrier;
A current detection step of detecting a charging current when applying the plurality of voltages;
A film thickness detecting step for detecting a film thickness provided on a peripheral surface of the image carrier based on an IV characteristic indicated by a charging current detected when a plurality of different voltages are applied;
An ambient environment value detecting step of detecting an ambient environment value comprising at least one of ambient temperature and ambient humidity of the charged body and the image carrier;
A film thickness correction step for correcting the detected film thickness using a correction value determined according to the detected ambient environment value;
A determining step for determining a charging voltage corresponding to the corrected film thickness;
A charging voltage control method comprising: applying a charging voltage to the charging body by a voltage applying unit using the determined voltage as a charging voltage at the time of image formation.