JP2013125263A - Image forming apparatus and charging control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable always maintaining a charge potential constant by correcting reduction in a charge potential due to the load increase of a charging member.SOLUTION: There is provided an image forming apparatus which comprises: a photoreceptor drum 11 for carrying an image on the surface: a charging roller 12 for charging the surface of the photoreceptor drum 11 by superimposing a charging DC bias and a charging AC bias; an AC current determination part 111 for detecting the charging AC current of the photoreceptor drum 11 charged by the charging roller 12; a control part 114 for controlling the charging AC current, the charging AC bias and the charging DC current, wherein the control part 114 determines the charging DC bias from the charging AC current detected by the AC current determination part 111, the charging AC bias controlled based on the detected charging AC current, and the instructed developing bias.

Description

  The present invention relates to an image forming apparatus and a charging control method, and more particularly to an image forming apparatus such as a copying machine using an electrophotographic method, a printer, a facsimile, or a digital composite machine that combines these functions, and the image forming apparatus. The present invention relates to a charge control method to be executed.

  As this type of technology, for example, the inventions described in Patent Documents 1 and 2 are known. Of these, the invention described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-172907) provides a high-quality image forming apparatus that can obtain a charged AC bias that is not affected by the state of a charged DC bias circuit. A charging member that is in contact with the body and the object to be charged (hereinafter referred to as “contact”), and a charging bias that applies a charging bias in which a DC component and an AC component are superimposed on the charging member. In an image forming apparatus including an applying unit, wherein an alternating current component is generated by a constant current power source and a direct current component is generated by a constant voltage power source, a current setting unit having a function capable of changing a current setting value of the constant current power source, Voltage setting means having a function capable of varying the voltage setting value of the voltage power supply, and control means for determining the current setting value based on the voltage setting value

  Further, the invention described in Patent Document 2 (Japanese Patent Application Laid-Open No. 2010-244019) is an image forming apparatus that uses a DC charging method, in order to charge the photosensitive drum to a target potential without using a potential sensor. A test bias in which a predetermined AC voltage and a predetermined DC voltage are superimposed is applied to the charging member so that discharge is performed between the photosensitive member and the charging member. And a control means for controlling the charging bias based on the output of the current detection means.

  In the invention described in Patent Document 1, in an image forming apparatus in which an alternating current component is generated by a constant current power source and a direct current component is generated by a constant voltage power source, a voltage setting circuit capable of changing a voltage setting value of the constant voltage power source Since the current setting value is determined based on the voltage setting value set by A, the AC component current setting value is determined based on the DC component voltage setting value. What is set here is an AC component current value, and a decrease in charging potential cannot be corrected. In the invention described in Patent Document 2, the direct current flowing when applied to the charging member is detected to control the charging bias. However, since the direct current is small, the charging bias cannot be determined with high accuracy. In any case, it is impossible to correct the decrease in the charging potential due to the increase in the load of the charging member, so it is impossible to keep the charging potential constant.

  Accordingly, a problem to be solved by the present invention is to correct a decrease in the charging potential due to an increase in the load on the charging member, and to keep the charging potential constant.

    In order to solve the above-described problems, the present invention provides an image carrier that carries an image, a charging unit that charges the image carrier by superimposing a charging DC bias and a charging AC bias, and the charging unit that is charged by the charging unit. A detection unit that detects a charging AC current of the image carrier, and a control unit that controls the charging AC current, the charging AC bias, and the charging DC bias. The control unit is detected by the detection unit. The charging DC bias is determined from the charging AC current, the charging AC bias set based on the detected charging AC current, and the designated developing bias.

  According to the present invention, it is possible to correct a decrease in the charging potential due to an increase in the load on the charging member, and to keep the charging potential constant.

1 is a diagram illustrating an overall configuration of a color copying machine as an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a schematic configuration of an engine unit for one color of the color copying apparatus illustrated in FIG. 1. FIG. 3 is an explanatory diagram showing control contents in a control configuration for controlling the voltage applied to the charging roller shown in FIG. 2. FIG. 6 is a characteristic diagram showing a relationship between a conventional charging member load characteristic (charging AC bias / charging AC current) and a charging potential. FIG. 6 is a characteristic diagram illustrating a relationship between a load characteristic (charging AC bias / charging AC current) of a charging member and a charging potential in the present embodiment.

  In the present invention, the charging DC bias is determined in accordance with the developing bias, the charging AC current, and the charging AC bias, and the decrease in the charging potential due to the increase in the load of the charging member is corrected, so that the charging potential can always be maintained constant It is characterized by.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an overall configuration of a color copying machine as an image forming apparatus according to an embodiment of the present invention. In the figure, the main body of the color copying machine 1 according to the present embodiment includes a document transport unit 3, a document reading unit 4, an optical writing unit (exposure unit) 6, a sheet feeding unit 7, process cartridges 10Y, 10M, 10C, and 10BK (hereinafter, referred to as a document cartridge). The intermediate transfer belt 17, the secondary transfer roller 18, the fixing unit 20, the toner container 28, and the like are provided.

  The document transport unit 3 transports the document to the document reading unit 4, and the document reading unit 4 reads image information of the document. The optical writing unit 6 emits laser light based on the input image information and performs optical writing on the photosensitive drums of the process cartridges 10Y, 10M, 10C, and 10BK. A recording medium P such as transfer paper is stored in the paper feeding unit 7 and fed to the secondary transfer unit (position of the second transfer roller 18) in accordance with the image forming timing. The process cartridges 10Y, 10M, 10C, and 10BK function as image forming units corresponding to the respective colors (yellow, magenta, cyan, and black), and are respectively described below as a photosensitive drum, a charging unit, a developing unit, a transfer unit, a cleaning unit, and A latent image is formed by the laser beam emitted from the optical writing unit 6 between the charging unit and the developing unit.

  On the intermediate transfer belt 17, toner images of yellow, magenta, cyan, and black developed with the process cartridges 10Y, 10M, 10C, and 10BK are superimposed and primarily transferred. The secondary transfer roller 18 secondarily transfers the full-color toner image formed on the intermediate transfer belt 17 to the recording medium P, and forms an image on the recording medium P. The fixing unit 20 fixes an unfixed image on the recording medium P, and after fixing, the recording medium P is discharged out of the apparatus. The toner container 28 contains toner for supplying toner of each color to the developing portions of the process cartridges 10Y, 10M, 10C, and 10BK.

  Each process cartridge 10Y, 10M, 10C, 10BK has a photosensitive drum 11 as an image carrier and a charging roller (charging member) as a charging unit, as shown in FIG. ) 12, a developing unit 13 (developing device), a cleaning unit (cleaning device), and a lubricant supply device (lubricant supply unit) 16 are integrated. The process cartridges 10Y, 10M, 10C, and 10BK are replaced with the main body of the color copying machine 1 when the service life is reached. A toner image of each color (yellow, magenta, cyan, black) is formed on the photosensitive drum 11 in each of the process cartridges 10Y, 10M, 10C, and 10BK. In FIG. 2, the arrangement of the photosensitive drum 11 and the primary transfer roller 14 is shown upside down from FIG.

  In the color copying machine 1, the document is transported from the document table by the transport roller of the document transport unit 3 and placed on the contact glass of the document reading unit 4. Then, the document reading unit 4 optically reads the image information of the document placed on the contact glass. Specifically, the document reading unit 4 scans an image of a document on the contact glass while irradiating light emitted from an illumination lamp. Then, the light reflected from the original is imaged on the color sensor via the mirror group and the lens. The color image information of the original is read for each color separation light of RGB (red, green, blue) by a color sensor, and then converted into an electrical image signal. Further, the image processing unit (not shown) performs color conversion processing, color correction processing, spatial frequency correction processing, and the like based on the RGB color separation image signals, and color image information for yellow, magenta, cyan, and black. Get.

  Image information of each color of yellow, magenta, cyan, and black is transmitted to the optical writing unit 6, and laser light (exposure light) based on the image information of each color is transmitted from the optical writing unit 6 to the corresponding process cartridge 10Y. Irradiation onto the photosensitive drum 11 of 10M, 10C, 10BK. On the other hand, each of the four photosensitive drums 11 rotates in the clockwise direction in the figure, and the surface of the photosensitive drum 11 is uniformly charged at a position facing the charging roller 12. Thus, a charged potential is formed on the photosensitive drum 11. Thereafter, the surface of the charged photosensitive drum 11 reaches the irradiation position of each laser beam.

  In the optical writing unit 6, laser light modulated in accordance with the image signal is emitted from the light source for each photosensitive drum 11. Although not shown, the laser light is incident on the polygon mirror and reflected, and then passes through a plurality of lenses. The laser light after passing through a plurality of lenses passes through different optical paths for each of the yellow, magenta, cyan, and black color components.

  Laser light corresponding to the yellow component is irradiated onto the surface of the photosensitive drum 11 of the first process cartridge 10Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotational axis direction (main scanning direction) of the photosensitive drum 11 by a polygon mirror (not shown) that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11 after being charged by the charging roller 12.

  Similarly, the cyan component laser light is applied to the surface of the photosensitive drum 11 of the second process cartridge 10 </ b> C from the left side of the sheet, thereby forming an electrostatic latent image of the cyan component. The laser beam corresponding to the magenta component is irradiated onto the surface of the photosensitive drum 11 of the third process cartridge 10M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The black component laser light is applied to the surface of the photosensitive drum 11 of the process cartridge 10BK (black image forming unit), which is fourth from the left side of the paper (most downstream with respect to the traveling direction of the intermediate transfer belt 17). An electrostatic latent image of the component is formed.

  The surface of the photosensitive drum 11 on which the electrostatic latent image of each color is formed reaches a position facing the developing unit 13. Then, each color toner is supplied from each developing unit 13 onto the photosensitive drum 11, and the latent image on the photosensitive drum 11 is developed. The surface of the photosensitive drum 11 after the development process reaches a position facing the intermediate transfer belt 17. Here, a primary transfer roller 14 is installed at each facing position so as to contact the inner peripheral surface of the intermediate transfer belt 17. Then, at the position of the primary transfer roller 14, the toner images of the respective colors formed on the photosensitive drum 11 are sequentially superimposed and transferred onto the intermediate transfer belt 17 (primary transfer).

  The surface of the photosensitive drum 11 after the primary transfer reaches a position facing the cleaning unit, and untransferred toner remaining on the photosensitive drum 11 is collected by the cleaning unit. Thereafter, the surface of the photosensitive drum 11 sequentially passes through the position of the lubricant application unit 16 and the position of the charge eliminating unit (not shown), and a series of image forming processes on the photosensitive drum 11 is completed. Although not shown in FIG. 2, the cleaning unit is disposed between the primary transfer roller 14 and the lubricant application unit 16.

  On the other hand, the surface of the intermediate transfer belt 17 on which the images of the respective colors on the photosensitive drum 11 are transferred in an overlapping manner travels in the direction of the arrow in the drawing and reaches the position of the secondary transfer roller 18. The full color image on the intermediate transfer belt 17 is secondarily transferred onto the recording medium P at the position of the secondary transfer roller 18. Thereafter, the surface of the intermediate transfer belt 17 reaches a position of an intermediate transfer belt cleaning unit (not shown), and untransferred toner on the intermediate transfer belt 17 is collected by the intermediate transfer belt cleaning unit, and a series of steps on the intermediate transfer belt 17 is performed. The transfer process is complete.

  Here, the recording medium P at the position of the secondary transfer roller 18 is conveyed from the paper supply unit 7 via the conveyance guide, the registration roller 19 and the like. Specifically, the transfer paper P fed by the paper feed roller 8 from the paper feed unit 7 that stores the recording medium P is guided to the registration roller 19 after passing through the conveyance guide. The recording medium P that has reached the registration roller 19 is conveyed toward the position of the secondary transfer roller 18 in synchronization with the toner image on the intermediate transfer belt 17. Thereafter, the recording medium P onto which the full color image has been transferred is guided to the fixing unit 20, and the color image is fixed on the recording medium P at the nip between the fixing roller and the pressure roller. The recording medium P after the fixing process is discharged as an output image outside the apparatus main body 1 by the paper discharge roller 29 and then stacked on the paper discharge unit 5 to complete a series of image forming processes.

  In FIG. 2, the engine unit EN includes a photosensitive drum 11 as an image carrier, a charging roller 12 arranged on the outer periphery of the photosensitive drum 11 along the rotation direction of the drum 11, an optical writing unit 6, and a developing device 13. A lubricant application unit 16, a primary transfer roller 14, and an intermediate transfer belt 17 that moves between the photoreceptor 11 and the primary transfer roller 14. The photosensitive drum 11, the charging roller 12, the developing device 13, and the lubricant application unit 16 are arranged as the process cartridge 10 in FIG. The charging roller 12 is connected to an AC current measuring unit 111, an AC power source 112, a DC power source 113, and a control unit 114 for controlling the voltage applied to the charging roller 12.

The photoreceptor drum 11 is a negatively charged organic photoreceptor, and a photosensitive layer or the like is provided on a drum-shaped conductive support. Although not shown, the photosensitive drum 11 is formed by sequentially laminating an undercoat layer as an insulating layer, a charge generation layer and a charge transport layer as a photosensitive layer, and a protective layer (surface layer) on a conductive support as a base layer. ing. As the conductive support (base layer) of the photosensitive drum 11, for example, a conductive material having a volume resistivity of 10 ¹⁰ (Ω · cm) or less is used.

The charging roller 12 is a roller member formed by coating an outer periphery of a conductive metal core with a medium-resistance elastic layer, and is disposed on the downstream side in the rotation direction of the photosensitive drum 11 with respect to the lubricant supply device 16. Yes. Further, the charging roller 12 is disposed so as to face the photosensitive drum 11 in a non-contact manner so that the lubricant supplied onto the photosensitive drum 11 by the lubricant supply device 16 does not adhere. Further, since the charging roller 12 and the photosensitive drum 11 are not in contact with each other, it is possible to suppress the toner or paper powder from adhering to the charging roller 12 from the photosensitive drum 11. As will be described later, a predetermined voltage (charging bias) is applied to the charging roller 12 from an AC power source 112 and a DC power source 113 serving as a power source unit, thereby uniformly charging the surface of the opposing photosensitive drum 11. If the resistance of the charging roller 12 is too low, no overcurrent flows when there is a pinhole in the photosensitive drum 11, and if the resistance is too high, the voltage drop becomes too large to be charged. Therefore, the charging roller 12 is preferably a conductive member having a volume resistivity of, for example, 10 ³ to 10 ⁷ (Ω · cm).

  The developing unit 13 mainly includes a developing roller 13a opposed to the photosensitive drum 11, a first conveying screw 13b1 opposed to the developing roller 13a, a second conveying screw 13b2 opposed to the first conveying screw 13b1 via a partition member, and The doctor blade 13c is opposed to the developing roller 13a. The developing roller 13a includes a magnet that forms a magnetic pole on the roller peripheral surface and a sleeve that rotates around the magnet. A plurality of magnetic poles are formed on the developing roller 13a (sleeve) by the magnet, and the developing roller 13a The developer is carried on the surface. In the developing unit 13, a two-component developer composed of a carrier and a toner is accommodated.

  Although not particularly shown, the cleaning unit is disposed on the upstream side in the rotation direction of the photosensitive drum 11 with respect to the lubricant supply device 16. The cleaning unit 15 is provided with a cleaning blade that comes into contact with the photosensitive drum 11, a transport coil that transports the toner collected in the cleaning unit 15 to the waste toner collection container as waste toner. The cleaning blade is made of a rubber material such as urethane rubber, and is in contact with the surface of the photosensitive drum 11 at a predetermined angle and a predetermined pressure. As a result, deposits such as untransferred toner adhering to the photosensitive drum 11 are mechanically scraped and collected in the cleaning unit. Here, examples of the deposit that adheres to the photosensitive drum 11 include paper powder generated from the recording medium P (paper) in addition to the untransferred toner, and a discharge product generated on the photosensitive drum 11 when discharged by the charging roller 12. And additives that are added to the toner.

  The lubricant supply device 16 urges the solid lubricant 16b, the lubricant supply roller 16a (brush roller) in contact with the photosensitive drum 11 and the solid lubricant 16b, and the solid lubricant 16b toward the lubricant supply roller 16a. And a blade-like member 16c for thinning the lubricant supplied onto the photosensitive drum 11 by the lubricant supply roller 16a. The blade-like member 16c is configured to contact the photosensitive drum 11 in the counter direction at a position downstream of the lubricant supply roller 16a in the rotation direction of the photosensitive drum 11. The lubricant supply device 16 configured as described above supplies the thinned lubricant on the photosensitive drum 11.

  In the engine unit EN having such a configuration, the surface of the photosensitive drum 1 is charged by the charging roller 12, and the optical writing unit 6 performs optical writing of an image by laser light. The latent image formed by the optical writing with the laser beam is developed with toner by the developing unit 13 to be visualized. The visualized toner image is primarily transferred onto the transfer belt 17 by the primary transfer roller 14 and transferred onto the transfer paper at a secondary transfer portion (not shown) on the downstream side in the rotation direction of the transfer belt 17 to form an image. Is done. As shown in FIG. 1, such engine units EN are arranged in parallel along the rotational direction of the YMCK four-color transfer belt 8, and a full-color image is formed on the transfer paper. Note that it is needless to say that the engine unit EN shown in FIG.

  FIG. 3 is an explanatory diagram showing the control contents in the control configuration for controlling the voltage applied to the charging roller 2 shown in FIG. The control unit 114 receives a charging AC current measurement value from the AC current measurement unit 111 and a development bias instruction value from the CPU of the main control device (not shown) of the color copying machine 1. The developing bias is a voltage applied between the electrostatic latent image carrier (photosensitive drum 11) and the developing electrode of the developing device 13 when the electrostatic latent image is visualized using a developer. The AC current is a current that flows through the charging member when an AC voltage is applied from the AC power source 112 to the charging member (here, the charging roller 12). The control unit 114 controls the charging AC bias so that the charging AC current becomes constant based on the measurement value measured by the AC current measuring unit 111 that detects the charging AC current, and the charging DC bias is set as described later. The determined charging AC bias is output from the AC power source 112 and the charging DC bias is output from the DC power source 113, and both are superimposed and applied to the charging roller 2.

  That is, as the charging AC bias, a bias higher than that causing forward / reverse discharge is necessary, and the control unit 114 controls the AC power source 112 so that the charging AC current becomes constant. Generally, it is set and controlled between 1.2 kV and 3.0 kV, for example. As the charging AC current, the measurement result measured by the AC current measuring unit 111 is input to the control unit 114, and the control unit 114 detects the linear velocity of the photosensitive drum 1 and the charging roller 2, the width in the longitudinal direction, and the gap. The charging AC bias is determined based on the size and the like. Specifically, the charging AC current is determined to be 0.4 mA to 3 mA. If the charging AC current is too small, insufficient charging will occur. If the charging AC current is too large, the photosensitive drum 1 or the charging roller 2 will be deteriorated due to excessive discharge. Therefore, the charging AC current in the above range is preferable.

  The charging AC bias and the charging AC current represent the load characteristics of the charging roller 12 (generally, a charging member). If this value is large, the load on the charging member is large. The load of the charging roller 12 is increased by energization. When the load increases, the charging AC bias and the charging DC bias become smaller. Since the charging AC current is made constant for AC, the necessary charging AC bias can be obtained without excess or deficiency, but for DC, the bias becomes small, resulting in a lower charging potential.

  FIG. 4 is a characteristic diagram showing the relationship between charging AC bias (Vac) / charging AC current (Iac) and charging potential (V). The charging potential is set to −800 V, but it can be seen that the charging potential decreases when the load rises above a certain threshold. This threshold value was Rth (corresponding to 6.18 in FIG. 3). This characteristic is obtained when the photosensitive drum 1 has a linear velocity of 255 mm / s, a charging width of 312 mm, a target surface potential of −800 V, a photosensitive drum diameter of 40 mm, and a charging roller diameter of 12.55 mm.

The charging DC bias (Vdc) determined by the control unit 14 is
When Vac / Iac ≦ Rth Vdc = Vb + α (1)
When Vac / Iac> Rth Vdc = Vb + α + β × (Log (Vac / Iac) −Log (Rth))
... (2)
However,
Vdc (V): charging DC bias Vb (V): development bias Vac (V): charging AC bias Iac (A): charging AC current
α, β: Fixed value
Rth: charging AC bias / charging AC current threshold.

  In the above formula, the sign changes between negative charging and positive charging. Negative charging will be described as an absolute value. The value of the fixed value α is preferably in the range of 40V to 200V, more preferably 80V to 140V.

  If the fixed value α is too small, the difference between the developing potential and the charging potential becomes small, and toner background smearing occurs. If the fixed value α is too high, the difference between the developing potential and the charging potential becomes large, and carrier adhesion occurs in two-component development. The value of the fixed value β corresponds to the slope on the high load side in FIG. 4 and represents the amount of decrease in the charged potential with respect to the load increase. A specific value is −300 to −10000.

  Further, (Vb + α) in equation (2) represents a value obtained by adding the background potential to the developing bias used in normal control, and charging AC bias (Vac) / charging AC current (Iac) corresponds to resistance. Represents.

Therefore, when the linear velocity of the image carrier and the charging member is 255 mm / s, the charging width is 312 mm, the image carrier diameter is 40 mm, and the charging member diameter is 12.55 mm, as described above.
Development bias: -700 (V)
α: -100 (V)
β: -3000 (V)
Rth: 10 ^6.18 (Ω)
When the charging AC bias (Vac) / charging AC current (Iac) and the charging potential (V) when the charging DC bias Vdc is determined based on the above equation and applied to the charging roller 12 are measured as shown in FIG. The characteristics are as shown.

  From this figure, when the charging DC bias is determined based on the above formula, it is possible to correct the decrease in the charging potential on the surface of the photosensitive drum 11 due to the increase in the load of the charging roller 12, and the charging potential is always kept constant. be able to.

  At this time, the developing bias is determined by the exposed portion potential of the image carrier 11 after exposure and the developing ability (development gamma characteristic). That is, in order to optimize the toner adhesion amount, the development bias becomes a point, but the toner adhesion amount is determined by the development potential and the development gamma characteristic which is the development ability. The development potential is the difference between the exposure portion potential and the development bias. To optimize the toner adhesion amount, an optimum development bias may be determined from the exposure portion potential and the development gamma characteristic.

  Also, as shown in FIG. 4, when the load on the charging roller 12 increases, a voltage drop occurs in the charging roller 12, so the charging potential decreases. Therefore, in this embodiment, the charging DC bias is raised as shown in the equation (2) according to the lowered charging potential, and the charging potential is always kept constant as shown in FIG. As a result, the load on the charging roller 12 is increased, the charging potential is lowered, and the toner background is not contaminated. The lowered charging potential can be predicted from the load of the charging roller 12, and the load (resistance) of the charging roller 12 can be obtained from the charging AC current (Iac) and the charging AC bias (Vac) as shown in FIG. it can.

  Furthermore, since the resistance of the charging roller 12 changes depending on the environment, the charging AC current changes when the charging AC bias is constant, resulting in insufficient charging or excessive charging. In contrast, in the present embodiment, the charging AC current is measured by the AC current measuring unit 111, and the charging AC bias is controlled so that the detected charging AC current is constant based on the measurement result. Regardless of the change, the charging AC current can be made constant.

As described above, according to the present embodiment,
1) It is possible to correct a charging potential that decreases due to an increase in the load on the charging roller, and to keep the charging potential constant.
2) Even if the resistance of the charging roller 2 changes depending on the environment, the charging AC bias is controlled so that the charging AC current is constant, so that insufficient charging or excessive charging is prevented regardless of the environment or environmental changes. can do.
(3) By determining the optimum developing bias from the exposed portion potential and the developing gamma, the toner adhesion amount can be optimized.
(4) Since the volume resistivity of the charging roller 12 is 10 ³ to 10 ⁷ (Ω · cm), a stable charging potential can be obtained.
(5) Since the charging roller 12 is provided so as to face the photosensitive drum 11 in a non-contact manner, it is possible to prevent toner or paper powder from adhering to the charging roller 12 from the photosensitive drum 11. Therefore, a stable charging potential can be obtained.
There are effects such as.

  In the embodiment, the image carrier in the claims is the photosensitive drum 11, the charging DC bias is Vdc, the charging AC bias is Vac, the charging unit is the charging roller 12, and the charging AC current is Iac, The detection unit corresponds to the AC current measuring unit 111, the control unit corresponds to the control unit 114, and the image forming apparatus corresponds to the color copying machine 1.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention, and all technical matters included in the technical idea described in the claims are included. The subject of the present invention. The above embodiment shows a preferable example, but those skilled in the art can realize various alternatives, modifications, variations, and improvements from the contents disclosed in this specification, These are included within the scope defined by the appended claims.

DESCRIPTION OF SYMBOLS 1 Color copier 11 Photosensitive drum 12 Charging roller 111 AC electric current measurement part 114 Control part Iac Charging AC electric current Vac Charging AC bias Vdc Charging DC bias

JP-A-2005-172907 JP 2010-244019 A

Claims (8)

An image carrier that carries an image on the surface;
Charging means for charging the surface of the image carrier by superimposing a charging DC bias and a charging AC bias;
Detecting means for detecting a charging AC current of the image carrier charged by the charging means;
Control means for controlling the charging AC current, the charging AC bias, and the charging DC bias;
An image forming apparatus comprising:
The control unit determines a charging DC bias from a charging AC current detected by the detecting unit, a charging AC bias controlled based on the detected charging AC current, and an instructed developing bias. An image forming apparatus. The image forming apparatus according to claim 1,
The charging DC bias (Vdc) is
When the developing bias is Vb, the charging AC current is Iac, the charging AC bias is Vac, α, β are fixed values, and Rth is a charging AC bias / charging AC current threshold,
When Vac / Iac ≦ Rth Vdc = Vb + α
When Vac / Iac> Rth Vdc = Vb + α + β × (Log (Vac / Iac) −Log (Rth))
An image forming apparatus determined by The image forming apparatus according to claim 1, wherein:
The image forming apparatus, wherein the control unit controls the charging AC bias based on the charging AC current detected by the detecting unit so that the charging AC current becomes constant. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus, wherein the developing bias is determined by an exposure portion potential and a developing gamma characteristic. The image forming apparatus according to any one of claims 1 to 4, wherein
The image forming apparatus, wherein the charging unit has a volume resistivity of 10 ³ to 10 ⁷ (Ω · cm). An image forming apparatus according to any one of claims 1 to 5,
An image forming apparatus, wherein the image carrier and the charging unit are not in contact with each other. The image forming apparatus according to any one of claims 1 to 6,
The image forming apparatus according to claim 1, wherein the developing bias is input from a host control unit. Charging the surface of the image carrier carrying the image by charging the charging DC bias and charging AC bias by a charging means;
Detecting a charging AC current of the image carrier charged by the charging unit by a detecting unit;
Controlling the charging AC bias based on the charging AC current detected in the detecting step;
Determining a charging DC bias based on the charging AC current detected in the detecting step, the charging AC bias controlled in the controlling step, and the designated developing bias;
Charge control method for an image forming apparatus.

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