JP2012003047A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of removing a deteriorated carrier from a developer even during an image forming operation and allowing no attachment of carrier to a solid-black exposure zone (i.e., of an image writing area, the zone irradiated with output light having the maximum output).SOLUTION: An image forming apparatus includes: a carrier removal section for generating an electric field between itself and a developer carrying member to remove a carrier which has deteriorated as compared to its initial stage from carriers carried on the developer carrying member; a carrier measurement section for measuring the degree of deterioration of the carrier removed by the carrier removal section; and an electric field strength change section for changing an electric field strength between the carrier removal section and developer carrying member based on a result of measurement by the carrier measurement section.

Description

  The present invention relates to an image forming apparatus that forms an image by an electrostatic copying process, such as a copying machine, a facsimile machine, and a printer.

  In an electrophotographic image forming apparatus such as a copying machine or a printer, an electrostatic latent image is formed on a uniformly charged surface of a photosensitive member by exposing it to light output from an image writing unit. The toner is developed with a developing device to form a toner image, and then the toner image is transferred to a transfer material such as recording paper. The transfer material onto which the toner image has been transferred passes through a fixing device, and heat and pressure are applied to fix the toner onto the transfer material.

  In such an image forming apparatus, the development of the electrostatic latent image on the photosensitive member is excellent in developability, and therefore, a development system (two-component developer) using a developer (two-component developer) composed of a toner and a carrier. Development system) is often used.

  In the two-component development method, the toner and carrier in the developer are stirred in a stirring tank attached to the developing device, and the toner is charged from the carrier by frictional charging and electrostatically attached to the outer surface of the carrier. Become. The carrier to which the toner is attached, that is, the developer, is transported to a developing region that is a portion facing the photosensitive member by a developer transporting member such as a developing sleeve containing a magnetic roll. In the developing area, the toner in the developer is separated from the carrier and adheres to the electrostatic latent image portion on the photoconductor to form a toner image. The toner and carrier remaining on the developer transport body are returned to the agitation tank and again used for development.

  In the two-component development system, the toner in the agitation tank is consumed and reduced by repeating the development operation, and thus is configured to replenish the consumed toner.

  On the other hand, the carrier is used repeatedly without being reduced by the developing operation. However, the carrier deteriorates when it is repeatedly stirred by repeated use. For example, the resin coat layer on the carrier surface is peeled off, and the resistance value is lower than that in the unused or initial state. The carrier having a lowered resistance value is easily reversed in charge polarity by charge injection under a developing electric field and easily transferred to the photoconductor. Therefore, the portion irradiated with the maximum output light of the image writing portion (toner on the photoconductor) (toner This is a portion with a large amount of adhesion, and induces problems such as carrier adhesion to the solid exposure portion). Therefore, it is necessary to remove the carrier that has been repeatedly used and deteriorated from the developer in the stirring tank.

  To solve this problem, in the process of replenishing the toner consumed by development, a new carrier is gradually replenished into the stirring tank together with the toner, and the development overflowing from the stirring tank by supplying the toner and the carrier. A so-called trickle-type developing device has been proposed that discharges the deteriorated carrier in the stirring tank by discharging the agent and suppresses the increase in the ratio of the deteriorated carrier of the developer in the stirring tank (for example, , See Patent Document 1).

  Further, a technique has been proposed in which the deteriorated carrier in the developer conveyed to the development region by the developer transport body is transferred onto the photosensitive member to discharge the deteriorated carrier in the developer (for example, Patent Documents). 2).

Japanese Patent Publication No. 2-21591 JP 2008-165061 A

  In the technique described in Patent Document 1, which suppresses an increase in the ratio of deteriorated toner in the developer by the so-called trickle development method, not only the deteriorated carrier but also the replenished developer is replenished. It is not efficient because it includes new carriers. Further, since the deteriorated carrier remains in the developer, it is difficult to suppress the occurrence of a problem caused by the deteriorated carrier, for example, a problem that the carrier adheres to the solid exposure portion.

  The technique proposed in Patent Document 2 is conveyed to the development area by making the background potential (difference between the charged potential of the photoconductor and the development bias potential) larger than the background potential during normal image formation. The carrier of the developed developer is transferred to the photoreceptor. However, due to the mechanism, it is difficult to selectively transfer only the deteriorated carrier to the photoconductor, and the carrier that has not deteriorated is transferred to the photoconductor together with the deteriorated carrier, which is inefficient. Further, since the deteriorated carrier remains in the developer, it is difficult to suppress the occurrence of a problem caused by the deteriorated carrier, for example, a problem that the carrier adheres to the solid exposure portion of the photoreceptor. In addition, when transferring deteriorated carriers to the photoconductor, it is necessary to set the background potential to be larger than the background potential during normal image formation. Therefore, it is necessary to remove the deteriorated carrier while performing normal image forming operations. There is also a problem that it is not possible.

  It is an object of the present invention to provide an image forming apparatus that can remove deteriorated carrier from a developer even during an image forming operation, and does not cause solid exposure part carrier adhesion.

  The above problem is solved by the following means.

1. A photoreceptor,
An image writing unit that irradiates the photosensitive member with output light and forms an electrostatic latent image on the photosensitive member;
A developing device having a developer conveying body that is rotatably disposed facing the photoconductor at a predetermined interval and carries a developer composed of toner and a carrier and conveys the developer to a position facing the photoconductor; Have
The toner in the developer carried on the developer transport body is transferred to the photoconductor by an electric field between the photoconductor and the developer transport body at a position where the photoconductor and the developer transport body face each other. In the image forming apparatus for developing the electrostatic latent image carried on the photoreceptor,
A carrier removing unit that forms an electric field between the developer transport body and removes the deteriorated carrier from the developer transport body from the initial stage;
A carrier measuring unit for measuring the degree of deterioration of the carrier removed by the carrier removing unit;
An electric field strength changing unit that changes the strength of the electric field between the carrier removing unit and the developer transport body based on the measurement result of the carrier measuring unit;
An image forming apparatus comprising:

2. The carrier removing unit is disposed on the upstream side in the rotation direction of the developer transport body from a position where the developer transport body and the photosensitive body face each other.
The strength of the electric field between the carrier removal unit and the developer transport body is at least between the irradiated portion of the photoconductor and the developer transport body irradiated with the output light of the maximum output of the image writing unit. 2. The image forming apparatus as described in 1 above, wherein the image forming apparatus is stronger than the electric field.

  3. 2. The image forming apparatus according to 1, wherein the carrier measuring unit measures the degree of deterioration of the carrier removed by the carrier removing unit based on a current value flowing through the carrier.

  4). 2. The image forming apparatus according to 1, wherein the carrier measuring unit measures the degree of deterioration of the carrier removed by the carrier removing unit based on the magnetic permeability of the carrier.

  5. The change of the electric field strength between the carrier removing unit and the developer transporting body by the electric field strength changing unit is performed by changing a voltage applied to the carrier removing unit. The image forming apparatus described in 1.

  6). The change of the electric field strength between the carrier removal unit and the developer transport body by the electric field strength changing unit is performed by changing the interval at the facing position between the carrier removal unit and the developer transport body. 2. The image forming apparatus as described in 1 above.

  According to the present invention, it is possible to provide an image forming apparatus that can remove deteriorated carrier from a developer even during an image forming operation and does not cause solid carrier exposure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an image forming apparatus according to a first embodiment of the present invention. FIG. 6 is a schematic diagram illustrating a configuration of a developing device 500 and a developing operation. FIG. 10 is a schematic diagram illustrating a configuration and developing operation of a developing device 500A incorporated in an image forming apparatus according to a second embodiment. It is a schematic diagram illustrating the configuration of the developing device 500B and the developing operation. It is a schematic diagram illustrating the configuration of the developing device 500P and the developing operation. It is a schematic diagram illustrating the configuration of the developing device 500T and the developing operation.

  Hereinafter, an image forming apparatus as an example of an embodiment of the present invention will be described. The present invention is not limited to this form.

  FIG. 1 is a diagram for explaining an image forming apparatus according to a first embodiment of the present invention.

  The image forming apparatus 10 is an image forming apparatus that prints and discharges images or characters on recording paper by an electrophotographic method.

  The image forming apparatus 10 includes a document reading unit 100, an image processing unit 200 (shown in FIG. 4), an image writing unit 300, an image forming unit 400, a transfer unit 450, a developing device 500, a fixing unit 600, a paper feed conveyance unit 700, An operation display unit 800 and a control unit 900 are provided.

  From the operation display unit 800, conditions for operating the image forming apparatus 10, for example, the number and size of recording sheets on which image formation is performed can be input as job information. The operation display unit 800 is provided with a start button. By turning on the start button, image formation of the image forming apparatus 10 can be started based on the input job information.

  The control unit 900 controls the operation of each unit of the image forming apparatus 10. In addition, the image forming operation executed by the image forming apparatus 10 is controlled based on the job information input from the operation display unit 800.

  An automatic document feeder DF is mounted on the upper part of the image forming apparatus 10. The document d placed on the document table of the automatic document feeder DF is conveyed in the direction of the arrow, the image of the document is read by the optical system of the document reading unit 100, and image information is acquired.

  The acquired image information is subjected to necessary image processing by the image processing unit 200 and sent to the image writing unit 300.

  The image writing unit 300 irradiates the photosensitive drum 410 of the image forming unit 400 of the image forming unit 400 with output light based on the image information with a semiconductor laser.

  The image forming unit 400 includes a photosensitive drum 410, an eraser lamp 420, a charger 430, and a cleaner 460.

  The photosensitive drum 410 rotated in the direction of the arrow shown by a driving means (not shown) is irradiated with the eraser lamp 420 to be neutralized, and then charged by the charger 430 and is based on the image information by the image writing unit 300. Irradiated with output light. By irradiating the output light from the image writing unit 300, an electrostatic latent image based on the image information is formed on the peripheral surface of the photosensitive drum 410. The photoconductor drum 410 functions as a photoconductor.

  The electrostatic latent image formed on the photosensitive drum 410 is developed by the developing device 500 and becomes a toner image. The configuration and operation of the developing device 500 will be described later.

  The toner image on the photosensitive drum 410 is transferred by the transfer unit 450 to the recording sheet S conveyed by the paper feeding / conveying unit 700, and the recording sheet S to which the toner image transferred through the fixing unit 600 is fixed is transferred to the recording sheet S. It is discharged outside the image forming apparatus 10.

  The cleaner 460 causes the cleaning blade 461 to contact the peripheral surface of the rotating photosensitive drum 410 to rub against the peripheral surface of the photosensitive drum 410 and scrape and remove the toner remaining on the peripheral surface.

  After the toner image is transferred to the recording paper S, the toner remaining on the outer peripheral surface of the photosensitive drum 410 is removed by the cleaner 460, and then the charge is removed by the eraser lamp 420 and charged by the charger 430. This is used for forming a new electrostatic latent image.

  The image forming apparatus and the developing device mounted will be described below.

  The image forming apparatus according to the first embodiment of the present invention is equipped with a developing device 500 described below.

  FIG. 2 is a schematic diagram illustrating the configuration of the developing device 500 and the developing operation.

  Reference numeral 510 denotes a developing device housing, which forms a developer storage chamber 513 that stores a developer (two-component developer) in which toner and a carrier are mixed and functions as a stirring tank.

  The developing device housing 510 is attached to the developing sleeve 551 functioning as a developer transport body, a magnetic roll 552 that is a magnetic field generating means included in the developing sleeve 551 and has a fixed magnetic pole, and the developing sleeve 551 that is transported. A layer thickness regulating member 555 that regulates the layer thickness of the developer to a predetermined amount and a pair of stirring screws 561 and 562 that stir the developer in the developer storage chamber 513 are disposed. Reference numeral 571 denotes a carrier adhesion roller, 572 a collection roller, 573 a scraper, and 574 a carrier discharge screw.

  A toner hopper 520 shown in the upper part of the developing device casing 510 is a carrier hopper for storing fresh toner, and 530 is a carrier hopper for storing fresh carrier. The toner or carrier stored in the developer storage chamber 513 from the toner hopper 520 and the carrier hopper 530 is supplied to the developer storage chamber 513 via a supply path (not shown).

  Reference numeral 514 denotes a toner concentration detection sensor for detecting the toner concentration of the developer in the developer storage chamber 513, and reference numeral 517 denotes a developer upper surface detection sensor for detecting the total amount of the developer in the developer storage chamber 513. is there.

  The agitating screws 561 and 562 rotate at mutually constant speeds in opposite directions to agitate the developer in the developer accommodating chamber 513, mix the toner and carrier, and triboelectrically charge the developer. The toner used as the developer in the image forming apparatus of the present embodiment has a negative charging characteristic, and the carrier has a resin particle constituting the toner and a resin that coats the surface of the carrier so as to have a positive charging characteristic. The material is selected, and the toner is negatively charged and the carrier is positively charged by being rubbed by stirring. The negatively charged toner adheres to the periphery of the positively charged carrier.

  The developing sleeve 551 is a non-magnetic cylindrical member using, for example, a stainless material, and maintains a predetermined gap (for example, 0.3 mm in the present embodiment) with respect to the peripheral surface of the photosensitive drum 410. The rotation driving means (not shown) is configured to rotate in opposite directions (clockwise rotation in FIG. 2) at positions facing each other with respect to the rotation of the photosensitive drum 410 (clockwise rotation in FIG. 2).

  The magnet roll 552 is fixed inside the developing sleeve 551 concentrically with the developing sleeve 551. A plurality of magnetic poles, for example, magnetic poles N 1, N 2, N 3, S 1, S 2, are alternately arranged on the magnet roll 552, and a magnetic force is applied to the peripheral surface of the nonmagnetic developing sleeve 551.

  Due to the magnetic force of the magnet roll 552, the developer in the developer accommodating chamber 513, that is, the carrier to which the toner is attached adheres to the peripheral surface of the developing sleeve 551.

  The rotating developing sleeve 551 conveys the developer adhering to the peripheral surface to a position (developing region) facing the photosensitive drum 410.

The layer thickness regulating member 555 is arranged in the developing device casing 510 so that a free end thereof is a predetermined gap (for example, 0.25 mm in the present embodiment) from the peripheral surface of the developing sleeve 551. The thickness of the developer layer that adheres to the circumferential surface of the rotating developing sleeve 551 and is conveyed, that is, the layer thickness is regulated within a predetermined range, and the developer conveyance amount is regulated. For example, the developer carrying amount of the developing sleeve 551 in the present embodiment is 200 g / m ² .

  After the surface of the photoconductive drum 410 is uniformly charged to a negative polarity by the charger 430, and the output light LB based on the image information is irradiated (written) by the image writing unit 300, the charged amount of the irradiated portion is increased. And an electrostatic latent image based on the image information is formed.

  In this embodiment, the charging potential of the surface of the photosensitive drum 410 by the charger 430 is −600 V, but is not limited thereto.

  The rotating photosensitive drum 410 is irradiated with the output light LB from the image writing unit 300, and the charged potential on the surface thereof changes depending on the irradiation amount (exposure amount) of the output light from the image writing unit 300, and the electrostatic latent image. Is formed. The potential of the surface of the photosensitive drum 410 in the developing device 500 is −600 V in the portion not irradiated with the output light (background portion), whereas the potential of the portion irradiated with the maximum output (solid exposure portion) is −. It is configured to be 100V.

  A developing bias voltage is applied to the developing sleeve 551 by a bias power source 559. The developing bias voltage in this embodiment is −500V. When the electrostatic latent image forming portion reaches the position facing the developing sleeve 551 (developing region) by the rotation of the photosensitive drum 410, the toner (negatively charged) of the developer conveyed by the developing sleeve 551 to the developing region. Is moved away from the carrier to the exposure portion of the photosensitive drum 410. At this time, the carrier is attracted to the developing sleeve 551 by the magnetic force of the magnet roll 552 and does not move to the photosensitive drum 410.

  The amount of toner transferred to the photosensitive drum 410 corresponds to the surface potential of the photosensitive drum 410, that is, the electrostatic latent image formed on the photosensitive drum 410, and the toner image in which the electrostatic latent image is a visible image. It becomes.

  Toner and carrier remaining on the peripheral surface of the developing sleeve 551 without moving to the photosensitive drum 410 pass through the developing region by the rotation of the developing sleeve 551, and are separated from the developing sleeve 551 by the action of the magnetic pole of the magnet roll 552. Then, the developer storage chamber 513 which is a stirring tank is returned. Then, it is stirred and mixed with the developer stored in the developer storage chamber 513 by the stirring screw 561, and used for new development.

  As described above, the carrier is not consumed by the development and is repeatedly used. However, since the toner is consumed by the development, the amount of toner in the developer storage chamber 513 is reduced by repeating the image forming operation.

  A developer supply port 511 is opened on the top plate in the upper part of the developer storage chamber 513. The developer supply port 511 communicates with a toner hopper 520 serving as a toner storage unit and a carrier hopper 530 serving as a carrier storage unit via a supply path (not shown), and depends on the state of the developer in the developer storage chamber 513. Then, toner or carrier is supplied into the developer storage chamber 513 through the developer supply port 511.

  The replenished toner or carrier is agitated and mixed with the developer accommodated in the developer accommodating chamber 513 by the agitating screws 561 and 562 to become a developer having a uniform toner concentration.

  Since the toner in the developer storage chamber 513 is transferred to the photosensitive drum 410 and consumed by development, the toner is reduced by repeating the development operation. On the other hand, the carrier is not consumed by development and is not reduced because it is used repeatedly. Therefore, by repeating the developing operation, the ratio (toner concentration) of the toner in the developer (mixture of toner and carrier) in the developer storage chamber 513 decreases. When the toner concentration in the developer decreases, appropriate development cannot be performed.

  When the toner concentration detection sensor 514 detects that the toner concentration in the developer storage chamber 513 has decreased below a predetermined toner concentration, the toner stored in the toner hopper 520 is supplied to the developer storage chamber 513.

  In the present embodiment, a shutter that closes the toner discharge port 521 of the toner hopper 520 when the toner concentration detection sensor 514 detects that the toner concentration in the developer storage chamber 513 is equal to or lower than a predetermined value. The toner discharge port 521 is opened by operating 522, and the toner stored in the toner hopper 520 is supplied to the developer storage chamber 513 via a toner supply path (not shown). By supplying the toner, the ratio of the toner in the developer in the developer storage chamber 513 is increased, and the toner density is increased.

  When the toner concentration of the developer in the developer storage chamber 513 reaches a predetermined value or more, the shutter 522 is operated to close the toner discharge port 521 and stop the supply of toner from the toner hopper 520.

  In this way, by supplying toner into the developer accommodating chamber 513 based on the detected toner concentration in the developer accommodating chamber 513, the toner concentration of the developer within the developer accommodating chamber 513 is set to a predetermined value. It is configured to keep in the range.

  The carrier is supplied from the carrier hopper 530 when the developer upper surface detection sensor 517 detects that the upper surface of the developer stored in the developer storage chamber 513 is lower than a predetermined height.

  In the image forming operation (development), the carrier is not consumed and the carrier is used repeatedly. The carrier that is repeatedly used is deteriorated by repeated stirring, the resin coat on the surface is peeled off, and the resistance value is lowered.

  Since the deteriorated carrier easily shifts to the photosensitive drum 410, a defect that shifts to the solid exposure portion of the electrostatic latent image, so-called solid exposure portion carrier adhesion is likely to occur.

  The developing device 500 includes a carrier removing unit 570 and can remove deteriorated carriers.

  The carrier removing unit 570 includes a carrier adhering roller 571, a collecting roller 572, and a scraper 573, and a deteriorated carrier, specifically, a carrier whose resistance value has been lowered to a level at which solid adhering unit carrier adhering is generated. From 551, the carrier adheres to the roller 571 and is removed.

  The carrier adhesion roller 571 is formed of a nonmagnetic columnar member such as a stainless material. The carrier adhering roller 571 maintains a predetermined gap (for example, 0.25 mm in this embodiment) with respect to the peripheral surface of the developing sleeve 551, and develops more than the position where the developing sleeve 551 and the photosensitive drum 410 face each other. The sleeve 551 is disposed on the upstream side in the rotation direction. Then, the developing sleeve 551 is rotated in the opposite direction (clockwise rotation in FIG. 2) at a position opposite to the rotation of the developing sleeve 551 (clockwise rotation in FIG. 2) by a rotation driving unit (not shown).

  A voltage is applied to the carrier adhesion roller 571 by a voltage variable DC power supply 590E. The voltage variable DC power supply 590E is a power supply that can change the output voltage, and the output voltage is changed under the control of the control unit 900. For example, in the present embodiment, +200 V is the default value.

  Carrier deteriorated by setting the strength of the electric field between the developing sleeve 551 and the carrier adhering roller 571 to be stronger than the strength of the electric field between the developing sleeve 551 and the solid exposure portion of the photosensitive drum 410, specifically In this case, a carrier having a resistance value lowered to a level at which solid exposure portion carrier adhesion occurs can be adhered to the carrier adhesion roller 571 and removed from the developing sleeve 551.

The strength of the electric field between two opposing parts can be represented by a numerical value obtained by dividing the potential difference between the two parts by the distance between the two parts. For example, the intensity E _SD of the electric field between the developing sleeve 551 and the solid exposure portion of the photosensitive drum 410 is V _S , and the potential of the developing sleeve 551 is V _S , and the potential of the solid exposure portion of the photosensitive drum 410 is V _D. If the distance between the developing sleeve 551 and the photosensitive drum 410 is d _SD ,
E _SD = (V _D -V _S ) / d _SD
It is represented by

Similarly, the intensity _{E S-B} of the electric field between the developing sleeve 551 and the carrier adhesion roller 571, the potential of the developing sleeve 551 _{V S,} the potential of the carrier deposition roller 571 _{V B,} carrier adhesion and the developing sleeve 551 When the distance between the rollers 571 and _{d S-B,}
E _S−B = (V _D −V _B ) / d _S−B
It is represented by

Greater than the strength E _S-D in the electric field between the solid exposed portions strength E _S-B of the electric field, the developing sleeve 551 and the photosensitive drum 410 between the developing sleeve 551 and the carrier adhesion roller 571 By doing so, it is possible to remove the deteriorated carrier, specifically, the carrier whose resistance value has been lowered to a level at which solid exposure portion carrier adhesion occurs.

Then, the electric field strength E _S-B between the developing sleeve 551 and the carrier adhesion roller 571, than the strength E _S-D in the electric field between the solid exposed portion of the developing sleeve 551 and the photosensitive drum 410 The larger the carrier capacity, the higher the carrier removal capability of the carrier adhesion roller 571. That is, even a carrier with a small degree of deterioration can be removed.

As described above, the potential at the solid exposure portion of the photosensitive drum 410 in the developing device 500 is −100 V, and the developing sleeve 551 rotates with a gap of 0.3 mm with respect to the peripheral surface of the photosensitive drum 410. Thus, the electric field strength E _SD between the developing sleeve 551 and the solid exposure portion of the photosensitive drum 410 is
E _SD = ((− 500 V − (− 100 V)) / 0.3 mm
= -1333 × 10 ³ V / m
It is.

The DC bias voltage applied to the developing sleeve 551 in the developing device 500 is −500 V, and the carrier adhesion roller 571 is configured to rotate with a gap of 0.25 mm with respect to the peripheral surface of the developing sleeve 551. Then, when the voltage applied to the carrier adhesion roller 571 to + 200V, which is the default value, for example, strength _{E S-B} of the electric field between the developing sleeve 551 and the carrier adhesion roller 571,
_{E S-B = ((-} 500V - (+ 200V)) / 0.25mm
= -2800 × 10 ³ V / m
It becomes.

Thus, when the voltage applied to the carrier adhesion roller 571 to + 200V, which is the default value, for example, strength _{E S-B} of the electric field between the developing sleeve 551 and the carrier adhesion roller 571 in the developing device 500, - 2800 × 10 ³ V / m. Further, the strength _{E S-D} in the electric field between the solid exposed portion of the developing sleeve 551 and the photosensitive drum 410 becomes -1333 × ¹⁰ 3 V / m. Therefore, the intensity E _S-B of the electric field between the developing sleeve 551 and the carrier adhesion roller 571, the deterioration becomes larger than the strength E _S-B of the electric field between the developing sleeve 551 and the carrier adhesion roller 571 The carrier whose resistance value has decreased to a level at which the solid exposure portion carrier adhesion occurs can be adhered to the carrier adhesion roller 571 and removed from the developing sleeve 551. A predetermined electric field is formed between the carrier removal portion disposed opposite to the developer transport body, and the developer transported to the position facing the photoconductor by the developer transport body is compared with the initial stage. It can be said that the process of attaching and removing the deteriorated carrier to the carrier removing portion is a deteriorated carrier removing process.

  Therefore, the developer from which the carrier whose resistance value has been reduced to a level at which the solid exposure portion carrier adhesion occurs is removed is transported to a position facing the photosensitive drum 410, so that the solid exposure portion carrier adheres to the photosensitive drum 410. Is not generated.

  The toner moves to the carrier adhesion roller 571 together with the deteriorated carrier. The carrier and toner transferred to the peripheral surface of the carrier adhesion roller 571 are conveyed to a position facing the collection roller 572 by the rotation of the carrier adhesion roller 571.

  The collection roller 572 is a magnetic roller provided with a plurality of magnetic poles, and is disposed with a predetermined gap (0.2 mm in this embodiment) with respect to the peripheral surface of the carrier adhesion roller 571, and is not shown in the drawing. The driving means rotates the carrier adhering roller 571 in the same direction (counterclockwise rotation in FIG. 2) at positions facing each other with respect to the rotation of the carrier adhesion roller 571 (clockwise rotation in FIG. 2).

  In the present embodiment, a voltage equal to the voltage applied to the carrier adhesion roller 571 is applied to the collection roller 572. Note that a voltage may be applied to each of the carrier adhesion roller 571 and the collection roller 572 by an independent power source, and the voltage applied to each may not be the same.

  The collection roller 572 attracts the deteriorated carrier from the carrier adhesion roller 571 by a magnetic force at a position facing the carrier adhesion roller 571 and conveys it to the position where the scraper 573 is disposed.

  The scraper 573 is a plate-like member made of a flexible material, for example, phosphor bronze, which is disposed with its front end in contact with the peripheral surface of the collection roller 572. The scraper 573 rubs the peripheral surface of the rotating collection roller 572 and scrapes off the carrier adsorbed and conveyed by the collection roller 572 from the collection roller 572.

  The carrier scraped off is temporarily stored in the carrier storage chamber 576 and discharged from the end of the carrier storage chamber 576 through a discharge path (not shown) by the operation of the carrier discharge screw 574.

  The toner remains on the peripheral surface of the carrier adhering roller 571 that has passed the position facing the collecting roller 572, but the remaining toner returns to the developing sleeve 551 again at the position facing the developing sleeve 551 and is used for development. The toner is not discarded as the deteriorated carrier is removed.

  Note that the carrier of the developer stored in the developer storage chamber 513 is reduced by discharging and removing the deteriorated carrier.

  When the carrier of the developer stored in the developer storage chamber 513 decreases, the total amount of developer stored in the developer storage chamber 513 decreases.

  A decrease in the total amount of developer accommodated in the developer accommodating chamber 513 results in a decrease in the height of the upper surface of the developer accommodated in the developer accommodating chamber 513. When the developer upper surface detection sensor 517 detects that the upper surface of the developer has fallen below a predetermined height, the shutter 532 that closes the carrier discharge port 531 of the carrier hopper 530 is operated to operate the carrier discharge port. 531 is opened, and the carrier (fresh and undegraded) stored in the carrier hopper 530 is supplied to the developer storage chamber 513 via a supply path (not shown).

  When the total amount of developer in the developer accommodating chamber 513 increases due to the supply of the carrier, and the upper surface of the developer accommodated in the developer accommodating chamber 513 exceeds a predetermined height, the shutter 532 is closed, and the carrier hopper The supply of the carrier from 530 is stopped.

  Further, although the toner concentration of the developer in the developer storage chamber 513 is reduced by the supply of the carrier, when the toner concentration detection sensor 514 detects that the toner concentration is equal to or lower than a predetermined value, the toner hopper 520 supplies the toner. Supply is performed, and the toner density of the developer in the developer storage chamber 513 is maintained within a predetermined range.

  By the way, the level of the resistance value of the carrier attached to the carrier attaching roller 571 changes when environmental conditions, for example, humidity changes.

  For example, when the humidity is lowered, the charge position of the carrier is increased, and the carrier is less likely to move to the carrier adhesion roller 571. Therefore, the deteriorated carrier does not move to the carrier adhesion roller 571 and is positioned at the position facing the photosensitive drum 410. May be transported to the surface, and the solid exposure part carrier adhesion may occur. Further, when the humidity is high, the charge level of the carrier is low, so that even the carrier whose resistance value has not decreased so much is transferred to the carrier adhesion roller 571 and discharged, so that wasteful discharge of the carrier increases. Consumption increases.

  The developing device 500 changes the strength of the electric field between the carrier removing unit 570 and the developer carrier based on the measurement result of the carrier measuring unit 580 and the carrier measuring unit 580 that measures the degree of deterioration of the removed carrier. Electric field strength changing section 590. And even if there is a change in humidity, while reliably removing the carrier that has deteriorated and the resistance value has decreased to a level that causes solid exposure part carrier adhesion, suppress the discharge of the carrier with a low degree of deterioration, Carrier consumption can be reduced.

  The electric field strength changing unit 590 includes a control unit 900 and a voltage variable DC power source 590E that generates a voltage to be applied to the carrier adhesion roller 571. The voltage variable DC power supply 590E is a DC power supply that can change the generated voltage, and the resistance value level of the carrier discharged by changing the voltage applied to the carrier adhesion roller 571 under the control of the control unit 900 is changed. change.

That is, by increasing the voltage applied to the carrier adhesion roller 571, since the strength E _S-B of the electric field between the developing sleeve 551 and the carrier adhesion roller 571 becomes stronger, until a small carrier having a degree of deterioration removal it can. Moreover, by lowering the voltage applied to the carrier adhesion roller 571, since the strength E _S-B of the electric field between the developing sleeve 551 and the carrier adhesion roller 571 becomes weaker, less carrier of degree of deterioration is removed It becomes difficult.

  The carrier measuring unit 580 detects and outputs the degree of deterioration of the discharged carrier based on the current value that flows when the carrier is energized under a predetermined condition.

  The carrier measuring unit 580 includes a temporary storage chamber 581 for temporarily storing the carrier discharged from the carrier storage chamber 576, and a degree of deterioration of the carrier stored in the temporary storage chamber 581 by a current value flowing through the carrier. And a current detection unit 582 for detection. Reference numeral 585 denotes a carrier amount detection sensor that detects whether or not the amount of carriers stored in the temporary storage chamber 581 has reached an amount capable of measuring carrier characteristics.

  In the carrier amount detection sensor 585, the upper surface of the carrier stored in the temporary storage chamber 581 exceeds the upper ends of the flat plate electrode 582PA and the flat plate electrode 582PB, which will be described later, that is, the opposing portion between the flat plate electrode 582PA and the flat plate electrode 582PB is temporarily. When the storage chamber 581 is filled with the stored carrier, a signal (carrier satisfaction signal) is transmitted to the connected control unit 900.

  The current detection unit 582 includes a detection unit in which the plate electrode 582PA and the plate electrode 582PB are arranged to face each other at a predetermined interval, a DC power supply 582E, and an ammeter 582A. The plate electrode 582PA is connected to a DC power source 582E, and the plate electrode 582PB is grounded via an ammeter 582A.

  The material, shape, and spacing of the plate electrode 582PA and the plate electrode 582PB, and the voltage of the DC power supply 582E may be determined as appropriate. For example, in the present embodiment, the flat plate electrode 582PA and the flat plate electrode 582PB are formed of a stainless steel plate having a width of 10 mm, a vertical length of 50 mm, and a thickness of 0.1 mm, and each flat portion in the temporary storage chamber 581 is 2 mm. It is arranged to face each other at an interval of. The voltage of the DC power supply 582E is set to 1 kV.

  The current detection unit 582 measures the current value stored in the temporary storage chamber 581 and flowing through the carrier sandwiched between the opposing portions of the flat plate electrode 582PA and the flat plate electrode 582PB, with an ammeter 582A.

  On the other hand, a predetermined amount of unused carrier that has not deteriorated is stored in the temporary storage chamber 581, and the current value measured by the current detection unit 582 is confirmed to be 10 to 13 μA.

  When the discharged carrier includes a carrier that has not deteriorated and is close to the initial resistance value, the electric resistance value of the carrier increases, and thus the flowing current decreases. On the other hand, when the ratio of deteriorated carriers is high, the flowing current becomes small. Therefore, the degree of deterioration of the discharged carrier can be determined based on the value of the current flowing through the carrier sandwiched between the opposed portions of the plate electrode 582PA and the plate electrode 582PB, that is, the output value of the ammeter 582A.

Control unit 900 changes the output voltage of the voltage variable DC power source 590E on the basis of the measured value of the ammeter 582A (current value), the electric field strength _{E S-B} between the developing sleeve 551 and the carrier adhesion roller 571 To change.

As described above, when the voltage applied to the carrier adhesion roller 571 is increased, that is, when the output voltage of the voltage variable DC power supply 590E is increased, for example, from a default value of +200 V, the voltage between the developing sleeve 551 and the carrier adhesion roller 571 is increased. since strength E _S-B of the electric field becomes stronger, it can be removed a small carrier of degree of deterioration. Further, the voltage applied to the carrier adhesion roller 571 lower, i.e. to lower the output voltage of the voltage variable DC power source 590E, smaller carrier of degree of deterioration since the strength E _S-B of the electric field is weakened becomes difficult to remove.

  The controller 900 waits for a carrier sufficiency signal when the carrier upper surface detection sensor 585 has reached an amount that allows the amount of carriers stored in the temporary storage chamber 581 to measure the carrier characteristics, and temporarily stores it in the current detection unit 582. Measurement of the carrier characteristics stored in the chamber 581 is started.

  The control unit 900 operates the voltage variable DC power source 590E to generate a predetermined voltage, and causes the ammeter 582A to measure the value of the current flowing through the carrier at the opposing portion of the plate electrode 582PA and the plate electrode 582PB, Output. When the current is detected by the current detector 582, the current is discharged from the carrier storage chamber 576 through a path (not shown). This step of measuring the degree of deterioration of the removed carrier can be said to be a carrier deterioration degree measuring step.

  When the current value is smaller than the lower limit value of the current value range determined in advance based on the level of resistance reduction of the carrier to be discharged, the control unit 900 lowers the output voltage value of the voltage variable DC power supply 590E, When the value is larger than the upper limit value of the predetermined current value range, the operation of the voltage variable DC power supply 590E is controlled to increase the output voltage value of the voltage variable DC power supply 590E.

  The controller 900 lowers the output voltage value of the voltage variable DC power supply 590E when the current value flowing through the carrier is smaller than the lower limit value of the predetermined current value range, and the current value is the upper limit of the predetermined current value range. When larger than the value, control is performed so as to increase the output voltage value of the voltage variable DC power supply 590E.

  In the developing device 500, the lower limit value of the current value is set to 15 μA, and the upper limit value is set to 20 μA.

  The lower limit value of 15 μA is a current value of a carrier having a resistance value at a level sufficiently safe with respect to a level at which the solid exposure portion carrier adhesion occurs, and the configuration of the developer 500 and the developer (carrier) to be used It is a value obtained separately based on the characteristics. The state in which the current value detected by the current detection unit 582 is smaller than the lower limit of 15 μA is a state in which the ratio of carriers with a small degree of deterioration in the removed carriers is high, and there is a possibility that useless carrier discharge is performed. State.

  When the current value detected by current detection unit 582 is smaller than the lower limit of 15 μA, control unit 900 controls to reduce the output voltage value of voltage variable DC power supply 590E. By reducing the output voltage value of the voltage variable DC power supply 590E, it is possible to suppress the discharge of carriers with a small degree of deterioration, and to suppress unnecessary carrier discharge. This process of controlling the degree of deterioration of the removed carrier by changing the strength of the electric field can be said to be a removed carrier deterioration degree control process.

  On the other hand, the upper limit value of 20 μA is a current value of a carrier at a dangerous level close to a level at which the resistance value decreases from the initial resistance value and causes solid exposure portion carrier adhesion. When the current value detected by the current detection unit 582 is larger than the upper limit value of 20 μA, the ratio of the carrier having a large degree of deterioration in the removed carrier is high, and is close to a level at which the solid exposure portion carrier adheres to the developing sleeve 551. There is a high possibility that carriers having a resistance value of a level remain, and there is no allowance for prevention of solid exposure portion carrier adhesion.

  When the current value detected by current detection unit 582 is greater than the upper limit value of 20 μA, control unit 900 controls to increase the output voltage value of voltage variable DC power supply 590E. By increasing the output voltage value of the voltage variable DC power supply 590E, it is possible to discharge the carrier having a smaller degree of deterioration, and to prevent the solid exposure part carrier from being attached with a margin.

  As described above, the developing device 500 according to the first embodiment of the present invention is disposed on the developing sleeve 551 by the carrier adhering roller that is arranged to face the developing sleeve 551 that is a developer conveying member and to which a predetermined voltage is applied. The deteriorated carrier in the developed developer is moved to and attached to the carrier adhesion roller 571 to be removed.

  Further, since the deteriorated carrier can be removed while performing the image forming operation, it is not necessary to interrupt the image forming operation for removing the deteriorated carrier, and the productivity of the image forming apparatus can be reduced. Absent.

  Then, by changing the applied voltage to the carrier adhesion roller according to the magnitude of the current flowing through the discharged carrier, the degree of deterioration of the discharged carrier is maintained at an appropriate level without being affected by changes in humidity. be able to.

  In this way, it is possible to prevent the occurrence of problems due to the deteriorated carrier, and it is possible to prevent the carrier having a small degree of deterioration from being discharged, so that wasteful consumption of the carrier can be suppressed.

  Then, the facing position between the carrier attaching roller 571 and the developing sleeve 551 is set on the upstream side in the rotational direction of the developing sleeve 551 with respect to the facing position between the developing sleeve 551 and the photosensitive drum 410, and the carrier attaching roller 571 and the developing sleeve 551. Is set to be larger than the strength of the electric field between the developing sleeve 551 and the solid exposure portion of the photosensitive drum 410. With this configuration, the carrier that has deteriorated to a level at which the solid exposure portion carrier adhesion in the developer carried and transported by the developing sleeve 551 occurs is opposed to the developing sleeve 551 and the photosensitive drum 410, that is, Since it is removed from the developing sleeve 551 before being transported to the developing area, it is possible to prevent the problem of solid carrier exposure.

  The second embodiment of the present invention is an image forming apparatus in which the developing device 500 in the image forming apparatus according to the first embodiment shown in FIG. 1 is replaced with a developing device 500A described later.

  The image forming apparatus according to the second embodiment has the same configuration as the image forming apparatus according to the first embodiment except for the developing device, and performs the same operation as the image forming apparatus according to the first embodiment. Description of operations other than the developer will be omitted, and the operation relating to the developing device will be mainly described below.

  FIG. 3 is a schematic diagram illustrating the configuration of the developing device 500A incorporated in the image forming apparatus according to the second embodiment and the developing operation.

  The developing device 500A includes the electric field strength changing section 590 in contrast to the developing device 500 in the first embodiment described above, but includes a different electric field strength changing section 590A. The developing device 500 has the same configuration except that the applied voltage is constant.

  The carrier removing unit 570 in the developing device 500A has the same configuration as the carrier removing unit 570 in the developing device 500, and includes a carrier adhesion roller 571, a collection roller 572, and a scraper 573. The carrier whose resistance value has been lowered to a level at which the exposure portion carrier adhesion occurs is adhered to the carrier adhesion roller 571 from the developing sleeve 551 and removed.

  In the developing device 500A, members having the same names and symbols as those of the developing device 500 described above have the same contents and configurations as the members having the same names and symbols constituting the developing device 500 unless otherwise specified. The developing device 500 is disposed in the same positional relationship.

  For example, the gap between the developing sleeve 551 of the developing device 500A and the photosensitive drum 410 is 0.3 mm, which is the same as that of the developing device 500.

  The voltage applied to the developing sleeve 551 of the developing device 500A is −500 V, which is the same as the voltage applied to the developing sleeve 551 of the developing device 500.

  A constant voltage, +200 V, +200 V is applied to each of the carrier adhesion roller 571 and the collection roller 572 by a DC power source 579.

  Further, the charging potential (background portion) of the photosensitive drum 410 by the charger 430 is −600 V, and the potential of the portion irradiated with the maximum output (solid exposure portion) is −100 V.

  The electric field strength changing unit 590A includes a control unit 900, a carrier adhesion roller substrate 591 and a motor 590M.

  In the developing device 500A, the carrier adhesion roller substrate 591, the collection roller 572, and the scraper 573 in the carrier removing unit 570 have a relative positional relationship between the carrier adhesion roller substrate 591, the collection roller 572, and the scraper 573 in the development device 500. It is attached to the carrier adhesion roller substrate 591 while maintaining the relationship.

  The carrier adhesion roller substrate 591 is configured such that the gap between the developing sleeve 551 and the carrier adhesion roller 571 can be changed by a motor 590M. The motor 590M is a stepping motor, and its rotation direction and rotation angle are controlled by the control unit 900. The controller 900 can change the gap between the developing sleeve 551 and the carrier adhesion roller 571 by controlling the rotation direction and rotation angle of the motor 590M.

  Note that a gap (default value) between the carrier adhesion roller 571 and the collection roller 572 attached to the carrier adhesion roller substrate 591 is 0.25 mm.

  A voltage is applied to the carrier adhesion roller 571 in the carrier removing unit 570 by a DC power source 579. The output voltage of the DC power supply 579 is + 200V.

Therefore, the intensity _{E S-D} in the electric field between the solid exposed portion of the developing sleeve 551 and the photosensitive drum 410 in the developing unit 500A, the
E _SD = ((− 500 V − (− 100 V)) / 0.3 mm
= -1333 × 10 ³ V / m
It becomes.

Further, the strength E _S-B of the electric field between the developing sleeve 551 and the carrier adhesion roller 571 is changed by changing the gap between the developing sleeve 551 and the carrier adhesion roller 571. In the developing device 500A, when the gap between the developing sleeve 551 and the carrier adhering roller 571 is 0.25 mm which is a default value, ES _−B = ((− 500 V − (+ 200 V)) / 0.25 mm
= -2800 × 10 ³ V / m
, And the intensity E _S-B of the electric field between the developing sleeve 551 and the carrier adhesion roller 571 than the strength E _S-D in the electric field between the solid exposed portion of the developing sleeve 551 and the photosensitive drum 410 It is configured to be strong.

  The developing device 500A changes the strength of the electric field between the carrier removing unit 570 and the developing sleeve 551 by the electric field strength changing unit 590A based on the measurement result of the carrier measuring unit 580 that measures the degree of deterioration of the removed carrier. . Therefore, even if the humidity fluctuates and the carrier discharge level fluctuates, the carrier that has deteriorated to a level that causes the solid-exposed-part carrier adhesion to be removed is surely removed, and the discharge of the carrier with a low degree of deterioration is suppressed. , Carrier consumption can be suppressed.

  Similarly to the developing device 500, the carrier amount detection sensor 585 is configured such that the upper surface of the carrier stored in the temporary storage chamber 581 is in the temporary storage chamber 581 and the opposite portion between the flat plate electrode 582 PA and the flat plate electrode 582 PB in the carrier measurement unit 580. Transmits a signal (carrier sufficiency signal) to the connected control unit 900 when it is filled with the stored carrier.

  When the control unit 900 confirms the carrier sufficiency signal from the carrier amount detection sensor 585, the control unit 900 operates the DC power source 582E, and the current value flowing through the carrier sandwiched between the opposing portions of the flat plate electrode 582PA and the flat plate electrode 582PB is ammetered. Measure at 582A.

When the value of the current flowing through the carrier is smaller than the lower limit value of the current value range determined in advance based on the level of resistance reduction of the carrier to be discharged, the controller 900 develops the developing sleeve 551 and the carrier adhesion roller 571. weakening the electric field strength E _S-B between, when larger than the upper limit of the current value within a predetermined range, the electric field strength E _S-B between the developing sleeve 551 and the carrier adhesion roller 571 Strengthen.

In the developing device 500A, when the value of the current flowing through the carrier is smaller than the lower limit value of the predetermined current value range, the developing sleeve 551 and the carrier attaching roller 571 are separated by separating the carrier attaching roller 571 from the developing sleeve 551. weakening the electric field strength E _S-B between. Further, when the value of the current flowing through the carrier is larger than the upper limit value of a predetermined current value range, the carrier adhering roller 571 is moved closer to the developing sleeve 551, so that the developing sleeve 551 and the carrier adhering roller 571 are positioned. It controls to enhance the strength E _S-B of the electric field.

  In the developing device 500A, similarly to the developing device 500, the lower limit value of the current value is set to 15 μA, and the upper limit value is set to 20 μA.

  When the measured value (current value) of the ammeter 582A is smaller than the lower limit (15 μA) of the current value range determined in advance based on the deterioration level of the carrier to be discharged, the control unit 900 moves the carrier adhesion roller 571. The operation of the motor 590M is controlled so that the carrier adhering roller 571 is separated from the developing sleeve 551 when it is separated from the developing sleeve 551 and the current value is larger than the upper limit (20 μA) of the predetermined current value range.

By approaching the carrier adhesion roller 571 to the developing sleeve 551, since the strength E _S-B of the electric field between the developing sleeve 551 and the carrier adhesion roller 571 becomes stronger, can be removed a small carrier of degree of deterioration. Accordingly, it is possible to discharge the carrier having a small degree of deterioration, and the solid exposure part carrier adhesion can be prevented with a margin. The step of controlling the degree of deterioration of the carrier to be removed by changing the distance between the carrier adhesion roller 571 and the developing sleeve 551 and changing the strength of the electric field is another form of the removal carrier deterioration degree control step. It can be said.

Further, by separating the carrier adhesion roller 571 from the developing sleeve 551, since the strength E _S-B of the electric field between the developing sleeve 551 and the carrier adhesion roller 571 becomes weaker, the discharge of small carriers having a degree of degradation It is possible to suppress wasteful carrier discharge.

  As described above, in the developing device 500A, similarly to the developing device 500, the carrier having a lowered resistance value out of the developer carried on the developing sleeve 551 is moved and attached to the carrier attaching roller 571 to be removed.

  Further, since the deteriorated carrier can be removed while performing the image forming operation, it is not necessary to interrupt the image forming operation for removing the deteriorated carrier, and the productivity of the image forming apparatus can be reduced. Absent.

  Then, by changing the applied voltage to the carrier adhesion roller according to the magnitude of the current flowing through the discharged carrier, the degree of deterioration of the discharged carrier is maintained at an appropriate level without being affected by changes in humidity. be able to.

  In this way, it is possible to prevent the occurrence of problems due to the deteriorated carrier, and it is possible to prevent the carrier having a small degree of deterioration from being discharged, so that wasteful consumption of the carrier can be suppressed.

  The third embodiment of the present invention is an image forming apparatus in which the developing device 500 in the image forming apparatus according to the first embodiment shown in FIG. 1 is replaced with a developing device 500B described later.

  The image forming apparatus according to the third embodiment has the same configuration as the image forming apparatus according to the first embodiment except for the developing device, and performs the same operation as the image forming apparatus according to the first embodiment. Description of operations other than the developer will be omitted, and the operation relating to the developing device will be mainly described below.

  FIG. 4 is a schematic diagram illustrating the configuration and developing operation of the developing device 500B incorporated in the image forming apparatus according to the third embodiment.

  The developing device 500B has the carrier measuring unit 580 that measures the degree of deterioration of the discharged carrier and the value of the current flowing through the discharged carrier, in the developing device 500 in the first embodiment described above. On the other hand, it has the same configuration as the developing device 500 except that it has a carrier measuring unit 580B that measures the permeability of the discharged carrier.

  In the developing device 500B, the members having the same names and symbols as those of the developing device 500 described above have the same contents and configurations as the members having the same names and symbols constituting the developing device 500 unless otherwise specified. The developing device 500 is disposed in the same positional relationship.

  For example, the gap between the developing sleeve 551 of the developing device 500B and the photosensitive drum 410 is 0.3 mm, which is the same as that of the developing device 500.

  The voltage applied to the developing sleeve 551 is the same as the voltage applied to the developing sleeve 551 of the developing device 500, and is −500V. Similarly to the developing device 500, a voltage is applied to the carrier adhesion roller 571 and the collection roller 572 by a voltage variable DC power source 590E. The voltage variable DC power supply 590E is a power supply that can change the output voltage, and the output voltage is changed under the control of the control unit 900. For example, in the present embodiment, +200 V is the default value.

  Further, the charging potential (background portion) of the photosensitive drum 410 by the charger 430 is −600 V, and the potential of the portion irradiated with the maximum output (solid exposure portion) is −100 V.

Therefore, the strength E _SD of the electric field between the developing sleeve 551 and the solid exposure portion of the photosensitive drum 410 in the developing device 500B is
E _SD = ((− 500 V − (− 100 V)) / 0.3 mm
= -1333 × 10 ³ V / m
It becomes.

Further, the strength _{E S-B} of the electric field between the developing sleeve 551 and the carrier adhesion roller 571, when the voltage applied to the carrier adhesion roller 571 to + 200V for example, the default value,
_{E S-B = ((-} 500V - (+ 200V)) / 0.25mm
= -2800 × 10 ³ V / m
Next, the strength E _S-B of the electric field between the developing sleeve 551 and the carrier adhesion roller 571 than the strength E _S-D in the electric field between the solid exposed portion of the developing sleeve 551 and the photosensitive drum 410 It is configured to be strong.

  In the developing device 500B, as in the developing device 500, the level of the degree of deterioration of the discharged carrier is changed by changing the voltage applied to the carrier adhesion roller 571.

  580B is a carrier measurement unit that measures the degree of deterioration of the carrier discharged from the carrier storage chamber 576.

  The carrier measuring unit 580B in the developing device 500B of the present embodiment detects the degree of deterioration of the discharged carrier based on the magnetic permeability of the carrier and outputs it.

  The carrier measurement unit 580B temporarily stores the carrier discharged from the carrier storage chamber 576, and outputs the degree of deterioration of the carrier stored in the temporary storage chamber 581 as a measured value of permeability. A sensor 583 is included. Reference numeral 585 denotes a carrier amount detection sensor 585 that detects whether or not the amount of carriers stored in the temporary storage chamber 581 has reached an amount capable of measuring carrier characteristics.

  The magnetic permeability sensor 583 is stored in the temporary storage chamber 581, measures the magnetic permeability of the carrier, and outputs it as a voltage value.

  When the ratio of undegraded carriers in the discharged carriers is high, the magnetic permeability is small, and the output value of the magnetic permeability sensor 583, that is, the voltage value is high. On the other hand, when the ratio of undegraded carriers is low, the magnetic permeability is increased and the output value of the magnetic permeability sensor 583, that is, the voltage value is decreased. Therefore, the degree of deterioration can be determined from the voltage value. This step of measuring the degree of deterioration of the carrier removed with magnetic permeability can be said to be another form of the carrier deterioration degree measuring step.

  As a result of storing a predetermined amount of unused carriers used in the developing device 500B, that is, carriers having an initial resistance value in the temporary storage chamber 581 and measuring the permeability with the permeability sensor 583, the output value is 1.6. It has been confirmed to be ˜1.8V.

  The control unit 900 changes the output voltage of the voltage variable DC power supply 590E based on the output value of the magnetic permeability sensor 583.

  When the output value of the magnetic permeability sensor 583 is smaller than the lower limit value of the output value range determined in advance based on the level of resistance reduction of the carrier to be discharged, the control unit 900 outputs the output voltage of the voltage variable DC power supply 590E. When the value is lowered and the output value is larger than the upper limit value of the predetermined output value range, the operation of the voltage variable DC power supply 590E is controlled to increase the output voltage value of the voltage variable DC power supply 590E.

  In the developing device 500B, the lower limit value of the output value is set to 2.0V, and the upper limit value is set to 2.5V.

  The lower limit value of 2.0 V is an output value of a carrier having a resistance value at a level sufficiently safe with respect to the level at which the solid exposure portion carrier adhesion occurs, and the configuration of the developing device 500B and the developer (carrier) ) Is a value obtained separately based on the characteristics of The state in which the output value detected by the magnetic permeability sensor 583 is smaller than the lower limit value of 2.0 V is a state in which the ratio of carriers with a small degree of deterioration in the removed carriers is high, and unnecessary carrier discharge may be performed. There is a state.

  When the output value of magnetic permeability sensor 583 is smaller than the lower limit value of 2.0 V, control unit 900 performs control so that the output voltage value of voltage variable DC power supply 590E is lowered. By reducing the output voltage value of the voltage variable DC power supply 590E, it is possible to suppress the discharge of carriers with a small degree of deterioration, and to suppress unnecessary carrier discharge.

  On the other hand, the upper limit value of 2.5 V is an output value of a carrier at a dangerous level close to a level at which the resistance value decreases from the initial resistance value and the solid exposure portion carrier adhesion occurs. When the output value detected by the magnetic permeability sensor 583 is larger than the upper limit value of 2.5 V, the ratio of the carrier having a large degree of deterioration in the removed carrier is high, and the level at which the solidified portion carrier adheres to the developing sleeve 551 is generated. There is a high possibility that carriers having a resistance value close to 2 remain, and there is no room for prevention of solid-exposed portion carrier adhesion.

  When the output value detected by magnetic permeability sensor 583 is larger than the upper limit value of 2.5 V, control unit 900 controls to increase the output voltage value of voltage variable DC power supply 590E. By increasing the output voltage value of the voltage variable DC power supply 590E, it is possible to discharge the carrier having a smaller degree of deterioration, and to prevent the solid exposure part carrier from being attached with a margin.

  As described above, the developing device 500 according to the first embodiment of the present invention is disposed on the developing sleeve 551 by the carrier adhering roller that is arranged to face the developing sleeve 551 that is a developer conveying member and to which a predetermined voltage is applied. The deteriorated carrier in the developed developer is moved to and attached to the carrier adhesion roller 571 to be removed.

  Further, since the deteriorated carrier can be removed while performing the image forming operation, it is not necessary to interrupt the image forming operation for removing the deteriorated carrier, and the productivity of the image forming apparatus can be reduced. Absent.

  And by changing the applied voltage to the carrier adhesion roller according to the magnitude of the permeability of the discharged carrier, the degree of deterioration of the discharged carrier can be kept at an appropriate level without being affected by the change in humidity. .

  In this way, it is possible to prevent the occurrence of problems due to the deteriorated carrier, and it is possible to prevent the carrier having a small degree of deterioration from being discharged, so that wasteful consumption of the carrier can be suppressed.

  When the output value is smaller than the lower limit value of a predetermined output value range, that is, smaller than 15 μA, control unit 900 performs control so that the output voltage value of voltage variable DC power supply 590E is lowered. By lowering the output voltage value of the voltage variable DC power supply 590E, it is possible to suppress discharge of carriers with a small degree of deterioration.

  Further, when the output value is larger than the upper limit value of the predetermined current value range, that is, when it is larger than 20 μA, control is performed to increase the output voltage value of the voltage variable DC power supply 590E. By increasing the output voltage value of the voltage variable DC power supply 590E, the discharge of carriers with a small degree of deterioration is promoted.

  Thus, the deteriorated carrier can be removed from the developer in the developer storage chamber 513 via the developing sleeve 551, the carrier adhesion roller 571, and the recovery roller 572.

  Then, the degree of deterioration of the discharged carrier can be set to an appropriate level by changing the voltage applied to the carrier adhesion roller depending on the magnetic permeability of the discharged carrier.

  Further, since the deteriorated carrier can be removed while performing the image forming operation, it is not necessary to interrupt the image forming operation for removing the deteriorated carrier, and the productivity of the image forming apparatus can be reduced. Absent.

  In this way, it is possible to prevent the occurrence of problems due to the deteriorated carrier, and it is possible to prevent the carrier having a low degree of deterioration from being discharged, so that wasteful consumption of the carrier can be suppressed.

  It was confirmed as follows that the image forming apparatus according to the embodiment of the present invention is effective in efficiently removing deteriorated carriers.

  Example 1 is an image forming apparatus incorporating the developing device 500 according to the first embodiment of the present invention shown in FIG.

The conditions in Example 1 are as follows:
Developer transport amount of developing sleeve 551 200 g / m ²
Carrier adhesion roller 571 Yes Recovery roller 572 Yes Layer thickness regulating member 555 Yes Applied voltage to developing sleeve 551 -500V
Applied voltage to carrier adhesion roller 571 (+ 200V)
The default voltage is + 200V. The voltage applied to the collection roller is changed according to the degree of deterioration of the discharged carrier.
The voltage applied to the carrier adhesion roller 571 is the same. The distance between the developing sleeve 551 and the carrier adhesion roller 571 is 0.25 mm.
The distance between the developing sleeve 551 and the carrier adhesion roller 571 is 0.25 mm.
Distance between carrier adhesion roller 571 and collection roller 572 0.2 mm
The distance between the developing sleeve 551 and the layer thickness regulating member 555 is 0.25 mm.
It is.

Further, the conditions related to the photosensitive drum 410 in Example 1 are as follows:
The distance between the photosensitive drum 410 and the developing sleeve 551 is 0.3 mm.
Background potential of photosensitive drum 410 -600V
Solid exposure part potential of photoconductor drum 410 -100V
It is.

  The second embodiment is an image forming apparatus incorporating the developing device 500A according to the second embodiment of the present invention shown in FIG.

The conditions in Example 2 are as follows:
Developer transport amount of developing sleeve 551 200 g / m ²
Carrier adhesion roller 571 Yes Recovery roller 572 Yes Layer thickness regulating member 555 No Applied voltage to developing sleeve 551 -500V
Applied voltage to carrier adhesion roller 571 + 200V
Applied voltage to collection roller + 200V
Same voltage applied to carrier adhesion roller 571 Distance between developing sleeve 551 and carrier adhesion roller 571 (0.25 mm)
The default value is changed to 0.25 mm according to the degree of deterioration of the discharged and discharged carriers.

Distance between carrier adhesion roller 571 and collection roller 572 0.2 mm
Further, the conditions related to the photosensitive drum 410 in Example 2 are as follows:
The distance between the photosensitive drum 410 and the developing sleeve 551 is 0.3 mm.
Background potential of photosensitive drum 410 -600V
Solid exposure part potential of photoconductor drum 410 -100V
It is.

  The third embodiment is an image forming apparatus incorporating the developing device 500B according to the third embodiment of the present invention shown in FIG.

  In the developing device 500B according to the third embodiment, the developing device 500 according to the first embodiment measures the degree of the resistance value of the carrier with the carrier measuring unit 580, and changes the output voltage value of the voltage variable DC power source 590E based on the measurement result. On the other hand, the carrier measurement unit 580B measures the degree of carrier resistance, and the only difference is that the output voltage value of the voltage variable DC power supply 590E is changed according to the measurement result. The conditions are the same as in the first embodiment. It is.

  Comparative Example 1 is an image forming apparatus in which the developing device 500 in the image forming apparatus according to the first embodiment shown in FIG. 1 is replaced with a later-described 500P.

  FIG. 5 is a schematic diagram illustrating the configuration of the developing device 500P and the developing operation.

  When the developing device 500P operates in the carrier discharge mode, the background potential (difference between the charging potential of the photosensitive drum and the developing bias potential applied to the developing sleeve) is made larger than when operating in the image forming mode. Then, the deteriorated carrier is transferred from the developing sleeve to the photosensitive drum and removed. Therefore, the carrier removal unit 570 in the developing device 500 in the first embodiment described above is not provided.

  In the developing device 500P, the members having the same names and reference numerals as the developing device 500 are the same as the members constituting the developing device 500, and their functions and operations are described in the description of the developing device 500. The description here will be omitted, and portions having different functions will be described.

Various conditions in the developing device 500P are as follows:
Developer transport amount of developing sleeve 551 200 g / m ²
Carrier adhering roller 571 None Collecting roller 572 None Applied voltage to developing sleeve 551 In image forming mode operation −500 V
-500V during carrier discharge mode operation
It is.

Further, the conditions related to the photosensitive drum 410 in the developing device 500P are as follows:
The distance between the photosensitive drum 410 and the developing sleeve 551 is 0.3 mm.
Photoreceptor drum 410 potential Image formation mode operation Background -600V
Solid exposure unit -100V
When in carrier discharge mode Background -800V
No solid exposure area.

  Here, the image forming mode is a normal image forming operation, that is, a mode for performing development, and the carrier discharge mode is for performing an operation of removing the deteriorated carrier from the developer in the developer storage chamber 513. Mode.

  In the carrier discharge mode, the charging potential is set to −800 V, and writing by the output light from the image writing unit 300 is not performed. By operating the photosensitive drums 410 and 500P under such conditions, the carrier having deteriorated developer conveyed to the developing region by the rotating developing sleeve 551 can be transferred to the photosensitive drum 410.

In the carrier discharge mode, the background potential (the difference between the charging potential of the photosensitive drum 410 and the developing bias potential applied to the developing sleeve 551) is
-800V-(-500V) =-300V
The background potential in the image forming mode −600V − (− 500V) = − 100V
Therefore, the carrier deteriorated from the developer conveyed to the developing region by the rotating developing sleeve 551 can be transferred to the photosensitive drum 410.

  As described above, when the developing device 500P is operated in the carrier discharge mode, the deteriorated carrier can be removed from the developer in the developer storage chamber 513 via the developing sleeve 551 and the photosensitive drum 410. The deteriorated carrier transferred to the photosensitive drum 410 is removed from the peripheral surface of the photosensitive drum 410 by the cleaning blade 461 of the cleaner 460 and discharged.

  In the developing device 500P, since the charging potential of the photosensitive drum 410 in the carrier discharge mode is different from the charging potential of the photosensitive drum 410 in the image forming mode, it is not possible to simultaneously execute the image forming mode and the carrier discharging mode. The image cannot be formed during operation in the carrier discharge mode. For this reason, it is preferable that the image is normally formed in the image forming mode and is operated in the carrier discharge mode when a predetermined condition is satisfied. For example, every time a predetermined number of image formations are completed, the image forming mode is switched to the carrier discharge mode, the carrier discharge mode is operated for a predetermined time, and the image forming mode is operated again. ing.

  In the carrier discharge mode, the voltage applied to the developing sleeve 551 by the bias power supply 559 is set to −800V. In addition, the photosensitive drum 410 has a charging potential of −900 V and does not perform writing with output light from the image writing unit 300. By operating in the carrier discharge mode under such conditions, the carrier having deteriorated developer conveyed to the developing region by the rotating developing sleeve 551 can be transferred to the photosensitive drum 410.

  By transferring the carrier having deteriorated developer to the photosensitive drum 410, the total amount of developer accommodated in the developer accommodating chamber 513 is reduced. When the developer upper surface detection sensor 517 detects that the upper surface of the developer has fallen below a predetermined height due to the decrease in the developer, the carrier (fresh and undegraded) stored in the carrier hopper 530 is removed. The developer is supplied to the developer storage chamber 513.

  Comparative Example 2 is an image forming apparatus in which the developing device 500 in the image forming apparatus according to the first embodiment shown in FIG. 1 is replaced with a developing device 500T described later.

  FIG. 6 is a schematic diagram illustrating the configuration of the developing device 500T and the developing operation. The developing device 500T is a type of developer that replenishes the developer by a so-called trickle system, and does not have the carrier removing unit 570 in the developing device 500 described above.

  The developing device 500T will be described below. In the developing device 500T, members having the same names and symbols as those of the developing device 500 are the same as the members constituting the developing device 500, and description of each function and operation is made in the description of the developing device 500. Therefore, description here is omitted, and portions having different functions will be described.

  On the right side of the developer accommodating chamber 513 in the developing device 500T, there are a developer outlet 512 for discharging the excess developer in the developer accommodating chamber 513, and the developer discharged from the developer outlet 512. A developer storage chamber 515 that stores the developer and a developer discharge screw 581 that discharges the developer in the developer storage chamber 515 are disposed.

A developer hopper 540 for storing a developer composed of toner and carrier mixed in a predetermined ratio is disposed above the developing device housing 510 in the figure, and the developer in the developer storage chamber 513 is in the state of the developer. Accordingly, the stored developer is supplied to the developer storage chamber 513 through a supply path (not shown). In the present embodiment, the mass ratio of the developer toner and the carrier stored in the developer hopper 540 is as follows.
Toner: Carrier = 9: 1
It is.

  When the toner concentration detection sensor 514 detects that the toner concentration in the developer storage chamber 513 is lower than a predetermined toner concentration, the developer stored in the developer hopper 540 is supplied to the developer storage chamber 513. .

  In the developing device 500T, when the toner concentration detection sensor 514 detects that the toner concentration in the developer storage chamber 513 has become a predetermined value or less by repeating development, the developer hopper 540 discharges the developer. The shutter 542 closing the outlet 541 is operated to open the developer discharge port 541, and the developer stored in the developer hopper 540 is supplied to the developer storage chamber 513 via a supply path (not shown). To do. By supplying the developer, the ratio of the toner in the developer in the developer storage chamber 513 is increased, and the toner concentration is increased.

  When the toner concentration of the developer in the developer storage chamber 513 reaches a predetermined value or more, the shutter 542 is operated to close the developer discharge port 541 and stop the supply of the developer from the developer hopper 540.

  The total amount of the developer stored in the developer storage chamber 513 is increased by the supply of the developer from the developer hopper 540, and the height of the upper surface of the developer stored in the developer storage chamber 513 is increased.

  When the upper surface of the developer stored in the developer storage chamber 513 reaches the developer discharge port 512, the developer overflows from the developer discharge port 512. The developer overflowing from the developer discharge port 512 is stored in the developer storage chamber 515 and discharged through a discharge path (not shown) by the operation of the developer discharge screw 581.

  The developer overflowing from the developer discharge port 512 to the outside of the developing device housing 510 is a mixture of toner and carrier stored in the developer storage chamber 513, and a developer hopper together with a carrier that has deteriorated after repeated use. The new carrier included in the developer supplied from 540 is also included.

Various conditions in Comparative Example 2 are:
Developer transport amount of developing sleeve 551 200 g / m ²
Carrier adhesion roller 571 None Collection roller 572 None Applied voltage to developing sleeve 551 -500V
It is.

Further, the conditions related to the photosensitive drum 410 in Comparative Example 2 are as follows:
The distance between the photosensitive drum 410 and the developing sleeve 551 is 0.3 mm.
Background potential of photosensitive drum 410 -600V
Solid exposure part potential of photoconductor drum 410 -100V
The same as in the first embodiment.

  Using Examples 1, 2, 3 and Comparative Examples 1, 2, a predetermined pattern was continuously printed out, and a test was performed to compare whether the deteriorated carrier was properly removed.

Test conditions Print pattern Print rate 5% (monochrome)
Paper size A4
Number of prints 200 × 10 ³ (continuous)
Developer transport amount of developing sleeve 551 200 g / m ²
In Comparative Example 1, every time 500 images were formed, the mode was switched to the carrier discharge mode, and the pattern operated for 20 seconds in the carrier discharge mode was repeated to print out a total of 200 × 10 ³ sheets.

Evaluation contents and method Solid exposure part carrier adhesion Deteriorated carrier tends to adhere to a solid exposure part. A large amount of solid-exposed portion carrier adhesion indicates a high ratio of deteriorated carriers in the developer. In the test, a total of 200 × 10 ³ prints were divided into 50 × 10 ³ prints, and each time 50 × 10 ³ prints were completed before the start of printing (0 sheets), A3 size paper was printed. Perform solid exposure, visually confirm the number of carriers adhering to the solid exposure part, and the number of carriers adhering to the solid exposure part is 10 or less. The super thing was made into x (poor).

The carrier emission Total 200 × 10 ³ sheets of print execution, and executes separated one by 50 × 10 ³ sheets were weighed amount of discharged carriers (mass) in the course of performing the respective 50 × 10 ³ prints .

  The test results are shown below.

Table 1 is a table showing the result of confirming that the solid-exposed portion carrier adheres when 200 × 10 ³ sheets are printed. As shown in Table 1, in Examples 1, 2, and 3, there is no occurrence of adhesion of more than 10 solid exposure part carriers in the process of printing 200 × 10 ³ sheets. That is, it can be said that the occurrence of defects due to the deteriorated carrier during execution of printing of 200 × 10 ³ sheets is suppressed, and the deteriorated carrier is appropriately removed from the developer. On the other hand, in Comparative Example 1, it was confirmed that more than 10 solid exposure part carriers were adhered after the 150 × 10 ^3rd and 200 × 10 ^3rd sheets were printed. In Comparative Example 2, it was confirmed that more than 10 solid exposed portion carriers were adhered after the printing of the 100 × 10 ^3rd sheet, 150 × 10 ^3rd sheet, and 200 × 10 ^3rd sheet was completed. In Comparative Examples 1 and 2, it can be said that the deteriorated carrier is not properly removed. Therefore, from the viewpoint of solid exposure part carrier adhesion, Example 1, Example 2, and Comparative Example 3 are evaluated as “good”, and Comparative Example 1 and Comparative Example 2 are Examples 1 and 2. In comparison with Comparative Example 3, it can be evaluated as x (poor).

Table 2 is a table showing measurement results of the carrier discharge amount when 200 × 10 ³ prints are divided into 50 × 10 ³ prints. As shown in Table 2, in Example 1, Example 2, and Example 3, the amount (mass) of the carrier discharged during printing between 50 × 10 ³ sheets is in the range of 34 to 43 g. On the other hand, in Comparative Example 1, it was 121-148 g, and in Comparative Example 2, it was 62-69 g. In Comparative Example 1 where a large number of carriers were discharged, as shown in Table 1, since the solid exposure part carrier adhesion occurred, the removal of the deteriorated carrier was not properly performed, and the carrier that was not deteriorated was considerable. The amount is considered to be discharged. Further, in Comparative Example 2, the amount (mass) of the discharged carrier is larger than that in Example 1, Example 2, and Example 3, but solid exposure part carrier adhesion occurs as shown in Table 1. Therefore, it is considered that the deteriorated carrier is not properly removed.

  Thus, the effectiveness of Examples 1, 2, and 3, that is, the effectiveness of the present invention was confirmed.

  As described above, the image forming apparatus 10 removes the deteriorated carrier from the developer composed of the toner and the carrier conveyed to the development area, and does not cause the solid exposure part carrier adhesion.

  This can be said to remove the deteriorated carrier from the repetitively used carrier and manage the characteristics of the carrier to a level that does not cause the solid exposure part carrier adhesion, but the image forming apparatus 10 generates the solid exposure part carrier adhesion. It can be said that the image forming operation is executed while applying the carrier management method for managing the characteristics of the carrier to a level that does not allow the carrier.

  The carrier management method applied by the image forming apparatus 10 is such that a predetermined electric field is formed between the carrier removing unit disposed facing the developer transport body, and the developer transport body faces the photoconductor. Deteriorated carrier removal process in which the carrier deteriorated compared to the initial stage is removed from the developer conveyed to the position by attaching it to the carrier removal unit, and the degree of carrier deterioration that measures the degree of deterioration of the carrier removed in the carrier removal process A removal carrier deterioration degree control step for controlling the degree of deterioration of the carrier to be removed by changing the electric field strength in the carrier removal step based on the measurement result in the measurement step and the carrier measurement step.

  By applying these deteriorated carrier removal step, carrier deterioration degree measuring step, and removed carrier deterioration degree control step, it is possible to remove the deteriorated carrier from the developer even during the image forming operation. It is possible to prevent the occurrence of partial carrier adhesion.

  Note that the measurement of the degree of carrier degradation in the carrier measurement step may be performed using the value of the current flowing through the carrier removed in the carrier removal step, or with the permeability of the carrier removed in the carrier removal step. You may go. In the carrier removal step, the electric field strength may be changed by changing the voltage applied to the carrier removal unit, or the distance between the carrier removal unit and the developer transport body may be changed. You may change the strength.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 100 Document reading part 200 Image processing part 300 Image writing part 400 Image forming part 410 Photosensitive drum 420 Eraser lamp 430 Charger 450 Transfer part 460 Cleaner 461 Cleaning blade 500, 500A, 500B, 500P, 500T Developer 510 Developer housing 513 Developer storage chamber 514 Toner density detection sensor 517 Developer upper surface detection sensor 520 Toner hopper 521 Toner discharge port 522 Shutter 530 Carrier hopper 531 Carrier discharge port 532 Shutter 540 Developer hopper 541 Developer discharge port 542 Shutter 551 Development Sleeve 552 Magnet roll 559 Bias power supply 555 Layer thickness regulating member 561, 562 Screw 570 Carrier removal part 571 Carrier adhesion low 572 Recovery roller 573 Scraper 574 Carrier discharge screw 576 Carrier storage chamber 579 DC power supply 580, 580B Carrier measurement unit 582 Current detection unit 582A Ammeter 582E DC power supply 583 Permeability sensor 590, 590A Electric field strength change unit 590E Voltage variable DC power supply 590M Motor 591 Carrier adhesion roller substrate 600 Fixing unit 700 Paper feed / conveying unit 800 Operation display unit 900 Control unit

Claims (6)

A photoreceptor,
An image writing unit that irradiates the photosensitive member with output light and forms an electrostatic latent image on the photosensitive member;
A developing device having a developer conveying body that is rotatably disposed facing the photoconductor at a predetermined interval and carries a developer composed of toner and a carrier and conveys the developer to a position facing the photoconductor; Have
The toner in the developer carried on the developer transport body is transferred to the photoconductor by an electric field between the photoconductor and the developer transport body at a position where the photoconductor and the developer transport body face each other. In the image forming apparatus for developing the electrostatic latent image carried on the photoreceptor,
A carrier removing unit that forms an electric field between the developer transport body and removes the deteriorated carrier from the developer transport body from the initial stage;
A carrier measuring unit for measuring the degree of deterioration of the carrier removed by the carrier removing unit;
An electric field strength changing unit that changes the strength of the electric field between the carrier removing unit and the developer transport body based on the measurement result of the carrier measuring unit;
An image forming apparatus comprising: The carrier removing unit is disposed on the upstream side in the rotation direction of the developer transport body from a position where the developer transport body and the photosensitive body face each other.
The strength of the electric field between the carrier removal unit and the developer transport body is at least between the irradiated portion of the photoconductor and the developer transport body irradiated with the output light of the maximum output of the image writing unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is stronger than an electric field.   The image forming apparatus according to claim 1, wherein the carrier measuring unit measures the degree of deterioration of the carrier removed by the carrier removing unit based on a current value flowing through the carrier.   The image forming apparatus according to claim 1, wherein the carrier measuring unit measures the degree of deterioration of the carrier removed by the carrier removing unit based on the magnetic permeability of the carrier.   The electric field strength change between the carrier removal unit and the developer transport body by the electric field strength changing unit is performed by changing a voltage applied to the carrier removal unit. The image forming apparatus according to 1.   The change of the electric field strength between the carrier removal unit and the developer transport body by the electric field strength changing unit is performed by changing the interval at the facing position between the carrier removal unit and the developer transport body. The image forming apparatus according to claim 1.

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