JP2012226127A - Image forming apparatus and developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of supplying a carrier with less excess and deficiency by accurately evaluating the electrification performance of the carrier, even while an image is formed.SOLUTION: A supply control part 900 supplies a toner of 0.5 g to the upstream side of a stirring chamber 402, while forming the image at the timing of each of image formations for 100 sheets. The supply control part 900 measures a mixture time T until the change of the dispersion state of the toner of a developer when the toner is supplied is converged by an optical sensor array 409 and supplies a carrier of 50 g from a carrier chamber 416, when the mixture time T is six seconds or more. When a toner supply amount for each image formation is less than 0.5 g, the supply of the toner is stopped until the cumulative total of the toner supply amount becomes 0.5 g and the measurement of the mixture time T is started.

Description

  The present invention relates to a developing device capable of supplying a carrier to a developer circulating in the developer circulation path, and more specifically, by accurately detecting the state of charge deterioration of the developer conveyed through the developer circulation path. The present invention relates to a developing device capable of executing carrier replenishment with a small amount of carrier.

  2. Description of the Related Art In electrophotographic image forming apparatuses, particularly image forming apparatuses that output full-color images, a two-component developing system that uses toner and a carrier as a developer is widely used. In the two-component developing system, when toner is consumed for development during image formation, toner corresponding to the toner consumption is replenished, while the carrier continues to circulate in the developing device regardless of the toner consumption. The charging performance gradually decreases. Therefore, a carrier mixing and replenishing type developing device that replenishes the developing device with a replenished developer mixed with a carrier in a certain ratio to the toner and overflows the developer that has become excessive due to the replenishment of the replenishing developer from the developing device. Has been put into practical use (Patent Document 1).

  However, in the carrier mixing and replenishing method, the carrier replenishment amount is automatically determined according to the toner consumption amount. On the other hand, the decrease in the charging performance of the carrier is mainly due to the carrier residence time (stirring accumulated time) in the developer circulation path. It progresses with. For this reason, if image formation with a large amount of toner consumption continues, a large amount of replenishment developer is unnecessarily discharged from the developing device before the charging performance of the carrier decreases. Conversely, if image formation with a small amount of toner consumption continues, replenishment cannot catch up with a decrease in the charging performance of the carrier, and various development defects and toner scattering will occur.

  On the other hand, Patent Document 2 discloses a developing device that can replenish a carrier to a developing device independently of toner replenishment. Here, since a certain amount of carrier is replenished to the developing device every predetermined operating time of the developing device, a carrier replenishing amount that does not vary according to the toner consumption is set.

  However, the deterioration of the charging performance of the carrier changes not only the accumulation of operation time but also the traveling speed due to various factors such as temperature and humidity, toner consumption, and toner type. For this reason, if the carrier is replenished simply based on the accumulated operation time, the replenishment amount may become inappropriate and the charging performance of the carrier may not be maintained in an appropriate state.

  Therefore, in Patent Document 3, the charging performance of the carrier in the developing device is periodically measured and fed back to the carrier replenishment amount to maintain the carrier charging performance in an appropriate state. Here, the image formation is interrupted, the development conditions that facilitate the development of the carrier are set, the carrier is intentionally attached to the image carrier (photosensitive drum), and the carrier attachment state of the image carrier is optically determined. It is detected and the charging performance of the carrier is evaluated. This is because when the charging performance of the carrier is lowered, the rate at which the carrier is injected and transferred to the image carrier (photosensitive drum) increases.

Japanese Patent Publication No. 02-21591 Japanese Patent Laid-Open No. 06-27809 JP 2007-79440 A

  The method for evaluating the charging performance of a carrier disclosed in Patent Document 3 cannot be performed during image formation because it uses development conditions different from those during image formation. If the frequency of carrier charge performance evaluation is reduced to reduce the impact on image formation productivity, a sudden drop in the carrier charge performance at the evaluation execution interval is overlooked and a large number of defective images are formed. There is a possibility that. Since the carrier is attached to the image carrier (photosensitive drum), the life of the image carrier (photosensitive drum) may be impaired.

  An object of the present invention is to provide an image forming apparatus equipped with a developing device capable of accurately evaluating the charging performance of a carrier even during image formation and performing carrier replenishment with little excess or shortage.

  An image forming apparatus according to the present invention supplements a developer carrying member, a developer circulation path that circulates the developer containing toner and a carrier to be supplied to the developer carrying member while stirring, and a consumed toner. A toner replenishing section for replenishing toner to the developer circulation path, a carrier replenishing section for replenishing the developer circulation path to replace the deteriorated carrier of the circulating developer, and carrier replenishment of the carrier replenishing section And a developer discharge section for discharging the developer from the developer circulation path. And detecting means capable of detecting a deviation in toner distribution in the developer conveyed along the developer circulation path based on the output; and a state of toner dispersion in the developer when the toner is replenished from the toner replenishing unit Control means for controlling the carrier replenishment by the carrier replenishing unit based on the output of the detecting means.

  In the image forming apparatus of the present invention, when the charging performance of the carrier is lowered, the flowability of the developer is lowered at the same time, so that the toner replenished to the developer conveyed through the developer circulation path becomes difficult to mix. It is used to evaluate the charging performance of carriers. When the replenished toner hardly mixes with the developer conveyed through the developer circulation path, a portion where the replenished toner is unevenly distributed in the conveyed developer becomes conspicuous. An optical density contrast is formed between the portion where the replenished toner is unevenly distributed and the portion where the replenished toner is not distributed, and the fluidity of the developer can be detected optically. Since it is an optical detection for the developer conveyed through the developer circulation path, it is not necessary to change the development conditions, and it can be performed even during image formation.

  Therefore, even during image formation, it is possible to accurately evaluate the charging performance of the carrier and execute carrier replenishment with little excess or shortage.

1 is an explanatory diagram of a configuration of an image forming apparatus. It is explanatory drawing of a structure of an image formation part. It is explanatory drawing of the photosensitive layer of a photosensitive drum. It is explanatory drawing of a structure of a developing device. It is a block diagram of a control system of the developing device. FIG. 2 is a schematic diagram in a longitudinal direction of a developing device in Embodiment 1. It is explanatory drawing of the relationship between deterioration of a carrier and the fall of the fluidity | liquidity of a developer. It is explanatory drawing of a structure of an optical sensor array. It is explanatory drawing of the imaging result of the developer by an optical sensor array. It is explanatory drawing of the histogram of the density distribution of a captured image. It is explanatory drawing of the change of the mixing state in the developing agent of the replenishment toner accompanying stirring. 3 is a flowchart of developer flowability evaluation in Example 1. It is explanatory drawing of the relationship between mixing time and a developer deterioration degree. 6 is a flowchart of carrier replenishment / developer discharge control according to the first exemplary embodiment. It is explanatory drawing of the comparison with the control of Example 1, and the control of an overflow system. It is explanatory drawing of the comparison of carrier consumption. It is explanatory drawing of the comparison of the abrasion amount of a photosensitive drum. FIG. 10 is an explanatory diagram of a configuration of a developing device according to Embodiment 2.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is also implemented in another embodiment in which part or all of the configuration of the embodiment is replaced with the alternative configuration as long as the carrier circulation amount is adjusted by optically detecting the developer circulation path. it can.

  Accordingly, an image forming apparatus using a two-component developer can be implemented without distinction between monochrome / full color, sheet-fed type / recording material conveying type / intermediate transfer type, toner image forming method, and transfer method.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. The image forming apparatus can be used for various purposes such as a printer.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus. FIG. 2 is an explanatory diagram of the configuration of the image forming unit. As shown in FIG. 1, the image forming apparatus 100 is a tandem intermediate transfer type full-color printer in which yellow, magenta, cyan, and black image forming portions PY, PM, PC, and PK are arranged along an intermediate transfer belt 54. is there.

  In the image forming unit PY, a yellow toner image is formed on the photosensitive drum 1Y and transferred to the intermediate transfer belt 54. In the image forming unit PM, a magenta toner image is formed on the photosensitive drum 1M and transferred to the intermediate transfer belt 54. In the image forming units PC and PK, a cyan toner image and a black toner image are formed on the photosensitive drums 1C and 1K, respectively, and sequentially transferred onto the intermediate transfer belt 54.

  The recording material P is taken out one by one from the recording material cassette 20 and waits at the registration roller 23. The recording material P is fed to the secondary transfer portion T2 by the registration roller 23 in synchronization with the toner image on the intermediate transfer belt 54, and the toner image is secondarily transferred from the intermediate transfer belt 54. The recording material P on which the four-color toner images are secondarily transferred is conveyed to the fixing device 6 and is heated and pressed by the fixing device 6 to fix the toner images, and then discharged to the external tray 25 by the discharge roller 24. Is done.

  The image forming units PY, PM, PC, and PK are configured substantially the same except that the color of toner used in the developing devices 4Y, 4M, 4C, and 4K is different from yellow, magenta, cyan, and black. In the following, the yellow image forming unit PY will be described, and redundant description regarding the other image forming units PM, PC, and PK will be omitted.

  As shown in FIG. 2, the image forming unit PY includes a corona charger 2Y, an exposure device 3, a developing device 4Y, a transfer roller 52Y, and a drum cleaning device 7Y around the photosensitive drum 1Y.

  The photosensitive drum 1Y will be described later. The corona charger 2Y irradiates charged particles associated with corona discharge to charge the surface of the photosensitive drum 1Y to a negative dark uniform potential VD. The exposure apparatus 3 scans a laser beam binary-modulated with an exposure signal obtained by developing image data with a polyhedral mirror, and lowers the potential of the exposed portion to the dark portion potential VL, thereby electrostatically impressing the image on the photosensitive drum 1Y. Form an image. As will be described later, the developing device 4Y develops the electrostatic image to form a toner image on the photosensitive drum 1Y. The transfer roller 52Y is applied with a positive voltage to primarily transfer the toner image on the photosensitive drum 1Y to the intermediate transfer belt 54. The transfer residual toner that escapes from the primary transfer and adheres to the photosensitive drum 1Y is scraped off by the drum cleaning device 7Y and collected in a toner container (not shown).

  The image density sensor 11Y is for adjusting the toner charge amount by optically measuring the density of the toner image on the photosensitive drum 1Y actually formed. The smaller the toner adhesion amount, the higher the reflectance. The output value increases.

<Photosensitive drum>
FIG. 3 is an explanatory diagram of the photosensitive layer of the photosensitive drum. As shown in FIG. 2, the photosensitive drum 1Y is an organic electrophotographic photosensitive member (OPC) in which an organic electrophotographic photosensitive layer having a negative charge polarity is provided on a drum-shaped conductive substrate having a diameter of 30 mm.

  As shown in FIG. 3, the photosensitive drum 1 </ b> Y is a function-separated type photoreceptor in which a charge generation layer 102 and a charge transport layer 103 are sequentially laminated on a conductive substrate 101. The function-separated type photoreceptor can be formed in a drum shape or a belt shape by laminating a charge generation layer and a charge transport layer on a conductive support. A function-separated type photoreceptor is most preferably used from the viewpoint of performance. An undercoat layer may be provided between the conductive substrate 101 and the charge generation layer 102 as necessary in order to improve adhesion and charge blocking properties.

  The conductive substrate 101 can employ a metal such as Al, Ni, Fe, or an alloy. Alternatively, a plastic film such as polycarbonate or an insulating substrate such as glass provided with a metal film such as Al, Ag, or Au or a metal oxide film such as In 2 O 3 or SnO 2 may be used.

  The charge generation layer 102 may be formed of only the charge generation material or may be formed by uniformly dispersing the charge generation material in the binder. The charge generation layer 102 is formed by dispersing these components in a suitable solvent, coating the conductive substrate 101 on the conductive substrate 101, and drying. Examples of the charge generation material include C.I. Pigment Blue 25 (Color Index (CI21180) and the like. Examples of the binder resin include polyamide and polyurethane. The amount of the binder resin is 5 with respect to 100 parts by weight of the charge generation material. The solvent is exemplified by tetrahydrofuran, cyclohexanone, etc. The average film thickness of the charge generation layer is 0.01-2 μm, preferably 0.1-1 μm, Here, the film thickness was 1 μm.

  The charge transport layer 103 is formed by dissolving a charge transport material, a binder resin and, if necessary, a plasticizer and a leveling agent in an appropriate solvent, coating the charge transport layer on the charge generation layer, and drying. Examples of the charge transport material include poly-N-vinylcarbazole and derivatives thereof, poly-γ-carbazolylethyl glutamate and derivatives thereof, and the like. Examples of the binder resin include polystyrene and styrene-acrylonitrile copolymer. Examples of the solvent include tetrahydrofuran, dioxane, toluene and the like. The charge transport layer has a thickness of 10 to 100 μm, preferably 20 to 40 μm, and here, 30 μm.

  In general, in the image forming apparatus 100, the surface of the photosensitive drum 1Y is in mechanical contact with not only the developing device 4Y but also the drum cleaning device 7Y, the intermediate transfer belt 54, and the like. The outermost layer of the photosensitive drum 1Y comes into contact with these members and is rubbed, and the film thickness decreases. In addition, when wear occurs, foreign matters such as metal pieces and carrier particles are mixed between the photosensitive drum 1Y and the member, whereby wear is further promoted and the life is shortened. Therefore, a protective layer may be provided on the outermost surface in order to improve wear resistance.

<Developer>
The developing device 4Y develops the electrostatic image on the photosensitive drum 1Y using a two-component developer in which a carrier (magnetic) and a toner (nonmagnetic) are mixed. A developer in which the carrier and the toner were mixed so that the weight ratio was 91: 9 (toner concentration: 9%) was used. The total weight of the initial developer accommodated in the developing device 4Y was 310 g.

As the carrier, ferrite particles coated with a silicone resin are used, and the specific resistance at an electric field strength of 24 Am ² / kg and 3000 V / cm is 1 × 10 ⁷ to 10 ⁸ Ω with respect to an applied magnetic field of 240 kA / m. -Cm and a weight average particle diameter of 50 micrometers.

  The carrier may be a resin magnetic carrier produced by a polymerization method using a binder resin, a magnetic metal oxide, and a nonmagnetic metal oxide as starting materials.

  The toner is composed of at least a binder, a colorant, and a charge control agent. Here, a styrene acrylic resin is used as the binder resin. However, resins such as styrene, polyester, and polyethylene can also be used. As the colorant, one type of colorant such as various pigments and various dyes may be used alone, or a plurality of types may be used in combination. As a charge control agent, you may contain the charge control agent for reinforcement as needed. As the charge control agent for reinforcement, nigrosine dyes, triphenylmethane dyes, and the like can be used.

  The toner may contain a wax or an external additive. The wax is contained for the purpose of improving the releasability from the fixing member during fixing and the fixing property. As the wax, paraffin wax, carnauba wax, polyolefin, or the like can be used, and kneaded and dispersed in a binder resin. Here, a resin obtained by kneading and dispersing a binder, a colorant, a charge control agent, and a wax by a mechanical pulverizer was used.

  Examples of the external additive include those obtained by subjecting amorphous silica to a hydrophobic treatment, or inorganic oxide fine particles such as titanium oxide and a titanium compound. It is preferable to externally add these fine particles to the toner to control the powder fluidity and charge amount of the toner. The particle diameter of the external additive particles is preferably about 1 nm to 100 nm. Here, titanium oxide having an average particle diameter of 50 nm and 0.5 wt% by weight ratio, and amorphous silica having an average particle diameter of 2 nm and 100 nm added by 0.5 wt% and 1.0 wt%, respectively, were used.

  When the particle size of the toner having the above-described configuration was measured with a powder particle size image analyzer FPIA-3000 manufactured by Sysmex Corporation, the weight average particle size was 5.7 μm.

<Developing device>
FIG. 4 is an explanatory diagram of the configuration of the developing device. As shown in FIG. 4, the developing device 4Y that can be mounted on the image forming apparatus is provided with a developing sleeve 415 that is an example of a developer carrier so as to be partially exposed from the opening 426 of the developing container 420. .

  The developing container 420 is divided into a developing chamber 401 and a stirring chamber 402 by a partition wall 421, and the developing chamber 401 and the stirring chamber 402 communicate with each other by openings provided at both ends in the longitudinal direction of the partition wall 421. This constitutes the circulation path. The developer in the circulation path is conveyed and circulated by the developing screw 407 and the stirring screw 408.

  A developing sleeve 415 is installed in the developing chamber 401, and a developing screw 407 is disposed in parallel with the developing sleeve 415. The developing screw 407 rotates in the direction of the arrow, and supplies the developer to the developing sleeve 415 while transporting the developer from the back side to the front side of the sheet.

  A stirring screw 408 is installed in the stirring chamber 402. The agitating screw 408 agitates the developer delivered from the developing screw 407 through the opening of the partition wall 421 on the near side of the paper surface from the near side to the far side of the paper surface, and frictionally charges the toner and the carrier. Let

  The developing sleeve 415, the developing screw 407, and the stirring screw 408 are gear-coupled outside the developing container 420, and are driven by a driving motor 427 to rotate integrally.

  The developing sleeve 415 is a rotatable cylinder made of a nonmagnetic metal such as aluminum or stainless steel, and the surface of the developing sleeve 415 has a surface roughness Rz (10-point average roughness) within a range of 10 to 20 μm. It is desirable to enter. A non-rotating magnet roller 425 is disposed inside the rotating developing sleeve 415. The magnet roller 425 has a plurality of magnetic poles, and a developer is carried on the surface of the non-magnetic developing sleeve 415 in which a magnetic flux formed between the plurality of magnetic poles of the magnet roller 425 rotates, and a predetermined rotational phase is obtained. A magnetic spike of developer is formed at the position. In the magnetic spike, the toner is electrostatically restrained with respect to each of the carrier particles that are magnetically restrained from the developing sleeve 415 and rise in a chain shape. At a position facing the photosensitive drum (1Y: FIG. 2), the magnetic spikes carried on the developing sleeve 415 rub against the photosensitive drum (1Y: FIG. 2).

  The power source 429 applies an oscillating voltage obtained by superimposing an AC voltage on the DC voltage Vdc to the developing sleeve 415 during image formation. With the magnetic brush sliding on the photosensitive drum (1Y: FIG. 2), an oscillating voltage is applied to the developing sleeve 415 so that the negatively charged toner is released from the positively charged carrier. Then, the photosensitive drum (1Y: FIG. 2) is transferred to the electrostatic image.

  The magnet roller 425 has a repulsive pole where magnetic poles of the same polarity are adjacent to each other at a phase position facing the developing screw 407. Here, since the magnetic force does not act between the repulsive poles, the developer cannot be carried. The developer that has been carried on the developing sleeve 415 and has finished consuming the toner and whose toner concentration has been lowered leaves the developing sleeve 415 here.

  Thereafter, the developer is conveyed again by the developing screw 407, flows into the stirring chamber 402 downstream of the developing chamber 401, and receives toner replenishment. The developer conveyed to the most downstream side of the stirring chamber 402 flows into the developing chamber 401 at a portion where the partition wall 421 that separates the stirring chamber 402 and the developing chamber 401 is partially interrupted. In the developing chamber 401, a part of the developer is carried on the developing sleeve 415, and only the toner is developed and consumed.

<Toner supply unit>
FIG. 5 is a block diagram of a control system of the developing device. In the two-component development system, toner is gradually consumed from the developer during image formation. For this reason, it is necessary to quickly replenish the developing container 420 with the amount of toner lost from the developing device 4Y through the developing sleeve 415 as the toner image is developed.

  The replenishment control unit 900 controls the driving of the toner replenishing screw 404 in the developing device 4Y to keep the toner concentration of the developer conveyed through the circulation path of the developing container 420 at 9% from the toner chamber 417. Adjust the amount of toner to be replenished.

  As shown in FIG. 5, a video counter 901, an image density sensor 11, and a developer toner density sensor 418 are connected to the input side of the supply control unit 900. To the output side of the replenishment control unit 900, a toner replenishment motor 434, a developer discharge solenoid 411, and a development drive motor 427 are connected.

  The video counter 901 calculates the integrated value of the density signal from the image information signal. The video count number integrated for one output image corresponds to the amount of toner consumed by the developing device 4Y to form one output image. The developer toner concentration sensor 418 measures the toner concentration in the developer by measuring the magnetic permeability of the developer in the developer container 420 using an inductor sensor. Note that a toner density detection sensor of an optical reflection light quantity detection method may be used instead.

  The replenishment control unit 900 drives the toner replenishing motor 434 so as to replenish toner of approximately the same amount as the calculated toner amount. The toner stored in the toner chamber 417 is supplied to the stirring chamber 402 from the supply port 403 at the upstream portion of the stirring chamber 402 by driving the toner supply screw 404.

  The replenishment control unit 900 detects the toner replenishment cumulative error based on the output of the video counter 901, and detects the toner concentration by detecting the inductance of the two-component developer. Is read and the toner density is calculated. The replenishment control unit 900 adjusts the toner replenishment amount based on the detection signal value of the toner concentration detection sensor 418, and performs control so that the toner concentration is constant at 9% as described above. The replenishment control unit 900 supplies the toner stored in the toner chamber 417 to the agitation chamber 402 from the replenishment port 403 located upstream of the agitation chamber 402 by driving the toner replenishment screw 404.

<Carrier Supply Department>
In the two-component development method, the carrier is not consumed during image formation, and the charging performance is lowered in the process of repeatedly circulating in the developing device. For this reason, in the past, the developer has been replaced in accordance with the service time of the image forming apparatus. In order to eliminate the need to replace the developer for the purpose of improving maintainability, an automatic replacement system in which a developer having a reduced charging performance, particularly a carrier, is gradually replaced with a new one has been put into practical use.

  In an example of the automatic replacement system, excess developer is discharged while replenishing toner containing a small amount of carrier. A developer in which a carrier is mixed with toner at a certain ratio is replenished, and excess developer in the developer container overflows from the discharge port. At the same time as toner replenishment, a fixed amount of carrier is supplied to the developing container, and the excess developer overflows accordingly.

  However, when the developer in which the carrier is mixed with the toner at a constant ratio is replenished, the developer is replaced regardless of the level of decrease in the charging performance of the carrier. Therefore, when the image area ratio is large and the toner consumption is large, the replacement of the developer becomes excessive, and when the image area ratio is small and the toner consumption is small, the replacement of the developer is insufficient.

  Therefore, when many images with a low image area ratio are output, the carrier is hardly replaced and the charging performance of the carrier is greatly reduced, and the carrier having the reduced charging performance continues to be used as it is. As a result, problems such as carrier adhesion, background contamination due to toner charging failure, and image quality deterioration are likely to occur. On the other hand, when a large number of images with a high image area ratio are output, a large amount of carrier replenishment results in a problem that unused carriers with high charging performance are discharged.

  Therefore, in the image forming apparatus 100, a carrier replenishment unit is provided separately from the toner replenishment unit so that the carrier can be replenished to the developing container 420 with a free replenishment amount. As a result, even when image formation that consumes a large amount of toner continues, normal carriers whose charging performance has not deteriorated are less likely to be discharged from the developing container 420.

  As shown in FIG. 4, the carrier stored in the carrier chamber 416 is supplied to the agitation chamber 402 from the replenishment port 403 in the upstream portion of the agitation chamber 402 when the solenoid 405 is driven and the carrier replenishment valve 406 is opened. The The carrier chamber 416 stores 100% of the carrier here, but considering the mixing property after being replenished to the developing container 420, a carrier replenishing developer in which several percent of toner is mixed. Also good.

<Developer discharge part>
FIG. 6 is a schematic view in the longitudinal direction of the developing device according to the first embodiment. The developing device 4Y includes a mechanism for discharging the developer in the developing container 420 to the outside. Specifically, a discharge port 412 is provided on the most downstream side of the developing chamber 407, and the developer can be discharged at a predetermined timing. In response to a signal to the developer discharge solenoid 411, the discharge valve 414 slides and the developer is discharged from the discharge port 412.

  As shown in FIG. 6, the toner and carrier supply port 403 is provided upstream of the stirring chamber 402. The toner supplied from the supply port 403 to the stirring chamber 402 is conveyed while being stirred by the stirring screw 408. With stirring, the toner particles and carrier particles are rubbed against each other, and the toner is negatively charged and the carrier is positively charged. The developer is transferred to the developing chamber 401 through the opening 428 of the partition wall 421 on the downstream side of the stirring chamber 402. The developer conveyed by the developing screw 407 is discharged from the discharge port 412 on the downstream side of the developing chamber 401. The discharged developer is accumulated in the collection container 413 and periodically recycled.

<Comparative example>
As for the automatic replacement of the developer in the two-component developing type developing device, there is one that directly detects the lowering state of the charging performance of the carrier in the developer for every predetermined number of image output sheets and adjusts the replenishment amount of the carrier. In the above-mentioned Patent Document 3, an optical sensor including a light emitting element and a light receiving element is disposed opposite to an image carrier, and a detection mode is controlled to detect a decrease in the charging performance of the carrier. . In the detection mode, the charging potential of the photosensitive drum and the development DC voltage are controlled to intentionally form a state where the carrier is easily developed on the image carrier. Then, the amount of carrier actually developed from the developer carrier to the image carrier is detected by an optical sensor to evaluate the state of deterioration of the charging performance of the carrier. An optical sensor detects the amount of reflected light from the background portion of the image carrier and the carrier adhesion portion to determine the ratio thereof, and detects the carrier adhesion amount on the image carrier in comparison with a preset reference value.

  In the detection mode, the carrier adhesion amount is detected under a plurality of development conditions in which the charging potential or the development DC voltage is varied in a plurality of stages. From the relationship between the development conditions and the carrier adhesion amount, the level of deterioration in the charging performance of the developer is determined. Calculated. Furthermore, the amount of carrier replenishment from the carrier chamber to the developing container is determined and replenished according to the calculated level of decrease in developer charging performance. A part of the developer that circulates along with the replenishment is discharged, so that the carrier in the developing container is replaced little by little.

  However, according to such control of the comparative example, there is a problem that when the detection mode is executed to detect the level of decrease in the charging performance of the carrier, the photosensitive drum is damaged by the carrier and wear is accelerated.

  Therefore, in the following embodiments, the state of deterioration of the charging performance of the carrier is evaluated without transferring the carrier to the photosensitive drum. Without developing the carrier on the photosensitive drum, the deterioration level of the carrier in the developing container is grasped, and the developer supply or carrier supply according to the deterioration level is performed. This makes it possible to form an image with low running cost while maintaining high quality with little background contamination and image quality deterioration due to toner charging failure over time.

<Example 1>
FIG. 7 is an explanatory diagram of the relationship between carrier deterioration and developer fluidity reduction. As shown in FIG. 4, a developing chamber 401 and an agitating chamber 402, which are examples of a developer circulation path, circulate a developer containing toner and a carrier while stirring, and a developing sleeve 415, which is an example of a developer carrier. To supply.

  A toner chamber 417, which is an example of a toner replenishing unit, replenishes toner on the upstream side of the agitation chamber 402, and supplements toner consumed in the previous image formation. The toner chamber 417 supplies toner corresponding to the amount of toner consumed in image formation to the upstream side of the stirring chamber 402 for each image formation. A carrier chamber 416, which is an example of a carrier replenishment unit, replenishes the carrier upstream of the agitation chamber 402 and replaces a part of the deteriorated carrier of the circulating developer. A discharge valve 414, which is an example of a developer discharge unit, discharges the developer on the downstream side of the developing chamber 401 and eliminates the excess of the developer accompanying the carrier supply from the carrier chamber 416.

  The replenishment control unit 900, which is an example of a control unit, is based on the output of the optical sensor array 409 so that the dispersion state of the toner in the developer when the toner is replenished from the toner chamber 417 is maintained within a predetermined allowable range. The carrier supply from the carrier chamber 416 is controlled. The replenishment control unit 900 replenishes a predetermined amount of carrier from the carrier chamber 416 when the toner dispersion state in the developer when the toner is replenished reaches a boundary of a predetermined allowable range.

  The replenishment control unit 900 detects the developer in the agitating chamber 402 at intervals of a predetermined number of images formed by the optical sensor array 409, and replenishes a constant amount of toner from the carrier chamber 416 for each detection. The replenishment control unit 900 executes the detection of the developer in the stirring chamber 402 by the optical sensor array 409 in parallel with the image formation.

  The replenishment control unit 900 sets the toner replenishment amount by the toner chamber 417 before and after the detection by the optical sensor array 409 so that the toner amount consumed in the image formation is supplemented with the toner amount used for the detection by the optical sensor array 409. adjust.

  One of the main reasons for the deterioration of the developer in the developing device is a phenomenon (hereinafter referred to as toner spent) in which the toner adheres to the carrier surface as a result of long-time stirring and mixing in the developing container. As the toner spent progresses, the surface area that can be involved in the frictional charging of the carrier decreases and the charging performance of the carrier decreases. As the charging performance of the carrier decreases, the average toner charge amount decreases, and problems such as white background fogging and toner scattering are likely to occur.

  Here, as the toner spent progresses, the toner pieces adhering to the carrier come into contact with the independent toner, so that the fluidity as a developer is lowered. When the fluidity of the developer is lowered, the carrier gap is enlarged on average, and the bulk density of the developer is lowered. In a state where the flowability of the developer is lowered, the time required for the newly supplied toner and the circulating developer to be uniformly mixed becomes longer.

  Therefore, the decrease in the charging performance of the developer extends the time until the newly supplied toner is uniformly mixed and diffused through the decrease in the fluidity of the developer. The decrease in the charging performance of the developer can be estimated by detecting the degree of mixing and diffusion of new toner in a state where new toner is supplied to the developer and mixed for a predetermined time.

  As shown in FIG. 6, 0.5 g of toner was replenished from the replenishing port 403 using toners of different colors, and the position distribution of the replenished toner after stirring for 6 seconds by the stirring screw 408 was measured. In the developing device 4Y, when 0.5 g of toner is replenished from the replenishing port 403, the fastest toner among the conveyed toner starts to flow into the developing chamber 401, that is, from upstream to downstream of the stirring chamber 402. It takes 6 seconds at the shortest to carry. 6 seconds is determined by the length of the stirring chamber 402, the number of rotations of the stirring screw 408, and the helical pitch. The position distribution of the replenishing toner was compared between the unused developer and the used developer having a cumulative image forming number of 50,000 sheets.

  As shown in FIG. 7A, when toner is replenished to an unused developer, the replenished toner is quickly taken into the developer and stirred and conveyed. Since the unused developer has high fluidity, the replenished toner is instantly taken into the developer and well dispersed, and the carrier and the toner mix well. The replenished toner quickly mixes with the developer conveyed through the stirring chamber 402 and has finished passing in front of the optical sensor array 409 at the center in the longitudinal direction. Therefore, with the unused developer, it is determined that the mixing in the vicinity of the optical sensor array 409 has been completed.

  As shown in FIG. 7B, when toner is replenished to the used developer, the replenished toner is not immediately taken into the developer, but the surface of the developer being conveyed. Floating. That is, the stirring screw 408 is not easily affected by stirring and transporting. In the used developer, the replenishment toner is not taken into the developer and floats on the surface, so that mixing is hardly completed.

  As shown in FIG. 7B, in the replenishment toner position distribution graph, the replenishment toner is distributed over the longitudinal direction of the agitating chamber 402, and at first glance, the dispersed state seems to be good. However, actually, the replenishment toner is present in an aggregated state without being finely dispersed, and in this state, mixing is poor. In fact, in this state, a large amount of toner particles that are not stirred and have an extremely low toner charge amount flow into the developing chamber 401 and are carried by the developing sleeve 415 and are involved in the development of the toner image. Lead to malfunctions. Therefore, in the used development, it is determined that mixing is incomplete.

  That is, it is the fluidity of the developer that dominates the characteristics of the replenishment toner mixing in the developer conveyed through the agitating chamber 402, and basically the deterioration of the developer.

  Therefore, in the first embodiment, a predetermined amount of toner is replenished to the stirring chamber 402 in the normal operation state of the developing device 4Y, and the mixed state of the newly replenished toner and the circulating developer is detected by the optical sensor array 409. Thus, the deterioration of the charging performance of the carrier is estimated by analogy.

  The optical sensor array 409 captures the dispersion state of the replenishment toner in the developer conveyed through the stirring chamber 402, and the replenishment control unit 900 quantifies the degree of mixing of the developer and the replenishment toner from the captured image.

  As shown in FIG. 5, an optical sensor array 409, a timer 903, and a page counter 902 are connected to the input side of the replenishment control unit 900. A carrier supply solenoid 405 is connected to the output side of the supply control unit 900.

  In the developing device 4Y, the replenishment control unit 900 performs developer replenishment / discharge control in accordance with the degree of decrease in developer charging performance. A mixed state of the developer and the replenished toner is detected as a parameter reflecting the deterioration degree of the charging performance of the developer.

  The replenishment control unit 900 detects the mixed state of toner replenished for each predetermined number of image output sheets, and replenishes the developing container 420 with more carriers so that the uniformity of the mixed state is lost.

  As shown in FIG. 6, 0.5 g of replenished toner replenished from the replenishing port 403 to the stirring chamber 402 is detected by the optical sensor array 409 in the middle of the stirring chamber 402 while being stirred by the stirring screw 408. The

  An optical sensor array 409 is provided near the center of the stirring chamber 402 in the longitudinal direction. The optical sensor array 409 is installed on the side surface of the stirring chamber 402. The replenished toner is stirred and conveyed by the stirring screw 408. The optical sensor array 409 captures the state of the replenishment toner mixing, and the replenishment control unit 900 digitizes the mixing state.

<Optical sensor array>
FIG. 8 is an explanatory diagram of the configuration of the optical sensor array. FIG. 9 is an explanatory diagram of the imaging result of the developer by the optical sensor array. FIG. 10 is an explanatory diagram of a histogram of the density distribution of the captured image. FIG. 11 is an explanatory diagram of a change in the mixed state of the replenishment toner in the developer accompanying stirring.

  As shown in FIG. 8, the optical sensor array 409, which is an example of a detection unit, can detect a deviation in toner distribution in the developer conveyed through the stirring chamber 402 based on the output. The transparent window 4094 of the optical sensor array 409 is disposed on the downstream side in the developer conveyance direction where the toner chamber 417 replenishes the stirring chamber 402 with toner. An LED 4092, which is an example of an illumination unit, illuminates the developer conveyed through the stirring chamber 402 via the transparent window 4094. An image sensor 4090 which is an example of an imaging unit images the developer illuminated by the LED 4092 through the transparent window 4094.

  The optical sensor array 409 has an image sensor 4090 composed of 16 × 16 pixels. In Example 1, an ADNSO Technologies ADNS-2051 was disposed as the image sensor 4090.

  The optical sensor array 409 includes a lens 4091 that gives an appropriate magnification and focus to the image sensor, an illumination LED 4092, an illumination lens 4093, and a transparent window 4094. Specifically, the optical sensor array 409 as a whole unit requires a resolution of about 25 μm to 200 μm to accurately measure the stirring time T. In Example 1, one having a resolution of 100 μm was used.

  Further, it is sufficient that the number of pixels of the image sensor is 16 × 16 pixels or more in this embodiment. In principle, when the number of pixels is smaller than that, it is difficult to measure the stirring time T. Conversely, when the number of pixels is large, the measurement accuracy is improved to some extent, but the cost of processing the measured image increases.

  The side beyond the transparent window 4094 is the inside of the stirring chamber 402. The transparent window 4094 has a fluororesin coated on the surface of the acrylic resin so that the developer does not adhere. By coating the surface with which the developer comes into contact with a fluororesin, the coefficient of friction of the surface is lowered, the stain resistance can be improved, and good photographing without toner adhesion can be performed.

  The replenishment control unit 900 causes the optical sensor array 409 to photograph the developer in synchronization with the rotation cycle of the stirring screw 408. In this way, by setting the shooting timing to be equal each time, it is possible to reduce variations in parameter values calculated from the images by aligning variations in shooting conditions due to differences in fin positions of the stirring screw 408.

  As shown in FIG. 9A, the captured image of the optical sensor array 409 is uniform when the toner and the developer are sufficiently agitated and in a uniform state, that is, when mixing is completed.

  As shown in FIG. 9B, when the replenishment toner is being stirred and mixing is not completed, a bright area with a large amount of replenishment toner and a high T / D ratio, and the T / D before the toner is replenished. There are dark areas where the D ratio is low, and intermediate color areas where toner is mixed.

  As shown in FIG. 10A, the luminance histogram of the image at the completion of mixing in which the toner and the developer are uniformly mixed shown in FIG. 9A has a single peak. On the other hand, as shown in FIG. 10B, the luminance histogram of the image when mixing is not completed shown in FIG. 9B is a broad histogram having a plurality of peaks. Then, when the standard deviation between the two is calculated, the standard deviation is smaller when mixing is completed as shown in FIG. 10A than when mixing is not completed as shown in FIG. 10B.

  As shown in FIG. 11, the transition of the standard deviation S when the toner mixing time T is actually measured is shown. When the stirring is insufficient immediately after the toner is replenished, the standard deviation of the density distribution obtained from the image photographed by the optical sensor array 409 is large, and thereafter, the standard deviation of the density distribution is increased as the conveyance and mixing proceed. Gradually get smaller. Therefore, by measuring the time until the standard deviation is reduced to some extent, the toner mixing time T required to diffuse the replenishment toner into the developer can be obtained.

<Control of Example 1>
FIG. 12 is a flowchart of developer fluidity evaluation in Example 1. FIG. 13 is an explanatory diagram of the relationship between the mixing time and the developer deterioration degree. FIG. 14 is a flowchart of carrier replenishment / developer discharge control according to the first exemplary embodiment.

  As shown in FIG. 5, the page counter 902 accumulates the number of image output sheets. The replenishment control unit 900 executes carrier replenishment / developer discharge control once for every 100 image outputs. In the carrier replenishment / developer discharge control, a developer replacement determination operation is performed to determine whether carrier replenishment and developer discharge are performed. Based on the output of the optical sensor array 409, the replenishment control unit 900 measures the mixing time T that is a parameter of the flowability of the developer in the developing device 4. Based on the mixing time T, the degree of decrease in the charging performance of the carrier is determined, and when the charging performance of the carrier has decreased to the limit state, the carrier is supplied and the developer is discharged.

  As shown in FIG. 12 with reference to FIG. 4, when the operation for measuring the mixing time T, which is a fluidity parameter, is started (S001), the replenishment control unit 900 first turns on the development drive motor 427 (S002). ), The developer is brought to a steady state by rotating the stirring screw 408.

  The replenishment control unit 900 processes the image picked up by the optical sensor array 409 and calculates the standard deviation of the density distribution of the image in real time.

The replenishment control unit 900 performs imaging once with the optical sensor array 409 before replenishing the replenishment toner for measuring the mixing time T. Standard deviation prior to replenishing the toner is stored as an initial value _{S 0} (S003).

  The replenishment control unit 900 resets the timer 903 to 0, turns on the toner replenishment motor 434 for a predetermined time (S004), and replenishes the replenishment toner by a predetermined amount (0.5 g in the first embodiment). The replenishment toner is replenished to the stirring chamber 402 and mixed by the stirring screw 408.

As shown in FIG. 11, the replenishment control unit 900 regards the time when the standard deviation S of the density distribution of the developer image taken by the optical sensor array 409 exceeds a predetermined threshold _Sth as the start of mixing (S005). YES), the timer 903 is started (S006). In Example 1, since the initial value S ₀ of the standard deviation was 41, the threshold value S _th was set to 45.1 which is 1.1 times the initial value S ₀ . However, other values may be used as long as they can define the time at which mixing starts.

As soon as mixing begins, the standard deviation S increases. If the stirring is further continued, dispersion of the replenishing toner by mixing proceeds and the standard deviation decreases. When the threshold value _Sth again _falls below, the timer 903 is stopped to finish mixing. The value of the elapsed time from the start of mixing to the end of mixing is defined as the mixing time T. In the measurement of FIG. 11, the mixing time T is 2 seconds.

  As shown in FIG. 13, the mixing time T increases as the developer deterioration degree increases. When the horizontal axis represents the developer deterioration degree and the vertical axis represents the mixing time T measured by the optical sensor array 409, the relationship is monotonously increased. As the cumulative number of images formed increases and as the amount of toner consumed in forming one image increases, the fluidity of the developer decreases significantly, and the replenishment toner becomes difficult to diffuse into the developer. The developer deterioration degree is defined as a deterioration degree equivalent to the number of images output with an image area ratio of 100%. When 20,000 images with an image area ratio of 100% are output, the developer deterioration degree is 20K. When 20,000 images with an image area ratio of 50% are output, the developer deterioration degree is 10K.

  As shown in FIG. 13, in Example 1, the developer deterioration degree 50K is defined as the developer use limit. The use limit mixing time Tth at that time is 6 seconds. Therefore, the replenishment control unit 900 images the developer with the optical sensor array 409 and measures the mixing time T. If the mixing time T is 6 seconds or more, the replenishment control unit 900 determines that the developer usage limit is reached. Then, carrier replenishment / developer discharge control is performed.

  As shown in FIG. 4, in the carrier replenishment / developer discharge control, the solenoid 405 is driven to open the carrier replenishment valve 406 to supply a predetermined amount of carrier from the replenishing port 403 to the stirring chamber 402. In parallel, the developer discharge solenoid 411 is driven to open the discharge valve 414 to discharge the old developer from the discharge port 412.

  As shown in FIG. 14 with reference to FIG. 4, when the number of developer replacement determination operations (100 sheets) is reached, at the start of image formation (S101), toner is supplied and the mixing time T is measured. (S102). As described above, the measurement of the mixing time T is executed based on the flowchart of FIG.

  If it is determined that the mixing time T is shorter than the predetermined use limit mixing time Tth and the developer has not deteriorated, the flow ends (S106). However, if the measured mixing time T is longer than the predetermined use limit mixing time Tth and it is determined that the carrier needs to be replaced, the developer discharge solenoid 411 is turned on for a predetermined time to discharge the carrier. A predetermined amount of developer is discharged from the outlet 412 (S104).

  In Example 1, about 60 g of developer corresponding to 20% of the whole was changed at a time. Furthermore, the carrier is replenished by the amount discharged from the replenishing port 403 by turning on the carrier replenishing solenoid 405 (S105). This completes the carrier replenishment / developer discharge control (S106).

  Incidentally, in the first embodiment, the measurement operation of the mixing time T is executed in parallel with the image formation without providing a downtime. In order to make the measurement conditions of the mixing time T uniform, the replenishment amount of the replenishment toner for measurement is constant at 0.5 g in each measurement of the mixing time T. On the other hand, the replenishment toner replenishment amount corresponding to the toner consumption amount of the output image determined by the video count value of the video counter 901 is not necessarily 0.5 g.

  Therefore, when the video count value is smaller than the value corresponding to the toner replenishment amount of 0.5 g, excessive toner replenishment is performed, so that the mixing time T is not measured and the toner is not replenished. The toner is carried over to the next image formation. Then, when the total amount of toner replenished and the amount of toner replenished at that time exceeds 0.5 g when the next image formation starts, 0.5 g of toner is replenished and the mixing time T Measure.

  On the contrary, when the video count value of the video counter 901 is larger than the value corresponding to the toner replenishment amount 0.5 g, after the toner replenishment of 0.5 g and the measurement of the mixing time T is completed, the insufficient toner replenishment amount. Replenish. In this way, when the mixing time T is measured, the replenishment toner amount is controlled to be always constant at 0.5 g.

<Effect of Example 1>
FIG. 15 is an explanatory diagram for comparison between the control of the first embodiment and the overflow control. FIG. 16 is an explanatory diagram of comparison of carrier consumption. FIG. 17 is an explanatory diagram for comparing the wear amount of the photosensitive drum.

  The developing device of Example 1, the developing device of the comparative example, and the conventional developing device of the overflow method using the replenishment developer mixed with the carrier at a constant ratio are mounted on the image forming apparatus of FIG. The degree of wear, the amount of carrier consumption and the degree of wear of the photosensitive drum were compared. The image area ratio was 100%, the developer capacity in the developing device was 310 g, and the image formation speed was 50 cpm (Copy Per Minutes). As shown in FIG. 13, the use limit deterioration degree of the developer was set to 50 k. The developer replacement determination operation was performed once for every 100 sheets of image formation. When it was determined that the developer needs to be replaced, about 50 g of developer was discharged.

  As shown in FIG. 15, in the control of the first embodiment, every time the developer deterioration degree reaches 50K, the carrier 50g is replenished to reduce the developer deterioration degree in a zigzag manner. The horizontal axis represents the number of images formed, and the vertical axis represents the relationship of the average deterioration degree of the developer.

  In the case where there is no developer replacement indicated by a broken line, the image area ratio is 100%. Therefore, according to the above definition, the cumulative image formation number and the developer deterioration degree (corresponding to × K sheets) have the same value.

  In the overflow method indicated by a thin line, the degree of developer deterioration increases relatively slowly as the number of durable sheets increases. This is because in the overflow method, the carrier is gradually changed from the initial stage where the developer has not deteriorated so much. In the overflow method, the degree of deterioration of the developer was saturated at about 50K.

  In the case of the comparative example and Example 1 indicated by the bold line, the deterioration degree of the developer increases linearly up to 50 k which is a preset use limit deterioration degree. In both the comparative example and the example 1, since the degree of decrease in the charging performance of the carrier is determined, the developer is not replaced until the use limit deterioration degree is reached. However, when the developer deterioration level reaches 50K, the developer is appropriately replaced after that, so that the developer deterioration level is saturated around 50K.

  As shown in FIG. 16, the total amount of carriers used up to 100,000 sheets of cumulative image formation in each developing device was compared. In the overflow method, the total used carrier amount was 4.2 kg, whereas in Example 1 and the comparative example, the total used carrier amount could be saved to 2.5 kg. In the overflow method, since the carrier is exchanged from the initial stage where the developer is not deteriorated so much, the developer discharged at the initial stage is considered to be a factor for reducing the carrier utilization efficiency. On the other hand, in Example 1, since the developer is not exchanged at the initial stage where the developer is not deteriorated so much, the carrier that is not deteriorated is not discharged.

  Further, even after the developer life is saturated, in the overflow method, the carrier is replenished and discharged very continuously. For this reason, an unused carrier that has just been replenished is discharged immediately after it contributes to image formation even though it is a very small amount. On the other hand, in Example 1, since a predetermined amount of developer replacement is performed collectively, the possibility of discharging unused carriers is low. That is, it is considered that the utilization efficiency of the replenished carrier becomes high, and as a result, the total amount of carrier used is small.

  As shown in FIG. 17, continuous image formation experiments were performed for the respective developing devices to compare the wear amount of the photosensitive drum. The amount of abrasion of the photosensitive drum was measured with an eddy current film thickness meter (FISCHERSCOPE MMS) manufactured by HelmutFisher.

  The initial film thickness of the charge transport layer, which is the outermost layer of the photosensitive drum used in the developing device of Example 1, is 30 μm. The use limit wear amount of the charge transport layer is 20 μm.

  As the image formation is accumulated, the photosensitive drum deteriorates and the wear amount increases. In the carrier adhesion method, the amount of wear reached the wear limit of 20 μm when the cumulative number of images formed reached 80,000. In contrast, in Example 1 and the overflow method, the wear limit of 20 μm was reached when the cumulative number of images formed was 150,000.

  This is because, in the carrier adhesion method, every time the developer deterioration degree is determined, the carrier is adhered on the photosensitive drum, and the adhesion amount is detected from the reflected light amount. It is considered that the wear of the photosensitive drum is promoted by the carrier particles that are not completely cleaned after the carrier adhesion amount is measured.

  In the developing device of the first embodiment, when the two-component developer composed of toner and carrier is used and the developer deteriorated due to the accumulation of image formation is replaced, the degree of deterioration of the developer is detected by the optical sensor array. In order to prevent photoconductor drum wear due to image formation accumulation and reduce the amount of carrier used, an agitation chamber is equipped with an optical sensor array, and the degree of developer deterioration is detected by measuring the replenishment toner agitation time. ing. Further, by replacing the developer according to the degree of deterioration of the developer, it is possible to prevent the photosensitive drum from being worn and reduce the amount of carrier used, and to maintain a long life of the developer. By replacing the developer according to the value of the degree of deterioration of the developer, it is possible to provide an image forming apparatus that is low in running cost while maintaining high quality with little background contamination and image quality deterioration due to poor charging of the toner over time. can do.

<Example 2>
FIG. 18 is an explanatory diagram of a configuration of the developing device according to the second embodiment. The developing device according to the second embodiment does not have the discharge port 412 of the developing chamber as in the first embodiment, and overflows excess developer from the discharge port 412 on the side surface of the stirring chamber. Since the other configuration is the same, in FIG. 18, the same reference numerals as those in FIG.

  As shown in FIG. 18, the overflow type developing device 4 </ b> Y does not have a mechanism for controlling the discharge amount of the developer in the developing container 420. When the amount of developer in the developing device 4Y increases due to carrier replenishment from the carrier chamber 416, the developer naturally overflows little by little from the side discharge port 412 and the developer is gradually replaced. That is, since a special mechanism is not provided for discharging the developer, it is inevitable that the unused carrier just supplied is discharged.

  Here, conventionally, the timing of carrier replenishment from the carrier chamber 416 is determined based on the cumulative number of image formations, the cumulative rotation time of the developing sleeve 415, and the like. Assuming that there is a certain relationship between the cumulative rotation time of the developing sleeve 415 and the deterioration level, the supply amount is determined by predicting the carrier deterioration level from the rotation time of the developing roller. However, in this case, when a large number of images with a large image area ratio are output, or when a large number of images with a small image area ratio are output, there is a possibility that the carrier supply is improperly executed. The problem based on the disadvantage that the degradation level varies depending on the image area ratio of the output image cannot be solved. The degree of deterioration of the carrier in the developer varies depending on the image area ratio (toner consumption) and the usage environment of the developing device. If the carrier deteriorates quickly, use the deteriorated carrier until the replacement time. become.

  However, similar to the first embodiment, such a problem can be solved by performing control for obtaining the toner mixing time T from the image captured by the optical sensor array 409. The replenishment control unit 900 executes carrier replenishment / developer discharge control once for every 100 image outputs. In the carrier replenishment / developer discharge control, a developer replacement determination operation is performed to determine whether carrier replenishment and developer discharge are performed. Based on the output of the optical sensor array 409, the replenishment control unit 900 measures the mixing time T that is a parameter of the flowability of the developer in the developing device 4. Based on the mixing time T, the degree of decrease in the charging performance of the carrier is determined, and when the charging performance of the carrier has decreased to the limit state, the carrier is supplied and the developer is discharged.

1Y, 1M, 1C, 1K Photosensitive drums 2Y, 2M, 2C, 2k Corona charger 3 Exposure device, 4Y, 4M, 4C, 4K Developing device 6 Fixing device, 20 Recording material cassette, 23 Registration roller 53 Secondary transfer roller, 54 Intermediate transfer belt 401 Development chamber, 402 Stir chamber, 403 Supply port 404 Toner supply motor, 405 Carrier supply solenoid 406 Carrier supply valve, 407 Development screw 408 Stir screw, 409 Optical sensor array 410 Image signal processing circuit, 411 Development Solvent for discharging agent 412 Developer discharge port, 413 collection container, 414 discharge valve 415 developing sleeve, 416 carrier chamber, 417 toner chamber 418 developer toner concentration sensor, 4090 image sensor 4091, 4093 lens, 4092 LED
4094 transparent window, 900 supply control unit, 901 video counter 902 page counter, 903 timer

Claims (6)

A developer carrier;
A developer circulation path for circulating the developer including toner and carrier while stirring to supply the developer carrying member;
A toner replenishing unit for replenishing the developer circulation path to supplement the consumed toner;
A carrier replenishing section for replenishing the developer circulation path to replace the deteriorated carrier of the circulating developer;
A developer discharging section for discharging the developer from the developer circulation path in order to eliminate the excess of the developer accompanying the carrier replenishment of the carrier replenishing section;
Detection means capable of detecting a deviation in toner distribution in the developer conveyed along the developer circulation path based on the output;
Control for controlling carrier replenishment by the carrier replenishment unit based on the output of the detection means so that the dispersion state of the toner in the developer when toner is replenished from the toner replenishment unit is maintained within a predetermined allowable range. And an image forming apparatus.   The control unit replenishes a predetermined amount of carrier from the carrier replenishment unit when a toner dispersion state in the developer when the toner is replenished reaches the boundary of the predetermined allowable range. Item 2. The image forming apparatus according to Item 1.   3. The control unit detects the developer in the developer circulation path at predetermined intervals by the detection unit, and replenishes a constant amount of toner from the toner replenishing unit for each detection. The image forming apparatus described.   The image forming apparatus according to claim 3, wherein the control unit executes detection of the developer in the developer circulation path by the detection unit in parallel with image formation. The toner replenishing unit supplies toner corresponding to the amount of toner consumed in image formation to the developer circulation path for each image formation,
The control unit adjusts the toner supply amount by the toner supply unit before and after detection by the detection unit so as to supplement the toner amount consumed in image formation in total with the toner amount used for detection by the detection unit. The image forming apparatus according to claim 4. A developer carrier;
A developer circulation path for circulating the developer including toner and carrier while stirring to supply the developer carrying member;
A toner replenishing unit for replenishing the developer circulation path to supplement the consumed toner;
A carrier replenishing section for replenishing the developer circulation path to replace the deteriorated carrier of the circulating developer;
A developer discharging section for discharging the developer from the developer circulation path in order to eliminate the excess of the developer accompanying the carrier replenishment of the carrier replenishing section;
A transparent window disposed on the downstream side in the developer conveying direction at a position where the toner replenishing portion replenishes the developer circulation path with toner;
Illuminating means for illuminating the developer conveyed through the developer circulation path through the transparent window;
6. The development mountable in the image forming apparatus according to claim 1, further comprising: an imaging unit configured to image the developer illuminated by the illumination unit through the transparent window. apparatus.

Images