JP2007047711A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus employing a trickle development system in which a fresh carrier is supplied to a development section by an optimum amount and which has high economic efficiency and environmental property. <P>SOLUTION: The image forming apparatus is equipped with the development section 23 which contains a developer G and develops a latent image formed on an image carrier 21 and a supply means 47 for newly supplying a carrier C into the development section 23. Then the supply amount of the carrier C is varied based upon at least the two of detection results: a detection result with respect to an image area rate, a detection result of a toner consumption, a detection result of an operation time of the development section, and a detection result of the number of output images per job. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a composite machine thereof, and in particular, a two-component developer composed of toner and a carrier is accommodated and a new carrier is provided. The present invention relates to an image forming apparatus including a developing unit that is appropriately supplied.

  Conventionally, in an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, or a combination machine thereof, a case where a two-component developer (additive or the like) composed of a toner and a carrier is included is included. (See, for example, Patent Document 1).

  In the developing unit using the two-component developer, toner is appropriately supplied into the developing unit from a toner supply port provided in a part of the developing unit in accordance with toner consumption in the developing unit. The replenished toner is stirred and mixed by a stirring member such as a transport screw together with the developer in the developing unit. Part of the stirred and mixed developer is supplied to the developing roller. The developer carried on the developing roller is regulated to an appropriate amount by a doctor blade (developer regulating member), and then the toner in the developer is placed on the photosensitive drum at a position facing the photosensitive drum (image carrier). It adheres to the latent image.

  As described above, since the carrier in the developer accommodated in the developing unit in the normal developing process remains in the developing unit without being consumed, the carrier deteriorates with time. Specifically, the carrier is agitated and mixed for a long time in the developing part, and the coating layer of the carrier wears or peels off, resulting in a “film scraping phenomenon” in which the charging ability of the carrier is reduced, or a toner component on the surface of the carrier. In addition, the “spent phenomenon” in which the charging ability of the carrier is reduced due to the adhesion of additives.

The trickle development method is for preventing the deterioration of the image quality of the output image due to such deterioration of the carrier over time. That is, a new carrier (or a new two-component developer) is appropriately replenished in the developing unit, and a part of the two-component developer accommodated in the developing unit is appropriately discharged to the outside of the developing unit. The amount of deteriorated carriers is reduced to maintain the amount of carriers accommodated in the developing unit and the charging ability.
The image forming apparatus using such a trickle development system has a stable output image quality over time compared to a device that requires replacement of the developing unit and carrier with a new one each time the carrier deteriorates over time. It will become.

  On the other hand, Patent Document 2 discloses an image forming apparatus that uses a trickle developing method and adjusts the replenishment amount of a new carrier to be replenished to the developing unit according to the amount of toner consumed in the developing unit. Is disclosed. Specifically, the image area ratio of the output image is detected by substituting the toner consumption amount described above, and when the detected image area ratio is large, the carrier replenishment amount is also proportionally increased according to the detected image area ratio.

JP-A-10-90991 JP-A-9-204105

The image forming apparatus using the conventional trickle developing system described above is wasteful because a new carrier may be excessively supplied to the developing unit in excess of a necessary amount.
That is, the degree to which the carrier accommodated in the developing unit deteriorates with time varies depending on the change in toner consumption in the developing unit and other conditions. However, the conventional image forming apparatus always replenishes the developing unit with a new carrier at a constant replenishment amount and timing regardless of the change in the conditions. Therefore, a new carrier may be excessively supplied to the developing unit.

  On the other hand, the technique disclosed in Patent Document 2 described above increases or decreases the supply amount of a new carrier to be supplied to the developing unit in proportion to the size of the image area ratio of the output image. However, since there is no perfect proportional relationship between the degree of deterioration of the carrier accommodated in the developing unit and the image area ratio of the output image, new carriers may be excessively supplied to the developing unit. It was.

  The present invention has been made to solve the above-described problems. An image using the trickle developing system, which is highly economical and environmentally friendly, in which an optimum amount of a new carrier is replenished to the developing unit without waste. It is to provide a forming apparatus.

  According to a first aspect of the present invention, there is provided an image forming apparatus containing a developer composed of toner and a carrier, developing a latent image formed on an image carrier, Replenishing means for newly replenishing the carrier, variable means for varying the replenishment amount of the carrier replenished by the replenishing means, and detecting means for directly or indirectly detecting the image area ratio of the image output from the apparatus A second detection unit that directly or indirectly detects a consumption amount of toner consumed in the development unit, a third detection unit that directly or indirectly detects an operation time of the development unit, And a fourth detecting means for directly or indirectly detecting the number of images output continuously without being intermittently operated, wherein the variable means includes the detecting means, the second detecting means, and the second detecting means. 3 detection means, the fourth detection It is to vary the supply amount of the carrier based on a result of detection by at least two of the means.

  According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect of the invention, wherein the variable means is configured to adjust the replenishment amount of the carrier based on the detection result detected by the second detection means. A reference value is determined, and the reference value is corrected based on the detection result detected by the fourth detection means.

  The image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the second aspect, wherein the variable means is configured such that when the number of images detected by the fourth detection means is 10 or less. The replenishment amount is corrected so as to be larger than the reference value.

  The image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to the first aspect, wherein the variable means determines the replenishment amount of the carrier based on a detection result detected by the third detecting means. A reference value is determined, and the reference value is corrected based on a detection result detected by the detection means.

  The image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to the fourth aspect, wherein when the image area ratio detected by the detecting means exceeds a predetermined value, the variable means The replenishment amount is corrected so as to be larger than the reference value.

  An image forming apparatus according to a sixth aspect of the present invention is the image forming apparatus according to the fifth aspect, wherein the predetermined value of the image area ratio is 10%.

  According to a seventh aspect of the present invention, there is provided an image forming apparatus containing a developer composed of toner and a carrier, a developing unit for developing a latent image formed on an image carrier, Replenishment means for newly replenishing the carrier in the developing unit, variable means for varying the amount of carrier replenished by the replenishment means, and detection for directly or indirectly detecting the image area ratio of the image output from the apparatus And the variable means compares the detection result detected by the detection means with a preset threshold value of the image area ratio or the plurality of image area ratios in a stepwise manner. It is variable.

  According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect of the present invention, the variable means controls the variable amount of the replenishment amount that varies stepwise so as not to be uniform. It is.

  According to a ninth aspect of the present invention, in the image forming apparatus according to the seventh or eighth aspect, the variable means has the detection result equal to or greater than an upper limit threshold among the plurality of thresholds. Sometimes the replenishment amount of the carrier is set to a fixed value.

  An image forming apparatus according to a tenth aspect of the present invention is the image forming apparatus according to the ninth aspect, wherein the upper limit threshold is set in a range of an image area ratio of 10 to 15%.

  An image forming apparatus according to an eleventh aspect of the present invention is the image forming apparatus according to any one of the seventh to tenth aspects, wherein the variable means has the detection result less than a lower limit threshold among the plurality of thresholds. The amount of replenishment of the carrier is reduced to zero.

  An image forming apparatus according to a twelfth aspect of the present invention is the image forming apparatus according to any one of the seventh to eleventh aspects, wherein the detection result detected by the detecting means is a predetermined number of sheets output from the apparatus. The image area ratios of the images are averaged.

  An image forming apparatus according to a thirteenth aspect of the present invention is the image forming apparatus according to any one of the seventh to twelfth aspects, comprising a plurality of the developing sections, and the threshold value is set for each of the plurality of developing sections. Is set.

  According to a fourteenth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to thirteenth aspects, wherein the discharging unit discharges a part of the developer accommodated in the developing section. Is further provided.

  An image forming apparatus according to a fifteenth aspect of the present invention is the image forming apparatus according to any one of the first to fourteenth aspects, wherein the replenishing unit replenishes toner into the developing unit together with a carrier. It is.

  According to a sixteenth aspect of the present invention, in the image forming apparatus according to any one of the first to fifteenth aspects, the variable unit varies the operating time or the number of operations of the replenishing unit. The replenishment amount of the carrier is variable.

  The image forming apparatus according to claim 17 is the image forming apparatus according to any one of claims 1 to 16, wherein the detection unit measures the number of pixels of the document and determines the number of pixels. The image area ratio is obtained by multiplying the original magnification.

  An image forming apparatus according to an eighteenth aspect of the present invention is the image forming apparatus according to any one of the first to sixteenth aspects, wherein the detecting means is based on the number of pixels of the document read by the document reading unit. The image area ratio is obtained.

  According to a nineteenth aspect of the present invention, in the image forming apparatus according to any one of the first to sixteenth aspects, the detection means is based on document data received via a communication circuit. The image area ratio is obtained.

  An image forming apparatus according to a twentieth aspect of the present invention is the image forming apparatus according to any one of the first to sixteenth aspects, wherein the detection means is formed on the image carrier by a writing unit. The image area ratio is obtained based on the number of pixels of the latent image.

  According to the present invention, since the replenishment amount of a new carrier to be replenished in the developing unit is optimally varied, the replenishment amount of the carrier is not wasted, and the image forming apparatus using the trickle developing system is highly economical and environmentally friendly Can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
The first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is an apparatus main body of a color copying machine as an image forming apparatus, 2 is a writing unit that emits laser light based on input image information, and 20Y, 20M, 20C, and 20BK are colors (yellow, magenta, cyan, black). ), A photosensitive drum as an image carrier accommodated in each of the process cartridges 20Y, 20M, 20C, and 20BK, 22 is a charging unit that charges the photosensitive drum 21, and 23Y, 23M, Reference numerals 23C and 23BK denote developing units (developing devices) for developing the electrostatic latent image formed on the photosensitive drum 21, and reference numeral 24 denotes a transfer bias for transferring the toner image formed on the photosensitive drum 21 to the intermediate transfer belt 27. A roller 25 indicates a cleaning unit that collects untransferred toner on the photosensitive drum 21.

  In addition, 27 is an intermediate transfer belt on which toner images of a plurality of colors are transferred in an overlapping manner, 28 is a second transfer bias roller for transferring the toner image formed on the intermediate transfer belt 27 to the recording medium P, and 29 is an intermediate transfer belt. 27 is an intermediate transfer belt cleaning unit that collects untransferred toner, 30 is a conveyance belt that conveys a recording medium P on which a four-color toner image is transferred, and 32Y, 32M, 32C, and 32BK are developing units 23Y and 23M. , 23C, 23BK, a toner replenishing unit for replenishing each color toner, 47Y, 47M, 47C, 47BK are replenishing means for replenishing each developing unit 23Y, 23M, 23C, 23BK, 51 A document conveying unit that conveys the document D to the document reading unit 55, 55 a document reading unit (scanner) that reads image information of the document D, and 61 a transfer sheet Paper feed unit in which the recording medium P is accommodated, 66 denotes a fixing unit for fixing the unfixed image on the recording medium P.

Here, each of the process cartridges 20Y, 20M, 20C, and 20BK is obtained by integrating the photosensitive drum 21, the charging unit 22, and the cleaning unit 25, respectively.
Image formation of each color (yellow, magenta, cyan, black) is performed on the photosensitive drum 21 in each of the process cartridges 20Y, 20M, 20C, and 20BK.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport roller of the document transport unit 51 and placed on the contact glass 53 of the document reading unit 55. Then, the document reading unit 55 optically reads the image information of the document D placed on the contact glass 53.

  Specifically, the document reading unit 55 scans the image of the document D on the contact glass 53 while irradiating light emitted from the illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each color separation light of RGB (red, green, blue) by the color sensor, and then converted into an electrical image signal. Further, the image processing unit (not shown) performs color conversion processing, color correction processing, spatial frequency correction processing, and the like based on the RGB color separation image signals, and performs yellow, magenta, cyan, and black processing. Get color image information.

  Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. Then, laser light (exposure light) based on the image information of each color is emitted from the writing unit 2 toward the photosensitive drums 21 of the corresponding process cartridges 20Y, 20M, 20C, and 20BK.

On the other hand, the four photosensitive drums 21 rotate in the clockwise direction in FIG. First, the surface of the photosensitive drum 21 is uniformly charged at a position facing the charging unit 22 (a charging process). Thus, a charged potential is formed on the photosensitive drum 21. Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of each laser beam.
In the writing unit 2, laser light corresponding to the image signal is emitted from the light source corresponding to each color. The laser light is incident on the polygon mirror 3 and reflected, and then passes through the lenses 4 and 5. The laser light after passing through the lenses 4 and 5 passes through different optical paths for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  The laser beam corresponding to the yellow component is reflected by the mirrors 6 to 8 and then irradiated onto the surface of the photosensitive drum 21 of the first process cartridge 20Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 21 by the polygon mirror 3 that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 21 charged by the charging unit 22.

  Similarly, the laser beam corresponding to the magenta component is reflected by the mirrors 9 to 11 and then irradiated to the surface of the photosensitive drum 21 of the second process cartridge 20M from the left side of the paper, thereby causing an electrostatic latent image corresponding to the magenta component. An image is formed. The cyan component laser light is reflected by the mirrors 12 to 14 and then irradiated to the surface of the photosensitive drum 12 of the third process cartridge 20C from the left side of the drawing to form a cyan component electrostatic latent image. The black component laser light is reflected by the mirror 15 and then irradiated on the surface of the photosensitive drum 21 of the fourth process cartridge 20BK from the left side of the paper, thereby forming an electrostatic latent image of black component.

Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent images of the respective colors are formed reaches positions facing the developing units 23Y, 23M, 23C, and 23BK, respectively. Then, each color toner is supplied onto the photosensitive drum 21 from the developing units 23Y, 23M, 23C, and 23BK, and the latent image on the photosensitive drum 21 is developed (this is a developing step).
Thereafter, the surface of the photosensitive drum 21 after the development process reaches a position facing the intermediate transfer belt 27. Here, the transfer bias roller 24 is installed at each facing position so as to contact the inner peripheral surface of the intermediate transfer belt 27. Then, at the position of the transfer bias roller 24, the images of the respective colors formed on the photosensitive drum 21 are sequentially superimposed and transferred onto the intermediate transfer belt 27 (first transfer step).

Then, the surface of the photosensitive drum 21 after the first transfer process reaches a position facing the cleaning unit 25. The untransferred toner remaining on the photosensitive drum 21 is collected by the cleaning unit 25 (this is a cleaning process).
Thereafter, the surface of the photosensitive drum 21 passes through a static elimination unit (not shown), and a series of image forming processes on the photosensitive drum 21 is completed.

On the other hand, the surface of the intermediate transfer belt 27 on which the images of the respective colors on the photosensitive drum 21 are transferred in an overlapping manner travels in the direction of the arrow in the drawing and reaches the position of the second transfer bias roller 28. Then, the full-color image on the intermediate transfer belt 27 is secondarily transferred onto the recording medium P at the position of the second transfer bias roller 28 (second transfer step).
Thereafter, the surface of the intermediate transfer belt 27 reaches the position of the intermediate transfer belt cleaning unit 29. Then, the untransferred toner on the intermediate transfer belt 27 is collected by the intermediate transfer belt cleaning unit 29, and a series of transfer processes on the intermediate transfer belt 27 is completed.

Here, the recording medium P at the position of the second transfer bias roller 28 is transported from the paper feeding unit 61 via the transport guide 63, the registration roller 64, and the like.
Specifically, the transfer paper P fed by the paper feed roller 62 from the paper feed unit 61 that stores the recording medium P passes through the conveyance guide 63 and is guided to the registration roller 64. The recording medium P that has reached the registration roller 64 is conveyed toward the position of the second transfer bias roller 28 in synchronization with the toner image on the intermediate transfer belt 27.

Thereafter, the recording medium P on which the full-color image is transferred is guided to the fixing unit 66 by the conveyance belt 30. In the fixing unit 66, the color image is fixed on the recording medium P at the nip between the heating roller 67 and the pressure roller 68.
Then, the recording medium P after the fixing process is discharged as an output image by the paper discharge roller 69 to the outside of the apparatus main body 1, and a series of image forming processes is completed.

Next, the image forming unit of the image forming apparatus will be described in detail with reference to FIGS.
FIG. 2 is a cross-sectional view showing the image forming section, and FIG. 3 is a cross-sectional view in the longitudinal direction (the direction perpendicular to the paper surface of FIG. 2) showing the developing section.
The four image forming units installed in the apparatus main body 1 have substantially the same structure except that the color of the toner T used in the image forming process is different. Therefore, alphabets of reference numerals in the process cartridge, the developing unit, and the toner replenishing unit. (Y, M, C, BK) is omitted for illustration.

  As shown in FIG. 2, the process cartridge 20 mainly contains a photosensitive drum 21 as an image carrier, a charging unit 22, and a cleaning unit 25 integrally in a case 26. The cleaning unit 25 is provided with a cleaning blade 25 a and a cleaning roller 25 b that are in contact with the photosensitive drum 21.

  The developing unit 23 mainly includes a developing roller 23a facing the photosensitive drum 21, a first conveying screw 23b facing the developing roller 23a, and a second conveying screw facing the first conveying screw 23b via a partition member 23e. 23c and a doctor blade 23d facing the developing roller 23a.

  Further, the developing unit 23 is provided with a first developer containing portion 23g and a second developer containing portion 23h separated by a partition member 23e. Referring to FIG. 3, the first developer accommodating portion 23g and the second developer accommodating portion 23h communicate with each other at both ends in the longitudinal direction (the range in which the partition member 23e is not interposed), and the developer circulation path. Is forming. A developing roller 23a, a first conveying screw 23b, and a doctor blade 23d are disposed in the first developer accommodating portion 23g. A second transport screw 23c and a magnetic sensor 40 are disposed in the second developer accommodating portion 23h.

  Referring to FIG. 3, the developing roller 23a includes a magnet 23a1 fixed inside and forming a magnetic pole on the roller peripheral surface, and a sleeve 23a2 made of a nonmagnetic material and rotating around the magnet 23a1. . A plurality of magnetic poles (main pole, transport pole, pumping pole, agent cutting pole, etc.) are formed on the developing roller 23a (sleeve 23a2) by the magnet 23a1.

  The developing roller 23a (sleeve 23a2) is connected to a drive motor (not shown) installed in the apparatus main body 1 and is rotationally driven by the drive motor. Although not shown, the developing roller 23a, the first transport screw 23b, and the second transport screw 23c are drivingly connected by a gear train. Thereby, as the developing roller 23a is rotationally driven by the drive motor, the first transport screw 23b and the second transport screw 23c are also rotationally driven following the development roller 23a.

A two-component developer G composed of toner T and carrier C is accommodated in the developing unit 23.
The toner T (the toner in the developer G and the toner in the toner replenishing unit 32) in the first embodiment contains toner base particles and additives made of a resin and a colorant.
In addition, the toner T according to the first exemplary embodiment is synthesized by a polymerization reaction such as emulsion polymerization or suspension polymerization using a monomer, or by a method in which the resin itself is melted and sprayed to form fine particles. Alternatively, it can be produced by a method in which an additive is mixed and adhered to a base particle obtained by dispersing in water or the like to a predetermined particle size using a Henschel mixer or the like.

  As the resin contained in the toner T, styrene such as polystyrene, polychlorostyrene, polyvinyltoluene, and the like, and a substituted polymer thereof; styrene / p-chlorostyrene copolymer, styrene / propylene copolymer, styrene / vinyl Toluene copolymer, styrene / vinyl naphthalene copolymer, styrene / methyl acrylate copolymer, styrene / ethyl acrylate copolymer, styrene / butyl acrylate copolymer, styrene / octyl acrylate copolymer, styrene / Methyl methacrylate copolymer, styrene / ethyl methacrylate copolymer, styrene / butyl methacrylate copolymer, styrene / α-chloromethyl methacrylate copolymer, styrene / acrylonitrile copolymer, styrene / vinyl methyl ether Copolymer, styrene / vinyl ethyl Ether copolymer, styrene / vinyl methyl ketone copolymer, styrene / butadiene copolymer, styrene / isoprene copolymer, styrene / acrylonitrile / indene copolymer, styrene / maleic acid copolymer, styrene / maleic acid ester Styrene copolymers such as copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyvinyl butyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, A phenol resin, an aliphatic or alicyclic hydrocarbon resin, an aromatic petroleum resin, chlorinated paraffin, paraffin wax and the like can be used alone or in combination of two or more.

  As the black colorant used for the toner T, carbon black, aniline black, furnace black, lamp black, and the like are used. Examples of cyan colorants include phthalocyanine blue, methyllene blue, Victoria blue, methyl violet, aniline blue, and ultramarine blue. As the magenta colorant, rhodamine 6G lake, dimethylquinacridone, watching red, rose bengal, rhodamine B, alizarin lake and the like are used. As the yellow colorant, chrome yellow, benzidine yellow, hansa yellow, naphthol yellow, molybdenum orange, quinoline yellow, tartrazine and the like are used.

  These toners T can contain a small amount of a charge imparting agent (for example, a dye or pigment, a polarity control agent, etc.) in order to impart the charge efficiently. As the polarity control agent, metal complex salts of monoazo dyes, nitrohumic acid and salts thereof, salicylic acid, naphthoic acid, metal complexes of dicarboxylic acid such as Co, Cr or Fe, organic dyes, quaternary ammonium salts and the like can be used.

  Examples of inorganic fine particles used as additives include silica, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, iron oxide, copper oxide, zinc oxide, tin oxide, silica sand, clay, Mica, wollastonite, diatomaceous earth, chromium oxide, cerium oxide, pengala, antimony trioxide, magnesium oxide, zirconium oxide, parium sulfate, barium carbonate, calcium carbonate, silicon carbide, silicon nitride, and the like can be used. Among these, when two types of silica and titanium oxide are used, the effect of suppressing the burying of the additive in the toner and the effect of stabilizing the charging of the toner are particularly exhibited.

Further, the carrier C in the developer G in the first embodiment is one in which a coating layer is formed on magnetic core particles.
As the core particles of the carrier C, ferromagnetic metals such as iron, cobalt and nickel, alloys such as magnetite, hematite and ferrite, or compounds thereof are used.

  Examples of the resin for forming the coating layer of the carrier C include polyolefin resins such as polyethylene, polypropylene, chlorinated polyethylene, and chlorosulfonated polyethylene; polyvinyl and polyvinylidene resins such as polystyrene, acrylic resin (eg, polymethyl methacrylate), Polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether and polyvinyl ketone; vinyl chloride / vinyl acetate copolymer; styrene / acrylic acid copolymer; straight silicone resin composed of organosiloxane bond Or modified products thereof (for example, modified products by alkyd resin, polyester, epoxy resin, polyurethane, etc.); fluorine resin, For example, polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene; polyamide; polyester, such as polyethylene terephthalate; polyurethane; polycarbonate; amino resin, such as urea / formaldehyde resin; it can. Among these resins, acrylic resin, silicone resin or a modified product thereof, and fluorine resin are preferable from the viewpoint of preventing toner spent (particularly silicone resin or modified product thereof is preferable). As a method for forming the coating layer, a method in which a resin is applied to the surface of the carrier core particles by a spraying method, a dipping method or the like is used.

  In addition, a fine powder can be added to the coating layer to the carrier C in order to adjust the carrier resistance. The fine powder dispersed in the coating layer preferably has a particle size of about 0.01 to 5.0 μm. Moreover, it is preferable that 2-30 weight part (especially 5-20 weight part) is added with respect to 100 weight part of coating resin. As the fine powder, metal oxides such as silica, alumina and titania, and pigments such as carbon black can be used.

The above-described image forming process will be described in more detail with a focus on the developing process.
The developing roller 23a rotates in the direction of the arrow in FIG. As shown in FIG. 3, the developer G in the developing unit 23 is generated by the rotation of the first conveying screw 23 b and the second conveying screw 23 c arranged so as to interpose the partition member 23 e therebetween in the arrow direction. It circulates in the longitudinal direction while being agitated and mixed with the toner T (new toner) replenished from the replenishing part 32 through the replenishing port 23f (circulation in the direction of the broken arrow in FIG. 3). The first transport screw 23b transports the developer G to the left side in FIG. 3, and the second transport screw 23c transports the developer G to the right side in FIG. 3 (in a direction opposite to the transport direction of the first transport screw 23b). Is transported to.

  Then, the toner T that is frictionally charged and adsorbed on the carrier C is carried on the developing roller 23 a together with the carrier C. The developer G carried on the developing roller 23a then reaches the position of the doctor blade 23d. The developer G on the developing roller 23a is adjusted to an appropriate amount at the position of the doctor blade 23d, and then reaches a position facing the photosensitive drum 21 (developing area).

  Thereafter, in the development area, the toner T in the developer G adheres to the electrostatic latent image formed on the surface of the photosensitive drum 21. Specifically, the toner T is latently exposed by the electric field formed by the potential difference (development potential) between the latent image potential (exposure potential) of the image area irradiated with the laser light L and the development bias applied to the development roller 23a. Adhere to the image.

  Thereafter, most of the toner T adhering to the photosensitive drum 21 in the developing process is transferred onto the intermediate transfer belt 27. The untransferred toner T remaining on the photosensitive drum 21 is collected in the cleaning unit 25 by the cleaning blade 25a and the cleaning roller 25b.

  Here, the toner replenishing unit 32 provided in the apparatus main body 1 includes a toner cartridge 33 configured to be replaceable, and a toner replenishing path 34 that guides the new toner T discharged from the toner cartridge 33 to the developing unit 23. It is configured. In addition, a new toner T (any of yellow, magenta, cyan, and black) is accommodated in the toner cartridge 33.

The toner T in the toner cartridge 33 is appropriately supplied into the developing unit 23 from the supply port 23f as the toner T in the developing unit 23 is consumed. The toner T in the developing unit 23 is consumed by a magnetic sensor 40 (toner density detecting means) installed below the second conveying screw 23c of the developing unit 23 or a photo sensor (not shown) facing the photosensitive drum 21. Is detected). Then, the toner supply unit 32 supplies the supply port 23f so that the detection result of the magnetic sensor 40 or the photo sensor becomes an output value corresponding to the target toner density (the ratio of the toner T in the developer G). The toner is supplied to the developing unit 23 via
Although illustration is omitted, adjustment of the toner replenishment amount replenished to the developing unit 23 is performed by controlling the rotation amount of the screw disposed in the toner replenishment path 34 by a pulse drive motor (toner transport motor).

Further, the developing unit 23 according to the first embodiment uses a trickle developing system.
As shown in FIG. 2, the image forming apparatus according to the first embodiment includes a discharge unit 23 k that discharges a part of the developer G stored in the developing unit 23 to the outside of the developing unit 23, and the inside of the developing unit 23. And a carrier replenishing section 47 as a replenishing means for newly replenishing the carrier C.

Specifically, a carrier replenishing portion 47 as a replenishing unit is provided above the second developer accommodating portion 23 h in addition to the toner replenishing portion 32. The carrier replenishing unit 47 includes a replaceable carrier cartridge 48 and a carrier replenishing path 49 that guides the new carrier C discharged from the carrier cartridge 48 to the developing unit 23 through the replenishing port 23f. . A new carrier C is accommodated in the carrier cartridge 48.
Although illustration is omitted, adjustment of the amount of carrier replenishment supplied to the developing unit 23 is performed by controlling the operation time or the number of operations of the screw disposed in the carrier replenishment path 49 with a pulse drive motor (variable means). The control of the variable means for changing the carrier replenishment amount from the carrier replenishment unit 47 will be described in detail later.
In addition to the screw mechanism described above, a powder pump mechanism can also be used as the conveying means in the toner supply path 34 and the carrier supply path 49.

On the other hand, a developer discharge port 23k as discharge means is provided in the vicinity of the upper end of the wall surface of the second developer storage portion 23h.
When the new carrier C is replenished from the carrier replenishing unit 47 into the developing unit 23 and the amount of developer in the developing unit 23 exceeds a predetermined amount, the excess developer G is discharged from the developer discharge port 23k. 23 is discharged outside. The developer G discharged from the developer discharge port 23k is conveyed to the developer recovery unit 44 via the developer recovery path 43.
In this way, as the new carrier C is replenished, the developer surface rises and the developer G exceeding the height of the developer discharge port 23k is discharged out of the developing unit 23, so that the development in the developing unit 23 is performed. The agent surface (developer amount) is always kept constant.
In the first embodiment, the overflow method is used as the discharging means for discharging the developer from the developing unit 23. However, an openable / closable shutter is provided at the developer discharge port 23k, and the developer is discharged by opening and closing the shutter. Can also be done.

In the image forming apparatus configured as described above, carrier replenishment is performed from the carrier replenishing unit 47 to the developing unit 23 according to the control flow shown in FIG.
Referring to FIG. 4, first, the toner replenishment amount detected from the operation time (rotation amount) of the above-described pulse drive motor (toner transport motor) or the like is detected by the control unit 45 as the second detection means. Indirect detection is made as the toner consumption amount consumed in step 23 (step S1).

  At the same time, the number of prints per job detected from user input information or the like (the number of images output continuously without intermittent operation of the apparatus 1) is used as the fourth detection means. It is detected by the control unit 45 (step S2). When the number of prints per job is 10 or less, the accumulated data is counted by multiplying the developing unit operating time ratio shown in FIG.

  Then, it is determined whether or not the value counted in step S1 has reached a certain value (step S3). As a result, when it is determined that the count value of the toner consumption amount has not reached a certain value, it is determined that it is not necessary to replenish the carrier from the carrier replenishing unit 47 to the developing unit 23, and after step S1 The steps are repeated. On the other hand, when it is determined that the count value of the toner consumption amount has reached a certain value, it is determined that the carrier needs to be replenished from the carrier replenishing unit 47 to the developing unit 23 and is variable. The carrier replenishment amount is determined by the control unit 45 as means (step S4).

  Here, in step S4, the carrier replenishment amount increases to a constant amount [A] (reference value) corresponding to the toner consumption amount by an amount [B] (increase in proportion to the count amount of prints per job). It is determined by adding a correction value. [A] and [B] described above are amounts determined by the durability of the carrier, and are values determined experimentally. [B] is calculated by multiplying the accumulated data of the number of prints per job by a constant [C].

Thereafter, based on the carrier replenishment amount determined in step S4, carrier replenishment to the developing unit 23 is performed (step S5). The variable control of the actual carrier replenishment amount is performed by increasing or decreasing the time or number of times that the carrier replenishment unit 47 is operated.
Then, the count of toner consumption and the count of the number of prints per job are reset (step S6), and then the steps after step S1 are repeated.

  As described above, in the first embodiment, when the number of prints per job decreases, the correction for increasing the replenishment amount of the carrier is performed. This is because when the number of prints per job is small, the operation time of the developing unit 23 required for each print increases, and the time for stirring and mixing the developer in the developing unit 23 also increases. This is because the “film scraping phenomenon” tends to occur in the carrier.

  FIG. 5 is a graph showing the relationship between “number of printed sheets / job” and “ratio of operating time of developing unit 23 required for one printed sheet”. In FIG. 5, the vertical axis indicates the relative ratio when the operating time of the developing unit 23 during continuous printing (the operating time required for one print) is 1. From FIG. 5, when the number of prints per job exceeds 10, the operation time is almost the same as that for continuous printing, but for one sheet / job, the operation time is about five times that for continuous printing. It can be seen that the job has twice the operating time. Therefore, if the number of prints per job decreases, the operating time of the developing unit increases regardless of the amount of toner consumption, and the carrier in the developing unit is likely to deteriorate due to stress.

Hereinafter, the operation time of the developing unit will be described in detail.
As described with reference to FIG. 1, the image forming apparatus 1 conveys the recording medium P accommodated in the paper feeding unit 61 to each image forming unit, forms a toner image on the recording medium P, and then transfers it to the fixing unit 66. Then, a fixing process is performed, and the recording medium P is discharged out of the apparatus as an output image. Therefore, when printing is started, it takes time to move the recording medium to the image forming unit and time to adjust the photosensitive drum and the developing unit in the image forming unit. Further, when the printing is finished, it is necessary to continue the operation until the last recording medium is discharged out of the apparatus. On the other hand, in the printing process on the way from the start to the end in the continuous printing operation, image formation is continuously performed in a short time with a slight space between the recording medium.
Therefore, when only one sheet is printed in one operation (one job), the time required for the paper feeding operation and the adjustment operation, the time for image formation, and the time for the paper discharge operation are required. The operation time per sheet becomes longer. On the other hand, when printing a large number of sheets in one operation (one job), the time required for image formation and the movement time between recording media increases with respect to the total operation time. The operating time per sheet of the developing unit is shortened.

Hereinafter, the deterioration of the carrier will be described in detail.
The carrier is a particle obtained by applying a coating layer for controlling the charging property to metal particles such as ferrite, and has two main causes of deterioration. The first cause of deterioration is that the coating layer is worn or peeled off by impact (“film scraping phenomenon”). The second cause of deterioration is that a toner component or an additive added to the toner adheres to the surface of the carrier (a “spent phenomenon”). In either case, the charging ability of the carrier is lowered and the carrier is deteriorated.

The “film scraping phenomenon” is likely to occur when the developing unit operates with a small amount of toner consumption, and friction between carriers and friction between the carrier and toner increases.
The “spent phenomenon” is a phenomenon that occurs when a large amount of toner is consumed when an image having a large image area ratio (image portion / (image portion + non-image portion)) is continuously output. A large amount of toner passes through the toner, and toner fine powders and additives are supplied one after another to the developer and are likely to stay in a state where they are released from the toner.

  In the first embodiment, the carrier supply for suppressing the “film scraping phenomenon” (with the developer discharge) is performed with reference to the carrier supply for suppressing the “spent phenomenon” (with the developer discharge). Is supplemented.) That is, the reference value of the carrier replenishment amount is determined based on the detection result (toner consumption amount) detected by the second detection unit, and based on the detection result (number of prints per job) detected by the fourth detection unit. The reference value is corrected.

Specifically, with reference to carrier replenishment proportional to toner consumption, when the number of printed sheets per job is 10 or less, a reference value for the amount of carrier replenishment is added by an increment corresponding to the number of printed sheets. Correction.
As a result, toner consumption is low, and deterioration due to carrier film scraping that occurs when stirring in the developing unit is performed for a long time can be prevented appropriately. When only carrier replenishment in proportion to the toner consumption amount is performed (control in the conventional image forming apparatus), the carrier replenishment amount is not set unless a certain amount of carrier replenishment amount corresponding to the toner consumption amount is set. Since deterioration cannot be prevented, a large amount of carriers are always replenished, resulting in low economic efficiency and environmental performance.

Hereinafter, in FIG. 6, it demonstrates in full detail by the drive control of a carrier replenishment part.
FIG. 6A is a graph showing an example of the relationship between the cumulative number of printed sheets and the cumulative toner consumption. FIG. 6B is a graph illustrating an example of a count state of toner consumption. When the toner consumption count reaches a certain value (H), carrier replenishment is performed, the toner consumption count is reset, and the next count is performed.
FIG. 6C is a timing chart when the carrier supply amount is adjusted by varying the operating time of the carrier supply unit. Carrier replenishment is performed when the toner consumption count reaches a certain value (H). However, since the carrier replenishment amount is corrected based on the detection result of the number of prints per job, the operation time of the carrier replenishment unit is variably controlled at the reference time (for example, t1) or at the time of correction (for example, t2). The
FIG. 6D is a timing chart when the carrier supply amount is adjusted by varying the number of times the carrier supply unit is operated. Carrier replenishment is performed when the toner consumption count reaches a certain value (H). However, since the carrier replenishment amount is corrected based on the detection result of the number of prints per job, the number of operations of the carrier replenishment unit is variable at the reference time (for example, 2 times) or at the time of correction (for example, 4 times). Be controlled.

  In the first embodiment, the carrier replenishment amount when a standard carrier mainly composed of ferrite is used is 1 gr to 10 gr per 1,000 image forming sheets (volume conversion is 0.4 ml to 4 ml). It is set. When the carrier is replenished for every 100 sheets, the volume is in the range of 0.04 ml to 0.4 ml, and a carrier replenishment unit capable of sufficiently controlling the amount of replenishment of the carrier can be configured.

  As described above, according to the first embodiment, since the replenishment amount of the new carrier C to be replenished in the developing unit 23 is optimally varied, the replenishment amount of the carrier C is not wasteful and economical. And can improve the environment.

  In the first embodiment, the new carrier C is supplied from the carrier supply unit 47, but a new developer G may be supplied from the carrier supply unit 47. Also in this case, the same effect as in the first embodiment is obtained.

  In the first embodiment, the process cartridges 20Y, 20M, 20C, and 20BK are configured by integrating the photosensitive drum 21, the charging unit 22, and the cleaning unit 25, respectively. Further, each developing unit 23Y, 23M, 23C, 23BK is configured as a single unit. On the other hand, the developing units 23Y, 23M, 23C, and 23BK can be integrated with the process cartridges 20Y, 20M, 20C, and 20BK. That is, the process cartridge 20 can also be configured by the photosensitive drum 21, the charging unit 22, the developing unit 23, and the cleaning unit 25. Also in this case, the same effect as in the first embodiment is obtained. Furthermore, the maintainability of the image forming unit is improved.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 7 is a flowchart showing carrier replenishment control performed by the developing unit in the second embodiment, and corresponds to FIG. 4 in the first embodiment. In the image forming apparatus according to the second embodiment, the carrier replenishment amount is varied based on the operating time of the developing unit and the image area ratio. The carrier is based on the toner consumption amount and the number of prints per job. This is different from that of the first embodiment in which the replenishment amount is variable.

In the image forming apparatus according to the second embodiment, the carrier supply from the carrier supply unit 47 to the developing unit 23 is performed as follows.
With reference to FIG. 7, first, the operation time of the developing unit 23 detected from the energization time of the drive motor that operates the developing unit 23 is detected by the control unit 45 as the third detecting means (step S11).

  At the same time, the image area ratio of the image to be output (printed) (the ratio of the image portion to the total area of the recording medium P) is detected by the control unit 45 serving as detection means (step S12). Here, the detecting means may measure the number of pixels of the document D and multiply the number of pixels by the magnification of the document D to obtain the image area ratio, or the number of pixels of the document D read by the document reading unit 55 may be obtained. The image area ratio may be obtained based on the image data, the image area ratio may be obtained based on the document data received via the communication circuit, or the latent image formed on the photosensitive drum 21 by the writing unit 2. The image area ratio may be obtained based on the number of pixels (lighting time of the laser light L).

  Then, it is determined whether or not the value counted in step S11 has reached a certain value (step S13). As a result, if it is determined that the count value of the operating time of the developing unit has not reached a certain value, it is determined that there is no need to replenish the carrier from the carrier replenishing unit 47 to the developing unit 23, and the step The steps after S11 are repeated. On the other hand, if it is determined that the count value of the operating time has reached a certain value, it is determined that the carrier needs to be replenished from the carrier replenishing unit 47 to the developing unit 23, and the variable means The carrier replenishment amount is determined by the control unit 45 (step S14).

  Here, in step S14, the replenishment amount of the carrier is a fixed amount [D] (reference value) corresponding to the operating time of the developing unit, and the image area ratio exceeds a predetermined value (10%). It is determined by adding an increment [E] (correction value) proportional to the excess amount. [D] and [E] described above are amounts determined by the durability of the carrier, and are values determined experimentally. [E] is calculated by multiplying an amount by which the image area ratio exceeds a predetermined value by a constant [F].

Thereafter, based on the carrier replenishment amount determined in step S14, carrier replenishment to the developing unit 23 is performed (step S15).
Then, the count of the operation time of the developing unit and the count of the image area ratio are reset (step S16), and then the steps after step S11 are repeated.

  As described above, in the second embodiment, when the image area ratio of the output image becomes large, correction is performed to increase the amount of carrier replenishment. This is because when the image area ratio of the image is large, a large amount of toner passes through the developer as a large amount of toner is consumed, and toner fine powder and additives are successively added to the developer. This is because a large amount of stays in the state of being supplied and released from the toner tends to cause a “spent phenomenon” in the carrier.

  In the first embodiment, carrier replenishment (with developer discharge) is used to suppress the “spent phenomenon” with reference to carrier replenishment (with developer discharge) that inhibits the “film scraping phenomenon”. Is supplemented.) That is, the reference value of the carrier replenishment amount is determined based on the detection result (operating time of the developing unit) detected by the third detection unit, and the reference value is determined based on the detection result (image area ratio) detected by the detection unit. It has been corrected.

Specifically, the carrier is replenished at every predetermined operating time with reference to the carrier replenishment proportional to the operating time of the developing unit. When the averaged image area ratio exceeds a predetermined value (10%), the carrier replenishment amount reference value is corrected by adding an increment corresponding to the degree exceeding the predetermined value. . Replenishment is performed by increasing the carrier replenishment amount until the image area ratio increases to some extent. The spent phenomenon appears prominently when the image area ratio exceeds 10%.
As a result, it is possible to appropriately prevent the deterioration due to the carrier spent when an image having a large image area ratio is output. When only carrier replenishment proportional to the operating time of the developing unit is performed (the control in the conventional image forming apparatus), a fixed amount of carrier replenishment amount corresponding to the operating time of the developing unit is set to be large. Otherwise, since deterioration of the carrier cannot be prevented, a large amount of carrier is always replenished, resulting in low economic efficiency and environmental performance.

  As described above, according to the second embodiment, since the replenishment amount of the new carrier C to be replenished in the developing unit 23 is optimally varied, as in the first embodiment, the carrier C There is no waste in the amount of replenishment, and it is possible to improve economy and environmental performance.

Embodiment 3 FIG.
A third embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 8 is a graph showing variable control of the carrier replenishment amount performed in the developing unit according to the third embodiment.
The image forming apparatus according to the third embodiment is also a trickle developing type apparatus provided with a carrier replenishing unit 47 as a replenishing unit, as in the above-described embodiments. Then, the amount of carrier replenishment supplied from the carrier replenishment unit 47 to the developing unit 23 is varied by the control unit 45 as a variable means. In the third embodiment, the amount of carrier replenishment is varied stepwise by comparing the image area ratio detected by the detecting means with a threshold value.

  Specifically, as shown in FIG. 3A, the detection result (image area ratio of the output image) detected by the detection means is compared with a preset threshold value M. As a result, when the detected image area ratio is smaller than the threshold value M, the carrier supply amount is set to B1. On the other hand, when the detected image area ratio is equal to or greater than the threshold value M, the carrier supply amount is set to B2 (> B1). As described above, the carrier replenishment amount is changed stepwise by comparing the image area ratio with the threshold value, so that the problem of excessive replenishment of carriers from the carrier replenishment unit 47 to the developing unit 23 can be suppressed.

This is due to the following contents obtained as a result of repeated research by the present inventors.
The deterioration of the carrier accommodated in the developing unit does not always progress in proportion to the increase in the image area ratio. When images with an image area ratio higher than a predetermined value are output continuously, carrier deterioration proceeds with an increase in the number of prints without depending on the image area ratio.
Specifically, when 10,000 images with an image area ratio of 10% are printed and when 10,000 images with an image area ratio of 20% are printed, the degree of carrier deterioration is the same. . Therefore, the amount of carrier replenishment when an image with an image area ratio of 20% is printed may be the same as that when an image with an image area ratio of 10% is printed.

That is, in a control method (conventional control method) in which carrier replenishment is performed in proportion to the size of the image area ratio, when an image with a high image area ratio is printed, more carrier replenishment (and developer) is required. ), The economy and the environment will be reduced.
Further, in the control method in which the carrier replenishment is performed in proportion to the size of the image area ratio, the control load on the control unit 45 is large, and the entire apparatus becomes complicated and expensive. For example, in the case of the conventional control method, when the carrier replenishment amount when the image area ratio is 5% is the reference (1), the carrier replenishment amount when the image area ratio is 5.5% is 1.1 times the reference. become. However, carrier replenishment, unlike toner replenishment, does not have to be so accurate, and even if the carrier replenishment amount is the same when the image area ratio is 5% and 5.5%, there is no problem in terms of image quality. Don't be.

FIG. 9 is a graph showing the relationship between the image area ratio and the carrier charging capability.
The experimental results in FIG. 9 show that the image area ratio is 0.5%, 1%, 3%, 5%, 7%, 10%, 15%, 20%, 30% at a temperature and humidity of 23 ° C. and 50%. The charging ability of the carrier after printing 10,000 sheets when the level is changed to 40% and 50% is measured.
From FIG. 9, when the image area ratio is 1% or less, the charging ability of the carrier is the same as that in the initial stage, and it is good. When the image area ratio is 1 to 10%, the charging ability decreases with the increase in the image area ratio. I can see it going. It can also be seen that when the image area ratio is 10% or more, the charging ability of the carrier is constant even if the image area ratio increases.

  For these reasons, there is a threshold value for the image area ratio, and when the image area ratio is smaller than the threshold value, carrier deterioration in the developing unit 23 proceeds as the cumulative toner consumption increases, and the threshold value is increased. It can be seen that when the image area ratio is larger than that, the carrier deterioration in the developing unit 23 progresses as the number of printed sheets increases. When the same experiment was performed by changing the type of toner or carrier, it was found that the threshold of the image area ratio at which the carrier deterioration pattern changes as described above was in the range of 10 to 15%.

A decrease in charging ability of the carrier is caused by adhesion of an additive in the toner to the surface of the carrier.
When the image area ratio is as low as 1% to 5%, as the image area ratio (toner consumption) increases, the amount of additive that is released from the toner and adheres to the carrier increases. As a result, carrier deterioration proceeds. However, when the image area ratio is high, the amount of the additive adhering to the carrier surface is hardly changed, so that the carrier deterioration does not depend on the image area ratio but proceeds as the number of prints increases. . Therefore, when the image area ratio is lower than the above-described threshold (10 to 15%), the carrier replenishment amount is controlled to be proportional to the image area ratio, and when the image area ratio is equal to or greater than the threshold value, the carrier replenishment amount. It is better to control so that becomes a fixed value.

However, as described above, the carrier replenishment amount does not need to be so accurate, and in order to achieve simplification and cost reduction of the apparatus, when the image area ratio is lower than the threshold value, the area of the low image area ratio A plurality of threshold values M1 to M5 are set, and a carrier replenishment amount B1 to B5 is set for each region divided by the plurality of threshold values M1 to M5, and the carrier replenishment amount is varied stepwise according to the image area ratio. It is preferable (see FIG. 8B).
At that time, with reference to FIG. 8C, it is possible to control so that the variable amount of the carrier replenishment amounts B1 to B5 that vary stepwise does not become uniform (for example, B2-B1 ≠ B3- B2.). Thereby, the freedom degree of variable control of carrier replenishment amount increases.

Referring to FIG. 8D, since the carrier deterioration proceeds in the high image area ratio region regardless of the image area ratio, the image area ratio is in the range of the upper limit threshold M3 (10 to 15%). ) When the above is reached, the carrier replenishment amount is set to the fixed value B3, thereby making it possible to replenish the carrier without waste.
Further, even when an image with an image area ratio of less than 1% is printed, the charging ability of the carrier does not decrease, so the lower limit threshold value M1 at which carrier deterioration does not proceed can be set. When the image area ratio is less than the lower limit threshold M1 (1%), the carrier replenishment amount is set to zero, so that the carrier replenishment without waste is possible.

Hereinafter, a method for determining the carrier replenishment amount in the third embodiment will be described.
First, a plurality of threshold values for the image area ratio are determined in advance, and the carrier replenishment amount in each region is determined. Then, the image area ratio is detected every time one sheet is printed, and the carrier replenishment amount is determined by the region where the detection result (image area ratio) is entered. The actual carrier replenishment may be performed immediately after the carrier replenishment amount is determined, or may be performed after the carrier replenishment amount per sheet is stored in the storage unit and the data is accumulated in a predetermined amount. Here, as the storage unit, an electrical storage unit such as a RAM or a rewritable ROM, or a magnetic storage unit such as a magnetic recording medium or a magneto-optical memory can be used.

  In the case where a plurality of developing units 23Y, 23M, 23C, and 23BK are provided as in the image forming apparatus according to the third embodiment, the deterioration of the carrier differs for each of the developing units 23Y, 23M, 23C, and 23BK. In particular, since the developing unit 23BK using black toner is frequently used, the carrier is more likely to deteriorate than the other developing units. Therefore, by setting a threshold value for each color developing unit and performing variable control of the carrier replenishment amount, the entire image forming apparatus can perform replenishment of carrier replenishment.

  As described above, according to the third embodiment, since the replenishment amount of the new carrier C to be replenished in the developing unit 23 is optimally varied, the replenishment amount of the carrier C is not wasteful and economical. And can improve the environment.

Example.
With reference to FIGS. 10 to 12, experiments (Examples and Comparative Examples) for confirming the effects of the third embodiment will be described.
FIG. 10 is a graph showing variable control of the carrier replenishment amount, where the horizontal axis represents the image area ratio and the vertical axis represents the carrier replenishment amount per print. In FIG. 10, a solid line shows variable control of the carrier replenishment amount in the third embodiment as an example, and a broken line shows conventional control of the carrier replenishment amount as a comparative example.

Specifically, in the embodiment, the carrier replenishment amount is variably controlled stepwise according to the image area ratio of the document. At that time, the upper limit threshold of the image area ratio was set to 10%, the lower limit threshold was set to 1%, and a threshold for each 1% was set therebetween. The carrier replenishment amount is set to zero when the image area ratio is less than 1%, and is set so as to increase in steps of 1% when the image area ratio is 1 to 10%. When the area ratio was 10% or more, the amount was fixed.
Further, every time one sheet was printed, the image area ratio was measured from the lighting time of the laser beam in the writing unit 2, and the carrier replenishment amount per sheet was determined and stored. By repeating this, when a certain amount of stored carrier replenishment amount data has been accumulated, carrier replenishment from the carrier replenishment unit 47 to the developing unit 23 is actually performed.

  On the other hand, in the comparative example, the carrier replenishment amount is controlled so as to be proportional to the image area ratio. Specifically, the image area ratio was measured every time one sheet was printed, and an amount of carrier proportional to the image area ratio was supplied to the developing unit. At this time, the weight ratio of the toner to be supplied and the carrier was about 9: 1.

FIG. 11 is a graph showing the relationship between the number of prints and the image quality in the example and the comparative example. FIG. 12 is a graph showing the relationship between the number of printed sheets and the accumulated carrier supply amount in the example and the comparative example. In the experiment, a total of 50,000 sheets were randomly printed on an original having an image area ratio of 1% to 100%, and the image quality evaluation of the output image and measurement of the cumulative carrier supply amount were performed. In the image quality evaluation, a chart with density gradation is printed, and the gradation, density uniformity, and presence / absence of an edge effect are visually evaluated.
From FIG. 11, it can be seen that the image quality is good up to 50,000 sheets in both the example (■ mark) and the comparative example (◯ mark). Also, from FIG. 12, it can be seen that the cumulative amount of carrier replenishment is far less in the example (marked with ■) than in the comparative example (marked with ◯). That is, it has been experimentally confirmed that the variable control of the carrier replenishment amount in the embodiment can improve the economic efficiency and the environmental performance without degrading the image quality.

  In addition to the experiment related to the above-described embodiment, the image area ratio is averaged every time 100 sheets are printed, and the carrier replenishment amount corresponding to the averaged image area ratio is determined based on FIG. An experiment was conducted in which the developing unit was replenished with 100 times the amount of carrier. As a result, it was possible to obtain experimental results almost similar to the experimental results related to the above-described embodiment.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view illustrating an image forming unit in the image forming apparatus of FIG. 1. It is sectional drawing which looked at the image development part to the longitudinal direction. It is a flowchart which shows control of carrier replenishment. 6 is a graph showing the relationship between the number of prints per job and the operating time of the developing unit. It is a timing chart which shows drive control of a carrier replenishment part. It is a flowchart which shows the control of the carrier replenishment performed in the image development part in Embodiment 2 of this invention. It is a graph which shows the variable control of the carrier replenishment amount performed in the developing part in Embodiment 3 of this invention. It is a graph which shows the relationship between an image area ratio and carrier charging ability. It is a graph which shows the relationship between an image area rate and the carrier replenishment amount per output image. 6 is a graph showing the relationship between the number of prints and image quality. It is a graph which shows the relationship between the number of printed sheets and the accumulation carrier replenishment amount.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20, 20Y, 20M, 20C, 20BK Process cartridge,
21 photosensitive drum (image carrier), 22 charging unit,
23, 23Y, 23M, 23C, 23BK Developing unit (developing device),
23a developing roller, 23b first conveying screw,
23c second conveying screw, 23d doctor blade,
23e partition member, 23f supply port,
23g first developer accommodating portion, 23h second developer accommodating portion,
23k developer outlet (discharge means),
32, 32Y, 32M, 32C, 32BK toner supply unit,
33 toner cartridge, 34 toner supply path,
43 developer collection path, 44 developer collection unit, 45 control unit,
47, 47Y, 47M, 47C, 47BK Carrier replenishment section (replenishment means),
48 carrier cartridge, 49 carrier supply route,
G Two-component developer (developer), C carrier, T toner.

Claims (20)

A developer that contains a developer composed of a toner and a carrier, and that develops a latent image formed on the image carrier;
Replenishment means for newly replenishing the carrier in the developing section;
Variable means for varying the amount of carrier replenished by the replenishing means;
Detection means for directly or indirectly detecting an image area ratio of an image output from the apparatus;
Second detection means for directly or indirectly detecting the amount of toner consumed in the developing unit;
Third detection means for directly or indirectly detecting the operating time of the developing unit;
A fourth detection means for directly or indirectly detecting the number of images output continuously without intermittent operation of the apparatus,
The variable means varies the replenishment amount of the carrier based on detection results detected by at least two of the detection means, the second detection means, the third detection means, and the fourth detection means. An image forming apparatus. The variable means determines a reference value for the replenishment amount of the carrier based on the detection result detected by the second detection means, and corrects the reference value based on the detection result detected by the fourth detection means. The image forming apparatus according to claim 1. The variable means corrects the replenishment amount to be larger than the reference value when the number of images detected by the fourth detection means is 10 or less. Image forming apparatus. The variable means determines a reference value for the replenishment amount of the carrier based on the detection result detected by the third detection means, and corrects the reference value based on the detection result detected by the detection means. The image forming apparatus according to claim 1, wherein: The variable means corrects the replenishment amount to be larger than the reference value when the image area ratio detected by the detection means exceeds a predetermined value. Image forming apparatus. The image forming apparatus according to claim 5, wherein the predetermined value of the image area ratio is 10%. A developer that contains a developer composed of a toner and a carrier, and that develops a latent image formed on the image carrier;
Replenishment means for newly replenishing the carrier in the developing section;
Variable means for varying the amount of carrier replenished by the replenishing means;
Detecting means for directly or indirectly detecting an image area ratio of an image output from the apparatus,
The variable means compares the detection result detected by the detection means with a preset threshold value of one or a plurality of image area ratios, and varies the replenishment amount of the carrier stepwise. Image forming apparatus. The image forming apparatus according to claim 7, wherein the variable unit performs control so that a variable amount of the replenishment amount that varies stepwise does not become uniform. 9. The image forming according to claim 7, wherein the variable unit sets the replenishment amount of the carrier to a fixed value when the detection result is equal to or more than an upper limit threshold among the plurality of thresholds. apparatus. The image forming apparatus according to claim 9, wherein the upper limit threshold is set in a range of an image area ratio of 10 to 15%. The said variable means makes the replenishment amount of the said carrier zero when the said detection result becomes less than a minimum threshold value among these threshold values, The Claim 1 characterized by the above-mentioned. Image forming apparatus. 12. The image according to claim 7, wherein the detection result detected by the detection means is obtained by averaging the image area ratio of a predetermined number of images output from the apparatus. Forming equipment. A plurality of the developing sections;
The image forming apparatus according to claim 7, wherein the threshold value is set for each of the plurality of developing units. The image forming apparatus according to claim 1, further comprising a discharging unit that discharges a part of the developer accommodated in the developing unit. 15. The image forming apparatus according to claim 1, wherein the replenishing unit newly replenishes toner in the developing unit together with a carrier. The image forming apparatus according to claim 1, wherein the variable unit varies a supply amount of the carrier by changing an operation time or the number of operations of the supply unit. The image forming apparatus according to claim 1, wherein the detecting unit measures the number of pixels of the document and multiplies the number of pixels by the magnification of the document to determine the image area ratio. apparatus. The image forming apparatus according to claim 1, wherein the detection unit obtains the image area ratio based on the number of pixels of the document read by the document reading unit. The image forming apparatus according to claim 1, wherein the detection unit obtains the image area ratio based on document data received via a communication circuit. The said detection means calculates | requires the said image area rate based on the pixel number of the said latent image formed on the said image carrier by the writing part, The Claim 1 characterized by the above-mentioned. Image forming apparatus.

Images