JP2015172671A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can suppress shock jitter, detect a toner pattern formed between sheets to correct image forming conditions without decreasing productivity, and suppress a reduction in the accuracy of correcting the image forming conditions.SOLUTION: When a toner pattern formed between sheets reaches a transfer nip such as a secondary transfer nip, and a transfer member such as a secondary transfer belt is separated from an image carrier such as an intermediate transfer belt, an image forming apparatus detects the toner pattern with first toner image detection means such as an intermediate transfer toner adhesion amount sensor. Meanwhile, when the transfer member is not separated from the image carrier, the image forming apparatus transfers the toner pattern to the transfer member and detects the toner pattern with second toner image detection means such as a secondary transfer toner adhesion amount sensor.

Description

  The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine.

  Conventionally, a toner image formed on the surface of a drum-shaped photoconductor is primarily transferred to an endless intermediate transfer belt by a known electrophotographic process, and the toner image on the intermediate transfer belt is transferred to a secondary transfer nip. 2. Description of the Related Art Image forming apparatuses that perform secondary transfer onto transfer paper that has been transported to the surface are known.

  In the image forming apparatus described in Patent Document 1, a toner pattern is formed in a portion corresponding to a space between sheets on the intermediate transfer belt, and this paper is used as a secondary transfer member that forms a secondary transfer nip in contact with the intermediate transfer belt. The toner pattern formed therebetween is transferred. The toner pattern on the secondary transfer member is detected by the toner image detecting means, and the image forming conditions are corrected based on the detection result detected by the toner image detecting means. In this image forming apparatus, an elastic intermediate transfer belt having an elastic layer is used as the intermediate transfer belt, and it is better to detect the toner pattern with the secondary transfer member than to detect the toner pattern with the elastic intermediate transfer belt. It is said that the toner pattern can be detected. The reason is explained as follows. In other words, the elastic intermediate transfer belt is flexible and has a low surface strength, and scratches are easily generated to reduce the glossiness. As the toner image detection means, an optical sensor is used, and prior to the detection of the toner pattern, the belt surface (background portion) without toner on the intermediate transfer belt is irradiated with light, and the output of the light receiving unit at that time The light quantity of the light emitting unit is adjusted so that becomes a predetermined voltage. When the glossiness of the belt surface is low, the amount of reflected light incident on the light receiving portion from the belt surface (background portion) of the intermediate transfer belt decreases. For this reason, the amount of light emitted from the light emitting unit increases. As a result, the amount of reflected light from the toner pattern on the intermediate transfer belt increases, the S / N ratio decreases, and the toner pattern cannot be detected satisfactorily. Therefore, stable image forming conditions can be corrected by detecting the toner pattern on the secondary transfer member in which such a decrease in glossiness is unlikely to occur.

  In addition, when a sudden speed change occurs in the intermediate transfer belt, an image transferred from the photosensitive member to the intermediate transfer belt at the primary transfer nip expands and contracts. For this reason, light and shade occurs in a portion of the image that should have a constant image density, and an abnormal image called a shock jitter occurs. The sudden change in the speed of the intermediate transfer belt described above occurs when the transfer paper enters the secondary transfer nip where the image on the intermediate transfer belt is secondarily transferred to the transfer paper.

  In Patent Document 2, in order to suppress an abnormal image called shock jitter, the secondary transfer member is separated from the intermediate transfer belt by a contact / separation mechanism based on the paper type conveyed to the secondary transfer nip. An image forming apparatus is described. Specifically, when the transfer paper transported to the secondary transfer nip is thick paper, the secondary transfer member is separated from the intermediate transfer belt by the contact / separation mechanism before entering the secondary transfer nip. Force to move. Thereby, a minute gap is formed between the secondary transfer member and the intermediate transfer belt, and the occurrence of shock jitter when the transfer paper enters the secondary transfer nip can be suppressed. Further, immediately after the leading edge of the transfer paper enters the minute gap, the separation of the secondary transfer member by the contact / separation mechanism is released, and the biasing force of the spring that biases the secondary transfer member toward the intermediate transfer belt side The secondary transfer member is pressed toward the intermediate transfer belt. As a result, the secondary transfer member comes into contact with the intermediate transfer belt, and a sufficient transfer pressure is exerted at the secondary transfer nip during the secondary transfer process to suppress the occurrence of transfer failure.

  On the other hand, when the transfer paper conveyed to the secondary transfer nip is plain paper, the secondary transfer member is not contacted / separated as described above, and the secondary transfer member is in contact with the intermediate transfer belt. Next transfer is performed.

  When the configuration described in Patent Document 2 is adopted in the image forming apparatus described in Patent Document 1, when the transfer paper conveyed to the secondary transfer nip is thick paper, productivity may be reduced. Occurred. When the toner pattern is not formed between the sheets, an operation of separating the secondary transfer member for the next thick sheet can be performed immediately after the thick sheet passes through the secondary transfer nip. However, when a toner pattern is formed between papers and this toner pattern is transferred to the secondary transfer member, the transfer paper passes through the secondary transfer nip and the toner pattern is transferred to the secondary transfer member. The secondary transfer member is separated for the thick paper. As a result, when a toner pattern is formed between papers, compared to a case where a toner pattern is not formed between papers, the distance between the papers is increased by the amount of transfer of the toner patterns to the secondary transfer member, and productivity is lowered. .

  Not only when an elastic intermediate transfer belt having an elastic layer is used, it is more preferable to detect the toner pattern on the secondary transfer member than when detecting the toner pattern on the intermediate transfer belt. This is because by detecting the toner pattern on the secondary transfer member, it is possible to correct the image forming conditions including the influence of the secondary transfer, and it is possible to correct the image forming conditions with high accuracy. It is.

  Similar problems also occur in the direct transfer type image forming apparatus that directly transfers the image bearing member to the transfer sheet.

  The present invention has been made in view of the above problems, and an object of the present invention is to detect a toner pattern formed between sheets of paper by suppressing shock jitter, and without reducing productivity. An object of the present invention is to provide an image forming apparatus capable of correcting the forming conditions and suppressing a decrease in correction accuracy of the image forming conditions.

  In order to achieve the above object, an invention according to claim 1 is directed to an endless belt-shaped image carrier that is rotatably supported by a plurality of tension members, and a front surface that is an outer peripheral surface of the image carrier. A transfer member that forms a transfer nip in contact with the image carrier, and contact / separation means that contacts and separates the transfer member with respect to the image carrier, and a toner image carried on the front surface of the image carrier is transferred to the transfer nip. A transfer device for transferring to a transfer material sandwiched inside, and when the transfer material conveyed in the transfer nip is a predetermined paper type, the transfer member is moved to the image carrier prior to the transfer material entering the transfer nip. In the image forming apparatus comprising: a control unit that controls the separation unit so that the transfer member is brought into contact with the image carrier after the transfer material has entered the transfer nip. The toner pattern formed on the body is detected. Based on the detection result of the first toner image detecting means, the second toner image detecting means for detecting the toner pattern transferred to the transfer member, and the detection result of the first toner image detecting means or the second toner image detecting means. And an image forming condition correcting means for correcting the image forming condition, and when the control for separating the transfer member from the image carrier between the sheets is not performed, the toner pattern is transferred to the transfer member and the first member is transferred to the transfer member. When the toner is detected by the two toner image detecting means and the transfer member is controlled to be separated from the image carrier between the papers, the toner pattern formed between the papers is detected by the first toner image detecting means, and the toner is detected. The separation operation is started without waiting for the trailing edge of the pattern to reach the transfer nip.

  According to the present invention, it is possible to suppress shock jitter and to correct the image forming conditions by detecting the toner pattern formed between the papers without reducing productivity. In addition, it is possible to suppress a decrease in correction accuracy of image forming conditions.

1 is a schematic configuration diagram illustrating an example of a printer according to an embodiment. FIG. 3 is an enlarged sectional view of a secondary transfer nip. AA sectional drawing of FIG. FIG. 2 is a block diagram showing a part of an electric circuit in the printer according to the embodiment. FIG. 3 is an enlarged schematic configuration diagram in the vicinity of a secondary transfer belt showing a gradation pattern and a secondary transfer toner adhesion amount sensor. FIG. 3 is an enlarged configuration diagram illustrating an enlarged secondary transfer toner adhesion amount sensor. 9 is a timing chart for explaining a conventional secondary transfer belt separation operation. FIG. 10 is a control flow diagram of second image density control according to the present embodiment. The figure explaining a mode that the same gradation pattern is detected with an intermediate transfer toner adhesion amount sensor and a secondary transfer toner adhesion amount sensor. The graph which shows the correlation with the detection result of an intermediate transfer toner adhesion amount sensor, and the detection result of a secondary transfer toner adhesion amount sensor. The graph which shows the correlation with the output value of the diffuse reflection light receiving element after sensitivity correction | amendment, and a toner adhesion amount.

Hereinafter, an embodiment in which the present invention is applied to a printer as an image forming apparatus that forms an image by an electrophotographic method will be described.
First, a basic configuration of the printer according to the embodiment will be described.
FIG. 1 is a schematic configuration diagram illustrating an example of a printer according to an embodiment.
This printer includes two optical writing units 1YM and 1CK and four process units 2Y, 2M, and 2Y for forming toner images of yellow (Y), magenta (M), cyan (C), and black (K). 2C, 2K. A paper feed path 30, a pre-transfer conveyance path 31, a manual paper feed path 32, a manual feed tray 33, a registration roller pair 34, and a conveyance belt unit 35 are provided. Further, a fixing device 40, a conveyance switching device 50, a paper discharge path 51, a paper discharge roller pair 52, a paper discharge tray 53, a first paper feed cassette 101, a second paper feed cassette 102, a retransmission device, and the like are also provided.

  Each of the first paper feed cassette 101 and the second paper feed cassette 102 accommodates a bundle of transfer papers P as recording media. Then, the uppermost transfer paper P in the paper bundle is sent out toward the paper feed path 30 by the rotational drive of the paper feed rollers 101a and 102a. The paper feed path 30 is followed by a pre-transfer conveyance path 31 for conveying transfer paper immediately before a secondary transfer nip described later. The transfer paper P sent out from the paper feed cassettes 101 and 102 enters the pre-transfer conveyance path 31 through the paper feed path 30.

  A manual feed tray 33 is disposed on the side surface of the printer housing so as to be openable and closable with respect to the housing, and a bundle of paper is manually fed to the upper surface of the tray in an open state with respect to the housing. The uppermost transfer paper P in the manually fed paper bundle is sent out toward the pre-transfer conveyance path 31 by the feed roller of the manual feed tray 33.

  Each of the two optical writing units 1YM and 1CK includes a laser diode, a polygon mirror, various lenses, and the like. Then, the laser diode is driven based on image information read by a scanner outside the printer or image information sent from a personal computer. As a result, the photoconductors 3Y, 3M, 3C, and 3K as the latent image carriers of the process units 2Y, 2M, 2C, and 2K are optically scanned. Specifically, the photoconductors 3Y, 3M, 3C, and 3K of the process units 2Y, 2M, 2C, and 2K are rotationally driven in a counterclockwise direction in the drawing by driving means (not shown). The optical writing unit 1YM performs an optical scanning process by irradiating the driven photosensitive members 3Y and 3M while deflecting the laser light in the rotation axis direction. Thereby, electrostatic latent images based on the Y image information and the M image information are formed on the photoreceptors 3Y and 3M, respectively. Further, the optical writing unit 1CK performs an optical scanning process by irradiating the driven photoconductors 3C and 3K while deflecting the laser light in the rotation axis direction. Thereby, electrostatic latent images based on the C image information and the K image information are formed on the photoreceptors 3C and 3K, respectively.

  The process units 2Y, 2M, 2C, and 2K have drum-shaped photoreceptors 3Y, 3M, 3C, and 3K as latent image carriers, respectively. The process units 2Y, 2M, 2C, and 2K support various devices arranged around the photoreceptors 3Y, 3M, 3C, and 3K as a single unit on a common support, It is detachable from the printer unit main body. The process units 2Y, 2M, 2C, and 2K have the same configuration except that the colors of the toners used are different from each other. Taking the process unit 2Y for Y as an example, this has a developing device 4Y for developing an electrostatic latent image formed on the surface of the photoreceptor 3Y into a Y toner image in addition to the photoreceptor 3Y. In addition, the charging device 5Y that uniformly charges the surface of the photoconductor 3Y that is driven to rotate, or the transfer residue that has adhered to the surface of the photoconductor 3Y after passing through the primary transfer nip for Y described later. A drum cleaning device 6Y for cleaning toner is also provided.

  The illustrated printer has a so-called tandem configuration in which four process units 2Y, 2M, 2C, and 2K are arranged along an endless movement direction with respect to an intermediate transfer belt 61 described later.

  As the photoreceptor 3 </ b> Y, a drum-like member is used in which a photosensitive layer is formed by applying a photosensitive organic photosensitive material to a raw tube such as aluminum. However, an endless belt may be used.

  The developing device 4Y develops a latent image using a two-component developer (hereinafter simply referred to as “developer”) containing a magnetic carrier (not shown) and non-magnetic Y toner. As the developing device 4Y, a type that performs development with a one-component developer not including a magnetic carrier may be used instead of the two-component developer. The developing device 4Y is appropriately replenished with Y toner in the Y toner bottle 103Y by a Y toner replenishing device (not shown).

  As the drum cleaning device 6Y, a system in which a polyurethane rubber cleaning blade as a cleaning member is pressed against the photoreceptor 3Y is used, but another system may be used. In order to improve the cleaning property, this printer employs a system in which a rotatable fur brush is brought into contact with the photoreceptor 3Y. This fur brush also serves to apply the lubricant to the surface of the photoreceptor 3Y while scraping the lubricant from a solid lubricant (not shown) into a fine powder.

  A neutralizing lamp (not shown) is disposed above the photoreceptor 3Y, and this neutralizing lamp is also a part of the process unit 2Y. The neutralization lamp neutralizes the surface of the photoreceptor 3Y after passing through the drum cleaning device 6Y by light irradiation. The surface of the photoreceptor 3Y that has been neutralized is uniformly charged by the charging device 5Y, and then optically scanned by the optical writing unit 1YM described above. The charging device 5Y is rotationally driven while receiving a charging bias from a power source (not shown). Instead of this method, a scorotron charger method in which the photosensitive member 3Y is charged without contact may be employed.

  The Y process unit 2Y has been described above, but the process units 2M, 2C, and 2K for M, C, and K have the same configuration as that for Y.

  A transfer unit 60 is arranged below the four process units 2Y, 2M, 2C, and 2K. In the transfer unit 60, an intermediate transfer belt 61 as an image carrier, which is an endless belt stretched by a plurality of support rollers, is brought into contact with the photoreceptors 3Y, 3M, 3C, and 3K. And it is made to drive | work (endless movement) in the clockwise direction in a figure by the rotational drive of any one support roller. As a result, primary transfer nips for Y, M, C, and K where the photoreceptors 3Y, 3M, 3C, and 3K and the intermediate transfer belt 61 abut are formed.

  In the vicinity of the primary transfer nips for Y, M, C, and K, primary transfer rollers 62Y, 62M, 62C, and 62K as primary transfer members are surrounded by the inner peripheral surface of the intermediate transfer belt, that is, in the belt loop. It is arranged. The intermediate transfer belt 61 is pressed toward the photoreceptors 3Y, 3M, 3C, and 3K by the primary transfer rollers 62Y, 62M, 62C, and 62K. A primary transfer bias is applied to the primary transfer rollers 62Y, 62M, 62C, and 62K by a power source (not shown). As a result, a primary transfer electric field for electrostatically moving the toner images on the photoreceptors 3Y, 3M, 3C, and 3K toward the intermediate transfer belt 61 is formed in the primary transfer nips for Y, M, C, and K. .

  In the drawing, toner images are sequentially superimposed on the outer peripheral surface of the intermediate transfer belt 61 that sequentially passes through the primary transfer nips for Y, M, C, and K along with the endless movement in the clockwise direction. The primary transfer. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as “four-color toner image”) is formed on the outer peripheral surface of the intermediate transfer belt 61.

  A secondary transfer device 70 as a transfer device is disposed below the intermediate transfer belt 61 in the drawing. The secondary transfer device 70 has a secondary transfer belt 77 as a transfer member stretched between a secondary transfer roller 72 and a unit facing roller 78. Outside the loop of the secondary transfer belt 77, a secondary transfer toner adhesion amount sensor 64 and a secondary transfer cleaning device 76, which are second toner image detection means, are disposed. The secondary transfer toner adhesion amount sensor 64 is opposed to the unit facing roller 78 with the secondary transfer belt 77 interposed therebetween. The secondary transfer cleaning device 76 has a secondary transfer belt cleaning blade that comes into contact with a portion of the secondary transfer belt 77 that is wound around the unit facing roller 78.

  The secondary transfer roller 72 is in contact with the portion of the intermediate transfer belt 61 that is wound around the secondary transfer counter roller 68 from the outer peripheral surface of the intermediate belt via the secondary transfer belt 77 to form a secondary transfer nip. As a result, a secondary transfer nip is formed in which the outer peripheral surface of the intermediate transfer belt 61 and the secondary transfer belt 77 abut.

  A secondary transfer bias is applied to the secondary transfer counter roller 68 from a power source (not shown). On the other hand, the secondary transfer roller 72 is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip.

  The registration roller pair 34 is disposed on the right side of the secondary transfer nip in the drawing, and the transfer paper P sandwiched between the rollers can be synchronized with the four-color toner image on the intermediate transfer belt 61. Send to the secondary transfer nip. In the secondary transfer nip, the four-color toner images on the intermediate transfer belt 61 are collectively transferred to the transfer paper P due to the influence of the secondary transfer electric field and the nip pressure, and become a full-color image combined with the white color of the transfer paper P.

  The transfer residual toner that has not been transferred to the transfer paper P at the secondary transfer nip adheres to the outer peripheral surface of the intermediate transfer belt 61 that has passed through the secondary transfer nip. This transfer residual toner is cleaned by a belt cleaning device 75 in contact with the intermediate transfer belt 61.

  The transfer paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 61 and transferred to the transport belt unit 35. The transport belt unit 35 endlessly moves the endless belt-shaped transport belt 36 endlessly in the counterclockwise direction in the figure by the rotational drive of the drive roller 37 while being stretched by the drive roller 37 and the driven roller 38. The transfer sheet P delivered from the secondary transfer nip is conveyed along with the endless movement of the conveyance belt 36 while being held on the tensioning surface of the outer circumferential surface of the conveyance belt, and is transferred to the fixing device 40 as a fixing unit. .

  In this printer, the transfer switching device 50, the retransmission path 54, the switchback path 55, the post-switchback transfer path 56, and the like constitute a retransmission means. Specifically, the conveyance switching device 50 switches the subsequent conveyance destination of the transfer paper P received from the fixing device 40 between the paper discharge path 51 and the retransmission path 54. When a single-side mode print job for forming an image only on the first surface of the transfer paper P is executed, the transfer destination of the transfer paper P is set to the paper discharge path 51. As a result, the transfer paper P on which an image is formed only on the first surface is sent to the paper discharge roller pair 52 via the paper discharge path 51 and discharged onto a paper discharge tray 53 outside the apparatus. In addition, when executing a double-sided mode print job for forming images on both sides of the transfer paper P, the transfer paper P is also received when the transfer paper P having images fixed on both sides is received from the fixing device 40. Is set to the paper discharge path 51. As a result, the transfer paper P on which images are formed on both sides is discharged onto a discharge tray 53 outside the apparatus. On the other hand, when a transfer sheet P having an image fixed only on the first side is received from the fixing device 40 during execution of a double-side mode print job, the transfer destination of the transfer sheet P is set to the retransmission path 54.

  A switchback path 55 is connected to the retransmission path 54, and the transfer paper P sent to the retransmission path 54 enters the switchback path 55. When the entire area in the conveyance direction of the transfer paper P enters the switchback path 55, the conveyance direction of the transfer paper P is reversed and the transfer paper P is switched back. In addition to the retransmission path 54, a post-switchback transport path 56 is connected to the switchback path 55, and the transferred transfer paper P enters the post-switchback transport path 56. At this time, the transfer paper P is turned upside down. Then, the transfer paper P that is turned upside down is retransmitted to the secondary transfer nip via the post-switchback transport path 56 and the paper feed path 30. The transfer sheet P on which the toner image is also transferred to the second surface at the secondary transfer nip is fixed on the second surface via the fixing device 40, and then the transfer switching device 50, the paper discharge path 51, and the like. The paper is discharged onto a paper discharge tray 53 via a pair of paper discharge rollers 52.

  The printer has a full-color image forming mode in which an image is formed with toners of four colors K, C, M, and Y, and a monochrome image forming mode in which an image is formed only with K toner, for example. It is arbitrarily set by the user on the operation section of the PC or the print screen of the personal computer.

  When the full color image forming mode is selected, toner images corresponding to the respective image information are formed on the photosensitive member by the four process units 2Y, 2M, 2C, and 2K. Next, the images are sequentially transferred to the intermediate transfer belt 61, and collectively transferred onto the transfer paper by paper transfer. Then, the process of melt-fixing with a fixing belt is performed. In the monochrome image formation mode using only K, the image data is related to K image formation, but only the process unit 2K is operated, and after transferring the intermediate transfer belt 61, an image is obtained by the same process as the full color image formation mode. .

  In addition, toner bottles 103Y, 103M, 103C, and 103K are disposed as toner containers that are disposed above the optical writing unit 1YM and filled with toner of each color of yellow, magenta, cyan, and black. . The toner bottles 103Y, 103M, 103C, and 103K are detachably attached to the apparatus main body. The toner of each color of yellow, cyan, magenta, and black in the toner bottles 103Y, 103C, 103M, and 103K is developed by the toner replenishing device by a predetermined replenishment amount in each of the process units 2Y, 2M, 2C, and 2K. Replenished to devices 4Y, 4M, 4C, 4K. The toner bottles 103Y, 103M, 103C, and 103K are consumables that are replaced when the internal toner runs out. When the toner runs out, the toner bottles 103Y, 103M, 103C, and 103K are detached from the apparatus main body and replaced.

  In recent years, in addition to plain paper that has been widely used as transfer paper, special transfer paper used for thermal transfer such as special paper having an uneven surface or iron print as a design has been increasingly used. When such special paper is used, transfer defects are more likely to occur when the toner image on the intermediate transfer belt 61 on which the color toners are superimposed is secondarily transferred onto the paper, as compared with the case of conventional plain paper. Therefore, in this printer, an elastic layer having low hardness is provided on the intermediate transfer belt 61 so that the toner layer and transfer paper with poor smoothness can be deformed at the secondary transfer nip. By providing the intermediate transfer belt 61 with an elastic layer having low hardness and imparting elasticity to the intermediate transfer belt 61, the surface of the intermediate transfer belt 61 can be deformed following local unevenness. As a result, good adhesion can be obtained without excessively increasing the secondary transfer pressure with respect to the toner layer, there is no loss of characters during transfer, and transfer unevenness is also caused on transfer paper with poor smoothness. A transfer image with excellent uniformity can be obtained.

  In this printer, the intermediate transfer belt 61 includes a base layer made of resin, an elastic layer made of an elastic member such as elastic rubber or elastomer, and a surface layer.

  The base layer of the intermediate transfer belt 61 is provided to prevent the intermediate transfer belt 61 from being stretched, and it is preferable to use a resin with little stretch. Specifically, polyimide resin, polyamideimide resin, polycarbonate, fluororesin (ETFE, PVDF), polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, Styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer) Styrene-octyl acrylate copolymer and styrene-phenyl acrylate copolymer), styrene-methacrylic acid ester copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene) -Phenyl methacrylate copolymer ), Styrene resins such as styrene-α-chloroacrylic acid methyl copolymer, styrene-acrylonitrile-acrylic acid ester copolymer (monopolymer or copolymer containing styrene or a styrene-substituted product), methyl methacrylate resin , Butyl methacrylate resin, ethyl acrylate resin, butyl acrylate resin, modified acrylic resin (silicone modified acrylic resin, vinyl chloride resin modified acrylic resin, acrylic / urethane resin, etc.), vinyl chloride resin, styrene-vinyl acetate copolymer , Vinyl chloride-vinyl acetate copolymer, rosin-modified maleic acid resin, phenol resin, epoxy resin, polyester resin, polyester polyurethane resin, polyethylene, polypropylene, polybutadiene, polyvinylidene chloride, ionomer resin, polyurethane resin, Recone resins, ketone resins, ethylene - can be used ethyl acrylate copolymer, xylene resin and polyvinyl butyral resin, polyamide resin, one kind or two kinds or more selected from the group consisting of modified polyphenylene oxide resin. However, it is a matter of course that the material is not limited to the above materials.

  The elastic layer of the intermediate transfer belt 61 is butyl rubber, fluorine rubber, acrylic rubber, EPDM, NBR, acrylonitrile-butadiene-styrene rubber natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, ethylene-propylene rubber, ethylene-propylene. Terpolymer, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, urethane rubber, syndiotactic 1,2-polybutadiene, epichlorohydrin rubber, ricone rubber, fluororubber, polysulfide rubber, polynorbornene rubber, hydrogenated nitrile 1 selected from the group consisting of rubber, thermoplastic elastomer (for example, polystyrene, polyolefin, polyvinyl chloride, polyurethane, polyamide, polyurea, polyester, fluororesin) It can be used kind or two kinds or more. However, it is a matter of course that the material is not limited to the above materials.

  There are no particular restrictions on the resistance value adjusting conductive agent contained in the resin layer or elastic layer of the intermediate transfer belt 61 in order to adjust the electric resistance value. For example, carbon black, graphite, metal powder such as aluminum or nickel, oxidation Conductive metal oxide such as tin, titanium oxide, antimony oxide, indium oxide, potassium titanate, antimony oxide-tin oxide composite oxide (ATO), indium oxide-tin oxide composite oxide (ITO), conductive metal oxidation The product may be coated with insulating fine particles such as barium sulfate, magnesium silicate, and calcium carbonate. Of course, the conductive agent is not limited thereto.

  The surface layer of the intermediate transfer belt 61 is required to prevent contamination of the photoconductor, reduce the frictional resistance of the surface of the intermediate transfer belt, reduce the adhesion of toner, and improve the cleaning property and secondary transfer property. . As the surface layer, for example, one kind or two or more kinds such as polyurethane, polyester, epoxy resin, etc. are used, and the surface energy is reduced to improve the lubricity, for example, fluorine resin, fluorine compound, carbon fluoride, and two oxides. One kind or two or more kinds of powders such as titanium and silicon carbide, or particles having different particle diameters can be dispersed and used. Further, it is also possible to use a material having a surface energy reduced by forming a fluorine-rich layer on the surface by performing a heat treatment like a fluorine-based rubber material.

  The intermediate transfer belt can be produced by, for example, a centrifugal molding method in which a material is poured into a rotating cylindrical mold to form a belt, or a spray coating method in which a liquid paint is sprayed to form a film. Also, a dipping method in which a cylindrical mold is dipped in a material solution and pulled up, a casting method in which the cylindrical mold is poured into an inner mold or an outer mold, and a method in which a compound is wound around a cylindrical mold and vulcanization polishing is used. You can also. However, the manufacturing method of the intermediate transfer belt is not limited to these, and in particular, in the laminated belt molding, the belt is generally manufactured by combining a plurality of manufacturing methods.

  In addition, in order to prevent the elastic layer made of a rubber material having a large elongation from extending, a core layer made of a material such as a canvas may be provided between the base layer and the elastic layer. Examples of materials for preventing elongation used in the core layer include natural fibers such as cotton and silk, polyester fibers, nylon fibers, acrylic fibers, polyolefin fibers, polyvinyl alcohol fibers, polyvinyl chloride fibers, and polyvinylidene chloride fibers. , One or more selected from the group consisting of synthetic fibers such as polyurethane fiber, polyacetal fiber, polyfluoroethylene fiber and phenol fiber, inorganic fibers such as carbon fiber and glass fiber, and metal fibers such as iron fiber and copper fiber Threaded or woven fabric can be used. Of course, the material is not limited to the above. The above-described yarn may be twisted in any manner, such as one or a plurality of filaments twisted, one-twisted yarn, various twisted yarns, double yarn, or the like. Further, for example, fibers of a material selected from the above material group may be blended. Of course, the yarn can be used after being subjected to an appropriate conductive treatment. On the other hand, the woven fabric can be any woven fabric such as knitted weave, and of course, a woven fabric that has been woven can also be used and can be subjected to a conductive treatment.

  The hardness of the elastic layer is preferably 10 ° ≦ HS ≦ 65 ° (JIS-A). Although the optimum hardness varies depending on the layer thickness of the intermediate transfer belt 61, if the hardness is lower than 10 ° JIS-A, transfer deficiency tends to occur. On the other hand, when the hardness is higher than 65 ° JIS-A, it is difficult to stretch the roller, and since it is stretched by long-term stretching, there is no durability and early replacement is necessary.

Next, a contact / separation mechanism as a separation unit that contacts and separates the secondary transfer belt 77 from the intermediate transfer belt 61 will be described.
FIG. 2 is an enlarged cross-sectional view of the secondary transfer nip.
In the same figure, the secondary transfer counter roller 68 that partially wraps the intermediate transfer belt 61 around its inner peripheral surface on the inner peripheral surface side of the intermediate transfer belt 61 has its deformable intermediate transfer belt 61 attached to its peripheral surface. It plays a role of backing up and maintaining the shape along a certain curvature. The secondary transfer belt 77 is in contact with the secondary transfer counter roller 68 on the intermediate transfer belt 61 from the front surface side of the intermediate transfer belt 61 to form a secondary transfer nip N.

  The secondary transfer roller 72 is rotatably held by the roller unit holder 80 via a bearing (not shown). The roller unit holder 80 is configured to be rotatable about a rotation shaft 80 a provided so as to take a posture parallel to the rotation axis of the secondary transfer roller 72. When the roller unit holding body 80 rotates counterclockwise in the figure around the rotation shaft 80a, the secondary transfer roller 72 held by the roller unit holding body 80 comes close to the secondary transfer counter roller 68. As a result, the secondary transfer belt 77 is pressed against the intermediate transfer belt 61 to come into contact with it, and a secondary transfer nip is formed. Further, when the roller unit holding body 80 rotates around the rotation shaft 80a in the clockwise direction in the drawing, the secondary transfer roller 72 held by the roller unit holding body 80 is separated from the secondary transfer counter roller 68. To go. As a result, the secondary transfer belt 77 is separated from the intermediate transfer belt 61.

  In the printer of this embodiment, the biasing coil spring 81 always biases the end of the roller unit holder 80 opposite to the rotation shaft 80 a toward the intermediate transfer belt 61. The biasing coil spring 81 always applies a force that rotates the roller unit holder 80 in the counterclockwise direction around the rotation shaft 80a to the secondary transfer roller 72 to the intermediate transfer belt 61. It is energizing towards. That is, the biasing means for biasing the secondary transfer roller 72 toward the intermediate transfer belt 61 is constituted by the biasing coil spring 81, the roller unit holder 80, the rotating shaft 80a of the roller unit holder 80, and the like. Yes.

  The secondary transfer roller 72 is rotationally driven in the counterclockwise direction in the figure by transmitting the rotational driving force of a roller drive motor (not shown) via a drive transmission means (not shown) such as a gear. These roller drive motors and drive transmission means are also held by the roller unit holder 80, and are configured to rotate together with the secondary transfer roller 72 and the roller unit holder 80.

FIG. 3 is a cross-sectional view taken along the line AA of FIG.
The secondary transfer roller 72 includes a roller portion 72A, a first shaft member 72B and a second shaft member 72C that protrude from both axial end surfaces of the roller portion 72A and extend in the rotation axis direction, and a first idling roller 134 described later. And a second idling roller 135. The roller portion 72A includes a cylindrical hollow metal core 72a and an elastic layer 72b made of an elastic material fixed to the peripheral surface thereof. Examples of the metal constituting the hollow core metal 72a include stainless steel and aluminum, but are not limited to these materials.

  The elastic layer 72b is preferably 70 [°] or less in terms of JIS-A hardness. Further, the elastic layer 72b having a JIS-A hardness of about 50 [°] may be formed of epichlorohydrin rubber exhibiting a certain degree of conductivity. As a rubber material exhibiting conductivity, EPDM or Si rubber in which carbon is dispersed, NBR having an ionic conductivity function, urethane rubber, or the like may be used instead of the above-described conductive epichlorohydrin rubber. The secondary transfer belt 77 wound around the secondary transfer roller 72 is a seamless belt made of polyimide resin or polyamide resin.

  The secondary transfer counter roller 68 around which the intermediate transfer belt 61 is wound has a roller portion 68b which is a cylindrical main body portion, and a roller portion 68b while penetrating in the rotation axis direction with respect to the rotation center portion of the roller portion 68b. And a through-shaft member 68a that idles on its surface. The penetrating shaft member 68a is made of a metal member, and the roller portion 68b is rotatably supported on its peripheral surface so as to be idled.

  The roller portion 68b as the main body includes a drum-shaped hollow cored bar 68c, an elastic layer 68d made of an elastic body fixed on the peripheral surface thereof, and balls press-fitted to both ends in the axial direction of the hollow cored bar 68c. And a bearing 68e. For this reason, the ball bearing 68e rotates on the through shaft member 68a together with the hollow core metal 68c while supporting the hollow core metal 68c. The elastic layer 68d is press-fitted into the outer peripheral surface of the hollow core metal 68c. The through shaft member 68 a is rotatably supported by a first bearing 152 fixed to the first side plate 128 of the transfer unit 60 that stretches the intermediate transfer belt 61 and a second ball bearing 153 fixed to the second side plate 129. Has been. However, most of the time during the print job, the through shaft member 68a is stopped without being driven to rotate. The penetrating shaft member 68a freely idles the roller portion 68b to be rotated along with the endless movement of the intermediate transfer belt 61 on its peripheral surface.

  The elastic layer 68d fixed on the peripheral surface of the hollow core metal 68c is composed of a conductive rubber material whose resistance value is adjusted by adding an ionic conductive agent so as to exhibit a resistance of 7.5 [LogΩ] or more. Has been. The reason why the electric resistance of the elastic layer 68d is adjusted within a predetermined range is as follows. That is, in the case of transfer paper having a relatively small size in the roller axis direction such as A5 size, the intermediate transfer belt 61 and the secondary transfer belt 77 are in direct contact with each other in the secondary transfer nip without any transfer paper. This is because the transfer current is not concentrated at the location. By making the electric resistance of the elastic layer 68d larger than the resistance of the transfer paper P, it is possible to suppress such transfer current concentration.

  As the conductive rubber material constituting the elastic layer 68d, foamed rubber is used so as to exhibit elasticity of about 40 [°] in Asker-C hardness. By forming the elastic layer 68d with such a foamed rubber, the secondary transfer nip having a certain size in the transfer paper conveyance direction is obtained by flexibly deforming the elastic layer 68d in the thickness direction in the secondary transfer nip N. N can be formed. The elastic layer 68d has a shape that is larger than the outer diameter of the end portion. That is, the secondary transfer counter roller 68 is formed in a shape of a Tyco having outer diameters that are smaller at the ends 68B and 68C than at the center 68A. By using a roller having a Tyco shape, when the secondary transfer roller 72 is urged toward the intermediate transfer belt 61 by the urging coil spring 81 (see FIG. 2) to form the secondary transfer nip N, bending is caused. It is possible to prevent the pressure at the central portion 68A from being released.

  In the penetrating shaft member 68a of the secondary transfer opposing roller 68, a pair of cams 150 constituting a part of the separating means are formed in both end regions that are not located in the roller portion 68b in the entire region in the longitudinal direction. 151 are fixed. In the first cam 150, a cam portion 150A and a true circular roller portion 150B are integrally formed side by side in the axial direction. The first cam 150 is fixed to one end region in the longitudinal direction of the penetrating shaft member 68a by screwing a screw 180 penetrating the roller portion 150B into the penetrating shaft member 68a. The second cam 151 includes a cam portion 151A and a true circular roller portion 151B which are integrally formed side by side in the axial direction. The second cam 151 has the same configuration as the first cam 150 and the other end in the longitudinal direction of the through shaft member 68a. It is fixed to the part area. A drive receiving pulley 154 is fixed to a region outside the second cam 151 in the axial direction of the through shaft member 68a. A disk 159 to be detected is fixed further outside the drive receiving pulley 154.

  On the second side plate 129 of the transfer unit 60, a cam driving motor 158 serving as cam driving means for rotating the pair of cams 150 and 151 in the forward direction and the reverse direction is fixed and arranged. The cam drive motor 158 rotates a motor pulley 157 provided on its output shaft, and transmits a driving force to a drive receiving pulley 154 fixed to the through shaft member 68a via a timing belt 156. With such a configuration, the penetrating shaft member 68a can be rotated by operating the cam drive motor 158. At this time, even if the through-shaft member 68a is rotated, the roller portion 68b can be freely idled on the through-shaft member 68a, so that the intermediate transfer belt 61 is prevented from rotating along with the roller portion 68b. There is no. In addition, by using a stepping motor as the cam drive motor 158, the motor rotation angle can be freely set without providing a rotation angle detection means such as an encoder. Of course, a rotation angle detection means may be provided to detect the rotation angle of the cam drive motor 158.

  The outer peripheral surfaces 150C and 151C of the cam portions 150A and 151A of the first cam 150 and the second cam 151 are formed as follows. That is, when the through-shaft member 68a stops rotating at a predetermined rotation angle, the respective cam portions 150A and 151A abut against the secondary transfer roller 72, and the secondary transfer roller 72 is biased by the biasing coil spring 81 of the roller unit holder 80. It is formed to push back against the urging force. That is, by controlling the rotational positions of the pair of cams 150 and 151, the secondary transfer roller 72 is moved in the direction closer to the secondary transfer counter roller 68 (and thus the intermediate transfer belt 61), thereby performing the secondary transfer. An inter-axis distance L between the opposing roller 68 and the secondary transfer roller 72 is adjusted. By adjusting the distance L between the axes of the secondary transfer counter roller 68 and the secondary transfer roller 72, the gap between the secondary transfer belt 77 and the intermediate transfer belt 61 in the secondary transfer nip N can be adjusted.

  In this embodiment, the distance L between the axes of the secondary transfer opposing roller 68 and the secondary transfer roller 72 is adjusted by at least a pair of the cam 150, the cam 151, and the cam drive motor 158. In other words, at least a pair of the cam 150, the cam 151, and the cam drive motor 158 constitute a separating unit 500 that separates the secondary transfer belt 77 from the intermediate transfer belt 61. The secondary transfer counter roller 68 as a rotatable support member freely idles the roller portion 68b on the penetrating shaft member 68a penetrated with respect to the cylindrical roller portion 68b. When the penetrating shaft member 68a rotates, the pair of cams 150 and 151 fixed to both ends in the axial direction of the penetrating shaft member 68a rotate as a unit. Accordingly, the cams 150 and 151 on both ends can be rotated by merely providing a drive transmission mechanism for transmitting drive to the penetrating shaft member 68a on one end in the axial direction.

  In this printer, while the hollow core metal 72 a of the secondary transfer roller 72 is grounded, a secondary transfer bias having the same polarity as the toner is applied to the hollow core metal 68 c of the secondary transfer counter roller 68. Thereby, in the secondary transfer nip N, a secondary transfer electric field for electrostatically moving the toner from the secondary transfer counter roller 68 side to the secondary transfer roller 72 side is formed between both rollers. That is, the first bearing 152 that rotatably receives the metal through-shaft member 68a of the secondary transfer counter roller 68 is composed of a conductive slide bearing. The conductive first bearing 152 is connected to a high voltage power supply 161 serving as transfer means for outputting a secondary transfer bias. The secondary transfer bias output from the high-voltage power supply 161 is supplied to the secondary transfer counter roller 68 via the conductive first bearing 152. In the secondary transfer facing roller 68, a metal penetrating shaft member 68a, a metal ball bearing 68e, a metal hollow core metal 68c, and a conductive elastic layer 68d are sequentially transmitted.

  The detected disk 159 fixed to one end of the through shaft member 68a has a test portion 159a that rises in the axial direction at a predetermined position in the rotation direction of the through shaft member 68a. On the other hand, an optical sensor 160 serving as a detection unit is fixed to the sensor bracket 501 fixed to the second side plate 129 of the transfer unit 60. When the through-shaft member 68a rotates, if the through-shaft member 68a is positioned within a predetermined rotation angle range, the test portion 159a of the detected disk 159 enters between the light emitting element and the light receiving element of the optical sensor 160. The optical path between the two is blocked. When the light receiving element of the optical sensor 160 receives light from the light emitting element, it transmits a light reception signal to the control means 600.

  The control means 600 is constituted by a well-known computer, and here, in particular, an optical sensor 160 and a cam drive motor 158 are connected. The control means 600 operates the cam drive motor 158 by calculating the timing at which the light reception signal from the light receiving element of the optical sensor 160 stops and the drive amount of the cam drive motor 158 from that timing. Further, based on the calculated driving amount, the rotational angle positions of the cam portions 150a and 151a of the cams 150 and 151 fixed to the through shaft member 68a are detected, and the pair of cams 150 and 151 are set at predetermined positions. Has the function to stop.

  The pair of cams 150 and 151 abut against the secondary transfer roller 72 at a predetermined rotation angle, and push the secondary transfer roller 72 away from the secondary transfer counter roller 68 against the urging force of the urging coil spring 81. (Hereafter, this push-back is referred to as “push down”). The amount of pushing back at this time (hereinafter referred to as “the amount of pushing down”) is determined by the rotational angle position of the pair of cams 150 and 151. As the amount by which the secondary transfer roller 72 is pushed down by the cams 150 and 151 increases, the inter-axis distance L between the secondary transfer counter roller 68 and the secondary transfer roller 72 increases. In the secondary transfer roller 72, a first idling roller 134 is provided on the first shaft member 72B that rotates integrally with the roller portion 72A so as to idle. The first idling roller 134 has a donut disk shape whose outer diameter is slightly larger than that of the roller portion 72A. And it has the function as a ball bearing itself, and can idle | slide on the surrounding surface of the 1st shaft member 72B. A second idling roller 135 having the same configuration as the first idling roller 134 is provided on the second shaft member 72C of the secondary transfer roller 72 so as to be idling. In the secondary transfer counter roller 68, the pair of cams 150 and 151 fixed to the through shaft member 68 a are in contact with the idling rollers 134 and 135 at a predetermined rotational angle position so that the outer peripheral surfaces 150 C and 150 A of the cam portions 150 A and 151 A 151C is formed. Specifically, the cam portion 150 </ b> A of the first cam 150 fixed to one end side of the penetrating shaft member 68 a hits the first idling roller 134 of the secondary transfer roller 72. At the same time, the cam portion 151A of the second cam 151 fixed to the other end side of the penetrating shaft member 68a hits the second idling roller 135 of the secondary transfer roller 72. The idling rollers 134 and 135 abutted against the cams 150 and 151 are prevented from rotating along with the abutment, but the rotation of the secondary transfer roller 72 is not prevented thereby. Even if the idling rollers 134 and 135 stop rotating, the idling rollers are ball bearings, so that the shaft members 72B and 72C of the secondary transfer roller 72 rotate freely independently of the idling rollers 134 and 135. Because it can. By stopping the rotation of the idle rollers 134 and 135 in accordance with the abutment by the cam portions 150A and 151A of the cam, the occurrence of friction between them is avoided, and the belt drive motor and the secondary transfer roller 72 caused by the friction are avoided. It is also possible to avoid an increase in torque of the drive motor.

  The pressing amount is preferably changed depending on the thickness of the transfer paper. In the printer, as shown in FIG. 3, a thickness information acquisition unit 700 for acquiring the thickness information of the transfer paper supplied to the secondary transfer nip N is provided. . As the thickness information acquisition unit 700, a thickness detection sensor that actually detects the thickness of the transfer paper conveyed in the paper feed path may be used, or a data input unit that receives thickness information data input from an operator. It may be used. Examples of the thickness detection sensor include an optical sensor that detects light transmittance in the thickness direction, and a sensor that detects the amount of roller movement when a sheet is sandwiched between a pair of conveyance rollers.

  The control unit 600 is configured to adjust the amount of depression of the secondary transfer roller 72 according to the acquisition result by the thickness information acquisition unit 700. Specifically, a data table indicating the relationship between the thickness information of the transfer sheet and the corresponding rotation stop position (agreement with the push-down amount) of the penetrating shaft member 68a is stored in a data storage unit such as a ROM in the control unit 600. I am letting.

  The control means 600 specifies the rotation stop position corresponding to the transfer sheet thickness acquisition result from the data table. The cam drive motor 158 is operated to rotate the through shaft member 68a to the rotation stop position. As described above, in this embodiment, the driving of the multistage cams 150 and 151 is stopped and the secondary transfer belt 77 is separated from the intermediate transfer belt 61 by a predetermined amount, and then the transfer paper enters the secondary transfer nip N. The control unit 600 is configured to execute the processing to be performed. Thereby, the shock jitter at the time of paper edge approach can be suppressed.

  The control unit 600 separates the cams 150 and 51 from the secondary transfer roller 72 until the leading edge of the image on the intermediate transfer belt 61 enters the secondary transfer nip N. As a result, when the image is secondarily transferred to the transfer paper P, a predetermined transfer pressure can be obtained by the urging coil spring 81, and a white image or the like is not generated at the leading end of the image, and a good image can be obtained. it can.

  As described above, the control unit 600 can be configured to perform the rotation stop position of the through-shaft member 68a at the timing when the optical sensor 160 detects the detected portion 159a of the detected disk 159. Further, the control means 600 may be configured to perform based on the drive amount of the stepping motor, which is the cam drive motor 158, from the timing when the optical sensor 160 detects the detected portion 159a of the detected disk 159.

  In the present embodiment, a pair of cams 150 and 151 for adjusting the distance between the secondary transfer belt 77 wound around the secondary transfer roller 72 and the intermediate transfer belt 61 wound around the secondary transfer counter roller 68 are provided as two. The case where it arrange | positions to the next transfer opposing roller 68 side was shown. However, it is of course possible to adjust the surface distance between the secondary transfer belt 77 and the intermediate transfer belt 61 by other methods. For example, a push-down member may be provided on the roller unit holder 80 and the surface distance (interval X) between the secondary transfer belt 77 and the intermediate transfer belt 61 may be adjusted by a pair of cams 150 and 151.

In this printer, image density control for optimizing the image density of each color is periodically executed.
FIG. 4 is a block diagram illustrating a part of an electric circuit in the printer according to the embodiment. In the figure, a potential control device 110 as an image forming condition correcting means includes a CPU (Central Processing Unit), a ROM (Read Only Memory) storing a control program and various data. Various peripheral devices are connected to the potential control device 110. In the figure, only those used mainly for image density control are shown.

  In this printer, the first image density control and the second image density control are performed. The first image density control is periodically performed exclusively with the operation of forming the image on the transfer paper, such as when the power is turned on, before the start of printing, after a predetermined number (for example, 500) of images is formed, or after the image forming operation is completed. This is image density control to be executed. On the other hand, the second image density control is image density control that is periodically executed in synchronism with an image forming operation between transfer paper sheets during continuous image formation on transfer paper.

  In the first image density control, first, as shown in FIG. 5, a gradation pattern Sk, Sm, Sc, Sy of each color as a toner pattern is applied to a secondary transfer toner adhesion amount sensor for each color on the secondary transfer belt 77. 64Y, M, C, and K are automatically formed at positions facing each other. The gradation pattern of each color is composed of 10 toner patches having an area of 2 [cm] × 2 [cm] having different image densities. The potential control device 110 controls the charging devices 5Y, M, C, and K for the respective colors when charging the photosensitive members 3Y, 3M, 3C, and 3K when creating the gradation patterns Sk, Sm, Sc, and Sy for the respective colors. Unlike the uniform drum charging potential in the printing process, the potential is gradually increased. Next, the potential control device 110 controls the optical charging units 1YM and 1CK with the photosensitive member 3 by the potential sensor and controls the optical writing units 1YM and 1CK to form a plurality of patch electrostatics for forming a gradation pattern image by scanning with laser light. A latent image is formed on each of the photoreceptors 3Y, 3M, 3C, and 3K. Next, the potential control device 110 measures the latent image potentials with the potential sensor 105 and then develops the latent images with the developing devices 4Y, M, C, and K for Y, M, C, and K. During this development, the value of the developing bias applied to the Y, M, C, and K developing rollers is gradually increased. By such development, gradation pattern images of Y, M, C, and K are formed on the photoreceptors 3Y, 3M, C, and K. These are secondarily transferred so as to be arranged at predetermined intervals in the main scanning direction (belt width direction) of the secondary transfer belt 77.

  The toner patterns Sk, Sm, Sc, and Sy formed on the secondary transfer belt 77 are connected to the secondary transfer toner adhesion amount sensors 64Y, 64M, 64C, and 64K along with the endless movement of the secondary transfer belt 77. Pass through the opposite position.

  Here, the secondary transfer toner adhesion amount sensors 64Y, M, C, and K will be described. Since the secondary transfer toner adhesion amount sensors 64Y, M, C, and K for the respective colors are the same, in the following description, the color code is appropriately omitted.

FIG. 6 is an enlarged configuration diagram showing the secondary transfer toner adhesion amount sensor 64 in an enlarged manner.
The secondary transfer toner adhesion amount sensor 64 is a reflective optical sensor including an LED 64a as a light emitting element, a regular reflection light receiving element 64b, a diffused light receiving element 64c, a glass cap 64d, a casing 64d, and the like. In addition, you may use a laser light emitting element etc. instead of LED as a light emitting element. In addition, as the regular reflection light receiving element 64b and the diffused light receiving element 64c, phototransistors are used, but it is also possible to use a photodiode or an amplifier circuit.

  The infrared light emitted from the LED 64 a passes through the glass cap 64 d and then reaches the toner pattern formed on the secondary transfer belt 77. A part of the infrared light is specularly reflected on the surface of the toner pattern to become specularly reflected light, and then retransmits through the glass cap 64d and is received by the specularly reflected light receiving element 64b. The regular reflection light receiving element 64b outputs a voltage corresponding to the amount of received light. The output value is converted into digital data by an A / D converter (not shown) and then input to the potential control device 110. The other part of the infrared light is diffusely reflected on the surface of the toner pattern to become diffusely reflected light, and then retransmits through the glass cap 64d and is received by the diffused light receiving element 64c. The diffused light receiving element 64c outputs a voltage corresponding to the amount of received light. The output value is converted into digital data by an A / D converter (not shown) and then input to the potential control device 110.

  The secondary transfer toner adhering amount sensor 64 receives the amount of light corresponding to the toner adhering amount per unit area with respect to the toner patch of each gradation pattern by the regular reflection light receiving element 64b and the diffused light receiving element 64c. The corresponding voltage is output.

  Next, the potential control device 110 uses the output voltages of the secondary transfer toner adhesion amount sensors 64Y, 64M, 64K, and the adhesion amount conversion algorithm when each color toner patch is detected, and each toner of the gradation pattern of each color. The amount of adhesion on the patch is calculated. Specifically, for example, as described in JP-A-2006-139180, the output value of the regular reflection light receiving element 64b of the toner patch or the regular reflection light receiving element 64b of the background portion of the secondary transfer belt. Is used to correct the sensitivity of the output value of the diffuse reflection light receiving element. Then, as shown in FIG. 11, the adhesion amount in each toner patch of the gradation pattern of each color is calculated based on the correlation between the output value of the diffusely reflected light receiving element after sensitivity correction and the toner adhesion amount.

  Next, the potential control device 110 adjusts the image forming condition based on the calculated adhesion amount. Specifically, a function (y = ax + b) indicating a straight line graph is calculated by regression analysis based on the result of detecting the toner adhesion amount on the toner patch and the development potential when each toner patch is imaged. The development potential when each toner patch is imaged is calculated from the latent image potential of each toner patch measured by the potential sensor 105 and the development bias when developing each toner patch. Then, an appropriate development bias value is calculated by substituting a target value of image density into this function, and development bias values for Y, M, C, and K are specified.

  The memory stores an image forming condition data table in which several tens of development bias values and appropriate drum charging potentials individually corresponding to the values are associated in advance. For each process unit 2Y, M, C, K, a developing bias value closest to the specified developing bias value is selected from the image forming condition table, and the drum charging potential associated therewith is specified.

  In the second image density control, an image density adjusting pattern of each color is formed between transfer paper sheets during continuous image formation. These image density adjustment patterns for each color are detected by the secondary transfer toner adhesion amount sensor 64. The potential control device 110 identifies the toner adhesion amount of the image density adjustment pattern from the output value of the secondary transfer toner adhesion amount sensor 64 when the image density adjustment pattern is detected, and stores the identified toner adhesion amount in the memory. Compare the target adhesion amount. Then, the toner supply device 104 is controlled so that the target adhesion amount is obtained. Specifically, when the detected adhesion amount is smaller than the target adhesion amount, the toner replenishment amount is increased and the toner concentration of the developer in the developing device is increased. When the detected adhesion amount is larger than the target adhesion amount, the toner replenishment amount is decreased and the toner concentration of the developer in the developing device is decreased.

  In this embodiment, as described above, an intermediate transfer belt having an elastic layer is used as the intermediate transfer belt 61. The intermediate transfer belt having such an elastic layer has lower gloss than the secondary transfer belt 77. Therefore, when an optical sensor similar to the secondary transfer toner adhesion amount sensor 64 is used, the output of the regular reflection light receiving element 64b has no sensitivity. Therefore, in calculating the toner adhesion amount, the output voltage of the regular reflection light receiving element 64b cannot be used. As a result, the sensitivity correction of the output voltage of the diffused light receiving element 64c cannot be performed by the method described in JP-A-2006-139180. Therefore, the accuracy of the detection result obtained by detecting the toner pattern on the intermediate transfer belt with the optical sensor is worse than when the toner pattern on the secondary transfer belt is detected with the optical sensor. Therefore, in the present embodiment, a gradation pattern or an image density adjustment pattern is transferred to the secondary transfer belt 77, and the toner adhesion amount is detected using the secondary transfer toner adhesion amount sensor. Thus, the image forming conditions are corrected. Thereby, highly accurate correction can be performed and a good image can be maintained.

  As described above, in the printer of this embodiment, in order to suppress shock jitter, when the transfer paper entering the secondary transfer nip is a thick paper, the secondary transfer is performed before the transfer paper enters the secondary transfer nip. The belt 77 is separated from the intermediate transfer belt. When the image density adjustment pattern is not formed between the sheets, the secondary transfer belt 77 is removed from the intermediate transfer belt 61 immediately after the transfer sheet passes through the secondary transfer nip as shown in FIG. An operation of separating can be performed. However, when the image density adjustment pattern is formed between the sheets, the secondary transfer belt 77 is transferred after the image density adjustment pattern is transferred to the secondary transfer belt 77 as shown in FIG. Is moved away from the intermediate transfer belt 61. Therefore, as shown in FIG. 7, when the second image density control is executed, the paper gap is opened by T-delay compared to when the second image density control is not executed. As a result, there is a problem that productivity falls.

  Therefore, in the present embodiment, as shown in FIG. 1, the intermediate transfer toner adhesion amount sensor 65 for detecting the adhesion amount of the toner pattern on the intermediate transfer belt is provided. When the secondary transfer belt 77 is controlled to be separated from the intermediate transfer belt 61 between sheets, the image density adjustment pattern is detected by the intermediate transfer toner adhesion amount sensor 65, and the image density adjustment pattern is transferred to the secondary transfer. The image was not transferred to the belt 77.

FIG. 8 is a control flow diagram of second image density control according to the present embodiment.
As shown in FIG. 8, an image density adjustment pattern is formed between sheets during a continuous image forming operation (S101 to S102). This image density adjustment pattern may be formed for every sheet interval, or may be formed for every plurality of sheets. Next, the potential control device 110 checks whether or not the secondary transfer belt 77 is separated from the intermediate transfer belt 61 between the sheets on which this image density adjustment pattern is formed (S103). Next, when the secondary transfer belt 77 is not separated from the intermediate transfer belt 61 between the sheets on which the image density adjustment pattern is formed, such as the transfer sheet conveyed to the secondary transfer nip is plain paper (Yes in S103). Then, the image density adjustment pattern is detected by the secondary transfer toner adhesion amount sensor 64 (S104). Then, the image forming condition is corrected based on the adhesion amount calculated using the detection result (output voltage corresponding to the adhesion amount) of the secondary transfer toner adhesion amount sensor 64 (S107).

  On the other hand, when the transfer sheet conveyed next to the secondary transfer nip is a thick sheet or the like, the secondary transfer belt 77 needs to be separated from the intermediate transfer belt 61 between the sheets on which this image density adjustment pattern is formed (S103). No), the intermediate transfer toner adhesion amount sensor 65 detects the image density adjustment pattern (S105). At this time, the separation of the secondary transfer belt 77 is started immediately after the transfer paper is removed from the secondary transfer nip, and the image density adjustment pattern detected by the intermediate transfer toner adhesion amount sensor 65 is transferred to the secondary transfer nip. When it reaches, the secondary transfer belt 77 is separated from the intermediate transfer belt 61. Therefore, the image density adjustment pattern detected by the intermediate transfer toner adhesion amount sensor 65 is removed by the belt cleaning device 75 without being transferred to the secondary transfer belt 77.

  As described above, in this embodiment, the operation of separating the secondary transfer belt 77 from the intermediate transfer belt 61 immediately after the transfer paper passes through the secondary transfer nip even between the papers on which the image density adjustment patterns are formed. You can start. Therefore, the delay of T-delay shown in FIG. 7 does not occur, and the decrease in productivity can be suppressed.

  As described above, in the present embodiment, the intermediate transfer belt 61 has elasticity, and glossiness cannot be expected, and regular reflection light receiving element output sensitivity cannot be expected. Therefore, the intermediate transfer toner adhesion amount sensor 65 uses an optical sensor having an LED as a light emitting element and a diffuse reflection light receiving element. When the intermediate transfer toner adhesion amount sensor 65 is used, unlike the case where the secondary transfer toner adhesion amount sensor 64 is used, the sensitivity of the output voltage of the diffuse reflection light receiving element that detects the toner patch cannot be corrected. For this reason, the adhesion amount detection accuracy is poor compared to the case where the adhesion amount is calculated based on the detection result of the secondary transfer toner adhesion amount sensor. Therefore, the detection result of the intermediate transfer toner adhesion amount sensor 65 is corrected based on the correlation between the detection result of the intermediate transfer toner adhesion amount sensor 65 and the detection result of the secondary transfer adhesion amount sensor 64 (S106).

  This correlation is acquired at the time of the first image density control, and the acquired correlation is stored in the memory. Specifically, as shown in FIG. 9, when the gradation pattern of the intermediate transfer belt 61 passes over the intermediate transfer toner adhesion amount sensor 65, each toner of the gradation pattern is detected by the intermediate transfer toner adhesion amount sensor 65. The output voltage of the diffusely reflected light receiving element in the patches P1, P2, P3. Further, this gradation pattern is transferred to the secondary transfer belt 77, and the secondary transfer toner adhesion amount sensor 64 detects the toner patches P1, P2, P3. Then, the output voltage of the diffusely reflected light receiving element in each toner patch whose sensitivity is corrected as described in JP-A-2006-139180 is obtained.

  Next, the potential control device 110 corrects the output value of the diffuse reflection light receiving element of the intermediate transfer toner adhesion amount sensor 65 of each toner patch P1, P2, P3... And the sensitivity of the secondary transfer toner adhesion sensor 64. The correlation is obtained based on the output value of the diffusely reflected light receiving element. Specifically, as shown in FIG. 10, the output value of the diffuse reflection light receiving element of the intermediate transfer toner adhesion amount sensor 65 is plotted on the horizontal axis, and the sensitivity of the secondary transfer toner adhesion amount sensor 64 is corrected. The slope E of the straight line graph (y = Ex) when the output value of is the vertical axis is obtained. The obtained inclination is stored in the memory as a correlation between the detection result of the intermediate transfer toner adhesion amount sensor 65 and the detection result of the secondary transfer toner adhesion amount sensor 64.

  In this embodiment, in order to obtain a correlation between the detection result of the intermediate transfer toner adhesion amount sensor 65 and the detection result of the secondary transfer toner adhesion amount sensor 64, the same toner patch is attached to the intermediate transfer toner adhesion amount sensor 65. It is necessary to detect with the secondary transfer toner adhesion amount sensor 64. Therefore, the intermediate transfer toner adhesion amount sensor 65 is disposed upstream of the two transfer nips in the movement direction of the intermediate transfer belt 61.

  When calculating the toner adhesion amount of the image density adjustment pattern from the output voltage of the diffusely reflected light receiving element of the intermediate transfer toner adhesion amount sensor 65, the coefficient E indicating the correlation stored in the memory is read. Next, the output voltage of the intermediate transfer toner adhesion amount sensor 65 is multiplied by the coefficient E. Thereby, the diffuse reflection light output voltage of the intermediate transfer toner adhesion amount sensor 65 is corrected to the diffuse reflection light output voltage whose sensitivity is corrected by the secondary transfer toner adhesion amount sensor. Then, the adhesion amount is calculated based on the correlation shown in FIG. As a result, the toner adhesion amount can be calculated with the same sensitivity as that detected by the secondary transfer toner adhesion amount sensor. From the detection result of the intermediate transfer adhesion amount sensor, the toner adhesion of the image density control pattern can be accurately performed. The amount can be detected. Therefore, highly accurate image density control can be performed based on the detection result of the intermediate transfer adhesion amount sensor.

  Further, when the image density adjustment pattern in the second image density control is such that a plurality of toner patches are arranged in the belt moving direction, the correlation may be acquired with the image density adjustment pattern. Specifically, when the secondary transfer belt 77 is not separated between sheets, the image density adjustment pattern is detected by both the intermediate transfer toner adhesion amount sensor 65 and the secondary transfer adhesion amount sensor 64. Then, the slope E of the straight line graph (y = Ex) shown in FIG. 10 is acquired from these detection results.

  Some of the plurality of toner patches of the image density adjustment pattern are transferred to the secondary transfer belt 77 and detected by the secondary transfer toner adhesion amount sensor, and the rest are detected by the intermediate transfer toner adhesion amount sensor. May be. In this case, after the transfer paper passes through the secondary transfer nip, the separation operation is started after waiting for a plurality of toner patches to be transferred to the secondary transfer belt. For this reason, the distance between the sheets becomes longer than when the separation operation starts immediately after the transfer sheet passes through the secondary transfer nip. However, the sheet interval can be shortened compared to the conventional configuration in which the separation operation is started after all the toner patches of the image density adjustment pattern are transferred to the secondary transfer belt 77.

What has been described above is an example, and the present invention has a specific effect for each of the following aspects.
(Aspect 1)
An image carrier such as an endless belt-like intermediate transfer belt 61 that is rotatably supported by a plurality of tension members, and a front surface that is the outer peripheral surface of the image carrier, such as a secondary transfer nip A transfer member such as a secondary transfer belt 77 that forms a transfer nip, and a contact / separation unit (in this embodiment, constituted by an urging unit and a separation unit 500) that contacts and separates the transfer member are provided. And a transfer device such as a secondary transfer device 70 for transferring the toner image carried on the front surface of the image carrier to a transfer material sandwiched in the transfer nip, and a transfer material such as transfer paper P conveyed in the transfer nip. Is a predetermined paper type, the transfer member is separated from the image carrier before the transfer material enters the transfer nip, and after the transfer material enters the transfer nip, the transfer member contacts the image carrier. Control means 600 for controlling the separation means so as to In an image forming apparatus such as a printer, a first toner image detection unit such as an intermediate transfer toner adhesion amount sensor 65 that detects a toner pattern formed on an image carrier and a toner pattern transferred to a transfer member are detected. A second toner image detection unit such as a secondary transfer toner adhesion amount sensor 64 and a potential control device 110 that corrects an image forming condition based on a detection result of the first toner image detection unit or the second toner image detection unit. An image forming condition correcting means, and when the control for separating the transfer member from the image carrier between the paper is not performed, the toner pattern is transferred to the transfer member and detected by the second toner image detecting means, When controlling the separation of the transfer member from the image carrier, the toner pattern formed between the sheets is detected by the first toner image detection means, and the trailing edge of the toner pattern is transferred to the transfer nip. Without waiting for reaching the and to start the separating operation.
According to (Aspect 1), when controlling the transfer member to be separated from the image carrier between papers, the toner pattern formed between the papers is detected by the first toner image detecting means, and the trailing edge of the toner pattern is detected. The separation operation is started without waiting for the toner to reach the transfer nip. Therefore, the distance between the sheets can be shortened compared to the case where the separation operation is started after the toner pattern is transferred to the transfer member at the transfer nip, and the decrease in productivity can be suppressed. Further, the image forming condition can be corrected based on the result of the first toner image detecting means. Further, by performing the separating operation between the sheets, it is possible to suppress shock jitter when the next transfer material enters the transfer nip.
Further, when the transfer member is not separated from the image carrier between the papers, the toner pattern formed between the papers is transferred to the transfer member and detected by the second toner image detecting means. As a result, a result including the effect of transfer from the image carrier to the transfer member can be detected, and the image forming conditions can be corrected with high accuracy. Accordingly, it is possible to suppress a decrease in the correction accuracy of the image forming condition as compared with the case where the image forming condition is corrected using only the first toner image detecting unit.

(Aspect 2)
In (Aspect 1), when the transfer member such as the secondary transfer belt 77 is controlled to be separated from the image carrier such as the intermediate transfer belt 8 between the sheets, the leading end of the toner pattern is the transfer nip such as the secondary transfer nip. The separation operation is started without waiting for the movement to reach.
By adopting such a configuration, it is possible to shorten the gap between the sheets and suppress a decrease in productivity as compared with the case where the separation operation is started after the leading edge of the toner pattern reaches the transfer nip such as the secondary transfer nip.

(Aspect 3)
In (Aspect 1) or (Aspect 2), the image forming condition correction means such as the potential control device 110 is based on the detection result of the toner pattern detected by the first toner image detection means such as the intermediate transfer toner adhesion amount sensor 65. When correcting the image forming conditions, the correlation between the detection result of the toner pattern detected by the first toner image detection unit and the detection result of the toner pattern detected by the second toner image detection unit such as the secondary transfer toner adhesion amount sensor 64 The detection result of the first toner image detection unit is corrected based on the relationship, and the image forming condition is corrected based on the corrected data.
According to (Aspect 2), as described in the embodiment, by correcting the detection result of the first toner image detection unit based on the correlation, the detection result of the first toner image detection unit is changed to the second toner. The detection result when the toner pattern on the transfer member such as the secondary transfer belt is detected by the image detection unit can be corrected. As a result, even if the accuracy of the detection result of the first toner image detection unit is worse than the accuracy of the detection result of the second toner image detection unit, a highly accurate image is obtained based on the detection result of the first toner image detection unit. The formation conditions can be corrected.
Further, by correcting the result of the first toner image detection means to the detection result of the second toner image detection means, the data indicating the relationship between the detection result of the second toner image detection means and the adhesion amount is the first data. The adhesion amount can be calculated from the detection result of the toner image detection means. As a result, the memory capacity can be reduced.

(Aspect 4)
In (Aspect 3), the toner pattern detected by the first toner image detecting means such as the intermediate transfer toner adhesion amount sensor 65 is transferred to a transfer member such as the secondary transfer belt 77, and the toner pattern transferred to this transfer member Is acquired by a second toner image detection unit such as a secondary transfer toner adhesion amount sensor 64, and an acquisition unit such as a potential control device 110 for acquiring a correlation is provided.
Thus, a highly accurate correlation can be acquired by detecting the same toner pattern by the first and second toner image detecting means. Thereby, the detection result of the first toner image detection means can be corrected with high accuracy.

(Aspect 5)
In (Aspect 4), an acquisition unit such as the potential control device 110 forms a toner pattern during non-image formation and acquires a correlation.
According to (Aspect 4), since the correlation is acquired at the time of non-image formation, the transfer is performed until the toner pattern for acquiring the correlation is transferred to the transfer member such as the secondary transfer belt 77 between the sheets. There is no need to wait for the operation of separating the member from the image carrier. Therefore, the correlation can be acquired without reducing the productivity as compared with the case of acquiring the correlation at the time of image formation.

(Aspect 6)
In (Aspect 3) to (Aspect 5), the toner pattern for obtaining the correlation is a gradation pattern composed of a plurality of toner images having different toner adhesion amounts.
According to (Aspect 6), the correlation can be obtained based on detection results of a plurality of toner images having different toner adhesion amounts, and the accuracy of the correlation can be improved.

(Aspect 7)
In (Aspect 3) to (Aspect 6), the first toner image detecting means such as the intermediate transfer toner adhesion amount sensor 65 receives a light emitting unit that emits light toward the toner pattern, and diffuse reflected light from the toner pattern. A second toner image detecting unit such as a secondary transfer toner adhesion amount sensor 64, and a light emitting unit that emits light toward the toner pattern and a positive light from the toner pattern. The optical sensor includes a regular reflection light receiving unit that receives reflected light and a diffuse reflection light receiving unit that receives diffuse reflection light from the toner pattern, and the correlation is a diffuse reflection light receiving unit in the first toner image detection unit. And the output value of the diffuse reflection light-receiving unit whose sensitivity has been corrected in the second toner image detecting means.
According to (Aspect 7), as described in the embodiment, based on the correlation, the output value of the diffuse reflection light receiving unit of the first toner image detecting unit such as the intermediate transfer toner adhesion amount sensor 65 is set to the second toner. It can be converted into the output value of the diffuse reflection light-receiving unit whose sensitivity has been corrected in the image detection means. Accordingly, the first toner image detection unit can accurately detect the adhesion amount from the low adhesion amount to the high adhesion amount.

(Aspect 8)
In (Aspect 1) to (Aspect 7), the image carrier such as the intermediate transfer belt 61 has an elastic layer.
By providing such a configuration, as described in the embodiment, it is possible to obtain a transfer image having excellent uniformity without transfer unevenness even on transfer paper having poor smoothness.

61: Intermediate transfer belt 64: Secondary transfer toner adhesion amount sensor 64b: Regular reflection light receiving element 64c: Diffuse light reception element 65: Intermediate transfer toner adhesion amount sensor 68: Secondary transfer counter roller 70: Secondary transfer device 72: Secondary transfer roller 77: Secondary transfer belt 80: Roller unit holder 80a: Rotating shaft 81: Energizing coil spring 110: Potential control device 500: Separating means 600: Control means 700: Information acquisition means N: Secondary transfer nip

JP 2013-182153 A JP-A-6-274051

Claims (8)

An endless belt-shaped image carrier that is rotatably stretched by a plurality of stretching members;
A transfer member that forms a transfer nip in contact with a front surface that is an outer peripheral surface of the image carrier, and contact / separation means that brings the transfer member into and out of contact with the image carrier; A transfer device for transferring a toner image carried on the front surface to a transfer material sandwiched in a transfer nip;
When the transfer material conveyed by the transfer nip is a predetermined paper type, the transfer member is separated from the image carrier before the transfer material enters the transfer nip, and the transfer material enters the transfer nip. Then, in an image forming apparatus comprising a control unit that controls the separation unit so that a transfer member is brought into contact with the image carrier,
First toner image detection means for detecting a toner pattern formed on the image carrier;
Second toner image detection means for detecting a toner pattern transferred to the transfer member;
An image forming condition correcting unit that corrects an image forming condition based on a detection result of the first toner image detecting unit or the second toner image detecting unit;
When the control for separating the transfer member from the image carrier between the sheets is not performed, the toner pattern is transferred to the transfer member and detected by the second toner image detection unit,
When controlling the transfer member to be separated from the image carrier between papers, the toner pattern formed between the papers is detected by the first toner image detecting means, and the trailing edge of the toner pattern is in the transfer nip. An image forming apparatus characterized in that a separation operation is started without waiting for arrival. The image forming apparatus according to claim 1,
When performing the control of separating the transfer member from the image carrier between sheets, the separation operation is started without waiting for the leading edge of the toner pattern to reach the transfer nip. Image forming apparatus. The image forming apparatus according to claim 1, wherein:
When the image forming condition correcting unit corrects the image forming condition based on the detection result of the toner pattern detected by the first toner image detecting unit, the detection result of the toner pattern detected by the first toner image detecting unit And the detection result of the first toner image detection unit is corrected based on the correlation between the detection result of the toner pattern detected by the second toner image detection unit, and the image forming condition is corrected based on the corrected data. An image forming apparatus. The image forming apparatus according to claim 3, wherein
An acquisition means for transferring the toner pattern detected by the first toner image detection means to the transfer member, detecting the toner pattern transferred to the transfer member by the second toner image detection means, and acquiring the correlation; An image forming apparatus comprising the image forming apparatus. The image forming apparatus according to claim 4,
The image forming apparatus, wherein the acquisition unit forms a toner pattern during non-image formation and acquires the correlation. The image forming apparatus according to claim 3, wherein
An image forming apparatus, wherein the toner pattern for obtaining the correlation is a gradation pattern composed of a plurality of toner images having different toner adhesion amounts. The image forming apparatus according to any one of claims 3 to 6,
The first toner image detection means is an optical sensor including a light emitting unit that irradiates light toward the toner pattern, and a diffuse reflection light receiving unit that receives diffuse reflection light from the toner pattern,
The second toner image detection means includes a light emitting unit that emits light toward the toner pattern, a regular reflection light receiving unit that receives regular reflection light from the toner pattern, and diffuse reflection light from the toner pattern. An optical sensor comprising a diffusely reflected light receiving part for receiving light;
The correlation is acquired based on an output value of the diffuse reflection light receiving unit in the first toner image detection unit and an output value of the diffuse reflection light reception unit whose sensitivity is corrected in the second toner image detection unit. An image forming apparatus. The image forming apparatus according to claim 1,
An image forming apparatus, wherein the image carrier has an elastic layer.

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