JP2005025159A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which stably detects a toner density without causing a cleaning failure. <P>SOLUTION: A reference toner patch is so formed that it slides in the direction of shaft centers 90Y, 90C, 90M, and 90K of image carriers 20Y, 20C, 20M, and 20K respectively for each of the image carriers 20Y, 20C, 20M, and 20K, in the image forming apparatus to obtain a color image by transferring a toner image that is formed on a plurality of rotated image carriers 20Y, 20C, 20M and 20K, by an electrophotography, to an intermediate transfer body. A detector 310 is so disposed that it slides in the direction of the shaft centers 90Y, 90C, 90M and 90K of the image carriers 20Y, 20C, 20M, and 20K, and faces the image carriers 20Y, 20C, 20M and 20K for each of the image carriers 20Y, 20C, 20M, and 20K. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a tandem color image forming apparatus such as a copying machine or a laser beam printer, and more particularly to a color image forming apparatus that detects toner density and controls image density using the result.

  In recent years, there has been an increasing demand for high productivity for image forming apparatuses that perform color image output by an electrophotographic method. As an image forming method that meets this demand, an image forming unit including a plurality of image carriers and developing devices is used as a transfer belt. An image forming apparatus called a tandem method, which is arranged in parallel at opposed positions and sequentially transfers toner images on an image carrier onto transfer paper (or transfer belt), has come to dominate.

  In such an image forming apparatus, a reference toner patch is formed on an image carrier or an intermediate transfer member, and image density control is performed based on the measurement result of the toner density using an optical toner density sensor. The technology has been put into practical use (for example, see Patent Document 1).

JP 2000-206761 A

  However, such an image forming apparatus has the following problems.

  1. The position of the toner density sensor arranged for each photoconductor is set to the same position with respect to the width direction of the photoconductor (width direction of the intermediate transfer belt), so that the toner density sensors can be detected. When one or more reference toner patches are formed in parallel at the same position in the width direction, the reference toner patches of these colors overlap on the intermediate transfer belt, and are input to the intermediate transfer belt cleaning and secondary transfer cleaning unit. The amount of toner increases, resulting in poor cleaning and toner scattering, which subsequently degrades image quality.

  2. In such an image forming apparatus, in order to prevent the reference toner patches from overlapping on the intermediate transfer belt, first, the image formation of one or more reference toner patches of one color is finished, and then the next color of the next color is finished. There is a method of forming a reference toner patch, but this method requires idle time, and when four colors are used, compared to a method of forming four color reference toner patches in parallel. It takes nearly four times longer, leading to increased user waiting time and reduced productivity.

  3. There is disclosed a technique for detecting the toner density of the reference toner patch by shifting the installation position of the toner density sensor corresponding to each color and the image forming position of the reference toner patch with respect to the width direction of the intermediate transfer belt. Since the intermediate transfer belt is rubbed with the transfer paper and easily damaged, the surface state of the transfer belt becomes non-uniform, and a plurality of (for each color) toner density sensors at different positions in the width direction of the intermediate transfer belt. Variations in detection during the period become large, and detection is not stable.

  4). In an image forming apparatus that detects the toner density on the intermediate transfer belt, when the toner density changes, whether the cause is the toner density in the developing device, the potential of the photosensitive member, or the transfer rate to the intermediate transfer belt. For example, even if the transfer rate to the intermediate transfer belt is abnormal and the toner density on the intermediate transfer belt is low, the toner replenishment amount in the developing device is increased and the toner is increased. If an attempt is made to increase the density, toner scattering may occur. Thus, a problem arises when detecting the toner density on the intermediate transfer belt.

  An object of the present invention is to provide an image forming apparatus that does not cause a cleaning failure and is capable of stable toner density detection.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of detecting a stable toner density without causing a cleaning defect, thereby reducing waiting time for a user, improving productivity, and stabilizing image quality. Is to provide.

  The invention according to claim 1 is an image forming apparatus that obtains a color image by transferring a toner image formed by electrophotography on a plurality of rotationally driven image carriers to an intermediate transfer member. A plurality of optical sensors for detecting the density of the toner image formed on the opposing image carrier are provided so as to face the carrier, and at least two of them are arranged shifted from each other in the axial direction of the image carrier. The detector is provided.

  Therefore, when a reference toner patch is formed as a toner image for image density control for each image carrier so that a plurality of detectors can detect the density, at least two images are associated with the detectors. What is necessary is just to form it shifting in the axial center direction of a support body. As a result, at least two reference toner patches are transferred on the intermediate transfer belt so as to be shifted from each other, so that the intermediate transfer cleaning, 2 and 2 are compared with the case where all the detectors are in the same position in the axial direction of the image carrier. It becomes possible to prevent the occurrence of cleaning failure in the next transfer cleaning and toner scattering due to transfer scattering in each transfer process.

  According to a second aspect of the present invention, there is provided an image forming apparatus for obtaining a color image by transferring a toner image formed by electrophotography on a plurality of rotationally driven image carriers to an intermediate transfer member. A plurality of detectors that are provided so as to face the carrier and are shifted from each other in the axial direction of the image carrier and optically detect the density of the toner image formed on the opposite image carrier. Prepare.

  Therefore, a reference toner patch may be formed as a toner image for image density control by shifting in the axial direction of the image carrier for each image carrier so that a plurality of detectors can detect the density. As a result, the reference toner patches corresponding to the respective image carriers are transferred on the intermediate transfer belt so as to be shifted from each other, so that toner due to poor cleaning in the intermediate transfer cleaning and the secondary transfer cleaning, and transfer scattering in each transfer process. It is possible to prevent the occurrence of scattering.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, a forming unit that forms a reference toner patch that is a toner image for each of the image carriers so that the plurality of detectors can detect the density; Image density control means for executing image density control based on the detection result of the detector.
Therefore, at least two of the reference toner patches corresponding to each image carrier for performing image density control are formed so as to be shifted in the axial direction of the image carrier in correspondence with the detector, and are formed on the intermediate transfer belt. As compared with the case where all the toner patches are formed at the same position in the axial center direction of the image carrier, the cleaning in the intermediate transfer cleaning and the secondary transfer cleaning, and in each transfer step, are transferred. It is possible to prevent toner scattering due to the transfer scattering.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect, a reference toner patch that is a toner image is provided for each of the image carriers so that the plurality of detectors can detect the density. Forming means for shifting in the direction, and image density control means for executing image density control based on the detection result of the detector.

  Accordingly, the reference toner patches corresponding to the respective image carriers for executing the image density control are transferred on the intermediate transfer belt so as to be shifted from each other. It is possible to prevent toner scattering due to transfer scattering in the process.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the plurality of detectors are arranged in the vicinity of the center of the image carrier in the axial direction.

  Accordingly, it is possible to suppress image density fluctuations between the detectors, which occur because the image density fluctuation method differs depending on the position of the image carrier in the axial direction.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the forming means includes an image forming operation and an image forming operation during a continuous image forming operation for transferring to a plurality of recording materials. The reference toner patch is formed during the image operation.

  Therefore, it is possible to perform image density control without providing a special image density control time.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the glossiness of the surface of the image carrier is higher than the glossiness of the surface of the intermediate transfer belt. .

  Therefore, the toner density can be detected more stably than when the toner density is detected on the intermediate transfer belt.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the glossiness of the surface of the intermediate transfer belt is 80 or less.

  Therefore, the toner density can be detected more stably than when the toner density is detected on the intermediate transfer belt.

  A ninth aspect of the present invention is the image forming apparatus according to any one of the first to eighth aspects, wherein the glossiness of the surface of the image carrier is 90 or more.

  Therefore, when a reflection type photosensor is used as a detector, the S / N can be maintained high. Therefore, a smaller light emitting / receiving element is employed as compared with the conventional case, and even in the tandem system, it is made to face the image carrier. Detectors can be arranged.

  According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, a linear velocity ratio between the surface of the image carrier and the surface of the intermediate transfer belt is approximately 1.

  Therefore, scratches caused by rubbing the surface of the image carrier with the intermediate transfer belt are less likely to occur.

  According to the first aspect of the present invention, in the image forming apparatus that obtains a color image by transferring a toner image formed by electrophotography on a plurality of rotationally driven image carriers to an intermediate transfer member, for each of the image carriers. Provided so as to face the image carrier, and at least two of them are shifted from each other in the axial direction of the image carrier, and optically detect the density of the toner image formed on the opposite image carrier. By providing a plurality of detectors, a reference toner patch is formed as a toner image for image density control on each image carrier so that the plurality of detectors can detect the density. Correspondingly, at least two of them may be formed shifted in the axial direction of the image carrier. As a result, at least two reference toner patches are transferred on the intermediate transfer belt so as to be shifted from each other, so that the intermediate transfer cleaning, 2 and 2 are compared with the case where all the detectors are in the same position in the axial direction of the image carrier. It is possible to prevent the occurrence of cleaning failure in the next transfer cleaning and toner scattering due to transfer scattering in each transfer process. Further, the cleaning load on the intermediate transfer belt can be reduced as compared with the case where all the detectors are set at the same position in the axial direction of the image carrier. In addition, since the reference toner patch can be formed on each image carrier in parallel, it is possible to reduce the waiting time of the user when performing a self-check such as potential control.

  According to a second aspect of the present invention, in the image forming apparatus for obtaining a color image by transferring a toner image formed by electrophotography on a plurality of rotationally driven image carriers to an intermediate transfer member, for each of the image carriers. A plurality of detections that are provided so as to face the image carrier and are shifted from each other in the axial direction of the image carrier, and optically detect the density of the toner image formed on the opposite image carrier. By providing an imager, a reference toner patch is formed as a toner image for image density control by shifting in the axial direction of the image carrier for each image carrier so that a plurality of detectors can detect the density. That's fine. As a result, the reference toner patches corresponding to the respective image carriers are transferred on the intermediate transfer belt so as to be shifted from each other, so that toner due to poor cleaning in the intermediate transfer cleaning and the secondary transfer cleaning, and transfer scattering in each transfer process. It is possible to prevent the occurrence of scattering. In addition, since the reference toner patch can be formed on each image carrier in parallel, it is possible to reduce the waiting time of the user when performing a self-check such as potential control.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the forming unit forms a reference toner patch that is a toner image for each of the image carriers so that the plurality of detectors can detect the density. Image density control means for executing image density control based on the detection result of the detector, so that at least two of the reference toner patches corresponding to each image carrier for executing image density control are provided. One of them is shifted in the axial direction of the image carrier corresponding to the detector and transferred onto the intermediate transfer belt so that all toner patches are formed at the same position in the axial direction of the image carrier. In comparison with the case, it is possible to prevent the occurrence of cleaning failure during intermediate transfer cleaning and secondary transfer cleaning, and toner scattering due to transfer scattering in each transfer process.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect, a reference toner patch, which is a toner image, is provided for each image carrier so that the plurality of detectors can detect the density. Each image carrier for performing image density control by comprising forming means that is formed by shifting in the axial direction and image density control means for performing image density control based on the detection result of the detector Since the reference toner patches corresponding to the above are transferred to each other on the intermediate transfer belt, it is possible to prevent the occurrence of poor toner cleaning during intermediate transfer cleaning and secondary transfer cleaning, and toner scattering due to transfer scattering in each transfer process. can do. In addition, since the reference toner patch can be formed on each image carrier in parallel, it is possible to reduce the waiting time of the user when performing a self-check such as potential control.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the plurality of detectors are arranged in the vicinity of the center in the axial direction of the image carrier. Therefore, it is possible to suppress image density fluctuations between the detectors that occur because the image density fluctuation method varies depending on the position of the image carrier in the axial direction.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the forming unit is configured to perform an image forming operation during a continuous image forming operation for transferring to a plurality of recording materials. By forming the reference toner patch between the image forming operation and the image forming operation, image density control can be performed without providing a special image density control time.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the glossiness of the surface of the image carrier is higher than the glossiness of the surface of the intermediate transfer belt. As a result, the toner density can be detected more stably than when the toner density is detected on the intermediate transfer belt.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, since the glossiness of the surface of the intermediate transfer belt is 80 or less, the toner is formed on the intermediate transfer belt. Toner density detection can be performed more stably than density detection.

  According to the ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, when the glossiness of the surface of the image carrier is 90 or more, the detector is a reflective type. When the optical sensor is employed, the S / N can be maintained high, and therefore, a detector that is smaller than that of the prior art can be employed and the detector can be disposed on the image carrier even in the tandem system.

  According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, a linear velocity ratio between the surface of the image carrier and the surface of the intermediate transfer belt is approximately 1. This makes it difficult to generate scratches caused by rubbing against the surface of the image bearing member with the intermediate transfer belt, and the toner density can be detected more stably than the intermediate transfer belt whose surface condition deteriorates due to rubbing with the transfer paper. .

  An embodiment of the present invention will be described with reference to the drawings. The present embodiment is an application example to a tandem type full-color electrophotographic copying machine (hereinafter simply referred to as “copying machine”) as an image forming apparatus.

  First, the configuration of the entire copying machine according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram showing the entire copying machine of the present embodiment. The copying machine includes a copying machine main body 100 that forms an image, a paper feeding device 200 on which the copying machine main body 100 is mounted and that supplies transfer paper 5 as a recording material to the copying machine main body 100, and a copying machine main body. A scanner 300 that is mounted on 100 and reads a document image, and an automatic document feeder (ADF) 400 that is mounted on the scanner 300 are provided. The copying machine main body 100 is provided with a manual feed tray 6 for manually feeding the transfer paper 5 and a paper discharge tray 7 for discharging the transfer paper 5 on which an image has been formed.

  FIG. 2 is an enlarged view showing the configuration of the copying machine main body 100. The copying machine main body 100 is provided with an endless belt-like intermediate transfer belt 10 which is an intermediate transfer member. As shown in FIG. 3, the intermediate transfer belt 10 has a three-layer structure including a base layer 11, an elastic layer 12, and a coat layer 13. The base layer 11 is configured, for example, by combining a fluorine resin having a small elongation or a rubber material having a large elongation with a material that hardly stretches such as a canvas. The elastic layer 12 is made of, for example, fluorine rubber or acrylonitrile-butadiene copolymer rubber, and is formed on the base layer 11. The coat layer 13 is formed by coating the surface of the elastic layer 12 with, for example, a fluorine resin. The intermediate transfer belt 10 is rotationally driven in the clockwise direction in FIG. 2 while being stretched around the three support rollers 14, 15 and 16.

  As shown in FIG. 2, four images of yellow, cyan, magenta, and black are formed on the belt stretch portion between the first support roller 14 and the second support roller 15 of the support rollers 14, 15, and 16. The forming units 18Y, 18C, 18M, and 18K are arranged side by side. Above these image forming units 18Y, 18C, 18M, and 18K, an exposure device 21 is provided as shown in FIG. The exposure apparatus 21 emits writing light by driving a semiconductor laser (not shown) by a laser control unit (not shown) based on the image information of the document read by the scanner 300, and each image forming unit. This is for forming an electrostatic latent image on the photoconductive drums 20Y, 20C, 20M, and 20K as image carriers provided on 18Y, 18C, 18M, and 18K. Here, the emission of the writing light is not limited to the laser, but may be an LED, for example.

  The configuration of the image forming units 18Y, 18C, 18M, and 18K will be described. In the following description, the image forming unit 18K that forms a black toner image will be described as an example, but the other image forming units 18Y, 18C, and 18M have the same configuration. Here, FIG. 4 is an enlarged view showing a configuration of two adjacent image forming units 18M and 18K. In addition, in the code | symbol in a figure, the symbol of "M" and "K" which shows distinction of a color is abbreviate | omitted, and a symbol is abbreviate | omitted suitably also in the following description.

  In the image forming unit 18, a charging device 60, a developing device 61, a photoconductor cleaning device 63, and a charge removal device 64 are provided around the photoconductor drum 20. Further, a primary transfer device 62 is provided at a position facing the photosensitive drum 20 via the intermediate transfer belt 10.

  The charging device 60 is of a contact charging type that employs a charging roller, and uniformly charges the surface of the photosensitive drum 20 by applying a voltage in contact with the photosensitive drum 20. As the charging device 60, a non-contact charging type using a non-contact scorotron charger or the like can be used.

  The developing device 61 uses a two-component developer composed of a magnetic carrier and a nonmagnetic toner. As the developer, a one-component developer may be used. The developing device 61 can be broadly divided into a stirring unit 66 and a developing unit 67 provided in the developing case 70. In the agitating unit 66, a two-component developer (hereinafter simply referred to as “developer”) is conveyed while being agitated and supplied onto a developing sleeve 65, which will be described later, as a developer carrying member. The stirring unit 66 is provided with two parallel screws 68, and a partition plate is provided between the two screws 68 for partitioning so that both ends communicate with each other. Further, a toner concentration sensor 71 for detecting the toner concentration of the developer in the developing device 61 is attached to the developing case 70. On the other hand, in the developing unit 67, the toner of the developer attached to the developing sleeve 65 is transferred to the photosensitive drum 20. The developing portion 67 is provided with a developing sleeve 65 that faces the photosensitive drum 20 through the opening of the developing case 70, and a magnet (not shown) is fixedly disposed in the developing sleeve 65. Further, a doctor blade 73 is provided so that the tip approaches the developing sleeve 65. In the present embodiment, the distance at the closest portion between the doctor blade 73 and the developing sleeve 65 is set to 0.9 mm.

  In the developing device 61, the developer is conveyed and circulated while being stirred by two screws 68, and is supplied to the developing sleeve 65. The developer supplied to the developing sleeve 65 is pumped and held by a magnet. The developer pumped up by the developing sleeve 65 is conveyed along with the rotation of the developing sleeve 65 and is regulated to an appropriate amount by the doctor blade 73. The regulated developer is returned to the stirring unit 66. Thus, the developer transported to the developing area facing the photosensitive drum 20 is brought into a spiked state by the magnet and forms a magnetic brush. In the developing region, a developing electric field for moving the toner in the developer to the electrostatic latent image portion on the photosensitive drum 20 is formed by the developing bias applied to the developing sleeve 65. As a result, the toner in the developer is transferred to the electrostatic latent image portion on the photosensitive drum 20, and the electrostatic latent image on the photosensitive drum 20 is visualized to form a toner image. The developer that has passed through the developing region is transported to a portion where the magnetic force of the magnet is weak, and thus is separated from the developing sleeve 65 and returned to the stirring unit 66. When the toner concentration in the stirring unit 66 becomes light by repeating such an operation, the toner concentration sensor 71 detects this, and the toner is supplied to the stirring unit 66 based on the detection result.

  The primary transfer device 62 employs a primary transfer roller, and is installed so as to be pressed against the photosensitive drum 20 with the intermediate transfer belt 10 interposed therebetween. The primary transfer device 62 may not be a roller shape, but may be a conductive brush shape, a non-contact corona charger, or the like.

  The photoconductor cleaning device 63 includes a cleaning blade 75 made of, for example, polyurethane rubber, which is disposed so that the front end is pressed against the photoconductor drum 20. In the present embodiment, a conductive fur brush 76 that contacts the photosensitive drum 20 is used in combination to improve the cleaning performance. A bias is applied to the fur brush 76 from a metal electric field roller 77, and the tip of a scraper 78 is pressed against the electric field roller 77. The toner removed from the photoconductor drum 20 by the cleaning blade 75 and the fur brush 76 is accommodated in the photoconductor cleaning device 63. Thereafter, the toner is brought to one side of the photoconductor cleaning device 63 by the recovery screw 79, returned to the developing device 61 through a toner recycling device 80 described later, and reused.

  The static eliminator 64 is composed of a static elimination lamp, and irradiates light to initialize the surface potential of the photosensitive drum 20.

  Further, the image forming unit 18 is provided with a toner density sensor 310 and a potential sensor 320 as detectors corresponding to the respective photosensitive drums 20. Specifically, as shown in FIG. 5, the toner density sensor 310 is provided so as to face the photosensitive drum 20 for each photosensitive drum 20, and is arranged so as to be shifted in the direction of the axis 90 of the photosensitive drum 20. Yes. The toner density sensor 310 is an optical infrared light reflection type sensor, and optically detects the density of the toner image formed on the surface of the photosensitive drum 20. Similarly, the potential sensor 320 is also provided so as to face the photoconductor drum 20 for each photoconductor drum 20, and is arranged so as to be shifted in the direction of the axis 90 of the photoconductor drum 20. These potential sensors 320 detect the potential on the surface of the photosensitive drum 20.

  Specific settings of the image forming unit 18 will be described. The diameter of the photosensitive drum 20 is 60 mm, and the photosensitive drum 20 is driven at a linear speed of 282 mm / s. The developing sleeve 65 has a diameter of 25 mm, and the developing sleeve 65 is driven at a linear speed of 564 mm / s. Further, the charge amount of the toner in the developer supplied to the development region is preferably in the range of about − (minus) 10 to −30 μC / g. The development gap, which is the gap between the photosensitive drum 20 and the development sleeve 65, can be set in the range of 0.5 to 0.3 mm, and the development efficiency can be improved by reducing the value. Further, the photosensitive layer of the photosensitive drum 20 has a thickness of 30 μm, the beam spot diameter of the optical system of the exposure device 21 is 50 × 60 μm, and the light quantity is about 0.47 mW. As an example, the surface of the photosensitive drum 20 is uniformly charged to −700 V by the charging device 60, and the potential of the electrostatic latent image portion irradiated with the laser by the exposure device 21 is −120 V. On the other hand, the developing bias voltage is set to -470V, and a developing potential of 350V is secured. Such process conditions are appropriately changed according to the result of the potential control.

  In the image forming unit 18 having the above configuration, first, the surface of the photosensitive drum 20 is uniformly charged by the charging device 60 as the photosensitive drum 20 rotates. Next, based on the image information read by the scanner 300, the exposure light is irradiated from the exposure device 21 to form an electrostatic latent image on the photosensitive drum 20. Thereafter, the electrostatic latent image is visualized by the developing device 61 to form a toner image. This toner image is primarily transferred onto the intermediate transfer belt 10 by the primary transfer device 62. The transfer residual toner remaining on the surface of the photosensitive drum 20 after the primary transfer is removed by the photosensitive member cleaning device 63, and thereafter, the surface of the photosensitive drum 20 is discharged by the static eliminating device 64, and the next image formation is performed. Provided.

  Next, as shown in FIG. 2, a secondary transfer roller 24 as a secondary transfer device is provided at a position facing the third support roller 16 among the support rollers. When the toner image on the intermediate transfer belt 10 is secondarily transferred onto the transfer paper 5, the secondary transfer roller 24 is pressed against the portion of the intermediate transfer belt 10 wound around the third support roller 16. Next transfer is performed. The secondary transfer device may not be configured using the secondary transfer roller 24 but may be configured using, for example, a transfer belt or a non-contact transfer charger. The secondary transfer roller 24 is in contact with a roller cleaning unit 91 that cleans toner adhering to the secondary transfer roller 24.

  Further, an endless belt-like transport belt 22 is stretched between the two rollers 23a and 23b on the downstream side of the secondary transfer roller 24 in the transport direction of the transfer paper 5. Further, a fixing device 25 for fixing the toner image transferred onto the transfer paper 5 is provided further downstream in the transport direction. The fixing device 25 has a configuration in which a pressure roller 27 is pressed against a heating roller 26. Further, a belt cleaning device 17 is provided at a position facing the second support roller 15 among the support rollers of the intermediate transfer belt 10. The belt cleaning device 17 is for removing residual toner remaining on the intermediate transfer belt 10 after the toner image on the intermediate transfer belt 10 is transferred to the transfer paper 5.

  Next, the configuration and operation of the toner recycling device 80 for reusing the transfer residual toner collected by the photoconductor cleaning device 63 in the developing device 61 will be described. FIG. 6 is an explanatory diagram showing a schematic configuration of the toner recycling device 80, and FIG. 7 is an enlarged view of one end portion of the recovery screw 79 of the photoconductor cleaning device 63.

  As shown in FIG. 7, the toner recycling device 80 includes a roller portion 82 provided at one end of the recovery screw 79 of the photoconductor cleaning device 63. The roller portion 82 is provided with a pin 81. The roller portion 82 stretches a belt-like collected toner conveying member 83 together with the roller portion 87 of the rotating shaft 86. At this time, the pin 81 of the roller portion 82 enters a long hole 84 provided in the collected toner conveying member 83. On the outer peripheral surface of the collected toner conveying member 83, blades 85 are provided at regular intervals.

  As shown in FIG. 6, the collected toner conveying member 83 is accommodated in the conveying path case 88 together with the rotating shaft 86. The transport path case 88 is integrally formed with a cartridge case 89 that integrally stores at least a part of the components of the image forming unit 18. One of the two screws 68 protrudes from the inside of the developing device 61 inside the conveyance path case 88.

  In such a toner recycling apparatus 80, the recovery screw 79 is rotated by transmitting a driving force from the outside, and the recovery toner conveying member 83 is rotationally driven. Thus, the toner collected by the photoconductor cleaning device 63 is transported toward the developing device 61 through the transport path case 88 and is accommodated in the developing device 61 by the screw 68. Thereafter, the collected toner is stirred and circulated together with the developer in the developing device 61 by the two screws 68 as described above, and contributes to development again.

  Further, as shown in FIG. 1, the copying machine main body 100 is provided with a conveyance path 48 that guides the transfer paper 5 fed from the paper feeding device 200 to the paper discharge tray 7 via the secondary transfer roller 24. Along the conveyance path 48, a conveyance roller 49a, a registration roller 49b, a discharge roller 56, and the like are provided. A switching claw 55 is provided on the downstream side of the transport path 48 to switch the transport direction of the transfer paper 5 after transfer to the paper discharge tray 7 or the paper reversing device 93. The paper reversing device 93 reverses the transfer paper 5 and sends it again toward the secondary transfer roller 24. Further, the copying machine main body 100 is provided with a manual feed path 53 that joins from the manual feed tray 6 to the transport path 48, and the transfer paper 5 set in the manual feed tray 6 is located upstream of the manual feed path 53. A sheet feeding roller 50 and a separation roller 51 are provided for feeding sheets one by one.

  The paper feeding device 200 includes a plurality of paper feeding cassettes 44 that store the transfer paper 5, a paper feeding roller 42 and a separation roller 45 that feed the transfer papers stored in these paper feeding cassettes 44 one by one, and the fed transfer paper Is composed of a transport roller 47 that transports the paper along the paper feed path 46. The paper feed path 46 is connected to the conveyance path 48 of the copying machine main body 100.

  The scanner 300 will be briefly described with reference to FIG. In the scanner 300, first and second traveling bodies 33 and 34 mounted with a document illumination light source and a mirror reciprocate in order to read and scan a document (not shown) placed on the contact glass 31. To do. The image information scanned by the traveling bodies 33 and 34 is collected by the imaging lens 35 on the imaging surface of the reading sensor 36 installed behind the imaging lens 35 and read by the reading sensor 36 as an image signal.

FIG. 8 is a block diagram showing the electrical connection of each part provided in the copying machine of the present embodiment. As shown in FIG. 8, the copying machine according to the present embodiment includes a main control unit 500 having a computer configuration, and the main control unit 500 controls driving of each unit. The main control unit 500 includes a ROM (Read Only Memory) 503 that stores in advance fixed data such as a computer program via a bus line 502 in a CPU (Central Processing Unit) 501 that executes various calculations and drive control of each unit. A RAM (Random Access Memory) 504 functioning as a work area for storing various data in a rewritable manner is connected.

  The ROM 503 stores a conversion table (not shown) that stores information related to conversion of the output value of the toner density sensor 310 into the toner adhesion amount per unit area.

  Connected to the main controller 500 are each part of the copying machine main body 100, a paper feeding device 200, a scanner 300, and an automatic document feeder 400. Here, the toner density sensor 310 and the potential sensor 320 of the copying machine main body 100 send the detected information to the main control unit 500.

  Next, the operation of the copying machine of this embodiment will be described. When copying a document using the copying machine having the above configuration, first, the document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 31 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it. Thereafter, when the user presses a start switch (not shown), when the document is set on the automatic document feeder 400, the document is conveyed onto the contact glass 31. Then, the scanner 300 is driven and the first traveling body 33 and the second traveling body 34 start traveling. Thereby, the light from the first traveling body 33 is reflected by the document on the contact glass 31, and the reflected light is reflected by the mirror of the second traveling body 34 and guided to the reading sensor 36 through the imaging lens 35. . In this way, the image information of the original is read.

  When the start switch is pressed by the user, a drive motor (not shown) is driven, and one of the support rollers 14, 15, 16 is rotationally driven to rotate the intermediate transfer belt 10. At the same time, the photosensitive drums 20Y, 20C, 20M, and 20K of the image forming units 18Y, 18C, 18M, and 18K are also rotationally driven. Thereafter, based on the image information read by the reading sensor 36 of the scanner 300, writing light is emitted from the exposure device 21 onto the photosensitive drums 20Y, 20C, 20M, and 20K of the image forming units 18Y, 18C, 18M, and 18K. Each is irradiated. As a result, electrostatic latent images are formed on the respective photosensitive drums 20Y, 20C, 20M, and 20K, and are visualized by the developing devices 61Y, 61C, 61M, and 61K. Then, yellow, cyan, magenta, and black toner images are formed on the photosensitive drums 20Y, 20C, 20M, and 20K, respectively.

  Each color toner image formed in this way is primarily transferred by the primary transfer devices 62Y, 62C, 62M, and 62K so as to sequentially overlap each other on the intermediate transfer belt 10. As a result, a composite toner image in which the toner images of the respective colors overlap is formed on the intermediate transfer belt 10. The transfer residual toner remaining on the intermediate transfer belt 10 after the secondary transfer is removed by the belt cleaning device 17.

  When the user presses the start switch, the paper feed roller 42 of the paper feed device 200 corresponding to the transfer paper 5 selected by the user rotates, and the transfer paper 5 is sent out from one of the paper feed cassettes 44. The transferred transfer paper 5 is separated into one sheet by the separation roller 45 and enters the paper feed path 46, and is conveyed by the conveyance roller 47 to the conveyance path 48 in the copying machine main body 100. The transfer sheet 5 thus transported is stopped when it abuts against the registration roller 49b. When the transfer paper 5 not set in the paper feed cassette 44 is used, the transfer paper 5 set on the manual feed tray 6 is fed out by the paper feed roller 50 and separated into one sheet by the separation roller 52, and then manually fed. It is conveyed through the paper path 53. Then, it stops when it hits the registration roller 49b.

  The registration roller 49 b starts to rotate in accordance with the timing at which the composite toner image formed on the intermediate transfer belt 10 as described above is conveyed to the secondary transfer unit facing the secondary transfer roller 24. Here, the registration roller 49b is generally used while being grounded, but a bias may be applied to remove the paper dust of the transfer paper 5. The transfer paper 5 sent out by the registration roller 49b is sent between the intermediate transfer belt 10 and the secondary transfer roller 24, and the secondary transfer roller 24 causes the composite toner image on the intermediate transfer belt 10 to be transferred onto the transfer paper 5. Secondary transfer is performed. Thereafter, the transfer paper 5 is conveyed to the fixing device 25 while being attracted to the secondary transfer roller 24, and heat and pressure are applied by the fixing device 25 to perform a toner image fixing process. The transfer paper 5 that has passed through the fixing device 25 is discharged to the paper discharge tray 7 by the discharge roller 56 and stacked. When image formation is performed also on the back surface of the surface on which the toner image is fixed, the transfer paper 5 that has passed through the fixing device 25 is switched by the switching claw 55 and sent to the paper reversing device 93. The transfer paper 5 is then reversed and guided to the secondary transfer roller 24 again.

  Next, potential control processing, which is image density control and self-check performed by the CPU 501 of the present embodiment based on a computer program, will be described with reference to FIGS. 9 is a flowchart showing a potential control routine, FIG. 10 is a diagram for explaining patch patterns formed on the photosensitive drum 20, FIG. 11 is a plan view showing patch patterns transferred onto the intermediate transfer belt 10, and FIG. An enlarged view showing the patch pattern, FIG. 13 is a graph showing the relationship between potential data at the time of potential control and toner adhesion amount data in each patch pattern, and FIG. 14 is potential data and control potential for the toner adhesion amount data at potential control. FIG. 15 is a schematic diagram showing a potential control table.

  In the potential control routine shown in FIG. 9, basically, at the time of starting the copying machine, a predetermined number of copies is made for each copy (that is, between the image forming operation and the image forming operation during the continuous image forming operation). This is done as needed, such as every hour. Here, the execution operation at the time of activation will be described. First, in order to distinguish the power-on state from an abnormal process such as a jam, the fixing temperature of the fixing device 25 is detected as a potential control execution condition in step S701. Based on the input signal from the fixing temperature sensor, it is determined whether or not the fixing temperature of the fixing device 25 exceeds 100 ° C. If the fixing temperature of the fixing device 25 exceeds 100 ° C. (in step S701). N), it is determined as abnormal, and the process is terminated without executing the potential control.

  If the fixing temperature of the fixing device 25 does not exceed 100 ° C. (Y in step S701), the surface potential of each photosensitive drum 20 uniformly charged under a predetermined condition is checked by the potential sensor 320 (step S701). Next, Vsg adjustment is performed in step S703 (step S703). In this Vsg adjustment, an output value for the background portion (surface) of the photosensitive drum 20 is taken from the toner concentration sensor 310, and the reflected light of the light irradiated from the toner concentration sensor 310 to the background portion of the photosensitive drum 20 becomes a constant value. The light emission amount of the toner density sensor 310 is adjusted so that Here, in steps S702 to S703, the image forming units 18 of the respective colors perform parallel processing.

  In step S704, it is checked whether there is any abnormality in the processing in steps S702 to 703. If there is an abnormality (Y in step S704), the process proceeds to step S717, an error code is set, and the process ends.

  If it is determined in step S704 that there is no abnormality in the processing in steps S702 to 703 (Y in step S704), it is determined whether the potential control method is set to automatic or fixed instead of automatic. (Step S5).

  In steps S703 to S704, the operation is performed prior to step S706 for use in other toner replenishment control regardless of the potential control method.

  If it is determined in step S705 that the potential control method is not automatic but fixed (N in step S705), an error code is set in step S717, and the process ends. On the other hand, if it is determined in step S705 that the potential control method is automatic (Y in step S705), the processes in steps S706 to 707 are performed on the image forming units 18 of the respective colors in parallel.

  In step S706, as shown in FIG. 5, a patch pattern (latent image pattern) 600 is formed on each photosensitive drum 20 as a reference toner patch that is a toner image (formation unit). The patch pattern 600 is formed by shifting each color with respect to the direction of the axis 90 (width direction) of the photosensitive drum 20. In this embodiment, N patch patterns 600 (600a, 600b, 600c,...) That are electrostatic latent images having N gradation densities are exposed for each color, for example, as shown in FIG. They are formed at predetermined intervals along the rotation direction of the body drum 20. In the present embodiment, 16 rectangular patch patterns 600 (600a, 600b, 600c,...) Each having a different gradation density and each side of 15 × 20 mm are arranged in the rotational direction of the photosensitive drum 20. And 10 mm apart. The interval between the patch patterns 600 for each color in the direction of the axis 90 of the photosensitive drum 20 is set to 5 mm.

  By forming the patch pattern 600 in this way, when the patch pattern 600 is transferred to the intermediate transfer belt 10, the patch patterns 600 of the respective colors are formed on the intermediate transfer belt 10 without overlapping as shown in FIG. Is done. Here, FIG. 12 shows an enlarged view of the patch pattern 600 on the intermediate transfer belt 10.

  In the next step S707, the output value of the potential sensor 320 with respect to the potential of these patch patterns 600 (600a, 600b, 600c...) On the photosensitive drum 20 is read and stored in the RAM 504. Then, the patch patterns 600 for the four colors on the photosensitive drum 20 are developed in the black developing device 61K, the cyan developing device 61C, the magenta developing device 61M, and the yellow developing device 61Y in a parallel operation to be visualized. Toner image.

  Next, the CPU 501 performs toner density detection by the toner density sensor 310 with respect to the patch pattern 600 of the photosensitive drum 20 (step S708). In this toner density detection, the output value of the toner density sensor 310 for the patch pattern 600 that is a toner image of each color is stored in the RAM 504 as Vpi (i = 1 to N) for each color.

  Next, the toner adhesion amount is calculated (step S709). That is, the output value of the toner density sensor 310 stored in the RAM 504 is converted into a toner adhesion amount per unit area with reference to a conversion table stored in the ROM 503 and stored again in the RAM 504. Then, steps S710 to 712 are executed. Hereinafter, these steps will be described in detail.

13 shows the relationship between the potential data obtained in step S707 and the toner adhesion amount data obtained in step S709 in each patch pattern 600 (600a, 600b, 600c...) On the XY plane. It is a plot. The X axis indicates the potential (the difference between the developing bias potential VB and the surface potential of the photosensitive drum 20) (unit V), and the Y axis indicates the toner adhesion amount (mg / cm ² ) per unit area.
Is shown. In the present embodiment, as described above, the toner density sensor 310 is configured by an optical sensor such as an infrared light reflection type sensor, and the infrared light reflection type sensor is generally shown in FIG. As shown, saturation characteristics are exhibited in a multi-adhesion portion where the toner adhesion amount is large, and the obtained detection value does not correspond to the actual toner adhesion amount. For this reason, if the toner adhesion amount is calculated by using the detection value of the toner density sensor 310 obtained in the multiple adhesion portion as it is, an adhesion amount different from the actual adhesion amount is obtained, and this toner adhesion is obtained. The toner replenishment control based on the amount cannot be performed accurately.

  Therefore, the CPU 501 according to the present embodiment uses the patch pattern 600 (600a, 600b, 600c) obtained from the potential sensor 320 and the toner density sensor 310 for each color patch pattern 600 (600a, 600b, 600c...). )) And the toner adhesion amount data after the visualization, as described later, the relationship between the potential data Xn (n = 1 to 10) and the toner adhesion amount data Yn (development of the developing device 61) By selecting only a straight section of (γ characteristics) and applying the least square method to the data in this section, a linear approximation of the developing characteristics of each developing device 61 is performed by a method as described later, and an approximate linear equation of the developing characteristics is obtained. (E) is obtained for each color, and the control potential is calculated for each color by the approximate linear equation (E).

The following formula is used for the calculation of the least square method.
Xave = ΣXn / k (1)
Yave = ΣYn / k (2)
Sx = Σ (Xn−Xave) × (Xn−Xave) (3)
Sy = Σ (Yn−Yave) × (Yn−Yave) (4)
Sxy = Σ (Xn−Xave) × (Yn−Yave) (5)
An approximate linear equation (E) obtained from the data of the potential of the patch pattern 600 (600a, 600b, 600c...) Obtained from the potential sensor 320 and the toner density sensor 310 and the toner adhesion amount after visualization is represented by Y = When A1 × X + B1, the coefficients A1 and B1 use the above variables,
A1 = Sxy / Sx (6)
B1 = Yave−A1 × Xave (7)
It can be expressed.

The correlation coefficient R of the approximate linear equation (E) is
R × R = (Sxy × Sxy) / (Sx × Sy) (8)
It can be expressed as In the present embodiment, until step S709, the CPU 501 has the potential data Xn of the patch pattern 600 (600a, 600b, 600c...) Obtained from the potential sensor 320 and the toner density sensor 310 for each color, and the visible image. A set of five data from the younger numerical value of the toner adhesion amount data Yn after conversion,
(X1-X5, Y1-Y5)
(X2-X6, Y2-Y6)
(X3-X7, Y3-Y7)
(X4 to X8, Y4 to Y8)
(X5 to X9, Y5 to Y9)
(X6-X10, Y6-Y10)
And the linear approximation calculation is performed according to the above-described equations (1) to (8), and the correlation coefficient R is calculated to calculate the following six sets of approximate linear equations and correlation coefficients (9) to (14). Get.
Y11 = A11 × X + B11; R11 (9)
Y12 = A12 × X + B12; R12 (10)
Y13 = A13 × X + B13; R13 (11)
Y14 = A14 × X + B14; R14 (12)
Y15 = A15 × X + B15; R15 (13)
Y16 = A16 × X + B16; R16 (14)
The CPU 501 selects one set of approximate linear equations corresponding to the maximum value in the correlation coefficients R11 to R16 as the approximate linear equation (E) from the obtained six sets of approximate linear equations.

Next, in step S710, the main control unit 500 (CPU 501) determines when the value of Y becomes the required maximum toner adhesion amount Mmax as shown in FIG. 14 in the above-described approximate linear equation (E) for each color. The value of X, that is, the value Vmax of the development potential is calculated. The developing bias potential VB of the black developing device 61K, the cyan developing device 61C, the magenta developing device 61M, and the yellow developing device 61Y and the surface potential (exposure potential) VL by image exposure of each color on the photosensitive drum 20 are obtained from the above formula. It is given by the following equations (15) and (16).
Vmax = (Mmax−B1) / A1 (15)
VB-VL = Vmax = (Mmax-B1) / A1 (16)
The relationship between VB and VL can be expressed using the coefficient of the approximate linear method (E). Therefore, equation (16) is
Mmax = A1 × Vmax + B1 (17)
It becomes.

Here, the relationship between the charging potential VD before exposure of the photosensitive drum 20 and the developing bias potential VB is a linear equation as shown in FIG.
Y = A2 * X + B2 (18)
From the X coordinate VK (development start voltage of the developing device 61) of the intersection of the X axis and the scumming margin voltage Vα obtained experimentally,
VD−VB = VK + Vα (19)
Given in.

  Therefore, the relationship among Vmax, VD, VB, and VL is determined by the equations (16) and (19). In this example, using Vmax as a reference value, the relationship between this and the control voltages VD, VB, and VL is obtained in advance through experiments or the like, tabulated as shown in FIG. 15, and stored in the ROM 503 as the potential control table T1.

  In step S711, the CPU 501 selects Vmax closest to the calculated Vmax for each color from the potential control table T1, and sets the control voltages (potentials) VB, VD, and VL corresponding to the selected Vmax as target potentials. To do.

  Next, in step S711, the laser emission power of the semiconductor laser is controlled to the maximum light amount via the laser control unit of the exposure apparatus 21, and the residual potential of the photosensitive drum 20 is acquired by taking in the output value of the potential sensor 320. Is detected (step S712). In step S713, when the residual potential is not 0, the target potentials VB, VD, and VL determined in step S711 are corrected to the target potential.

  In step S714, it is determined whether or not there is an error in steps S705 to 713 above. If there is an error even for one color (N in step S714), the image density fluctuation becomes large even if only the other colors are controlled, and the operation in step S715 to be performed thereafter is wasted. A code is set (step S717), and the process ends. In this case, the image forming conditions are not updated, and image forming is performed under the same image forming conditions as before until the next self-check is successful.

  If it is determined in step S714 that there is no error (Y in step S714), in step S715, a power supply circuit (FIG. 5) is arranged so that the charging potential VD by the charging device 60 of the photosensitive drum 20 becomes the target potential in parallel with each color. (Not shown), the laser emission power of the semiconductor laser is adjusted via a laser control unit (not shown) so that the surface potential VL of the photosensitive drum 20 becomes the target potential, and the black developing device 61K. The power supply circuit is adjusted so that the developing bias potentials VB of the cyan developing device 61C, the magenta developing device 61M, and the yellow developing device 61Y become the target potential, respectively (image density control means).

  In step S716, it is determined whether or not there is an error in step S715. If there is no error in step S715 (Y in step S716), the process ends. On the other hand, if there is an error in step S715 (N in step S716), the process proceeds to step S717, an error code is set, and the process is terminated.

  Such potential control is an important control particularly in a color image forming apparatus in order to maintain a constant image quality.

  Then, the patch patterns 600 (600a, 600b, 600c,...) Of the respective colors on the respective photosensitive drums 20 formed in such potential control processing are formed on the intermediate transfer belt 10 as shown in FIG. The patch patterns 600 for each color are transferred without overlapping.

  As described above, in this embodiment, the patch pattern 600 corresponding to each photosensitive drum 20 for executing the potential control that is the image density control is provided on the intermediate transfer belt 10 as shown in FIG. Since the images are transferred out of alignment with each other, the load applied to the belt cleaning device 17 and the roller cleaning unit 91 is lightened. Therefore, it is possible to prevent poor cleaning and toner scattering due to transfer scattering in each transfer process. can do. In addition, since the patch pattern 600 can be formed on each photosensitive drum 20 in parallel, it is possible to reduce the waiting time of the user when executing the potential control.

  Further, in this potential control that is self-checking, defective cleaning in the belt cleaning device 17 and the roller cleaning unit 91 is prevented, so that normal image formation can be performed following the self-checking.

  In addition, the toner patch formation in the potential control is performed between the image forming operation and the image forming operation during the continuous image forming operation for transferring to a plurality of recording materials. It is possible to control image density without providing it.

  In the present embodiment, a copying machine has been described as an example of the image forming apparatus. However, the present invention is not limited to this, and a printer or the like may be used.

  In the present exemplary embodiment, the example in which all the toner density sensors 310 and all the patch patterns 600 for each color are shifted in the direction of the axis 90 of the photosensitive drum 20 has been described. However, the present invention is not limited to this. The at least two toner density sensors 310 and the patch patterns 600 corresponding to these toner density sensors 310 need only be shifted in the direction of the axis 90 of the photosensitive drum 20. For example, the configuration may be such that only the black toner density sensor 310 and the black patch pattern 600 corresponding thereto are shifted from the toner density sensors 310 and patch patterns 600 of other colors. In this case, the cleaning load of the intermediate transfer belt 10 with respect to the color toner is higher than when all the toner density sensors 310 and the toner patches 60 are shifted in the direction of the axial center 90. However, even in this case, all the toner density sensors The cleaning load on the intermediate transfer belt 10 can be reduced as compared with the case where 310 is set at the same position in the axial center 90 direction and all the toner patches 600 are set at the same position in the axial center 90 direction. In general, the frequency of color image output is less than the frequency of black image output. Therefore, only when adjusting the color of the color image, control over the black image and control over the color image are performed so that sufficient cleaning is performed over time. If different, the device can be established as such. In addition, in this case, there is also an advantage that the color density deviation due to the position of the toner patch 600 can be reduced.

  Next, examples of the present invention will be described. In this embodiment, since the toner density sensor 310 is disposed on the tandem photosensitive drum 20, the toner density sensor 310 is downsized. What is important for downsizing is how small the components of the light emitting / receiving element can be. In general, as the light receiving / emitting element is downsized, the light emission intensity and the light receiving sensitivity (S / N) decrease. Therefore, in this embodiment, the glossiness of the image carrier is set to GS (20)> 90. In this embodiment, the glossiness of the surface of the intermediate transfer belt is 80 or less.

  In this embodiment, the linear speed ratio between the surface of the photosensitive drum 20 and the surface of the intermediate transfer belt is set to approximately 1, and they are driven.

  In this embodiment, the developing sleeve 65 is disposed approximately 10 degrees above the horizontal line passing through the axis 90 of the photosensitive drum 20 in order to secure a space for disposing the toner density sensor 310.

  In this embodiment, in order to process the outputs of the potential sensor 320 and the toner density sensor 310 in parallel for the four colors, A / D having an independent sampling period of 4 msec is adopted for each channel.

  Further, in this embodiment, in order to minimize the difference in fluctuation at the detection position, the patch patterns 600 that are the reference toner patches for the respective colors are brought close to each other and centered in the direction of the axis 90 of the photosensitive drum 20. The arrangement was collected, and specifically, within the A6 width.

  With such a configuration, the glossiness of the surface of the photosensitive drum 20 is higher than the glossiness of the surface of the intermediate transfer belt 10, so that the toner density is detected on the intermediate transfer belt 10. The toner density can be detected stably.

  Further, since the glossiness of the surface of the intermediate transfer belt 10 is 80 or less, the toner density can be detected more stably than when the toner density is detected on the intermediate transfer belt 10.

  Further, since the glossiness of the surface of the photoconductor drum 20 is GS (20)> 90, the S / N of the toner density sensor 310 can be maintained high, so that a smaller light emitting / receiving element than that in the past can be obtained. The toner density sensor 310 can be disposed so as to face the photosensitive drum even in the tandem method.

  Further, since the linear velocity ratio between the surface of the photosensitive drum 20 and the surface of the intermediate transfer belt 10 is approximately 1, scratches caused by rubbing against the surface of the photosensitive drum 20 with the intermediate transfer belt 10 are less likely to occur. Further, it is possible to perform more stable detection than the intermediate transfer belt 10 whose surface condition is deteriorated due to rubbing with the transfer paper 5.

  Further, since the plurality of toner density sensors 310 are arranged in the vicinity of the center in the direction of the axis 90 of the photosensitive drum 20 so that their widths are within A6 width, normally output images are A6. Since the width is greater than or equal to the width, the variation in the position of the patch pattern 600 of each color is small, the detection error for each color due to the detection position is reduced, and a high-speed and high-precision copying machine can be provided.

  Of the toner density sensors 310, only the black toner density sensor 310 is shifted from the toner density sensors 310 of other colors in the direction of the axis 90, and the positions of the other density sensors 310 are aligned in the direction of the axis 90. Correspondingly, when only the black toner patch 600 is shifted from the other toner patches 600 in the direction of the axial center 90, compared to the case where all the toner density sensors 310 and the toner patches 60 are shifted in the direction of the axial center 90. Although it takes time to clean the intermediate transfer belt 10, there is no error due to the color toner detection position. Further, the cleaning load on the intermediate transfer belt 10 is reduced and the color reproducibility is improved as compared with the case where all the toner patch 600 positions are the same in the axial direction 90.

1 is a schematic configuration diagram illustrating an entire copying machine according to an embodiment of the present invention. FIG. 2 is an enlarged view showing a configuration of a copying machine main body. FIG. 3 is a cross-sectional view illustrating a structure of an intermediate transfer belt. 2 is an enlarged view showing a configuration of two adjacent image forming units. FIG. It is a top view which shows a reflection density sensor, an electric potential sensor, and a photoreceptor. 2 is an explanatory diagram illustrating a schematic configuration of a toner recycling apparatus. FIG. It is an enlarged view showing one end portion of a recovery screw of the photoconductor cleaning device. FIG. 2 is a block diagram showing electrical connections of respective units provided in the copying machine. It is a flowchart which shows an electric potential control routine. It is explanatory drawing for demonstrating the patch pattern formed on a photoconductor drum. FIG. 3 is a plan view showing a patch pattern transferred onto an intermediate transfer belt. It is an enlarged view which shows the patch pattern. 6 is a graph showing a relationship between potential data and toner adhesion amount data for each patch pattern during potential control. 6 is a graph showing linear approximation of potential data and control potential data with respect to toner adhesion amount data during potential control. It is a schematic diagram which shows an electric potential control table.

Explanation of symbols

10 Intermediate transfer belt (intermediate transfer member)
20 Photosensitive drum (image carrier)
90 Axle 310 Toner concentration sensor (detector)
600 patch pattern (reference toner patch)
S706 Formation unit S715 Image density control unit

Claims (10)

In an image forming apparatus for obtaining a color image by transferring a toner image formed by electrophotography on a plurality of rotationally driven image carriers to an intermediate transfer member,
Each image carrier is provided so as to face the image carrier, and at least two of them are arranged so as to be shifted from each other in the axial direction of the image carrier, and the toner image formed on the opposite image carrier is arranged. An image forming apparatus comprising a plurality of detectors for optically detecting density. In an image forming apparatus for obtaining a color image by transferring a toner image formed by electrophotography on a plurality of rotationally driven image carriers to an intermediate transfer member,
Each of the image carriers is provided so as to face the image carrier, and is arranged so as to be shifted from each other in the axial direction of the image carrier, and the density of the toner image formed on the opposed image carrier is optically determined. An image forming apparatus comprising: a plurality of detectors for detecting; Forming means for forming a reference toner patch that is a toner image for each of the image carriers so that the plurality of detectors can detect the density;
Image density control means for performing image density control based on the detection result of the detector;
The image forming apparatus according to claim 1, further comprising: Forming means for forming a reference toner patch, which is a toner image, for each of the image bearing members by shifting in the axial direction of the image bearing member so that the plurality of detectors can detect the density;
Image density control means for performing image density control based on the detection result of the detector;
The image forming apparatus according to claim 2, further comprising:   5. The image forming apparatus according to claim 1, wherein the plurality of detectors are arranged in the vicinity of the center in the axial direction of the image carrier.   6. The forming unit according to claim 1, wherein the forming unit forms the reference toner patch between an image forming operation and an image forming operation during a continuous image forming operation for transferring to a plurality of recording materials. The image forming apparatus according to claim 1.   7. The image forming apparatus according to claim 1, wherein the glossiness of the surface of the image carrier is higher than the glossiness of the surface of the intermediate transfer belt.   The image forming apparatus according to claim 1, wherein the surface of the intermediate transfer belt has a glossiness of 80 or less.   9. The image forming apparatus according to claim 1, wherein the glossiness of the surface of the image carrier is 90 or more.   10. The image forming apparatus according to claim 1, wherein a linear velocity ratio between the surface of the image carrier and the surface of the intermediate transfer belt is approximately 1.

Images