JP5807504B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an intermediate transfer type image forming apparatus.

  Conventionally, in color image forming apparatuses (copiers, printers, facsimiles, etc.) using electrophotographic process technology, an intermediate transfer system using an intermediate transfer member such as an intermediate transfer belt has become the mainstream. The intermediate transfer method is a method in which toner images of C (cyan), M (magenta), Y (yellow), and K (black) formed on a photosensitive drum are transferred (primary transfer) to an intermediate transfer member, and intermediate transfer is performed. This is a system in which toner images of four colors are superimposed on the body and then transferred (secondary transfer) to a sheet.

  In such an image forming apparatus, the image quality of the output image (image formed on the paper) is deteriorated due to deterioration over time of the photosensitive drum, developer, etc., environment around the apparatus (temperature and humidity fluctuations), and the like. Specifically, a phenomenon occurs in which the gradation of the input image is not faithfully reproduced in the output image. Therefore, in a conventional image forming apparatus, image stabilization control is performed to stably reproduce the gradation of an input image on an output image (for example, Patent Document 1).

  As image stabilization control, for example, the density of each CMYK color toner pattern formed on the intermediate transfer member is detected by an optical sensor, and tone correction data (so-called gamma correction curve) is based on the detection result (tone characteristics). ) And is fed back to image forming conditions such as a charging potential, a developing potential, and an exposure amount.

  In Patent Document 1, when forming a single color image, a transparent toner image is formed on the intermediate transfer belt as a background of a colored toner image, thereby forming a single color image and a case of forming a multicolor image. The toner density of a specific color is disclosed to be uniform.

JP 2009-1380 A

  Image stabilization control (gradation correction) in the intermediate transfer type image forming apparatus is performed based on the detection results of the CMYK color toner patterns. Therefore, by performing the gradation correction, the input image (monochromatic image) of the primary colors (C, M, Y, K primary colors) is faithfully reproduced in the output image (gradation reproducibility is guaranteed).

  However, the actually output image is not necessarily a primary color, and is a secondary color or tertiary color such as R (red), G (green), B (blue), or Pk (process black). Often reproduced. When such a secondary color or tertiary color is reproduced as an output image, the gradation is affected by the retransfer on the downstream photosensitive drum, so that the stabilization control is performed on the primary color. However, the gradation of the secondary color or the tertiary color is not always guaranteed.

  Hereinafter, the relationship between retransfer and image stabilization control will be briefly described.

  First, the case where a single color (primary color) image of each colored component is formed will be described. Table 1 shows the toner retransfer status when a single color (primary color) image of each colored component is formed.

  As shown in Table 1, for example, when forming a single color image of yellow (Y), a part of the Y toner transferred from the Y-component photosensitive drum 413Y to the intermediate transfer belt 421 is part of the M-component photosensitive drum 413M. , C component photosensitive drum 413C and K component photosensitive drum 413K are transferred again (see FIG. 1).

  When a magenta (M) single color image is formed, a part of the M toner transferred from the M component photosensitive drum 413M to the intermediate transfer belt 421 is part of the C component photosensitive drum 413C and the K component. Retransferred to the photosensitive drum 413K (see FIG. 2). When a cyan (C) single color image is formed, a part of the C toner transferred from the C component photosensitive drum 413C to the intermediate transfer belt 421 is retransferred to the K component photosensitive drum 413K.

The toner remaining on the intermediate transfer belt 421 when it passes through the photosensitive drum 413K located on the most downstream side is transferred to the paper S in the secondary transfer portion.

  In image stabilization control, original image formation is performed in consideration of the amount of toner (retransfer rate) retransferred to the downstream photosensitive drum (photosensitive drums 413M, 413C, and 413K when forming a yellow monochrome image). The image forming conditions are controlled so that an appropriate amount of toner (amount to be transferred to the paper S in order to reproduce an image with a desired density (tone value)) is transferred to the intermediate transfer belt 421. By performing this image stabilization control, even if a part of the toner is transferred to the downstream photosensitive drum, an appropriate amount of toner is transferred to the paper S. can get. That is, for the output image of the primary color, the gradation characteristics are guaranteed by performing the image stabilization control.

  Next, a case where a multicolor (secondary color or tertiary color) image is formed will be described. Table 2 shows the toner retransfer status when a multicolor image is formed.

  As shown in Table 2, for example, when a red multicolor image in which magenta is superimposed on yellow is formed, M toner is transferred immediately after Y toner is transferred to the intermediate transfer belt 421 (see FIG. 3). In the case of forming a yellow single color image, Y toner retransfer occurs three times, whereas in the case of a red multicolor image, Y toner retransfer does not occur. Different.

In addition, after the M toner is transferred to the intermediate transfer belt 421, the toners of other colors are not transferred thereon, so that the retransfer of the M toner occurs twice (see FIG. 3). That is, the transfer rate of M toner when forming a red multicolor image is the same as when forming a magenta single color image.

  In this way, when a multicolor image is formed, the toner of the uppermost layer is retransferred to the photosensitive drum of that color every time it passes through the primary transfer portion of the color where the image is not formed. That is, for the toner that is not the uppermost layer at the time of secondary transfer (Y toner in FIG. 3), when the toner is the uppermost layer, depending on the number of times of passing through the primary transfer portion of the color on which no image is formed. The amount of toner retransfer changes. For example, the retransfer amount of Y toner differs between when a red multicolor image is formed and when a green multicolor image is formed.

  However, in the above-described image stabilization control, the image forming conditions are set so as to guarantee the gradation reproducibility of a single color image, and the change in the transfer rate of each toner when forming a multicolor image is taken into consideration. It has not been. For the toner that does not eventually become the uppermost layer, an excessive amount of toner is transferred to the paper (the density is increased). For this reason, it is difficult to obtain a desired hue in the output image. Specifically, the maximum density and the halftone density are deviated from the design values, and it is difficult to obtain gradation characteristics as designed.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can guarantee desired gradation characteristics even for a multicolor (secondary color or tertiary color) image. And

The image forming apparatus according to the present invention is sequentially arranged along the circulation path of the intermediate transfer belt, each of which forms a toner image of each color, and sequentially transfers the toner image of each color onto the intermediate transfer belt. , a photosensitive drum for a plurality of organic color,
Said and along the circular path of the intermediate transfer belt is disposed between the chromatic color light-sensitive light drum, the color toner adhering a transparent toner on the intermediate transfer belt is transferred, a plurality of transparent toner A photosensitive drum;
A plurality of toner adhesion amounts that are disposed between the plurality of color photosensitive drums and downstream of the most downstream color photosensitive drum, and detect the adhesion amount of the color toners on the intermediate transfer belt. A sensor,
A retransfer amount of the toner image to each of the colored photosensitive drums is calculated using detection values obtained by the at least two toner adhesion amount sensors arranged so as to sandwich each of the colored photosensitive drums. A transfer amount calculation unit;
A transparent toner amount control unit that controls the amount of the transparent toner to be adhered by each of the transparent toner photosensitive drums based on the calculated retransfer amount of the toner image to each of the colored photosensitive drums;
It comprises.

According to the present invention, the transparent toner for the photosensitive drum, onto the intermediate transfer member, since the transparent toner image on the color toner image is formed, passes through the photosensitive drum chromatic color of not be imaged is downstream At this time, the transparent toner is transferred to the photosensitive drum for the color component. Accordingly, since the transfer rate of all the colored toners to the paper becomes 100%, it is not necessary to consider the retransfer of the colored toners to the downstream photoreceptor in the image stabilization control, and the desired gradation characteristics are obtained. An output image can be easily formed.

  In addition, since the amount of transparent toner is optimized by the toner adhesion amount sensor, the retransfer amount calculation unit, and the control unit, the gradation characteristics of the multicolor image can be more reliably ensured, and unnecessary transparent toner So you do n’t have to spend.

Schematic diagram showing a toner state on an intermediate transfer belt when a yellow single color image is formed by a conventional image forming apparatus Schematic diagram showing the toner state on the intermediate transfer belt when forming a magenta monochrome image with a conventional image forming apparatus Schematic diagram showing a toner state on an intermediate transfer belt when a red multicolor image is formed by a conventional image forming apparatus 1 schematically shows an overall configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a main part of a control system of an image forming apparatus according to an embodiment. Flow chart showing processing procedure for re-transfer amount detection The figure which shows the press-contact / separation state of the primary transfer roller of each color with respect to a detection object color Schematic diagram showing how the retransfer amount of the yellow toner pattern is detected Flowchart showing processing procedure for image formation on intermediate transfer belt Schematic diagram showing the toner state on the intermediate transfer belt when forming a yellow monochrome image Diagram for explaining the transparent toner adhesion amount sensor A flowchart showing a processing flow in the case where control is performed so that the amount of transparent toner becomes a target value with reference to a detection result by the transparent toner adhesion amount sensor. Diagram showing the relationship between the amount of transparent toner attached and the image forming conditions

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[1] Overall Configuration FIG. 4 is a diagram schematically showing the overall configuration of the image forming apparatus 1 according to the embodiment of the present invention. FIG. 5 shows the main part of the control system of the image forming apparatus 1 according to the embodiment. FIG.

  The image forming apparatus 1 shown in FIGS. 4 and 5 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. That is, the image forming apparatus 1 transfers (primary transfer) each color toner image of Y (yellow), M (magenta), C (cyan), and K (black) formed on the photosensitive drum to the intermediate transfer member, An image is formed by superimposing four color toner images on the intermediate transfer member and then transferring (secondary transfer) to a sheet.

  In addition, the image forming apparatus 1 employs a tandem system in which photoreceptors corresponding to four colors of YMCK are arranged in series in the running direction of the intermediate transfer member, and each color toner image is sequentially transferred to the intermediate transfer member in a single procedure. Has been.

  4 and 5, the image forming apparatus 1 includes a control unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a conveyance unit 50, a fixing unit 60, a storage unit 70, and a communication unit 80. It has.

  The control unit 10 includes a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, and the like. The CPU 11 reads a program corresponding to the processing content from the ROM 12 and develops it in the RAM 13, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the developed program. At this time, various data stored in the storage unit 70 are referred to. The storage unit 70 is configured by, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive.

  The control unit 10 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 80. Do. For example, the control unit 10 receives image data transmitted from an external device, and forms an image on a sheet based on the image data (input image data). The communication unit 80 is configured by a communication control card such as a LAN card, for example.

  Further, the control unit 10 controls the image processing unit 30 to perform gradation correction based on the gradation correction data, and a gradation correction unit 14 that generates gradation correction data used for gradation correction. The unit 15 functions as a transparent image data generation unit 16 that generates transparent image data for forming a transparent toner image, and a transparent toner amount control unit 17 that controls the amount of transparent toner to be adhered by each transparent toner photosensitive drum. .

  The operation display unit 20 is configured by, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, an image status display, an operation status of each function, and the like according to a display control signal input from the control unit 10. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 10.

  The image processing unit 30 includes a circuit that performs digital image processing corresponding to initial settings or user settings on input image data. For example, the image processing unit 30 performs gradation correction based on the gradation correction data (gradation correction table) under the control of the control unit 10. Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, a compression process, and the like on the input image data in addition to the gradation correction. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 is based on input image data, and image forming units 41Y, 41M, 41C, and 41K, and transparent component toners for forming an image using each color toner of Y component, M component, C component, and K component Image forming units 41CLR1 to 41CLR3 for forming an image using (transparent toner), an intermediate transfer unit 42, a density sensor 43, and the like are provided.

  The image forming units 41Y, 41M, 41C, 41K, 41CLR1 to 41CLR3 for the Y component, M component, C component, K component, and transparent component have the same configuration. For convenience of illustration and description, common components are denoted by the same reference numerals, and in order to distinguish each, Y, M, C, K, or CLR1 to CLR3 are added to the reference numerals. In FIG. 4, reference numerals are given only to the constituent elements of the image forming unit 41Y for the Y component, and reference numerals are omitted for the constituent elements of the other image forming units 41M, 41C, 41K, 41CLR1 to 41CLR3.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

  The photosensitive drum 413 includes, for example, an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube). : A negatively charged organic photoconductor (OPC) in which Charge Transport Layers are sequentially stacked.

  The charging device 414 uniformly charges the surface of the photoconductive drum 413 to a negative polarity.

  The exposure device 411 is composed of, for example, a semiconductor laser, and irradiates the photosensitive drum 413 with laser light corresponding to the image of each color component. A positive charge is generated in the charge generation layer of the photosensitive drum 413 and is transported to the surface of the charge transport layer, whereby the surface charge (negative charge) of the photosensitive drum 413 is neutralized. An electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to a potential difference from the surroundings.

  The developing device 412 contains a developer of each color component (for example, a two-component developer composed of a toner having a small particle diameter and a magnetic material), and the toner of each color component is attached to the surface of the photosensitive drum 413. The electrostatic latent image is visualized to form a toner image.

  The drum cleaning device 415 includes a drum cleaning blade that is in sliding contact with the surface of the photosensitive drum 413. Transfer residual toner remaining on the surface of the photosensitive drum 413 after the primary transfer is scraped off and removed by a drum cleaning blade.

  The image forming units 41CLR1 to 41CLR3 for transparent components are provided between the image forming units 41Y, 41M, 41C, and 41K for colored components. That is, a transparent toner image can be formed by the transparent component image forming units 41CLR1 to 41CLR3 as an upper layer of the Y, M, and C colored toner images formed on the intermediate transfer belt 421. The image forming units 41CLR1 to 41CLR3 form a transparent toner image based on the transparent image data generated by the transparent image data generation unit 16 (control unit 10).

  In the image forming units 41CLR1-41CLR3, the amount of the transparent toner to be attached is controlled by the transparent toner amount control unit 17. The amount of the transparent toner to be attached means the thickness of the transparent toner to be attached.

  In addition to this configuration, density sensors 43-1, 43-2, and 43-3 are provided between the color image forming units 41Y, 41M, 41C, and 41K. A density sensor 43-4 is also provided on the downstream side of the most downstream colored image forming unit 41K. These density sensors 43-1, 43-2, 43-3, and 43-4 are provided as toner adhesion amount sensors that detect the adhesion amount of each color toner on the intermediate transfer belt 421. That is, the toner adhesion amount can be estimated from the density detection result because the toner adhesion amount increases as the detected density increases. Here, the density sensors 43-1, 43-2, and 43-3 are respectively between the colored photosensitive drums 413 Y, 413 M, 413 C, and 413 K, and the density sensor 43-4 is the most downstream of the colored photosensitive drums 413 K. What is necessary is just to arrange | position in the downstream.

  The density detection results obtained by the density sensors 43-1, 43-2, 43-3, and 43-4 are used to calculate the retransfer amounts of the colored photosensitive drums 413Y, 413M, 413C, and 413K. The density detection result by the density sensor 43-4 is used when generating gradation correction data. Incidentally, when the tone correction data is generated, the density sensor 43-4 detects the non-image forming area of the intermediate transfer belt 421 (for example, between images when images are continuously formed on a large number of sheets). The density of the toner pattern for gradation correction formed in (region) is detected.

As the density sensors 43-1, 43-2, 43-3, 43-4, for example, a light emitting element such as a light emitting diode (LED) and a light receiving element such as a photodiode (PD) are provided. A reflection type optical sensor that detects the reflection density of the toner pattern can be applied. The reflection density of the toner pattern, the amount of light incident on the measurement object I _0, when the amount of reflected light from the measuring object was I, represented by -log (I / I _0).

  When the intermediate transfer belt 421 is made of a translucent material, the light emitting element and the light receiving element are used as the density sensors 43-1, 43-2, 43-3, 43-4, and the intermediate transfer belt 421. It is possible to apply a transmissive optical sensor that is opposed to each other.

  The density detection results obtained by the density sensors 43-1, 43-2, 43-3, and 43-4 are output to the retransfer amount calculation unit 90. The retransfer amount calculation unit 90 is obtained by at least two density sensors 43-1, 43-2, 43-3, and 43-4 that are arranged so as to sandwich the colored photosensitive drums 413Y, 413M, 413C, and 413K. Using the detected value, the retransfer amount of the toner image to each of the colored photosensitive drums 413M, 413C, and 413K is calculated. Specifically, the retransfer amount to the colored photosensitive drum 413M is calculated from the difference value of the detection values of the density sensors 43-1 and 43-2, and the detection values of the density sensors 43-2 and 43-3. The retransfer amount to the color photosensitive drum 413C is calculated from the difference value of the color, and the retransfer amount to the color photosensitive drum 413K is calculated from the difference value of the detection values of the density sensors 43-3 and 43-4. The

  Information on the retransfer amount of the toner image to each of the colored photosensitive drums 413M, 413C, and 413K calculated by the retransfer amount calculation unit 90 is output to the transparent toner amount control unit 17. The transparent toner amount control unit 17 controls the amount of transparent toner attached by each of the transparent toner photosensitive drums 413CLR1, 413CLR2, 413CLR3 based on the retransfer amount of the toner image to each of the colored photosensitive drums 413M, 413C, 413K. To do. Specifically, the transparent toner amount control unit 17 corresponds to the amount of toner retransferred to the adjacent color photosensitive drums 413M, 413C, and 413K on the downstream side by the transparent toner photosensitive drums 413CLR1, 413CLR2, and 413CLR3. The transparent toner photosensitive drums 413CLR1, 413CLR2, and 413CLR3 are controlled so that the transparent toner is attached. That is, the transparent toner photosensitive drum 413CLR1 adheres transparent toner corresponding to the retransfer amount on the colored photosensitive drum 413M, and the transparent toner photosensitive drum 413CLR2 is transparent toner corresponding to the retransfer amount on the colored photosensitive drum 413C. The transparent toner photosensitive drum 413CLR3 attaches a transparent toner corresponding to the retransfer amount on the colored photosensitive drum 413K.

  By doing so, the amount of transparent toner is optimized, so that the gradation characteristics of a multicolor image can be more reliably ensured, and unnecessary transparent toner can be eliminated. Therefore, the quality of multilayer reproduction colors can be improved and the running cost of the apparatus can be reduced.

  The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a secondary transfer roller 423, a driving roller 424, a driven roller 425, a belt cleaning device 426, and the like.

  The intermediate transfer belt 421 travels at a constant speed in the direction of arrow A by the rotation of the driving roller 424. When the intermediate transfer belt 421 is brought into pressure contact with the photosensitive drum 413 by the primary transfer roller 422, the respective color toner images are sequentially superimposed and primarily transferred onto the intermediate transfer belt 421. When the intermediate transfer belt 421 is pressed against the sheet S by the secondary transfer roller 423, the toner image primarily transferred to the intermediate transfer belt 421 is secondarily transferred to the sheet S.

  The belt cleaning device 426 includes a belt cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 421. Transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer is scraped off and removed by a belt cleaning blade.

  The fixing unit 60 includes a pressure unit that forms a nip for nipping and conveying the paper S, a heating unit that contacts the paper S on which the toner image is transferred, and heats the paper S at a fixing temperature. A known technique can be applied to the fixing unit 60. The fixing unit 60 fixes the toner image on the paper S by heating and pressurizing the conveyed paper S at the nip portion.

  The transport unit 50 includes a paper feed unit 51, a transport mechanism 52, a paper discharge unit 53, and the like. In the two paper feed tray units 51a and 51b constituting the paper feed unit 51, paper (standard paper, special paper) S identified based on the basis weight, size, etc. of the paper is stored for each preset type. Is done.

  The sheets S accommodated in the sheet feed tray units 51a and 51b are sent out one by one from the top, and are conveyed to the image forming unit 40 by a conveyance mechanism 52 having a plurality of conveyance rollers such as registration rollers 52a. At this time, the registration section provided with the registration rollers 52a corrects the inclination of the fed paper S and adjusts the conveyance timing.

  In the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred onto one side of the sheet S at a time, and a fixing process is performed in the fixing unit 60. The sheet S on which the image has been formed is discharged out of the apparatus by a discharge unit 53 having a discharge roller 53a.

[2] Retransfer Amount Detection Processing FIG. 6 is a flowchart showing a retransfer amount detection processing procedure in the present embodiment. The processing flow of FIG. 6 is performed for each color of Y, M, C, and K.

  When the re-transfer amount detection process is started, first, information on the created color and information on the toner pattern are acquired (step S1). Next, the primary transfer roller 422 for colored toner is pressed (step S2), and the primary transfer roller 422 for transparent toner is separated from the intermediate transfer belt 421 (step S3). In this state, the target color (in step S1) A toner pattern of a color corresponding to the acquired created color information is formed (step S4). Next, the density sensor 43 detects the density (step S5), and the retransfer amount / retransfer when the retransfer amount calculation unit 90 passes through the image forming units 41M, 41C, 41K based on the detected density. The rate is calculated (step S6). Next, the retransfer amount / retransfer rate at each position (each image forming unit 41M, 41C, 41K) is stored (step S7).

  FIG. 7 is a chart showing the pressure contact / separation state of the primary transfer roller 422 for each color with respect to the detection target color. As can be seen from the figure, since retransfer occurs on the colored photosensitive drums 413M, 413C, and 413K on the downstream side of the target color, when the retransfer amount is detected, the colored photosensitive drum for the target color, and A colored photosensitive drum on the downstream side of the target color may be pressed.

  FIG. 8 is a schematic diagram showing how the retransfer amount of the yellow toner pattern is detected.

  The yellow toner pattern formed on the yellow photosensitive drum 413Y is retransferred when passing through the photosensitive drums 413M, 413C, and 413K of other colors (M, C, and K).

  The retransfer amount / retransfer rate of the toner pattern retransferred to the photosensitive drum 413M when the yellow toner pattern passes through the magenta photosensitive drum 413M is a density sensor 43-1 provided before and after the photosensitive drum 413M. It calculates from the difference of the detected value of 43-2. Subsequently, the retransfer amount or the retransfer rate when passing through the cyan photosensitive drum 413C and when passing through the black photosensitive drum 413K is calculated in the same manner.

[3] Adhesion Processing of Transparent Toner FIG. 9 is a flowchart showing a processing procedure for image formation on the intermediate transfer belt 421. FIG. 9 is a flowchart mainly focusing on the transparent toner forming process.

  When the image forming apparatus 1 starts the image forming process, the image forming apparatus 1 receives and acquires image data separated into yellow, magenta, cyan, and black (step S11). At this time, image data for image formation is acquired as YMCK image information for each pixel. Incidentally, thereafter, image data for forming a transparent toner image is generated based on the retransfer amount stored in advance by the retransfer amount calculation process.

  In step S12, the image forming apparatus 1 determines whether there is a request for Y image formation. If it is determined that there is no request, the process proceeds to step S15. On the other hand, if there is a request for Y image formation, image forming conditions for the Y image are set in step S13. Note that the image forming conditions here are such that the amount of Y toner is set on the assumption that there is no retransfer of Y toner on the downstream side. In step S14, a Y image is formed by the photosensitive drum 413Y according to the image forming conditions.

  In step S15, the image forming apparatus 1 determines whether or not there is a request for M image formation. If there is a request, the image forming apparatus 1 proceeds to step S16 and sets M image formation conditions. Here, the image forming conditions are such that the amount of M toner is set on the assumption that there is no retransfer of M toner on the downstream side. In step S17, an M image is formed by the photosensitive drum 413M according to the image forming conditions.

  On the other hand, when the image forming apparatus 1 determines that there is no request for M image formation, the image forming apparatus 1 proceeds to step S18 and determines whether there is a Y image. If it is determined in step S18 that there is a Y image, it means that there is a Y image and no M image is formed. Therefore, if there is no transparent toner, the Y toner is retransferred on the M photosensitive drum 413M. The Therefore, if it is determined in step S18 that there is a Y image, a transparent toner forming process is performed in steps S19 to S22.

  First, in step S19, the transparent toner amount control unit 17 reads storage information of the retransfer amount on the M photosensitive drum 413M, and generates image data of the transparent toner photosensitive drum 413CLR1 in step S20. In step S21, the image forming condition of the transparent toner photosensitive drum 413CLR1 is set in consideration of the retransfer amount on the M photosensitive drum 413M. In step S22, a transparent toner image is formed by the transparent toner photosensitive drum 413CLR1. Thus, a transparent toner corresponding to the retransfer amount on the M photosensitive drum 413M is formed.

  In step S23, the image forming apparatus 1 determines whether or not there is a request for C image formation. If there is a request, the image forming apparatus 1 proceeds to step S24 and sets C image forming conditions. Note that the image forming conditions here are such that the amount of C toner is set on the assumption that there is no retransfer of C toner on the downstream side. In step S25, a C image is formed by the photosensitive drum 413C according to the image forming conditions.

  In contrast, if the image forming apparatus 1 determines that there is no request for C image formation, the image forming apparatus 1 proceeds to step S26 and determines whether there is a Y image or an M image. If it is determined in step S26 that there is a Y image or M image, it means that there is a Y image or M image and no C image is formed. The image is retransferred on the photosensitive drum 413C. Therefore, when it is determined in step S26 that there is a Y image or M image, a transparent toner forming process is performed in steps S27 to S30.

  First, in step S27, the transparent toner amount control unit 17 reads storage information of the retransfer amount in the C photosensitive drum 413C, and generates image data of the transparent toner photosensitive drum 413CLR2 in step S28. In step S29, the image forming conditions of the transparent toner photosensitive drum 413CLR2 are set in consideration of the retransfer amount on the C photosensitive drum 413C. In step S30, a transparent toner image is formed by the transparent toner photosensitive drum 413CLR2. Thus, a transparent toner corresponding to the retransfer amount on the C photosensitive drum 413C is formed.

  In step S31, the image forming apparatus 1 determines whether or not there is a request for K image formation. If there is a request, the image forming apparatus 1 proceeds to step S32 and sets K image forming conditions. In step S33, a K image is formed by the photosensitive drum 413K according to the image forming conditions.

  In contrast, if the image forming apparatus 1 determines that there is no request for K image formation, the image forming apparatus 1 proceeds to step S34 and determines whether there is a Y image, an M image, or a C image. If it is determined in step S34 that there is a Y image, an M image, or a C image, it means that there is a Y image, an M image, or a C image, and no K image is formed. The toner, M toner, or K toner is retransferred on the K photosensitive drum 413K. Therefore, if it is determined in step S34 that there is a Y image, M image, or C image, a transparent toner forming process is performed in steps S35 to S38.

  First, in step S35, the transparent toner amount control unit 17 reads storage information of the retransfer amount in the K photosensitive drum 413K, and generates image data of the transparent toner photosensitive drum 413CLR3 in step S36. In step S37, the image forming conditions of the transparent toner photosensitive drum 413CLR3 are set in consideration of the retransfer amount on the K photosensitive drum 413K. In step S38, a transparent toner image is formed by the transparent toner photosensitive drum 413CLR3. Thus, a transparent toner corresponding to the retransfer amount on the K photosensitive drum 413K is formed.

Next, a case where a Y (yellow) image is formed will be described as an example with reference to FIG.
When a yellow (Y) single color image is formed, the transparent toner of the transparent toner photosensitive drum 413CLR1 is transferred again to the M photosensitive drum 413M, and the transparent toner photosensitive drum 413CLR2 is transparent to the C photosensitive drum 413C. The toner is transferred again, and the transparent toner photosensitive drum 413CLR3 toner is transferred again to the K component photosensitive drum 413K. That is, the Y toner transferred from the Y photosensitive drum 413Y to the intermediate transfer belt 421 is not retransferred to the photosensitive drums 413M, 413C, and 413K for color components on which no image is formed.

  Further, since the retransfer of the yellow toner is reliably prevented by the transparent toner, the yellow toner adhesion amount may be controlled by a process setting condition in which the retransfer is not considered, that is, the adhesion amount on the paper.

  As described above, the image forming apparatus 1 according to the present embodiment has the density arranged between the colored photosensitive drums 413Y, 413M, 413C, and 413K and on the downstream side of the most downstream colored photosensitive drum 413K. Sensors 43-1, 43-2, 43-3, 43-4 and at least two density sensors 43-1, 43-2, which are arranged so as to sandwich each of the colored photosensitive drums 413Y, 413M, 413C, 413K, The retransfer amount calculation unit 90 that calculates the retransfer amount of the toner image to each of the colored photosensitive drums 413Y, 413M, 413C, and 413K is calculated using the detection values obtained by 43-3 and 43-4. The transparent toner photosensitive drums 413CLR1, 41 based on the retransfer amount of the toner image to the colored photosensitive drums 413Y, 413M, 413C, 413K. Having a transparent toner amount control unit 17 for controlling the amount of the transparent toner deposited by CLR2,413CLR3, the.

  As a result, retransfer of colored toner does not occur at all, so that it is possible to form an image with an appropriate amount of adhesion, and consumption of colored toner due to retransfer can be suppressed. Cost can be reduced.

  In addition, since the amount of the transparent toner is optimized, the gradation characteristics of the multicolor image can be more reliably ensured, and unnecessary transparent toner can be eliminated.

[4] Other Embodiments In the above-described embodiment, as shown in FIG. 8, the colored photosensitive drums 413Y, 413M, 413C, and 413K are sandwiched between the colored photosensitive drums 413M, 413C, and 413K. One density sensor 43-1, 43-2, 43-3, 43-4 is provided for each, and the re-transfer amount at each of the colored photosensitive drums 413M, 413C, 413K is obtained.

  In addition to this, as shown in FIG. 11, the transparent toner adhesion amount sensor 43-5 for detecting the adhesion amount of the transparent toner at a position adjacent to the downstream side of the transparent toner photosensitive drums 413CLR1, 413CLR2, 413CLR3. 43-6, 43-7, and the transparent toner amount control unit 17 refers to the detection results of the transparent toner adhesion amount sensors 43-5, 43-6, 43-7, and the amount of the transparent toner is the target value. If the control is performed, the amount of the transparent toner is optimized, the gradation characteristics of the multicolor image can be more reliably ensured, and unnecessary transparent toner can be prevented from being consumed more.

  FIG. 12 shows a processing flow in the case where control is performed so that the amount of transparent toner becomes a target value with reference to detection results by the transparent toner adhesion amount sensors 43-5, 43-6, and 43-7. Steps S1-S7 are the same as in FIG. In step S41, the transparent toner primary transfer roller is pressure-bonded so that the transparent toner can be attached. In step S42, while changing the image forming conditions of the transparent toner, the transparent toner adhesion amount sensors 43-5, 43-6, and 43-7 adjacent to the transparent toner photosensitive drums 413CLR1, 413CLR2, and 413CLR3 adjoin the transparent toner. Detect adhesion amount. In step S43, image forming conditions of the transparent toner photosensitive drums 413CLR1, 413CLR2, and 413CLR3 are determined so that the transparent toner has a target adhesion amount (= retransfer amount).

  As shown in FIG. 13, as the image forming conditions, the transparent toner adhesion amount sensors 43-5, 43-6, 43-6, 43-6, while changing the development DC bias of the transparent toner photosensitive drums 413CLR1, 413CLR2, 413CLR3 or the amount of writing light. The characteristic curve L1 indicating the relationship between the development DC bias or the write light quantity and the transparent toner adhesion amount is obtained in advance by detecting the adhesion amount of the transparent toner at 43-7. Then, the development DC bias or the write light quantity corresponding to the target transparent toner adhesion amount on the characteristic curve L1 is determined as the image forming condition.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the above embodiment, and can be changed without departing from the gist thereof.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 17 Transparent toner amount control part 43-1, 43-2, 43-3, 43-4, 43-5, 43-6, 43-7 Density sensor 90 Retransfer amount calculation part 413Y, 413M, 413C 413K Colored photosensitive drums 413CLR1, 413CLR2, 413CLR3 Transparent toner photosensitive drums 421 Intermediate transfer belt

Claims (3)

Are sequentially arranged along a circular path of the intermediate transfer belt, respectively, the toner images of the respective colors are formed on the surface, the toner images of the respective colors are sequentially transferred to the intermediate transfer belt, a photosensitive drum for a plurality of chromatic colors ,
Said and along the circular path of the intermediate transfer belt is disposed between the chromatic color light-sensitive light drum, the color toner adhering a transparent toner on the intermediate transfer belt is transferred, a plurality of transparent toner A photosensitive drum;
A plurality of toner adhesion amounts that are disposed between the plurality of color photosensitive drums and downstream of the most downstream color photosensitive drum, and detect the adhesion amount of the color toners on the intermediate transfer belt. A sensor,
A retransfer amount of the toner image to each of the colored photosensitive drums is calculated using detection values obtained by the at least two toner adhesion amount sensors arranged so as to sandwich each of the colored photosensitive drums. A transfer amount calculation unit;
A transparent toner amount control unit that controls the amount of the transparent toner to be adhered by each of the transparent toner photosensitive drums based on the calculated retransfer amount of the toner image to each of the colored photosensitive drums;
An image forming apparatus comprising: Each of the transparent toner photosensitive drums adheres a transparent toner corresponding to the amount of toner retransferred to the adjacent colored photosensitive drum on the downstream side.
The image forming apparatus according to claim 1. And a plurality of transparent toner adhesion amount sensors for detecting the adhesion amount of the transparent toner at positions adjacent to the downstream side of the respective photosensitive drums for transparent toner,
The transparent toner amount control unit controls the amount of the transparent toner to be adhered by each of the transparent toner photosensitive drums based on the transparent toner adhesion amount detected by the transparent toner adhesion amount sensor.
The image forming apparatus according to claim 1.

Images