JP6349893B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter, or the like, or a multifunction machine having a plurality of functions.

  A method for detecting a test pattern formed on an intermediate transfer belt with a detection device and estimating the image density from detection data of the test pattern to control image forming conditions is widely known (for example, Patent Documents). 1 and Patent Document 2). As a detection device for detecting a test pattern, a reflection type optical sensor is generally used. The reflective optical sensor includes a light emitting element and a light receiving element, and light emitted from the light emitting element is reflected by a detection target having a test pattern, received by the light receiving element, and converted into a signal. By reading the change in the signal, the information of the test pattern can be inferred.

  The optical sensor is set so that the output signal on the surface (background portion) of the intermediate transfer belt as a photoreceptor or endless intermediate transfer member without a test pattern is a reference. For this reason, when using an optical sensor, it is used after performing calibration at the initial stage, every use, or at an appropriate timing. There are various calibration methods depending on the system to be used. For example, when a predetermined output signal is set as a reference, the input signal of the sensor is adjusted so that the output signal is obtained.

  Specifically, the control parameter (here, LED current) of the light emitting element is adjusted so that the output of the background portion becomes a predetermined output signal. Under the same LED current, the density can be detected when the output of the background portion and the test pattern are present or not, or by detecting the output difference between a plurality of different test patterns. As described above, the toner image whose adhesion amount is controlled on the intermediate transfer belt is transferred to the recording medium by the secondary transfer device as the next step. At this time, not all the toner on the intermediate transfer belt is transferred to the recording medium, but remains on the intermediate transfer belt at a constant rate, and the remaining toner is an intermediate transfer provided downstream of the secondary transfer device. It is cleaned with a belt cleaning device.

  As described above, in the apparatus that detects the test pattern on the intermediate transfer belt and stabilizes the toner adhesion amount, the ratio at which the toner on the intermediate transfer belt is transferred to the recording medium, that is, the secondary transfer efficiency, becomes what. It is decided beforehand. Then, the target value of the test pattern on the intermediate transfer belt is determined by calculating backward from the desired toner adhesion amount on the recording medium. The secondary transfer efficiency is known to vary depending on various conditions such as the environment such as temperature and humidity, and the charged state of the toner. However, the secondary transfer efficiency is stabilized by correcting the secondary transfer current depending on the temperature and humidity. New inventions have also been published.

  However, even when stable secondary transfer efficiency is achieved, when an image is formed by superimposing a plurality of toner images, the image is transferred to a recording medium as compared with the case of forming an image with a single toner image. The amount of toner in the toner image varies. Specifically, in the first toner image first transferred to the intermediate transfer belt, the second toner image created by another image carrier is overlaid on the first toner image. The overlapped toner image is transferred onto the recording medium in the secondary transfer step, but most of the second toner image on the recording medium side is transferred onto the recording medium, while the first toner image on the intermediate transfer belt side is transferred. The toner image remains on the intermediate transfer belt under the influence of transfer efficiency.

As described above, when an image is formed by superimposing a plurality of toner images even if the toner image on the intermediate transfer belt is stabilized from a single toner image by calculating backward from the secondary transfer efficiency, a recording medium is used. There is a problem that the amount of toner transferred to the top changes.
Hereinafter, for the sake of simplifying the sentence, “when a toner image created by a plurality of image carriers is overlapped to form an image” is omitted, and “created by an image carrier” is omitted. This is also referred to as “when a plurality of toner images are superimposed to form an image”. For the same purpose, “when an image is formed with a toner image created with a single image carrier” is also referred to as “when an image is formed with a single toner image”.

  The present invention has been made in view of the above-described problems of the prior art, and in the case of forming an image by superimposing a plurality of toner images, image formation capable of stabilizing the toner adhesion amount on the recording medium. An object is to provide an apparatus.

To achieve the above object, the present invention provides a plurality of image carriers, charging means for charging the surface of the image carrier, and exposure for forming an electrostatic latent image by exposing the surface of the image carrier. Means, a developing means for supplying a developer to the electrostatic latent image formed on the surface of the image carrier to form a visible image, and a visible image formed on the surface of the image carrier on the intermediate transfer member. A primary transfer means for performing a next transfer, and a secondary transfer means for secondary transfer of a visible image on the intermediate transfer body to a recording medium, and a secondary transfer rotating body that contacts the intermediate transfer body. An image forming apparatus configured to transfer a visible image on the intermediate transfer body to the recording medium when the recording medium is passed through a contact portion between the secondary transfer rotating body and the intermediate transfer body, In the case of forming an image by superimposing toner images created by the plurality of image carriers, Comprises a first correcting means for applying different correction to the image processing for forming an image with toner image produced in one image bearing member, said image processing is a processing for correcting the dot coverage, the When performing a process of correcting the dot coverage for a toner image other than the toner image first transferred to the intermediate transfer member among the toner images created by a plurality of image carriers, the toner image is created by the plurality of image carriers. When forming an image by superimposing the toner images, the dot coverage is corrected so that the amount of toner adhesion is smaller than when forming an image with a toner image created with a single image carrier. When the first correction unit forms an image with a toner image created by a single image carrier, the first correction unit does not perform the process of correcting the dot coverage and does not execute the first correction unit. When the toner image formed by the plurality of image bearing members is overlapped to form an image and the toner image is first transferred to the intermediate transfer member, the transfer is performed on the recording medium. In anticipation of a reduction in the amount of toner to be transferred, transfer to the intermediate transfer member is performed by performing a correction that increases the dot coverage as compared with the case of forming an image with a toner image created with a single image carrier. The amount of toner to be applied is increased, and the first correction unit is a case where an image is formed by superimposing toner images created by the plurality of image carriers, and is first transferred to the intermediate transfer member. If the toner image is not a toner image, the amount of toner transferred onto the recording medium is anticipated and the dot coverage is reduced compared to the case where an image is formed with a toner image created with a single image carrier. Lowering By performing positive, the amount of toner transferred to the intermediate transfer member is reduced .

  According to the present invention, due to the above-described configuration, the amount of secondary transferred toner differs between when an image is formed with a single toner image and when an image is formed by superimposing a plurality of toner images. Since the color variation is corrected by performing image processing, stable image output is possible.

1 is a schematic configuration diagram of a printer as an image forming apparatus according to a first embodiment. 1A is a schematic enlarged view showing an overlapping state of Y and M toners adhered and formed on the intermediate transfer belt in the secondary transfer portion of the printer of FIG. 1, and FIG. FIG. 4 is a schematic enlarged view showing a state in which M toner is secondarily transferred to a recording sheet and a state in which Y toner remains on the intermediate transfer belt as a transfer residual toner. It is a block diagram which shows the control structure of 1st Embodiment. It is a flowchart which shows the control flow of 1st Embodiment. It is a schematic block diagram of a printer as an image forming apparatus according to first , fourth, and fifth reference examples . It is a block diagram which shows the control structure of a 1st reference example , and the one part control structure of a 2nd reference example . It is a flowchart which shows the control flow of a 1st reference example . It is a timing chart of the 1st reference example . It is a block diagram which shows the control structure of the 3rd and 4th reference example . It is a flowchart which shows the control flow of the 3rd and 4th reference example . FIG. 10 is a front view around a secondary transfer device for explaining a control method according to a fourth reference example . FIG. 10 is a front view around a secondary transfer device for explaining a specific example of a control method according to a fourth reference example . In the secondary transfer portion of the printer of the fifth reference example , after the secondary transfer, the Y and M toners on the intermediate transfer belt are secondarily transferred to the recording paper, and the Y toner is transferred as residual toner on the intermediate transfer belt. It is a typical enlarged view which shows the state which remains in. It is a block diagram which shows the control structure of the 5th reference example .

Hereinafter, embodiments of the present invention including examples will be described in detail with reference to the drawings. In each embodiment , each reference example, and the like, components (members and components) having the same function and shape are described once by giving the same reference numerals after being described once unless there is a possibility of confusion. Is omitted. In order to simplify the drawings and the description, even if the components are to be represented in the drawings, the components that do not need to be specifically described in the drawings may be omitted as appropriate. When quoting and explaining constituent elements such as published patent gazettes, the reference numerals are shown in parentheses to distinguish them from those of the embodiments. The “second embodiment” described below is referred to as a “first reference example”, the “third embodiment” as a “second reference example”, and the “fourth embodiment” as a “third reference”. Reference Example ”,“ Fifth Embodiment ”are read as“ Fourth Reference Example ”, and“ Sixth Embodiment ”is read as“ Fifth Reference Example ”.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS.
A basic configuration of a printer that forms an image by an electrophotographic method will be described with reference to FIG. 1 as an image forming apparatus to which the present invention is applied. FIG. 1 is a schematic configuration diagram of a printer as an image forming apparatus showing the first embodiment.
The printer shown in FIG. 1 includes four process units 2Y, 2M, 2C, and 2K for forming toner images of different colors of yellow (Y), magenta (M), cyan (C), and black (K). ing. Further, the sheet feeding path 30, the pre-transfer conveying path 31, the manual sheet feeding path 32, the manual feed tray 33, the registration roller pair 34, the conveying belt unit 35, the fixing device 40, the conveyance switching device 50, the sheet discharging path 51, and the sheet discharging roller. A pair 52, a paper discharge tray 53, a first paper feed cassette 101, a second paper feed cassette 102, a retransmission device, and the like are also provided. Two optical writing units 1YM and 1CK are also provided. The process units 2Y, 2M, 2C, and 2K have drum-shaped photoreceptors 3Y, 3M, 3C, and 3K as image carriers or latent image carriers corresponding to different color toner images.

Each of the first paper feed cassette 101 and the second paper feed cassette 102 accommodates a bundle of recording paper P as a recording medium. Then, the uppermost recording sheet P in the bundle of recording sheets P is sent out toward the sheet feeding path 30 by the rotational driving of the sheet feeding rollers 101 a and 102 a. Connected to the paper feed path 30 is a pre-transfer conveyance path 31 for conveying a recording sheet immediately before a secondary transfer nip described later. The recording paper selectively sent out from the first paper feed cassette 101 or the second paper feed cassette 102 enters the pre-transfer conveyance path 31 through the paper feed path 30.
A manual feed tray 33 is disposed on the side surface of the printer chassis so as to be openable and closable with respect to the chassis (meaning that the manual feed tray 33 is provided by being arranged and positioned). A bundle or one sheet of recording paper (not shown) is manually fed onto the upper surface of the tray 33. The uppermost recording paper in the bundle of manually fed recording papers is sent out toward the pre-transfer conveyance path 31 by the sending roller of the manual feed tray 33.

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

  The process units 2Y, 2M, 2C, and 2K each support a photosensitive member as an image carrier or a latent image carrier and various devices arranged around the photosensitive member as a single unit on a common support. They are detachable from the printer unit main body. The configuration is the same except that the colors of the toners used are different. The Y process unit 2Y will be described as a representative. In addition to the photoreceptor 3Y, a developing device 4Y is provided as a developing unit for developing an electrostatic latent image formed on the surface of the photoreceptor 3Y into a Y toner image. doing. In addition, it adheres to the surface of the photoreceptor 3Y after passing through a primary transfer nip for Y, which will be described later, or a charging device 5Y as a charging means for uniformly charging the surface of the photoreceptor 3Y that is driven to rotate. A drum cleaning device 6Y for cleaning the transfer residual toner is also provided.

The illustrated printer has a so-called tandem configuration in which four process units 2Y, 2M, 2C, and 2K are arranged along an endless moving direction with respect to an intermediate transfer belt 61 described later.
As the photoreceptor 3 </ b> Y, a drum-like member is used in which a photosensitive layer is formed by applying a photosensitive organic photosensitive material to a base tube made of aluminum or the like. However, an endless belt-shaped so-called photoreceptor belt may be used.

  The developing device 4Y develops an electrostatic latent image using a two-component developer (hereinafter simply referred to as “developer”) containing a magnetic carrier (not shown) and non-magnetic Y toner. The developing device 4Y is appropriately replenished with Y toner in the Y toner bottle 103Y by a Y toner replenishing device (not shown). In the developing device 4Y, a toner density detecting means (not shown) is provided. This toner concentration detecting means detects the magnetic permeability caused by the carrier that is a magnetic material, and calculates the toner concentration from the amount of carrier contained in a certain volume. The toner density detection means detects the toner density in the developing device Y and controls the toner density in the developing device Y to be kept within a certain range (for example, 5 to 9 wt%).

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

A neutralizing lamp (not shown) is disposed above the photoreceptor 3Y, and this neutralizing lamp is also a part of the process unit 2Y. The neutralization lamp neutralizes the surface of the photoreceptor 3Y after passing through the drum cleaning device 6Y by light irradiation. The surface of the photoreceptor 3Y that has been neutralized is uniformly charged by the charging device 5Y, and then optically scanned by the optical writing unit 1YM described above. The charging device 5Y is of a charging roller type that is rotated while receiving a supply of a charging bias from a power source (not shown) (contacted with the photoconductor 3Y, or close to the photoconductor 3Y). Instead of this method, a scorotron charger method in which the photosensitive member 3Y is charged without contact may be employed.
The Y process unit 2Y has been described above, but the process units 2M, 2C, and 2K for M, C, and K have the same configuration as the process unit 2Y for Y.

  A transfer unit 60 is disposed below the four process units 2Y, 2M, 2C, 2K. The transfer unit 60 includes an intermediate transfer belt 61 as an endless intermediate transfer member that is stretched by a plurality of support rollers 63, 67, etc., while abutting the photosensitive members 3Y, 3M, 3C, and 3K. It is moved endlessly in the clockwise direction in the figure by the rotational drive of one roller. As a result, primary transfer nips for Y, M, C, and K in which the photoreceptors 3Y, 3M, 3C, and 3K abut on the intermediate transfer belt 61 are formed. Of the support rollers 63 and 67, the support roller 63 is a driving roller, and the support roller 67 is a driven roller. “Tension” means to hang up in a state where tension is applied, and “abutment” means to make contact in a state of abutment.

  In the vicinity of the primary transfer nips for Y, M, C, and K, the intermediate transfer belt 61 is exposed to light by primary transfer rollers 62Y, 62M, 62C, and 62K as primary transfer rotators disposed inside the belt loop. It is pressing toward the bodies 3Y, 3M, 3C, 3K. A primary transfer bias is applied to the primary transfer rollers 62Y, 62M, 62C, and 62K by a primary transfer bias power source (not shown) for each color. As a result, a primary transfer electric field for electrostatically moving the toner images on the photoreceptors 3Y, 3M, 3C, and 3K toward the intermediate transfer belt 61 is formed in the primary transfer nips for Y, M, C, and K. Has been. “Pressing” means pressing with pressure. Each primary transfer roller 62Y, 62M, 62C, 62K and a primary transfer bias power source (not shown) for each color constitute a primary transfer device as a primary transfer unit.

  In the drawing, the photosensitive drum passes through the primary transfer nip for Y, M, C, and K in sequence with the endless movement in the clockwise direction on the front surface of the intermediate transfer belt 61 at each primary transfer nip. The toner images on the bodies 3Y, 3M, 3C, and 3K are sequentially superimposed and primarily transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as “four-color toner image”) is formed on the front surface of the intermediate transfer belt 61.

A secondary transfer roller 72 as a secondary transfer rotator is disposed below the intermediate transfer belt 61 in the drawing. The secondary transfer roller 72 abuts from the front surface of the intermediate transfer belt 61 to a place where the intermediate transfer belt 61 is wound around the secondary transfer backup roller 68, and a secondary transfer nip as a contact portion or a contact / holding portion. Is forming. As a result, a secondary transfer nip where the front surface of the intermediate transfer belt 61 and the secondary transfer roller 72 abut is formed.
A secondary transfer bias is applied to the secondary transfer roller 72 by a secondary transfer bias power source (not shown). On the other hand, the secondary transfer backup roller 68 in the belt loop of the intermediate transfer belt 61 is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip. The secondary transfer roller 72 and a secondary transfer bias power source (not shown) constitute a secondary transfer unit 70 (secondary transfer device as a secondary transfer unit).

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

  On the intermediate transfer belt 61 between the primary transfer nip and the secondary transfer nip and in the vicinity of the support roller 67, a toner adhesion amount sensor 64 as a test pattern detection unit is disposed. The toner adhesion amount sensor 64 is a reflective optical sensor, and includes a light emitting element and a light receiving element, but may have a function as a toner density detecting unit. Light emitted from the light emitting element of the toner adhesion amount sensor 64 is reflected by a toner patch (not shown) as a test pattern created on the intermediate transfer belt 61, and is received by the light receiving element and converted into a signal. . By reading the change in the signal, the test pattern information is inferred and the toner patch adhesion amount is detected.

The transfer residual toner that has not been transferred to the recording paper P at the secondary transfer nip is attached to the front surface of the intermediate transfer belt 61 that has passed through the secondary transfer nip. This untransferred toner is cleaned by a belt cleaning device 75 having a cleaning blade in contact with the intermediate transfer belt 61. A cleaning blade backup roller 69 is disposed at a position facing the cleaning blade of the belt cleaning device 75 with the intermediate transfer belt 61 interposed therebetween. A tension roller 66 that applies a predetermined tension to the intermediate transfer belt 61 is disposed near the downstream of the belt cleaning device 75 in the rotational traveling direction.
The recording paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 61 and transferred to the transport belt unit 35. The transport belt unit 35 is endlessly moved in the counterclockwise direction in the figure by the rotational driving of the drive roller 37 while the endless transport belt 36 is stretched by the drive roller 37 and the driven roller 38. The recording paper delivered from the secondary transfer nip is conveyed with the endless movement of the conveyance belt 36 while being held on the upper stretched surface of the conveyance belt 36 and is delivered to the fixing device 40.

  The recording paper P that has passed through the secondary transfer nip is sent into the fixing device 40 and is sandwiched between the fixing nips. Then, the toner image is fixed by an action such as pressurization or heating. The recording paper P on which the toner image is transferred to the first surface at the secondary transfer nip and the toner image is fixed on the first surface by the fixing device 40 is sent out toward the conveyance switching device 50.

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

  On the other hand, when the recording paper P having the image fixed only on the first side is received from the fixing device 40 during execution of the double-side mode print job, the transport destination is set to the retransmission path 54. A switchback path 55 is connected to the retransmission path 54, and the recording paper P sent to the retransmission path 54 enters the switchback path 55. When the entire area in the conveyance direction of the recording paper P enters the switchback path 55, the conveyance direction of the recording paper P is reversed and the recording paper P is switched back. In addition to the retransmission path 54, a post-switchback transport path 56 is connected to the switchback path 55, and the recording paper P that has been switched back enters the post-switchback transport path 56. At this time, the upper and lower sides of the recording paper P are reversed. Then, the recording paper P that is turned upside down is retransmitted to the secondary transfer nip via the post-switchback transport path 56 and the paper feed path 30 described above. The recording paper P on which the toner image is also transferred to the second surface at the secondary transfer nip is fixed on the second surface via the fixing device 40, and then the conveyance switching device 50 and the paper discharge path 51. And the paper discharge roller pair 52, the paper is discharged onto the paper discharge tray 53.

  Hereinafter, the stabilization control of the toner adhesion amount unique to the present embodiment will be described. In an electrophotographic system in which an image is formed by charging toner, the amount of toner adhesion varies depending on environmental changes such as ambient temperature and humidity where the apparatus is placed and changes in the state of the developer in the developing apparatus. A test pattern (not shown) is created on the top. This test pattern is formed by first transferring the test pattern created on the plurality of photoconductors onto the surface of the intermediate transfer belt 61. Then, the toner adhesion amount of the test pattern is detected by the toner adhesion amount sensor 64 to perform feedback control for stabilizing the toner adhesion amount. The toner adhesion amount sensor 64 may have a function as a test pattern detection unit, a toner concentration detection unit, or a positional deviation detection unit.

In this embodiment, as described above, the toner adhesion amount on the intermediate transfer belt 61 is detected by the toner adhesion amount sensor 64, but the toner on the intermediate transfer belt 61 is applied to the recording paper P by the secondary transfer unit 70. A part of the toner remains on the intermediate transfer belt 61 during the transfer. Therefore, in order to achieve a desired toner adhesion amount on the recording paper P, a larger amount of toner adheres on the intermediate transfer belt 61 at a constant rate than the target toner adhesion amount on the recording paper P. The target adhesion amount of the intermediate transfer belt 61 is controlled.
Here, the toner target adhesion amount on the recording paper P is defined as Mp [mg / cm ² ], and the ratio of the toner that can be transferred onto the recording paper P by the secondary transfer (hereinafter also referred to as “secondary transfer efficiency”) is represented by α [ %], The target adhesion amount Mb [mg / cm ² ] on the intermediate transfer belt 61 is expressed by the following equation (1).
Mb = Mp / (α / 100) (1)

As described above, when a toner image is created with a single photosensitive member and a developing device (hereinafter, also simply referred to as “single photosensitive member”), the toner adhesion amount on the intermediate transfer belt 61 is stabilized. The toner adhesion amount on the recording paper P can be stabilized. However, when a toner image is created by a plurality of photoconductors and a developing device (hereinafter, also simply referred to as “multiple photoconductors”), and an image is formed by superimposing them, intermediate transfer is performed according to the order in which the toner images overlap. The percentage of toner remaining on the belt 61 changes.
Thus, for example, consider the case where an image is formed with Y toner and M toner on the intermediate transfer belt 61 with reference to FIG. Here, the following description will be made assuming that each toner is a solid image filled with no gap. As described with reference to FIG. 1, the process units 2Y, 2M, 2C, and 2K are arranged in the order of Y → M → C → K from the upstream side in the endless movement direction of the intermediate transfer belt 61 at positions facing the intermediate transfer belt 61. ing. Therefore, as shown in FIG. 2A, the Y toner first adheres onto the intermediate transfer belt 61, and the M toner adheres in an overlapping state thereon. The toner on the intermediate transfer belt 61 is conveyed to the secondary transfer unit 70 and transferred onto the recording paper P. At this time, as shown in FIG. Due to the secondary transfer efficiency, the toner remains on the intermediate transfer belt 61 as a transfer residual toner. If the M toner amount and Y toner amount on the intermediate transfer belt 61 are Mb _M and Mb _Y , respectively, and the secondary transfer efficiency is α [%], the Y toner on the recording paper P after the secondary transfer at the time of toner superposition Mp ′ _Y which is the amount of is represented by the following formula (2).
Mp ′ _Y = (Mb _M + Mb _Y ) × (α / 100) −Mp ′ _M (2)

For the meanings of Mb _M , Mb _Y , Mp ′ _Y , Mp ′ _{M in the} above formula (2), the leftmost capital letter “M” from the subscript letter represents the toner amount (Mass), and the second on the left The small letter “b” represents the intermediate transfer belt, and the small letter “p” represents the recording paper. Further, “M” on the right side of the subscript English letter represents M toner, and “Y” on the right side represents Y toner. Hereinafter, the meaning of the symbols shown in the above formula (2) and the following also conforms to the above-described content. Hereinafter, the toner superposition is also simply referred to as “color superposition”.

On the other hand, Mp ′ _M , which is the amount of M toner on the recording paper P after secondary transfer at the time of color superposition,
Mp ′ _M = Mb _M.

Assuming that the amount of Y toner on the recording paper P after secondary transfer during color superposition is Mp ′ _Y , the above equation (2) is
Mp ′ _Y = Mb _Y × (α / 100) − (1−α / 100) × Mb _M
It is expressed.
Mp ′ _Y , which is the amount of Y toner on the recording paper P after the secondary transfer in a single color,
Since Mp ′ _Y = Mb _Y × (α / 100) and 0 <α <100, the amount of Y toner on the recording paper P after the secondary transfer at the time of color superposition is after the secondary transfer at the time of a single color. Is smaller than the amount of Y toner on the recording paper P by (1−α / 100) × Mb _M.

  On the recording paper P when a toner image is formed with a single photoconductor (single color) and when an image is formed by overlapping toner images created with a plurality of M and Y photoconductors (when M & Y is overlaid) Table 1 below summarizes the amount of adhesion.

  In the present invention, the case where an image is formed from a toner image created with a single photoconductor in this way is different from the case where an image is formed by superimposing toner images created with a plurality of photoconductors. Correction is performed by image processing so that the toner adhesion amount on the recording paper becomes constant. Specifically, the dot coverage (image area ratio) is corrected so that the amount of toner adhesion on the recording paper that has increased or decreased compared to the case of single color during color superposition will be the same amount of toner adhesion as in the case of single color. It is. Here, “dot coverage” represents the proportion of dots (toner) per certain area.

The control configuration of the main part of the first embodiment will be described with reference to FIG. 3A. As shown in FIG. 3A, the printer of this embodiment includes an image processing correction device 10. The image processing correction device 10 corrects dot coverage based on the input image information (image data signal) and executes a control flow relating to image data development shown in FIG. 3B. The image processing correction device 10 functions as a first correction unit that performs correction different from the image processing in the case of forming an image with a single toner image when an image is formed by superimposing a plurality of toner images. In addition, it has the functions described later. The image processing correction apparatus 10 includes, for example, a microcomputer including a CPU, an I / O (input / output) port, a ROM, a PROM, a RAM, a timer, and the like, which are connected by a signal bus. The ROM or PROM stores in advance a program (for example, the flowchart of FIG. 3B) and related data (for example, dot coverage) for exhibiting the arithmetic and control functions of the CPU. The PROM may be configured to be changed and set based on an appropriate request from the user or the like.
The image data as the image information relates to an image mode transmitted from, for example, a computer such as a personal computer connected externally, an image reading apparatus / scanner appropriately disposed in a printer, or an operation display unit appropriately disposed. Data (mixed color image or single color image) and the like are included.

The control flow of the first embodiment will be described with reference to FIG. 3B. When image data expansion is started and image data as image information is sent to the image processing correction apparatus 10 in the printer, the image data is expanded into four colors Y, M, C, and K as shown in FIG. 3A. The dot coverage for each color is determined. In step S1, it is determined whether the image is a color overlay or a single color. If yes, it is determined whether or not the toner image (color) is first transferred to the intermediate transfer belt (step S2). In the case of No which is a single color, the control is terminated. In the case of YES, which is the toner image that is first transferred to the intermediate transfer belt, as described above, the amount of toner remaining on the intermediate transfer belt as the transfer residual toner is larger than that in single color printing. Will decrease. In anticipation of this decrease, the amount of toner placed on the intermediate transfer belt is increased by increasing dot coverage (step S3).
On the other hand, in step S2, when the color is superimposed and the toner image (color) that is first transferred to the intermediate transfer belt is NO, as described above, the amount remaining on the intermediate transfer belt as the transfer residual toner is monochromatic printing. Compared to less. As a result, the amount of toner transferred onto the recording paper increases. In anticipation of this increase, the amount of toner placed on the intermediate transfer belt is reduced by reducing dot coverage (step S4).

How to correct the dot coverage will be described below with a specific example. In Table 1 above, the toner adhesion amount on the recording paper for the single color and the M & Y overlap is shown for each of the M toner and Y toner. If the dot coverage of M toner and Y toner at the time of single color is DC _M and DC _Y , respectively, the dot coverage of M toner and Y toner at the time of color superposition may be corrected by the change shown in Table 1 above. Specifically, the following expressions (3) and (4) are obtained. The corrected dot coverages are DC ′ _M and DC ′ _Y , respectively, the toner adhesion amounts on the recording paper at the time of single color are Mp _M and Mp _Y, and the toner adhesion amounts on the recording paper at the time of color superposition are Mp ′ _M and Mp ′ _Y. When the toner adhesion amount on the intermediate transfer belt is Mb _M and Mb _Y ,
DC ′ _M = DC _M × Mp _M / Mp ′ _{M
= DC M × (Mb M ×} α / 100) / Mb M ··· (3)
DC ′ _Y = DC _Y × Mp _Y / Mp ′ _Y
= DC _Y × (Mb _Y × α / 100) / (Mb _Y × α / 100−
(1-α / 100) × Mb _M ) (4)

As described above, the dot coverage after correction can be calculated using Mb _M , Mb _Y , and α, which are known values. In addition, although the example using the photosensitive member and the developing device as two image carriers has been described, the invention is not limited thereto, and the same applies to three or more photosensitive members and developing devices using toner of three or more colors. Of course, it is possible to calculate the corrected dot coverage.

  As described above, according to the present embodiment, when a plurality of colors are overlaid using a photosensitive member and a developing device as a plurality of image carriers, the target toner adhesion amount is deviated due to the influence of the secondary transfer efficiency. Since the correction is performed, it is possible to provide an image forming apparatus having a stable color.

1st Embodiment described above is an example of this invention, and this invention has an effect peculiar to every following aspect.
[Aspect 1]
A plurality of image carriers such as photoreceptors 3Y, 3M, 3C, and 3K, charging devices 5Y, 5M, 5C, and 5K for charging the surface of the image carrier, and the surface of the image carrier are exposed. Exposure units such as optical writing units 1YM and 1CK that form an electrostatic latent image, and developing devices 4Y, 4M that supply a developer to the electrostatic latent image formed on the surface of the image carrier to form a visible image. Development means such as 4C and 4K, and primary transfer rollers 62Y, 62M, 62C, and 62K that primarily transfer a visible image formed on the surface of the image carrier to an intermediate transfer body such as the intermediate transfer belt 61. A secondary transfer unit that has a transfer unit and a secondary transfer rotating member such as a secondary transfer roller 72 that contacts the intermediate transfer member, and that secondarily transfers a visible image on the intermediate transfer member to a recording medium such as recording paper P. Secondary transfer means such as 70, and the secondary transfer rotating body and the inside An image forming apparatus configured to transfer a visible image on an intermediate transfer body to a recording medium when the recording medium is passed through a contact portion such as a secondary transfer nip with the transfer body. An image processing correction device that performs correction different from the image processing in the case of forming an image with a toner image created with a single image carrier when forming an image by superimposing toner images created with a body First correction means such as 10 is provided.
According to this aspect 1, as described in the above embodiment, the amount of toner to be secondarily transferred differs between the case of forming an image with a single toner image and the case of forming an image with a plurality of toner images. Since the color variation due to this is corrected by performing image processing, stable image output becomes possible.

[Aspect 2]
In [Aspect 1], the image processing is dot coverage.

[Aspect 3]
In [Aspect 1] or [Aspect 2],
The first correction unit corrects the image processing of the toner image first transferred to the intermediate transfer body among the toner images created by the plurality of image carriers.

[Aspect 4]
In [Aspect 3], when the first correction unit forms an image by superimposing toner images created by a plurality of image carriers, the first correction unit displays an image using a toner image created by a single image carrier. The image processing is corrected so that the toner adhesion amount is increased as compared with the case of forming.

[Aspect 5]
In any one of [Aspect 1] to [Aspect 4], the first correction unit includes a toner image created by a plurality of image carriers other than the toner image first transferred to the intermediate transfer member. Correction is applied to the image processing of the toner image.

[Aspect 6]
In [Aspect 5], in the case of forming an image by superimposing toner images created by a plurality of image carriers, compared to the case of forming an image by a toner image created by a single image carrier, Image processing is corrected so as to reduce the toner adhesion amount.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS.
The object of the invention according to the second embodiment has been made in view of the above-mentioned problems of the background art according to the present invention. When forming an image with a single toner image, a plurality of toner images are superimposed. In other words, the image quality in the case of forming an image is made compatible. In other words, an object of the present invention is to provide an image forming apparatus capable of stabilizing the toner adhesion amount on a recording medium even when an image is formed by superimposing a plurality of toner images.

  First, the configuration of a printer as an image forming apparatus according to the second embodiment will be described with reference to FIG. FIG. 4 is a schematic configuration diagram of a printer as an image forming apparatus according to the second embodiment. The printer according to the second embodiment shown in FIG. 4 uses a secondary transfer device 71 instead of the secondary transfer unit 70 as compared with the printer according to the first embodiment shown in FIG. The main difference is that the arrangement position is changed to the secondary transfer device 71 and a control configuration described later is used. Other than these differences, the second embodiment is the same as the first embodiment. Hereinafter, the second embodiment will be described in detail with a focus on differences from the first embodiment.

  The secondary transfer device 71 is installed below the intermediate transfer belt 61 in FIG. 4 and functions as a secondary transfer unit in the second embodiment. The secondary transfer device 71 includes a secondary transfer roller 72, a secondary transfer belt 77, a secondary transfer drive roller 73, a secondary transfer bias power source 28 and a secondary transfer belt cleaning device 76 shown in FIG. . The secondary transfer belt 77 is made of the same material as the intermediate transfer belt 61 and is stretched between the secondary transfer roller 72 and the secondary transfer drive roller 73. From the front surface of the intermediate transfer belt 61, a secondary transfer roller 72 is in contact with the intermediate transfer belt 61 via a secondary transfer belt 77 to form a secondary transfer nip. As a result, a secondary transfer nip where the front surface of the intermediate transfer belt 61 and the secondary transfer belt 77 abut is formed. In the present embodiment, the secondary transfer belt 77 functions as a secondary transfer rotator.

  A secondary transfer bias is applied to the secondary transfer roller 72 by a secondary transfer bias power source 28 shown in FIG. On the other hand, the secondary transfer backup roller 68 in the loop of the intermediate transfer belt 61 is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip. In this printer, when the recording paper P is passed through a secondary transfer nip that is a contact portion between a secondary transfer belt 77 as a secondary transfer rotating body and an intermediate transfer belt 61 as an intermediate transfer body, the intermediate transfer belt 61 is passed. The upper visible image is transferred to the recording paper P.

  In the secondary transfer device 71, a toner adhesion amount sensor 64, which is a reflective optical sensor having the same configuration as that described in the first embodiment, is disposed to face the secondary transfer belt 77. The reflective optical sensor has a light emitting element and a light receiving element, and light emitted from the light emitting element is reflected by a toner patch (not shown) as a test pattern created on the secondary transfer belt 77. The light receiving element receives the light and converts it into a signal. By reading the change in the signal, the test pattern information is inferred to detect the amount of toner patch adhesion. The toner on the secondary transfer belt 77 is cleaned by the secondary transfer belt cleaning device 76. The toner adhesion amount sensor 64 functions as a test pattern detection unit that detects a test pattern.

The printer of the second embodiment includes test pattern forming means for forming a test pattern for inspecting image characteristics on the surfaces of the photoreceptors 3Y, 3M, 3C, and 3K, the above-described toner adhesion amount sensor 64, and its test. Image forming condition correcting means for correcting the image forming condition based on the pattern detection result.
The test pattern forming method is basically the same as the above-described image forming operation, and is formed on the surfaces of the photoreceptors 3Y, 3M, 3C, and 3K at a predetermined timing according to instructions from the overall control unit of the printer. That is, the test pattern forming means includes the process units 2Y, 2M, 2C, and 2K, the optical writing units 1YM and 1CK shown in FIG. 4, and the overall control unit that controls them.
The image forming condition correction unit is configured by, for example, an overall control unit (not shown) of the printer. The overall control unit is configured to optimally control image forming conditions (parameters) such as a developing bias, a charging bias, and a laser exposure power based on data obtained by detecting a test pattern.

  Test patterns (not shown) formed on the photoreceptors 3Y, 3M, 3C, and 3K are formed on the intermediate transfer belt 61 at the primary transfer nip where the photoreceptors 3Y, 3M, 3C, and 3K are in pressure contact with the intermediate transfer belt 61. Is transcribed. Next, the test pattern transferred onto the intermediate transfer belt 61 is transferred to the secondary transfer belt 77 at a secondary transfer nip where the intermediate transfer belt 61 and the secondary transfer roller 72 are in pressure contact with each other.

The control configuration of the main part of the second embodiment will be described with reference to FIG. The printer of this embodiment includes a transfer bias correction device 20 shown in FIG. The transfer bias correction device 20 passes through the transfer bias control device 21 based on input image information (image data signal) and information (data signal) related to each test pattern detection result from the toner adhesion amount sensor 64. The primary transfer bias power source 27 and the secondary transfer bias power source 28 are controlled. The transfer bias correction device 20 includes, for example, a microcomputer including a CPU, an I / O (input / output) port, a ROM, a PROM, a RAM, a timer, and the like, which are connected by a signal bus. The ROM and PROM calculate a program (flowchart in FIG. 6 and timing chart in FIG. 7) and related data (primary and secondary transfer bias correction values) for demonstrating the arithmetic and control functions of the CPU. Calculation formulas, fixed data, etc.) are stored in advance. The transfer bias control device 21 may also include the above-described microcomputer. Of course, the control performed by either or both of the transfer bias correction device 20 and the transfer bias control device 21 may be performed by the overall control unit of the printer.
In FIG. 5, the data signal input from the toner adhesion amount sensor 64 relates to the adhesion amount of a toner patch (not shown) as a test pattern created on the secondary transfer belt 77 as described above. Data. The toner adhesion amount sensor 64 may be configured to be connected to the transfer bias correction device 20 via the overall control unit.
Note that image information indicated by a one-dot chain line input to the transfer bias controller 21 is for a third embodiment to be described later.

  The transfer bias correction device 20 calculates a primary transfer bias correction value as a primary transfer condition and a secondary transfer bias correction value as a secondary transfer condition in a control flow as shown in FIG. The transfer bias correction device 20 is operated when the printer is turned on or after printing a predetermined number of sheets, and updates the primary and secondary transfer bias correction values. It is executed exclusively with the printing operation for forming an image on a recording sheet. The transfer bias correcting device 20 includes a primary transfer condition of the primary transfer unit and a secondary transfer unit in a case where an image is formed by superimposing a plurality of toner images and an image is formed using a single toner image. It functions as a second correction unit that corrects at least one of the secondary transfer conditions.

As shown in FIG. 6, the transfer bias correction device 20 calculates correction values for the primary transfer bias and the secondary transfer bias in the order of magenta (M) and yellow (Y). In FIG. 6 and the following description, “pattern” means a test pattern. Hereinafter, specifically, the primary transfer current refers to the primary transfer bias, and the secondary transfer current refers to the secondary transfer bias.
First, in step S5, a magenta (M) single-color solid pattern and a cyan (C) single-color solid pattern are created by the photoconductors 3M and 3C as described above, and then the intermediate transfer belt 61 is formed at the primary transfer nip. Primary transfer.
Next, each of the patterns transferred to the intermediate transfer belt 61 is secondarily transferred to the secondary transfer belt 77 at the secondary transfer nip. Then, the toner adhesion amount sensor 64 detects the toner adhesion amounts of the magenta (M) single-color solid pattern and the cyan (C) single-color solid pattern, and the magenta (M) toner adhesion amount (M ) And cyan (C) toner adhesion amount (C).

Next, primary transfer is performed to the intermediate transfer belt 61 at the primary transfer nip so that the magenta (M) pattern and the cyan (C) pattern created by the photoconductors 3M and 3C are superimposed, and further at the secondary transfer nip. Secondary transfer is performed on the secondary transfer belt 77. The toner adhesion amount sensor 64 detects the toner adhesion amount of the two-color mixed pattern in which the magenta (M) and cyan (C) patterns are superimposed, and obtains the toner adhesion amount (MC) of the two-color mixed pattern (step). S6).
Whether the primary transfer bias and the secondary transfer bias need to be corrected based on the toner adhesion amount (M), toner adhesion amount (C), and toner adhesion amount (MC) of the two-color mixed pattern detected in steps S5 and S6. Is determined by the following judgment formula (5).
{Toner adhesion amount (M) + toner adhesion amount (C)} × α> toner adhesion amount (MC) (5)
Here, α is a correction determination threshold value, takes a numerical value of 0 to 1, and is set to 0.95 in this embodiment. α is a value determined in advance for each image forming apparatus, and is an allowable value for executing correction.

  When the determination formula (5) is satisfied, it is determined that correction is necessary. This is a case where α times the total of the two color toner adhesion amounts for each single color is larger than the toner adhesion amount (MC) when two colors are superimposed. In other words, when the secondary transfer efficiency drops when two colors are overlaid and the residual toner of magenta (M) becomes large, correction is performed to increase the secondary transfer efficiency of magenta (M). To do. Specifically, the primary transfer bias color overlap correction value (M) is determined to be smaller than the primary transfer bias single color correction value (M) for magenta (M) single color. The secondary transfer bias color overlay correction value (MC) is determined to be larger than the secondary transfer bias single color correction value (M).

By setting the primary transfer bias small, the electric field received by the magenta (M) toner during the primary transfer is reduced, and the force received by the toner is reduced, so that the adhesion force between the intermediate transfer belt 61 and the toner is reduced. Secondary transfer efficiency is improved. Therefore, the color where the toner does not contact the intermediate transfer belt 61 has little effect even if the primary transfer bias is set small. For this reason, the correction of the primary transfer bias is performed on the color toner first transferred to the intermediate transfer belt 61. By setting the secondary transfer bias large, the transfer electric field at the secondary transfer nip increases, so that the secondary transfer efficiency at the time of superimposing two colors is improved. However, if the secondary transfer bias is increased too much, the secondary transfer efficiency is decreased due to the influence of discharge during single-color transfer, and therefore it is desirable to perform an upper limit process for the secondary transfer bias.
After the primary transfer bias color overlay correction value (M) and the secondary transfer bias color overlay correction value (MC) are determined, the same processing is performed for magenta (M) and yellow (Y) (step). S8 to step S10). At this time, the value determined immediately before is used as the primary transfer bias color superposition correction value (M) when two colors are superposed. In this manner, the transfer bias correction device 20 determines correction values for the primary transfer bias and the secondary transfer bias during color superposition.

Next, a method for switching the transfer bias during image formation will be described. In the present embodiment, the transfer bias control device 21 shown in FIG. 5 is provided, and the transfer bias control device 21 switches the transfer bias during image formation. The transfer bias control device 21 switches the transfer bias during image formation based on the image information and the primary / secondary transfer bias information determined by the transfer bias correction device 20. “During image formation” means, for example, that the primary / secondary transfer bias, which is a transfer condition, is switched within the same page.
Since the transfer bias can only have the same value in the sub-scanning direction, if there is single-color image data and color-superimposed image data depending on the position in the main-scanning direction, the transfer bias for either single color or color superposition should be used. It is necessary to judge whether or not. In this embodiment, when a single color pattern and a color superposition pattern coexist depending on the position in the main scanning direction, a transfer bias for color superposition is used. The sub-scanning direction is also the conveyance direction of the recording medium, and the main scanning direction means a width direction orthogonal to the conveyance direction of the recording medium.

  A transfer bias changing method will be described with reference to FIG. The upper part of FIG. 7 shows a print image PA, which is an image composed of a magenta (M) single color pattern and a magenta (M) + cyan (C) color overlap pattern. The middle and lower stages of FIG. 7 indicate the primary / secondary transfer bias at each time, and the time is corrected at the timing when the print image passes. Actually, the timing at which the head of the magenta (M) pattern passes differs between the primary transfer nip and the secondary transfer nip, but the horizontal axis is corrected so as to be the same timing T1. In the case where there is no pattern or a magenta (M) single color pattern, the primary transfer bias (M) and the secondary transfer bias for magenta (M) are the biases for single color. The primary transfer bias (M) and the secondary transfer bias are changed to biases for color superposition at timing T2 when the head of the color superposition pattern of magenta (M) + cyan (C) reaches each transfer nip. Thereafter, the bias for color superposition is maintained at the timing when the magenta (M) single color pattern disappears, and is returned to the bias for single color at timing T3 when the rear end of the color superposition pattern passes through each transfer nip. At this time, the primary transfer bias (C) for cyan (C) is set to a constant value regardless of the single color pattern and the color overlapping pattern. Thus, by changing the primary / secondary transfer bias to the optimum value according to the image pattern of the print image, a high-quality image can be provided.

  As described above, according to the present embodiment, by changing the transfer condition between the single color and the color overlay, it is possible to transfer to the recording medium under the optimum transfer condition. Images can be provided.

(Third embodiment)
A third embodiment of the present invention will be described with reference to FIGS. 1 and 5 to 7.
The object of the invention according to the third embodiment has been made in view of the above-mentioned problems of the background art according to the present invention. In the case of forming an image with a single toner image, a plurality of toner images are superimposed. In other words, the image quality in the case of forming an image is made compatible.

The basic configuration of a printer as an image forming apparatus according to the third embodiment is the same as that shown in FIG. In this printer, when the recording paper P is passed through the secondary transfer nip, which is a contact portion between the secondary transfer roller 72 and the intermediate transfer belt 61, as in the first embodiment described above, The visible image is transferred to the recording paper P.
The third embodiment is mainly different from the second embodiment in that the transfer bias correction device 20 is removed from the control configuration of the second embodiment shown in FIG. The configuration of the third embodiment other than this difference is the same as that of the second embodiment.

In this embodiment, since the transfer bias correction device 20 is not provided, the toner adhesion amount detection by the toner adhesion amount sensor 64 is not performed. In the present embodiment, the transfer bias control device 21 functions as a second correction unit. Therefore, unnecessary waiting time for the user can be reduced. The transfer bias for color superposition is determined in advance by performing a test or the like in advance, and is stored in advance in the ROM of the transfer bias controller 21 or the like. By doing so, it is possible to provide a high-quality image by changing the transfer bias for single color and color superposition to the optimum values according to the image pattern of the print image without waiting time. it can. In other words, each image can be transferred to a recording medium under optimum transfer conditions, so that a good image can be obtained regardless of toner overlap.
Note that the specific configuration and effects of the third embodiment can be easily understood and implemented by those skilled in the art from the details described in the second embodiment. Therefore, further explanation is omitted from the point of avoiding duplicate explanation.

The second and third embodiments described above are examples of the present invention, and the present invention has a unique effect for each of the following modes.
[Aspect 7]
A plurality of image carriers such as photoreceptors 3Y, 3M, 3C, and 3K, charging devices 5Y, 5M, 5C, and 5K for charging the surface of the image carrier, and the surface of the image carrier are exposed. Exposure units such as optical writing units 1YM and 1CK that form an electrostatic latent image, and developing devices 4Y, 4M that supply a developer to the electrostatic latent image formed on the surface of the image carrier to form a visible image. Development means such as 4C and 4K, primary transfer means such as a primary transfer roller 62 that primarily transfers a visible image formed on the surface of the image carrier onto an intermediate transfer body such as the intermediate transfer belt 61, and intermediate transfer Secondary transfer such as a secondary transfer device 71 having a secondary transfer rotating body such as a secondary transfer belt 77 in contact with the body and secondary transferring a visible image on the intermediate transfer body to a recording medium such as recording paper P And a secondary transfer nib between the secondary transfer rotating body and the intermediate transfer body. An image forming apparatus configured to transfer a visible image on an intermediate transfer body to a recording medium when the recording medium is passed through a contact portion such as a toner image created by a plurality of image carriers. The primary transfer condition of the primary transfer unit and the secondary transfer condition of the secondary transfer unit in the case of forming an image by superimposing and the case of forming an image with a toner image created by a single image carrier And a second correction means such as a transfer bias control device 21 for correcting at least one of them.
According to Aspect 7, as described in the above embodiment, the above configuration allows transfer onto a recording medium under optimum primary / secondary transfer conditions, respectively, so that a good image can be obtained regardless of toner superposition. It is done.

[Aspect 8]
In [Aspect 7], the process units 2Y, 2M, 2C, and 2K, the optical writing units 1YM and 1CK, and the overall control unit that form a test pattern for inspecting the image characteristics on the surface of the image carrier. Image forming such as the configured test pattern forming means, the test pattern detecting means such as the toner adhesion amount sensor 64 for detecting the test pattern, and the overall control section for correcting the image forming condition based on the detection result of the test pattern. And a condition correction unit configured to transfer the test pattern formed on the image carrier to the intermediate transfer member, and to transfer the test pattern on the intermediate transfer member to the secondary transfer rotating member. The test pattern transferred to the transfer rotator is detected by the test pattern detection means, and the test pattern detection means Based on known results, when forming an image with a toner image created with a single image carrier and when forming an image by superimposing toner images created with a plurality of image carriers. Second correction means such as a transfer bias correction device 20 for correcting at least one of the primary transfer condition and the secondary transfer condition is provided.
According to this aspect, as described in the above embodiment, each of the above structures can be transferred to a recording medium under optimum transfer conditions, so that a good image can be obtained regardless of toner superposition. Furthermore, since the optimum transfer conditions are fed back by the test pattern detection means, more accurate conditions can be calculated.

[Aspect 9]
In [Aspect 8], a test pattern created by a single image carrier and a test pattern formed by superimposing test patterns created by a plurality of image carriers are detected by a test pattern detection unit, and the test pattern is detected. Based on the result detected by the detection means, at least one of the primary transfer condition and the secondary transfer condition is corrected.
According to this aspect, as described in the above embodiment, with the above-described configuration, more accurate primary / secondary transfer conditions can be calculated, and a good image can be obtained regardless of toner superposition. It is done.

[Aspect 10]
In [Aspect 7], the toner adhesion amount per unit area when the toner images are superimposed on a plurality of image carriers is the toner adhesion amount per unit area when the toner image is formed on a single image carrier. When the value exceeds the maximum value, at least one of the primary transfer condition and the secondary transfer condition is corrected.
According to this aspect, as described in the above embodiment, with the above configuration, the correction can be performed only when the optimal primary / secondary transfer conditions are changed. An image is obtained.

[Aspect 11]
In [Aspect 7] or [Aspect 8], the primary transfer condition of the toner image first transferred to the intermediate transfer member among the toner images created by the plurality of image carriers is corrected.
According to this aspect, as described in the above embodiment, the above-described configuration can correct the toner adhesion state that is easily affected by a decrease in secondary transfer efficiency, so that a good image can be obtained regardless of toner superposition. It is done.

[Aspect 12]
In any one of [Aspect 7] to [Aspect 9], when toner images are overlapped with a plurality of image carriers, primary transfer is performed as compared with a case where a toner image is formed with a single image carrier. The primary transfer current as a condition is lowered.
According to this aspect, as described in the above embodiment, by reducing the primary transfer current, the adhesive force between the intermediate transfer member and the toner can be reduced. can get.

[Aspect 13]
In any one of [Aspect 7] to [Aspect 10], when the toner images are overlapped with a plurality of image carriers, the secondary transfer conditions are compared with the case where the toner images are formed with a single image carrier. As a secondary transfer current.
According to this aspect, by increasing the secondary transfer current, it is possible to maintain the secondary transfer efficiency at the time of superimposition, so that a good image can be obtained regardless of toner superposition.

(Fourth embodiment)
A fourth embodiment of the present invention will be described with reference to FIGS. 1, 2, 8, and 9.
In an electrophotographic image forming apparatus, when the power is turned on, before starting printing, after printing a predetermined number of sheets (for example, 500 sheets), after printing, etc., process control is executed periodically to keep the toner adhesion amount constant. It is controlled. In this process control, a plurality of single-color toner patterns having different densities are formed, and the electrostatic latent image potential, the adhesion amount, and the like of each pattern are detected. Thereby, it is possible to give image forming conditions such as a charging bias, a developing bias, and an exposure amount so that the solid toner adhesion amount becomes a target value.
The object of the invention according to the fourth embodiment has been made in view of the above-mentioned problems of the background art according to the present invention, and the toner on the recording medium is formed even when a plurality of toner images are superimposed to form an image. An object of the present invention is to provide an image forming apparatus capable of stabilizing the adhesion amount. In particular, the present invention has been made to solve the problem that the color superposition toner adhesion amount in the image forming unit (process unit) on the upstream side is lowered due to the influence of the secondary transfer.

  The basic configuration of a printer as an image forming apparatus according to the fourth embodiment is the same as that shown in FIG. In this printer, when the recording paper P is passed through the secondary transfer nip, which is a contact portion between the secondary transfer roller 72 and the intermediate transfer belt 61, as in the first embodiment described above, The visible image is transferred to the recording paper P.

A control configuration of a main part of a printer as an image forming apparatus according to the fourth embodiment will be described with reference to FIG. As shown in FIG. 8, a potential control device 23 is provided as one of image density control means. The potential control device 23 includes, for example, a microcomputer including a CPU, an I / O (input / output) port, a ROM, a PROM, a RAM, a timer, and the like, which are connected by a signal bus. In the ROM and PROM, there are a program (flowchart in FIG. 9) for demonstrating the arithmetic and control functions of the CPU and related data (calculation formulas and fixed data for changing / correcting image forming conditions). Stored in advance.
The potential control device 23 also has a function as the third correcting means of the present invention. The potential control device 23 periodically executes image density control exclusive of printing operations such as when the power is turned on, before printing is started, after printing a predetermined number of sheets (for example, 500 sheets), after printing is completed. The control of the potential control device 23 may be executed by the overall control unit described above.

  The potential sensor 24 measures the potential of an electrostatic latent image of a plurality of test patterns having different densities (hereinafter also simply referred to as “patterns” or “toner patterns”) formed on the photoreceptors 3Y, 3M, 3C, and 3K. Is. The toner adhesion amount sensor 64 detects the adhesion amount of the pattern on the intermediate transfer belt 61 as described above. The toner density sensor 25 corresponds to the time when the potential of the electrostatic latent image is measured by the potential sensor 24 and the time when the toner adhesion amount sensor 64 detects the adhesion amount of the toner pattern on the intermediate transfer belt 61. , 4C, and 4K toner densities are detected.

  The potential control device 23 includes a detection value detected by the toner adhesion amount sensor 64, a toner concentration detected by the toner concentration sensor 25, a surface potential after exposure of the photosensitive member detected by the potential sensor 24, and a developing bias. And the target adhesion amount and image information are input. Based on the above input data, the potential controller 23 applies charging bias to the charging devices 5Y, 5M, 5C, 5K, developing bias to the developing devices 4Y, 4M, 4C, 4K, and optical writing units 1YM, 1CK. The exposure amount and the toner density control target value are output. In the printer of this embodiment, a stable image density is obtained by controlling each bias and toner supply in accordance with the optimum image forming conditions by the potential control device 23.

  The fourth embodiment and the control flow will be described with reference to FIG. In an image forming apparatus to which the present invention is applied, in order to stabilize the toner adhesion amount on a recording medium of a superimposed image of a plurality of toner images (hereinafter also referred to as “mixed color image”), for example, In this way, image density stabilization control is performed. First, a printer (potential control device 23) as an image forming apparatus acquires image information (step S20). Next, the process proceeds to step S21, and it is determined whether or not the image information is a mixed color image. At this time, in the case of a monochromatic image, the control is terminated, and in the case of a mixed color image, a determination is made as to whether or not control execution of image forming condition (image forming condition) correction is necessary (step S22). A specific method for determining whether or not to perform image forming condition correction will be described later with reference to FIG. 2 in the fourth embodiment and FIG. 10 with respect to a fifth embodiment to be described later. If it is determined that control execution is unnecessary, the control is terminated.

  On the other hand, if it is determined that control execution is necessary, the process proceeds to step S23 to calculate the image forming condition correction amount. In the image forming apparatus to which the present invention is applied, the image forming conditions (image forming conditions) to be corrected at this time are exposure conditions and exposure amounts. The exposure condition / exposure correction amount is set to such a value that the toner adhesion amount of the mixed color image becomes the target value. Further, the correction amount of the exposure condition may be changed according to image information such as dot coverage, toner density, time, environment, or the like, or the correction amount may be changed depending on the position in the same image. The image forming apparatus corrects the exposure condition by the exposure condition correction amount determined as described above, that is, changes the exposure condition during printing (step S24).

In the image forming apparatus configured to detect the test pattern (not shown) on the intermediate transfer belt 61 as shown in FIG. 1, the toner adhesion amount is stabilized by using the process control by the control configuration shown in FIG. It is as follows. That is, as described with reference to a specific example in FIG. 2, as shown in FIG. 2A, first, Y toner adheres, and M toner adheres in an overlapping state thereon. The toner on the intermediate transfer belt 61 is conveyed to the secondary transfer unit 70 and transferred onto the recording paper P. At this time, as shown in FIG. 2B, the Y toner on the intermediate transfer belt 61 side is transferred. Residual toner remains on the intermediate transfer belt 61. Therefore, in order to achieve a desired toner adhesion amount on the recording paper P, a larger amount of toner adheres on the intermediate transfer belt 61 at a constant rate than the target toner adhesion amount on the recording paper P. The target adhesion amount of the intermediate transfer belt 61 is controlled.
Here, if the target toner adhesion amount on the recording paper P is Mp [mg / cm ² ] and the secondary transfer efficiency, which is the ratio of toner that can be transferred onto the recording paper P by secondary transfer, is α [%], The target adhesion amount Mb [mg / cm ² ] on the transfer belt 61 is expressed by the following formula (1) as described above.
Mb = Mp / (α / 100) (1)

  In the image forming apparatus to which the present invention is applied, the secondary transfer efficiency α is determined in advance, and the target value Mb of the test pattern on the intermediate transfer member is determined by calculating back from the desired toner adhesion amount on the recording medium. ing. It is known that the secondary transfer efficiency varies depending on various conditions such as the environment such as temperature and humidity, and the charging state of the toner. However, the secondary transfer efficiency is stabilized by correcting the secondary transfer current depending on the temperature and humidity. New inventions have also been published. As described above, when a toner image is created by a single photoconductor / developing device, the toner adhesion amount on the recording paper can be stabilized by stabilizing the adhesion amount on the intermediate transfer belt. However, even when stable secondary transfer efficiency is achieved, when an image is formed by superimposing a plurality of toner images, the image is transferred to a recording medium as compared with a case where an image is formed with a single toner image. The adhesion amount of the toner image varies.

  Specifically, as illustrated in FIG. 2, the first toner image (for example, Y toner created by the photoreceptor 3 </ b> Y) first transferred to the intermediate transfer belt 61 is another photoreceptor (for example, the photoreceptor). A second toner image (for example, M toner) created by 3M) is overlaid. This overlapped toner image is transferred onto the recording paper P in the secondary transfer step, but most of the second toner image (for example, M toner) on the recording paper P side is transferred onto the recording paper P. On the other hand, the first toner image (for example, Y toner) on the intermediate transfer belt 61 side remains on the intermediate transfer belt 61 under the influence of the secondary transfer efficiency. As described above, even when the toner image on the intermediate transfer body is stabilized from a single toner image by calculating backward from the secondary transfer efficiency, when a plurality of toner images are formed to form an image, the image is formed on the recording medium. The amount of toner transferred changes.

  Therefore, in this embodiment, the potential control device 23 changes and corrects the image forming conditions between the case where an image is formed by superimposing a plurality of toner images and the case where an image is formed using a single toner image. It is configured to apply. The image forming conditions for printing the color superimposed image are corrected from the time of printing the single color image based on the image data, and the toner image of the mixed color image on the recording medium is stabilized. Therefore, according to the present embodiment, it is possible to provide an image forming apparatus capable of stabilizing the toner adhesion amount on the recording paper even when an image is formed by superimposing a plurality of toner images.

  Further, the execution determination of the correction in the present embodiment is determined to be necessary only when it is determined that the toner adhesion amount at the time of mixed color printing is larger than the maximum toner adhesion amount at the time of monochrome printing. That is, when the toner adhesion amount per unit area when a plurality of toner images are superposed is larger than the maximum toner adhesion amount per unit area when a single toner image is formed, the image forming condition Apply correction to.

  Further, the correction of the image forming condition in the present embodiment is performed by correcting the image forming condition of the toner image first transferred to the intermediate transfer member in the process unit (image forming unit) constituting the mixed color image. . This is because, as shown in FIG. 2, when the adhesion amount is reduced at the time of creating the mixed color image, the adhesion amount of the toner image (toner image located on the upper side of the recording paper) first transferred to the intermediate transfer member is reduced. Therefore, the image forming conditions of the toner image first transferred to the intermediate transfer member are corrected. That is, the image forming conditions of the toner image first transferred to the intermediate transfer member among the plurality of toner images are corrected.

  Further, the correction in the present embodiment is performed so that the toner adhesion amount is increased as compared with the case of forming an image with a single toner image in order to compensate for the adhesion amount of the transfer residual toner. That is, when a plurality of toner images are overlapped, the image forming conditions are corrected so that the amount of toner adhesion is larger than when a single toner image is formed.

  Further, in the correction of the image forming conditions in the present embodiment, the exposure conditions are corrected. That is, the correction of the image forming condition is correction of the exposure amount of the exposure unit. Therefore, according to the present embodiment, even when a mixed color image portion and a single color image portion exist at the same time or when images with different dot coverage exist at the same time in the main scanning direction, the exposure condition is changed according to the image location. it can. Therefore, compared with the case where the charging condition and the development condition are changed, the toner adhesion amount of the mixed color image can be maintained at the target value while the toner adhesion amount of the single color image is maintained at the target value.

  Further, the correction amount of the image forming condition may be a value that makes the toner adhesion amount of the mixed color image a target value, and may be changed depending on image information such as dot coverage, toner density, time, environment, and the like. In the present embodiment, an example of correcting the image forming condition of a two-color superimposed image has been described. However, the present invention can be similarly applied to a case where three or more colors are superimposed.

  As described above, according to the present embodiment, it is possible to provide an image forming apparatus capable of stabilizing the toner adhesion amount on a recording medium even when an image is formed by superimposing a plurality of toner images. it can.

(Fifth embodiment)
A fifth embodiment of the present invention will be described with reference to FIGS. 4 and 8 to 11.
The object of the invention according to the fifth embodiment has been made in view of the above-mentioned problems of the background art according to the present invention. Even when a plurality of toner images are superimposed to form an image, the toner on the recording medium is used. An object of the present invention is to provide an image forming apparatus capable of stabilizing the adhesion amount. In particular, the present invention has been made to solve the problem that the color superposition toner adhesion amount in the image forming unit (process unit) on the upstream side is lowered due to the influence of the secondary transfer.

  The basic configuration of a printer as an image forming apparatus according to the fifth embodiment is the same as that of the second embodiment shown in FIG. In this printer, when the recording paper P is passed through the secondary transfer nip, which is a contact portion between the secondary transfer belt 77 and the intermediate transfer belt 61, as in the second embodiment described above, The visible image is transferred to the recording paper P. Further, when the process control described with reference to FIG. 8 is executed, a toner image including a test pattern can be transferred onto the secondary transfer belt 77, and the toner adhesion amount on the secondary transfer belt 77 can be determined based on the toner adhesion. This is configured to be detected by the quantity sensor 64.

  A control method according to the fifth embodiment will be described with reference to FIG. FIG. 10 is a front view of the periphery of the secondary transfer apparatus for explaining the control method according to the fifth embodiment. As shown in FIG. 10, in the present embodiment, a toner pattern, which is a test pattern of a plurality of colors (three colors) with different densities, is transferred onto the intermediate transfer belt 61. Next, when the toner pattern passes through the secondary transfer nip, the toner pattern is transferred onto the secondary transfer belt 77 by the secondary transfer electric field, and the toner pattern on the secondary transfer belt 77 is transferred by the toner adhesion amount sensor 64. Detect the toner adhesion amount. Based on this detection result, the process control shown in FIG. 8 is executed. Therefore, in this embodiment, the amount of toner image attached after secondary transfer is detected. Therefore, the influence of the secondary transfer residual toner or the like of the mixed color toner image (two colors in FIG. 2) shown in FIG. 2 can be fed back to the control from the detection result of the toner adhesion amount.

A specific control method according to the fifth embodiment will be described with reference to FIG. FIG. 11 is a front view around the secondary transfer apparatus for explaining a specific example of the control method according to the fifth embodiment. As shown in FIG. 11, test patterns A and B created with a single photoreceptor on the secondary transfer belt 77 and a test pattern C overlaid with test patterns created with multiple (two) photoreceptors. Are transferred from the intermediate transfer belt 61 to the secondary transfer belt 77. Then, the toner adhesion amounts MA [mg / cm ² ], MB [mg / cm ² ], and MC [mg / cm ² ] on the secondary transfer belt 77 are measured using the toner adhesion amount sensor 64. In accordance with the detection result, the potential control device 23 in FIG. 8 performs execution determination of image forming condition correction at the time of color superposition and determination of a correction amount. Note that the single color test patterns A ′ and B ′ and the mixed color test pattern C ′ on the intermediate transfer belt 61 shown in FIG. 11 represent the transfer residual toner remaining on the intermediate transfer belt 61.

In the case of detection on the secondary transfer belt 77, for example, the execution determination of the image forming condition correction and the determination of the correction amount are performed by the following method. The potential control device 23 of FIG. 8 uses the sum (MA + MB) of the toner adhesion amount of a test pattern created by a single photoconductor and the toner adhesion amount of a test pattern in which patterns created by a plurality of photoconductors are superimposed. Compare (MC). At this time, the amount of toner adhesion is compared using the following equation (6).
(MA + MB)> β × MC, β: constant of 0 <β <1) (6)
As a result of the comparison, if the latter (toner adhesion amount (MC)) is smaller than a certain threshold calculated by the equation (6), it is determined that the amount of residual toner at the time of creating the mixed color image is large, and the mixed color In order to increase the toner adhesion amount of the image, it is determined that the image forming condition correction needs to be executed, and the correction amount is calculated.
On the contrary, when the latter (toner adhesion amount (MC)) is larger than a certain threshold value, it is determined that the amount of residual toner to be transferred at the time of creating the mixed color image is within an allowable range, and it is determined that it is not necessary to perform image formation condition correction. To do. Further, it is determined that the image forming condition correction execution determination at the time of mixed color printing is necessary only when it is determined that the toner adhesion amount at the time of mixed color printing is larger than the maximum toner adhesion amount at the time of monochrome printing. That is, when the toner adhesion amount per unit area when a plurality of toner images are superposed is larger than the maximum toner adhesion amount per unit area when a single toner image is formed, the image forming condition Apply correction to.

In the image forming condition correction, the image forming condition of the toner image first transferred to the intermediate transfer member in the image forming unit constituting the mixed color image is corrected. As described with reference to FIG. 2, when the adhesion amount is reduced at the time of creating a mixed color image, the adhesion amount of the toner image (the toner image positioned on the upper side on the recording paper) first transferred to the intermediate transfer belt 61 is reduced. Therefore, the image forming conditions of the toner image first transferred to the intermediate transfer belt 61 are corrected. That is, the image forming conditions of the toner image first transferred to the intermediate transfer member among the plurality of toner images are corrected.
In addition, the above correction is performed so as to increase the adhesion amount as compared with the case of forming an image with a single toner image in order to compensate for the adhesion amount of the transfer residual toner. That is, when a plurality of toner images are overlapped, the image forming conditions are corrected so that the amount of toner adhesion is larger than when a single toner image is formed.

  Further, in the correction of the image forming conditions in the present embodiment, the exposure conditions are corrected. That is, the correction of the image forming condition is correction of the exposure amount of the exposure unit. According to this embodiment, even when a mixed color image portion and a single color image portion exist in the main scanning direction at the same time or when images with different dot coverage exist at the same time, the exposure condition can be changed according to the image location. Therefore, compared with the case where the charging condition and the development condition are changed, the toner adhesion amount of the mixed color image can be maintained at the target value while the toner adhesion amount of the single color image is maintained at the target value.

  Further, the correction amount is set to a value at which adhesion of the mixed-color image becomes a target value, and not only the difference in adhesion amount between the single color and the color overlay but also image information such as dot coverage, toner density, time, It may be changed depending on the environment. Here, an example of correcting the image forming conditions of a two-color superimposed image has been described, but it goes without saying that the present invention can be similarly applied to a case where three or more colors are superimposed. Also, the control described in FIG. 11 is executed exclusively independently of the printing operation, that is, periodically when the power is turned on, before starting printing, after printing a predetermined number of sheets (for example, 500 sheets), after printing, etc. May be.

  As described above, according to the present embodiment, it is possible to provide an image forming apparatus capable of stabilizing the toner adhesion amount on a recording medium even when an image is formed by superimposing a plurality of toner images. it can.

(Sixth embodiment)
A sixth embodiment of the present invention will be described with reference to FIGS. 4, 12, and 13.
The object of the invention according to the sixth embodiment has been made in view of the above-mentioned problems of the background art according to the present invention, and the toner on the recording medium is formed even when a plurality of toner images are superimposed to form an image. An object of the present invention is to provide an image forming apparatus capable of stabilizing the adhesion amount.

The basic configuration of a printer as an image forming apparatus according to the sixth embodiment is the same as that of the second and fifth embodiments shown in FIG. In this printer, when the recording paper P is passed through the secondary transfer nip, which is the contact portion between the secondary transfer belt 77 and the intermediate transfer belt 61, as in the second and fifth embodiments, the intermediate transfer is performed. The visible image on the belt 61 is transferred to the recording paper P. Thereby, it is possible to perform the same overall operation as that of the second and fifth embodiments described with reference to FIG. 4 except for the operation peculiar to the second and fifth embodiments.
Further, when executing the process control, a toner image including a test pattern can be transferred onto the secondary transfer belt 77, and the toner adhesion amount on the secondary transfer belt 77 is detected by the toner adhesion amount sensor 64. It is the composition to do.

Hereinafter, the stabilization control of the toner adhesion amount unique to the present embodiment will be described. As described above, when the toner on the intermediate transfer belt 61 is transferred to the recording paper P at the secondary transfer portion (secondary transfer nip) of the secondary transfer device 71, a part of the toner is transferred onto the intermediate transfer belt 61. Remains. Therefore, in order to achieve a desired toner adhesion amount on the recording paper P, a larger amount of toner adheres on the intermediate transfer belt 61 at a constant rate than the target toner adhesion amount on the recording paper P. The target adhesion amount of the intermediate transfer belt 61 is controlled.
As described above, the target toner adhesion amount on the recording paper P is Mp [mg / cm ² ], and the ratio of the toner that can be transferred onto the recording paper P by secondary transfer (the above-mentioned secondary transfer efficiency) is α [%]. Then, the target adhesion amount Mb [mg / cm ² ] on the intermediate transfer belt 61 was expressed by the formula (1).
Mb = Mp / (α / 100) (1)

As described above, when a toner image is created with a single photoconductor and developing device, the toner adhesion amount on the recording paper P can be stabilized by stabilizing the toner adhesion amount on the intermediate transfer belt 61. . However, when a toner image is created by a plurality of photoconductors and developing devices and an image is formed by superimposing them, the ratio of the toner remaining on the intermediate transfer belt 61 varies depending on the order in which the toner images overlap.
Thus, for example, a case where an image is formed with Y toner and M toner on the intermediate transfer belt 61 will be considered with reference to FIG. Here, the following description will be made assuming that each toner is a solid image filled with no gap. As described with reference to FIG. 4, the process units 2Y, 2M, 2C, and 2K are arranged in the order of Y → M → C → K from the upstream side in the endless movement direction of the intermediate transfer belt 61 at positions facing the intermediate transfer belt 61. ing. Therefore, the Y toner first adheres on the intermediate transfer belt 61, and the M toner adheres thereon in an overlapping state. The toner on the intermediate transfer belt 61 is conveyed to the secondary transfer nip of the secondary transfer device 71 and transferred onto the recording paper P. At this time, as shown in FIG. 12, a certain amount of toner remains on the intermediate transfer belt 61 side as the transfer residual Y toner due to the above-described secondary transfer efficiency. After the secondary transfer, the transfer residual Y toner selectively remains on the intermediate transfer belt 61 side, and the M toner and Y toner on the recording paper P side are transferred to the recording paper P side. That is, the amount of toner image transferred to the recording paper P varies between the case where a toner image is created using a single photoconductor and the case where a toner image is created using a plurality of photoconductors.

  In this embodiment, since the toner adhesion amount detection sensor 64 for detecting the toner adhesion amount is provided on the secondary transfer belt 77, it is possible to detect the toner adhesion amount after the secondary transfer. That is, the toner adhesion on the recording paper P is detected by the toner adhesion amount sensor 64 detecting a test pattern in which a toner image is created with a single photoreceptor and a test pattern in which a toner image is created with a plurality of photoreceptors. The same effect as detecting the amount is obtained.

  The control configuration of the main part of the present embodiment will be described with reference to FIG. The printer of this embodiment includes an image processing correction device 11 as shown in FIG. The image processing correction device 11 corrects dot coverage based on input image information (image data signal) and information (data signal) related to the detection result of each test pattern from the toner adhesion amount sensor 64 and A control flow relating to image data development substantially similar to that shown in 3B is executed. The image processing correction device 11 functions as a first correction unit that performs correction different from the image processing in the case of forming an image with a single toner image when an image is formed by superimposing a plurality of toner images. In addition, it has the functions described later. The image processing correction apparatus 11 includes, for example, a microcomputer including a CPU, an I / O (input / output) port, a ROM, a PROM, a RAM, a timer, and the like, which are connected by a signal bus. In the ROM and PROM, a program (for example, the flowchart shown in FIG. 3B) and related data (for example, dot coverage) for exhibiting the calculation function and control function of the CPU are stored in advance.

  In the present embodiment, the case where an image is formed from a toner image created with a single photoconductor in this way is different from the case where an image is formed by superimposing toner images created from a plurality of photoconductors. The correction is performed by image processing so that the toner adhesion amount on the coming recording paper P becomes constant.

  Specifically, as described in modes 14 to 19 to be described later, the toner adhesion amount on the recording paper P that has increased or decreased compared to the single color when the colors are superimposed is the same as that for the single color. The dot coverage is corrected so that A dot coverage correction method will be described with reference to FIG. In FIG. 12, a toner image that is an image created by the photosensitive member 3Y and the developing device 4Y of the process unit 2Y and the photosensitive member 3M and the developing device 4M of the process unit 2M will be considered. A Y toner image (hereinafter, simply referred to as “Y toner”) and an M toner image (hereinafter, simply referred to as “M toner”) are formed on the intermediate transfer belt 61, and further, the secondary transfer belt 72 causes the secondary transfer belt 72. 77 is transferred onto. At this time, a part of the Y toner on the intermediate transfer belt 61 side remains on the intermediate transfer belt 61 as a transfer residual toner. On the other hand, since the Y toner transferred first on the intermediate transfer belt 61 is covered with the M toner, all the M toner on the intermediate transfer belt 61 is transferred onto the recording paper P.

  As described above, the amount of toner that is first transferred onto the intermediate transfer belt 61 at the time of color superposition increases as the amount of toner remaining on the intermediate transfer belt 61 as the transfer residual toner, and the amount of toner transferred onto the recording paper P decreases. In anticipation of this, the dot coverage of the image is increased so that the toner amount becomes the same as that when the image is formed with a single photoconductor.

  On the other hand, with respect to the toner transferred onto the intermediate transfer belt 61 after color superposition, the amount of toner remaining on the intermediate transfer belt 61 as a transfer residual toner decreases, and the amount of toner transferred onto the recording paper P increases. In anticipation, the dot coverage of the image is lowered so that the toner amount becomes the same as that when the image is formed with a single photoconductor.

  As described above, according to the present embodiment, when a plurality of colors are overlaid using a photosensitive member and a developing device as a plurality of image carriers, the target toner adhesion amount is deviated due to the influence of the secondary transfer efficiency. Since the correction is performed, it is possible to provide an image forming apparatus having a stable color.

The sixth embodiment described above (corresponding to the aspects 14 to 19) is an example of the present invention, and the present invention has a specific effect for each of the following aspects.
[Aspect 14]
A plurality of image carriers such as photoreceptors 3Y, 3M, 3C, and 3K, charging devices 5Y, 5M, 5C, and 5K for charging the surface of the image carrier, and the surface of the image carrier are exposed. Exposure units such as optical writing units 1YM and 1CK that form an electrostatic latent image, and developing devices 4Y, 4M that supply a developer to the electrostatic latent image formed on the surface of the image carrier to form a visible image. Development means such as 4C and 4K, and primary transfer rollers 62Y, 62M, 62C, and 62K that primarily transfer a visible image formed on the surface of the image carrier to an intermediate transfer body such as the intermediate transfer belt 61. A secondary transfer device having a transfer means and a secondary transfer rotating member such as a secondary transfer belt 77 in contact with the intermediate transfer member, and secondarily transferring a visible image on the intermediate transfer member to a recording medium such as recording paper P Secondary transfer means such as 71, and a secondary transfer rotator; An image forming apparatus configured to transfer a visible image on an intermediate transfer body to a recording medium when the recording medium is passed through a contact portion such as a secondary transfer nip with an intermediary transfer body. Test pattern forming means configured by the process units 2Y, 2M, 2C, 2K, the optical writing units 1YM, 1CK, the overall control unit of the printer, and the like for forming a test pattern for inspection on the surface of the image carrier And a test pattern detecting means such as a toner adhesion amount sensor 64 for detecting the test pattern, and an image forming condition correcting means such as the overall control section for correcting the image forming condition based on the test pattern detection result. The test pattern formed on the image carrier is transferred to the intermediate transfer member, and the test pattern on the intermediate transfer member is transferred to the secondary transfer rotator. And the test pattern transferred to the secondary transfer rotator is detected by the test pattern detection means, and created by a plurality of image carriers based on the result detected by the test pattern detection means. When forming an image by superimposing toner images, the first image processing correction device 11 or the like that performs correction different from the image processing in the case of forming an image with a toner image created by a single image carrier. The correction means is provided.
According to this aspect 14, as described in the above embodiment, with the above configuration, secondary transfer is performed when an image is formed with a single toner image and when an image is formed with a plurality of toner images. Color variations due to different toner amounts are corrected through image processing, so that stable image output is possible.

[Aspect 15]
In [Aspect 14], the image processing is dot coverage.
According to this aspect 15, there exists an effect similar to the said aspect 14.

[Aspect 16]
In [Aspect 14] or [Aspect 15],
The first correction unit corrects the image processing of the toner image first transferred to the intermediate transfer body among the toner images created by the plurality of image carriers.
According to this aspect 16, there are the same effects as in the above aspect 14.

[Aspect 17]
In [Aspect 16], when the first correction unit forms an image by superimposing toner images created by a plurality of image carriers, the first correction unit displays an image using a toner image created by a single image carrier. The image processing is corrected so that the toner adhesion amount is increased as compared with the case of forming.
According to this aspect 17, there are the same effects as in the above aspect 14.

[Aspect 18]
In any one of [Aspect 14] to [Aspect 17], the first correction means is a toner image created by a plurality of image carriers, other than the toner image first transferred to the intermediate transfer member. Correction is applied to the image processing of the toner image.
According to this aspect 18, there are the same effects as in the above aspect 14.

[Aspect 19]
In [Aspect 18], when an image is formed by overlapping toner images created by a plurality of image carriers, compared to a case where an image is formed by a toner image created by a single image carrier, Image processing is corrected so as to reduce the toner adhesion amount.
According to this aspect 19, there are the same effects as in the above aspect 14.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above. For example, the first to sixth embodiments may be appropriately combined.

  For example, the second, fifth, or sixth embodiments are not limited to this, and the toner adhesion amount sensor 64 is arranged at a position on the secondary transfer belt 77 shown in FIG. It may be arranged at a position on the intermediate transfer belt 61 described below. As a result, in addition to the stabilization control of the toner adhesion amount peculiar to the second, fifth or sixth embodiment, the same process control in the image forming unit as in the conventional case, that is, the process units 2Y, 2M, 2C and 2K. Process control may be performed.

  For example, the image forming apparatus to which the present invention is applied is not limited to the type of image forming apparatus described above, and may be another type of image forming apparatus. That is, the image forming apparatus to which the present invention is applied may be an image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter, or a multifunction machine having a plurality of functions.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

1YM, 1CK optical writing unit (an example of exposure means / exposure device)
2Y, 2M, 2C, 2K process unit (process cartridge)
3Y, 3M, 3C, 3K photoconductor (an example of an image carrier)
4Y, 4M, 4C, 4K developing device (an example of developing means)
5Y, 5M, 5C, 5K Charging device (an example of charging means)
6Y, 6M, 6C, 6K Drum cleaning device (cleaning means)
10. Image processing correction apparatus (an example of first correction means)
11 Image processing correction apparatus (an example of first correction means)
20 Transfer bias correction device (an example of second correction means)
21 Transfer bias control device (example of second correction means)
23 Potential control device (example of third correcting means)
24 Potential sensor 25 Toner concentration sensor 61 Intermediate transfer belt (intermediate transfer member)
64 Toner adhesion amount sensor (an example of test pattern detection means)
68 Secondary transfer backup roller (secondary transfer means / secondary transfer device)
70 Secondary transfer section (example of secondary transfer means and secondary transfer device)
71 Secondary transfer device (an example of secondary transfer means)
72 Secondary transfer roller (an example of a secondary transfer rotator, constituting secondary transfer means and secondary transfer device)
77 Secondary transfer belt (an example of a secondary transfer rotating body)
A, B, C Test pattern

JP 2007-121943 A JP 2010-128070 A

Claims (3)

A plurality of image carriers;
Charging means for charging the surface of the image carrier;
Exposure means for exposing the surface of the image carrier to form an electrostatic latent image;
Developing means for supplying a developer to the electrostatic latent image formed on the surface of the image carrier to form a visible image;
Primary transfer means for primarily transferring a visible image formed on the surface of the image carrier to an intermediate transfer body;
A secondary transfer rotator that contacts the intermediate transfer member, and a secondary transfer unit that secondarily transfers a visible image on the intermediate transfer member to a recording medium,
An image forming apparatus configured to transfer a visible image on the intermediate transfer body to the recording medium when the recording medium is passed through a contact portion between the secondary transfer rotating body and the intermediate transfer body,
In the case of forming an image by superimposing toner images created by the plurality of image carriers, correction different from image processing in the case of forming an image by toner images created by a single image carrier is performed. First correction means for applying ,
The image processing is processing for correcting dot coverage,
When performing the process of correcting the dot coverage for a toner image other than the toner image first transferred to the intermediate transfer member among the toner images created by the plurality of image carriers, the plurality of image carriers When an image is formed by superimposing the created toner images, the dot coverage is reduced so that the amount of toner adhesion is smaller than when forming an image with a toner image created with a single image carrier. Perform the correction process,
When the first correction unit forms an image with a toner image created by a single image carrier, the first correction unit does not perform the process of correcting the dot coverage;
The first correction unit is a case where an image is formed by superimposing toner images created by the plurality of image carriers, and when the first correction unit is a toner image first transferred to the intermediate transfer member, In anticipation of a reduction in the amount of toner transferred onto the recording medium, the dot coverage is corrected by performing correction to increase the dot coverage as compared with the case of forming an image with a toner image created with a single image carrier. Increase the amount of toner transferred to the intermediate transfer body,
The first correction means is a case where an image is formed by superimposing toner images created by the plurality of image carriers, and when the toner image is not first transferred to the intermediate transfer body, In anticipation of an increase in the amount of toner transferred onto the medium, the intermediate is achieved by performing a correction that lowers the dot coverage as compared with the case of forming an image with a toner image created with a single image carrier. An image forming apparatus that reduces the amount of toner transferred to a transfer body . The image forming apparatus according to claim 1.
An image forming apparatus that performs a process of correcting the dot coverage on a toner image first transferred to the intermediate transfer body among toner images created by the plurality of image carriers . The image forming apparatus according to claim 2 .
When an image is formed by superimposing toner images created by the plurality of image carriers, the toner adhesion amount is larger than when an image is formed by toner images created by a single image carrier. An image forming apparatus that performs a process of correcting the dot coverage as described above .

Images