JP2016040634A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can appropriately reduce unevenness in density in terms of a plurality of types of images having different densities from each other.SOLUTION: An image forming apparatus forms a toner image of a first image pattern on an intermediate transfer belt 1, determines first image forming conditions on the basis of a result of detection of the density of the toner image, and controls toner image forming means on the basis of the determined first image forming conditions. The image forming apparatus forms a toner image of a second image pattern different from the first image pattern on the intermediate transfer belt 1, determines second image forming conditions on the basis of a result of detection of the density of the toner image, and controls the toner image forming means on the basis of the determined second image forming conditions.SELECTED DRAWING: Figure 8

Description

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

Conventionally, as this type of image forming apparatus, an image forming apparatus that performs correction and control to reduce density unevenness of a toner image formed on an image carrier is known.
For example, Patent Document 1 discloses a recording apparatus (image formation) that records a latent image by modulating and scanning a laser beam on a photosensitive drum (image carrier), and developing and transferring the image by an electrophotographic process. Device) prior to outputting the image, a solid black image is recorded on the photosensitive drum, the solid black image is read and stored, and the image density at each recording position is corrected based on the read information. Is disclosed.
Further, Patent Document 2 discloses at least one of a charging voltage, an exposure light amount, a developing voltage, and a transfer voltage, based on periodically stored image density periodic fluctuation data or periodic fluctuation data on the charging potential of an image carrier. There has been disclosed an image forming apparatus that reduces striped density unevenness periodically generated in an image by controlling one image forming condition. In this image forming apparatus, periodic fluctuation data such as image density used for controlling image forming conditions is measured in advance using one type of image data (for example, image data of a solid image).
Further, in Patent Document 3, the rotation cycle of the developing roller is detected by a developing roller cycle detecting device, the density unevenness amount of the toner density of the pattern formed on the image carrier is detected by the density unevenness detecting device, and the density is detected. An image forming apparatus that controls the developing bias so as to match the phases of the output signal of the unevenness amount detecting device and the output signal of the developing roller rotation period detecting device is disclosed. In this image forming apparatus, density unevenness of a solid image can be corrected by changing the development potential by controlling the development bias.
Further, in Patent Document 4, a test image is formed on an image carrier or a transfer medium, a frequency of periodic image density unevenness generated in the test image is detected, and image density unevenness is detected based on the detected frequency. An image forming apparatus that specifies a generation source and controls the operation of the specified image density unevenness generation source to reduce the image density unevenness is disclosed.

However, the conventional image forming apparatus has a problem that density unevenness cannot be appropriately reduced for each of a plurality of types of images having different image densities (for example, a solid image and a halftone image).
For example, since the image forming apparatus disclosed in Patent Document 1 performs correction based on information obtained by reading a black solid image, the density unevenness of the solid image can be reduced. However, when forming a halftone image, the density unevenness is reduced. There is a risk that it cannot be mitigated and it gets worse.
In the image forming apparatus disclosed in Patent Document 2, periodic variation data such as image density used for controlling image forming conditions is measured using image data of one type of image (for example, a solid image). The image density unevenness profile may differ slightly depending on the image density level (for example, the density level of the solid portion or the density level of the halftone portion). For this reason, in the image forming apparatus of Patent Document 2, even if the density unevenness can be corrected successfully in the image (for example, a solid image) used in the measurement of the variation data, the density (for example, a halftone image) different from that image is corrected. There is a possibility that density unevenness cannot be corrected.
In the image forming apparatus disclosed in Patent Document 3, since the development potential is changed by controlling the development bias, the background potential is changed at the same time, and the density of the halftone image that is affected by the background potential change is reversed. Resulting in. Therefore, although it functions well for density correction of solid images, it is highly likely that it does not function well for density correction of halftone images.
Further, in the image forming apparatus of Patent Document 4, when detecting the frequency of periodic image density unevenness for each of the solid image and the halftone image, the same is true regardless of the source of density unevenness of each image being different. A frequency characteristic may be detected. In that case, the density unevenness source of each image cannot be accurately specified, and there is a possibility that the density unevenness cannot be reduced appropriately.

  The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus capable of appropriately reducing density unevenness for a plurality of types of images having different densities.

In order to achieve the above object, the invention of claim 1 includes a toner image forming unit that forms a toner image on an image carrier, a density detector that detects the density of the toner image formed on the image carrier, And forming a toner image of a first image pattern that is a single density pattern on the image carrier, and density unevenness of the toner image based on a detection result of the density of the toner image And detecting the control parameter value of the first image forming condition based on the detection result of the periodic fluctuation component of the density unevenness of the toner image, and the density of the toner image of the first image pattern. A first control unit that determines a control table changed at the same cycle as the variation cycle of unevenness, and controls the toner image forming unit based on the control table of the determined first image forming condition; and the image carrier Said first to the body A toner image of a second image pattern, which is a single density pattern having a density different from the image pattern, is formed, and a periodic fluctuation component of density unevenness of the toner image is detected based on the density detection result of the toner image. Based on the detection result of the periodic fluctuation component of the density unevenness of the toner image, the control parameter value of the second image forming condition is set to the same period as the fluctuation period of the density unevenness of the toner image of the second image pattern. And a second control unit that determines the changed control table and controls the toner image forming unit based on the control table of the determined second image forming condition. .
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the toner image of the second image pattern in the second control unit is formed by the first control unit. It is characterized in that it is carried out in a controlled state based on the first image forming conditions.
According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the toner image forming means forms a latent image by charging the surface of the image carrier and exposing the charged surface. The latent image is developed with toner to form a toner image on the surface of the image carrier, and the image pattern on the high density side of the first image pattern and the second image pattern. The image forming conditions determined in (1) are at least one of development conditions and exposure conditions, and the image forming conditions determined by the low-density image pattern are charging conditions.
According to a fourth aspect of the present invention, in the image forming apparatus according to the second or third aspect, the toner image formation and density detection of the first image pattern, the periodic fluctuation component of the density unevenness of the toner image, and the Determination of the control table for the first image forming condition, control of toner image formation based on the control table for the first image forming condition, toner image formation and density detection of the second image pattern, The detection of a periodic variation component of density unevenness, the determination of the control table for the second image forming condition, and the control of toner image formation based on the control table for the second image forming condition are repeated a plurality of times. To do.
According to a fifth aspect of the present invention, the image forming apparatus according to any one of the first to fourth aspects further comprises a rotational position detecting means for detecting a rotational position of a rotating body that is a source of image unevenness. The control table for the first image forming condition and the control table for the second image forming condition are determined in synchronization with the detection signal of the detecting means.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the formation and density detection of the toner image of the image pattern, the detection of the periodic fluctuation component of the density unevenness of the toner image, and the The determination of the image formation condition control table based on the detection result of the periodic variation component of density unevenness is performed after the image carrier is mounted on the main body of the image forming apparatus, and then toner image formation on the image carrier is started. It is characterized by being performed before
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the image forming apparatus further comprises transfer means for transferring the toner image formed on the image carrier to a recording medium, and the toner image of the image pattern. Formation and density detection, detection of periodic fluctuation component of density unevenness of toner image, and determination of control table of image forming condition based on detection result of periodic fluctuation component of density unevenness, toner image is transferred The present invention is characterized in that it is performed at intervals of a certain number of recording media.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the image forming apparatus further comprises transfer means for transferring the toner image formed on the image carrier to a recording medium, and the toner image of the image pattern. And the detection of the periodic fluctuation component of the density unevenness of the toner image and the determination of the control table of the image forming condition based on the detection result of the periodic fluctuation component of the density unevenness are the environment in the image forming apparatus. It is characterized by being performed when conditions change.

According to the present invention, among a plurality of types of images having different densities, one of the high density side image and the low density side image has a single density pattern suitable for correcting the density unevenness of the one image. A toner image having a first image pattern is formed on the image carrier. Then, based on the detection result of the density of the toner image, a periodic fluctuation component of the density unevenness of the toner image is detected, and based on the detection result of the periodic fluctuation component of the density unevenness of the toner image, the one image A control table in which the value of the control parameter of the first image forming condition that is influenced by the density unevenness of the first image pattern is changed in the same cycle as the fluctuation cycle of the density unevenness of the toner image of the first image pattern is determined. The toner image forming unit is controlled based on a control table of one image forming condition. By this control, density unevenness can be reduced for one of the high density side image and the low density side image.
Further, the other one of the high density side image and the low density side image is a single density pattern having a density different from that of the first image pattern, which is suitable for correcting the density unevenness of the other image. A toner image having a second image pattern is formed on the image carrier. Based on the detection result of the density of the toner image, a periodic fluctuation component of the density unevenness of the toner image is detected. Based on the detection result of the periodic fluctuation component of the density unevenness of the toner image, the other image A control table is determined by changing the control parameter value of the second image forming condition that is affected by the density unevenness of the image in the same cycle as the fluctuation cycle of the density unevenness of the toner image of the second image pattern. The toner image forming unit is controlled based on the control table of the second image forming condition. By this control, density unevenness can be reduced for the other of the high density side image and the low density side image.
As described above, according to the present invention, density unevenness can be appropriately reduced for a plurality of types of images having different densities.

1 is a schematic configuration diagram illustrating a configuration example of an image forming apparatus to which the present invention is applicable. FIG. 6 is a schematic configuration diagram illustrating another configuration example of an image forming apparatus to which the present invention is applicable. FIG. 10 is a schematic configuration diagram illustrating still another configuration example of an image forming apparatus to which the present invention is applicable. FIG. 7 is a partial perspective view illustrating an example of an installation state of a toner image detection sensor. FIG. 3 is a block diagram illustrating an example of a main part of a control system of the image forming apparatus. Explanatory drawing which shows an example of each of the 1st image pattern and 2nd image pattern used for correction control of image density nonuniformity. Explanatory drawing which shows the other example of each of the 1st image pattern and 2nd image pattern used for correction control of image density nonuniformity. 7 is a flowchart illustrating an example of density unevenness correction control using the image pattern of FIG. 6. 8 is a flowchart showing an example of density unevenness correction control using the image pattern of FIG. 7. 10 is a flowchart illustrating another example of density unevenness correction control. 10 is a flowchart showing still another example of density unevenness correction control. 6 is a graph illustrating the relationship between a rotational position detection signal (A), a toner adhesion amount detection signal (B) by a toner image detection sensor, and a value (C) of an image formation condition (control table).

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating a configuration example of an image forming apparatus to which the present invention can be applied. FIG. 1 shows a configuration example of a full color machine of a four-tandem type intermediate transfer system as an electrophotographic image forming apparatus to which the present invention can be applied. The present invention can also be applied to other image forming apparatuses such as a direct transfer type full color machine and a one-drum intermediate transfer type full color machine. Furthermore, the present invention can also be applied to a monochrome machine such as a one-drum direct transfer system.

  In FIG. 1, photosensitive drums 2Y, 2M, 2C, and 2K that are latent image carriers are juxtaposed along a stretched surface (stretching surface) of an intermediate transfer belt 1 that is an intermediate transfer member as an image carrier. ing. The symbol Y indicates yellow, M indicates magenta, C indicates cyan, and K indicates black. The yellow image forming station will be described as a representative example. The charging unit 3Y as the charging unit, the optical writing unit 4Y as the exposing unit, and the developing unit 5Y as the developing unit are arranged around the photosensitive drum 2Y in the rotation direction. A primary transfer roller 6Y as a primary transfer unit, a photosensitive member cleaning unit 7Y as a latent image carrier cleaning unit, and a quenching lamp 8Y as a charge eliminating unit are arranged. A toner image forming means for forming a toner image on the intermediate transfer belt 1 as an image carrier is configured using a photosensitive drum 2Y, a charging charger 3Y, an optical writing unit 4Y, a developing unit 5Y, a primary transfer roller 6Y, and the like. ing. The same applies to imaging stations of other colors. Above the optical writing unit 4, a scanner unit 9 as an image reading unit, an ADF 10 as an automatic document supply unit, and the like are provided.

  The intermediate transfer belt 1 is rotatably supported by rollers 11, 12, and 13 as a plurality of support members, and a belt cleaning unit 15 is provided at a portion facing the rollers 12. A secondary transfer roller 16 as a transfer unit is provided at a portion facing the roller 13.

  A plurality of paper feed trays 17 as a plurality of paper feed units are provided at the lower part of the apparatus main body, and a recording paper 20 as a recording medium accommodated in these trays is fed by a pickup roller 21 and a paper feed roller 22. The paper is transported by the transport roller pair 23, and sent to the secondary transfer portion by the registration roller pair 24 at a predetermined timing. A fixing unit 25 as a fixing unit is provided on the downstream side of the secondary transfer portion in the sheet conveying direction. In FIG. 1, reference numeral 26 denotes a paper discharge tray, and 27 denotes a switchback roller pair.

  In the configuration shown in FIG. 1, an image forming operation will be described. When a print start command is input, the rollers around the photosensitive drum, the intermediate transfer belt, and the paper feed path start to rotate at a predetermined timing, and the recording paper feed starts from the lower paper feed tray. Is done.

  On the other hand, the surface of each photoconductive drum 2 is charged to a uniform potential by the charging charger 3, and the surface is exposed according to the image data by the writing light emitted from the optical writing unit 4. The potential pattern after the exposure is called an electrostatic latent image. The toner is supplied from the developing unit 5 to the surface of the photosensitive drum 2 carrying the electrostatic latent image, so that it is carried on the photosensitive drum 2. The electrostatic latent image is developed to a specific color. In the configuration of FIG. 1, since there are four photosensitive drums 2, toner images of yellow, magenta, cyan, and black (color order varies depending on the system) are developed on each photosensitive drum 2. .

  The toner image developed on each photosensitive drum 2 is intermediated by a primary transfer bias and a pressing force applied to a primary transfer roller 6 disposed opposite to the photosensitive drum 2 at a contact point with the intermediate transfer belt 1. Transferred onto the transfer belt 1. By repeating this primary transfer operation for four colors at the same timing, a full-color toner image is formed on the intermediate transfer belt 1.

  The full-color toner image formed on the intermediate transfer belt 1 is transferred to the recording paper 20 conveyed at the timing by the registration roller pair 24 in the secondary transfer roller portion. At this time, the secondary transfer is performed by the secondary transfer bias and the pressing force applied to the secondary transfer roller 16. The recording paper 20 on which the full-color toner image has been transferred passes through the fixing unit 25, whereby the toner image carried on the surface of the recording paper 20 is heat-fixed.

  If it is single-sided printing, it is straightly conveyed and conveyed to the paper discharge tray 26. If it is double-sided printing, the conveying direction is changed downward and conveyed to the paper reversing unit. The recording paper 20 that has reached the paper reversing section is reversed in the conveying direction by the switchback roller pair 27 and exits the paper reversing section from the rear end of the paper. This is called a switchback operation, and the front and back of the recording paper 20 can be reversed by this operation. The recording paper 20 that is turned upside down does not return to the fixing unit direction, passes through the refeed conveyance path, and joins the original feed path. Thereafter, the toner image is transferred in the same manner as the front surface printing, and is discharged through the fixing unit 25. This is a double-sided printing operation.

  The operation of each part will be explained to the last. The photosensitive drum 2 that has passed through the primary transfer part carries the primary transfer residual toner on its surface, and this is transferred to the photosensitive drum cleaning unit 7 constituted by a blade, a brush and the like. Removed. Thereafter, the surface is uniformly discharged by a quenching lamp (QL) 8 to prepare for charging for the next image. The intermediate transfer belt 1 that has passed through the secondary transfer portion also carries secondary transfer residual toner on its surface, which is also removed by the belt cleaning unit 15 composed of blades and brushes. In preparation for the transfer of the next toner image. By repeating such an operation, single-sided printing or double-sided printing is performed.

  The image forming apparatus shown in FIG. 1 includes a toner image detection sensor (optical sensor unit) 30 constituted by an optical sensor or the like as density detection means for detecting the density of a toner image formed on the outer peripheral surface of the intermediate transfer belt 1. ing. The toner of the various image patterns (for example, a first image pattern and a second image pattern described later) formed on the surface of the intermediate transfer belt 1 so as to be used for image unevenness correction control by the toner image detection sensor 30. The density of the image can be detected. In the example of FIG. 1, the toner image detection sensor 30 is disposed at a position P1 (position before secondary transfer) facing the portion of the intermediate transfer belt 1 that is wound around the roller 11. The toner image detection sensor 30 can also be disposed at a downstream position (position after secondary transfer) P2 of the secondary transfer portion. In the case where the roller 14 is disposed between the supporting rollers as in the position P2 on the downstream side of the secondary transfer portion in FIG. 1, a roller 14 is provided on the inner side of the intermediate transfer belt 1 so as to face the roller 14. Thus, a toner image detection sensor 30 is provided.

  Of the two types of arrangement positions of the toner image detection sensor 30, the position P1 before the secondary transfer is a position where the toner pattern on the intermediate transfer belt 1 before the secondary transfer process can be detected, and there are restrictions on the machine layout. Otherwise, this configuration is often adopted. Since the toner image of the image pattern for correction control can be formed and detected immediately, there is less waiting time, and it is not necessary to slip through the secondary transfer part to the toner image of the image pattern. It is. However, many models have a secondary transfer position immediately after the image forming station for the fourth color (black in the example of FIG. 1). In this case, it is difficult to install a sensor at the position P1. In such a case, after the toner image detection sensor 30 is installed at the position P2, which is the position after the secondary transfer, and the toner image of the image pattern formed on the intermediate transfer belt 1 is passed through the secondary transfer portion. Therefore, the toner image detection sensor 30 detects the density of the toner image. As a method of passing through the secondary transfer portion, separation of the secondary transfer roller 16, application of a reverse bias to the secondary transfer roller 16, and the like can be considered, but there is no particular limitation here.

  FIG. 2 is a schematic configuration diagram illustrating another configuration example of the image forming apparatus to which the present invention is applicable. In FIG. 2, members and devices similar to those in the image forming apparatus in FIG. 1 are given the same reference numerals, and descriptions thereof are omitted. The image forming apparatus of FIG. 2 is a one-drum type intermediate transfer type full-color machine, and includes a drum-shaped photosensitive drum 2 and a revolver developing unit 50 facing the drum-shaped photosensitive drum 2. The revolver developing unit 50 holds four developing devices 51Y, 51M, 51C, and 51K by a holding body that rotates about a rotation axis. These developing units develop the electrostatic latent image on the photosensitive drum 2 with yellow (Y), magenta (M), cyan (C), and black (K) toners. The revolver developing unit 50 rotates the holding member to move the developing device of any color among Y, M, C, and K to the developing position facing the photosensitive drum 2, so that the top of the photosensitive drum 2 is moved. The electrostatic latent image can be developed into an arbitrary color. When forming a full-color image, for example, an electrostatic latent image for Y, M, C, and K is sequentially formed on the photosensitive drum 2 in the process of rotating the endless intermediate transfer belt 1 about four times, Development is performed sequentially by developing units 51Y, 51M, 51C, and 51K for Y, M, C, and K. Then, Y, M, C, and K toner images obtained on the photosensitive drum 2 are sequentially superimposed and transferred onto the intermediate transfer belt 1. At the secondary transfer position where the roller 13 which is a support member of the intermediate transfer belt 1 and the secondary transfer roller 16 of the secondary transfer unit 28 face each other, the transfer conveyance belt of the intermediate transfer belt 1 and the secondary transfer unit 28 is provided. The secondary transfer nip is formed by contacting with 28a at a predetermined nip width. When the four-color superimposed toner image on the intermediate transfer belt 1 passes through the secondary transfer nip, the recording medium that has been transported by the transfer transport belt 28a of the secondary transfer unit 28 is synchronized with the passage. The four-color superimposed toner image on the intermediate transfer belt 1 is secondarily transferred onto the recording paper 20 at once. When images are formed on both sides of the recording paper 20, the recording paper 20 that has passed through the fixing unit 25 is conveyed to the double-sided unit 17 ′, and the recording paper 20 that has been turned upside down by the double-sided unit 17 ′ is again subjected to the secondary transfer. The four-color superimposed toner image on the intermediate transfer belt 1 is secondarily transferred onto the back surface of the recording paper 20 at a time.

  In the image forming apparatus having the configuration shown in FIG. 2, the toner image detection sensor 30 is disposed at a position (position before secondary transfer) P <b> 3 that faces a portion of the intermediate transfer belt 1 that is wound around the roller 11.

  FIG. 3 is a schematic configuration diagram showing still another configuration example of an image forming apparatus to which the present invention can be applied. In FIG. 3, the same members and apparatuses as those in the image forming apparatus in FIG. The image forming apparatus in FIG. 3 is a four-drum tandem direct transfer type full-color machine, and toner images formed on the photosensitive drums 2Y, 2M, 2C, and 2K are recorded below the four image forming stations. A transfer unit 29 for transferring to the paper 20 is provided. The transfer unit 29 has an endless transfer conveyance belt 29a rotatably supported by rollers 11a to 11d as a plurality of support members. The transfer conveying belt 29a is wound around the driving roller 11a and the driven rollers 11b to 11d, and supports the recording paper 20 while being driven to rotate counterclockwise in the drawing at a predetermined timing. Transport to pass through. Further, inside the transfer conveyance belt 29a, transfer rollers 6Y, 6M, 6C, which transfer toner images on the photosensitive drums 2Y, 2M, 2C, 2K to the recording paper 20 by applying a transfer charge at the transfer position. 6K is provided.

  In the image forming apparatus of FIG. 3, for example, when the four-color superposition full color mode is selected by an operation unit (not shown), the toner images of the respective colors on the photosensitive drums 2Y, 2M, 2C, and 2K of the image forming stations of the respective colors. The image forming process for forming the image is executed in synchronization with the conveyance of the recording paper 20. On the other hand, the recording paper 20 fed from the paper feed tray 17 is fed at a predetermined timing by the registration roller pair 24 and is carried on the transfer conveyance belt 29a, and conveyed so as to pass the transfer position of each image forming station. The The recording paper 20 on which the toner images of the respective colors are transferred and the four-color superimposed color image is formed is discharged onto the paper discharge tray 26 after the toner image is fixed by the fixing unit 25.

  In the image forming apparatus having the configuration shown in FIG. 3, the toner image detection sensor is located at a position (position before fixing) P4 facing the portion of the transfer unit 29 that is wound around the roller 11a on the most downstream side in the recording sheet conveyance direction. 30 is arranged. Further, a toner image detection sensor 30 is also disposed at a position P5 in FIG.

  In the configuration example of the image forming apparatus in FIGS. 1 to 3, the toner image of the image pattern for correction control is formed on the photosensitive drum 2, and the downstream belt (the intermediate transfer belt 1 or the transfer conveyance belt 28a, 29a), the toner image detection sensor 30 may be installed so as to face the surface of the photosensitive drum 2. The installation position of the toner image detection sensor 30 in this case is from the development position by the development unit 5 to the transfer position to the belt (the intermediate transfer belt 1 or the transfer conveyance belts 28a and 29a).

  Next, density unevenness correction control based on the image pattern density detection result in the image forming apparatus configured as described above will be described. In the following description, the case where the present invention is applied to the image forming apparatus having the configuration shown in FIG. 1 will be described. However, the present invention can be similarly applied to the image forming apparatus having the configuration shown in FIGS.

  FIG. 4 is a partial perspective view showing an example of the installation state of the toner image detection sensor 30. FIG. 4 shows an example in which a toner image detection sensor (optical sensor unit) 30 is installed at a position P1 before secondary transfer in the image forming apparatus of FIG. This toner image detection sensor 30 is a three-head type (three-head toner image detection sensor 30) in which sensor heads (optical sensors) 31a, 31b and 31c as three density detection means are mounted on a sensor substrate 32. . That is, the example of FIG. 4 is a configuration example of the toner image detection sensor 30 in which three sensor heads (optical sensors) are installed in the main scanning corresponding direction (axial direction of the photosensitive drum 2) orthogonal to the recording paper conveyance direction. Show. With this configuration, it is possible to simultaneously measure the toner adhesion amounts at three locations in the main scanning corresponding direction (the axial direction of the photosensitive drum 2). The number of sensor heads in the toner image detection sensor 30 is not limited to the above three. For example, the configuration may be a one-piece or two-piece toner image detection sensor 30 having one or two sensor heads, or four heads to seven having a sensor head dedicated to each color. The configuration of the individual toner image detection sensor 30 may be used.

  FIG. 5 is a block diagram illustrating an example of a main part of a control system of the image forming apparatus according to the present exemplary embodiment. In FIG. 5, a control unit 200 as a control unit is configured by, for example, a microcomputer, a CPU (Central Processing Unit) 201 as an arithmetic processing unit, a RAM (Random Access Memory) 202 and a ROM of a nonvolatile memory as a storage unit. (Read Only Memory) 203 and the like. The control unit 200 is electrically connected to the image forming stations 40Y, 40M, 40C, 40K, the optical writing unit 4, the toner image detection sensor (optical sensor unit) 30, and the like. The control unit 200 controls these various devices based on the control program. The RAM 202 which is a nonvolatile memory stores output conversion data (described later) as output conversion information used when calculating the toner density (toner adhesion amount) from the detection values of the sensor heads (optical sensors) of the toner image detection sensor 30. Conversion table), output conversion formula (algorithm), and the like.

  The control unit 200 functions as a first control unit and a second control unit that perform correction control so as to optimize the image density of each color, for example, when the power is turned on or every time a predetermined number of prints are performed. When functioning as the first control means, a toner image of the first image pattern is formed on the intermediate transfer belt 1, and the first image forming condition is determined based on the detection result of the density of the toner image. Based on the determined first image forming condition, the toner image forming unit configured as described above is controlled. Further, when functioning as the second control means, a toner image having a second image pattern different from the first image pattern is formed on the intermediate transfer belt 1, and based on the detection result of the density of the toner image. The second image forming condition is determined, and the toner image forming unit configured as described above is controlled based on the determined second image forming condition.

  FIG. 6 is an explanatory diagram showing an example of each of the first image pattern and the second image pattern used for the correction control of the image density unevenness. The example of FIG. 6 is an example in which only the center sensor head 31b of the toner image detection sensor 30 having the configuration of FIG. 4 is used for image pattern detection. In this example, a strip-shaped first image pattern 901 and a second image pattern 902 are sequentially formed on a portion of the outer peripheral surface of the intermediate transfer belt 1 facing the central sensor head 31b. The lengths of the image patterns 901 and 902 are set to a length equal to or longer than the photosensitive member circumferential length Lp because at least density unevenness of the photosensitive member period needs to be detected. The first image pattern 901 and the second image pattern 902 are sequentially formed, but the shape is the same and only the image density is different. The method of changing the image density may be an area gradation method or an analog method.

  FIG. 7 is an explanatory diagram showing other examples of the first image pattern and the second image pattern used for the correction control of the image density unevenness. The example of FIG. 7 is an example in the case where two different sensor heads 31a and 31b of the toner image detection sensor 30 having the configuration of FIG. 4 are used for image pattern detection. In this example, a belt-like toner image of the first image pattern 901 and a toner image of the second image pattern 902 are formed side by side on portions of the outer peripheral surface of the intermediate transfer belt 1 facing the two sensor heads 31a and 31b. doing. In this case, the toner image formation of the image pattern and its detection can be performed in parallel.

  FIG. 8 is a flowchart showing an example of density unevenness correction control using the image patterns 901 and 902 in FIG. 6 in the image forming apparatus in FIG. In this control flow example, first, a toner image of the first image pattern 901 and a toner image of the second image pattern 902 are sequentially formed on the intermediate transfer belt 1, and the toner images of the image patterns 901 and 902 are formed. Detection is performed by the sensor head 31b at the center of the toner image detection sensor 30 (steps 101 and 102). That is, the first image pattern formation / detection process (step 101) and the second image pattern formation / detection process (step 102) are executed in order.

  After toner image formation and detection of the image patterns 901 and 902, based on the detection results, a photosensitive member periodic component corresponding to the rotation cycle of the photosensitive drum 2 of the density unevenness of each image pattern is detected (extracted); Image forming condition calculation processing (steps 103a and 103b) for determining image forming conditions based on the photosensitive member periodic components, and image forming condition reflection processing (steps 104a and 104b) for reflecting the calculated image forming conditions to the control unit 200. ) And execute. Here, the image forming condition calculation process is a process of creating a control table of image forming conditions in the control unit 200, for example. The image forming condition reflecting process is a process for setting the created control table to be used for controlling the toner image forming unit, for example. Further, the image formation condition calculation process and the image formation condition reflection process, which are calculation processes, may be performed by parallel processing as shown in FIG. 8, or by serial processing (sequential processing, sequential processing) (not shown). Also good.

  In the control flow of FIG. 8, the image formation condition calculation process (steps 103 a and 103 b) and the image formation condition reflection process (steps 104 a and 104 b) are mutually different in the first system and the second system different from each other in the control unit 200. Performed independently. That is, in the first system, after the toner image formation and detection of the first image pattern 901, based on the detection result, the photosensitive body periodic component of density unevenness of the first image pattern is detected (extracted), A first image forming condition calculation process (step 103a) for determining a first image forming condition based on the photosensitive member periodic component, and a control unit that functions the calculated first image forming condition as a first control unit. The first image forming condition reflecting process (step 104a) to be reflected on the 200 is executed. Further, in the second system, after the toner image formation and detection of the second image pattern 902, based on the detection result, the photosensitive member periodic component of density unevenness of the second image pattern is detected (extracted), and A second image forming condition calculation process (step 103b) for determining a second image forming condition based on the photoconductor periodic component, and a control unit that functions the calculated second image forming condition as a second control unit. The second image forming condition reflecting process (step 104b) to be reflected in the 200 is executed.

  FIG. 9 is a flowchart showing an example of density unevenness correction control using the image patterns 901 and 902 in FIG. 7 in the image forming apparatus in FIG. In this control flow example, the toner images of the image patterns 901 and 902 are formed at positions corresponding to the two different sensor heads 31a and 31b of the toner image detection sensor 30, respectively. The toner image formation and the detection thereof can be performed in parallel. That is, in the control flow of FIG. 9, unlike the control flow of FIG. 8, the first image pattern formation / detection process (step 201a) and the second image pattern formation / detection process (step 201b) are abbreviated. It is executed in parallel at the same time. Therefore, in the control flow of FIG. 9, a series of processing from image pattern formation / detection to image formation condition reflection processing is performed independently of each other in the first system (201a to 203a) and the second system (201b to 203b). Run in parallel.

  FIG. 10 is a flowchart showing another example of density unevenness correction control in the image forming apparatus of FIG. In this control flow, the toner image formation (step 304) of the second image pattern 902 is controlled by the first control unit according to the first image forming condition (steps 301 to 301). 303). In order to form the second image pattern 902 in a state where the first image forming condition (control table) is reflected on the first control means (control unit 200), the first image pattern forming / detecting process starts with the first image forming condition (control table). The first system (steps 301 to 303) up to the process of reflecting one image forming condition to the first control means (control unit 200), and the second image pattern formation / detection process to the second image formation The second system (steps 304 to 306) up to the process of reflecting the condition on the second control means (control unit 200) has a serial relationship. The control flow of such a processing method has an advantage that the control by the first control unit can detect an adverse effect on the second image pattern 902 and reflect it on the second control unit. Theoretically, if the gain for calculating the image forming conditions (control table) is appropriately determined, correction control may be performed according to the control flow shown in FIGS. Because there is a difference, the predetermined gain is not always optimal for each machine. Therefore, there is a possibility that the correction control by the first control unit may adversely affect the density unevenness of the second image pattern 902. In contrast, the control flow shown in FIG. 10 has an advantage that the second image forming condition (control table) can be determined so as to reduce the density unevenness generated in the second image pattern 902.

  FIG. 11 is a flowchart showing still another example of density unevenness correction control in the image forming apparatus of FIG. This control flow is an example of control when the first image pattern 901 and the second image pattern 902 are single density patterns having different densities. In this control example, the image forming conditions determined by the pattern on the high density side are the developing conditions (for example, developing bias) in the developing units 5Y, 5M, 5C, and 5K or the optical writing units 4Y, 4M, 4C, and 4K. The exposure conditions (for example, exposure power) are used, and the image forming conditions determined by the low density side pattern are charging conditions (for example, charging bias).

  In the control flow of FIG. 11, first, a toner image of a typical solid image pattern (first image pattern 901) is formed on the intermediate transfer belt 1 as a high density side pattern, and the density of the toner image of the solid image pattern is set. It is detected by the toner image detection sensor 30 (step 401). Then, based on the detection result of the toner image detection sensor 30, the photosensitive member periodic component of the density unevenness of the solid image pattern is detected (extracted), and based on the photosensitive member periodic component, the first image forming condition is set. A calculation process for determining development conditions or exposure conditions is performed (step 402). In the example shown in the figure, a control table for the developing bias applied to the developing roller of the developing unit 5 or a table for the exposure power of the optical writing unit 4 is created. The control parameters (development bias and exposure power) of these two image forming conditions are both effective parameters for solid image density control, and the control table created for these control parameters (control factors) is corrected by the control unit 200. (Step 403), solid image density unevenness can be reduced.

  On the other hand, when these control parameters (control factors) are changed according to the photosensitive member cycle according to the control table, the development potential is periodically changed and the ratio to the background potential is changed. For this reason, density unevenness occurs in the halftone density portion. Therefore, in the control flow of FIG. 11, the halftone density image pattern is applied to the intermediate transfer belt 1 as the second image pattern in a state where the control parameters (development bias and exposure power) of the two image forming conditions are applied. The formed toner image density of the halftone density image pattern is detected by the toner image detection sensor 30 (step 404). Then, based on the detection result of the toner image detection sensor 30, the photosensitive member periodic component of density unevenness in the halftone density image pattern is detected (extracted), and the second image forming condition is determined based on the photosensitive member periodic component. A calculation process for determining the charging condition is performed (step 405). In the illustrated example, a control table for the charging bias applied to the charging charger 3 is created, which is a control parameter (control factor) effective for halftone density control (fluctuating the background potential). By applying this charging bias control table to the correction control by the control unit 200 (step 406), density unevenness occurring in the halftone density unit can be reduced.

  It should be noted that the control flow in which the order of the upper half processing (steps 401 to 403) and the lower half processing (steps 404 to 406) in FIG. 11 is switched is performed, and halftone density unevenness is performed before solid image density unevenness correction control. You may make it carry out correction control. That is, similar control may be performed using a halftone density pattern as the first image pattern and a solid image pattern as the second image pattern. The effect of development bias control table or exposure power control table for solid image density control on halftone density unevenness is more apparent than the effect of charging bias control table for halftone density control on solid image density unevenness. Cheap. For this reason, there is a difficult aspect in the control flow in which the halftone density pattern is first used as the first image pattern. However, if the gain at the time of creating the control table is appropriate, the same control effect can be obtained in either control flow. Will be obtained.

  Further, the control flows shown in FIGS. 10 and 11 may be repeated a plurality of times. In an actual machine, there is a possibility that the gain at the time of creating the control table is set to be weak in order to prevent overcorrection, but this may not completely remove image density unevenness with a single correction control. In such a case, it is possible to further reduce density unevenness by repeating a series of correction control. However, since the image pattern is drawn repeatedly, there is a possibility that it is disadvantageous in terms of control time and toner yield. Therefore, it is more preferable to set the gain setting so that the control effect is obtained with one correction as much as possible and finish the correction control without repeating a plurality of times.

  Further, in the image forming apparatus having the above-described configuration, a rotation position detection unit (for example, a home position sensor or a rotary encoder) that detects the rotation position of the photosensitive drum 2 that is a rotating body that is a generation source of image unevenness is provided. The first image forming condition and the second image forming condition may be determined and controlled in synchronization with the detection signal of the rotational position detecting means.

  FIG. 12 shows a rotational position detection signal (A) and a toner image when determining and controlling each of the first image forming condition and the second image forming condition in synchronization with the detection signal of the rotational position detecting means. 6 is a graph illustrating a relationship between a toner adhesion amount detection signal (B) by a detection sensor 30 and a value (C) of an image forming condition (control table) created based on the signal. In the example shown in the drawing, signals for two rotations of the photosensitive drum 2 are drawn. The toner adhesion amount detection signal (B) fluctuates in the same cycle as the rotation position detection signal (A), and the image forming condition (control table) is in the opposite phase to the toner adhesion amount detection signal (B). Determine the value of. The charging bias, the developing bias, and the exposure power that can be used as parameters (control factors) for actual image density control have a minus sign, and when the absolute value increases, the toner adhesion amount decreases. For this reason, it is not appropriate to uniformly express the value of the image forming condition (control table) as “reverse phase”, but here, the direction to cancel the fluctuation of the toner adhesion amount indicated by the toner adhesion amount detection signal (B) This is expressed as “reverse phase” in the sense that a control table is created, that is, a control table that creates a toner adhesion amount fluctuation in the opposite phase is created.

  What is the gain for determining the control table, that is, what is the change amount of the control table with respect to the change amount [V] of the toner adhesion amount detection signal (B)? Ideally, it can be obtained from theoretical values, but when installed on actual machines, there is a high possibility that actual machines will be verified based on theoretical values and ultimately determined from experimental data. The control table determined with the gain determined in this way has the timing relationship shown in FIG. 12 with the rotational position detection signal (A). Here, it is assumed that the head of the control table is the time when the rotational position detection signal (A) is generated. If this control table is a development bias control table, it is necessary to determine the application timing of the control table in consideration of the distance between the development nip and the toner image detection sensor 30. If the distance between the developing nip and the toner image detection sensor is an integral multiple of the circumferential length of the photosensitive drum 2, it is applied from the top of the control table in accordance with the timing of the rotational position detection signal (A). That's fine. If the distance between the development nip and the toner image detection sensor is deviated from an integral multiple of the circumferential length of the photosensitive drum 2, the control table may be applied by shifting the timing by the deviation distance. Similarly, the exposure power control table takes into account the distance between the exposure position and the toner image detection sensor, and the charge bias control table takes into account the distance between the charge position and the toner image detection sensor. Will be applied.

  Further, in the image forming apparatus having the above-described configuration, the timing of determining the image forming conditions (control table creation / updating) in the image unevenness correction control illustrated in FIGS. It may be the timing immediately after is set (at the time of initial setting, at the time of replacement, at the time of detachment, etc.). In this case, when the photosensitive drum 2 is mechanically removed, there is a high possibility that the occurrence state of image density unevenness in the rotation cycle of the photosensitive drum 2 is changed. Another reason is that the positional relationship with the installed photoconductor home position sensor is shifted. In the initial setting of the latent image carrier (photosensitive drum) for which no control table is originally created, it is necessary to first create a control table by performing a series of correction controls. When the photosensitive drum is replaced, the control table corresponding to the new photosensitive drum is re-created because the new photosensitive drum has a difference in the flare characteristic and the light sensitivity characteristic compared to the photosensitive drum 2 used so far. There is a need. In addition, even when the photosensitive drum 2 is simply attached / detached for maintenance, a change in the mounting state of the photosensitive drum 2 (change in how the photosensitive drum shaft and the rotating shaft are displaced) accompanying the removal of the photosensitive drum may occur. In addition, the position of the flare characteristic and the photosensitivity characteristic unevenness of the photosensitive drum 2 and the position of the photosensitive member home position sensor deviate, and it is necessary to recreate the control table. For the above reasons, it is necessary to determine the image forming conditions (creation / update of the control table) immediately after the photosensitive drum 2 is set.

  In the image forming apparatus having the above-described configuration, the image forming conditions may be determined (control table creation / update) at intervals of a predetermined number of recording sheets 20. As the number of prints of the recording paper 20 increases, the photoreceptor deterioration progresses, so that there may be a change in the light sensitivity characteristic unevenness. In addition, the set state of the photoconductive drum 2 gradually shifts due to long-term use, and the occurrence of eccentricity due to the shift between the shaft of the photoconductive drum 2 and the rotation shaft, and the positional relationship with the photoconductor home position sensor. There is also a possibility of shifting. In order to cancel the influence of these deviations, the image forming conditions may be determined (control table creation / update) at intervals of a certain number of recording sheets 20.

  In the image forming apparatus having the above-described configuration, determination of image forming conditions (creation / update of a control table) may be performed when environmental conditions in the apparatus change. Of the environmental conditions, especially when the temperature condition changes, the photosensitive element tube expands and contracts in accordance with the thermal expansion coefficient of the photosensitive element tube of the photosensitive drum 2. For this reason, there is a possibility that the occurrence of density unevenness changes due to the change in the profile of the photosensitive drum 2 and the change in the development gap. In order to cope with this change, the image forming conditions may be determined (control table creation / update) when the environmental conditions change. As a method for determining the trigger for determining the image forming conditions in this case, for example, “there is a temperature change of N [deg] or more compared to the previous determination of the image forming conditions (control table creation / update). It ’s OK to decide.

  As described above, according to the present embodiment, among the plurality of types of images having different densities, one of the high density side image and the low density side image is suitable for correction control of density unevenness of the one image. A toner image having the image pattern is formed on the image carrier. Then, based on the detection result of the density of the toner image, a first image forming condition that is affected by the density unevenness of the one image is determined, and the charging charger is determined based on the determined first image forming condition. 3. Control toner image forming means such as the optical writing unit 4 and the developing unit 5. By this control, density unevenness can be reduced for one of the high density side image and the low density side image. In addition, a toner image having a second image pattern suitable for correction control of density unevenness of the other image is formed on the image carrier for the other of the high density side image and the low density side image. Then, based on the detection result of the density of the toner image, a second image forming condition that is affected by the density unevenness of the other image is determined, and the toner is determined based on the determined second image forming condition. Control the image forming means. By this control, density unevenness can be reduced for the other of the high density side image and the low density side image. As described above, according to the present embodiment, density unevenness can be appropriately reduced for a plurality of types of images having different densities.

  In particular, an image formed by the electrophotographic image forming apparatus of this embodiment may have periodic density unevenness (toner adhesion amount unevenness) in the recording paper conveyance direction. There are several possible causes of this density unevenness (toner adhesion amount unevenness). Among them, the development electric field fluctuation caused by the fluctuation of the development gap (gap between the development roller and the photosensitive drum) in the development unit 5 is particularly important. And electrostatic latent image unevenness due to photoreceptor sensitivity unevenness. The two factors (development electric field fluctuation and electrostatic latent image unevenness) are considered to be the main causes of density unevenness (toner adhesion unevenness) that occurs at the time of development. A profile that is a distribution characteristic may differ depending on the density of image density (for example, between a solid density part and a halftone density part). The following can be considered as the cause. That is, in the halftone density portion, the amount of latent image potential drop due to the writing light is relatively small, so that the charging unevenness due to the charging means (charging charger 3) remains as the electrostatic latent image unevenness in the image portion. On the other hand, in the solid density portion, since the latent image potential drop amount due to the writing light is large, the charging unevenness due to the charging means (charging charger 3) hardly remains as the electrostatic latent image unevenness in the image portion. This is considered to be because the influence of the photosensitivity unevenness of the photosensitive member becomes strong. Therefore, in this embodiment, toner images of two types of image patterns having different densities are formed, and the density unevenness of the high density image (solid image) and the density unevenness of the low density image (halftone image) are separately measured. Thus, density unevenness at each image density is accurately grasped, and control is performed so as to feed back to an image forming condition having an influence on each image density. By this control, it is possible to appropriately reduce density unevenness at the image densities of the high density image (solid image) and the low density image (halftone image).

Further, according to the present embodiment, the detection result of density unevenness of a high density image (solid image) is fed back to the development potential, and the result of density unevenness detection of the low density image (halftone image) is fed back to the background potential. doing. Since the development potential and the background potential are mutually related control parameters (control factors), if the density unevenness of the high density image (solid image) is controlled by controlling the development potential, the effect is low density image (halftone image). ) And density unevenness in a low density image (halftone image) may be created. The converse is also true. When density unevenness of a low density image (halftone image) is controlled by controlling the background potential, the effect appears on the high density image (solid image), and the high density image (solid image). ) May cause uneven density. Of course, it is basic to determine the gain when creating the control table so as not to create density unevenness at other image densities, but there may be cases where the conditions are slightly shifted to create density unevenness.
Therefore, in the present embodiment (see the control flow in FIG. 10), the correction control by the first control unit performed based on the first image forming condition determined using the first image pattern is reflected. Toner image formation and density detection of the second image pattern, determination of the second image formation condition based on the density detection result, and correction control by the second control means based on the second image formation condition Yes. By performing correction control in two steps in this way, even when density unevenness is created in the toner image of the second image pattern by the first control means, the density unevenness can be detected and reduced. it can. Accordingly, appropriate image density unevenness correction can be performed on both the high density image (solid image) and the low density image (halftone image).

  In the image forming apparatus according to the present exemplary embodiment, development conditions and exposure conditions are typical control factors for high-density images (solid images), and charging conditions are typical control factors for low-density images (halftone portions). . Therefore, according to the present embodiment (see the control flow of FIG. 11), the development condition or the exposure condition is determined and controlled based on the detection result of the density unevenness of the high density image (solid image). By determining and controlling the charging conditions based on the detection result of density unevenness in the tone adjustment section, more appropriate density unevenness correction is possible for both high density images (solid images) and low density images (halftone images). It becomes.

  Further, in the image forming apparatus according to the present embodiment, if the gain for determining each image forming condition is appropriately determined, the control accuracy should be achieved by performing a series of correction control once. However, since there are individual differences in the state of the actual machine, it is considered better not to set the gain to an optimum value but to set a slightly weaker gain so as not to overcorrect. In this case, the density unevenness may not be completely corrected by a single correction control. Therefore, according to the present embodiment, a series of correction control including toner image formation and density detection of an image pattern, determination of image formation conditions based on the density detection result, and control based on the image formation conditions are performed a plurality of times (for example, By repeating twice, the level of density unevenness can be further reduced.

  Further, in the image forming apparatus of the present embodiment, when density unevenness correction control is performed based on the determined image forming conditions, it is necessary to perform control in synchronization with the generated image density unevenness. . For this purpose, a rotating position detection means (for example, a home position sensor) for detecting a rotating position is provided on a rotating body (for example, the photosensitive drum 2) that is a generation source of the density unevenness cycle, and the rotation of the rotating body is performed. It is necessary to grasp the cycle. Therefore, according to the present embodiment, the determined image is determined by specifying the relationship between the generated image density unevenness and the rotational position of the rotating body based on the detection result of the rotation period of the rotating body. Formation conditions (specifically, a control table that changes image formation conditions over time) can be applied at an appropriate timing.

  Further, in the image forming apparatus of the present embodiment, the causes of the image density unevenness (toner adhesion amount unevenness) occurring at the stage of the toner image on the photosensitive drum 2 are insufficient roundness of the photosensitive drum 2 and Variations in the development gap due to eccentricity caused by rotational axis deviation at the time of setting, and post-exposure potential (VL) unevenness due to photosensitive layer coating unevenness of the photosensitive drum 2 are two major factors. Since these factors are errors of the photosensitive drum itself and errors generated when the photosensitive drum is set, once the photosensitive drum 2 is set, image density unevenness due to these factors hardly changes thereafter. it is conceivable that. Therefore, according to the present embodiment, the image forming conditions (control table) are created only immediately after the photosensitive drum 2 is set, so that the image forming conditions effective until the next removal of the photosensitive drum are effective. (Control table) can be obtained.

  Further, in the image forming apparatus according to the present embodiment, when the number of output sheets of recording paper 20 increases, the photoreceptor deterioration proceeds. Further, the set state of the photosensitive drum 2 may be gradually shifted. In such a case, the image forming conditions (control table) stored in the control unit 200 may not function effectively. Therefore, according to the present embodiment, it is possible to maintain the effectiveness of the density unevenness correction control by recreating the image forming conditions (control table) at intervals of a certain number of recording sheets 20.

    Further, in the image forming apparatus of the present embodiment, when the environment (particularly temperature) in the apparatus varies, the photosensitive drum 2 may be slightly deformed according to the thermal expansion coefficient of the photosensitive element tube. Due to the deformation of the photosensitive drum 2, the development gap fluctuates, and the aspect of image density unevenness may change. Therefore, according to the present embodiment, the effectiveness of the density unevenness correction control can be maintained by recreating the image forming conditions (control table) when the environment changes.

1: Intermediate transfer belt 2: Photoconductor drum 3: Charger charger 4: Optical writing unit 5: Development unit 6: Primary transfer roller 20: Recording paper 30: Toner image detection sensor (optical sensor unit)
31a, 31b, 31c, 31d: sensor head (optical sensor)
40Y, 40M, 40C, 40K: imaging station 200: control unit 901: first image pattern 902: second image pattern

Japanese Patent Laid-Open No. 62-145266 JP-A-9-62042 Japanese Patent No. 3825184 JP 2006-106556 A

Claims (8)

An image forming apparatus comprising: a toner image forming unit that forms a toner image on an image carrier; and a density detector that detects a density of the toner image formed on the image carrier.
Forming a toner image of a first image pattern which is a single density pattern on the image carrier, detecting a periodically varying component of density unevenness of the toner image based on a detection result of the density of the toner image; Based on the detection result of the periodic fluctuation component of the density unevenness of the toner image, the control parameter value of the first image forming condition is changed at the same period as the fluctuation period of the density unevenness of the toner image of the first image pattern. A first control unit that controls the toner image forming unit based on the control table of the determined first image forming condition;
A toner image of a second image pattern, which is a single density pattern having a density different from that of the first image pattern, is formed on the image carrier, and the density of the toner image is determined based on the detection result of the density of the toner image. A periodic fluctuation component of unevenness is detected, and based on the detection result of the periodic fluctuation component of density unevenness of the toner image, the control parameter value of the second image forming condition is set to the value of the toner image of the second image pattern. A second control unit that determines a control table that is changed at the same cycle as the variation cycle of density unevenness and controls the toner image forming unit based on the determined control table of the second image forming condition;
An image forming apparatus comprising: The image forming apparatus according to claim 1.
The toner image formation of the second image pattern in the second control unit is performed in a state where the toner image forming unit is controlled based on the first image forming condition by the first control unit. An image forming apparatus. The image forming apparatus according to claim 1 or 2,
The toner image forming means is configured to charge the surface of the image carrier, to expose the charged surface to form a latent image, and to develop the latent image with toner to thereby form the surface of the image carrier. To form a toner image,
Of the first image pattern and the second image pattern, the image forming condition determined by the image pattern on the high density side is at least one of the developing condition and the exposure condition, and determined by the image pattern on the low density side. The image forming apparatus is characterized in that the image forming condition is a charging condition. The image forming apparatus according to claim 2 or 3,
Toner image formation and density detection of the first image pattern, detection of periodic fluctuation components of density unevenness of the toner image, determination of the control table of the first image formation condition, and the first image formation condition Control of toner image formation based on control table, formation and density detection of toner image of second image pattern, detection of periodic fluctuation component of density unevenness of toner image, and control table of second image formation condition And determining the toner image based on the control table of the second image forming condition and repeating the determination a plurality of times. The image forming apparatus according to claim 1,
Rotation position detection means for detecting the rotation position of the rotating body that is the source of image unevenness,
An image forming apparatus, wherein a control table for the first image forming condition and a control table for a second image forming condition are determined in synchronization with a detection signal of the rotation position detecting means. The image forming apparatus according to claim 1,
Toner image formation and density detection of the image pattern, detection of periodic fluctuation component of density unevenness of the toner image, and determination of a control table of image formation conditions based on the detection result of periodic fluctuation component of the density fluctuation An image forming apparatus, which is performed after an image carrier is mounted on a main body of the image forming apparatus and before the start of toner image formation on the image carrier. The image forming apparatus according to claim 1,
A transfer means for transferring the toner image formed on the image carrier to a recording medium;
Toner image formation and density detection of the image pattern, detection of periodic fluctuation component of density unevenness of the toner image, and determination of a control table of image forming conditions based on the detection result of periodic fluctuation component of the density unevenness, An image forming apparatus, wherein the image forming apparatus performs the recording at intervals of a predetermined number of recording media onto which toner images are transferred. The image forming apparatus according to claim 1,
A transfer means for transferring the toner image formed on the image carrier to a recording medium;
Toner image formation and density detection of the image pattern, detection of periodic fluctuation component of density unevenness of the toner image, and determination of a control table of image formation conditions based on the detection result of periodic fluctuation component of the density fluctuation An image forming apparatus, which is performed when an environmental condition in the image forming apparatus changes.

Images