JP6663592B2 - Image forming device - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Conventionally, a first control for determining a first image forming condition so as to correct periodic density unevenness in a high-density image portion and a second control to correct periodic density unevenness in a low-density image portion 2. Description of the Related Art An image forming apparatus that performs second control for determining image forming conditions is known. In the first control, a toner density of a high-density first image pattern is formed on an image carrier, and control data of a first image forming condition is determined based on a density detection result of the first image pattern. . In the second control, the toner density of the low-density second image pattern is formed on the image carrier in a state where the control data of the first image forming condition is applied, and the density detection result of the second image pattern is formed. The control data of the second image forming condition is determined based on. The toner image formation in the image forming operation is controlled based on the control data of the first image forming condition and the control data of the second image forming condition thus determined.

  Patent Document 1 discloses an image forming apparatus that performs such first and second controls, in which control data of a developing bias is determined as a first image forming condition, and control of a charging bias is determined as a second image forming condition. What determines the data is described. In the first control, a high-density solid band pattern (first image pattern) is created, and a developing bias (first image forming condition) is generated based on the density detection result of the periodic density unevenness of the solid band pattern. Are determined and created so as to periodically change the developing bias. In the second control, a low-density halftone pattern (second image pattern) is created with the created development bias control data applied. Then, control data of the charging bias is created so as to periodically change the charging bias (second image forming condition) based on the density detection result of the periodic density unevenness of the halftone pattern. In this image forming apparatus, by performing the image forming operation by applying the control data of the charging bias and the developing bias that are changed periodically after the correction, the high-density image portion and the low-density image portion It is said that density unevenness can be reduced.

  However, when the present inventors conducted an experimental study on the image forming apparatus that performs the first and second controls, it was found that there were the following problems. That is, when the density unevenness of the high-density first image pattern detected in the first control is large, the first image forming condition determined in the execution of the first control is changed to the second image in the second control. When applied at the time of forming a toner image of an image pattern, large density unevenness occurs in a low density image portion at the same cycle as high density unevenness. As a result, it was found that even when the second image forming condition determined by the second control was applied, the density unevenness of the low density image portion could not be reduced.

  In order to solve the above problems, the present invention provides an image carrier comprising a rotating body, a toner image forming means for forming a toner image on a surface of the image carrier, and a toner image formed on the image carrier. Density detecting means for detecting a density, forming a toner image of a high-density first image pattern on the image carrier, and forming a first image based on a density detection result of the toner image of the first image pattern A first control unit for determining control data of a condition, and the first image on the image carrier in a state in which the control data of the first image forming condition created by the first control unit is applied. Forming a toner image of a second image pattern having a lower density than the pattern, and determining control data of a second image forming condition based on a density detection result of the toner image of the second image pattern; Means and control of the first image forming condition. An image forming control unit for controlling the toner image forming unit during an image forming operation based on data and control data of the second image forming condition, wherein the second control The means determines the control data of the second image forming condition based on a density detection result of the toner image of the first image pattern and a density detection result of the toner image of the second image pattern. It is characterized by the following.

  ADVANTAGE OF THE INVENTION According to this invention, when the density unevenness of a high density image part is large, the density unevenness of a low density image part can be reduced reliably.

FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment. FIG. 2 is an explanatory diagram illustrating a configuration example of a tandem image forming unit of the image forming apparatus according to the embodiment. FIG. 3A is an explanatory diagram illustrating a configuration example of a black toner adhesion amount sensor. FIG. 3B is an explanatory diagram illustrating a configuration example of a color toner adhesion amount sensor. FIG. 2 is a block diagram illustrating an example of a main configuration of a control system of the image forming apparatus according to the embodiment. 9 is a flowchart illustrating an example of correction control for correcting periodic density unevenness in the image forming apparatus according to the embodiment. FIGS. 4A and 4B are diagrams illustrating an example of an image pattern used in the first control and the second control, respectively. FIG. 5 is an explanatory diagram illustrating an example of measurement of an output signal of a toner adhesion amount sensor and a photoconductor rotation position signal when an image pattern is detected. FIG. 6 is a block diagram showing a flow until density unevenness information is obtained from a toner adhesion amount sensor signal and a photoconductor rotation position signal. FIG. 4 is an explanatory diagram illustrating an example of density unevenness information. FIG. 9 is a diagram for explaining a method of applying image forming conditions in the first control and the second control. 7A and 7B are graphs showing examples of measurement results of density unevenness in a high-density portion and a low-density portion before and after the first and second controls are applied, respectively, when the image density unevenness is small. (A) and (b) show the case where the density unevenness of the first image pattern detected by the first control is large compared to the case of FIG. 9 is a graph showing an example of a measurement result of density unevenness in a low density portion. A correction coefficient of a gain applied to the second image forming condition (charging bias) for canceling the high density unevenness detected in the first control (amplitude of the fluctuation of the toner adhesion amount) and the low image density unevenness. 6 is a graph showing an example of the relationship with the graph. 9 is a graph showing an example of a profile as a time change of a toner adhesion amount (density) of each of a first image pattern and a second image pattern before reflecting a first image forming condition. 4 is a graph illustrating an example of a relationship between a time change of a toner adhesion amount (density) of each of the first image pattern and the second image pattern and a time change of a value of a control table (control data) of a first image forming condition. . 9 is a graph illustrating an example of a change over time in the toner adhesion amount (density) of each of a first image pattern and a second image pattern after applying a first image forming condition. 9 is a graph illustrating an example of a measurement result of a relationship between a change amount of a background potential and a change amount of a toner adhesion amount (density) of a second image pattern.

Hereinafter, embodiments will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present embodiment. Referring to FIG. 1, an image forming apparatus 1 according to the present embodiment includes an apparatus main body (printer unit) 100, a paper feed table 200 as a recording medium supply unit on which the apparatus main body is mounted, and an image forming apparatus 1 mounted on the apparatus main body 100. And a scanner 300 as an image reading device. Further, the image forming apparatus 1 of the present embodiment includes an automatic document feeder (ADF) 400 mounted on the scanner 300.

  The apparatus main body 100 is provided at the center thereof with an intermediate transfer belt 10 composed of an endless belt as an intermediate transfer body. The intermediate transfer belt 10 is stretched around support rollers 14, 15, and 16 as three support rotating bodies, and rotates clockwise in the drawing. Among these three support rollers, an intermediate transfer belt cleaning device 17 for removing residual toner remaining on the intermediate transfer belt 10 after image transfer is provided on the left side of the second support roller 15 in the drawing. In addition, a tandem image forming unit 20 as an image forming unit is arranged to face a belt portion stretched between the first support roller 14 and the second support roller 15 among the three support rollers.

  As shown in FIG. 1, the tandem image forming unit 20 includes four image forming units 18Y of yellow (Y), magenta (M), cyan (C), and black (K) along the belt moving direction of the belt portion. , 18M, 18C, and 18K are arranged side by side. In the present embodiment, the third support roller 16 is a driving roller. An exposure device 21 as an exposure unit is provided above the tandem image forming unit 20.

  On the opposite side of the tandem image forming unit 20 with the intermediate transfer belt 10 therebetween, a secondary transfer device 22 as a second transfer unit is provided. In the secondary transfer device 22, a secondary transfer belt 24 which is an endless belt as a transfer sheet conveying member is stretched between two rollers 231 and 232. The secondary transfer belt 24 is provided so as to be pressed against the third support roller 16 via the intermediate transfer belt 10. The toner image on the intermediate transfer belt 10 is transferred to a transfer sheet S, which is a transfer material as a recording medium, by the secondary transfer device 22. As shown in FIG. 1, a cleaning device 170 for cleaning the outer peripheral surface of the secondary transfer belt 24 may be provided.

  A fixing device 25 for fixing the toner image transferred onto the transfer sheet S is provided on the left side of the secondary transfer device 22 in the drawing. The fixing device 25 has a configuration in which a pressure roller 27 is pressed against a fixing belt 26 which is an endless belt to be heated.

  Further, the secondary transfer device 22 has a sheet conveying function of conveying the transfer sheet S after transferring the toner image from the intermediate transfer belt 10 to the transfer sheet S to the fixing device 25. Below the secondary transfer device 22 and the fixing device 25, a sheet reversing device 28 for reversing the transfer sheet S to record images on both sides of the transfer sheet S is provided in parallel with the tandem image forming unit 20. I have.

  When making a copy using the image forming apparatus 1 having the above configuration, a document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed. Then, when the start switch of the operation unit is pressed, when the original is set in the automatic document feeder 400, the original is conveyed and moved onto the contact glass 32.

  On the other hand, when an original is set on the contact glass 32, the scanner 300 is immediately driven to cause the first traveling body 33 and the second traveling body 34 to travel. The first traveling body 33 emits light from the light source, and further reflects the light reflected from the document surface toward the second traveling body 34, and reflects the light on the mirror of the second traveling body 34 to form the imaging lens 35. And enters the image reading sensor 36 to read the contents of the document.

  In parallel with the reading of the original, the drive roller 16 is driven to rotate by a drive motor as a drive source. As a result, the intermediate transfer belt 10 moves in the clockwise direction in the figure, and the remaining two support rollers (driven rollers) 14 and 15 rotate together with this movement.

  At the same time as the reading of the document and the movement of the intermediate transfer belt 10, the drum-shaped photoconductors 40Y, 40M, 40C, and 40K as image carriers are rotated in the individual image forming units 18. Then, each of the photoconductors 40Y, 40M, 40C, and 40K is exposed and developed using yellow, magenta, cyan, and black color-specific information, thereby forming a single-color toner image (visible image).

  At a position facing each of the photoconductors 40Y, 40M, 40C, and 40K with the belt portion between the support rollers 14 and 15 of the intermediate transfer belt 10 therebetween, a primary transfer device 62Y including a primary transfer roller as a primary transfer unit is provided. 62M, 62C and 62K are provided. By the primary transfer devices 62Y, 62M, 62C, and 62K, the toner images on the photoconductors 40Y, 40M, 40C, and 40K are sequentially transferred onto the intermediate transfer belt 10 so as to overlap each other, and are synthesized on the intermediate transfer belt 10. A color toner image is formed.

  In parallel with the image forming operation, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated, and the transfer sheet S is fed out from one of the paper feed cassettes 44 provided in the paper bank 43 in multiple stages. Then, the fed transfer sheet S is separated one by one by a separation roller 45 and put into a paper feed path 46, transported by a transport roller 47, guided to a paper feed path in the apparatus main body 100, and abutted against a registration roller 49. Stop. Alternatively, the transfer sheet S on the manual feed tray 51 is fed out by rotating the paper feed roller 50, separated one by one by the separation roller 52, put into the manual feed path 53, and similarly stopped against the registration roller 49.

  Next, the registration roller 49 is rotated in synchronization with the synthetic color toner image on the intermediate transfer belt 10, and the transfer sheet S is sent between the intermediate transfer belt 10 and the secondary transfer device 22, and the secondary transfer device 22 is rotated. To transfer the color toner image onto the transfer sheet S.

  The transfer sheet S after the transfer of the toner image is conveyed by the secondary transfer belt 24 and sent to the fixing device 25, and the fixing device 25 applies heat and pressure by the fixing belt 26 and the pressure roller 27 to transfer the transfer toner image. To establish. After this fixing, the sheet is switched by the switching claw 55 and discharged by the discharge roller 56, and is stacked on the discharge tray 57. Alternatively, the sheet is switched by the switching claw 55 to enter the sheet reversing device 28, where it is reversed and guided again to the transfer position, the image is also recorded on the back surface, and then discharged onto the discharge tray 57 by the discharge roller 56.

  The intermediate transfer belt 10 after the transfer of the toner image is removed by an intermediate transfer belt cleaning device 17 to remove the residual toner remaining on the intermediate transfer belt 10 after the transfer of the toner image, and the tandem image forming unit 20 forms the image again. Prepare. Here, the registration roller 49 is generally often used with being grounded, but it is also possible to apply a bias for removing paper dust from the sheet.

  Further, the apparatus main body 100 serves as a density detecting unit for detecting the density of the toner image formed on the outer peripheral surface of the intermediate transfer belt 10, and a toner adhesion amount as a density detecting sensor which is an optical sensor unit including an optical sensor and the like. The sensor 310 is provided. The toner adhering amount sensor 310 functions as a density detecting unit that detects the amount of toner adhering on the intermediate transfer belt 10 and detects the density of the toner image on the intermediate transfer belt 10 in order to detect the density unevenness of the image. It is also called a toner image detection sensor or a toner adhesion amount detection sensor. The toner adhering amount sensor 310 detects the density of a toner image of an image pattern for correction control described later formed on the surface of the intermediate transfer belt 10 to be used for correction control of image unevenness. In addition, at a position facing the toner adhesion amount sensor 310 with the intermediate transfer belt 10 therebetween, a facing roller 311 may be provided as shown in FIG.

  FIG. 2 is an explanatory diagram illustrating a configuration example of a tandem-type image forming unit of the image forming apparatus 1 according to the present embodiment. Here, the K (black) image forming unit 18K will be described, but the Y (yellow), M (magenta), and C (cyan) image forming units 18Y, 18M, and 18C have the same configuration. I have.

  For example, as shown in FIG. 2, the image forming unit 18K includes a charging device 60K as a charging unit, a potential sensor 70K, a developing device 61K as a developing unit, and a photoconductor cleaning device 63K around a drum-shaped photoconductor 40K. And a static eliminator.

  During the image forming operation, the photoreceptor 40K is driven to rotate in the direction of arrow A by a drive motor as an image carrier rotation drive unit. After the surface of the photoreceptor 40K is uniformly charged by the charging device 60K, the photoreceptor 40K is exposed by the writing exposure L from the exposure device 21 controlled based on the image signal of the original or the like from the scanner 300 described above. , An electrostatic latent image is formed. A color image signal based on image data from the scanner 300 is subjected to image processing such as color conversion processing in an image processing unit, and is output to the exposure device 21 as an image signal of each color of transparent, K, Y, M, and C. . The exposure device 21 converts the K image signal from the image processing unit into an optical signal, and scans and exposes the surface of the uniformly charged photoconductor 40K based on the optical signal to expose the electrostatic latent image. To form

  A developing bias is applied to a developing roller 61Ka as a developer carrier of the developing device 61K, and a developing potential, which is a potential difference, is formed between the electrostatic latent image on the photoconductor 40K and the developing roller 61Ka. I have. The toner on the developing roller 61Ka is transferred from the developing roller 61Ka to the electrostatic latent image on the photoconductor 40K by the developing potential, whereby the electrostatic latent image is developed and a toner image is formed. In addition, a toner concentration sensor 312 that can detect the toner concentration in the developer is provided on the bottom surface of the developer transport unit in which the developer transport screw 61Kb in the developing device 61K is provided.

  The K toner image formed on the photoconductor 40K is primarily transferred onto the intermediate transfer belt 10 by the primary transfer device 62K. The photoreceptor 40K is cleaned of residual toner by the photoreceptor cleaning device 63K after the transfer of the toner image, and is discharged by the discharger to prepare for the next image formation. Similarly, the image forming units 18Y, 18M, and 18C include a charging device, a potential sensor, a developing device, a photoconductor cleaning device, and a static eliminator around the drum-shaped photoconductors 40Y, 40M, and 40C. Then, Y, M, and C toner images are formed on the photoconductors 40Y, 40M, and 40C, and these are primary-transferred onto the intermediate transfer belt 10 in a superimposed manner.

  In the image forming apparatus 1 having the above configuration, the exposure device 21 and the charging devices 60Y, 60M, 60C, and 60K function as a latent image forming unit that forms an electrostatic latent image on the surface of the photoconductors 40Y, 40M, 40C, and 40K. . The exposure device 21, the charging devices 60Y, 60M, 60C, and 60K and the developing devices 61Y, 61M, 61C, and 61K function as toner image forming units that form toner images on the surfaces of the photoconductors 40Y, 40M, 40C, and 40K. I do.

  Further, the image forming apparatus 1 according to the present embodiment has a photo interrupter 71K as a rotational position detecting unit capable of detecting the rotational position of the photoconductor 40K and a photo interrupter 72K as a rotational position detecting unit capable of detecting the rotational position of the developing roller 61Ka. And The photo-interrupter 71K and the photo-interrupter 72K optically detect the rotational positions of the photoconductor 40K and the developing roller 61Ka, which are rotating bodies, respectively. In this photointerrupter, for example, a light-emitting element and a light-receiving element are arranged opposite to each other, and a detected part provided in a rotationally moving part of the rotary body passes between the light-intercepting element and the light-intercepting element to block light. This is for detecting the rotational position of. The rotation position detecting means for detecting the rotation positions of the photoreceptor 40K and the developing roller 61Ka, which are rotating bodies, may be other than a photo interrupter.

  FIG. 3 is an explanatory diagram of a configuration example of the toner adhesion amount sensor 310 as a density detecting unit that detects the density of a toner image in the image forming apparatus 1 according to the present embodiment. 3A shows a configuration example of a black toner adhesion amount sensor 310 (K) suitable for detecting the density of a black toner image, and FIG. 3B shows a configuration suitable for detecting the density of a color toner image other than black. 4 shows a configuration example of a color toner adhesion amount sensor 310 (Y, M, C).

  As shown in FIG. 3A, the black toner adhesion amount sensor 310 (K) includes a light emitting element 310a including a light emitting diode (LED) and a light receiving element 310b for receiving specularly reflected light. The light emitting element 310a irradiates light onto the intermediate transfer belt 10, and the irradiated light is reflected by the intermediate transfer belt 10. The light receiving element 310b receives specularly reflected light of the reflected light.

  On the other hand, as shown in FIG. 3B, the color toner adhesion amount sensor 310 (Y, M, C) includes a light emitting element 310a including a light emitting diode (LED) and a light receiving element 310b that receives specularly reflected light. , And a light receiving element 310c that receives diffuse reflected light. The light emitting element 310a irradiates the intermediate transfer belt 10 with light, as in the case of the black toner adhesion amount sensor, and the irradiated light is reflected by the surface of the intermediate transfer belt 10. The regular reflection light receiving element 310b receives the regular reflection light of the reflected light, and the diffuse reflection light receiving element 310c receives the diffuse reflection light of the reflection light.

  In this embodiment, a GaAs infrared light emitting diode having a peak wavelength of emitted light of 950 nm is used as the light emitting element, and a Si phototransistor having a peak light receiving sensitivity of 800 nm is used as the light receiving element. . A light emitting element and a light receiving element having different peak wavelengths and peak light receiving sensitivities may be used. Further, between the black toner adhesion amount sensor 310 (K) and the color toner adhesion amount sensor 310 (Y, M, C), and the belt surface of the intermediate transfer belt 10 onto which the toner image to be detected is transferred. Are arranged with a distance (detection distance) of, for example, about 5 mm.

  In the present embodiment, the toner adhesion amount sensor 310 is provided near the intermediate transfer belt 10, and transfers a toner image of a predetermined image pattern formed on each of the photoconductors 40 Y, 40 M, 40 C, and 40 K to the intermediate transfer belt 10. To detect the density of the toner image. Image forming conditions (image forming conditions) are determined based on the detection result of the toner concentration (toner adhesion amount) detected on the intermediate transfer belt. Although the toner adhesion amount sensor 310 is provided near the intermediate transfer belt 10 in this manner, the toner adhesion amount sensor 310 is located near each of the photoconductors 40Y, 40M, 40C, and 40K, and is a transfer member that conveys the transfer sheet S. It may be arranged near the conveyor belt. Then, the density of the toner image formed on the photoconductors 40Y, 40M, 40C, and 40K is detected directly without passing through the intermediate transfer belt 10, or the toner image is transferred from each photoconductor to the transfer conveyance belt and detected. Or you may.

  Outputs from the black toner adhesion amount sensor 310 (Y, M, C) and the color toner adhesion amount sensor 310 (Y, M, C) are converted into a toner adhesion amount by an adhesion amount conversion algorithm. An algorithm similar to the prior art can be used as the adhesion amount conversion algorithm.

FIG. 4 is a block diagram illustrating an example of a main configuration of a control system of the image forming apparatus 1 according to the present embodiment.
The image forming apparatus 1 includes a control unit 500 including a computer device such as a microcomputer. The control unit 500 controls the image forming units 18 (Y, M, C, and K) in accordance with the input image information, and performs image quality adjustment control for adjusting the image quality of the output image. Function. In the image quality adjustment control according to the present embodiment, at least the periodic image density unevenness that occurs in the rotation cycle of the photosensitive member 40 and the developing roller 61a, which are the rotating members, in each of the image forming units 18 (Y, M, C, and K). Image forming condition determination control for determining an image forming condition for reducing image quality.

  The control unit 500 includes a CPU (Central Processing Unit) 501. Further, a read only memory (ROM) 503 and a random access memory (RAM) 504 as storage means connected to the CPU 501 via a bus line 502 and an I / O interface unit 505 are provided. The CPU 501 executes various calculations and drive control of each unit by executing a control program, which is a computer program incorporated in advance. The ROM 503 stores in advance fixed data such as a computer program and control data. The RAM 504 functions as a work area for storing various data in a rewritable manner.

  Various sensors such as a toner adhesion amount sensor 310, a toner density sensor 312, and a potential sensor 70 of the apparatus main body (printer unit) 100 are connected to the control unit 500 via an I / O interface unit 505. Here, various sensors such as the toner adhesion amount sensor 310, the toner density sensor 312, and the potential sensor 70 send information detected by each sensor to the control unit 500. Further, a charging bias setting unit (charging bias power supply) 330 for applying a predetermined charging bias to the charging device (charging roller) 60 is connected to the control unit 500 via an I / O interface unit 505. Further, a developing bias setting unit (developing bias power supply) 340 for applying a predetermined developing bias to the developing roller 61a of the developing device 61 is connected.

  Further, the control unit 500 has a primary transfer bias setting unit (a primary transfer bias setting unit) that applies a predetermined primary transfer bias to the primary transfer roller of the primary transfer device 62 (Y, M, C, K) via the I / O interface unit 505. A primary transfer bias power supply) 350 is connected. Further, an exposure setting section (light source power supply section) 360 for applying a predetermined voltage or supplying a predetermined current to the light source of the exposure apparatus 21 is connected.

  Further, a paper feeder (paper feed table) 200, a scanner 300, and an automatic document feeder 400 are connected to the controller 500 via an I / O interface 505. The control unit 500 controls each unit based on control target values of image forming conditions (for example, a charging bias, a developing bias, an exposure amount, a primary transfer bias, and the like).

  The ROM 503 or the RAM 504 stores, for example, a conversion table that stores information regarding conversion of the output value of the toner adhesion amount sensor 310 into the amount of toner adhesion per unit area. Further, in the ROM 503 or the RAM 504, a control target of image forming conditions (for example, charging bias, developing bias, exposure amount, primary transfer bias) of each image forming unit 18 (Y, M, C, K) in the image forming apparatus 1 is stored. The value is stored.

  Note that the control unit 500 may be configured using, for example, an IC as a semiconductor circuit element manufactured for control in the image forming apparatus 1 instead of a computer device such as a microcomputer.

  FIG. 5 is a flowchart illustrating an example of correction control for correcting periodic density unevenness in the image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 according to the present embodiment includes a first control for determining a first image forming condition so as to reduce density unevenness in a high-density image portion, and a second control for determining density unevenness in a low-density image portion. The second control for determining the second image forming condition is executed.

  In the first control (S1, S2), first, a toner image (see FIG. 6 described later) of a predetermined density image pattern (solid image pattern) is formed on each photoconductor 40 (Y, M, C, K). I do. Then, the density (toner adhesion amount) of the toner image is detected on the intermediate transfer belt 10 by the toner adhesion amount sensor 310. The detection of the toner image density (toner attachment amount) is performed while the rotational position of each photoconductor 40 (Y, M, C, K) is detected by a photo interrupter 71 (Y, M, C, K). As a result, for example, an output signal as shown in FIG. 7 described later is obtained.

  Next, using the toner adhesion amount detection signal (toner image density detection signal) detected by the toner adhesion amount sensor 310 and the rotation position signal of the photoconductor 40 detected by the photo interrupter 71, as shown in FIG. Density unevenness phase information and density unevenness amplitude information of one rotation period of the photoconductor are obtained. Then, based on the density unevenness phase information and the density unevenness amplitude information, the first image forming condition (for each rotation position of the photoconductor 40 (Y, M, C, K) applied during the image forming operation (at the time of printing)). The control data which is the control target value of the imaging condition is determined. Specifically, the control data of the developing bias applied to the developing roller 61a of each developing device 61 at each rotational position of the photoconductor 40 (Y, M, C, K) is transferred to the first image forming condition (image forming condition). ) Is determined (see FIG. 10 described later). A development bias control table in which the thus determined development bias control data is associated with the rotational position of the photoconductor 40 is created and stored in the control unit 500.

  The second control (S3 to S6) is executed following the first control (S1, S2). In the second control, in a state where the control data of the first image forming condition (development bias) obtained in the first control is applied, a predetermined value is applied on each photoconductor 40 (Y, M, C, K). A toner image of a second image pattern (halftone image pattern) having a density is formed. Then, the toner adhesion amount sensor 310 detects the density (toner adhesion amount) of the toner image of the image pattern formed on each photoconductor on the intermediate transfer belt 10. The detection of the density of the toner image (toner adhesion amount) is also performed while detecting the rotational position of each photoconductor 40 (Y, M, C, K) by the photointerrupter 71 (Y, M, C, K). Will be

  Next, using the toner adhesion amount signal (toner image density detection signal) detected by the toner adhesion amount sensor 310 and the rotation position signal of the photoconductor 40 detected by the photo interrupter 71, the density unevenness of one rotation cycle of the photoconductor is used. Phase information and density unevenness amplitude information are obtained. Then, based on the density unevenness phase information and the density unevenness amplitude information, a control that is a control target value of a second image forming condition (image forming condition) for each rotational position of the photoconductor 40 (Y, M, C, K). Provisionally determine the data. Specifically, control data of the charging bias applied to the charging device 60 at each rotation position of the photoconductor 40 (Y, M, C, K) is temporarily determined.

  Next, in the image forming apparatus of the present embodiment, the control data of the tentatively determined second image forming condition (charging bias) is corrected. This correction is performed according to the density unevenness detected for the toner image of the first image pattern in the first control (see FIGS. 11 to 13 described later). Specifically, the control data of the tentatively determined second image forming condition (charging bias) is corrected based on the density unevenness phase information and the density unevenness amplitude information in the first control described above. The control data of the second image forming condition (charging bias) after this correction is applied to the second rotational position of the photoconductor 40 (Y, M, C, K) applied during the image forming operation (at the time of printing). This is finally determined as control data which is a control target value of an image forming condition (image forming condition). A charging bias control table in which the thus determined charging bias control data is associated with the rotational position of the photoconductor 40 is created and stored in the control unit 500.

  Although the flowchart of FIG. 5 shows the control flow for the density unevenness in one rotation cycle of the photoconductor, the same first control and the second control are applied to the density unevenness in one rotation cycle of the developing roller. be able to.

Hereinafter, a more detailed embodiment of each step shown in FIG. 5 will be described.
FIG. 6 is a diagram illustrating an example of an image pattern used in the first control and the second control described in FIG.
FIG. 6A is an explanatory diagram illustrating an example of an image pattern detected using only the toner adhesion amount sensor 310 (central sensor head) disposed at the center of the intermediate transfer belt 10 in the width direction. In this example, a band-shaped single-density image pattern 320 (Y, M, C, K) of each color extending in the belt movement direction V is provided in a detection area of the toner adhesion amount sensor 310 (center sensor head). Are sequentially formed. Then, the toner adhering amount (density unevenness of the toner image) of the band-shaped single-density image pattern 320 (Y, M, C, K) of each color is detected by the toner adhering amount sensor 310. The length of each image pattern 320 (Y, M, C, K) in the belt moving direction V is determined by calculating at least the peripheral length Lp of the photoconductor 40 and the developing roller 61a in order to calculate the later-described variation in the image density unevenness information. The length of each circumference is at least one cycle. The length of each image pattern 320 (Y, M, C, K) in the belt movement direction V is at least two cycles of the circumference Lp of the photoconductor 40 and the circumference of the developing roller 61a. You may.

  FIG. 6B is an explanatory diagram illustrating an example of an image pattern detected using a plurality of toner adhesion amount sensors 310 (sensor heads). In this example, a band-shaped single-density image pattern 320 (Y, M, C, K) of each color extending in the belt moving direction V is provided in a detection area of each of the plurality of toner adhesion amount sensors 310 (sensor heads). A toner image is formed. Then, the density unevenness of the toner image of the band-shaped single density image pattern 320 (Y, M, C, K) of each color is detected by the corresponding toner adhesion amount sensor 310. Also in this case, as in the example of FIG. 6A, each image pattern 320 (Y, M, C, K) is a band-shaped single-density pattern, and at least the peripheral length Lp of each color and the development The length of the circumference of each roller is at least one cycle. The length of each image pattern 320 (Y, M, C, K) in the belt moving direction V is also at least two cycles of the circumference Lp of the photoconductor 40 and the circumference of the developing roller 61a. There may be.

  In the present embodiment, the first image pattern used for the first control is formed as a solid image pattern by a solid band pattern so as to form a shadow portion having a high image density. Further, the second image pattern used for the second control is formed as a halftone image pattern which is a halftone band pattern so as to form a halftone portion having a lower image density than the first image pattern.

  Here, the first image pattern is a solid image pattern in the present embodiment, but may be an image having a lower density as long as a change in the image density is detected. The solid band pattern forming the first image pattern means a high-density pattern in the detection sensitivity region of the toner adhesion amount sensor 310. In the present embodiment, the solid band pattern is a high-density pattern with an image density of 100% for color colors, that is, yellow, cyan, and magenta. In addition to such an image pattern, black may be a high density pattern of about 70% image density, and the second image pattern may be an image pattern of 40% image density.

  FIG. 7 is an explanatory diagram illustrating an example of measurement of the output signal of the toner adhesion amount sensor 310 and the photoconductor rotation position signal when the image pattern illustrated in FIG. 6 is detected. The upper part of FIG. 7 is a measurement example of the photoconductor rotation position detection signal detected from the photo interrupter 71 (Y, M, C, K) when the image pattern shown in FIG. 6 is formed and detected. . 7 is a measurement example of a toner adhesion amount detection signal in which the toner adhesion amount sensor 310 detects the toner adhesion amount (density of the toner image) of the image pattern shown in FIG. Here, an example of a signal for three periods of the photoconductor circumference Lp is shown. As shown in FIG. 7, the toner adhesion amount detection signal fluctuates at the same cycle as the rotation position detection signal.

  FIG. 7 shows a measurement example in which the photoconductor rotation position signal is measured together with the output signal of the toner adhesion amount sensor 310. However, the developing roller rotation position signal is output together with the output signal of the toner adhesion amount sensor 310. Similar measurement results are obtained when measurement is performed.

FIG. 8 is a block diagram showing a flow of processing until density unevenness information is obtained from the toner adhesion amount sensor signal and the photoconductor rotation position signal described in FIG. FIG. 9 is an explanatory diagram illustrating an example of the density unevenness information of the image pattern acquired in FIG.
In the image forming apparatus of the present embodiment, in the signal processing 520 of the control unit 500, a process 521 of separating the toner adhesion amount detection signal 511 from the toner adhesion amount sensor 310 for each rotation cycle (photoconductor cycle) of the photoconductor is executed. I do. In this process 521, the photoconductor rotation position signal 510 from the photo interrupter 71 is used. For example, in FIG. 7, the detection start portion of the photoconductor rotation position signal 510 (where the output starts to drop) is set to time 0, and the toner adhesion amount detection signal 511 for one cycle of the photoconductor is extracted. Thus, as shown in FIG. 9, density unevenness information for one cycle of the photoconductor (for one rotation of the photoconductor) can be obtained for three cycles (for three rotations).

  The toner adhesion amount detection signal 511 for one cycle of the photoconductor (one rotation of the photoconductor) includes a measurement error as shown in FIG. 9 and the phase and amplitude of the density unevenness vary. Therefore, in the signal processing 520 of the control unit 500, the amplitudes A1, A2,... And the phases θ1, θ2,. The process 522 for calculating the value “・” is performed. For example, the amplitudes A1, A2, A3 and the phases θ1, θ2, θ3 of the toner adhesion amount sensor signals for three cycles of the photoconductor (three rotations of the photoconductor) in FIG. 9 are calculated. For these calculations, for example, quadrature detection processing can be used. In the image forming apparatus of the present embodiment, the information of the amplitudes A1, A2, A3, and the information of the phases θ1, θ2, θ3,... Are stored as the amplitude information 530 and the phase information 531 of the image density unevenness, respectively. Used to determine image forming conditions.

  In the example of FIG. 8, the phase information 531 and the amplitude information 530 of the density unevenness are obtained from the raw output of the toner adhesion amount detection signal for one cycle of the photoconductor output from the toner adhesion amount sensor 310. The average of the toner adhesion amount detection signals for several cycles of the photoconductor may be averaged, processed into data of the toner adhesion amount detection signal for one cycle, and density unevenness information may be obtained in the same manner as the above method. Further, in the example of FIG. 8, the amplitude information of the toner adhesion amount detection signal output from the toner adhesion amount sensor 310 has been described as the image density unevenness information. The amplitude information may be obtained by converting into the toner adhesion amount.

  In the examples of FIGS. 8 and 9, the acquisition of the density unevenness information with the photoconductor circumference (one rotation of the photoconductor) as one cycle has been described. However, the development roller circumference (one rotation of the development roller) is assumed to be one cycle. The obtained density unevenness can be obtained in a similar manner. The image density unevenness having one cycle of the circumferential length of the developing roller (one rotation of the developing roller) has a shorter cycle and a smaller amplitude of the density unevenness than the case of the photoconductor. Therefore, even if the density unevenness detection signal is divided for each cycle of the developing roller as shown in FIG. 9, the density unevenness of the circumferential cycle of the developing roller is buried in the density unevenness of the cycle of the photoconductor, and the detection error of the density unevenness information increases. there is a possibility. Therefore, when detecting the density unevenness information in which the circumferential length of the developing roller (one rotation of the developing roller) is detected as one cycle, the density unevenness may be detected as follows. That is, the density unevenness of the detected photoconductor circumference cycle is removed from the toner adhesion amount detection signal 511, and the waveform of the toner adhesion amount detection signal 511 is processed. Good.

  FIG. 10 is a diagram illustrating a method of applying the image forming conditions in the first control and the second control described in FIG. In FIG. 10, in addition to the rotation position detection signal 510 and the toner adhesion amount detection signal 511 when the predetermined image pattern illustrated in FIG. 7 is formed, an image determined by the control unit 500 based on these signals 510 and 511. The example of the relationship of the control data 512 (control table) of formation conditions is shown. Here, a measurement example for two cycles of the rotating body (photoconductor 40 or developing roller 61a) is shown. The toner adhesion amount detection signal 511 fluctuates in the same cycle as the rotation position detection signal 510, and the image forming condition for the rotation position of the rotating body is set so as to be “in opposite phase” with the toner adhesion amount detection signal 511. A control table including the control data 512 is determined. The sign of the charging bias and the developing bias, which are the actual image density control parameters, is negative, or the toner adhesion amount decreases as the absolute value increases. For this reason, it is not appropriate to uniformly represent “opposite phase”, but control data (control table) is created in a direction to cancel the fluctuation of the toner adhesion amount indicated by the toner adhesion amount detection signal 511. In other words, the term “opposite phase” is used to mean that a control table that generates the toner adhesion amount fluctuation in the opposite phase is created.

  The "gain" for determining the control table is ideally obtained from a theoretical value. However, when the actual device is mounted, the actual device is verified based on the theoretical value and finally determined from experimental data. Here, the “gain” is a parameter that determines what [V] the amount of variation of the control data in the control table is with respect to the amount of variation [V] of the toner adhesion amount detection signal 511. The control table including the control data 512 determined by the gain determined in this manner has the timing relationship shown in FIG. 10 with the rotation position detection signal 510. Here, it is assumed that the head of the control table is the time when the rotation position detection signal 510 is generated. If this control table is a developing bias control table, it is necessary to determine the timing of application of the control table in consideration of the distance between the developing nip (the position where the developing roller and the photoreceptor face each other) and the toner adhesion amount sensor 310. If the distance between the development nip and the toner adhesion amount sensor 310 (the distance between the development nip and the toner adhesion amount sensor) is exactly an integral multiple of the photoconductor circumferential length, the timing of the rotation position detection signal 510 In addition, it is only necessary to apply from the top of the control table (control data) 512. If the distance between the developing nip and the toner adhesion amount sensor is deviated from an integral multiple of the circumference of the photoconductor, the control table (control data) 512 may be applied by shifting the timing by the distance of the deviation. .

  The case where the developing bias is periodically changed has been described above, but the same applies to the charging bias. As in the case of the developing bias, if the control table includes control data of the charging bias, the charging bias control table may be applied in consideration of the distance between the charging position of the charging device 60 and the toner adhesion amount sensor 310. become.

11 to 13 are diagrams illustrating the second image forming condition correction method (S6) described with reference to FIG.
FIGS. 11A and 11B show a high-density image portion (hereinafter also referred to as a “high-density portion”) and a low-density image portion (hereinafter, also referred to as “high-density portion”) before and after the first and second controls are applied, respectively, when the image density unevenness is small. 6 is a graph showing an example of a measurement result of density unevenness of a “low density portion”.
In the present embodiment, the first image forming condition determined by the first control is the developing bias. That is, in the first control, the density unevenness phase information and the density unevenness amplitude information are calculated from the density unevenness obtained from the high-density solid image pattern, and the developing bias is modulated so as to cancel the density unevenness based on the information. . This modulation method is the same as the method described in Patent Document 1. Here, in the first control described above, the developing bias is controlled to change the developing potential. Therefore, at the same time, the background potential, which is the potential difference between the charging potential and the developing bias (development potential), fluctuates, and the density of the halftone image affected by the fluctuation in the background potential also fluctuates.

  Therefore, in the present embodiment, the above-described second control reduces the density unevenness of the halftone image that fluctuates due to the application of the first image forming condition. In the second control, a halftone density image pattern (band pattern) is formed with a control table for modulating the control data of the first image forming condition (development bias) applied. Then, the density (toner adhering amount) of the toner image of the halftone density image pattern is detected, and based on the detection result, the density unevenness of the low-density portion that is deteriorated by canceling the density unevenness of the high-density portion is suppressed. . Specifically, control data of the second image forming condition (charging bias) effective for controlling the background potential is controlled so as to suppress the density unevenness of the low-density portion which is deteriorated by canceling out the density unevenness of the high-density portion. Create a control table to be modulated. Then, as shown in the measurement data C103 and C203 in FIGS. 11A and 11B, during the image forming operation (during printing), each of the image forming conditions determined by the first control and the second control is satisfied. Apply control tables. As a result, it is possible to reduce the density unevenness in each of the high density portion and the low density portion.

FIGS. 12A and 12B respectively show high density before and after the first and second control applications when the density unevenness of the first image pattern detected by the first control is larger than that in the case of FIG. 7 is a graph showing an example of a measurement result of density unevenness of a part and a low density part.
As shown in the figure, as the density unevenness of the high-density first image pattern detected by the first control is greater, control of the first image forming condition (developing bias) necessary to cancel the high-density unevenness of the pattern is performed. The data modulation amount (the amplitude of the developing bias control table) naturally increases. Under the influence, the fluctuation of the background potential increases, and the density unevenness of the halftone image (low-density portion) also greatly deteriorates.

  Measurement data C403 in FIG. 12B indicates measurement data of density unevenness in a low density portion when the control data of the second image forming condition is applied in the above-described second control. As shown by the measurement data C403, when the density unevenness in the high-density portion is large, the level of the density unevenness in the low-density portion becomes worse than before the application even when the control data of the second image forming condition is applied. ing. In the second control, the gain is adjusted so as to cancel the influence of the density unevenness that has been deteriorated by applying the control data of the first image forming condition determined in the first control, and the second image forming condition (charge Bias) control data is determined. However, even when the control table of the second image forming condition (charging bias) determined by adjusting the gain is applied, the low density deteriorated by the application of the control data of the first image forming condition (developing bias). The density unevenness of the part cannot be canceled sufficiently.

  Therefore, in the present embodiment, when the density unevenness of the high-density portion is large, the control table of the second image forming condition (charging bias) provisionally determined by the second control is corrected and used during the image forming operation. I have.

  The measurement data C304 and C404 in FIG. 12 are measurement data of the density unevenness of the high density portion and the low density portion when the modulation table of the charging bias is corrected. As shown in the measurement data C404 in FIG. 12B, by correcting the control table of the second image forming condition (charging bias), it is possible to reduce the density unevenness in the low density portion.

  When the second image forming condition (charging bias) is corrected in the case of FIG. 11 in which the density unevenness in the high density portion is not so large, the correction becomes excessively conversely, and the density unevenness in the low density portion deteriorates. In addition, the density unevenness of the high-density portion also becomes worse as the value of the control data of the second image forming condition (charging bias) increases. Therefore, the gain applied to the second image forming condition (charging bias) of the present embodiment (what [V] should the variation amount of the control table be with respect to the variation amount [V] of the toner adhesion amount detection signal)? Is different depending on the density unevenness of the high density portion detected by the first control. The optimum value of the gain applied to the second image forming condition (charging bias) differs depending on the first image forming condition (developing bias) determined by the first control.

FIG. 13 is applied to the second image forming condition (charging bias) in order to cancel the high density unevenness (amplitude of fluctuation of the toner adhesion amount) detected in the first control and the density unevenness in the low image area. 9 is a graph illustrating an example of a relationship between a gain and a correction coefficient.
With respect to the control table of the second image forming condition (charging bias) calculated by the provisional determination in the second control, a correction coefficient set according to the density unevenness (horizontal axis) of the high density portion in FIG. Apply the corrected gain. Accordingly, when the density unevenness of the high density portion detected by the first control is large, and the side effect on the low density portion caused by applying the first image forming condition (development bias) determined by the first control is large. However, density unevenness in the low density portion can be reduced. That is, it is possible to appropriately reduce the density unevenness of the low density portion without the density unevenness of the high image portion being deteriorated again by the second control.

In the example of FIG. 13, the second image is not changed until the variation (density unevenness) of the toner adhesion amount in the high-density portion reaches a predetermined threshold (about 8 × 10 ³ mg / cm ^{2 in the} illustrated example). The gain applied to the control table of the forming condition (charging bias) is not corrected (correction coefficient = 1). Then, when the variation (density unevenness) of the toner adhesion amount in the high density portion becomes larger than a predetermined threshold value, the following correction is performed. That is, the correction is performed by multiplying the gain applied to the control table of the second image forming condition (charging bias) by a correction coefficient set so as to be proportional to the variation (density unevenness) of the toner adhesion amount. The correction equation used for such correction and the threshold value are not limited to those shown in FIG. 13, and are set, for example, according to the occurrence of density unevenness in the high density portion and the low density portion in an actual apparatus. You.

  In the present embodiment, the control data of the second image forming condition (charging bias) before correction is temporarily determined in the second control. Then, the control data of the temporarily determined second image forming condition is corrected based on the density detection result of the toner image of the high-density first image pattern detected by the first control. The control data of the second image forming condition (charging bias) after this correction is finally determined as the control data of the second image forming condition (charging bias) used during the image forming operation. In another embodiment, the second control may be executed without tentatively determining and correcting the control data of the second image forming condition (charging bias). For example, when it is determined in the second control that the high density unevenness is large, the control data of the second image forming condition (charging bias) may be determined as follows. That is, control data of the second image forming condition (charging bias) is determined based on the density detection result of the toner image of the first image pattern and the density detection result of the toner image of the second image pattern. You may.

Next, the execution determination of the first control and the second control will be described.
The execution determination as to whether to execute the first control and the second control is made, for example, at a timing when the rotational positions of the photosensitive drums 40Y, 40M, 40C, and 40K can be changed in the apparatus main body of the image forming apparatus. Do. This timing is immediately after the photosensitive drum is set (at the time of initial setting, at the time of replacement, at the time of attachment / detachment, etc.).

  The first control and the second control are executed at the above-described timing because, when the photoconductor 40 is mechanically removed from the apparatus main body 100 of the image forming apparatus, the occurrence state of the image density unevenness in the photoconductor cycle is reduced. This is because the possibility of change is high. Another reason is that the positional relationship between the rotational position of the photoconductor 40 and the photo interrupter 71 is shifted. At the time of initial setting of the photoreceptor in which the control table of the image forming conditions has not been prepared, it is necessary to perform a series of the first control and the second control to prepare the control table. When the photoconductor is replaced, the control table corresponding to the new photoconductor 40 needs to be re-created because the new photoconductor has differences in deflection characteristics and light sensitivity characteristics unevenness from the photoconductor previously used. Further, even when the photoconductor is simply detached for maintenance, there is a possibility that a change in the mounting state of the photoconductor accompanying the detachment of the photoconductor (change in the manner of displacement between the photoconductor shaft and the rotation axis) may occur. Further, the position of the fluctuation characteristic and the light sensitivity characteristic unevenness of the photoconductor 40 and the position of the photo interrupter 71 are shifted. Therefore, it is necessary to re-create the control table of the image forming conditions described above. For the above reasons, it is necessary to determine the image forming conditions (create / update the control table) immediately after the photoconductor 40 is set.

  Similarly, the determination of the execution of the first control and the second control may be performed when the environmental conditions in the apparatus change. When the temperature condition among the environmental conditions changes, the photoconductor tube expands and contracts in accordance with the thermal expansion coefficient of the photoconductor tube. For this reason, there is a possibility that the appearance profile of the photoreceptor 40 changes, and the state of occurrence of density unevenness changes due to a change in the state of fluctuation of the development gap. In order to cope with this change, it is necessary to execute first and second controls for determining image forming conditions (creating / updating a control table) when environmental conditions change. The method of determining the trigger for executing the first and second controls is as follows: "when there is a temperature change of N [deg] or more compared to the time when the previous image forming conditions were determined (control table creation / update). ]. Further, the execution determination of the first and second controls may be similarly performed at a printing interval of a fixed number of sheets.

  Similarly, the determination of execution of the first control and the second control may be performed when the toner concentration of the developer in the developing device changes. When the toner density decreases, the situation of occurrence of the density unevenness may change. In order to cope with this change, it is necessary to execute first and second controls for determining image forming conditions (creating / updating a control table) when the toner density changes. The trigger for executing the first and second controls may be determined as follows: “A change in toner density that is equal to or more than a predetermined reference change amount compared to the previous determination of the image forming conditions (creation / update of the control table)” If there is ". Alternatively, control may be performed such that the first and second controls are executed when the measured value of the toner density becomes equal to or less than a predetermined reference value.

  Next, another example of the second control of the present embodiment will be described. In the second control of this example, as shown below, the density responsiveness indicating the relationship between the change in the second image forming condition and the change in the toner adhesion amount (density) of the toner image of the second image pattern is measured. Then, the control data of the second image forming condition is determined based on the measurement result.

  In this example, a high-density solid image is formed as the first image pattern, and a halftone image is created as the second image pattern. Further, in the present embodiment, a case in which the density fluctuation occurs only in the rotation period of the photoconductor will be described. However, the second control of the present embodiment described later can be applied to the following case. That is, the second control of the present embodiment is also applicable to a case where a density fluctuation occurs in the rotation period of the developing roller or a case where a density fluctuation corresponding to both the photoconductor period and the rotation period of the developing roller occurs.

  Further, the second control of this example may be performed without being combined with the correction of the control table of the second image forming condition when the density unevenness of the high density portion is large, or the second image forming This may be performed in combination with the correction of the condition control table. For example, when the density unevenness of the high-density portion is large, the control table of the second image forming condition is corrected, and the control table of the second image forming condition after the correction is measured. The correction may be made based on the result.

  14 and 15 are diagrams for explaining a problem to be solved by the control for determining the control data of the second image forming condition in the present example. FIG. 14 is a graph showing an example of a profile as a time change of the toner adhesion amount (density) of each of the first image pattern and the second image pattern before reflecting the first image forming condition. FIG. 15 shows the relationship between the time change of the toner adhesion amount (density) of each of the first image pattern and the second image pattern and the time change of the value of the control table (control data) of the first image forming condition. It is a graph which shows an example. FIG. 16 is a graph illustrating an example of a change over time of the toner adhesion amount (density) of each of the first image pattern and the second image pattern after applying the first image forming condition. FIG. 16 also shows a time change of the toner adhesion amount (density) of the second image pattern before the first image forming condition is applied, for comparison reference.

  In the image forming apparatus of the present embodiment, as shown in FIG. 14, in a state where the density of the image pattern fluctuates, the toner adhesion amount (density) C501 of the first image pattern is detected. In this state, the toner adhesion amount (density) C502 of the first image pattern also changes as shown in FIG. Next, based on the detection result of the toner adhesion amount (density) C501 of the first image pattern, as shown in FIG. 8 and FIG. And the amplitude Ab.

  Next, as shown in FIG. 15, the image forming apparatus creates a control table C503 of the first image forming condition based on the detection result of the toner adhesion amount (density) C501 of the first image pattern. This control table generates a time variation of the toner adhesion amount (density) having a phase opposite to the waveform of the detected adhesion amount unevenness (density unevenness) in order to cancel the adhesion amount unevenness (density unevenness) of the first image pattern. Decide to create. However, the control table may be created by adjusting the correction gain to prevent overcorrection or undercorrection. At this time, the first image forming condition may be a developing condition or an exposure condition for changing an electric field between the developing roller and the photoconductor. In this example, the developing condition is changed as the first image forming condition.

  Next, as shown in FIG. 16, the image forming apparatus determines the toner adhesion amount (density) C504 of the first image pattern formed in a state in which the control table of the first image forming condition is reflected and the second image pattern. The toner adhesion amount (density) C505 is detected. Then, from the detection result, the amplitude Ac and the phase Pc of the toner adhesion amount unevenness (density unevenness) of the second image pattern are acquired. At this time, if the toner adhesion amount unevenness (density unevenness) of the first image pattern is correctly detected without error, as shown by C504 in FIG. 16, the toner adhesion amount unevenness (density unevenness) of the first image pattern Is canceled out and is in a flat state. On the other hand, in the second image pattern, toner adhesion amount unevenness (density unevenness) caused by the potential fluctuation at the time of forming the image pattern and the potential fluctuation at the time of forming the image pattern by the first control is superimposed. It is in a state.

  Next, the image forming apparatus determines a control table (control data) for the second image forming condition from the detection result of the amplitude Ac and the phase Pc of the toner adhesion amount unevenness (density unevenness) of the second image pattern. create. This control table is designed so that the toner adhesion amount fluctuation of the opposite phase to the waveform of the detected adhesion amount unevenness (density unevenness) occurs in order to cancel the toner adhesion amount unevenness (density unevenness) of the second image pattern. Decide and create. The second image forming condition at this time is a charging condition (charging bias) of the photoconductor. According to the control table of the second image forming conditions, the density unevenness of the second image pattern (halftone image) can be reduced without impairing the effect of reducing the density unevenness of the first image pattern (solid image) by the first control. Can be reduced.

  In the control method for determining and creating the control data of the image forming conditions as described above, it is necessary to create a charging bias control table so as to cancel out the density unevenness of the detected second image pattern (halftone image). For this reason, a relationship between the amount of change in the background potential determined by the charging condition (charging bias) as the second image forming condition and the amount of change in the toner adhesion amount (density) is given in advance, and an appropriate value is determined based on this relationship. A control table for charging conditions (charging bias) is determined. That is, density responsiveness indicating the relationship of the toner adhesion amount (density) of the toner image of the second image pattern to the change of the second image forming condition is given in advance, and an appropriate charging condition is determined based on the density responsiveness. (Charge bias) control table is determined.

  However, the relationship between the amount of change in the background potential and the amount of change in the toner adhesion amount (density) determined by the charging condition (charging bias) as the second image forming condition depends on environmental (temperature and humidity) conditions, toner characteristics, and the like. It may change and is not always constant. If this relationship is erroneously set and a control table for the charging bias as the second image forming condition is created, overcorrection or undercorrection occurs, and the variation in the toner adhesion amount (density) of the halftone image is appropriately reduced. In some cases, it is not possible to make it worse.

  Therefore, in this example, in order to avoid the overcorrection and the undercorrection, the density responsiveness indicating the change of the toner adhesion amount (density) of the second image pattern with respect to the change of the charging bias includes the change amount of the background potential and the change amount of the background potential. The relationship with the amount of change in the toner adhesion amount (density) is measured. Then, control is performed so that a control table for the charging bias is determined based on the measurement result.

FIG. 17 is a graph showing an example of the measurement result of the relationship between the change amount of the background potential and the change amount of the toner adhesion amount (density) of the second image pattern in this example.
This control is performed, for example, as follows.
First, a toner image of a halftone image pattern having the same image area ratio as the second image pattern is created by changing a charging bias as a charging condition which is a second image forming condition. Next, the charged potential in the created image pattern is detected by the potential sensor 70, and the toner adhesion amount of the toner image of the image pattern is measured by the toner adhesion amount sensor 310. These measurements were performed at least at two or more levels, and as shown in FIG. 17, a density response indicating the relationship between the variation in the background potential (charging potential-developing potential (developing bias)) and the variation in the amount of toner attached to the image pattern. Obtain gender measurement results.

Next, based on the measurement result of the density responsiveness, a control table of the second image forming condition (charging bias) is determined as exemplified below. Here, it is assumed that the amount of change in the amount of toner attached to the halftone image, which is the second image pattern described above with reference to FIGS. 14 to 16, is a sine wave having an amplitude X [mg / cm ² ]. It is also assumed that the slope of the change amount of the background potential and the change amount of the toner adhesion amount as measured in FIG. 17 are Y [mg / cm ² / V]. In this case, the control table of the charging bias as the charging condition, which is the second image forming condition, indicates that the amplitude is X / Y [V] and the phase of the toner adhesion is opposite to that of the toner adhesion amount profile of the halftone image. It is determined so as to be a sine wave of a phase [deg] that gives a quantity variation. With the control table of the charging bias determined in this way, it is possible to cancel the fluctuation of the toner adhesion amount of the second image pattern.

  The control for determining the second image forming condition based on the measurement result of the density responsiveness described with reference to FIGS. 14 to 17 is performed by controlling the relationship between the background potential variation amount and the toner adhesion amount variation amount. It may be executed at a timing when the concentration responsiveness can change. For example, the control is performed when environmental conditions such as temperature and humidity in the image forming apparatus fluctuate, or every fixed number of transfer sheets S as a recording medium on which an image is formed by the image forming apparatus of the present embodiment. It may be performed or when the toner concentration of the developer fluctuates.

  In addition, if the control is performed each time the responsiveness of the toner adhesion amount changes due to environmental conditions or the like, the user may wait for an image forming operation for forming an image on a recording medium (transfer sheet) by using a “waiting time”. May increase. Therefore, a second image pattern was formed at a predetermined timing, the density responsiveness was measured, and the measurement result of the density responsiveness was evaluated with time, based on environmental conditions, developing ability and toner density in the developing device, and image formation. It may be corrected and changed depending on the number of output sheets of the transfer sheet. Then, the second image forming condition may be determined by using the corrected and changed measurement result of the responsiveness of the toner adhesion amount.

  In the above-described embodiment, the case where the image forming apparatus is an electrophotographic copying machine employing a tandem type and an intermediate transfer (indirect transfer) method is described. However, other image forming apparatuses such as a printer and a facsimile are used. Is also good.

What has been described above is merely an example, and each embodiment has a specific effect.
(Aspect A)
An image carrier such as a photoconductor 40 composed of a rotating body, an exposure device 21 for forming a toner image on the surface of the image carrier, a toner image forming means such as a charging device 60 and a developing device 61, and an image carrier formed on the image carrier. Density detecting means such as a toner adhesion amount sensor 310 for detecting the density of the toner image, and forming a high-density toner image of the first image pattern on the image carrier, and the density of the toner image of the first image pattern. A first control unit such as the control unit 500 that determines control data of the first image forming condition based on the detection result, and control data of the first image forming condition created by the first control unit are applied. In the state, the toner image of the second image pattern having a lower density than the first image pattern is formed on the image carrier, and the second image is formed based on the density detection result of the toner image of the second image pattern. Control data for forming conditions Control means for controlling the toner image forming means during the image forming operation based on the control data of the first image forming condition and the control data of the second image forming condition. An image forming control unit such as a unit 500, wherein the second control unit determines the control data of the second image forming condition by determining the control data of the toner image of the first image pattern. This is performed based on the density detection result and the density detection result of the toner image of the second image pattern.
According to this, as described in the embodiment, when the density unevenness of the high-density first image pattern detected by the first control is large, the high-density Large density unevenness occurs in the low-density image area in the same cycle as the density unevenness. In order to reduce the density unevenness of the low-density image portion, the density detection result of the toner image of the first image pattern and the density detection of the toner image of the second image pattern including the density unevenness having the same cycle as the density unevenness Based on the result, the control data of the second image forming condition can be determined. By applying the thus determined second image forming condition during the image forming operation, the density unevenness of the low density image portion can be reliably reduced.
(Aspect B)
In the above aspect A, the second control means temporarily determines control data of a second image forming condition based on a density detection result of the toner image of the second image pattern, and controls the toner image of the first image pattern. The control data of the second image forming condition is determined by correcting the provisionally determined control data of the second image forming condition based on the density detection result.
According to this, as described in the above embodiment, it is possible to confirm the density unevenness of the low-density image portion when the provisionally determined second image forming condition control data is applied to the image forming operation.
(Aspect C)
In the above aspect A or B, the toner adhesion amount sensor 310 and the potential sensor 70 for measuring a density responsiveness indicating a relationship between a change in the density of the toner image of the second image pattern and a change in the second image forming condition. The second control means determines control data of the second image forming condition based on the measurement result.
According to this, as described in the above embodiment, even when the density responsiveness fluctuates with time, the control data of the second image forming condition is appropriately determined, and the density unevenness of the low density image portion is reduced. It can be surely reduced.
(Aspect D)
In the above-mentioned aspect C, the measuring unit may be configured to change the density response of the toner image of the second image pattern when the second image pattern is formed by changing a second image forming condition. Measure gender.
According to this, as described in the above embodiment, the concentration responsiveness can be accurately measured.
(Aspect E)
In the above aspect D, the image forming apparatus further includes a potential detecting unit that detects a potential in a latent image of the image pattern when the image pattern is formed on the image carrier, wherein the measuring unit includes a toner image of a second image pattern on the image carrier. The second image forming condition is controlled so as to change the potential in the second image pattern when forming the image, and the relationship between the amount of change in the potential and the amount of change in the density of the toner image of the second image pattern Is measured as the concentration responsiveness.
According to this, as described in the embodiment, it is possible to measure the density responsiveness indicating the relationship between the change in the charging condition and the change in the density of the toner image of the second image pattern.
(Aspect F)
In the above aspects D or E, the formation of the second image pattern when the second image forming condition is changed is performed at least at two or more levels.
According to this, as described in the above embodiment, the concentration responsiveness can be accurately measured.
(Aspect G)
In any one of the above modes C to F, the toner image forming means forms a latent image on the surface of the image carrier by charging the surface of the image carrier to a predetermined potential and exposing the charged surface to light. , A toner image is formed by developing a latent image with a developer containing toner, and a toner density detecting unit for detecting a toner density of the developer is provided. The measurement result is corrected based on at least one of the number of recording media on which an image is formed and the detection result of the toner density, and control data of a second image forming condition is corrected based on the corrected measurement result. decide.
According to this, as described in the above embodiment, even when environmental conditions in the image forming apparatus fluctuate with time, the control data of the second image forming condition is appropriately determined, and the low-density image section Can be surely reduced. In addition, by using the corrected measurement result to determine the control data of the second image forming condition over time, it is not necessary to measure the density responsiveness when the environmental condition or the toner density changes. Therefore, it is not necessary to delay the start of the image forming operation or interrupt the image forming operation for measuring the density responsiveness, and it is possible to reduce the waiting time of the user during the image forming.
(Aspect H)
In any one of the above modes A to G, the density detection result in each of the first control means and the second control means may be a periodic density of the toner image repeated in one rotation cycle of the image carrier. Includes amplitude information and phase information of unevenness.
According to this, as described in the above embodiment, the density unevenness of the high-density image portion and the low-density image portion that occurs over one rotation cycle of the image carrier can be reliably reduced.
(Aspect I)
In any one of the above modes A to H, the toner image forming unit forms a latent image on the surface of an image carrier such as the photoconductor 40, and forms the latent image on the surface of a developer carrier such as a developing roller 61a composed of a rotating body. The latent image on the image carrier is developed using the carried developer to form a toner image, and the density detection result used by the first control unit and the second control unit is the developer carrier. The amplitude information and the phase information of the periodic density unevenness of the toner image repeated in one rotation cycle.
According to this, as described in the above embodiment, the density unevenness of the high-density image portion and the low-density image portion that occurs over one rotation cycle of the developing carrier can be reliably reduced.
(Aspect J)
In any of the above aspects A to I, the length of each of the first image pattern and the second image pattern in the image carrier surface moving direction is at least one circumference of a rotating body such as the photoconductor 40 and the developing roller 61a. Is the length of
According to this, as described in the above embodiment, it is possible to detect the density unevenness of each image pattern for one rotation cycle or more of the rotating body, so that the high density image portion and the low density image portion generated over one rotating cycle of the rotating body are detected. Can be more reliably reduced.
(Aspect K)
In any one of the above modes A to J, the toner image forming unit charges the surface of the image carrier such as the photoconductor 40 to a predetermined potential, and exposes the charged surface to the surface of the image carrier to expose the surface of the image carrier. A latent image is formed, and a toner image is formed by developing the latent image. The first image pattern and the second image pattern are single density patterns, and the first image forming condition is The second image forming condition is a charging condition such as an anti-static bias when the surface of the image carrier is charged when the latent image on the image carrier is developed.
According to this, as described in the above embodiment, each image pattern is a single density pattern in which density unevenness can be easily detected. In addition, since the first image forming condition is a developing condition for easily controlling the density unevenness in the high density image area, and the second image forming condition is a charging condition for easily controlling the density unevenness in the low density image area, Density unevenness of the density image portion and the low density image portion can be more reliably reduced.
(Aspect L)
In any one of the above modes A to K, the image forming apparatus further includes a rotation position detecting unit such as photo-interrupters 71 and 72 for detecting a rotation position of a rotating body such as the photoreceptor 40 and the developing roller 61a. The determination of the control data for each of the image forming conditions and the image forming control based on the control data are executed in synchronization with the rotational position of the rotator based on the detection result of the rotational position detecting means.
According to this, as described in the above embodiment, the control data of the first image forming condition and the second image forming condition are determined in synchronization with the rotational position of the rotating body that causes the density unevenness. Since the image forming control is executed, density unevenness can be reduced more reliably.
(Aspect M)
In any of the above aspects A to L, the determination of the control data for each of the first image forming condition and the second image forming condition is executed when the mounting rotational position of the rotating body changes.
According to this, as described in the above-described embodiment, the density unevenness can be reliably reduced even when the rotation position of the rotating body where the relationship between the rotational position of the rotary body and the density unevenness changes changes.
(Aspect N)
In any one of the above aspects A to M, the determination of the control data of each of the first image forming condition and the second image forming condition is performed for each fixed number of recording media on which an image is formed by the image forming apparatus. Be executed.
According to this, as described in the above embodiment, even when image formation on a recording medium is repeated, density unevenness can be reliably reduced.
(Aspect O)
In any one of the above aspects A to N, the determination of the control data of each of the first image forming condition and the second image forming condition is executed when the environmental condition in the image forming apparatus changes.
According to this, as described in the above-described embodiment, the density unevenness can be reliably reduced even when the environmental condition changes in which the relationship between the rotational position of the rotating body and the density unevenness changes.
(Aspect P)
In any one of Aspects A to O, the toner image forming means may form a latent image on the surface of the image carrier by charging the surface of the image carrier to a predetermined potential and exposing the charged surface to light. Is configured to form a toner image by developing a latent image with a developer containing toner, and the determination of the control data for each of the first image forming condition and the second image forming condition is performed by the developer. This is executed when the toner density changes.
According to this, as described in the above embodiment, even when the toner concentration of the developer fluctuates, it is possible to reduce the density unevenness in the high density image portion and the low density image portion.

1 Image Forming Apparatus 10 Intermediate Transfer Belt 18 (Y, M, C, K) Image Forming Section 20 Tandem Image Forming Section 21 Exposure Apparatus 40 (Y, M, C, K) Photoconductor 60 (Y, M, C, K) ) Charging device 61 (Y, M, C, K) Developing device 61 (Y, M, C, K) a Developing roller 62 (Y, M, C, K) Primary transfer device 70 Potential sensor 100 Device body (printer unit) )
310 toner adhesion amount sensor 500 control unit

JP 2014-178404 A

Claims (16)

An image carrier comprising a rotating body,
Toner image forming means for forming a toner image on the surface of the image carrier,
Density detection means for detecting the density of the toner image formed on the image carrier,
A first image forming unit configured to form a high-density toner image of a first image pattern on the image carrier and determine control data of a first image forming condition based on a density detection result of the toner image of the first image pattern; Control means;
In a state where the control data of the first image forming condition created by the first control means is applied, a toner image of a second image pattern having a lower density than the first image pattern is formed on the image carrier. A second control means for determining the control data of the second image forming conditions based on the density detection result of the toner image of the second image pattern,
An image forming apparatus comprising: an image forming control unit configured to control the toner image forming unit during an image forming operation based on control data of the first image forming condition and control data of the second image forming condition. And
The second control means determines the control data of the second image forming condition based on a density detection result of the toner image of the first image pattern and a density detection result of the toner image of the second image pattern. The image forming apparatus is characterized in that it is performed based on the following. The image forming apparatus according to claim 1,
The second control means tentatively determines control data of a second image forming condition based on a toner image density detection result of the second image pattern, and detects the density of the toner image of the first image pattern. An image forming apparatus, wherein the control data of the second image forming condition is determined by correcting the provisionally determined control data of the second image forming condition based on the result. The image forming apparatus according to claim 1, wherein
Measuring means for measuring density responsiveness indicating a relationship between a change in the density of the toner image of the second image pattern and a change in the second image forming condition,
The image forming apparatus, wherein the second control means determines control data of the second image forming condition based on a measurement result of the density responsiveness . The image forming apparatus according to claim 3,
The measuring unit measures the density responsiveness by an amount of change in density of a toner image of the second image pattern when the second image pattern is formed by changing the second image forming condition. An image forming apparatus comprising: The image forming apparatus according to claim 4,
A potential detecting unit that detects a potential in the image pattern when the image pattern is formed on the image carrier;
The measuring unit controls the second image forming condition so as to change a potential in the second image pattern when forming a toner image of the second image pattern on the image carrier, and An image forming apparatus, wherein a relationship between a change amount of a potential and a change amount of a density of a toner image of the second image pattern is measured as the density responsiveness. The image forming apparatus according to claim 4, wherein
The image forming apparatus according to claim 1, wherein forming the second image pattern when the second image forming condition is changed is performed at least at two or more levels. The image forming apparatus according to claim 3, wherein
The toner image forming means charges the surface of the image carrier to a predetermined potential, forms a latent image on the surface of the image carrier by exposing the charged surface, and forms the latent image with a developer containing toner. Configured to form a toner image by developing the latent image,
A toner concentration detecting unit for detecting a toner concentration of the developer,
Correcting the measurement result of the density responsiveness based on at least one of environmental conditions in the image forming apparatus, the number of recording media on which an image is formed by the image forming apparatus, and the detection result of the toner density; An image forming apparatus, wherein control data of the second image forming condition is determined based on a measurement result obtained later. The image forming apparatus according to claim 1, wherein
The result of the density detection in each of the first control means and the second control means includes amplitude information and phase information of periodic density unevenness of the toner image repeated in one rotation cycle of the image carrier. An image forming apparatus comprising: The image forming apparatus according to any one of claims 1 to 8,
The toner image forming means forms a latent image on the surface of the image carrier, and develops the latent image on the image carrier using a developer carried on the surface of a developer carrier composed of a rotating body. Configured to form a toner image,
The density detection result used by the first control means and the second control means includes amplitude information and phase information of periodic density unevenness of the toner image repeated in one rotation cycle of the developer carrier. An image forming apparatus comprising: The image forming apparatus according to any one of claims 1 to 9,
The image forming apparatus according to claim 1, wherein a length of each of the first image pattern and the second image pattern in a direction of moving the surface of the image carrier is equal to or longer than one circumference of the rotating body. The image forming apparatus according to any one of claims 1 to 10,
The toner image forming unit charges the surface of the image carrier to a predetermined potential, forms a latent image on the surface of the image carrier by exposing the charged surface, and develops the latent image. Is configured to form a toner image by
The first image pattern and the second image pattern are a single density pattern,
The first image forming conditions are development conditions for developing a latent image on the image carrier,
The image forming apparatus according to claim 1, wherein the second image forming condition is a charging condition for charging a surface of the image carrier. The image forming apparatus according to any one of claims 1 to 11,
A rotating position detecting unit that detects a rotating position of the rotating body,
The determination of the control data for each of the first image forming condition and the second image forming condition and the image forming control based on the control data are performed based on the detection result of the rotation position detection unit. The image forming apparatus is executed in synchronization with the image forming apparatus. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the determination of the control data for each of the first image forming condition and the second image forming condition is executed when a mounting rotational position of the rotating body changes. The image forming apparatus according to any one of claims 1 to 13,
The image forming apparatus according to claim 1, wherein the determination of the control data for each of the first image forming condition and the second image forming condition is performed for every fixed number of recording media on which images are formed by the image forming apparatus. apparatus. The image forming apparatus according to any one of claims 1 to 14,
The image forming apparatus according to claim 1, wherein the determination of the control data for each of the first image forming condition and the second image forming condition is performed when an environmental condition in the image forming device changes. The image forming apparatus according to any one of claims 1 to 15,
The toner image forming means charges the surface of the image carrier to a predetermined potential, forms a latent image on the surface of the image carrier by exposing the charged surface, and forms the latent image with a developer containing toner. Configured to form a toner image by developing the latent image,
The image forming apparatus according to claim 1, wherein the control data for each of the first image forming condition and the second image forming condition is determined when the toner concentration of the developer changes.