JP2011170009A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, which can simultaneously perform the formation of a density detection image and the forcible discharge of developer and can prevent the useless consumption of toner. <P>SOLUTION: A control section 32 repeatedly forms a patch image M, and calculates an amount ΔS<SB>n</SB>of change in area from a patch image M<SB>n</SB>formed immediately before according to the detected densities A<SB>n</SB>, A<SB>n-1</SB>, and A<SB>n-2</SB>of the patch images M<SB>n</SB>, M<SB>n-1</SB>and M<SB>n-2</SB>. Then, based on the calculated amount ΔS<SB>n</SB>of change in area, the control section varies the area S<SB>n+1</SB>of the patch image M<SB>n+1</SB>to be formed next, to form the patch image M<SB>n+1</SB>, thereby performing the forcible discharge of toner. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using electrophotography, and more particularly to forced discharge of a developer from a developing device in the image forming apparatus.

  Conventionally, as a development method using dry toner in an image forming apparatus using an electrophotographic process, a one-component development method using no carrier and a two-component developer charging a nonmagnetic toner using a magnetic carrier are used. In addition, a two-component development system is known in which an electrostatic latent image on an image carrier (photoconductor) is developed by a magnetic brush composed of toner and a carrier formed on a developing roller.

  The one-component development method is suitable for high image quality because the electrostatic latent image on the image carrier is not disturbed by the magnetic brush. On the other hand, the toner is charged by the charge roller, and the elastic regulating blade is used on the development roller. In order to regulate the layer thickness, the toner additive adheres to the charge roller, the charging ability is lowered, and it is difficult to stably maintain the charge amount of the toner. In addition, toner may adhere to the regulating blade, resulting in non-uniform layer formation and image defects.

  In the case of color printing in which color superposition is performed, since the color toner is required to be transparent, it needs to be a non-magnetic toner. Therefore, in a full-color image forming apparatus, a two-component development system in which toner is charged and conveyed using a carrier is often employed. However, the two-component development method can maintain a stable charge amount for a long time and is suitable for extending the life of the toner, but is disadvantageous in terms of image quality due to the influence of the magnetic brush described above.

  As one of means for solving these problems, when a developer is transferred onto a developing roller (toner carrier) installed in a non-contact manner with respect to the image carrier using a magnetic roller (toner supply member), A developing method is proposed in which only a non-magnetic toner is transferred onto the developing roller while leaving the magnetic carrier on the magnetic roller to form a thin toner layer, and the toner is attached to the electrostatic latent image on the image carrier by an AC electric field. Has been.

  Here, when the toner in the developer is consumed by development, the toner is replenished from the toner container into the developing device according to the consumption amount, and the toner in the developing device is sequentially replaced. When the replacement of toner in the developing device is reduced, such as when image formation at a printing rate is continuous, the toner staying time in the developing device becomes longer.

  When the staying time becomes longer as described above, the stirring of the toner and the rubbing of the surface are repeated by mixing with the carrier, and the toner moves back and forth between the magnetic roller and the developing roller many times. As a result, the toner is likely to be deteriorated, such as irregular shape of the toner, uneven distribution of the particle size, or external additives buried in or detached from the toner surface. Image defects such as reduction, ghost, toner scattering, and fogging are likely to occur. Therefore, a method for forcibly discharging the deteriorated toner has been proposed.

  For example, in Patent Document 1, the configuration of the developing device is complicated by collecting the residual toner on the developing roll with a magnetic brush while the developing roll and the magnetic roll are rotated and in an equipotential state between the two rolls. There has been disclosed a method for preventing the occurrence of a residual image (ghost) during continuous development and supplying a reliably charged toner to a developing roll to obtain stable image quality over a long period of time. Patent Document 1 discloses that toner consumption is estimated from the dot amount (printing rate) of an image to be printed, and toner is forcibly discharged to an intermediate transfer belt based on a magnetic permeability sensor value.

  However, in such a method for forcibly discharging toner based on the printing rate, there is a possibility that the toner cannot be forcibly discharged sufficiently when environmental conditions such as temperature and humidity, image density, and the like change. Therefore, a method for forcibly discharging the toner in consideration of these has been proposed.

  For example, Japanese Patent Laid-Open No. 2004-228867 discloses a method for forcibly discharging toner at the time of non-development based on an integrated value of toner replenishment motor driving time every fixed time, thereby reducing the printing rate and temperature without complicating the developing device. A method is disclosed in which a constant toner can be discharged without being influenced.

  Further, Patent Document 3 detects an image area ratio per unit moving distance of the developer carrier, and controls the forced consumption of toner based on the detection result, thereby preventing unnecessary deterioration of the developer. A method for eliminating the progress and stably forming a high-quality image is disclosed.

  Further, in Patent Document 4, it is determined whether to execute the forced toner consumption mode based on the image ratio calculation result and the image density detection result, thereby suppressing a decrease in image quality and image density, and excessively. A method for reducing toner consumption and useless downtime is disclosed.

  In Patent Document 5, a developer image for measurement is formed under the same image forming conditions as that for a reference developer image, and the developer is measured when the image density of the developer image for measurement is equal to or lower than the image density of the reference developer image. A method of suppressing wasteful consumption of developer by executing a forced consumption operation is disclosed.

  In Patent Document 6, a plurality of images having different image densities are formed, each image density of the plurality of images is detected, and it is determined whether or not to refresh the developer carrier based on the detection result. Thus, a method is disclosed in which the developer adhered on the developer carrier is moved onto the image carrier in consideration of the deterioration of the developer.

JP 2003-015380 A JP 2005-055842 A Japanese Patent Laid-Open No. 2005-043388 JP 2006-337699 A Japanese Patent Publication No. 2007-147782 JP 2009-145488 A

  However, in the methods of Patent Document 2 and Patent Document 3, based on the prediction that the toner will be deteriorated from the driving time of the toner replenishing motor and the image area ratio per unit moving distance of the developer carrier. Since toner is forcibly discharged, the degree of toner deterioration and the amount of toner forcible discharge may be different, and toner may be discharged wastefully.

  Further, in the methods of Patent Document 4, Patent Document 5, and Patent Document 6, although toner is forcibly discharged based on the detection result of image density, an image for density detection and an image for forced toner discharge are used. Therefore, there is a possibility that toner is wasted.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of simultaneously performing formation of an image for density detection and forced discharge of a developer to prevent wasteful consumption of toner.

  In order to achieve the above object, the present invention provides an image carrier, an exposure device that forms an electrostatic latent image on the image carrier, and a developer carrier that has an electrostatic latent image formed by the exposure device. An image forming unit including a developing device that develops an image; a detecting unit that detects a density of a reference image formed on the image carrier by the image forming unit; and a reference image detected by the detecting unit. And a control unit that forcibly discharges the developer by moving the developer carrier to the image carrier based on the detected density. The control unit forms the reference image. The forced discharge is performed by repeatedly forming the reference image, calculating an area change amount from the reference image formed immediately before according to the detected density of the reference image, and calculating the area Next shape based on the amount of change It is characterized by varying the area of the reference image.

  Further, the present invention is characterized in that the control means calculates the area change amount based on a difference between a detected density of the reference image and a target density.

  According to the present invention, when the control means uses the area change amount as the first reference image as the reference image formed immediately before, the detection density of the first reference image and the first reference And calculating based on the detected density of the second reference image formed immediately before the image and the detected density of the third reference image formed immediately before the first reference image. It is a feature.

According to the present invention, the control means calculates the area of the reference image to be formed next according to the following equations (1) and (2).
S _{n + 1} = S _n + ΔS _n (1)
_{ΔS n = {K i · e} n + K p (e n -e n-1) + K d (e n -e n - 2)} ··· (2)
However,
n: 3 or more natural number S _n: the area of the reference image formed on the n-th [Delta] S _n: area change amount of the reference image formed on the n-th e _n: goals detected density of the reference image formed on the n-th Differences K _i , K _p , K _d for the concentration: coefficients

  Further, the present invention is characterized in that the control means calculates the area change amount based on a detected density of a reference image formed immediately before.

According to the present invention, the control means calculates the area of the reference image to be formed next according to the following equations (3), (4) and (5).
S _{n + 1} = S _c + ΔS _n (3)
ΔS _n = −R (e _n ≧ 0) (4)
ΔS _n = R (e _n <0) (5)
However,
n: natural number S _c: constant area value [Delta] S _n: area change amount of the reference image formed on the n-th e _n: difference from the target density of the detected density of the reference image formed on the n-th R: positive constant value

  In the invention, it is preferable that the control unit stops the forced discharge when the detected density of the reference image continuously becomes equal to or higher than the target density.

  According to the first configuration of the present invention, the control unit executes the forced discharge by forming the reference image, repeatedly forms the reference image, and is formed immediately before according to the detected density of the reference image. By calculating the area change amount from the reference image, and changing the area of the reference image to be formed next based on the calculated area change amount, the density detection image (reference image) is formed and the developer is changed. Forcible discharge can be executed at the same time, and wasteful consumption of the developer can be prevented.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, the area change amount is more appropriately calculated based on the difference between the detected density of the reference image and the target density. Since the area change amount can be calculated, the area of the reference image to be formed next can be varied more appropriately.

  According to the third configuration of the present invention, in the image forming apparatus having the second configuration, when the area change amount is set to the first reference image as the reference image formed immediately before, the first reference The detected density of the image, the detected density of the second reference image formed immediately before the first reference image, and the detected density of the third reference image formed two times before the first reference image Therefore, the area change amount can be calculated in more detail, so that the area of the reference image to be formed next can be varied in more detail.

  According to the fourth configuration of the present invention, in the image forming apparatus having the third configuration, the control unit calculates the area of the reference image to be formed next according to the equations (1) and (2). Thus, the area of the reference image to be formed next can be varied in more detail.

  According to the fifth configuration of the present invention, in the image forming apparatus having the second configuration, the control unit calculates the area change amount based on the detected density of the reference image formed immediately before. Since the area change amount can be calculated more easily, the area of the reference image to be formed next can be varied in more detail.

  According to the sixth configuration of the present invention, in the image forming apparatus having the fifth configuration, the control unit determines the area of the reference image to be formed next using the expressions (3), (4), and (5). ), The area of the reference image to be formed next can be changed more easily.

  According to the seventh configuration of the invention, in the image forming apparatus having any one of the second to sixth configurations, when the control unit continuously detects the detected density of the reference image equal to or higher than the target density. By stopping the forced discharge, wasteful consumption of the developer can be further prevented.

1 is a schematic diagram showing the overall configuration of a color image forming apparatus of the present invention. Schematic side view showing the configuration of a density detection sensor used in the color image forming apparatus of the present invention. 1 is a block diagram showing a control path of a color image forming apparatus of the present invention. The figure which shows typically the patch image formed in each image formation part The figure which shows typically the state in which the patch image in which the area was changed in the image formation part Pa is formed. Flow chart showing the procedure of the first control example Flow chart showing the procedure of the second control example The figure which shows the detection density of the patch image of Example 1, the area of a patch image, an area change rate, and an output image density. The graph which shows the relationship between the number of printed sheets and output image density of Example 1, and the relationship between the number of printed sheets and an area change rate. The figure which shows the detection density of the patch image of Example 2, the area of a patch image, an area change rate, and an output image density. The graph which shows the relationship between the number of printed sheets and output image density of Example 2, and the relationship between the number of printed sheets and an area change rate. The figure which shows the detection density of the patch image of a comparative example, the area of a patch image, an area change rate, and an output image density Graph showing the relationship between the number of printed sheets and output image density in the comparative example, and the relationship between the number of printed sheets and the area change rate

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a color image forming apparatus of the present invention. In the main body of the image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (magenta, cyan, yellow, and black), and magenta, cyan, and yellow are respectively subjected to charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  Photosensitive drums (image carriers) 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors are disposed in the image forming portions Pa to Pd, and these photosensitive drums 1a. 1d are sequentially transferred (primary transfer) onto the intermediate transfer belt 8 that moves adjacent to each image forming portion while rotating clockwise in FIG. 1 by a driving means (not shown). Then, the toner image is transferred onto the paper 28 at the same time (secondary transfer) by the secondary transfer roller 9 and further fixed on the paper 28 by the fixing unit 7 and then discharged from the apparatus main body. . An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The paper 28 onto which the toner image is transferred is accommodated in the paper cassette 16 at the lower part of the apparatus, and is conveyed to the secondary transfer roller 9 via the paper feed roller 12a and the registration roller pair 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used. Further, a cleaning blade 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure device 4 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the toner (developer) remaining on the photosensitive drums 1a to 1d are removed. Cleaning units 5a, 5b, 5c and 5d are provided.

  When the start of image formation is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated by the exposure device 4 to each of the photosensitive drums 1a to 1d. An electrostatic latent image corresponding to the image signal is formed on the top. The developing devices 3a to 3d have developing rollers (developer carrying members) 3aa, 3ba, 3ca, and 3da (see FIG. 2), and toners of magenta, cyan, yellow, and black are supplied to the replenishing devices (see FIG. 2). A predetermined amount is filled. The toner is supplied onto the photosensitive drums 1 a to 1 d by the developing rollers 3 aa to 2 da and electrostatically attached to form a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 4. Is done.

  After an electric field is applied to the intermediate transfer belt 8 at a predetermined transfer voltage, magenta, cyan, yellow, and black toner images on the photosensitive drums 1a to 1d are transferred to the intermediate transfer belt 8 by the primary transfer rollers 6a to 6d. Primary transferred onto. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched over a driven roller 10, a drive roller 11, and a tension roller 20, and the intermediate transfer belt 8 starts to rotate clockwise as the drive roller 11 is rotated by a drive motor (not shown). Then, the sheet 28 is conveyed from the registration roller 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and the sheet 28 is conveyed at the nip portion (secondary transfer nip portion) with the intermediate transfer belt 8. A full color image is secondarily transferred onto 28. The paper 28 to which the toner image has been transferred is conveyed to the fixing unit 7.

  The paper 28 conveyed to the fixing unit 7 is heated and pressurized when passing through the nip part (fixing nip part) of the pair of fixing rollers 13 to fix the toner image on the surface of the paper 28, and a predetermined full-color image is formed. It is formed. The paper 28 on which the full-color image is formed is distributed in the transport direction by the branching section 14 that branches in a plurality of directions. When an image is formed on only one side of the paper 28, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when images are formed on both sides of the paper 28, a part of the paper 28 that has passed through the fixing unit 7 is once projected from the discharge roller 15 to the outside of the apparatus. Thereafter, the paper 28 is distributed to the paper conveyance path 18 by the branching portion 14 by rotating the discharge roller 15 in the reverse direction, and is conveyed again to the secondary transfer roller 9 with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the paper 28 where the image is not formed by the secondary transfer roller 9 and conveyed to the fixing unit 7 to fix the toner image, It is discharged to the discharge tray 17.

  As shown in FIGS. 1 and 2, a density detection sensor 21 is disposed on the downstream side of the image forming unit Pd and the upstream side of the secondary transfer roller 9. The density detection sensor 21 irradiates the patch image (reference image) formed on the intermediate transfer belt 8 in the image forming portions Pa to Pd with measurement light, receives reflected light from the patch image, photoelectrically converts it, and receives the light. A signal is output, and the output value is A / D converted and then transmitted to the control unit 32 described later as a sensor output value (detected density).

  As the density detection sensor 21, an optical sensor including a light emitting element composed of an LED or the like and a light receiving element composed of a photodiode or the like is generally used. When measuring the density of the density correction pattern, when the measurement light is sequentially irradiated from the light emitting element to each patch image on the intermediate transfer belt 8, the measurement light is reflected as light reflected by the toner and light reflected by the belt surface. Incident on the light receiving element.

  When the toner adhesion amount is large, the reflected light from the belt surface is blocked by the toner, so that the light reception amount of the light receiving element is reduced. On the other hand, when the adhesion amount of toner is small, conversely, the amount of reflected light from the belt surface increases, resulting in an increase in the amount of light received by the light receiving element.

  Since the density detection sensor 21 needs to strictly define the distance to the measurement object, as shown in FIGS. 1 and 2, the density detection sensor 21 faces the driving roller 11 having a small distance variation to the surface of the intermediate transfer belt 8. The intermediate transfer belt 8 is positioned in the width direction according to the patch image (reference image) formation position on the intermediate transfer belt 8.

  The density detection sensor 21 may be disposed at another position where the patch image on the intermediate transfer belt 8 can be detected. For example, when the density detection sensor 21 is disposed on the downstream side of the secondary transfer roller 9, the image forming units Pa to. There is a possibility that the time from when the patch image is formed by Pd until density detection is performed becomes longer, and when the patch image comes into contact with the secondary transfer roller 9, the surface state of the patch image may change. Therefore, as shown in FIG. 1, it is preferable to dispose on the downstream side of the image forming unit Pd and the upstream side of the contact position of the secondary transfer roller 9. The patch image formed on the intermediate transfer belt 8 is removed by the cleaning blade 19.

  Further, for example, the density detection sensor 21 is disposed on the downstream side of the developing units 3a to 3d and on the upstream side of the transfer rollers 6a to 6d in the rotational direction of the photosensitive drums 1a to 1d, respectively, on the photosensitive drums 1a to 1d. It is also possible to detect the density of the patch image (toner image) formed on the surface. In such a case, the patch images on the photosensitive drums 1 a to 1 d are removed by the cleaning units 5 a to 5 d or transferred to the intermediate transfer belt 8 and then removed by the cleaning blade 19.

  FIG. 3 is a block diagram showing a control path of the image forming apparatus according to the present invention. Portions common to FIGS. 1 and 2 are denoted by the same reference numerals and description thereof is omitted. The image forming apparatus 100 includes an image forming unit Pa to Pd, an image input unit 30, an AD conversion unit 31, a control unit (control means) 32, a storage unit 33, an operation panel 34, a fixing unit 7, an intermediate transfer belt 8, and density detection. The configuration includes the sensor 21 and the like.

  When the image forming apparatus 100 is a color copying machine, the image input unit 30 includes a scanning lamp mounted with a scanner lamp that illuminates the original during copying and a mirror that changes the optical path of reflected light from the original, and reflection from the original. 1 is an image reading unit that includes a condenser lens that collects light to form an image and a CCD that converts the formed image light into an electrical signal. In the case of a printer, the receiving unit receives image data transmitted from a personal computer or the like. The image signal input from the image input unit 30 is converted into a digital signal by the AD conversion unit 31 and then sent to the image memory 40 in the storage unit 33.

  The storage unit 33 stores print image data input from the image input unit 30 and digitally converted by the AD conversion unit 31 in units of pages, necessary data generated during control of the image forming apparatus 100, and image formation. A readable / writable RAM (Random Access Memory) 41 in which data and the like temporarily required for the control of the apparatus 100 are stored, and the image forming apparatus 100 such as a control program for the image forming apparatus 100 and numerical values necessary for the control. A read-only ROM (Read Only Memory) 42 that stores data that is not changed during use is provided.

  The RAM 41 also includes a parameter that associates the output value of the density detection sensor 21 with the density of the patch image, a target density of the patch image, a parameter that associates the density of the patch image with the area of the patch image, and the patch image. Are also stored, such as parameters (coefficients) for calculating the area of the image, parameters that associate the area of the patch image with the writing timing of the exposure apparatus 4, and the like. In addition, the RAM 41 stores the number of patch image formations, the detected density of the patch image, the difference between the detected density of the patch image and the target density, the area of the patch image, the area change amount from the immediately preceding patch image, The area of the patch image to be formed next is stored.

  The operation panel 34 displays the state of the image forming apparatus 100, the image forming status, and the number of copies to be printed, and as a touch panel, functions such as double-sided printing and black-and-white reversal, various settings such as magnification setting and density setting, and the number of printing copies When the image forming apparatus 100 has a FAX function, a numeric keypad for inputting the FAX number of the other party, a start button for instructing the user to start image formation, and when stopping image formation. A stop / clear button, a reset button used when setting various settings of the image forming apparatus 100 to a default state, and the like are provided. The user operates the operation panel 34 to input an instruction, whereby the image forming apparatus 100 is set. Are set to execute various functions such as image formation.

  The control unit 32 is, for example, a central processing unit (CPU), and according to a set program, the image input unit 30, the image forming units Pa to Pd, the fixing unit 7, and the sheet 28 from the sheet cassette 16 (see FIG. 1). In addition to overall control of conveyance and the like, the image signal input from the image input unit 30 is converted into image data by scaling processing or gradation processing as necessary. The exposure device 4 irradiates laser light based on the processed image data, and forms latent images on the photosensitive drums 1a to 1d.

  Further, when the forced toner discharge mode is set, the control unit 32 counts the number of prints, or forms a patch image when the number of prints from the previous patch image formation reaches a preset set number of prints. The function and the sensor output value from the density detection sensor 21 are received, the function of calculating the difference of the detected density of the patch image with respect to the target density, and the area change amount from the previous patch image formation based on the calculated difference. A function to calculate, a function to calculate the area of the next patch image to be formed from the calculated area change amount, a function to forcibly discharge toner by forming a patch image based on the calculated patch area, etc. ing.

  Next, a first control example of forced toner discharge in the image forming apparatus according to the present invention will be described. FIG. 4 is a diagram schematically illustrating patch images formed by the image forming units. In FIG. 4, a solid line arrow indicates the rotation direction of the intermediate transfer belt 8.

In each of the image forming units Pa to Pd, the patch images M, C, Y, and B (toner images) are formed each time the number of printed sheets N reaches a preset set number of printed sheets N _s (for example, 10 sheets). It has become. As shown in FIG. 4, the patch images M to B formed by the image forming units Pa to Pd are transferred to the intermediate transfer belt 8 and detected by the density detection sensor 21 (see FIG. 1). Further, the toner is forcibly discharged in each of the developing devices 3a to 3d by forming the patch images M to B.

  Since the toner discharge control operation is the same in the developing devices 3a to 3d of the image forming units Pa to Pd, the image forming unit Pa will be described as a representative. FIG. 5 is a diagram schematically illustrating a state in which a patch image having a variable area is formed in the image forming unit Pa. In FIG. 5, solid arrows indicate the rotation direction of the intermediate transfer belt 8.

First, in the image forming unit Pa, the first patch image M ₁ and the second patch image M are respectively set so as to have preset areas S ₁ , S ₂ , S ₃ with a constant developing bias. _{2 A} third patch image M ₃ is formed. The patch images M _{1 to} M ₃ are detected by the density detection sensor 21, and when the detected densities A ₁ , A ₂ and A _{3 of} the patch images M _{1 to} M ₃ are transmitted to the control unit 32, the control unit 32 calculates a detected density a ₁ to a _3, the difference e ₁ between the target concentration a _s of the stored patch image in the storage unit 33, e _2, e _3, the.

That is, the control unit 32, the detected density A ₁ of first patch images M ₁ is transmitted, calculates a difference e ₁ between the detected density A ₁ and the target density A _s, the second patch image detection When the concentration a ₂ is transmitted, calculates a difference e ₂ between the detected density a ₂ and a target concentration a _s, the third detection density a ₃ is transmitted, and the target density a _s detected density a ₃ The difference e ₃ is calculated.

After calculating the _third difference e ₃ , the control unit 32 uses the parameters K _i , K _p and K _d stored in the storage unit 33 to change the area change ΔS from the patch image M ₃ formed immediately before. ₃ is calculated. These e ₁ , e ₂ , e _3, and ΔS ₃ are stored in the storage unit 33. Specifically, the difference e ₃ , the difference between the difference e ₃ and the difference e ₂ (e ₃ −e ₂ ), the difference between the difference e ₂ and the difference e ₁ (e ₂ −e ₂ ), and the parameter K _i, using K _p and _{K d, ΔS 3 = K i} · e 3 + K p (e 3 -e 2) + K d {(e 3 -e 2 + e 2 -e 1)} , based on the area change The rate ΔS ₃ is calculated.

Then, after calculating thus the area rate of change [Delta] S _3, the patch image area change rate [Delta] S ₃ M
By adding the _third area S _3, and calculates a fourth area S ₄ of the patch image M ₄ of the subsequently formed _{(S 4 = S 3 + ΔS} 3), like the exposing device 4 becomes the area S ₄ The patch image M ₄ is formed by adjusting the writing timing.

4 and subsequent, this operation is repeated and the n-th (n is an integer of 3 or more) is detected density A _n of the latest to form patch images as (first patch image) M _n is sent, the control unit 32 calculates a difference e _n between detected density a _n and the target concentration a _s of the patch image M _n, n-1-th patch image already calculated (second patch images) detection of M _n-1 difference e _n-1 between the concentration a _n-1 and the target density a _s, and, n-2-th patch image (third patch images) M _n-2 of the detected density a _n-2 and the target density a _s difference e _n-2, and using, in the same manner as described above, calculates the area change amount [Delta] S _n from the patch image M _n which is formed just before.

That is, the difference e _n , the difference between the difference e _n and the difference e _n−1 (e _n −e _n−1 ), and the difference between the difference e _{n− 1} and the difference e _n−2 (e _n−1 − e _n-2), with a K _i, K _p and _{K d, ΔS n = K i} · e n + K p (e n -e n-1) + K d {(e n -e n-1 + e n ₋₁₋ e _n−2 )}, the area change amount ΔS _n is calculated. It should be noted that the area change amount [Delta] S _n from the patch image M _n which is formed just before, from the time of formation of the formed patch image M _n just before, when forming a patch image M _{n + 1} to be subsequently formed The area amount of the patch image to be changed to.

Then, after calculating thus the area change amount [Delta] S _n, by adding the area change amount [Delta] S _n to the area S _n of the patch image M _n, it is then formed (n + 1) th area of the patch image M _{n + 1} of S _{n + 1} is calculated (S _{n + 1} = S _n + ΔS _n ), and the writing timing of the exposure apparatus 4 is adjusted so as to be the area S _{n + 1} to form the patch image M _{n + 1} .

Thus, the patch image M _n, M _n-1, M to calculate the area change amount [Delta] S _n from the patch image M _n in accordance with the _n-2 of the detected density A _n, patch image subsequently formed M _{n + 1} of the area S _{n + 1} variable, by forming the patch image M _{n + 1,} it is possible to perform the forced discharge of toner.

An example of the patch images M _n−2 , M _n−1 , M _n and M _{n + 1} formed as described above is shown in FIG. Here, the area _{Sn + 1} is changed in the main scanning direction (the direction perpendicular to the rotation direction of the intermediate transfer belt 8) by adjusting the writing timing of the exposure apparatus 4, and therefore the area _{Sn + 1} is variable. Becomes easy. However, the sub-scanning direction can be changed, or the area _{Sn + 1} can be varied in both the main scanning direction and the sub-scanning direction.

Incidentally, further solving the right-hand side of the equation [Delta] S _n, it is expressed as _{ΔSn = K i · e n +} K p (e n -e n-1) + K d (e n -e n-2). K _i , K _p, and K _d can be appropriately set by a preliminary experiment or the like. For example, K _i = −10, K _p = −2, and K _d = −5.

Further, here, it was decided to store the detected density A, the detected density difference e, all the calculated area S storage unit 33 relative to the target concentration A _s of A. Thus, for example, after forming the patch image M _n-1 of the n-1 th, if the job is completed, the area S _n of the patch image M _n to be formed next, the patch image M _n- Differences e _n−1 and e _{n−2 of the} densities of ₁ and M _n−2 are stored in the storage unit 33.

Then, for example, if the patch image M _n is formed in the next job, the area S _n of the patch image M _n is set by reading the area S _n stored in the storage unit 33, which is formed in such an area S _n calculates a difference e _n between detected density a _n and the target concentration a _s of the patch image M _n, calculated as the difference e _n and e _n-1, e _n-2 stored in the storage unit 33, by, calculates the area change amount [Delta] S _n from the patch image M _n, the area S _{n + 1} of the patch image M _{n + 1} to be formed next can be calculated. In addition, the value of the preset area S can be stored in the storage unit 33, and an initial patch image M such as the first sheet or the second sheet of the next job can be formed using the area S.

Incidentally, the area S _n of the patch image M _n to be initially formed in the next job, each density of the patch image M _n-1, M _n-2 only difference _{e n-1, e n-} 2, Data can be stored in the storage unit 33 as necessary, such as setting to store in the storage unit 33. Further, when the number of times of forming the patch image M is reset, the patch image M is newly formed from the first time.

Further, the formation interval of the patch images M can be appropriately set by a preliminary experiment or the like according to the apparatus configuration. For example, the number N of printed sheets can be set to every 10 sheets (set number of printed sheets N _s ). In addition, for example, it can be set according to the driving time of the developing device 3a from the patch image M formed immediately before.

  Next, the procedure of the first control example will be described. FIG. 6 is a flowchart showing the procedure of the first control example. With reference to FIG. 3, the forced toner discharge control procedure will be described along the steps of FIG.

The storage unit 33, the area S _n of the patch image M _n should then be formed, the difference e _n-1 of the previous two times of the patch image M _n-1, M _n-2 concentrations, e _n-2 Is remembered. First, when the number of copies to be set is set by the user on the operation panel 34 and printing is started (step S1), the density detection sensor 21 starts detection (step S2), and the control unit 32 reads the patch formed immediately before. The number of printed sheets N from the image M _n-1 is counted, and it is determined whether or not the number of printed sheets N has reached the set number of printed sheets N _s (for example, 10 sheets) since the last formation of the patch image M _n-1 (step). S3).

When reaching the set number of printed sheets _{N s (N ≧ N s)} , based on the area S _n which has been stored in the storage unit 33, to form a patch image M _n of n-th and forces out the toner (step S4). Next, when the detected density A _n of the patch image M _n transferred to the intermediate transfer belt 8 is sent, the control unit 32 calculates the difference e _n between detected density A _n and the target concentration A _s (step S5) From the difference e _n and the density differences e _n-1 and e _{n-2 of} the patch images M _n-1 and M _n-2 stored in the storage unit 33, the difference from the patch image M _n An area change amount ΔS _n is calculated (step S6).

That is, the formula _{ΔS n = K i · e n} + K p (e n -e n-1) + K d {(e n -e n-1 + e n-1 -e n-2)} ··· ( wherein ( 2)), the area change amount ΔS _n is calculated. Using this calculation result, the control unit 32 calculates the area S _{n + 1} of the patch image S _{n + 1} to be formed next (step S7). That is, the area S _{n + 1} is calculated from the expression ΔS _{n + 1} = S _n + ΔS _n (Expression (1)). Then, store the area S _{n + 1} of the patch image M _{n + 1,} the density of the patch image M _n and the difference e _n, in the storage unit 33. (Step 8).

Next, the number of prints set on the operation panel 34 is reached, and it is determined whether or not printing is finished (step S9). When the set number of prints is reached, the process ends. On the other hand, if the set number of prints has not been reached, the process returns to step S1 and steps S1 to S9 are repeated. At this time, a patch image M _{n + 1} is formed in step S4. In the case where the print number N has not reached the set number of printed sheets N _s in step S3, it executes step S9.

As described above, in this control, the control unit 32, repeatedly to form a patch image M, the patch image _{M n, M n-1,} M n-2 of the detected density _{A n, A n-1,} A n-2 area of area change amount [Delta] S _n is calculated, and the patch image M _{n + 1} to be subsequently formed on the basis of the calculated area change amount [Delta] S _n from the formed patch image M _n immediately before according to S _{n + Since} the toner is forcibly discharged by changing ₁ to form the patch image M _{n + 1} , the formation of the image density detection patch image M and the forcible discharge of the toner are executed at the same time. Consumption can be prevented.

Further, in the present control example, the control unit 32 sets the area change amount ΔS _n to the target density A _n , A _n-1 , A _n-2 of the patch images M _n , M _n-1 , M _n-2. Since the calculation is based on the differences e _n , e _n−1 , and e _n−2 with respect to the concentration As, the area change amount ΔS _n can be calculated more appropriately. Thereby, the area S _{n + 1} of the patch image M _{n + 1} to be formed next can be varied more appropriately.

Further, in the present control example, the control unit 32, the area change amount [Delta] S _n, and the detected density A _n of the patch image M _n, 1 previous to form a detection of the patch image M _n-1 of the patch image M _n calculating the concentration a _n-1, and the patch image M 2 previous patch image M _n-2 which is formed on the detected density a _n-2 of _n, because calculated based, the area change amount S _n more detail it can. Thereby, the area S _{n + 1} of the patch image M _{n + 1} can be varied in more detail.

Further, in this control example, the control unit 32 sets n as a natural number of 3 or more and sets the area of the patch image M _{n + 1} to be formed next to the expression ΔS _{n + 1} = S _n + ΔS _n and the expression ΔS. _{n = K i · e n +} K p (e n -e n-1) + K d {(e n -e n-1 + e n-1 -e n-2)} for calculated accordingly greater detail patch image M the area S _{n + 1} of the _{(n + 1)} can be varied.

Note that the control of the image forming apparatus according to the present invention is not particularly limited to this control example. For example, the control unit 32 determines that the detected density A of the patch image M is continuously _{equal to} or higher than the target density As. When this happens, the forced discharge can be stopped. Thereby, wasteful consumption of the developer can be further prevented.

Next, a second control example of forced toner discharge in the image forming apparatus according to the present invention will be described. In this control example, the image forming unit Pa, to form a first patch images M ₁ of the first so that the area S _c is a preset constant area value. When the detected density A ₁ of the patch image M ₁ transferred to the intermediate transfer belt 8 and detected by the density detection sensor 21 is transmitted to the control unit 32, the control unit 32 stores the detected density A ₁ and the storage unit 33. It calculates a difference e ₁ between the stored target concentration a _s.

At this time, the detected density A ₁ is the target concentration A _s or more, i.e., if the difference e ₁ is 0 or more (e ₁ ≧ 0), the area S ₂ of the patch image M ₂ to be subsequently formed, the area S _c Less than R, which is a positive constant value set in advance. That is, the area change amount ΔS ₁ from the patch image M ₁ formed immediately before is set to −R. On the other hand, if the difference e ₁ is less than 0 (e ₁ <0), it is made larger than the area _Sc by R. That is, let R be the area change amount ΔS ₁ from the patch image M ₁ formed immediately before.

Further, here, also second and subsequent, area change amount at the time of each patch image formed of the area S _c delta
S was added. That is, when the n-th (n is a natural number) the concentration A _n latest the formed patch image M _n as transmitted, the control unit 32, the patch image M _n detected density of A _n and the target density A _s and calculates the difference e _n.

The difference if e _n ≧ 0, the area change amount [Delta] S _n of the patch image M _n and -R, such [Delta] S _n, in addition to the area S _C, the patch image M _{n + 1} of the area S _{n + 1} And

On the other hand, if the difference e _n <0, the area change amount ΔS _n of the patch image M _n is set as R, and the Δ
Adding S _n to the area S _c, and the area S _{n + 1} of the patch image M _{n + 1.} That is, let n be a natural number, and formulas S _{n + 1} = S _c + ΔS _n (formula (3)), ΔS _n = −R (e _n ≧ 0) (formula (4)), ΔS _n = R (e _n <0) (ΔS _{n + 1} is calculated based on (Expression (5))).

Further, for example, after forming the patch image M _n-1 of the n-1 th, the job is finished, when the patch image M _n in the next job is formed, reads the area S _c stored in the storage unit 33 As a result, a patch image M _n is formed. The patch according to the patch image M _n detecting calculates a difference e _n between the concentration A _n and the target density A _s, the area rate of change [Delta] S _n based on the calculated difference e _n is calculated and then formed it is possible to calculate the area S _{n + 1} of the image M _{n + 1.}

Note that the above-described areas S _c and R can be appropriately set by preliminary experiments or the like according to the apparatus configuration, and for example, S _c = 2 and R = 1 can be set. Other configurations are the same as those in the first control example, and thus the description thereof is omitted.

  Next, the procedure of the second control example will be described. FIG. 7 is a flowchart showing the procedure of the second control example. With reference to FIG. 3, the toner forced discharge control procedure will be described along the steps of FIG.

The storage unit 33, the area S _c is stored as a constant value. First, when the user sets the number of copies to be printed in the job on the operation panel 34 and printing is started (step S1), the density detection sensor 21 starts detection (step S2), and the control unit 32 reads the previous patch. The number N of prints from the formation of the image M _n-1 is counted, and it is determined whether or not the number N of prints has reached the set number of prints N _s from the formation of the previous patch image M _n-1 (step S3). .

When reaching the set number of printed sheets _{N s (N ≧ N s)} , based on the area S _n which has been stored in the storage unit 33, to form a patch image M _n of n-th and forces out the toner (step S4). Next, when the detected density A _n of the patch image M _n transferred to the intermediate transfer belt 8 is sent, the control unit 32 calculates the difference e _n between detected density A _n and the target concentration A _s (step S5), such difference e _n is 0 or more (e _n ≧ 0) determines whether (step S6).

For e _n ≧ 0, and ΔS _n = -R (step S7), and the area of the patch image M _{n + 1} S _{n + 1}
Is calculated by S _{n + 1} = S _c −R (step S8). On the other hand, if e _n <0, ΔS
_n = R is set (step S9), and the area S _{n + 1} of the patch image M _{n + 1} is calculated by S _{n + 1} = S _C + R (step S10). Then, the area S _{n + 1} of the patch image M _{n + 1} calculated in step S9 or step S10 is stored in the storage unit 33. (Step 11).

Next, the number of prints set on the operation panel 34 is reached, and it is determined whether or not printing has been completed (step S12). If the set number of prints has been reached, the process ends. On the other hand, if the set number of prints has not been reached, the process returns to step S1 and steps S1 to S11 are repeated. At this time, a patch image M _{n + 1} is formed in step S4. In the case where the print number N has not reached the set number of printed sheets N _s in step S3, it executes Step S12.

As described above, in this control, the control unit 32, repeatedly to form a patch image M, the area change from the patch image M _n which is formed just before on the basis of the detected density A _n of the patch image M _n [Delta] S _n And the area S _{n + 1} of the patch image M _{n + 1} to be formed next is changed based on the calculated area change amount ΔS _n to form the patch image M _{n + 1,} thereby Since the forced discharge is executed, the formation of the patch image M for image density measurement and the forced discharge of the toner can be executed at the same time, thereby preventing wasteful consumption of toner.

Also in the present control example, the control unit 32, the area change amount [Delta] S _n, because it was decided to calculate on the basis of the difference e _n to the target concentration As the detected density A _n of the patch image M _n, more appropriately area The change amount ΔS _n can be calculated. Thereby, the area S _{n + 1} of the patch image M _{n + 1} to be formed next can be varied more appropriately.

Further, in the present control example, the control unit 32, the area change amount [Delta] S _n, because it was decided to calculate on the basis of the detected density A _n of the patch image M _n, which can be more easily calculate the area change amount [Delta] S,
In more detail, the area S _{n + 1} of the patch image M _{n + 1} to be formed next can be varied.

Further, in this control example, n is a natural number, and the expressions S _{n + 1} = S _c + ΔS _n , ΔS _n = −R (e _n
≧ 0), ΔS _n = R (e _n <0), so that ΔS _{n + 1} is calculated. Therefore, the area change amount ΔS _n is more easily calculated, and the patch image M _{n + 1 is} more easily calculated. Therefore, it is possible to further prevent wasteful consumption of the developer.

Further, here, has been calculated area Sn + 1 of the patch image Mn + 1, which is formed next with a certain area S _c, and other, using the area Sn of the patch image Mn formed immediately before the formula S _{n + 1} = S _n + ΔS _n , ΔS _n = −R (e _n ≧ 0), ΔS _n = R (e _n <0),
ΔS _{n + 1} can also be calculated.

  In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, the intermediate transfer belt 8 is used as a print medium, and the density of the patch image is detected by transferring the patch image to the intermediate transfer belt 8, but the patch image is also transferred to the paper (print medium) 28. It is also possible to detect the patch image transferred onto the paper 28.

  In addition, for example, in the case of using a direct transfer type tandem color image forming apparatus, it is also possible to detect a patch image formed on the transport belt by using a transport belt for transporting paper as a print medium. When such a direct transfer tandem color image forming apparatus is used, the toner can be removed by detecting the density of the patch image on the photosensitive drum and transferring the patch image to the paper 28.

  The present invention is not limited to a tandem color image forming apparatus that transfers a full color image formed by sequentially laminating toner images of each color onto the intermediate transfer belt 8 as shown in FIG. Of course, the present invention can be applied to various image forming apparatuses such as rotary color image forming apparatuses, monochrome copying machines, monochrome printers, and facsimiles.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a present Example.

Using the image forming apparatus shown in FIG. 1, according to the first control example described above, 130 sheets are printed while forcibly discharging toner every 10 print sheets (set print sheet number N _s ). The output image density of the printed image formed on P was examined. Here, the image forming portion Pa was examined as a representative.

Further, in the equation of the first control example _{ΔS n = K i · e n} + K p (e n -e n-1) + K d {(e n -e n-1 + e n-1 -e n-2)} K _i = −10, K _p = −2, and K _p = −5. In addition, the target density A _s and 0.22. Further, when a patch image formed of first time (n = 1), the area S stored in the storage unit 33, and to form a patch image M1 reads the difference e from the target concentration A _s concentration A. In addition, printing was started from a state where the image density was lowered in advance, and the first control example was implemented.

Shown at each patch image formed at this time, the detected density A _n of the patch image M _n, the area S _n of the patch image M _n calculated in FIG. In addition, first patch images M ₁ of the area S ₁ (here, 1) as a reference value, the area change ratio of the area S _n of each patch image M _n with respect to a reference value (%), formula (S _n - The area change rate calculated by S ₁ ) / S ₁ × 100 and the output image density of the print image are shown in FIG. FIG. 9 shows the relationship between the number of printed sheets N and the output image density, and the relationship between the number of printed sheets N and the area change rate.

Using the image forming apparatus shown in FIG. 1, according to the second control example described above, 130 sheets are printed while the toner is forcibly discharged every 10 print sheets (set print sheet number N _s ). The output image density of the printed image formed on P was examined. In the equations S _{n + 1} = S _c + ΔS _n , ΔS _n = −R (e _n ≧ 0), ΔS _n = R (e _n <0), S _c = 2 and R = 1.
In addition, the target density A _s and 0.22.

In addition, printing was started from a state in which the output image density was lowered in advance, and the second control example was implemented. Also, at the time of first (n = 1), second (n = 2), and third (n = 3) patch image formation, the areas S ₁ , S ₂ , S ₃ (here, Using 3), a patch image M ₁ was formed.

Shown at each patch formed at this time, the patch image M _n detected density A _n, the area S _n of the patch image M _n calculated in Figure 10. In addition, the reference value area change rate of the area S _n of each patch image M _n for (1 in this case) of the area S (percent) was calculated by the formula (S _n -1) / 1 × 100, such area change The rate and the output image density of the printed image are shown in FIG. FIG. 11 shows the relationship between the number of printed sheets N and the output image density, and the relationship between the number of printed sheets N and the area change rate.

Comparative example

  Using the image forming apparatus shown in FIG. 1, the patch image M was formed with a constant area S (here, 1) without forcibly discharging the toner, and 130 sheets were printed to form the sheet P. The density of the printed image (output image) was detected. In addition, printing was started from a state in which the image density was lowered in advance.

At each patch image formed at this time, the detected density A _n of the patch image M _n, the area S _n of the patch image M _n calculated is shown in FIG. 12. In addition, first patch images M ₁ of the area S ₁ (here, 1) as a reference value, the area change ratio of the area S _n of each patch image M _n with respect to a reference value (%), formula (S _n - FIG. 12 shows the area change rate calculated by S ₁ ) / S ₁ × 100 and the output image density of the print image. FIG. 13 shows the relationship between the number of printed sheets N and the output image density, and the relationship between the number of printed sheets N and the area change rate.

In Example 1, as shown in FIG. 8, the area S _{n + 1} of the patch image M _{n + 1} to be formed next is changed according to the densities A _n , A _n−1 , and A _n−2 . As shown in FIG. 9, the area change rate once increased and then decreased and maintained at about 100%. By changing the area in this way, the output image density increased, and after about 40 sheets, the target density of the output image, 1.2, was almost reached, and then the output image density up to 130 sheets was substantially maintained. . As a result, it was found that the output image density, which was initially low, can be corrected to the target density, and a stable image can be obtained.

Also in the second embodiment, sensing concentration based on A _n as shown in FIG. 10, the result of changing the area S _{n + 1} of the patch image M _{n + 1} to be subsequently formed, as shown in FIG. 11, The area change rate fluctuated around 100%. By changing the area in this way, the output image density increased, and after reaching the target density 1.2 of the output image between about 30 and 40 sheets, it fluctuated around 1.2 as the center. . Although varied in this way, the output image density was stable with a variation range of about ± 10% with respect to 1.2. In addition, the output image density is significantly higher than that at the start of printing.

  On the other hand, as shown in FIG. 12, in the comparative example in which the area of the patch image M is not changed, as shown in FIG. 13, the output image density remains low, and a sufficient output image density cannot be obtained. .

  As a result, it was found that in Example 1 and Example 2 according to the present invention, the output image density can be stabilized by forcibly discharging the toner. In addition, it has been found that because toner can be forcibly discharged simultaneously with the formation of the image density detection patch image M, wasteful consumption of toner can be prevented.

  According to the present invention, the control unit executes forced discharge by forming a reference image, repeatedly forming the reference image, and an area change amount from the reference image formed immediately before according to the detected density of the reference image And the area of the reference image to be formed next is varied based on the calculated area change amount.

  As a result, wasteful consumption of the developer can be prevented, so that the amount of developer replenishment can be reduced, thereby reducing costs and improving workability.

  In addition, the area change amount can be calculated more appropriately by calculating the area change amount based on the difference between the detected density of the reference image and the target density. Further, when the reference image formed immediately before is used as the first reference image, the area density is detected density of the first reference image and the second density formed immediately before the first reference image. By calculating based on the detected density of the reference image and the detected density of the third reference image formed two times before the first reference image, the area change amount can be calculated in more detail.

  Also, the area of the reference image to be formed next can be varied in more detail by calculating the area of the reference image to be formed next according to the above formulas (1) and (2). . In addition, the control unit can calculate the area change amount more easily by calculating the area change amount based on the detected density of the reference image formed immediately before.

  Further, the control means calculates the area of the reference image to be formed next according to the above formulas (3), (4) and (5), so that the area of the reference image to be formed next can be changed more easily. can do. In addition, when the detected density of the reference image is continuously equal to or higher than the target density, the control unit stops execution of forced discharge, thereby further preventing wasteful consumption of the developer.

Pa to Pd Image forming section 1a to 1d Photosensitive drum (image carrier)
2a to 2d charger 3a to 3d developing device 3aa to 3da developing roller (developing device)
DESCRIPTION OF SYMBOLS 4 Exposure apparatus 6a-6d Primary transfer roller 7 Fixing part 8 Intermediate transfer belt 9 Secondary transfer roller 21 Density detection sensor (detection means)
32 Control unit (control means)
33 Storage Unit 34 Operation Panel 41 RAM
42 ROM
100 Image forming apparatus

Claims (7)

Image formation comprising an image carrier, an exposure device that forms an electrostatic latent image on the image carrier, and a development device that has a developer carrier and develops the electrostatic latent image formed by the exposure device And
Detecting means for detecting the density of a reference image formed on the image carrier by the image forming unit;
An image forming apparatus comprising: a control unit configured to move the developer carrier to the image carrier based on the detected density of the reference image detected by the detection unit, and to forcibly discharge the developer.
The control means performs the forced discharge by forming the reference image, repeatedly forming the reference image, and an area from the reference image formed immediately before according to the detected density of the reference image An image forming apparatus, wherein a change amount is calculated, and an area of a reference image to be formed next is varied based on the calculated area change amount.   The image forming apparatus according to claim 1, wherein the control unit calculates the area change amount based on a difference between a detected density of the reference image and a target density. When the control unit uses the area change amount as the first reference image, the reference image formed immediately before the area change amount,
The detected density of the first reference image, the detected density of the second reference image formed immediately before the first reference image, and the first density formed two times before the first reference image. The image forming apparatus according to claim 2, wherein the image forming apparatus calculates the density based on the detected density of the three reference images. The image forming apparatus according to claim 3, wherein the control unit calculates an area of the reference image to be formed next according to the following expressions (1) and (2).
S _{n + 1} = S _n + ΔS _n (1)
_{ΔS n = {K i · e} n + K p (e n -e n-1) + K d (e n -e n - 2)} ··· (2)
However,
n: 3 or more natural number S _n: the area of the reference image formed on the n-th [Delta] S _n: area change amount of the reference image formed on the n-th e _n: goals detected density of the reference image formed on the n-th Differences K _i , K _p , K _d for the concentration: coefficients   The image forming apparatus according to claim 2, wherein the control unit calculates the area change amount based on a detected density of a reference image formed immediately before. 6. The image forming apparatus according to claim 5, wherein the control unit calculates an area of the reference image to be formed next according to the following equations (3), (4), and (5).
S _{n + 1} = S _c + ΔS _n (3)
ΔS _n = −R (e _n ≧ 0) (4)
ΔS _n = R (e _n <0) (5)
However,
n: natural number S _C : constant area value ΔS _n : area change amount of the reference image formed at the nth time e _n : difference between the detected density of the reference image formed at the nth time and the target density R: positive constant value   7. The image formation according to claim 2, wherein the control unit stops executing the forced discharge when the detected density of the reference image continuously becomes equal to or higher than the target density. apparatus.

Images