JP2006258903A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture an image forming apparatus capable of accurately detecting toner concentration in a developer container, without generating difference between the toner concentration detected and the practical toner concentration. <P>SOLUTION: The image forming apparatus is provided with a toner concentration detecting means (toner concentration detection sensor) 43 for magnetically detecting toner concentration in a developer container 33; an agitating/carrying means (first screw) 39 for agitating and carrying a developer 35 in the developer container 33; and a toner concentration control means (control part) 45 for feeding the toner, on the basis of the detection value of a detection signal of the toner concentration detection sensor 43 and a previously set reference value. The toner concentration detection sensor 43 detects the periodical waveform to be varied by the rotation of the first screw 39, and the control part 45 corrects the detection value of the detection signal of the toner concentration detection sensor 43 or the reference value of toner concentration control. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly to an image forming apparatus that performs process control by detecting the toner concentration of a developer in a developing container.

  In general, in an image forming apparatus such as a copying machine or a printer, an image forming apparatus that detects a toner concentration of a developer in a developing device by a toner concentration detection sensor and performs process control such as toner replenishment based on the detection result is well known. It is. For example, in a developing device using a two-component developer composed of toner and carrier, it is necessary to appropriately control the toner replenishment amount so that the toner concentration becomes a predetermined concentration in order to maintain the developing ability.

  The toner density of the two-component developer is detected by utilizing the fact that the magnetic permeability of the developer varies depending on the toner density, or by utilizing the fact that the optical reflection density with respect to the developer varies depending on the toner density. . That is, in the conventional image forming apparatus, the toner density is directly determined from the detection result such as magnetic permeability or optical reflection density, and process control such as toner replenishment is performed.

  However, in an image forming apparatus that performs various controls using a toner concentration detection sensor, the developer density changes and the output of the toner concentration detection sensor changes despite the same toner concentration due to the deterioration of the developer. There is a problem that will be. Therefore, when the control is performed with the belief in the density sensor as it is, the toner density may fluctuate and the image density may fluctuate, or the toner may scatter due to the increase in toner density, or the carrier may adhere due to the toner density reduction.

  On the other hand, in the prior art described in Patent Document 1, periodic vibration is applied to the developer, and the output waveform corresponding to the bulk density of the developer is generated by the vibration of the developer with one density sensor. The degree of developer deterioration and the toner density are determined by combining the amplitude value of the output amplitude waveform corresponding to the difference in the generated fluidity and the minimum and maximum values of the amplitude.

Japanese Patent No. 3308126

  However, the conventional technique described in Patent Document 1 determines the degree of developer deterioration by using a density sensor, but currently used carriers have high durability and little change in charge amount with time. In reality, changes in bulk density and fluidity greatly affect fluctuations in the output of the toner density sensor. This change is caused by so-called toner deterioration in which the additive on the toner surface is buried by stirring, and thus is different from the deterioration of the carrier, and occurs when the developing container is simply agitated empty ( FIG. 15).

  In normal image formation, if a certain amount of image is formed, the toner inside the developing container is discharged and new toner is replenished, so that the overall toner deterioration is small. However, even when the image area is small or the color image forming apparatus drives four color developing containers, only a limited amount of toner in the developing containers is consumed, and other developing containers are stirred. If only the remaining state continues, the output of the toner density sensor decreases despite the same toner density, and it is determined that the toner density is high. For this reason, in a machine that replenishes toner using a toner density sensor, toner replenishment is not performed, so that the image density is lowered. That is, there is a problem that taking an image close to a blank sheet causes a phenomenon that the image density decreases in a chained manner.

  An object of the present invention is to provide an image forming apparatus capable of accurately detecting the toner concentration in the developing container without causing a deviation between the detected toner concentration and the actual toner concentration.

  In order to solve the above-mentioned problems, the invention described in claim 1 includes a toner concentration detecting means for magnetically detecting the toner concentration in the developing container, and an agitating / conveying means for stirring and conveying the developer inside the developing container. And a toner concentration control means for replenishing toner based on the detection value of the detection signal of the toner concentration detection means and a preset reference value, and the toner concentration detection means is a periodic variable that varies with the rotation of the stirring and conveying means. The toner concentration control unit corrects the detection value of the detection signal of the toner concentration detection unit or the reference value of the toner concentration control based on a specific parameter of the output waveform detected by the toner concentration detection unit. It is characterized by.

  According to a second aspect of the present invention, there is provided a toner concentration detecting means for magnetically detecting the toner concentration in the developing container, an agitating and conveying means for stirring and conveying the developer inside the developing container, and detection by the toner concentration detecting means. A toner concentration control unit that replenishes toner based on a detection value of the signal and a preset reference value, and the toner concentration detection unit detects a periodic waveform that fluctuates due to rotation of the stirring and conveying unit; The toner density control means corrects the setting range of the reference value for toner density control based on a specific parameter of the output waveform detected by the toner density detection means.

  The invention described in claim 3 is the invention described in claim 1 or 2, wherein the agitating and conveying means is a screw-shaped conveying member, and the tip of the conveying member is substantially in contact with or close to the inner wall of the developing container. It is characterized by being.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the toner density control means calculates the rise time of the output waveform detected by the toner density detection means and the average value of the output waveform. The toner density is controlled as a specific parameter.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to third aspects, the toner concentration control means is a ratio of a rise time and a fall time of the output waveform detected by the toner density detection means. The toner density is controlled using the average value of the output waveform as a specific parameter.

  According to a sixth aspect of the present invention, the image forming apparatus according to any one of the first to fifth aspects includes a plurality of developing containers, and repeats development on the image carrier to superimpose toner images. After that, a color image is formed by batch transfer to a transfer material, and the toner density control means performs toner density control for each developing container.

  According to the present invention, the detected value of the toner density detecting means or the reference value of the toner density control is corrected based on the specific parameter of the output waveform of the toner density detecting means. The toner concentration in the developing container can be accurately detected without causing a deviation in the toner concentration.

  Hereinafter, as an example of an embodiment of an image forming apparatus to which the present invention is applied, a basic configuration of an electrophotographic printer (hereinafter simply referred to as a printer) will be described. As shown in FIG. 14, the printer 100 has colors of yellow (Y), cyan (C), magenta (M), and black (K). Four sets of toner image forming portions 6Y, 6C, 6M, and 6K are sequentially arranged from the upstream side in the moving direction of the intermediate transfer belt 8. The toner image forming units 6Y, 6C, 6M, and 6K are provided with photosensitive members 1Y, 1C, 1M, and 1K on a drum as latent image carriers.

  An exposure device 7 is disposed below the toner image forming units 6Y, 6C, 6M, and 6K. This is a tandem type color printer provided with four sets of process cartridge-like toner image forming portions 6Y, 6C, 6M, and 6K for forming an exposure device image. The toner image forming units 6Y, 6C, 6M, and 6K use toners of different colors as image forming substances, but otherwise have the same configuration, and are replaced when the lifetime is reached.

  Above the four sets of toner image forming units 6Y, 6C, 6M, and 6K, an intermediate transfer unit 15 is provided that moves an endless intermediate transfer belt 8 as an intermediate transfer member to be described later while stretching. The exposure device 7 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each of the photoreceptors 1Y, 1C, 1M, and 1K while scanning with laser light based on image data. By this light irradiation, electrostatic latent images of yellow, magenta, cyan and black are formed on the photoreceptors 1Y, 1C, 1M and 1K.

  The toner image forming units 6Y, 6C, 6M, and 6K use yellow, magenta, cyan, and black toners of different colors as the developer, but the other configurations are the same. A description will be given using the formation portion 6Y as a representative example.

  FIG. 1 is a schematic configuration diagram of a yellow toner image forming unit 6Y. The toner image forming unit 6Y includes a drum-shaped photoreceptor 1Y, a cleaning device 2Y, a charge eliminating device, a charging device 4Y, a developing device 5Y, and the like. The toner image forming unit 6Y can be attached to and detached from the printer 100 main body, and the consumable parts can be exchanged at the same time when the life is reached.

  The charging device 4Y uniformly charges (for example, −700 V) the surface of the photoreceptor 1Y that is driven to rotate clockwise in the drawing by a driving unit (not shown). The surface of the uniformly charged photoreceptor 1Y is irradiated with laser light L from the exposure device 7 to form an electrostatic latent image for a yellow image. This electrostatic latent image is developed by the developing device 5Y using yellow toner. Then, primary transfer is performed on the intermediate transfer belt 8. The cleaning device 2Y removes the toner remaining on the surface of the photoreceptor 1Y after the primary transfer process. Further, the static eliminator neutralizes residual charges on the photoreceptor 1Y after cleaning. By this charge removal, the surface of the photoreceptor 1Y is initialized and prepared for the next image formation. In the other toner image forming units 6C, 6M, and 6K, magenta, cyan, and black toner images are similarly formed on the photoreceptors 1C, 1M, and 1K.

  In addition to the intermediate transfer belt 8, the intermediate transfer unit 15 includes four primary transfer bias rollers 9Y, 9C, 9M, and 9K, an intermediate transfer belt cleaning device 10, and the like. A secondary transfer backup roller 12, a cleaning backup roller 13, a tension roller 14 and the like are also provided. The intermediate transfer belt 8 is endlessly moved in the counterclockwise direction in the figure by the rotational drive of at least one of the rollers while being stretched around these three rollers.

  The primary transfer bias rollers 9Y, 9C, 9M, and 9K sandwich the intermediate transfer belt 8 that is moved endlessly between the photoreceptors 1Y, 1C, 1M, and 1K to form primary transfer nips, respectively. Yes. In these methods, a transfer bias having a polarity opposite to that of toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 8. All the rollers except the primary transfer bias rollers 9Y, 9C, 9M, and 9K are electrically grounded. The intermediate transfer belt 8 sequentially passes through the primary transfer nips for yellow, magenta, cyan, and black along with its endless movement, and yellow, magenta, and cyan on the photoreceptors 1Y, 1C, 1M, and 1K. The black toner image is primarily transferred so as to overlap. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 8.

  Below the exposure device 7, paper supply means having a paper storage cassette 26, a paper supply roller 27, a registration roller pair 28 and the like are disposed. Further, a secondary transfer roller 19 is provided so as to face the secondary transfer backup roller 12 on the downstream side of the toner image forming portion 6K of the intermediate transfer belt 8. Here, the secondary transfer backup roller 12 sandwiches the intermediate transfer belt 8 with the secondary transfer roller 19 to form a secondary transfer nip. Further, a fixing unit 20 and a paper discharge roller pair 29 are provided above the secondary transfer nip.

  The paper storage cassette 26 stores a plurality of transfer papers P as recording media, and a paper feed roller 27 is in contact with the uppermost transfer paper P. The sheet feeding roller 27 is rotated counterclockwise in the drawing by a driving unit (not shown), and feeds the uppermost transfer sheet P toward the gap between the registration roller pair 28. The registration roller pair 28 rotationally drives both rollers to sandwich the transfer paper P, but temporarily stops rotating immediately after sandwiching. Then, the transfer paper P is sent out toward the secondary transfer nip at an appropriate timing. In the sheet feeding means having such a configuration, the conveying means is configured by a combination of the sheet feeding roller 27 and the registration roller pair 28 as the timing roller. This transport means transports the transfer paper P from the paper storage cassette 26 serving as the storage means to the secondary transfer nip. The four-color toner image formed on the intermediate transfer belt 8 is transferred to the transfer paper P at the secondary transfer nip. Untransferred toner that has not been transferred onto the transfer paper P adheres to the intermediate transfer belt 8 after passing through the secondary transfer nip. This is cleaned by the cleaning device 10.

  In the secondary transfer nip, the transfer paper P is sandwiched between the intermediate transfer belt 8 and the secondary transfer roller 19 whose surfaces move in the forward direction, and is conveyed in the direction opposite to the registration roller pair 28 side. When the transfer paper P sent out from the secondary transfer nip passes between the rollers of the fixing device 20, the four-color toner image transferred to the surface is fixed by heat and pressure. Thereafter, the transfer paper P is discharged out of the apparatus through a pair of paper discharge rollers 29.

  A stack unit 30 is formed on the upper surface of the printer main body, and the transfer paper P discharged outside the apparatus by the discharge roller pair 29 is sequentially stacked on the stack unit 30. A reflection type photosensor 40 as an image density detecting means is disposed above the secondary transfer backup roller, and is configured to output a signal corresponding to the light reflectance on the intermediate transfer belt 8.

  Next, the developing device 5Y according to the present embodiment will be described. As shown in FIG. 1, the developing device 5 </ b> Y includes a developing sleeve 31 and a developing container 33. The developing container 33 contains a two-component developer 35 composed of toner and carrier, and a first screw (agitating and conveying means) 39 and a second screw 41 are disposed across the partition 37. Yes. Further, a fin 40 protruding outward in the radial direction is attached to the shaft of the first screw 39, and an elastically deformable mylar 42 is attached to the tip of the fin 40. The mylar 42 moves along with the stirring of the conveying screw while being in sliding contact with the inner peripheral wall 33a of the developing container 33. In this embodiment, the mylar 42 is in sliding contact with the inner peripheral wall 33a of the developing container 33. However, the mylar 42 may be provided close to the inner peripheral wall 33a of the developing container 33.

  The toner in the developing container 33 is conveyed to the first screw 39 and the second screw 41 while being stirred. At this time, the toner in the two-component developer 35 is charged to a predetermined charge amount by friction with the carrier and adheres to the surface of the carrier particles. The sufficiently charged toner moves to the developing sleeve 31.

  The developing sleeve 31 is configured by fixing a magnetic pole inside a cylindrical nonmagnetic sleeve, and rotates in the direction of the arrow. The developing sleeve 31 attracts the toner moved from the second screw 41 by an internal magnetic pole, and attaches the toner to the surface of the developing sleeve 31. Then, an electrostatic field is formed between the photosensitive member 1Y and the developing sleeve 31 by the developing bias applied to the developing sleeve 31, and the toner is attracted to the electrostatic latent image on the photosensitive member 1Y for development.

  A toner concentration detection sensor (toner concentration detection means) 43 for detecting the toner concentration in the developing container 33 is disposed on the side of the developing container 33 where the first screw 39 is provided. Is detected, information to that effect is transmitted to the control unit (toner density control means) 45.

  The control unit 45 is connected to a drive motor 47 that rotationally drives the first screw 39 and the second screw 41, and based on information from the toner concentration detection sensor 43, the rotation speed of the conveying screws 39, 41 can be varied. I have control.

  Next, since the toner density is output by the configuration based on the above-described configuration, a description will be given below. FIG. 5 is a graph showing the output waveform of the toner concentration at the initial stage of stirring, and FIG. 6 is a graph showing the output waveform of the toner density when stirring is performed for about 2 hours. As shown in FIG.5 and FIG.6, it turned out that an output waveform changes with stirring time. The period is seen in the output waveform when the Mylar 42 shown in FIGS. 2 and 3 passes through the toner concentration detection sensor 43, and the maximum value of the output waveform is determined by the Mylar 42 at the toner concentration detection sensor 43. The minimum value of the output waveform that occurs at the abutting position is formed when the mylar 42 passes through the toner concentration detection sensor 43. Further, the reason why the output waveform is different between FIG. 5 and FIG. 6 is considered that the fluidity and bulk density of the developer are changed.

  As shown in FIG. 7, an additive is added to the toner in the initial state for reasons such as improving fluidity and preventing aggregation. However, when the developer is replenished and stirring is continued in the developing device, the additive is buried in the binder of the toner and changes into a shape as shown in FIG. The output waveform of the toner concentration detection sensor 43 at this time is shown in FIG. The horizontal axis shown in FIG. 9 is the time during which the developing container 33 is idlely stirred without development (empty stirring time), and the vertical axis indicates the output voltage. In FIG. 9, the rhombus plot shows the maximum value of the toner density sensor output, the round plot shows the minimum value of the toner density sensor output, and the square plot shows the average value of the toner density sensor output.

  Further, the graph shown in FIG. 10 shows the relationship between the empty stirring time and the bulk density. Furthermore, the graph shown in FIG. 11 shows the relationship between the empty stirring time and the degree of burying of the additive. The vertical axis of FIG. 11 ranks the degree of additive burying, and the additive burying degree rank is 5 for an initial state and 1 for a state where no additive is present on the surface.

  As shown in FIGS. 9 to 11 above, as the stirring time of the developing container 33 elapses, the additive adhering to the surface of the toner is buried, and the fluidity and bulk density of the developer are reduced, and the toner concentration sensor. It turned out that the average value of the output is also decreasing.

Next, correction of toner density control will be described. Toner concentration detection sensor 43 shown in FIG.
In the output waveform according to, rise time from the time when the output waveform reaches the value of 10% between the minimum value and the maximum value to the value of 90% rise, and 90% between the minimum value and the maximum value. The fall time until the value drops to a value of 10% from the time when the value is reached is set as fall.

  As can be seen from a comparison between FIG. 5 and FIG. 6, there was no significant change in the fall time of the output waveform due to the stirring of the developing container 33 between the initial stirring and the stirring for 2 hours. However, with regard to the rise time (rise), it was found that a large change occurred between the case of the initial stirring and the case of stirring for 2 hours. This is because the developer is pressed against the toner concentration detection sensor 43 by the Mylar 42, but as the fluidity is lower and the bulk density is higher, and the state where the developer is pressed against the toner concentration detection sensor 43 becomes longer, the rise time is increased. This is due to an increase in (rise).

  When the mylar 42 passes through the toner concentration detection sensor 43 due to the rotation of the first screw 39, the developer does not follow and an empty space is formed in the toner concentration detection sensor 43. Therefore, the output waveform has the lowest output. Form the value (min).

  Further, regarding the output waveform detected by the toner concentration detection sensor 43, parameters such as amplitude, maximum value (max), minimum value (min), rise time (rise), fall time (fall), and the toner concentration detection sensor 43 are used. As a result of multivariate analysis of the correlation between the output fluctuation and the case of stirring for 2 hours, the rise time (rise) in the initial stage of stirring and the rise time (rise) in the case of stirring for 2 hours The ratio or the correlation between the rise time (rise) and the fall time (fall) was the highest.

  Next, the correlation between each parameter of the output waveform detected by the toner concentration detection sensor 43 and the stirring time will be described. FIG. 12 is a graph showing the correlation between the rise time (rise) and fall time (fall) of the output waveform (rise × 1000 / fall) and the agitation time, and FIG. 13 is the agitation time and the rise of the output waveform. It is a graph which shows correlation with time (rise) or fall time (fall).

  As shown in FIG. 12, it was found that the ratio (rise × 1000 / fall) between the rise time (rise) and the fall time (fall) of the output waveform gradually decreased as the stirring time passed. As shown in FIG. 13, as the stirring time elapses, there is no particular change in the fall time (fall) of the output waveform, but the rise time (rise) of the output waveform gradually decreases with time. I found out that Therefore, it was found that the state of the developer is closely related to the rise time (rise) of the output waveform.

  The waveform of the rise time (rise) is formed not only by the presence of the conveyance member close to the inner wall of the developing container 33 such as Mylar 42 but also by the combination with the screw-shaped conveyance member that is fed in the axial direction. It is effective. This is because the screw-shaped conveying member is weak in feeding the developer in the axial direction, and the developer conveyed by the Mylar 42 receives the pressure of the developer existing in the helical shape of the screw. On the other hand, in the case of a paddle type conveyance member, the force for conveying the developer in the axial direction is strong and the force for pressing the developer against the toner concentration detection sensor 43 is weakened. Change is difficult to obtain.

  The control unit 45 is based on the rise time (rise), which is a feature amount of the output waveform of the toner concentration detection sensor 43, and the average value of the output waveform, or the ratio between the rise time and fall time of the output waveform and the average value of the output waveform. Thus, the correction of the detection value of the toner density detection sensor 43 or the reference value of the toner density control is corrected. As described above, since the detection value of the toner concentration detection sensor 43 or the reference value of the toner concentration control is corrected based on the specific parameter (feature amount) of the output waveform of the toner concentration detection sensor 43, the detected toner is corrected. The toner density in the developing container 33 can be accurately detected without causing a deviation between the density and the actual toner density.

  By taking a rising waveform as a specific parameter (feature amount) of the output waveform of the toner concentration detection sensor 43, changes in bulk density and fluidity due to developer deterioration can be captured. Further, by taking a ratio in comparison with the falling waveform time, it is possible to detect a change in developer characteristics with reduced sampling error and stability.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. In the above-described embodiment, the toner density control reference value is corrected based on the feature value of the output waveform of the toner density detection sensor 43. However, the toner density control reference value setting range (upper / lower limiter) is corrected. May be. By correcting the setting range of the reference value for toner density control, it is possible to prevent problems such as toner scattering that is too high and toner scattering or carrier adhesion that is too low. In this case, since normal control is not affected, normal control can be reflected without sacrificing.

1 is a cross-sectional view schematically showing a developing device according to the present embodiment. FIG. 2 is a diagram illustrating a main part of the developing device illustrated in FIG. 1, and a cross-sectional view illustrating a state in which a mylar of a stirring screw is in a position in front of a toner concentration detection sensor. It is a figure which shows the principal part of the image development apparatus shown in FIG. 1, and is sectional drawing which shows the state in which the mylar of a stirring screw exists in the position which passed the toner concentration detection sensor. FIG. 4 is a transverse cross-sectional view of a main part of the developing device shown in FIG. 2 or FIG. 3. It is a graph which shows the output waveform of the toner density in the initial stage of stirring. 6 is a graph showing an output waveform of toner concentration when a developing container is stirred for a predetermined time. FIG. 6 is a cross-sectional view illustrating a state of toner when not used. FIG. 6 is a cross-sectional view illustrating a toner state when the developing container is air-stirred for a predetermined time. 6 is a graph showing the relationship between the stirring time of a developing container and the output voltage of toner concentration. It is a graph which shows the relationship between the stirring time of a developing container, and a bulk density. It is a graph which shows the relationship between the stirring time of a developing container, and the burial degree of an additive. 6 is a graph showing a correlation between a ratio between a rise time (rise) and a fall time (fall) of an output waveform of a toner concentration detection sensor and a stirring time of a developing container. 6 is a graph showing a correlation between a developing container agitation time and a rise time (rise) or fall time (fall) of an output waveform of a toner concentration detection sensor. 1 is a cross-sectional view schematically illustrating an entire image processing apparatus according to the present embodiment. 6 is a graph comparing the relationship between the toner density and the output voltage of the toner density detection sensor between normal times and after stirring for a predetermined time.

Explanation of symbols

33 Developing container 39 First screw (stirring conveyance means)
43 Toner density detection sensor (toner density detection means)
45 Control unit (toner density control means)
100 printer (image forming apparatus)

Claims (6)

  Toner density detecting means for magnetically detecting the toner density in the developing container, agitating / conveying means for stirring and conveying the developer in the developing container, detection values of detection signals of the toner density detecting means and preset reference Toner density control means for replenishing toner based on the value, the toner density detection means detects a periodic waveform that fluctuates due to the rotation of the agitation transport means, and the toner density control means An image forming apparatus, wherein a detection value of a detection signal of a toner density detection unit or a reference value of toner density control is corrected based on a specific parameter of a detected output waveform.   Toner density detecting means for magnetically detecting the toner density in the developing container, agitating / conveying means for stirring and conveying the developer in the developing container, detection values of detection signals of the toner density detecting means and preset reference Toner density control means for replenishing toner based on the value, the toner density detection means detects a periodic waveform that fluctuates due to the rotation of the agitation transport means, and the toner density control means An image forming apparatus, wherein a setting range of a reference value for toner density control is corrected based on a specific parameter of a detected output waveform.   The image forming apparatus according to claim 1, wherein the stirring and conveying unit is a conveying member having a spiral blade, and an outer edge of the blade of the conveying member is substantially in contact with or close to the inner wall of the developing container. apparatus.   The toner density control means controls the toner density using the rise time of the output waveform detected by the toner density detection means and the average value of the output waveform as specific parameters. The image forming apparatus described in 1.   The toner density control means controls the toner density by using the ratio of the rise time and fall time of the output waveform detected by the toner density detection means and the average value of the output waveform as specific parameters. The image forming apparatus according to any one of 1 to 3. The image forming apparatus according to any one of claims 1 to 5 includes a plurality of developing containers, and repeatedly develops the image carrier to superimpose toner images, and then collectively transfers the images onto a transfer material. An image forming apparatus, wherein a color image is formed, and toner density control means performs toner density control for each developing container.

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