JP2015155965A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of insufficient image concentration and toner scattering after the continuation of a high image density output state over a long period, and suppress the occurrence of excessive image concentration and solid carrier adhesion after the continuation of a low image density output state over a long period.

SOLUTION: A main control unit is configured to perform, in addition to processing to correct a target value of toner concentration, processing to correct a developing potential Vpot, which is a difference in potential between an electrostatic latent image and a developing sleeve of a developing device, to a smaller value when having corrected the target value to a larger value, and to correct the developing potential to a larger value when having corrected the target value to a smaller value.

COPYRIGHT: (C)2015,JPO&INPIT

Description

  In the present invention, the toner replenishing means is driven to replenish toner to the developing device so that the toner density of the developer in the developing device approaches a predetermined target value, or the image area ratio of the output image within the most recent predetermined period The present invention relates to an image forming apparatus that corrects the target value based on the above.

  2. Description of the Related Art Conventionally, an image forming apparatus that forms a toner image using a developer containing toner and a carrier is known. In this type of image forming apparatus, the toner in the developer and the carrier are mixed and stirred in the developing device and pumped up to the surface of the developing roller, and the developing roller rotates to face the latent image carrier such as a photosensitive member. Transport to area. A latent image is written on the latent image carrier by scanning with a laser beam or the like. In the developing area, the toner of the developer on the developing roller is selectively transferred to the latent image on the latent image carrier. Thereby, the latent image is developed to obtain a toner image. The toner image formed on the surface of the latent image carrier in this way is transferred to a recording sheet directly or via an intermediate transfer member. In parallel with the development of the latent image, the toner concentration of the developer in the developing device is detected by the toner concentration sensor, and when the detection result is below the target value, the toner replenishing device is driven to develop the developing device. Supply toner inside. This prevents the toner in the developer from being depleted by maintaining the toner concentration of the developer in the developing device within a certain range.

  In such a configuration, if the output frequency of an image with a high image area ratio is relatively high (hereinafter referred to as a high image density output state) to some extent, toner consumed by the developer in the developing device and toner due to toner replenishment The replacement of becomes active. The agitation cycle from toner replenishment in the developing device through mixing and agitation to contribution to development is shortened, and the toner charge amount Q / M is reduced due to the agitation failure. Then, the electrostatic attraction force of the toner to the magnetic carrier is weakened, and the toner is easily separated from the surface of the magnetic carrier, so that the image density becomes excessive. On the other hand, if the output frequency of the low image area ratio image is relatively high (hereinafter referred to as a low image density output state) to some extent, the toner agitation cycle in the developing device becomes long, and excessive agitation The charge amount Q / M of the toner increases. Then, it becomes difficult for the toner to be detached from the surface of the magnetic carrier, so that the image density becomes insufficient.

  On the other hand, Patent Document 1 discloses the following image forming apparatus. That is, this image forming apparatus corrects the target value of the toner density to a lower value when the average value or moving average value of the image area ratio of the image output in the past predetermined period becomes relatively high. As a result, the toner is more actively rubbed against the magnetic carrier in the developing device to promote the frictional charging of the toner, thereby suppressing an increase in image density due to a decrease in the toner charge amount Q / M. . On the other hand, when the aforementioned average value or moving average value becomes relatively low, the target value of toner density is corrected to a higher value. Accordingly, it is difficult to cause the toner to rub against the magnetic carrier in the developing device and the frictional charging of the toner is suppressed, thereby suppressing a decrease in image density due to an increase in the toner charge amount Q / M. By correcting the target value in this way, a stable image density can be obtained regardless of the variation in the image area ratio of the output image.

  However, in this image forming apparatus, the occurrence of toner scattering when the high image density output state continues for a long period of time cannot be suppressed. Further, it has not been possible to suppress the occurrence of solid carrier adhesion when the low image density output state continues for a long period of time.

  Specifically, when the high image density output state continues to some extent, as described above, the toner charge amount Q / M tends to decrease. Then, the toner density target value is corrected to a lower value, thereby suppressing an increase in image density. However, if the high image density output state continues further in this state, the target value of the toner density eventually reaches a predetermined lower limit value and is not corrected to a lower value. Although there is no specific description of the reason why such a lower limit is set in Patent Document 1, in the experiments of the present inventors, if the target value is corrected to a value lower than a certain value, the toner density is reversed. The image density was lowered due to the lack. In order to avoid such a decrease in image density, it is considered that the target value is not corrected to a value lower than a predetermined lower limit value. If the high image density output state continues with the target value corrected to the lower limit value, the toner charge amount Q / M will decrease significantly, and the toner particles will be attracted to the magnetic carrier particles well on the rotating developing roller. This makes it difficult to keep the toner and causes toner scattering. When the toner scatters, each part in the machine is soiled with toner, and the image is smeared due to toner dropping.

  On the other hand, when the low image density output state continues to some extent, as described above, the toner charge amount Q / M tends to increase. Then, by correcting the target value of the toner density to a higher value, a decrease in image density can be suppressed. However, if the low image density output state further continues in this state, the target value of the toner density eventually reaches a predetermined upper limit value and is not corrected to a higher value. Although there is no specific description about the reason why such an upper limit is set in Patent Document 1, in the experiments of the present inventors, if the target value is corrected to a value higher than a certain value, the toner density is reversed. The image density has increased due to the excessive amount. In order to avoid such an increase in image density, it is considered that the target value is not corrected to a value higher than a predetermined upper limit value. If the low density image output state continues with the target value corrected to the upper limit value, the toner particles rub against the magnetic carrier particles with a strong electrostatic force, so that the surface layer of the magnetic carrier particles is scraped and causes dielectric breakdown. . Then, a phenomenon called solid carrier adhesion in which the dielectric breakdown magnetic carrier particles are transferred from the developing roller onto the solid image of the latent image carrier is caused. Solid carrier adhesion appears as white spots on the image and lowers the image quality. Also, the surface layer of the latent image carrier is scraped, the cleaning blade for cleaning the latent image carrier is damaged, and the carrier in the developer is insufficient. It causes image quality degradation due to.

  The present invention has been made in view of the above background, and an object thereof is to provide the following image forming apparatus. That is, insufficient image density and toner scattering when the high image density output state continues for a long period of time are suppressed, and excessive image density and solid carrier when the low image density output state continues for a long period of time. An image forming apparatus capable of suppressing the occurrence of adhesion.

  In order to achieve the above object, the present invention develops a latent image on a latent image carrier with a latent image carrier that carries the latent image on its surface and a developer containing toner and carrier. The detection results obtained by the developing means for obtaining the toner image, the toner density detecting means for detecting the toner density of the developer in the developing means, the toner supplying means for supplying toner to the developing means, and the detection result by the toner density detecting means are predetermined. The target value is corrected based on the toner replenishing process for driving the toner replenishing unit so as to be close to the target value of the toner and replenishing toner to the developing unit, and the respective image area ratios of the output image within the latest predetermined period In the image forming apparatus including the control unit for performing the density target correction process, the target value is set to a larger value in addition to the process of correcting the target value in the density target correction process. When corrected, the developing potential, which is the potential difference between the latent image and the developer carrying member of the developing means, is corrected to a smaller value, while when the target value is corrected to a smaller value, the developing potential is corrected. The control means is configured to perform a process of correcting the value to a larger value.

  According to the present invention, it is possible to suppress the occurrence of insufficient image density and toner scattering when the high image density output state continues for a long period of time, and the image density when the low image density output state continues for a long period of time. The occurrence of excess and solid carrier adhesion can be suppressed.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 2 is a block diagram showing a main part of an electric circuit of the printer. The graph which shows an example of a time-dependent change of scattering prevention upper limit density | concentration TcDust, adhesion prevention lower limit density | concentration TcCar, and target value TcOpt in the continuous print mode which prints the image of average image area ratio DC = 0 [%] continuously. The graph which shows an example of a time-dependent change of scattering prevention upper limit density | concentration TcDust, adhesion prevention lower limit density | concentration TcCar, and target value TcOpt in the continuous printing mode which prints the image of average image area ratio DC = 10 [%] continuously. The graph which shows an example of a time-dependent change of scattering prevention upper limit density | concentration TcDust, adhesion prevention lower limit density | concentration TcCar, and target value TcOpt in the continuous printing mode which prints the image of average image area ratio DC = 100 [%] continuously. 6 is a graph showing the relationship between development γ and toner concentration Tc. The graph which shows the relationship between the number of continuous prints in a 1st continuous print test or a 2nd continuous print test, and the image area ratio DC in each test print. The graph which shows the relationship between target value TcOpt and the number of continuous prints in a 1st continuous print test and a 2nd continuous print test. 6 is a graph showing the relationship between the degree of occurrence of toner scattering and the number of continuous prints in the first continuous print test and the second continuous print test. The graph which shows the relationship between the generation | occurrence | production degree of solid carrier adhesion in the 1st continuous print test and the 2nd continuous print test, and the number of continuous printing. 7 is a graph showing the relationship between the development potential Vpot and the number of continuous prints in the first continuous print test and the second continuous print test. The graph which shows the relationship between the image density in the 1st continuous print test and the 2nd continuous print test, and the number of continuous prints.

An embodiment of an electrophotographic printer will be described below as an image forming apparatus to which the present invention is applied.
FIG. 1 is a schematic configuration diagram illustrating a printer according to an embodiment. In FIG. 1, a printer 100 includes a paper feed unit (paper feed table) that supplies a recording sheet accommodated therein to a paper feed path, and a printer unit mounted thereon. Subscripts Y, M, C, and K attached to the end of the reference numerals in the drawing indicate members for yellow, magenta, cyan, and black (black).

  In the vicinity of the center of the printer unit, an endless intermediate transfer belt 10 is provided that is wound around a plurality of support rollers 14, 15, 15 ', 16, and 63 and can move endlessly clockwise in the drawing. The cleaning device 17 is in contact with the cleaning backup roller from the belt front surface side in the entire area in the circumferential direction of the intermediate transfer belt 10 that is a surface endless moving body. The cleaning device 17 removes transfer residual toner remaining on the intermediate transfer belt 10 after passing through a secondary transfer nip described later.

  Of the entire region of the intermediate transfer belt 10 in the circumferential direction, the region between the support roller 14 and the support roller 15 extends substantially in the horizontal direction. A tandem image forming unit 20 is disposed on the area. The tandem image forming unit 20 has four image forming units 18Y, 18M, 18C, and 18K for yellow, magenta, cyan, and black disposed along the belt front surface facing the belt front surface. Yes.

  An optical writing device 21 as a latent image writing unit is provided on the tandem image forming unit 20. The image forming units 18Y, 18M, 18C, and 18K of the tandem image forming unit 20 are drum-shaped photoconductors 40Y, 40M, and 40C as latent image carriers on which latent images of yellow, magenta, cyan, and black are formed. , 40K. The optical writing device 21 that drives the light source based on the image data after the surfaces of the photoconductors 40Y, 40M, 40C, and 40K are uniformly charged by the charging devices 60Y, 60M, 60C, and 60K (for example, −650 V). Is optically scanned. The light irradiation portions on the surfaces of the photoconductors 40Y, 40M, 40C, and 40K generated by this optical scanning attenuate the potential (for example, −50 V) to form an electrostatic latent image.

  The electrostatic latent images formed on the surfaces of the photoreceptors 40Y, 40M, 40C, and 40K are developed by the developing devices 59Y, 59M, 59C, and 59K to become Y, M, C, and K toner images. The developing devices 59Y, 59M, 59C, and 59K are supplied with Y, M, C, and K toners from the toner bottles 50Y, 50M, 50C, and 50K as necessary. In the developing devices 59Y, 59M, 59C, and 59K, they are agitated as Y, M, C, and K developers in which Y, M, C, and K toners and magnetic carriers are mixed. The Y, M, C, and K toners in the Y, M, C, and K developers are triboelectrically charged to a negative polarity (for example, −30 μC / g). Developing rollers for Y, M, C, and K are disposed in the developing devices 59, 59M, 59C, and 59K, respectively. The developing rollers for Y, M, C, and K are exposed to the outside through a part of the peripheral surface of the developing roller that is provided in the casing, and face the photoreceptors 40Y, 40M, 40C, and 40K. The Y, M, C, and K developers pumped up by the developing rollers for Y, M, C, and K are conveyed to a developing area that faces the photoreceptors 40Y, 40M, 40C, and 40K as the rollers rotate. . In the development area, negative toner is transferred from the roller side to the latent image side between the electrostatic latent images of the photoconductors 40Y, 40M, 40C, and 40K and the developing roller to which a developing bias (for example, −500 V) is applied. The developing potential Vpot to be moved acts. Due to the developing potential Vpot (potential difference between the developing roller and the electrostatic latent image), the Y, M, C, and K toners on the Y, M, C, and K developing rollers are separated from the magnetic carrier, and the photoreceptors 40Y, 40Y, Transfer to 40M, 40C, 40K electrostatic latent images. As a result, the electrostatic latent images on the photoreceptors 40Y, 40M, 40C, and 40K are developed with the Y, M, C, and K toners to become Y, M, C, and K toner images.

  Primary transfer rollers 62Y, 62M, 62C, and 62K are disposed under the photoreceptors 40Y, 40M, 40C, and 40K, and press the intermediate transfer belt 10 toward the photoreceptors 40Y, 40M, 40C, and 40K. ing. As a result, primary transfer nips for Y, M, C, and K in which the photoreceptors 40Y, 40M, 40C, and 40K contact the intermediate transfer belt 10 are formed. Around the primary transfer nips for Y, M, C, and K, primary transfer rollers 62Y, 62M, 62C, and 62K to which a primary transfer bias is applied, and electrostatic latent images on the photoreceptors 40Y, 40M, 40C, and 40K During this, a primary transfer electric field is formed.

  When receiving the image data, the printer 100 rotates the support roller 14 by a driving unit (not shown) to move the intermediate transfer belt 10 endlessly in the clockwise direction in the drawing. At the same time, the image forming units 18Y, 18M, 18C, and 18K are driven to form Y, M, C, and K toner images on the photoreceptors 40Y, 40M, 40C, and 40K. These toner images are primarily transferred while being superimposed on the front surface of the intermediate transfer belt 10 at the primary transfer nips for Y, M, C, and K. As a result, a four-color superimposed toner image is formed on the front surface of the intermediate transfer belt 10.

  When a black single color image is formed on the intermediate transfer belt 10, the support rollers 15, 15 'other than the drive roller 14 are moved so that the yellow, magenta, and cyan photoconductors 40Y, 40M, and 40C are in the middle. It can also be separated from the transfer belt 10.

  Transfer residual toner that has not been primarily transferred to the intermediate transfer belt 10 adheres to the surfaces of the photoreceptors 40Y, 40M, 40C, and 40K after passing through the primary transfer nips for Y, M, C, and K. The transfer residual toner is removed from the surfaces of the photoreceptors 40Y, 40M, 40C, and 40K by the drum cleaning devices 61Y, 61M, 61C, and 61K, and then conveyed to a waste toner bottle (not shown).

  The surfaces of the photoreceptors 40Y, 40M, 40C, and 40K after cleaning are uniformly charged again by the charging devices 60Y, 60M, 60C, and 60K.

  The printer 100 selectively rotates one of the paper feed rollers 42 on the paper feed table 200 of the paper feed unit. As a result, the recording sheet is fed out from one of a plurality of paper feed cassettes 44 provided in multiple stages in the paper bank 43. Then, after the recording sheets are separated one by one by the separation roller 45 and sent to the paper feed path 46, the recording sheet is transported by the transport roller 47 to enter the paper feed path 48 of the printer unit. The recording sheet that has entered the paper feed path 48 of the printer unit stops by hitting the registration nip of the registration roller pair 49.

  A secondary transfer device 22 is disposed below the intermediate transfer belt 10. The secondary transfer device 22 forms a secondary transfer nip by bringing the secondary transfer roller 16 ′ into contact with a portion of the intermediate transfer belt 10 in the circumferential direction that is wound around the secondary transfer counter roller 16. ing.

  The registration roller pair 49 starts rotational driving at a timing at which the recording sheet can be superimposed on the four-color superimposed toner image on the belt at the secondary transfer nip, and sends the recording sheet toward the secondary transfer nip. In the secondary transfer nip, the four-color superimposed toner image on the intermediate transfer belt 10 is secondarily transferred to the recording sheet by the action of the secondary transfer electric field and nip pressure.

  The recording sheet that has passed through the secondary transfer nip is sent to the fixing device 25. The fixing device 25 includes a fixing belt unit and a pressure roller 25d. The fixing belt unit includes a heating roller 25b, a fixing roller 25c, and a fixing belt 25a that can be moved endlessly while being wound around these rollers. The fixing belt 25a and the pressure roller 25d are brought into contact with each other to form a fixing nip.

  The endless fixing belt 25a is a multilayer belt having at least a base material layer made of a material such as nickel, stainless steel or polyimide and an elastic layer made of silicon rubber or the like laminated on the front surface side. It is. The heating roller 25b disposed inside the loop of the fixing belt 25a includes a heat source such as a halogen heater inside a hollow roller made of metal such as aluminum or iron.

  The fixing belt 25a is endlessly moved in the clockwise direction in the drawing by the rotational driving of the fixing roller 25c while being stretched by the heating roller 25b and the fixing roller 25c disposed inside the loop. In the process of endless movement, it is heated by the heating roller 25b.

  Of the entire area in the circumferential direction of the fixing belt 25a, the pressure roller 25d is in contact with the fixing roller 25c from the belt front surface to form a fixing nip. The recording sheet sent to the fixing device 25 is heated and pressurized when passing through the fixing nip, whereby the four-color superimposed toner image is fixed on the surface.

  The recording sheet that has passed through the fixing device 25 is discharged out of the apparatus via the discharge roller pair 56 and then stacked on the discharge tray 57. In the double-sided print mode in which images are formed on both sides of the recording sheet, the recording sheet in which the toner image is fixed only on the first side of both sides passes through the fixing device 25 and is then discharged to the pair of discharge rollers. Instead of 56, it is sent to the retransmission device 28. Then, the image is retransmitted to the paper feed path 48 while being turned upside down by the retransmission device 28. After the four-color superimposed toner image is secondarily transferred from the paper feed path 48 to the secondary transfer nip and also on the second surface thereof, the machine passes through the fixing device 25 and the paper discharge roller pair 56. It is discharged outside.

  The intermediate transfer belt 10 that has passed through the secondary transfer nip enters the primary transfer nip for Y, M, C, and K again after the transfer residual toner adhering to the surface is removed by the belt cleaning device 17. To do. The toner accommodated in the belt cleaning device 17 is collected in a waste toner bottle (not shown) by a conveying means (not shown).

  FIG. 2 is a block diagram showing the main part of the electric circuit of the printer. In the figure, a writing control unit 151 controls the driving of the optical writing device 21 to write an electrostatic latent image by optically scanning a Y, M, C, K photoconductor (not shown). Is. The main control unit 150 includes a RAM, a ROM, a non-volatile memory, a CPU, and the like, and executes various arithmetic processes and controls driving of each device. Connected to the main controller 150 are Y, M, C, and K image forming units 18Y, 18M, 18C, and 18K, a K process motor 152, a color process motor 153, and the like. The image forming units 18Y, 18M, 18C, and 18K have toner density sensors 58Y, 58M, 58C, and 58K mounted on the developing devices, respectively. The toner density sensors 58Y, 58M, 58C, and 58K detect the Y, M, C, and K toner concentrations in the Y, M, C, and K developers stored in the developing devices for Y, M, C, and K, respectively. To do. Specifically, the toner density sensors 58Y, 58M, 58C, and 58K are magnetic permeability sensors, and output voltages corresponding to the magnetic permeability of the Y, M, C, and K developers. Since the magnetic permeability of the Y, M, C, and K developers is correlated with the Y, M, C, and K toner concentrations of the Y, M, C, and K developers, the toner density sensors 58Y, 58M, 58C, and 58K are correlated. Means that the Y, M, C, and K toner densities are detected. As the Y, M, C, and K toner concentrations increase, the output voltage values from the toner concentration sensors 58Y, 58M, 58C, and 58K decrease.

  The main control unit 150 includes a belt drive motor 154, toner supply motors 155Y, 155M, 155C, and 155K for Y, M, C, and K, a first pickup motor 156, a second pickup motor 157, a registration motor 161, a paper feed A motor 162 and the like are also connected. Further, primary transfer power sources 158Y, 158M, 158C, and 158K for Y, M, C, and K, development power sources 160Y, 160M, 160C, and 160K for secondary transfer power sources 154Y, 154M, 154C, and 154K, and an adhesion amount detection sensor 165 Etc. are also connected.

  The K process motor 152 is a motor that is a drive source of each device such as a photoconductor in the K image forming unit 18K. The color process motor is a motor serving as a drive source for each of the image forming units 18Y, 18M, and 18C for Y, M, and C. The belt drive motor 154 is a motor that is a rotational drive source of a roller that moves the intermediate transfer belt (10) endlessly.

  The toner supply motors 155Y, 155M, 155C, and 155K for Y, M, C, and K are for Y, M, C, and K developing devices (59Y, 59M, 59C, and 59K). This motor serves as a drive source for replenishing Y, M, C, and K toner in the toner bottle. That is, the toner replenishing motors 155Y, 155M, 155C, and 155K each constitute part of the toner replenishing means. When the toner supply motors 155Y, 155M, 155C, and 155K rotate, the toner supply mechanism of the toner supply device for Y, M, C, and K operates. As a result, the Y, M, C, and K toners in the toner bottles 50Y, 50M, 50C, and 50K are supplied to the developing devices 59Y, 59M, 59C, and 59K.

The main control unit 150, the non-volatile in memory (not shown), a toner density sensor 58Y, 58M, 58C, the output voltage _Y Vt from _58K, M _Vt, and stores C _Vt, the target value of K Vt respectively. Specifically, target voltages _Y Vtref, _M Vtref, _C Vtref, and _K Vtref corresponding to each color of Y, M, C, and _K are stored. Output voltage _{Y Vt, M Vt, C Vt} , K Vt is the target voltage _{Y Vtref, M Vtref, C Vtref} , and becomes higher than K Vtref. In this case, it means that the Y, M, C, and K toner concentrations of the Y, M, C, and K developers are lower than the target values. Therefore, the main control unit 150 performs toner supply processing during the print job. Then, the output voltage _{Y Vt, M Vt, C Vt} , K Vt is the target voltage _{Y Vtref, M Vtref, C Vtref} , if it becomes higher than K Vtref, the toner supply motor drive amount corresponding to the difference between them 155Y, 155M, 155C, and 155K are driven. Accordingly, the Y, M, C, and K toners corresponding to the difference are supplied to the developing devices 59Y, 59M, 59C, and 59K, so that the Y, M, and C of the Y, M, C, and K developers are supplied. , K toner density is maintained within a certain range.

Incidentally, as already mentioned, Y, M, C, taking the increase or decrease in K toner concentration, the output voltage _{Y Vt, M Vt, C Vt} , the opposite behavior is the increase or decrease in K Vt. Thus, as practiced in the actual machine, the output voltage _{Y Vt, M Vt, C Vt} , K Vt or target voltage _{Y Vtref, M Vtref, C Vtref} , based on the K Vtref Y, M, C, K toner It is easy to get confused when trying to understand the right or wrong concentration. Therefore, the toner replenishment process will be described below with a content different from the process actually performed in the actual machine. For example, when the target values of Y, M, C, and K toner densities are made higher, the target voltages _Y Vtref, _MV Tref, _C Vtref, and _K Vtref are made lower in the actual machine. However, it is easy to get confused. Therefore, instead of explaining that the target voltages _Y Vtref, _M Vtref, _C Vtref, and _K Vtref are lower, the target values _Y TcCar, _M TcCar, _C TcCar, and _K TcCar of the Y, M, C, and K toner densities are set as follows. Explain that it is higher.

  The first pickup motor 156 is a motor that serves as a drive source for feeding a recording sheet from one of the two sheet feeding cassettes (44). The second pickup motor 157 is a motor serving as a drive source for feeding the recording sheet from the other paper feed cassette (44). The registration motor 161 is a motor that is a driving source of the registration roller pair (49). The paper feed motor 162 is a motor that is a driving source for various transport roller pairs disposed in the paper feed path. The primary transfer power sources 158Y, 158M, 158C, and 158K for Y, M, C, and K are primary applied to the primary transfer rollers (62Y, 62M, 62C, and 62K) for Y, M, C, and K. The transfer bias is output. The secondary transfer power source 154 outputs a secondary transfer bias to be applied to the secondary transfer roller (16 '). Further, Y, M, C, and K developing power supplies 160Y, 160M, 160C, and 160K are applied to developing rollers of Y, M, C, and K developing devices (59Y, 59M, 59C, and 59K). A developing bias is output.

  When the main control unit 150 receives image data sent from an external personal computer or the like, the main control unit 150 controls driving of various devices based on the received image data. Also, the image data is transmitted to the writing control unit 151, and various processes such as a toner replenishment process and a density target correction process described later are performed. The writing control unit 151 controls the driving of the optical writing device 21 based on the image data, and uses the number of dots optically written with one print for Y, M, C, and K for each print. Data of a certain number of writing dots is transmitted to the main control unit 150. The main control unit 150 calculates the image area ratio of the image in each print based on the data of the number of write dots sent from the write control unit 151, and temporarily stores the result in the RAM.

Next, a characteristic configuration of the printer will be described.
The main control unit 150 performs density target correction processing when a continuous print mode in which images are continuously formed on a plurality of recording sheets P is performed or when the frequency of execution of print jobs is relatively high. To do. Then, Y, M, C, respectively for each color of K, appropriately corrected toner concentration of _{Y TcCar, M TcCar, C TcCar} , the K TcCar. The density target correction process will be described below. In the following description, the same processing is performed for each of the colors Y, M, C, and K, and therefore, for convenience, the description and subscripts relating to the colors Y, M, C, and K will be omitted.

  The chargeability of the toner in the developer in the developing device is influenced by the spent amount of the magnetic carrier (fixed amount of the external additive of the toner) and the surface layer scraping amount, and the spent amount and the surface layer scraping amount are individually measured within the latest predetermined period. Can be predicted based on the image area ratio of the print. Specifically, based on the image area ratio of each print, the most recent image output state is a high image density output state, a low image density output state, or a normal image density output state. It is possible to predict whether there is. Then, based on the predicted output state, the spent amount and the surface layer scraping amount can be predicted.

  Further, based on the predicted spent amount, it is possible to predict an anti-scattering upper limit concentration TcDust that is a limit value that does not cause toner scattering with respect to the toner concentration Tc of the developer. Further, based on the predicted surface layer scraping amount, it is also possible to predict an adhesion preventing lower limit concentration TcCar, which is a lower limit value that does not cause solid carrier adhesion, with respect to the toner concentration Tc of the developer. The intermediate value between the scattering prevention upper limit density TcDust and the adhesion prevention lower limit density TcCar is the optimum target value TcOpt of the toner density.

  Note that the cause of toner scattering is that the toner concentration Tc is excessively increased and that the target value TcOpt has a lower limit. Specifically, when the toner concentration Tc is excessively increased, the external additive added to the toner adheres to the magnetic carrier particles, thereby reducing the charging ability of the magnetic carrier. As a result, the charge amount Q / M of the toner is lowered, resulting in insufficient image density and toner scattering. The anti-scattering upper limit density TcDust is an upper limit value of the target value TcOpt that does not cause this kind of toner scattering, and is irrelevant to the toner scattering caused by setting the lower limit value to the target value TcOpt. When the lower limit is set, toner scattering occurs as follows. That is, when the high image density output state continues for a long period of time, the target value TcOpt is continuously corrected to a lower value by the density target correction process, and the target value TcOpt eventually decreases to the lower limit value. Thereafter, when the high image density output state further continues, the toner charge amount Q / M decreases and toner scattering occurs.

  In addition, the cause of the occurrence of solid carrier adhesion is that the toner concentration Tc is remarkably lowered, and the target value TcOpt is provided with an upper limit value. Specifically, when the toner concentration Tc is remarkably reduced, a phenomenon occurs in which the magnetic carrier particles are rubbed while being in direct contact with the surface of the developing roller. As a result, the surface layer of the magnetic carrier particles is scraped to cause dielectric breakdown, thereby causing solid carrier adhesion. The adhesion preventing lower limit concentration TcCar is a lower limit value of the target value TcOpt that does not cause this kind of solid carrier adhesion, and is irrelevant to the solid carrier adhesion resulting from the upper limit being set for the target value TcOpt. When an upper limit is provided, solid carrier adhesion occurs as follows. That is, when the low image density output state continues for a long period of time, the target value TcOpt is continuously corrected to a higher value by the density target correction process, and the target value TcOpt eventually increases to the upper limit value. Thereafter, when the low image density output state continues further, the toner charge amount Q / M increases, and the toner particles are rubbed against the magnetic carrier particles with strong electrostatic force, so that the surface layer of the magnetic carrier particles is scraped. Causes dielectric breakdown. And this carrier breakdown causes solid carrier adhesion.

  The main control unit 150 performs density target correction processing every time the cumulative number of prints requiring consideration reaches 100. The prints requiring consideration are prints that contribute to fluctuations in the toner charge amount Q / M. Specifically, as described above, the toner charge amount Q / M decreases when the high image density output state continues, while the toner charge amount Q / M increases when the low image density output state continues. . Therefore, the toner charge amount Q / M varies according to the average image area ratio in the latest print. For this reason, it is possible to grasp the fluctuation tendency of the toner charge amount Q / M based on the average image area ratio in the latest print. However, the toner charge amount Q / M cannot be accurately grasped simply by referring to the respective image area ratios for the predetermined number of sheets in the past. This is for the reason explained below. That is, when the toner is well charged by stirring, the charge amount Q / M is maintained for a while even after the stirring is stopped. However, the charge amount Q / M is gradually decreased as the standing time elapses. Go. For this reason, in order to grasp the charge amount Q / M of the toner, it is necessary to consider the standing time after the stirring is stopped. If the standing time is relatively long, it is not necessary to consider the image area ratio in the print before stopping the stirring, but if the standing time is relatively short, it is also necessary to consider the image area ratio in the print before stopping the stirring. There is. Therefore, when the target value TcOpt is corrected in the density target correction process, when printing is performed during a period from the time point traced back in the past by a predetermined time to the present time, the target value is taken into consideration for each print in consideration of the image area ratio. Determine TcOpt. A past print that should take into account the image area ratio is a print requiring consideration. When the continuous print mode is performed, all the prints in the continuous print mode are prints requiring consideration.

  For example, at the start of the continuous print mode, the main control unit 150 sets the initial value of the number of required prints to 5 when the number of prints that need to be considered by previous prints is five. . Then, when the first to 95th prints are performed in the continuous print mode, since the accumulation reaches 100 sheets, the density target correction process is performed. At this time, the image density output state is grasped based on the respective image area ratios in the prints for 100 sheets.

  As for the image density output state, characteristics that can grasp the image area output frequency for 100 sheets such as the average image area ratio DC, which is the average value of the image area ratio for 100 sheets, the moving average value, and the output dot number ratio, etc. If so, it is possible to grasp any characteristics. Hereinafter, a method of determining the target value TcOpt while grasping the image density output state based on the average image area ratio DC will be described as an example. However, the image density output state is determined based on characteristics different from the average image area ratio DC. You may grasp. However, whichever characteristic is used, each image area ratio in each print is referred to. Even if we refer to the output dot number rate, it is agreed that it refers to the image area rate.

  If the waiting time without executing the print job becomes a certain length of time, the toner charge amount Q / M in the developing device is considerably reduced. In this case, if a print command is issued, before the print job starts. Then, the idling operation is performed and the frictional charging of the toner is promoted. For this reason, it is not necessary to consider the shortage of the toner charge amount when the leaving time becomes considerably long in determining the target value TcOpt.

When starting the density target correction process, the main control unit 150 obtains the scattering prevention upper limit density TcDust by the following formula using the average image area ratio DC in the prints requiring consideration for the past 100 sheets.
“TcDust = TcDust (previous value) + kDust (DC) × (TcDustLim (DC) −TcDust (previous value))”.
In this equation, TcDustLim (DC) is the convergence value of the anti-scattering upper limit density TcDust when continuous printing is performed at a specific average image area ratio DC, and is an average constructed based on the experimental results of previous experiments. It is a function of the image area ratio DC. Further, kDust (DC) is a time constant representing the speed until the scattering prevention upper limit concentration TcDust converges to the convergence value TcDustLim (DC), and is a function of the average image area ratio DC constructed based on the experiment. is there.

  When the inventors conducted an experiment using a printer tester having the same configuration as the printer according to the embodiment, the convergence value TcDustLim (DC) is a function of “10−2 × log (DC + 1)”. Became. Further, the time constant kDust (DC) is a constant of “0.0015”.

Next, the main control unit 150 obtains the adhesion prevention lower limit concentration TcCar by the following equation.
“TcCar = TcCar (previous value) + kCar (DC) × (TcCarLim (DC) −TcCar (previous value))”.
In this equation, TcCarLim is the convergence value of the adhesion prevention lower limit density TcCar when continuous printing is performed at a certain specific average image area ratio DC, and is the average image area ratio constructed based on the experimental results of previous experiments. It is a function of DC. KCar is a time constant of the convergence value TcCarLim and is a function of the average image area ratio DC constructed based on the experimental result.

  As a result of an experiment using a printer tester, the convergence value TcCarLim (DC) was a function of “5.5−0.5 × log (DC + 1)”. Further, the time constant kCar (DC) is a function of “0.0010−0.0001 × log (DC + 1)”.

Next, the main control unit 150 obtains the target value TcOpt by substituting the calculated new scattering prevention upper limit concentration TcDust and adhesion prevention lower limit concentration TcCar into the following equations.
“TcOpt = (TcDust + TcCar) ÷ 2”

The present inventors conducted experiments using a printer testing machine, and TcDust (initial value), which is an upper limit TcDust for preventing scattering when performing a print job after idling after waiting for a long period of time, and an anti-adhesion lower limit concentration An appropriate value of TcCar (initial value) which is TcCar was obtained. The values were as follows:
・ TcDust (initial value) = 9.0 [wt%]
・ TcCar (initial value) = 4.0 [wt%]

  After the idling operation, the scattering prevention upper limit density TcDust, the adhesion prevention lower limit density TcCar, and the target value in a continuous print mode (actually simply continuous paper passing) in which images with an average image area ratio DC = 0 [%] are continuously printed. An example of the change over time of TcOpt is shown in FIG. In addition, an example of changes over time of the scattering prevention upper limit density TcDust, the adhesion prevention lower limit density TcCar, and the target value TcOpt in the continuous print mode in which images with an average image area ratio DC = 10 [%] are continuously printed after the idling operation. As shown in FIG. In addition, an example of temporal changes of the scattering prevention upper limit density TcDust, the adhesion prevention lower limit density TcCar, and the target value TcOpt in the continuous print mode in which images with an average image area ratio DC = 100 [%] are continuously printed after the idling operation. As shown in FIG.

  Assume that the low image density output state continues for a long period of time. In this case, as indicated by a solid line in FIG. 3, the target value TcOpt is increased as the number of printed sheets is increased, so that the toner is excessively charged. The occurrence of adhesion can be avoided over a long period of time. However, in the conventional configuration, the upper limit value is set for the target value TcOpt (the lower limit value is set for the target voltage Vtref) with the aim of avoiding the occurrence of excessive image density caused by excessively increasing the target value TcOpt. ) For this reason, when the low image density output state continues for a long period of time, as shown by the dotted line in the figure, when the target value TcOpt is gradually increased, the target value TcOpt is eventually reached to reach the upper limit value. Cannot be corrected to a high value. Then, the upper limit value was lower than the adhesion preventing lower limit concentration TcCar, causing solid carrier adhesion.

  On the other hand, it is assumed that the high image density output state continues for a long period of time. In this case, as shown in FIG. 5, by decreasing the target value TcOpt as the number of printed sheets increases, an increase in image density and toner scattering due to insufficient charging of the toner occur over a long period of time. Can be avoided. However, in the conventional configuration, the lower limit value is set for the target value TcOpt (the upper limit value is set for the target voltage Vtref) in order to avoid the occurrence of insufficient image density due to the target value TcOpt being too small. ) For this reason, when the high image density output state continues for a long period of time, as shown by the dotted line in the figure, when the target value TcOpt is gradually decreased, the target value TcOpt is eventually reached to reach the lower limit value. Cannot be corrected to a lower value. The lower limit value exceeds the scattering prevention upper limit concentration TcDust, causing toner scattering.

  When an image with an image area ratio of 10% is continuously output over a long period of time, as shown in FIG. 4, the target value TcOpt is also set between the anti-scattering upper limit concentration TcDust and the anti-adhesion lower limit concentration TcCar even in the conventional configuration. I was able to keep the value in between. That is, continuous output can be performed without causing toner scattering and solid carrier adhesion.

FIG. 6 is a graph showing the relationship between development γ and toner density Tc. Development γ [mg / cm ² / kV] is a slope of a graph showing the relationship between the toner adhesion amount M / A of the toner image and the development potential Vpot. That is, when the toner adhesion amount M / A is represented by the vertical axis, the development ability increases as the development γ increases. When the toner density Tc of the developer is changed due to the correction of the target value TcOpt in the density target correction process, the developing ability is also changed accordingly. Specifically, when the target value TcOpt is corrected to a lower value and the toner concentration Tc is lowered to suppress the occurrence of excessive image density and toner scattering due to insufficient charging of the toner, as shown in the figure. In addition, the development γ (= development ability) is further reduced. In this case, the developing ability is reduced. However, since the developing ability has been increased more than usual due to insufficient charging of the toner in the previous stage, the high image density output state must be continued for a long period of time. For example, the developing ability is reduced to an appropriate value. Thereby, the target image density can be obtained. However, if the high image density output state continues for a considerably long period of time, the decrease in the developing ability due to the decrease in the toner concentration Tc becomes larger than the increase in the developing ability due to insufficient charging of the toner. As a result, insufficient image density occurs.

  On the other hand, when the target value TcOpt is corrected to a higher value and the toner concentration Tc is increased in order to suppress the occurrence of insufficient image density and carrier adhesion due to excessive charging of the toner, as shown in FIG. γ (= development ability) is further increased. In this case, the developing ability is increased. However, since the developing ability was lowered than usual due to the excessive charging of the toner in the previous stage, the low image density output state must be continued for a long period of time. For example, the developing ability is increased to an appropriate value. Thereby, the target image density can be obtained. However, when the low image density output state continues for a considerably long time, the increase in the development capability due to the increase in the toner concentration Tc becomes larger than the decrease in the development capability due to the excessive charging of the toner. As a result, excessive image density occurs.

  The development γ varies depending on the toner density Tc, and also varies depending on the environment and the image density output state. However, the present inventor has shown through experiments that the ratio between the change amount of the toner concentration Tc and the change amount of the development γ when the toner concentration Tc is changed (development γ (Tc1) / γ (Tc2) depends on the printing conditions. The development γ has a good correlation with the development potential Vpot, which can maintain the image density constant by correcting the development potential Vpot as follows. That is, when the function G (Tc) of the dependence of the developing potential Vpot on the toner Tc is examined in advance, and the target value TcOpt is corrected in the density target correction processing, the developing potential Vpot is changed to the function G. In more detail, “Vpot = Vpot (value before correction) × G (Tc (value before correction))”. The developing potential Vpot is corrected to a value obtained by the equation “÷ G (TC (corrected value)).” Then, in the density target correction processing, the developing potential Vpot is developed by correcting the target value TcOpt. Correction is made so as to be inversely proportional to the fluctuation of γ.

  Therefore, the main control unit 150 corrects the target value TcOpt without limiting the upper and lower limits in the density target correction process. When the target value TcOpt is corrected to a larger value, the development potential Vpot is corrected to a smaller value. On the other hand, when the target value TcOpt is corrected to a smaller value, the development potential Vpot is corrected to a larger value.

  As described above, in this printer, when the target value TcOpt is corrected in the density target correction process, the development potential Vpot is corrected on the opposite side (increase or decrease) to the correction of the target value TcOpt as follows. I was able to. That is, even when the high image density output state continues for a long period of time, the occurrence of excessive image density and toner scattering due to toner charging failure, and the occurrence of insufficient image density due to insufficient toner density Tc. Was able to be suppressed. Furthermore, even when the low image density output state continues for a long period of time, the image density is insufficient due to excessive charging of the toner, the solid carrier adheres, and the image density is excessive due to the excessive toner density Tc. Was able to be suppressed.

  The present inventors prepared a printer tester, and thereby performed a first continuous print test and a second continuous print test. In the first continuous print test, the density target correction processing was performed every 100 prints while continuously printing images with various image area ratios. In each density target correction process, a process of correcting the target value TcOpt within the range from the upper limit value to the lower limit value as in the image forming apparatus described in Patent Document 1 is executed (conventional configuration).

  On the other hand, in the second continuous print test, density target correction processing is performed every 100 prints while continuously printing images with various image area ratios, and the following processing is performed in each density target correction processing. I let them. That is, similarly to the printer according to the embodiment, the target value TcOpt is corrected without limitation on the upper and lower limits, and when the target value TcOpt is corrected, the process of correcting the developing potential Vpot to a value that is inversely proportional is performed.

  In each continuous print test, the change over time in the target value TcOpt, the change over time in the degree of occurrence of toner scattering, the change over time in the degree of occurrence of solid carrier adhesion, the change over time in the development potential Vpot, and the change over time in the image density. Examined.

  FIG. 7 is a graph showing the relationship between the number of continuous prints in the first continuous print test and the second continuous print test and the image area ratio DC in each test print. As shown in the figure, in these continuous print tests, a test image with a low image area ratio DC and a test image with a high image area ratio DC are switched and printed at a predetermined timing.

  FIG. 8 is a graph showing the relationship between the target value TcOpt and the number of continuous prints in the first continuous print test and the second continuous print test. FIG. 9 is a graph showing the relationship between the degree of occurrence of toner scattering and the number of continuous prints in the first continuous print test and the second continuous print test. FIG. 10 is a graph showing the relationship between the occurrence of solid carrier adhesion and the number of continuous prints in the first continuous print test and the second continuous print test. FIG. 11 is a graph showing the relationship between the development potential Vpot and the number of continuous prints in the first continuous print test and the second continuous print test. FIG. 12 is a graph showing the relationship between the image density and the number of continuous prints in the first continuous print test and the second continuous print test.

  As shown in FIG. 8, in the second continuous print test corresponding to the embodiment, the target value TcOpt is always maintained at a value between the scattering prevention upper limit density TcDust and the adhesion prevention lower limit density TcCar regardless of the number of continuous prints. doing. Therefore, as shown in FIGS. 9 and 10, toner scattering and solid carrier adhesion did not occur during the test period.

  On the other hand, as shown in FIGS. 7 and 8, in the first continuous print test corresponding to the conventional configuration, the target value TcOpt is increased to the upper limit value when images with a low image area ratio DC are continuously output. After that, it is lower than the lower limit concentration TcCar for preventing adhesion. As a result, as shown in FIGS. 7 and 10, noticeable solid carrier adhesion occurs when images with a low image area ratio DC are continuously output. Further, as shown in FIGS. 7 and 8, when an image having a high image area ratio DC is continuously output, the target value TcOpt is lowered to the lower limit value, and is then made higher than the scattering prevention upper limit density TcDust. End up. As a result, as shown in FIGS. 7 and 9, significant toner scattering occurs when images having a high image area ratio DC are continuously output.

  As shown in FIG. 12, in both the first continuous print test and the second continuous print test, the image density variation with time can be maintained at a relatively small value. In the first continuous print test corresponding to the conventional configuration, an upper limit value and a lower limit value are provided for the target value TcOpt, so that excessive increase and decrease in the toner concentration Tc are suppressed, and fluctuations in image density over time are relatively suppressed. This is because it can be maintained at a small value. On the other hand, in the second continuous print test, since the upper limit value and the lower limit value are not provided for the target value TcOpt, the toner density Tc is largely changed as shown in FIG. This fluctuation range far exceeds the range between the upper limit value and the lower limit value. The reason why the image density variation with time can be maintained at a relatively small value in spite of the large variation in the toner density Tc is as follows. That is, as shown in FIGS. 8 and 11, when the target value TcOpt is corrected, the development potential Vpot is corrected in the direction opposite to the target value TcOpt. Thus, the development performance can be maintained constant by offsetting the increase or decrease in the development performance due to the correction of the target value TcOpt by the decrease in the development performance due to the reverse correction of the development potential Vpot.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
[Aspect A]
Developing means for developing a latent image on the surface of the latent image carrier with a latent image carrier (for example, photoconductor 40) carrying the latent image on its surface and a developer containing toner and carrier to obtain a toner image (For example, a developing device 59), a toner concentration detecting unit (for example, a toner concentration sensor 58) for detecting the toner concentration of the developer in the developing unit, and a toner replenishing unit (for example, a toner replenishing motor) for supplying toner to the developing unit. 155 and a toner replenishing process for replenishing toner to the developing unit by driving the toner replenishing unit so that the detection result by the toner density detecting unit approaches a predetermined target value (for example, TcOpt). Or control means for performing density target correction processing for correcting the target value based on the image area ratio of each output image within the most recent predetermined period ( For example, in the image forming apparatus including the main control unit 150), in the density target correction process, in addition to the process of correcting the target value, the latent image is corrected when the target value is corrected to a larger value. When the developing potential (for example, Vpot), which is the potential difference between the developing means and the developer carrying member (for example, the developing roller) is corrected to a smaller value, the developing potential is corrected when the target value is corrected to a smaller value. The control means is configured to perform a process of correcting the value to a larger value.

  In such a configuration, when a high image density output state continues, in order to suppress an increase in image density due to toner charging failure, the target value of the toner density is corrected to a lower value and the developing means converts the toner into a magnetic carrier. Rubbing more positively. This promotes frictional charging of the toner and suppresses a decrease in the toner charge amount Q / M, thereby suppressing an increase in image density due to a decrease in the charge amount Q / M. At this time, if the target value is simply corrected to a lower value, if the high image density output state continues for a long period of time, the developing ability may be insufficient due to a significant decrease in toner density, which may cause insufficient image density. Therefore, it is necessary to set a lower limit for the target value. However, in the present invention, when the target value is corrected to a lower value, the development potential is corrected to a higher value in accordance with the correction, and the development capability resulting from the correction of the target value to a lower value. Reduce the decline. As a result, even if the lower limit value is not set for the target value, it will not cause insufficient image density due to insufficient development capability, so the target value is reduced to a sufficient value and the high image density output state is maintained for a long period of time. Thus, excessive image density and toner scattering can be suppressed. On the other hand, when the low image density output state continues, in order to suppress a decrease in image density due to excessive charging of the toner, the target value of the toner density is corrected to a higher value and the developing means rubs the toner against the magnetic carrier. Suppress. Accordingly, the frictional charge of the toner is suppressed to suppress the increase in the toner charge amount Q / M, thereby suppressing the decrease in the image density due to the increase in the charge amount Q / M. At this time, if the target value is simply corrected to a higher value, if the low image density output state continues for a long period of time, there is a risk of excessive development capacity due to a significant increase in toner density, resulting in excessive image density. Therefore, it is necessary to set an upper limit value for the target value. However, in the present invention, when the target value is corrected to a higher value, the development potential is corrected accordingly to a lower value, and the development capability resulting from the correction of the target value to a higher value. Suppress the increase. As a result, an excessive image density due to an excessive development capability does not occur without setting an upper limit value for the target value. For this reason, the target value can be increased to a sufficient value to suppress the occurrence of insufficient image density and solid carrier adhesion when the low image density output state continues for a long period of time. As described above, it is possible to suppress the occurrence of insufficient image density and toner scattering when the high image density output state continues for a long period of time, and excessive image density when the low image density output state continues for a long period of time. And solid carrier adhesion can be suppressed.

[Aspect B]
Aspect B corrects the target value to a larger value and lowers the development potential when the output frequency of an image with a relatively high image area ratio within the predetermined period is relatively high. The control means is configured so that the process of correcting to a value is performed in the density target correction process.

[Aspect C]
Aspect C corrects the target value to a smaller value and increases the development potential when the output frequency of an image with a relatively low image area ratio is relatively high within the predetermined period in aspect B The control means is configured so that the process of correcting to a value is performed in the density target correction process.

[Aspect D]
Aspect D is a toner adhesion amount detection means for detecting the toner adhesion amount per unit area of the image density detection toner image obtained by developing the latent image on the latent image carrier in any one of the aspects A to C. (For example, an adhesion amount detection sensor 165) is provided, and a toner image for image density detection is formed each time a predetermined timing arrives, and a desired value is determined based on the result of detecting the toner adhesion amount of the image density detection toner image A developing ability adjustment process for adjusting the developing potential so as to obtain the developing ability is performed separately from the density target correction process, and the development potential adjustment in the developing ability adjustment process is performed in the density target correction process. The control means is configured to perform a process of correcting the development potential based on the value. In such a configuration, the development potential adjustment process is periodically performed, whereby the development potential can be adjusted to a value suitable for the environment, and a stable image density can be obtained regardless of the environment. Further, in the density target correction process, the development potential is corrected based on the adjustment value of the development potential in the development capability adjustment process, thereby correcting the development potential to a value suitable for both the environment and the image density output state. be able to.

40Y, M, C, K: photoconductor (latent image carrier)
58Y, M, C, K: toner density sensor (toner density detection means)
59Y, M, C, K: Developing device (developing means)
150: Main control unit (control means)
155Y, M, C, K: Toner supply motor (part of toner supply device)
165: Adhesion amount detection sensor (adhesion amount detection means)

JP 2007-133235 A

Claims (4)

A latent image carrier that carries a latent image on its surface; a developing unit that develops the latent image on the latent image carrier with a developer containing toner and a carrier to obtain a toner image; A toner density detecting means for detecting the toner density of the developer, a toner supplying means for supplying toner to the developing means, and the toner supplying means so that the detection result by the toner density detecting means approaches a predetermined target value. Control means for performing toner supply processing for driving and replenishing toner to the developing means, and density target correction processing for correcting the target value based on the respective image area ratios of output images within the most recent predetermined period. In the image forming apparatus provided,
In the density target correction process, in addition to the process of correcting the target value, when the target value is corrected to a larger value, development is a potential difference between the latent image and the developer carrier of the developing unit. The control unit is configured to perform a process of correcting the development potential to a larger value when the target value is corrected to a smaller value while the potential is corrected to a smaller value. An image forming apparatus. The image forming apparatus according to claim 1.
When the output frequency of an image having a relatively high image area ratio is relatively high within the predetermined period, the processing for correcting the target value to a larger value and correcting the developing potential to a smaller value is performed. An image forming apparatus, characterized in that the control means is configured to perform the target correction process. The image forming apparatus according to claim 2.
When the output frequency of an image with a relatively low image area ratio is relatively high within the predetermined period, the processing for correcting the target value to a smaller value and correcting the development potential to a larger value is performed. An image forming apparatus, characterized in that the control means is configured to perform the target correction process. The image forming apparatus according to any one of claims 1 to 3,
A toner adhesion amount detecting means for detecting the toner adhesion amount per unit area of the image density detection toner image obtained by developing the latent image on the latent image carrier;
Each time the predetermined timing arrives, the image density detecting toner image is formed, and the developing potential is obtained so that a desired developing ability can be obtained based on the result of detecting the toner adhesion amount of the image density detecting toner image. The development potential adjustment process for adjusting the development potential is performed separately from the density target correction process, and the development potential is corrected based on the adjustment value of the development potential in the development capacity adjustment process in the density target correction process. An image forming apparatus comprising the control unit so as to perform processing.

Images