JP5790406B2 - Control device, image forming apparatus, and program - Google Patents

Description

  The present invention relates to a control device, an image forming apparatus, and a program.

  In an electrophotographic image forming apparatus, when an electrostatic latent image is developed, a voltage applied between a photosensitive drum as an electrostatic latent image holding member and the developing device is referred to as a developing bias. The development bias is represented by a potential difference with respect to a predetermined reference potential. Further, a potential called a development potential is represented by a difference between a potential of an exposure area that is an exposed area on the photosensitive drum and a development bias. Hereinafter, this development potential is referred to as Vdev. The potential difference between the charging potential when the photosensitive drum is charged and the developing bias is called a cleaning field. The cleaning field is a potential for cleaning the photosensitive drum by preventing toner from adhering to a non-exposed portion, which is an unexposed portion of the charged photosensitive drum, by electrostatic force. Hereinafter, the cleaning field is referred to as Vcf. When control is performed so that the ratio between Vdev and Vcf is maintained at a certain value within a predetermined range (hereinafter, the ratio is maintained), the above-described various potential controls cause highlights and halftone levels. It is known that correction can be performed while suppressing fluctuations in density in tone characteristics.

  FIG. 10 is a diagram illustrating an example of changes in Vdev and Vcf when the potential is controlled in the image forming apparatus. In FIG. 10, the horizontal axis represents time t, and the vertical axis represents potential v. In order to suppress an image quality defect called a pattern defect in an image, an upper limit and a lower limit are provided for Vdev and Vcf. In FIG. 10, the Vdev upper limit, the Vdev lower limit, the Vcf upper limit, and the Vcf lower limit are indicated by broken lines, respectively. A range indicated by an arrow A1 represents a period during which the ratio of Vdev and Vcf is maintained. A range indicated by an arrow A2 represents a period in which the ratio between Vdev and Vcf is not maintained. A range indicated by an arrow B1 surrounded by two alternate long and short dash lines represents a range of Vdev that can be changed while maintaining a ratio to Vcf. Arrows S1 and S2 represent the timing at which the setup process is performed. The setup process includes a first setup process and a second setup process. An arrow S1 represents the timing at which the first setup process is performed, and this first setup process is executed, for example, when the image forming apparatus is turned on. An arrow S2 represents a timing at which the second setup process is performed. This second setup process is executed, for example, during a period in which an image forming process is performed in the image forming apparatus. In the setup process, for example, a potential such as Vdev or Vcf is corrected based on the detected density of a patch image having a uniform density. Vdev and Vcf vary depending on such a setup process, but as shown in FIG. 10, control is performed so that the ratio between Vdev and Vcf is maintained in the period A1. In the case where this ratio is not maintained, it is impossible to suppress density fluctuations by only potential control in a low gradation area or an intermediate gradation area called so-called highlight. Patent Document 1 describes that when the contrast potential, which is the sum of the development potential and the cleaning field, is corrected, the correction is performed so as to maintain the ratio of the cleaning field to the contrast potential. Japanese Patent Application Laid-Open No. 2004-228561 describes that control is performed so that a development potential representing a development potential and a background potential representing a cleaning field have a predetermined target ratio.

  Here, when the range between the upper limit and the lower limit of Vcf, that is, the variable range of Vcf is narrower than the variable range of Vdev linked to the ratio of Vdev and Vcf, as shown in the graph of period A2, Vcf is When the potential corresponding to the upper limit or the lower limit is fixed by the setup process as described above, the ratio of Vdev and Vcf is not maintained at a constant level. Here, the fact that the ratio is maintained at a constant level means that the ratio is within an allowable range determined from a certain value. Hereinafter, the ratio is simply referred to as “the ratio is maintained”. In this case, even if the setup process is performed at the timings indicated by arrows S1 and S2 and Vdev is corrected, Vcf maintains its upper or lower limit value, so the ratio between Vdev and Vcf is not maintained.

  FIG. 11 is a diagram showing the relationship between the gradation value and density of an image. In FIG. 11, the horizontal axis represents the gradation value of the image, and the vertical axis represents the density of the image. In FIG. 11, a curve L1 represents the relationship between the gradation value and the density of the image before Vdev and Vcf are corrected. In FIG. 11, a curve L2 represents the relationship between the gradation value and the density of the image when the ratio of Vdev and Vcf is maintained. In FIG. 11, a curve L3 represents the relationship between the gradation value and the density of the image when Vcf is fixed at the upper limit or the lower limit. When Vcf is fixed at the upper limit or the lower limit, the ratio between Vdev and Vcf is not maintained, and therefore, as shown by the curve L3 in FIG. 11, fluctuations in density in the highlight and halftone gradation characteristics cannot be suppressed. . On the other hand, in the curve L2, when Vdev is corrected in order to adjust the high density range, the ratio between Vdev and Vcf is maintained, so that fluctuations in density in highlight and halftone gradation characteristics are suppressed. The

Japanese Patent Laid-Open No. 05-307302 JP 2010-44218 A

  An object of the present invention is to extend the period during which the ratio between the cleaning field and the development potential represented by the difference between the development bias and the charge potential of the image carrier is maintained when an image is formed by electrophotography. It is in.

  According to a first aspect of the present invention, there is provided an image forming apparatus for controlling an operation of an image forming unit that exposes a charged image carrier to form an electrostatic latent image, develops the image by a developing device, and transfers the image onto a medium. When the time for satisfying the first condition that is determined in advance is reached by the control means, the first setup is executed to cause the image forming means to form a first image with a certain density as a target. Based on the difference between the formation control means, the acquisition means for acquiring the reading result of the density of the first image, and the certain density that is the target of the first image and the reading result acquired by the acquisition means Determining means for determining a development potential which is a difference between a potential of an exposed area on the image carrier and a development bias which is a voltage applied between the image carrier and the developing device; The setup is performed When the first image is formed, a cleaning field represented by a difference between the developing bias and a charging potential for charging the image carrier is set to a value less than a predetermined upper limit in advance. A setting means for setting a value exceeding a determined lower limit; and a specifying means for specifying a ratio between the cleaning field set by the setting means and the development potential determined by the determination means, and the image formation control means Is characterized in that the operation of the image forming means is controlled so as to maintain the ratio specified by the specifying means.

  According to a second aspect of the present invention, when the time when the image forming control unit satisfies a predetermined second condition different from the predetermined first condition is reached, the first image forming control unit A second setup different from the setup is executed to cause the image forming unit to form a second image with a certain density as a target, and the acquisition unit performs the second setup with the certain density as a target. The determination unit obtains the development potential based on a difference between the read result acquired by the acquisition unit and the certain density that is a target of the second image. The setting means sets the cleaning field based on the ratio specified by the specifying means and the development potential determined by the determining means.

  In the control device according to a third aspect of the present invention, the image formation control unit is configured such that a difference between the cleaning field set by the setting unit and the upper limit or the lower limit when the second setup is executed is equal to or greater than a threshold value. In this case, the first setup is executed to form the first image on the image forming means.

  In the control device according to claim 4 of the present invention, the image formation control unit is configured to execute the cleaning field set by the setting unit when the second setup is executed and the second setup. When the ratio with the development potential determined by the determining unit deviates more than a threshold from the ratio specified by the specifying unit, the first setup is executed, and the first image is displayed. The image forming unit forms the image.

  According to a fifth aspect of the present invention, the control device stores a plurality of first gradation values and a second gradation value corresponding to each of the first gradation values, and the acquisition Update means for updating the second gradation value corresponding to each of the first gradation values stored in the storage means on the basis of the reading result acquired by the means, and the image forming control The means converts the gradation value of each pixel represented by the image data based on the correspondence relationship between the second gradation value updated by the updating means and the first gradation value, and the conversion An image corresponding to the subsequent image data is formed on the image forming means.

  The control device according to claim 6 of the present invention is characterized in that the setting means sets the cleaning field to a value obtained by weighted averaging the upper and lower limits of the cleaning field with a predetermined ratio.

  The control device according to claim 7 of the present invention is characterized in that the setting means sets the cleaning field to a value separated from the upper limit or lower limit by a predetermined value.

  In the control device according to an eighth aspect of the present invention, the setting unit has a value less than a predetermined upper limit when the image forming control unit cannot maintain the ratio specified by the specifying unit. And a value exceeding a predetermined lower limit.

  According to a ninth aspect of the present invention, there is provided an image forming apparatus comprising: an image holding member; a charging unit that charges the image holding member; and an image holding member charged by the charging unit that exposes the electrostatic latent image. An exposure unit for forming, a developing device for developing an electrostatic latent image formed by the exposure unit and forming an image on the surface of the image carrier, and an image formed on the surface of the image carrier as a medium A transfer unit that transfers the image to the medium; a fixing unit that fixes the image transferred to the medium to the medium; and the control device according to claim 1.

  In the image forming apparatus according to the tenth aspect of the present invention, when the predetermined first condition is satisfied, when the power of the apparatus is turned on, the power saving operation state is changed from the power saving operation state. The developer is replenished to the developing device after the toner shortage is detected, when a predetermined condition is satisfied at the start of the image forming process, when the image forming process is completed Or at least one of the parts constituting the device is replaced.

  According to an eleventh aspect of the present invention, there is provided a program for controlling an operation of an image forming unit that causes a computer to expose a charged image carrier to form an electrostatic latent image, develop the image by a developing device, and transfer the image to a medium. In step, when the time when a predetermined first condition is satisfied is reached, a first setup is executed to cause the image forming means to form a first image targeting a certain density. The second step of obtaining the reading result of the density of the first image, the reading result obtained by the second step, and the certain density that is the target of the first image. Based on the difference, a third step of determining a developing potential that is a difference between a potential of an exposed area on the image carrier and a developing bias that is a voltage applied between the image carrier and the developing device. And said When the first image is formed by executing the first setup, the cleaning field expressed by the difference between the developing bias and the charging potential for charging the image carrier is set to a predetermined upper limit. A ratio between the cleaning step set by the fourth step and the developing potential determined by the third step is set to a value less than a predetermined lower limit, and the cleaning field set by the fourth step. A fifth step of specifying and a sixth step of controlling the operation of the image forming unit so as to maintain the ratio specified by the fifth step are executed.

According to the control device of the first aspect, the image forming control unit does not have a configuration for controlling the operation of the image forming unit so as to maintain the ratio between the developing potential specified by the specifying unit and the cleaning field. In contrast, when an image is formed by the electrophotographic method, the period during which the ratio between the cleaning field and the developing potential, which is represented by the difference between the developing bias and the charging potential of the image carrier, is maintained is longer.
According to the control device of the second aspect, when the second setup is executed, the cleaning field is set based on the ratio specified by the specifying unit and the development potential determined by the determining unit. When an image is formed by the electrophotographic method, the period during which the ratio between the cleaning field and the developing potential represented by the difference between the developing bias and the charging potential of the image carrier is maintained is longer than when the image is not formed. .
According to the control device of the third aspect, even if the ratio between the developing potential and the cleaning field is not maintained, this is maintained again.
According to the control device of the fourth aspect, even if the ratio between the developing potential and the cleaning field is not maintained, this is maintained again.
According to the control device of claim 5, based on the reading result acquired by the acquisition unit, the plurality of first gradation values and the second gradation corresponding to each of the first gradation values. The accuracy of gradation correction is improved as compared with the case where the second gradation value corresponding to each first gradation value stored in the storage means for storing the value is not provided. .
According to the control device of claim 6, the cleaning field has an upper limit or a lower limit as compared with a case where the cleaning field is not configured to set the upper limit and the lower limit to a weighted average value with a predetermined ratio. The period to reach is longer.
According to the control device of the seventh aspect, the cleaning field has its upper limit or lower limit compared to a case where the cleaning field is not configured to be set to a value separated from the upper limit or lower limit by a predetermined value. The period until reaching the lower limit becomes longer.
According to the control device of the eighth aspect, even when the ratio between the developing potential and the cleaning field is not maintained, this is maintained again.
According to the image forming apparatus of the ninth aspect, the image forming control unit does not have a configuration for controlling the operation of the image forming unit so as to maintain the ratio between the developing potential specified by the specifying unit and the cleaning field. Compared to the case, when an image is formed by the electrophotographic method, the period during which the ratio between the cleaning field and the developing potential represented by the difference between the developing bias and the charging potential of the image holding member is maintained becomes longer.
According to the image forming apparatus of claim 10, the time when the predetermined first condition is satisfied is consumed from the power saving operation state to the power saving operation state when the power of the apparatus is turned on. When power is restored to a high operating state, when a predetermined condition is established at the start of the image forming process, when the image forming process is completed, when developer is supplied to the developing device after the toner shortage is detected Alternatively, compared to a case where at least one of the components constituting the device itself is not replaced, a variation in density in highlight and halftone gradation characteristics is suppressed.
According to the program of the eleventh aspect of the present invention, as compared with the case where there is no configuration for controlling the operation of the image forming unit so as to maintain the ratio between the development potential specified in the fifth step and the cleaning field, When an image is formed by the electrophotographic method, the period during which the ratio between the cleaning field and the development potential expressed by the difference between the development bias and the charging potential of the image carrier is maintained is longer.

Block diagram showing hardware configuration of image forming apparatus The figure which shows an example of a structure of an image formation part A diagram showing the positional relationship between the image sequence formed on the surface of the intermediate transfer belt and the density sensor Block diagram showing the functional configuration of the control unit Flow chart of processing performed by control unit based on patch image for potential control during setup processing The figure showing an example of transition of the development potential and cleaning field concerning an embodiment Flow chart of processing performed by the control unit based on the patch image for gradation correction during the setup processing The figure showing the image row | line | column formed on the surface of an intermediate transfer belt based on the modification 1. The figure showing the image row | line | column formed on the surface of an intermediate transfer belt based on the modification 2. The figure showing an example of transition of the development potential and cleaning field in the conventional control system Diagram showing the relationship between gradation value and density of image

<Embodiment>
Embodiments of the present invention will be described below with reference to the drawings.
<Configuration>
FIG. 1 is a block diagram illustrating a hardware configuration of an image forming apparatus 10 according to an embodiment of the present invention. Here, the image forming apparatus 10 is an electrophotographic printer. The image forming apparatus 10 includes a control unit 11, a storage unit 12, a communication unit 13, a UI (User Interface) unit 14, and an image forming unit 15. Each part is electrically connected by a bus.

  The control unit 11 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), and makes it possible to use time measuring means for measuring time and the image forming apparatus 10 in a suitable state. It functions as a sheet number measuring means for measuring the number of output sheets after the setup process. The setup process will be described later. The CPU controls each unit connected to the control unit 11 by executing a control program stored in the ROM or the storage unit 12. The processing executed by the control unit 11 includes image processing for image data. In addition to binarization and screen processing, this image processing uses a look-up table (LUT) stored in the storage unit 12 to correct the tone characteristics of the image (hereinafter referred to as “tone correction”). )including. The LUT is an output gradation value associated with an input gradation value expressed in 256 gradations from 0 to 255, for example. The input tone value corresponds to the first tone value, and the output tone value corresponds to the second tone value.

  The storage unit 12 is a storage device such as a hard disk, and stores, for example, a control program and the LUT. The communication unit 13 is means for transmitting / receiving data to / from an external device. The external device here is a device for transmitting image data to the image forming device 10 or instructing the image forming device 10 to form an image, such as an image reading device such as a flat head scanner for reading an image, It is a client device such as a personal computer connected via communication means. The UI unit 14 is a means for presenting information to the user and receiving user operations. The UI unit 14 includes, for example, a display device having a touch screen and various buttons.

  The image forming unit 15 is an example of a unit that forms an image through each process of electrophotography such as charging, exposure, development, transfer, and fixing. The image forming unit 15 forms an image represented by the image data on a sheet using image forming parameters corresponding to each of these processes. The image forming parameters include, for example, a charging potential when the photosensitive drum is charged, an exposure potential when exposing the photosensitive drum, a developing potential when developing the electrostatic latent image, and a mixing ratio of toner and carrier in the developing device. These are various parameters relating to image formation, such as a transfer potential when a toner image is transferred. The image forming unit 15 is a unit that forms a color image in this embodiment, but may be a unit that forms a monochrome image.

  Here, when the electrostatic latent image is developed, a voltage applied between the photosensitive drum as a holding member of the electrostatic latent image and the developing device is referred to as a developing bias. The development bias is represented by a potential difference with respect to a predetermined reference potential. The development potential described above is represented by the difference between the potential of the exposed area on the photosensitive drum and the development bias. Hereinafter, the developing potential is referred to as Vdev. The potential difference between the charging potential and the developing bias is called a cleaning field. The cleaning field is a potential for preventing toner from adhering to an unexposed area of the charged photosensitive drum. Hereinafter, the cleaning field is referred to as Vcf.

  The control unit 11 determines the values of Vdev and Vcf and stores them in the RAM every time the setup process is executed. In addition, as described above, in order to suppress image quality defects called pattern defects in an image, upper and lower limits are provided for Vdev and Vcf, which are stored in the storage unit 12. As described above, when control is performed so that the ratio between Vdev and Vcf is within an allowable range determined from a certain value (hereinafter, the ratio is maintained), highlight or halftone gradation It is known that correction can be performed while suppressing variation in density in characteristics. The ratio between Vdev and Vcf is determined by the control unit 11 based on at least one of environmental factors such as temperature and humidity, the deterioration state of the photosensitive drum, and the deterioration state of the developer, for example. The control unit 11 causes the storage unit 12 to store the determined ratio between Vdev and Vcf. Since this ratio is used as a reference in subsequent processing, it is hereinafter referred to as a reference ratio.

  FIG. 2 is a diagram illustrating an example of the configuration of the image forming unit 15. The image forming unit 15 illustrated in FIG. 2 forms an image using toner of four colors of yellow (Y), magenta (M), cyan (C), and black (K) by a so-called intermediate transfer method. is there. The image forming unit 15 includes toner cartridges 151Y, 151M, 151C, and 151K, transfer units 152Y, 152M, 152C, and 152K, an exposure device 153, an intermediate transfer belt 154, a plurality of support rolls 155, and a secondary transfer roll. 156, a plurality of transport rolls 157, a fixing device 158, and a density sensor 159.

  Note that among the components shown in FIG. 2, those with the alphabet (Y, M, C, or K) at the end of the reference sign indicate that the component corresponds to one of the above four colors. ing. Although these components are different in the color of the toner to be used, the main components and functions are common. Therefore, in the following description, when it is not necessary to distinguish each other in the description of these constituent elements, they are collectively referred to as “toner cartridge 151” and “transfer unit 152” by omitting the suffix. It shall be.

  The toner cartridge 151 is a unit that stores toner of each color and supplies it to the developing unit of the transfer unit 152 as necessary. The transfer unit 152 includes a photosensitive drum that is an image holding member, a charger that charges the photosensitive drum, a developing device, a primary transfer roll, and the like, and is a unit that transfers a toner image of each color to the intermediate transfer belt 154. The exposure device 153 includes a laser emission source, a polygon mirror, and the like, and irradiates the peripheral surface of the photosensitive drum charged by the charger with laser light modulated based on image data, that is, performs exposure. It is an example of a means for forming an electrostatic latent image. The developing device is an example of a unit that develops the electrostatic latent image formed by the exposure device 153 and forms an image on the surface of the photosensitive drum. The primary transfer roll is an example of a unit that transfers an image formed on the surface of the photosensitive drum to the intermediate transfer belt 154.

  The intermediate transfer belt 154 is supported by a plurality of support rolls 155 and moves while circling in a direction indicated by an arrow A1 in the drawing. A toner image transferred by the transfer unit 152, that is, an image is formed on the intermediate transfer belt 154. The intermediate transfer belt 154 is an example of a transfer medium to which an image is transferred. The process of forming an image on the intermediate transfer belt 154 is called an image forming process. The secondary transfer roll 156 is a means for transferring the toner image transferred to the intermediate transfer belt 154 to a sheet. The transport roll 157 is a means for transporting the paper along a route along the broken line arrow A2 in the drawing. The fixing device 158 is means for fixing the toner image on the paper by heating and pressurizing the paper on which the toner image has been transferred by the secondary transfer roll 156.

  The density sensor 159 is a unit that optically reads the toner image formed on the intermediate transfer belt 154. The density sensor 159 supplies the read result, that is, density information indicating the density of the toner image to the control unit 11. The density here is a numerical value representing the color density of the toner image, and is determined by, for example, the ratio of the light applied to the toner image and the reflected light.

  The image forming apparatus 10 performs image processing on image data supplied from an external device, and forms an image on a sheet. Further, the image forming apparatus 10 executes a setup process for making the image forming apparatus 10 usable in a suitable state at an appropriate timing. The setup process is executed by the control unit 11 using the image forming unit 15. The setup process includes at least a process of forming a process control toner image on the intermediate transfer belt 154. The toner image for process control is a toner image used for detecting the state of each process in the electrophotographic system for the purpose of stabilizing the image quality of the image output from the image forming apparatus 10. This is a patch image for density control targeting a certain density. This target density is called a target density.

  The setup process includes a first setup process and a second setup process. The first setup process is performed, for example, when a predetermined condition is satisfied when the image forming apparatus 10 is turned on, when returning from a so-called sleep state, or when the image forming process is started. Here, when a predetermined condition is satisfied, the predetermined amount of toner is used every time a predetermined time elapses, a predetermined number of sheets are used, or the like. Every time, or each time the temperature or humidity changes more than a predetermined level. Further, the first setup process may be performed after replenishing the developer after the toner shortage is detected or after replacing the parts of the image forming apparatus 10. Thus, the first setup process is executed at the break of the image forming process. The timing at which the first setup process is performed is an example of a timing that satisfies a predetermined first condition.

  On the other hand, in the second setup process, a predetermined number such as 50 sheets is output from the previous setup process or a predetermined number such as 40 sheets is output from the previous setup process during the period in which the image forming process is being executed. This is performed at the end of the image forming process after output exceeding the number of sheets. In other words, when the image forming process is continuously performed in the image forming apparatus 10, the second setup process is performed more times than the first setup process. Further, the setup process may be executed at a timing when a plurality of these conditions are satisfied. Further, the setup process is not limited to the case where such a predetermined condition is satisfied, and may be executed as needed at a timing designated by the user. The timing at which the second setup process is performed is an example of a timing that satisfies a predetermined second condition.

  In the setup process, the control unit 11 causes the image forming unit 15 to form on the intermediate transfer belt 154 an image sequence in which the above-described patch images are arranged in the sub-scanning direction. Accordingly, for example, patch images having two-step area ratios of 100% and 40% are arranged on the intermediate transfer belt 154 at predetermined intervals. In the present embodiment, the area ratio is represented by a toner coverage on the image forming surface (the surface of the intermediate transfer belt 154) per unit area. The patch image has a uniform density with respect to a predetermined area by toner of any one color of Y, M, C, and K.

  FIG. 3 is a diagram showing the positional relationship between the image row G1 formed on the surface of the intermediate transfer belt 154 and the density sensor 159, as viewed from a direction perpendicular to the belt surface of the intermediate transfer belt 154. Represents. K, C disposed along the sub-scanning direction of the intermediate transfer belt 154 at a position near the center of the direction (main scanning direction) intersecting the moving direction b (sub-scanning direction) of the surface of the intermediate transfer belt 154. An image sequence G1 composed of M, Y patch images is formed. Here, the main scanning direction is the scanning direction when the exposure device 153 performs exposure scanning in accordance with the rotation of the polygon mirror. In each patch image indicated by a rectangular area included in the image row G1, “K” represents black, “C” represents cyan, “M” represents magenta, and “Y” represents yellow. The number at the end represents the difference in density, and the smaller the value, the higher the density. For example, a patch image represented by “C1a” indicates a cyan patch image having an area ratio of 100%, and “C2a” is a cyan patch image having an area ratio of 40%. The density sensor 159 is provided at a position where the patch image included in the image row G1 can be read.

  The density sensor 159 supplies density information indicating the density of the patch image to the control unit 11. The control unit 11 corrects the image forming parameter based on the supplied density information, calculates a gradation value from the density information, and updates the LUT based on the calculated gradation value. For example, in the case of a patch image having an area ratio of 100% in the high density area, the control unit 11 determines the charging potential when charging the photosensitive drum, the exposure potential when exposing the photosensitive drum, or the like based on the density information. , Developing bias, Vdev, Vcf, and the like are corrected. Such a patch image is referred to as a potential control patch image. Further, for example, in the case of a patch image with an area ratio of 40%, which is a medium density region to a low density region, the control unit 11 updates the LUT based on the calculated gradation value. Such a patch image is referred to as a tone correction patch image.

FIG. 4 is a block diagram illustrating a functional configuration of the control unit 11.
An image formation control unit 111 realized by the control unit 11 controls the operation of the image forming unit 15 that exposes a charged image carrier to form an electrostatic latent image, develops it with a developing device, and transfers it to a medium. When the time when the predetermined first condition is satisfied is reached, the first setup is executed, and the first image targeted for a certain density is sent to the image forming unit 15. It is an example of the image formation control means to form. The acquisition unit 112 realized by the control unit 11 is an example of an acquisition unit that acquires the reading result of the density of the first image formed with a certain density as a target. Based on the difference between the reading result acquired by the acquisition unit 112 and the target density of the first image, the determination unit 113 realized by the control unit 11 determines the potential of the region exposed on the image carrier and the image. FIG. 5 is an example of a determining unit that determines a developing potential that is a difference from a developing bias that is a voltage applied between a holding body and a developing device. FIG. The setting unit 114 realized by the control unit 11 includes a developing bias and an image that are voltages applied between the image carrier and the developing device when the first setup is executed and the first image is formed. This is an example of setting means for setting a cleaning field represented by a difference from a charging potential when charging a holding body to a value that is less than a predetermined upper limit and that exceeds a predetermined lower limit. The specifying unit 115 realized by the control unit 11 is an example of a specifying unit that specifies the ratio between the cleaning field set by the setting unit 114 and the development potential determined by the determining unit 113. The image forming control unit 111 controls the operation of the image forming unit 15 so as to maintain the ratio specified by the specifying unit 115.

<Operation>
Next, the operation for controlling the ratio of Vdev and Vcf to be maintained will be described in detail.
FIG. 5 is a flowchart of processing performed by the control unit 11 based on the patch image for potential control during the setup processing. First, the control unit 11 acquires density information of a patch image for potential control from the density sensor 159 (step S1a). Then, the control unit 11 calculates a difference density that is a difference between the target density of the patch image and the density represented by the density information acquired in Step S1a (Step S2a). Next, the control part 11 calculates Vdev according to the following formula | equation (1) based on difference density (step S3a).
New Vdev = Current Vdev + α × Differential density (1)
In equation (1), α is a predetermined coefficient. Further, the current Vdev in the equation (1) is the latest Vdev stored in the RAM.

  Next, the control unit 11 compares Vdev calculated in step S3a with the upper limit and lower limit of Vdev stored in the storage unit 12, and when Vdev calculated in step S3a exceeds the upper limit, Vdev is set to the upper limit value. If it is below the lower limit, Vdev is set to the lower limit value (step S4a).

Next, when the setup process being executed is the first setup process (step S5a; YES), the control unit 11 advances the process to step S6a. In step S6a, the control unit 11 calculates Vcf according to the following equation (2).
New Vcf = (Vcf upper limit + Vcf lower limit) / 2 (2)
That is, in step S6a, the control unit 11 calculates the median between the upper limit and the lower limit as a new Vcf. Based on the new Vdev and the new Vcf calculated as described above, the control unit 11 calculates V_ratio, which is a new ratio between Vdev and Vcf, according to the following equation (3) (step S7a). ).
V_ratio = new Vdev / new Vcf (3)

On the other hand, after the end of step S4a, when the setup process being executed is the second setup process (step S5a; NO), the control unit 11 advances the process to step S8a. In step S8a, the control unit 11 calculates Vcf according to the following equation (4).
New Vcf = New Vdev / V_ratio (4)
Next, the control unit 11 compares Vcf calculated in step S8a with the upper limit and lower limit of Vcf stored in the storage unit 12, and if Vcf calculated in step S8a exceeds the upper limit, Vcf is set to the upper limit value. If the value is below the lower limit, Vcf is set to the lower limit value (step S9a).

  After step S7a or step S9a, the control unit 11 controls image forming parameters such as a charging potential, a developing bias, and an exposure potential based on the calculated new Vdev and new Vcf (step S10a). . In step S10a, specifically, when the Vcf has not reached the upper limit or the lower limit, the control unit 11 controls the image forming parameters so that Vdev and Vcf become a predetermined ratio. The predetermined ratio is V_ratio when V_ratio is calculated, and is a reference ratio stored in the storage unit 12 when V_ratio is not calculated.

  As described above, the first setup process is executed at the break of the image forming process. Therefore, each time the first setup process is executed, a new Vdev and a new Vcf are calculated, and the image forming parameters are controlled so that the ratio between Vdev and Vcf is maintained. As a result, when a new image forming process is performed, it starts from a state in which the ratio of Vdev and Vcf is maintained, so that fluctuations in density in highlight and halftone gradation characteristics are suppressed.

  Further, after executing the second setup process, that is, after step S10a is performed through steps S8a and S9a in FIG. 5, the control unit 11 determines the difference between Vcf calculated in step S8a and its upper limit or lower limit. When the value becomes equal to or greater than a predetermined threshold value, the first setup process is executed. Vcf calculated based on Vdev and V_ratio in the second setup process approaches its upper and lower limits as time elapses. Therefore, even if the ratio between Vdev and Vcf does not become constant, the first setup process is executed and Vcf is again calculated as a value within the upper and lower limits, so the ratio between Vdev and Vcf is again It can be controlled constantly.

  Further, after step S9a, the control unit 11 calculates the ratio between the two by dividing Vdev by Vcf (hereinafter, this ratio is referred to as a comparison ratio because it is used as a reference for comparison with V_ratio). The comparison ratio is calculated according to the same equation (3) as V_ratio, except that V_ratio is calculated in the first setup process, whereas the comparison ratio is calculated in the second setup process. The control unit 11 executes the first setup process when the comparison ratio and V_ratio deviate by a predetermined value or more. The fact that the two deviate by a predetermined value or more means that Vcf has reached the upper limit or lower limit or is close to the upper and lower limits, and the ratio of Vdev to Vcf is constant. It means that it has been greatly changed from the value of. The new Vcf is set between the upper limit and the lower limit by the first setup process, and the gradation correction based on the patch image for gradation control is performed, so that the ratio of Vdev and Vcf is maintained again. Be controlled.

  Further, the control unit 11 changes the image forming parameter so that Vcf changes and reaches the upper limit or the lower limit, and as a result, the ratio between Vdev and Vcf becomes a predetermined ratio such as V_ratio or the reference ratio. Is not controllable, Vcf is calculated according to equation (2). As a result, in a situation where the ratio between Vdev and Vcf is not maintained as Vcf approaches its upper limit or lower limit, control is performed so that the ratio between Vdev and Vcf is maintained again. That is, even if the ratio between Vdev and Vcf is not maintained, control is performed so that this is maintained again.

  FIG. 6 is a diagram illustrating an example of changes in Vdev and Vcf according to the embodiment. In FIG. 6, the horizontal axis represents time t, and the vertical axis represents potential v. In FIG. 6, the Vdev upper limit, the Vdev lower limit, the Vcf upper limit, and the Vcf lower limit are indicated by broken lines, respectively. A range indicated by an arrow A1 represents a period during which the ratio between Vdev and Vcf is maintained. A range indicated by an arrow A3 represents a period in which the ratio between Vdev and Vcf is not maintained. A range indicated by an arrow A4 represents a period during which the ratio of Vdev and Vcf is maintained again. A range indicated by an arrow B1 surrounded by two alternate long and short dash lines represents a range of Vdev that can be changed while maintaining a ratio to Vcf. Arrows S1 and S2 represent the timing at which the setup process is performed. Arrow S1 represents the timing at which the first setup process is performed, and arrow S2 represents the timing at which the second setup process is performed. As shown in FIG. 6, in the period A1, the ratio between Vdev and Vcf is maintained and controlled. On the other hand, in the period A3, Vdev is controlled in a state where Vcf is fixed at the upper limit, and thus the ratio between Vdev and Vcf is not maintained. In the present embodiment, as described with reference to FIG. 5, when a patch image for potential control is formed in the first setup process, a new Vcf between the upper limit and the lower limit of Vcf is calculated. As a result, Vcf is not fixed at the upper limit or the lower limit, and therefore, in the period A4 after the setup process is performed, the control unit 11 controls both to maintain the ratio of Vdev and Vcf. To do.

FIG. 7 is a flowchart of processing performed by the control unit 11 based on the patch image for gradation correction during the setup processing.
First, the control unit 11 acquires density information of a patch image for gradation correction from the density sensor 159 (step S1b). Then, the control unit 11 calculates a difference density that is a difference between the target density of the patch image and the density represented by the density information acquired in Step S1b (Step S2b). Based on the calculated difference density and the LUT stored in the storage unit 12, the control unit 11 calculates an output tone value according to the equation (5) (step S3b).
New output tone value = output tone value based on the current LUT + β × difference density (5)
In Expression (5), the output tone value based on the current LUT is a storage unit when the tone value before applying the LUT of each pixel included in the image data representing the patch image is used as the input tone value. 12 is an output gradation value corresponding to this in the LUT stored in FIG. In equation (5), β is a predetermined coefficient. Thus, in this embodiment, it is assumed that the LUT is also applied to the patch image.

  Next, the control unit 11 compares the output gradation value calculated in step S3b with the upper and lower limits that the gradation value can take in the LUT stored in the storage unit 12, and the output gradation value calculated in step S3b. When the value exceeds the upper limit, the output gradation value is set to the upper limit value, and when the value is lower than the lower limit, the output gradation value is set to the lower limit value (step S4b). Then, the control unit 11 updates the LUT using the calculated output gradation value (step S5b). Specifically, in step S5b, the control unit 11 uses the gradation value before applying the LUT of each pixel included in the image data representing the patch image whose density information is acquired in step S1b as the input gradation value. The input gradation value and the calculated output gradation value are associated with each other in the LUT and stored in the storage unit 12. By updating the LUT in this way, the output tone value of the patch image formed by the control unit 11 on the image forming unit 15 tends to satisfy the target density. That is, the accuracy of gradation correction is improved.

  As described above, according to the embodiment, when the setup process is performed, the control unit 11 calculates a new Vdev and sets a new Vcf different from the upper limit and the lower limit and between the upper limit and the lower limit. Calculate to be a value. As a result, Vcf is not in a state of being fixed at the upper limit or the lower limit, so that the control unit 11 has a longer period during which the ratio of Vdev and Vcf is maintained. Further, when the setup process is the second setup process, the control unit 11 performs a new operation based on the new ratio V_ratio between the Vdev and Vcf calculated in the first setup process and the new Vdev. Vcf is calculated. That is, in this case, since the control unit 11 calculates Vcf based on V_ratio and Vdev at the time of processing, not only the reference ratio stored in the storage unit 12, Vdev and Vcf in the latest state. The period during which the ratio is maintained becomes longer. As described above, according to this embodiment, when an image is formed by electrophotography, the period during which the ratio between the cleaning field and the development potential expressed by the difference between the development bias and the charge potential of the image carrier is maintained. Becomes longer.

<Modification>
The above embodiment can be modified as follows. Note that the following modifications may be implemented in combination as appropriate.
(Modification 1)
The image sequence formed on the intermediate transfer belt 154 in the setup process is not limited to that in the embodiment, and may be as follows.
FIG. 8 is a diagram illustrating an image row formed on the surface of the intermediate transfer belt 154 according to the first modification, and shows a view when viewed from a direction perpendicular to the belt surface of the intermediate transfer belt 154. The daytime transfer belt 154 and the density sensor 159 are the same as those described with reference to FIG. K, C disposed along the sub-scanning direction of the intermediate transfer belt 154 at a position near the center of the direction (main scanning direction) intersecting the moving direction b (sub-scanning direction) of the surface of the intermediate transfer belt 154. , M, Y patch images G2 are formed. In FIG. 8, for example, a patch image represented by “C1b” indicates a cyan potential control patch image with an area ratio of 100%, and “C2b” is for cyan gradation correction with an area ratio of 70%. "C3b" indicates a patch for cyan gradation correction with an area ratio of 40%, and "C4b" indicates a patch for cyan gradation correction with an area ratio of 15%. Indicates an image.

  In the first modification, when the first setup process is performed, the control unit 11 causes the image transfer unit 15 to form the image row G2 illustrated in FIG. 8 on the intermediate transfer belt 154. On the other hand, when the second setup process is performed, the control unit 11 causes the image transfer unit 15 to form the image row G1 shown in FIG. In the image sequence G1, there is one patch image for potential control and one patch image for gradation correction. On the other hand, the image sequence G2 has a larger number of patch images for gradation correction than the image sequence G1. Accordingly, in the first setup process, tone correction is performed based on a plurality (three in this case) of tone correction patch images, so that the input tone value and the output tone value in the LUT are associated with each other. The accuracy is improved, that is, the accuracy of gradation correction is increased.

  In the second setup process, the number of gradation correction patch images is smaller than that in the first setup process, so that the gradation correction is performed based on the density information of the patch image read by the density sensor 159. The time required for the process to be performed is less than that of the first setup process. As a result, compared to the case where the same number of patch images are formed in the first setup process and the second setup process, the time required for the gradation correction process is shortened, that is, the image forming process. As a result, the productivity of the image forming apparatus 10 is improved. In Modification 1, since the number of patch images formed by the second setup process is small, toner consumption can be suppressed.

  As described above, according to the first modification, the number of patch images formed in the first setup process is larger than that formed in the second setup process, so that the accuracy of gradation correction is high. Become. Further, according to the first modification, the number of patch images formed in the second setup process is smaller than that formed in the first setup process, thereby suppressing toner consumption and improving productivity. I can plan.

(Modification 2)
The image sequence formed on the intermediate transfer belt 154 in the setup process may be as follows.
FIG. 9 is a diagram illustrating an image row formed on the surface of the intermediate transfer belt 154 according to the second modification, and illustrates a view when viewed from a direction perpendicular to the belt surface of the intermediate transfer belt 154. The intermediate transfer belt 154 and the density sensor 159 are the same as those described with reference to FIG. K, C disposed along the sub-scanning direction of the intermediate transfer belt 154 at a position near the center of the direction (main scanning direction) intersecting the moving direction b (sub-scanning direction) of the surface of the intermediate transfer belt 154. An image row G3 composed of patch images of M, Y, and Y is formed. In FIG. 9, for example, a patch image represented by “C1c” indicates a patch image for cyan potential control with an area ratio of 100%, and “C2c” indicates a patch for cyan potential control with an area ratio of 100%. Indicates an image. Here, “C1c” is a patch image for first potential control, and “C2c” is a patch image for second potential control. “C3c” indicates a patch image for cyan gradation correction with an area ratio of 70%, “C4c” indicates a patch image for cyan gradation correction with an area ratio of 40%, “C5c” indicates a patch image for cyan gradation correction with an area ratio of 15%.

In the second modification, when the first setup process is performed, the control unit 11 causes the intermediate transfer belt 154 to form the image row G3 illustrated in FIG. On the other hand, when the second setup process is performed, the control unit 11 causes the intermediate transfer belt 154 to form the image row G2 shown in FIG. When the first setup process is performed in the second modification, the control unit 11 first, based on the density information obtained by reading the first potential control patch image in the image sequence G3 in step S3a of FIG. To calculate Vdev (referred to as Vdev_1). In the second modification, the control unit 11 calculates Vdev_1 according to the following equation (6).
Vdev_1 = current Vdev + α × difference density + predetermined first potential (6)
The first potential determined in advance in Expression (6) is stored in the storage unit 12, and an example of the value is “−55 V”, but it depends on the environmental factors of the image forming apparatus 10, the usage status, and the like. The user can arbitrarily set using the UI unit 14. Next, the control unit 11 calculates Vdev based on the density information of the second potential control patch image in the image sequence G3 (referred to as Vdev_2). In the second modification, the control unit 11 calculates Vdev_2 according to the following equation (7).
Vdev_2 = current Vdev + α × difference density + predetermined second potential (7)
The second potential determined in advance in Expression (7) is stored in the storage unit 12, and an example of the value is “+50 V”. Can be arbitrarily set using the UI unit 14.

  Then, for example, when the control unit 11 sets Vdev as the variable x on the horizontal axis and creates a two-dimensional plane coordinate with the concentration set as the variable y on the vertical axis and stores it in the RAM, A set of density information of the first potential control patch image and Vdev_1 when Vdev_1 is calculated, and a set of density information and Vdev_2 of the second potential control patch image when Vdev_2 is calculated. Plot. A straight line connecting the two points plotted in this way is represented by an equation such as y = −ax + b (a and b are constants). Next, the control unit 11 substitutes the target density for y in this equation, and calculates Vdev corresponding to the target density as a new Vdev. The subsequent processing is performed according to FIG.

  As described above, according to the second modification example, in the first setup process, based on the density information of two different potential control patch images, the Vdev_1 and Vdev_2 calculated based on the density information, and the target density. A new Vdev is calculated. At this time, Vdev calculated based on the density information of the two different potential control patch images is such that the density information read from the patch image more satisfies the target density. Therefore, according to the second modification, by applying Vdev and Vcf calculated based on the density information of the patch image for potential control to the subsequent patch image for tone correction, the tone characteristics are more stable. Control becomes possible. Further, in the second modification, the control unit 11 calculates the ratio between them (the comparison ratio described above) by dividing Vdev by Vcf after step S9a. When the comparison ratio and the reference ratio stored in the storage unit 12 deviate by a predetermined value or more, the control unit 11 executes a first setup process. In Modification 2, since the number of gradations of the patch image for gradation correction in the first setup process is larger than in the second setup process, the calculated ratio is stable even if the calculated ratio deviates greatly from the reference ratio. The provided gradation characteristics can be provided. Here, instead of the comparison between the comparison ratio calculated after step S9a and the reference ratio, a comparison between the comparison ratio and V_ratio calculated in step S7a may be performed.

(Modification 3)
The calculation method of Vdev and Vcf is not limited to that in the embodiment, and may be as follows. The sum of Vdev and Vcf is called the contrast potential and is expressed as V_cont. Here, Vdev and Vcf may be calculated so as to satisfy a predetermined ratio with respect to V_cont. Predetermined ratios of Vdev and Vcf to V_cont are stored in the storage unit 12.
In the third modification, the control unit 11 calculates V_cont according to the following equation (6) before step S7a and before S8a in FIG.
V_cont = Vdev + Vcf (6)
Moreover, in the modification 3, the control part 11 calculates V_ratio according to the following formula | equation (7) by S7a of the step of FIG.
V_ratio = Vcf / Vcont (7)
Moreover, in the modification 3, the control part 11 calculates Vcf according to the following formula | equation (8) by step S8a of FIG.
New Vcf = V_cont × V_ratio (8)
In Modification 3, only the concept of the ratio of Vdev and Vcf is different from that in the embodiment, so that Modification 3 can also achieve the same effects as in the embodiment.

(Modification 4)
In the embodiment, the setup process performed at the end of the image forming process is the second setup process. Alternatively, the first setup process may be used instead. For example, when the number of tone correction patch images formed in the first setup process is larger than that in the second setup process as in Modification 1, the first setup process is performed at the end of the image formation process. As a result, the accuracy of gradation correction is improved compared to when the second setup process is executed. If the next image forming process is not waiting during the execution of the setup process, the productivity is unlikely to decrease even if the setup process takes a long time. In such a case, the first image forming process is terminated at the end of the image forming process. The setup process may be executed.

(Modification 5)
Further, it is preferable to use the same image forming parameters when the patch image is formed on the intermediate transfer belt 154 in the second setup process as when the image forming process was performed immediately before. Since the second setup process may be performed during the execution of the image forming process, abrupt fluctuations in the density of the image formed on the intermediate transfer belt 154 can be suppressed in this way.

(Modification 6)
In the embodiment, the control unit 11 calculates the median value between the upper limit and the lower limit as a new Vcf in step S6a of FIG. 5, but the following may be used instead. For example, the control unit 11 may calculate Vcf according to the following equation (8) using a weighted average.
New Vcf = Vcf upper limit × β + Vcf lower limit × (1−β) (8)
In Expression (8), β is a predetermined coefficient, and is a real number between 0 and 1. The coefficient β may be stored in the storage unit 12 and may be changed by the user using the UI unit 14. When the equation (8) is followed, the control unit 11 calculates a new Vcf as a result of weighting each of the upper limit and the lower limit of the Vcf. As a result, in the modified example 6, the new Vcf is not a median value, but is a value close to either the upper limit or the lower limit of Vcf. When Vcf shifts to either the upper limit or the lower limit due to any factor such as the usage tendency, usage environment, or usage state of the image forming apparatus 10, the weighting by the above coefficient is possible, There are effects like this. That is, since the difference between the upper limit or the lower limit of the new Vcf is controlled to be the median value, the period until the Vcf reaches the upper limit or the lower limit can be increased. Thereby, the period controlled by the control part 11 becomes long so that the ratio of Vcf and Vdev is maintained.

(Modification 7)
The new Vcf calculated by the control unit 11 in step S6a of FIG. 5 may be as follows. For example, the control unit 11 may calculate Vcf according to the following formula (9) or formula (10).
New Vcf = Vcf upper limit−γ (9)
New Vcf = Vcf lower limit + ε (10)
In equation (9), γ is a predetermined coefficient. In the equation (10), ε is a predetermined coefficient. The coefficients γ and ε may be stored in the storage unit 12 and may be changed by the user using the UI unit 14. As a result of following the formula (9) or the formula (10) in the modified example 7, the control unit 11 calculates a new Vcf as a value separated from the Vcf upper limit or lower limit by a predetermined value. As in the sixth modification, when Vcf changes depending on an environmental factor in the image forming apparatus 10 and shifts to either the upper limit or the lower limit, the value is shifted from the upper limit or the lower limit to the median value. By calculating Vcf, the following effects can be obtained. That is, since the difference between the upper limit or the lower limit of the new Vcf is controlled to be the median value, the period until the Vcf reaches the upper limit or the lower limit can be increased. Thereby, the period controlled by the control part 11 becomes long so that the ratio of Vcf and Vdev is maintained.

(Modification 8)
The present invention can also be specified as a program for causing a computer to function as a control device. Such a program may be provided in a form recorded on a recording medium such as an optical disc, or may be provided in a form such that the program is downloaded to a computer via a communication line such as the Internet, and is installed and used. .

  DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus, 11 ... Control part, 12 ... Memory | storage part, 13 ... Communication part, 14 ... UI part, 15 ... Image forming part, 151K, 151C, 151M, 151Y ... Toner cartridge, 152K, 152C, 152M, 152Y ... transfer unit, 153 ... exposure device, 154 ... intermediate transfer belt, 155 ... support roll, 156 ... secondary transfer roll, 157 ... conveyance roll, 158 ... fixing device, 159 ... density sensor, G1, G2, G3 ... image sequence

Claims (11)

An image forming control unit that controls an operation of an image forming unit that exposes a charged image carrier to form an electrostatic latent image, develops the image by a developing device, and transfers the image to a medium. An image forming control unit that executes a first setup and causes the image forming unit to form a first image targeting a certain density;
Obtaining means for obtaining a reading result of the density of the first image;
Based on the difference between the reading result acquired by the acquisition unit and the certain density that is the target of the first image, the potential of the area exposed on the image carrier, the image carrier, and the developing device Determining means for determining a developing potential that is a difference from a developing bias that is a voltage applied between
When the first image is formed by executing the first setup, a cleaning field represented by a difference between the developing bias and a charging potential when charging the image carrier is determined in advance. Setting means for setting a value that is less than the upper limit and exceeds a predetermined lower limit;
A specifying means for specifying a ratio between the cleaning field set by the setting means and the development potential determined by the determining means;
The image forming control unit controls the operation of the image forming unit so as to maintain the ratio specified by the specifying unit. The image formation control means
When it is time to satisfy a second predetermined condition that is different from the first predetermined condition, a second setup different from the first setup is executed to target a certain concentration Forming a second image on the image forming means;
The acquisition means includes
Obtaining a reading result of the density of the second image formed with the certain density as a target;
The determination unit determines the development potential based on a difference between the reading result acquired by the acquisition unit and the certain density that is a target of the second image.
The setting means includes
The control device according to claim 1, wherein the cleaning field is set based on a ratio specified by the specifying unit and a development potential determined by the determining unit. The image formation control means
When the difference between the cleaning field set by the setting means and the upper limit or lower limit thereof is equal to or greater than a threshold when the second setup is executed, the first setup is executed, and the first setup is executed. The control apparatus according to claim 2, wherein the image forming unit is configured to form an image of The image formation control means
A ratio between the cleaning field set by the setting unit when the second setup is executed and the developing potential determined by the determining unit when the second setup is executed is 4. The apparatus according to claim 2, wherein the first setup is executed to cause the image forming unit to form the first image when the ratio deviates more than a threshold from the ratio specified by the specifying unit. 5. Control device. Storage means for storing a plurality of first gradation values and second gradation values respectively corresponding to the first gradation values;
Updating means for updating the second gradation value corresponding to each of the first gradation values stored in the storage means based on the reading result obtained by the obtaining means;
The image formation control means
Based on the correspondence relationship between the second gradation value updated by the updating means and the first gradation value, the gradation value of each pixel represented by the image data is converted, and the converted image The control device according to claim 1, wherein the image forming unit forms an image according to data. The setting means includes
The control device according to any one of claims 1 to 5, wherein the cleaning field is set to a value obtained by weighted averaging the upper limit and the lower limit with a predetermined ratio. The setting means includes
The control device according to any one of claims 1 to 5, wherein the cleaning field is set to a value separated from the upper limit or lower limit by a predetermined value. The setting means sets the cleaning field to a value that is less than a predetermined upper limit and exceeds a predetermined lower limit when the image formation control means cannot maintain the ratio specified by the specifying means. The control device according to claim 1, wherein An image carrier,
Charging means for charging the image carrier;
Exposure means for exposing the image carrier charged by the charging means to form an electrostatic latent image; and
A developing device that develops the electrostatic latent image formed by the exposure unit and forms an image on the surface of the image carrier;
Transfer means for transferring an image formed on the surface of the image carrier to a medium;
Fixing means for fixing the image transferred to the medium to the medium;
An image forming apparatus comprising: the control device according to claim 1. When the predetermined first condition is satisfied, when the power of the apparatus is turned on, when the power saving operation state returns to the operation state in which the power consumption is larger than the power saving operation state, the image is displayed. When a predetermined condition is satisfied at the start of the forming process, when the image forming process is completed, when the developer is supplied to the developing apparatus after the toner shortage is detected, or the parts constituting the apparatus are replaced. The image forming apparatus according to claim 9, wherein the image forming apparatus is at least one of the following. On the computer,
The charged image carrier is exposed to form an electrostatic latent image, developed by a developing device, and transferred to a medium to control the operation of the image forming means, and a predetermined first condition is satisfied. A first step of executing a first setup to cause the image forming means to form a first image with a certain density as a target when the time for satisfying has arrived;
A second step of obtaining a reading result of the density of the first image;
Based on the difference between the reading result obtained in the second step and the certain density that is the target of the first image, the potential of the region exposed on the image carrier, the image carrier, and the image carrier A third step of determining a developing potential that is a difference from a developing bias that is a voltage applied between the developing devices;
When the first image is formed by executing the first setup, a cleaning field represented by a difference between the developing bias and a charging potential when charging the image carrier is determined in advance. A fourth step of setting a value that is less than the upper limit and exceeds a predetermined lower limit;
A fifth step of specifying a ratio between the cleaning field set by the fourth step and the development potential determined by the third step;
And a sixth step of controlling the operation of the image forming means so as to maintain the ratio specified in the fifth step.

Images