JP6662734B2 - Image forming apparatus, control program, and control method - Google Patents

Description

  The present invention relates to an image forming apparatus, a control program, and a control method, and more particularly to, for example, an image forming apparatus, a control program, and a control method for forming an image on a recording medium by an electrophotographic method.

  An example of the image forming apparatus of the background art is disclosed in Patent Document 1. Patent Document 1 discloses a two-component developing an electrostatic latent image using a two-component developer including a toner and a carrier for imparting charge to the toner in an image forming apparatus using an electrophotographic method. A development system is disclosed.

  The image forming apparatus disclosed in Patent Document 1 includes a density sensor for detecting the magnetic permeability of the developer in a developing tank, and calculates the toner concentration in the developer based on the measurement result of the density sensor. Based on the obtained toner concentration, toner concentration control for controlling the toner concentration in the developing tank is performed.

JP 2015-72460 A

  In the image forming apparatus of this background art, since a density sensor that detects magnetic permeability is used, the bulk density of the developer changes due to a change in the material of the developer over time or a change in the amount of charge of the developer. May be incorrectly calculated. If the toner density is incorrectly calculated, the toner density in the developing tank cannot be properly controlled, and there is a problem that image quality defects occur when an image is formed on a recording medium.

  Therefore, a main object of the present invention is to provide a novel image forming apparatus, a control program, and a control method.

  It is another object of the present invention to provide an image forming apparatus, a control program, and a control method that can appropriately control the toner concentration in a developing tank.

According to a first aspect of the invention, there is provided an electrophotographic system including an image carrier, and a developing device having a developing roller that accommodates a developer in which toner and carrier are mixed in a developing housing and supplies the toner to the image carrier. An image forming apparatus for forming an image on a recording medium by using the image forming apparatus. The image carrier is, for example, an intermediate transfer belt or a photosensitive drum. The image forming apparatus includes a density detecting unit, a control voltage setting unit, a toner density adjusting unit, a reference toner image forming unit, an adhesion amount detecting unit, and a correcting unit. The density detecting means is a magnetic permeability sensor, which is provided at the bottom of the developing housing and detects the toner concentration (T / D: T is toner and D is developer) in the developer in the developing housing. I do. The control voltage setting means sets a control voltage for calibrating the output value (output voltage) of the concentration detecting means. The toner density adjusting means adjusts the toner density in the developing housing according to the output value of the density detecting means. For example, the toner density adjusting means replenishes the toner in the developing housing, stops replenishing the toner in the developing housing, or consumes the toner in the developing housing. The reference toner image forming means is provided by the developing means in the circumferential direction of the developing roller for density correction including at least a part of a range of a first rotation of the developing roller and at least a part of a range of a second rotation of the developing roller. A reference toner image (toner patch) is formed on the image carrier. The adhesion amount detection means is an optical sensor, and detects the adhesion amount of the toner in the reference toner image formed on the image carrier by the reference toner image forming means. The correction unit detects the amount of toner attached to the reference toner image in the first rotation of the developing roller and the amount of toner attached to the reference toner image in the second rotation of the developing roller. The control voltage set by the control voltage setting means is corrected in accordance with the ratio (adhesion amount ratio).
When correcting the control voltage, the characteristic of the ghost phenomenon (developing memory) generated when the reference toner image is formed on the image carrier is used. When the ghost phenomenon occurs, the image of the first portion becomes darker or lighter depending on the toner density. That is, when the ghost phenomenon occurs, the amount of toner attached to the first portion increases or decreases depending on the toner density. However, since the ghost phenomenon is eliminated after the second rotation of the developing roller, the image density becomes a preset image density. That is, the second portion has the preset image density. Therefore, the ratio of the amount of adhesion between the first portion and the second portion changes according to the toner density.

  According to the first aspect of the present invention, according to the adhesion amount ratio between the adhesion amount in the first rotation of the developing roller in the reference toner image and the adhesion amount in the second rotation of the developing roller in the reference toner image, Correct the control voltage. For this reason, it is possible to correct a change in the output value of the concentration detecting means based on a change in the apparent magnetic permeability. Therefore, the toner concentration in the developing housing can be appropriately controlled.

  According to a second aspect, in the image forming apparatus according to the first aspect, a part of a leading end of the reference toner image in the transport direction protrudes downstream in the transport direction of the reference toner image.

  According to the second aspect, since a part of the leading end of the reference toner image in the transport direction protrudes downstream in the transport direction of the reference toner image, a ghost phenomenon easily occurs, and the toner adheres to the first portion. The ratio of the amount of toner to the amount of toner adhered to the second portion is likely to change. Thereby, the toner concentration in the developing housing can be appropriately controlled.

  A third invention is an image forming apparatus according to the second invention, wherein a front end of the reference toner image is inclined with respect to a direction perpendicular to a conveyance direction of the reference toner image.

  According to the third aspect, the tip of the reference toner image is inclined with respect to the direction perpendicular to the transport direction of the reference toner image, so that the ghost phenomenon easily occurs, as in the second aspect. The ratio of the amount of toner attached to the portion and the amount of toner attached to the second portion is likely to change. Thereby, the toner concentration in the developing housing can be appropriately controlled.

  A fourth invention is the image forming apparatus according to the second invention, wherein a front end of the reference toner image is curved in a direction perpendicular to a conveyance direction of the reference toner image.

  According to the fourth aspect, the tip of the reference toner image is curved in a direction perpendicular to the transport direction of the reference toner image, so that the ghost phenomenon easily occurs as in the second aspect, and The ratio of the amount of toner attached to the portion and the amount of toner attached to the second portion is likely to change. Thereby, the toner concentration in the developing housing can be appropriately controlled.

  A fifth invention is an image forming apparatus according to any one of the first to fourth inventions, wherein the correction means corrects a control voltage in accordance with information on a use state of the image forming apparatus. To change.

  According to the fifth aspect, the toner density in the developing housing can be more appropriately controlled.

  A sixth invention provides an image forming apparatus including: an image carrier; and a developing device that accommodates a developer in which toner and carrier are mixed in a developing housing and has a developing roller that supplies the toner to the image carrier. Control program for controlling the computer of the image forming apparatus by detecting density of toner in the developing housing; control voltage setting means for setting a control voltage for calibrating an output value of the density detecting means; A toner density adjusting means for adjusting the toner density in the developing housing in accordance with the output value of the means, and at least a part of the range of the first rotation of the developing roller in the circumferential direction of the developing roller and the developing roller by the developing device. A reference toner image forming means for forming a reference toner image for density correction including at least a part of the range of the circumference on the image carrier; Attachment amount detection means for detecting the amount of toner attached to the reference toner image formed on the image carrier by the image forming means, and toner in the first rotation of the developing roller in the reference toner image detected by the attachment amount detection means In accordance with the ratio between the amount of toner adhered and the amount of toner adhered to the reference toner image in the range of the second rotation of the developing roller, it functions as correction means for correcting the control voltage set by the control voltage setting means.

  A seventh invention provides an image forming apparatus including: an image carrier; and a developing device that accommodates a developer in which toner and carrier are mixed in a developing housing and has a developing roller that supplies the toner to the image carrier. Wherein the computer of the image forming apparatus comprises: (a) detecting the toner concentration in the developing housing; (b) setting a control voltage for calibrating the output value in step (a); (D) adjusting the toner concentration in the developing housing according to the output value of step (a), and (d) at least part of the range of the first rotation of the developing roller and the developing device in the circumferential direction of the developing roller by the developing device. A reference toner image for density correction including at least a part of the range of the second rotation of the roller is formed on the image carrier, and (e) the reference toner image formed on the image carrier in step (d) (F) detecting the amount of toner adhered in the first rotation of the developing roller in the reference toner image, which is detected in step (e); According to the ratio with the amount of toner adhered in the range of the circumference, the control unit functions as a correction unit that corrects the control voltage set in step (b).

  Also in the sixth and seventh inventions, similarly to the first invention, the toner density in the developing housing can be appropriately controlled.

  According to the present invention, the toner concentration in the developing housing can be appropriately controlled.

FIG. 1 is a schematic configuration diagram of an entire image forming apparatus according to a first embodiment of the present invention as viewed from the front. FIG. 2 is a block diagram showing an example of an electrical configuration of the image forming apparatus shown in FIG. FIG. 3 is an enlarged sectional view schematically showing the toner adhesion amount detection sensor. FIG. 4 is an illustrative view showing one example of a shape of a toner patch. FIG. 5 is a graph showing the relationship between the ghost occurrence level and the toner density. FIG. 6 is a graph showing the toner adhesion amount on the intermediate transfer belt with respect to the adhesion amount ratio between the first and second rotations of the developing roller in the toner patch. FIG. 7 is a table showing correction values for correcting the control voltage according to the adhesion amount ratio between the first and second rotations of the developing roller in the toner patch. FIG. 8 is an illustrative view showing one example of a memory map of a RAM shown in FIG. 2; FIG. 9 is a flowchart showing a part of an example of the toner density control process of the CPU of the image forming apparatus 10 shown in FIG. FIG. 10 is a flowchart showing another part of the toner density control processing of the image forming apparatus 10 and subsequent to FIG. FIG. 11 is an illustrative view showing one example of a shape of a toner patch in the second embodiment. FIGS. 12A to 12D are illustrative views showing another example of the shape of the toner patch in the second embodiment. FIG. 13 is a table for determining the usage environment level of the image forming apparatus according to the third embodiment. FIG. 14 is a table for determining a basic correction value in the case where the idle time is short and the printing rate is low in the third embodiment. FIG. 15 is a table for determining a basic correction value in the case where the idle time is short and the printing rate is high in the third embodiment. FIG. 16 is a table for determining a basic correction value in the case where the idle time is long and the printing rate is low in the third embodiment. FIG. 17 is a flowchart illustrating a part of an example of the toner density control process of the CPU of the image forming apparatus 10 according to the third embodiment. FIG. 18 is a flowchart showing another part of the toner density control process of the CPU of the image forming apparatus 10 according to the third embodiment, which is subsequent to FIG. FIG. 19 is a flowchart showing another part of the toner density control process of the CPU of the image forming apparatus 10 according to the third embodiment, which is subsequent to FIG.

[First embodiment]
FIG. 1 is a schematic configuration diagram of an entire image forming apparatus 10 according to an embodiment of the present invention as viewed from the front.

  Referring to FIG. 1, an image forming apparatus 10 according to a first embodiment is a color printer, and forms a multi-color or single-color image on paper (recording medium) by an electrophotographic method. However, the image forming apparatus 10 may be a monochrome printer. Further, the image forming apparatus 10 does not need to be limited to a printer, and may be a copier, a facsimile, or a multifunction peripheral having these functions.

  First, a basic configuration of the image forming apparatus 10 will be schematically described. As shown in FIG. 1, the image forming apparatus 10 includes an image forming unit 100. The image forming unit 100 includes components such as a photosensitive drum 12, a developing device 14, a charger 16, a cleaning unit 18, an exposing device 20, an intermediate transfer belt unit 22, a secondary transfer roller 24, and a fixing unit 26. An image is formed on the sheet conveyed from the tray 28, and the sheet on which the image has been formed is discharged to the discharge tray 30. As image data for forming an image on paper, image data input from an external computer is used. However, when the image forming apparatus 10 has a scanner function, not only image data input from the outside but also image data read from a document by a scanner can be used.

  Each of the above components is housed in a housing 10a of the image forming apparatus 10. A control unit including a CPU 110, a RAM 114, and the like (see FIG. 2) is provided in the housing 10a of the image forming apparatus 10. The CPU 110 transmits a control signal to each part of the image forming apparatus 10 and causes the image forming apparatus 10 to execute various operations.

  Here, the image data handled in the image forming unit 100 (image forming apparatus 10) corresponds to four color images of black (BK), magenta (M), cyan (C), and yellow (Y). is there. For this reason, each of the photoconductor drum 12, the developing device 14, the charger 16 and the cleaning unit 18 is provided so as to form four types of latent images corresponding to each color. Be composed. The four image stations are arranged in a line along the running direction (circulating movement direction) of the surface of the intermediate transfer belt 36, and are arranged from the downstream side in the running direction of the intermediate transfer belt 36, that is, to the secondary transfer roller 24. From the near side, they are arranged in the order of black, magenta, cyan and yellow. However, the arrangement order of each color can be changed as appropriate.

  In each image station, a charger 16, a developing device 14, and a cleaning unit 18 are arranged in this order around the rotation direction of the photosensitive drum 12 (clockwise in FIG. 1). The developing device 14 is arranged such that the rotation axis of the developing roller 14 a is arranged in parallel with the rotation axis of the photosensitive drum 12. The charger 16 is arranged so that its own rotation axis is parallel to the rotation axis of the photosensitive drum 12. Further, the cleaning unit 18 is arranged such that the longitudinal direction of a cleaning blade (not shown) coincides with the rotation axis direction of the photosensitive drum 12.

  The photoconductor drum 12 is an image carrier in which a photoconductive layer (photoconductive layer) is formed on a surface of a conductive base, and is rotatable around an axis by a driving unit (not shown). The substrate can take various shapes such as a cylindrical shape, a columnar shape, and a thin film sheet shape. The photosensitive layer is formed of a material that becomes conductive when irradiated with light. As the photoconductor drum 12 of the first embodiment, a cylindrical substrate made of aluminum and amorphous silicon (a-Si), selenium (Se), or organic light formed on the outer peripheral surface of the substrate are used. And a photosensitive layer comprising a semiconductor (OPC).

  The developing device 14 visualizes an electrostatic latent image formed on the surface of the photosensitive drum 12 with toner (forms a toner image). A toner cartridge 32 is connected to the developing device 14 via a toner supply pipe 34.

  The toner cartridge 32 is a container for storing unused toner and carrier, and is provided above the developing device 14 to supply (supply) toner to the developing device 14 and replenish the carrier. Although not shown, the toner cartridge 32 has a discharge port for discharging the toner and the carrier. Further, an auger screw that functions as a transport member is provided inside the toner cartridge 32, and the auger screw transports the toner and the carrier to an outlet.

  The toner supply pipe 34 connects the discharge port of the toner cartridge 32 and a toner supply port formed in the developing device 14.

  The charger 16 is a device that charges the surface of the photoconductor drum 12 to a predetermined polarity and potential. As the charger 16, a brush type charging device, a roller type charging device, a corona discharging device, an ion generating device, or the like can be used.

  After the toner image is transferred from the photosensitive drum 12 to the intermediate transfer belt 36, the cleaning unit 18 removes and collects the toner remaining on the surface of the photosensitive drum 12, and cleans the surface of the photosensitive drum 12. . The cleaning unit 18 includes, for example, a cleaning blade, which is a plate-like member for scraping off toner, and a collection container for collecting the scraped toner.

  The exposure device 20 is provided below the developing device 14. The exposure device 20 is configured as a laser scanning unit (LSU) including a laser emitting unit, a reflection mirror, and the like, and exposes the charged surface of the photosensitive drum 12 to an electrostatic latent image corresponding to image data. It is formed on the surface of the photosensitive drum 12.

  The intermediate transfer belt unit 22 includes an intermediate transfer belt 36, a driving roller 38, a driven roller 40, four intermediate transfer rollers (primary transfer rollers) 42, and the like, and is disposed above the photosensitive drum 12.

  The intermediate transfer belt 36 is an endless belt having flexibility, and is formed of a synthetic resin or rubber into which a conductive material such as carbon black is appropriately mixed. The intermediate transfer belt 36 is stretched by a plurality of rollers such as a driving roller 38 and a driven roller 40, and is arranged such that its surface (outer peripheral surface) contacts the surface of the photosensitive drum 12. Then, the intermediate transfer belt 36 rotates (circularly moves) in a predetermined direction (counterclockwise in FIG. 1) as the driving roller 38 is driven to rotate.

  The drive roller 38 is provided rotatably around its axis by a drive unit (not shown). The driven roller 40 rotates with the orbital movement of the intermediate transfer belt 36 and applies a constant tension to the intermediate transfer belt 36 to prevent the intermediate transfer belt 36 from being loosened.

  The intermediate transfer roller 42 is disposed at a position facing each of the photosensitive drums 12 with the intermediate transfer belt 36 interposed therebetween. The intermediate transfer roller 42 is pressed against the inner peripheral surface of the intermediate transfer belt 36 and rotates with the orbital movement of the intermediate transfer belt 36. I do. Although not shown, a transfer power supply for applying a transfer bias is connected to the intermediate transfer roller 42. At the time of image formation, a voltage having a polarity opposite to the charging polarity of the toner constituting the toner image formed on the surface of the photosensitive drum 12 is applied to the intermediate transfer roller 42. As a result, a transfer electric field is formed between the photosensitive drum 12 and the intermediate transfer belt 36, and the toner image formed on the photosensitive drum 12 is transferred to the outer peripheral surface of the intermediate transfer belt 36 by the action of the transfer electric field. You. For example, when a color image is formed, the toner images of the respective colors formed on the respective photosensitive drums 12 are sequentially superimposed on the intermediate transfer belt 36 and transferred (primary transfer), and are transferred onto the outer peripheral surface of the intermediate transfer belt 36. A multicolor toner image is formed.

  The secondary transfer roller 24 is disposed at a position facing the drive roller 38 with the intermediate transfer belt 36 interposed therebetween. A transfer power supply (not shown) is connected to the secondary transfer roller 24, and a voltage (secondary transfer voltage) is applied to the secondary transfer roller 24 by the transfer power supply during image formation. Then, while the paper passes through the transfer nip area between the intermediate transfer belt 36 and the secondary transfer roller 24 by the action of the transfer electric field formed by the secondary transfer roller 24 to which the voltage is applied, the intermediate transfer belt The toner image formed on the outer peripheral surface of the sheet 36 is transferred (secondarily transferred) to the sheet. Thereafter, the toner remaining on the surface of the intermediate transfer belt 36 is removed and collected by a transfer belt cleaning unit (not shown).

  The fixing unit 26 includes a heat roller, a pressure roller, and the like, and is disposed above the secondary transfer roller 24. The heat roller is set to have a predetermined fixing temperature.When the sheet passes through a fixing nip area between the heat roller and the pressure roller, the toner image transferred to the sheet is melted, mixed and mixed. The toner image is heat-fixed to the sheet by pressing.

  Further, in the housing 10 a of the image forming apparatus 10, there is provided a sheet conveyance path for sending the sheet placed on the sheet feed tray 28 to the sheet discharge tray 30 via the secondary transfer roller 24 and the fixing unit 26. It is formed. In this sheet conveyance path, sheet conveyance means such as conveyance rollers 44, 46, and 48 and registration rollers 50 are appropriately arranged.

  At the time of image formation, the paper placed on the paper feed tray 28 is guided one by one to a paper transport path by a pickup roller (not shown), and transported to the registration roller 50 by the transport roller 44. Then, the registration roller 50 conveys the sheet to the secondary transfer roller 24 at a timing when the leading end of the sheet and the leading end of the toner image on the intermediate transfer belt 36 are aligned, and the toner image is transferred onto the sheet. Thereafter, the unfixed toner on the sheet is melted and fixed by heat by passing through the fixing unit 26, and the sheet is discharged onto the sheet discharge tray 30 via the conveying rollers 46 and 48.

  In the image forming apparatus 10 of the first embodiment, a developer (two-component developer) including black, cyan, magenta or yellow toner and a carrier is accommodated in a developing tank (developing housing) provided in the developing device 14. . The carrier is a magnetic material such as iron powder or ferrite. When this two-component developer is used, for example, it is conceivable to use a developing device 14 of a trickle developing system, but it is not necessary to be limited to this.

  FIG. 2 is a block diagram showing an example of an electrical configuration of the image forming apparatus 10 shown in FIG. As shown in FIG. 2, the image forming apparatus 10 includes a CPU 110, and the CPU 110 controls the toner concentration detection sensor 60, the toner supply control unit 62, the toner adhesion amount detection sensor 70, the image forming unit 100 via a bus 112. The RAM 114 and the HDD 116 are connected. Although not shown, the image forming apparatus 10 also includes the above-described components, and is connected to the CPU 110 via the bus 112.

  The CPU 110 controls the overall control of the image forming apparatus 10 and comprehensively controls the operation of each component of the image forming apparatus 10 described above.

  The RAM 114 is used as a work area and a buffer area for the CPU 110. The HDD 116 is a main storage device of the image forming apparatus 10 that stores table data 304a described later and the like.

  Although not shown, the toner concentration detection sensor 60 is provided at the bottom of the developing housing in the developing device 14, and the toner concentration (T / D: T is a toner and D is a developer) in the developing housing. ) Is a sensor for detecting (calculating). In the first embodiment, a magnetic permeability sensor is used as the toner concentration detection sensor 60.

  The magnetic permeability changes depending on the ratio of the magnetic material in the developer. Specifically, when the mixing ratio of the magnetic material (carrier) and the non-magnetic material (toner) in the developer, that is, the relative concentration of the magnetic material changes, the magnetic permeability changes, and the toner density changes according to the changed magnetic permeability. The output value (output voltage) of the detection sensor 60 changes. As the concentration of the non-magnetic toner increases, the magnetic permeability of the developer decreases. In addition, when the toner concentration decreases, the magnetic permeability of the developer increases. For example, the output voltage of the toner concentration detection sensor 60 decreases as the magnetic permeability of the developer decreases, and increases as the magnetic permeability of the developer increases. That is, the output voltage of the toner density detection sensor 60 decreases as the toner density increases, and increases as the toner density decreases.

  The output of the toner density detection sensor 60 (magnetic permeability sensor) is changed within a predetermined fluctuation range by adjusting a control voltage to the toner density detection sensor 60. Therefore, normally, in order to maximize the sensitivity of the toner concentration detection sensor 60, the toner concentration detection is performed when the initial developer is supplied into the development housing or when the initial developer is stored in the development housing. The control voltage is adjusted so that the output voltage of the sensor 60 becomes the center value of the fluctuation range. That is, the output voltage of the toner density detection sensor 60 is calibrated, and the reference value (the voltage value of the reference output voltage) for determining the density (size) when controlling the toner density is set at the center of the fluctuation range. Set to value. The voltage value corresponding to the control voltage at this time is the reference value of the control voltage, and the reference value set to the center value is the initial value of the reference value.

  However, the initial developer refers to an initial developer whose toner concentration has been adjusted so that a good image is formed by the image forming apparatus 10.

  The toner replenishment control unit 62 is a motor driver for driving and controlling a motor for rotating the August screw of the toner cartridge 32.

  After the output voltage of the toner density detection sensor 60 is calibrated, the toner density is controlled based on the output voltage of the toner density detection sensor 60. That is, the image forming apparatus 10 (CPU 110) replenishes new toner from the toner cartridge 32 into the developing housing or consumes toner in the developing housing so that the output voltage of the toner density detecting sensor 60 becomes equal to the median value. Or For example, when the output voltage of the toner concentration detection sensor 60 is lower than the reference value, the toner is supplied into the developing housing to increase the toner concentration. When the output voltage of the toner concentration detection sensor 60 is higher than the reference value, the supply of the toner is stopped or the toner in the developing housing is forcibly consumed.

  For example, when new toner is replenished, the toner replenishment control unit 62 drives a motor in accordance with an instruction from the CPU 110, and the August screw provided in the toner cartridge 32 is rotated. Then, the toner in the housing of the toner cartridge 32 is transported to the discharge port by the August screw, and the toner discharged from the discharge port is supplied with toner into the developing housing. As described above, the discharge port provided in the housing of the toner cartridge 32 and the supply port provided in the developing housing are connected by the toner supply pipe.

  When the toner in the developing housing is consumed, the supply of the toner to the developing housing is stopped (the toner is not supplied) until the output voltage of the toner concentration detection sensor 60 matches the reference value. When the supply of the toner to the developing housing is stopped, the toner is consumed every time the image forming process is performed, and the toner density gradually decreases. However, when the toner concentration is relatively high, that is, when the output voltage of the toner concentration detection sensor 60 is larger than a predetermined threshold, a process for forcibly consuming the toner in the developing housing is executed. Is done. When the toner is forcibly consumed, a toner image for printing a solid image (for example, a solid black toner image) is formed on the photosensitive drum 12, and the toner image is transferred to the intermediate transfer belt 36. After the transfer, the sheet is not transferred to the sheet but is removed and collected by the transfer belt cleaning unit.

  In the first embodiment, since the image forming apparatus is a tandem image forming apparatus provided with a plurality of developing devices 14, the toner image of the solid image transferred to the intermediate transfer belt 36 is removed and collected by the transfer belt cleaning unit. I have to do it. However, the solid image toner image may be removed and collected by the cleaning unit 18 without being transferred to the intermediate transfer belt 36.

  The toner adhesion amount detection sensor 70 is a sensor that is disposed close to the image carrier (the photosensitive drum 12 or the intermediate transfer belt 36) and detects the toner adhesion amount of the toner image on the image carrier. Hereinafter, in the first embodiment, a case where the toner adhesion amount detection sensor 70 is disposed close to the intermediate transfer belt 36 will be described as an example.

  FIG. 3 is an enlarged sectional view schematically showing the toner adhesion amount detection sensor 70. As shown in FIG. 3, the toner adhesion amount detection sensor 70 includes a semiconductor laser 72, a condensing lens 74, and a photo sensor (light receiving element) 76 in a housing 70a. The semiconductor laser 72 irradiates the surface of the intermediate transfer belt 36 with laser light. The focusing lens 74 narrows the light emitted from the semiconductor laser 72 onto the intermediate transfer belt 36. The photo sensor 76 receives the reflected light of the laser light reflected by the toner image on the intermediate transfer belt 36, and outputs an electric signal corresponding to the light amount.

  Since the amount of light received by the photo sensor 76 is correlated with the amount of toner attached to the toner image formed on the intermediate transfer belt 36, the current value or voltage value of the electric signal output in accordance with the amount of received light, By previously acquiring the correlation as a correlation equation or table data, the toner adhesion amount (image density) of the toner image formed on the surface of the intermediate transfer belt 36 can be measured.

  The output of the toner adhesion amount detection sensor 70 is mainly used for process control. The process control refers to an environment in which the image forming apparatus 10 is installed, various development process conditions such as a charging potential, an exposure amount, and a development potential are adjusted so as to correspond to changes in the material of the developer with time, and are always constant. Means that the image quality is obtained.

  In performing this process control, a reference toner image (toner patch) 80 for density correction is formed on the intermediate transfer belt 36. In the process control, the amount of toner attached to the toner patch 80 formed on the intermediate transfer belt 36 (image density of the toner patch 80) is detected according to the output of the toner attached amount detection sensor 70. The developing process conditions are adjusted in accordance with the amount of toner adhered to the intermediate transfer belt 36 detected by the toner amount sensor 70.

  In the first embodiment, the toner patch 80 is conveyed along the running direction (sub-scanning direction) of the surface of the intermediate transfer belt 36. That is, the transport direction of the toner patch 80 is the sub-scanning direction.

  When the toner adhesion amount detection sensor 70 is disposed close to the photoconductor drum 12, the development process conditions are adjusted according to the toner adhesion amount on the toner patch 80 formed on the photoconductor drum 12. You. In this case, the rotation direction (sub-scanning direction) of the photosensitive drum 12 is the toner patch conveyance direction.

  As described above, in the image forming apparatus 10 of the first embodiment, according to the output voltage (output value) of the toner concentration detection sensor 60, the output voltage in the developing housing is adjusted so as to match the reference value of the fluctuation range. The toner density control for adjusting the toner density is performed.

  However, the bulk density of the developer changes due to a change in the material and the amount of charge of the developer over time, and the apparent magnetic permeability of the developer changes accordingly. For this reason, the output of the toner density detection sensor 60 changes, and the toner density cannot be properly controlled. If the toner density is not properly controlled, the toner density may deviate from an allowable range. For example, when the toner density is too high, image fogging occurs, and when the toner density is too low, the formed image becomes thin. That is, there is a problem that a defect occurs in the image quality of the output image.

  For this reason, in the image forming apparatus 10 of the first embodiment, the control voltage of the toner density detection sensor 60 is corrected in accordance with the detection result of the toner adhesion amount detection sensor 70, so that the toner based on the change of the apparent magnetic permeability is corrected. A change in the output of the density detection sensor 60 is corrected.

  FIG. 4 is an illustrative view showing one example of the toner patch 80 in the first embodiment. As shown in FIG. 4, the toner patch 80 is formed in a rectangular (rectangular) shape. The length of the toner patch 80 in the transport direction (corresponding to the sub-scanning direction) of the toner image (including the toner patch 80) is perpendicular to the toner image transport direction (sub-scan direction) (in the main scanning direction). Equivalent) longer than the length. However, the length of the toner patch 80 in the main scanning direction is set to include the size (length) of the detection range of the toner adhesion amount detection sensor 70 in the main scanning direction.

  Further, the toner patch 80 includes a first portion 802 and a second portion 804, and the first portion 802 and the second portion 804 are provided continuously (connected). In the first embodiment, the length of the first portion 802 and the second portion 804 in the sub-scanning direction corresponds to the length L of one rotation of the developing roller 14a. In the first embodiment, the first portion 802 is a portion that is developed in the first rotation of the developing roller 14a, and the second portion 804 is a portion that is developed in the second rotation of the developing roller 14a. For this reason, the shape of the tip of the toner patch 80 in the transport direction is formed parallel to the direction perpendicular to the transport direction of the toner patch 80.

  As described above, the toner patch 80 is composed of the first portion 802 and the second portion 804 because the ratio of the amount of toner attached to the first portion 802 to the amount of toner attached to the second portion 804 (hereinafter, referred to as “the amount of toner attached”). This is for correcting the control voltage in accordance with the “adhesion amount ratio”.

  In the first embodiment, the characteristic of the ghost phenomenon (developing memory) generated when the toner patch 80 is formed on the intermediate transfer belt 36 is used to determine the ratio of the amount of toner adhered between the first portion 802 and the second portion 804. The control voltage is corrected accordingly. The ghost phenomenon means a phenomenon that causes a difference in the development density on the surface of the image carrier.

  For example, when the ghost phenomenon occurs, the developing density of the first portion 802 becomes higher or lower than the developing density of the second portion 804. That is, in the first portion 802, the image becomes darker or lighter than the set image density. This is due to the toner concentration in the developing housing. Here, high development density (high image density) means that the amount of toner attached is large, and low development density (light image) means that the amount of toner adhesion is small. .

  However, since the amount of toner to be developed is adjusted in the second and subsequent rotations of the developing roller 14a, the ghost phenomenon is eliminated, and the second portion 804 of the toner patch 80 has a preset image density.

  As described above, while the amount of toner attached to the first portion 802 changes according to the toner density, the amount of toner attached to the second portion 804 is not affected by the toner density. It is considered that the ratio of the amount of adhesion to the second portion 804 changes according to the toner density.

  An experiment was conducted to quantify the relationship between the level of occurrence of the ghost phenomenon and the toner concentration. The result of this experiment is shown in FIG.

  In this experiment, the ghost occurrence level was visually evaluated in nine levels. However, when the ghost phenomenon does not occur, that is, when the image density in the first part 802 and the image density in the second part 804 are almost the same, it is set to “0”. The case where the image density in the first portion 802 is higher than the image density in the second portion 804 is divided into four stages, and the case where the image density is highest is “4”. Furthermore, the case where the image density of the first portion 802 is lower than the image density of the second portion 804 is divided into four stages, and the case where the image density is the lowest is "-4".

  However, the allowable range when the image density in the first part 802 is higher than the image density in the second part 804 is up to “1”, and the image density in the first part 802 is the image in the second part 804. The allowable range when the density is smaller than the density is set to "-1". That is, the allowable range of the ghost phenomenon occurrence level is “1” to “−1”.

  As can be seen from FIG. 5, according to the experimental results, when the toner density exceeds 5%, the image density in the first portion 802 becomes larger than the image density in the second portion 804. In particular, when the toner concentration exceeds 6%, the ghost occurrence level exceeds “1”. That is, when the toner concentration exceeds 6%, the ghost phenomenon occurrence level falls outside the allowable range. Therefore, when the toner concentration exceeds 5%, it is considered desirable to lower the toner concentration.

  On the other hand, when the toner density is lower than 5%, the image density in the first portion 802 becomes smaller than the image density in the second portion 804. In particular, when the toner concentration is lower than 4.5%, the ghost phenomenon occurrence level is lower than “−1”. That is, when the toner density is lower than 4.5%, the ghost phenomenon occurrence level falls outside the allowable range. Therefore, when the toner concentration falls below 5%, it is considered desirable to increase the toner concentration.

  According to the experimental results shown in FIG. 5, the image density in the first portion 802 changes according to the toner density. Further, it can be seen that the ratio of the amount of adhesion between the first portion 802 and the second portion 804 changes according to the toner density.

  Next, an experiment was conducted to quantify the relationship between the amount of toner attached to the first portion 802 and the ratio of the amount of attachment between the first portion 802 and the second portion 804. FIG. 6 shows the results of this experiment.

  However, the adhesion amount ratio R between the first portion 802 and the second portion 804 shown in FIG. 6 is the ratio of the adhesion amount of the toner in the first portion 802 to the adhesion amount of the toner in the second portion 804. That is, the attachment amount ratio R is a value obtained by dividing the amount of toner attached to the second portion 804 by the amount of toner attached to the first portion 802. As described above, since the amount of toner attached to the second portion 804 is not affected by the toner density, the ratio R of the attached amount between the first portion 802 and the second portion 804 is equal to the amount of attached toner of the first portion 802. Varies by.

  As shown in FIG. 6, when the amount of toner adhered to the first portion 802 is larger than 0.25, the ratio R of the amount of adhesion between the first portion 802 and the second portion 804 is smaller than “1”. That is, the amount of toner attached to the first portion 802 is larger than the amount of toner attached to the second portion 804. In this case, since the amount of toner attached to the first portion 802 is considered to be larger than the preset amount of attachment, the ghost phenomenon occurrence level shown in FIG. 5 is likely to be “0” or more. That is, when the adhesion amount ratio R is smaller than “1”, it is considered that the toner density is high. Therefore, when the adhesion amount ratio R between the first portion 802 and the second portion 804 is smaller than “1”, it is considered desirable to lower the toner density.

  When the amount of toner attached to the first portion 802 is smaller than 0.25, the ratio R between the first portion 802 and the second portion 804 is larger than “1”. That is, the amount of toner attached to the first portion 802 is smaller than the amount of toner attached to the second portion 804. In this case, since the amount of toner attached to the first portion 802 is considered to be smaller than the preset amount of attachment, the ghost phenomenon occurrence level shown in FIG. 5 is likely to be “0” or less. That is, when the adhesion amount ratio R is larger than “1”, it is considered that the toner density is low. Therefore, when the adhesion amount ratio R between the first portion 802 and the second portion 804 is larger than “1”, it is considered desirable to increase the toner density.

  Hereinafter, a method of correcting the control voltage according to the adhesion amount ratio R between the first portion 802 and the second portion 804 shown in FIG. 6 will be described. As described later, when the control voltage is corrected, the reference value is changed from the median value, and the toner density is controlled based on the changed reference value.

  FIG. 7 is a table showing correction values for correcting the control voltage according to the adhesion amount ratio R between the first portion 802 and the second portion 804.

  However, the voltage value (0 to 10 V) of the control voltage is represented by a numerical value of 0 to 255 (8-bit data), and the correction value shown in FIG. 7 is a numerical value for correcting the control voltage represented by 0 to 255. It is. When the voltage value of the control voltage is represented by a numerical value of 0 to 255 (8 bits), one count corresponds to about 0.039 V (10 (V) / 256).

  When the correction value is larger than “0” (when the toner density based on the adhesion amount ratio R is low), the control voltage is increased by the voltage corresponding to the correction value. In this case, the reference value is set to be larger than the median value. Therefore, when the operation of replenishing the toner is being performed, the replenishment amount of the toner is increased. If the operation of consuming toner is being performed, the operation is switched to an operation of replenishing toner, or the amount of toner consumption is reduced. For example, when the correction value is “10 (“ 00001010 ”)”, the control voltage is increased by about 0.39V.

  When the correction value is smaller than “0” (when the toner density based on the adhesion amount ratio R is high), the control voltage is reduced by the voltage corresponding to the correction value. In this case, the reference value is set smaller than the median. Therefore, when the operation of replenishing the toner is being performed, the replenishment of the toner is stopped, the operation is switched to the operation of consuming the toner, or the amount of the replenished toner is reduced. In addition, when the operation of consuming toner is being performed, the amount of toner consumption is increased.

  When the correction value is “0”, the control voltage is not corrected (changed), so that the reference value does not change.

  As described above, the control voltage is corrected and the reference value is changed, but when the voltage value of the control voltage is corrected by the correction value, the amount by which the reference value is changed from the center value of the change range is obtained in advance. When the control voltage is corrected, the reference value is changed (changed) according to the corrected control voltage.

  As shown in FIG. 7, if the adhesion amount ratio R between the first portion 802 and the second portion 804 is “1.1” or more, the correction value is set to a value larger than “0”. Specifically, when the adhesion amount ratio R between the first portion 802 and the second portion 804 is equal to or greater than “1.2”, the correction value is “10” (first correction value). When the adhesion amount ratio R is equal to or more than “1.1” and less than “1.2”, the correction value is “5” (second correction value). As described above, when the adhesion amount ratio R is equal to or more than “1.1” (when the toner density based on the adhesion amount ratio R is low), in the first embodiment, the correction value (first correction) corresponding to the adhesion amount ratio R is used. Value or the second correction value).

  If the adhesion ratio R between the first portion 802 and the second portion 804 is less than “0.9”, the correction value is set to a value smaller than “0” (minus side). Specifically, when the adhesion amount ratio R is less than “0.9” and is “0.8” or more, the correction value is “−5” (third correction value). When the adhesion amount ratio R is less than “0.8” and equal to or more than “0.6”, the correction value is “−10” (fourth correction value). Further, when the adhesion amount ratio R is less than “0.6”, the correction value is “−15” (fifth correction value). As described above, when the adhesion amount ratio R is less than “0.9” (when the toner density based on the adhesion amount ratio R is high), in the first embodiment, the correction value corresponding to the adhesion amount ratio R (third value) The control voltage is reduced by the correction value, the fourth correction value, or the fifth correction value).

  However, when the adhesion amount ratio R is equal to or more than “0.9” and less than “1.1”, the correction value is “0”.

  The above operation of the image forming apparatus 10 is realized by the CPU 110 executing a control program of the image forming apparatus 10 stored in the RAM 114. Specific processing will be described later using a flowchart.

  FIG. 8 is an illustrative view showing one example of a memory map 300 of the RAM 114 shown in FIG. As shown in FIG. 8, the RAM 114 includes a program storage area 302 and a data storage area 304. The control program is stored in the program storage area 302 of the RAM 114 as described above. The control programs include an image forming program 302a, a density detecting program 302b, a toner patch forming program 302c, an adhesion amount detecting program 302d, a control voltage setting program 302e, a correction program 302f, and a toner density adjusting program 302g.

  The image forming program 302a is a program for controlling each component of the image forming apparatus 10 based on image data or the like input from an external computer to form a multi-color or single-color image on a sheet.

The density detection program 302b is a program for detecting (calculating) the toner density in the developing housing according to the output voltage of the toner density detection sensor 60. However,
The toner patch forming program 302c is a program for controlling the developing device 14 and the exposing device 20 to form a toner patch 80 for density correction on the photosensitive drum 12 and the intermediate transfer belt 36.

  The attached amount detection program 302 d is a program for detecting the amount of attached toner on the toner patch 80 on the intermediate transfer belt 36 according to the output of the toner attached amount detection sensor 70. However, the attached amount detection program 302d of the first embodiment detects the attached amount of toner in the first portion 802 and the attached amount of toner in the second portion 804, respectively.

  The control voltage setting program 302e determines whether the output voltage of the toner concentration detection sensor 60 is high when the initial developer is supplied to the developing housing or when the developing device 14 in which the initial developer is accommodated is mounted. This is a program for setting the control voltage so as to match the median of the fluctuation range. That is, the reference value for controlling the toner density is set to the center value of the fluctuation range.

  The correction program 302f is set by the control voltage setting program 302e according to an adhesion amount ratio R between the toner adhesion amount in the first portion 802 and the toner adhesion amount in the second portion 804 detected according to the adhesion amount detection program 302d. This is a program for correcting the reference control voltage.

  The toner density adjustment program 302g controls the image forming unit 100 to execute the operation of replenishing the toner or stop the operation of replenishing the toner such that the output voltage of the toner density detection sensor 60 matches the reference value. And a program for forcibly consuming the toner.

  Although not shown, the program storage area 302 also stores a program for selecting and executing various functions executable by the image forming apparatus 10.

  The data storage area 304 of the RAM 114 stores table data 304a, reference value data 304b, control voltage data 304c, and the like.

  The table data 304a is, for example, data on a control voltage correction value table shown in FIG. 7, and is read from the HDD 116 into the RAM 114 as needed.

  The reference value data 304b is a numerical value for a reference value for controlling the toner density. However, the output voltage of the toner concentration detection sensor 60 when the control voltage is set according to the control voltage setting program 302e is set as a reference value, and when the control voltage is corrected, the reference value is changed accordingly. When the reference value changes, the reference value data 304b is updated.

  The control voltage data 304c is numerical data on the voltage value of the control voltage for adjusting the output of the toner density detection sensor 60 (magnetic permeability sensor). The control voltage is set according to the control voltage setting program 302e, and is corrected according to the correction program 302f. When the control voltage is corrected, the control voltage data 304c is updated.

  Although not shown, the data storage area 304 stores other data required for executing the control program, and is provided with a timer (counter) and a register required for executing the control program.

  FIGS. 9 and 10 are flowcharts showing an example of the toner density control process of the CPU 110 of the image forming apparatus 10 shown in FIG. This toner density control process is executed at a different timing from the image forming process for forming an image on a sheet. For example, the toner density control process is performed when the image forming process is not executed, when one print job is completed, when a predetermined time has elapsed since the previous toner density control process was performed, or when the previous toner density control process was performed. It is executed at a timing such as when the number of images formed by the image forming apparatus 10 exceeds a predetermined number after the control process is performed. However, a print job is a job such as a copy job or a print job that forms an image on a sheet and outputs it.

  As shown in FIG. 9, when starting the toner density control process, the CPU 110 controls the image forming unit 100 to form the toner patch 80 on the intermediate transfer belt 36 in step S1. Although illustration is omitted, when the toner density control process is started, the CPU 110 resets the reference value data 304b and the control voltage data 304c. That is, the reference value and the control voltage are each set to the initial value.

  In the next step S3, the toner adhesion amount of the first portion 802 is detected based on the output of the toner adhesion amount detection sensor 70. In step S5, the second portion 804 is detected based on the output of the toner adhesion amount detection sensor 70. Is detected.

  Subsequently, in step S7, an adhesion amount ratio R between the toner adhesion amount of the first portion 802 detected in step S3 and the toner adhesion amount of the second portion 804 detected in step S5 is calculated, and the process proceeds to step S9. . However, the adhesion amount ratio R calculated in step S7 is a value obtained by dividing the toner adhesion amount of the second portion 804 by the toner adhesion amount of the first portion 802, as described above. Then, in a step S9, it is determined whether or not the adhesion amount ratio R is "1.2" or more.

  If “YES” in the step S9, that is, if the adhesion amount ratio R is equal to or more than “1.2”, a first correction value (here, “10”) is acquired from the table data 304a in a step S11. In step S13, the control voltage is corrected by the first correction value, and the process proceeds to step S15 described below. However, in step S13, the CPU 110 applies the corrected control voltage to the toner density detection sensor 60, and stores the control voltage data 304c corresponding to the corrected control voltage in the RAM 114. Hereinafter, the same applies to the case where the control voltage is corrected.

  On the other hand, if “NO” in the step S9, that is, if the adhesion amount ratio R is less than “1.2”, it is determined in a step S21 whether the adhesion amount ratio R is “1.1” or more. I do. If “YES” in the step S21, that is, if the adhesion amount ratio R is equal to or more than “1.1” and less than “1.2”, a second correction value (here, Then, “5”) is acquired, and in step S25, the control voltage is corrected with the second correction value, and the process proceeds to step S15.

  On the other hand, if “NO” in the step S21, that is, if the adhesion amount ratio R is less than “1.1”, as shown in FIG. Is determined. If “YES” in the step S27, that is, if the adhesion amount ratio R is equal to or more than “0.9” and less than “1.1”, the process proceeds to the step S17 without correcting the control voltage.

  On the other hand, if “NO” in the step S27, that is, if the adhesion amount ratio R is less than “0.9”, it is determined in a step S29 whether the adhesion amount ratio R is “0.8” or more. to decide.

  If “YES” in the step S29, that is, if the adhesion amount ratio R is equal to or more than “0.8” and less than “0.9”, in a step S31, the third correction value (here, Then, “−0.5”) is acquired, the control voltage is corrected by the third correction value in step S33, and the process proceeds to step S15.

  On the other hand, if “NO” in the step S29, that is, if the adhesion amount ratio R is less than “0.8”, it is determined whether or not the adhesion amount ratio R is “0.6” or more in a step S35. to decide. If “YES” in the step S35, that is, if the adhesion amount ratio R is equal to or more than “0.6” and less than “0.8”, in a step S37, the fourth correction value (here, Then, “−10”) is obtained, the control voltage is corrected by the fourth correction value in step S37, and the process proceeds to step S15.

  On the other hand, if “NO” in the step S35, that is, if the adhesion amount ratio R is less than “0.6”, a fifth correction value (here, “−15”) from the table data 304a in a step S41. Is obtained, the control voltage is corrected by the fifth correction value in step S43, and the process proceeds to step S15.

  In step S15, the reference value is changed according to the corrected control voltage. That is, the CPU 110 updates the reference value data 304b. In the next step S17, the output of the toner density detection sensor 60 is detected, and in step S19, as described above, the toner density is adjusted so that the output of the toner density detection sensor 60 detected in step S17 matches the reference value. After the control, the toner density control process ends.

  According to the first embodiment, the amount of adhesion of the first round portion (first portion 802) of the developing roller 14a on the toner patch 80 and the second round portion (second portion) of the developing roller 14a on the toner patch 80 are determined. Since the control voltage is corrected and the reference value for controlling the toner density is changed in accordance with the ratio of the adhesion amount to the adhesion amount of the portion 804), the output of the toner concentration detection sensor 60 based on the change in the apparent magnetic permeability. Can be corrected. Therefore, the toner concentration in the developing housing can be appropriately controlled.

  Further, in the first embodiment, as shown in the table of FIG. 7, the correction value is set in six steps according to the adhesion amount ratio R, but the present invention is not limited to this. For example, according to the adhesion amount ratio R, the correction value may be set in seven or more steps, or the correction value may be set in five or less steps. Further, the correction value may be calculated by a mathematical expression based on the adhesion amount ratio R.

  Further, in the first embodiment, the toner patch 80 is formed by connecting (adjacent) the first round part (first part 802) of the developing roller 14a and the second round part (second part 804) of the developing roller 14a. However, the present invention is not limited to this. For example, the toner patch 80 may be formed such that a portion of the first rotation of the developing roller 14a (first portion 802) and a portion of the second rotation of the developing roller 14a (second portion 804) are separated.

Further, the length of the toner patch 80 in the sub-scanning direction may be set to a length of one rotation or more and two or less rotations of the developing roller 14a. Therefore, the toner patch 80 has at least a part of the length L of one rotation of the developing roller 14a in the first rotation and a part of the length L of one rotation of the developing roller 14a in the second rotation in the sub-scanning direction. What is necessary is just to be formed so that it may have. Further, the shape of the toner patch 80 does not need to be limited to a rectangular shape.
[Second embodiment]
The image forming apparatus 10 according to the second embodiment is the same as the image forming apparatus 10 according to the first embodiment except that the shape of the toner patch 80 is different. Will be omitted.

  FIG. 11 is an illustrative view showing one example of a shape of the toner patch 80 in the second embodiment. FIGS. 12A to 12D are illustrative views showing another example of the shape of the toner patch 80 in the second embodiment.

As shown in FIGS. 11 and 12A to 12D, in the second embodiment, the shape of the toner patch 80 is different from the shape of the toner patch 80 shown in the first embodiment.
Therefore, a part of the leading edge 802a of the toner patch 80 in the transport direction (sub-scanning direction) is formed so as to protrude downstream (the distal end of the toner patch 80) in the transport direction of the toner patch 80. However, in the second embodiment, the range from the leading edge 802a of the toner patch 80 to the length L of one round of the developing roller 14a is the first portion 802, and the portion other than the first portion 802 of the toner patch 80 is the first portion 802. Two parts 804.

  As an example in which the shape of the tip of the toner patch 80 is modified, one end of the tip of the toner patch 80 in the main scanning direction is projected more downstream than the other end in the transport direction of the toner patch 80. Can be considered.

  In the example shown in FIG. 11, the toner patch 80 is formed in a fan shape surrounded by two radii (line segments) and an arc. In the example shown in FIG. 11, the angle between the two radii is 90 °. Further, the toner patch 80 has two radii (line segments) constituting the fan shape such that one radius extends in a direction parallel to the main scanning direction and the other radius extends in a direction parallel to the sub-scanning direction. Is arranged. Accordingly, the leading edge 802a (circular arc) of the toner patch 80 connects one end in the main scanning direction at the downstream end in the conveying direction of the toner patch 80 and the other end in the main scanning direction at the upstream end in the conveying direction of the toner patch 80. . For this reason, on the downstream side in the transport direction of the toner patch 80, the other end side in the main scanning direction protrudes more downstream than the one end side in the transport direction.

  Although not shown, the toner patch 80 may be formed in a triangular shape. In this case, for example, in the fan-shaped toner patch 80 shown in FIG. 11, instead of a curve, two radii (line segments) are connected by a straight line.

  Although not shown, the fan-shaped or triangular-shaped toner patches 80 may be reversed in a line-symmetric manner with respect to a straight line parallel to the toner patch 80 conveyance direction in the case shown in FIG.

  In the examples shown in FIGS. 12A to 12D, the shape of the tip of the toner patch 80 shown in the first embodiment is deformed. In the second embodiment, the leading end of the toner patch 80 is the downstream end in the transport direction (sub-scanning direction) of the toner patch 80. When the shape of the tip of the toner patch 80 is deformed, the leading edge 802a of the toner patch 80 is not parallel to the direction (main scanning direction) perpendicular to the direction in which the toner patch 80 is transported.

  For example, in the example of the toner patch 80 shown in FIGS. 12A and 12B, at the downstream end side in the transport direction of the toner patch 80, the central portion in the main scanning direction is larger than both ends in the main scanning direction. The toner patch 80 protrudes toward the front end side. That is, the center of the leading edge 802a of the toner patch 80 protrudes downstream of the toner patch 80 in the conveying direction from both ends.

  In the example illustrated in FIG. 12A, the toner patch 80 has a shape in which a semicircle is combined on one short side of a rectangle, or a horizontally long track shape (an oval shape) at a central portion in the horizontal direction. It is formed in one shape when divided. In this case, the circular arc portion of the toner patch 80 is disposed downstream of the toner patch 80 in the transport direction. Therefore, the leading edge 802a of the toner patch 80 curves so as to protrude downstream in the transport direction of the toner patch 80.

  In the example illustrated in FIG. 12B, the toner patch 80 is formed in a shape obtained by combining a triangle on one short side of a rectangle, or a shape obtained by diagonally cutting two corners on one short side of the rectangle. You. In this case, the toner patch 80 has a vertex of a triangle or a corner formed by cutting two corners obliquely, and is disposed downstream of the toner patch 80 in the transport direction.

  In the example of the toner patch 80 illustrated in FIGS. 12C and 12D, both ends in the main scanning direction at the downstream end in the toner patch conveyance direction are smaller than the center in the main scanning direction. It protrudes to the tip side of the patch 80. That is, both ends of the leading edge 802a of the toner patch 80 protrude downstream of the toner patch 80 in the transport direction from the center.

  In the example shown in FIG. 12C, the toner patch 80 is formed in a shape obtained by cutting out a semicircular (arc) shape on one short side of a rectangle. In this case, the portion of the toner patch 80 cut out in a semicircular shape is arranged on the downstream side in the transport direction of the toner patch 80.

  In the example shown in FIG. 12D, the toner patch 80 has a shape obtained by combining two right triangles on one short side of the rectangle, or a vertex angle on one short side of the rectangle in the transport direction of the toner patch 80. It is formed in a shape formed by cutting out a triangular shape facing the upstream side. In this case, the toner patches 80 are arranged such that the apexes of the two triangles face downstream in the transport direction of the toner patches 80, respectively. However, in the two right-angled triangles, the oblique sides facing the respective right-angled corners face each other, and the opposite sides facing the respective apex angles are connected to a rectangle.

  In the second embodiment, only the shape of the toner patch 80 generated in step S5 of the toner density control process shown in the first embodiment is different.

  According to the second embodiment, a part of the leading edge 802a of the toner patch 80 in the transport direction projects toward the leading end of the toner patch 80. Therefore, the toner is first supplied to the protruding portion of the leading edge 802a. With this configuration, the first toner supply range is narrower than when the leading edge 802a is parallel to the main scanning direction (when toner is supplied to the entire leading edge 802a at the same time). The difference in shade of 802 is likely to appear. Therefore, the ratio of the amount of toner adhered to the first portion 802 and the amount of toner adhered to the second portion 804 can easily change, and the amount-of-adhesion ratio R can be calculated appropriately. Thereby, the toner concentration in the developing housing can be appropriately controlled.

  Note that the shape of the toner patch 80 shown in FIGS. 11 and 12A to 12D is merely an example, and the shape may be appropriately changed as long as a part of the leading edge 802a projects toward the leading end of the toner patch 80. It is possible to

For example, in the examples shown in FIGS. 11 and 12A to 12D, the rear end of the toner patch 80 in the transport direction is formed in parallel with the main scanning direction. There is no need to be limited. The rear end of the toner patch 80 in the transport direction may be deformed with respect to the main scanning direction like the front end of the toner patch 80 in the transport direction.
[Third embodiment]
The image forming apparatus 10 according to the third embodiment is the same as the image forming apparatus 10 according to the first embodiment except that the correction value for correcting the control voltage is changed according to the information on the usage status of the image forming apparatus 10. Therefore, only the contents different from those of the first embodiment will be described, and the repeated description will be omitted.

  In brief, in the third embodiment, a basic correction value serving as a basis of a correction value in correction control is set in accordance with information on the usage status of the image forming apparatus 10. This basic correction value is added to the correction value of the control voltage shown in FIG. That is, the correction value of the control voltage is further corrected with the basic correction value in accordance with the information on the usage state of the image forming apparatus 10, and the correction value for correcting the control voltage is changed.

  However, the information on the usage status of the image forming apparatus 10 used in the third embodiment includes the temperature and humidity of the installation location of the image forming apparatus 10 and the idle time since the previous print job ended (hereinafter, simply referred to as The image forming apparatus 10 prints (hereinafter simply referred to as “integrated number”), the travel distance of the developing roller 14a, and the average printing rate in the image forming apparatus 10 (hereinafter simply referred to as “printing rate”). ) Is included.

  Further, the image forming apparatus 10 of the third embodiment includes a temperature sensor, a humidity sensor, a timer, and the like for acquiring each piece of information on the use state of the image forming apparatus 10 described above. The temperature sensor is used to detect the temperature (° C.) of the place where the image forming apparatus 10 is installed. The humidity sensor is used to detect the humidity (%) at the place where the image forming apparatus 10 is installed. The timer is used to measure the idle time since the previous print job ended.

  Further, the integrated number of sheets printed by the image forming apparatus 10, the traveling distance of the developing roller 14a, and the printing rate in the image forming apparatus 10 are acquired according to the operation of the image forming apparatus in the image forming process. The obtained or detected information is stored in the HDD 116.

  FIG. 13 is a table for determining the usage environment level of the image forming apparatus according to the third embodiment. As shown in FIG. 13, eight use environment levels from “1” to “8” are set according to the temperature (° C.) and the humidity (%). However, if the temperature is high, the use environment level tends to be high, and if the temperature is low, the use environment level tends to be low. Also, the use environment level tends to increase when the humidity is high, and the use environment level tends to decrease when the humidity is low.

  For example, when the temperature of the installation location of the image forming apparatus 10 is 22 ° C. and the humidity is 65%, the use environment level is “5”.

  Next, a table of corresponding conditions is selected from 12 types of tables set according to the idle time, the total number of sheets, and the printing rate. Then, the basic correction value is determined according to the selected table.

  However, in the third embodiment, whether or not the idle time is long is determined if the idle time is long if it is 60 minutes or more after the end of the previous print job, and it is determined that the idle time is long after the previous print job is ended. If it is less than minutes, it is determined that the leaving time is short. Whether the number of integrated sheets is large is determined when the number of integrated sheets is 1000 or more, that the number of integrated sheets is large. When the number of integrated sheets is less than 1,000, it is determined that the number of integrated sheets is small. Further, the printing rate in the image forming apparatus 10 is determined in three stages of a low printing rate, a medium printing rate, and a high printing rate. If the printing rate in the image forming apparatus 10 is less than 6%, it is determined that the printing rate is low. If the printing rate in the image forming apparatus 10 is 6% or more and less than 21%, it is determined that the printing rate is medium. If the printing rate is 21% or more, it is determined that the printing rate is high.

  FIGS. 14 to 16 show six types of tables among the twelve types of tables in order to explain the tendency of the tables for determining the basic correction value. FIG. 14 is a table for determining the basic correction value when the idle time is short and the integrated printing rate is low. FIG. 15 is a table for determining a basic correction value when the idle time is short and the printing rate is high. FIG. 16 is a table for determining a basic correction value when the idle time is long and the printing rate is low. FIGS. 14A to 16A each show a table in the case where the total number is less than 1000, and FIGS. 14 to 16 each show a table in the case where the total number is 1000 or more. Show the table.

  As shown in FIGS. 14 to 16, in each of the tables, a basic correction value is set according to the usage environment level and the traveling distance of the developing roller 14a. However, the traveling distance of the developing roller 14a is divided into stages every 7 km.

  In any of the tables, the basic correction value tends to decrease when the use environment level is high, and the basic correction value tends to increase when the use environment level is low. Furthermore, if the traveling distance of the developing roller 14a is long, the absolute value of the basic correction value tends to increase, and if the traveling distance of the developing roller 14a is short, the absolute value of the basic correction value tends to decrease. Furthermore, if the number of integrated sheets is large, the absolute value of the basic correction value tends to increase, and if the number of integrated sheets is small, the absolute value of the basic correction value tends to decrease.

  FIG. 14 and FIG. 15 show tables where the idle time is short and the print ratios are different. As can be seen from a comparison between FIG. 14 and FIG. 15, when the printing rate is high, the basic correction value tends to decrease when the use environment level is “1” to “3” (low temperature and / or low humidity). It is in. That is, if the printing rate is low, the basic correction value tends to increase when the use environment level is “1” to “3”. However, when the use environment level is “4” to “8” (high temperature and / or high humidity), the basic correction value does not change even if the printing rate changes.

  FIG. 14 and FIG. 16 show tables in the case where the printing rate is low and the leaving time is different. As can be seen from a comparison between FIG. 14 and FIG. 16, if the leaving time is long, the basic correction value becomes large when the use environment level is “1” to “2” (low temperature and / or low humidity), When the use environment level is "5" to "8" (high temperature and / or high humidity), the basic correction value tends to be small. However, when the use environment level is “4”, the basic correction value does not change even if the idle time changes.

  For example, if the idle time is less than 60 minutes, the accumulated number of sheets is less than 1000, and the printing rate is less than 6%, the table in FIG. 14A is used. If the traveling distance of the developing roller 14a is 35 km and the use environment level is “3”, the basic correction value is “1”. Here, for example, when the adhesion amount ratio R is “1.2” or more, the correction value indicated by the table shown in FIG. 7 is “10”. In this case, the basic correction value “1” is added to the correction value “10”, and the correction value becomes “11”.

  Hereinafter, the toner density control processing in the third embodiment will be described with reference to a flowchart. The same reference numerals are given to the same processing as the toner density control processing described in the first embodiment, and the duplicated contents will be described. , Will be omitted or briefly described.

  FIGS. 17 to 19 are flowcharts showing a part of an example of the toner density control process of the CPU 110 of the image forming apparatus 10 in the third embodiment. However, FIG. 18 and FIG. 19 are substantially the same as the processing of steps S1 to S43 shown in the first embodiment, and a description of overlapping contents will be omitted.

  As shown in FIG. 17, when the CPU 110 of the image forming apparatus 10 starts the toner density control process, the temperature of the installation location of the image forming apparatus 10 is detected in step S51, and the installation location of the image forming apparatus 10 is detected in step S53. Is detected, and the process proceeds to step S55.

  However, in step S51, the temperature of the installation location of the image forming apparatus 10 is detected in accordance with the output of the temperature sensor, and in step S53, the humidity of the installation location of the image forming apparatus 10 is detected in accordance with the output of the humidity sensor. Although illustration is omitted, also in the third embodiment, the CPU 110 resets the reference value data 304b and the control voltage data 304c when starting the toner density control process.

  In step S55, the use environment level is determined with reference to the table shown in FIG. 13 according to the temperature detected in step S51 and the humidity detected in step S53, and the process proceeds to step S57.

  In a succeeding step S57, a leaving time is detected, in a step S59, a printing rate is read, and in a step S61, an integrated number is read, and the process proceeds to a step S63. The idle time is detected according to the output of the timer. The printing rate and the cumulative number of sheets are read from the HDD 116.

  In step S63, a table for setting a basic correction value is selected. Here, a table with corresponding conditions is selected from 12 types of tables set according to whether the idle time is long, whether the number of accumulated sheets is large, and whether the printing rate in the image forming apparatus 10 is high.

  In a succeeding step S65, the travel distance of the developing roller is read, and the process proceeds to a step S67. Then, in step S67, according to the table set in step S63, a basic correction value corresponding to the use environment level determined in step S55 and the travel distance of the developing roller read in step S65 is acquired. The process proceeds to step S1 shown in FIG.

  As shown in FIG. 18, in the third embodiment, when the first correction value is acquired from the table data 304a in step S11, the control voltage is corrected by the first correction value and the basic correction value in step S13a, and Proceed to S15. However, the CPU 110 applies the control voltage corrected by the first correction value and the basic correction value to the toner density detection sensor 60 in step S13a, and stores the control voltage data 304c corresponding to the corrected control voltage in the RAM 114. I do. Hereinafter, the same applies to step S25a for correcting the control voltage and to steps S33a, S39a, and S43a shown in FIG.

  As shown in FIG. 19, in the third embodiment, if “YES” in the step S27, that is, if the control voltage is not corrected according to the adhesion amount ratio R, the process proceeds to a step S81. In step S81, the control voltage is corrected with the basic correction value, and the process proceeds to step S15. As described above, even when the control voltage is not corrected according to the adhesion amount ratio R, the control voltage may be corrected with the basic correction value. However, if the basic correction value acquired in step S67 is “0”, the control voltage is not corrected in step S81. In this case, since the control voltage is not corrected and the reference value is not changed, the process proceeds to step S17 without correcting the reference value in step S15. When the reference value is not corrected in this way, in step S19, the toner density is controlled so that the output of the toner density detection sensor 60 detected in step S17 matches the initial reference value.

  According to the third embodiment, the control voltage can be corrected according to the use condition of the image forming apparatus 10, and the toner density in the developing housing can be appropriately controlled.

  The modification shown in the third embodiment can be applied to the image forming apparatus 10 of the second embodiment.

  In addition, regardless of the amount of toner attached to the first portion 802, the process control may be performed according to the amount of toner attached to the second portion 804. As described above, in the process control, the development process conditions are adjusted in accordance with the amount of toner adhered on the intermediate transfer belt 36 detected by the toner amount detection sensor 70.

  Specifically, development bias correction or toner density correction is performed, and the image density (toner image density) of the toner image formed on the image carrier (photosensitive drum 12 or intermediate transfer belt 36) is controlled.

  In the process control, a plurality of toner patches 80 whose toner density (toner adhesion amount) continuously changes are formed on the surface of the photosensitive drum 12 by continuously changing the developing bias voltage. At this time, the development process conditions (development bias voltage value and / or toner density) of each toner patch are stored in the data storage area 304 of the RAM 114.

  The amount of toner attached to each of the toner patches 80 formed on the surface of the photosensitive drum 12 is detected according to the output of the toner attached amount detection sensor 70. The CPU 110 compares the detection result of the toner adhesion amount of each toner patch 80 with a toner adhesion amount (reference toner adhesion amount) corresponding to a preset reference toner density, and determines the toner adhesion amount that is the largest in the reference toner adhesion amount. Is determined (selected). Subsequently, the CPU 110 reads the developing bias voltage value applied to the formation of the selected toner patch 80, and uses the difference between the read developing bias voltage value and the developing bias voltage value at the reference toner density as a developing bias correction value. Set.

  At the time of image formation, a toner image is formed using a developing bias voltage corresponding to a voltage value obtained by correcting a developing bias voltage value applied to the formation of the selected toner patch 80 with a developing bias correction value. By doing so, a toner image having a toner adhesion amount equal to the reference toner adhesion amount is stably formed. That is, the toner image density is stabilized.

  For example, when the toner image density is low, control for increasing the toner image density is performed by process control. When the toner image density is low, the developing bias voltage value is lower than the developing bias voltage value at the reference toner density. Therefore, the developing bias correction value is set to increase the developing bias voltage value. Therefore, the developing bias voltage value is increased. However, when the toner image density is low, it is conceivable that the toner density is low. In this case, the control voltage of the toner concentration detection sensor 60 is corrected so that the detected toner concentration becomes low. Further, the same control as in the case where the toner density is low based on the adhesion amount ratio R is performed, and the control voltage of the toner density detection sensor 60 is increased.

  When the toner image density is high, control is performed to reduce the toner image density. When the toner image density is high, the developing bias voltage value is higher than the developing bias voltage value at the reference toner density. Therefore, the developing bias correction value is set so as to lower the developing bias voltage value. Therefore, the developing bias voltage value is reduced. Further, control for lowering the toner density may be performed. In this case, the control voltage of the toner concentration detection sensor 60 is corrected so that the detected toner concentration becomes higher. Further, the same control as in the case where the toner density is high based on the above-described adhesion amount ratio R is performed, and the control voltage of the toner density detection sensor 60 is reduced.

  In this process control, the toner adhesion amount of the second portion 804 is used instead of the toner adhesion amount of the first portion 802. As described above, the ghost phenomenon is eliminated after the second rotation of the developing roller 14a. Therefore, the process control is not affected by the ghost phenomenon by using the toner adhesion amount of the second portion 804 in which the ghost phenomenon has been eliminated. Therefore, it is possible to appropriately control the toner image density.

  Further, specific numerical values, screen configurations, and the like described in the above-described embodiments are merely examples, and can be changed according to actual products. Further, the order of processing of the steps in the flowchart shown in the above-described embodiment can be appropriately changed as long as the same result is obtained.

10 image forming apparatus 14 developing apparatus 14a developing roller 112 CPU
114… RAM
Reference numeral 60: concentration detection sensor 70: adhesion amount detection sensor 80: toner patch 802: first part 804: second part

Claims (7)

An image forming apparatus comprising: an image carrier, and a developing device that accommodates a developer in which a toner and a carrier are mixed in a developing housing and has a developing roller that supplies the toner to the image carrier.
Density detection means for detecting the toner density in the developing housing,
Control voltage setting means for setting a control voltage for calibrating the output value of the concentration detection means,
Toner density adjusting means for adjusting the toner density in the developing housing according to the output value of the density detecting means,
By the developing device, in the circumferential direction of the developing roller, a reference toner image for density correction including at least a part of a range of a first rotation of the developing roller and at least a part of a range of a second rotation of the developing roller is used. Reference toner image forming means for forming on the image carrier,
An adhesion amount detection unit that detects an adhesion amount of toner in the reference toner image formed on the image carrier by the reference toner image formation unit; and the development in the reference toner image detected by the adhesion amount detection unit. The control set by the control voltage setting means in accordance with a ratio between the amount of toner attached in the first rotation of the roller and the amount of toner attached in the second rotation of the developing roller in the reference toner image. An image forming apparatus including a correction unit that corrects a voltage.   The image forming apparatus according to claim 1, wherein a part of a leading end of the reference toner image in a transport direction protrudes downstream in the transport direction of the reference toner image.   The image forming apparatus according to claim 2, wherein the front end of the reference toner image is inclined with respect to a direction perpendicular to a conveyance direction of the reference toner image.   The image forming apparatus according to claim 2, wherein the front end of the reference toner image is curved in a direction perpendicular to a conveyance direction of the reference toner image.   The image forming apparatus according to claim 1, wherein the correction unit changes a correction value for correcting the control voltage in accordance with information on a use state of the image forming apparatus. A control program for an image forming apparatus, comprising: an image carrier; and a developing device that accommodates a developer in which toner and carrier are mixed in a developing housing and has a developing roller that supplies the toner to the image carrier. hand,
The computer of the image forming apparatus,
Density detection means for detecting the toner density in the developing housing,
Control voltage setting means for setting a control voltage for calibrating the output value of the concentration detection means,
Toner density adjusting means for adjusting the toner density in the developing housing according to the output value of the density detecting means,
By the developing device, in the circumferential direction of the developing roller, a reference toner image for density correction including at least a part of a range of a first rotation of the developing roller and at least a part of a range of a second rotation of the developing roller is used. Reference toner image forming means for forming on the image carrier,
An adhesion amount detection unit that detects an adhesion amount of toner in the reference toner image formed on the image carrier by the reference toner image formation unit; and the development in the reference toner image detected by the adhesion amount detection unit. The control set by the control voltage setting means in accordance with a ratio between the amount of toner attached in the first rotation of the roller and the amount of toner attached in the second rotation of the developing roller in the reference toner image. A control program for an image forming apparatus that functions as a correction unit that corrects a voltage. A method for controlling an image forming apparatus, comprising: an image carrier; and a developing device that accommodates a developer in which toner and carrier are mixed in a developing housing and has a developing roller that supplies the toner to the image carrier. hand,
The computer of the image forming apparatus includes:
(A) detecting the toner concentration in the developing housing,
(B) setting a control voltage for calibrating the output value of step (a);
(C) adjusting the toner concentration in the developing housing according to the output value of step (a);
(D) the developing device, in the circumferential direction of the developing roller, a reference toner for density correction including at least a part of a range of a first round of the developing roller and at least a part of a range of a second round of the developing roller. Forming an image on the image carrier;
(E) detecting the amount of toner attached to the reference toner image formed on the image carrier in the step (d); and (f) detecting the amount of toner in the reference toner image detected in the step (e). The ratio set in the step (b) according to the ratio between the amount of toner attached in the first rotation of the developing roller and the amount of toner attached in the second rotation of the developing roller in the reference toner image. A method for controlling an image forming apparatus, wherein the method functions as a correction unit for correcting a control voltage.

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