JP2020046560A - Image forming apparatus - Google Patents

Abstract

To prevent image fogging and density difference immediately after supply of toner into a developing unit, while ensuring miniaturization of the developing unit.SOLUTION: An image forming apparatus comprises: charging means that charges an image holding body to a predetermined charging potential; exposure means that exposes the image holding body charged by the charging means to form an electrostatic latent image; developing means including a developing roller that holds a developer containing a toner on its surface to develop the electrostatic latent image with the toner; calculation means that calculates a supply amount of toner supplied to the developing means; and changing means that, when the supply amount of toner calculated by the calculation means exceeds a predetermined threshold, changes the magnitude of a cleaning electric field in an axial direction of the image holding body, the cleaning electric field formed by a background part potential of the electrostatic latent image and a developing bias potential.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an image forming apparatus.

  An image forming apparatus for forming an image by scanning and exposing light modulated in accordance with image data representing an image in two main and sub two-dimensional directions to visualize an electrostatic latent image as a toner image, and forming an image in a main scanning direction. Calculating means for calculating the amount of image data to be formed in the image data for each of the divided areas, based on the calculation result of the calculating means, There is known an image forming apparatus including a correcting unit for correcting unevenness in density in a main scanning direction of a toner image caused by a distance to the image forming apparatus (Patent Document 1).

JP 2007-192888 A

  SUMMARY OF THE INVENTION It is an object of the present invention to suppress image fog and a density difference immediately after toner supply into a developing device, while ensuring the size of the developing device.

In order to solve the above problem, the image forming apparatus according to claim 1,
Charging means for charging the image carrier to a predetermined charging potential,
Exposure means for exposing the image carrier charged by the charging means to form an electrostatic latent image,
Developing means comprising a developing roll for holding a developer containing toner on the surface thereof and developing the electrostatic latent image with the toner;
Calculating means for calculating a replenishment amount of the toner supplied to the developing means;
When the replenishment amount of the toner calculated by the calculation means exceeds a predetermined threshold, the cleaning electric field of the image holding member formed by the background potential of the electrostatic latent image and the development bias potential is adjusted. Changing means for changing the size in the axial direction,
An image forming apparatus comprising:

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
The changing unit expands the cleaning electric field over a predetermined area from a supply position of the toner supplied to the developing unit to the developing roll in an axial direction of the image holding member.
It is characterized by the following.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect,
A developing unit for irradiating the image carrier with static elimination light to eliminate the charge on the image carrier; and before the charging of the image carrier by the charging unit, the developing roll of the toner supplied to the developing unit. From a supply position to a predetermined area, the discharge light is weakened compared to a normal state in which the replenishment amount of the toner does not exceed a predetermined threshold, and the post-discharge potential of the image holding member is increased.
It is characterized by the following.

According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect,
The changing unit may set the background portion potential to a predetermined threshold from a supply position of the toner supplied to the developing unit of the image holding member to the developing roll from a supply position to a predetermined region. Expand the cleaning electric field by making it higher than normal not to exceed,
It is characterized by the following.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect,
Exposing the image holding member to a region serving as a background portion of an image on the image holding member excluding a region extending from a supply position of the toner supplied to the developing unit to the developing roll to a predetermined region from the supply position by the exposure unit Performing, the background portion potential is increased by making the toner supply amount smaller than a normal time when the toner supply amount does not exceed a predetermined threshold value,
It is characterized by the following.

In order to solve the above problem, the image forming apparatus according to claim 6,
Charging means for charging the image carrier to a predetermined charging potential,
Exposure means for exposing the image carrier charged by the charging means to form an electrostatic latent image,
Developing means comprising a developing roll for holding a developer containing toner on the surface thereof and developing the electrostatic latent image with the toner;
Calculating means for calculating a replenishment amount of the toner supplied to the developing means;
When the replenishment amount of the toner calculated by the calculation unit exceeds a predetermined threshold, a developing electric field formed by an exposure portion potential of the electrostatic latent image and a developing bias potential of the image holding member is used. Changing means for changing the size in the axial direction,
It is characterized by the following.

According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect,
The changing unit may be configured such that the amount of exposure of the toner supplied to the developing unit of the image holding member from the supply position to the developing roll from a supply position to the developing roll is predetermined by the amount of exposure by the exposing unit. Increase the exposed portion potential to be smaller than the normal time does not exceed the threshold,
It is characterized by the following.

According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth aspect,
The changing unit includes an area gradation ratio Cin of an image to be an exposure unit of the electrostatic latent image from a supply position of the toner supplied to the developing unit of the image holding member to the developing roll from a predetermined position. Lower than the normal time when the toner supply amount does not exceed a predetermined threshold,
It is characterized by the following.

According to a ninth aspect of the present invention, in the image forming apparatus according to the first or sixth aspect,
The calculating unit calculates the toner supply amount based on the number of rotations per unit time of a toner supply unit that supplies the toner to the developing unit.
It is characterized by the following.

According to a tenth aspect of the present invention, in the image forming apparatus according to the first or sixth aspect,
The calculation unit calculates the toner supply amount based on the number of pixels per unit area of the electrostatic latent image formed on the image holding member,
It is characterized by the following.

According to an eleventh aspect of the present invention, in the image forming apparatus according to the first or sixth aspect,
The calculating means calculates a toner replenishment amount by detecting a toner recovery operation for the developing means,
It is characterized by the following.

  According to the first aspect of the invention, it is possible to suppress image fog immediately after toner supply into the developing device.

  According to the second aspect of the present invention, the cleaning electric field can be expanded over a predetermined area from the toner supply position to the developing roll.

  According to the third aspect of the present invention, it is possible to increase the cleaning electric field by setting the post-static potential of the image carrier higher than usual.

  According to the fourth aspect of the present invention, it is possible to enlarge the cleaning electric field by setting the background potential of the image carrier higher than usual.

  According to the fifth aspect of the present invention, the cleaning electric field can be expanded by setting the charging potential of the image holding member higher than usual.

  According to the sixth aspect of the invention, it is possible to suppress a difference in image density immediately after toner supply into the developing device.

  According to the seventh aspect of the present invention, it is possible to reduce the developing electric field by increasing the potential of the exposed portion of the electrostatic latent image on the image holding member as compared with the normal case.

  According to the eighth aspect of the present invention, the area gradation ratio Cin of an image serving as an exposed portion of the electrostatic latent image on the image holding member can be reduced as compared with a normal case, so that the developability can be reduced.

  According to the ninth aspect, it is possible to detect a sudden toner supply into the developing device.

  According to the tenth aspect, it is possible to detect a sudden toner supply into the developing device.

  According to the eleventh aspect, it is possible to detect a sudden toner supply into the developing device.

FIG. 2 is a schematic vertical cross-sectional view illustrating an internal configuration of the image forming apparatus according to the embodiment. FIG. 2 is a schematic vertical cross-sectional view illustrating a main configuration of an image forming unit. FIG. 3 is a schematic cross-sectional view developed in a horizontal direction along a line ABC in FIG. 2 for explaining conveyance of a developer in a developing device. FIG. 4 is a diagram for explaining a relationship between a charging potential and an exposure portion potential of the photosensitive drum and a developing potential of the developing device when an AC superimposed bias is applied. FIG. 2 is a functional block diagram illustrating a functional configuration of an image forming unit. FIG. 4 is a diagram schematically illustrating a distribution of a TC value of a developer in a developer accommodating portion of the developing device. 6 is a flowchart illustrating a flow of cleaning electric field control in the image forming apparatus. FIG. 6 is a diagram illustrating a relationship between a charging potential and a developing potential in cleaning electric field control. 9 is a flowchart illustrating a flow of cleaning electric field control in the image forming apparatus according to Modification 1. 11 is a flowchart illustrating a flow of cleaning electric field control in an image forming apparatus according to Modification 2. 13 is a flowchart illustrating a flow of cleaning electric field control in an image forming apparatus according to Modification 3. FIG. 6 is a diagram illustrating a relationship between a charging potential and a developing potential in cleaning electric field control. 8 is a flowchart illustrating a flow of a developing electric field control in the image forming apparatus according to the second embodiment. FIG. 4 is a diagram illustrating a relationship between a charging potential and a developing potential in developing electric field control. 9 is a flowchart illustrating a flow of image density control in a modification of the image forming apparatus according to the second embodiment. FIG. 6 is a diagram illustrating a distribution of Cin in an axial direction of a photosensitive drum in image density control.

Next, the present invention will be described in more detail with reference to the drawings and embodiments and specific examples, but the present invention is not limited to these embodiments and specific examples.
In the following description using the drawings, it should be noted that the drawings are schematic and ratios of respective dimensions and the like are different from actual ones. Illustrations other than members are omitted as appropriate.
In order to facilitate understanding of the following description, in the drawings, the front-back direction is defined as an X-axis direction, the left-right direction is defined as a Y-axis direction, and the up-down direction is defined as a Z-axis direction.

(1) Overall Configuration and Operation of Image Forming Apparatus (1.1) Overall Configuration of Image Forming Apparatus FIG. 1 is a schematic cross-sectional view showing an example of a schematic configuration of an image forming apparatus 1 according to the present embodiment.
The image forming apparatus 1 includes an image forming unit 10, a sheet feeding device 20 mounted at one end of the image forming unit 10, and a sheet discharging unit that is provided at the other end of the image forming unit 10 and discharges printed sheets. The image processing apparatus includes a unit 30, an operation display unit 40, and an image processing unit 50 that generates image information from print information transmitted from a higher-level device.

  The image forming unit 10 includes a system control device 11 (not shown), an exposure device 12, a photoconductor unit 13, a developing device 14, a transfer device 15, a sheet transport device 16a, 16b, 16c, a fixing device 17, and a drive device 18 (not shown). The image information received from the image processing unit 50 is formed as a toner image on a sheet fed from the sheet feeding device 20.

  The paper feed device 20 supplies paper to the image forming unit 10. That is, a plurality of sheet stacking units for storing sheets P of different types (for example, material, thickness, sheet size, and grain size) are provided, and sheets fed from any one of the plurality of sheet stacking units are provided. It is configured to supply to the image forming unit 10.

  The paper discharge unit 30 discharges the paper on which the image has been output by the image forming unit 10. For this purpose, the paper discharge unit 30 includes a paper discharge storage unit into which the paper P after image output is discharged. Note that the paper discharge unit 30 may have a function of performing post-processing such as cutting and stapling (staple binding) on a sheet bundle output from the image forming unit 10.

  The operation display unit 40 is used for inputting various settings and instructions and displaying information. That is, it corresponds to a so-called user interface, and is specifically configured by combining a liquid crystal display panel, various operation buttons, a touch panel, and the like.

(1.2) Configuration and Operation of Image Forming Unit In the image forming apparatus 1 having such a configuration, the sheet stacking device designated for each print job in the print job among the sheet feeding devices 20 in accordance with the image forming timing. The paper fed from the copying section is sent to the image forming section 10.

  Each of the photoconductor units 13 is provided below the exposure device 12 in parallel, and includes a photoconductor drum 31 as an image holder that is driven to rotate. Along with the rotation direction of the photosensitive drum 31, a charging device 32 as a charging device, an exposure device 12 as an exposure device, a developing device 14 as a developing device, a primary transfer roller 52, a cleaning device 33, and a charge removing device 34 (FIG. 2) See).

The developing device 14 has a developing housing 41 in which a developer is stored. A developing roller 42 is disposed in the developing housing 41 so as to face the photosensitive drum 31. A trimmer TM (see FIG. 2) for regulating the layer thickness of the developer is disposed close to the developing roller 42. Have been.
Each of the developing devices 14 is configured in substantially the same manner except for the developer housed in the developing housing 41, and each of the developing devices 14 forms a yellow (Y), magenta (M), cyan (C), and black (K) toner image. Form.

  A replaceable toner cartridge T containing a toner (toner including a carrier) and a guide for inserting and removing the toner cartridge T are provided above the developing device 14, and the toner is supplied from each toner cartridge T to the developing device 14. The toner supply device 100 is provided.

  The surface of the rotating photosensitive drum 31 is charged by the charging device 32, and an electrostatic latent image is formed by the latent image forming light L1 (see FIG. 2) emitted from the exposure device 12. The electrostatic latent image formed on the photosensitive drum 31 is developed by the developing roller 42 as a toner image.

The transfer device 15 includes an intermediate transfer belt 51 on which each color toner image formed on the photosensitive drum 31 of each photosensitive unit 13 is multiplex-transferred, and an intermediate transfer belt for transferring each color toner image formed on each photosensitive unit 13. A primary transfer roller 52 that sequentially transfers (primary transfer) to the image transfer belt 51, and a secondary transfer belt 53 that collectively transfers (secondarily transfers) the color toner images superimposed and transferred on the intermediate transfer belt 51 to a sheet. I have.
The secondary transfer belt 53 is stretched by a secondary transfer roller 54 and a peeling roller 55, and is sandwiched between a backup roller 65 and a secondary transfer roller 54 disposed on the back side of the intermediate transfer belt 51, and the secondary transfer is performed. A part TR is formed.

  Each color toner image formed on the photoconductor drum 31 of each photoconductor unit 13 is intermediately transferred by a primary transfer roller 52 to which a predetermined transfer voltage is applied from a power supply or the like (not shown) controlled by the system controller 11. Electrostatic transfer (primary transfer) is sequentially performed on the belt 51 to form a superimposed toner image in which toners of the respective colors are superimposed.

  The superimposed toner image on the intermediate transfer belt 51 is conveyed to the secondary transfer section TR on which the secondary transfer belt 53 is disposed as the intermediate transfer belt 51 moves. When the superimposed toner image is conveyed to the secondary transfer unit TR, the paper P is supplied from the paper feeding device 20 to the secondary transfer unit TR at the same timing. Then, a predetermined transfer voltage is applied from a power supply device or the like controlled by the system control device 11 to the backup roller 65 facing the secondary transfer roller 54 via the secondary transfer belt 53, and the intermediate transfer belt The multiple toner images on 51 are collectively transferred.

  The residual toner on the surface of the photosensitive drum 31 is removed by the cleaning device 33 and collected in a waste toner storage unit (not shown). The surface of the photosensitive drum 31 from which the residual toner has been removed is neutralized by the neutralization device 34 and then recharged by the charging device 32.

The fixing device 17 includes an endless fixing belt 17a that rotates in one direction, and a pressure roller 17b that contacts the peripheral surface of the fixing belt 17a and rotates in one direction, and presses the fixing belt 17a with the pressure roller 17b. A nip portion (fixing region) is formed by the region.
The sheet P to which the toner image has been transferred in the transfer device 15 is conveyed to the fixing device 17 via the sheet conveying device 16a in a state where the toner image has not been fixed. The paper P conveyed to the fixing device 17 is fixed with a toner image by the action of heating and pressing by a pair of fixing belts 17a and pressure rollers 17b.

The sheet on which the fixing has been completed is sent to the sheet discharging unit 30 via the sheet conveying device 16b.
When an image is to be output on both sides of the sheet, the sheet is turned over by the sheet conveying device 16c and sent again to the secondary transfer unit TR in the image forming unit 10. Then, after the transfer of the toner image and the fixing of the transferred image are performed, the toner image is sent to the paper discharge unit 30. The sheet P sent to the sheet discharge unit 30 is subjected to post-processing such as cutting and stapling (staple binding) as necessary, and then discharged to the sheet discharge storage unit.

(2) Configuration and Operation of Principal Parts FIG. 2 is a schematic vertical cross-sectional view showing the configuration of the main parts of the image forming unit 10, and FIG. 3 is a view illustrating the transport of the developer in the developing device 14. FIG. 4 is a schematic cross-sectional view developed in a horizontal direction along the line ABC in FIG. 2. FIG. 4 shows a charging potential VH and an exposure portion potential VL in the photosensitive drum 31 and an AC superimposed bias in the developing device 14. FIG. 5 is a functional block diagram illustrating a functional configuration of the image forming unit 10, and FIG. 6 is a schematic diagram illustrating a distribution of a TC value of a developer in a developer storage unit 41 </ b> B of the developing device 14. FIG.
Hereinafter, the configuration and operation of the main part of the image forming unit 10 will be described with reference to the drawings.

(2.1) Charging Device The charging device 32 is replaceably disposed downstream of the cleaning device 33 with respect to the rotation direction of the photosensitive drum 31 (the direction of arrow R in FIG. 2).
As shown in FIG. 2, the charging device 32 includes a shield case 32A having an open side on the photosensitive drum 31 side. A constant voltage (for example, -700 V) is applied to the shield case 32A.

  In the shield case 32A, corona wires 32B are stretched one by one (two in total), and these corona wires 32B are connected to a high-voltage power supply (not shown) so that the current to the corona wires 32B is constant. Constant current control is performed so as to be a current. As a result, the corona wire 32 </ b> B generates a negative charge and supplies a corona ion current to the photosensitive drum 31.

On the opening side of the shield case 32A, a grid electrode 32E is arranged between the corona wire 32B and the photosensitive drum 31 in the longitudinal direction of the shield case 32A. The grid electrode 32E is arranged so that the distance from the photoconductor drum 31 is constant, and a constant voltage equal to a charging set potential of the photoconductor drum 31 (a preset charging potential VH before exposure) is applied. .
The charging device 32 configured as described above charges the surface of the photosensitive drum 31 to a predetermined charging potential VH by corona discharge of the corona wire 32B.

(2.2) Developing Device The developing device 14 includes a developing housing 41 that stores the developer, a developing roller 42 that is arranged to face the photosensitive drum 31, a stirring auger 43 that conveys the developer while stirring, a developing process. A supply auger 44 for supplying the developer to the roller 42 is provided.

  The developing roller 42 has a magnet inside, and sends the developer from the developing housing 41 to a developing position facing the photosensitive drum 31 by attracting and rotating the developer by a magnetic force on the surface. At the developing position, the electrostatic latent image formed on the surface of the photosensitive drum 31 is developed, and the developer after the development returns to the developing housing 41 by the rotation of the developing roller 42.

FIG. 3 is a schematic cross-sectional view developed in a horizontal direction along the line ABC in FIG. 2 to explain the transport (movement) of the developer in the developing device 14.
In the developing housing 41, a partition wall 41a is provided upright between the stirring auger 43 and the supply auger 44, and the developing housing 41 is partitioned into two developer accommodating portions 41A and 41B, and both ends in the longitudinal direction of the partition wall 41a. The portions are formed with openings 45 and 46, respectively.

The stirring auger 43 and the supply auger 44 include spiral blades 43b around rotation axes 43a, 44a.
A developer 44b is formed and receives a rotational force from a driving source (not shown) to rotate along the inner walls of the developer accommodating portions 41A and 41B, thereby causing the developer to move in a predetermined direction in the developer accommodating portions 41A and 41B. Transport.
Specifically, the stirring auger 43 conveys the developer in the developer accommodating portion 41A in the direction of the arrow (-Y) while agitating the developer, and the supply auger 44 agitates the developer in the developer accommodating portion 41B with the arrow. It is transported in the (Y) direction. The developer transported in the arrow (-Y) direction moves from the opening 45 to the developer accommodating portion 41B, and the developer transported in the arrow (Y) direction moves from the opening 45 to the developer accommodating portion 41A. .
Thus, the developer in the developing housing 41 circulates while being stirred by the two stirring augers 43 and the supply auger 44. The toner in the developer is charged by such stirring of the developer.

  A receiving port 47 (see FIG. 5) for receiving toner supplied from a toner supply device 100 driven by a dispense motor M (see FIG. 5) is provided on an upper surface portion on one end side (Y direction: rear side of the apparatus) of the developing housing 41. 3 is schematically shown to explain the function). The toner received by the developing device 14 at the receiving port 47 is transported by the stirring auger 43 and moves to the developer accommodating portion 41A of the developing housing 41 to be mixed with the developer.

  The toner replenished from the toner supply device 100 through the receiving port 47 is agitated by the agitation auger 43 from the back side (IN side: described in the Y direction and the subsequent IN side) to the front side (OUT side: in the −Y direction and thereafter). OUT side) and is moved to the supply auger 44 on the near side (OUT side: -Y direction). Then, the toner supplied from the supply auger 44 is supplied to the developing roller 42.

  The developing device 14 is provided with an ATC sensor SR that measures a ratio (TC) of the developer to the carrier of the developer circulating in the developing housing 41. In the image forming apparatus 1, the TC value of the developer is maintained at a predetermined value by the control unit instructing toner supply from the toner cartridge T based on the value measured by the ATC sensor SR.

  In the present embodiment, since the toner is supplied to the developing roller 42 from the OUT side toward the IN side, the toner supply amount is reduced by the time the toner reaches the IN side. The ATC sensor SR is provided on the OUT side of the agitation auger 43 in order to perform the above control.

  In addition, a discharge port 48 is provided on a lower surface portion on one end side (Y direction: rear side of the apparatus) of the developing housing 41. Between the developing housing 41 and the discharge port 48, there is provided a reverse spiral blade 44c in which the direction of the spiral is reversed with respect to the spiral blade 44b at another location. Most of the developer conveyed in the direction of the arrow (Y) is guided to the opening 46 by the reverse spiral blade 44c and moves to the developer accommodating portion 41A, but a part of the developer is transferred to the reverse spiral blade 44c. And is discharged out of the developing device 14 from a discharge port 48 (schematically shown in FIG. 3 for explaining the function).

(2.3) Static elimination device The static elimination device 34 irradiates light to the area of the photosensitive drum 31 after the remaining toner has been removed by the cleaning device 33, and the photosensitive drum 31 emits light from the static elimination device 34. The electricity is removed by irradiation.

The static eliminator 34 is, for example, an LED array including a large number of LEDs (Light Emitted Diodes), and emits light at a predetermined emission angle. The light emitted from the LED array irradiates the photosensitive drum 31 as shown by an arrow L2 in FIG.
In this manner, the photosensitive drum 31 is irradiated with light and discharged at any point in the rotation axis direction.

(2.4) Development Potential Control The developing roller 42 is supplied with an AC developing bias Vdv-AC containing an AC component superimposed on a DC developing bias Vdv-DC containing a DC component. Here, the DC developing bias Vdv-DC is for moving toner from the developing roller 42 to the photosensitive drum 31, and the AC developing bias Vdv-AC is a photosensitive drum from the developing roller 42 by the DC developing bias Vdv-DC. This is for promoting the movement of the toner to the body drum 31 by vibrating the toner.

Here, the charging potential VH is determined by the current (constant current control) supplied to the corona wire 32B and the magnitude of the grid voltage applied to the grid electrode 32E, and the exposure portion potential VL is determined by the charging potential and the exposure device 12. It depends on the exposure energy.
The development potential VB is determined by the magnitude of the DC development bias Vdv-DC. In FIG. 5, the magnitude of the AC developing bias Vdv-AC is represented by a peak-to-peak value since the magnitude is an alternating current.

In the present embodiment, as shown in FIG. 5, the charging potential VH and the exposed portion potential VL are both negative, but the magnitude of the exposed portion potential VL is smaller in absolute value than the charging potential VH. (| VL | <| VH |). The value of the developing potential VB, that is, the value of the DC developing bias Vdv-DC is negative, and its absolute value is set to a magnitude between the charging potential VH and the exposure portion potential VL (| VL | <| VB | <| VH |).
When the charging potential VH, the exposure portion potential VL, and the developing potential VB have such a magnitude relationship, the toner (negatively charged) on the developing roller 42 passing through the developing area is charged on the photosensitive drum 31. To the exposed portion potential VL (image portion) which becomes relatively positive potential (flying) (Vdv), while the charging potential VH (background portion) becomes relatively negative potential on the photosensitive drum 31. Becomes difficult to move (fly) (Vc = VH-VB: cleaning electric field).

(2.4) Cleaning Electric Field Control As shown as a functional block diagram in FIG. 5, an exposure device 12, a photoconductor unit 13, a developing device 14, a toner supply device 100, which are main components of the image forming unit 10 in the present embodiment, The static eliminator 34 is controlled by the system controller 11 to predetermined image forming conditions (parameters) via the exposure controller 112, the charging controller 113, the development controller 114, the toner supply controller 145, and the light amount controller 134, respectively. The print control is performed by setting.

  The system controller 11 controls the cleaning electric field (Vc = VH−VB) formed by the charging potential VH of the photosensitive drum 31 and the developing potential VB, which is the developing bias potential, in the axial direction (Y direction) of the photosensitive drum 31. It functions as changing means for changing the size.

  The toner supply amount calculation unit 110 as an example of a calculation unit that calculates the toner supply amount is supplied to the developing device 14 based on the toner supply time per unit time of the dispense motor M that drives the toner supply device 100. Calculate the toner supply amount. The system controller 11 changes the cleaning electric field (Vc) based on the toner supply amount calculated by the toner supply amount calculator 110.

FIG. 6 schematically shows the distribution of the TC value of the developer in the developer accommodating section 41B which transports the developer in the developing device 14 while supplying the developer to the developing roller 42 by the supply auger 44.
As shown in FIG. 6, the toner supplied to the developing device 14 is transported from the IN side to the OUT side while being stirred by the stirring auger 43 in the developer accommodating portion 41A, but the amount of the supplied toner sharply increases. In this case, even if the toner is agitated by the agitating auger 43, the toner charge is not sufficiently increased, and a fixed area in the axial direction (Y direction) of the developing roller 42 with the opening 45 on the OUT side as a base end (see W in FIG. 6). In this case, image fogging may occur.
Examples of the case where the replenishment toner amount rapidly increases include a case where an image having a high image density is continuously printed, a case where the toner cartridge T is replaced and a toner recovery operation is started, and the like.

FIG. 7 is a flowchart showing the flow of the cleaning electric field control in the image forming apparatus 1, and FIG. 8 is a diagram showing the relationship between the charging potential and the developing potential in the cleaning electric field control.
In the image forming apparatus 1 according to the present embodiment, image formation is performed by controlling the cleaning electric field according to the operation flow shown in FIG.
When the image forming apparatus 1 receives a print job (S101), the toner supply amount calculation unit 110 calculates a toner supply time (rotation time) A1 of the dispense motor M per unit time (S102). Then, the system controller 11 determines whether the toner supply time (rotation time) A1 per unit time is longer than a predetermined threshold value Ath (S103). Here, the threshold value Ath is stored in a threshold value storage unit (not shown) of the system control device 11.

  When the toner supply time A1 per unit time of the dispense motor M exceeds the threshold value Ath (S103: Yes), the axial light amount distribution of the charge removing light L2 of the charge removing device 34 is determined (S104). Specifically, as shown in FIG. 8A, in the axial direction (Y direction) of the photosensitive drum 31, the rotation axle direction (Y direction) of the supply auger 44 in the developer accommodating portion 41 </ b> B from the opening 45 of the developing device 14. 8A, the amount of static elimination light L2 is made weaker than in a normal state in which the toner supply time A1 does not exceed the threshold value Ath over a predetermined area (see W in FIG. 8A). Note that the light amount of the charge removing light L2 is in a range where the charging potential VH of the photosensitive drum 31 is excessively increased and the cleaning electric field Vc is not expanded more than necessary (a range in which the developer does not adhere to the surface of the photosensitive drum 31). It is determined.

  Then, the light amount control unit 134 calculates the light emission amount of each light source element (LED) so as to obtain the determined light amount distribution in the axial direction of the static elimination device 34 (S105). Is changed to the calculated light amount to form an image (S106). As a result, as shown in FIG. 8B, in the axial direction of the photosensitive drum 31, a fixed area (Y direction) from the opening 45 of the developing device 14 in the rotation axis direction (Y direction) of the supply auger 44 in the developer container 41 </ b> B. The cleaning electric field Vc is enlarged over W (see W in FIG. 8B), and image fogging can be suppressed.

"Modification 1"
FIG. 9 is a flowchart illustrating a flow of the cleaning electric field control in the image forming apparatus 1 according to the first modification.
In the image forming apparatus 1 according to the first modification, the toner supply amount calculation unit 110 calculates the toner supply amount based on the number of pixels per unit area of the electrostatic latent image formed on the photosensitive drum 31.

When the image forming apparatus 1 receives a print job (S201), the toner supply amount calculation unit 110 calculates the number of pixels P1 per unit area of the image of the print job (S202). The pixel number P1 can be obtained from the result of the image processing in the image processing unit 50.
Then, the system control device 11 determines whether or not the number of pixels P1 per unit area is larger than a predetermined threshold Pth (S203). Here, the threshold value Pth is stored in a threshold value storage unit (not shown) of the system control device 11.

When the number of pixels P1 per unit area of the image of the print job exceeds the threshold value Pth (S203: Yes), the axial light amount distribution of the static elimination light L2 of the static eliminator 34 is determined (S204).
Then, the light amount control unit 134 calculates the light emission amount of each light source element (LED) so as to obtain the determined light amount distribution in the axial direction of the static eliminator 34 (S205). Is changed to the calculated light amount to form an image (S206). As a result, as shown in FIG. 8B, in the axial direction of the photosensitive drum 31, from the opening 45 of the developing device 14 to a certain area in the rotation axis direction (Y direction) of the supply auger 44 in the developer accommodating portion 41 </ b> B. Accordingly, the cleaning electric field Vc is enlarged, and image fogging can be suppressed.

"Modification 2"
FIG. 10 is a flowchart illustrating a flow of the cleaning electric field control in the image forming apparatus 1 according to the second modification.
In the image forming apparatus 1 according to the second modification, the toner supply amount calculation unit 110 detects the toner recovery operation for the developing device 14 and calculates the toner supply amount.

When the image forming apparatus 1 receives a print job (S301), the toner supply amount calculation unit 110 detects whether or not a toner recovery operation has been performed (S302).
In the toner recovery operation, when the toner cartridge T becomes near-end or empty and the toner cartridge T is replaced, the TC value in the developing device 14 is detected by the ATC sensor SR, and the necessary toner supply amount is calculated. This is an operation of replenishing toner from the toner cartridge T replaced with the developing device 14 based on the toner replenishing amount, and driving and stirring the developing device 14. When the toner recovery operation is started, the toner is rapidly replenished into the developing device 14, and even if the toner is stirred by the stirring auger 43, the toner charge is not sufficiently increased. Image fog may occur in a certain area in the axial direction (Y direction).

If it is detected that the toner recovery operation has been performed (S302: Yes), the axial light amount distribution of the neutralization light L2 of the neutralization device 34 is determined (S303).
Then, the light amount control unit 134 calculates the light emission amount of each light source element (LED) so as to obtain the determined light amount distribution in the axial direction of the static elimination device 34 (S304). The image forming is performed by changing the static elimination light to the calculated light amount (S305). As a result, as shown in FIG. 8B, in the axial direction of the photosensitive drum 31, the developer abutment unit 41 </ b> B moves from the opening 45 to a certain area in the rotation axis direction (Y direction) of the supply auger 44 in the developer accommodating unit 41 </ b> B. Accordingly, the cleaning electric field Vc is enlarged, and image fogging can be suppressed.

"Modification 3"
FIG. 11 is a flowchart showing the flow of the cleaning electric field control in the image forming apparatus 1 according to Modification 3, and FIG. 12 is a diagram showing the relationship between the charging potential and the developing potential in the cleaning electric field control.
In the image forming apparatus 1 according to the third modification, the toner supply amount calculation unit 110 supplies toner to the developing device 14 based on the toner supply time per unit time of the dispense motor M that drives the toner supply device 100. Calculate the amount. Based on the toner supply amount calculated by the toner supply amount calculation unit 110, the system control device 11 increases the charging potential VH of the background portion as compared with a normal state where the toner supply amount does not exceed a predetermined threshold. To increase the cleaning electric field Vc.

  When the image forming apparatus 1 receives a print job (S401), the toner supply amount calculation unit 110 calculates a toner supply time (rotation time) A1 of the dispense motor M per unit time (S402). Then, the system controller 11 determines whether the toner supply time (rotation time) A1 per unit time is longer than a predetermined threshold value Ath (S403).

  When the toner supply time A1 per unit time of the dispense motor M exceeds the threshold value Ath (S403: Yes), first, the normal charging potential (VH0) of the photosensitive drum 31 is uniformly increased (S404). Specifically, as shown in FIG. 12A, the charging control unit 113 raises the bias voltage of the grid electrode 32E of the charging device 32 to charge the photosensitive drum 31 by the charging device 32 at the normal time ( VH0) is uniformly increased (VH1). The bias voltage of the grid electrode 32E is in a range where the charging potential VH of the photosensitive drum 31 is excessively increased and the cleaning electric field Vc is not expanded more than necessary (a range where the developer does not adhere to the surface of the photosensitive drum 31). Is determined.

  Then, the exposure control unit 112 determines an exposure amount distribution for the background portion of the exposure device 12 (S405). Specifically, as shown in FIG. 12A, in the axial direction (Y direction) of the photosensitive drum 31, the rotational axis direction (Y) of the supply auger 44 in the developer accommodating portion 41 </ b> B from the opening 45 of the developing device 14. The exposure amount distribution is determined such that the exposure device 12 performs exposure with a weak exposure amount on an area serving as a background portion of an image except for an area (see W in FIG. 12A) over a certain area in the direction (FIG. 12A). (See FIG. 12 (a)).

  Then, by changing the exposure amount of the exposure device 12 with respect to the background portion to the exposure amount distribution determined in step S405 and performing image formation (S406), as shown in FIG. In the axial direction, the cleaning electric field Vc is expanded from the opening 45 of the developing device 14 to a certain region (see W in FIG. 12B) in the rotation axis direction (Y direction) of the supply auger 44 in the developer accommodating portion 41B. Image fog can be suppressed.

  In the third modification, the example in which the toner supply amount calculation unit 110 calculates the toner supply amount to be supplied to the developing device 14 based on the toner supply time per unit time of the dispense motor M has been described. The calculation of the amount may be performed based on the number of pixels per unit area of the electrostatic latent image formed on the photosensitive drum 31 as in the first modification. Further, similarly to the second modification, the toner replenishment amount may be calculated by detecting the toner recovery operation for the developing device 14.

"Second embodiment"
The image forming apparatus 1A according to the present embodiment has the same configuration as the image forming apparatus 1 according to the first embodiment, and is a main part of the image forming unit 10 as shown in a functional block diagram in FIG. The system controller 11 controls the exposure device 12, the photoconductor unit 13, the developing device 14, and the toner supply device 100 via the exposure controller 112, the charging controller 113, the development controller 114, and the toner supply controller 145, respectively. The print control is performed by setting a predetermined image forming condition (parameter).

  In the image forming apparatus 1A, the toner supplied to the developing device 14 is transported from the IN side to the OUT side while being stirred by the stirring auger 43 in the developer accommodating section 41A, but the amount of the supplied toner sharply increases. In this case, even when the toner is stirred by the stirring auger 43, the toner charge does not sufficiently rise, and the developing characteristic changes in a fixed region in the axial direction (Y direction) of the developing roller 42 with the opening 45 on the OUT side as a base end. There is a possibility that a density difference (in-plane uniformity) occurs in the axial direction (left and right).

  In the image forming apparatus 1A according to the present embodiment, the system controller 11 changes the developing electric field (Vdv) based on the toner supply amount calculated by the toner supply amount calculation unit 110. That is, the system controller 11 controls the photosensitive drum 31 of the developing electric field Vdv (Vdv = VB-VL: see FIG. 5) formed by the exposure portion potential VL of the photosensitive drum 31 and the developing potential VB which is the developing bias potential. , The density difference (in-plane uniformity) in the axial direction (left and right) is suppressed.

FIG. 13 is a flowchart showing the flow of the developing electric field control in the image forming apparatus 1A according to the present embodiment, and FIG. 14 is a diagram showing the relationship between the charging potential and the developing potential in the developing electric field control.
When the image forming apparatus 1A receives a print job (S501), the toner supply amount calculation unit 110 calculates a toner supply time (rotation time) A1 per unit time of the dispense motor M (S502). Then, the system controller 11 determines whether the toner supply time (rotation time) A1 per unit time is longer than a predetermined threshold value Ath (S503).

If the toner supply time A1 per unit time of the dispense motor M exceeds the threshold value Ath (S503: Yes), the axial exposure amount distribution of the exposure device 12 is determined (S504).
Specifically, as shown in FIG. 14, in the axial direction (Y direction) of the photoconductor drum 31, the opening 45 of the developing device 14 extends in the rotation axis direction (Y direction) of the supply auger 44 in the developer accommodating portion 41 </ b> B. Over a certain region (see W in FIG. 14), the image portion exposure amount L1 of the exposure device 12 is made smaller than in a normal case where the toner supply time A1 does not exceed the threshold value Ath.

  The exposure control unit 112 changes the exposure amount of the exposure device 12 so as to obtain the determined exposure amount distribution of the exposure device 12 in the axial direction, and performs image formation (S505). As a result, as shown in FIG. 14, in the axial direction of the photosensitive drum 31, a certain area (in the Y direction) from the opening 45 of the developing device 14 in the rotation axis direction (Y direction) of the supply auger 44 in the developer accommodating portion 41B in the axial direction. W), the developing electric field Vdv becomes smaller, and the difference in left and right density can be suppressed.

"Modification"
FIG. 15 is a flowchart illustrating a flow of image density control in the image forming apparatus 1A according to the modification, and FIG. 16 is a diagram illustrating an axial distribution of Cin of the photosensitive drum 31 in the image density control.
When the image forming apparatus 1A receives a print job (S601), the toner supply amount calculation unit 110 calculates a toner supply time (rotation time) A1 per unit time of the dispense motor M (S602). Then, the system controller 11 determines whether the toner supply time (rotation time) A1 per unit time is longer than a predetermined threshold value Ath (S603).

If the toner supply time A1 per unit time of the dispense motor M exceeds the threshold value Ath (S603: Yes), the axial direction of the photosensitive drum 31 at the area gradation ratio Cin of the image to be the exposed portion of the photosensitive drum 31 The distribution is determined (S604).
Specifically, as shown in FIG. 16, in the axial direction (Y direction) of the photosensitive drum 31, the opening 45 of the developing device 14 extends in the rotation axis direction (Y direction) of the supply auger 44 in the developer accommodating portion 41 </ b> B. Over a certain area (see W in FIG. 14), Cin of the image is made lower than the normal time when the toner supply time A1 does not exceed the threshold value Ath.

  Then, the image processing unit 50 changes the Cin so as to obtain the axial Cin distribution of the determined image and forms an image (S605). Thereby, in the axial direction of the photosensitive drum 31, the developing property extends from the opening 45 of the developing device 14 to a certain region (see W in FIG. 16) in the rotation axis direction (Y direction) of the supply auger 44 in the developer accommodating portion 41 </ b> B. And the density difference between the right and left sides can be suppressed.

  In the present embodiment, an example has been described in which the toner supply amount calculation unit 110 calculates the toner supply amount to be supplied to the developing device 14 based on the toner supply time per unit time of the dispense motor M. The amount may be calculated based on the number of pixels per unit area of the electrostatic latent image formed on the photosensitive drum 31. The amount of toner replenishment is calculated by detecting a toner recovery operation for the developing device 14. Is also good.

1, 1A Image forming apparatus 10 Image forming section 11 System control apparatus 110 Toner supply amount calculating section 12 Exposure apparatus 13 Photoconductor unit 31 Photosensitive Body drum 32 Charging device 33 Cleaning device 34 Static eliminator 14 Developing device 41 Developing housing 41A, 41B Developing agent container 42 Developing roller 43 Agitating auger 44 supply auger 15 transfer device 16 paper transport device 17 fixing device 20 paper supply device 30 discharge unit 40 operation display unit 50 image processing unit 100 toner supply device

Claims (11)

Charging means for charging the image carrier to a predetermined charging potential,
Exposure means for exposing the image carrier charged by the charging means to form an electrostatic latent image,
Developing means comprising a developing roll for holding a developer containing toner on the surface thereof and developing the electrostatic latent image with the toner;
Calculating means for calculating a replenishment amount of the toner supplied to the developing means;
When the replenishment amount of the toner calculated by the calculation means exceeds a predetermined threshold, a cleaning electric field formed by a background potential of the electrostatic latent image and a development bias potential of the image holding member is used. Changing means for changing the size in the axial direction,
An image forming apparatus comprising: The changing unit expands the cleaning electric field over a predetermined area from a supply position of the toner supplied to the developing unit to the developing roll in an axial direction of the image holding member.
The image forming apparatus according to claim 1, wherein: A developing unit for irradiating the image carrier with static elimination light to eliminate the charge on the image carrier; and before the charging of the image carrier by the charging unit, the developing roll of the toner supplied to the developing unit. From a supply position to a predetermined area, the discharge light is weakened compared to a normal state in which the replenishment amount of the toner does not exceed a predetermined threshold, and the post-discharge potential of the image holding member is increased.
The image forming apparatus according to claim 2, wherein: The changing unit may set the background portion potential to a predetermined threshold from a supply position of the toner supplied to the developing unit of the image holding member to the developing roll from a supply position to a predetermined region. Expand the cleaning electric field by making it higher than normal not to exceed,
The image forming apparatus according to claim 2, wherein: Exposing the image holding member to a region serving as a background portion of an image on the image holding member excluding a region extending from a supply position of the toner supplied to the developing unit to the developing roll to a predetermined region from the supply position by the exposure unit Performing, the background portion potential is increased by making the toner supply amount smaller than a normal time when the toner supply amount does not exceed a predetermined threshold value,
The image forming apparatus according to claim 4, wherein: Charging means for charging the image carrier to a predetermined charging potential,
Exposure means for exposing the image carrier charged by the charging means to form an electrostatic latent image,
Developing means comprising a developing roll for holding a developer containing toner on the surface thereof and developing the electrostatic latent image with the toner;
Calculating means for calculating a replenishment amount of the toner supplied to the developing means;
When the replenishment amount of the toner calculated by the calculation means exceeds a predetermined threshold, a developing electric field formed by an exposure portion potential of the electrostatic latent image and a developing bias potential of the image holding member is used. Changing means for changing the size in the axial direction,
An image forming apparatus comprising: The changing unit may be configured such that the amount of exposure of the toner supplied to the developing unit of the image holding member from the supply position to the developing roll from a supply position to the developing roll is predetermined by the amount of exposure by the exposing unit. Increase the exposed portion potential to be smaller than the normal time does not exceed the threshold,
The image forming apparatus according to claim 6, wherein: The changing unit includes an area gradation ratio Cin of an image to be an exposure unit of the electrostatic latent image from a supply position of the toner supplied to the developing unit of the image holding member to the developing roll from a predetermined position. Lower than the normal time when the toner supply amount does not exceed a predetermined threshold,
The image forming apparatus according to claim 6, wherein: The calculating unit calculates the toner supply amount based on the number of rotations per unit time of a toner supply unit that supplies the toner to the developing unit.
The image forming apparatus according to claim 1, wherein: The calculation unit calculates the toner supply amount based on the number of pixels per unit area of the electrostatic latent image formed on the image holding member,
The image forming apparatus according to claim 1, wherein: The calculating means calculates a toner replenishment amount by detecting a toner recovery operation for the developing means,
The image forming apparatus according to claim 1, wherein:

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