JP2007264398A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent image quality deterioration even when many images of a low printing rate are formed, and also, to improve productivity. <P>SOLUTION: The image forming apparatus includes a plurality of units comprising a photoreceptor drum 1, a corona electrifier 2 for electrifying the surface of the photoreceptor drum 1 so as to form an electrostatic latent image, an exposure means 3, a developing unit 4, a primary transfer roller 53 for transferring the developed electrostatic latent image to an intermediate transfer belt 51, and a cleaner 6 for removing developer and foreign substances left on the photoreceptor drum 1. Regarding the image forming apparatus also including a secondary transfer means for transferring the image to a recording material and a control means, the control means controls the developing unit 4 to discharge the developer onto the photoreceptor drum 1, and when the discharged developer quantity reaches a previously set value, the developer is discharged from the developing unit 4 in response to the discharge control by the control means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and is particularly suitable for application to an electrostatic copying machine, a printer, or the like that forms an image based on digital signalized image information.

  2. Description of the Related Art Conventionally, an image forming apparatus including a developing unit that develops an electrostatic latent image formed on the surface of a photoreceptor, which is an image carrier, with toner in a powder developer has been widely put into practical use. As an example, as shown in FIG. 5, there is a full-color electrophotographic image forming apparatus having four photosensitive drums 1 and using an intermediate transfer belt 51 as an intermediate transfer member.

  In this image forming apparatus, a corona charger 2 as a charging unit, an exposure device 3, a developing unit 4 as a developing unit, an intermediate transfer unit 5 and a cleaner 6 as a cleaning unit are provided around the photosensitive drum 1. Four process units are provided. Since each process unit has the same configuration except for the toner to be used, the process unit Pa will be used as an example in the description below, and the symbol a and the like will be omitted.

  First, after the surface of the photosensitive drum 1 is uniformly charged by the corona charger 2, an electrostatic latent image is formed on the surface by the exposure device 3. The electrostatic latent image formed on the photosensitive drum 1 in each process unit is developed by a developer (toner) (not shown) as an image of each color of yellow, magenta, cyan, and black in the developing unit 4. Visualized. The toner image is primarily transferred onto the intermediate transfer belt 51 at the primary transfer portion N1. The intermediate transfer member 51 is configured to slide and pass while in contact with the photosensitive drum 1. The toner image transferred onto the intermediate transfer belt 51 is secondarily transferred to a recording material such as paper at the secondary transfer portion N2.

After the toner image has been transferred, the photosensitive drum 1 is removed by the cleaner 6 to remove deposits such as residual toner. The cleaner 6 includes a cleaning blade 61 and a conveying screw 62. The cleaning blade 61 is in contact with the photosensitive drum 1 by a pressurizing unit (not shown) at a predetermined angle and pressure, and collects residual toner on the surface of the photosensitive drum 1. The photosensitive drum 1 from which the residual toner has been removed by the cleaner 6 returns again to the charging process, and the above-described series of image forming operations is executed.
JP 2001-074433 A

  However, the color image forming apparatus configured as described above has the following problems.

  That is, in the image forming apparatus having the plurality of photosensitive drums described above, when one-point color image formation or single-color image formation is performed, there is an advantage that the same productivity as a full-color image can be obtained. The intermediate transfer belt 51 and the photosensitive drum 1 on which image formation is not performed are in contact with each other even when a monochrome image is formed in the monochrome image formation mode. In this case, local shaving and scratches occur in the primary transfer portion N1, and it is difficult to form a good image. Therefore, in order to prevent this, the photosensitive drum 1 on which image formation is not performed is also rotationally driven in synchronization with the driving of the intermediate transfer belt 51.

The cleaning blade 61 is configured to clean the surface of the photosensitive drum 1 by sliding contact with the surface of the photosensitive drum 1. The toner and external additives remaining on the surface of the photosensitive drum 1 after the first transfer process have an important role in maintaining lubricity between the cleaning blade 61 and the surface of the photosensitive drum 1. For example, external additives that improve lubricity, such as titanium oxide or alumina fine powder, and external materials that improve abrasiveness, such as strontium titanate powder, cerium oxide powder, or calcium titanate powder. When an additive is used, the effect of this external additive is great.

  That is, the external additive and the toner cause the friction coefficient of the surface of the photoreceptor to be too low, and the components in the toner adhere to the surface of the photoreceptor drum 1 and cause image defects (cleaning defects). Further, the external additive prevents the friction coefficient of the surface of the photosensitive member from being increased excessively and prevents the cleaning blade 61 from slipping.

  Accordingly, when the photosensitive drum on which no image is formed is rotated for a long period of time, the amount of toner or external additive as a lubricant gradually decreases. As a result of the reduction in the amount of toner and external additives, the sliding of the cleaning blade is worsened, and eventually, cleaning failure, blade squealing, and wobbling occur.

  Therefore, conventionally, there is a method in which the photosensitive drum 1 and the developing device 4 are not always driven to rotate even in a process unit as an image forming unit that does not perform image formation. Here, in detail, the developing device 4 has a screw 45s, 46s for agitating and conveying the developer composed of toner and carrier in the developing device 4, and a photosensitive drum 1 carrying the developer. And a developing sleeve 42 to be supplied.

  On the other hand, after a predetermined amount of toner is developed on the photosensitive drum 1, the interval between continuous image formation (paper interval) or image formation is temporarily stopped at a predetermined timing, and this toner is intermediately transferred in the primary transfer portion N1. There is also a method for preventing transfer to the transfer belt. In this case, a bias having a reverse polarity to that at the time of transfer is applied to the transfer member, and the cleaning blade 61 collects the toner (see Patent Document 1).

  Further, in the configuration in which the developing device 4 continues to rotate for a long time in a state where toner is hardly consumed and replenished, the toner is excessively friction-charged (charged up). As a result of this charge-up, the amount of developer applied per unit area on the photosensitive drum 1 decreases. A predetermined amount of developer cannot be supplied due to the decrease in the amount of developer applied.

  Further, the external additive attached to the toner T is peeled off due to the rubbing with the carrier and the regulating blade 44 for a long time on the photosensitive drum 1. This tends to make it difficult to maintain high image quality.

  Certainly, a configuration in which a predetermined amount of toner is consumed and replenished by a predetermined number of image forming sheets can maintain high image quality. However, on the other hand, in image formation with an extremely low image ratio, there is a problem that productivity is significantly reduced.

  Therefore, the object of the present invention is to prevent overcharging of the developer and deterioration of the developer in the developing means, and even when many images with a low printing rate are formed, it is possible to prevent deterioration of image quality and improve productivity. An object of the present invention is to provide an image forming apparatus capable of achieving the above.

In order to achieve the above object, the present invention provides:
Electrostatic image forming means for forming an electrostatic image based on image information composed of pixels on an image carrier;
Developing means for developing the electrostatic image with a developer;
Integrating means for integrating the number of pixels;
Image forming sheet number detecting means for detecting the number of image forming sheets;
Control means for controlling the discharge of the developer from the developing means at a time other than the image forming operation according to the integrated value by the integrating means and the number of detected sheets by the image forming number detecting means;
In an image forming apparatus having
When the number of sheets detected by the image forming sheet number detecting unit is a predetermined number and the integrated value by the integrating unit is equal to or greater than a predetermined value, the control unit determines a predetermined amount from the developing unit. The control of discharging the developer is performed.

  According to the present invention, even when a large number of images with a low printing rate are formed, it is possible to prevent image quality deterioration and improve productivity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings of the following embodiments, the same or corresponding parts are denoted by the same reference numerals. The embodiments described below are illustrative of the present invention and do not limit the scope of the present invention.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. As an image forming apparatus according to the first embodiment, a full color electrophotographic image forming apparatus having four photosensitive drums and using an intermediate transfer member will be described as an example. FIG. 1 shows an image forming apparatus according to the first embodiment.

(Operation of image forming apparatus)
As shown in FIG. 1, each process unit P (PA, Pb, Pc, Pd) that forms an image of each color of yellow, magenta, cyan, and black has a photosensitive drum 1 (1A, 1b, 1c, 1d) are arranged. These photosensitive drums are rotatable in the direction of the arrow. Further, around each photosensitive drum 1 (1a to 1d), a corona charger 2 (2a to 2d) as a primary charging unit, an exposure device 3 (3a to 3d), a developing device 4 (4a to 4d), The cleaners 6 (6a to 6d) are sequentially arranged along the rotation direction of the photosensitive drum 1.

  Hereinafter, the process unit will be described with reference to FIG. Since the four process units have the same configuration, the following description will be made with the symbols a, b, c, and d omitted. Also, each process means that acts on the photosensitive drum 1 in image formation is controlled by a control means (not shown).

  As shown in FIG. 2, the process unit P includes a photosensitive drum 1 as an image carrier that is rotatably supported. The photosensitive drum 1 is basically a cylindrical electrophotographic photosensitive member composed of a conductive substrate 11 such as aluminum and a photoconductive layer 12 formed on the outer periphery thereof. A support shaft is provided at the center parallel to the cylindrical direction of the cylinder, and the photosensitive drum 1 is driven to rotate in the direction of arrow R1 around the support shaft at a process speed (Ps) of, for example, 300 mm / s.

A corona charger 2 is disposed above the photosensitive drum 1. The corona charger 2 includes a wire 21, a grid 22, and a shield member 23. The corona charger 2 is disposed at a distance of 5 mm from the surface of the photosensitive drum 1 and uniformly and uniformly charges the surface of the photosensitive drum 1 with a predetermined polarity and potential.

  Specifically, a current of 1 mA, for example, is passed through the wire 21 by constant current control by a power source (not shown). A voltage of −720 V is applied to the grid 22 by constant voltage control. As a result, the surface of the photosensitive drum 1 is uniformly charged at −700V. An exposure device 3 is disposed on the downstream side of the corona charger 2 along the rotation direction of the photosensitive drum 1.

  The exposure apparatus 3 serving as an electrostatic image forming unit scans while turning on / off a laser beam corresponding to image data, and the surface potential of the irradiated photosensitive drum 1 becomes −150 V, whereby the photosensitive drum 1 is exposed. An electrostatic latent image is formed on the surface.

  Further, the exposure apparatus 3 is connected to a pixel counter 9 as an integration unit provided in an image forming apparatus main body controller (not shown). The pixel counter 9 is configured to measure pixels of image data as image information input to the exposure unit. The pixel counter 9 may be provided in an image forming controller (not shown).

  In addition, the control controller of the image forming apparatus main body is provided with an image forming number detecting means (not shown) that integrates an integrated value of the number of pixels and an image forming number electrically or magnetically.

  The developing device 4 as a developing unit is disposed on the downstream side of the exposure device 3. The developing device 4 has a developing container 41 that contains a two-component developer composed of toner and a carrier (magnetic material). A developing sleeve 42 configured to be rotatable is installed in an opening of the developing container 41 facing the photosensitive drum 1. A magnet roller 43 that holds toner on the developing sleeve 42 is fixed inside the developing sleeve 42. In addition, a regulating blade 44 that regulates the developer carried on the developing sleeve 42 to form a thin developer layer is installed below the developing sleeve 42 of the developing container 41.

  Further, a developing chamber 45 and a stirring chamber 46 are provided inside the developing container 41. The developing chamber 45 and the stirring chamber 46 are provided with screws 45s and 46s for stirring and transporting the developer. Further, a replenishment chamber 47 containing replenishment toner is provided above the developing container 41.

  A developer concentration detecting means 49 is provided on the upstream side in the developer conveyance direction of the opening where toner is supplied to the stirring chamber 46. The developer concentration detecting means 49 is a sensor that detects magnetic permeability.

  When the toner formed on the developer layer, which is a thin layer, is conveyed to the development area facing the photosensitive drum 1, the spikes are generated by the magnetic force of the development main pole located in the development area of the magnet roller 43. Occurs and a magnetic brush is formed.

The surface of the photosensitive drum 1 is rubbed by the magnetic brush, and the developing sleeve 42 is powered by a power source (not shown), for example, a DC voltage of −500 V, for example, and a frequency Vp of 1.2 × 10 ⁵ Hz, for example. -p is applied in an overlapping manner with an AC voltage of 1800V. As a result, the toner attached to the carrier constituting the ears of the magnetic brush adheres to the exposed portion of the electrostatic latent image and is developed to form a toner image on the photosensitive drum 1.

Thus, the toner in the developer is consumed by the development process. As the toner is consumed, new toner corresponding to the amount of consumed toner is replenished from the replenishing chamber 47 by a change in toner density detected by the developer concentration detecting means 49 and the like. As a result, the image density is kept constant.

  A primary transfer roller 53 as a primary transfer unit is disposed below the photosensitive drum 1 on the downstream side of the developing device 4. The primary transfer roller 53 is pressed against the surface of the photosensitive drum 1 with a pressing force of, for example, 9.8 N (1000 gf) through the intermediate transfer belt 51.

  A primary transfer portion N1 is formed between the photosensitive drum 1 and the primary transfer roller 53. In the transfer nip portion, a DC voltage of +1000 V is applied to the transfer roller 53 from a power source (not shown). As a result, the negatively charged toner is transferred from the surface of the photosensitive drum 1 to the surface of the intermediate transfer belt 51.

  Depositors such as residual toner on the photosensitive drum 1 after the toner image is transferred are removed by the cleaner 6. The cleaner 6 includes a cleaning blade 61 and a conveying screw 62. The cleaning blade 61 is brought into contact with the photosensitive drum 1 at an angle of 60 ° from the horizontal, for example, with a pressure of 19.6 N (2000 gf), and collects toner remaining on the surface of the photosensitive drum 1. The photosensitive drum 1 from which the residual toner has been removed by the cleaner 6 returns to the charging process again, and then the series of image forming operations described above are repeated.

  Further, as shown in FIG. 1, intermediate transfer units 5 are disposed below the respective photosensitive drums 1. The intermediate transfer unit 5 includes an intermediate transfer belt 51, transfer rollers 53 (53a, 53b, 53c, 53d), an intermediate transfer belt cleaner 55, and secondary transfer rollers 56, 57.

  The respective color toner images formed on the photosensitive drum 1 (1a, 1b, 1c, 1d) are sequentially transferred onto the intermediate transfer belt 51 as described above. Thereafter, as the intermediate transfer belt 51 rotates, the toner images of the respective colors are conveyed to the secondary transfer portion N2.

  On the other hand, before the toner image is conveyed to the secondary transfer portion N2, the recording material taken out from the feeding cassette is supplied to a conveying roller (none of which is shown) through a pickup roller. Thereafter, the toner image is further conveyed leftward in FIG. 1, and the toner image is transferred onto the recording material S by the secondary transfer bias applied between the secondary transfer rollers 56 and 57 in the secondary transfer portion N2. The transfer residual toner on the intermediate transfer belt 51 is removed and collected by the intermediate transfer belt cleaner 55.

  The recording material is further conveyed, and is pressurized and heated by a fixing means (not shown). As a result, the unfixed toner image on the surface of the recording material is melted and fixed, and a full-color image is formed on the recording material.

  Further, in the toner used in the first embodiment, strontium titanate powder and hydrophobic alumina fine powder are externally added to color toner particles made of polyester resin. The color toner particles have an average particle diameter of 6 μm, for example, the strontium titanate powder has an average length particle diameter of 1 μm, for example, and the hydrophobic alumina fine powder has a length average particle diameter of 0.1 μm. As the carrier, a ferrite carrier having an average particle diameter of 50 μm is used. The toner is negatively charged to −25 μC / mg by rubbing with the carrier.

  In the image forming apparatus configured as described above, when the toner consumption amount for a predetermined number of sheets is low, image formation is temporarily stopped, and a predetermined amount of toner is consumed and replenished.

Specifically, the yellow printing rate is 2.0%, for example, and the magenta printing rate is 1.0%, for example.
An image of a low printing rate pattern having a cyan printing rate of, for example, 2.0% and a black printing rate of, for example, 6.0% is formed on 4500 continuous recording materials using A4 size paper. In addition, when the average printing rate at the 100th sheet is less than 2.0% in terms of A4 size paper, the ejection control is performed so that the average printing rate is 2.0%. That is, as an example, when the printing rate is 1.5%, ejection of 0.5% is performed. The maximum discharge amount corresponds to an average printing rate of 2.0% for 100 sheets of A4 size, that is, a solid image for two sheets of A4 size.

  As a sequence at the time of ejection, image formation is temporarily stopped, and deteriorated toner is ejected. At this time, if the toner discharged to the photosensitive drum 1 is transferred to the intermediate transfer belt 51, the secondary transfer roller 57 is soiled. For this reason, it is desirable to apply a bias having a polarity opposite to that at the time of image formation, specifically, for example, a voltage of −1000 V to the primary transfer roller 53.

  In order to reliably switch the bias, it is desirable to stop the image formation of at least three sheets. The average printing rate can be calculated by accumulating the number of pixels of the image data calculated by the pixel counter up to the 100th and dividing by the total number of pixels of 100 sheets of A4 size paper.

  As a result of such control, it is possible to prevent a decrease in density due to toner charge-up and an increase in graininess in a halftone image due to toner deterioration and to form a good image over a long period of time. Therefore, for example, if discharge control is performed once for every 100 sheets, 44 times of discharge control is executed, and productivity is significantly reduced.

  Therefore, in the first embodiment, image formation is continued until the toner discharge amount reaches a predetermined amount, and discharge control is performed when the toner discharge amount reaches a predetermined value or more. This control will be described with reference to the flowchart of FIG.

First, in step ST1, the number of image formation sheets N (Na to Nd) and the number of integrated pixels stored in the CPU as the control means for controlling the ejection of the image forming apparatus main body in terms of A4 size and the image formation number detection means. Vsum (Vsuma to Vsumd) is read (loaded).

  Next, the process proceeds to step ST2, and the control unit measures the 2.0% pixel number Vref and the integrated pixel number Vsum up to the Nth sheet in the A4 size up to the Nth sheet, and further, the difference between them is calculated. Calculated. The value corresponds to the discharge amount on the Nth sheet. Then, this value is compared with the corresponding number of pixels V of two solid images of A4 size.

As a result of the comparison in step ST2, when the discharge amount is smaller, the process proceeds to step ST3. In step ST3, 1 is added to the number N of image formations, and the number of pixels of the next image data is added to the total number of pixels Vsum, and then the result is stored in the CPU (control means) of the main body, and the process ends. On the other hand, when the discharge amount is larger or when the discharge amount is equal to V, the process proceeds to step ST4 and discharge control is started.

That is, first, after image formation is temporarily stopped in step ST5, the process proceeds to step ST6. In step ST6, the bias applied to the primary transfer roller 53 is switched to the reverse polarity. Subsequently, in step ST7, toner is refreshed by discharging and supplying toner for two solid images of A4 size. Subsequently, the process proceeds to step ST8, and the values of the image forming number N and the cumulative pixel number Vsum stored in the CPU in the main body are reset. In step ST9, the bias applied to the primary transfer roller 53 is switched to positive polarity, discharge control is terminated (step ST10), and normal image formation is resumed (step ST11).

Specifically, a low printing rate pattern with a yellow printing rate of 2.0%, a magenta printing rate of 1.0%, a cyan printing rate of 2.0%, and a black printing rate of 6.0%. Images are continuously formed on 4500 sheets of A4 size paper. Under this condition, the ejection amount for the 100th sheet of magenta image formation can be calculated from the difference between Vref and Vsum. Specifically,
Vref = (100 sheets × 2.0%) pixels equivalent to two A4 solids Vsum = total number of pixels of 100 with a printing rate of 1.0% ≈A4 solid one equivalent In this case, the discharge amount is A4 solid 1 It corresponds to a sheet. This discharge amount is less than a solid image for two A4 sizes, which is a predetermined amount. As a result, the values of Vref and Vsum are stored in the CPU (control means) in the image forming apparatus main body without performing the discharge control. Thereafter, normal image formation is continued.

Furthermore, after image formation was performed on 100 A4 size recording sheets, Vref
And Vsum are as follows.
Vref = (200 sheets × 2.0%) pixels equivalent to four A4 solids Vsum = total number of 200 pixels with a printing rate of 1.0% ≈A4 solid equivalents In this case, Vref−Vsum≈A4 solids Since it reaches two sheets, discharge control is performed.

  From the above, the discharge control interval is doubled as compared with the conventional control, and the number of times of stopping image formation can be reduced by half by the discharge control.

  As described above, in the first embodiment, the difference between the A4 size 2.0% number of pixels Vref up to the Nth sheet and the pixel integration number Vsum of the image data by the pixel counter 9 is a predetermined value set in advance. The discharge control is performed when the number of pixels V is reached. Therefore, it is possible to prevent a decrease in density and an increase in graininess, and it is possible to widen the discharge control interval, thereby achieving an improvement in productivity.

(Second Embodiment)
In the first embodiment described above, the difference between the number of pixels Vref when the A4 size printing rate up to the Nth sheet is 2.0% and the accumulated number of pixels Vsum of the image data measured by the pixel counter 9 is obtained. When the predetermined number of pixels V is reached, ejection control is performed. According to the discharge control at this time, productivity can be improved. However, if the printing ratios of the respective colors are different and the timing for performing the discharge control is shifted, the number of times of stopping image formation increases, and the productivity may decrease.

  Specifically, a low printing rate pattern with a yellow printing rate of 1.0%, a magenta printing rate of 1.6%, a cyan printing rate of 1.3%, and a black printing rate of 6.0%. Then, an image is formed on 4500 continuous A4 size sheets. At this time, yellow discharge control is performed every 200 sheets, magenta discharge control is performed every 500 sheets, and cyan discharge control is performed every 300 sheets, and image formation is stopped each time.

  Therefore, in the second embodiment, discharge control is performed as follows. That is, it is assumed that at least one process unit among the plurality of process units satisfies the discharge control condition, and the discharge control is executed at this time. At this time, if the difference between the number of pixels Vref of A4 size up to the Nth sheet and the printing rate of 2.0% and the total number of pixels Vsum up to the Nth sheet is positive, it corresponds to (Vref−Vsum). The amount of toner to be discharged is controlled to be discharged simultaneously. Specifically, when the discharge control is performed in the yellow process unit, the toner corresponding to 0.8 sheets of A4 solid is simultaneously ejected in the magenta process unit, and 1.4 sheets of toner is ejected in A4 solid in the cyan process unit. Is done.

The above control is demonstrated using the flow of FIG. That is, as shown in FIG. 4, in step ST21, the image forming number N (Na to Nd) of each color stored in the control unit of the image forming apparatus main body converted to A4 size, and the total number of pixels Vsum (Vsuma to Vsumd) is loaded.

  Next, the process proceeds to step ST22, and the difference between the 2.0% pixel number Vref in the A4 size up to the Nth sheet and the integrated pixel number Vsum up to the Nth sheet is calculated by the control unit. The value corresponds to the discharge amount on the Nth sheet. Then, this value is compared with the corresponding number of pixels V of two solid images of A4 size.

As a result of the comparison in step ST22, when the discharge amount is smaller, the process proceeds to step ST23. In step ST23, 1 is added to the number N of image formations by the control means, the number of pixels of the next image data is added to the integrated pixel number Vsum, and then the information is stored in the control means of the apparatus main body. Ends. On the other hand, when the discharge amount is larger or when the discharge amount is equal to V, the process proceeds to step ST24 and discharge control is started.

  That is, first, in step ST25, image formation is temporarily stopped. Subsequently, in step ST26, the bias applied to the primary transfer roller 53 is switched to the reverse polarity.

  Next, in step ST27, by the control means, in the process units other than the at least one process unit described above, the integrated pixel number Vref of 2.0% in the A4 size up to the Nth sheet and the integrated pixels up to the Nth sheet. The difference from the number Vsum is calculated.

  When the calculation result in step ST27 is positive, the process proceeds to step ST28. In step ST28, a toner amount corresponding to V is discharged in a process unit that satisfies the conditions for discharge control, and a toner amount corresponding to (Vref−Vsum) is discharged in a process unit that satisfies Vref−Vsum ≧ 0. Is done. Thereafter, the process proceeds to step ST29.

On the other hand, in step ST27, in all other process units, (Vref−
If Vsum) <0, the process proceeds to step ST29.

Subsequently, in step ST29, in the process unit extracted as a result of the comparison process in step ST22 described above, toner for two A4 size solid images is discharged and replenished. Thereby, toner refresh is executed. Subsequently, the process proceeds to step ST30, and the values of the image forming number N and the accumulated pixel number Vsum stored in the control device in the apparatus main body are reset. Thereafter, in step ST31, the bias applied to the primary transfer roller 53 is switched to positive polarity, the discharge control is terminated (step ST32), and normal image formation is resumed (step ST33).

As described above, when at least one process unit satisfies the discharge control condition, the number of pixels Vref having an A4 size and a discharge rate of 2.0% up to the Nth sheet in another process unit.
If the difference from the integrated pixel number Vsum is positive, the difference is discharged simultaneously. As a result, productivity can be improved even when the printing rates of the respective colors are different and the ejection timing is different.

As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible. For example, the numerical values given in the above embodiment are merely examples, and different numerical values may be used as necessary.

  Further, for example, in the above-described embodiment, the reference for performing the discharge control is the number of pixels V corresponding to the solid image for two A4 sizes. However, depending on the capacity of the developer inside the developing device 4 and the degree of developer compression in the vicinity of the regulating blade, toner charge-up and toner deterioration can be reduced, and the reference value can be further increased. As a result, as in the first and second embodiments, it is possible to prevent an increase in graininess in a halftone image due to a decrease in density due to toner charge-up or toner deterioration. Furthermore, a good image can be formed over a long period of time, and the interval for performing the discharge control can be further increased, thereby improving the productivity.

1 is a schematic diagram illustrating an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic diagram illustrating a process unit of an image forming apparatus according to a first embodiment of the present invention. 3 is a flowchart showing a control flow of the image forming apparatus according to the first embodiment of the present invention. 7 is a flowchart illustrating a control flow of an image forming apparatus according to a second embodiment of the present invention. It is a basic diagram which shows the image forming apparatus by a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Corona charger 3 Exposure apparatus 4 Developer 5 Intermediate transfer unit 6 Cleaner 9 Pixel counter 11 Conductive base 12 Photoconductive layer 21 Wire 22 Grid 23 Shield member 41 Developer container 42 Developer sleeve 43 Magnet roller 44 Regulating blade 45 Developing chamber 45s, 46s Screw 46 Stirring chamber 47 Replenishment chamber 49 Developer concentration detection means 51 Intermediate transfer belt 53 Primary transfer roller 55 Intermediate transfer belt cleaner 56, 57 Secondary transfer roller 61 Cleaning blade 62 Conveying screw P, Pa, Pb , Pc, Pd Process unit

Claims (3)

Electrostatic image forming means for forming an electrostatic image based on image information composed of pixels on an image carrier;
Developing means for developing the electrostatic image with a developer;
Integrating means for integrating the number of pixels;
Image forming sheet number detecting means for detecting the number of image forming sheets;
Control means for controlling the discharge of the developer from the developing means at a time other than the image forming operation according to the integrated value by the integrating means and the number of detected sheets by the image forming number detecting means;
In an image forming apparatus having
The control means is determined in advance from the developing means when the number of sheets detected by the image forming number detection means is a predetermined number and the integrated value by the integrating means is equal to or greater than a predetermined value. An image forming apparatus that controls discharge of an amount of developer. 2. The image formation according to claim 1, wherein, after execution of the ejection control, the integrated value integrated by the integration unit and the detected number of sheets detected by the image forming number detection unit are returned to an initial state. apparatus. A plurality of the developing means;
The integrating means is configured to integrate the number of pixels of the image developed by each of the plurality of developing means,
In the case where the predetermined amount of developer is discharged in at least one developing unit among the plurality of developing units, the control unit is configured so that each developing unit other than the one developing unit 3. The image forming apparatus according to claim 1, wherein the developer discharge control is performed in an amount corresponding to an integrated value of the number of pixels corresponding to the developing unit.

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