JP2013033171A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that easily removes stains on a developer carrier of a developing device without adopting a cleaning member.SOLUTION: In an image forming apparatus, a cleaning control unit is provided to a developer carrier of at least one developing device in an image forming unit. The cleaning control unit determines accumulated contamination degree of the developer carrier on the basis of image information; forms an electrostatic latent image for cleaning a developer carrier on an image carrier 1 in the amount of one revolution or more of the developer carrier depending on the accumulated contamination degree when the accumulated contamination degree exceeds a predetermined accumulated contamination degree; and causes the developing device to develop the electrostatic latent image to clean the developer carrier.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine combining two or more of these, and particularly relates to a developing device used in the image forming apparatus.

  A developing device for developing an electrostatic latent image formed on an image carrier in an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine combining two or more of these using today's mainstream dry developer. From the viewpoint of the developer, a one-component developing device using a so-called one-component developer mainly composed of toner and a two-component developing device using a so-called two-component developer mainly composed of toner and carrier are known. Yes.

  In both of these one-component developing devices and two-component developing devices, the developing device carries a developer carrying member for carrying the developer and transporting the electrostatic latent image on the image carrier to a developing area. The developer carrying member is applied with a developing bias for forming a developing electric field for transferring toner from the developer carrying member to the image carrying member for developing an electrostatic latent image.

  As the developing bias, a developing bias in which an alternating current component and a direct current component are superimposed may be employed in order to improve the developing efficiency regardless of whether the developing device is a one-component developing device or a two-component developing device. In particular, such development bias tends to be employed when speeding up of the image forming apparatus is required.

  In the two-component developing device, the developer is held on the surface of the developer carrier in the form of a magnetic brush by the action of the magnetic field generator built in the developer carrier and conveyed to the development area. The bodies are separated with a development gap.

  On the other hand, in a one-component developing device, when a DC voltage is adopted as the developing bias, the developer carrier is usually placed in contact with the image carrier, but a developing bias in which an AC component and a DC component are superimposed is adopted. In general, the developer carrier and the image carrier are generally separated with a development gap.

  In any case, when a developing bias in which an alternating current component and a direct current component are superimposed is adopted, the alternating current component to be superimposed is improved in order to improve the development efficiency in order to meet the demand for speeding up of today's image forming apparatuses. The peak-to-peak voltage Vpp and / or frequency is about to be set high. As a result, problems arise. This will be described by taking the two-component developing device shown in FIG. 10 as an example.

  The two-component developing device 4 shown in FIG. 10 includes a developing housing 40 that stores the developer D, a developing roller (an example of a developer carrying member) 41 that is provided in the developing housing 40 in the form of a rotatable drive sleeve, A magnetic field generator 42 built in the developing roller 41 and a developer regulating member 43 facing the developing roller 41 are included.

The developing device 4 further includes a rotationally driven developer conveying member 441 that distributes the developer D in the developing housing 40 to the developing roller 41 as a whole while conveying it.
As shown in FIG. 10, the developer conveying member 441 is generally arranged with the rotation center axis lined up on the developing roller 41.

  In the illustrated example, another developer conveying member 442 is disposed in parallel with the developer conveying member 441. The developer transport member 442 is disposed in parallel with the developer transport member 441 with a partition wall 400 having developer flow holes formed at both ends (the front and back ends in the drawing). The developer is distributed to the developing roller 41 while being reciprocally conveyed.

  The magnetic field generator 42 adsorbs the developer to be developed in the developing housing 40 on the surface of the developing roller 41, while returning to the developing housing 40 while being adsorbed on the developing roller 41 without being developed. This is a magnetic field generator having a plurality of magnetic poles for providing a low magnetic field LM for separating the developer from the developing roller 41.

  The magnetic poles in the magnetic field generator 42 are not limited thereto, but in the example of FIG. 10, the magnetic poles pass through the restricting pole N2 and the restricting member 43 at positions corresponding to the restricting member 43 and the catch pole S2 that sucks the developer D to the developing roller 41. The repulsive magnetic field between the transport pole S1 for transporting the developer thus developed toward the development area Da for developing the electrostatic latent image on the image carrier 1, the development pole N1 corresponding to the development area Da, and the catch pole S2. And a developer separation pole S3 that forms the low magnetic field LM.

  The developer adsorbed on the surface of the developing roller 41 by the magnetic force of the magnetic field generator 42 is conveyed to the developer amount regulating gap where the developer regulating member 43 faces the developing roller 41 under the action of frictional force by the rotation of the developing roller 41. Therefore, it is regulated to a predetermined amount, conveyed to the electrostatic latent image developing area Da, and used for developing the electrostatic latent image on the electrostatic latent image carrier 1.

  The developer returning to the developing housing 40 while being held by the developing roller 41 without being consumed in the developing area Da is peeled off from the developing roller 41 in the low magnetic force area LM.

  However, when a developing bias in which an AC component and a DC component are superimposed is used as the developing bias, and the peak-to-peak voltage Vpp and / or frequency of the AC component is set high in order to increase development efficiency, the direction of the electric field is very small. As shown in FIG. 11, the toner between the developing roller 41 and the image carrier 1 slightly vibrates when observed in a minute time.

  The toner and the carrier are frictionally charged and adsorbed to each other. However, when the toner vibrates in this way, the toner and the carrier are easily separated from each other, and are close to the image carrier 1 but are not used for development. When the developer returning to the developing housing 40 while being adsorbed on the developing roller 41 is separated from the developing roller 41 in the low magnetic field LM, a part of the toner is separated from the carrier, and only the carrier from the developing roller 41 is separated. The toner may leave and remain on the developing roller 41 as it is.

  When the toner remaining on the developing roller 41 is accumulated on the developing roller 41 in this manner, this becomes a developer carrying body (developing roller 41 in this example) called so-called sleeve dirt.

  When such a developer carrying member (developing roller 41 in this example) is smudged, an increase in the apparent development bias due to the charge of the toner causing the smearing and / or a unit on the developer carrying member. Compared with the case where the developer carrying member stain is not generated even when the same developing bias is applied due to the increase in the toner amount per area, the image density in the stain corresponding portion in the toner image to be developed is Get higher. For this reason, when an image that should have a uniform density is output, image density unevenness occurs in which the image becomes darker according to the developer carrying member contamination.

  In this regard, for example, in Japanese Patent Application Laid-Open No. 7-191552 (Patent Document 1), in a two-component developing device, a part of a developer carrying member (a developing sleeve fitted on a built-in magnetic field generator) is partially provided. A cleaning member that rotates while in contact is provided, and a magnetic member is disposed inside the cleaning member, and before supplying the developer to the development area, the two-component developer on the developer carrier is removed by the cleaning member. It is described that one end is peeled off.

  Japanese Patent Laid-Open No. 2000-66503 (Patent Document 2) forms a coat layer having the same polarity as the charged polarity of the toner so that the toner hardly remains on the surface of the developer carrying member in the two-component developing device. It is described to do.

JP-A-7-191552 JP 2000-66503 A

  However, in the developing device described in Patent Document 1, a cleaning member having a built-in magnetic member must be disposed in contact with the developer carrying member. In the developing device described in Patent Document 2, toner is placed on the surface of the developer carrying member. A coating layer, which can be said to be one type of cleaning member, has the same polarity as the charging polarity, and in either case, the cost of the developing device is increased or the configuration is further complicated.

  Accordingly, the present invention provides an image bearing member, a charging device for charging the surface of the image bearing member, and an exposure that forms an electrostatic latent image by performing image exposure on the charging area of the image bearing member by the charging device according to image information. At least one image forming unit including a developing device that develops an electrostatic latent image formed on the image carrier by the apparatus and the exposure device to form a visible toner image, and at least one of the image forming units. A developing device that faces the image carrier with a development gap in a development zone for developing the electrostatic latent image on the image carrier, and carries the developer to support the electrostatic latent image on the image carrier. A developer carrying member for transporting the toner to a developing area where the developer is carried, and a direct current component and an alternating current component are provided between the developer carrying member and the image carrier facing the developer carrying member by an electric field forming device. The electrostatic latent image is formed by forming a superimposed developing electric field. An image forming apparatus which is a DC / AC superimposed bias developing device for developing, and at least one of the DC / AC superimposed bias developing devices can easily remove toner stains on a developer carrying member without using a special cleaning member. It is an object of the present invention to provide an image forming apparatus capable of forming an image that can be cleaned easily and image density unevenness can be suppressed accordingly.

In order to solve the above problems, the present invention
Image bearing member, charging device for charging surface of image bearing member, exposure device for performing image exposure on charging area of image bearing member by charging device according to image information and forming electrostatic latent image, and exposure device And at least one image forming unit including a developing device that develops an electrostatic latent image formed on the image carrier to form a visible toner image,
The developing device in at least one of the image forming units faces the image carrier with a development gap in a development area for developing the electrostatic latent image on the image carrier, and carries the developer to support the image carrier. A developer carrying member for transporting the electrostatic latent image on the body to a developing area for developing, and the electric field forming device between the developer carrying member and the image carrier facing the developer carrying member. An image forming apparatus that is a DC / AC superimposed bias developing device that develops the electrostatic latent image by forming a developing electric field in which a DC component and an AC component are superimposed on each other,
A cleaning controller for a developer carrier of the developing device is provided for at least one of the DC / AC superimposed bias type developing device,
The cleaning control unit should be developed by the developing device using a degree of contamination of the developer carrying member determined by toner according to image information for forming an electrostatic latent image to be developed by the developing device. When the cumulative contamination level of the developer carrier under the history of the image information for forming an electrostatic latent image is obtained, and the cumulative contamination level exceeds a predetermined cumulative contamination level, the exposure is performed. An electrostatic latent image for cleaning the developer carrier corresponding to one or more rounds of the developer carrier corresponding to the accumulated stain degree is formed on the image carrier, and the electrostatic latent image is applied to the developing device. An image forming apparatus for developing and cleaning a developer carrying member of the developing device is provided.

  An image forming apparatus according to the present invention has at least one image forming unit including an image carrier, a charging device, an exposure device, and a developing device, and the developing device in at least one of the image forming units is the DC / AC superimposed bias type developing. The developer carrying member cleaning control unit of the developing device is provided for at least one of the DC / AC superimposed bias developing devices.

  The cleaning control unit obtains a cumulative stain level of the developer carrier under the history of the image information for forming an electrostatic latent image to be developed by the developing device, and the cumulative stain level is determined in advance. When the accumulated contamination level is exceeded, the exposure apparatus causes the developer carrying member cleaning electrostatic latent image corresponding to one or more rounds of the developer carrying member corresponding to the accumulated contamination degree to be formed on the image carrier. The electrostatic latent image is developed by the developing device to clean the developer carrying member of the developing device.

  As described above, according to the image forming apparatus of the present invention, at least one of the DC / AC superimposed bias type developing devices can easily remove the toner on the developer carrying member without requiring a special cleaning member as in the prior art. Therefore, it is possible to form an image in which unevenness in image density is suppressed.

  The image forming apparatus according to the present invention may include one image forming unit or a plurality of image forming units, as is generally seen in a monochrome image forming apparatus. Examples of the image forming apparatus including a plurality of the image forming units include so-called tandem type and cycle type color image forming apparatuses.

  The tandem type image forming apparatus includes an intermediate transfer member that is rotationally driven and a plurality of image forming units that are sequentially arranged along the intermediate transfer member, and each image forming unit faces the intermediate transfer member. An electrostatic latent image corresponding to the assigned color is formed on the image carrier, and the electrostatic latent image is developed by a developing device to which the assigned color toner is assigned. A toner image is formed, and the toner image is primarily transferred to the intermediate transfer member by a primary transfer device, and a multi-toner comprising a monochrome toner image or a toner image of two or more colors on the intermediate transfer member by the primary transfer. The image forming apparatus is capable of forming an image, secondarily transferring the primary transfer toner image onto a recording medium such as recording paper by a secondary transfer apparatus, and fixing the image.

  The cycle type image forming apparatus forms an electrostatic latent image on an image carrier, and corresponds to the electrostatic latent image among a plurality of developing devices capable of moving the electrostatic latent image to an electrostatic latent image developing area. A toner image is formed by developing with a developing device that holds the assigned color toner, and the toner image is primarily transferred to the intermediate transfer member, whereby a monochrome toner image or a toner image of two or more colors is transferred onto the intermediate transfer member. An image forming apparatus capable of forming a multi-toner image and secondarily transferring and fixing the toner image on the intermediate transfer member to a recording medium.

  In the cycle type image forming apparatus, one image carrier is usually used, but it can be considered that it is commonly used in a plurality of image forming units.

  When there is only one image forming unit including the DC / AC superimposed bias type developing device, it is sufficient that the developing device can clean the toner stain on the developer carrier by the cleaning control unit. In the case where there are a plurality of image forming units including a developing device, one or two or more of them may be cleaned by the cleaning control unit.

The following can be raised as a more specific example of the cleaning control unit. That is,
In grasping the history of the image information, the developer carrier is divided into a plurality of ranges in the width direction crossing the developer carrier surface movement direction, and the image information history for each of the divided plural ranges is grasped. For each of the image information histories, the degree of accumulated dirt of the developer carrying member is obtained, and when the degree of accumulated dirt in any of the plurality of divided ranges exceeds a predetermined accumulated dirt degree, the exposure apparatus For each divided range of the developer carrier, an electrostatic latent image for cleaning the developer carrier corresponding to one or more rounds of the developer carrier is formed on the image carrier in accordance with the accumulated degree of dirt. The electrostatic latent image is developed by the developing device to clean the developer carrying member of the developing device.

  In any case, the cleaning control unit can grasp the image information history based on, for example, exposure information from the exposure apparatus on the image carrier.

  In this case, as the cleaning control unit, for example, the exposure information obtained by the exposure apparatus is grasped as a print rate, the history of the print rate is adopted as the image information history, and a predetermined development according to the image information is performed. Examples of the degree of smearing of the agent carrier with the toner include the printing rate and the toner smearing degree of the developer carrier determined in advance according to the printing rate.

  Further, the cleaning control unit grasps exposure information from the exposure device as a printing rate, adopts the printing rate history as the image information history, and determines a developer carrier predetermined according to the image information. As the degree of contamination by toner, the printing rate and the toner contamination level of the developer carrier determined in advance according to the printing rate are adopted, and the number of image formations is taken into account when determining the cumulative degree of contamination of the developer carrier. Alternatively, it may be obtained as a cumulative stain degree corresponding to the number of formed images.

  As described above, according to the present invention, an image carrier, a charging device for charging the surface of the image carrier, and a charging area of the image carrier by the charging device are subjected to image exposure according to image information to perform electrostatic latent. At least one image forming unit including an exposure device that forms an image and a developing device that develops an electrostatic latent image formed on the image carrier by the exposure device to form a visible toner image. The developing device in at least one of the forming portions faces the image carrier with a development gap in a development area for developing the electrostatic latent image on the image carrier, and carries the developer on the image carrier. A developer carrying member for transporting the electrostatic latent image to a developing area for developing, and a direct current between the developer carrying member and the image carrier facing the developer carrying member by an electric field forming device. A developing electric field is formed by superimposing the AC component and the component. And an image forming apparatus that is a DC / AC superimposed bias type developing device that develops the electrostatic latent image, wherein at least one of the DC / AC superimposed bias type developing devices has a toner stain on a developer carrier. It is possible to provide an image forming apparatus that can be easily cleaned without employing a cleaning member and that can form an image in which unevenness in image density is suppressed.

1 is a diagram illustrating an outline of a configuration of an example of an image forming apparatus according to the present invention. FIG. 2 is a block diagram schematically showing a control circuit of the image forming apparatus in FIG. 1. It is a figure which shows the example of a waveform of the developing bias potential applied to the developing sleeve of a developing device. 1A is a view showing an example of a print (printed) image by the image forming apparatus of FIG. 1, and FIG. 1B is a view showing toner adhering dirt on the developing sleeve by this image print. FIG. 4 is a diagram showing uneven image density due to the dirt. It is a figure which shows the relationship between a printing rate and the image density nonuniformity on the output image by developing sleeve dirt. FIG. 6 is a diagram illustrating a relationship between a surface potential of an image carrier and a removal rate of dirt on a developing sleeve when developing for one round of the developing sleeve is performed. The upper part in FIG. 7 shows the printing rate of the printed image of FIG. 4A, the middle part shows the degree of stain on the developing sleeve at that printing rate, and the lower part shows the degree of dirt on the developing sleeve when 6 images are output. Show. FIG. 6 is a diagram illustrating the surface potential of the image carrier when the developing sleeve is removed. It is a figure which shows a mode that image density nonuniformity is suppressed. It is a figure which shows the prior art example of a two-component developing apparatus. FIG. 11 is a diagram illustrating the occurrence of developer carrying member contamination due to toner adhesion in the developing device of FIG. 10.

Hereinafter, an example of an image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 schematically shows the configuration of an example of an image forming apparatus according to the present invention. FIG. 2 is a block diagram schematically showing a control circuit of the image forming apparatus of FIG.
An image forming apparatus 10 shown in FIG. 1 is an electrophotographic image forming apparatus that forms a monochrome image on a recording sheet S such as recording paper under the instruction of the control unit C shown in FIG.

  The image forming apparatus 10 includes a drum-type photoconductor 1 as an image carrier, and a charging device 2, an image exposure device 3, a developing device 4, a transfer roller 5, and a cleaning device 6 are arranged in this order around the photoconductor 1. Has been placed. In addition to these, the image forming apparatus 10 includes a recording sheet supply unit (not shown), and the fixing device 7 and the sheet are disposed downstream of the transfer roller 5 in the transport direction of the sheet S supplied from the recording sheet supply unit. A discharge tray (not shown) is provided.

The photoreceptor 1 is a negatively chargeable photoreceptor, and its surface can be uniformly charged to a predetermined negative potential by a charging device 2 to which a charging voltage is applied from a charging power supply PW1 (see FIG. 2).
The image exposure device 3 forms an electrostatic latent image corresponding to an image to be formed by exposing the photosensitive member charged area by the charging device 2 to an image. Image exposure is performed according to image information provided from a machine or the like.

  The developing device 4 is the same as the developing device 4 shown in FIG. 10, and is a two-component developing device that develops an electrostatic latent image on the photoreceptor 1 using a two-component developer containing toner and a magnetic carrier. The electrostatic latent image is converted into a visible toner image by reversal development with a charged toner.

  More specifically, as described above, the developing device 4 includes a developing sleeve 41 having a built-in magnetic field generator 42. The developing sleeve 41 can be driven to rotate by a developing motor (not shown), and an image is held in the developing area Da. A developing gap is disposed with respect to the body (in this example, the drum-type photosensitive member 1 that is rotationally driven). For developing the electrostatic latent image on the photosensitive member 1, a developing bias power source PW2 (see FIG. 2) is used. A developing bias in which a DC component is superimposed on an AC component is applied.

According to the image forming apparatus 10, a toner image can be formed on the sheet S as follows under the instruction of the control unit C shown in FIG.
The surface of the photoreceptor 1 that is rotationally driven clockwise in the figure by a photoreceptor drive motor (not shown) is uniformly charged to a predetermined potential by a charging device 2 to which a charging voltage is applied from a charging power supply PW1. An image is exposed from the image exposure device 3 to the charged area to form an electrostatic latent image corresponding to the image to be formed, and the electrostatic latent image is developed by the two-component developing device 4 to form a toner image. .

  On the other hand, the recording sheet S is supplied from a recording sheet supply unit (not shown) to a timing roller (not shown), and the recording sheet S is transferred by the timing roller to the photosensitive member 1 at a timing when the toner image is transferred to the image formation target area. And a transfer portion between the transfer roller 5 and the transfer roller 5. At this time, a transfer voltage is applied to the transfer roller 5 from a transfer power supply (not shown), and the toner image on the photoreceptor 1 is transferred to the sheet S.

The recording sheet S to which the toner image has been transferred in this manner passes through the fixing device 7 so that the toner image is fixed under heat and pressure, and is discharged to the sheet discharge tray.
The surface of the photoreceptor 1 after the toner image transfer is cleaned by a cleaning device 6 and is prepared for the next image formation.

  Although an image is formed as described above, it should be noted that the image forming apparatus 10 can particularly easily clean the toner stain on the developing sleeve 41 of the developing device 4. This will be described below.

Prior to the formation of the electrostatic latent image, the surface of the photoreceptor 1 is charged by the charging device 2, and the photoreceptor surface potential at that time is approximately −400 V in this example.
The surface potential of the photosensitive member 1 by image exposure for forming an electrostatic latent image by the exposure device 3 is -40 V by exposure at a portion to be a black image, and a portion to be a white image to which toner is not attached is exposed. It remains at -400V.

Further, the developing bias applied from the developing bias power source PW2 to the developing sleeve 41 of the two-component developing device 4 in developing the electrostatic latent image is a bias whose waveform is shown in FIG.
That is, the bias is obtained by superimposing an AC voltage (a square waveform voltage of Vpp = 1.6 kV, frequency f = 2.5 kHz) on a DC voltage (−300 V).

  Under such a development bias in which an alternating current component and a direct current component are superposed, the development that is close to the photosensitive member 1 but is not used for development and is attracted onto the development sleeve 41 and returns to the development housing 40. When the agent is separated from the developing sleeve 41 in a low magnetic force region, a part of the toner is separated from the carrier, only the carrier is separated from the developing sleeve 41, the toner remains on the developing sleeve 41 as it is, and the developing sleeve is soiled. This contamination may cause image density unevenness that cannot be ignored in subsequent image formation.

  For example, when the image of FIG. 4 (A) is developed and formed, the developing sleeve 41 is contaminated with the toner shown in FIG. 4 (B). The image density unevenness that the image becomes dark corresponding to the sleeve contamination occurs.

  FIG. 5 is a diagram showing an example of the relationship between the printing rate and the image density unevenness on the output image due to the developing sleeve stain. In FIG. 5, the image information for forming an electrostatic latent image to be developed by the developing device 4 is grasped by the exposure information by the exposure device 3, and the exposure information is grasped by the printing rate. The level of image density unevenness is evaluated by measuring the reflection density (ID) of an image with a reflection densitometer known per se, and evaluating the density difference (ΔID) between a dark part and a thin part in the image.

  In the experimental example of FIG. 5, the maximum density difference in an image when a gray image is output continuously after continuously outputting an image whose printing rate does not change in the rotation center line (rotating axis) direction of the developing sleeve 41 is expressed as a printing rate. This is shown in relation to the accumulated (cumulative) rotation speed of the developing sleeve 41 when images with no change are continuously output.

  From FIG. 5, it can be seen that density unevenness is more likely to occur when the printing rate is low, and that when the printing rate exceeds 15%, the density difference does not need to be regarded as a problem.

  The surface potential of the opposing image carrier (photosensitive member 1 in this example) and the removal rate of the sleeve stain when developing for one rotation of the developing sleeve in a state where a certain amount of sleeve stain has occurred are as follows: As shown in FIG. 6, when an image close to a black image is output, the accumulated dirt on the sleeve is eliminated.

  Therefore, the image forming apparatus 10 includes a cleaning control unit CL in the control unit C as means for reducing the image density unevenness caused by the developing sleeve contamination. The cleaning controller CL basically has a toner stain on the developing sleeve 41 that is predetermined according to image information for forming an electrostatic latent image to be developed by the developing device 4 (in this example, the printing rate is adopted). The degree of accumulated stain of the developing sleeve 41 based on the history of the image information for forming the electrostatic latent image to be developed by the developing device 4 is obtained using the degree, and the accumulated stain degree is accumulated in advance. When the contamination level is exceeded, the exposure device 4 forms an electrostatic latent image for cleaning the developing sleeve corresponding to the circumference of the developing sleeve corresponding to the accumulated contamination level on the photosensitive member 1, and develops the electrostatic latent image. The developing sleeve 41 is cleaned by developing the apparatus 4.

  The toner contamination level of the developing sleeve 41 determined in advance according to the image information (printing rate in this example) is determined by experiments from the viewpoint of removing the toner contamination of the developing sleeve 41. Here, Then, it is determined as follows according to the printing rate for one rotation of the developing sleeve.

Print rate Less than 1% 1% or more but less than 5% 5% or more but less than 10% 10% or more but less than 15% Stain degree 6 5 4 2
Printing rate 15% or more and less than 20% 21% or more
Degree of contamination 1 0

  More specifically, the cleaning control unit CL basically cleans the stain on the developing sleeve 41 as follows. That is, when the integrated value (cumulative contamination degree) of the above-mentioned sleeve contamination degree determined by the printing rate per rotation of the developing sleeve 41 exceeds a predetermined value (250 in this case), the sleeve contamination is caused by uneven image density. It is determined that the limit has been reached, and at the timing when the photoconductor 1 does not output an image on the recording sheet S, charging and exposure are performed so that the surface potential of the photoconductor 1 becomes −40V, and development for one circumference of the developing sleeve is performed. . Further, when the printing rate per one round of the sleeve exceeds 80%, the stain level is reduced by 10 (the stain level is set to −10). However, it will not be negative. When the development for cleaning the developing sleeve is performed, the integrated value (cumulative contamination level) of the contamination level is reset.

  More specifically, the cleaning controller CL cleans the developing sleeve 41 dirt as follows. That is, the developing sleeve 41 is divided into a plurality of ranges in the width direction crossing the surface movement direction, the image information history (here, the printing rate history) for each of the divided plurality of ranges is grasped, and each image information history is developed. When the accumulated dirt degree of the sleeve 41 is obtained and the accumulated dirt degree in any range exceeds the limit value 250, the surface potential of the photoreceptor 1 is output at a timing when the photoreceptor 1 does not output an image to the recording sheet S. However, charging and exposure are performed so that the accumulated value (accumulated dirt degree) is −40 V for a range of 150 or more, and −300 V for other ranges, and development for one round of the developing sleeve is performed. Thereafter, the accumulated value of the degree of contamination is reset for a range where development is performed at a surface potential of −40V. At this time, the toner discharged to the photosensitive member 1 by the cleaning development is cleaned by the cleaning device 6.

This will be described by taking as an example a case where the image of FIG. 4A is actually printed on a recording sheet. The developing sleeve 41 at this time has a width of 330 mm in the developing sleeve rotation center line direction and a circumferential length of 50 mm, and a recording sheet size of 300 mm in width and 400 mm in the conveyance direction (developing sleeve surface movement direction). .

As shown in FIG. 7, the developing sleeve 41 is divided into a range of a1 to a11 in the width direction (developing sleeve rotation center line direction) crossing the surface moving direction, and the printing rate history of each divided range is grasped. For each history, the accumulated contamination degree of the developing sleeve 41 is obtained (see the contamination degree table in the middle of FIG. 7), and further, the accumulated contamination degree in any range exceeds the limit value of 250, which corresponds to six recording sheets. FIG. 8 shows the accumulated dirt degree when the image is output (see the dirt degree table at the bottom of FIG. 7), and before outputting the seventh sheet, according to the accumulated dirt degree for each range of a1 to a11. As shown in the figure, development is performed for one round of the developing sleeve by charging and exposing so that the accumulated value (cumulative stain degree) is −40 V when the range is 150 or more, and −300 V for the other ranges. To. Thereby, the developing sleeve 41 is cleaned.
Thus, image density unevenness is suppressed as shown in FIG. In FIG. 9, CL is the cleaning control part CL. “End” and “center” in parentheses are the end and center of the developing sleeve 41.

  The image forming apparatus described above forms a monochrome image. However, the present invention can also be applied to an image forming apparatus that forms a color image. The present invention can be applied to one or more of a plurality of developing devices housed therein. The present invention can also be applied to a one-component developing device in which a developer carrying member is disposed with a developing gap with respect to an image carrier and a developing bias in which a direct current component is superimposed on an alternating current component is used as the developing bias. .

  INDUSTRIAL APPLICABILITY The present invention can be used to provide an image forming apparatus that can easily clean the developer carrying member of the developing device without using a cleaning member.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus S Recording sheet 1 Photoconductor 2 Charging apparatus 3 Image exposure apparatus 5 Transfer roller 6 Cleaning apparatus 7 Fixing apparatus 4 Two-component developing apparatus 40 Developing housing 41 Developing sleeve 42 Magnetic field generator 43 Developer regulating members 441 and 442 Developing Agent conveying member 400 Partition wall D between conveying members Developer S2 Catch pole N2 Regulating pole S1 Conveying pole N1 Developing pole S3 Separating pole LM Low magnetic field area C Control section CL Cleaning control section

Claims (5)

Image bearing member, charging device for charging surface of image bearing member, exposure device for performing image exposure on charging area of image bearing member by charging device according to image information and forming electrostatic latent image, and exposure device And at least one image forming unit including a developing device that develops an electrostatic latent image formed on the image carrier to form a visible toner image,
The developing device in at least one of the image forming units faces the image carrier with a development gap in a development area for developing the electrostatic latent image on the image carrier, and carries the developer to support the image carrier. A developer carrying member for transporting the electrostatic latent image on the body to a developing area for developing, and the electric field forming device between the developer carrying member and the image carrier facing the developer carrying member. An image forming apparatus that is a DC / AC superimposed bias developing device that develops the electrostatic latent image by forming a developing electric field in which a DC component and an AC component are superimposed on each other,
A cleaning controller for a developer carrier of the developing device is provided for at least one of the DC / AC superimposed bias type developing device,
The cleaning control unit should be developed by the developing device using a degree of contamination of the developer carrying member determined by toner according to image information for forming an electrostatic latent image to be developed by the developing device. When the cumulative contamination level of the developer carrier under the history of the image information for forming an electrostatic latent image is obtained, and the cumulative contamination level exceeds a predetermined cumulative contamination level, the exposure is performed. An electrostatic latent image for cleaning the developer carrier corresponding to one or more rounds of the developer carrier corresponding to the accumulated stain degree is formed on the image carrier, and the electrostatic latent image is applied to the developing device. An image forming apparatus for developing and cleaning a developer carrying member of the developing device.   The cleaning control unit divides the developer carrier into a plurality of ranges in a width direction crossing the developer carrier surface movement direction in grasping the history of the image information, and images for each of the divided plurality of ranges. Ascertaining the information history, for each image information history, to determine the accumulated dirt degree of the developer carrier, when the accumulated dirt degree of any of the divided multiple ranges exceeds a predetermined accumulated dirt degree, In the exposure apparatus, an electrostatic latent image for cleaning the developer carrier corresponding to one or more rounds of the developer carrier for each divided range of the developer carrier on the image carrier is displayed on the image carrier. The image forming apparatus according to claim 1, wherein the electrostatic latent image is developed by the developing device and the developer carrying member of the developing device is cleaned.   The image forming apparatus according to claim 1, wherein the cleaning control unit grasps the image information history based on exposure information from the exposure apparatus to the image carrier.   The cleaning control unit grasps exposure information from the exposure apparatus as a printing rate, adopts the printing rate history as the image information history, and uses a toner of a developer carrier predetermined according to the image information. The image forming apparatus according to claim 3, wherein the degree of smearing employs the printing rate and a toner smearing level of a developer carrier determined in advance according to the printing rate. The cleaning control unit grasps exposure information from the exposure apparatus as a printing rate, adopts the printing rate history as the image information history, and uses a toner of a developer carrier predetermined according to the image information. As the degree of smearing, the printing rate and the toner smearing degree of the developer carrying member determined in advance according to the printing rate are adopted, and the cumulative smearing degree of the developer carrying member is obtained as the cumulative smearing degree according to the number of images formed. The image forming apparatus according to claim 3.