JP5040157B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a recording medium such as a recording sheet using an electrophotographic system such as a copying machine, a printer, a facsimile machine, and a multifunction machine of these, and a control method thereof.

  An image forming apparatus such as a copying machine or a printer using an electrophotographic system develops, for example, an electrostatic latent image formed on a photosensitive drum with a developer (toner) by a developing device to form a toner image. The toner image formed on the body drum is configured to be transferred and fixed on the recording medium. The toner remaining on the photosensitive drum after the toner image is transferred onto the recording medium is removed and collected by the cleaning device.

As a developing device used in such an image forming apparatus, there are a one-component developing method using a magnetic toner and a two-component developing method using a two-component developer in which a toner and a magnetic carrier are mixed. In recent years, particularly in color image forming apparatuses, a two-component development method using color toners that do not contain magnetic particles has become mainstream.
As such a two-component developing type developing device, a housing provided with a developing roll is provided with two spiral augers that rotate in reverse to each other in parallel with the developing roll, and the housing is stirred while the developer is stirred by the rotation of the spiral auger. There is a configuration in which toner is circulated and charged, and the toner is charged by friction with a carrier and supplied to a developing roll (see Patent Document 1).
In the two-component development system, only the toner is consumed with the development action, and the toner content in the developer changes. For this reason, new toner is supplied with consumption to the most upstream side in the transport direction of the developer, and the toner content is kept constant. The toner content mentioned here is defined by (toner weight / total developer weight) × 100 (%).

By the way, in the image forming apparatus, a configuration (toner recycling) in which the toner (collected toner) collected by the cleaning device is returned to the developing device and reused is known (see Patent Document 2).
In the electrophotographic apparatus in Patent Document 2, a residual toner discharge port is provided in the cleaning device, while a residual toner recovery port is provided at a position lower than the residual toner discharge port of the developing device. It is configured by connecting with a residual toner collection port of the apparatus by a conveyance path (conveyance path). The residual toner removed by the cleaning device is naturally dropped in the conveyance path and returned to the developing device.

JP 2005-266280 A JP 2001-22181 A

As described above, in the developing device configured to supply the developer while being conveyed in parallel with the developing roll (that is, in parallel with the photosensitive drum), the toner is consumed from the upstream side in the developer moving direction, and thus goes downstream. There is a characteristic that the toner content of the developer is lowered.
For this reason, in particular, when a large number of high-density images are continuously formed, there is a problem in that the toner content on the downstream side is significantly reduced, and density unevenness (density difference) occurs on the formed image.
FIG. 11 shows a graph in which the density difference on the image corresponding to the upstream side and the downstream side in the developer moving direction is examined when high-density images are continuously formed. In the figure, the horizontal axis represents the number of image forming pages, and the vertical axis represents the difference in image density on both sides of the recording paper corresponding to the upstream side and the downstream side in the developer moving direction. The size of the recording paper is A3, and the density of the formed image is 100%. From this figure, it can be seen that the density difference expands according to the number of image-formed pages up to about 50 sheets on A3 size recording paper, and then stabilizes with a large density difference. In addition, the density | concentration parameter | index in a figure is based on the parameter | index of the 404A density | concentration inspection apparatus by X-Rite.

In the toner recycling configuration described above, some toner (recycled toner) returned from the cleaning device has deteriorated chargeability, and such toner requires a long stirring time to be charged. For this reason, in the image forming apparatus that performs toner recycling, the density difference between the upstream and the downstream during the above-described continuous high-density image formation is more likely to occur.
Furthermore, some recycled toners are charged with a reverse polarity, and there is a problem that such toners adhere to portions other than the electrostatic latent image on the photosensitive member to cause toner fog.

  The present invention has been made to solve such a technical problem, and an image forming apparatus and a control method therefor that are less likely to cause density unevenness and reduce toner fog even when a high-density image is continuously formed. The purpose is to provide.

In order to achieve such an object, an image forming apparatus according to the present invention develops an image carrier on which an electrostatic latent image is formed, and the electrostatic latent image formed on the image carrier with a developer containing toner. A developing device, and when performing continuous image formation under a predetermined condition with high toner consumption, the continuous image formation is interrupted and the idle operation is performed for a predetermined time.
An image forming apparatus according to another invention of the present application includes an image carrier on which an electrostatic latent image is formed, and a developing device that develops the electrostatic latent image formed on the image carrier with a developer containing toner. In the case of continuous image formation under predetermined conditions with high toner consumption, the interval between successive image formations is set wider than that in normal image formation, and idle operation is performed during the image formation interval. And

Here, the predetermined condition may be a value determined in advance by the image density and the number of continuous pages. The image processing apparatus further includes storage means for storing the value, and determination means for determining that the image formation consumes a large amount of toner before or during image formation using the value stored in the storage means. Can be characterized.
The apparatus further comprises a cleaning device that removes and collects the toner on the image carrier, and a toner reuse mechanism that transports the collected toner collected by the cleaning device to the developing device for reuse. When used, the predetermined condition that consumes a large amount of toner may be set lower by a predetermined amount than when the collected toner is not reused.
In addition, when an image is formed under a predetermined condition that consumes a large amount of toner, the toner content of the developer may be set higher by a predetermined amount.
In addition, when continuous image formation under a predetermined condition with high toner consumption is set, the interval between successive image formations is set wider than that during normal image formation. The predetermined condition is determined by the image density and the number of continuous pages. The image forming interval can be changed in accordance with the image density, and the image forming interval can be increased to a certain value when the image density is equal to or higher than a predetermined value.

A method for controlling an image forming apparatus according to the present invention is a method for controlling an image forming apparatus that develops an electrostatic latent image of an image formed on an image carrier with a developer containing toner, before or after image formation. Obtaining information on image density and number of continuous pages during formation, comparing image density and number of continuous pages with a predetermined reference value to determine continuous image formation with high toner consumption, and toner And a step of performing high-density continuous control different from normal image formation when it is determined that continuous image formation is highly consumed.
A control method for an image forming apparatus according to another invention of the present application is a control method for an image forming apparatus that develops an electrostatic latent image of an image formed on an image carrier with a developer containing toner, before image formation. Alternatively, the step of obtaining information on the image density and the number of continuous pages during image formation and the product of the image density and the number of continuous pages are compared with a predetermined reference value to determine continuous image formation with high toner consumption. And a step of performing high-density continuous control different from normal image formation when it is determined that continuous image formation is high in toner consumption.
Here, the high-density continuous control in the above control method can be characterized in that the continuous image formation is interrupted every predetermined number of pages and the idle operation is executed for a predetermined time.
Further, the high density continuous control can be characterized in that the interval between successive image formations is set wider than that during normal image formation, and idle operation is performed during the image formation interval.

  According to the image forming apparatus and the control method of the present invention configured as described above, it is possible to suppress the occurrence of density unevenness even when high-density images are continuously formed. Further, toner fog can be suppressed.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a block diagram of an image forming apparatus 1 to which this embodiment is applied.

The image forming apparatus 1 includes a photosensitive drum 11 as an image carrier having a photosensitive layer on the surface, an intermediate transfer belt 20 on which a toner image formed on the photosensitive drum 11 is primarily transferred, and an intermediate transfer belt 20. A secondary transfer unit 30 that transfers the toner image transferred thereon onto the recording paper P and a fixing device 40 that fixes the toner image onto the recording paper P are provided.
In addition, the image forming apparatus 1 includes a control device 50 that performs all mechanism control and image processing.
The present invention is not limited to the configuration provided with the intermediate transfer belt, and may be a configuration in which the toner image is directly transferred from the photosensitive drum to the recording paper. In addition, a plurality of image forming units each including a photosensitive drum are disposed facing the intermediate transfer belt, and the image forming units perform image formation with toners of different colors (yellow, magenta, cyan, black), and as a whole, The present invention may be applied to a so-called tandem color image forming apparatus that forms an image.

Around the photosensitive drum 11, a charging roll 12 that uniformly charges the photosensitive drum 11, a laser exposure device 13 that scans the charged photosensitive drum 11 with laser light to form an electrostatic latent image, and A developing device 60 that attaches toner to the electrostatic latent image to form a toner image, a transfer roll 14 that transfers the toner image formed on the photosensitive drum 11 to the intermediate transfer belt 20, and the photosensitive drum 11 after transfer. And a cleaning device 70 for removing the toner remaining on the toner.
The laser exposure device 13 is controlled by the control device 50, emits a laser beam from the laser diode based on the image information, and performs exposure scanning (main scanning) of the photosensitive member on the peripheral surface of the photosensitive drum 11 in the rotation axis direction. ) To form an electrostatic latent image corresponding to the image information.

  The developing device 60 is a two-component developing type developing device using a developer in which toner and a carrier are mixed. A housing 61 for containing the developer is provided with a developing roll 62, and the developing roll 62 is provided to face the photosensitive drum 11. Inside the housing 61, two screw augers 63 are provided in parallel with the developing roll 62, and the developer in the housing 61 is conveyed along the developing roll 62 while being stirred by the screw auger 63. The inside of the housing 61 is circulated. The housing 61 is provided with a toner concentration sensor 64.

  The toner concentration sensor 64 detects the magnetic permeability of the developer inside the housing 61 and outputs the detected information to the control device 50 as information for proper maintenance control of the toner content of the developer. The proper maintenance control of the toner content of the developer is not limited to the information based on the detection information by the toner density sensor 64. For example, an image for toner density detection may be formed on the intermediate transfer belt 20 and the image density read by a sensor.

  Further, the developing device 60 is connected to a toner replenishing device 80 and a collected toner transport mechanism 90 as a toner reusing mechanism, and new toner is supplied from the toner replenishing device 80 and recycled toner is supplied from the recovered toner transport mechanism 90. It has become so. The supply of new toner from the toner replenishing device 80 and the supply of recycled toner from the collected toner transport mechanism 90 are controlled by the control device 50. The toner supply control by the controller 50 will be described in detail later.

  The primary transfer roll 14 is opposed to the photosensitive drum 11 with the intermediate transfer belt 20 interposed therebetween, and this is a primary transfer portion. A voltage (primary transfer bias) having a polarity opposite to the charging polarity of the toner is applied to the primary transfer roll 14, and the toner image on the photosensitive drum 11 is electrostatically attracted to the intermediate transfer belt 20. Primary transfer.

The intermediate transfer belt 20 is stretched around a predetermined path by a plurality of stretching rolls so as to be able to go around.
A secondary transfer roll 31 is disposed facing a predetermined position of the intermediate transfer belt 20, and a secondary transfer backup roll 32 is disposed outside the path with the secondary transfer roll 31 and the intermediate transfer belt 20 interposed therebetween. This is the secondary transfer unit 30. A secondary transfer bias is applied to the backup roll 32, and the secondary transfer roll 31 is grounded, and the toner image carried by the intermediate transfer belt 20 is transferred onto the recording paper P that is conveyed by a conveyance mechanism (not shown). Secondary transfer to.

  The cleaning device 70 includes a cleaning blade 72 in a housing 71, and is provided in pressure contact with the photosensitive drum 11. The toner remaining on the photosensitive drum 11 after the toner image is transferred to the intermediate transfer belt 20 at the primary transfer portion is scraped off by the cleaning blade 72 and collected in the housing 71. The housing 71 is connected to the collected toner transport mechanism 90, and the collected toner accumulated in the housing 71 is transferred to the collected toner transport mechanism 90.

The collected toner transport mechanism 90 includes a collected toner storage container 91 that stores toner transferred from the cleaning device 70, and a toner transport path (re-use) that connects the recovered toner storage container 91 to the developing device 60 and a waste toner box (not shown). A use conveyance path 92 and a discard conveyance path 93). As a result, the collected toner removed from the photosensitive drum 11 by the cleaning device 70 is temporarily stored in the collected toner storage container 91 and conveyed to the developing device 60 or the waste toner box.
A reuse transport path 92 that connects the collected toner storage container 91 and the developing device 60 is connected to the bottom of the recovered toner storage container 91, and an open / close control valve 92V is interposed in the middle. On the other hand, a waste conveyance path 93 that connects the collected toner storage container 91 to the developing device 60 and the waste toner box is connected to a side portion having a predetermined height from the bottom surface of the recovered toner storage container 91. Each toner transport path (reuse transport path 92, discard transport path 93) is provided with transport means such as a screw auger for transporting the collected toner.

In the collected toner conveyance mechanism 90 having such a configuration, the collected toner transferred from the cleaning device 70 is once stored in the collected toner storage container 91, and when the amount exceeds a predetermined amount, the excess collected toner passes through the waste conveyance path 93. Thus, a state where a constant amount of recovered toner is always stored in the recovered toner storage container 91 is maintained. As a result, by always opening the opening / closing control valve 92V, the collected toner can be supplied to the developing device 60 via the reuse conveyance path 92. The controller 50 controls the driving of the conveying means of each toner conveyance path (reuse conveyance path 92, discard conveyance path 93) and the opening / closing operation of the open / close control valve 92V. In other words, the control device 50 controls switching between implementation and non-execution of toner recycling.
The fixing device 40 is configured such that a pressure roll 42 is disposed in pressure contact with a heated fixing roll 41, and the recording paper P onto which a toner image has been transferred is sandwiched between the fixing roll 41 and the pressure roll 42 and heated and heated. To fix the toner image on the recording paper P.

The control device 50 includes a mechanism control unit 51, an image control unit 52, and an image memory 53.
Although not shown, the mechanism control unit 51 includes a memory as a storage unit that stores control information. Based on the control information stored in the memory, the toner content rate control and toner recycling in the developing device 60 are performed. Control of each mechanism related to the image forming process, including control of the above (control of the collected toner transport mechanism 90) and the like.
In the toner content rate control, new toner is replenished from the toner replenishing device 80 so as to maintain a predetermined toner content rate based on the toner content rate obtained from the magnetic permeability of the developer detected by the toner density sensor 64. .
The toner recycling control opens and closes an open / close control valve 92V provided in a reuse conveyance path 92 from the collected toner conveyance mechanism 90 to the developing device 60 based on a user's selection operation via an operation panel (not shown). In addition to the operation, the conveyance means in the reuse conveyance path 92 is turned on / off.

  The image control unit 52 converts image information input from the image reading device SC, the computer PC, or the like into image formation data and outputs the image formation data to the laser exposure device 13. In the configuration shown in the figure, the copy image information read by the image reading device SC is input as it is to form an image for each sheet, and the print image information from the computer PC or the like is temporarily stored in the image memory 53 and then image forming data. In this way, image formation is continuously performed. Further, the image density and page number information is read from the image information stored in the image memory 53 and used as control information.

The image forming apparatus 1 is controlled by the control device 50 to perform image formation as described below.
That is, the photosensitive drum 11 is rotated to uniformly charge the photosensitive member on the surface with the charging roll 12, and the laser exposure device 13 is driven based on the image formation data formed by the image control unit 52. Exposure is performed to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 60 to be a toner image, and the toner image is transferred to the recording paper P by the primary transfer unit. Next, the toner image transferred onto the recording paper P is fixed by the fixing device 40 and discharged. The toner remaining on the photosensitive drum 11 after the toner image is transferred to the recording paper P is removed by the cleaning device 70. Further, toner recycling is performed based on a user's selection operation via an operation panel (not shown).

Here, the control device 50 performs different control (hereinafter referred to as image density continuous correspondence control) according to the image density and the number of continuous pages during image formation.
In the image density continuous correspondence control, it is determined whether or not high-density image formation is continued based on image information or the like. If high-density image formation is continued, the developer toner inside the developing device 60 is determined. High density continuous control is performed to prevent density unevenness on the formed image due to the difference in content. When it is determined that the high density is not continuous, normal control is performed.
The method of determining that high-density images are continuous differs depending on the input status of image information.
That is, the image information input mode includes, for example, a case where the control device 50 can acquire page number information in advance, such as when image output information of a plurality of pages is collectively input from the personal computer PC, and image reading. There is a case where the control device 50 cannot acquire the page number information in advance as in the case of taking a so-called copy in which the device SC reads a document sent by the feeder and forms an image each time.
For this reason, when the page number information can be acquired in advance, a high-density continuous control can be performed by setting a schedule. However, when the page number information cannot be acquired in advance, a judgment is made each time, Density continuous control will be performed.

Hereinafter, the image density continuous correspondence control will be described in detail.
[Embodiment 1]
FIG. 2 shows a flowchart of an example of image density continuous correspondence control when page number information can be acquired in advance. Refer to FIG. 1 for the reference numerals of the constituent mechanisms.
First, information on the image density and the number of pages is read from the image information stored in the image memory 53 via the image control unit 52 (S101). Then, it is determined whether the high-density images are continuous (S102). That is, it is determined whether the average image density is equal to or higher than a predetermined value and the number of continuous pages is equal to or higher than the predetermined number of pages. If it is determined that the high-density images are continuous, image formation is started (S103), idle operation is performed for a predetermined time every predetermined number of pages (S104), and thereafter this is repeated. On the other hand, if it is determined that high-density images are not continuous, image formation is performed under normal control (S105).
The criteria for continuous determination of high-density images in S102 are, for example, average image density: 80% and number of continuous pages: 30 sheets. The value of this criterion is determined in advance and stored in the storage device of the control device 50. Needless to say, the number of continuous pages varies depending on the size of the recording paper P. Further, the idle operation in S104 is, for example, an idle operation for 10 pages of image formation every 30 sheets. In this control flow, the step of performing idling for a predetermined time every predetermined number of pages (S104) is high-density continuous control.

FIG. 3 is a flowchart of an example of image density continuous correspondence control when page number information cannot be acquired in advance.
In this control, image formation is started by normal control (S201), and thereafter image density information and page number information are obtained one by one (S202). If image formation continues, continuous image formation from the start of image formation is obtained. The average image density is calculated (S203). Then, it is determined whether or not the high-density images are continuous (S204). Here, when it is determined that the high-density images are continuous, the idling is performed for a predetermined time (S205). In other cases, image formation under normal control is continued (S201), and thereafter this is repeated.
The image density information acquired in S202 can be obtained from the lighting time of the laser diode of the laser exposure apparatus at the time of image formation, for example. Further, the criteria for determining whether or not the high-density images in S204 are continuous are, for example, an average image density of 80% and a continuous page number of 30. The idle operation in S205 is, for example, 10 pages of image formation. In this control flow, when it is determined that high-density images are continuous, the step of performing idling for a predetermined time (S205) is high-density continuous control.

Here, the idling operation in the high-density continuous control in the above embodiment is performed by causing various mechanisms of the image forming process to function in the same manner as in the image forming except for the laser exposure device 13. That is, the charging roll 12 charges the photosensitive drum 11, and the developing device 60 performs agitation and conveyance of the developer and supplies the developer to the developing roll 62, and also controls toner density.
As a result, when the toner content of the developer of the developing device 60 has decreased due to continuous high-density image formation, new toner from the toner replenishing device 80 is replenished and the toner content is increased. Is adjusted to the specified value. Further, in the developing device 60, the developer is agitated to promote toner charging, and the difference in toner content in the axial direction of the photosensitive drum 11 is also eliminated. Thereby, it is possible to suppress the occurrence of uneven density in the image in the axial direction of the photosensitive drum 11. Further, if there is toner charged in reverse polarity in the developer in the developing device 60 due to deterioration or the like, it adheres to the photosensitive drum 11 and is removed from the developing device 60, and the toner in the subsequent formed image Can suppress fog.

FIG. 4 shows a graph of test results obtained by actually forming a high-density image continuously and performing idling in the middle and examining the density difference on the image corresponding to the upstream side and the downstream side in the developer moving direction. In the figure, the horizontal axis represents the number of image forming pages, and the vertical axis represents the difference in image density at both sides of the recording paper corresponding to the upstream end and the downstream end in the developer moving direction. The index on the vertical axis is based on the index of the 404A concentration inspection apparatus manufactured by X-Rite.
In the test, image formation was continuously performed with a recording paper size of A3 and a density of formed images of 100%, and when the number of continuous pages reached 40, blank operation corresponding to 10 image formations was performed. is there.
As a result, the density difference was smaller than that of the conventional example shown in FIG. 11, and the density unevenness suppressing effect was confirmed.

In the image density continuous correspondence control, the criterion for determining that the high-density image is continuous is not limited to using the average image density and the number of continuous pages as independent determination elements. A product obtained by multiplying a number may be used as a criterion.
For example, as described above, on the condition that it is determined that the high-density image is continuous with the average image density of 80% and the number of continuous pages: 30, the average image density × the number of continuous pages = 80 × 30 = 2400 is set as the reference value. In this case, when images with an image density of 90% are continuous, 2400 ÷ 90≈27, which is 27 sheets. Accordingly, it is determined that if the average image density is 90% and 27 pages are continuous, the high-density image is continuous. When images with an image density of 60% are continuous, it is determined that 40 high-density images are continuous.
According to such control, fine control according to the image density is possible as compared with the control with a single reference value, and it is possible to respond more quickly when image formation with higher density continues. be able to.

Further, the image forming apparatus 1 according to the present embodiment includes the collected toner transport mechanism 90 that returns the collected toner removed from the photosensitive drum 11 by the cleaning device 70 to the developing device 60 for reuse as described above. The toner can be recycled. Here, some of the collected toner once subjected to the developing action has a deteriorated charging performance. Such toner takes time to charge, and when high-density images are continuously formed, uneven density of the image in the axial direction of the photosensitive drum 11 is likely to occur. For this reason, when toner recycling is performed, the reference value for high-density continuous control is decreased by a predetermined amount, and high-density continuous control is performed from an earlier stage.
In other words, a standard value for determination when toner recycling is not performed (normal standard value) and a standard value for determination when toner recycling is lower than this (toner recycling standard value) are determined. In addition, the presence / absence of toner recycling is confirmed, and the continuity of high-density images is determined based on the respective determination reference values.

For example, the toner recycling reference value is set to about 2/3 of the normal reference value in which toner recycling is not performed.
By such control, when toner recycling in which toner having deteriorated charging performance is supplied is performed, high-density continuous control can be performed from an earlier stage, and the shaft of the photosensitive drum 11 can be controlled. The image density difference in the direction can be suppressed. In addition, toner charged to a reverse polarity, which is higher than usual, can be excluded from the developing device 60, and toner fogging in subsequent formed images can be suppressed.
In the case where the supply amount of the collected toner to the developing device 60 can be variably controlled during toner recycling, the toner recycling reference value may be changed according to the supply amount. .

[Embodiment 2]
Next, image density continuous correspondence control, which is different from the first embodiment in high density continuous control, will be described. In this high-density continuous control, the interval between pages for image formation is increased more than usual, and the idle operation is performed during that interval.
FIG. 5 is a flowchart of an example of image density continuous correspondence control when page number information can be acquired in advance, and FIG. 6 is a flowchart of image density continuous correspondence control when page number information cannot be acquired in advance. In this embodiment, the determination step that the high-density images are continuous is the same as that in the first embodiment, and only the content of the high-density continuous control is different.
In the image density continuous correspondence control in the case where the page number information can be acquired in advance as shown in FIG. 5, the image density and page number information is read from the image information stored in the image memory 53 via the image control unit 52 (S301). Then, it is determined whether or not the high-density images are continuous (S302). If it is determined that high-density images are continuous, the image formation interval is set wide (S303), and image formation is performed (S303). On the other hand, if it is determined that high-density images are not continuous, image formation is performed under normal control (normal image formation interval) (S305). In this control flow, the step of widening the image formation interval (S303) is high-density continuous control.

  In the image density continuous correspondence control when the page number information cannot be acquired in advance as shown in FIG. 6, image formation is started by normal control (S401), and thereafter image density information is acquired one by one (S402), and image formation continues. If so, the average of the continuous image formation density from the start of image formation is calculated (S403). Then, it is determined whether or not the high-density images are continuous (S404). If it is determined that the high-density images are continuous, the image formation interval is set wide (S405), and image formation is performed. In other cases, image formation under normal control is continued (S401), and thereafter this is repeated. In this control flow, when it is determined that high-density images are continuous, the step of widening the image formation interval (S405) is high-density continuous control.

5 and 6, the various mechanisms of the image forming process are controlled so as to function in the same manner as in the image forming except for the laser exposure device 13 during the image forming interval.
This makes it possible to replenish toner to the developing device 60 during individual image formation, promote charging of the toner by stirring the developer in the developing device 60, uniformize the toner content in the axial direction, and eliminate deteriorated toner. Can be done. As a result, it is possible to suppress the occurrence of density unevenness of the image in the axial direction of the photosensitive drum 11 and to suppress the toner fog of the formed image thereafter.
The interval between image formations is, for example, 1.5 times that during normal image formation.
Further, the image forming interval may be variably controlled according to the average image density and the number of continuous pages.
FIG. 7 shows an example of such a control map.
By using such a control map and variably controlling the interval between the recording sheets according to the average image density and the number of continuous pages, it becomes possible to form a rational image as required in a more detailed manner.

FIG. 8 shows a graph of test results obtained by actually forming a high-density image continuously at a wider image forming interval than usual and examining the density difference on the image corresponding to the upstream side and the downstream side in the developer movement direction.
In the figure, the horizontal axis represents the number of image forming pages, and the vertical axis represents the difference in image density on both sides of the recording paper corresponding to the upstream side and the downstream side in the developer moving direction.
In the test, image formation was continuously performed with a recording paper size of A3 and a density of formed images of 100%, and the image forming interval was doubled when the number of continuous pages reached 40.
As a result, the density difference was smaller and more stable than the conventional example shown in FIG. 13, and the effect of suppressing density unevenness was confirmed.
In the second embodiment as well, the control configuration in which the product obtained by multiplying the average image density by the number of continuous pages and the determination reference value for high density continuation described in the first embodiment and the presence / absence of toner recycling are used. A control configuration that changes the determination criteria may be applied.

Furthermore, in the second embodiment, when high-density images are continuous, control for setting the toner content of the developer in the developing device 60 high may be added.
That is, when it is determined that the high-density images are continuous, the control target value of the toner content of the developer in the developing device 60 performed by the control device 50 is set high. For example, when the target value of the toner content rate during normal control is 9%, it is set to 11% during high-density continuous control.

FIG. 9 is a graph showing the relationship between the toner content and the image density.
As can be seen from this graph, as the toner content increases, the rate of change in image density with respect to that change decreases. That is, when the toner content is increased, the density difference of the image is compressed. For this reason, at the time of forming a high-density image, by setting the toner content rate high, even if the image density unevenness occurs in the axial direction of the photosensitive drum 11, the density difference is reduced and made inconspicuous. Can do.
FIG. 10 shows the results of a test similar to the test shown in FIG. 8 in the second embodiment with the toner content increased. The test conditions were that the recording paper size was A3, the density of the formed image was 100%, and the toner content was increased to 11% compared to 9% in the test of FIG.
As a result, the density difference was smaller than the result shown in FIG. 8, and it was confirmed that a larger density unevenness suppressing effect could be obtained.

  As described above, according to the above-described embodiment, even in the case where high-density image formation is continuously performed, the difference in the toner content of the developer in the developing device 60 in the axial direction of the photosensitive drum 11 is achieved. Can be reduced and toner charging can be promoted, and the occurrence of uneven density in the image in the axial direction of the photosensitive drum 11 can be suppressed. In addition, toner fogging can be suppressed by removing the toner charged to the opposite polarity in the developer in the developing device 60. Furthermore, since the toner content of the developer in the developing device 60 can be averaged, troubles in the machine due to poor toner charging caused by a part of the toner content being too high, and part of the toner content being too low. The occurrence of white spots and the like due to the carrier adhering to the photoreceptor can be suppressed.

  In addition, this invention is not limited to said embodiment, For example, the reference value etc. of a high density continuation judgment can be changed suitably. Further, the image forming apparatus to be applied is not limited to the configuration described in the embodiment.

1 is a block configuration diagram of an image forming apparatus to which an exemplary embodiment is applied. It is a flowchart of an example of image density continuous correspondence control in a case where page number information can be acquired in advance. It is a flowchart of an example of continuous control of image density when page number information cannot be acquired in advance. It is a graph of the test result which implemented the idle driving | running in the middle of continuous image formation, and measured the upstream and downstream density | concentration difference. It is a flowchart of an example of image density continuous correspondence control in a case where page number information can be acquired in advance. It is a flowchart of an example of continuous control of image density when page number information cannot be acquired in advance. It is an example of the control map of variable control of the interval between recording sheets based on an average image density and the number of continuous pages. It is a graph of the test result which expanded the image formation space | interval and formed the high-density image continuously and measured the upstream and downstream density difference. 6 is a graph showing the relationship between toner content and image density. It is a graph which shows the test result which measured the density difference of the upstream and downstream by performing image formation by making toner content rate high. It is a graph which shows the test result as a prior art example which performed continuous image formation and measured the upstream and downstream density | concentration difference.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 11 ... Photosensitive drum (image carrier), 50 ... Control device, 60 ... Developing device, 70 ... Cleaning device, 90 ... Collected toner conveyance mechanism (toner reuse mechanism)

Claims (7)

An image carrier on which an electrostatic latent image is formed;
A developing device for developing the electrostatic latent image formed on the image carrier with a developer containing toner;
A cleaning device for removing and collecting the toner on the image carrier;
A toner reuse mechanism for transporting the collected toner collected by the cleaning device to the developing device for reuse ;
With
When continuous image formation under a predetermined condition with a large amount of toner consumption is performed, continuous image formation is interrupted and idle operation is performed for a predetermined time, and when the collected toner is reused, An image forming apparatus characterized in that many predetermined conditions are set lower by a predetermined amount than when the collected toner is not reused . An image carrier on which an electrostatic latent image is formed;
A developing device for developing the electrostatic latent image formed on the image carrier with a developer containing toner;
A cleaning device for removing and collecting the toner on the image carrier;
A toner reuse mechanism for transporting the collected toner collected by the cleaning device to the developing device for reuse ;
With
During continuous image formation under a predetermined condition with high toner consumption, the interval between successive image formations is set wider than that during normal image formation, the idle operation is performed during the image formation interval , and the collected toner is removed. An image forming apparatus characterized in that, when reusing, a predetermined condition that consumes a large amount of toner is set lower by a predetermined amount than when the collected toner is not reused .   The image forming apparatus according to claim 1, wherein the predetermined condition is a value determined in advance by an image density and a number of continuous pages. Storage means for storing the value;
A determination unit that determines that the image formation consumes a large amount of toner before or during the image formation using the value stored in the storage unit;
The image forming apparatus according to claim 3, further comprising: 3. The image forming apparatus according to claim 1, wherein the toner content of the developer is set higher by a predetermined amount when an image is formed under a predetermined condition in which toner consumption is high.   The image forming apparatus according to claim 2, wherein the predetermined condition is determined by an image density and the number of continuous pages, and the image forming interval is changed according to the image density.   The image forming apparatus according to claim 2, wherein the predetermined condition is determined by an image density and a number of continuous pages, and the image forming interval is expanded to a constant value when the image density is equal to or higher than a predetermined value.

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