JP5699534B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Conventionally, as the image forming apparatus, for example, an electrostatic latent image formed on the surface of a photosensitive drum is visualized using a toner by a developing device, and the toner image is recorded directly or via an intermediate transfer member. Some are configured to form an image by fixing after being transferred onto a sheet.

  By the way, in such an image forming apparatus, when an image with a low image density is formed frequently, the toner in the developing device is hardly consumed and the time in which the toner stays inside becomes long, and the toner is excessively charged by friction. Deteriorated image quality, such as the amount of toner that is electrostatically attached to the electrostatic latent image formed on the surface of the photosensitive drum and develops the electrostatic latent image is reduced, and the image density is reduced. Cause.

  Therefore, as a technique that can suppress the deterioration in image quality when the frequency with which an image with a low image density is formed in the image forming apparatus is high, for example, Japanese Patent Application Laid-Open Nos. 2000-206744 and 2003-76079, or Those disclosed in JP-A-2005-43388 and JP-A-2008-170562 have been proposed.

  An image forming apparatus according to the above Japanese Patent Laid-Open No. 2000-206744 includes an image carrier on which an electrostatic latent image is formed and carried, and an electrostatic latent image forming unit that forms an electrostatic latent image on the image carrier. An image forming apparatus having a developing device that develops the electrostatic latent image formed by the electrostatic latent image forming unit using a developer, wherein the electrostatic latent image is formed by the electrostatic latent image forming unit. An image density detecting means for detecting an image density of an image to be formed on the image carrier before forming, and when a value detected by the image density detecting means is determined to be lower than a desired value; And a forcible discharge means for forming a predetermined electrostatic latent image and forcibly consuming the developer of the developing device.

  Further, an image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 2003-76079 is an image forming apparatus that forms an electrostatic latent image on an image carrier and develops the electrostatic latent image with a developer supplied from the developing device. The image area ratio detecting means for detecting the area ratio of the image to be formed and the development driving time detecting means for detecting the development driving time of the developing device, and according to the image area ratio per unit driving time of development. The developer is forcibly consumed.

Further, an image forming apparatus according to the above Japanese Patent Application Laid-Open No. 2005-43388 includes an image carrier,
A latent image forming means for forming an electrostatic latent image on the image carrier; and
In an electrophotographic image forming apparatus having a developer carrying member and provided with developing means for developing the formed electrostatic latent image by moving the developer carrying member.
A moving distance detecting unit that detects a moving distance of the developer carrying member; an image area rate detecting unit that detects an image area rate per unit moving distance of the developer carrying member; and a control unit; The means detects the image area ratio per unit movement distance based on the image data and the detection result of the movement distance detection means, and the control means detects the toner based on the detection result of the image area ratio detection means. It is configured to control the forced consumption.

Further, an image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 2008-170562 includes a latent image forming unit that forms an electrostatic latent image on an electrostatic latent image carrier,
A developer for supplying toner to the electrostatic latent image formed on the electrostatic latent image carrier to form a toner image;
Toner supply means for supplying toner to the developer;
Transfer means for transferring a toner image formed on the electrostatic latent image carrier onto a transfer material, or sequentially transferring a plurality of color toner images formed on the electrostatic latent image carrier. A transfer means for transferring the image onto the transfer material after being superimposed on the body;
Cleaning means for removing toner on the electrostatic latent image carrier;
When using a transfer unit that uses an intermediate transfer member, an intermediate transfer member cleaning unit that removes toner on the intermediate transfer member;
The latent image forming means and the developing device are operated at a predetermined timing to forcibly attach the toner in the developing device to the electrostatic latent image carrier, and transfer to the transfer material is performed by the transfer means. Without using the cleaning means, the toner forcible consumption means for removing the toner on the intermediate transfer body by the intermediate transfer body cleaning means,
Image amount integration means for integrating and counting the amount of image formed until the predetermined number of printed sheets is reached or until a predetermined developer drive time elapses;
A developer drive amount integrating means for integrating and counting the total area of the areas where image formation has been performed or the developer drive time until a predetermined number of printed sheets is reached or until a predetermined developer drive time elapses;
Integrated value storage means for storing each integrated value by the image amount integrating means and the developer drive amount integrating means;
Divide the integrated image amount until the predetermined number of printed sheets is reached or until the predetermined developer drive time elapses by the total area of the image forming area or the integrated developer drive time. An average image density calculating means for calculating an average image density;
Toner supply amount integration means for integrating a value corresponding to the amount of toner supplied until a predetermined number of printed sheets is reached or until a predetermined developer drive time elapses;
The average image density calculated by the average image density calculating means is less than or equal to a predetermined value set in advance, and is integrated by the toner supply amount integrating means with respect to the image amount integrated value stored in the integrated value storage means. Control means for controlling to forcibly consume the toner by the toner forcible consumption means when the two conditions that the ratio of the integrated value of the toner supply amount is not less than a predetermined value are satisfied. It is comprised so that it may be provided.

JP 2000-206744 A JP 2003-76079 A JP 2005-43388 A JP 2008-170562 A

  Incidentally, the problem to be solved by the present invention is an image forming apparatus capable of maintaining good image quality while avoiding a decrease in productivity due to frequent execution of forced developer consumption. Is to provide.

That is, the invention described in claim 1 includes an image forming unit that forms an image by forming an electrostatic latent image on an image holding member into a visible image using a developer by a developing unit;
A cumulative image number detecting means for cumulatively detecting the number of images formed by the image forming means;
An average image density detecting unit for detecting an average image density of an image over a predetermined number of images formed in the past by the image forming unit;
When the cumulative value of the number of images detected by the cumulative image number detection means is equal to or greater than the first image threshold value, and the average image density detected by the average image density detection means is less than the first density threshold value. A forcible consumption means for forcibly consuming the developer of the developing means after the image forming operation being executed by the image forming means is completed ,
The forced consumption means executes a forced consumption operation of the developer by the forced consumption means in addition to the first operation mode in which the developer of the development means is forcibly consumed after the ongoing image forming operation is completed. A second operation mode for forcibly consuming the developer of the developing means even during a series of image forming operations when the conditions to be satisfied are satisfied, the first operation mode, and the second operation And a third operation mode that combines the mode,
The forced consumption means automatically changes from the first operation mode to the second operation mode when the cumulative value of the number of images detected by the cumulative image number detection means is equal to or greater than a third image threshold. Or an image forming apparatus that automatically switches to a third operation mode that uses both the first operation mode and the second operation mode .
According to a second aspect of the present invention, there is provided an image forming means for forming an image by forming an electrostatic latent image on an image holding member into a visible image using a developer by a developing means;
A cumulative image number detecting means for cumulatively detecting the number of images formed by the image forming means;
An average image density detecting unit for detecting an average image density of an image over a predetermined number of images formed in the past by the image forming unit;
When the cumulative value of the number of images detected by the cumulative image number detection means is equal to or greater than the first image threshold value, and the average image density detected by the average image density detection means is less than the first density threshold value. A forcible consumption means for forcibly consuming the developer of the developing means after the image forming operation being executed by the image forming means is completed,
The forced consumption means executes a forced consumption operation of the developer by the forced consumption means in addition to the first operation mode in which the developer of the development means is forcibly consumed after the ongoing image forming operation is completed. A second operation mode for forcibly consuming the developer of the developing means even during a series of image forming operations when the conditions to be satisfied are satisfied, the first operation mode, and the second operation And a third operation mode that combines the mode,
The forced consumption means is an image forming apparatus comprising switching means for selectively switching a user among the first operation mode, the second operation mode, and the third operation mode.

According to a third aspect of the present invention, the forcible consumption means forms a belt-like toner image in an image-equivalent area corresponding to the image formed by the image forming means, and the belt-like toner image is formed. and including the image corresponding area, claims average image density detected by said mean image density detecting means is characterized in that forcibly consumed developer of the developing unit to reach the first density threshold The image forming apparatus according to 1 or 2 .

Further, in the invention described in claim 4, when the cumulative image number detecting means ends the forced consumption operation of the developer by the forced consumption means, the cumulative number of images by the cumulative image number detecting means is reached. 4. The image forming apparatus according to claim 1 , wherein the value is returned to a reference value.

Further, in the invention described in claim 5 , even if the forced consumption means satisfies the condition for executing the forced consumption operation of the developer by the forced consumption means, the cumulative image number detecting means When the cumulative value of the number of detected images is equal to or greater than a second image threshold value that is greater than the first image threshold value, the average image density detected by the average image density detection means is the first density threshold value. 5. The image forming apparatus according to claim 3 , wherein the developer of the developing unit is forcibly consumed until a second density threshold value greater than the second density threshold value is reached.

According to a sixth aspect of the present invention, there is provided a plurality of image formations in which images of different colors are formed by visualizing an electrostatic latent image on an image carrier with a developer using a developer. Means,
Cumulative image number detecting means for cumulatively detecting the number of images formed by each of the image forming means;
Average image density detection means for detecting an average image density of an image over a predetermined number of images formed in the past by each of the image forming means;
In any one or more of the plurality of image forming units, the cumulative value of the number of images detected by the cumulative image number detecting unit is equal to or greater than a first image threshold, and the average image density When the average image density detected by the detecting unit becomes less than the first density threshold, the developer of the developing unit is forcibly consumed after the image forming operation being performed by the corresponding image forming unit is completed. With forced consumption means ,
The forced consumption means executes a forced consumption operation of the developer by the forced consumption means in addition to the first operation mode in which the developer of the development means is forcibly consumed after the ongoing image forming operation is completed. A second operation mode for forcibly consuming the developer of the developing means even during a series of image forming operations when the conditions to be satisfied are satisfied, the first operation mode, and the second operation And a third operation mode that combines the mode,
The forced consumption means automatically changes from the first operation mode to the second operation mode when the cumulative value of the number of images detected by the cumulative image number detection means is equal to or greater than a third image threshold. Or an image forming apparatus that automatically switches to a third operation mode that uses both the first operation mode and the second operation mode .

According to the first aspect of the present invention, the image quality can be reduced while avoiding the decrease in productivity due to the frequent execution of the forced consumption operation of the developer as compared with the case without this configuration. It can be maintained well.
According to the first aspect of the present invention, as compared with the case where the present configuration is not provided, even if the user performs one image forming operation over a large number of images, the forced consumption of the developer is performed. It is possible to maintain good image quality while avoiding a decrease in productivity due to frequent operations.
Further, according to the first aspect of the present invention, the compulsory consumption operation of the developer is frequently executed while responding to various needs of the user as compared with the case where the present configuration is not provided. It is possible to maintain good image quality while avoiding the accompanying decrease in productivity.
Furthermore, according to the second aspect of the present invention, the forced consumption operation of the developer is frequently executed while responding to the various needs of the user as compared with the case without this configuration. It is possible to maintain good image quality while avoiding the accompanying decrease in productivity.

In addition, according to the invention described in claim 3 , it is possible to reliably avoid the deterioration of the image quality as compared with the case where the present configuration is not provided.

Furthermore, according to the fourth aspect of the present invention, the configuration of the cumulative image number detecting means can be simplified as compared with the case where the present configuration is not provided.

Further, according to the invention described in claim 5 , compared with the case where the present configuration is not provided, even when a single image forming operation covers a large number of images, the forced consumption of the developer is performed. It is possible to maintain good image quality while avoiding a decrease in productivity due to frequent operations.

Further, according to the invention described in claim 6 , in the image forming apparatus originally required to have high productivity as compared with the case without this configuration, the forced consumption operation of the developer is frequently performed. It is possible to maintain good image quality while avoiding a decrease in productivity due to execution.

It is explanatory drawing which shows operation | movement of the image forming apparatus which concerns on the reference example 1 of this invention. 1 is a configuration diagram illustrating a tandem type full-color printer as an image forming apparatus according to Reference Example 1 of the present invention. FIG. It is a block diagram which shows an image formation part. It is a block diagram which shows the control apparatus of the image forming apparatus which concerns on the reference example 1 of this invention. It is explanatory drawing which shows the structure of an image panel. It is explanatory drawing which shows the formation state of an image. 3 is a timing chart showing an image forming operation. FIG. 3 is a configuration diagram illustrating a toner band formation state. 6 is a flowchart showing the operation of the image forming apparatus according to Reference Example 1 of the present invention. 6 is a flowchart showing an operation of an image forming apparatus according to Reference Example 2 of the present invention. It is explanatory drawing which shows operation | movement of the image forming apparatus which concerns on the reference example 2 of this invention. 1 is a block diagram showing a control device of an image forming apparatus according to Embodiment 1 of the present invention. 3 is a flowchart showing the operation of the image forming apparatus according to Embodiment 1 of the present invention. 3 is a flowchart showing the operation of the image forming apparatus according to Embodiment 1 of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings.

Reference example 1
FIG. 2 shows a tandem full-color printer as an image forming apparatus according to Reference Example 1 of the present invention. The tandem full-color printer includes an image reading device and is configured to function as a full-color copier. However, the tandem full-color printer may not include the image reading device. In addition, this full-color printer has a high productivity, which is the number of recording sheets on which image formation is possible per unit time. For example, 100 sheets per minute on an A4 size LEF (Long Edge Feed) recording sheet. An image can be formed to some extent. However, the present invention is not limited to a high-speed tandem image forming apparatus.

  In FIG. 2, reference numeral 1 denotes a main body of the image forming apparatus, and an image reading device 4 that reads an image of the document 2 is disposed at one upper end (left end in the illustrated example) of the image forming apparatus main body 1. ing. The image reading device 4 illuminates a document 2 placed on a platen glass 5 while being pressed by a document pressing member 3 with a light source 6, and reflects a reflected light image from the document 2 with a full rate mirror 7 and a half rate mirror 8. The image reading element 11 reads the image of the document 2 at a predetermined dot density by performing scanning exposure on the image reading element 11 made of a CCD or the like through a reduction optical system including the image forming lens 10 and the image forming lens 10. It is configured.

  The image of the document 2 read by the image reading device 4 is sent to the image processing device 12 as, for example, three-color image data of red (R), green (G), and blue (B) (each 8 bits), In this image processing device 12, predetermined image processing such as shading correction, position shift correction, lightness / color space conversion, gamma correction, frame removal, color / moving editing, etc. is performed on the image data of the document 2. The In addition, image data that has been subjected to predetermined image processing by the image processing device 12 as described above is similarly processed by the image processing device 12 to yellow (Y), magenta (M), cyan (C), black (K) ( Each image data is converted into 4-bit image data of 8 bits). Of course, the image data input to the image processing device 12 may be sent from a personal computer or the like via a communication line (not shown).

By the way, this reference example is configured to include a plurality of image forming means for forming an image using toners having different colors.

That is, inside the image forming apparatus main body 1 according to this reference example , as shown in FIG. 2, as a plurality of image forming means, yellow (Y), magenta (M), cyan (C), black (K) The image forming units 13Y, 13M, 13C, and 13K corresponding to the respective colors are arranged in parallel at regular intervals along the horizontal direction, and the image forming units 13Y, 13M, 13C, and 13K are arranged in parallel. On the upstream side, for example, an image forming unit 13CT of a specific color that forms an image using transparent toner (CT) is arranged at an equal interval from other image forming units. As described above, the transparent toner image forming unit 13CT is arranged on the upstream side so that an image made of transparent toner used for giving gloss to a full-color image is a full-color image on the recording medium. This is because the image is transferred and fixed on the surface of the image. Further, by disposing the transparent toner image forming unit 13CT on the upstream side, when the transparent toner image is not formed, downstream yellow (Y), magenta (M), cyan (C), black (K The image forming operation can be started immediately in each of the image forming units 13Y, 13M, 13C, and 13K), and even if the image forming unit 13CT of transparent toner is arranged, it is desirable that the productivity is not lowered.

  The arrangement order of the yellow (Y), magenta (M), cyan (C), and black (K) image forming units 13Y, 13M, 13C, and 13K and the transparent toner image forming unit 13CT is shown in the drawing. The transparent toner image forming unit 13CT may be used instead of the transparent toner image forming unit 13CT, or a plurality of specific toners such as color toners having different densities may be used together with the transparent toner image forming unit 13CT. A color image forming unit may also be arranged. In addition, one or a plurality of specific color image forming units may be mounted on the main body of the image forming apparatus so as to be exchangeable with other image forming units as necessary.

  Examples of the transparent toner include resins constituting toners used in the other image forming portions 13Y, 13M, 13C, and 13K of yellow (Y), magenta (M), cyan (C), and black (K). What remove | excluded the pigment as a coloring agent from material is used. The image processing apparatus 12 outputs image data corresponding to the transparent toner to the transparent toner image forming unit 13CT. The image data corresponding to the transparent toner is, for example, one that forms a transparent toner image uniformly at a predetermined image density on the entire surface of the recording medium, or yellow (Y), magenta (M), cyan (C). , One that forms a transparent toner image uniformly at a predetermined image density only in an area where image data of each color of black (K) exists, or yellow (Y), magenta (M), cyan (C) The transparent toner image may be uniformly formed at a predetermined image density only in an area where no image data of each color of black (K) exists.

These five image forming units 13CT , 13Y, 13M , 13C, and 13K are basically the same except for the type of toner to be used, as shown in FIG. 2, and are roughly driven at a predetermined rotational speed along the direction of arrow A. A photosensitive drum 15 as an image holding member, a scorotron 16 as a primary charging means for uniformly charging the surface of the photosensitive drum 15, and an image corresponding to each color on the surface of the photosensitive drum 15. Then, an image exposure device 14 as a latent image forming means for forming an electrostatic latent image, and a developing device 17 as a developing means for developing the electrostatic latent image formed on the photosensitive drum 15 with a corresponding color toner. And a cleaning device 18.

  As shown in FIG. 2, the image exposure device 14 modulates the semiconductor laser 19 according to the image data, and emits a laser beam LB from the semiconductor laser 19 according to the image data. The laser beam LB emitted from the semiconductor laser 19 is deflected and scanned by the rotary polygon mirror 22 via the reflecting mirrors 20 and 21, and the focal length is adjusted according to the scanning angle by an unshown f-θ lens. Then, scanning exposure is performed on the photosensitive drum 15 as an image holding member through a plurality of reflecting mirrors 23 and 24 and the like.

From the image processing device 12, the image forming unit 13CT for each color of transparent toner (CT), yellow (Y), magenta, cyan (C), and black (K) is provided. , 13Y, 13M , 13C, 13K image exposure device 14CT , 14Y, 14M , 14C, and 14K, image data of each color is sequentially output. These image exposure apparatuses 14CT , 14Y, 14M , 14C, and 14K, the laser light LB emitted in accordance with the image data corresponds to the corresponding photosensitive drum 15CT. , 15Y, 15M , 15C and 15K are scanned and exposed along the main scanning direction to form electrostatic latent images. Each of the photosensitive drums 15CT , 15Y, 15M , 15C, and 15K, the electrostatic latent image is developed by the developing device 17CT. , 17Y, 17M , 17C, and 17K, the toner images are developed as transparent toner (CT), yellow (Y), magenta, cyan (C), and black (K) toner images, respectively.

Development device 17CT , 17Y, 17M 17C and 17K, as shown in FIG. 3, for example, a two-component developing device in which a two-component developer 171 composed of toner and a carrier is accommodated in the developing device main body 170 is used. The developing device main body 170 is replenished with toner from toner cartridges 175CT to 175K (see FIG. 2) at a predetermined timing, and the toner density in the developing device main body 170 is maintained within a predetermined range. It is configured as follows. The toner supplied into the developing device main body 170 is agitated with the developer 171 in the developing device main body 170 by the two agitators 172 and 173 for stirring and conveying the developer, is frictionally charged, and circulates. In the meantime, it is supplied to the developing roll 174 and conveyed to a developing region facing the surface of the photosensitive drum 15 as a magnetic brush of the developer 171 formed on the surface of the developing roll 174, and the surface of the photosensitive drum 15. It is used for development of the electrostatic latent image formed.

  Transparent toner (CT), yellow (Y), magenta (M), sequentially formed on the photosensitive drums 15CT, 15Y, 15M, 15C, and 15K of the image forming units 13CT, 13Y, 13M, 13C, and 13K. As shown in FIG. 2, toner images of cyan (C) and black (K) colors are transferred to intermediate transfer belts as intermediate transfer members disposed below the image forming units 13CT, 13Y, 13M, 13C, and 13K. 25, primary transfer is performed in a state of being superposed on each other by primary transfer rolls 26CT, 26Y, 26M, 26C, and 26K.

  The intermediate transfer belt 25 includes a driving roll 27, a tension applying roll 28, a driven roll 29, a driven roll 30, a back support roll 31 of the secondary transfer unit, and a plurality of rolls including a driven roll 32. The photosensitive drums 15CT, 15Y, 15M, 15C, 15C, 15C, 15C, 15C, 15C, 15C, 15C, 15C, 15C, 15C, 15C, 15C, 15C, 15C, 15C, 15C, 15C It is driven to circulate at a predetermined speed substantially equal to the rotational speed (circumferential speed) of 15K. As the intermediate transfer belt 25, for example, a flexible synthetic resin film such as polyimide or polyamideimide formed in an endless belt shape is used.

  The transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred in multiple onto the intermediate transfer belt 25 are intermediately transferred to the back support roll 31. The recording sheet 34, which is secondarily transferred onto a recording sheet 34 as a recording medium and transferred onto the recording sheet 34 as a recording medium by the secondary transfer roll 33 that is in pressure contact with the transfer belt 25, and the toner images of the respective colors are transferred, is transported in a double series. It is conveyed to a fixing device 37 by belts 35 and 36. The recording paper 34 onto which the toner images of the respective colors have been transferred is subjected to a fixing process with heat and pressure by a heating belt 38 and a pressure roll 39 of a fixing device 37, and in the case of single-sided printing, the image forming apparatus main body as it is. 1 is discharged onto a discharge tray 40 provided outside of 1.

  As shown in FIG. 2, for example, the recording paper 34 has a predetermined size or material from any one of the plurality of paper feed trays 41 and 42, and a paper feed roller 43 and a paper transport roller. The paper is once transported to the registration roll 47 via the paper transport path 46 composed of the pairs 44 and 45 and stopped. The recording paper 34 supplied from one of the paper feed trays 41 and 42 is sent out to the secondary transfer position of the intermediate transfer belt 25 by a registration roll 47 that is rotationally driven at a predetermined timing.

  Further, when images are formed on both sides of the recording paper 34 by the image forming apparatus, the recording paper 34 on which the image is fixed on one side by the fixing device 37 is not discharged out of the apparatus as it is, but a switching gate (not shown). As a result, the transport path of the recording paper 34 is switched downward and transported to the reverse paper transport path 48 once. Then, the recording paper 34 conveyed to the reversing paper conveyance path 48 is reversed, with the conveyance direction reversed, through the double-sided paper conveyance path 49 and the normal paper conveyance path 46. In this state, the sheet is conveyed again to the secondary transfer position of the intermediate transfer belt 25 and an image is formed on the back surface, and then subjected to a fixing process with heat and pressure by the heating belt 38 and the pressure roll 39 of the fixing device 37. Then, the image is discharged onto a discharge tray 40 provided outside the image forming apparatus main body 1.

  Note that the surface of the photosensitive drum 16 after the primary transfer of the toner image is completed is cleaned by the cleaning device 18. The intermediate transfer belt 25 after the secondary transfer of the toner image is cleaned by a belt cleaning device 50 whose surface is disposed in the vicinity of the drive roll 27.

By the way, in the image forming apparatus configured as described above, the transparent toner (CT), yellow (Y), magenta, cyan (C), and black (K) image forming units 13CT. , 13Y, 13M , 13C, 13K, at least one image forming unit 13CT , 13Y, 13M , 13C, and 13K, if the frequency with which the image density is low is formed, the toner in the developing device 17 of the corresponding image forming unit 13 is hardly consumed and the residence time in the developing device main body 170 is long. As a result, the toner is excessively frictionally charged and deteriorates, the amount of toner contributing to developing the electrostatic latent image formed on the surface of the photosensitive drum 15 is reduced, and the image density is lowered. Causes a drop.

Therefore, in the image forming apparatus according to the reference example , the number of images formed by the image forming unit is cumulatively detected, and the number of images formed in advance is formed by the image forming unit. An average image density detecting means for detecting an average image density of the obtained image, and a cumulative value of the number of images detected by the cumulative image number detecting means is equal to or greater than a first image threshold and is detected by the average image density detecting means. Forcibly consuming means for forcibly consuming the developer of the developing means after the image forming operation being executed by the image forming means is completed when the average image density is less than a first density threshold. It is configured as follows.

FIG. 4 is a block diagram showing a control circuit of the image forming apparatus according to this reference example .

  In FIG. 4, reference numeral 100 denotes a control circuit as a control unit including a CPU, MCU, or the like that controls an image forming operation of the image forming apparatus. The control circuit 100 is, for example, according to a program stored in the ROM 101. Based on the control data stored in the NVRAM (nonvolatile memory) 102, the transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) image forming units 13CT, 13Y, It also has a function as a control means for controlling the image forming conditions of the respective color toner images in 13M, 13C, and 13K.

  Reference numerals 13CT, 13Y, 13M, 13C, and 13K denote the above-described transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) image forming units, respectively. .

As shown in FIG. 5A, the control circuit 100 includes transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) image forming units 13CT, 13Y, It also has a function as a cumulative image number detecting means for cumulatively detecting the number of images 60 ₁ , 60 ₂ ,... Formed by 13M, 13C, and 13K.

In the control circuit 100, as shown in FIG. 5 (a), when an image formed immediately before the N-th image 60 _N, The current image one sheet 60 _N-1, 62 sheets ... The current The image is 60 _N-62 , the image before 63 sheets is 60 _N-63 , and the image before 64 sheets is 60 _N-64 .

  In the image forming apparatus, as shown in FIG. 2, an image can be formed on the recording paper 34 of any size by feeding the recording paper 34 from the paper feed tray 41 or the paper feed tray 42. However, in this embodiment, as shown in FIG. 5B, the A4 size recording paper 34 is fed starting from one side 34a having a relatively long length (LEF: The image area set to perform (Long Edge Feed) is used as a reference image panel 61 to count the number of images. That is, one image panel 61 corresponds to one image 60. Here, for the sake of simplification, the recording paper 34 having a size equal to or smaller than the recording paper of A4 size (LEF) is counted as “1” for all the image panels 61 and is larger than the recording paper of A4 size (LEF). The recording sheets 34 up to A3 size, which is the size, are all counted with the number of image panels 61 being “2”. However, the number of images is not limited to this, and the recording paper 34 of A4 size (LEF) is set to the image panel “1”, and the recording paper 34 of other sizes has an A4 size (LEF) recording paper 34 of the area. Of course, it may be configured to count by multiplying by a coefficient corresponding to the ratio to.

  In addition, the control circuit 100 uses the past in each of the transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) image forming units 13CT, 13Y, 13M, 13C, and 13K. The image forming unit 13CT, 13Y, 13M, 13C, and 13K are configured to function as an average image density detecting unit that detects the average image density over a plurality of images formed in the image forming units 13CT, 13Y, 13M, 13C, and 13K. The average image density is used as a parameter for evaluating the degree of toner deterioration in the developing devices 17CT, 17Y, 17M, 17C, and 17K of the image forming units 13CT, 13Y, 13M, 13C, and 13K.

  More specifically, the average image density is determined in advance by determining the total number of pixels of the image panel on which images have been formed in the past by the image forming units 13CT, 13Y, 13M, 13C, and 13K. It is given as a value divided by the cumulative driving time of the developing device required to develop the image over the specified number.

  As shown in FIG. 2, the control circuit 100 receives image forming units 13CT from the image processing apparatus 12 for transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K). Based on the image data output to 13Y, 13M, 13C, and 13K, the total number of pixels of the image formed by the image exposure device 14 of each of the image forming units 13CT, 13Y, 13M, 13C, and 13K is calculated. It is obtained by cumulatively counting the number of pixels. In the image exposure device 14, as shown in FIG. 6, based on the image data output from the image processing device 12, image exposure is performed for each dot according to the resolution of the image data. Reference numeral 100 denotes a cumulative count of the number of pixels of image data output from the image processing device 12, thereby obtaining the total number of pixels per image panel 61.

As shown in FIG. 5, the control circuit 100 sets the total number of pixels of the first image 60 to K ₁ , the total number of pixels of the second image 60 to K ₂ ,. If the total number of pixels is K _N , among the images formed in the past by the image forming units 13CT, 13Y, 13M, 13C, and 13K, for example, the image 60 covers a predetermined number (for example, 64) immediately before. The cumulative number of pixels ΣK = K _N , K _N−1 ,... K _N−63 of the image panel 61 on which is formed is counted.

On the other hand, as shown in FIG. 7, the control circuit 100 is required to develop a predetermined number (for example, 64) of images in the past by the image forming units 13CT, 13Y, 13M, 13C, and 13K. drive time oT = T _N of the developing device 17 which, T _N-1, by counting ··· T _N-63 cumulatively required to develop the image 60 over a predetermined number in the past The accumulated driving time of the developing device 17 is obtained.

Then, the control circuit 100 predetermines the total number of pixels ΣK of the image panel 61 on which the image 60 is formed in the past by the image forming units 13CT, 13Y, 13M, 13C, and 13K. It is obtained by calculating an average image density K _AVE = ΣK / ΣT as a value divided by the cumulative driving time ΣT of the developing device required to develop the image over the specified number.

Further, in the control circuit 100, as shown in FIG. 5A, the (latest) image is formed immediately before by the image forming units 13CT, 13Y, 13M, 13C, and 13K as the average image density K _AVE . With the Nth image panel 61 as a reference, a moving average image density is always obtained by taking a so-called moving average obtained by averaging the image densities K of images traced back in the past by a predetermined number.

  Further, the control circuit 100 determines that the cumulative value of the number of images 60 detected by the cumulative image number detection unit is equal to or greater than the first image threshold value P1, and the average image density K detected by the average image density detection unit is When the density is less than the first density threshold K1, the developer of the developing device 17 is forcibly applied after the image forming operation being executed by the image forming units 13CT, 13Y, 13M, 13C, and 13K that satisfies the condition is completed. It also functions as a compulsory consumption means.

  As shown in FIG. 8, the forced consumption operation of the developer is performed by a predetermined image density (for example, about 50 to 60%) by the image forming units 13CT, 13Y, 13M, 13C, and 13K that satisfy the conditions. ) Over a predetermined length along the moving direction of the intermediate transfer belt 25, yellow (Y), magenta (M), cyan (C), black (K), transparent toner (CT) and spare (#). Are formed in a belt-like toner image 62Y, 62M, 62C, 62K, 62CT, 62 # (hereinafter referred to as “toner band”), and the toner bands 62Y, 62M, 62C, 62K, 62CT, 62 # are intermediately formed. This is performed by transferring onto the transfer belt 25. The operation of forming the toner bands 62Y, 62M, 62C, 62K, 62CT, 62 # is basically executed under the same conditions as the normal image forming operation, but the toner bands 62Y, 62M, 62C, 62K, 62CT, Of course, as long as 62 # can be formed, it may be executed under conditions different from the normal image forming operation. The toner bands 62Y, 62M, 62C, 62K, 62CT, and 62 # transferred onto the intermediate transfer belt 25 are formed without passing the recording paper 34, and are removed by the cleaning device 50 for the intermediate transfer belt 25. The

  The toner bands 62Y, 62M, 62C, 62K, 62CT, 62 # are transferred to the toner band panel 63 set corresponding to the image panel 61 as shown in FIG. A toner image having a predetermined length L along the rotation direction of the photosensitive drum 15 is formed at a predetermined image density (for example, 50 to 60%) over the entire width in the longitudinal direction. The length L of the toner image may be variable so that it can be set as appropriate.

  If any one of the image forming units 13CT, 13Y, 13M, 13C, and 13K does not satisfy the toner band forming conditions, the areas of the opened toner bands 62Y, 62M, 62C, 62K, 62CT, and 62 # are displayed. Alternatively, other color toner bands may be formed.

  More specifically, as shown in FIG. 8, the toner bands 62Y, 62M, 62C, 62K, 62CT, and 62 # are, for example, yellow, magenta, cyan, and cyan from the head along the traveling direction of the toner band panel 63. It is formed in the order of black, transparent toner, and preliminary. A patch region 64 for forming a patch for detecting image density and image position is provided at the tip of the toner band panel 63. The toner bands 62Y, 62M, 62C, 62K, 62CT, and 62 # are formed with a gap 65 required to switch the voltage applied to the primary transfer roll 26 on the downstream side of the patch region 64.

  The toner bands 62Y, 62M, 62C, 62K, 62CT, 62 # are set to, for example, an image density of 50% or 60% & degree, but are not limited to this, and are formed at other densities. Of course, it may be.

  Further, the toner bands 62Y, 62M, 62C, 62K, 62CT and 62 # are used until the average image density K including the toner bands 62Y, 62M, 62C, 62K, 62CT and 62 # reaches a predetermined threshold value. Done. That is, the toner bands 62Y, 62M, 62C, 62K, 62CT, 62 # are used when the average image density reaches a predetermined threshold value in the developing device 17 for all the colors in one toner band panel 63. The formation of the bands 62Y, 62M, 62C, 62K, 62CT, 62 # is completed, but the average image density does not reach a predetermined threshold value in the developing device 17 for all the colors in one toner band panel 63. The toner bands 62Y, 62M, 62C, 62K, 62CT, and 62 are continuously set by continuously setting new toner band panels 63 until the average image density reaches a predetermined threshold value in the developing devices 17 of all colors. The # forming operation is repeated.

  The developing device 17 whose average image density has reached a predetermined threshold is stopped at that time.

As described above, as the average image density, as described above, the cumulative number of pixels over a predetermined number of images in which images have been formed in the past in each of the image forming units 13CT, 13Y, 13M, 13C, and 13K. Device 17CT , 17Y, 17M , 17C, and 17K, and is not limited to a value divided by the cumulative driving time, but is accumulated over a predetermined number of images in which images have been formed in the past in each of the image forming units 13CT, 13Y, 13M, 13C, and 13K. The number of pixels may be substituted with a value obtained by dividing the number of pixels by a predetermined number (for example, “64”) in which images are formed by the image forming units 13CT, 13Y, 13M, 13C, and 13K. good.

  That is, the cumulative driving time of the developing device 17 is proportional to the total number of images formed by the image forming units 13CT, 13Y, 13M, 13C, and 13K, the number of prints, the total driving time of the photosensitive drum 15, and the like. Therefore, the total number of images formed by these image forming units 13CT, 13Y, 13M, 13C, and 13K, the number of prints, the total driving time of the photosensitive drum 15, and the like may be used.

  However, since the cumulative driving time of the developing device 17 serves as an index for directly evaluating the deterioration state of the toner causing the image quality deterioration as described above, the cumulative driving time of the developing device 17 is used. desirable.

With the above configuration, in the image forming apparatus according to this reference example , the image quality is improved while avoiding a decrease in productivity due to frequent execution of the forced developer consumption operation as follows. It is possible to maintain.

  That is, in the image forming apparatus, as shown in FIG. 2, for example, based on the image data input to the image processing apparatus 12, transparent toner (CT), yellow (Y), magenta (M), cyan (C ) And black (K) image forming portions 13CT, 13Y, 13M, 13C, and 13K, toner images of respective colors are formed, and transparent toner formed by these image forming portions 13CT, 13Y, 13M, 13C, and 13K. The toner images of each color (CT), yellow (Y), magenta (M), cyan (C), and black (K) are transferred onto the intermediate transfer belt 25 in a multiple manner, and then from the intermediate transfer belt 25. Secondary transfer is performed collectively on the recording paper 34.

  In the image forming apparatus, as shown in FIG. 2, toners of colors according to image data such as transparent toner (CT), yellow (Y), magenta (M), cyan (C), black (K), etc. The recording sheet 34 onto which the image has been transferred undergoes a fixing process by the fixing device 37 and is discharged onto a discharge tray 40 provided outside the image forming apparatus main body 1.

  At that time, in the image forming apparatus, as shown in FIG. 9, when an image forming operation is executed in each of the image forming units 13CT, 13Y, 13M, 13C, and 13K (step 101), the control circuit 100 in FIG. As shown in FIG. 4, the number of image panels 61 on which images are formed in each of the image forming units 13CT, 13Y, 13M, 13C, and 13K is cumulatively counted, and one of the image forming units 13CT, 13Y, 13M, 13C, It is determined whether or not the cumulative value of the image panel 61 at 13K has reached a predetermined value P1 or more stored in the NVRAM 102 (step 102).

  When the control circuit 100 determines that the cumulative value ΣP of the image panel 61 has not reached a predetermined value P1 or more in any of the image forming units 13CT, 13Y, 13M, 13C, and 13K, the print job is processed. It is determined whether or not the print job is finished (step 105), and if the print job is not finished, the process returns to step 101 to execute the image forming operation.

On the other hand, when the control circuit 100 determines that the cumulative value ΣP of the image panel 61 has reached the predetermined value P1 or more in any one of the image forming units 13CT, 13Y, 13M, 13C, and 13K, the image panel 61 It is determined whether or not the average image density K _AVE of the past N (for example, 64) panels in the image forming unit 13 in which the cumulative value ΣP of the image has reached the predetermined value P1 or more is less than the first density threshold K1. (Step 103). In the control circuit 100, the average image density K _AVE of the past N (for example, 64) panels in the image forming unit 13 in which it is determined that the accumulated value of the image panel 61 has reached the predetermined value P1 or less is less than the first density threshold K1. If it is determined that the print job is not completed, it is determined whether or not the print job is completed (step 105). If the print job is not completed, the process returns to step 101 to execute the image forming operation.

  On the other hand, in the control circuit 100, as shown in FIG. 1, the average image density of past N (for example, 64) panels in the image forming unit 13 in which it is determined that the cumulative value of the image panel 61 has reached a predetermined value P1 or more. If it is determined that the toner density is less than the first density threshold value K1, it is determined that the toner band forming conditions in the corresponding image forming unit 13 are satisfied, and a toner band entry operation is performed (step 104). It is determined whether or not (step 105), and if the print job has not ended, the process returns to step 101 to execute the image forming operation.

  When the control circuit 100 determines that the print job being executed has been completed (step 105), the control circuit 100 determines whether or not there is a toner band entry (step 106). End the operation.

  Further, the control circuit 100 determines that there is a toner band entry (step 106), starts the toner band forming operation (step 107), and in the corresponding image forming unit 13 as shown in FIG. An image forming operation of the toner band 62 is executed (step 108).

  Next, the control circuit 100 determines whether or not the average image density of the past N (for example, 64) panels in the image forming unit 13 has reached the first density threshold value K1 and is equal to or higher than the first density threshold value K1. If the average image density of the past N (for example, 64) panels in the image forming unit 13 is not equal to or higher than the first density threshold value K1, the process returns to step 108 and the image forming unit 13 concerned. Then, the image forming operation of the toner band 62 is executed.

  Here, the average image density of the past N (for example, 64) panels in the image forming unit 13 determined in step 109 in the control circuit 100 includes the toner band forming panel 62 of the toner band 62 formed immediately before. The image density is calculated.

  When the control circuit 100 determines that the average image density of the past N (for example, 64) panels in the image forming unit 13 is equal to or higher than the first density threshold K1 (step 109), the image formation of the toner band 62 is performed. When the operation is finished (step 110), a zero reset operation is performed to reset the accumulated value of the image panel 61 to the reference value “0” and reset (step 111), and the printing operation is finished.

Thus, in the above reference example , whether or not the formation conditions of the toner bands 62Y, 62M, 62C, 62K, 62CT, and 62 # are satisfied according to the cumulative value of the number of images and the average image density by the control circuit 100 is determined. If it is determined and the formation conditions of the toner bands 62Y, 62M, 62C, 62K, 62CT, 62 # are satisfied and a series of print jobs are being executed, the print job being executed is completed. Thereafter, the forming operation of the toner bands 62Y, 62M, 62C, 62K, 62CT, and 62 # is executed in the corresponding image forming units 13CT, 13Y, 13M, 13C, and 13K.

Therefore, in the above reference example , even for a user who frequently forms a relatively small number of images, the printing operation is interrupted unnecessarily in order to form the toner bands 62Y, 62M, 62C, 62K, 62CT, 62 #. If the toner bands 62Y, 62M, 62C, 62K, 62CT, 62 # are satisfied, the toner bands 62Y, 62M, 62C, 62K, 62CT, 62 # are completed after the print job is completed. Therefore, it is possible to maintain the image quality while maintaining the productivity.

Reference example 2
FIG. 10 shows Reference Example 2 of the present invention. The same reference numerals are given to the same parts as in Reference Example 1 , and in this Reference Example 2 , the forced consumption means includes the forced consumption. Even when the condition for executing the forced developer consumption operation by the means is satisfied, a second value in which the cumulative value of the number of images detected by the cumulative image number detection means is larger than the first image threshold value. When the image threshold value is exceeded, the developer of the developing unit is forced until the average image density detected by the average image density detecting unit reaches a second density threshold value that is larger than the first density threshold value. It is configured to be consumed.

In the reference example 1 , as shown in FIG. 9, the control circuit 100 determines that the conditions for forming the toner bands 62Y, 62M, 62C, 62K, 62CT, and 62 # are satisfied, and the toner band forming operation is entered. Even in such a case, the print operation being executed is continued until the print job is completed.

Therefore, in the first reference example , the number of recording sheets 34 printed after the determination that the condition for forming the toner band 62 is satisfied by the control circuit 100 and the end of the print job being executed is relative. If the amount of toner is too large, the toner in the developing device 17 may deteriorate during that time.

Therefore, in the reference example 2 , as shown in FIG. 10, the control circuit 100 satisfies the toner band 62 formation condition, that is, even when the toner band is entered (step 104), the toner When creating the band 62, it is determined whether or not the cumulative value of the number of images counted by the control circuit 100 is greater than or equal to the second image threshold P2 that is greater than the first image threshold P (step 120).

  Then, as shown in FIG. 10, when the toner band 62 is created, the control circuit 100 is less than the second image threshold P2 in which the cumulative value of the number of images counted by the control circuit 100 is larger than the first image threshold P1. When the density parameter K3 is determined to be the first density threshold value K1, the toner band is set until the average image density detected by the control circuit 100 reaches the first density threshold value K1 (step 121). The image forming operation 62 is continued (step 109).

  On the other hand, when the toner band 62 is created, if it is determined that the cumulative value of the number of images counted by the control circuit 100 is greater than or equal to the second image threshold P2 that is greater than the first image threshold P1, the density parameter K3. Is set to the second density threshold value K2 (step 121), and as shown in FIG. 11, the average image density detected by the control circuit 100 is set to the second density threshold value K2 that is larger than the first density threshold value K1. The image forming operation of the toner band 62 is continued until the toner band 62 is reached (step 109).

In this way, in Reference Example 2 , the number of recording sheets 34 printed after the determination that the condition for forming the toner band 62 is satisfied and before the print job being executed is completed is relatively large. In this case, since the image forming operation of the toner band 62 is continued until the average image density detected by the control circuit 100 reaches the second density threshold value k2 that is larger than the first density threshold value K1, the development is performed during that time. It is possible to suppress or avoid the deterioration of the toner in the apparatus 17 and the deterioration of the image quality of an image to be formed next.

Other configurations and operations are the same as those in the reference example, and thus the description thereof is omitted.

Embodiment 1
FIGS. 12 to 14 show Embodiment 1 of the present invention. The same reference numerals are given to the same parts as those in the reference example , and in this Embodiment 1 , the forced consumption means is In addition to the first operation mode in which the developer of the developing unit is forcibly consumed after completion of the image forming operation being executed, the condition for executing the forced consumption of developer by the forced consumption unit is satisfied. In this case, even in the middle of a series of image forming operations, the second operation mode for forcibly consuming the developer of the developing unit, the first operation mode, and the second operation mode are used in combination. 3 operation modes.

In the first embodiment , the forcible consumption unit is configured such that when the cumulative value of the number of images detected by the cumulative image number detection unit becomes equal to or greater than a third image threshold value that is greater than the second image threshold value. Automatically switches from the first operation mode to the second operation mode, or automatically switches to the third operation mode using both the first operation mode and the second operation mode. It is configured.

That is, in the first embodiment , as shown in FIG. 12, an operation mode changeover switch 200 as an operation mode changeover means is provided, and the control circuit 100 causes the accumulated image number detection means to operate. When the cumulative value of the number of images detected by the above becomes equal to or greater than a third image threshold value that is larger than the second image threshold value, the developer of the developing unit is forcibly applied after the image forming operation being executed is completed. When the condition for executing the forced developer consumption operation is satisfied from the first operation mode to be consumed, the second developer forcibly consuming the developer in the developing unit even during the series of image forming operations. The operation mode can be switched to the third operation mode in which the first operation mode and the second operation mode are used together.

More specifically, in the first embodiment , as shown in FIG. 12, when the operation mode changeover switch 200 is used to switch to the first operation mode, the operation of the reference example 1 described above is executed.

In the first embodiment , as shown in FIG. 12, when the operation mode changeover switch 200 switches to the second operation mode, the control circuit 100 determines the number of images detected by the cumulative image number detection means. Until the cumulative value reaches the third image threshold value that is larger than the second image threshold value (if less), the operation of Reference Example 2 described above is executed.

  That is, when the mode is switched to the second operation mode, as shown in FIG. 13, the control circuit 100 determines whether or not the print job is ended in step 105 and determines that the print job is not ended. However, instead of returning to step 101 as it is, it is determined whether or not the cumulative value of the image panel is equal to or greater than a third image threshold value P3 that is larger than the second image threshold value P2, and the cumulative value of the image panel is the first value. If it is determined that it is not greater than or equal to the third image threshold value P3, the process returns to step 101, and the above-described operation of the second embodiment is executed.

  On the other hand, in step 131 of FIG. 13, the control circuit 100 determines that the cumulative value of the number of images detected by the cumulative image number detection means is equal to or greater than a third image threshold P3 that is greater than the second image threshold P2. Then, it is determined whether the operation mode selected by the operation mode changeover switch 200 is the second operation mode or the third operation mode (step 132).

  Then, as shown in FIG. 13, when it is determined that the operation mode is the second operation mode (step 132), the control circuit 100 determines whether there is a toner band entry (step 133). If it is determined that there is no toner band entry, a printing operation is executed (step 138).

  If the control circuit 100 determines that there is an entry for the toner band, it starts a toner band forming operation (step 134), and as shown in FIG. The image forming operation is executed (step 135).

  Next, the control circuit 100 continues the image forming operation of the toner band 62 until the average image density detected by the control circuit 100 reaches the first density threshold value K1 (step 136). When the detected average image density reaches the first density threshold value K1, the image forming operation of the toner band 62 is finished (step 137), and the printing operation is executed (step 138).

  Thereafter, the control circuit 100 determines whether or not the average image density detected by the control circuit 100 is less than the first density threshold K1 (step 139), and the average image density is less than the first density threshold K1. In this case, after the entry of the toner band is made (step 140), it is determined whether or not the print job is finished (step 141), and the average image density is equal to or higher than the first density threshold K1. In step 141, it is determined whether the print job is completed. Then, the control circuit 100 returns to step 133 when the print job is not completed, and ends the printing operation as it is when the print job is completed.

  On the other hand, when the control circuit 100 determines that the operation mode is the third operation mode, as shown in step 132 of FIG. 13, the operation shown in the flowchart of FIG. 14 is executed.

That is, when the mode is switched to the third operation mode, as shown in FIG. 14, in the control circuit 100, after the print image forming operation is executed (step 151), any one of the image forming units 13CT, 13Y, Also in 13M, 13C, and 13K, it is determined whether or not the average image density K _AVE of the past N (for example, 64) panels in the image forming unit 13 is less than the first density threshold K1 (step 1152).

In the control circuit 100, the average image density K _AVE of the past N (for example, 64) panels in the image forming unit 13 in which it is determined that the accumulated value of the image panel 61 has reached the predetermined value P1 or less is less than the first density threshold K1. If not, it is determined whether or not the print job is finished (step 154). If it is determined that the average image density K _AVE of the image panel is less than the first density threshold K1, the entry of the toner band is determined. (Step 153), it is determined whether or not the print job is finished (Step 154).

  When the control circuit 100 determines that the print job is completed (step 154), the first operation mode is executed in the same manner as the operation modes shown in step 106 to step 111 in FIG. Steps 156 to 163).

  On the other hand, as shown in FIG. 14, when it is determined that the print job is not finished (step 154), the control circuit 100 determines whether or not there is a toner band entry (step 164), and there is no toner band entry. Return to step 151.

  Further, as shown in FIG. 14, when it is determined that there is a toner band entry (step 164), the control circuit 100 starts the toner band forming operation (step 165), and as shown in FIG. Then, the image forming operation of the toner band 62 is executed in the corresponding image forming unit 13 (step 166).

  Next, the control circuit 100 continues the image forming operation of the toner band 62 until the average image density detected by the control circuit 100 reaches the first density threshold K1 (step 167). When the detected average image density reaches the first density threshold value K1, the image forming operation of the toner band 62 is finished (step 168), and the process returns to step 151 to execute the printing operation (step 151).

As described above, in the first embodiment , when the number of recording sheets 34 to be printed in one job is significantly large, the operation mode changeover switch 200 causes the second operation mode or the third operation mode. By switching to, it is possible to effectively suppress deterioration in image quality by executing an operation for forcibly consuming the developer of the developing device 17 even during a series of image forming operations.

Other configurations and operations are the same as those in the reference example, and thus the description thereof is omitted.

In the reference example and the embodiment, the image forming apparatus including a plurality of image forming units that form images of different colors has been described. However, the present invention is not limited to this, and the image is not limited to this. Needless to say, the present invention can also be applied to an image forming apparatus having only one image forming unit to be formed or a so-called four-cycle image forming apparatus for sequentially forming images of different colors on one image carrier. .

  13CT, 13Y, 13M, 13C, 13K: Transparent toner (CT), yellow (Y), magenta, cyan (C), black (K) image forming units, 62Y, 62M, 62C, 62K, 62CT: toner band 100: Control circuit (cumulative image number detection means, average image density detection means, forced consumption means).

Claims (6)

An image forming means for forming an image by making the electrostatic latent image on the image carrier visible by a developing means using a developer; and
A cumulative image number detecting means for cumulatively detecting the number of images formed by the image forming means;
An average image density detecting unit for detecting an average image density of an image over a predetermined number of images formed in the past by the image forming unit;
When the cumulative value of the number of images detected by the cumulative image number detection means is equal to or greater than the first image threshold value, and the average image density detected by the average image density detection means is less than the first density threshold value. A forcible consumption means for forcibly consuming the developer of the developing means after the image forming operation being executed by the image forming means is completed ,
The forced consumption means executes a forced consumption operation of the developer by the forced consumption means in addition to the first operation mode in which the developer of the development means is forcibly consumed after the ongoing image forming operation is completed. A second operation mode for forcibly consuming the developer of the developing means even during a series of image forming operations when the conditions to be satisfied are satisfied, the first operation mode, and the second operation And a third operation mode that combines the mode,
The forced consumption means automatically changes from the first operation mode to the second operation mode when the cumulative value of the number of images detected by the cumulative image number detection means is equal to or greater than a third image threshold. Or an image forming apparatus that automatically switches to a third operation mode that uses both the first operation mode and the second operation mode . An image forming means for forming an image by making the electrostatic latent image on the image carrier visible by a developing means using a developer; and
A cumulative image number detecting means for cumulatively detecting the number of images formed by the image forming means;
An average image density detecting unit for detecting an average image density of an image over a predetermined number of images formed in the past by the image forming unit;
When the cumulative value of the number of images detected by the cumulative image number detection means is equal to or greater than the first image threshold value, and the average image density detected by the average image density detection means is less than the first density threshold value. A forcible consumption means for forcibly consuming the developer of the developing means after the image forming operation being executed by the image forming means is completed,
The forced consumption means executes a forced consumption operation of the developer by the forced consumption means in addition to the first operation mode in which the developer of the development means is forcibly consumed after the ongoing image forming operation is completed. A second operation mode for forcibly consuming the developer of the developing means even during a series of image forming operations when the conditions to be satisfied are satisfied, the first operation mode, and the second operation And a third operation mode that combines the mode,
The image forming apparatus , wherein the forcible consumption means includes a switching means for a user to selectively switch between the first operation mode, the second operation mode, and the third operation mode . The forced consumption means forms a belt-like toner image in an image equivalent area corresponding to an image formed by the image forming means, and includes the image equivalent area in which the belt-like toner image is formed, and the average image density 3. The image forming apparatus according to claim 1, wherein the developer of the developing unit is forcibly consumed until an average image density detected by the detecting unit reaches the first density threshold value. The cumulative image number detecting means, after completing the forced consumption operation of the developer by the forced consumption unit, claims and returning the number of images of the cumulative value by the cumulative image number detecting means to the reference value Item 4. The image forming apparatus according to any one of Items 1 to 3 . The forced consumption means has a cumulative value of the number of images detected by the cumulative image number detection means even when a condition for executing a forced developer consumption operation by the forced consumption means is satisfied. Until the average image density detected by the average image density detection means reaches a second density threshold value greater than the first density threshold value. The image forming apparatus according to claim 3, wherein the developer of the developing unit is forcibly consumed. A plurality of image forming means for forming images of different colors from each other by visualizing the electrostatic latent image on the image carrier with a developer using a developing means;
Cumulative image number detecting means for cumulatively detecting the number of images formed by each of the image forming means;
Average image density detection means for detecting an average image density of an image over a predetermined number of images formed in the past by each of the image forming means;
In any one or more of the plurality of image forming units, the cumulative value of the number of images detected by the cumulative image number detecting unit is equal to or greater than a first image threshold, and the average image density When the average image density detected by the detecting unit becomes less than the first density threshold, the developer of the developing unit is forcibly consumed after the image forming operation being performed by the corresponding image forming unit is completed. With forced consumption means ,
The forced consumption means executes a forced consumption operation of the developer by the forced consumption means in addition to the first operation mode in which the developer of the development means is forcibly consumed after the ongoing image forming operation is completed. A second operation mode for forcibly consuming the developer of the developing means even during a series of image forming operations when the conditions to be satisfied are satisfied, the first operation mode, and the second operation And a third operation mode that combines the mode,
The forced consumption means automatically changes from the first operation mode to the second operation mode when the cumulative value of the number of images detected by the cumulative image number detection means is equal to or greater than a third image threshold. Or an image forming apparatus that automatically switches to a third operation mode that uses both the first operation mode and the second operation mode .

Images