JP2008292734A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To extend the service life of an image forming section, to downsize an image forming apparatus, and to effectively suppress image deterioration such as a density decrease and density nonuniformity while shortening an operating time, except for printing, in the image forming apparatus, which includes an image carrier 1, a developing device 5 for developing a latent image on the image carrier, an intermediate transfer body 10 to which a developer image is primarily transferred from a primary transfer means 7 in contact with the image cattier, a means 17 for secondarily transferring the developer image on the intermediate transfer body onto a recording material 12, a first cleaning device 8 for removing the primary transfer residual developer from the image carrier; and a second cleaning device 21 for removing secondary transfer residual developer from the intermediate transfer body, and performs a developing device refresh operation, by which, in accordance with the frequency of the use of the developing device, a developer is forcibly transferred to the image carrier from the developing device when an image is not formed. <P>SOLUTION: In the developing device refresh operation, the developer transferred to the image carrier is recovered to both the first cleaning device 8 and the second cleaning device 21. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system or the like.

  Here, the electrophotographic image forming apparatus forms an image on a recording medium using an electrophotographic image forming system. For example, an electrophotographic copying machine, an electrophotographic printer (for example, a laser beam printer, an LED printer, etc.), a facsimile machine, a word processor, and the like are included.

  In addition, the process cartridge is a cartridge in which the electrophotographic photosensitive member (image carrier) and the image forming process means acting on the electrophotographic photosensitive member are integrally formed, and the cartridge is attached to and detached from the main body of the electrophotographic image forming apparatus. It is possible. The image forming process means acts on the electrophotographic photosensitive member and means at least one of a charging means, a developing means, and a cleaning means.

  Conventionally, in an image forming apparatus using an electrophotographic image process, when an image with a low printing rate is continuously printed, the toner is changed by circulating in the developing unit without being consumed, and the density is low. In some cases, image deterioration such as density unevenness may occur.

  Therefore, a “developing device refresh operation” is performed in which the toner in the developing device is forcibly transferred to the photosensitive drum (image carrier) side and consumed during non-image formation at a predetermined interval or the like. The toner forcibly transferred to the photosensitive drum is collected by a cleaning device provided on the photosensitive drum. As a result, there is an example in which a change in toner caused by the same toner circulating in the developing device is suppressed (Patent Document 1).

  Specific examples of the “developing device refresh operation” include the following 1) to 3).

1) Force transfer of a fixed amount of toner with a certain number of sheets 2) Set a low printing rate where toner change is noticeable in advance as a threshold value, and average the result when the average printing rate is less than the threshold value The difference printing area is calculated so that the printing rate becomes substantially the same as the threshold value, and the toner is forcibly transferred by that amount. 3) When the difference between the printing rate during printing and the threshold value is integrated and reaches a certain value, “Developer refresh operation” that forcibly transfers toner for the area corresponding to the fixed value is executed at the time of standby mode without print signal, or at the end of continuous printing or inserted during continuous printing. There are many.

In addition to the purpose of refreshing the developing device, the developer is forcibly transferred from the developing device to the photosensitive member for the purpose of maintaining the cleaning performance of the cleaning device and preventing the cleaning blade from turning over. Further, there has been proposed a technique in which the forcibly transferred developer is transferred to an intermediate transfer member and then collected by an intermediate transfer member cleaning device (Patent Document 2).
JP 2006-91314 A JP 2006-209107 A

  By the way, in particular, many full-color printers, copiers, and the like use a process cartridge system in which the photosensitive drum and the developing device can be integrally replaced. In such an image forming apparatus, 1) the direction of extending the life of the process cartridge, and 2) the volume of the waste toner container of the cleaning device for the photosensitive drum, which greatly affects the pitch of the image forming station, due to the downsizing of the apparatus. There is a direction to want to make as small as possible. For this reason, it has become difficult to accommodate all the toner forcibly transferred by the developing device refresh operation together with the waste toner in the photosensitive drum cleaning device.

  Further, when the intermediate transfer member is collected by the cleaning device and the collected toner is further collected in the waste toner container on the image forming apparatus side, the frequency of replacement of the waste toner container may be increased. Further, when the waste toner container is unitized on the intermediate transfer member, it is conceivable that the life of the unit is shortened. Further, if the waste toner container on the image forming apparatus side is enlarged in order to reduce the replacement frequency, the image forming apparatus may be enlarged as a result.

  Therefore, as the next improvement, there is a demand for an image forming apparatus capable of effectively suppressing image deterioration such as low density and uneven density while achieving a longer process cartridge life and a smaller image forming apparatus.

  Further, the developing device refresh operation itself is performed separately from the original print operation, and the user may feel that the print operation is temporarily stopped from the viewpoint of the user. Therefore, at the time of execution, it is desired to finish the execution in a shorter time.

  The present invention meets the above needs. That is, the object is to effectively suppress image deterioration such as density thinning and density unevenness while achieving a longer life of the image forming unit, a reduction in the size of the image forming apparatus, and a reduction in apparatus operating time other than printing. And

  In order to achieve the above object, a typical configuration of an image forming apparatus according to the present invention includes a rotating image carrier and development of a latent image formed on the image carrier with a developer to form a developed image. An intermediate transfer member that rotates in contact with the image carrier and receives a primary transfer of the developed image by a primary transfer unit; and a development image primarily transferred to the intermediate transfer member as a recording material. A secondary transfer means for performing the next transfer, a first cleaning device for removing the primary transfer residual developer from the image carrier, and a second cleaning device for removing the secondary transfer residual developer from the intermediate transfer member; In the image forming apparatus for performing the developing device refresh operation for forcibly transferring the developer from the developing device to the image carrier during non-image formation according to the frequency of use of the developing device, the image in the developing device refresh operation Transferred to the carrier A developer, said first cleaning unit, and recovering both the second cleaning device.

  According to the present invention, it is possible to effectively suppress image deterioration such as low density and uneven density while achieving longer life of the image forming unit, downsizing of the image forming apparatus, and shortening of the apparatus operating time other than printing. can do.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings and embodiments. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. . Further, the materials, shapes, etc. of the members once described in the following description are the same as those in the first description unless otherwise described.

[Example 1]
(1) Overall Configuration of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus 100 is an inline (tandem) type-intermediate transfer type full color electrophotographic image forming apparatus (full color laser beam printer). That is, on the periphery of an intermediate transfer member on which a plurality of image forming units rotate, including a rotating image carrier and a developing device that develops a latent image formed on the image carrier with a developer to form a developed image. Are arranged in parallel along the circumference.

  In the image forming apparatus main body 100A, four image forming units (image forming stations: hereinafter referred to as stations) Y, M, C, and Y arranged in parallel in the horizontal direction in order from right to left in the drawing. Bk is disposed. Each of these stations is an electrophotographic image forming mechanism having a rotating drum type electrophotographic photosensitive member 1 (Y, M, C, Bk) as an image carrier. Hereinafter, the electrophotographic photosensitive member is referred to as a photosensitive drum. Each of the stations Y, M, C, and Bk has a yellow (Y) developer image, a magenta (M) developer image, a cyan (C) developer image, and a black (Bk) on the photosensitive drum 1, respectively. The developer image is formed. Hereinafter, the developer is referred to as toner, and the developer image is referred to as toner image.

  In each of the stations Y, M, C, and Bk, the photosensitive drum 1 is driven to rotate clockwise at a predetermined speed by a driving unit (not shown). Around the photosensitive drum 1, the following components are arranged in order according to the rotation direction. That is, a charging roller 2 (Y, M, C, Bk) as a charging unit that uniformly charges the surface of the photosensitive drum 1 and the charged surface of the photosensitive drum 1 are exposed to form a latent image (electrostatic latent image). Laser irradiating means 3 (Y, M, C, Bk) is arranged as an exposing means. The laser irradiation means 3 is a laser scanning exposure apparatus that scans and exposes the surface of the photosensitive drum 1 with laser light 4 (Y, M, C, Bk) modulated in accordance with an image signal of a corresponding color. Further, a developing device 5 (Y, M, C, Bk) as developing means for developing the electrostatic latent image with toner, and a toner supply unit 6 (Y. M, C, Bk) are arranged. 1 is a primary transfer means (electrode member) that transfers a toner image (development image) on the photosensitive drum 1 to a flexible endless belt-shaped intermediate transfer body (hereinafter referred to as a belt) 10. Next transfer rollers 7 (Y, M, C, Bk) are arranged. Further, a photoreceptor cleaning device 8 (Y, M, C, and the like) that removes primary transfer residual toner (primary transfer residual developer) remaining on the surface of the photosensitive drum after the toner image is transferred to the belt 10 (after primary transfer). Bk). Hereinafter, this photoreceptor cleaning device is referred to as a first cleaning device.

  In each station Y, M, C, and Bk, the photosensitive drum 1, the charging roller 2, the developing device 5, and the cleaning device 8 are integrally formed as a process cartridge 9 (Y, M, C, and Bk) to form an image. It is configured to be detachable from the apparatus main body 100A. Further, the toner supply unit 6 (Y, M, C, Bk) is also detachable from the image forming apparatus main body 100A.

  The belt 10 is suspended and stretched between the driving roller 10a and the tension roller 10b, and faces the lower surfaces of all the photosensitive drums 1 of the respective cartridges 9 (Y, M, C, and Bk). The belt 10 is circulated and driven counterclockwise at substantially the same speed as the rotational speed of the photosensitive drum 1 when the driving roller 10a is rotationally driven.

  The primary transfer rollers 7 (Y, M, C, and Bk) of the stations Y, M, C, and Bk are disposed on the inner side of the belt 10 so as to be rotatably supported by the vertical movable member 11. . The vertically movable member 11 is moved up and down by a drive means (not shown) controlled by the intermediate transfer member separation and contact drive means 125 (FIG. 3). That is, the image forming apparatus has a mechanism capable of contacting and separating the photosensitive drum (Y, M, C, Bk) and the belt 10. When the vertically movable member 11 is moved up to a predetermined position, the belt portion on the ascending side of the belt 10 is lifted by the primary transfer rollers 7 (Y, M, C, Bk) against the tension, 1, the state is held in contact with the lower surface of each photosensitive drum 1 (belt contact state). A contact portion between each photosensitive drum 1 and the belt 10 is a primary transfer portion T1. Image formation (printing) is executed in this belt contact state.

  In addition, when the vertically movable member 11 is moved down to a predetermined position, the belt portion on the ascending side of the belt 10 is also lowered by the downward movement of each primary transfer roller 7 (Y, M, C, Bk). As a result, as shown in FIG. 2, the belt 10 is held in a state of being separated from each photosensitive drum 1 by the tension (belt separation state).

  The driving means for the vertically movable member 11 is, for example, an elevation mechanism using a motor and a cam, an elevation mechanism using an electromagnetic solenoid, or the like.

  Image forming operations at the stations Y, M, C, and Bk are as follows. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2. In this embodiment, the charging polarity of the photosensitive drum 1 is negative. Then, scanning exposure is performed on the uniformly charged surface of the photosensitive drum 1 with the laser beam 4 that is output from the laser irradiation unit 3 and modulated according to the image information of each color. As a result, an electrostatic latent image corresponding to the image information (scanning exposure pattern) is formed on the photosensitive drum surface. In this embodiment, the electrostatic latent image (image portion) corresponding to the image information has a negatively charged uniformly charged surface of the photosensitive drum 1 exposed to a negatively charged charge by exposure with laser light 4 from the laser irradiation means 3. Formed in the attenuated part. The electrostatic latent image is visualized as a toner image by the developing device 5. In this embodiment, the developing method is a reversal developing method. For this reason, the negative polarity toner in the present embodiment, which has the same polarity as the charged charge, adheres to the portion (image portion) of the photosensitive drum 1 where the negative charged charge is attenuated. The toner is supplied from the toner supply unit 6 (Y, M, C, Bk) as the toner storage unit to the developing device 5 (Y, M, C, Bk) in a timely manner according to each color. Then, the toner image formed on the photosensitive drum 1 is circulated and driven from the photosensitive drum 1 side in the primary transfer portion T1 which is a contact portion between the photosensitive drum 1 and the belt 10 in a belt contact state. Primary transfer is performed on the 10 side. That is, the belt 10 rotates in contact with the photosensitive drum 1 and receives the primary transfer of the toner image by the primary transfer roller 7. In the primary transfer, a predetermined primary transfer bias having a polarity opposite to the charging polarity of the toner is applied to the primary transfer roller 7 from a primary transfer bias application power source (not shown) at a predetermined control timing. This is done electrostatically by the transfer electric field. The predetermined primary transfer bias is a voltage at which the toner image is transferred from the photosensitive drum 1 to the belt 10. Further, the primary transfer residual toner remaining on the surface of the photosensitive drum 1 without being transferred to the belt 10 side is removed by the first cleaning device 8. Thus, the photosensitive drum 1 is cleaned and prepared for the subsequent image forming operation. The first cleaning device 8 includes a blade-shaped cleaning member, and scrapes off the primary transfer residual toner from the surface of the photosensitive drum and collects it in a waste toner storage portion (cleaning container portion) of the cleaning device 8.

  By the electrophotographic image forming process as described above, a Y toner image corresponding to the yellow component of the full color image is formed on the photosensitive drum 1Y of the first station Y. Then, the Y toner image is primarily transferred onto the belt 10 that is rotationally driven.

  An M toner image corresponding to the magenta component of the full-color image is formed on the photosensitive drum 1M of the second station M. Then, the M toner image is primary-transferred superimposed on the Y toner image already transferred onto the belt 10 that is rotationally driven.

  A C toner image corresponding to the cyan component of the full-color image is formed on the photosensitive drum 1C of the third station C. Then, the C toner image is primary-transferred superposedly on the Y toner image + M toner image already transferred onto the belt 10 that is rotationally driven.

  A Bk toner image corresponding to the black component of the full-color image is formed on the photosensitive drum 1Bk of the fourth station Bk. Then, the Bk toner image is primary-transferred superposedly on the Y toner image + M toner image + C toner image already transferred on the belt 10 that is rotationally driven.

  Thus, four full-color unfixed toner images of Y + M + C + Bk are synthesized and formed on the belt 10.

  On the other hand, the paper feed roller 14 is driven at a predetermined control timing. As a result, the recording material (transfer material) 12 stacked and accommodated in the recording material cassette 13 is separated and fed, and is sent to the registration roller 16 through the sheet path 15a. The registration roller 16 controls the skew correction of the recording material 12 and the secondary transfer timing of the toner image from the belt 10 to the recording material 12. The registration roller 16 controls the recording material 12 fed from the recording material cassette 13. Receive the tip and stop it.

  A secondary transfer roller 17 as a secondary transfer unit (electrode member) is in contact with the driving roller 10a of the belt 10 with the belt 10 interposed therebetween. A contact portion between the belt 10 and the secondary transfer roller 17 is a secondary transfer portion T2.

  Then, the recording material 12 stopped at the position of the registration roller 16 is fed again by the roller 16 that is rotationally driven at a predetermined control timing. The recording material 12 is introduced into the secondary transfer portion T2 through the sheet path 15b and is nipped and conveyed. Meanwhile, a predetermined secondary transfer bias having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller 17 from a secondary transfer bias application power source (not shown). The predetermined secondary transfer bias is a voltage at which the toner image is transferred from the belt 10 to the recording material 12. As a result, the full-color unfixed toner image on the belt 10 is secondarily transferred collectively onto the recording material 12 electrostatically by a transfer electric field.

  The recording material 12 exiting the secondary transfer portion T2 is separated from the surface of the belt 10 and introduced into the fixing device 18 through the sheet path 15c. The unfixed toner image carried on the recording material 12 is heated by a fixing member (heat roller) 18a provided in the fixing device 18 and pressurized by a pressure member (pressure roller) 18b, and recorded. It is fixed on the material 12.

  The recording material 12 that has exited the fixing device 18 passes through a sheet path 15d and is discharged as an image formed product (print) onto a discharge tray unit 20 by a discharge roller 19.

  The secondary transfer residual toner (secondary transfer residual developer) remaining on the surface of the belt 10 without being transferred to the recording material 12 is removed by the belt cleaning device 21. Hereinafter, this belt cleaning device is referred to as a second cleaning device. As a result, the belt 10 is cleaned to prepare for the subsequent image forming operation. The second cleaning device 21 includes a blade-shaped cleaning member, and scrapes off secondary transfer residual toner from the surface of the belt 10. The secondary transfer residual toner scraped off is carried out of the second cleaning device 21 by the transport screw 21a, and is collected via a transport path 22 into a waste toner box 23 provided on the image forming apparatus main body side. The

  The above is the outline of the full color image forming operation of the image forming apparatus 100 of the present embodiment. Note that the order of forming the color toner images is not limited to the above order.

(2) Developing Device Refresh Operation As described above, the developing device refresh operation is an operation control mode in which the developer is forcibly transferred from the developing device to the image carrier during non-image formation according to the frequency of use of the developing device. . In other words, at a predetermined control timing, during non-image formation, the toner in the toner is forcibly transferred to the photosensitive drum side (toner discharge) and consumed according to the frequency of use of the developing device. By this developing device refresh operation, the toner change caused by the same toner circulating in the developing device is suppressed. The forced transfer of toner during the refresh operation of the developing device forms an electrostatic latent image for refresh operation (for example, an electrostatic latent image by full-surface scanning exposure) on the photosensitive drum surface, and develops the electrostatic latent image with the developing device. You can make it happen. The developing device refresh operation is performed at the time of non-image formation, for example, in a standby mode without a print signal, or at the end of continuous printing or inserted during continuous printing.

  The developing device refresh operation in the image forming apparatus of this embodiment will be described below with reference to the block diagram of the control system of the image forming apparatus in FIG. 3, the control flowchart in FIG. 4, and the sequence diagram in FIG.

  In this embodiment, the timing for executing the developing device refresh operation is determined by the printing rates of the first to fourth stations Y, M, C, and Bk during image formation.

  Printing is started in response to a print request from the host computer 120, which is an external input device connected to the control unit of the image forming apparatus via an interface (step 1).

  Further, based on the image forming signal obtained by converting the image information from the host computer 120 by the image processing circuit 122, the printing rate calculation unit 123 calculates the printing rate Cvg of the image (step 2).

  Next, the CPU 121 determines the low printing rate threshold value Cvg. A difference ΔCvg between th (setting a printing rate of 1% in this embodiment) and the printing rate Cvg of the image is calculated (step 3).

ΔCvg = Cvg. th-Cvg ··· Formula (1)
Further, the CPU 121 calculates an area S (paper size S) of the recording material 12 (paper and sheet material to be finally printed) used for printing (step 4).

  Then, the CPU 121 multiplies the difference ΔCvg in the above equation (1) by the area S (step 4) of the recording material 12 used for printing, and integrates it to the forced transfer amount integrated value ΣΔCvg (step 5).

ΣΔCvg = ΣΔCvg + ΔCvg × S (2)
This forced transfer amount integrated value ΣΔCvg is the average print rate is set to the low print rate threshold Cvg. The toner consumption area that is insufficient to make th is shown.

  When the value of the forced transfer amount integrated value ΣΔCvg is 0 or −, the average printing rate is the low printing rate threshold Cvg. It is more than th. In this case, in this embodiment, the CPU 121 determines that the developing device refresh operation is not necessary (step 6), and resets the forced transfer amount integrated value ΣΔCvg (= 0) (step 7).

  When this value is +, the average printing rate is the low printing rate threshold Cvg. Since it is less than th and it is necessary to refresh the developing device in this embodiment, the integration of the forced transfer amount integration value ΣΔCvg is continued. At this time, if the toner corresponding to the area of the forced transfer amount integrated value ΣΔCvg is forcibly transferred from the developing device 4 to the photosensitive drum 1 side, the average print rate in the integrated section becomes the low print rate threshold Cvg. Same as th.

  In this embodiment, in each color, that is, in each of the first to fourth stations Y, M, C, and Bk, the forced transfer amount of the toner is measured on the first cleaning device 8 on the photosensitive drum 1 side and on the belt 10 side. It is set so that it is collected half by half with a certain second cleaning device 21.

  That is, a partial amount (half amount in this embodiment) of the developer to be transferred to the photosensitive drum in the developing device refresh operation is transferred from the developing device to the photosensitive drum, and further transferred to the belt. Thereafter, the remaining amount (the remaining half amount in this embodiment) of the developer is transferred from the developing device to the photosensitive drum, and is not transferred to the belt, but is left on the photosensitive drum, and the partial amount of developer is second cleaned. The remaining amount of developer is collected in the first cleaning device 8 in the device 21.

  Further, the maximum length D in the belt circumferential direction (intermediate transfer member circumferential direction) of toner transferred to the belt 10 side by one developing device refresh operation is set as a station pitch L (FIG. 2) between the stations. The station pitch L is a pitch on the circumference of the intermediate transfer body of a plurality of image forming units, and is a distance between photosensitive drum axes between adjacent stations or a distance between primary transfer units.

Therefore, the execution timing of the developing device refresh operation is set when the forced transfer amount integrated value ΣΔCvg reaches the developable width × 2L. In this embodiment, the station pitch L is 94 mm and the developable width is 312 mm. That is, the developing device refresh operation execution threshold Z is
Z = 312 × 94 × 2 = 58656 (mm ² ) (3)
It is.

  The CPU 121 compares the forced transfer amount integrated value ΣΔCvg of each of the first to fourth stations Y, M, C, and Bk with the developing device refresh operation execution threshold value Z (step 8).

  When any of the stations reaches the threshold value Z, the developing device refresh operation is performed (step 9).

  When the developing device refreshing operation is performed, at a station that is a trigger for the execution determination, toner having an area of 312 mm × 94 mm is collected by the cleaning device 8 on the photosensitive drum 1 side and the cleaning device 21 on the belt 10 side, respectively. .

  At other stations, half of the accumulated forced transfer amount accumulated value ΣΔCvg is collected by the cleaning device 8 on the photosensitive drum 1 side and half by the cleaning device 21 on the belt 10 side.

  In the station where the forced transfer amount integrated value ΣΔCvg = 0, the toner is not forcedly transferred.

  The area control of the forced transfer of the toner in each station Y, M, C, and Bk is performed by controlling the exposure time of the laser irradiation means 3 (Y, M, C, and Bk) from the CPU 121 through the image processing circuit 122. Is called.

  When the developing device refresh operation is started, the CPU 121 gives a command to the intermediate transfer member separation and contact drive control means 125 through the image forming operation control means 124 to drive the drive means of the vertically movable member 11 in the belt contact direction. That is, the vertically movable member 11 is moved up to a predetermined position, and the belt 10 is brought into contact with the lower surface of the photosensitive drum 1 of each station as shown in FIG. 1 (step 10).

  After that, at the same timing, at each station Y, M, C, and Bk, the primary charging (negative charging) by the charging roller 2 to the photosensitive drum 1 and the area of half of the forced transfer amount integrated value ΣΔCvg Laser scanning exposure is performed from the laser irradiation means 3 so as to be. By this exposure, an electrostatic latent image for refresh operation is formed on the surface of the photosensitive drum. Then, the electrostatic latent image is developed by a developing device. That is, toner is forcibly transferred from the developing device 5 to the photosensitive drum 1 side (step 11).

  At the station where the execution determination of the developing device refresh operation is triggered, at the timing when the toner having the same length as the station pitch L is transferred onto the belt 10, the CPU 121 places the belt 10 in the belt separation state (step 12). That is, the CPU 121 gives a command to the intermediate transfer member separation and contact driving control unit 125 through the image forming operation control unit 124 to drive the driving unit of the vertically movable member 11 in the belt separation direction. As a result, the belt 10 is held in a belt-separated state away from each photosensitive drum 1 as shown in FIGS.

  Here, if the same forced transfer amount integrated value ΣΔCvg is the same in all the stations Y, M, C, and Bk, the transfer of toner from the photosensitive drum 1 to the belt 10 in each station Y, M, C, and Bk is performed. As shown in FIG. Since exposure is started at the same timing, the same timing is applied to all stations Y, M, C, and Bk.

  Thereafter, in the belt separation state (FIG. 2 and FIG. 6B), the photosensitive drum 1 has the same area at half of the forced transfer amount integrated value ΣΔCvg in each of the stations Y, M, C, and B. Is exposed to form an electrostatic latent image for refresh operation. The electrostatic latent image is developed by the developing device 5 and toner is forcibly transferred from the developing device 5 to the photosensitive drum 1 (step 13). Since the belt 10 and the photosensitive drum 1 are in a separated state, the toner transferred from the developing device 5 to the photosensitive drum 1 is collected as it is by the first cleaning device 8 on the photosensitive drum 1 side (step 14).

  Further, the toner transferred to the belt 10 in the belt contact state is held and moved on the rotating belt 10 as it is, and is removed by the second cleaning device 21 on the belt 10 side, and further, a waste toner box. 23 is collected (step 15).

  Here, in order to prevent the toner held on the belt 10 from adhering to the secondary transfer roller 17 in the secondary transfer portion T2, control is performed to separate the secondary transfer roller 17 from the belt 10 during the refresh operation. . Alternatively, the secondary transfer roller 17 is kept in contact with the belt 10 and a bias having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller 17 to pass through the secondary transfer portion T2. Control is performed to prevent the toner to adhere from adhering to the secondary transfer roller 17.

  Thereafter, the CPU 121 resets the forced transition amount integrated value ΣΔCvg (= 0) (step 16).

  The above is the developing device refresh operation of this embodiment.

  In other words, this embodiment has a mechanism capable of contacting and separating the photosensitive drum and the belt. In the developing device refresh operation, the developer transferred from the developing device to the photosensitive drum is transferred to the belt and collected in the second cleaning device 21 by bringing the photosensitive drum and the belt into contact with each other. Further, by setting the photosensitive drum and the belt apart from each other, the developer transferred from the developing device to the photosensitive drum is collected by the first cleaning device 8 without being transferred to the belt.

  As in this embodiment, the toner that is forcibly transferred to the photosensitive drum 1 by the developing device refresh operation is distributed and collected by the cleaning devices 8 and 21 of both the photosensitive drum 1 and the intermediate transfer member 10, as follows. Effects can be obtained.

  That is, it is possible to effectively suppress the occurrence of low density and uneven density throughout the life of the process cartridge 9 (Y, M, C, B). At the same time, the amount of toner collected in the conventional process cartridge cleaning device can be reduced, the station pitch L can be shortened, and the process cartridge can be set to have a long service life.

  In this embodiment, half of the toner forcedly transferred to the photosensitive drum 1 by the developing device refresh operation is collected by the cleaning device 21 of the intermediate transfer member 10. Therefore, the following effects can be obtained as compared with the case where it is assumed that all the process cartridges 9 are simply collected in the cleaning device 8 (Y, M, C, B). That is, the volume of the waste toner storage portion of the cleaning device 8 (Y, M, C, B) of the process cartridge 9 (Y, M, C, B) is 0.7 times, and the waste toner storage portion of the process cartridge is filled. The life setting at can be set to 1.4 times.

  In the developing device refresh operation, first, toner transfer to the intermediate transfer member 10 side is performed first, and then toner collection to the photosensitive drum 1 side is performed, thereby obtaining the following effects. That is, the recovery end timing of the toner on the intermediate transfer body 10 to the cleaning device 21 that restricts the shortening of the operation time of the developing device refresh operation can be made earliest. This is because the distance from the intermediate transfer member contact portion (primary transfer portion T1) of the photosensitive drum 1 to the cleaning device 8 of the photosensitive drum 1 is the distance from the photosensitive drum 1 and intermediate transfer member contact portion to the intermediate transfer member cleaning device 21. Because it is much smaller. Thereby, it is possible to minimize waiting for the user to wait for a time other than printing.

  Further, by setting the maximum length D in the circumferential direction of the intermediate transfer member to be transferred to the intermediate transfer member in one developing device refresh operation as the pitch L of the image forming station, the following effects can be obtained. That is, even when the developing device refresh operation of each of the stations Y, M, C, and B is performed at the same time, the toner of two or more colors does not overlap on the intermediate transfer member 10 as shown in FIG. This contributes to shortening the operation time of the developing device refresh operation, and can reduce the load on the intermediate transfer member cleaning device 21 that removes the forcibly transferred toner from the intermediate transfer member 10. In other words, when cleaning a much larger amount of toner than the amount of untransferred toner during an image forming operation, such as a developing device refresh operation, a cleaning failure that rarely occurs in a low temperature environment or the like. The probability of occurrence can be lowered. However, when the cleaning performance of the cleaning device 21 is sufficiently high with respect to the developing device refresh operation, the timing may be controlled so that two or more colors overlap.

  The distribution ratio of the forcibly transferred toner to the first cleaning device 8 and the second cleaning device 21 (ratio between the partial amount and the remaining amount) can be set as appropriate. That is, in the design of the image forming apparatus, it is possible to appropriately select an optimum value for the above-described distribution ratio depending on which waste toner storage unit has a capacity and how the life is set. A desirable configuration is as follows.

  1) The waste toner container of the cleaning device 8 of 9 (Y, M, C, B) of the process cartridge is set large within a range that does not greatly affect the station pitch L.

  2) The toner distribution ratio to the photoconductor side is determined based on the set volume of the waste toner container so that the toner is collected to the photoconductor side as much as possible without affecting the life of the process cartridge.

  3) The capacity of the waste toner container of the intermediate transfer member for collecting the remaining ratio on the intermediate transfer member side is determined in consideration of the replacement frequency and the like.

  This is because the process cartridge is originally replaced as appropriate due to consumption due to printing (no toner, consumption of the photoconductor, etc.). By collecting as much toner as possible on the photosensitive member side so as not to increase the replacement frequency, the replacement frequency of the waste toner container on the intermediate transfer member side can be reduced as much as possible (or the volume is reduced = the main body is reduced). Because.

  In addition to the purpose of “refreshing the developing device” for the purpose of this embodiment, for example, when the toner is sent to both cleaning devices for the purpose of preventing the photosensitive drum and the intermediate transfer member cleaning blade from turning up, for example. An appropriate distribution ratio may be set.

  Further, when it is desired that two or more colors of toner images when the toner is collected on the intermediate transfer member do not overlap, the following 4) is preferable.

  4) Based on the toner distribution ratio on the intermediate transfer body side determined as described above, the amount of toner (length D in the circumferential direction of the intermediate transfer body) transferred to the intermediate transfer body side in one developing device refresh operation is the station pitch L Do not exceed. The developing device refresh operation execution threshold value Z may be adjusted so that the developing device refresh operation is executed at such timing.

  In this case, the execution frequency can be minimized by setting the amount of toner to be transferred to the intermediate transfer member side in one developing device refresh operation (length D in the circumferential direction of the intermediate transfer member) = station pitch L. I can do it.

[Example 2]
In the first exemplary embodiment, an intermediate transfer member abutment / separation mechanism is used as a method for distributing the collection destination of the toner forcibly transferred from the developing device 5 to the photosensitive drum 1. However, the belt 10 as an intermediate transfer member may be maintained in a state where the photosensitive drum 1 is in contact with the belt, and the voltage applied to the primary transfer roller 7 may be controlled to distribute the toner collection destination. . That is, it is possible to perform control for transferring the toner forcibly transferred onto the photosensitive drum 1 to the belt 10 side and control for remaining on the photosensitive drum 1 side.

  In this embodiment, the voltage applied to the primary transfer roller 7 is controlled to distribute the toner collection destinations.

  That is, during the developing device refresh operation, a voltage at which the developer is transferred from the photosensitive drum 1 to the belt 10 is applied to the primary transfer roller 7. As a result, the developer transferred from the developing device 5 to the photosensitive drum 1 is transferred to the belt 10 and collected by the second cleaning device 21. Further, a voltage that makes it difficult for the developer to transfer from the photosensitive drum 1 to the belt 10 is applied to the primary transfer roller 7. As a result, the developer transferred from the developing device 5 to the photosensitive drum 1 is collected by the first cleaning device 8 without being transferred to the belt 10.

  The developing device refresh operation in this embodiment will be described below with reference to the control flowchart of FIG. 7 and the sequence diagram of FIG. In this embodiment, since the schematic configuration of the image forming apparatus and the outline of the image forming operation are the same as those in the first embodiment, the description thereof will be omitted.

  By the same procedure (steps 1 to 8) as in the first embodiment, the timing for performing the developing device refresh operation is determined by the printing rate of each station Y, M, C, and B during image formation.

  When the developing device refreshing operation is performed (step 9), toner having an area of 312 mm × 94 mm is collected by the cleaning device 8 on the photosensitive drum 1 side and the cleaning device 21 on the belt 10 side at the station that has caused the execution determination. The

  At other stations, half of the accumulated forced transfer amount accumulated value ΣΔCvg is collected by the cleaning device 8 on the photosensitive drum 1 side and half by the cleaning device 21 on the belt 10 side.

  In the image forming station where the forced transfer amount integrated value ΣΔCvg = 0, the toner is not forcedly transferred.

  The area control of the forced transfer of the toner is performed by the exposure time control of the exposure unit 3 from the CPU 121 through the image processing circuit 122.

  When the developing device refresh operation is started, exposure to the photosensitive drum 1 is performed so that the area of the forced transfer amount integrated value ΣΔCvg becomes half the area at each of the stations Y, M, C, and B at the same time. An electrostatic latent image for time is formed. The electrostatic latent image is developed by the developing device 5, and the forced transfer of toner from the developing device 5 to the photosensitive drum 1 is performed (step 10).

  The CPU 121 applies a voltage (transfer voltage) in a direction in which the toner on the photosensitive drum 1 is transferred to the belt 10 side to the primary transfer roller 7 (Y, M, C, B) through the image forming operation control unit 124 ( step 11). In this embodiment, +500 V is applied, and about 95% of the toner can be transferred to the belt 10 side.

  Thereafter, the toner is forcibly transferred so that the toner to be collected comes to the cleaning device 8 on the photosensitive drum 1 side after the timing when the Y toner of the first station Y passes the primary transfer portion T1 of the fourth station Bk. In the forced transfer of the toner, the photosensitive drum 1 is exposed so that the area is half the forced transfer amount integrated value ΣΔCvg, and the toner is forcedly transferred from the developing device 5 to the photosensitive drum 1 (step 12). .

  In synchronism with the second toner forced transfer, a voltage (non-transfer voltage) in a direction in which the toner on the photosensitive drum 1 does not transfer to the belt 10 side to the primary transfer roller 7 (Y, M, C, B) 1. ) Is applied (step 13). In this embodiment, −300 V is applied, so that approximately 95% of the toner can be left on the photosensitive drum 1 side.

  The toner remaining on the photosensitive drum 1 side is collected as it is by the cleaning device 8 on the photosensitive drum 1 side (step 14).

  Further, the toner transferred to the belt 10 is held and moved on the rotating belt 10 as it is, removed by the cleaning device 21 on the belt 10 side, and further collected in a waste toner box 23 (step 15).

  Thereafter, the CPU 121 resets (= 0) the forced transfer amount integrated value ΣΔCvg (step 16).

  The above is the developing device refresh operation of this embodiment.

[Example 3]
FIG. 9 is a schematic configuration diagram of an image forming apparatus according to the third embodiment. This image forming apparatus is a one-drum-intermediate transfer type full-color electrophotographic image forming apparatus (full-color laser beam printer). That is, toner images of a plurality of colors corresponding to image information are sequentially formed on one image carrier by an electrophotographic process. The toner images of the respective colors are primarily transferred so as to be sequentially superimposed on the surface of the intermediate transfer member that circulates. Then, the multiple toner image formed on the surface of the intermediate transfer member is secondarily transferred to a recording material at a time and then fixed to output a full-color image formed product.

  In the image forming apparatus of FIG. 9, a photosensitive drum 1 as an image carrier is rotationally driven in the counterclockwise direction indicated by an arrow and receives uniform primary charging by a charging roller 2. The charged surface of the photosensitive drum 1 is subjected to image exposure by the laser irradiation unit 3 to form an electrostatic latent image. The electrostatic latent image is developed as a toner image by the rotary developing unit 50.

  The rotary developing unit 50 includes four developing devices 5Y, 5M, 5C, which form toner images by attaching toner to the electrostatic latent image formed on the surface of the photosensitive drum 1 on the circumferential portion of the rotary unit 51. It is equipped with 5Bk. A developer having Y toner is accommodated in the developing device 5Y. The developing device 5M stores a developer having M toner. The developing device 5C contains a developer having C toner. The developing device 5Bk contains a developer having Bk toner. The developing device 5Y, 5M, 5C, and 5Bk is selectively set at a developing position facing the photosensitive drum 1 by rotating the rotary unit 51 in a counterclockwise direction indicated by an arrow at a predetermined angle at a predetermined control timing. The developing roller faces the photosensitive drum 1.

  The toner image formed on the surface of the photosensitive drum 1 is primarily transferred to the surface of the intermediate transfer belt 10. The belt 10 is suspended around a plurality of rollers 10a to 10g. The rollers 10b, 10c and 10d are brought into contact with the photosensitive drum 1. A contact portion between the photosensitive drum 1 and the belt 10 is a primary transfer portion T1. The belt 10 is rotationally driven at a speed corresponding to the rotational speed of the photosensitive drum 1 in the clockwise direction indicated by an arrow, for example, using the roller 10a as a driving roller. The roller 10c is a primary transfer roller, and a predetermined primary transfer voltage having a polarity opposite to the toner charging polarity is supplied to the roller 10c from a primary transfer bias application power source (not shown) at a predetermined control timing. Is applied. As a result, the toner image on the photosensitive drum 1 is moved to the surface of the belt 10.

  Further, the roller 10g is a secondary transfer counter roller, and the secondary transfer roller 17 is disposed so as to be able to contact and separate with the belt 10 sandwiched between the secondary transfer counter roller 10g. A contact portion when the secondary transfer roller 17 is in contact with the belt 10 is a secondary transfer portion T2. The secondary transfer roller 17 has a shift mechanism (not shown) between a first state in which the belt 10 is pressed against the secondary transfer counter roller 10g and a second state separated from the outer surface of the belt 10. Is controlled by switching. The secondary transfer roller 17 is normally switched and held in a second state separated from the outer surface of the belt 10. By switching to the first state, the secondary transfer portion T2 is formed between the belt 10 and the outer surface.

  Further, a second cleaning device 21 is disposed so as to face the belt suspension portion of the roller 10a. The cleaning device 21 is controlled to be switched between a first state in which the cleaning member is in contact with the belt 10 and a second state in which the cleaning member is separated from the outer surface of the belt 10 by a shift mechanism (not shown). The belt cleaning device 21 is normally switched and held in the second state separated from the outer surface of the belt 10.

  A full color image is formed as follows. First, for example, a Y toner image as the first color is formed on the photosensitive drum 1 by the above-described image forming process of charging, exposure, and development. Then, the Y toner image is primarily transferred onto the belt 10 by the primary transfer roller 10c to which the primary transfer voltage is applied in the primary transfer portion T1. The primary transfer residual toner that is not transferred to the belt 10 and remains on the surface of the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the first cleaning device 8. The photosensitive drum 1 cleaned by the cleaning device 8 is repeatedly used for image formation.

  The image forming process (charging, exposure, development, primary transfer) similar to the above is repeated in the order of, for example, M toner image, C toner image, and Bk toner image for the second, third, and fourth colors. Thus, primary transfer is performed so as to sequentially overlap the surface of the belt 10. As a result, an unfixed full-color toner image (multiple toner image) formed by sequentially superimposing and transferring a Y toner image, an M toner image, a C toner image, and a K toner image is synthesized and formed on the belt 10. Note that the order of forming the color toner images is not limited to the above order.

  On the other hand, a sheet feeding unit (not shown) recording material 12 is separated and sent out at a predetermined control timing and sent to the registration roller 16. Further, the secondary transfer roller 17 is switched to the first state at a predetermined control timing. Then, the recording material 12 stopped at the position of the roller 16 is fed again from the roller 16 at a predetermined control timing, and 2 between the secondary transfer roller 17 and the belt 10 which are switched to the first state. The ink is introduced into the next transfer portion T2 and is conveyed while being held between the secondary transfer portions T2. Meanwhile, a predetermined secondary transfer voltage is applied to the secondary transfer roller 17, and the full-color toner image on the belt 10 is electrostatically transferred onto the recording material 12 collectively.

  The secondary transfer residual toner that is not transferred to the recording material 12 and remains on the surface of the belt 10 is removed from the belt surface by the second cleaning device 21, and the cleaned belt 10 is repeatedly used for image formation. When the secondary transfer of the toner image from the belt 10 to the recording material 12 is performed at the secondary transfer portion T2, the cleaning device 12 is switched to a state in which the cleaning device 12 is in contact with the outer surface of the belt 10 at a predetermined control timing. The second cleaning device 21 is separated from the belt 10 during full-color image formation, and is controlled so as to be always in contact during monochromatic image formation. The second cleaning device 21 includes a blade-shaped cleaning member, and scrapes off secondary transfer residual toner from the surface of the belt 10. The secondary transfer residual toner scraped off is carried out of the second cleaning device 21 by the transport screw 21a, and is collected via a transport path 22 into a waste toner box 23 provided on the image forming apparatus main body side. The

  The recording material 12 that has exited the secondary transfer portion T2 is separated from the surface of the belt 10, conveyed to the fixing device 18 by the conveying belt 24, and introduced into the fixing nip portion. As a result, the full-color toner image is fixed by heating and pressing on the surface of the recording material 12. The recording material 12 exiting the fixing device 18 is discharged to a discharge tray (not shown).

  In the image forming apparatus according to the present exemplary embodiment, the photosensitive drum 1, the charging roller 2, and the cleaning device 8 are integrally formed as a process cartridge 9 so as to be detachable from the main body of the image forming apparatus.

  Also in the image forming apparatus of the present embodiment, the developing device refresh operation is sequentially executed for the developing devices 5Y, 5M, 5C, and 5Bk. The timing for executing the developing device refresh operation is determined by the printing rate of image formation using the developing devices 5Y, 5M, 5C, and 5Bk as in the first and second embodiments. Then, in each of the developing devices 5Y, 5M, 5C, and 5Bk, the toner that is forcibly transferred to the photosensitive drum 1 is the same as in the first and second embodiments, and the first cleaning device 8 and the second cleaning device 21. Both of them are sorted and collected at a predetermined ratio.

  Also in the case of the image forming apparatus of this embodiment, the developer sequentially transferred from each developing device to the photosensitive drum 1 is controlled by the same developing device refresh operation control as in the case of the image forming apparatus of Embodiment 1 or 2. Then, it is collected in both the first and second cleaning devices 8 and 21. As a result, the same effects as those of the image forming apparatuses according to the first and second embodiments can be obtained.

  Here, in the image forming apparatus of the present invention, the image forming process is not limited to the electrophotographic image forming process. An electrostatic recording image forming process using an electrostatic recording dielectric as an image carrier, a magnetic recording image forming process using a magnetic recording magnetic material as an image carrier, and the like may be used.

1 is a schematic diagram of an image forming apparatus in Embodiment 1. FIG. It is a partial view at the time of a belt separation state. It is a block diagram of a control system. It is a control flowchart. It is a sequence diagram. FIG. 10 is an operation explanatory diagram during a developing device refresh operation. 10 is a control flowchart in Embodiment 2. It is a sequence diagram. 6 is a schematic diagram of an image forming apparatus in Embodiment 3. FIG.

Explanation of symbols

Y, M, C, Bk) .. First to fourth image forming units (image forming stations)
1 (Y, M, C, Bk) ... Photosensitive drum (image carrier)
2 (Y ・ M ・ C ・ Bk) ・ ・ Charging roller (charging means)
3 (Y ・ M ・ C ・ Bk) ・ ・ Laser irradiation means (exposure means)
5 (Y, M, C, Bk), Development device 6 (Y, M, C, Bk), Toner supply unit 7 (Y, M, C, Bk), Primary transfer means 8 (Y, M ..C.Bk) .. Photosensitive drum cleaning device 9 (Y.M.C.Bk) .. Process cartridge 12..Recording material 10..Intermediate transfer member (intermediate transfer belt)
14. · Feeding roller 17 ·· Secondary transfer means 18 ·· Fixing device 21 ·· Intermediate transfer member cleaning device 23 ·· Intermediate transfer member waste toner box

Claims (6)

A rotating image carrier, a developing device that develops a latent image formed on the image carrier with a developer to form a developed image, and a developer that rotates in contact with the image carrier and is developed by a primary transfer unit. An intermediate transfer member that receives the primary transfer of the image, a secondary transfer unit that secondary-transfers the developed image primary-transferred to the intermediate transfer member onto a recording material, and a primary transfer residual developer from the image carrier. A first cleaning device to remove, and a second cleaning device to remove the secondary transfer residual developer from the intermediate transfer member, and the developer is applied during non-image formation according to the frequency of use of the developing device. In an image forming apparatus that performs a developing device refresh operation for forcibly transferring from a developing device to an image carrier,
An image forming apparatus, wherein the developer transferred to the image carrier in the developing device refresh operation is collected by both the first cleaning device and the second cleaning device.   A plurality of image forming units having a rotating image carrier and a developing device that develops a latent image formed on the image carrier with a developer to form a developed image are arranged on the circumference of the intermediate transfer member. The image forming apparatus according to claim 1, wherein the image forming apparatus is arranged in parallel along the line.   The image carrier and the intermediate transfer member have a mechanism capable of contacting and separating, and the image carrier and the intermediate transfer member are in contact with each other when the developing device is refreshed. The developer transferred to the body is transferred to the intermediate transfer member and collected by the second cleaning device, and the image carrier and the intermediate transfer member are separated from each other, whereby the image is transferred from the developing device. 3. The image forming apparatus according to claim 1, wherein the developer transferred to the carrier is collected by the first cleaning device without being transferred to the intermediate transfer member.   During the developing device refresh operation, the developer transferred from the developing device to the image carrier by applying a voltage at which the developer transfers from the image carrier to the intermediate transfer member is applied to the primary transfer unit. The intermediate transfer member is transferred to the second cleaning device, and is applied to the primary transfer unit by applying a voltage that makes it difficult for the developer to transfer from the image carrier to the intermediate transfer member. 3. The image forming apparatus according to claim 1, wherein the developer transferred from the developing device to the image carrier is collected by the first cleaning device without being transferred to the intermediate transfer member.   In the developing device refresh operation, a part of the developer to be transferred to the image carrier is transferred from the developing device to the image carrier, further transferred to the intermediate transfer member, and then the remaining amount of developer is transferred. Transfer from the developing device to the image carrier and remain on the image carrier without being transferred to the intermediate transfer member, and the remaining amount of developer is transferred to the second cleaning device. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is recovered by the first cleaning device. When the pitch on the periphery of the intermediate transfer body of the plurality of image forming units is L, the maximum length D in the circumferential direction of the intermediate transfer body of the developer transferred to the intermediate transfer body in one developing device refresh operation is set. ,
D ≦ L
The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus.

Images