Image forming apparatus

Abstract

To provide an image forming apparatus that prevents occurrence of cleaning failure even after formation of a high print image.SOLUTION: An image forming apparatus comprises a plurality of image forming units each having an image carrier, a developer carrier that supplies developer to an electrostatic latent image formed on the image carrier on the basis of image information to form a developer image, and a cleaning member that is in contact with the image carrier to remove the developer from the surface of the image carrier. The image forming apparatus comprises: an intermediate transfer body to which the plurality of developer images formed on the plurality of image forming units is sequentially transferred in a superimposed manner; a transfer unit that transfers the developer images transferred in the superimposed manner to the intermediate transfer body to a recording material; and a control unit that executes toner supply processing of supplying the developer from the developer carrier to an area where the image carrier and the cleaning member are in contact with each other, at timing after first image formation with a high printing ratio is performed and before second image formation is performed which is image formation subsequent to the first image formation.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] There are known image forming apparatuses using an electrophotographic or electrostatic recording method, such as copying machines, printers, facsimile machines, etc. In such image forming apparatuses, a process cartridge that integrates a photosensitive drum, a developing unit, etc., may be configured to be detachably attached to the main body of the apparatus.

[0003] Also, an in-line color type image forming apparatus is known that has a configuration in which a plurality of photosensitive drums are arranged in the rotation direction of an intermediate transfer belt. In such an in-line type image forming apparatus, an electrostatic latent image formed on a photosensitive drum is developed into a toner image by toner supplied from a developing means. The toner image is then primarily transferred to the intermediate transfer belt. Thereafter, a full-color toner image is formed on the intermediate transfer belt by repeating the same primary transfer for a plurality of colors. The full-color toner image is secondarily transferred to a recording material and fixed by a fixing means. Note that toner remaining on the intermediate transfer belt without being transferred to the recording material in the secondary transfer process is removed by a cleaning device that contacts the intermediate transfer belt.

[0004] After the toner image is primarily transferred onto the photosensitive drum, there is a toner-derived substance called transfer residue. Toner and external additives are attached. A blade cleaning device is used to clean the residual toner and external additives remaining on the photosensitive drum. The blade cleaning device removes the residual toner and external additives by contacting an elastic blade with the photosensitive drum. A layer of external additives (external additive particles added as auxiliary particles to toner particles) of the toner that has migrated from the toner to the photosensitive drum is formed on the edge of the blade, and serves as a barrier for cleaning the photosensitive drum. Hereinafter, such a layer will be referred to as a "blocking layer." Patent Document 1 (JP Patent Publication 2020-003718 A) shows a configuration in which the thickness of the blocking layer is increased by supplying toner containing an external additive from a developing means to a cleaning blade in advance, thereby improving cleaning performance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-003718 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above-mentioned configuration, when forming many images with a high printing rate (high printing images), a part of the blocking layer of the cleaning blade may be destroyed in the image forming section located downstream of the intermediate transfer belt. When an image is formed in this state, cleaning failure (toner passing through) may occur in the part where the blocking layer is destroyed, and vertical streaks may occur on the image.

[0007] This cleaning defect caused by the destruction of the blocking layer often occurs during image formation after a calibration operation that adjusts the image density and color shift. The reason is that during the calibration operation, a high-density image is formed for image adjustment, so a large amount of toner with a higher charge than during normal image formation enters the cleaning blade, and the destruction of the blocking layer formed on the cleaning blade progresses.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus that suppresses occurrence of cleaning defects even after forming a high-print image. [Means for solving the problem]

[0009] The present invention employs the following configuration. An image forming apparatus including a plurality of image forming units, each of which includes an image carrier, a developer carrier that supplies a developer to an electrostatic latent image formed on the image carrier based on image information to form a developer image, and a cleaning member that contacts the image carrier to remove the developer from a surface of the image carrier, an intermediate transfer body onto which the developer images formed in the image forming units are sequentially transferred in a superimposed manner; a transfer section that transfers the developer image transferred to the intermediate transfer body in a superimposed state onto a recording material; a control unit that executes a toner supply process for supplying the developer from the developer carrier to a region where the image carrier and the cleaning member contact each other after a first image formation, which is a high-printing image formation, is performed and before a second image formation, which is a subsequent image formation following the first image formation, is performed; The image forming apparatus is characterized by comprising: Effect of the Invention

[0010] According to the present invention, it is possible to provide an image forming apparatus that suppresses occurrence of cleaning defects even after formation of a high-print image. [Brief description of the drawings]

[0011] [Figure 1] Flowchart of toner discharge sequence in embodiment 1 [Diagram 2] Schematic cross-sectional view of an image forming apparatus according to a first embodiment. [Diagram 3] Cross section of the process cartridge in the first embodiment [Figure 4] Control block diagram of an image forming apparatus according to a first embodiment [Diagram 5] FIG. 1 is a patch image for color shift correction according to the first embodiment. [Figure 6] FIG. 1 is a patch image for density correction according to the first embodiment. [Figure 7] Close-up of the cleaning blade edge [Figure 8] Flowchart of toner discharge sequence in embodiment 2 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, exemplary embodiments for carrying out the present invention will be described with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, and relative positions of the components described in the embodiments are not intended to limit the scope of the present invention to those alone. Furthermore, the materials, shapes, and the like of the members once described in the following description are the same as those described initially unless otherwise specified. Well-known or publicly known technologies in the relevant technical field can be applied to configurations and processes that are not particularly illustrated or described. Furthermore, duplicated descriptions may be omitted.

[0013] [Example 1] <Description of Image Forming Apparatus> The overall configuration of an electrophotographic image forming apparatus in the first embodiment will be described. Here, the image forming apparatus forms an image on a recording material (recording medium). Examples of the image forming apparatus include copying machines, printers (laser beam printers, LED printers, etc.), facsimile machines, word processors, and combination machines (multifunction printers) of these.

[0014] 2 is a schematic cross-sectional view of the image forming apparatus 100 according to the first embodiment. Reference numeral 100 denotes a full-color laser printer employing an in-line system and an intermediate transfer system. The image forming apparatus 100 forms a full-color image on a recording material S (e.g., recording paper, a plastic sheet, cloth, etc.) according to image information. The image information is input to the image forming apparatus 100 from an image reading device such as a scanner connected to the image forming apparatus 100, or from a host device such as a personal computer connected to the image forming apparatus 100 so as to be able to communicate with the image forming apparatus 100.

[0015] <Explanation of process cartridge and image formation> The image forming apparatus 100 has a plurality of image forming units, ie, first, second, third and fourth image forming units SY, SM, SC and SK for forming images of each color, yellow (Y), magenta (M), cyan (C) and black (K). When there is no need to distinguish between them, the subscripts indicating the colors are omitted and only the reference numerals are shown. The image forming apparatus 100 has four drum-shaped electrophotographic photosensitive members (also called photosensitive drums, hereinafter referred to as photosensitive members 1) arranged in a direction intersecting with the vertical direction. The photosensitive members 1 and the image forming units (SY, SM, SC and SK) are integrated to form a process cartridge 7. The photosensitive members 1 are image carriers that carry electrostatic latent images.

[0016] As shown in FIG. 3, the photoconductor 1 is rotated in the direction of the arrow A by a driving means (not shown). The charging roller 2, which is a charging member, is a single-layer roller made of a conductive core metal and a conductive rubber layer. The charging voltage application unit 71, which serves as a high-voltage power source described later, applies a charging voltage (-1000V) to the charging roller 2, so that the surface of the photoconductor 1 is uniformly charged (-500V). Here, a DC voltage of "Vd+Vth" is applied to the charging roller 2, and the photoconductor 1 is uniformly charged to Vd by discharge. Vd is the dark potential (-500V). Also, Vth is the discharge start voltage. Here, when the charging voltage applied to the charging roller 2 by the charging voltage application unit 71 is smaller than the discharge start voltage Vth, the surface potential on the photoconductor 1 does not increase by discharge, but when the charging voltage exceeds the discharge start voltage Vth, the surface potential of the photoconductor 1 increases by discharge. The discharge start voltage Vth in the first embodiment is -500V.

[0017] After the charging roller 2 charges the surface of the photoreceptor 1, the surface of the photoreceptor 1 is irradiated with laser light from the exposure unit 30. The exposure unit 30 is an exposure means that irradiates a laser based on image information to form an electrostatic latent image on the surface of the photoreceptor 1. The surface potential of the portion of the photoreceptor 1 irradiated with the laser light changes to a light area potential Vl (-100V), thereby forming an electrostatic latent image on the surface of the photoreceptor 1.

[0018] FIG. 3 is a cross-sectional view of the process cartridge 7 of the first embodiment as viewed in the longitudinal direction (rotation axis direction) of the photoconductor 1. The process cartridge 7 is composed of a development unit 3 and a photoconductor unit 13. The development unit 3 includes a development roller 4 as a developer carrier and a supply roller 5 as a toner supply member. By receiving a driving force from a driving motor (not shown), the development roller 4 rotates in the direction of the arrow D in FIG. 2, and the supply roller 5 rotates in the direction of the arrow R in FIG. 2. When a development voltage (−300V) is applied from a development voltage application unit 72 to the development roller 4, the development roller 4 supplies developer (toner) to the electrostatic latent image (i.e., the above-mentioned light area potential Vl portion) formed on the surface of the photoconductor 1. As a result, the electrostatic latent image is developed into a developer image (toner image).

[0019] The toner image developed on the surface of the photoreceptor 1 is transferred to an intermediate transfer belt 31, which serves as an intermediate transfer member, shown in Fig. 2. The intermediate transfer belt 31 is formed of an endless belt that faces the photoreceptors 1 of the image forming units SY, SM, SC, and SK. The intermediate transfer belt 31 comes into contact with the photoreceptors 1 of the image forming units SY, SM, SC, and SK, and circulates (rotates) in the direction of arrow B in Fig. 2 (counterclockwise).

[0020] The inner peripheral surface of the intermediate transfer belt 31 is provided with photosensitive members for the image forming units SY, SM, SC, and SK. A primary transfer roller 32, which is a transfer member, is disposed to face the photoconductor 1. A voltage of a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer roller 32 from a primary transfer voltage application unit 73. This causes the toner image on the photoconductor 1 to be transferred (primary transfer) onto the intermediate transfer belt 31. Note that the normal polarity of the toner in the first embodiment is negative. Therefore, the primary transfer voltage application unit 73 applies a voltage of positive polarity as the primary transfer voltage.

[0021] Here, the recording material S stored in a cassette at the bottom of the apparatus body is transported by a pickup roller and a transport roller to a secondary transfer section. In the secondary transfer section, a secondary transfer roller 33 serving as a secondary transfer means is disposed on the outer peripheral surface side of the intermediate transfer belt 31. A voltage of a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 33 from a secondary transfer voltage application section 74 serving as a secondary transfer voltage application section. As a result, the toner image on the intermediate transfer belt 31 is transferred (secondarily transferred) to the recording material S.

[0022] When a full-color image is formed, the images of each color formed in the image forming stations SY, SM, SC, and SK are sequentially primarily transferred onto the intermediate transfer belt 31. Thereafter, the recording material S is conveyed to the secondary transfer station in synchronization with the movement of the intermediate transfer belt 31. Then, the four-color toner images on the intermediate transfer belt 31 are secondarily transferred collectively onto the recording material S by the action of the secondary transfer roller 33 that is in contact with the intermediate transfer belt 31 via the recording material S.

[0023] The recording material S onto which the toner image has been transferred is transported to the fixing device 34. The fixing device 34 applies heat and pressure to the recording material S to fix the toner image onto the recording material S, and the recording material S is discharged outside the image forming apparatus 100.

[0024] Here, the toner remaining on the surface of the photoreceptor 1 without being transferred to the intermediate transfer belt 31 by the primary transfer roller 32 is scraped off from the surface of the photoreceptor 1 by a cleaning blade 8 serving as a cleaning member in contact with the photoreceptor 1, as shown in Fig. 3. The toner is then stored in a waste toner storage chamber 9 provided below the cleaning blade 8. Similarly, the toner remaining on the intermediate transfer belt 31 without being transferred to the recording material S by the secondary transfer roller 33 is transported to an intermediate transfer body cleaning device 35 serving as a cleaning device and removed.

[0025] <Explanation of the control block diagram> 4 is a block diagram showing logical relationships between components of the image forming apparatus 100 in the first embodiment. A control unit 202 that controls the operation of the image forming apparatus 100 receives and outputs signals indicating various information via electrical connections. The control unit 202 processes signals input from various process devices and sensors, and processes signals output to instruct the various process devices to operate. The controller 200 inputs and outputs various signals to and from a host device, and inputs and outputs various signals to and from the control unit 202 via an interface 201, thereby comprehensively controlling the image forming operation of the image forming apparatus 100 according to a predetermined control program and a reference table.

[0026] The control unit 202 has a CPU 155 which is a central element for performing various calculation processes, and memories 15 such as RAM and ROM which are storage elements. The RAM stores the detection results of the sensors, the count results of the counters, the calculation results, etc., and the ROM stores a control program, a data table obtained in advance by experiments, etc.

[0027] The control unit 202 is connected to various control objects, sensors, counters, etc. in the image forming apparatus 100. The control unit 202 controls the input and output of various signals, the timing of driving each unit, etc., and performs control of a predetermined image formation sequence. For example, it controls a high-voltage power supply and a device for forming a toner image on the surface of the photoconductor 1. The control objects include, for example, a charging voltage application unit 71 as a charging power supply, a developing voltage application unit 72 as a developing power supply, a power supply for the supply roller 5, and a power supply for the supply roller 6. There is a supply voltage application section 75 that supplies a toner supply voltage, a development blade voltage application section 76 as a power source for the toner regulating member 6, and an exposure unit 30. The controlled objects further include a primary transfer voltage application section 73 as a primary transfer power source for forming a toner image on the recording material S, a secondary transfer voltage application section 74 as a secondary transfer power source, a contact / separation mechanism 50 that controls the contact and separation between the development roller 4 and the photoconductor 1, a torque detection mechanism 51 for the drive motor of the photoconductor 1, and a cartridge memory communication mechanism 52 that records the usage history of the cartridge. Each voltage application section may be configured with a common power source or may be separate.

[0028] <Calibration explanation> Calibration for correcting image density deviation and color deviation caused by the usage environment of the image forming apparatus and the number of printed sheets will be described. In calibration, the control unit corrects the conditions during image formation. Calibration is performed at a predetermined timing, such as when the image forming apparatus 100 is first used, when the number of printed sheets reaches a predetermined number, or when the usage time of the apparatus reaches a predetermined value. Calibration may also be performed at any timing by the user.

[0029] 5 shows an example of a patch image (reference image) for color misregistration correction used in calibration. In this embodiment, reference images of each color, black, cyan, magenta, and yellow, are formed with solid density at both ends of the intermediate transfer belt 31 in the width direction. The patch image is not limited to this example, and is appropriately changed to an image suitable for calibration. For example, it may be a horizontal band image of uniform density.

[0030] The density sensor 60 of this embodiment is provided facing the intermediate transfer belt 31 so as to detect the image density of the region where the reference image is formed in the width direction of the intermediate transfer belt 31. The density sensor 60 detects the reference images of each color conveyed and compares their positional relationship with a predetermined reference position. For example, if the detection result of the black reference image is shifted from the predetermined reference position in the main scanning direction (the direction perpendicular to the conveying direction of the intermediate transfer belt 31), a color shift in the main scanning direction occurs in black. Therefore, when correcting the color shift in the main scanning direction, the control unit 202 adjusts the exposure start position of the exposure unit 30. Similarly, when correcting the color shift in the sub-scanning direction (the conveying direction of the intermediate transfer belt 31, which intersects (typically perpendicular) with the main scanning direction), the control unit 202 performs the color shift correction by adjusting the exposure start timing of the exposure unit 30.

[0031] Next, the density correction of the calibration will be described using an example of the black image forming unit SK. Fig. 6 is a diagram showing an example of a patch image (reference image) for density correction used in the calibration. At the end of the width direction of the intermediate transfer belt 31, a reference image K consisting of patch images K1 to K8 of eight levels of density from a light-colored image K1 to a darkest image K8 (solid image) is formed along the belt traveling direction. Adjacent patch images are each formed in a single color so that the density changes at the boundary.

[0032] The image density sensor 60 as a detection means detects the density of the patch image K. The control unit 202 compares the detected density with a predetermined standard density to calculate the density difference between each toner density and the reference density. The control unit 202 then reads out a parameter value used for density correction from a density correction table according to the obtained density difference, and executes density correction. For example, if the density of the patch image K is lighter than the standard density, the amount of toner during image formation may be increased according to the density difference. Note that for colors other than black, the density can be similarly corrected based on the difference between the detected density and the standard density.

[0033] <Toner supply to cleaning blade> Next, regarding the toner supply process to the cleaning blade 8, An explanation will be given using an example of SK. In this embodiment, toner is supplied to the cleaning blade 8 during non-image formation. Here, non-image formation refers to a period when image formation is not performed according to instructions using a host or an operation panel, and may be, for example, when the device is first used, during regular maintenance, or at any time desired by the user, as with the timing of calibration. During the toner supply process to the cleaning blade 8, the developing roller 4 and the photoconductor 1 are continuously in contact with each other since the time of image formation, and the toner supply process to the cleaning blade 8 is performed after the image formation is completed.

[0034] The supply of toner to the cleaning blade 8 is performed by the same process as the formation of a toner image during image formation. That is, the developing roller 4 supplies toner to an electrostatic latent image formed by charging and exposing the surface of the photoconductor 1, thereby forming a toner image. In this embodiment, a solid horizontal band image that is uniform in the longitudinal direction is formed. During toner purging, in order to leave this toner image on the photoconductor 1, a negative voltage is applied to the primary transfer roller 32 to suppress the transfer of the toner image onto the intermediate transfer belt 31. All of the toner images on the photoconductor 1 that have not been transferred are supplied to the edge of the cleaning blade 8.

[0035] <Explanation of the formation of blocking layer> The cleaning mechanism and the formation of the blocking layer X will be described with reference to an enlarged view of the edge portion 8a of the cleaning blade 8 in FIG. 7. The cleaning blade 8 abuts against the photoreceptor 1 in the counter direction to the rotation direction A, and the edge portion 8a of the cleaning blade is rolled in as the photoreceptor 1 rotates. Toner external additives smaller in size than the toner particles T enter the wedge-shaped space formed by this rolling in. In this way, the toner external additives accumulated in the wedge portion form the blocking layer X. That is, when toner is supplied to the cleaning blade 8, the external additives contained in the supplied toner gather at the edge portion, forming the blocking layer X.

[0036] This blocking layer X acts as a barrier for cleaning the toner on the photoreceptor 1. Without the blocking layer X, the toner would easily slip into the wedge portion formed by the edge portion 8a being rolled in, causing the toner to slip through the cleaning blade 8 and resulting in poor cleaning.

[0037] <About the destruction of the blocking layer> Next, the mechanism by which the blocking layer X is destroyed will be described. The toner image formed on the photoconductor 1 is transferred to the intermediate transfer belt 31 at the transfer section at the transfer position. At this time, discharge occurs at the transfer section, and highly charged toner is generated. Some of this highly charged toner transfers to the photoconductor 1. Highly charged toner and external additives have a strong electrical adhesion to the photoconductor 1. For this reason, when the highly charged toner and external additives penetrate the edge of the cleaning blade 8, a large force is required to peel them off from the photoconductor 1, and part of the blocking layer X is destroyed.

[0038] Furthermore, if a large amount of highly charged toner enters, the destruction of the blocking layer X is accelerated, and the blocking layer X breaks down in part of the longitudinal direction of the edge portion, and the blocking layer X is depleted. If the next image formation is performed with the blocking layer X depleted, the toner cannot be sufficiently cleaned, and the toner slips through, causing vertical streaks on the image.

[0039] The highly charged toner adhering to the intermediate transfer belt 31 is the toner image on the photoconductor 1 that has been transferred to the intermediate transfer belt 31 by the transfer bias at the transfer position. The amount of highly charged toner adhering to the intermediate transfer belt 31 gradually increases as the transfer proceeds from the upstream image forming unit to the downstream image forming unit. The most downstream image forming unit in the transport direction of the intermediate transfer belt 31 (typically the black image forming unit) is affected by the toner images formed in all the upstream image forming units. As a result, the image forming unit downstream in the travel direction of the intermediate transfer belt 31 is affected by the toner images formed in all the upstream image forming units. The closer to the forming section, the more likely it is that the amount of highly charged toner collected will increase, and cleaning defects will be more likely to occur due to depletion of the blocking layer X. From the above, in order to prevent cleaning defects, even if the blocking layer X is once destroyed, it is necessary to form a blocking layer before the next image formation is performed, and this is particularly necessary in the image forming section that is downstream in the traveling direction.

[0040] <Toner discharge sequence in this case> The timing of performing the toner discharge sequence in this embodiment will be described with reference to the flow chart in Fig. 1. The image forming apparatus 100 starts its operation, and in step S101, the control unit 202 determines whether it is time to perform calibration based on the number of printed sheets. If it is determined that it is not time to perform calibration (S101 = No), the process ends.

[0041] On the other hand, when it is determined that it is time to perform calibration (S101=Yes), the control unit 202 forms a color shift patch image by the above-mentioned method (step S102) and performs color shift adjustment (step S103). Next, the control unit 202 forms a density patch image (step S104) and performs density adjustment (step S105). The control unit 202 confirms that the calibration has been completed through the above procedure (step S106).

[0042] After the calibration is completed, the control unit 202 executes the toner supply to the cleaning blade 8 in each image forming unit SM, SC, and SK located downstream in the transport direction of the intermediate transfer belt 31 (step S107). In this embodiment, a horizontal band image composed of a solid image was used as an image for supplying toner to the cleaning blade 8 of each image forming unit. The width of the horizontal band in the transport direction is 20 mm for the image forming unit SM, 40 mm for the image forming unit SC, and 60 mm for the image forming unit SK. Here, as described above, the destruction of the blocking layer X is promoted in the image forming unit located downstream in the transport direction of the intermediate transfer belt 31. Therefore, in this embodiment, the toner supply to the cleaning blade 8 is increased in the image forming unit located downstream of the intermediate transfer belt 31. Note that the image forming unit SY located at the most upstream of the intermediate transfer belt 31 does not have an image forming unit upstream, so the destruction of the blocking layer X due to the collection of the highly charged toner is not promoted. Therefore, in this embodiment, the toner supply to the cleaning blade 8 after the calibration is not executed for the image forming unit SY. However, in order to reliably form the blocking layer X also in the upstream image forming unit SY, toner supply may be performed.

[0043] <Effects> The effects of Example 1 will be described with reference to Table 1. The effect was confirmed in the black image forming unit SK located at the most downstream of the intermediate transfer belt 31. Printing was performed after calibration under each condition, and the presence or absence of vertical streaks caused by poor cleaning was confirmed. The conditions for Example 1, Comparative Example 1, and Comparative Example 2 are as follows. Example 1: Toner supply to cleaning blade 8 after calibration Comparative Example 1: Toner supply to cleaning blade 8 before calibration Comparative Example 2: Toner supply to cleaning blade 8 not performed [Table 1]

[0044] As shown in Table 1, no cleaning failure occurred in the configuration of this embodiment. However, in Comparative Example 1, slight vertical streaks occurred due to cleaning failure. Furthermore, in Comparative Example 2, vertical streaks occurred due to cleaning failure. This is because in this embodiment, by supplying toner to the cleaning blade 8, the blocking layer X, which acts as a barrier layer, is reformed at the edge of the cleaning blade 8, and the cleaning performance of the cleaning blade 8 is restored when the next image formation is performed. On the other hand, in Comparative Example 1, in which toner was supplied before calibration, the blocking layer was destroyed due to image formation with a high printing rate during calibration, and thus a slight image failure occurred. Furthermore, in Comparative Example 2, in which toner was not supplied, a severe image failure occurred.

[0045] As described above, according to the configuration of this embodiment, even if a large amount of toner with a large charge enters the cleaning blade 8 due to high-print image formation (first image formation) such as calibration, the blocking layer X is reformed by supplying toner thereafter. Therefore, it is possible to provide an image forming apparatus that does not cause cleaning defects even in the image formation (second image formation) following the formation of a high-print image.

[0046] In this embodiment, the toner image supplied to the cleaning blade 8 is a solid horizontal band image extending in the width direction of the intermediate transfer belt 31, but the same effect can be obtained even if the toner image when supplied is appropriately changed. For example, the same effect can be obtained even with an image in which a large amount of toner is supplied to an area corresponding to the position of a calibration patch image (reference image).

[0047] [Example 2] A second embodiment will be described. The description of the parts common to the first embodiment will be simplified. In the first embodiment, the timing of calibration is determined and toner is supplied. In the second embodiment, high-print image formation is detected, and toner is supplied after image formation.

[0048] The timing of execution of the toner discharge sequence in this embodiment will be described with reference to the flow chart in Fig. 8. The image forming apparatus 100 starts operation, and the control unit 202 acquires image information from the controller 200. The control unit 202 calculates the amount of toner to be transferred to the intermediate transfer belt 31 based on the acquired image information (step S201). In this embodiment, the intermediate transfer belt 31 is divided into 10 equal parts in the width direction (main scanning direction), and the toner amount in each area is calculated. The length in the sub-scanning direction may be, for example, the length of one sheet of recording material.

[0049] Next, the control unit 202 judges whether the calculated toner amount on the intermediate transfer belt 31 is greater than a predetermined threshold for each area (step S202). If there is no area with a toner amount greater than the threshold, the process ends. On the other hand, if there is an area with a toner amount greater than the threshold, the control unit 202 judges the next and subsequent image information in order, and determines whether the toner amount is greater than the threshold. It is determined whether the high state continues for a predetermined number of sheets or more (step S203). If it is determined that the number of images in which the toner amount transferred to the intermediate transfer belt 31 exceeds the threshold continues for a predetermined number of sheets or more (S203=Yes), the process proceeds to step S204, where image formation based on the image information is started. Then, after the image formation is completed in step S205, the control unit 202 executes toner supply to the cleaning blade 8 (step S206).

[0050] <Effects> The effect of Example 2 will be described with reference to Table 2. Here, the effect of this Example and Comparative Example was confirmed in the black image forming unit SK located at the most downstream of the intermediate transfer belt 31. In this Example, assuming that an image is formed on two sheets of A4 paper, the number of divisions in the main scanning direction was 1 (that is, the toner amount was calculated without division in the main scanning direction). Therefore, the target area for toner amount calculation is 210 mm wide and 594 mm long (two sheets of A4 paper). The control unit 202 of this Example calculated the toner amount of the target area based on the image information of two sheets. That is, the same process as that in the case of S202=Yes and S202=Yes (the predetermined number is two sheets) in FIG. 8 was performed. The threshold value here was set to 80% of the maximum toner amount that can be set and placed on the intermediate transfer belt 31. In this Example, the image for supplying toner to the cleaning blade 8 was a horizontal band image composed of a solid image, and the supply width (thickness of the horizontal band) of the image forming unit SK was set to 60 mm.

[0051] Table 2 shows the results of confirming whether or not vertical streaks occur due to poor cleaning by performing continuous printing at high print rates under the conditions of Example 2, Comparative Example 3, and Comparative Example 4, after performing continuous printing at high print rates, and then performing image formation again. Here, continuous printing at high print rates corresponds to continuous printing on two sheets of A4 paper at a rate higher than the threshold (80% of the maximum toner amount). The conditions of Example 2, Comparative Example 3, and Comparative Example 4 are as follows. Example 2: Toner supply to cleaning blade 8 after high-density image formation Comparative Example 3: Toner supply to cleaning blade 8 before high-density image formation Comparative Example 4: Toner supply to cleaning blade 8 not performed [Table 2]

[0052] As shown in Table 2, in the configuration of this embodiment, no cleaning failure occurred. However, in Comparative Example 3, slight vertical streaks occurred due to cleaning failure. Furthermore, in Comparative Example 4, vertical streaks occurred due to cleaning failure. This is due to the same cause as in Example 1. That is, in this embodiment, by supplying toner to the cleaning blade 8, the blocking layer X, which acts as a barrier layer, is reformed at the edge of the cleaning blade 8, and the cleaning performance is restored when the next image formation is performed, suppressing cleaning failure. On the other hand, in Comparative Example 3, in which toner was supplied before the high-print image formation, the blocking layer was destroyed due to the high-print image formation, and a slight image failure occurred. Furthermore, in Comparative Example 4, in which toner was not supplied, a severe image failure occurred.

[0053] As described above, according to the configuration of this embodiment, even if a large amount of toner with a large charge enters the cleaning blade 8 due to successive high-print images, an image forming device can be provided that does not cause cleaning failures in subsequent image formation.

[0054] In this embodiment, a solid horizontal band image is used as the toner image supplied to the cleaning blade 8, but the same effect can be obtained by supplying toner only to those parts of the divided area of ​​the intermediate transfer belt 31 that have reached the supply condition. Furthermore, when determining high print image formation based on image information, the number and method of dividing the intermediate transfer belt 31 are not limited to those described above, and division is not necessary.

[0055] As described above, according to the present invention, after the first image formation (for example, image formation with a high printing rate or calibration), a depleted blocking layer can be formed by supplying toner to the cleaning blade. As a result, cleaning failure during the next image formation (second image formation) can be suppressed.

[0056] [Configuration 1] An image forming apparatus including a plurality of image forming units, each of which includes an image carrier, a developer carrier that supplies a developer to an electrostatic latent image formed on the image carrier based on image information to form a developer image, and a cleaning member that contacts the image carrier to remove the developer from a surface of the image carrier, an intermediate transfer body onto which the developer images formed in the image forming units are sequentially transferred in a superimposed manner; a transfer section that transfers the developer image transferred to the intermediate transfer body in a superimposed state onto a recording material; a control unit that executes a toner supply process for supplying the developer from the developer carrier to a region where the image carrier and the cleaning member contact each other after a first image formation, which is a high-printing image formation, is performed and before a second image formation, which is a subsequent image formation following the first image formation, is performed; An image forming apparatus comprising: [Configuration 2] the transfer of the developer image from the plurality of image forming units to the intermediate transfer body is performed sequentially from the image forming unit on the upstream side to the image forming unit on the downstream side in a transport direction of the intermediate transfer body, The control unit performs control such that the amount of the developer supplied in the toner supply process increases toward the downstream side of the image forming unit. 2. The image forming apparatus according to claim 1, [Configuration 3] The first image formation is a calibration for correcting the conditions during image formation. 3. The image forming apparatus according to claim 1, wherein the first and second components are arranged in a same plane. [Configuration 4] the control unit forms the developer image as a reference image on the intermediate transfer body for the calibration; The image forming apparatus further includes a detection unit for detecting a density of the reference image, The control unit performs the calibration by comparing the density of the reference image detected by the detection unit with a predetermined standard density. 4. The image forming apparatus according to claim 3, [Configuration 5] When a direction perpendicular to a transport direction of the intermediate transfer body is defined as a width direction, the control unit applies the developer to an area corresponding to the reference image in the width direction during the toner supply process. Supply 5. The image forming apparatus according to claim 4, [Configuration 6] When a direction perpendicular to a conveying direction of the intermediate transfer body is defined as a width direction, the control unit supplies the developer using a horizontal band image extending in the width direction during the toner supply process. 5. The image forming apparatus according to claim 4, [Configuration 7] The control unit calculates an amount of toner when an image is formed in the image forming unit based on the image information, and when the amount of toner is greater than a predetermined threshold, executes the toner supply process before a next image formation. 7. The image forming apparatus according to any one of configurations 1 to 6, [Configuration 8] When a direction perpendicular to a transport direction of the intermediate transfer body is defined as a width direction, the control unit calculates the toner amount for each of a plurality of regions divided in the width direction, and supplies the developer to the region in which the toner amount is greater than the predetermined threshold value. 8. The image forming apparatus according to claim 7, [Configuration 9] When a direction perpendicular to a conveying direction of the intermediate transfer body is defined as a width direction, the control unit supplies the developer using a horizontal band image extending in the width direction during the toner supply process. 8. The image forming apparatus according to claim 7, [Explanation of symbols]

[0057] 1: photoconductor, 4: developing roller, 8: cleaning blade, 31: intermediate transfer belt, 100: image forming apparatus, 202: control unit, S: image forming unit

Claims

1. An image forming apparatus including a plurality of image forming units, each of which includes an image carrier, a developer carrier that supplies a developer to an electrostatic latent image formed on the image carrier based on image information to form a developer image, and a cleaning member that contacts the image carrier to remove the developer from a surface of the image carrier, an intermediate transfer body onto which the developer images formed in the image forming units are sequentially transferred in a superimposed manner; a transfer section that transfers the developer image transferred to the intermediate transfer body in a superimposed state onto a recording material; a control unit that executes a toner supply process for supplying the developer from the developer carrier to a region where the image carrier and the cleaning member contact each other, at a timing after a first image formation, which is a high-printing image formation, is performed and before a second image formation, which is a subsequent image formation following the first image formation, is performed; An image forming apparatus comprising:

2. the transfer of the developer image from the plurality of image forming units to the intermediate transfer body is performed sequentially from the image forming unit on the upstream side to the image forming unit on the downstream side in a transport direction of the intermediate transfer body, The control unit performs control such that the amount of the developer supplied in the toner supply process increases toward the downstream side of the image forming unit.

2. The image forming apparatus according to claim 1,

3. The first image formation is a calibration for correcting the conditions during image formation.

3. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

4. the control unit forms the developer image as a reference image on the intermediate transfer body for the calibration; The image forming apparatus further includes a detection unit for detecting a density of the reference image, The control unit performs the calibration by comparing the density of the reference image detected by the detection unit with a predetermined standard density.

4. The image forming apparatus according to claim 3.

5. When a direction perpendicular to a transport direction of the intermediate transfer body is defined as a width direction, the control unit supplies the developer to an area corresponding to the reference image in the width direction during the toner supply process.

5. The image forming apparatus according to claim 4.

6. When a direction perpendicular to a conveying direction of the intermediate transfer body is defined as a width direction, the control unit supplies the developer using a horizontal band image extending in the width direction during the toner supply process.

5. The image forming apparatus according to claim 4.

7. The control unit calculates an amount of toner when an image is formed in the image forming unit based on the image information, and when the amount of toner is greater than a predetermined threshold, executes the toner supply process before a next image formation.

3. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

8. When a direction perpendicular to a transport direction of the intermediate transfer body is defined as a width direction, the control unit calculates the toner amount for each of a plurality of regions divided in the width direction, and supplies the developer to the region in which the toner amount is greater than the predetermined threshold value.

8. The image forming apparatus according to claim 7,

9. When a direction perpendicular to a conveying direction of the intermediate transfer body is defined as a width direction, the control unit supplies the developer using a horizontal band image extending in the width direction during the toner supply process.

8. The image forming apparatus according to claim 7,

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