JP2022151914A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can effectively prevent a foreign substance from being bitten between a belt cleaning blade for cleaning an intermediate transfer belt and the intermediate transfer belt, while reducing a printing waiting time and toner consumption.SOLUTION: An image forming apparatus comprises: a plurality of image forming units; an intermediate transfer belt; primary transfer members; a secondary transfer member; a belt cleaning device; a paper feeding unit; a pressure variable mechanism; and a control unit. The belt cleaning device has a cleaning blade that removes a residual toner on the intermediate transfer belt. The paper feeding unit feeds a sheet to a secondary transfer nip part by using a pickup roller. The control unit can supply a protective toner to the belt cleaning blade at a timing earlier than the timing at which a first sheet is supplied to the secondary transfer nip part at the start of image formation. As the amount of paper powder of the sheet increases, the control unit increases the load on the pickup roller and the amount of protective toner supplied to the belt cleaning blade.SELECTED DRAWING: Figure 7

Description

The present invention relates to image forming apparatuses such as copiers, printers, facsimiles, and multifunction machines, and more particularly to a method for suppressing foreign matter such as paper dust from getting caught in a belt cleaning blade that cleans an intermediate transfer belt. be.

In electrophotographic image forming apparatuses such as copiers and printers, after a toner image is transferred from an image carrier to a transfer material such as paper, a small amount of toner remains on the outer peripheral surface of the image carrier. There is Residual toner, paper dust, and other deposits on the outer peripheral surface of the image carrier hinder the next new image formation, so cleaning is necessary. As a method for cleaning the outer peripheral surface of the image carrier, a method of scraping off deposits such as residual toner by bringing a cleaning blade into contact with the outer peripheral surface of the image carrier is widely known.

In the image forming apparatus using the above method, there is a concern that foreign matter such as paper dust may get caught and stay between the tip of the cleaning blade and the outer peripheral surface of the image carrier. As a result, cleaning failure may occur.

Therefore, methods have been proposed to prevent remnants from being caught between the edge (tip) of the cleaning blade and the image bearing member. In an image forming apparatus having intermediate transfer member cleaning means for collecting toner and a detection sensor for detecting the surface property of the intermediate transfer member, the detection sensor detects the surface property of the intermediate transfer member, and according to the detected value, , an image forming apparatus having a mode for supplying toner swaths to a photoreceptor is disclosed.

Further, Japanese Patent Application Laid-Open No. 2002-100000 discloses that an image carrier is rotated in the reverse direction by a drive unit during non-image formation, and a region of the outer peripheral surface of the image carrier in contact with a cleaning blade is rotated more forward than the toner supply unit. Further, the drive unit rotates the image carrier forward, the toner supply unit supplies toner to the outer peripheral surface of the image carrier, and the supplied toner is moved to the cleaning blade to reach the edge of the cleaning blade. An image forming apparatus capable of executing a foreign matter removal mode for removing the foreign matter together with the foreign matter staying in the part is disclosed.

JP 2018-54652 A JP 2020-112737 A

Since the surface properties of the intermediate transfer member (intermediate transfer belt) tend to vary greatly in the width direction depending on the print pattern, the method of Patent Document 1 requires a large number of sensors for detecting the surface properties. Further, since the toner bands are supplied to all the photoreceptors, the amount of toner consumed for purposes other than printing increases. Furthermore, the method of Patent Document 1 suppresses foreign matter that has slipped through the cleaning blade of the intermediate transfer member from being caught by the cleaning blade of the photoreceptor. was enough.

In addition, the method of Patent Document 2 requires execution of the foreign matter removal mode during non-image formation, and thus printing must be interrupted, which causes a print waiting time and lowers the image forming efficiency. Furthermore, since the image carrier is rotated in the reverse direction in the foreign matter removal mode, there is also the problem that the waiting time for printing becomes longer depending on the layout of the image forming apparatus.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an image forming apparatus capable of effectively suppressing foreign matter from getting caught in a belt cleaning blade that cleans an intermediate transfer belt while suppressing print waiting time and toner consumption. for the purpose.

In order to achieve the above object, a first configuration of the present invention includes a plurality of image forming units, an intermediate transfer belt, a primary transfer member, a secondary transfer member, a belt cleaning device, a paper feed unit, and a pressure transfer unit. An image forming apparatus including a variable mechanism and a control unit. The plurality of image forming units include an image carrier having a surface on which a toner image is formed, and form a toner image of each color. The intermediate transfer belt is endless and arranged adjacent to the image carrier. The primary transfer member is arranged to face the image carrier with the intermediate transfer belt interposed therebetween, and primarily transfers the toner image formed on the image carrier onto the intermediate transfer belt. The secondary transfer member forms a secondary transfer nip portion in contact with the intermediate transfer belt, and secondarily transfers the toner image that has been primarily transferred onto the intermediate transfer belt onto a sheet passing through the secondary transfer nip portion. The belt cleaning device has a belt cleaning blade that cleans residual toner on the intermediate transfer belt. The paper feed unit feeds the paper to the secondary transfer nip using a pickup roller that is pressed against the upper surface of the paper. The variable pressure mechanism changes the load of the pickup roller with respect to the paper. The control section controls the image forming section and the variable pressure mechanism. The control unit primarily transfers the belt-shaped protective toner formed by the image forming unit at the start of image formation onto the intermediate transfer belt, and protects the toner at an earlier timing than the first sheet of paper is fed to the secondary transfer nip. Toner can be moved to a belt cleaning device and supplied to a belt cleaning blade. The controller estimates the amount of paper dust on the paper, and increases the load on the pickup roller and the amount of protective toner supplied to the belt cleaning blade as the estimated amount of paper dust increases.

According to the first configuration of the present invention, by estimating the amount of paper dust on the paper and changing the load of the pickup roller according to the estimated amount of paper dust, even paper with a large amount of paper dust can be slipped. Therefore, it is possible to suppress problems such as poor paper feeding and non-feeding of paper. Further, by changing the amount of protective toner supplied to the belt cleaning blade according to the amount of paper dust on the paper, it is possible to supply an appropriate amount of protective toner according to the amount of paper dust adhering to the intermediate transfer belt. Therefore, it is possible to suppress the consumption of toner for purposes other than printing as much as possible while suppressing paper dust from being caught in the belt cleaning blade.

FIG. 1 is a side cross-sectional view showing the internal configuration of an image forming apparatus 100 according to one embodiment of the present invention; FIG. 1 is a partial enlarged view of the periphery of an image forming portion Pa in FIG. FIG. 2 is a cross-sectional side view showing the structure of the intermediate transfer unit 30 mounted in the image forming apparatus 100; 4 is a partially enlarged view showing the structure around the belt cleaning device 31 in FIG. FIG. 2 is a cross-sectional side view showing the structure around a paper feeding unit 40 that feeds paper S from a paper cassette 16; FIG. 2 is a block diagram showing an example of a control path of the image forming apparatus 100; 3 is a flow chart showing an example of load control of the pickup roller 41 and supply control of protective toner to the belt cleaning device 31 in the image forming apparatus 100 of the present embodiment;

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view showing the internal structure of an image forming apparatus 100 according to one embodiment of the invention. FIG. 2 is an enlarged view of the vicinity of the image forming portion Pa in FIG.

The image forming apparatus 100 shown in FIG. 1 is a so-called tandem color printer, and has the following configuration. Four image forming units Pa, Pb, Pc, and Pd are arranged in order from the left side in FIG. These image forming units Pa to Pd are provided corresponding to images of four different colors (yellow, cyan, magenta and black). and black images are sequentially formed.

Photoreceptor drums (image carriers) 1a to 1d for carrying visible images (toner images) of respective colors are provided in these image forming portions Pa to Pd, respectively. Further, an intermediate transfer belt 8 that rotates counterclockwise in FIG. 1 is provided adjacent to each of the image forming stations Pa to Pd. The toner images formed on these photoreceptor drums 1a to 1d are sequentially transferred onto an intermediate transfer belt 8 that moves while being in contact with each of the photoreceptor drums 1a to 1d. The image is transferred onto a sheet S, which is an example, at one time, fixed onto the sheet S by the fixing device 13, and then discharged from the main body of the image forming apparatus 100. FIG. An image forming process is performed on each of the photosensitive drums 1a to 1d while rotating the photosensitive drums 1a to 1d clockwise in FIG.

The paper S onto which the toner image is to be transferred is housed in a paper cassette 16 at the bottom of the device, and is formed by an intermediate transfer belt 8 and a secondary transfer roller 9 via a paper feeder 40 and a pair of registration rollers 12. It is conveyed to the secondary transfer nip portion N (see FIG. 3). A dielectric resin sheet is used for the intermediate transfer belt 8, and a seamless belt is mainly used. The intermediate transfer belt 8 and the secondary transfer roller 9 are rotationally driven at the same linear velocity as the photosensitive drums 1a to 1d by a belt drive motor 51 (see FIG. 6). A belt cleaning device 30 for removing residual toner remaining on the surface of the intermediate transfer belt 8 is arranged above the image forming portion Pd.

Next, the image forming units Pa to Pd will be described. The image forming portion Pa will be described in detail below, but the image forming portions Pb to Pd are basically of the same configuration, and thus description thereof will be omitted. As shown in FIG. 2, a charging device 2a, a developing device 3a, and a cleaning device 7a are provided around and below the rotatably disposed photosensitive drum 1a along the drum rotation direction (clockwise direction in FIG. 2). , and a primary transfer roller 6a is arranged with the intermediate transfer belt 8 interposed therebetween.

Next, an image forming procedure in the image forming apparatus 100 will be described. When the user inputs the start of image formation, the rotation of the photosensitive drums 1a to 1d is first started by the main motor 50 (see FIG. 6), and the photosensitive drums 1a to 1d are driven by the charging rollers 20 of the charging devices 2a to 2d. uniformly charge the surface of the Next, the surfaces of the photosensitive drums 1a to 1d are irradiated with beam light (laser light) emitted from the exposure device 5 to form electrostatic latent images corresponding to image signals on the respective photosensitive drums 1a to 1d.

The developing devices 3a to 3d are filled with predetermined amounts of magenta, cyan, yellow and black toners, respectively. When the ratio of the toner in the two-component developer filled in each of the developing devices 3a to 3d falls below a specified value due to the formation of a toner image, which will be described later, each of the developing devices 3a to 3d is removed from the toner containers 4a to 4d. Toner is supplied to the The toner in this developer is supplied onto the photosensitive drums 1a to 1d by the developing rollers 21 of the developing devices 3a to 3d, and adheres electrostatically. As a result, a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 5 is formed.

Then, an electric field is applied between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d by the primary transfer rollers 6a to 6d with a predetermined transfer voltage, and magenta, cyan, yellow, and magenta on the photosensitive drums 1a to 1d are transferred. A black toner image is primarily transferred onto the intermediate transfer belt 8 . These four-color images are formed with a predetermined positional relationship for predetermined full-color image formation. After that, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning blades 22 and rubbing rollers 23 of the cleaning devices 7a to 7d in preparation for subsequent new electrostatic latent image formation.

When the intermediate transfer belt 8 starts rotating in the counterclockwise direction as the drive roller 10 is rotated by the belt drive motor 51, the sheet S is conveyed from the pair of registration rollers 12 to the secondary transfer nip portion N at a predetermined timing. A full-color image is secondarily transferred to S. The sheet S on which the toner image has been secondarily transferred is conveyed to the fixing section 13 . Toner remaining on the surface of the intermediate transfer belt 8 is removed by the belt cleaning device 31 .

The sheet S conveyed to the fixing section 13 is heated and pressed by the pair of fixing rollers 13a to fix the toner image on the surface of the sheet S, forming a predetermined full-color image. The paper S on which the full-color image is formed is distributed in the conveying direction by the branching unit 14 branched in a plurality of directions, and is discharged by the discharge roller pair 15 as it is (or after being sent to the double-sided conveying path 18 and printed on both sides). It is discharged to tray 17 .

FIG. 3 is a side sectional view of the intermediate transfer unit 30 mounted on the image forming apparatus 100. As shown in FIG. FIG. 4 is a partially enlarged view showing the structure of the belt cleaning device 31 in FIG. As shown in FIG. 3, the intermediate transfer unit 30 includes an intermediate transfer belt 8 stretched between a driving roller 10 on the downstream side and a tension roller 11 on the upstream side; 1d, a belt cleaning device 31, and a cleaning facing roller 37. The belt cleaning device 31 is arranged downstream of the drive roller 10 (secondary transfer nip portion N) in the rotational direction of the intermediate transfer belt 8 and upstream of the tension roller 11 in the rotational direction of the intermediate transfer belt 8 .

As shown in FIG. 4, the belt cleaning device 31 includes a housing 32, a belt cleaning blade 33, a collection screw 34, and sheet-like first and second sealing members 35 and 36. As shown in FIG.

The housing 32 has an opening 32 a that faces the intermediate transfer belt 8 and a waste toner storage section 32 b that stores waste toner scraped from the surface of the intermediate transfer belt 8 .

The belt cleaning blade 33 is fixed on the downstream side (left side in FIG. 3) of the opening 32a of the housing 32 with respect to the rotation direction of the intermediate transfer belt 8. As shown in FIG. The belt cleaning blade 33 contacts the outer peripheral surface of the intermediate transfer belt 8 and removes foreign matter such as residual toner adhering to the intermediate transfer belt 8 . As the belt cleaning blade 33 , for example, a blade made of polyurethane rubber is used, and is attached at a predetermined angle so that the leading end thereof faces the upstream side in the rotation direction of the intermediate transfer belt 8 . The material, hardness, size, amount of bite into the intermediate transfer belt 8 , pressing force, etc. of the belt cleaning blade 33 are appropriately set according to the specifications of the intermediate transfer belt 8 .

A cleaning facing roller 37 that receives the pressure contact force of the belt cleaning blade 33 is arranged at a position facing the belt cleaning blade 33 with the intermediate transfer belt 8 interposed therebetween. The cleaning facing roller 37 is rotated counterclockwise in FIG.

Residual toner removed from the surface of the intermediate transfer belt 8 by the belt cleaning blade 33 is discharged outside the belt cleaning device 31 as the recovery screw 34 rotates, and is conveyed to a waste toner recovery container (not shown). stored.

The first seal member 35 is attached to the opening 32a of the housing 32 on the upstream side in the rotation direction of the intermediate transfer belt 8 (right side in FIG. 4). The second seal member 36 is located upstream of the opening 32a of the housing 32 in the rotational direction of the intermediate transfer belt 8 (right side in FIG. 4) and downstream of the first seal member 35 in the rotational direction of the intermediate transfer belt 8 (in FIG. 4). left side). The first sealing member 35 and the second sealing member 36 prevent waste toner from leaking from the housing 32 through the gap between the housing 32 and the intermediate transfer belt 8 . As the first sealing member 35 and the second sealing member 36, for example, a urethane sheet having a thickness of 100 μm is used.

FIG. 5 is a side cross-sectional view showing the structure around the paper feed unit 40 that feeds the paper S from the paper cassette 16. As shown in FIG. The paper feed unit 40 includes a pickup roller 41, a paper feed roller pair 43, and a variable pressure mechanism 45 (see FIG. 6).

The pickup roller 41 rotates in contact with the upper surface of the stack of sheets S stacked on the sheet stacking plate 16a of the sheet cassette 16, thereby sending out one to a plurality of sheets S from the stack of sheets S. As shown in FIG. The paper feed roller pair 43 is composed of a feed roller 43a and a retard roller 43b, and feeds a plurality of sheets S sent out by the pickup roller 41 while handling them one by one.

The pressure variable mechanism 45 varies the pressure when the pickup roller 41 is pressed against the upper surface of the stack of sheets S. As shown in FIG. As the variable pressure mechanism 45, for example, a configuration combining an eccentric cam and a compression spring, or a configuration using a clutch may be used.

Further, a paper detection unit 47 is arranged in the vicinity of the paper feed roller pair 43 on the downstream side with respect to the paper feed direction. A paper detection sensor 47 detects whether or not the paper S has passed through the paper feed roller pair 43 . Examples of the paper detection sensor 47 include a PI (photointerrupter) sensor having a detection portion having a light emitting portion and a light receiving portion, and a structure in which a PI sensor and an actuator are combined.

FIG. 6 is a block diagram showing an example of control paths of the image forming apparatus 100 of this embodiment. Since various parts of the apparatus are controlled when the image forming apparatus 100 is used, the overall control path of the image forming apparatus 100 is complicated. Therefore, here, the portion of the control path that is necessary for implementing the present invention will be mainly described.

The control unit 90 includes a CPU (Central Processing Unit) 91 as a central processing unit, a read-only memory (ROM) 92, a readable/writable memory (RAM) (Random Access Memory) 93, a temporary A temporary storage unit 94 for temporarily storing image data and the like, a timer 95, and a plurality (here, two) for transmitting control signals to each device in the image forming apparatus 100 and receiving input signals from the operation unit 70. at least an I/F (interface) 96 of Also, the control unit 90 can be arranged at any place inside the main body of the image forming apparatus 100 .

The ROM 92 stores a program for controlling the image forming apparatus 100 and data such as numerical values necessary for control that are not changed while the image forming apparatus 100 is in use. The RAM 93 stores necessary data generated during control of the image forming apparatus 100, data temporarily necessary for controlling the image forming apparatus 100, and the like. The RAM 93 (or ROM 92) stores the relationship between the amount of paper dust on the paper S, the load of the pickup roller 41, and the amount of toner supplied, which is used to determine the load of the pickup roller 41 and the amount of toner supplied to the belt cleaning blade 33, which will be described later. A table (see Table 1), etc. that defines . The timer 95 measures the time from when the pickup roller 41 starts driving to when the paper detection sensor 47 detects the paper.

Further, the control unit 90 transmits a control signal from the CPU 91 to each part and device in the image forming apparatus 100 through the I/F 96 . Signals and input signals indicating the state of each part and device are transmitted to the CPU 91 through the I/F 96 . The parts and devices controlled by the control unit 90 include, for example, the image forming units Pa to Pd, the paper feed unit 40, the main motor 50, the belt drive motor 51, the voltage control circuit 61, the operation unit 70, and the like.

The voltage control circuit 61 is connected to a charging voltage power supply 62 , a developing voltage power supply 63 and a transfer voltage power supply 64 , and operates these power supplies according to output signals from the control section 90 . These power sources are controlled by a control signal from a voltage control circuit 61, a charging voltage power source 62 to the charging rollers 20 in the charging devices 2a to 2d, a developing voltage power source 63 to the developing rollers 21 in the developing devices 3a to 3d, A transfer voltage power supply 64 applies predetermined voltages to the primary transfer rollers 6a to 6d and the secondary transfer roller 9, respectively.

The operation unit 70 is provided with a liquid crystal display unit 71 and LEDs 72 indicating various states. Various settings of the forming apparatus 100 are set to the default state. The liquid crystal display unit 71 indicates the state of the image forming apparatus 100, and displays the image forming state and the number of print copies. Various settings of the image forming apparatus 100 are performed from the printer driver of the personal computer.

As described above, when foreign matter such as paper dust gets stuck between the edge portion of the belt cleaning blade 33 and the intermediate transfer belt 8 and stays there, a gap is generated between the belt cleaning blade 33 and the intermediate transfer belt 8. Poor cleaning may occur. In particular, when the amount of paper dust on the paper S is large, jamming is likely to occur.

As a method of suppressing foreign matter from being caught, there is a method of supplying toner to the edge portion of the belt cleaning blade 33 and removing the foreign matter together with the toner. However, if toner is always supplied to the edge portion, the amount of toner consumed for purposes other than printing increases, leading to an increase in the running cost of the image forming apparatus 100 . Further, if the toner is supplied during non-image formation, the waiting time for printing becomes long.

Therefore, in the image forming apparatus 100 of the present embodiment, protective toner is supplied to the edge portion of the belt cleaning blade 33 prior to feeding the sheet S during image formation in order to prevent foreign matter from being caught. Then, the supply amount of protective toner is adjusted according to the amount of paper dust of the sheet S fed to the secondary transfer roller 9 .

There is a correlation between the amount of paper dust and the amount of slippage of the paper S, and the amount of slippage increases in proportion to the amount of paper dust. Therefore, the amount of paper dust on the paper S can be estimated based on the amount of slippage of the paper S in the paper feed section 40 .

As a method for detecting the amount of slippage of the paper S, the time from the start timing of driving the pickup roller 41 to the timing of detection of the paper S by the paper detection unit 47 is measured, and the paper S is determined by comparing with the time when there is no slippage. Calculate the amount of slippage. Alternatively, as the amount of paper dust on the paper S increases, the load on the pickup roller 41 required for feeding the paper S also increases. It is also possible to calculate the amount of slippage of the sheet S from the load when the feeding of the sheet S is detected by the unit 47 .

By storing the relationship between the amount of paper dust on the paper S, the load on the pickup roller 41, and the amount of toner supplied in advance in the RAM 93 (or ROM 92), the amount of slippage of the pickup roller 41 is calculated based on the calculated amount of slippage of the paper S. The load and supply of protective toner can be determined. Table 1 shows a table for determining the load of the pickup roller 41 and the supply amount of protective toner.

As shown in Table 1, since the amount of paper dust is as small as 2 mg/m ² in paper A, it is possible to feed the paper without slipping by setting the load of the pickup roller 41 to the reference value (5 N). In addition, since there is no risk of paper dust getting caught in the edge portion of the belt cleaning blade 33, the protective toner is not supplied to the edge portion of the belt cleaning blade 33 either.

Since the amount of paper dust in the paper B is slightly large at 10 mg/m ² , it is necessary to increase the load of the pickup roller 41 (10 N) from the reference value. In addition, since there is a risk of paper dust getting caught in the edge portion of the belt cleaning blade 33 , a certain amount (5 g) of protective toner is supplied to the edge portion of the belt cleaning blade 33 . Since the amount of paper dust in the paper C is as large as 15 mg/m ² , it is necessary to further increase the load of the pickup roller 41 (15 N) from the reference value. Also, the amount of protective toner supplied to the edge portion of the belt cleaning blade 33 is increased to 8 g.

FIG. 7 is a flowchart showing an example of load control of the pickup roller 41 and supply control of protective toner to the belt cleaning device 31 in the image forming apparatus 100 of this embodiment. A procedure for determining the load of the pickup roller 41 and the toner supply amount to the belt cleaning device 31 will be described in detail along the steps of FIG. 7 while referring to FIGS. 1 to 6 as necessary.

When print data is input from a personal computer or the like to the control unit 90, the control unit 90 transmits control signals to each unit of the image forming apparatus 100 to drive the image forming units Pa to Pd and the intermediate transfer belt 8 to perform a printing operation. start (step S1). At the same time, feeding of the sheet S from the sheet feeding section 40 is also started. The controller 90 detects the slippage amount of the paper S in the paper feeder 40 (step S2).

Specifically, the timer 95 measures the time from the start timing of driving the pickup roller 41 to the timing of detection of the paper S by the paper detection unit 47, and the amount of slippage of the paper S is calculated. Alternatively, the load of the pickup roller 41 is gradually increased by the variable pressure mechanism 45, and the amount of slippage of the paper S is calculated from the load when the paper detection unit 47 detects the feeding of the paper S. Then, the controller 90 estimates the amount of paper dust on the sheet S based on the calculated amount of slippage of the sheet S (step S3).

Next, the controller 90 determines the load of the pickup roller 41 based on the estimated amount of paper dust (step S4). The load of the pickup roller 41 is determined based on a table (see Table 1) stored in the RAM 93 (or ROM 92). Further, when calculating the amount of slippage by increasing the load of the pickup roller 41 stepwise by the variable pressure mechanism 45, the load may be determined to feed the paper S without slippage when calculating the amount of slippage.

Further, the control unit 90 determines the amount of protective toner to be supplied to the belt cleaning blade 33 based on the estimated amount of paper dust (step S5). The supply amount of protective toner is determined based on a table (see Table 1) stored in the RAM 93 (or ROM 92).

Next, the controller 90 supplies protective toner to the belt cleaning blade 33 in the amount determined in step S5 (step S6). Specifically, a strip-shaped toner image (solid image) is formed on the photosensitive drums 1a to 1d in one of the image forming portions Pa to Pd. The toner images are primarily transferred onto the intermediate transfer belt 8 from the photosensitive drums 1a to 1d. With the secondary transfer roller 9 separated from the intermediate transfer belt 8 , the primarily transferred toner image is moved to the belt cleaning device 31 and supplied to the edge portion of the belt cleaning blade 33 . The toner image is supplied in a predetermined length in the circumferential direction of the intermediate transfer belt 8 over the entire width of the intermediate transfer belt 8 . The supply amount of protective toner can be adjusted by changing the circumferential length of the toner image.

It should be noted that the protective toner must be supplied prior to the execution of the printing operation. is determined. Therefore, the time for forming toner images (solid images) on the photosensitive drums 1a to 1d is limited. Therefore, it is preferable to form a toner image for supplying the protective toner in the image forming portion Pd closest to the secondary transfer nip portion N. FIG.

Following the supply of protective toner to the belt cleaning blade 33, printing is performed (step S7). Specifically, toner images of respective colors for printing are formed on the photosensitive drums 1a to 1d, sequentially primary-transferred onto the intermediate transfer belt 8, and secondary-transferred onto the sheet S conveyed to the secondary transfer nip portion. to form a full-color image. After that, it is determined whether or not the printing is completed (step S8), and if the printing is continued (No in step S8), the process returns to step S7. If printing has ended (Yes in step S8), the process ends.

According to the control example of FIG. 7, by estimating the amount of paper dust of the paper S and changing the load of the pickup roller 41 according to the estimated amount of paper dust, even if the paper S has a large amount of paper dust, It is possible to feed the sheet S without slipping, and it is possible to suppress troubles such as defective feeding of the sheet S and non-feeding of the sheet. Further, by changing the amount of protective toner supplied to the belt cleaning blade 33 according to the amount of paper dust on the paper S, it is possible to supply an appropriate amount of protective toner according to the amount of paper dust adhering to the intermediate transfer belt 8 . can. Therefore, it is possible to suppress the consumption of toner for purposes other than printing as much as possible while suppressing paper dust from being caught in the belt cleaning blade 33 .

In addition, since the amount of paper dust on the paper S can be easily and accurately estimated based on the amount of slippage of the paper S in the paper feeding unit 40, it is necessary to mount means for detecting the amount of paper dust on the paper S. It also contributes to cost reduction of the image forming apparatus 100 .

Note that when the load of the pickup roller 41 is changed by the pressure variable mechanism 45 and the amount of slippage of the paper S is calculated from the load when the paper detection unit 47 detects the feeding of the paper S, the paper S is fed. The load of the pick-up roller 41 that enables feeding varies depending on the thickness of the paper S. As shown in FIG. Specifically, even if the amount of slippage (amount of paper dust) of the paper S is the same, the load on the pickup roller 41 is greater for thick paper than for plain paper by the thickness of the paper.

Therefore, it is preferable to change the threshold value of the load of the pickup roller 41 when determining the toner supply amount according to the thickness of the sheet S. FIG. Specifically, a plurality of tables for determining the load of the pickup roller 41 and the supply amount of protective toner as shown in Table 1 are stored in the RAM 93 (or ROM 92) according to the thickness of the sheet S. The control unit 90 determines the supply amount of protective toner using a table corresponding to the type of paper S set in the operation unit 70 .

In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention. For example, in the above embodiment, the belt cleaning device 31 that removes the toner remaining on the intermediate transfer belt 8 with the belt cleaning blade 33 has been described as an example, but the present invention is not limited to this. For example, a belt cleaning device having a cleaning brush (fur brush) in contact with the intermediate transfer belt 8 and a belt cleaning blade arranged downstream of the cleaning brush with respect to the moving direction of the intermediate transfer belt 8 can be used in exactly the same way. Applicable.

INDUSTRIAL APPLICABILITY The present invention can be used in an image forming apparatus having a belt cleaning blade for cleaning an intermediate transfer belt. By using the present invention, it is possible to provide an image forming apparatus capable of effectively suppressing foreign matter from getting caught in a belt cleaning blade that cleans an intermediate transfer belt while suppressing print waiting time and toner consumption.

Pa to Pd image forming unit 1a to 1d photosensitive drum (image carrier)
2a to 2d charging device 3a to 3d developing device 5 exposure device 6a to 6d primary transfer roller (primary transfer member)
7a to 7d cleaning device 8 intermediate transfer belt 9 secondary transfer roller (secondary transfer member)
13 fixing device 30 intermediate transfer unit 31 belt cleaning device 33 belt cleaning blade 40 paper feeding section 41 pickup roller 43 paper feeding roller pair 45 variable pressure mechanism 47 paper detection section 70 operation section (input section)
90 control unit 92 ROM
93 RAM
100 image forming apparatus

Claims (5)

a plurality of image forming units each including an image carrier on which a toner image is formed and which forms a toner image of each color;
an endless intermediate transfer belt arranged adjacent to the image carrier;
a primary transfer member arranged to face the image carrier with the intermediate transfer belt interposed therebetween, for primarily transferring the toner image formed on the image carrier onto the intermediate transfer belt;
A secondary transfer member that contacts the intermediate transfer belt to form a secondary transfer nip and secondarily transfers the toner image that has been primarily transferred onto the intermediate transfer belt onto a sheet that passes through the secondary transfer nip. When,
a belt cleaning device having a belt cleaning blade for cleaning residual toner on the intermediate transfer belt;
a paper feed unit that feeds the paper to the secondary transfer nip using a pickup roller that is pressed against the upper surface of the paper;
a variable pressure mechanism that changes the load of the pickup roller with respect to the paper;
a control unit that controls the image forming unit and the variable pressure mechanism;
In an image forming apparatus comprising
The control unit
At the start of image formation, the band-shaped protective toner formed by the image forming unit is primarily transferred to the intermediate transfer belt, and the first sheet of paper is fed to the secondary transfer nip portion at a timing earlier than that. protective toner can be moved to the belt cleaning device and supplied to the belt cleaning blade;
An image forming apparatus, comprising: estimating the amount of paper dust on the paper; and increasing the load of the pickup roller and the supply amount of the protective toner to the belt cleaning blade as the estimated amount of paper dust increases. . A paper detection unit arranged downstream of the paper supply unit with respect to the paper supply direction and detecting passage of the paper,
The control unit measures the time from the timing when the pickup roller starts driving to the timing when the paper detection unit detects the paper, and calculates the amount of slippage of the paper by comparing it with the time when there is no slippage. 2. The image forming apparatus according to claim 1, wherein the amount of paper dust is estimated based on the calculated amount of slippage. The control unit increases the load of the pickup roller stepwise by the variable pressure mechanism to feed the paper, and the load of the pickup roller when the paper detection unit detects the feeding of the paper. 2. The image forming apparatus according to claim 1, wherein the amount of slippage of the paper is calculated from the calculated amount of slippage, and the amount of paper dust is estimated based on the calculated amount of slippage. An input unit for inputting the thickness information of the paper,
4. The image forming method according to claim 3, wherein the control unit changes a threshold value of the load of the pickup roller used for estimating the amount of paper dust based on the thickness information input from the input unit. Device. 5. The protective toner according to any one of claims 1 to 4, wherein the protective toner is formed in one of the image forming units, which is positioned immediately upstream of the secondary transfer nip portion. The image forming apparatus according to .

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