JP2010122329A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately clean an intermediate transfer belt without deteriorating the efficiency of forming an image. <P>SOLUTION: In the image forming apparatus, reflectance based on an output voltage of an optical sensor related to filming at which paper powder or a residual toner left after transfer adheres to the intermediate transfer belt is detected. When the reflectance exceeds a first threshold and a situation that the filming occurs much is decided, a cleaning blade made to press-contact with an outer peripheral surface of the intermediate transfer belt is separated from the outer peripheral surface thereof in a frequency of one time per 50 sheets so as to suppress the filming, and when the reflectance exceeds a second threshold and a situation that the filming occurs much more is decided, the cleaning blade is separated from the outer peripheral surface thereof in a frequency of one time per 10 sheets so as to suppress the growth of a filming layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine or a combination machine combining two or more of them, and more particularly to a toner image carrier (intermediate transfer body, intermediate) in the image forming apparatus. The present invention relates to a technique for suppressing the deterioration of the cleaning function of the transfer belt.

  In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine combining two or more of them, which normally forms a toner image, an electrostatic latent image is usually formed on an image carrier such as a photosensitive member in an exposure process. And developing the electrostatic latent image in a development process to form a visible toner image, and transferring the visible toner image to a recording medium such as a recording paper in a transfer process, or temporarily using an intermediate transfer belt or the like The toner image transferred to the recording medium in the fixing process can be fixed on the recording medium by primary transfer to the intermediate transfer body and secondary transfer from the intermediate transfer body to the recording medium.

  In the transfer process, when the recording medium is recording paper, residual toner is not transferred on the surface of the photoreceptor after transfer of the toner image to the recording paper or on the surface of the intermediate transfer body after transfer of the toner image to the recording paper. In addition to adhering, paper powder, toner external additives and the like are adhering. Therefore, in order to repeatedly use the photosensitive member and the intermediate transfer member, transfer residual toner and paper dust or the like (hereinafter referred to as “paper residual etc.”) A cleaning device for removal is provided. As one of such cleaning apparatuses, there is an apparatus that mechanically removes paper dust and the like by bringing a cleaning blade formed of an elastic member such as rubber into contact with an intermediate transfer belt as an intermediate transfer body. This cleaning device is configured such that the paper blade or the like overcomes the adhesion force that adheres to the intermediate transfer belt, the cleaning blade scrapes the paper powder or the like from the intermediate transfer belt, and the paper dust or the like does not pass under the cleaning blade. There are many things.

  In such a cleaning device, when paper dust or the like passes under the cleaning blade, a thin layer, that is, a filming layer in which paper dust or the like is formed into a film on the intermediate transfer belt may be formed (hereinafter, referred to as “filming layer”). The formation of the filming layer may be simply described as filming). When the filming layer grows, wiping of paper dust and the like, chipping (chips, etc.) of the cleaning blade or peeling may occur. As countermeasures, (1) improving the releasability of the intermediate transfer belt, (2) introducing an air feeding device that suppresses the generation of paper dust, and (3) providing a cooling fan or the like in the device. (4) A speed difference is provided between the photosensitive member and the intermediate transfer belt so that the contact between the cleaning blade and the intermediate transfer belt is suppressed. (5) Secondary transfer pressure, that is, pressure when the recording paper is pressed against the intermediate transfer belt by the secondary transfer member when the toner image on the intermediate transfer belt is secondarily transferred to the recording paper. , To prevent the paper powder from adhering to the intermediate transfer belt. However, countermeasures (1), (2), and (3) have a problem of cost increase, and countermeasure (4) has a problem that the photosensitive member may be damaged. Countermeasure (5) has a low secondary transfer pressure. As a result, there is a problem in that the transferability of the toner image to thick paper or rough paper is deteriorated. For this reason, in practice, the pressure at which the tip of the cleaning blade comes into contact with the intermediate transfer belt is separated by moving the cleaning blade pressed against the intermediate transfer belt away from the intermediate transfer belt or reversing the intermediate transfer belt. There are cases where measures for improving the cleaning performance are ensured to be suitable for belt cleaning (for example, Patent Document 1: Japanese Patent Application Laid-Open No. 8-63071).

  In the image forming apparatus disclosed in Patent Document 1, measures for improving the cleaning performance are performed to suppress cleaning defects as follows.

  When the four-cycle full-color copying machine is in the monochrome mode, the cleaning blade is always in contact with the intermediate transfer belt. Therefore, the cleaning performance deteriorates when paper dust or the like (including toner) aggregates at the tip of the cleaning blade. For example, when about 10 single-color copies are made with spherical toner, cleaning failure occurs. Therefore, the cleaning blade is brought into contact with the intermediate transfer belt until the paper transfer is completed and the cleaning of the next image forming area on the intermediate transfer belt is completed, and then the cleaning blade is in contact with the intermediate transfer belt. Are separated from each other and brought into contact again before the transfer residual toner area of the next image reaches the tip of the cleaning blade. The agglomerated toner is removed from the tip of the cleaning blade by using an impact when the cleaning blade is released from the intermediate transfer belt. Further, the intermediate transfer belt is temporarily reversed between the images (at this time, the intermediate transfer belt is separated from the paper transfer roller), thereby removing the aggregated toner from the tip of the cleaning blade.

JP-A-8-63071

  However, in the measures for improving the cleaning performance of the intermediate transfer belt in the image forming apparatus disclosed in Patent Document 1, for example, when about 10 single-color copies are made regardless of the growth state of the filming layer on the intermediate transfer belt, the cleaning blade The intermediate transfer belt is rotated reversely. That is, the cleaning blade is separated or the intermediate transfer belt is rotated in reverse regardless of whether or not such measures for improving the cleaning performance are actually necessary. Assuming that the cleaning blade is spaced apart and the intermediate transfer belt is reversely rotated every 10 sheets, when 55 copies are made continuously, 5 of the 55 continuous copies are included. Since the cleaning blades are spaced apart and the intermediate transfer belt is rotated in the reverse direction, it takes extra time for continuous copying as compared with the case where such measures for improving the cleaning performance are not performed. This means that if it is not necessary to take measures to improve the cleaning performance, the frequency of separating the cleaning blade or rotating the intermediate transfer belt reversely increases, and as a result, the efficiency of image formation deteriorates. It shows that.

  On the other hand, even if the cleaning blade is separated or the intermediate transfer belt is reversely rotated every 100 sheets, depending on the amount of paper dust generated (depending on the quality of the recording paper), the intermediate transfer There may be cases where measures for improving the belt cleaning performance are sufficient or insufficient. For this reason, setting the measures for improving the cleaning performance of the intermediate transfer belt by the number of copies cannot be said to improve the cleaning performance of the intermediate transfer belt appropriately. For example, the number of copies can be used to improve the cleaning performance of the intermediate transfer belt, whether it is a user who uses high-quality paper that does not easily cause filming, or a user who uses poor-quality paper that easily causes filming. If it is set, the user who uses the high quality paper is taking an excessive measure for improving the cleaning performance. For this reason, a user who uses high-quality paper is disadvantageous in that the efficiency of image formation (copy efficiency) is deteriorated.

  Therefore, the present invention is an image forming apparatus that forms an image by an electrophotographic method, and has an image forming portion that forms a toner image and an endless outer peripheral surface that rotates in a predetermined direction, and is formed by the image forming portion. The transferred toner image is primarily transferred to the outer peripheral surface, and then the toner image on the outer peripheral surface is secondarily transferred to the recording paper, a rotational drive unit that rotates the intermediate transfer member, and the post-secondary transfer It is an object of the present invention to provide an image forming apparatus that properly cleans an intermediate transfer member without reducing the efficiency of image formation, including a cleaning unit that includes a cleaning blade that removes foreign matters attached to the outer peripheral surface.

In order to solve the above-described problems, the present invention provides the following image forming apparatus.
An image forming apparatus that forms an image on recording paper by an electrophotographic method, and has an image forming unit that forms a toner image and an endless outer peripheral surface that rotates in a predetermined direction, and is formed by the image forming unit An intermediate transfer member on which the toner image is primarily transferred to the outer peripheral surface, and then the toner image on the outer peripheral surface is secondarily transferred to the recording paper, a rotational drive unit for rotating the intermediate transfer member, and the outer peripheral surface after the secondary transfer And a cleaning unit having a cleaning blade for removing foreign matter adhering to the
A physical quantity related to the adhesion state of the foreign matter on the outer peripheral surface is detected, and a process for suppressing the deterioration of the foreign matter removing function by the cleaning part based on the physical quantity is executed by controlling at least one of the cleaning part and the rotation driving part. An image forming apparatus further including a control unit.

  According to this image forming apparatus, the control unit detects a physical quantity related to the adhesion state of foreign matter on the outer peripheral surface of the intermediate transfer member. Based on this physical quantity, the control unit performs a process for suppressing the deterioration of the foreign matter removing function by the cleaning unit. In this process, at least one of the cleaning unit and the rotation driving unit is controlled. That is, the control unit determines the adhesion state of the foreign matter on the outer peripheral surface of the intermediate transfer member, and if the adhesion state is not preferable for the foreign matter removing function by the cleaning unit, at least one of the cleaning unit and the rotation driving unit. To control the deterioration of the foreign matter removal function. For this reason, this process is performed only when a process for suppressing the deterioration of the foreign matter removal function is necessary. Therefore, a process for separating the cleaning blade, which is an example of a process for suppressing the reduction of the foreign matter removal function, or intermediate transfer The frequency of the reverse rotation of the belt does not increase easily, and as a result, it is possible to suppress deterioration in the efficiency of image formation.

  Further, in the cleaning unit of the image forming apparatus according to the present invention, the cleaning blade is provided on the outer peripheral surface so as to be capable of being pressed away from the outer peripheral surface, and the control unit controls the cleaning unit to temporarily remove the cleaning blade pressed against the outer peripheral surface from the outer peripheral surface. Therefore, it is possible to configure so as to execute a process for suppressing the deterioration of the foreign substance removing function by separating them. In this case, the cleaning blade that is in pressure contact with the intermediate transfer member is temporarily separated from the intermediate transfer member and is brought into pressure contact again, so that chipping can be suppressed or returned from the mesh, so that the cleaning blade can be moved to the intermediate transfer member. The pressure that comes into contact with the intermediate transfer member can be brought close to an appropriate pressure for removing the foreign matter on the intermediate transfer member, and the deterioration of the foreign matter removing function of the cleaning blade can be suppressed.

  Further, in the image forming apparatus according to the present invention, the control unit controls the rotation driving unit to execute a process for suppressing a decrease in the foreign matter removing function by rotating the intermediate transfer member in a direction opposite to a predetermined direction. It can be configured as follows. By doing so, the intermediate transfer member is rotated in the reverse direction and the pressure contact state between the cleaning blade and the intermediate transfer member is changed, so that the chipping can be suppressed or returned from the crease, so that the cleaning blade is moved to the intermediate transfer member. The pressure that comes into contact with the intermediate transfer member can be brought close to an appropriate pressure for removing the foreign matter on the intermediate transfer member, and the deterioration of the foreign matter removing function of the cleaning blade can be suppressed.

  Further, in the image forming apparatus according to the present invention, the frequency of executing the processing for suppressing the deterioration of the foreign matter removing function is defined using the number of recording sheets on which the image is formed, and the control unit determines whether the foreign matter is attached. Until the state 1 is exceeded, the process for suppressing the deterioration of the foreign matter removal function is not executed, and the state of attachment of the foreign matter exceeds the first state and exceeds the second state where the foreign matter adheres more than the first state. Until, the processing for suppressing the deterioration of the foreign matter removal function is executed at the first frequency, and when the adhesion state of the foreign matter exceeds the second state, the processing for suppressing the reduction of the foreign matter removal function is performed more than the first frequency. It can be configured to execute at a second frequency which is a high frequency. In this way, the adhesion state of the foreign matter to the intermediate transfer member is determined, and if necessary, the frequency is changed according to the state to take measures to suppress the degradation of the cleaning performance. If not, the cleaning performance is degraded. No suppression measures are taken. For this reason, it is possible to suppress a decrease in the foreign matter removing function of the cleaning blade without degrading the image forming efficiency.

  Further, the physical quantity is detected by an optical sensor including a light projecting unit that projects light onto the intermediate transfer member, and a light receiving unit that receives light reflected from a foreign substance in the projected light. Can be configured. In this way, it is possible to determine the adhesion state of the foreign matter on the intermediate transfer member, for example, using an optical sensor originally provided to adjust the toner density on the intermediate transfer member.

  As described above, according to the present invention, an image forming apparatus that forms an image by an electrophotographic method includes an image forming unit that forms a toner image, and an endless outer peripheral surface that rotates in a predetermined direction, An intermediate transfer member in which the toner image formed in the image forming unit is primarily transferred to the outer peripheral surface, and then the toner image on the outer peripheral surface is secondarily transferred to the recording paper; a rotation driving unit that rotates the intermediate transfer member; The present invention provides an image forming apparatus that properly cleans an intermediate transfer member without reducing the efficiency of image formation, including a cleaning unit that includes a cleaning blade that removes foreign matter adhering to the outer peripheral surface after secondary transfer. Can do.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

<First Embodiment>
The image forming apparatus according to the first embodiment of the present invention will be described below.
[Entire configuration of image forming apparatus]
FIG. 1 shows an image forming apparatus 10 according to the present embodiment. The image forming apparatus 10 in FIG. 1 is a so-called four-cycle color image forming apparatus. In the following description, the recording medium is described as recording paper.

  The image forming apparatus 10 includes a drum-type photosensitive member 1 (hereinafter referred to as a photosensitive member 1), and a charger 2, a developing device 4, an intermediate transfer belt 6, and a cleaning device 5 are arranged around the drum-type photosensitive member 1 in this order. An image exposure device 3 that performs image exposure on the photosensitive member 1 from between the charger 2 and the developing device 4 is provided, and a recording paper supply unit 9 is provided below the image exposure device 3.

  The photoreceptor 1 is rotationally driven in the clockwise direction in the figure by a photoreceptor drive motor (not shown). A photosensitive member charging voltage is applied to the charger 2 at a predetermined timing from a charging power source (not shown) whose output is variable.

  The developing device 4 has a developing device rack 40 mounted with a black developing device 4K, a cyan developing device 4C, a magenta developing device 4M, and a yellow developing device 4Y. The developing device rack 40 can be driven to rotate counterclockwise in the figure by a driving unit (not shown) including a stepping motor. The developing devices are mounted on the developing device rack 40 in the order of the developing devices 4K, 4C, 4M, and 4Y in the rack rotation direction at equal central angle intervals of 90 degrees.

  Black toner cartridge KC can be replaced with black developer unit 4K, cyan toner cartridge CC with cyan developer unit 4C, magenta toner cartridge MC with magenta developer unit 4M, and yellow toner cartridge YC with yellow developer unit 4Y. It is mounted on. Each developing device is equipped with a developing roller (toner carrier roller) 41 for developing the electrostatic latent image on the photoreceptor 1. Each developing roller 41 has an elastic surface layer.

  In addition to the developing roller 41, each developing device includes a toner supply roller that supplies toner to the roller, a toner regulating blade that regulates the layer thickness of the toner supplied from the toner supply roller on the developing roller 41, and the like. Each developing device can reversely develop the electrostatic latent image on the photoreceptor 1 using negatively chargeable toner.

  Each developing device can be arranged at a developing position where the developing device 41 develops the electrostatic latent image on the photoreceptor 1 by rotating the developing device rack 40. The developing roller 41 disposed at the developing position faces the surface of the photosensitive member 1, and a developing bias can be applied from a developing bias power source (not shown) whose output is variable. Further, the developing roller 41 arranged at the developing position can be driven to rotate counterclockwise in the drawing by a developing roller driving motor (not shown). Further, a toner supply bias can be applied to the toner supply roller from a power supply (not shown), and a regulation bias can be applied to the toner regulation blade.

  The intermediate transfer belt 6 is connected to a driving roller 61, a driven counter roller 62 opposite to the driving roller 61, a primary transfer roller 63 disposed opposite to the photosensitive member 1, and a primary transfer roller 63, so that the intermediate transfer belt 6 is attached to the photosensitive member 1. It is wound around a roller group composed of rollers 64 to be brought into contact with each other.

  A primary transfer voltage can be applied to the primary transfer roller 63 from a primary transfer power supply (not shown). The intermediate transfer belt 6 can be rotated counterclockwise by driving the drive roller 61 counterclockwise in the figure by a transfer belt drive motor (not shown).

  A secondary transfer roller 7 is disposed on a portion of the intermediate transfer belt 6 that is wound around the driving roller 61. The secondary transfer roller 7 is brought into contact with and separated from the intermediate transfer belt 6 at a predetermined timing. A secondary transfer voltage can be applied to the secondary transfer roller 7 from a secondary transfer power supply (not shown).

  A cleaning device 65 that removes and cleans paper dust and the like (including secondary transfer residual toner) is disposed on the portion of the intermediate transfer belt 6 that is wound around the opposing roller 62. The cleaning device 65 is provided with a cleaning blade BL for removing paper dust and the like from the intermediate transfer belt 6. The cleaning device 65 is provided with a pressure contact / separation mechanism (not shown) that switches between a state in which the cleaning blade BL is brought into contact (pressure contact) with the intermediate transfer belt 6 and a state in which the cleaning blade BL is separated. This pressure contact / separation mechanism is used when full color copying is performed using four developing devices (when two or more developing devices are used), and after the toner image of the first color is formed on the intermediate transfer belt 6, 2, 3, While the fourth color is formed on the intermediate transfer belt 6, the cleaning blade BL is separated from the intermediate transfer belt 6 so as not to disturb the toner image on the intermediate transfer belt 6, and the intermediate transfer after the transfer to the recording paper S is performed. It is provided in order to bring the original cleaning function into contact with the intermediate transfer belt 6 again at the timing of cleaning the belt 6. The pressure contact / separation mechanism includes, for example, a separation pressure contact solenoid that separates the cleaning blade BL from the intermediate transfer belt 6 when energized, and presses the cleaning blade BL against the intermediate transfer belt 6 when power is turned off. The energization control to the solenoid is performed by a control unit described later.

  A fixing device 8 is provided above the secondary transfer roller 7, and a recording paper discharge roller R3 and a recording paper discharge tray T are sequentially provided downstream thereof.

  Below the secondary transfer roller 7, a timing roller pair R2 and a guide roller pair Rl for guiding the recording paper S from the recording paper storage unit 9 to the timing roller pair R2 are arranged.

  An image density adjustment sensor 66 that detects the amount of toner on the intermediate transfer belt 6 is provided in the vicinity of the opposing roller 62 and at a position facing the intermediate transfer belt 6. The image density adjusting sensor 66 is an optical sensor, and includes a light projecting unit and a light receiving unit, and receives reflected light of light projected from the light projecting unit toward the intermediate transfer belt 6 as an object. And outputs a voltage corresponding to the amount of light received by the light receiving unit. When the filming layer formed by paper dust or the like on the intermediate transfer belt 6 grows, the projected light is reflected more and the amount of received light increases (the reflectance (= the amount of received light / the amount of light emitted) increases. To do). When the reflectance increases, the output voltage from the image density adjusting sensor 66 decreases. In the image forming apparatus 10 according to the present embodiment, the growth state of the filming layer formed on the intermediate transfer belt 6 is determined on the basis of the output voltage from the image density adjustment sensor 66, and according to the state. Thus, the cleaning blade BL is separated from the intermediate transfer belt 6 and the countermeasure for suppressing the deterioration of the cleaning function (the countermeasure for suppressing the deterioration of the cleaning function and the countermeasure for reducing the growth (progression) of filming) is executed. In this embodiment, the filming layer growth state is determined based on the output voltage from the image density adjustment sensor 66 which is an optical sensor originally provided in the image forming apparatus 10. The invention is not limited to this. Another sensor may be used as long as it detects a physical quantity having a correlation (a negative correlation or a positive correlation) with the growth state of the filming layer.

  According to the image forming apparatus 10 described above, a toner image on the recording paper S is used using one or more of 4K, 4C, 4M, and 4Y developing devices under the instruction of a control unit (not shown in FIG. 1). Can be formed. An example in which a full color image is formed using four developing devices will be described below.

  First, the developing device rack 40 is rotated by a rack driving unit (not shown) so that the yellow developing device 4Y is disposed at a developing position where the developing roller 41 contacts the photoconductor 1, and the photoconductor 1 is rotated in the clockwise direction in the drawing. The intermediate transfer belt 5 is also rotated. At this stage, the secondary transfer roller 7 is separated from the intermediate transfer belt 6.

  The surface of the rotating photosensitive member 1 is uniformly charged to a predetermined potential by a charger 2 to which a charging voltage is applied from a charging power source, and the charged region is turned from the image exposure device 3 through folding reflection mirrors 31 and 32 to yellow. Image exposure for the image is performed to form a yellow electrostatic latent image, and the latent image is developed by the developing device 4Y to form a yellow toner image. The yellow toner image is primarily transferred onto the intermediate transfer belt 6 by a primary transfer roller 63 to which a primary transfer voltage is applied.

  Further, in the same manner as in the case of forming the yellow toner image, the magenta developing device 4M is arranged at the development position to form a magenta toner image on the photosensitive member 1, and this is transferred onto the intermediate transfer belt 6, and then cyan. The developing unit 4C is arranged at the developing position to form a cyan toner image on the photosensitive member 1, and this is transferred onto the intermediate transfer belt 6, and then the black developing unit 4K is arranged at the developing position and placed on the photosensitive member 1. A black toner image is formed and transferred onto the intermediate transfer belt 6. The formation of each color toner image on the photosensitive member 1 and the primary transfer onto the intermediate transfer belt 6 are performed at the timing when these toner images are superimposed and transferred onto the intermediate transfer belt 6.

  When primary transfer to the intermediate transfer belt 6 is being performed, the cleaning blade BL of the cleaning device 65 is separated from the intermediate transfer belt 6 by a press-contact separation mechanism.

  On the other hand, when the recording paper S is pulled out from the recording paper supply unit 9 by the supply roller 91 and supplied to the timing roller pair R2, and the leading edge of the recording paper is detected by a timing sensor (not shown) on the exit side of the timing roller pair R2. Then, the timing roller pair R2 is stopped, and the recording paper S is kept waiting there.

  Prior to the multiple toner image on the intermediate transfer belt 6 reaching the secondary transfer roller 7 by the rotation of the intermediate transfer belt 6, the roller 71 is brought into contact with the intermediate transfer belt 6 so that the multiple toner image is transferred to the secondary transfer region. The recording paper S is also fed to the secondary transfer area by the tamming roller pair R2 at the timing of reaching.

  Thus, the multiple toner image is secondarily transferred onto the recording paper S. The recording sheet S to which the multiple toner images have been transferred is fixed on the toner image by the fixing device 8 and discharged onto the discharge tray T by the recording sheet discharge roller R3. Thus, the recording paper S on which a full color image is formed can be obtained.

  The primary transfer residual toner or the like on the photoreceptor 1 is removed and cleaned by the cleaning device 5, and the paper dust or the like (including the secondary transfer residual toner) on the intermediate transfer belt 6 is removed and cleaned by the cleaning device 65. At this time, the cleaning blade BL of the cleaning device 65 is in pressure contact with the intermediate transfer belt 6 by a pressure contact / separation mechanism.

  In this image forming apparatus 10, when the monochrome mode is selected, only the developing device for that color is set in the developing operation state, and the intermediate transfer belt 6 is driven at a constant speed while being in contact with the photoreceptor 1. Let the action take place. During the copying operation in the monochrome mode, the intermediate transfer belt 6 after the toner image transferred on the belt is transferred to the recording paper S passes through the cleaning device 65. Therefore, from the viewpoint of not disturbing the toner image formed on the intermediate transfer belt 6 before the secondary transfer, it is not necessary to separate the cleaning blade BL of the cleaning device 65 from the intermediate transfer belt 6. In general, the copying operation is performed in a state where the surface remains in contact.

  However, as described above, the copying operation is performed while the cleaning blade BL of the cleaning device 65 is kept in contact with the surface of the intermediate transfer belt 6 without being separated from the intermediate transfer belt 6, and paper dust or the like is filled on the intermediate transfer belt 6. A mingling layer is easily formed. As a result, the cleaning performance decreases. This is because the cleaning blade BL is always in pressure contact with the intermediate transfer belt 6 in the monochrome mode, so that the tip of the cleaning blade BL is pulled by the intermediate transfer belt 6, and as a result, the tip of the cleaning blade BL contacts the intermediate transfer belt 6. This is due to the fact that the abutting pressure is reduced to a level that does not have sufficient scraping ability. Therefore, in the image forming apparatus 10 according to the present embodiment, during the copying operation in which the monochrome mode is selected, the output voltage from the image density adjustment sensor 66 (this sensor itself is originally provided in the image forming apparatus 10) is used. Based on this, the growth state of the filming layer formed on the intermediate transfer belt 6 is determined, and the cleaning blade BL pulled by the intermediate transfer belt 6 is separated from the intermediate transfer belt 6 according to the state. (The separation pressure contact switching mechanism of the cleaning blade BL itself is originally provided in the four-cycle image forming apparatus 10), and the cleaning blade BL is brought close to the original state to suppress the deterioration of the cleaning function.

[Cleaning function deterioration suppression mechanism]
FIG. 2 is a control block diagram of the image forming apparatus 10 according to the present embodiment provided with a cleaning function lowering suppression mechanism. Note that the control block diagram shown in FIG. 2 shows only the portion related to the cleaning function lowering suppression mechanism in the control block of the image forming apparatus 10.

  As shown in FIG. 2, the control device of the image forming apparatus 10 is connected to a control unit 68 that controls the entire image forming apparatus 10 and an input port (not shown) of the control unit 68 according to the amount of received light. An image density adjusting sensor 66 that outputs a voltage to the control unit 68, and a separation pressure contact solenoid 67 that is connected to an output port (not shown) of the control unit 68 and operates the cleaning blade BL of the intermediate transfer belt 6. Furthermore, other signals (for example, signals from the operation panel for inputting copy mode (color, monochrome, recording paper size, recording paper type, etc.)) are input to the control unit 68 via the input port of the control unit 68. In addition, other signals are output from the control unit 68 via the output port of the control unit 68.

  FIG. 3 shows the time change of the output voltage from the image density adjustment sensor (optical sensor) 66. FIG. 3 shows the time change of the output voltage during the time that the intermediate transfer belt 6 makes one round. As shown in FIG. 3, the sheet passing length (the length in the feeding direction of the recording sheet S) is shorter than one turn of the intermediate transfer belt 6, and the sheet passing length in one turn of the intermediate transfer belt 6. The distance between the paper and the paper passing length is between the images. A large amount of paper dust is generated at the paper end (start end) and paper end (end end) of the recording paper S with relatively few images such as characters. Therefore, a filming layer is easily formed on the intermediate transfer belt 6 at this portion. As the detection region of the filming layer, it is also possible to appropriately select a paper end (start end and / or end end), the entire area of the intermediate transfer belt 6, or a portion with few images such as characters.

  As shown in FIG. 3, the output voltage from the image density adjustment sensor (optical sensor) 66 corresponding to the paper edge drops. This is because when a filming layer made of paper dust or the like is formed, a large amount of light projected from the light projecting portion of the image density adjusting sensor 66 is reflected by the filming layer, and the amount of light received by the light receiving portion increases. Reflectivity increases. Since the image density adjusting sensor 66 is a sensor whose output voltage decreases as the reflectance increases, the output voltage decreases at the edge of the paper as shown in FIG. Depending on the definition of reflectance, the correlation between the growth state of the filming layer and the reflectance may be reversed, and depending on the sensor specifications, the correlation between the growth state of the filming layer and the output voltage is reversed. Sometimes it becomes. The present invention includes all of these cases, and the correlation between the growth state of the filming layer and the reflectance is not limited to the above-described relationship.

  If the filming layer formed on the intermediate transfer belt 6 grows, the filming layer reflects more light, the reflectance increases, and the output voltage decreases. If this is detected by the control unit 68 and the control unit 68 determines the growth state of the filming layer based on the reflectance, and there is a problem in image formation, the cleaning device 65 is left unwiped. The cleaning blade BL that is in pressure contact with the intermediate transfer belt 6 is temporarily separated from the intermediate transfer belt 6 so as not to enter the region (in order to suppress the deterioration of the cleaning function). By temporarily separating the cleaning blade BL from the intermediate transfer belt 6 and press-contacting it again, the pressure at which the cleaning blade BL abuts against the intermediate transfer belt 6 can be reduced by suppressing chipping or returning from the mesh. 6 can be brought close to an appropriate pressure to remove paper dust or the like (the tip stress of the cleaning blade BL can be brought close to an appropriate stress). Note that the determination timing of the growth state of the filming layer may be the same as that at the time of normal image density correction, such as when the image forming apparatus 10 is turned on or returned from the standby state.

[Cleaning function deterioration suppression operation]
With reference to FIG. 4 to FIG. 6, the cleaning function lowering suppression operation in the image forming apparatus 10 according to the present exemplary embodiment will be described.

  FIG. 4 shows a change in reflectance (filming growth state) with respect to the number of image formations when the image forming apparatus 10 according to the present embodiment is copied in the monochrome mode without causing the cleaning blade BL to be in contact with the separation. Show. As shown in FIG. 4, since the cleaning blade BL is always in contact with the intermediate transfer belt 6 in the monochrome mode as described above, the filming layer grows more easily than in the color mode. In particular, in the case of poor paper, more paper dust is generated than fine paper, so that unwiping is generated with a smaller number of image formations. Note that the thicker paper among the bad papers is more strongly pressed by the intermediate transfer belt 6 during the secondary transfer, and therefore the filming layer is more likely to grow.

  FIG. 5 shows a case where the image forming apparatus 10 according to the present embodiment has the cleaning blade BL brought into pressure contact with the frequency of 50 image formations once and when it is made pressure contact once with 10 sheets. Shows the change in reflectivity (filming growth state) with respect to the number of images of bad paper. As shown in FIG. 5, the filming layer can be prevented from growing as the cleaning blade BL is separated and pressed more frequently. In the present embodiment, based on the type of paper (bad paper, high-quality paper), the thickness of the paper, the number of images to be formed, etc., the frequency at which the cleaning blade BL is press-contacted by separation is set to once every 50 sheets and once every 10 sheets. It is set to. This frequency may be obtained experimentally, and it should be confirmed that the present invention is not limited to this frequency.

  As described above, the frequency at which the cleaning blade BL is separated and pressed is set to a frequency of once per 50 sheets and a frequency of once per 10 sheets, and after confirming that the effect is appropriate, FIG. As shown, the first threshold value and the second threshold value are set for the reflectance. During the copying operation in the monochrome mode, when the reflectance exceeds the first threshold value, the control unit 68 causes the cleaning blade BL to be spaced and pressed once every 50 sheets, so that the reflectance is the second level. When the threshold value is exceeded, the cleaning blade BL is brought into pressure contact with each other once every 10 sheets, thereby suppressing the deterioration of the cleaning function.

  More specifically, for example, when the power is turned on or when returning from the standby state, the control unit 68 calculates the growth state of the filming layer on the intermediate transfer belt 6 from the output voltage from the image density adjustment sensor 66. The determination is made based on the reflectance. When the monochrome mode is selected and the copy operation is started, the control unit 68 performs the copy operation without bringing the cleaning blade BL into contact with pressure when the reflectance does not exceed the first threshold value. . When the number of images formed in the monochrome mode increases, the cleaning blade BL remains in contact with the intermediate transfer belt 6 in the monochrome mode, so that a filming layer easily grows on the intermediate transfer belt 6. As the filming layer grows, the reflectance gradually increases (solid line in FIG. 6).

  For example, at the time of a copy operation in the next monochrome mode (it may be performed when the power is turned on or after returning from standby), the control unit 68 exceeds the first threshold value and sets the second threshold value. If not, the copying operation is performed with the cleaning blades BL being spaced and pressed once every 50 sheets. As the number of images formed in the monochrome mode increases, the filming layer tends to grow on the intermediate transfer belt 6, but since the cleaning blade BL is separated and pressed once every 50 sheets, the filming layer grows. It is suppressed (dotted line in FIG. 6).

  Further, during the copying operation in the next monochrome mode, if the reflectance exceeds the second threshold value, the control unit 68 causes the cleaning blade BL to be separated and pressed with a frequency of once per 10 sheets. Perform a copy operation. When the number of images formed in the monochrome mode is further increased, a filming layer grows on the intermediate transfer belt 6 even if the cleaning blade BL is separated and pressed once every 50 sheets, but 10 cleaning blades BL are formed. Therefore, the growth of the filming layer is further suppressed (thick dotted line in FIG. 6).

  As shown in FIG. 6, if the cleaning blade BL is not brought into contact with pressure, the filming layer on the intermediate transfer belt 6 grows with the increase in the number of image formations, and the remaining unwiped image with a small number of image formations as indicated by the alternate long and short dash line. It reached the area and caused an image defect. In the image forming apparatus 10 according to the present embodiment, the growth of the filming layer can be allowed until the reflectance exceeds the first threshold value. Therefore, the cleaning blade BL is not brought into pressure contact with priority on copy efficiency. Until the reflectance exceeds the first threshold value and exceeds the second threshold value, the growth of the filming layer is suppressed and the copy efficiency is prioritized, and the cleaning blade BL is spaced once every 50 sheets. Press contact. Further, when the reflectance exceeds the second threshold value, the cleaning blade BL is pressed and contacted at a frequency of once every 10 sheets in order to further suppress the growth of the filming layer.

  As described above, the image forming apparatus according to the present embodiment determines the state of the filming layer on the intermediate transfer belt, and if necessary, changes the frequency according to the state to suppress deterioration in cleaning performance. Take measures and do not take measures to prevent degradation of cleaning performance until it is not necessary. For this reason, it is possible to suppress unwiping of the intermediate transfer belt due to filming and to suppress image defects resulting therefrom without reducing the image forming efficiency.

<Second Embodiment>
An image forming apparatus according to the second embodiment of the present invention will be described below with reference to FIG. Detailed description of the same configuration as in the first embodiment will not be repeated here.
[Entire configuration of image forming apparatus]
FIG. 7 shows an example of an image forming apparatus according to the present embodiment. An image forming apparatus 100 shown in FIG. 7 is a so-called tandem type color image forming apparatus.

  The image forming apparatus 100 includes a driving roller 181 and an endless intermediate transfer belt 108 wound around a roller 182 facing the driving roller 181. The intermediate transfer belt 108 is rotated counterclockwise (arrow direction in the figure) α in the figure by a driving roller 181 driven by a belt drive unit (including an intermediate transfer belt drive motor 167 described later).

  A secondary transfer roller 109 faces the driving roller 181 via the intermediate transfer belt 108, and a cleaning device 183 that cleans residual toner and the like faces a roller 182 facing the driving roller 181. The cleaning device 183 is provided with a cleaning blade BL that removes paper dust and the like of the intermediate transfer belt 108. The cleaning device 183 is provided with a pressure contact / separation mechanism that is provided in the image forming apparatus 10 according to the first embodiment described above and switches between a state in which the cleaning blade BL is brought into contact with the intermediate transfer belt 108 and a state in which the cleaning blade BL is separated from the intermediate transfer belt 108. It is not done.

  A surface layer portion of the secondary transfer roller 109 is formed of an elastic material, and is pressed against a portion of the intermediate transfer belt 108 supported by the driving roller 181 by a pressing unit (not shown), and a nip is formed between the secondary transfer roller 109 and the intermediate transfer belt 108. And can be rotated in accordance with the rotation of the intermediate transfer belt 108 or in accordance with the movement of the recording sheet S fed into the nip portion as will be described later. A secondary transfer bias can be applied to the secondary transfer roller 109 at a predetermined timing from a power supply (not shown).

  A fixing device FX is disposed above the intermediate transfer belt 108 and the secondary transfer roller 109, a timing roller pair TR is disposed below the intermediate transfer belt 108, and a recording paper containing the recording paper S is further disposed below the fixing device FX. A cassette 110 is arranged.

  The fixing device FX includes a fixing heating roller incorporating a heat source such as a halogen lamp heater and a pressure roller pressed against the fixing heating roller. The recording paper S stored in the recording paper storage cassette 110 can be pulled out one by one by the recording paper supply roller 111 and supplied to the timing roller pair TR.

  Between the driving roller 181 and the roller 182 around which the intermediate transfer belt 108 is wound, the yellow image forming unit Y, the magenta image forming unit M, the roller 182 toward the driving roller 181 along the intermediate transfer belt 108. The cyan image forming unit C and the black image forming unit K are arranged in this order.

  Each of the image forming units Y, M, C, and K includes a drum-type photoconductor 101 as an electrostatic latent image carrier, and a charger 102, an image exposure device 103, and a development device 104 are provided around the photoconductor. The primary transfer roller 105 and the cleaning device 106 are arranged in this order.

  In each image forming unit, a process cartridge including a photoreceptor 101, a charger 102, a developing device 104, and a cleaning device 106 is formed. That is, the yellow process cartridge YC for forming the yellow image forming portion Y, the magenta process cartridge MC for forming the magenta image forming portion M, the cyan process cartridge CC for forming the cyan image forming portion C, and the black image forming This is a black process cartridge KC for forming the portion K. Each process cartridge is detachable from the main body of the image forming apparatus.

  The primary transfer roller 105 is opposed to the photosensitive member 101 with the intermediate transfer belt 108 therebetween, and is rotated as the intermediate transfer belt 108 travels. A primary transfer bias for primary transfer of a toner image formed on the photoreceptor 101 to the intermediate transfer belt 108 can be applied to the primary transfer roller 105 from a power supply (not shown) at a predetermined timing. The image exposure apparatus 103 can perform image exposure by dot (point) exposure on the photosensitive member 101 by blinking of a laser beam according to image information.

  The photoconductor 101 in each image forming unit is a negatively chargeable photoconductor here, and can be driven to rotate clockwise in the drawing by a photoconductor drive motor (not shown). The charger 102 in each image forming unit is not limited to this, but is a scorotron charger in this example, and a charging voltage is applied from a power source at a predetermined timing.

  The developing device 104 in each image forming unit can reversely develop the electrostatic latent image formed on the photoreceptor 1 with a developing roller 141 to which a developing bias is applied from a power supply (not shown).

  An image density adjustment sensor 66 that detects the amount of toner on the intermediate transfer belt 108 is provided in the vicinity of the roller 182 and at a position facing the intermediate transfer belt 108. The image density adjusting sensor 66 is the same as that in the first embodiment.

  According to the image forming apparatus 100, an image is formed using one or more of Y, M, C, and K image forming units under the instruction and control of a control unit that controls the image forming apparatus 100. be able to. Taking a case where a full color image is formed using all of the image forming portions Y, M, C, and K as an example, first, a yellow toner image is formed in the yellow image forming portion Y, and this is applied to the intermediate transfer belt 108 by 1. Next transfer.

  That is, in the yellow image forming portion Y, the photosensitive member 101 is rotationally driven in the clockwise direction in the drawing, and the surface is uniformly charged to a predetermined potential by the charger 102. Image exposure is performed, and a yellow electrostatic latent image is formed on the photoreceptor 101. The electrostatic latent image is developed by a developing roller 141 to which a developing bias of a developing device 104 having yellow toner is applied to become a visible yellow toner image, and the toner image is transferred onto the intermediate transfer belt 108 by a primary transfer roller 105. Primary transfer. At this time, a primary transfer bias is applied to the primary transfer roller 105 from a power supply (not shown).

  Similarly, a magenta toner image is formed in the magenta image forming unit M and transferred to the intermediate transfer belt 108, and a cyan toner image is formed in the cyan image forming unit C and transferred to the intermediate transfer belt 108, and the black image forming unit. A black toner image is formed at K and transferred to the intermediate transfer belt 108.

  Yellow, magenta, cyan, and black toner images are formed at a timing at which these toner images are transferred onto the intermediate transfer belt. Thus, the multiple toner image formed on the intermediate transfer belt 108 moves toward the secondary transfer roller 109 by the rotation of the intermediate transfer belt 108.

  On the other hand, the recording paper S is pulled out from the recording paper storage cassette 110 by the recording paper supply roller 111, supplied to the timing roller pair TR, and is on standby.

  Thus, the recording sheet S waiting at the timing roller pair TR is supplied to the nip portion between the intermediate transfer belt 108 and the secondary transfer roller 109 in accordance with the multiple toner images sent by the intermediate transfer belt 108. The multiple toner image is secondarily transferred onto the recording paper S by a secondary transfer roller 109 to which a secondary transfer bias is applied from a power supply (not shown). Thereafter, the recording paper S is passed through the fixing device FX, where the multiple toner images are fixed on the recording paper S under heat and pressure. The recording sheet S is continuously discharged to the discharge tray T by the discharge roller pair DR.

  Transfer residual toner or the like remaining on the photoreceptor 101 in the primary transfer of the toner image to the intermediate transfer belt 108 is cleaned by the cleaning device 106, and secondary transfer residual toner or the like remaining on the intermediate transfer belt 108 by the secondary transfer. Is cleaned by a cleaning device 183.

  Thus, unlike the cycle type image forming apparatus 10, the tandem type image forming apparatus 100 performs intermediate transfer for the second, third, and fourth colors after the toner image of the first color is formed on the intermediate transfer belt 108. Even during the formation on the belt 108, it is not necessary to separate the cleaning blade BL from the intermediate transfer belt 108. For this reason, basically, there is no pressure contact / separation mechanism for switching between a state where the cleaning blade BL is brought into contact with the intermediate transfer belt 108 and a state where the cleaning blade BL is separated.

[Cleaning function deterioration suppression mechanism]
The image forming apparatus 100 according to the present embodiment does not include a pressure contact / separation mechanism. Therefore, in the image forming apparatus 100 according to the present embodiment, the growth state of the filming layer formed on the intermediate transfer belt 108 is determined based on the output voltage from the image density adjustment sensor 66, and the state is determined. Accordingly, the intermediate transfer belt 108 is reversely rotated (a minute amount of reverse rotation equivalent to inching is performed once), and the cleaning blade BL pulled by the intermediate transfer belt 108 is brought close to the original state for cleaning. Reduces functional degradation.

  FIG. 8 is a control block diagram of the image forming apparatus 100 according to the present embodiment, which is provided with a cleaning function lowering suppression mechanism. Note that the control block diagram shown in FIG. 8 shows only the portion related to the cleaning function lowering suppression mechanism in the control block of the image forming apparatus 100, as in FIG.

  As shown in FIG. 8, the control device of the image forming apparatus 100 is connected to a control unit 168 that controls the entire image forming apparatus 100 and an input port (not shown) of the control unit 168 according to the amount of received light. An image density adjustment sensor 66 that outputs a voltage to the control unit 168 and an intermediate transfer belt drive motor 167 that is connected to an output port (not shown) of the control unit 168 and rotates the drive roller 181 are included. Further, other signals (for example, signals from an operation panel for inputting a copy mode (color, monochrome, recording paper size, recording paper type, etc.)) are input to the control unit 168 via the input port of the control unit 168. In addition, other signals are output from the control unit 168 via the output port of the control unit 68.

  In response to a signal from the control unit 168, the intermediate transfer belt drive motor 167 is normally rotated counterclockwise in FIG. When it is necessary to suppress the deterioration of the cleaning function, the intermediate transfer belt drive motor 167 is rotated by a minute amount in the clockwise direction in FIG. As described above, when the reverse rotation is performed even by a minute amount, the pressure contact state between the cleaning blade BL and the intermediate transfer belt 108 is changed, so that the chipping can be suppressed or the recovery can be resumed from the mesh. Can be brought close to an appropriate pressure for removing paper dust and the like on the intermediate transfer belt 108 (the tip stress of the cleaning blade BL can be brought close to an appropriate stress). .

[Cleaning function deterioration suppression operation]
In the image forming apparatus 100 according to the present embodiment, as in the image forming apparatus 10 according to the first embodiment described above, the filming growth state is determined according to the reflectance, and the first threshold value is determined. Using the value and the second threshold value, the intermediate transfer belt 108 is reversely rotated as a cleaning function lowering suppression operation. The difference from the first embodiment described above is that the operation for suppressing the deterioration of the cleaning function is not the separation pressure contact operation of the cleaning blade BL but the reverse rotation operation of the intermediate transfer belt 108. Is the same as in the first embodiment. Needless to say, the reverse rotation of the intermediate transfer belt 108 is performed without causing any problem in image formation.

  That is, in the image forming apparatus 100 according to the present embodiment, since the growth of the filming layer can be allowed until the reflectance exceeds the first threshold value, the intermediate transfer belt 108 is rotated in reverse with priority on copy efficiency. I won't let you. Until the reflectivity exceeds the first threshold value and exceeds the second threshold value, the growth of the filming layer is suppressed and the copy efficiency is prioritized, and the intermediate transfer belt 108 is rotated once every 50 sheets. Perform at the frequency of Further, when the reflectance exceeds the second threshold value, the intermediate transfer belt 108 is reversely rotated once every 10 sheets in order to further suppress the growth of the filming layer.

  As described above, according to the state of the filming layer on the intermediate transfer belt, the image forming apparatus according to the present embodiment changes the frequency according to the state of the filming layer, if necessary, and takes measures to suppress deterioration in cleaning performance. Do not take measures to prevent degradation of the cleaning performance until it is not necessary. For this reason, it is possible to suppress unwiping of the intermediate transfer belt due to filming and to suppress image defects resulting therefrom without reducing the image forming efficiency.

<Modification>
Note that the image forming apparatus according to the present invention may perform the above-described separation pressure contact of the cleaning blade BL and reverse rotation of the intermediate transfer belt in an appropriate combination. In particular, when the separation pressure contact of the cleaning blade BL and the reverse rotation of the intermediate transfer belt differ from each other in the effect of suppressing the deterioration of the cleaning function and the time required, the reflection is performed so as not to easily reach the unwiped area even if the number of image formations increases. It is also possible to set a rate threshold and operate a more appropriate cleaning function lowering suppression mechanism (separate pressure contact of the cleaning blade BL and / or reverse rotation of the intermediate transfer belt).

  The embodiment disclosed this time is merely an example, and the present invention is not limited to the embodiment described above. The scope of the present invention is indicated by each claim in the claims after taking into account the description of the detailed description of the invention, and all modifications within the meaning and scope equivalent to the wording described therein are intended. Including.

1 is a diagram illustrating an outline of a configuration of a printer that is an example of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a control block diagram of the image forming apparatus in FIG. 1. It is a figure which shows the relationship between an intermediate transfer belt and the output value of an optical sensor. FIG. 6 is a diagram (part 1) illustrating a relationship between the number of image formations and reflectance. FIG. 6 is a diagram (part 2) illustrating a relationship between the number of formed images and the reflectance. FIG. 6 is a third diagram illustrating the relationship between the number of formed images and the reflectance. FIG. 5 is a diagram illustrating an outline of a configuration of a printer that is an example of an image forming apparatus according to a second embodiment of the present invention. FIG. 8 is a control block diagram of the image forming apparatus in FIG. 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 Photoconductor 2,102 Charger 3,103 Image exposure apparatus 4,104 Development apparatus 5,65,106,183 Cleaning apparatus 6,108 Intermediate transfer belt 8, FX fixing apparatus 10,100 Image forming apparatus 66 Image density Adjustment sensor 67 Separation pressure contact solenoid 68, 168 Control unit 167 Intermediate transfer belt drive motor BL Cleaning blade

Claims (5)

An image forming apparatus that forms an image on recording paper by an electrophotographic method, and has an image forming unit that forms a toner image and an endless outer peripheral surface that rotates in a predetermined direction, and is formed by the image forming unit. An intermediate transfer member on which the toner image is primarily transferred to the outer peripheral surface, and then the toner image on the outer peripheral surface is secondarily transferred to a recording sheet; a rotation drive unit that rotates the intermediate transfer member; A cleaning unit having a cleaning blade for removing foreign matter adhering to the outer peripheral surface after the next transfer,
A process of detecting a physical quantity related to the adhesion state of the foreign matter on the outer peripheral surface and suppressing a decrease in the foreign matter removing function by the cleaning unit based on the physical quantity is performed on at least one of the cleaning unit and the rotation driving unit. An image forming apparatus, further comprising a control unit that performs control. In the cleaning unit, the cleaning blade is provided so as to be capable of being pressed against the outer peripheral surface,
The control unit controls the cleaning unit to execute a process of suppressing a decrease in a foreign matter removing function by temporarily separating the cleaning blade pressed against the outer peripheral surface from the outer peripheral surface. The image forming apparatus according to claim 1.   2. The control unit according to claim 1, wherein the control unit controls the rotation driving unit to perform a process of suppressing a decrease in a foreign matter removing function by rotating the intermediate transfer member in a direction opposite to a predetermined direction. The image forming apparatus described. The frequency of executing the processing for suppressing the deterioration of the foreign matter removing function is defined using the number of recording sheets on which images are formed,
The controller is
Until the adhesion state of the foreign matter exceeds the first state, do not execute a process for suppressing the deterioration of the foreign matter removal function,
The process of suppressing the deterioration of the foreign matter removal function is executed at the first frequency until the foreign matter attachment state exceeds the first state and exceeds the second state where the foreign matter adheres more than the first state. And
The processing for suppressing a decrease in the foreign matter removal function is executed at a second frequency that is higher than the first frequency when the foreign matter adhesion state exceeds the second state. The image forming apparatus according to claim 3.   The physical quantity is detected by an optical sensor including a light projecting unit that projects light onto the intermediate transfer member, and a light receiving unit that receives light reflected from the foreign matter in the projected light. The image forming apparatus according to claim 1.

Images