JP4947067B2 - Image forming apparatus - Google Patents

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 these that can form an image by electrophotography.

  Various types of electrophotographic image forming apparatuses are known, in which an electrostatic latent image is formed on an electrostatic latent image carrier, and the electrostatic latent image is transferred to the electrostatic latent image. A toner image is formed by developing with a developing device that holds the color toner corresponding to the electrostatic latent image among a plurality of developing devices that can move to the image developing area, and the toner image is primarily transferred to an intermediate transfer member As a result, a multi-toner image composed of a monochrome toner image or a toner image of two or more colors is formed on the intermediate transfer member, and the toner image on the intermediate transfer member is secondarily transferred to a recording medium, and then transferred to the recording medium. There is known a cycle type color image forming apparatus that can be fixed and removes foreign matter on the surface of an intermediate transfer member after secondary transfer with a cleaning blade.

  Here, as the “intermediate transfer member”, there is a drum type, but generally a belt type (intermediate transfer belt) is often used.

  The foreign matter on the surface of the intermediate transfer member includes secondary transfer residual toner, recording medium powder (especially paper powder when the recording medium is recording paper), toner external additives, and the like.

  The cleaning blade is usually formed of an elastic member such as rubber, and is used for mechanically scraping and removing foreign matter on the surface by being pressed against the surface of the intermediate transfer member.

  In such a cleaning device for cleaning the surface of the intermediate transfer member by the cleaning blade, the cleaning blade overcomes the adhesion force of the foreign matter to the surface of the intermediate transfer member, and the cleaning blade scrapes off the foreign matter from the intermediate transfer member, so that the foreign matter does not pass under the cleaning blade. Many are structured as follows.

  In such a cleaning device, when a foreign substance, particularly paper dust or an external additive of toner, passes under the cleaning blade, a thin layer, that is, a filming layer in which the paper dust or the like is formed into a film on the intermediate transfer member, is formed. (Hereinafter, the formation of the filming layer may be simply described as the occurrence of 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 surface of the intermediate transfer member, (2) introducing an air sheet feeding device that suppresses the generation of paper dust, (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 member to prevent the cleaning blade from decreasing the contact pressure with the intermediate transfer member. (5) Secondary transfer pressure, that is, when the toner image on the intermediate transfer member is secondarily transferred to the recording paper, the recording paper is pressed against the intermediate transfer member by the secondary transfer member. For example, the pressure may be lowered to suppress the adhesion of paper dust to the intermediate transfer member.

  However, the measures (1), (2) and (3) increase the cost, and the measure (4) may damage the photoconductor. In the measure (5), there is a possibility that the transferability of the toner image onto the thick paper or the rough paper is lowered by lowering the secondary transfer pressure. Therefore, in reality, the pressure at which the tip of the cleaning blade comes into contact with the intermediate transfer member is separated by moving the cleaning blade pressed against the intermediate transfer member away from the intermediate transfer member or reversing the intermediate transfer member. In some cases, measures for improving the cleaning performance are ensured to be suitable for cleaning (for example, Japanese Patent Application Laid-Open No. 8-63071).

  In the image forming apparatus described in Patent Document 1, measures for improving the cleaning performance are taken to suppress defective cleaning 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 member. Therefore, when paper dust or the like aggregates at the tip of the cleaning blade, the cleaning performance deteriorates. For example, when about 10 single-color copies are made with spherical toner, cleaning failure occurs. For this reason, the cleaning blade is brought into contact with the intermediate transfer member until the paper transfer is finished and the cleaning of the next image forming area on the intermediate transfer member is finished, and then the cleaning blade in contact with the intermediate transfer member. 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. In this way, the aggregated toner and the like are removed from the tip of the cleaning blade by using the impact when the cleaning blade is released from the intermediate transfer member. Further, the intermediate transfer member is temporarily reversed between the images (at this time, the intermediate transfer member is separated from the paper transfer roller), thereby removing the agglomerated toner and the like 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 described 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 Or the intermediate transfer belt is rotated in the reverse direction. 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 separated or the intermediate transfer belt is reversely rotated every 10 sheets, when 55 copies are made continuously, 5 out of 55 continuous copies are required. 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 taken. 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, resulting in a decrease in image productivity. It means to end.

  On the other hand, even if the cleaning blade is separated or the intermediate transfer member is reversely rotated every 100 sheets, depending on the amount of paper dust generated (depending on the quality of the recording paper, etc.), the intermediate transfer There may be cases where measures for improving body cleaning performance are sufficient or insufficient. For this reason, setting the countermeasure for improving the cleaning performance of the intermediate transfer member only by the number of images formed cannot be said to improve the cleaning performance of the intermediate transfer member appropriately.

  For example, the intermediate transfer belt can be cleaned by both users who use high-quality paper and poor-quality paper, which are less likely to generate paper dust and therefore less likely to cause filming. If the performance improvement measure is set by the number of image formations, it means that an excessive cleaning performance improvement measure is taken for a user who uses high-quality paper. For this reason, there is a disadvantage that the image productivity is lowered for a user who uses high-quality paper.

  Therefore, the present invention forms an electrostatic latent image on the electrostatic latent image carrier, and converts the electrostatic latent image to the electrostatic latent image among a plurality of developing units that can move to the electrostatic latent image developing area. A toner image is formed by developing with a developing device that holds the corresponding color toner, and the toner image is primarily transferred to the intermediate transfer member, whereby a monochrome toner image or two or more toners are transferred onto the intermediate transfer member. A multi-toner image consisting of an image can be formed, the toner image on the intermediate transfer member can be secondarily transferred to a recording medium and fixed on the recording medium, and foreign matter on the surface of the intermediate transfer member can be removed after the secondary transfer. A cycle-type color image forming apparatus that performs processing with a cleaning blade, the image forming apparatus capable of appropriately removing foreign matter on the surface of the intermediate transfer member with the cleaning blade over a long period of time without degrading image productivity. The issue is to provide.

In order to solve the above-described problems, the present invention provides the following image forming apparatus.
Color toner corresponding to the electrostatic latent image among a plurality of developing units capable of forming the electrostatic latent image on the electrostatic latent image carrier and moving the electrostatic latent image to the electrostatic latent image developing area The toner is developed with a developing device that holds toner, and a toner image is formed, and the toner image is primarily transferred to the intermediate transfer member, whereby a multi-toner composed of a monochrome toner image or a toner image of two or more colors on the intermediate transfer member An image is formed, and the toner image on the intermediate transfer member is secondarily transferred to a recording medium and fixed on the recording medium. The foreign matter on the surface of the intermediate transfer member after the secondary transfer is removed with a cleaning blade. A cycle type color image forming apparatus for performing,
A blade drive unit that presses and separates the cleaning blade from the surface of the intermediate transfer member, and a control unit for the blade drive unit,
The control unit should at least temporarily separate the cleaning blade from the surface of the intermediate transfer body for every coefficient α indicating the image forming mode, a coefficient β indicating the running distance of the surface of the intermediate transfer body, and for every image forming sheet number γ. The surface of the intermediate transfer member is calculated using the formula [y = α × (1-1 / γ) × β] for calculating the filming coefficient y due to the foreign matter on the surface of the intermediate transfer member expressed as a function of the number γ of image formations When the accumulated value Y of the obtained filming coefficient y exceeds a predetermined threshold according to the accumulated travel distance of the surface of the intermediate transfer member, the filming coefficient y is sequentially calculated at a predetermined timing. An image forming apparatus that causes a blade driving unit to perform a frequency of separating and pressing a cleaning blade against an intermediate transfer member in a monochrome image forming mode at a predetermined increased frequency.

  Here, the “image forming mode” refers to an image forming mode such as a color image forming mode or a monochrome image forming mode.

  According to the cycle image forming apparatus, in the monochrome image forming mode, for the primary transfer of the toner image to the intermediate transfer member, the cleaning blade may be kept in contact with the intermediate transfer member.

  On the other hand, in the color image forming mode, after the toner image of one color is primarily transferred onto the intermediate transfer member, the toner image of the next color is superimposed on the toner image that has been primary transferred first, and then the primary image. Since the toner image is transferred, the cleaning blade is separated from the intermediate transfer member when the previous toner image passes through the cleaning device. Accordingly, in the color image forming mode, the frequency of separation pressure contact with the intermediate transfer member of the cleaning blade is high, and the cleaning performance of the cleaning blade is easily maintained in the expected state.

  For this reason, as for the coefficient α indicating the image forming mode, an example in which the coefficient α indicating the monochrome image forming mode is larger than the coefficient α indicating the color image forming mode can be given.

As the coefficient β indicating the travel distance on the surface of the intermediate transfer member, the travel distance on the surface of the intermediate transfer member itself may be adopted, or the rotation speed of the intermediate transfer member representing the travel distance may be adopted.
In any case, the coefficient β is a coefficient indicating the travel distance of the surface of the intermediate transfer member between the previous calculation of the filming coefficient y and the calculation of the next filming coefficient y. Here, the “previous filming coefficient y calculation” includes the case of the start of image formation, and therefore β = 0.

  Regarding the number of image forming sheets γ, the number of image forming sheets γ for temporarily separating the cleaning blade from the surface of the intermediate transfer member, the state of the intermediate transfer member (for example, the surface material), the state of the cleaning blade (For example, blade material) and the like, and is determined from the viewpoint of extending the life of the cleaning blade as much as possible without degrading image productivity. For example, γ = 3 , Γ = 5 etc. can be exemplified.

  The “predetermined timing for obtaining the filming coefficient y using the calculation formula” is, for example, every predetermined number of rotations (for example, every 100 rotations) of the intermediate transfer member (in other words, the surface of the intermediate transfer member). (For each predetermined travel distance).

  In any case, when calculating the filming coefficient y, the control unit may calculate the coefficient value at the time of calculation (α value, β value, γ value, etc. at the time of calculation).

  The “threshold value determined in advance according to the travel distance of the surface of the intermediate transfer member” is an intermediate transfer member from the viewpoint that the foreign matter removal treatment on the surface of the intermediate transfer member by the cleaning blade can be appropriately performed over a long period of time. Until the cumulative travel distance of the surface reaches a predetermined distance L, the cleaning blade performs the foreign matter removal processing function in a state where the cumulative value Y of the filming coefficient y on the surface of the intermediate transfer member is suppressed to an allowable level or less. In other words, it is determined on the assumption that it is desired to extend the life of the cleaning blade at least until the cumulative travel distance of the surface of the intermediate transfer member reaches a predetermined distance L.

  Furthermore, according to the filming coefficient calculated by the filming coefficient calculation formula, the cumulative value of the filming coefficient exceeds the allowable level before the cumulative travel distance on the surface of the intermediate transfer member reaches the distance L (therefore, accordingly). If the cleaning blade falls into a state where it cannot perform the foreign substance removal processing function), if the increase rate of the filming coefficient is reduced at a certain intermediate transfer member cumulative travel distance L ′ (<L), the intermediate Until the cumulative travel distance on the surface of the transfer body reaches the distance L, the cumulative travel distance L ′ of the intermediate transfer body when the cumulative value Y of the filming coefficient y on the surface of the intermediate transfer body can be suppressed to an allowable level or less. The cumulative filming coefficient Y at the time.

  Such a threshold cumulative filming coefficient may be determined in advance by an experiment or the like according to the image forming mode, or further, the recording paper quality and / or the recording paper thickness, etc. The increased separation pressure contact frequency with respect to the intermediate transfer member of the cleaning blade in the monochrome image forming mode, which is adopted when the cumulative value Y exceeds the threshold value, may be determined in advance by an experiment or the like.

  For example, in the monochrome image forming mode, in order to avoid a decrease in image productivity, the cleaning blade is not pressed against and separated from the intermediate transfer member up to a certain distance on the surface of the intermediate transfer member (therefore, the 1 / In the case where γ is considered to be 0), in the increasing line of the cumulative value Y of the filming coefficient y derived from the filming coefficient calculation formula, if the value exceeds that (threshold cumulative filming coefficient), a predetermined increase is made as a γ value. By adopting a γ value (for example, γ = 3) indicating the frequency of pressure contact and separation, the intermediate transfer member is calculated using the filming coefficient calculation formula until the cumulative travel distance on the surface of the intermediate transfer member reaches the distance L. The cumulative filming coefficient such that the cumulative value Y of the filming coefficient y on the surface can be suppressed below an allowable level can be used as a threshold value. Kill.

  According to the image forming apparatus of the present invention, at least the coefficient α indicating the image forming mode, the coefficient β indicating the travel distance of the surface of the intermediate transfer member, and the number of sheets of image forming sheet γ are temporarily attached to the surface of the intermediate transfer member. An expression [y = α × (1-1 / γ) × β] for calculating a filming coefficient y due to foreign matter on the surface of the intermediate transfer member, which is expressed as a function of the number γ of image formations as to whether the images are separated from each other. The filming coefficient y on the surface of the intermediate transfer member is sequentially obtained at a predetermined timing, and the accumulated value Y of the obtained filming coefficient y exceeds a predetermined threshold according to the cumulative traveling distance on the surface of the intermediate transfer member. Thereafter, the frequency of the separation pressure contact with the intermediate transfer body of the cleaning blade in the monochrome image forming mode is performed at a predetermined increased frequency.

  Therefore, the foreign matter removal processing on the surface of the intermediate transfer member by the cleaning blade can be appropriately performed over a long period of time without degrading image productivity.

  The above-mentioned γ value indicates whether the recording medium to be used is high-quality paper with relatively little paper dust generation (and therefore less filming), or poor paper with more paper dust generation (and hence filming is likely to occur). Or may be determined in consideration of other conditions (such as the state of the intermediate transfer member) including this point.

  Also, the thick paper is more strongly pressed against the intermediate transfer body during the secondary transfer of the toner image than the plain paper, and the paper powder is likely to adhere to the intermediate transfer body, so the γ value is whether the recording medium used is thick paper or plain paper Or may be determined in consideration of other conditions (such as the state of the intermediate transfer member) including this point.

  In any case, when the recording medium is recording paper, if the paper quality is also taken into consideration, an example in which the γ value is smaller when the recording paper is poor paper than when the recording paper is high quality paper is adopted. Can be mentioned.

  In any case, if the thickness is taken into account when the recording medium is recording paper, the γ value is smaller when the recording paper is thick paper than when the recording paper is plain paper. An example can be given.

  In calculating the filming coefficient, when the recording medium is recording paper, if the paper quality (whether fine paper or poor paper) is taken into consideration, the coefficient p indicating the paper quality can be adopted. If the thickness (thick paper or plain paper) is taken into consideration, a coefficient q indicating the thickness can be adopted.

Then, as a formula for calculating the filming coefficient y, the coefficient p and / or q are added to the y = α × (1-1 / γ) × β],
y = α × (1-1 / γ) × β] × p, or y = α × (1-1 / γ) × β] × q, or y = α × (1-1 / γ) × β] * P * q etc. can also be adopted.

In this case, for p, for example, the value of p in the case of bad paper is made larger than the value of p in the case of fine paper (for example, fine paper: p = 1, bad paper: p = 1.5) Can be mentioned.
As for q, for example, the q value for thick paper can be made larger than the q value for plain paper (for example, plain paper: q = 1, thick paper: q = 1.5). .

  In any case, suitable coefficients α, γ, p, q, etc. may be determined in advance according to various conditions of image formation through experiments and experiences.

  As described above, according to the present invention, an electrostatic latent image is formed on an electrostatic latent image carrier, and the electrostatic latent image can be moved to the electrostatic latent image developing area. A toner image is formed by developing with a developing device that holds the assigned color toner corresponding to the electrostatic latent image, and the toner image is primarily transferred to the intermediate transfer member, whereby a monochrome toner image or An intermediate transfer body that can form a multiple toner image composed of toner images of two or more colors, secondarily transfer the toner image on the intermediate transfer body to a recording medium, and fix the toner image on the recording medium. A cycle type color image forming apparatus that removes foreign matter on the surface with a cleaning blade, and appropriately removes foreign matter on the surface of the intermediate transfer member with the cleaning blade over a long period of time without degrading image productivity. To provide an image forming apparatus capable of performing It can be.

1 is a diagram schematically illustrating a configuration of an example of an image forming apparatus according to the present invention. FIG. 2 is a block diagram illustrating an outline of a control circuit of the image forming apparatus in FIG. 1. FIG. 6 is a diagram illustrating a growth state of a filming layer on an intermediate transfer belt accompanying an increase in the number of image formations when a clique blade is constantly in contact with an intermediate transfer member. FIG. 6 is a diagram showing that filming growth on an intermediate transfer belt is slowed with an increase in the frequency of separation of a cleaning blade from an intermediate transfer body even when an image is formed on poor paper in a monochrome mode. In the example of change in the cumulative value Y of the filming coefficient y calculated by the filming coefficient calculation formula, when the γ value is set to 10, 5, and 3 in the monochrome image forming mode, the blade is separated from the intermediate transfer belt. FIG. 6 is a diagram illustrating the case of the color image forming mode when there is no color image. FIG. 6 is a diagram illustrating an example of changing a γ value when a cumulative value Y of a filming coefficient y at a predetermined cumulative travel distance of the intermediate transfer belt exceeds a threshold value.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 schematically shows the configuration of an example of an image forming apparatus according to the present invention.
FIG. 2 is a block diagram showing an outline of a control-related circuit in the image forming apparatus shown in FIG.

  An image forming apparatus 10 shown 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) that is an electrostatic latent image carrier here, and a charger 2, a developing device 4, an intermediate transfer member 6, and a cleaning device around the drum-type photosensitive member 1. The devices 5 are arranged 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. Here, the intermediate transfer member 6 is an intermediate transfer belt in the form of an endless belt.

  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 provided 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 blade driving unit BLD 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 from the intermediate transfer belt 6. This blade drive unit BLD is essentially provided for the following.

  That is, when forming a color image using two or more developing devices, after the first color toner image is formed on the intermediate transfer belt 6, the next second color toner image, or the third color toner image, or Further, while the toner image of 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. Then, after all the desired toner images are formed on the recording paper S, the cleaning blade BL is again brought into pressure contact with the intermediate transfer belt 6 at the timing of cleaning the intermediate transfer belt 6 to exhibit the original cleaning function.

  The blade driving unit BLD includes, but is not limited to, 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 the current is interrupted. It has been. The energization control of the remote pressure contact solenoid is performed by the control unit Cont shown in FIG.

  Although not limited thereto, in this example, the blade BL is made of urethane rubber. On the other hand, the intermediate transfer belt 6 is a friction made of polycarbonate, polyimide, or the like that has not been subjected to surface coating treatment or the like for cost reduction. This is a resin-based belt having a high coefficient and a relatively high rigidity of each part.

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.

  Further, when the filming layer formed by paper dust or the like on the intermediate transfer belt 6 grows, the sensor 66 reflects more projected light and increases the received light amount (reflectance (= received light amount / projected light amount). Light intensity). 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 exemplary embodiment, the growth state of the filming layer formed on the intermediate transfer belt 6 can be determined based on the output voltage from the image density adjustment sensor 66.

  The image forming apparatus 10 described above operates under the instruction of the control unit Cont shown in FIG. An operation panel PA is connected to the control unit Cont. On the operation panel PA, the user sets the number of images to be formed, sets the size of the recording paper, sets the type of recording paper (whether fine paper, poor paper, or thick paper (plain paper)), monochrome image formation mode, or color image. It is possible to set an image forming mode as a forming mode.

  The operation of the blade drive unit BLD of the cleaning device 65 (operation to press and separate the blade BL from the intermediate transfer belt 6) is controlled by the control unit Cont.

  According to the image forming apparatus 10, a toner image can be formed on the recording sheet S using one or more of 4K, 4C, 4M, and 4Y developing devices under the instruction of the control unit Cont. An example of forming a full-color image using four developing units will be described below.

  First, if necessary, the developing device rack 40 is rotated by a rack driving unit (not shown) to place the yellow developing device 4Y at a developing position where the developing roller 41 faces the photosensitive member 1, and the photosensitive member 1 is shown in the drawing. The intermediate transfer belt 6 is also rotated in the clockwise direction. 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 performed in this color image formation, the cleaning blade BL of the cleaning device 65 is moved by the pressure contact / separation mechanism BLD under the instruction of the control unit Cont. It is separated from.

  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 pressed against the intermediate transfer belt 6 by the blade driving unit BLD.

  As described above, in the color image forming mode, the cleaning blade BL is frequently temporarily separated from the intermediate transfer belt 6 and is pressed again. Therefore, in the color image forming mode, the frequency of separation pressure contact with the intermediate transfer belt of the cleaning blade is high, and the cleaning performance of the cleaning blade is easily maintained in the expected state.

  On the other hand, when the monochrome mode is selected, the controller Cont puts only the developing device of that color into the developing operation state, and the intermediate transfer belt 6 is driven at a constant speed while being kept in contact with the photoreceptor 1. An image forming operation is performed. During the operation in the monochrome mode, the intermediate transfer belt 6 after the toner image transferred to the belt 6 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, an image forming operation is performed while being in contact with the surface.

  However, as described above, when image formation 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, paper dust or the like is formed on the intermediate transfer belt 6. A filming layer is easily formed.

  This is because, when the cleaning blade BL is always in pressure contact with the intermediate transfer belt 6, the tip of the cleaning blade BL is pulled by the intermediate transfer belt 6, and the pressure at which the blade tip contacts the intermediate transfer belt 6 decreases. This means that the scraping ability by the cleaning blade BL is lowered relatively early.

  As described above, the sensor 66 can also determine the growth state of the filming layer formed on the intermediate transfer belt 6. Therefore, when the cleaning blade BL is always pressed against the intermediate transfer belt 6 in the monochrome mode, the change in the filming level on the intermediate transfer belt 6 is viewed from the reflectance of the surface of the intermediate transfer belt 6 detected by the sensor 66. As illustrated in FIG.

  That is, as shown in FIG. 3, as the number of images formed increases, the reflectance of the surface of the intermediate transfer belt 6 increases, and the filming layer on the surface of the intermediate transfer belt 6 grows. Therefore, the cleaning blade BL is cleaned. It can be seen that the performance decreases. In particular, it can be seen that when a rough paper having more paper dust than the high quality paper is used as the recording paper, the foreign matter removing function of the cleaning blade BL is deteriorated earlier than the case of the high quality paper, and unwiping is generated.

  On the other hand, even when the image is formed in the monochrome mode and on the poor paper, as shown in FIG. 4, when the frequency of temporary separation of the Crye blade BL from the intermediate transfer belt 6 is increased, It can be seen that the filming growth on the intermediate transfer belt 6 is slowed down, and that the greening blade can exhibit its original function for such a long time.

Therefore, in the image forming apparatus 10, the control unit Cont is as follows.
That is, the controller Cont temporarily moves the cleaning blade BL to the surface of the intermediate transfer belt with respect to the coefficient α indicating the image forming mode, the coefficient β indicating the traveling distance of the surface of the intermediate transfer belt 6 and the number of image forming sheets γ. An expression [y = α × (1-1 / 1 /) for calculating a filming coefficient y relating to filming generated by paper dust or the like on the surface of the intermediate transfer belt 6 expressed as a function of the number of image formations γ as to whether the image is separated. γ) × β] is used to sequentially obtain the filming coefficient y on the surface of the intermediate transfer belt 6 for every 100 image forming sheets. In this case, β at each calculation is β = 100.

  The controller Cont further determines a threshold value (in this example, the accumulated value Y of the filming coefficient y determined in advance according to the accumulated travel distance of the surface of the intermediate transfer belt 6 (in this example, the accumulated belt speed 500). 500), thereafter, the blade drive unit BLD is caused to increase the separation pressure contact frequency of the cleaning blade BL with respect to the intermediate transfer belt 6 in the monochrome image forming mode by a predetermined increased frequency (γ = 3) higher than the current frequency. ).

5 and 6 illustrate this.
In this example, the coefficient α indicating the image formation mode is set to α = 1 in the monochrome image formation mode and α = 0.25 in the color image formation.

  In this example, the rotation speed (rotation speed) of the intermediate transfer belt 6 is employed as the coefficient β indicating the travel distance of the surface of the intermediate transfer belt 6.

  Here, such coefficients α and β are adopted as the coefficients α and β, and the value of (1 / γ) in the monochrome image forming mode is 0 (the state in which the blade BL is always pressed against the belt 6), γ = 10 (blade BL is spaced once every 10 images), γ = 5 (blade BL is spaced once every 5 sheets), γ = 3 (blade BL is spaced once every 3 sheets), and The (1 / γ) value in the color image forming mode is regarded as 0, and the filming coefficient y in each case is calculated using the above-described calculation formula y = α × (1-1 / γ) × β] When calculation is performed every 100 image formation sheets (in each calculation, β = 100), the cumulative value Y of the filming coefficient y changes as shown in FIG.

  As shown in FIG. 5, in the monochrome mode, the blade BL is not separated from the belt 6, and the blade BL is always kept in pressure contact with the belt 6, that is, (1 / γ) is substantially 0, or the γ value is 10 (If the frequency is low even if the separate pressure welding is repeated), the foreign matter removing ability of the cleaning belt 6 decreases, and the cumulative rotational speed of the belt indicating the cumulative travel distance on the surface of the belt 6 is (1 / γ). When = 0, when it exceeds about 800, when γ = 10, when it exceeds about 900, each of the filming layers becomes practically negligible, such as paper dust on the intermediate transfer belt 6 by the blade BL. It can be seen that the foreign matter removal processing capability due to the pressure decreases before reaching the belt cumulative rotation speed (1000 in this example) corresponding to the predetermined belt travel distance L in this example. .

    On the other hand, in the color image forming mode, it can be seen that the removal capability of foreign matters caused by paper dust on the intermediate transfer belt 6 by the blade BL is maintained for a long time.

  Therefore, here, assuming that image formation is started in the monochrome image formation mode, the blade BL is initially kept in constant pressure contact with the belt 6 so as not to reduce image productivity as shown in FIG. In this state, an image is formed, and the cumulative value Y of the filming coefficient y at the belt cumulative rotational speed 500 corresponding to the predetermined cumulative travel distance of the belt 6 exceeds the threshold value 500. After that, the blade driving unit BLD is caused to perform the separation pressure contact frequency of the cleaning blade BL with respect to the intermediate transfer belt 6 in the monochrome image forming mode at a predetermined frequency (γ = 3).

  Thus, the foreign matter removal processing on the surface of the intermediate transfer belt 6 by the cleaning blade BL is performed until the belt cumulative rotation speed corresponding to the predetermined belt travel distance L in this example is reached without degrading the image productivity. It can be done properly over a long period of time.

  The above-mentioned γ value indicates whether the recording medium to be used is high-quality paper with relatively little paper dust generation (and therefore less filming), or poor paper with more paper dust generation (and hence filming is likely to occur). As described above, it may be determined according to the above, or may be determined in consideration of other conditions (the state of the intermediate transfer member, etc.) including this point.

  Also, the thick paper is more strongly pressed against the intermediate transfer body during the secondary transfer of the toner image than the plain paper, and the paper powder is likely to adhere to the intermediate transfer body, so the γ value is whether the recording medium used is thick paper or plain paper As described above, it may be determined according to the above, or may be determined in consideration of other conditions (such as the state of the intermediate transfer member) including this point.

  In calculating the filming coefficient, when the recording medium is recording paper, if the paper quality (whether fine paper or poor paper) is taken into consideration, the coefficient p indicating the paper quality can be adopted. If the thickness (thick paper or plain paper) is taken into consideration, a coefficient q indicating the thickness can be adopted.

Then, as a formula for calculating the filming coefficient y, the coefficients p and / or q are added to the above y = α × (1-1 / γ) × β],
y = α × (1-1 / γ) × β] × p, or y = α × (1-1 / γ) × β] × q, or y = α × (1-1 / γ) × β] * P * q etc. can also be adopted.

In this case, with respect to p, an example can be given in which p = 1 for fine paper and p = 1.5 for poor paper.
As for q, an example can be given in which q = 1 for plain paper and q = 1.5 for thick paper.

  According to the present invention, there is provided a cycle type color image forming apparatus, which can appropriately remove foreign matter on the surface of an intermediate transfer body by a cleaning blade over a long period of time without degrading image productivity. It can be used for that.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 1 Photoconductor 2 Charger 3 Image exposure apparatus 4 Developing device 5, 65, Cleaning device BL Cleaning blade BLD Blade drive part 6 Intermediate transfer belt 8 Fixing device 66 Image density adjustment sensor Cont. Control unit

Claims (4)

Color toner corresponding to the electrostatic latent image among a plurality of developing units capable of forming the electrostatic latent image on the electrostatic latent image carrier and moving the electrostatic latent image to the electrostatic latent image developing area The toner is developed with a developing device that holds toner, and a toner image is formed, and the toner image is primarily transferred to the intermediate transfer member, whereby a multi-toner composed of a monochrome toner image or a toner image of two or more colors on the intermediate transfer member An image is formed, the toner image on the intermediate transfer member is secondarily transferred to a recording medium, and fixed on the recording medium. A cycle type color image forming apparatus for performing,
A blade drive unit that presses and separates the cleaning blade from the surface of the intermediate transfer member, and a control unit for the blade drive unit,
The control unit should at least temporarily separate the cleaning blade from the surface of the intermediate transfer body for every coefficient α indicating the image forming mode, a coefficient β indicating the running distance of the surface of the intermediate transfer body, and for every image forming sheet number γ. The surface of the intermediate transfer member is calculated using the formula [y = α × (1-1 / γ) × β] for calculating the filming coefficient y due to the foreign matter on the surface of the intermediate transfer member expressed as a function of the number γ of image formations When the accumulated value Y of the obtained filming coefficient y exceeds a predetermined threshold according to the accumulated travel distance of the surface of the intermediate transfer member, the filming coefficient y is sequentially calculated at a predetermined timing. An image forming apparatus characterized by causing a blade driving unit to perform a frequency of separating press contact with an intermediate transfer body of a cleaning blade in a monochrome image forming mode at a predetermined increased frequency. When the recording medium is recording paper, the control unit adopts a coefficient p indicating the paper quality, and the coefficient p is set to y = α × (1-1 / γ) × β as a formula for calculating the filming coefficient y. The image forming apparatus according to claim 1, wherein y = α × (1-1 / γ) × β × p is used in consideration of When the recording medium is recording paper, the control unit employs a coefficient q indicating the paper thickness, and sets y = α × (1-1 / γ) × β as a formula for calculating the filming coefficient y. The image forming apparatus according to claim 1, wherein y = α × (1-1 / γ) × β × q in consideration of the coefficient q is used. When the recording medium is recording paper, the control unit employs a coefficient p indicating the paper quality and a coefficient q indicating the paper thickness, and y = α × ( The image forming apparatus according to claim 1, wherein y = α × (1-1 / γ) × β × p × q in which coefficients p and q are added to (1/1 / γ) × β.

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