JP5136220B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Conventionally, an electrostatic latent image is formed on an image carrier such as a photoconductor, and a plurality of toner images obtained by developing the electrostatic latent image are sequentially transferred (primary transfer) onto an image carrier such as a transfer belt. There is a so-called electrophotographic image forming apparatus in which formed toner images are collectively transferred (secondary transfer) onto a recording medium such as paper, and an image is formed on a storage medium. In the case of such an image forming apparatus, a part of the toner image may remain on one or a plurality of each image carrier during transfer. Hereinafter, the toner remaining on the image carrier is referred to as residual toner.

  Residual toner may become an unintended adhering toner in subsequent image formation, reducing image quality, and in the case of an intermediate image carrier, may cause problems such as soiling a recording medium such as paper. For this reason, the image forming apparatus is provided with a configuration for cleaning each image carrier to remove residual toner. In such a configuration, the image carrier is slidably brought into contact with the surface of the image carrier, and the brush is brought close to or slid in contact with the image carrier, and the brush roller is charged to cause electrostatic coulomb force. A device that collects the residual toner is known. In recent years, as the toner particle size has become smaller and spherical, the toner may pass between the blade and the image carrier. ing.

  In the case of an electrophotographic image forming apparatus, the toner has a positive or negative polarity. Here, a negative polarity toner will be described as an example. Negative polarity toner has the property of being attracted to a positive polarity member or medium by Coulomb force. Accordingly, the brush roller that collects the negative polarity residual toner is charged to have a positive polarity.

By the way, the toner is exposed to a potential different from the potential of the image carrier during transfer. At this time, the toner may be charged, and the polarity of the toner may change. For this reason, a part of the remaining toner may have a positive polarity. Many residual toners having a positive polarity are weakly charged with a weak positive polarity.
When the residual toner has a positive polarity, the toner may remain on the image carrier without being collected by the positive polarity brush roller. Therefore, by providing two brush rollers, the brush roller that approaches and slides in contact with the image carrier first has the opposite polarity to the toner, and the brush roller that approaches and slides in contact with the image carrier later has the same polarity as the toner. A configuration in which the charged toner is further collected by a later brush roller is known (for example, Patent Document 1, Patent Document 2, etc.).
JP 2002-229344 A JP 2005-315987 A

  However, in the case of the configuration shown in each of the above-mentioned patent documents, there is a possibility that the remaining toner cannot be sufficiently collected even with the subsequent brush roller. This is because the remaining toner is further reversely charged by the subsequent brush roller and has the same polarity as that of the subsequent brush roller, and may not be collected by the subsequent brush roller.

  An object of the present invention is to provide an image forming apparatus that can satisfactorily collect residual toner.

According to a first aspect of the present invention, in an image forming apparatus for forming an image by transferring toner carried on an image carrier onto a sheet, the toner is located on the upstream side of the image carrier in the moving direction from the image carrier. A first brush roller that removes toner, a second brush roller that is located downstream of the first brush roller and removes toner from the image carrier, and a voltage that charges the first brush roller and the second brush roller An inflection point potential in the voltage-current characteristics of the first brush roller and / or the second brush roller, wherein the polarity of the voltage applied to the applying means and the first brush roller is opposite to the charging polarity of the toner. And a voltage having an absolute value smaller than the absolute value of the inflection point potential is applied to the second brush roller with the same polarity as the charging polarity of the toner. Applied Comprising a voltage control means for controlling said voltage applying means so that the discrimination means toner carried on the image carrier, it is determined whether the remaining toner after transfer, wherein the voltage control means, said As a result of determination by the determination means, when the toner carried on the image carrier is not the residual toner after transfer, the first toner is compared with the case where the residual toner after transfer is carried on the image carrier. The absolute value of the voltage value of the brush roller is reduced .
The “paper” is not limited to paper, but includes all recording media that can be printed by OHP film or other toner transfer.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the voltage-current characteristics of the first brush roller and / or the second brush roller are such that no toner adheres to the image carrier. It is the characteristic in.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the conductive member is grounded at a position facing the first brush roller and / or the second brush roller with the image carrier interposed therebetween. Is provided.

  According to the present invention, it is possible to provide an image forming apparatus capable of suppressing the residual toner collection failure caused by the reverse charging of the residual toner due to the charging of the brush roller and collecting the residual toner satisfactorily.

(First embodiment)
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic cross-sectional configuration diagram of an image forming apparatus 1 according to the first embodiment.

  As shown in FIG. 1, the image forming apparatus 1 reads an image from a document, forms a read image on a sheet P, and outputs it, page data including image data from an external device or the like, and each image data A print function for receiving a job including the image forming conditions, and forming and outputting an image on the paper P based on the received job. As shown in FIG. 1, the image forming apparatus 1 includes an image reading unit 20, a printing unit 40, and the like.

  The image reading unit 20 includes an automatic document feeder 21 called an ADF (Auto Document Feeder) and a reading unit 22. The document d placed on the document tray 21a of the automatic document feeder 21 is conveyed to a contact glass which is a reading location, and an image on one or both sides of the document d is read by an optical system, and a CCD (Charge Coupled Device) 22a. As a result, the image of the document d is read. Here, the image means not only image data such as graphics and photographs but also text data such as characters and symbols.

  An image (analog image signal) read by the image reading unit 20 is output to the control unit 100 to be described later, subjected to various image processing such as A / D conversion in the control unit 100, and then to the printing unit 40. Is output.

  The print unit 40 performs an electrophotographic image forming process based on the input print data, and includes a paper feed unit 41, a conveyance unit 42, an image formation unit 43, a fixing unit 44, an unloading unit 45, an unloading unit 45. A standby unit 46 is provided.

  The paper feed unit 41 includes a plurality of paper feed trays 41a, a paper feed unit 41b, a manual feed tray 41c, and the like. The paper feed tray 41a stores standard paper, special paper, insertion paper, and other paper P identified for each paper feed tray 41a on the basis of the amount and size of the paper for each preset type. The paper P is transported one by one from the top toward the transport unit 42 by the paper feeding means 41b. The manual feed tray 41c is a paper feed tray on which various types of paper P can be stacked according to the user's needs, and transports the paper P stacked by the paper feed rollers one by one from the top to the transport unit 42. To do.

  The transport unit 42 transports the paper P transported from the paper feed tray 41a or the manual feed tray 41c to the secondary transfer roller 42b through a plurality of intermediate rollers, registration rollers 42a, and the like. The registration roller 42a functions as a first standby unit that temporarily waits for the paper conveyed to the secondary transfer roller 42b. The secondary transfer roller 42b receives the toner image on the intermediate transfer member (intermediate transfer belt 43b). It functions as a secondary transfer section that performs secondary transfer onto the paper.

  In addition, the conveyance unit 42 conveys the sheet P on which the single-sided image formation processing has been performed to the double-side conveyance path 42c by the conveyance path switching plate, and again conveys the sheet P to the secondary transfer roller 42b via the intermediate roller and the registration roller 42a. By the secondary transfer roller 42b, a toner image primarily transferred to an intermediate transfer belt 43b described later is secondarily transferred onto the paper P.

  For example, when forming an image of four colors (yellow (Y), magenta (M), cyan (C), and black (K)), the image forming unit 43 is provided for each color that can be filled with toner of different colors. The image forming units 43Y, 43M, 43C, and 43K, an intermediate transfer belt 43b, and a cleaning unit 50 are provided.

  For example, the image forming unit 43Y primarily transfers a charging device, an exposure device, a developing device, and a toner image on which an electrostatic latent image based on image data developed around the photosensitive drum is developed onto the intermediate transfer belt 43b. A primary transfer roller 43Ya that functions as a primary transfer unit and a cleaning device are provided to form a yellow (Y) image.

Specifically, an electrostatic latent image is formed by irradiating the photosensitive drum charged by the charging device with light according to yellow (Y) image data from the exposure device. The developing device develops the electrostatic latent image by attaching charged yellow (Y) toner to the surface of the photosensitive drum on which the electrostatic latent image is formed. The photosensitive drum to which toner is attached by the developing device is primarily transferred to the intermediate transfer belt 43b while being rotated at a constant speed to a transfer position where the primary transfer roller 43Ya is disposed. After the toner is primarily transferred to the intermediate transfer belt 43b, the cleaning device removes residual charges, residual toner, and the like on the surface of the photosensitive drum.

  The image forming units 43M, 43C, and 43K have the same configuration as the image forming unit 43Y, and form magenta (M), cyan (C), and black (K) images, respectively.

The intermediate transfer belt 43b is a semiconductive endless belt that is suspended and supported rotatably by a plurality of rollers, and is driven and moved in accordance with rotation of a roller such as the drive roller 56.
The intermediate transfer belt 43b is pressure-bonded to the respective photosensitive drums by primary transfer rollers 43Ya, 43Ma, 43Ca, and 43Ka of the image forming units 43Y, 43M, 43C, and 43K. As a result, the toner developed on the surface of each photosensitive drum is primarily transferred to the intermediate transfer belt 43b at the transfer positions by the primary transfer rollers 43Ya, 43Ma, 43Ca, and 43Ka, and the paper is transferred at the transfer position by the secondary transfer roller 42b. Yellow, magenta, cyan, and black toners are sequentially superimposed on P and secondarily transferred.

  The intermediate transfer belt 43b secondarily transfers the toner image onto the paper P by the secondary transfer roller 42b, and then separates the paper P from the curvature and electrostatically, and the cleaning unit 50 removes the residual toner.

  The fixing unit 44 includes a rotary fixing member 44a having a heat source and a pressure roller 44b that presses against the rotary fixing member 44a to form a nip portion N, and thermally fixes the toner image secondarily transferred onto the paper P. To do. Examples of the rotation fixing member 44a include a heating roller and a heating belt.

  The carry-out unit 45 includes a plurality of paper discharge rollers, a carry-out port 45a, and a paper discharge surface switching path 45b. The paper P on which the toner image is fixed is sandwiched between the paper discharge rollers by the conveyance path switching plate. A discharge function that functions as a paper discharge surface switching unit that switches the paper surface of the paper discharged from the outlet 45a to the carry standby unit 46, or the paper P on which the toner image is fixed is sandwiched between the paper discharge rollers. After being transported to the paper surface switching path 45b, it is unloaded from the unloading port 45a to the unloading standby unit 46.

  The carry-out standby unit 46 is provided between the secondary transfer roller 42b and the paper discharge tray 47, and includes a plurality of paper discharge rollers, a first carry-out path 46a, and a second carry-out path 46b. The sheet carried in from the carry-out port 45a is conveyed by the plate to the first carry-out path 46a or the second carry-out path 46b, and then discharged to the paper discharge tray 47.

  The first carry-out path 46a is a path for discharging the paper carried in from the carry-out port 45a to the paper discharge tray 47 on the same surface as the paper surface carried in from the carry-out port 45a. The second carry-out path 46b functions as a second standby unit that temporarily waits for the paper carried in from the carry-out port 45a, and is a path that discharges the paper to the paper discharge tray 47 at a predetermined timing. The first carry-out path 46a This is a path for discharging paper to the paper discharge tray 47 on the reverse side to the paper surface carried out to the paper discharge tray 47.

  In the present embodiment, toner that is negatively charged (hereinafter referred to as negative toner) is used. The intermediate transfer belt 43b is made of polyimide (PI) resin and has a volume resistance of 10 ^ 9 [Ω] and a surface resistance of 10 ^ 11 [Ω].

  Further, as shown in FIG. 1, a sensor 70 is provided on the downstream side of the transport unit 42 and on the upstream side of the cleaning unit 50 in the moving direction of the intermediate transfer belt 43 b. The sensor 70 determines the type of residual toner. The type of remaining toner and its determination will be described later.

FIG. 2 shows a control block diagram of the image forming apparatus 1.
As illustrated in FIG. 2, the image forming apparatus 1 includes an operation display unit 30 and a control unit 100.

  The operation display unit 30 includes an LCD (Liquid Crystal Display) 31, a touch panel 32, and the like, and can perform various information display regarding the image forming apparatus 1, various input operations by an operator, and the like.

  The control unit 100 includes a CPU 101, a RAM 102, a ROM 103, and the like, and performs various processes related to the operation of the image forming apparatus 1 by so-called software processing. The control unit 100 is connected to the image reading unit 20, the operation display unit 30, the printing unit 40, the cleaning unit 50, the sensor 70 and other units of the image forming apparatus 1, and performs operation control of each unit as necessary. The input content from the operation display unit 30 is interpreted and processed by the control unit 100.

  The control unit 100 includes an A / D conversion unit 104, a voltage control unit 105, and the like. The A / D conversion unit 104 converts analog data input to the control unit 100 into digital data and inputs the digital data to the CPU 101. The voltage control unit 105 controls the polarity and voltage value of the voltage applied to two brush rollers 51 and 52 of the cleaning unit 50 described later.

FIG. 3 is a schematic cross-sectional configuration diagram of the cleaning unit 50 and its surroundings.
As shown in FIG. 3, the cleaning unit 50 includes two brush rollers 51 and 52 having brushes arranged radially from the center of a cylindrical member such as an aluminum cylinder, and two brush rollers. Two toner collecting rollers 53 and 54 that are provided for each of the 51 and 52 and are in contact with the tip of the brush of each brush roller, and close to each of the two toner collecting rollers 53 and 54 Scrapers 55 and 55 provided as described above. The core material of the two brush rollers 51 and 52 is not limited to the cylindrical member, and may be a hollow cylinder or the like.

The two brush rollers 51 and 52 are provided so that the tips of the brushes are close to or slidably contact the outer peripheral surface of the intermediate transfer belt 43b at a position facing the driving roller 56 with the intermediate transfer belt 43b interposed therebetween. The brush rollers 51 and 52 are provided so as to be rotatable about their respective cores as rotation axes, and rotate in the same direction as the drive direction of the drive roller 56. That is, at the position where the brush tip of each brush roller and the intermediate transfer belt 43b are close to or in sliding contact with each other, the moving direction of the brush tip is opposite to the moving direction of the intermediate transfer belt 43b. The two brush rollers 51 and 52 have the tips of the respective brushes positioned on substantially the same circumference with the core material as the center.
In the following description, of the two brush rollers, the brush roller positioned relatively upstream in the traveling direction of the intermediate transfer belt 43b is the first brush roller 51, and the brush roller positioned relatively downstream is the first. This is referred to as a second brush roller 52.

  In this embodiment, the brush of each brush roller is made of conductive nylon and has a wire diameter of about 0.027 [mm].

The toner collection rollers 53 and 54 are provided so as to contact the two brush rollers 51 and 52, respectively. Specifically, the outer peripheral surface of each toner collection roller is in contact with the tip of the brush of each brush roller. Each toner collecting roller is provided so as to be rotatable about its cylindrical shaft. The rotation direction of each toner collecting roller is opposite to the rotation direction of the brush roller.
In the following description, the toner collecting roller that contacts the first brush roller is referred to as a first toner collecting roller 53, and the toner collecting roller that contacts the second brush roller is referred to as a second toner collecting roller 54.

  Each toner collecting roller is connected to power sources 501 and 502 via the control unit 100. The controller 100 connects the first toner collecting roller 53 to the positive electrode of the power source 501 and the second toner collecting roller 54 to the negative electrode of the power source 502. The power supplies 501 and 502 are power supply devices that function as so-called constant current power supplies.

  Accordingly, the first brush roller 51 is charged to have a positive charge, and the second brush roller 52 is charged to have a negative charge. Therefore, with respect to the toner on the outer peripheral surface of the intermediate transfer belt 43b, the first brush roller attracts and collects negative toner, and the second brush roller attracts and collects positively charged toner (hereinafter referred to as positive toner).

  On the other hand, the drive roller 56 is grounded. Accordingly, the current from the power source 501 flows to the ground of the driving roller 56 via the first toner collecting roller 53 and the first brush roller 51, and the current from the power source 502 passes from the ground of the driving roller 56 to the second brush roller 52. Then, it flows to the power source 502 side through the second toner collecting roller. Ground refers to a connection to a reference potential point and does not necessarily need to be connected to the ground.

  In the present embodiment, each toner collecting roller is made of stainless steel, and the amount of biting of each toner collecting roller with respect to each brush roller in sliding contact is 1 [mm]. The biting amount refers to a length in which the length from the rotation center of the brush roller to the tip of the brush overlaps with the diameter of the toner recovery roller.

  One scraper 55, 55 is provided at a position near each of the two toner collecting rollers 53, 54. As shown in FIG. 3, each scraper is provided such that its blade portion 55 a is inclined to face the rotation direction of each adjacent toner collection roller, that is, the movement direction of the outer peripheral surface of each toner collection roller. Each scraper cleans each toner collecting roller by scraping off residual toner adhering to the outer peripheral surface of each rotating toner collecting roller.

  In this embodiment, each scraper is a stainless steel plate having a thickness of 0.05 [mm].

Next, the operation of the cleaning unit 50 will be described in detail.
FIG. 4 shows an example of the voltage-current characteristic of the toner recovery roller 53. FIG. 5 shows a verification example of the correspondence between the relationship between the voltage value and current value of each toner collecting roller and the cleaning result of the intermediate transfer belt 43b.

  The voltage-current characteristics shown in FIG. 4 are characteristics measured under conditions where no toner adheres to the intermediate transfer belt 43b.

In FIG. 5 and the following description, “untransferred toner” refers to the cleaning unit 50 without passing through the process of transferring the toner secondarily transferred to the intermediate transfer belt 43b to the printing medium such as paper. This is the residual toner in the case of As a case where untransferred toner is generated, for example, a case where the image forming apparatus generates a patch image for controlling the toner density can be cited.
The “transfer residual toner” in FIG. 5 and the following description refers to the intermediate transfer belt that is not transferred when the toner secondarily transferred to the intermediate transfer belt 43b is transferred to a printing medium such as paper. The toner remaining on the outer peripheral surface of 43b.

  The cleaning results A, B, and X in FIG. 5 indicate the evaluation of the cleaning result of the intermediate transfer belt 43b. In this evaluation, after the cleaning of the intermediate transfer belt 43 by the cleaning unit 50, the residual toner on the outer peripheral surface of the intermediate transfer belt 43b is collected with an adhesive medium such as a tape, and the residual toner is pasted on a white paper. This is based on a value obtained by measuring the light reflection density of the residual toner. In FIG. 5, the measured value is evaluated as A when the relative concentration is 0.003 or less, B when the relative concentration is greater than 0.003 and less than 0.005, and X when the relative concentration exceeds 0.005. , B, the cleaning results are considered to be good, and X is considered to be poor cleaning.

  As shown in FIG. 4, the proportionality coefficient of the voltage-current characteristic of the toner recovery roller 53 changes at a certain potential. Hereinafter, a point that becomes the boundary of the change of the proportional coefficient is referred to as an inflection point (for example, the inflection points C1, C2, and C3), and the potential at the inflection point is referred to as an inflection point potential. The voltage-current characteristics applied to the toner collection roller 54 have the same relationship as the toner collection roller 53 by replacing the applied voltage [V] in FIG. 4 with a negative voltage value.

  The voltage-current characteristic of each toner collecting roller varies depending on the resistance value of the brush of each brush roller. 4 and 5, as an example, the case where the logarithm of the resistance value of the brush is 11.5 [logΩ], 9 [logΩ], and 13 [logΩ] is shown.

As shown in Examples 1 to 9 in FIG. 5, the first toner collecting roller 53 is applied with a voltage having an absolute value larger than the absolute value of the inflection point potential. The second toner collecting roller 54 is applied with a voltage having an absolute value smaller than the absolute value of the inflection point potential.
The inflection point potential can also have an inflection point in each of the first brush roller and the second brush roller according to the voltage-current characteristics of the first brush roller and the second brush roller. Here, a brush roller having the same brush resistance is used, and the measurement is performed under the condition of the same inflection point potential.

  When recovering untransferred toner, the voltage of the first toner recovery roller 53 that charges the first brush roller 51 is lower than when recovering untransferred toner. Yes. Hereinafter, a detailed description will be given together with a mechanism for collecting residual toner by two brush rollers.

  FIG. 6 shows an example of the relationship between the magnitude of the potential of the first brush roller 51 and the charge amount distribution of the residual toner before and after passing through the first brush roller 51 for each type of residual toner. In the graph shown in the explanatory diagram of FIG. 6, the dotted line graph indicates the polarity distribution of the residual toner before passing through the first brush roller 51, and the solid line graph indicates the residual toner after passing through the first brush roller 51. Shows the polarity distribution.

  First, the case of untransferred toner will be described. As indicated by T in FIG. 6, when the potential of the first brush roller 51 is large, that is, when a high voltage (for example, 2000 [V]) is applied to the first toner collection roller, the first brush roller 51 is moved. Most of the residual toner after passing, that is, the residual toner not collected by the first brush roller, passes as a toner having a strong positive potential. This is because the residual toner is charged by the first brush roller 51 having a large potential.

  Since the transfer residual toner is exposed to a positive potential when transferred to a printing medium such as paper, a part of the toner may be charged and remain on the intermediate transfer belt 43b with a positive polarity. Therefore, the untransferred toner may be in a state in which plus toner and minus toner are mixed. In this case, the first brush roller 51 having a large potential collects the negative toner out of the remaining toner with Coulomb force, and charges the positive toner that cannot be collected into a strong positive polarity toner. As a result, the residual toner that passes through the first brush roller 51 has a strong positive polarity and is favorably collected by the second brush roller 52 that is negatively charged.

  At this time, a voltage having an absolute value smaller than the absolute value of the inflection point potential (for example, 700 [V]) is applied to the second toner collecting roller 54 that charges the second brush roller 52. As a result, the second brush roller 52 draws the residual toner having a strong positive polarity by the first brush roller 51, and does not negatively charge the residual toner again by the potential of the second brush roller. Collect well. Accordingly, there is no or very little residual toner passing through the second brush roller, and good recovery of the residual toner is realized.

  On the other hand, as shown in FIG. 6Q, when the potential of the first brush roller 51 is small, that is, when a low voltage (for example, 1530 [V]) is applied to the first toner collecting roller, the first brush roller The residual toner after passing through 51, that is, the residual toner not collected by the first brush roller, passes as a toner having a weak positive polarity as compared with the case where the first brush roller 51 has a large potential. In consideration of the recovery of the residual toner by the second brush roller 52, when the transfer residual toner is recovered, the first brush roller 51 has a large potential so that the residual toner can be recovered better.

  Next, the case of untransferred toner will be described. As shown in R of FIG. 6, when the toner is collected by the first brush roller 51 having a large potential with respect to the untransferred toner, a part of the untransferred toner is exposed to the large potential of the first brush roller. The first brush roller 51 passes through the first brush roller 51 without being collected.

  On the other hand, as shown in S of FIG. 6, when the toner is collected by the first brush roller 51 having a small potential with respect to the untransferred toner, the untransferred toner does not become a positive polarity, and the first brush roller It is recovered well at 51 and does not pass or is very small even if it passes. Therefore, when collecting untransferred toner, the first brush roller 51 having a small potential can collect better residual toner. In this case, the voltage applied to the first toner collecting roller 53 for charging the first brush roller 51 is compared with the voltage (for example, 2000 [V]) applied when collecting the transfer residual toner better. Thus, the voltage is low (for example, 1530 [V]), that is, a voltage having a small absolute value.

  As shown in FIGS. 1 and 2, a sensor 70 is provided on the upstream side of the cleaning unit 50 in the moving direction of the intermediate transfer belt 43b. The sensor 70 detects the toner carried on the outer peripheral surface of the intermediate transfer belt 43b, and determines the type of the carried toner, that is, whether the toner is untransferred toner or untransferred toner. The discrimination may be performed by any means capable of discriminating the remaining toner, such as optics, potential measurement and the like.

The controller 100 controls the voltage applied to each toner collecting roller in order to optimally adjust the potential of each brush roller according to the type of residual toner.
The control unit 100 controls the voltage applied to each toner collecting roller according to the determination result of the remaining toner type by the sensor 70.

  For example, as shown in Example 3 in FIG. 5, there is a voltage setting that can satisfactorily collect both untransferred toner and untransferred toner. The control unit 100 may vary the voltage applied to each toner collecting roller when collecting the residual toner according to the type of the residual toner, or collects the good residual toner regardless of the type of the residual toner. You may apply the voltage which can perform.

  The voltage-current characteristics shown in FIG. 4 are shown for the first toner collecting roller 53 and the second toner collecting roller 54 by replacing the applied voltage [V]. The same is true for the voltage-current characteristics of the two brush rollers.

  Next, processing relating to cleaning of the intermediate transfer belt 43b in the operation of the image forming apparatus 1 will be described with reference to the flowchart of FIG. In the flowchart of FIG. 7 and the following description, the image output signal is ON when the image forming apparatus 1 forms an image on a print medium such as paper, and the cleaning unit 50 finishes cleaning the intermediate transfer belt 43b. The image output process ends. When the patch creation sequence is ON, a patch image is formed. When the cleaning of the intermediate transfer belt 43b by the cleaning unit 50 is finished, the patch creation sequence processing is finished. The toner of the patch image is untransferred toner.

  First, the control unit 100 determines whether the image output signal is ON (step S1). When ON (step S1: YES), the control unit 100 applies a voltage (for example, voltage V1) having an absolute value larger than the absolute value of the inflection point potential to the first toner collecting roller 53 and the second toner. A voltage having an absolute value (for example, voltage V2) smaller than the absolute value of the inflection point potential (for example, the inflection point potential W) is applied to the collection roller 54 (step S2). Then, the control unit 100 drives the drive roller 56 and other parts for moving the intermediate transfer belt 43b to drive the intermediate transfer belt 43b (step S3). Thereafter, when the image output process ends (step S4: YES), the control unit 100 ends the application of voltage to the two toner recovery rollers (step S5), and stops the intermediate transfer belt 43b (step S6).

  On the other hand, when the image output signal in step S1 is OFF (step S1: NO) and the patch creation sequence is ON (step S7: YES), the control unit 100 applies the inflection point potential to the first toner recovery roller 53. A voltage having an absolute value larger than the absolute value (for example, voltage V3) is applied, and a voltage having an absolute value smaller than the absolute value of the inflection point potential (for example, voltage V4) is applied to the second toner collecting roller 54. (Step S8). Then, the controller 100 drives the drive roller 56 and other parts for moving the intermediate transfer belt 43b to drive the intermediate transfer belt 43b (step S9). Thereafter, when the patch creation sequence process ends (step S10: YES), the control unit 100 ends the application of voltage to the two toner recovery rollers (step S5), and stops the intermediate transfer belt 43b (step S6).

  In the above-described processing, the voltages V1 and V3 have a relationship of V1 ≧ V3> W with respect to the inflection point potential W. That is, the voltage applied to the first toner collecting roller 53 in step S8 is equal to or lower than the voltage value applied to the first toner collecting roller 53 in step S2. The voltage V2 or V4 applied to the second toner collection roller 54 is optimally controlled with respect to the voltage V1 or V3 applied to the first toner collection roller 53. For example, the voltage value applied to each toner collecting roller in step S2 is the voltage shown in the first embodiment of FIG. 5, and the voltage value applied to each toner collecting roller in step S8 is the voltage shown in FIG. The case where it is the voltage shown in Example 2 is mentioned.

  According to the first embodiment, the control unit 100 applies a voltage higher than the absolute value of the inflection point potential to the first brush roller 51 via the two toner collection rollers 53 and 54, and the second A voltage having an absolute value smaller than the absolute value of the inflection point potential is applied to the brush roller 52. The polarity of the first brush roller 51 is controlled to be opposite to the polarity of the toner, and the polarity of the second brush roller 52 is controlled to be the same as the polarity of the toner. As a result, the reversely charged toner in the secondary transfer is charged by the first brush roller 51 and sent out as a toner having a reverse polarity strong to the polarity of the original toner. Is done. Therefore, it is possible to provide an image forming apparatus capable of suppressing the residual toner collection failure due to the reverse charging of the residual toner due to the charging of the brush roller and collecting the residual toner satisfactorily.

  Further, since the voltage-current characteristics shown in FIG. 4 are characteristics measured under the condition where toner is not attached to the intermediate transfer belt, the voltage is not affected by factors such as the position distribution and amount of the residual toner. -The current characteristics can be measured. Therefore, the control unit 100 can perform accurate voltage control based on the voltage-current characteristics, and can provide an image forming apparatus that can collect toner more favorably.

  Further, the drive roller 56 is provided at a position facing the two brush rollers 51 and 52 with the intermediate transfer brush 43b interposed therebetween, and is grounded. As a result, the drive roller functions as one electrode of the current flowing through the two brush rollers 51 and 52. Therefore, it becomes easy to apply individual polarities and voltages to the brush rollers 51 and 52, respectively.

  Further, the sensor 70 determines the type of the residual toner carried on the intermediate transfer belt, that is, the untransferred toner or the transfer residual toner. The control unit 100 charges the first brush roller 51 when the residual toner carried on the intermediate transfer belt 43b is untransferred toner, compared to when the residual transfer toner is carried on the intermediate transfer belt 43b. The absolute value of the voltage value of the first toner collecting roller 53 is reduced. As a result, the cleaning unit 50 can collect the untransferred toner satisfactorily without reverse charging.

(Second Embodiment)
In the first embodiment, the cleaning unit 50 is configured to clean the intermediate transfer belt 43b, but may be used for other image carriers. Hereinafter, an embodiment in which a similar configuration is provided in a cleaning device for a photosensitive drum will be described.
FIG. 8 shows a schematic cross-sectional configuration diagram of the photosensitive drum cleaning device 60 and its periphery. In addition, the same code | symbol is attached | subjected about the structure similar to 1st Embodiment, and description is abbreviate | omitted.

The photosensitive drum cleaning device 60 includes a first brush roller 61, a second brush roller 62, a first toner recovery roller 53, a second toner recovery roller 54, and scrapers 55 and 55. Prepare. The first toner collecting roller 53 and the second toner collecting roller 54 are connected to power sources 501 and 502 via the control unit 100, respectively.
The first brush roller 61 and the second brush roller 62 are provided such that the tips of the brushes are close to or in sliding contact with the outer peripheral surface of the photosensitive drum 63, and the photosensitive layer 63 a provided on the outer peripheral surface of the photosensitive drum 63. The remaining toner is collected.

Specifically, after charging and exposure processing of the photosensitive layer 63a by the charging / exposure device 64, the toner is attracted from the developing device 65 to the exposed portion of the photosensitive layer 63a and so-called development processing is performed, so that the photosensitive drum is obtained. 63 carries toner. Thereafter, transfer is performed by a transfer device such as a transfer roller (not shown), and then the residual toner on the photosensitive layer 63a is collected by each brush roller of the cleaning device 60.
Regarding other features, the first brush roller 61 and the second brush roller 62 are the same as the first brush roller 51 and the second brush roller 52 shown in the first embodiment.

  Accordingly, the first brush roller 61 is charged with a polarity (for example, plus) opposite to the polarity (for example, minus) of the toner (for example, minus toner) carried on the photosensitive drum 63, and the second brush roller 62 is photosensitive. The toner is charged to the same polarity (for example, minus) as the polarity of the toner carried on the body drum 63. The voltage applied to the first toner collecting roller 53 is a voltage having an absolute value larger than the absolute value of the inflection point potential, and the voltage applied to the second toner collecting roller 54 is the inflection point potential. The voltage is an absolute value smaller than the absolute value.

  Furthermore, the aluminum base tube 63b provided inside the photosensitive layer 63a of the photosensitive drum 63 is grounded, and the current flowing through each brush roller faces each brush roller with the photosensitive layer 63a serving as an image carrier interposed therebetween. It flows between the aluminum elementary tube 63b and the toner collecting rollers.

  Note that the photosensitive drum 63 described above may be a photosensitive drum included in the image forming units 43Y, 43M, 43C, and 43K of the respective colors of the image forming unit 43 of the first embodiment, or other image bearings. It may be a body. For example, it may be a photosensitive drum as an image carrier for secondary transfer used like the intermediate transfer belt 43b of the first embodiment.

  According to the second embodiment, the same effects as those of the first embodiment can be obtained.

  The embodiment of the present invention should be considered that the embodiment disclosed this time is illustrative and not restrictive in all respects. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  For example, the toner of the image forming apparatus is not limited to minus toner. Plus toner may be used. At this time, the polarity of each brush roller to be charged corresponds to the polarity of the toner. Specifically, the upstream brush roller is charged to have a polarity opposite to the polarity of the toner, and the downstream brush roller is charged to have the same polarity as the polarity of the toner. Therefore, when the toner is positively charged, the upstream brush roller is charged to have a negative charge, and the downstream brush roller is charged to have a positive charge.

  Further, the above-described materials such as the intermediate transfer belt 43b, the two brush rollers 51 and 52, the scrapers 55 and 55, and the numerical values and other matters relating to the resistance value are merely examples, and indicate other materials and other resistance values. It goes without saying that can be used. A voltage control unit (for example, the control unit 100) controls the voltages of the two brush rollers based on the inflection point potential obtained by the configuration of each unit of the image forming apparatus.

  In addition, it goes without saying that the configuration of each part of the image forming apparatus can be added, deleted or replaced without departing from the characteristics of the present invention. For example, the image forming apparatus may have a communication unit capable of communicating with a computing device such as a PC, or may be configured to allow only monochrome printing. The power sources 501 and 502 may be a single power source, and the polarity applied to each toner collecting roller may be set by wiring. In each of the above-described embodiments, the member made of aluminum, stainless steel, or the like may be another conductor.

  In each embodiment described above, one control unit 100 performs both charging polarity and voltage for each brush roller. However, polarity control and voltage control may be performed by separate control units. For example, a switch or the like for switching the polarity may be provided so that the operator or the like can manually switch the polarity of each brush roller according to the polarity of the toner to be used. The voltage control is the same as in the above-described embodiments.

1 is a schematic cross-sectional configuration diagram of an image forming apparatus according to a first embodiment. 2 is a control block diagram of the image forming apparatus. FIG. It is a schematic cross-sectional block diagram of the cleaning part and its circumference. FIG. 6 is a diagram illustrating an example of voltage-current characteristics of a toner recovery roller. FIG. 10 is a diagram illustrating a verification example of the correspondence between the relationship between the voltage value and current value of each toner recovery roller and the cleaning result of the intermediate transfer belt. It is a figure which shows an example of the relationship between the magnitude of the electric potential of a 1st brush roller, and the charge amount distribution of the residual toner before and behind passage of a 1st brush roller for every kind of residual toner. 6 is a flowchart illustrating processing related to cleaning of an intermediate transfer belt. FIG. 2 is a schematic cross-sectional configuration diagram of a photosensitive drum cleaning device and its surroundings.

Explanation of symbols

43b Intermediate transfer belt 50 Cleaning unit 51 First brush roller 52 Second brush roller 53 First toner recovery roller 54 Second toner recovery roller 55 Scraper 100 Control units 501 and 502 Power supply

Claims (3)

In an image forming apparatus for forming an image by transferring toner carried on an image carrier onto a sheet,
A first brush roller located upstream in the moving direction of the image carrier to remove toner from the image carrier;
A second brush roller located downstream of the first brush roller for removing toner from the image carrier;
Voltage applying means for charging the first brush roller and the second brush roller;
From the absolute value of the inflection point potential in the voltage-current characteristics of the first brush roller and / or the second brush roller, the polarity of the voltage applied to the first brush roller is opposite to the charging polarity of the toner. A voltage having an absolute value that is greater than the absolute value of the inflection point potential and having the same polarity as the charging polarity of the toner. Voltage control means for controlling the voltage application means;
Discriminating means for discriminating whether or not the toner carried on the image carrier is residual toner after transfer ,
When the toner carried on the image carrier is not the residual toner after transfer as a result of the discrimination by the discrimination means, the voltage control unit is configured to carry the residual toner after transfer onto the image carrier. An image forming apparatus characterized in that the absolute value of the voltage value of the first brush roller is made smaller than that of the image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the voltage-current characteristics of the first brush roller and / or the second brush roller are characteristics under a condition in which toner does not adhere to the image carrier. .   3. The image forming apparatus according to claim 1, wherein a grounded conductive member is provided at a position facing the first brush roller and / or the second brush roller with the image carrier interposed therebetween.

Images