JP2014235225A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the possibility of the reduction of a cleaning effect, in an image forming apparatus in which a constant current is made to flow between a transfer belt and a cleaning member by constant current control.SOLUTION: The image forming apparatus includes a constant current source 20 making a current Ic flow between an intermediate transfer belt 11 and a brush roller 45a, an image forming speed control part 311 switching a speed for moving the intermediate transfer belt 11 between a first moving speed and a second moving speed lower than the first moving speed, and a cleaning speed control part 312 driving the brush roller 45a, so that the relative speed of the second peripheral surface of the brush roller 45a to the intermediate transfer belt 11 becomes a first relative speed, when the moving speed of the intermediate transfer belt 11 is the first moving speed and driving the brush roller 45a, so that the relative speed of the second peripheral surface of the brush roller 45a to the intermediate transfer belt 11 becomes a second relative speed higher than the first relative speed, when the moving speed of the intermediate transfer belt 11 is the second moving speed.

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet using toner.

  Conventionally, an image carrier, a developing device that visualizes an electrostatic latent image on the image carrier to form a toner image, and a cleaning device that collects toner remaining on the image carrier after the toner image is transferred There is known an electrophotographic image forming apparatus including

  As such a cleaning device, a voltage is applied between the transfer belt and the cleaning roller in a state where the cleaning roller as the cleaning member is in contact with the transfer belt as the image carrier, and the charged toner on the transfer belt is coulombic. Techniques for collecting on a cleaning roller by force are known (see, for example, Patent Document 1 and Patent Document 2).

JP-A-7-306602 JP 2003-345212 A

  Incidentally, when a voltage is applied between the transfer belt and the cleaning member, constant current control may be performed so that a constant current flows between the transfer belt and the cleaning member. Since the movement of the charged toner appears as a current between the transfer belt and the cleaning member, in order to obtain a sufficient cleaning effect, it is necessary to pass a certain amount of current by constant current control.

  However, when a constant current is passed between the transfer belt and the cleaning member by constant current control, an excessive voltage may be applied between the transfer belt and the cleaning member because the voltage is not a control target. When an excessive voltage is applied between the transfer belt and the cleaning member, a discharge occurs between the transfer belt and the cleaning member, and the toner is charged with a reverse polarity by the discharge charge. The toner charged to the reverse polarity has a reduced charge amount or a reverse charge polarity. For this reason, the toner charged to the opposite polarity is not affected by the Coulomb force that moves from the transfer belt to the cleaning member, so that the transfer belt cleaning effect is reduced.

  An object of the present invention is to provide an image forming apparatus capable of reducing a possibility that a cleaning effect is reduced in an image forming apparatus in which a constant current is passed between a transfer belt and a cleaning member by constant current control. .

  An image forming apparatus according to the present invention includes an image carrier having a first circumferential surface that bears a toner image formed by charged toner, a first driving unit that moves around the first circumferential surface, and the first driving unit. A transfer portion that is disposed at a facing position facing the peripheral surface and transfers the toner image carried on the first peripheral surface to the sheet at the facing position; and a downstream portion in the circumferential movement direction from the facing position. A cleaning member having a second peripheral surface in contact with the first peripheral surface, a second drive unit that moves the second peripheral surface relative to the first peripheral surface, and the first peripheral surface and the cleaning member. A constant current source that moves the charged toner on the first peripheral surface to the cleaning member by passing a predetermined constant current between the first drive and the member, and the first driving unit by the first driving unit. The speed at which the surface is moved is a predetermined first shift. An image forming speed control unit that switches between a speed and a second moving speed that is slower than the first moving speed, and a speed at which the first driving unit moves the first peripheral surface is the first moving speed. The second driving unit moves the second peripheral surface so that the relative speed of the second peripheral surface with respect to the first peripheral surface becomes a predetermined first relative speed, and the first driving unit moves the first peripheral surface. When the speed for moving the peripheral surface is the second moving speed, the second driving unit is configured such that the relative speed of the second peripheral surface with respect to the first peripheral surface is a second relative speed higher than the first relative speed. And a cleaning speed control unit that moves the second peripheral surface.

  According to this configuration, of the toner carried on the first circumferential surface of the image carrier, residual toner that has not been transferred by the transfer unit is removed by the cleaning member. At this time, a constant current flows between the first circumferential surface of the image carrier and the cleaning member by a constant current source. In this state, when the moving speed of the first peripheral surface of the image carrier is switched from the first moving speed to the second moving speed by the image forming speed control unit, and the moving speed of the first peripheral surface of the image carrier is reduced, The electrical resistance between the first peripheral surface of the image carrier and the cleaning member increases. Since the constant current source continues to pass a constant current, when the electric resistance between the first circumferential surface of the image carrier and the cleaning member increases, the voltage between the first circumferential surface of the image carrier and the cleaning member is increased. There is a risk of discharge and discharge. When discharging is performed between the first circumferential surface of the image carrier and the cleaning member, the residual toner carried on the first circumferential surface of the image carrier may be charged with a reverse polarity. For this reason, even if the constant current source passes a current, residual toner does not move from the image carrier to the cleaning member, and there is a possibility that a sufficient cleaning effect cannot be obtained. Therefore, the cleaning speed control unit is configured such that when the moving speed of the first circumferential surface of the image carrier is the first moving speed, the relative speed of the second circumferential surface of the cleaning member with respect to the first circumferential surface is a predetermined first relative speed. When the second peripheral surface is moved so that the moving speed of the first peripheral surface of the image carrier is the second moving speed, the relative speed of the second peripheral surface of the cleaning member to the first peripheral surface is the first speed. The second peripheral surface of the cleaning member is moved so that the second relative speed is higher than the first relative speed. As a result, the electric resistance between the first peripheral surface of the image carrier and the cleaning member is apparently reduced, so that the possibility of causing discharge is reduced, so that the possibility of reducing the cleaning effect can be reduced.

  In addition, a humidity detection unit that detects humidity related to the image carrier is further provided, and the cleaning speed control unit is configured to detect the first and second when the humidity detected by the humidity detection unit is lower than a predetermined reference humidity. It is preferable to increase each relative speed.

  When the humidity decreases, the electrical resistance between the first peripheral surface of the image carrier and the cleaning member increases, which may cause discharge. Therefore, the cleaning speed control unit increases the first and second relative speeds when the humidity detected by the humidity detection unit is lower than the predetermined reference humidity, thereby cleaning the first circumferential surface of the image carrier. The electrical resistance between the members is apparently reduced. Thereby, since the possibility that discharge will occur is reduced, the possibility that the cleaning effect is reduced can be reduced.

  In addition, the sheet on which the toner image is transferred by the transfer unit is heated while being conveyed, thereby fixing the toner image to the sheet, and a thickness for acquiring thickness information indicating the thickness of the sheet. An image information acquisition unit, and the image formation speed control unit sets a predetermined conveyance speed of the sheet by the fixing unit when the thickness of the sheet indicated by the thickness information is a predetermined first thickness. And the first drive unit moves the first peripheral surface to the first moving speed, and the thickness of the sheet indicated by the thickness information is the first thickness. When the second thickness is greater than the first thickness, the sheet conveyance speed by the fixing unit is set to a second conveyance speed that is slower than the first conveyance speed, and the first driving unit moves the first circumferential surface. The second moving speed Rukoto is preferable.

  Since the thick sheet has a large heat capacity, it takes time to heat and melt the toner image and fix it on the sheet. In view of this, the image forming speed control unit causes the sheet conveyance speed by the fixing unit to be lower than that at the first thickness when the sheet thickness indicated by the thickness information is the second thickness larger than the first thickness. Since the two conveying speeds are used, the toner image can be fixed onto the sheet satisfactorily even when the sheet is thick. Further, the image forming speed control unit, when the sheet thickness is a predetermined first thickness, causes the first driving unit to move the first peripheral surface to a speed at which the first peripheral surface is moved, thereby increasing the sheet thickness. Is a second thickness that is greater than the first thickness, the speed at which the first drive unit moves the first peripheral surface is set to the second moving speed, so that the moving speed of the first peripheral surface of the image carrier is That is, the speed of forming the toner image on the sheet and the sheet conveyance speed by the fixing unit can be linked, so that the sheet can be conveyed smoothly.

  The image forming apparatus having such a configuration can reduce the possibility of reducing the cleaning effect in the image forming apparatus in which a constant current is passed between the transfer belt and the cleaning member by constant current control.

1 is a perspective view illustrating an appearance of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic vertical sectional view showing a schematic structure of the image forming apparatus shown in FIG. 1. FIG. 3 is a schematic vertical sectional view showing a schematic structure in the vicinity of a belt cleaning unit of the image forming unit shown in FIG. 2. FIG. 2 is a block diagram schematically showing an electrical configuration of the image forming apparatus shown in FIG. 1. 5 is a flowchart illustrating an example of an intermediate transfer belt cleaning process performed by the image forming apparatus illustrated in FIG. 4. 5 is a flowchart illustrating an example of an intermediate transfer belt cleaning process performed by the image forming apparatus illustrated in FIG. 4. FIG. 5 is a conceptual explanatory diagram for explaining a cleaning process of the intermediate transfer belt by the image forming apparatus shown in FIG. 4. It is a graph which shows the relationship between the voltage between an intermediate transfer belt and a brush roller, and an electric current.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing an appearance of an image forming apparatus 1 according to an embodiment of the present invention. Here, a printer is illustrated as the image forming apparatus 1, but the image forming apparatus may be a copier, a facsimile machine, or a multifunction machine having these functions. Further, the image forming apparatus is not limited to a color-compatible image forming apparatus, and may be a monochrome-compatible image forming apparatus. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

  The image forming apparatus 1 includes an apparatus main body 2 having a substantially rectangular parallelepiped housing structure. The apparatus main body 2 forms an image on a sheet using toner. The apparatus main body 2 accommodates various devices for image formation. A discharge tray 9 is formed on the upper surface of the apparatus main body 2.

  An operation panel 25 (thickness information acquisition unit) is provided on the upper front surface of the apparatus main body 2. The operation panel 25 includes operation keys 251 and an LCD touch panel 252 and receives various operation instructions input from the user. Further, the operation panel 25 receives input of thickness information indicating the thickness of the paper P from the user. The thickness information is, for example, information indicating whether the paper P is a plain paper having a first thickness or a thick paper having a second thickness larger than the first thickness.

  A sheet feeding cassette 211 that stores a sheet P (sheet) on which an image forming process is performed is mounted at the lower part of the apparatus main body 2. The paper feed cassette 211 can be pulled out from the front surface of the apparatus main body 2 in the forward direction.

  A maintenance door 212 that exposes the inside of the apparatus main body 2 is attached to the front surface of the apparatus main body 2 and the upper portion of the paper feed cassette 211. The maintenance door 212 is rotatably attached to the apparatus main body 2 at the lower end edge thereof, and can be opened and closed.

  FIG. 2 is a schematic vertical sectional view showing a schematic structure of the image forming apparatus 1 shown in FIG.

  The image forming apparatus 1 is a so-called tandem color image forming apparatus, and includes a paper feeding unit 200, a vertical conveyance path 202, a registration roller pair 3, an image forming unit 50, a fixing unit 7, a discharge conveyance path 8, and a discharge tray 9. It is configured to include. The image forming unit 50 includes image forming units 5B, 5M, 5C, and 5Y (hereinafter collectively referred to as "image forming unit 5") for each color of black (B) magenta (M), cyan (C), and yellow (Y). Are arranged in parallel, the belt conveyance unit 4 is disposed above the image forming unit 5, and the secondary transfer unit 6 (transfer unit) is disposed behind the belt conveyance unit 4.

  The image forming apparatus 1 performs the following image forming process. The sheet P is conveyed from the sheet feeding cassette 1 a of the sheet feeding unit 200 to the vertical conveyance path 202 by the pickup roller 1 b and is conveyed to the secondary transfer unit 6 through the registration roller pair 3.

  In the image forming unit 50, the intermediate transfer belt 11 (image carrier) is sent in the direction of the arrow by the driving roller 41. On the peripheral surface (first peripheral surface) of the intermediate transfer belt 11, toner images of yellow, cyan, magenta, and black are formed on the respective photosensitive drums 51 in the image forming units 5Y, 5C, 5M, and 5B. Are successively transferred to form a color toner image. The toner image formed here is secondarily transferred by the secondary transfer section 6 onto the paper P conveyed from the intermediate transfer belt 11 from the paper feed cassette 1a. A color toner image is formed on the paper P.

  Thereafter, the sheet P on which the unfixed toner image is transferred is conveyed from the secondary transfer unit 6 to the fixing unit 7. The fixing unit 7 includes a heating roller 7a and a pressure roller 7b that are rotationally driven by a motor (not shown) while being pressed against each other. The heating roller 7a and the pressure roller 7b convey the paper P to the discharge conveyance path 8 by rotating while the nip of the transferred paper P is pressed. A heater (not shown) is built in the heating roller 7a. The toner image is fixed on the paper P by being heated by the heat generated by the heater while the paper P is pressurized at the nip portion between the heating roller 7a and the pressure roller 7b.

  The rotation speed of the heating roller 7a and the pressure roller 7b, that is, the conveyance speed of the paper P by the fixing unit 7 is controlled by the image forming speed control unit 311 (FIG. 4).

  After the fixing process is performed by the fixing unit 7, the paper P is discharged to the discharge tray 9 through the discharge conveyance path 8.

  Next, the configuration of the image forming unit 50 that is a main component of the image forming apparatus 1 will be described in detail. The image forming unit 50 includes a belt conveyance unit 4, an image forming unit 5, and a belt cleaning unit 45.

  As shown in FIG. 2, the belt conveyance unit 4 includes a drive roller 41, a driven roller 42, and an endless intermediate transfer belt 11 that is stretched over the two rollers. The intermediate transfer belt 11 is maintained at an appropriate tension by a tension roller 44. In this state, the driving roller 41 receives driving force from the belt driving motor 411 (FIG. 4) and rotates in the clockwise direction in the drawing. When the driving roller 41 rotates in the clockwise direction, the intermediate transfer belt 11 wound around the driving roller 41 and the driven roller 42 rotates in the clockwise direction, and the driven roller 42 is driven to rotate in the clockwise direction.

  The drive roller 41 is driven so that the surface speed of the outer peripheral surface of the photosensitive drum 51 of each image forming unit and the feed speed of the intermediate transfer belt 11 are constant speeds close to constant speed. ing.

  The image forming units 5Y, 5C, 5M, and 5B are arranged side by side below the belt conveyance unit 4. The image forming units 5Y, 5C, 5M, and 5B are for yellow (Y), cyan (C), magenta (M), and black (B) in order from the front. Each of the image forming units 5Y, 5C, 5M, and 5B includes an unillustrated toner tank that stores the corresponding color toner. Each image forming unit 5 is composed of image forming units having substantially the same configuration except that the color of toner stored in the toner tank is different.

  The image forming unit 5 includes a photosensitive drum 51, a main charging device 52, an exposure device 53, a primary transfer roller 54, a cleaning device 55, and a developing device 56, and is assembled into a housing made of resin or the like as one unit. It is attached to the device body. The photosensitive drum 51 is charged by the main charging device 52 so that the dark potential at the development position becomes a predetermined potential. An electrostatic latent image is formed on the surface of the photosensitive drum 51 by the exposure device 53 irradiating the charged surface of the photosensitive drum 51 with light corresponding to image information.

  The developing device 56 charges toner particles supplied from a toner tank (not shown) to, for example, a positive charge and applies the toner particles to the surface of the developing roller 57. The charged toner particles are supplied from the developing roller 57 to the electrostatic latent image formed on the surface of the photosensitive drum 51, thereby developing the toner image on the photosensitive drum 51. Residual toner that has not been transferred onto the photosensitive drum 51 is removed by the cleaning device 55.

  Subsequently, in order to lower the residual potential on the surface of the photoconductive drum 51 and make it uniform, the photoconductive drum 51 is decharged by the static eliminating lamp 58 and is prepared for the next series of processes. As described above, the image forming apparatus 1 develops images corresponding to black, magenta, cyan, and yellow on the photosensitive drum 51 and sequentially repeats them on the intermediate transfer belt 11 in each image forming unit 5. By performing multiple transfer without deviation, one color image is formed.

  FIG. 3 is a schematic vertical sectional view showing a schematic structure in the vicinity of the belt cleaning unit 45 of the image forming unit 50 shown in FIG.

  The belt cleaning unit 45 includes a brush roller 45a (cleaning member), a recovery roller 45b, a cleaning blade 45c, a pre-brush 45d, a toner recovery screw 45e, and a casing 45f that accommodates these members.

  The brush roller 45 a is disposed to face the driven roller 42 with the intermediate transfer belt 11 interposed between the brush roller 45 a and the driven roller 42. The brush roller 45a is formed by brush hairs 452 being uniformly planted on the outer periphery of an axis 451 extending in parallel with the rotation axis of the driven roller 42. The tip end portion of the brush bristles 452 constitutes a virtual outer peripheral surface (second peripheral surface) of the brush roller 45a. Hereinafter, the virtual outer peripheral surface of the brush roller 45a is simply referred to as the outer peripheral surface of the brush roller 45a. The outer peripheral surface of the brush roller 45 a is in contact with the intermediate transfer belt 11.

  The brush roller 45a is rotationally driven in a counterclockwise direction (a direction opposite to the driven roller 42) by a brush drive motor 453 (FIG. 4). A current supplied from the constant current source 20 (FIG. 4) flows between the intermediate transfer belt 11 and the brush roller 45a. As a result, the residual toner attached to the peripheral surface of the intermediate transfer belt 11 is scraped off by the brush roller 45a, and the scraped residual toner moves from the intermediate transfer belt 11 to the brush roller 45a.

  The shaft core 451 and the brush bristles 452 are made of, for example, a material obtained by mixing a conductive material with acrylic. Thereby, electroconductivity is provided to the brush roller 45a.

  The collection roller 45b is a cylindrical member extending in parallel with the axis 451 of the brush roller 45a. The collection roller 45b is disposed such that the outer peripheral surface is in contact with the outer peripheral surface of the brush roller 45a. The collection roller 45b is made of, for example, sulfur composite free-cutting steel (SUM).

  The collection roller 45b is rotationally driven in a counterclockwise direction (the same direction as the brush roller 45a) by a motor (not shown).

  A current supplied from the constant current source 20 (FIG. 4) flows between the brush roller 45a and the collection roller 45b. Thereby, the residual toner adhering to the brush roller 45a adheres to the peripheral surface of the collection roller 45b.

  The cleaning blade 45c abuts against the collection roller 45b to scrape off residual toner attached to the peripheral surface of the collection roller 45b. The residual toner scraped off by the cleaning blade 45c is stored at the bottom of the casing 45f and is transported to a waste toner container (not shown) by the toner recovery screw 45e.

  The pre-brush 45d is disposed on the upstream side in the moving direction of the intermediate transfer belt 11 with respect to the brush roller 45a so as to contact the peripheral surface of the intermediate transfer belt 11. The prebrush 45d cleans the surface of the intermediate transfer belt 11 prior to the brush roller 45a. In this cleaning process, residual toner adhering to the surface of the intermediate transfer belt 11 is lifted off from the intermediate transfer belt 11, so that the brush roller 45 a can more effectively clean the residual toner from the intermediate transfer belt 11. Can be done.

  FIG. 4 is a block diagram schematically showing an electrical configuration of the image forming apparatus 1 shown in FIG. The image forming apparatus 1 includes a control unit 300 that controls operation of the entire apparatus. The control unit 300 includes, for example, a CPU (Central Processing Unit) that executes predetermined arithmetic processing, a ROM (Read Only Memory) that stores a predetermined control program, and a RAM (Random Access Memory) that temporarily stores data. And these peripheral circuits and the like. The control unit 300 functions as an image formation control unit 310, an image formation speed control unit 311, and a cleaning speed control unit 312 by executing a control program stored in, for example, a ROM.

  The control unit 300 includes a belt drive motor 411 (first drive unit), a brush drive motor 453 (second drive unit), a constant current source, in addition to the operation panel 25, the fixing unit 7 and the image forming unit 50 described above. 20, a paper transport mechanism 400, a humidity sensor 21 (humidity detection unit), a temperature sensor 22, and a communication I / F unit 23 are connected. The paper transport mechanism 400 includes a paper feed unit 200, a vertical transport path 202, and a motor, a gear mechanism, and the like that rotationally drive a paper transport roller included in the discharge transport path 8.

  The belt drive motor 411 rotates the drive roller 41 to move the intermediate transfer belt 11 around. The brush drive motor 453 moves the outer peripheral surface of the brush roller 45 a relative to the peripheral surface of the intermediate transfer belt 11 by driving and rotating the brush roller 45 a.

  The constant current source 20 is a constant current circuit configured by, for example, a switching power supply circuit. The constant current source 20 causes a predetermined current Ic to flow between the intermediate transfer belt 11 and the brush roller 45a in accordance with a control signal from the control unit 300, thereby causing the constant current source 20 on the peripheral surface of the intermediate transfer belt 11 to flow. The charged residual toner is moved to the brush roller 45a.

  The humidity sensor 21 is disposed, for example, in the vicinity of the driven roller 42 and detects the humidity of the air around the intermediate transfer belt 11 as the humidity H related to the intermediate transfer belt 11. The humidity sensor 21 is not necessarily limited to the example in the vicinity of the driven roller 42 and the intermediate transfer belt 11. The humidity of the air near the intermediate transfer belt 11 has a correlation with the humidity inside the image forming apparatus 1 and the environmental humidity outside the image forming apparatus 1. Therefore, the humidity sensor 21 may be configured to detect the humidity inside the image forming apparatus 1 or the environmental humidity outside the image forming apparatus 1 as the humidity H related to the intermediate transfer belt 11.

  The temperature sensor 22 detects the temperature ta of the surrounding environment of the image forming apparatus 1.

  The communication I / F unit 23 is a communication interface circuit such as a wired LAN (Local Area Network), a wireless LAN, or a USB (Universal Serial Bus) interface. The communication I / F unit 23 transmits / receives data to / from an external terminal device such as a personal computer (not shown) via a communication cable (not shown) or by wireless communication. As a result, the communication I / F unit 23 receives image data representing an image to be formed on the paper P from the external terminal device.

  The image formation control unit 310 forms an image on the paper P by controlling the operation of each unit in the image forming apparatus 1 based on the image data received by the communication I / F unit 23.

  The image forming speed control unit 311 switches the conveyance speed of the paper P by the fixing unit 7 between a preset first conveyance speed Sf1 and a second conveyance speed Sf2 that is slower than the first conveyance speed Sf1. The image forming speed control unit 311 also has a first moving speed Sm1 that is set in advance as a speed at which the belt drive motor 411 moves the peripheral surface of the intermediate transfer belt 11, and a second moving speed that is slower than the first moving speed Sm1. Switch between Sm2.

  Specifically, when the thickness information acquired by the operation panel 25 indicates plain paper, the image forming speed control unit 311 sets the transport speed of the paper P by the fixing unit 7 to the first transport speed Sf1, and The speed at which the belt drive motor 411 moves the peripheral surface of the intermediate transfer belt 11 is set to the first movement speed Sm1. Further, when the thickness information acquired by the operation panel 25 indicates thick paper, the image forming speed control unit 311 sets the transport speed of the paper P by the fixing unit 7 to the second transport speed Sf2, and the belt drive motor 411. Causes the speed of moving the peripheral surface of the intermediate transfer belt 11 to the second moving speed Sm2.

  When the movement speed of the peripheral surface of the intermediate transfer belt 11 is the first movement speed Sm1, the cleaning speed control unit 312 determines that the relative speed of the outer peripheral surface of the brush roller 45a with respect to the peripheral surface of the intermediate transfer belt 11 is the first relative speed Sc1. The brush roller 45a is rotationally driven by the brush drive motor 453 so that Further, the cleaning speed control unit 312 determines that the relative speed of the outer peripheral surface of the brush roller 45a with respect to the peripheral surface of the intermediate transfer belt 11 is the first relative speed when the moving speed of the peripheral surface of the intermediate transfer belt 11 is the second moving speed Sm2. The brush roller 45a is rotationally driven by the brush drive motor 453 so that the second relative speed Sc2 is higher than the speed Sc1.

  Further, the cleaning speed control unit 312 increases the first relative speed Sc1 and the second relative speed Sc2, respectively, when the humidity H detected by the humidity sensor 21 is lower than a preset reference humidity Href. For example, 40% can be suitably used as the reference humidity Href.

  5 and 6 are flowcharts showing an example of the cleaning process for the intermediate transfer belt 11 by the image forming apparatus 1 shown in FIG. FIG. 7 is a conceptual explanatory diagram for explaining the cleaning process of the intermediate transfer belt 11 by the image forming apparatus 1 shown in FIG. First, the user operates the operation panel 25 to input thickness information indicating whether the paper P is plain paper or thick paper. Thereby, thickness information is acquired by the operation panel 25 (step S1).

  Note that the thickness information is not limited to information indicating whether the paper P is plain paper or thick paper. For example, the thickness information may be information representing the thickness of the paper P as a numerical value. For example, when the thickness of the paper P is equal to or less than a preset reference thickness, the image forming speed control unit 311 determines that the thickness of the paper P is the first thickness, and the thickness of the paper P is greater than the reference thickness. When it is thick, the thickness of the paper P may be determined as the second thickness.

  Further, the thickness information is not limited to the example acquired by the operation panel 25. For example, the thickness information may be transmitted from the external terminal device (not shown) to the communication I / F unit 23. In this case, the communication I / F unit 23 corresponds to a thickness information acquisition unit.

  Next, the image formation control unit 310 determines whether or not the paper P is a thick paper based on the thickness information acquired by the operation panel 25 (step S2). If the paper P is plain paper and not thick paper (NO in step S2), the image forming control unit 310 sets the print mode to the normal print mode (step S3).

  In the normal printing mode, the image formation control unit 310 performs the first conveyance in which the conveyance speed of the paper P by the fixing unit 7 is set in advance so that the fixing time in the fixing unit 7 is a time suitable for plain paper. The speed Sf1 is set (step S4). Further, in the normal printing mode, the image forming control unit 310 controls the rotational speed of the belt drive motor 411 so that the moving speed Sb of the peripheral surface of the intermediate transfer belt 11 is set to the first moving speed Sm1 (step S5). Then, the process proceeds to step S11.

  The conveyance speed of the sheet P conveyed from the secondary transfer unit 6 to the fixing unit 7 is equal to the moving speed of the peripheral surface of the intermediate transfer belt 11. Therefore, in order to smoothly carry the paper P from the secondary transfer unit 6 to the fixing unit 7, the speed at which the fixing unit 7 carries the paper P and the moving speed Sb of the peripheral surface of the intermediate transfer belt 11 are as follows. Need to be linked. Therefore, in the normal printing mode, the image forming control unit 310 sets the speed at which the fixing unit 7 transports the paper P as the first transport speed Sf1, and sets the moving speed Sb of the peripheral surface of the intermediate transfer belt 11 as the first moving speed Sm1. And The first moving speed Sm1 is a movement that allows the paper P to be smoothly transported from the secondary transfer unit 6 to the fixing unit 7 when the speed at which the fixing unit 7 transports the paper P is the first transport speed Sf1. The speed Sb is set in advance.

  On the other hand, if the sheet P is a thick sheet in step S2 (YES in step S2), the image formation control unit 310 sets the printing mode to the half-speed printing mode (step S6).

  When the paper P is a thick paper, the heat capacity of the paper P is larger than that of the plain paper. For this reason, the time required for the toner image formed on the paper P by the fixing unit 7 to be heated and melted and fixed on the paper P is longer when the paper P is a thick paper than when it is a plain paper.

  Therefore, if the paper P is a thick paper (YES in step S2), the image formation control unit 310 sets the printing mode to the half-speed printing mode (step S6), and sets the conveyance speed of the paper P by the fixing unit 7 to the second speed. The conveyance speed Sf2 is set (step S7). The second transport speed Sf2 is set to a speed slower than the first transport speed Sf1, for example, half the first transport speed Sf1.

  As a result, when the heat capacity of the paper P is larger than that of the plain paper because the paper P is a thick paper, the fixing time of the toner image onto the paper P by the fixing unit 7 becomes long. Therefore, regardless of the thickness of the paper P, the paper Fixing of the toner image onto P is good.

  Further, in the half-speed printing mode, the image formation control unit 310 controls the rotational speed of the belt drive motor 411 so that the moving speed Sb of the peripheral surface of the intermediate transfer belt 11 is set to the second moving speed Sm2 (step S8). ), The process proceeds to step S11. The second movement speed Sm2 is set to a speed slower than the first movement speed Sm1, for example, half the first movement speed Sm1. As a result, the conveyance of the paper P from the secondary transfer unit 6 to the fixing unit 7 can be performed smoothly.

  In step S11, the humidity sensor 21 measures the humidity H (step S11).

  Next, the cleaning speed control unit 312 compares the humidity H measured by the humidity sensor 21 with the reference humidity Href (step S12). When the humidity H is equal to or higher than the reference humidity Href and the humidity is high (NO in step S12), the cleaning speed control unit 312 proceeds to step S13 and determines whether or not the printing mode is the half speed printing mode. (Step S13).

  In step S13, when the printing mode is the normal printing mode (NO in step S13), that is, when the moving speed Sb of the intermediate transfer belt 11 is the first moving speed Sm1, the cleaning speed control unit 312 is the outer peripheral surface of the brush roller 45a. The rotational speed of the brush drive motor 453 is controlled so that the moving speed Sr of the toner becomes 1.2 times the moving speed Sb of the intermediate transfer belt 11 (step S14).

  In this case, the first relative speed Sc1, which is the relative speed of the outer peripheral surface of the brush roller 45a with respect to the intermediate transfer belt 11, is (Sb × 0.2).

  On the other hand, in step S13, when the printing mode is the half-speed printing mode (YES in step S13), that is, when the moving speed Sb of the intermediate transfer belt 11 is the second moving speed Sm2, the cleaning speed control unit 312 performs the brush roller 45a. The rotational speed of the brush drive motor 453 is controlled so that the movement speed Sr of the outer peripheral surface of the intermediate transfer belt 11 is 1.5 times the movement speed Sb of the intermediate transfer belt 11 (step S15).

  In this case, the second relative speed Sc2, which is the relative speed of the outer peripheral surface of the brush roller 45a with respect to the intermediate transfer belt 11, is (Sb × 0.5).

  In other words, the cleaning speed control unit 312 performs the processing of steps S13, S14, and S15 so that the brush roller 45a moves with respect to the peripheral surface of the intermediate transfer belt 11 when the movement speed of the peripheral surface of the intermediate transfer belt 11 is the first movement speed Sm1. The brush roller 45a is rotationally driven by the brush drive motor 453 so that the relative speed of the outer peripheral surface becomes the first relative speed Sc1 (= Sb × 0.2) (step S14), and the moving speed of the peripheral surface of the intermediate transfer belt 11 Is a second relative speed Sc2 (= Sb) in which the relative speed of the outer peripheral surface of the brush roller 45a with respect to the peripheral surface of the intermediate transfer belt 11 is higher than the first relative speed Sc1 (= Sb × 0.2). The brush roller 45a is rotationally driven by the brush drive motor 453 so as to be × 0.5) (step S15).

  On the other hand, when the humidity H is less than the reference humidity Href in step S12 and the humidity is low (YES in step S12), the cleaning speed control unit 312 proceeds to step S16 and determines whether the print mode is the half speed print mode. It is determined whether or not (step S16).

  In step S16, when the printing mode is the normal printing mode (NO in step S16), that is, when the moving speed Sb of the intermediate transfer belt 11 is the first moving speed Sm1, the cleaning speed control unit 312 performs the outer peripheral surface of the brush roller 45a. The rotational speed of the brush drive motor 453 is controlled so that the moving speed Sr of the intermediate transfer belt 11 becomes 1.5 times the moving speed Sb of the intermediate transfer belt 11 (step S15).

  In this case, the first relative speed Sc1, which is the relative speed of the outer peripheral surface of the brush roller 45a with respect to the intermediate transfer belt 11, is (Sb × 0.5).

  On the other hand, in step S16, when the printing mode is the half speed printing mode (YES in step S16), that is, when the moving speed Sb of the intermediate transfer belt 11 is the second moving speed Sm2, the cleaning speed control unit 312 performs the brush roller 45a. The rotation speed of the brush drive motor 453 is controlled so that the movement speed Sr of the outer peripheral surface of the intermediate transfer belt 11 becomes 2.0 times the movement speed Sb of the intermediate transfer belt 11 (step S17).

  In this case, the second relative speed Sc2, which is the relative speed of the outer peripheral surface of the brush roller 45a with respect to the intermediate transfer belt 11, is (Sb × 1.0).

  In other words, the cleaning speed control unit 312 performs the processing of steps S16, S15, and S17 so that the brush roller 45a moves relative to the peripheral surface of the intermediate transfer belt 11 when the movement speed of the peripheral surface of the intermediate transfer belt 11 is the first movement speed Sm1. The brush roller 45a is rotationally driven by the brush drive motor 453 so that the relative speed of the outer peripheral surface becomes the first relative speed Sc1 (= Sb × 0.5) (step S15), and the moving speed of the peripheral surface of the intermediate transfer belt 11 Is a second relative speed Sc2 (= Sb) in which the relative speed of the outer peripheral surface of the brush roller 45a with respect to the peripheral surface of the intermediate transfer belt 11 is higher than the first relative speed Sc1 (= Sb × 0.5). The brush roller 45a is rotationally driven by the brush drive motor 453 so as to be × 1.0) (step S17).

  Further, the case where the humidity H is different under the same conditions for the moving speed (printing mode) of the peripheral surface of the intermediate transfer belt 11 is as follows.

  When the humidity H is equal to or higher than the reference humidity Href (NO in step S12) and the moving speed of the peripheral surface of the intermediate transfer belt 11 is the first moving speed Sm1 (NO in step S13), the first relative speed Sc1 is ( Sb × 0.2) (step S14), when the humidity H is less than the reference humidity Href (YES in step S12), and the movement speed of the peripheral surface of the intermediate transfer belt 11 is the first movement speed Sm1 (step S14). The first relative speed Sc1 is set to (Sb × 0.5) (NO in S16) (step S15).

  That is, the cleaning speed control unit 312 increases the first relative speed Sc1 when the humidity H is lower than the reference humidity Href (step S15) and when the humidity H is equal to or higher than the reference humidity Href (step S14).

  When the humidity H is equal to or higher than the reference humidity Href (NO in step S12) and the moving speed of the peripheral surface of the intermediate transfer belt 11 is the second moving speed Sm2 (YES in step S13), the second relative speed Sc2 is ( Sb × 0.5) (step S15), when the humidity H is less than the reference humidity Href (YES in step S12), and the movement speed of the peripheral surface of the intermediate transfer belt 11 is the second movement speed Sm2 (step S15). The second relative speed Sc2 is set to (Sb × 1.0) (YES in S16) (step S17).

  That is, the cleaning speed control unit 312 increases the second relative speed Sc2 when the humidity H is lower than the reference humidity Href (step S17) and when the humidity H is equal to or higher than the reference humidity Href (step S15).

  Through the processing in steps S1 to S17, the sheet conveyance speed of the fixing unit 7, the moving speed Sb of the intermediate transfer belt 11, and the moving speed Sr of the outer peripheral surface of the brush roller 45a are set. The brush roller 45a is driven.

  Next, the image formation control unit 310 causes the constant current source 20 to cause a constant current Ic to flow between the driven roller 42 and the cleaning blade 45c (step S18). As a result, a current Ic flows through a current path from the driven roller 42 to the cleaning blade 45c via the intermediate transfer belt 11, the brush roller 45a, and the recovery roller 45b.

  Next, with reference to FIG. 7, the effect obtained by the processing of steps S11 to S18 described above will be described.

  First, when the printing mode is set to the normal printing mode (step S3) and the moving speed Sb of the intermediate transfer belt 11 is set to the first moving speed Sm1 (step S5), the moving distance of the intermediate transfer belt 11 per unit time is The movement distance Lb1. On the other hand, when the printing mode is set to the half speed printing mode (step S6) and the moving speed Sb of the intermediate transfer belt 11 is set to the second moving speed Sm2 (step S8), the moving distance of the intermediate transfer belt 11 per unit time. Is the moving distance Lb2. The movement distance Lb2 is shorter than the movement distance Lb1.

  Here, when the current Ic flows through the contact position A between the intermediate transfer belt 11 and the brush roller 45a, the area of the intermediate transfer belt 11 through which the current Ic flows during the unit time is the moving distance per unit time. The shorter it is, the narrower it is. Therefore, the area of the intermediate transfer belt 11 through which the current Ic flows during the unit time is narrower when the printing mode is the half-speed printing mode than when in the normal printing mode. A reduction in the area of the region of the intermediate transfer belt 11 through which the current Ic flows during the unit time means that the current density flowing through the intermediate transfer belt 11 increases.

  When the density of the current flowing through the intermediate transfer belt 11 is increased, the same effect as that of increasing the electrical resistance between the intermediate transfer belt 11 and the brush roller 45a is brought about. Since the constant current source 20 causes a constant current Ic to flow between the intermediate transfer belt 11 and the brush roller 45a, if the electrical resistance between the intermediate transfer belt 11 and the brush roller 45a increases, the intermediate transfer is performed according to Ohm's law. The voltage between the belt 11 and the brush roller 45a increases.

  When the voltage between the intermediate transfer belt 11 and the brush roller 45a rises and exceeds a predetermined voltage, a discharge occurs between the residual toner T on the intermediate transfer belt 11 and the brush roller 45a, and the residual toner T is charged to the opposite polarity. That is, the residual toner T that has been positively charged is negatively charged by discharge. The negatively charged residual toner T does not move from the intermediate transfer belt 11 to the brush roller 45a even when a current Ic is supplied from the intermediate transfer belt 11 to the brush roller 45a. As a result, the cleaning effect of the residual toner T by the brush roller 45a cannot be sufficiently obtained.

  Therefore, the cleaning speed control unit 312 changes the moving speed Sr of the outer peripheral surface of the brush roller 45a according to the printing mode, that is, according to the moving speed Sb of the intermediate transfer belt 11, by the processing of steps S13 to S17. Further, it is possible to reduce the possibility that the cleaning effect of the residual toner T is lowered by the discharge.

  Specifically, as described above, when the moving speed Sb of the intermediate transfer belt 11 is low (YES in Step S13), the cleaning speed control unit 312 moves the brush roller 45a relative to the intermediate transfer belt 11 in the half-speed printing mode. The relative speed of the outer peripheral surface is made faster (step S15) than when the moving speed Sb is high in the normal printing mode (step S14).

  As a result, when the moving speed Sb of the intermediate transfer belt 11 decreases and the voltage between the intermediate transfer belt 11 and the brush roller 45a increases, the unit of the outer peripheral surface of the brush roller 45a with respect to the intermediate transfer belt 11 The relative travel distance per time is increased. If the relative movement distance per unit time of the outer peripheral surface of the brush roller 45a with respect to the intermediate transfer belt 11 is increased, an effect of lowering the electrical resistance between the intermediate transfer belt 11 and the brush roller 45a is generated. An increase in voltage between the belt 11 and the brush roller 45a can be suppressed.

  As a result, the possibility that electric discharge is generated between the intermediate transfer belt 11 and the brush roller 45a is reduced, so that the possibility that the cleaning effect of the residual toner T is lowered by electric discharge can be reduced.

  Also in steps S15 to S17, the same effects as in steps S13 to S15 described above can be obtained.

  In addition, the electrical resistance between the intermediate transfer belt 11 and the brush roller 45a may increase due to the influence of humidity. That is, when the humidity is high, moisture absorption occurs in the residual toner T, the intermediate transfer belt 11, the brush roller 45a, and the like. As a result, the electrical resistance between the intermediate transfer belt 11 and the brush roller 45a decreases. On the other hand, when the humidity is low, the residual toner T, the intermediate transfer belt 11, the brush roller 45a, and the like are dried, and the electrical resistance between the intermediate transfer belt 11 and the brush roller 45a increases. Since the constant current source 20 causes a constant current Ic to flow between the intermediate transfer belt 11 and the brush roller 45a, if the electrical resistance between the intermediate transfer belt 11 and the brush roller 45a increases, the intermediate transfer is performed according to Ohm's law. The voltage between the belt 11 and the brush roller 45a increases.

  Therefore, when the humidity around the intermediate transfer belt 11 is low, as in the case of the half-speed printing mode, a discharge occurs between the residual toner T on the intermediate transfer belt 11 and the brush roller 45a, and the residual toner generated by the brush roller 45a. A sufficient T cleaning effect cannot be obtained.

  Therefore, the cleaning speed control unit 312 increases the first relative speed Sc1 when the humidity H is lower than the reference humidity Href (YES in Step S12) than when the humidity H is equal to or higher than the reference humidity Href (Step S14) ( Step S15). Further, the cleaning speed control unit 312 increases the second relative speed Sc2 when the humidity H is lower than the reference humidity Href (YES in step S12) than when the humidity H is equal to or higher than the reference humidity Href (step S15) ( Step S17).

  As a result, an effect of lowering the electrical resistance between the intermediate transfer belt 11 and the brush roller 45a is produced, so that an increase in voltage between the intermediate transfer belt 11 and the brush roller 45a can be suppressed. And the possibility of electric discharge between the brush roller 45a is reduced. As a result, it is possible to reduce the possibility that the cleaning effect of the residual toner T is lowered due to discharge at low humidity.

  FIG. 8 is a graph showing the relationship between the voltage Vc between the intermediate transfer belt 11 and the brush roller 45a and the current Ic. The horizontal axis represents current Ic, and the vertical axis represents voltage Vc. In FIG. 8, the current Ic represents the current in the direction from the brush roller 45a to the driven roller 42 as + polarity, and the voltage Vc represents the intermediate transfer belt when the potential of the intermediate transfer belt 11 (driven roller 42) is 0V. 11 and the voltage between the brush roller 45a.

  In the graph shown in FIG. 8, a cleanable area B surrounded by a frame line indicates an area in which no discharge is generated between the intermediate transfer belt 11 and the brush roller 45a, and therefore the intermediate transfer belt 11 can be cleaned. ing. Hereinafter, the ratio of the moving speed Sr of the outer peripheral surface of the brush roller 45a to the moving speed Sb of the intermediate transfer belt 11 is referred to as a linear speed ratio. Further, a temperature of 23 ° C. and a humidity of 50% are referred to as normal temperature and normal humidity, and a temperature of 10 ° C. and a humidity of 15% are referred to as low temperature and low humidity.

  Graph G1 is a graph when the normal printing mode is set at normal temperature and humidity and the linear speed ratio is 1.2. Graph G2 is a graph when the half-speed printing mode is set at normal temperature and humidity and the linear speed ratio is 1.2. Graph G3 is a graph when the half-speed printing mode is set at normal temperature and humidity and the linear speed ratio is 1.5. Graph G4 is a graph when the normal printing mode is set at low temperature and low humidity and the linear velocity ratio is 1.2. Graph G5 is a graph when the normal printing mode is set at low temperature and low humidity and the linear speed ratio is 1.5. Graph G6 is a graph when the low-temperature and low-humidity mode is set to the half-speed printing mode and the linear speed ratio is 1.2. Graph G7 is a graph when the low-temperature and low-humidity mode is set to the half-speed printing mode and the linear speed ratio is 2.0.

  The graph G2 is out of the range of the cleanable area B when the current Ic is −10.0 μA. Under the conditions of the graph G2, the cleaning speed control unit 312 is NO in step S12, YES in step S13, and sets the linear speed ratio to 1.5 (step S15). Thereby, the conditions of the graph G3 are satisfied. Since the graph G3 is within the range of the cleanable region B when the current Ic is −10.0 μA, the cleaning speed control unit 312 changes the condition of the graph G2 to the condition of the graph G3 that can be cleaned. .

  The graph G4 is out of the range of the cleanable area B when the current Ic is −5.0 μA. Under the conditions of the graph G4, the cleaning speed control unit 312 becomes YES in step S12, NO in step S16, and sets the linear speed ratio to 1.5 (step S15). Thereby, the condition of the graph G5 is satisfied. Since the graph G5 is within the cleanable region B when the current Ic is −5.0 μA, the cleaning speed control unit 312 changes the condition of the graph G4 to the condition of the graph G5 that can be cleaned. .

  The graph G6 is out of the range of the cleanable area B when the current Ic is −5.0 μA. Under the condition of the graph G6, the cleaning speed control unit 312 becomes YES in step S12, YES in step S16, and sets the linear speed ratio to 2.0 (step S17). Thereby, the conditions of the graph G7 are satisfied. Since the graph G7 is within the range of the cleanable region B when the current Ic is −5.0 μA, the cleaning speed control unit 312 changes the condition of the graph G6 to the condition of the graph G7 that can be cleaned. .

  As described above, it was confirmed from the graph shown in FIG. 8 and the flowchart shown in FIG. 6 that the image forming apparatus 1 can reduce the possibility that the cleaning effect is reduced.

  Note that, under normal weather conditions, the humidity decreases in a low temperature environment such as winter, and the humidity increases in a high temperature environment such as summer. Therefore, for example, the reference temperature tref is set in advance, and in step S11, the temperature ta is measured by the temperature sensor 22 in addition to the humidity H. In step S12, when the humidity H <Href and the temperature ta <tref. You may make it transfer to step S16. In this case, for example, a temperature of about 15 ° C. can be used as the reference temperature tref.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 4 Belt conveyance part 5 Image forming unit 6 Secondary transfer part (transfer part)
7 Fixing part 7a Heating roller 7b Pressure roller 11 Intermediate transfer belt (image carrier)
20 Constant current source 21 Humidity sensor (humidity detector)
22 Temperature sensor 23 Communication I / F part (Thickness information acquisition part)
25 Operation panel (thickness information acquisition unit)
41 Driving roller 42 Followed roller 44 Tension roller 45 Belt cleaning unit 45a Brush roller (cleaning member)
45b Recovery roller 45c Cleaning blade 45d Pre-brush 45e Toner recovery screw 45f Casing 50 Image forming unit 51 Photoreceptor drum 52 Main charging device 53 Exposure device 54 Primary transfer roller 55 Cleaning device 56 Development device 57 Development roller 58 Static elimination lamp 251 Operation key 252 LCD touch panel 300 Control unit 310 Image formation control unit 311 Image formation speed control unit 312 Cleaning speed control unit 411 Belt drive motor (first drive unit)
451 Shaft core 452 Brush hair 453 Brush drive motor (second drive part)
B Cleanable area H Humidity Href Reference humidity Ic Current P Paper (sheet)
Sb, Sr Travel speed Sf1 First transport speed Sf2 Second transport speed Sm1 First travel speed Sm2 Second travel speed T Residual toner

Claims (3)

An image carrier having a first peripheral surface for carrying a toner image formed by charged toner;
A first drive unit that moves around the first circumferential surface;
A transfer unit disposed at a facing position facing the first circumferential surface, and transferring the toner image carried on the first circumferential surface to the sheet at the facing position;
A cleaning member disposed on the downstream side in the circumferential movement direction with respect to the facing position and having a second peripheral surface in contact with the first peripheral surface;
A second drive unit that moves the second peripheral surface relative to the first peripheral surface;
A constant current source that moves the charged toner on the first peripheral surface to the cleaning member by flowing a predetermined constant current between the first peripheral surface and the cleaning member;
An image forming speed control unit that switches a speed of moving the first circumferential surface by the first driving unit between a predetermined first moving speed and a second moving speed that is slower than the first moving speed;
When the speed of moving the first peripheral surface by the first drive unit is the first movement speed, the relative speed of the second peripheral surface to the first peripheral surface is set to a predetermined first relative speed. When the second drive unit moves the second peripheral surface and the first drive unit moves the first peripheral surface at the second movement speed, the second peripheral surface with respect to the first peripheral surface An image forming apparatus comprising: a cleaning speed control unit that moves the second peripheral surface by the second driving unit so that a relative speed becomes a second relative speed higher than the first relative speed. A humidity detector for detecting the humidity of the image carrier;
The image forming apparatus according to claim 1, wherein the cleaning speed control unit increases the first and second relative speeds when the humidity detected by the humidity detection unit is lower than a predetermined reference humidity. A fixing unit that fixes the toner image on the sheet by heating the sheet on which the toner image has been transferred by the transfer unit while heating the sheet;
A thickness information acquisition unit that acquires thickness information indicating the thickness of the sheet;
The image forming speed control unit
When the thickness of the sheet indicated by the thickness information is a predetermined first thickness, the sheet conveying speed by the fixing unit is set to a predetermined first conveying speed, and the first driving unit is The speed of moving one circumferential surface is the first moving speed,
When the thickness of the sheet indicated by the thickness information is a second thickness that is greater than the first thickness, the conveyance speed of the sheet by the fixing unit is set to a second conveyance speed that is slower than the first conveyance speed, The image forming apparatus according to claim 1, wherein a speed at which the first driving unit moves the first peripheral surface is set to the second moving speed.

Images