JP2015194777A - Belt unit and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a belt unit which can prevents toner falling from an endless belt from being deposited on a read surface of a read part, and an image forming apparatus.SOLUTION: An image forming apparatus 100 includes an intermediate transfer unit 2 comprising an intermediate transfer belt 21, a read part 25, and an auxiliary roller 26. The intermediate transfer belt 21 is stretched on a driving roller 22 and a driven roller 23, and moves along a predetermined circulation path. The read part 25 reads density of a toner image from a surface of the intermediate transfer belt 21. The auxiliary roller 26 comes into contact with a rear face of the intermediate transfer belt 21 so that a distance between a read surface of the read part 25 and the surface of the intermediate transfer belt 21 is constant. The auxiliary roller 26 is arranged downstream of the read part 25 in a horizontal direction by a predetermined distance S. The predetermined distance S is a distance from a center O of the read part 25 in the horizontal direction to a contact point P where the auxiliary roller 26 comes into contact with the intermediate transfer belt 21.

Description

  The present invention relates to a belt unit and an image forming apparatus including a reading unit that reads a toner image carried on the surface of an endless belt.

  Some electrophotographic image forming apparatuses include a belt unit that transfers a toner image onto a transfer target using an endless belt.

  The belt unit cannot maintain the density of the toner image carried on the endless belt properly due to changes in the environment such as temperature and humidity, and changes over time such as deterioration of the image carrier and toner. May occur. Therefore, the belt unit forms a reference toner image on the endless belt under predetermined image forming conditions, reads the density of the reference toner image from the surface of the endless belt by the reading unit, and the read density is equal to the predetermined reference density. In some cases, the density of the toner image is adjusted by changing the image forming conditions (see, for example, Patent Document 1). In order for the reading unit to accurately read the density, it is necessary to prevent the endless belt from wavy while keeping the distance between the reading unit and the surface of the endless belt constant. The roller is in contact.

  Some reading units are used for detecting the amount of meandering of the endless belt when adjusting the meandering of the endless belt.

JP 2008-241958 A

  However, in the endless belt, the contact portion with the auxiliary roller is curved, so that the toner may fall from the curved surface. If the dropped toner adheres to the reading surface, the reading unit cannot accurately read the toner image from the surface of the endless belt.

  An object of the present invention is to provide a belt unit and an image forming apparatus that can prevent toner dropped from an endless belt from adhering to a reading surface of a reading unit.

  The belt unit of the present invention includes an endless belt, a reading unit, an auxiliary roller, and a moving mechanism. The endless belt is stretched between a driving roller and a driven roller, and a surface carrying a toner image is supported so as to be freely circulated along a predetermined moving direction. The reading unit is disposed below the endless belt in the vertical direction, and reads a toner image from the surface of the endless belt. The auxiliary roller is spaced from the back surface and the abutting position where it contacts the back surface of the endless belt on the upstream side of the driving roller and on the downstream side of the driven roller so that the distance between the reading surface of the reading unit and the surface of the endless belt is constant. The center of rotation is positioned downstream from the center of the reading surface by a distance equal to or greater than the radius in the horizontal direction. The moving mechanism positions the auxiliary roller at the contact position only during reading by the reading unit.

  A shutter configured to be movable between an open position that opens the reading surface and a closed position that closes the reading surface; and an open / close mechanism that positions the shutter in the open position only when reading by the reading unit. Is preferred.

  A sensor configured to detect whether or not the auxiliary roller is located at the contact position; a shutter configured to be movable between an open position that opens the reading surface and a closed position that closes the reading surface; and an auxiliary roller It is preferable to further include an opening / closing mechanism that positions the shutter in the open position when the sensor detects that the shutter is in the contact position.

  The image forming apparatus of the present invention includes a photoreceptor, the above-described belt unit, and a transfer member. The photoreceptor carries a toner image on the surface. The transfer member transfers the toner image from the surface of the photoreceptor to an intermediate transfer belt that is an endless belt.

  According to the present invention, it is possible to prevent the toner dropped from the endless belt from adhering to the reading surface of the reading unit.

1 is a schematic diagram of a part of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged view of a vicinity of a reading unit and an auxiliary roller of the image forming apparatus. The toner adhesion state, the reading result, and the measurement result of the reading result. 2 is a block diagram of a control unit of the image forming apparatus. FIG. It is a flowchart which shows the density | concentration adjustment process in the same control part.

  An image forming apparatus including an intermediate transfer unit which is a belt unit of the present invention will be described with reference to the drawings. As illustrated in FIG. 1, the image forming apparatus 100 includes, for example, a process unit 1, an intermediate transfer unit 2, and a control unit 200, and an image input from an external device (not shown) based on an instruction from the control unit 200. An image forming process is performed on the paper by electrophotography using the data.

  The process unit 1 includes an exposure unit 11 and photosensitive drums 12A to 12D. The process unit 1 irradiates image light based on the image data from the exposure unit 11 to form electrostatic latent images on the surfaces of the photosensitive drums 12A to 12D, and supplies toner to visualize the electrostatic latent images as toner images. To do.

  The intermediate transfer unit 2 includes an intermediate transfer belt (corresponding to an endless belt of the present invention) 21, a driving roller 22, a driven roller 23, primary transfer rollers 24A to 24D, a reading unit 25, and an auxiliary roller 26. The intermediate transfer belt 21 is stretched around the driving roller 22 and the driven roller 23, and moves along a circulation path that passes through the photosensitive drums 12D, 12C, 12B, and 12A in this order.

The primary transfer rollers 24A to 24D are disposed to face the photosensitive drums 12A to 12D with the intermediate transfer belt 21 interposed therebetween. The primary transfer rollers 24 </ b> A to 24 </ b> D are between a contact position where the surface of the intermediate transfer belt 21 contacts the photosensitive drums 12 </ b> A to 12 </ b> D and a separation position where the surface of the intermediate transfer belt 21 is separated from the photosensitive drums 12 </ b> A to 12 </ b> D. It is configured to be movable. The primary transfer rollers 24 </ b> A to 24 </ b> D primarily transfer the toner images from the surfaces of the photosensitive drums 12 </ b> A to 12 </ b> D to the surface of the intermediate transfer belt 21 when a primary transfer voltage is applied.
The reading unit 25 is an optical sensor having a light emitting element such as an LED and a light receiving element such as a photodiode, and reads the density of the toner image from the surface of the intermediate transfer belt 21. The reading unit 25 is disposed with the reading surface facing the surface side of the intermediate transfer belt 21. The reading unit 25 irradiates the surface of the intermediate transfer belt 21 with measurement light from the light emitting element, and receives the reflected light reflected on the surface of the intermediate transfer belt 21 by the light receiving element. The reading unit 25 reads the density of the toner image according to the amount of light received by the light receiving element because the amount of light differs between the reflected light on the surface of the intermediate transfer belt 21 and the reflected light of the toner.

  As shown in FIG. 2, a shutter 251 is provided between the reading surface of the reading unit 25 and the surface of the intermediate transfer belt 21. The shutter 251 is configured to be movable between a closed position where the reading surface of the reading unit 25 is closed and an open position where the reading surface of the reading unit 25 is opened. The shutter 251 is connected to a shutter solenoid 45 and moves to an open position when the shutter solenoid 45 is energized, and moves to a closed position when the shutter solenoid 45 is not energized.

  The auxiliary roller 26 is in contact with the back surface of the intermediate transfer belt 21 and spaced apart from the back surface of the intermediate transfer belt 21 so that the distance between the reading surface of the reading unit 25 and the surface of the intermediate transfer belt 21 is constant. It is configured to be movable between positions. The auxiliary roller 26 is connected to an auxiliary roller solenoid 44 and moves to a contact position when the auxiliary roller solenoid 44 is energized, and moves to a separated position when the auxiliary roller solenoid 44 is not energized.

  The auxiliary roller 26 is disposed downstream of the reading unit 25 in the horizontal direction by a predetermined distance S. The predetermined distance S is a distance from the center O of the reading unit 25 in the horizontal direction to the contact point P where the auxiliary roller 26 contacts the intermediate transfer belt 21.

  FIG. 3 shows the measurement of toner adhesion, readability, and read result for each predetermined distance S when the radius R of the auxiliary roller 26 is 5 mm and the distance L from the center of the reading unit 25 to one end is 2 mm. Results are shown.

  The toner adhesion state indicates the degree to which the toner dropped from the intermediate transfer belt 21 has adhered to the reading surface of the reading unit 25. ◎ indicates no adhesion, ○ indicates almost no adhesion, Δ indicates slight adhesion, and X indicates a large amount of adhesion.

  The readability indicates whether or not the toner image can be read from the surface of the intermediate transfer belt 21 using the reading unit 25 where the toner is not attached to the reading surface. ◎ indicates good readability, ○ indicates readability, Δ indicates partial readability, and X indicates non-readability.

  The reading result indicates whether or not the reading result by the reading unit 25 after use for a predetermined period is correct. ○ indicates correct reading, Δ indicates incorrect reading, and x indicates imprecise reading.

  When the predetermined distance S is shorter than the radius R of the auxiliary roller 26, the toner adheres to the reading surface of the reading unit 25, so the density cannot be read accurately. When the predetermined distance S is made to coincide with the radius R of the auxiliary roller 26, toner does not adhere to the reading surface of the reading unit 25, and the waviness of the intermediate transfer belt 21 can be prevented, so that the density can be read accurately. In addition, when the predetermined distance S is longer than the radius R of the auxiliary roller 26, the waviness of the intermediate transfer belt 21 cannot be prevented, and thus the density cannot be read accurately.

  From the above, the predetermined distance S is the distance of the radius R of the auxiliary roller 26. As a result, the toner does not adhere to the reading surface dropped from the surface of the intermediate transfer belt 21 and the wavyness of the intermediate transfer belt 21 can be prevented, so that the reading unit 25 accurately detects the toner image from the surface of the intermediate transfer belt 21. The density can be read.

  As shown in FIG. 4, the control unit 200 is connected to the operation unit 40, the reading unit 25, the auxiliary roller solenoid 44, the shutter solenoid 45, and the motor 46.

  The operation unit 40 receives an image formation process start instruction, a density adjustment process start instruction, and the like. In the density adjustment process, the density of the toner image carried on the surface of the intermediate transfer belt 21 is detected, and the image forming condition is changed according to the detected density. The image forming conditions are, for example, the amount of toner supplied to the electrostatic latent image, the amount of image light by the exposure unit 11, the voltage value of the primary transfer voltage, and the like. The density adjustment process is also performed when the image forming apparatus 100 is turned on, every predetermined number of image forming processes, or during an error process in the image forming process.

  Each of the solenoid drivers 441 and 451 selectively energizes each of the auxiliary roller solenoid 44 and the shutter solenoid 45 based on the switching data. The motor driver 461 selectively supplies power to the motor 46 based on the drive data. The motor 46 is connected to the drive mechanism 30. The drive mechanism 30 displaces the primary transfer rollers 24 </ b> A to 24 </ b> D to the contact position or the separation position when supplying power to the motor 46, so that the color attitude, which is the attitude when forming a color image, and the attitude when forming a monochrome image. It moves in order to a monochrome posture and a standby posture that is a posture during non-image formation. In the color posture, the primary transfer rollers 24A to 24D are positioned at the contact positions. In the monochrome posture, the primary transfer roller 24A is located at the contact position, and the primary transfer rollers 24B to 24D are located at the separated positions. In the standby posture, the primary transfer rollers 24A to 24D are positioned at the standby position.

  The control unit 200 includes a CPU 41, a ROM 42, a RAM 43, solenoid drivers 441 and 451, and a motor driver 461. The CPU 41 reads out various programs stored in the ROM 42 and executes the various programs using the RAM 43 as a working area.

  The CPU 41 performs image formation processing and density adjustment processing. The CPU 41 outputs drive data to the motor driver 461 so as to supply power to the motor 46 during the image forming process and the density adjustment process. Further, the CPU 41 outputs switching data to the solenoid drivers 441 and 451 so as to energize the auxiliary roller solenoid 44 and the shutter solenoid 45 only during the density adjustment processing.

  Hereinafter, the density adjustment processing by the control unit 200 will be described with reference to FIG. As shown in FIG. 5, the control unit 200 waits until the start timing of the density adjustment process (S11). At the start timing of the density adjustment process, the control unit 200 drives the motor 46 to move to the color posture (S12). The control unit 200 energizes the auxiliary roller solenoid 44 to move the auxiliary roller 26 to the contact position (S13). The control unit 200 determines whether or not the position of the auxiliary roller 26 is the contact position based on a detection result of a sensor (not shown) that detects whether or not the auxiliary roller 26 is positioned at the contact position. (S14). When the auxiliary roller 26 is not located at the contact position, the control unit 200 performs error processing (S15) and ends the processing.

  When the auxiliary roller 26 is located at the contact position, the controller 200 energizes the shutter solenoid 45 to move the shutter 251 to the open position (S16). The control unit 200 determines whether the position of the shutter 251 is the open position based on the detection result of a sensor (not shown) that detects whether the shutter 251 is located at the open position (S17). When the shutter 251 is not located at the open position, the control unit 200 performs error processing (S15) and ends the processing.

  When the shutter 251 is located at the open position, the control unit 200 instructs the process unit 1 to form toner images for each hue on the surfaces of the photosensitive drums 12A to 12D (S18), and the primary transfer roller 24A. A primary transfer voltage is applied to .about.24D, and a toner image for each hue is sequentially transferred from the surface of each of the photosensitive drums 12A to 12D so as not to overlap the intermediate transfer belt 21 (S19). The control unit 200 acquires the density of the toner image for each hue read by the reading unit 25 (S20). The controller 200 stops energization of the shutter solenoid 45 and moves the shutter 251 to the closed position (S21). The controller 200 stops energization of the auxiliary roller solenoid 44 and moves the auxiliary roller 26 to the separated position (S22). The control unit 200 drives the motor 46 to move to the standby posture (S23). Based on the toner image density for each hue acquired from the reading unit 25, the control unit 200 changes the image forming conditions for all hue toner images (S24).

  As described above, since the shutter 251 is positioned at the closed position except when the density is read by the reading unit 25, the toner dropped from the intermediate transfer belt 21 does not reliably adhere to the reading surface of the reading unit 25. For this reason, it is possible to reliably prevent the reading surface of the reading unit 25 from being contaminated by the dropped toner.

  Further, the auxiliary roller 26 is moved to the contact position before the reading surface of the reading unit 25 is opened by the shutter 251, and the auxiliary roller 26 is moved to the separation position after the reading surface of the reading unit 25 is closed by the shutter 251. The toner that falls due to the impact force when the auxiliary roller 26 contacts the transfer belt 21 does not adhere to the reading surface of the reading unit 25.

  In the above-described embodiment, the density adjustment processing is performed by moving to the color posture. However, the density adjustment processing may be performed by moving to the monochrome posture. In the monochrome posture, it is possible to adjust the image forming condition regarding the black toner image.

  In the image forming apparatus 100 of the present invention, the toner image is transferred to the sheet via the intermediate transfer belt 21. However, the present invention is not limited to this, and the sheet passing between the photosensitive drums 12A to 12D and the transfer belt is used. The toner images may be directly transferred from the photosensitive drums 12A to 12D.

  The endless belt of the present invention is not limited to the intermediate transfer belt 21 and may be any belt that carries a toner image. The reading unit 25 may read the meandering amount of the endless belt when adjusting the meandering of the endless belt such as the intermediate transfer belt 21, the secondary transfer belt, or the transfer belt. In this case, the endless belt is not limited to a belt carrying a toner image.

  The intermediate transfer unit 2 that is a belt unit of the present invention includes an intermediate transfer belt 21 that is an endless belt, a reading unit 25, and an auxiliary roller 26. The intermediate transfer belt 21 is supported such that a surface carrying a toner image can be circulated and moved along a predetermined movement direction. The reading unit 25 is disposed below the intermediate transfer belt 21 in the vertical direction, and reads a toner image from the surface of the intermediate transfer belt 21. The auxiliary roller 26 is in contact with the back surface of the intermediate transfer belt 21 so that the distance between the reading surface of the reading unit 25 and the surface of the intermediate transfer belt 21 is constant, and is a predetermined distance S on the downstream side of the reading unit 25 in the horizontal direction. To position. The predetermined distance S is a distance from the center O of the reading surface to the contact point P where the auxiliary roller 26 contacts the intermediate transfer belt 21 in the horizontal direction.

  The contact portion of the intermediate transfer belt 21 with the auxiliary roller 26 is curved by the contact of the auxiliary roller 26. The toner on the curved surface of the intermediate transfer belt 21 drops from the lower side in the vertical direction of the auxiliary roller 26 to the downstream side of the auxiliary roller 26 in the moving direction due to the gravity of the toner and the inertial force accompanying the movement of the surface of the intermediate transfer belt 21. There are things to do. The dropped toner hardly adheres to the reading surface of the reading unit 25 located on the upstream side of the auxiliary roller 26 in the horizontal direction. The reading unit 25 can accurately read the toner image from the surface of the intermediate transfer belt 21 because the toner hardly adheres to the reading surface.

  The auxiliary roller 26 is located between a contact position that contacts the intermediate transfer belt 21 and a spaced position that separates from the intermediate transfer belt 21 so that the distance between the reading surface of the reading unit 25 and the surface of the intermediate transfer belt 21 is constant. In the case of being configured to be movable, it is preferable to further include an auxiliary roller solenoid 44 and a control unit 200 which are moving mechanisms that position the auxiliary roller 26 at the contact position only when reading by the reading unit 25.

  The auxiliary roller 26 moves from the separated position to the contact position during reading by the reading unit 25. The toner on the surface of the intermediate transfer belt 21 falls to the downstream side of the reading unit 25 in the horizontal direction due to the impact force when the auxiliary roller 26 contacts the intermediate transfer belt 21. The reading unit 25 can accurately read the toner from the surface of the intermediate transfer belt 21 because the toner dropped from the surface of the intermediate transfer belt 21 is difficult to adhere to the reading surface.

  A shutter 251 configured to be movable between an open position for opening the reading surface and a closed position for closing the reading surface, and an opening / closing mechanism that positions the shutter 251 in the open position only when reading by the reading unit 25 is performed. It is preferable to further include a shutter solenoid 45 and a control unit 200.

  Except when reading by the reading unit 25, the reading surface of the reading unit 25 is closed by the shutter 251, so that the dropped toner is not attached.

  The predetermined distance S is preferably a distance of the radius R of the auxiliary roller 26.

  Since the auxiliary roller 26 is in contact with a position separated from the center O of the reading unit 25 by a distance of the radius R of the auxiliary roller 26 in the horizontal direction, the undulation of the intermediate transfer belt 21 facing the center O of the reading unit 25 is prevented. can do. As a result, the reading unit 25 can accurately read the toner image from the surface of the intermediate transfer belt 21. Further, the reading unit 25 can hardly read the toner image from the surface of the intermediate transfer belt 21 because the toner dropped from the surface of the intermediate transfer belt 21 is difficult to adhere to the reading surface.

  An image forming apparatus 100 according to the present invention includes photosensitive drums 12A to 12D that are photosensitive members, the above-described intermediate transfer unit 2, and primary transfer rollers 24A to 24D that are transfer members. The photoconductor drums 12A to 12D carry toner images on their surfaces. The primary transfer rollers 24 </ b> A to 24 </ b> D transfer toner images from the surfaces of the photosensitive drums 12 </ b> A to 12 </ b> D to the intermediate transfer belt 21.

  In the image forming apparatus 100, since toner hardly adheres to the reading surface of the reading unit 25, the toner image can be accurately read from the surface of the intermediate transfer belt 21, and the toner image density adjustment and the intermediate transfer belt 21 meandering adjustment are possible. Therefore, poor image quality can be prevented.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

2. Intermediate transfer unit 21 Intermediate transfer belt 25 Reading unit 26 Auxiliary roller

Claims (4)

An endless belt that is stretched between a driving roller and a driven roller and is supported so that a surface carrying a toner image can be circulated and moved along a predetermined movement direction;
A reading unit that is disposed below the endless belt in the vertical direction and reads a toner image from the surface of the endless belt;
A contact position that contacts the back surface of the endless belt on the upstream side of the driving roller and the downstream side of the driven roller so that the distance between the reading surface of the reading unit and the surface of the endless belt is constant, and the back surface An auxiliary roller configured to be movable between a separation position and a separation position separated from the auxiliary roller, wherein the rotation center in the horizontal direction is located downstream from the center of the reading surface by a distance equal to or greater than the radius thereof;
A belt unit comprising: a moving mechanism that positions the auxiliary roller at the contact position only when reading by the reading unit. A shutter configured to be movable between an open position for opening the reading surface and a closed position for closing the reading surface;
The belt unit according to claim 1, further comprising an opening / closing mechanism that positions the shutter in the open position only when reading by the reading unit. A sensor for detecting whether or not the auxiliary roller is located at the contact position;
A shutter configured to be movable between an open position for opening the reading surface and a closed position for closing the reading surface;
The belt unit according to claim 1, further comprising: an opening / closing mechanism that positions the shutter in the open position when the sensor detects that the auxiliary roller is in the contact position. A photoreceptor carrying a toner image on the surface;
The belt unit according to any one of claims 1 to 3,
An image forming apparatus comprising: a transfer member that transfers a toner image from the surface of the photoreceptor to an intermediate transfer belt that is the endless belt.

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