JP2005084463A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of banding by reducing a change in the speed of an image carrier which results in a separation streak on an intermediate transfer body. <P>SOLUTION: An image forming apparatus includes: a latent image formation means for forming an electrostatic latent image on the image carrier 3; a development means for developing the electrostatic latent image into a toner image; a transfer means 13 for transferring the toner image to the intermediate transfer body 12; and a cleaning means which is brought into contact with the intermediate transfer body and separated therefrom in order to remove toner remaining on the intermediate transfer body. In the image forming apparatus, a countermeasure image 26 is formed on the intermediate transfer body upstream of a cleaning means separation position C1 in the direction of the advancement of the intermediate transfer body 12, and the formation of the latent image by the latent image formation means is initiated before the countermeasure image reaches a transfer position T1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic method, and more particularly to an image forming apparatus provided with a cleaning unit that removes toner remaining on an intermediate transfer member.

  In the image forming apparatus, the toner image primarily transferred from a latent image carrier such as a photosensitive member to an intermediate transfer member such as an intermediate transfer belt is secondarily transferred onto a recording medium such as transfer paper. Then, after the secondary transfer, the transfer residual toner remaining on the intermediate transfer member is removed from the intermediate transfer member by a cleaning means such as a cleaning blade that contacts the surface of the intermediate transfer member and scrapes the transfer residual toner. ing.

However, in the image forming apparatus having such a cleaning unit, when the cleaning blade is separated from the surface of the intermediate transfer member, a streak-like cleaning mark (hereinafter referred to as a separation line) is generated. In this image forming process, there arises a problem that the toner image is primarily transferred onto the intermediate transfer member. Therefore, conventionally, the separation timing of the cleaning unit is controlled on the basis of the toner image primarily transferred onto the intermediate transfer member so that the separation line of the cleaning unit does not enter the image area (see Patent Document 1). ).
JP 2000-231276 A

  FIG. 1 is a view showing a state in which the above-mentioned separating muscle 24 passes the transfer position T1. FIG. (A) shows a state in which the separation stripe 24 remains on the intermediate transfer body 12 and the separation position C1 advances to the primary transfer position T1, and FIG. (B) shows the separation stripe 24 at the primary transfer position T1. FIG. 8C shows a state where the separation line 24 passes through the primary transfer position T1, and the electrostatic latent image formed on the image carrier 3 is developed by the developing roller 6a.

  By the way, when the present inventor conducted various experiments, as described above, even if the separation line of the cleaning unit does not enter the image area, that is, the separation position is set to a predetermined position in the non-image area, the following is performed. It was found that such a problem occurred. That is, when the latent image writing operation is performed on the image carrier 3 when the separating stripe 24 is at the primary transfer position T1 as shown in FIG. It has been found that density unevenness and color misregistration accompanying so-called speed unevenness, so-called banding occurs. This is because if there is a separation line (toner) between the intermediate transfer member and the image carrier, the frictional force between the two decreases, and as a result, the image carrier slips and speed fluctuation occurs. ing.

FIG. 2 is a diagram showing experimental data obtained by measuring the speed fluctuation of the image carrier. In this experiment, the peripheral speed of the intermediate transfer member is set 0.7% faster than the peripheral speed of the image carrier, and Bk (black), C (cyan), M (magenta), and Y (yellow) are set on the intermediate transfer member. The toner images are transferred in this order. In FIG. 2, the vertical axis represents speed unevenness, the horizontal axis represents time,
(Rotation speed of the intermediate transfer member−rotation speed of the image carrier) / Rotation speed of the image carrier × 100. Therefore, the plus of the speed unevenness is slower than the intermediate transfer member, and the minus of the speed unevenness is It shows that the image carrier is faster than the intermediate transfer member. Here, the first large speed irregularity appears because of the disturbance of the signal that hits the belt joint of the encoder that detects the rotation, and it is ignored because it does not directly indicate the disturbance of the rotation.

  According to this, it can be seen that when the distance between the intermediate transfer members reaches the primary transfer position, remarkable speed unevenness occurs as shown by the arrows in FIG.

  This phenomenon is particularly remarkable when there is a speed difference between the rotation of the image carrier and the intermediate transfer member. Hereinafter, a case where the intermediate transfer member has a higher peripheral speed than the image carrier will be described. In general, a frictional force and an electrostatic attraction force act between the image carrier and the intermediate transfer member, and these two forces drive the image carrier to be pulled by the intermediate transfer member. However, if a separation line (toner) is locally present in the primary transfer region, the frictional force at that portion is rapidly reduced, and the force with which the intermediate transfer member pulls the image carrier is reduced. As a result, the image carrier is instantaneously slowed down. When a latent image is written on the image carrier at this time, the writing position is shifted and the above banding occurs.

  Further, the speed fluctuation of the image carrier is further promoted by the image carrier cleaning means. Hereinafter, a case where a cleaning blade is used as the cleaning means will be described. The cleaning blade uses a stick-slip phenomenon to remove toner. Therefore, stress is always applied to the tip of the cleaning blade, and when the speed of the image carrier is decreased for a moment, the stress at the tip of the blade is released, and this further promotes speed fluctuation.

  Further, at the primary transfer position, an electrostatic attraction force acts between the image carrier and the intermediate transfer member as described above, and the speed variation also depends on this force. That is, even if the frictional force due to the separating muscle is reduced, if the electrostatic attraction force is large, the influence of the change can be reduced. Conversely, if the electrostatic attraction force is weak, the speed fluctuation becomes large.

  The present invention solves the above-described conventional problems, and provides an image forming apparatus capable of reducing the fluctuation in the speed of the image carrier caused by the separation stripe on the intermediate transfer member and preventing the occurrence of banding. The purpose is to do.

Therefore, an image forming apparatus according to the present invention includes a latent image forming unit that forms an electrostatic latent image on an image carrier, a developing unit that develops the electrostatic latent image into a toner image, and the toner image that is an intermediate transfer member. In the image forming apparatus, the image forming apparatus includes: a transfer unit that transfers to the intermediate transfer member; and a cleaning unit that removes the toner remaining on the intermediate transfer member by contacting the intermediate transfer member. A countermeasure image is formed on the upstream side in the advancing direction of the body, and the latent image is formed by the latent image forming means after the countermeasure image has passed the transfer position.
The countermeasure image is a surface image including a cleaning unit separation position. Further, the toner amount of the countermeasure image is formed with a toner amount smaller than the toner amount at the cleaning unit separation position.
Further, the peripheral speeds of the image carrier and the intermediate transfer member are different at the transfer position.
The image carrier and the intermediate transfer member are each driven by a single drive motor via a gear train.

  According to the present invention, it is possible to reduce the speed fluctuation of the image carrier due to the separation stripe on the intermediate transfer member and to prevent the occurrence of banding.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a diagram showing an embodiment of an image forming apparatus according to the present invention, in which 1 is an image forming apparatus, 2 is a main body case, 3 is an image carrier such as a photoconductor, 4 is a charging device, 5 Is an exposure device (latent image forming means), 6 is a developing device (developing means), 7 is a photoreceptor cleaner, 12 is an intermediate transfer member comprising an intermediate transfer belt, 13 is a primary transfer roller (transfer means), 15 is 2 The next transfer roller, 16 is a power supply device, 17 is a paper feed tray, 20 is a fixing device, and 21 is a paper discharge tray.

  As shown in FIG. 3, the image forming apparatus 1 according to the present embodiment includes a paper discharge tray 21 formed on the upper portion of the main body case 2 and a front cover 2 a that is openably and detachably inserted on the front surface. In the main body case 2, a developing device 6 having a plurality of developing cartridges, an image carrier 3 on which an electrostatic latent image is formed and developed to form a toner image, and a toner image on the image carrier 3 are transferred. An intermediate transfer unit, a control unit for controlling each drive motor and bias, a power supply device 16, a paper feed tray 17 for storing a recording medium, a fixing device 20 for fixing a toner image on the recording medium, and the like are disposed. A paper transport unit 19 for transporting the recording medium from the paper feed tray 17 to the fixing device 20 through the secondary transfer roller 15 is disposed in the front cover 2a. Each unit and device is configured to be detachable from the main body, and can be removed and repaired or replaced integrally during maintenance or the like.

  The photoreceptor 3 as an image carrier has a thin cylindrical conductive substrate and a photosensitive layer formed on the surface thereof. On the outer periphery of the photosensitive member 3, a charging device 4 for uniformly charging the photosensitive member 3 along the rotation direction, an exposure device 5 for forming an electrostatic latent image on the photosensitive member 3, an electrostatic latent A developing device 6 for developing an image, an intermediate transfer belt 12 for transferring a toner image on the photoreceptor 3, a photoreceptor cleaner 7 for cleaning the surface of the photoreceptor 3 after primary transfer, and the like are provided. Yes.

  The intermediate transfer unit is composed of a driving roller 10 and a driven roller 11 and an endless intermediate transfer belt 12. The intermediate transfer unit is wound around both rollers 10 and 11 and is driven in the direction of the arrow in the drawing to transfer the toner image on the photoreceptor 3. An intermediate transfer belt 12, a primary transfer roller 13 that is disposed on the back surface of the intermediate transfer belt 12 so as to face the photoreceptor 3 and primarily transfers the toner image on the photoreceptor 3 to the intermediate transfer belt 12, and intermediate transfer A transfer belt cleaning unit 14 that removes residual toner on the belt 12 and a drive roller 10 are arranged to face the four-color full-color toner image formed on the intermediate transfer belt 12 as a recording medium (paper or the like). ) And a secondary transfer roller 15 for secondary transfer.

  A power supply device 16 is disposed below the exposure device 5, and a paper feed cassette 17 is disposed at the bottom of the main body case 2. A recording medium in the paper feed cassette 17 is a pickup roller 18, a sheet material conveyance path. 19, the secondary transfer roller 15, and the fixing device 20 are conveyed to the paper discharge tray 21. The paper feed cassette 17 is attached to the front of the apparatus by a handle 17b so that it can be pulled out, and an auxiliary cassette 17a is attached so that it can be pulled out so as to protrude toward the rear of the apparatus so as to cope with a large paper size. Yes.

  In the image forming apparatus 1 configured as described above, when an image forming signal is input to the exposure device 5, the photoreceptor 3, the developing roller 6 a of the developing device 6, and the intermediate transfer belt 12 are controlled in accordance with the drive motor and bias control by the control unit. Is rotated, and first, the outer peripheral surface of the photoreceptor 3 is uniformly charged by the charging device 4. Thereafter, the exposure device 5 selectively exposes the surface of the photoreceptor 3 in accordance with the image information to form an electrostatic latent image. At this time, the developing device 6 rotates so that the developing roller 6 a of the developing cartridge comes into contact with the photoreceptor 3. As a result, a toner image of an electrostatic latent image is formed on the photoreceptor 3. The toner image formed on the photoreceptor 3 is transferred onto the intermediate transfer belt 12 by the primary transfer roller 13 to which a primary transfer voltage having a polarity opposite to the toner charging polarity is applied, and remains on the photoreceptor 3. The remaining toner is removed by the photoreceptor cleaner 7.

  In the full-color image forming apparatus, yellow Y, magenta M, cyan C, and black K developing cartridges 6Y, 6M, 6C, and 6K are detachably mounted on the developing device 6. In the image forming operation, the exposure device 5 selectively exposes the surface of the photoreceptor 3 in accordance with image information of the first color, for example, yellow Y, to form a yellow Y electrostatic latent image. At this time, the developing device 6 rotates so that the developing roller 6a of the yellow Y developing cartridge 6Y contacts the photoreceptor 3, and a yellow Y electrostatic latent image toner image is formed on the photoreceptor 3. Subsequently, the toner image is transferred onto the intermediate transfer belt 12 by the primary transfer roller 13 to which a primary transfer voltage having a polarity opposite to the charging polarity of the toner is applied.

  During this time, the transfer belt cleaning means 14 and the secondary transfer roller 15 are separated from the intermediate transfer belt 12. A four-color full-color image is obtained by repeating this series of processes corresponding to the second color, the third color, and the fourth color of the image formation signal, thereby obtaining yellow Y, Magenta M, cyan C, and black K toner images are sequentially superimposed and transferred from the photoreceptor 3 onto the intermediate transfer belt 12. Note that the order of yellow Y, magenta M, cyan C, and black K is arbitrary.

  The recording medium on the paper feed tray 17 is conveyed from the pickup roller 18 to the secondary transfer roller 15 through the registration roller and the sheet material conveyance path 19 at the timing when the superimposed image of each color toner image reaches the secondary transfer roller 15. The secondary transfer roller 15 is pressed against the intermediate transfer belt 12 and a secondary transfer voltage is applied to transfer the toner image on the intermediate transfer belt 12 onto the recording medium. The recording medium onto which the toner image has been transferred in this manner is conveyed to the fixing device 20, and the toner image on the recording medium is heated and pressed by the fixing device 20 to be fixed. The toner remaining on the intermediate transfer belt 12 is removed by the cleaning unit 14.

  In the case of double-sided printing, the recording medium exiting the fixing device 20 is switched back so that its trailing edge is the leading edge, and is supplied again to the secondary transfer roller 15 via the double-sided printing conveyance path 22. The full-color toner image on the intermediate transfer belt 12 is transferred onto the recording medium, is heated and pressed again by the fixing device 20, and is discharged onto the paper discharge tray 21.

  In the developing device 6 of the present embodiment, the four developing cartridges 6Y, 6M, 6C, and 6K are detachably mounted as described above to form a four-color full-color image forming device, but a monochrome image forming device. As shown in FIG. 2, only the black K developing cartridge 6K is mounted and mounted, the developing cartridge 6K waits at the standby position (home position), and the black K developing cartridge 6K rotates and moves from the standby position during image formation. The electrostatic latent image on the photoreceptor 3 may be developed into a toner image at the position. This makes it possible to use the developing device 6 with the same design specifications for full color and mono color, and maintenance management and design compared to designing an image forming apparatus dedicated to full color and mono color by sharing full color and mono color. Manufacturing costs can be greatly reduced.

  Next, a mechanism related to the speed unevenness of the image carrier and the countermeasures will be described. FIG. 4 is a diagram for explaining a drive system for the image carrier 3 and the intermediate transfer member 12 in FIG. A drive gear 3a is connected to one end of the image carrier 3, and the drive gear 3a is connected to an output gear 23a of the drive motor 23 via transmission gears 3b and 3c. A driving gear 10a is connected to one end of the driving roller 10 that drives the intermediate transfer body 12, and is connected to an output gear 23a of the driving motor 23 through a transmission gear 10b.

  As described above, since the image carrier 3 and the intermediate transfer member 12 are each driven by the single drive motor 23 via the gear train, there is a minute gap in the meshing portion of each gear, and the primary transfer. When the frictional force between the image carrier 3 and the intermediate transfer member 12 changes in the portion, the gears shake at the gear meshing portion, and the peripheral speed of the image carrier 3 or the intermediate transfer member 12 changes. Speed unevenness occurs in the carrier 3.

  5 to 8 are diagrams for explaining an embodiment of the present invention. FIG. 5 is a diagram showing an outline of an operation sequence of the color image forming apparatus. FIG. 6 is a diagram for explaining the operation of FIG. FIG. 7 is a diagram showing the positional relationship between the separating muscle and the countermeasure image, and FIG. 8 is a diagram showing measurement data.

  FIG. 5 shows a vsync signal, an image signal, a color switching operation of the developing device, a developing operation, a primary transfer position, and a transfer cleaner operation. This operation sequence will be described with reference to FIGS. The surface of the image carrier 3 is uniformly charged by the charging device 4 and the image signal is turned on in synchronization with the vsync signal. First, an electrostatic latent image 26 ′ as a countermeasure image is formed on the surface of the image carrier 3. Is done. Next, the surface of the image carrier 3 is selectively exposed according to the first color image information to form an electrostatic latent image. At this time, the developing device 6 is rotated so that the first color developing roller 6a contacts the image carrier 3, and the countermeasure image and the first color toner image are formed on the image carrier 3, and subsequently. The countermeasure image 26 and the first color toner image are transferred onto the intermediate transfer body 12 by the primary transfer roller 13 to which the primary transfer voltage is applied.

  During this time, the transfer belt cleaning unit 14 and the secondary transfer roller 15 are separated from the intermediate transfer body 12. In a four-color full-color image, this series of processing is repeatedly executed corresponding to the second color, the third color, and the fourth color of the image formation signal, so that a toner image corresponding to the content of each image formation signal is obtained. From the image carrier 3, the images are sequentially superimposed and transferred onto the intermediate transfer body 12. The recording medium S is conveyed to the secondary transfer roller 15 at a timing when the superimposed image of each color toner image reaches the secondary transfer roller 15, and the secondary transfer roller 15 is pressed against the intermediate transfer belt 12 and 2. The next transfer voltage is applied, and the toner image on the intermediate transfer body 12 is transferred onto the recording medium S.

  Next, the toner remaining on the intermediate transfer belt 12 is removed by the cleaning unit 14. The cleaning unit 14 is in contact with the intermediate transfer body 12 after the trailing edge of the third color image has passed the cleaning blade position, and the leading edge of the first color image of the (second) image formed in the next step. Is separated from the intermediate transfer body 12 before reaching the cleaning blade position. By the separation contact of the cleaning unit 14, the toner image on which the fourth color is superimposed is transferred to the recording medium S, and the toner remaining on the intermediate transfer body 12 is removed by the cleaning unit 14.

  As shown in FIG. 6, when the cleaning unit 14 is separated from the intermediate transfer body 12, a separation stripe 24 is generated. In this embodiment, as shown in FIG. 7, a non-image area (transfer image) of the intermediate transfer body 12 is formed. In a region G) where no cleaning image is formed, a countermeasure image 26 consisting of a surface image is formed upstream of the separation position C1 on the intermediate transfer body 12 by the cleaning means 14 in the traveling direction of the intermediate transfer body 12, and the countermeasure image 26 is the primary image. Control is performed so that an electrostatic latent image is formed by turning on an image signal and writing an image before a predetermined time t before reaching the transfer position T1. Accordingly, since the countermeasure image 26 passes before the separating stripe 24 reaches the primary transfer position T1, there is no sudden change in the frictional force between the image carrier 3 and the intermediate transfer member 12, and the speed of the image carrier 3 is increased. Unevenness can be reduced.

FIG. 8 is a diagram showing experimental data obtained by measuring the speed variation of the image carrier. In this experiment, the peripheral speed of the intermediate transfer member is set 0.7% faster than the peripheral speed of the image carrier, and the toner image is transferred to the intermediate transfer member. In FIG. 8, the vertical axis represents speed unevenness, the horizontal axis represents time,
(Rotation speed of the intermediate transfer member−rotation speed of the image carrier) / Rotation speed of the image carrier × 100. Therefore, the plus of the speed unevenness is slower than the intermediate transfer member, and the minus of the speed unevenness is It shows that the image carrier is faster than the intermediate transfer member. Here, the first large speed irregularity appears because of the disturbance of the signal that hits the belt joint of the encoder that detects the rotation, and it is ignored because it does not directly indicate the disturbance of the rotation.
According to FIG. 8, it can be seen that the non-uniformity of speed is reduced at the position of the arrow when the separation line passes through the primary transfer position.

  FIG. 9 is a diagram for explaining another embodiment of the present invention and is a diagram showing a positional relationship between a separation line and a countermeasure image. In this embodiment, the countermeasure image 26 is formed so as to include the separation stripes 24, and control is performed so that an electrostatic latent image is formed by writing an image before the countermeasure image 26 passes the primary transfer position T1. Yes. Also in this embodiment, the frictional force between the image carrier 3 and the intermediate transfer member 12 is not rapidly changed, and the speed unevenness of the image carrier 3 can be reduced.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, the electrostatic latent image is formed on the image carrier by the exposure device. However, the electrostatic latent image may be formed by the charging / writing device. It is defined as forming means. Although the intermediate transfer belt has been described in the above embodiment, it can be applied to an intermediate transfer drum, and in the present invention, these are defined as intermediate transfer members.

It is a figure which shows the state in which a separating muscle passes the transcription | transfer position. It is a figure which shows the experimental data which measured the speed fluctuation | variation of the image carrier by a separating muscle. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 4 is a diagram for explaining a drive system for an image carrier and an intermediate transfer member in FIG. 3. FIG. 2 is a diagram for explaining an embodiment of the present invention, and is a diagram showing an outline of an operation sequence of a color image forming apparatus. It is a figure for demonstrating operation | movement of embodiment of FIG. FIG. 6 is a diagram illustrating a positional relationship between a separation line and a countermeasure image in the embodiment of FIG. 5. It is a figure which shows the experimental data which measured the speed fluctuation | variation of the image carrier in embodiment of FIG. It is a figure for demonstrating other embodiment of this invention, and is a figure which shows the positional relationship of a separation line and a countermeasure image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Image carrier, 5 ... Latent image formation means, 6 ... Development means, 12 ... Intermediate transfer body 13 ... Primary transfer roller (transfer means), 14 ... Cleaning means 23 ... Drive motor, 24 ... Spacer, 26 ... Countermeasure images 3a to 3c, 10a to 10b ... gear train C1 ... cleaning unit separation position, T1 ... primary transfer position (transfer position)

Claims (5)

A latent image forming unit that forms an electrostatic latent image on an image carrier, a developing unit that develops the electrostatic latent image into a toner image, a transfer unit that transfers the toner image to an intermediate transfer member, and the intermediate transfer In an image forming apparatus provided with a cleaning unit that separates and abuts on a body and removes toner remaining on an intermediate transfer body,
A countermeasure image is formed upstream of the intermediate transfer member in the advancing direction of the intermediate transfer member from the cleaning unit separation position on the intermediate transfer member, and latent image formation by the latent image forming unit is started before the countermeasure image reaches the transfer position. An image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the countermeasure image is a surface image including a cleaning unit separation position. 3. The image forming apparatus according to claim 2, wherein a toner amount of the countermeasure image is formed with a toner amount smaller than a toner amount at a cleaning unit separation position. The image forming apparatus according to claim 1, wherein peripheral speeds of the image carrier and the intermediate transfer member are different at the transfer position. The image forming apparatus according to claim 4, wherein the image carrier and the intermediate transfer member are each driven by a single drive motor via a gear train.

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