JP2005077829A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of banding, without being affected by the changes in the speed of an image carrier. <P>SOLUTION: The image forming apparatus includes a latent image formation means for forming a latent image on an image carrier 3; a developing means 6a for developing the electrostatic latent image into a toner image by the application of an AC overlap bias to a developing roller; and a transfer means 13 for transferring the toner image to an intermediate transfer body 12. In the image forming apparatus, the latent image is formed by the latent image forming means after a bias application start position B1 on the image carrier passes through 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, or a facsimile using an electrophotographic method, and in particular, an AC superimposing bias is applied to a developing roller to develop an electrostatic latent image into a toner image. The present invention relates to an image forming apparatus that transfers onto an intermediate transfer member.

In the image forming apparatus, the high pressure is not stable when the development bias application is started, and the toner locally adheres to the image carrier due to toner scattering, fogging, or the like. Therefore, conventionally, an AC superimposing bias is applied before the latent image on the image carrier reaches the development area (that is, the non-image portion) to stabilize the bias before development, thereby preventing toner scattering and fogging. (See Patent Document 1).
Japanese Examined Patent Publication No. 3-64073

  However, as shown in FIG. 1, if an AC superimposed bias is applied before the latent image on the image carrier 3 reaches the development area (that is, the non-image portion), the toner in the area Y is transferred to the image carrier at the start of bias application. To fly to. The flying toner causes the developing roller 6a and the image carrier 3 to rotate in the direction of the arrow shown in the figure, so that the gap between the image carrier 3 and the developing roller 6a is increased and the electric field is weakened, so that the toner returns to the developing roller 6a. Can not. Further, the power supply may become unstable at the start of bias application, so-called overshoot may occur, and toner may fly to the image carrier 3. The toner formed in the non-image area at the start of bias application in this way is hereinafter referred to as AC bias application stripe 25.

  FIG. 2 is a diagram showing the relationship between the AC bias applying muscle 25 and the primary transfer position. In the figure, 12 is an intermediate transfer belt, 13 is a primary transfer roller, and 26 is an AC superimposed bias power source. As shown in FIG. (A), the AC bias application line 25 advances to the primary transfer position T1, and as shown in FIG. (B), the application line 25 reaches the primary transfer position T1, and FIG. As shown in FIG. 4, the application stripe 25 is transferred to the intermediate transfer belt 12 and passes 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 inventor conducted various experiments, it was found that the following problems occur. That is, when the latent image writing operation is performed on the image carrier 3 when the bias application start position B1, that is, the AC bias application line 25 is at the primary transfer position T1, as shown in FIG. It was found that fluctuations occurred and density unevenness and color misregistration due to speed unevenness of the image carrier 3, so-called banding occurred. This is because, if there is an AC bias application 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 slides and speed fluctuation occurs. Is attributed.

  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 an AC bias application line (toner) is locally present in the primary transfer region, the frictional force of 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 toner streaks 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 can prevent the occurrence of banding without being affected by fluctuations in the speed of the image carrier caused by the AC bias application line. An object is to provide a forming apparatus.

Therefore, the image forming apparatus of the present invention includes a latent image forming unit that forms an electrostatic latent image on an image carrier, and a developing unit that applies an AC superimposing bias to a developing roller to develop the electrostatic latent image into a toner image. And a transfer means for transferring the toner image to the intermediate transfer body, the latent image forming means forms a latent image after the bias application start position on the image carrier has passed the transfer position. It is characterized by that.
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, after the AC bias applying stripe on the image carrier passes through the transfer position, the latent image forming means forms a latent image, so that even if the image carrier speed fluctuations caused by the AC bias applying stripe occur. The occurrence of banding can be prevented without being affected by this.

  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.

  Thus, since the image carrier 3 and the intermediate transfer member 12 are each driven by the single drive motor 23 through the gear train, there is a minute gap in the meshing portion of the gear, and the primary transfer portion. When the frictional force between the image carrier 3 and the intermediate transfer member 12 is changed, the gear meshing portion is shaken, and the peripheral speed of the image carrier 3 or the intermediate transfer member 12 is changed. Speed unevenness will occur.

FIG. 5 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 images are transferred to the intermediate transfer member in the order of K (Bk), C, M, and Y. . In FIG. 5, 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, in FIG. 2, when the bias application start position B1 of each color, that is, the AC bias application line 25 comes to the primary transfer position T1, significant speed unevenness occurs as shown by the arrows in FIG. It shows that.

  This phenomenon can be explained as follows. For example, when the peripheral speed of the intermediate transfer member is larger than that of the image carrier, a frictional force and an electrostatic attraction force act between the image carrier and the intermediate transfer member, and the two forces cause the image carrier to move to the intermediate transfer member. It is driven to be pulled. However, if an AC bias application line (toner) is locally present in the primary transfer region, the frictional force of 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.

  FIG. 6 is a diagram illustrating an outline of an operation sequence of the color image forming apparatus according to the present embodiment, and FIG. 7 is a diagram illustrating control timing. FIG. 6 shows the vsync signal, the image signal, the color switching operation of the developing device, the AC application operation, and the primary transfer position. This operation sequence will be described with reference to FIG. The surface of the image carrier 3 is uniformly charged by the charging device 4, the image signal is turned on in synchronization with the vsync signal, and the surface of the image carrier 3 is selectively exposed according to the image information of the first color. And an electrostatic latent image is formed. At this time, the developing device 6 rotates so that the first color developing roller 6 a contacts the image carrier 3, and a first color toner image is formed on the image carrier 3. Is transferred onto the intermediate transfer body 12 by the primary transfer roller 13 to which a 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 is conveyed to the secondary transfer roller 15 at a timing when the superimposed images of the respective color toner images reach the secondary transfer roller 15, and the secondary transfer roller 15 is pressed against the intermediate transfer belt 12 and the secondary transfer roller 15. A transfer voltage is applied, and the toner image on the intermediate transfer body 12 is transferred onto the recording medium by the secondary transfer roller 15.

  Next, the toner remaining on the intermediate transfer belt 12 is removed by the cleaning unit 14. The cleaning unit 14 comes into contact with the intermediate transfer body 12 after the rear end of the third color image has passed the cleaning blade position, and corresponds to the first color of the (second) image formed in the next step. Is separated from the intermediate transfer body 12 before reaching the cleaning blade position.

  When an AC bias is applied, an AC bias applying streak is generated in the image carrier 3 as described in FIG. 1. In the present invention, as shown in detail in FIG. 6, the bias application start position B1, that is, the AC bias applying streak is generated. After 25 reaches the primary transfer position T1, the image signal is turned on after a predetermined time t, and image writing is performed to form an electrostatic latent image. Therefore, as shown in FIG. 7, since the image writing is performed after the AC bias applying stripe passes the primary transfer position, the occurrence of banding can be prevented without being affected by the speed unevenness of the image carrier. .

  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 for demonstrating the AC bias application line | wire which concerns on this invention. It is a figure which shows the relationship between an AC bias application line | wire and a primary transfer position. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a diagram for explaining a drive system for an image carrier and an intermediate transfer member in FIG. 1. It is a figure which shows the experimental data which measured the speed fluctuation | variation of the image carrier. It is a figure for demonstrating the operation | movement sequence of this invention. It is a figure which shows the latent image writing timing in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Image carrier, 5 ... Latent image formation means, 6 ... Developing means, 12 ... Intermediate transfer body 13 ... Primary transfer roller (transfer means), 14 ... Cleaning means 23 ... Drive motor, 3a-3c, 10a-10b ... Gear train B1 ... Bias application start position, T1 ... Primary transfer position (transfer position)

Claims (3)

A latent image forming unit that forms an electrostatic latent image on the image carrier, a developing unit that applies an AC superimposing bias to a developing roller to develop the electrostatic latent image into a toner image, and the toner image is used as an intermediate transfer member. An image forming apparatus comprising: a transfer means for transferring; wherein the latent image forming means forms a latent image after the bias application start position on the image carrier has passed the transfer position. 2. 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. 3. The image forming apparatus according to claim 2, wherein the image carrier and the intermediate transfer member are each driven by a single drive motor through a gear train.

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