JP5504582B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus having a belt-like intermediate transfer member. More specifically, the present invention relates to an image forming apparatus capable of forming a color image by superimposing and transferring toner images of respective colors on an intermediate transfer member.

  Conventionally, there is a type of image forming apparatus called a so-called four-cycle machine. In this type of apparatus, each color developing device incorporated in a rotating rack or the like faces one photoconductor in order. A toner image of that color is formed and transferred to the intermediate transfer member. By repeating this procedure for each color, the toner images of the respective colors are sequentially transferred to the same position on the intermediate transfer body and are superimposed.

  In the 4-cycle machine, since the intermediate transfer member is rotated once for each color, the cleaner device and the secondary transfer device are pressed and separated from the intermediate transfer member in synchronization with each process for image formation. . Therefore, the load state for driving the intermediate transfer member varies depending on whether the cleaner device or the secondary transfer device is pressed or separated.

  As this intermediate transfer member, there is one in which a belt-like member stretched by a plurality of rollers or the like is used. A belt-like intermediate transfer member may be partially bent. In particular, it may bend temporarily due to the impact of the shock at the time of contact and separation of the cleaner device. Further, the drive state may temporarily change due to the bending. For this reason, there is a problem in that if a cleaner device or the like is contacted or separated during primary transfer, color misregistration occurs at that timing.

On the other hand, for example, in the image forming apparatus described in Patent Document 1, the timing of primary transfer and the timing of contact and separation of the cleaner device are shifted. That is, color shift due to shock is prevented by setting the timing at which primary transfer is started after the separation of the cleaner device is completed. In addition, in the image forming apparatus described in Patent Document 2, the latent image writing position is shifted in advance so as to cancel out the color shift due to the load fluctuation at the time of contact and separation of the cleaner device or the like. Yes.
JP-A-9-146438 JP 2002-278204 A

  However, the conventional image forming apparatus described above has the following problems. In the apparatus described in Patent Document 1, the start of the primary transfer is delayed as compared with the apparatus that contacts and separates the cleaner device during the primary transfer. For this reason, there is a problem that the productivity of the entire apparatus is low. In addition, the apparatus described in Patent Document 2 has a problem that it is difficult to cancel out variations caused by fluttering of an intermediate transfer member due to color shift due to a contact / separation shock of a cleaner apparatus or the like.

  In recent years, as the toner diameter is reduced, the pressure contact force of the cleaner device tends to be increased. For this reason, the fluctuation range of the load fluctuation due to the pressure contact / separation of the cleaner device is also increasing. Therefore, there is a problem that the color shift due to the shock of the load fluctuation tends to increase.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. That is, an object of the present invention is to provide an image forming apparatus that can effectively prevent color misregistration due to shock of contact / separation of the cleaner device without reducing productivity.

The image forming apparatus of the present invention, which has been made for the purpose of solving this problem, has an image forming unit that forms a toner image on a rotating photoconductor, and rotates while contacting the photoconductor, and the toner image is transferred from the photoconductor. An image forming apparatus having a transfer belt, wherein the transfer belt is in contact with the transfer belt, and a moving member which is movable between a position where the transfer belt is pressed against the toner image carrying surface and a position where the image is separated from the toner image carrying surface. A fixing member that is fixed and arranged to be a sliding resistance against the rotation of the transfer belt, a voltage applying unit that applies a voltage to the fixing member, a control unit that controls the moving member and the voltage applying unit , and a toner sensor for detecting the toner images on the belt, the control unit, during the period in which the toner image to the transfer belt from at least a photosensitive member is transferred, the fixing member by the voltage application unit irrespective of the position of the moving member With applying a voltage, the movement of the moving member state, and are not the voltage application by the voltage application unit to perform during the period that has been done, the fixing member is disposed on the rear surface of the sensing position of the toner sensor Monodea Ru.

  According to the image forming apparatus of the present invention, the voltage is applied to the fixing member during the transfer period of the toner image from the photoconductor to the transfer belt. For this reason, an adsorption force acts between the fixing member and the transfer belt at the contact portion. This adsorption force becomes a load for the running of the transfer belt. On the other hand, when the moving member moves away from the press contact with the transfer belt or vice versa, the load on the running of the transfer belt changes. The ratio of the change in the load to the total load is relatively small by the load due to the fixed member. For this reason, the influence of the movement of the moving member on the running state of the transfer belt is small. Therefore, even if the position of the moving member is changed during the transfer period, the deviation of the toner image during transfer is prevented. As a result, the image forming apparatus can effectively prevent color misregistration due to the shock of contact and separation of the cleaner device without reducing productivity.

In the present invention, fixed member is disposed on the rear surface of the sensing position of the toner sensor. Sensing the position of the bets Nasensa is provided at a position less fluttering of the transfer belt. Therefore, in Rukoto to place the fixing member on the back surface, the fixing member and the transfer belt is stably slide. Therefore, fluctuations in the adsorption state can be suppressed.

Further, in the present invention, the toner images of the respective colors are primarily transferred at the same position on the transfer belt, and the color images are formed by performing the secondary transfer by collectively transferring the superimposed toner images from the transfer belt. desirable.
In such an image forming apparatus, it is necessary to remove the secondary transfer residual toner on the transfer belt.

Further, in the present invention, it is desirable that the image forming unit has one photosensitive member and a plurality of developing members that face the photosensitive member in turn one by one.
The present invention is particularly effective for such a so-called four-cycle type image forming apparatus.

Further, in the present invention, the control unit separates the moving member from the transfer belt before the leading edge of the first color toner image reaches the moving member, and the trailing end of the toner image superimposed up to the second color from the last is displayed. It is desirable that the moving member is brought into contact with the transfer belt after passing through the moving member.
In this way, it is not necessary to idle the transfer belt for cleaning. Therefore, the image forming apparatus has high productivity.

  According to the image forming apparatus of the present invention, it is possible to effectively prevent color misregistration due to a contact / separation shock of the cleaner device without reducing productivity.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a so-called four-cycle image forming apparatus.

  The color printer 1 of this embodiment is a so-called four-cycle machine as shown in FIG. One photosensitive member 11 is provided near the center in the figure, and a charging device 12, an exposure device 13, a developing device 14, and a cleaner device 15 are arranged around the lower portion thereof. In the developing device 14, developing units 14Y, 14M, 14C, and 14K for respective colors are mounted on a rotatable developing rack 14a. As for the inside, the schematic configuration is shown only for the yellow developing section 14Y, but the other colors have almost the same configuration.

  Further, the color printer 1 has an intermediate transfer belt 21 above the photoconductor 11 in FIG. The intermediate transfer belt 21 is a belt-like member and is wound around each of a cleaner facing roller 23, a primary transfer roller 24, a driving roller 25, and a tension roller 26. The tension roller 26 is pushed upward by a tension spring 27 in the upper right direction in the figure.

  Further, a belt cleaner 28 is provided so as to face the cleaner facing roller 23. The belt cleaner 28 of this embodiment is a cleaning blade, and is pressed against or separated from the intermediate transfer belt 21 as indicated by an arrow in the drawing. A toner sensor 29 is disposed above the intermediate transfer belt 21. The toner sensor 29 is for inspecting the toner image on the intermediate transfer belt 21.

  Further, a sheet cassette 31 is provided below the color printer 1 in FIG. 1, and sheets are stored therein. During image formation, sheets are pulled out from the sheet cassette 31 one by one. In this embodiment, a secondary transfer roller 32 is provided so as to face the driving roller 25. Further, a fixing device 33, a paper discharge roller 34, and a paper discharge tray 35 are provided downstream in the paper transport direction.

  An operation for forming a color image by the color printer 1 of this embodiment will be briefly described. The photoreceptor 11 is charged substantially uniformly by the charging device 12. Next, an electrostatic latent image based on yellow image data is formed on the surface of the photoreceptor 11 by the exposure device 13. Further, the developing rack 14a is stopped at a position where the yellow developing portion 14Y faces the photoconductor 11. The electrostatic latent image on the photoconductor 11 is developed by the yellow developing unit 14 </ b> Y, and a yellow toner image is formed on the photoconductor 11. The formed toner image is transferred to the intermediate transfer belt 21 by the primary transfer roller 24.

  Subsequently, residual toner is removed from the surface of the photoconductor 11 by the cleaner device 15, and a second color (magenta) toner image is formed in the same procedure as described above. During this time, the intermediate transfer belt 21 is rotated once, and the magenta toner image is transferred to the position where it is combined with the yellow toner image. Further, cyan and black toner images are superimposed on the intermediate transfer belt 21 in the same procedure. Then, the superimposed four color toner images are transferred onto the paper by the secondary transfer roller 32. The toner image is fixed on the sheet by the fixing device 33. In this way, the sheet on which the color image is formed is discharged to the discharge tray 35 by the discharge roller 34.

  Next, FIG. 2 shows a peripheral portion of the intermediate transfer belt 21 which is a characteristic portion of the present invention. The intermediate transfer belt 21 of the present embodiment is rotated by a driving roller 25 as indicated by an arrow in the drawing during image formation. The belt cleaner 28 and the secondary transfer roller 32 are pressed and separated in accordance with the timing of image formation. Therefore, the load for driving the intermediate transfer belt 21 varies at that timing. Furthermore, in the present embodiment, the intermediate transfer belt 21 is a belt member, so that some bending occurs. One of the causes of color misregistration is that the bending state changes between when the belt cleaner 28 is pressed and when it is separated. In particular, it is not preferable that the length of the intermediate transfer belt 21 between the contact point of the primary transfer roller 24 and the drive point of the drive roller 25 varies.

  As shown in FIG. 2, the color printer 1 of the present embodiment includes an electrode member 41 slightly downstream of the cleaner facing roller 23 in the rotational direction of the intermediate transfer belt 21. The electrode member 41 is fixedly disposed so as to be in contact with the inner surface of the intermediate transfer belt 21 at a position between the cleaner facing roller 23 and the primary transfer roller 24. Accordingly, when the intermediate transfer belt 21 rotates, the electrode member 41 slides with respect to the intermediate transfer belt 21. Further, a high voltage power source 42 is connected to the electrode member 41. Thereby, the electrode member 41 can receive application of a voltage. Furthermore, this embodiment has a control unit 43 that controls the pressure contact / separation of the belt cleaner 28 and the secondary transfer roller 32 with respect to the intermediate transfer belt 21 and ON / OFF of the high-voltage power supply 42.

  The electrode member 41 of this embodiment is formed of a conductive or semiconductive member. For example, a metal member, a metal member having a conductive or semiconductive film attached thereto, and the like can be used. Further, the intermediate transfer belt 21 of the present embodiment is formed of a material that can flow current in the in-plane direction and the thickness direction. The cleaner facing roller 23 is grounded. When the high voltage power source 42 is turned on by the control unit 43, a voltage is applied to the electrode member 41 by the high voltage power source 42. The voltage application method applied to the electrode member 41 by the high voltage power source 42 may be a constant voltage or a constant current.

  As a result, an electric attractive force acts between the intermediate transfer belt 21 and the electrode member 41. That is, it becomes a load for driving the intermediate transfer belt 21. The driving roller 25 can overcome the load and rotate the intermediate transfer belt 21 at an appropriate speed. By doing so, the driving load of the intermediate transfer belt 21 is increased. Accordingly, it is possible to minimize the influence of the load fluctuation caused by the shock when the belt cleaner 28 is pressed against or separated from the intermediate transfer belt 21, and color misregistration can be prevented.

  Next, the timing of voltage application by the high-voltage power supply 42 when forming a color image will be described with reference to FIG. FIG. 3 shows the passage of time from left to right in the figure. Each period delimited by a dashed dotted vertical line indicates the time required for the intermediate transfer belt 21 to make one revolution. One color image is formed by sequentially transferring Y color, M color, C color, and K color and superimposing them on the intermediate transfer belt 21. Then, the intermediate transfer belt 21 makes one round for each primary transfer period of each color.

  Of the period in which the intermediate transfer belt 21 makes one turn, the period indicated by shading in the upper part of FIG. 3 is a period in which primary transfer is performed. Furthermore, in this embodiment, as shown in the lower part of the figure, a voltage is applied to the electrode member 41 by the high-voltage power source 42 at least during the period when the primary transfer is being performed. Further, the pressure contact / separation state of the belt cleaner 28 is changed as shown in the middle part of the figure. That is, the belt cleaner 28 is separated from the pressure contact state with the intermediate transfer belt 21 during the primary transfer of Y color. Then, the belt cleaner 28 is pressed against the intermediate transfer belt 21 during the primary transfer of K color. Accordingly, the timing at which the belt cleaner 28 is moved is during the period when the voltage is applied to the electrode member 41 by the high voltage power source 42.

  The procedure for forming a toner image for one color image according to this embodiment is as follows. First, a Y-color toner image is formed on the photoconductor 11 and is primarily transferred to the intermediate transfer belt 21. In the case of continuous processing from the previous image formation, the belt cleaner 28 is pressed against the intermediate transfer belt 21 and starts the primary transfer of the current Y color in parallel while cleaning the previous secondary transfer residual toner. To do. The belt cleaner 28 is separated before the head of the current Y color toner image reaches the position of the belt cleaner 28. That is, the belt cleaner 28 is separated from the intermediate transfer belt 21 from the press contact state during the Y-color primary transfer. Accordingly, a voltage is applied to the electrode member 41 by the high voltage power source 42 at the timing when the belt cleaner 28 is separated.

  During the second and third primary transfer of M and C colors, it is necessary to keep the toner image on the intermediate transfer belt 21, so that the belt cleaner 28 remains in the separated state. When the trailing edge of the three color superimposed toner images passes the position of the belt cleaner 28, the belt cleaner 28 is pressed against the intermediate transfer belt 21. At the timing of the press contact, primary transfer of K color is being executed, and a voltage is applied to the electrode member 41 by the high voltage power source 42. The toner remaining on the intermediate transfer belt 21 even after the end of the secondary transfer is removed by the belt cleaner 28.

  In the present embodiment, since the voltage is applied to the electrode member 41 during the primary transfer, the intermediate transfer belt 21 is attracted to the electrode member 41. For this reason, even if the belt cleaner 28 is pressed and separated during the primary transfer, the rate of fluctuation of the load due to the shock is very small. Therefore, it is not necessary to idle the intermediate transfer belt 21 for cleaning. As a result, the entire circumference of the intermediate transfer belt 21 can be cleaned without delaying image formation, resulting in high productivity.

  The voltage application period to the electrode member 41 may be during the same period as the primary transfer execution period and may not be applied during other periods. Alternatively, it may be applied constantly during image formation, including other periods. However, the high voltage power source 42 is not switched during the primary transfer.

  Next, FIG. 4 shows the relationship between the magnitude of the voltage applied to the electrode member 41 by the high-voltage power supply 42 and the driving load at that time. Note that the notation such as “2 mm” and “4 mm” in the figure is the contact width between the electrode member 41 and the intermediate transfer belt 21. That is, the electrode member 41 is in contact with the intermediate transfer belt 21 in an area of this contact width × transfer area width. As shown in the figure, the driving load increases as the applied voltage is increased except for the “rotary” type, that is, the fixed type. And the increase rate of the drive load with respect to an applied voltage is so large that a contact width is large. Therefore, the contact width and the applied voltage may be selected so that an appropriate driving load can be obtained.

  In this embodiment, for example, the contact width is 8 mm and the applied voltage is 700 V so that the driving load by the electrode member 41 is about 17N. By doing so, the amount of color misregistration that was about 0.17 mm at the maximum without the conventional high-voltage power supply 42 was reduced to about 0.04 mm at the maximum.

  The results shown in FIG. 4 were obtained using the intermediate transfer belt 21 as described below. The material of the intermediate transfer belt 21 is polycarbonate (PC), and its circumference is 500 mm and the thickness is 0.15 mm. The intermediate transfer belt 21 was stretched with a tension of 30 N and driven at a rotational speed of 150 mm / s. A metal member was used as the electrode member 41. Further, in the rotary electrode member 41, as shown in the lowermost graph in the drawing, even if a voltage is applied, the driving load does not change, so that no effect is obtained.

  Instead of providing the electrode member 41, as shown in FIG. 5, a high voltage power source 42 may be connected to the primary transfer member 51 so as to act as an electrode member. The primary transfer member 51 is a member that has a roller-like shape but does not rotate. The end of the shaft of the primary transfer member 51 is D-cut as shown and is fixed to a part of the housing. Thereby, the primary transfer member 51 always contacts and slides on the inner surface side of the intermediate transfer belt 21 at the same location. Note that the primary transfer member 51 does not necessarily have a roller shape. A plate shape or a prismatic shape may be used.

  In this case, the location where the primary transfer member 51 is in contact with the intermediate transfer belt 21 is about 4 to 6 mm in the traveling direction of the intermediate transfer belt 21 from the location where the photoconductor 11 is in contact with the intermediate transfer belt 21. It is in the downstream position. By separating the distance from the photoconductor 11 to this extent, discharge from the primary transfer member 51 to the toner on the photoconductor 11 is prevented.

  Alternatively, as shown in FIG. 6, a high voltage power source 42 can be connected to the opposing member 52 of the toner sensor 29 to be used as an electrode member. In general, the toner sensor 29 is arranged at a position where the flutter of the intermediate transfer belt 21 is small in order to detect a toner image as accurately as possible. For example, it is disposed slightly upstream of the cleaner facing roller 23. The opposing member 52 is fixedly disposed on the back side of the intermediate transfer belt 21 in order to stabilize the detection state at the sensing position of the toner sensor 29.

  The opposing member 52 is also a member that slides on the intermediate transfer belt 21, and a driving load can be increased by applying a voltage thereto. As described above, it is preferable that the electrode member of the present embodiment is fixedly provided at a position where the intermediate transfer belt 21 has little flutter and the sliding state is difficult to change.

  As described above in detail, according to the color printer 1 of the present embodiment, the electrode member 41 is fixed at a position where it slides on the inner peripheral side of the intermediate transfer belt 21. Further, a voltage is applied to the electrode member 41 by a high voltage power source 42 during the primary transfer. As a result, an attracting force acts between the electrode member 41 and the intermediate transfer belt 21, so that the driving load of the intermediate transfer belt 21 increases. Therefore, even if the belt cleaner 28 is brought into contact with or separated from the intermediate transfer belt 21 during the primary transfer, the rate of load fluctuation due to the shock is relatively small. Therefore, it is possible to effectively prevent color misregistration due to the shock of contact / separation of the cleaner device without reducing productivity.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, the belt cleaner is not limited to a blade type but may be a cleaning roller or a cleaning brush.
Further, the voltage may be applied to the electrode member 41 at the timing when the secondary transfer roller 32 is pressed against and separated from the intermediate transfer belt 21.
Further, during the primary transfer of the M color and the C color, the pressure contact / separation of the belt cleaner 28 is not performed, so that it is not necessary to apply a voltage to the electrode member 41. However, in that case, it is necessary to match the belt traveling speed with the primary transfer of Y color or K color.

1 is a schematic configuration diagram illustrating a color printer according to an embodiment. FIG. 6 is an explanatory view showing the periphery of an intermediate transfer belt. It is a timing diagram which shows the timing of voltage application. It is a figure which shows the relationship between the magnitude | size of the voltage applied to a primary transfer roller, and a drive load. It is explanatory drawing of the example which shared the primary transfer member and the electrode member. FIG. 6 is an explanatory diagram of an example in which a facing member and an electrode member of a toner sensor are shared.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color printer 11 Photoconductor 14 Developing apparatus 21 Intermediate transfer belt 28 Belt cleaner 41 Electrode member 42 High voltage power supply 43 Control part 51 Primary transfer member 52 Opposing member

Claims (4)

In an image forming apparatus comprising: an image forming unit that forms a toner image on a rotating photoconductor; and a transfer belt that rotates while being in contact with the photoconductor and to which a toner image is transferred from the photoconductor.
A moving member which is movable between a position where it is pressed against the toner image carrying surface of the transfer belt and a position where it is separated;
A fixing member arranged in contact with and fixed to the transfer belt, and having sliding resistance against rotation of the transfer belt;
A voltage application unit for applying a voltage to the fixing member;
A control unit for controlling the moving member and the voltage application unit ;
A toner sensor for detecting a toner image on the transfer belt;
The control unit applies a voltage to the fixed member by the voltage applying unit regardless of the position of the moving member, and at least during the period when the toner image is transferred from the photoconductor to the transfer belt. The movement of the member is performed during the period in which the voltage is applied by the voltage application unit ,
The image forming apparatus according to claim 1, wherein the fixing member is disposed on a back surface of a sensing position of the toner sensor . The image forming apparatus according to claim 1 ,
A color image is formed by performing primary transfer by superimposing toner images of respective colors on the same position on the transfer belt and performing secondary transfer of the superimposed toner images collectively from the transfer belt. Image forming apparatus. The image forming apparatus according to claim 1, wherein:
The image forming apparatus, wherein the image forming unit includes one photoconductor and a plurality of developing members that face the photoconductor in turn one by one. The image forming apparatus according to claim 2 or claim 3, wherein the control unit,
Separating the moving member from the transfer belt before the top of the first color toner image reaches the moving member;
An image forming apparatus, wherein the end of a toner image superimposed from the last to the second color passes the moving member and then the moving member is brought into contact with the transfer belt.

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