JP2014109656A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing an influence of a temporary reduction in speed of an intermediate transfer belt in association with the entry of a recording medium into a secondary transfer nip.SOLUTION: An image forming apparatus includes a plurality of photoreceptors 2, an intermediate transfer belt 8 that comes into contact with the respective photoreceptors 2, and a secondary transfer member 12 that comes into contact with the intermediate transfer belt 8; and a part of the plurality of photoreceptors 2 and the intermediate transfer belt 8 can be separated from each other. When a small number of the photoreceptors 2 is in contact with the intermediate transfer belt 8, the image forming apparatus controls to decrease the linear velocity of the photoreceptors 2 in contact with the intermediate transfer belt 8, with respect to the intermediate transfer belt 8.

Description

  The present invention relates to an image forming apparatus that transfers images on a plurality of photosensitive members to a recording medium via an intermediate transfer belt.

  As an electrophotographic image forming apparatus, a so-called tandem type intermediate transfer type image forming apparatus is known in which images on a plurality of photoconductors are transferred to a recording medium such as paper via an intermediate transfer belt. Generally, in this image forming apparatus, a primary transfer roller that forms an intermediate transfer nip by sandwiching an intermediate transfer belt with each photoconductor, and a secondary transfer nip that forms a contact with the intermediate transfer belt is formed. A secondary transfer roller is provided. The toner image formed on each photoconductor is transferred onto the intermediate transfer belt at each primary transfer nip position, and then the toner image transferred onto the intermediate transfer belt is recorded onto the recording medium at the secondary transfer nip position. It is supposed to be transferred to.

  Also, a technique is known in which an intermediate transfer belt is separated from a color photoconductor in order to suppress unnecessary wear of a color photoconductor that is not used when a monochrome image is formed. (See Patent Document 1).

  By the way, in the tandem intermediate transfer type image forming apparatus as described above, when the recording medium enters the secondary transfer nip, the rotational speed of the intermediate transfer belt is caused by a load caused by the recording medium coming into contact with the intermediate transfer belt. May decrease temporarily. If such a temporary speed reduction of the intermediate transfer belt occurs during image transfer to the intermediate transfer belt, there is a possibility that good transfer cannot be performed.

  For example, as shown in FIG. 10, when the toner transfer T is transferred from the photosensitive member 2 to the intermediate transfer belt 8 at equal intervals as shown in FIG. The distance between the toner patches becomes short at the point A where the surface speed of the belt is lowered. As a result, the image transferred to the recording medium at the position of the secondary transfer nip is shaded due to the difference in the distance between the toner patches. 10 and 11, the case where the toner patch T is transferred has been described for convenience of explanation, but the same can be said for a normal output image such as a character image or a photographic image.

  In addition, the effect of the temporary reduction in the speed of the intermediate transfer belt as described above is caused when the number of contact of the photosensitive member is small, such as when forming a monochrome image in which only one photosensitive member is in contact with the intermediate transfer belt. It was found to be particularly remarkable.

  Therefore, in view of such circumstances, the present invention intends to provide an image forming apparatus capable of suppressing the influence due to the temporary speed reduction of the intermediate transfer belt accompanying the entry of the recording medium into the secondary transfer nip. Is.

  In order to solve the above problems, the present invention includes a plurality of photoconductors, an intermediate transfer belt that comes into contact with each of the photoconductors, and a secondary transfer member that comes into contact with the intermediate transfer belt. In the image forming apparatus in which a part of the photosensitive members and the intermediate transfer belt are configured to be separated from each other, the contact is made when the number of contact of the photosensitive member with the intermediate transfer belt is small. Control is performed so that the linear velocity ratio of the photosensitive member in contact with the intermediate transfer belt is reduced as compared with the case where the number is large.

  According to the present invention, when the number of contact of the photosensitive member with respect to the intermediate transfer belt is small, the linear speed ratio of the photosensitive member in contact with the intermediate transfer belt is made smaller than when the number of contact is large. By controlling this, the tension of the intermediate transfer belt can be loosened and the intermediate transfer belt can be loosened. As a result, it is possible to suppress fluctuations in the position of the intermediate transfer belt accompanying the entry of the recording medium into the contact portion between the intermediate transfer belt and the secondary transfer member.

1 is a schematic configuration diagram of a printer as an image forming apparatus according to an embodiment of the present invention. FIG. 4 is a diagram illustrating a state where an intermediate transfer belt is separated from a color photoconductor. It is a figure which shows the structure of the characteristic part of the printer which concerns on this embodiment. FIG. 6 is a diagram illustrating an example of a linear velocity ratio of a photoconductor set based on an image forming mode and a paper type. FIG. 6 is an image diagram of a state where the tension of the intermediate transfer belt is loosened. FIG. 4 is a diagram illustrating an embodiment configured to control the rotation speed of an intermediate transfer belt. FIG. 3 is a diagram illustrating an embodiment configured to control the rotational speeds of both a photoreceptor and an intermediate transfer belt. It is a figure which shows embodiment provided with the environmental condition detection sensor. FIG. 4 is a diagram illustrating linear speeds of an intermediate transfer belt and a photosensitive member when a sheet enters the secondary transfer nip, during passage, and when discharged. FIG. 6 is a diagram illustrating a state where toner patches are transferred at equal intervals. FIG. 6 is a diagram illustrating a state in which a distance between toner patches to be transferred is shortened as a result of a temporary speed reduction in the intermediate transfer belt.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each drawing, components such as members and components having the same function or shape are denoted by the same reference numerals as much as possible, and once described, the description is omitted.

  FIG. 1 is a schematic configuration diagram of a printer as an image forming apparatus according to an embodiment of the present invention. First, the overall configuration and operation of the printer will be described with reference to FIG.

  As shown in FIG. 1, at the center of the printer apparatus main body (image forming apparatus main body) 100, yellow (Y), magenta (M), cyan (C), black (Bk) corresponding to the color separation components of the color image. ) Four image forming sections 1Y, 1M, 1C, and 1Bk that form images of different colors. Each of the image forming units 1Y, 1M, 1C, and 1Bk includes a photoreceptor 2 carrying an electrostatic latent image on the surface, a charging roller 3 as a charging unit that charges the surface of the photoreceptor 2, and a static on the photoreceptor 2. The image forming apparatus includes a developing device 4 as a developing unit that supplies toner to the electrostatic latent image and develops, and a cleaning blade 5 as a cleaning unit that cleans the surface of the photoreceptor 2.

  In FIG. 1, only the photoconductor 2, the charging roller 3, the developing device 4, and the cleaning blade 5 included in the image forming unit 1 </ b> Y that forms a yellow image are denoted by reference numerals, and the other image forming units 1 </ b> M and 1 </ b> C are provided. , 1Bk, the reference numerals are omitted. In this embodiment, each of the image forming units 1Y, 1M, 1C, and 1Bk is integrally provided with the photoreceptor 2, the charging roller 3, the developing device 4, and the cleaning blade 5, and is detachable from the apparatus main body 100. It is configured as a process unit.

  In FIG. 1, an exposure device 6 as a latent image forming means for forming an electrostatic latent image on the surface of each photoconductor 2 is disposed above each image forming unit 1Y, 1M, 1C, 1Bk. The exposure apparatus 6 of the present embodiment includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and is configured to irradiate the surface of each photoconductor 2 with laser light based on image data. The LED array may be used.

  On the other hand, below the respective image forming units 1Y, 1M, 1C, and 1Bk, a transfer device 7 that transfers a toner image onto a sheet as a recording medium is disposed. The transfer device 7 has an intermediate transfer belt 8 formed of an endless belt as a transfer body. The intermediate transfer belt 8 is stretched around a driving roller 9, a driven roller 10, a primary transfer roller 11, and a cleaning counter roller 21. Both ends of the driven roller 10 are urged toward the intermediate transfer belt 8 by springs, whereby tension is applied to the intermediate transfer belt 8. Further, when the driving roller 9 rotates counterclockwise in the figure, the intermediate transfer belt 8 is configured to run (rotate) in the direction indicated by the arrow in the figure.

  The four primary transfer rollers 11 are disposed at positions facing the four photoconductors 2. Each primary transfer roller 11 presses the inner peripheral surface of the intermediate transfer belt 8 at each position, and a primary transfer nip is formed at a place where the pressed portion of the intermediate transfer belt 8 and each photoconductor 2 abut. ing. In the present embodiment, each primary transfer roller 11 is offset in the moving direction of the intermediate transfer belt 8 and the vertically upward direction in the drawing with respect to the lowest point of the photoconductor 2 in the drawing. Each primary transfer roller 11 is connected to a power source (not shown), and a predetermined direct current voltage (DC) and / or alternating current voltage (AC) is applied to the primary transfer roller 11. In this embodiment, a metal roller is used as the primary transfer member, but a conductive blade, a conductive sponge roller, or the like can also be used in addition to this.

  Further, a secondary transfer roller 12 as a secondary transfer member is disposed at a position facing the drive roller 9. The secondary transfer roller 12 presses the outer peripheral surface of the intermediate transfer belt 8, and a secondary transfer nip is formed at a position where the secondary transfer roller 12 and the intermediate transfer belt 8 come into contact with each other. Similar to the primary transfer roller 11, the secondary transfer roller 12 is connected to a power source (not shown) so that a predetermined direct current voltage (DC) and / or alternating current voltage (AC) is applied to the secondary transfer roller 12. It has become. The secondary transfer roller 12 is configured by covering a metal cored bar with an elastic body made of a conductive material. As the secondary transfer roller 12, for example, a conductive roller, an electronic conductive type roller, or the like can be used.

  A belt cleaning device 13 for cleaning the surface of the intermediate transfer belt 8 is disposed on the outer peripheral surface of the intermediate transfer belt 8 on the right end side in the drawing. The belt cleaning device 13 includes a cleaning blade 22 that removes toner and foreign matter on the intermediate transfer belt 8, a cleaning counter roller 21 disposed at a position facing the cleaning blade 22 with the intermediate transfer belt 8 interposed therebetween, and the like. . The cleaning blade 22 is made of urethane rubber or the like, and is in contact with the moving direction of the intermediate transfer belt 8 in the counter direction. A waste toner transfer hose (not shown) extending from the belt cleaning device 13 is connected to the entrance of a waste toner container 14 disposed below the transfer device 7.

  A toner mark sensor 23 used to adjust the density and position of each color image by measuring the amount and position of toner transferred onto the intermediate transfer belt 8 is disposed on the left side of the intermediate transfer belt 8 in the drawing. Has been. Here, the toner mark sensor 23 is an optical sensor that combines a regular reflection method and a diffuse reflection method.

  In the lower part of the figure of the apparatus main body 100, a paper feed tray 15 for storing paper P as a recording medium, a paper feed roller 16 for feeding paper P from the paper feed tray 15, and the like are provided. Here, the paper P includes thick paper, postcard, envelope, plain paper, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like. Further, an OHP sheet, an OHP film, or the like can be used as a recording medium.

  On the other hand, a pair of paper discharge rollers 17 for discharging the paper to the outside are disposed on the upper portion of the apparatus main body 100 in the drawing. A discharge tray 18 for stocking sheets discharged outside the apparatus is provided on the upper surface of the apparatus main body 100.

  In the apparatus main body 100, a transport path B for transporting the paper P from the paper feed tray 15 through the secondary transfer nip to the paper discharge tray 18 is disposed. In the conveyance path B, a pair of registration rollers 19 as timing rollers for conveying the sheet to the secondary transfer nip at the conveyance timing is arranged upstream of the position of the secondary transfer roller 12 in the sheet conveyance direction. Yes. On the other hand, a fixing device 20 for fixing the unfixed image transferred to the paper is disposed downstream of the position of the secondary transfer roller 12 in the paper transport direction.

Next, a basic operation of the printer according to the present embodiment will be described with reference to FIG.
When the image forming operation is started, the respective photoconductors 2 of the respective image forming units 1Y, 1M, 1C, and 1Bk are rotationally driven clockwise by a driving device (not shown), and the surface of each photoconductor 2 is charged with the charging roller 3. Are uniformly charged to a predetermined polarity. An electrostatic latent image is formed on the charging surface of each photoconductor 2 by exposure from the exposure device 6 based on image information from a reading device or a computer (not shown). At this time, the image information to be exposed on each photoconductor 2 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. As the electrostatic latent image formed on the photosensitive member 2 is supplied with toner by each developing device 4, the electrostatic latent image is visualized (visualized) as a toner image.

  When the image forming operation is started, the intermediate transfer belt 8 starts to rotate in the direction of the arrow in the figure. Further, a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 11. Thereby, a transfer electric field is formed in the primary transfer nip.

  Thereafter, when each color toner image on the photoconductor 2 reaches the primary transfer nip as the photoconductor 2 rotates, the toner image on each photoconductor 2 is formed by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 8. Thus, a full-color toner image is carried on the surface of the intermediate transfer belt 8. Further, the toner on each photoreceptor 2 that could not be transferred to the intermediate transfer belt 8 is removed by the cleaning blade 5. Next, the surface of each photoconductor 2 is subjected to a static elimination action by a static elimination device (not shown), and the surface potential is initialized to prepare for the next image formation.

  Further, the paper feed roller 16 starts to rotate, and the paper P is sent from the paper feed tray 15 to the transport path B. The paper P sent to the transport path B is timed by the registration roller 19 and sent to the secondary transfer nip. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 8 is applied to the secondary transfer roller 12, thereby forming a transfer electric field in the secondary transfer nip. .

  Thereafter, when the toner image on the intermediate transfer belt 8 reaches the secondary transfer nip with the rotation of the intermediate transfer belt 8, the transfer electric field formed in the secondary transfer nip causes the transfer on the intermediate transfer belt 8. The toner images are collectively transferred onto the paper P. Further, the toner on the intermediate transfer belt 8 that could not be transferred onto the paper P is removed by the cleaning blade 22 of the belt cleaning device 13 and then conveyed to the waste toner container 14.

  Thereafter, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 17 and stocked on the paper discharge tray 18.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single-color image is formed using any one of the four image forming units 1Y, 1M, 1C, and 1Bk. Two or three image forming units can be used to form a two-color or three-color image.

Hereinafter, an operation when a monochrome image is formed in the printer of this embodiment will be described with reference to FIG.
As shown in FIG. 2, when forming a monochrome image, the color primary transfer rollers 11Y, 11M, and 11C except for the black primary transfer roller 11Bk are opposite to the direction in which they are pressed against the intermediate transfer belt 8. Move in the direction. Specifically, brackets 30 that support both ends of the color primary transfer rollers 11Y, 11M, and 11C are provided, and the brackets 30 are moved downward in the figure using cams, solenoids, or the like (not shown). As a result, the intermediate transfer belt 8 is moved from the position indicated by the two-dot chain line in the drawing to the position indicated by the solid line, and the intermediate transfer belt 8 is separated from each of the photoconductors 2Y, 2M, 2C other than the black photoconductor 2Bk. It becomes. That is, the bracket 30 functions as a separation mechanism that separates the photoreceptors 2Y, 2M, and 2C from the intermediate transfer belt 8. As described above, when the monochrome image is formed, the color photoreceptors 2Y, 2M, and 2C that are not used are separated from the intermediate transfer belt 8 so that the color photoreceptors 2Y, 2M, and 2C are worn. And the deterioration of color toner is suppressed. When the image forming operation is started, an image is formed only on the black photoconductor 2Bk. The image is transferred to a sheet, fixed, and discharged out of the apparatus in the same manner as in the above-described full-color image formation.
The primary transfer rollers 11Y, 11M, and 11C for color may be separately separated from each other.

Hereinafter, characteristic portions of the printer according to the present embodiment will be described.
As shown in FIG. 3, the printer according to the present embodiment includes a control unit 27 that controls the linear rotation speed of each of the photoreceptors 2Y, 2M, 2C, and 2Bk. In the present embodiment, a stepping motor is used as a drive motor that rotates the photoreceptors 2Y, 2M, 2C, and 2Bk, and the control unit 27 adjusts the number of pulses input to the stepping motor. The rotation angle of the motor shaft is adjusted. A DC motor may be used as the drive motor. In this case, it is possible to control the rotation linear velocity of each of the photoreceptors 2Y, 2M, 2C, and 2Bk by adjusting the voltage value applied to the DC motor.

  As a method for adjusting or confirming the rotational speed of the drive motor, for example, there is a method using a stroboscope. Specifically, the flashing light emitted from the stroboscope is irradiated to the rotating drive motor, the emission frequency is adjusted so that the drive motor appears to be stationary, and the frequency is used as the rotation speed of the drive motor. .

  As another method, there is a method of detecting an FG signal. The FG signal is a signal obtained by converting a change in the magnetic field caused by the rotation of the magnet inside the drive motor. By detecting this FG signal, the rotational speed of the drive motor can be adjusted or confirmed.

  The control unit 27 is configured to control the linear rotation speed of each of the photosensitive members 2Y, 2M, 2C, and 2Bk based on information input from the operation panel 28 provided in the apparatus main body. Specifically, the information that the control unit 27 obtains from the operation panel 28 is information related to the image forming mode, which is a monochrome image or a full-color image, and information related to the type of paper used for image formation. In this embodiment, in order to obtain the paper type information easily and at low cost, the input information of the operation panel 28 is used. However, it is possible to separately provide a detection means for detecting the paper type.

FIG. 4 shows an example of the linear velocity ratio of the photoconductor set based on the image forming mode and the paper type.
The linear velocity ratio of the photoreceptor shown here is the linear velocity ratio with respect to the intermediate transfer belt. When the linear velocity of the photosensitive member is V1 and the linear velocity of the intermediate transfer belt is V2, the linear velocity ratio of the photosensitive member is ((V1−V2) / V2) × 100 (%). For example, when the linear speed ratio of the photosensitive member is −0.5%, this means that when the linear speed of the intermediate transfer belt at that time is 100%, the linear speed of the black photosensitive member is the linear speed of the intermediate transfer belt. It is 0.5% slower than the speed.

  As shown in FIG. 4, in this embodiment, plain paper and thicker and thicker thick paper are used, but the linear velocity ratio of the photosensitive member when using plain paper is the default value. Specifically, when using plain paper, in the monochrome mode, the linear velocity ratio of the black photosensitive member is set to -0.5%, and in the full color mode, the linear velocity ratio of the black photosensitive member is the same as that in the monochrome mode. The linear speed ratio of the color photoconductor is set to -0.5%. As described above, the linear velocity ratio of the black photosensitive member and the color photosensitive member is set to a negative value. When the linear velocity ratio is set to a positive value, the toner image on the photosensitive member is set. This is because a part of the toner is not transferred to the intermediate transfer belt, and so-called insect erosion may occur. However, the conditions that cause worm erosion are caused not only by the linear speed ratio of the photoconductor but also by factors such as the properties of the toner and the releasability of the intermediate transfer belt. Therefore, the default linear speed ratio of the photoconductor is negative. The value is not limited to ± 0 and may be a positive value.

  When medium thick paper or thick paper is used, the linear speed ratio between the black photoconductor and the color photoconductor in the full color mode is the same as the linear speed ratio when the plain paper is used. However, if the linear speed of the intermediate transfer belt, which is the comparison target, is set to the normal speed for plain paper, it is set to a slower medium speed for medium thick paper and a slower speed for thick paper. In this case, even if the linear velocity ratio is the same, the linear velocity itself of the photoreceptor varies depending on the paper type.

On the other hand, when medium thick paper or thick paper is used and in the monochrome mode, the linear velocity ratio of the black photoconductor is different from the linear velocity ratio (−0.5%) when using the plain paper. Specifically, when the monochrome mode is executed using medium thick paper or thick paper, the linear velocity ratio of the black photoconductor is set to -2.5%. That is, in this case, the linear speed of the black photoconductor is set to be slower than the linear speed of the intermediate transfer belt. Further, the linear velocity ratio (−2.5%) of the black photoconductor in the monochrome mode is set to be smaller than the linear velocity ratio (−0.5%) of the black photoconductor in the full color mode.
Note that the linear velocity ratio of the black photoconductor in the monochrome mode may be set more finely according to the type of paper used. For example, the linear speed ratio when using plain paper is set to -0.5%, the linear speed ratio when using medium thick paper is set to -1.5%, and the linear speed ratio when using thick paper is set to -2.5%. May be.

  In this way, when the monochrome mode is executed using medium thick paper or thick paper, the linear velocity of the black photoconductor is made slower than the linear velocity of the intermediate transfer belt (the linear velocity ratio of the black photoconductor is If it is made smaller, the resistance against the movement of the intermediate transfer belt increases at the contact portion between the transfer belt and the black photoconductor. As a result, as shown in FIG. 5, the intermediate transfer belt 8 is loosened and the belt tension is loosened on the upstream side in the belt movement direction of the black photoconductor 2Bk. In FIG. 5, the slack of the belt is exaggerated in order to easily understand the state where the tension of the intermediate transfer belt 8 has been loosened. However, in actuality, it is difficult to judge visually. It is slack.

  As a result, even when the linear speed of the intermediate transfer belt temporarily decreases due to the load when the paper enters the secondary transfer nip, the tension of the intermediate transfer belt is loosened, so the temporary linear speed decrease It is possible to absorb the belt position fluctuation due to. That is, when a temporary speed reduction of the intermediate transfer belt 8 occurs, a load F (see FIG. 5) in the direction opposite to the belt moving direction is applied, but the load F can be reduced by loosening the intermediate transfer belt 8. Thus, the portion of the intermediate transfer belt 8 that is pulled can be absorbed. As a result, it is possible to suppress the influence due to the temporary speed reduction of the intermediate transfer belt accompanying the entry of the sheet into the secondary transfer nip.

  In the case of plain paper, the load when the paper enters the secondary transfer nip is less likely to occur than in the case of medium-thick paper or thick paper, so that the tension of the intermediate transfer belt may not be loosened too much. For this reason, in the present embodiment, when executing the monochrome mode using plain paper, the linear velocity ratio of the photosensitive member for black is set to −0.5%, and the linear velocity difference of the photosensitive member with respect to the intermediate transfer belt is set. It is small. Also, if the difference in the linear velocity of the photosensitive member relative to the intermediate transfer belt is too large, the belt running performance becomes unstable and the possibility of image erosion increases. Therefore, if the linear velocity of the photosensitive member can be increased, There is also a reason that closer to the linear velocity is preferable.

  Also, in this embodiment, even when using medium-thick paper or thick paper that increases the load on the intermediate transfer belt, in the full-color mode, the linear speed ratio of each photoconductor is set in the same manner as when using plain paper. doing. The reason for this is that in the full color mode, the number of photoconductors in contact with the intermediate transfer belt is larger than in the monochrome mode, so the belt accompanying the entry of the paper into the secondary transfer nip as described above. This is because the position fluctuations of are difficult to occur.

  For this reason, in the present embodiment, in the full color mode in which the belt position does not easily change as paper enters, even if medium-thick paper or thick paper is used, the linear velocity ratio of the photoconductor to the intermediate transfer belt is reduced. It corresponds without. As a result, in the full-color mode, the belt running performance becomes unstable, and the problem of causing image worm-feeding is reliably prevented. Even in the full color mode, if the influence of the belt position change due to the paper entering is large, the difference in the linear velocity of the photosensitive member with respect to the intermediate transfer belt is increased, and the linear velocity of the photosensitive member becomes the linear velocity of the intermediate transfer belt. However, it may be set to be slower.

  As described above, in this embodiment, in particular, in the monochrome mode in which the number of contact of the photoconductor is small and the belt position is likely to change as the paper enters, the linear velocity of the photoconductor is changed to the linear velocity of the intermediate transfer belt. On the other hand, by making it slower, the influence accompanying the entry of the paper is suppressed. That is, by reducing the linear velocity ratio of the photosensitive member to the intermediate transfer belt, the influence due to the intrusion of the paper is suppressed.

  By the way, in the configuration in which the intermediate transfer belt 8 is stretched between the driving roller 9 and the driven roller 10 as in this embodiment, the intermediate transfer belt 8 is pulled upstream of the driving roller 9 in the belt moving direction. It is done. Accordingly, in the intermediate transfer belt 8, the portion where the belt moves from the driven roller 10 toward the driving roller 9 is relatively tight, and conversely, the portion where the belt moves from the driving roller 9 toward the driven roller 10. Therefore, it becomes relatively slack side. In this embodiment, the photoreceptor 2 is brought into contact with the intermediate transfer belt 8 on the slack side. For this reason, it is easy to give the intermediate transfer belt 8 slack as compared with the configuration in which the photosensitive member 2 is brought into contact with the tension side. As described above, in this embodiment, since the photosensitive member is easily arranged to give looseness to the intermediate transfer belt, when the monochrome mode is executed using medium-thick paper or thick paper, there is more influence due to paper entry. It can be effectively suppressed.

  Similarly, in the configuration in which the intermediate transfer belt 8 is stretched by the driving roller 9 and the plurality of driven rollers 10, the intermediate transfer belt 8 is brought into contact with the intermediate transfer belt 8 on the slack side. It becomes easy to give a bend.

  In the above embodiment, when medium thick paper or thick paper is used, the linear speed ratio of each photoconductor is set to a negative value in the full color mode. The linear velocity ratio of each photoconductor can be set to ± 0 or a positive value. Accordingly, there are the following three patterns for setting the relative linear velocity of the photoconductor when the number of contact of the photoconductor is large and small.

  First, when the number of contact of the photosensitive member with the intermediate transfer belt is large, the linear speed of the photosensitive member in the contact state with respect to the intermediate transfer belt is set to be low, and the number of contact of the photosensitive member with the intermediate transfer belt is small. In this case, the linear velocity of the photosensitive member in contact with the intermediate transfer belt is set slower than that in the case where the number of contacts is large.

  Second, when the number of contact of the photosensitive member with the intermediate transfer belt is large, the linear speed of the photosensitive member in the contact state is set equal to the linear speed of the intermediate transfer belt, and the contact of the photosensitive member with the intermediate transfer belt is set. A pattern in which, when the number of contacts is small, the linear velocity of the photosensitive member in contact is set slower than the linear velocity of the intermediate transfer belt.

  Third, when the number of contact of the photosensitive member with the intermediate transfer belt is large, the linear speed of the photosensitive member in the contact state is set higher than the linear speed of the intermediate transfer belt, and the contact of the photosensitive member with the intermediate transfer belt is set. When the number of contacts is small, the linear speed of the photosensitive member in the contact state is set to be slower than the linear speed of the intermediate transfer belt.

  Which one of the above three patterns is selected may be determined in consideration of conditions that cause image erosion.

  In the above embodiment, the linear speed ratio of the photosensitive member to the intermediate transfer belt is changed by controlling the rotational linear velocity of the photosensitive member. However, the rotational speed of the intermediate transfer belt is controlled. It is also possible to control the rotational speeds of both the photoreceptor and the intermediate transfer belt.

FIG. 6 is a diagram illustrating an embodiment configured to control the rotation speed of the intermediate transfer belt.
In this case, the control unit 27 controls the rotational speed of the intermediate transfer belt 8 by controlling the rotational speed of the driving roller 9 based on the input information of the operation panel 28. For example, when the monochrome mode is executed using medium-thick paper or thick paper, the linear speed of the intermediate transfer belt is made faster than that in the full-color mode, so that the relative speed of the photoconductor in the monochrome mode is the same as in the above embodiment. The target line speed can be reduced. That is, the linear velocity ratio of the black photoconductor in the monochrome mode can be reduced.

FIG. 7 is a diagram showing an embodiment configured to control the rotational speeds of both the photoreceptor and the intermediate transfer belt.
In this case, the control unit 27 controls the rotational linear speed of each of the photoreceptors 2Y, 2M, 2C, and 2Bk and the rotational speed of the drive roller 9 based on information input from the operation panel 28. As a result, the relative linear velocity of the photosensitive member can be reduced, particularly in the monochrome mode when using medium-thick paper or thick paper, as in the above-described embodiment. That is, the linear velocity ratio of the black photoconductor in the monochrome mode can be reduced.

FIG. 8 is a diagram showing an embodiment in which an environmental condition detection sensor is further provided.
The rigidity of the paper varies depending on the temperature and humidity in the usage environment of the image forming apparatus. Therefore, at a certain temperature or humidity, even if the load on the intermediate transfer belt is small when the sheet enters the secondary transfer nip, the load applied to the intermediate transfer belt increases as a result of the temperature or humidity change. In some cases.

  Therefore, as shown in FIG. 8, in addition to the configuration of the above embodiment, an environmental condition detection sensor 29 for detecting at least one of temperature and humidity in the usage environment may be further provided. In this case, the control unit 27 changes the linear speed ratio of the photoreceptor to the intermediate transfer belt based on at least one of the temperature and humidity measured by the environmental condition detection sensor 29. This makes it possible to control the linear speed of the photoconductor in consideration of the rigidity of the paper that changes depending on the temperature or humidity of the usage environment, and temporarily reduces the speed of the intermediate transfer belt as the paper enters the secondary transfer nip. It is possible to more effectively suppress the influence of.

  In FIG. 8, the control unit 27 is configured to control the rotational linear speed of each of the photosensitive members 2Y, 2M, 2C, and 2Bk. It may be a case where the rotational speed of both of the transfer belts is controlled.

  Further, the load received by the intermediate transfer belt varies depending on when the sheet enters the secondary transfer nip, during passage, and when discharged, so as shown by a solid line in FIG. The linear speed V2 of the intermediate transfer belt in each state at the time of ejection E3 is also different. For this reason, it is desirable to change the linear velocity ratio of the photosensitive member to the intermediate transfer belt in accordance with each state.

  Specifically, in the example shown in FIG. 9, the linear speed V2 of the intermediate transfer belt greatly decreases at the time of entry E1, returns to the normal linear speed during the passage E2, and is not as high as the entry time E1 at the time of discharge E3. descend. That is, when the linear speed of E1 when the intermediate transfer belt enters is V2a, the linear speed of E2 during passing is V2b, and the linear speed at discharge is V2c, the relationship is V2a <V2c <V2b. Then, following the change in the linear velocity of the intermediate transfer belt, the linear velocity V1 of the photosensitive member indicated by a two-dot chain line in the drawing is greatly reduced at the time of entry E1, and returned to the normal linear velocity during the passage E2, and discharged. At time E3, control is performed so that the voltage is lowered with a small width. That is, assuming that the linear velocity of E1 when the photosensitive member enters is V1a, the linear velocity of E2 during passing is V1b, and the linear velocity at the time of ejection is V1c, V1a <V1c <V1b. Further, if the linear speed ratio of the photosensitive member to the intermediate transfer belt at the time of entry E1 is S1, the linear speed ratio of E2 during passing is S2, and the linear speed ratio of E3 at the time of ejection is S3, S1 <S3 <S2. The linear speed ratio in each state is set. Thus, as the width of the speed reduction of the intermediate transfer belt is large and problems caused by belt position fluctuations are likely to occur, the intermediate transfer belt is more easily bent by making the linear speed ratio smaller. It is possible to suppress the problem caused by the position fluctuation of the image to a higher degree.

  As described above, according to the present invention, when the contact number of the photosensitive member with respect to the intermediate transfer belt is small, the linear velocity of the photosensitive member in the contact state with respect to the intermediate transfer belt is larger than when the contact number is large. By controlling the ratio to be small, the tension of the intermediate transfer belt can be loosened and the intermediate transfer belt can be loosened upstream of the most upstream photoconductor in the belt moving direction. As a result, it is possible to suppress the belt position fluctuation accompanying the paper entering the secondary transfer nip, and to obtain a good image free from density change caused by the belt position fluctuation.

  Further, as in the above-described embodiment, each photosensitive member is disposed so as to abut on the portion (slack side) where the intermediate transfer belt moves from the driving roller toward the driven roller, thereby relaxing the intermediate transfer belt. It becomes easy to give, and the malfunction resulting from the positional variation of a belt can be suppressed more effectively.

  In addition, this invention is not limited to the above-mentioned embodiment, Of course, a various change can be added in the range which does not deviate from the summary of this invention. In the above-described embodiment, the case where only the black photoconductor is brought into contact with the intermediate transfer belt in the monochrome mode has been described as an example. However, only one photoconductor to be brought into contact is a photoconductor for colors other than black. Also good. In the above-described embodiment, in the monochrome mode, one photosensitive member for black is brought into contact and three photosensitive members for color are separated from each other. The body may be separated to form an image. That is, the present invention can be applied to any configuration that includes two or more photoconductors, and a part of the photoconductors are separated from the intermediate transfer belt. Further, a belt-shaped secondary transfer belt may be used as the secondary transfer member.

  The present invention is also applicable to a configuration having three or more image forming modes in which the contact number of the photosensitive member is different. In this case, the mode in which the number of contact of the photosensitive member is small is more easily affected by the paper entering the secondary transfer nip, so that the intermediate transfer of the photosensitive member becomes smaller as the number of contact of the photosensitive member decreases. It is desirable to set the linear velocity ratio with respect to the belt to be smaller.

  The image forming apparatus according to the present invention is not limited to a printer, and may be a copier, a facsimile, or a complex machine of these.

2 Photoconductor 8 Intermediate transfer belt 9 Drive roller 10 Driven roller 12 Secondary transfer roller (secondary transfer member)
27 Control unit 29 Environmental condition detection sensor

JP 2010-134149 A

Claims (8)

A plurality of photoreceptors;
An intermediate transfer belt in contact with each of the photosensitive members;
A secondary transfer member in contact with the intermediate transfer belt,
In the image forming apparatus configured such that some of the plurality of photosensitive members and the intermediate transfer belt can be separated from each other.
When the contact number of the photosensitive member with respect to the intermediate transfer belt is small, the linear speed ratio of the photosensitive member in contact with the intermediate transfer belt is controlled to be smaller than when the contact number is large. An image forming apparatus. Setting the linear speed of the photoconductor slower than the linear speed of the intermediate transfer belt;
2. The image according to claim 1, wherein when the number of contact of the photoconductor with the intermediate transfer belt is smaller than when the photoconductor is in contact with the intermediate transfer belt, the linear velocity difference between the photoconductor and the intermediate transfer belt with respect to the intermediate transfer belt is controlled to be large. Forming equipment. The intermediate transfer belt is stretched by a driving roller and a driven roller,
The image forming apparatus according to claim 1, wherein the photosensitive member is disposed in contact with a portion where the intermediate transfer belt moves from the driving roller toward the driven roller.   The image forming apparatus according to claim 1, further comprising: a mode in which a plurality of the photoconductors are brought into contact with the intermediate transfer belt and a mode in which an image is formed by bringing the one photoconductor into contact with the intermediate transfer belt. Image forming apparatus.   The linear velocity ratio of the photosensitive member in the contact state with respect to the intermediate transfer belt can be changed according to the type of the recording medium entering the contact portion between the secondary transfer member and the intermediate transfer belt. The image forming apparatus according to 1. When the recording medium entering the contact portion between the secondary transfer member and the intermediate transfer belt is thin, even if the number of contact of the photoconductor with the intermediate transfer belt increases or decreases, Without changing the linear speed ratio to the intermediate transfer belt,
When the recording medium entering the contact portion between the secondary transfer member and the intermediate transfer belt is thick, when the number of contact of the photoconductor with the intermediate transfer belt is small, compared to when the contact number is large. The image forming apparatus according to claim 1, wherein the linear speed ratio of the photosensitive member in contact with the intermediate transfer belt is controlled to be small.   The image forming apparatus according to claim 1, wherein a linear speed ratio of the photosensitive member in contact with the intermediate transfer belt can be changed based on at least one of temperature and humidity in a use environment.   When the recording medium enters the abutting portion between the secondary transfer member and the intermediate transfer belt, the recording medium passes through the abutting portion, and the recording medium is ejected from the abutting portion, depending on whether the recording medium is discharged. The image forming apparatus according to claim 1, wherein the linear speed ratio of the photosensitive member in contact with the intermediate transfer belt is changed.

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