JP5974941B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Japanese Patent Application Laid-Open No. 2004-133830 discloses a first generation unit that generates a first speed corresponding value corresponding to the peripheral speed of the image carrier, and a second speed that generates a second speed corresponding value corresponding to the moving speed of the recording medium. An image forming apparatus is disclosed that includes: a generating unit configured to control the driving unit of the image carrier to equalize the first and second velocity correspondence values.

JP 2000-172148 A

  It is an object of the present invention to suppress fluctuations in the conveyance speed at the leading end side and the trailing end side of a recording medium in the nip region.

  According to a first aspect of the present invention, there is provided an image holding body that holds an image and a transfer body that conveys the recording medium in a nip area between the image holding body and transfers the image onto the recording medium, and the nip area. It is disposed closest to the nip region on the upstream side in the conveyance direction, has a conveyance force smaller than the conveyance force by the image holding body and the transfer body, and the conveyance speed of the recording medium by the image holding body and the transfer body. And an conveying member that conveys the recording medium to the nip region at a conveying speed equal to or less than a constant velocity.

The invention according to claim 1 is further arranged on the upstream side in the transport direction with respect to the transport member, and the transport member has a transport force larger than the transport force by the transport member after aligning the front end of the recording medium in the width direction. upstream transport member for transporting the recording medium to the conveying member at a higher conveying speed than the conveying speed by, Ru comprising a.

  According to the configuration of the first aspect of the present invention, it is possible to suppress the speed fluctuation of the conveyance speed at the front end side and the rear end side of the recording medium in the nip region as compared with the case where the conveyance member in this configuration is not provided.

According to the configuration of the first aspect of the present invention, compared to the case where the upstream conveying member in the present configuration is not provided, the fluctuation in the conveyance speed at the leading end side and the trailing end side of the recording medium in the nip region is suppressed, and the recording is performed. Both suppression of the skew of the medium can be achieved.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment. It is a side view which shows the structure of the registration roll pair and conveyance roll pair which concern on this embodiment. It is the figure which looked at the registration roll pair and conveyance roll pair which concern on this embodiment in the axial direction. It is the figure which looked at the photosensitive drum concerning this embodiment, the transfer roll, and the registration roll pair in the axial direction. It is the figure which looked at the photoconductive drum which concerns on a comparative example, the transfer roll, and the registration roll pair in the axial direction. It is the figure which looked at the photosensitive drum concerning the modification, the transfer roll, the conveyance roll pair before transfer, and the registration roll pair in the axial direction. FIG. 6 is a schematic diagram illustrating a modification in which an intermediate transfer member is applied as an image holding member.

  Below, an example of an embodiment concerning the present invention is described based on a drawing.

(Configuration of image forming apparatus 10)
First, the configuration of the image forming apparatus 10 will be described. FIG. 1 is a schematic diagram illustrating a configuration of the image forming apparatus 10.

  As shown in FIG. 1, the image forming apparatus 10 includes an apparatus main body 11 in which each component is housed. Inside the apparatus main body 11, a plurality of storage units 12 that store recording media P such as paper, an image forming unit 14 that forms an image on the recording medium P, and an image forming unit 14 are formed on the recording medium P. A fixing device 56 that fixes the image to the recording medium P, a transport unit 16 that transports the recording medium P from the storage unit 12 to the image forming unit 14, and a control unit 20 that controls the operation of each unit of the image forming apparatus 10. , Is provided. Further, a discharge unit 18 for discharging the recording medium P on which the image is fixed by the fixing device 56 is provided at the upper part of the apparatus main body 11.

  The image forming unit 14 includes a photosensitive drum 32 (an example of an image holding member) that holds an image. The photosensitive drum 32 rotates in one direction (for example, counterclockwise in FIG. 1). Around the photosensitive drum 32, a charging roll 23 as a charging device for charging the photosensitive drum 32 and the photosensitive drum 32 charged by the charging roll 23 are exposed in order from the upstream side in the rotation direction of the photosensitive drum 32. An exposure device 36 that forms an electrostatic latent image on the photosensitive drum 32, a developing device 80 that develops the electrostatic latent image formed on the photosensitive drum 32 by the exposure device 36 to form a black toner image, and A transfer roll 26 (an example of a transfer body) that transfers a black toner image formed on the photosensitive drum 32 by the developing device 80 to the recording medium P is provided.

  The exposure device 36 is configured to form an electrostatic latent image based on the image signal sent from the control unit 20. Examples of the image signal sent from the control unit 20 include an image signal acquired by the control unit 20 from an external device.

  A toner storage container 58 that stores toner is provided above the exposure device 36. A toner storage chamber 58 </ b> A that stores toner is formed inside the toner storage container 58. Between the toner storage container 58 and the developing device 80, a toner transport device 60 that transports toner from the toner storage chamber 58A of the toner storage container 58 toward the developing device 80 is provided.

  The transfer roll 26 is in contact with the photosensitive drum 32, and a nip region T that sandwiches the recording medium P between the transfer roll 26 and the photosensitive drum 32 is formed. The transfer roll 26 conveys the recording medium P sandwiched between the photosensitive drum 32 in the nip region T, and transfers the toner image formed on the photosensitive drum 32 to the recording medium P in the nip region T. It has become. That is, the nip region T is a transfer position (transfer portion) at which the toner image formed on the photosensitive drum 32 is transferred to the recording medium P.

  The transport unit 16 includes a delivery roll 46 that sends out the recording medium P accommodated in each storage unit 12, a transport path 48 that transports the recording medium P sent out by the delivery roll 46, and a downstream direction in which each delivery roll 46 is transported. A pair of conveyance rolls 50 that convey the recording medium P provided on the side to the downstream side (a nip area TA described later) and the recording medium P conveyed by each pair of conveyance rolls 50 are nip areas T. A registration roll pair 70 (an example of a conveyance member). The specific configuration of the registration roll pair 70 will be described later.

  The fixing device 56 includes a heating roll 56A and a pressure roll 56B. In the fixing device 56, the toner image transferred to the recording medium P by the transfer roll 26 is fixed to the recording medium P by heating by the heating roll 56A and pressing by the pressure roll 56B. A discharge roll 52 that discharges the recording medium P on which the toner image is fixed to the discharge unit 18 is provided above the fixing device 56 (downstream in the transport direction).

  Further, the reverse conveyance path 37 for reversing the recording medium P having the toner image fixed on one side and feeding it back to the nip region T is opposite to the photosensitive drum 32 with respect to the transfer roll 26 (right side in FIG. 1). ). When images are formed on both sides of the recording medium P, the recording medium P with the toner image fixed on one side is switched back by the discharge roll 52 and guided to the reverse conveyance path 37 and sent back to the nip region T. It is like that.

  Next, an image forming operation for forming an image on the recording medium P in the image forming apparatus 10 will be described.

  In the image forming apparatus 10, the recording medium P sent out from any of the storage units 12 by the sending roll 46 is sent to the nip region T by the transport roll pair 50 and the registration roll pair 70.

  On the other hand, in the image forming unit 14, the photosensitive drum 32 is charged by the charging roll 23, and then exposed by the exposure device 36, so that an electrostatic latent image is formed on the photosensitive drum 32. The electrostatic latent image is developed by the developing device 80, and a black toner image is formed on the photosensitive drum 32. This black toner image is transferred to the recording medium P in the nip region T by the transfer roll 26.

  The recording medium P onto which the toner image has been transferred is conveyed to the fixing device 56 and the toner image is fixed by the fixing device 56. When an image is formed only on one side of the recording medium P, the recording medium P is discharged to the discharge unit 18 by the discharge roll 52 after the toner image is fixed.

  When images are formed on both sides of the recording medium P, after the image is fixed on one side, the recording medium P is switched back by the discharge roll 52, reversed, and sent to the reverse conveyance path 37. Further, the recording medium is again fed into the nip region T from the reverse conveyance path 37, and an image is formed on the opposite surface where no image is recorded in the same manner as described above, and is discharged to the discharge unit 18 by the discharge roll 52. . As described above, a series of image forming operations are performed.

(Specific configuration of registration roll pair 70)
As shown in FIG. 1, the registration roll pair 70 is disposed immediately before the nip area T by the photosensitive drum 32 and the transfer roll 26 (upstream in the conveyance direction with respect to the nip area T and closest to the nip area T). A nip area TA that sandwiches the recording medium P is formed between the registration roll pair 70.

  In addition, the registration roll pair 70 has a function of aligning the leading end of the recording medium P conveyed from the conveyance roll pair 50 in the width direction (the front-rear direction of the paper surface in FIG. 1) and conveying it to the nip region T.

  Specifically, the registration roll pair 70 stops driving in a predetermined period after the leading end of the recording medium P conveyed from the conveyance roll pair 50 reaches the registration roll pair 70, and then drives to register the recording medium. P is conveyed.

  As a result, as shown in FIG. 2, even when the recording medium P is skewed and conveyed to the nip area TA of the registration roll pair 70, the nip area TA is reached first in the width direction of the recording medium P. 2 (the left side portion of the recording medium P in FIG. 2) is blocked by the registration roll pair 70, and further, the recording medium P is pushed into the nip area TA by the conveying roll pair 50, so that the nip area TA is reached first. The portion (the right portion in FIG. 2) opposite to the portion (the left portion of the recording medium P in FIG. 2) reaches the nip area TA. Thereby, the front ends of the recording media P are aligned in the width direction. At this time, a slack (loop) RA is formed on the recording medium P as shown in FIG. This sagging (loop) RA is larger in the portion (left portion of the recording medium P in FIG. 2) that has reached the registration roll pair 70 earlier than the opposite side (right portion of the recording medium P in FIG. 2).

  The registration roll pair 70 starts transporting the recording medium P in a state where the leading ends of the recording medium P are aligned in the width direction, so that the skew of the recording medium P is eliminated and the nip between the photosensitive drum 32 and the transfer roll 26 is removed. The recording medium P is conveyed to the area T.

  Note that the recording medium P indicated by a two-dot chain line in FIG. 2 is not skewed (skewed) and is conveyed in a direction orthogonal to the axis of the conveying roll pair 50 (registration roll pair 70). Yes. In FIG. 2, the alternate long and short dash line TA indicates the nip area TA (start position of the nip area TA) of the registration roll pair 70.

  Further, the registration roll pair 70 is configured to transport the recording medium P to the nip region T at a predetermined timing so as to match the transfer position (transfer start position) and the leading end position of the recording medium P.

  The photosensitive drum 32 and the transfer roll 26 are configured to transport the recording medium P whose leading ends are aligned in the width direction by the registration roll pair 70 to the fixing device 56.

  Here, the registration roll pair 70 is configured to transport the recording medium P to the nip region T with a transport force smaller than the transport force of the photosensitive drum 32 and the transfer roll 26. That is, the conveying force by the photosensitive drum 32 and the transfer roll 26 is made larger than the conveying force by the registration roll pair 70. The conveyance force is a frictional force (dynamic frictional force) that acts on the recording medium along the recording medium conveyance direction between the registration roll pair 70 (photosensitive drum 32 and transfer roll 26) and the recording medium P. , Friction coefficient (dynamic friction coefficient) μ × nip load N

  Further, the registration roll pair 70 is configured to transport the recording medium P at a transport speed that is equal to or lower than the transport speed of the recording medium P by the photosensitive drum 32 and the transfer roll 26.

(Operation according to the embodiment)
Next, the operation according to the embodiment will be described.

  In the present embodiment, the recording medium P sent out from any of the accommodating portions 12 by the sending roll 46 is transported by the transport roll pair 50 to the nip area TA of the registration roll pair 70. The recording medium P transported to the nip area TA is transported to the nip area T by the photosensitive drum 32 and the transfer roll 26 with the leading edges aligned by the registration roll pair 70.

  The recording medium P conveyed to the nip region T is conveyed to the fixing device 56 by the photosensitive drum 32 and the transfer roll 26.

  Here, as shown in FIG. 4, the recording medium P whose leading end has reached the nip region T is sandwiched between the photosensitive drum 32 and the transfer roll 26 and the photosensitive drum 32 and the transfer roll. 26, and the rear end side is sandwiched by the nip area TA of the registration roll pair 70 and is conveyed by the registration roll pair 70.

  Since the registration roll pair 70 transports the recording medium P at a transport speed equal to or lower than the transport speed of the recording medium P by the photosensitive drum 32 and the transfer roll 26, between the nip region T and the nip region TA, The slack (loop) R (see FIG. 5) of the recording medium P is not formed.

  Further, since the conveyance force by the photosensitive drum 32 and the transfer roll 26 is larger than the conveyance force by the registration roll pair 70, the conveyance speed of the registration roll pair 70 is the conveyance speed of the recording medium P by the photosensitive drum 32 and the transfer roll 26. Even in a later case, the photosensitive drum 32 and the transfer roll 26 convey the recording medium P from the nip region T toward the fixing device 56 against the conveyance load from the registration roll pair 70. At this time, the recording medium P is pulled by the photosensitive drum 32 and the transfer roll 26 to be applied with tension, and the rear end side is slipped (slid) between the registration roll pair 70 and is conveyed by the registration roll pair 70. Is done.

  As described above, in this embodiment, the recording medium P is not pushed from the nip area TA to the nip area T, and the conveyance speed of the recording medium P is controlled by the photosensitive drum 32 and the transfer roll 26.

  On the other hand, in a comparative example (see FIG. 5) in which the conveyance speed of the registration roll pair 70 is higher than the conveyance speed of the recording medium P by the photosensitive drum 32 and the transfer roll 26, as described later, the nip region T and the registration roll. A slack (loop) R of the recording medium P is formed between the pair 70.

  That is, in the comparative example, there is no slack (loop) R of the recording medium P when the leading edge of the recording medium P conveyed by the registration roll pair 70 reaches the nip region T (see the two-dot chain line in FIG. 5). In a state where the leading end side of the recording medium P is conveyed by the photosensitive drum 32 and the transfer roll 26 and the trailing end side of the recording medium P is conveyed by the registration roll pair 70, the conveyance speed (conveyance amount) of the registration roll pair 70 is the photosensitive element. A slack (loop) R of the recording medium P is gradually formed by being larger than the conveyance speed (conveyance amount) of the recording medium P by the drum 32 and the transfer roll 26.

  At this time, a pushing force for pushing the recording medium P into the nip region T is generated, and the pushing force increases as the slack (loop) of the recording medium P increases. For this reason, the conveyance speed of the recording medium P in the nip region T is gradually increased.

  Further, since the slack (loop) of the recording medium P is gradually formed, the posture (entry direction) changes when entering the nip region T between the front end side and the rear end side of the recording medium P. That is, on the leading end side of the recording medium P, the nip region T is entered in a posture shown by a two-dot chain line in FIG. 5, and on the trailing end side of the recording medium P, the nip region T is entered in a posture shown by a solid line in FIG. . For this reason, it becomes a factor for promoting the speed fluctuation of the recording medium P in the nip region T.

  As described above, in the comparative example, in the nip region T, the speed fluctuation of the conveyance speed occurs at the front end side and the rear end side of the recording medium P. Due to this speed fluctuation, the partial magnification of the toner image to be transferred fluctuates between the front end side and the rear end side of the recording medium P. That is, the toner image transferred to the recording medium P is extended at a portion where the conveyance speed is high, and the toner image transferred to the recording medium P is contracted at a portion where the conveyance speed is low.

  In contrast, in the present embodiment, as described above, the recording medium P is not pushed from the nip area TA to the nip area T, and the conveyance speed of the recording medium P is controlled by the photosensitive drum 32 and the transfer roll 26. The sag (loop) of the recording medium P is formed between the nip area T and the nip area TA by increasing the conveying speed of the registration roll pair 70 than the conveying speed of the recording medium P by the photosensitive drum 32 and the transfer roll 26. Compared with the comparative example (see FIG. 5), the speed fluctuation of the conveyance speed at the front end side and the rear end side of the recording medium P in the nip region T is suppressed.

  Further, in this embodiment, since no slack (loop) R (see FIG. 5) of the recording medium P is formed between the nip area T and the nip area TA, the recording medium is between the nip area T and the nip area TA. Compared with the comparative example (see FIG. 5) in which the slack (loop) of P is formed, the posture (entry direction) when entering the nip region T does not change between the leading end side and the trailing end side of the recording medium P, and the nip In the region T, fluctuations in the conveyance speed at the leading end side and the trailing end side of the recording medium P are suppressed.

  Since fluctuations in the conveyance speed of the recording medium P in the nip region T are suppressed, fluctuations in the partial magnification of the transferred toner image are suppressed on the front end side and the rear end side of the recording medium P.

(Modification)
In the above embodiment, the registration roll pair 70 is arranged immediately before the nip region T (upstream in the conveyance direction with respect to the nip region T and closest to the nip region T). As shown, a configuration in which the pre-transfer conveying roll pair 72 is disposed between the nip area TA and the nip area T of the registration roll pair 70 may be employed. That is, the pre-transfer conveyance roll pair 72 may be disposed immediately before the nip region T (upstream in the conveyance direction with respect to the nip region T and closest to the nip region T).

  The pre-transfer transport roll pair 72 transports the recording medium P to the nip region T with a transport force smaller than the transport force of the photosensitive drum 32 and the transfer roll 26. That is, the conveying force by the photosensitive drum 32 and the transfer roll 26 is made larger than the conveying force by the pre-transfer conveying roll pair 72.

  Further, the pre-transfer conveyance roll pair 72 conveys the recording medium P at a conveyance speed equal to or lower than the conveyance speed of the recording medium P by the photosensitive drum 32 and the transfer roll 26. A nip region TB that sandwiches the recording medium P is formed between the pre-transfer conveyance roll pair 72. Note that the pre-transfer conveyance roll pair 72 does not have a function of aligning the leading end of the recording medium P in the width direction.

  In the modified example, the registration roll pair 70 transports the recording medium P to the nip region TB with a transport force larger than the transport force of the pre-transfer transport roll pair 72. Further, the registration roll pair 70 is configured to transport the recording medium P at a transport speed faster than the transport speed of the recording medium P by the pre-transfer transport roll pair 72.

  Also in this modification, the registration roll pair 70 has a function of aligning the leading ends of the recording media P in the width direction. Also in this modified example, the registration roll pair 70 conveys the recording medium P to the nip region TB at a predetermined timing so as to match the transfer position (transfer start position) and the leading end position of the recording medium P. It has become.

  In this modification, the conveyance force by the registration roll pair 70 may be larger, smaller, or the same as the conveyance force by the photosensitive drum 32 and the transfer roll 26. Further, the conveyance speed by the registration roll pair 70 may be faster, slower, or the same as the conveyance speed by the photosensitive drum 32 and the transfer roll 26.

  As described above, in this modification, the pre-transfer conveyance roll pair 72 is used as an example of the conveyance member disposed immediately before the nip region T (upstream in the conveyance direction with respect to the nip region T and closest to the nip region T). . Further, in this modified example, as an example of an upstream conveyance member that is arranged upstream in the conveyance direction with respect to the pre-transfer conveyance roll pair 72 and conveys the recording medium to the pre-transfer conveyance roll pair 72 after aligning the front end of the recording medium in the width direction. A registration roll pair 70 is used.

(Operation of modification)
According to the configuration of this modified example, the recording medium P conveyed to the nip area TA of the registration roll pair 70 is conveyed to the nip area TB by the pre-transfer conveyance roll pair 72 with the leading end aligned by the registration roll pair 70. The recording medium P transported to the nip region TB is transported to the nip region T by the photosensitive drum 32 and the transfer roll 26 by the pre-transfer transport roll pair 72.

  Here, as shown in FIG. 6, the recording medium P whose leading end has reached the nip region T is sandwiched between the nip region T between the photosensitive drum 32 and the transfer roll 26, and the photosensitive drum 32 and the transfer roll. 26, and the rear end side is sandwiched by the nip region TB of the pre-transfer conveyance roll pair 72 and is conveyed by the pre-transfer conveyance roll pair 72.

  The pre-transfer conveyance roll pair 72 conveys the recording medium P at a conveyance speed equal to or lower than the conveyance speed of the recording medium P by the photosensitive drum 32 and the transfer roll 26, so that the nip region T and the nip region TB are separated. In the meantime, the slack (loop) R (see FIG. 5) of the recording medium P is not formed.

  Further, since the conveyance force between the photosensitive drum 32 and the transfer roll 26 is larger than the conveyance force due to the pre-transfer conveyance roll pair 72, the conveyance speed of the pre-transfer conveyance roll pair 72 is determined by the photosensitive drum 32 and the transfer roll 26. Even if it is slower than the conveyance speed of the recording medium P, the photosensitive drum 32 and the transfer roll 26 face the conveyance load from the pre-transfer conveyance roll pair 72 toward the fixing device 56 from the nip region T. The recording medium P is conveyed. At this time, the recording medium P is pulled by the photosensitive drum 32 and the transfer roll 26 to be applied with tension, and the rear end side slips (slids) between the pair of pre-transfer conveying rolls 72 before being transferred. It is conveyed by the conveyance roll pair 72.

  As described above, in this modification, the recording medium P is not pushed into the nip area T, and the conveyance speed of the recording medium P is controlled by the photosensitive drum 32 and the transfer roll 26. Variations in the conveyance speed on the side and rear end sides are suppressed.

  Further, in this modified example, since no slack (loop) R (see FIG. 5) of the recording medium P is formed between the nip region T and the nip region TB, the nip is formed between the leading end side and the trailing end side of the recording medium P. The posture at the time of entering the region T does not change, and the speed fluctuation of the conveyance speed on the front end side and the rear end side of the recording medium P in the nip region T is suppressed. Thereby, fluctuations in the partial magnification of the transferred toner image are suppressed on the front end side and the rear end side of the recording medium P.

  Furthermore, since the registration roll pair 70 transports the recording medium P with a transport force larger than the transport force of the pre-transfer transport roll pair 72, compared to the case of transporting with a transport force smaller than the transport force of the pre-transfer transport roll pair 72, The recording medium P is conveyed in a state in which the posture of the recording medium P with the front end aligned is maintained. That is, the posture of the recording medium P whose posture is corrected so that the leading ends are aligned is suppressed from returning to the original skew state.

  As described above, the conveyance force of the registration roll pair 70 is larger than the conveyance force of the pre-transfer conveyance roll pair 72, but the conveyance speed of the recording medium P by the registration roll pair 70 is the recording medium by the pre-transfer conveyance roll pair 72. Since the slack (loop) R of the recording medium P is formed between the nip area TA and the nip area TB, and the registration roll pair 70 acting on the pre-transfer conveyance roll pair 72 is formed. The conveyance load is suppressed.

(Other variations)
In the above embodiment, the example using the photosensitive drum 32 has been described as an example of the image holding body. However, the present invention is not limited to this. For example, as illustrated in FIG. An intermediate transfer member 132 (an intermediate transfer belt, an intermediate transfer drum, or the like) that transfers an image formed by the image forming unit 133 to the recording medium P may be used.

  In the above-described embodiment, the registration roll pair 70 (in the above modification, the pre-transfer conveyance roll pair 72) is configured to convey upward toward the nip region T. In the modification, the transport direction of the pre-transfer transport roll pair 72) may be, for example, the horizontal direction (see FIG. 7) or the downward direction, and the transport direction of the transport member and the direction of gravity are irrelevant.

  The present invention is not limited to the above embodiment, and various modifications, changes, and improvements can be made. For example, the modification examples described above may be appropriately combined.

10 Image forming apparatus 26 Transfer roll (an example of a transfer body)
32 Photosensitive drum (an example of an image carrier)
70 registration roll pair (an example of a conveying member, an example of an upstream conveying member)
72 Pre-transfer conveyance roll pair (an example of a conveyance member)
P Recording medium T Nip area

Claims (1)

An image carrier for holding an image;
A transfer body that conveys the recording medium in a nip region with the image holding body, and transfers the image to the recording medium;
The recording medium is transported by the image holding body and the transfer body, which is disposed closest to the nip area on the upstream side in the transport direction with respect to the nip area and has a transporting force smaller than the transporting force by the image holding body and the transfer body. A transport member that transports the recording medium to the nip region at a transport speed equal to or less than a speed, the transport member not having a function of aligning the front end of the recording medium in the width direction;
Arranged upstream in the conveying direction with respect to the conveying member, the leading edge of the recording medium is aligned in the width direction, and the conveying force is larger than the conveying force by the conveying member and faster than the conveying speed by the conveying member. An upstream conveying member that conveys the recording medium to the conveying member;
An image forming apparatus comprising:

Images