JP3571864B2 - Sheet conveying device and image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sheet conveying apparatus and an image forming apparatus that can avoid skewing, wrinkling, and the like when conveying a sheet.
[0002]
[Prior art]
In a copying machine, a laser beam printer, or the like, a sheet of paper or the like is transported by using a roller made of a hard material such as iron (hereinafter referred to as an “iron roller”) and a roller formed by winding a soft material such as rubber around a hard roller shaft such as an iron. In general, a pair of rubber rollers is used. A load is applied to the ends of the roller pair to press both rollers, and a rotational force is applied to one or both of the rollers to convey the sheet sandwiched therebetween. FIG. 4 shows a model of the roller pair. 50 is an iron roller and 51 is a rubber roller.
[0003]
The soft material such as rubber is used to secure a contact area between the rollers 50 and 51 called a nip. The nip is necessary for transmitting the conveying force and for applying heat and pressure to the sheet material in the fixing roller. For accurate conveyance and fixing, it is required that the nip width is uniform in the axial direction.
[0004]
However, in an actual roller, as shown by an arrow F in FIG. 4 , since both ends of the roller shaft are pressed by a spring or the like to secure the nip, the roller shaft may be bent. Therefore, the nip pressure is concentrated at the end, and the nip width is narrow at the center of the roller and wide at the end. FIG. 5 shows the state of the nip with diagonal lines.
[0005]
As is clear from FIG. 5 , a difference in the amount of distortion in the nip is generated between the center and the end of the rubber roller 51, and the sheet conveyance speed is different. FIG. 6 shows the distribution of the conveying speed V of the sheet 52 as viewed from each part when the nip width is not uniform. It is considered that this speed distribution causes a change in magnification and wrinkles.
[0006]
In addition, if there is a difference between the left and right pressing loads due to the floating force of the drive gear, etc., the left and right nip widths also become non-uniform. This also causes a speed difference between both ends of the shaft of the sheet, which causes a conveyance failure such as a deviation in parallelism (skew).
[0007]
In order to solve these problems, the rigidity of the roller shaft has been increased or the distribution of pressure has been corrected by attaching a crown or an inverted crown to the roller so that the roller shaft is hardly bent. Regarding the non-uniformity of both ends in the longitudinal direction of the roller, the non-uniformity is corrected by changing the strength of the springs on both sides. However, it is difficult to make the nip width completely uniform.
[0008]
[Problems to be solved by the invention]
Here, the mechanism of the occurrence of the conveyance failure due to the non-uniform nip width during the sheet conveyance will be examined in further detail.
[0009]
As described above, the nip width when a load is applied only to the ends of the roller shaft, as shown in FIG. 5, the central portion is narrower end becomes wider type. This is because pressure is concentrated on the end of the nip due to the bending of the roller, and the rubber roller is pushed into the gap. This difference in the amount of rubber pushed in results in a difference in the amount of distortion on the rubber surface. The harder the rubber is pushed, the more the rubber tries to escape from its incompressible nature and stretches the rubber surface. FIG. 7 shows a cross-sectional view when the roller pair is pressed.
[0010]
In FIG. 7 , where the rubber roller 51 is not deformed, the rubber surface should be advanced by d when rotated by the central angle ω. However, in the nip, the surface is extended by d '(d <d') as much as the surface is stretched by pressing. Therefore, if the rubber roller 51 is a driving roller, the sheet 52 is fed at an increased speed.
[0011]
The sheet 52 sent in contact with the rubber surface is fed faster as the rubber surface has a larger elongation. Therefore, the amount by which the sheet 52 is fed differs between the central portion and the end portion of the roller. For this reason, as shown in FIG. 6 , a force is applied in a direction different from the traveling direction, which causes transport failure such as parallelism and wrinkles.
[0012]
Further, in most of the actual apparatuses, the rollers are driven on one side of the roller shaft via a gear. In this case, when the roller is rotating, a floating force is generated in the gear, and the left and right pressures become uneven. As a result, the left and right nibs become uneven. FIG. 8 shows an example of this nip. For the same reason as described above, this causes non-uniform transport speeds on the right and left sides of the roller, which causes a transport failure such as a deviation in parallelism.
[0013]
In order to solve the above problem, a method is adopted in which the left and right pressing forces are unbalanced from the beginning in anticipation of the gear levitation force, but in order to make the nip non-uniform when not rotating, It is considered that a deviation occurs when the end of the sheet material is pressed against the roller before the rotation to adjust the direction, thereby causing skew.
[0014]
The present invention has been made in view of the above points, and an object of the present invention is to provide a sheet conveying apparatus and an image forming apparatus that eliminate non-uniformity of a nip width of a roller pair and do not cause a conveyance failure. .
[0015]
[Means for Solving the Problems]
A typical configuration according to the present invention for achieving the above object is, in a sheet conveying apparatus that conveys a sheet by rotating a pair of pressed rollers, a first roller and a lower hardness than the first roller. A second roller having a roller portion, and a driven rotatable urging roller for urging the first roller or the second roller toward the other roller , wherein the urging roller is in a roller axial direction. It is characterized in that it is configured to be movable .
[0016]
In the above configuration, by biasing one roller to the other roller by the biasing roller, a load can be applied even at the center of the roller, for example, where the nip width is likely to be narrow, and the entire roller is evenly distributed. A nip width can be provided.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, a sheet conveying apparatus according to an embodiment of the present invention and an image forming apparatus using the same will be described with reference to the drawings.
[0018]
[First Embodiment]
Referring to FIGS about the first embodiment will be described. FIG. 1 is a schematic diagram of a sheet conveying device according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of an image forming apparatus using the sheet conveying device.
[0019]
Here, as the order of the description, first, the overall configuration of the image forming apparatus using the sheet transport apparatus will be described with reference to FIG . 2, and then the configuration of the sheet transport apparatus will be described with reference to FIGS.
[0020]
<< Overall Configuration of Image Forming Apparatus >>
As shown in FIG. 2, an image forming apparatus (laser beam printer) A according to the present embodiment irradiates a drum-shaped electrophotographic photosensitive member with information light based on image information from a laser scanner 1 to the photosensitive member. A latent image is formed, and the latent image is developed to form a toner image. In synchronism with the formation of the toner image, a plurality of recording sheets S are separated and fed one by one from a detachable cassette 2 in which a plurality of recording sheets S are stacked and stored by a feeding roller 3, and a pair of conveying rollers 4 serving as a sheet conveying device. The sheet is conveyed by the registration roller pair 5 and is guided by the guide plate 6 to be conveyed to the image forming means.
[0021]
The registration roller pair 5 conveys the recording sheet S to the image forming means in synchronization with the image forming operation. The image forming unit of the present embodiment is configured such that a photosensitive drum 7 which is an electrophotographic photosensitive member, and a process cartridge B in which a primary charging unit, a developing unit, and a cleaning unit (not shown) are formed into a cartridge are detachably mountable to the image forming apparatus A. Make up. Then, the photosensitive drum 7 is rotated in synchronization with the conveyance of the recording sheet S, and the surface thereof is uniformly charged by a charging unit, and the information light from the laser scanner 1 is exposed to the photosensitive drum 7 via an exposure unit. To form a latent image. The toner frictionally charged by the developing means is transferred in accordance with the latent image to form a toner image, and the toner image is applied to a transfer roller 8 as a transfer means by applying a voltage having a polarity opposite to that of the toner image to the recording sheet S. The image is transferred to an image and recorded. The toner remaining on the photosensitive drum 7 after the transfer of the toner image is removed by a cleaning unit.
[0022]
The recording sheet S on which an image is formed by the image forming unit is conveyed to the fixing unit 11 by the conveying belt 9 and the guide plate 10, and the toner image transferred to the recording sheet S by applying heat and pressure in the fixing unit 11 Is established.
[0023]
The recording sheet S on which the image has been fixed is discharged to a discharge section 15 formed on the upper portion of the apparatus by the discharge roller pairs 12 and 13 and the guide member 14.
[0024]
｝ Configuration of sheet transport device｝
Next, the configuration of a transport device that transports the recording sheet S will be described with reference to FIG.
[0025]
The sheet conveying device is configured to convey and hold the sheet S between the pair of rollers by rotating a pair of rollers such as a pair of conveying rollers 4 or a pair of registration rollers 5. Here, the configuration of the roller pair will be described using the registration roller pair 5 as an example.
[0026]
As shown in FIG. 1, the registration roller pair 5 includes a first roller 20 having a high hardness roller portion 20b made of iron, plastic, or the like on a roller shaft 20a, and a lower hardness than the roller portion 20b on a roller shaft 21a. And a second roller 21 having a roller portion 21b made of rubber or the like. Then, both ends of the roller shaft 20a of the first roller 20 are urged by a force F by a spring or the like, and the first roller 20 is pressed against the second roller 21 to form a nip between the two rollers.
[0027]
Further, a biasing roller 22 is pressed against a substantially central portion in the longitudinal direction of the first roller 20 by a biasing force F0. The urging roller 22 urges the roller portion 20b of the first roller 20 toward the roller portion 21b of the second roller 21, and is mounted so as to be rotated by the rotation of the first roller 20. .
[0028]
As described above, the urging roller 22 urges a portion where the nip width at the central portion is smaller than that at both ends in the longitudinal direction of the roller portion 20b due to the bending of the roller shaft 20a, and applies a load to the portion. For this reason, the nip width becomes uniform throughout the longitudinal direction of the roller, and wrinkling and skew during sheet conveyance can be prevented. Since the urging roller 22 is driven to rotate, it does not affect the rotation of the roller pair.
[0029]
The urging force of the urging roller 22 is set to a value such that a portion where the nip width is narrowed is uniform with a portion where the nip width is wide.
[0030]
Then, in this embodiment the biasing roller 22 slidably configured in the longitudinal direction of the first roller 20 constitutes a longitudinal any position of the first roller 20 so as to urge.
[0031]
For example, as shown in FIG. 3, the pressing force of the first roller 20 becomes non-uniform with F1 and F2 at both ends of the roller shaft due to the floating force of a drive gear (not shown) attached to the roller shaft of the second roller 21. In this case (F1 <F2), the nip width is wide on the right and left sides of the left and right hands in the longitudinal direction of the roller and narrow on the left side 24 as it is. Therefore, the urging roller 22 is arranged to urge the first roller 20 at a position deviated leftward from the center where the nip width becomes narrow.
[0032]
By moving the urging roller 22 by an appropriate distance in this manner, uneven load distribution on the left and right is corrected, and uneven nip width and nip pressure can be corrected.
[0033]
[Other embodiments]
In the above-described embodiment, the example in which the first roller 20 is urged by the correction roller 22 has been described. However, instead of the first roller 20, the second roller 21 is urged by the urging roller 22. Can obtain the same effect.
[0034]
Further, in the above-described embodiment, an example is shown in which the first roller of the registration roller pair 5 is made of iron or plastic, and the second roller is made of rubber, but the material of the roller is not limited to this. Instead, it is only necessary that the hardness of the second roller is lower than that of the first roller.
[0035]
In the above-described embodiment, the configuration of the rollers has been described by exemplifying the pair of registration rollers 5. However, similar effects can be obtained by applying the configuration to the rollers of the pair of rollers such as the pair of transport rollers 4 and the pair of discharge rollers 12, 13. Obtainable.
[0036]
Furthermore, in the above-described embodiment, an example in which the sheet conveying apparatus is applied to an image forming apparatus that conveys a recording sheet has been described. However, the present invention can be suitably applied to a document reading apparatus that conveys a document as a sheet. it is obvious.
[0037]
【The invention's effect】
Since the present invention is configured as described above, by urging one roller to the other roller by the urging roller, for example, a load can be applied even at the central portion of the roller where the nip width tends to be narrow, and the entire roller Can have a uniform nip width. Then, by moving the urging roller by an appropriate distance, uneven load distribution on the left and right sides is corrected, and uneven nip width and nip pressure can be corrected. For this reason, skew and wrinkling of the sheet are prevented, and in an image forming apparatus using the same, sheet conveyance accuracy is enhanced, and a high-quality image can be formed.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view of a sheet conveying device according to the present invention.
FIG. 2 is a schematic explanatory view of an image forming apparatus using a sheet conveying device.
FIG. 3 is an explanatory diagram of an embodiment in which an urging roller is arranged at a biased position.
FIG. 4 is an explanatory diagram of a roller pair for conveying a sheet.
FIG. 5 is an explanatory diagram of a nip width of a roller pair.
FIG. 6 is an explanatory diagram of a sheet conveying speed when a nip width of a roller pair is uneven.
FIG. 7 is an explanatory diagram of a sheet conveyance amount when a nip width of a roller pair is narrow and when it is wide.
FIG. 8 is an explanatory diagram in the case where the nip width is uneven at both ends in the longitudinal direction of the roller.
[Explanation of symbols]
A image forming apparatus B process cartridge S recording sheet 1 laser scanner 2 cassette 3 feeding roller 4 transport roller pair 5 registration roller pair 6 guide plate 7 photosensitive drum 8 transfer roller 9 Conveyor belt
10… Guide plate
11 ... fixing means
12 ... discharge roller pair
13… Discharge roller pair
14… Guide member
15 ... discharge section
20… First roller
20a… Roller shaft
20b… Roller part
21… Second roller
21a… Roller shaft
21b… Roller part
22 ... biasing roller

Claims (3)

In a sheet conveying device that conveys a sheet by rotating a pair of pressed rollers,
The first roller,
A second roller having a roller portion having a lower hardness than the first roller,
A driven rotatable urging roller for urging the first roller or the second roller toward the other roller,
Has,
A sheet conveying device, wherein the urging roller is configured to be movable in a roller axis direction . The sheet conveying device according to claim 1 , wherein the second roller is driven via a gear provided on one side of a roller shaft of the second roller . In an image forming apparatus that conveys a sheet to form an image,
A sheet conveying device according to claim 1 or 2 for conveying a sheet;
Image forming means for forming an image on a conveyed sheet,
An image forming apparatus comprising:

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