JP2008273725A - Sheet conveying apparatus and image forming apparatus - Google Patents

Abstract

A sheet conveying apparatus capable of accurately correcting and conveying a curl that varies greatly depending on the material of the sheet, and an image forming apparatus including the sheet conveying apparatus.
A sheet conveying apparatus that conveys a sheet by a plurality of driving rollers 20 provided on a driving shaft 21 that rotates by transmitting driving force, and a roller 22 that rotates in contact with the driving roller 20. The rotation center of each drive roller 20 is decentered and is decentered by rotation of the drive shaft 21, and the phase of the eccentricity of the adjacent drive roller 20 is shifted.
[Selection] Figure 3a

Description

  The present invention relates to a sheet conveying apparatus capable of correcting and conveying a sheet curl, and an image forming apparatus represented by a copying machine, a printer, and a facsimile apparatus using the sheet conveying apparatus.

  In an image forming apparatus using an electrophotographic system such as a copying machine or a printer, a toner image transferred to a sheet in an image forming unit is fixed by heat and pressure in a fixing unit. A conventional fixing device includes a heating roller and a pressure roller that rotate while being pressed against each other, and an unfixed image is passed between the rollers to perform fixing.

  However, in such a fixing device, when the recording sheet is passed between the heating roller and the pressure roller, the temperature on the heating roller side surface of the recording sheet becomes higher than that on the pressure roller side surface. This inevitably curls the recording sheet, impairs the stackability of the recording sheet on the discharge tray and intermediate tray after passing through the fixing, and causes jamming due to the curling of the recording sheet during duplex copying. Or

  It is known that the strength and direction of curl generated on a recording sheet varies depending on the usage environment such as temperature and humidity, the paper quality, the moisture content that varies depending on the storage state of the paper, and the like. Furthermore, the curl state also changes depending on the amount of toner applied to the recording sheet, such as differences in image data such as photographic images and text documents.

  In order to avoid such a situation, a plurality of discharge rollers having a large diameter and a small diameter are combined and arranged alternately to form a corrugated shape in the sheet width direction intersecting the sheet conveying direction of the recording sheet. Some of them give waist (rigidity) and correct curl. For example, as shown in FIG. 8 a, a plurality of discharge rubber rollers 101 are fastened to the discharge roller shaft 100. The rotation center of the discharge rubber roller 101 coincides with the axis of the discharge roller shaft 100. A discharge roller 102 urged by a spring is in contact with a position facing the discharge rubber roller 101. A plurality of discharge roller / roller pairs are arranged on the same shaft, and a waist rubber roller 103 having no opposing roller is disposed between the discharge roller / roller pair. The diameter is slightly larger than the discharged rubber roller 101. As a result, the sheet on which the toner is fixed by being heated and pressed is seated.

  That is, as shown in FIG. 8b, the sheet is slightly waved, the portion where the discharge rubber roller 101 and the discharge roller 102 are located is convex upward, and the portion where the waist rubber roller 103 is located is convex downward. In this case, the sheet S is curled up and down in the upstream and downstream of the sheet conveying direction, and is formed with a crest and a trough in the sheet width direction intersecting the sheet conveying direction. , Curling is suppressed.

  In addition, a pair of discharge rollers is arranged on the downstream side of the heating roller and pressure roller, the position of the discharge roller pair is made variable in the vertical direction, and the sheet clamping position relationship between the discharge roller pair is changed to change the curl correction force. (Patent Document 1).

JP-A-8-290857

  In the configuration in which the large and small rollers are regularly arranged as described above, a general recording sheet is used in a standard use environment, and the curling in the sheet conveyance direction of the recording sheet having a certain standard image is performed. Demonstrate a temporary effect.

  However, with respect to the curling action in the sheet width direction in which the end of the recording sheet moves up and down in the direction intersecting the sheet conveyance direction, the sheet does not have a deformation that stretches, so the correction force is weakened and a satisfactory correction effect is obtained. It becomes difficult.

  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 capable of accurately correcting and conveying curls that vary greatly depending on the material of the sheet, and an image forming apparatus including the sheet conveying apparatus. Is to provide.

  A representative means in the present invention for solving the above-described problem has a plurality of drive rollers provided on a drive shaft that rotates by transmitting a driving force, and rotation of adjacent drive rollers among the plurality of drive rollers. The center is eccentric and provided on the drive shaft, and the eccentric phases of the adjacent drive rollers are out of phase.

  In the present invention, a plurality of ridges and valleys having no directionality are formed on the conveyed sheet by the plurality of rollers rotating eccentrically, and the entire surface is seated. For this reason, it is possible to correct curls that vary greatly depending on the usage environment, the material of the sheet, etc., and the upper curl and lower curl on the leading edge / rear edge, or left / right edge of the sheet can be reduced to a predetermined amount or less. It becomes possible.

  Next, a sheet conveying apparatus according to an embodiment of the present invention will be described with reference to the drawings together with an image forming apparatus including the sheet conveying apparatus.

[First Embodiment]
1 to 5 show a sheet conveying apparatus and an image forming apparatus according to a first embodiment of the present invention.

[Entire configuration of image forming apparatus]
First, the overall configuration of the image forming apparatus according to the present embodiment will be described together with the image forming operation with reference to FIG. The image forming apparatus A of this embodiment is a color laser printer that forms an image by electrophotography.

  The apparatus main body 1 is provided with image forming means using an electrophotographic system. The image forming unit of the present embodiment includes a process cartridge P and a belt conveying unit 9 described later. Process cartridges P (Pa, Pb, Pc, Pd) that form four-color toner images of cyan, yellow, magenta, and black are arranged in order from the bottom. Each process cartridge has the same configuration except for the color of the toner, and is provided with charging means, developing means 3 (3a, 3b, 3c, 3d), etc. around the photosensitive drum 2 (2a, 2b, 2c, 2d). ing. When forming an image, the exposure unit 4 (4a, 4b, 4c, 4d) irradiates the photosensitive drum 2 with light based on each color image information to form an electrostatic image, which is developed by the developing unit 3 with toner. Visualize by developing.

  A sheet feeding unit that conveys a sheet stored in a feeding cassette 5 that is detachably mounted to the image forming unit is provided at a lower portion of the apparatus main body 1. The sheet feeding unit separates and feeds the sheets in the feeding cassette 5 one by one by the pickup roller 6 and the separation roller 7, and conveys the sheet to the belt conveying unit 9 by the conveyance roller 8.

  The belt conveying means 9 serving as a transfer means has a conveying belt 9a stretched and supported by a driving roller 9b and driven rollers 9c, 9d and 9e, and is arranged to face all four photosensitive drums 2. When the sheet S fed to the conveyance belt 9a is electrostatically attracted and conveyed while being in contact with each photosensitive drum 2, the above-described toner image is transferred to the sheet S by applying a bias.

  The sheet onto which the toner image has been transferred is conveyed to the fixing means 10 by the conveyance belt 9a, where the toner image is fixed on the sheet by being heated and pressurized, and is discharged by a pair of discharge rollers constituting the sheet conveying apparatus B. It is discharged to the discharge unit 11 at the upper part of the apparatus main body.

[Sheet Conveying Device]
Next, the sheet conveying apparatus B according to the present embodiment will be described. The sheet conveying apparatus according to the present embodiment is disposed downstream of the fixing unit 10 in the sheet conveying direction, and is configured as a discharge roller pair that discharges a sheet heated and pressed by the fixing unit 10.

  Of the pair of discharge rollers, the driving roller 20 that rotates is constituted by a rubber roller, and a driving shaft 21 is eccentrically attached to the driving roller 20 as shown in FIG. For this reason, when a driving force is transmitted from a driving source (not shown) and the driving shaft 21 rotates, the driving roller 20 rotates eccentrically. Further, as shown in FIG. 3a, a plurality of the drive rollers 20 are provided in the longitudinal direction of the drive shaft 21, and the eccentric phases of the adjacent drive rollers 20 are attached with a 180 ° shift.

  Each of the drive rollers 20 has a roller 22 that is a driven roller in contact with the drive roller by a spring 23 and is rotated by the rotation of the drive roller 20. The drive roller 20 and the roller 22 sandwich and convey the sheet.

  When the sheet is nipped and conveyed, since the driving roller 20 rotates eccentrically as described above, the contact pressure with the sheet S periodically changes with each rotation of the driving roller 20, and the sheet S in the sheet conveying direction changes. Unevenness changes with the roller period. Therefore, as shown in FIG. 3b, irregularities are formed in the sheet conveying direction.

  Further, since the eccentric phases of the adjacent drive rollers 20 are shifted by 180 °, unevenness is also formed in the sheet width direction intersecting the sheet conveyance direction. Even if the eccentric phase difference between the adjacent drive rollers is not 180 ° as in the present embodiment, irregularities are formed in the sheet width direction as long as they are shifted by a predetermined amount.

  Here, FIG. 4 and FIG. 5 show images of the unevenness formed when the roller is conveyed by the driving roller 20 and the roller 22. 4 shows an image of the cross section in the sheet width direction of FIG. 3b, and FIG. 5 shows an image of the cross section in the sheet conveyance direction of FIG. 3b. FIG. 5 is a cross section of the sheet S at the position of two adjacent drive rollers 20. Naturally, the cycle of the two peaks is the same as the rotation cycle of the drive roller 20. The phase difference between the two rotation cycles is approximately 180 °, and the drive roller 20 is eccentric with an opposite phase.

  By performing the phase shift of the driving roller 20 over the entire width of the sheet S, a number of valleys and valleys having no back-up direction such as the sheet conveying direction or the direction intersecting the sheet conveying direction are formed on the sheet S. The whole surface will be seated. Thereby, the curl of the sheet can be corrected regardless of the curl of the rear end of the front end and the right end of the left end.

  Further, in this embodiment, the distance between adjacent drive rollers whose phases are shifted by 180 ° is made substantially the same as the circumferential length of the drive roller 20. As a result, the relationship between the peaks and valleys that are traced obliquely with respect to the sheet conveying direction can be arranged at approximately 45 ° with respect to the sheet conveying direction. The arrangement in which this is 0 ° is close to that of the prior art. When this angle is 0 or 90 degrees, the peaks and valleys formed on the sheet coincide with each other in the sheet conveyance direction or the sheet width direction, and the sheet conveyance direction curl or the sheet width direction curl is weak. A configuration that is strong against both curls is the relationship of the valleys and valleys arranged at approximately 45 degrees as in the present embodiment.

  As described above, in the present embodiment, the sheet seating direction by the peaks and valleys formed on the sheet is set to 45 ° with respect to the sheet conveying direction, but the angle of the seating direction is limited to 45 °. There is no need. The angle in the seating direction can be directed in the desired direction by adjusting the outer diameter (circumferential length) of the drive roller 20 and the interval between the adjacent drive rollers 20.

  As described above, in the sheet conveying apparatus according to the present embodiment, a plurality of ridges and valleys having no orientation of the seat are formed on the conveyed sheet by the plurality of eccentric rotating rollers, and the whole surface is seated. It will be. For this reason, it is possible to correct curls that vary greatly depending on the usage environment, the material of the sheet, etc., and the upper curl and lower curl on the leading edge / rear edge, or left / right edge of the sheet can be reduced to a predetermined amount or less. It becomes possible.

  In this embodiment, all of the plurality of rollers provided on the same axis are decentered. However, at least one of the plurality of rollers adjacent to each other may be attached with a relative phase difference. It is sufficient that a roller that is not eccentric is included in the plurality of rollers. However, in order to sit on the entire surface, it is necessary to dispose an eccentric roller over the entire width of the sheet S.

  Moreover, although the structure which a driven roller contact | abuts all the several drive rollers provided on the same axis | shaft is demonstrated as this Embodiment, the structure which contacted every other driven roller may be sufficient, for example. By arranging every other pair of rollers for nipping and conveying the sheet, wrinkles generated on the sheet between adjacent drive rollers can be suppressed.

[Second Embodiment]
Next, an apparatus according to a second embodiment will be described with reference to FIGS. Note that the basic configuration of the apparatus of this embodiment is the same as that of the above-described embodiment, and thus a duplicate description is omitted. Here, a configuration that is a feature of this embodiment will be described. Moreover, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above.

  This embodiment differs from the first embodiment in the eccentric phase of the drive roller 20. That is, in the first embodiment, the eccentric phases of the adjacent drive rollers 20 are alternately shifted by approximately 180 ° in the width direction of the sheet S. However, in the present embodiment, the sheets S to be conveyed are arranged at symmetrical positions with respect to the center in the width direction, and arranged so that the phase shift of the eccentricity of the adjacent drive rollers is less than 180 °.

  FIG. 6A is a diagram showing the eccentric phase of the driving roller 20 of the present embodiment, and FIG. 6B is a diagram showing the deviation of the eccentric phase of the adjacent driving roller 20. As shown in FIG. 6a, the drive rollers 20 arranged at the center in the width direction of the conveyed sheet S are arranged so that the eccentric phases of the drive rollers 20 are symmetrical. In this embodiment, as shown in FIG. 6b, the adjacent rollers are out of phase by about 90 °. In FIG. 6a, a → b → c → d → a from the center in the sheet width direction. And it is arranged to be shifted every 90 °.

  By disposing the driving roller 20 as described above, a strong nip pressure starting from the center in the sheet width direction is directed toward the outer side of the conveyed sheet S. Therefore, as shown in FIG. 7, the sheet S is conveyed while extending outward in the width direction. As a result, the sheet is less likely to wrinkle.

  If the eccentric phase difference between the adjacent drive rollers 20 is 180 °, the rightward extending force becomes zero, so that the effect of extending the wrinkles is lost. Therefore, in order to exert a stretching force in the left-right direction, the eccentric phase difference between adjacent drive rollers 20 needs to be less than 180 °.

  Further, in the driving roller 20 of the present embodiment, the roller whose eccentric phase difference is shifted by nearly 180 ° corresponds to the second roller from a certain roller. The distance between the driving rollers 20 shifted by 180 ° is made substantially the same as the circumferential length of the driving roller 20. As described in the above-described embodiment, this makes it possible to arrange the relationship between the peaks and valleys slanted with respect to the sheet conveyance direction at approximately 45 ° with respect to the sheet conveyance direction.

  The arrangement in which this is 0 ° is close to that of the prior art. When this angle is 0, 90 °, the valleys enter the sheet conveyance direction or the sheet width direction, and the leading edge trailing edge curl or the left edge right edge curl is weak. A configuration strong against both curls is a configuration arranged at approximately 45 ° as in the present embodiment. Note that it is not necessary to limit the seating direction to approximately 45 °, and this angle can be set to a desired angle by adjusting the outer diameter of the driving roller 20 and the interval between the driving rollers 20, as in the above-described embodiment. It is.

  As described above, in the sheet conveying apparatus of the present embodiment, by performing the phase shift of the driving roller 20 over the entire width of the sheet S, the conveyed sheet has a large number of valleys and valleys that do not have a sitting direction. It can be formed and seated on the entire surface. As a result, wrinkles in the sheet width direction can be prevented.

1 is a schematic diagram of an image forming apparatus. It is a perspective view of an eccentric drive roller. It is explanatory drawing of the roller pair used as a sheet conveying apparatus. It is an image figure of the unevenness | corrugation formed in the sheet | seat conveyed by the sheet conveying apparatus. It is an image figure of the unevenness | corrugation formed in a sheet width direction. It is an image figure of the unevenness | corrugation formed in a sheet conveyance direction. It is explanatory drawing of the roller pair used as the sheet conveying apparatus which concerns on 2nd Embodiment. It is explanatory drawing which shows the eccentric phase difference of an adjacent drive roller. It is explanatory drawing conveyed, extending a wrinkle on the sheet width direction outer side. It is explanatory drawing of the roller pair used as the sheet conveying apparatus of a prior art. It is an image figure of the unevenness | corrugation formed in the sheet | seat conveyed by the sheet conveying apparatus of the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS A ... Image forming apparatus B ... Sheet conveyance apparatus P ... Process cartridge S ... Sheet 1 ... Main body 2 ... Photoconductor drum 3 ... Developing means 4 ... Exposure means 5 ... Feed cassette 6 ... Pickup roller 7 ... Separation roller 8 ... Conveyance Roller 9 ... Belt conveying means 9a ... Conveying belt 9b ... Driving roller 9c, 9d, 9e ... Drive roller
10… Fixing means
11… discharge section
20… Drive roller
21… Drive shaft
22… Kolo
23… Spring

Claims (6)

A plurality of drive rollers provided on a drive shaft that is rotated by driving force transmission;
The sheet conveying apparatus, wherein a rotation center of an adjacent drive roller among the plurality of drive rollers is eccentrically provided on the drive shaft, and an eccentric phase of the adjacent drive roller is shifted.   2. The sheet conveying apparatus according to claim 1, wherein the phase of the eccentricity of the adjacent drive rollers is shifted by 180 [deg.], And the distance between the adjacent drive rollers is substantially the same as the circumference of the drive roller. .   The plurality of drive rollers are arranged at symmetrical positions with respect to the center in the width direction of the sheet to be conveyed, and the phase shift of the eccentricity of adjacent drive rollers is less than 180 °. Sheet conveying device.   The sheet conveying device according to any one of claims 1 to 3, wherein the plurality of driving rollers are provided over the entire width of the sheet to be conveyed. In an image forming apparatus that conveys a sheet to form an image,
An image forming apparatus comprising the sheet conveying device according to claim 1.   6. The image forming apparatus according to claim 5, wherein the sheet conveying device is disposed downstream of a fixing unit that heats and fixes an image formed on the sheet in the sheet conveying direction.

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