JP2010047351A - Sheet conveying device and image forming device with the same - Google Patents

Abstract

To provide a sheet conveying apparatus and an image forming apparatus including the sheet conveying apparatus that can effectively prevent the occurrence of conveyance failure due to penetration of a leading end of a sheet from a nip portion in a registration roller pair.
A sheet conveying apparatus includes a registration roller pair that conveys a sheet in a predetermined sheet conveyance direction X, and a reverse conveyance path S ′ that is curved upstream of the registration roller pair in the sheet conveyance direction X. And a first conveyance straight line β1 along the sheet conveyed at the upstream end P1 in the sheet conveyance direction X on the reverse conveyance path S ′, and a downstream end in the sheet conveyance direction X on the reverse conveyance path S ′. The tip of the thick paper Q2, which is stronger than plain paper, is prevented from penetrating from the nip portion of the registration roller pair 106 by the reversal angle α formed with the second transport straight line β2 along the sheet transported by the portion P2. .
[Selection] Figure 2

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus including the sheet conveying apparatus.

  For example, in an electrophotographic image forming apparatus, generally, an electrostatic latent image is formed on the surface of an image carrier such as a photosensitive drum, and the electrostatic latent image on the surface of the image carrier is developed with a developer. Then, a toner image is formed on the surface of the image carrier, and the toner image is transferred from the image carrier to the sheet while being conveyed by sandwiching a sheet of plain paper or OHP between the image carrier and the transfer member. The toner image is fixed on the sheet by heating and pressing the sheet. In some cases, the toner image is temporarily transferred from the image carrier to the intermediate transfer member, and the toner image on the intermediate transfer member is transferred from the intermediate transfer member to the sheet, and then the toner image is fixed on the sheet.

  In such an image forming apparatus, a sheet conveying apparatus is incorporated, and the sheet is pulled out from a sheet feeding unit such as a sheet feeding tray and conveyed by the sheet conveying apparatus. Further, in the conveyance path of the sheet conveyance apparatus, a registration roller (PS) is disposed upstream of the nip portion between the image carrier and the transfer member or the nip portion between the intermediate transfer member and the transfer member in the sheet conveyance direction. (Paper Stop) roller) and a counter roller opposite to it are provided, and the leading edge of the sheet (the downstream end in the sheet conveyance direction) is applied to the nip portion of the stopped registration roller pair. Then, the sheet is bent, and the leading edge of the sheet is aligned parallel to the registration roller pair by the elastic force of the sheet, and then the sheet is conveyed to the nip portion by the registration roller pair. This prevents the sheet from being inclined and passing through the nip portion, so that the toner image is not transferred obliquely to the sheet.

  FIG. 14 is a diagram for explaining an example of a conveying operation of a conventional sheet conveying apparatus. FIG. 14A shows a state immediately before the sheet Q reaches the registration roller pair 106, and FIG. 14B shows a state where the leading edge of the sheet Q hits the registration roller pair 106 in a stopped state. FIG. 14C shows a state in which the sheet Q is conveyed as the registration roller pair 106 rotates. FIG. 14D is a timing chart showing the rotational driving state of the registration roller pair 106 and the pre-registration roller pair 19. In FIG. 14D, “registration roller pair ON” or “registration roller pair OFF” indicates the “drive state” or “drive stop state” of the registration roller pair 106, respectively. “ON” or “pre-registration roller pair OFF” indicates “drive state” or “drive stop state” of the pre-registration roller pair 19, respectively.

  The conventional sheet conveying apparatus shown in FIG. 14 is disposed on the upstream side in the sheet conveying direction X with respect to the registration roller pair 106 that conveys the sheet Q in a predetermined sheet conveying direction (X direction in the drawing). A sheet conveyance path having a pair of pre-registration rollers 19 and a sheet bending forming portion 75 for causing the leading edge of the sheet Q conveyed by the pair of pre-registration rollers 19 to abut against the registration roller pair 106 to bend the leading edge side of the sheet Q. S. The registration roller pair 106 includes a registration roller 101 and a counter roller 105 facing the registration roller 101. The pre-registration roller pair 19 includes a pre-registration roller 191 and a counter roller 192 facing the roller. The sheet conveyance path S is linearly formed between the registration roller pair 106 and the pre-registration roller pair 19.

  In the conventional sheet conveying apparatus shown in FIG. 14, as shown in FIG. 14A, the sheet Q is conveyed toward the registration roller pair 106 by the pre-registration roller pair 19, and immediately before the registration roller pair 106 in the stopped state. (See a in FIG. 14D). Thereafter, the pre-registration roller pair 19 is rotated at a timing earlier than the registration roller pair 106 by a predetermined time (see b in FIG. 14D). Then, as shown in FIG. 14B, the sheet Q is in a state of being bent by abutting the leading end against the resist roller pair 106 in a stopped state. Thereby, the leading edge of the sheet Q is aligned in parallel with the registration roller pair 106, and the oblique feeding of the sheet Q can be corrected. Then, as shown in FIG. 14C, the registration roller pair 106 is rotated at a synchronous timing that synchronizes the toner image formed on the image carrier with the sheet Q or the toner image formed on the intermediate transfer member. (See c in FIG. 14D).

By the way, in the conventional sheet conveying apparatus, not only plain paper (for example, standard paper of about 64 g / m ² (basis weight)) but also a sheet (for example, 200 g / m ²⁾ stronger than plain paper as a sheet to be conveyed. (Basis weight) grade paper) may be used. Then, even if it is possible to correct the skew feeding properly and carry it with the proper image formation timing with plain paper, the leading edge may penetrate through the nip portion of the registration roller pair with a sheet that is stiffer than plain paper, As a result, there is a risk of sheet conveyance failure such that the correction performance of the oblique sheet feeding is deteriorated or the synchronization timing is shifted. This will be described below with reference to FIG.

  FIG. 15 is a schematic side view for explaining penetration of the leading end of the sheet from the nip portion N in the registration roller pair 106 in the conventional sheet conveying apparatus. FIG. 15A shows a conveyance state in which the sheet to be conveyed is plain paper Q1, and FIG. 15B shows a conveyance state in which the sheet to be conveyed is thick paper Q2.

  In the conventional sheet conveying apparatus, as shown in FIG. 15A, when conveying the plain paper Q1, the leading edge side of the plain paper Q1 is appropriately bent by the sheet bending forming portion 75, whereby the plain paper Q1. Can be properly corrected and can be conveyed at an appropriate synchronization timing.

  On the other hand, when the thick paper Q2 is transported, as shown in FIG. 15B, since it is stronger than the plain paper Q1, the leading end side of the thick paper Q2 can be sufficiently bent by the sheet bending forming portion 75. Accordingly, the tip easily penetrates from the nip portion N of the registration roller pair 106 (see d in FIG. 15B). In this case, the thick paper Q2 causes an oblique feed and a synchronization timing shift.

With respect to this point, for example, Japanese Patent Application Laid-Open No. H10-228667 describes the strength of the waist of the sheet when the leading end of the sheet comes into contact with the registration roller pair on the outer side of the reversing unit upstream of the registration roller pair. The guide member that rotates is formed, and a curved portion for accommodating the bent portion of the sheet is formed in the guide member. When the sheet comes into contact, the leading end of the sheet is registered by the elastic member that is bent in the curved portion. A configuration has been disclosed in which the effect of aligning the front end of the sheet with the pair of registration rollers in contact with the roller pair is more reliable.
JP-A-6-191686

  However, in the configuration as described above, the bent portion of the sheet that is bent by abutting the tip against the registration roller pair is pressed toward the registration roller pair from the outside of the reverse portion by the guide member and the elastic member. Therefore, the leading edge of the sheet (especially thick paper) is likely to penetrate from the nip portion of the registration roller pair, and rather, the conveyance failure due to penetration of the leading edge of the sheet from the nip portion of the registration roller pair is promoted.

  SUMMARY An advantage of some aspects of the invention is that it provides a sheet conveying apparatus and an image forming apparatus including the sheet conveying apparatus that can effectively prevent the occurrence of a conveyance failure due to the penetration of the leading end of a sheet from a nip portion in a registration roller pair.

  In order to solve the above-mentioned problems, the present inventor found the following and completed the present invention. That is, in the reverse conveyance path that is curved upstream of the registration roller pair in the sheet conveyance direction, the reverse angle of the conveyed sheet, that is, along the sheet conveyed at the upstream end (entrance) in the sheet conveyance direction. The reversing angle between the first conveying straight line and the second conveying straight line along the sheet conveyed at the downstream end (exit part) in the sheet conveying direction causes the leading end of the sheet to be stronger than plain paper. It has been found that penetration of the registration roller pair from the nip portion can be prevented.

  FIG. 13 shows a conventional synchronization timing shift characteristic and sheet oblique feed characteristic when standard plain paper (broken line) is used as a sheet and when thick paper (solid line) stronger than plain paper is used. It is the graph compared with. FIG. 13A shows the deviation characteristic of the synchronization timing and the oblique sheet feeding characteristic in the conventional sheet conveying apparatus in which the sheet conveying path is linearly formed as shown in FIG. 14, and FIG. FIG. 5 shows a synchronization timing shift characteristic and a sheet oblique feeding characteristic in a sheet conveying apparatus configured to prevent a through end from a nip portion of a registration roller pair at a leading end of a sheet that is stiffer than plain paper by a reversal angle. .

  In FIG. 13, the “deviation amount” on the vertical axis indicates the deviation amount in the sheet conveyance direction with reference to the reference position where the sheet image is to be formed. Further, the “slanting amount” on the vertical axis indicates the sheet feeding amount based on a reference line parallel to the registration roller pair. On the other hand, the “registration amount adjustment value” on the horizontal axis indicates the difference in activation timing between the pair of pre-registration rollers 19 and the pair of registration rollers for bending the sheet.

In the conventional sheet conveying apparatus in which the sheet conveying path is formed linearly, as shown in FIG. 13A, when the sheet is plain paper (for example, standard paper having a basis weight of about 64 g / m ² ). (Refer to the broken line) When the registration amount adjustment value is equal to or larger than the predetermined value γ, the deflection amount is secured well, and the synchronization timing deviation characteristic and the sheet oblique feeding characteristic are desired, and the sheet can be conveyed almost without any trouble. strong waist than paper sheets (e.g., 200 g / m ² (basis weight) of cardboard approximately) when it is (see the solid line), the amount of deflection resist amount adjustment value is even higher than a predetermined value γ is sufficiently ensured In other words, both the synchronization timing shift characteristic and the sheet oblique feed characteristic deteriorate. In contrast, the first conveying straight line along the sheet conveyed at the upstream end (inlet part) in the sheet conveying direction and the sheet conveyed at the downstream end (exit part) in the sheet conveying direction. As shown in FIG. 13 (b), by adopting a structure that prevents the sheet roller that is stiffer than plain paper from penetrating from the nip portion of the registration roller pair by the reversal angle formed with the second conveyance straight line, Even for sheets that are stiffer than plain paper (see the broken line) (see the solid line), the amount of resist adjustment is greater than or equal to the predetermined value γ, and a good amount of deflection can be secured. It is possible to achieve the same characteristics as plain paper.

  The present invention is based on such knowledge, and in order to solve the above problems, a registration roller pair that conveys a sheet in a predetermined sheet conveyance direction, and a curve on the upstream side of the sheet conveyance direction of the registration roller pair. A first conveying straight line along a sheet conveyed at an upstream end (entrance) in the sheet conveying direction on the reverse conveying path, and the sheet conveying direction on the reverse conveying path. The leading edge of the sheet that is stiffer than plain paper penetrates from the nip portion of the registration roller pair due to the reversal angle formed with the second conveyance straight line along the sheet conveyed at the downstream end (exit portion) of A sheet conveying device and an image forming apparatus including the sheet conveying device are provided.

  According to the sheet conveying apparatus and the image forming apparatus according to the present invention, the nip of the registration roller pair at the leading edge of the sheet that is stiffer than plain paper by the reversal angle formed by the first conveying straight line and the second conveying straight line. It is possible to effectively prevent the sheet from penetrating from the portion, and thus it is possible to prevent the occurrence of conveyance failure due to the sheet tip penetrating from the nip portion.

Assuming that the inversion angle is α, the inversion angle α may be an angle within a range of 90 ° ≦ α ≦ 100 °. As described above, when the inversion angle α is set to an angle within the range of 90 ° ≦ α ≦ 100 °, the sheet is more effective than the plain paper, particularly for thick paper of about 200 g / m ² (basis weight). It is.

  In the present invention, the reversing conveyance path forms a curved portion between the outer guide member and the inner guide member facing each other, and is movable in the direction in which the path width of the curved portion becomes wider. It is preferable that the guide member is provided. In this case, when the inversion angle is α, the inversion angle α can be an angle within a range of 60 ° ≦ α ≦ 80 °.

As described above, the inner guide member is provided so as to be movable in the direction in which the path width of the curved portion becomes wider even when the inversion angle α is an angle in the range of 60 ° ≦ α ≦ 80 °. By adopting the configuration, even if the sheet is stiffer than plain paper, especially thick paper of about 200 g / m ² (basis weight), the conveyance failure due to the penetration of the leading edge of the sheet from the nip portion in the registration roller pair. Generation | occurrence | production can be prevented effectively. Moreover, since the inversion angle α is set to an angle in the range of 60 ° ≦ α ≦ 80 °, the sheet conveying apparatus can be reduced in size accordingly.

  As described above, according to the sheet conveying device and the image forming apparatus including the same according to the present invention, the leading edge of the sheet that is stiffer than plain paper penetrates from the nip portion of the registration roller pair according to the reversal angle. Therefore, it is possible to prevent the occurrence of conveyance failure due to penetration of the leading edge of the sheet from the nip portion.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. In addition, the following embodiment is an example which actualized this invention, Comprising: The thing of the character which limits the technical scope of this invention is not.

  FIG. 1 is a side view schematically showing an image forming apparatus D to which an embodiment of a sheet conveying apparatus according to the present invention is applied. The image forming apparatus D includes a document reading device B that reads an image of a document, and an image of the document read by the document reading device B or an image received from the outside in color or single color, such as plain paper or OHP. An apparatus main body A for recording and forming.

  In the document reading device B, when the document is set on the document setting tray 41, the pickup roller 44 is pressed against the surface of the document and rotated, the document is pulled out from the tray 41, and the document passes between the suction roller 45 and the separation pad 46. Then, after being separated one by one, it is transported to the transport path 47.

  In this conveyance path 47, the leading edge of the document comes into contact with the registration roller 49, and the leading edge of the document is aligned in parallel with the registration roller 49. After that, the document is conveyed by the registration roller 49 and between the reading guide 51 and the reading glass 52. Pass through. At this time, the light of the light source of the first scanning unit 53 is irradiated on the surface of the document through the reading glass 52, and the reflected light is incident on the first scanning unit 53 through the reading glass 52. The image is reflected by the mirrors of the second scanning units 53 and 54 and guided to the imaging lens 55, and an image on the surface of the document is formed on a CCD (Charge Coupled Device) 56 by the imaging lens 55. The CCD 56 reads an image on the document surface and outputs image data indicating the image on the document surface. Further, the document is conveyed by the conveyance roller 57 and is discharged to the paper discharge tray 59 via the paper discharge roller 58.

  In addition, it is possible to read a document placed on the platen glass 61. The registration roller 49, the reading guide 51, the paper discharge tray 59, and the like and the members above them form an integrated cover body, and around the axis along the document conveying direction on the back side of the document reading device B It is pivotally supported so that it can be opened and closed. When the upper cover body is opened, the document table glass 61 is released, and a document can be placed on the document table glass 61. When the document is placed and the cover body is closed, the first and second scanning units 53 and 54 are moved in the sub-scanning direction, and the first scanning unit 53 exposes the document surface on the document table glass 61. Reflected light from the document surface is guided to the imaging lens 55 by the first and second scanning units 53 and 54, and an image on the document surface is formed on the CCD 56 by the imaging lens 55. At this time, the first and second scanning units 53 and 54 are moved while maintaining a predetermined speed relationship with each other, and reflection of the document surface → first and second scanning units 53 and 54 → imaging lens 55 → CCD 56 is performed. The positional relationship between the first and second scanning units 53 and 54 is always maintained so that the length of the optical path of the light does not change, and thereby the focus of the image on the original surface on the CCD 56 is always accurately maintained.

  The entire original image read in this way is sent and received as image data to the apparatus main body A of the image forming apparatus D, and the apparatus main body A records the image on a recording sheet.

  On the other hand, the apparatus main body A of the image forming apparatus D includes an exposure apparatus 1, a developing apparatus 2 (2a, 2b, 2c, 2d), a photosensitive drum 3 (3a, 3b, 3c, 3d) acting as an image carrier, and charging. Intermediate transfer belt device 8 including a container 5 (5a, 5b, 5c, 5d), a cleaner device 4 (4a, 4b, 4c, 4d), and an intermediate transfer roller 6 (6a, 6b, 6c, 6d) acting as a transfer portion. A fixing device 12, a sheet conveying device 100, a paper feed tray 10 that functions as a paper feed unit, and a paper discharge tray 15 that functions as a paper discharge unit.

  The image data handled in the apparatus main body A of the image forming apparatus D is data corresponding to a color image using each color of black (K), cyan (C), magenta (M), yellow (Y), or a single color (for example, This corresponds to a monochrome image using (black). Accordingly, the developing device 2 (2a, 2b, 2c, 2d), the photosensitive drum 3 (3a, 3b, 3c, 3d), the charger 5 (5a, 5b, 5c, 5d), and the cleaner device 4 (4a, 4b, 4c, 4d) and four intermediate transfer rollers 6 (6a, 6b, 6c, 6d) are provided so as to form four types of images corresponding to the respective colors. Is associated with black, b with cyan, c with magenta, and d with yellow to form four image stations. Hereinafter, the description will be made with the suffixes a to d omitted.

  The photoconductor drum 3 is disposed at substantially the center in the vertical direction of the apparatus main body A.

  The charger 5 is a charging means for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential. In addition to a contact type roller type or brush type charger, a charger type charger is used. .

  Here, the exposure apparatus 1 is a laser scanning unit (LSU) provided with a laser diode and a reflection mirror, and exposes the surface of the charged photosensitive drum 3 according to image data, and according to the image data on the surface. An electrostatic latent image is formed.

  The developing device 2 develops the electrostatic latent image formed on the photosensitive drum 3 with (K, C, M, Y) toner. The cleaner device 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  In addition to the intermediate transfer roller 6, the intermediate transfer belt device 8 disposed above the photosensitive drum 3 includes an intermediate transfer belt 7, an intermediate transfer belt drive roller 21, a driven roller 22, a tension roller 23, and an intermediate transfer belt. A cleaning device 9 is provided.

  Roller members such as the intermediate transfer belt drive roller 21, the intermediate transfer roller 6, the driven roller 22, and the tension roller 23 stretch and support the intermediate transfer belt 7, and the intermediate transfer belt 7 is supported in a predetermined sheet conveyance direction (in the drawing). Move around in the direction of arrow C).

  The intermediate transfer roller 6 is rotatably supported inside the intermediate transfer belt 7 and is pressed against the photosensitive drum 3 via the intermediate transfer belt 7.

  The intermediate transfer belt 7 is provided so as to be in contact with each photoconductive drum 3, and a color toner image (each color is transferred by sequentially superimposing and transferring the toner image on the surface of each photoconductive drum 3 onto the intermediate transfer belt 7. Toner image). Here, the transfer belt 7 is formed in an endless belt shape using a film having a thickness of about 100 μm to 150 μm.

  The transfer of the toner image from the photosensitive drum 3 to the intermediate transfer belt 7 is performed by an intermediate transfer roller 6 that is in pressure contact with the inner side (back surface) of the intermediate transfer belt 7. A high voltage transfer bias (for example, a high voltage having a polarity (+) opposite to the toner charging polarity (−)) is applied to the intermediate transfer roller 6 in order to transfer the toner image. Here, the intermediate transfer roller 6 is a roller based on a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm and whose surface is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). With this conductive elastic material, a high voltage can be uniformly applied to the recording sheet.

  The apparatus main body A of the image forming apparatus D further includes a secondary transfer apparatus 11 including a transfer roller 11a that functions as a transfer unit. The transfer roller 11 a is in contact with the outside of the intermediate transfer belt 7.

  As described above, the toner images on the surfaces of the respective photosensitive drums 3 are stacked on the intermediate transfer belt 7 and become a color toner image indicated by the image data. The stacked toner images of the respective colors are transported together with the intermediate transfer belt 7 and transferred onto the recording sheet by the secondary transfer device 11.

  The intermediate transfer belt 7 and the transfer roller 11a of the secondary transfer device 11 are pressed against each other to form a nip region. The transfer roller 11a of the secondary transfer device 11 has a voltage (for example, a polarity (+) opposite to the toner charging polarity (-)) for transferring the toner image of each color on the intermediate transfer belt 7 to the recording sheet. Is applied). Further, in order to constantly obtain the nip region, either the transfer roller 11a of the secondary transfer device 11 or the intermediate transfer belt drive roller 21 is made of a hard material (metal or the like), and the other is a soft material such as an elastic roller. (Elastic rubber roller, foaming resin roller, etc.).

  In addition, the toner image on the intermediate transfer belt 7 may not be completely transferred onto the recording sheet by the secondary transfer device 11, and the toner may remain on the intermediate transfer belt 7. Causes color mixing. Therefore, the residual toner is removed and collected by the intermediate transfer belt cleaning device 9. The intermediate transfer belt cleaning device 9 includes, for example, a cleaning blade that contacts the intermediate transfer belt 7 as a cleaning member, and residual toner can be removed and collected by the cleaning blade. The driven roller 22 supports the intermediate transfer belt 7 from the inside (back side), and the cleaning blade is in contact with the intermediate transfer belt 7 so as to press the driven roller 22 from the outside.

  The paper feed tray 10 is a tray for storing recording sheets, and is provided below the image forming unit of the apparatus main body A. A paper discharge tray 15 provided on the upper side of the image forming unit is a tray for placing printed recording sheets face down.

  In addition, the apparatus main body A is provided with a sheet conveying device 100 for sending the recording sheet in the paper feed tray 10 to the paper discharge tray 15 via the secondary transfer device 11 and the fixing device 12. This sheet conveying apparatus 100 has an S-shaped sheet conveying path S, and along the sheet conveying path S, a pickup roller 16, a roller roller 14a, a separation roller 14b, each conveying roller 13, a pre-registration roller pair 19, Conveying members such as the registration roller pair 106, the fixing device 12, and the paper discharge roller 17 are disposed.

  The pickup roller 16 is a pull-in roller that is provided at the downstream end of the sheet feeding tray 10 in the sheet conveying direction and supplies recording sheets from the sheet feeding tray 10 to the sheet conveying path S one by one. The separating roller 14a passes the recording sheet between the separating roller 14b and conveys it to the sheet conveying path S while separating the recording sheets one by one. Each conveyance roller 13 and the pre-registration roller pair 19 are small rollers for promoting and assisting conveyance of the recording sheet. Each conveying roller 13 is provided at a plurality of locations along the sheet conveying path S. The pre-registration roller pair 19 is provided in the immediate vicinity of the registration roller pair 106 on the upstream side in the sheet conveyance direction, and conveys the recording sheet to the registration roller pair 106. The sheet conveyance path S is provided with a registration roller front sheet detection device (not shown) that detects the timing of the leading edge of the recording sheet (the downstream end in the sheet conveyance direction).

  In addition, the image forming apparatus D includes a control unit (not shown). This control means is based on the recording sheet leading edge timing signal from the registration roller front sheet detecting device, and after the predetermined time has elapsed since the detection of the recording sheet leading edge (that is, immediately before the stopped registration roller pair 106). The rotational drive to the pair 19 is temporarily stopped. Further, the control means resumes the rotation of the pre-registration roller pair 19 after a predetermined time has elapsed (that is, the recording sheet in a state of being bent by abutting the leading end against the resist roller pair 106 in the stopped state is an intermediate transfer belt. The registration roller pair 106 is driven to rotate (at an image formation timing synchronized with the toner image formed on the upper surface 7). As a result, the registration roller pair 106 records the toner image on the intermediate transfer belt 7 in the nip area between the intermediate transfer belt 7 and the secondary transfer device 11 so that the toner image on the recording sheet is to be formed. A sheet can be conveyed.

  The fixing device 12 receives the recording sheet on which the toner image is transferred, and conveys the recording sheet by sandwiching the recording sheet between the heat roller 31 and the pressure roller 32.

  The temperature of the heat roller 31 is controlled to be a predetermined fixing temperature, and the recording sheet is thermocompression bonded together with the pressure roller 32 to melt, mix, and press the toner image transferred to the recording sheet. On the other hand, it has a function of heat fixing.

  The recording sheet after fixing the toner images of the respective colors is discharged onto the paper discharge tray 15 by the paper discharge roller 17.

  It is also possible to form a monochrome image using only one of the four image forming stations and transfer the monochrome image to the intermediate transfer belt 7 of the intermediate transfer belt device 8. Similarly to the color image, this monochrome image is also transferred from the intermediate transfer belt 7 to the recording sheet and fixed on the recording sheet.

  In addition, when performing image formation on both the front side and the front side of the recording sheet, the image on the surface of the recording sheet is fixed by the fixing device 12, and then the recording sheet is discharged on the sheet conveying path S in the sheet discharge roller 17. In the middle of the conveyance, the paper discharge roller 17 is stopped and then reversely rotated, the recording sheet is passed through the front / back reversing path Sr, the recording sheet is reversed, and the recording sheet is transferred to the registration roller pair 106 again. As in the case of the front surface of the recording sheet, the image is recorded and fixed on the back surface of the recording sheet, and the recording sheet is discharged to the paper discharge tray 15.

  By the way, when the sheet conveyance path between the registration roller pair and the pre-registration roller pair is formed linearly, in a recording sheet that is stiffer than plain paper, the leading edge of the recording sheet is the nip of the registration roller pair. In this case, the sheet feeding failure may be caused such that the correction performance of the oblique sheet feeding is deteriorated or the synchronization timing is shifted.

[Description of Features of the Present Invention]
Therefore, in the sheet conveying apparatus 100 according to the embodiment of the present invention, as illustrated in FIGS. 2 to 7, a reverse conveying path S ′ is provided between the registration roller pair 106 and the pre-registration roller pair 19 in the sheet conveying path S. Even if the recording sheet is stiffer than plain paper, the leading end of the recording sheet is effectively prevented from penetrating from the nip portion N of the registration roller pair 106.

(First embodiment)
FIG. 2 is a cross-sectional view schematically showing the vicinity of the reverse conveying path S ′ in the sheet conveying apparatus 100 according to the first embodiment.

  As shown in FIG. 2, the sheet conveying apparatus 100 according to the first embodiment includes a registration roller pair 106 that conveys a recording sheet in a predetermined sheet conveyance direction (the arrow X direction in the drawing), and a registration roller pair 106. And a reverse conveyance path S ′ having a curved portion 71 that is curved on the upstream side in the sheet conveyance direction X. Specifically, the sheet conveying apparatus 100 includes a pair of pre-registration rollers 19 disposed on the upstream side of the registration roller pair 106 in the sheet conveyance direction X in addition to the registration roller pair 106 and the reverse conveyance path S ′. The registration roller pair 106 includes a registration roller 101 and a counter roller 105 facing the registration roller 101. The pre-registration roller pair 19 includes a pre-registration roller 191 and a counter roller 192 facing the roller.

  Here, the reverse conveyance path S ′ is a sheet deflection forming portion (space) for the leading edge of the recording sheet conveyed by the pair of pre-registration rollers 19 to abut against the registration roller pair 106 to bend the leading edge side of the recording sheet. 75. The sheet deflection forming portion 75 is provided outside the reverse conveyance path S ′ between the registration roller pair 106 and the pre-registration roller pair 19.

  More specifically, the reverse conveyance path S ′ is formed between an outer guide member (hereinafter referred to as an outer guide) 72 and an inner guide member (hereinafter referred to as an inner guide) 73, and in the sheet conveyance direction X, a resist is formed. It is located upstream from the roller pair 106 and downstream from the pre-registration roller pair 19. The curved portion 71 of the reverse conveyance path S ′ is configured to bend gradually so that the sheet conveyed by the pre-registration roller pair 19 faces the registration roller pair 106.

  Further, the sheet deflection forming portion 75 provided in the reverse conveyance path S ′ is configured to contact the leading end of the recording sheet so as to be aligned in parallel with the registration roller pair 106 so as to bend the recording sheet with certainty. In the sheet deflection forming portion 75, in the vicinity of the upstream side in the sheet conveying direction X of the registration roller pair 106, a part 76 of the outer guide 72 of the reverse conveying path S ′ is concave in a sectional view (as viewed from the section). It is provided so as to be recessed. In other words, the sheet deflection forming portion 75 is provided in the vicinity of the upstream side of the registration roller pair 106 in the sheet conveyance direction X, and the sheet is formed so that the recording sheet that is bent by hitting the registration roller pair 106 in a stopped state is accommodated. It is assumed that the width of the transport path S is widened outward.

  The sheet conveying apparatus 100 is an upstream end (entrance) IN in the sheet conveying direction X on the reverse conveying path S ′ (here, at the position of the pre-registration roller pair 19 at the pre-registration roller pair 19). At the first conveyance straight line β1 along the conveyed sheet and the downstream end (exit portion) OUT in the sheet conveyance direction X on the reverse conveyance path S ′ (here, the registration roller pair 106 uses the registration roller pair 106). The reversal angle α formed with the second conveyance straight line β2 along the conveyed sheet is a predetermined angle, and the reversal angle α causes the leading edge of the sheet that is stronger than plain paper to be a registration roller. The pair 106 is prevented from penetrating from the nip portion N. In other words, the reversal angle α is equal to the first conveyance straight line β1 orthogonal to the virtual straight line γ1 passing through the rotation centers P1 and P2 around the axis of the pre-registration roller 191 and the counter roller 192 of the pre-registration roller pair 19, and the registration roller. This is an angle formed by a virtual straight line γ2 passing through the rotation centers P3 and P4 around the axis of the pair of registration rollers 101 and the opposing roller 105 and a second transport straight line β2.

  FIG. 3 is a cross-sectional view schematically showing a state in which the cardboard Q2 is being conveyed in the sheet conveying apparatus 100 according to the first embodiment. 3A shows a state in which the thick paper Q2 is directed from the pre-registration roller pair 19 to the registration roller pair 106, and FIG. 3B shows that the leading end of the thick paper Q2 is in contact with the registration roller pair 106. The state where the front end side of the thick paper Q2 is bent is shown.

In the sheet conveying device 100 according to the first embodiment, for example, is conveyed to the curved portion 71 64 g / m ² (basis weight) of about standard plain paper (not shown) through the resist roller pair 19 Since the plain paper has sufficient flexibility, the plain paper easily bends along the curved portion 71, and the plain paper smoothly passes through the curved portion 71 so that the leading end of the plain paper is reliably bent. Mu Thus, when the recording sheet is plain paper, the sheet can be conveyed without hindrance.

On the other hand, a strong thick chewy than plain paper (e.g., 200 g / m ² (basis weight) of about cardboard) in the case of Q2, the cardboard Q2 has passed through the is the inversion angle α reverse conveying path S ' In this case, as shown in FIG. 3 (a), the cardboard Q2 conveyed along the first conveyance straight line β1 at the inlet portion IN is changed to the second portion at the outlet portion OUT as shown in FIG. 3 (b). The cardboard Q2 bent in the direction along the conveyance straight line β2, that is, passing through the reverse conveyance path S ′, is directed toward the registration roller pair 106 while the inner facing surface Q2 ′ facing the inner guide 73 is in contact with the inner guide 73. Then, after the outer facing surface Q2 ″ facing the outer guide 72 on the front end side contacts the outer guide 72 through the sheet deflection forming portion 75, the front end contacts the registration roller pair 106. At this time, the registration roller pair 106 rotation temporarily stopped Are, while the tip of the cardboard Q2 is brought into contact with the registration roller pair 106, the conveying of cardboard Q2 by the registration roller pair 19 is continued, the leading end side of the cardboard Q2 is bent in the forming portion 75 bending sheet.

  In this way, the thick paper Q2 along the first conveyance straight line β1 at the inlet portion IN is bent in the direction along the second conveyance straight line β2 toward the outlet portion OUT, so that the thick paper Q2 at the sheet deflection forming portion 75 is bent. The leading end side can be easily bent, and accordingly, the leading end of the thick paper Q2 can be made difficult to penetrate from the nip portion N in the registration roller pair 106. That is, as described above, the thick paper Q2 is bent, so that the direction of conveyance in the outlet portion (position of the registration roller pair 106) OUT of the thick paper Q2 and the entrance portion of the thick paper Q2 (position of the pre-registration roller pair 19). Since the cardboard Q2 can be curved by changing the direction of the conveyance direction at IN, it contributes to an increase in the amount of deflection on the leading end side of the cardboard Q2, and accordingly, in the registration roller pair 106 at the tip of the cardboard Q2. The penetration from the nip portion N can be effectively prevented. Thereby, the leading end of the thick paper Q2 is aligned in parallel with the registration roller pair 106 by the elastic force of the bent thick paper Q2.

  Accordingly, the reversal angle α formed by the first virtual tangent β1 and the second virtual tangent β2 allows the penetration of the leading end of the thick paper Q2, which is stronger than the plain paper, from the nip portion N in the registration roller pair 106 to an allowable level. This can be reduced or eliminated, and it is possible to prevent the occurrence of conveyance failure such as the correction of oblique sheet feeding correction performance and the synchronization timing being deviated. Here, the inversion angle α is an angle within a range of 90 ° ≦ α ≦ 100 °.

(Second Embodiment)
FIG. 4 is a cross-sectional view schematically showing the vicinity of the reverse conveyance path S ′ of the sheet conveyance path S in the sheet conveyance apparatus 100a according to the second embodiment. In the sheet conveying apparatus 100a according to the second embodiment, differences from the sheet conveying apparatus 100 according to the first embodiment shown in FIGS. 2 and 3 will be mainly described. In FIG. 4, the same components as those of the sheet conveying apparatus 100 of the first embodiment are denoted by the same reference numerals. The same applies to FIGS. 5 to 7 described later.

  In the reverse conveying path S ′ of the sheet conveying apparatus 100 according to the first embodiment shown in FIGS. 2 and 3, the sheet conveying apparatus 100 a according to the second embodiment reduces the inversion angle α and the path width of the bending portion 71. The inner guide 73 is provided so as to be movable in the direction in which J becomes wider.

  Specifically, the inner guide 73 can be moved in a direction in which the path width J of the curved portion 71 is widened by a recording sheet that is curved along the curved portion 71 of the reverse conveyance path S ′.

  More specifically, the inner guide 73 is supported so as to be rotatable around a pivot shaft 73a along the axial direction of the registration roller pair 106, and the path of the bending portion 71 while the inner guide 73 is stationary. The width J is maintained constant, and the path width J of the bending portion 71 is widened in a state where the inner guide 73 rotates around the pivot shaft 73a.

  Here, the outer guide 72 is fixed. The inner guide 73 is pivotally supported so as to be rotatable around a pivot shaft 73a. The inner guide 73 is provided upstream of the sheet deflection forming portion 75 in the sheet conveyance direction X. The inner guide 73 is positioned with its own weight around the pivot shaft 73a and the end opposite to the pivot shaft 73a abutting against the stopper 74, and the rotation to the reverse conveyance path S ′ is restricted. . The stopper 74 is fixed at a position where it does not contact or interfere with the recording sheet passing through the bending portion 71 with respect to the apparatus main body A.

  The first conveyance straight line β1 along the sheet conveyed at the inlet portion IN on the reverse conveyance path S ′ and the second conveyance straight line β2 along the sheet conveyed at the outlet portion OUT on the reverse conveyance path S ′. The reversal angle α is set to an angle in the range of 60 ° ≦ α ≦ 80 °.

  FIG. 5 is a cross-sectional view schematically showing a state in which the thick paper Q2 is being conveyed in the sheet conveying apparatus 100a according to the second embodiment. 5A shows a state in which the thick paper Q2 is directed from the pre-registration roller pair 19 to the registration roller pair 106, and FIG. 5B shows that the leading end of the thick paper Q2 is in contact with the registration roller pair 106. The state where the front end side of the thick paper Q2 is bent is shown.

In the sheet conveying apparatus 100a according to the second embodiment, for example, is conveyed to the curved portion 71 64 g / m ² (basis weight) of about standard plain paper (not shown) through the resist roller pair 19 Since the plain paper has sufficient flexibility, the plain paper easily bends along the curved portion 71, and the plain paper smoothly passes through the curved portion 71 so that the leading end of the plain paper is reliably bent. Mu At this time, even if the plain paper comes into contact with the inner guide 73, a force enough to displace the inner guide 73 does not act on the inner guide 73, and the path width J between the outer guide 72 and the inner guide 73 is kept constant. Plain paper can be conveyed as it is. Thus, when the recording sheet is plain paper, the sheet can be conveyed without hindrance.

On the other hand, in the case of thick paper (for example, thick paper of about 200 g / m ² (basis weight)) Q2 which is stronger than plain paper, the thick paper Q2 is conveyed to the curved portion 71 as shown in FIG. Then, since the thick paper Q2 is strong, the thick paper Q2 cannot be curved along the curved portion 71. For this reason, as shown in FIG. 5B, the inner guide 73 is pressed by the cardboard Q2, and the inner guide 73 is rotated and displaced in the direction in which the path width J becomes wider around the pivot point 73a. 73 is separated from the outer guide 72 and the path width J of the curved portion 71 is increased.

  Then, the thick paper Q2 that has been transported along the first transport straight line β1 at the entrance portion IN is bent in the direction along the second transport straight line β2 at the exit portion OUT, that is, the thick paper Q2 that passes through the reverse transport path S ′. The inner facing surface Q 2 ′ facing the inner guide 73 is bent toward the registration roller pair 106 side while being in contact with the inner guide 73, and the outer facing surface facing the outer guide 72 on the front end side through the sheet deflection forming portion 75. After Q2 ″ contacts the outer guide 72, the leading end abuts against the registration roller pair 106. At this time, the rotation of the registration roller pair 106 is temporarily stopped, and the leading end of the cardboard Q2 contacts the registration roller pair 106. Conveying the thick paper Q2 by the pair of pre-registration rollers 19 is continued while being in contact, and the leading end side of the thick paper Q2 is bent in the sheet bending forming portion 75. Here, the path width J of the curved portion 71 is The inner guide 73 is pushed in according to the waist strength of the cardboard Q2 and is rotated by rotating around the pivot shaft 73a.

  According to the sheet conveying apparatus 100a according to the second embodiment, the direction in the conveying direction at the exit portion (position of the registration roller pair 106) OUT of the thick paper Q2 and the entrance portion of the thick paper Q2 (position of the pre-registration roller pair 19). Since the cardboard Q2 can be curved by changing the direction of the conveyance direction at IN, the leading end side of the cardboard Q2 is easily bent. Moreover, when the reversal angle α is set to an acute angle within the range of 60 ° ≦ α ≦ 80 °, the sheet conveying apparatus 100a can be made compact, while the leading end of the thick paper Q2 extends from the nip portion N of the registration roller pair 106. Where it is easy to penetrate, the inner guide 73 is provided so as to be movable in the direction in which the path width J of the bending portion 71 becomes wider in the reversing conveyance path S ′, so that it is curved along the bending portion 71 of the reversing conveyance path S ′. The inner guide 73 that comes into contact with the inner facing surface Q2 ′ of the thick paper Q2 is pushed inward by the thick paper Q2, so that the place of the thick paper Q2 can be secured, and therefore the leading end of the thick paper Q2 can hardly penetrate the nip portion N. Accordingly, it is possible to effectively prevent the sheet conveying apparatus 100a from penetrating from the nip portion N at the leading end of the thick paper Q2 while realizing a compact size.

(Modification 1 of 2nd Embodiment)
FIG. 6 is a cross-sectional view illustrating a modified example 100a ′ of the sheet conveying apparatus of the second embodiment. 6A shows a state in which the thick paper Q2 is directed from the pre-registration roller pair 19 to the registration roller pair 106, and FIG. 6B shows that the leading end of the thick paper Q2 is in contact with the registration roller pair 106. The state where the front end side of the thick paper Q2 is bent is shown.

  This sheet conveying apparatus 100a ′ is the same as the sheet conveying apparatus 100a of the second embodiment shown in FIGS. 4 and 5, except that the inner guide 73 provided inside the reverse conveying path S ′ is positioned at a predetermined position. It is biased toward the direction in which the path width J becomes narrower. That is, the sheet conveying apparatus 100a of FIGS. 4 and 5 further includes an urging member (here, a coil spring) 82 such as a spring that urges the inner guide 73 toward the conveying path. Here, the coil spring 82 is inserted and connected between a support member (here, a frame) 81 that supports the inner guide 73 so as to be rotatable around the pivot shaft 73 a and an upper portion 73 b of the inner guide 73.

  For example, in a state where the cardboard Q2 is not passed, the coil spring 82 is in a natural length state or slightly contracted as shown in FIG. 6A, and the elastic force of the coil spring 82 causes the inner guide 73 to move. The end opposite to the pivot shaft 73 a is pressed against the stopper 74 and is in contact with the stopper 74. At this time, the path width J between the outer guide 72 and the inner guide 73 is constant. On the other hand, in the state in which the thick paper Q2 is being passed, the path width J is wide against the urging force of the coil spring 82 by the thick paper Q2 in which the inner guide 73 is curved along the curved portion 71 of the reverse conveyance path S ′. It rotates around the pivot shaft 73a in the direction of

(Modification 2 of the second embodiment)
FIG. 7 is a cross-sectional view showing another modification 100a ″ of the sheet conveying apparatus of the second embodiment. In FIG. 7A, the thick paper Q2 is directed from the pre-registration roller pair 19 toward the registration roller pair 106. FIG. 7B shows a state in which the leading end of the thick paper Q2 is bent while the leading end of the thick paper Q2 is in contact with the registration roller pair 106.

  The sheet conveying apparatus 100a ″ is formed with a concave portion 73c for supporting one end side of the coil spring 82 in the inner guide 73 in the sheet conveying apparatus 100a of the second embodiment shown in FIGS. A recess 81b for supporting the other end of the inner guide 73 is formed in the frame 81 that supports the inner guide 73, and the coil spring 82 is disposed and enclosed inside the recess 73c of the inner guide 73 and the recess 81b of the frame 81. The coil spring 82 is sandwiched between the inner guide 73 and the frame 81.

  Specifically, the inner guide 73 is attached so as to be rotatable with respect to the frame 81, and a coil spring 82 is disposed and enclosed inside the recess 73c of the inner guide 73 and the recess 81b of the frame 81. Yes.

  The inner guide 73 is detachably attached to the frame 81. When the frame 81 is attached to the apparatus main body, movement of the inner guide 73 with respect to the frame 81 is prohibited. It is configured.

  A specific arrangement configuration of the coil spring 82 will be further described with reference to FIGS. 8 to 11. FIG. 8 is an exploded perspective view showing the outer guide 72, the inner guide 73, and the support frame 81 as seen from the back side. FIG. 9 is a perspective view showing the inner guide 73 and the support frame 81 upside down. FIG. 10 is an exploded perspective view showing the inner guide 73 and the support frame 81 upside down. Further, FIG. 11 is an enlarged side view showing a connecting portion between the inner guide 73 and the support frame 81.

  As shown in FIGS. 7 to 11, two recesses 73 c are formed on the upper surface 73 b of the inner guide 73, and the respective shafts 73 a protrude from the side walls 73 e on both sides of the inner guide 73.

  In addition, two concave portions 81b are formed in the bottom surface 81a of the support frame 81, side walls 81c on both sides of the support frame 81 project toward the bottom surface 81a, and bearing holes 81d are formed in these side walls 81c.

  By inserting the shafts 73a on both sides of the inner guide 73 into the bearing holes 81d on both sides of the support frame 81, the inner guide 73 is connected to the support frame 81 so as to be rotatable around the pivot shaft 73a. In addition, coil springs 82 are respectively fitted between the recesses 73c on the upper surface 73b of the inner guide 73 and the recesses 81b on the bottom surface 81a of the support frame 81, and the side walls 73d of the recesses 73c and the sidewalls 81f of the recesses 81b respectively. The coil spring 82 is covered and hidden.

  Next, the assembly procedure of the inner guide 73 and the support frame 81 will be described. First, as shown in FIG. 10, one end side of the coil spring 82 is fitted into and supported by the two concave portions 81 b of the bottom surface 81 a of the support frame 81.

  Then, as shown in FIGS. 10 and 11, the shafts 73 a on both sides of the inner guide 73 are inserted into the bearing holes 81 d on the side walls 81 c on both sides of the support frame 81. The shafts 73a on both sides of the inner guide 73 are elliptical when viewed from the side, with both sides in the radial direction of the cylinder having a diameter slightly smaller than the diameter of the bearing hole 81d. Further, the bearing holes 81d in the side walls 81c on both sides of the support frame 81 have notches 81e. The opening width of the notch 81e is narrower than the diameter of the bearing hole 81d and slightly larger than the thickness of the elliptical short diameter portion of the shaft 73a of the inner guide 73. Therefore, as shown in FIG. 11, the shafts 73a on both sides of the inner guide 73 can be passed through the notches 81e of the bearing holes 81d on both sides. Subsequently, the inner guide 73 is rotated 90 degrees around the shaft 73a so that the shaft 73a of the inner guide 73 does not come off from the bearing holes 81d on both sides. At this time, the upper surface 73 b of the inner guide 73 overlaps and faces the bottom surface 81 a of the support frame 81, and the other end sides of the two coil springs 82 are fitted into the respective recesses 73 c of the upper surface 73 b of the inner guide 73. In this state, one end side of each coil spring 82 is fitted and supported in each recess 81 b on the bottom surface 81 a of the support frame 81, and the other end side of each coil spring 82 is fitted and supported on each recess 73 c on the upper surface 73 b of the inner guide 73.

  Then, the notches 81e of the bearing holes 81d of the side walls 81c on both sides of the support frame 81 are directed to the outer guide 72 side, and both ends in the width direction of the support frame 81 are used as outer guides 72 using screws as shown in FIG. Install and fix. At this time, as shown in FIG. 7, the inner guide 73 comes into contact with the stopper 74, and a gap is formed between the support frame 81 and the inner guide 73 and the outer guide 72. Become. Further, the inner guide 73 escapes between the upper surface 73b of the inner guide 73 and the bottom surface 81a of the support frame 81 so that the inner guide 73 can be rotated and displaced in the direction in which the path width J becomes wider around the shaft 73a. A space R is formed.

  According to the first and second modifications of the second embodiment shown in FIGS. 6 and 7, the coil spring is such that the tip of the thick paper Q2 does not penetrate from the nip portion N of the registration roller pair 106 according to the stiffness of the thick paper Q2. 82 biasing forces can be set. By doing so, it is possible to reliably bend the leading end side of the thick paper Q2 while effectively preventing the leading end of the thick paper Q2 from penetrating from the nip portion N in the registration roller pair 106.

  Note that the sheet conveying apparatuses 100 and 100a of the first and second embodiments and the modified examples 100a ′ and 100a ″ of the sheet conveying apparatus of the second embodiment are applied to the main body of the image forming apparatus to convey the recording sheet. However, the present invention is not limited to this. For example, the present invention may be applied to a document reading device in an image forming apparatus to convey a document sheet.

(Example)
Next, in the sheet conveying apparatus according to the present invention, the paper-feeding property such as jamming (JAM) or conveyance delay with respect to the reversal angle α, and the presence or absence of penetration from the nip portion of the registration roller pair at the leading end of the thick paper were examined. This will be described below.

Example 1 is the sheet conveying apparatus 100 according to the first embodiment in which the inner guide 73 is fixed, and Example 2 is the sheet conveying apparatus 100a according to the second embodiment in which the inner guide 73 is movable. By continuously passing 100 sheets of thick paper of about 200 g / m ² (basis weight) in an environment of normal temperature and humidity (25 ° C., 55 RH) and changing the reversal angle α from 50 ° to 10 °, The paper passing property and the presence or absence of penetration were evaluated. In addition, regarding the paper passing property of thick paper, “○” indicates that there is no paper jam or conveyance delay, “×” indicates that there is a paper jam, and “○” indicates that the leading edge of the thick paper does not come out of the nip portion of the registration roller pair. The case was evaluated as “×”. The results of Example 1 and Example 2 are shown in FIGS. 12 (a) and 12 (b), respectively.

  In Example 1, as shown in FIG. 12A, when the reversal angle α is 90 ° or more, the paper passing property of the thick paper is good, and when it exceeds 100 °, the leading edge of the thick paper slips out from the nip portion of the registration roller pair. . Thereby, in the sheet conveying apparatus 100 of 1st Embodiment which fixed the inner side guide 73, it turned out that 90 degrees-100 degrees are preferable as the inversion angle (alpha). Further, in Example 2, as shown in FIG. 12B, when the reversal angle α is 60 ° to 80 °, the paper passing property of the thick paper is good, and the leading edge of the thick paper does not come out from the nip portion of the registration roller pair. It was. Thereby, in the sheet conveying apparatus 100a of 2nd Embodiment which enabled the inner side guide 73 to move, it turned out that 60 degrees-80 degrees are preferable as the inversion angle (alpha).

1 is a side view schematically illustrating an image forming apparatus to which an embodiment of a sheet conveying apparatus according to the present invention is applied. FIG. 3 is a cross-sectional view schematically illustrating the vicinity of a reverse conveyance path in the sheet conveyance apparatus according to the first embodiment. FIG. 2 is a cross-sectional view schematically showing a state in which thick paper is being conveyed in the sheet conveying apparatus according to the first embodiment, and FIG. (A) is a state in which the thick paper is directed from the pair of pre-registration rollers to the registration roller pair. FIG. 4B is a diagram showing a state in which the leading end of the thick paper is bent while the leading end of the thick paper is in contact with the registration roller pair. FIG. 10 is a cross-sectional view schematically illustrating the vicinity of a reverse conveyance path of a sheet conveyance path in a sheet conveyance apparatus according to a second embodiment. FIG. 9 is a cross-sectional view schematically illustrating a state in which thick paper is being conveyed in the sheet conveying apparatus according to the second embodiment, and FIG. FIG. 4B is a diagram showing a state in which the leading end of the thick paper is bent while the leading end of the thick paper is in contact with the registration roller pair. FIG. 9A is a cross-sectional view illustrating a modified example of the sheet conveying apparatus of the second embodiment, and FIG. 9A is a diagram illustrating a state in which thick paper is directed from a pair of pre-registration rollers to a pair of registration rollers, and FIG. FIG. 6 is a diagram illustrating a state where the leading end of the thick paper is bent while the leading end of the thick paper is in contact with the registration roller pair. FIG. 9A is a cross-sectional view illustrating another modified example of the sheet conveying apparatus according to the second embodiment, and FIG. 9A is a diagram illustrating a state in which thick paper is directed from a pair of pre-registration rollers to a pair of registration rollers. FIG. 7B is a diagram illustrating a state in which the leading end of the thick paper is bent while the leading end of the thick paper is in contact with the registration roller pair. It is a disassembled perspective view which shows an outer side guide, an inner side guide, and a support frame seeing from the back side. It is a perspective view which shows an inner side guide and a support frame upside down. It is a disassembled perspective view which shows an inner side guide and a support frame upside down. It is a side view which expands and shows the connection location of an inner side guide and a support frame. FIG. 5 is a diagram showing the results of the example, in which FIG. (A) is a table showing the results of Example 1, and (b) is a table showing the results of Example 2. FIG. FIG. 9A is a graph comparing the synchronization timing shift characteristic and the sheet oblique feed characteristic when plain paper or thick paper is used as a sheet, and FIG. FIG. 7B is a diagram showing characteristics of the sheet conveying apparatus configured to prevent the sheet roller, which is stiffer than plain paper, from penetrating through the nip portion of the registration roller pair depending on the reversal angle. It is a figure for demonstrating an example of the conveyance operation of the conventional sheet conveying apparatus. FIG. 10 is a schematic side view for explaining penetration of a sheet front end from a nip portion in a registration roller pair in a conventional sheet conveying apparatus.

Explanation of symbols

71 Curved portion 72 of the reverse conveyance path Outer guide member 73 Inner guide member 100 Sheet conveyance device 100a of the first embodiment Sheet conveyance device 100a 'of the second embodiment Modification 1 of the sheet conveyance device of the second embodiment
100a "Modification 2 of the sheet conveying device of the second embodiment
106 Registration roller pair D Image forming apparatus J Path width P1 Upstream end (inlet part) of reverse conveyance path
Downstream end (exit part) of P2 reverse conveyance path
S 'Reversed conveyance path Q1 Plain paper Q2 Thick paper (an example of a sheet that is stronger than plain paper)
X Sheet transport direction β1 First transport straight line β2 Second transport straight line

Claims (4)

A pair of registration rollers for conveying a sheet in a predetermined sheet conveying direction;
A reverse conveyance path that is curved on the upstream side in the sheet conveyance direction from the registration roller pair,
A first conveyance straight line along the sheet conveyed at the upstream end in the sheet conveyance direction on the reverse conveyance path, and a sheet conveyed at the downstream end in the sheet conveyance direction on the reverse conveyance path. A sheet conveying apparatus that prevents a leading end of a sheet that is stiffer than plain paper from penetrating through a nip portion of the pair of registration rollers by an inversion angle formed with a second conveying straight line. In the sheet conveying apparatus according to claim 1,
The inversion angle α is in a range of 90 ° ≦ α ≦ 100 °. In the sheet conveying apparatus according to claim 1,
The reverse conveying path is formed with a curved portion between the outer guide member and the inner guide member facing each other, and the inner guide member is provided so as to be movable in a direction in which the path width of the curved portion becomes wider. Is configured as
The inversion angle α is in a range of 60 ° ≦ α ≦ 80 °.   An image forming apparatus comprising the sheet conveying device according to claim 1.

Images