JP2010089900A - Sheet carrying device, sheet length detecting device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet carrying device capable of preventing the occurrence of a gouge and the occurrence of tearing to a soft roller, without arranging a guide just before the soft roller. <P>SOLUTION: In carrier roller pairs 51 for carrying a sheet S1 from carrier roller pairs 50, the lower side is a hard roller 13, and the upper side is a soft roller 12. An auxiliary guide member 18 slidingly contacted with a lower guide plate 17 by folding back downward after introducing the sheet S1 upward, is arranged on the upstream side in the carrying direction of these carrier roller pairs 51. When the sheet S1 reaches the carrier roller pairs 51 by the auxiliary guide member 18, its chip becomes the lower side than a tangent (t) of a nip 51a, and the upward curled sheet S1 is guide to the nip 51a without abutting on the soft roller 12. Thus, the occurrence of a hit mark or tearing is prevented, and there is no need to arrange the guide just before the soft roller 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sheet conveying apparatus that conveys a sheet, a sheet length detection apparatus, and an image forming apparatus, and more particularly to an apparatus that includes a pair of conveying rollers with a second conveying roller that is softer than a first conveying roller.

  Conventionally, for example, in an image forming apparatus such as a copying machine, a printer, or a multifunction peripheral, conveyance using a conveyance force of a roller pair has been adopted as a sheet conveyance method. In general, the roller pair includes a driving roller on one side and a driven roller on the other side, and conveys the sheet by sandwiching the sheet between the driving roller and the driven roller. Further, in this roller pair, a roller made of a relatively hard material (hereinafter referred to as “hard roller”) and a roller made of a soft material softer than the hard roller (hereinafter referred to as “soft roller”) face each other. Arranged and configured.

  If this is a combination of soft rollers, if the edge of the leading edge of the sheet is caught on the surface of the soft roller, there is a risk that a dent will be formed on the soft roller or the sheet will be torn. For this reason, this problem is solved by combining a soft roller and a hard roller and carrying the sheet so that the leading edge of the sheet positively hits the hard roller. Also, if a hard roller is used on the drive side, slippage may occur due to the high surface slidability, and the sheet conveying force may not be obtained. Used.

  That is, when the sheet passes through such a pair of rollers, the sheet is pressed against the hard roller by the soft roller, so that the sheet is provided with a curl having a concave shape on the hard roller side. In the sheet conveyance path, the arrangement of the hard roller and the soft roller is continuously made the same so that the leading edge of the sheet curled by the previous roller pair hits the hard roller side of the next roller pair. It is conceivable to prevent the occurrence of dents and tears as described above.

  By the way, in such an image forming apparatus, the soft roller and the hard roller used for the sheet conveyance described above are usually attached to a unit including the conveyance guide. Since the soft roller is on the drive side as described above, a drive source such as a motor, and a drive transmission member such as a gear and a belt are disposed in the unit on the soft roller side. On the other hand, in the image forming apparatus, a plurality of units constituting the sheet conveying unit and the image forming unit are arranged in a housing of the image forming apparatus main body. For this reason, the unit on the soft roller side is not necessarily arranged on the same side with respect to the conveyance path due to space restrictions, and the hard roller may not be continuously arranged on the same side.

  Further, when the hard rollers are continuously arranged on the same side as described above, the curled sheet is continuously curled to the same side, so that only the curl amount is increased. Therefore, it is necessary to remove the curl of the sheet by appropriately changing the positional relationship between the hard roller and the soft roller.

  Accordingly, in the sheet conveying path, for example, the upper roller in the upstream conveying roller pair is a hard roller and the lower roller is a soft roller, the upper roller in the downstream conveying roller pair is a soft roller, and the lower roller is a hard roller. There is a case. In this case, there is a possibility that the sheet curls upward in the upstream conveying roller pair and the leading edge of the sheet hits the soft roller in the downstream conveying roller pair.

  The cause of the curling direction toward the soft roller is not only the change in the vertical relationship between the hard roller and the soft roller, but also other causes. For example, the direction of curling generated by a fixing device that heats and pressurizes a toner image and fixes the toner image on the sheet may be on the soft roller side.

  In order to prevent the curled sheet from hitting the soft roller and causing the above-described dents, tears, etc., it is also conceivable to provide a collision prevention guide in front of the soft roller (see Patent Document 1). In other words, as shown in FIG. 7A, a guide 72 is provided in front of the soft roller 71a in front of the roller nip 70 formed by the soft roller 71a and the hard roller 71b. As a result, the leading edge of the sheet S2 curled toward the upper side is in contact with the guide 72 even when it is separated from the lower surface guide plate 73 toward the soft roller 71a. Then, as shown in FIG. 7B, the sheet S2 is guided to the roller nip 70 without colliding with the soft roller 71a. As a result, the edge at the end of the curl is not caught by the soft roller 71a, and it is possible to prevent the occurrence of a dent on the soft roller 71a, the tearing of the sheet S2, and the like.

JP 2004-334102 A

  However, in the case where the guide 72 is provided in front of the soft roller 71a as described above, it is necessary to cover the front end of the sheet with the guide 72 until just before the roller nip 70 so as not to touch the soft roller 71a. For this reason, for example, when a jam occurs at the roller nip 70 and a jammed sheet enters between the guide 72 and the soft roller 71a, there is a problem that the margin for the jamming problem is small, such as it becomes difficult to remove the sheet.

  Accordingly, the present invention provides a sheet conveying device, a sheet length detecting device, and an image forming device that do not provide a guide immediately before the soft roller and can prevent the occurrence of dents and tearing of the soft roller. Is intended to provide.

The present invention includes a sheet conveying unit that conveys a sheet;
Arranged on the downstream side in the sheet conveying direction with respect to the sheet conveying portion, the first conveying roller and the second conveying roller that is softer than the first conveying roller are arranged to face each other with the second conveying roller facing upward. A pair of transport rollers,
An upper guide plate and a lower guide plate, which are arranged between the sheet conveying unit and the conveying roller pair and constitute a sheet conveying path for guiding the sheet;
In a sheet conveying apparatus comprising:
Auxiliary guide member that is arranged on the upstream side in the sheet conveyance direction with respect to the pair of conveyance rollers and guides the sheet guided upward in the sheet conveyance path and then folds the sheet downward and makes sliding contact with the lower guide plate With
When the conveyed sheet reaches the pair of conveying rollers by the auxiliary guide member, the leading end of the sheet is positioned on the lower guide plate side with respect to the tangent line of the nip of the conveying roller pair. To do.

  According to the present invention, for example, when a sheet whose front end is curled upward is conveyed, the auxiliary guide member guides the sheet upward and then folds the sheet downward to make sliding contact with the lower guide plate. Let the pair reach. Therefore, when the sheet reaches the conveying roller pair, the leading edge of the sheet can be positioned on the lower guide plate side with respect to the tangent line of the nip of the conveying roller pair, and the leading edge of the sheet hits the second conveying roller. Can be prevented. As a result, it is possible to prevent the occurrence of dents on the second conveying roller and the occurrence of tearing of the sheet. Further, since the auxiliary guide member and the conveying roller pair are sufficiently separated from each other, for example, a jammed sheet is not clogged, that is, the margin can be increased against adverse effects such as jamming.

  Hereinafter, the best mode of the present invention will be described in detail with reference to the drawings.

  First, an image forming apparatus 40 provided with a sheet conveying apparatus according to the present invention will be described with reference to FIGS. FIG. 3 is a cross-sectional view of an intermediate transfer tandem color image forming apparatus. FIG. 4 is a perspective view of the color image forming apparatus. 5A and 5B are diagrams illustrating a duplex conveyance path, where FIG. 5A is a diagram illustrating a state in which a guide for a duplex conveyance path is closed, and FIG. 5B is a diagram illustrating a state in which the guide for a duplex conveyance path is opened during jam processing or the like. FIG.

  As shown in FIG. 3, the sheet S is stacked and stored on a lift-up device 42 included in the paper supply storage 41 and is supplied by the paper supply unit 43 in accordance with the image formation timing of the image forming apparatus 40. Is done. Examples of the paper feeding means 43 include a system that uses frictional separation by a paper feed roller and the like, a system that uses separation and adsorption by air, and the like. In this embodiment, a separation and suction system by air is used. The sheet S sent out by the paper supply unit 43 passes through a transport path 44 a included in the transport unit 44 and is transported to the registration unit 45. After the skew correction and timing correction are performed in the registration unit 45, the registration unit 45 is sent to the secondary transfer unit 420. The secondary transfer portion 420 is a toner image transfer nip portion to the sheet S formed by the substantially opposite secondary transfer inner roller 403 and secondary transfer outer roller 46, and has a predetermined pressure and electrostatic load bias. The unfixed image is adsorbed on the surface of the sheet S. The conveyance path for conveying the sheet S is guided while conveying the sheet S while suppressing the behavior of the conveyance means (for example, a roller pair and a suction belt) arranged at an appropriate interval for holding and delivering the sheet S. It is comprised by the conveyance guide to do.

  With respect to the conveyance process of the sheet S up to the secondary transfer unit described above, an image formation process sent to the secondary transfer unit 420 at the same timing will be described. The image forming unit 415 includes four sets of stations 413 and an intermediate transfer belt 406. The station 413 mainly includes a photosensitive member 408, an exposure device 411, a developing device 410, a primary transfer device 407, and a photosensitive member cleaner 409. Etc. The exposure device 411 emits light on the basis of the image information signal sent to the photosensitive member 408 whose surface has been uniformly charged in advance by a charging means (not shown) and which rotates in the direction of arrow A in the figure, and is diffracted. A latent image is formed through the means 412 and the like as appropriate.

  The electrostatic latent image formed on the photoconductor 408 in this manner is subjected to toner development by the developing device 410, and a toner image (toner image) is formed on the photoconductor 408. Thereafter, a predetermined pressure and an electrostatic load bias are applied by the primary transfer device 407, and the toner image is transferred onto the intermediate transfer belt 406. Thereafter, the transfer residual toner slightly remaining on the photoconductor 408 is collected by the photoconductor cleaner 409, and is again prepared for the next image formation. The station 413 described above includes four sets (four colors) of yellow (Y), magenta (M), cyan (C), and black (Bk) in the image forming apparatus 40. Of course, the number of stations is not limited to four sets (four colors), and the arrangement order is not limited to this.

  Next, the intermediate transfer belt 406 will be described. The intermediate transfer belt 406 is stretched by rollers such as a driving roller 404, a tension roller 405, and a secondary transfer inner roller 403, and is conveyed and driven in the direction of arrow B in the drawing. Therefore, the image forming process of each color processed in parallel by the above-described Y, M, C, and Bk stations 413 is performed at the timing of overlapping with the upstream toner image primarily transferred onto the intermediate transfer belt 406. As a result, a full-color toner image is finally formed on the intermediate transfer belt 406 and conveyed to the secondary transfer unit 420.

  As described above, the full-color toner image is secondarily transferred onto the sheet S in the secondary transfer unit 420 by the conveyance process of the sheet S and the image formation process of the image forming unit 415 described above. Thereafter, the sheet S is conveyed from the pre-fixing conveying means 47 to the fixing device (fixing unit) 48, where the toner image is melted by pressurization / heating or the like (at least one of pressurization / heating is sufficient). Secure. The sheet S having a fixed image obtained in this manner is discharged as it is onto the paper discharge tray 400 by the branch conveyance device 49, or when the double-sided image formation is required, the reverse conveyance device 401 to the double-side conveyance device 402. The route is selected as to whether it is conveyed.

  As shown in FIG. 4, at the lower part of the image forming apparatus 40, the paper storage 41 is provided so that it can be pulled out in the front direction. Further, each part (particularly including a double-sided conveyance device 402 described later in detail) located above the sheet storage 41 is covered with front covers 61 and 62. The front covers 61 and 62 are configured to be supported so as to be able to open the doors, and are configured to be able to open each part of the image forming apparatus 40.

  Next, explanation will be given on the double-sided image formation. As shown in FIG. 3, the uppermost sheet S stored in the sheet storage 41 is separated by the sheet feeding means 43 (here, an air suction belt), and the first sheet S immediately after the downstream is separated. It is nipped and conveyed by a drawing roller pair and a second drawing roller pair (both not shown). Subsequently, the sheet is fed to a double-sided pass roller, a registration roller, and a secondary transfer roller (all not shown), and heat and pressure are applied to the sheet when passing through the fixing roller, and the image on one side is fixed to the sheet S. At this time, the sheet S curls upward in FIG. Thereafter, the sheet S is conveyed to the reverse conveyance device 401 by the branch conveyance device 49 and further conveyed to the double-sided conveyance path 402 a of the double-sided conveyance device 402. Then, the sheet conveyed to the double-sided conveyance path 402a is re-conveyed to the secondary transfer unit 420 with the top and bottom (front and back) being reversed.

  As shown in FIG. 5A, the double-sided conveying device 402 includes an upstream unit 100 that is upstream in the conveying direction (sheet material conveying direction) and a downstream unit 101 that is downstream in the conveying direction. ing. The upstream unit 100 includes an upper guide plate 14 and a lower guide plate 15. A drive transmission member such as a motor and a gear and a plurality of soft rollers are arranged on the lower guide plate 15, and a unit of the drive side roller. Is configured. Further, a plurality of hard rollers are rotatably supported on the upper guide plate 14 to constitute a driven roller unit. One downstream unit 101 includes an upper guide plate 16 and a lower guide plate 17. A drive transmission member such as a motor and a gear and a plurality of soft rollers are arranged on the upper guide plate 16, and a drive side roller is provided. The unit is configured. In addition, a plurality of hard rollers are rotatably supported on the lower guide plate 17 to constitute a driven roller unit. The soft roller is made of a softer material than the hard roller. The soft roller is made of a material such as soft rubber or sponge, and the hard roller is made of hard rubber or metal.

  As described above, in the double-sided conveyance device 402, the upstream unit 100 and the downstream unit 101 have the upper and lower arrangements of the soft roller and the hard roller reversed. In the present embodiment, the sheet conveying apparatus 1 according to the present invention is applied to such a sheet conveying path between the upstream unit 100 and the downstream unit 101 (that is, a part of the double-sided conveying path 402a). Yes.

  In the double-sided conveyance device 402, for example, when a sheet is removed due to the occurrence of a jam or the like, as shown in FIG. 5B, the opening direction of the guide plate is upside down due to the configuration of the image forming apparatus. That is, the lower guide plate 15 is opened in the upstream unit 100 and the upper guide plate 16 is opened in the downstream unit 101. When the lower guide plate 15 and the upper guide plate 16 are closed as shown in FIG. 5A, a nip is formed between each soft roller and each hard roller, and the respective rollers are arranged to face each other. A roller pair is formed.

  Next, the sheet conveying apparatus 1 according to the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic cross-sectional view showing a sheet conveying apparatus provided with an auxiliary guide member according to the present invention, and FIG. 2 is a schematic cross-sectional view showing a sheet conveying apparatus not provided with an auxiliary guide member.

  As shown in FIG. 1, the sheet conveying apparatus 1 according to the present invention includes an upper guide plate 14 and a lower guide plate 15 of the upstream unit 100 and an upper guide plate 16 and a lower guide plate 17 of the downstream unit 101. A sheet conveyance path for guiding the sheet is configured. This sheet conveyance path (sheet conveyance path) constitutes a part of the double-sided conveyance path 402a of the double-sided conveyance apparatus 402. In other words, the sheet conveyance apparatus 1 is disposed at a part of the double-sided conveyance path 402a. ing.

  The sheet conveying apparatus 1 includes a pair of conveying rollers (sheet conveying unit) 50 on the upstream side (upstream side in the sheet conveying direction). The upstream conveying roller pair 50 includes a hard roller (third conveying roller) 10 supported by the upper guide plate 14 and a soft roller (fourth conveying roller) 11 supported by the lower guide plate 15. The conveying roller pair 50 forms a nip 50 a between the hard roller 10 and the soft roller 11 with the lower guide plate 15 of the upstream unit 100 closed (see FIG. 5).

  Further, the sheet conveying apparatus 1 includes a conveying roller pair 51 on the downstream side in the conveying direction F (downstream side in the sheet conveying direction) with respect to the upstream conveying roller pair 50. The downstream conveyance roller pair 51 includes a hard roller (first conveyance roller) 13 supported by the lower guide plate 17 and a soft roller (second conveyance roller) 12 supported by the upper guide plate 16. The conveying roller pair 51 forms a nip 51a between the hard roller 13 and the soft roller 12 with the upper guide plate 16 of the downstream unit 101 closed (see FIG. 5).

  In the sheet conveying apparatus 1, an auxiliary guide member 18 made of a flexible plate spring-like member is disposed between the upstream conveying roller pair 50 and the downstream conveying roller pair 51. The auxiliary guide member 18 has a lower base portion fixed to the lower guide plate 17 and is inclined so as to approach the upper guide plate 16 as it proceeds from the lower guide plate 17 in the transport direction F. ing. That is, the auxiliary guide member 18 is disposed so as to be inclined so as to intersect the sheet conveyance direction F as a whole. The distal end portion 18a of the auxiliary guide member 18 is on the upper guide plate side with respect to a line connecting the nip 50a of the upstream conveying roller pair 50 and the nip 51a of the downstream conveying roller pair 51 (nip between both rollers), Preferably, it extends so as to contact the upper guide plate 16.

  Next, a sheet conveying operation in the sheet conveying apparatus 1 will be described. As described above, the sheet conveying apparatus 1 is disposed in a part of the duplex conveying path 402a, and the sheet S1 made of, for example, plain paper conveyed to the sheet conveying apparatus 1 is fixed to the fixing apparatus 48 (see FIG. 3). 1) is curled on the upper side in FIG. In addition, since the plurality of transport roller pairs arranged in the upstream unit 100 (see FIG. 5) are hard rollers on the upper side and soft rollers on the lower side, they are pressed against the hard rollers by the soft rollers when transported and sandwiched. It is done. Therefore, in each pair of transport rollers (including the transport roller pair 50), a predetermined amount (radius R with O as the center) of the sheet S1 is similarly imparted to the upper side.

  As shown in FIG. 2, for example, when the sheet conveying apparatus 1 does not include the auxiliary guide member 18, that is, in the normal double-sided conveying path 402 a, the curled sheet S <b> 4 is delivered from the conveying roller pair 50. Then, it goes to the lower guide plate 17. Since the sheet S4 is grounded to the lower guide plate 17 as it is and heads toward the conveying roller pair 51, the height of the leading end of the sheet S4 to which a predetermined amount (radius R with O as the center) is applied is the hard roller 13. It becomes higher than (nip 51a). For this reason, when the sheet S4 reaches the conveying roller pair 51, the leading end of the sheet S4 comes into contact with the soft roller 12, and for example, if there is an edge at the leading end of the sheet S4, there is a possibility that a dent is formed or the sheet is torn. There is.

  On the other hand, as shown in FIG. 1, in the sheet conveying apparatus 1 according to the present invention, when the sheet S1 sent from the upstream conveying roller pair 50 contacts the auxiliary guide member 18, it is guided upward. The sheet S 1 guided upward by the auxiliary guide member 18 is pressed against the upper guide plate 16, folded back at the pressed portion and rotated downward, and the lower guide near the front of the conveying roller pair 51. It faces the plate 17 and is in sliding contact with the lower guide plate 17. That is, the sheet S1 proceeds in a triangular shape in side view with the pressed portion as a vertex, and the contact angle with the lower guide plate 17 is increased as compared with the case of FIG.

  Therefore, when the conveyed sheet S1 reaches the conveying roller pair 51, the leading edge of the sheet S1 is positioned closer to the lower guide plate 17 side (lower guide plate side) than the tangent t of the nip 51a of the conveying roller pair 51. . That is, when reaching the pair of conveying rollers 51, the height of the leading edge of the sheet S1 is lower than that of the hard roller 13 (nip 51a), and is guided to the nip 51a without coming into contact with the soft roller 12. Thereby, for example, even if there is an edge at the leading edge of the sheet S1, it is possible to prevent the soft roller 12 from being dented or the sheet S1 from being torn. Further, since the auxiliary guide member 18 is not disposed in proximity to the soft roller 12, even if a jam or the like occurs in the conveyance roller pair 51, for example, the sheet is easily removed, that is, a margin for adverse effects such as a jam. Becomes larger.

  Further, when the sheet S1 is conveyed, the auxiliary guide member 18 has flexibility as described above. Therefore, when the sheet S1 is slidably contacted with the upper guide plate 16, the sheet S1 is conveyed to the surface of the sheet S1. Can be reduced.

  In the present embodiment, the case where the sheet S1 is, for example, plain paper is described. However, when the sheet is hard and has rigidity (rigidity) such as an OHP sheet, the auxiliary guide member 18 is bent. It is conceivable to set the flexibility of the auxiliary guide member 18. When the sheet is rigid, the curl generated is small or hardly curled. Therefore, when the rigidity of the sheet is stronger than that of the auxiliary guide member 18, the auxiliary guide member 18 bends, the sheet advances substantially straight without facing upward, and then falls due to its own weight, so that the leading edge of the sheet reaches the hard roller 13. Will progress towards.

  Next, another embodiment in which the above-described sheet conveying apparatus is applied to a sheet length detection system (sheet length detection apparatus) will be described with reference to FIG. FIG. 6 is a schematic cross-sectional view showing a sheet length detection system according to the present invention.

  The sheet length detection system 26 removes curl of the sheet S3 as much as possible and accurately conveys it to the sensors (detection means) 24 and 25 in order to accurately measure the length of the sheet S3 that has been conveyed. By doing so, the length of the sheet S3 is measured. That is, in order to measure the length of the sheet S3 in the conveyance direction F with high accuracy, the sheet conveyance device 2 in the sheet length detection system 26 needs to use a combination of conveyance roller pairs with stable sheet conveyance force. Therefore, in the sheet length detection system 26, the upstream side conveyance roller pair (sheet conveyance unit) 52 includes a hard roller (third conveyance roller) 21 on the upper side and a soft roller (fourth conveyance roller) 20 on the lower side. Configuration is adopted. Further, the conveying roller pair 53 employs a configuration of a soft roller (second conveying roller) 23 on the upper side and a driving hard roller (first conveying roller) 22 on the lower side. In particular, for the transport roller pair 53 on the downstream side in the transport direction F, a blast roller (hard roller) 22 having a rough iron surface is used as the lower drive side, and a rubber roller (soft roller) 23 is used on the upper driven side. As a result, the friction coefficient is large and the conveyance force is stable.

  Further, since the combination of the soft roller and the hard roller in the upper and lower rollers is switched between the upstream conveying roller pair 52 and the downstream conveying roller pair 53, the curling direction for the sheet S3 is switched. That is, in the conveying roller pair 52 in which the hard roller 21 is used on the upper side and the soft roller 20 is used on the lower side, the upward curling is applied to the sheet S3. On the contrary, in the conveyance roller pair 53 in which the soft roller 23 is used on the upper side and the hard roller 22 is used on the lower side, the downward curling is applied to the sheet S3. Therefore, for example, even if the sheet S3 curled upward or downward is conveyed to the sheet length detection system 26, the same amount of curl is applied vertically by the conveyance roller pairs 52 and 53, and the sheet S3 The curl can be removed.

  Then, the sheet S3 that has been curled and thus stably conveyed is based on the ON / OFF signals of the sensors 24 and 25 including, for example, a light emitting element and a light receiving element. The length in the transport direction is detected with high accuracy.

  Also in the sheet conveying apparatus 2 in the sheet length detection system 26 as described above, an auxiliary guide member 27 whose tip 27a contacts the upper guide plate 28 is disposed between the conveying roller pair 52 and the conveying roller pair 53. Has been. That is, even in the sheet conveying apparatus 2, the sheet S3 sent from the upstream conveying roller pair 52 is guided upward by the auxiliary guide member 27, pressed against the upper guide plate 28, and rotated downward. It is slidably contacted with the lower guide plate 29 in the vicinity of the front of the conveying roller pair 53. Therefore, when the sheet S3 reaches the conveying roller pair 53, the leading edge of the sheet S3 is positioned on the lower guide plate 29 side with respect to the tangent t of the nip 53a of the conveying roller pair 53 without contacting the soft roller 23. To the nip 53a. As a result, for example, even if there is an edge at the leading edge of the sheet S3, it is possible to prevent the soft roller 23 from being dented or the sheet S3 from being torn. Similarly, since the auxiliary guide member 27 is not arranged close to the soft roller 23, for example, even if a jam or the like occurs in the conveyance roller pair 53, the sheet is easily removed, that is, against the harmful effects such as a jam. The margin increases.

FIG. 3 is a schematic cross-sectional view illustrating a sheet conveying apparatus in which an auxiliary guide member according to the present invention is disposed. FIG. 4 is a schematic cross-sectional view illustrating a sheet conveying device that does not include an auxiliary guide member. 1 is a cross-sectional view of an intermediate transfer tandem color image forming apparatus. 1 is a perspective view of a color image forming apparatus. 4A and 4B are diagrams illustrating a duplex conveyance path, where FIG. 5A is a diagram illustrating a state in which a guide for a duplex conveyance path is closed, and FIG. 5B is a diagram illustrating a state in which the guide for a duplex conveyance path is opened during jam processing or the like. The cross-sectional schematic diagram which shows the sheet length detection system which concerns on this invention. 2A and 2B are diagrams illustrating an apparatus in which a guide is provided in front of a soft roller, in which FIG. 3A is a diagram illustrating a state where a sheet is in contact with the guide, and FIG.

Explanation of symbols

1, 2 ... Sheet conveying device 10, 21 ... Third conveying roller (hard roller)
11, 20 ... Fourth transport roller (soft roller)
12, 23 ... second conveying roller (soft roller)
13, 22 ... 1st conveying roller (hard roller)
16, 28 ... upper guide plates 17, 29 ... lower guide plates 18, 27 ... auxiliary guide members 18a, 27a ... tip portions 24, 25 ... detection means (sensors)
26... Sheet length detection device 40... Image forming device 48.
50, 52... Sheet conveying section, upstream side conveying roller pair 51, 53... Conveying roller pair 50a, 51a, 52a, 53a .. nip 402a ... sheet conveying path, duplex conveying path 415. Image forming unit 420 ... transfer unit (secondary transfer unit)
F: Sheet transport direction S1, S3 ... Sheet t ... Tangent

Claims (7)

A sheet conveying section for conveying the sheet;
The first conveyance roller and the second conveyance roller that is softer than the first conveyance roller are disposed opposite to the sheet conveyance unit with the second conveyance roller facing upward. A pair of transport rollers,
An upper guide plate and a lower guide plate, which are arranged between the sheet conveying section and the conveying roller pair and constitute a sheet conveying path for guiding the sheet;
In a sheet conveying apparatus comprising:
Auxiliary guide member that is arranged on the upstream side in the sheet conveyance direction with respect to the pair of conveyance rollers and guides the sheet guided upward in the sheet conveyance path and then folds the sheet downward and makes sliding contact with the lower guide plate With
When the conveyed sheet reaches the pair of conveying rollers by the auxiliary guide member, the leading end of the sheet is positioned on the lower guide plate side with respect to the tangent line of the nip of the conveying roller pair. Sheet transport device.   The said auxiliary guide member has flexibility, and is arrange | positioned so that the front-end | tip part of the sheet conveyance direction downstream of the said auxiliary guide member may contact the said upper guide plate. Sheet transport device.   The auxiliary guide member is disposed so as to intersect the sheet material conveyance direction so as to approach the upper guide plate from the lower guide plate toward the sheet conveyance direction. The sheet conveying apparatus according to 1.   The leading end of the auxiliary guide member on the downstream side in the sheet conveying direction is located on the upper guide plate side with respect to the upstream conveying roller pair and a line connecting nips of both rollers of the conveying roller pair. The sheet conveying apparatus according to claim 1. A sheet conveying device according to any one of claims 1 to 4,
A sheet length detection apparatus, comprising: a detection unit that is disposed on the downstream side in the conveyance direction of the sheet conveyance apparatus and detects the length of the conveyed sheet. An image forming unit for forming an image on a sheet;
An image forming apparatus comprising: the sheet conveying device according to claim 1 disposed on an upstream side or a downstream side of the image forming unit. A transfer unit for transferring a toner image to a sheet;
A fixing unit that fixes the toner image transferred by the transfer unit to a sheet using at least one of pressure and heat;
A double-sided conveyance path for reversing the sheet on which the image is fixed on one side by the fixing unit and re-transporting the sheet to the transfer unit,
5. The image forming apparatus according to claim 1, wherein the sheet conveying apparatus according to claim 1 is disposed in a part of the double-sided conveying path.

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