JP2008087907A - Sheet conveying path switching device, sheet conveying device, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easy-to-use, inexpensive, and small sheet conveying device, which can stably and separately convey not only sheets of a fixed size that are normally used, but also highly rigid sheets and special sheets, and can further separately convey a bent sheet reliably. <P>SOLUTION: In this sheet conveying path switching device having a sheet loading path and a switching/separating claw, the outlines of two separating/conveying paths near the separating/branching claw out of a plurality of separating/conveying paths 27, 28 positioned on the downstream side of the switching/separating claw 22 are configured by the surface of a movable belt 53. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a conveyance path switching apparatus that switches a sheet conveyance direction in an image forming apparatus such as a copying machine, a printer, and a facsimile, and a sheet conveyance apparatus and an image forming apparatus using the conveyance path switching apparatus.

  In order to reduce the size of the entire image forming apparatus, it is desired to reduce the size of a sheet conveying apparatus that conveys a recording medium (paper, recording sheet) from a sheet storage unit such as a sheet feeding cassette or a sheet feeding tray. In recent years, in image forming apparatuses, models corresponding to various sizes and paper types are becoming popular. In such a model, several sizes and types of paper are stored in advance in a paper storage unit, and a paper whose size or type is appropriately selected by the user from the paper storage unit or automatically selected by the image forming apparatus. Paper can be fed. For this reason, since the sheet storage means occupies more space in the image forming apparatus, there is an increasing demand for downsizing the sheet conveying apparatus. From the viewpoint of sheet conveyance, there is a similar request for ADF documents.

  Furthermore, recently, in an image forming apparatus, a model capable of performing image formation by selecting one side or both sides of a sheet is becoming common. In an image forming apparatus capable of forming an image on both sides of a sheet, a sheet having an image fixed on one side is sent out to a recording material stacking unit (discharge tray) provided in the apparatus body, or In order to form an image on the back side, it is conveyed to a recording body reversing unit (double-sided conveyance means). Therefore, branching means for selectively switching the sheet conveyance direction is provided in the sheet conveyance path. Even when images are formed on only one side, it is necessary to switch the conveyance path when the fixed sheets are sorted and discharged. As the branching means, as shown in Patent Document 1, a simple and low-cost one using a branching claw is widely adopted. In order to reduce the size of the conveyance path formed in the branching section in the sheet conveyance apparatus, the conveyance direction is largely changed to reduce the occupied space of the conveyance path itself, depending on the positional relationship of the apparatus. ing. As a result, a curvature portion having a predetermined curved shape is provided on the conveyance path in order to continuously and smoothly change the conveyance direction, and the curvature radius of the curvature portion is a standard shape usually used in an image forming apparatus. The radius is set so as to be small enough to convey the sheet.

  FIG. 7 is a cross-sectional view schematically illustrating a configuration of a sheet conveying apparatus that uses a branching claw as a branching unit and has a reduced curvature radius of a curvature portion of a branching conveyance path. FIG. 7A shows a first posture in which the claw member of the branching claw 22 guides the paper P to the discharge tray side, and FIG. 7B shows the switchback conveyance path and the re-conveyance path side for the double-sided printing of the paper P. The second posture for guiding is shown. FIG. 6 is a perspective view of the branching device. In this figure, in order to make the depiction easy to understand, the upper guide plate 23 that forms the branched conveyance path and the upper roller of the conveyance roller pair are omitted.

  The branch claw 22 has a configuration in which a plurality of claw members 22a are coaxially arranged on a shaft 22b. The tip of the claw member 22a can be fitted into holes (may be concave) 18a, 19a provided in the lower left guide plate 18 and the lower right guide plate 19 as viewed in FIG. The direction is branched. The shaft 22b is in a first posture in which the shutter 22c for detecting the rotational position is fixed, and the edge of the shutter 22c is detected by the photosensor 21 so that the branching claw 22 guides the paper to the paper discharge unit. Can be detected. A pulley 22d is fixed to the shaft 22b on the side opposite to the shutter portion 22c, and is connected to the shaft 22b by a stepping motor 20 via a timing belt 24. The branching claw 22 has a driving force of the stepping motor 20. Is supposed to work with.

  In FIG. 7, a carry-in path 26 into which a sheet is carried in from a fixing device (only a fixing roller pair 25 a is shown) on the upstream side of the sheet conveyance, and two conveyance paths 27 and 28 located on the downstream side of the sheet conveyance beyond the branching claw 22. A branch conveyance path is formed by these conveyance paths 26, 27, and 28. The first branch transport path 27 guides the paper to the paper discharge unit side, and the second branch transport path 28 guides the paper to the switchback transport path side.

JP-A-2005-178554 Japanese Patent No. 3257712

  In the paper conveyance device configured as described above, when trying to convey a stiff, such as thick paper, that is, high-rigidity paper or special paper such as an envelope, the curvature radius of the curvature portion is small. Will come into contact with the wall surface of the curvature and the frictional resistance will increase. For this reason, there is a problem in that a highly rigid paper or special paper cannot travel along the transport path formed by the curvature portion, and a stable transport operation cannot be performed due to a jam or a transport failure. In order to prevent such a problem, it is conceivable to use a suction-type conveying means using air. However, since a suction device is required, the device becomes complicated and large, and the cost is greatly increased. There was a demerit.

  Accordingly, the present applicant realizes a device that can reliably feed a sheet to each intended conveyance path at a low cost even if the sheet is conveyed on the conveyance path at a very small sheet interval in response to an increase in the speed of the apparatus. With this in mind, the proposal of Patent Document 2 was made. Considering switching of the paper transport path using one of the proposed configurations, as shown in FIG. 8, the paper P passes through the nip of the roller pair 31 and is on an extension line in the paper transport direction so that the forward / reverse rotation is performed. By providing a possible switching belt 41 and changing the rotation direction of the switching belt 41, the transport direction of the paper P transported by the roller pair 31 is switched.

  FIG. 8A shows a state in which the leading edge of the sheet P is slightly pushed out by the roller pair 31 on an extension line in the sheet conveying direction passing through the nip of the roller pair. At this time, the switching belt 41 has already been rotated in the counterclockwise direction indicated by the arrow in order to send the paper P to the transport path 27 side. When the leading edge Pa of the paper P comes into contact with the switching belt 41, the leading edge Pa of the paper P1 is guided to the conveyance path 27 side by the rotation of the switching belt 41 in the direction of the arrow as shown in FIG. Thereafter, the sheet P is guided by the guide plates 36 and 37 as shown in FIG. 8C and is held by the pair of transport rollers 33 and moves up in the transport path 27.

  In the conveyance of the paper to another branch conveyance path 28, as shown in FIG. 9A, the leading edge of the paper P is nipped by the roller pair 31, while the switching belt 41 sends the paper P to the conveyance path 28 side. Rotate clockwise as indicated by the arrow. When the paper P reaches the switching belt 41 and the leading edge Pa contacts the belt, the leading edge Pa of the paper is guided in the rotation direction indicated by the arrow of the switching belt 41 as shown in FIG. Accordingly, the sheet P advances while being guided by the guide plates 36 and 38 and is conveyed downward in the conveyance path 28 while being held by the conveyance roller pair 35 as shown in FIG. 9C.

  Such a sheet conveying device using a switching belt can apply a conveying force to the sheet at the sheet conveying turning section, and is smooth even on a stiff sheet compared to a fixed curved guide path having a small curvature radius. Enables transportation. However, in the configuration shown in FIGS. 8 and 9, it is not guaranteed that the leading edge of the sheet contacts the desired branch conveyance path side of the switching belt 41 when the sheet is fed into the desired branch conveyance path, and switching between different branch conveyance paths is performed. There is a possibility that a situation may occur in which the front end of the sheet is pushed back to a desired branch conveyance path after coming into contact with the belt portion. That is, the sheet after fixing is particularly warped or wrinkled. For example, when the sheet P is warped downward in FIG. 8, the leading edge of the sheet first contacts the oblique lower right side of the switching belt 41. While the sheet P is fed by the roller pair 31, the leading edge of the sheet is lifted and pushed back toward the conveyance path 27, so that there is a high risk of jamming.

  The present invention has been made in view of the above background, and the object of the present invention is to stably branch and convey high-rigidity paper and special paper in addition to the regular form paper that is normally used. An object of the present invention is to provide a simple and inexpensive small-sized sheet conveying apparatus and image forming apparatus that can surely branch and convey even attached paper.

  According to the present invention, in the sheet conveyance path switching device having a sheet carry-in path and a switching branch claw, the above-described problem is that of two branch conveyance paths close to the branch claw among a plurality of branch conveyance paths on the downstream side of the switching branch claw. This can be solved by configuring the outer shell with a movable belt surface. In the case of the following embodiments related to the drawings, there are only two downstream branch conveyance paths, but the invention can also be applied to three or more branch conveyance paths, and the movable belt surface is close to the branch claw of them. Consists of the outline of two branch transport paths.

  It is preferable that the outer wall of the two branch conveyance paths is constituted by a belt surface of a single endless belt. A rotating member facing the belt tension rotating member that stretches the belt is disposed inside the branch conveyance path, and the sheet is sandwiched and conveyed between the opposite rotating member and the belt surface that is wound around the belt tension rotating member. If it is, it is more convenient. The belt tension rotating member may be directly driven. However, a belt capable of rotating in the forward and reverse directions may be driven in a driven manner by driving a rotating member facing the belt stretching rotating member. It is preferable if one of the belt tension rotating members also serves as one of the pair of paper discharge rollers.

It is also advantageous to provide a torque limiter on the rotating member facing the belt tension rotating member and that the belt is conductive.
It is preferable that the switching branch claw is composed of a fixed guide portion and a movable tip switching claw piece. It is preferable that the bottom side portion of the solid guide portion is as close as possible to the belt surface constituting the outline of the branch conveyance path. However, the endless belt may be composed of a belt portion that is divided into a plurality of portions in a direction orthogonal to the paper transport direction. In this case, it is advantageous that the bottom side portion of the fixed guide portion enters the endless belt region rather than the belt surface constituting the outline of the branch conveyance path.

The switching operation of the branching claws is preferably switched prior to the belt rotation direction switching operation.
In a sheet conveyance path switching device having a sheet carry-in path, a switching branch claw, and a plurality of branch conveyance paths downstream from the switching branch claw, the switching branch claw is constituted by a fixed guide portion and a movable tip switching claw piece. However, the above problem can be solved. In that case, it is more effective that a pair of sandwiching rollers is arranged near both ends of the bottom of the fixed guide portion, and the top corner of the bottom is directed to a roller constituting the outline of the branch conveyance path in the pair of sandwiching rollers.

  According to the first aspect of the present invention, in the sheet conveyance path switching device having the sheet carry-in path and the switching branch claw, two branch conveyance paths close to the branch claw among the plurality of branch conveyance paths existing downstream of the switching branch claw. Because the outer shell is constructed with a movable belt surface, in addition to the standard paper that is normally used, highly rigid paper and special paper can be stably branched and conveyed, even with warped paper. Branch conveyance is possible.

  According to the second aspect of the present invention, the outer contour of the two branch conveyance paths is constituted by the belt surface of a single endless belt, so that the configuration is simplified. According to the third aspect of the present invention, the rotating member facing the belt tension rotating member is arranged inside the branch conveyance path, and the sheet is nipped and conveyed between the opposed rotating member and the belt surface. The pressure applied to the belt can be adjusted without depending on the tension of the belt, and the frictional resistance can be adjusted. The belt tension rotation member may be directly driven to stabilize the belt drive. However, as in the invention according to claim 4, by driving the counter rotation member, the belt capable of rotating forward and reverse is driven. If it is driven in this manner, there is no need to dispose a drive member up to the belt rotation shaft located outside the sheet conveying path, which not only provides a merit in layout but also reduces the number of parts. . According to the fifth aspect of the present invention, since one of the belt tension rotating members also serves as one of the pair of paper discharge rollers, the paper transportability in the paper discharge transport is reliably improved only by extending the belt length.

  According to the sixth aspect of the present invention, since the torque limiter is provided on the counter rotating member, the counter rotating member is driven when a load exceeding the specification acts on each of the transport members provided in the transport path switching device due to a jam or the like. By stopping, the load applied to the belt can be kept within the specifications, the belt damage can be avoided, and a sheet conveying apparatus with few failures can be provided. According to the seventh aspect of the present invention, since the belt is conductive, it is possible to prevent the occurrence of frictional charging on the contact surface and to prevent the occurrence of an abnormal image during the second surface printing.

  According to the eighth aspect of the present invention, since the switching branch claw is composed of the fixed guide portion and the movable tip switching claw piece, the functions of switching the conveyance path and turning in the sheet conveyance direction can be divided for each piece. Even if the curvature of the side of the fixed guide portion is increased and the sheet conveyance path is switched in a compact manner, the leading edge of the sheet slides on the side piece of the fixed guide portion, and conveyance failure can be suppressed. According to the ninth aspect of the present invention, since the bottom side portion of the solid guide portion is as close as possible to the belt surface constituting the outline of the branch conveyance path, the sheet is conveyed from the side of the fixed guide portion to the belt surface. The bridge becomes smooth. According to the invention of claim 10, since the endless belt is constituted by a belt portion divided into a plurality of parts in a direction orthogonal to the sheet conveying direction, not only the member cost can be suppressed, but also the invention of claim 11 can be achieved. As described above, the bottom portion of the fixed guide portion can enter the endless belt region rather than the belt surface constituting the outline of the branch conveyance path, and the sheet conveyance from the side of the fixed guide portion to the belt surface can be further bridged. Smooth.

  According to the twelfth aspect of the present invention, since the switching operation of the branching claw is switched prior to the rotation direction switching operation of the belt, the sheet spacing can be reduced in a state where the sheet continuously enters the carry-in path. Even when the sheet is small, the sheet can be reliably guided from the carry-in path to any one of the branch conveyance paths, and a sheet conveyance apparatus with excellent productivity can be provided.

  According to the thirteenth aspect of the present invention, in the sheet conveyance path switching device having a sheet carry-in path, a switching branch claw, and a plurality of branch conveyance paths downstream of the switching branch claw, the switching branch claw is movable with the fixed guide portion. Since it is composed of a leading edge switching claw piece, highly rigid paper and special paper can be stably branched and conveyed in addition to the standard paper that is usually used, and even if the paper is warped, it can be reliably branched Can be transported. In that case, as in the invention according to claim 14, a pair of sandwiching rollers is arranged in the vicinity of both ends of the bottom of the fixed guide portion, and the top corner of the bottom faces the roller constituting the outline of the branch conveyance path in the pair of sandwiching rollers. If this is the case, the possibility of jam occurrence can be further suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional configuration diagram showing an outline of a full-color printer (hereinafter referred to as “printer”) 100 as an example of an image forming apparatus according to the present invention. A printer 100 shown in FIG. 1 includes a belt-like photoreceptor 1 as a latent image carrier. Around the photosensitive member 1, a charging device (not shown), a writing optical unit 2 as an exposure device, a multi-stage developing unit 3 as a developing device, an intermediate transfer belt 11 as a transfer device, a cleaning (not shown), and the like. Is arranged. The multi-stage developing unit 3 includes developing devices 3K, 3C, 3M, and 3Y that store black, cyan, magenta, and yellow developers in order from the bottom in a detachable and multi-stage manner. Here, subscripts K, C, M, and Y of the respective symbols indicate members for black, cyan, magenta, and yellow, respectively. Further, a primary transfer roller 12 as a primary transfer unit is provided inside the intermediate transfer belt 11 at a position facing the photoreceptor 1 (right side in the figure). In addition, at the lower part of the printer 100, three-stage paper feed cassettes 45a, 45b, and 45c that store paper are provided. Separating and feeding means 46a, 46b, and 46c are provided corresponding to the respective paper feeding cassettes 45a, 45b, and 45c. A manual feed tray 63 is provided on the right side surface of the printer 100 so that it can be pulled out and stored. FIG. 1 shows a state where the manual feed tray 63 is pulled out. In order to feed paper from the manual feed tray 63, separation feeding means 46d is provided. A grip roller pair 47 is provided to transport the paper fed by these separating and feeding means 46a, 46b, 46c and 46d. A registration roller pair 48 is provided above the grip roller pair 47 (on the downstream side in the paper transport direction). Above the registration roller pair 48, a secondary transfer roller 49 as a secondary transfer unit is provided to face the transfer counter roller 13 that is one of the rollers on which the intermediate transfer belt 11 is stretched. The separating / feeding means 46, the grip roller pair 47, the registration roller pair 48, and the like are each configured to be independently driven by a clutch, a stepping motor, or the like.

  A fixing device 25 is provided above the secondary transfer roller 49, and a conveyance path switching device 51 that selectively branches the conveyance direction is provided above the fixing device 25. Reference numerals 64 to 70 are paper sensors appropriately disposed in the paper conveyance path. The paper is appropriately guided by a guide member (not labeled) such as a guide plate provided in the paper transport path. The upper surface of the main body of the printer 100 is configured as a paper discharge tray 62, and a paper discharge roller pair 61 for discharging paper to the paper discharge tray 62 is provided at the upper left of the fixing device 25.

  A reversing device 80 for reversing the paper is provided on the right side of the printer 100 main body. The reversing device 80 includes a reversing forward path 81 as a switchback path and a reversing return path 82. In addition, a switchback roller pair 83 that sandwiches the sheet sent to the reversing forward path 81, an inlet sensor 84 provided on the upstream side of the switchback roller pair 83, and a reversing unit switching claw 85 are provided.

  Next, the operation of the printer will be described. When the printer receives full-color image data, the photoconductor 1 rotates clockwise (clockwise) in FIG. 1, and the surface thereof is uniformly charged by the charging device. Next, the photoconductor 1 is irradiated with laser light corresponding to each color image by the writing optical unit 2, and a latent image corresponding to the image data is formed on the surface of the photoconductor. The developing devices 3K, 3C, 3M, and 3Y corresponding to the formed colors are selectively opposed to the photoconductor 1 as the latent image reaches the position of the multi-stage development unit 3 by rotating the photoconductor 1. Then, toner is supplied onto the photoreceptor 1 from any of the developing devices 3K, 3C, 3M, and 3Y that face each other, and a toner image is formed. The toner image on the photoreceptor 1 is once transferred onto the intermediate transfer belt 11 by the primary intermediate transfer roller 12. On the other hand, the surface of the photoreceptor 1 after the toner image transfer is cleaned by a cleaning device (not shown). Such a cycle is repeated for each color, and the yellow, magenta, cyan, and black toner images are sequentially transferred onto the intermediate transfer belt, and a four-color superimposed full-color toner image is formed.

  On the other hand, when a paper feed command is issued in accordance with the timing of toner image formation, the paper is selectively separated from the feed cassettes 45a, 45b, 45c or the manual feed tray 63, and any one of the separation feed units 46a, 46b, 46c, 46d. Are fed one by one, pass through the grip roller pair 47, reach the registration roller pair 48, and temporarily stop. Then, the registration roller pair 48 sends out the toner image carried on the intermediate transfer belt 11 toward the secondary transfer position in timing. At the secondary transfer position, the toner image on the surface of the intermediate transfer belt 11 is collectively transferred onto the sheet by the secondary transfer roller 49. When the paper on which the toner image is transferred passes through the fixing device 25, the toner image is melted and fixed on the paper by heat and pressure. On the other hand, the intermediate transfer belt 11 after the toner image is transferred is cleaned by an intermediate transfer belt cleaning device (not shown) and is prepared for the next formation of an electrostatic latent image.

  The transport path switching device 51 switches the transport direction so that the paper after the toner image is fixed by the fixing device 25 is directed to either the paper discharge tray 62 or the reversing device 80. FIG. 2 shows an enlarged schematic configuration of the transport path switching device 51. The conveyance path switching device 51 has a branch claw 22 as a paper conveyance direction branching unit, and the branch claw 22 is switched to the left and right in the figure by an actuator (not shown) such as a solenoid. The conveyance path 27 conveys the sheet to the discharge tray 62 side, and the conveyance path 28 conveys the sheet to the reversing device 80 side. The sheet on which the toner image has been fixed by the fixing device 25 is introduced from the carry-in path 26 to the position of the branching claw 22, and is conveyed toward the conveyance paths 27 and 28 by the branching claw 22. A part of each outline of the branch conveyance paths 27 and 28 is carried by the belt surface of the endless belt 53. Incidentally, it is possible to divide the endless belt 53 into two to be an endless belt for the branch conveyance path 27 and an endless belt for the branch conveyance path 28. A substantially Y-shaped transport path is formed by the carry-in path 26 and the branch transport paths 27 and 28. For example, when single-sided printing is selected, the sheet is conveyed to the conveyance path 27 in the direction of the discharge tray 62 by switching the branch claw 22 of the conveyance path switching device 51, and the upper surface of the printer 100 main body is discharged by the discharge roller pair 61. The paper is discharged to a paper discharge tray 62 configured as described above. A thick solid line in FIG. 1 indicates a sheet conveyance path during single-sided printing (in the case of feeding from the feeding cassettes 45a, 45b, 45c or the manual feed tray 63). When double-sided printing is selected, the sheet is transported to the transport path 28 on the reversing device 80 direction side by switching the branch claw 22 of the transport path switching device 51. The paper fed into the reverse forward path 81 of the reversing device 80 by switching the transport path switching device 51 is sandwiched between the switchback roller pair 83 and sent to the reverse reverse path 82 by the reversing operation. In the reverse forward path 81, when the inlet sensor 84 provided on the upstream side of the switchback roller pair 83 detects the trailing edge of the sheet, the detection is used as a trigger to reverse the rotation direction of the switchback roller and reverse the switchback roller pair 83. The sheet is conveyed in the direction opposite to the approach direction with the trailing edge as the leading edge. The sheet sandwiched between the switchback roller pair 83 is transported by the transport action, and the reversing unit switching claw 85 is driven by a solenoid (not shown) so that it can enter the reversing return path 82. The sheet reversed through the reverse return path 82 is conveyed to the registration roller pair 48 from the reverse exit 86 for backside printing. A broken line in FIG. 1 indicates a sheet conveyance path in the reversing device 80 at the time of duplex printing. Then, the toner image is transferred to the transfer position of the intermediate transfer belt 11 by the registration roller pair 48 in synchronization with the toner image. After the transfer, the sheet is conveyed to the fixing device 25 where the toner image is fixed on the sheet. The sheet on which the image formation on the second side has been completed is conveyed to the discharge roller 61 along the path indicated by the thick solid line by the transfer path switching device 51 and is discharged onto the discharge tray 62 outside the apparatus.

  A more detailed configuration and operation of the transport path switching device 51 will be described. In the printer 100 of this embodiment, after being guided to one of the two transport paths 27 and 28 by the branching claw 22, the front end of the sheet contacts the surface of the belt 53 that is driven when transported to the paper discharge tray 62 or the reversing device 80. Thus, an endless belt 53 stretched by two rollers 29 and 30 is provided so as to turn in the corresponding transport direction. More specifically, in the conveyance path switching device 51, the leading end of the sheet is gripped on the surface of the endless belt 53, and the leading end of the sheet is moved and guided toward the downstream clamping unit. The belt 53 is configured to be able to switch between forward and reverse rotations, and is rotated in accordance with a predetermined conveyance direction to the paper discharge tray 62 or the reversing device 80, so that the resistance when the front end of the paper contacts can be reduced. For this reason, it is possible to stably convey not only regular form papers that are normally used but also highly rigid papers and special papers without causing jamming or poor conveyance. In addition, the space (curvature radius) required for changing the paper transport direction can be reduced simply by providing such a stretched belt, so that the size can be reduced and the cost increase can be suppressed. In the illustrated example, a single belt 53 that can be switched between forward and reverse rotations constitutes a rotational conveying means for conveying in both directions of the paper discharge tray 62, the reversing device 80, and both directions. It is of course possible to arrange a smaller endless belt to share the conveyance in the direction of the paper discharge tray 62 and the direction of the reversing device 80. It is also possible to configure the belt tension rotating member 29 to be one of the paper discharge roller pair 61. In this case, the counter rotating member 54 can be reduced, and the paper discharge roller pair 61 can be shifted to the right side in the drawing, so that a large mounting area for the paper discharge tray 62 can be secured.

  For the endless belt 53, a known conductive material is used such as carbon black dispersed in silicone rubber. By using the conductive member, it is possible to prevent the occurrence of frictional charging at the contact surface with the paper, and in particular, it is possible to prevent the occurrence of an abnormal image when printing on the second surface. In addition, when attaching the endless belt 53 to the belt tension rotating members 29 and 30, the endless belt 53 may be hung around the belt tension rotating members 29 and 30. In this case, an expansion ratio that allows the front end of the sheet to be securely gripped on the belt surface, an expansion ratio that is equal to the linear velocity with the counter rotating members 54 and 55 (when the belt side is driven), or interference with the bottom of the branching claw. It is preferable that the elongation ratio is such that it does not.

  Further, the belt 53 can be switched between forward and reverse rotations by applying a driving force to at least one of the belt tension rotating members 29 and 30 from a belt driving unit (not shown) that can be driven to rotate in both forward and reverse directions. Specifically, when the paper is branched and conveyed to the conveyance path 27 on the discharge tray 62 side, the rotation direction of the belt 53 is clockwise (CW) in the drawing, and is branched and conveyed to the conveyance path 28 on the reversing device 80 side. In this case, the counterclockwise direction (CCW) is used. Alternatively, the belt 53 may be driven to rotate by applying a driving force to the rotation members 54 and 55 facing the belt stretching rotation members 29 and 30 via the belt 53 by the drive unit. Torque limiters 56 and 57 may be provided in such a rotating member drive unit or opposed rotating members 54 and 55. In this way, the belt 53 can be reliably switched to a different conveyance path, and damage to the belt 53 can be prevented even when a malfunction such as a jam occurs. Furthermore, a configuration in which the conveyance path is opened so as to release the sandwiched state of the belt 53 and the counter rotating members 54 and 55 can be easily achieved. In addition, by disposing the rotation members 54 and 55 at positions facing the rotation axis of the belt 53, regardless of which of the belt stretching rollers 29 and 30 and the opposite rotation members 54 and 55 are given a driving force, the sheet Therefore, the frictional resistance between the belt 53 and the paper is increased, and the paper conveyance performance is improved.

  The branch claw 22 includes a movable tip switching claw piece 22a and a fixed guide portion 22b. By dividing into the movable part and the fixed part in this way, even when the bottom part of the fixed guide part 22b is brought very close to the belt 51, the bottom part of the branching claw can come into contact with the belt surface when switching the paper transport path. In addition, the sheet guide can be ensured. If the curved portion of the branch conveyance path is formed by curving the side of the fixed guide portion 22b, the sheet conveyance can be performed smoothly.

  As shown in FIG. 3, the belt 51 may be divided into a plurality of parts in a direction orthogonal to the paper transport direction. By dividing the belt, the fixed guide portions 22b ', 22b "between the partial belts 51a, 51b, 51c (only three belt pieces are shown in the drawing, but two or four or more are possible). With this arrangement, the bottom portion of the fixed guide portion (the flat portion of the fixed guide portion visible in FIG. 3) is positioned above the lower surface of the partial belts 51a, 51b, 51c, and the branching claw 22 is endless. The belt can be configured so as to enter the belt region, and the configuration can smoothly guide the sheet from the side of the fixed guide portion to the belt surface.

  The switching operation of the branch claw 22 (movable tip switching claw piece 22 a) is performed in advance by the switching operation of the rotation direction of the belt 53. In this way, it is possible to reliably guide the paper to different transport paths without increasing the paper transport interval. FIG. 4 is a flowchart regarding an operation example of the branch claw 22 and the endless belt 53. When a double-sided printing command is input (step 1) in a control unit (not shown) in the printer 100 main body, the detection state of a photo sensor (not shown, corresponding to reference numeral 21 in FIG. 6) at the branching claw is confirmed. (Step 2) If the detection is off, the tip switching claw opens the branch conveyance path 28 to the reversing device 80, so that the position of the endless belt 53 is maintained while maintaining its position (for example, stepping motor excitation). , The printing operation is started (step 4). On the other hand, if the detection state of the photo sensor is ON in step 2, the tip switching claw opens the branch conveyance path 27 to the discharge tray 62 and closes the branch conveyance path 28 to the reversing device 80. The stepping motor (not shown, corresponding to reference numeral 20 in FIG. 6) is normally rotated until it becomes (steps 5 and 6). If the timer is used (step 7) and no OFF detection is detected within a predetermined time (step 8), the operation of the image forming apparatus is stopped because there is a possibility of component failure. A failure display is made at (Step 9).

  As described above, according to the present embodiment, the rotatable belt 53 in which the leading end of the sheet is in contact between the branching claw 22 and the two transport paths 27 and 28 can be used to enter the leading end of the sheet. The load can be greatly reduced. For this reason, in addition to the standard paper that is normally used, highly rigid paper and special paper can be stably conveyed without causing jamming or poor conveyance.

  As another embodiment, as shown in FIG. 5, sandwiching roller pairs 72 and 74 are disposed in the vicinity of both ends of the bottom of the fixed guide portion of the branch claw 22 composed of the movable tip switching claw piece 22a and the fixed guide portion 22b. . Moreover, the base apex corner portions 22c and 22d of the fixed guide portion 22b are shaped to guide the leading edge of the sheet to the sandwiching portions of the pair of sandwiching rollers 72 and 74. With such a configuration, the paper guide becomes smooth.

  Further, since the branching claw 22 is composed of the fixed guide portion 22b and the movable tip switching claw piece 22a, the paper is placed on the pair of sandwiching rollers 72 and 74 without considering the rotation area of the branching claw. In the case of a conventional type of branching claw having a guide surface close to the pair of sandwiching rollers 72 and 74 for easy guidance, the downstream tip of the claw interferes with the inner guide when rotated, and the paper is conveyed. The fixed guide 22b can be as close as possible to the bottom apex corners 22c and 22d, and the paper can be smoothly guided. In other words, in the case of the conventional configuration, a step is generated between the bottom of the switching claw and the outer guide surface, and thus a load due to this step is generated. However, the above configuration eliminates the step, thereby reducing the transport load. can do.

  In this case, a plurality of fixed guide portions 22b and movable tip switching claw pieces 22a may be arranged in a direction orthogonal to the paper transport direction, as in the form shown in FIG. With this configuration, the pair of sandwiching rollers 72 and 74 and the bottom apex portions 22c and 22d can be arranged alternately in the width direction. With this configuration, there is no step between the pair of sandwiching rollers 72 and 74 and the bottom apex corner portions 22c and 22d in the transport direction, so that the leading edge of the sheet can be prevented from colliding with the antinodes of the pair of sandwiching rollers 72 and 74. As a result, the paper can be smoothly guided to the clamping portions of the clamping roller pairs 72 and 74.

  In the above embodiment, the conveyance path switching device 51 is disposed so as to be close to the bottom of the branch claw. Therefore, the conventional branch claw interferes with the belt 53 when the branch claw rotates. End up. Therefore, instead of the fixed guide portions 22b 'and 22b "described with reference to FIG. 3, if a conventional branching claw is similarly disposed between the belts, interference with the belt can be prevented.

  In the above embodiment, the description has been given of the sheet switching position after fixing (the paper discharge tray and the double-sided reverse path), but the present invention is not limited to this form. For example, the document conveyance path switching position of an automatic document conveyance device (ADF) that conveys and reads a document, the switching position when discharging paper after image formation to a plurality of stacking units, and the conveyance path branch into two or more. It can also be applied to branching positions. Furthermore, the image forming apparatus may be an apparatus that forms a stacking space between the image reading unit and the image forming unit, and the image forming unit is not limited to the electrophotographic type, and may be applied to various methods. it can.

1 is a schematic configuration diagram of an image forming apparatus. It is a figure which shows an example of the sheet conveyance path switching apparatus which concerns on this invention. FIG. 6 is a perspective view illustrating a state in which an endless belt is divided in a direction orthogonal to a sheet conveying direction. It is a flow explaining the drive timing of a branch claw and a belt. It is a figure which shows another example of a sheet conveyance path switching apparatus. It is a schematic perspective view of a conventionally well-known branch apparatus. It is a figure explaining the change of the branch claw of the branch apparatus of FIG. It is a figure which shows the conventionally well-known branch apparatus of another structure, and shows a mode that a sheet | seat is branched upward by (a) to (c). FIG. 9 shows how the sheet is branched downward from (a) to (c) in the branching device of FIG. 8.

Explanation of symbols

22 Branch claw 26 Carry-in path 27, 28 Branch transport path 29, 30 Belt tension roller 51 Transport path switching device 53 Endless belt 54, 55 Opposing rotating member 56, 57 Torque limiter 61 Paper discharge roller 62 Paper discharge tray 80 Reversing device 85 Reverse unit switching claw

Claims (16)

  It has a sheet carry-in path and a switching branch claw, and out of a plurality of branch conveyance paths existing downstream of the switching branch claw, an outer shell of two branch conveyance paths close to the branch claw is configured by a movable belt surface. Sheet transport path switching device.   2. The sheet conveyance path switching device according to claim 1, wherein an outer shell of the two branch conveyance paths is configured by a belt surface of a single endless belt.   A rotating member facing the belt stretching rotary member that stretches the belt is disposed inside the branch conveyance path, and the sheet is sandwiched and conveyed between the opposing rotating member and the belt surface that is wound around the belt stretching rotating member. The sheet conveying path switching device according to claim 2.   4. The sheet conveyance path switching device according to claim 3, wherein a belt capable of rotating in the forward and reverse directions is driven by driving the counter rotating member.   3. The sheet conveying path switching device according to claim 2, wherein one of the belt tension rotating members also serves as one of the pair of discharge rollers.   The sheet conveying path switching device according to any one of claims 3 to 5, wherein a torque limiter is provided on the counter rotating member.   The sheet conveying path switching device according to any one of claims 1 to 6, wherein the belt is conductive.   The sheet conveyance path switching device according to any one of claims 1 to 7, wherein the switching branch claw includes a fixed guide portion and a movable tip switching claw piece.   9. The sheet conveyance path switching device according to claim 8, wherein a bottom portion of the solid guide portion is as close as possible to a belt surface constituting an outline of the branch conveyance path.   9. The sheet conveying path switching device according to claim 8, wherein the endless belt is constituted by a belt portion divided into a plurality of parts in a direction orthogonal to the sheet conveying direction.   11. The sheet conveyance path switching device according to claim 10, wherein the bottom side portion of the fixed guide portion enters the endless belt region rather than the belt surface constituting the outline of the branch conveyance path.   The sheet conveyance path switching device according to any one of claims 2 to 11, wherein the switching operation of the branching claw is switched prior to the rotation direction switching operation of the belt.   In a sheet conveyance path switching device having a sheet carry-in path, a switching branch claw, and a plurality of branch conveyance paths downstream from the switching branch claw, the switching branch claw is constituted by a fixed guide portion and a movable tip switching claw piece. A sheet conveying path switching device characterized by the above.   14. The sheet according to claim 13, wherein a pair of sandwiching rollers is disposed in the vicinity of both ends of the bottom of the fixed guide portion, and a top corner of the bottom is directed to a roller that forms an outline of the branch conveyance path in the pair of sandwiching rollers. Transport path switching device.   A sheet conveying apparatus comprising the sheet conveying path switching device according to claim 1.   An image forming apparatus comprising the sheet conveyance path switching device according to claim 1.

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