JP2007070004A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device for performing the double-side printing which is capable of reducing the number of components at a changing part of its conveying path, and facilitating the access to a vicinity of a fixing unit when a paper sheet is jammed. <P>SOLUTION: The image forming device has a branch claw 30 which is turnably and pivotably supported at the branching position of a main conveying path 11 and a double-side conveying path 15 on the upstream side of a paper discharge unit 18. The branch claw 30 has a first guide face 30b for guiding a transfer sheet from a fixing unit 12 to the paper discharge unit 18 between the fixing unit 12 and the paper discharge unit 18 of the main conveying path 11, and a second guide face 30c for guiding the transfer sheet reversely fed from the paper discharge unit 18 in an area in which the transfer sheet is guided from the paper discharge unit 18 of the double-side conveying path 15 to the position for avoiding the fixing unit 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus provided with a branch path that enables double-sided printing on a transfer sheet.

  In an image forming apparatus such as a copying machine, an image is formed on a transfer sheet such as plain paper or OHP, and an electrophotographic method is often employed because of high speed image formation, image quality, cost, and the like. The electrophotographic method is a method in which a toner image is formed on a transfer sheet and the formed toner image is fixed to the transfer sheet with heat and pressure. In this type of image forming apparatus, an apparatus that can form an image on both sides of a transfer sheet by a series of printing operations is widely used.

  FIG. 1 is a sectional view conceptually showing a general configuration of an image forming apparatus capable of double-sided printing of this type. In the figure, the image forming apparatus includes a double-sided conveyance path 15 in addition to the main conveyance path 11 for image formation for double-sided printing. In the image forming apparatus shown in the figure, the exposure unit 3 performs optical writing on the four image forming units 4 to 7, and each of the image forming units 4 to 7 forms a color toner image on the intermediate transfer belt 8. The transfer sheet loaded on the sheet feeding cassette 1 is fed by the sheet feeding roller 2, passes through the registration roller 9, and the toner image is transferred to the transfer sheet by the secondary transfer roller 10. Thereafter, the toner image transferred by the fixing unit 12 through the main conveyance path 11 is fixed as an image on the transfer sheet, and the transfer sheet on which the image is formed is removed from the housing by the discharge roller 13 of the discharge unit 18. Is discharged.

  In the case of single-sided printing, this completes the image forming process. However, when images are to be obtained on both sides, the paper discharge roller 13 is driven in reverse rotation before the transfer sheet is discharged onto the tray from the paper discharge roller 13. Is done. As a result, the transfer paper is again drawn into the housing. At that time, the branching claw 14 is switched and driven, whereby the transfer sheet is sent to the double-sided conveyance path 15. The transfer sheet is sent again to the registration roller 9 through the double-sided conveyance path 15, and this time the image is transferred and fixed in the same manner as the single-sided side with its back side facing the secondary transfer roller 10 side. And discharged outside the housing.

  FIG. 2 is an enlarged cross-sectional view of the peripheral portion of the branching claw 14 of FIG. 1, which shows the structure of the branching claw 14 having a conventional configuration. In the figure, (a) shows the state when the transfer sheet after the fixing step is discharged to the discharge portion, and (b) shows the state when the transfer sheet of the discharge portion is fed back to the duplex conveyance path, (C) shows the state during the paper jam processing.

  As shown in these drawings, the branching claw 14 is disposed at the joining position of the main conveyance path 11 and the double-sided conveyance path 15 on the downstream side of the fixing unit 12. The branch claw 14 is controlled to rotate by a solenoid or other driving means (not shown). When the transfer sheet on which the image has been fixed is discharged, the branching claw 14 is driven in the clockwise direction to open the main transport path 11 as shown in FIG. The transfer sheet that has passed through is guided to the paper discharge roller 13 of the discharge unit 18. In the case of double-sided printing, when the trailing edge of the transfer sheet comes to a position beyond the branching claw 14 from the state of FIG. 11A, the branching claw 14 is driven counterclockwise, and the state shown in FIG. As described above, the main transport path 11 is closed, and the double-sided transport path 15 is opened instead. In parallel with this, the paper discharge roller 13 is reversely driven, and the transfer sheet nipped by the paper discharge roller 13 is fed back and guided into the double-sided conveyance path 15.

  When a paper jam occurs in the vicinity of the fixing unit 12, the exterior cover 17 is opened upward and the jammed paper is taken out as shown in FIG. When a paper jam occurs on the main transport path 11, the guide member 16 constituting the double-side transport path 15 is further opened so that the user can access the fixing unit 12. Patent Documents 1 and 2 are image forming apparatuses having such a configuration.

JP 2002-274747 A JP 2003-215874 A JP-A-11-236159

  In recent years, even in such an image forming apparatus, further downsizing and cost reduction of the apparatus are required. On the other hand, in order to improve the workability, it is required to facilitate the processing work at the time of paper jam. However, in the image forming apparatus having the conventional configuration, for double-sided printing processing, compared to a model that performs only single-sided printing, a branching claw and a drive mechanism for operating this are additionally required. There is a problem that the number of parts increases and the cost increases. In addition, in this type of image forming apparatus, there is a branch claw on the downstream side of the fixing unit, so the visibility near the fixing unit is poor, and the problem is that this is an obstacle during jam processing and the workability is poor. There is.

  Patent Document 3 discloses an image forming apparatus that reduces costs by operating a switching claw without using a solenoid. However, even in this conventional example, although the problem in terms of cost can be improved somewhat, the problem of workability at the time of jam processing has not been solved.

  In view of the above, the present invention provides an image forming apparatus that performs double-sided printing by simplifying the configuration of the branching unit in the path branching portion to reduce the cost and facilitate access to the vicinity of the fixing unit at the time of paper jam. The purpose is to improve workability.

  According to a first aspect of the present invention, an image forming unit that transfers a toner image to a transfer sheet to be fed, a fixing unit that fixes the toner image on the transfer sheet, and a transfer sheet after image fixing are out of the casing. A paper discharge unit to be discharged, a first conveyance path for feeding a transfer sheet from the image forming unit to the paper discharge unit, and a transfer sheet that is fed back from the paper discharge unit to the image while avoiding the fixing unit. An image forming apparatus comprising: a second conveyance path that feeds the transfer sheet to the upstream side of the forming unit so that the conveyance surface of the transfer sheet is reverse; and the first conveyance path on the upstream side of the paper discharge unit; A branching means pivotally supported at a branch position with respect to the second transport path, wherein the branch leading end portion of the branch transport section is located at the first transport path with respect to the paper discharge section. Or one of the second transport paths is opened. The branching unit includes a first guide surface that guides a transfer sheet from the fixing unit to the paper discharge unit between the fixing unit and the paper discharge unit of the first conveyance path, and the second conveyance. And a second guide surface for guiding the transfer sheet that is fed back from the paper discharge unit in a region that guides the transfer sheet from the paper discharge unit to a position that avoids the fixing unit.

  According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the branching unit is pivotally supported in the vicinity of the downstream side of the second guide surface so as to be able to rotate downstream of the fixing unit. It is characterized by being configured to open.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the branching unit has a first position at which the branch leading end opens the first transport path with respect to the paper discharge unit, and A driving means for rotationally driving the branching means is provided between the branching tip and a second position where the second transport path is opened with respect to the paper discharge part, and the driving means is configured to An urging means for urging to the first or second position and a cam mechanism that is driven by the power source to rotate the branching means to the other position are provided.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the cam mechanism includes an eccentric cam.

  According to a fifth aspect of the present invention, in the image forming apparatus of the third aspect, the cam mechanism includes a pinion gear and a rack having a cam surface.

  According to a sixth aspect of the present invention, in the image forming apparatus of the fourth or fifth aspect, the gum mechanism is operated by a power source of a driving unit that feeds a transfer sheet in the paper discharge unit.

  According to the present invention, in the image forming apparatus that performs double-sided printing, the branching unit also serves as a guide portion of the conveyance path in the vicinity thereof, so that the number of parts can be reduced and the vicinity of the fixing unit at the time of paper jam. Is easy to access, and its workability is improved.

  The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

  Embodiments of the present invention will be described below with reference to the drawings. The present invention can be widely applied to image forming apparatuses such as electrophotographic copying machines and printers having a double-sided printing function as shown in FIG. That is, the image forming apparatus according to the present invention includes a secondary transfer roller 10 that transfers a toner image to a transfer sheet fed from the paper feed cassette 1, and a fixing unit 12 that fixes the toner image on the transfer sheet. And a paper discharge unit including a paper discharge roller 13 for discharging the transfer sheet after image fixing to the outside of the housing. Further, the main transfer path 11 for feeding the transfer sheet from the secondary transfer roller 10 to the paper discharge unit, and the transfer sheet fed back from the paper discharge unit to the upstream side of the secondary transfer roller 10 avoiding the fixing unit 12. And a double-sided conveyance path 15 for feeding.

  FIG. 3 is an enlarged cross-sectional view showing a main part of the image forming apparatus provided with the branching claw according to the embodiment of the present invention. FIGS. 9A to 9C correspond to FIGS. 2A to 2C, respectively, showing a conventional example, that is, FIG. 9A shows that the transfer sheet after the fixing process is discharged to the discharge unit. (B) shows the state when the transfer sheet of the discharge section is fed back to the double-sided conveyance path, and (c) shows the state when the paper jam is processed. 4 (a) and 4 (b) are side views illustrating the state of the branching claw in FIGS. 3 (a) and 3 (b) with the drive mechanism further enlarged.

  In these drawings, the branching claw 30 according to the present invention has a shape like a fin of a surfboard, and is provided at a branching position between the main transport path 11 and the double-sided transport path 15 on the upstream side of the paper discharge unit 18. . The branch claw 30 has a branch tip 30a, and the opposite end thereof is pivotally supported on the housing side at a position near the track of the double-sided transport path 15 away from the track of the main transport path 11.

  The branching claw 30 also has a concavely curved first guide surface 30 b that guides the transfer sheet from the fixing unit 12 to the paper discharge unit 18 between the downstream of the fixing unit 12 in the main transport path 11 and the paper discharge unit 18. have. The downstream side of the first guide surface 30b is continuous with the branching tip 30a, and the upstream side extends to the vicinity of the nip portion of the roller pair 12a, 12a (fixing roller and pressure roller) of the fixing unit 12. . That is, in the conventional configuration, a guide member that forms the main transport path 11 is provided between the upstream side of the branching claw and the fixing unit 12. In the configuration of this embodiment, such a guide member is provided. Is not provided, and the first guide surface 30b of the branch claw 30 serves as a guide member.

  The branching claw 30 further guides the transfer sheet that is fed back from the paper discharge unit 18 in a region from the paper discharge unit 18 to the straight line portion of the double-sided conveyance path 15 (an area parallel to the main conveyance path 11). It has the 2nd guide surface 30c of convex curve shape. The paper discharge unit 18 side (upstream side in the double-sided conveyance path 15) of the second guide surface 30c is continuous with the branching tip part 30a, and the downstream side is continuous with the straight line part of the double-sided conveyance path 15; It extends to this area. That is, in the conventional configuration, a guide member that forms the double-sided conveyance path 15 is provided on the downstream side of the branching claw in the double-sided conveyance path. However, in the configuration of this embodiment, such a guide member is provided. First, the second guide surface 30c of the branch claw 30 serves as the guide member.

  The branch claw 30 is rotationally driven by a drive mechanism described later, so that the branch tip 30a opens either the main transport path 11 or the double-sided transport path 12 with respect to the paper discharge unit 18. FIGS. 3A and 4A show a state in which the main conveyance path 11 is released. In this state, the transfer sheet on which the image is fixed from the fixing unit 12 is the first of the branching claws 30. While being guided by one guide surface 30b, it is guided into the paper discharge section 18. The transfer sheet guided into the paper discharge unit 18 is nipped by the paper discharge roller 12 and further sent out of the casing. On the other hand, FIGS. 3B and 4B show a state where the double-sided conveyance path 15 is opened. In this state, the transfer sheet in the paper discharge unit is guided to the double-sided conveyance path 15. That is, in the double-sided printing mode, when the trailing edge of the transfer sheet comes to a position beyond the branching claw 30 from the state of FIG. 11A, the branching claw 30 is driven counterclockwise, and FIG. As described above, the main transport path 11 is closed and the double-sided transport path 15 is opened instead. In parallel with this, the sheet discharge roller 13 is driven to rotate reversely, and the transfer sheet nipped by the sheet discharge roller 13 is fed back and guided into the duplex conveyance path 15 while being guided by the second guide surface 30c of the branch claw 30. Will be.

  Further, as shown in FIG. 3C, the branching claw 30 can be rotated approximately 90 degrees in the clockwise direction in the drawing around the pivot point. Since there are no members other than the branching claw 30 on the downstream side of the fixing unit 12, when the branching claw 30 is opened as shown in the figure when a paper jam occurs, the downstream side of the fixing unit 12 is completely exposed upward. The Rukoto. This makes it very easy for the user to access the fixing unit 12, and the jam handling operation can be performed efficiently.

  Next, the drive mechanism of the branch claw 30 will be described with reference to FIG. As shown in the figure, the branching claw 30 is urged to rotate counterclockwise about its axis by a spring 31 having one end fixed to the housing side. A protrusion 30 d is formed on the side surface of the branch claw 30, and is pressed against the eccentric cam 32 by the biasing force of the spring 31. The eccentric cam 32 is rotationally driven by a power source (not shown), and the rotation of the branch claw 30 is rotated along the cam surface. That is, the branching claw 30 opens the main transport path 11 at the position where the projection 30d is pushed up, and opens the main transport path 11 to discharge the transfer sheet fed from the fixing unit 18 as shown in FIG. To pass to the side. The fed transfer sheet passes through the gap between the branching claw 30 and the guide member 33 along the first guide surface 30b of the branching claw 30, reaches the paper discharge unit 18, and the paper discharge roller shown in FIG. 12 is nipped and fed out of the housing. Further, the branching claw 30 is abutted against the guide member 33 at the position where the eccentric cam 32 is substantially half-rotated and the projection 30d is lowered, as shown in FIG. Thus, the main conveyance path 11 is closed, and on the other hand, the double-sided conveyance path 15 is opened so that the transfer sheet fed back from the paper discharge unit 18 can pass through the double-sided conveyance path 15. The transfer sheet to be fed is guided to the straight portion of the double-sided conveyance path 15 along the second guide surface 30c of the branching claw 30 and the inner surface of the exterior cover 17 shown in FIG. The paper is fed toward the upstream side of the transfer roller 10.

  Next, another driving mechanism of the branching claw 30 will be described. FIG. 5 is a side view showing another embodiment of the branch claw 30. FIG. 5A shows a state in which the main transport path 11 is opened as in FIG. 4A, and FIG. Similarly to FIG. 4B, the double-sided conveyance path 15 is shown open. As shown in the figure, the branching claw 30 is urged to rotate counterclockwise about its axis by a spring 31 having one end fixed to the housing side. A cylindrical projection 30 e is formed on the side surface of the branch claw 30, and is pressed against the positioning surface of the rack 34 by the biasing force of the spring 31. The rack 34 meshes with the pinion gear 35 and is driven in the horizontal direction by the rotation thereof. The pinion gear 35 is connected to the paper discharge roller 13 shown in FIG. 1 via a torque limit mechanism. Therefore, the rack 34 is synchronized with the paper discharge roller 13 by the power source of the paper discharge roller 13. Driven. That is, the branching claw 30 is fed from the fixing unit by opening the main conveyance path 11 at a position where the projection 30e is on the first positioning surface 34a of the rack 34, as shown in FIG. The transferred sheet is allowed to pass to the discharge unit 18 side. The fed transfer sheet passes through the gap between the branching claw 30 and the guide member 33 along the first guide surface 30b of the branching claw 30, reaches the paper discharge unit 18, and the paper discharge roller shown in FIG. 12 is nipped and fed out of the housing.

  On the other hand, when the paper discharge roller 13 is reversely driven in the double-sided printing mode, the pinion gear 35 is rotated clockwise in synchronism with this, and the rack 34 receives the driving force as shown in FIG. To the left. When one end of the rack 34 abuts against the positioning portion 36, the torque limit mechanism works to cut off the driving force from the power source and stop. By the movement of the rack 34, the protrusion 30e is pushed down by the biasing force of the spring 31 to the surface height of the second positioning surface 34b. As a result, the branch claw 30 is rotated in the counterclockwise direction, and the branch tip 30a is abutted against the guide member 33 to close the main transport path 11, while the double-side transport path 15 is opened. Thus, the transfer sheet fed back from the paper discharge unit 18 can pass through the double-sided conveyance path 15. The transfer sheet to be fed is guided to the straight portion of the double-sided conveyance path 15 along the second guide surface 30c of the branching claw 30 and the inner surface of the exterior cover 17 shown in FIG. The paper is fed toward the upstream side of the transfer roller 10. In the case of this embodiment, since the power source of the paper discharge roller is used as the power source of the rack and pinion mechanism for operating the branching claw 30, it is not necessary to provide a separate power source for driving the power source. Since the branch claw 30 is mechanically operated as described above, it is not necessary to provide a separate position detection sensor or the like in order to control this.

1 is a cross-sectional view conceptually showing a general configuration of an image forming apparatus capable of duplex printing. It is sectional drawing which expands and shows the peripheral part of the branch nail of FIG. 1, and has shown the branch nail of the conventional structure. It is sectional drawing which expands and shows the peripheral part of the branch nail of FIG. 1, and has shown the branch nail which concerns on one Example of this invention. It is the side view which expanded further and showed the state of the branching claw in FIG. 3 with the drive mechanism. It is a side view which shows the other Example of a branch nail | claw.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Paper feed cassette 2 Paper feed roller 3 Exposure unit 4-7 Image formation unit 8 Intermediate transfer belt 9 Registration roller 10 Secondary transfer roller 11 Main conveyance path 12 Fixing unit 13 Paper discharge roller 14 Branching claw 15 Both-side conveyance path 16 Guide member 17 exterior cover 18 paper discharge unit 30 branch claw 30a branch tip 30b first guide surface 30c second guide surface 30d, 30e projection 31 spring 32 eccentric cam 33 guide member 34 rack 34a first positioning surface 34b second positioning surface 35 Pinion gear 36 Positioning part

Claims (6)

An image forming unit that transfers a toner image to a transferred transfer sheet, a fixing unit that fixes the toner image on the transfer sheet, a paper discharge unit that discharges the transfer sheet after image fixing to the outside of the housing, A first conveyance path for feeding a transfer sheet from the image forming unit to the paper discharge unit, and a transfer sheet fed back from the paper discharge unit to the upstream side of the image forming unit by avoiding the fixing unit. An image forming apparatus including a second conveyance path for feeding the transfer sheet so that a conveyance surface of the transfer sheet is reverse;
A branching means pivotally supported at a branching position between the first transporting path and the second transporting path on the upstream side of the paper discharge unit, the branching unit depending on the pivoting position. The leading end opens either the first transport path or the second transport path with respect to the paper discharge section, and the branching unit discharges the paper from the fixing section of the first transport path. A first guide surface that guides the transfer sheet from the fixing unit to the paper discharge unit, and a region that guides the transfer sheet from the paper discharge unit to a position that avoids the fixing unit in the second conveyance path. An image forming apparatus comprising: a second guide surface that guides a transfer sheet that is fed back from the paper discharge unit. 2. The branching device according to claim 1, wherein the branching unit is pivotally supported in the vicinity of the downstream side of the second guide surface, and is configured to open the downstream side of the fixing unit by the rotation. Image forming apparatus. The branching means has a first position where the branch tip end opens the first transport path with respect to the paper discharge section, and the branch tip opens a second transport path with respect to the paper discharge section. Drive means for rotationally driving the branch means between the second position, the drive means for biasing the branch means to the first or second position, and the power The image forming apparatus according to claim 1, further comprising a cam mechanism that is driven by a source to rotate the branching unit to the other position. The image forming apparatus according to claim 3, wherein the cam mechanism includes an eccentric cam. The image forming apparatus according to claim 3, wherein the cam mechanism includes a pinion gear and a rack having a cam surface. 6. The image forming apparatus according to claim 4, wherein the gum mechanism is operated by a power source of a driving unit that feeds a transfer sheet in the paper discharge unit.

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