JP4804749B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus in which a sheet having an image formed on the front surface (one surface) is conveyed again to an image forming unit to form an image, and in particular, re-conveying a sheet again to the image forming unit. It relates to the structure of the road.

  2. Description of the Related Art Conventionally, for example, there is an image forming apparatus such as a printer having a digital optical system in which a sheet having an image formed on the front surface (one surface) is conveyed again to an image forming unit to form an image. Such an image forming apparatus includes a re-conveying path that conveys a sheet having an image formed on the front surface (one surface) again to the image forming unit.

  Such an image forming apparatus sequentially feeds sheets stored in a paper feed cassette to an image forming unit and a fixing unit by a sheet feeding device, forms an image on the sheet, and then discharges the sheet to a paper discharge unit. It is supposed to be. When images are formed on both sides of a sheet, the sheet is conveyed to a reconveying path and conveyed to an image forming unit again (see Patent Document 1).

  By the way, as a sheet conveying apparatus, a sheet having a sheet conveying unit that conveys a sheet while being sandwiched between a pair of rotating cylindrical rollers, a cylindrical roller, and a cylindrical roller and a pad is widely used. These sheet conveying sections are arranged in a sheet conveying path such as a re-conveying path to convey the sheet. The movement of the sheet can be easily controlled by changing the rotational speed of these sheet conveying units and the ON / OFF timing.

  By the way, the adjacent sheet conveying units are arranged with an interval at which the sheets having the shortest length in the conveying direction (hereinafter referred to as “shortest sheet”) can be sandwiched at the same time even if they are arranged farthest apart. Yes. Further, the sheet conveyance path may be curved due to the downsizing of the apparatus and the configuration of each process. When the sheet conveying unit is provided in such a curved sheet conveying path, the two sheets are conveyed until the sheet is nipped by the downstream sheet conveying unit after being conveyed from the upstream sheet conveying unit. The sheet is conveyed along a sheet conveyance guide unit provided between the conveyance units.

FIG. 8 is a diagram showing a schematic configuration of a conventional image forming apparatus 201 provided with such a sheet conveying apparatus. Sheet P more discharged the feeding device 251 from a paper feed cassette 250 for accommodating the sheet P, first, by the sheet conveying section 253,252 which are located respectively at the same time be clamped position the shortest sheet downstream of the feeding device 251 The toner image formed by the image forming unit 260 is transferred to the image forming unit 260.

  Next, the sheet P to which the toner image has been transferred is conveyed to the fixing device 261, where the toner image is fixed, and thereafter, the sheet P passes through the paper discharge conveyance path 271 and is paired with a discharge roller. The paper is discharged to the paper discharge stacking portion 272 by 270.

By the way, this image forming apparatus 201 can perform double-sided printing for forming images on both sides of the sheet P and multiple printing for forming images on the sheet P in an overlapping manner. When performing double-sided printing or multiple printing, the image forming apparatus 201 partially discharges a sheet having an image formed on one side through the fixing device 261 to the paper discharge stacking unit 272. The paper is conveyed to the re-conveying path 280 by the reverse rotation of the paper discharge roller pair 270 and a switching mechanism (not shown), and is conveyed again to the image forming unit 260 via the re-conveying path 280.

  As in the case of single-sided printing, the sheet P thus transported to the image forming unit 260 is transferred with the toner image in the image forming unit 260, and then the toner image is fixed in the fixing device 261. Then, the sheet is discharged to the discharge stacking portion 272 through the discharge conveyance path 271.

JP 07-267461 A

  By the way, the conventional image forming apparatus includes a re-conveying path 280 in the vertical direction above the sheet cassette 250 as shown in FIG. The re-conveying path 280 is provided with, for example, a U-shaped passage 281 on the downstream side for changing the conveying direction of the sheet P conveyed downward to the image forming unit 260.

  For this reason, the conventional image forming apparatus has a problem that the height of the apparatus main body is increased by the length of the U-shaped passage 281 in the vertical direction and the size of the entire apparatus is increased.

  An object of the present invention is to provide an image forming apparatus provided with a re-conveying path capable of reducing the height of the apparatus main body.

To achieve the above object, the present invention provides an image forming apparatus for forming an image on a sheet, an apparatus main body, an image forming means provided on the apparatus main body for forming an image on the sheet, and the apparatus main body. A lower guide member provided in the sheet stacking unit, wherein a part of a transport path for transporting the sheet is provided in the image forming apparatus. And an upper guide member disposed in the apparatus main body so as to face the lower guide member with a gap through which the conveyed sheet enters the sheet stacking unit side from the apparatus main body and through which the conveyed sheet can pass. The upper guide member and the lower guide member are a plurality of plate-like members arranged in a direction intersecting with the attaching / detaching direction of the sheet stacking means and arranged in parallel to the attaching / detaching direction. Is formed, and the plate-like member of the lower guide member and the plate-like member of the upper guide member, wherein are arranged at a position not to interfere with attachment and detachment direction of the sheet stacking means, it is characterized.

  In the image forming apparatus of the present invention, a part of the conveyance path is provided by projecting the upper guide member provided in the apparatus main body into the attachment / detachment locus of the sheet stacking unit, and a part of the conveyance path on the apparatus main body side is provided in the sheet. By providing the stacking means, the height of the apparatus main body can be reduced, and the entire apparatus can be reduced in size.

  The upper guide member and the lower guide member are formed of a plurality of plate-like members arranged in a direction intersecting with the attachment / detachment direction of the sheet stacking unit and facing the attachment / detachment direction, Because the plate-like member of the lower guide member is arranged at a position where it does not interfere with the attaching / detaching direction, the re-conveying path can be opened by pulling out the sheet stacking means from the apparatus main body, and jammed sheets can be easily Can be removed.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings. Note that the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

  FIG. 1 is a diagram showing a schematic configuration of a laser beam printer which is an example of an image forming apparatus according to the first embodiment of the present invention.

  A laser beam printer (hereinafter simply referred to as “printer”) 100 as an image forming apparatus includes a photosensitive drum 1 a and a transfer roller in a laser beam printer main body (hereinafter simply referred to as “printer body”) 101 as an apparatus main body. An image forming unit 1 as an image forming unit including 1b and the like, a sheet feeding unit 2 disposed below the image forming unit 1 and feeding the sheet P to the image forming unit 1, and above the image forming unit 1 A fixing unit 3 and the like that are arranged and fix an image on a sheet are provided.

  The printer main body 101 can also form an image on the back side of a sheet on which an image is formed on one side, and the sheet P after the image is formed on one side is again input to the image forming unit 1. A re-transport path 8A for transport is also provided. However, the U-turn passage 25 at the lower end of the re-conveyance path 8A is formed in the paper feed cassette 4.

Further, a sheet feeding cassette 4 as a sheet stacking unit is detachably provided below the printer main body 101 (below the image forming unit 1). The paper feed cassette storage space 102 is a space for storing the paper feed cassette 4 formed in the lower part of the printer main body 101. An option feeder 4A is provided at the bottom of the printer main body 101.

  In order to form an image on the sheet P, the printer 100 having such a configuration first exposes the surface of the photosensitive drum by the scanner unit 1c in accordance with the image signal and electrostatic latent image on the peripheral surface of the photosensitive drum 1a. After that, the electrostatic latent image is developed with toner by the developing device 1d to form a toner image.

  The sheets P stored in the paper feed cassette 4 or the optional feeder 4A are separated one by one by the paper feed roller 2a and the separation pad 2b in parallel with the toner image forming operation, and only the uppermost sheet is registered. The roller pair 5 is fed. Thereafter, the leading edge of the sheet P is abutted against the stopped registration roller pair 5 to form a loop, and skew is corrected.

  Next, after correcting the skew of the sheet P, the printer 100 synchronizes the leading edge of the toner image on the circumferential surface of the photosensitive drum with the print start position of the sheet P, that is, synchronizes with the image writing position. As a result, the registration roller pair 5 is started to rotate, and the sheet P is conveyed to a transfer portion constituted by the photosensitive drum 1a and the transfer roller 1b. The transfer unit transfers the toner image on the photosensitive drum to a sheet.

  Next, the sheet P to which the toner image has been transferred is carried into the fixing unit 3 and heated and pressed by the pressure roller 3a and the heating roller 3b of the fixing unit 3, whereby the toner image is thermally fixed. Thereafter, the paper is discharged onto the paper discharge stacking unit 10 with the image forming surface down by the paper discharge roller pair 6a, 6b.

  On the other hand, during double-sided printing, the printer 100 causes a pair of paper discharge rollers to be discharged by a control unit (not shown) while the sheet P having the toner image fixed on the front surface (one side) is discharged to the paper discharge stacking unit 10. 6a and 6b are reversed and sent to the re-transport path 8A. The sheet is conveyed again to the image forming unit 1, and the toner image is transferred to the back surface in the same manner as when the toner image is transferred to the front surface, and the toner image is fixed by the fixing unit 3. Finally, the sheet is discharged to the paper discharge stacking unit 10 by the paper discharge roller pair 6a and 6b.

  FIG. 2 is an enlarged view of a main part of the printer main body 101 having such a configuration. The first guide member 21 a is a member that guides the uppermost sheet separated from the other sheets by the paper feed roller 2 a and the separation pad 2 b to the registration roller pair 5. The first conveyance path 21 conveys the sheet P on which the toner image is transferred to the fixing unit 3. The second conveyance path 22 conveys the sheet P on which the toner image is fixed to the paper discharge roller pair 6a, 6b.

Note that the second transport path 22 joins the re-transport path 8 which is the printer main body side portion of the re-transport path 8A at the downstream side portion thereof. A flapper 23 is provided at the junction of the second transport path 22 and the re-transport path 8. Here, the flapper 23 is located at the position shown in the figure when guiding the sheet P on which the image is formed to the paper discharge stacking unit 10, and when the image is formed on both sides of the sheet P, the trailing edge of the sheet P is formed. After passing through the flapper 23, it is moved counterclockwise by a control unit (not shown). As a result, when the paper discharge roller pair 6a, 6b is reversed thereafter, the sheet P passes through the upper surface of the flapper 23 and enters the reconveying path 8A (reconveying path 8).

  The sheet P that has entered the re-conveying path 8A is guided into the printer main body and conveyed to the registration roller pair 5, and thereafter, the same conveying form as in the case of single-sided printing is used, and finally the sheet stacking is performed. The image is discharged to the unit 10, and a series of image forming processes is completed.

  By the way, when images are formed on both sides of the sheet, the lower opening 8a of the re-conveyance passage 8 is positioned above the paper feed cassette storage space 102 (see FIG. 1) as shown in the figure. Then, the sheet discharged from the lower opening 8 a of the re-conveyance path 8 is guided again to the inside of the printer body by the U-turn path 25 provided below, and is conveyed to the registration roller pair 5. It has become so.

  That is, the re-conveying path 8 </ b> A for conveying the sheet P on which the image is formed to the image forming unit 1 again includes the re-conveying path 8 and the U-turn path 25.

  As shown in FIG. 3, the U-turn passage 25 is provided between the drawer handle 41 of the sheet feeding cassette 4 and the sheet storage portion 42. In the figure, a sheet placing plate 43 is provided in the sheet storage portion 42 so as to be rotatable in the vertical direction, and the sheet P is placed thereon, and the sheet P is pressed against the sheet feeding roller 2a by a spring or the like. It is like that. The side regulating plate 44 regulates both side ends of the sheet P placed on the sheet placing plate 43 in the width direction orthogonal to the sheet conveying direction (arrow a direction). The rear end regulation plate 45 regulates the rear end position of the sheet P.

  The lower guide 46 is provided at the front end of the sheet feeding cassette 4 that is the end in the sheet conveyance direction. A separation pad 2b is disposed at a position of the lower guide 46 facing the paper feed roller 2a.

On the other hand, the U-turn passage 25 of the paper feed cassette 4 has a lower guide portion 25a formed between the drawer handle 41 and the sheet storage portion 42 and extending in the width direction and smoothly curved downward, and the lower guide portion 25a. The upper guide portion 25b is provided with a gap through which the sheet P can pass. The upper guide portion 25 b is provided in the printer main body 101. Upper guide portion 25b protrudes in the sheet feeding cassette 4 side from the printer main body 101 side in the space for attaching and detaching the paper supply cassette 4, so the advance input state inside the trajectories of detachable sheet cassette 4 Yes.

Therefore, as shown in FIG. 4, the lower guide portion 25 a and the upper guide portion 25 b are arranged in a direction intersecting with the attachment / detachment direction (arrow A direction) of the paper feed cassette 4 and arranged in parallel with the attachment / detachment direction. The sheet passing ribs 25aa and 25ba are formed as a plurality of plate-like members. Both of the sheet passing ribs 25aa and 25ba are disposed at positions where they do not interfere with each other in the mounting / demounting direction of the sheet feeding cassette 4. That is, the paper passing ribs 25aa and 25ba are arranged in a comb-teeth shape. For this reason, the paper feed cassette 4 can be easily attached to and detached from the printer main body 101.

  By forming the U-turn passage 25 in the paper feed cassette 4, as described above, the sheet P discharged from the lower opening 8a of the re-conveyance passage 8 enters the U-turn passage 25 from the direction indicated by the arrow d. Thereafter, it passes through the U-turn passage 25 and is conveyed in the direction indicated by the arrow e, is again guided into the printer body, and is conveyed to the registration roller pair 5.

  By arranging the U-turn passage 25 at the drawer side end of the paper feed cassette 4 as described above, that is, by arranging a part (downstream portion) of the re-conveyance path 8A in the paper feed cassette 4, FIG. In the re-conveying path 280 of the conventional image forming apparatus shown in FIG. 5, for example, the re-conveying path 8 which is the re-conveying path portion on the printer main body side as compared with the vertical distance H0 between the paper feed roller 202a and the registration roller pair 205. The distance H1 between the sheet feeding roller 2a and the registration roller pair 5 can be shortened. In particular, in the case of a so-called vertical path type printer in which the conveyance path and the re-conveyance path extend vertically as in the present embodiment, the overall height of the apparatus tends to be high, and the configuration of the present invention is effective. In addition, the overall height of the printer can be reduced.

  The height of the printer main body 101 is lowered by shortening the distance H1 between the paper feed roller 2a and the registration roller pair 5 in the reconveying path 8, that is, by shortening the vertical length of the reconveying path 8. can do. As a result, the size of the entire printer can be reduced.

The upper guide portion 25b, so has a shape that has entered the sheet cassette 4 side, it is conceivable to include an upper guide portion 25b in the paper feed cassette 4. However, when the upper guide portion 25b is provided in the sheet feeding cassette 4, when the sheet feeding cassette 4 is pulled out from the printer main body 101 in a state where the sheet is stopped in the U-turn passage 25, the upper guide portion There is a possibility that 25b is torn off from the paper feed cassette 4. However, by providing the upper guide portion 25b in the printer main body 101, when the paper feed cassette 4 is pulled out from the printer main body 101, the upper guide portion 25b may remain in the printer main body 101 together with the stationary sheet and be torn off. Absent.

  Further, by forming a part of the reconveying path 8A (U-turn path 25) on the paper feeding cassette 4 side, when the paper feeding cassette 4 is pulled out from the printer main body 101, the reconveying path 8A can be opened. Thus, it is possible to easily remove the jam sheet, clean it, and the like.

(Second Embodiment)
FIG. 5 shows a sheet conveying apparatus of an image forming apparatus according to the second embodiment of the present invention.

1 to 4, the upper guide portion 25b on the printer main body side that forms the U-turn passage 25 is fixed. On the other hand, when the upper guide portion 55b on the printer body 101 side in the U-turn passage 55 of the sheet conveying apparatus shown in FIG. 5 is pressed by the spring 51 toward the lower guide portion 55a, the paper feed cassette 4 is mounted. The lower guide portion 55a is positioned with a predetermined gap. That is, the upper guide portion 55b is biased downward by the spring 51, and the projections 53 protruding from the side surfaces of the upper guide portion 55b are mounted in the concave grooves 52 formed in the both side frames of the paper feed cassette 4. The printer main body 101 is provided to be movable up and down. The bottom of the concave groove 52 forms an inclined surface 52a .

  By the way, in the U-turn passage 25 shown in FIGS. 1 to 5, as shown in FIG. When trying to pull out from the main body 101 in the direction of the arrow B, the lower guide portion 25a, the upper guide portion 25b, etc. will not be damaged, but the stationary sheet Pa has a comb-tooth shape of the lower guide portion 25a and the upper guide portion 25b. The paper passing ribs 25aa and 25ba may be torn between them.

  In this case, if the user does not notice that a part of the torn sheet remains in the printer main body 101 and restarts the laser printer 100, the remaining sheet may cause a jam. There is.

  However, as shown in FIG. 5, the upper guide portion 55 b has an arrow against the spring 51 due to the contact between the inclined surface 52 a of the groove 52 and the protrusion 53 when the paper feed cassette 4 is pulled out in the arrow B direction. Since it retracts in the C direction, it is possible to prevent the stationary sheet Pa from being torn. Further, if the upper guide portion 55b can be retracted in the direction of arrow C, the jam sheet can be easily removed.

(Third embodiment)
FIG. 7 shows a sheet conveying apparatus of an image forming apparatus according to the third embodiment of the present invention.

  The lower guide portion 65a in the U-turn passage 65 of the sheet conveying apparatus shown in FIG. 7 is rotatably provided on the shaft 63 on the sheet feeding cassette side. The lower guide portion 65a is pressed toward the upper guide portion 65b by the spring 61 and is received by a stopper (not shown), and forms a gap necessary for conveying the sheet between the lower guide portion 65a. The lower guide 65a rotates to a position where there is no guide step with respect to the sheet conveying guide 9 on the downstream side of the U-turn passage 65. In addition, the lower guide portions 65b and 65a are also formed of comb-like paper passing ribs, similarly to the lower guide portion 25a and the upper guide portion 25b shown in FIG.

Incidentally, the upper guide portion 65b, like the upper guide portion 55 b shown in FIG. 5, may be adapted escape away from the lower guide portion 55 a.

  When a sheet Pb having strong rigidity (waistness) such as cardboard is conveyed, the lower guide portion 65a is pushed by the sheet Pb, and a position having a step with respect to the sheet conveyance guide 9 (FIG. 7A). To the position where there is no step with respect to the sheet conveyance guide 9 (FIG. 7B).

  Here, as shown in FIG. 7A, assuming that a rigid sheet passes through the lower guide portion 65a with a step between the sheet conveyance guide 9 and the lower guide portion 65a, The bent rear end of the sheet is struck with force to the sheet conveyance guide 9 and the sheet jumping sound is generated. Further, when the U-turn passage 65 has a narrow passage width (width in the thickness direction of the sheet) for a rigid sheet, the sheet becomes difficult to pass through the U-turn passage 65 and the conveyance load increases, and the U-turn passage 65 is damaged. May be attached. Further, when the conveyance load increases, the sheet conveyance speed becomes unstable, and the image may be stretched and distorted. Therefore, it is conceivable to increase the width of the U-turn passage 65 from the beginning. However, if the passage width is wide, there is a possibility that sheets having low rigidity such as thin paper cannot be guided and accumulated.

  However, in the U-turn passage 65 shown in FIG. 7, the lower guide portion 65a escapes and the passage width widens according to the rigidity of the sheet, so that the highly rigid sheet may be damaged. Almost disappear. Furthermore, even for a wide variety of sheets, the conveyance load can be reduced, the sheet conveyance speed becomes constant, and the image is not distorted.

  Further, when the lower guide portion 65a escapes, the level difference between the lower guide portion 65a and the sheet conveyance guide 9 is reduced, and the sheet jump sound can be reduced.

  Further, if the lower guide portion 65a can be retracted downward, the jam sheet can be easily removed.

1 is a diagram illustrating a schematic configuration of a laser beam printer as an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is an enlarged view of a main part of the printer main body of FIG. 1. FIG. 2 is an external perspective view of a paper feed cassette in the laser beam printer of FIG. 1. FIG. 2 is an external perspective view of a paper feed cassette in the laser beam printer of FIG. 1. (A) is the figure which looked at the paper feed cassette from the upstream of the sheet discharge direction. (B) is the elements on larger scale of an upper guide part and a lower guide part. It is an enlarged view of the upper guide part and lower guide part of the U-turn channel | path which concerns on 2nd Embodiment of this invention. It is a figure for demonstrating the problem of a U-turn channel | path. FIG. 6 is a schematic configuration diagram illustrating a periphery of a sheet conveyance guide according to a third embodiment of the present invention. (A) is a figure when the lower guide part has not escaped. (B) is the figure which showed the state which the lower guide part escaped. FIG. 10 is a diagram illustrating a schematic configuration of an image forming apparatus including a conventional sheet conveying device.

Explanation of symbols

100 Laser beam printer 101 Laser beam printer body (device body)
102 Paper cassette storage space 1 Image forming section (image forming means)
1a Photosensitive drum 3 Fixing unit 4 Paper feed cassette (sheet stacking means)
4A Option feeder 5 Registration roller pair 8 Re-transfer path (re-transfer path)
8a Lower opening 8A Re-conveying path 9 Sheet conveying guide 25 U-turn path 25a Lower guide part (lower guide member)
25ab Paper passing rib (plate-like member)
25b Upper guide part (upper guide member)
25ba Paper passing rib (plate member)
51 Spring 52 Concave groove 52a Inclination 55 U-turn passage 55a Lower guide part (lower guide member)
55b Upper guide part (upper guide member)
61 Spring 63 Shaft 65 U-turn passage 65a Lower guide part (lower guide member)
65b Upper guide part (upper guide member)

Claims (4)

In an image forming apparatus for forming an image on a sheet,
The device body;
An image forming means provided in the apparatus main body for forming an image on a sheet;
A sheet stacking means that is detachable from the apparatus main body and on which sheets are stacked,
Is provided in the image forming apparatus, a sheet part of the conveying path for conveying the sheet, and the lower guide member provided on said sheet stacking means, which enters from the apparatus main body to said sheet stacking means side, it is conveyed Is formed with an upper guide member disposed in the apparatus body so as to face the lower guide member with a gap through which it can pass,
The upper guide member and the lower guide member are each formed by a plurality of plate-like members arranged in a direction intersecting with the attaching / detaching direction of the sheet stacking unit and arranged in parallel with the attaching / detaching direction,
The plate-like member of the upper guide member and the plate-like member of the lower guide member are disposed at positions that do not interfere with each other in the attaching / detaching direction of the sheet stacking means.
An image forming apparatus. The sheet stacking unit is disposed below the image forming unit, a transport path extending upward to transport the sheet fed from the sheet stacking unit to the image forming unit, and an image is formed by the image forming unit. A re-conveying path for conveying the sheet again to the image forming unit is arranged to extend downward, and the lower side of the re-conveying path is formed in a U shape by the upper guide member and the lower guide member. Connected to the transport passage,
The image forming apparatus according to claim 1. In an image forming apparatus for forming an image on a sheet,
The device body;
An image forming means provided in the apparatus main body for forming an image on a sheet;
A sheet stacking means that is detachable from the apparatus main body and on which sheets are stacked,
Is provided in the image forming apparatus, a sheet part of the conveying path for conveying the sheet, and the lower guide member provided on said sheet stacking means, which enters from the apparatus main body to said sheet stacking means side, it is conveyed Is formed with an upper guide member disposed in the apparatus body so as to face the lower guide member with a gap through which it can pass,
The upper guide member is movable in a direction away from the lower guide member when the sheet stacking means is attached or detached.
An image forming apparatus. The upper guide member is biased toward the lower guide member by a spring and enters the sheet stacking means side.
The image forming apparatus according to claim 3.

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