JP2005298186A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus including a switch-back mechanism, accurately detecting the presence of a paper sheet with a sheet detection switch without fluttering the leading edge of a paper sheet carried in a reversing tray and with large deflection of a paper sheet even if both sides of the paper sheet are held by a registration member. <P>SOLUTION: The switch-back mechanism includes: the reversing tray 1; and a pair of switch-back rollers 2 for carrying in the paper sheet to the reversing tray 1 and carrying out the paper sheet from the reversing tray 1. The mechanism is provided with an upper guide member 3 disposed opposite to the reversing tray 1, and a paper sheet detection switch 4 is fitted to the upper guide member 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an apparatus capable of forming an image on both sides of a sheet.

  An apparatus that forms images on both sides of a sheet is provided with a switchback mechanism that reverses the sheet on which an image is formed on one side. FIG. 5 shows a conventional switchback mechanism. In the conventional switchback mechanism, the detection rod 41 protrudes from the reversing tray 1 ′, the switchback roller pair 2 ′ provided on the conveyance opening side of the reversing tray 1 ′, and the opening 12 formed in the reversing tray 1 ′. And a sheet detection switch 4 arranged to do so. The paper detection switch 4 detects a jam of the paper P on the reverse tray 1 '.

The paper P on which an image is formed on one side is carried into the reversing tray 1 ′ from the transport port 8 by the switchback roller pair 2 ′. When the rear end of the paper P reaches the nip portion of the switchback roller pair 2 ′, the switchback roller pair 2 ′ rotates in the reverse direction, and the paper P is sent out from the reverse tray 1 ′ to the conveyance path. Then, after an image is formed on the other side of the fed paper P, it is discharged out of the apparatus.
JP 2003-312915 A (Claims, FIGS. 1 to 3)

  In such a conventional switchback mechanism, the leading end of the paper P carried into the reversing tray 1 'flutters. Further, in order to adjust the position in the width direction of the paper, when the paper on the reverse tray 1 ′ is sandwiched from both sides by an alignment member (not shown) provided so as to be movable in the central direction on both sides of the reverse tray 1 ′. In some cases, the central portion in the width direction of the sheet is bent so as to extend upward. This is the main cause of the erroneous detection of the paper detection switch 4.

  Further, in the conventional switchback mechanism, the pressure contact between the switchback roller pair is dependent on the weight of the upper roller 21, but such a roller pair 2 'can carry in / out the sheet in the case of a thick sheet. There was something I couldn't do enough.

  The present invention has been made in view of the above-described conventional problems. The object of the present invention is to prevent the leading edge of the paper that has been carried into the reversing tray from flapping, and to align the both sides of the paper with the alignment member. An object of the present invention is to provide an image forming apparatus that can accurately detect the presence of a sheet with a sheet detection switch without causing the center of the sheet to be greatly bent even if it is pinched.

  Another object of the present invention is to ensure that even a thick sheet can be carried in and out with a switchback roller pair.

  According to the present invention, in the image forming apparatus that includes the switchback mechanism that reverses the paper on which the image is formed on one side, and forms the image on both sides of the paper, the switchback mechanism reverses the reverse tray and the paper. An image comprising: a pair of switchback rollers that are carried into the tray and carried out of the reversing tray; an upper guide member provided so as to face the reversing tray; and a sheet detecting means attached to the upper guide member. A forming apparatus is provided.

  Here, from the viewpoint of surely loading and unloading even thick paper with the switchback roller pair, the upper roller of the switchback roller pair is pivotally supported on the support member and the upper surface of the upper guide member is covered with the cover. It is preferable that a biasing member is interposed between the cover and the support member and the cover so that the upper roller is biased in the direction of the lower roller.

  In addition, in the case of a high-speed image forming apparatus, it is necessary to reduce the time for carrying paper into and out of the reversing tray, so that the upper roller can be moved between a position where it contacts the lower roller and a position where it does not contact. It is preferable to further provide a holding mechanism for holding the upper roller at a position where it does not contact the lower roller. The holding mechanism includes a solenoid, a locking claw that holds the support member so that the upper roller does not contact the lower roller, a lever that is swung by the solenoid, and a lever that locks the support member. It is recommended to have a biasing means for biasing.

  In the image forming apparatus of the present invention, since the upper guide member is provided so as to face the reversing tray, flapping of the leading edge of the sheet carried into the reversing tray can be suppressed. In addition, it is possible to suppress bending that extends upward from the center of the sheet when both sides of the sheet are sandwiched between alignment members. In addition, since the sheet detecting means is attached to the upper guide member, even if the sheet central portion is bent so as to extend upward, it is not erroneously detected.

  Further, the upper roller of the switchback roller pair is pivotally supported on the support member, the upper surface of the upper guide member is covered with a cover, a biasing member is interposed between the support member and the cover, and the upper roller is lowered. When urged in the direction of the side roller, the pressure contact force of the switchback roller pair increases and even a thick sheet can be reliably carried in and out by the switchback roller pair.

  In addition, when the upper roller can be moved to a position where it does not contact the lower roller and a position where it does not contact the lower roller, and a holding mechanism that holds the upper roller at a position where it does not contact the lower roller is further provided, -The time for carrying out can be shortened, and the speed of the image forming apparatus can be coped with. Here, as the holding mechanism, there are a solenoid, a locking claw that holds the support member so that the upper roller does not contact the lower roller, a lever that is swung by the solenoid, and a direction in which the support member is locked. If a device including an urging means for urging the lever is used, it can be reliably held in a non-contact position with the upper roller with a simple mechanism.

  The image forming apparatus of the present invention will be described below with reference to the drawings. The present invention is not limited to these embodiments.

  FIG. 1 is a schematic configuration diagram showing an example of the image forming apparatus of the present invention. The papers fed one by one from the paper feed cassette 81 by the paper feed roller 82 pass through the transport path 83, have their leading ends adjusted by the registration roller pair 84, wait, and are transported to the photosensitive drum 91 at a predetermined timing. . On the other hand, the latent image on the photosensitive drum 91 is visualized as a toner image by a developing device (not shown), and is transferred to the fed paper by the transfer unit 92. The sheet on which the toner image is placed is conveyed to the fixing roller pair 93 and is heated and pressed by the heating roller and the pressure roller, and the toner image is fixed on the sheet.

  Next, the sheet on which the toner image is fixed on one side is conveyed to the switchback mechanism M via the conveyance path 86 by the branching device 85, and the sheet is changed to the conveyance path 87 by changing the front and rear of the conveyance direction. Be transported. Details of the switchback mechanism M will be described later. Then, the sheet is conveyed again to the registration roller pair 84 through the conveying path 87, and after the toner image is transferred and fixed on the other side of the sheet in the same manner as described above, the sheet is transferred to the discharge tray 94 by the branching device 85. Discharged.

  A sectional view of a switchback mechanism M used in the image forming apparatus of the present invention is shown in FIG. 2, and a partial perspective view is shown in FIG. In addition, the same code | symbol is attached | subjected to the same member and part as FIG. The switchback mechanism M includes a reversing tray 1 and a pair of switchback rollers 2 provided on the reversing tray 1 on the conveying port 8 side. The lower roller 22 of the switchback roller pair 2 is rotatably attached to the apparatus. On the other hand, the upper roller 21 of the switchback roller pair 2 is pivotally supported by a support member 6 that is swingably mounted on a conveyance guide plate 88 about a shaft 61. Then, as will be described later, when the support member 6 swings, the upper roller 21 moves to a position where it contacts the lower roller 22 and a position where it does not contact.

  An upper guide member 3 is attached to the reversing tray 1 at the center in the width direction on the opposite side of the switchback roller so as to face the reversing tray 1. A cover 5 is attached so as to cover the upper surface of the upper guide member 3. An opening 31 is formed at the center in the width direction of the upper guide member 3. The paper detection switch 4 is disposed on the lower surface of the recess 52 formed in the cover 5 so that the detection rod 41 protrudes from the opening 31. The paper detection switch 4 detects paper jam on the reversing tray 1 as in the prior art.

  A concave portion 62 is formed in the support member 6, and a convex portion 51 of the cover 5 is formed vertically above the concave portion 62. A spring (biasing member) S is interposed between the concave portion 62 of the support member 6 and the convex portion 51 of the cover 5 to constantly bias the support member 6 downward. As a result, the upper roller 21 is always urged in the direction of contact with the lower roller 22, and the pressing force is much larger than that of the conventional pressing by only the weight of the upper roller 21, so that even thick paper can be easily conveyed. Become. As will be described later, in this embodiment, a holding mechanism that holds the upper roller 21 in a position not in contact with the lower roller 22 is provided, and the upper roller 21 is controlled to contact the lower roller 22 only when necessary. The As a result, it is possible to carry out processing such as carrying paper into the reversing tray 1 while carrying out paper from the reversing tray 1, thereby increasing the paper transport speed and corresponding to high-speed image formation. Of course, an elastic member such as rubber may be used instead of the spring S as the biasing member.

  Next, a holding mechanism for the support member 6 will be described. FIG. 4 shows a schematic diagram of the holding mechanism. A lever 71 having a locking claw 711 for holding the support member 6 is supported by a shaft 73 in a swingable manner on a vertical plate portion of the apparatus main body. The lever 71 is connected to a rod 74 that enters the solenoid 72 by the activation of the solenoid 72 by a pin m, and is always in the direction of the support member 6 by a torsion coil spring (biasing means) 75 that is externally fitted to the shaft 73. It is energized. On the other hand, a notch 63 that engages with the locking claw 711 of the lever 71 is formed on the side surface of the support member 6. Instead of the torsion coil spring 75, a compression coil spring may be used to bias the lever 71 in the direction of the support member 6.

  As shown in FIG. 4A, in the normal state, the torsion coil spring 75 urges the lever 71 in the direction of the support member 6 and the locking claw 711 is engaged with the notch 63 of the support member 6. The upper roller 21 that is pivotally supported by the support member 6 is held at a position where it does not contact the lower roller 22. On the other hand, as shown in FIG. 5B, when the solenoid 72 is activated, the rod 74 enters the solenoid, and the lever 71 rotates clockwise. Then, the engagement between the locking claw 711 of the lever 71 and the notch 63 of the support member 6 is released, and the support member 6 moves downward about the shaft 61 (shown in FIG. 2) by the spring S and its own weight. The upper roller 21 is in pressure contact with the lower roller 22. As a result, the sheet can be conveyed while being sandwiched between the upper roller 21 and the lower roller 22.

  Next, the movement of the switchback mechanism will be described with reference to FIG. The sheet on which the image is formed on one side is carried into the reverse tray 1 from the conveyance port 8 by the switchback roller pair 2. At this time, the detection rod 41 of the paper detection switch 4 rotates in contact with the paper that has been carried in, and the presence of the paper is detected. When the trailing edge of the sheet reaches the nip portion of the switchback roller pair 2, the switchback roller pair 2 rotates in the reverse direction, and the sheet is sent out from the reverse tray 1 to the conveyance path. Then, an image is formed on the other side of the fed sheet, and is discharged to a discharge tray 94 (shown in FIG. 1) outside the apparatus.

  Note that the mounting position of the upper guide member is not limited to the central portion in the width direction on the opposite side of the switchback roller as in the above embodiment, but the size of the paper to be transported and the transport reference (center reference or side end reference). Or the like). Also, the size of the upper guide is not particularly limited, and may be a size facing the entire surface of the reversing tray. However, if taking out of paper when a paper conveyance error occurs in the reversing tray, the upper guide is considered. Is preferably large enough to cover a portion of the reversing tray.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus of the present invention. It is a sectional side view which shows an example of a switchback mechanism. It is a perspective view of a switchback mechanism. It is a schematic diagram of a holding mechanism. It is a sectional side view which shows the conventional switchback mechanism.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reverse tray 2 Switch back roller pair 3 Upper guide member 4 Paper detection switch (paper detection member)
5 Cover 6 Support Member 7 Holding Mechanism m Pin P Paper S Spring (Biasing Member)
21 Upper roller 22 Lower roller 31 Opening portion 41 Detection rod 51 Protruding portion 52 Recessing portion 61 Shaft 62 Recessing portion 63 Notch portion 71 Lever 72 Solenoid 73 Shaft 74 Rod 75 Torsion coil spring 711 Locking claw

Claims (4)

In an image forming apparatus that includes a switchback mechanism that reverses a sheet of paper on which an image is formed on one side and forms an image on both sides of the sheet,
The switchback mechanism is attached to a reversing tray, a pair of switchback rollers for carrying paper into and out of the reversing tray, an upper guide member provided to face the reversing tray, and an upper guide member. And an image forming apparatus.   The upper roller of the switchback roller pair is pivotally supported by a support member, the upper surface of the upper guide member is covered with a cover, an urging member is interposed between the support member and the cover, and the upper roller is The image forming apparatus according to claim 1, wherein the image forming apparatus is urged toward the lower roller.   The image forming apparatus according to claim 1, further comprising a holding mechanism that is movable between a position where the upper roller contacts the lower roller and a position where the upper roller does not contact the upper roller, and holds the upper roller at a position where the upper roller does not contact the lower roller.   The holding mechanism has a solenoid, a locking claw for holding the support member so that the upper roller does not come into contact with the lower roller, a lever that is swung by the solenoid, and a lever that locks the support member. The image forming apparatus according to claim 3, further comprising an urging unit that urges the image forming apparatus.

Images