JP2008170787A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of preventing wrinkles and ensuring good jam handling performance.
A guide member 4 for guiding a sheet to the fixing nip N is provided on the upstream side of the fixing nip N between the fixing roller 2 and the pressure roller 3 in the sheet conveying direction so as to be rotatable in the vertical direction. The guide member 4 is selectively set to a first position where the fixing nip side end 4a of the guide member 4 is located above the extension line L of the fixing nip N and a second position located below the extension line L. Turn to. Then, the reverse rotation mechanism rotates at least one of the fixing roller 2 and the pressure roller 3 in the reverse direction so as to move the sheet sandwiched between the fixing roller 2 and the pressure roller 3 in the direction opposite to the sheet conveying direction, and the reverse rotation mechanism. When the guide member 4 is in the first position when the sheet is moved in the direction opposite to the sheet conveying direction, the guide member 4 is rotated to the second position by the rotation unit 5.
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus, and more particularly to a jam process in a fixing unit including a fixing roller and a pressure roller.

  2. Description of the Related Art Conventionally, some image forming apparatuses such as copying machines, facsimile machines, and laser printers form an image on a sheet by an electrophotographic method. In such an image forming apparatus, when an image is formed on a sheet, first, the photosensitive drum is exposed in accordance with image information to form an electrostatic latent image on the photosensitive drum.

  Next, the electrostatic latent image is developed with toner in a developing device to be visualized as a toner image, and the toner image is transferred to a sheet supplied from a paper feeding unit in a transfer unit. . Thereafter, the sheet is conveyed to a fixing nip between a fixing roller and a pressure roller provided in the fixing unit, and the toner image is fixed on the sheet as a permanent image.

  Incidentally, in such a conventional image forming apparatus, a guide member is provided between the transfer unit and the fixing unit so as to guide the sheet to the fixing unit. In some cases, when the distance between the transfer unit and the fixing unit is relatively long, a sheet conveyance unit is arranged between the guide member and the transfer unit so that the sheet is conveyed on a rubber belt.

  By the way, as an image forming apparatus provided with a guide member, the guide member is provided so as to be pivotable in the vertical direction from the viewpoint of preventing wrinkling of the sheet and transportability of a small size sheet such as a postcard. (For example, refer to Patent Document 1).

  In such an image forming apparatus, the front end height (position) of the guide member on the fixing unit side can be changed in two stages according to the sheet size and the like. For example, when the sheet size is large, the rotation tip position of the guide member 54 is rotated to the upper position as shown in FIG. .

JP 05-224547 A

  By the way, in such a conventional image forming apparatus, a jam may occur when the sheet is sandwiched in the fixing nip. In this case, in order to prevent the sheet from being wound around the fixing roller, the sheet is transferred to the transfer unit side. Jam processing is performed by sending it out.

  Here, in order to prevent wrinkling of the sheet, the fixing roller 52 and the pressure roller of the fixing unit 51 are in a state where the rotation tip position of the guide member 54 is set to the upper position as shown in FIG. In some cases, jamming of the sheet S may occur in a state where the sheet S is sandwiched between the fixing nip N and the fixing nip 53.

  In this case, when the jammed sheet S is sent out to the transfer portion side by rotating the fixing roller 52 and the pressure roller 53 in the opposite directions, the jammed sheet S becomes the guide member 54 as shown in FIG. It may become difficult to handle jams.

  In other words, in order to prevent wrinkling of the sheet, when the guide member 54 is set to the upper position, if the sheet S is sent out to the transfer portion side for jam processing, the jammed sheet S enters under the guide member 54. Therefore, there is a case where the jam processing becomes difficult.

  Therefore, the present invention has been made in view of such a current situation, and an object of the present invention is to provide an image forming apparatus that can prevent wrinkles and ensure good jam processing performance. is there.

  The present invention relates to an image forming apparatus that transports a sheet on which an unfixed toner image is transferred to a fixing nip between a fixing roller and a pressure roller and fixes the unfixed toner image on the sheet. A guide member that guides a sheet to the fixing nip and is provided on the upstream side in the sheet conveyance direction, and the guide member includes a guide nip side end portion of the guide member from a tangent line of the fixing nip. The sheet is jammed in a state of being sandwiched by the fixing roller and the pressure roller, and a rotating portion that selectively rotates to a first position that is also located above, a second position that is located below the tangent line, and the fixing roller. A reversing mechanism that reversely rotates at least one of the fixing roller and the pressure roller so as to move the jammed sheet in the direction opposite to the sheet conveying direction. When the guide member is in the first position when the sheet is moved in the direction opposite to the sheet conveying direction, the guide member is rotated to the second position by the rotating unit. It is a feature.

  As in the present invention, when the sheet is moved in the direction opposite to the sheet conveying direction for jam processing, the guide member is rotated so that the end portion on the fixing nip side is positioned below the tangent line of the fixing nip, It is possible to prevent the generation of wrinkles and ensure good jam handling properties.

  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 a first embodiment of the present invention.

  In FIG. 1, reference numeral 100 denotes a laser beam printer, and 101 denotes a laser beam printer main body (hereinafter referred to as a printer main body). The laser beam printer 100 includes an image forming unit 102, cassette feeding devices 105 and 106 that feed the sheet S to the image forming unit 102, and a transfer unit 103 that transfers a toner image to the sheet S. Further, the image forming apparatus includes a fixing unit 1 that fixes the toner image transferred by the transfer unit 103 to the sheet S, and a manual sheet feeding device 105 provided on a side surface of the printer main body 101.

  The image forming unit 102 exposes the surface of the photosensitive drum 31 and the process cartridge 30 including the photosensitive drum 31, the charging roller 32, the developing sleeve 33, a toner container (not illustrated), and the like to electrostatically charge the photosensitive drum. And a laser scanner 116 for forming a latent image. The laser scanner 116 includes a laser light emitting unit (not shown), a rotating polygon mirror 21, a folding mirror 22, and the like.

  The cassette feeding devices 105 and 106 include sheet feeding trays 105a and 106a for stacking sheets S, a feeding roller 26 for feeding the sheets S on the sheet feeding tray one by one, and a retard separation type sheet separating unit. 108,109. The transfer unit 103 includes the photosensitive drum 31 and the transfer charger 8.

  Next, an image forming operation in the laser beam printer 100 configured as described above will be described.

  When the image forming operation is started, the photosensitive drum 31 first rotates in the direction of the arrow, and is uniformly charged to a predetermined polarity and a predetermined potential by the charging roller 32. Then, laser light L is emitted from the laser light emitting unit of the laser scanner 116 to the photosensitive drum 31 whose surface has been charged based on image information, and this laser light L passes through the polygon mirror 21 and the folding mirror 22. Irradiated. As a result, an electrostatic latent image is formed on the photosensitive drum 31.

  Next, the electrostatic latent image is developed as a toner image when toner that has been appropriately charged with the rotation of the developing sleeve 33 is supplied onto the photosensitive drum 31 and attached to the electrostatic latent image. Visualized.

  On the other hand, in parallel with the toner image forming operation, the sheets S stacked and stored in the paper feed trays 105a and 106a are sent out by the feed roller 26 and then separated by the sheet separation units 108 and 109 to be registered. It is conveyed to the roller 110. Alternatively, the sheet S stacked and stored on the manual feed tray is fed by the feeding roller 26 and then conveyed to the registration roller 110.

  The sheet S thus transported to the registration roller 110 is transported to the transfer unit 103 at the timing of the latent image formed on the photosensitive drum 31 after the skew is corrected by the registration roller 110. Is done. Thereafter, the toner image formed on the photosensitive drum by the transfer unit 103 is transferred to a predetermined position on the sheet S.

  Next, the sheet S on which the toner image has been transferred in this manner is conveyed to the fixing unit 1 including the pressure roller 3 and the fixing roller 2 including the heater via the conveying unit 6 including the conveying belt 6a. Thereafter, in the fixing unit 1, the unfixed toner image is heated and pressurized and fixed on the sheet surface.

  The laser beam printer 100 has a duplex printing mode for performing duplex printing on the sheet S and a simplex printing mode. In the single-sided print mode, the sheet S after the fixing process is discharged onto the discharge tray 18 outside the apparatus by the inner discharge roller pair 16 and the outer discharge roller 17.

  In the double-sided print mode, the paper is temporarily stacked and stored on the intermediate tray 24 via the refeed path 20 and the double-sided conveyance path 23 by the internal discharge roller pair 16 or the switchback roller pair 19. Thereafter, the sheet S stored on the intermediate tray 24 is conveyed again to the registration roller 110 for image formation by the refeed device 25, and thereafter discharged outside the apparatus through the same process as that for single-sided printing.

  By the way, as shown in FIG. 2, between the fixing unit 1 and the conveying unit 6 is a guide member for guiding the sheet to the fixing nip N where the fixing roller 2 and the pressure roller 3 are in pressure contact. A sheet guide 4 is arranged.

  The sheet guide 4 is pivotally supported by a printer main body frame (not shown) so as to be pivotable in the vertical direction via a pivot shaft 4b provided at the upstream end in the sheet conveying direction. Further, a guide lever 4c having one end connected to the rod 5a of the solenoid 5 is fixed to the rotating shaft 4b. The guide lever 4c is provided with a tension coil spring (not shown) whose other end is fixed to the printer main body frame.

  When the solenoid 5 is turned on to operate the rod 5a, the guide lever 4c moves from the position shown in FIG. 2A to the position shown in FIG. 2B while resisting the tension coil spring. When the solenoid 5 is turned OFF, the guide lever 4c is moved from the position shown in FIG. 2B to the position shown in FIG. Thus, the guide lever 4c rotates in the vertical direction according to the ON / OFF state of the solenoid 5, and the sheet guide 4 also rotates in the vertical direction accordingly.

  Here, the solenoid 5 is turned on and off according to the sheet size. For example, when the sheet size is a large size such as A3, the fixing nip side end 4a of the sheet guide 4 is located at the upper position shown in FIG. 2A, the sheet size is postcard, B5, etc. In the case of the small size, it is at the lower position shown in FIG.

  That is, in the present embodiment, the sheet guide 4 rotates in the vertical direction according to the sheet size, and accordingly, the fixing nip side end portion (hereinafter referred to as a rotating end) 4a of the sheet guide 4 is the fixing nip N. The tangent line L is selectively positioned at the upper and lower positions. The tangent L of the fixing nip N is a tangent to the outer periphery of the fixing roller 2 and the pressure roller 3 and is a line passing through the fixing nip N. When the width of the fixing nip N in the sheet conveying direction is wide, the inlet (the nip end on the upstream side in the sheet conveying direction) and the outlet (the nip end on the downstream side in the sheet conveying direction) of the fixing nip N are connected. The line is defined as tangent L.

  FIG. 3 is a control block diagram of the laser beam printer 100. In FIG. 3, reference numeral 60 denotes a control unit that controls the entire image forming operation of the laser beam printer 100, and 61 denotes a sheet size detection sensor 61 that is a sheet size detection unit that detects the size of a sheet to be transferred. A jam detection unit 62 detects a jam of the sheet. The control unit 60 holds the sheet S in the fixing nip N based on a detection signal from the jam detection unit 62, and a rear end of the sheet guide 4 It can be detected that it is on the downstream side of the rotation end 4a.

  Here, the position switching operation of the sheet guide 4 according to the present embodiment will be described.

  When the sheet size to be transferred is recognized by the sheet size detection sensor 61 shown in FIG. 3, the control unit 60 configures a rotating unit that rotates the sheet guide 4 when the sheet size is a large size, for example. The solenoid 5 is turned off. As a result, the rotation end 4a of the sheet guide 4 moves to a first position higher than the tangent L of the fixing nip N as shown in FIG.

  When the sheet guide 4 is in such a state, when the sheet is conveyed, first, the leading edge of the sheet is conveyed from the position higher than the fixing nip N to the fixing nip N, and thereafter, the leading edge of the sheet is fixed to the fixing roller. 2 abuts. Here, the surface of the fixing roller 2 is coated with a fluorine-based resin having a small friction coefficient such as Teflon (registered trademark) in order to improve heat resistance and releasability.

  For this reason, after contacting the fixing roller 2, the leading edge of the sheet advances while sliding along the surface of the fixing roller 2. At this time, the sheet advances while sliding along the surface of the fixing roller while being pushed upward by the rotating end 4a of the sheet guide 4 that has moved to the first position.

  Thereafter, when entering the fixing nip N, the sheet is sandwiched between the transfer unit 103 and the fixing nip N and is conveyed while being pushed up by the rotating end 4a of the sheet guide 4. become.

  As a result, the sheet advances while being pressed against the surface of the fixing roller. As a result, when the leading edge of the sheet is undulated, the undulation of the sheet is planarized along the surface of the fixing roller 2. Thereafter, the leading edge of the sheet enters the fixing nip N in such a flattened state, so that the sheet passes smoothly through the fixing nip N without generating wrinkles.

  When the sheet size is a small size, the sheet is transported by the transport unit 6 in a state of being separated from the registration rollers 110 (see FIG. 1). Only the force, and the force to convey the sheet is low. For this reason, the control unit 60 turns on the solenoid 5 when the sheet size is a small size (small size). As a result, the rotation end 4a of the sheet guide 4 moves to a second position lower than the tangent L of the fixing nip N as shown in FIG.

  In this way, the rotation end 4a of the sheet guide 4 is moved to the second position, so that a small-sized sheet having a low conveying force can be easily entered into the fixing nip N, and problems such as sheet non-feeding are caused. It can be smoothly carried into the fixing nip N without being generated.

  Next, the position switching operation of the sheet guide 4 during jam processing will be described with reference to FIG. During the jam processing, the fixing roller 2 and the pressure roller 3 are rotated in a direction opposite to the sheet conveying direction by manually operating a jam handle which is a reverse rotation mechanism (not shown).

  Here, the jammed sheet is not only a sheet jammed in the state of being nipped by the fixing nip N, but also the fixing nip N when the operation of the laser beam printer 100 is stopped due to the sheet jamming in another conveyance path. Including a sheet stopped in a state of being sandwiched between the two.

  First, as shown in FIG. 4A, a case where the sheet S is jammed in a state where the sheet trailing edge is sandwiched in the fixing nip N when the sheet guide 4 is in the first position will be described.

  In this case, that is, when the jam detection unit (see FIG. 3) detects that the sheet S is sandwiched in the fixing nip N and the rear end is downstream of the rotation end 4a of the sheet guide 4, the control unit 60 Immediately after detecting a jam, the solenoid 5 is turned ON. As a result, as shown in FIG. 4B, the sheet guide 4 moves to the second position.

  Next, after the sheet guide 4 is moved to the second position, the user turns a jam handle (not shown) for jam sheet processing. When the jam handle is rotated in this way, the sheet S passes over the rotating end 4a without entering the lower side of the sheet guide 4 as shown in FIG. Thereby, the jam sheet S can be easily processed.

  As described above, in the present embodiment, when the sheet S is moved in the direction opposite to the sheet conveyance direction for jam processing, when the sheet guide 4 is in the first position, the sheet guide 4 is moved to the second position. I am doing so.

  That is, during the jam processing, the sheet guide 4 is rotated so that the rotation end 4 a is positioned below the tangent line of the fixing nip N. Accordingly, when the user performs jam processing, the sheet S can be prevented from entering the lower side of the sheet guide 4. As a result, generation of wrinkles can be prevented and good jam processing performance can be ensured.

  In the above description, the case where the sheet guide 4 is moved to the second position by the solenoid 5 when a jam is detected has been described. However, the present invention is not limited to this. For example, in the case of an image forming apparatus that turns off the power when a jam is detected, the sheet guide 4 is manually moved to the second position.

  Next, a second embodiment of the present invention in which the sheet guide 4 is manually moved to the second position will be described.

  FIG. 5 is a diagram illustrating a configuration between the conveyance unit and the fixing unit in the image forming apparatus according to the present exemplary embodiment. In FIG. 5, the same reference numerals as those in FIG. 2 described above indicate the same or corresponding parts.

  In FIG. 5, reference numeral 10 denotes an idler gear. The idler gear 10 is connected to the fixing roller 2 via a gear (not shown). The idler gear 10 is connected to a jam handle gear 9 rotatably attached to a gear shaft (not shown) rotatably supported on the printer main body frame.

  The jam handle gear 9 rotates integrally with a jam handle (not shown), and is attached to the gear shaft via a one-way clutch (not shown) and a tri-limiter (not shown) provided on the gear shaft. Via the pivot shaft 4b of the sheet guide 4.

  When the fixing roller 2 is rotated clockwise in the sheet conveyance direction by this one-way clutch (during normal copying), the idler gear 10 and the jam handle gear 9 accompanying the rotation of the fixing roller 2 rotate the gear shaft. Is not transmitted to. For this reason, the sheet guide 4 does not rotate during such normal copying.

  As will be described later, when the jam handle is rotated in the direction in which the fixing roller 2 is reversely rotated during the jam processing, the rotation of the jam handle is transmitted from the handle gear 9 to the idler gear 10 and further through the idler gear 10. 2 is transmitted. The rotation of the jam handle gear 9 is transmitted to the gear shaft through the one-way clutch, and further transmitted to the rotating shaft 4b of the seat guide 4 through the gear shaft and the trilimiter. As a result, the sheet guide 4 rotates downward.

  Next, the position switching operation of the sheet guide 4 at the time of jam processing in the present embodiment will be described.

  For example, as shown in FIG. 5A, when a jam occurs with the trailing edge of the sheet sandwiched between the fixing nip N when the rotation end 4a of the sheet guide 4 is at the first position, the user performs jam sheet processing. Therefore, the jam handle is rotated, and the jam handle gear 9 is rotated counterclockwise. At this time, since the solenoid 5 (see FIG. 4) is OFF, the rotation of the jam handle (jam handle gear 9) constituting the auxiliary rotating portion is not hindered.

  Here, when the jam handle gear 9 is rotated in this direction, the rotation is transmitted to the rotating shaft 4b via the one-way clutch and the gear shaft, thereby, as shown in FIG. 5B, the seat guide. The rotation end 4a of 4 rotates downward and moves to the second position.

  Since the torque limiter is connected to the rotation shaft 4b of the sheet guide 4, the sheet guide lever 4c contacts the stopper 4d provided on the printer main body frame 101A after the sheet guide 4 has moved to the second position. Then, the jam handle gear 9 idles.

  Further, when the jam handle gear 9 is rotated counterclockwise as described above, the fixing roller 2 is rotated counterclockwise via the idler gear 10, and the jam sheet S is conveyed toward the transfer portion. That is, due to the counterclockwise rotation of the jam handle gear 9, the fixing roller 2 conveys the sheet toward the transfer portion, and at the same time, the sheet guide 4 moves to the second position.

  Thus, in the present embodiment, as shown in FIG. 5A, when the user rotates the jam handle for jam sheet processing, the sheet guide 4 is shown in FIG. 5B accordingly. Move to the second position. Further, when the jam handle that also functions as a reverse rotation mechanism for rotating the fixing roller 2 in the reverse direction is rotated, the fixing roller 2 is rotated in a direction in which the jam sheet S is conveyed toward the transfer portion.

  As a result, even when the solenoid 5 does not operate during jam processing, if the jam handle is turned, the sheet S can be prevented from entering the lower side of the sheet guide 4, and as a result, wrinkles are generated. Can be prevented and good jam handling properties can be secured.

  In the first and second embodiments described so far, the first position is set to a position where wrinkles can be prevented, and the second position is optimal so that the sheet-conveying property of a small size sheet is good. However, the present invention is not limited to this. For example, the height of the sheet guide 4 is set in three stages, and the second position is a position that is lower than the position of the sheet guide 4 (see FIGS. 2B and 5B) when a small-size sheet is passed. It is also good.

  By setting the second position to such a position, the sheet S can enter the lower side of the sheet guide 4 even when the sheet guide 4 is at a position determined by the sheet conveyance performance of the small size sheet. This can be surely prevented, and the jam handling property can be further improved. In the above description, the fixing roller 2 is rotated in order to convey the sheet toward the transfer portion. However, the present invention is not limited to this, and at least one of the fixing roller 2 and the pressure roller 3 is reversed. It should be rotated.

1 is a diagram showing a schematic configuration of a laser beam printer which is an example of an image forming apparatus according to a first embodiment of the present invention. FIG. 4 is a diagram illustrating a configuration of a sheet guide provided between a fixing unit and a conveyance unit of the laser beam printer. FIG. 3 is a control block diagram of the laser beam printer. The figure explaining the position switching operation | movement at the time of the jam processing of the said sheet guide. FIG. 6 is a diagram illustrating a configuration between a conveyance unit and a fixing unit in an image forming apparatus according to a second embodiment of the present invention. FIG. 10 is a diagram illustrating a position switching operation during jam processing of a sheet guide provided between a conventional conveyance unit and a fixing unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing part 2 Fixing roller 3 Pressure roller 4 Sheet guide 4a Rotating end 4b Rotating shaft 4c Guide lever 5 Solenoid 6 Conveying part 8 Transfer charger 9 Jam handle gear 10 Idler gear 60 Control part 61 Sheet size detection sensor 62 Jam Detection unit 100 Laser beam printer 101 Laser beam printer main body 102 Image forming unit L Tangent line of fixing nip N Fixing nip S Sheet

Claims (5)

In an image forming apparatus for conveying a sheet on which an unfixed toner image is transferred to a fixing nip between a fixing roller and a pressure roller and fixing the unfixed toner image on the sheet,
A guide member provided on the upstream side in the sheet conveyance direction of the fixing nip so as to be rotatable in the vertical direction, and for guiding the sheet to the fixing nip;
The guide member is selectively rotated to a first position where an end portion of the guide member on the fixing nip side is located above a tangent line of the fixing nip and a second position located below the tangent line. A rotating part;
A reversing mechanism that reversely rotates at least one of the fixing roller and the pressure roller so as to move the jammed sheet in a direction opposite to the sheet conveying direction when the sheet is jammed between the fixing roller and the pressure roller. With
When the jamming sheet is moved in the direction opposite to the sheet conveying direction by the reversing mechanism, when the guide member is in the first position, the guide member is rotated to the second position by the rotating unit. An image forming apparatus characterized by that. A jam detection unit for detecting that the sheet is jammed in a state of being sandwiched between the fixing roller and the pressure roller;
A control unit that controls the rotating unit to rotate the guide member to the second position based on a detection signal of the jam detecting unit when the guide member is in the first position. The image forming apparatus according to claim 1. It has a sheet size detector that detects the size of the sheet,
2. The control unit according to claim 1, wherein the guide member is selectively moved to the first position or the second position by the rotation unit based on sheet size information from the sheet size detection unit. Or the image forming apparatus of 2.   The image forming apparatus according to claim 1, wherein the reverse rotation mechanism manually rotates at least one of the fixing roller and the pressure roller. An auxiliary rotation unit that manually rotates the guide member from the first position to the second position;
The image forming apparatus according to claim 4, wherein the auxiliary rotation unit is also configured to serve as the reverse rotation mechanism.

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