JP2009186692A - Fixing device and image forming apparatus provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which can detect a jam, without causing the delay of the detection of the jam and degrading printing quality and which is simply structured; and to provide an image forming apparatus provided with the same. <P>SOLUTION: The lever 31 of a sheet detecting means 30 can be arranged in the vicinity of a nip N between a heating-rotation means 21 and a pressure-rotation means 22, so that the delay of the detection of the jam is never caused. A rotation roller 42 attached to the top end of the lever 31 comes into roll-contact with the rear face 2b of a sheet 2, to prevent the lever 31 from rubbing against the rear face 2b of the sheet 2, so that even when a toner image is printed on the rear face 2b of the sheet 2 by both-side printing, the toner image is never scraped by the lever 31. Thus, the jam can be detected without degrading the printing quality. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device for fixing a toner image transferred on a sheet (copy paper, plastic film, etc.) to the sheet, and an electrophotographic image forming apparatus (copier, printer, facsimile apparatus, and the like) having the same. Multifunctional devices).

  FIG. 5 shows a conventionally known electrophotographic image forming apparatus 100. As shown in FIG. 5, the electrophotographic image forming apparatus 100 sends a sheet 102 from a paper feeding unit 101 to an image forming unit 103, and transfers a toner image onto the sheet 102 by the image forming unit 103. The sheet 102 on which the toner image is transferred is sent to the fixing device 104, the toner image is fixed to the sheet 102 by the fixing device 104, and the fixed sheet 102 is sent to the paper discharge tray 105 or a duplex printing unit (not shown). Yes.

  In the fixing device 104, the heating rotation unit 106 and the pressure rotation unit 107 are in contact with each other while rotating, and the contact portion forms a nip N that feeds the sheet 102 to the sheet conveyance path 108 on the downstream side in the sheet conveyance direction while sandwiching the sheet 102. It is like that. Then, the toner image is heated and pressurized by the nip N that is a contact portion between the heating rotation unit 106 and the pressure rotation unit 107, so that the toner image is welded to the sheet 102.

  The sheet 102 sent out from the nip N between the heating rotation means 106 and the pressure rotation means 107 to the downstream side in the sheet conveying direction is wound around the heating rotation means 106 side because the welded toner image is in contact with the heating rotation means 106 side. Jam (paper jam) is likely to occur. Therefore, a separating unit 110 is disposed at a position downstream of the heating rotating unit 106 in the sheet conveying direction and in the vicinity of the nip N between the heating rotating unit 106 and the pressure rotating unit 107, and the sheet 102 after fixing is separated by the separating unit 110. Is separated from the heating rotation means 106.

  Further, on the downstream side of the separation unit 110 of the fixing device 104 in the sheet conveying direction, the sheet detection for detecting whether or not the sheet 102 sent out from the nip N is normally conveyed along the sheet conveying path 108. Means 111 is arranged, and a controller (not shown) for controlling the operation of the image forming apparatus 100 determines whether or not a jam has occurred in the fixing device 104 based on the operating state of the sheet detecting means 111. It has become.

  The sheet detection means 111 includes a non-contact type and a contact type. Photosensors are known as non-contact type sheet detecting means. However, since the photosensor is vulnerable to heat, it cannot be placed close to the heating rotation means 106, which may cause a delay in jam detection. In addition, the photosensor has a problem that the structure of the fixing device 104 becomes complicated because a cooling unit or the like must be installed in order to prevent failure due to heat. For this reason, as the sheet detecting means 111, many contact-type sheet detecting means are employed. If the jam detection delay is large, the amount of the jammed sheet 102 wound around the heating rotation unit 106 increases, and it becomes extremely difficult to remove the jammed sheet 102 from the fixing device 104.

  6 and 7 show a conventional contact type sheet detecting means 111. The contact-type sheet detection means 111 shown in these drawings includes a lever 112 disposed in the sheet conveyance path 108 on the downstream side in the sheet conveyance direction from the separation means 110 and in the vicinity of the separation means 110, and the movement of the lever 112. It has a light shielding member 113 that interlocks, and a photo interrupter 114 whose optical path is opened or blocked by the light shielding member 113. The contact-type sheet detecting unit 111 operates in conjunction with the lever 112 when the lever 112 is tilted by the leading end of the sheet 102 fed from the nip N between the heating rotation unit 106 and the pressure rotation unit 107. When the member 113 is positioned between the light emitting unit 114a and the light receiving unit 114b of the photo interrupter 114 and blocks the optical path, the rear end of the sheet 102 passes the sheet detection position and the lever 112 returns to the original posture. 113 opens the optical path between the light emitting unit 114a and the light receiving unit 114b of the photo interrupter 114. Here, if the sheet detection unit 111 cannot detect the arrival of the sheet 102 even after a predetermined time has elapsed from the detection start reference position of the sheet 102, it is assumed that a jam such as the winding of the sheet 102 has occurred in the fixing device 104. To be judged. If the sheet detecting unit 111 cannot detect the passage of the trailing end of the sheet 102 within a predetermined time after the sheet detecting unit 111 detects the leading edge of the sheet 102, it is determined that a jam has occurred in the fixing device 104. (See Patent Document 1).

Note that such a contact-type sheet detection unit 111 can dispose the photo interrupter 114, which is vulnerable to heat, at a position away from the lever 112 (a position away from the heating rotation unit 106, which is a heat source). Compared with the sheet detecting means of the type, the sheet detecting position by the lever 112 can be arranged in the vicinity of the nip N between the heating rotating means 106 and the pressure rotating means 107.
Japanese Patent Laying-Open No. 2005-301165

  However, in the fixing device 104 as shown in FIGS. 6 and 7, the lever 112 of the sheet detecting unit 111 is tilted by the leading end of the sheet 102 fed from the nip N of the heating rotating unit 106 and the pressure rotating unit 107. After that (after turning to the dotted line position in FIG. 6), the leading end comes into sliding contact with the back surface 102b of the sheet 102. At this time, in the case of single-sided printing in which the toner image is printed only on the front surface 102a side of the sheet 102, there is no particular problem. In some cases, the toner image on the back surface 102b side of the sheet 102 is rubbed off at the tip of the lever 112, causing the toner image to be disturbed, resulting in a decrease in print quality.

  Therefore, the present invention provides a fixing device having a simple structure that does not cause a delay in jam detection and can detect jam without deteriorating print quality, and an image forming apparatus including the same. The purpose is to do.

  According to the first aspect of the present invention, (1) the sheet is disposed in the sheet conveyance path on the downstream side in the sheet conveyance direction with respect to the image forming unit capable of transferring the toner image on both surfaces of the sheet, and the sheet is heated while rotating. And (2) a pressure rotating means that is pressed against the heating rotating means and rotates together with the heating rotating means while forming a nip at a contact portion with the heating rotating means, (3) The sheet is heated and pressed in the nip, a toner image is fixed on the sheet, and the sheet on which the toner image is fixed is sent out downstream in the sheet conveying direction by the heating rotating unit and the pressing rotating unit. The present invention relates to a fixing device configured as described above. In the present invention, the heating rotation means and the pressure rotation means are accommodated in a housing. Further, a sheet detection unit that detects whether or not the sheet fed from the nip is moving along the sheet conveyance path is disposed downstream of the nip in the sheet conveyance direction. The sheet detection means includes a swingable lever that protrudes into the sheet conveyance path, and a rotating roller that is rotatably attached to the tip of the lever. In the fixing device of the present invention, when the lever is pushed down by the leading edge of the sheet fed from the nip, the rotating roller rolls on the back surface of the sheet so that the back surface of the sheet does not slide on the lever. The movement of the sheet is guided by contact. In the fixing device of the present invention, when the trailing end of the sheet passes through the rotating roller, the lever returns to the original posture.

  The invention of claim 2 is characterized in that the sheet detecting means in the invention of claim 1 is characterized. That is, in the present invention, the sheet detecting means is attached to (1) the lever and (2) a pivot center portion of the lever so as to be integrally rotatable, and the housing along the pivot center line of the lever. A connecting shaft extending to the outside of the housing, (3) a light shielding plate that is located outside the housing of the connecting shaft and swings integrally with the lever through the connecting shaft, and (4) outside the housing. And a photo interrupter in which the light path between the light emitting part and the light receiving part is blocked or opened by the light shielding plate.

  The invention of claim 3 limits both the configurations of the invention of claim 1 or 2. That is, in the present invention, the length (L1) along the sheet conveying direction from the position where the sheet detecting means detects the leading edge of the sheet to the center position of the nip, and the sheet of the housing from the center position of the nip. The sum (L1 + L2) of the length (L2) along the sheet conveyance direction to the upstream end in the sheet conveyance direction at the entrance is the length (L1 + L2) along the sheet conveyance direction of the smallest size sheet among the sheets ( It is characterized by being smaller than Lx).

  The invention according to claim 4 is an image forming unit that forms a toner image on a sheet, a duplex printing unit that enables printing on both sides of the sheet, and a fixing device according to the invention of claim 1 or 2; The present invention relates to an image forming apparatus.

  According to a fifth aspect of the present invention, an image forming unit that forms a toner image on a sheet, a duplex printing unit that enables printing on both sides of the sheet, and the fixing device according to the third aspect are provided. The present invention relates to an image forming apparatus. According to the present invention, a sheet conveyance path adjacent to the sheet entrance of the fixing device is movably disposed, and the sheet conveyance path adjacent to the sheet entrance is moved to move around the sheet entrance. It is characterized by the fact that the space can be expanded so that the operator's hand can be inserted.

  In the present invention, the sheet detection is not performed directly by a non-contact type sensor such as a heat-sensitive photosensor, but the sheet is detected by bringing the lever of the sheet detection unit into contact with the leading edge of the sheet. Therefore, compared with the case where the sheet detection is performed by the non-contact type sensor, the lever of the sheet detection unit can be disposed in the vicinity of the nip between the heating rotation unit and the pressure rotation unit, and the jam detection is delayed. There is no such thing.

  Further, the present invention can prevent the rotating roller attached to the tip of the lever from rolling and coming into contact with the back of the sheet and rubbing the lever against the back of the sheet. Even when the image is printed, the toner image is not scraped off by the lever, and jam detection can be performed without deteriorating the print quality.

  In addition, the present invention does not directly detect the sheet with a non-contact type sensor such as a photosensor, so that a complicated configuration for protecting the sensor from heat is not required. Therefore, the structure of the fixing device and the image forming apparatus provided with the fixing device can be simplified.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic structural diagram of an image forming apparatus 1 according to an embodiment of the present invention.

(Overall structure of image forming apparatus)
The image forming apparatus 1 shown in FIG. 1 is a sheet feeding unit that feeds sheets (sheet-shaped recording media such as copy sheets and plastic films) 2 having a square shape from a sheet feeding cassette 3 to a sheet conveying path 4 one by one. 5, a sheet conveying unit 6 that conveys the sheet 2 fed by the sheet feeding unit 5 along the sheet conveying path 4, and a registration roller that feeds the sheet 2 conveyed by the sheet conveying unit 6 to the image forming position P. 7, an image forming unit 8 that forms (transfers) a toner image on the sheet 2 fed by the registration roller 7, and a fixing that fixes the toner image transferred to the sheet 2 by the image forming unit 8 on the sheet 2. Apparatus 10, double-sided printing unit 11 that reverses the sheet 2 sent out from fixing apparatus 10 and sends the sheet 2 to registration roller 7 again, and fixing apparatus 10 A sheet discharge unit 13 that discharges the fed sheet 2 onto the sheet discharge tray 12, a sheet discharge tray 12 that can stack the sheet 2 fed out from the sheet discharge unit 13, and an upper portion of the apparatus main body 14. And an image reading unit 15 which is attached to the image reading unit and reads an image of a document or the like. In the image forming apparatus 1 according to the present exemplary embodiment, when a jam (paper jam) occurs in the fixing device 10, in order to easily remove the jammed sheet 2, the upstream side in the sheet conveyance direction adjacent to the fixing device 10. Part of the sheet conveyance path 4 (conveyance guide 16) can be swung so that the space around the sheet entrance 17 of the fixing device 10 can be sufficiently opened, and the operator's hand can It can be inserted in the vicinity of the entrance 17 (see FIG. 2). 1 and 2, the conveyance guide 16 maintains the posture of the solid line position during normal sheet conveyance, and swings to the two-dot chain line position during jam processing of the fixing device 10.

(Fixing device)
Hereinafter, the fixing device 10 according to the present embodiment will be described with reference to FIGS. 1 to 4. FIG. 2 is a structural diagram of the fixing device 10 according to the present embodiment. FIG. 3 is a structural diagram of the sheet detecting means viewed along the Ya direction in FIG. FIG. 4 is a side view of a portion of the sheet detecting means shown in FIG. 3 located outside the housing, and is a view seen along the Yb direction of FIG.

  1 and 2 is housed in a substantially rectangular parallelepiped housing 20 having a space 18 therein so that a heating rotation means 21 and a pressure rotation means (pressure roller) 22 can rotate. ing.

  The heating rotation unit 21 includes a heating roller 23, a fixing roller 24, and an endless fixing belt 25 that is stretched over the heating roller 23 and the fixing roller 24.

  Among these, the heating roller 23 has a coating layer of a resin (for example, a fluororesin) excellent in heat resistance on the surface of a metal cylindrical member such as aluminum (Al) or iron (Fe) excellent in thermal conductivity. A film is formed, and a heater (heat source) 26 for heating the fixing belt 25 is accommodated in the internal space of the metal cylindrical member. Both ends of the heating roller 23 are rotatably supported by bearings (not shown) of the housing 20.

  The fixing roller 24 includes a cored bar and a cylindrical elastic body layer (for example, silicon rubber or a sponge member (for example, foamed silicon rubber)) formed on the outer peripheral surface of the cored bar. ing. Both ends of the fixing roller 24 are rotatably supported by bearings (not shown) of the housing 20 and are rotated by a motor (not shown).

  The fixing belt 25 is formed by forming a silicon rubber film on the outer peripheral surface of an endless belt base material (for example, a thin plate of nickel (Ni) or polyimide resin), and further coating the outer surface of the silicon rubber film with a fluororesin. A layer or film is formed, and the molten toner is difficult to adhere.

  In such a heating rotation means 21, when the fixing roller 24 is rotationally driven by a motor (not shown), the heating roller 23 is rotated by a fixing belt 25 that rotates in the clockwise direction together with the fixing roller 24. Yes.

  The pressure rotating means (pressure roller) 22 is formed by integrally forming a cylindrical elastic body (for example, silicon rubber) on the outer peripheral side of the core metal, and it is difficult for molten toner to adhere to the outer peripheral surface thereof. It has become. Both ends of the pressure rotating means 22 are rotatably supported by bearings (not shown) of the housing 20 and are pressed against the fixing roller 24 via a fixing belt 25 by a spring member (not shown). A nip N is formed at a contact portion with the fixing belt 25 constituting the heating rotation means 21, and a driven rotation (counterclockwise direction) is performed as the fixing roller 24 and the fixing belt 25 rotate (clockwise rotation). To rotate).

  A sheet separating blade 27 as a separating unit is disposed on the downstream side of the nip N between the heating rotating unit 21 and the pressure rotating unit 22 in the sheet conveying direction and in the vicinity of the nip N. The base end 27a of the sheet separating blade 27 is fixed to a blade fixing frame 28 that protrudes into the space 18 inside the housing 20, and the leading end 27b is positioned near the nip, and is attached to the fixing belt 25 and wound up. Is separated from the fixing belt 25.

  A sheet detection unit 30 is disposed downstream of the nip N between the heating rotation unit 21 and the pressure rotation unit 22 in the sheet conveyance direction and downstream of the sheet separation blade 27 in the sheet conveyance direction.

  As shown in FIGS. 2 to 4, the sheet detection unit 30 includes a lever 31 that protrudes into the sheet conveyance path 4 on the downstream side in the sheet conveyance direction with respect to the nip N between the heating rotation unit 21 and the pressure rotation unit 22. A connecting shaft 32 whose one end is fitted to the swinging fulcrum portion of the lever 31 so as to be integrally rotatable, a light shielding plate 33 integrally formed on the other end of the connecting shaft 32, and the light path by the light shielding plate 33. A photo interrupter 34 that is interrupted or released, and a sensor spring 36 that presses the light shielding plate 33 against the stopper 35 of the housing 20 so that the lever 31 is held at the initial position (solid line position in FIG. 2). Yes. The sensor spring 36 shown in FIG. 4 is wound around the shaft end side of the connecting shaft 32 protruding to the outside of the housing 20, one end side supports the lower surface side of the end portion 33a of the light shielding plate 33, and the other end side is the housing. The connecting shaft 32 is always urged to rotate in one direction. The photo interrupter 34 is connected to a controller (CPU) 37 of the image forming apparatus 1, and a signal for blocking and opening an optical path between the light emitting unit 34 a and the light receiving unit 34 b constituting the photo interrupter 34 is transmitted to the image forming apparatus 1. The controller (CPU) 37 is input (see FIG. 1).

  One end side of the connecting shaft 32 of the sheet detecting means 30 is rotatably supported by a bearing portion 38 formed on the housing 20, and the other end side thereof is rotatably supported by a bearing portion 40 formed on the housing 20. (See FIG. 3).

  The lever 31 attached to one end side of the connecting shaft 32 is assembled so that the first lever portion 31a and the second lever portion 31b face each other, and the second lever portion 31b extends from the distal end side of the first lever portion 31a. A roller shaft 41 extending toward the distal end side is positioned so as to be parallel to the connecting shaft 32, and a disk-shaped rotating roller 42 is fitted to the roller shaft 41 so as to freely rotate (see FIG. 3). ). The outer diameter dimension of the rotating roller 42 is larger than the width dimension d of the lever 31, and the lever 31 is tilted so as to be in the horizontal direction in FIG. 2 (parallel to the sheet conveying direction indicated by the arrow). Also, the back surface 2b side of the sheet 2 is in contact with the rotating roller 42, and the back surface 2b of the sheet 2 is dimensioned so as not to slide on the lever 31 (see FIG. 2). Here, the rotating roller 42 is formed of a material (for example, a fluororesin) that at least the surface that contacts the back surface 2b of the sheet 2 is not easily contaminated with toner (toner does not easily adhere). In this embodiment, for example, the angle θ formed by the lever 31 and the sheet conveyance direction is 33 ° and the swing angle α of the lever 31 is 20 °. However, the present invention is not limited to this. An optimal numerical value is selected according to the shape of the conveyance path 4 and the like. In FIG. 3, the rotary roller 42 is disposed at a substantially central portion in the sheet passing width direction of the sheet conveying path 4, but may be a position where the leading edge and the trailing edge of the minimum size sheet can be detected.

  As shown in FIG. 3, the light shielding plate 33 on the other end side of the connecting shaft 32 is exposed to the outside of the housing 20, and is connected to the connecting shaft 32 by the same swing angle α as the swing angle α of the lever 31. And the optical path between the light emitting part 34a and the light receiving part 34b of the photo interrupter 34 attached to the outside of the housing 20 is blocked or opened.

  In the sheet detecting means 30, the rotary roller 42 is formed by forming a fluororesin coating layer or film on the outer peripheral surface of a heat resistant resin (for example, PPS), or entirely formed of a fluororesin. ing. The lever 31, the connecting shaft 32, and the light shielding plate 33 are made of a heat resistant resin (for example, PET). The connecting shaft 32 may be made of metal (for example, SUS), and a resin or metal light shielding plate 33 may be attached to the end of the connecting shaft 32 so as to be integrally rotatable.

  The housing 20 is formed of a heat resistant resin (for example, PET), and a sheet entrance 17 for receiving the sheet 2 conveyed along the sheet conveyance path 4 from the image forming unit 8 side into the internal space 18; A sheet discharge port 43 is formed through which the sheet 2 sent out from the nip N between the heating rotation means 21 and the pressure rotation means 22 is sent to the sheet conveyance path 4 on the downstream side in the sheet conveyance direction (see FIGS. 1 and 2). . The housing 20 has a structure in which heat hardly leaks from other than the sheet entrance 17 and the sheet discharge port 43.

  As shown in FIG. 2, the sheet entrance 17 is arranged so that the opening area gradually decreases from the upstream side in the sheet conveying direction toward the downstream side (the nip N side of the heating rotation unit 21 and the pressure rotation unit 22). An edge-side inclined wall 44 and a lower edge-side guide wall 45 are formed. And the lower edge side guide wall 45 located on the lower side (the back surface 2b side of the sheet 2) of the sheet entrance 17 includes a flange portion 45a protruding from the side wall 20a of the housing 20 toward the upstream side in the sheet conveying direction, and this flange The sheet 2 has an inclined wall portion 45b extending from the end of the portion 45a (the side wall 20a of the housing 20) to the vicinity of the nip N of the heating rotation means 21 and the pressure rotation means 22, and to which unfixed toner is not transferred. The front surface of the sheet 2 is guided to the nip N between the heating rotation means 21 and the pressure rotation means 22. Further, the upper edge side inclined wall 44 of the sheet entrance 17 is largely separated from the lower inclined wall portion 45b of the sheet entrance 17, and the unfixed toner image of the sheet 2 sent out from the image forming unit 8 is transferred. It is devised so that it does not contact the surface 2a.

  As shown in FIG. 2, the sheet 2 fed from the nip N between the heating rotation unit 21 and the pressure rotation unit 22 is placed on the upper edge side and the lower edge side of the sheet discharge port 43 in the sheet conveyance direction from the fixing device 10. Guide walls 46 and 47 are formed to guide the sheet conveying path 4 on the downstream side. These guide walls 46 and 47 are formed so that the opening area gradually decreases from the upstream side in the sheet conveying direction toward the downstream side in the sheet conveying direction. An opening 48 that allows the lever 31 to swing is formed in the guide wall 47 on the lower edge side of the sheet discharge port 43.

  Further, in the fixing device 10 of the present embodiment, the lever 31 of the sheet detection unit 30 is pushed down by the leading end of the sheet 2 fed from the nip N between the heating rotation unit 21 and the pressure rotation unit 22, and the sheet detection unit 30 is moved to the sheet. The heating rotation means 21 and the pressure rotation means from the position where the tip of 2 is detected (the rotation center position of the rotating roller 42 when the light shielding plate 33 blocks the optical path between the light emitting portion 34a and the light receiving portion 34b of the photo interrupter 34). The length along the sheet conveyance direction to the center position of the nip N of 22 is L1, and the upstream position in the sheet conveyance direction of the sheet entrance 17 of the housing 20 from the center position of the nip N of the heating rotation means 21 and the pressure rotation means 22 is L1. When the length along the sheet conveying direction to the side end (upstream side end in the sheet conveying direction of the flange portion 45a of the lower edge guide wall 45) is L2, the lengths of L1 and L2 The lever 31 of the sheet detection means 30, the heating rotation means 21, and the pressure rotation means 22 are set so that (L1 + L2) is smaller than the length (Lx) along the sheet conveyance direction of the minimum size sheet 2 to be printed. The upstream end portion in the sheet conveying direction of the flange portion 45a of the sheet entrance 17 is formed. The upstream end of the sheet entrance 17 in the sheet conveying direction is not limited to the flange 45a of the lower edge guide wall 45. If the flange 45a is not provided, the lower edge side of the sheet entrance 17 of the housing 20 is provided. Side wall 20a. In the present embodiment, the minimum size sheet is usually assumed to be the minimum size postcard of postcards, and the length is 148 mm. The center of the nip N is a position w / 2 from one end of the nip N along the sheet conveyance direction when the length of the nip N along the sheet conveyance direction is a predetermined width (w).

(Jam detection in fixing device)
The sheet detection means 30 in the fixing device 10 of the present embodiment configured as described above is a lever 31 at the front end of the fixed sheet 2 that is fed and moved from the nip N of the heating rotation means 21 and the pressure rotation means 22. Is pushed, and the lever 31 is pushed down (rotated) to a predetermined angle against the spring force of the sensor spring 36 using the connecting shaft 32 as a swinging shaft, and the light shielding plate 33 that rotates integrally with the connecting shaft 32. When the light path between the light emitting part 34a and the light receiving part 34b constituting the photo interrupter 34 is interrupted, an off signal is output to the controller (CPU) 37 of the image forming apparatus 1. Note that after the leading end of the sheet 2 reaches the rotating roller 42 at the leading end of the lever 31, the rotating roller 42 rolls into contact with the back surface 2 b of the sheet 2.

  Then, when the rear end of the sheet 2 passes through the rotating roller 42, the sheet detecting means 30 rotates the lever 31 around the connecting shaft 32 by the spring force of the sensor spring 36 to return to the original standing position (initial position). ), The light shielding plate 33 that rotates integrally with the connecting shaft 32 opens the optical path between the light emitting unit 34 a and the light receiving unit 34 b constituting the photo interrupter 34, and sends an on signal to the controller 37 of the image forming apparatus 1. It is designed to output.

  Here, after the off signal output from the photo interrupter 34 of the sheet detection unit 30 is input to the controller 37 of the image forming apparatus 1, within the time until the sheet trailing edge detection determined according to the sheet size and the sheet conveyance speed. If the on signal is not output from the photo interrupter 34 of the sheet detection unit 30 to the controller 37 of the image forming apparatus 1, the controller 37 of the image forming apparatus 1 determines that a jam has occurred in the fixing device 10, and the controller of the image forming apparatus 1. A control signal for jam processing is output from 37, and the operation of the fixing device 10 and the like is stopped.

  If the registration roller 7 feeds the sheet 2 to the image forming unit 8, the controller 37 of the image forming apparatus 1 sets the reference position for starting the sheet detection in the sheet detection unit 30 of the fixing device 10. A predetermined time has elapsed from the time of operation (when the motor 50 driving the registration roller 7 is operated) (a time determined from the distance in the sheet conveyance direction from the registration roller 7 to the sheet leading edge detection position by the lever 31 and the sheet conveyance speed). Even if the off signal is not output from the photo interrupter 34 to the controller 37 of the image forming apparatus 1, it is determined that a jam has occurred in the fixing device 10, a control signal for jam processing is output, and the fixing device 10 or the like is output. The operation is stopped. Note that the reference position for starting sheet detection is not limited to the above-described aspect, and a position at which a sheet detection sensor (not shown) disposed between the fixing device 10 and the image forming unit 8 detects the leading edge of the sheet. In addition, an optimal position is set on the configuration of the image forming apparatus 1 such as a position where a paper feed sensor (not shown) of the paper feeding unit 5 detects the leading edge of the sheet 2.

(Effect of this embodiment)
The fixing device 10 configured as described above prevents the rotating roller 42 attached to the tip of the lever 31 from rollingly contacting the back surface 2b of the sheet 2 and rubbing the lever 31 against the back surface 2b of the sheet 2. Therefore, even when a toner image is printed on the back surface 2b of the sheet 2 by double-sided printing, the toner image on the back surface 2b of the sheet 2 is not scraped off and is not disturbed, and the print quality is deteriorated. Jam detection can be performed without causing it to occur.

  Further, the fixing device 10 of the present embodiment detects the sheet 2 by bringing the lever 31 and the rotating roller 42 of the sheet detecting unit 30 into contact with the sheet 2, and the photo interrupter 34 that is weak against heat in the sheet detecting unit 30. Since the photo interrupter 34 is arranged outside the housing 20 and shields the heat inside the housing 20 from the heat, the lever 31 of the sheet detecting means 30 is compared with the case where the sheet is detected by a non-contact type sensor. Can be disposed in the vicinity of the nip N between the heating rotation means 21 and the pressure rotation means 22, and there is no delay in jam detection.

  Further, since the fixing device 10 according to the present embodiment does not directly detect the sheet 2 with a non-contact type sensor such as a photosensor, a complicated cooling mechanism or the like for protecting the sensor from heat. No configuration is required. Therefore, according to the present embodiment, the structure of the fixing device 10 and the image forming apparatus 1 including the fixing device 10 can be simplified.

  Further, in the fixing device 10 of the present embodiment, even when printing on the minimum size sheet 2, the rear end of the jammed sheet 2 along the sheet conveyance direction is upstream of the sheet entrance 17 of the housing 20 in the sheet conveyance direction. Since it protrudes from the end portion, it becomes easy to pick the rear end of the sheet 2 jammed by the operator, and the jam handling operation is facilitated.

  As shown in FIG. 1, the fixing device 10 according to the present exemplary embodiment is illustrated as being disposed in the sheet conveyance path 4 extending in the horizontal direction. However, the fixing device 10 is not limited to this, and the vertical direction (direction orthogonal to the horizontal direction) is illustrated. ) May be disposed on the sheet conveyance path extending in the direction of the sheet, or may be disposed on the sheet conveyance path extending in an oblique direction (a direction inclined obliquely with respect to the horizontal direction).

1 is a schematic structural diagram of an image forming apparatus according to an embodiment of the present invention. 1 is a structural diagram of a fixing device according to an embodiment of the present invention. FIG. 3 is a structural diagram of a sheet detection unit viewed along the Ya direction in FIG. 2. FIG. 4 is a side view of a portion of the sheet detection unit shown in FIG. 3 that is located outside the housing, and is a view taken along the Yb direction of FIG. 3. 1 is a structural diagram of a conventional image forming apparatus. FIG. 10 is a diagram illustrating a relationship between a conventional fixing device and a sheet detection unit. FIG. 7 is a plan view of the conventional sheet detection unit shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Sheet, 2a ... Back side, 4 ... Sheet conveyance path, 8 ... Image forming part, 10 ... Fixing device, 11 ... Duplex printing unit, 16 ... Conveyance guide ( Part of sheet conveyance), 17 ... Sheet entrance, 20 ... Housing, 21 ... Heating rotation means, 22 ... Pressure rotation means, 30 ... Sheet detection means, 31 ... Lever, 32 ... Linked Shaft, 33 ... Light-shielding plate, 34 ... Photo interrupter, 34a..Light emitting portion, 34b..Light receiving portion, 42 ... Rotating roller, N..Nip

Claims (5)

A heating rotation unit that is disposed in a sheet conveyance path downstream of the image forming unit capable of transferring a toner image on both sides of the sheet and that heats the sheet while rotating;
A pressure rotating means that is pressed against the heating rotating means and rotates together with the heating rotating means while forming a nip at a contact portion with the heating rotating means,
The sheet is heated and pressed at the nip, a toner image is fixed on the sheet, and the sheet on which the toner image is fixed is sent to the downstream side in the sheet conveying direction by the heating rotation unit and the pressure rotation unit. Fixing device,
The heating rotation means and the pressure rotation means are accommodated in a housing,
Sheet detection means for detecting whether or not the sheet sent out from the nip is moving along the sheet conveyance path is disposed downstream of the nip in the sheet conveyance direction,
The sheet detection means includes a swingable lever that protrudes into the sheet conveyance path, and a rotating roller that is rotatably attached to the tip of the lever.
When the lever is pushed down by the leading edge of the sheet fed from the nip, the rotating roller rolls and contacts the back surface of the sheet to guide the movement of the sheet so that the back surface of the sheet does not slide on the lever. And
When the rear end of the sheet passes through the rotating roller, the lever returns to the original posture.
A fixing device. The sheet detecting means includes: (1) the lever; and (2) a connecting shaft that is attached to the swing center portion of the lever so as to be integrally rotatable, and extends to the outside of the housing along the swing center line of the lever. (3) a light-shielding plate located on the outside of the housing with respect to the connecting shaft and swinging integrally with the lever via the connecting shaft; and (4) located on the outside of the housing, and the light-shielding plate. A light interrupter that blocks or opens an optical path between the light emitting unit and the light receiving unit,
The fixing device according to claim 1. The length (L1) along the sheet conveyance direction from the position where the sheet detection means detects the leading edge of the sheet to the center position of the nip, and the sheet conveyance direction of the sheet entrance of the housing from the center position of the nip The sum (L1 + L2) of the length (L1 + L2) along the sheet conveyance direction to the upstream end is smaller than the length (Lx) along the sheet conveyance direction of the smallest sheet among the sheets.
The fixing device according to claim 1, wherein   An image forming unit that forms a toner image on a sheet, a duplex printing unit that enables printing on both sides of the sheet, and the fixing device according to claim 1 or 2. Image forming apparatus. An image forming unit that forms a toner image on a sheet, a duplex printing unit that enables printing on both sides of the sheet, and the fixing device according to claim 3,
The sheet conveyance path adjacent to the sheet entrance of the fixing device is movably disposed, and the sheet conveyance path adjacent to the sheet entrance is moved so that the space around the sheet entrance is freed by an operator. An image forming apparatus, wherein the image forming apparatus is widened so as to be inserted.

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