JP2008145904A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus easily carrying out a jam processing when jamming occurs on an upstream side or downstream side of a paper transporting direction of a fixing device without an increase in manufacturing cost or enlarging of an apparatus main body. <P>SOLUTION: A rocking bearing 51 supporting a pressurizing roller 42 is composed to be rockable against a housing 40. An energizing spring 53 is set to connect a separating/contacting lever 52 revolving along with attaching/detaching of a paper transporting unit 37 and the rocking bearing 51. Then, when the paper transporting unit 37 is attached, the pressurizing roller 42 is brought into a pressurized contact with the fixing roller 41 by a prescribed pressurizing contact force by energizing force of the energizing spring 53. Furthermore, a switching lever 54 which can rock the rocking bearing 51 against the energizing spring 53 is installed in a vicinity of the separating/contacting lever 52. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a facsimile, a copying machine, and a printer using an electrophotographic method, and more particularly, an image forming apparatus having a mechanism for changing a pressure contact force between a pair of rollers provided in a fixing device. It is about.

  Conventionally, copiers, facsimiles, laser printers, and the like are known as image forming apparatuses using an electrophotographic system. In these image forming apparatuses, a photosensitive drum whose surface is uniformly charged is selectively exposed. As a result, an electrostatic latent image is formed, and this electrostatic latent image is developed into a toner image. Then, the toner image is transferred to a sheet, and finally, an unfixed toner is fixed on the sheet by a fixing device so that an image is formed.

  A fixing device used in the image forming apparatus as described above has a heating roller having a built-in heater and a pressure roller that is pressed against the heating roller to form a fixing nip portion, and a toner image is formed in a predetermined transfer region. The transferred sheet is nipped and conveyed by a heating and pressure roller, and the sheet passing through the fixing nip is heated and pressed to fix the unfixed toner image on the sheet.

  In recent years, in addition to plain paper, an image is formed on a special sheet such as a resin sheet such as an OHP film or an envelope, and a heating roller and a pressure roller for fixing such special paper. Since the proper pressure contact force between the two is different from that at the time of fixing the plain paper, various mechanisms having a mechanism capable of switching the pressure contact force between both rollers have been proposed (for example, Patent Documents 1 and 2). Further, in such a device, when a paper jam occurs with the paper being sandwiched between both rollers, a press contact force switching mechanism is used to easily perform jam processing, so that the heating roller and the pressure roller are in contact with each other. It is comprised so that the press-contact of can be cancelled | released.

  However, in the image forming apparatuses described in Patent Documents 1 and 2, when the paper is jammed between both rollers during fixing, if the leading edge of the paper is about several cm downstream of the fixing nip portion, the pressure contact force Jam processing can be easily performed by releasing the pressure contact between the heating roller and the pressure roller using the switching mechanism. However, if the leading edge of the paper has stopped immediately after the fixing nip, There was a problem that became very difficult.

Therefore, various image forming apparatuses that can easily perform jam processing even when the leading edge of the sheet is stopped immediately after the fixing nip portion have been proposed. The cover is configured to have a cover that can be opened and closed on the downstream side in the sheet conveyance direction of the housing of the fixing device on which the heating and pressure rollers are supported. An image forming apparatus that can visually recognize the leading edge of a sheet that can be easily jammed is disclosed.
JP-A-6-337612 JP 2003-186337 A JP-A-2005-55817

  However, in the image forming apparatuses described in Patent Documents 1 to 3, jamming is performed from the downstream side of the fixing device in the paper conveyance direction for a paper jam that occurs after the leading edge of the conveyed paper passes through the fixing nip portion. However, if the leading edge of the paper has stopped inside the fixing device and upstream of the fixing nip portion, for example, the jamming process is performed after the fixing device is removed from the image forming apparatus main body or the fixing device is mounted. Jam processing must be performed by opening and closing the exterior cover of the image forming apparatus.

  Therefore, it is necessary to configure the fixing device to be detachable from the image forming apparatus, or to secure a space in the image forming apparatus where a jam processing operation can be performed. However, when the fixing device is configured to be detachable. However, it is necessary to provide a drawer or the like in the fixing device, which leads to an increase in manufacturing cost. When a jam processing space is secured in the image forming apparatus, there is a problem that the apparatus is increased in size.

  In the present invention, in view of the above-described circumstances, jamming is easily performed when a paper jam occurs upstream and downstream in the sheet conveyance direction of the fixing device without increasing the manufacturing cost and increasing the size of the apparatus main body. An object of the present invention is to provide an image forming apparatus that can perform the above-described process.

  In order to achieve the above-mentioned object, the present invention has a pair of rollers in which at least one roller is provided with a heat source, and a pressure contact force switching capable of switching a pressure contact force between the rollers between a normal pressure state and a low pressure normal state. A fixing device having a mechanism, and a paper transport unit that forms a transport path on the upstream side of the paper transport direction of the fixing device, and is configured to be detachable by being pulled out in a direction opposite to the paper transport direction with respect to the apparatus main body. In the image forming apparatus, the pressing force switching mechanism is configured to release the pressing force between the rollers when the paper transport unit is pulled out from the apparatus main body.

  According to the present invention, in the image forming apparatus configured as described above, the fixing device includes a housing that accommodates the roller pair, and the pressure contact force switching mechanism rotatably supports one of the roller pairs. A swing bearing supported to be swingable with respect to the housing; a contact lever that is rotatably supported with respect to the housing and rotates in accordance with the attachment / detachment of the paper transport unit; An urging spring that urges the oscillating bearing in a direction in which the roller supported by the oscillating bearing is pressed against the other roller. The switching lever is rotatably supported by the housing and can swing the rocking bearing against the biasing force of the biasing spring.

  According to the present invention, in the image forming apparatus configured as described above, the fixing device is supported by the fixing device so as to be rotatable with respect to the housing on the downstream side in the paper conveyance direction, and is configured to be openable and closable in the paper conveyance direction. A cover is provided.

  According to the first configuration of the present invention, when a paper jam occurs in a state where a part of the paper is nipped by the nip portion after the leading edge of the paper has passed through the nip portion of the roller pair, the pressure contact force switching is performed. Jam processing can be easily performed by setting the pressure contact force between the roller pair to a low pressure state using the mechanism. In addition, when the leading edge of the paper is nipped in the nip portion of the roller pair or stops upstream of the nip portion, the pressure contact between the roller pair is automatically released when the paper transport unit is pulled out. When the transport unit is pulled out, the paper is not pulled out together with the paper transport unit and remains inside the fixing device, and the paper is prevented from being damaged inside the main body. By pulling it out, it can be removed from the apparatus main body, and jamming can be easily performed.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, the pressure contact force switching mechanism is configured by a rocking bearing, a separation contact lever, a biasing spring, and a switching lever. Since a power source or the like is not required for force switching, the pressure contact force switching mechanism can be configured easily and at low cost.

  According to the third configuration of the present invention, in the image forming apparatus having the first or second configuration, the jam processing cover is closed by providing the jam processing cover on the downstream side in the sheet transport direction of the fixing device. In this case, the fixing nip formed between the pair of rollers is covered with the jam processing cover, and the user is prevented from accidentally contacting the rollers. When a paper jam occurs in the fixing device, even if the leading edge of the paper is not discharged to the outside of the housing and stops immediately after the fixing nip, the paper is removed by opening the jam processing cover. Therefore, it is possible to easily perform the jam processing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram illustrating the overall configuration of an image forming apparatus according to the present invention, and the right side is illustrated as the front side of the image forming apparatus. 2 is an overall perspective view in the middle of pulling out the paper feed cassette, FIG. 3 is an overall perspective view in which the manual feed tray is opened, FIG. 4 is an overall perspective view in the middle of removing the toner container, and FIG. It is a whole perspective view which shows the state pulled out. Here, in this embodiment, a color laser printer is illustrated as an example of an image forming apparatus, but it goes without saying that the present invention can be applied to a copying machine other than a printer, for example, a copying machine.

  A paper feed cassette 2 for storing a bundle of paper is provided at the lower part of the image forming apparatus main body 1. The paper P stored above the paper feed side (right side in FIG. 1) of the paper feed cassette 2 is provided. Is disposed in order from the uppermost sheet, and further, on the downstream side in the sheet conveying direction, a feed roller 4 is disposed to convey the sheet P fed by the pickup roller 3 further downstream. Yes.

  The sheet feeding cassette 2 is provided with a retard roller 5 so as to be in pressure contact with the feed roller 4. When a plurality of sheets P are simultaneously fed from the pickup roller 3, the feed roller 4 and the retard roller 5 are retarded. By rolling the paper P at the nip portion with the roller 5, double feeding is prevented. The paper feed cassette 2 is configured to be detachable from the apparatus main body 1 and can be removed by being pulled out to the front side of the apparatus main body 1 as shown in FIG.

  A manual feed tray 6 is provided on the front side of the apparatus main body 1 so as to constitute a part of the exterior cover. The manual feed tray 6 is configured such that a lower end portion thereof is rotatably supported by a rotation fulcrum 6a with respect to the apparatus main body 1, and is configured to be able to be opened and closed by rotating about this, as shown in FIG. By opening the manual feed tray 6, paper can be placed on the manual feed tray 6. In the vicinity of the rotation fulcrum 6a, a manual transport path R2 for transporting the paper P placed on the manual feed tray 6 to a paper transport path R1 described later is provided, and along this manual transport path R2. A paper feed roller 7 is disposed.

  A reversing roller 8 is disposed above the feed roller 4 to convey the paper P supplied from the paper feed cassette 2 or the manual feed tray 6 to the rear of the apparatus main body 1. In the apparatus main body 1, a paper conveyance path R1 for conveying the paper P from the reverse roller 8 to the rear of the apparatus main body 1 is provided, and the paper is reversed in order from the upstream in the paper conveyance direction along the paper conveyance path R1. A roller 8, a registration roller pair 9, a secondary transfer roller 10, and a fixing device 11 are arranged.

  An intermediate transfer belt 12 that is an intermediate transfer member is rotatably disposed above the sheet conveyance path R1. The intermediate transfer belt 12 is stretched around a driving roller 13, a driven roller 14, a tension roller 15 and a primary transfer roller 16, and when the driving roller 13 is rotationally driven, a clock as indicated by an arrow A along with the above-described rollers. It is designed to rotate in the direction. A sheet made of dielectric resin is used for the intermediate transfer belt 12, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is preferably used.

  The driving roller 13 abuts on the secondary transfer roller 10 via the intermediate transfer belt 12 to form a secondary transfer area, and downstream of the abutting portion (secondary transfer area) in the rotation direction of the intermediate transfer belt 12. On the side, the cleaning roller 17 is pressed against the intermediate transfer belt 12 so as to face the driving roller 13. Further, the primary transfer roller 16 is in contact with a photosensitive drum 18 which is an image carrier via the intermediate transfer belt 12.

  The photosensitive drum 18 is driven to rotate counterclockwise by a driving device (not shown), and the charging roller 19, which is a contact type charger, the developing unit 20, the primary transfer roller 16, and the cleaning unit 21 are sequentially arranged from above along the rotation direction. Is arranged. The charging roller 19 abuts on the upper portion of the photosensitive drum 18 and rotates following the rotation of the photosensitive drum 18. A toner container 22 that supplies toner to the developing unit 20 is disposed above the cleaning unit 21, and a laser optical unit 23 that uses a known optical system is disposed above the developing unit 20. Yes.

  The toner container 22 disposed in the apparatus main body 1 is configured to be detachable from the apparatus main body 1 in order to facilitate toner replenishment work, and the apparatus main body 1 can be attached and detached. A part of the exterior cover on the front side is an openable / closable cover 24. Then, as shown in FIG. 4, the opening / closing cover 24 is pivoted about the pivot fulcrum 24a and opened to open the portion, and the toner container 22 can be replaced through the opening. It has become.

  Further, in the apparatus main body 1 according to the present invention, the opening formed by opening the opening / closing cover 24 is made larger so that maintenance of the intermediate transfer belt 12 and the like can be performed from this opening. On the front side of the main body 1, almost the entire surface except for the paper feed cassette 2 is an open / close cover 24. For this reason, the above-described manual feed tray 6 is also a part of the opening / closing cover 24. By providing the rotation fulcrum 24a of the opening / closing cover 24 on the axis concentric with the rotation fulcrum 6a of the manual feed tray 6, the manual feed tray 6 is provided. Can be opened and closed together with the opening / closing cover 24. When the opening / closing cover 24 is opened, the manual feed tray 6 is also opened at the same time.

  The developing unit 20 has a substantially cylindrical shape as a whole, and is supported rotatably at both ends thereof. The interior of the developing unit 20 is divided into four rooms by a cross-shaped partition wall, which corresponds to toners of each color of black (K), cyan (C), magenta (M), and yellow (Y). Four developing units 25K, 25C, 25M, and 25Y are configured. In addition, arrangement | positioning of the image development apparatus to illustrate is an example, Comprising: It is not limited to this.

  Each of the developing devices 25K to 25Y includes developing rollers 26, 27, 28, and 29 that are individually driven to rotate. Further, a driving unit (not shown) is connected to the developing unit 20, and by driving the driving unit, the developing unit 20 rotates, and any of the developing rollers 26 to 29 of the developing devices 25K to 25Y. These are selectively arranged to face the photosensitive drum 18 so that the developing operation is performed.

  The downstream end portion of the paper transport path R1 is provided with a paper discharge path R3 for transporting the paper P after image fixing upward and discharging it to the discharge tray 30 so as to be continuous therewith. A transport roller pair 31 is disposed along R3, and a discharge roller pair 32 is disposed at the downstream end of the paper discharge path R3.

  Further, a rear tray 33 is provided on the back side of the apparatus main body 1 so as to constitute a part of the exterior cover. The rear tray 33 is configured such that a lower end portion thereof is rotatably supported by a rotation fulcrum 33a with respect to the apparatus main body 1, and can be opened by rotating the rear tray 33 toward the back side of the apparatus main body 1. When the rear tray 33 is opened, the sheet P from the fixing device 11 is not conveyed to the sheet discharge path R3 but is discharged from the sheet conveyance path R1 to the upper surface of the rear tray 33.

  Further, the transport roller pair 31 and the discharge roller pair 32 also serve as switchback rollers when performing duplex printing, and the upstream end of the paper discharge path R3 is connected to the transport roller pair 31 and the discharge roller R3. A duplex printing conveyance path R4 is provided for conveying the paper P switched back by the discharge roller pair 32 to the secondary transfer region again.

  This duplex printing conveyance path R4 extends from the upstream end of the paper discharge path R3 to the lower side of the apparatus main body 1, changes the paper conveyance direction to the front of the apparatus main body 1 at the upper part of the paper feed cassette 2, and its downstream end is a reverse roller. 8 and upstream of the registration roller pair 9 are formed so as to merge with the sheet conveyance path R1. The fixing device 11 is provided later in order along the double-sided printing conveyance path R4 from the upstream in the sheet conveyance direction. A double-sided conveyance roller 34 and double-sided conveyance roller pairs 35 and 36 constituting a roller pair in contact with one of the discharge roller pair 43 (see FIG. 6) are arranged.

  In the image forming apparatus configured as described above, the paper P transported in the apparatus main body 1 may be jammed in the middle of the paper transport path R1 or the duplex printing transport path R4. Therefore, a portion surrounded by a broken line in FIG. 1 is unitized as a paper transport unit 37 and configured to be able to be pulled out from the apparatus main body 1. By removing the paper transport unit 37, jamming can be easily performed. Can be done.

  Specifically, as shown by a broken line in FIG. 1, a part of the sheet conveyance path R1, and a pickup roller 3, a feed roller 4, a reversing roller 8, a registration roller pair 9 disposed along the sheet conveyance path R1, and The secondary transfer roller 10 and a pair of double-sided conveyance rollers 35 and 36 arranged along the manual conveyance route R2 and the double-sided printing conveyance route R4 are unitized as a paper conveyance unit 37.

  In addition, when paper is fed from the manual feed tray 6, the paper P may be jammed at a position straddling the manual feed tray 6 and the manual feed path R2, so that jam processing in such a case is facilitated. The manual feed tray 6 is also configured to be pulled out integrally with the paper transport unit 37. Further, since the paper P may be jammed at a position straddling the paper feed cassette 2 and the paper transport path R1, when the paper transport unit 37 is pulled out, the paper feed cassette 2 is pulled out at the same time as shown in FIG. It is supposed to be.

  Regarding the image forming operation by the image forming apparatus configured as described above, first, the operation during single-sided printing will be described. When the photosensitive drum 18 is rotationally driven, the charging roller 19 is driven to rotate, and the surface of the photosensitive drum 18 is uniformly charged. Based on the input image signal, the laser optical unit 23 operates to irradiate the charged photosensitive drum 18 with laser light, and an electrostatic latent image is formed on the surface of the photosensitive drum 18. The electrostatic latent image thus formed is developed by the developing unit 20 as described above, and is primarily transferred by the primary transfer roller 16 onto the intermediate transfer belt 12 that rotates clockwise.

  That is, in the case of monochrome image formation, a black toner image is formed on the photosensitive drum 18 by disposing only the developing roller 26 of the developing device 25K so as to face the photosensitive drum 18 on which the electrostatic latent image is formed. The black toner image formed on the photosensitive drum 18 is transferred onto the rotating intermediate transfer belt 12 by the primary transfer roller 16 to form a monochrome image.

  In the case of color image formation, the developing unit 20 is rotated by driving the driving unit, and the developing rollers 26 to 29 of the four developing devices 25K to 25Y are sequentially and selectively arranged to face the photosensitive drum 18. The toner images of the respective colors are formed on the photosensitive drum 18, and the toner images of the respective colors formed on the photosensitive drum 18 are transferred onto the intermediate transfer belt 12 that is sequentially rotated by the primary transfer roller 16, and these are transferred. A color image is formed by superposition. In the case of color image formation, the cleaning roller 17 is separated from the intermediate transfer belt 12 during the primary transfer operation.

  Then, in a predetermined secondary transfer region, intermediate transfer is performed by the secondary transfer roller 10 onto the paper P that is supplied from the paper feed cassette 2 or the manual feed tray 6 and further transported through the paper transport path R1 by the registration roller pair 9. A monochrome image or a color image on the belt 12 is secondarily transferred at once. The sheet P on which the monochrome image or the color image is transferred in this way is conveyed along the sheet conveyance path R1, and the toner image on the sheet P is heated and fixed by the fixing device 11. After fixing, when the rear tray 33 is closed, the paper P is transported from the paper transport path R1 to the paper discharge path R3, and is discharged to the discharge tray 30 by the transport roller pair 31 and the discharge roller pair 32. When 33 is open, it is discharged from the paper transport path R1 onto the rear tray 33.

  The untransferred toner that remains on the photosensitive drum 18 without being primary transferred is removed by the cleaning unit 21, and the untransferred toner that remains on the intermediate transfer belt 12 without being secondary transferred is removed by the cleaning roller 17. Removed. The removed toner is conveyed to a waste bottle (not shown) by a toner collecting device such as a collecting screw.

  Next, the operation during duplex printing will be described. First, an image is formed on the surface of the paper P in the same manner as in the single-side printing described above. Then, the sheet P that has undergone single-sided printing is discharged from the sheet transport path R1 to the discharge tray 30 via the discharge path R3. In the case of double-sided printing, the trailing edge of the sheet P is the discharge path R3. When entering, the rotation direction of the conveyance roller pair 31 and the discharge roller pair 32 is reversed, and the paper P is pulled back into the apparatus main body 1. The pulled-back paper P is not returned to the paper transport path R1, but is transported to the duplex printing transport path R4.

  The sheet P conveyed to the duplex printing conveyance path R4 is conveyed by the discharge roller pair 43 (see FIG. 6) of the fixing device 11 and the duplex conveyance roller 34 and the duplex conveyance roller pairs 35 and 36 constituting the roller pair. After returning to the upstream side of the registration roller pair 9 in the paper conveyance path R1 and forming an image on the remaining back surface in the same manner as in the above-described single-side printing, the paper discharge path 30 passes through the paper conveyance path R1 and the paper discharge path R3. Is discharged.

  Next, the configuration of the fixing device mounted in the image forming apparatus of the present invention will be described with reference to FIGS. FIG. 6 is a side sectional view of the fixing device, and FIG. 7 is a perspective view of the fixing device as viewed from the downstream side in the sheet conveyance direction. FIG. 8 is a perspective view of the fixing device as seen from the downstream side in the paper conveyance direction, as in FIG. 7, and shows a state in which the jam processing cover is opened. FIG. 9 is a side cross-sectional view showing a pressing force switching mechanism provided in the fixing device. 6 to 9 show a state in which the pressure roller is in pressure contact with the fixing roller with a pressure contact force suitable for fixing a plain paper.

  In FIG. 9, the right side is shown as the front side of the fixing device, and for convenience of explanation, a part of the paper transport unit is shown together, and the fixing roller housing and the jam processing cover are excluded. Yes. Furthermore, in FIG. 9, attention is paid only to the pressure contact force switching mechanism disposed on one side surface of the pressure roller housing, and the description of the pressure contact force switching mechanism disposed on the other side surface is omitted. However, the configuration is the same except that both are arranged symmetrically.

  As shown in FIG. 6, the fixing device 11 includes a housing 40, a fixing roller 41 rotatably held in the housing 40, a pressure roller 42, a discharge roller pair 43, and the like. The housing 40 constitutes the main body skeleton of the fixing device 11 and includes a fixing roller housing 40a and a pressure roller housing 40b. The fixing roller housing 40a adds the fixing roller 41 and the pressure roller housing 40b adds. Each of the pressure rollers 42 is covered, and a sheet conveyance path R1 is formed between the fixing roller housing 40a and the pressure roller housing 40b.

  The fixing roller 41 is a so-called hard roller in which a fluororesin coating or a tube is simply coated on a cylindrical metal core made of a metal such as aluminum or iron having excellent heat conductivity. Inside, a heat source such as a halogen heater (not shown) is provided. The pressure roller 42 is a resin in which an elastic layer such as silicon rubber is formed on a cylindrical base material made of synthetic resin, metal or other material, and the surface of the elastic layer is excellent in releasability such as fluororesin. A so-called soft roller covered with is used.

  The fixing roller 41 and the pressure roller 42 are rotatably supported by the housings 40a and 40b so as to be parallel to each other and to intersect at right angles to the transport direction of the paper P. A fixing nip portion N is formed by pressing the pressure roller 42 against the fixing roller 41 with a predetermined pressure. The sheet P conveyed to the fixing nip N is heated and pressed to melt and fix the powdered toner. The sheet P after the fixing is discharged from the housing 40 by the discharge roller pair 43. It is supposed to be discharged.

  Further, the toner image is transferred to the upper surface (the surface that contacts the fixing roller 41) of the conveyed paper P, and the paper P that has passed through the fixing nip N may be wound around the fixing roller 41. Therefore, as shown in FIG. 6, the fixing roller housing 40 a is provided with a separation claw 44 for separating the paper P from the fixing roller 41 on the downstream side of the fixing nip portion N in the paper conveyance direction.

  Further, the housing 40 is provided with a jam processing cover 45 on the downstream side in the paper transport direction. The lower end of the jam handling cover 45 is supported so as to be rotatable with respect to the pressure roller housing 40b, and is opened and closed in the paper transport direction to select the closed position shown in FIG. 7 and the open position shown in FIG. It is configured so that it can be arranged. The discharge roller pair 43 is rotatably supported by the jam processing cover 45, and is positioned downstream of the fixing nip N on the paper transport path R1 when the jam processing cover 45 is in the closed position.

  When the jam cover 45 is in the closed position, as shown in FIG. 7, the fixing nip N formed between the fixing roller 41 and the pressure roller 42 is covered and this is covered. Thus, even when the rear tray 33 is opened, the user is prevented from accidentally coming into contact with the fixing roller 41 or the pressure roller 42. When the rear tray 33 is opened, the jam processing cover 45 can be opened. By opening the jam processing cover 45 as shown in FIG. 8, the fixing nip portion N can be viewed from the back side of the apparatus main body 1.

  Furthermore, the fixing device 11 is provided with a pressure contact force switching mechanism 50. As shown in FIG. 9, the pressure contact force switching mechanism 50 includes a rocking bearing 51, a separation lever 52, a biasing spring 53, a switching lever 54, and the like, and is provided at both end portions of the pressure roller housing 40b. Is provided.

  The rocking bearing 51 rotatably supports the rotating shaft 42a of the pressure roller 42, and the rocking bearing 51 swings with respect to the support portion 55 provided in the pressure roller housing 40b by a hooking portion 51a formed at the front end portion. It is supported movably. In addition, an arm portion 51b is formed on the rear side facing the hooking portion 51a across the portion of the rocking bearing 51 that supports the rotating shaft 42a, and a contact portion 51c is provided at the tip of the arm portion 51b. It has been.

  The separation lever 52 is disposed on the rear side of the pressure roller 42, and is rotatably supported by a fulcrum pin 56 formed in the pressure roller housing 40b, and a lower end portion thereof is for the pressure roller. It protrudes downward from the housing 40b, and a contact portion 52a is provided at the tip. Further, an engaging portion 52b is formed at the upper part of the separation lever 52, and this engaging portion 52b is connected to an engaging hole 51d provided in the vicinity of the abutting portion 51c of the swing bearing 51. A biasing spring 53 is stretched.

  As shown in FIG. 9, in the state where the paper transport unit 37 is mounted on the apparatus main body 1, the rear end portion of the paper transport unit 37 abuts on the abutment portion 52 a of the separable lever 52. The lever 52 is positioned so that the upper edge of the lever 52 abuts on a regulating portion 57 provided in the pressure roller housing 40 b. At this time, the swinging bearing 51 is centered on the support portion 55 by the biasing spring 53. 9, the pressure roller 42 is pressed against the fixing roller 41 with a pressing force suitable for fixing plain paper. In addition, the state in which the pressing force is suitable at the time of fixing the plain paper is referred to as a normal pressure state.

  Further, the switching lever 54 is positioned in the vicinity of the contact portion 51c of the swing bearing 51 in the state where the swing bearing 51 is positioned so that the upper end edge thereof contacts the restriction portion 57 as described above. And is rotatably supported by a fulcrum pin 58 provided in the pressure roller housing 40b. The switching lever 54 is formed with a fan-shaped opening 54b, and a restriction pin 59 provided in the pressure roller housing 40b is engaged with the opening 54b. The rotation is restricted to a predetermined position.

  Hereinafter, with reference to FIGS. 9 to 12, jam processing when a paper jam occurs in the fixing device will be described. 10 to 12 are side cross-sectional views of the fixing device. FIG. 10 illustrates a state in which the pressing force is being switched by the switching lever, FIG. 11 illustrates a state in which the pressing force is reduced, and FIG. 12 illustrates a state in which the pressing is released. ing. 10 to 12, as in FIG. 9, the right side is the front side of the fixing device and a part of the sheet transport unit is shown together, and the fixing roller housing and the jam processing cover are excluded. Furthermore, attention is paid only to the pressure contact force switching mechanism disposed on one side surface of the pressure roller housing, and the description of the pressure contact force switching mechanism disposed on the other side surface is omitted.

  First, a description will be given of a jam processing when a paper jam occurs in a state where a part of the paper is nipped by the fixing nip N after the leading edge of the paper passes through the fixing nip N. In this way, when a paper jam occurs after the leading edge of the sheet has passed through the fixing nip portion N, the switching lever 54 can be opened without opening the jam handling cover 45 if the leading edge of the sheet is discharged to the outside of the housing 40. Is rotated counterclockwise in FIG.

  As a result, as shown in FIG. 10, the protrusion 54 a of the switching lever 54 contacts the contact portion 51 c of the swing bearing 51, and the swing bearing 51 is resisted against the biasing force of the biasing spring 53. 9 so as to swing counterclockwise in FIG. In this way, the rocking bearing 51 is swung counterclockwise about the support portion 55, whereby the pressure roller 42 supported by the rocking bearing 51 moves downward, and the pressure roller 42 The pressure contact force to the fixing roller 41 is reduced.

  After the pressure contact force of the pressure roller 42 is reduced, the leading edge of the paper discharged to the outside of the housing 40 is picked, and the jammed paper is removed by pulling it out to the downstream side in the paper transport direction. As described above, since the pressure contact force of the pressure roller 42 can be switched from the normal pressure state to the low pressure state by the switching lever 54, even when a paper jam occurs in a state where the paper is nipped by the fixing nip portion N. The jam processing can be easily performed by reducing the pressure contact force.

  If the leading edge of the sheet is not discharged to the outside of the housing 40, the jamming cover 45 is opened after the pressure contact force of the pressure roller 42 is reduced by the switching lever 54 as described above. Then, the leading end of the sheet stopped immediately after the fixing nip portion N is picked, and the jammed sheet is removed by drawing it to the downstream side in the sheet conveying direction. Thus, by opening the jam treatment cover 45, even when the leading edge of the sheet is not discharged to the outside of the housing 40 and stops immediately after the fixing nip portion N, the leading edge of the sheet can be visually recognized. Jam processing can be easily performed.

  Further, when the switching lever 54 is further rotated, the projection 54a of the switching lever 54 comes into contact with the upper surface of the contact portion 51c, as shown in FIG. The oscillating bearing 51 urged to be biased so as to rotate counterclockwise. Here, the switching lever 54 is more counter-rotated than the position shown in FIG. The pivoting bearing 51 can be locked at this position when the switching lever 54 is pivoted to the position shown in FIG. 11. The state where the pressure contact force is reduced in this way is referred to as a low pressure state.

  As described above, since the switching lever 54 and the rocking bearing 51 can be locked in a low pressure state, it is not always necessary to hold the switching lever 54 when removing the paper, and the jam handling operation is further facilitated. be able to. In addition, since the low pressure state can be maintained, for example, when forming an image on special paper such as an envelope, the pressure contact force of the pressure roller 42 can be used to form an image, and the fixing nip portion N can be formed. The generation of wrinkles on the passing envelope or the like can be prevented.

  Next, a description will be given of the jam processing when the leading end of the sheet is nipped by the fixing nip portion N or stopped upstream of the fixing nip portion N. In such a case, when the jam processing is performed, the sheet transport unit 37 is pulled out to the front side of the apparatus main body 1 as shown in FIG. As a result, the manual feed path R2, a part of the sheet transport path R1, and the duplex printing transport path R4 can be exposed to the outside of the apparatus body 1, and the paper P jammed in each transport path can be easily removed.

  Here, in a state where the paper transport unit 37 is mounted on the apparatus main body 1, as shown in FIG. 9, the rear end portion of the paper transport unit 37 contacts the contact portion 52 a of the contact lever 52, and the The contact lever 52 is positioned so that the upper edge of the contact lever 52 is in contact with the restricting portion 57. However, when the paper transport unit 37 is pulled out, the paper transport unit 37 does not contact the contact portion 52a. The lever 52 is rotated to the position shown in FIG. 12 by its own weight.

  When the contact lever 52 rotates, the urging force of the urging spring 53 does not act on the oscillating bearing 51. Therefore, the oscillating bearing 51 also has a position shown in FIG. So that the pressure roller 42 supported by the rocking bearing 51 also moves downward so that the pressure contact of the pressure roller 42 to the fixing roller 41 is released. Become.

  That is, when the paper transport unit 37 is pulled out to the front side of the apparatus main body 1, the pressure contact of the pressure roller 42 to the fixing roller 41 is automatically released. As a result, even when a paper jam occurs in the state where the leading edge of the paper is nipped by the fixing nip portion N, when the paper transport unit 37 is pulled out, the paper is not pulled out together with the paper transport unit 37 and remains in the fixing device 11. And the paper is prevented from being damaged inside the apparatus main body 1, and the paper jammed on the upstream side of the fixing nip portion N can be removed by pulling out the paper transport unit 37, and jam processing is performed. Can be easily performed.

  The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, the pressure roller 42 is pressed against the fixing roller 41. However, it may be configured such that the fixing roller 41 is pressed against the pressure roller 42. In the above embodiment, only the fixing roller 41 is provided with a heat source. However, both the fixing roller 41 and the pressure roller 42 may be provided with a heat source.

  INDUSTRIAL APPLICABILITY The present invention can be used in an image forming apparatus such as a facsimile, a copying machine, and a printer using an electrophotographic system, and in particular, an image having a mechanism that changes a pressure contact force between a pair of rollers provided in a fixing device. It can be used for a forming apparatus.

FIG. 1 is a schematic configuration diagram showing an overall configuration of an image forming apparatus according to the present invention. FIG. 4 is an overall perspective view in the middle of pulling out a paper feed cassette. FIG. 3 is an overall perspective view showing a state where a manual feed tray is opened. FIG. 4 is an overall perspective view showing the middle of removing the toner container. FIG. 4 is an overall perspective view showing a state in which the paper transport unit is pulled out. FIG. 3 is a side sectional view showing an internal configuration of the fixing device. FIG. 5 is a perspective view of the fixing device as viewed from the downstream side in the paper conveyance direction. FIG. 10 is a perspective view of the fixing device as seen from the downstream side in the paper conveyance direction, showing a state in which the jam treatment cover is opened. FIG. 3 is a side sectional view showing a pressing force switching mechanism provided in the fixing device. FIG. 3 is a side sectional view of the fixing device showing a state in the middle of switching of the pressing force by the switching lever. FIG. 4 is a side cross-sectional view of the fixing device showing a state in which the pressure contact force is reduced. FIG. 2 is a side cross-sectional view of the fixing device showing a state where pressure contact is released.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Fixing apparatus 33 Rear tray 37 Paper conveyance unit 40 Housing 41 Fixing roller 42 Pressure roller 43 Discharge roller pair 44 Separation claw 45 Jam processing cover 50 Pressing force switching mechanism 51 Swing bearing 52 Separation lever 53 Energizing spring 54 switching lever 55 support portion 56 fulcrum pin 57 restricting portion 58 fulcrum pin 59 restricting pin N fixing nip portion P paper

Claims (3)

A fixing device having a pair of rollers each having at least one roller provided with a heat source, and a pressure contact force switching mechanism capable of switching the pressure contact force between the rollers between a normal pressure state and a low pressure normal state;
An image forming apparatus comprising: a sheet conveyance unit that forms a conveyance path on the upstream side of the sheet conveyance direction of the fixing device, and is configured to be detachable by being pulled out of the apparatus main body in a direction opposite to the sheet conveyance direction.
The image forming apparatus, wherein the pressure contact force switching mechanism is configured to release the pressure contact force between the rollers when the paper transport unit is pulled out from the apparatus main body. The fixing device has a housing that houses the roller pair,
The pressure contact force switching mechanism includes a swing bearing that rotatably supports one of the roller pair and is swingably supported with respect to the housing.
A separation lever supported rotatably with respect to the housing, and rotated according to the attachment and detachment of the paper transport unit;
An urging spring for urging the oscillating bearing in a direction in which the roller supported by the oscillating bearing is pressed against the other roller, and is stretched so as to connect the separating lever and the oscillating bearing; ,
2. A switching lever that is rotatably supported by the housing and is capable of swinging the swing bearing against the biasing force of the biasing spring. The image forming apparatus described in 1.   The jamming cover is provided on the downstream side of the sheet conveying direction so as to be rotatable with respect to the housing and configured to be openable and closable in the sheet conveying direction. The image forming apparatus according to claim 1.

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