Image forming apparatus

Abstract

To provide an image forming apparatus that allows a user to replace a fixing device without impairing operability in taking out the fixing device, in a configuration in which nipping of the fixing device is released in conjunction with a door.SOLUTION: An engagement mechanism has a first engagement part, and a pressurization release mechanism has a first part to be engaged that is engaged with the first engagement part. In a process through which a first opening and closing member is opened from a state where it is closed, an urging force is reduced or released, which is applied to a fixing nip part by the first engagement part located closer to a second opening than the first part to be engaged pressing the first part to be engaged from the side of the second opening. In a state in which the first opening and closing member is closed, the engagement of the first engagement part with the first part to be engaged is released, and the first engagement part is retreated from a path of the first part to be engaged in taking out a fixing unit from the second opening.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, and more particularly to a configuration in which, when a paper jam occurs, pressure applied to a fixing device is released in conjunction with the opening of a door in order to clear the jam. [Background technology]

[0002] Image forming devices such as printers and facsimiles include a fixing device that applies heat and pressure to a toner image formed on a sheet to fix the toner image to the sheet. The fixing device is configured to form a nip portion with a pressure member and a heating unit, and to fix the toner image by applying heat and pressure to the sheet as it passes through the nip portion.

[0003] Patent Document 1 proposes a configuration in which a gear train mechanism releases pressure at the nip portion of the fixing device in conjunction with the opening and closing of a door. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-032833 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the configuration of Patent Document 1, a gear train is installed between the arm member connected to the door and the fixing device, and the fixing device cannot be removed from the image forming apparatus unless the gear is removed. Therefore, there is a concern that it may be difficult to remove the fixing device when servicing the image forming apparatus.

[0006] The present invention has been made in consideration of the current situation, and aims to provide an image forming apparatus in which the nip of the fixing device is released in conjunction with the opening of the door, and in which the fixing device can be replaced without compromising the ease of removal of the fixing device. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention has the following configuration.

[0008] a fixing unit for fixing a toner image formed on a sheet to the sheet, the fixing unit having a heating unit for heating the sheet, a pressure member for pressing against the heating unit to form a fixing nip portion for fixing, a biasing member for applying a biasing force to bring the pressure member and the heating unit into pressure contact, and a pressure release mechanism for reducing or releasing the biasing force applied to the fixing nip portion; and an apparatus main body for detachably housing the fixing unit, the apparatus main body having a first opening / closing member provided so as to be openable and closable relative to a first opening of the apparatus main body, the pressure release mechanism, and an engagement mechanism that engages with the first opening / closing member and is linked to the opening and closing of the first opening / closing member, and a second opening for attaching and detaching the fixing unit, wherein when the first opening / closing member is closed, the biasing member applies the biasing force to the fixing nip portion, and .... an image forming apparatus in which the pressure release mechanism reduces or releases the biasing force applied to the fixing nip portion as the engagement mechanism moves in a process in which an opening / closing member is opened from a closed state; the engagement mechanism has a first engagement portion, and the pressure release mechanism has a first engaged portion that engages with the first engagement portion, and in a process in which the first opening / closing member is opened from a closed state, the first engagement portion that is closer to the second opening side than the first engaged portion presses the first engaged portion from the second opening side to reduce or release the biasing force applied to the fixing nip portion, and when the first opening / closing member is in a closed state, the engagement between the first engagement portion and the first engaged portion is released, and the first engagement portion is retracted from the path of the first engaged portion when the fixing unit is removed from the second opening. Effect of the Invention

[0009] According to the present invention, in a configuration in which the nip of the fixing device is released in conjunction with the opening of the door, it is possible to provide an image forming apparatus in which the fixing device can be replaced without compromising the ease of removal of the fixing device. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus. [Diagram 2] Schematic diagram of fixing device 9 [Diagram 3] Cross-sectional view of the heating unit 10 [Figure 4] FIG. 1 is a schematic diagram showing a pressure release mechanism of a fixing device 9. [Diagram 5] Schematic diagram of the front cam 34, the rear cam 35, and the shaft member 37 [Figure 6] FIG. 2 is an external perspective view of a rear door 20. [Figure 7] FIG. 2 is an explanatory diagram showing the operation of the pressure release mechanism of the fixing device 9 by opening and closing the rear door 20. [Figure 8] FIG. 13 is a perspective view showing an engagement mechanism that engages with a pressure release mechanism of the fixing device in conjunction with the front door. [Figure 9] FIG. 13 is an explanatory diagram showing the operation of the front door 19 and the engagement mechanism on the front side of the image forming apparatus main body. [Figure 10] FIG. 13 is an explanatory diagram showing the operation of the cam engagement member 51 and the pressure release mechanism (when the front door 19 is closed). [Figure 11] FIG. 13 is an explanatory diagram showing the operation of the cam engagement member 51 and the pressure release mechanism (the state in which the cam engagement member 51 and the front cam 34 begin to engage with each other). [Figure 12] FIG. 13 is an explanatory diagram showing the operation of the cam engagement member 51 and the pressure release mechanism (pressure release process) [Figure 13] FIG. 13 is an explanatory diagram showing the operation of the cam engagement member 51 and the pressure release mechanism (front door 19 is in an open state). [Figure 14] FIG. 2 is an explanatory diagram showing how to attach and detach the rear door 20. [Figure 15] FIG. 1 is an explanatory diagram showing a path of attachment and detachment of the fixing device 9 in the first embodiment. [Figure 16] 1 is a perspective view showing the operation of the cam engagement member 61 and the pressure release mechanism; [Figure 17] A top view showing the operation of the cam engagement member 61 and the pressure release mechanism. [Figure 18] FIG. 11 is an explanatory diagram showing a path of attachment and detachment of the fixing device 9 in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Example 1 A first embodiment of the present invention will be described below. FIG. 1 is a cross-sectional view showing the schematic configuration of a monochrome laser printer, which is an example of an image forming apparatus. However, the dimensions, materials, shapes, and relative positions of the components described in the following embodiment should be appropriately changed depending on the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless otherwise specified, the scope of the present invention is not limited thereto. Here, the overall configuration of the image forming apparatus will be described first, followed by the configuration of the fixing device.

[0012] The image forming apparatus 101 shown in FIG. 1 has a sheet feeding section, an image forming section for forming an image on a sheet, a fixing section, a paper discharge reversing section, and a duplex conveying section. The image forming apparatus 101 has a process cartridge 1 that is detachable from the main body of the apparatus. The process cartridge 1 is a process unit for forming a toner image on a sheet using an electrophotographic process, and has a photosensitive drum 2 and a developing section (not shown) and a charging roller and other process means. A scanner unit 3 is disposed vertically above the process cartridge 1, and exposes the photosensitive drum 2 based on an image signal. The photosensitive drum 2 is charged to a predetermined negative potential by a charging roller (not shown). Then, the scanner unit 3 scans the photosensitive drum 2 with a laser beam, forming an electrostatic latent image on the photosensitive drum 2. Then, a developing section (not shown) in the process cartridge 1 attaches toner to the electrostatic latent image on the photosensitive drum 2 to form a toner image.

[0013] The sheet feeding section has a paper feed roller 4 in the image forming apparatus 101 and a paper feed cassette 5 that stores sheets and is detachable from the image forming apparatus 101. The sheets S stored in the paper feed cassette 5 are separated and fed one by one from the paper feed cassette 5 by the paper feed roller 4 that is rotated by the power of a paper feed drive unit (not shown). The fed sheet S is transported to a registration roller pair 7 by a transport roller pair 6, where skew correction is performed, and the sheet S is transported to a transfer section. In the transfer section, a positive bias is applied to a transfer roller 8 by a bias application means (not shown). As a result, the toner image on the photosensitive drum 2 is transferred to the sheet S transported to the transfer section.

[0014] The sheet S onto which the toner image has been transferred is transported to a fixing device (fixing unit) 9 provided downstream in the transport direction as viewed from the transfer section. The fixing device 9 fixes the toner image transferred onto the sheet S onto the sheet, and has a heating unit 10 equipped with a heater, which is a heating means (not shown), and a pressure roller 11, which is a pressure member that is in pressure contact with the heating unit 10 and rotates around a rotation axis. The sheet S onto which the toner image has been formed is sandwiched and transported in a fixing nip portion N formed by the heating unit 10 and the pressure roller 11, and the toner image is fixed onto the surface of the sheet S by applying heat and pressure.

[0015] The sheet S on which the toner image has been fixed is transported from the fixing device 9 to a discharge / reversal section. The discharge / reversal section has a triple roller set including a discharge roller 13, a discharge roller 14, and a reversal roller 15, and a double-sided flapper 12. In the case of single-sided image formation (single-sided printing), the double-sided flapper 12 waits at a position where it guides the sheet S to the discharge nip section formed by the discharge roller 13 and the discharge roller 14, and the sheet S is discharged onto the discharge tray 16 by the discharge roller 13 and the discharge roller 14.

[0016] In the case of double-sided image formation (double-sided printing), the double-sided flapper 12 waits at a position where it guides the sheet S to the inversion nip formed by the discharge roller 13 and the inversion roller 15, and the fixing device 9 conveys the sheet S to the inversion nip. The discharge roller 13 rotates in the reverse direction by a rotation direction switching means (not shown) at the timing when the rear end of the sheet S reaches a predetermined position. As a result, the sheet S passes through the pair of double-sided conveying rollers 17 and the pair of re-feed rollers 18 with the rear end at the front, and is re-sent in an inverted state to the pair of registration rollers. After that, the double-sided flapper 12 waits at a position where it guides the sheet S to the discharge nip formed by the discharge roller 13 and the discharge roller 14. Then, the toner image on the photosensitive drum 2 is transferred to the second side of the sheet S in the same manner as in single-sided printing, and is then fixed by the fixing device 9. The sheet S is then discharged onto the discharge tray 16 by the discharge roller 13 and the discharge roller 14, and double-sided printing is completed. If a sheet jam occurs in the fixing device 9 during sheet transport, the jam can be cleared by opening the front door (first opening / closing member) 19 covering the first opening or the rear door (second opening / closing member) 20 covering the second opening, depending on where the jam occurred.

[0017] Next, the fixing device 9 will be described with reference to Figs. 2 to 4. Fig. 2(a) is a schematic diagram of the fixing device 9 in this embodiment 1, and Fig. 2(b) is a schematic diagram of the fixing device 9 excluding a paper transport guide. The fixing device 9 is detachably housed in the image forming apparatus 101. The fixing device 9 has side plates 21 and 22, an upper stay 23, and a lower stay 24. A pressure roller 11 as a pressure member is rotatably supported by the side plates 21 and 22 via a ball bearing 25 and a bearing 26. The heating unit 10 is attached to the side plates 21 and 22 via a flange member 28. The pressure roller 11 is disposed on the opposite side of the heating unit 10 to form a fixing nip N and sandwich the sheet.

[0018] 3 is a cross-sectional view showing the heating unit. The heating unit 10 mainly has a heater 30, a pressure stay 29, a fixing film 31, and a film guide 32. The fixing film 31 is cylindrical (sleeve-shaped) and flexible, and is fitted onto the outside of the film guide 32. The heater 30, which is a heat source, is fitted and fixed into a recessed groove provided along the longitudinal direction of the film guide 32. The pressure stay 29 has a substantially U-shaped cross-section, is disposed inside the film guide 32, and presses the film guide 32 and heater 30 toward the pressure roller 11 when subjected to a pressure force.

[0019] Fig. 4 is a side view seen from the direction A in Fig. 2, and is a schematic diagram of a pressure mechanism and a pressure release mechanism in the fixing device 9. Fig. 4(a) shows a contact state in which a predetermined pressure is applied by the heating unit 10 being biased against the pressure roller 11, and Fig. 4(b) shows a pressure release state in which the pressure of the heating unit 10 against the pressure roller 11 is reduced (or zero) compared to the contact state. When the pressure spring 33 biases the pressure plate 27, the biasing force is transmitted to the heating unit 10 via the flange member 28, and when the heating unit 10 is biased against the pressure roller 11, a predetermined pressure is applied to the fixing nip N.

[0020] The pressure release mechanism of the fixing device 9 includes a front cam (cam member) 34 that is linked to the opening and closing of the front door 19, and a rear cam 35 that rotates in conjunction with the opening and closing of the rear door 20. The pressure release arm 36 switches the fixing nip N between a pressurized state and a pressure-released state by lifting the pressure plate 27, and a pressure release arm holder 40 that holds the pressure release arm 36. The front cam 34 and the rear cam 35 rotate in conjunction with the front door 19 and the rear door 20 changing from a closed state to an open state, and the fixing device 9 switches from the abutting state shown in FIG. 4(a) to the pressure-released state shown in FIG. 4(b). Note that FIG. 4(b) shows a pressure-released state in which both the front door 19 and the rear door 20 are open and both the front cam 34 and the rear cam 35 have rotated. FIG. 5 is a diagram showing the relationship between the front cam 34, the rear cam 35, and the shaft member 37. As shown in FIG. 5, the front cam 34 and the rear cam 35 are held by the shaft member 37 in such a manner that the hole 35D of the rear cam 35 engages with the shaft portion 34D of the front cam 34. This allows the front cam 34 and the rear cam 35 to rotate independently, and when either the front door 19 or the rear door 20 is open, only the cam corresponding to the open door is rotated. The front cam 34, the rear cam 35, the pressure release arm 36, and the pressure release arm holder 40 are disposed on both longitudinal sides of the fixing device 9, and the front cams 34 disposed on both sides are connected by the shaft member 37. The front cam 34 and the rear cam 35 are provided with cam surfaces for lifting the pressure release arm 36 upward, and the fixing device 9 is put into a pressure release state by rotating. Since the front cam 34 and the rear cam 35 can rotate independently, the pressure release state is achieved if at least one of the front cam 34 and the rear cam 35 is rotating. That is, when at least one of the front door 19 and the rear door 20 is open, the pressure is released. Next, the pressure release linked to the rear door 20 will be described with reference to Fig. 6. Fig. 6 is a perspective view showing the rear door 20, and Fig. 7 is an explanatory diagram showing the operation of the pressure release mechanism of the fixing device 9 by opening and closing the rear door 20, and is a cross-sectional view of the rear cam 35. As shown in Fig. 6, the rear door 20 has a first rear door engaging portion 20A and a second rear door engaging portion 20B at both ends for releasing the pressure of the fixing device 9.This is because, as mentioned above, the rear cams 35 located at both longitudinal ends of the fixing device 9 can rotate independently of each other, and the rear cams 35 on both sides can be rotated by the first rear door engagement portion 20A and the second rear door engagement portion 20B.

[0021] Next, the operation of the pressure release mechanism of the fixing device 9 when the rear door 20 is opened and closed will be described with reference to FIG. 7. FIG. 7(a) shows the rear door 20 in a closed state, and the fixing nip N is in a pressurized state as shown in FIG. 4(a). FIG. 7(b) shows the rear door 20 in an open state, and the fixing nip N is in a depressurized state as shown in FIG. 4(b). When the rear door 20 starts to open, the first rear door engagement portion 20A of the rear door 20 comes into contact with the surface 35G of the rear cam 35. When the rear door 20 is further opened, the second rear door engagement portion 20B provided on the rear door 20 comes into contact with the surface 35F of the rear cam. As a result, the rear cam 35 rotates clockwise in FIG. 7 in conjunction with the rotation of the rear door 20 in the opening direction. Finally, the rotation of the rear cam 35 stops at a position where the arc portion 35B, which is concentric with the rotation axis center of the rear cam 35, comes into contact with the pressure release arm 36 as shown in FIG. 7(b). Here, the second rear door engagement portion 20B and the surface 35F of the rear cam are in contact. When the rear door 20 is moved from the open state to the closed state, the first rear door engagement portion 20A of the rear door 20 abuts against the surface 35E of the rear cam 35, causing the rear cam 35 to rotate counterclockwise, and finally reaching the abutment state shown in FIG. 4(a).

[0022] Next, pressure release linked to the front door 19 will be described with reference to Figs. 8 to 12. Fig. 8 is a perspective view showing an engagement mechanism that engages with the pressure release mechanism of the fixing device 9 in conjunction with the front door 19. The engagement mechanism is a mechanism for applying pressure to and releasing pressure from the fixing nip N in conjunction with the opening and closing of the front door 19. The engagement mechanism includes a front door engagement member 38 that engages with the front door 19, a slide member 50 that is movable in the horizontal direction, and a cam engagement member (swing member) 51 that engages with the front cam 34 to rotate the front cam 34. In this embodiment 1, the cam engagement member 51 is connected to the slide member 50 so as to be rotatable around an axis parallel to the rotation axis of the pressure roller 11. Note that this embodiment is not limited to this configuration, and another member may be rotatably connected between the cam engagement member 51 and the slide member 50.

[0023] The front door engaging member 38 is rotatably held by the slide member 50 and has an elongated hole 38A. A boss 19A extending from the front door 19 in the direction of the rotation axis of the front door 19 engages with the elongated hole 38A. The cam engaging member 51 is rotatably held by the shaft 50A of the slide member 50 and has a first engaging portion 51B provided at the tip side of the U-shaped portion of the cam engaging member 51 for engaging with the guide boss 51A and the front cam 34, and a second engaging portion 51C provided at the rear end side. The front cam 34 has a boss 34C for engaging with the engaging portion 51B and the engaging portion 51C. The guide boss 51A and the boss 34C of the front cam 34 are provided in parallel, and the guide boss 51A engages with a guide groove 52 provided in the image forming apparatus main body. The slide member is held in the image forming apparatus main body by a component (not shown) so as to be horizontally movable.

[0024] Next, the operation of the engagement mechanism linked to the opening and closing operation of the front door 19 will be described with reference to Figs. 9 to 13. Fig. 9 is an explanatory diagram showing the operation of the front door 19 and the engagement mechanism on the front side of the image forming apparatus main body, Fig. 9(a) is a diagram showing the front door 19 in a closed state, Fig. 9(b) is a diagram showing the state where the slide member 50 starts to move horizontally, and Fig. 9(c) is a diagram showing the front door 19 in an open state. When the front door 19 starts to rotate clockwise in Fig. 9(a) around the rotation shaft 19B from the closed state, the boss 19A slides in the elongated hole 38A, and the front door engagement member 38 rotates clockwise around the rotation shaft 38C. At this time, the slide member 50 does not move horizontally. Then, the end surface 38B of the elongated hole 38A comes into contact with the boss 19A of the front door 19, resulting in the state shown in Fig. 9(b). When the front door 19 rotates further, the boss 19A and the end face 38B of the elongated hole 38A move while remaining in contact with each other, and the slide member 50 moves horizontally by a predetermined distance L1, finally moving to the open position shown in FIG.

[0025] FIG. 10 is an explanatory diagram showing the operation of the cam engagement member 51 and the pressure release mechanism. FIG. 10 is a diagram showing the front door 19 in a closed state, and FIG. 11 to FIG. 13 sequentially show the operation of the cam engagement member 51 and the pressure release mechanism in the process of opening the front door 19. As shown in FIG. 10, when the front door 19 is in a closed state, the engagement portion 51B of the cam engagement member 51 is in a position separated from the boss 34C of the front cam 34. When the front door 19 opens, the slide member 50 moves horizontally. Then, the guide boss 51A of the cam engagement member 51 moves along the inclined surface portion 52A of the guide groove 52, and the cam engagement member 51 moves while rotating around the shaft 50A which is the engagement portion with the slide member 50. As a result, the first engagement portion 51B moves upward, and the engagement portion 51B abuts against the first engaged portion 34E1, which is the left surface in the figure of the boss 34C of the front cam 34, from the second opening side, resulting in the state shown in FIG. 11. When the slide member 50 moves further horizontally, the guide boss 51A of the cam engagement member 51 moves along the horizontal portion of the guide groove 52, and the cam engagement member 51 moves horizontally together with the slide member 50. At that time, the engagement portion 51B of the cam engagement member 51 rotates the front cam 34, resulting in the state shown in Fig. 12. When the slide member has finally moved a predetermined distance L1, it reaches the pressure-released state shown in Fig. 13.

[0026] When the front door 19 is moved from the open state to the closed state, the movement of the cam engagement member 51 is the reverse of the movement described above. The second engaged portion 34E2, which is the right surface of the boss 34C of the front cam 34 in the figure, is located closer to the second opening side than the second engaging portion 51C of the cam engagement member 51. In the process in which the front door 19 is moved from the open state to the closed state, the second engaging portion 51C of the cam engagement member 51 pushes the second engaged portion 34E2 of the front cam 34 toward the second opening side, causing the front cam 34 to rotate, and a biasing force is applied to the fixing nip portion N. As shown in FIG. 10, when the front door 19 is in the closed state, the second engaging portion 51C of the cam engagement member 51 and the second engaged portion 34E2 of the front cam 34 are not in contact with each other. Note that when the front door 19 is in the closed state, the cam engagement member 51 may move to a position where the second engaging portion 51C and the boss 34C are in contact with each other. Furthermore, the embodiment in which the boss 34C has the first engaged portion and the second engaged portion has been described, but the first engaged portion and the second engaged portion may each be provided on a separate boss portion.

[0027] Next, the procedure for removing the fixing device 9 will be described. Fig. 14(a) is a perspective view of the image forming apparatus 101 as viewed from the left rear, Fig. 14(b) is an explanatory diagram showing how to remove the rear door 20, Fig. 14(c) is a perspective view of the image forming apparatus 101 with the rear door removed, and Fig. 14(d) is an explanatory diagram showing how to remove the fixing device 9. The rear door 20 is rotatably supported by the rear cover 70 shown in Fig. 14(a), and after removing the fastening screws 80, the rear door 20 and the rear cover 70 are removed together as a unit as shown in Fig. 14(b). This allows access to the fixing device 9 for installation and removal.

[0028] As described above, in FIG. 10 where the front door 19 is in the closed state, the first engaging portion 51B is in a position retracted from the path along which the first engaged portion 34E1 moves when the fixing device 9 is removed from the image forming apparatus 101. Therefore, as shown in FIG. 15, the fixing device 9 can be removed in the X direction. The path along which the first engaged portion 34E1 moves is indicated by P in FIG. 15, which is the path along which the first engaged portion 34E1 moves directly in front as viewed from the second opening side. The user can replace the fixing device 9 without having to release the engagement between the engagement mechanism and the fixing device 9, and the fixing device 9 can be replaced without impairing usability.

[0029] In addition, the pressure release mechanism in this embodiment is independently linked to the front door 19 and the rear door 20. Therefore, regardless of whether the pressure release mechanism linked to the rear door 20 is in a pressurized state or a pressure release state, the fixing device 9 can be attached and detached when the front door 19 is closed. In addition, in this embodiment, the first engaging portion 51B is in a position completely removed from the path of the first engaged portion 34E1 when the fixing device 9 is removed from the image forming device 101. However, it does not have to be in a completely removed position. The first engaging portion 51B can move by the first engaged portion 34E1 pushing the first engaging portion 51B due to the clearance of the engaging portion between the parts constituting the engaging mechanism. In other words, the first engaging portion 51B may be configured to be removed from the path of the first engaged portion 34E1 by the first engaged portion 34E1 pushing the first engaging portion 51B when the fixing device 9 is removed from the image forming device 101.

[0030] In this embodiment, the engagement mechanism that engages with the fixing device 9 in conjunction with the front door 19 has been described as being composed of three parts: the front door engagement member 38, the slide member 50, and the cam engagement member 51. However, the engagement mechanism may be composed of a number of parts other than three. Thus, unless otherwise specified, the functions, materials, shapes, and arrangements of the components described in the above embodiment do not limit the present invention to these, and may be modified as appropriate within the spirit and scope of the present invention.

[0031] Example 2 Next, a second embodiment of the present invention will be described with reference to Figures 16 and 17. The same or corresponding parts as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. The engagement mechanism in this embodiment is composed of a front door engagement member 38 that connects with the front door 19, a slide member 60 that is movable in the horizontal direction, and a cam engagement member 61 that engages with the front cam 34 to rotate the front cam 34.

[0032] In this second embodiment, the cam engagement member 61 is rotatably connected to the shaft 60A of the slide member 60. That is, the cam engagement member 61 is rotatably connected to the slide member 60 around an axis perpendicular to the rotation axis of the pressure roller 11. Another member may be rotatably connected between the cam engagement member 61 and the slide member 60. Also, the guide boss 61A has an engagement portion 61B for engaging with the front cam 34. The front cam 34 has an extending boss 34C for engaging with the engagement portion 61B. The guide boss 61A and the boss 34C of the front cam 34 are provided so as to be perpendicular to each other, and the guide boss 61A engages with a guide groove 62 provided in the image forming apparatus main body. The slide member is held in the image forming apparatus main body by a component (not shown) so as to be horizontally movable.

[0033] Fig. 16 is a perspective view showing the operation of the cam engagement member 61 and the pressure release mechanism, and Fig. 17 is a top view seen from above the main body. Figs. 16(a) and 17(a) are views showing the front door 19 in a closed state, Figs. 16(b) and 17(b) are views showing the state in which the cam engagement member 61 and the front cam 34 begin to engage, and Figs. 16(c) and 17(c) are views showing the front door 19 in an open state. As shown in Fig. 16(a), when the front door 19 is in a closed state, the engagement portion 61B of the cam engagement member 61 is in a position spaced apart from the boss 34C of the front cam. When the slide member 60 starts to move horizontally, the cam engagement member 61 moves horizontally, and the guide boss 61A moves along the inclined surface portion 62A of the guide groove 62, so that the cam engagement member 61 moves while rotating around the axis 60A of the slide member 60. As a result, engaging portion 61B moves in a direction approaching fixing device 9 and comes into contact with boss 34C of front cam 34, resulting in the state shown in FIG. 16(b). When slide member 60 further moves horizontally, guide boss 61A of cam engaging member 61 moves along the vertical portion of guide groove 62, and cam engaging member 61 moves horizontally together with slide member 60. At that time, engaging portion 61B of cam engaging member 61 rotates front cam 34. When slide member 60 has finally moved a predetermined distance L1, as in FIG. 9(c) of embodiment 1, it reaches the pressure-released state shown in FIG. 16(c).

[0034] When the front door 19 is moved from the open state to the closed state, the reverse operation to that described above is performed. As described above, when the front door 19 is in the closed state shown in Fig. 16(a) and Fig. 17(a), the engagement mechanism (cam engagement member 61) is in a position retracted from the attachment / detachment path of the front cam 34. Therefore, as shown in Fig. 18, the fixing device 9 is attachable and detachable in the X direction. The user can replace the fixing device 9 without having to release the engagement portion between the engagement mechanism and the fixing device 9, and the fixing device 9 can be replaced without impairing usability.

[0035] In addition, the pressure release mechanism in this embodiment is independently linked to the front door 19 and the rear door 20. Therefore, regardless of whether the pressure release mechanism linked to the rear door 20 is in the abutting state or the pressure release state, the fixing device 9 can be attached and detached when the front door 19 is closed. In this embodiment, the cam engagement member 61 is in a position completely retracted from the attachment / detachment path of the fixing device 9. However, it does not have to be in a completely retracted position. For example, in the process of removing the fixing device 9, the front cam 34 may push the cam engagement member 61 to rotate the cam engagement member 61, thereby retracting the cam engagement member 51 from the attachment / detachment path.

[0036] In this embodiment, the engagement mechanism that engages with the fixing device 9 in conjunction with the front door 19 has been described as being composed of three parts: the front door engagement member 38, the slide member 60, and the cam engagement member 61. However, the engagement mechanism may be composed of a number of parts other than three. Thus, unless otherwise specified, the functions, materials, shapes, and arrangements of the components described in the above embodiment do not limit the present invention to these, and may be modified as appropriate within the spirit of the present embodiment.

[0037] [Note] The above-described embodiment discloses at least the following image forming apparatus.

[0038] (Item 1) a fixing unit for fixing a toner image formed on a sheet to the sheet, the fixing unit including: a heating unit for heating the sheet; a pressure member for pressing against the heating unit to form a fixing nip portion for fixing; a biasing member for applying a biasing force to bring the pressure member and the heating unit into pressure contact; and a pressure release mechanism for reducing or releasing the biasing force applied to the fixing nip portion; an apparatus main body that detachably houses the fixing unit, the apparatus main body having a first opening / closing member that is openable and closable relative to a first opening of the apparatus main body, the pressure release mechanism, and an engagement mechanism that engages with the first opening / closing member and is linked to the opening and closing of the first opening / closing member, and a second opening for attaching and detaching the fixing unit; In an image forming apparatus, when the first opening / closing member is in a closed state, the biasing member applies the biasing force to the fixing nip portion, and when the first opening / closing member is being opened from a closed state, the engagement mechanism moves, and the pressure release mechanism reduces or releases the biasing force applied to the fixing nip portion; the engagement mechanism has a first engagement portion, and the pressure release mechanism has a first engaged portion that engages with the first engagement portion; In the process in which the first opening / closing member is opened from a closed state, the first engaging portion, which is located closer to the second opening than the first engaged portion, presses the first engaged portion from the second opening side, thereby reducing or releasing the biasing force applied to the fixing nip portion; An image forming apparatus characterized in that, when the first opening / closing member is closed, the engagement between the first engaging portion and the first engaged portion is released, and the first engaging portion is retracted from the path of the first engaged portion when the fixing unit is removed from the second opening.

[0039] (Item 2) Item 1. The image forming apparatus according to item 1, The image forming apparatus according to claim 1, wherein the first engaging portion engages with the first engaged portion while the first opening / closing member is being opened.

[0040] (Item 3) 3. The image forming apparatus according to claim 1, The engagement mechanism has a second engagement portion, the pressure release mechanism has a second engaged portion, the second engaged portion is located closer to the second opening than the second engaging portion, An image forming apparatus characterized in that, during the process of closing the first opening / closing member, the second engagement portion engages with the second engaged portion, and the second engagement portion presses the second engaged portion, thereby applying the biasing force to the fixing nip portion.

[0041] (Item 4) 4. The image forming apparatus according to any one of claims 1 to 3, 2. An image forming apparatus, comprising: a first engaging portion disposed on a side of the second opening relative to the second engaging portion;

[0042] (Item 5) 5. The image forming apparatus according to any one of claims 1 to 4, The pressure release mechanism has a rotatable cam member that can adjust the biasing force by acting on the biasing member, and the cam member has the first engaged portion, characterized in that the pressure release mechanism has a rotatable cam member that can adjust the biasing force by acting on the biasing member, and the cam member has the first engaged portion.

[0043] (Item 6) 6. The image forming apparatus according to any one of claims 1 to 5, The pressure member is a pressure roller having a rotation shaft, The engagement mechanism includes a slide member that is held so as to be movable in a horizontal direction in response to opening and closing of the first opening and closing member; a swing member supported by the slide member so as to be rotatable about an axis parallel to a rotation axis of the pressure roller; and the pivotable member has the first engagement portion.

[0044] (Item 7) 6. The image forming apparatus according to any one of claims 1 to 5, The pressure member is a pressure roller having a rotation shaft, The engagement mechanism includes a slide member that is held so as to be movable in a horizontal direction in response to opening and closing of the first opening and closing member; a swing member supported by the slide member so as to be rotatable about an axis perpendicular to the rotation axis of the pressure roller; and the pivotable member has the first engagement portion.

[0045] (Item 8) 8. The image forming apparatus according to any one of claims 1 to 7, The image forming apparatus is characterized in that the device main body has a second opening / closing member for handling jams in the fixing nip portion in a position covering at least a portion of the second opening, and the opening and closing operation of the second opening / closing member is linked to the pressure release mechanism to reduce or release the biasing force applied to the fixing nip portion.

[0046] (Item 9) Item 9. An image forming apparatus according to item 8, An image forming apparatus, wherein the opening and closing operation of the second opening and closing member is not linked to the engagement mechanism. [Explanation of symbols]

[0047] 9 Fixing device 19 Front Door 20 Rear door 34 Front Cam 35 Rear Cam 38 Front door connecting member 50, 60 Slide member 51, 61 Cam engagement member

Claims

1. a fixing unit for fixing a toner image formed on a sheet to the sheet, the fixing unit including: a heating unit for heating the sheet; a pressure member for pressing against the heating unit to form a fixing nip portion for fixing; a biasing member for applying a biasing force to bring the pressure member and the heating unit into pressure contact; and a pressure release mechanism for reducing or releasing the biasing force applied to the fixing nip portion; an apparatus main body for detachably housing the fixing unit, the apparatus main body having a first opening / closing member that is openable and closable relative to a first opening of the apparatus main body, the pressure release mechanism, and an engagement mechanism that engages with the first opening / closing member and is linked to the opening and closing of the first opening / closing member, and a second opening for attaching and detaching the fixing unit; In an image forming apparatus, when the first opening / closing member is in a closed state, the biasing member applies the biasing force to the fixing nip portion, and when the first opening / closing member is being opened from a closed state, the engagement mechanism moves, and the pressure release mechanism reduces or releases the biasing force applied to the fixing nip portion; the engaging mechanism has a first engaging portion, and the pressure release mechanism has a first engaged portion that engages with the first engaging portion; In the process in which the first opening / closing member is opened from a closed state, the first engaging portion, which is located closer to the second opening than the first engaged portion, presses the first engaged portion from the second opening side, thereby reducing or releasing the biasing force applied to the fixing nip portion; An image forming apparatus characterized in that, when the first opening / closing member is closed, the engagement between the first engaging portion and the first engaged portion is released, and the first engaging portion is retracted from the path of the first engaged portion when the fixing unit is removed from the second opening.

2. 2. The image forming apparatus according to claim 1, wherein the first engaging portion engages with the first engaged portion while the first opening / closing member is being opened.

3. The engagement mechanism has a second engagement portion, the pressure release mechanism has a second engaged portion, the second engaged portion is located closer to the second opening than the second engaging portion, 2. The image forming apparatus according to claim 1, wherein, during the process of closing the first opening / closing member, the second engaging portion engages with the second engaged portion, and the second engaging portion presses the second engaged portion, thereby applying the biasing force to the fixing nip portion.

4. 4. The image forming apparatus according to claim 3, wherein the first engaging portion is located closer to the second opening than the second engaging portion.

5. 2. The image forming apparatus according to claim 1, wherein the pressure release mechanism has a rotatable cam member that can adjust the urging force by acting on the urging member, and the cam member has the first engaged portion.

6. The pressure member is a pressure roller having a rotation shaft, The engagement mechanism includes a slide member that is held so as to be movable in a horizontal direction in response to opening and closing of the first opening / closing member; a swing member supported by the slide member so as to be rotatable about an axis parallel to a rotation axis of the pressure roller; 2. The image forming apparatus according to claim 1, wherein the pivotable member has the first engaging portion.

7. The pressure member is a pressure roller having a rotation shaft, The engagement mechanism includes a slide member that is held so as to be movable in a horizontal direction in response to opening and closing of the first opening / closing member; a swing member supported by the slide member so as to be rotatable about an axis perpendicular to the rotation axis of the pressure roller; 2. The image forming apparatus according to claim 1, wherein the pivotable member has the first engaging portion.

8. The image forming apparatus according to claim 1, characterized in that the device main body has a second opening / closing member for handling jams in the fixing nip portion in a position covering at least a portion of the second opening, and the opening and closing operation of the second opening / closing member is linked to the pressure release mechanism to reduce or release the biasing force applied to the fixing nip portion.

9. 9. The image forming apparatus according to claim 8, wherein the opening and closing operation of the second opening and closing member is not linked to the engagement mechanism.

Images