Image forming apparatus

Abstract

It suppresses the decline in jam processing efficiency. [Solution] The image forming apparatus has a fixing device configured to move from a first position to a second position. The fixing device has a contact portion that contacts the sheet at a position between the fixing nip and the transport nip when the sheet jams while straddling the fixing nip and the transport nip, by initiating a movement operation. The biasing portion is configured such that when the biasing force of the biasing portion acts on the sheet straddling the fixing nip and the transport nip via the contact portion, the tension acting on the sheet between the fixing nip and the contact portion due to the component of the biasing force is smaller than the restraining force on the sheet by the fixing nip, and the tension acting on the sheet between the transport nip and the contact portion due to the component of the biasing force is smaller than the restraining force on the sheet by the transport nip.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that forms a toner image on a sheet.

Background Art

[0002] Conventionally, an image forming apparatus has been proposed that includes a pair of arm members rotatably provided in an apparatus main body and a fixing device held at the tip of the arm member (see Patent Document 1). The fixing device is configured to be movable between an internal mounting position and a temporary holding position closer to the opening of the apparatus main body than the internal mounting position by rotating the pair of arm members.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the image forming apparatus described in Patent Document 1, when a sheet jams across the fixing nip of the fixing device and another pair of conveyance rollers, moving the fixing device from the internal mounting position to the temporary holding position causes the sheet to be greatly deformed. Then, jam processing becomes difficult and the jam processing performance deteriorates.

[0005] An object of the present invention is to provide a form of an image forming apparatus capable of suppressing a decrease in jam processing performance.

Means for Solving the Problems

[0006] One aspect of the present invention is an image forming apparatus that forms a toner image on a sheet, including a device body having an opening, an opening / closing member that is supported by the device body so as to be openable and closable between a closed position covering the opening and an open position opening the opening, and a fixing device that is detachably supported by the device body via the opening and fixes the toner image on the sheet by applying heat and pressure to the sheet. The fixing device includes a heating unit that can heat the toner image on the sheet, and a pressure roller that forms a fixing nip for sandwiching the sheet together with the heating unit. The image forming apparatus further includes a pair of conveyance rotators that have a conveyance nip for sandwiching and conveying the sheet and are arranged so as to be able to convey the sheet together with the fixing nip, and a moving unit provided in the device body that can move the fixing device from a first position to a second position different from the first position and has a biasing portion that biases the fixing device from the first position toward the second position. The fixing device is restricted from moving from the first position to the second position when the opening / closing member is in the closed position, and the moving operation of the fixing device by the moving unit is allowed when the opening / closing member is in the open position. When a sheet jams across the fixing nip and the conveyance nip, a contact portion that contacts the sheet at a position between the fixing nip and the conveyance nip is formed by starting the moving operation. The biasing portion is configured such that when the biasing force of the biasing portion acts on the sheet in a state where the sheet straddles the fixing nip and the conveyance nip via the contact portion, the tension acting on the sheet between the fixing nip and the contact portion due to the component force of the biasing force is smaller than the restraining force of the sheet by the fixing nip, and the tension acting on the sheet between the conveyance nip and the contact portion due to the component force of the biasing force is smaller than the restraining force of the sheet by the conveyance nip. This is a feature of the image forming apparatus.

Advantages of the Invention

[0007] According to the present invention, it is possible to suppress a decrease in jam processing performance.

Brief Description of the Drawings

[0008] [Figure 1] A cross-sectional view showing an image forming apparatus according to the first embodiment. [Figure 2] A cross-sectional view showing an image forming apparatus with the door open. [Figure 3] A cross-sectional view showing an image forming apparatus with the fixing device raised to the second position. [Figure 4] A cross-sectional view showing an image forming apparatus with the transfer unit and tray unit pulled out from the opening. [Figure 5] (a) is a perspective view showing the image forming apparatus with the door open, (b) is a perspective view showing the fixing device in the second position, (c) is a perspective view showing the fixing device removed from the moving unit, and (d) is a perspective view showing the image forming apparatus with the cover open. [Figure 6] (a) is a cross-sectional view showing the sheet jammed while straddling the fixing nip and the discharge nip, and (b) is a cross-sectional view showing the fixing device moved to the second position in the state of Figure 6(a). [Figure 7] A cross-sectional view showing the forces acting on the sheet. [Figure 8] (a) is a cross-sectional view showing the fixing device in the first position, (b) is a cross-sectional view showing the case where the fixing device has moved to the second position, and (c) is a cross-sectional view showing the situation when the upward movement of the fixing device is restricted. [Figure 9] (a) is a cross-sectional view showing a fixing device according to the second embodiment, and (b) is a cross-sectional view showing the sheet jammed while straddling the fixing nip and the discharge nip. [Figure 10] A cross-sectional view showing the tip of the partition member in contact with the sheet. [Figure 11] A cross-sectional view showing the forces acting on the sheet. [Modes for carrying out the invention]

[0009] <First Embodiment> [Overall structure] The image forming apparatus 1 according to the first embodiment is an electrophotographic full-color laser beam printer. Figure 1 is a cross-sectional view showing the image forming apparatus 1.

[0010] Furthermore, an image forming apparatus includes printers, copiers, facsimile machines, and multifunction devices, and refers to a device that forms an image on a sheet used as a recording medium based on image information input from an external PC or image information read from a document. In addition to the main unit with image forming function, an image forming apparatus may be connected to auxiliary equipment such as optional feeders, image readers, and sheet processing devices, and the entire system with such auxiliary equipment connected is also a type of image forming apparatus. Furthermore, the sheet includes paper such as paper and envelopes, plastic films such as overhead projector sheets (OHP), cloth, etc.

[0011] As shown in Figure 1, the image forming apparatus 1 includes an apparatus body 1A having an opening 1A1, and a door 20 as an opening / closing member that is supported on the apparatus body 1A so as to be able to open and close between a closed position that covers the opening 1A1 and an open position that opens the opening 1A1. The door 20 is configured to be rotatable about a pivot axis 20b.

[0012] The main body 1A of the device houses an image forming unit 70 for forming an image on a sheet S, a feeding unit 30, a fixing device 80, a pair of discharge rollers 7, and a moving unit 140, which will be described later. The image forming unit 70 has a transfer unit 40, a tray unit 50 positioned above the transfer unit 40, and a scanner 2 positioned above the tray unit 50.

[0013] The tray unit 50 has a tray 51 that can be pulled out from the main unit 1A, and four process cartridges PY, PM, PC, and PK that form toner images of four colors: yellow (Y), magenta (M), cyan (C), and black (K). The four process cartridges PY, PM, PC, and PK are placed on the tray 51. The tray 51 has a tray handle 52 that can be grasped by the user.

[0014] Note that the four process cartridges PY, PM, PC, and PK have the same configuration except for the color of the image they form. Therefore, only the configuration and image formation process of process cartridge PY will be explained, and the explanations of process cartridges PM, PC, and PK will be omitted.

[0015] The process cartridge PY includes a photosensitive drum 61, a charging roller 62, and a developing roller 63. The photosensitive drum 61 is constructed by coating the outer circumference of an aluminum cylinder with an organic photoconductive layer and is rotated by a drive motor (not shown). The rotation axes of the photosensitive drum 61, the developing roller 63, and the charging roller 62 are parallel to each other.

[0016] The transfer unit 40 includes a drive roller 46 and a tension roller 47, and an intermediate transfer belt 41 wrapped around the drive roller 46 and the tension roller 47. Primary transfer rollers 42Y, 42M, 42C, and 42K are provided inside the intermediate transfer belt 41. A secondary transfer roller 45 is provided opposite the drive roller 46, sandwiching the intermediate transfer belt 41. The intermediate transfer belt 41 and the secondary transfer roller 45 form a transfer nip that transfers an image to the conveyed sheet S. The image forming unit 70 is equipped with an optical sensor 44 that detects the toner image transferred to the intermediate transfer belt 41. The rotation axes of the primary transfer rollers 42Y, 42M, 42C, and 42K, the drive roller 46, the tension roller 47, and the secondary transfer roller 45 are parallel to each other.

[0017] The feeding unit 30 is located at the bottom of the image forming apparatus 1 and includes a cassette 31 for loading sheets S and a pickup roller 32 for feeding the sheets S supported by the cassette 31. The cassette 31 is configured to be detachably attached to the apparatus body 1A on the same side as the opening 1A1. An discharge tray 1f is provided at the top of the apparatus body 1A on which the sheets S discharged by the discharge roller pair 7, which are a discharge rotating body pair, are loaded.

[0018] The fixing device 80 includes a pressure roller 81, a heating roller 82, a guide member 5, and a pair of reversing rollers 132. The heating roller 82 has a built-in heater (not shown), and the pressure roller 81 is in contact with the heating roller 82 at a predetermined pressure. These heating roller 82 and pressure roller 81 grip the sheet S and form a fixing nip N1 that fixes the toner image on the sheet S to the sheet by applying heat and pressure to the sheet S. The guide member 5 is configured to be rotatable between an discharge position that guides the sheet S toward the discharge path 1d and a reversing position that guides the sheet S toward the reversing path 1e.

[0019] Next, the image forming operation of the image forming apparatus 1 configured in this way will be described. The image forming apparatus 1 has a control unit 3 that is connected to an external host device 400. Based on the image signals received from the external host device 400 and the reading unit, the control unit 3 controls the scanner 2 to irradiate the photosensitive drum 61 of the process cartridge PY with laser light corresponding to the image signal. The external host device 400 is, for example, a personal computer, an image reader, and a facsimile machine.

[0020] At this time, the surface of the photosensitive drum 61 is uniformly charged to a predetermined polarity and potential by the charging roller 62, and an electrostatic latent image is formed on the surface when laser light is shone from the scanner 2. The electrostatic latent image formed on the photosensitive drum 61 is developed by the developing roller 63, and a yellow (Y) toner image is formed on the photosensitive drum 61.

[0021] The developing roller 63 is configured to be able to contact or separate from the photosensitive drum 61. When the image forming apparatus 1 is not performing an image forming operation, the developing roller 63 can be separated from the photosensitive drum 61, thereby extending the lifespan of both the photosensitive drum 61 and the developing roller 63.

[0022] Similarly, laser light from scanner 2 is shone onto each photosensitive drum of process cartridges PM, PC, and PK, forming magenta (M), cyan (C), and black (K) toner images on each drum. The toner images of each color formed on each drum are transferred to the intermediate transfer belt 41 by primary transfer rollers 42Y, 42M, 42C, and 42K, and transported to the transfer nip by the intermediate transfer belt 41, which is rotated by the drive roller 46. The image formation process for each color is performed at a timing that overlaps with the upstream toner image that has been primary transferred onto the intermediate transfer belt 41. Any remaining toner on the photosensitive drum 61 is removed by the cleaning blade.

[0023] In parallel with this image formation process, the sheet S housed in the cassette 31 of the feeding unit 30 is sent to the transport path 1c by the pickup roller 32. The sheet S is then corrected for skew by the registration roller pair 4 provided on the transport path 1c and transported at a predetermined transport timing in accordance with the image transfer timing at the transfer nip.

[0024] Then, the full-color toner image from the intermediate transfer belt 41 is transferred to the sheet S at the transfer nip by the secondary transfer bias applied to the secondary transfer roller 45. Any remaining toner on the intermediate transfer belt 41 is removed by a cleaning blade 43A provided in the cleaning unit 43. The sheet S, on which the toner image has been transferred, is subjected to predetermined heat and pressure by the heating roller 82 and pressure roller 81 of the fixing device 80, causing the toner to melt and solidify (fix) to the sheet S. After passing through the fixing device 80, the sheet S is guided by the guide member 5 to the discharge path 1d or the reversal path 1e.

[0025] When a single-sided printing job is entered, in which an image is printed on only one side, the guide member 5 is positioned at the discharge position, and the sheet S is guided to the discharge path 1d. The sheet S guided to the discharge path 1d is discharged outside the machine by the discharge roller pair 7 and loaded onto the discharge tray 1f.

[0026] When a double-sided printing job is input to form an image on both sides of a sheet S, the sheet S, on which the image has been formed on the first side by the transfer nip, is guided to the reversal path 1e by a guide member 5 located at the reversal position. The reversal roller pair 132 provided on the reversal path 1e reverses after the rear end of the sheet S has passed the guide member 5, causing the sheet S to switch back. During this time, the guide member 5 moves to the discharge position, and the switched-back sheet S is guided by the guide member 5 to the double-sided transport path 20a.

[0027] The sheet S, guided along the double-sided transport path 20a, is transported to the transport path 1c by multiple transport roller pairs, where an image is formed on the second surface at the transfer nip. After the toner image is fixed by the fuser 80 as described above, the sheet S is discharged to the discharge tray 1f by the discharge roller pair 7.

[0028] [Outline configuration of the mobile unit] Next, the general configuration of the mobile unit 140 will be described using Figure 5(c). Figure 5(c) is a perspective view showing the mobile unit 140 with the fixing device 80 removed. The mobile unit 140 is positioned between a right-side plate and a left-side plate (not shown) that constitute part of the main body 1A of the device, and as shown in Figure 5(c), it has a support part 91 and a lifting part 100.

[0029] In the following description and drawings, the vertical direction when the image forming apparatus 1 is installed on a horizontal surface is defined as the Z-axis direction. The rotation axis direction of the photosensitive drum 61 provided by the image forming apparatus 1 is defined as the Y-axis direction. The direction that intersects both the Z-axis direction and the Y-axis direction is defined as the X-axis direction. The X-axis direction, Y-axis direction, and Z-axis direction are preferably orthogonal to each other. That is, the X-axis direction and the Y-axis direction are in the same direction. In addition, one side of the X-axis direction (the side indicated by the X arrow) may be called the X direction, and the other side of the X-axis direction may be called the -X direction. Similarly, one side of the Y-axis direction (the side indicated by the Y arrow) may be called the Y direction, and the other side of the Y-axis direction may be called the -Y direction, and one side of the Z-axis direction (the side indicated by the Z arrow) may be called the Z direction, and the other side of the Z-axis direction may be called the -Z direction.

[0030] The X direction can be referred to as the front side of the image forming apparatus 1, and is the direction from which the door 20 opens. Furthermore, using the image forming apparatus 1 as viewed from the front, the Y direction side can be referred to as the right side, and the -Y direction side can be referred to as the left side.

[0031] The lifting unit 100 has an arm unit positioned on one side in the Y-direction parallel to the longitudinal direction of the fixing device 80, and an arm unit positioned on the other side in the Y-direction of the fixing device 80. These two arm units have similar configurations, and below, only the arm unit on one side (right side) of the fixing device 80 in the Y-direction will be described.

[0032] As shown in Figures 2 and 3, the arm unit includes arms 90a, 90b, and 90c, and a biasing member 97 which acts as a biasing part for biasing the arms 90a, 90b, and 90c. The arms 90a, 90b, and 90c constitute a link mechanism. In this embodiment, the biasing member 97 is made of a coil spring, but is not limited to this. For example, the biasing member 97 may be made of other springs such as a leaf spring, or the biasing member 97 may be made of multiple types of springs.

[0033] The support section 91 has a metal frame 91a and a shaft member 91b extending in the Y direction. The metal frame 91a is formed in a substantially U-shape in plan view, and when the metal frame 91a is connected to the shaft member 91b, the entire support section 91 is formed in a rectangular shape. This improves the rigidity of the support section 91. The support section 91 is connected to the lifting section 100 and moves up and down together with the lifting section 100. The support section 91 supports the bottom surface of the fixing device 80. In other words, the support section 91 supports the fixing device 80 so that it can be attached and detached from below.

[0034] When the door 20 is in the closed position, the fixing device 80 is housed inside the image forming apparatus 1, as shown in Figure 1, and is in a first position where it can fix the toner image to the sheet S during the image forming operation. The moving unit 140 can move the fixing device 80 to the second position shown in Figure 3 while supporting the fixing device 80 with the support part 91. Hereafter, the position of the moving unit 140 when the door 20 is in the closed position will be referred to as the storage position, and the position of the moving unit 140 that can support the fixing device 80 in the second position will be referred to as the support position. That is, the moving unit 140 is configured to be able to rise from the storage position (position shown in Figure 1) to the support position (position shown in Figure 3) by the biasing force of the biasing member 97.

[0035] [Movement of the transfer unit and tray unit] Next, the movement of the transfer unit 40 and the tray unit 50 will be explained using Figures 2 to 4. Figure 2 is a cross-sectional view showing the image forming apparatus 1 with the door 20 open. Figure 3 is a cross-sectional view showing the image forming apparatus 1 with the fixing device 80 raised to the second position. Figure 4 is a cross-sectional view showing the image forming apparatus 1 with the transfer unit 40 and the tray unit 50 pulled out from the opening 1A1.

[0036] As shown in Figure 2, when the door 20 is opened, the opening 1A1 of the main body 1A is opened. When the door 20 is moved to the open position, the fixing device 80 is exposed to the outside of the image forming apparatus 1 through the opening 1A1. In particular, as shown in Figures 1 and 2, the door 20 has a side surface 20c that constitutes one side of the image forming apparatus 1 and a top surface 20d that constitutes part of the top surface of the image forming apparatus 1, and is formed in a substantially L-shape overall. That is, when the door 20 is moved to the open position, the space above the fixing device 80 that was covered by the top surface 20d of the door 20 in the closed position is opened. As a result, the fixing device 80 can move upward from the first position to the second position. In other words, when the door 20 is in the closed position, the upward movement (movement) of the fixing device 80 from the first position to the second position is restricted, and when the door 20 is in the open position, the upward movement is permitted. In this embodiment, the fixing device 80 located in the first position does not overlap with the door 20 in the closed position when viewed in the Y direction, as shown in Figures 1 and 2, while the fixing device 80 located in the second position overlaps with the door 20 in the open position, at least in part, when viewed in the Y direction.

[0037] Furthermore, when the door 20 is opened from the closed position to the open position, the opening 1A1 is opened, and the transport path 1c and the double-sided transport path 20a are exposed. This allows for the processing of jammed sheets S in the transport path 1c or the double-sided transport path 20a. The door 20 also rotatably supports the secondary transfer frame 25, which supports the secondary transfer roller 45. By rotating the secondary transfer frame 25 with the door 20 in the open position, the double-sided transport path 20a can be opened wider. In the following, when a sheet S gets stuck and stops in the transport path, it is referred to as jamming, and the operation to clear the jam is referred to as jamming.

[0038] Then, as shown in Figure 3, when the movable unit 140 rises from the storage position to the support position, the fixing device 80 moves to the second position, and the space below the fixing device 80 becomes open. As a result, the transfer unit 40 and the tray unit 50, which are image forming units for forming a toner image on the sheet, become detachable from the main body 1A through the opening 1A1 and the space below the fixing device 80.

[0039] The transfer unit 40 and the tray unit 50 can be attached to and detached from the device body 1A even when the fixing device 80 is attached to the support part 91, as long as the moving unit 140 is raised to the support position. That is, when the fixing device 80 is in the second position, the transfer unit 40 and the tray unit 50 are configured to be attached to and detached from the device body 1A via the opening 1A1. The transfer unit 40 and the tray unit 50 are pulled out in the X direction or mounted in the -X direction relative to the device body 1A.

[0040] As shown in Figure 4, when the transfer unit 40 and tray unit 50 are pulled out from the main body 1A of the apparatus, the process cartridges PY, PM, PC, and PK can be attached to and detached from the tray 51. Therefore, the process cartridges PY, PM, PC, and PK can be replaced. The transfer unit 40 can also be replaced.

[0041] Thus, the fixing unit 80, the transfer unit 40, and the tray unit 50 are all configured to be detachable from the door 20 side of the image forming apparatus 1. Therefore, when attaching or detaching the fixing unit 80, the transfer unit 40, and the tray unit 50, they can be accessed from one side of the image forming apparatus 1, improving usability and saving installation space when setting up the image forming apparatus 1. In addition, the cassette 31 is also configured to be detachable from the main body 1A on the same side as the opening 1A1, thereby improving usability and saving space.

[0042] On the other hand, the fixing device 80 located in the first position overlaps with the movement trajectory when the transfer unit 40 and the tray unit 50 are attached to and detached from the device body 1A. Therefore, the image forming apparatus 1 can be miniaturized. In this embodiment, the transfer unit 40 and the tray unit 50 are configured to be attached to and detached from the device body 1A independently of each other, but they may also be configured to be attached to and detached from the device body 1A as a single unit.

[0043] [Attachment and detachment of the fixing device] Next, the attachment and detachment operation of the fixing device 80 will be explained using Figures 5(a) to 5(d). Figure 5(a) is a perspective view showing the image forming apparatus 1 with the door 20 open. Figure 5(b) is a perspective view showing the fixing device 80 in the second position. Figure 5(d) is a perspective view showing the image forming apparatus 1 with the cover 83 open.

[0044] First, the procedure for removing the fixing device 80 from the support portion 91 of the mobile unit 140 will be described. As shown in Figure 5(a), the user first moves the door 20 from the closed position to the open position. The fixing device 80 is provided with a fixing locking member (not shown), and the fixing locking member engages with a locking portion (not shown) provided on the device body 1A, thereby holding the fixing device 80 in the first position. That is, when the fixing locking member of the fixing device 80 is engaged with the locking portion of the device body 1A, the movement of the mobile unit 140 is restricted from rising from the storage position to the support position. For example, when performing jam processing on the transport path 1c or the double-sided transport path 20a, the user can perform jam processing in the state shown in Figure 5(a).

[0045] As shown in Figures 5(a) and 5(b), restricting members 92 and locking members 93 are provided on both sides of the movable unit 140 in the Y direction, respectively. A release lever 96 is provided on the other side (right side) of the movable unit 140 in the Y direction. These restricting members 92, locking members 93, and release lever 96 are rotatably supported with respect to the shaft member 91b. That is, the restricting members 92, locking members 93, and release lever 96 are each rotatable relative to each other around the shaft member 91b, which is the same axis.

[0046] The restricting member 92 is shaped to cover the locking member 93. The locking member 93 is provided with an engaging claw (not shown) on its side that elastically deforms under a predetermined force. The restricting member 92 is provided with a projection (not shown) that the engaging claw can overcome under a predetermined force. When the engaging claw is engaged with the projection of the restricting member 92, the locking member 93 rotates together with the restricting member 92.

[0047] On the other hand, by rotating the locking member 93, the locking member 93 can rotate relative to the regulating member 92 while releasing the engagement between the engaging claw of the locking member 93 and the projection of the regulating member 92. Furthermore, as shown in Figure 2, a claw portion 93a is provided at the tip of the locking member 93. The fixing device 80 is also provided with a recess 84 into which the claw portion 93a can engage. When the claw portion 93a engages with the recess 84, the upward movement of the fixing device 80 is restricted. In other words, when the claw portion 93a is engaged with the recess 84, the fixing device 80, which is supported by the support portion 91, is restricted from being removed from the support portion 91.

[0048] The locking member 93 is movable between a removal-restricting position in which the claw portion 93a engages with the recess 84 and a removal-permitting position in which the claw portion 93a is separated from the recess 84. That is, in the removal-restricting position, the locking member 93 restricts the removal of the fixing device 80 from the support portion 91, and in the removal-permitting position, it permits the removal of the fixing device 80 from the support portion 91.

[0049] Furthermore, the restricting member 92 is held in an upright position by a restricting spring (not shown). The position in which no external force acts on the restricting member 92 and the restricting member is held in an upright position by the restricting spring is defined as the home position. When the restricting member 92 is in the home position and the engaging claw of the locking member 93 is engaged with the projection of the restricting member 92, the locking member 93 is in the release restricting position.

[0050] The regulating member 92, located in the home position, faces the fixing device 80, which is mounted on the support portion 91, in the X direction, and prevents the fixing device 80 from falling off the support portion 91. More specifically, the regulating member 92, as a regulating portion, prevents the fixing device 80 from falling off the support portion 91 toward the door 20, which is in the open position.

[0051] As shown in Figure 4, when the movable unit 140 is in the support position, the restricting member 92 protrudes above the upper surface 1g of the device body 1A. That is, at least a portion of the restricting member 92 is located above the upper surface 1g of the device body 1A when the movable unit 140 is in the support position. Also, at least a portion of the restricting member 92 is located above the upper end 81a of the pressure roller 81 when the movable unit 140 is in the support position. By configuring the restricting member 92 in this way, even if a strong force is applied to the fixing device 80, it is possible to prevent the fixing device 80 from falling off the support portion 91.

[0052] Furthermore, since the regulating member 92 protrudes above the upper surface 1g of the device body 1A, the user can intuitively recognize the position where the fixing device 80 is to be attached when attaching the fixing device 80 to the support part 91, as will be described later. This improves the ease of attachment and detachment and usability of the fixing device 80.

[0053] The release lever 96 is configured to be rotatable vertically by the user, and by operating the release lever 96, the user can move the aforementioned fixing lock member (not shown) of the fixing device 80. The fixing lock member is movably supported on the frame member of the fixing device 80 between a restricted position and an allowable position, and is biased to the restricted position by a biasing member (not shown).

[0054] The fixing locking member, in the restricted position, engages with the locked portion of the device body 1A, thereby restricting the movement of the fixing device 80 from the first position to the second position, i.e., the upward movement of the moving unit 140. In the permitted position, the fixing locking member releases its engagement with the locked portion, allowing the fixing device 80 to move from the first position to the second position. When the user operates the release lever 96, the fixing locking member moves from the restricted position to the released position.

[0055] As shown in Figures 5(a) and 5(b), when the door 20 is opened from the closed position to the open position and the release lever 96 is operated by the user, the fixing lock member of the fixing device 80 moves from the restricted position to the permitted position, and the upward movement of the movable unit 140 begins. That is, the movable unit 140 rises from the stored position to the supported position due to the biasing force of the biasing member 97, and the fixing device 80 rises from the first position to the second position.

[0056] Next, the user rotates the locking member 93 from the restricted position to the permitted position, as shown in Figure 5(c). This causes the claw portion 93a of the locking member 93 to separate from the recess 84 of the fixing device 80, allowing the fixing device 80 to be removed from the support portion 91.

[0057] In this state, the user can remove the fixing device 80 from the support unit 91 by lifting the pair of gripping parts 85 provided on the upper surface of the fixing device 80. Since the fixing device 80 is simply resting on the metal frame 91a and shaft member 91b of the support unit 91, it can be easily removed from the support unit 91 by simply lifting the fixing device 80.

[0058] Furthermore, when the mobile unit 140 is raised to the support position, the gripping portion 85 is located above the upper surface 1g of the device body 1A. Therefore, the user can easily lift the fixing device 80, improving operability.

[0059] When the fixing device 80 is removed from the support unit 91, the support unit 91 is visible, as shown in Figure 5(c). Furthermore, the metal frame 91a and shaft member 91b of the support unit 91 extend in the Y direction over substantially the entire length of the fixing device 80, allowing the user to intuitively recognize the position where the fixing device 80 will be placed. Moreover, when the fixing device 80 is removed from the support unit 91, the movable unit 140 is held in the support position, so the support unit 91 is located near the opening 9, improving the visibility of the support unit 91.

[0060] For example, when the wear parts of the fixing device 80 reach the end of their lifespan, the fixing device 80 is replaced. When attaching a new fixing device 80 to the support unit 91, the user places their fingers on the gripping part 85 and moves the fixing device 80 from above toward the support unit 91. At this time, if the locking member 93 is in the removal restriction position, the lower surface of the fixing device 80 will come into contact with the locking member 93.

[0061] In this embodiment, the locking member 93 is provided with a tapered surface, and the fixing device 80 presses against this tapered surface, moving the locking member 93 to the removable position. Therefore, even when the locking member 93 is in the removal restriction position, the fixing device 80 can be attached to the support part 91. In this embodiment, the engaging claw of the locking member 93 engages with the projection of the restricting member 92, allowing the locking member 93 to remain in the removal restriction position.

[0062] Subsequently, the user pushes the fixing device 80 or the moving unit 140 downwards, moving the fixing device 80 downwards until its movement is restricted by the locking portion. The fixing device 80 is in the first position when the fixing locking member provided on the fixing device 80 engages with the locking portion of the device body 1A. Therefore, the user can intuitively determine how far down to push the fixing device 80. Then, the user closes the door 20, completing the replacement of the fixing device 80.

[0063] Furthermore, the door 20 may be provided with a pressing rib positioned opposite the locking member 93. This pressing rib presses against the locking member 93 just before the door 20 reaches the closed position. When the door 20 reaches the closed position, the locking member 93 is pressed against the pressing rib, causing it to rotate to the release restriction position, and the fixing device 80 is locked by the locking member 93. As a result, the fixing device 80 is reliably locked to the support portion 91, and the fixing device 80 can be reliably held in the first position when the door 20 is closed.

[0064] Furthermore, consider the case where the door 20 is closed from the open position to the closed position while the mobile unit 140 is in a support position and the fixing device 80 is detached from the support portion 91 of the mobile unit 140. Since the regulating member 92 is supported so as to be rotatable around the shaft member 91b, it is pressed towards the discharge tray 1f by the door 20 while the door 20 is moving from the open position to the closed position. As a result, the regulating member 92 rotates around the shaft member 91b. This prevents damage to the regulating member 92. In addition, the door 20 can move to the closed position even when the fixing device 80 is not mounted on the support portion 91 of the mobile unit 140.

[0065] [Jam removal in the fixing device] Next, a method for clearing jammed sheets S from the fixing device 80 will be explained using Figures 5(b) and 5(d). As shown in Figures 5(b) and 5(d), when removing a sheet S held by the fixing nip N1 of the fixing device 80, the fixing device 80 is raised to the second position using the same procedure as for removing the fixing device 80 described above. Then, the sheet S held by the fixing nip N1 can be pulled out either downwards or upwards and towards the user. When pulling out the sheet S downwards, as shown in Figure 5(b), the user pulls out the sheet S downwards while the fixing device 80 remains on the support 91.

[0066] On the other hand, when pulling the sheet S upward and towards the user, the user first opens the retractable cover 83 provided on the fixing device 80, as shown in Figure 5(d). This allows the user to access the fixing nip N1 of the fixing device 80. When the user pulls the sheet S upward and towards the user, a force acts on the fixing device 80 through the sheet S, upward in the Z direction and towards the user in the X direction.

[0067] However, the fixing device 80 is positioned in the X direction by the restricting member 92, and in the Z direction by the support portion 91 and the claw portion 93a of the locking member 93. As a result, even when jamming the sheet S held by the fixing device 80, the restricting member 92 and the locking member 93 prevent the fixing device 80 from falling from the support portion 91 toward the door 20 which is in the open position. After jamming is complete, the user closes the cover 83, moves the fixing device 80 to the first position, and closes the door 20.

[0068] As mentioned above, when the door 20 is closed, the fixing device 80 is locked by the restricting member 92. Therefore, when jamming the sheet S held in the fixing device 80, it is possible to prevent the restricting member 92 from separating from the fixing device 80. Furthermore, the jamming process can be performed not only when the fixing device 80 is in the second position, but also when it is in the first position. Even in this case, the restricting member 92 and the locking member 93 prevent the fixing device 80 from falling from the support part 91 toward the door 20 in the open position.

[0069] Furthermore, in this embodiment, the fixing device 80 is moved upward by the moving unit 140 and exposed upward from the opening 9. Since the upward movement of the fixing device 80 is performed in an upward direction approximately vertically (Z direction), the travel distance is shorter than, for example, when the fixing device 80 is rotated to move it upward. Therefore, the time required for replacing the fixing device 80 and jamming can be reduced, and the ease of attaching and detaching the fixing device 80 and the ease of jamming can be improved.

[0070] Furthermore, the pair of regulating members 92 are positioned outside the cover 83 of the fixing device 80 in the Y direction. This allows the regulating members 92 to be designed without considering constraints on the sheet S transport path, thereby improving design flexibility. For example, the regulating members 92 can be positioned close to the fixing device 80, thus restricting the positional displacement of the fixing device 80. Also, with the fixing device 80 mounted on the support 91, the opening angle of the cover 83 can be increased, improving workability when removing jammed sheets S from the fixing nip N1. In addition, the regulating members 92 do not interfere with the sheet S that can be pulled by the user, improving jam handling efficiency.

[0071] [The fixing device rises during jamming] Next, using Figures 6(a) to 8(c), we consider the case where the sheet S jams while straddling the fixing nip N1 and the discharge nip N2 of the discharge roller pair 7, and the fixing device 80 begins to move upward. Figure 6(a) is a cross-sectional view showing the sheet S jammed while straddling the fixing nip N1 and the discharge nip N2 of the discharge roller pair 7, and Figure 6(b) is a cross-sectional view showing the fixing device 80 having moved to the second position in the state shown in Figure 6(a). Figure 7 is a cross-sectional view showing the forces acting on the sheet S. Figure 8(a) is a cross-sectional view showing the fixing device 80 in the first position, Figure 8(b) is a cross-sectional view showing the case where the fixing device 80 has moved to the second position, and Figure 8(c) is a cross-sectional view showing the upward movement of the fixing device 80 being restricted.

[0072] As shown in Figure 6(a), the discharge roller pair 7, which is a conveying rotating body pair provided in the fixing device 80, has a first roller 7a and a second roller 7b, and these first roller 7a and second roller 7b form a discharge nip N2 that grips and conveys the sheet S. The discharge nip N2, as a conveying nip, discharges the sheet S to the outside of the device body 1A and loads it onto the discharge tray 1f. Either the first roller 7a or the second roller 7b is a drive roller driven by a drive motor (not shown), and the other of the first roller 7a or the second roller 7b is a driven roller that rotates in conjunction with the drive roller. In this embodiment, the first roller 7a is the drive roller, and the second roller 7b is a driven roller that presses against the first roller 7b with a predetermined pressure.

[0073] As shown in Figure 6(a), the sheet S may jam while straddling the fixing nip N1 and the discharge nip N2. That is, the discharge roller pair 7 is positioned to transport the sheet S together with the fixing nip N1. In this state, if, for example, the user accidentally raises the fixing device 80 from the first position to the second position, the contact portion 88 of the fixing device 80 will come into contact with the sheet S between the fixing nip N1 and the discharge nip N2. The contact portion 88 may be, for example, part of a transport guide that forms a transport path through which the sheet S passes, or it may be a driven roller that can rotate in accordance with the sheet being transported along the transport path. Furthermore, if the sheet S jams, the drive transmission to the fixing device 80 and the discharge roller pair 7 stops.

[0074] As shown in Figure 6(b), if the fixing device 80 rises from the first position to the second position, the sheet S, which is held between the fixing nip N1 and the discharge nip N2, will be significantly curved. At this time, the sheet S is pulled in the direction of movement of the fixing device 80 by the contact portion 88 of the fixing device 80, and the sheet S slips at at least one of the fixing nip N1 and the discharge nip N2. When the sheet S is significantly curved in this way, the force required to remove the sheet S, that is, the force required to pull out the sheet S during jamming, increases, and the jamming efficiency decreases.

[0075] As shown in FIG. 7, when the sheet S jams across the fixing nip N1 and the discharging nip N2 and the fixing device 80 starts to move upward, various forces act on the sheet S. These forces will be specifically described below. The fixing nip N1 has a restraining force F nip on the sheet S, and the sheet S is stably conveyed by the restraining force F nip . The restraining force F nip of the sheet S by the fixing nip N1 is the product of the friction coefficient (frictional force) μ nip between the heating roller 82 and the pressure roller 81 and the pressing force P nip of the pressure roller 81 against the heating roller 82.

[0076] Similarly, the discharging nip N2 has a restraining force F FD on the sheet S, and the sheet S is stably conveyed by the restraining force F FD . The restraining force F FD of the sheet S by the discharging nip Nl is the product of the friction coefficient (frictional force) μ FD between the first roller 7a and the second roller 7b and the pressing force P FD of the second roller 7b against the first roller 7a. That is, the restraining forces F nip , F FD of the sheet S by the fixing nip N1 and the discharging nip N2 are respectively expressed by the following formulas (1) and (2). F nip = μ nip ·P nip ···(1) F FD = μ FD ·P FD ···(2)

[0077] Further, an urging force of an urging member 97 (see FIG. 3) that urges the fixing device 80 from the first position to the second position acts on the sheet S via the contact portion 88. The urging force of the urging member 97 is shown as an urging force F LU in FIG. 7. That is, the moving direction of the fixing device 80 is the same as the direction of the urging force F LU . Between the fixing nip N1 and the contact portion 88 and between the contact portion 88 and the discharging nip N2, an urging force FLU A tension is exerted due to the component force. Here, the tension acting on the sheet S between the fixing nip N1 and the contact portion 88 is called the first tension TF1, and the tension acting on the sheet S between the contact portion 88 and the discharge nip N2 is called the second tension TF2. The sheet S and biasing force F between the contact portion 88 and the fixing nip N1 LU The angle formed by the angle θ nip , the sheet S and biasing force F between the contact portion 88 and the discharge nip N2 LU The angle formed by the angle θ FD In this case, the first tension TF1 and the second tension TF2 are expressed by the following equations (3) and (4). TF1=F LU · Cosθ nip ...(3) TF2=F LU · Cosθ FD ...(4)

[0078] Then, the first tension TF1 is the restraining force F of the sheet S by the fixing nip N1. nip If it is greater than this, when the fixing device 80 performs an upward movement, the sheet S pulled by the fixing device 80 becomes able to move the fixing nip N1. Also, the second tension TF2 is the restraining force F of the sheet S by the discharge nip N2. FD If the value is greater than the specified value, when the fixing device 80 performs an upward movement, the sheet S pulled by the fixing device 80 becomes able to move the discharge nip N2. In this case, the fixing device 80 becomes able to move from the first position to the second position.

[0079] Conversely, the first tension TF1 is the restraining force F of the sheet S due to the fixing nip N1. nip Smaller than the second tension TF2, and the restraining force F of the sheet S due to the nip N2 is released. FD If the value is smaller than the specified value, the sheet S is restrained by the fixing nip N1 and the discharge nip N2. This restricts the upward movement of the fixing device 80, i.e., its movement from the first position to the second position.

[0080] The pressure applied by the pressure roller 81 to the heating roller 82 is generally set to a pressure of 10 [N / m2] or more in order to fix the toner image to the sheet by applying pressure to the molten, unfixed toner image. On the other hand, from the viewpoint of jam handling when the sheet S is held between the fixing nip N1 and the discharge nip N2, it is desirable to keep the restraining force (clamping pressure) of the sheet S in the fixing nip N1 and the discharge nip N2 as small as possible. Furthermore, in order for the fixing device 80 to perform the upward movement, the biasing force F of the biasing member 97 is LU It needs to be above a specified value.

[0081] Furthermore, in this embodiment, the biasing force F of the biasing member 97 LU And the restraining force F of sheet S due to fixing nip N1 nip And the restraining force F of the sheet S due to the discharge nip N2. FD And are set such that they satisfy the following relationships (5) and (6). TF1=(F LU · Cosθ nip ) < F nip ...(5) TF2=(F LU · Cosθ FD ) < F FD ...(6)

[0082] Furthermore, since the contact portion 88 of the fixing device 80 is in contact with the sheet S between the fixing nip N1 and the discharge nip N2, the biasing force F of the biasing member 97 LU The first tension TF1 and the second tension TF2, due to the component forces, are in opposite directions along the sheet S. Therefore, the first tension TF1 and the restraining force F nip These forces act in opposite directions along sheet S, forming a second tension TF2 and a restraining force F FD These forces act in opposite directions along the sheet S. Therefore, if the above relations (5) and (6) are satisfied, the upward movement of the fixing device 80 is restricted by the sheet S jammed across the fixing nip N1 and the discharge nip N2.

[0083] As shown in Figure 8(a), the transport path between the fixing device 80 located at the first position in this embodiment and the pair of discharge rollers 7 is configured to be relatively linear. Furthermore, in the sheet transport direction, there is no pair of rollers between the fixing nip N1 and the discharge nip N2 for gripping and transporting the sheet. And, as shown in Figure 8(b), if the sheet S jams while straddling the fixing nip N1 and the discharge nip N2, and the fixing device 80 moves to the second position, it is clear that jamming will become difficult.

[0084] In this configuration, as shown in Figure 8(c), when the sheet S jams while straddling the fixing nip N1 and the discharge nip N2, and the upward movement of the fixing device 80 begins, various forces act on the sheet S as shown in Figure 8(c). When the upward movement of the fixing device 80 begins, the contact portion 88 of the fixing device 80 comes into contact with the sheet S. At this time, the forces acting on the sheet S are the same as those described in Figure 7.

[0085] In this case, since this embodiment satisfies the above-described relational equations (5) and (6), even if the user mistakenly performs the upward movement of the fixing device 80 when the sheet S is jammed while straddling the fixing nip N1 and the discharge nip N2, the upward movement is restricted. Therefore, the sheet S is prevented from becoming significantly curved as shown in Figure 8(b), and a decrease in jamming efficiency can be suppressed.

[0086] <Second Embodiment> Next, a second embodiment of the present invention will be described. The second embodiment is configured by adding a partition member 8 to the fixing device 80 of the first embodiment. For this reason, the same configuration as in the first embodiment will be omitted from the illustration or will be described using the same reference numerals in the illustration.

[0087] Figure 9(a) is a cross-sectional view showing the fixing device 180 according to the second embodiment, and Figure 9(b) is a cross-sectional view showing the sheet S jammed while straddling the fixing nip N1 and the discharge nip N2 of the discharge roller pair 7. Figure 10 is a cross-sectional view showing the tip 188 of the partition member 8 in contact with the sheet S. Figure 11 is a cross-sectional view showing the force acting on the sheet S.

[0088] As shown in Figure 9(a), the fixing device 180 according to the second embodiment has a partitioning member 8. The partitioning member 8 partitions the transport space SP through which the sheet S that has passed through the fixing nip N1 passes. Also, as shown in Figure 9(b), when the fixing device 180 is in the first position, the partitioning member 8 is located below the transport space SP and in a position that does not obstruct the transport of the sheet S. The partitioning member 8 extends along the transport space SP and has a tip portion 188 that is closer to the discharge nip N2 than to the fixing nip N1. The tip portion 188, which acts as a contact portion, is located near the discharge nip N2 when the fixing device 180 is in the first position.

[0089] In this configuration, when the sheet S jams while straddling the fixing nip N1 and the discharge nip N2, and the upward movement of the fixing device 180 begins, various forces act on the sheet S as shown in Figure 11. When the upward movement of the fixing device 180 begins, the tip 188 of the partition member 8 comes into contact with the sheet S. At this time, the force acting on the sheet S is the same as that described in Figure 7. That is, between the fixing nip N1 and the tip 188, the biasing force F of the biasing member 97 acts. LU A first tension TF1 resulting from the component force acts on the sheet S. Also, between the tip portion 188 and the discharge nip N2, the biasing force F of the biasing member 97 acts. LU A second tension TF2, resulting from the component force, acts on the sheet S.

[0090] In this case, since this embodiment satisfies the relational equations (5) and (6) described in the first embodiment, even if the user mistakenly performs the upward movement of the fixing device 180 when the sheet S is jammed while straddling the fixing nip N1 and the discharge nip N2, the upward movement is restricted. Therefore, the sheet S is prevented from becoming significantly curved, and the decrease in jam handling efficiency can be suppressed.

[0091] Furthermore, in this embodiment, the tip 188 of the partition member 8 that contacts the sheet S is positioned near the discharge nip N2. Therefore, the upward movement of the fixing device 180 is restricted immediately after the upward movement of the fixing device 180 begins. This is because the contact point of the sheet S that contacts the tip 188 is affected by the biasing force F LU This is because the distance that can be moved in that direction is small. Therefore, the upward movement of the fixing device 180 can be restricted more quickly than in the first embodiment, and a decrease in jam handling performance can be suppressed. In addition, by changing the arrangement of the partition members 8, the degree of freedom in the direction of movement during the upward movement of the fixing device 180 can be improved.

[0092] <Other Embodiments> In all the configurations described above, the example used was a sheet S jammed while straddling the fixing nip N1 and the discharge nip N2, but the system is not limited to this. For example, a pair of conveying rollers having a conveying nip may be provided between the fixing nip N1 and the discharge nip N2. In this case, the discharge nip N2 described above can be replaced with a conveying nip, and the above-described relationships (5) and (6) must be satisfied.

[0093] Furthermore, in all of the embodiments described above, the fixing devices 80, 180 were biased from the first position to the second position by one biasing member 97 of the moving unit 140, but this is not limited to this. For example, multiple biasing members 97 may be provided on the moving unit 140.

[0094] Furthermore, although the mobile unit 140 is provided with a pair of restricting members 92 in all of the embodiments described above, it is not limited to this. For example, the mobile unit 140 may be provided with one restricting member or three or more restricting members.

[0095] Furthermore, although the movable unit 140 is provided with a pair of locking members 93 in all of the embodiments described above, it is not limited to this. For example, the movable unit 140 may be provided with one locking member or three or more locking members.

[0096] Furthermore, in all of the embodiments described above, the detachment of the fixing device 80 from the support portion 91 was suppressed by the restricting member 92 and the locking member 93, but this is not limited to these embodiments. For example, the locking member 93 may be omitted, and the detachment of the fixing device 80 from the support portion 91 may be suppressed by the restricting member 92. Alternatively, the restricting member 92 may be omitted, and the detachment of the fixing device 80 from the support portion 91 may be suppressed by the locking member 93.

[0097] Furthermore, in all of the embodiments described above, the restricting member 92 and the locking member 93 were rotatably supported on the same shaft member 91b, but this is not limited to this. For example, the locking member 93 may be rotatably supported on the restricting member 92.

[0098] Furthermore, in all of the embodiments described above, the second position of the fixing device 80 was above the first position, but this is not limited to this. For example, the fixing device 80 may be moved horizontally from the first position to the second position, or it may be moved diagonally downward.

[0099] Furthermore, in all of the embodiments described above, the lifting unit 100 had a link mechanism composed of multiple arms, but is not limited to this. For example, the lifting unit 100 may have a rack section, and the support section 91 may be raised and lowered by the engagement of the rack section with a pinion gear provided on the support section 91. Alternatively, the support section 91 may be provided with a pinion gear, and the lifting unit 100 may be provided with a rack member. Thus, the configuration of the lifting unit 100 is not limited.

[0100] Furthermore, in all of the embodiments described above, the fixing device 80 has a heating roller 82 and a pressure roller 81, but is not limited thereto. For example, instead of the heating roller 82, a heating unit including a heater such as a ceramic heater and a fixing film heated by the heater may be applied. Alternatively, instead of the heating roller 82, a fixing belt having a heating layer that generates heat by induction heating may be applied.

[0101] Furthermore, in all of the above-described configurations, the photosensitive drum 61, the charging roller 62, and the developing roller 63 were provided on the process cartridge (PY~PK), but are not limited to this. That is, the photosensitive drum 61, the charging roller 62, and the developing roller 63 may be provided on either the process cartridge or the tray 51.

[0102] Furthermore, in all of the embodiments described above, the door 20 is provided so as to be rotatable about the pivot axis 20b, but is not limited to this. For example, instead of the door 20, a cover that is slidable or removable relative to the device body 1A may be provided.

[0103] Summary of this disclosure This disclosure includes at least the following: (Composition 1) In an image forming apparatus that forms a toner image on a sheet, A device body having an opening, An opening / closing member is supported by the main body of the device so as to be able to open and close between a closed position that covers the opening and an open position that opens the opening, A fixing device that is detachably supported to the main body of the device through the aforementioned opening and fixes a toner image to a sheet by applying heat and pressure to the sheet, comprising: a heating unit capable of heating the toner image on the sheet; and a pressure roller that forms a fixing nip that holds the sheet together with the heating unit; A pair of conveying rotating bodies, each having a conveying nip for gripping and transporting a sheet, and arranged so that the sheet can be transported together with the fixing nip, The apparatus body is provided with a movable unit capable of moving the fixing device from a first position to a second position different from the first position, and the movable unit has a biasing part that biases the fixing device from the first position to the second position, The fixing device has a contact portion that contacts the sheet at a position between the fixing nip and the conveying nip when the sheet jams while straddling the fixing nip and the conveying nip, and when the fixing device is in the closed position, the movement of the fixing device by the moving unit is initiated. The biasing portion is configured such that, when the biasing force of the biasing portion acts on a sheet that straddles the fixing nip and the transport nip via the contact portion, the tension acting on the sheet between the fixing nip and the contact portion due to the component of the biasing force is smaller than the restraining force on the sheet by the fixing nip, and the tension acting on the sheet between the transport nip and the contact portion due to the component of the biasing force is smaller than the restraining force on the sheet by the transport nip. An image forming apparatus characterized by the following: (Configuration 2) The aforementioned biasing force is F LU The restraining force of the sheet by the fixing nip is F nip The restraining force of the sheet by the transport nip is F FD , the angle θ between the sheet and the biasing force between the contact portion and the fixing nip nip , the angle θ between the sheet and the biasing force between the contact portion and the transport nip FD When this is the case, the following relationship is satisfied: F LU · Cosθ nip < F nip F LU · Cosθ FD < F FD The image forming apparatus according to configuration 1, characterized in that it is a picture forming apparatus. (Composition 3) The fixing device has a partitioning member that divides the transport space through which the sheet that has passed through the fixing nip passes, The contact portion is the tip of the partition member that is closer to the transport nip than the fixing nip. An image forming apparatus according to configuration 1 or 2, characterized by the above. (Composition 4) The aforementioned pair of conveying rotating bodies is a pair of discharge rollers that discharge the sheet on which the toner image has been fixed by the fixing device to the outside of the device body. An image forming apparatus according to any one of configurations 1 to 3, characterized by the above. (Composition 5) The fixing device located in the first position does not overlap with the opening / closing member located in the closed position when viewed in the longitudinal direction of the fixing device. The fixing device located in the second position overlaps, at least in part, with the opening / closing member located in the closed position when viewed in the longitudinal direction of the fixing device. An image forming apparatus according to any one of configurations 1 to 4, characterized by the above. (Composition 6) The second position is a position above the first position. An image forming apparatus according to any one of configurations 1 to 5, characterized by the above. (Composition 7) The moving unit includes a support portion that detachably supports the fixing device located at the second position, and a restricting portion that prevents the fixing device supported by the support portion from falling off the support portion. An image forming apparatus according to any one of configurations 1 to 6 characterized by the above. (Composition 8) The regulating portion is rotatably supported by the support portion. The image forming apparatus according to configuration 7, characterized by the features described above. (Composition 9) The movable unit is movable between a storage position in which the opening / closing member is located when it is in the closed position and a support position in which it can support the fixing device located in the second position. At least a portion of the regulating portion is located above the upper end of the pressure roller when the moving unit is in the support position. The image forming apparatus according to configuration 7 or 8, characterized by the above. (Composition 10) In the sheet transport direction, no pair of rollers for gripping and transporting the sheet is provided between the fixing nip and the transport nip. An image forming apparatus according to any one of configurations 1 to 9, characterized by the above. (Composition 11) The device further includes an image forming unit for forming a toner image on a sheet, The image forming unit is configured to be detachably attached to the main body of the device via the opening when the fixing device is moved to the second position by the moving unit. An image forming apparatus according to any one of configurations 1 to 10, characterized by the above. [Explanation of Symbols]

[0104] 1: Image forming apparatus / 1A: Apparatus body / 1A1: Opening / 7: Transfer rotating body pair (discharge roller pair) / 8: Partition member / 20: Opening / closing member (door) / 40, 50: Image forming section (transfer unit, tray unit) / 80, 180: Fixing device / 81: Pressure roller / 81a: Upper end / 82: Heating unit (heating roller) / 88, 188: Contact section, tip section / 91: Support section / 92: Regulating section (regulating member) / 97: Biasing section (biasing member) / 140: Moving unit / N1: Fixing nip / N2: Transfer nip (discharge nip) / SP: Transfer space

Claims

1. In an image forming apparatus that forms a toner image on a sheet, A device body having an opening, An opening / closing member is supported by the main body of the device so as to be able to open and close between a closed position that covers the opening and an open position that opens the opening, A fixing device that is detachably supported to the main body of the device through the aforementioned opening and fixes a toner image to a sheet by applying heat and pressure to the sheet, comprising: a heating unit capable of heating the toner image on the sheet; and a pressure roller that forms a fixing nip that holds the sheet together with the heating unit; A pair of conveying rotating bodies, each having a conveying nip for gripping and transporting a sheet, and arranged so that the sheet can be transported together with the fixing nip, The apparatus body is provided with a moving unit capable of moving the fixing device from a first position to a second position different from the first position, and the moving unit has a biasing part that biases the fixing device from the first position to the second position, The fixing device has a contact portion that contacts the sheet at a position between the fixing nip and the conveying nip when the sheet jams while straddling the fixing nip and the conveying nip, and when the fixing device is in the closed position, the movement of the fixing device by the moving unit is initiated. The biasing portion is configured such that, when the biasing force of the biasing portion acts on a sheet that straddles the fixing nip and the transport nip via the contact portion, the tension acting on the sheet between the fixing nip and the contact portion due to the component of the biasing force is smaller than the restraining force on the sheet by the fixing nip, and the tension acting on the sheet between the transport nip and the contact portion due to the component of the biasing force is smaller than the restraining force on the sheet by the transport nip. An image forming apparatus characterized by the following features.

2. The biasing force is F ＬＵ The restraining force of the sheet by the fixing nip is F ｎｉｐ F is the restraining force of the sheet by the transport nip. ＦＤ , the angle θ between the sheet and the biasing force between the contact portion and the fixing nip ｎｉｐ , the angle θ between the sheet and the biasing force between the contact portion and the transport nip ＦＤ When this is the case, the following relationship is satisfied: F ＬＵ ・Cosθ ｎｉｐ < F ｎｉｐ F ＬＵ ・Cosθ ＦＤ < F ＦＤ The image forming apparatus according to feature 1.

3. The fixing device has a partitioning member that divides the transport space through which the sheet that has passed through the fixing nip passes, The contact portion is the tip of the partition member that is closer to the transport nip than the fixing nip. The image forming apparatus according to feature 1.

4. The aforementioned pair of conveying rotating bodies is a pair of discharge rollers that discharge the sheet on which the toner image has been fixed by the fixing device to the outside of the device body. The image forming apparatus according to feature 1.

5. The fixing device located at the first position does not overlap with the opening / closing member located at the closed position when viewed in the longitudinal direction of the fixing device. The fixing device located at the second position overlaps, at least in part, with the opening / closing member located at the closed position when viewed in the longitudinal direction of the fixing device. The image forming apparatus according to feature 1.

6. The second position is a position above the first position. The image forming apparatus according to feature 1.

7. The moving unit includes a support portion that detachably supports the fixing device located at the second position, and a restricting portion that prevents the fixing device supported by the support portion from falling off the support portion. The image forming apparatus according to feature 1.

8. The regulating portion is rotatably supported by the support portion. The image forming apparatus according to feature 7.

9. The movable unit is movable between a storage position in which the opening / closing member is located when it is in the closed position and a support position in which it can support the fixing device located in the second position. At least a portion of the regulating portion is located above the upper end of the pressure roller when the moving unit is in the support position. The image forming apparatus according to feature 7.

10. In the sheet transport direction, no pair of rollers for gripping and transporting the sheet is provided between the fixing nip and the transport nip. The image forming apparatus according to any one of claims 1 to 9.

11. The device further includes an image forming unit for forming a toner image on a sheet, The image forming unit is configured to be detachably attached to the main body of the device via the opening when the fixing device is moved to the second position by the moving unit. The image forming apparatus according to any one of claims 1 to 9.

Images