Image forming apparatus

Abstract

We provide a new image forming apparatus that builds upon conventional technology. [Solution] An image forming apparatus comprising: a main frame; a fixing unit that heats and fixes a toner image to a sheet while transporting the sheet in a nip section; a shutter that can move between a shielding position that closes the upstream entrance of the nip section and an open position that opens the entrance of the nip section; a cartridge; a rear opening / closing cover; a switching mechanism for switching the state of the fixing unit between a first state in which the pressure in the nip section is a first pressure and a second state in which the pressure is lower than the first pressure or zero; a cover interlocking mechanism that interlocks the switching mechanism with the rear opening / closing cover and is provided at the third end of the main frame; and a shutter interlocking mechanism that interlocks the cartridge attachment / detachment operation with the shutter and is provided at the third end of the main frame.

Description

Technical Field

[0001] The present invention relates to an electrophotographic image forming apparatus.

Background Art

[0002] Patent Document 1 describes an image forming apparatus provided with a link mechanism that releases the pressure applied to a fixing nip portion in conjunction with the opening operation of a door.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a new image forming apparatus that develops on the basis of the conventional technology.

Means for Solving the Problems

[0005] One aspect of the present invention is a fixing unit comprising: a main frame having a first end and a second end opposite to the first end in a first horizontal direction, and a third end and a fourth end opposite to the third end in a second horizontal direction perpendicular to the first direction; a heating unit; and a pressure roller that together with the heating unit forms a nip portion, wherein the fixing unit heats and fixes a toner image to a sheet while conveying the sheet at the nip portion, the fixing unit having a fixing provided on the side of the first end of the main frame in the first direction A unit comprising: a shutter movable between a shielding position that closes the upstream entrance of the nip portion and an open position that opens the entrance of the nip portion in the transport direction in which the nip portion transports a sheet; a photosensitive drum rotatable about a rotation axis extending in the second direction; and a developing roller that develops the toner image on the photosensitive drum by supplying toner to the photosensitive drum; a cartridge that is detachable from the main body frame, the cartridge mounted on the second end side of the main body frame in the first direction; and the main body A rear opening / closing cover rotatably supported with respect to the main frame at the first end of the frame, which rotates between an open position that allows access to the fixing unit from the first end of the main frame and a closed position that prevents access to the fixing unit from the first end of the main frame; a switching mechanism for switching the state of the fixing unit between a first state where the pressure of the nip portion is a first pressure and a second state where the pressure is a second pressure lower than the first pressure or zero; a cover interlocking mechanism that interlocks the switching mechanism with the rear opening / closing cover such that the fixing unit is in the first state when the rear opening / closing cover is in the closed position and the fixing unit is in the second state when the rear opening / closing cover is in the open position; and a cover interlocking mechanism provided at the third end of the main frame such that the shutter is in the open position when the cartridge is mounted on the main frame and the shutter is in the shielded position when the cartridge is not mounted on the main frame.The image forming apparatus is characterized by comprising a shutter interlocking mechanism that links the attachment / detachment operation of the cartridge with the shutter, the shutter interlocking mechanism being provided at the third end of the main frame. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a new image forming apparatus that is an advancement of the conventional technology. [Brief explanation of the drawing]

[0007] [Figure 1] A view of the first side plate according to this embodiment, seen from the left side. [Figure 2] A schematic diagram of an image forming apparatus according to an embodiment. [Figure 3] A perspective view of an image forming apparatus according to an embodiment. [Figure 4] A schematic diagram of the fixing device according to the embodiment. [Figure 5] Cross-sectional view of the fixing device according to the embodiment. [Figure 6] Exploded view of the fixing device according to this embodiment. [Figure 7] A perspective view of the cover interlocking mechanism and switching mechanism according to an embodiment. [Figure 8] A cross-sectional view of the cover interlocking mechanism and fixing device according to an embodiment. [Figure 9] A cross-sectional view of the cover interlocking mechanism and fixing device according to an embodiment. [Figure 10] Front view (a) and cross-sectional views (b, c, d) of the fixing device according to the embodiment. [Figure 11] Cross-sectional views (a, b) of the fixing device according to the embodiment. [Figure 12] An exploded view of the frame of the fixing device according to this embodiment. [Figure 13] A perspective view showing a process cartridge according to an embodiment. [Figure 14] A view of a portion of the first side plate according to this embodiment, seen from the left side. [Figure 15] A view of a portion of the first side plate according to this embodiment, seen from the right side. [Figure 16] Diagrams (a, b) showing the shutter interlocking mechanism according to an embodiment. [Figure 17] Perspective views (a, b) for explaining shutter opening and closing according to an embodiment. [Figure 18] Side views (a, b) of the fixing device for explaining shutter opening and closing according to an embodiment. [Figure 19] Perspective views (a, b) of the switching mechanism, cover interlocking mechanism, and shutter interlocking mechanism according to an embodiment. [Figure 20] Top view showing the positional relationship of the switching mechanism, cover interlocking mechanism, and shutter interlocking mechanism according to an embodiment. [Figure 21] Diagrams (a, b) showing the positional relationship of the switching mechanism, cover interlocking mechanism, and shutter interlocking mechanism according to an embodiment.

MODE FOR CARRYING OUT THE INVENTION

[0008] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings.

[0009] FIG. 2 is a cross-sectional view of an image forming apparatus 1 according to an embodiment. The image forming apparatus 1 is capable of executing an image forming operation, which is a series of operations for forming an image on a sheet S while transporting the sheet S one by one. The image forming apparatus 1 of the present embodiment is a monochrome laser printer that forms an image on a sheet S by an electrophotographic process using laser light. As the sheet S, which is a recording material (recording medium), various sheet materials with different sizes and materials can be used, such as paper such as plain paper and thick paper, sheet materials with surface treatment such as coated paper, special-shaped sheet materials such as envelopes and index papers, plastic films, cloth, etc.

[0010] In the present disclosure, the “image forming apparatus” is not limited to a single-function printer that only performs printing, and may be a copying machine or a multifunction machine. Further, the “image forming apparatus” may have an image forming apparatus main body provided with an image forming unit and attached devices (original scanners, finishers, optional feeders, etc.) connected to the image forming apparatus main body.

[0011] In the following description, when the image forming apparatus 1 is installed on a horizontal plane, the vertical direction is defined as the Z-axis direction. One of the horizontal directions is defined as the X-axis direction. The direction orthogonal to both the Z-axis direction and the X-axis direction is defined as the Y-axis direction. In the present embodiment, the X-axis direction can be referred to as the front-rear direction of the image forming apparatus 1, and the Y-axis direction can be referred to as the width direction or the left-right direction of the image forming apparatus 1. As necessary, the directions of the arrows X, Y, and Z shown in each drawing are represented by positive signs (+) respectively, and the opposite sides are represented by negative signs (-).

[0012] In the present embodiment, the +X direction may be referred to as the front side or the front face side of the image forming apparatus 1, and the -X direction may be referred to as the rear side or the back face side of the image forming apparatus 1. Also, when viewing the image forming apparatus 1 from the front side, the left side (+Y direction) may be referred to as the left side of the image forming apparatus 1, and the opposite side (-Y direction) may be referred to as the right side of the image forming apparatus 1 (see FIG. 3). Further, the Y-axis direction is the direction of the rotation axis of the photosensitive drum 11 provided in the image forming apparatus 1, and the X-axis direction is an example of a direction intersecting the direction of the rotation axis of the photosensitive drum 11.

[0013] The overall configuration of the image forming apparatus 1 will be described using FIG. 2. The image forming apparatus 1 includes an apparatus main body 2 and a process cartridge 10 that is detachable from the apparatus main body 2. In the present embodiment, the apparatus main body 2 refers to the portion of the image forming apparatus 1 excluding the process cartridge 10.

[0014] The apparatus main body 2 includes a feed tray 3, a sheet feeding unit 4, a registration roller pair 44, a sheet conveyance path P, a transfer roller 51, a fixing device 6, a discharge roller pair 71, a discharge tray 72, and a laser scanner LS. The process cartridge 10 includes a photosensitive drum 11, a charger such as a charging roller or a corona discharger, a developing roller 12, and a toner storage unit (developing container) that stores toner as a developer. The process cartridge 10, the laser scanner LS, and the transfer roller 51 constitute an image forming unit 1A that forms an image on the sheet S.

[0015] Furthermore, the device body 2 includes a main frame 2A provided with a front opening 2a and a rear opening 2b, and a front opening / closing cover 21 and a rear opening / closing cover 22, which are supported by the main frame 2A, respectively.

[0016] The front opening / closing cover 21 is a cover that is rotatably supported relative to the main frame 2A at the front end 2F (second end) side of the main frame 2A. The front opening / closing cover 21 has a pivot shaft 21a supported by the main frame 2A. The front opening / closing cover 21 is rotatable relative to the main frame 2A about a pivot axis passing through the center of the pivot shaft 21a. The front opening / closing cover 21 is configured to be movable between a closed position that closes the front opening 2a and an open position that opens the front opening 2a. The pivot shaft 21a is provided at the lower end of the front opening / closing cover 21, with reference to the posture when the front opening / closing cover 21 is in the closed position. The process cartridge 10 can be attached to and detached from the main frame 2A through the front opening 2a when the front opening / closing cover 21 is in the open position.

[0017] The rear opening / closing cover 22 is a cover that is rotatably supported relative to the main frame 2A at the rear end 2B (first end) side of the main frame 2A. The rear opening / closing cover 22 has a pivot shaft 22a supported by the main frame 2A. The rear opening / closing cover 22 is rotatable relative to the main frame 2A about a pivot axis passing through the center of the pivot shaft 22a. The rear opening / closing cover 22 is configured to move between a closed position that closes the rear opening 2b and an open position that opens the rear opening 2b. In other words, the rear opening / closing cover 22 rotates between an open position that allows access to the fuser 6 from the rear end 2B (first end) side of the main frame 2A and a closed position that prevents access to the fuser 6 from the rear end 2B (first end) side of the main frame 2A. The pivot shaft 22a is provided at the lower end of the rear opening / closing cover 22, with reference to the posture of the rear opening / closing cover 22 when it is in the closed position. With the rear opening / closing cover 22 in the open position, the user can access the sheet transport path P through the rear opening 2b and remove the sheets S (jam paper) that are trapped inside the device body 2.

[0018] The photosensitive drum 11 is an electrophotographic photoreceptor in which a photosensitive layer, such as an organic photosensitive material, is formed on the outer circumference of a cylindrical conductive substrate. The photosensitive drum 11 is rotatable about a rotation axis extending in the left-right direction (second direction). The developing roller 12 is a developer carrier that holds the toner in the toner storage section. The developing roller 12 is configured to develop a toner image on the photosensitive drum 11 by supplying toner to the photosensitive drum 11.

[0019] The laser scanner LS is an exposure apparatus that exposes the photosensitive drum 11. The laser scanner LS includes a laser light source and a scanning optical system that guides light from the laser light source to the photosensitive drum 11 and scans the surface of the photosensitive drum 11 in the main scanning direction (Y-axis direction). In this embodiment, the laser scanner LS is positioned above the process cartridge 10. Alternatively, an LED exposure apparatus using multiple LED elements arranged in the main scanning direction as light sources may be used as the exposure apparatus.

[0020] The feeding tray 3 is a storage section where sheets S are loaded and stored. The sheet feeding section 4 includes a feeding roller 41, a separation roller 42, a separation pad 42a, and a pair of transport rollers 43. The feeding roller 41 is an example of a feeding member that feeds sheets S from the feeding tray 3, and a belt-shaped feeding member may be used, for example. The separation pad 42a is an example of a separation member that separates sheets S by frictional force, and a roller-shaped separation member may be used, for example.

[0021] The transfer roller 51 is an example of a transfer member that transfers the toner image. The transfer roller 51 is positioned opposite the photosensitive drum 11. A transfer nip is formed between the photosensitive drum 11 and the transfer roller 51, serving as a transfer area. The fuser 6 is a thermal fixing type image fixing device (image heating device). The fuser 6 has a heating unit 61 and a pressure roller 62. A nip portion np1 (fixing nip) is formed between the heating unit 61 and the pressure roller 62. Details of the fuser 6 will be described later.

[0022] The discharge roller pair 71 is a discharge member that discharges the sheet S from the inside to the outside of the device body 2. The discharge tray 72 is a loading section on which the sheets S on which the image is formed are stacked. In this embodiment, the discharge tray 72 is formed on the upper surface of the device body 2.

[0023] The sheet transport path P is a route from the feed roller 41, through the nip portion of the separation roller 42 and separation pad 42a, the transport roller pair 43, the registration roller pair 44, the transfer nip, the nip portion np1 of the fuser 6, and the discharge roller pair 71, to the discharge tray 72. The main body of the device 2 has a plurality of guide members that form the sheet transport path P.

[0024] Furthermore, the image forming apparatus 1 has an operation unit 1P for operating the image forming apparatus 1. The operation unit 1P is located at the left end of the upper surface of the apparatus body 2. The operation unit 1P includes a display unit such as a liquid crystal panel and LED lamps, and an input unit such as an execution button and a selection button for instructing the execution of an image forming operation. When the control unit of the image forming apparatus 1 detects a jam in the sheet S, it can notify the user of the jam by methods such as displaying a text message on the operation unit 1P, flashing a lamp, sounding a buzzer, or giving a voice message.

[0025] (Image formation process) The image forming process will now be explained. The control unit of the image forming apparatus 1 starts the image forming process based on image information received from, for example, an external device. Once the image forming process starts, the sheets S stored in the feed tray 3 are fed one by one to the sheet transport path P by the sheet feed unit 4. The fed sheets S are corrected for skew and their timing adjusted by the registration roller pair 44 before being transported toward the transfer nip.

[0026] Simultaneously with the transport of the sheet S, the image forming unit 1A begins creating a toner image. The photosensitive drum 11 is rotated by a drive source (motor) located in the main body of the device 2. The charger uniformly charges the surface of the photosensitive drum 11 to a predetermined potential. The laser scanner LS scans the surface of the photosensitive drum 11 with laser light based on image information to expose it and write an electrostatic latent image to the photosensitive drum 11. The developing roller 12 carries toner and supplies it to the photosensitive drum 11, developing the electrostatic latent image into a toner image.

[0027] The transfer roller 51 receives voltage from the high-voltage substrate of the main body 2, and transfers the toner image from the photosensitive drum 11 to the sheet S as the sheet S passes through the transfer nip. After that, the sheet S undergoes image fixing in the fuser 6. The fuser 6 holds the sheet S between the heating unit 61 and the pressure roller 62 in a nip section np1 and transports it while heating and pressurizing the unfixed image on the sheet S to fix it to the surface of the sheet S. After passing through the fuser 6, the sheet S is discharged to the discharge tray 72 via the discharge roller pair 71.

[0028] (Main frame) The main frame 2A of the apparatus body 2 will be explained using Figure 3. Figure 3 is a perspective view of the image forming apparatus 1. As shown in Figure 3, the main frame 2A, which is the frame of the apparatus body 2, comprises a first side plate 23 (first frame member, right side plate) and a second side plate 24 (second frame member, left side plate) which are spaced apart in the left-right direction (Y-axis direction).

[0029] The main frame 2A has a rear end 2B as the first end and a front end 2F as the second end opposite to the first end in the horizontal front-to-back direction (X-axis direction, first direction). The main frame 2A also has a right end 2R as the third end and a left end 2L as the fourth end opposite to the third end in the horizontal left-to-right direction (Y-axis direction, second direction) which is perpendicular to the front-to-back direction. The first side plate 23 is positioned at the right end 2R and the second side plate 24 is positioned at the left end 2L.

[0030] Each of the first side plate 23 and the second side plate 24 extends in a direction intersecting the left-right direction, which is the direction of the rotation axis of the photosensitive drum 11. Each of the first side plate 23 and the second side plate 24 is, for example, a sheet metal extending in the front-back direction and the up-down direction, with its thickness direction oriented in the left-right direction.

[0031] In the left-right direction, a mounting space for the process cartridge 10 is formed between the first side plate 23 and the second side plate 24. Also, for example, the fuser 6 is positioned between the first side plate 23 and the second side plate 24 in the left-right direction. The first side plate 23 is located on one side (right side) of the process cartridge 10 and the fuser 6 in the left-right direction. The second side plate 24 is located on the other side (left side) of the process cartridge 10 and the fuser 6 in the left-right direction.

[0032] In this embodiment, the fuser 6 is positioned on the rear end 2B side (the side of the first end) of the main frame 2A in the front-rear direction (X-axis direction, first direction) (Figure 2). In other words, the distance from the nip portion np1 to the rear end 2B of the main frame 2A in the front-rear direction is shorter than the distance from the nip portion np1 to the front end 2F of the main frame 2A in the front-rear direction.

[0033] Furthermore, in this embodiment, the process cartridge 10 is mounted on the front end 2F side (second end side) of the main frame 2A in the front-rear direction (first direction). In other words, the distance from the rearmost end of the process cartridge 10 to the rear end 2B of the main frame 2A in the front-rear direction is shorter than the distance from the foremost end of the process cartridge 10 to the front end 2F of the main frame 2A in the front-rear direction.

[0034] Furthermore, a power supply board PS is located at the left end 2L (fourth end) of the main frame 2A. The power supply board PS supplies power to, for example, the operating unit 1P and the drive source (motor) of the main unit 2. The operating unit 1P and the power supply board PS are located on the opposite side in the left-right direction (second direction) from the cover interlocking mechanism 8 and shutter interlocking mechanism 9, which will be described later. This allows for an efficient arrangement of the electrical circuit including the operating unit 1P and the power supply board PS, and the cover interlocking mechanism 8 and shutter interlocking mechanism 9 related to the fuser 6, thereby enabling miniaturization of the image forming apparatus 1.

[0035] When the image forming apparatus 1 is viewed in the left-right direction, at least a portion of the cover interlocking mechanism 8 and / or at least a portion of the shutter interlocking mechanism 9 may overlap with the power supply board PS (Figure 1).

[0036] (Fuser) Next, the configuration of the fuser 6 as the fixing unit in this embodiment will be described. Figure 4 is a schematic diagram of the fuser 6 viewed in the left-right direction. As shown in Figure 4, the fuser 6 has a heating unit 61 and a pressure roller 62 that together with the heating unit 61 forms a nip section np1, and heats and fixes the toner image to the sheet S while transporting the sheet S at the nip section np1.

[0037] The heating unit 61 comprises a heater 611, a holder 612, a stay 613, and a belt 614. The heater 611, holder 612, stay 613, and belt 614 are each elongated members in the left-right direction. The pressure roller 62 rotates around a rotation axis that extends in the left-right direction. Hereafter, the left-right direction may be referred to as the longitudinal direction of the fuser 6.

[0038] The belt 614 is a rotatable heating element. The belt 614 may be an endless (tubular) film. The heater 611 is provided on the inner surface side of the belt 614 and heats the belt 614. The heater 611 is plate-shaped with its thickness direction intersecting both the sheet conveying direction D and the longitudinal direction (Y-axis direction). The heater 611 has a first surface 611a and a second surface 611b opposite to the first surface 611a, and the first surface 611a is supported by the holder 612.

[0039] The holder 612 is made of a heat-resistant resin such as PPS or liquid crystal polymer. The holder 612 has a guide surface 612a and a support wall 612b. The guide surface 612a contacts the inner circumferential surface 614a of the belt 614 to guide the belt 614. The support wall 612b has a support surface 612b1 that abuts against the first surface 611a of the heater 611 and supports the heater 611. The stay 613 is a member (support member, reinforcing member) that supports the holder 612. The stay 613 is a metal member made of a plate material with greater rigidity than the holder 612, for example, a steel plate with a thickness of 1.6 mm bent into a roughly U-shape.

[0040] The belt 614 is an endless belt that is heat-resistant and flexible, and is composed of, for example, a metal sleeve such as stainless steel coated with fluororesin, or a laminate of polyimide resin, silicone rubber, fluororesin, etc. A heater 611, a holder 612, and a stay 613 are arranged inside the belt 614, and the belt 614 is configured to rotate around these. The inner circumferential surface 614a of the belt 614 is in contact with the second surface 611b of the heater 611, and the belt 614 is heated by heat conduction from the heater 611.

[0041] The pressure roller 62 (pressure rotating body) has a metal shaft 62a and an outer circumference 62b made of an elastic material that covers the shaft 62a. The pressure roller 62 is pressed by the heater 611 with the belt 614 in between. As a result, a nip portion np1 for nipping, heating, and pressurizing the sheet S is formed between the belt 614 and the pressure roller 62. In other words, the pressure roller 62, together with the heater 611 via the belt 614, forms the nip portion np1.

[0042] Hereinafter, the direction in which the sheet S is transported in the nip section np1 will be referred to as the sheet transport direction D in the fuser 6, or simply as the sheet transport direction D. The sheet transport direction D is oriented in the direction from the front to the rear of the image forming apparatus 1 (-X direction) with respect to the front-to-back direction. The direction perpendicular to both the sheet transport direction D and the longitudinal direction (Y-axis direction) will be referred to as the nip pressure direction H.

[0043] The pressure roller 62 is configured to rotate when a driving force is transmitted from a drive source provided by the image forming apparatus 1. As the pressure roller 62 rotates, the belt 614 rotates in accordance with the pressure roller 62 due to the force it receives from the pressure roller 62 at the nip portion np1.

[0044] Next, the frame configuration of the fuser 6 and the shutter 69 will be described using Figure 5. Figure 5 is a cross-sectional view showing a section of the fuser 6 cut by a virtual plane perpendicular to the longitudinal direction. The fuser 6 has an upper frame 64 and a lower frame 63. The lower frame 63 can also be called the first frame, and the upper frame 64 can be called the second frame.

[0045] The lower frame 63 is a frame that supports the heating unit 61 and the pressure roller 62. The upper frame 64 is located above the lower frame 63 and covers the heating unit 61. The lower frame 63 and the upper frame 64 may be made of resin and formed from a non-conductive molded member (resin member). The upper frame 64 has an upper guide surface 64a located downstream of the heating unit 61 in the sheet conveying direction D. The upper guide surface 64a guides the upper surface of the sheet S being conveyed in the sheet conveying direction D. The lower frame 63 has a lower guide surface 63a located downstream of the heating unit 61 in the sheet conveying direction D. The lower guide surface 63a guides the lower surface of the sheet S being conveyed in the sheet conveying direction D.

[0046] Furthermore, the fuser 6 has a shutter 69 and an inlet 6i that opens toward the upstream side of the conveying direction (sheet conveying direction D) in which the nip portion np1 conveys the sheet S. The inlet 6i is an opening for the fuser 6 to receive the sheet S on the upstream side of the nip portion np1. The inlet 6i is formed between the upper frame 64 and the lower frame 63. The shutter 69 is movable between a shielded position that shields the inlet 6i (see also Figure 17(b)) and an open position that opens the inlet 6i (see also Figure 17(a)). The shutter 69 in this embodiment is supported by the upper frame 64 and rotates around a pivot axis that extends in the left-right direction.

[0047] The configuration of the lower frame 63 will be further explained using Figure 6. Figure 6 is an exploded perspective view of the fuser 6. The lower frame 63 has rails 63b provided at both ends in the Y-axis direction, which is the longitudinal direction of the fuser 6. Each rail 63b extends in the nip pressing direction H, which is perpendicular to both the sheet transport direction D and the longitudinal direction (Y-axis direction).

[0048] The two rails 63b face each other in the longitudinal direction of the fuser 6. Each rail 63b engages with grooves 651a1 and 651b1 provided in each of the two transmission members 651 (transmission members 651a and 651b), which will be described later. The transmission members 651 are supported by the rails 63b so as to be movable in the nip pressurization direction H.

[0049] The fixing unit 6 also includes bearings 62c, 62c. One end of the shaft 62a of the pressure roller 62 is rotatably supported by one bearing 62c, and the other end of the shaft 62a is rotatably supported by the other bearing 62d. The bearing 62c is positioned when its protrusion 62c1 fits into a recess 63d1 (groove) provided in the lower frame 63. Similarly, the bearing 62d is positioned when its protrusion 62d1 fits into a recess 63d2 (groove) provided in the lower frame 63. The bearings 62c are electrically conductive. In this embodiment, the bearings 62c and 62d are provided with protrusions 62c1 and 62d1, and the lower frame 63 is provided with recesses 63d1 and 63d2, but the orientation of the protrusions and recesses may be reversed. Also, the means for fixing the bearings 62c and 62d to the lower frame 63 is not limited to the fitting of the recess (groove) and the protrusion.

[0050] (Pressurization mechanism) Next, the pressurizing mechanism of the fuser 6 will be explained. Figure 10(a) is a front view of the fuser 6 as seen in the sheet transport direction D. Figures 10(b) to (d) are cross-sectional views of the fuser 6 along lines AA, BB, and CC in Figure 10(a), respectively.

[0051] As shown in Figures 10(a) to (d), the fuser 6 has a pressurizing mechanism 65 for pressurizing the nip portion np1. In this embodiment, the pressurizing mechanism 65 presses the heating unit 61 against the pressurizing roller 62.

[0052] The pressurizing mechanism 65 is provided at both the +Y direction end and the -Y direction end of the lower frame 63. In other words, the pressurizing mechanism 65 can be said to be supported by the lower frame 63. The structure of the pressurizing mechanism 65 provided at the +Y direction end of the lower frame 63 and the pressurizing mechanism 65 provided at the -Y direction end of the lower frame 63 are substantially the same. Therefore, the pressurizing mechanism 65 will be described below without distinguishing between the two.

[0053] As shown in Figures 10(b),(c), and(d), the pressurizing mechanism 65 includes a transmission member 651, a pressurizing arm 652, and a pressurizing spring 653. The pressurizing arm 652 is supported by a lower frame 63. More specifically, the pressurizing arm 652 is supported by a support portion 64d of the lower frame 63 and is rotatable around the rotation axis Ax1 of the support portion 64d. The support portion 64d is a substantially cylindrical projection.

[0054] The pressure arm 652 has a pressing portion 652a that contacts the transmission member 651 from above and presses the transmission member 651 downward. The transmission member 651 transmits the pressing force received from the pressure arm 652 to the stay 613. When the stay 613 receives the pressing force, the holder 612 and heater 611 supported by the stay 613 are pressed against the pressure roller 62.

[0055] The pressure spring 653 biases the pressure arm 652 in the direction in which the pressing portion 652a presses against the transmission member 651. In other words, the pressure spring 653 is a biasing member that biases the pressure arm 652 so that the nip portion np1 is pressurized. The pressure spring 653 is, for example, a conductive tension coil spring. One end 653b of the pressure spring 653 is engaged with the lower frame 63, and the other end 653a of the pressure spring 653 is engaged with the pressure arm 652.

[0056] Furthermore, the pressurizing arm 652 has a contact portion 674 (Figures 8 and 9) that contacts the cam 672 of the pressure release mechanism 67.

[0057] (Pressure release mechanism) Next, the configuration of the pressure release mechanism 67 of the fuser 6 will be explained using Figures 11(a)(b) and 12. The pressure release mechanism 67 is a mechanism (pressure release section) that changes the nip pressure in the nip section np1 between the heating unit 61 and the pressure roller 62.

[0058] Figures 11(a) and 11(b) are cross-sectional views of the fuser unit 6. Figure 11(a) shows the pressurized state in which the pressure release mechanism 67 allows pressurization of the nip portion np1. Figure 11(b) shows the pressure release state in which the pressure release mechanism 67 releases pressurization of the nip portion np1. Figure 12 is an exploded perspective view showing the upper frame 64, lower frame 63, and camshaft 671 of the fuser unit 6. In Figure 12, some parts of the fuser unit 6, such as the heating unit 61 and the pressure roller 62, are omitted.

[0059] As shown in Figures 11(a)(b) and 12, the pressure release mechanism 67 comprises a camshaft 671 and a cam 672.

[0060] As shown in Figure 11(a), the camshaft 671 is rotatable about the rotation axis Ax2 (second rotation axis). The camshaft 671 is an axial member that extends axially in the left-right direction (longitudinal direction of the fuser 6). The camshaft 671 is made of a conductive material, such as metal.

[0061] As shown in Figure 12, cams 672 are mounted on the +Y end and the -Y end of the camshaft 671, respectively. The cams 672 are supported on the camshaft 671 so as to rotate with it. One cam 672 is located at the +Y end of the lower frame 63, and the other cam 672 is located at the -Y end of the lower frame 63. The two cams 672 have the same shape and rotational phase.

[0062] The cam 672 is rotatable between the pressurized position shown in Figure 11(a) and the depressurized position shown in Figure 11(b). The state of the fuser 6 when the cam 672 is in the pressurized position is called the pressurized state, and the state of the fuser 6 when the cam 672 is in the depressurized position is called the depressurized state.

[0063] The pressurized state can be described as the first state, where the pressure at the nip portion np1 is the first pressure. The depressurized state can be described as the second state, where the pressure at the nip portion np1 is the second pressure, which is lower than the first pressure. Note that the pressure at the nip portion np1 in the second state may be zero. In other words, when the cam 672 is in the depressurized position, the heating unit 61 may be separated from the pressurizing roller 62 (non-contact state).

[0064] The cam 672 can move the pressure arm 652 against the biasing force of the pressure spring 653. That is, the rotation of the cam 672 changes the position of the pressure arm 652 around the rotation axis Ax1, and changes the positions of the transmission member 651, stay 613, holder 612, and heater 611 in the nip pressure direction H. As a result, the amount of penetration of the heating unit 61 into the pressure roller 62 changes. This amount of penetration refers to the distance that the outer surface of the pressure roller 62 is displaced in the nip pressure direction H by the force received from the heating unit 61 at the nip section np1, with reference to the position of the outer surface of the pressure roller 62 when the outer circumference 62b of the elastic pressure roller 62 is not elastically deformed. In this way, the switching mechanism 66 switches the pressure acting between the belt 614 and the pressure roller 62 in the nip pressure direction H (nip pressure) at the nip section np1 by changing the amount of penetration of the heating unit 61 into the pressure roller 62 according to the rotation angle of the cam 672.

[0065] Furthermore, the moment of force that the pressurizing arm 652 receives around the rotation axis Ax1 due to the biasing force of the pressurizing spring 653 balances the moment received by the pressurizing arm 652 due to the reaction force that the contact portion 674 receives from the cam 672 and the reaction force that the pressing portion 652a receives from the transmission member 651. The change in nip pressure described above can also be rephrased as a change in the distribution ratio of the biasing force between the contact portion 675 and the pressing portion 652a, while satisfying the balance condition, according to the rotation angle of the cam 672. In other words, the switching mechanism 66 can be rephrased as being configured to change the pressing force of the pressurizing arm 652 on the pressurizing roller 62 of the heating unit 61 by rotating the cam 672.

[0066] The cam 672 of this embodiment has a first cam surface 673a and a second arc-shaped cam surface 673b centered on the rotation axis Ax2 of the camshaft 671. The first cam surface 673a corresponds to the end face obtained by cutting a part of the circumference centered on the rotation axis Ax2 with a straight line. The minimum distance from the rotation axis Ax2 to the first cam surface 673a is shorter than the distance from the rotation axis Ax2 to the second cam surface 673b.

[0067] The pressurized position of cam 672 is when the first cam surface 673a contacts the contact portion 674 of pressurized arm 652. The depressurized position of cam 672 is when the second cam surface 673b contacts the contact portion 674 of pressurized arm 652.

[0068] Next, the support configuration for the camshaft 671 will be described using Figure 12. The lower frame 63 has support walls 631 that support the camshaft 671. The support walls 631 are provided at the +Y end and the -Y end of the lower frame 63, respectively. The support walls 631 extend in the nip pressurization direction H. Each support wall 631 has a hole 631h that rotatably supports the camshaft 671. The hole 631h is formed to penetrate the support wall 631 in the longitudinal direction of the fuser 6. The two holes 631h may have the same shape. The camshaft 671 is inserted through the hole 631h.

[0069] The upper frame 64 has support walls 641 that support the camshaft 671. The support walls 641 extend in the nip pressurization direction H. The support walls 641 are provided at both the +Y end and the -Y end of the upper frame 64. The support walls 641 have holes 641h that rotatably support the camshaft 671. The holes 641h are formed to penetrate the support wall 641 in the longitudinal direction of the fuser 6. The two holes 631h may have the same shape. The camshaft 671 is inserted through the holes 631h.

[0070] The support wall 631 of the lower frame 63 and the support wall 641 of the upper frame 64 each function as a shaft support part that supports the camshaft 671. The shaft support part may consist of only one of the support wall 631 of the lower frame 63 or the support wall 641 of the upper frame 64.

[0071] As shown in Figure 7, a fourth link 84 is attached to the -Y end of the camshaft 671, which is outside the cam 672. The fourth link 84 is supported so as to rotate together with the camshaft 671. The fourth link 84 protrudes in a direction intersecting the rotation axis Ax2 of the camshaft 671, and a boss 841 is formed at its tip. The boss 841 is connected to the third link 83 of the cover interlocking mechanism 8, which will be described later. The base of the fourth link 84 is a support portion 842 fixed to the camshaft 671.

[0072] The fourth link 84 can be described as a connecting part that links the switching mechanism 66 and the cover interlocking mechanism 8. The fourth link 84 is a component that rotates integrally with the camshaft 671 and constitutes part of the pressure release mechanism 67. Furthermore, the fourth link 84, together with the links (81-83) of the cover interlocking mechanism 8, can be described as part of a linkage mechanism that transmits force to rotate the camshaft 671 in conjunction with the opening and closing of the rear opening / closing cover 22. Therefore, the fourth link 84 can also be described as part of the cover interlocking mechanism 8.

[0073] (Switching mechanism) The aforementioned pressurizing mechanism 65 and pressure release mechanism 67 are combined to form a switching mechanism 66 that switches the state of the fuser 6 in relation to the pressurizing of the nip portion np1. In other words, the image forming apparatus 1 has a switching mechanism 66 that switches the state of the fuser 6, and the switching mechanism 66 includes the pressurizing mechanism 65 and the pressure release mechanism 67.

[0074] Thus, the switching mechanism 66 is configured to switch the state of the fuser 6 between a first state in which the pressure at the nip portion np1 is the first pressure, and a second state in which the pressure at the nip portion np1 is lower than the first pressure, or zero.

[0075] The switching mechanism 66 includes a pressure arm 652 (arm) that pressurizes the heating unit 61 toward the pressure roller 62, and a pressure spring 653 (biasing member) that biases the pressure arm 652. The pressure spring 653 (biasing member) biases the pressure arm 652 so that the heating unit 61 is pressed toward the pressure roller 62 by the pressure arm 652. The switching mechanism 66 also has a cam 672 that rotates around a second rotation axis, with the rotation axis of the photosensitive drum 11 as the first rotation axis. By rotating around the second rotation axis, the cam 672 moves the pressure arm 652 to a first position where the fuser 6 is in a pressurized state (first state) and to a second position where the fuser 6 is in a depressurized state (second state).

[0076] (Cover interlocking mechanism) The cover interlocking mechanism 8 will be explained using Figures 7 to 9. The cover interlocking mechanism 8 is a linkage mechanism that operates the pressure release mechanism 67 in conjunction with the opening and closing of the rear opening / closing cover 22.

[0077] Figure 7 is a perspective view of the cover interlocking mechanism 8. Figures 8 and 9 are diagrams showing the cover interlocking mechanism 8, the rear opening / closing cover 22, the pressure release mechanism 67, and the fuser 6, and are cross-sectional views representing a part of the image forming apparatus 1 cut by a virtual plane perpendicular to the left-right direction. Figure 8 shows the rear opening / closing cover 22 in the closed position, and Figure 9 shows the rear opening / closing cover 22 in the open position.

[0078] As shown in Figures 7 to 9, the cover interlocking mechanism 8 connects (links) the pressure release mechanism 67 and the rear opening / closing cover 22. In other words, the cover interlocking mechanism 8 connects (links) the switching mechanism 66 and the rear opening / closing cover 22. The cover interlocking mechanism 8 is located on the right side and rear side of the main body 2 of the device.

[0079] The cover interlocking mechanism 8 comprises a first link 81, a second link 82, a third link 83, and a fourth link 84.

[0080] The first link 81 engages with the rear opening / closing cover 22. The second link 82 engages with the first link 81 and is rotatable about a rotation axis (third rotation axis) extending in the left-right direction (second direction). The third link 83 engages with both the second link 82 and the switching mechanism 66 and is movable in the direction from the rear end 2B (first end) of the main frame 2A toward the front end 2F (second end) and from the front end 2F (second end) toward the rear end 2B (first end). The fourth link 84 engages with the third link 83 and is rotatable about a rotation axis (fourth rotation axis) extending in the left-right direction (second direction).

[0081] The components of the cover interlocking mechanism 8 will be described in more detail below. The first link 81 is a substantially straight member connected to the rear opening / closing cover 22. The first link 81 has a hole 811 formed on the first end side and a hole 812 formed on the side. The hole 811 is rotatably fitted into the boss 221 of the rear opening / closing cover 22. The boss 221 of the rear opening / closing cover 22 is located at a position different from the rotation axis R1 of the rear opening / closing cover 22 (above the rotation axis R1 when the rear opening / closing cover 22 is in the closed position).

[0082] The second link 82 is a substantially disc-shaped member connected to the first link A1. The second link 82 is rotatably supported about the rotation axis R3 by a boss 821 protruding from the first side plate 23. The second link 82 has a first arm portion that protrudes outward from the outer circumference of the disc in a direction intersecting the rotation axis R3, and a boss 822 that protrudes in the +Y direction from the tip of the first arm portion. The boss 822 is rotatably fitted into the hole 812 of the first link 81. The second link 82 also has a second arm portion that protrudes outward from the outer circumference of the disc in a direction intersecting the rotation axis R3 and opposite to the first arm portion, and a boss 823 that protrudes in the -Y direction from the tip of the second arm portion. The three bosses 821, 822, and 823 can be said to be arranged in a line along a virtual straight line perpendicular to the rotation axis R3.

[0083] The third link 83 is a substantially linear member connected to the second link 82 and the pressure release mechanism 67. The third link 83 has a hole 831 formed on the first end side and a hole 832 formed on the other end side. The boss 823 of the second link 82 is rotatably fitted into the hole 831. The boss 841 of the fourth link 84 is rotatably fitted into the hole 832. In this embodiment, the third link 83 is longer than the first link 81.

[0084] The cover interlocking mechanism 8 is configured such that, as shown in Figure 8, when the rear opening / closing cover 22 is in the closed position, the cam 672 is in the pressurized position, and as shown in Figure 9, when the rear opening / closing cover 22 is in the open position, the cam 672 is in the release position.

[0085] Specifically, as shown in Figure 8, when the rear opening / closing cover 22 is in the closed position, the first link 81, second link 82, and third link 83 of the cover interlocking mechanism 8 are folded in a Z-shape. The range from one end to the other of the first link 81 in the front-rear direction and the range from one end to the other of the third link 83 in the front-rear direction overlap on the X-axis. In other words, when the rear opening / closing cover 22 is in the closed position, the range occupied by the cover interlocking mechanism 8 in the front-rear direction is narrow.

[0086] The position of the third link 83 when the rear opening / closing cover 22 is in the closed position determines the position of the hole 832 of the third link 83 and the boss 841 of the fourth link 84, which engage with each other. The position of the boss 841 of the fourth link 84 determines the positions of the camshaft 671 and cam 672 around the rotation axis Ax2. As a result, when the rear opening / closing cover 22 is in the closed position, the cam 672 is positioned in the pressurized position.

[0087] As mentioned above, when the cam 672 is in the pressurized position, the heating unit 61 is pressed against the pressurized roller 62 by the biasing force of the pressurized spring 653, and the nip portion np1 is pressurized. In other words, when the rear opening / closing cover 22 is in the closed position, the fuser 6 is in a state where the nip portion np1 is pressurized so that it can fix the image.

[0088] When the rear opening / closing cover 22 is moved from the closed position to the open position, the first link 81 is pulled by the rear opening / closing cover 22 and moves rearward (-X direction) in the front-rear direction. The movement of the first link 81 causes the second link 82 to be pulled by the first link 81 and rotate clockwise in the figure. The rotation of the second link 82 pushes the third link 83 forward (+X direction) in the front-rear direction. The movement of the third link 83 presses on the fourth link 84, and the fourth link 84 rotates clockwise in the figure together with the camshaft 671 and cam 672. As a result, in conjunction with the movement of the rear opening / closing cover 22 from the closed position to the open position, the cam 672 rotates clockwise in the figure from the pressurized position to the release position (Figure 9).

[0089] As mentioned above, when the cam 672 is in the release position, the second cam surface 673b of the cam 672 pushes up the pressurizing arm 652 against the biasing force of the pressurizing spring 653. This releases the pressure on the nip portion np1. In other words, when the rear opening / closing cover 22 is in the open position, the fuser 6 is in a state where the pressure on the nip portion np1 is released, making jam processing easier for the user.

[0090] While the rear opening / closing cover 22 moves from the closed position to the open position, the first link 81, second link 82, and third link 83 of the cover interlocking mechanism 8 unfold from their Z-shaped folded state. In the state shown in Figure 9, the range from one end to the other of the first link 81 in the front-rear direction and the range from one end to the other of the third link 83 in the front-rear direction do not overlap on the X-axis. In other words, the range occupied by the cover interlocking mechanism 8 in the front-rear direction when the rear opening / closing cover 22 is in the open position is wider than the range occupied by the cover interlocking mechanism 8 when the rear opening / closing cover 22 is in the closed position.

[0091] Incidentally, as shown in Figure 8, when the rear opening / closing cover 22 is in the closed position, the connection points (812, 822) between the first link 81 and the second link 82 are located in front of (+X direction) the rotation axis R3 of the second link 82 in the front-rear direction. Also, when the rear opening / closing cover 22 is in the closed position, the connection points (823, 831) between the second link 82 and the third link 83 are located behind (-X direction) the rotation axis R3 of the second link 82 in the front-rear direction.

[0092] As shown in Figure 9, when the rear opening / closing cover 22 is in the open position, the connection points (812, 822) between the first link 81 and the second link 82 are located behind (-X direction) the rotation axis R3 of the second link 82 in the front-rear direction. Also, when the rear opening / closing cover 22 is in the open position, the connection points (823, 831) between the second link 82 and the third link 83 are located in front (+X direction) the rotation axis R3 of the second link 82 in the front-rear direction.

[0093] In this way, as the rear opening / closing cover 22 opens and closes, the connection between the first link 81 and the second link 82, and the connection between the second link 82 and the third link 83, each move in the front-rear direction from one side to the other along the rotation axis R3 of the second link 82. This configuration increases the amount of rotation of the second link 82 and the amount of movement of the third link 83 in the front-rear direction when the rear opening / closing cover 22 opens and closes, allowing the switching mechanism 66 to pressurize and depressurize the fuser 6 more reliably.

[0094] In this embodiment, the cover interlocking mechanism 8 interlocks the switching mechanism 66 with the rear opening / closing cover 22 so that when the rear opening / closing cover 22 is in the closed position, the fuser 6 is in a pressurized state (first state), and when the rear opening / closing cover 22 is in the open position, the fuser 6 is in a depressurized state (second state). This allows the fuser 6 to be switched between a pressurized state capable of fixing images and a depressurized state capable of jamming, depending on whether the rear opening / closing cover 22 is opened or closed.

[0095] Furthermore, since the second link 82 is a rotating member, the movement of the first link 81 in the front-rear direction is converted into rotation of the second link 82, and the rotation of the second link 82 is further converted into movement of the third link 83 in the front-rear direction. This configuration has the advantage of keeping the amount of vertical movement of each link constituting the cover interlocking mechanism 8 small. As a result, the image forming apparatus 1 can be made smaller in the vertical direction. In addition, the cover interlocking mechanism 8 can also be made smaller by consolidating the rear opening / closing cover 22 and the fuser 6 at the rear end.

[0096] (Drum shaft) Figure 13 is a perspective view of the process cartridge 10. As shown in Figure 13, the photosensitive drum 11 has a drum shaft 11a. The drum shaft 11a protrudes from the right end face of the process cartridge 10 toward the right (-Y direction), that is, toward the first side plate 23 of the main frame 2A.

[0097] The drum shaft 11a functions as an engaging part that engages with the shutter interlocking mechanism 9, described later, when the process cartridge 10 is attached to and removed from the main frame 2A. Note that the drum shaft 11a is just one example of an engaging part, and the process cartridge 10 may be configured so that a part other than the drum shaft 11a functions as the engaging part.

[0098] (1st side plate) The first side plate 23 of the main frame 2A will be explained using Figures 1, 14, and 15. Figure 1 is a view of the first side plate 23 from the left side (i.e., the center side of the main frame 2A) looking to the right (-Y direction). Figure 14 is an enlarged view of a part of Figure 1. Figure 15 is a view of a part of the first side plate 23 from the right side (i.e., the outside of the main frame 2A) looking to the left (+Y direction).

[0099] As shown in Figures 1 and 14, the first side plate 23 includes a front frame 23A and a rear frame 23B. The front frame 23A and the rear frame 23B are plate-shaped members that extend in directions intersecting the left-right direction. The front frame 23A forms the front portion of the first side plate 23, and the rear frame 23B forms the rear portion of the first side plate 23. The front frame 23A and the rear frame 23B are joined or fastened together to form a first side plate 23 that is continuous in the front-rear direction. The first side plate 23 may also be a single plate-shaped member in which the portion corresponding to the front frame 23A and the portion corresponding to the rear frame 23B are integrally formed.

[0100] As shown in Figure 1, the front frame 23A has a cartridge rail 231 and a contact rail 232. The cartridge rail 231 is provided on the left side of the front frame 23A (Figure 14), and the contact rail 232 is provided on the right side of the front frame 23A.

[0101] The cartridge rail 231 is a guide section that guides the drum shaft 11a (Figure 13) of the photosensitive drum 11. The contact piece rail 232 is a guide section that guides the contact piece 90 (Figure 16(a)(b)) of the shutter interlocking mechanism 9, which will be described later.

[0102] As shown in Figure 14, the cartridge rail 231 is a groove that opens to the left and extends in a direction intersecting the left-right direction. In this embodiment, the cartridge rail 231 opens forward when viewed in the left-right direction and inclined downward toward the rear. The inclination angle of the cartridge rail 231 with respect to the horizontal is not necessarily constant and may be bent as shown in the figure.

[0103] The cartridge rail 231 receives the drum shaft 11a (Figure 13) of the photosensitive drum 11 and guides the drum shaft 11a when the process cartridge 10 is attached to and removed from the apparatus body 2. The process cartridge 10 is attached to the apparatus body 2 from front to rear and removed from rear to front. In this way, the first side plate 23 (front frame 23A) guides the drum shaft 11a by the cartridge rail 231 when the process cartridge 10 is attached to and removed.

[0104] As shown in Figure 15, the contact rail 232 is a groove that opens to the right and extends in a direction intersecting the left-right direction. In this embodiment, the contact rail 232 opens forward when viewed in the left-right direction and is inclined downward toward the rear.

[0105] The cartridge rail 231 has a front section 231a, a middle section 231b, and a rear section 231c. The abutment rail 232 also has a front section 232a, a middle section 232b, and a rear section 232c. The middle section 231b of the cartridge rail 231 and the middle section 232b of the abutment rail 232 overlap when viewed in the left-right direction and communicate with each other. The middle sections 231b and 232b of the cartridge rail 231 and the abutment rail 232 have through holes 23C that penetrate the front frame 23A in the left-right direction.

[0106] In other words, the overlapping portion of the middle section 231b of the cartridge rail 231 and the middle section 232b of the contact rail 232 is the through hole 23C. This overlap makes it possible to form the cartridge rail 231 and the contact rail 232 with common materials.

[0107] When viewed from the outside (right side) of the first side plate 23, the drum shaft 11a is exposed through the through hole 23C when the drum shaft 11a passes through the middle part 231b of the cartridge rail 231 during the process cartridge 10 to and from the main body 2 of the apparatus.

[0108] Furthermore, the front portion 232a of the contact rail 232 extends upward above the front portion 231a of the cartridge rail 231. The rear portion 232c of the contact rail 232 extends upward above the rear portion 231c of the cartridge rail 231. In other words, the front and rear ends of the contact rail 232 are located above the cartridge rail 231. Also, the length of the contact rail 232 in the front-rear direction is shorter than the length of the cartridge rail 231 in the front-rear direction.

[0109] (Shutter interlocking mechanism) The shutter interlocking mechanism 9 will be explained using Figures 1 and 16(a) to 18(b). Figure 16(a) is a diagram of the shutter interlocking mechanism 9 as viewed from the outside towards the center in the left-right direction (viewed in the +Y direction), similar to Figure 15. Figure 16(b) is a diagram of the shutter interlocking mechanism 9 as viewed from the center towards the outside in the left-right direction (viewed in the -Y direction). Figures 17(a) and 17(b) are perspective views showing the fuser 6 and a part of the shutter interlocking mechanism 9. Figures 18(a) and 18(b) show the fuser 6 and a part of the shutter interlocking mechanism 9 as viewed in the left-right direction. Figures 17(a) and 18(a) correspond to the case when the process cartridge 10 is mounted on the main body 2 of the device. Figures 17(b) and 18(b) correspond to the case when the process cartridge 10 is removed from the main body 2 of the device.

[0110] As shown in Figures 1 and 16(a) and 16(b), the main body 2 of the device is equipped with a shutter interlocking mechanism 9. The shutter interlocking mechanism 9 has the function of opening and closing the shutter 69 in conjunction with the installation and removal of the process cartridge 10. Specifically, the shutter interlocking mechanism 9 interlocks the shutter 69 with the installation and removal of the process cartridge 10 such that the shutter 69 is in the open position when the process cartridge 10 is installed on the main body frame 2A, and the shutter 69 is in the closed position when the process cartridge 10 is not installed on the main body frame 2A.

[0111] The shutter interlocking mechanism 9 is located in the left-right direction on the opposite side of the process cartridge 10 from the front frame 23A of the first side plate 23 (i.e., to the right of the front frame 23A).

[0112] As shown in Figures 1 and 16(a) and 16(b), the shutter interlocking mechanism 9 includes a contact piece 90, a first rotational link 91, a linear link 92, a second rotational link 93, and a third rotational link 94. Furthermore, as shown in Figures 17(a) to 18(b), the shutter interlocking mechanism 9 also includes a shutter link 95 and a coil spring 96.

[0113] The shutter link 95 is an arm member that engages with the shutter 69 and rotates the shutter 69 between the shielded position and the open position by rotating around the rotation axis Ax2 (second rotation axis) independently of the cam 672 of the switching mechanism 66 described above. The third rotation link 94 rotates the shutter link 95 by rotating around the rotation axis Ax2 (second rotation axis) which is common to the cam 672 and the shutter link 95. The linear link 92 is movable in the direction from the rear end 2B (first end) to the front end 2F (second end) of the main frame 2A (+X direction) and in the opposite direction (-X direction) in order to rotate the third rotation link 94. The contact piece 90 is an engaged part that can engage with the drum shaft 11a (engaging part) of the process cartridge 10.

[0114] During the process of mounting the process cartridge 10 onto the main frame 2A, the contact piece 90 (engaged portion) engages with the drum shaft 11a (engaged portion) of the process cartridge 10. The force received by the contact piece 90 (engaged portion) from the drum shaft 11a (engaged portion) causes the linear link 92 to move in the -X direction from the front end 2F (second end) to the rear end 2B (first end) of the main frame 2A. The movement of the linear link 92 causes the shutter link 95 to rotate. The rotation of the shutter link 95 then rotates the shutter 69 from the open position to the closed position.

[0115] The components of the shutter interlocking mechanism 9 will now be described in detail. As shown in Figures 16(a) and 16(b), the contact piece 90 is a component that moves in contact with a part of the process cartridge 10. In this embodiment, the contact piece 90 is configured to contact the drum shaft 11a of the photosensitive drum 11. The contact piece 90 is slidably engaged with the contact piece rail 232. The contact piece rail 232 guides the contact piece 90 as it moves in contact with the drum shaft 11a.

[0116] The contact piece 90 comprises a main body portion 901, a connecting portion 902, a first projection 903, and a second projection 904. The main body portion 901 is a plate-shaped member with its thickness direction oriented in the left-right direction. The connecting portion 902 is a convex portion (boss) that protrudes to the right from the right side of the main body portion 901. The first projection 903 and the second projection 904 are convex portions (pins) that protrude to the left from the left side of the main body portion 901. Both the first projection 903 and the second projection 904 are engaged with the contact piece rail 232 of the first side plate 23 and are guided by the contact piece rail 232.

[0117] The second projection 904 is located downstream of the first projection 903 in the mounting direction of the process cartridge 10. The mounting direction of the process cartridge 10 refers to the direction in which the process cartridge 10 moves along the cartridge rail 231 when it is mounted on the main body 2 of the apparatus. In this embodiment, the mounting direction of the process cartridge 10 is forward (+X direction) and inclined downward in the front-rear direction.

[0118] The contact piece 90 is located on the opposite side of the process cartridge 10 relative to the front frame 23A of the first side plate 23 (i.e., to the right of the front frame 23A). The first projection 903 and the second projection 904 are located in positions that do not protrude toward the side of the process cartridge 10 relative to the front frame 23A of the first side plate 23 (i.e., to the left).

[0119] The first projection 903 contacts the drum shaft 11a when the process cartridge 10 is mounted on the device body 2. The second projection 904 contacts the drum shaft 11a when the process cartridge 10 is removed from the device body 2. In other words, the first projection 903 contacts the drum shaft 11a of the process cartridge 10 when it is mounted on the device body 2, and the second projection 904 contacts the drum shaft 11a of the process cartridge 10 when it is removed from the device body 2.

[0120] The first projection 903 contacts the drum shaft 11a of the process cartridge 10 through the through hole 23C in the middle portion 232b (through hole 23C) of the contact rail 232. The second projection 904 also contacts the drum shaft 11a of the process cartridge 10 through the through hole 23C in the middle portion 232b (through hole 23C) of the contact rail 232.

[0121] The drum shaft 11a may contact the first projection 903 and the second projection 904 inside the through hole 23C, or it may contact the first projection 903 and the second projection 904 at a position that extends to the right of the through hole 23C in the left-right direction.

[0122] The first rotating link 91 is a linear member connected to the contact piece 90, and is located to the right of the front frame 23A of the first side plate 23 in the left-right direction. The front end of the first rotating link 91 has a fitting portion 911 into which the connecting portion 902 of the contact piece 90 fits, and the rear end has a boss 912 that protrudes to the left. The first rotating link 91 is inclined so that the fitting portion 911 is located above and in front of the boss 912. The fitting portion 902 into the fitting portion 911 connects the first rotating link 91 to the contact piece 90, and it rotates as the contact piece 90 moves.

[0123] The linear motion link 92 is a linear member that extends in the front-rear direction and is connected to the first rotational motion link 91. The linear motion link 92 is located to the right of the front frame 23A of the first side plate 23 in the left-right direction. The front end of the linear motion link 92 has a fitting portion 921 into which the boss 912 of the first rotational motion link 91 fits, and the rear end has a connecting hole 922. The linear motion link 92 is connected to the first rotational motion link 91 by the fitting of the boss 912 into the fitting portion 921, and moves linearly in the front-rear direction as the first rotational motion link 91 rotates.

[0124] The second pivot link 93 is connected to the linear link 92 and supported by the first side plate 23. The second pivot link 93 has a support portion 931 that is rotatably supported by the first side plate 23, a first arm 932 extending downward from the support portion 931, and a second arm 933 extending upward. The tip of the first arm 932 has an engagement pin 932a that protrudes to the left, and the tip of the second arm 933 has a connecting hole 933a.

[0125] The engagement pin 932a of the first arm 932 is engaged with the connecting hole 922 of the linear link 92 from the right side. The engagement pin 932a moves by being pressed against the inner wall of the connecting hole 922 as the linear link 92 moves in the front-rear direction. The second pivot link 93 is connected to the linear link 92 via the engagement of the engagement pin 932a and the connecting hole 922, and rotates around the support portion 931 as the linear link 92 moves.

[0126] The third rotating link 94 is connected to the second rotating link 93 and is rotatably supported on the camshaft 671 of the fuser 6. The third rotating link 94 is rotatable around the rotation axis Ax2 independently of the camshaft 671. In other words, the third rotating link is rotatable independently of the aforementioned pressure release mechanism 67. Furthermore, the shutter interlocking mechanism 9 can operate independently of the cover interlocking mechanism 8 and the switching mechanism 66.

[0127] The third rotation link 94 has a support portion 941 that is rotatably supported on the camshaft 671, an engagement pin 942 extending from the support portion 941, and a connecting hole 943 formed at a different phase from the engagement pin 942 in the rotational direction around the support portion 941. The engagement pin 942 protrudes to the right in the left-right direction (second direction). The engagement pin 942 engages with the connecting hole 933a, which is a hole in the second rotation link 93, from the left side. The engagement pin 942 is pressed against the inner wall of the connecting hole 933a when the second rotation link 93 rotates. The third rotation link 94 is connected to the second rotation link 93 via the engagement of the engagement pin 942 and the connecting hole 933a, and rotates around the camshaft 671 as the second rotation link 93 rotates.

[0128] As shown in Figures 17(a) to 18(b), the shutter link 95 is connected to the third rotation link 94 and is rotatably supported on the camshaft 671 of the fuser 6. The shutter link 95 is rotatable independently of the camshaft 671 around the rotation axis Ax2. In other words, the third rotation link is rotatably supported without affecting the switching mechanism 66 described above. The shutter link 95 moves with the movement of the third rotation link 94, moving the shutter 69 of the fuser 6 between the closed and open positions. The shutter link 95 is located at the right end of the fuser 6.

[0129] The shutter link 95 includes a support portion 951, an arm portion 952, an engaging portion 953, and an engaging pin 954.

[0130] The support portion 951 of the shutter link 95 is rotatably supported on the camshaft 671. The camshaft 671 has a projection 671a that protrudes to the right from the right end of the upper frame 64 (Figure 17(a)(b)). The support portion 951 is supported by the projection 671a of the camshaft 671. The arm portion 952 extends forward from the support portion 951. The engaging portion 953 is located at the front end of the arm portion 952 and has an elongated oval engaging hole 953a that is long in the front-rear direction. An opening / closing pin 691 that protrudes to the right from the right end of the shutter 69 engages with the engaging hole 953a.

[0131] The shutter link 95 is rotatable around the support portion 951 in a direction in which the engaging portion 953 moves up and down. When the engaging portion 953 moves downward, the shutter 69 moves from the open position (Figures 17(a), 18(a)) to the closed position (Figures 17(b), 18(b)). When the engaging portion 953 moves upward, the shutter 69 moves from the closed position to the open position.

[0132] The engagement pin 954 of the shutter link 95 protrudes to the right from the rear of the arm portion 952. The engagement pin 954 is engaged with the connecting hole 943 of the third rotation link 94 from the left side.

[0133] The coil spring 96 is a torsion spring attached to the support portion 941 of the third rotation link 94. The coil spring 96 has a first arm portion 961 and a second arm portion 962. The first arm portion 961 extends from the inner diameter side to the outer diameter side of the connecting hole 943 and enters into the connecting hole 943. Similarly, the second arm portion 962 extends from the inner diameter side to the outer diameter side of the connecting hole 943 from a position different from that of the first arm portion 961 in the circumferential direction and enters into the connecting hole 943.

[0134] The first arm 961 is located above the engagement pin 954 within the connecting hole 943, and the second arm 962 is located below the engagement pin 954. The coil spring 96 rotates in conjunction with the rotation of the third pivot link 94. As the third pivot link 94 rotates, either the first arm 961 or the second arm 962 engages with the engagement pin 954. The shutter link 95 is connected to the third pivot link 94 via the engagement of the engagement pin 954 with either the first arm 961 or the second arm 962. As a result, the shutter link 95 moves in conjunction with the rotation of the third pivot link 94, moving the shutter 69 between the closed and open positions.

[0135] The coil spring 96 may be positioned so that the engagement pin 954 is sandwiched between the first arm portion 961 and the first end portion 943a of the connecting hole 943. In this case, when the third pivot link 94 rotates counterclockwise in Figures 18(a) and 18(b), the first arm portion 961 of the coil spring 96 presses the engagement pin 954 downward in the figure. Also, when the third pivot link 94 rotates clockwise in Figures 18(a) and 18(b), the first end portion 943a of the connecting hole 943 presses the engagement pin 954 upward in the figure.

[0136] In this embodiment, when the process cartridge 10 is attached to or removed from the device body 2, the contact piece 90 (engaged portion) of the shutter interlocking mechanism 9 engages with the drum shaft 11a (engaged portion) of the process cartridge 10 and moves along the contact piece rail 232. The movement of the contact piece 90 is then transmitted to the shutter 69 via the first rotational link 91, the linear link 92, the second rotational link 93, the third rotational link 94, and the shutter link 95, causing the shutter 69 to move between the closed and open positions.

[0137] The shutter interlocking mechanism 9 in this embodiment is composed of a contact piece 90, a first rotational link 91, a linear link 92, a second rotational link 93, a third rotational link 94, a shutter link 95, and a coil spring 96, but is not limited thereto. The shutter interlocking mechanism 9 can also be composed of a single link that is connected to the shutter 69 and opens and closes the shutter 69 by contacting the process cartridge 10. Furthermore, the manner of movement of each link member constituting the shutter interlocking mechanism 9 (modes such as rotation and linear motion, and direction of movement) is not limited to those described in this embodiment. The manner of movement of each link member is sufficient as long as it opens and closes the shutter 69 with appropriate operation in response to the insertion and removal of the process cartridge 10.

[0138] In this embodiment, force is transmitted from the third rotational link 94 to the shutter link 95 via a coil spring 96. This configuration has the advantage of preventing difficulty in removing the process cartridge 10 or damage to the shutter interlocking mechanism 9 when, for example, jam paper is retained at the inlet 6i of the fuser 6 and the user attempts to remove the process cartridge 10 from the main body 2. Specifically, when removing the process cartridge 10, force is transmitted in the order of contact piece 90, first rotational link 91, linear link 92, second rotational link 93, and third rotational link 94, causing the third rotational link 94 to attempt to rotate counterclockwise from the position shown in Figure 18(a). At this time, if the movement of the shutter 69 from the open position to the closed position (Figure 18(b)) is obstructed by the jam paper, the rotation of the shutter link 95 is also obstructed, and the engagement pin 954 cannot move downward from the position shown in Figure 18(a) to the position shown in Figure 18(b). However, due to the elastic deformation of the coil spring 96, the first arm 961 is allowed to move relative to the third pivot link 94 so as to approach the second end 943b of the connecting hole 943. Therefore, even when the shutter 69 and shutter link 95 are not moving, the third pivot link 94 can move to a position corresponding to the removal state of the process cartridge 10 (Figure 18(b)).

[0139] In other words, the coil spring 96 allows the rotation of the third pivot link 94 and the movement of the contact piece 90 which is linked to the third pivot link 94, even if the shutter 69 cannot move from the open position to the closed position. Therefore, it is possible to prevent a situation where the movement of the contact piece 90 stops before the second projection 904 of the contact piece 90 passes from the middle part 232b (through hole 24C) of the contact piece rail 232 to the front part 232a, making it impossible to remove the process cartridge 10. In addition, it is possible to prevent damage to the shutter interlocking mechanism 9 by a user who is prevented from removing the process cartridge 10 and pulls on it forcefully.

[0140] (Locking mechanism) As shown in Figures 16(a) and 16(b), the main body of the device 2 is equipped with a locking mechanism 97 that controls the movement of the shutter interlocking mechanism 9. Specifically, the locking mechanism 97 can restrict the movement of the linear motion link 92 in the forward and backward directions by pressing down on the linear motion link 92.

[0141] The locking mechanism 97 includes an arm 98 that contacts the upper surface of the linear link 92, and a locking spring 99 that presses the tip of the arm 98 against the upper surface of the linear link 92. The locking spring 99 is an example of a biasing means that presses the tip of the arm 98 against the linear link 92.

[0142] The arm 98 has a support portion 971 that is rotatably supported on the first side plate 23, a contact portion 972 that contacts the upper surface of the linear link 92, and a spring receiving portion 973 that receives the lock spring 99. The arm 98 extends from the support portion 971, which is the base end, toward the contact portion 972, which is the tip, in a direction that intersects the left-right direction (approximately the front-back direction), with the contact portion 972 located at the front end. The arm 98 is rotatable around an axis that extends in the left-right direction. The contact portion 972 is movable in the vertical direction around the support portion 971. The spring receiving portion 973 is located above the contact portion 972.

[0143] The upper end of the lock spring 99 is supported by the first side plate 23, and the lower end is attached to the spring receiving portion 973 of the arm 98. The lock spring 99 biases the arm 98 so as to press the contact portion 972 of the arm 98 against the upper surface of the linear link 92.

[0144] On the upper surface of the linear link 92, a link projection 923 is formed between the fitting portion 921 and the connecting hole 922, projecting toward the locking mechanism 97 side (upwards). The link projection 923 has a convex shape including a first inclined surface 923a that slopes downward toward the rear, and a second inclined surface 923b that is formed continuously in front of the first inclined surface 923a and slopes downward toward the front.

[0145] The contact portion 972 of the arm 98 moves to overcome the link projection 923 against the biasing force of the lock spring 99 as the linear link 92 moves in the front-rear direction. The contact portion 972 of the arm 98 can be stably positioned on the rear side of the first inclined surface 923a of the link projection 923, or on the front side of the second inclined surface 923b.

[0146] When the contact portion 972 of the arm 98 is located behind the link projection 923, the contact portion 972 engages with the first inclined surface 923a, thereby restricting the rearward movement of the linear link 92. When the contact portion 972 of the arm 98 is located in front of the link projection 923, the contact portion 972 engages with the second inclined surface 923b, thereby restricting the forward movement of the linear link 92.

[0147] In other words, the locking mechanism 97 can restrict the operation of the shutter interlocking mechanism 9 by having the arm 98 contact the linear link 92 at the rear of the link projection 923, thereby restricting the rearward movement of the linear link 92. The locking mechanism 97 can also restrict the operation of the shutter interlocking mechanism 9 by having the arm 98 contact the linear link 92 at the front of the link projection 923, thereby restricting the forward movement of the linear link 92. The locking mechanism 97 can prevent the shutter 69 from opening and closing unintentionally when the process cartridge 10 is not installed or removed. In this way, the locking mechanism 97 restricts the movement of the linear link 92 by having the arm 98 press against it, and the locking mechanism 97 can be constructed with a simple structure.

[0148] The specific configuration of the locking mechanism 97 is not limited to that described in this embodiment. For example, instead of providing a locking mechanism 97 which is composed of a separate component from the shutter interlocking mechanism 9, the link member constituting the shutter interlocking mechanism 9 itself may have the function of holding the shutter 69 in the open or closed position.

[0149] (Positional relationship between the switching mechanism, cover interlocking mechanism, and shutter interlocking mechanism) As described above, the main body 2 of the image forming apparatus 1 of this embodiment has a switching mechanism 66, a cover interlocking mechanism 8, and a shutter interlocking mechanism 9. As previously mentioned, both the cover interlocking mechanism 8 and the shutter interlocking mechanism 9 are provided on the right end 2R (third end) side of the main body frame 2A in the left-right direction (second direction), as shown in Figure 1.

[0150] In other words, the cover interlocking mechanism 8 and the shutter interlocking mechanism 9 are concentrated and arranged on the right end 2R (third end) side of the main frame 2A. This configuration makes it possible to miniaturize the main body 2 of the image forming apparatus 1 in the left-right direction (second direction) in a device that has the function of switching the pressure applied to the nip section np1 in conjunction with the opening and closing of the rear opening / closing cover 22, and the function of opening and closing the shutter 69 of the fuser 6 in conjunction with the attachment and detachment operation of the process cartridge 10.

[0151] The cover interlocking mechanism 8 and the shutter interlocking mechanism 9 are positioned at the ends of the main frame 2A in the left-right direction so as not to interfere with the process cartridge 10, the fuser 6, and the transport rollers and transport guides of the sheet transport path P. If the cover interlocking mechanism 8 were positioned on the right end 2R side of the main frame 2A and the shutter interlocking mechanism 9 were positioned on the left end 2L side of the main frame 2A, the size of the device body 2 in the left-right direction (second direction) would increase. According to this embodiment, since the cover interlocking mechanism 8 and the shutter interlocking mechanism 9 are concentrated on the right end 2R (third end) side of the main frame 2A, the increase in size of the device body 2 in the left-right direction (second direction) can be suppressed.

[0152] The positional relationship between the switching mechanism 66, the cover interlocking mechanism 8, and the shutter interlocking mechanism 9 will be further explained using Figures 19(a) to 21(b).

[0153] Figures 19(a) and 19(b) are perspective views of the switching mechanism 66, the cover interlocking mechanism 8, and the shutter interlocking mechanism 9. Figure 20 is a top view of a part of the switching mechanism 66, the cover interlocking mechanism 8, and the shutter interlocking mechanism 9, viewed from above in the direction of gravity. Figure 21(a) is a view of a part of the switching mechanism 66, the cover interlocking mechanism 8, and the shutter interlocking mechanism 9, viewed from the rear end 2B side of the main frame 2A toward the front (+X direction). Figure 21(b) is a view of a part of the switching mechanism 66, the cover interlocking mechanism 8, and the shutter interlocking mechanism 9, viewed from the front end 2F side of the main frame 2A toward the rear (-X direction).

[0154] As shown in Figures 19(a)(b) and 20, in the left-right direction (second direction), the cover interlocking mechanism 8 is positioned differently from the switching mechanism 66. In other words, in the left-right direction (second direction), the range Y8 in which the links (81, 82, 83, 84) constituting the cover interlocking mechanism 8 are positioned is different from the range Y6 in which the pressure arm 652, pressure spring 653 (biasing member), and cam 672 of the switching mechanism 66 are positioned. This configuration allows the cover interlocking mechanism 8 and the switching mechanism 66 to be positioned without interference in the left-right direction (second direction).

[0155] Furthermore, as shown in Figures 19(a) to 21(b), in the left-right direction (second direction), the shutter interlocking mechanism 9 is positioned differently from the switching mechanism 66. In other words, in the left-right direction (second direction), the range Y9 in which the elements (90-95) constituting the shutter interlocking mechanism 9 are positioned is different from the range Y6 in which the pressurizing arm 652, pressurizing spring 653 (biasing member), and cam 672 of the switching mechanism 66 are positioned. This configuration allows the shutter interlocking mechanism 9 and the switching mechanism 66 to be positioned without interference in the left-right direction (second direction).

[0156] Furthermore, as shown in Figures 19(a) to 21(b), in the left-right direction (second direction), the fourth link 84 of the cover interlocking mechanism 8 is located outside the shutter link 95 of the shutter interlocking mechanism 9. This configuration allows the fourth link 84 of the cover interlocking mechanism 8 and the shutter link 95 of the shutter interlocking mechanism 9 to be positioned without interference in the left-right direction (second direction).

[0157] In particular, in this embodiment, both the fourth link 84 and the shutter link 95 are components that can rotate independently of each other around the rotation axis Ax2 (second rotation axis). By arranging the fourth link 84 and the shutter link 95, which rotate around a common rotation axis Ax2 (second rotation axis), in a left-right direction (second direction), the cover interlocking mechanism 8 and the shutter interlocking mechanism 9 can be arranged without difficulty.

[0158] Furthermore, as shown in Figures 19(a) to 21(b), in the left-right direction (second direction), the fourth link 84 of the cover interlocking mechanism 8 is located inside the linear link 92 of the shutter interlocking mechanism 9. This allows the linear link 92 to be positioned as far outward as possible.

[0159] As shown in Figure 21(b), the position of the fourth link 84 in the left-right direction (second direction) coincides with the position of the contact piece 90 (engaged portion) of the shutter interlocking mechanism 9 in the left-right direction (second direction) (Figure 20). In other words, when viewed in at least one direction perpendicular to the left-right direction, the fourth link 84 overlaps with the contact piece 90. Therefore, the device can be miniaturized in the left-right direction compared to the case where the position of the contact piece 90 (engaged portion) and the position of the fourth link 84 are arranged far apart in the left-right direction (second direction). Furthermore, the linear link 92, which does not directly engage with the process cartridge 10, is located further out than the fourth link 84 in the left-right direction (second direction), thus avoiding contact with the process cartridge 10.

[0160] As described above, in the left-right direction (second direction), a portion of the shutter interlocking mechanism 9 is located inside the fourth link 84, and another portion of the shutter interlocking mechanism 9 is located outside the fourth link 84. In this case, the shutter interlocking mechanism 9 is provided with a portion that overlaps with the fourth link 84 when viewed in a direction perpendicular to the left-right direction (second direction), and which is capable of transmitting force from the outside to the inside relative to the fourth link 84.

[0161] In this embodiment, the support portion 941 of the third rotational link 94 of the shutter interlocking mechanism 9 is located inward from the fourth link 84 in the left-right direction (second direction). Also, the support portion 931 of the second rotational link 93 is located outward from the fourth link 84 in the left-right direction (second direction) (Figure 21(a)). The third rotational link 94 has an engagement pin 942 as the connected portion, and the second rotational link 93 has a connecting hole 933a as the connecting portion that connects to the engagement pin 942.

[0162] Furthermore, at least one of the connecting hole 933a (connecting part) and the engaging pin 942 (connected part) overlaps with the fourth link 84 when viewed in at least one direction perpendicular to the left-right direction. Therefore, the connecting hole 933a and the engaging pin 942 of the shutter interlocking mechanism 9 function as parts capable of transmitting force from the outside to the inside of the fourth link 84 in the left-right direction (second direction). Alternatively, a connecting hole may be provided in the third rotational link 94, and an engaging pin that engages with the connecting hole may be provided in the second rotational link 93.

[0163] Furthermore, when viewed in the left-right direction (second direction), the support portion 842 of the fourth link 84 and the support portion 951 of the shutter link 95 may overlap. Also, when viewed in the left-right direction (second direction), the support portion 842 of the fourth link 84 and the support portion 941 of the third pivot link 94 may overlap.

[0164] Furthermore, in this embodiment, the third rotation link 94 (rotation link) and shutter link 95 of the shutter interlocking mechanism 9 are arranged coaxially with the cam 672 of the switching mechanism 66 and are supported to rotate independently of the cam 672. Therefore, the size of the device equipped with the shutter interlocking mechanism 9 and the switching mechanism 66 can be reduced compared to the case where at least one of the third rotation link 94 and the shutter link 95 is arranged on an axis different from the rotation axis Ax2 of the cam 672.

[0165] Summary of this disclosure This disclosure includes at least the following: (Composition 1) A main frame having a first end and a second end opposite to the first end in a first horizontal direction, and a third end and a fourth end opposite to the third end in a second horizontal direction perpendicular to the first direction, A fixing unit comprising a heating unit and a pressure roller that together with the heating unit forms a nip portion, wherein the fixing unit heats and fixes a toner image to a sheet while conveying the sheet in the nip portion, wherein the fixing unit is provided on the side of the first end of the main body frame in the first direction, A shutter is provided that is movable between a shielding position that closes the upstream entrance of the nip portion and an open position that opens the entrance of the nip portion in the conveying direction in which the nip portion conveys the sheet. A cartridge having a photosensitive drum rotatable about a rotation axis extending in the second direction, and a developing roller that develops a toner image on the photosensitive drum by supplying toner to the photosensitive drum, and a cartridge that is detachable from the main body frame, the cartridge being mounted on the side of the second end of the main body frame in the first direction, A rear opening / closing cover that is rotatably supported with respect to the main frame at the first end of the main frame, and which rotates between an open position that allows access to the fixing unit from the first end of the main frame and a closed position that prevents access to the fixing unit from the first end of the main frame. A switching mechanism for switching the state of the fixing unit between a first state in which the pressure of the nip portion is a first pressure, and a second state in which the pressure is lower than the first pressure or zero. A cover interlocking mechanism that interlocks the switching mechanism with the rear opening / closing cover such that the fixing unit enters the first state when the rear opening / closing cover is in the closed position, and the fixing unit enters the second state when the rear opening / closing cover is in the open position, the cover interlocking mechanism provided at the third end of the main frame, A shutter interlocking mechanism that links the attachment / detachment of the cartridge with the shutter such that the shutter is in the open position when the cartridge is mounted on the main frame and the shutter is in the closed position when the cartridge is not mounted on the main frame, comprising a shutter interlocking mechanism provided at the third end of the main frame, An image forming apparatus characterized by comprising: (Configuration 2) When the aforementioned axis of rotation is defined as the first axis of rotation, The switching mechanism includes an arm that pressurizes the heating unit toward the pressure roller, a biasing member that biases the arm so that the heating unit is pressed toward the pressure roller by the arm, and a cam that rotates the arm about a second rotation axis to move the arm to a first position in which the fixing unit is in the first state and to a second position in which the fixing unit is in the second state. The image forming apparatus according to configuration 1, characterized in that it is a picture forming apparatus. (Composition 3) The cartridge has an engaging portion, The shutter interlocking mechanism includes a shutter link that engages with the shutter and rotates independently of the cam about the second rotation axis, thereby rotating the shutter between the shielded position and the open position; a rotating link that rotates the shutter link by rotating about the second rotation axis; a linear link that is movable in a direction from the first end toward the second end and in a direction from the second end toward the first end in order to rotate the rotating link; and an engaged portion that can engage with the engaging portion of the cartridge. In the process of mounting the cartridge onto the main frame, the engaged portion engages with the engaged portion of the cartridge, causing the linear link to move from the second end to the first end, the movement of the linear link causes the shutter link to rotate, and the rotation of the shutter link causes the shutter to rotate from the open position to the closed position. The image forming apparatus according to configuration 2, characterized in that... (Composition 4) The cover interlocking mechanism includes a first link that engages with the rear opening / closing cover, a second link that engages with the first link and is rotatable about a third rotation axis extending in the second direction, a third link that engages with both the second link and the switching mechanism and is movable in the direction from the first end toward the second end and from the second end toward the first end, and a fourth link that engages with the third link and is rotatable about a fourth rotation axis extending in the second direction. The image forming apparatus according to configuration 3, characterized by having the following features. (Composition 5) In the second direction, the position of the cover interlocking mechanism is arranged to be different from the position of the arm, biasing member, and cam of the switching mechanism. An image forming apparatus according to any one of configurations 2 to 4, characterized by the above. (Composition 6) In the second direction, the fourth link is located outside the shutter link. The image forming apparatus according to configuration 4 or 5, characterized by the above. (Composition 7) In the second direction, the fourth link is located inside the linear link. An image forming apparatus according to any one of configurations 4 to 6, characterized by the features described above. (Composition 8) The position of the fourth link in the second direction coincides with the position of the engaged portion in the second direction. An image forming apparatus according to any one of configurations 4 to 7, characterized by the features described above. (Composition 9) The switching mechanism has a camshaft that supports the cam and the fourth link and extends in the second direction, The aforementioned rotating link has a support portion that is rotatably supported with respect to the camshaft, In the second direction, the fourth link is provided outside the support portion. An image forming apparatus according to any one of configurations 4 to 8, characterized by the above. (Composition 10) The aforementioned pivot link and shutter link are arranged coaxially with the cam and are supported to be rotatable independently of the cam. An image forming apparatus according to any one of configurations 3 to 9, characterized by the above. (Composition 11) The heating unit comprises a cylindrical film and a heater provided on the inner surface side of the film. The pressure roller, together with the heater via the film, forms the nip portion. An image forming apparatus according to any one of configurations 1 to 10, characterized by the above. (Composition 12) An operating section for operating the image forming apparatus is provided at the end of the image forming apparatus on the side of the fourth end in the second direction. A power supply for supplying power to the operating unit is provided at the fourth end of the main frame. An image forming apparatus according to any one of configurations 1 to 11, characterized by the above. [Explanation of Symbols]

[0166] 2A…Main frame / 2B…Rear end (1st end) / 2F…Front end (2nd end) / 2L…Left end (4th end) / 2R…Right end (3rd end) / 6…Fuser (fuser unit) / 8…Cover interlocking mechanism / 9…Shutter interlocking mechanism / 10…Process cartridge (cartridge) / 11…Photosensitive drum / 12…Developing roller / 22…Rear opening / closing cover / 61…Heating unit / 62…Pressure roller / 66…Switching mechanism / 69…Shutter

Claims

1. A main frame having a first end and a second end opposite to the first end in a first horizontal direction, and a third end and a fourth end opposite to the third end in a second horizontal direction perpendicular to the first direction, A fixing unit comprising a heating unit and a pressure roller that together with the heating unit forms a nip portion, wherein the fixing unit heats and fixes a toner image to a sheet while conveying the sheet in the nip portion, wherein the fixing unit is provided on the side of the first end of the main body frame in the first direction, A shutter is provided that is movable between a shielding position that closes the upstream entrance of the nip portion and an open position that opens the entrance of the nip portion in the conveying direction in which the nip portion conveys the sheet. A cartridge having a photosensitive drum rotatable about a rotation axis extending in the second direction, and a developing roller that develops a toner image on the photosensitive drum by supplying toner to the photosensitive drum, and a cartridge that is detachable from the main body frame, the cartridge being mounted on the side of the second end of the main body frame in the first direction, A rear opening / closing cover that is rotatably supported with respect to the main frame at the first end of the main frame, and which rotates between an open position that allows access to the fixing unit from the first end of the main frame and a closed position that prevents access to the fixing unit from the first end of the main frame. A switching mechanism for switching the state of the fixing unit between a first state in which the pressure of the nip portion is a first pressure, and a second state in which the pressure is lower than the first pressure or zero. A cover interlocking mechanism that interlocks the switching mechanism with the rear opening / closing cover such that the fixing unit enters the first state when the rear opening / closing cover is in the closed position, and the fixing unit enters the second state when the rear opening / closing cover is in the open position, the cover interlocking mechanism provided at the third end of the main frame, A shutter interlocking mechanism that links the attachment / detachment of the cartridge with the shutter such that the shutter is in the open position when the cartridge is mounted on the main frame, and the shutter is in the closed position when the cartridge is not mounted on the main frame, comprising a shutter interlocking mechanism provided at the third end of the main frame, An image forming apparatus characterized by comprising:

2. When the aforementioned axis of rotation is defined as the first axis of rotation, The switching mechanism includes an arm that pressurizes the heating unit toward the pressure roller, a biasing member that biases the arm so that the heating unit is pressed toward the pressure roller by the arm, and a cam that rotates the arm about a second rotation axis to move the arm to a first position in which the fixing unit is in the first state and to a second position in which the fixing unit is in the second state. The image forming apparatus according to feature 1.

3. The cartridge has an engaging portion, The shutter interlocking mechanism includes a shutter link that engages with the shutter and rotates independently of the cam about the second rotation axis, thereby rotating the shutter between the shielded position and the open position; a rotating link that rotates the shutter link by rotating about the second rotation axis; a linear link that is movable in a direction from the first end toward the second end and in a direction from the second end toward the first end in order to rotate the rotating link; and an engaged portion that can engage with the engaging portion of the cartridge. In the process of mounting the cartridge onto the main frame, the engaged portion engages with the engaged portion of the cartridge, causing the linear link to move from the second end to the first end, the movement of the linear link causes the shutter link to rotate, and the rotation of the shutter link causes the shutter to rotate from the open position to the closed position. The image forming apparatus according to feature 2.

4. The cover interlocking mechanism includes a first link that engages with the rear opening / closing cover, a second link that engages with the first link and is rotatable about a third rotation axis extending in the second direction, a third link that engages with both the second link and the switching mechanism and is movable in the direction from the first end toward the second end and from the second end toward the first end, and a fourth link that engages with the third link and is rotatable about a fourth rotation axis extending in the second direction. The image forming apparatus according to claim 3, characterized by having the following features.

5. In the second direction, the position of the cover interlocking mechanism is different from that of the arm, biasing member, and cam of the switching mechanism. The image forming apparatus according to feature 2.

6. In the second direction, the fourth link is provided outside the shutter link. The image forming apparatus according to feature 4.

7. In the second direction, the fourth link is located inside the linear link. The image forming apparatus according to feature 4.

8. The position of the fourth link in the second direction coincides with the position of the engaged portion in the second direction. The image forming apparatus according to feature 7.

9. The switching mechanism has a camshaft that supports the cam and the fourth link and extends in the second direction, The aforementioned rotating link has a support portion that is rotatably supported with respect to the camshaft, In the second direction, the fourth link is provided outside the support portion. The image forming apparatus according to feature 4.

10. The aforementioned pivot link and shutter link are arranged coaxially with the cam and are supported to be rotatable independently of the cam. The image forming apparatus according to feature 3.

11. The heating unit comprises a cylindrical film and a heater provided on the inner surface side of the film. The pressure roller, together with the heater via the film, forms the nip portion. The image forming apparatus according to any one of claims 1 to 10.

12. An operating section for operating the image forming apparatus is provided at the end of the image forming apparatus on the side of the fourth end in the second direction. A power supply for supplying power to the operating unit is provided at the fourth end of the main frame. The image forming apparatus according to any one of claims 1 to 10.

Images