Fixing device

Abstract

To provide a fixing device comprising a shutter that opens and closes an entrance of the fixing device and a cam for changing a nip pressure, and to prevent increase in a size of an image forming apparatus.SOLUTION: A fixing device 1 comprises a first rotating body (belt BL), a second rotating body (pressure roller 3), a frame 4, a shutter 50, a pressure arm, and a cam for changing a nip pressure at a nip part NP. The second rotating body forms the nip part NP with the first rotating body. The frame 4 has an opening 4A through which a sheet S conveyed toward the nip part NP passes. The shutter 50 is rotatable between a closing position to close the opening 4A and an opening position to open the opening 4A. The pressure arm presses the first rotating body toward the second rotating body. The cam rotates centered on a first axis X1 to press the pressure arm. The shutter 50 is rotatable centered on the first axis X1.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a fixing device for fixing an image on a sheet.

Background Art

[0002] Conventionally, as a fixing device, there is known one provided with a shutter for opening and closing an inlet of a sheet of the fixing device (see Patent Document 1). In this technology, the rotation axis of the shutter is disposed near the inlet of the housing of the fixing device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, as a fixing device, there is known one provided with a nip pressure changing mechanism for changing the nip pressure applied between a heating roller and a pressure roller. The nip pressure changing mechanism includes, for example, a pressing arm and a spring for pressing the pressure roller toward the heating roller, and a cam capable of reducing the nip pressure by pressing the pressing arm against the biasing force of the spring. When such a nip pressure changing mechanism is provided in a conventional fixing device, if the rotation axis of the cam is disposed at a position different from the rotation axis of the shutter, there is a risk that the image forming apparatus becomes large-sized.

[0005] Therefore, an object of the present invention is to suppress an increase in the size of an image forming apparatus in a configuration including a shutter for opening and closing an inlet of a fixing device and a cam for changing a nip pressure.

Means for Solving the Problems

[0006] To solve the aforementioned problems, the fixing device according to the present invention comprises a first rotating body, a second rotating body, a frame, a shutter, a pressure arm, and a cam. The second rotating body forms a nip section with the first rotating body. The frame has an opening through which a sheet being transported toward the nip section passes. The frame supports the first and second rotating bodies. The shutter is rotatable between a closed position that closes the opening and an open position that opens the opening. The pressurizing arm pushes the first rotating body toward the second rotating body. The cam rotates around the first axis, pressing against the pressure arm and changing the nip pressure at the nip section. The shutter is rotatable around the first axis.

[0007] With this configuration, by making the pivot point of the shutter the first axis, which is the pivot point of the cam, it is not necessary to independently provide the pivot point of the shutter on the frame of the fixing device, thus preventing the image forming apparatus from becoming larger.

[0008] Furthermore, the fixing device may include a shaft that supports the cam and is rotatable about the first axis, and the shutter may be rotatably supported on the shaft.

[0009] This configuration allows a single shaft to support both the cam and the shutter, thus reducing the number of parts.

[0010] The fixing device may also include a connecting arm connected to the shutter and rotating independently of the cam around a first axis to rotate the shutter between a closed position and an open position, and an arm cam that rotates around the first axis to push the connecting arm at a position offset from the first axis, thereby rotating the connecting arm.

[0011] Furthermore, the fixing device may include a spring that can contact the connecting arm, and the arm cam may press the connecting arm via the spring to position the shutter in the closed position.

[0012] Furthermore, the fixing device may include a spring that can contact the connecting arm, and the arm cam may press the connecting arm via the spring to position the shutter in the open position.

[0013] Furthermore, the shutter includes a shutter body that opens and closes the opening, and a shutter arm that extends from the shutter body toward the first axis, and the shutter arm may be curved so as to be convex toward the opposite side from the nip portion.

[0014] Furthermore, the first axis may be located downstream of the nip section in the sheet transport direction.

[0015] This configuration allows for a larger distance between the part that closes the shutter opening and the first axis, enabling the shutter to be opened and closed with a small amount of rotation.

[0016] Furthermore, the fixing device may include a substrate and a heater having a resistance heating element, and the first rotating body may be an endless belt heated by the heater and rotating around the heater. [Effects of the Invention]

[0017] According to the present invention, in a configuration that includes a shutter for opening and closing the aperture of the fixing device and a cam for changing the nip pressure, it is possible to suppress the increase in size of the image forming apparatus. [Brief explanation of the drawing]

[0018] [Figure 1] This diagram shows the configuration of a laser printer according to an embodiment. [Figure 2] (a) is a cross-sectional view showing the fixing device, and (b) is a close-up cross-sectional view showing the area around the heater. [Figure 3] Figure (a) shows the side of the heater where the resistance heating element is arranged, Figure (b) shows the heater and heat conduction member as seen from the back of the heater, and Figure (c) shows a cross-sectional view of the heater etc. cut along the longitudinal direction. [Figure 4]Cross-sectional view (a) showing the nip pressure changing mechanism when the nip pressure is the first nip pressure, and enlarged cross-sectional view (b) showing around the heater. [Figure 5] Cross-sectional view (a) showing the nip pressure changing mechanism when the nip pressure is the second nip pressure, and enlarged cross-sectional view (b) showing around the heater. [Figure 6] Perspective view showing the shutter, shaft, and frame disassembled. [Figure 7] Cross-sectional view showing the structure around the fixing device when the shutter is in the closed position. [Figure 8] Cross-sectional view showing the structure around the fixing device when the shutter is in the open position. [Figure 9] Perspective view showing the shutter operating mechanism. [Figure 10] Perspective view showing the shutter operating mechanism disassembled. [Figure 11] Side view (a) showing the fixing device when the shutter is in the closed position, and diagram (b) showing the relationship between the pressing portion, spring, and second boss of the shutter operating mechanism. [Figure 12] Side view (a) showing the fixing device when the shutter is in the open position, and diagram (b) showing the relationship between the pressing portion, spring, and second boss of the shutter operating mechanism.

Embodiments for Carrying Out the Invention

[0019] Next, embodiments of the present invention will be described in detail with appropriate reference to the drawings. As shown in FIG. 1, the laser printer 100 includes a main body housing 120, a supply unit 130, an exposure device 140, a process cartridge 150, a fixing device 1, and a control unit 500.

[0020] The main casing 120 includes a front cover 121 that opens and closes a first opening H1, a manual feed tray 122, a rear cover 123 that opens and closes a second opening H2, and an output tray 124. The first opening H1 is an opening through which a process cartridge 150 can pass. The manual feed tray 122 is a tray used when printing on sheets S, such as thick paper like postcards, transported along a straight transport path. In the following description, printing performed along a straight transport path will also be referred to as "straight printing".

[0021] The second opening H2 is an opening through which the sheet S discharged from the fuser 1 passes when straight printing is performed. The rear cover 123 is in an open state when straight printing is performed and supports the sheet S discharged from the second opening H2. The discharge tray 124 is a tray for supporting the sheet S discharged from inside the main housing 120 when the rear cover 123 is closed.

[0022] The laser printer 100 is further equipped with a cover sensor SE1 that detects when the rear cover 123 is closed. The information detected by the cover sensor SE1 is output to the control unit 500.

[0023] The supply unit 130 is a mechanism that supplies sheets S to the photosensitive drum 151, which will be described later. The supply unit 130 comprises a supply tray 131 for holding the sheets S, a pressing plate 132, and a supply mechanism 133. The sheets S in the supply tray 131 are pushed upward by the pressing plate 132 and separated one by one by the supply mechanism 133 and supplied to the process cartridge 150.

[0024] The exposure apparatus 140 includes a laser light source (not shown), a polygon mirror, lenses, a reflector, and the like. The exposure apparatus 140 exposes the surface of the photosensitive drum 151 with laser light based on image data emitted from the laser light source.

[0025] The process cartridge 150 is detachable from the main body housing 120 through the first opening H1. The process cartridge 150 includes a photosensitive drum 151, a charger 152, a developing roller 153, and a transfer roller 154.

[0026] The charger 152 charges the surface of the photosensitive drum 151. The exposure device 140 exposes the charged surface of the photosensitive drum 151 to form an electrostatic latent image on the surface of the photosensitive drum 151.

[0027] The developing roller 153 supplies toner from the process cartridge 150 to the electrostatic latent image on the photosensitive drum 151. This forms a toner image on the photosensitive drum 151. Subsequently, the sheet S supplied from the supply unit 130 passes between the photosensitive drum 151 and the transfer roller 154, transferring the toner image on the photosensitive drum 151 to the sheet S.

[0028] The fixing device 1 is a device that fixes the toner image onto the sheet S. The sheet S, on which the toner image has been fixed, is discharged onto the discharge tray 124 by the discharge roller 125.

[0029] As shown in Figure 2(a), the fixing device 1 comprises a heating unit 2, a pressure roller 3 as an example of a second rotating body, and a frame 4 that supports the heating unit 2 and the pressure roller 3.

[0030] The pressure roller 3 is a rotatable roller. The pressure roller 3 has a cylindrical shaft 3A and a cylindrical roller portion 3B. The shaft 3A is made of, for example, metal. The roller portion 3B is made of, for example, rubber. The roller portion 3B covers a part of the shaft 3A. The pressure roller 3 forms a nip portion NP (see Figure 2(b)) between itself and the heating unit 2, and more specifically, the belt BL described later.

[0031] The heating unit 2 includes a heater 10, a holder 20, a heat conductive member 30 shown in Figure 2(b), a stay ST, a belt BL as an example of a first rotating body, and a temperature sensor SE2 shown in Figure 2(b). The heater 10 heats the belt BL, and heats the sheet S via the belt BL. The temperature sensor SE2 detects the temperature of the heater 10. The temperature sensor SE2 outputs the detected temperature to the control unit 500. The temperature sensor SE2 is in contact with the heat conductive member 30.

[0032] As shown in Figure 2(b), the heater 10 comprises a substrate 11, a resistive heating element 12 disposed on the substrate 11, and a cover 13. The substrate 11 is made of an elongated rectangular plate of ceramic made of aluminum oxide. The heater 10 is a so-called ceramic heater. The resistive heating element 12 is formed on one surface of the substrate 11 by printing. As shown in Figure 3(a), in this embodiment, two resistive heating elements 12 are provided. The two resistive heating elements 12 are each elongated in the longitudinal direction of the heater 10 and are arranged parallel to each other in the short direction perpendicular to the longitudinal direction. In other words, the two resistive heating elements 12 are arranged on the substrate 11 in the direction of conveying the sheet S. In the following description, the direction of conveying the sheet S at the nip section NP will also simply be referred to as the "conveying direction". A conductor 19A is connected to one end 12A of each resistive heating element 12, and a power supply terminal 18 for supplying power to the resistive heating element 12 is provided at each end of the conductor 19A.

[0033] The power supply terminal 18 is electrically connected to the resistive heating element 12 via a conductor 19A. The power supply terminal 18 is located at one end 11E in the longitudinal direction of the circuit board 11. As shown in Figure 3(c), a connector C that supplies electricity to the heater 10 is connected to the power supply terminal 18. The connector C is detachable from one end in the longitudinal direction of the heater 10. Electricity is supplied to the power supply terminal 18 from the connector C. For convenience, the resistive heating element 12, cover 13, and belt BL are not shown in Figure 3(c).

[0034] As shown in Figure 3(a), the other end 12B of each resistance heating element 12 is connected to one another by a conductor 19B. The number of resistance heating elements 12 is not particularly limited. Furthermore, the heat distribution in the longitudinal direction may be adjusted by providing resistance heating elements in which the heat generation in the longitudinal center is greater than that in the longitudinal ends, and resistance heating elements in which the heat generation in the longitudinal ends is greater than that in the longitudinal center, and by individually controlling each resistance heating element.

[0035] As shown in Figure 2(b), the cover 13 covers the resistance heating element 12. The cover 13 is made of, for example, glass.

[0036] As shown in Figure 2(a), the holder 20 supports the heater 10 and also guides the belt BL. The holder 20 is made of, for example, resin.

[0037] The stay ST supports the holder 20. The stay ST is made of, for example, metal.

[0038] The belt BL is endless and made of metal or resin. The belt BL rotates around the heater 10 while being guided by the holder 20. The belt BL has an outer circumferential surface and an inner circumferential surface. The outer circumferential surface is in contact with the pressure roller 3 or the sheet S to be heated. The inner circumferential surface is in contact with the heater 10.

[0039] The heat conduction member 30 is a member that conducts heat in the longitudinal direction of the heater 10 to equalize the temperature of the heater 10 in the longitudinal direction. The heat conduction member 30 is a plate-shaped member that is located between the heater 10 and the holder 20 and is in contact with the other surface of the substrate 11. When the heating unit 2 sandwiches the sheet S between the pressure roller 3, the heat conduction member 30 is sandwiched between the heater 10 and the holder 20. The heat conduction member 30 is made of, for example, aluminum.

[0040] As shown in Figures 3(a) and 3(b), one end 12A and the other end 12B of the resistance heating element 12 are located outside the maximum width W1 of the sheet usable by the heating unit 2 in the longitudinal direction, and inside the one end 30A and the other end 30B of the heat conductive member 30. In other words, in the longitudinal direction, the length of the heat conductive member 30 is longer than the length of the resistance heating element 12.

[0041] In the longitudinal direction, the length of the substrate 11 is longer than the length of the heat conductive member 30. One end 30A of the heat conductive member 30 is located inward in the longitudinal direction than one end 11A of the substrate 11. The other end 30B of the heat conductive member 30 is located outward in the longitudinal direction than the other end 11B of the substrate 11.

[0042] As shown in Figure 4(a), the fixing device 1 further includes a nip pressure changing mechanism NM. The nip pressure changing mechanism NM is a mechanism that changes the nip pressure at the nip section NP between a first nip pressure and a second nip pressure that is smaller than the first nip pressure. The nip pressure changing mechanism NM includes a shaft SF, a pressure arm 60, a pressure spring 70, and a cam 80. The frame 4 supports the pressure spring 70 and also rotatably supports the pressure arm 60 and the cam 80.

[0043] The pressure arm 60, pressure spring 70, and cam 80 are positioned at one end and the other end of the frame 4 in the axial direction of the pressure roller 3. In the following description, "axial direction of the pressure roller 3" will also be simply referred to as "axial direction." Since the structure of one side of the nip pressure changing mechanism NM in the axial direction and the structure of the other side are substantially the same, the following description will mainly refer to the structure of the one side in the axial direction.

[0044] As shown in Figure 6, the shaft SF extends in the axial direction. The shaft SF is made of, for example, metal. Cams 80 are fixed to each axial end of the shaft SF. The cams 80 rotate as the shaft SF rotates. The frame 4 rotatably supports the shaft SF. As shown in Figure 4(a), the shaft SF is rotatable about the first axis X1.

[0045] The pressurizing arm 60 is an arm that presses the heating unit 2 toward the pressurizing roller 3. The frame 4 rotatably supports the pressurizing arm 60.

[0046] The pressure spring 70 is a tension coil spring that biases the pressure arm 60 toward the pressure roller 3. One end of the pressure spring 70 is attached to the pressure arm 60, and the other end is attached to the frame 4.

[0047] The cam 80 is capable of pressing the pressurizing arm 60 against the biasing force of the pressurizing spring 70. Specifically, the cam 80 is rotatable about the first axis X1 between a first position shown in Figure 4(a) and a second position shown in Figure 5(a). The cam 80 rotates when a driving force is supplied from a motor (not shown). The cam 80 may also rotate via a link mechanism that is linked to the opening and closing operation of the rear cover 123 that opens and closes the second opening H2.

[0048] When cam 80 is in the first position, the nip pressure is the first nip pressure. When cam 80 is in the second position, the nip pressure is the second nip pressure, which is smaller than the first nip pressure.

[0049] As shown in Figure 4(b), the nip width Ln, which is the length of the nip section NP in the conveying direction, is greater than the length Lr from the upstream end E1 of the resistance heating element 12 located furthest upstream in the conveying direction to the downstream end E2 of the resistance heating element 12 located furthest downstream in the conveying direction, when the nip pressure is the first nip pressure. The two resistance heating elements 12 are located within the range of the nip section NP in the conveying direction.

[0050] As shown in Figure 5(b), when the nip pressure is the second nip pressure, the nip width Ln is smaller than the length Lr from the upstream end E1 of the resistance heating element 12 located furthest upstream in the conveying direction to the downstream end E2 of the resistance heating element 12 located furthest downstream in the conveying direction. The nip portion NP is located within the range from the upstream end E1 to the downstream end E2 in the conveying direction.

[0051] As shown in Figure 5(a), the heating unit 2 has side guides SG at each axial end. The side guides SG support the axial ends of the stay ST. The side guides SG are movably supported on the frame 4. The pressure arm 60 presses the side guides SG toward the pressure roller 3.

[0052] As shown in Figure 6, the fixing device 1 further includes a shutter 50. The shutter 50 is rotatably supported on the shaft SF. As a result, the shutter 50 is rotatable about the first axis X1, as shown in Figures 7 and 8.

[0053] Frame 4 has an opening 4A through which the sheet S being conveyed toward the nip section NP passes. The opening 4A is located upstream of the nip section NP in the conveying direction.

[0054] The shutter 50 is rotatable between the closed position shown in Figure 7 and the open position shown in Figure 8. When the shutter 50 is in the closed position, it closes the opening 4A. When the shutter 50 is in the open position, it opens the opening 4A.

[0055] The first axis X1, which is the pivot point of the shutter 50, is located downstream of the nip section NP in the conveying direction. More specifically, the first axis X1 is located downstream of the belt BL of the heating unit 2 in the conveying direction. Also, in the opposing direction where the belt BL of the heating unit 2 and the pressure roller 3 face each other, the first axis X1 is located closer to the belt BL than the nip section NP.

[0056] In the following explanation, the direction indicated by the opposing arrows in the diagram will be considered one side of the opposing direction. For example, the pressure roller 3 is located on one side of the heating unit 2 in the opposing direction.

[0057] The shutter 50 comprises a shutter body 51 and a shutter arm 52. The shutter body 51 is the part that opens and closes the opening 4A and extends parallel to the first axis X1. The shutter arm 52 extends from the shutter body 51 toward the first axis X1.

[0058] The shutter arm 52 is rotatably supported at one end on the shaft SF. The shutter body 51 is integrally formed at the other end of the shutter arm 52. The portion of the shutter arm 52 between the one end and the other extends parallel to the first axis X1. The shutter arm 52 is curved so as to be convex toward the opposite side of the nip portion NP. The heating unit 2 is located between the shutter arm 52 and the pressure roller 3 in the opposing direction.

[0059] The fixing device 1 further includes a sheet guide G1. The sheet guide G1 is a guide that guides the sheet S toward the nip portion NP. The sheet guide G1 is located upstream of the nip portion NP in the conveying direction. The upstream end G11 of the sheet guide G1 in the conveying direction is located on the pressure roller 3 side of the nip portion NP in the opposing direction. In this embodiment, the entire sheet guide G1 is located on the pressure roller 3 side of the nip portion NP in the opposing direction.

[0060] The sheet guide G1 is positioned such that the sheet S can pass between it and the tip 51A of the shutter 50 when the shutter 50 is in the open position. Here, the tip 51A of the shutter 50 is the end located furthest downstream in the direction of rotation when the shutter 50 rotates from the open position to the closed position.

[0061] The tip 51A of the shutter 50 is closer to the sheet guide G1 when it is in the closed position than when it is in the open position. The tip 51A of the shutter 50 is located downstream in the transport direction when it is in the closed position than when it is in the open position. When the shutter 50 is in the closed position, the tip 51A of the shutter 50 is located downstream of the upstream end G11 of the sheet guide G1 in the transport direction. When the shutter 50 is in the closed position, the shutter body 51 extends diagonally with respect to the transport direction from the shutter arm 52 toward the downstream direction of transport.

[0062] In other words, the outer surface 51B of the shutter body 51, including the tip 51A, is inclined with respect to the transport direction such that it is located downstream in the transport direction as it moves toward one side in the opposite direction. Note that the outer surface 51B is the side of the shutter body 51 opposite to the heating unit 2.

[0063] As shown in Figures 1 and 8, the laser printer 100 further comprises a wall 160 and a main unit-side sheet guide G2. The wall 160 is located between the process cartridge 150 and the fuser unit 1 in the transport direction. The wall 160 extends substantially vertically. The main unit-side sheet guide G2 is a guide that guides the sheet S toward the sheet guide G1. The main unit-side sheet guide G2 is located upstream of the sheet guide G1 in the transport direction.

[0064] The main body sheet guide G2 is positioned vertically away from the wall 160. The sheet S can pass between the wall 160 and the main body sheet guide G2. The tip 51A of the shutter 50 is closer to the main body sheet guide G2 when it is in the closed position than when it is in the open position.

[0065] More specifically, when the shutter 50 is in the open position, in the vertical direction, the tip 51A of the shutter 50 is above the tip 161 of the wall 160 on the main body side sheet guide G2 side. When the shutter 50 is in the closed position, in the vertical direction, the tip 51A of the shutter 50 is below the tip 161 of the wall 160.

[0066] In other words, when the shutter 50 is in the open position, in the direction in which the wall 160 extends, the tip 51A of the shutter 50 is located further from the main body side sheet guide G2 than the tip 161 of the wall 160. Also, when the shutter 50 is in the closed position, in the direction in which the wall 160 extends, the tip 51A of the shutter 50 is located closer to the main body side sheet guide G2 than the tip 161 of the wall 160.

[0067] Hereinafter, the upstream end of the sheet S in the transport direction will be referred to as the rear end of the sheet S. As shown in Figure 8, if a curled sheet S gets jammed in the fixing device 1, the rear end of the sheet S may be positioned above the tip 161 of the wall 160 and become invisible to the user. However, in this case, by rotating the shutter 50 from the open position to the closed position, as shown in Figure 7, the tip 51A of the shutter 50 presses down on the sheet S from above, moving the rear end of the sheet S between the wall 160 and the main body side sheet guide G2, so that the user can see the rear end of the sheet S.

[0068] As shown in Figure 9, the fixing device 1 further includes a shutter operating mechanism 90 for opening and closing the shutter 50. As shown in Figure 10, the shutter operating mechanism 90 includes a connecting arm 91, an arm cam 92, and a spring 93. The connecting arm 91 and the arm cam 92 are made of resin or the like. The spring 93 is made of metal or the like.

[0069] The shutter arm 52 has a first boss 52A that protrudes in the axial direction. The first boss 52A is located offset from the first axis X1.

[0070] The connecting arm 91 is connected to the first boss 52A and is an arm that rotates the shutter 50 between the closed position and the open position. The connecting arm 91 is rotatable around the first axis X1 independently of the cam 80. The connecting arm 91 has a first hole 91A, a second boss 91B, and a second hole 91C.

[0071] The first hole 91A is the hole into which the first boss 52A of the shutter 50 fits. The shutter 50 and the connecting arm 91 are rotatably connected by the first boss 52A and the first hole 91A.

[0072] The second boss 91B protrudes axially. The second boss 91B is located between the first hole 91A and the second hole 91C. The second hole 91C is the hole into which the third boss 92A of the arm cam 92, described later, fits. The connecting arm 91 and the arm cam 92 are rotatably connected by the second hole 91C and the third boss 92A.

[0073] The spring 93 is a torsion spring. The spring 93 has a coil portion 93A, a first arm portion 93B extending from one end of the coil portion 93A, and a second arm portion 93C extending from the other end of the coil portion 93A. The first arm portion 93B and the second arm portion 93C of the spring 93 are capable of contacting the second boss 91B in the rotational direction of the connecting arm 91.

[0074] The arm cam 92 is a component that rotates around the first axis X1, thereby pushing the connecting arm 91 at a position offset from the first axis X1 and causing the connecting arm 91 to rotate. The arm cam 92 has a third boss 92A, an elongated hole 92B, and a pressing portion 92C as shown in Figure 11(b).

[0075] The third boss 92A is rotatably supported on the shaft SF. The third boss 92A enters inside the coil portion 93A of the spring 93 and supports the coil portion 93A. The third boss 92A also enters the second hole 91C of the connecting arm 91 and rotatably supports the connecting arm 91.

[0076] The elongated hole 92B is the slot into which the second boss 91B of the connecting arm 91 fits. The elongated hole 92B is arc-shaped with the first axis X1 as its center.

[0077] As shown in Figure 11(b), the pressing portion 92C is located between the first arm portion 93B and the second arm portion 93C of the spring 93 in the rotational direction of the arm cam 92. The arm cam 92 is rotatable between the closed position shown in Figure 11(a) and the open position shown in Figure 12(a). When the arm cam 92 is in the closed position, the shutter 50 is in the closed position. When the arm cam 92 is in the open position, the shutter 50 is in the open position.

[0078] As the arm cam 92 rotates from the open position to the closed position, as shown in Figure 11(b), the pressing portion 92C pushes the second arm portion 93C of the spring 93, causing the spring 93 to rotate counterclockwise as shown. The spring 93, rotating counterclockwise as shown, pushes the second boss 91B of the connecting arm 91 with its first arm portion 93B. As a result, the arm cam 92 rotates the shutter 50 from the open position to the closed position via the spring 93 and the connecting arm 91.

[0079] As shown in Figures 11(a) and (b), when the shutter 50 is in the closed position, the pressing portion 92C contacts the second arm portion 93C of the spring 93, and the first arm portion 93B of the spring 93 contacts the second boss 91B of the connecting arm 91. In other words, the arm cam 92 presses the connecting arm 91 via the spring 93, thereby positioning the shutter 50 in the closed position.

[0080] As the arm cam 92 rotates from the closed position to the open position, as shown in Figure 12(b), the pressing portion 92C pushes the first arm portion 93B of the spring 93, causing the spring 93 to rotate clockwise as shown. The spring 93, rotating clockwise as shown, pushes the second boss 91B of the connecting arm 91 with its second arm portion 93C. As a result, the arm cam 92 rotates the shutter 50 from the closed position to the open position via the spring 93 and the connecting arm 91.

[0081] As shown in Figures 12(a) and (b), when the shutter 50 is in the open position, the pressing portion 92C contacts the first arm portion 93B of the spring 93, and the second arm portion 93C of the spring 93 contacts the second boss 91B of the connecting arm 91. In other words, the arm cam 92 presses the connecting arm 91 via the spring 93, thereby positioning the shutter 50 in the open position.

[0082] The arm cam 92 is configured to rotate in conjunction with the attachment and detachment of the process cartridge 150 to the main housing 120 by an interlocking mechanism (not shown). The interlocking mechanism may include, for example, one that comprises multiple links. When the process cartridge 150 is attached to the main housing 120, the interlocking mechanism contacts a part of the process cartridge 150, transmitting the force applied to the process cartridge 150 to the arm cam 92, causing the arm cam 92 to rotate from the closed position to the open position. When the process cartridge 150 is detached from the main housing 120, the interlocking mechanism contacts a part of the process cartridge 150, transmitting the force applied to the process cartridge 150 to the arm cam 92, causing the arm cam 92 to rotate from the open position to the closed position.

[0083] Next, we will explain the effects and benefits of Shutter 50. As shown in Figure 8, if a curled sheet S jams in the fixing device 1, the rear end of the sheet S may be positioned above the front end 161 of the wall 160. Even in this case, when the user removes the process cartridge 150 from the main housing 120, the arm cam 92, which receives force from the interlocking mechanism, rotates from the open position to the closed position, as shown in Figures 12 and 11. As a result, the arm cam 92 pushes the shutter 50 via the spring 93 and connecting arm 91, causing the shutter 50 to rotate from the open position to the closed position.

[0084] As the shutter 50 rotates from the open position to the closed position, the tip 51A of the shutter 50 slides along the surface of the sheet S, pushing the sheet S downwards, as shown in Figure 7. This moves the rear end of the sheet S below the tip 161 of the wall 160, allowing the user to access the rear end of the sheet S located below the wall 160 through the first opening H1 and perform jamming, as shown in Figure 1.

[0085] As described above, the following effects can be obtained according to this embodiment. By making the pivot point of the shutter 50 the first axis X1, which is the pivot point of the cam 80, it is not necessary to independently provide the pivot point of the shutter 50 on the frame 4 of the fixing device 1, thus preventing the laser printer 100 from becoming larger.

[0086] Since a single shaft SF supports both the cam 80 and the shutter 50, the number of parts can be reduced.

[0087] By positioning the first axis X1 downstream of the nip section NP in the transport direction, the distance between the shutter body 51 and the first axis X1 can be increased, allowing the shutter 50 to be opened and closed with a small amount of rotation.

[0088] In particular, in this embodiment, since the first axis X1 is located downstream of the heating unit 2 in the conveying direction, the distance between the shutter body 51 and the first axis X1 can be increased, and the shutter 50 can be opened and closed with a smaller amount of rotation.

[0089] Since the tip 51A of the shutter 50 is closer to the sheet guide G1 when it is in the closed position than when it is in the open position, even if the rear end portion of the sheet S jammed in the nip portion NP is curved away from the sheet guide G1, closing the shutter 50 allows the shutter 50 to push the sheet S towards the sheet guide G1. As a result, the user can easily grasp the sheet S that has been pushed towards the sheet guide G1, and the efficiency of jam removal can be prevented from being compromised.

[0090] In the opposing direction, the first axis X1 is located on the heating unit 2 side of the nip section NP, and the upstream end G11 of the sheet guide G1 in the transport direction is located on the pressure roller 3 side of the nip section NP. Therefore, compared to, for example, the case where the first axis is positioned on the pressure roller side in the opposing direction, the shutter 50 can be made smaller.

[0091] When the tip 51A of the shutter 50 is in the closed position it is located downstream in the conveying direction more than when it is in the open position. As a result, when the shutter 50 rotates from the open position to the closed position, the tip 51A of the shutter 50 moves downstream in the conveying direction. Therefore, when the tip 51A of the shutter 50 pushes the sheet S jammed in the nip section NP, the tip 51A of the shutter 50 slides along the surface of the sheet S, allowing the tip 51A of the shutter 50 to gently push the sheet S.

[0092] When the shutter 50 is in the closed position, the shutter body 51 extends diagonally with respect to the transport direction from the shutter arm 52 toward the downstream direction of transport. Therefore, compared to a configuration in which, for example, the shutter body extends toward the upstream direction of transport from the shutter arm, it is possible to suppress the sheet S jammed in the nip portion NP from being hidden by the shutter 50.

[0093] When the shutter 50 is in the closed position, the tip 51A of the shutter 50 is located downstream of the upstream end G11 of the sheet guide G1. This reduces the gap between the tip 51A of the shutter 50 and the sheet guide G1, thereby more reliably preventing the user's fingers from entering the opening 4A.

[0094] The present invention is not limited to the embodiments described above, and can be used in various forms as illustrated below. In the above embodiment, the shutter body and the shutter arm are formed as a single unit, but the shutter body and the shutter arm may be separate components.

[0095] In the above embodiment, the arm cam was linked to the loading and unloading operation of the process cartridge, but for example, the arm cam may be linked to the opening and closing of the front cover.

[0096] The spring is not limited to a torsion spring; for example, it could be a leaf spring or a wire spring.

[0097] The first rotating body is not limited to a belt; for example, it may be a heating roller having a cylindrical metal tube.

[0098] The second rotating body is not limited to a pressure roller, but may also be, for example, the belt of a pressure unit having a pressure pad and a belt. In this case, the belt, as the second rotating body, may be sandwiched between the pressure pad and the first rotating body.

[0099] The first rotating body may also be a pressure roller or a belt in a pressure unit. The second rotating body may also be a belt or heating roller that is heated by a heater.

[0100] The first axis may be located at the same position as the nip section in the sheet transport direction, or it may be located upstream of the nip section.

[0101] The heater is not limited to a ceramic heater; for example, it may be a halogen lamp or the like. In this case, the heating unit may be configured to include a belt, a nip plate that sandwiches the belt between a pressure roller, and a heater that heats the nip plate.

[0102] The elements described in the above embodiments and modifications may be implemented in any combination. [Explanation of Symbols]

[0103] 1. Fixing device 3. Pressure roller 4 frames 4A aperture 50 shutters 60 Pressure Arms 80 Cam BL belt NM Nip Pressure Adjustment Mechanism NP Nipple S Seat X1 1st axis

Claims

1. The first rotating body and, A second rotating body that forms a nip portion with the first rotating body, A frame having an opening through which a sheet being conveyed toward the nip portion passes, and supporting the first rotating body and the second rotating body, A shutter that can rotate between a closed position that closes the opening and an open position that opens the opening, A pressurizing arm that presses the first rotating body toward the second rotating body, The device comprises a cam that rotates around a first axis to press the pressurizing arm and change the nip pressure at the nip portion, The fixing device is characterized in that the shutter is rotatable about the first axis.

2. The cam is supported by a shaft that is rotatable about the first axis, The fixing device according to claim 1, characterized in that the shutter is rotatably supported on the shaft.

3. A connecting arm is connected to the shutter and rotates independently of the cam around the first axis, thereby rotating the shutter between the closed position and the open position. The fixing device according to claim 1, further comprising an arm cam that rotates about the first axis to push the connecting arm at a position offset from the first axis and rotate the connecting arm.

4. The connecting arm is equipped with a spring that can come into contact with it, The fixing device according to claim 3, characterized in that the arm cam presses the connecting arm via the spring to position the shutter in the closed position.

5. The connecting arm is equipped with a spring that can come into contact with it, The fixing device according to claim 3, characterized in that the arm cam presses the connecting arm via the spring to position the shutter in the open position.

6. The aforementioned shutter is, A shutter body that opens and closes the aforementioned opening, It has a shutter arm extending from the shutter body toward the first axis, The fixing device according to claim 1, characterized in that the shutter arm is curved so as to be convex toward the opposite side from the nip portion.

7. The fixing device according to claim 1, characterized in that the first axis is located downstream of the nip portion in the conveying direction of the sheet.

8. It comprises a heater having a circuit board and a resistive heating element. The fixing device according to any one of claims 1 to 7, characterized in that the first rotating body is an endless belt heated by the heater and rotating around the heater.

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