Image forming apparatus

Abstract

To cope with the reduction in space of an apparatus when rotational shafts of two cam members for pushing up respective pressure members are different in an image forming apparatus in which pressure force applied to a fixing nip portion is released in conjunction with an open of a door.SOLUTION: An image forming apparatus includes a first door and a second door provided so as to be open and closed, in which a first cam member rotates in conjunction with an open and close of the first door, and a second cam member rotates in conjunction with an open and close of the second door. In the image forming apparatus, a rotational center of the second cam member is arranged coaxially with a rotational center of the first cam member.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, and particularly to a configuration in which, when a paper jam occurs in a fixing device, the pressing force of the fixing device is released in conjunction with the opening of a user access door for jam clearing. Background Art

[0002] Image forming apparatuses such as printers and facsimile machines include a fixing device that applies heat and pressure to a toner image formed on a sheet to fix the toner image onto the sheet. The fixing device forms a nip portion between a pressure roller and a heating unit, and is configured such that when the sheet passes through the nip portion, heat and pressure are applied to fix the toner image.

[0003] In the image forming apparatuses as described above, there is known a technology of releasing the pressing force of the fixing device in conjunction with opening of a door during jam clearing. Patent Document 1 proposes a technology that releases the pressing force of the fixing device in conjunction with the opening of either a front door or a rear door of the image forming apparatus when clearing a jam in the fixing device. According to the technology described in Patent Document 1, when the front door is opened, a cam member corresponding to the front door rotates to push up a pressing member, thereby releasing the pressing force of the fixing device. Further, when the rear door is opened, another cam member corresponding to the rear door rotates to push up the pressing member, thereby releasing the pressing force of the fixing device. Prior Art Documents Patent Documents

[0004] Patent Document 1 Japanese Unexamined Patent Publication No. 2010-032833 Summary of the Invention Problem to be Solved by the Invention

[0005] However, in the technology described in Patent Document 1 above, the rotation axes of the two cam members that push up the pressurizing member are on different axes, so there is room for improvement in terms of reducing the space required for the device. [Means for solving the problem]

[0006] To solve the above problems, the present invention provides a fixing unit for fixing a toner image formed on a sheet to the sheet, comprising: a heating unit for heating the sheet; a pressure roller that forms a fixing nip portion for pressing against the heating unit to perform the fixing, and for applying a predetermined pressure to the fixing nip portion during the fixing; and a first cam member and a second cam member having a pivot center, wherein the position of the heating unit is moved by the rotation of the first cam member or the second cam member to a first position and a front position such that the predetermined pressure is applied to the fixing nip portion. An image forming apparatus comprising: a fixing unit having a pressure release means for switching to a second position in which the predetermined pressure applied to the fixing nip portion is reduced or released; and a device body having a first door and a second door that are provided to be openable and closable, and housing the fixing unit, wherein the first cam member rotates in conjunction with the opening and closing of the first door, and the second cam member rotates in conjunction with the opening and closing of the second door, characterized in that the pivot center of the second cam member is arranged coaxially with the pivot center of the first cam member. [Effects of the Invention]

[0007] According to the present invention, an image forming apparatus can be provided that achieves miniaturization of the apparatus, in which an image forming apparatus has a pressure release configuration for a fixing device linked to the opening and closing of multiple doors. [Brief explanation of the drawing]

[0008] [Figure 1] Schematic diagram of the image forming apparatus in this embodiment 1 [Figure 2] Schematic diagram of the fixing device in this embodiment 1 [Figure 3]Cross-sectional view showing the configuration of the heating unit in this embodiment 1. [Figure 4] Schematic diagram of the pressure-releasing mechanism and pressure-relieving mechanism of the fixing device in this embodiment 1. [Figure 5] Perspective view of the pressure release mechanism of the fixing device in this embodiment 1. [Figure 6] Diagram illustrating the front cam of the pressure release mechanism in this embodiment 1. [Figure 7] Diagram illustrating the rear cam of the pressure release mechanism in this embodiment 1. [Figure 8] Diagram illustrating the pressure release arm of the pressure release mechanism in this embodiment 1. [Figure 9] Diagram illustrating the relationship between the front cam and rear cam in this embodiment 1. [Figure 10] Perspective view showing the pressure release method linked to the front door in this embodiment 1. [Figure 11] This diagram illustrates the operation of the pressure release mechanism of the fixing device due to the opening and closing of the front door in this embodiment 1. [Figure 12] Perspective view showing the configuration of the rear door in this embodiment 1. [Figure 13] This diagram illustrates the operation of the pressure release mechanism of the fixing device caused by opening and closing the rear door in this embodiment 1. [Figure 14] Explanatory diagram showing the shape of the shaft member in this embodiment 2. [Figure 15] Diagram illustrating the shape of the front cam in this embodiment 2. [Figure 16] Side view showing the interlocking configuration of the shaft member and front cam in this embodiment 2. [Figure 17] Diagram illustrating the pressure release arm of the pressure release mechanism in this embodiment 3. [Figure 18] Diagram illustrating the front cam of the pressure release mechanism in this embodiment 3. [Figure 19] Schematic diagram of the pressure-releasing mechanism and pressure-relieving mechanism of the fixing device in this embodiment 3. [Figure 20] This diagram illustrates the shape of the projection on the rear door for rotating the rear cam in this embodiment 4. [Figure 21] Diagram illustrating the shape of the rear cam in this embodiment 4. [Figure 22] Explanatory diagram of the pressure release method interlocked with rear door opening and closing in Example 4 Mode for Carrying Out the Invention

[0009] Example 1 As an example of the configuration of the image forming apparatus according to the present invention, an embodiment where the invention is applied to an electrophotographic laser printer will be specifically described. In this description, the overall configuration of the image forming apparatus will be described first, followed by the configuration of the fixing device of the image forming apparatus.

[0010] FIG. 1 shows an example of the image forming apparatus according to Example 1. FIG. 1 is a cross-sectional view showing the configuration of an electrophotographic laser printer having a double-sided image forming function. However, unless specifically stated otherwise, the dimensions, materials, shapes, relative arrangements and the like of the components described in this embodiment are not intended to limit the scope of the present invention only thereto. Further, the image forming apparatus according to the present invention is not limited only to laser printers, and may be applied to other image forming apparatuses such as copying machines and facsimile machines.

[0011] The image forming apparatus 101 shown in FIG. 1 broadly includes a sheet feeding unit, an image forming unit that forms an image on a sheet, a fixing unit, a paper discharge reversing unit, and a double-sided conveyance unit.

[0012] The image forming apparatus 101 is equipped with a process cartridge 1 that is detachable from the main body of the apparatus. The process cartridge 1 is a process unit necessary for forming a toner image on a sheet using an electrophotographic process, and includes a photoreceptor drum 2, a developing unit (not shown), a charging roller, and other processing means. A scanner unit 3 is positioned vertically above the process cartridge 1 and performs exposure on the photoreceptor drum 2 based on an image signal. The photoreceptor drum 2 is charged to a predetermined negative potential by a charging roller (not shown). Subsequently, the scanner unit 3 scans the photoreceptor drum 2 with laser light, forming an electrostatic latent image on the photoreceptor drum 2. This electrostatic latent image is inverted and developed onto the sheet by the developing unit (not shown) in the process cartridge 1, and negative polarity toner is deposited onto the sheet, thereby forming a toner image on the sheet.

[0013] The sheet feeding unit includes a paper feed roller 4 mounted on the image forming apparatus 101 and a paper feed cassette 5 for storing sheets, which is detachable from the image forming apparatus 101. The sheets S stored in the paper feed cassette 5 are separated and fed one by one from the paper feed cassette 5 by the paper feed roller 4, which is rotated by the power of a paper feed drive unit (not shown). The fed sheets S are transported by a transport roller pair 6 to a registration roller pair 7, where the registration roller pair 7 performs skew correction and then transports them to the transfer unit.

[0014] In the transfer section, a positive bias is applied to the transfer roller 8 by a bias application means (not shown). As a result, the toner image is transferred to the sheet S that has been transported to the transfer section.

[0015] The sheet S onto which the toner image has been transferred is transported to a fixing device 9 located downstream in the transport direction from the transfer unit. The fixing device 9 fixes the toner image transferred to the sheet S to the sheet and includes a heating unit 10 equipped with a heater (not shown) and a pressure roller 11 which is a pressing member that presses against the heating unit 10 and rotates. The sheet on which the toner image has been formed is held and transported by a nip formed by the heating unit 10 and the pressure roller 11, and the toner image is fixed to the surface of the sheet S by the application of heat and pressure.

[0016] The sheet S, on which the toner image has been fixed, is transported from the fuser unit 9 to the paper output reversal unit. The paper output reversal unit has a triple roller system with a paper output roller 13, a paper output roller 14, and a reversal roller 15, and a double-sided flapper 12. In the case of single-sided image formation (single-sided printing), the double-sided flapper 12 waits in a position to guide the sheet S towards the paper output nip section formed by the paper output roller 13 and the paper output roller 14, and the sheet is discharged onto the paper output tray 16 by the paper output roller 13 and the paper output roller 14.

[0017] In addition, in the case of double-sided image formation (double-sided printing), the double-sided flapper 12 is positioned (dotted line position) to guide the sheet S to the inversion nip section formed by the paper discharge roller 13 and the inversion roller 15, and the sheet S is transported to the inversion nip section by the fuser 9. The paper discharge roller 13 rotates in the reverse direction by a rotation direction switching means (not shown) when the rear end of the sheet S reaches a predetermined position. As a result, the sheet S passes through the double-sided transport roller pair 17 and the re-feed roller pair 18 with the rear end leading, and is re-fed in an inverted state to the registration roller pair 7. After that, the sheet S is transferred to the second side by the transfer roller 8 and fixed by the fuser 9, similar to single-sided printing, and discharged to the paper discharge tray 16 by the paper discharge roller 13 and the paper discharge roller 14, completing double-sided printing.

[0018] Furthermore, if a jam occurs in the fixing device 9 while the sheets are being transported, the system is configured to open either the front door 19 or the rear door 20 depending on where the jam occurred to clear the jam.

[0019] Next, the fixing device 9 will be described using Figures 2 to 11. Note that fastening members such as screws will not be shown in the following description. Figure 2 is a schematic diagram of the fixing device 9 in this embodiment 1. The fixing device 9 has a first side plate 21, a second side plate 22, an upper stay 23, and a lower stay 24. The pressure roller 11 is rotatably supported on the first side plate 21 and the second side plate 22 via ball bearings 25 and bearings 26. The heating unit 10 is attached to the first side plate 21 and the second side plate 22 via flange members 28. The pressure roller 11 is positioned on the opposite side of the heating unit 10 to form a nip portion and clamp the sheet.

[0020] Figure 3 is a cross-sectional view showing the configuration of the heating unit. The heating unit 10 mainly comprises a heater 30, a pressure stay 29, a fixing film 31, and a film guide 32. The fixing film 31 is cylindrical (endless belt-shaped, sleeve-shaped) and flexible, and is loosely fitted onto the film guide 32. The heater 30, which is the heating source, is fitted into a groove provided along the longitudinal direction of the film guide 32 and fixed in place. The pressure stay 29 has a roughly U-shaped cross-section and is positioned inside the film guide 32, and when pressure is applied, it pressurizes the film guide 32 and the heater 30 toward the pressure roller 11.

[0021] Figure 4 is a side view of Figure 2 as seen in direction A, and is a schematic diagram of the pressurizing mechanism and pressure release mechanism in the fixing device 9. Figure 4(a) shows the contact state in which a predetermined pressurizing force is applied to the pressurizing roller 11 by the heating unit 10 being biased, and Figure 4(b) shows the pressure release state in which the pressurizing force of the heating unit 10 on the pressurizing roller 11 is weaker than in the contact state (including zero pressurizing force). The pressurizing spring 33 biases the pressurizing plate 27, and the biasing force is transmitted to the heating unit 10 via the flange member 28, thereby applying pressurizing force to the nip portion as the heating unit 10 is biased on the pressurizing roller 11.

[0022] Furthermore, the pressure release mechanism of the fixing device 9 has a front cam 34 that rotates in conjunction with the opening and closing of the front door 19, and a rear cam 35 that rotates in conjunction with the opening and closing of the rear door 20. In addition, it has a pressure release arm 36 for adjusting the pressure plate 27 between a contact state and a pressure release state, and a pressure release arm holder 40 for holding the pressure release arm 36. The fixing device 9 is configured such that the front cam 34 and the rear cam 35 rotate in conjunction with the front door 19 and the rear door 20 moving from a closed state to an open state, switching from the contact state in Figure 4(a) to the pressure release state in Figure 4(b). Note that Figure 4(b) shows the pressure release state where both the front door 19 and the rear door 20 are open and both the front cam 34 and the rear cam 35 are rotated. If only one of the front door 19 or the rear door 20 is open, only the cam corresponding to the open door will rotate. Furthermore, the front cam 34, rear cam 35, pressure release arm 36, and pressure release arm holder 40 are arranged on both sides in the longitudinal direction of the fixing device 9.

[0023] Here, the pressure release arm 36 may be composed of multiple parts, or it may be composed of multiple power transmission systems such as gears.

[0024] Figure 5 is a perspective view of the pressure release mechanism in the fixing device 9. The pressure release arm 36 contacts the front cam 34 and the rear cam 35, converting the radial fluctuation caused by the rotation of either cam into a fluctuation in the Y direction. As a result, the pressure release arm 36 moves in the Y direction, pushing up the pressure plate 27 and adjusting the pressure applied by the pressure spring 33.

[0025] Figures 6-8 are detailed diagrams illustrating each component of the pressure release mechanism. Figure 6 is an explanatory diagram of the front cam 34, Figure 7 is an explanatory diagram of the rear cam 35, and Figure 8 is an explanatory diagram of the pressure release arm 36. As shown in Figure 6, the front cam 34 has a surface 34A that contacts the pressure release arm 36 when the nip portion is in the contact state shown in Figure 4(a), and an arc portion 34B that contacts the pressure release arm 36 when the nip portion is in the pressure release state shown in Figure 4(b). Here, the center of the arc portion 34B is the same as the rotation axis of the cam, and the distance between the arc portion 34B and the rotation axis of the cam is greater than the distance between the surface 34A and the rotation axis of the cam. The front cam 34 also has a boss portion 34C for interlocking with the opening and closing of the front door, and a substantially circular bearing portion 34D for supporting the rear cam 35.

[0026] As shown in Figure 7, the rear cam 35 has an arc portion 35A that contacts the pressure release arm 36 when in the contact state shown in Figure 4(a), an arc portion 35B that contacts the pressure release arm 36 when in the pressure release state shown in Figure 4(b), and an arc portion 35C which is shaped to impart rotational force to the cam by the fixing pressure. Here, the centers of both the arc portion 35A and the arc portion 35B are the same as the rotation axis of the cam, and the radius of curvature of the arc portion 35B is larger than that of the arc portion 35A. The center position of the arc portion 35C is different from the center of the rotation axis of the cam, and the distance between the arc portion 35C and the rotation axis of the cam is greater than the distance between the arc portion 35B and the rotation axis of the cam. The rear cam 35 also has a substantially circular inner circumferential surface 35D for fitting with the bearing portion 34D of the front cam 34, and an engaging portion 35E for interlocking with the opening and closing of the rear door 20. As shown in Figure 8, the pressure release arm 36 has a first contact surface 36A that contacts the front cam 34, a second contact surface 36B that contacts the rear cam 35, and a pressure plate contact portion 36C that contacts the pressure plate 27.

[0027] Figure 9 is an explanatory diagram showing the relationship between the front cam 34 and the rear cam 35. Figure 9(a) is a perspective view, and Figure 9(b) is a cross-sectional view at the center of the cam's rotation axis. As shown in Figure 9(a), the front cam 34 and the rear cam 35 are arranged on both sides of the longitudinal direction of the fixing device 9, and the rear cam 35 has the same rotation axis as the front cam 34. By making the rotation axes of the two types of cams the same, the two cams can be arranged in a smaller space compared to when they are not the same. As shown in Figure 9(b), the basic cross-sectional shape of the shaft member 37 is a substantially circular axis, and D-cut shapes 37A are provided at both ends of the shaft. In addition, the front cam 34 is provided with a D-cut groove 34E, and the front cam 34 and the shaft member 37 are linked at this D-cut section, so that the front cams 34 on both sides rotate in conjunction. Furthermore, the inner circumferential surface 35D of the rear cam 35 is positioned on the bearing portion 34D of the front cam 34, so that the rear cam 35 rotates independently of the front cam 34. Since the rear cam 35, which rotates independently of the front cam 34, is not fastened to the shaft member 37, the rear cams 35 on both sides can also rotate independently of each other.

[0028] As shown in the relationship between the front cam 34 and the rear cam 35 in Figure 9(b), the front cam 34 also serves as the bearing for the rear cam 35. This results in a configuration where the front cam 34 and the rear cam 35 overlap in the direction of the cam's rotation axis, allowing the two cams to be placed in a smaller space than in a configuration where they do not overlap.

[0029] Next, the pressure release method linked to the front door will be explained using Figures 10-11. Figure 10 is a perspective view showing the pressure release method linked to the front door, and Figure 11 is an explanatory diagram showing the operation of the pressure release mechanism of the fixing device 9 when the front door is opened and closed, as viewed from direction B in Figure 10. Note that in Figures 10-19, parts that are not necessary for explaining the pressure release method linked to the front door have been omitted. The image forming apparatus 101 has a connecting member for rotating the front cam 34 in accordance with the opening and closing of the front door 19. The connecting member consists of a front door connecting member 38 that connects to the front door 19, and a cam-side connecting member 39 that contacts the front cam 34 and rotates the front cam 34. The front door connecting member 38 and the cam-side connecting member 39 are connected to rotate the front cam 34 in accordance with the opening and closing of the front door 19. The operation of the pressure release mechanism of the fixing device 9 when the front door is opened and closed will be explained using Figure 11. Figure 11(a) shows the front door closed, with the nip portion in the contact state as in Figure 4(a), and Figure 11(b) shows the front door 19 open, with the nip portion in the pressure-release state as in Figure 4(b). The cam-side connecting member 39 has an engagement hole 39A for engaging with the boss portion 34C of the front cam 34. As the front door 19 opens from the closed state in Figure 11, the cam-side connecting member 39 moves in conjunction with the front door 19 toward the front side of the image forming apparatus 101 (direction C in Figure 11). As the cam-side connecting member 39 moves in direction C, the boss portion 34C is pushed by the engagement hole 39A, and the front cam 34 rotates counterclockwise. When the front door 19 is fully open, it reaches the state shown in Figure 11(b). At this time, as the front door 19 opens, the surface of the front cam 34 that contacts the pressure-release arm 36 changes from a surface 34A to an arc portion 34B. Since the distance of the arc portion 34B from the rotation axis of the cam is greater than the distance of the surface 34A from the rotation axis of the cam, the pressure release arm 36 is pushed up when the front door 19 opens, and the nip portion switches from the contact state in Figure 4(a) to the pressure release state in Figure 4(b). Also, at this time, since the rear cam 35 and the front cam 34 are configured to rotate independently of each other, the rear cam 35 does not rotate from the rotation phase in Figure 11(a) even when the front cam 34 switches to the pressure release state.

[0030] Next, the pressure release method linked to the rear door 20 will be explained using Figures 12-13. Figure 12 is a perspective view showing the configuration of the rear door 20, and Figure 13 is an explanatory diagram showing the operation of the pressure release mechanism of the fixing device 9 due to the opening and closing of the rear door 20, and is a cross-sectional view of the rear cam portion. As shown in Figure 12, the rear door 20 has projections 20A at both ends for releasing pressure on the fixing device 9. This is because the rear cams 35 located at both ends in the longitudinal direction of the fixing device 9 are configured to rotate independently of each other, and the two projections 20A can rotate the rear cams 35 on both sides.

[0031] The operation of the pressure release mechanism of the fixing device 9 when the rear door 20 is opened and closed will be explained using Figure 13. Figure 13(a) shows the rear door 20 closed, with the nip portion in the contact state as shown in Figure 4(a). Figure 13(b) shows the pressure release arm 36 in contact with the arc portion 35C, and the rear cam 35 receives a rotational force in the direction that closes the rear door 20 due to the biasing force of the pressure spring 33 transmitted from the pressure release arm 36. Figure 13(c) shows the pressure release arm 36 in contact with the arc portion 35C, and the rear cam 35 receives a rotational force in the direction that opens the rear door 20 due to the biasing force of the pressure spring 33 transmitted from the pressure release arm 36. Thus, since the center of the arc of the arc portion 35C is different from the rotation axis center of the cam, the direction in which the rear cam 35 rotates changes depending on the contact position of the arc portion 35C with respect to the pressure release arm 36, due to the biasing force of the pressure spring 33 transmitted from the pressure release arm 36. Figure 13(d) shows the rear door 20 open and the nip portion in the pressure release state. As the rear door 20 begins to open as shown in Figure 13(a), the projection 20A of the rear door 20 rotates along the trajectory L and comes into contact with the surface 35F of the engaging portion 35E of the rear cam 35. As a result, the rear cam 35 rotates in conjunction with the opening and closing of the rear door 20. Up to the state shown in Figure 13b, the direction of the pressure applied to the rear cam 35 from the pressure release arm 36 is directed towards the rear door 20 side from the rotation center of the rear cam 35, so a force is applied in the direction that closes the rear door. Therefore, the rear cam 35 is rotated by the projection 20A of the rear door 20 until it reaches the state shown in Figure 13(b).

[0032] Subsequently, as the rear cam 35 rotates beyond the state shown in Figure 13(b), and the contact position between the arc portion 35C and the pressure release arm 36 changes as shown in Figure 13(c), a force acts on the rear cam 35 in the direction of the arrow shown in Figure 13(c) due to the pressure applied by the pressure release arm 36. This causes the rear cam 35 to rotate in the direction that opens the rear door 20. As a result, from the state shown in Figure 13(c) onward, the rear cam 35 rotates in advance due to the pressure applied by the pressure release arm 36, and the rotation of the rear cam 35 due to the engagement between the rear door 20 and the rear cam 35 ceases. Then, as shown in Figure 13(d), the rear cam 35 stops rotating at the arc portion 35B, which is concentric with the rotation axis of the cam. At this point, because the rear cam 35 rotates in advance, no pressure is applied from the pressure release arm 36 during user operation after the initial rotation. At the same time, when the rear door 20 is open, the engagement between the projection 20A of the rear door 20 and the engagement portion 35E of the rear cam 35 is released, so the pressure applied by the fixing device 9 is no longer applied to the projection 20A of the rear door 20 via the pressure release arm 36. Therefore, there is no risk of creep of the projection 20A of the rear door 20. In this state, the rear cam 35 receives the pressurizing force from the pressure release arm 36 on the surface of the arc portion 35B, so a sufficiently large contact area can be secured, and the force applied per unit area is reduced, so there is no risk of creep for the rear cam 35 either. Furthermore, in the state shown in Figure 13(d), the surface 35F of the rear cam 35 stops with a gap between it and the rotational trajectory L of the projection 20A of the rear door 20. Therefore, when closing the rear door 20 from the state shown in Figure 13(d), the configuration is designed to prevent the projection 20A from catching on the surface 35F.

[0033] Here, the arc portion 35B is not limited to being concentric with the rotation axis of the cam, but can be any shape as long as it is such that the pressure release arm 36 is supported by the rear cam 35 and its rotation stops, as shown in Figure 13(d).

[0034] Furthermore, the rear cam 35 is positioned at both ends in the longitudinal direction of the fixing device 9, and the projection 20A of the rear door 20 is similarly positioned at both ends in the longitudinal direction. Therefore, when the rear door 20 is opened, the nip portion is uniformly released in the longitudinal direction. In addition, since the rear cam 35 and the front cam 34 rotate independently of each other, even when the rear cam 35 switches to the release state, the front cam 34 remains in the rotational phase corresponding to the contact state in Figure 13(a).

[0035] Furthermore, the rear cams 35 located at both ends in the longitudinal direction are configured to rotate independently of each other. This configuration offers the following advantages compared to the case where both rear cams 35 are linked: When both rear cams 35 are linked, if the timing of contact between the projection 20A of the rear door 20 and both rear cams 35 is staggered due to part variations, the pressure release operation will only be performed by the rear cam 35 that made contact first. As a result, the pressing force of the fixing device 9 acts on one of the rear cams 35, increasing the user's operating force. In contrast, when both rear cams 35 rotate independently of each other, the projection 20A of the rear door 20 always makes contact with both rear cams 35. Therefore, pressure release is performed by both rear cams 35, and the pressing force of the fixing device 9 is distributed to both sides, resulting in a smaller and more stable user operating force compared to the case where both rear cams 35 are linked.

[0036] In this way, by arranging the rotation centers of the rear cam 35 and the front cam 34 on the same axis, and by allowing the rear cams 35 located at both ends in the longitudinal direction to rotate independently of each other and independently of the front cam 34, a simple configuration can be achieved and the components can be installed in a small space.

[0037] The configuration of this embodiment can provide an image forming apparatus that achieves miniaturization, cost reduction, and a stable pressure release mechanism.

[0038] Example 2 Next, Embodiment 2 of the present invention will be described using Figures 14 to 16. In this embodiment, parts common to the first embodiment are omitted from the description. The difference from Embodiment 1 is the configuration of the shaft member 137 that interlocks the front cams 134 at both ends in the longitudinal direction.

[0039] Figure 14 is an explanatory diagram showing the shape of the shaft member 137, Figure 15 is an explanatory diagram showing the shape of the front cam 134, and Figure 16 is a side view showing the interlocking configuration of the shaft member 137 and the front cam 134. From Figure 14, the shaft member 137 is a roughly V-shaped rotating shaft formed by bending sheet metal. The angle of the bent portion of the shaft member 137 is less than 90°. From Figure 15, the front cam 134 has an engaging portion 134E for engaging with the roughly V-shaped cross-section of the shaft member 137. From Figure 16, the engagement of the engaging portion 134E of the front cam 134 with the V-shaped cross-section of the shaft member 137 causes the front cam 134 and the shaft member 137 to rotate in conjunction.

[0040] Thus, by making the shaft member 137 a rotating shaft with a V-shape bent in only one place from sheet metal, it is possible to reduce costs compared to a roughly circular turned shaft as in Embodiment 1.

[0041] Example 3 Next, Embodiment 3 of the present invention will be described using Figures 17-19. In this embodiment, parts common to the first embodiment are omitted from the description. Also, the configuration of the shaft member that interlocks the front cams 234 at both ends in the longitudinal direction is the same as in the second embodiment, so the description is omitted. In this embodiment, the parts that differ from the first and second embodiments are the shape of the surface 236A of the pressure release arm 236 and the surface 234A and arc portion 234B of the front cam 234.

[0042] Figure 17 is an explanatory diagram showing the shape of the pressure release arm 236. The pressure release arm 236 has a common surface 236A that contacts both the front cam 234 and the rear cam 235. The pressure plate contact portion 236C that contacts the pressure plate 27 is the same as in Embodiment 1.

[0043] Figure 18 is an explanatory diagram showing the shape of the front cam 234, where Figure 18(a) is a perspective view and Figure 18(b) is a side view of Figure 18(a) viewed in direction A. The front cam 234 has a surface 234A that contacts the surface 236A of the pressure release arm 236 when in the contact state shown in Figure 4(a), and an arc portion 234B that contacts the surface 236A of the pressure release arm 236 when in the pressure release state shown in Figure 4(b). Here, the arc portion 234B is concentric with the rotation axis of the cam, and the distance between the arc portion 234B and the rotation axis of the cam is greater than the distance between the surface 234A and the rotation axis of the cam. The boss portion 234C for interlocking with the opening and closing of the front door and the substantially circular bearing portion 234D for supporting the rear cam 235 are the same as in Embodiment 1.

[0044] Figure 19 is a schematic diagram of the pressure-releasing mechanism and pressure-relieving mechanism of the fixing device in this embodiment, viewed from direction A in Figure 2. Note that the front cam 234 is not shown in Figure 19 for explanatory purposes. As shown in section A of Figure 19, the pressure-relieving arm 236 and the rear cam 235 are not in a relationship that overlaps when viewed from the side.

[0045] In this embodiment, the shaft member is a rotating axis made of sheet metal bent into a V-shape in only one place, similar to Embodiment 2, thus achieving cost reduction compared to Embodiment 1. In addition, in this embodiment, the surface 236A of the pressure release arm 236 has a common cam shape for the front cam 234 and the rear cam 235. As a result, the pressure release arm 236 and the rear cam 235 do not overlap when viewed from the side, eliminating the need to lift the pressure release arm 36 upwards and assemble the rear cam 35 around it during assembly, as in the configuration of Embodiment 1. In this embodiment, the rear cam 235 can be assembled without moving the pressure release arm 236, resulting in an improved assembly configuration compared to Embodiment 1.

[0046] Example 4 Embodiment 4 of the present invention will be described using Figures 20-22. In this embodiment, parts common to the first and second embodiments are omitted from the description. Also, the configuration of the shaft member that interlocks the front cams at both ends in the longitudinal direction is the same as in the second embodiment, so the description is omitted. In this embodiment, the difference from the first and second embodiments is the configuration of the pressure release mechanism of the fixing device 9 when the rear door 320 is opened and closed.

[0047] Figure 20 is an explanatory diagram showing the shape of the projection on the rear door 320 for rotating the rear cam 335. The rear door 320 has a first engaging portion 320A and a second engaging portion 320B that engage with the rear cam 335 and rotate the cam.

[0048] Figure 21 is an explanatory diagram showing the shape of the rear cam 335. The rear cam 335 has an arc portion 335A that contacts the pressure release arm 336 when in the contact state shown in Figure 4(a), an arc portion 335B that contacts the pressure release arm 336 when in the pressure release state shown in Figure 4(b), and an arc portion 335C that smoothly connects the arc portions 335A and 335B. Here, the arc portions 335A and 335B are concentric with the rotation axis center of the cam, while the arc portion 335C has a configuration where the center of the arc is different from the rotation axis center of the cam. The rear cam 335 also has a first engaged portion 335E that engages with the first engaging portion of the rear door 320, and a second engaged portion 335F that engages with the second engaging portion.

[0049] Figure 22 is an explanatory diagram of the pressure release method linked to the opening and closing of the rear door 320. Figure 22(a) shows the rear door 320 closed, with the nip portion in the contact state as shown in Figure 4(a). Figure 22(b) shows the timing when the rotation of the rear cam 335 by the first engaging portion of the rear door 320 ends. Figure 22(c) shows the timing when the rotation of the rear cam 335 by the second engaging portion of the rear door 320 begins. Figure 22(d) shows the rear door 320 open, with the nip portion in the pressure release state as shown in Figure 4(b). When the rear door 320 begins to open from the state shown in Figure 22(a), the first engaging portion 320A of the rear door 320 contacts the surface of the first engaged portion 335E of the rear cam 335, causing the rear cam 335 to rotate to the state shown in Figure 22(b). When the rear door 320 is in the state shown in Figure 22(b), the first engaging portion 320A of the rear door 320 and the first engaged portion 335E of the rear cam 335 are released. At this time, the rear cam 335 is in contact with the pressure release arm 336 at the arc portion 335B which is concentric with the rotation axis of the cam, so the rotation of the rear cam 335 stops, and the rear door 320 rotates to the state shown in Figure 22(c). Then, from the state shown in Figure 22(c), the second engaging portion 320B of the rear door 320 comes into contact with the second engaged portion 335F of the rear cam 335, causing the rear cam 335 to rotate to the state shown in Figure 22(d), and the nip portion rotates to the pressure release state shown in Figure 4(b). In the state shown in Figure 22(d), the tip portion 335G of the rear cam 335 stops with a gap between it and the rotation trajectory L2 of the first engaging portion 320A of the rear door 320. Therefore, the configuration is designed to prevent the first engaging portion 320A from catching on the tip 335G when closing the rear door 320 from the state shown in Figure 22(d).

[0050] Here, when the first engaging portion 320A of the rear door 320 and the first engaged portion 335E of the rear cam 335 are disengaged in the state shown in Figure 22(b), the rotation of the rear cam 335 is not limited to a stopped state. For example, the shape of the rear cam 335 may be such that the rear cam 335 rotates in a direction in which the second engaged portion 335F approaches the second engaging portion 320B of the rear door 320.

[0051] Furthermore, Figure 22(e) is an explanatory diagram showing the timing at which the rear cam 335 begins to rotate ahead of the rotation of the rear door 320 due to engagement when the rear door 320 is closed from an open position. When the rear door 320 closes from Figure 22(d), the rear cam 335 begins to rotate ahead of the rear cam 335 when it is in contact with the pressure release arm 336 at the arc portion 335C, as shown in Figure 22(e). This is because the direction of the pressure applied to the rear cam 335 from the pressure release arm 336 is directed towards the rear door 320 from the center of rotation of the rear cam 335, so that a force is applied to the rear cam 335 in the direction that closes the rear door 320. At the timing when the preceding rotation occurs as shown in Figure 22(e), the gap between the first engaging portion 320A and the first engaged portion 335E is as small as possible, or they are already in an engaged position. In this embodiment, the shaft member is a rotating axis made of sheet metal bent into a V-shape at only one point, similar to Embodiment 2, thus achieving cost reduction compared to Embodiment 1. Furthermore, in this embodiment, the rear door 320 is provided with a first engaging portion 320A and a second engaging portion 320B, and the second engaging portion 320B rotates the tip 335G of the rear cam 335 to a state where there is a gap with respect to the rotation trajectory L2 of the first engaging portion 320A. This configuration does not overcome the preceding rotation during the opening process of the rear door 320 as in Embodiments 1 and 2, and therefore requires less force to open the rear door 320 compared to Embodiment 1, resulting in improved operability. Moreover, in this embodiment, at the timing when the preceding rotation of the rear cam 335 begins during the closing process of the rear door 320, the gap between the first engaging portion 320A and the first engaged portion 335E is kept to a minimum, or they are already engaged. Therefore, compared to Example 1, the collision energy with the first engagement portion 320A of the rear door 320 due to the preceding rotation of the rear cam 335 is smaller, resulting in an improved collision noise configuration.

[0052] The embodiments of the present invention have been described in detail above, but this invention is based on the above-described embodiments. This invention is not limited to this, and various modifications based on the technical concept of this invention are possible. [Explanation of symbols]

[0053] 1 Process Cartridge 2 Photoconductor drum 3 Scanner Unit 4 Paper feed rollers 5. Paper feed cassette 6 Conveyor roller pairs 7 Resistola vs. 8 Transfer Roller 9. Fixing device 10 Heating Units 11 Pressure roller 11 Conveyor roller pair 12 Double-sided flappers 13 Paper output roller 14 Paper output roller 15 Reversal Roll 16 Paper output tray 17 Double-sided conveyor roller pair 18 Refeed roller pair 19 Front Door 20,320 Rear Door 21 First side plate 22 Second side plate 23 Upper Stay 24 Stay down 25 ball bearings 26 bearings 27 Pressure plate 28 Flange member 29 Pressurized Stay 30 Heater 31 Fixing film 32 Film Guide 33 Pressure spring 34, 134, 234 Front Cam 35, 135, 235, 335 Rear Cam 36, 136, 236, 336 Pressure release arm 37, 137 Shaft members 38 Front door connecting member 39 Cam-side connecting member 40 Pressure release arm holder 101 Image forming apparatus

Claims

1. A fixing unit for fixing a toner image formed on a sheet to the sheet, comprising: a heating unit for heating the sheet; a pressure roller that forms a fixing nip portion for pressing against the heating unit to perform the fixing, and for applying a predetermined pressure to the fixing nip portion during the fixing; and a pressure release means having a first cam member and a second cam member having a pivot center, which switches the position of the heating unit between a first position where the predetermined pressure is applied to the fixing nip portion and a second position where the predetermined pressure applied to the fixing nip portion is reduced or released by the rotation of the first cam member or the second cam member; The device comprises a main body that houses the fixing unit and has a first door and a second door that are provided to be openable and closable, In an image forming apparatus in which the first cam member rotates in conjunction with the opening and closing of the first door, and the second cam member rotates in conjunction with the opening and closing of the second door, The image forming apparatus is characterized in that the pivot center of the second cam member is arranged coaxially with the pivot center of the first cam member.

2. The first cam member is arranged one at each end of the fixing unit in the longitudinal direction of the fixing unit, The second cam member is arranged one at each end of the fixing unit in the longitudinal direction of the fixing unit. The image forming apparatus according to claim 1, characterized in that the fixing unit has a shaft member connecting the two first cam members.

3. The second door has engaging portions at both ends in the longitudinal direction of the fixing unit that engage with the two second cam members in order to rotate the two second cam members, and the second cam members have engaged portions that engage with the engaging portions. The image forming apparatus according to feature 2.

4. The main body of the device has a shaft member for linking the opening and closing of the first door with the rotation of the first cam member, The two first cam members rotate in the same phase by being coupled by the shaft member in conjunction with the opening and closing of the first door. The image forming apparatus according to claim 3, characterized in that the two second cam members are each rotatable independently of the first cam member.

5. The first cam member has a substantially circular protrusion that extends in the direction of the rotation axis when viewed in the direction of the rotation axis, The second cam member has a substantially circular hole when viewed in the direction of the rotation axis, The diameter of the hole and the diameter of the protrusion are approximately the same. The image forming apparatus according to claim 4, characterized in that the second cam member is rotatable independently of the first cam member when the convex portion and the hole portion overlap in the rotation axis direction of the second cam member.

6. The image forming apparatus according to claim 1, characterized in that the first door is a door for attaching and detaching a process unit necessary for forming a toner image on a sheet using an electrophotographic process, and the second door is a door for jamming the sheet when jamming occurs in the fixing unit.

7. The fixing unit has a pressure plate for applying pressure to the fixing nip portion, The pressure release means comprises a movable member having a first contact surface that contacts the first cam member, a second contact surface that contacts the second cam member, and a third contact surface that contacts the pressure plate. The image forming apparatus according to claim 3, characterized in that the position of the heating unit is switched between a first position and a second position by changing the position of the moving member and the pressure plate by the rotation of the first cam member or the second cam member.

8. The image forming apparatus according to claim 7, characterized in that the first contact surface and the second contact surface are surfaces located at different distances from the third contact surface.

9. The image forming apparatus according to claim 7, characterized in that the first contact surface and the second contact surface are surfaces that are at the same distance from the third contact surface.

10. The image forming apparatus according to claim 7, characterized in that the moving member consists of a single component.

11. When the heating unit is in the first position, the first door is closed and the second door is closed. The image forming apparatus according to claim 7, characterized in that when the heating unit is in the second position, at least one of the first door and the second door is open.

12. The second cam member has a contact surface that contacts the moving member, The first arc portion is located in a range where the distance from the pivot axis center of the cam is greater than the contact surface, and has a center different from the pivot axis center of the second cam member, When the second door is in the open position, the second cam member contacts the moving member with the contact surface. When the second door is at a first angle between the closed state and the open state, the second cam member contacts the moving member at the first arc portion. The image forming apparatus according to claim 11, characterized in that when the second door moves from the closed state to the open state, the engaging portion and the engaged portion engage up to the first angle, causing the second cam member to rotate, and when the first angle is exceeded, a rotational force is applied to the second cam member by a biasing force applied from the moving member in the direction that the second door opens, and the second cam member rotates to the contact surface by the biasing force.

13. The image forming apparatus according to claim 12, characterized in that the contact surface has a second arc portion that is centered on the same axis as the pivot axis of the second cam member.

14. The second door has a first engaging portion that engages with the second cam member from the closed phase to a first angle between the closed and open states, and a second engaging portion that engages with the second cam member from the first angle to the open state. The second cam member has a first engaged portion that engages with the first engaging portion and a second engaged portion that engages with the second engaging portion. The second cam member has a third arc portion that is centered at the same point as the pivot axis center of the second cam member, and a fourth arc portion that is centered at the same point as the pivot axis center of the second cam member and has a larger radius than the third arc portion. When the second door is in the closed position, the second cam member contacts the moving member at the third arc portion. When the second door is opened by a predetermined angle relative to the closed state, the second cam member contacts the moving member at the fourth arc portion. The image forming apparatus according to claim 11, characterized in that, until the engagement between the second door and the second cam member switches from the first engagement portion to the second engagement portion, no rotational force is applied to the second cam member by the biasing force applied from the moving member in the direction that the second door opens.

15. The image forming apparatus according to claim 14, characterized in that the second cam member has a fifth arc portion that connects the third arc portion and the fourth arc portion, with the center position being different from the pivot axis center of the second cam member.

16. The image forming apparatus according to claim 7, characterized in that when the second door is in the open position, no biasing force from the moving member is applied to the engaging portion of the second door.

Images