Pressure / depressurization switching mechanism and image forming apparatus

Abstract

To provide a pressurization and depressurization switching mechanism that can be reduced in a size in a pressure direction of a contact member to a member to be contacted.SOLUTION: A pressurization and depressurization switching mechanism switches pressurization and depressurization of a contact member 20 to a member to be contacted 21, and the mechanism has: a support and rotation member 26 that rotates around a first rotation shaft 26a to support the contact member movably in a contact and separation direction with respect to the member to be contacted; an urging member 27 that is connected with a part to be urged 26b of the support and rotation member located on an opposite side of the first rotation shaft with respect to a virtual line NV, and applies urging force to rotate the support and rotation member in a direction in which the contact member is brought into contact with the member to be contacted; and a switching and rotation member 28 that is connected with the urging member, and rotates around a second rotation shaft 28a parallel to the first rotation shaft between a pressurization rotation position where the same increases the urging force of the urging member and a depressurization rotation position where the same decreases the urging force of the urging member. A rotation operation end 28c operating the rotation of the switching and rotation member is located on an opposite side of the second rotation shaft during pressurization with respect to the virtual line.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a pressure application and release switching mechanism and an image forming apparatus.

Background Art

[0002] Conventionally, a pressure application and release switching mechanism for switching the pressure application and release of a contact member with respect to a contact target member has been known.

[0003] For example, Patent Document 1 discloses a support module (pressure application and release switching mechanism) capable of switching the pressure application and release of a pressure belt (contact member) with respect to a heating roll (contact target member) of a fixing device. In this support module, a belt support member (support rotating member) that supports the pressure belt is configured to be rotatable with respect to a roll support member that supports the heating roll, and one end of a tension spring (biasing member) is attached to a spring attachment portion of this belt support member. During pressure application, the pressure belt is pressed against the heating roll via the belt support member by the biasing force of this tension spring. A lever that is operated to switch the pressure application and release of the pressure belt with respect to the heating roll is provided rotatably with respect to the roll support member in this support module. The other end of the tension spring is attached to a spring receiving portion of this lever.

[0004] In the support module, in the nip state where the pressure belt is pressed against the heating roll, the lever takes a rotation position (pressure application rotation position) such that its longitudinal direction substantially coincides with the tension direction of the tension spring. At this time, the other end of the tension spring is in a state of being hooked on a spring attachment portion provided on the roll support member, and is in a state of being disengaged from the spring receiving portion of the lever. The lever is held loosely with respect to the roll support member in the nip state. When the lever is rotated from this nip state, the other end of the tension spring is disengaged from the spring attachment portion of the roll support member and is hooked on the spring receiving portion of the lever. Then, the spring receiving portion of the lever rotates around the rotation axis, and the extension amount of the tension spring becomes smaller. Thereby, the pressure belt is released from the heating roll.

Summary of the Invention

[0005] However, conventional pressure / depressure switching mechanisms had the problem of the contact member's dimensions in the pressure direction becoming larger relative to the contacted member. [Means for solving the problem]

[0006] To solve the above-mentioned problems, the present invention provides a pressure-depressure switching mechanism for switching between applying and depressurizing pressure to a contact member against a member to be contacted, comprising: a support rotating member that rotates around a first pivot axis to support the contact member so that it can move toward and away from the member to be contacted; a biasing member that, when viewed from the axial direction of the first pivot axis, is connected to a biased portion of the support rotating member located on the opposite side of the first pivot axis with respect to a virtual line parallel to the pressure direction that passes through the contact point between the contact member and the member to be contacted when pressure is applied, and applies a biasing force to rotate the support rotating member in the direction in which the contact member contacts the member to be contacted; and a switching rotating member that is connected to the end of the biasing member opposite to the end of the support rotating member that is connected to the biased portion, and rotates around a second pivot axis parallel to the first pivot axis between a pressure rotation position that increases the biasing force of the biasing member and a depressurization rotation position that decreases the biasing force of the biasing member. When the switching rotating member is in the pressurized rotating position, a restricting member restricts the rotation of the switching rotating member to the opposite side of the depressurized rotating position. The rotating end that operates the rotation of the switching rotating member is positioned on the opposite side of the second rotating shaft from the imaginary line when viewed from the axial direction of the second rotating shaft when pressurized. Furthermore, when the switching rotating member is in the pressurized rotation position, the biasing force of the biasing member is configured to rotate the switching rotating member toward the opposite side of the depressurized rotation position, and as the switching rotating member rotates from the pressurized rotation position to the depressurized rotation position, the direction of rotation of the switching rotating member due to the biasing force of the biasing member is configured to switch toward the depressurized rotation position. It is characterized by the following. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress the increase in size of the contact member in the direction of pressure applied to the member to be contacted. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram of the image forming apparatus in an embodiment. [Figure 2] This diagram illustrates the internal structure of the fixing device in the image forming apparatus, viewed from the paper width direction. [Figure 3] This diagram illustrates the configuration of the pressure / depressurization switching mechanism used in the fixing device. [Figure 4] This diagram illustrates the configuration of the pressure-reducing / depressurizing switching mechanism used in the same fixing device. [Figure 5] A schematic diagram illustrating the pressure and depressurization switching mechanism. [Figure 6] This diagram illustrates the lengths L1 to L6 of various parts in the pressure-reducing switching mechanism. [Figure 7] A schematic diagram illustrating a conventional pressure / depressurization switching mechanism. [Figure 8] An explanatory diagram showing the configuration in which the pressure release lever is linked to the opening and closing cover of the image forming apparatus when it is in the pressurized rotation position. [Figure 9] An explanatory diagram showing the configuration in which the pressure release lever is linked to the opening and closing cover of the image forming apparatus when it is in the depressurization rotation position. [Modes for carrying out the invention]

[0009] The following describes one embodiment in which the pressure-relieving switching mechanism according to the present invention is applied to the fixing device of an electrophotographic image forming apparatus. In this embodiment, the pressurization and depressurization switching mechanism in the fixing device of an image forming apparatus is used as an example to explain how to pressurize and depressurize a fixing belt, which acts as a contact member, against a pressure roller, which acts as a contact member. However, the invention is not limited to this. For example, the present invention can also be applied to a pressurization and depressurization switching mechanism in an image forming apparatus that switches on and off the pressurization and depressurization of another location (such as a pair of transport rollers) that contacts a contact member with a contact member. The image forming apparatus is not limited to electrophotographic image forming apparatuses, but may also be other types of image forming apparatuses such as inkjet recording apparatuses, and may be printers, copiers, facsimile machines, or combination machines thereof.

[0010] Figure 1 is a schematic diagram of the image forming apparatus in this embodiment. The image forming apparatus 100 of this embodiment comprises four image forming units 1Y, 1M, 1C, and 1Bk, which constitute the image forming section. Each image forming unit 1Y, 1M, 1C, and 1Bk is configured to be detachable from the main body 103 of the image forming apparatus and has the same configuration except that it contains different colored developers of yellow, magenta, cyan, and black, corresponding to the color separation components of a color image. Specifically, each image forming unit 1Y, 1M, 1C, and 1Bk comprises a drum-shaped photoreceptor 2 as a latent image carrier. Each image forming unit also comprises a charging device 3 for charging the surface of the photoreceptor 2, a developing device 4 for supplying toner as a developer to the surface of the photoreceptor 2 to form a toner image, and a cleaning device 5 for cleaning the surface of the photoreceptor 2.

[0011] The image forming apparatus 100 also includes an exposure device 6 that exposes the surface of each photoreceptor 2 to form an electrostatic latent image, a paper feed device 7 that supplies paper P as a recording material, and a transfer device 8 that transfers the toner image formed on each photoreceptor 2 to the paper P. The image forming apparatus 100 also includes a fixing device 9 that fixes the toner image transferred to the paper P, and a paper discharge device 10 that discharges the paper P outside the apparatus.

[0012] The transfer device 8 has an endless intermediate transfer belt 11 as an intermediate transfer body stretched by a plurality of rollers. The transfer device 8 also has four primary transfer rollers 12 as primary transfer members that transfer the toner image on each photoreceptor 2 to the intermediate transfer belt 11, and a secondary transfer roller 13 as a secondary transfer member that transfers the toner image transferred on the intermediate transfer belt 11 to the paper P. Each of the plurality of primary transfer rollers 12 is in contact with the photoreceptor 2 via the intermediate transfer belt 11. As a result, the intermediate transfer belt 11 and each photoreceptor 2 are in contact with each other, and a primary transfer nip is formed between them. On the other hand, the secondary transfer roller 13 is in contact with one of the rollers that stretch the intermediate transfer belt 11 via the intermediate transfer belt 11. As a result, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11.

[0013] Furthermore, a paper transport path 14 is formed inside the image forming apparatus 100 through which the paper P fed from the paper feed device 7 is transported. A pair of timing rollers 15 are provided along this paper transport path 14, from the paper feed device 7 to the secondary transfer nip (secondary transfer roller 13).

[0014] Next, the printing operation of the image forming apparatus of this embodiment will be described. When a print operation start command is received, in each image unit 1Y, 1M, 1C, and 1Bk, the photoreceptor 2 is driven to rotate clockwise as shown in Figure 1, and the surface of the photoreceptor 2 is charged to a uniform high potential by the charging device 3. Next, based on the image information of the original document read by the document reader or the print command issued from the terminal, the exposure device 6 exposes the surface of each photoreceptor 2, causing the potential of the exposed area to decrease and forming an electrostatic latent image. Then, toner is supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoreceptor 2.

[0015] Each toner image formed on each photoreceptor 2, upon reaching the primary transfer nip (position of the primary transfer roller 12) as the photoreceptor 2 rotates, is transferred onto the intermediate transfer belt 11, which rotates counterclockwise as shown in Figure 1, so that the images overlap each other. The toner images transferred onto the intermediate transfer belt 11 are then transported to the secondary transfer nip (position of the secondary transfer roller 13) as the intermediate transfer belt 11 rotates, and are transferred to the paper P that has been transported to the secondary transfer nip. This paper P is supplied from the paper feeder 7. The paper P supplied from the paper feeder 7 is stopped by the timing roller 15, and then transported to the secondary transfer nip in time with the toner images on the intermediate transfer belt 11 reaching the secondary transfer nip. Thus, a full-color toner image is carried on the paper P. After the toner image is transferred, any toner remaining on each photoreceptor 2 is removed by the cleaning devices 5.

[0016] The sheet P onto which the toner image has been transferred is conveyed to the fixing device 9, and the toner image is fixed to the sheet P by the fixing device 9. Thereafter, the sheet P is discharged outside the apparatus by the paper discharge device 10, and a series of printing operations is completed.

[0017] Next, the configuration of the fixing device 9 of the present embodiment will be described. FIG. 2 is an explanatory view when the internal structure of the fixing device 9 in the present embodiment is viewed from the width direction of the sheet P (recording material width direction). The fixing device 9 of the present embodiment includes a fixing belt (also referred to as a fixing sleeve) 20 formed of an endless belt member as a fixing member which is an abutting member, and a pressure roller 21 as an opposing member which is an abutted member that contacts the outer peripheral surface of the fixing belt 20 to form a nip portion N which is a fixing nip, and a heating device 19 that heats the fixing belt 20. The heating device 19 includes a planar heater 22 as a heating member that heats the fixing belt from the inner peripheral surface side of the fixing belt 20, and a heater holder 23 as a holding member that holds the heater 22. Further, the heating device 19 includes a stay 24 as a support member that supports the heater holder 23 in the recording material width direction (the direction perpendicular to the paper surface in FIG. 2).

[0018] The fixing belt 20 has, for example, a hollow base made of polyimide (PI) with an outer diameter of 25 mm and a thickness of 40 to 120 μm. On the outermost layer of the fixing belt 20, a release layer with a thickness of 5 to 50 μm made of a fluororesin such as PFA or PTFE is formed in order to enhance durability and ensure release properties. An elastic layer made of rubber or the like with a thickness of 50 to 500 μm may be provided between the base and the release layer. Further, the base of the fixing belt 20 is not limited to polyimide, and may be a heat-resistant resin such as PEEK, or a metal base such as nickel (Ni) or SUS. The inner peripheral surface of the fixing belt 20 may be coated with polyimide, PTFE, or the like as a sliding layer.

[0019] The pressure roller 21 has, for example, an outer diameter of 25 mm and is composed of a solid iron core 21a, an elastic layer 21b formed on the surface of the core 21a, and a release layer 21c formed on the outside of the elastic layer 21b. The elastic layer 21b is made of silicone rubber and has a thickness of, for example, 3.5 mm. To improve release properties, it is desirable to form a release layer 21c on the surface of the elastic layer 21b, which is a fluororesin layer with a thickness of, for example, about 40 μm.

[0020] The heater 22 is elongated in the width direction (recording material width direction) of the fixing belt 20 and is positioned to contact the inner circumferential surface of the fixing belt 20. The heater 22 may not be in contact with the fixing belt 20, or may be in indirect contact via a low-friction sheet or the like, but direct contact between the heater 22 and the fixing belt 20 improves the heat transfer efficiency to the fixing belt 20. It is also possible to have the heater 22 in contact with the outer circumferential surface of the fixing belt 20, but if the outer circumferential surface of the fixing belt 20 is damaged by contact with the heater 22, the fixing quality may deteriorate, so it is preferable for the heater 22 to be in contact with the inner circumferential surface of the fixing belt 20.

[0021] The heater holder 23 and the stay 24 are positioned on the inner circumference side of the fixing belt 20. The stay 24 is made of a metal channel material and is pressurized toward the pressure roller 21 by a pressure / depressure switching mechanism described later. Because the side of the heater holder 23 opposite to the heater 22 side is supported by the stay 24, the heater 22 and the heater holder 23 are kept from bending significantly under the contact pressure with the pressure roller 21, and a nip portion N is formed between the fixing belt 20 and the pressure roller 21.

[0022] Since the heater holder 23 is prone to becoming hot due to the heat from the heater 22, it is desirable that it be made of a heat-resistant material. For example, if the heater holder 23 is made of a heat-resistant resin with low thermal conductivity such as LCP or PEEK, heat transfer from the heater 22 to the heater holder 23 is suppressed, making it possible to efficiently heat the fixing belt 20.

[0023] The pressure roller 21 and the fixing belt 20 are pressed against each other via the stay 24 by the biasing force of the tension spring 27, which acts as a biasing member of the pressure / depressure switching mechanism described later. This forms a nip portion N between the fixing belt 20 and the pressure roller 21. The pressure roller 21 also functions as a drive roller, which is rotated by a driving force transmitted from a driving means provided on the image forming apparatus body 103. On the other hand, the fixing belt 20 is configured to rotate in conjunction with the rotation of the pressure roller 21. During rotation, the fixing belt 20 slides against the heater 22. To improve the sliding properties of the fixing belt 20, a lubricant such as oil or grease may be interposed between the heater 22 and the fixing belt 20.

[0024] When the printing operation starts, the pressure roller 21 is driven to rotate, and the fixing belt 20 begins to rotate in response. Power is also supplied to the heater 22, which heats the fixing belt 20. When the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), the paper P carrying the unfixed toner image is transported between the fixing belt 20 and the pressure roller 21 (nip section N), as shown in Figure 2. As a result, the unfixed toner image is heated and pressurized and fixed to the paper P.

[0025] Figures 3 and 4 are explanatory diagrams showing the configuration and operation of the pressure / depressurization switching mechanism used in the fixing device 9 of this embodiment. Figure 5 is a schematic diagram illustrating the pressure and depressurization switching mechanism of this embodiment. Figure 6 is an explanatory diagram illustrating the lengths L1 to L6 of various parts in the pressure-relieving switching mechanism of this embodiment. Figures 3, 5, and 6 show the state of the pressurization / depressurization switching mechanism during pressurization, while Figure 4 shows the state of the pressurization / depressurization switching mechanism during depressurization.

[0026] In this embodiment, the fixing device 9 has the core metal 21a of the pressure roller 21 rotatably supported by the fixing frame 25 of the fixing device body. The stay 24 that presses the fixing belt 20 against the pressure roller 21 is supported by a pressure lever 26, which is a support rotating member that can rotate around the first pivot axis 26a.

[0027] One end of the pressure lever 26 has a hook groove, which can be hooked onto the fixing frame 25, allowing the lever to rotate with the hook point as the first pivot axis 26a. The other end of the pressure lever 26 is provided with a spring mounting portion 26b, which is the biased part to which one end 27a of a tension spring 27, which acts as a biasing member, is attached. When viewed from the axial direction of the first pivot axis 26a, the spring mounting portion 26b is located on the opposite side from the first pivot axis 26a with respect to an imaginary line NV (hereinafter referred to as the "nip normal") that is parallel to the direction of pressure and passes through the contact point (fixing nip) between the fixing belt 20 and the pressure roller 21 when pressure is applied. The pressure lever 26 supports the stay 24 at a point (stay pressure point) 26c between the first pivot axis 26a and the spring mounting portion 26b.

[0028] With this configuration, when pressurized, the tension spring 27 acts as a biasing force (counterclockwise in the figure) that causes the pressurizing lever 26 to rotate around the first pivot axis 26a so that the fixing belt 20 comes into contact with the pressurizing roller 21. This biasing force causes the pressurizing lever 26 to bias the stay 24, which is supported at the stay pressurizing point 26c, toward the pressurizing roller 21. As a result, the stay 24 presses the fixing belt 20 against the pressurizing roller 21, forming a nip portion N.

[0029] The other end 27b of the tension spring 27 is attached to a spring mounting portion 28b provided on a pressure release lever 28, which serves as a switching rotating member. The pressure release lever 28 is configured to rotate around a second pivot axis 28a, which is parallel to the first pivot axis 26a, between a pressurizing rotation position (rotation position in Figure 3) that increases the biasing force of the tension spring 27 and a depressurizing rotation position (rotation position in Figure 4) that decreases the biasing force of the tension spring 27. The pressure release lever 28 is preferably composed of a single component, but it may also be composed of a combination of multiple components.

[0030] When the pressure release lever 28 is in the pressurized rotation position (rotation position in Figure 3), the spring length of the tension spring 27 becomes L1, and when the pressure release lever 28 is in the depressurized rotation position (rotation position in Figure 4), the spring length of the tension spring 27 becomes L2 (L1 > L2). In other words, the pressure release lever 28 has the function of switching the spring length of the tension spring 27.

[0031] In this embodiment, when pressurized, as shown in Figure 3, the line connecting the spring mounting portion 28b of the pressure release lever 28 and the spring mounting portion 28b of the pressurizing lever 26 is located on the side of the pressurizing point 26c of the pressurizing lever 26 relative to the second pivot axis 28a. Therefore, the pressure release lever 28 is subjected to a biasing force by the tension spring 27 that causes it to rotate counterclockwise around the second pivot axis 28a (in the direction of arrow A in the figure). At this time, the rotation operating end 28c that operates the rotation of the pressure release lever 28 abuts against the first rotation stopper portion 25a, which is a restricting member of the fixing frame 25, as shown in Figure 3, and further rotation is prohibited. As a result, the pressure release lever 28 is held in the pressurized rotation position as shown in Figure 3. At this time, the spring length of the tension spring 27 is configured to be L1.

[0032] On the other hand, when depressurizing, as shown in Figure 4, the line connecting the spring mounting portion 28b of the pressure release lever 28 and the spring mounting portion 28b of the pressure application lever 26 is located on the opposite side of the pressure application point 26c of the pressure application lever 26 with respect to the second pivot axis 28a. Therefore, the pressure release lever 28 is subjected to a biasing force by the tension spring 27 that causes it to rotate clockwise around the second pivot axis 28a (in the direction of arrow B in the figure). At this time, as shown in Figure 4, the pressure release lever 28 abuts against the second anti-rotation portion 25b provided on the fixing frame 25, and further rotation is prohibited. As a result, the pressure release lever 28 is held in the depressurization rotation position as shown in Figure 4. At this time, the spring length of the tension spring 27 is configured to be L2.

[0033] Figure 7 is a schematic diagram illustrating a conventional pressure / depressurization switching mechanism. In conventional pressurization / depressurization switching mechanisms, when pressurized, the biasing direction of the tension spring 27 is configured to substantially coincide with the longitudinal direction of the pressure release lever 28, as shown in Figure 7(a). In other words, when the pressure release lever 28 is pressed, the rotating end 28c of the pressure release lever 28 is configured to be on the same side as the second pivot shaft 28a with respect to the nip normal NV when viewed from the axial direction of the second pivot shaft 28a.

[0034] In this configuration, the longitudinal direction of the pressure release lever 28 during pressurization will be close to the direction in which the fixing belt 20 is pressed against the pressure roller 21. In particular, in order to efficiently pressurize the fixing belt 20 against the pressure roller 21 by the biasing force of the tension spring 27, it is preferable that the direction in which the fixing belt 20 is pressed against the pressure roller 21 (direction of the nip normal NV) and the biasing direction of the tension spring 27 (direction of L1) are oriented in approximately the same direction during pressurization. In this preferred configuration, the longitudinal direction of the pressure release lever 28 during pressurization will approximately coincide with the direction in which the fixing belt 20 is pressed against the pressure roller 21.

[0035] Here, if we want to reduce the force required to rotate the pressure release lever 28, we can either lower the spring constant of the tension spring 27 or increase the distance (length) L6 between the rotating end 28c of the pressure release lever 28 and the second pivot shaft 28a. However, there is a limit to how much we can lower the spring constant of the tension spring 27, since the required nip pressure is fixed, and increasing the spring length would lead to an increase in the size of the fixing device 9 (pressure / depressure switching mechanism) in the direction of the spring length of the tension spring 27. Therefore, increasing the length L6 of the pressure release lever 28 is an effective method.

[0036] However, if the method of increasing the length L6 of the pressure release lever 28 is adopted, the conventional pressure / depressure switching mechanism faces the problem of increasing the size of the fixing device 9 (pressure / depressure switching mechanism) in the direction of pressure application (direction of the nip normal NV) to the fixing belt 20 on the pressure roller 21 when pressurized.

[0037] Therefore, in this embodiment, as shown in Figures 3, 5, and 6, the rotating end 28c of the pressure release lever 28 is configured such that, when viewed from the axial direction of the second pivot shaft 28a, it is located on the opposite side of the second pivot shaft 28a from the nip normal NV when pressurized. With this configuration, the longitudinal direction (L6 direction) of the pressure release lever 28 when pressurized is in a direction that is greatly inclined or perpendicular to the pressurizing direction (nip normal NV direction) of the fixing belt 20 relative to the pressure roller 21. As a result, even if the longitudinal length L6 of the pressure release lever 28 is increased, it is possible to suppress an increase in the size of the fixing device 9 (pressure / depressurization switching mechanism) in the direction of the nip normal NV.

[0038] Furthermore, the dimensions of the fixing device 9 (pressure / depressure switching mechanism) in the direction perpendicular to the direction of pressure applied to the fixing belt 20 on the pressure roller 21 (direction of the nip normal NV) (paper transport direction) must originally be such that the longitudinal length L1 of the pressure lever 26 is secured. Therefore, even if the longitudinal length L6 of the pressure release lever 28 is increased, the dimensions of the fixing device 9 (pressure / depressure switching mechanism) in that direction will not increase as long as it does not exceed the length of L1.

[0039] Based on the above, according to this embodiment, even when the longitudinal length L6 of the pressure release lever 28 is increased to reduce the force required to rotate the pressure release lever 28, it is possible to suppress an increase in the size of the fixing device 9 (pressure / depressure switching mechanism) in the direction of the nip normal NV.

[0040] Figures 8 and 9 are explanatory diagrams showing a configuration in which the pressure release lever 28 is rotated to the pressurizing rotation position and the depressurizing rotation position in conjunction with the opening and closing operation of the opening / closing cover 101 of the image forming apparatus 100. Figure 8 shows the pressure release lever 28 in the pressurized rotation position, while Figure 4 shows the pressure release lever 28 in the depressurized rotation position.

[0041] In this embodiment, when the opening / closing cover 101 of the image forming apparatus 100 is opened from the state shown in Figure 8, the pressure release part 101a provided on the inside of the opening / closing cover 101 catches on the rotating end 28c of the pressure release lever 28 of the fixing device 9 during the rotation (opening operation D) of the opening / closing cover 101. Then, as the opening / closing cover 101 rotates further (opening operation D), the movement (rotation) of the pressure release part 101a that accompanies this movement pushes the rotating end 28c of the pressure release lever 28, causing the pressure release lever 28 to rotate from the pressurized rotation position to the depressurized rotation position. As a result, when the rotation (opening operation D) of the opening / closing cover 101 is completed, the pressure release lever 28 is in the depressurized rotation position, as shown in Figure 9, and the device is in a depressurized state.

[0042] Furthermore, in this embodiment, when the opening / closing cover 101 of the image forming apparatus 100 is closed from the state shown in Figure 9, the rotating end 28c of the pressure release lever 28, which is in the depressurization rotation position, abuts against the guide portion 101b provided on the inside of the opening / closing cover 101 during the rotation (closing operation E) of the opening / closing cover 101. Subsequently, as the opening / closing cover 101 rotates further (closing operation E), the rotating end 28c of the pressure release lever 28 slides along the guide portion 101b and the inner wall of the opening / closing cover 101, causing the pressure release lever 28 to rotate from the depressurization rotation position toward the pressurization rotation position. When the rotation (closing operation E) of the opening / closing cover 101 is completed, as shown in Figure 8, the pressure release lever 28 is in the pressurization rotation position and is in a pressurized state.

[0043] In this embodiment, a configuration has been described in which the pressure release lever 28 is rotated to the pressurizing rotation position and the depressurizing rotation position in conjunction with the opening and closing operation of the opening / closing cover 101 of the image forming apparatus 100, but this is not the only configuration. For example, an operator may manually operate the rotating end 28c of the pressure release lever 28 to rotate the pressure release lever 28 to the pressurizing rotation position and the depressurizing rotation position.

[0044] Furthermore, since the pressure release switching mechanism in this embodiment is provided in the fixing device 9, it is positioned near the heater 22 of the fixing device 9, which is a heat-generating element. In this case, if the pressure release lever 28 is positioned in the vertically upper region of the heater 22, it is particularly prone to becoming extremely hot due to exposure to the heat from the heater 22. In this embodiment, as shown in Figure 3, the pressure release lever 28 is positioned outside the vertically upper region of the heater 22, specifically, to the side of the heater 22. This makes it less likely for the pressure release lever 28 to become extremely hot compared to a configuration where the pressure release lever 28 is positioned in the vertically upper region of the heater 22.

[0045] If the pressure release lever 28 is designed to be less prone to high temperatures, the heat resistance requirements for the pressure release lever 28 are relaxed. As a result, the freedom of material selection for the pressure release lever 28 increases, allowing for the selection of materials such as those with low heat resistance but high strength. For example, a resin material can be suitably used as the pressure release lever 28.

[0046] Furthermore, in this embodiment, when the pressure release lever 28 is in the depressurization rotation position, the rotational operating end 28c is positioned lower than when it is in the pressurization rotation position. In this configuration, as shown in Figure 4, if an object falls on the pressure release lever 28 or a load is applied to it from above when the pressure release lever 28 is in the depressurization rotation position, the pressure release lever 28 will come into contact with the second anti-rotation part 25b and will not be able to rotate, which may cause damage to the pressure release lever 28.

[0047] In cases where such damage is likely, the pressure release lever 28 should be configured such that when it is in the depressurization rotation position, the rotating end 28c is positioned higher than when it is in the pressurization rotation position. With this configuration, if an object falls on the pressure release lever 28 or a load is applied from above while it is in the depressurization rotation position, the pressure release lever 28 can rotate toward the pressurization rotation position, thereby preventing damage to the pressure release lever 28.

[0048] The above is just one example; each of the following embodiments produces its own unique effects. [First aspect] The first embodiment is a pressure / depressure switching mechanism for switching the pressure on and depressurization of a contact member (e.g., a fixing belt 20) against a contacted member (e.g., a pressure roller 21), comprising: a support rotating member (e.g., a pressure lever 26) that rotates around a first pivot axis 26a to support the contact member so that it can move toward and away from the contacted member; and a biased portion (e.g., a spring mounting portion 26b) of the support rotating member located on the opposite side of the first pivot axis with respect to a virtual line (e.g., nip normal NV) that passes through the contact point between the contact member and the contacted member when pressure is applied, when viewed from the axial direction of the first pivot axis, and the contact member comes into contact with the contacted member The device includes a biasing member (e.g., a tension spring 27) that applies a biasing force to rotate the support rotating member in the direction of rotation, and a switching rotating member (e.g., a pressure release lever 28) connected to the end 27b of the biasing member opposite to the end 27a of the support rotating member that is connected to the biased portion of the support rotating member, and which rotates around a second rotating axis 28a parallel to the first rotating axis between a pressurizing rotating position that increases the biasing force of the biasing member and a depressurizing rotating position that decreases the biasing force of the biasing member, wherein the rotating operating end 28c that operates the rotation of the switching rotating member is located on the opposite side of the second rotating axis with respect to the imaginary line when viewed from the axial direction of the second rotating axis when pressurized. The support rotating member rotates around the first rotation axis, thereby supporting the contact member so that it can move toward and away from the contacted member. One end of the biasing member is attached to the biased portion of this support rotating member. When viewed from the axial direction of the first rotation axis, this biased portion is located on the opposite side of the first rotation axis from a virtual line parallel to the pressurizing direction that passes through the contact point between the contact member and the contacted member when pressurized. The other end of the biasing member is connected to a switching rotating member. This switching rotating member can be rotated around the second axis by operating its rotational end, thereby taking on a pressurizing rotation position that increases the biasing force of the biasing member and a depressurizing rotation position that decreases the biasing force of the biasing member. In such a configuration, in order to efficiently pressurize the contact member against the contacted member by the biasing force of the biasing member, the direction in which the contact member pressurizes the contact member against the contacted member and the direction in which the biasing member biases should be oriented in approximately the same direction. In conventional pressurization / depressurization switching mechanisms, when pressurization is performed, the direction in which the biasing member biases is oriented is configured to approximately coincide with the longitudinal direction of the switching rotating member (roughly the direction passing through the connection portion where the rotating end of the switching rotating member, the second rotating shaft, and the other end of the biasing member are connected). Therefore, when pressurization is performed, the longitudinal direction of the switching rotating member approximately coincides with the direction in which the contact member pressurizes the contact member against the contacted member. Here, the longer the distance (length) between the rotating end of the switching rotating member and the second rotating shaft, that is, the longer the longitudinal length of the switching rotating member, the smaller the force required to rotate the switching rotating member can be. However, in conventional pressurization / depressurization switching mechanisms, as described above, the longitudinal direction of the switching rotating member during pressurization substantially coincides with the direction of pressurization of the contact member against the contacted member. Therefore, if the longitudinal length of the switching rotating member is increased, the dimensions of the pressurization / depressurization switching mechanism in that pressurization direction become larger. In this embodiment, the rotating end of the switching rotating member is configured such that, when viewed from the axial direction of the second rotating shaft, it is positioned on the opposite side of the second rotating shaft from the second rotating shaft with respect to the imaginary line (an imaginary line parallel to the pressurizing direction that passes through the contact point between the contact member and the contacted member when pressurized). With this configuration, the longitudinal direction of the switching rotating member when pressurized is inclined or perpendicular to the pressurizing direction of the contact member relative to the contacted member. Therefore, even if the longitudinal length of the switching rotating member is increased, the increase in the size of the pressurizing / depressurizing switching mechanism in the pressurizing direction is suppressed.

[0049] [Second aspect] The second embodiment is characterized in that, in the first embodiment, when the switching rotating member is in the pressurized rotating position, it has a restricting member (for example, a first rotation stopper 25a) that restricts the rotation of the switching rotating member to the opposite side of the depressurized rotating position, and when the switching rotating member is in the pressurized rotating position, the biasing force of the biasing member is configured to rotate the switching rotating member to the opposite side of the depressurized rotating position. According to this, the biasing force of the biasing member allows the switching rotation member to be stably held in the pressurized rotation position.

[0050] [Third aspect] The third embodiment is characterized in that, in the first or second embodiment, the switching rotation member is composed of a single member. This allows for a reduction in the number of parts.

[0051] [Fourth aspect] The fourth embodiment is characterized in that, in any of the first to third embodiments, the biasing member is positioned in the vertically upper region or vertically lower region of the contact point (nip portion N). According to this, the longitudinal direction of the switching rotating member is positioned so that it is approximately oriented vertically, which helps to suppress an increase in the height of the pressure / depressurization switching mechanism.

[0052] [Fifth aspect] The fifth embodiment is characterized in that, in any of the first to fourth embodiments, the switching rotating member is configured such that when it is in the depressurization rotating position, the rotating operating end is positioned higher than it is in the pressurization rotating position. According to this, even if an object falls on the switching rotating member or a load is applied from above while the switching rotating member is in the depressurization rotation position, the switching rotating member can still rotate toward the pressurization rotation position, thereby suppressing damage to the switching rotating member.

[0053] [Sixth aspect] The sixth embodiment is an image forming apparatus 100, characterized by comprising a pressure-relieving switching mechanism according to any of the first to fourth embodiments. According to this, it is possible to suppress the increase in size of the image forming apparatus in the direction of pressure applied by the contacting member to the member to be contacted.

[0054] [Seventh aspect] The seventh aspect is characterized in that, in the sixth aspect, the image forming apparatus body 103 has an opening / closing cover 101, and the switching rotating member rotates from the pressurizing rotating position to the depressurizing rotating position in conjunction with the opening operation of the opening / closing cover, and the switching rotating member rotates from the depressurizing rotating position to the pressurizing rotating position in conjunction with the closing operation of the opening / closing cover. According to this, the switching rotating member can be rotated in conjunction with the opening and closing of the opening and closing cover of the image forming apparatus body, eliminating the need to rotate the switching rotating member separately from the opening and closing of the opening and closing cover.

[0055] [8th aspect] The eighth aspect is characterized in that, in the sixth or seventh aspect, the pressure / depressurization switching mechanism is located near a heat-generating element (e.g., heater 22) within the main body of the image forming apparatus, and the switching rotation member is located outside the vertically upper region of the heat-generating element. According to this, compared to a configuration where the switching rotating member is positioned in the vertically upper region of the heating member, the switching rotating member is less likely to become hot. As a result, the heat resistance requirements for the switching rotating member are relaxed, and the degree of freedom in selecting the material for the switching rotating member is increased.

[0056] [Ninth aspect] The ninth aspect is characterized in that, in any of the sixth to eighth aspects, the switching rotating member is made of resin. According to this, a resin-made switching and rotating member can be provided. [Explanation of Symbols]

[0057] 1: Image creation unit 2: Photoreceptor 3: Charging device 4: Developing equipment 5: Cleaning device 6: Exposure equipment 7: Paper feeder 8: Transfer device 9: Fixing device 10: Paper ejection device 11: Intermediate transfer belt 12: Primary transfer roller 13: Secondary transfer roller 14: Paper transport path 15: Timing Roller 19: Heating device 20: Fixing belt 21: Pressure roller 21a: Core metal 21b: Elastic layer 21c: Release layer 22: Heater 23: Heater holder 24: Stay 25: Fixing frame 25a: First anti-rotation part 25b: Second anti-rotation part 26: Pressurized lever 26a: First rotation axis 26b: Spring mounting section 26c: Stay pressurization point 27: Tension spring 28: Pressure release lever 28a: Second rotation axis 28b: Spring mounting section 28c: Rotating end 100: Image forming apparatus 101: Open / Close Cover 101a: Pressure release section 101b: Guide section [Prior art documents] [Patent Documents]

[0058] [Patent Document 1] Patent No. 6503800

Claims

1. A pressure and depressurization switching mechanism that switches between applying and depressurizing pressure to a contact member against a contact member, A support rotating member that rotates around a first pivot axis to support the contact member so that it can move toward and away from the contacted member, When viewed from the axial direction of the first pivot axis, a biasing member is connected to the biased portion of the support pivot member located on the opposite side of the first pivot axis with respect to a virtual line parallel to the pressurizing direction that passes through the contact point between the contact member and the contacted member when pressurized, and applies a biasing force that causes the support pivot member to rotate in the direction in which the contact member contacts the contacted member. A switching rotating member is connected to the end of the biasing member opposite to the end of the support rotating member connected to the biased portion, and rotates around a second rotating axis parallel to the first rotating axis between a pressurizing rotating position that increases the biasing force of the biasing member and a depressurizing rotating position that decreases the biasing force of the biasing member, The switching rotating member has a restricting member that restricts the rotation of the switching rotating member to the opposite side of the depressurization rotating position when the switching rotating member is in the pressurization rotation position, The rotating end that operates the rotation of the switching rotating member is, when pressurized, located on the opposite side of the second rotating shaft from the imaginary line when viewed from the axial direction of the second rotating shaft. When the switching rotating member is in the pressurized rotating position, the biasing force of the biasing member is configured to rotate the switching rotating member to the opposite side from the depressurized rotating position. A pressure-relieving switching mechanism characterized in that, while the switching rotating member is rotated from the pressure-relieving position to the pressure-relieving position, the direction of rotation of the switching rotating member due to the biasing force of the biasing member is switched toward the pressure-relieving position.

2. In the pressurization / depressurization switching mechanism according to Claim 1, The pressure-relieving switching mechanism is characterized in that the switching rotating member is composed of a single member.

3. In the pressurization / depressurization switching mechanism according to either claim 1 or 2, The pressure-relieving switching mechanism is characterized in that the biasing member is positioned in the vertically upper region or the vertically lower region of the contact point.

4. In the pressurization / depressurization switching mechanism according to any one of claims 1 to 3, The pressure-relieving switching mechanism is characterized in that the switching rotating member is configured such that when it is in the pressure-relieving rotating position, the rotating operating end is positioned higher than when it is in the pressure-relieving rotating position.

5. An image forming apparatus characterized by comprising a pressure and depressurization switching mechanism according to any one of claims 1 to 4.

6. In the image forming apparatus according to claim 5, The image forming apparatus has an opening and closing cover. An image forming apparatus characterized by comprising at least one of the following configurations: a configuration in which the switching rotating member rotates from the pressurizing rotation position to the depressurizing rotation position in conjunction with the opening operation of the opening / closing cover; and a configuration in which the switching rotating member rotates from the depressurizing rotation position to the pressurizing rotation position in conjunction with the closing operation of the opening / closing cover.

7. In the image forming apparatus according to claim 5 or 6, The aforementioned pressure / depressurization switching mechanism is located near the heat-generating element inside the main body of the image forming apparatus. The image forming apparatus is characterized in that the switching rotating member is positioned outside the vertically upper region of the heating member.

8. In the image forming apparatus according to any one of claims 5 to 7, The image forming apparatus is characterized in that the switching rotating member is made of resin.

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