Image forming apparatus

Abstract

To provide an image forming apparatus that restricts, with a relatively simple configuration, fall of a pressure release lever in a rotation axis direction.SOLUTION: An image forming apparatus of the present invention comprises: a pressure mechanism that applies pressure to a pressure application body against a pressure application target body; and an opening and closing member that is openable and closable relative to an apparatus body accommodating the pressure mechanism, and the image forming apparatus applies pressure to the pressure application body against the pressure application target body or releases the applied pressure, in conjunction with an opening operation or a closing operation of the opening and closing member. The pressure mechanism has: a pressure lever that is rotatably and pivotably supported at one end, is provided with an elastic body at the other end, and can apply pressure to the pressure application body against the pressure application target body; and a pressure release lever that is rotatably supported, and is connected to the pressure lever with the elastic body therebetween. The pressure release lever is movable between a holding position where pressure is applied to the pressure application body against the pressure application target body, and a release position where the pressure applied to the pressure application body against the pressure application target body is released. The opening and closing member has a pressure part that applies pressure to the pressure release lever during the closing operation to move it from the release position to the holding position. The pressure part has an inclined part that is in contact with the pressure release lever to restrict fall of the pressure release lever in a rotation axis direction.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] A fixing device equipped with a pair of rollers consisting of a fixing roller and a pressure roller is widely used in image forming devices such as copiers, printers, and facsimiles. This type of image forming device is equipped with a pressure mechanism that presses a pressure roller against the fixing roller, and uses a configuration in which the pressure roller is pressed against or released from the fixing roller in conjunction with the opening and closing of a cover or door.

[0003] For example, Patent Document 1 discloses a configuration having a pressure release lever 25 that can move between a position that maintains the pressed state of the roller pair 21, 22 and a position that releases the pressed state, and returns the lever from the release position to the holding position in conjunction with the action of closing the door 7 that has been opened to clear a jam.

[0004] When the opening / closing member is opened, the pressure contact state of the roller pair is automatically released, which makes it possible to handle the jam, such as removing the recording material stuck between the roller pair, thereby improving convenience. Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, efforts have been made to optimize designs to reduce the weight and parts costs of fixing units while maintaining the fixing function. However, it has been discovered that the strength of the rotation shaft (support part) of the pressure release lever is insufficient.

[0006] Specifically, when the pressure release lever is pressed in conjunction with the closing door, it may tip over in the direction of its rotation axis, causing the pressure release lever to not move to the correct position, resulting in the problem of not being able to pressurize and release the pressure on the roller pair properly.

[0007] To address this issue, efforts have been made to strengthen the components of the fixing unit or to add new components such as a mechanism to prevent the unit from tipping over, but these efforts would not achieve weight reduction or cost reduction. Also, if a guide mechanism that controls the operating range of the pressure release lever were provided in the fixing unit, this would mean that the guide mechanism would also need to be replaced when the unit is replaced, which is not economical.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus that has a relatively simple structure and that prevents the pressure release lever from tilting in the direction of the rotation axis. [Means for solving the problem]

[0009] The above problem is solved by an image forming apparatus comprising a pressure mechanism that pressurizes a pressure body against a pressure target body, and an opening / closing member that can be opened or closed relative to the apparatus main body that houses the pressure mechanism, and which pressurizes or releases pressure on the pressure target body in conjunction with the opening or closing operation of the opening / closing member, wherein the pressure mechanism comprises a pressure lever that is rotatably supported at one end and has an elastic body at the other end, and is capable of pressurizing the pressure body against the pressure target body, and a pressure release lever that is rotatably supported and connected to the pressure lever via the elastic body, and the pressure release lever is movable between a holding position where the pressure body is pressed against the pressure target body and a release position where the pressure body is released from the pressure target body, the opening / closing member has a pressing portion that presses the pressure release lever during a closing operation, moving it from the release position to the holding position, and the pressing portion has an inclined portion that comes into contact with the pressure release lever and restricts the pressure release lever from tilting in the direction of the rotation axis. [Effects of the Invention]

[0010] The image forming apparatus of the present invention can restrict the pressure release lever from tilting in the direction of the rotation axis with a relatively simple configuration. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. [Figure 2] 1 is a schematic cross-sectional view of a fixing device according to an embodiment of the present invention; [Figure 3] 1A and 1B are schematic cross-sectional configuration diagrams of a pressure mechanism and an opening / closing member according to an embodiment of the present invention, in which FIG. 1A shows the opening operation of the opening / closing member, and FIG. 1B shows the closing operation of the opening / closing member. [Figure 4] 5A and 5B are diagrams showing the mounting structure of the pressure release lever, in which (a) is a perspective view and (b) is a plan view. [Figure 5] FIG. 4 is a plan view showing a pressing portion of an opening / closing member according to an embodiment of the present invention. [Figure 6] FIG. 10 is a plan view (part 1) showing a pressing portion of an opening / closing member according to a modified example of the present invention. [Figure 7] FIG. 10 is a second plan view showing the pressing portion of the opening / closing member according to the modified example of the present invention. [Figure 8] FIG. 10 is a plan view showing a pressure release lever according to a modified example of the present invention. [Figure 9] FIG. 10 is a schematic top view of a fixing device according to a modified example of the present invention. [Figure 10] FIG. 2 is a view showing the plane heater in the width direction. DETAILED DESCRIPTION OF THE INVENTION

[0012] The configuration of an image forming apparatus according to one embodiment of the present invention will be described below with reference to Figure 1. The image forming apparatus 100 shown in Figure 1 is a tandem color printer in which image forming units that form multiple color images are arranged side by side along the extension direction of the belt. However, the present invention is not limited to this type, and can also be applied to not only printers but also copiers, facsimile machines, etc.

[0013] The image forming apparatus 100 employs a tandem structure in which photosensitive drums 20Y, 20C, 20M, and 20Bk are arranged side by side as image carriers capable of forming images corresponding to the colors separated into yellow, cyan, magenta, and black.

[0014] In the image forming apparatus 100, the visible images formed on the photosensitive drums 20Y, 20C, 20M, and 20Bk are primarily transferred to an intermediate transfer body (hereinafter referred to as a transfer belt) 11, which is an endless belt that can move in the direction of arrow A1 while facing each photosensitive drum. By carrying out this primary transfer process, the images of each color are superimposed and transferred, and then, by carrying out a secondary transfer process, they are transferred all at once to a recording material S, such as a recording sheet.

[0015] Devices for performing image formation processing in accordance with the rotation of the photosensitive drum 20 are arranged around each photosensitive drum 20. Taking photosensitive drum 20Bk, which forms black images, as a representative example, a charging device 30Bk, a developing device 40Bk, a primary transfer roller 12Bk, and a cleaning device 50Bk, which perform image formation processing, are arranged along the direction of rotation of photosensitive drum 20Bk. An optical writing device 8 is used for writing using writing light Lb, which is performed after charging the photosensitive drum 20.

[0016] In the process of transfer belt 11 moving in the A1 direction, the superimposed transfer onto transfer belt 11 involves transferring the visible images formed on each of photosensitive drums 20Y, 20C, 20M, and 20Bk onto the same position on transfer belt 11 in a superimposed manner. Therefore, transfer is performed with shifted timing from the upstream side to the downstream side in the A1 direction by applying voltage to primary transfer rollers 12Y, 12C, 12M, and 12Bk disposed opposite each of photosensitive drums 20Y, 20C, 20M, and 20Bk across transfer belt 11.

[0017] The photoconductor drums 20Y, 20C, 20M, and 20Bk are arranged in this order from the upstream side in the A1 direction. The photoconductor drums 20Y, 20C, 20M, and 20Bk are provided in image stations for forming yellow, cyan, magenta, and black images, respectively.

[0018] The image forming apparatus 100 includes four image stations that perform image formation processing for each color, and a transfer belt unit 10 that is disposed above and facing each photosensitive drum 20 and includes a transfer belt 11 and primary transfer rollers 12Y, 12C, 12M, and 12Bk. It also includes a secondary transfer roller 5 that is disposed opposite the transfer belt 11 and serves as a transfer member that rotates in conjunction with the transfer belt 11, and a belt cleaning device 13 that is disposed opposite the transfer belt 11 and cleans the surface of the transfer belt 11. The image forming apparatus 100 also includes an optical writing device 8 that is disposed below and facing these four image stations.

[0019] The optical writing device 8 is equipped with a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a folding mirror, and a rotating polygonal mirror as a polarizing means. The optical writing device 8 is configured to emit writing light Lb corresponding to each color to each of the photoconductor drums 20Y, 20C, 20M, and 20Bk, forming electrostatic latent images on the photoconductor drums 20Y, 20C, 20M, and 20Bk. For convenience, only the image station for the black image is labeled in Figure 1, but the same applies to the other image stations.

[0020] The image forming apparatus 100 is provided with a sheet feeding device 61 serving as a paper feed cassette that holds recording material S to be transported toward between the photosensitive drums 20Y, 20C, 20M, and 20Bk and the transfer belt 11. Also provided is a pair of registration rollers 4 that feeds out the recording material S transported from the sheet feeding device 61 toward a transfer section between each photosensitive drum 20 and the transfer belt 11 at a predetermined timing that matches the timing of toner image formation by the image station. Furthermore, a sensor (not shown) is provided that detects when the leading edge of the recording material S has reached the pair of registration rollers 4.

[0021] The image forming apparatus 100 is provided with a fixing device 200 as a fixing unit of a roller fixing type for fixing a toner image onto a recording material S onto which the toner image has been transferred, and a paper discharge roller 7 for discharging the recording material S with the fixed toner image to the outside of the main body of the image forming apparatus 100. Also, at the top of the main body of the image forming apparatus 100, a paper discharge tray 17 is provided for stacking the recording material S discharged to the outside of the main body of the image forming apparatus 100 by the paper discharge roller 7. Below the paper discharge tray 17, toner bottles 9Y, 9C, 9M, and 9Bk filled with toner of each color, yellow, cyan, magenta, and black, are provided.

[0022] The transfer belt unit 10 includes a transfer belt 11, primary transfer rollers 12Y, 12C, 12M, and 12Bk, as well as a drive roller 72 and a driven roller 73 around which the transfer belt 11 is wound.

[0023] The driven roller 73 also functions as a tension applying means for the transfer belt 11, and for this purpose, a spring or other such applying means is provided on the driven roller 73. The transfer belt unit 10, primary transfer rollers 12Y, 12C, 12M, and 12Bk, secondary transfer roller 5, and belt cleaning device 13 constitute a transfer device 71.

[0024] The sheet feeding device 61 is disposed in the lower part of the main body of the image forming apparatus 100, and has a feeding roller 3 as a paper feeding roller that contacts the upper surface of the uppermost recording material S. The feeding roller 3 is driven to rotate counterclockwise in the drawing, thereby feeding the uppermost recording material S toward the pair of registration rollers 4.

[0025] Although not shown in detail, the belt cleaning device 13 provided in the transfer device 71 has a cleaning brush and a cleaning blade disposed to face and contact the transfer belt 11. The belt cleaning device 13 cleans the transfer belt 11 by scraping off and removing foreign matter such as residual toner on the transfer belt 11 with the cleaning brush and cleaning blade.

[0026] The belt cleaning device 13 also has a discharge means (not shown) for carrying out and discarding the residual toner removed from the transfer belt 11 .

[0027] Fig. 2 is a schematic cross-sectional view of a fixing device according to one embodiment of the present invention. As shown in Fig. 2, fixing device 200 includes fixing belt 201 as a rotatable fixing member and pressure roller 203 as a rotatable pressure member disposed opposite to fixing belt 201. Furthermore, fixing belt 201 is directly heated from its inner peripheral side by radiant heat from halogen heaters 202A and 202B as multiple heat sources.

[0028] Temperature sensors 230A and 230B are attached to detect the temperature of fixing belt 201 in a non-contact manner. A control unit of fixing device 200 controls the lighting rates of halogen heaters 202A and 202B based on the detected temperatures, thereby controlling the temperature of fixing belt 201 to a desired temperature.

[0029] The fixing belt 201 is made of a metal belt such as nickel or SUS, or an endless belt or film made of a resin material such as polyimide. The surface of the belt has a release layer such as a PFA or PTFE layer to provide release properties to prevent toner from adhering. It is preferable to have an elastic layer made of silicone rubber or the like between the belt base material and the PFA or PTFE layer.

[0030] Without the silicone rubber layer, the heat capacity is reduced and the fixing performance is improved, but when the unfixed image is crushed and fixed, the minute irregularities on the belt surface are transferred to the image, which can leave a citrus peel-like uneven gloss (citrus peel image) on the solid parts of the image. To improve this, a silicone rubber layer of 100 μm or more can be provided. The deformation of the silicone rubber layer absorbs the minute irregularities, improving the citrus peel image.

[0031] Pressure roller 203 has a configuration in which elastic rubber layer 204 is provided on core metal 205, and a release layer (PFA or PTFE layer) is provided on the surface of the elastic rubber layer 204 to provide release properties. Pressure roller 203 rotates by a driving force transmitted via gears from a driving source such as a motor provided in image forming apparatus 100. Pressure roller 203 is pressed against fixing belt 201 by a spring or the like, and elastic rubber layer 204 is crushed and deformed to provide a predetermined nip width.

[0032] Pressure roller 203 may be a hollow roller, and may have a heat source such as a halogen heater inside pressure roller 203. Elastic rubber layer 204 may be solid rubber, but if there is no heater inside pressure roller 203, sponge rubber may be used. Sponge rubber is more preferable because it has high heat insulation properties and makes it difficult for heat to be lost from fixing belt 201.

[0033] Provided inside fixing belt 201 are nip forming member 206 disposed opposite pressure roller 203 and heat transfer assisting member 216 covering the surface of nip forming member 206 facing the inner surface of fixing belt 201. Also provided is stay member 207 that holds nip forming member 206 against the pressure from pressure roller 203.

[0034] The nip forming member 206 forms a fixing nip N between the pressure roller 203 and the fixing belt 201 via the fixing belt 201 , and also slides indirectly against the inner surface of the fixing belt 201 via the heat transfer assisting member 216 .

[0035] End heaters 226, which serve as end heat sources separate from the main heat source (fixing heat source), are integrally attached to both longitudinal ends of nip forming member 206. End heaters 226 are generally contact heat transfer type heat sources that are resistance heating elements such as ceramic heaters.

[0036] The heat transfer assisting member 216 prevents the heat from the end heater 226 from accumulating locally and actively transfers the heat in the longitudinal direction, reducing temperature non-uniformity in the longitudinal direction. For this reason, the heat transfer assisting member 216 is preferably made of a material that allows heat to be transferred in a short time, and is preferably made of a material with high thermal conductivity such as copper, aluminum, or silver. When cost, availability, thermal conductivity characteristics, and processability are all taken into consideration, it is most desirable to use aluminum or copper.

[0037] In this embodiment, the surface of the heat transfer assist member 216 that faces the inner surface of the fixing belt 201 is the surface that comes into direct contact with the fixing belt 201 and serves as the nip forming surface. A low-friction, wear-resistant sliding coating is applied to the surface of the heat transfer assist member 216, i.e., the surface that comes into contact with the inner surface of the fixing belt 201. Materials that are used for the sliding coating include a low-friction fluorine coating and highly wear-resistant DLC.

[0038] 2, the heat transfer assistance member 216 has a flat shape, but it may have a concave shape or other shapes. When the heat transfer assistance member 216 has a concave shape, the leading edge of the recording material S is discharged toward the pressure roller 203, improving separation performance and suppressing jams.

[0039] Stay member 207 is a support member for supporting nip forming member 206 and fixing nip portion N. Stay member 207 prevents bending of nip forming member 206 when pressure is applied from pressure roller 203, thereby making it possible to obtain a uniform nip width in the axial direction. Stay member 207 is held and fixed to side plates at both ends for positioning.

[0040] Stay member 207 has standing portions 207a and 207b that stand on the side opposite to fixing nip portion N, and halogen heaters 202A and 202B are disposed between standing portions 207a and 207b as fixing heat sources. Therefore, fixing belt 201 is directly heated from the inner surface by radiant heat from halogen heaters 202A and 202B.

[0041] Furthermore, a reflecting member 209 is provided between the halogen heater 202 and the stay member 207 to prevent unnecessary energy consumption caused by the stay member 207 being heated by radiant heat from the halogen heater 202. Instead of providing the reflecting member 209, the same effect can be obtained by insulating or mirror-finishing the surface of the stay member 207.

[0042] In this embodiment, as shown in Fig. 2, a reflecting member 209 is provided between halogen heaters 202A and 202B. By preventing each heater from heating the other's glass tube, fixing belt 201 can be heated efficiently.

[0043] The fixing device 200 of this embodiment includes a pressure mechanism 250 that brings the fixing belt 201 and the pressure roller 203 into contact with or separates them, thereby applying or depressurizing pressure to the fixing nip N. The pressure mechanism 250 includes a pressure lever 254 that rotates around a rotation shaft 66. When the pressure mechanism 250 brings the fixing belt 201 and the pressure roller 203 closer to each other, the fixing nip N is formed at the contact point between them, and when they are separated, the fixing nip N is dissolved.

[0044] If pressure roller 203 is pressed against fixing belt 201 for a long time, elastic rubber layer 204 may become deformed and stiffen, which may cause abnormal noise or glossy streaks in the next print. Therefore, after a predetermined time (for example, one minute) has passed since fixing, pressure mechanism 250 is activated to release pressure from fixing nip N. This leaves pressure roller 203 in an undeformed state or in a state with only a small amount of deformation, preventing deformation of elastic rubber layer 204.

[0045] Furthermore, even if a paper jam or the like occurs, the pressure mechanism 250 is activated to release pressure from the fixing nip N, making it easier for the user to remove the jammed paper.

[0046] In the fixing device 200 of this embodiment, the fixing belt 201 is rotated together with the pressure roller 203. Specifically, the pressure roller 203 is rotated by a drive source, and the fixing belt 201 rotates as a result of a driving force being transmitted to the belt at the fixing nip portion N. The fixing belt 201 rotates while being sandwiched in the fixing nip portion N, and is guided by flanges (not shown) at both ends and travels outside the fixing nip portion N. The toner image on the recording material S is heated and pressurized in the fixing nip portion N and fixed.

[0047] With the above-described configuration, it is possible to realize a fixing device that is inexpensive and has a fast warm-up time.

[0048] FIG. 3 is a schematic cross-sectional view of a pressure mechanism and an opening / closing member according to one embodiment of the present invention, where (a) shows the opening operation of the opening / closing member, and (b) shows the closing operation of the opening / closing member.

[0049] The image forming apparatus 100 includes a fixing device 200, a pressure mechanism 250 that applies pressure to a fixing belt 201 that is a pressure target by a pressure roller 203 that is a pressure applying member, and an opening / closing member 260 that can be opened and closed relative to the apparatus main body.

[0050] The pressure mechanism 250 has a pressure lever 254 rotatably supported at one end and having a pressure spring 252, which is an elastic body, attached to the other end, and a pressure release lever 256 that is rotatably supported and connected to the pressure lever 254 via the pressure spring 252.

[0051] The pressure release lever 256 is movable between a release position (Figure 3(a)) in which the pressure roller 203 is released from the fixing belt 201 and a holding position (Figure 3(b)) in which the pressure roller 203 is pressed against the fixing belt 201 by the pressure lever 254.

[0052] The opening / closing member 260 is configured to be openable and closable relative to the main body of the image forming apparatus 100, which houses the fixing device 200, the pressure mechanism 250, etc. The opening / closing member 260 also has a guide portion 262 that guides the pressure release lever 256 during the opening / closing operation, and a pressing portion 264 that presses the pressure release lever 256 during the closing operation, moving it from the release position to the holding position.

[0053] With the above-described configuration, the pressure roller 203 can be pressed or released against the fixing belt 201 in conjunction with the opening or closing operation of the opening / closing member 260.

[0054] Next, the problem to be solved by the present invention will be described in detail.

[0055] 4A and 4B are diagrams showing the mounting configuration of the pressure release lever, where (a) is a perspective view and (b) is a plan view. As shown in Fig. 4A, the pressure release lever 256 is rotatably supported by a rotation shaft 258 on a support member 200a of the fixing device 200. Only one end of the rotation shaft 258 is fixed to the support member 200a, so the pressure release lever 256 is cantilevered.

[0056] 4(b), while it is held (restrained) in the direction of arrow A (toward the support member 200a), it is not held (restrained) in the direction of arrow B (opposite the support member 200a). If the pressure release lever 256 is pressed by the pressing portion 264 during the closing operation of the open / close member 260, it may fall toward the rotation shaft 258 (here, the direction of arrow B), which may damage the rotation shaft 258.

[0057] In response to this, it is conceivable to support the pressure release lever 256 on both sides, but this is not preferable from the viewpoint of reducing weight and parts costs. Also, since the fixing unit including the fixing device 200 may need to be replaced over time, it is desirable for the structure to be as simple as possible.

[0058] 5A and 5B are plan views showing the pressing portion of an opening / closing member according to one embodiment of the present invention. As shown in Fig. 5A, pressing portion 264 of opening / closing member 260 has inclined portion 266, which is an inclined plane that slopes in one direction. When opening / closing member 260 is closed, pressing portion 264 presses pressure release lever 256 with inclined portion 266, moving it from the release position to the hold position.

[0059] 4(b), the cantilevered pressure release lever 256 is prone to tipping in the direction of arrow B. In contrast, as shown in FIG. 5(b), the inclined portion 266 of the pressing portion 264 is a slope that increases in the direction of arrow B (decreases in the direction of arrow A), so that the movement of the pressure release lever 256 in the direction B is restricted and it can be moved in the direction of arrow A.

[0060] The movement (tilt) of the pressure release lever 256 in direction A is held (restrained) by the support member 200a, so that the pressure release lever 256 is less likely to tip over. Therefore, the image forming apparatus 100 of this embodiment restricts the pressure release lever 256 from tipping over in the direction of the rotation axis, and the pressure mechanism 250 can stably pressurize and release the roller pair.

[0061] As described above, the image forming apparatus 100 of this embodiment does not require any additional members to the fixing unit, and there are essentially no additional members to the opening / closing member 260. Therefore, there is almost no need to change the layout, and the configuration is relatively simple.

[0062] (Variation) Fig. 6 is a plan view (part 1) showing a pressing portion of an opening / closing member according to a modified example of the present invention. As shown in Fig. 6, the inclined portion 266a of the pressing portion 264 has two inclined planes facing each other. In other words, the inclined portion 266a of the pressing portion 264 has a V-shaped cross section.

[0063] In this case, the inclined portion 266a of the pressing portion 264 can restrict movement of the pressure release lever 256 toward the center Lc of the inclined portion 266a when pressed. Therefore, the amount of movement of the pressure release lever 256 can be made smaller compared to the configuration of FIG.

[0064] Fig. 7 is a second plan view showing a pressing portion of an opening / closing member according to a modified example of the present invention. As shown in Fig. 7, the inclined portion 266b of the pressing portion 264 has two inclined curved surfaces facing each other. In other words, the inclined portion 266b of the pressing portion 264 has a U-shaped cross section.

[0065] In this configuration, if the amount of movement of the pressure release lever 256 pressed by the inclined portion 266b is small, the force received by the pressure release lever 256 is also small, thereby reducing the stress in the tilting direction.

[0066] Next, advantageous configurations will be described.

[0067] FIG. 8 shows a pressure release lever according to a modified example of the present invention, where (a) is a plan view, and (b) and (c) are schematic diagrams showing the shape of the pressure release lever.

[0068] 8(b), it is desirable that the pressure release lever 256 has a tapered shape that narrows toward the tip 256a, and that the tip 256a contacts the inclined portion 266. In this case, the tip 256a of the pressure release lever 256 easily fits along the inclined portion 266 of the pressing portion 264, and the pressure release lever 256 can be reliably prevented from falling.

[0069] 8(c), it is desirable that the tip 256a of the pressure release lever 256 is rounded. In this case as well, the tip 256a of the pressure release lever 256 can easily fit along the inclined portion 266 of the pressing portion 264, and the pressure release lever 256 can be reliably prevented from falling over.

[0070] (supplement) The present invention can also be applied to a fixing device that includes a planar heater as a heat source, instead of the fixing device shown in Fig. 2. Such a fixing device 300 will be described with reference to Figs.

[0071] 9, fixing device 300 installed in image forming apparatus 100 includes fixing belt 321 as a fixing rotor, pressure roller 331 as a pressure rotor, and planar heater 324 as heating means (heat source).

[0072] The fixing device 300 is configured such that the fixing belt 321 is pressed against the pressure roller 331 by pressure applied by a pressure lever 352 (pressure mechanism 351) via a flange member 342. The pair of flange members 342 guide both widthwise ends of the fixing belt 321 from the inner peripheral surface side so that the substantially cylindrical posture of the fixing belt 321 is maintained.

[0073] A sheet heater 324, a holder 323, a stay 330, and the like are provided on the inside (inner peripheral surface side) of the fixing belt 321. Here, the sheet heater 324 is arranged so as to extend in the width direction (the left-right direction in FIG. 9 and the up-down direction in FIG. 10). The sheet heater 324 is in pressure contact with the pressure roller 331 via the fixing belt 321 on the inside (inner peripheral surface side) of the fixing belt 321, forming a nip portion (fixing nip) through which the sheet P is conveyed.

[0074] Referring to FIG. 10, the sheet heater 324 is formed of a substrate 325 (base portion), a resistor pattern 326 (heat generating resistor), a conductor pattern 327 (relay portion), a power supply electrode 328 as an electrode, and the like.

[0075] At least the front surface (the surface facing the inner circumferential surface of the fixing belt 321 in the nip portion) of the base material 325 is made of an insulating material. In this embodiment, the base material 325 is entirely made of an insulating material (in this embodiment, aluminum nitride (AIN)).

[0076] Resistor pattern 326 is formed on the front surface of substrate 325. Similarly, conductor pattern 327 is also formed on the front surface of substrate 325. Resistor pattern 326 functions as a heating resistor that generates heat due to the resistance when a current flows through it (is energized). Resistor pattern 326 is formed by applying a paste prepared to a desired resistance value to the surface of substrate 325 by screen printing or the like, and then baking it to form a pattern.

[0077] The conductor pattern 327 is electrically connected to the resistor pattern 326 (and the power supply electrode 328), and functions as a relay section that passes a current input from the power supply electrode 328 to the resistor pattern 326. The conductor pattern 327 is formed by applying a paste made of a highly conductive material to the surface of the base material 325 by screen printing or the like, and then baking the paste to form a pattern.

[0078] The power supply electrode 328 is electrically connected to the conductor pattern 327 and is formed so as to be connectable to a connector (not shown) that serves as an external terminal. Therefore, even if a surface layer having insulating properties and low friction is formed over the entire surface of the sheet heater 324, only the power supply electrode 328 will be exposed from the surface layer so as to be able to supply power.

[0079] The power supply electrode 328 is made of a silver-based material such as silver (Ag) or silver palladium (AgPd) in order to reduce heat generation due to current flow. In this embodiment, the power supply electrode 328 is formed by printing on the surface of the base material 325 by screen printing and then baking.

[0080] In the plane heater 324, a thermistor 340 (heat-sensitive element) is provided in direct contact (or indirect contact or facing) with the surface opposite to the surface forming the nip portion.

[0081] In the fixing device 300 configured as described above, when power is supplied from the power supply unit to the resistor pattern 326 (heating resistor), the resistor pattern 326 generates heat due to its resistance, thereby heating the fixing belt 321.

[0082] In order to reduce the sliding resistance between the fixing belt 321 and the plane heater 324, the surface of the plane heater 324 may be covered with a sheet-like member made of a low-friction material such as PTFE or provided with a surface layer.

[0083] The present invention has been described in detail above using examples. These examples are merely examples, and various modifications can be made without departing from the spirit and scope of the invention. For example, the embodiments, modifications, and advantageous configurations may be combined with each other.

[0084] For example, aspects of the present invention are as follows. (Aspect 1) a pressurizing mechanism that presses a pressurizing body against a pressurized body; an opening / closing member that can be opened and closed relative to a device main body that houses the pressurizing mechanism, In an image forming apparatus, the pressurizing member presses or releases pressure against the pressure-receiving member in conjunction with an opening or closing operation of the opening / closing member, The pressure mechanism includes a pressure lever having one end rotatably supported by a shaft and the other end provided with an elastic body, and capable of applying pressure to the pressure applying body against the pressure receiving body; a pressure release lever that is rotatably supported and connected to the pressure lever via the elastic body, the pressure release lever is movable between a holding position where the pressurizing body presses the pressurized body and a release position where the pressurizing body is released from the pressurized body, the opening / closing member has a pressing portion that presses the pressure release lever during a closing operation to move the lever from the release position to the holding position, The image forming apparatus according to claim 1, wherein the pressing portion has an inclined portion that comes into contact with the pressure release lever and restricts tilting of the pressure release lever in the direction of the rotation axis. (Aspect 2) 2. The image forming apparatus according to claim 1, wherein the inclined portion has an inclined plane inclined in one direction. (Aspect 3) 2. The image forming apparatus according to claim 1, wherein the inclined portion has two inclined planes facing each other. (Aspect 4) 2. The image forming apparatus according to claim 1, wherein the inclined portion has two inclined curved surfaces facing each other. (Aspect 5) The inclined portion contacts the tip of the pressure release lever, 5. The image forming apparatus according to claim 1, wherein the pressure release lever has a tapered shape that narrows toward the tip. (Aspect 6) 6. The image forming apparatus according to claim 1, wherein the tip of the pressure release lever is rounded. [Explanation of symbols]

[0085] 3 Feeding roller 4 Registration roller pair 5 Secondary transfer roller 7 Paper ejection roller 8 Optical writing device 9Bk, 9C, 9M, 9Y toner bottles 10 Transfer belt unit 11 Transfer belt 12Bk, 12C, 12M, 12Y Primary transfer roller 13 Belt cleaning device 17 Paper output tray 20Bk, 20C, 20M, 20Y photoconductor drum 30Bk, 30C, 30M, 30Y charging device 40Bk, 40C, 40M, 40Y developing device 50Bk, 50C, 50M, 50Y cleaning device 61 Sheet feeding device 66 Rotation axis 71 Transcription device 72 Drive roller 73 Driven roller 100 Image forming device 200, 300 fixing unit 200a support member 201, 321 Fixing belt 202A, 202B halogen heater 203, 331 Pressure roller 204 Elastic rubber layer 205 Core 206 Nip forming member 207 Stay member 207a, 207b Standing part 209 Reflective material 216 Heat transfer auxiliary member 226 End Heater 230A, 230B Temperature Sensor 250, 351 Pressure mechanism 252 Pressure spring 254, 352 Pressure lever 256 Pressure release lever 256a (Pressure release lever) tip 258 Rotation Axis 260 Opening and closing members 262 Guide section 264 Pressing part 266, 266a, 266b Slope 323 Holder 324 Planar heater 325 Base material 326 Resistor Pattern 327 Conductor Pattern 328 Power supply electrode 330 Stay 331 Pressure roller 340 Thermistor 342 Flange member N Fixing nip S recording material [Prior art documents] [Patent documents]

[0086] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-201975

Claims

1. a pressurizing mechanism that presses a pressurizing body against a pressurized body; an opening / closing member that can be opened and closed relative to a device main body that houses the pressurizing mechanism, In an image forming apparatus, the pressurizing member presses or releases pressure against the pressure-receiving member in conjunction with an opening or closing operation of the opening / closing member, The pressure mechanism includes a pressure lever having one end rotatably supported by a shaft and the other end provided with an elastic body, and capable of applying pressure to the pressure applying body against the pressure receiving body; a pressure release lever that is rotatably supported and connected to the pressure lever via the elastic body, the pressure release lever is movable between a holding position where the pressurizing body presses the pressurized body and a release position where the pressurizing body is released from the pressurized body, the opening / closing member has a pressing portion that presses the pressure release lever during a closing operation to move the lever from the release position to the holding position, The image forming apparatus according to claim 1, wherein the pressing portion has an inclined portion that comes into contact with the pressure release lever and restricts tilting of the pressure release lever in the direction of the rotation axis.

2. 2. The image forming apparatus according to claim 1, wherein the inclined portion has an inclined plane inclined in one direction.

3. 2. The image forming apparatus according to claim 1, wherein the inclined portion has two inclined planes facing each other.

4. 2. The image forming apparatus according to claim 1, wherein the inclined portion has two inclined curved surfaces facing each other.

5. The inclined portion contacts the tip of the pressure release lever, 5. The image forming apparatus according to claim 2, wherein the pressure release lever has a tapered shape that tapers toward the tip.

6. 6. The image forming apparatus according to claim 5, wherein the tip of the pressure release lever is rounded.

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