JP7119281B2 - Fixing device and image forming device - Google Patents

Description

The present invention relates to a fixing device and an image forming apparatus.

2. Description of the Related Art In an electrophotographic image forming apparatus, a toner image transferred onto a recording material such as paper is fixed onto the recording material by a fixing device. The fixing device includes a fixing member such as a fixing belt, a pair of flanges having guide portions that support both ends of the fixing member, a pressure member such as a pressure roller that contacts the outer peripheral surface of the fixing member, and a nip forming unit that forms a fixing nip by pressing the fixing member against the pressure member.

In the fixing device, in addition to fixing performance to the recording material, good peeling performance of the recording material from the fixing member is required. For example, Japanese Patent Application Laid-Open No. 2002-100002 discloses a configuration that improves the peeling performance by changing the nip pressure between the upstream side and the downstream side of the fixing nip in the conveying direction of the recording material. Further, Patent Document 2 discloses a configuration in which a nip forming surface on the downstream side in the conveying direction protrudes, as shown in FIG. 4 of the document, in order to improve peeling performance.

When the corners of the nip forming unit come into contact with the fixing member at the longitudinal ends of the nip forming unit, a high load is applied to the fixing member. In order to suppress damage to the fixing member due to such load, the above Patent Document 2 also has a configuration in which corners are removed at the ends in the longitudinal direction of the nip forming surface as shown in FIG. 9 of the document. disclosed.

Patent Documents 3 and 4 similarly disclose configurations related to suppression of damage to the fixing member. In Patent Document 3, in order to suppress damage to the fixing member due to contact with a protective member (driven ring) provided at the end of the fixing member, the end of the fixing member is tilted toward the inner peripheral side to prevent the protective member from breaking. The surface of the protective member is slanted so as to come into contact with the In Patent Document 4, the positional relationship between the fixing member and the flange is defined so as to suppress damage to the fixing member when the fixing member is shifted in the longitudinal direction.

In general, the fixing member has a greater width in the longitudinal direction than the pressure member. Therefore, the end of the fixing member protrudes from the pressure member. Since the end portion of the fixing member is supported by the guide portion of the flange, it has a shape similar to that of the guide portion when viewed in a cross section orthogonal to the longitudinal direction, for example. On the other hand, in the section including the nip forming unit and the pressure member, the fixing member deforms according to the shape of the nip forming surface. If this shape change occurs over a short distance, the load applied to the fixing member increases, and the fixing member may break.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a fixing device capable of reducing a load caused by a change in shape of a fixing member in the longitudinal direction, and an image forming apparatus including the fixing device.

In order to solve the above-described problems, a fixing device according to one aspect of the present invention includes a rotatable fixing member, a pressure member that contacts an outer peripheral surface of the fixing member, a heat source that heats the fixing member, and a nip forming unit having a nip forming surface that is pressed against the pressure member via a fixing member to form a fixing nip between the fixing member and the pressure member; and an end portion of the fixing member in the longitudinal direction. and a flange having a guide surface that supports the inner surface of the fuser member. The nip forming surface is positioned between a first region and an end portion of the nip forming surface and the first region in the longitudinal direction. and a second region that is smaller than the first region. In the longitudinal direction, the end of the pressure member is positioned between the end of the guide surface inserted inside the fixing member and the end of the fixing member. Furthermore, in the longitudinal direction, the end of the guide surface is located between the boundary between the first region and the second region and the end of the pressure member. Further, the nip forming surface has a first corner located upstream in the transport direction from the fixing nip and a second corner located downstream from the fixing nip in the transport direction. At least one of the first corner portion and the second corner portion has a smaller curvature in the second area than in the first area and is displaced in the inner diameter direction of the fixing member.

According to the present invention, it is possible to provide a fixing device capable of reducing the load caused by the shape change in the longitudinal direction of the fixing member, and an image forming apparatus including the fixing device.

1 is a diagram showing a schematic configuration of an image forming apparatus according to one embodiment; FIG. 1 is a schematic plan view of a fixing device according to one embodiment; FIG. FIG. 3 is a schematic cross-sectional view of the fixing device taken along line F3-F3 in FIG. 2; 1 is a schematic exploded perspective view of a nip forming unit according to one embodiment; FIG. The perspective view which shows an example of a structure of the flange which concerns on one Embodiment. FIG. 4 is a schematic perspective view showing a guide surface of a flange according to one embodiment; FIG. 5 is a schematic cross-sectional view of the vicinity of a flange of a fixing device according to a comparative example; 8A and 8B are schematic cross-sectional views of the fixing device taken along lines F8a-F8a, F8b-F8b, and F8c-F8c in FIG. 7; Schematic perspective view, side view, and front view of an auxiliary member included in the fixing device according to one embodiment. 4 is a schematic cross-sectional view of the vicinity of the flange of the fixing device according to one embodiment; FIG. 11A and 11B are schematic cross-sectional views of the fixing device taken along lines F11a-F11a, F11b-F11b, and F11c-F11c in FIG. 10; Schematic perspective view, bottom view and front view of an auxiliary member according to a modified example.

An embodiment of the present invention will be described with reference to the drawings. In this embodiment, a tandem color printer is disclosed as an example of an image forming apparatus. Further, a fixing device included in the color printer is disclosed as an example of the fixing device. However, the configuration disclosed in this embodiment can also be applied to other types of image forming apparatuses such as four-cycle color printers, monochrome printers, copiers, and facsimile machines, and fixing devices provided in these image forming apparatuses. .

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 1 according to this embodiment. The image forming apparatus 1 includes four image forming apparatuses 2 (2Y, 2C, 2M, and 2K) corresponding to yellow (Y), cyan (C), magenta (M), and black (K), and image forming apparatuses 2 (2Y, 2C, 2M, and 2K). The device 2 is provided with four toner bottles 3 (3Y, 3C, 3M, 3K) containing toner to be replenished. In the reference numerals of this embodiment, the suffixes Y, C, M, and K attached to the numbers indicate members related to yellow, cyan, magenta, and black, respectively. These suffixes may be omitted when the members of each color are not particularly distinguished.

Each image forming device 2 includes a photoreceptor 4 as an image carrier, a charging device 5 for charging the surface of the photoreceptor 4 , a developing device 6 for supplying toner to the photoreceptor 4 , and a cleaning device for cleaning the photoreceptor 4 . device 7; In FIG. 1, each element included in the imaging device 2K is represented by a reference numeral, and the reference numerals for the elements included in the other imaging devices 2Y, 2C, and 2M are omitted.

The image forming apparatus 1 further includes a writing device 8 , an intermediate transfer belt 9 , and a primary transfer roller 10 provided for each image forming device 2 . The writing device 8 has, for example, a laser as a light source, various lenses and mirrors, and writes an electrostatic latent image on the photoreceptor 4 . A developing device 6 supplies toner to this electrostatic latent image to form a toner image. Each primary transfer roller 10 forms a primary transfer nip together with the photoreceptor 4 of each image forming device 2 , and transfers the toner image formed on each photoreceptor 4 to the intermediate transfer belt 9 .

As elements related to the transport of the paper S, the image forming apparatus 1 includes a transport path 11, a paper feeder 12, a secondary transfer roller 13, a registration roller pair 14, a discharge roller 15, a paper discharge tray 16, and a fixing device 100 . The paper S is an example of a recording material in this embodiment.

The paper feeder 12 includes a paper feed cassette 12a and a paper feed roller 12b. The paper feed cassette 12a accommodates the stacked paper sheets S. As shown in FIG. The paper feed roller 12 b supplies the paper S from the paper feed cassette 12 a to the transport path 11 . In the example of FIG. 1, only one sheet feeding device 12 is shown. However, the image forming apparatus 1 may be provided with a plurality of paper feeding devices 12 . In this case, each sheet feeding device 12 may be capable of accommodating sheets S of different sizes.

The secondary transfer roller 13 forms a secondary transfer nip with the intermediate transfer belt 9, and transfers the toner image on the intermediate transfer belt 9 onto the sheet S passing through the nip. The registration roller pair 14 is provided upstream of the secondary transfer roller 13 in the transport direction of the sheet S in the transport path 11, and temporarily makes the sheet S transported to the secondary transfer nip wait. The fixing device 100 fixes the toner image transferred to the sheet S onto the sheet S. As shown in FIG. The discharge roller 15 is arranged at the end of the paper S transport path.

Next, a series of operations by the image forming apparatus 1 will be described. Image information representing an image to be formed on the sheet S is transmitted from an external electronic device to the image forming apparatus 1, for example. During image formation based on this image information, the photosensitive member 4 of each image forming device 2 rotates and is uniformly charged by the charging device 5 . The writing device 8 forms an electrostatic latent image on the photosensitive member 4 based on the image information, and the developing device 6 develops the electrostatic latent image. By executing such an operation for each color (Y, C, M, K), a toner image is formed on the intermediate transfer belt 9 as a visible image.

In the paper feeder 12 , the paper feed roller 12 b supplies the paper S from the paper feed cassette 12 a to the transport path 11 . The sheet S waits with its leading edge in contact with the nip of the pair of registration rollers 14 . Then, the registration roller pair 14 starts rotating at the timing when the sheet S is superimposed on the toner image on the intermediate transfer belt 9, and the sheet S is sent out to the secondary transfer nip. The sheet S onto which the toner image has been transferred by the secondary transfer nip is sent to the fixing device 100 .

The fixing device 100 heats and presses the paper S to fix the toner image on the paper S. As shown in FIG. After passing through the fixing device 100 , the paper S is ejected onto the paper ejection tray 16 by the ejection rollers 15 . In each image forming device 2 , the toner remaining on the surface of the photoreceptor 4 that has passed through the primary transfer nip is removed and collected from the photoreceptor 4 by the cleaning device 7 .

The image forming apparatus 1 illustrated in FIG. 1 has an intermediate transfer system configuration for transferring the toner image on the photosensitive member 4 to the sheet S via the intermediate transfer belt 9 . The image forming apparatus 1 may have a configuration compatible with other types of methods, such as a direct method of directly transferring a toner image from the photoreceptor 4 to the paper S.

Next, details of the fixing device 100 will be described. FIG. 2 is a schematic plan view of the fixing device 100 according to this embodiment. The fixing device 100 includes a first flange 20</b>A, a second flange 20</b>B, an endless fixing belt 30 and a pressure roller 40 . The fixing belt 30 is pressed against the pressure roller 40 . As a result, a fixing nip N through which the sheet of paper S passes is formed between the fixing belt 30 and the pressure roller 40 . In this embodiment, the fixing belt 30 is an example of a fixing member, and the pressure roller 40 is an example of a pressure member.

The fixing belt 30 and the pressure roller 40 have elongated shapes in the width direction of the sheet S passing through the fixing nip N. As shown in FIG. In this embodiment, the longitudinal direction of the fixing belt 30 and pressure roller 40 is defined as a first direction X. As shown in FIG. Further, the direction in which the fixing belt 30 and the pressure roller 40 are arranged is defined as a second direction Y, and the direction in which the paper S passing through the fixing nip N is conveyed is defined as a third direction Z. FIG. In this embodiment, the first direction X, the second direction Y and the third direction Z intersect each other perpendicularly, but they may intersect at other angles.

Both ends of the fixing belt 30 in the first direction X are slidably supported by flanges 20A and 20B, respectively. The pressure roller 40 is rotatably supported by a hollow metal core 41 . Hereinafter, the end portion of the fixing belt 30 supported by the first flange 20A will be referred to as a first end portion 30a, and the end portion of the fixing belt 30 supported by the second flange 20B will be referred to as a second end portion 30b. The end of the pressure roller 40 on the side of the first flange 20A is called a first end 40a, and the end of the pressure roller 40 on the side of the second flange 20B is called a second end 40b.

FIG. 3 is a schematic cross-sectional view of the fixing device 100 taken along line F3-F3 in FIG. The fixing device 100 includes a nip forming unit 50 , a first reflecting member 61 , a second reflecting member 62 , a first heater 71 and a second heater 72 inside the fixing belt 30 .

The nip forming unit 50 includes a pressure pad 51 , a heat transfer assisting member 52 (hereinafter simply referred to as the assisting member 52 ), and a stay 53 . The pressure pad 51 faces the pressure roller 40 with the fixing belt 30 interposed therebetween. The auxiliary member 52 is arranged between the pressure pad 51 and the fixing belt 30 and attached to the pressure pad 51 . In the example of FIG. 3, the surface of the auxiliary member 52 facing the pressure roller 40 is flat, but this surface may not be flat as shown in FIG. 9, which will be described later.

The stay 53 is supported by the flanges 20A and 20B shown in FIG. In the example of FIG. 3, the stay 53 includes a first member 54 and a second member 55. As shown in FIG. The first member 54 has a horizontal portion 54a extending in the second direction Y and a vertical portion 54b extending in the third direction Z. As shown in FIG. Similarly, the second member 55 has a horizontal portion 55a extending in the second direction Y and a vertical portion 55b extending in the third direction Z. As shown in FIG. The first member 54 and the second member 55 are fixed to each other with the horizontal portions 54a and 55a in contact with each other. The pressing force from the pressure roller 40 against the pressure pad 51 and the auxiliary member 52 is received by the stay 53 .

The first heater 71 is arranged above the stay 53 in the figure (third direction Z). The second heater 72 is arranged below the stay 53 in the figure (opposite direction to the third direction Z). Each of the heaters 71 and 72 is an example of a heating element that emits radiant heat for heating the fixing belt 30, and halogen heaters, for example, can be used. Instead of the heaters 71 and 72 , or together with the heaters 71 and 72 , other types of heating elements may be arranged in the fixing device 100 .

The first reflecting member 61 is arranged between the first member 54 and the first heater 71 . The second reflecting member 62 is arranged between the second member 55 and the second heater 72 . The first reflecting member 61 reflects the radiant heat generated by the first heater 71 toward the inner circumferential surface of the fixing belt 30 . Similarly, the second reflecting member 62 reflects the radiant heat emitted by the second heater 72 toward the inner circumferential surface of the fixing belt 30 . By providing the reflecting members 61 and 62, the heating of the stay 53 by the radiant heat of the heaters 71 and 72 and the heating of the heaters 71 and 72 can be suppressed, and the fixing belt 30 can be efficiently heated. . Instead of providing the reflecting members 61 and 62, the surface of the stay 53 may be heat-insulated or mirror-finished.

In the example of FIG. 3, a first sensor 81 and a second sensor 82 are arranged outside the fixing belt 30 . Each sensor 81, 82 detects the temperature of the fixing belt 30, for example, in a non-contact manner. By controlling the lighting rates of the heaters 71 and 72 based on the temperatures detected by the sensors 81 and 82, the fixing belt 30 can be controlled to a desired temperature.

The pressure roller 40 has an elastic layer 42 provided on the outer peripheral surface of the metal core 41 described above. The pressure roller 40 is rotated by driving force transmitted from a driving source such as a motor provided in the image forming apparatus 1 . Further, the pressure roller 40 is pressed against the auxiliary member 52 via the fixing belt 30 by an urging member such as a spring. As a result, the elastic layer 42 in contact with the fixing belt 30 is deformed so as to be crushed, and a fixing nip N having a predetermined width is formed between the fixing belt 30 and the elastic layer 42 .

The rotational force of the pressure roller 40 is transmitted to the fixing belt 30 at the fixing nip N. As shown in FIG. As a result, the fixing belt 30 is driven to rotate by the pressure roller 40 . The paper S is conveyed in the third direction Z and passes through the fixing nip N. As shown in FIG. The toner image on the paper S is heated and pressed in the fixing nip N and fixed to the paper S. As shown in FIG.

The auxiliary member 52 plays a role of uniforming the temperature distribution of the fixing nip N in the first direction X. As shown in FIG. Therefore, the auxiliary member 52 is preferably made of a material with excellent thermal conductivity, such as copper, aluminum, or silver.

The fixing belt 30 can be made of, for example, a metal material such as nickel or stainless steel, or a resin material such as polyimide. A release layer made of, for example, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) or PTFE (polytetrafluoroethylene) may be provided on the outer peripheral surface of the fixing belt 30 . In this case, an elastic layer made of silicon rubber or the like may be provided between the base material of the fixing belt 30 and the release layer. If the elastic layer is not provided, the heat capacity is reduced and the fixability is improved. On the other hand, when an elastic layer is provided, fine unevenness is absorbed by its elasticity, so uneven gloss can be suppressed. As an example, the elastic layer preferably has a thickness of 100 μm or more.

For example, a heat source such as a halogen heater may be arranged inside the metal core 41 . A release layer made of PFA, PTFE, or the like may be provided on the outer peripheral surface of the elastic layer 42 . The elastic layer 42 may be made of solid rubber, for example, but may be made of sponge rubber if the heat source is not provided. When the elastic layer 42 is made of sponge rubber, the heat insulating property of the pressure roller 40 is enhanced, and the heat of the fixing belt 30 is less likely to be lost.

FIG. 4 is a schematic exploded perspective view of the nip forming unit 50 in this embodiment. The stay 53 (the first member 54 and the second member 55), the pressure pad 51 and the auxiliary member 52 all have elongated shapes in the first direction X. As shown in FIG. The pressure pad 51 is attached to the vertical portions 54 b and 55 b of the first member 54 and the second member 55 .

The auxiliary member 52 is bent in a shape surrounding the upper surface, lower surface and right surface of the pressure pad 51 in the figure. The auxiliary member 52 is attached to the pressure pad 51 with the pressure pad 51 accommodated inside (see FIG. 3). In this embodiment, the outer surface of the auxiliary member 52 constitutes the nip forming surface NS. The above fixing nip N is formed by pressing the nip forming surface NS against the pressure roller 40 via the fixing belt 30 . In FIG. 4, the range in which the fixing nip N is formed is illustrated with diagonal lines.

The nip forming surface NS has, in the first direction X, a first end 52a and a second end 52b. The first end 52a is the end on the first flange 20A side, and the second end 52b is the end on the second flange 20B side. For example, a fusing nip N is formed between the first end 52a and the second end 52b.

The nip forming surface NS has a first corner portion 52c on the upstream side of the fixing nip N in the conveying direction (third direction Z) and a second corner portion 52d on the downstream side of the fixing nip N in the conveying direction. ing. The first corner portion 52c and the second corner portion 52d are corner portions formed by bending the auxiliary member 52 toward the stay 53 side. In the example of FIG. 4, both corners 52c and 52d extend linearly from the first end 52a to the second end 52b. The shape of the corner portions 52c and 52d applicable to this embodiment will be described later with reference to FIG.

In the example of FIG. 4, heaters 56 and 57 are arranged at both ends of the pressure pad 51 in the first direction X. As shown in FIG. As the heaters 56 and 57, for example, contact heat transfer heaters such as ceramic heaters can be used. By providing the heaters 56 and 57, the temperature of the end portion of the fixing nip N can be preferably controlled. Heat generated by the heaters 56 and 57 is made uniform in the first direction X by the auxiliary member 52 . As another example, the pressure pad 51 may not be provided with the heaters 56 and 57 .

FIG. 5 is a perspective view showing an example of a configuration applicable to the flanges 20A, 20B. Although the first flange 20A is illustrated here as a representative example, the same configuration can be applied to the second flange 20B. In the example of FIG. 5, the first flange 20A has a mounting portion 21, a collar portion 22, and a guide portion 23. As shown in FIG.

The mounting portion 21 has a plurality of through holes for fixing the first flange 20A to a member inside the image forming apparatus 1 with bolts. The collar portion 22 is arranged between the mounting portion 21 and the guide portion 23 and has an outer diameter larger than that of the guide portion 23 .

The guide portion 23 protrudes from the collar portion 22 in the first direction X and has a guide surface 23 a for guiding the inner surface of the fixing belt 30 . The guide surface 23 a corresponds to the outer peripheral surface of the guide portion 23 . Further, the guide portion 23 has an opening portion 23b for arranging the nip forming unit 50. As shown in FIG. That is, in a cross section (a cross section on the YZ plane) that intersects with the first direction X, the guide surface 23a has a substantially arc shape with an open portion where the nip forming unit 50 is arranged. Here, the term “substantially arcuate” refers not only to the case where the cross-sectional shape of the guide surface 23a is an arc corresponding to a part of a perfect circle as a whole, but also to the case where the cross-sectional shape has a plurality of portions with different curvatures and flat portions. This means that it includes the case where is a shape close to a circular arc when viewed as a whole.

As shown in FIG. 5, an inclined portion 24 may be provided at the tip of the guide portion 23 . The outer surface of the slant portion 24 is slanted so as to approach the central axis of the guide portion 23 as it moves away from the guide surface 23a. By providing such an inclined portion 24 , the guide portion 23 can be easily inserted inside the fixing belt 30 .

FIG. 6 is a schematic perspective view showing each guide surface 23a of the flanges 20A, 20B. In this embodiment, a virtual cylindrical surface VS including each guide surface 23a of the flanges 20A and 20B is defined.

The virtual cylindrical surface VS is a curved surface whose cross-sectional shape on the YZ plane is circular at any position in the first direction X. As shown in FIG. For example, when the cross-sectional shape of the guide surface 23a on the YZ plane is an arc corresponding to a part of a perfect circle as a whole, the cross-sectional shape of the virtual cylindrical surface VS matches the perfect circle. However, when the cross-sectional shape of the guide surface 23a includes portions with different curvatures as described above, the cross-sectional shape of the virtual cylindrical surface VS may be a shape that approximates the cross-sectional shape of the guide surface 23a to a perfect circle or an ellipse. good.

In the fixing device 100 configured as described above, the shape of the fixing belt 30 may change in the vicinity of the first end 30a and the second end 30b of the fixing belt 30 . This shape change will be described below with reference to a comparative example with this embodiment.

FIG. 7 is a schematic cross-sectional view in the vicinity of the first flange 20A of the fixing device 100C according to the comparative example. This cross-sectional view corresponds to a cross-section in the XY plane of the region including the fixing nip N, and is other than the flange portion 22 and the guide portion 23 of the first flange 20A, the fixing belt 30, the pressure roller 40, the core metal 41 and the auxiliary member 52. elements are omitted.

Here, the maximum paper passing position A is the position at which the edge of the paper S having the maximum width in the first direction X passes through the fixing nip N among the plurality of types of paper S on which image formation can be performed by the image forming apparatus 1 . Define. As an example, the maximum width corresponds to A3 vertical size (297 mm).

Further, in the first direction X, the position corresponding to the end portion 23c (the end portion of the guide portion 23) of the guide surface inserted inside the fixing belt 30 is B, and the position corresponding to the first end portion 40a of the pressure roller 40. A position corresponding to the first end 52a of the nip forming surface NS is defined as D, and a position corresponding to the first end 30a of the fixing belt 30 is defined as E.

In the comparative example of FIG. 7, these positions A to E are arranged in the first direction X in the order of positions E, B, D, C, and A. In FIG. In this case, the position C also corresponds to the end of the fixing nip N. As shown in FIG. That is, the fixing nip N is formed from the maximum sheet passing position A to the first end portion 30a side of the fixing belt 30 . As a result, even when an image is formed on a sheet of paper S having the maximum width, a good conveying force is applied to the edge of the sheet of paper S, so slippage of the sheet of paper S can be suppressed. Further, since the pressure roller 40 does not press the fixing belt 30 at the first end portion 52a of the nip forming surface NS, it is possible to prevent the fixing belt 30 from being pressed against the first end portion 52a and being damaged.

8A, 8B, and 8C are schematic cross-sectional views of the fixing device 100C taken along lines F8a-F8a, F8b-F8b, and F8c-F8c in FIG. 7, respectively. In FIG. 8A, a fixing nip N is formed between the fixing belt 30 and the pressure roller 40 . The fixing nip N and the nip forming surface NS of the auxiliary member 52 are parallel to the third direction Z on the upstream side of the fixing nip N in the transport direction of the sheet S.

On the other hand, downstream of the fixing nip N in the transport direction, the nip forming surface NS is inclined so as to protrude toward the pressure roller 40 (second direction Y). Accordingly, the second corner portion 52d of the nip forming surface NS protrudes further toward the pressure roller 40 than the first corner portion 52c and the fixing nip N. As shown in FIG. The fixing belt 30 is curved according to the shape of the nip forming surface NS. The sheet S is discharged from the fixing nip N at an angle inclined toward the pressure roller 40 with respect to the third direction Z according to the shape of the fixing belt 30 . As a result, the separation between the fixing belt 30 and the paper S is improved, and the occurrence of jams in the fixing device 100C can be suppressed.

In FIG. 8A, the fixing nip N is positioned inside the virtual cylindrical surface VS, and the corners 52c and 52d protrude outside the virtual cylindrical surface VS. Therefore, the fixing belt 30 is curved so as to enter the inside of the virtual cylindrical surface VS in the vicinity of the fixing nip N and protrude outside the virtual cylindrical surface VS in the vicinity of the corners 52c and 52d. Further, since the guide portion 23 does not exist in this section and is separated from the guide portion 23 to some extent, the fixing belt 30 is not restrained by the guide surface 23a. Therefore, in the area opposite to the fixing nip N in the second direction Y, the fixing belt 30 is inside the imaginary cylindrical surface VS.

In the cross section of FIG. 8B, the pressure roller 40 is not in contact with the fixing belt 30 . The shape of the auxiliary member 52 is the same as in FIG. 8(a). That is, the auxiliary member 52 has a uniform cross section in the first direction X in this comparative example.

8B is closer to the guide portion 23, the fixing belt 30 is more affected by the guide surface 23a than the position of the cross section of FIG. 8A. Therefore, in the area opposite to the fixing nip N in the second direction Y, the fixing belt 30 has a shape similar to the virtual cylindrical surface VS. On the other hand, on the nip forming surface NS side, the fixing belt 30 is positioned outside the virtual cylindrical surface VS due to the influence of the corners 52c and 52d. As a result, the fixing belt 30 becomes oblong in the second direction Y as a whole.

In the cross section of FIG. 8(c), the guide portion 23 exists and the auxiliary member 52 does not exist. The fixing belt 30 is aligned with the virtual cylindrical surface VS except for the area of the opening 23b. In the area of the opening 23b, the fixing belt 30 enters slightly inside the virtual cylindrical surface VS. As a result, the fixing belt 30 has a shape closer to the virtual cylindrical surface VS than the cross section of FIG. 8B.

Here, the distance between position B and position C is defined as L, as shown in FIG. When the distance L is small or when there is no distance L (including the case where the positions B and C are interchanged), the fixing belt 30 in the first direction X changes from the cross-sectional shape shown in FIG. 8B to the cross-sectional shape shown in FIG. abruptly changes to the cross-sectional shape of When a force causing such a sudden change in shape acts on the fixing belt 30, the sliding friction at the contact portion between the nip forming surface NS and the fixing belt 30 in FIG. 8B and the guide surface 23a in FIG. The fixing belt 30 may be damaged due to sliding friction at the contact portion between the fixing belt 30 and the torsional stress acting on the fixing belt 30 .

On the other hand, if the distance L is increased, the change in the shape of the fixing belt 30 in the first direction X becomes gentle, so damage to the fixing belt 30 can be suppressed. However, in this case, the size of the fixing device 100C in the first direction X becomes large.

Next, the configuration of the fixing device 100 according to this embodiment will be described. 9A, 9B and 9C are a schematic perspective view, a side view and a front view of the auxiliary member 52 provided in the fixing device 100, respectively. Although the vicinity of the first end 52a is shown here, a similar shape can be applied to the vicinity of the second end 52b.

In the example of FIG. 9, the auxiliary member 52 does not have a uniform shape in the first direction X, unlike the comparative example described above. That is, the nip forming surface NS has a first region R1 and a second region R2. A dashed line in the drawing represents a boundary BL between the first region R1 and the second region R2. The second region R2 is positioned in the first direction X between the first end 52a and the first region R1. The shapes of the auxiliary member 52 and the nip forming surface NS in the first region R1 are the same as in FIGS. 8A and 8B, and are uniform in the first direction X.

As shown in FIGS. 9A and 9B, in the second region R2, the first corner portion 52c and the second corner portion 52d have a smaller curvature than the corner portions 52c and 52d in the first region R1. rounded to .

As shown in FIG. 9C, the width of the nip forming surface NS in the third direction Z is W1 in the first region R1 and W2 smaller than W1 in the second region R2 (W1>W2). In the example of FIG. 9(c), both edges of the nip forming surface NS in the third direction Z are inclined with respect to the first direction X, so that the width W2 increases from the boundary BL toward the first end 52a. It is gradually decreasing.

Since the nip forming surface NS has such a shape, as indicated by an arrow Q1 in FIG. It is displaced in the opposite direction of the second direction Y and in the third direction Z. Furthermore, as indicated by an arrow Q2, the position of the second corner portion 52d is displaced in the direction opposite to the second direction Y and the direction opposite to the third direction Z as it moves from the boundary BL toward the first end portion 52a. . Here, the direction opposite to the second direction Y corresponds to the direction away from the pressure roller 40 described above.

FIG. 10 is a schematic cross-sectional view in the vicinity of the first flange 20A of the fixing device 100 according to this embodiment. This cross-sectional view corresponds to a cross-section in the XY plane of the region including the fixing nip N as in FIG. Elements other than the auxiliary member 52 are omitted. Positions A, B, C, D, and E in the drawing are the same as in FIG. Portion 52a and first end 30a of fuser belt 30 are shown.

In the example of FIG. 10, positions A to E are arranged in the first direction X in the order of positions E, D, C, B, and A. In the example of FIG. That is, the first end 40 a of the pressure roller 40 is positioned between the end 23 c of the guide surface 23 a and the first end 30 a of the fixing belt 30 in the first direction X. As shown in FIG. Furthermore, the end portion 23c of the guide surface 23a is located between the boundary BL between the first region R1 and the second region R2 and the first end portion 40a of the pressure roller 40 in the first direction X. As shown in FIG.

In such a configuration, the fixing nip N and the guide surface 23a overlap in the second direction Y. As shown in FIG. As a result, the width of the entire fixing belt 30 in the first direction X can be reduced while maintaining the same width of the fixing nip N in the first direction X as in the case of FIG. 7, for example. As a result, the size of the fixing device 100 can be reduced.

However, since the distance L shown in FIG. 7 does not exist in the configuration of FIG. join. In this embodiment, as shown in FIG. 9, the auxiliary member 52 is provided with the second region R2, and the position of the boundary BL is determined between the positions A and B, thereby suppressing the load applied to the fixing belt 30. . The operation of such a configuration will be described below.

11A, 11B, and 11C are schematic cross-sectional views of the fixing device 100 along lines F11a-F11a, F11b-F11b, and F11c-F11c in FIG. 10, respectively. FIG. 11(a) corresponds to a cross section including the first region R1 of the nip forming surface NS, and the shapes of the fixing belt 30 and the auxiliary member 52 are the same as those in FIG. 8(a). 11(c) corresponds to a cross section including the guide portion 23 and not including the fixing nip N, and the shape of the fixing belt 30 is the same as that of FIG. 8(c).

FIG. 11(b) corresponds to a cross section including the position P shown in FIG. Position P is included in second region R2. In the second region R2, the width W2 of the nip forming surface NS is smaller than the width W1 in the first region. Further, the corners 52 c and 52 d are displaced away from the pressure roller 40 . At the position P, as shown in FIG. 11(b), both the corners 52c and 52d match the virtual cylindrical surface VS.

In FIG. 11B, the pressure roller 40 presses the fixing belt 30 against the nip forming surface NS. Therefore, the fixing belt 30 bulges outward from the virtual cylindrical surface VS on the upstream and downstream sides of the fixing nip N in the conveying direction. Moreover, since the corners 52c and 52d both coincide with the virtual cylindrical surface VS, the corners 52c and 52d and the fixing belt 30 do not come into contact with each other. As a result, the fixing belt 30 does not largely deviate from the virtual cylindrical surface VS as shown in FIG. 8B in the comparative example, and has a shape similar to that shown in FIG. 11C.

Between the position P and the boundary BL in FIG. 10, the corners 52c and 52d protrude from the virtual cylindrical surface VS, but the amount of protrusion is smaller than that of the first region R1. Therefore, in this range, the fixing belt 30 does not contact the corners 52c and 52d, or even if it does contact, it does not protrude toward the pressure roller 40 as much as in FIG. 11(a).

Between the position P and the first end portion 52a, the nip forming surface NS including the corner portions 52c and 52d is located inside the virtual cylindrical surface VS. Therefore, the fixing belt 30 does not contact the corners 52c and 52d in this range, and the fixing belt 30 approaches the shape shown in FIG. 11C as it approaches the first end 52a. As an example, between the position P and the first end portion 52a, the fixing belt 30 and the nip forming surface NS may not contact each other except for the portion where the pressure roller 40 presses the fixing belt 30 against the nip forming surface NS. preferable.

Thus, in the present embodiment, shape change in the first direction X of the fixing belt 30 is reduced in the vicinity of the first end portion 30a. Similar effects can be obtained by applying a configuration similar to that shown in FIGS. 9 to 11 in the vicinity of the second end portion 30b shown in FIG.

The width of the fixing nip N in FIG. 11(b) is preferably at least equal to the width of the fixing nip N in FIG. 11(a). As a result, even when the sheet S having the maximum width is conveyed to the fixing nip N, the frictional force necessary for conveying the sheet S can be favorably applied to the edges of the sheet S.

In the present embodiment described above, since the fixing nip N overlaps the first flange 20A in the second direction Y, the size of the fixing belt 30, the fixing device 100, or the image forming apparatus 1 can be reduced. Further, a first region R1 and a second region R2 are provided on the nip forming surface NS, and the guide surface 23a is formed between the boundary BL of these regions and the first end 40a of the pressure roller 40 (end of the fixing nip N). The end 23c is positioned. As a result, the shape of the fixing belt 30 shown in FIG. 11B is realized in the vicinity of the guide surface 23a, and the shape change of the fixing belt 30 can be mitigated, so that the load applied to the fixing belt 30 can be suppressed.

Further, in the present embodiment, the corner portions 52c and 52d are separated from the fixing belt 30 at least at the first end portion 52a of the nip forming surface NS. If the corners 52c and 52d of the first end portion 52a are in contact with the fixing belt 30, a large load may be applied to the fixing belt 30, but such a load can be suppressed in the present embodiment.

Furthermore, since the nip forming surface NS is positioned inside the virtual cylindrical surface VS in the range from the position P to the first end portion 52a, at least in this range, the fixing belt 30 and the nip forming surface except for the portion of the fixing nip N No contact with NS. As a result, the load applied to the fixing belt 30 can be suppressed not only at the corners 52c and 52d of the first end 52a, but also at the corners 52c and 52d.

Further, in the first region R1, the second corner portion 52d protrudes from the fixing nip N toward the pressure roller 40 side. This improves the peelability between the fixing belt 30 and the sheet S conveyed to the fixing nip N in the first region R1, thereby suppressing the occurrence of a jam.

Furthermore, the boundary BL between the first area R1 and the second area R2 is located between the maximum sheet passing position A and the end portion 23c of the guide surface 23a. As a result, even when the toner image formed on the sheet S having the maximum width on which the image can be formed by the image forming apparatus 1 is fixed, the entire sheet S passes through the first region R1 having excellent peelability.

In addition to the above, various favorable effects can be obtained from this embodiment. Moreover, this embodiment does not limit the scope of the present invention to the configuration disclosed in the embodiment. The present invention can be implemented by modifying the configuration disclosed in the present embodiment into various aspects.

For example, in this embodiment, between the position P and the first end portion 52a, both the corner portions 52c and 52d are separated from the fixing belt 30 (see FIG. 11B). However, between the position P and the first end portion 52 a , one of the corner portions 52 c and 52 d may be separated from the fixing belt 30 and the other may be in contact with the fixing belt 30 . In this case, as shown in FIG. 9C, instead of inclining both edges in the third direction Z of the nip forming surface NS in the second region R2 with respect to the first direction X, one edge You may incline only.

On the upstream side of the fixing nip N in the conveying direction, the fixing belt 30 is pulled into the fixing nip N by the frictional force of the pressure roller 40, so that the fixing belt 30 receives a strong load from the first corner portion 52c. On the other hand, on the downstream side of the fixing nip N in the conveying direction, as shown in FIG. 30 receives a strong load from the second corner 52d. Even if only one of the corners 52 c and 52 d is separated from the fixing belt 30 , one of these loads can be reduced, which contributes to suppressing damage to the fixing belt 30 .

Further, even if at least one of the corner portions 52c and 52d contacts the fixing belt 30 between the position P and the first end portion 52a, if the nip forming surface NS has the shape shown in FIG. The shape change of the fixing belt 30 can be reduced toward the one end portion 52a. Therefore, compared to the case where the nip forming surface NS has a uniform cross-sectional shape in the first direction X, the load on the fixing belt 30 can be suppressed.

The shape of the auxiliary member 52 is not limited to that shown in FIG. FIG. 12 is a diagram showing a schematic configuration of an auxiliary member 152 according to one modification. Here, FIG. 12(a) is a schematic perspective view of the auxiliary member 152, FIG. 12(b) is a schematic bottom view of the auxiliary member 152, and FIG. 12(c) is a schematic diagram of the auxiliary member 152. It is a typical front view. Parts similar to those of the auxiliary member 52 shown in FIG. 9 are denoted by the same reference numerals, and descriptions thereof are omitted.

The auxiliary member 152 has a first region R1 and a second region R2, as shown in FIG. 12(a). As shown in FIG. 12(c), the auxiliary member 152 has a thickness T1 in the first region R1. In the second region R2, the nip forming surface NS is rounded in an arc shape. Accordingly, the thickness T2 of the auxiliary member 152 in the second region R2 is smaller than the thickness T1 (T1>T2) and decreases toward the first end portion 52a.

As shown in FIG. 12(c), the relationship between the width W1 in the first region R1 of the nip forming surface NS and the width W2 in the second region R2 is the same as in the example of FIG. However, in the second region R2, both edges of the nip forming surface NS in the third direction Z are rounded in an arc shape.

Even with the auxiliary member 152 having such a shape, it is possible to obtain the same effects as in the above embodiment. Furthermore, since the nip forming surface NS is rounded as a whole in the second region R2, even if the fixing belt 30 comes into contact with the fixing belt 30, the fixing belt 30 is less likely to be damaged.

9 and 12 illustrate the case where the outer surfaces of the auxiliary members 52 and 152 constitute the nip forming surface NS, but the present invention is not limited to this example. For example, when the nip forming unit 50 does not include the auxiliary members 52 and 152 and the pressure pad 51 slides on the inner surface of the fixing belt 30, the outer surface of the pressure pad 51 serves as the nip forming surface NS. In addition, the nip forming surface NS can be realized in various ways.

Reference Signs List 1 image forming apparatus 20A, 20B first and second flanges 23a guide surface 30 fixing belt 40 pressure roller 50 nip forming unit 52, 152 auxiliary member 52c first corner 52d second corner 71, 72 first and second heaters 100 fixing device N fixing nip NS nip forming surface R1 first area R2 second area VS … imaginary cylindrical surface, S … paper.

Japanese Patent No. 4770453 JP 2017-116921 A JP 2017-203873 A JP 2012-252186 A

Claims (6)

a rotatable fuser member;
a pressing member that contacts the outer peripheral surface of the fixing member;
a heat source for heating the fixing member;
a nip forming unit having a nip forming surface that is pressed against the pressure member via the fixing member to form a fixing nip between the fixing member and the pressure member;
a flange disposed at an end in the longitudinal direction of the fixing member and having a guide surface for supporting the inner surface of the fixing member;
The nip forming surface is positioned between a first region and an end portion of the nip forming surface and the first region in the longitudinal direction. a second region that is smaller than the first region;
in the longitudinal direction, an end of the pressure member is positioned between an end of the guide surface inserted inside the fixing member and an end of the fixing member;
In the longitudinal direction, an end of the guide surface is positioned between a boundary between the first region and the second region and an end of the pressure member ;
The nip forming surface has a first corner located upstream in the transport direction from the fixing nip and a second corner located downstream from the fixing nip in the transport direction,
The fixing device , wherein at least one of the first corner portion and the second corner portion has a smaller curvature in the second area than in the first area and is displaced in an inner diameter direction of the fixing member . 2. The fixing device according to claim 1, wherein at least one of the first corner portion and the second corner portion is separated from the fixing member at the end portion of the nip forming surface in the longitudinal direction. Device. 3. The fixing device according to claim 2, wherein in the first area, the second corner protrudes toward the pressure member from the fixing nip. The guide surface has a substantially arcuate shape with an open portion where the nip forming unit is arranged in a cross section that intersects with the longitudinal direction,
In the first region, at least a portion of the nip forming surface protrudes outside an imaginary cylindrical surface including the guide surface,
4. Any one of claims 1 to 3, wherein the nip forming surface is positioned inside the virtual cylindrical surface in a range from a predetermined position in the second region to an end of the nip forming surface. 10. The fixing device according to claim 1. An image forming apparatus comprising the fixing device according to any one of claims 1 to 4. The boundary between the first region and the second region is defined by a position in the longitudinal direction at which an end of a recording material having a maximum width on which image formation is possible by the image forming apparatus passes through the fixing nip, and a boundary between the guide surface and the guide surface. 6. The image forming apparatus according to claim 5, wherein the image forming apparatus is positioned between the end portion.

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