Patent Application
20240288803
This application claims priority from Japanese Patent Application No. 2023-030499 filed on Feb. 28, 2023. The entire content of the priority application is incorporated herein by reference.
There has been conventionally known a fixing device provided inside a main body of an image-forming apparatus and configured to fix a toner image onto a sheet. Such a conventional fixing device includes a pressure roller having a so-called inverted crown shape in which an outer diameter at each axial end thereof is greater than that at an axial center thereof. By virtue of the inverted crown shape of the pressure roller, the fixing device conveys a sheet while stretching the same from the center toward the respective axial ends, thereby restraining generation of wrinkles on the sheet.
However, in the fixing device including the pressure roller having the inverted crown shape described above, there occurs a problem that a nipping width at each axial end becomes greater among the entire axial length of the pressure roller.
In view of the foregoing, it is an object of the present disclosure to provide a fixing device in which an increase in a nipping width at each end of a pressure roller in an axial direction can be restrained.
In order to attain the above and other object, the present disclosure provides a fixing device including: an endless belt; a heater; a holder; a stay; and a pressure roller. The heater is positioned in a space encircled by the endless belt. The heater includes: a base plate; and a resistance heating element provided on the base plate. The holder holds the heater. The holder has: a heater supporting surface; and a contacting surface. The heater supporting surface supports the heater. The contacting surface is opposite the heater supporting surface. The stay is in contact with the contacting surface. The pressure roller is rotatable about a rotation axis extending in an axial direction. The pressure roller is configured to nip the endless belt between the pressure roller and the heater. The pressure roller includes: a shaft; and an elastic layer covering an outer circumferential surface of the shaft. The pressure roller has a diameter that varies in the axial direction such that the diameter becomes smaller from each end of the pressure roller toward a center of the pressure roller. In a state prior to assembling the holder with both the stay and the heater, a distance in an orthogonal direction between the heater supporting surface and the contacting surface at a center of the holder in the axial direction is longer than a distance in the orthogonal direction between the heater supporting surface and the contacting surface at each end of the holder in the axial direction. The orthogonal direction is orthogonal to the axial direction.
In the above structure, the pressure roller has a so-called inverted crown shape in which the diameter of the pressure roller varies in the axial direction such that the diameter becomes smaller from each end of the pressure roller toward the center of the pressure roller. Accordingly, the fixing device can convey the sheet while applying a stretching force to the sheet directed from a center of the sheet in the axial direction toward each end of the sheet S in the axial direction, thereby restraining formation of wrinkles on the sheet.
Further, the contacting surface is provided such that the distance in the orthogonal direction between the heater supporting surface and the contacting surface at the center of the holder in the axial direction is greater than the distance between the heater supporting surface and the contacting surface at each end of the holder in the axial direction in a state prior to assembling the holder with both the stay and the heater. This structure can restrain a nipping pressure at the center in the axial direction from becoming smaller relative to that at each end in the axial direction. Accordingly, an increase in a nipping width at each end in the axial direction of the pressure roller can be suppressed irrespective of the inverted crown shape of the pressure roller.
According to another aspect, the present disclosure also provides a fixing device including: an endless belt; a heater; a holder; a stay; and a pressure roller. The heater is positioned in a space encircled by the endless belt. The heater includes: a base plate; and a resistance heating element provided on the base plate. The holder holds the heater. The holder has: a heater supporting surface; and contacting surfaces. The heater supporting surface supports the heater. The contacting surfaces are opposite the heater supporting surface. The stay is in contact with each contacting surface. The pressure roller is rotatable about a rotation axis extending in an axial direction. The pressure roller is configured to nip the endless belt between the pressure roller and the heater. The pressure roller includes: a shaft; and an elastic layer covering an outer circumferential surface of the shaft. The pressure roller has a diameter that varies in the axial direction such that the diameter becomes smaller from each end of the pressure roller toward a center of the pressure roller. In a state prior to assembling the holder with both the stay and the heater, a distance in an orthogonal direction between the heater supporting surface and a first contacting surface of the contacting surfaces is longer than a distance in the orthogonal direction between the heater supporting surface and a second contacting surface of the contacting surfaces. The first contacting surface is positioned closer to a center of the holder in the axial direction than the second contacting surface is to the center of the holder in the axial direction. The orthogonal direction is orthogonal to the axial direction.
The fixing device according to the other aspect also can exhibit the same advantages as the fixing device according to the aspect, since the pressure roller has a so-called inverted crown shape in which the diameter of the pressure roller varies in the axial direction such that the diameter becomes smaller from each end of the pressure roller toward the center of the pressure roller.
Further, since the contacting surfaces are arranged such that the distance between the heater supporting surface and the first contacting surface, which is positioned closer to the center of the holder in the axial direction than the second contacting surface, is greater than the distance between the heater supporting surface and the second contacting surface, the nipping pressure at the center in the axial direction from becoming smaller relative to that at each end in the axial direction. Accordingly, an increase in the nipping width at each end in the axial direction of the pressure roller can be suppressed irrespective of the inverted crown shape of the pressure roller.
Hereinafter, one embodiment of the present disclosure will be described while referring to the accompanying drawings.
A fixing device 1 illustrated in
In the following description, a conveying direction in which the sheet S is conveyed will be simply referred to as “conveying direction”, and an axial direction of the pressure roller 3 will be simply referred to as “axial direction”. The axial direction is parallel to a width direction of the sheet S, and is orthogonal to the conveying direction. Also, a direction orthogonal to both the conveying direction and the axial direction will be referred to as “orthogonal direction”.
The heating unit 2 includes a heater 10, a holder 20, a stay 40, and a belt 50. A portion of the heater 10 is positioned in a space encircled by the belt 50. The heater 10 is configure to apply heat to a sheet S through the belt 50.
As illustrated in
In the following description, a direction in which the long side of the rectangular base plate 11 extends will be referred to as “long-side direction” and a direction in which the short side of the rectangular base plate 11 extends will be referred to as “short-side direction”. The long-side direction and the short-side direction are orthogonal to each other. Note that the long-side direction is a direction parallel to the axial direction, and the short-side direction is a direction parallel to the conveying direction.
As illustrated in
As illustrated in
As illustrated in
One of the belt guides 23 extends from the base portion 21 along an inner peripheral surface of the belt 50 toward the upstream side in the conveying direction, while the other of the belt guides 23 extends from the base portion 21 along the inner peripheral surface of the belt 50 toward the downstream side in the conveying direction. As illustrated in
As illustrated in
The plurality of protrusions 24 include protrusions 24A positioned in the vicinity of a center C in the axial direction, and protrusions 24B positioned at each end in the axial direction. A protruding amount of each protrusion 24A, which is positioned close to the center C in the axial direction, from the base portion 21 is greater than a protruding amount of each protrusion 24B, which is positioned at each end in the axial direction, from the base portion 21. More specifically, a protruding amount T1 of the protrusion 24A which is positioned closest to the center C in the axial direction is greater than a protruding amount T2 of the protrusion 24B which is positioned farthest from the center C in the axial direction (T2<T1). Also, the protrusions 24 are arranged such that protruding amounts of the protrusions 24 become greater from each end in the axial direction toward the center C in the axial direction.
Each of the plurality of protrusions 24 has a rectangular distal end surface 24M. Each distal end surface 24M faces in a direction opposite the direction in which the heater supporting surface 22A faces. Each distal end surface 24M constitutes a contacting surface that is in contact with the stay 40. That is, each distal end surface 24M is an example of the contacting surface. In other words, the holder 20 has the plurality of distal end surfaces 24M constituting the contacting surface in contact with the stay 40.
As illustrated in
In other words, in a state prior to assembling the holder 20 with both the stay 40 and the heater 10, a distance in the orthogonal direction between the distal end surfaces 24M at a center of the holder 20 in the axial direction and the heater supporting surface 22A is greater than a distance in the orthogonal direction between the distal end surfaces 24M at each end of the holder 20 in the axial direction and the heater supporting surface 22A.
Further in other words, in a state prior to assembling the holder 20 with both the stay 40 and the heater 10, a distance in the orthogonal direction between one distal end surface 24M of the distal end surfaces 24M and the heater supporting surface 22A is equal to or greater than a distance in the orthogonal direction between another one distal end surface 24M, which is positioned farther from the center of the holder 20 in the axial direction than the one distal end surface 24M is from the center of the holder 20 in the axial direction, of the distal end surfaces 24M and the heater supporting surface 22A.
Specifically, a distance D1 between the distal end surface 24M of the protrusion 24A, which is positioned closest to the center C in the axial direction, and the virtual plane P1 is greater than a distance D2 between the distal end surface 24M of the protrusion 24B, which is positioned farthest from the center C, and the virtual plane P1 (D2<D1). In other words, the distance D1 in the orthogonal direction between the distal end surface 24M of the protrusion 24A and the heater supporting surface 22A is greater than the distance D2 in the orthogonal direction between the distal end surface 24M of the protrusion 24B and the heater supporting surface 22A.
Note that a difference between the distance D2 and the distance D1 is not less than 25 μm and not more than 700 μm, for example. Preferably, the difference between the distance D2 and the distance D1 is not less than 100 μm and not more than 450 μm. More preferably, the difference between the distance D2 and the distance D1 is not less than 150 μm and not more than 350 μm.
Note that the proper value for the difference between the distance D2 and the distance D1 varies depending on a shape of the stay 40 and a shape of the pressure roller 3, and therefore is determined by conducting experiments as appropriate.
The heating unit 2 further includes a heat conductive member (not illustrated). The heat conductive member is configured to conduct heat in the long-side direction so as to provide uniform temperature along the entire length of the heater 10 in the long-side direction. The heat conductive member has a plate shape and is positioned between the heater 10 and the holder 20. The heat conductive member is made of aluminum, for example.
The stay 40 supports the holder 20. The stay 40 is made of, for example, metal. The stay 40 has a U-shape when viewed in the axial direction. Specifically, the stay 40 includes a first wall 41, a second wall 42, and a third wall 43, and has holder supporting surfaces 40A.
The first wall 41 extends in the orthogonal direction. The first wall 41 has one end in the orthogonal direction that is in contact with the distal end surfaces 24M.
The second wall 42 is arranged to be spaced apart from the first wall 41 in the conveying direction. The second wall 42 extends in the orthogonal direction. The second wall 42 has one end in the orthogonal direction that is in contact with the distal end surfaces 24M.
The third wall 43 extends in the conveying direction. The third wall 43 connects another end of the first wall 41 in the orthogonal direction and another end of the second wall 42 in the orthogonal direction to each other.
Surfaces of the one end in the orthogonal direction of the first wall 41 and the one end in the orthogonal direction of the second wall 42 serve as the holder supporting surfaces 40A. That is, the holder supporting surfaces 40A are in contact with the holder 20. The holder supporting surfaces 40A extend parallel to the axial direction.
The belt 50 is an endless belt. The belt 50 is circularly movable around the heater 10 while being guided by the holder 20. The belt 50 has an outer peripheral surface, and the inner peripheral surface. The outer peripheral surface makes contact with the pressure roller 3, or a sheet S which is a target to be heated. The inner peripheral surface makes contact with the heater 10. The belt 50 is configured to convey the sheet S in cooperation with the pressure roller 3 by circularly moving.
The pressure roller 3 is rotatable about a rotation axis X3 extending in the axial direction. The pressure roller 3 is configured to nip the belt 50, in cooperation with the heater 10 of the heating unit 2, between the pressure roller 3 and the heater 10. Further, the pressure roller 3 is configured to nip the sheet S, in cooperation with the belt 50, between the pressure roller 3 and the belt 50. The pressure roller 3 is configured to convey the sheet S in cooperation with the belt 50 by rotating.
The pressure roller 3 includes a shaft 3A, and an elastic layer 3B. The shaft 3A has a solid cylindrical shape, and is made of metal, for example. The elastic layer 3B has a hollow cylindrical shape, and is made of silicone rubber, for example. The elastic layer 3B covers an outer circumferential surface of the shaft 3A.
As illustrated in
As illustrated in
The shaft 3A has a diameter that varies in the axial direction such that the diameter becomes greater from each end of the shaft 3A toward a center of the shaft 3A. A diameter B1 of the shaft 3A at the center of the shaft 3A in the axial direction is greater than a diameter B2 of the shaft 3A at each end of the shaft 3A in the axial direction (B2<B1). Specifically, a difference between the diameter B1 of the shaft 3A at the center in the axial direction and the diameter B2 of the shaft 3A at each end in the axial direction is not less than 0.1 mm and not more than 9 mm.
The elastic layer 3B has a thickness that varies in the axial direction such that the thickness becomes thinner from each end of the elastic layer 3B toward a center of the elastic layer 3B. A thickness C1 of the elastic layer 3B at the center of the elastic layer 3B in the axial direction is smaller than a thickness C2 of the elastic layer 3B at each end of the elastic layer 3B in the axial direction (C1<C2). Specifically, a difference between the thickness C1 of the elastic layer 3B at the center in the axial direction and the thickness C2 of the elastic layer 3B at each end in the axial direction is not less than 0.1 mm and not more than 1 mm.
With a configuration described above, the following technical advantages can be obtained according to the present embodiment.
In the fixing device 1 according to the present embodiment, the pressure roller 3 has a so-called inverted crown shape in which the diameter of the pressure roller 3 varies in the axial direction such that the diameter becomes smaller from each end of the pressure roller 3 toward the center of the pressure roller 3. With such a shape of the pressure roller 3, the fixing device 1 can convey the sheet S using the pressure roller 3 and the belt 50 while applying a stretching force to the sheet S directed from a center of the sheet S in the axial direction (the width direction) toward each end of the sheet S in the axial direction (the width direction), thereby restraining generation of wrinkles on the sheet S.
In the meantime, in a case where a pressure roller having an inverted crown shape is employed in a fixing device, there occurs a problem that the nipping width at each end of the pressure roller in the axial direction becomes greater.
However, in the fixing device 1 according to the embodiment described above, the plurality of distal end surfaces 24M, which constitutes the contacting surface, are arranged such that the closer the distal end surfaces 24M are positioned to the center in the axial direction, the greater the distance between the virtual plane P1, which extends parallel to both the axial direction and the conveying direction and containing the heater supporting surface 22A, and each distal end surface 24M becomes, thereby suppressing a nipping pressure at the center in the axial direction from becoming smaller than that at each end in the axial direction. Accordingly, an increase in the nipping width at each end in the axial direction can be suppressed irrespective of the employment of the pressure roller 3 having the inverted crown shape.
In this way, the fixing device 1 can attain a uniform nipping width along the entire length of the pressure roller 3 in the axial direction, since an increase in the nipping width at each end in the axial direction can be suppressed.
Further, since the shaft 3A of the pressure roller 3 has a diameter that varies in the axial direction such that the diameter becomes greater from each end of the shaft 3A toward the center of the shaft 3A, each end of the elastic layer 3B in the axial direction of is expanded more than the center of the elastic layer 3B in the axial direction in a case where the elastic layer 3B of the pressure roller 3 undergoes thermal expansion. Hence, a stretching force directed from the center in the axial direction toward each end in the axial direction can be applied to the sheet S being conveyed even when the elastic layer 3B undergoes thermal expansion, thereby suppressing formation of wrinkles on the sheet S.
Further, since the elastic layer 3B of the pressure roller 3 has a thickness that varies in the axial direction such that the thickness becomes smaller from each end of the elastic layer 3B toward the center of the elastic layer 3B, each end of the elastic layer 3B in the axial direction is expanded more than the center of the elastic layer 3B in the axial direction in a case where the elastic layer 3B of the pressure roller 3 undergoes thermal expansion. Accordingly, a stretching force directed from the center in the axial direction toward each end in the axial direction can be applied to the sheet S being conveyed even when the elastic layer 3B undergoes thermal expansion, thereby suppressing formation of wrinkles on the sheet S.
While the invention has been described in conjunction with various example structures outlined above and illustrated in the figures, various alternatives, modifications, variations, improvements, and/or substantial equivalents, whether known or that may be presently unforeseen, may become apparent to those having at least ordinary skill in the art. Accordingly, the example embodiments of the disclosure, as set forth above, are intended to be illustrative of the invention, and not limiting the invention. Various changes may be made without departing from the spirit and scope of the disclosure. Therefore, the disclosure is intended to embrace all known or later developed alternatives, modifications, variations, improvements, and/or substantial equivalents. Some specific examples of potential alternatives, modifications, or variations in the described invention are provided below:
In the embodiment described above, each of the holder supporting surfaces 40A, at which the stay 40 is in contact with the holder 20, extends parallel to the axial direction. However, the present disclosure need not be limited to the above configuration.
Each of the protrusions of the second wall 142 has an end surface, and the holder supporting surface 140A is constituted by the end surfaces of the protrusions. That is, the holder supporting surface 140A has such a shape that a center of the holder supporting surface 140A in the axial direction protrudes further than each end of the holder supporting surface 140A in the axial direction does.
Note that, although not illustrated in detail in the drawings, the first wall (not illustrated) has a configuration similar to the second wall 142 of this modification.
According to the modification in
Note that, although not illustrated in detail in the drawings, the first wall (not illustrated) has a configuration similar to the second wall 242 of this modification.
Also in this modification illustrated in
In the embodiment described above, the heater supporting surface 22A of the holder 20 extends parallel to the axial direction. However, the present disclosure need not be limited to this configuration.
In a state prior to assembling the holder 120 with both the stay 40 and the heater 10, the protrusions 122 are arranged such that the closer the protrusions 122 are positioned to the center C, the greater a protruding amount of the protrusions 122 become. Each of the protrusions 122 has an end surface, and the heater supporting surface 122M are constituted by end surfaces of the protrusions 122. That is, in a state prior to assembling the holder 120 with both the stay 40 and the heater 10, the heater supporting surface 122M has such a shape that a center of the heater supporting surface 122M in the axial direction protrudes further than each end of the heater supporting surface 122M in the axial direction does.
With the modification illustrated in
In a state prior to assembling the holder 220 with both the stay 40 and the heater 10, a protruding amount of the heater supporting surface 222M varies in the axial direction such that the protruding amount becomes greater from each end of the heater supporting surface 222M toward a center of the heater supporting surface 222M. That is, in a state prior to assembling the holder 220 with both the stay 40 and the heater 10, the heater supporting surface 222M has such a shape that the center of the heater supporting surface 222M in the axial direction protrudes further than each end of the heater supporting surface 222M in the axial direction does.
With the configuration in the modification of
Although the shaft 3A of the pressure roller 3 has such a shape that the diameter of the shaft 3A becomes greater from each end in the axial direction toward the center in the axial direction in the embodiment described above, the present disclosure need not be limited to this configuration.
Similar to the embodiment described above, the pressure roller 103 in this modification can restrain increase in the nipping width at each end of the pressure roller 103 in the axial direction.
Similar to the embodiment described above, the pressure roller 203 can restrain the nipping width at each end of the pressure roller 203 in the axial direction from becoming greater than that at the center in the axial direction.
In the embodiment described above, not less than 20 (twenty) protrusions 24 are arranged in the axial direction at regular intervals. However, the number of the protrusions 24 arranged in the axial direction at regular intervals may be less than 20 (twenty).
In the embodiment described above, the contacting surface, which makes contact with the stay 40, is configured of the distal end surfaces 24M of the plurality of protrusions 24. However, other configurations may be employed. For example, the plurality of protrusions 24 may be omitted, and another surface of the base portion 21 of the holder 20 that faces the stay 40 (an opposite surface of the one surface of the base portion 21) may make contact with the stay 40. In this case, the other surface of the base portion 21 serves as the contacting surface.
The elastic layer 3B of the pressure roller 3 may be made of a material other than silicone rubber. Further, the holder 20 may be made of a material other than resin. Still further, the stay 40 may be made of a material other than metal.
Parts and components used in the embodiment and modifications described above may be suitably combined to be implemented.
Hereinafter, examples according to the present disclosure will be described.
Three fixing devices according to an example 1 and an example 2 of the present disclosure, and a comparative example were prepared. The nipping width, which is the length in the conveying direction of the nipping region NP formed between the pressure roller 3 and the heating unit 2, was measured in each of the above three fixing devices.
In each fixing device, the nipping width was measured at five positions with respect to the axial direction, i.e., an end position 1, an end position 2, a center position, an end position 3, and an end position 4 which are illustrated in
In the example 1, a difference AT in a protruding amount between the center in the axial direction of the holder 20 and each end in the axial direction of the holder 20 was 150 μm.
In the example 2, the difference AT in the protruding amount between the center in the axial direction of the holder 20 and each end in the axial direction of the holder 20 was 350 μm.
In the comparative example, the difference AT in the protruding amount between the center in the axial direction of the holder 20 and each end in the axial direction of the holder 20 was 0 (zero) μm.
Note that the difference AT in the protruding amount denotes the difference between the distance D1 between the virtual plane P1, which extends parallel to both the axial direction and the conveying direction and containing the heater supporting surface 22A, and the distal end surface 24M (constituting the contacting surface) at the center C in the axial direction and the distance D2 between the virtual plane P1 and the distal end surface 24M (constituting the contacting surface) at each end in the axial direction (ΔT=D1−D2).
A table in
Note that, in each fixing device, the base plate 11 of the heater 10 had a length of 7+0.2 mm in the short-side direction, and the cover 13 of the heater 10 had a length of 6.4 mm in the short-side direction.
In the comparative example, the nipping width at the center position was smallest, and the nipping width became grater from the center position toward the end positions 1 and 4. That is, in the comparative example, the nipping width at the end positions 1 and 4 was much greater than the nipping width at the center position. Accordingly, in the fixing device according to the comparative example, uniform fixing performance in the widthwise direction of the sheet S cannot be expected.
In the example 1, the nipping width at the end positions 1 and 4 was greater than the nipping width at the center position. However, a difference in the example 1 between the nipping width at the end positions 1 and 4 and the nipping width at the center position was less than the difference in the comparative example. Accordingly, in the fixing device according to the example 1, relative uniform fixing performance can be expected over the entire area of the sheet S in the widthwise direction.
In the example 2, the nipping width at the center position was approximately the same as the nipping width at the end positions 1 and 4. Further, the nipping width at the end position 2 and 3 was smaller than the nipping width at the end positions 1 and 4. Accordingly, in fixing device according to the example 2, relatively uniform fixing performance can be expected over the entire area of the sheet S.
The above results indicate that the difference AT is preferably not less than 150 μm and not more than 350 μm.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-030499 | Feb 2023 | JP | national |
