Fixation device

Abstract

To provide a fixation device capable of equalizing a nip width of a pressure area in a width direction.SOLUTION: A fixation device comprises a fixture belt 31, a heater holder 35, a stay 37, an end part holder and a pressure roller 23, and forms a pressure area N by pressing the stay 37 toward the pressure roller 23. The stay 37 has a pair of lateral plates 37b; the heater holder 35 has a pedestal rib 43 on which the pair of lateral plates 37b is placed; the pair of lateral plates 37b of the stay 37 is formed such that their central parts in a width direction protrude toward the pressure area N more than both end parts; and the pedestal rib 43 of the heater holder 35 is formed such that its central part in the width direction is higher than both end parts. The value of α-X-Y is set close to zero, where X is a protrusion amount of the lateral plates 37b at a prescribed position in the width direction; Y is the height of the pedestal rib 43; and α is a deformation amount of the stay 35 in the pressure area N.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a fixing device that fixes a toner image onto a sheet of paper. [Background technology]

[0002] The fixing device includes a fixing belt heated by a heater and a pressure roller. The heater is held by a heater holder and heats the fixing belt by contacting the inner circumferential surface of the fixing belt. The heater holder is reinforced by stays. Both ends of the fixing belt, heater holder, and stay in the width direction of the paper are supported by end holders. The stay is pressed against the pressure roller while being supported by the end holders, thereby forming a pressure area between the pressure roller and the fixing belt. When the paper to which the toner image has been transferred passes through the pressure area, the toner image is heated and pressurized to be fixed to the paper.

[0003] In a fixing device with such a configuration, both ends of the stay are pressed against the pressure roller, so that the center of the stay is deformed so as to be curved toward the opposite side of the pressure roller, which causes the pressure applied from the stay to the fixing belt in the width direction of the paper to be uneven, and as a result, the nip width in the pressure area becomes uneven in the width direction, causing a problem of reduced fixing performance and conveyance performance.

[0004] Therefore, in the fixing device described in Patent Document 1, the center of the side plate of the stay is formed to protrude further toward the pressure area than both ends. As a result, when the stay is supported by the end holder and pressed toward the pressure roller, the surface of the stay facing the pressure roller becomes almost linear, making it possible to uniformize the pressure applied by the stay to the fixing belt. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] WO2020 / 217802 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the fixing device described in Patent Document 1, the stay may not necessarily deform as desired due to variations and dimensional accuracy of parts such as the stay, heater holder, and end holder.

[0007] In consideration of the above circumstances, an object of the present invention is to provide a fixing device capable of making the nip width uniform in the width direction of the pressure region. [Means for solving the problem]

[0008] In order to solve the above problems, the fixing device of the present invention includes a rotatable endless fixing belt, a heater in contact with an inner peripheral surface of the fixing belt, a heater holder that holds the heater, a stay that reinforces the heater holder, end holders that support both ends of the fixing belt, the heater holder, and the stay in the width direction of the paper, and a pressure roller that is arranged to face the heater across the fixing belt, and presses the stay against the pressure roller while supporting it with the end holders, thereby forming a pressure region between the pressure roller and the fixing belt where the paper onto which a toner image has been transferred is heated and pressed, and the stay is supported by a top plate and a pressure roller that supports the stay. and a pair of side plates arranged opposite each other in a direction intersecting the width direction of paper, the heater holder having a bottom plate having a recess in which the heater is housed, and a base rib provided on the bottom plate on which the pair of side plates of the stay are placed, the pair of side plates of the stay are formed so that a central portion in the width direction protrudes toward the pressurized area further than both end portions, the base rib of the heater holder is formed so that a central portion in the width direction is higher than both end portions, the amount of protrusion of the side plates of the stay at a predetermined position in the width direction is X, the height of the base rib of the heater holder is Y, and the amount of deformation of the stay in the pressurized area is α, where the value of α-XY is set to a value close to zero.

[0009] In the present invention, the maximum value of the protrusion amount X of the side plate of the stay may be 0.1 mm.

[0010] In the present invention, the stay may have a plate thickness of 2 mm. Effect of the Invention

[0011] According to the present invention, even when taking into account the dimensional tolerances of the stays and heater holder, it is possible to suppress the protrusion of the central parts of both side plates of the stay toward the pressure area when forming the pressure area, and to make the nip width of the pressure area uniform in the width direction. [Brief description of the drawings]

[0012] [Figure 1] 1 is a front view showing a schematic internal configuration of an image forming apparatus including a fixing device according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a side view showing a fixing device according to an embodiment of the present invention. [Diagram 3] 1 is a front cross-sectional view showing a fixing device according to an embodiment of the present invention; [Figure 4] FIG. 2 is a perspective view showing a heater holder and a stay of a fixing device according to an embodiment of the present invention. [Diagram 5] FIG. 2 is a cross-sectional view showing a heater holder and a stay of a fixing device according to an embodiment of the present invention. [Figure 6] FIG. 4 is a side view showing a stay of the fixing device according to the embodiment of the present invention. [Figure 7] FIG. 2 is a side view showing a stay, a heater holder, and a pressure roller of a fixing device according to an embodiment of the present invention. [Figure 8] 5 is a graph showing an example of a relationship between a dimensional tolerance and the number of stays in the fixing device according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fixing device according to an embodiment of the present invention will now be described with reference to the accompanying drawings.

[0014] First, with reference to Fig. 1, an image forming apparatus 1 equipped with a fixing device 9 will be described. Fig. 1 is a front view showing a schematic view of the inside of the image forming apparatus 1. Fr, Rr, L, and R shown in each drawing indicate the front side, rear side, left side, and right side of the image forming apparatus 1, respectively.

[0015] The image forming apparatus 1 is provided with a paper feed cassette 3 that stores paper, a paper feed device 5 that feeds paper from the paper feed cassette 3, an image forming section 7 that forms a toner image on the paper, a fixing device 9 that fixes the toner image on the paper, a paper discharge device 11 that discharges the paper, and a paper discharge tray 13 on which the discharged paper is stacked. Furthermore, the image forming apparatus 1 is provided with a transport path 15 along which paper is transported from the paper feed device 5 through the image forming section 7 and the fixing device 9 to the paper discharge device 11.

[0016] The paper fed from paper feed cassette 3 by paper feed device 5 is transported along transport path 15 to image forming unit 7, where a toner image is formed on the paper. The paper on which the toner image has been formed is transported along transport path 15 to fixing device 9, where the toner image is fixed to the paper. The paper on which the toner image has been fixed is discharged by paper discharge device 11 onto paper discharge tray 13.

[0017] Next, the fixing device 9 will be described with reference to Figures 2 and 3. Figure 2 is a side view showing the fixing device 9, and Figure 3 is a cross-sectional view showing the fixing device 9. The fixing device 9 includes a belt assembly 21 and a pressure roller 23. The belt assembly 21 and the pressure roller 23 are contained in a housing (not shown).

[0018] First, a description will be given of the belt assembly 21. The belt assembly 21 includes a fixing belt 31, a heater 33 (see FIG. 3) that heats the fixing belt 31, a heater holder 35 that holds the heater 33, a stay 37 that reinforces the heater holder 35, and end holders 39 that support both end portions of the fixing belt 31, the heater holder 35, and the stay 37 in the width direction W of the paper.

[0019] First, the fixing belt 31 will be described. The fixing belt 31 is an endless belt having a predetermined inner diameter and a width greater than the width of the paper. The fixing belt 31 is made of a flexible material and has a base layer, an elastic layer provided on the outer peripheral surface of the base layer, and a release layer provided on the outer peripheral surface of the elastic layer. The base layer is made of a metal such as SUS or Ni. The elastic layer is made of silicone rubber or the like. The release layer is made of a PFA tube or the like.

[0020] Next, the heater 33 will be described. The heater 33 is a flat-plate heater having a width equal to that of the fixing belt 31 and a predetermined length and thickness. The heater 33 has a laminated structure in which a stainless steel or ceramic substrate, a glass electrical insulating layer, a resistance heating layer having electrodes, and a protective layer are laminated in this order from the back side to the front side. The surface of the protective layer is formed flat and serves as a sliding surface that contacts the inner circumferential surface of the fixing belt 31. The resistance heating layer generates heat when electricity is passed through the electrodes.

[0021] Next, the heater holder 35 will be described with reference to Figures 4 and 5. Figure 4 is a perspective view showing the heater holder 35 and the stay 37, and Figure 5 is a cross-sectional perspective view showing the heater holder 35 and the stay 37.

[0022] As shown in FIG. 4 and FIG. 5, the heater holder 35 is a member having a bottom plate 35a and a pair of side plates 35b, and has a substantially U-shaped cross section. The width of the heater holder 35 is greater than the widths of the fixing belt 31 and the heater 33. A recess 41 (see FIG. 5) in which the heater 33 is accommodated is formed on the outer surface of the bottom plate 35a. A plurality of pedestal ribs 43 are formed on the inner surface of the bottom plate 35a. The pedestal rib 43 has a rectangular parallelepiped shape having a predetermined length along a cross direction crossing the width direction of the paper and a predetermined height. The plurality of pedestal ribs 43 are disposed at both ends of the inner surface of the bottom plate 35a in the cross direction at predetermined intervals in the width direction W. The height Y (see FIG. 7) of the pedestal rib 43 is formed so that it is highest at the center of the width direction W and gradually decreases toward both ends. The height Y of the pedestal rib 43 will be described later with reference to FIG. 7.

[0023] A plurality of guide ribs 45 are formed on the outer surfaces of the pair of side plates 35b at predetermined intervals in the width direction W. The guide ribs 45 have a substantially semicircular shape along the circumferential direction of the fixing belt 31. Furthermore, support ribs 47 (see FIG. 4) are formed on the inner surfaces of the pair of side plates 35b at predetermined intervals in the width direction W and along the height direction of the side plates 35b.

[0024] 2, the heater holder 35 penetrates the hollow portion of the fixing belt 31, and both ends thereof protrude outward from both sides of the fixing belt 31. The heater holder 35 is made of a heat-resistant resin such as a liquid crystal polymer.

[0025] Next, the stay 37 will be described with reference to FIG. 4, FIG. 5, and FIG. 6. FIG. 6 is a cross-sectional view of the stay 37. The stay 37 is a member having a substantially U-shaped cross section, including a top plate 37a and a pair of side plates 37b. As shown in FIG. 6, the pair of side plates 37b are formed such that the center portion in the width direction W is higher than both ends. In other words, the center portion of the pair of side plates 37b protrudes more than both ends, and the protrusion amount X is highest in the center and gradually decreases toward both ends. The width of the stay 37 is longer than the width of the fixing belt 31. The stay 37 is made of sheet metal, and has a plate thickness of 2 mm. The protrusion amount of both side plates 37b will be described later with reference to FIG. 7.

[0026] 5, the stay 37 is disposed between both side plates 35b of the heater holder 35 with the opening between the pair of side plates 37b facing the opening between the both side plates 35b of the heater holder 35. Both side plates 37b of the stay 37 are supported by both support ribs 47 (see FIG. 4) of the heater holder 35, and the end faces of both side plates 37b are placed on the base rib 43 of the heater holder 35. As shown in FIG. 2, both end portions of the stay 37 protrude outward from both sides of the fixing belt 31.

[0027] Next, the end holder 39 will be described with reference to Figures 2 and 3. The end holder 39 rotatably supports both end portions of the fixing belt 31, and also supports both end portions of the heater holder 35 and the stay 37 protruding outward from the fixing belt 31.

[0028] Next, the pressure roller 23 will be described with reference to Fig. 2 and Fig. 3. The pressure roller 23 has a core metal 23a and an elastic layer 23b provided on the outer peripheral surface of the core metal 23a. The elastic layer 23b is made of silicone rubber or the like. A release layer may be provided on the outer peripheral surface of the elastic layer 23b.

[0029] As described above, the belt assembly 21 and the pressure roller 23 are housed in a housing (not shown). The pressure roller 23 is rotatably supported between the lower portions of a pair of side plates (not shown) of the housing. The pressure roller 23 is connected to a motor (not shown). The belt assembly 21 is disposed above the pressure roller 23, and the end holder 39 is supported by the upper portions of the pair of side plates of the housing. The heater 33 faces the pressure roller 23 via the fixing belt 31. The end holder 39 is biased toward the pressure roller 23 by a pressing plate and a coil spring (both not shown). In detail, both side plates 37b of the stay 37 bias the seat rib 43 (bottom plate 35a) of the heater holder 35 toward the pressure roller 23. This forms a pressure region N (see FIGS. 2 and 3) between the fixing belt 31 and the pressure roller 23.

[0030] The fixing operation of the fixing device 9 having the above configuration will be described. During the fixing operation, the pressure roller 23 is driven by the motor to rotate. Then, the fixing belt 31 is guided by the guide rib 45 of the heater holder 35 and rotates in the opposite direction to the pressure roller 23, following the rotation of the pressure roller 23. As a result, the paper onto which the toner image has been transferred passes through the pressure area N. At that time, the toner image is heated and pressurized to be fixed to the paper.

[0031] Here, an example of a method for setting the amount of protrusion of the center of the side plate 37b of the stay 37 and the height of the base rib 43 of the heater holder 35 will be described with reference to Fig. 7. Fig. 7 is a side view showing the stay 37, the heater holder 35, and the pressure roller 23. As described above, the center of both side plates 37b of the stay 37 protrudes toward the pressure region N side (referred to as the negative direction) further than both end portions. Furthermore, the center of the base rib 43 of the heater holder 35 is formed to be the highest.

[0032] As described above, when the stay 37 is pressed toward the pressure roller 23 while being supported by the end holders 39 in forming the pressure region N (see arrow A), the central portion of the stay 37 is deformed so as to be curved in the opposite direction (positive direction) from the pressure roller 23 (see arrow B). To compensate for such deformation of the stay 37, the central portions of both side plates 37b of the stay 37 are made to protrude toward the pressure roller 23, and the central pedestal rib 43 of the heater holder 35 is formed so as to be higher than the ends.

[0033] Here, the deformation amount of the center of both side plates 37b of the stay 37 is α, the protrusion amount of the center of both side plates 37b of the stay 37 is X, and the height of the seat rib 43 at the center of the heater holder 35 is Y. Then, when the pressurized area N is formed, the center of both side plates 35b of the stay 37 protrudes toward the side of the pressurized area N (in the negative direction) by α-XY. As an example, if this protrusion amount becomes larger than 0.39 mm (when the center of both side plates 37b of the stay 37 protrudes toward the side of the pressurized area N), the nip width of the pressurized area N changes in the width direction W. For this reason, when the pressurized area is formed, it is necessary to set the center of both side plates 37b of the stay 37 not to protrude toward the side of the pressurized area N as much as possible, that is, to make the value of α-XY as close to zero as possible.

[0034] The deformation amount α generally depends on the rigidity of the stay 37. In the present invention, since the plate thickness of the stay 37 is set to 2 mm, the maximum deformation amount α is set to +0.148 mm to +0.173 mm. The protrusion amount X of the central portion of each of the side plates 37b of the stay 37 is set to -0.1 mm. In addition, the dimensional tolerance of the pedestal rib 43 of the heater holder 35 is set to ±0.05 mm. To make the value of α-XY as close to zero as possible, the height Y of the central pedestal rib 43 is 0.22±0.05 mm. In this case, the nip width in the pressurized region N is maintained within a desired range in the width direction W.

[0035] As described above, by setting the amount of protrusion of the center of the side plate 37b of the stay 37 and the height of the base rib 43 of the heater holder 35, it is possible to suppress the protrusion of the center of the side plate 37b of the stay 37 toward the pressure area N when the pressure area N is formed, even when taking into consideration the dimensional tolerance of the stay 37 and the heater holder 35, and to make the nip width of the pressure area N uniform in the width direction W. In particular, by setting the plate thickness of the stay 37 to 0.2 mm, it is possible to suppress deformation of the stay 37 when the pressure area N is formed. Therefore, even in the fixing device 9 configured to form the pressure area N by pressing the stay 37 toward the pressure roller 23 while supporting it with the end holder 39, it is possible to make the nip width of the pressure area N uniform in the width direction W, and stabilize the fixing performance and the conveying performance.

[0036] Next, the dimensional tolerance of the stay 37 will be described with reference to FIG. 8. The horizontal axis of the graph in FIG. 8 indicates the dimensional tolerance, and the vertical axis indicates the number of stays 37. It is assumed that the dimensional tolerance of the stay 37 due to processing appears in a normal distribution indicated by the solid line in the graph. If the protrusion amount of the center of both side plates 37b of the stay 37 is 0 to 0.1 mm, the stay 37 included in the range indicated by the arrow C in the graph will be used. In this case, if the center of both side plates 37b of the stay 37 is made protruding by 0.05 mm, the dimensional tolerance of the stay 37 due to processing shifts to a normal distribution indicated by the two-dot chain line in the graph. As a result, the number of stays 37 included in the range indicated by the arrow C can be increased, and the probability that the nip width can be made uniform in the width direction W can be increased as described above.

[0037] In this embodiment, the thickness of the stay 37 is set to 2 mm to suppress deformation. Alternatively, the stay 37 may be provided with reinforcing ribs along the width direction W to suppress deformation.

[0038] Furthermore, the above description of the embodiments of the present invention describes preferred embodiments of the present invention, and therefore may include various technically preferable limitations. However, the technical scope of the present invention is not limited to these aspects unless there is a specific description that limits the present invention. [Explanation of symbols]

[0039] 1. Image forming device 9 Fixing device 23 Pressure Roller 31 Fixing belt 33 Heater 35 Heater holder 35a bottom plate 37 Stay 37a Tabletop 37b side plate 39 End holder 43 Pedestal rib

Claims

1. a rotatable endless fixing belt; a heater in contact with an inner circumferential surface of the fixing belt; A heater holder for holding the heater; A stay for reinforcing the heater holder; an end holder for supporting both end portions of the fixing belt, the heater holder, and the stay in a width direction of the paper; a pressure roller disposed opposite the heater with the fixing belt interposed therebetween, a fixing device in which the stay is supported by the end holder and pressed against the pressure roller to form a pressure region between the pressure roller and the fixing belt in which a sheet having a transferred toner image is heated and pressed, The stay is The top plate and a pair of side plates disposed opposite to each other in a direction intersecting the width direction of the paper; The heater holder is a bottom plate having a recess in which the heater is accommodated; a base rib provided on the bottom plate on which the pair of side plates of the stay are placed, The pair of side plates of the stay are formed such that a central portion in the width direction protrudes toward the pressurized region side more than both end portions, The base rib of the heater holder is formed so that a center portion in the width direction is higher than both end portions, a protrusion amount of the side plate of the stay at a predetermined position in the width direction is X, a height of the base rib of the heater holder is Y, and a deformation amount of the stay in the pressure application area is α, and a value of α-X-Y is set to a value close to zero.

2. 2. The fixing device according to claim 1, wherein the maximum value of the protrusion amount X of the side plate of the stay is 0.1 mm.

3. 3. The fixing device according to claim 2, wherein the thickness of the stay is 2 mm.

Images