Fixing device, and image forming apparatus

Abstract

To prevent the state of contact of a thermistor with a heater from becoming unstable due to interference of an insulating sheet with components around the thermistor, while extending the length of the insulating sheet wound around the thermistor to extend the insulation distance of the thermistor and well prevent entry of grease to an area around the thermistor.SOLUTION: In a fixing device 20, in a process of mounting a thermistor 43 and an insulating sheet 44 on a heater holder 24, the heater holder 24 is brought into contact with an end of the insulating sheet 44 to deform the insulating sheet 44. Upon completion of mounting of the thermistor 43 and the insulating sheet 44 on the heater holder 24, an inclined surface 24f releases the end of the insulating sheet 44 from the contact with the heater holder 24.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a fixing device and an image forming apparatus that fix an image formed on a recording sheet by passing the recording sheet through a nip area between an endless fixing belt and a pressure roller. [Background technology]

[0002] One type of fixing device has a pressure roller pressed against an endless fixing belt to form a nip area between the endless fixing belt and the pressure roller, and passes recording paper through this nip area to fix the image formed on the recording paper.

[0003] For example, in the fixing device described in Patent Document 1, a nip area is formed between a cylindrical fixing film and a pressure roller, the temperature of a heater that heats the fixing film is detected by a thermistor, heat generation of the heater is controlled based on the temperature detected by the thermistor, and recording paper is passed through the nip area to fix an image formed on the recording paper. Also, ceramic paper is interposed between the thermistor and the heater to stabilize the contact state of the thermistor with the heater. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-97143 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, as described above, ceramic paper is interposed between the thermistor and the heater to stabilize the contact state of the thermistor with the heater, thereby reducing errors in the temperature detected by the thermistor.

[0006] On the other hand, it is desirable to increase the insulation distance of the thermistor and effectively prevent the intrusion of surrounding grease, etc. However, the ceramic paper described in Patent Document 1 is only provided near the thermistor, and therefore does not increase the insulation distance or effectively prevent the intrusion of surrounding grease, etc.

[0007] Furthermore, if the size of an insulating sheet such as ceramic paper is increased, the insulating sheet may interfere with surrounding components. This interference may cause the insulating sheet to deform, which may result in unstable contact between the thermistor and the heater.

[0008] The present invention has been made in consideration of the above circumstances, and aims to lengthen the insulating sheet wrapped around the thermistor, thereby increasing the insulating distance of the thermistor and effectively preventing the intrusion of surrounding grease and the like into the thermistor, while preventing the contact state of the thermistor with the heater from becoming unstable due to interference of the insulating sheet with surrounding parts. [Means for solving the problem]

[0009] A fixing device according to one aspect of the present invention comprises an endless fixing belt, a pressure roller pressed against the fixing belt, a heater disposed inside the fixing belt and receiving the pressure of the pressure roller through the fixing belt to heat the fixing belt, a thermistor disposed on a surface of the heater facing away from the fixing belt, a flexible insulating sheet wrapped around the thermistor, a heater holder that holds the heater and on which the thermistor wrapped with the insulating sheet is attached, and a biasing member that presses the thermistor attached to the heater holder against the surface of the heater via the insulating sheet, wherein the heater holder is shaped to have a notch that contacts an end of the insulating sheet to deform the insulating sheet during the process of attaching the thermistor and the insulating sheet to the heater holder, and releases the end of the insulating sheet from said contact when the attachment of the thermistor and the insulating sheet to the heater holder is complete.

[0010] An image forming apparatus according to one aspect of the present invention comprises the fixing device of the present invention described above and an image forming section that forms an image on recording paper, and the fixing device sandwiches the recording paper in a nip area between the fixing belt and the pressure roller, and thermally pressurizes the image formed on the recording paper. [Effects of the Invention]

[0011] According to the present invention, the insulating sheet wrapped around the thermistor is lengthened, thereby increasing the insulating distance of the thermistor and effectively preventing the intrusion of surrounding grease and the like into the thermistor, while stabilizing the contact state of the thermistor with the heater due to the interference of the insulating sheet with surrounding components. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view showing the appearance of an image forming apparatus to which a fixing device according to an embodiment of the present invention is applied; [Figure 2] 1 is a cross-sectional view schematically illustrating an image forming unit and a fixing device in an image forming apparatus. [Figure 3] FIG. 2 is a perspective view illustrating the appearance of the fixing device according to the embodiment. [Figure 4] 1A is a perspective view showing the main configuration of a fixing device, and FIG. 1B is a cross-sectional view showing the fixing device taken along line aa in FIG. 1A. [Figure 5] (A) is an oblique view showing the fixing device with the fixing belt removed, showing the stay metal plate and a pair of holding parts, and (B) is a plan view showing the fixing device with the fixing belt and stay metal removed, showing the heater holder, heat insulating holder, the thermistor holding part that presses the thermistor unit, and a pair of holding parts. [Figure 6] (A) is an oblique view of the thermistor unit and heater holder viewed from above, (B) is an oblique view of the heater holder viewed from above with the thermistor unit removed, and (C) is an oblique view of the thermistor unit viewed from the side. [Figure 7] 10(A) to 10(D) are cross-sectional views showing the procedure for mounting the thermistor unit on the heater holder. [Figure 8] 10A and 10B are perspective views showing the thermistor holder as viewed from above and below, respectively. [Figure 9] FIG. 1A is a perspective view showing the thermistor holding portion, thermistor unit, and heater holder, and FIG. 1B is a cross-sectional view showing the thermistor holding portion, thermistor unit, and heater holder assembled together. [Figure 10] FIG. 10 is a perspective side view of a thermistor unit of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a perspective view showing the appearance of an image forming apparatus to which a fixing device according to an embodiment of the present invention is applied. In Figs. 1 to 10, the arrow direction x is the depth direction, the arrow direction y is the width direction, and the arrow direction z is the height direction.

[0014] 1, a device body 2 of an image forming device 1 is provided with a plurality of components for realizing various functions of the image forming device 1. For example, the device body 2 is provided with an image forming unit, a fixing device, an operation unit 3, a paper feed cassette 4, an output tray 5, etc.

[0015] The image forming unit forms an image represented by image data on recording paper supplied from a paper feed cassette 4. The recording paper on which the image has been formed undergoes a fixing process by a fixing device and is then discharged onto a discharge tray 5.

[0016] The operation unit 3 includes, for example, a start key, a decision key for confirming operation input, and numeric input keys for inputting numeric values, and receives instructions from the operator regarding various operations and processes, etc. The operation unit 3 also includes a display unit for displaying operation guides, etc. to the operator.

[0017] 2 is a cross-sectional view that schematically shows the image forming unit and fixing device in the image forming apparatus 1. The image forming unit 11 is for forming a toner image on recording paper P supplied from a paper feed cassette 4 by electrophotography, and includes a photosensitive drum 12 that rotates in the direction of the arrow, a charge eliminating unit 13 that eliminates charge from the surface of the photosensitive drum 12, a cleaning unit 14 that cleans the surface of the photosensitive drum 12, a charging unit 15 that uniformly charges the surface of the photosensitive drum 12, a developing device 16 that develops into a toner image an electrostatic latent image formed on the surface of the photosensitive drum 12 by exposure from an exposure unit (not shown), and a toner container 19 that supplies toner to the developing device 16.

[0018] The photosensitive drum 12 is pressed against a transfer roller 18 provided below the photosensitive drum 12 , forming a nip area between the photosensitive drum 12 and the transfer roller 18 .

[0019] When recording paper P is supplied from paper feed cassette 4, this recording paper P is transported through transport path 17 in the direction of arrow A. This recording paper P passes through the nip area between photosensitive drum 12 and transfer roller 18, and the toner image on the surface of photosensitive drum 12 is transferred onto the recording paper P. Subsequently, the recording paper P is transported to fixing device 20, which applies heat and pressure to the recording paper P, thereby fixing the toner image on the recording paper P. Furthermore, the recording paper P is transported from fixing device 20 through transport path 17, which curves upward, and is discharged onto discharge tray 5, which is provided above image forming apparatus 1.

[0020] Fig. 3 is a perspective view showing the appearance of the fixing device 20 of this embodiment. As shown in Fig. 3, the fixing device 20 includes a main body frame 30 formed by combining a synthetic resin molded member and a metal plate, and the various components of the fixing device 20 are supported by the main body frame 30. The main body frame 30 is provided with an inlet 31 for the recording paper P.

[0021] Fig. 4(A) is a perspective view showing the main components of the fixing device 20, and Fig. 4(B) is a cross-sectional view showing the fixing device 20 taken along line aa in Fig. 4(A). As shown in Figs. 4(A) and (B), the fixing device 20 includes a fixing belt 21, a pressure roller 22, a planar heater 23, a heater holder 24, a thermistor unit 41, a stay metal plate 26, and a pair of holding portions 27.

[0022] The fixing belt 21 is an endless belt, and is a flexible sheet-like layer made up of a base layer made of metal or synthetic resin, an elastic layer made of silicone rubber, and a release layer made of synthetic resin.

[0023] On the inside of the fixing belt 21, there are provided a sheet heater 23 that is in sliding contact with the lower portion of the inner circumferential surface of the fixing belt 21, a heater holder 24 that supports the sheet heater 23, a heat insulating holder 25, and a stay metal plate 26 that supports the heater holder 24. The stay metal plate 26 extends in the longitudinal direction of the fixing belt 21 and protrudes from both ends of the fixing belt 21. The heater holder 24 and the heat insulating holder 25 are molded products of synthetic resin.

[0024] The thermistor 43 (shown in Figures 6, 7, etc.) of the thermistor unit 41 protrudes toward the sheet heater 23 through an opening in the heater holder 24 and detects the temperature of the upper surface of the sheet heater 23. The temperature of the sheet heater 23 is controlled based on the temperature of the upper surface of the sheet heater 23 detected by the thermistor 43.

[0025] The stay metal plate 26 is formed, for example, by sheet metal processing into a U-shaped cross section, and has sufficient strength and rigidity. Each holding portion 27 is supported by the main body frame 30 of the fixing device 20, both ends of the stay metal plate 26 are supported by the respective holding portions 27, the heater holder 24 and the heat insulating holder 25 are supported by the stay metal plate 26, and the planar heater 23 is held by the heater holder 24. Therefore, the stay metal plate 26 is supported by each holding portion 27 and supports the heater holder 24, the heat insulating holder 25, and the planar heater 23. As a result, each holding portion 27, the stay metal plate 26, the heater holder 24, the heat insulating holder 25, and the planar heater 23 are supported integrally.

[0026] The pressure roller 22 is a metal cylinder or columnar body whose outer surface is covered with a layer of synthetic resin, etc. The shaft of the pressure roller 22 is rotatably supported by bearings on both sides of the pressure roller 22 and is arranged parallel to the center of rotation of the fixing belt 21.

[0027] When the rotational driving force of a motor (not shown) is transmitted to the shaft of the pressure roller 22 and the pressure roller 22 is rotated in the direction of the arrow, the fixing belt 21 is rotated in the opposite direction to the pressure roller 22. In addition, the planar heater 23 is made to generate heat to heat the fixing belt 21, and the temperature of the fixing belt 21 is set to a specified temperature suitable for fixing.

[0028] In this state, when the recording paper P is conveyed to the nip area N, the recording paper P is heated and pressed in the nip area N, and the toner image on the recording paper P is fixed by thermocompression.

[0029] Figure 5(A) is an oblique view showing the heat insulating holder 25, the stay metal plate 26, and a pair of holding portions 27, etc., with the fixing belt 21 removed, and Figure 5(B) is a plan view showing the heater holder 24, the heat insulating holder 25, the thermistor holding portion 51 that presses down the thermistor unit 41 (shown in Figures 6, 7, etc.), and a pair of holding portions 27, etc., with the fixing belt 21 and the stay metal plate 26 removed.

[0030] As shown in Figures 5(A) and (B), the pair of holding portions 27 each have an annular frame portion 27A, and each annular frame portion 27A is inserted inside both end portions of the fixing belt 21, and the outer surface of each annular frame portion 27A contacts the inner surface of the end portion of the fixing belt 21, thereby holding the fixing belt 21.

[0031] When the stay metal plate 26 shown in Fig. 5(A) is removed, the heater holder 24 and thermistor holding portion 51, etc., are exposed as shown in Fig. 5(B). At least one thermistor unit 41 is provided on the heater holder 24. When multiple thermistor units 41 are provided, the thermistor units 41 are arranged spaced apart along the longitudinal direction of the heater holder 24.

[0032] Figure 6(A) is a perspective view of the thermistor unit 41 and heater holder 24 viewed from above, Figure 6(B) is a perspective view of the heater holder 24 viewed from above with the thermistor unit 41 removed, and Figure 6(C) is a perspective view of the thermistor unit 41 viewed from the side.

[0033] As shown in FIG. 6(C), the thermistor unit 41 includes a frame 42, a thermistor 43 located approximately in the center of the frame 42, and a flexible insulating sheet 44 wrapped around the frame 42 to cover the thermistor 43. The frame 42 is narrowed in the center, and one end of the frame 42 is formed with a pair of protrusions 42a that protrude outward from both sides of the frame 42, while the other end of the frame 42 is formed with a protrusion 42b that protrudes upward. A hollow annular portion 42c protrudes toward the other end of the frame 42. One end of the insulating sheet 44 is engaged with the frame 42 and wrapped around the frame 42 to form a cylindrical shape, and the other end is also engaged with the frame 42 and wrapped around the frame 42. The length L of the cylindrical insulating sheet 44 is longer than the length of the upper half.

[0034] As shown in Figure 6(B), a rectangular opening 24a is formed in the heater holder 24. The sheet heater 23 is placed on the underside of the heater holder 24, and the sheet heater 23 is exposed through the opening 24a. A hook 24b is provided at one end of the opening 24a, and a boss 24c that protrudes upward is provided at the other end of the opening 24a, with shelf portions 24d provided on both sides of the opening 24a. In addition, as shown in Figure 6(A), the heater holder 24 is provided with a fitting recess 24e at a position spaced apart from the opening 24a.

[0035] 6(A), the thermistor unit 41 is placed and attached to the rectangular opening 24a of the heater holder 24. The thermistor 43 of the thermistor unit 41 is placed on the upper surface of the sheet heater 23 via an insulating sheet 44, and detects the temperature of the sheet heater 23.

[0036] 7(A) to 7(D) are cross-sectional views showing the procedure for attaching the thermistor unit 41 to the heater holder 24. As shown in Fig. 7(A), the thermistor unit 41 is lowered from above the rectangular opening 24a of the heater holder 24 onto the heater holder 24 before the thermistor unit 41 is attached, as shown in Fig. 7(B), and the bosses 24c of the heater holder 24 are fitted into the hollow annular portions 42c of the frame 42 of the thermistor unit 41. As shown in Fig. 7(C), the pair of protrusions 42a protruding from both sides of the frame 42 of the thermistor unit 41 are brought into contact with the shelf portions 24d on both sides of the opening 24a of the heater holder 24. In this way, the thermistor unit 41 is attached to the heater holder 24.

[0037] Furthermore, the thermistor unit 41, when placed on the heater holder 24, is pressed down by a thermistor holding portion 51 as shown in Figures 8(A) and (B). Figures 8(A) and (B) are perspective views showing the thermistor holding portion 51 as seen from above and below, respectively.

[0038] 8(A) and 8(B), the thermistor holder 51 includes a frame 52 and a coil spring 53. The frame 52 includes side walls 52a on both sides, positioning pieces 52b protruding from one end of each side wall 52a, and engaging portions 52c protruding downward from each side wall 52a. The coil spring 53 protrudes downward from approximately the center of the frame 52.

[0039] Figure 9(A) is an oblique view showing the thermistor holding portion 51, thermistor unit 41, and heater holder 24, and Figure 9(B) is a cross-sectional view showing the thermistor holding portion 51, thermistor unit 41, and heater holder 24 assembled together.

[0040] 9(A) and 9(B), the thermistor holding portion 51 is lowered from above the thermistor unit 41, the positioning piece 52b of the thermistor holding portion 51 is inserted into the fitting recess 24e of the heater holder 24, and the engaging portion 52c of the thermistor holding portion 51 is hooked onto the hook 24b of the heater holder 24, thereby engaging the thermistor holding portion 51 with the heater holder 24. At this time, the coil spring 53 of the thermistor holding portion 51 is compressed, and the biasing force of the coil spring 53 presses the thermistor 43 of the thermistor unit 41 via the insulating sheet 44. In this way, the thermistor unit 41 is attached to the heater holder 24.

[0041] As can be seen from Figure 9(B), the thermistor 43 of the thermistor unit 41 is biased downward by the force of the coil spring 53 and pressed against the upper surface of the planar heater 23 via the insulating sheet 44, thereby entering a state in which it detects the temperature of the planar heater 23.

[0042] Here, the insulating sheet 44 is provided to increase the insulation distance of the thermistor 43 and to prevent the intrusion of surrounding grease and the like into the thermistor 43, and it is desirable to increase the length of the insulating sheet 44 (the length in the longitudinal direction of the sheet heater 23). Therefore, as shown in Figure 6(C), the length L of the lower half of the cylindrical insulating sheet 44 is made longer than the length of its upper half, thereby increasing the insulation distance and further improving the effect of preventing the intrusion of surrounding grease and the like into the thermistor 43.

[0043] Fig. 10 is a perspective side view of a thermistor unit 41A of the comparative example. The length of the lower half of the insulating sheet 44 of the thermistor unit 41A of the comparative example shown in Fig. 10 is shorter than the length L of the lower half of the insulating sheet 44 of the thermistor unit 41 of this embodiment. Therefore, the thermistor unit 41A of the comparative example has a shorter insulation distance and is more susceptible to penetration of surrounding grease and the like into the thermistor 43 than the thermistor unit 41 of this embodiment.

[0044] However, if the length L of the insulating sheet 44 is increased, as shown in Figures 7(B) and (C), when the thermistor unit 41 is attached to the heater holder 24, the end of the insulating sheet 44 will interfere with the boss 24c of the heater holder 24, causing the insulating sheet 44 to deform. If the insulating sheet 44 remains deformed, the thermistor 43 will be urged downward by the coil spring 53, and even when the insulating sheet 44 is sandwiched between the thermistor 43 and the sheet heater 23, the flatness of the insulating sheet 44 will not be maintained, and the thermistor 43 will not be pressed uniformly against the top surface of the sheet heater 23 via the insulating sheet 44, resulting in a large error in the temperature detected by the thermistor 43 against the sheet heater 23.

[0045] The inventors of the present invention have discovered that such deformation of the insulating sheet 44 due to interference with the heater holder 24 causes an increase in the error in the temperature of the sheet heater 23 detected by the thermistor 43 .

[0046] Therefore, in this embodiment, as shown in Figure 7(A), the lower portion of the boss 24c of the heater holder 24 facing the end of the insulating sheet 44 is cut out, and a downward and outward inclined surface (cutout portion) 24f is formed in this lower portion, and a space SP is provided below the boss 24c.

[0047] Therefore, even if the end of the insulating sheet 44 interferes with the heater holder 24 and is bent and deformed during the process of lowering the thermistor unit 41 from above the rectangular opening 24a of the heater holder 24 and fitting the boss 24c of the heater holder 24 into the hollow annular portion 42b of the frame 42 of the thermistor unit 41 as shown in Figures 7(B) and (C), when the thermistor unit 41 is attached to the heater holder 24 as shown in Figure 7(D), the bent end of the insulating sheet 44 slides along the downward, outward inclined surface 24f of the heater holder 24 and stretches in the space SP, causing the end of the insulating sheet 44 to return to its original shape.

[0048] That is, in the process of attaching the thermistor 43 and the insulating sheet 44 to the heater holder 24, the heater holder 24 comes into contact with the end of the insulating sheet 44 and deforms the insulating sheet 44. Then, when the thermistor 43 and the insulating sheet 44 have been attached to the heater holder 24, the inclined surface 24f releases the end of the insulating sheet 44 from contact with the heater holder 24.

[0049] This maintains the flatness of the insulating sheet 44 between the thermistor 43 and the surface heater 23, and the thermistor 43 is pressed evenly against the upper surface of the surface heater 23 via the insulating sheet 44, allowing the thermistor 43 to accurately detect the temperature of the surface heater 23.

[0050] The configuration and processing described with reference to FIGS. 1 to 10 are merely one embodiment of the present invention, and the present invention is not limited to these configurations and processing. [Explanation of symbols]

[0051] 1. Image forming device 2. Device body 3 Control section 4 Paper cassette 5 Output tray 11 Image forming unit 20 Fixing device 21 Fixing belt 22 Pressure roller 23 Planar heater 24 Heater holder 26 Stay sheet metal 27 Holding part 41 Thermistor unit 43 Thermistor 44 Insulation sheet 51 Thermistor holder 53 Coil spring

Claims

1. an endless fixing belt; a pressure roller that is in pressure contact with the fixing belt; a heater provided inside the fixing belt, receiving the pressure from the pressure roller through the fixing belt and heating the fixing belt; a thermistor disposed on a surface of the heater facing away from the fixing belt; a flexible insulating sheet wrapped around the thermistor; a heater holder that holds the heater and to which the thermistor wrapped with the insulating sheet is attached; a biasing member that presses the thermistor attached to the heater holder against a surface of the heater via the insulating sheet, The heater holder is In the process of attaching the thermistor and the insulating sheet to the heater holder, the insulating sheet is deformed by contacting an edge of the insulating sheet; The fixing device has a shape having a notch that releases the end of the insulating sheet from the contact when the thermistor and the insulating sheet are completely attached to the heater holder.

2. 2. The fixing device according to claim 1, wherein the notch of the heater holder is formed by an inclined surface facing the end of the insulating sheet and facing outward from the heater holder.

3. a fixing device according to claim 1 or 2; an image forming unit that forms an image on a recording sheet; The fixing device is an image forming apparatus that sandwiches the recording paper in a nip area between the fixing belt and the pressure roller, and heat-pressure-bonds the image formed on the recording paper.

Images