Fixing device and image forming apparatus

Abstract

A fixing device capable of suppressing damage to a substrate caused by thermal expansion of a resistance heating element. [Solution] The fixing device comprises a fixing belt that heats the toner on the paper while rotating around its axis, a pressure roller that pressurizes the toner on the paper as it passes through a pressure area while rotating around its axis, and a heater 22 that contacts the inner surface of the fixing belt facing the pressure area and heats the fixing belt, the heater 22 having a plurality of resistance heating elements 31, 32 formed on one side of a substrate 30 at intervals in the axial direction, the plurality of resistance heating elements 31, 32 having a first resistance heating element 31 and a second resistance heating element 32 formed at a position shifted to one side of the transport direction of the paper P that is perpendicular to the axial direction relative to the first resistance heating element 31, and the amount of shift G2 between the first resistance heating element 31 and the second resistance heating element 32 is less than the dimension of the pressure area N in the transport direction and is set in the range of 0.1 mm or more and less than 4.5 mm.

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes a toner image on a medium and an image forming apparatus. [Background technology]

[0002] A fixing device is known that heats toner on paper as the paper passes between a fixing belt and a pressure roller (Patent Document 1). A heating element extending in the axial direction of the fixing belt is in contact with the inner surface of the fixing belt. The heating element has multiple resistance heating elements formed on one surface of a substrate. The multiple resistance heating elements are formed at positions offset in a stepped pattern in the width direction of the substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-122938 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned multiple resistance heating elements are presumably arranged in a stepped pattern, taking into consideration the wiring on the substrate, etc. This configuration may allow for a compact heater while ensuring an insulation distance (creepage distance) between adjacent resistance heating elements. However, when the resistance heating elements thermally expand due to the passage of current, forces in opposite directions act between adjacent resistance heating elements, which creates a problem in that if the amount of misalignment of the resistance heating elements exceeds a certain level, the substrate becomes more susceptible to damage.

[0005] In consideration of the above circumstances, the present invention provides a fixing device and an image forming apparatus that can suppress damage to a substrate caused by thermal expansion of a resistance heating element. [Means for solving the problem]

[0006] A fixing device of the present invention includes a fixing belt formed in a cylindrical shape and rotating around its axis to heat toner on a medium, a pressure member forming a pressure region between the fixing belt and the pressure member and pressing the toner on the medium as the medium passes through the pressure region while rotating around its axis, and a heater extending in the axial direction of the fixing belt and contacting the inner surface of the fixing belt facing the pressure region to heat the fixing belt, wherein the heater has a plurality of resistance heating elements formed on one surface of a substrate at intervals in the axial direction, and the plurality of resistance heating elements include at least one first resistance heating element and at least one second resistance heating element formed at a position shifted to one side in a medium transport direction perpendicular to the axial direction with respect to the first resistance heating element, The amount of deviation between the first resistance heating element and the second resistance heating element is less than the dimension of the pressure region in the conveyance direction, and is set in the range of 0.1 mm or more and less than 4.5 mm.

[0007] An image forming apparatus according to the present invention includes the fixing device described above. [Effects of the Invention]

[0008] According to the present invention, damage to the substrate caused by the thermal expansion of the resistance heating element can be suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram (side view) showing the internal structure of an image forming apparatus according to one embodiment of the present invention. [Figure 2] FIG. 1 is a perspective view showing a fixing device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2. [Figure 4] FIG. 2 is a bottom view showing a heater of a fixing device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, Fr, Rr, L, R, U, and D indicate front, rear, left, right, top, and bottom. The front-to-back direction (transport direction), left-to-right direction (axial direction), and top-to-bottom direction are perpendicular to one another. Terms indicating directions and positions are used in this specification, but these terms are used for convenience of explanation and do not limit the technical scope of the present invention. Furthermore, the terms "upstream," "downstream," and similar terms refer to "upstream" and "downstream" in the transport direction of paper P (medium) and similar concepts. In each drawing, the dimensions and angles of components are not accurate and are shown schematically for the purpose of explanation.

[0011] An image forming apparatus 1 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram (side view) showing the image forming apparatus 1.

[0012] The image forming apparatus 1 is an electrophotographic printer. The image forming apparatus 1 has an apparatus main body 2 that has a substantially rectangular parallelepiped appearance. A paper feed cassette 3 that stores, for example, paper P (medium) is detachably provided at the bottom of the apparatus main body 2. A paper output tray 4 is provided on the top surface of the apparatus main body 2. Note that the paper P, which is an example of a medium, is not limited to being made of paper, and may be a resin sheet or the like.

[0013] The image forming apparatus 1 includes a paper feeder 5, an imaging device 6, and a fixing device 7. The paper feeder 5 is provided at the upstream end of a transport path 9A that extends from the paper feed cassette 3 to the paper output tray 4, and sends out paper P stored in the paper feed cassette 3 one sheet at a time to the transport path 9A. The imaging device 6 is provided in the middle of the transport path 9A, and forms a toner image on the transported paper P. The fixing device 7 is provided downstream of the transport path 9A, and thermally fixes the toner image to the paper P.

[0014] The conveying path 9A is provided with a pair of registration rollers 10A that temporarily block the conveyed paper P to correct (skew correct) the inclination of the paper P. Below the conveying path 9A, a reversing conveying path 9B is provided that branches off on the downstream side of the conveying path 9A and merges with the upstream side of the conveying path 9A. The reversing conveying path 9B is provided with a plurality of pairs of conveying rollers 10B that convey the paper P.

[0015] The image forming device 6 includes a toner container 11, a drum unit 12, and an optical scanning device 13. The toner container 11 is located at the upper front of the device main body 2 and contains, for example, black toner (developer). The drum unit 12 includes a photosensitive drum 14, a charging device 15, a developing device 16, and a transfer roller 17. The photosensitive drum 14 is formed in a substantially cylindrical shape and is driven to rotate about its axis by a motor (not shown). The charging device 15, the developing device 16, and the transfer roller 17 are arranged around the photosensitive drum 14 in the order of the image formation process. The transfer roller 17 contacts the photosensitive drum 14 from below to form a transfer nip. The optical scanning device 13 is located above the photosensitive drum 14 and emits scanning light toward the surface of the photosensitive drum 14.

[0016] The image forming apparatus 1 is provided with a control device 8 that controls the entire apparatus. The control device 8 may be configured with a processor, or may be configured with a logic circuit (hardware) formed in an integrated circuit or the like. When configured with a processor, the processor reads and executes programs stored in memory to perform various processes.

[0017] [Image formation processing] A control device 8 that controls the image forming apparatus 1 performs the following image forming process based on image data input from an external terminal.

[0018] The charging device 15 charges the surface of the photosensitive drum 14, and the optical scanning device 13 emits scanning light based on image data to form an electrostatic latent image on the photosensitive drum 14. The developing device 16 develops a toner image on the photosensitive drum 14 using toner supplied from the toner container 11. The paper feeder 5 feeds paper P one sheet at a time from the paper feed cassette 3 to the transport path 9A. The paper P is transported along the transport path 9A, skew-corrected by a pair of registration rollers 10A, and enters the transfer nip. The transfer roller 17 transfers the toner image on the photosensitive drum 14 to the surface of the paper P as it passes through the transfer nip. The fixing device 7 thermally fixes the toner image to the paper P. In the case of single-sided printing, the paper P that has passed through the fixing device 7 is discharged to the paper output tray 4.

[0019] In the case of double-sided printing, the paper P that has passed through the fixing device 7 switches back at the downstream end of the conveying path 9A and is sent to the reverse conveying path 9B. The paper P is conveyed by the conveying roller pair 10B, returned from the reverse conveying path 9B to the conveying path 9A again, and after skew correction by the registration roller pair 10A, is sent to the transfer nip. Thereafter, the toner image is transferred onto the paper P and thermally fixed, and the double-sided printed paper P is discharged onto the paper output tray 4.

[0020] [Fusing device] Next, the fixing device 7 will be described with reference to Figures 2 to 4. Figure 2 is a perspective view showing the fixing device 7. Figure 3 is a cross-sectional view taken along line III-III in Figure 2. Figure 4 is a bottom view showing the heater 22.

[0021] 2 and 3, the fixing device 7 includes a fixing belt 20, a pressure roller 21, a heater 22, and a heat equalizing member 23. The fixing belt 20 and the pressure roller 21 are supported by a frame (not shown), and the frame is fixed to the device body 2.

[0022] <Fixing belt> The fixing belt 20 is an endless belt formed in a generally cylindrical shape that is long in the left-right direction (axial direction). The fixing belt 20 is made of a heat-resistant and flexible material (polymer resin, metal, or a combination of polymer resin and metal). A pair of holding members 24 (see FIG. 2) is inserted into both left and right ends of the fixing belt 20. The pair of holding members 24 guide the fixing belt 20 to rotate around its axis while maintaining its generally cylindrical shape. The fixing belt 20 is supported by a frame (not shown) via the pair of holding members 24.

[0023] As shown in FIG. 3, a bridge member 25 and a support member 26 are provided in the space surrounded by the fixing belt 20. The bridge member 25 is formed, for example, from a metal material such as stainless steel into a generally rectangular cylindrical shape that is elongated in the left-right direction (axial direction), and is bridged between the pair of holding members 24. The support member 26 is fixed to the lower part of the bridge member 25. The support member 26 is formed, for example, from a heat-resistant and abrasion-resistant synthetic resin into a generally semi-cylindrical shape that is elongated in the left-right direction. The support member 26 curves along the inner surface of the fixing belt 20 and contacts the lower side of the inner surface of the fixing belt 20 (the side of the pressure region N). A fitting portion 26A into which the heater 22 is fitted is recessed in the lower part of the support member 26.

[0024] <Pressure roller> As shown in FIGS. 2 and 3, pressure roller 21, an example of a pressure member, is formed in a generally cylindrical shape that is long in the left-right direction. Pressure roller 21 has a metal core 21A and an elastic layer 21B, such as a silicone sponge, laminated on the outer circumferential surface of the metal core 21A (see FIG. 3). A drive motor M is connected to the left end of core 21A via a gear train (not shown) (see FIG. 2). Pressure roller 21 contacts fixing belt 20 from below, forming a pressure region N between itself and fixing belt 20. A toner image is fixed onto paper P as it passes through pressure region N. Note that pressure region N refers to the region extending from an upstream position where the pressure is 0 Pa, through a position where pressure is applied, to a downstream position where the pressure returns to 0 Pa.

[0025] The paper sheet P is transported with the center of its width in the left-right direction roughly aligned with the center of the pressure area N in the left-right direction (axial direction). For this reason, the fixing belt 20 (or the pressure area N) has a passing area A1 in the axial center that contacts the paper sheet P, and non-passing areas A2 on both sides in the axial direction that do not contact the paper sheet P (see FIG. 4). The transported paper sheet P always contacts the passing area A1 near the axial center, regardless of the size (left-right dimension) of the paper sheet P. In contrast, normal-sized paper sheets P (e.g., A4 size) contact both sides of the passing area A1 in the axial direction, but small-sized paper sheets P (e.g., A5, B5 size, etc.) do not contact the passing area A1.

[0026] <Heater> 3 and 4, heater 22 extends in the left-right direction (axial direction) of fixing belt 20 and is fitted into fitting portion 26A of support member 26. Heater 22 comes into contact with the inner surface of fixing belt 20 facing pressure region N, and heats fixing belt 20. As shown in FIG. 4, heater 22 has a substrate 30 and a plurality of (e.g., three) resistance heating elements 31 and 32.

[0027] (substrate) The substrate 30 is made of an insulator (electrically insulating material) such as ceramic, and is formed in the shape of a generally rectangular plate that is long in the left-right direction (axial direction). The axial dimension of the substrate 30 (heater 22) is set to be equal to or smaller than the axial dimension of the fixing belt 20. The dimension of the substrate 30 (heater 22) in the front-rear direction (transport direction) is set to be equal to or smaller than the dimension (D2) of the pressure region N in the transport direction (see FIG. 3).

[0028] (resistance heating element) The three resistance heating elements 31, 32 are each formed in a substantially rectangular shape from a metal material with high electrical resistance. As shown in FIG. 4, the three resistance heating elements 31, 32 are formed on the lower surface (one surface) of the substrate 30 at intervals in the left-right direction (axial direction). One resistance heating element 31 is disposed in the central region of the substrate 30 in the axial direction, and two resistance heating elements 32 are disposed on both sides of the substrate 30 in the axial direction, with a gap G1 between them. For ease of explanation, in this specification, the one resistance heating element 31 disposed in the central region of the axial direction will be referred to as the "first resistance heating element 31," and the two resistance heating elements 32 disposed on both sides of the axial direction will be referred to as the "second resistance heating element 32." The gap G1 is set to an insulation distance (creepage distance) that can prevent creepage discharge between adjacent resistance heating elements 31, 32.

[0029] The first resistance heating element 31 is formed shorter in the left-right direction (axial direction) than the second resistance heating element 32. As will be described in detail later, the heater 22 includes three resistance heating elements 31 and 32 to efficiently heat paper P of various sizes. The first resistance heating element 31 corresponds to the left-right width of a small-sized paper P, and all resistance heating elements 31 and 32 correspond to the left-right width of a normal-sized paper P. The three resistance heating elements 31 and 32 are arranged in a stepped pattern, for example, taking into consideration the wiring (such as individual electrodes 33 and 34 described later) on the substrate 30. Specifically, the second resistance heating element 32 is formed in a position shifted to one side in the transport direction (for example, downstream (rearward)) from the first resistance heating element 31. Arranging the three resistance heating elements 31 and 32 in a stepped pattern enables the heater 22 to be made compact while ensuring the insulation distance (creepage distance) between adjacent resistance heating elements 31 and 32. The amount of misalignment G2 between the first resistance heating element 31 and the second resistance heating element 32 refers to the distance between the center of the first resistance heating element 31 in the conveyance direction and the center of the second resistance heating element 32 in the conveyance direction. The amount of misalignment G2 is set to an insulation distance (creepage distance) that can prevent creepage discharge between the adjacent resistance heating elements 31, 32.

[0030] The left-right (axial) dimensions of the three resistance heating elements 31, 32, in other words, the dimension between both ends of the two second resistance heating elements 32 in the axial direction, are set to be shorter than the entire axial length of the fixing belt 20 and longer in the axial direction than the passing area A1 of the fixing belt 20. In other words, both axial sides of the two second resistance heating elements 32 face the non-passing area A2 of the fixing belt 20. In addition, the front-rear (conveying direction) dimensions of the three resistance heating elements 31, 32, in other words, the dimension (D1) between both ends of the first resistance heating element 31 and the second resistance heating element 32 in the conveying direction (see FIG. 4), are set to be equal to or smaller than the dimension (D2) in the conveying direction of the pressure area N (see FIG. 3).

[0031] As shown in FIG. 4, three individual electrodes 33, 34 and a common electrode 35 are formed on the lower surface of the substrate 30. The three individual electrodes 33, 34 and the common electrode 35 are formed, for example, from a metal material having a lower electrical resistance than the resistance heating elements 31, 32. The individual electrode 33 is connected to the downstream end (rear end) of the first resistance heating element 31, and the other individual electrodes 34 are connected to the downstream end of the second resistance heating element 32. The common electrode 35 is connected to the upstream ends (front ends) of all the resistance heating elements 31, 32. The individual electrodes 33, 34 and the common electrode 35 extend from the portions connected to the resistance heating elements 31, 32 toward both sides in the axial direction of the substrate 30. The individual electrodes 33, 34 and the common electrode 35 are electrically connected to devices (not shown) such as a power supply on both sides in the axial direction of the substrate 30.

[0032] The resistance heating elements 31 and 32, the individual electrodes 33 and 34, and the common electrode 35 are covered with a coating layer (not shown). The heater 22 is fitted into the fitting portion 26A of the support member 26, with the coating layer in contact with the inner surface of the fixing belt 20. The heater 22 receives the fixing belt 20 pressed against the pressure roller 21, thereby forming a pressure region N at the contact portion between the fixing belt 20 and the pressure roller 21. Electric power supplied from a power source is passed through the resistance heating elements 31 and 32 in the conveyance direction (short direction), causing the resistance heating elements 31 and 32 to generate heat. The fixing device 7 is provided with a temperature detection unit (not shown) that detects the temperature of the heater 22. The heater 22, the drive motor M, the temperature detection unit, etc. are electrically connected to the control device 8, the power source (not shown), etc. The control device 8 appropriately controls the power source, the heater 22, etc.

[0033] <Heat-equalizing member> In the fixing device 7 according to this embodiment, a heat equalizing member 23 is provided on the heater 22 to prevent excessive temperature rise in the non-passage region A2 and both axial ends of the pass region A1 where the paper P does not pass (see FIG. 3). The heat equalizing member 23 is formed in a substantially rectangular plate shape from a metal material such as an aluminum alloy. The heat equalizing member 23 extends in the axial direction so as to be equal to or smaller than the left-right (axial) dimension of the heater 22. The heat equalizing member 23 contacts the upper surface of the heater 22 (substrate 30) on the side opposite the fixing belt 20 (pressure region N) and is supported by a support member 26 (see FIG. 3). The heat equalizing member 23 absorbs heat emitted from the heater 22 and transfers it in the axial direction, thereby making the temperature of the heater 22 uniform in the axial direction. As a result, the temperature of the fixing belt 20 is also generally uniform in the axial direction, preventing excessive temperature rise in the non-passage region A2.

[0034] [Fixing process] Here, the operation (fixing process) of the fixing device 7 will be described. The control device 8 controls the drive motor M to rotate the pressure roller 21 around its axis. The fixing belt 20 rotates following the rotation of the pressure roller 21 (see the arrow in FIG. 3). The control device 8 also receives a detection signal from the temperature detection unit and controls the heater 22 (or power supply) to maintain a preset target temperature. The resistance heating elements 31 and 32 of the heater 22 generate heat when energized, and heat the fixing belt 20 (pressure region N).

[0035] At this time, the control device 8 changes which of the three resistance heating elements 31, 32 is heated (energized) depending on the size of the paper P. For example, when a normal-sized paper P passes through the pressure region N, the control device 8 executes control to cause all of the resistance heating elements 31, 32 to generate heat. On the other hand, when a small-sized paper P passes through the pressure region N, the control device 8 executes control to cause one resistance heating element 31 to generate heat. This makes it possible to heat only the necessary portion of the fixing belt 20 (pressure region N) in accordance with the size of the paper P. As a result, it is possible to minimize the amount of power used. It is also possible to prevent excessive temperature rise at both ends of the fixing belt 20 in the axial direction.

[0036] When the fixing belt 20 (heater 22) reaches the target temperature, the control device 8 starts the image formation process already described. The paper P onto which the toner image has been transferred enters the pressure area N. The fixing belt 20 heats the toner (toner image) on the paper P as it passes through the pressure area N while rotating around its axis. The pressure roller 21 pressurizes the toner on the paper P as it passes through the pressure area N while rotating around its axis. The toner image is then fixed to the paper P, forming a fixed image on the paper P. The paper P with the fixed image is then discharged to the paper output tray 4.

[0037] [Misalignment of adjacent resistance heating elements] Incidentally, since the resistance heating elements 31 and 32 generate heat and thermally expand on the substrate 30, forces in opposite directions may act between adjacent resistance heating elements 31 and 32 (see the arrows indicated by two-dot chain lines in FIG. 4 (only the right side is shown in FIG. 4)). As already explained, the second resistance heating element 32 is shifted downstream from the first resistance heating element 31. If the amount of shift G2 exceeds a certain level, the opposite forces caused by the thermal expansion of the resistance heating elements 31 and 32 may cause cracks or other damage to the substrate 30. Therefore, in the fixing device 7 according to this embodiment, the amount of shift G2 between the first resistance heating element 31 and the second resistance heating element 32 is set to be less than the dimension (D2) of the pressure region N in the transport direction, in the range of 0.1 mm or more and less than 4.5 mm. 4, the arrows indicating the opposing forces are shown pointing in the transport direction, but more precisely, the opposing forces also point in various directions on the plane because the resistance heating elements 31 and 32 thermally expand in all directions (axial direction and transport direction) on a plane. As such, because the opposing forces point in various directions on a plane, it is estimated that complex forces act on the substrate 30 between the adjacent resistance heating elements 31 and 32.

[0038] In the fixing device 7 according to the present embodiment described above, the second resistance heating element 32 is positioned offset to one side (downstream) in the transport direction relative to the first resistance heating element 31. The offset G2 between the first resistance heating element 31 and the second resistance heating element 32 is less than the dimension of the pressure region N in the transport direction and is set in the range of 0.1 mm to less than 4.5 mm. The applicant has estimated through experiments that this range of offset G2 is effective in weakening the forces acting in opposite directions between adjacent resistance heating elements 31 and 32 when the heater 22 is operating. This effectively prevents damage to the substrate 30 due to thermal expansion of the resistance heating elements 31 and 32.

[0039] In the fixing device 7 according to the present embodiment, the heater 22 includes three resistance heating elements 31 and 32, but this is not limiting and the heater may include two or more resistance heating elements 31 and 32. The heater 22 includes one first resistance heating element 31 and two second resistance heating elements 32, but the present invention is not limited to this. The heater 22 may include, for example, two or more first resistance heating elements 31 and one or three or more second resistance heating elements 32 (not shown). In this case, the three or more resistance heating elements 31 and 32 may be arranged in a single staircase or a staggered pattern (not shown).

[0040] Furthermore, in the heater 22 of the fixing device 7 according to this embodiment, the second resistance heating element 32 is formed at a position shifted downstream in the transport direction from the first resistance heating element 31, but this is not limiting and the second resistance heating element 32 may be formed at a position shifted upstream in the transport direction from the first resistance heating element 31 (not shown).

[0041] Furthermore, in the fixing device 7 according to this embodiment, the paper P passes through the center of the pressure region N in the axial direction, but this is not limiting, and the paper P may pass through a position closer to one side in the axial direction of the pressure region N (not shown). In this case, the non-passing region A2 is set only on one side in the axial direction of the fixing belt 20 (or the pressure region N).

[0042] Furthermore, in the fixing device 7 according to this embodiment, the pressure roller 21 is driven to rotate, and the fixing belt 20 is driven to rotate, but this is not limited to this, and the fixing belt 20 may be driven to rotate, and the pressure roller 21 may be driven to rotate.

[0043] Furthermore, in the description of the above embodiment, the present invention has been applied to a monochrome image forming device 1 as an example, but this is not limiting and the present invention may also be applied to, for example, a color printer, a copier, a facsimile, or a multifunction device.

[0044] The above-described embodiment shows one aspect of the fixing device and image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above-described embodiment. The present invention may be variously changed, substituted, or modified without departing from the spirit of the technical concept, and the claims include all embodiments that may fall within the scope of the technical concept. [Explanation of symbols]

[0045] 1. Image forming device 7 Fixing device 20 Fixing belt 21 Pressure roller (pressure member) 22 Heater 30 boards 31 First resistance heating element 32 Second resistance heating element G2 deviation amount N pressure area P Paper (media)

Claims

1. a fixing belt formed in a cylindrical shape and rotating around its axis to heat the toner on the medium; a pressure member that forms a pressure region between itself and the fixing belt and that pressurizes the toner on the medium that passes through the pressure region while rotating around its axis; a heater extending in the axial direction of the fixing belt, contacting the inner surface of the fixing belt facing the pressure area, and heating the fixing belt; the heater has a plurality of resistance heating elements formed on one surface of the substrate at intervals in the axial direction, Multiple of the aforementioned resistance heating elements are at least one first resistive heating element; The present invention comprises at least one second resistance heating element formed at a position offset from the first resistance heating element in one direction of transport of the medium that is perpendicular to the axial direction, The fixing device is characterized in that the amount of displacement between the first resistance heating element and the second resistance heating element is less than the dimension of the pressurized area in the transport direction and is set to a range of 0.1 mm or more and less than 4.5 mm.

2. An image forming apparatus comprising the fixing device according to claim 1.

Images