Fixing device, and image forming apparatus

Abstract

To simplify a current path for grounding by using only a single resistance element.SOLUTION: A fixing device 20 comprises: an endless fixing belt 21; a pressure roller 22 that is brought into pressure contact with the fixing belt 21; a planar heater 23 that is provided inside the fixing belt 21, receives pressure-contact pressure by the pressure roller 22 through the fixing belt 21, and heats the fixing belt 21; a stay sheet metal 25 that is provided inside the fixing belt 21, and support the planar heater 23; a torsion spring 33 that is in contact with an end of a stay sheet metal 25 projecting to the outside of an end of the fixing belt 21; an upper conductive plate 34 that is in contact with an end of the pressure roller 22; and a resistance element 35. The torsion spring 33 is locked and connected to the upper conductive plate 34, and the upper conductive plate 34 is connected to a body frame with the resistance element 35 therebetween.SELECTED DRAWING: Figure 4

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] In some fixing devices, a pressure roller is pressed against an endless fixing belt to form a nip area between the endless fixing belt and the pressure roller, and recording paper is passed through this nip area to fix an image formed on the recording paper. In such fixing devices, for safety reasons, it is preferable that the fixing belt and the pressure roller are appropriately connected to ground points of the fixing device.

[0003] The image forming apparatus described in Patent Document 1 is equipped with a film heating type fixing unit. This fixing unit includes a cylindrical film, a heater that contacts the inner surface of the film, and a pressure roller that forms a nip area with the heater via the film. The heater is grounded to the frame ground (hereinafter referred to as FG) of the apparatus body via the film, the pressure roller, and a resistive element. In this configuration, if a discharge occurs between the film and FG, the voltage dividing effect of the resistive element between the pressure roller and FG cannot be obtained, and a high potential surge voltage is applied to the heater's protective layer, causing insulation breakdown of the heater's protective layer. Therefore, a lightning arrester that discharges at a stable voltage regardless of the surge voltage polarity is installed in the power line connected to the heater to prevent the application of such a high potential surge voltage.

[0004] Furthermore, the fixing device described in Patent Document 2 includes a fixing film, a heater for heating the fixing film, and a pressure roller that is pressed against the fixing film to form a nip area between it and the fixing film, and the pressure roller has a conductive rubber and an insulating or highly resistive release layer. Two resistance elements with different resistance values ​​are provided in parallel between the pressure roller and a grounded portion, and the pressure roller is grounded by appropriately selecting the two resistance elements, and the voltage applied to the fixing belt is gradually increased until it reaches a specified voltage value, thereby preventing pinhole leaks in the release layer of the pressure roller. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-257466 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-117672 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, in Patent Document 1, the heater is grounded via the film, pressure roller, and resistive element. However, because the film is made of an insulating material, it cannot be said that the heater, film, and pressure roller are grounded for direct current, and the configuration is designed to deal with pulsed surge voltages.

[0007] Furthermore, in Patent Document 2, the pressure roller is grounded through one of two resistance elements, but there is no mention of grounding the heater.

[0008] Here, if a jam occurs between the fixing belt and the pressure roller, for example, the user will have to remove the recording paper, so to ensure safety, it is preferable to ground the fixing belt, heater, pressure roller, etc. through resistor elements with appropriate resistance values.

[0009] However, neither Patent Document 1 nor Patent Document 2 is configured to ground the fixing belt and the pressure roller through their respective resistance elements.

[0010] Furthermore, when two current paths are provided to ground the fixing belt and the pressure roller through their respective resistance elements, there is a problem that the fixing device becomes larger and the structure becomes more complicated.

[0011] The present invention has been made in view of the above circumstances, and has as its object to use only a single resistance element while grounding both the fixing belt and the pressure roller, and to simplify the current path for grounding. [Means for solving the problem]

[0012] 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 provided inside the fixing belt that receives the pressure of the pressure roller through the fixing belt and heats the fixing belt, a support metal plate provided inside the fixing belt and supporting the heater, a first conductive member that contacts the end of the support metal plate that protrudes outside the end of the fixing belt, a second conductive member that contacts the end of the pressure roller, and a resistance element, wherein the first conductive member is connected by engaging with the second conductive member, and the second conductive member is connected to the device main body via the resistance element.

[0013] 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]

[0014] According to the present invention, while both the fixing belt and the pressure roller are grounded, only a single resistance element is used, and the current path for grounding can be simplified. [Brief explanation of the drawings]

[0015] [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 showing the internal structure of the image forming apparatus. [Figure 4] 2 is a perspective view showing one end of a main body frame on the front side where a fixing device is provided, viewed obliquely from below. FIG. [Figure 5] FIG. 2 is a perspective view showing a fixing device. [Figure 6] 7A and 7B are a front view and a cross-sectional view of the fixing device taken along line bb in FIG. 7A. [Figure 7] 6(A) and 6(B) are a side view showing the fixing device and a cross-sectional view showing the fixing device taken along line aa in FIG. 6(A). [Figure 8] FIG. 2 is an enlarged side view showing one front end of the main body frame. [Figure 9] 3 is an enlarged perspective view showing the periphery of one end of a stay metal plate, a torsion spring, and an upper conductive plate in the fixing device. FIG. [Figure 10] FIG. 2 is an enlarged perspective view showing the periphery of an upper conductive plate and a shaft of a pressure roller in the fixing device. [Figure 11] FIG. 4 is a cross-sectional view showing the shape of the end of the shaft of the pressure roller. [Figure 12] 2 is an enlarged perspective view showing the periphery of an upper conductive plate, a resistance element, and a lower conductive plate in the fixing device; FIG. [Figure 13] 10 is a diagram used to explain a first current path from a stay metal plate to a main body frame in a fixing device, and a second current path from a pressure roller to a main body frame. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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 12, 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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 .

[0022] 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. Next, the recording paper P is transported to fixing device 20, which heats and pressurizes 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.

[0023] Fig. 3 is a perspective view showing the internal structure of image forming apparatus 10 of this embodiment. As shown in Fig. 3, image forming apparatus 10 has a main body frame 30 made by combining synthetic resin molded members and sheet metal, and each component of image forming apparatus 10 is supported by main body frame 30. A space Sp into which paper feed cassette 4 is inserted and removed is provided below main body frame 30, and image forming unit 11 is provided at the back side above this space Sp, and fixing device 20 is provided at the front side.

[0024] 4 shows the front end of the main body frame 30 on which the fixing device 20 is mounted, viewed from diagonally below. As shown in Fig. 4, a metal frame side plate 31 is provided at the front end of the main body frame 30, and supports one end of a shaft 22A of a pressure roller 22 of the fixing device 20, which will be described in detail later, and one end 25A of a stay metal plate 25 of the fixing belt 21 protrudes from the frame side plate 31.

[0025] Next, the fixing device 20 of this embodiment will be described in detail. Fig. 5 is a perspective view showing the fixing device 20. Figs. 6A and 6B are a front view showing the fixing device 20 and a cross-sectional view showing the fixing device 20 taken along line bb in Fig. 7A. Figs. 7A and 7B are a side view showing the fixing device 20 and a cross-sectional view showing the fixing device 20 taken along line aa in Fig. 6A.

[0026] 5, 6(A), (B), and 7(A), (B), the fixing device 20 includes a fixing belt 21, a pressure roller 22, a planar heater 23, a heater holder 24, a stay metal plate 25, and a pair of holding portions 26. The planar heater 23 corresponds to the heater in the claims, and the stay metal plate 25 corresponds to the support metal plate in the claims.

[0027] 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.

[0028] The pair of holding portions 26 are molded products of synthetic resin and each have an annular frame portion 26A, and each annular frame portion 26A is inserted inside both end portions of the fixing belt 21, with the outer surface of each annular frame portion 26A contacting the inner surface of the end portion of the fixing belt 21 to hold the fixing belt 21.

[0029] 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, and a stay metal plate 25 that supports the heater holder 24. The sheet heater 23, heater holder 24, and stay metal plate 25 are provided to extend in the longitudinal direction of the fixing belt 21 and protrude from both ends of the fixing belt 21. The heater holder 24 is a molded product made of synthetic resin.

[0030] The stay metal plate 25 is formed, for example, by sheet metal processing into a U-shaped cross section, and has sufficient strength and rigidity. Each holding portion 26 is supported by the main body frame 30 of the fixing device 20, both ends of the stay metal plate 25 are supported by the respective holding portions 26, the heater holder 24 is supported by the stay metal plate 25, and the sheet heater 23 is held by the heater holder 24 made of synthetic resin. Therefore, the stay metal plate 25 is supported by each holding portion 26 and supports the heater holder 24 and the sheet heater 23. As a result, each holding portion 26, the stay metal plate 25, the heater holder 24, and the sheet heater 23 are supported integrally.

[0031] Pressure roller 22 is a metal cylinder or columnar body whose outer surface is covered with a layer of synthetic resin or the like. Shaft 22A of pressure roller 22 is rotatably supported by slide bearing 27 and is provided parallel to the center of rotation of fixing belt 21. Slide bearing 27 is a molded part made of synthetic resin and is open on the top side, receiving and rotatably supporting shaft 22A of pressure roller 22 through this open space.

[0032] The pair of holding parts 26 are supported on both sides of the main body frame 30 of the fixing device 20 so as to be movable in directions toward and away from the shaft 22A of the pressure roller 22, and the fixing belt 21 is disposed above the pressure roller 22. Each holding part 26 is urged downward by a spring or the like (not shown) to move closer to the shaft 22A of the pressure roller 22, and the stay metal plate 25, heater holder 24, and planar heater 23 are also urged downward to move. As a result, the fixing belt 21 approaches and is pressed against the pressure roller 22, and the pressure roller 22 is pressed against the planar heater 23 via the fixing belt 21, so that the outer circumferential surfaces of the pressure roller 22 and the fixing belt 21 are pressed against each other over a wide range, forming a nip region N over this wide range.

[0033] When the rotational driving force of a motor (not shown) is transmitted to shaft 22A of pressure roller 22 and pressure roller 22 is rotated in the direction of the arrow, fixing belt 21 is rotated in the opposite direction to pressure roller 22. Furthermore, planar heater 23 is made to generate heat to heat fixing belt 21, and the temperature of fixing belt 21 is set to a specified temperature suitable for fixing.

[0034] 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.

[0035] If a jam or the like occurs between the fixing belt 21 and the pressure roller 22, the user will have to remove the recording paper P, so to ensure the safety of the work, the stay metal plate 25 and the pressure roller 22 are grounded through resistive elements with appropriate resistance values. Also, because the fixing belt 21, the planar heater 23, and the heater holder 24 are in contact with the stay metal plate 25 or the insulation distance is very short, the fixing belt 21, the planar heater 23, and the heater holder 24 are also grounded through the resistive elements.

[0036] However, providing two current paths that ground the stay metal plate 25 and the pressure roller 22 through their respective resistance elements would result in an increase in the size of the device and a more complicated configuration. For this reason, the fixing device 20 of this embodiment uses only a single resistance element, and aims to simplify the current path for grounding.

[0037] As shown in FIG. 4, one end of the main body frame 30 supports one end of the shaft 22A of the pressure roller 22 of the fixing device 20, and one end 25A of the stay metal plate 25 protrudes from the fixing belt 21.

[0038] 8 is an enlarged side view showing one end of the front side of the main body frame 30. As shown in FIGS. 4 and 8, one end of the main body frame 30 is provided with a frame side plate 31, a torsion spring 33, an upper conductive plate 34, a resistance element 35, a lower conductive plate 36, and a screw 37. The torsion spring 33, the upper conductive plate 34, the lower conductive plate 36, and the screw 37 are made of metal and are conductive. The torsion spring 33 corresponds to a first conductive member in the claims, the upper conductive plate 34 corresponds to a second conductive member in the claims, and the lower conductive plate 36, the screw 37, and the frame side plate 31 correspond to at least one other conductive member in the claims.

[0039] As described above, the main body frame 30 is a combination of a synthetic resin molded member and a metal sheet member. The upper conductive plate 34 and the lower conductive plate 36 are fixed in their respective predetermined positions in the synthetic resin molded member of the main body frame 30 and are insulated from each other. The resistor element 35 is connected to the upper conductive plate 34 and the lower conductive plate 36 via lead wires 35A and 35B of the resistor element 35. The screws 37 connect and fix the lower conductive plate 36 to the metal frame side plate 31, thereby establishing electrical continuity between the lower conductive plate 36 and the frame side plate 31.

[0040] 9 is an enlarged perspective view showing the periphery of one end 25A of the stay metal sheet 25, the torsion spring 33, and the upper conductive plate 34. As shown in FIGS. 9 and 8, the ring-shaped portion 33A of the torsion spring 33 is fitted into a protrusion 28 that is a separate member provided at one end of the holding portion 26, thereby supporting the torsion spring 33. One arm 33B of the torsion spring 33 contacts one end 25A of the stay metal sheet 25 for electrical conduction, and the other arm 33C of the torsion spring 33 is bent and inserted into an engagement hole 34A of the upper conductive plate 34 for contact and electrical conduction. The torsion spring 33 biases each arm 33B, 33C of the torsion spring 33 in a direction that spreads them apart, so that even if the stay metal plate 25 moves in conjunction with the movement of each holding portion 26, the contact of one arm 33B with one end 25A of the stay metal plate 25 and the contact of the other arm 33C with the engagement hole 34A of the upper conductive plate 34 are maintained.

[0041] Fig. 10 is an enlarged perspective view showing the periphery of the upper conductive plate 34 and the shaft 22A of the pressure roller 22. As shown in Fig. 10, the upper conductive plate 34 has a bent portion 34B, and a U-shaped tip portion 34C is formed on the tip side of this bent portion 34B when viewed from above. The bent portion 34B is elastically deformed, and the elastic force of the bent portion 34B presses the tip portion 34C against the shaft 22A of the pressure roller 22, thereby establishing electrical continuity.

[0042] Figure 11 shows the cross-sectional shape of the end of shaft 22A of pressure roller 22. As shown in Figure 11, the end of shaft 22A of pressure roller 22 has a conical shape with an apex that protrudes most outward in the direction of extension of shaft 22A, at the portion that serves as the center of rotation of pressure roller 22. Therefore, even when shaft 22A of pressure roller 22 rotates, the position of the apex of shaft 22A does not change, and the apex of shaft 22A is always pressed against a fixed position of tip end 34C of bent portion 34B, thereby stably maintaining conductivity between shaft 22A of pressure roller 22 and upper conductive plate 34.

[0043] 12 is an enlarged perspective view showing the periphery of the upper conductive plate 34, the resistive element 35, and the lower conductive plate 36. As shown in FIGS. 12 and 8, lead wires 35A and 35B are drawn out from both ends of the resistive element 35, respectively.

[0044] The upper conductive plate 34 has a bent portion 34D, and a tip portion 34E is formed at the tip side of the bent portion 34D, which is bent into a triangular shape when viewed from above. The bent portion 34D is elastically deformed, and the elastic force of the bent portion 34D causes the lead wire 35A at one end of the resistor element 35 to be sandwiched between the tip portion 34E of the bent portion 34D and the synthetic resin molded member of the main body frame 30, and the lead wire 35A at one end of the resistor element 35 is pressed against the upper conductive plate 34, thereby establishing electrical continuity.

[0045] Similarly, the lower conductive plate 36 has a bent portion 36A, and a tip portion 36B bent into a triangular shape when viewed from above is formed at the tip side of this bent portion 36A. The bent portion 36A is elastically deformed, and the elastic force of the bent portion 36A sandwiches the lead wire 35B at the other end of the resistance element 35 between the tip portion 36B of the bent portion 36A and the synthetic resin molded member of the main body frame 30, so that the lead wire 35B at the other end of the resistance element 35 is pressed against the lower conductive plate 36, thereby establishing electrical conduction.

[0046] Furthermore, as shown in Figure 12, screws 37 are screwed into the metal frame side plate 31 from the holes in the lower conductive plate 36 through the synthetic resin molded member of the main frame 30, thereby fixing the lower conductive plate 36 and establishing electrical continuity between the lower conductive plate 36 and the frame side plate 31.

[0047] As described above, one arm 33B of torsion spring 33 is in contact with one end 25A of stay metal plate 25 and is electrically connected, the other arm 33C of torsion spring 33 is in contact with upper conductive plate 34 and is electrically connected, one end 22B of shaft 22A of pressure roller 22 is in contact with bent portion 34B of upper conductive plate 34 and is electrically connected, bent portion 34D of upper conductive plate 34 is in contact with lead wire 35A at one end of resistor element 35 and is electrically connected, bent portion 36A of lower conductive plate 36 is in contact with lead wire 35B at the other end of resistor element 35 and is electrically connected, and screws 37 provide electrical connection between lower conductive plate 36 and frame side plate 31. In addition, frame side plate 31 is fixed to a sheet metal member of main body frame 30 and is electrically connected.

[0048] 13 , a first current path is formed from the stay metal plate 25 → torsion spring 33 → upper conductive plate 34 → resistance element 35 → lower conductive plate 36 → screw 37 → frame side plate 31 → main frame 30, and the stay metal plate 25 is grounded to the main frame 30 via the resistance element 35. Furthermore, because the fixing belt 21, sheet heater 23, and heater holder 24 are in contact with the stay metal plate 25 or the insulation distance is very short, the fixing belt 21, sheet heater 23, and heater holder 24 are also grounded to the main frame 30 via the resistance element 35. Furthermore, a second current path is formed from the shaft 22A of the pressure roller 22 → upper conductive plate 34 → resistance element 35 → lower conductive plate 36 → screw 37 → frame side plate 31 → main frame 30, and the pressure roller 22 is grounded to the main frame 30 via the resistance element 35.

[0049] Both the first current path and the second current path pass AC and DC currents, ensuring safety when the user performs tasks such as removing recording paper stuck between the fixing belt 21 and the pressure roller 22.

[0050] Furthermore, when comparing the first and second current paths, the upper conductive plate 34, resistive element 35, lower conductive plate 36, screws 37, and frame side plate 31 are shared, and only the torsion spring 33 is a component exclusive to the first current path. Therefore, only a single resistive element is used, and the current path for grounding is simplified.

[0051] Furthermore, since the stay metal plate 25 is connected to the upper conductive plate 34 via the torsion spring 33 and the pressure roller 22 is connected to the upper conductive plate 34, the potential of the stay metal plate 25 and the potential of the pressure roller 22 can be kept equal and stable.

[0052] In the above embodiment, a monochrome printer is used as the image forming apparatus according to the present invention, but this is merely an example, and other image forming apparatuses such as color printers or other electronic devices, for example, multifunction machines, copiers, facsimile machines, etc., may also be used.

[0053] Furthermore, the configuration and processing described with reference to FIGS. 1 to 13 are merely one embodiment of the present invention, and the present invention is not limited to these configurations and processing. [Explanation of symbols]

[0054] 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 25 Stay sheet metal 26 Holding part 27 Plain bearing 30 Main frame 31 Frame side panel 33 Torsion spring 34 Upper conductive plate 35 Resistor element 36 Lower conductive plate 37 Bis

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 support plate provided inside the fixing belt and supporting the heater; a first conductive member that contacts an end of the support metal plate that protrudes outward from an end of the fixing belt; a second conductive member that contacts an end of the pressure roller; a resistive element; The fixing device has the first conductive member engaged and connected to the second conductive member, and the second conductive member connected to the device main body via the resistance element.

2. The end of the shaft of the pressure roller is formed into a conical shape with a top portion that protrudes most outward in the direction of extension of the shaft, the top portion being the rotation center of the pressure roller, 2. The fixing device according to claim 1, wherein the second conductive member is pressed against the top of the cone by the elastic force of the second conductive member.

3. 2. The fixing device according to claim 1, wherein the first conductive member is pressed against the supporting metal plate by the elastic force of the first conductive member.

4. 2. The fixing device according to claim 1, wherein the resistance element is connected to a main body frame of the fixing device via at least one other conductive member.

5. 2. The fixing device according to claim 1, wherein the shaft of the pressure roller is rotatably supported by a sliding bearing made of synthetic resin.

6. a fixing device according to any one of claims 1 to 5; 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