Fixing device and image forming apparatus

Abstract

To provide a fixing device that achieves space saving, and can prevent a reduction in durability due to damage to constituent members.SOLUTION: A fixing device comprises: a pair of rollers; a swingable pressure lever 10 that is pivotally supported at one end and has a spring 15 locked to the other end, and presses one of the pair of rollers to the other; a cam member 20 that displaces the pressure lever 10 between a position for maintaining the pressure contact state of the pair of rollers and a position for releasing the state; and a cam receiving member 30 that is disposed at a portion to be pressed of the pressure lever 10 pressed by the cam member 20. The cam receiving member 30 has a cross-sectional U-shape fitting to the pressure lever 10 so that a concave part covers the portion to be pressed. In a width direction orthogonal to a longitudinal direction of the pressure lever 10, the length W of an area where the cam member 20 and the cam receiving member 30 are in contact with each other is three times or more and seven times or less the thickness t of the pressure lever, and the center L of the load of a pressing force applied by the cam member 20 via the cam receiving member 30 matches the center C of the thickness of the pressure lever 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fixing device and an image forming apparatus. [Background technology]

[0002] A known fixing device installed in an image forming device such as a copier, printer, or facsimile machine is equipped with a heating roller and a pressure roller, which are pressed together to form a fixing nip where a recording medium is passed through and an image on the recording medium is fixed by heat and pressure.

[0003] The pressure / release mechanism of the pressure roller in such a fixing device is made up of a plurality of members for operating the pressure lever (see, for example, Patent Documents 1 and 2).

[0004] Patent Document 1 discloses a fixing device having a pressure mechanism including a pressure arm and a rotating arm, pressure application and depressurization operations performed by a cam and a cam follower, a stopper mechanism to prevent the pressure roller from getting too close to the fixing roller, and a configuration in which the pressure force (axis-to-axis distance) is controlled by an adjustment lever and an adjustment screw. Patent document 2 discloses a configuration that includes a pressure lever, a release lever, a member for rotating the pressure lever in the pressure release direction against the biasing direction of the pressure lever, a fixing lever for fixing the fixing device to the mounting table, and a connecting member that is linked to the rotation of the release lever, making it possible to release the fixing device in conjunction with the release of pressure.

[0005] In recent years, there has been a demand for space-saving and cost-reducing features in image forming apparatuses, and the same is true for the fixing devices installed in them. However, the fixing device of Patent Document 1 has a complex configuration with a large number of components constituting the pressure / release mechanism, which requires space to accommodate them. Furthermore, the fixing device of Patent Document 2 is configured to require space inside the main body for a pressure release lever that operates only when the fixing device is removed. Summary of the Invention [Problem to be solved by the invention]

[0006] Furthermore, in the fixing device of Patent Document 2, when the fixing device is removed from the main body to clear a jam, the release lever and pressure release cam work together to release the pressure, resulting in a depressurized state. Therefore, when the fixing device is installed, continuous load is applied to the fixing member and pressure member, which causes deformation of the nip portion due to compressive strain of the members and durability issues such as shortened part life.

[0007] One way to save space in a fixing device is to make the components smaller and thinner, but this can lead to problems due to reduced strength, etc. In particular, if the pressure lever is made of a single sheet metal member to save space, the repeated load on the part that receives pressure from the cam member can cause deformation or damage to the member (see Figure 8), which poses a problem of reducing the durability of the fixing device.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fixing device that can achieve space saving and prevent a decrease in durability due to damage to constituent members. [Means for solving the problem]

[0009] In order to solve the above problem, the fixing device of the present invention comprises a pair of rollers that are pressed against each other so as to be able to come into and out of contact with each other and that sandwich and transport a recording medium; a pressure lever that is pivotally supported at one end and has a spring attached to the other end and that presses one of the pair of rollers against the other; a cam member that displaces the pressure lever between a position that maintains the pressure contact state of the pair of rollers and a position that releases it; and a cam receiving member that is disposed on the pressed portion of the pressure lever that is pressed by the cam member, wherein the cam receiving member has a substantially U-shaped cross section and a recess that fits into the pressure lever so as to cover the pressed portion, and the length of the area where the cam member and the cam receiving member contact in the width direction perpendicular to the longitudinal direction of the pressure lever is between three and seven times the thickness of the pressure lever, and the center of the load of the pressing force exerted by the cam member via the cam receiving member coincides with the center of the thickness of the pressure lever. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a fixing device that can achieve space saving and prevent a decrease in durability due to damage to constituent members. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating the configuration of a fixing device according to an embodiment of the present invention. [Figure 2] FIG. 10 is an explanatory diagram of dimensions of a pressure lever and a cam receiving member. [Figure 3] 10 is a table showing the relationship between the dimensions of the pressure lever and the cam receiving member and whether or not they are damaged. [Figure 4] 10A and 10B are explanatory views showing an example of a cam receiving member constituted by a cover member and an intermediate member. [Figure 5] FIG. 4 is an explanatory diagram of dimensions of a cover member and an intermediate member. [Figure 6] 10A and 10B are explanatory views showing an example of a cam receiving member constituted by a cover member and an intermediate member. [Figure 7] 1 is a schematic diagram illustrating the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 8] FIG. 1 is a schematic diagram illustrating an example of a conventional fixing device. DETAILED DESCRIPTION OF THE INVENTION

[0012] The fixing device and image forming apparatus according to the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments, and can be modified, added, modified, deleted, or otherwise altered within the scope of what can be conceived by a person skilled in the art. Any embodiment that achieves the functions and effects of the present invention is within the scope of the present invention.

[0013] [Fixing device] FIG. 1A is a side view showing a schematic configuration of a fixing device according to one embodiment of the present invention, and FIGS. 1B and 2 are cross-sectional views of a portion indicated by AA in FIG. 1A. As shown in FIG. 1(A), the fixing device of this embodiment comprises a pair of rollers 1 and 2 that are capable of pressing against each other and moving toward and away from each other to sandwich and transport a recording medium, a pressure lever 10 that is pivotally supported at one end and has a spring 15 attached to the other end, and that presses one of the pair of rollers (the roller indicated by reference numeral 2) against the other (the roller indicated by reference numeral 1), a cam member 20 that displaces the pressure lever 10 between a position that maintains the pressure contact state of the pair of rollers 1 and 2 and a position that releases it, and a cam receiving member 30 that is disposed in the pressed portion of the pressure lever 10 that is pressed by the cam member 20.

[0014] The pair of rollers 1 and 2 comprises a heating roller 1 heated by a heating means 6 such as a heater, and a pressure roller 2 pressed against the heating roller 1 by a pressure lever 10 . In a mode in which the fixing device of this embodiment is installed in an electrophotographic image forming apparatus, the heating roller 1 is sometimes called a fixing roller.

[0015] A temperature detection member is disposed near the surface of the heating roller 3. The device also includes an entrance guide plate 4 that guides the recording medium, which is the object to be conveyed and has been conveyed to the fixing device, between the rollers, and a separation claw 5 that separates the recording medium that has been discharged from between the rollers.

[0016] The pressure lever 10 is made of a single sheet metal member and has a fulcrum 12 which is supported by a shaft and serves as the center of rotation, and a hook portion 13 which engages the spring 15. The pressure lever 10 presses the pressure roller 2 by the elastic force of the spring 15.

[0017] A cam member 20 and a cam receiving member 30 are disposed between the pressure roller 2 and the hook portion 13 in the longitudinal direction (the X direction in FIG. 1(A)). The pressure lever 10 is actuated by the forward and reverse rotation of the cam member 20. The cam member 20 rotates (pushes down) the pressure lever 10 against the action of the spring 15, thereby releasing the pressure on the pressure roller 2. Meanwhile, when the cam member 20 reaches the bottom dead center, the elastic force of the spring 15 causes the pressure lever 10 to press against the pressure roller 2.

[0018] 1(B), 2(A) and 2(B) are cross-sectional views of the pressing lever 10 taken along the line AA in the width direction perpendicular to the longitudinal direction of the pressing lever 10. FIG. The cam receiving member 30 is a member having a substantially U-shaped cross section that fits with the pressing lever 10 so that the recess covers the pressed portion, and is provided so as to surround the plate thickness of the pressing lever 10 in the width direction. Furthermore, the cam receiving member 30 is arranged so that in the width direction (Y direction in Figure 1(B)) perpendicular to the longitudinal direction (X direction in Figure 1(A)) of the pressure lever 10, the length W of the area where the cam member 20 and the cam receiving member 30 contact each other is at least three times and at most seven times the thickness t of the pressure lever 10, and so that the center L of the load of the pressing force by the cam member 20 via the cam receiving member 30 coincides with the center C of the thickness of the pressure lever 10.

[0019] FIG. 2(A) shows an example in which the length W of the contact area between the cam member 20 and the cam receiving member 30 is three times the thickness t of the pressing lever 10. The thickness wa of each side that constitutes the U-shaped shape of the cam receiving member 30 is equal to the thickness t of the cam receiving member 30 (wa = t). As a result, the widthwise length of the area that faces the cam member 20 and comes into contact with and receives the load is three times the thickness of the cam receiving member 30 (W = 3t). FIG. 2(B) shows an example in which the length W of the contact area between the cam member 20 and the cam receiving member 30 is seven times the thickness t of the pressing lever 10. The thickness wb of each side that constitutes the U-shaped portion of the cam receiving member 30 is three times the thickness t of the cam receiving member 30 (wb = 3t). As a result, the widthwise length of the area that faces the cam member 20 and comes into contact with and receives the load is seven times the thickness of the cam receiving member 30 (W = 7t).

[0020] As shown in Fig. 2, the cam receiving member 30 has a U-shaped configuration with each side having a uniform thickness. By providing a uniform thickness without uneven thickness, it is possible to reduce molding defects such as warpage, sink marks, and voids that occur during molding of the member, and to prevent a decrease in the strength of the member.

[0021] FIG. 8 is a diagram showing an example of the configuration of a conventional fixing device. In the example of FIG. 8, in the pressing lever 10 formed of a single sheet metal member for space saving, a bending portion 35 is formed in the pressed portion pressed by the cam member 20. The center L of the load of the pressing force by the cam member 20 does not coincide with the center of the thickness of the pressing lever 10 and is away from the fulcrum 12, unlike the example of the present embodiment. Therefore, a force that causes the bending portion 35 to fall in the direction indicated by the arrow B is generated. As a result, the fulcrum 12 of the pressing lever 10 is caught by an unnecessary load, preventing the smooth operation of the pressing lever 10. In addition, the portion of the cam member 20 that receives the load may cause a decrease in strength or breakage due to the repeatedly received load, which may reduce the durability of the member and thus the durability of the fixing device.

[0022] On the other hand, according to the configuration of the present embodiment shown in FIGS. 1 and 2, it is possible to provide a fixing device that realizes space saving and prevents a decrease in durability due to breakage of the constituent members.

[0023] FIG. 3 is a table showing the dimensional relationship between the pressing lever 1 and the cam receiving member 30 and the presence or absence of breakage. Specifically, regarding the thickness t in the direction orthogonal to the longitudinal direction of the pressing lever 10 and the length W of the contact area between the cam member 20 and the cam receiving member 30, five levels are provided respectively, and the occurrence of breakage of the cam receiving member 30 when the cam member 20 applies a constant load to the cam receiving member 30 in each combination of levels is shown.

[0024] The thickness t (t1 to t5) of the pressing lever 10 is a value that satisfies the relationship of 0 < t1 < t2 < t3 < t4 < t5. Also, the length W (W1 to W5) of the contact area between the cam member 20 and the cam receiving member 30 is a value that satisfies the relationship of 0 < W1 < W2 < W3 < W4 < W5. In the table, combinations where no breakage occurred are represented by "〇", combinations where minor damage / breakage was observed are represented by "△", and combinations where breakage occurred are represented by "×". In the present embodiment, the cam receiving member 30 is a member formed of a resin material such as POM, PA, or PPS.

[0025] In the table, "◯" indicates a combination where the ratio K (=W / t) of the thickness t of the pressure lever 10 to the length W of the contact area between the cam member 20 and the cam receiving member 30 is 3 or more. "△" and "×" indicate a combination where the ratio K (=W / t) is less than 3. From the above results, it was found that damage to the components can be prevented by making the length W of the contact area between the cam member 20 and the cam receiving member 30 at least three times the thickness t of the pressure lever 10, and by arranging the center L of the load of the pressing force from the cam member 20 via the cam receiving member 30 to coincide with the center C of the thickness of the pressure lever 10.

[0026] Increasing the length W of the contact area between the cam member 20 and the cam receiving member 30 relative to the thickness t of the pressing lever 10 is preferable in terms of strength, but may be disadvantageous in terms of cost and space saving. Therefore, it is preferable that the ratio K (= W / t) be 3 or more and 7 or less.

[0027] 4 and 5 are explanatory diagrams showing an example of a cam receiving member 30 composed of a cover member 30a and an intermediate member 30b. Fig. 4(A) is an exploded perspective view of the pressure lever 10 and the cam receiving member 30 at the pressed portion pressed by the cam member 20, and Fig. 4(B) is a schematic cross-sectional view in the width direction thereof. Fig. 5 is a diagram explaining the dimensions of each member.

[0028] As shown in Figures 4(A) and 4(B), the cam receiving member 30 can be configured to include a cover member 30a that abuts against the cam member 20, and an intermediate member 30b that is arranged inside the cover member 30a and abuts against the pressure lever 10.

[0029] 5, the length W of the area where the cam member 20 and the cam receiving member 30 contact each other is the width of the cover member 30a, and the width wc of the area where the intermediate member 30b abuts against the cover member 30a. The cover member 30a and the intermediate member 30b each have a substantially U-shaped cross section, and each side of the U-shape is formed to a uniform thickness. The cover member 30a and the intermediate member 30b are both made of a resin material such as POM, PA, or PPS.

[0030] In this way, by combining multiple resin members, the overall thickness can be increased. Also, by providing the intermediate member 30b, the load that the cover member 30a, which contacts the cam member 20, receives from the pressure lever 10 can be reduced, preventing breakage and improving the durability of the part.

[0031] As shown in FIG. 4(A), the portion of the pressure lever 10 that is pressed by the cam member 20 can be a groove portion 10b into which the cam receiving member 30 fits.

[0032] The cam receiving member 30 is preferably disposed detachably with respect to the pressure lever 10 so that it can be easily replaced in the unlikely event that it is damaged by the repeated load from the cam member 20 . Even in an embodiment in which the cam receiving member 30 is composed of a cover member 30a and an intermediate member 30b, it is preferable that the cover member 30a be detachable from the intermediate member 30b, and similarly, it is preferable that the intermediate member 30b be detachable from the pressure lever 10.

[0033] 6A and 6B are explanatory diagrams showing another example of a cam receiving member 30 composed of a cover member 30a and an intermediate member 30b, in which FIG. 6A is an exploded perspective view of the pressure lever 10 and the cam receiving member 30 at the pressed portion pressed by the cam member 20, and FIG. 6B is a schematic cross-sectional view in the width direction thereof. In the example shown in FIG. 6, the cover member 30a is detachable from the intermediate member 30b, and the intermediate member 30b is also detachable from the pressing lever . The portion of the pressure lever 10 that is pressed by the cam member 20 can be a groove portion 10b into which the cam receiving member 30 fits.

[0034] The cam receiving member 30 may have a convex portion that engages with the pressure applying lever 10 , and the pressure applying lever 10 may have an engaging and fixing portion 10 a that engages with the convex portion of the cam receiving member 30 . In the example of FIG. 6, the intermediate member 30b has a convex portion 33 that engages with the engaging and fixing portion 10a of the pressing lever 10. The engaging and fixing portion 10a may be an opening that passes through the pressure lever 10 in the thickness direction, or may be a groove-like recess that does not pass through. As shown in FIG. 6, the cover member 30a is provided with a protrusion 31 that engages with an end surface 32 of the intermediate member 30b.

[0035] In this way, the pressure lever 10, the cover member 30a, and the intermediate member 30b have a structure in which they engage with each other, so that they are stable when attached, and can be easily attached and detached when replaced.

[0036] In this embodiment, it is preferable that the pressure lever 10, the cam member 20, and the cam receiving member 30 that constitute the pressure mechanism are each made of a material having sufficient strength. Furthermore, when the strength of the material of the pressure lever 10 is S1, the strength of the material of the cam member 20 is S2, and the strength of the material of the cam receiving member 30 is S3, it is preferable that the relationship S1>S2>S3 be satisfied.

[0037] By constructing the cam member 20 from a material with higher bending strength and tensile strength than the cam receiving member 30 (cover member 30a and intermediate member 30b), it is possible to prevent the cam member 20 from being destroyed by creep or fatigue before the cam receiving member 30. When replacing the cam member 20, it is necessary to remove more parts than the cam receiving member 30, so it is preferable to prevent damage to the cam member 20 from the standpoint of ease of replacement due to damage to the parts.

[0038] The pressure lever 10 is made of a metal material, and the cam member 20 and the cam receiving member 30 are made of a resin material. The cover member 30a and the intermediate member 30b constituting the cam receiving member 30 may be made of the same resin material or different resin materials. In either case, it is preferable that the strength of the cam member 20 is greater than that of the cover member 30a and the intermediate member 30b.

[0039] [Image forming equipment] FIG. 7 is an explanatory diagram of the essential configuration of a laser printer as an embodiment of an image forming apparatus equipped with a fixing device according to the present invention, illustrating the principle in a simplified manner. The fixing device according to the present invention can be applied to both electrophotographic and inkjet image formation. In an inkjet image formation apparatus, the fixing device can be used, for example, as a means for heating a recording medium with a heating roller to dry the ink.

[0040] In the following embodiments, the "recording medium" will be described as "paper," but the "recording medium" is not limited to paper (paper). The "recording medium" includes not only paper (paper), but also transparencies, fabrics, metal sheets, plastic films, and prepreg sheets made of carbon fiber pre-impregnated with resin. Media to which developer or ink can be attached, recording paper, and recording sheets are all included in the "recording medium." Furthermore, "paper" includes not only plain paper, but also cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like.

[0041] Furthermore, the term "image formation" used in the following description refers not only to the application of meaningful images such as letters and figures to a medium, but also to the application of meaningless images such as patterns to a medium.

[0042] As shown in FIG. 7, the image forming apparatus according to this embodiment includes a paper feed unit, a pair of registration rollers 60, a photosensitive drum 80 as an image carrier, a transfer unit 110, and a fixing device 100.

[0043] The paper feed means includes a paper feed tray 140 in which recording media (paper) P are stored in a stacked state, and a paper feed roller 116 that separates and feeds the paper P stored in the paper feed tray 140 one by one, starting from the top one. The paper P sent out by the paper feed roller 116 is stopped once by the pair of registration rollers 60, and after any misalignment has been corrected, the paper P is sent to the transfer section 111 by the pair of registration rollers 60 at a timing synchronized with the rotation of the photosensitive drum 80, that is, at a timing when the leading edge of the toner image formed on the photosensitive drum 80 coincides with a predetermined position of the leading edge of the paper P in the transport direction.

[0044] Around the photosensitive drum 80, in the order of rotation indicated by the arrow, there are arranged a charging roller 118 as a charging means, a mirror 128 constituting part of an exposure means (not shown), a developing means 122 equipped with a developing roller 122a, a transfer means 110, and a cleaning means 124 equipped with a cleaning blade 124a.

[0045] Between the charging roller 118 and the developing means 122, the exposure light Lb is irradiated onto an exposure portion 126 on the photosensitive drum 80 via a mirror 128, and is scanned. The image forming operation in the printer is performed in the same manner as known operations. That is, when the photosensitive drum 80 starts to rotate, the surface of the photosensitive drum 80 is uniformly charged by the charging roller 118, and exposure light Lb is irradiated onto the exposure section 126 based on the image information, and scanning is performed to form an electrostatic latent image corresponding to the image to be created. This electrostatic latent image is moved to the developing means 122 by the rotation of the photosensitive drum 80, where toner is supplied to make it visible, thereby forming a toner image.

[0046] The toner image formed on the photosensitive drum 80 is transferred onto the paper P that has entered the transfer section 111 at a predetermined timing by the application of a transfer bias by the transfer means 110. The paper P carrying the toner image is transported toward the fixing device 100, where the toner image is fixed, and then the paper P is discharged and stacked on a paper discharge tray (not shown).

[0047] Residual toner that is not transferred at the transfer site 111 and remains on the photosensitive drum 80 reaches the cleaning means 124 as the photosensitive drum 80 rotates, and is scraped off and cleaned by the cleaning blade 124a while passing through this cleaning means 124. Thereafter, the residual potential on the photosensitive drum 80 is removed by a discharging means (not shown) to prepare for the next image forming process.

[0048] The image forming apparatus of this embodiment is equipped with the fixing device according to the present invention described above, thereby realizing space saving and cost reduction, as well as improving operability and durability when clearing jams. [Explanation of symbols]

[0049] 1 Heating roller 2 Pressure roller 10 Pressure lever 13 Hook part 15 Spring 20 Cam member 30 Cam receiving member 30a Cover member 30b Intermediate member 100 Fixing device [Prior art documents] [Patent documents]

[0050] [Patent Document 1] Patent No. 3896235 [Patent Document 2] Patent No. 3404453

Claims

1. a pair of rollers that are in contact with and separate from each other and press against each other to sandwich and transport a recording medium; a pressure lever having one end pivotally supported and the other end connected to a spring, the pressure lever pressing one of the pair of rollers against the other; a cam member that displaces the pressure lever between a position that maintains the pressure contact state of the pair of rollers and a position that releases the pressure contact state; a cam receiving member disposed at a portion of the pressure lever that is pressed by the cam member, the cam receiving member has a generally U-shaped cross section, and the recess fits into the pressure lever so as to cover the pressed portion; a fixing device characterized in that, in a width direction perpendicular to the longitudinal direction of the pressure lever, the length of the area where the cam member and the cam receiving member contact each other is between three and seven times the thickness of the pressure lever, and the center of the load of the pressing force by the cam member via the cam receiving member coincides with the center of the thickness of the pressure lever.

2. 2. The fixing device according to claim 1, wherein the pair of rollers comprises a heating roller heated by a heating means and a pressure roller pressed against the heating roller by the pressure lever.

3. 3. The fixing device according to claim 1, wherein the cam receiving member comprises a cover member that contacts the cam member, and an intermediate member that is disposed inside the cover member and contacts the pressure lever.

4. 4. The fixing device according to claim 3, wherein the cover member of the cam receiving member is detachable from the intermediate member.

5. 5. The fixing device according to claim 1, wherein the cam receiving member has a convex portion that engages with the pressure lever, and the pressure lever has an engaging and fixing portion that engages with the convex portion of the cam receiving member.

6. An image forming apparatus comprising the fixing device according to any one of claims 1 to 5.

Images