Fixing device and image forming apparatus using the same

Abstract

To reduce a variation in the amount of separation between a heating structure and a pressure structure in a pressure-contact released state of a fixing device, and thereby stabilize the amount of paper jam processing power.SOLUTION: A fixing device comprises a contact-pressure state switching mechanism 100 that selectively switches a contact-pressure state between a heating structure and a pressure structure to any one of a first pressure-contact state, a second pressure-contact state, and a pressure-contact release state. The pressure-contact state switching mechanism 100 includes: a cam for separation 141 that is transferred with driving force through a gear (intermediate gear 144) meshing with a driving member 138 when the pressure-contact state is transitioned to the pressure-contact release state, and is brought into contact with a contact part 125 on a side of the pressure structure to separate the pressure structure from the heating structure; and urging means (torsion coil spring 147) that constantly urges the cam for separation 141 in a direction to separate from the contact part 125. After the driving member 138 meshes with the intermediate gear 144, the cam for separation 141 is driven against the urging force of the urging member to be brought into contact with the contact part 125.SELECTED DRAWING: Figure 6B

Description

Technical Field

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

Background Art

[0002] In an electrophotographic image forming apparatus, the surface of a photoreceptor is exposed and scanned based on image data of a document to form an electrostatic latent image. Next, the image forming apparatus supplies toner to this electrostatic latent image to generate a toner image. Then, after transferring the toner image onto a recording sheet, the image forming apparatus thermally fixes it using a fixing device.

[0003] The fixing device forms a nip portion between a heating structure (for example, a fixing belt whose inner peripheral surface is slidably supported by a heating roller, a pad, etc.) and a pressure structure (for example, a pressure roller) pressed against it. The fixing device passes a recording sheet through this nip portion and conveys it forward while thermally fixing it.

[0004] The pressing force (nip pressure) at the nip portion can be changed according to the type of paper being passed. Specifically, for example, when fixing normal plain paper, it is set to the full contact state. Also, when passing special paper such as envelopes, if the pressing force is too strong, wrinkles may occur, so it is set to a light contact state that is smaller than the pressing force when passing plain paper.

[0005] Also, when a jam occurs in the recording paper at the nip portion, it is necessary to separate the pressure structure from the heating structure to release the contact state for jam processing.

[0006] Therefore, in recent years, a fixing device provided with a contact state switching mechanism capable of switching the contact state between a fixing rotating body and a pressure rotating body among three stages: a full contact state, a light contact state, and a contact release state has been proposed (for example, Patent Document 1).

[0007] Figs. 11A, 11B, and 11C are schematic side views showing the configuration of a pressure contact state switching mechanism in the fixing device according to Patent Document 1. As shown in Fig. 11A, the fixing device includes an endless fixing belt 51, a fixing pad 52 fixedly supported by a support member (not shown) so as to contact the inner peripheral surface of the fixing belt 51, a guide member 53 that contacts the inner peripheral surface of the fixing belt 51 and guides the fixing belt 51, a heating roller 54 that heats the fixing belt 51, and a pressure roller 55 that presses the outer peripheral surface of the fixing belt 51.

[0008] The heating roller 54 is rotatably supported by a main frame 56 via a bearing member (not shown). The bearing member is biased downward by an elastic member, and applies a certain tension to the fixing belt 51 stretched between the heating roller 54 and the fixing pad 52.

[0009] A sub-frame 57 is rotatably supported by the main frame 56 via a first support shaft 58 on a plane parallel to the main surface of the main frame 56. A pressure roller 55 is supported by the sub-frame 57 via a holding plate 59. The pressure contact state between the fixing belt 51 and the pressure roller 55 is switched by changing the swing angle of the sub-frame 57 with respect to the main frame 56.

[0010] A pressure contact cam 60 for switching the pressure contact state between a light pressure contact state and a full pressure contact state is pivotally supported by the main frame 56 via a second support shaft 61. A tension spring 62 for full pressure contact is installed between a spring locking portion 63 provided on the sub-frame 57 and a spring locking pin 64 provided on the pressure contact cam 60. Also, a tension spring 65 for light pressure contact is installed between a spring locking portion 66 provided on the main frame 56 and a spring locking portion 67 provided on the sub-frame 57.

[0011] The cam 60 for press - fitting is formed with a crank mechanism (driving - force conversion mechanism) in which a driving pin 71 erected on a driving member 70 is inserted into a long hole 68 formed in the cam 60 for press - fitting. Therefore, by driving the driving member 70 to swing the cam 60 for press - fitting, the press - fitting state can be switched between a full - press - fitting state and a light - press - fitting state.

[0012] Also, in order to switch from the press - fitting state to the press - fitting release state, as shown in FIGS. 11B and 11C, an intermittent gear 72, an intermediate gear 73, and a separating cam 74 provided on the driving member 70 are provided.

[0013] The separating cam 74 is pivotally supported by the same support shaft (second support shaft 61) as the cam 60 for press - fitting. This separating cam 74 has a protruding cam portion 75 protruding toward the sub - frame side and a partial gear 76 provided on the opposite side of the protruding cam portion 75. The partial gear 76 is constantly meshed with the intermediate gear 73. On the other hand, the intermittent gear 72 meshes with the intermediate gear 73 and transmits the rotational force only when the driving member 70 is in a specific rotational phase. The rotational force transmitted to the intermediate gear 73 is further transmitted to the partial gear 76, causing the separating cam 74 to swing.

[0014] As a result, the tip of the protruding cam portion 75 abuts against a contact portion 77 provided on the holding plate 59 of the sub - frame 57, pressing and pushing back the contact portion 77 against the biasing force of the tension spring 65. As a result, the swing angle of the sub - frame 57 opens, the fixing belt 51 and the pressure roller 55 are separated, and the press - fitting state is released.

Prior Art Documents

Patent Documents

[0015]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0016] However, the separation cam 74 of the conventional fixing device is pivotally supported so as to be rotatable with respect to the support shaft 61. Therefore, until the drive member 70 engages with the intermediate gear 73, the separation cam 74 is rotatable within a range where rotation is restricted from the position where it abuts against the abutting portion 77 that forms part of the pressurizing structure to a position separated from the abutting portion 77 (the separation cam 74 has a play angle in the rotational direction). As a result, since the position where the drive member 70 of the intermediate gear 73 that rotates together with the separation cam 74 engages changes, there is a problem that the separation amount between the fixing belt 51 (heating structure) and the pressure roller 55 (pressurizing structure) varies. As a result, there is a concern that the amount of jam processing power varies and the operability of the user deteriorates.

[0017] The present invention has been made in view of such circumstances, and the main problem is to eliminate variations in the separation amount between the heating structure and the pressurizing structure and to make the amount of jam processing power constant.

Means for Solving the Problems

[0018] In order to achieve the above problems, the fixing device according to the present invention is A fixing device that forms a nip portion by pressing a pressurizing structure against a heating structure, passes a recording sheet on which an unfixed toner image has been transferred through this nip portion, and fixes the toner image to the recording sheet, A pressure contact state switching mechanism that selectively switches the pressure contact state between the heating structure and the pressurizing structure to any one of a first pressure contact state, a second pressure contact state having a different pressure contact force from the first pressure contact state, and a pressure contact release state, The pressure contact state switching mechanism is When shifting to the pressure contact release state, a separation cam that presses the abutting portion of the pressurizing structure to separate the pressurizing structure from the heating structure by transmitting a driving force from a driving member through a gear meshing therewith, Biasing means for constantly biasing the separation cam in a direction away from the abutting portion, and The separation cam is configured to abut against the abutting portion by being driven against the biasing force of the biasing means after the drive member engages with the gear.

[0019] The image forming apparatus according to the present invention is an image forming apparatus including a transfer unit that transfers a toner image onto a recording sheet and a fixing unit that fixes the transferred toner image onto the recording sheet, wherein the fixing device described above is used as the fixing unit.

Advantages of the Invention

[0020] According to the above configuration, the separating cam that separates the pressing structure from the heating structure is constantly biased by the biasing means in a direction away from the contact portion of the pressing structure. Thus, until the driving member meshes with the gear that transmits the driving force, the separating cam is held at a position where it is separated from the contact portion by the biasing means and is restricted from rotating. Therefore, the position where the driving member meshes with the gear becomes constant, the variation in the separation amount between the heating structure and the pressing structure is eliminated, and the amount of jam processing power can be made constant.

Brief Description of the Drawings

[0021] The advantages and features provided by the embodiments of the present invention are described by way of example and are not intended to limit the present invention. They will be more fully understood from the following detailed description and the accompanying drawings.

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5A

Figure 5B

Figure 6A

Figure 6B

Figure 7A

Figure 7B

Figure 7C

Figure 8

Figure 9A

Figure 9B

Figure 9C

Figure 10A

Figure 10B

Figure 11A

Figure 11B

Figure 11C

Embodiments for Carrying Out the Invention

[0022] Hereinafter, an example in which the pressure contact state switching mechanism according to the embodiment of the present invention is applied to a fixing device of a tandem type color printer (hereinafter simply referred to as "printer"), which is an image forming apparatus, will be described with reference to the drawings. However, the scope of the present invention is not limited to the disclosed embodiments.

[0023] (1) Overall Configuration of Printer FIG. 1 is a schematic cross-sectional view showing the overall configuration of the printer 1.

[0024] As shown in the figure, the printer 1 includes an image forming unit 10, a paper feeding unit 20, and a fixing device 30.

[0025] The image forming unit 10 includes image forming units 11Y, 11M, 11C, and 11K corresponding to each color of Y (yellow), M (magenta), C (cyan), and K (black), and an intermediate transfer belt 13.

[0026] The image forming unit 11K includes a photosensitive drum 12, a charging unit 16, an exposure unit 17, a developing unit 18, and a cleaner 19 arranged along the circumferential direction of the photosensitive drum 12.

[0027] The exposure unit 17 includes a light emitting element such as a laser diode and a lens, etc., and modulates laser light according to a drive signal from a control unit (not shown) to perform exposure scanning on the photosensitive drum 12.

[0028] The photosensitive drum 12 is rotationally driven by a drive source (not shown). Before receiving the above exposure, after the residual toner on the surface is removed by the cleaner 19, it is uniformly charged by the charging unit 16. In this uniformly charged state, when it receives the exposure by the above laser light, an electrostatic latent image is formed on the surface of the photosensitive drum 12.

[0029] The electrostatic latent image formed on the photosensitive drum 12 is developed by the developing unit 18, and thereby a toner image of K color is formed on the surface of the photosensitive drum 12. This K-color toner is primarily transferred from the photosensitive drum 12 onto the intermediate transfer belt 13 by the primary transfer roller 14 arranged on the side opposite to the photosensitive drum 12 via the circulating intermediate transfer belt 13.

[0030] The image forming units 11Y, 11M, and 11C also have the same configuration as the image forming unit 11K. For each image forming unit, a toner image of the corresponding color (Y, M, or C color) is formed on the photosensitive drum 12 and is primarily transferred onto the intermediate transfer belt 13 by the primary transfer roller 14.

[0031] The operating operations in each of the image forming units 11Y to 11K are executed with their timings shifted so that the toner images are primarily transferred while being superimposed at the same position on the intermediate transfer belt 13. Thereby, a color toner image of Y to K colors is formed on the intermediate transfer belt 13.

[0032] The paper feeding unit 20 includes paper feeding cassettes 21 and 22 for accommodating the recording sheet S, feeding rollers 21a and 22a, a conveying roller 23, and a timing roller 24.

[0033] Each of the feeding rollers 21a and 22a is under the control of the control unit 40, contacts the uppermost recording sheet S from the selected paper feeding cassette 21 or 22, and feeds it out to the conveyance path 25.

[0034] The conveying roller 23 conveys the recording sheet S fed out by the feeding rollers 21a and 22a toward the timing roller 24. The timing roller 24 feeds out the recording sheet S to the downstream side at the timing instructed by a control unit (not shown).

[0035] The color toner image multiply transferred onto the intermediate transfer belt 13 in the image forming unit 10 moves to the secondary transfer position 15a, which is the contact position between the intermediate transfer belt 13 and the secondary transfer roller 15, due to the circumferential running of the intermediate transfer belt 13.

[0036] In accordance with the movement timing of the toner image on the circumferentially running intermediate transfer belt 13, the recording sheet S is fed on the conveyance path 25 from the timing roller 24 of the paper feeding unit 20. When the recording sheet S passes through the secondary transfer position 15a, the color toner image on the intermediate transfer belt 13 is secondarily transferred onto the recording sheet S by the secondary transfer roller 15. The recording sheet S that has passed through the secondary transfer position 15a is sent to the fixing device 30.

[0037] The fixing device 30 passes the recording sheet S conveyed from the secondary transfer roller 15 in the direction indicated by the arrow D (sheet conveyance direction) through the fixing nip 3, and fixes the color toner image (unfixed image) on the recording sheet S to the recording sheet S by heating and pressurization.

[0038] The recording sheet S that has passed through the fixing device 30 is discharged outside the machine by the discharge roller 26 and is housed in the paper discharge tray 27.

[0039] (2) Configuration of the fixing device FIG. 2 is a schematic cross-sectional view showing the configuration of the main part of the fixing device 30. Here, in this figure, the X-axis direction is the left-right direction when the printer 1 is viewed from the front side. The Y-axis direction represents the up-down direction. The Z-axis direction is a direction orthogonal to both the X-axis and the Y-axis and corresponds to the depth direction of the printer 1. This figure is a cross-sectional view when the fixing device 30 is cut in the X-Y plane orthogonal to the Z-axis.

[0040] As shown in Fig. 2, the fixing device 30 includes an endless fixing belt 31, a fixing pad 32 in contact with the inner peripheral surface of the fixing belt 31, a guide member 33 in contact with the inner peripheral surface of the fixing belt 31 for guiding the fixing belt 31, a support member 34 for fixedly supporting the fixing pad 32 and the guide member 33, a heating roller 35 for heating the fixing belt 31, a heater 36 for applying heat to the heating roller 35, and a pressure roller 39 for pressing the outer peripheral surface of the fixing belt 31.

[0041] The fixing belt 31 is wound around the fixing pad 32, the heating roller 35, and the guide member 33. As will be described later, the heating roller 35 is biased in a direction away from the fixing pad 32 by an elastic member such as a compression spring, so that a certain tension is applied to the fixing belt 31.

[0042] The fixing belt 31 is formed by laminating, in this order, an elastic layer made of a highly heat-resistant material such as silicone rubber or fluororubber and a release layer having releasability such as a fluorine tube and a fluorine coating on a base layer made of polyimide, SUS (stainless steel), Ni (nickel) electroforming, or the like.

[0043] The pressure roller 39 is formed by laminating, in this order, a solid core metal 39a made of aluminum, iron, or the like, an elastic layer 39b made of a highly heat-resistant material such as silicone rubber or fluororubber, and a release layer 39c having releasability such as a fluorine tube and a fluorine-based coating.

[0044] The axis 399 of the rotation axis of the pressure roller 39 is parallel to the Z axis, and the pressure roller 39 is held so as to be able to be pressed against and separated from the fixing belt 31 by a pressure contact state switching mechanism described later. Fig. 2 shows a state in which the pressure roller 39 is pressed against the fixing belt 31.

[0045] This pressure roller 39 is rotationally driven at a predetermined rotational speed in the direction indicated by arrow A by the rotational driving force of the fixing conveyance motor 220. Due to the rotation of this pressure roller 39, the fixing belt 31 is driven to rotate (travel) in the direction indicated by arrow B (belt circumferential direction) as a follower. Note that the core metal 39a is not limited to being solid and may be, for example, a metal pipe or the like.

[0046] The fixing pad 32 and the guide member 33 are arranged so as to be aligned along the circumferential direction of the fixing belt 31. These are non-rotating bodies that do not rotate with the rotation of the fixing belt 31, and the length in the Z-axis direction is substantially the same as the length in the Z-axis direction (belt width) of the fixing belt 31.

[0047] The fixing pad 32 is arranged on the side opposite to the pressure roller 39 that is located outside the belt with the fixing belt 31 interposed therebetween, and receives the pressing force from the pressure roller 39. As a result, the outer peripheral surface of the pressure roller 39 and the outer peripheral surface of the fixing belt 31 are in pressure contact, and a fixing nip 3 is formed between the fixing belt 31 and the pressure roller 39.

[0048] The guide member 33 is located on the downstream side in the belt circumferential direction from the fixing pad 32 and on the upstream side in the belt circumferential direction from the heating roller 35, and is arranged at a position closer to the fixing pad 32 than the heating roller 35. Further, the guide member 33 guides the belt portion immediately after passing through the fixing nip 3 of the fixing belt 31 downstream in the circumferential direction.

[0049] This guide member 33 is provided to make the circumferential path of the fixing belt 31 that is wound around the fixing pad 32 and the heating roller 35 into a smooth curved shape.

[0050] The fixing pad 32 and the guide member 33 are formed of the same material here. For example, resins such as polyphenylene sulfide, polyimide, and liquid crystal polymer are used, and those with excellent heat resistance are desirable. Also, they may be composed of metals such as aluminum and iron, ceramics, etc., or those obtained by combining these with silicone rubber, fluorine rubber, etc. Further, the fixing pad 32 and the guide member 33 may be made of different materials.

[0051] The support member 34 is a member made of metal such as aluminum, iron, or SUS with a C-shaped cross-section, and fixedly supports the fixing pad 32 on one of the adjacent side surfaces and fixedly supports the guide member 33 on the other side surface.

[0052] In addition, in order to reduce the wear caused by the rubbing between the fixing pad 32 and the guide member 33 and the inner peripheral surface of the fixing belt 31, it is desirable to coat the surface of the portion of the fixing pad 32 and the guide member 33 that contacts the fixing belt 31 with a low-friction material such as fluororesin. Alternatively, it is desirable to take wear suppression measures such as applying a lubricant to the inner peripheral surface of the fixing belt 31.

[0053] (3) Pressure contact state switching mechanism FIGS. 3A and 3B are views of the fixing device 30 including a pressure contact state switching mechanism 100 for switching the pressure contact state of the pressure roller 39 with respect to the fixing belt 31. Note that FIG. 3A is an overall side view of the fixing device 30, and FIG. 3B is a view in which the pressure contact cam 131, the crank mechanism, and the tension spring 133 described later are omitted from FIG. 3A.

[0054] The heating roller 35 is rotatably supported by the main frame (first holding member) 110 via a ring-shaped bearing member 351. The bearing member 351 is biased downward by an elastic member (not shown), for example, a compression spring, so that a constant tension is applied to the fixing belt 31 stretched between the heating roller 35 and the fixing pad 32.

[0055] Also, a sub-frame (second holding member) 120 is pivotally supported on the main frame 110 via a first support shaft 121 so as to be swingable within a plane parallel to the main surface of the main frame 110. A pressure roller 39 is pivotally supported on this sub-frame 120 via a holding plate 122. The pressure contact state between the fixing belt 31 and the pressure roller 39 can be switched by changing the swing angle formed by the sub-frame 120 with respect to the main frame 110.

[0056] The crimping state switching mechanism 100 is a mechanism for selectively switching the crimping state among three states: the full crimping state, the light crimping state, and the crimping release state. The crimping state switching mechanism 100 includes a first switching unit 130 (FIG. 3A) that switches between the full crimping state and the light crimping state, and a second switching unit 140 (FIG. 3B) that switches between the light crimping state and the crimping release state.

[0057] <Configuration of the First Switching Unit 130> As shown in FIG. 3A, the first switching unit 130 mainly includes a crimping cam 131 pivotally supported on the main frame 110 via a second support shaft 132 so as to be swingable, a tension spring 133 for full crimping, a tension spring 134 for light crimping, and a drive member 138 connected to an end of a drive rod (drive shaft) 137 that protrudes forward through a through hole in the main frame 110.

[0058] A drive pin 136 erected on the drive member 138 is inserted into a long hole 135 formed in the crimping cam 131 to form a crank mechanism (drive force conversion mechanism).

[0059] Here, the long hole 135 extends toward the second support shaft 132. The long hole 135 is formed such that the circumferential width of the crimping cam 131 reduces the gap with the drive pin 136 on the side closer to the second support shaft 132. Also, the long hole 135 is formed such that the gap with the drive pin 136 increases on the side farther from the second support shaft 132. The portion with a small gap with the drive pin 136 is formed with a constant width from approximately the center in the extending direction of the long hole 135 to the end on the second support shaft side.

[0060] A pinion (not shown) attached to the motor shaft of the crimping state switching motor 230 meshes with a spur gear 139. Thereby, the rotational force of the crimping state switching motor 230 is transmitted to the drive member 138 via the drive rod (drive shaft) 137. When the drive member 138 rotates, the crimping cam 131 swings vertically about the second support shaft 132 due to the above-described crank action.

[0061] Note that the driving force conversion mechanism is not limited to the crank mechanism as described above, and other known link mechanisms or the like may be used.

[0062] FIG. 4 is a schematic perspective view of the entire fixing device 30 in FIG. 3A as viewed obliquely upward from the pressure roller side. In this figure, the main frame 110 shown in FIG. 3A is omitted in order to clarify the state of the cam mechanism.

[0063] As also shown in FIG. 4, the tension spring 133 is installed between a spring latching portion 123 provided on the upper part of the sub-frame 120 and a spring latching pin 1311 arranged on the side opposite to the long hole 135 of the pressure contact cam 131.

[0064] As the oscillating motion of the pressure contact cam 131 occurs, the distance between the spring latching portion 123 and the spring latching pin 1311 varies, so the biasing force of the tension spring 133 also varies, and the pressure contact force on the fixing belt 31 (fixing pad 32) changes.

[0065] On the other hand, the light pressure contact tension spring 134 is installed between a spring latching portion 112 on the upper part of the main frame 110 and a spring latching portion 124 on the upper part of the sub-frame 120 (see FIG. 3B).

[0066] <Pressure contact state switching operation by the first switching portion 130> (Light pressure contact state) FIG. 5A is a schematic diagram showing the state when the first switching portion 130 is in the light pressure contact state. For convenience of explanation, the illustration of the main frame 110 is omitted (the rotational phase of the drive member 138 at this time is referred to as the "first rotational phase").

[0067] As shown in this figure, in the light pressure contact state, the drive member 138 pushes the drive pin 136 upward against the long hole 135 portion of the pressure contact cam 131 (the portion where the gap between the long hole 135 and the pin is small), causing the pressure contact cam 131 to swing clockwise about the second support shaft 132. At this time, since the spring latching pin 1311 of the pressure contact cam 131 approaches the sub-frame 120 direction (the first swinging position), the tension spring 133 for full pressure contact becomes its natural length and does not exert a biasing force.

[0068] However, the sub-frame 120 is biased in the direction of the main-frame 110 by the biasing force of the tension spring 134. Therefore, the pressure-contact state between the pressure roller 39 and the fixing belt 31 becomes a light pressure-contact state where they are pressure-contacted only by the spring force of the tension spring 134.

[0069] (Full pressure-contact state) Rotate the drive member 138 clockwise from the state of FIG. 5A and stop it at the rotational phase (second rotational phase) shown in FIG. 6A.

[0070] At this time, since the pressure-contact cam 131 rotates counterclockwise by a crank action (second swinging position), the spring-latching pin 1311 moves away from the spring-latching portion 123. As a result, since the tension spring 133 extends from its natural length, the biasing force of the tension spring 133 acts on the sub-frame 120.

[0071] The spring constant of the tension spring 133 is set larger than the spring constant of the tension spring 134. Therefore, the swing angle of the sub-frame 120 becomes smaller than the swing angle shown in FIG. 5A (the sub-frame 120 is brought closer to the main-frame 110 side).

[0072] Therefore, the distance between the spring-latching portion 112 on the main-frame 110 side where the tension spring 134 was installed and the spring-latching portion 124 of the sub-frame 120 becomes shorter, and the extension amount of the tension spring 134 becomes smaller. As a result, the biasing force that brings the sub-frame 120 closer to the main-frame 110 becomes smaller, but the state of pressure-contacting the pressure roller 39 to the fixing belt 31 becomes a full pressure-contact state where they are pressure-contacted by the spring forces of both the tension spring 133 and the tension spring 134.

[0073] <Configuration of the second switching portion 140> Next, the configuration of the second switching portion 140 for switching the pressure-contact state from the light pressure-contact state to the pressure-contact release state will be described.

[0074] Figures 7A and 7B are diagrams showing the state of release of pressure welding. Figure 7A is an overall side view of the fixing device 30. Figure 7B is a diagram in which the pressure welding cam 131, the crank mechanism, and the tension spring 133 are omitted from Figure 7A.

[0075] As shown in FIGS. 3B, 5B, 6B, and 7B, the second switching unit 140 mainly includes a separating cam 141, an intermediate gear 144, and an intermittent gear 145 provided on the drive member 138.

[0076] The separating cam 141 is pivotally supported by the same support shaft (the second support shaft 132) as the pressure welding cam 131. This separating cam 141 has a protruding cam portion 142 protruding toward the sub-frame 120 side and a partial gear 143 provided on the opposite side of the protruding cam portion 142, and has a shape like a ginkgo leaf as a whole.

[0077] The intermittent gear 145 provided on the drive member 138 meshes with the intermediate gear 144 and transmits the rotational force only while the drive member 138 is in a specific rotational phase. The rotational force transmitted to the intermediate gear 144 is further transmitted to the partial gear 143 of the separating cam 141 to swing the separating cam 141 (intermittent transmission mechanism).

[0078] The separating cam 141 and the intermediate gear 144 are always in a meshing and cooperating relationship. However, the intermittent gear 145 of the drive member 138 is not yet meshed with the intermediate gear 144 as shown in FIG. 6B in the fully pressure-welded state, and the driving force is not transmitted to the separating cam 141. In the lightly pressure-welded state, as shown in FIG. 5B, the intermittent gear 145 of the drive member 138 begins to mesh with the intermediate gear 144, and the driving force begins to be transmitted to the separating cam 141. Note that in this lightly pressure-welded state, the intermittent gear 145 may not be meshed with the intermediate gear 144 yet.

[0079] Here, on the rotation locus of the protruding cam portion 142 of the separating cam 141, a support member 34 that supports the fixing pad 32 and the guide member 33 on the heating structure side as viewed from the protruding cam portion 142 is arranged. Also, an abutting portion 125 described later is arranged on the pressure structure side.

[0080] <Operation of switching the pressing state by the second switching unit 140> The operation when the pressing state is switched from the light pressing state shown in FIGS. 5A and 5B to the pressing release state (separated state) by the second switching unit 140 will be described.

[0081] When the drive member 138 is rotated counterclockwise from the light pressing state shown in FIG. 5A, as shown in FIG. 7B, the intermittent gear 145 of the drive member 138 rotates the separation cam 141 counterclockwise via the intermediate gear 144 meshing therewith. As a result, the protruding cam portion 142 of the separation cam 141 swings upward about the second support shaft 132.

[0082] Then, the tip of the protruding cam portion 142 abuts against the contact portion 125 provided on the holding plate 122 of the sub-frame 120, and presses and pushes back the contact portion 125 against the biasing force of the tension spring 134. For this reason, the swing angle of the sub-frame 120 opens, the fixing belt 31 and the pressure roller 39 are separated, and the pressing state is released.

[0083] In this pressing release state, as also shown in FIG. 7C, the straight line connecting the center of the second support shaft 132, which is the rotation fulcrum of the separation cam 141, and the contact portion of the contact portion 125 is brought into contact so as to be perpendicular to the surface of the contact portion 125.

[0084] Note that, in this example, the pressing release state is described as being completely separated from the fixing belt 31 by the pressure roller 39, but the pressure roller 39 may be in a state of lightly contacting the fixing belt 31.

[0085] Also, as shown in the schematic perspective view of the fixing device 30 in FIG. 4, a pressure contact state switching mechanism similar to that on the front side is provided on the back side of the fixing device 30. However, the drive member on the back side is a spur gear 139 that meshes with a pinion attached to the motor shaft of a pressure contact state switching motor (not shown). This spur gear 139 is connected to the drive member 138 on the front side via a drive rod 137. The intermediate gear 144' on the back side is composed of a partial gear connected to the intermediate gear 144 on the front side by a connecting rod 146. The swing drive of the separation cam 141' on the back side swings in synchronization with the separation cam 141 on the front side.

[0086] (4) Rotation Direction Position Fluctuation Prevention Mechanism of Separation Cam By the way, in the above-described pressure contact state switching mechanism, the separation cam 141 meshes with the intermediate gear 144 only while the drive member 138 is in a specific rotational phase, and rotational power is transmitted through this intermediate gear 144. As a result, the protruding cam portion 142 of the separation cam 141 abuts against the contact portion 125 provided on the holding plate 122 of the sub-frame 120, and presses and pushes back the contact portion 125 against the biasing force of the tension spring 134. As a result, the swing angle of the sub-frame 120 with respect to the main frame 110 increases, and the pressure roller 39 is separated from the fixing belt 31.

[0087] However, the separation cam 141 is rotatable about the second support shaft 132 in the range from the position where the protruding cam portion 142 abuts against the contact portion 125 to the position where it abuts against the support member 34 until the intermittent gear 145 of the drive member 138 meshes with the intermediate gear 144. For this reason, the position where the intermediate gear 144 that drives the separation cam 141 starts to mesh with the intermittent gear 145 of the drive member 138 becomes unstable. That is, the rotation amount of the separation cam 141 varies, and the amount of separating the pressure roller 39 from the fixing belt 31 becomes unstable.

[0088] Therefore, it is preferable to hold the rotational direction position of the separation cam 141 at a fixed predetermined position until a rotational force is applied to the separation cam 141 (until the intermittent gear 145 of the drive member 138 meshes with the intermediate gear 144).

[0089] At this time, it is also conceivable to position the separation cam 141 in the swinging direction by bringing the protruding cam portion 142 of the separation cam 141 into contact with the contact portion 125 of the pressing structure. However, due to the thermal expansion of the pressing roller 39 or the variation in the sag or hardness of the pressing roller 39, the position of the contact portion 125 varies. There is a concern that this may cause the meshing position between the intermittent gear 145 and the intermediate gear 144 to shift or tooth tip contact to occur.

[0090] Therefore, in this embodiment, as shown in FIG. 8, a torsion coil spring 147 as a biasing means is attached around the second support shaft 132 that rotatably supports the separation cam 141. One end is locked to the separation cam 141 and the other end is locked to the main frame 110. By providing such a biasing means, the separation cam 141 is constantly biased in a direction away from the contact portion 125 of the pressing structure (constantly biased in a direction of contacting the support member 34). For this reason, when the drive member 138 (intermittent gear 145) is not engaged with the intermediate gear 144, the protruding cam portion 142 of the separation cam 141 is constantly in contact with the support member 34 by the biasing force of the torsion coil spring 147. As a result, it becomes possible to make the rotational direction position of the protruding cam portion 142 of the separation cam 141 wait at a predetermined position until immediately before the intermittent gear 145 meshes with the intermediate gear 144.

[0091] Then, after the drive member 138 (intermittent gear 145) meshes with the intermediate gear 144, the separation cam 141 is driven against the biasing force of the biasing means. After that, after the separation cam 141 contacts the contact portion 125, it pushes back the contact portion to separate the fixing pad from the fixing belt 31.

[0092] Therefore, since the position where the intermittent gear 145 of the drive member 138 meshes with the intermediate gear 144 is always the same position, it becomes possible to prevent the inconvenience that the meshing position changes and the separation amount between the fixing belt 31 and the pressing roller 39 varies.

[0093] (5) Gear guiding mechanism In addition to such biasing means, a guiding mechanism 150 for aligning the positions of both before their tooth tips mesh with each other is provided at the meshing portion between the driving member 138, which is the driving source of the separating cam 141, and the intermediate gear 144, as also shown in FIGS. 9A to 9C. This guiding mechanism 150 is configured, for example, by providing a guiding guide 144a that protrudes radially from the intermediate gear 144, and providing a guide contact portion 145a that contacts the guiding guide 144a in the circumferential direction at the front end portion in the rotational direction where the intermittent gear 145 of the driving member 138 starts to mesh. Since such a guiding mechanism 150 is provided, the guide contact portion 145a contacts the guiding guide 144a immediately before the intermittent gear 145 meshes with the intermediate gear 144. As a result, the timing for driving the intermediate gear 144 following the driving member 138 is adjusted, and it becomes possible to smoothly mesh their tooth tips with each other.

[0094] (6) Pressing state detection mechanism As described above, the light pressing state and the full pressing state are switched by the movement of the pressing cam 131. Therefore, by detecting the position of the pressing cam 131 in the rotational direction, it becomes possible to detect whether it is in the full pressing state or the light pressing state.

[0095] Therefore, in order to detect the rotational position of the pressing cam 131, as shown in FIGS. 10A and 10B, an optical sensor including a light projecting portion 161 that projects light and a light receiving portion 162 that receives light is provided on the inner surface of the exterior of the fixing machine facing the pressing cam 131 (shown by a broken line). Further, a light shielding plate 160 is fixed to the side surface of the pressing cam 131, and this light shielding plate 160 is made movable between the light projecting portion 161 and the light receiving portion 162 of the optical sensor. In the full pressing state shown in FIG. 10A, the light shielding plate 160 protrudes between the light projecting portion 161 and the light receiving portion 162 of the optical sensor, blocks the light from the light projecting portion 161, and prevents the light from being received by the light receiving portion 162 (the output signal from the light receiving portion 162 becomes OFF). Also, in the light pressing state shown in FIG. 10B, the light shielding plate 160 is removed from between the light projecting portion 161 and the light receiving portion 162 of the optical sensor, and the light from the light projecting portion 161 can be received by the light receiving portion 162 (the output signal from the light receiving portion 162 becomes ON). Accordingly, it is possible to determine whether the pressing state is the full pressing state or the light pressing state based on the presence or absence of light reception by the light receiving unit 162 (ON / OFF of the signal output from the light receiving unit 162).

[0096] At this time, if the circumferential width of the long hole 135 formed in the pressing cam 131 is made considerably larger than the diameter of the drive pin 136 (if a large gap is formed between the drive pin 136 and the peripheral edge of the long hole 135), when switching between the full pressing state and the light pressing state, the swing angle of the pressing cam 131 becomes smaller by the amount of the gap, and the detection accuracy of the switching deteriorates. Therefore, the circumferential width of the long hole 135 (the clearance between the inner surface of the long hole 135 and the drive pin 136) is made narrowest at the portion where the drive pin 136 is located when switching between the full pressing state and the light pressing state. That is, the circumferential width of the long hole 135 formed in the pressing cam 131 is made narrow on the side closer to the second support shaft 132, thereby reducing the play of the pressing cam 131 associated with the switching of the pressing state (switching between the full pressing state and the light pressing state) and ensuring a large swing angle. Therefore, since the swing angle at the time of switching is increased, it is possible to improve the detection accuracy of the switching of the pressing state. Further, since the circumferential width is widened on the side away from the second support shaft 132, it is possible to prevent deterioration of the assemblability of the fixing device.

[0097] (6) Summary of Effects According to the present embodiment, biasing means for constantly biasing the separating cam 141 in a direction away from the contact portion 125 is provided, and the separating cam 141 is brought into contact with the contact portion 125 by driving it against the biasing force of the biasing means after the drive member 138 meshes with the intermediate gear 144. As a result, the meshing position between the drive member 138 and the intermediate gear 144 is always constant, and it is possible to eliminate variations in the separation amount of the pressure roller 39 from the fixing belt 31 in the pressure release state.

[0098] In addition, a guiding mechanism 150 for aligning the positions of both members is provided at the meshing portion between the driving member 138, which is the driving source of the separating cam 141, and the intermediate gear 144 before the tooth tips of both members mesh with each other. Therefore, it is possible to prevent a temporary increase in torque and the generation of abnormal noise due to the contact of the tooth tips of the intermittent gear 145 of the driving member 138 and the intermediate gear 144.

[0099] When shifting to the pressure release state, a straight line connecting the contact portion between the rotation fulcrum (the second support shaft 132) of the separating cam and the contact portion 125 is perpendicular to the surface of the contact portion 125. Therefore, the force received from the pressurizing structure can be received by the rotation fulcrum (the second support shaft 132) of the separating cam 141, improving the positional accuracy when the heating structure and the pressurizing structure are separated and suppressing the load applied to the driving member 138 when the pressure release state is maintained.

[0100] Also, in the pressure release state, by making the pressure roller (pressurizing structure) 39 and the fixing belt (heating structure) 31 lightly contact without completely separating them, it is possible to prevent toner stains caused by paper dropping.

[0101] Furthermore, the width of the long hole 135 provided in the pressure-applying cam 131 for switching the pressure contact state is formed to be the narrowest at the portion where the driving pin 136 is located when the pressure contact state is switched. Therefore, it is possible to accurately detect the pressure contact state by the movement of the pressure-applying cam 131.

[0102] <Modification Example> As described above, the present invention has been described based on the embodiments, but the present invention is not limited to the above-described embodiments, and the following modification examples are conceivable.

[0103] In the above-described embodiment, an example was shown in which a biasing member made of a coil spring was provided on the separation cam 141 on the front side in FIG. 4. However, instead of such a configuration of the separation cam 141, or together with such a configuration of the separation cam 141, a similar biasing member may be provided on the separation cam 141' on the back side. Further, the biasing member may be replaced with another elastic member as long as it can obtain the effect of constantly biasing the separation cam 141 in a direction away from the contact portion 125 instead of a torsion coil spring.

[0104] In the pressure contact state switching mechanism 100 in the above-described embodiment, a configuration in which the first switching portion 130 and the second switching portion 140 are driven by the same drive motor was shown. However, the present invention is not limited to this, and each switching portion may have a dedicated drive source.

[0105] Further, in the above-described embodiment, the support shaft of the pressure contact cam 131 and the support shaft of the separation cam 141 are shared by the same drive shaft. However, they may be pivotally supported at different positions as long as each switching portion can achieve the above-described pressure contact state switching operation.

[0106] In the above-described embodiment, the sub-frame 120 is biased in a direction approaching the main frame 110 by the tension springs 133 and 134. However, as the elastic member for biasing, not limited to the tension spring, a compression spring, a helical spring, a leaf spring, etc. may be used.

[0107] In the above-described embodiment, an example in which a fixing belt is stretched between a heating roller and a fixing pad as a heating structure was described. However, a configuration may be adopted in which a fixing nip is directly formed by a fixing roller and a pressure roller without passing through the fixing belt.

[0108] In this case, the separation cam 141 that is constantly biased in a direction away from the contact portion 125 by the biasing means may be brought into contact with the rotation shaft of the fixing roller or the like.

[0109] The pressurizing structure is not limited to a rotating body such as a pressurizing roller, and a fixing pad may be used. That is, any fixing device having a configuration in which a fixing nip is formed by a heated heating structure and a pressurizing structure for pressurizing the same, and a recording sheet is passed through the fixing nip for fixing can be applied.

[0110] Further, the heat source for heating the heating structure is not limited to the method of heating the fixing belt 31 with a halogen heater, and may be a method of electromagnetic induction heating the heat generating layer of the fixing belt 31 using an exciting coil, a method of heating the fixing belt 31 with a resistance heating element, or the like.

[0111] In the above embodiment, the pressure contact state is switched by fixing the heating structure side and moving the pressurizing structure side. However, the present invention is not limited to this, and the heating structure may be moved to the pressurizing structure side.

[0112] In the above embodiment, a tandem type printer has been described. However, the present invention is not limited to this, and an image forming apparatus such as a FAX, a copying machine, or an MFP (Multiple Function Peripheral) may be used.

[0113] Further, the above-described configuration is applicable not only to an image forming apparatus but also to a pressure contact state switching device that needs to switch the pressure contact state between a first pressure contact state and a second pressure contact state having different pressing forces and a pressure contact release state for releasing these pressure contact states between a first member (first structure) and a second member (second structure).

[0114] <Supplementary Note> Regarding the fixing device and the image forming apparatus according to the present invention, embodiments and modified examples have been described. However, the present invention is not limited to the above-described embodiments and modified examples. Forms obtained by applying various modifications conceivable by those skilled in the art to the above-described embodiments and modified examples, and forms realized by arbitrarily combining the components and functions in the embodiments and modified examples without departing from the spirit of the present invention are also included in the present invention. The scope of the present invention should be interpreted by the appended claims.

Industrial Applicability

[0115] The present invention is effective as a technique for switching the pressure contact state between a heating structure and a pressurizing structure in a pressure contact state in a fixing device.

Explanation of Signs

[0116] 1 Printer 10 Image forming unit 20 Paper feeding unit 30 Fixing device 31 Fixing belt 32 Fixing pad 35 Heating roller 39 Pressurizing roller 100 Pressure contact state switching mechanism 110 Main frame 120 Sub-frame 130 First switching unit 131 Cam for pressure contact 133, 134 Tension springs 135 Long hole 136 Driving pin 138 Driving member 140 Second switching unit 141, 141' Cams for separation 142 Protruding cam portion 143 Partial gear 144, 144' Intermediate gears 145 Intermittent gear 147 Twisted coil spring

Claims

1. A fixing device that forms a nip portion by pressing a pressure structure against a heating structure, passes a recording sheet having an unfixed toner image transferred to the nip portion, and fixes the toner image to the recording sheet, wherein a pressure contact state switching mechanism is provided for selectively switching the pressure contact state between the heating structure and the pressure structure to any one of a first pressure contact state, a second pressure contact state having a different pressure contact force from the first pressure contact state, and a pressure contact release state; the pressure contact state switching mechanism when shifting to the pressure contact release state, a separation cam that presses the contact portion of the pressure structure to separate the pressure structure from the heating structure by transmitting a driving force from a driving member through a gear meshing therewith; biasing means for constantly biasing the separation cam in a direction away from the contact portion; and the separation cam contacts the contact portion by being driven against the biasing force of the biasing means after the driving member meshes with the gear. A fixing device characterized by the above.

2. The gear for transmitting the driving force from the driving member to the separation cam includes an intermittent gear provided on the driving member and an intermediate gear that can mesh with the intermittent gear and mesh with the separation cam, the separation cam is constantly meshed with the intermediate gear, the intermittent gear meshes with the intermediate gear only when the driving member is in a specific rotational phase, The fixing device according to claim 1, wherein a guiding mechanism for aligning the positions of the intermittent gear and the intermediate gear with each other before meshing is provided between the intermittent gear and the intermediate gear.

3. The separation cam in the pressure contact release state contacts such that a straight line connecting the support shaft and the contact portion of the contact portion is perpendicular to the surface of the contact portion. The fixing device according to claim 1.

4. The pressure contact state between the pressure structure and the heating structure in the pressure contact release state is a state in which the pressure structure and the heating structure are in light contact. The fixing device according to claim 1.

5. The second holding member for holding the pressure structure is pivotally supported relative to the first holding member for holding the heating structure via a first support shaft so as to be relatively swingable, The switching portion for switching between the first pressure contact state and the second pressure contact state includes a pressure contact cam swingably held on the first holding member via a second support shaft and a drive pin provided on the drive member for swinging the pressure contact cam. The cam for pressing is formed with an elongated hole into which the drive pin is inserted to form a crank mechanism, and includes a detected portion that detects the pressing state by detecting its own rocking position. The fixing device according to claim 1, wherein the width of the elongated hole is formed to be the narrowest at a portion where the drive pin is located when the pressing state is switched.

6. The fixing device according to claim 5, wherein the cam for pressing and the cam for separating are driven by the same drive source and are non-interlocked.

7. The heating structure has a fixing belt stretched between a heating roller and a fixing pad, and the separating cam is in contact with a support member that supports the fixing pad by the biasing means until the drive member meshes with the gear. The fixing device according to claim 1, characterized in that.

8. The fixing device according to claim 1, wherein the pressing force between the heating structure and the pressurizing structure is set to be smaller in the first pressing state than in the second pressing state, and the transition to the pressing release state is from the first pressing state.

9. An image forming apparatus including a transfer unit that transfers a toner image onto a recording sheet and a fixing unit that fixes the transferred toner image onto the recording sheet, wherein the fixing unit uses the fixing device according to any one of claims 1 to 8. An image forming apparatus characterized by that.

Images