JP5632275B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly to a fixing device and an image forming apparatus capable of improving the pressure-bonding / separation (pressure-release) characteristics of a pressure roller with respect to a fixing roller.

  Image forming apparatuses such as copying machines, printers, and fax machines form a toner image based on image information on an image carrier, transfer the toner image to a recording material, and pass the recording material carrying the toner image through a fixing device. The toner image is fixed on the recording material by heat and pressure. As the fixing device, a heat roller method and a belt (or film) method are generally employed.

  A heat roller type fixing device has a fixing roller and a pressure roller, and the fixing roller itself is heated (see Patent Document 1). On the other hand, a belt-type fixing device has a fixing roller and a pressure roller, and a heated belt is supplied to the fixing roller (see Patent Document 2). In a normal operation state, the pressure roller is pressed against the fixing roller by a pressure spring and rotates. When the recording material carrying the toner image is passed between the pressure-bonded rollers, the toner image is melted by the heat of the fixing roller (or belt) and fixed on the recording material.

  However, if the pressure-bonded state of the roller is maintained over a long-time operation stop state, the roller may be deformed or the belt may be damaged. For this reason, for example, when the operation is stopped for a long time, when the recording material is jammed, or when the fixing roller is rapidly heated, the pressure roller is moved from the fixing roller against the urging force of the pressure spring. Separate.

  Usually, the pressure roller is pressed and separated from the fixing roller by a simple lever mechanism using a cam (see Patent Documents 1 and 2). The simple lever mechanism includes a pressure lever that holds the pressure roller, a pressure spring that urges the pressure roller to the fixing roller through the pressure lever, and a cam that operates the pressure lever. In the simple lever mechanism, the pressure roller is pressed against or separated from the fixing roller by moving the pressure lever toward / separating from the fixing roller by rotation of the cam.

JP 2005-326524 A JP 2009-237188 A

  However, when forming a high-quality image or a high-speed image, a wide fixing nip is required in the recording material conveyance direction in order to secure the fixing time of the fixing roller with respect to the recording material. Therefore, it is necessary to ensure a large pressure contact (compression) distance and separation distance of the pressure roller with respect to the fixing roller.

  Therefore, in the conventional fixing device, the operating distance of the pressure roller is increased by increasing the operating radius of the cam (difference between the maximum radius and the minimum radius) or increasing the lever ratio. However, as a result, there is a problem that the space for accommodating the cam and the pressure lever is increased, and the fixing device itself is further increased in size.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fixing device and an image forming apparatus capable of improving the pressure-bonding / separation (pressure-release release) characteristics of the pressure roller with respect to the fixing roller.

  According to an aspect of the present invention, the fixing roller, the pressure roller, the cam, and one end are rotatably supported, the other end has a contact point with the cam, and an intermediate point between the one end and the other end. It has a first link, a first end, a second end, and a third end, the first end is rotationally joined to the intermediate point of the first link, and the second end is capable of rotating the pressure roller in the roller axial direction. A second link to be supported, a third link whose one end is rotationally supported and whose other end is rotationally joined to the third end of the second link, and a biasing force which biases the pressure roller toward the fixing roller through the first link A fixing device is provided. In the fixing device, when the first link moves in the direction approaching the fixing roller by the rotational operation of the cam against the urging force of the urging member, the second link is intermediate between the rotation support point of the first link. The second end is moved so that the second end moves to the opposite side of the fixing roller from the reference line when the first link moves in a direction away from the fixing roller from the reference line connecting the points. Control the rotation of the link.

  The maximum operating distance (d2 ′) of the pressure roller is the distance (L3) between the rotation support point of the first link and the rotation support point of the pressure roller, and the contact point of the rotation support point of the first link and the cam. It may be larger than a value obtained by multiplying the ratio (L3 / L4) to the distance (L4) between the two and the cam operating radius (d3).

  The reference angle Θ between the auxiliary line extending perpendicularly to the operating direction of the pressure roller from the first end and the second end located on the opposite side of the auxiliary line with respect to the first end is determined by the pressure roller Is in the range of 160 ° to 270 ° when it is farthest from the fixing roller, and the operation distance of the pressure roller gradually increases in the vicinity where the pressure roller approaches the fixing roller and the operation distance becomes maximum. Also good.

  The reference angle between the auxiliary line extending perpendicularly to the operation direction of the pressure roller from the first end and the second end located on the opposite side of the auxiliary line with respect to the first end is determined by the pressure roller It may be 180 ° −α or 180 ° + α when it is farthest from the fixing roller, and 180 ° + α or 180 ° −α when it is closest.

  According to another aspect of the present invention, an image forming apparatus having the above-described fixing device is provided.

  According to the present invention, it is possible to provide a fixing device and an image forming apparatus capable of improving the pressure-bonding / separation (pressure-release release) characteristics of the pressure roller with respect to the fixing roller.

1 is a diagram illustrating an outline of a general color image forming apparatus. It is a figure which shows an example of a structure and operation | movement (crimping operation | movement) of a fixing device which has a simple lever mechanism. It is a figure which shows an example of a structure and operation | movement (separation operation | movement) of a fixing device which has a simple lever mechanism. It is a figure which shows an example of a structure and operation | movement (crimping operation | movement) of a fixing device which has a four-bar linkage mechanism which concerns on embodiment of this invention. It is a figure which shows an example of a structure and operation | movement (separation operation | movement) of a fixing device which has a four-bar linkage mechanism which concerns on embodiment of this invention. It is a figure which shows the increase tendency of the operating distance of a pressure roller. It is a figure for demonstrating the change of the increase tendency of the operating distance of a pressure roller according to arrangement | positioning of a link mechanism. It is a figure for demonstrating the definition of a reference angle.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

[1. Configuration of image forming apparatus]
FIG. 1 is a diagram showing an outline of a general color image forming apparatus. As shown in FIG. 1, the image forming apparatus includes an image forming unit 1 that forms a superimposed toner image on a recording material P, and a fixing device 2 that fixes the superimposed toner image on the recording material P.

  The image forming means 1 includes first to fourth image carriers 3Y, 3M, 3C, and 3BK configured as drum-shaped photoconductors. Yellow, magenta are provided on the image carriers 3Y, 3M, 3C, and 3BK, respectively. , Cyan and black toner images are respectively formed. A transfer belt 4 is arranged to face the first to fourth image carriers 3Y, 3M, 3C, 3BK. The transfer belt 4 is wound around a drive roller 4a and a driven roller 4b and is driven to travel in the direction of arrow A. Is done.

  For example, the image carrier 3Y carrying a yellow toner image is rotated in the clockwise direction, and the surface of the image carrier 3Y is uniformly charged to a predetermined polarity by the charging roller 5. Next, the charged surface is irradiated with a laser beam L that is optically modulated from the laser writing unit 6. As a result, an electrostatic latent image is formed on the image carrier 3Y, and the electrostatic latent image is visualized as a yellow toner image by the developing device 7.

  On the other hand, a recording material P is fed from a paper feeding unit (not shown), and the recording material is fed between the image carrier 3Y and the transfer belt 4 as indicated by an arrow B, and is carried by the transfer belt 4 and conveyed. Is done. A transfer roller 8 is disposed at a position substantially opposite to the image carrier 3Y across the transfer belt 4, and a voltage having a polarity opposite to the charging polarity of the toner on the image carrier 3Y is applied to the transfer roller 8. The As a result, the toner image on the image carrier 3Y is transferred to the recording material P. The residual toner that is not transferred to the recording material P and remains on the image carrier 3Y is removed by the cleaning device 9.

  Similarly, magenta, cyan, and black toner images are respectively formed on the second to fourth image carriers 3M, 3C, and 3BK, and the yellow toner image is sequentially superimposed and transferred onto the transferred recording material P. Is done. In this way, an “overlapped toner image” is formed on the recording material P by superimposing four color toner images.

  The recording material P carrying the superimposed toner image is fed into the fixing device 2 as indicated by an arrow C. In the fixing device 2, the pressure roller 12 is pressed against the fixing roller 11 by the pressure spring 14 and rotates. When the recording material P carrying the superimposed toner image is passed between the pressure-bonded rollers 11 and 12, the toner image is melted and fixed to the recording material P by the heat of the fixing roller 11. Then, the recording material P that has passed through the fixing device 2 is discharged to a paper discharge tray (not shown).

[2. Fixing device 10 having a simple lever mechanism]
2A and 2B are diagrams illustrating an example of the configuration and operation of the fixing device 10 having a simple lever mechanism. FIG. 2A shows a transition from the separated state to the crimped state, and FIG. 2B shows a transition from the crimped state to the separated state. Note that the separated state is a state in which the pressure roller 12 is separated from the fixing roller 11, and the pressure-bonded state is a state in which the pressure roller 12 is pressure-bonded to the fixing roller 11.

  2A and 2B, the fixing device 10 includes a fixing roller 11, a pressure roller 12, a pressure lever 13, a pressure spring 14, and a cam 15. The fixing roller 11 is rotatably supported by a frame (not shown) of the image forming apparatus via a rotation support point 11a. The pressure roller 12 is rotationally joined to the pressure lever 13 via a rotation support point 12a. The pressure lever 13 is a substantially rod-shaped member, one end (rotation support point 13 a) is rotatably supported by a frame or the like, the other end has a contact point 13 b with the cam 15, and the intermediate point 13 c is the pressure roller 12. Is rotatably supported in the direction of the roller shaft 12a. The pressure spring 14 has one end 14 a fixed to the frame and the other end 14 b fixed to the pressure lever 13. The cam 15 is rotatably supported by a frame or the like so as to contact the other end of the pressure lever 13 at the contact point 13b, and is driven to rotate by a motor or the like (not shown).

  Here, the distance from the rotation support point 13a of the pressure lever 13 to the intermediate point 13c is L1, and the distance from the rotation support point 13a of the pressure lever 13 to the contact point 13b is L2. The maximum radius of the cam 15 is d3, and the minimum radius is d4.

  FIG. 2A shows a transition from the separated state to the crimped state. In the pressure-bonded state, the pressure lever 13 is urged toward the side closer to the fixing roller 11 by the pressure spring 14. The cam 15 is in contact with the pressure lever 13 with a minimum radius d4. The pressure lever 13 rotates counterclockwise from the separated state with the rotation support point 13a as a reference (M2) according to the rotation of the cam 15 (M1), and presses the pressure roller 12 to the fixing roller 11 (M3). ). As a result, the pressure roller 12 compresses the surface of the fixing roller 11 by a pressure (compression) distance d1 in a direction connecting the roller shaft 12a of the fixing roller 12 and the roller shaft 11a of the fixing roller 11. The crimping distance d1 is approximately d1 = (d3−d4) × (L1 / L2).

  FIG. 2B shows a transition from the crimped state to the separated state. In the separated state, the cam 15 is in contact with the pressure lever 13 with a maximum radius d3. The pressure lever 13 rotates to the side away from the fixing roller 11 against the pressure spring 14. In response to the rotation of the cam 15 (M4), the pressure lever 13 rotates clockwise (M5) from the above-described pressure-bonded state with the rotation support point 13a as a reference, thereby separating the pressure roller 12 from the fixing roller 11. (M6). As a result, the pressure roller 12 is separated from the surface of the fixing roller 11 compressed by the pressure contact distance d1 by a separation distance d2 (d1 ≦ d2) in the direction of the roller shaft 12a of the pressure roller 12. The separation distance d2 is approximately d2 = (d3−d4) × (L1 / L2). When the pressure contact distance d1 = the separation distance d2, the pressure roller 12 contacts the fixing roller 11 without compressing the surface of the fixing roller 11.

  Here, in order to realize a wide fixing nip N in the conveyance direction of the recording material P, it is necessary to ensure a large pressing distance d1 and a separation distance d2, that is, a maximum operating distance of the pressure roller 12 (= separation). A large distance d2) must be ensured. For this reason, the operating radius of the cam 15 (difference between the maximum radius and the minimum radius: d3-d4) is increased, or the lever ratio (L1 / L2) of the pressure lever 13 is increased. Then, the operation occupation range of the cam 15 is increased, or the distance between the rotation support point 13a of the pressure lever 13 and the pressure roller 12 is increased. Therefore, there arises a problem that the fixing device 2 itself further increases in size of the image forming apparatus.

[3. Fixing device 20 having a four-bar linkage mechanism]
3A and 3B are diagrams illustrating a configuration example of the fixing device 20 having the four-bar linkage mechanism according to the embodiment of the present invention. 3A shows a transition from the separated state to the crimped state, and FIG. 3B shows a transition from the crimped state to the separated state.

  As shown in FIG. 3, the fixing device 20 includes a fixing roller 21, a pressure roller 22, a first link 23, a second link 24, a third link 25, a pressure spring 26 (biasing member), and a cam 27. Become. The fixing roller 21 is rotatably supported by a frame (not shown) of the image forming apparatus. The pressure roller 22 is rotationally joined to the first link 23. The first link 23 is a substantially rod-like member, one end (rotation support point 23a) is rotatably supported by a frame or the like, the other end has a contact point 23b with the cam 27, and the rotation support point 23a and the contact point 23b. Has an intermediate point 23c. The second link 24 is a substantially triangular member, and has a first end 24 a, a second end 24 b, and a third end 24 c at each vertex of the triangle, and the first end 24 a is an intermediate point of the first link 23. The second end 24b rotatably supports the pressure roller 22 in the direction of the roller shaft 22a. The third link 25 is a substantially rod-shaped member, one end (rotation support point 25 a) is rotatably supported, and the other end 25 b is rotationally joined to the third end 24 c of the second link 24. The pressure spring 26 has one end 26 a fixed to the frame and the other end 26 b fixed to the first link 23. The cam 27 is rotatably supported by a frame or the like so as to contact the other end of the first link 23 at the contact point 23b, and is driven to rotate by a motor or the like (not shown).

  3A and 3B, the rotation support point 23a of the first link 23 and the rotation support point 25a of the third link 25 are in a direction connecting the roller shaft 21a of the fixing roller 21 and the roller shaft 22a of the pressure roller 22. It is arrange | positioned substantially parallel with respect to. Further, the second link 24 is arranged such that the distance from the rotation support point 23a of the first link 23 is the largest at the first end 24a, then the largest at the third end 24c, and the smallest at the second end 24b. Has been.

  Here, the distance from the rotation support point 23a of the first link 23 to the second end 24b (the roller shaft 22a of the pressure roller 22) of the second link 24 is L3, and the cam support from the rotation support point 23a of the first link 23 is set to L3. The distance to the contact 23b is L4. The maximum radius of the cam 27 is d3 + d4, and the minimum radius is d4.

  FIG. 3A shows a transition from the separated state to the crimped state. In the pressure-bonded state, the first link 23 is biased toward the side closer to the fixing roller 21 by the pressure spring 26. The cam 27 is in contact with the first link 23 with a minimum radius d4. The second link 24 presses the pressure roller 22 against the fixing roller 21 in a state where the rotation is controlled by the third link 23.

  In the transition from the separated state to the crimped state, the four-bar linkage mechanism operates as follows. The cam 27 is rotationally driven from a state in which the cam 27 is in contact with the first link 23 with a maximum radius d3 to a state in which the cam 27 is in contact with a minimum radius d4 (M11). In response to the rotation of the cam 27, the first link 23 rotates counterclockwise with respect to the rotation support point 23a (M12). The second link 24 moves to the side closer to the fixing roller 21 in conjunction with the rotation of the first link 23 through the joining of the first end 24a and the intermediate point 23c of the first link 23 (M13). The third link 25 rotates counterclockwise with the rotation support point 25a as a reference in conjunction with the movement of the second link 24 through the joining of the other end 25b and the third end 24c of the second link 24 (M14). . The second link 24 rotates clockwise with respect to the first end 24a in conjunction with the rotation of the third link 25 through the joining of the third end 24c and the other end 25b of the third link 25 (M15).

  That is, the second link 24 moves to the side closer to the fixing roller 21 in conjunction with the rotation of the first link 23 (M13), while the second link 24 operates in conjunction with the rotation of the third link 25 with respect to the first end 24a as a reference. Rotate in the direction (M15). Then, the second link 24 moves to the fixing roller 21 side with respect to the reference line RL connecting the rotation support point 23a of the first link 23 and the intermediate point 23c, that is, the second end 24b is fixed to the fixing roller. The pressure roller 22 is pressed against the fixing roller 21 (M16). As a result, the pressure roller 22 compresses the surface of the fixing roller 21 in the direction of the roller shaft 21a of the fixing roller 21 by a pressure (compression) distance d1 ′.

  FIG. 3B shows a transition from the crimped state to the separated state. In the separated state, the cam 27 is in contact with the first link 23 with a maximum radius d3. The first link 23 rotates to the side away from the fixing roller 21 against the pressure spring 26. The second link 24 separates the pressure roller 22 from the fixing roller 21 while the rotation is controlled by the third link 25.

  In the transition from the crimping state to the separated state, the four-bar linkage mechanism operates as follows. The cam 27 is rotationally driven from a state where it abuts against the first link 23 with a minimum radius d4 to a state where it abuts with a maximum radius d3 (M17). The first link 23 rotates clockwise based on the rotation support point 23a according to the rotation of the cam 27 (M18). The second link 24 moves to the side away from the fixing roller 21 in conjunction with the rotation of the first link 23 through the joining of the first end 24a and the intermediate point 23c of the first link 23 (M19). The third link 25 rotates clockwise with the rotation support point 25a as a reference in conjunction with the movement of the second link 24 through the joining of the other end 25b and the third end 24c of the second link 24 (M20). The second link 24 rotates counterclockwise with the first end 24a as a reference in conjunction with the rotation of the third link 25 through the joining of the third end 24c and the other end 25b of the third link 25 (M21). .

  That is, the second link 24 moves to the side away from the fixing roller 21 in conjunction with the rotation of the first link 23 (M19), and counteracts with the first end 24a as a reference in conjunction with the rotation of the third link 25. Rotate clockwise (M21). Then, the second link 24 moves to the opposite side of the fixing roller 21 from the reference line RL connecting the rotation support point 23a of the first link 23 and the intermediate point 23c, that is, the second end 24b is moved. The pressure roller 22 is moved away from the fixing roller 21 to move away from the fixing roller 21 (M22). As a result, the pressure roller 22 is separated from the surface of the fixing roller 21 by a separation distance d2 ′ in the direction of the roller shaft 22a of the pressure roller 22.

  FIG. 4 is a diagram showing an increasing tendency of the operating distance of the pressure roller 22. In FIG. 4, the horizontal axis indicates the change in the operation amount of the cam 27, and the vertical axis indicates the change in the operation distance of the pressure roller 22.

  Here, the operation amount of the cam 27 is a function of the distance between the cam shaft 27a and the cam contact point 23b on the first link 23, and is 0 in the separated state (the maximum radius of the cam 27: d3). The maximum value is obtained by (the minimum radius of the cam 27: d4). Similarly, the operating distance of the pressure roller 22 is a function of the distance between the roller shaft 21a of the fixing roller 21 and the roller shaft 22a of the pressure roller 22, and is 0 in the separated state and the maximum value in the pressure-bonded state. .

  FIG. 4 shows the increasing tendency of the operating distance of the pressure rollers 12 and 22 between the simple lever mechanism and the four-bar linkage mechanism. In both mechanisms, the lever ratio of the pressure lever 13 and the first link 23 is substantially the same (L1 / L2≈L3 / L4≈0.5), and the maximum radius d3 and the minimum radius d4 of the cams 15 and 27 are the same. It is.

  In this case, in the simple lever mechanism, the operating distance of the pressure roller 12 is approximately 0.5 times the operating amount of the cam 15. On the other hand, in the four-bar linkage mechanism, the operation distance of the pressure roller 22 is approximately one time the operation amount of the cam 27, that is, twice the simple lever mechanism. Therefore, the maximum operating distance of the pressure roller 22 can be increased from the maximum operating distance (d3 × L3 / L4 = 0.5d3) obtained from the lever ratio without increasing the cam operating radius and lever ratio. it can. Further, the operating distance of the pressure roller 22 increases substantially linearly in proportion to the operating amount of the cam 27.

  The operating distance of the pressure roller 22 in the four-bar linkage described above is merely an example, and the operating distance of the pressure roller 22 can be changed by changing the arrangement / shape of the link mechanism and the arrangement / shape of the cam 27. Can be set to approximately one time or more of the operation amount of the cam 27. Therefore, the design freedom of the fixing device 2 can be improved.

  FIG. 4 shows an increasing trend that gradually increases in the vicinity of the maximum operating distance, along with a substantially linear increasing trend. In the fixing device 2, it may be desired to gradually increase the operating distance of the pressure roller 22 in the vicinity of the maximum operating distance. This is because the fixing conditions such as the crimping distance fluctuate due to an error in the mechanism of the fixing device 2, but it is desirable to suppress the fluctuation of the fixing conditions as much as possible near the maximum operating distance that greatly affects the formation of the fixing nip N. is there. By gradually increasing the operating distance of the pressure roller 22 in the vicinity of the maximum operating distance, it is possible to relatively suppress the influence of fluctuations in the fixing conditions on the operating distance of the pressure roller 22.

  Further, in the fixing device 22, it may be desired to maximize the operating distance of the pressure roller 22. By maximizing the operating distance, it is possible to reduce the size of the fixing device 2 and the image forming apparatus while ensuring a sufficient fixing nip N.

  FIG. 5 is a diagram for explaining a change in the increasing tendency of the operating distance of the pressure roller 22 according to the arrangement of the link mechanism. In FIG. 5, the horizontal axis indicates the operation amount of the cam 27, and the vertical axis indicates the operation distance of the pressure roller 22. FIG. 5 schematically shows the movement locus of the second end 24 b of the second link 24 according to the rotation of the cam 27, that is, the roller shaft 22 a of the pressure roller 22.

  In connection with FIG. 5, FIG. 6 defines the angle between the auxiliary line AL and the second end 24b of the second link 24 around the first end 24a of the second link 24 as a reference angle Θ. Yes. Here, the auxiliary line AL is a line extending perpendicularly to the operation direction of the pressure roller 22 (the direction connecting the roller shaft 21a of the fixing roller 21 and the roller shaft 22a of the pressure roller 22) from the first end 24a. Defined. The reference angle Θ changes as the pressure roller 22 transitions between the separated state and the pressure-bonded state. For example, in the example of FIGS. 3A and 3B, the reference angle Θ increases when the pressure roller 22 transitions from the separated state to the pressure-bonded state. The range in which the reference angle Θ changes is determined according to the arrangement of the link mechanism.

  Here, the second link 24 rotates in a state in which the rotation is controlled by the third link 25 according to the rotation of the cam 27, and the second end 24 b moves by the rotation of the second link 24. The distance by which the second end 24b moves in the direction of operation of the pressure roller 22 is greater as the reference angle is closer to Θ = 180 ° and is further away from Θ = 180 ° with respect to changes in the amount of motion of the cam 27. Get smaller.

  That is, as shown in FIG. 5, the operating distance of the pressure roller 22 increases as the reference angle becomes closer to Θ = 180 ° (inclination), and increases as the reference angle moves away from Θ = 180 ° ( (Slope) becomes low. More specifically, the operation distance of the pressure roller 22 increases in a convex shape as the operation amount of the cam 27 increases in the range where the reference angle is Θ = 180 ° or more, and in the range where the reference angle is less than Θ = 180 °. Increasing in a concave shape.

  Therefore, in order to gradually increase the operating distance of the pressure roller 22 in the vicinity of the maximum operating distance, a range in which the increasing tendency of the operating distance gradually decreases in the vicinity of the maximum operating distance, for example, Θ = 160 ° to 270. The reference angle Θ may be changed within the range R1. For example, if the reference angle is changed within the range R2 of Θ = 160 ° to 220 °, the operating distance tends to increase in the range of Θ = 160 ° to 200 °, and the operation is performed in the range of Θ = 200 ° to 220 °. The increasing tendency of distance becomes relatively low. Of course, the reference angle Θ is not limited to the above range, and may be changed, for example, in a range R3 of Θ = 180 ° to 220 °, or may be changed in a range R4 of Θ = 230 ° to 270 °. In any range, the operating distance of the pressure roller 22 gradually increases in the vicinity of the maximum operating distance.

  Further, in order to maximize the operating distance of the pressure roller 22, the range in which the increasing tendency of the operating distance is maximized, that is, Θ = 180 ° −α to 180 ° + α centered on the reference angle Θ = 180 °. The reference angle Θ may be changed within the range. For example, if the reference angle is changed in the range R5 (α = 20 °) from Θ = 160 ° to 200 °, the operating distance is changed between Θ = 160 ° to 180 ° and Θ = 180 ° to 200 °. Any increase trend can be increased to maximize the total operating distance. Further, for example, the reference angle may be changed in a range R6 (α = 10 °) of Θ = 170 ° to 190 °. In either range, the operating distance of the pressure roller 22 is maximized.

  As shown in FIG. 4, in order to increase the operating distance of the pressure roller 22 substantially linearly, the range in which the increasing tendency of the operating distance is approximately linear, that is, the reference angle is Θ = 180 °. It is only necessary to change the reference angle within a narrow range in the vicinity.

[4. Summary]
As described above, according to the fixing device 2 and the image forming apparatus according to the embodiment of the present invention, by using the four-bar link mechanism, the pressure-contact / separation (pressure-release release) characteristics of the pressure roller 22 with respect to the fixing roller 21. Can be improved. As the pressure contact / separation characteristics, the maximum operating distance of the pressure roller 22 can be increased, the operating distance can be gradually increased near the maximum operating distance, or the operating distance can be maximized.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  For example, in the above description, the case where the cam 27 is rotationally driven by a motor or the like has been described, but the cam 27 may be manually rotationally driven. In the above description, the case where the pressure roller 22 is biased by the pressure spring 26 has been described. However, the pressure roller 22 may be biased by a biasing means (elastic means) other than the pressure spring 26. . In the above description, the embodiment of the color image forming apparatus has been described. However, the present invention is similarly applied to a monochrome image forming apparatus.

10, 20 Fixing device 11, 21 Fixing roller 12, 22 Pressing roller 13 Pressing lever 14, 26 Pressing spring 15, 27 Cam 23 First link 24 Second link 25 Third link

Claims (5)

A fixing roller, a pressure roller, a cam,
A first link having one end rotatably supported, the other end having a contact point with the cam, and an intermediate point between the one end and the other end;
The first end has a first end, a second end, and a third end, the first end is rotationally joined to the intermediate point of the first link, and the second end is capable of rotating the pressure roller in the roller axial direction. A second link to support,
A third link whose one end is rotationally supported and whose other end is rotationally joined to the third end of the second link;
A biasing member that biases the pressure roller toward the fixing roller through the first link;
When the first link moves in a direction approaching the fixing roller by the rotational operation of the cam against the urging force of the urging member, the second link is supported by the rotation of the first link. When the first link moves in a direction away from the fixing roller with respect to the reference line connecting the point and the intermediate point, the second end is closer to the fixing roller than the reference line. A fixing device that controls rotation of the second link so as to move to the opposite side.   The maximum operating distance (d2 ′) of the pressure roller is the distance (L3) between the rotation support point of the first link and the rotation support point of the pressure roller, and the rotation support of the first link. The fixing device according to claim 1, wherein the fixing device is larger than a value (L3 / L4) of a distance (L3 / L4) between a point and the contact point of the cam multiplied by an operating radius (d3) of the cam.   A reference angle between an auxiliary line extending perpendicularly to the operation direction of the pressure roller from the first end and the second end located on the opposite side of the auxiliary line with respect to the first end is When the pressure roller is farthest from the fixing roller, the pressure roller is in a range of 160 ° to 270 °. The operating distance of the pressure roller is the maximum when the pressure roller approaches the fixing roller. The fixing device according to claim 1, wherein the fixing device gradually increases in the vicinity of   A reference angle between an auxiliary line extending perpendicularly to the operation direction of the pressure roller from the first end and the second end located on the opposite side of the auxiliary line with respect to the first end is The pressure roller is 180 ° −α or 180 ° + α when the pressure roller is farthest from the fixing roller, and 180 ° + α or 180 ° −α when closest to the pressure roller. Fixing device. An image forming apparatus comprising the fixing device according to claim 1.

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