Fixing device and image forming apparatus

Abstract

To provide a fixing device that prevents excessive rotation of an eccentric cam rotating reciprocatingly, and an image forming apparatus.SOLUTION: A fixing device 12 comprises: a fixing belt 31; a pressure application roller 32 that forms a pressure application area N with the fixing belt 31; and a pressure changing unit 34 that can be changed between a pressure application state S1 where it applies pressure to the pressure application area N and a pressure reduction state where it reduces the pressure in the pressure application area N. The pressure changing unit 34 has an eccentric cam 50 that reciprocatingly rotates about an axis while bringing its outer peripheral surface into contact with or opposite to a cam follower 45 of a support part 40, and a regulation part 55 that regulates the rotation of the eccentric cam 50 exceeding a reciprocating rotation range. The eccentric cam 50 has a pressure application surface part 52A that brings the pressure application area N into the pressure application state S1, and a pressure reduction surface part that brings the pressure application area N into the pressure reduction state. The regulation part 55 regulates the rotation of the eccentric cam 50 by interfering with part of the support part 40 while bringing the pressure application surface part 52A or the pressure reduction surface part into contact with or opposite to the cam follower 45.SELECTED DRAWING: Figure 10

Description

[Technical field]

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

[0002] A fixing device is known that includes a pressure mechanism that applies nip pressure between a heating member and a pressure member, and a pressure adjustment mechanism that varies the nip pressure (Patent Document 1). The pressure adjustment mechanism has an eccentric cam whose distance from the rotation center to its outer circumferential surface changes in the circumferential direction, and the eccentric cam rotates forward and backward (reciprocating), applying nip pressure by the pressure mechanism at a large diameter portion formed on the outer circumferential surface, and releasing the nip pressure at a small diameter portion. When nip pressure is applied using the large diameter portion of the eccentric cam, a reaction force that tends to rotate the eccentric cam in the direction of the small diameter portion is always acting on the eccentric cam. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-107034 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned technology, when the nip pressure is applied, the eccentric cam in contact with the pressurizing mechanism may rotate past the large diameter portion against the reaction force. Similarly, when the nip pressure is released, the eccentric cam in contact with the pressurizing mechanism may rotate past the small diameter portion. When the eccentric cam rotates past the large diameter portion or the small diameter portion, it becomes locked so that it cannot rotate forward or backward, and there is a problem that it is necessary to restore it by disassembling the fixing device, for example.

[0005] SUMMARY OF THE PRESENT DISCLOSURE In consideration of the above circumstances, the present invention provides a fixing device and an image forming apparatus that prevent excessive rotation of an eccentric cam that reciprocates. [Means for solving the problem]

[0006] The fixing device includes a fixing member that heats toner on a medium while rotating about an axis, a pressure member that forms a pressure area between the fixing member and the pressure member while rotating about an axis and pressurizes the toner on the medium passing through the pressure area, and a pressure change unit that is configured to be switchable between a pressurized state in which one of the fixing member and the pressure member is pressed against the other to pressurize the pressure area, and a depressurized state in which the pressure of the fixing member and the pressure member is released to depressurize the pressure area, and the pressure change unit includes a support unit that rotatably supports either the fixing member or the pressure member and moves within a range corresponding to the pressurized state and the depressurized state, and a support unit that rotates around the axis while bringing an outer circumferential surface into contact with or facing a cam follower provided on the support unit. the eccentric cam has a pressure surface portion formed at one end of the reciprocating rotation range of the outer circumferential surface and bringing the pressurized region into the pressurized state, and a pressure reduction surface portion formed at the other end of the reciprocating rotation range of the outer circumferential surface and bringing the pressurized region into the depressurized state, and the pressure reduction surface portion is arranged in a state where the pressure surface portion is in contact with or facing the cam follower and interferes with a part of the support portion to reduce the rotation of the eccentric cam toward one side of the reciprocating rotation range, and the pressure reduction surface portion is arranged in a state where the pressure reduction surface portion is in contact with or facing the cam follower and interferes with a part of the support portion to reduce the rotation of the eccentric cam toward the other side of the reciprocating rotation range.

[0007] In this case, the pressure change unit further has a drive unit that rotates the eccentric cam back and forth, and when an overcurrent occurs in the drive unit while the regulating unit is interfering with a part of the support unit, the drive unit stops.

[0008] The image forming apparatus includes the fixing device described above. Effect of the Invention

[0009] According to the present invention, excessive rotation of the reciprocating eccentric cam can be prevented. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view (front view) showing an outline of the inside of an image forming apparatus according to one embodiment of the present invention. [Diagram 2] FIG. 1 is a perspective view showing a fixing device according to an embodiment of the present invention. [Diagram 3] 1 is a cross-sectional view (front view) showing a fixing device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view (rear view) showing a pressure changing section and the like of the fixing device (in a pressure applying state) according to one embodiment of the present invention. [Diagram 5] FIG. 4 is a cross-sectional view (rear view) showing a pressure changing unit and the like of the fixing device (in a reduced pressure state) according to one embodiment of the present invention. [Figure 6] FIG. 4 is a rear view showing the eccentric cam of the pressure changing portion of the fixing device according to the embodiment of the present invention. [Figure 7] FIG. 4 is a perspective view showing an eccentric cam of a pressure changing portion of the fixing device according to an embodiment of the present invention. [Figure 8] FIG. 4 is a cross-sectional view (rear view) showing a transmission type optical sensor and the like of a pressure changing unit of a fixing device (in a pressured state) according to one embodiment of the present invention. [Figure 9] FIG. 4 is a cross-sectional view (rear view) showing a transmissive optical sensor and the like of a pressure changing unit of a fixing device (in a reduced pressure state) according to one embodiment of the present invention. [Figure 10] 10 is a cross-sectional view (rear view) illustrating the operation of a regulating portion of a pressure changing portion of the fixing device (in a pressured state) according to an embodiment of the present invention. FIG. [Figure 11] 11 is a cross-sectional view (rear view) illustrating the operation of a regulating portion of a pressure changing unit of a fixing device (in a reduced pressure state) according to an embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. Note that Fr, Rr, L, R, U, and D shown in the drawings indicate front, rear, left, right, top, and bottom. Terms indicating directions and positions are used in this specification, but these terms are used for convenience of explanation and do not limit the technical scope of the present invention.

[0012] An image forming apparatus 1 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view (front view) showing an outline of the inside of the image forming apparatus 1.

[0013] [Image forming device] The image forming apparatus 1 is a color printer that forms an image by transferring a full-color toner image formed by an electrophotographic method onto paper P (medium). The image forming apparatus 1 includes an apparatus main body 2 that has a substantially rectangular parallelepiped appearance. A cassette 3 that stores paper P is removably provided at the bottom of the apparatus main body 2, and a paper output tray 4 onto which paper P with an image formed thereon is output is provided on the top surface of the apparatus main body 2. Four toner containers 5 that store refill toner (developers) of four colors (magenta, cyan, yellow, and black) are removably attached below the paper output tray 4. The medium is not limited to paper P made of paper, and may be a resin sheet or the like.

[0014] On the right side inside the device body 2, a transport path 6 and a reversing transport path 7 are formed as paths for transporting the paper P. The transport path 6 is formed in a roughly S-shape along the vertical direction, and is a path for transporting the paper P from the cassette 3 to the paper output tray 4. The reversing transport path 7 branches off to the right on the downstream side of the transport path 6, extends downward, and merges with the upstream side of the transport path 6. The reversing transport path 7 is a path for reversing the paper P and transporting it again to the imaging device 11 described below. In this specification, the terms "upstream" and "downstream" refer to "upstream" and "downstream" in the transport direction of the paper P (medium).

[0015] Provided inside the apparatus main body 2 are a paper feeder 10, an image forming device 11, a fixing device 12, and a control unit 13. The paper feeder 10 is provided at the upstream end of the transport path 6, and sends out the paper P stored in the cassette 3 to the transport path 6 while separating the paper P one by one. The image forming device 11 is provided downstream of the paper feeder 10, and the fixing device 12 is provided downstream of the image forming device 11. The fixing device 12 applies pressure to the toner image on the paper P while heating it, thereby thermally fixing the toner image on the paper P. The control unit 13 has overall control over the image forming apparatus 1.

[0016] <Imaging device> The imaging device 11 has an intermediate transfer belt 14, four drum units 15, and an optical scanning device 16. The intermediate transfer belt 14 is provided below the toner container 5, stretched over a number of rollers, and rotates in the direction indicated by the arrow in FIG. 1. The four drum units 15 correspond to the four colors of toner, and are aligned in the left-right direction below the intermediate transfer belt 14. The optical scanning device 16 is provided below the drum units 15. Note that the four drum units 15 have the same structure, so the following description will focus on one drum unit 15.

[0017] The drum unit 15 has a photoconductor drum 20, a charging device 21, a developing device 22, a primary transfer roller 23, and a cleaning device 24. The photoconductor drum 20 rotates around its axis while contacting the underside of the intermediate transfer belt 14. The charging device 21, the developing device 22, the primary transfer roller 23, and the cleaning device 24 are arranged around the photoconductor drum 20 in the order of the image formation process. The primary transfer roller 23 faces the photoconductor drum 20 from above, sandwiching the intermediate transfer belt 14 between them. A secondary transfer roller 25 contacts the right end of the intermediate transfer belt 14 to form a transfer nip. A pair of registration rollers 26 is provided upstream of the secondary transfer roller 25.

[0018] <Control Unit> The control unit 13 has a storage unit that stores programs, data, etc., a calculation processing unit that executes calculation processing according to the programs, etc., and a communication unit that is communicatively connected to each control target (all not shown). The storage unit, the calculation processing unit, and the communication unit are electrically connected to each other and configured to be communicatively connected to each other. The storage unit includes, for example, a storage medium such as a ROM (Read Only Memory) or a RAM (Random Access Memory), and the calculation processing unit includes, for example, a CPU (Central Processing Unit). Note that the control unit 13 may be realized by a logic circuit (hardware) formed in an integrated circuit or the like instead of a CPU.

[0019] [Image formation processing] Here, there will be described an operation of the image forming apparatus 1. For example, the control unit 13 executes an image forming process as follows, based on image data input from an external terminal.

[0020] The charging device 21 charges the surface of the photoconductor drum 20. The optical scanning device 16 exposes the photoconductor drum 20 to light, forming an electrostatic latent image corresponding to image data on the surface of the photoconductor drum 20. The developing device 22 develops the electrostatic latent image on the photoconductor drum 20 into a toner image using toner supplied from the toner container 5. The four-color toner images carried on the four photoconductor drums 20 are sequentially transferred to the rotating intermediate transfer belt 14 by a primary transfer roller 23 to which a primary transfer bias is applied. The intermediate transfer belt 14 carries a full-color toner image in which the four-color toner images are superimposed while rotating. The cleaning device 24 removes toner remaining on the surface of the photoconductor drum 20 after the primary transfer.

[0021] The paper feeder 10 takes out the paper P stored in the cassette 3 and sends it out to the transport path 6. The pair of registration rollers 26 temporarily block the paper P and send the skew-corrected paper P downstream. A secondary transfer roller 25 to which a secondary transfer bias is applied performs a second transfer of the toner image on the intermediate transfer belt 14 onto the surface of the paper P passing through the transfer nip. The fixing device 12 applies pressure to the toner transferred to the paper P and heats it to thermally fix it onto the paper P. In the case of single-sided printing, the paper P with the fixed toner image (image formed) is discharged to the paper output tray 4.

[0022] When double-sided printing is performed, the paper P that has passed through the fixing device 12 switches back at the downstream end of the conveying path 6 and is sent to the reversing conveying path 7. The paper P conveyed along the reversing conveying path 7 re-enters the conveying path 6, and an image is formed on the back side of the paper P in the same procedure as in the single-sided printing described above.

[0023] [Fixing device] Next, the fixing device 12 will be described with reference to Figs. 2 to 9. Fig. 2 is a perspective view showing the fixing device 12. Fig. 3 is a cross-sectional view (front view) showing the fixing device 12. Fig. 4 is a cross-sectional view (rear view) showing the pressure changing unit 34 and the like of the fixing device 12 (pressurized state S1). Fig. 5 is a cross-sectional view (rear view) showing the pressure changing unit 34 and the like of the fixing device 12 (reduced pressure state S2). Fig. 6 is a rear view showing the eccentric cam 50 of the pressure changing unit 34. Fig. 7 is a perspective view showing the eccentric cam 50 of the pressure changing unit 34. Fig. 8 is a cross-sectional view (rear view) showing the transmission type optical sensor 53 and the like of the fixing device 12 (pressurized state S1). Fig. 9 is a cross-sectional view (rear view) showing the transmission type optical sensor 53 and the like of the fixing device 12 (reduced pressure state S2).

[0024] As shown in FIGS. 2 and 3, the fixing device 12 includes a fixing belt 31, a pressure roller 32, a heat generating section 33, and a pressure changing section .

[0025] <Fixing belt> The fixing belt 31, which is an example of a fixing member, is made of a material in which metal and synthetic resin are laminated, and is formed into a substantially cylindrical shape that is long in the front-rear direction. As shown in FIG. 3, a belt support material 35, a pressure pad 36, and a belt guide 37 are provided inside the fixing belt 31. The belt support material 35 penetrates the fixing belt 31 in the axial direction, and both ends thereof are supported by the fixing frame 30 (see FIG. 2). The pressure pad 36 is made of a heat-resistant synthetic resin, is fixed to the belt support material 35 at a position facing the pressure roller 32, and is in contact with the inner surface of the fixing belt 31. The belt guide 37 is made of metal and is formed into a substantially semi-cylindrical shape that is long in the axial direction. The belt guide 37 is fixed to the belt support material 35 on the opposite side of the pressure pad 36, and is in contact with the inner surface of the fixing belt 31 to maintain the fixing belt 31 in a substantially cylindrical shape. The fixing belt 31 is rotatably supported by the belt support material 35 via a pair of caps 38 attached to both front and rear ends (see FIG. 2).

[0026] <Pressure roller> The pressure roller 32, which is an example of a pressure member, is formed in a generally cylindrical shape long in the front-rear direction and is disposed on the right side of the fixing belt 31. The pressure roller 32 is formed, for example, by laminating an elastic layer 32B made of synthetic resin on the outer peripheral surface of a metal core 32A. Both front and rear ends of the pressure roller 32 (core 32A) are rotatably supported by a pair of movable frames 41 (described later). The pressure roller 32 rotates around its axis by receiving a driving force from a motor (not shown) connected via a gear train or the like. The pressure roller 32 forms a pressure region N in which the pressure roller 32 is pressed against the fixing belt 31 and conveys the paper P while sandwiching it between the pressure roller 32 and the fixing belt 31. The pressure region N refers to a region from an upstream position where the pressure is 0 Pa, through a position where the pressure is maximum, to a downstream position where the pressure is 0 Pa again. In this embodiment, the pressure roller 32 (the surface) is always in contact with the fixing belt 31 (the surface).

[0027] <Heater> The heat generating unit 33 is disposed to the left of the fixing belt 31 with a gap therebetween. The heat generating unit 33 is an induction heating type heater that generates a magnetic field to cause the fixing belt 31 to self-heat. The belt guide 37 described above absorbs leakage magnetic flux that has passed through the fixing belt 31 and self-heats, thereby assisting in heating the fixing belt 31.

[0028] The motor for rotating the pressure roller 32 and the heat generating unit 33 are electrically connected to the control unit 13 and a power circuit (not shown) and are appropriately controlled by the control unit 13. In the present embodiment, the pressure roller 32 is driven to rotate, and the fixing belt 31 is driven to rotate, but the present invention is not limited to this. The fixing belt 31 may be driven to rotate, and the pressure roller 32 may be driven to rotate (not shown). In addition, the induction heating type heat generating unit 33 is disposed on the outside of the fixing belt 31 as a heat source. Instead of this, a halogen heater, a carbon heater, or the like may be disposed inside the fixing belt 31, or a heat generating resistor may be disposed in contact with the inner surface of the fixing belt 31 (neither of these are shown).

[0029] <Pressure change section> The pressure changing unit 34 is configured to be switchable between a pressurized state S1 (see FIG. 4) in which the pressurized roller 32 is pressed against the fixing belt 31 to pressurize the pressurized area N, and a reduced pressure state S2 (see FIG. 5) in which the pressure of the pressurized roller 32 is released to reduce the pressure of the pressurized area N. Note that the pressurized area N is in the pressurized state S1 during image formation processing, and the pressurized area N is in the reduced pressure state S2 during standby or the like. In the pressurized state S1, the fixing belt 31 is pressed by the pressurized roller 32 to deform, and rotates following the pressurized roller 32. In addition, even in the reduced pressure state S2, the pressurized roller 32 is in contact with the fixing belt 31.

[0030] 2 and 4, the pressure changing unit 34 has a support unit 40, a pair of eccentric cams 50, a pair of regulating units 55, a drive unit 60, and a control unit 13. Since the pair of eccentric cams 50 have substantially the same structure, this specification will mainly describe one (rear) eccentric cam 50. Similarly, this specification will mainly describe one (rear) regulating unit 55. The control unit 13 is a component included in the image forming apparatus 1, but is also a component of the pressure changing unit 34. The pressure changing unit 34 may include a dedicated control unit (not shown) instead of the control unit 13 that controls the image forming apparatus 1.

[0031] (Support part) 4 and 5, the support portion 40 has a pair of movable frames 41, a pair of pressing frames 42, and a pair of urging members 43. Since the pair of movable frames 41 have substantially the same structure, this specification will mainly describe one (rear) movable frame 41. Similarly, this specification will mainly describe one (rear) pressing frame 42 and one (rear) urging member 43.

[0032] (movable frame) The pair of movable frames 41 are disposed inside the fixing frame 30 on both sides in the front-rear direction with the pressure roller 32 sandwiched therebetween. The movable frame 41 is a metal plate having a substantially rectangular shape that is long in the vertical direction. The pair of movable frames 41 support both ends in the axial direction (front-rear direction) of the core metal 32A of the pressure roller 32 so as to be rotatable about the axis. The pressure roller 32 is supported at approximately the center in the vertical direction of the movable frame 41. The lower portion of the movable frame 41 is supported by a support shaft portion 44 provided on the fixing frame 30, and the movable frame 41 swings (reciprocates) in the left-right direction around the support shaft portion 44.

[0033] (Press frame) The pair of pressing frames 42 are disposed on the right side (opposite side of the fixing belt 31) of the pair of movable frames 41. The pressing frame 42 is a metal plate bent into a substantially L-shape. The lower part of the pressing frame 42 is supported by a support shaft portion 44, and the pressing frame 42 swings (reciprocates) in the left-right direction around the support shaft portion 44. In addition, a substantially disk-shaped (cylindrical) cam follower 45 is supported slightly above the pressing frame 42 so as to be rotatable about an axis.

[0034] (urging member) The biasing member 43 is, for example, a compression coil spring, and is installed between the upper part of the movable frame 41 and the upper part of the pressing frame 42 (above the cam follower 45). A guide bar 48 fixed to the fixing frame 30 passes through the upper parts of the movable frame 41 and the pressing frame 42, and the biasing member 43 is provided so as to be wound around the guide bar 48. The left end of the guide bar 48 is formed in a stepped rod shape, and a flange-shaped stopper 49 is provided at the right end of the guide bar 48. The biasing member 43 presses the pressure roller 32 supported by the movable frame 41 against the fixing belt 31, using the pressing frame 42 as a base. In addition, the biasing member 43 presses the cam follower 45 provided on the pressing frame 42 against an eccentric cam 50 (described later), using the movable frame 41 as a base.

[0035] (Eccentric cam) The pair of eccentric cams 50 are fixed to both sides in the front-rear direction of a cam shaft portion 51 provided on the fixing frame 30. The cam shaft portion 51 is formed in a round bar shape extending in the front-rear direction to the right of the pressure roller 32, and is disposed approximately parallel to the pressure roller 32. Both ends in the front-rear direction of the cam shaft portion 51 are supported by the fixing frame 30 so as to be rotatable about their axes. As shown in Figs. 6 and 7, the eccentric cam 50 is a so-called plate cam formed in a roughly magatama shape, with the distance (radius) from the axis (of the cam shaft portion 51) to the outer circumferential surface 52 being non-uniform. As shown in Figs. 4 and 5, the eccentric cam 50 is disposed on the lower right side of the cam follower 45 provided on the pressing frame 42 (support portion 40), and its outer circumferential surface 52 is in contact with (or faces) the outer circumferential surface of the cam follower 45. The eccentric cam 50 receives a driving force from a driving portion 60 and rotates back and forth about its axis while bringing an outer circumferential surface 52 into contact with or facing the cam follower 45 .

[0036] As shown in FIG. 6, the eccentric cam 50 has a pressure surface portion 52A formed at one end of the reciprocating rotation range A1 of the outer circumferential surface 52, and a pressure reduction surface portion 52B formed at the other end of the reciprocating rotation range A1 of the outer circumferential surface 52. The pressure reduction surface portion 52A is a part of the outer circumferential surface 52 having a certain range in the circumferential direction, which corresponds roughly to the maximum radius of the eccentric cam 50. The pressure reduction surface portion 52B is a part of the outer circumferential surface 52 having a certain range in the circumferential direction, which corresponds roughly to the minimum radius of the eccentric cam 50. The angle θ about the center of the reciprocating rotation range A1 is an angle exceeding 180 degrees (for example, 225 degrees). The reciprocating rotation range A1 is a rotation range of the eccentric cam 50 in the normal state, which is a range of the outer circumferential surface 52 that contacts or faces the cam follower 45. In the reciprocating rotation range A1, the radius of the eccentric cam 50 gradually (continuously) increases from the pressure reduction surface portion 52B toward the pressure reduction surface portion 52A. That is, the outer peripheral surface 52 in the reciprocating rotation range A1 forms a smoothly curved surface. In this embodiment, the pressure application surface portion 52A contacts (the outer peripheral surface of) the cam follower 45 (see FIG. 4), and the pressure reduction surface portion 52B faces (the outer peripheral surface of) the cam follower 45 with a gap therebetween (see FIG. 5). Note that the pressure reduction surface portion 52B may be configured to contact the cam follower 45 (not shown).

[0037] In the range excluding the reciprocating rotation range A1 (hereinafter referred to as the non-contact range A2 (180 degrees - angle θ)), the radius of the eccentric cam 50 changes drastically, and a step is formed on the outer circumferential surface 52. The non-contact range A2 is a range of the outer circumferential surface 52 that does not come into contact with or face the cam follower 45 under normal conditions.

[0038] For example, when the eccentric cam 50 with the pressure reducing surface 52B facing the cam follower 45 rotates clockwise in Fig. 5, the pressing frame 42 rotates (is pushed out) clockwise (in the direction approaching the fixing belt 31) as shown in Fig. 4, compressing the urging member 43. The urging member 43 increases the force pressing the movable frame 41 by being compressed, and presses the pressure roller 32 supported by the movable frame 41 against the fixing belt 31. The pressure surface 52A of the eccentric cam 50 comes into contact with the cam follower 45 to bring the pressure region N into the pressure state S1.

[0039] Conversely, when the eccentric cam 50 with the pressure surface portion 52A in contact with the cam follower 45 rotates counterclockwise in FIG. 4, the pressing frame 42 is biased by the biasing member 43 to rotate counterclockwise (in the direction away from the fixing belt 31) as shown in FIG. 5, and hits the stopper 49 of the guide bar 48. Then, the biasing member 43 extends (returns to approximately its natural length) to reduce the force pressing the movable frame 41, and releases the pressure roller 32 from pressing against the fixing belt 31. The pressure reduction surface portion 52B of the eccentric cam 50 faces the cam follower 45 with a gap therebetween, thereby putting the pressure region N into a pressure reduction state S2. Note that even in the pressure reduction state S2, the pressure roller 32 is in contact with the fixing belt 31, but may be configured to be separated from the surface of the fixing belt 31 (not shown).

[0040] As described above, the eccentric cam 50 is rotated forward and backward, and the pressure application surface portion 52A and the pressure reduction surface portion 52B are selectively brought into contact with or opposed to the cam follower 45, whereby the support portion 40 moves within a range corresponding to the pressure application state S1 and the pressure reduction state S2. The support portion 40 (the movable frame 41 and the pressing frame 42) moves within the range of the guide bar 48.

[0041] As shown in Figs. 8 and 9, a transmission type optical sensor 53 is provided at the rear of the fixing frame 30, and a light shielding plate 54 formed in a substantially fan shape is fixed to the rear of the cam shaft portion 51. The light shielding plate 54 rotates back and forth around the same axis as the eccentric cam 50, and moves in and out between the light emitting portion and the light receiving portion of the transmission type optical sensor 53. The transmission type optical sensor 53 is electrically connected to the control portion 13 and transmits a light receiving signal to the control portion 13. When the pressure surface portion 52A of the eccentric cam 50 contacts the cam follower 45, the light shielding plate 54 is disposed between the light emitting portion and the light receiving portion to block the light emitted from the light emitting portion (see Fig. 8). When the pressure reducing surface portion 52B of the eccentric cam 50 faces the cam follower 45, the light shielding plate 54 leaves between the light emitting portion and the light receiving portion, and the light emitted from the light emitting portion enters the light receiving portion (see Fig. 9).

[0042] (Regulations Department) As shown in Figs. 6 and 7, the restricting portion 55 is provided on the eccentric cam 50. In detail, the restricting portion 55 protrudes in the axial direction (front-rear direction) from an end face (back face) of the eccentric cam 50 that is approximately the maximum radius. The restricting portion 55 is a substantially block-shaped protrusion molded integrally with the eccentric cam 50. As shown in Figs. 4 and 5, the restricting portion 55 is provided so as to be capable of interfering with a part of the support portion 40 in a state in which the pressure surface portion 52A or the pressure reduction surface portion 52B of the eccentric cam 50 is in contact with or facing the cam follower 45. In detail, the restricting portion 55 is provided so as to be capable of interfering with the pressure interference portion 46 or the pressure reduction interference portion 47 formed on the pressing frame 42. The pressure interference portion 46 is a part of the support portion 40 (pressing frame 42) that protrudes to the right below the cam follower 45. The decompression interference portion 47 is located below the pressurization interference portion 46 with a gap therebetween, and is a part of the support portion 40 (pressing frame 42) that is inclined upward from the right to the left.

[0043] (Drive unit) As shown in Fig. 2, the drive unit 60 has a DC motor 61, a power supply circuit 62, and an overcurrent protection element 63. The DC motor 61 is connected to one end (e.g., the rear end) of the camshaft unit 51 via a gear train 64. The DC motor 61 reciprocates the eccentric cam 50 (camshaft unit 51). The power supply circuit 62 is electrically connected to the control unit 13, a power source (not shown), etc., and controls the power supplied to the DC motor 61. The overcurrent protection element 63 is mounted on the power supply circuit 62, and protects the power supply circuit 62 when a current (overcurrent) exceeding the allowable current occurs in the power supply circuit 62.

[0044] [Fixing process] Here, the operation of the fixing device 12 will be described with reference to Figures 4, 5, 8 to 11. Figure 10 is a cross-sectional view (rear view) for explaining the operation of the regulating portion 55 of the fixing device 12 (pressurized state S1). Figure 11 is a cross-sectional view (rear view) for explaining the operation of the regulating portion 55 of the fixing device 12 (reduced pressure state S2).

[0045] The control unit 13 executes the fixing process while appropriately controlling the fixing device 12 during the image forming process described above. Note that before the start of the image forming process (fixing process) (initial state), the pressure region N is in the reduced pressure state S2. That is, the reduced pressure surface portion 52B of the eccentric cam 50 faces the cam follower 45, and the light shielding plate 54 is removed from between the light emitting portion and the light receiving portion (see Figs. 5 and 9). Also, in the initial state, the restriction portion 55 is separated from (not interfering with) the reduced pressure interference portion 47 (see Fig. 5).

[0046] First, when the image forming process (fixing process) is started, the driving unit 60 rotates the cam shaft portion 51 (the eccentric cam 50 and the light shielding plate 54) clockwise in Figs. 5 and 9 under the control of the control unit 13. The cam follower 45 moves relatively from the decompression surface portion 52B to the pressure surface portion 52A (see Fig. 4), and the light shielding plate 54 enters between the light emitting portion and the light receiving portion of the transmission type optical sensor 53 (see Fig. 8). The transmission type optical sensor 53 transmits light reception information indicating that the light from the light emitting portion has been blocked by the light shielding plate 54 to the control unit 13, and the control unit 13 stops driving the driving unit 60 based on the received light reception information. As a result, the pressure surface portion 52A is held in contact with the cam follower 45, and the pressure region N is in the pressure state S1 (see Fig. 4). In this state, the regulating portion 55 is separated from the pressure interference portion 46 (does not interfere (see Fig. 4)).

[0047] Next, the control unit 13 drives the heating unit 33, the motor, etc., to start the image forming process already described. The heating unit 33 heats the fixing belt 31. The fixing belt 31 heats the toner image on the paper P passing through the pressure area N while rotating about its axis. The pressure roller 32 pressurizes the toner on the paper P passing through the pressure area N while rotating about its axis. As the paper P passes through the pressure area N, the toner image on the paper P melts and is fixed to the paper P.

[0048] When the image forming process (fixing process) is completed, the driving unit 60 rotates the cam shaft portion 51 (the eccentric cam 50 and the light shielding plate 54) counterclockwise in Fig. 4 and Fig. 8 under the control of the control unit 13. The cam follower 45 moves relatively from the pressure surface portion 52A to face the pressure reduction surface portion 52B (see Fig. 5), and the light shielding plate 54 leaves between the light emitting portion and the light receiving portion of the transmission type optical sensor 53 (see Fig. 9). The transmission type optical sensor 53 transmits light reception information indicating that the light receiving portion has received the light from the light emitting portion to the control unit 13, and the control unit 13 stops driving the driving unit 60 after a predetermined time has elapsed since the reception of the light reception information. As a result, the pressure reduction surface portion 52B is held in contact with the cam follower 45, and the pressure region N is in the pressure reduction state S2 (see Fig. 5). The pressure changing unit 34 also sets the pressure region N to the pressure reduction state S2 when the paper P is jammed in the pressure region N or the like. This allows the jammed paper P to be easily removed.

[0049] However, if the transmission type optical sensor 53 does not function normally due to a breakdown or the like, the drive unit 60 may not be stopped, and the contact position between the outer circumferential surface 52 of the eccentric cam 50 and the cam follower 45 may shift. For example, if the eccentric cam 50 rotates too much and the cam follower 45 passes relatively past the pressure surface 52A or the pressure reduction surface 52B, the cam follower 45 falls into the non-contact range A2 where it should not come into contact. Then, the eccentric cam 50 is locked and cannot rotate, and the fixing device 12 must be disassembled or the like to restore it.

[0050] Therefore, in the fixing device 12 according to the present embodiment, the regulating portion 55 regulates the rotation of the eccentric cam 50 beyond the reciprocating rotation range A1. Specifically, as shown in Fig. 10, the regulating portion 55 regulates the (clockwise) rotation of the eccentric cam 50 toward one side (non-contact range A2) of the reciprocating rotation range A1 by interfering with (butting against) the pressure interference portion 46 with the pressure surface portion 52A of the eccentric cam 50 in contact with the cam follower 45. Also, as shown in Fig. 11, the regulating portion 55 regulates the (counterclockwise) rotation of the eccentric cam 50 toward the other side (non-contact range A2) of the reciprocating rotation range A1 by interfering with (butting against) the pressure reduction interference portion 47 with the pressure reduction surface portion 52B of the eccentric cam 50 facing the cam follower 45. According to this configuration, since the restricting portion 55 physically interferes with a part of the support portion 40 (pressing frame 42), it is possible to prevent the eccentric cam 50 from rotating excessively such that the cam follower 45 relatively passes over the pressure applying surface portion 52A or the pressure reducing surface portion 52B. This makes it possible to effectively prevent the eccentric cam 50 from being locked so as not to be able to rotate.

[0051] Furthermore, if the drive unit 60 continues to be driven while the restricting portion 55 is interfering with a part of the support portion 40, an overcurrent will be generated in the power supply circuit 62 of the drive unit 60. If an overcurrent continues to flow through the power supply circuit 62, an excessive load will be applied to the power supply circuit 62, and there is a risk that the power supply circuit 62 and the like will be damaged.

[0052] Therefore, in the fixing device 12 according to the present embodiment, when an overcurrent occurs in the drive unit 60 (power supply circuit 62) while the regulating portion 55 is interfering with a part of the support portion 40, the drive unit 60 (DC motor 61) stops. Specifically, when an overcurrent occurs in the power supply circuit 62, the resistance value of the overcurrent protection element 63 (see FIG. 2) rises suddenly, the power supply to the DC motor 61 is cut off, and the DC motor 61 stops. With this configuration, even if the transmissive optical sensor 53 breaks down, the drive unit 60 can be stopped when the drive unit 60 detects an overcurrent. This makes it possible to suppress problems such as an excessive load being applied to the drive unit 60 and damage to the power supply circuit 62.

[0053] In the fixing device 12 according to the present embodiment, the support section 40 is configured by connecting the movable frame 41 and the pressing frame 42 with the biasing member 43, but the present invention is not limited to this. For example, the pressing frame 42 and the biasing member 43 may be omitted, and the support section 40 may be configured only with the movable frame 41. In this case, the cam follower 45, the pressure interference section 46, and the pressure reduction interference section 47 are provided on the movable frame 41, and a spring or the like that presses the movable frame 41 (cam follower 45) against the eccentric cam 50 may be provided (not shown).

[0054] In addition, in the fixing device 12 according to the present embodiment, the support section 40 (the pair of movable frames 41) rotatably supports the pressure roller 32, but the present invention is not limited to this. For example, the support section 40 (the pair of movable frames 41) may rotatably support the fixing belt 31. That is, the pressure change section 34 may be configured to be switchable between a pressurized state S1 in which the fixing belt 31 is pressed against the pressure roller 32 and a reduced pressure state S2 in which the pressing of the fixing belt 31 is released (not shown).

[0055] In the fixing device 12 according to the present embodiment, the eccentric cam 50 (camshaft portion 51) is disposed on the opposite side of the pressure roller 32 across the support portion 40 (the right side of the pressing frame 42 in FIG. 4), the pressure surface portion 52A corresponds to the approximate maximum radius of the eccentric cam 50, and the pressure reduction surface portion 52B corresponds to the approximate minimum radius of the eccentric cam 50, but the present invention is not limited thereto. For example, the eccentric cam 50 (camshaft portion 51) may be disposed between the movable frame 41 and the pressing frame 42, and may contact or face the cam follower 45 from the left side of the pressing frame 42 in FIG. 4 (not shown). In this case, the pressure surface portion 52A corresponds to the approximate minimum radius of the eccentric cam 50, and the pressure reduction surface portion 52B corresponds to the approximate maximum radius of the eccentric cam 50 (not shown). In this case, the pressure surface portion 52A may contact the cam follower 45 or may face the cam follower 45 with a gap therebetween (not shown). The pressure reduction surface portion 52B contacts the cam follower 45. In this case, the biasing member 43 may be a tension coil spring that presses the cam follower 45 against the eccentric cam 50 .

[0056] In addition, in the fixing device 12 according to this embodiment, the reciprocating rotation range A1 (angle θ) of the eccentric cam 50 is an angle exceeding 180 degrees, but is not limited thereto and may be 90 degrees or more and 180 degrees or less (not shown).

[0057] In addition, in the fixing device 12 according to the present embodiment, the transmissive optical sensor 53 detects the rotation angle of the eccentric cam 50, but the present invention is not limited to this. For example, instead of the transmissive optical sensor 53 and the light blocking plate 54, a reflective optical sensor and a reflector may be used, or a microswitch and a member for pressing it may be used (neither is shown).

[0058] In addition, in the fixing device 12 according to the present embodiment, the regulating portion 55 is molded integrally with the eccentric cam 50, but the present invention is not limited to this. For example, the regulating portion 55 may be manufactured as a separate member from the eccentric cam 50 and fixed to the side surface of the eccentric cam 50 by means of adhesion, screws, or the like (not shown).

[0059] In addition, in the fixing device 12 according to the present embodiment, one regulating portion 55 interferes with both the pressure interference portion 46 and the pressure reduction interference portion 47, but the present invention is not limited to this. For example, two regulating portions 55 may be provided on the side surface of the eccentric cam 50 so as to correspond to the two interference portions 46, 47 (not shown). That is, a first regulating portion that interferes with the pressure interference portion 46 when the pressure surface portion 52A is in contact with the cam follower 45, and a second regulating portion that interferes with the pressure reduction interference portion 47 when the pressure reduction surface portion 52B is in contact with the cam follower 45 may be provided on the side surface of the eccentric cam 50 (neither is shown).

[0060] In addition, in the fixing device 12 according to the present embodiment, the DC motor 61 of the drive unit 60 rotates the eccentric cam 50, but this is not limiting, and a motor capable of controlling the angle, such as a stepping motor, may be used instead of the DC motor 61. In this case, the transmissive optical sensor 53 and the like become unnecessary.

[0061] In addition, in the fixing device 12 according to the present embodiment, the fixing belt 31 is used as an example of a fixing member, but the present invention is not limited to this, and a roller member similar to the pressure roller 32 may be used (not shown). In addition, the pressure roller 32 is used as an example of a pressure member, but the present invention is not limited to this, and a belt member similar to the fixing belt 31 may be used (not shown).

[0062] Furthermore, the image forming apparatus 1 according to the present embodiment is a color printer, but the present invention is not limited to this and may be applied to, for example, a monochrome printer, a copier, a facsimile, or a multifunction machine.

[0063] The above embodiment shows one aspect of the fixing device and image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above embodiment. The present invention may be modified, substituted, or altered in various ways without departing from the spirit of the technical idea, and the claims include all embodiments that may be included within the scope of the technical idea. [Explanation of symbols]

[0064] 1. Image forming device 12 Fixing device 31 Fixing belt (fixing member) 32 Pressure roller (pressure member) 34 Pressure change section 40 Support part 45 Cam follower 46 Pressurized interference part (part of the support part) 47 Pressure reducing interference part (part of the support part) 50 Eccentric Cam 52 Outer surface 52A Pressure surface 52B Pressure reducing surface 55 Regulatory Department 60 Drive unit A1 Reciprocating rotation range P Paper (medium) S1 Pressurized state S2 Decompression state

Claims

1. A fixing member that heats the toner on the medium while rotating about an axis; a pressure member that rotates around an axis to form a pressure region between itself and the fixing member and pressurizes the toner on the medium passing through the pressure region; a pressure changing unit that is switchable between a pressurized state in which one of the fixing member and the pressure member is pressed against the other to pressurize the pressurized area, and a reduced pressure state in which the pressing of the fixing member and the pressure member is released to reduce the pressure of the pressurized area, The pressure changing unit is a support section that rotatably supports one of the fixing member and the pressure member and moves within a range corresponding to the pressurized state and the depressurized state; an eccentric cam that reciprocates about an axis while its outer circumferential surface is in contact with or facing a cam follower provided on the support portion; a restricting portion provided on the eccentric cam and restricting rotation of the eccentric cam beyond a reciprocating rotation range, The eccentric cam is a pressure surface portion that is formed at one end of the reciprocating rotation range of the outer circumferential surface and that puts the pressure region into the pressure state; a pressure reducing surface portion formed at the other end of the reciprocating rotation range of the outer circumferential surface and configured to reduce the pressure in the pressurized region; The fixing device is characterized in that the regulating portion regulates the rotation of the eccentric cam toward one side of the reciprocating rotation range by interfering with a part of the support portion when the pressure surface portion is in contact with or facing the cam follower, and regulates the rotation of the eccentric cam toward the other side of the reciprocating rotation range by interfering with a part of the support portion when the pressure reduction surface portion is in contact with or facing the cam follower.

2. The pressure changing unit further includes a drive unit that reciprocates the eccentric cam, 2. The fixing device according to claim 1, wherein, when an overcurrent occurs in the drive unit while the regulating portion is in contact with a part of the support portion, the drive unit stops.

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

Images