JP5836251B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and a composite machine using an electrophotographic method, and more particularly to an image forming apparatus capable of changing a nip pressure between a heating member and a pressure member. is there.

  Conventionally, an image forming apparatus is provided with a fixing device for fixing a toner image transferred from an image carrier onto a recording material. As this fixing device, a roller system including a fixing roller (heating member) and a pressure roller (pressure member) rotating in contact with each other, a belt system using an endless fixing belt as a heating member, and the like are known. It has been. For example, a roller-type fixing device heats and presses a toner image carried on a recording material at a nip portion between a fixing roller and a pressure roller that are pressed against each other, and fixes the toner image on the recording material.

  In the fixing device as described above, the temperature of the heating member and the nip pressure of the nip portion are set in consideration of the toner fixing property to the recording material. However, when fixing a toner image on a recording material such as an envelope of a different type under heating / pressurization conditions set in consideration of toner fixing properties to a sheet-like recording material such as plain paper, Wrinkles are likely to occur on the recording material. Therefore, there is a fixing device in which the nip pressure between the heating member and the pressure member is variable according to the type of recording material on which the toner image is fixed (see, for example, Patent Document 1).

  As shown in FIG. 9, the above-mentioned Patent Document 1 includes a fixing unit 1030 having a fixing roller 1131 and a pressure roller 1132 pressed against the fixing roller 1131, and a nip portion where the fixing roller 1131 and the pressure roller 1132 are pressed. A fixing device 1013 including a pressure mechanism 1050 that applies a nip pressure and a nip pressure switching unit 1060 that changes the nip pressure of the nip portion is disclosed.

  As shown in FIGS. 9 and 10, the pressurizing mechanism 1050 includes a first arm member 1051 made of metal having a first abutting portion 1051a supported in a swingable manner around a support shaft 1054, and a second abutting mechanism. A metal second arm member 1052 having a contact portion 1052a and an elastic member 1053 wound around the rotation shaft 1055 of the first arm member 1051 are included. The first arm member 1051 holds the pressure roller 1132. The elastic member 1053 is disposed so that one end thereof is in contact with the first contact portion 1051a and the other end is in contact with the second contact portion 1052a, and the first contact portion 1051a and the second contact portion 1052a are separated from each other. The nip pressure is applied to the nip portion by energizing in the direction of the nip. The second arm member 1052 is provided with a through hole 1052b into which a rotation connecting shaft 1063 (described later) of the nip pressure switching unit 1060 is inserted and slid.

  The nip pressure switching unit 1060 has a roller 1061 provided on the second arm member 1052, an eccentric cam 1062 that contacts the roller 1061 and changes in the distance from the rotation center to the outer peripheral surface, and the eccentric cam 1062 are fixed. A rotation connecting shaft 1063 made of metal, and a drive unit 1070 including a gear train for rotating the rotation connecting shaft 1063 and the eccentric cam 1062.

  In the fixing device 1013, as shown in FIGS. 10 and 11, when the rotation connecting shaft 1063 and the eccentric cam 1062 are rotated, the distance between the roller 1061 and the rotation connecting shaft 1063 changes, and the elastic member 1053 The amount of compression changes. As a result, the first arm member 1051 swings about the support shaft 1054, so that the nip pressure of the nip portion is changed.

JP 2012-128222 A

  In Patent Document 1, when the rotation coupling shaft 1063 and the eccentric cam 1062 are rotated and the distance between the roller 1061 and the rotation coupling shaft 1063 changes, the rotation coupling shaft 1063 slides along the through hole 1052b. Move. At this time, there is a problem that sliding sound (metal sound) is generated due to rubbing between the rotation connecting shaft 1063 and the through hole 1052b.

  The present invention has been made to solve the above problems, and an object of the present invention is to suppress the generation of sliding noise when changing the nip pressure between the heating member and the pressure member. It is an object of the present invention to provide an image forming apparatus capable of performing the above.

  In order to achieve the above object, an image forming apparatus of the present invention has a heating member and a pressure member pressed against the heating member, and heats and pressurizes a toner image carried on the recording material to form a recording material. A fixing unit for fixing, a pressure mechanism for applying a nip pressure to a nip portion where the heating member and the pressure member are in pressure contact, and a nip pressure switching unit for changing the nip pressure of the nip portion. A first arm member that is supported so as to be swingable about a support shaft, has a first engagement portion, and holds one member of a pressure member and a heating member; and a second arm portion that has a second engagement portion. The arm member is disposed so that one end engages with the first engagement portion and the other end engages with the second engagement portion, and the first engagement portion and the second engagement portion are separated from or approach each other. And an elastic member that applies nip pressure to the nip portion by urging in the direction, and nip pressure switching The portion includes a roller provided on the second arm member, an eccentric cam in which the outer peripheral surface abuts on the roller and a distance from the rotation center to the outer peripheral surface changes, a rotary shaft to which the eccentric cam is fixed, and a rotary shaft The second arm member is provided with a through hole into which the rotary shaft is inserted, and the rotary shaft is provided with a bearing member that slides with respect to the through hole. ing.

  According to the present invention, the second arm member is provided with a through hole into which the rotary shaft is inserted, and the rotary shaft is provided with a bearing member that slides with respect to the through hole. Thereby, when the rotation shaft and the eccentric cam are rotated and the distance between the roller and the rotation shaft changes (when the nip pressure between the heating member and the pressure member is changed), the rotation shaft and the eccentric cam are provided on the rotation shaft. The bearing member slides with respect to the through hole. Since the bearing member is excellent in slidability, it is possible to suppress the generation of sliding noise when the bearing member slides with respect to the through hole. Further, since the through-hole of the second arm member can be smoothly slid with respect to the bearing member, the first engagement portion and the second engagement portion can be smoothly separated from or approached to each other. Thereby, the nip pressure of a nip part can be changed smoothly.

1 is a cross-sectional view schematically showing the structure of an image forming apparatus according to an embodiment of the present invention. It is sectional drawing which showed the structure of the fixing device of one Embodiment of this invention. It is the perspective view which showed the structure of the fixing | fixed part of one Embodiment of this invention, a pressurization mechanism, and a nip pressure switching part. FIG. 3 is a cross-sectional view illustrating a structure around a nip portion of a fixing device according to an embodiment of the present invention. It is the perspective view which showed the structure of the 1st arm member of one Embodiment of this invention, a 2nd arm member, and an elastic member periphery. It is the perspective view which showed the structure of the 1st arm member of one Embodiment of this invention, a 2nd arm member, and an elastic member periphery. It is the top view which showed the structure of the 1st arm member of one Embodiment of this invention, a 2nd arm member, and an elastic member periphery. FIG. 3 is a cross-sectional view illustrating a structure around a nip portion of a fixing device according to an embodiment of the present invention. It is the perspective view which showed an example of the conventional fixing device. FIG. 6 is a cross-sectional view showing a structure around a nip portion of a conventional fixing device. FIG. 6 is a cross-sectional view showing a structure around a nip portion of a conventional fixing device.

  Embodiments of the present invention will be described below with reference to the drawings.

  With reference to FIGS. 1-8, the image forming apparatus 1 by one Embodiment of this invention is demonstrated. In FIG. 1, the right side is illustrated as the front side of the image forming apparatus 1. As shown in FIG. 1, an image forming unit P is disposed in the image forming apparatus 1 (here, a monochrome printer). The image forming unit P forms a predetermined image through each process of charging, exposure, development, and transfer.

  The image forming portion P is provided with a photosensitive drum (image carrier) 2 that carries a visible image (toner image), and the toner image formed on the photosensitive drum 2 is printed on paper (recording material). ) And transferred onto the sheet 6 by the fixing unit 13 and then discharged from the apparatus main body. An image forming process is performed on the photosensitive drum 2 while rotating the photosensitive drum 2 clockwise in FIG. 1 by a drum drive motor (not shown).

  Next, the image forming unit P will be described in detail. Around and around the photosensitive drum 2 rotatably disposed (right side in FIG. 1), a charging roller 3 that charges the photosensitive drum 2 and an exposure that exposes image information to the photosensitive drum 2. A unit 4; a developing unit 5 that forms a toner image on the photosensitive drum 2; a cleaning device 9 that collects developer (toner) remaining on the photosensitive drum 2; and a static eliminator that removes an electrostatic latent image. 10 are provided.

  First, the surface of the photosensitive drum 2 is uniformly charged by the charging roller 3, and then light is irradiated by the exposure unit 4 to form an electrostatic latent image corresponding to the image signal on the photosensitive drum 2. The developing unit 5 includes a developing roller 5 a disposed so as to face the photosensitive drum 2, and the developing unit 5 is filled with a predetermined amount of a magnetically charged positive component toner by a toner container 11. The toner is supplied to the surface of the photosensitive drum 2 by a developing roller 5a to which a developing bias is applied by a developing bias applying device (not shown), and is formed by exposure from the exposure unit 4 by electrostatic adhesion. A toner image corresponding to the electrostatic latent image is formed.

  The paper 6 onto which the toner image is transferred is stored in a paper feed cassette 12 that stores the paper 6 and is directed to the photosensitive drum 2 on which the toner image is formed via the paper feed roller 7 and the registration roller pair 14. Are transported. At this time, the image writing signal is turned on, and an image is formed on the photosensitive drum 2 so that the toner image is transferred to a predetermined position on the paper 6. A toner image on the photosensitive drum 2 is transferred onto the paper 6 by applying an electric field to the lower portion of the photosensitive drum 2 with a transfer roller 17 to which a predetermined transfer bias is applied. The transfer roller 17 is applied with a negative transfer bias having a polarity opposite to that of the toner during image formation (printing operation).

  The sheet 6 on which the toner image is transferred is conveyed to the fixing device 13. In addition, the photosensitive drum 2 after the toner image is transferred is collected by the cleaning device 9 in preparation for the subsequent formation of a new electrostatic latent image. The sheet 6 conveyed to the fixing device 13 is heated and pressed by a fixing roller 131 and a pressure roller 132, which will be described later, and the toner image is fixed on the surface of the sheet 6 to form a predetermined image. The paper 6 on which the image is formed is then discharged to a discharge tray 19 by a discharge roller pair 18. Details of the fixing device 13 will be described later.

  A charging roller 3 is disposed in front of the photosensitive drum 2 so as to be in contact with the drum surface in a rotatable manner and to charge the drum surface. A cleaning brush 8 is disposed in front of the charging roller 3 to press the surface of the charging roller 3 and clean the roller surface.

  The photosensitive drum 2 is connected to the above-described drum drive motor via a drive gear (not shown), and rotates clockwise in the figure as described above.

  The charging roller 3 is rotatably supported by the apparatus main body. The charging roller 3 is pressed against the photosensitive drum 2 with a predetermined nip pressure, and is rotated by being driven by the photosensitive drum 2. In addition, a charging bias having the same polarity as the toner (here, positive polarity) is applied to the charging roller 3 during image formation (printing operation).

  As shown in FIG. 2, the fixing device 13 includes a fixing unit 30 including a fixing roller 131 that is a heating member and a pressure roller 132 that is a pressure member. 2 shows a state viewed from the back side of FIG. 1, and the arrangement of each member is reversed from that of FIG.

  As the fixing roller 131, a so-called hard roller is used in which a cylindrical metal core made of a metal such as aluminum or iron having excellent thermal conductivity is coated with a fluororesin coating or a tube. Further, a halogen heater 133 as a heat source is provided inside the cored bar of the fixing roller 131, and the surface of the fixing roller 131 is held at a predetermined temperature. The pressure roller 132 is a resin in which an elastic layer such as silicon rubber is formed on a cylindrical base material made of synthetic resin, metal or other material, and the surface of the elastic layer is excellent in releasability such as fluororesin. The one covered with is used.

  As shown in FIG. 3, the fixing roller 131 is rotatably held by the apparatus main body, and the pressure roller 132 is rotatably held by a first arm member 51 of a pressure mechanism 50 described later. A gear 134 is provided on the left side (A1 direction side) of the fixing roller 131, and a gear 135 is provided on the right side (A2 direction side). A rotational driving force is transmitted to the fixing roller 131 through a gear 134 from a driving source (not shown) such as a motor. This rotational driving force is also transmitted to the pressure roller 132 via the gear 135 and a gear (not shown) provided on the A2 direction side of the pressure roller 132.

  The fixing device 13 includes a pressure mechanism 50 and a nip pressure switching unit 60 in addition to the fixing unit 30 including the fixing roller 131 and the pressure roller 132 described above. In FIG. 3, only the fixing unit 30, the pressure mechanism 50, and the nip pressure switching unit 60 are illustrated for convenience of explanation.

  The pressure mechanism 50 presses the pressure roller 132 and the fixing roller 131 and applies a nip pressure to the nip portion N (see FIG. 2) to be pressed, and includes a first arm member 51 and a second arm member. 52 and an elastic member 53, and a pair of pressure rollers 132 are disposed on both ends in the longitudinal direction.

  The nip pressure switching unit 60 changes the nip pressure of the nip portion N by changing the urging force of the elastic member 53. The nip pressure switching portion 60 includes a drive unit 70 including a motor, a gear train, an eccentric cam 62, an eccentricity, and the like. A roller 61 that engages with the cam 62 and a rotation connecting shaft (rotating shaft) 63 are provided. The drive unit 70 is disposed on the right side (A2 direction side) of the pressure roller 132, and a pair of the eccentric cam 62 and the roller 61 are disposed on both ends of the pressure roller 132. The rotary connecting shaft 63 is provided integrally with the eccentric cams 62 on both sides, and transmits the rotational driving force of the drive unit 70 to the right eccentric cam 62 and the left eccentric cam 62. Accordingly, the nip pressure switching unit 60 changes the urging force of the elastic members 53 on both sides of the pressure roller 132 at the same time.

  As shown in FIG. 4, the first arm member 51 is formed in a predetermined shape with a metal plate such as iron. A pressure roller 132 is rotatably supported at a substantially central portion of the first arm member 51. A hole that fits into a support shaft 54 that is fixed to the apparatus main body is formed in the lower portion of the first arm member 51. The first arm member 51 has a front-rear direction centered on the support shaft 54 (the left-right direction in FIG. 4). ) Is swingably held. One end of a fixed shaft 55 extending in the forward direction (left direction in FIG. 4) is fixed to the upper portion of the first arm member 51, and the other end (left end in FIG. 4) of the fixed shaft 55 is flat. A first contact portion (first engagement portion) 51a is formed. An elastic member 53 is wound around the fixed shaft 55, and one end of the elastic member 53 is in contact with the first contact portion 51a.

  The second arm member 52 is formed in a predetermined shape with a metal plate such as iron. At the rear end (the right end in FIG. 4) of the second arm member 52, a second contact portion (second engagement portion) 52a having a flat plate shape is formed. The second contact portion 52a is fixed so as to face the first contact portion 51a of the first arm member 51 and to be movable in the front-rear direction (the axial direction of the fixed shaft 55) with respect to the fixed shaft 55. There is a hole 52d (see FIG. 5) through which the shaft 55 is inserted. Further, the other end of the elastic member 53 is in contact with the second contact portion 52a.

  Further, as shown in FIGS. 5 to 7, the second arm member 52 is formed with a pair of side wall portions 52 b that sandwich the eccentric cam 62, the elastic member 53, and the like from both sides in the axial direction of the rotary connecting shaft 63. . And each of a pair of side wall part 52b is provided with the through-hole 52c in which the rotation connection shaft 63 is inserted.

  As shown in FIG. 4, the elastic member 53 is for applying a nip pressure to the nip portion N. The elastic member 53 is composed of a compression coil spring, and both ends of the elastic member 53 in a compressed state are connected to the first contact portion 51a and the second contact portion. It is in contact with the contact part 52a. Therefore, a forward biasing force (leftward in FIG. 4) acts on the first contact portion 51a, and a backward biasing force (rightward in FIG. 4) acts on the second contact portion 52a. . The first contact portion 51 a and the second contact portion 52 a are urged away from each other by the elastic member 53, and the pressure roller 132 is pressed against the fixing roller 131.

  The second arm member 52 is formed to extend forward from the second contact portion 52a, and a cylindrical roller 61 is rotatably attached to the front end portion thereof.

  An eccentric cam 62 is engaged with the roller 61. The eccentric cam 62 is fixed to the rotary connecting shaft 63. As shown in FIGS. 5 to 7, bearing members 64 a and 64 b that slide with respect to the through holes 52 c of the second arm member 52 are provided on the rotary connecting shaft 63 with respect to the eccentric cam 62. Are provided on both sides in the axial direction. The bearing members 64a and 64b are sliding bearings, and are formed of, for example, a Cu-based metal. Further, the bearing member 64 a is provided with a flange portion 64 c that comes into contact with the side wall portion 52 b of the second arm member 52 in the axial direction of the rotary connecting shaft 63.

  Further, the eccentric cam 62 is rotatable around the rotation center of the rotary connecting shaft 63, and is formed such that the distance from the rotation center to the outer peripheral surface changes. When the rotary connecting shaft 63 is rotated by the drive unit 70, the state is switched between the state shown in FIG. 4 and the state shown in FIG.

  In the state shown in FIG. 4, the interval between the second contact portion 52a of the second arm member 52 and the first contact portion 51a of the first arm member 51 is a predetermined distance, and the elastic member 53 is a predetermined amount. Only compressed. In the state shown in FIG. 8, the second arm member 52 is displaced rearward (rightward in FIG. 5) with respect to the state of FIG. 4, and the second contact portion 52a, the first contact portion 51a, , And the elastic member 53 is extended.

  Therefore, in the state of FIG. 8, the urging force by the elastic member 53 is smaller than in the state of FIG. 4, and accordingly, the nip pressure of the nip portion N is reduced and the pressure is reduced. Since the nip pressure of the nip portion N is reduced, the first arm member 51 slightly swings backward (rightward in FIG. 8) about the support shaft 54.

  Since the urging direction of the elastic member 53 (the axial direction of the fixed shaft 55) substantially coincides with the alignment direction of the fixing roller 131 and the pressure roller 132, the urging force of the elastic member 53 does not lose and the nip portion N To be told.

  As shown in FIG. 3, a drive unit 70 is provided to rotate the eccentric cam 62. The drive unit 70 includes a motor 72, a motor gear 73 formed of a worm gear, gear trains 74 to 76, and the like, and a base plate 71 fixed to the apparatus main body. The gear 76 is fixed to the end of the rotary connecting shaft 63 on the A2 direction side.

  The motor 72 is composed of a DC motor, for example. When the motor 72 is rotated by a motor drive circuit (not shown), the rotary connecting shaft 63 and the eccentric cam 62 rotate via the gear trains 74 to 76 and the like.

  The motor 72 is controlled by a control unit (not shown). The control unit includes a microcomputer, a storage element such as a RAM and a ROM, and controls the motor drive circuit according to a program set in the storage element. Specifically, when the user operates an operation panel (not shown) to set the type of paper 6, the control unit controls the motor drive circuit so that the motor 72 rotates a predetermined number of times. As a result, the rotary connecting shaft 63 and the eccentric cam 62 rotate by a predetermined amount, and the nip pressure of the nip portion N is changed.

  In the present embodiment, as described above, the second arm member 52 is provided with the through hole 52c into which the rotary connecting shaft 63 is inserted, and the rotary connecting shaft 63 slides with respect to the through hole 52c. Bearing members 64a and 64b are provided. As a result, the rotation connecting shaft 63 and the eccentric cam 62 are rotated to change the distance between the roller 61 and the rotation connecting shaft 63 (when the nip pressure between the fixing roller 131 and the pressure roller 132 is changed). Further, the bearing members 64a and 64b provided on the rotary connecting shaft 63 slide with respect to the through hole 52c. Since the bearing members 64a and 64b are excellent in slidability, it is possible to suppress the generation of sliding noise when the bearing members 64a and 64b slide with respect to the through hole 52c. Further, since the through hole 52c of the second arm member 52 can be smoothly slid with respect to the bearing members 64a and 64b, the first contact portion 51a and the second contact portion 52a can be smoothly separated from each other. Can do. Thereby, the nip pressure of the nip part N can be changed smoothly.

  Further, since the through hole 52c of the second arm member 52 can be smoothly slid with respect to the bearing members 64a and 64b, the first contact portion 51a and the second contact portion 52a are separated or approach each other. In addition, it is possible to suppress the load on the second arm member 52 in the axial direction of the rotary connecting shaft 63. Accordingly, the second arm member 52 can be prevented from moving in the axial direction of the rotary connecting shaft 63 and the hole 52d of the second arm member 52 and the fixed shaft 55 are brought into contact with each other. Generation of sliding noise between the hole 52d and the fixed shaft 55 can also be suppressed. In addition, when the bearing member 64a and 64b are not provided in the rotation connection shaft 63, since the frictional force between the through-hole 52c of the 2nd arm member 52 and the rotation connection shaft 63 is large, the through-hole of the 2nd arm member 52 When the slide 52c slides with respect to the rotary connecting shaft 63, the second arm member 52 generates a considerable amount of frictional force in the axial direction of the rotary connecting shaft 63. And when the 1st contact part 51a and the 2nd contact part 52a mutually space | interval or approach, a load is applied to the axial direction of the rotation connection shaft 63 with respect to the 2nd arm member 52. FIG. For this reason, the second arm member 52 moves in the axial direction of the rotary connecting shaft 63 so that the hole 52d of the second arm member 52 and the fixed shaft 55 come into contact with each other, and the hole 52d of the second arm member 52 and the fixed shaft 55 There may be a sliding noise between the two.

  In addition, as described above, the bearing member 64 a is provided with the flange portion 64 c that comes into contact with the side wall portion 52 b of the second arm member 52 in the axial direction of the rotary connecting shaft 63. Thereby, since it can suppress more that the 2nd arm member 52 moves to the axial direction of the rotation connection shaft 63, it suppresses further that the hole 52d of the 2nd arm member 52 and the fixed shaft 55 contact. be able to. For this reason, it is possible to further suppress the generation of sliding noise between the hole 52d of the second arm member 52 and the fixed shaft 55.

  Further, as described above, the bearing members 64 a and 64 b are provided on both sides in the axial direction of the rotary connecting shaft 63 with respect to the eccentric cam 62, and the second arm member 52 rotationally connects the eccentric cam 62. The shaft 63 has a pair of side wall portions 52b sandwiched from both sides in the axial direction, and a through hole 52c is provided in each of the pair of side wall portions 52b. Thereby, since the 2nd arm member 52 can be stably moved with respect to the rotation connection shaft 63, the nip pressure of the nip part N can be changed more smoothly.

  Further, as described above, the urging direction of the elastic member 53 (the axial direction of the fixed shaft 55) substantially coincides with the alignment direction of the fixing roller 131 and the pressure roller 132. Thereby, the urging force of the elastic member 53 can be transmitted to the nip portion N without loss.

  Further, as described above, the bearing members 64a and 64b are made of metal. Thereby, it can prevent easily that the bearing members 64a and 64b deform | transform with the heat from a heating roller. Further, the slidability of the bearing members 64a and 64b can be easily improved by forming the bearing members 64a and 64b from a Cu-based metal.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, although an example in which the present invention is applied to a monochrome printer has been shown, the present invention is not limited to this. Needless to say, the present invention can be applied to various image forming apparatuses capable of changing the nip pressure between the heating member and the pressure member, such as a color printer, a monochrome copying machine, a digital multifunction peripheral, and a facsimile machine.

  In the above embodiment, an example in which the present invention is applied to a roller type fixing device has been described. However, the present invention is not limited to this, and a belt type using an endless fixing belt as a heating member, or a heating member is fixedly supported. Further, the present invention may be applied to a fixing device having a heating body and a heat-resistant film that slides in close contact with the heating body and presses the heating body and a pressure roller through the heat-resistant film. In addition, a heating unit that heats by electromagnetic induction may be used as a heat source, and a pressurizing mechanism may be provided on the heating member side.

  Moreover, in the said embodiment, while using the compression coil spring as an elastic member, the structure which urges | biases a 1st contact part and a 2nd contact part in the direction which mutually spaces apart was shown, but this invention is not limited to this Absent. A tension coil spring is used as the elastic member, and the first engagement portion and the second engagement portion are arranged opposite to the above-described embodiment, and the first engagement portion and the second engagement portion are moved closer to each other. It may be energized. Moreover, you may use elastic members other than a spring.

  In the above embodiment, an example using a metal bearing member has been described. However, the present invention is not limited to this, and a resin bearing member may be used as long as it can withstand heat during fixing.

1 Image forming device 6 Paper (recording material)
30 fixing portion 50 pressure mechanism 51 first arm member 51a first contact portion (first engagement portion)
52 2nd arm member 52a 2nd contact part (2nd engaging part)
52b Side wall portion 52c Through hole 53 Elastic member 54 Support shaft 60 Nip pressure switching portion 61 Roller 62 Eccentric cam 63 Rotating connecting shaft
64a, 64b bearing member 64c collar 70 driving unit 131 fixing roller (heating member)
132 Pressure roller (Pressure member)
N Nip part

Claims (4)

A fixing unit having a heating member and a pressure member pressed against the heating member, and fixing the toner image carried on the recording material by heating and pressurizing the recording material;
A pressure mechanism for applying a nip pressure to a nip portion where the heating member and the pressure member are in pressure contact;
A nip pressure switching portion for changing the nip pressure of the nip portion;
With
The pressurizing mechanism is supported so as to be swingable about a support shaft, has a first engaging portion, holds a first arm member that holds one member of the pressurizing member and the heating member, and a second arm member. A second arm member having an engagement portion, and one end engaged with the first engagement portion and the other end engaged with the second engagement portion; An elastic member that applies a nip pressure to the nip portion by urging the two engaging portions in a direction of separating or approaching each other,
The nip pressure switching unit includes a roller provided on the second arm member, an eccentric cam in which an outer peripheral surface is in contact with the roller and a distance from a rotation center to the outer peripheral surface is changed, and the eccentric cam is fixed. A rotating shaft that is driven, and a drive unit that rotationally drives the rotating shaft,
The second arm member is provided with a through hole into which the rotating shaft is inserted,
The rotating shaft is provided with a bearing member that slides with respect to the through hole ,
The urging direction of the elastic member substantially coincides with the alignment direction of the heating member and the pressure member,
The first arm member is provided with a fixed shaft that extends in a predetermined direction and is wound with the elastic member, and has an end portion formed with the first engagement portion.
The rotating shaft and the roller are disposed on an extension line of the fixed shaft,
A line connecting the support shaft and the center of one of the pressure member and the heating member is disposed substantially perpendicular to a line connecting the center of the pressure member and the center of the heating member. An image forming apparatus. The second arm member has a side wall portion disposed on at least one side in the axial direction of the rotation shaft with respect to the eccentric cam,
The image forming apparatus according to claim 1, wherein the bearing member is provided with a flange portion that abuts in the axial direction of the rotation shaft with respect to the side wall portion of the second arm member. The bearing member is provided on both sides in the axial direction of the rotary shaft with respect to the eccentric cam,
The second arm member has a pair of side wall portions that sandwich the eccentric cam from both sides in the axial direction of the rotating shaft,
The image forming apparatus according to claim 1, wherein the through hole is provided in each of the pair of side wall portions. The bearing member is an image forming apparatus according to any one of claims 1 to 3, characterized in that it is made of metal.

Images