JPWO2018020824A1 - Variable pressing force mechanism, fixing device including the same, and image forming apparatus - Google Patents

Abstract

A variable pressing force mechanism capable of suppressing overrun of an eccentric cam, a fixing device including the mechanism, and an image forming apparatus are provided. This variable pressing force mechanism includes an eccentric cam (82), a pressed member (81) pressed by the eccentric cam, a drive source (61), and an intermediate gear that transmits the driving force generated by the drive source to the eccentric cam. (62). The eccentric cam is provided on the downstream side from the top dead center (P2) in the moving direction of the contact position with the member to be pressed, and the distance from the rotation center (O82) to the outer peripheral surface is the same radius area as the top dead center. (R3) and a radius increasing region (R2) that is provided upstream of the top dead center in the moving direction of the contact position with the pressed member, and the distance from the rotation center to the outer peripheral surface increases as the top dead center is approached. ) And. The sliding resistance between the equal radius region and the pressed member is larger than the sliding resistance between the radius increasing region and the pressed member.

Description

  The present invention relates to a pressing force variable mechanism, a fixing device including the same, and an image forming apparatus, and more particularly to a pressing force variable mechanism including an eccentric cam and an intermediate gear that transmits a driving force generated by a driving source to the eccentric cam. And a fixing device and an image forming apparatus including the same.

  Conventionally, an image forming apparatus is provided with a fixing device for fixing a toner image transferred from an image carrier onto a recording medium. 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 medium 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 medium.

  The fixing device is provided with a pressing force variable mechanism for pressing the pressure roller against the fixing roller. The pressing force variable mechanism includes, for example, an eccentric cam, a pressed member pressed by the eccentric cam, a drive source that generates a driving force for driving the eccentric cam, and a driving force generated by the drive source. A plurality of intermediate gears for transmission. When the driving force is transmitted to the eccentric cam via the intermediate gear and the eccentric cam rotates, the eccentric cam presses the pressed member, and the pressure roller is pressed against the fixing roller by the pressed member.

  Note that a fixing device including a pressing force variable mechanism having an eccentric cam is disclosed in, for example, Patent Document 1.

JP 2011-95320 A

  By the way, in the fixing device having the above-described variable pressing force mechanism, the eccentric torque rotates and the shaft torque acting on the eccentric cam as the pressing position of the pressed member moves from the bottom dead center to the top dead center. Rises. At this time, the intermediate gear disposed between the drive source and the eccentric cam is distorted by the shaft torque. When the pressing position with respect to the pressed member reaches the top dead center, the shaft torque acting on the eccentric cam is released. At this time, distortion is eliminated by the restoring force of the intermediate gear, and the eccentric cam further rotates (overruns) from a predetermined angle, so that the eccentric cam cannot be stopped at a predetermined stop angle (stop position). There is a problem.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a variable pressing force mechanism capable of suppressing overrun of the eccentric cam, a fixing device including the same, and An image forming apparatus is provided.

  A variable pressing force mechanism according to a first aspect of the present invention includes an eccentric cam, a member to be pressed against the eccentric cam, a drive source that generates a driving force for driving the eccentric cam, the eccentric cam, and the drive. And one or more intermediate gears that are disposed between the power source and transmit the driving force generated by the power source to the eccentric cam. The eccentric cam is provided on the downstream side from the top dead center in the moving direction of the contact position with the member to be pressed, an equal radius region where the distance from the rotation center to the outer peripheral surface is the same as the top dead center, And a radius-increasing region that is provided on the upstream side of the top dead center in the moving direction of the contact position and in which the distance from the rotation center to the outer peripheral surface increases as the top dead center is approached. The sliding resistance between the equal radius region and the pressed member is larger than the sliding resistance between the radius increasing region and the pressed member.

  According to the pressing force variable mechanism according to the first aspect of the present invention, the sliding resistance between the equal radius region and the pressed member is larger than the sliding resistance between the radius increasing region and the pressed member. . Thereby, even if the eccentric cam rotates and the pressing position with respect to the pressed member reaches the top dead center, the eccentric cam can be suppressed from sliding with respect to the pressed member. That is, the eccentric cam can be prevented from rotating. For this reason, the overrun of the eccentric cam can be suppressed.

  Further, in the moving direction of the contact position between the eccentric cam and the pressed member, an equal radius region where the distance from the rotation center to the outer peripheral surface is the same as the top dead center is provided downstream from the top dead center. Compared to the case where a radius-reducing region is provided near the downstream side of the top dead center in the direction of movement of the contact position between the eccentric cam and the pressed member and the distance from the rotation center to the outer peripheral surface decreases as the distance from the top dead center increases. Thus, the overrun of the eccentric cam can be further suppressed.

  Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the description of embodiments described below.

1 is a cross-sectional view schematically illustrating a structure of an image forming apparatus including a pressing force variable mechanism according to an embodiment of the present invention. It is the side view which showed the structure of the eccentric cam periphery of the pressing force variable mechanism of one Embodiment of this invention, and is the figure which showed the state which the bottom dead center area | region of eccentric cam contact | abuts to the to-be-pressed member. It is the side view which showed the structure around the eccentric cam of the pressing force variable mechanism of one Embodiment of this invention, and is the figure which showed the state in which the top dead center of the eccentric cam is contacting the to-be-pressed member. It is the side view which showed the structure around the eccentric cam of the pressing force variable mechanism of one Embodiment of this invention, and is the figure which showed the state in which the equal radius area | region of an eccentric cam is contacting the to-be-pressed member. It is the perspective view which showed the structure of the eccentric cam and intermediate gear periphery of the pressing force variable mechanism of one Embodiment of this invention. It is the side view which showed the structure of the eccentric cam and intermediate gear periphery of the pressing force variable mechanism of one Embodiment of this invention. It is the side view which showed the structure of the eccentric cam and pressed member of the pressing force variable mechanism of one Embodiment of this invention. It is the side view which showed the structure of the eccentric cam of the pressing force variable mechanism of one Embodiment of this invention. It is the figure which showed the relationship between the axial torque which acts on an eccentric cam when rotating the eccentric cam of the pressing force variable mechanism of one Embodiment of this invention, and time.

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

  With reference to FIGS. 1-9, the image forming apparatus 1 provided with the variable pressing force mechanism 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 a sheet (recording medium). ) And transferred onto the paper 6 and then fixed on the paper 6 by the fixing device 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).

  In addition, a charging roller 3 that charges the photosensitive drum 2 and image information on the photosensitive drum 2 are exposed around and in front of the photosensitive drum 2 that is rotatably arranged (right side in FIG. 1). The exposure unit 4, the developing unit 5 that forms a toner image on the photosensitive drum 2, the cleaning device 9 that collects the developer (toner) remaining on the photosensitive drum 2, and the electrostatic latent image is removed. A static eliminator 10 is provided.

  The sheet 6 on which the toner image is transferred by the photosensitive drum 2 is conveyed to the fixing device 13. 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.

  As shown in FIG. 2, the fixing device 13 includes a fixing roller 131 that is a heating member that heats unfixed toner carried on the paper 6, and a pressure member that rotates while contacting the fixing roller 131 with a predetermined pressure. A fixing unit 30 including a pressure roller 132 is provided. 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 (see FIG. 2), which is 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 this elastic layer is excellent in releasability such as fluororesin. The one covered with is used.

  The fixing roller 131 is rotatably held by a fixing frame (not shown), and the pressure roller 132 is rotatably held by the pair of pressure levers 51 at both ends of the rotation shaft 132a.

  The pressure lever 51 is made of a metal plate such as iron and has a predetermined shape. A hole for fitting into a first support shaft 54 fixed to a fixing frame (not shown) is formed in the upper portion of the pressure lever 51, and the pressure lever 51 is front and rear with the first support shaft 54 as a center. It is held so as to be swingable in the direction (left-right direction in FIG. 2). One end of a biasing member 53 made of a tension coil spring is engaged with the lower portion of the pressure lever 51. As shown in FIGS. 3 and 4, the lower portion of the pressure lever 51 is urged in a predetermined direction (left direction in FIG. 3) by the urging member 53, whereby the pressure roller 132 is fixed with a predetermined pressure contact force. Pressed against the roller 131.

  The other end of the urging member 53 is engaged with a pressed member 81 that is pressed by the eccentric cam 82. The pressed member 81 is formed in a predetermined shape with a metal plate such as iron. In the upper part of the pressed member 81, a hole that fits into a second support shaft 55 provided in a fixing frame (not shown) is formed. The pressed member 81 has a longitudinal direction about the second support shaft 55. It is held so that it can swing in the left-right direction in FIG. Then, the lower portion of the pressed member 81 pulls the urging member 53 in a predetermined direction (left direction in FIG. 2), so that the urging force for urging the pressing lever 51 is increased on the urging member 53.

  The pressed member 81 is pressed forward (left side in FIG. 2) by the eccentric cam 82. The eccentric cam 82 can rotate around the rotation center O82 of the rotation shaft 82a in a state where it is in contact with the pressed member 81, and is formed such that the distance from the rotation center O82 to the outer peripheral surface changes. For this reason, if the eccentric cam 82 rotates, it will switch to the state shown, for example in FIG.2, FIG.3, FIG.4.

  In the state shown in FIG. 2 (the state where the distance from the rotation center O82 to the contact position between the eccentric cam 82 and the pressed member 81 is the shortest), the tensile force of the pressed member 81 against the biasing member 53 is small. The urging force transmitted from the urging member 53 to the pressure lever 51 is small. On the other hand, the eccentric cam 82 rotates from the state shown in FIG. 2 to the state shown in FIG. 3 (the state where the distance from the rotation center O82 to the contact position between the eccentric cam 82 and the pressed member 81 is the largest). As a result, the tensile force of the pressed member 81 against the biasing member 53 increases. For this reason, the urging force transmitted from the urging member 53 to the pressure lever 51 is increased, and the nip pressure of the fixing nip portion N is increased. In this way, the urging force transmitted from the urging member 53 to the pressure lever 51 can be switched by rotating the eccentric cam 82. The detailed structure of the eccentric cam 82 will be described later.

  The eccentric cam 82, the pressed member 81, the urging member 53, and the pressure lever 51 are provided substantially symmetrically on both sides in the longitudinal direction of the fixing unit 30. The pair of eccentric cams 82 are fixed to both ends of one rotation shaft 82a, and a rotational driving force is transmitted through the rotation shaft 82a.

  Specifically, as shown in FIGS. 5 and 6, on one end portion side of the rotating shaft 82 a, a drive source 61 such as a motor and a plurality of resin-made intermediates from which the drive force is transmitted from the drive source 61. A gear 62 and an input gear 63 that is fixed to one end of the rotating shaft 82a and transmits the driving force from the intermediate gear 62 to the pair of eccentric cams 82 via the rotating shaft 82a are provided. The plurality of intermediate gears 62 includes a plurality of intermediate gears 62a constituting a first gear train, a clutch gear 62b coupled to the intermediate gear 62a, and a plurality of intermediate gears coupled to the clutch gear 62b to constitute a second gear train. 62c.

  The eccentric cam 82 rotates counterclockwise in FIG. 7 about the rotation center O82. Therefore, the contact position between the eccentric cam 82 and the pressed member 81 moves in the direction of arrow A (clockwise direction) in FIG. The eccentric cam 82 includes a bottom dead center P1 at which the distance from the rotation center O82 to the outer peripheral surface is minimum, and a top dead center P2 at which the distance from the rotation center 82 to the outer peripheral surface is maximum.

  In the present embodiment, as shown in FIG. 8, the eccentric cam 82 has a bottom dead center region in the moving direction (arrow A direction) of the contact position between the bottom dead center region R 1 including the bottom dead center P 1 and the pressed member 81. A radius increasing region R2 provided downstream of R1 and upstream of top dead center P2, an equal radius region R3 provided downstream from top dead center P2, and an equal radius region R3 and a bottom dead center region R1. And a radius-decreasing region R4 provided therebetween.

  The bottom dead center region R1 has a constant distance from the rotation center O82 to the outer peripheral surface and is the same as the bottom dead center P1. In the radius increase region R2, the distance from the rotation center O82 to the outer peripheral surface increases as the top dead center P2 is approached. The equiradius region R3 has a constant distance from the rotation center O82 to the outer peripheral surface and is the same as the top dead center P2. In the radius decreasing region R4, the distance from the rotation center O82 to the outer peripheral surface decreases as the distance from the top dead center P2 increases.

  The outer peripheral surface of the equal radius region R3 is subjected to a textured process, and the outer peripheral surface of the equal radius region R3 is used for other regions of the eccentric cam 82 (the bottom dead center region R1, the radius increasing region R2, the radius decreasing region R4). The surface roughness is larger than the outer peripheral surface. For this reason, the sliding resistance between the equal radius region R3 and the pressed member 81 is the other region (the bottom dead center region R1, the radius increasing region R2, the radius decreasing region R4) of the eccentric cam 82 and the pressed member 81. It is larger than the sliding resistance between.

  From the state of FIG. 2 (the state where the bottom dead center region R1 and the pressed member 81 are in contact with each other, T1 of FIG. 9), the driving force is transmitted from the driving source 61 to the eccentric cam 82 via the intermediate gear 62. When the cam 82 rotates counterclockwise in FIG. 2, the radius increasing region R2 presses the pressed member 81, and the shaft torque acting on the eccentric cam 82 increases (T2 in FIG. 9). At this time, the intermediate gear 62 and the like disposed between the drive source 61 and the eccentric cam 82 are distorted by the shaft torque.

  And after the pressing position with respect to the to-be-pressed member 81 reached | attained the top dead center P2 (state of FIG. 3, T3 of FIG. 9), if the top dead center P2 passes through a predetermined angle, the clutch gear 62b will be switched to a disconnection state, The state shown in FIG. 4 (printing state) is obtained.

  At this time, when the pressing position with respect to the pressed member 81 reaches the top dead center P2, the shaft torque acting on the eccentric cam 82 is released. For example, unlike the present embodiment, when the constant radius region R3 of the eccentric cam 82 is not subjected to the texture processing, the distortion is eliminated by the restoring force of the intermediate gear 62 when the shaft torque acting on the eccentric cam is released. At the same time, the eccentric cam further rotates (overruns) from a predetermined angle (T4 ′ in FIG. 9). For this reason, it is difficult to stop the eccentric cam at a predetermined stop angle (stop position).

  On the other hand, in the present embodiment, the constant radius region R3 of the eccentric cam 82 is subjected to a texture process so that the sliding resistance between the constant radius region R3 and the pressed member 81 is relatively large. Even if the pressing position with respect to 81 reaches the top dead center P <b> 2, the eccentric cam 82 can be prevented from sliding with respect to the pressed member 81. That is, it is possible to suppress the eccentric cam 82 from rotating. For this reason, since the overrun of the eccentric cam 82 can be suppressed (state of FIG. 4, T4 of FIG. 9), the eccentric cam 82 can be stopped in a state close to a predetermined stop angle (stop position).

  Further, when the clutch gear 62b is switched from the state shown in FIG. 4 to the connected state, the eccentric cam 82 further rotates counterclockwise in FIG. 4, and the pressing position with respect to the pressed member 81 passes through the radius decreasing region R4 ( T5 in FIG. 9) Move to the bottom dead center region R1. When the pressing position with respect to the pressed member 81 reaches the bottom dead center region R1, the clutch gear 62b is switched to the disconnected state, and the state shown in FIG. 2 (non-printing state) is obtained.

  In the present embodiment, as described above, the sliding resistance between the equal radius region R3 and the pressed member 81 is larger than the sliding resistance between the radius increasing region R2 and the pressed member 81. Thereby, even if the eccentric cam 82 rotates and the pressing position with respect to the pressed member 81 reaches the top dead center P <b> 2, the eccentric cam 82 can be prevented from sliding with respect to the pressed member 81. That is, it is possible to suppress the eccentric cam 82 from rotating. For this reason, the overrun of the eccentric cam 82 can be suppressed.

  Further, in the moving direction (arrow A direction) of the contact position between the eccentric cam 82 and the pressed member 81, the distance from the top dead center P2 to the downstream side and the rotation center O82 to the outer peripheral surface is the same as the top dead center P2. Since the equiradius region R3 is provided, for example, in the vicinity of the downstream side of the top dead center P2 in the moving direction of the contact position between the eccentric cam 82 and the pressed member 81, from the rotation center O82 as the distance from the top dead center P2 increases. Unlike the case of providing the radius reduction region R4 in which the distance to the outer peripheral surface is reduced, the eccentric cam 82 is not pressed in the counterclockwise direction of FIG. 2 by the reaction force of the pressed member 81. Overrun can be further suppressed.

  Further, as described above, the outer peripheral surface of the equal radius region R3 has a larger surface roughness than the outer peripheral surface of the radius increase region R2. Thereby, the sliding resistance between the equal radius region R3 and the pressed member 81 can be easily made larger than the sliding resistance between the radius increasing region R2 and the pressed member 81.

  As described above, the intermediate gear 62 is made of resin. As described above, when the intermediate gear 62 is made of resin, the intermediate gear 62 is easily distorted by the axial torque. Therefore, it is particularly effective to apply the present invention when the intermediate gear 62 is made of resin. .

  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, and further includes meanings equivalent to the scope of claims and all modifications within the scope.

  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 including a fixing device including a heating member and a pressure roller, 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 pressing force variable mechanism is applied to the fixing device has been described. However, the present invention is not limited thereto, and the pressing force variable mechanism may be applied to devices other than the fixing device.

  Further, in the above embodiment, the outer peripheral surface of the equiradius region is subjected to embossing to reduce the slide resistance between the equiradius region and the pressed member and the slide resistance between the other region and the pushed member. Although an example of larger than the above is shown, the present invention is not limited to this. For example, by attaching another member to the equal radius region, the sliding resistance between the equal radius region and the pressed member may be larger than the sliding resistance between the other region and the pressed member. .

Claims (5)

An eccentric cam,
A member to be pressed against the eccentric cam;
A drive source for generating a drive force for driving the eccentric cam;
One or more intermediate gears disposed between the eccentric cam and the drive source and transmitting the driving force generated by the drive source to the eccentric cam;
With
The eccentric cam is provided on the downstream side from the top dead center in the moving direction of the contact position with the member to be pressed, and an equal radius region in which the distance from the rotation center to the outer peripheral surface is the same as the top dead center; A radius increasing region that is provided upstream of the top dead center in the direction of movement of the contact position with the pressed member, and the distance from the rotation center to the outer peripheral surface increases as the top dead center is approached. Including
A pressing force variable mechanism, wherein a sliding resistance between the equal radius region and the pressed member is larger than a sliding resistance between the radius increasing region and the pressed member.   2. The pressing force variable mechanism according to claim 1, wherein the outer peripheral surface of the equal radius region has a larger surface roughness than the outer peripheral surface of the radius increasing region.   The pressing force variable mechanism according to claim 1, wherein the intermediate gear is made of resin. A pressing force variable mechanism according to claim 1;
A heating member for heating the unfixed toner image carried on the recording medium;
A pressure member that rotates while contacting the heating member at a predetermined pressure;
With
The fixing device, wherein the pressing member is pressed against the heating member by a force received from the pressed member.   An image forming apparatus comprising the fixing device according to claim 4.

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