JP6590168B2 - Eccentric cam - Google Patents

Description

  The present invention relates to an eccentric cam that is rotationally driven by a motor while contacting a roller rotatably supported by a predetermined member.

  For example, the fixing device disclosed in Japanese Patent Application Laid-Open No. 2004-151620 prevents wrinkles when an envelope or the like is passed through, or has a concave permanent distortion generated when the fixing roller is left in a pressed state for a long time, so-called C set. In order to prevent the phenomenon, a nip pressure adjusting mechanism for adjusting the nip pressure of the nip portion is provided.

  This nip pressure adjusting mechanism reverses the eccentric cam by 180 ° by a motor through a drive gear train and switches between the minimum radius portion and the maximum radius portion, thereby reducing the spring pressure of the compression spring that presses the pressure roller against the fixing roller. The pressure at the nip is adjusted by increasing or decreasing.

JP 2001-201976 A

  In the nip pressure adjusting mechanism of Patent Document 1, when the eccentric cam rotates in the direction to switch from the minimum radius portion to the maximum radius portion, the compression spring gradually extends, so that the eccentric cam stops at that position simultaneously with the stop of the motor. .

  However, on the contrary, when the eccentric cam rotates in the direction of switching from the maximum radius portion to the minimum radius portion, the spring pressure of the compression spring is released, so the eccentric cam is rotated by the repulsive force. The eccentric cam rotates more than the motor rotates, and a predetermined nip pressure may not be obtained.

  This invention is made | formed in view of this point, The place made into the objective is providing the eccentric cam which can be made to stop at a regular stop position.

The eccentric cam according to the present invention is rotationally driven by a motor while abutting a roller rotatably supported by a predetermined member.
The roller is urged toward the eccentric cam by an urging member, and the eccentric cam is a minimum radius composed of a maximum radius portion and a bottom surface of a recess provided at a position away from the maximum radius portion. The concave portion has a depth on the upstream side in the rotational direction that is deeper than a depth on the downstream side in the rotational direction.

  According to this configuration, when the eccentric cam is switched from the maximum radius portion to the minimum radius portion, the roller faces the recess, so that even if the spring pressure of the compression spring is released, the eccentric cam is rotated by the repulsive force. The eccentric cam does not rotate more than the motor rotates, and stops at the specified stop position. Moreover, while the roller smoothly faces the recess, the eccentric cam is reliably prevented from rotating excessively.

  Further, it is preferable that a gap is formed between the roller and the bottom surface of the recess in a state where the roller faces the minimum radius portion.

  According to this configuration, the spring pressure of the compression spring is applied to the pressure member without loss.

  According to the present invention, since the roller faces the concave portion of the eccentric cam, it is possible to eliminate the situation where the eccentric cam rotates more than the motor is rotated by the repulsive force of the compression spring and the motor rotates. Can be stopped at a specified stop position.

FIG. 1 is a schematic diagram showing the internal structure of the image forming apparatus. FIG. 2 is an external perspective view of the fixing device. FIG. 3 is a cross-sectional view showing the internal structure of the fixing device. FIG. 4 is an enlarged view of a portion A in FIG. FIG. 5 is an enlarged view of the eccentric cam. FIG. 6 is a perspective view illustrating a driving configuration of the fixing device. FIG. 7 is an explanatory diagram of power transmission during rotation of the fixing roller. FIG. 8 is an explanatory diagram of power transmission in a state where the nip pressure is reduced or released from the state shown in FIG. FIG. 9 is an explanatory diagram of a state in which the nip pressure is reduced or released from the state of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment.

  FIG. 1 shows an image forming apparatus 1, which is a tandem type color copier of a cylinder discharge type in this example. The image forming apparatus 1 includes a lower apparatus main body 2 and an upper apparatus main body 3.

  In the lower apparatus main body 2, a paper feeding unit 4, an image forming unit 5, a fixing device 6 and the like are accommodated, and in the upper apparatus main body 3, an image reading unit 7 is accommodated. A paper discharge space 8 is formed between the lower apparatus main body 2 and the upper apparatus main body 3, and a paper discharge tray 9 is provided in the paper discharge space 8.

  A plurality of transport rollers 10 that sandwich and transport the paper P are disposed in the paper transport path L from the paper feed unit 4 to the paper discharge space 8.

  The paper feed unit 4 includes a paper feed cassette 11 in which the paper P is accommodated, and a pickup roller 12 for taking out the paper P in the paper feed cassette 11 and sending it out to the paper transport path L. The paper P sent out from the paper feed cassette 11 is supplied to the image forming unit 5 by the transport roller 10.

  The image forming unit 5 includes four image forming units 13M, 13C, 13Y, and 13K arranged in order from the right side of FIG. 1 for magenta, cyan, yellow, and black, and these image forming units 13M, 13C, and 13Y. , 13K, an endless intermediate transfer belt 14 is arranged to be stretched between a driving roller 15 and a tension roller 16.

  Each of the image forming units 13M, 13C, 13Y, and 13K includes a photosensitive drum 17 that is an image carrier, and a developing device 18, an exposure device 19, a charging device 20, and a cleaning device 21 are disposed around the photosensitive drum 17. ing.

  The charger 20 uniformly charges the peripheral surface of the photosensitive drum 17. The exposure device 19 is provided with a laser light source, a polygon mirror, and the like (not shown), and laser light emitted from the laser light source is applied to the peripheral surface of the photosensitive drum 17 through the polygon mirror. An electrostatic latent image corresponding to predetermined image data (for example, document image data read by the image reading unit 7) is formed on the peripheral surface of the photosensitive drum 17 by the irradiated laser light. The developing unit 18 supplies toner to the electrostatic latent image on the peripheral surface of the photosensitive drum 17 to visualize it as a toner image.

  The photosensitive drum 17 is in contact with the intermediate transfer belt 14 from below, and is pressed against the intermediate transfer belt 14 by a primary transfer roller 22 to form a primary transfer portion. In the primary transfer portion, as the intermediate transfer belt 14 rotates, the toner images on the photosensitive drums 17 are sequentially transferred to the intermediate transfer belt 14 at a predetermined timing. As a result, a toner image is formed on the surface of the intermediate transfer belt 14 by superimposing four color toner images of magenta, cyan, yellow, and black.

  The cleaning device 21 cleans the toner remaining on the peripheral surface of the photosensitive drum 17 after the transfer. Although not shown, a static eliminator for removing residual charges on the peripheral surface of the photosensitive drum 17 is disposed around the photosensitive drum 17. Thus, the image forming unit 5 is configured.

  Below the fixing device 6 in the paper conveyance path L, a secondary transfer roller 23 to which a bias potential is applied is disposed to face the driving roller 15, and the secondary transfer roller 23 is connected to the driving roller 15 and the intermediate transfer belt 14. A secondary transfer portion is formed in pressure contact with the intermediate transfer belt 14. In the secondary transfer portion, the toner image on the surface of the intermediate transfer belt 14 is transferred onto the paper P, and the paper P after the transfer is supplied to the fixing device 6. After the transfer, a belt cleaning device (not shown) cleans the toner remaining on the intermediate transfer belt 14.

  The fixing device 6 includes a fixing roller (fixing member) 25 and a pressure roller (pressure member) 26 accommodated in a fixing housing 24 (see FIGS. 2 and 3). The fixing roller 25 incorporates a halogen heater as a heat source and is heated by the halogen heater. The pressure roller 26 is pressed against the fixing roller 25, and a nip portion N (see FIG. 1) is formed therebetween. The paper P carrying the unfixed toner image supplied from the image forming unit 5 to the fixing device 6 is sandwiched and heated and pressed by the nip N between the fixing roller 25 and the pressure roller 26. Thus, the unfixed toner image is melted and fixed on the paper P.

  The paper P on which the toner image is fixed by the fixing device 6 is sent out to the downstream side of the paper transport path L by the fixing roller 25 and the pressure roller 26, and is transported to the paper discharge tray 9 in the paper discharge space 8 by the transport roller 10. Discharged.

  As shown in FIG. 3, a support shaft 27 protrudes from both ends of the pressure roller 26, and the support shaft 27 is supported by a bearing 28. The bearing 28 is fixed to the upper end side of an arm member 29 extending vertically. The upper end of the arm member 29 is supported on the fixing housing 24 by a rotation shaft (not shown). The arm member 29 supports the pressure roller 26 rotatably on the upper end side, and moves up and down around the rotation shaft. It is designed to rotate.

  A fixing plate 30 is attached to the lower end of the fixing housing 24, and one end (left end in FIG. 3) of a horizontally extendable plate-like bar 31 that extends horizontally is fixed to the fixing plate 30. On the other end (right end in FIG. 3) side of the bar 31, a wide portion 31a (see FIGS. 7 to 9) that is wide in the lateral direction (the front and back sides of the drawing) is formed. To 9), and the tip of the arm member 29 is inserted into the insertion hole 31b with play in the longitudinal direction of the bar 31. The other end (right end in FIG. 3) of the bar 31 is narrow, and is supported by the lever 34 through a lower end side of a lever 34 described later.

  A lower compression spring 32 is wound around the bar 31. The lower compression spring 32 is contracted between the fixed plate 30 and the end edge 31 c of the wide portion 31 a of the bar 31, extends the bar 31 with spring pressure, and presses the lower end side of the arm member 29 with the bar 31. Thus, the arm member 29 is rotated counterclockwise in FIG. 3 with the rotation axis as a fulcrum, and the pressure roller 26 is pressed against the fixing roller 25.

  An upper compression spring 33 is juxtaposed in the vicinity of the upper side of the lower compression spring 32. One end (the left end in FIG. 3) of the upper compression spring 33 is fixed to the fixing plate 30, and the other end (the right end in FIG. 3) is The arm member 29 is fixed. The upper compression spring 33 presses the arm member 29 counterclockwise in FIG. 3 with a weak spring pressure of about 1/10 of the lower compression spring 32 when the lower compression spring 32 is almost extended. It has become.

  On the opposite side to the lower compression spring 32 and the upper compression spring 33 on the lower end side of the arm member 29, as shown in an enlarged view in FIG. 4, a lever 34 extending vertically is arranged in parallel, and the upper end of the lever 34 is the fixing housing. 24, the lever 34 is pressed together with the arm member 29 by the spring pressure of the lower compression spring 32 so as to rotate up and down. A roller 35 is rotatably supported on the lever 34 by a shaft 36.

  On the side opposite to the arm member 29 side of the lever 34, an eccentric cam 37 that contacts the roller 35 is rotatably supported by the cam shaft 38 and arranged in parallel. As shown in an enlarged view in FIG. 5, the eccentric cam 37 includes a maximum radius portion R1 far from the cam shaft 38 and a minimum radius portion R2 provided at a position 180 ° away from the maximum radius portion R1 and close to the cam shaft 38. The maximum radius portion R1 is configured with a width having a central angle θ of about 60 ° so as not to protrude from the maximum radius portion R1 even if the position of the roller 35 varies.

  The minimum radius portion R2 of the eccentric cam 37 is configured by the bottom surface of the concave portion 39, and a part of the roller 35 is fitted into the concave portion 39 when the roller 35 faces the minimum radius portion R2. As a result, when the eccentric cam 37 is switched from the maximum radius portion R1 to the minimum radius portion R2, the spring pressure of the lower compression spring 32 is released, and the roller 35 fits into the recess 39 vigorously, and the repulsive force of the lower compression spring 32 As a result, the roller 35 tends to jump out of the recess 39, but the roller 35 is restricted from jumping out by the side wall of the recess 39. Accordingly, the roller 35 does not go too far over the minimum radius portion R2, but stably stops at the minimum radius portion R2, and the eccentric cam 37 is prevented from being rotated forward, and the eccentric cam 37 does not rotate beyond the rotation of the motor described later. Since it stops at the specified stop position, the nip pressure is stabilized and the fixing performance of the fixing device 6 can be improved.

  In FIG. 5, the eccentric cam 37 is formed on the inclined surface 37a on the lower side (upstream in the rotational direction) from the concave portion 39 and on the downward inclined surface 37b on the upper side (downstream in the rotational direction) from the concave portion 39. Since the depth D1 of the rising inclined surface 37a of the recess 39 is deeper than the depth D2 of the descending inclined surface 37b of the recess 39, the eccentric cam 37 is asymmetric. Thereby, the roller 35 can be smoothly opposed to the concave portion 39 of the eccentric cam 37 rotated clockwise as indicated by an arrow in FIG. 5, while the eccentric cam 37 can be prevented from excessively rotating. Further, since the depth D2 of the descending inclined surface 37b is shallower than the depth D1 of the ascending inclined surface 37a, the descending inclined surface 37b becomes gentle, and the eccentric cam 37 changes from the maximum radius portion R1 to the minimum radius portion R2. When switching to, the force with which the eccentric cam 37 is rotated can be minimized.

  When the roller 35 faces the concave portion 39 (minimum radius portion R2), as shown in FIGS. 3 and 4, the bar 31 is extended by the spring pressure of the lower compression spring 32 and the lever 34 rotates counterclockwise in FIG. To turn. Accordingly, the arm member 29 rotates counterclockwise in FIG. 3 with the rotation axis as a fulcrum, so that the pressure roller 26 comes into pressure contact with the fixing roller 25 via the lever 34 and the arm member 29, and the nip portion. N generates a predetermined nip pressure. A gap C is formed between the roller 35 and the bottom surface of the recess 39 (minimum radius portion R2) in a state where the roller 35 faces the minimum radius portion R2 (see FIG. 4). As a result, the spring pressure of the lower compression spring 32 can be applied to the pressure roller 26 without loss.

  On the other hand, when the roller 35 opposes the maximum radius R1 that is 180 ° opposite to the minimum radius R2, the lever 34 is pushed by the maximum radius R1 and rotates clockwise, and the bar 31 is moved to the lower compression spring 32. Shrinks against spring pressure. Accordingly, the arm member 29 rotates clockwise in FIG. 3 with the rotation axis as a fulcrum, so that the pressure roller 26 moves away from the fixing roller 25 via the lever 34 and the arm member 29. The nip pressure at the nip portion N is reduced or released.

  Such adjustment of the nip pressure is performed by the nip pressure adjusting mechanism 100 including the arm member 29, the bar 31, the lower compression spring 32, the upper compression spring 33, the lever 34, the roller 35, the eccentric cam 37, and the like.

  The nip pressure adjusting mechanism 100 also includes a drive gear train as shown in FIGS. 6 to 9 that transmits a driving force to the eccentric cam 37 to rotate the eccentric cam 37. That is, the drive input gear 40 connected to a motor (not shown) (stepping motor), the fixing roller gear 41 attached so as to rotate integrally with the fixing roller 25, and the cam attached so as to rotate integrally with the eccentric cam 37. A drive gear 42, a planetary gear 43 that moves following the rotation of the drive input gear 40, and intermediate gears 44 and 45 disposed between the drive input gear 40 and the planetary gear 43 are provided. The drive input gear 40 includes a one-way clutch (not shown). An actuator (not shown) is attached to the camshaft 38, and this actuator is detected by a PI sensor (Photo Interrupter Sensor) (not shown), so that the direction of the eccentric cam 37 is inverted by 180 °.

  Then, during normal rotation of the fixing roller 25, a rotational driving force is input counterclockwise from the motor to the drive input gear 40, and the planetary gear 43 is separated from the cam drive gear 42 to disengage the cam drive gear 42. . Further, the one-way clutch built in the drive input gear 40 is rotated in the meshing direction, and the rotational drive of the drive input gear 40 is transmitted to the fixing roller gear 41 as indicated by an arrow in FIG. At this stage, as shown in FIGS. 3 and 4, the eccentric cam 37 has the minimum radius R2 opposed to the roller 35 and a part of the roller 35 is fitted in the recess 39, so that the arm member 29 and the lever 34 are The pressure roller 26 is pressed against the fixing roller 25 by rotating counterclockwise by the spring pressure of the lower compression spring 32, and a predetermined nip pressure is generated in the nip portion N.

  On the other hand, when adjusting the nip pressure of the nip portion N in order to prevent wrinkling when an envelope or the like is passed through or to prevent the C-set phenomenon of the fixing roller 25, the motor is driven to rotate clockwise from the motor to the drive input gear 40. When the force is input, the planetary gear 43 approaches the cam drive gear 42 and meshes with the cam drive gear 42. Further, the one-way clutch built in the drive input gear 40 is rotated in the sliding direction, and the rotational drive of the drive input gear 40 is cammed from the intermediate gears 44 and 45 through the planetary gear 43 as shown by arrows in FIGS. It is transmitted only to the drive gear 42. The eccentric cam 37 rotates 180 ° by the rotation of the cam drive gear 42, the roller 35 comes out of the recess 39, and the maximum radius portion R 1 of the eccentric cam 37 faces the roller 35. As a result, as shown in FIGS. 8 to 9, the arm member 29 and the lever 34 rotate clockwise while contracting the lower compression spring 32 to move the pressure roller 26 away from the fixing roller 25. The nip pressure at the nip portion N is reduced or released.

  From this state, when the eccentric cam 37 is switched from the maximum radius portion R1 to the minimum radius portion R2, the roller 35 opposes the recess 39 as described above and restricts the forward rotation of the eccentric cam 37 so that the eccentric cam 37 is defined. Since the image forming apparatus 1 can be stopped at the stop position, the image forming apparatus 1 including a fixing device having a stable fixing function can be obtained.

  In the above-described embodiment, the roller fixing method is exemplified as the fixing device 6. However, the fixing device 6 is not limited to this and can be applied to a belt fixing method.

  In the above embodiment, the case where the image forming apparatus 1 is a color copying machine has been described. However, the present invention is not limited to this, and various image forming apparatuses such as a color printer, a monochrome copying machine, a monochrome printer, a digital multifunction peripheral, a facsimile machine, and the like. Applicable to.

  As described above, the present invention has a nip pressure adjusting mechanism that adjusts the nip pressure of the nip portion formed by pressure contact between a fixing member such as a fixing roller or a fixing belt and a pressure member such as a pressure roller. It is useful for an apparatus and an image forming apparatus provided with the apparatus.

1 Image forming device 6 Fixing device 25 Fixing roller (fixing member)
26 Pressure roller (Pressure member)
29 Arm member 32 Lower compression spring 34 Lever (predetermined member)
35 Roller 37 Eccentric cam 39 Concave 40 Drive input gear 41 Fixing roller gear 42 Cam drive gear 43 Planetary gears 44 and 45 Intermediate gear 100 Nip pressure adjusting mechanism C Clearance D1 Depth of rotation in upstream of recess D2 Downstream of recess in rotational direction Side depth N Nip part P Paper R1 Maximum radius R2 Minimum radius

Claims (3)

An eccentric cam that is rotationally driven by a motor while abutting a roller rotatably supported by a predetermined member,
The roller is biased to the eccentric cam side by a biasing member,
The eccentric cam has a maximum radius portion formed with a width of a predetermined center angle, and a minimum radius portion formed by a bottom surface of a recess provided at a position away from the range of the center angle of the maximum radius portion. And
The eccentric cam is characterized in that the depth on the upstream side in the rotational direction is deeper than the depth on the downstream side in the rotational direction. The eccentric cam according to claim 1,
An eccentric cam, wherein a gap is formed between the roller and the bottom surface of the recess in a state where the roller faces the minimum radius portion. The eccentric cam according to claim 1 or 2,
The eccentric cam, wherein the minimum radius portion is located on the opposite side of the maximum radius portion with the shaft center of the eccentric cam interposed therebetween.

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