JP6425053B2 - Fixing device and image forming apparatus - Google Patents

Description

  The present invention is provided with a fixing device having a nip pressure adjusting mechanism for adjusting a nip pressure of a 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, The present invention relates to an image forming apparatus.

  The fixing device disclosed in Patent Document 1, for example, prevents wrinkles when passing through an envelope or the like, and a concave permanent distortion caused by the fixing roller being left in a pressure-contacted state for a long time, a so-called C set A nip pressure adjustment mechanism is provided to adjust the nip pressure of the nip portion in order to prevent the phenomenon.

  The nip pressure adjusting mechanism reverses the eccentric cam by 180 ° by the motor via the drive gear train to switch between the minimum radius portion and the maximum radius portion, thereby the spring pressure of the compression spring pressing 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 the eccentric cam stops at the same position as the motor stops. .

  However, conversely, when the eccentric cam rotates in the direction to switch from the maximum radius to the minimum radius, the spring pressure of the compression spring is released, so that the eccentric cam is pre-rotated by its repulsive force. The eccentric cam may rotate more than the motor rotates, and a predetermined nip pressure may not be obtained.

  The present invention has been made in view of such a point, and the purpose thereof is a fixing device in which the fixing performance is improved by stopping the eccentric cam at a specified stop position and stabilizing the nip pressure. And providing an image forming apparatus provided with the same.

In the fixing device according to the present invention, a fixing member and a sheet carrying an unfixed toner image in pressure contact with the fixing member are held between the fixing member and the unfixed toner image is melted and fixed on the sheet A fixing device including a pressing member forming the nipping portion and a nipping pressure adjusting mechanism adjusting the nipping pressure of the nipping portion, the nipping pressure adjusting mechanism rotatably supporting the pressing member. And an arm member rotatably supported on a predetermined axis, an eccentric cam having an axial center extending in parallel with the predetermined axis, and having a maximum radius portion and a minimum radius portion, and a predetermined movement interlocking with the arm member A rotatable roller disposed movably along the path and in contact with the eccentric cam, and a drive unit for driving the eccentric cam, the eccentric cam being rotated by the drive unit, Contact position between the eccentric cam and the roller Is configured to rotate the arm member about the predetermined axis to adjust the nip pressure by switching between the maximum radius portion and the minimum radius portion, and the minimum radius portion is the eccentric cam The recess is provided at a position apart from the maximum radius portion and is formed of the bottom surface of the recess, and the recess on the upstream side in the rotational direction is deeper than the depth on the downstream side in the rotational direction .

According to this configuration, when the eccentric cam switches from the maximum radius portion to the minimum radius portion, the roller faces the recess, so the eccentric cam is not rotated first, and the eccentric cam rotates more than the motor rotates. Without stopping at the specified stop position. Therefore, a stable nip pressure is obtained, and the fixing performance of the fixing device is improved .

Further , according to the above configuration, while the roller smoothly faces the recess, the excessive rotation of the eccentric cam is reliably prevented.

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

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

  An image forming apparatus according to the present invention includes the above-described fixing device.

  According to this configuration, the image forming apparatus includes the fixing device with improved fixing performance.

  According to the present invention, the roller is opposed to the recess of the eccentric cam, the situation where the eccentric cam is rotated more than the cam is rotated earlier and the motor is rotated is eliminated, and the eccentric cam is set to the specified stop position. The fixing performance can be improved by stopping and stabilizing the nip pressure.

FIG. 1 is a schematic view 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 of FIG. FIG. 5 is an enlarged view of the eccentric cam. FIG. 6 is a perspective view showing a drive configuration of the fixing device. FIG. 7 is an explanatory view of power transmission when the fixing roller rotates. FIG. 8 is an explanatory view of power transmission in a state of being ready to reduce or release the nip pressure from the state of FIG. 7. FIG. 9 is an explanatory view 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 based on the drawings. The present invention is not limited to the following embodiments.

  FIG. 1 shows an image forming apparatus 1, and in this example, it is a tandem type color copying machine of an in-body delivery type. The image forming apparatus 1 includes a lower apparatus main body 2 and an upper apparatus main body 3.

  In the lower apparatus body 2, the sheet feeding unit 4, the image forming unit 5, the fixing device 6 and the like are accommodated, and in the upper apparatus body 3, the 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.

  In the sheet conveyance path L from the sheet feeding unit 4 to the sheet discharge space 8, a plurality of conveyance rollers 10 which sandwich and convey the sheet P are disposed.

  The sheet feeding unit 4 includes a sheet feeding cassette 11 in which the sheet P is stored, and a pickup roller 12 for taking out the sheet P in the sheet feeding cassette 11 and feeding the sheet P to a sheet conveyance path L. The sheet P fed from the sheet feeding cassette 11 is supplied to the image forming unit 5 by the conveyance roller 10.

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

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

  The charger 20 uniformly charges the circumferential 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 the laser light emitted from the laser light source is irradiated onto the circumferential surface of the photosensitive drum 17 via the polygon mirror. An electrostatic latent image corresponding to predetermined image data (for example, data of an original image read by the image reading unit 7) is formed on the circumferential surface of the photosensitive drum 17 by the irradiated laser light. The developing unit 18 supplies toner to the electrostatic latent image on the circumferential surface of the photosensitive drum 17 to make it visible 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 the primary transfer roller 22 to form a primary transfer portion. At the primary transfer portion, the toner images of the photosensitive drums 17 are sequentially transferred to the intermediate transfer belt 14 at predetermined timing as the intermediate transfer belt 14 rotates. As a result, a toner image in which toner images of four colors of magenta, cyan, yellow and black are superimposed is formed on the surface of the intermediate transfer belt 14.

  The cleaning device 21 cleans the toner adhering and remaining on the circumferential surface of the photosensitive drum 17 after transfer. Although not shown, around the photosensitive drum 17, a static eliminator for removing the residual charge on the circumferential surface of the photosensitive drum 17 is disposed. The image forming unit 5 is configured of these components.

  A secondary transfer roller 23 to which a bias potential is applied is disposed below the fixing device 6 of the sheet conveyance path L so as to face the drive roller 15, and the secondary transfer roller 23 and the drive roller 15 form an intermediate transfer belt 14. Is pressed against the intermediate transfer belt 14 to form a secondary transfer portion. In the secondary transfer portion, the toner image on the surface of the intermediate transfer belt 14 is transferred to the sheet P, and the sheet P after transfer is supplied to the fixing device 6. After 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 the fixing housing 24 (see FIGS. 2 and 3). The fixing roller 25 incorporates a halogen heater which is a heat source, and is heated by the halogen heater. The pressure roller 26 is in pressure contact with the fixing roller 25 and a nip portion N (see FIG. 1) is formed therebetween. The sheet P carrying the unfixed toner image supplied from the image forming unit 5 to the fixing device 6 is nipped by the nip portion N between the fixing roller 25 and the pressure roller 26 to be heated and pressed. Thus, the unfixed toner image is melted and fixed on the sheet P.

  The sheet P on which the toner image is fixed by the fixing device 6 is sent to the downstream side of the sheet conveyance path L by the fixing roller 25 and the pressure roller 26, and is conveyed to the sheet discharge tray 9 of the sheet discharge space 8 by the conveyance roller 10. Exhausted.

  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 the arm member 29 extending vertically. The upper end of the arm member 29 is supported by the fixing housing 24 by a pivot shaft (not shown), and the arm member 29 rotatably supports the pressure roller 26 on the upper end side and vertically with the pivot shaft as a fulcrum It is supposed to rotate.

  A fixing plate 30 is attached to the lower end in the fixing housing 24, and one end (left end in FIG. 3) of an expandable plate-like bar 31 extending horizontally is fixed to the fixing plate 30. At the other end (right end in FIG. 3) of the bar 31, a wide part 31a (see FIGS. 7 to 9) wide in the lateral direction (paper surface front and back direction) is formed. 9) is formed, and the tip end 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 the lower end side of the lever 34 described later.

  The lower compression spring 32 is wound around the bar 31. The lower compression spring 32 is compressed between the fixed plate 30 and the end edge 31c of the wide portion 31a of the bar 31, extends the bar 31 by spring pressure, and presses the lower end side of the arm member 29 with the bar 31. The pressure roller 26 is pressed against the fixing roller 25 by turning the arm member 29 counterclockwise in FIG.

  An upper compression spring 33 is juxtaposed in the upper vicinity of the lower compression spring 32, and one end (left end in FIG. 3) of the upper compression spring 33 is fixed to the fixing plate 30, and the other end (right end in FIG. It is fixed to the arm member 29. 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 fully extended. It has become.

  On the opposite side of the lower compression spring 32 and the upper compression spring 33 at the lower end side of the arm member 29, a lever 34 extending vertically is juxtaposed as shown in FIG. 4 in an enlarged manner, and the upper end of the lever 34 is a fixing housing The lever 34 is supported by the fixed side 24 a 24 and 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. Further, a roller 35 is rotatably supported by a shaft 36 on the lever 34.

  On the side opposite to the arm member 29 side of the lever 34, an eccentric cam 37 in contact with the roller 35 is rotatably supported by the cam shaft 38 and arranged in parallel. The eccentric cam 37, as shown enlarged in FIG. 5, includes a maximum radius R1 far from the cam shaft 38 and a minimum radius R2 provided at a position 180 ° away from the maximum radius R1 and near the cam shaft 38 The maximum radius R1 is configured to have a central angle .theta. Of about 60.degree. So as not to protrude from the maximum radius R1 even if the position of the roller 35 varies.

The minimum radius portion R2 of the eccentric cam 37 is formed by the bottom surface of the recess 39, and when the roller 35 faces the minimum radius portion R2, a part of the roller 35 is fitted in the recess 39. As a result, when the eccentric cam 37 switches from the maximum radius R1 to the minimum radius R2, the spring pressure of the lower compression spring 32 is released and the roller 35 snaps into the recess 39 and the repulsion force of the lower compression spring 32 As a result, the roller 35 tries to jump out of the recess 39, but the side wall of the recess 39 restricts the projection of the roller 35. Therefore, the roller 35 does not overrun the minimum radius portion R2 and stably stops at the minimum radius portion R2, and the first rotation of the eccentric cam 37 is prevented, and the eccentric cam 37 does not rotate more than the motor described later rotates. In order to stop at the specified stop position, the nip pressure can be stabilized, and the fixing performance of the fixing device 6 can be improved.

  The eccentric cam 37 is formed on the upper side (the upstream side in the rotational direction) below the recess 39 in FIG. 5 on the upward inclined surface 37a, and on the upper side (the downstream side in the rotational direction) than the recess 39 on the downstream inclined surface 37b. Since the depth D1 of the upward inclined surface 37a of the recess 39 is deeper than the depth D2 of the downward inclined surface 37b of the recess 39, the eccentric cam 37 is asymmetric. As a result, the roller 35 can be made to smoothly face the recess 39 of the eccentric cam 37 rotated clockwise as shown by the arrow in FIG. 5, while over rotation of the eccentric cam 37 can be prevented. Further, since the depth D2 of the downward inclined surface 37b is smaller than the depth D1 of the upward inclined surface 37a, the downward inclined surface 37b becomes gentle, and the eccentric cam 37 has a minimum radius R2 from the maximum radius R1. When switching to the above, the force by which the eccentric cam 37 is pre-turned can be minimized.

  Then, when the roller 35 faces the recess 39 (minimum radius portion R2), as shown in FIGS. 3 and 4, the bar 31 extends by the spring pressure of the lower compression spring 32, and the lever 34 rotates counterclockwise in FIG. To rotate. In conjunction with this, when the arm member 29 pivots counterclockwise in FIG. 3 with the pivot shaft as a fulcrum, the pressure roller 26 is in pressure contact with the fixing roller 25 via the lever 34 and the arm member 29, and the nip portion A predetermined nip pressure is generated at N. In the state where the roller 35 is opposed to the minimum radius portion R2, a gap C is formed between the roller 35 and the bottom surface of the recess 39 (minimum radius portion R2) (see FIG. 4). Thereby, 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 faces the maximum radius R1 opposite to the minimum radius R2 by 180 °, the lever 34 is pushed by the maximum radius R1 to rotate clockwise, and the bar 31 is moved to the lower compression spring 32 Shrink against spring pressure. Accordingly, the pressure roller 26 is moved away from the fixing roller 25 via the lever 34 and the arm member 29 by the arm member 29 rotating clockwise in FIG. The nip pressure of 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 described above.

  The nip pressure adjusting mechanism 100 also includes a drive gear train as shown in FIGS. 6 to 9 for transmitting the driving force to the eccentric cam 37 to rotate the eccentric cam 37. That is, a drive input gear 40 connected to a motor (stepping motor) (not shown), a fixing roller gear 41 attached to rotate integrally with the fixing roller 25, and a cam attached to rotate integrally with the eccentric cam 37 The drive gear 42, a planetary gear 43 moving following the rotational movement 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 incorporates a one-way clutch (not shown). An actuator (not shown) is attached to the cam shaft 38, and the direction of the eccentric cam 37 is reversely controlled by detecting the actuator with a PI sensor (Photo Interrupter Sensor) (not shown).

  Then, when the fixing roller 25 normally rotates, the rotational drive force is input counterclockwise from the motor (drive unit) to the drive input gear 40, and the planetary gear 43 separates from the cam drive gear 42 and meshes with the cam drive gear 42. Is eliminated. Further, the one-way clutch contained 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 shown by the arrow in FIG. At this stage, as shown in FIGS. 3 and 4, the eccentric cam 37 has the minimum radius R2 facing the roller 35, a part of the roller 35 is fitted in the recess 39, and the arm member 29 and the lever 34 The spring pressure of the lower compression spring 32 rotates counterclockwise to press the pressure roller 26 against the fixing roller 25 to generate a predetermined nip pressure at the nip portion N.

  On the other hand, when adjusting the nip pressure of the nip portion N to prevent wrinkles when an envelope or the like is fed and to prevent C set phenomenon of the fixing roller 25, the motor is driven to rotate clockwise to the drive input gear 40 The force is input, and the planetary gear 43 approaches the cam drive gear 42 and meshes with the cam drive gear 42. In addition, 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 passes from the intermediate gears 44 and 45 through the planetary gear 43 as shown by the arrows in FIGS. Only the drive gear 42 is transmitted. The rotation of the cam drive gear 42 rotates the eccentric cam 37 by 180 °, the roller 35 comes out of the recess 39, and the maximum radius R1 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 in the direction away from the fixing roller 25. , Reduce or cancel the nip pressure of the nip portion N.

  From this state, when switching the eccentric cam 37 from the maximum radius portion R1 to the minimum radius portion R2, as described above, the roller 35 faces the recess 39 and restricts the first rotation of the eccentric cam 37 to specify the eccentric cam 37. Since the image forming apparatus 1 can be stopped at the stop position, it is possible to obtain the image forming apparatus 1 provided with a fixing device having a stable fixing function.

  Although the roller fixing method is exemplified as the fixing device 6 in the above embodiment, the present invention is not limited to this, and it is needless to say that it can be applied to the belt fixing method.

  In the above embodiment, the image forming apparatus 1 is a color copying machine. 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, etc. Applicable to

  As described above, the present invention is a fixing device having a nip pressure adjusting mechanism for adjusting the nip pressure of the nip portion formed by pressure contact between a fixing member such as a fixing roller or fixing belt and a pressure member such as a pressure roller. The present invention 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 35 Roller 37 Eccentric cam 39 Recess 40 Drive input gear 41 Fixing roller gear 42 Cam drive gear 43 Planet gear 44, 45 Intermediate gear 100 Nip pressure adjustment mechanism C Clearance D1 Recess in upstream rotation direction Depth D2 of the side Depth of the downstream side in the rotational direction of the recess N Nip portion P Paper R1 Maximum radius portion R2 Minimum radius portion

Claims (4)

A fixing member,
A pressure member which is in pressure contact with the fixing member, and forms a nip portion for fixing the unfixed toner image on the sheet by holding the sheet carrying the unfixed toner image between the fixing member and the sheet;
And a nip pressure adjusting mechanism for adjusting the nip pressure of the nip portion.
The above nip pressure adjustment mechanism
An arm member rotatably supporting the pressing member and rotatably supported on a predetermined shaft;
An eccentric cam having an axis extending parallel to the predetermined axis and having a maximum radius and a minimum radius;
A rotatable roller disposed so as to be movable along a predetermined movement path in conjunction with the arm member and in contact with the eccentric cam;
A drive unit for driving the eccentric cam;
The arm member is rotated by the drive unit to switch the contact position between the eccentric cam and the roller between the maximum radius portion and the minimum radius portion, thereby the arm member Is rotated about the predetermined axis to adjust the nip pressure,
The minimum radius portion is provided at a position apart from the maximum radius portion of the eccentric cam, and is formed of the bottom surface of the recess ,
In the fixing device, the recess 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 . In the fixing device according to claim 1,
A fixing device, wherein a minimum radius portion of the eccentric cam is provided at a position 180 ° apart from the maximum radius portion around an axis of the eccentric cam. In the fixing device according to claim 1 or 2 ,
In a state in which the roller is opposed to the minimum radius portion, the gap between the rollers and the bottom surface of the recess is formed, the fixing device. An image forming apparatus comprising the fixing device according to any one of claims 1 to 3 .

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