JP2009192767A - Fixing device and image forming apparatus provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which is capable of easily varying fixing pressure by simultaneously operating a pair of right and left fixing pressure varying mechanisms provided at both ends in the axial direction of a pressure roller. <P>SOLUTION: In the fixing device 22, the fixing pressure varying mechanisms are provided at both ends in the axial direction of the pressure roller respectively. Each fixing pressure varying mechanism is configured to include a rotatable pressure lever pressing the pressure roller to a heating roller, a pressure plate engaged with the pressure lever, an opening/closing lever, and a pressure spring interposed between the opening/closing lever and the pressure plate. A fixing pressure varying lever 35 whose both ends in a longitudinal direction have acting portions 35a and 35b acting on the pressure plates of each fixing pressure varying mechanism is provided so that the fixing pressure varying lever 35 is slide-operated to vary the fixing pressure. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device having a mode (fixing pressure reduction mode) for reducing a fixing pressure, which is a contact force of a pressure roller to a heating roller, and an image forming apparatus having the same.

  In an image forming apparatus such as a copying machine or a printer that forms an image on a sheet by electrophotography, the electrostatic latent image formed on the image carrier is developed by a developing device and visualized as a toner image. Transfer the image onto the paper. The sheet onto which the toner image has been transferred is conveyed to a fixing device, and after the toner image is fixed by heat and pressure by the fixing device, it is discharged out of the apparatus, thereby completing a series of image forming operations. .

  The fixing device includes a heating roller and a pressure roller that rotate in contact with each other, and presses the pressure roller against the heating roller to provide a predetermined fixing pressure (fixing nip pressure) therebetween. I try to secure it.

When a paper jam (jam) occurs in such a fixing device, normally, after opening the opening / closing cover, the pressure roller is separated from the heating roller to release the pressure, and jammed paper sandwiched between the two rollers. In order to improve the workability of the jam processing, a fixing device that employs a method in which the pressure roller is in a pressure state or a pressure release state in conjunction with the opening / closing operation of the opening / closing cover is proposed. (For example, refer to Patent Document 1).
There has also been proposed a fixing device including a fixing pressure variable mechanism that adjusts the fixing pressure in order to suppress variations in fixing pressure or to variably control the glossiness of an image (see, for example, Patent Document 2).
JP 2001-166627 A JP 2003-186337 A

  By the way, in a fixing device having a variable fixing pressure mechanism, the fixing pressure variable mechanisms are provided at both ends (left and right) in the axial direction of the pressure roller in order to make the fixing pressure uniform in the paper width direction. When the pressure is varied, it is necessary to operate the left and right fixing pressure varying mechanisms, which is troublesome.

  The present invention has been made in view of the above problems, and its object is to easily change the fixing pressure by simultaneously operating a pair of left and right fixing pressure variable mechanisms provided at both axial ends of the pressure roller. It is an object of the present invention to provide a fixing device that can perform the above and an image forming apparatus including the same.

In order to achieve the above object, according to the first aspect of the present invention, there is provided a variable fixing pressure mechanism for changing a fixing pressure, which is a contact pressure between a heating roller and a pressure roller rotating in contact with each other. The fixing pressure variable mechanism is provided at both ends in the direction, the rotatable pressure lever for pressing the pressure roller against the heating roller, a pressure plate engaged with the pressure lever, an opening / closing lever, A pressure spring interposed between the opening / closing lever and the pressure plate, and rotating the opening / closing lever to change the pressure applied by the pressure spring. In the fixing device to be in a pressure state or a pressure release state,
A fixing pressure variable lever provided with action portions acting on the pressure plate of each fixing pressure variable mechanism at both longitudinal ends is provided, and the fixing pressure is varied by sliding the fixing pressure variable lever. To do.

  According to a second aspect of the present invention, in the first aspect of the invention, the variable fixing pressure lever is configured to be detachable from the fixing frame.

  According to a third aspect of the present invention, in the second aspect of the invention, an operation projection is provided at one end in the longitudinal direction of the fixing pressure variable lever, the other end in the longitudinal direction is inserted into a guide hole of the fixing frame, and the other end in the longitudinal direction is inserted. The fixing pressure variable lever is rotated as a center to incorporate the operation protrusion into the fixing frame, and the fixing pressure variable lever is slid in the longitudinal direction to form engagement protrusions formed on the operation protrusion. The fixing pressure is varied by selectively engaging with the engaging groove.

  An image forming apparatus according to a fourth aspect includes the fixing device according to any one of the first to third aspects.

  According to the first aspect of the present invention, by sliding the fixing pressure variable lever, the action portions provided at both ends in the longitudinal direction of the fixing pressure variable lever are applied to the pressure plates of the pair of left and right fixing pressure variable mechanisms. The fixing pressure can be easily varied by acting simultaneously.

  According to the second aspect of the present invention, the fixing pressure variable lever can be attached to and detached from the fixing frame in accordance with whether or not the fixing pressure needs to be varied, and when there is no need to vary the fixing pressure, the fixing pressure can be varied. The lever can be removed from the fixing frame.

  According to the third aspect of the present invention, when it is necessary to vary the fixing pressure, the fixing pressure variable lever is inserted into the guide hole of the fixing frame at one end in the longitudinal direction of the fixing pressure variable lever, and the fixing pressure variable lever is centered on the one end in the longitudinal direction. The fixing pressure variable lever can be easily attached to the fixing frame by assembling the operation projection provided at the other end in the longitudinal direction to the fixing frame, and the assemblability is improved. Then, an operation protrusion of the fixing pressure variable lever mounted on the fixing frame is operated to slide the fixing pressure variable lever in the longitudinal direction, and a plurality of engagement protrusions formed on the operation protrusion are formed on the fixing frame. By selectively engaging with the engaging groove, the fixing pressure can be easily and reliably varied.

  According to the invention of claim 4, for example, when passing thick paper such as an envelope, an image is stably fixed on the thick paper without reducing the fixing pressure and generating wrinkles or the like on the thick paper. Can be made.

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

[Image forming apparatus]
FIG. 1 is a cross-sectional view of a color laser printer as an embodiment of an image forming apparatus according to the present invention, and FIG. 2 is a perspective view of the color laser printer with an open / close cover opened.

  The color laser printer according to the present embodiment is a tandem type, and as shown in FIG. 1, a magenta image forming unit 1M, a cyan image forming unit 1C, and a yellow image forming unit 1Y are arranged at the center of the main body 100. The black image forming units 1K are arranged in tandem at regular intervals.

  Each of the image forming units 1M, 1C, 1Y, and 1K is provided with photosensitive drums 2a, 2b, 2c, and 2d, and charging rollers 3a, 3b, 3c, and 3d are disposed around the photosensitive drums 2a to 2d. 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d and drum cleaning devices 6a, 6b, 6c, 6d are arranged, respectively.

  Here, the photosensitive drums 2a to 2d are drum-shaped photosensitive members, and are rotationally driven at a predetermined process speed in a direction indicated by an arrow (clockwise) by a variable speed stepping motor (not shown). The charging rollers 3a to 3d uniformly charge the surfaces of the photosensitive drums 2a to 2d to a predetermined potential by a charging bias applied from a charging bias power source (not shown).

  Further, the developing devices 4a to 4d contain magenta (M) toner, cyan (C) toner, yellow (Y) toner, and black (BK) toner, respectively, and are formed on the respective photosensitive drums 2a to 2d. In addition, the toner of each color is attached to each electrostatic latent image to visualize each electrostatic latent image as a toner image of each color.

  The transfer rollers 5a to 5d are arranged so as to be able to contact the photosensitive drums 2a to 2d via the intermediate transfer belt 7 in the respective primary transfer portions. Here, the intermediate transfer belt 7 is stretched between the secondary transfer counter roller 8 and the tension roller 9 and is disposed on the upper surface side of each of the photosensitive drums 2a to 2d. The roller 8 is disposed so as to be in contact with the secondary transfer roller 10 via the intermediate transfer belt 7 in the secondary transfer portion. A belt cleaning device 11 is provided in the vicinity of the tension roller 9.

  Incidentally, toner containers 12a, 12b, 12c, and 12d for supplying toner to the developing devices 4a to 4d are arranged in a line above the image forming units 1M, 1C, 1Y, and 1BK in the apparatus main body 100. It is installed.

  In addition, a laser scanner unit (LSU) 13 is disposed below the image forming units 1M, 1C, 1Y, and 1BK in the apparatus main body 100, and a paper feed cassette 14 is detachably attached to the bottom of the main body 100 below the image forming units. is set up. A plurality of sheets (not shown) are stacked and accommodated in the paper feed cassette 14, and a pickup roller 15 for taking out the paper one by one from the paper feed cassette 14 is taken out in the vicinity of the paper feed cassette 14. A feed roller 16 and a retard roller 17 are provided for feeding the fed paper to the transport path L.

  The conveyance path L extending in the vertical direction on the side of the apparatus main body 100 includes a conveyance roller pair 18 that conveys the sheet, and the secondary transfer counter roller 8 and the second transfer opposing roller 8 at a predetermined timing after the sheet is temporarily held. A registration roller pair 19 is provided to be supplied to the secondary transfer portion which is a contact portion with the next transfer roller 10. Next to the conveyance path L, another conveyance path L ′ used for forming an image on both sides of the sheet is formed, and a plurality of conveyance roller pairs 20 are appropriate for this conveyance path L ′. Are provided at regular intervals.

  By the way, the conveyance path L arranged in the vertical direction on one side in the apparatus main body 100 extends to the paper discharge tray 21 provided on the upper surface of the apparatus main body 100, and the fixing device 22 and the discharge path are in the middle. A paper roller pair 23 is provided. As shown in FIG. 2, an opening / closing cover (front cover) 101 that can be opened and closed is provided on the front surface of the main body 100. When a sheet jams in the fixing device 22 or the like, the opening / closing cover 101 is provided. Is opened as shown in the figure and processing such as removing jammed paper is performed.

  Next, an image forming operation by the color laser printer having the above configuration will be described with reference to FIG.

  When an image formation start signal is issued, the photosensitive drums 2a to 2d are driven to rotate at a predetermined process speed in the direction of the arrow in FIG. 1 (clockwise) in each of the image forming units 1M, 1C, 1Y, and 1BK. The drums 2a to 2d are uniformly charged by the charging rollers 3a to 3d. The laser scanner unit 13 emits a laser beam modulated by a color image signal for each color, irradiates the surface of each photosensitive drum 2a to 2d with the laser beam, and each color is applied to each photosensitive drum 2a to 2d. An electrostatic latent image corresponding to the color image signal is formed.

  First, magenta toner is attached to the electrostatic latent image formed on the photosensitive drum 2a of the magenta image forming unit 1M by the developing device 4a to which a developing bias having the same polarity as the charged polarity of the photosensitive drum 2a is applied. The electrostatic latent image is visualized as a magenta toner image. This magenta toner image is transferred to the arrow shown in FIG. 1 by the action of the transfer roller 5a to which a primary transfer bias having a polarity opposite to that of the toner is applied at the primary transfer portion (transfer nip portion) between the photosensitive drum 2a and the transfer roller 5a. Primary transfer is performed on the intermediate transfer belt 7 which is rotationally driven in the direction.

  The intermediate transfer belt 7 on which the magenta toner image has been primarily transferred as described above moves to the next cyan image forming unit 1C. In the cyan image forming unit 1C as well, the cyan toner image formed on the photosensitive drum 2b is transferred to the magenta toner image on the intermediate transfer belt 7 in the primary transfer portion in the same manner as described above.

  Similarly, yellow and black toners respectively formed on the photosensitive drums 2c and 2d of the yellow and black image forming units 1Y and 1BK on the magenta and cyan toner images superimposed and transferred on the intermediate transfer belt 7, respectively. The images are sequentially superimposed at each primary transfer portion, and a full-color toner image is formed on the intermediate transfer belt 7. The transfer residual toner which is not transferred onto the intermediate transfer belt 7 and remains on the photosensitive drums 2a to 2d is removed by the drum cleaning devices 6a to 6d, and the photosensitive drums 2a to 2d are prepared for the next image formation. It is done.

  Then, the pickup from the paper feed cassette 14 is performed in accordance with the timing at which the front end of the full color toner image on the intermediate transfer belt 7 reaches the secondary transfer portion (transfer nip portion) between the secondary transfer counter roller 8 and the secondary transfer roller 10. The sheet fed to the conveyance path L by the roller 15, the feed roller 16 and the retard roller 17 is conveyed to the secondary transfer unit by the registration roller pair 19. Then, a full-color toner image is collectively transferred from the intermediate transfer belt 7 to the sheet conveyed to the secondary transfer unit by the secondary transfer roller 10 to which a secondary transfer bias having a polarity opposite to that of the toner is applied. .

  Thus, the sheet on which the full-color toner image has been transferred is conveyed to the fixing device 22, and the sheet on which the full-color toner image has been fixed by being heated and pressurized and thermally fixed on the surface of the sheet. Then, the paper is discharged onto the paper discharge tray 21 by the paper discharge roller pair 23 to complete a series of image forming operations. The transfer residual toner that is not transferred onto the sheet and remains on the intermediate transfer belt 7 is removed by the belt cleaning device 11, and the intermediate transfer belt 7 is prepared for the next image formation.

[Fixing device]
Next, details of the fixing device 22 according to the present invention will be described with reference to FIGS.

  3 is a perspective view of the fixing device, FIG. 4 is a side view showing a state of the identification fixing device during normal pressure application, and FIG. 5 is a partial perspective view showing a state of the identification fixing device variable fixing pressure mechanism during normal pressure application. FIG. 6 is a partial perspective view showing a state when the identification pressure varying mechanism is released from the fixing pressure, and FIG. 7 is a side view showing a state when the identification pressure varying mechanism is normally pressed and when the fixing pressure is released.

  As shown in FIG. 3, between the left and right side plates 24, a heating roller 25 and a pressure roller 26 that rotate in contact with each other are supported while being rotatably supported at both ends in the axial direction. Is pressed against the heating roller 25 by a fixing pressure variable mechanism 30 described later, thereby forming a fixing nip having a predetermined pressure (fixing pressure) therebetween. Although not shown, a heater is passed through the hollow heating roller 25.

  Thus, as described above, the sheet on which the full-color toner image is secondarily transferred collectively from the intermediate transfer belt 7 by the secondary transfer roller 10 is conveyed to the fixing device 22, and the fixing device 22 is heated. A full-color toner image is fixed by being heated and pressed in the process of being sandwiched and conveyed by a fixing nip between the roller 25 and the pressure roller 26. Then, the sheet on which the toner image is fixed is discharged to the discharge tray 21 by the discharge roller pair 23.

  Next, a fixing pressure variable mechanism for changing the pressure (fixing pressure) applied to the heating roller 25 by the pressure roller 26 will be described.

  As shown in FIG. 3, the fixing pressure variable mechanisms 30 are provided at both ends in the axial direction of the pressure roller 26, and the configuration of the pair of left and right fixing pressure variable mechanisms 30 is the same. Only the variable pressure mechanism 30 will be described.

  As shown in FIGS. 4 and 5, a pressure lever 28 is rotatably supported at the axial end portion of the rotation shaft 27 of the pressure roller 26, and above and below one end of the pressure lever 28. Claws 28 a and 28 b are formed, and these claws 28 a and 28 b are engaged with rectangular holes 24 a and 24 b formed in the side plate 24, respectively. Therefore, if the pressure lever 28 is rotated within an angular range in which the other claw 28b can move within the rectangular hole 24b with the one claw 28a as the center, the pressure roller 26 together with the rotary shaft 27 also has the claw 28a as the center. If the respective pressure levers 28 are rotated in the clockwise direction in FIG. 4, the pressure roller 26 is pressed against the heating roller 25, and a fixing nip having a predetermined pressure is formed therebetween.

  Further, an engagement groove 28c is formed at the other end (tip) of each pressure lever 28, and a pressure plate 29 bent in an L shape in side view is engaged with the engagement groove 28c. . That is, as shown in FIG. 5, the pressure plate 29 is formed with a rectangular engagement hole 29a that is long in the vertical direction, and the tip of the pressure lever 28 is passed through the engagement hole 29a. The engagement groove 28 c formed in the portion engages with the engagement hole 29 a of the pressure plate 29.

  On the other hand, as shown in FIG. 3, in the vicinity of the pressure lever 28, there is an open / close lever 32 that rotates about a shaft 33 in conjunction with the open / close operation of the open / close cover 101 (see FIGS. 1 and 2). The upper end of a rod 33 is connected to one end of the opening / closing lever 32. The rod 33 passes through a guide plate 24c formed integrally with the pressure plate 29 and the side plate 24, and extends below them. A pressure spring 34 is interposed between the opening / closing lever 32 on the outer periphery of the rod 33 and the pressure plate 29.

  When plain paper is passed through the fixing device 22 configured as described above, when the open / close cover 101 is closed as shown in FIG. 1, as shown in FIGS. 4, 5, and 7 (dashed line). In addition, since the opening / closing lever 32 is rotated in the direction of arrow a about the shaft 31 by the opening / closing cover 101 and pushes down the rod 33 as shown in the figure, the pressurization interposed between the opening / closing lever 32 and the pressure plate 29 is performed. The spring 34 is pressed and contracted, the reaction force (spring force) is transmitted to the pressure lever 28 via the pressure plate 29, and the tip of the pressure lever 28 is pushed down by the reaction force of the pressure spring 34. For this reason, the pressure lever 28 rotates around the claw 28a in the clockwise direction in FIGS. 4 and 7 to pressurize the pressure roller 26 against the heating roller 25, and thereby between the pressure roller 26 and the heating roller 25. Is formed with a fixing nip having a predetermined pressure, and when the plain paper passes through the fixing nip, the toner image is heated and pressurized and fixed on the plain paper (normal pressure mode).

  Then, for example, when the opening / closing cover 101 is opened as shown in FIG. 2 because a jam has occurred in the fixing device 22, the restriction of the opening / closing lever 32 by the opening / closing cover 101 is released, and the pressure spring 34 extends to a free length. As shown in FIGS. 6 and 7 (solid line), the open / close lever 32 rotates in the direction of arrow b about the shaft 31. For this reason, the reaction force that has been pushing down the pressure plate 29 by the pressure spring 34 until now becomes zero, so the pressure applied by the pressure roller 26 is also zero and the fixing pressure is released (fixing pressure released state). The jammed paper that is nipped in the fixing nip between the pressure roller 26 and the heating roller 25 can be easily removed.

  By the way, when passing thick paper such as an envelope while the image forming operation is performed with the open / close cover 101 closed, fixing is performed using a fixing pressure variable lever 35 (see FIGS. 8 and 9) described below. Pressure is reduced (fixing pressure reduction mode).

  8 is a perspective view of the fixing pressure variable lever, FIG. 9 is a perspective view showing how to attach the identification pressure variable lever to the fixing frame, FIG. 10 is an enlarged detail view of part A in FIG. 9, and FIG. 11 is a fixing pressure variable lever. FIGS. 12A and 12B are partial perspective views showing the state of the pressure release lever during normal pressurization and when the fixing pressure is reduced. FIG.

  As shown in FIG. 8, the fixing pressure variable lever 35 includes action portions 35 a and 35 b that act on the pressure plates 29 of the pair of left and right fixing pressure variable mechanisms 30 at both ends in the longitudinal direction. An operation projection 36 is provided at one end. Here, as shown in FIG. 11, the operation protrusion 36 is integrally connected to the lever body 35A by a connection plate 36a, and a gap δ having a width B is formed between the guide portion 36b and the lever body 35A. In addition, two upper and lower engaging projections 36c (only one is shown in FIG. 11) project from the back surface of the guide portion 36b. As shown in FIG. 10, a triangular mark 36d indicating the position of the engagement protrusion 36c is formed on the guide portion 36b of the operation protrusion 36.

  On the other hand, as shown in FIG. 11, at one end (right end) in the longitudinal direction of the fixing frame 37, a rectangular hole 37a having a size through which one action portion 35b of the fixing pressure variable lever 35 can pass is formed. On the surface of the fixing frame 37, a slit-like engagement hole 37b extending horizontally from the rectangular hole 37a is formed. Then, slit-like engagement grooves 37c and 37d that are long in the longitudinal direction are formed at two intervals in the middle of the engagement hole 37b. Here, the width B of the gap δ between the guide portion 36b of the operation projection 36 and the lever main body 35A is set slightly larger than the plate thickness t of the fixing frame 37 (B> t).

  Further, as shown in FIG. 9, a rectangular guide hole 37e is formed at the other end of the fixing frame 37 (left end in FIG. 9).

  Thus, the fixing pressure variable lever 35 configured as described above can be attached to and detached from the fixing frame 37, and when it is necessary to reduce the fixing pressure, the fixing frame 37 can be simply attached to the fixing frame 37 as follows. Can be installed.

  That is, as shown in FIG. 9, one end in the longitudinal direction (left end in FIG. 9) provided with the action portion 35a of the fixing pressure variable lever 35 is inserted into the guide hole 37e of the fixing frame 37, and the fixing is performed with the inserted end as a center. The pressure variable lever 35 is rotated in the direction of the arrow c in FIG. 9, and the operation protrusion 36 at the other end (right end in FIG. 9) of the fixing pressure variable lever 35 is incorporated in the fixing frame 37 as shown in FIG. That is, the other action portion 35b of the fixing pressure variable lever 35 is inserted into a rectangular hole 37a formed in the fixing frame 37, and a connection plate 36a for connecting the operation projection 36 to the lever body 35A is formed on the fixing frame 37. The fixing pressure variable lever 35 can be easily attached to the fixing frame 37 by being fitted into and engaged with the joint hole 37b. Then, the operation protrusion 36 is operated to slide the fixing pressure variable lever 35 in the lateral direction, and the engagement protrusion 36c protruding from the back surface of the guide portion 36b of the operation protrusion 36 is one side as shown in FIG. The engagement groove 37c is engaged.

  Thus, at the time of normal pressure when plain paper is passed through the fixing device 22, the action portions 35 a and 35 b provided at both ends in the longitudinal direction of the fixing pressure variable lever 35 are respectively pressed by the pair of left and right fixing pressure variable mechanisms 30. The fixing pressure variable mechanism 30 maintains the state shown in FIGS. 4 and 5 without acting on the plate 29 and ensures a predetermined nip pressure (fixing pressure) between the heating roller 25 and the pressure roller 26.

  When passing the thick paper such as an envelope while the image forming operation is being performed with the open / close cover 101 closed, the open / close cover 101 is opened and the fixing pressure is set as shown in FIGS. 6 and 7 (solid line). In a state where the operation protrusion 36 is released, the operation protrusion 36 is operated to slide the fixing pressure variable lever 35 in the direction of the arrow d from the state shown in FIG. The protrusion 36c is engaged with the engagement groove 37d as shown in FIG.

  Then, the action portions 35 a and 35 b provided at both ends in the longitudinal direction of the fixing pressure variable lever 35 enter between the pressure plates 29 of the left and right fixing pressure variable mechanisms 30 and the guide plates 24 c of the side plates 24. At this time, since the fixing pressure is released, both operating portions 35 a and 35 b of the fixing pressure variable lever 35 easily enter between the pressure plate 29 of each fixing pressure variable mechanism 30 and the guide plate 24 c of the side plate 24. be able to. If the opening / closing cover 101 is closed in this state, the pressure plates 29 of the left and right fixing pressure variable mechanisms 30 are positioned at the chain line positions by the thickness of the action portions 35a and 35b of the fixing pressure variable lever 35 as shown in FIG. Is pushed upward to the solid line position.

  When the pressurizing plate 29 is pushed up as described above, the reaction force of the pressurizing spring 34 increases, but the pressurizing plate 29 moves upward relative to the pressurizing lever 28 so that the pressurizing lever by the pressurizing plate 29 is used. As a result, the pressing force applied to the pressure roller 26 by the pressure lever 28 is weakened and the pressure (fixing pressure) applied to the pressure roller 26 is reduced, so that the envelope passes through the fixing nip. There is no problem such as wrinkles on the thick paper.

  As described above, according to the fixing device 22 according to the present invention, when the fixing pressure variable lever 35 is slid, the action portions 35a and 35b provided at both ends in the longitudinal direction of the fixing pressure variable lever 35 are paired on the left and right sides. The fixing pressure can be easily varied by simultaneously acting on the pressure plates 29 of the variable fixing pressure mechanism 30.

  Further, the fixing pressure variable lever 35 can be attached to and detached from the fixing frame 37 according to the necessity of changing the fixing pressure. When the fixing pressure does not need to be changed, the fixing pressure variable lever 35 is fixed to the fixing frame 37. Can be removed from.

  When it is necessary to reduce the fixing pressure, as shown in FIG. 9, the fixing pressure variable lever 35 is inserted into the guide hole 37e of the fixing frame 37 at one end in the longitudinal direction of the fixing pressure variable lever 35, and the fixing pressure variable lever is centered on the one end in the longitudinal direction. By rotating the operation projection 36 provided at the other end in the longitudinal direction by rotating the 35, the fixing pressure variable lever 35 can be easily attached to the fixing frame 37, and its assembling property is improved. . Then, the operation protrusion 36 of the fixing pressure variable lever 35 mounted on the fixing frame 37 is operated to slide the fixing pressure variable lever 35 in the longitudinal direction, and the engagement protrusion 36c formed on the operation protrusion 36 is shown in FIG. As shown in (b), the fixing pressure can be easily and reliably varied by engaging with the engaging groove 37d formed in the fixing frame 37.

  In the above, the embodiment in which the present invention is applied to the color laser printer and the fixing device provided therewith has been described. However, the present invention also applies to a monochrome image forming apparatus and a fixing device provided therein. Of course, the same applies.

1 is a cross-sectional view of a color laser printer according to the present invention. FIG. 3 is a perspective view of the color laser printer according to the present invention with an open / close cover opened. 1 is a perspective view of a fixing device according to the present invention. FIG. 3 is a side view showing a state of the fixing device according to the present invention during normal pressure application. FIG. 6 is a partial perspective view showing a state during normal pressurization of a fixing pressure variable mechanism in the fixing device according to the present invention. FIG. 6 is a partial perspective view showing a state when a fixing pressure is released by a variable fixing pressure mechanism in the fixing device according to the present invention. FIG. 6 is a side view showing a state of the fixing pressure variable mechanism in the fixing device according to the present invention at the time of normal pressing and when the fixing pressure is released. It is a perspective view of a fixing pressure variable lever. FIG. 5 is a perspective view showing a procedure for mounting a fixing pressure variable lever to a fixing frame. FIG. 10 is an enlarged detail view of a part A in FIG. 9. FIG. 5 is a perspective view showing an engagement relationship between an operation protrusion of a fixing pressure variable lever and a fixing frame. (A), (b) is a fragmentary perspective view which shows the state of the pressure release lever at the time of normal pressurization, and at the time of reduction of fixing pressure.

Explanation of symbols

1M Magenta image forming unit 1C Cyan image forming unit 1Y Yellow image forming unit 1BK Black image forming unit 2a to 2d Photosensitive drum 3a to 3d Charging roller 4a to 4d Developing device 5a to 5d Transfer roller 6a to 6d Drum cleaning device 7 Intermediate transfer belt 8 Secondary transfer counter roller 9 Tension roller 10 Secondary transfer roller 11 Belt cleaning device 12a to 12d Toner container 13 Laser scanner unit (LSU)
DESCRIPTION OF SYMBOLS 14 Paper feed cassette 15 Pickup roller 16 Feed roller 17 Retard roller 18 Conveyance roller pair 19 Registration roller pair 20 Conveyance roller pair 21 Paper discharge tray 22 Fixing device 23 Paper discharge roller pair 24 Side plate 24a, 24b Rectangular hole 24c Guide plate 25 Heating roller 26 Pressure roller 27 Rotating shaft of pressure roller 28 Pressure lever 28a, 28b Claw of pressure lever 28c Engaging groove of pressure lever 29 Pressure plate 29a Engagement hole of pressure plate 30 Fixing pressure variable mechanism 31 Axis 32 Opening / closing lever 33 Rod 34 Pressure spring 35 Fixing pressure variable lever 35A Lever main body 35a, 35b Actuating portion of fixing pressure variable lever 36 Operation projection 36a Operation projection coupling plate 36b Operation projection guide portion 36c Operation projection engagement projection 36d Marking of operation protrusion 37 Wearing frame 37a engaging hole 37c of the rectangular hole 37b fixing frame fixing frame, the engagement groove 37e fixing frame 37d fixing frame guide hole 100 the image forming apparatus main body 101 cover L, L 'conveying path δ gap

Claims (4)

Fixing pressure variable mechanisms that vary the fixing pressure, which is the contact pressure between the heating roller and the pressure roller rotating in contact with each other, are provided at both ends in the axial direction of the pressure roller, and each of the fixing pressure variable mechanisms is A rotatable pressure lever that presses the pressure roller against the heating roller, a pressure plate that engages the pressure lever, an opening / closing lever, and an opening / closing lever and the pressure plate. A fixing device that includes a pressure spring, and rotates the opening / closing lever to change the pressure applied by the pressure spring, thereby bringing the pressure roller into a pressure state or a pressure release state.
A fixing pressure variable lever provided with action portions acting on the pressure plate of each fixing pressure variable mechanism at both longitudinal ends is provided, and the fixing pressure is varied by sliding the fixing pressure variable lever. Fixing device to do.   The fixing device according to claim 1, wherein the fixing pressure variable lever is configured to be detachable from the fixing frame.   An operation protrusion is provided at one end in the longitudinal direction of the fixing pressure variable lever, the other end in the longitudinal direction is inserted into a guide hole of the fixing frame, and the operation protrusion is fixed by rotating the fixing pressure variable lever around the other end in the longitudinal direction. The fixing pressure can be varied by incorporating a fixing pressure variable lever into the frame and sliding the lever in the longitudinal direction to selectively engage the engaging protrusions formed on the operation protrusion with the plurality of engaging grooves formed on the fixing frame. The fixing device according to claim 2, wherein the fixing device is used. An image forming apparatus comprising the fixing device according to claim 1.

Images