JP2008287242A - Fixing device and image forming apparatus provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of preventing the occurrence of wrinkles of a recording material by reducing the pressure force of a pressure roller with simple operation. <P>SOLUTION: In the fixing device 8 which is provided with a fixing roller 20 having a heat source 25 inside and the pressure roller 21 brought into press-contact with the fixing roller 20 by a pressure spring 28 and heats and pressurizes a toner image carried on the recording material supplied to between these fixing roller 20 and pressure roller 21, to fix the toner image on the recording material, a spring holder 29 for holding the pressure spring 28 is movably supported and is moved by a cam action by a release lever 30, to adjust the pressure force of the pressure roller 21. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device for fixing a toner image transferred onto a recording material by an electrophotographic process to the recording material, and an image forming apparatus including the fixing device.

  2. Description of the Related Art Image forming apparatuses such as copying machines and printers that employ an electrophotographic system include a fixing device for fixing a toner image transferred from an image carrier onto a recording material. As this fixing device, a two-roller system including a fixing roller and a pressure roller rotating in contact with each other and a belt system using an endless fixing belt as a heating member are known.

  For example, a fixing device adopting a two-roller system includes a fixing roller having a heat source therein and a pressure roller pressed against the fixing roller by a pressure spring, and is supplied between the heating roller and the pressure roller. The toner image carried on the recording material is heated and pressed to be fixed on the recording material.

By the way, in such a fixing device, since heat and pressure are applied to a recording material such as paper, wrinkles may occur in the recording material. In particular, wrinkles are frequently generated in folded cardboard such as envelopes. For this reason, when passing thick paper such as an envelope that is likely to wrinkle, a pressure releasing mechanism has been proposed that reduces the pressure applied to the thick paper by reducing the pressure applied to the thick paper to suppress wrinkling (for example, Patent Documents 1 to 3).
JP-A-2-130574 JP-A-8-006425 JP-A-10-142994

  However, the pressure release mechanisms described in Patent Documents 1 to 3 have a complicated structure. In actual operation, the pressure release mechanism is operated by opening the opening / closing cover of the image forming apparatus main body and operating the release lever attached to the fixing device. Since the method of canceling was adopted, there was a problem that operability was poor.

  Further, since the position of the release lever cannot be confirmed from the outside of the apparatus main body after the pressure is released, there is a possibility that an image defect may occur due to forgetting to return the release lever.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fixing device capable of reducing the pressure applied by the pressure roller and preventing the occurrence of wrinkling of the recording material with a simple operation. An image forming apparatus is provided.

  Another object of the present invention is to provide a fixing device capable of improving operability and preventing image defects due to forgetting to return the release lever, and an image forming apparatus having the fixing device.

  In order to achieve the above object, a first aspect of the present invention comprises a fixing roller having a heat source therein, and a pressure roller pressed against the fixing roller by a pressure spring, and the fixing roller and the pressure roller. In a fixing device that heats and pressurizes a toner image carried on a recording material supplied therebetween and fixes the toner image on the recording material, a spring holder that holds the pressure spring or a bearing that supports the pressure roller is moved. It is possible to adjust the pressure applied by the pressure roller by moving the spring holder or the bearing by a cam action by a release lever.

  According to a second aspect of the present invention, in the first aspect of the invention, the release lever is provided on an opening / closing cover of the image forming apparatus main body.

  According to a third aspect of the present invention, in the first aspect of the present invention, a link mechanism that links the opening / closing operation of the opening / closing cover and the operation of the release lever is provided.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the link mechanism is constituted by a member separate from the opening / closing cover.

  According to a fifth aspect of the present invention, in the invention according to any one of the second to fourth aspects, the pressure roller is separated from the fixing roller in conjunction with an opening operation of the opening / closing cover. .

  The invention described in claim 6 is characterized in that, in the invention described in any one of claims 1 to 5, adjustment of the pressing force of the pressure roller and switching of the speed mode are performed simultaneously.

  According to a seventh aspect of the invention, in the sixth aspect of the invention, when the pressure applied by the pressure roller is reduced, the speed mode is switched to the low speed mode.

  The invention according to claim 8 is characterized in that, in the invention according to claim 6 or 7, the speed mode is switched in conjunction with the operation of the release lever.

  According to a ninth aspect of the present invention, in the invention according to any of the sixth to eighth aspects, a position detection sensor for detecting the position of the release lever is provided, and the speed mode is automatically set based on the detection result of the position detection sensor. It is characterized in that it is switched with.

  According to a tenth aspect of the present invention, there is provided an image carrier for forming a latent image, developing means for developing the latent image formed on the image carrier as a toner image, and a toner image on the image carrier as a recording material. 10. An image forming apparatus comprising: a transfer unit that transfers the toner image; and a fixing unit that heats and pressurizes and fixes the toner image transferred onto the recording material by the transfer unit. It is characterized by comprising the above fixing device.

  According to the first aspect of the present invention, since the pressing force of the pressure roller can be adjusted by moving the spring holder or the bearing by the cam action of the release lever, the pressing force of the pressure roller can be reduced by a simple operation. Generation of wrinkles on the recording material can be prevented.

  According to the second aspect of the present invention, since the release lever is provided on the opening / closing cover of the image forming apparatus main body, it is not necessary to open the opening / closing cover to operate the release lever, and the release lever is operated with good operability while the opening / closing cover is closed. Thus, the pressing force of the pressure roller can be adjusted. In addition, since the position of the release lever can be confirmed from the outside of the apparatus main body after the pressure is reduced, it is possible to prevent an image defect caused by forgetting to return the release lever.

  According to the invention of claim 3, since the release lever can be operated in conjunction with the opening / closing operation of the opening / closing cover, for example, from the state where the plain paper is discharged face-down with the opening / closing cover closed, When the cover is opened and the thick paper such as an envelope is discharged face-up, the pressure applied by the pressure roller can be reduced without manually operating the release cover. When the open / close cover is closed, the pressure applied by the pressure roller is automatically returned and the plain paper is discharged face-down, preventing the occurrence of image defects due to forgetting to return the release lever.

  According to the fourth aspect of the present invention, for example, when it is desired to open the opening / closing cover and eject plain paper face-up, the separate link mechanism is removed to release the interlocking between the opening / closing cover and the release lever. Is possible.

  According to the fifth aspect of the present invention, the pressure roller is separated from the fixing roller in conjunction with the opening operation of the opening / closing cover. If the pressure roller is separated from the fixing roller to release the pressure, the jammed recording material can be easily taken out, and the maintainability is improved.

  According to the sixth and seventh aspects of the present invention, when the pressure applied to the pressure roller is reduced, the speed mode is switched to the low speed mode. Fixing failure does not occur and image failure is prevented.

  According to the eighth aspect of the invention, the speed mode can be automatically switched in conjunction with the operation of the release lever, and a high-quality image can be output while preventing occurrence of fixing failure regardless of the type of recording material. Can do.

  According to the ninth aspect of the invention, since the speed mode is automatically switched according to the position of the release lever detected by the position detection sensor, it is possible to prevent a fixing failure regardless of the type of the recording material and to produce a high quality image. Can be output.

  According to the tenth aspect of the present invention, it is possible to stably obtain a high quality image by preventing generation of wrinkles and fixing failure of the recording material after fixing the toner image.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
[Image forming apparatus]
FIG. 1 is a side sectional view of a laser beam printer as an embodiment of an image forming apparatus according to the present invention.

  The illustrated laser beam printer 1 includes a box-shaped main body (housing) 2, and an inclined concave discharge tray 3 is provided at the center of the upper surface of the main body 2. An openable / closable manual feed tray 4 is provided at the top of the front surface of the main body 2 (the right side in FIG. 1 is the front), and a rectangular box-shaped paper feed cassette 5 that can be pulled out toward the front side is provided at the lower portion of the main body 2. It has been.

  Thus, the laser beam printer 1 uses a recording material based on image data transmitted from a terminal (not shown) while conveying the recording material such as paper along a conveyance path L provided in the main body 2. An image is formed, and the conveyance path L is substantially L-shaped in a side view and extends to the paper discharge tray 3.

  Further, the laser beam printer 1 includes a paper feeding unit 6 provided at a lower portion of the main body 2, an image forming unit 7 provided at a substantially central portion in the main body 2 above the paper feeding unit 6, and the image forming unit. A fixing device 8 disposed behind the unit 7 and a concave paper discharge unit 9 provided on the upper surface of the main body 2 above the fixing device 8 are provided.

  The paper feed unit 6 accommodates a recording material and feeds the recording material toward the image forming unit 7 and includes the paper feed cassette 5 and the manual feed tray 4. Yes. Here, the paper feed cassette 5 has a rectangular box shape with an open upper surface, and a plurality of recording materials are stacked and accommodated therein.

  The paper feed unit 6 is rotatably provided with a paper feed roller 10 and a reverse roller 11 that take out recording materials in the paper feed cassette 5 one by one and send them to the transport path L. Is provided with a registration roller 12 for temporarily feeding the recording material that has been fed out and supplying the recording material to the image forming unit 7 at a predetermined timing.

  The image forming unit 7 forms an image on a recording material supplied from the paper supply unit 6, and includes a photosensitive drum 13 as an image carrier that is rotatably disposed at a substantially central portion in the main body 2. , A primary charger 14 arranged around it, a developing device 15 as developing means, a transfer roller 16 as a transferring means and a cleaning device 17, a laser scanner unit (LSU) 18 arranged above them, and a toner hopper 19 etc.

  The fixing device 8 is for fixing the toner image transferred to the recording material in the image forming unit 7 to the recording material. The fixing device 8 includes a fixing roller 20 and a pressure roller 21 that rotate while being pressed against each other. I have.

  Further, the paper discharge unit 9 is for discharging the recording material on which the toner image is fixed in the fixing device 8 to the outside of the main body 2, and is a pair of paper discharge rollers provided at the end of the conveyance path L. 22 and 23, and a plurality of longitudinal rib-shaped conveyance guide ribs 24 for guiding the recording material conveyed along the conveyance path L to the paper discharge rollers 22 and 23, and the recording material discharged outside the main body 2 are stacked. The paper discharge tray 3 is provided. One paper discharge roller 23 is composed of a rubber roller in order to increase the conveying force of the recording material.

  Next, an image forming operation of the laser beam printer 1 having the above configuration will be described.

  For example, when a print start signal is transmitted to the laser beam printer 1 from a terminal such as a personal computer (personal computer), in the image forming unit 7, the photosensitive drum 13 is driven in the direction indicated by the arrow (clockwise) in FIG. And the surface thereof is uniformly charged to a predetermined potential by the primary charger 14. When a laser beam based on the image data transmitted from the terminal is output from the laser scanner unit 18 and irradiated onto the photosensitive drum 13, an electrostatic latent image is formed on the photosensitive drum 13. Then, the electrostatic latent image formed on the photosensitive drum 13 is developed by the developing device 15 using toner as a developer to be visualized as a toner image.

  At the same time, in the paper feed unit 6, for example, the recording materials stored in the paper feed cassette 5 are picked up one by one from the uppermost one by the paper feed roller 10, and pass through the reverse roller 11 while being reversed 180 °. It is conveyed to the registration roller 12. At this time, the paper feed roller 10 rotates by receiving a driving force until the leading edge of the recording material reaches the registration roller 12.

  In the registration roller 12, the recording material is temporarily put into a standby state and then supplied to the image forming unit 7 at a predetermined timing synchronized with the toner image on the photosensitive drum 13. At this time, the sheet feeding roller 10 does not receive a driving force and rotates following the conveyance of the recording material by the registration roller 12, so that the recording material is pulled between the sheet feeding roller 10 and the registration roller 12. In this state, the reverse roller 11 fulfills the function of preventing the recording material from wrinkling.

  In the image forming unit 7, the recording material supplied to the transfer nip between the photosensitive drum 13 and the transfer roller 16 is conveyed while being pressed against the photosensitive drum 13 by the transfer roller 16, so that the surface (transfer) is transferred. The toner image on the photosensitive drum 13 is transferred onto the surface. The recording material onto which the toner image has been transferred is conveyed to the fixing device 8 where the toner image is heated and pressed in the process of being sandwiched and conveyed by the fixing roller 20 and the pressure roller 21. Get fixed. The toner remaining on the surface of the photosensitive drum 13 (transfer residual toner) after the transfer of the toner image onto the recording material is removed by the cleaning device 17.

Thus, the recording material having the toner image fixed on the surface thereof by the fixing unit 8 is conveyed upward along the conveyance path L, and the sheet discharge tray 3 provided on the upper portion of the main body 2 by the sheet discharge rollers 22 and 23. A series of image forming operations is completed.
[Fixing device]
Next, an embodiment of the fixing device 8 according to the present invention will be described with reference to the accompanying drawings.

<Embodiment 1>
2 is a partial perspective view of the fixing device according to the first exemplary embodiment of the present invention in a normal state (plain paper mode), FIG. 3 is a partial perspective view of the identification fixing device in a pressure reduction state (envelope mode), and FIG. FIG. 5 is a side sectional view of the fixing device in a normal state (plain paper mode), and FIG.

  A heat source 25 such as a halogen heater is accommodated inside the fixing roller 20, and both axial ends of the fixing roller 20 are rotatably supported by the main body frame 26 although not shown. A pressure roller 21 is arranged in parallel below the fixing roller 20, and both end portions in the axial direction of the pressure roller 21 are rotatably supported by bearings 27 supported so as to be movable up and down. ing. 2 to 5 show the configuration of only one end portion of the fixing device 8, but the configuration of the other end portion is the same as that of the one end portion, so that the illustration thereof is omitted.

  Since the bearing 27 is biased upward by the pressure spring 28, the pressure roller 21 rotatably supported by the bearing 27 is in pressure contact with the fixing roller 20 with a predetermined pressure. Here, the lower end of the pressure spring 28 is held by a spring holder 29, and the spring holder 29 is supported by the main body frame 26 so as to be movable up and down.

  On the other hand, a release lever 30 is provided below the spring holder 29 of the main body frame 26 so as to be movable in a direction perpendicular to the axial direction of the fixing roller 20 and the pressure roller 21 (left and right direction in FIGS. 4 and 5). ing. Here, the upper surface of the release lever 30 forms a cam surface, and the cam surface has a mountain-shaped convex portion 30a and a flat portion 30b having a height lower than that of the convex portion 30a.

  Meanwhile, the lower portion of the spring holder 29 penetrates the main body frame 26 and protrudes downward from the main body frame 26, and the lower end surface thereof is in contact with the cam surface on the upper surface of the release lever 30.

  Thus, when the recording material is thin plain paper (in the plain paper mode), the release lever 30 is pushed into the back side (right side in FIG. 4) as shown in FIGS. At this time, since the lower end surface of the spring holder 29 is in contact with the convex portion 30a of the cam surface of the release lever 30, the spring holder 29 is pushed upward. Therefore, the pressure spring 28 is compressed by the spring holder 29 to increase the spring force, and the pressure roller 21 is pressed against the fixing roller 20 by the pressure spring 28 with a relatively large pressure.

  Accordingly, the toner image transferred onto the plain paper is heated and pressurized in the process of passing through the fixing nip formed between the rotating fixing roller 20 and the pressure roller 21 and is fixed onto the plain paper.

  On the other hand, when the recording material is thick paper such as an envelope that tends to wrinkle (in the envelope mode), the release lever 30 is pulled toward the front side (in the direction of the arrow in the drawing) as shown in FIGS. Then, the lower end surface of the spring holder 29 comes into contact with the flat surface 30 b having a low cam surface of the release lever 30. For this reason, the spring holder 29 moves downward, the pressure spring 28 extends, the spring force of the pressure spring 28 decreases, and the pressure applied by the pressure roller 21 is reduced.

  Accordingly, the pressure applied to the thick paper such as an envelope passing through the fixing nip portion between the fixing roller 20 and the pressure roller 21 is reduced, and wrinkles are prevented from occurring on the thick paper passing through the fixing nip portion.

  By the way, if the pressure is reduced as described above when passing thick paper such as an envelope (in the envelope mode), the fixability may be reduced. In this case, the mode for passing the recording material is switched to the low speed mode so as to reduce the passing speed of thick paper such as envelopes. In the present embodiment, the speed mode is switched in conjunction with the operation of the release lever 30, and the pressure applied to the pressure roller 21 is reduced by pulling the release lever 30 toward the front as shown in FIGS. 3 and 5. Then, the speed mode is switched to the low speed mode in conjunction with this operation, and when the release lever 30 is pushed back to restore the original pressure as shown in FIGS. 2 and 4, the speed is interlocked with this operation. The mode is returned to the original high speed mode.

  As described above, in this embodiment, since the spring holder 29 can be moved up and down by the cam action by the pushing and pulling operation of the release lever 30, the pressure applied by the pressure roller 21 can be adjusted. Thus, the pressure applied by the pressure roller 21 can be reduced to prevent wrinkling of the recording material.

  Further, when the pressure applied to the pressure roller 21 is reduced, the speed mode is switched to the low speed mode. Therefore, even if the pressure applied to the pressure roller 21 is reduced, a toner image fixing defect does not occur. The occurrence of image defects can be prevented. In particular, if the speed mode is automatically switched in conjunction with the operation of the release lever 30, it is possible to stably output a high-quality image by preventing the occurrence of fixing failure regardless of the type of recording material. .

  In this embodiment, the pressing force of the pressure roller 21 is adjusted in two stages, “normal” and “pressure reduction”, but it can be adjusted in three stages including “pressure release”, and the fixing device 8 is jammed, if the pressure roller 21 is separated from the fixing roller 20 to release the pressure, the jammed recording material can be easily taken out, and maintenance is easy. Enhanced. Further, the adjustment stage of the pressing force of the pressure roller 21 is arbitrary, and may be adjusted in four stages or more or infinitely.

<Embodiment 2>
Next, a fixing device according to Embodiment 2 of the present invention will be described with reference to FIGS.

  FIG. 6 is a side sectional view of the fixing device according to the second embodiment of the present invention in a normal state (plain paper mode), and FIG. 5 is a side sectional view of the identification fixing device in a pressure reducing state (envelope mode). In the figure, the same elements as those shown in FIGS. 2 to 5 are denoted by the same reference numerals, and description thereof will be omitted below.

  The present embodiment is characterized in that a link mechanism for linking the opening / closing operation of the rear cover 33, which is an opening / closing cover provided in the image forming apparatus main body so as to be openable / closable, and the operation of the release lever 30 is provided. Here, the link mechanism is constituted by a tension spring 36 that is contracted between the release lever 30 and the main body frame 26, and a belt 37 that connects the release lever 30 and the rear cover 33. The release lever 30 is a tension spring. 36 is always urged to the right (plain paper mode side) in FIG. The belt 37 is made of polypropylene (PP) or cloth, which is a separate member from the rear cover 33, and can be removed from the rear cover 33 as necessary.

  Thus, when the recording material is thin plain paper (in the plain paper mode), the rear cover 33 is closed as shown in FIG. 6 is pulled to the right in the right limit position, and the lower end surface of the spring holder 29 is in contact with the convex portion 30a of the cam surface of the release lever 30, so that the spring holder 29 is pushed upward. Yes. Therefore, the pressure spring 28 is compressed by the spring holder 29 to increase the spring force, and the pressure roller 21 is pressed against the fixing roller 20 by the pressure spring 28 with a relatively large pressure.

  Therefore, the toner image transferred on the plain paper is heated and pressed in the process of passing through the fixing nip formed between the rotating fixing roller 20 and the pressure roller 21, and is fixed on the plain paper. The plain paper on which the image is fixed is discharged face-down upward.

  On the other hand, when the recording material is thick paper such as an envelope that tends to wrinkle (in the envelope mode), as shown in FIG. 76, when the rear cover 33 is rotated in the direction of the arrow and opened, the rear cover 33 The belt 37 with one end fixed is pulled, and the release lever 30 is moved to the left (arrow direction) in FIG. 7 against the urging force of the tension spring 36. Then, since the lower end surface of the spring holder 29 comes into contact with the flat surface 30b having a low cam surface of the release lever 30, the spring holder 29 moves downward and the pressure spring 28 extends, and the spring of the pressure spring 28 is extended. The force is reduced and the pressure applied by the pressure roller 21 is reduced.

  Accordingly, the pressure applied to the thick paper such as an envelope passing through the fixing nip portion between the fixing roller 20 and the pressure roller 21 is reduced, and wrinkles are prevented from occurring on the thick paper passing through the fixing nip portion.

  By the way, when thick paper such as an envelope is passed (in the envelope mode), if the pressure is reduced as described above, the fixability may be lowered. Therefore, the pressure is also reduced in this embodiment. In this case, the mode for passing the recording material is switched to the low speed mode so as to reduce the passing speed of thick paper such as envelopes. In the present embodiment, the speed mode is switched in conjunction with the opening / closing operation of the rear cover 33. When the rear cover 33 is opened and the pressure applied to the pressure roller 21 is reduced as shown in FIG. Then, when the speed mode is switched to the low speed mode and the rear cover 33 is closed as shown in FIG. 6, the speed mode is returned to the original high speed mode in conjunction with this operation.

  As described above, in the present embodiment, the release lever 30 can be operated in conjunction with the opening / closing operation of the rear cover 33. Therefore, as shown in FIG. When the rear cover 33 is opened and the thick paper such as an envelope is face-up discharged from the paper-covered state as shown in FIG. 7, the pressure applied to the pressure roller 21 is reduced without operating the release cover 30 by hand. can do. When the rear cover 33 is closed, the release lever 30 is returned to the position shown in FIG. 6 by the tension spring 36, and the pressure applied by the pressure roller 21 is also automatically returned, so that the plain paper is discharged face-down. The occurrence of image defects due to forgetting to return the release lever 30 is prevented.

  In the present embodiment, the belt 37 is configured as a separate member from the rear cover 33. For example, when the rear cover 33 is opened and plain paper is discharged face up, the separate belt 37 is removed and the rear cover is removed. It becomes possible to deal with the problem by releasing the interlocking between 33 and the release lever 30.

  As shown in FIG. 8, the release lever 30 is formed with a convex portion 30a and two flat surfaces 30b and 30c having different steps, and in the plain paper mode in which the rear cover 33 is closed, the spring holder 29 contacts the convex portion 30a. In the envelope mode in which a large pressure is applied to the pressure roller 21 and the rear cover 33 is opened as shown in FIG. 7, the release lever 33 is pulled by the belt 37 by the opening operation of the rear cover 33, and the left side of FIG. The spring holder 29 comes into contact with the flat surface 30b of the release lever 30 to reduce the pressure applied by the pressure roller 21, and when the rear cover 33 is fully opened as shown in FIG. The lever 30 may be further moved so that the spring holder 29 abuts against the flat surface 30c so that the pressure applied by the pressure roller 21 is released (pressure release).

<Embodiment 3>
Next, a fixing device according to Embodiment 3 of the present invention will be described with reference to FIGS.

  9 is a partial perspective view of the fixing device according to Embodiment 3 of the present invention, and FIG. 10 is a view in the direction of arrow A in FIG.

  As shown in FIG. 9, both ends in the axial direction of the pressure roller 21 are rotatably supported by a pair of bearings 31, and each bearing 31 is biased upward by a pressure spring (not shown). The pressure roller 21 is pressed against a fixing roller (not shown).

  Further, a release arm 32 is cam-engaged with the upper portion of each bearing 31, and the release arm 32 moves in a direction perpendicular to the axial direction of the pressure roller 21 (directions of arrows a and b in FIG. 9). As a result, the bearing 31 moves up and down to adjust the spring force of a pressure spring (not shown), that is, the pressure applied to the pressure roller 21.

  On the other hand, the image forming apparatus main body is provided with a rear cover 33 that can be opened and closed. A release lever 34 is provided on the rear cover 33 so as to be movable in the axial direction of the pressure roller 21 (directions c and d in FIG. 9). It has been. The operation portion 34A of the release arm 34 is exposed on the outer surface side of the rear cover 33 as shown in FIG. The rear cover 33 is opened during maintenance. For example, when a paper jam occurs in the fixing device, the rear cover 33 is opened and the jammed recording material is removed.

  Both end portions in the longitudinal direction of the release lever 34 constitute a convex cam 34B, and the inclined cam surface 34a of each cam 34B is engaged with the inclined cam surface 32a of the release arm 32.

  Thus, when the recording material is plain thin paper, the release lever 34 moves in the “normal” direction shown in FIG. Is pushed up by a predetermined spring force, the pressure roller 21 is pressed against a fixing roller (not shown) by a relatively large pressure by the pressure spring.

  Therefore, the toner image transferred to the plain paper is heated and pressed in the process of passing through the fixing nip formed between the rotating fixing roller and the pressure roller 21 and is fixed on the plain paper.

  On the other hand, when the recording material is thick paper such as an envelope that is likely to wrinkle, the operation portion 34A of the release lever 34 is operated to move the release lever 34 in the “pressure release” direction of FIG. Then, the release arm 32 that engages the cam 34B of the release lever 34 moves in the direction of arrow a in FIG. 9 and pushes down the bearing 31, so that the pressure applied by the pressure roller 21 is reduced, and the fixing roller and the pressure roller 21 are reduced. The pressure applied to the thick paper such as an envelope passing through the fixing nip is also reduced, and wrinkles are prevented from occurring on the thick paper that has passed through the fixing nip.

  By the way, if the pressure is reduced as described above when passing a thick paper such as an envelope, the fixability may be lowered. Therefore, also in this embodiment, when the pressure is reduced, recording is performed. The material passing speed mode is switched to the low speed mode to reduce the passing speed of thick paper such as envelopes. In the present embodiment, the speed mode is switched in conjunction with the operation of the release lever 34. When the release lever 34 is moved in the “pressure release” direction of FIG. When the speed mode is switched to the low speed mode and the release lever 34 is moved in the “normal” direction in FIG. 10 to restore the pressure applied to the pressure roller 21, the speed mode is restored to the original. Return to fast mode.

  Thus, in this embodiment, the same effect as in the first and second embodiments can be obtained. However, in this embodiment, since the release lever 34 is provided on the rear cover 33, the operation of the release lever 34 is performed by the rear cover. It is not necessary to open the opening 33, and the pressing force of the pressure roller 21 can be adjusted by operating the release lever 34 with good operability while the opening / closing cover 33 is closed.

  Further, since the position of the release lever 34 can be confirmed from the outside of the apparatus main body after the pressure is reduced, the occurrence of image defects due to forgetting to return the release lever 34 is prevented.

  If the pressure roller 21 is separated from the fixing roller to release the pressure in conjunction with the opening operation of the rear cover 33, the pressure roller 21 is separated from the fixing roller at the same time as the rear cover 33 is opened during maintenance such as jam processing. Since the pressure is released, the jammed recording material can be easily removed, and the maintainability is improved.

<Embodiment 4>
Next, a fixing device according to Embodiment 4 of the present invention will be described with reference to FIG.

  FIG. 11 is a partial perspective view of a fixing device according to Embodiment 3 of the present invention. In FIG. 11, the same components as those shown in FIGS. 9 and 10 are denoted by the same reference numerals. The re-explanation about is omitted.

  In the present embodiment, a position detection sensor 35 for detecting the position of the release arm 32, that is, the position of the release lever 34 (“release position” or “normal position”) is provided. The speed mode is automatically switched based on this, and the other configuration is the same as that of the third embodiment.

  Thus, in this embodiment, the same effect as in the first to third embodiments can be obtained, but the speed mode is automatically switched depending on the position of the release lever 34 detected by the position detection sensor 35. Regardless of the type of recording material, it is possible to prevent the occurrence of fixing failure and stably output a high-quality image.

  Although the present invention has been described with respect to the embodiment in which the present invention is applied particularly to the laser beam printer and the two-roller fixing device provided in the laser beam printer, the present invention is not limited to the printer, but may be any other optional device such as a copying machine or a facsimile machine. Of course, the present invention can be similarly applied to the image forming apparatus and a belt-type fixing device provided in the image forming apparatus.

1 is a side sectional view of an image forming apparatus (laser beam printer) according to the present invention. FIG. 3 is a partial perspective view of the fixing device according to the first exemplary embodiment of the present invention in a normal state (plain paper mode). FIG. 3 is a partial perspective view of a pressure reducing state (envelope mode) of the fixing device according to the first embodiment of the present invention. FIG. 3 is a side sectional view of the fixing device according to the first exemplary embodiment of the present invention in a normal state (plain paper mode). FIG. 3 is a side cross-sectional view of a pressure reducing state (envelope mode) of the fixing device according to the first embodiment of the present invention. FIG. 6 is a side sectional view of a fixing device according to a second embodiment of the present invention in a normal state (plain paper mode). FIG. 6 is a side cross-sectional view of a fixing device according to a second embodiment of the present invention in a pressure reduction state (envelope mode). FIG. 9 is a cross-sectional view showing a relationship between a rear cover, a release lever, and a spring holder, showing a modification of the fixing device according to Embodiment 2 of the present invention. FIG. 9 is a partial perspective view of a fixing device according to Embodiment 3 of the present invention. It is a figure of the arrow A direction of FIG. FIG. 6 is a partial perspective view of a fixing device according to Embodiment 4 of the present invention.

Explanation of symbols

1 Laser beam printer (image forming device)
2 Main body 3 Paper discharge tray 4 Manual feed tray 5 Paper feed cassette 6 Paper feed unit 7 Image forming unit 8 Fixing device 9 Paper discharge unit 10 Paper feed roller 11 Reverse roller 12 Registration roller 13 Photosensitive drum (image carrier)
14 Primary charger 15 Developing device (developing means)
16 Transfer roller (transfer means)
17 Cleaning device 18 Laser scanner unit (LSU)
DESCRIPTION OF SYMBOLS 19 Toner hopper 20 Fixing roller 21 Pressure roller 22, 23 Paper discharge roller 24 Conveying guide rib 25 Heat source 26 Main body frame 27 Bearing 28 Pressure spring 29 Spring holder 30 Release lever 30a Release lever convex part 30b Release lever flat surface 30c Release Flat surface of lever 31 Bearing 32 Release arm 32a Cam surface of release arm 33 Rear cover (open / close cover)
34 Release lever 34A Release lever operation part 34B Release lever cam 34a Release lever cam surface 35 Position detection sensor 36 Tension spring (link mechanism)
37 Belt (link mechanism)
L transport path

Claims (10)

A fixing roller having a heat source therein and a pressure roller pressed against the fixing roller by a pressure spring, and a toner image carried on a recording material supplied between the fixing roller and the pressure roller In a fixing device for fixing to a recording material by heating and pressing,
A spring holder that holds the pressure spring or a bearing that pivotally supports the pressure roller is movably supported, and the spring holder or the bearing is moved by a cam action by a release lever to apply pressure to the pressure roller. A fixing device characterized in that it can be adjusted.   The fixing device according to claim 1, wherein the release lever is provided on an opening / closing cover of the main body of the image forming apparatus.   The fixing device according to claim 1, further comprising a link mechanism that links an opening / closing operation of the opening / closing cover and an operation of the release lever.   The fixing device according to claim 3, wherein the link mechanism is formed of a member different from the opening / closing cover.   The fixing device according to claim 2, wherein the pressure roller is separated from the fixing roller in conjunction with an opening operation of the opening / closing cover.   6. The fixing device according to claim 1, wherein adjustment of the pressure of the pressure roller and switching of the speed mode are performed simultaneously.   The fixing device according to claim 6, wherein when the pressure applied by the pressure roller is reduced, the speed mode is switched to the low speed mode.   8. The fixing device according to claim 6, wherein the speed mode is switched in conjunction with the operation of the release lever.   9. The fixing according to claim 6, wherein a position detection sensor for detecting the position of the release lever is provided, and the speed mode is automatically switched based on a detection result of the position detection sensor. apparatus. An image carrier that forms a latent image; a developing unit that develops the latent image formed on the image carrier as a toner image; and a transfer unit that transfers the toner image on the image carrier onto a recording material; In an image forming apparatus provided with a fixing unit that is transferred onto a recording material by the transfer unit and fixes the toner image by heating and pressing.
An image forming apparatus comprising the fixing device according to any one of claims 1 to 9.

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