JP2011149990A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device that can automatically release or reduce the pressure of a fixing nip, and eliminate the need for a dedicated driving means. <P>SOLUTION: The fixing device includes: a switching gear 31 to which rotating force is transmitted from a driving means; an operation gear 32 in which two gear parts 32a and 32b disposed in different positions in an axial direction are provided with intermittent gear parts 321 and 322; a pressure releasing member 33 rotated integrally with the operation gear 32 and switched between the pressing state, in which a support member 25 is pressed against a bias means 27, and the non-pressing state in which the support member 25 is not pressed; and axially moving means 29 and 30 which make the switching gear 31 perform reciprocal motion in the axial direction and switch the switching gear 31 between the two gear parts 32a and 32b to arrange the switching gear 31 so as to mesh. The fixing device is provided with a stopper 34 for restricting rotation of the pressure releasing member 33, in a state where the pressure releasing member 33 is disposed in the non-pressing state and one intermittent gear part 321 is disposed in a position opposite to the switching gear 31. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fixing device that fixes an unfixed image on a recording medium to the recording medium, and an image forming apparatus including the fixing device.

  In general, an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine of these includes a fixing device that fixes an image on a recording medium such as paper. The fixing device includes a pair of fixing members, and the fixing member includes, for example, a fixing roller having a heating source therein and a pressure roller that presses the fixing roller. Then, the toner image is fixed on the recording medium by passing the recording medium through a fixing nip formed by press-contacting the fixing roller and the pressure roller.

  However, if the image forming operation is not performed for a long period of time, creep may occur due to the pressing of the fixing roller or the pressure roller for a long period of time. Further, when a paper jam occurs in the fixing nip, there is a problem that it is difficult to remove the paper because the paper is sandwiched between the fixing roller and the pressure roller at a predetermined pressure.

  Therefore, in order to solve the above-described problems of creep and paper jam processing, a fixing device having means for releasing or reducing the pressure applied between the fixing roller and the pressure roller has been proposed. For example, the fixing device described in Patent Document 1 includes a pressure release lever that releases the pressure of the fixing nip. In this case, by manually operating the pressure exclusion lever, the pressure roller is separated from the fixing roller, and the pressure in the fixing nip is released. Further, as described in Patent Document 2, there is also a fixing device including a pressure releasing mechanism that can electrically release the pressure of the fixing nip.

  However, in the configuration in which the nip pressure is manually released, there is a problem that the operation of the pressure release lever is troublesome or the lever is forgotten to be operated. Further, since the pressure release lever is often provided near the fixing device, and the pressure release lever may be heated when the fixing device is heated, it is not preferable for safety to operate the lever manually. .

  In recent years, the fixing performance has been reduced by reducing the nip width of the fixing nip by reducing the diameter of the fixing roller or the like with the downsizing of the image forming apparatus, and by reducing the amount of heat applied to the paper as the paper passing speed increases. Therefore, in order to improve the fixability, the pressure applied by the pressure roller is increased to ensure a sufficient fixing nip. As described above, in the configuration in which the pressing force of the pressure roller is set strongly, it is particularly difficult to operate the pressure release lever.

  On the other hand, in the configuration in which the nip pressure is released electrically, the above problem in the configuration in which the pressure is released manually can be solved. However, in this case, it is necessary to provide a dedicated motor or the like for driving the pressure release mechanism, and there is a problem that the apparatus is increased in size and cost.

  In view of such circumstances, the present invention provides a fixing device that can automatically release or reduce the pressure of the fixing nip and that does not require a dedicated driving unit, and an image forming apparatus including the fixing device. To do.

  According to the first aspect of the present invention, a pair of fixing members that fix an image on a recording medium to the recording medium, a driving unit that applies a rotational force to the fixing member, and a pair of members that support the fixing member so as to be close to and away from each other. In a fixing device comprising a support member and an urging means for urging the support member in a direction in which the fixing member approaches each other, a switching gear to which a rotational force is transmitted from the drive means and a position different in the axial direction An operation gear provided with a toothless portion on one of the two gear portions disposed in the shaft, and the one of the pair of support members are pressed against the biasing means by rotating integrally with the operation gear. A pressure release member that is switched to a pressed state that does not press the support member, and a reciprocating movement of the switching gear and the operation gear relative to each other in the axial direction so that the switching gear is Switch between the two gears An axially moving means that can be arranged, and the discontinuous portion is disposed at a position facing the switching gear in a state where the pressure release member is disposed in the non-pressed state, A stopper for restricting the rotation of the pressure release member is provided in a state of being disposed at a position facing the switching gear.

  In order to release the pressure between the pair of fixing members, the switching gear is moved to the gear portion where the toothless portion of the operation gear is not provided by the axial movement means and meshed. In this state, when the switching gear is applied with a rotational force from the driving means, the operation gear and the pressure release member rotate integrally. Then, when the pressure release member presses one of the support members against the urging means, the pair of fixing members are moved away from each other, and the pressure therebetween is released. Further, when the pressure releasing member is in a pressing state in which the supporting member is pressed, the driving of the driving unit is stopped. Thereby, the pressure between the fixing members is maintained in a released state.

  Further, when the pressure between the fixing members is returned, the switching gear is moved to the gear portion provided with the tooth missing portion of the operation gear by the axial movement means and meshed. In this state, when the switching gear is applied with a rotational force from the driving means, the operation gear and the pressure release member rotate integrally, and the pressure release member is switched from the pressed state to the non-pressed state in which the support member is not pressed. . As a result, the pair of fixing members move in a direction approaching each other, and the pressure between them is restored. Further, when the non-pressed state is established, the toothless portion is disposed at a position facing the switching gear, so that the meshing between the switching gear and the operation gear is released. For this reason, even if the switching gear continues to rotate thereafter, the rotational force is not transmitted to the operation gear. Thus, in the state where the pressure between the fixing members is returned (the pressure releasing member is not pressed), the pressure releasing member does not rotate even if the driving unit is driven to perform the fixing operation. The pressure is not released during operation.

  In addition, when the pressure release member is rotated to the non-pressed position, the rotation of the pressure release member can be restricted by the stopper in a state where the missing tooth portion faces the switching gear. Can be prevented from deviating from the opposite position. As a result, the operation gear and the switching gear do not unexpectedly mesh with each other, and the non-pressed pressure release member does not receive a rotational force from the switching gear and is not pressed. Occurrence of fixing failure due to the release of pressure can be prevented.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the stopper abuts on the pressure release member rotated from the pressed state to the non-pressed state and restricts movement in the rotation direction. It is configured.

  When the pressure release member is returned from the pressed state to the non-pressed state, an inertial force in the rotational direction at that time acts on the pressure release member, but the stopper is in contact with the pressure release member to resist the inertial force. Thus, the pressure release member can be stopped at a predetermined position. As a result, the toothless portion of the operation gear does not rotate beyond the position facing the switching gear, so that the operation gear and the switching gear do not unexpectedly mesh with each other, and the pressure release member does not rotate from the switching gear. Will not be pressed. As described above, since the pressure release member can be reliably stopped at a predetermined position by the stopper, it is possible to prevent occurrence of fixing failure due to unexpected release of the pressure between the fixing members during the fixing operation.

  According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the driving unit is configured to be able to rotate forward and reversely during a fixing operation, and the axial movement unit is moved forward by the driving unit. A pair of helical gears that are reciprocally movable in the axial direction by being reversely rotated, and one of the helical gears is provided so as to be integrally rotatable with the switching gear, and the axial direction between the helical gears that occurs during normal rotation The switching gear is moved to the gear portion provided with the toothless portion by movement, and the switching gear is moved to a different gear portion by axial movement between the helical gears that occurs during reverse rotation. It is.

  Due to the axial movement between the helical gears caused by the positive rotation during the fixing operation, the switching gear can be moved to the gear portion provided with the missing tooth portion, and the meshing between the switching gear and the operation gear can be released. Thus, even if the switching gear continues to rotate normally during the fixing operation, the rotational force is not transmitted to the operation gear, so that the pressure between the fixing members is not released. Further, in this case, the rotational force obtained from the drive means can be converted and applied to the axial moving force by the pair of helical gears, so that the rotational force can be used more effectively than a separate actuator. Therefore, the size and cost can be reduced.

  According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the gear portion different from the gear portion provided with the missing tooth portion is provided with another missing tooth portion, The another missing tooth portion is disposed at a position facing the switching gear in a state where the pressure release member is disposed in the pressed state.

  In this case, when the pressure release member is in the pressed state, the missing tooth portion is disposed at a position facing the switching gear, so that the meshing between the switching gear and the operation gear is released. As a result, when the pressure release member is in the pressed state, the rotational force is not transmitted to the operation gear without stopping the driving of the drive means. The state in which the pressure is released can be maintained.

  According to a fifth aspect of the present invention, in the fixing device according to any one of the first to fourth aspects, the pressing surface for pressing the support member of the pressure releasing member is formed in a flat shape.

  By forming the pressing surface of the pressure releasing member into a flat shape, the pressure releasing member is unlikely to rotate unexpectedly in a state where the supporting member is pressed by the pressure releasing member, so that the pressing state can be stably maintained. .

  According to a sixth aspect of the present invention, in the fixing device according to any one of the first to fifth aspects, the rotation center is greater than the distance between the rotation center of the pressure release member and a pressing surface that presses the support member. The distance between the pressing surface and the surfaces disposed on both sides in the rotational direction is set to be long.

  In a state where the pressure release member presses the support member by setting the distance between the rotation center and the surface disposed on both sides in the rotation direction of the pressure surface longer than the distance between the rotation center of the pressure release member and the pressure surface. The pressure release member can be prevented or suppressed from rotating unexpectedly.

  According to a seventh aspect of the present invention, in the fixing device according to any one of the first to sixth aspects, when the support member pressed by the pressure release member is configured to be swingable, the pressure release member is The support member is configured to slide and press from the side far from the center of swing to the side closer to the support member.

  When the pressure release member slides from the side far from the center of swing to the side closer to the support member, the support member is pressed with a smaller force than when sliding in the opposite direction. Is possible. Thereby, while being able to reduce the load concerning the pressure release member, each gear, etc. at the time of pressing a support member, pressure release can be performed reliably.

  According to an eighth aspect of the present invention, in the fixing device according to the third aspect, the helical gear is made of an injection molded resin.

  As a result, the helical gear can be produced in a small size and at a low cost.

  According to a ninth aspect of the present invention, in the fixing device according to the eighth aspect, the resin is a polyphenylene sulfide resin, a polyamide resin, a polyamideimide resin, a polyimide resin, a polyphenylene ether resin, a polyphenylene oxide resin, a polyacetal resin, or a polybutylene terephthalate resin. , Polycarbonate resin, and these alloy resins.

  As a result, the helical gear can be produced in a small size and at a low cost.

  A tenth aspect of the present invention is an image forming apparatus including the fixing device according to any one of the first to ninth aspects.

  Since the image forming apparatus includes the fixing device according to any one of the first to ninth aspects, the above-described effects of these fixing devices can be obtained.

  According to the present invention, since the pressure between the fixing members can be automatically released, there is no troublesome operation and forgetting to operate the pressure release lever as in the past, and operability and reliability can be improved. it can. Moreover, since it is not necessary to manually operate the pressure release lever which may become hot, safety is also improved.

  Further, according to the present invention, it is possible to release the pressure between the fixing members by using the driving force of the driving means for applying a rotational force to the fixing member. That is, according to the present invention, it is possible to perform the fixing operation and the pressure releasing operation using the driving force of one driving unit, so that it is not necessary to provide a dedicated driving unit for releasing the pressure. As a result, the fixing device and the image forming apparatus can be reduced in size and cost.

  Further, according to the present invention, since the rotation of the pressure release member can be restricted by the stopper in a state where the tooth missing portion faces the switching gear, the pressure between the fixing members is unexpectedly released during the fixing operation. Therefore, it is possible to prevent the occurrence of fixing failure.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. FIG. 2 is an external perspective view of one end side of the fixing device according to the present invention. FIG. 2 is a side view of the fixing device. (A) is a figure which shows the non-pressing state in which the pressure releasing member provided in the said fixing member is not pressing the pressurizing plate, (b) is the said pressure releasing member pressing the pressurizing plate. It is a figure which shows a press state. It is an enlarged view of the said pressure release member. FIG. 2 is an external perspective view of one end portion side of the fixing device. It is a figure for demonstrating operation | movement of the pressure release mechanism of this invention. It is a figure for demonstrating operation | movement of the said pressure release mechanism. It is a figure for demonstrating operation | movement of the said pressure release mechanism. It is a figure for demonstrating operation | movement of the said pressure release mechanism. It is a figure for demonstrating operation | movement of the said pressure release mechanism. It is a figure which shows the structure of the fixing device which concerns on other embodiment in this invention.

  Hereinafter, the present invention will be described with reference to the accompanying drawings. In the drawings for explaining the present invention, components such as members and components having the same function or shape are denoted by the same reference numerals as much as possible, and once described, the description will be given. Omitted.

  FIG. 1 is a schematic configuration diagram of a color image forming apparatus according to the present invention. The image forming apparatus illustrated in FIG. 1 includes four process units 1Y, 1C, 1M, and 1Bk configured to be detachable from the image forming apparatus main body 100. The process units 1Y, 1C, 1M, and 1Bk have the same configuration except that they contain toners of different colors of yellow, cyan, magenta, and black corresponding to the color separation components of the color image.

  Each process unit 1Y, 1C, 1M, and 1Bk includes a photosensitive drum 2 as an image carrier, a charging roller 3 as a charging unit that charges the surface of the photosensitive drum 2, and toner on the surface of the photosensitive drum 2. A developing device 4 as a developing unit that forms (develops) a toner image by supplying, and a cleaning blade 5 as a cleaning unit that cleans the surface of the photosensitive drum 2 are integrally provided.

  Above each process unit 1Y, 1C, 1M, 1Bk, an exposure device 6 is disposed as an exposure means for exposing the surface of the photosensitive drum 2. A transfer device 7 is disposed below each process unit 1Y, 1C, 1M, 1Bk. The transfer device 7 has an intermediate transfer belt 8 constituted by an endless belt as a transfer body. The intermediate transfer belt 8 is stretched around the driving roller 9 and the driven roller 10 and is configured to be rotatable (circular running) in the direction of the arrow in the figure.

  Four primary transfer rollers 11 as primary transfer means are disposed at positions facing the four photosensitive drums 2. Each primary transfer roller 11 presses the inner peripheral surface of the intermediate transfer belt 8 at each position, and a primary transfer nip is formed at a location where the pressed portion of the intermediate transfer belt 8 and each photosensitive drum 2 come into contact with each other. Has been. A secondary transfer roller 12 as a secondary transfer unit is disposed at a position facing the drive roller 9. The secondary transfer roller 12 presses the outer peripheral surface of the intermediate transfer belt 8, and a secondary transfer nip is formed at a location where the secondary transfer roller 12 and the intermediate transfer belt 8 are in contact with each other.

  A belt cleaning device 13 for cleaning the surface of the intermediate transfer belt 8 is disposed on the outer peripheral surface on the right end side of the intermediate transfer belt 8 in the drawing. A waste toner transfer hose (not shown) extending from the belt cleaning device 13 is connected to an inlet portion of a waste toner container 14 disposed below the transfer device 7.

  A lower part of the image forming apparatus main body 100 is provided with a paper feed tray 15 that stores recording paper P as a recording medium, a paper feed roller 16 that carries the recording paper P out of the paper feed tray 15, and the like. On the other hand, a pair of paper discharge rollers 17 for discharging recording paper to the outside and a paper discharge tray 18 for stocking the discharged recording medium are disposed on the upper portion of the image forming apparatus main body 100. .

  In the image forming apparatus main body 100, a conveyance path R1 for guiding the recording paper P from the lower paper feed tray 15 to the upper paper discharge tray 18 is formed. A pair of registration rollers 19 is disposed on the conveyance path R1 in the middle from the paper feed roller 16 to the secondary transfer roller 12. In addition, a fixing device 20 for fixing an image on the recording paper is provided on the way from the secondary transfer roller 12 to the paper discharge roller 17.

  Further, the image forming apparatus according to the present embodiment includes a mechanism for forming an image on both sides of the recording paper P. Specifically, a reversing path R2 is formed in the image forming apparatus main body 100 for reversing and feeding the recording paper P. The reversing path R2 branches before the downstream end of the transport path R1 in the transport direction, and joins the transport path R1 before the registration roller 19. The paper discharge roller 17 functions as a switchback roller that rotates the recording paper P back to the reverse path R2 by rotating in the direction opposite to the rotation direction in which the recording paper P is discharged.

The basic operation of the image forming apparatus will be described below with reference to FIG.
When the image forming operation is started, the photosensitive drums 2 of the process units 1Y, 1C, 1M, and 1Bk are rotationally driven clockwise by a driving device (not shown), and the surface of each photosensitive drum 2 is charged with the charging roller 3. Are uniformly charged to a predetermined polarity. The surface of each charged photoconductive drum 2 is irradiated with laser light from the exposure device 6 to form an electrostatic latent image on the surface of each photoconductive drum 2. At this time, the image information to be exposed to each photosensitive drum 2 is single-color image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. Thus, the electrostatic latent image is visualized as a toner image (developer image) by supplying toner to the electrostatic latent image formed on the photosensitive drum 2 by each developing device 4. .

  By driving the drive roller 9 counterclockwise in the figure, the intermediate transfer belt 8 is driven to travel in the direction indicated by the arrow in the figure. Further, a constant voltage or a constant current controlled voltage having a polarity opposite to the toner charging polarity is applied to each primary transfer roller 11. Thereby, a transfer electric field is formed at the primary transfer nip between each primary transfer roller 11 and each photosensitive drum 2. Then, the toner images of the respective colors formed on the photosensitive drums 2 of the process units 1Y, 1C, 1M, and 1Bk are sequentially superimposed and transferred onto the intermediate transfer belt 8 by the transfer electric field formed in the primary transfer nip. Is done. Thus, the intermediate transfer belt 8 carries a full-color toner image on its surface.

  Residual toner adhering to the surface of each photosensitive drum 2 after the toner image is transferred is removed by the cleaning blade 5, and then the surface is subjected to a neutralizing action by a neutralizing device (not shown) so that the surface potential is reduced. Initialized to prepare for the next image formation.

  Further, in the lower part of the image forming apparatus, the recording paper P accommodated in the paper feed tray 15 is sent out to the transport path R1 by rotating the paper feed roller 16. The recording paper P sent to the transport path R1 is timed by the registration roller 19 and sent to the secondary transfer nip between the secondary transfer roller 12 and the driving roller 9 facing it. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 8 is applied to the secondary transfer roller 12, thereby forming a transfer electric field in the secondary transfer nip. Then, the toner images on the intermediate transfer belt 8 are collectively transferred onto the recording paper P by the transfer electric field formed in the secondary transfer nip. The recording paper P to which the toner image has been transferred is conveyed to the fixing device 20 where the toner image is fixed on the recording paper P. Then, the recording paper P on which the toner image is fixed is discharged to a paper discharge tray 18 by a discharge roller 17. Further, the toner remaining on the intermediate transfer belt 8 after the transfer is removed by the belt cleaning device 13, and the removed toner is conveyed to the waste toner container 14 and collected.

  When images are formed on both sides of the recording paper P, the rotation direction in which the recording paper P is discharged by the paper discharge roller 17 after fixing the toner image on one side (front side) of the recording paper P as described above. And the recording paper P is switched back to the reverse path R2. As the recording paper P passes through the reversing path R2, the front and back of the recording paper P are reversed and guided again to the transport path R1. In the same manner as described above, after the toner image is transferred and fixed on the back surface of the recording paper P, the recording paper P is discharged to the paper discharge tray 18.

  The above description is an image forming operation when a full-color image is formed on a recording sheet. A single-color image can be formed using any one of the four process units 1Y, 1C, 1M, and 1Bk. Two or three process units may be used to form a two or three color image.

Next, the configuration and operation of the fixing device provided in the image forming apparatus of this embodiment will be described.
As shown in FIG. 1, the fixing device 20 of this embodiment includes a fixing roller 21 as a fixing rotating member, a pressure roller 22 as a pressing rotating member, and the like as a pair of fixing members for fixing an image on a recording sheet. Have. Here, the fixing roller 21 is formed of an elastic material such as silicone rubber, fluorine rubber, and foamable silicone rubber on a cylindrical body (thickness: 1 mm, outer diameter: 30 mm) made of a metal material such as aluminum or iron ( The thickness is about 1 mm), and PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer resin) and PTFA (polytetrafluoroethylene) are formed on the surface layer as a release layer with a thickness of several tens of μm. A heater 23 as a heat source is fixed inside the cylindrical body. The heater 23 is a halogen heater, and both ends thereof are fixed to the frame of the fixing device 20. Then, the cylindrical body made of the metal material is heated by the radiant heat from the heater 23 whose output is controlled by the power supply unit (AC power supply) of the image forming apparatus main body, and further the heat is transmitted to the elastic material and the release layer, and the recording medium Heat is applied to the upper toner image. The output control of the heater 23 is performed based on the detection result of the roller surface temperature by a thermopile (not shown) that faces the surface of the fixing roller 21 in a non-contact manner. Specifically, the AC voltage is applied to the heater 23 for the energization time determined based on the detection result of the thermopile. By such output control of the heater 23, the temperature of the fixing roller 21 (fixing temperature) can be adjusted and controlled to a desired temperature (target control temperature). The fixing roller 21 is driven to rotate by a drive motor (not shown).

Subsequently, the pressure roller 22 is formed by forming an elastic material having a thickness of 4 mm made of silicone rubber, fluorine rubber, foamable silicone rubber or the like on a metal core. The pressure roller 22 has an outer diameter set to about 35 mm. A release layer made of PFA, PTFE, or the like can be provided on the surface layer of the elastic material. The pressure roller 22 is pressed against the fixing roller 21 by a pressure mechanism described later. Thus, a desired nip (fixing nip) is formed between the pressure roller 22 and the fixing roller 21. In the present embodiment, it is also possible to install a heating means such as a heater that directly heats the pressure roller 22, or to use a thermistor that contacts and faces the roller surface for output control of the heater 23.

  A guide plate (not shown) for guiding the conveyance of the recording paper is disposed on the entrance side of the contact portion (nip) between the fixing roller 21 and the pressure roller 22. Further, in the vicinity of the exit side of the nip at a position where it abuts on the fixing roller 21, a separation plate that suppresses the trouble that the recording paper (recording paper after the fixing process) sent out from the nip is wound around the fixing roller 21. (Not shown) is installed.

The fixing device 20 configured as described above operates as follows.
When the power switch of the image forming apparatus main body is turned on, an AC voltage is applied (powered) from the AC power source to the heater 23, and the fixing roller 21 is started to rotate by a drive motor (not shown). The pressure roller 22 is driven to rotate. Thereafter, the recording paper P is fed from the paper feed tray 15 and an unfixed image is carried on the recording paper P at the position of the secondary transfer nip. The recording paper P carrying an unfixed image (toner image) is conveyed to the fixing device 20 and fed into the nip between the fixing roller 21 and the pressure roller 22 in a pressure contact state. The toner image is fixed on the surface of the recording paper P by the heating by the fixing roller 21 and the pressing force of the fixing roller 21 and the pressure roller 22. Thereafter, the recording paper P sent out from the nip by the rotating fixing roller 21 and the pressure roller 22 is discharged to the paper discharge tray 18 by the paper discharge roller 17.

Hereinafter, the structure of the characteristic part of this invention is demonstrated based on FIGS.
2 is an external perspective view of one end portion side of the fixing device 20, and FIG. 3 is a side view thereof. As shown in FIGS. 2 and 3, the fixing device 20 of the present embodiment includes a fixing plate 24 as a supporting member that rotatably supports the fixing roller 21 and a supporting member that rotatably supports the pressure roller 22. The pressure plate 25 is provided. The fixing plate 24 and the pressure plate 25 are connected to each other via a support shaft 26 provided at the lower portion thereof, and the pressure plate 25 is configured to be swingable about the support shaft 26. Thereby, the pressure roller 22 is configured to be able to approach and separate from the fixing roller 21.

  In the present embodiment, the fixing plate 24 is fixed to the image forming apparatus main body, and the pressure plate 25 is configured to swing. However, the present invention is not limited to this configuration. Conversely, the pressure plate 25 may be fixed and the fixing plate 24 may be swung. Further, both the fixing plate 24 and the pressure plate 25 may be configured to be swingable.

  The fixing plate 24 and the pressure plate 25 are urged in a direction in which the fixing roller 21 and the pressure roller 22 are brought close to each other by a pressure spring 27 as a biasing unit. Here, a compression spring is used as the pressure spring 27, but an urging force may be applied similarly by a tension spring. By the urging force of the pressure spring 27, the fixing roller 21 and the pressure roller 22 are pressed against each other to form a fixing nip.

  In addition, the fixing device 20 includes a pressure release mechanism that releases the pressure contact between the fixing roller 21 and the pressure roller 22. Specifically, as shown in FIG. 2 or 3, the pressure release mechanism includes a drive gear 28, a fixing gear 29, a moving force generation gear 30, a switching gear 31, an operation gear 32, and pressure release. It is comprised by the member 33 grade | etc.,.

  The drive gear 28 is rotatably provided on the fixing plate 24. Further, the drive gear 28 is connected to a drive device (drive means) (not shown) provided in the image forming apparatus main body so that the drive force is transmitted.

  The fixing gear 29 is provided at one end of the fixing roller 21. The fixing gear 29 is in mesh with the drive gear 28. As a result, the rotational force from the drive gear 28 is transmitted to the fixing gear 29 so that the fixing roller 21 rotates.

  The moving force generating gear 30 and the switching gear 31 are disposed on the same axis and at different positions in the axial direction, and are rotatably provided on the fixing plate 24, respectively. Further, the moving force generating gear 30 and the switching gear 31 are supported so as to be capable of reciprocating in the axial direction indicated by arrows A and B in FIG. Further, the moving force generating gear 30 is engaged with the fixing gear 29, and the moving force generating gear 30 and the fixing gear 29 are each constituted by a helical gear. The helical gear is a gear whose tooth row is arranged to be inclined with respect to the rotation direction of the gear and can transmit the driving force between the gears in the axial direction. For this reason, when the moving force generating gear 30 and the fixing gear 29 rotate forward or backward, a moving force is generated between these gears in the axial direction indicated by the arrow A or B in FIG. That is, in the present embodiment, the moving force generating gear 30 and the fixing gear 29 also function as an axial direction moving unit. The driving gear 28 that meshes with the fixing gear 29 is also a helical gear, but the driving gear 28 and the fixing gear 29 are configured not to move in the axial direction by a stopper (not shown).

  In the present embodiment, the moving force generating gear 30 and the switching gear 31 are integrally formed of injection molded resin. Thereby, it is small and can be produced inexpensively. As the resin material, polyphenylene sulfide resin, polyamide resin, polyamideimide resin, polyimide resin, polyphenylene ether resin, polyphenylene oxide resin, polyacetal resin, polybutylene terephthalate resin, polycarbonate resin, and alloy resins thereof can be applied. It is. The moving force generating gear 30 and the switching gear 31 can be configured separately. In the present embodiment, the diameters of the reference pitch circles of the respective tooth rows in the moving force generating gear 30 and the switching gear 31 are different. As a result, the degree of freedom of the arrangement of the gears 28 to 32 and the pressure release member 33 is increased, and the space of the gear arrangement can be saved and the fixing device 20 can be downsized. Even if the diameters of the reference pitch circles of the respective tooth rows in the moving force generating gear 30 and the switching gear 31 are set to be the same, it does not depart from the essence of the present invention. Further, the moving force generating gear 30 and the switching gear 31 can be constituted by one gear formed continuously in the axial direction.

  The operation gear 32 includes a first gear portion 32a and a second gear portion 32b that are disposed on different positions in the axial direction on the same axis. In the present embodiment, the first gear portion 32a and the second gear portion 32b are integrally configured by the injected resin. Thereby, it is possible to produce small and inexpensive. As the resin material, polyphenylene sulfide resin, polyamide resin, polyamideimide resin, polyimide resin, polyphenylene ether resin, polyphenylene oxide resin, polyacetal resin, polybutylene terephthalate resin, polycarbonate resin, and alloy resins thereof can be applied. It is. In addition, it is also possible to comprise each gear part 32a, 32b separately. Moreover, you may comprise each gear part 32a, 32b by the one gear formed continuously in the axial direction. The gear portions 32a and 32b are provided with partial teeth 321 and 322 having no tooth row in a part of the circumferential direction. The missing tooth portions 321 and 322 provided in the gear portions 32a and 32b are disposed at different positions in the circumferential direction.

  The switching gear 31 is reciprocated in the axial direction so as to be switched and meshed between the first gear portion 32a and the second gear portion 32b. In the present embodiment, if the inclination of the tooth row (husba) of the moving force generating gear 30 and the fixing gear 29 is formed in the opposite direction, the axial moving force generated with the rotation is generated in the opposite direction. The arrangement of the first gear portion 32a and the second gear portion 32b can be exchanged. In the present embodiment, the tooth rows of the gear portions 32a and 32b are configured with the same spur teeth as the switching gear 31, but the gear portions 32a and 32b and the switching gear 31 may be configured with a helical bar. It does not depart from the essence of the present invention.

  The pressure release member 33 is configured to be rotatable integrally with the operation gear 32. In the present embodiment, the pressure release member 33 and the operation gear 32 are integrally configured by the injected resin. Thereby, it is possible to produce small and inexpensive. As the resin material constituting the pressure release member 33, a material used for the operation gear 32 described above can be applied. The pressure release member 33 and the operation gear 32 may be configured separately. Further, the pressure release member 33 is configured to rotate integrally as the operation gear 32 rotates and to contact and press against the pressure plate 25.

4A is a diagram illustrating a non-pressed state in which the pressure release member 33 is not pressing the pressure plate 25, and FIG. 4B is a diagram illustrating the pressure release member 33 pressing the pressure plate 25. It is a figure which shows the pressed state.
In the non-pressed state shown in FIG. 4A, the missing tooth portion 321 of the first gear portion 32 a out of the missing tooth portions 321 and 322 of the first gear portion 32 a and the second gear portion 32 b is the switching gear 31. It is arrange | positioned in the position facing. On the other hand, in the pressed state shown in FIG. 4 (b), the toothless portion 322 of the second gear portion 32 b is disposed to face the switching gear 31. As described above, in the present embodiment, different missing tooth portions 321 and 322 are configured to face the switching gear 31 in the non-pressed state and the pressed state.

FIG. 5 is an enlarged view of the pressure release member 33.
As shown in FIG. 5, in this embodiment, the pressing surfaces 33 a that press the pressure plate 25 of the pressure release member 33 are formed in a flat shape, and are disposed on both sides of the pressing surface 33 a in the rotational direction. The surfaces 33b and 33c are formed in a convex curved surface shape. Here, the distances Db and Dc between the rotation center Q of the pressure release member 33 and the convex curved surfaces 33b and 33c are set to be longer than the distance Da between the rotation center Q and the pressing surface 33a. Yes. However, the shape of the pressure release member 33 is not limited to the shape shown in FIG.

  As shown in FIG. 3, the fixing device 20 is provided with a stopper 34 that restricts the rotation of the pressure release member 33. The stopper 34 is composed of a rod-like member protruding from the fixing plate 24 (see FIG. 6). When the stopper 34 contacts the non-pressed pressure release member 33, the counterclockwise rotation of the pressure release member 33 in FIG. 3 is restricted. Further, the position of the stopper 34 is set so that the missing tooth portion 321 of the first gear portion 32 a faces the switching gear 31 in a state where the stopper 34 and the pressure releasing member 33 are in contact with each other.

  In the present embodiment, the stopper 34 is configured to abut against the pressure release member 33 and restrict its rotation. However, by restricting the rotation of the operation gear 32, the rotation of the pressure release member 33 is restricted. It is also possible. For example, a protrusion may be provided on the rotation shaft of the operation gear 32 and the stopper 34 may be brought into contact with the protrusion to restrict the rotation of the operation gear 32. Further, the stopper 34 may be provided so as to be able to be locked and detached with respect to the pressure release member 33, and the stopper 34 may be configured to restrict the rotation of the pressure release member 33 in both directions.

Hereinafter, the operation and effect of the pressure release mechanism will be described.
When the pressure between the fixing roller 21 and the pressure roller 22 is released, a driving device (driving means) (not shown) provided in the image forming apparatus main body is rotated in the reverse direction to the rotation direction (forward rotation) during the fixing operation. As a result, as shown in FIG. 7, the driving gear 28 that has received the driving force from the driving device rotates counterclockwise in the figure, and the fixing gear 29, the moving force generating gear 30 and the switching gear 31 are respectively indicated by the arrows in the figure. Rotate in the direction. At this time, the switching gear 31 at the start of rotation is opposed to the toothless portion 321 provided in the first gear portion 32 a of the operation gear 32, so that the rotational force of the switching gear 31 is not transmitted to the operation gear 32. . For this reason, the operation gear 32 does not rotate when the switching gear 31 starts to rotate.

  As described above, when each gear rotates, an axial force in the direction indicated by arrow A in FIG. 7 is generated between the fixing gear 29 and the moving force generating gear 30. Thereby, the switching gear 31 moves from the position facing the first gear portion 32a to the position facing the second gear portion 32b, and enters the state shown in FIG. Further, when the switching gear 31 moves to a position facing the second gear portion 32b, the movement in the axial direction (direction of arrow A in the figure) is stopped by a stopper (not shown).

  As shown in FIG. 8, when the switching gear 31 and the second gear portion 32 b face each other, the toothless portion 322 of the second gear portion 32 b is disposed at a position not facing the switching gear 31. Therefore, the switching gear 31 meshes with the second gear portion 32b, and the rotational force from the switching gear 31 is transmitted to the second gear portion 32b. As a result, the operation gear 32 rotates clockwise in FIG. Further, when the operation gear 32 rotates, the pressure release member 33 also rotates integrally therewith.

  As described above, when the pressure release member 33 rotates, the pressure release member 33 contacts the pressed portion 25a of the pressure plate 25 as shown in FIG. The pressure release member 33 presses the pressure plate 25 against the pressure spring 27 and moves the pressure plate 25 in a direction in which the pressure plate 25 is separated from the fixing plate 24. Along with this, the pressure roller 22 is moved away from the fixing roller 21, and the pressure between the fixing roller 21 and the pressure roller 22 is released. Thereafter, the driving of the driving device provided in the image forming apparatus main body is stopped.

  As described above, the release of the pressure between the fixing roller 21 and the pressure roller 22 can suppress or prevent the occurrence of creep on the fixing roller 21 and the pressure roller 22. Further, when a paper jam occurs in the fixing nip, the paper removal process is facilitated by releasing the pressure between the fixing roller 21 and the pressure roller 22. The “pressure release” referred to in the present invention is not limited to the case where the fixing roller and the pressure roller are completely separated so that no contact pressure acts between the two rollers. Includes a case where the contact pressure is reduced but the contact pressure is reduced.

  Further, as shown in FIG. 9, when the pressure release member 33 is in a pressing state in which the pressure plate 25 is pressed, the toothless portion 322 of the second gear portion 32 b is disposed at a position facing the switching gear 31. Therefore, the meshing between the second gear portion 32b and the switching gear 31 is released. As a result, even after the switching gear 31 rotates for a while after the pressing state is reached, the operation gear 32 does not rotate and the pressure release member 33 does not rotate, so that the pressing state can be reliably maintained. is there.

  In the present embodiment, as described above, since the pressing surface 33a of the pressure releasing member 33 is formed in a flat shape (see FIG. 5), the pressing plate 25 (the pressed portion) is pressed by the pressing surface 33a of the pressure releasing member 33. In the state where 25a) is pressed, the pressure release member 33 hardly rotates unexpectedly, and the pressed state is stably maintained. Further, the distances Db and Dc between the convex curved surfaces 33b and 33c disposed on both sides of the pressing surface 33a and the rotation center Q are set to be longer than the distance Da between the pressing surface 33a and the rotation center Q. For this reason (see FIG. 5), the convex curved surfaces 33b and 33c can prevent or suppress the unexpected rotation of the pressure release member 33. Thereby, it is possible to maintain a pressing state more stably.

  In this embodiment, when the pressure release member 33 presses the pressed portion 25a of the pressure plate 25, the pressure release member 33 slides from the top to the bottom of FIG. 9 with respect to the pressed portion 25a. It is like that. That is, the pressure release member 33 is configured to slide from the far side to the near side from the support shaft 26 as the swing center with respect to the pressed portion 25a, and therefore slides in the opposite direction. Compared to the case, the pressing plate 25 can be pressed and moved away with a small force. As a result, it is possible to reduce the load applied to the pressure release member 33, each gear, and the like when the pressure plate 25 is pressed, and to reliably release the pressure.

Next, the case where the fixing operation is performed by returning the pressure between the fixing roller 21 and the pressure roller 22 to the original state will be described.
When starting the fixing operation, a drive device (drive means) (not shown) provided in the image forming apparatus main body is rotated forward. Thereby, in FIG. 10, the drive gear 28 rotates clockwise in the figure, and the fixing gear 29, the moving force generating gear 30, and the switching gear 31 rotate in the directions of the arrows in the figure. At this time, the switching gear 31 at the start of rotation is opposed to the toothless portion 322 provided in the second gear portion 32 b of the operation gear 32, so that the rotational force of the switching gear 31 is not transmitted to the operation gear 32. . For this reason, the operation gear 32 does not rotate when the switching gear 31 starts to rotate.

  As described above, when each gear rotates, an axial force in the direction indicated by arrow B in FIG. 10 is generated between the fixing gear 29 and the moving force generating gear 30. Thereby, the switching gear 31 moves from a position facing the second gear portion 32b to a position facing the first gear portion 32a, and enters the state shown in FIG. Further, the movement of the switching gear 31 in the axial direction (the direction of arrow B in the figure) is stopped by a stopper (not shown) at a position where the switching gear 31 faces the first gear portion 32a.

  As shown in FIG. 11, in a state where the switching gear 31 and the first gear portion 32 a face each other, the toothless portion 321 of the first gear portion 32 a is disposed at a position not facing the switching gear 31. Therefore, the switching gear 31 meshes with the first gear portion 32a, and the rotational force from the switching gear 31 is transmitted to the first gear portion 32a. As a result, the operation gear 32 rotates counterclockwise in FIG. 11, and the pressure release member 33 also rotates integrally therewith and returns to the non-pressed state shown in FIG. At this time, the pressure release member 33 contacts the stopper 34 and its rotation is restricted (see FIG. 3). At the same time as the pressure release member 33 is returned to the non-pressed state, the pressure roller 22 approaches and contacts the fixing roller 21, and the pressure between the rollers 21 and 22 is restored. Thereafter, the toner image is fixed on the recording paper as the recording paper passes between the fixing roller 21 and the pressure roller 22 that rotate in the forward direction.

  Further, in the non-pressed state shown in FIG. 7, since the toothless portion 321 of the first gear portion 32 a is disposed at a position facing the switching gear 31, the meshing between the first gear portion 32 a and the switching gear 31 is released. The As a result, the operation gear 32 does not rotate and the pressure release member 33 does not rotate even if the switching gear 31 continues to rotate normally after the non-pressed state, and therefore the pressure is released by the pressure release member 33 during the fixing operation. It will not be released.

  Further, when the pressure release member 33 is returned from the pressed state to the non-pressed state, an inertial force in the rotational direction at that time acts on the pressure release member 33, but by providing the stopper 34, the inertial force is applied to the inertial force. Accordingly, the pressure release member 33 can be stopped at a predetermined position. Thereby, since the toothless portion 321 of the first gear portion 32a does not rotate beyond the position facing the switching gear 31, the first gear portion 32a and the switching gear 31 do not unexpectedly mesh with each other. The pressure release member 33 does not receive a rotational force from the switching gear 31 and is not pressed. In this way, the pressure release member 33 can be reliably stopped at a predetermined position by the stopper 34, so that the fixing caused by the unexpected release of the pressure between the fixing roller 21 and the pressure roller 22 during the fixing operation. The occurrence of defects can be prevented.

FIG. 12 shows a configuration of a fixing device according to another embodiment of the present invention.
In the embodiment shown in FIG. 12, the missing tooth portion 322 of the second gear portion 32 b is omitted as compared with the embodiment. That is, the missing tooth portion 321 is formed only in the first gear portion 32a. Further, in this embodiment, the moving force generating gear 30 composed of a helical gear is also omitted. Instead, the switching gear 31 is configured to be reciprocally movable in the axial direction indicated by the arrow A or B in the figure by an actuator (not shown). However, the use of a pair of helical gears as the axial movement means has the advantage that the rotational force obtained from the drive device can be used more effectively than a separate actuator, and the size and cost can be reduced. . In addition, it is possible to configure the operation gear 32 to reciprocate in the axial direction instead of the switching gear 31 by the actuator.

  In the embodiment shown in FIG. 12, when the pressure between the fixing roller 21 and the pressure roller 22 is released, the switching gear 31 is moved in the direction of the arrow A in the drawing by an actuator (not shown), and the second gear portion 32b. Mesh with. Then, when the rotational force is transmitted from the switching gear 31 to the second gear portion 32b, the pressure release member 33 rotates and presses the pressure plate 25 to release the fixing nip pressure. At this time, in this embodiment, it is necessary to stop the reverse rotation of the drive device in a state where the pressure release member 33 presses the pressure plate 25.

  Further, when the pressure between the fixing roller 21 and the pressure roller 22 is returned, the switching gear 31 is moved in the direction of the arrow B in the figure by the actuator and meshed with the first gear portion 32a. Then, when the rotational force is transmitted from the switching gear 31 to the first gear portion 32a, the pressure release member 33 rotates and returns to the state where the pressure plate 25 is not pressed, and the fixing nip pressure is restored. In this case, similarly to the above-described embodiment, the toothless portion 321 of the first gear portion 32a is disposed at a position facing the switching gear 31, so that the pressure release member 33 is maintained even if the switching gear 31 continues to rotate normally. Does not rotate, and the pressure is not released during the fixing operation. In the embodiment shown in FIG. 12, the configuration other than the above-described configuration is the same as that of the above-described embodiment shown in FIG.

  The embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention. In the above-described embodiment, the fixing roller 21 functions as a main driving roller and the pressure roller 22 functions as a driven roller. However, the pressure roller 22 can function as a main driving roller and the fixing roller 21 as a driven roller. is there. Further, instead of the fixing roller 21 or the pressure roller 22, a fixing member constituted by an endless belt or the like can be applied. Further, the fixing device of the present invention is not limited to the color image forming apparatus shown in FIG. 1, but can be mounted on a monochrome image forming apparatus, a copying machine, a printer, a facsimile, or a complex machine thereof.

  As described above, according to the present invention, the pressure release of the fixing nip can be automatically performed, so that there is no troublesome operation and forgetting to operate the pressure release lever as in the conventional case, and operability and reliability. Can be improved. Moreover, since it is not necessary to manually operate the pressure release lever which may become hot, safety is also improved.

  Further, according to the present invention, it is possible to release the pressure of the fixing nip using the driving force of the driving means (driving device) for applying a rotational force to the fixing member. That is, according to the present invention, it is possible to perform the fixing operation and the pressure releasing operation using the driving force of one driving unit, so that it is not necessary to provide a dedicated driving unit for releasing the pressure. This makes it possible to reduce the size and cost of the fixing device and the image forming apparatus.

  Further, according to the present invention, when the pressure release member is rotated to the non-pressing position, the rotation of the pressure release member can be restricted by the stopper, so that the pressure between the fixing roller and the pressure roller during the fixing operation is reduced. Is not canceled unexpectedly, and it is possible to prevent the occurrence of fixing failure.

20 Fixing device 21 Fixing roller (fixing member)
22 Pressure roller (fixing member)
24 Fixing plate (support member)
25 Pressure plate (support member)
26 Support shaft 27 Pressure spring (biasing means)
31 switching gear 32 operation gear 32a first gear part 32b second gear part 33 pressure release member 33a pressing surface 34 stopper 321 missing tooth part 322 missing tooth part Da, Db, Dc distance from rotation center Q rotation center

JP 2009-122243 A JP 2009-139682 A

Claims (10)

A pair of fixing members for fixing an image on the recording medium to the recording medium; a driving unit for applying a rotational force to the fixing member; a pair of supporting members for supporting the fixing member so as to be close to and away from each other; and the fixing member And a biasing unit that biases the support member in a direction in which the two are moved closer to each other.
A switching gear to which a rotational force is transmitted from the driving means;
An operation gear provided with a missing tooth portion on one of two gear portions disposed at different positions in the axial direction;
Pressure release that rotates integrally with the operation gear and is switched between a pressing state in which one of the pair of supporting members is pressed against the biasing means and a non-pressing state in which the supporting member is not pressed. Members,
An axial movement means for reciprocally moving the switching gear and the operation gear in the axial direction and switching the switching gear between the two gear portions so as to be meshed with each other.
The missing tooth portion is disposed at a position facing the switching gear in a state where the pressure releasing member is disposed in the non-pressed state,
A fixing device comprising a stopper for restricting the rotation of the pressure release member in a state where the tooth missing portion is disposed at a position facing the switching gear.   The fixing device according to claim 1, wherein the stopper is configured to abut against the pressure release member that has rotated from the pressed state to the non-pressed state to restrict movement in the rotation direction. The drive means is configured to be able to rotate forward and reverse during the fixing operation,
The axial direction moving means has a pair of helical gears that are reciprocally movable in the axial direction by being rotated forward and backward by the driving means,
One of the helical gears is provided to be rotatable integrally with the switching gear,
The switching gear is moved to the gear portion provided with the toothless portion by the axial movement between the helical gears that occurs during normal rotation, and the switching gear is made different by the axial movement between the helical gears that occurs during reverse rotation. The fixing device according to claim 1, wherein the fixing device is configured to be moved to a gear portion.   Another gear missing portion is provided in the gear portion different from the gear portion provided with the tooth missing portion, and the other tooth missing portion is switched in a state where the pressure release member is disposed in the pressed state. The fixing device according to claim 1, wherein the fixing device is disposed at a position facing the gear.   The fixing device according to claim 1, wherein a pressing surface that presses the support member of the pressure release member is formed in a flat shape.   The distance between the rotation center of the pressure release member and the pressing surface that presses the support member is set to be longer than the distance between the rotation center and surfaces disposed on both sides of the pressing surface in the rotation direction. The fixing device according to any one of 1 to 5.   When the support member pressed by the pressure release member is configured to be swingable, the pressure release member is slid from the side far from the swing center to the side closer to the support member. The fixing device according to claim 1, wherein the fixing device is configured to be pressed.   The fixing device according to claim 3, wherein the helical gear is made of an injection molded resin.   9. The resin is composed of a polyphenylene sulfide resin, a polyamide resin, a polyamideimide resin, a polyimide resin, a polyphenylene ether resin, a polyphenylene oxide resin, a polyacetal resin, a polybutylene terephthalate resin, a polycarbonate resin, and an alloy resin thereof. The fixing device according to 1.   An image forming apparatus comprising the fixing device according to claim 1.

Images