JP2010048965A - Fixing device and image forming apparatus - Google Patents

Abstract

When a pressure roller is switched from a pressure contact state to a pressure release state, a means for braking the switching speed is provided to reliably switch the contact / separation operation of each roller.
A swing cam that rotates in one direction when a rotational driving force is transmitted by a driving means and a pressure roller 32 are pivotally supported, and the pressure roller 32 is displaced so as to contact and separate from a fixing roller. The displacement frame 71, the pressure release cam 76 that is in sliding contact with the displacement frame 71, the one-way clutch and torque limiter 79 provided on the shaft 76 a of the pressure release cam 76, and the one-way clutch are connected to be in sliding contact with the swing cam. The torque limiter 79 applies a constant load to the shaft 76a to brake the rotational speed so that the shaft 76a rotates more than the one-way clutch 7 is fed. To prevent.
[Selection] Figure 8

Description

  The present invention relates to a fixing device that can be applied to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and an image forming apparatus including the same.

  In this type of electrophotographic image forming apparatus, an electrostatic latent image is formed on the surface of an image carrier such as a photoconductive drum, and the electrostatic latent image on the surface of the image carrier is developed with a developer, thereby carrying the image A toner image is formed on the surface of the body, the toner image is transferred from the image carrier to a recording sheet, and the recording sheet is heated and pressurized to fix the toner image on the recording sheet.

  The toner image on the recording sheet is fixed by a fixing device. That is, in the fixing device, usually, a pressure contact means for pressing the pressure roller toward the fixing roller is provided, and the recording sheet is sandwiched and conveyed in the fixing nip region between the fixing roller and the pressure roller, The recording sheet is heated and pressurized by each roller, and the toner on the recording sheet is heated and melted and fixed.

  In such a conventional fixing device, depending on the type of recording sheet being conveyed, the pressure contact force between the rollers may affect the state of the recording sheet when passing through the fixing nip region. For example, when a thick recording sheet formed in a bag shape like an envelope is fixed with a pressing force suitable for fixing ordinary plain paper, there is a risk of causing a conveyance failure or fixing failure such as wrinkles. is there.

  As described above, from the viewpoint of avoiding the occurrence of a recording sheet conveyance failure or fixing failure such as an envelope, in the conventional fixing device, a pressure contact release means for releasing the pressure roller from the pressure roller to the fixing roller is provided. There is an apparatus in which an appropriate pressure contact force is obtained by releasing the pressure contact between the rollers as required by the pressure release means (for example, see Patent Document 1).

  The purpose is not to release the pressure contact according to the thickness of the recording sheet, but when the fixing roller and the pressure roller are stopped, the rollers are separated so that the elastic layer of each roller is not left in a deformed state. A fixing device provided with a pressure release mechanism for achieving the above is also disclosed (see, for example, Patent Documents 2 and 3).

  The fixing device disclosed in Patent Document 1 is a heat roller type fixing device including a fixing roller and a pressure roller that is in pressure contact with the fixing roller, and the pressure contact load of the pressure roller to the fixing roller is variable. A pressing lever that engages with the pressing lever and can be protruded and retracted, and an opening and closing member that supports the protruding member provided in the vicinity of the fixing device. When closed, the projecting member presses the pressing lever to switch the pressure contact load. That is, when the protruding member presses the pressing lever, the pressing load is reduced, and it is suitable for fixing a thick recording sheet.When the protruding member does not press the pressing lever, the pressing load is restored, It is suitable for fixing a general plain paper recording sheet.

  Further, as shown in FIG. 10, the fixing device disclosed in Patent Document 2 includes a fixing roller 341 disposed so as to face the pressure roller 342 and connected to a connecting portion 344b of a connecting member 344. The pressure spring 343 presses the fixing roller 341 against the pressure roller 342 with a predetermined pressure via the connecting member 344. On the other hand, the pressure release cam 345 is disposed substantially opposite to the pressure spring 343 across the connecting member 344, and is provided so as to be rotatable in the direction of the arrow R around the rotation shaft 345a by a drive source (not shown). ing. The pressure release cam 345 is a cam follower surface X extending from 345b to 345c which is the lowest point when the fixing roller 341 is pressed, a cam follower surface Y extending from 345c to 345d, and a cam follower surface Z extending from 345d to 345e to 345b. It is composed of

  When the image forming apparatus is in operation (image formation), the cam follower surface X of the pressure release cam 345 is opposed to the connecting member 344 as shown in FIG. As a result, the pressure release cam 345 does not act on the connecting member 344, and the fixing roller 341 presses against the pressure roller 342 with a predetermined pressure, so that the recording paper on which the image is formed is stably fixed. ing.

  On the other hand, unnecessarily high pressure is required when handling paper jams that occur during image formation, when entering a low power mode that is not used for a certain period of time, or when the image forming apparatus is turned off. Is applied to the pressure roller 342 and the fixing roller 341, the pressure release cam 345 is rotated approximately 90 degrees. As a result, as shown in FIG. 10B, the cam follower surface X of the pressure release cam 345 depresses the connecting member 344 against the urging force of the pressure spring 343, and is further applied by the flat surface of the cam follower surface Y. By maintaining the posture of the pressure release cam 345, the fixing roller 341 is separated from the pressure roller 342.

  Further, after the paper jam processing, in order to bring the image forming apparatus main body into an image formable state, when the pressure state shown in FIG. 10A is reproduced from the pressure release state shown in FIG. The pressure release cam 345 in the state shown in FIG. 10B is rotated again approximately 270 degrees in the direction of arrow R, and the connecting member 344 is gradually returned to the pressure position by the cam follower surface Z.

  That is, the fixing device disclosed in Patent Document 2 is provided with gentle portions on the cam follower surfaces X, Y, and Z of the pressure release cam 345, and the pressure release cam 345 when operating from the pressure release state to the pressure state. By performing the rotation over half a rotation (approximately 270 degrees in the above example), acceleration of rotation due to the urging force from the pressure spring 343 is suppressed.

Further, the fixing device disclosed in Patent Document 3 movably supports a frame body that pivotally supports a pressure roller, and is provided with a cam that is slidably contacted with the frame body. The pressure roller can be separated from the fixing roller. At the time of fixing, the forward rotation of the output shaft of the drive motor is transmitted to the fixing roller via the gear unit and the one-way clutch, and the recording sheet is sandwiched and conveyed in the fixing nip area between the rollers. Further, during non-fixing, the reverse rotation of the output shaft of the drive motor is transmitted to the cam via the other gear unit and the one-way clutch, and the frame is moved by the cam to separate the pressure roller from the fixing roller. . Accordingly, it is possible to switch between the rotational driving of each roller and the contact / separation operation of each roller by using one driving motor. In the fixing device disclosed in Patent Document 3, braking means is provided in the pressure contact / pressure release mechanism including the cam, the gear unit, and the one-way clutch so as to alleviate abrupt operation. The braking means comprises a notch gear and a torque limiter. The notch gear is not provided with teeth in a first phase in which the cam rotates in the direction in which the biasing force of the coil spring increases, and the cam has a first force in which the biasing force of the coil spring decreases. Teeth are provided in two phases and a third phase in which the biasing force of the coil spring does not change. Accordingly, the cam is not braked in the first phase of the cam rotation, and the cam is braked by the torque limiter in the second phase and the third phase. By such braking means comprising a torque limiter and a notch gear, the rapid rotational movement of the cam is mitigated, and as a result, noise and vibration when the operation of the fixing device is stopped are effectively prevented.
JP-A-2005-258135 JP 2007-253349 A JP 2003-280308 A

  According to the fixing device of Patent Document 1, when the opening / closing member is closed, the protruding member provided on the opening / closing member pushes down the pressing lever of the pressure roller, so that the pressure roller is separated from the fixing roller. Oscillates to reduce the pressure contact force, resulting in a pressure contact force suitable for a thick recording sheet. In other words, since the pressing lever is operated in conjunction with the opening / closing operation of the opening / closing member, it is not possible to finely adjust the pressing down of the pressure roller, and an appropriate pressure contact force suitable for a thick recording sheet may not necessarily be obtained. There is. For this reason, there is a problem that a normal fixing nip region cannot be obtained, and there is a possibility that a conveyance failure such as a wrinkle or a fixing failure may be caused.

  In addition, the fixing device disclosed in Patent Document 2 has a problem that a driving source for driving the pressure release cam is required in addition to the pressure roller and the driving system for the fixing roller, resulting in a complicated structure. In addition, by performing the rotation of the pressure release cam when operating from the pressure release state to the pressure state over half a turn, the acceleration of rotation due to the urging force from the pressure spring is suppressed, No consideration is given to suppressing acceleration of the rotation of the pressure release cam when operating from the pressure state to the pressure application / removal state. For this reason, depending on the magnitude of the urging force of the pressure spring, the rotational operation of the pressure release cam may be accelerated, and the pressure release cam may be held in the half pressure release state.

  By the way, the driving motor of the fixing device is not necessarily dedicated to the fixing device, and rotationally drives the recording sheet conveyance roller on the upstream side or the downstream side in the recording sheet conveyance direction, or the developing or transfer roller. It is often used for this purpose. That is, various rollers are rotationally driven by one driving motor. Accordingly, when the output shaft of the drive motor is rotated in the reverse direction, the various rollers are also rotated in the reverse direction, causing various inconveniences. In this case, if several one-way clutches are incorporated in the gear unit as in Patent Document 3, it is possible to prevent reverse rotation of various rollers even if the output shaft of the drive motor is reversely rotated. Since the one-way clutch is incorporated in the gear unit itself, there is a problem that the configuration of the gear unit becomes complicated. In addition, a braking means comprising a notch gear and a torque limiter is provided to mitigate the rapid rotational movement of the cam and prevent noise and vibration when the fixing device is deactivated. And the torque limiter are combined, the drive control for releasing the pressure is complicated, and it is difficult to ensure the reliability of the apparatus.

  The present invention was devised to solve such problems, and the object thereof is to press the pressure roller without reversely rotating the drive motor and without complicating the configuration of the gear unit around the fixing device. In addition, it is possible to switch between the rotation driving of the fixing roller and the contact / separation operation of each roller, and to provide a means for reducing the switching speed when the pressure roller is switched from the pressure contact state to the pressure release state. Another object of the present invention is to provide a fixing device capable of switching the contact / separation operation of each roller with certainty and an image forming apparatus including the same.

  In order to solve the above-described problems, a fixing device according to the present invention includes a pressing unit that presses a second roller against a first roller that is fixed to a shaft, and a pressing unit that switches between pressing and releasing the pressing of the first roller by the pressing unit. In a fixing device including a pressure release switching unit and a driving unit that rotates the first and second rollers, when the second roller is switched from a pressure release state to a pressure state by the pressure contact / pressure release switching unit. In this configuration, the speed reducing means for braking the switching speed is provided.

  More specifically, as shown in FIG. 3, the pressure contact / pressure contact release switching means is transmitted with the rotational driving force by the drive means (drive gear 84) and rotated in one direction, and the first cam A displacement frame 71 that is a displacement support member that pivotally supports a pressure roller 32 that is two rollers and is displaced so that the pressure roller 32 contacts and separates from the fixing roller 31 that is the first roller, and a displacement frame 71 A pressure release cam 76 that slides on the shaft, a one-way clutch 77 provided on a shaft 76a of the pressure release cam 76, a swing lever 78 that is connected to the one-way clutch 77 and is urged so as to slide on the swing cam 81. When the swing cam 81 is rotated in one direction by the rotational driving force of the drive means, the swing lever 78 slidably contacting the swing cam 81 swings repeatedly, and the swing lever 78 Oscillation is transmitted to the pressure release cam 76 as one-way intermittent rotation via the one-way clutch 77, and the pressure release cam 76 rotates to cause a pressure contact force (contraction force) of the coil spring 74 that is the displacement frame 71 as a pressure contact means. ), The displacement frame 71 and the pressure roller 32 are displaced, so that the pressure roller 32 operates so as to reduce the pressure contact force against the fixing roller 31 (this state is shown in FIG. 9). (B)). Then, when the swing cam 81 is further rotated in one direction by the rotational driving force of the driving means from this state, the swing lever 78 slidably contacting the swing cam 81 swings repeatedly, and the swing lever 78 Is transmitted as a one-way intermittent rotation to the pressure release cam 76 via the one-way clutch 77, and the rotation of the pressure release cam 76 causes the displacement frame 71 and the pressure roller 32 to have a pressure contact force ( The pressure roller 32 operates so as to increase the pressure contact force with respect to the fixing roller 31 (that is, restore to the original pressure contact force) by being displaced so as to be pulled to the original position by the contraction force). (This state is shown in FIGS. 3 and 9A). In such an operation, the speed reducing means acts to constantly brake the rotational speed of the pressure release cam 76. Specifically, the deceleration means is a torque limiter 79 provided on the shaft 76 a of the pressure release cam 76.

  Here, when the speed reduction means is not provided, when the pressure release cam 76 reaches the pressure release position (position shown in FIG. 9B) that most protrudes the displacement frame 71, the displacement frame due to the biasing force of the coil spring 74 is reached. On the contrary, the pressure force of 71 acts as a rotational force of the pressure release cam 76, and the pressure release cam 76 may pass through the pressure release position shown in FIG. 9B and rotate. When the pressure release cam 76 rotates after passing through the pressure release position shown in FIG. 9B, the displacement frame 71 and the pressure spooler 32 are slightly displaced toward the fixing roller 31 to press the pressure in the fixing nip region. The power will increase slightly. For this reason, the pressing force in the fixing nip region is slightly higher than the optimal pressing force for fixing a thick recording sheet such as an envelope, so that fixing failure may occur. On the other hand, as in the present invention, a torque limiter 79 is provided on the shaft 76a of the pressure release cam 76 so that a constant load is always applied to the shaft 76a. Even when a thick recording sheet is fixed, stable fixing performance can be obtained.

  In addition, the fixing device of the present invention includes a control unit that is connected to the swing lever 78 and moves the swing lever 78 so as to be separated from the swing cam 81. Further, reverse rotation blocking means for blocking the rotation of the shaft of the pressure release cam 76 in the same direction as the one-way clutch 77 rotates in the idling direction is also provided.

  According to the present invention, when the second roller is switched from the pressure release state to the pressure contact state, the second roller can be reliably switched to the pressure contact state by braking the switching speed by the speed reduction means and decelerating. That is, by providing a brake mechanism that is a deceleration means on the shaft of the pressure release cam and applying a constant load to the shaft to suppress the rotational force, the pressure release cam is prevented from rotating too much beyond the stop position, The pressure release cam can be stopped at the normal position.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. In addition, the following embodiment is an example which actualized this invention, Comprising: The thing of the character which limits the technical scope of this invention is not.

  FIG. 1 is a schematic view of an internal configuration of an image forming apparatus D to which an embodiment of a fixing device according to the present invention is applied, viewed from the side. The image forming apparatus D includes an original reading apparatus B that reads an image of an original, and an apparatus that records and forms an image of the original read by the original reading apparatus B or an image received from outside on a recording sheet such as paper in color or single color. And a main body A.

  In the document reading apparatus B, when the document is set on the document set tray 41, the pickup roller 44 is pressed against the surface of the document and rotated, the document is pulled out from the tray 41, and the document passes between the suction roller 45 and the separation pad 46. Then, after being separated one by one, it is transported to the transport path 47.

  In this conveyance path 47, the leading edge of the document comes into contact with the registration roller 49, and the leading edge of the document is aligned in parallel with the registration roller 49. After that, the document is conveyed by the registration roller 49 and between the reading guide 51 and the reading glass 52. Pass through. At this time, the light of the light source of the first scanning unit 53 is irradiated on the surface of the document through the reading glass 52, and the reflected light is incident on the first scanning unit 53 through the reading glass 52. The image is reflected by the mirrors of the second scanning units 53 and 54 and guided to the imaging lens 55, and an image on the surface of the document is formed on a CCD (Charge Coupled Device) 56 by the imaging lens 55. The CCD 56 reads an image on the document surface and outputs image data indicating the image on the document surface. Further, the document is conveyed by the conveyance roller 57 and is discharged to the paper discharge tray 59 via the paper discharge roller 58.

  In addition, it is possible to read a document placed on the platen glass 61. The registration roller 49, the reading guide 51, the paper discharge tray 59, and the like and the members above them form an integrated cover body, and around the axis along the document conveying direction on the back side of the document reading device B It is pivotally supported so that it can be opened and closed. When the upper cover body is opened, the document table glass 61 is released, and a document can be placed on the document table glass 61. When the document is placed and the cover body is closed, the first and second scanning units 53 and 54 are moved in the sub-scanning direction, and the first scanning unit 53 exposes the document surface on the document table glass 61. Reflected light from the document surface is guided to the imaging lens 55 by the first and second scanning units 53 and 54, and an image on the document surface is formed on the CCD 56 by the imaging lens 55. At this time, the first and second scanning units 53 and 54 are moved while maintaining a predetermined speed relationship with each other, and reflection of the document surface, the first and second scanning units 53 and 54, the imaging lens 55, and the CCD 56 is performed. The positional relationship between the first and second scanning units 53 and 54 is always maintained so that the length of the optical path of the light does not change, and thereby the focus of the image on the document surface on the CCD 56 is always accurately maintained.

  The entire original image read in this way is sent and received as image data to the apparatus main body A of the image forming apparatus D, and the apparatus main body A records the image on a recording sheet.

  On the other hand, the apparatus main body A of the image forming apparatus D includes an exposure apparatus 1, a developing apparatus 2 (2a, 2b, 2c, 2d), a photosensitive drum 3 (3a, 3b, 3c, 3d) acting as an image carrier, and charging. Intermediate transfer belt device 8 including a container 5 (5a, 5b, 5c, 5d), a cleaner device 4 (4a, 4b, 4c, 4d), and an intermediate transfer roller 6 (6a, 6b, 6c, 6d) acting as a transfer portion. A fixing device 12, a sheet conveying device 18, a paper feed tray 10 that functions as a paper feed unit, and a paper discharge tray 15 that functions as a paper discharge unit.

  The image data handled in the apparatus main body A of the image forming apparatus D is data corresponding to a color image using each color of black (K), cyan (C), magenta (M), yellow (Y), or a single color (for example, This corresponds to a monochrome image using (black). Accordingly, the developing device 2 (2a, 2b, 2c, 2d), the photosensitive drum 3 (3a, 3b, 3c, 3d), the charger 5 (5a, 5b, 5c, 5d), and the cleaner device 4 (4a, 4b, 4c, 4d) and four intermediate transfer rollers 6 (6a, 6b, 6c, 6d) are provided so as to form four types of images corresponding to the respective colors. Is associated with black, b with cyan, c with magenta, and d with yellow to form four image stations. Hereinafter, the description will be made with the suffixes a to d omitted.

  The photoconductor drum 3 is disposed at substantially the center in the vertical direction of the apparatus main body A.

  The charger 5 is a charging means for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential. In addition to a contact type roller type or brush type charger, a charger type charger is used. .

  Here, the exposure apparatus 1 is a laser scanning unit (LSU) provided with a laser diode and a reflection mirror, and exposes the surface of the charged photosensitive drum 3 according to image data, and according to the image data on the surface. An electrostatic latent image is formed.

  The developing device 2 develops the electrostatic latent image formed on the photosensitive drum 3 with (K, C, M, Y) toner. The cleaner device 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  In addition to the intermediate transfer roller 6, the intermediate transfer belt device 8 disposed above the photosensitive drum 3 includes an intermediate transfer belt 7, an intermediate transfer belt drive roller 21, a driven roller 22, a tension roller 23, and an intermediate transfer belt. A cleaning device 9 is provided.

  Roller members such as the intermediate transfer belt drive roller 21, the intermediate transfer roller 6, the driven roller 22, and the tension roller 23 stretch and support the intermediate transfer belt 7, and the intermediate transfer belt 7 is supported in a predetermined sheet conveyance direction (in the drawing). Move around in the direction of arrow C).

  The intermediate transfer roller 6 is rotatably supported inside the intermediate transfer belt 7 and is pressed against the photosensitive drum 3 via the intermediate transfer belt 7.

  The intermediate transfer belt 7 is provided so as to be in contact with each photoconductive drum 3, and a color toner image (each color is transferred by sequentially superimposing and transferring the toner image on the surface of each photoconductive drum 3 onto the intermediate transfer belt 7. Toner image). Here, the transfer belt 7 is formed in an endless belt shape using a film having a thickness of about 100 μm to 150 μm.

  The transfer of the toner image from the photosensitive drum 3 to the intermediate transfer belt 7 is performed by an intermediate transfer roller 6 that is in pressure contact with the inner side (back surface) of the intermediate transfer belt 7. A high voltage transfer bias (for example, a high voltage having a polarity (+) opposite to the toner charging polarity (−)) is applied to the intermediate transfer roller 6 in order to transfer the toner image. Here, the intermediate transfer roller 6 is a roller based on a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm and whose surface is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). With this conductive elastic material, a high voltage can be uniformly applied to the recording sheet.

  The apparatus main body A of the image forming apparatus D further includes a secondary transfer apparatus 11 including a transfer roller 11a that functions as a transfer unit. The transfer roller 11 a is in contact with the outside of the intermediate transfer belt 7.

  As described above, the toner images on the surfaces of the respective photosensitive drums 3 are stacked on the intermediate transfer belt 7 and become a color toner image indicated by the image data. The stacked toner images of the respective colors are transported together with the intermediate transfer belt 7 and transferred onto the recording sheet by the secondary transfer device 11.

  The intermediate transfer belt 7 and the transfer roller 11a of the secondary transfer device 11 are pressed against each other to form a transfer nip region. The transfer roller 11a of the secondary transfer device 11 has a voltage (for example, a polarity (+) opposite to the toner charging polarity (-)) for transferring the toner image of each color on the intermediate transfer belt 7 to the recording sheet. Is applied). Further, in order to constantly obtain the transfer nip area, either the transfer roller 11a of the secondary transfer device 11 or the intermediate transfer belt drive roller 21 is made of a hard material (metal or the like), and the other is made of a soft material such as an elastic roller. Material (elastic rubber roller, foaming resin roller, etc.) is used.

  In addition, the toner image on the intermediate transfer belt 7 may not be completely transferred onto the recording sheet by the secondary transfer device 11, and the toner may remain on the intermediate transfer belt 7. Causes color mixing. Therefore, the residual toner is removed and collected by the intermediate transfer belt cleaning device 9. The intermediate transfer belt cleaning device 9 includes, for example, a cleaning blade that contacts the intermediate transfer belt 7 as a cleaning member, and residual toner can be removed and collected by the cleaning blade. The driven roller 22 supports the intermediate transfer belt 7 from the inside (back side), and the cleaning blade is in contact with the intermediate transfer belt 7 so as to press the driven roller 22 from the outside.

  The paper feed tray 10 is a tray for storing recording sheets, and is provided below the image forming unit of the apparatus main body A. A paper discharge tray 15 provided on the upper side of the image forming unit is a tray for placing printed recording sheets face down.

  In addition, the apparatus main body A is provided with a sheet conveying device 100 for sending the recording sheet in the paper feed tray 10 to the paper discharge tray 15 via the secondary transfer device 11 and the fixing device 12. The sheet conveying device 18 has an S-shaped sheet conveying path S, and along the sheet conveying path S, a pickup roller 16, a roller roller 14a, a separation roller 14b, each conveying roller 13, a pre-registration roller 19, a resist Conveying members such as a roller 14, a fixing device 12, and a paper discharge roller 17 are arranged. The fixing device 12 will be described in detail later.

  The pickup roller 16 is a pull-in roller that is provided at the downstream end of the sheet feeding tray 10 in the sheet conveying direction and supplies recording sheets from the sheet feeding tray 10 to the sheet conveying path S one by one. The suction roller 14a passes the recording sheet between the separation roller 14b and conveys it to the sheet conveyance path S while separating the recording sheets one by one. Each conveyance roller 13 and the pre-registration roller 19 are small rollers for promoting and assisting the conveyance of the recording sheet. Each conveying roller 13 is provided at a plurality of locations along the sheet conveying path S.

  In the stopped state, the registration roller 14 abuts the leading edge of the recording sheet that has been conveyed, aligns the leading edge of the recording sheet, and is intermediate in the transfer nip region between the intermediate transfer belt 7 and the secondary transfer device 11. The recording sheet is conveyed in a timely manner in synchronism with the toner image formed on the intermediate transfer belt 7 so that the toner image on the transfer belt 7 is transferred to the recording sheet. For example, the registration roller 14 is arranged so that the toner image on the intermediate transfer belt 7 matches the position where the image on the recording sheet is to be formed in the transfer nip region between the intermediate transfer belt 7 and the secondary transfer device 11. Transport.

  The fixing device 12 receives the recording sheet on which the toner image is transferred, and conveys the recording sheet by sandwiching the recording sheet between the fixing roller 31 and the pressure roller 32.

  The recording sheet after fixing the toner images of the respective colors is discharged onto the paper discharge tray 15 by the paper discharge roller 17.

  It is also possible to form a monochrome image using only one of the four image forming stations and transfer the monochrome image to the intermediate transfer belt 7 of the intermediate transfer belt device 8. Similarly to the color image, this monochrome image is also transferred from the intermediate transfer belt 7 to the recording sheet and fixed on the recording sheet.

  Further, in the case of forming not only the front (front) surface of the recording sheet but also both sides, the recording sheet is fixed on the surface of the recording sheet by the fixing device 12, and then the recording sheet is discharged on the sheet conveying path S. In the middle of the conveyance, the paper discharge roller 17 is stopped and then reversely rotated, the recording sheet is passed through the reversing path Sr, the recording sheet is reversed, and the recording sheet is guided to the registration roller 14 again. Similarly to the front surface of the recording sheet, an image is recorded and fixed on the back surface of the recording sheet, and the recording sheet is discharged to the paper discharge tray 15.

  FIG. 2 is a schematic side view showing a state in which the pressure roller 32 is in pressure contact with the fixing roller 31 in the fixing device 12 according to the present embodiment.

  In the fixing device 12 of the present embodiment, as shown in FIG. 2, fixing in which a recording sheet is sandwiched between the fixing roller 31 and the pressure roller 32 with the pressure roller 32 being in pressure contact with the fixing roller 31. A nip area N is formed, and the recording sheet is heated and pressed through the fixing nip area N while the fixing roller 31 is driven to rotate in the direction of the arrow and the pressure roller 32 is driven to rotate. The image is melted, mixed, and pressed, and thermally fixed to the recording sheet.

  Specifically, the fixing roller 31 is a three-layered roller in which an elastic layer is provided on the outer surface of the core metal and a release layer is formed on the outer surface of the elastic layer. For the core metal, for example, a metal such as iron, stainless steel, aluminum, copper, or an alloy thereof can be used. Silicon rubber can be used for the elastic layer, and fluorine resin such as PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) or PTFE (polytetrafluoroethylene) can be used for the release layer. Can do.

  Inside the fixing roller 31 (inside the cored bar), a heat source (here, a halogen heater lamp) 33 for heating the roller 31 is provided.

  Similarly to the fixing roller 31, the pressure roller 32 is also composed of a core metal made of metal such as iron, stainless steel, aluminum, copper, or an alloy thereof, an elastic layer such as silicon rubber on the surface of the core metal, and further thereon. The roller has a three-layer structure composed of a release layer such as PFA or PTFE.

  Here, for example, when a thick recording sheet formed in a bag shape like an envelope is fixed with a pressing force suitable for fixing a general plain paper, a conveyance failure such as a wrinkle is generated. In order to avoid this, in the fixing device 12 of the present embodiment, when the fixing roller 31 and the pressure roller 32 are stopped, the fixing roller 31 is moved in a direction in which the pressure roller 32 is released from the pressure contact with the fixing roller 31. The pressure contact force between the pressure roller 32 and the pressure roller 32 is a predetermined first pressure contact force (for example, a plain paper recording sheet pressure contact force) and a predetermined second pressure contact force weaker than the first pressure contact force (for example, like an envelope). The recording sheet pressure).

  FIG. 8 is a perspective view schematically showing the configuration of both ends of the pressure roller 32 in the fixing device of the present embodiment. 3 and 4 are schematic cross-sectional views showing the configuration of one end side (right front side in FIG. 8) of the fixing roller 31 and the pressure roller 32 in the fixing device 12 in the axial direction. 3 and 4 are different in cross-sectional position, and the configuration of FIG. 4 is located outside the configuration of FIG.

  As shown in FIG. 8, body frames 89a and 89b of the fixing device 12 are arranged on both sides of the pressure roller 32, and both ends of the shaft 31a of the fixing roller 31 are pivotally supported by these body frames 89a and 89b.

  As shown in FIGS. 3 and 4, the fixing device 12 includes a fixing roller 31, a pressure roller 32, and a pressure contact device 100 that is an example of a pressure contact unit that presses the pressure roller 32 toward the fixing roller 31. And a pressure release device 200 which is an example of a pressure release unit that releases the pressure contact of the pressure roller 32 to the fixing roller 31 by the pressure device 100, and a fixing nip region between the fixing roller 31 and the pressure roller 32. A recording sheet is sandwiched between N and conveyed.

[About pressure welding equipment]
In this embodiment, the pressure welding device 100 includes a displacement support member (here, a displacement frame) 71 and a biasing member (here, a coil spring 74). The fixing roller 31 is pivotally supported by a main body frame (see main body frames 89a and 89b in FIG. 8) of the fixing device 12 so as to be rotatable about an axis, and is rotated by a rotational driving force transmitted from a driving source (not shown). It has become.

  The displacement frame 71 pivotally supports the pressure roller 32 so as to be rotatable about its axis, and is in a direction in which the pressure roller 32 is pressed against the fixing roller 31 or a direction in which the pressure roller 32 is released from the pressure contact with the fixing roller 31. It will be displaced. Specifically, the displacement frame 71 supports the shaft 32a of the pressure roller 32 via a bearing (not shown), and pivotally supports the fixing device 12 main body along the axial direction of the pressure roller 32. The shaft 71a is supported so as to be swingable around the shaft 71a (more specifically, the shaft 71a supported on the main body frame side of the fixing device 12).

  The displacement frame 71 is urged by a coil spring 74 in a direction in which the pressure roller 32 is pressed against the fixing roller 31. Specifically, hooks 74 a at both ends of the coil spring 74 are respectively hooked on a pin 72 positioned radially outward centering on the shaft 71 a of the displacement frame 71 and a pin 73 of the main body frame, and the coil spring 74 causes the displacement frame 71 to The pin 72 is attracted toward the pin 73 of the main body frame, whereby the displacement frame 71 is urged toward the fixing roller 31 around the shaft 71a, and the pressure contact force of the pressure roller 32 to the fixing roller 31 is increased. The first pressure contact force is used.

[Pressure release device]
In this embodiment, the pressure release device 200 includes a pressure release cam (eccentric cam) 76, a one-way clutch 77, a swing lever 78, and a swing cam (eccentric cam) 81. The automatic pressure contact release means that automatically switches between the first pressure contact force of the pressure roller 32 to the fixing roller 31 and the second pressure contact force released from the first pressure contact force.

  The pressure release cam 76 is in sliding contact with the displacement frame 71. The one-way clutch 77 is provided on the shaft 76 a of the pressure release cam 76 along the axial direction of the pressure roller 32. The swing lever 78 is connected to the one-way clutch 77 and is urged so as to be in sliding contact with the swing cam 81. The swing cam 81 is rotated in one direction by receiving a rotational driving force from a driving source (not shown).

  In the pressure release device 200, when the swing cam 81 is rotated in one direction by the rotational driving force from the drive source, the swing lever 78 slidingly contacting the swing cam 81 repeatedly swings, and the swing lever The swing of 78 is transmitted as one-way intermittent rotation to the pressure release cam 76 via the one-way clutch 77, and the displacement frame 71 is pushed out against the urging force of the coil spring 74 by the pressure release cam 76. 71 is displaced together with the pressure roller 32 to release the pressure contact force of the pressure roller 32 to the fixing roller 31 from the first pressure contact force to the second pressure contact force.

  Specifically, a roller 75 is provided on the outer side in the radial direction around the axis 71 a of the displacement frame 71. A shaft 76a is supported on the main body frame side of the fixing device 12, and the shaft 76a protrudes through an opening (not shown) of the displacement frame 71 outside the main body frame, and a portion of the protruding shaft 76a. A pressure release cam 76 is fixed to the head. The roller 75 provided on the displacement frame 71 is brought into pressure contact with the pressure release cam 76 by the pin 72 of the displacement frame 71 being attracted by the coil spring 74 toward the pin 73 of the main body frame.

  A one-way clutch 77 is provided on the shaft 76 a of the pressure release cam 76. A swing lever 78 is connected and fixed to the one-way clutch 77. Here, the one-way clutch 77 is juxtaposed outside the pressure release cam 76 in the axial direction. The one-way clutch 77 is interposed between the swing lever 78 and the shaft 76 a of the pressure release cam 76, and only the rotation of the swing lever 78 in the other direction (for example, clockwise in the figure) is via the one-way clutch 77. When the swing lever 78 is transmitted to the shaft 76a and rotates in one direction (for example, counterclockwise in the figure), the one-way clutch 77 is idled so that this one-way rotation is not transmitted to the shaft 76a. . The shaft 76a of the pressure release cam 76 is provided with a torque limiter 79 (see also FIG. 8) inside the main body frame 89a. The torque limiter 79 applies a constant load to the shaft 76a of the pressure release cam 76 to suppress the rotational force, and brakes and decelerates the rotational speed of the shaft 76a.

  The swing lever 78 is biased in a direction toward the swing cam 81 about a shaft 76a of the pressure release cam 76 by a biasing means (for example, a spring) (not shown).

  Further, on the main body frame side of the fixing device 12, a shaft 83 along the axial direction of the fixing roller 31 is supported so as to be rotatable about the axis. A rocking cam 81 and a rocking gear 82 are pivotally supported by the shaft 83 so as not to rotate relative to each other. The rocking gear 82 is engaged with a drive gear 84 fixed to the shaft 31 a of the fixing roller 31. Thus, when the fixing roller 31 is rotationally driven, the drive gear 84 is rotated, and the swinging gear 82 is rotated together with the swinging cam 81.

  In FIG. 4, the control lever 91 is rotatably supported around a shaft 91 a along the axial direction of the fixing roller 31 with respect to the main body frame side of the fixing device 12. 91 b protrudes inward along the axial direction of the fixing roller 31. The swing lever 78 is provided with a frame portion 78 a that protrudes outward along the axial direction of the fixing roller 31 and extends along the outer peripheral edge. The pin 91b of the control lever 91 is located inside the frame portion 78a. That is, the frame portion 78a of the swing lever 78 is edged by a rib, and the pin 91b at one end of the control lever 91 is hooked on the rib.

  A clamping part 91c is projected from the opposite side of the pin 91b with the shaft 91a of the control lever 91 therebetween. The clamping portion 91c is connected to a plunger 92 of a solenoid 93 that is arranged so as to be orthogonal to the shaft 91a. Specifically, the clamping portion 91c has a “U” -shaped engagement portion as viewed from the top at the tip, and the constricted portion 92a of the plunger 92 is formed in the “U” -shaped engagement portion. It is designed to be pinched. The plunger 92 is inserted into a hole provided in the solenoid 93 so as to be movable along the hole. When the solenoid 93 is not operated, the plunger 92 is urged in a protruding direction by a spring (not shown). While projecting from the solenoid 93, the plunger 92 is pulled into the solenoid 93 against the biasing force of the spring when the solenoid 93 is activated.

  FIG. 4 shows a state of the control lever 91 in which the solenoid 93 is in an inoperative state. As shown in FIG. 4, when the solenoid 93 is deactivated, the plunger 92 protrudes from the solenoid 93, and the holding portion 91c of the control lever 91 that holds the constricted portion 92a of the plunger 92 is pushed out, so that the control lever 91 pivots about the shaft 91a in the direction in which the pin 91b engages with the frame portion 78a of the swing lever 78, and the pin 91b engages with the frame portion 78a. That is, the pin 91b is hooked inside the frame portion 78a and rotates the swing lever 78 in a direction away from the swing cam 81 against a biasing force by a spring (not shown). As a result, the sliding contact edge 78 b of the swing lever 78 with the swing cam 81 is separated from the outer peripheral surface of the swing cam 81.

  When the sliding contact edge 78b of the swing lever 78 is thus separated from the outer peripheral surface of the swing cam 81, the fixing roller 31 is driven to rotate, the drive gear 84 is rotated, and the swing gear 82 is rotated. Even when the rotation lever 81 is rotated, the stop state of the swing lever 78 can be maintained.

  FIG. 5 is a diagram illustrating a state of the control lever 91 in which the solenoid 93 is in the activated state in the pressure release device 200.

  In FIG. 5, when the solenoid 93 is activated and the plunger 92 is pulled into the solenoid 93, the holding portion 91 c of the control lever 91 that holds the constricted portion 92 a of the plunger 92 is drawn, and the control lever 91 is pivoted. The pin 91b rotates in a direction to release the engagement with the frame 78a of the swing lever 78 around the center 91a, and the engagement with the frame 78a of the pin 91b is released. That is, the swing lever 78 is rotated about the shaft 76a of the pressure release cam 76 by a biasing force of a spring (not shown) to contact the swing cam 81. As a result, the sliding contact edge 78 b of the swing lever 78 contacts the outer peripheral surface of the swing cam 81.

  In this state, when the fixing roller 31 is driven to rotate, the drive gear 84 rotates, and the swinging gear 82 rotates together with the swinging cam 81, the sliding contact edge 78b of the swinging lever 78 is the outer peripheral surface of the swinging cam 81. To slide. As a result, the swing lever 78 swings around the shaft 76a.

  6 and 7 are schematic cross-sectional views showing the configuration of one end side in the axial direction of the fixing roller 31 and the pressure roller 32 in the fixing device 12, and FIG. 6 is a state in which the pressure roller 32 is pressed against the fixing roller 31. FIG. FIG. 7 is a diagram illustrating a state in which the pressure roller 32 is released from the pressure contact with the fixing roller 31. 6 and 7 show cross sections outside of FIG.

  As shown in FIG. 6, the pressure release device 200 further includes a cam 94 and a pressure control sensor 95.

  The cam 94 is supported on the shaft 76a of the pressure release cam 76 so as not to be relatively rotatable. As a result, the cam 94 can rotate together with the shaft 76 a of the pressure release cam 76. Here, the cam 94 is juxtaposed outside the one-way clutch 77 and the swing lever 78 in the axial direction. Then, the cam 94 is positioned in the circumferential direction by the pressure control sensor 95, and thus the pressure contact state or the pressure release state of the pressure roller 32 with respect to the fixing roller 31 (that is, the pressure roller 32 is in contact with the fixing roller 31 in the first pressure contact state). Whether it is pressed by force or whether it is pressed by the second pressing force).

  Specifically, the pressure control sensor 95 includes a light emitting element 95a that emits light, a light receiving element 95b that receives light from the light emitting element 95a, and a light that is displaced by the rotation of the cam 94 to light from the light emitting element 95a to the light receiving element 95b. A detection member 96 configured to be able to take an incident posture that allows the incidence of light and a blocking posture that blocks light from the light emitting element 95a to the light receiving element 95b. And the position of the circumferential direction of the cam 94 can be detected now by detecting with the light receiving element 95b.

  More specifically, the cam 94 is formed by forming a notch 94a in a part of a disk, and the detection member 96 of the pressure control sensor 95 is rotated by a shaft 96a along the axial direction of the pressure roller 32. It is supported freely. The detection member 96 is provided with a fan-shaped sliding contact portion 96b on the radially inner side centered on the shaft 96a and an arc wall portion 96c on the radially outer side centered on the shaft 96a.

  As shown in FIG. 6, when the outer peripheral surface on the short diameter side of the pressure release cam 76 faces the roller 75, the cam 94 has a notch portion 94a with the shaft 76a in between and a sliding contact portion 96b of the detection member 96. It is designed to face in the opposite direction. Then, the outer peripheral surface of the cam 94 pushes up the sliding contact portion 96b, and the arc wall portion 96c of the detection member 96 moves between the light emitting element 95a and the light receiving element 95b of the pressure control sensor 95, and from the light emitting element 95a to the light receiving element. The light irradiated to 95b is interrupted.

  On the other hand, as shown in FIG. 7, when the outer peripheral surface on the long diameter side of the pressure release cam 76 is pressed against the roller 75, the cam 94 is arranged so that the cutout portion 94 a faces the sliding contact portion 96 b of the detection member 96. It has become. Then, the detection member 96 rotates by its own weight around the shaft 96a, the sliding contact portion 96b moves to the notch portion 94a, and the arc wall portion 96c of the detection member 96 moves from between the light emitting element 95a and the light receiving element 95b. By retracting, the light irradiation from the light emitting element 95a to the light receiving element 95b is allowed.

  Accordingly, the pressure control sensor 95 presses the circumferential position of the cam 94 and thus the pressure roller 32 against the fixing roller 31 with the first pressure contact force based on the light reception output of the light receiving element 95b, or the first It is possible to detect whether the pressure contact is made with two pressure contact forces.

  FIG. 8 is a perspective view schematically showing a part of the pressure contact device 100 and the pressure release device 200 in the fixing device 12.

  As shown in FIG. 8, body frames 89a and 89b are disposed on both sides of the pressure roller 32, and shafts 31a (not shown in FIG. 8) of the fixing roller 31 are disposed on these body frames 89a and 89b. Both ends are pivotally supported. Further, the displacement frame 71 is disposed outside the one main body frame 89a, and the displacement frame 71 is also disposed outside the other main body frame 89b. Both ends of the shaft 32a of the pressure roller 32 protrude outside the main body frames 89a and 89b and are supported by the respective displacement frames 71, and each displacement frame 71 is urged by a coil spring 74 (not shown in FIG. 8). The pressure roller 32 is in pressure contact with the fixing roller 31.

  In addition, a pressure release cam 76 is provided on each of the main body frames 89a and 89b, and a roller 75 that presses against the pressure release cam 76 is provided on the displacement frame 71 side. The shaft 76a of the pressure release cams 76 on both sides is a common one, and the pressure release cams 76 on both sides are rotated by the rotation of the shaft 76a.

  Further, as described above, the torque limiter 79 is provided inside the one body frame 89 a of the shaft 76 a of the pressure release cam 76. Further, a one-way clutch 97 for preventing reverse rotation is fixed inside the main body frame 89b, and a shaft 76a of the pressure release cam 76 is passed through the one-way clutch 97 for preventing reverse rotation. The one-way clutch 97 for preventing reverse rotation is idle when the one-way clutch 77 on the main body frame 89a side transmits rotation in the other direction to the shaft 76a, and enables rotation in the other direction of the shaft 76a. When the shaft 76a is about to rotate by being dragged by one-way clutch 77 idling around one direction, the rotation of the shaft 76a around one direction is prohibited. Accordingly, in the one-way clutch 77 on the main body frame 89a side and the one-way clutch 97 for preventing reverse rotation on the inner side of the main body frame 89b, the direction of transmitting rotation and the direction of idling are reversed.

[Operation of pressure release device]
In performing the fixing operation in the fixing device 12 described above, as shown in FIG. 5, the solenoid 93 is activated and the plunger 92 is pulled into the solenoid 93. Then, the engagement of the pin 91b at one end of the control lever 91 with the frame portion 78a of the swing lever 78 is released, and the swing lever 78 rotates toward the swing cam 81, and a spring biasing force (not shown) is applied. As a result, the swing lever 78 contacts the swing cam 81. The sliding contact edge 78 b of the swing lever 78 is brought into contact with the outer peripheral surface of the swing cam 81.

  FIG. 9 is a diagram illustrating the operation of the swing lever 78 and the pressure release cam 81. FIG. 9A shows an operation of transition from the pressure contact state of the first pressure contact force of the pressure roller 32 to the fixing roller 31 to the pressure release state of the second pressure contact force, and FIG. The pressure release state of the second pressure contact force of the pressure roller 32 to the fixing roller 31 is shown.

  When the fixing roller 31 is driven to rotate with the sliding contact edge 78b of the swing lever 78 in contact with the outer peripheral surface of the swing cam 81, the drive gear 84 rotates and meshes with the drive gear 84. The swinging gear 82 rotates together with the swinging cam 81, whereby the swinging lever 78 swings around the shaft 76a.

  At this time, only the rotation of the swing lever 78 in the other direction is transmitted to the shaft 76a of the pressure release cam 76 via the one-way clutch 77, and the rotation in the other direction is intermittently transmitted to the shaft 76a of the pressure release cam 76. Is done. As a result, as shown in FIG. 9A, the pressure release cam 76 rotates intermittently in the other direction.

  Further, when the swing lever 78 rotates in one direction and the one-way clutch 77 rotates idly, the one-way clutch 97 for preventing reverse rotation on the main body frame 79b side in FIG. Rotation is prohibited. Thereby, the shaft 76a of the pressure release cam 76 does not rotate in one direction by being dragged by the rotation in one direction of the one-way clutch 77, and the pressure release cam 76 surely performs intermittent rotation in the other direction. be able to.

  In the fixing device 12 having the above-described configuration, when a fixing operation is performed on a general plain paper recording sheet, the solenoid 93 is inactivated and the plunger 92 is moved from the solenoid 93 as shown in FIG. The plunger 92 pushes up the clamping portion 91c of the control lever 91, and the pin 91b of the control lever 91 moves downward. The swing lever 78 is rotated clockwise by this pin 91b, and the right side of the swing lever 78 The sliding contact edge 78 b is separated from the outer peripheral surface of the swing cam 81.

  As shown in FIG. 3, the circumferential surface on the short diameter side of the pressure release cam 76 faces the roller 75 of the displacement frame 71, and the pressure roller 32 is in pressure contact with the fixing roller 31. The fixing nip region N1 between the pressure roller 32 and the fixing roller 31 at this time is a nip region with the first pressure contact force suitable for fixing ordinary plain paper. The recording sheet can be fixed.

  That is, in this state, the fixing roller 31 of the fixing device 12 is driven to rotate, the pressure roller 32 is driven to rotate, and the recording sheet is passed through the fixing nip region N1 between the rollers 31 and 32 to be stably heated. And pressurized.

  At this time, although the driving gear 84 rotates together with the fixing roller 31 and the swinging gear 82 and the swinging cam 81 rotate, the swinging lever 78 is separated from the outer peripheral surface of the swinging cam 81, so that the swinging lever 78 stopped states are maintained. For this reason, the contact / separation operation | movement of each roller 31 and 32 which is mentioned later is not performed.

  Therefore, when the fixing roller 31 is rotated in a state where the solenoid 93 is in the non-operating state and the sliding contact edge 78b on the right side of the swing lever 78 is separated from the outer peripheral surface of the swing cam 81, each roller 31, Thus, the fixing of the recording sheet of plain paper by 32 can be performed stably.

  On the other hand, when a thick recording paper such as an envelope is fixed, first, as shown in FIG. 5, the solenoid 93 is activated, the plunger 92 is pulled into the solenoid 93, and the control lever 91 is moved. It rotates counterclockwise about the shaft 91a, the pin 91b of the control lever 91 rises, and the swing lever 78 can rotate clockwise and counterclockwise, and a spring (not shown) The oscillating lever 78 rotates counterclockwise by the urging force, and the sliding contact edge 78 b on the right side of the oscillating lever 78 is brought into contact with the outer peripheral surface of the oscillating cam 81.

  In this state, when the fixing roller 31 of the fixing device 12 is driven to rotate, the drive gear 84 rotates, the swinging gear 82 and the swinging cam 81 rotate, and come into contact with the outer peripheral surface of the swinging cam 81. The sliding contact edge 78b on the right side of the swing lever 78 reciprocates up and down, and the swing lever 78 reciprocally rotates clockwise and counterclockwise around the shaft 76a of the pressure release cam 76.

  At this time, only the clockwise rotation of the swing lever 78 is transmitted to the shaft 76a of the pressure release cam 76 via the one-way clutch 77, and the clockwise rotation is intermittently transmitted to the shaft 76a of the pressure release cam 76. Is done. As a result, as shown in FIG. 9A, the pressure release cam 76 rotates intermittently clockwise. At this time, the pressure release cam 76 rotates slowly and reliably because a constant load is applied to the shaft 76a by the torque limiter 79 and the rotational force is suppressed. That is, even if a pressing force that gives a rotational force from the displacement frame 71 by the urging force of the coil spring 74 is applied to the pressure release cam 76, the load is applied to the shaft by the torque limiter 79. It does not rotate beyond being fed out by the one-way crack 77.

  Further, when the swing lever 78 rotates counterclockwise and the one-way clutch 77 rotates idly, the counterclockwise rotation of the shaft 76a of the pressure release cam 76 is caused by the one-way clutch 97 for preventing reverse rotation on the main body frame 89b side in FIG. Since the rotation around is prohibited, the pressure release cam 76 is intermittently rotated clockwise without being dragged by the counterclockwise rotation of the one-way clutch 77 and the shaft 76a of the pressure release cam 76 rotating counterclockwise. Rotate surely to go.

  Then, as shown in FIG. 9B, when the pressure release cam 76 rotates 180 degrees clockwise, the circumferential surface on the long diameter side of the pressure release cam 76 projects the roller 75 of the displacement frame 71, and the displacement frame 71 The pressure roller 32 moves slightly away from the fixing roller 31 by rotating counterclockwise around the shaft 71a. That is, the pressure roller 32 operates so as to reduce the pressing force against the fixing roller 31. As a result, the fixing nip area N2 between the pressure roller 32 and the fixing roller 31 is a nip area with the second pressure contact force suitable for fixing a thick recording sheet, so that the thick recording sheet is stabilized. Can be established. .

  By the way, as shown in FIG. 9B, when the pressure release cam 76 rotates 180 degrees clockwise to project the roller 75, the pressure release cam 76 moves the displacement frame 71 and the roller 75 from the opposite direction. Thus, the biasing force (contraction force) of the coil spring 74 is received, and this biasing force is applied to the pressure release cam 76 as a rotational force.

  In this case, when the torque limiter 79 serving as a speed reduction means is not provided, when the pressure release cam 76 reaches the pressure release position (position shown in FIG. 9B) that most protrudes the displacement frame 71, the coil spring 74 On the contrary, the pressure applied to the displacement frame 71 by the urging force acts as a rotational force of the pressure release cam 76, and the pressure release cam 76 passes through the pressure release position shown in FIG. 9B and rotates clockwise. There is a possibility. When the pressure release cam 76 passes through the pressure release position shown in FIG. 9B and rotates clockwise, the displacement frame 71 and the pressure spooler 32 are slightly displaced back to the fixing roller 31 side. Therefore, the pressure contact force in the fixing nip area N slightly increases. For this reason, the pressing force in the fixing nip region N is slightly higher than the second pressing force optimum for fixing a thick recording sheet such as an envelope, so that fixing failure may occur. On the other hand, as in the present invention, a torque limiter 79 is provided on the shaft 76a of the pressure release cam 76 so that a constant load is always applied to the shaft 76a. Even when a thick recording sheet is fixed, stable fixing performance can be obtained.

  Further, as shown in FIG. 3, when the circumferential surface on the short diameter side of the pressure release cam 76 faces the roller 75 of the displacement frame 71 and the pressure roller 32 is in pressure contact with the fixing roller 31, it is shown in FIG. As described above, the notch 94a of the cam 94 is directed downward, and the circumferential surface of the cam 94 pushes up the sliding contact portion 96b of the detection member 96, so that the arc wall portion 96c of the detection member 96 is connected to the light emitting element 95a of the pressure control sensor 95. Moving to between the light receiving elements 95b, the light emitting element 95a and the light receiving element 95b are blocked.

  Further, as shown in FIG. 9B, the circumferential surface on the long diameter side of the pressure release cam 76 projects the roller 75 of the displacement frame 71, and the displacement frame 71 rotates and moves counterclockwise around the shaft 71a. When the pressure roller 32 moves in a direction slightly away from the fixing roller 31, the cam 94 also rotates 180 degrees as shown in FIG. 7, and the notch 94a of the cam 94 faces upward, and the detection member The sliding contact part 96b of 96 moves to the notch part 94a, the detection member 96 rotates around the axis 96a, the arc wall part 96c of the detection member 96 comes off between the light emitting element 95a and the light receiving element 95b, and the light emitting element 95a. And the light receiving element 95b are opened.

  Therefore, the rotation angle of the cam 94 and the pressure release cam 76 is detected based on the light reception output of the light receiving element 95b of the pressure control sensor 95, and the pressure roller 32 is generally used with respect to the fixing roller 31 from the rotation angle. Whether the fixing nip region N1 is formed with a first pressing force suitable for fixing a recording sheet of plain paper, or the fixing nip region N2 is formed with a first pressing force suitable for fixing a thick recording sheet. Can be determined.

  Furthermore, it is possible to control the contact / separation operation of each of the rollers 31 and 32 based on such a determination result.

  For example, after determining that the pressure roller 32 is in contact with the fixing roller 31 based on the light receiving output of the light receiving element 95 b of the pressure control sensor 95, the solenoid 93 is activated to slide the right side of the swing lever 78. With the edge 78b in contact with the outer peripheral surface of the swing cam 81, the fixing roller 31 of the fixing device 12 is driven to rotate, the swing cam 81 is rotated, and the swing lever 78 is swung to The release cam 76 is intermittently rotated clockwise. Then, based on the light receiving output of the light receiving element 95 b of the pressure control sensor 95, the outer peripheral surface on the longer diameter side of the pressure release cam 76 projects the roller 75 of the displacement frame 71, so that the pressure roller 32 is thicker than the fixing roller 31. The pressure release cam 76 is rotated until it is determined that the fixing nip region N2 is formed with the second pressure contact force suitable for fixing the recording sheet. Thus, the rollers 31 and 32 can be separated from each other until a fixing nip region suitable for fixing a thick recording sheet is obtained.

  Further, when shifting from the fixing operation of the thick recording sheet to the fixing operation of the recording sheet of plain paper, the solenoid 93 is operated and the sliding contact edge 78 b on the right side of the swing lever 78 is brought into contact with the outer peripheral surface of the swing cam 81. In the contact state, the fixing roller 31 of the fixing device 12 is driven to rotate, the swing cam 81 is rotated, the swing lever 78 is swung, and the pressure release cam 76 is intermittently rotated clockwise. Resume. Based on the light reception output of the light receiving element 95b of the pressure control sensor 95, the pressure roller 32 is determined to be in pressure contact with the fixing roller 31 with the first pressure contact force that is the pressure contact force of the recording sheet of plain paper. Then, the pressure release cam 76 is rotated. Specifically, the circumferential surface on the short diameter side of the pressure release cam 76 again faces the roller 75 of the displacement frame 71, and the nip area between the pressure roller 32 and the fixing roller 31 is a general plain paper recording sheet. The pressure release cam 76 is rotated until it is pressed with a first pressing force suitable for fixing. Thereafter, the solenoid 93 is deactivated and the swing lever 78 is separated from the swing cam 81.

  As described above, in the fixing device 12 according to the present embodiment, the rotation driving force of the fixing roller 31 can be used to bring the rollers 31 and 32 into contact and separation without changing the rotation direction of the rollers 31 and 32. . For this reason, even if the driving motor of the fixing device 12 is used to drive the registration roller 14, the transport roller 13, or the photosensitive drum 3 or the developing device 2, the rollers and the photosensitive drum are reversed. It does not rotate.

  Further, it is not necessary to incorporate a one-way clutch into the gear unit that transmits the rotational driving force from the driving motor to the fixing roller 31 or the like, and the gear unit is not complicated.

  Further, since the swing lever 78 can be moved toward and away from the swing cam 81, during the fixing operation, the swing lever 78 is moved away from the swing cam 81 and the rollers 31 and 32 are moved toward and away from each other. Can be stopped. Therefore, the rotational drive of each roller 31 and 32 and the contact / separation operation | movement of each roller 31 and 32 can be switched and performed.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. It is understood.

1 is a schematic view of an internal configuration of an image forming apparatus to which an embodiment of a fixing device according to the present invention is applied, viewed from the side. 2 is a side view illustrating a schematic configuration of a roller portion of the fixing device according to the exemplary embodiment. FIG. 4 is a cross-sectional view illustrating a configuration on one end side of each roller in the fixing device of the present embodiment. FIG. 4 is a cross-sectional view showing a configuration of one end side of each roller in the fixing device of the present embodiment, and shows a cross section on the outer side than FIG. 3. FIG. 5 is a cross-sectional view showing the configuration of one end of each roller in the fixing device of the present embodiment, and is a view showing the operation of the control lever of FIG. 4. FIG. 5 is a cross-sectional view showing a configuration of one end side of each roller in the fixing device of the present embodiment, and shows a cross section on the outer side than FIG. 4. FIG. 7 is a cross-sectional view showing the configuration of one end side of each roller in the fixing device of the present embodiment, and is a view showing the operation of the cam of FIG. 6. FIG. 2 is a perspective view schematically showing a configuration of both ends of a pressure roller in the fixing device of the present embodiment. (A), (b) is sectional drawing which shows the structure of the one end side of each roller in the fixing device of this embodiment, and is a figure which shows operation | movement of the rocking lever and pressure release cam in FIG. It is explanatory drawing which shows an example of the conventional press-contact / pressure-contact cancellation | release mechanism of a fixing device.

Explanation of symbols

A Image forming apparatus B Document preparation apparatus D Image forming apparatus S Sheet conveyance path 1 Optical scanning device 2 (2a, 2b, 2c, 2d) Developing device 3 (3a, 3b, 3c, 3d) Photosensitive drum 4 (4a, 4b, 4c, 4d) Cleaner device 5 (5a, 5b, 5c, 5d) Charger 7 Intermediate transfer belt 8 Intermediate transfer belt device 10 Paper feed tray 11 Secondary transfer device 12 Fixing device 15 Paper discharge tray 31 Fixing roller (first roller) 1 roller)
32 Pressure roller (second roller)
41 Document setting tray 44 Pickup roller 51 Document guide 52 Reading glass 53 First scanning unit 54 Second scanning unit 55 Imaging lens 56 CCD
71 Displacement frame 74 Coil spring 75 Roller 76 Pressure release cam 77 One-way clutch 78 Oscillating lever 79 Torque limiter 81 Oscillating cam 84 Drive gear 91 Control lever 92 Plunger 93 Solenoid 94 Cam 95 Pressure control sensor 97 One-way clutch 100 for preventing reverse rotation Pressure welding device 200 Pressure welding release device

Claims (4)

Pressure-contacting means for pressing the second roller against the first roller fixed on the shaft, pressure-contact / pressure-contact releasing switching means for switching between pressure-contacting and pressure-releasing to the first roller by the pressure-contacting means, and the first and second rollers In a fixing device comprising a driving means for rotating
A fixing device, comprising: a decelerating unit that applies braking to a switching speed when the second roller is switched from the press release state to the press contact state by the press contact / pressure release switching unit. The fixing device according to claim 1,
The pressure contact / pressure contact release switching means pivotally supports the second cam and a swing cam that rotates in one direction upon receiving a rotational driving force from the drive means, and the second roller with respect to the first roller. A displacement support member that is displaced so as to be in contact with and away from, a pressure release cam that is slidably contacted with the displacement support member, a one-way clutch provided on a shaft of the pressure release cam, and the swing cam connected to the one-way clutch And a swing lever urged to slidably contact
When the rocking cam is rotated in one direction by the rotational driving force of the driving means, the rocking lever slidingly contacting the rocking cam repeatedly rocks, and the rocking lever rocks the one-way clutch. Is transmitted to the pressure release cam as one-way intermittent rotation, and the displacement support member is ejected against the pressure contact force of the pressure contact means by the rotation of the pressure release cam. When the second roller is displaced, the second roller operates so as to reduce the pressure contact force with respect to the first roller, and the displacement support member is pressed by the pressure contact means by the rotation of the pressure release cam. When the displacement support member and the second roller are displaced by being pulled by each other, the second roller operates to increase the pressure contact force with respect to the first roller. ,
The fixing device according to claim 1, wherein the speed reducer is provided so as to brake the rotational speed of the pressure release cam. The fixing device according to claim 2,
The fixing device, wherein the speed reducing means is a torque limiter provided on a shaft of the pressure release cam.   An image forming apparatus comprising the fixing device according to any one of claims 1 to 3.

Images