JP5383941B2 - IH fixing device - Google Patents

Description

  The present invention relates to a fixing device that performs a fixing process on an image-transferred sheet by an IH (induction heating) method.

  The fixing device in the image forming apparatus includes a fixing roller and a pressure roller, and the toner image is applied to the sheet by passing the sheet on which the toner image is transferred to a fixing nip formed by these rollers and applying heat and pressure. To fix. In such a fixing device, an IH fixing device employing induction heating as a method for generating heat is known. The IH fixing device includes an IH unit including an induction heating coil for generating magnetic flux and a core member for forming a magnetic path, and a fixing roller having a heating roller (or a heating belt) that is induction-heated by the IH unit. Including units.

  The fixing unit may need to be replaced due to factors such as deterioration over time. In this case, since it is uneconomical to replace the entire IH fixing device even though there is no problem with the IH unit, the IH unit and the fixing unit have separate structures. That is, the IH unit is mounted on the apparatus main body side of the image forming apparatus, and the fixing unit is detachable from the apparatus main body. A problem with these separate structures is how to keep the distance relationship between the induction heating coil and the heating roller constant before and after the fixing unit is attached and detached. When the distance between the two changes, the induction heating effect changes, and the heating roller cannot accurately generate the desired fixing heat. For this reason, in this type of IH fixing device, a positioning mechanism that can keep the distance between the induction heating coil and the heating roller constant is attached (for example, Patent Documents 1 and 2).

  By the way, a fixing unit having a nip pressure adjusting mechanism for switching the nip pressure in the fixing nip portion between a normal pressure (high pressure) state and a pressure reduction (low pressure) state is known. The nip pressure adjusting mechanism is configured to set the nip pressure to a normal pressure state when passing a sheet having a normal paper thickness through the fixing nip portion, while passing a thick paper or a thin paper such as an envelope or to jam processing. The nip pressure is set to the reduced pressure state. The rotation shaft of the pressure roller is supported by the housing of the fixing unit so as to be able to shift in a direction toward or away from the fixing roller, and the nip pressure adjusting mechanism uses the driving force of the motor to switch the state. Do. By such switching of the nip pressure, generation of wrinkles or the like is suppressed when passing through the fixing nip portion for thick paper or thin paper, and the user can easily perform jam processing.

JP 2006-350054 A JP 2009-258457 A

  In the conventional apparatus, the pressure roller is selected as the roller to be shifted and moved in order to keep the positional relationship between the fixing roller (heating roller) and the induction heating coil constant. That is, if the fixing roller side does not move, the position relative to the induction heating coil is determined when the fixing unit is mounted at a predetermined position in the main body of the image forming apparatus. Accordingly, there is no occurrence of positional deviation when the fixing nip portion is formed.

Further, in the conventional apparatus, transmission of the rotational driving force from the driving means of the apparatus main body to each roller of the fixing unit is realized by driving input to the rotating shaft of the pressure roller. This is because the fixing roller is a sponge-like roller, whereas the pressure roller is a roller having higher rigidity than the fixing roller. When a fixing roller that easily causes a change in outer diameter is selected as a roller for driving input, the peripheral speed of the roller varies, and accurate roller rotation control cannot be performed.

  However, as described above, since the pressure roller is a roller whose rotational axis is shifted, a mechanical device is required for driving input to the pressure roller. In other words, the mechanism for driving input to the pressure roller whose axis moves along with the change of the pressure contact state and the release state becomes complicated, and the cost is increased.

  The present invention has been made in view of the above problems, and in an IH fixing device including an IH type fixing unit that can be attached to and detached from the apparatus main body, a mechanism for inputting a rotational driving force to the fixing unit is simplified. The purpose is to make it possible.

  An IH fixing device according to an aspect of the present invention includes a housing, a first rotating shaft, and a first roller that is rotatably supported by the housing in a state in which the first rotating shaft is not capable of shifting. A second roller that has two rotating shafts and is rotatably supported by the housing in a state in which the second rotating shaft is shiftable, and forms a fixing nip portion that performs a fixing process on the sheet together with the first roller; A first posture in which the second roller is brought into pressure contact with the first roller with a first pressure, and the second rotating shaft is shifted from the state of the first posture to shift the second roller from the first pressure. A nip pressure adjusting mechanism for changing the posture between the second posture pressed against the first roller with the reduced second pressure, and an induction heating unit for generating heat necessary for the fixing process; The second b Ra and the relative position between the induction heating unit, and a maintaining mechanism for maintaining a constant in both the time the first orientation and when the second position of the second roller.

  According to this configuration, the second roller is a roller that shifts, but the relative position between the second roller and the induction heating unit is kept constant by the maintenance mechanism regardless of the posture changing operation by the nip pressure adjustment mechanism. Be drunk. On the other hand, the first roller is supported by the housing in a state incapable of shift movement, and a rotational driving force is applied to the first roller from the drive mechanism. Therefore, it is possible to simplify the input mechanism of the rotational driving force while keeping the distance relationship of the second roller with respect to the induction heating unit constant.

  In the above configuration, when the first roller is formed of a material having a first hardness, and the second roller is formed of a material having a second hardness lower than the first hardness. Thus, the advantages of the present invention can be further enjoyed.

  According to this configuration, since the first roller has a higher hardness than the second roller, the first input is the drive input in that the peripheral speed of the outer periphery of the roller does not vary during rotational driving. The first rotation axis of the roller is suitable.

  In the above-described configuration, the housing includes a main body frame and a moving frame assembled to be movable with respect to the main body frame, the first roller is supported by the main body frame, and the second roller is the moving frame. The maintaining mechanism includes an engaging structure portion that positions and engages the induction heating unit and the moving frame, and an urging mechanism that applies an urging force to maintain the engagement to the induction heating unit. It is desirable to include.

  According to this configuration, the nip pressure adjusting mechanism can change the posture of the second roller with a simple configuration of moving the moving frame. Further, positioning of the induction heating unit and the moving frame can be realized with a simple configuration.

  In the above configuration, a third roller having a third rotating shaft, supported by the moving frame and induction-heated by the induction heating unit, and a belt member spanned between the second roller and the third roller, , May be further provided.

  According to this configuration, the heat of the third roller that is heated by induction is conveyed to the fixing nip portion by the belt member. In such a configuration, the distance relationship between the induction heating unit and the third roller is maintained constant.

  In this case, the induction heating unit includes an induction heating coil for generating magnetic flux, a core member for forming a magnetic path, and a holding member for holding the induction heating coil and the core member, and the moving frame Is provided with a shaft support portion that supports the third rotation shaft of the third roller, and both end portions of the third rotation shaft project from the moving frame, and the engagement structure portion is configured to perform the third rotation. It is desirable that the shaft comprises both end portions of the shaft and positioning recesses formed on the holding member and fitted with the both end portions of the third rotating shaft.

  According to this configuration, the induction heating unit is positioned using both ends of the third rotating shaft of the third roller. Since the third rotating shaft itself is used as a positioning member, the induction heating coil and the third roller can be accurately positioned.

  The said structure WHEREIN: The wall part arrange | positioned facing the said induction heating unit is further provided, and the said urging | biasing mechanism is a 1st spring seat with which the one end side of the said compression spring contact | abuts on a compression spring and the said wall part side And a second spring seat with which the other end side of the compression spring abuts on the induction heating unit side, and the induction heating unit can be moved following the movement of the moving frame.

  According to this configuration, the induction heating unit can be moved by following the movement of the moving frame using the biasing force of the compression spring. Therefore, even if the nip pressure adjusting mechanism executes the posture change of the second roller, the induction heating unit moves following the second roller by the biasing force.

  In this case, a duct member attached to the induction heating unit and forming a ventilation path for cooling the induction heating unit, a cooling duct provided in the wall portion and connected to the duct member, and the cooling duct It is desirable to further include a stretchable seal member disposed at a connecting portion between the air passage and the ventilation path.

  According to this configuration, the induction heating unit can be cooled, and even if the induction heating unit is moved by the compression spring, the airtightness of the ventilation path can be maintained by the elastic seal member.

  According to the present invention, in an IH fixing device including an IH fixing unit having a housing structure that can be attached to and detached from the apparatus main body, a mechanism for inputting a rotational driving force to the fixing unit can be simplified. Therefore, the structure of the apparatus can be simplified, and the size and cost of the IH fixing apparatus can be reduced.

1 is a cross-sectional view showing an internal structure of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a simplified diagram illustrating a state where the fixing unit (first housing) is detached from the apparatus main body (second housing). FIG. 2 is a cross-sectional view illustrating an internal structure of a fixing device according to an embodiment of the present invention. FIG. 3 is a partially broken perspective view of the fixing device. FIG. 3 is an exploded perspective view of the fixing device and its peripheral devices. FIG. 3 is an end perspective view of a fixing device showing a configuration of a nip pressure adjusting mechanism. FIG. 4 is a cross-sectional view of the fixing device for explaining the movement of the rotation shafts of the fixing roller and the heating roller. FIG. 5 is a cross-sectional view of the fixing device, for illustrating a configuration of a maintenance mechanism. (A) is a side view of the fixing device, and (B) is another side view for explaining the configuration of the maintenance mechanism.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing an internal structure of an image forming apparatus 1 according to an embodiment of the present invention. Here, a copying machine is illustrated as the image forming apparatus 1, but the image forming apparatus 1 may be a printer, a facsimile machine, or a multifunction machine having these functions as long as the IH fixing method is adopted. Good.

  The image forming apparatus 1 includes an apparatus main body 10 having a substantially rectangular parallelepiped housing structure, and an automatic document feeder 20 disposed on the apparatus main body 10. Inside the apparatus main body 10 are a reading unit 25 that optically reads a document image to be copied, an image forming unit 30 that forms a toner image on a sheet, and a fixing device 60 (IH fixing device) that fixes the toner image on the sheet. ), A sheet feeding unit 40 for storing sheets conveyed to the image forming unit 30, and a conveyance path 50 for conveying the sheet from the sheet feeding unit 40 to the sheet discharge port 10E via the image forming unit 30 and the fixing device 60. And a conveyance unit 55 having therein a sheet conveyance path constituting a part of the conveyance path 50 is accommodated.

  The right side surface 10 </ b> R of the apparatus main body 10 is provided with a main body cover 101 that is opened and closed when a unit such as the image forming unit 30 and the fixing device 60 is removed from the apparatus main body 10 during jam processing or maintenance. The main body cover 101 is rotatably attached to the apparatus main body 10 at the base end portion (lower end portion) (see also FIG. 2).

  The automatic document feeder 20 is rotatably attached to the upper surface of the apparatus body 10. The automatic document feeder 20 automatically feeds a document sheet to be copied toward a predetermined document reading position (position where the first contact glass 241 is assembled) in the apparatus body 10. On the other hand, when the user manually places the document sheet on a predetermined document reading position (position of the second contact glass 242), the automatic document feeder 20 is opened upward. The automatic document feeder 20 includes a document tray 21 on which a document sheet is placed, a document transport unit 22 that transports a document sheet via an automatic document reading position, and a document discharge in which a document sheet after reading is discharged. A tray 23.

The reading unit 25 is a first contact glass 241 for reading a document sheet automatically fed from the automatic document feeder 20 on the upper surface of the apparatus body 10 or a second contact glass for reading a manually placed document sheet. Through 242, the image of the original sheet is optically read. In the reading unit 25, a scanning mechanism including a light source, a movable carriage, a reflection mirror, and the like, and an image sensor are accommodated (not shown). The scanning mechanism irradiates the original sheet with light and guides the reflected light to the image sensor. The image sensor photoelectrically converts the reflected light into an analog electric signal. The analog electric signal is converted into a digital electric signal by an A / D conversion circuit and then input to the image forming unit 30.

  The image forming unit 30 performs a process of generating a full-color toner image and transferring it onto a sheet. Yellow (Y), magenta (M), cyan (C), and black (Bk) arranged in tandem. An image forming unit 32 including four units 32Y, 32M, 32C, and 32Bk for forming the respective toner images, an intermediate transfer unit 33 disposed adjacent to the image forming unit 32, and an intermediate transfer unit 33. And a toner replenishing section 34 disposed in the.

  Each of the image forming units 32Y, 32M, 32C, and 32Bk includes a photosensitive drum 321 and a charger 322, an exposure device 323, a developing device 324, a primary transfer roller 325, and a cleaning device disposed around the photosensitive drum 321. 326.

  The photosensitive drum 321 rotates about its axis, and an electrostatic latent image and a toner image are formed on its peripheral surface. As the photosensitive drum 321, a photosensitive drum using an amorphous silicon (a-Si) material can be used. The charger 322 uniformly charges the surface of the photosensitive drum 321. The exposure device 323 includes a laser light source and optical system devices such as a mirror and a lens, and forms an electrostatic latent image by irradiating the peripheral surface of the photosensitive drum 321 with light based on image data of a document image. .

  The developing device 324 supplies toner to the peripheral surface of the photosensitive drum 321 in order to develop the electrostatic latent image formed on the photosensitive drum 321. The developing device 324 is for a two-component developer and includes a stirring roller, a magnetic roller, and a developing roller. The stirring roller charges the toner by circulating and conveying the two-component developer while stirring. A two-component developer layer is carried on the circumferential surface of the magnetic roller, and a toner layer formed by the transfer of toner by a potential difference between the magnetic roller and the developing roller is carried on the circumferential surface of the developing roller. The The toner on the developing roller is supplied to the peripheral surface of the photosensitive drum 321 and the electrostatic latent image is developed.

  The primary transfer roller 325 forms a nip portion with the photosensitive drum 321 across the intermediate transfer belt 331 provided in the intermediate transfer unit 33, and the toner image on the photosensitive drum 321 is primary transferred onto the intermediate transfer belt 331. To do. The cleaning device 326 includes a cleaning roller and the like, and cleans the peripheral surface of the photosensitive drum 321 after the toner image is transferred.

  The intermediate transfer unit 33 includes an intermediate transfer belt 331, a driving roller 332, a driven roller 333, a tension roller 334, and a backup roller 336. The intermediate transfer belt 331 is an endless belt that is stretched over the rollers 332, 333, 334, and 336 and the primary transfer roller 325, and the intermediate transfer belt 331 has toner from a plurality of photosensitive drums 321. The image is transferred to the same place and transferred (primary transfer).

  The drive roller 332 is a roller formed by molding sponge-like conductive rubber into a cylindrical shape on a metal conductive shaft, and a driving force for rotating the intermediate transfer belt 331 is applied. A secondary transfer roller 35 is disposed to face the peripheral surface of the drive roller 332. The secondary transfer roller 35 is also a conductive roller. A nip portion between the driving roller 332 and the secondary transfer roller 35 becomes a secondary transfer portion 35A that transfers a full-color toner image overcoated on the intermediate transfer belt 331 to a sheet.

  A secondary transfer bias potential having a polarity opposite to that of the toner image is applied to the secondary transfer roller 35, and the drive roller 332 is grounded. The driven roller 333 is a roller that is driven according to the rotation of the intermediate transfer belt 331, the tension roller 334 is a roller that applies a predetermined tension to the intermediate transfer belt 331, and the backup roller 336 is in the rotating direction of the intermediate transfer belt 331. A roller that bends the intermediate transfer belt 331 immediately upstream of the secondary transfer portion 35A.

  The toner supply unit 34 includes a yellow toner container 34Y, a magenta toner container 34M, a cyan toner container 34C, and a black toner container 34Bk. These toner containers 34Y, 34C, 34M, and 34Bk respectively store toner of each color, and are supplied to the developing devices 324 of the image forming units 32Y, 32M, 32C, and 32Bk corresponding to each color of YMCBk through a supply path (not shown). Supply toner of each color.

  The paper feed unit 40 includes two-stage paper feed cassettes 40A and 40B for storing sheets on which image forming processing is performed, and a paper feed tray 46 for manual paper feed. These paper feed cassettes 40A and 40B can be pulled out from the front of the apparatus body 10 toward the front. The paper feed cassettes 40 </ b> A and 40 </ b> B are cassettes provided for automatic paper feed, but the paper feed tray 46 for manual paper feed is provided on the right side surface 10 </ b> R of the apparatus main body 10. The paper feed tray 46 is attached to the main body cover 101 at its lower end so as to be freely opened and closed. When performing manual sheet feeding, the user opens the sheet feeding tray 46 as shown in the drawing and places a sheet thereon.

  The sheet feeding cassette 40A (40B) includes a sheet storage unit 41 that stores a sheet bundle formed by stacking a plurality of sheets, and a lift plate 42 that lifts up the sheet bundle for feeding. A pickup roller 43 and a roller pair of a paper feed roller 44 and a retard roller 45 are arranged on the upper right side of the paper feed cassette 40A (40B). By driving the pickup roller 43 and the paper feed roller 44, the uppermost sheet of the sheet bundle in the paper feed cassette 40A is fed out one by one and carried into the upstream end of the transport path 50. On the other hand, the sheet placed on the paper feed tray 46 is similarly carried into the conveyance path 50 by driving the pickup roller 461 and the paper feed roller 462.

  The conveyance path 50 includes a main conveyance path 50A that conveys a sheet from the paper feeding unit 40 to the exit of the fixing device 60 through the image forming unit 30, and a sheet that is printed on one side when performing duplex printing on the sheet. A reverse conveyance path 50B for returning to the image forming unit 30, a switchback conveyance path 50C for directing the sheet from the downstream end of the main conveyance path 50A to the upstream end of the reverse conveyance path 50B, and the downstream end of the main conveyance path 50A To a sheet discharge port 10E provided on the left side surface 10L of the apparatus main body 10 and a horizontal conveyance path 50D for conveying the sheet in the horizontal direction. Most of the horizontal conveyance path 50 </ b> D is configured by a sheet conveyance path provided inside the conveyance unit 55.

  A registration roller pair 51 is disposed on the upstream side of the main transfer path 50A from the secondary transfer portion 35A. The sheet that has been transported through the main transport path 50A comes into contact with the resist roller pair 51 in a stopped state and is temporarily stopped to perform skew correction. Thereafter, the registration roller pair 51 is rotationally driven by a drive motor (not shown) at a predetermined timing for image transfer, whereby the sheet is sent out to the secondary transfer portion 35A. In addition, a plurality of conveyance roller pairs 52 for conveying the sheet are arranged in the main conveyance path 50A. The same applies to the other transport paths 50B, 50C, and 50D.

  A paper discharge unit 530 having a paper discharge roller pair 53 is disposed adjacent to the left side of the transport unit 55 in FIG. The sheet discharge roller pair 53 feeds the sheet through a sheet discharge port 10E to a post-processing apparatus (not shown) that is connected to the apparatus body 10 on the left side surface 10L side of the apparatus body 10. In the image forming apparatus to which the post-processing apparatus is not attached, a sheet discharge tray is provided below the sheet discharge port 10E.

  The transport unit 55 is a unit that transports the sheet unloaded from the fixing device 60 to the sheet discharge port 10E. In the image forming apparatus 1 of the present embodiment, the fixing device 60 is disposed on the right side 10R side of the apparatus main body 10, and the sheet discharge port 10E is disposed on the left side 10L side of the apparatus main body 10 facing the right side 10R. Yes. Accordingly, the transport unit 55 transports the sheet in the horizontal direction from the right side surface 10R of the apparatus main body 10 toward the left side surface 10L.

  The fixing device 60 is an induction heating type fixing device that performs a fixing process for fixing a toner image on a sheet, and includes a heating roller 61 (third roller), a fixing roller 62 (second roller), and a pressure roller 63 (first roller). 1 roller), a fixing belt 64 (belt member), an induction heating unit 65, and a conveying roller pair 66. The fixing device 60 is disposed in a housing space 102 provided in the vicinity of the right side surface 10 </ b> R of the apparatus main body 10.

  As shown in FIG. 2, the above-described constituent members excluding the induction heating unit 65 are accommodated in a housing 600 and unitized as a fixing unit 60U. The fixing unit 60U can be attached to and detached from the apparatus main body 10. On the other hand, the induction heating unit 65 is attached at an appropriate position in the accommodation space 102 of the apparatus main body 10, and only the induction heating unit 65 remains in the accommodation space 102 when the fixing unit 60 </ b> U is removed from the apparatus main body 10. Will do. With such a configuration, when the fixing unit 60U needs to be replaced due to deterioration with time or the like, if there is no problem with the induction heating unit 65, the induction heating unit 65 remains in the apparatus main body 10 while the fixing unit 60U remains. It becomes possible to exchange only.

  3 is a cross-sectional view showing the internal structure of the fixing device 60, FIG. 4 is a partially broken perspective view of the fixing device 60, FIG. 5 is an exploded perspective view of the fixing device 60 and its peripheral devices, and FIG. 3 is an end perspective view of the fixing device 60 showing the configuration of the nip pressure adjusting mechanism 80. FIG. The detailed structure of the fixing device 60 will be described below with reference to FIGS.

  The housing 600 of the fixing unit 60U has a substantially rectangular cross-sectional shape and accommodates a member for performing a fixing process. The housing 600 includes a main body frame 601 that is fixed to the housing 600 and a moving frame 602 that is assembled so as to be movable with respect to the main body frame 601. Although not shown, the moving frame 602 is rotatably attached to a turning fulcrum provided on the main body frame 601. The housing 600 has an opening at the position of the upper right corner in FIG. 3, and the opening is covered with a cover member 68 that can be freely opened and closed. When a problem such as a sheet jam occurs in the fixing unit 60U, the cover member 68 is opened upward.

  The heating roller 61 is a roller that is induction-heated by the induction heating unit 65 and is made of a magnetic metal such as iron or stainless steel, and a release layer made of PFA or the like is formed on the surface thereof. The heating roller 61 has a rotation shaft (third rotation shaft 61S) and is driven to rotate around the third rotation shaft 61S.

  The fixing roller 62 and the pressure roller 63 are rollers that form a fixing nip portion 60N by pressing the peripheral surfaces with the fixing belt 64 interposed therebetween. The sheet on which the toner image has been secondarily transferred in the secondary transfer portion 35A passes through the fixing nip portion 60N, and is heated and pressed to fix the toner image on the sheet surface.

  The fixing roller 62 is an elastic roller having an elastic layer as a surface layer. As the elastic layer, an elastic layer made of silicon sponge can be used. The fixing roller 62 has a rotation shaft (second rotation shaft 62S), and is driven to rotate about the second rotation shaft 62S.

  The pressure roller 63 is a roller for pressing the fixing roller 62 to form a fixing nip portion 60N having a predetermined width. One of the preferable configurations of the pressure roller 63 includes a metal core material such as iron or aluminum, a silicon rubber layer formed on the core material, and a fluororesin layer formed on the surface of the silicon rubber layer. It is the composition provided. The pressure roller 63 has a surface layer hardness (first hardness) higher than the surface layer hardness (second hardness) of the fixing roller 62, and a heating element such as a halogen heater is provided therein. ing. The pressure roller 63 has a rotation shaft (first rotation shaft 63S) and is driven to rotate about the first rotation shaft 63S as will be described later.

  The fixing belt 64 is a belt that is stretched between the heating roller 61 and the fixing roller 62 and is induction-heated by the induction heating unit 65 in the same manner as the heating roller 61. A tension roller 641 for applying tension to the fixing belt 64 is in contact with the inner peripheral surface of the fixing belt 64. The fixing belt 64 is formed by sequentially forming a silicon rubber elastic layer and a PFA release layer on a base material made of a ferromagnetic material such as nickel. In the case where the fixing belt 64 is not provided with a function to be heated and is merely a carrier of heat generated by the heating roller 61, a resin belt such as polyimide (PI) can be used.

  The first rotating shaft 63 </ b> S of the pressure roller 63 is rotatably supported by a main body frame 601 in the housing 600. On the other hand, the third rotation shaft 61 </ b> S of the heating roller 61 and the second rotation shaft 62 </ b> S of the fixing roller 62 are rotatably supported by a moving frame 602 in the housing 600. In other words, the first rotation shaft 63S of the pressure roller 63 is supported in a state in which the shift movement is substantially impossible in the housing 600, whereas the third rotation shaft 61S of the heating roller 61 and the fixing roller 62 are supported. The second rotation shaft 62 </ b> S is supported in a state in which shift movement is possible in the housing 600. As shown in FIG. 9, both end portions 61E of the third rotating shaft 61S and both end portions 62E of the second rotating shaft 62S protrude outward from the moving frame 602. The main body frame 601 is provided with a long hole 601H, and an end 62E of the second rotating shaft 62S that shifts is fitted into the long hole 601H.

  Specifically, the heating roller 61, the fixing roller 62, the tension roller 641, and the fixing belt 64 are mounted on the moving frame 602 to form a belt unit 64U, and the belt unit 64U is moved by the nip pressure adjusting mechanism 80 shown in FIG. Thus, the second rotating shaft 62S and the third rotating shaft 61S are configured to shift. Although described in detail later with reference to FIGS. 7 to 9, the nip pressure adjusting mechanism 80 adjusts the nip pressure of the fixing nip portion 60 </ b> N by moving the moving frame 602. That is, a normal pressure posture (first posture) in which the peripheral surface of the fixing roller 62 is pressed against the peripheral surface of the pressure roller 63 with a relatively strong pressure (first pressure), and a relatively low pressure (second state). The posture of the fixing roller 62 is changed between a pressure-reduced posture (second posture) that is pressed by pressure.

  The nip pressure adjusting mechanism 80 includes a motor 81 that generates a driving force for moving the moving frame 602 and a driving gear train 83. The motor 81 is mounted on the side wall of the housing 600, and its output gear 82 is meshed with the first gear 84 of the drive gear train 83. The drive gear train 83 includes a plurality of reduction gears and a sect gear that is not shown in FIG. 6, and transmits the drive force generated by the motor 81 to the moving frame 602, so that the normal pressurization posture and the decompression posture are The moving frame 602 is moved between them.

As schematically shown in FIG. 4, the first rotation shaft 63 </ b> S of the pressure roller 63 is provided on the apparatus main body 10.
A rotational driving force is input from a motor M (drive mechanism) provided on the side via a predetermined speed reduction mechanism. Due to the rotation of the pressure roller 63, the heating roller 61, the fixing roller 62, the tension roller 641, and the fixing belt 64 are driven to rotate. As described above, the pressure roller 63 has a higher hardness than the fixing roller 62. For this reason, the first rotating shaft 63S of the pressure roller 63 is suitable for driving input from the motor M in that the peripheral speed of the outer periphery of the roller does not vary during rotational driving.

  The induction heating unit 65 is a unit for generating heat necessary for fixing processing, and accommodates an induction heating coil 651, a core member composed of a center core 652, a plurality of pairs of arch cores 653 and a pair of side cores 654, and these. A unit housing 650 (holding member).

  The induction heating coil 651 generates magnetic flux for inductively heating the heating roller 61 and the fixing belt 64, and has an arcuate surface in a virtual sectional view opposite to the arcuate surface in the sectional view of the heating roller 61 and the fixing belt 64. Is placed on top. The center core 652, the plurality of pairs of arch cores 653, and the pair of side cores 654 are core members made of ferrite, and are arranged to form a magnetic path that passes through a part of the heating roller 61 and the fixing belt 64. When the magnetic flux generated by the induction heating coil 651 passes through the magnetic path, an eddy current is generated in the heating roller 61 and the fixing belt 64, and the accompanying Joule heat is generated.

  The unit housing 650 is a housing member that holds the induction heating coil 651 and the core member, and includes an arcuate recess 65H into which a part of the heating roller 61 and the fixing belt 64 enters. The unit housing 650 of the induction heating unit 65 and the side surface (the left side surface in FIG. 3) of the fixing unit housing 600 are fitted in a positioned state, and between the inner peripheral surface of the recess 65H and the surface of the fixing belt 64. Are formed with a gap of a predetermined interval.

  The gap (that is, the relative position between the heating roller 61 and the fixing roller 62 and the induction heating unit 65) is moved by the belt unit 64U by the nip pressure adjusting mechanism 80, so that either of the normal pressure posture and the pressure-reduced posture is selected. Even if it becomes a posture, it is kept constant by the maintenance mechanism. In the present embodiment, as the maintenance mechanism, the housing 600 of the fixing unit 60U includes a positioning pin 600A and a receiving portion 602E. The unit housing 650 of the induction heating unit 65 is fitted with an insertion hole 65A corresponding to the positioning pin 600A, a contact portion 650E corresponding to the receiving portion 602E, and an end portion 61E of the third rotating shaft 61S. A groove 650C (see FIG. 9) is provided (the engaging structure portion).

  The maintenance mechanism further includes a coil spring 65B (biasing mechanism). The coil spring 65B is a compression spring and is arranged to urge the unit housing 650 toward the housing 600 and maintain the gap constant. That is, the contact portion 650E is pressed against the receiving portion 602E by the urging force of the coil spring 65B, and the end portion 61E of the third rotating shaft 61S is pressed against the receiving groove 650C. Needless to say, when the fixing unit 60U is removed from the apparatus body 10, the positioning pin 600A is removed from the insertion hole 65A, the contact portion 650E is separated from the receiving portion 602E, and the fitting between the end portion 61E and the receiving groove 650C is also eliminated. .

  Referring to FIG. 3, conveyance roller pair 66 is a conveyance roller pair for sending the sheet that has passed through fixing nip portion 60 </ b> N to horizontal conveyance path 50 </ b> D on the downstream side of housing 600. The conveyance roller pair 66 includes a first conveyance roller 661 that is rotatably supported by the housing 600 and a second conveyance roller 662 that is rotatably supported by the cover member 68. The first transport roller 661 is a drive roller to which rotational driving force is input from the apparatus body 10 side, and the second transport roller 662 is a driven roller that is driven to rotate as the first transport roller 661 rotates. The second conveying roller 662 is pressed against the first conveying roller 661 with a predetermined nip pressure in order to provide a sheet conveying force.

  A pair of guide members 671 and 672 for guiding a sheet carried toward the fixing nip 60N are disposed upstream of the fixing nip 60N in the sheet conveyance direction. A pair of guide members 673 and 674 for guiding the sheet discharged from the fixing nip portion 60N toward the conveyance roller pair 66 is disposed downstream of the fixing nip portion 60N in the sheet conveyance direction. Further, an actuator 67A for detecting the passage of the sheet is disposed in a swingable state on the downstream side in the sheet conveyance direction of the fixing nip 60N.

  In FIG. 3, the fixing roller 62 and the fixing belt 64 rotate counterclockwise, and the pressure roller 63 rotates clockwise. A separation plate 675 is disposed on the circumferential surface of the fixing belt 64 and a separation claw 676 is disposed on the circumferential surface of the pressure roller 63 on the downstream side in the rotational direction from the fixing nip 60N. The separation plate 675 and the separation claw 676 are arranged to peel off a sheet to be wound around the peripheral surface of the fixing belt 64 or the pressure roller 63. The separation plate 675 is a plate-like member that extends in the axial direction of the fixing roller 62, and a minute space is provided between the tip of the separation plate 675 and the peripheral surface of the fixing belt 64. On the other hand, the separation claw 676 is a member having a width of about several millimeters in the axial direction of the pressure roller 63, and the tip thereof is in contact with the peripheral surface of the pressure roller 63. The separation plate 675 is a single plate member having a length corresponding to the sheet passing width, whereas a plurality of separation claws 676 are arranged at predetermined intervals in the axial direction of the pressure roller 63.

  3 to 5, a duct member 69 is integrally attached to the back surface of the unit housing 650. A main body frame 70 (wall portion) of the apparatus main body 10 is disposed on the back surface of the duct member 69 (the main body frame 70 is omitted in FIG. 5). The coil spring 65B described above is disposed between the main body frame 70 and the duct member 69.

  Two coil springs 65 </ b> B are disposed at two locations, two in each location, spaced apart in the axial direction of the heating roller 61. Each coil spring 65B is inserted through the shaft 65S. The shaft 65 </ b> S is a member that protrudes in a direction perpendicular to the roller axis direction from a pressing plate 691 (second spring seat) that contacts the back surface of the duct member 69, and a tip portion thereof is provided on the main body frame 70. It penetrates a hole (not shown). One end of the coil spring 65B is in contact with a spring seat 701 (first spring seat) that is in pressure contact with the main body frame 70, and the other end is in contact with a pressing plate 691 (FIG. 3).

  Inside the duct member 69, a space D (ventilation path) through which cooling air can flow is provided. As shown in FIG. 5, main body cooling ducts 71, 71 provided on the apparatus main body 10 side are connected to the back surfaces near both ends of the duct member 69. In this connecting portion, the duct member 69 is open, and the space D communicates with the inside of the main body cooling ducts 71 and 71.

  An exhaust duct 72 is connected to the main body cooling duct 71 on the downstream side of the cooling air flow path. A cooling fan 73 for sucking cooling air is provided in the main body cooling duct 71 on the upstream side of the cooling air flow path, and the cooling air is provided between the main body cooling duct 71 and the exhaust duct 72 on the downstream side of the cooling air flow path. The cooling fan 74 for blowing out is assembled. When the cooling fans 73 and 74 are driven, cooling reaches the main body cooling duct 71 and the duct member 69 on the upstream side of the cooling air flow path, and the main body cooling duct 71 and the exhaust duct 72 on the downstream side of the cooling air flow path. A wind ventilation path AF is formed, and the induction heating unit 65 is cooled.

  As shown in FIG. 4, a stretchable seal member 71 </ b> S is interposed at a connecting portion between the main body cooling duct 71 and the duct member 69. Although the main body frame 70 does not move, the duct member 69 integrated with the induction heating unit 65 is pressed by the coil spring 65B and moves. Even if such movement is performed, a seal member 71S having elasticity is arranged so that cooling air does not leak from the connecting portion between the main body cooling duct 71 and the duct member 69.

  Subsequently, the movement operation of the belt unit 64U by the nip pressure adjusting mechanism 80 will be described with reference to FIGS. 7A shows a state in which the fixing roller 62 (belt unit 64U) is set to the normal pressure posture in the fixing nip portion 60N, and FIG. 7B shows the state in which the fixing roller 62 is set to the reduced pressure posture. Each state is shown. The normal pressure posture is a state where a high nip pressure is formed in the fixing nip portion 60N, and is set when a sheet having a normal paper thickness is passed through the fixing nip portion 60N. On the other hand, the depressurization posture is a state in which a slight nip pressure is formed in the fixing nip portion 60N. When a thick paper or a thin paper such as an envelope is passed through the fixing nip portion 60N, or a sheet jam occurs in the fixing unit 60U. This is set when an error occurs.

  As described above, the first rotating shaft 63S of the pressure roller 63 is supported by the main body frame 601 fixed in the housing 600, and thus does not shift in both the normal pressure posture and the pressure-reduced posture. That is, the position of the first rotating shaft 63S remains unchanged from P1. In the present embodiment, the rotational driving force is input from the motor M (FIG. 4) provided in the apparatus main body 10 to the first rotating shaft 63S that does not shift in this way. For this reason, the input mechanism of the rotational driving force can be simplified.

  On the other hand, the belt unit 64U is supported by the moving frame 602 of the housing 600. When the nip pressure adjusting mechanism 80 moves the moving frame 602 to change the posture from the normal pressure posture to the pressure-reduced posture, the second of the fixing roller 62 is obtained. The rotation shaft 62S and the third rotation shaft 61S of the heating roller 61 shift. That is, the position of the second rotating shaft 62S is shifted by a distance d1 from P21 to P22, and the position of the third rotating shaft 61S is shifted by a distance d2 from P31 to P32. Of course, d1 = d2.

  In the present embodiment, since the above-described maintenance mechanism is provided, the induction heating unit 65 also moves following the movement of the belt unit 64U. When the pressure reducing posture of FIG. 7B shifts to the normal pressure posture of FIG. 7A, the belt unit 64U moves in a direction approaching the pressure roller 63. At this time, the state in which the unit housing 650 of the induction heating unit 65 is pressed against the housing 600 of the fixing unit 60U is maintained by the biasing force of the coil spring 65B. Specifically, the contact portion 650E of the unit housing 650 is pressed against the receiving portion 602E by the urging force, and the state where the end portion 61E of the third rotating shaft 61S is pressed against the receiving groove 650C (FIG. 9) is maintained. It is what is done. Furthermore, the state where the positioning pin 600A is in contact with the insertion hole 65A is also maintained.

  On the other hand, when the normal pressure posture of FIG. 7A is shifted to the pressure-reduced posture of FIG. 7B, the belt unit 64U moves in a direction away from the pressure roller 63. At this time, the induction heating unit 65 receives a pressing force against the urging force of the coil spring 65B from the belt unit 64U. As a result, the induction heating unit 65 moves to the left in FIG. 7, and the coil spring 65B is compressed. That is, the position of the induction heating unit 65 (shown here as the position of the duct member 69) shifts by a distance d3 from P41 to P42 in the normal pressurizing posture. Needless to say, d3 = d2 = d1. Therefore, the relative position between the belt unit 64U and the induction heating unit 65 is always kept constant regardless of the posture changing operation by the nip pressure adjusting mechanism 80.

  In this embodiment, the device which makes the adhesiveness of the induction heating unit 65 and the belt unit 64U favorable is given. This point will be described with reference to FIGS. Two coil springs 65B are arranged side by side in the vertical direction (referred to as upper coil spring 65B1 and lower coil spring 65B2 respectively). The 3rd rotating shaft 61S of the heating roller 61 is arrange | positioned in the position eccentrically upward rather than the intermediate point of upper coil spring 65B1 and lower coil spring 65B2 (a1 <a2).

  As shown in FIGS. 9A and 9B, the end 61E of the third rotating shaft 61S is fitted in a U-shaped receiving groove 650C. Accordingly, the unit housing 650 of the induction heating unit 65 can swing around the end 61E. Then, the pressing force F1 of the upper coil spring 65B1 and the pressing force F2 (F1 = F2) of the lower coil spring 65B2 are respectively applied to the action points where the distance difference of a1: a2 exists. Therefore, a rotational moment in the direction indicated by arrow B in the figure acts on the unit housing 650, and the unit housing 650 has an arrow B around the axis of the end 61E within the range of fitting play between the positioning pin 600A and the insertion hole 65A. Swing in the direction. Accordingly, the contact portion 650E is naturally pressed against the receiving portion 602E, and the induction heating unit 65 and the belt unit 64U can be accurately positioned.

  According to the IH fixing type image forming apparatus 1 of the present embodiment described above, the relative position between the induction heating unit 65 and the belt unit 64U (fixing roller 62) is irrespective of the posture changing operation by the nip pressure adjusting mechanism 80. It is kept constant by a maintenance mechanism including the coil spring 65B. On the other hand, the pressure roller 63 having a hardness higher than that of the fixing roller 62 is supported by the housing 600 (main body frame 601) in a state in which the shift movement is impossible, and a rotational driving force is applied to the pressure roller 63 from the motor M. Therefore, the rotational drive force input mechanism can be simplified while keeping the distance relationship between the induction heating unit 65 and the belt unit 64U constant.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to said structure. For example, in the above-described embodiment, the fixing unit 60U including the heating roller 61 and the fixing belt 64 is illustrated. However, a fixing unit of a type in which these units do not exist may be used. Specifically, a cylindrical belt made of a magnetic material similar to the fixing belt 64 is wound around the outer periphery of the fixing roller 62. In this modified embodiment, the induction heating unit 65 performs induction heating of the cylindrical belt.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Apparatus main body 30 Image forming part 60 Fixing apparatus 60N Fixing nip part 600 Housing 600A Positioning pin (engaging structure part)
601 Body frame 602 Moving frame 602E Receiving part (engaging structure part)
61 Heating roller (third roller)
61S Third rotating shaft 61E End 62 Fixing roller (second roller)
62S Second rotating shaft 63 Pressure roller (first roller)
63S First rotating shaft 64 Fixing belt (belt member)
65 Induction heating unit 65B Coil spring (biasing mechanism / maintenance mechanism)
650 Unit housing (holding member)
650C receiving groove (engagement structure)
650E Contact part (engagement structure part)
651 Induction heating coil 652, 653, 654 Center core, arch core, side core (core member)
69 Duct member 70 Body frame 71 Body cooling duct 71S Seal member 80 Nip pressure adjusting mechanism M Motor (drive mechanism)
D Ventilation path

Claims (7)

A housing;
A first roller having a first rotating shaft and rotatably supported by the housing in a state in which the first rotating shaft is not capable of shifting;
A second roller having a second rotating shaft, which is rotatably supported by the housing in a state in which the second rotating shaft can be shifted, and that forms a fixing nip portion for fixing the sheet together with the first roller; ,
A first posture in which the second roller is brought into pressure contact with the first roller with a first pressure, and the second rotating shaft is shifted from the state of the first posture to shift the second roller from the first pressure. A nip pressure adjusting mechanism for changing the posture between a second posture that presses against the first roller with a reduced second pressure;
An induction heating unit for generating heat necessary for the fixing process;
A maintenance mechanism for maintaining the relative position of the second roller and the induction heating unit constant both in the first posture and in the second posture of the second roller;
An IH fixing device. The IH fixing device according to claim 1,
The first roller is formed of a material having a first hardness;
The IH fixing device, wherein the second roller is formed of a material having a second hardness lower than the first hardness. The IH fixing device according to claim 1 or 2,
The housing includes a main body frame and a moving frame assembled to be movable with respect to the main body frame,
The first roller is supported by the body frame, the second roller is supported by the moving frame,
The maintenance mechanism includes an engagement structure portion that positions and engages the induction heating unit and the moving frame, and an urging mechanism that applies an urging force to maintain the engagement to the induction heating unit. IH fixing device. The IH fixing device according to claim 3,
A third roller having a third rotating shaft, supported by the moving frame, and induction-heated by the induction heating unit;
An IH fixing device, further comprising: a belt member that spans between the second roller and the third roller. The IH fixing device according to claim 4,
The induction heating unit includes an induction heating coil for generating magnetic flux, a core member for forming a magnetic path, and a holding member for holding the induction heating coil and the core member,
The moving frame includes a shaft support portion that supports the third rotating shaft of the third roller, and both end portions of the third rotating shaft protrude from the moving frame,
The IH fixing device, wherein the engaging structure portion includes both end portions of the third rotating shaft and positioning recesses formed on the holding member and fitted with both end portions of the third rotating shaft. In the IH fixing device according to any one of claims 3 to 5,
A wall portion disposed opposite to the induction heating unit;
The biasing mechanism is
A compression spring; a first spring seat with which one end side of the compression spring abuts on the wall side; and a second spring seat with which the other end side of the compression spring abuts on the induction heating unit side;
An IH fixing device that moves the induction heating unit following the movement of the moving frame. The IH fixing device according to claim 6,
A duct member attached to the induction heating unit and forming a ventilation path for cooling the induction heating unit;
A cooling duct provided on the wall and connected to the duct member;
An IH fixing device, further comprising: a stretchable seal member disposed at a connection portion between the cooling duct and the ventilation path.

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