JP6464792B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that includes a heater and a pressure device and performs printing and fixing on a recording material that passes through a nip region thereof, and an image forming apparatus including the fixing device.

  Conventionally, in an image forming apparatus adopting an electrophotographic method, a recording paper on which an unfixed toner image is transferred is conveyed to a fixing nip region between a heater heated by a heat source and a pressurizer in contact with the heater. It is widely performed to fix an unfixed toner image on a recording sheet by heating and pressurizing. As a fixing device for fixing toner on the recording paper, a fixing device that heats the fixing belt with a heat source such as a halogen heater or a ceramic heater and presses the recording paper simultaneously with the fixing belt is used conventionally. Has been.

  In such a fixing device, since the heat capacity of the fixing belt is small, when the fixing belt is stopped due to a malfunction, the time until smoke and ignition is as short as a few seconds. Therefore, it is necessary to quickly detect that the fixing belt has stopped.

  Therefore, in the fixing device described in Patent Document 1, a plurality of through holes are formed in the fixing belt at equal intervals along the rotation direction, and light emitted from an infrared heater and passed through these through holes is detected by a light detection sensor. Thus, the rotation state of the fixing belt is monitored to quickly detect that the fixing belt has stopped.

JP 2011-048134 A

  However, in the fixing device described in Patent Document 1, since the light emitted from the infrared heater and passed through the through hole is irradiated other than the light detection sensor, the temperature of members around the light detection sensor rises. There is a problem of causing thermal degradation. In addition, since it is necessary to use a heat-resistant member that can withstand such a temperature rise, there is a problem that the cost of the fixing device increases.

  In view of such a problem, the present invention provides a fixing device and an image forming apparatus that can quickly detect that the fixing belt has stopped while suppressing an increase in temperature of members around the light detection sensor. With the goal.

In order to achieve the above object, a fixing device according to the present invention includes a cylindrical fixing member that is rotatably supported and has a plurality of through holes at equal intervals in the rotation direction, and an outer peripheral surface of the fixing member. A pressure member that forms a fixing nip portion by pressure contact, a heat source that heats the fixing member from the inner peripheral surface side, and a position that covers a part of the outer peripheral surface of the heat source in the width direction. And a detector that is provided on the outer peripheral surface side of the fixing member and detects light of the heat source that has passed through the through hole . And in the said reflecting plate, the opening width of the part facing the said detection part is narrower than the opening width of another part.

  Moreover, the opening width of the part which opposes the said detection part in the said reflecting plate may be smaller than the diameter of the said heat source.

  Moreover, the opening direction of the part which opposes the said detection part in the said reflecting plate may differ from the opening direction of another part.

  An infrared cut filter may be provided between the fixing member and the detection unit.

  A shielding member that shields heat may be provided around the detection unit.

  A condensing lens may be provided between the fixing member and the detection unit.

  Further, in the heat source, the amount of light in a portion facing the detection unit may be lower than the amount of light in other portions.

  Moreover, the reflectance of the part which opposes the said detection part in the said reflecting plate may be lower than the reflectance of another part.

  Further, the shape of the through hole may be longer in the direction perpendicular to the rotation direction than in the direction along the rotation direction.

  The image forming apparatus of the present invention includes any one of the above-described fixing devices.

  According to the present invention, since the shape of the part facing the detection unit in the reflector is different from the shape of the other part, the light emitted from the heat source is different between the part facing the detection unit and the other part. The range can be different. Thereby, it is possible to easily limit the range of light leaking from the through hole, and as a result, it is possible to easily suppress the temperature rise of the members around the detection unit.

1 is a schematic configuration diagram illustrating an internal configuration of an image forming apparatus. FIG. 3 is a diagram schematically illustrating a characteristic part of the first embodiment of the fixing device. 1 is a diagram illustrating an overall configuration of a first embodiment of a fixing device. FIG. FIG. 4 is a diagram showing a cross section (cross section AA in FIG. 3) of the first embodiment of the fixing device. FIG. 6 is a diagram showing a cross section (XX cross section of FIG. 4) of the first embodiment of the fixing device. FIG. 6 is a view showing a cross section (YY cross section of FIG. 4) of the first embodiment of the fixing device. FIG. 6 is a diagram for explaining a control method of the first embodiment of the fixing device. It is a figure which shows simply the characteristic part of 2nd Example of a fixing device. It is a figure which shows the cross section of 2nd Example of a fixing device. It is a figure which shows simply the characteristic part of 3rd Example of a fixing device. FIG. 6 is a cross-sectional view of a third embodiment of the fixing device. It is a figure which shows simply the characteristic part of 4th Example of a fixing device. FIG. 7 is a cross-sectional view of a fourth embodiment of the fixing device. FIG. 10 is a diagram illustrating a cross section of a fifth embodiment of the fixing device. It is a figure which shows the cross section of 6th Example of a fixing device. It is a figure which shows the cross section of 7th Example of a fixing device. It is a figure which shows the cross section of 8th Example of a fixing device.

  Hereinafter, an embodiment embodying the present invention will be described with reference to the drawings in a case where the embodiment is applied to a tandem color digital printer which is an example of an image forming apparatus. In the following description, when using terms indicating a specific direction or position (for example, “left / right”, “up / down”, etc.) as necessary, the direction perpendicular to the paper surface in FIG. ing. These terms are used for convenience of explanation, and do not limit the technical scope of the present invention.

<Overall configuration of image forming apparatus>
First, an outline of the image forming apparatus 1 will be described with reference to FIG. As shown in FIG. 1, the image forming apparatus 1 includes an image processing device 3, a paper feeding device 4, a fixing device 5, and the like in an outer casing 2. Although not shown in detail, the image forming apparatus 1 is connected to a network such as a LAN, and is configured to execute printing based on the command when receiving a print command from an external terminal (not shown). Has been.

  The paper feeding device 4 located at the lower part in the outer casing 2 includes a paper feeding cassette 21 that accommodates the recording material P1, a pickup roller 22 that feeds the recording material P1 in the paper feeding cassette 21 from the uppermost layer, and a fed recording material. A pair of separation rollers 23 for separating P1 one by one and a pair of timing rollers 24 for conveying the recording material P1 separated into one sheet to the image processing apparatus 3 at a predetermined timing are provided. . The recording material P <b> 1 in each paper feed cassette 21 is sent out one by one from the top layer to the transport path 30 by the rotation of the pickup roller 22 and the separation roller pair 23. The conveyance path 30 passes from the paper feed cassette 21 of the paper feed device 4 to the outer casing 2 via the nip portion of the timing roller pair 24, the secondary transfer nip portion of the image processing device 3, and the fixing nip portion of the fixing device 5. It reaches the discharge roller pair 26 at the top.

  The recording material P <b> 1 in the paper feeding cassette 21 is set so that the center of the paper passing width becomes the center reference when transporting toward the transport path 30. The paper feed cassette 21 is provided with a pair of side portion regulating plates (not shown) for shifting the recording material P1 before paper feed to the center reference. The pair of side part restricting plates are configured to move in close proximity to each other in the sheet passing width direction. By sandwiching the recording material P1 in the paper feed cassette 21 from both sides in the sheet passing width direction with a pair of side portion regulating plates, the recording material P1 in the paper feed cassette 21 is set to the center reference regardless of the standard. Therefore, the transfer process in the image processing apparatus 3 and the fixing process in the fixing apparatus 5 are also executed on the basis of the center.

  The image processing device 3 positioned above the paper feeding device 4 plays a role of transferring a toner image formed on a photosensitive drum 13 which is an example of an image carrier to a recording material P1, and is an intermediate transfer member. And a total of four image forming sections 7 corresponding to the respective colors of yellow (Y), magenta (M), cyan (C) and black (K).

  The intermediate transfer belt 6 is an endless belt made of a conductive material, and is also an example of an image carrier. The intermediate transfer belt 6 is wound around a driving roller 8 located on the right side of the central portion in the outer casing 2 and a driven roller 9 located on the left side of the central portion. A secondary transfer roller 10 is disposed outside the portion of the intermediate transfer belt 6 that is wound around the drive roller 8. The intermediate transfer belt 6 rotates in the counterclockwise direction in FIG. 1 by rotating the driving roller 8 counterclockwise in FIG. 1 by power transmission from a main motor (not shown).

  A secondary transfer roller 10 is disposed on the outer peripheral side of the portion of the intermediate transfer belt 6 that is wound around the drive roller 8. The secondary transfer roller 10 is in contact with the intermediate transfer belt 6, and a portion between the intermediate transfer belt 6 and the secondary transfer roller 10 (contact portion) is a secondary transfer nip portion as a secondary transfer region. . The secondary transfer roller 10 rotates in the clockwise direction in FIG. 1 with the rotation of the intermediate transfer belt 6 or with the movement of the recording material P1 held and conveyed by the secondary transfer nip portion. A transfer belt cleaner 12 for removing untransferred toner on the intermediate transfer belt 6 is disposed on the outer peripheral side of the portion of the intermediate transfer belt 6 wound around the driven roller 9. The transfer belt cleaner 12 is in contact with the intermediate transfer belt 6.

  The four image forming units 7 are arranged along the intermediate transfer belt 6 in the order of yellow (Y), magenta (M), cyan (C), and black (K) from the left in FIG. They are arranged side by side. In FIG. 1, for convenience of explanation, symbols Y, M, C, and K are attached to each image forming unit 7 according to the reproduction color. Each image forming unit 7 includes a photosensitive drum 13 as an example of an image carrier that rotates clockwise in FIG. Around the photosensitive drum 13, a charging device 14, an exposure device 19, a developing device 15, a primary transfer roller 16, and a photosensitive cleaner 17 are arranged in this order along the clockwise rotation direction in FIG. 1.

  The photosensitive drum 13 is negatively charged and is configured to rotate clockwise in FIG. 1 by power transmission from the main motor. A charging bias voltage output at a predetermined timing from a charging power source (not shown) is applied to the charging device 14. The developing device 15 makes the electrostatic latent image formed on the photosensitive drum 13 visible by reversal development using toner having a negative polarity.

  The primary transfer roller 16 is located on the inner peripheral side of the intermediate transfer belt 6 and faces the photosensitive drum 13 of the corresponding image forming unit 7 with the intermediate transfer belt 6 interposed therebetween. The primary transfer roller 16 also rotates counterclockwise in FIG. 1 as the intermediate transfer belt 6 rotates. Between the intermediate transfer belt 6 and the primary transfer roller 16 (contact portion) is a primary transfer nip portion as a primary transfer region. The photoreceptor cleaner 17 is for removing untransferred toner remaining on the photoreceptor drum 13, and is in contact with the photoreceptor drum 13. An exposure device 19 is disposed below the four image forming units 7. The exposure device 19 forms an electrostatic latent image on each photosensitive drum 13 by laser light based on image information from an external terminal or the like.

  The density of the toner image on the intermediate transfer belt 6 is detected on the most downstream side in the circumferential direction of the intermediate transfer belt 6, that is, between the image forming portion 7K closest to the secondary transfer roller 10 and the secondary transfer nip portion. An IDC sensor (not shown) is arranged. The IDC sensor basically may be referred to as a reference pattern (test toner image) of each color formed on the intermediate transfer belt 6 during image stabilization processing such as color misregistration, gradation, and image density reproduction correction. ) Is detected. A hopper (not shown) that accommodates toner supplied to each developing device 15 is disposed above the intermediate transfer belt 6.

  In each image forming unit 7, when a laser beam corresponding to an image signal is projected from the exposure device 19 onto the photosensitive drum 13 charged by the charging device 14, an electrostatic latent image is formed. The electrostatic latent image is reversely developed with toner supplied from the developing device 15 and becomes a toner image of each color. The toner images on the respective photosensitive drums 13 are primarily transferred from the photosensitive drum 13 to the outer peripheral surface of the intermediate transfer belt 6 in the order of yellow, magenta, cyan, and black at the corresponding primary transfer nip portions, and are superimposed. . Untransferred toner remaining on the photosensitive drum 13 is scraped off by the photosensitive cleaner 17 and removed from the photosensitive drum 13. Then, when the recording material P1 passes through the secondary transfer nip portion, the superimposed four color toner images are collectively transferred onto the recording material P1. Untransferred toner remaining on the intermediate transfer belt 6 is scraped off by the transfer belt cleaner 12 and removed from the intermediate transfer belt 6.

  The fixing device 5 positioned above the secondary transfer roller 10 in the image processing apparatus 3 includes a heater (fixing device) 31 having a built-in heat source such as a halogen lamp heater and a pressurizer 32 facing the heater 31. ing. A contact portion between the heater 31 and the pressurizer 32 is a fixing nip portion which is a fixing region. The recording material P1 on which the unfixed toner image is placed after passing through the secondary transfer nip portion is heated and pressurized when passing through the fixing nip portion between the heater 31 and the pressurizer 32, and the recording material P1 is placed on the recording material P1. The unfixed toner image is fixed to the toner image. Thereafter, the recording material P <b> 1 is discharged onto the paper discharge tray 27 by the rotation of the discharge roller pair 26.

  A control unit 28 that performs overall control of the image forming apparatus 1 is disposed between the image processing apparatus 3 and the sheet feeding apparatus 4 in the outer casing 2. The controller 28 incorporates a controller (not shown) that executes various arithmetic processes, storage, and control.

<First Embodiment of Fixing Device>
A first example of the fixing device in the image forming apparatus of the present embodiment will be described below with reference to the drawings.

  FIG. 2 is a diagram schematically showing a characteristic part of the first embodiment of the fixing device 5, FIG. 3 is a diagram showing an entire configuration of the fixing device 5, and FIG. 4 is a cross-sectional view of the fixing device 5 ( FIG. 5 is a view showing a cross section of the fixing device 5 (cross section XX of FIG. 4), and FIG. 6 is a cross section of the fixing device 5 (FIG. 4). FIG. 7 is a diagram for explaining a control method of the fixing device 5.

  As shown in FIG. 3, the fixing device 5 includes a heater 31 that presses the fixing belt 311 that is an endless belt against the pressure device 32, and a pressure device that includes a pressure roller that has a cylindrical cored bar 321 as an axis. 32. The pressurizer 32 is rotationally driven by the cored bar 321 being pivotally supported by the roller support frame 33 and being connected to the drive motor 39 so that power can be transmitted. Further, the heater 31 is supported at a position where the fixing belt 311 is pressed against the pressurizer 32 to form a fixing nip portion by being sandwiched by the guide member 35 via the seal member 34 from both edge sides thereof. As a result, the fixing belt 311 of the heater 31 rotates following the rotation of the pressurizer 32.

  As shown in FIG. 5, the heater 31 includes a pressing member (sliding pad) 312 that is provided inside the fixing belt 311 and presses the fixing belt 311 against the pressurizer 32. In order to arrange the pressing member 312 so as to press the fixing belt 311 from the inside, a holding frame 313 for fixing the pressing member 312 is installed in the fixing belt 311. A heat source 318 for heating the fixing belt 311 to a predetermined target temperature (for example, a fixing temperature within a range of 150 ° C. to 180 ° C.) is disposed inside the fixing belt 311 so as to extend in the sheet passing width direction. Yes. A halogen heater or the like is employed as the heat source 318.

  A reflective plate 36 for reflecting the light from the heat source 318 is provided at a position covering a part of the outer peripheral surface of the heat source 318 in the width direction. As shown in FIG. 2, the reflection plate 36 is fixed to the holding frame 313. As shown in FIG. 5, the cross-sectional shape of the reflecting plate 36 is a U-shape that opens in a predetermined direction (left direction in FIG. 5). Thus, the fixing belt 311 can be efficiently heated. In addition, as shown in FIG. 2, the shape of the cross section of the reflecting plate 36 is different from the other portions only in one end portion (left end portion in FIG. 2) of the reflecting plate 36. The reason will be described later. .

  The fixing belt 311 includes a base layer 315 that takes heat resistance, strength, and surface smoothness into consideration, and has a configuration in which the outer side of the base layer 315 is covered with a release layer 314 having releasability. The pressing member 312 includes an elastic pressing member 316 that elastically deforms and presses the fixing belt 311, and a rigid pressing member 317 made of a material having a higher hardness than the elastic pressing member 316, and is elastically pressed by the rigid pressing member 317. The member 316 is gripped.

  The pressurizer 32 has a configuration in which an outer peripheral surface of a metal core 321 made of a metal material is coated with an elastic layer 322 and a release layer 323 in order. The elastic layer 322 is made of an elastic material having heat resistance, and has heat resistance with respect to the fixing temperature and elasticity for ensuring the length of the fixing nip portion. The release layer 323 not only has heat resistance with respect to the fixing temperature and release property that assists in peeling of the recording material P1 that has passed through the fixing nip portion, but also has a property that it is difficult to transmit ultrafine particles generated from the elastic layer 322 ( Gas barrier properties). The roller support frame 33 is urged and supported by a spring, so that the pressurizer 32 comes into pressure contact with the fixing belt 311.

  With the above-described configuration, the elastic pressing member 316 and the rigid pressing member 317 sequentially press the fixing belt 311 from the downstream side to the upstream side in the conveyance direction of the recording material P1, thereby fixing the toner image on the recording material P1. . That is, the recording material P1 is heated and pressed in a fixing nip portion formed by pressing due to elastic deformation of the elastic pressing member 316, whereby the toner on the paper surface is melted and fixed. Thereafter, the rigid pressing member 317 having high hardness presses the pressurizer 32 via the fixing belt 311, thereby deforming the elastic layer 322 of the pressurizer 32 and peeling the recording material P <b> 1 that has passed through the fixing nip portion.

  Next, a configuration for holding the fixing belt 311 will be described below with reference to FIGS. 3 and 4. The fixing belt 311 has a part of the guide member 35 inserted therein so that both edge portions in the width direction (left and right direction in FIGS. 3 and 4) are covered with the guide member 35. The guide member 35 includes a cylindrical frame holding portion 351 inserted inside the fixing belt 311 and a ring-shaped belt holding portion 352 protruding outward from the outer peripheral surface of the frame holding portion 351.

  The guide member 35 configured as described above is inserted from both the front and rear edges of the fixing belt 311 so that the frame holding portion 351 enters the inside of the base layer 315 of the fixing belt 311. The frame holding portions 351 of the two guide members 35 are connected to the holding frame 313. That is, the guide members 35 installed at the front and rear ends of the fixing belt 311 are supported by the holding frame 313. Note that both ends of the holding frame 313 are fixed to the outer casing 2 of the image forming apparatus 1 as shown in FIG.

  Further, both front and rear edges of the fixing belt 311 are covered with a seal member 34 that is externally fitted to the outer peripheral surface of the frame holding portion 351 of the guide member 35. The seal member 34 is fixed by contacting the end surface of the belt holding portion 352 of the guide member 35. As a result, the fixing belt 311 is held by the belt holding portion 352 of the guide member 35 fixed to the holding frame 313 via the seal member 34, and is supported rotatably.

  As shown in FIG. 4, the seal member 34 seals the inside of the fixing belt 311 connected to the guide member 35 by slidingly contacting the end surface and the inner and outer peripheral surfaces of the edge portion of the fixing belt 311. The seal member 34 is formed of an elastic material such as foamed resin or rubber, and a low friction member is provided on the contact surface with the edge of the fixing belt 311 so that the fixing belt 311 slides. The mobility is good.

  As shown in FIGS. 2 and 3, the fixing belt 311 has a plurality of through holes 319 formed at equal intervals along the rotation direction (circumferential direction). These through holes 319 are provided in an area outside the “sheet passing area” shown in FIG. 3 (hereinafter referred to as a non-sheet passing area) so as not to affect fixing of the toner image onto the recording material P1. The “paper passing area” is an area in the fixing belt 311 that can come into contact with the recording material P1 passing through the fixing nip portion.

  As shown in FIG. 3, a photo sensor 41 (photodiode, phototransistor, etc.) is disposed at a position facing the through hole 319 of the fixing belt 311. Most of the light from the heat source 318 is directly or after being reflected by the reflecting plate 36 and then irradiated to the inner peripheral surface of the fixing belt 311, but part of the light from the heat source 318 passes through the fixing belt 311. It passes through the hole 319 and leaks to the outside of the fixing belt 311. When the light that has passed through the through hole 319 is irradiated onto the photosensor 41 in this way, the photosensor 41 detects the light.

  The detection result of the photo sensor 41 is notified to the control unit 28 as needed. When the fixing belt 311 rotates normally, the photo sensor 41 periodically detects light at time intervals according to the rotation speed of the fixing belt 311. However, the fixing belt 311 stops due to some trouble. If this happens, light will not be detected periodically. Thereby, the control unit 28 can quickly detect the stop of the fixing belt 311.

  The shape of the through hole 319 is longer in the direction (width direction) perpendicular to the rotation direction than in the direction along the rotation direction (circumferential direction). Therefore, even if the position of the through hole 319 is slightly shifted in the width direction due to the displacement or deformation of the fixing belt 311, the light that has passed through the through hole 319 can be normally detected by the photo sensor 41. .

  A part of the light of the heat source 318 leaking from the through hole 319 is irradiated to the photo sensor 41 and used for detecting the operation state of the fixing belt 311 as described above. However, the remaining light of the heat source 318 leaking from the through hole 319 not only becomes useless light, but also causes a rise in the temperature around the photosensor 41, and the heat of the peripheral members It will cause deterioration.

  Therefore, in the first embodiment, as shown in FIG. 2, the bending angle of the portion facing the photosensor 41 in the reflector 36 is set so as to reduce the unnecessary light as described above. By making it smaller than the bending angle, the opening width (W2 in FIG. 6) of the portion facing the photosensor 41 is made narrower than the opening width of other portions (W1 in FIG. 5). Thereby, the range of light leaking from the through hole 319 becomes narrower, and useless light can be reduced. In particular, the opening width (W2 in FIG. 6) of the portion facing the photosensor 41 is preferably smaller than the diameter of the heat source 318. Thereby, useless light can be greatly reduced.

  In addition, by making the opening width of the reflecting plate 36 narrower, the temperature of the reflecting plate 36 is more likely to rise. If it is desired to suppress such a temperature rise of the reflecting plate 36, for example, the reflecting plate 36 may be disposed so as to be in contact with another member having high thermal conductivity to promote heat dissipation. In the first embodiment, as shown in FIG. 6, the cross-sectional shape of the reflector 36 is substantially U-shaped, and the contact range between the reflector 36 and the holding frame 313 is widened. Heat is easily transferred from 36 to the holding frame 313.

  Next, a control method of the fixing device 5 will be described with reference to FIG. As shown in FIG. 7, the fixing device 5 includes a temperature sensor 40 that measures the temperature of the surface of the fixing belt 311 and the photosensor 41 described above.

  If the temperature sensor 40 is a contact type, the surface of the fixing belt 311 to be measured may be damaged. For example, a non-contact type such as a thermistor is used. The temperature sensor 40 is arranged at a position on the outer periphery of the fixing belt 311 so that the measurement surface faces the surface of the fixing belt 311.

  The control unit 28 gives a control signal to the drive motor 39 to control the rotational drive of the drive motor 39 and to control the rotation operation of the heater 31 and the pressurizer 32 in the fixing device 5, while A control signal is given to control the heating amount in the heater 31. The drive motor 39 has a rotation speed detection unit 42 such as a hall sensor, and notifies the control unit 28 of the rotation speed of the drive motor 39. The control unit 28 adjusts the temperature of the heat source 318 based on the rotation speed of the driving motor 39 and the temperature measured by the temperature sensor 40. In addition, the control unit 28 monitors the operation state of the fixing belt 311 based on the detection result of the photosensor 41, and immediately stops the heat source 318 and the drive motor 39 when an abnormality is detected. In response to this, an error notification is given by the operation panel or the like of the image forming apparatus 1.

<Second Embodiment of Fixing Device>
Next, a second embodiment of the fixing device will be described with reference to the drawings. FIG. 8 is a diagram schematically illustrating a characteristic portion of the second embodiment of the fixing device 5, and FIG. 9 is a diagram illustrating a cross section of the fixing device 5 (a cross section intersecting with the plurality of through holes 319).

  In the second embodiment, in the reflecting plate 36, a shielding portion 361 that shields a part of the opening is provided in a portion facing the photosensor 41, so that the opening width of the portion facing the photosensor 41 is changed to the other portion. The opening width is narrower. Thereby, the opening width of the part facing the photosensor 41 can be easily narrowed.

<Third embodiment of fixing device>
Next, a third embodiment of the fixing device will be described with reference to the drawings. FIG. 10 is a diagram schematically illustrating a characteristic portion of the third embodiment of the fixing device 5, and FIG. 11 is a diagram illustrating a cross section of the fixing device 5 (a cross section intersecting with the plurality of through holes 319).

  In the third embodiment, a shielding portion 361 that shields a part of the opening is provided in a portion of the reflecting plate 36 that faces the photosensor 41, and a guide portion 362 that extends from the tip of the shielding portion 361 toward the photosensor 41. Is provided. Accordingly, the opening width of the portion facing the photosensor 41 can be narrower than the opening width of the other portions, and the directivity of light from the heat source 318 toward the photosensor 41 can be further increased (that is, the through hole). The range of light leaking from 319 can be made narrower). Thereby, the temperature rise around the photosensor 41 can be further suppressed.

<Fourth Embodiment of Fixing Device>
Next, a fourth embodiment of the fixing device will be described with reference to the drawings. FIG. 12 is a diagram schematically illustrating a characteristic portion of the fourth embodiment of the fixing device 5, and FIG. 13 is a diagram illustrating a cross section of the fixing device 5 (a cross section intersecting with the plurality of through holes 319).

  In the fourth embodiment, in the reflecting plate 36, the bending angle of the portion facing the photosensor 41 is reduced as in the first embodiment, and at the portion facing the photosensor 41 as in the second embodiment. A shielding part 361 is provided. As a result, the same effects as those of the first and second embodiments can be obtained.

<Fifth Embodiment of Fixing Device>
Next, a fifth embodiment of the fixing device will be described with reference to the drawings. FIG. 14 is a view showing a cross section of the fixing device 5 (a cross section intersecting with the plurality of through holes 319).

  The fifth embodiment is different from the first embodiment in that an infrared cut filter 50 is provided between the fixing belt 311 and the photo sensor 41. In the first embodiment, in the reflector 36, the opening width of the portion facing the photosensor 41 is reduced, so that the range of light leaking from the through hole 319 becomes narrower and the temperature of the photosensor 41 rises. It becomes easy. In the fifth embodiment, the infrared rays applied to the photosensor 41 can be suppressed, so that the temperature rise of the photosensor 41 can be prevented.

<Sixth Embodiment of Fixing Device>
Next, a sixth embodiment of the fixing device will be described with reference to the drawings. FIG. 15 is a diagram illustrating a cross section of the fixing device 5 (a cross section intersecting with the plurality of through holes 319).

  The sixth embodiment is different from the first embodiment in that a shielding plate 51 that shields heat is provided around the photosensor 41. Thereby, it is possible to prevent the light around the photosensor 41 from being irradiated with the light from the heat source 318, so that the temperature rise of the members around the photosensor 41 can be suppressed.

<Seventh Embodiment of Fixing Device>
Next, a seventh embodiment of the fixing device will be described with reference to the drawings. FIG. 16 is a diagram illustrating a cross section of the fixing device 5 (a cross section intersecting with the plurality of through holes 319).

  The seventh embodiment is different from the first embodiment in that a condensing lens 52 is provided between the fixing belt 311 and the photosensor 41. As a result, the light traveling from the heat source 318 toward the members around the photosensor 41 can be condensed on the photosensor 41, so that the temperature rise of the members around the photosensor 41 can be suppressed.

<Eighth Embodiment of Fixing Device>
Next, an eighth embodiment of the fixing device will be described with reference to the drawings. FIG. 17 is a view showing a cross section of the fixing device 5 (a cross section intersecting with the plurality of through holes 319).

  The eighth embodiment is different from the first embodiment in that the opening direction of the portion facing the photosensor 41 in the reflecting plate 36 is different from the opening direction of the other portions. Specifically, in FIG. 17, the opening direction of the part facing the photosensor 41 is downward, while the opening direction of the other part is leftward. As a result, the photosensor 41 can be arranged more freely.

<Other embodiments>
Note that two or more of the first to eighth embodiments described above may be arbitrarily combined. For example, the shielding plate 361 is provided on the reflector 36 as in the second embodiment, the infrared cut filter 50 is provided as in the fifth embodiment, and the condensing lens 52 is provided as in the seventh embodiment. May be.

  In addition to the characteristics of any of the above-described embodiments, the light amount of the portion facing the photosensor 41 in the heat source 318 may be smaller than the light amount of the other portions. Thereby, since the light quantity leaking out from the through hole 319 becomes smaller, the temperature rise of members around the photosensor 41 can be suppressed.

  Further, in addition to the characteristics of any of the above-described embodiments, the reflectance of the portion facing the photosensor 41 in the reflector 36 may be smaller than the reflectance of the other portions. Thereby, since the light quantity leaking out from the through hole 319 becomes smaller, the temperature rise of members around the photosensor 41 can be suppressed.

  In the above embodiment, the fixing device 5 has been described by taking the fixing device of the free belt system shown in FIGS. 3 to 5 as an example. You can also use the method of winding.

  The image forming apparatus 1 has been described by taking an image forming apparatus using an intermediate transfer method as an example. However, if the image forming apparatus 1 includes a fixing device, an image forming apparatus using another method such as a direct transfer method or a rotary arrangement type may be used. It does not matter. The image forming apparatus may be an MFP (Multifunction Peripheral) having a copy function, a scanner function, a printer function, and a fax function, or may be a printer, a copier, a facsimile, or the like. In addition, the structure of each part is not limited to embodiment of illustration, A various change is possible in the range which does not deviate from the meaning of this invention.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Outer housing 5 Fixing apparatus 28 Control part 30 Conveyance path 31 Heater 311 Fixing belt 313 Holding frame 318 Heat source 319 Through hole 32 Pressurizer 321 Core metal 33 Roller support frame 34 Seal member 35 Guide member 351 Frame holding 352 Belt holding part 36 Reflector 361 Shielding part 362 Guide part 40 Temperature sensor 41 Photosensor 42 Rotational speed detection part 50 Infrared filter 51 Shielding plate 52 Condensing lens

Claims (10)

A cylindrical fixing member that is rotatably supported and has a plurality of through holes at equal intervals along the rotation direction;
A pressure member that presses against the outer peripheral surface of the fixing member to form a fixing nip portion; and
A heat source for heating the fixing member from the inner peripheral surface side;
A reflection plate provided at a position covering a part of the outer peripheral surface of the heat source over the width direction, and reflecting light of the heat source;
A fixing unit provided on an outer peripheral surface side of the fixing member, and detecting a light of the heat source that has passed through the through hole ,
The fixing device, wherein an opening width of a portion of the reflecting plate facing the detection unit is narrower than an opening width of other portions. In the reflection plate, the opening width of the portion opposed to the detecting unit is smaller than the diameter of the heat source, a fixing device according to claim 1. In the reflection plate, the opening direction of the portion opposed to the detecting portion is different from the opening direction of the other parts, the fixing device according to claim 1.   The fixing device according to claim 1, wherein an infrared cut filter is provided between the fixing member and the detection unit.   The fixing device according to claim 1, wherein a shielding member that shields heat is provided around the detection unit.   The fixing device according to claim 1, wherein a condensing lens is provided between the fixing member and the detection unit.   The fixing device according to claim 1, wherein in the heat source, a light amount of a portion facing the detection unit is lower than a light amount of other portions.   2. The fixing device according to claim 1, wherein a reflectance of a portion facing the detection unit in the reflecting plate is lower than a reflectance of another portion.   The fixing device according to claim 1, wherein the shape of the through hole is longer in a direction perpendicular to the rotation direction than in a direction along the rotation direction. Comprising a fixing device according to any one of claims 1 to 9 image forming apparatus.

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