JP5672640B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

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

  2. Description of the Related Art Image forming apparatuses such as copiers, printers, facsimiles, and multifunction peripherals thereof are provided with a fixing device that fixes a toner image carried on a recording medium such as paper. Generally, a fixing device includes a fixing member that is heated by a heating source such as a heater, and an opposing member that forms a nip portion in contact with the fixing member. When the image forming operation is started in the image forming apparatus and the toner image is transferred to the sheet, the sheet passes through the nip portion between the fixing member heated to a predetermined temperature and the opposing member. The toner carried on the paper is heated and melted to fix the image.

  In the fixing device, since the heat of the fixing member is taken away by the sheet passing through the nip portion, the fixing member is managed to be maintained at an appropriate temperature by a temperature sensor or the like. On the other hand, in the non-sheet passing area where the sheet does not pass, the heat of the fixing member tends not to be taken away. For this reason, there is a problem that the fixing member overheats in the non-sheet passing region, particularly when the sheet is continuously passed.

  In order to solve this problem, Patent Document 1, Patent Document 2, and Patent Document 3 are provided with a shielding member that can shield heat from the heating source toward the fixing member and can increase or decrease the shielding area by rotation. A fixing device has been proposed.

  However, none of Patent Documents 1 to 3 discloses a specific structure for supporting the shielding member while allowing its rotation. Depending on the configuration of the support structure for the shielding member, the peripheral structure of the shielding member may be complicated or enlarged, and the degree of freedom in layout may be reduced when designing the fixing device and further the image forming apparatus.

  In view of such circumstances, an object of the present invention is to provide a fixing device capable of rotatably supporting a shielding member with a compact and simple mechanism, and an image forming apparatus including the fixing device.

  In order to achieve the above object, the present invention provides a stationary member, a fixing member that is rotatably supported, a heating source that heats the fixing member, and an opposing surface that abuts the outer peripheral surface of the fixing member to form a nip portion. In a fixing device including a member and a rotation side member including a shielding member, the shielding member can shield heat from the heating source toward the fixing member, and the rotation area is increased or decreased by the rotation. Each of the members is provided with opposing surfaces that are opposed to each other in the axial direction, a female portion is formed on one of the opposing surfaces, and a male portion that can be fitted to the female portion is provided on the other side. The portion is slidable in the circumferential direction of the shielding member.

  According to the present invention, the load of the shielding member is supported by the stationary member by the fitting of the male part and the female part, and the rotation direction of the shielding member is guided by the sliding of the male part and the female part in the circumferential direction. Therefore, the shielding member can be rotatably supported with a compact and simple configuration, and the degree of freedom in layout of the fixing device and the image forming apparatus can be increased, and the cost thereof can be reduced.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to the present invention. FIG. 2 is a cross-sectional view illustrating a schematic configuration of a fixing device mounted on the image forming apparatus. FIG. 3 is a cross-sectional view illustrating the fixing device in a state where a shielding member is moved to a retracted position. It is a figure which shows the relationship between the shape of a shielding member, the heat generating part of a halogen heater, and paper size. It is a figure which shows the state which moved the shielding member to the shielding position. It is a figure which shows other embodiment of a shielding member. It is a figure which shows the state which moved the shielding member to the shielding position. It is a figure which shows the support structure of a shielding member. It is a perspective view which shows the drive mechanism of a shielding member. It is a perspective view of a fixing device. FIG. 3 is a perspective view showing a fixing belt support structure. It is a perspective view of a holding member and a slide member. It is a front view which shows the state which accumulated the slide member on the holding member. It is a perspective view which shows the support structure of a shielding member. It is sectional drawing in the XX line in FIG. It is sectional drawing which expands and shows the fitting part of a guide groove and a protrusion.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings for explaining the embodiments of the present invention, constituent elements such as members and components having the same function or shape are described once by giving the same reference numerals as much as possible. Then, the explanation is omitted.

First, an overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.
An image forming apparatus 1 shown in FIG. 1 is a color laser printer, and four image forming units 4Y, 4M, 4C, and 4K are provided in the center of the apparatus main body. Each of the image forming units 4Y, 4M, 4C, and 4K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K has a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and a surface of the photoconductor 5. A developing device 7 for supplying toner and a cleaning device 8 for cleaning the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are denoted by reference numerals. In the other image forming units 4 </ b> Y, 4 </ b> M, and 4 </ b> C, The reference numerals are omitted.

  Under the image forming units 4Y, 4M, 4C, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as an intermediate transfer member, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, a secondary transfer backup roller 32, A cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35 are provided.

  The intermediate transfer belt 30 is an endless belt, and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. Further, a power source (not shown) is connected to each primary transfer roller 31 so that a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31.

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, a power source (not shown) is also connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has come to be.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30. A waste toner transfer hose (not shown) extending from the belt cleaning device 35 is connected to an entrance of a waste toner container (not shown).

  A bottle container 2 is provided in the upper part of the printer body, and four toner bottles 2Y, 2M, 2C, and 2K that store replenishing toner are detachably attached to the bottle container 2. . A replenishment path (not shown) is provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7, and each development from each toner bottle 2Y, 2M, 2C, 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, at the lower part of the printer main body, a paper feed tray 10 that stores paper P as a recording medium, a paper feed roller 11 that carries the paper P out of the paper feed tray 10, and the like are provided. In addition to plain paper, the recording medium includes cardboard, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. Although not shown, a manual paper feed mechanism may be provided.

  In the printer main body, a transport path R is provided for discharging the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as timing rollers for transporting the paper P to the secondary transfer nip at a transport timing is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction. ing.

  Further, a fixing device 20 for fixing the unfixed image transferred onto the paper P is disposed downstream of the position of the secondary transfer roller 36 in the paper transport direction. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. A discharge tray 14 for stocking sheets discharged outside the apparatus is provided on the upper surface of the printer main body.

Next, a basic operation of the printer according to the present embodiment will be described with reference to FIG.
When the image forming operation is started, the respective photoconductors 5 in the respective image forming units 4Y, 4M, 4C, and 4K are rotationally driven clockwise by a driving device (not shown), and the surface of each photoconductor 5 is charged by the charging device 6. Are uniformly charged to a predetermined polarity. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure. Further, by applying a constant voltage having a polarity opposite to the toner charging polarity or a voltage controlled by a constant current to each primary transfer roller 31, the primary transfer nip between each primary transfer roller 31 and each photoreceptor 5 is applied. A transfer electric field is formed.

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 5 is generated by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Then, the surface of each photoconductor 5 is neutralized by a neutralizing device (not shown), and the surface potential is initialized.

  In the lower part of the printer, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The paper P sent to the transport path R is temporarily stopped by the registration rollers 12.

  Thereafter, rotation of the registration roller 12 is started at a predetermined timing, and the paper P is conveyed to the secondary transfer nip in accordance with the timing at which the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip. . Then, the toner images on the intermediate transfer belt 30 are collectively transferred onto the paper P by this transfer electric field. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container (not shown) and collected.

  Thereafter, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

FIG. 2 is a cross-sectional view of the fixing device of this embodiment.
Hereinafter, the configuration of the fixing device 20 will be described with reference to FIG.
As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a fixing member, a pressure roller 22 as an opposing member that contacts the outer peripheral surface of the fixing belt 21, and a heating source that heats the fixing belt 21. Halogen heater 23, nip forming member 24 that contacts pressure roller 22 from the inner peripheral side of fixing belt 21 to form nip portion N, stay 25 as a support member that supports nip forming member 24, halogen heater A reflection member 26 that reflects heat from the fixing belt 21 to the fixing belt 21, a shielding member 27 that shields heat from the halogen heater 23, a temperature sensor 28 as temperature detecting means for detecting the temperature of the fixing belt 21, and the like.

  The fixing belt 21 is composed of a thin and flexible endless belt member (including a film). Specifically, the fixing belt 21 includes a base material on the inner peripheral side formed of a metal material such as nickel or SUS or a resin material such as polyimide (PI), and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). Or it is comprised by the release layer of the outer peripheral side formed with polytetrafluoroethylene (PTFE) etc. Further, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer.

  Also, when there is no elastic layer, the heat capacity is reduced and the fixability is improved. It can happen. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing an elastic layer having a thickness of 100 μm or more, minute unevenness can be absorbed by elastic deformation of the elastic layer, so that occurrence of uneven gloss can be avoided.

  In this embodiment, in order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is thin and has a small diameter. Specifically, the thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, and the overall thickness is set. It is set to 1 mm or less. The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is desirably 0.2 mm or less, and more desirably 0.16 mm or less. The diameter of the fixing belt 21 is desirably 30 mm or less.

  The pressure roller 22 includes a cored bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, or fluorine rubber provided on the surface of the cored bar 22a, and a PFA provided on the surface of the elastic layer 22. Alternatively, it is constituted by a release layer 22c made of PTFE or the like. The pressure roller 22 is pressed toward the fixing belt 21 by a pressure unit (not shown) and is in contact with the nip forming member 24 via the fixing belt 21. At the place where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer 22b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. Note that the fixing member and the facing member are not limited to being in pressure contact with each other, and may be configured to simply contact without pressing.

  The pressure roller 22 is configured to be rotationally driven by a drive source such as a motor (not shown) provided in the printer main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the nip portion N, and the fixing belt 21 is driven to rotate.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heating source such as a halogen heater may be disposed inside the pressure roller 22. The elastic layer 22b may be solid rubber, but if there is no heat source inside the pressure roller 22, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away.

  The halogen heater 23 is disposed on the inner peripheral side of the fixing belt 21 and on the upstream side of the nip portion N in the sheet conveyance direction. Specifically, in FIG. 2, assuming that a virtual straight line passing through the center Q of the nip portion N in the paper transport direction and the rotation center O of the pressure roller 22 is L, the halogen heater 23 is closer to the paper transport direction than the virtual straight line L. It is arranged on the upstream side (lower side in FIG. 2). The halogen heater 23 is configured to generate heat by being output controlled by a power supply unit provided in the printer body, and the output control is performed based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 28. Is called. By such output control of the heater 23, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature. A temperature sensor (not shown) for detecting the temperature of the pressure roller 22 is provided in place of the temperature sensor for detecting the temperature of the fixing belt 21, and the temperature of the fixing belt 21 is predicted based on the temperature detected by the temperature sensor. You may make it do.

  In this embodiment, two halogen heaters 23 are provided, but the number of halogen heaters 23 may be one or three or more according to the size of the paper used in the printer. In addition to the halogen heater, a resistance heating element, a carbon heater, or the like can be used as a heating source for heating the fixing belt 21.

  The nip forming member 24 includes a base pad 241 and a low friction sliding sheet 240 provided on a surface of the base pad 241 facing the fixing belt 21. The base pad 241 is disposed in a longitudinal shape over the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22. The shape of the nip portion N is determined by the base pad 241 receiving the pressure applied by the pressure roller 22. In the present embodiment, the shape of the nip portion N is flat, but may be a concave shape or other shapes. The sliding sheet 240 is provided to reduce sliding friction when the fixing belt 21 rotates. Note that when the base pad 241 itself is formed of a low-friction member, the sliding sheet 240 may not be provided.

  The base pad 241 is made of a heat resistant material having a heat resistant temperature of 200 ° C. or higher. With such a configuration, it is possible to prevent the nip forming member 24 from being deformed by heat in the toner fixing temperature range, to secure a stable state of the nip portion N, and to stabilize the output image quality. In addition, the base pad 241 is required to have appropriate rigidity to ensure strength. The material of the base pad 241 that satisfies the above conditions includes polyethersulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyethernitrile (PEN), polyamideimide (PAI), polyetheretherketone. Resins such as (PEEK) and liquid crystal polymer (LCP) can be used. In addition, the base pad 241 can be formed of metal or ceramic.

  The base pad 241 is fixedly supported by the stay 25. Thus, the nip forming member 24 is prevented from being bent by the pressure of the pressure roller 22, and a uniform nip width is obtained in the axial direction of the pressure roller 22. The stay 25 is preferably formed of a metal material having high mechanical strength such as stainless steel or steel in order to satisfy the function of preventing the nip forming member 24 from bending.

  The reflection member 26 is fixedly supported by the stay 25 so as to face the halogen heater 23. By reflecting the heat (or light) radiated from the halogen heater 23 to the fixing belt 21 by the reflecting member 26, the heat is suppressed from being transmitted to the stay 25 and the like, and the fixing belt 21 is efficiently heated. At the same time, we are trying to save energy. As the material of the reflecting member 26, aluminum, stainless steel or the like is used. In particular, in the case of using a material obtained by vapor-depositing silver having a low emissivity (high reflectivity) on an aluminum base material, the heating efficiency of the fixing belt 21 can be improved.

  The shielding member 27 is made of, for example, a thin metal plate having a thickness of 0.1 mm to 1.0 mm, and the whole is formed in a partial cylindrical surface shape having a cross section orthogonal to the longitudinal direction as an end. The shielding member 27 is close to the inner peripheral surface of the belt inside the fixing belt 21 and rotates substantially coaxially with the fixing belt 21 in a non-contact state with the belt. In the present embodiment, in the circumferential region of the fixing belt 21, a direct heating region in which the halogen heater 23 directly heats the fixing belt 21 is heated, and other than the shielding member 27 between the halogen heater 23 and the fixing belt 21. There is a non-direct heating region in which members (reflection member 26, stay 25, nip forming member 24, etc.) are interposed. When it is necessary to perform heat shielding, as shown in FIG. 2, the shielding member 27 is directly arranged at the shielding position on the heating region side. On the other hand, when there is no need for heat shielding, as shown in FIG. 3, the shielding member 27 is rotated and moved to the retracted position on the non-direct heating region side, and the shielding member 27 is moved to the back side of the reflecting member 26 and the stay 25. It is possible to evacuate. By rotating the shielding member 27 in this manner, the amount of heat supplied from the halogen heater 23 to the fixing belt 21 is adjusted by increasing or decreasing (including the case where the shielding area 27 is set to 0). Yes. Since the shielding member 27 requires heat resistance, it is preferable to use a metal material such as aluminum, iron, stainless steel, or ceramic as the material.

FIG. 4 is a diagram showing the relationship between the shape of the shielding member 27, the heat generating portion of the halogen heater 23, and the paper size.
First, the shape of the shielding member 27 will be described in detail with reference to FIG.
As shown in FIG. 4, the shielding member 27 according to the present embodiment includes a pair of shielding portions 48 provided at both ends for shielding heat from the halogen heater 23 and a connecting portion 49 that connects the shielding portions 48 to each other. And have. Further, an opening 50 is provided between the shielding portions 48 for releasing heat from the halogen heater 23 without shielding it.

  Moreover, the straight part 51 parallel to the rotation direction of the shielding member 27 and the inclination part 52 which inclines with respect to the rotation direction are formed in the inner edge which each shielding part 48 mutually opposes. In FIG. 4, when the side on which the shielding member 27 rotates to the shielding position is defined as the shielding side Y, each inclined portion 52 is continuously provided on the shielding portion side Y of the straight portion 51 and faces the shielding side Y with respect to each other. Tilted away. Thereby, the opening part 50 is formed in the same width | variety between the straight parts 51 toward the shielding side Y, and is formed so that a width | variety may spread between the inclination parts 52. FIG.

Next, the relationship between the heat generating part of the halogen heater and the paper size will be described.
As shown in FIG. 4, in the present embodiment, the length and arrangement position of the heat generating portions of the halogen heaters 23 are varied in order to change the heating area according to the paper size. Of the two halogen heaters 23, the heat generating part 23a of one (lower side in the figure) of the halogen heater 23 is disposed on the central part in the longitudinal direction, and the heat generating part 23b of the other halogen heater 23 (upper side in the figure). Are disposed on both ends in the longitudinal direction. In this example, the heat generating part 23a on the center side is disposed in a range corresponding to the medium-size sheet passing width W2, and the heat generating part 23b on both ends is larger than the medium-sized sheet passing width W2 and has a large size. And an extra large size sheet passing width W3, W4.

  In addition, in the relationship between the shape of the shielding member 27 and the paper size, each straight portion 51 is disposed in the width direction inner side with respect to the end portion of the large size paper passing width W3, and each inclined portion 52 is the large size. Is disposed at a position straddling the end of the sheet passing width W3.

  In this embodiment, for example, the medium size is letter size (sheet passing width 215.9 mm) or A4 size (sheet feeding width 210 mm), and the large size is double letter size (sheet feeding width 279.4 mm) or A3 size ( The paper passing width is 297 mm), and the extra large size is A3 Nobi (paper passing width 329 mm). However, the paper size example is not limited to this. Further, the medium size, large size, and extra large size referred to here indicate the relative size relationship of each size, and the specific numerical value of the sheet passing width is not limited to the above example.

Hereinafter, the basic operation of the fixing device according to the present embodiment will be described with reference to FIG.
When the power switch of the printer main body is turned on, power is supplied to the halogen heater 23 and the pressure roller 22 starts to rotate clockwise in FIG. As a result, the fixing belt 21 is driven to rotate counterclockwise in FIG. 2 by the frictional force with the pressure roller 22.

  Thereafter, the paper P carrying the unfixed toner image T in the above-described image forming process is conveyed in the direction of the arrow A1 in FIG. 2 while being guided by a guide plate (not shown), and the fixing belt 21 in the pressure contact state and It is fed into the nip N of the pressure roller 22. Then, the toner image T is fixed on the surface of the paper P by heat from the fixing belt 21 heated by the halogen heater 23 and pressure applied between the fixing belt 21 and the pressure roller 22.

  The paper P on which the toner image T is fixed is carried out from the nip portion N in the direction of the arrow A2 in FIG. At this time, the paper P is separated from the fixing belt 21 by the leading edge of the paper P coming into contact with the leading edge of a separation member (not shown). Thereafter, the separated paper P is discharged out of the apparatus by the paper discharge roller as described above, and stocked on the paper discharge tray.

Next, the control of the halogen heater and the control of the shielding member 27 for each paper size will be described.
First, when the medium-size paper P2 shown in FIG. 4 is passed, only the heat generating portion 23a on the center side is heated, so that only the range corresponding to the medium-size paper passing width W2 is heated. When passing oversized paper P4, in addition to the heat generating portion 23a on the center side, the heat generating portions 23b on both ends are also heated, and the range corresponding to the oversized paper passing width W4 is heated.

  The heating range of the halogen heater 23 corresponds only to the medium size sheet passing width W2 and the extra large size sheet passing width W4. For this reason, when passing large size paper P3, if only the heat generating part 23a on the center side is heated, the necessary range is not heated, and the heat generating parts 23a, 23b on the center side and both ends are heated. As a result, the heated range exceeds the large sheet passing width W3. If the large-size sheet P3 is passed as it is in a state in which the heat generating portions 23a and 23b on the both ends on the center side are heated, the fixing belt in the non-sheet-passing area outside the large-size sheet passing width W3. There is a problem that the temperature of 21 rises excessively.

  Therefore, in the present embodiment, when passing the large size paper P3, as shown in FIG. 5, the shielding member 27 is moved to the shielding position. As a result, the shield 48 on both ends can cover the outer area from the vicinity of the end of the large sheet passing width W3, so that the temperature rise of the fixing belt 21 can be suppressed in the non-sheet passing area.

  Further, when it is no longer necessary to shield the heat, such as when the fixing process is completed, or when the temperature of the non-sheet passing area of the fixing belt 21 is equal to or lower than a predetermined threshold, the shielding member 27 is returned to the retracted position. . In this way, by moving the shielding member 27 to the shielding position as necessary, good fixing can be performed without reducing the sheet passing speed.

  In the present embodiment, since the inclined portion 52 is provided in the shielding portion 48, it is possible to adjust the range in which the halogen heater 23 b is covered by the shielding portion 48 by changing the rotational position of the shielding member 27. . For example, the temperature of the fixing belt 21 in the non-sheet passing area tends to increase as the number of sheets passed and the sheet passing time increase. Therefore, when the number of sheets passed reaches a predetermined number or when the sheet passing time reaches a predetermined time. Is reached, the shielding member 27 is rotated in a direction to cover the heat generating portion 23b on both ends. Thereby, it is possible to reliably suppress an abnormal temperature rise of the fixing belt 21.

The temperature sensor 28 that detects the temperature of the fixing belt 21 is preferably disposed in a region where the temperature increase in the axial direction of the fixing belt 21 is significant.
In the case of the present embodiment, the temperature is likely to rise particularly in a region outside the large-size sheet passing width W3. Therefore, it is desirable to dispose the temperature sensor 28 outside the large-sized sheet passing width W3 (FIG. 4). reference). Further, in the present embodiment, of the two halogen heaters 23, it is the halogen heater 23 having the heat generating portions 23 b on both end sides that is largely caused by the temperature rise, and therefore the heat generating portion 23 b of the halogen heater 23. It is desirable to dispose the temperature sensor 28 at a position opposite to.

FIG. 6 shows another configuration example of the shielding member.
In the shielding member 27 shown in FIG. 6, the shielding portions 48 on both ends are integrally formed in a shape having two step portions. That is, each shielding part 48 is comprised by the small shielding part 48a with a small longitudinal direction width | variety, and the large shielding part 48b with a large longitudinal direction width | variety. The small shielding parts 48a are located at both ends in the longitudinal direction of the shielding member 27, and protrude to the shielding side Y from the large shielding part 48b. The two shielding parts 48 are connected via a connecting part 49. Further, the inner edges of the small shielding part 48a facing each other and the inner edges of the large shielding part 48 facing each other are inclined parts 52a and 52b that are inclined so as to be separated from each other toward the shielding side Y. In this type of shielding member 27, the straight portion 51 as in the shielding member 27 shown in FIG. 4 is not formed.

  In the embodiment shown in FIG. 6, at least four types of paper are used: small size paper P1, medium size paper P2, large size paper P3, and extra large size paper P4. In this embodiment, for example, the small size is a postcard size (sheet feeding width 100 mm), the middle size is A4 size (sheet feeding width 210 mm), the large size is A3 size (sheet feeding width 297 mm), and the extra large size is A3 nobi (Paper width 329 mm). However, the paper size example is not limited to this.

  Here, the paper passing width W1 of the small size paper P1 is in a range smaller than the length of the heat generating portion 23a on the center side. Further, in relation to the shape of the shielding member 27, each inclined portion 52b of the large shielding portion 48b is disposed at a position straddling the end of the small size sheet passing width W1, and each inclined portion 52a of the small shielding portion 48a is The sheet is disposed at a position straddling the end of the large sheet passing width W3. Note that the positional relationship between the paper sizes other than the small size (medium, large, extra large) and each of the heat generating portions 23a, 23b is the same as in the above embodiment, and thus the description thereof is omitted.

  When the small size paper P1 is passed, only the heat generating portion 23a on the center side is heated. However, in this case, since the range heated by the heat generating part 23a on the central side exceeds the small sheet passing width W1, the shielding member 27 is moved to the shielding position as shown in FIG. As a result, the large shielding portion 48b can cover the outer area from the vicinity of the end portion of the small sheet passing width W1, so that the temperature rise of the fixing belt 21 can be suppressed in the non-sheet passing area.

  Note that the control of the halogen heater 23 and the shielding member 27 when passing other size sheets (medium, large, extra large) is basically the same as in the above embodiment. In this case, the function as the shielding part 48 in the embodiment is performed by the small shielding part 48a.

  In the case of the embodiment shown in FIG. 6 as well, since the inclined portions 52a and 52b are provided in the small shielding portion 48a and the large shielding portion 48b, respectively, similarly to the shielding portion 48 in the above embodiment, the rotation of the shielding member 27 is performed. By changing the position, it is possible to adjust the range in which the heat generating portions 23a and 23b are covered by the shielding portions 52a and 52b.

  In the fixing device 20 of the present invention, when the shielding member 27 is moved between the retracted position and the shielding position or when the shielding position is adjusted, it is necessary to rotate the shielding member 27 in the forward and reverse directions.

FIG. 8 is a perspective view showing a drive mechanism 50 that rotationally drives the shielding member 59 in the forward and reverse directions.
As shown in FIG. 8, the drive mechanism 60 is arranged on one end side in the axial direction of the shielding member 27 (left side in FIG. 9), and includes a motor 61 as a drive source and a plurality of transmission gears 62, 63, 64. The gear train which consists of. Of the gear train, the gear 62 on one end side is connected to the output shaft of the motor 61. Further, the gear 64 on the other end side meshes with a gear portion 415 formed on the outer peripheral surface of the slide member 41 (described in detail later). Accordingly, when the motor 42 is driven in the forward and reverse directions, the driving force is transmitted to the slide member 41 via the gear train, and the shielding member 27 rotates in the forward and reverse directions.

  FIG. 9 is a perspective view showing a support structure of the fixing belt 21, and FIG. 10 shows the nip portion N by vertically inverting the support structure at the non-driving side end portion (right side in FIG. 9) of the shielding member 27. It is the perspective view seen from the side. In the following description, the terms “axial direction”, “circumferential direction”, and “radial direction” mean respective directions when the rotation axis of the shielding member 27 is used as a reference. For example, the axial direction coincides with the longitudinal direction of the shielding member 27.

  As shown in FIG. 9, the fixing belt 21 is rotatably supported by holding members 40 disposed at both ends in the axial direction. As shown in FIG. 10, the holding member 40 is detachably attached to the side plate 29 of the fixing device 20 using screws or the like.

  As shown in FIG. 8, the shielding member 27 is rotatably supported by a support structure having a holding member 40 and a slide member 41.

  As shown in FIG. 11, the holding member 40 has a hollow shape that is open on both sides in the axial direction, and integrally includes a receiving portion 401 that extends in the axial direction and a flange portion 402 that protrudes radially from the receiving portion 401. The receiving portion 401 is formed in a partial cylindrical shape having a notch 403 in a partial region in the circumferential direction. The nip forming member 24 is inserted into the space formed by the notch 403 as shown in FIG. An end portion of the nip forming member 24 is fixed to the side plate 29 through the inner periphery of the flange portion 402. Although not shown in FIG. 10, each end of the halogen heater 23 and the stay 25 arranged inside the fixing belt is also fixed to the side plate 29 through the inner periphery of the receiving portion 401 and the inner periphery of the flange portion 402. Has been.

  As shown in FIG. 11, the slide member 41 is disposed so as to face the holding member 40 in the axial direction in a region opposite to the mounting side of the fixing belt 21 in the axial direction. In the following description, the opposing surface 404 of the holding member 40 that faces the slide member 41 in the axial direction is referred to as the outer surface of the holding member 40, and the opposing surface of the slide member 41 that faces the holding member 40 in the axial direction. 411 is referred to as the inner surface of the slide member 41.

  The slide member 41 has an arc shape when viewed from the holding member 40 side, and a protrusion 412 extending in the circumferential direction as a male portion is formed on the inner side surface 411 thereof. Further, a raised portion 413 is formed on the inner peripheral surface of the slide member 41. An arcuate hole 414 extending in the circumferential direction of the shielding member 27 is formed on the inner side surface of the raised portion 413. A projection 27a provided at the end of the shielding member 27 is inserted into the hole 414 (see FIG. 13), whereby the shielding member 27 and the slide member 41 are coupled to each other so that both can rotate integrally. Yes.

The holding member 40 and the slide member 41 are assembled to the fixing device 20 in a state in which they are in close contact with each other in the axial direction. FIG. 12 is a front view showing the holding member 40 and the slide member 41 in the assembled state.
As shown in the figure, a guide groove 405 extending in the circumferential direction as a female portion is formed on the outer surface 404 of the holding member 40. In the guide groove 405, the protrusion 412 of the slide member 41 is fitted. The circumferential length of the guide groove 405 is longer than the circumferential length of the protrusion 412. In the holding member 40, the region where the guide groove 405 is formed and the region where the receiving portion 401 is formed substantially coincide with each other in the axial direction.

  Both the holding member 40 and the slide member 41 described above can be formed by resin injection molding. At this time, the holding member 40 and the slide member can be formed of a resin material having high heat resistance and slidability, such as a liquid crystal polymer or polyimide. In addition, both may be formed of the same kind of resin or different kinds of resins. Considering the processing cost, it is desirable that both the holding member 40 and the slide member 41 be resin injection-molded products. If this point is not a problem, either the holding member 40 or the slide member 41 is used. One or both can be made of metal.

  10 to 12, among the support structures at both ends in the axial direction of the shielding member 27, the support structure of the non-driving side end portion where the drive mechanism 50 is not disposed, the holding member 40 that constitutes the support structure, and the slide member 41 is illustrated. On the other hand, as shown in FIGS. 8 and 13, the support structure of the drive side end portion where the drive mechanism 50 is arranged basically has the same configuration as the non-drive side support structure. In the drive side end support structure, a gear portion 415 that meshes with the gear 54 of the drive mechanism 50 is provided on the outer peripheral surface of the slide member 41. In this respect, the non-drive side end that does not have such a gear portion is provided. The structure is different from that of the slide member 41 of the support structure.

FIG. 14 is a cross-sectional view taken along line XX in FIG.
As shown in FIG. 14, when the protrusion 412 of the slide member 41 is fitted into the guide groove 405 of the holding member 40, the shielding member 27 coupled to the slide member 41 is supported by the holding member 40. At this time, the protrusion 412 can slide in the circumferential direction in a region other than the axial center with respect to the guide groove 405. Therefore, when the slide member 41 is rotationally driven by the drive mechanism 50, the slide member 41 is guided in the circumferential direction by sliding between the protrusion 412 and the guide groove 405, and the slide member 41 rotates around the specified position as the rotation center. Thereby, the shielding member 27 can be moved between the shielding position and the retracted position, and the amount of heat given from the halogen heater 23 to the fixing belt 21 can be controlled. Thus, the holding member 40 according to the present invention has a function of rotatably supporting not only the fixing belt 21 but also the shielding member 27.

  By the way, the shielding member 27 of the present embodiment is formed of a thin-walled material in a partial cylindrical shape, and has a fragile portion (connecting portion 49 (see FIG. 4)) having an extremely narrow width, so that rigidity is ensured. Difficult to do. Therefore, if the sliding resistance between the guide groove 405 and the protrusion 412 is large, the shielding member 27 may be twisted and the left and right shielding areas may vary. In order to prevent such inconvenience, as shown in FIG. 14, gaps (α1, α2) of an appropriate size are provided between the guide groove 405 and the protrusion 412 in the radial direction and the axial direction of the shielding member 27 to slide. It is preferable to try to reduce the resistance. The gaps α1 and α2 also have a role of suppressing an increase in sliding resistance between the guide groove 405 and the protrusion 412 even during thermal expansion at a high temperature. In order to reduce the sliding resistance between the guide groove 405 and the protrusion 412, a plurality of minute protrusions 420 may be formed on the opposing inner surface of the guide groove 405 as shown in FIG. 15. The minute protrusions 420 can be formed on the inner surface of the guide groove 405 or on the peripheral surface of the protrusion 412.

  The support structure of the shielding member 27 described above has the following characteristics.

  The necessary space on both sides in the axial direction of the fixing belt 21 is sufficient to accommodate the holding member 40 and the slide member 41 which are in close contact with each other in the axial direction. Therefore, the support structure of the shielding member 29 can be made compact, and the degree of freedom in layout around the fixing device 20 is improved.

  When a substantially cylindrical member such as the shielding member 27 is rotatably supported, a configuration in which a shaft is arranged at the center of rotation of the member and the shaft is supported by a bearing is common. However, when such a configuration is adopted, the axial space increases. Further, a member for connecting the shaft and the shielding member 27 is required, and the heat capacity of the entire shielding member 27 is increased, resulting in an increase in energy loss. Furthermore, if the connecting member is integrated with the shielding member 27, it becomes difficult to manufacture the shielding member 27 only by plastic processing of the metal plate, and if the connecting member is a separate member, the number of parts increases. Therefore, in any case, the cost increases.

  On the other hand, in the present invention, the opposing surfaces 404 and 411 facing each other in the axial direction are provided on each of the slide member 41 that is the rotation side member and the holding member 40 that is the stationary side member, and the opposing surface 404 of the holding member 40 is provided. A guide groove 405 (female part) is formed on the (outer side surface), and a protrusion 412 (male part) that can be fitted to the guide groove 405 is provided on the opposing surface 411 (inner side surface) of the slide member 41. Further, the guide groove The 405 and the protrusion 412 can slide in the circumferential direction of the shielding member 27. According to this configuration, the load of the shielding member 27 is supported by the holding member 40 by the fitting of the guide groove 405 and the protrusion 412, and the rotation direction of the shielding member 27 is guided by the sliding of the guide groove 405 and the protrusion 412. Is done. Therefore, the shielding member 27 can be rotatably supported with a compact configuration. In this case, it is not necessary to arrange the shaft at the rotation center of the shielding member 27 and it is not necessary to connect the shaft and the shielding member 27. Therefore, the above problem can be solved.

  Even if a pin is fitted as a male part to the guide groove 405, the shielding member 27 can be supported rotatably. However, in such a configuration, since the guide groove and the pin are in point contact or line contact with each other, the posture of the shielding member 27 is not stable, and it is difficult to accurately control the amount of heat applied to the fixing belt 21. On the other hand, in the present invention, since the protrusion 412 having a certain length in the circumferential direction is fitted into the guide groove 405 and both are brought into surface contact, the posture of the shielding member 27 is stabilized. Can do.

  If the driving mechanism 50 for rotationally driving the fixing belt 21 is disposed at one end in the axial direction of the shielding member 27, the configuration of the fixing device 20 can be simplified as compared with the case where the driving mechanism 50 is disposed at both ends. Therefore, the degree of freedom in layout can be further improved.

  As shown in FIG. 14, in the region on the side where the fixing belt 21 is mounted on the both sides in the axial direction of the holding member 40, both of them are between the axial end of the fixing belt 21 and the flange portion 402 of the holding member 40. A slip ring 42 is disposed to prevent direct contact between the two. As described above, since the slip ring is interposed, the guide groove 405 is formed on one of the rotating side and the stationary side in the region of the holding member 40 on the side where the fixing belt 21 is mounted, and the protrusion on the other side. Even when 412 is formed, it is difficult to fit them together. On the other hand, in the present invention, the slide member 41 is coupled to the shielding member 27, and the slide member 41 is opposed to the holding member 40 in a region opposite to the fixing belt 21 in the axial direction, and the guide is guided to the opposed portion. Grooves 405 and protrusions 412 are arranged. Therefore, regardless of the slip ring 42, the guide groove 405 and the protrusion 412 can be reliably fitted.

  By forming both the holding member 40 and the slide member 41 with resin, it is possible to further reduce the sliding resistance between the guide groove 405 and the protrusion 412 and to reliably prevent the shielding member 27 from being twisted.

  As shown in FIG. 3, when the shielding member 27 rotates in a direction to reduce the shielding area (especially when the shielding member 27 moves to the retracted position), one end of the shielding member 27 is disposed inside the fixing belt. The nip forming member 24 is approached.

  Here, for example, when a coupling portion (hole portion 414) between the slide member 41 and the shielding member 27 is provided near the middle in the circumferential direction of the slide member 41, the slide member 41 may be rotated even if the shielding member 27 is rotated in the retracting direction. Interferes with the nip forming member 24 and further rotation is restricted. Therefore, there is a possibility that the retreat of the shielding member 27 is insufficient. On the other hand, as shown in FIG. 12, when the shielding member 27 of the slide member 41 is rotated in the retracting direction to reduce the shielding area, the shielding member 27 is located at the end approaching the nip forming member 24. If the connecting portion is arranged, the moving stroke of the shielding member 27 can be maximized, and the shielding member 27 can be reliably moved to the retracted position.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. In the above embodiment, the case where the present invention is applied to a fixing device using a fixing belt has been described as an example. However, a configuration in which a hollow (cylindrical) or solid fixing roller is used instead of the fixing belt. It is possible to apply the present invention. Further, the shape of the shielding member is not limited to the above-described embodiment. Depending on the paper size used, the shielding member may be formed in a shape having three or more step portions. Further, the image forming apparatus equipped with the fixing device according to the present invention is not limited to the printer as shown in FIG. 1, but can be a copying machine, a facsimile, or a complex machine thereof.

  Moreover, in the said embodiment, although the protrusion 412 as a male part was formed in the slide member 41 of a movable side, and the case where the guide groove 405 as a female part was formed in the holding member 40 of a fixed side was illustrated, Conversely, a guide groove as a female part may be formed in the movable slide member 41, and a protrusion 412 as a male part may be formed in the holding member 40 on the fixed side. Further, the slide member 41 is omitted, and a protrusion 412 is formed at one end of the shielding member 27 serving as the rotation side member, and this is directly fitted into the guide groove 405 provided on the outer surface 404 of the holding member 40. You can also.

20 Fixing device 21 Fixing belt (fixing member)
22 Pressure roller (opposing member)
23 Halogen heater (heating source)
24 Nip forming member 25 Stay (support member)
26 Reflecting member 27 Shielding member 40 Holding member 41 Slide member 404 Outer surface (opposing surface)
405 Guide groove (female part)
411 Inner side (opposite side)
412 ridge (male)
414 hole (joint part)
415 Gear part P paper (recording medium)

Japanese Patent No. 4130898 JP 2008-58833 A JP 2008-139779 A

Claims (9)

A stationary member, a fixing member rotatably supported, a heating source for heating the fixing member, an opposing member that contacts the outer peripheral surface of the fixing member to form a nip portion, and a rotating member including a shielding member; In the fixing device, the shielding member can shield heat from the heating source toward the fixing member, and the shielding area is increased or decreased by the rotation thereof.
Each of the rotation-side member and the stationary-side member is provided with opposing surfaces that face each other in the axial direction, and a female portion is formed on one of the opposing surfaces, and a male portion that can be fitted to the female portion is provided on the other. A fixing device provided with a male part and a female part slidable in the circumferential direction of the shielding member.   The fixing device according to claim 1, wherein the female portion is a guide groove extending in a circumferential direction of the shielding member, and the male portion is a protrusion extending in the circumferential direction of the shielding member.   The stationary member and the rotating member are taken as one set, and one set of the stationary member and the rotating member are arranged at both ends in the axial direction of the shielding member, and a driving mechanism for rotationally driving the shielding member is provided in the axial direction of the shielding member. The fixing device according to claim 1, wherein the fixing device is disposed at one end.   The fixing device according to claim 1, wherein the entire shielding member is formed of a thin plate material in a partial cylindrical surface shape.   The fixing member is an endless fixing belt having a heating source and a shielding member disposed therein, and the stationary side member is a holding member that is fitted to both axial ends of the fixing belt and rotatably supports the fixing belt. The fixing device according to any one of 1 to 4.   The rotation side member is constituted by a shielding member and a sliding member coupled to the shielding member, and the sliding member is opposed to the holding member in a region opposite to the fixing belt in the axial direction, so that each of the holding member and the sliding member is provided. The fixing device according to claim 5, wherein the facing surface is formed. The fixing device according to claim 6, wherein both the holding member and the slide member are made of resin.
  A nip forming member that forms the nip portion is arranged inside the fixing belt, and among the slide members, an end portion that approaches the nip forming member when the shielding member rotates in a direction to reduce the shielding area, The fixing device according to claim 6, wherein a coupling portion with the shielding member is disposed.   An image forming apparatus comprising the fixing device according to claim 1.

Images