JP2015025957A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that can accurately stop a shielding member at a target position.SOLUTION: There is provided a fixing device including a shielding member 27 that can be moved between a fixing member and a heat source in the regular direction and reverse direction to change the area of a heating target area to be heated by the heat source, a holding member 41 that movably holds the shielding member 27, and position detection means 63 and 64 for directly detecting the position of the holding member 41, where the fixing device controls the movement of the shielding member 27 on the basis of position information on the holding member 41 detected by the position detection means 63 and 64.

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 Documents 1, 2, and 3 propose a fixing device provided with a shielding member that shields heat from a heating source in a non-sheet passing region of the fixing member. In these fixing devices, the shielding member is configured to be movable, and by arranging the shielding member at an appropriate position according to the paper size, the heat is shielded in a necessary range, and the paper width is supported. The heated area can be secured.

  However, in the fixing devices described in Patent Documents 1 to 3, it is difficult to accurately stop the shielding member at the target position. For this reason, there is a possibility that an excessive temperature rise occurs in the non-sheet passing region and the shielding member is deformed, or that the image quality is deteriorated due to insufficient heating.

  SUMMARY An advantage of some aspects of the invention is that it provides a fixing device that can accurately stop a shielding member at a target position, and an image forming apparatus including the fixing device.

  In order to solve the above problems, the present invention provides a rotatable fixing member, a heating source for heating the fixing member, a facing member that abuts an outer peripheral surface of the fixing member to form a nip portion, and the fixing member A shielding member capable of moving in a forward direction and a reverse direction between the heating source and the moving member, and capable of changing an area of a heated region heated by the heating source of the fixing member, and the shielding member. In a fixing device comprising: a holding member that is movably held; and a power transmission mechanism that transmits power from a driving source to the shielding member to move the shielding member, a position detection unit that directly detects the position of the holding member. And the movement of the shielding member is controlled based on the position information of the holding member detected by the position detecting means.

  According to the present invention, by controlling the movement of the shielding member based on the position information of the holding member directly detected by the position detecting means, it is possible to reduce the variation in the position of the shielding member due to the dimensional tolerance of components, mounting errors, and the like. . Thereby, it becomes possible to arrange | position a shielding member to the target position with high precision.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 3 is a cross-sectional view of a fixing device mounted on the image forming apparatus. It is sectional drawing which shows the state which moved the shielding member to the non-heating area | region. It is a perspective view of the fixing device. It is a perspective view which shows the support structure of a shielding member. It is a perspective view which shows the drive means of a shielding member. 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 structure of the characteristic part of this invention. It is a figure which shows operation | movement of a shielding member. It is a figure which shows an example of the specific control flow of a shielding member. It is a figure which shows the structure of a comparative example. It is a figure which shows return operation | movement to the initial position of the shielding member in the structure which is not equipped with the sensor for initial position detection.

  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 the heat from the fixing belt 21 to the fixing belt 21, a shielding member 27 that shields the heat from the halogen heater 23, a temperature sensor 28 as a first temperature detecting means for detecting the temperature of the fixing belt 21, and the like. Prepare.

  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 pressurized toward the fixing belt 21 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. The nip portion N is switched between a pressurized state and a depressurized state by a switching mechanism (not shown). Note that the fixing belt 21 and the pressure roller 22 are not limited to being brought into pressure contact with each other, and may be configured to simply contact each other without applying pressure.

  The pressure roller 22 is configured to be rotationally driven by a drive source such as a fixing motor (not shown) provided in the printer 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. In place of the temperature sensor for detecting the temperature of the fixing belt 21, a temperature sensor 29 is provided as a second temperature detecting means for detecting the temperature of the pressure roller 22, and the fixing belt is detected based on the temperature detected by the temperature sensor 29. 21 temperatures may be predicted.

  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, an IH, 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 this configuration, the nip forming member 24 is prevented from being deformed by heat in the toner fixing temperature range, and a stable state of the nip portion N is secured 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. A resin such as (PEEK) 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 iron 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 radiant heat from the halogen heater 23 to the fixing belt 21 by the reflection member 26, heat is prevented from being transmitted to the stay 25 and the like, thereby efficiently heating the fixing belt 21 and saving energy. Yes. 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 configured by forming a metal plate having a thickness of 0.1 mm to 1.0 mm into an arc-shaped cross-sectional shape along the inner peripheral surface of the fixing belt 21. The shielding member 27 is movable between the fixing belt 21 and the halogen heater 23 in the circumferential direction. In the present embodiment, as shown in FIG. 3, the circumferential region of the fixing belt 21 is opposed to the halogen heater 23 and is directly heated by the halogen heater 23. Other members (reflecting member 26, stay 25, nip forming member 24, etc.) fixed to the side plate or the like are interposed, and a non-heated region β that is not directly heated by the halogen heater 23 is formed. When it is necessary to perform heat shielding, as shown in FIG. 2, the shielding member 27 is disposed at a shielding position set at one place or a plurality of places on the heated region α side. On the other hand, when there is no need for heat shielding, as shown in FIG. 3, the shielding member 27 is moved to the non-heating region β side, and the entire shielding member 27 is retracted to the back side of the reflecting member 26 and the stay 25. It is possible. By rotating the shielding member 27 in this manner, the area of the heated region α of the fixing belt 21 is changed, and the amount of radiant heat applied to the fixing belt 21 from the halogen heater 23 is adjusted. 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 perspective view of the fixing device of this embodiment.
As shown in FIG. 4, flange members 40 as belt holding members are inserted into the inner circumferences of both ends of the fixing belt 21, and the fixing belt 21 is rotatably held by the flange members 40. . Each flange member 40, halogen heater 23 and stay 25 are fixedly supported by a pair of side plates (not shown) of the fixing device 20.

FIG. 5 is a diagram illustrating a support structure of the shielding member.
As shown in FIG. 5, the shielding member 27 is held by an arcuate slide member 41 as a holding member attached to the flange member 40. Specifically, the projection 27 a provided at the end of the shielding member 27 is inserted into the hole 41 a provided in the slide member 41, so that the shielding member 27 is attached to the slide member 41. Further, the projecting portion 41b is provided on the slide member 41, and when the projecting portion 41b is inserted into the arc-shaped groove portion 40a provided on the flange member 40, the slide member 41 slides along the groove portion 40a. It is possible. Thereby, the shielding member 27 can rotate and move integrally with the slide member 41 in the circumferential direction of the flange member 40. In the present embodiment, the flange member 40 and the slide member 41 are made of resin.

  In FIG. 5, only the support structure of one end portion is shown, but the other end portion is similarly held rotatably via the slide member 41.

FIG. 6 is a diagram illustrating a driving mechanism of the shielding member.
As shown in FIG. 6, in the present embodiment, as a drive mechanism for the shielding member 27, a motor 42 that is a drive source and a power transmission mechanism 47 having a gear train composed of a plurality of gears 43, 44, 45, 46 are provided. Prepare. In the gear train, the gear 43 on one end side is a worm gear provided on the rotating shaft of the motor 42, and the gear 46 on the other end side is connected to a gear portion 41 c provided in the circumferential direction of the slide member 41. When the motor 42 is driven, the driving force is transmitted to the slide member 41 through the gear train, and the shielding member 27 is moved in the forward direction (rotation direction from the non-heated region β to the heated region α) and in the reverse direction (heated region). The rotational movement is made in the direction of rotation from α to the non-heated region β.

FIG. 7 is a diagram showing the relationship between the shape of the shielding member, the heat generating portion of the halogen heater, 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. 7, 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. 7, when the side where 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 side Y of the straight portion 51, and the interval between the inner edges is shielded. The side Y is inclined so as to be separated. 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. 7, in the present embodiment, the length and the 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.

  As an example of the paper size in the present embodiment, for example, the medium size is letter size (paper passing width 215.9 mm) or A4 size (paper passing width 210 mm), and the large size is double letter size (paper passing width 279.4 mm) or A3 size (sheet passing width 297 mm), extra large size A3 Nobi (sheet passing width 329 mm), and the like. However, the paper size example is not limited to this. The medium size, large size, and extra large size referred to here indicate the relative relationship between the sizes, and may be a small size, a medium size, a large size, or the like.

Next, the control of the halogen heater and the control of the shielding member for each paper size will be described.
First, when passing the medium-size paper P2 shown in FIG. 7, only the range corresponding to the medium-size paper passing width W2 is heated by heating only the heat generating portion 23a on the center side. 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.

  However, in the present embodiment, 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 while the heat generating portions 23a and 23b on the center side and both end sides 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. 8, 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. 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.

  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 moved to the non-heating area β. Return to.

  Further, 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 heat generating portion 23b 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. The temperature rise can be suppressed to a higher degree by rotating the shielding member 27 in such a direction as to cover the heat generating portions 23b on both ends.

The temperature sensor 28 for detecting the temperature of the fixing belt 21 is disposed in a region where the temperature rise in the axial direction of the fixing belt 21 is remarkable.
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. 7). 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. Although FIG. 7 illustrates the case where the temperature sensors 28 are disposed at both ends of the sheet passing width, either one of the temperature sensors 28 can be omitted. Further, the temperature sensor 28 can be arranged at a place other than the illustrated location (for example, the central portion of the sheet passing width). The number of the temperature sensors 28 can be set arbitrarily, and can be arranged at three or more locations in the axial direction of the fixing belt 21.

FIG. 9 shows another embodiment of the shielding member.
In the shielding member 27 shown in FIG. 9, the shielding portions 48 on both ends are each 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 large shielding parts 48b are connected to each other via a connecting part 49, and the small shielding part 48a is provided continuously on the shielding side Y of the large shielding part 48b. Further, the inner edges of the small shielding part 48a facing each other and the inner edges of the large shielding part 48b facing each other are inclined parts 52a and 52b that are inclined away from each other toward the shielding side Y. The straight part 51 like the shielding member 27 shown in FIG. 7 is not formed.

  In the embodiment shown in FIG. 9, 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. As an example of the paper size in this embodiment, for example, a small size is a postcard size (paper passing width 100 mm), a medium size is A4 size (paper passing width 210 mm), a large size is A3 size (paper passing width 297 mm), and an extra large size is A3. Nobi (sheet passing 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 center 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.

  The control of the halogen heater 23 and the shielding member 27 when passing other size sheets (medium, large, extra large) is 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. 9 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 of 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 48a and 48b.

  Thus, in order to arrange the shielding member 27 at an appropriate position in accordance with the paper size or the like, it is necessary to provide a position detection means for detecting the rotational position of the shielding member 27 and to manage the rotational position. As the position detection means, for example, as shown in FIG. 14, a substantially fan-shaped filler 200 as a detected portion that rotates in conjunction with the shielding member 27 and a sensor 300 that detects the position of the filler 200 are provided. Things.

  The filler 200 is attached to a frame or the like (not shown) so as to be rotatable in the forward and reverse directions around the support shaft 200a. In addition, the filler 200 is connected to the slide member 41 via a long connecting member 400. Therefore, when the shielding member 27 rotates, that is, when the slide member 41 moves, the filler 200 rotates in conjunction with this.

  The sensor 300 is a photo interrupter having a light emitting part and a light receiving part, and is attached to a frame or the like (not shown). In this case, when the shielding member 27 rotates, the filler 200 rotates, and when the filler 200 enters between the light emitting unit and the light receiving unit of the sensor 300 and the light is blocked (shielded state), the sensor 300 is high. Send a signal. On the contrary, when the filler 200 comes out from between the light emitting part and the light receiving part and light is transmitted (translucent state), a Low signal is emitted. Thus, the position of the shielding member 27 can be indirectly detected by detecting the timing when the filler 200 shields light or transmits light. The position of the shielding member 27 is stopped by stopping the movement of the shielding member 27 at a specified rotation angle based on the time when the output signal of the sensor 300 is switched from Low to High, or the time when the output signal is switched from High to Low. Can be determined.

  However, in the configuration shown in FIG. 14, the length of the connecting member 400, the angular accuracy error of the filler 200, the positional accuracy error of the filler 200, the backlash between the rotation center of the filler 200 and the support portion, and the like are accumulated. The variation in the relative position between the filler 200 and the shielding member 27 may increase. As a result, the position of the shielding member 27 may not be determined with high accuracy.

Therefore, in the embodiment of the present invention, a configuration as shown in FIG. 11 is adopted so that the position of the shielding member 27 can be accurately determined.
As shown in FIG. 11, in the embodiment of the present invention, two reflective sensors 63 and 64 are provided as position detection means, and the position of the slide member 41 is directly detected by each sensor 63 and 64. Yes. In the present embodiment, the slide member 41 has an encoder section 61 formed of a convex pattern provided so as to be arranged in the moving direction, and the pattern of the encoder section 61 is detected by the sensors 63 and 64. A planar pattern may be printed on the slide member 41, or a sheet on which the pattern is formed may be attached to the slide member 41. Each sensor 63, 64 is adapted to receive the reflected light of the light irradiated from the light emitting unit to the encoder unit 61 at the light receiving unit, and there is a convex pattern of the encoder unit 61 at a position opposed to the light receiving unit. The reflected light is received and a Low output signal is emitted. In other cases, a high output signal is generated. In the present embodiment, of the two sensors 63 and 64, the upper sensor 63 in FIG. 11 is used as the initial position detection sensor 63 for detecting the initial position of the shielding member 27. On the other hand, the lower sensor 64 in the figure is used as the rotation angle control sensor 64.

FIG. 12A shows a state in which the shielding member 27 is disposed at the initial position.
The initial position here is a position where the shielding member 27 does not shield the radiant heat from the halogen heater 23 and the area of the heated region α of the fixing belt 21 is maximized (see FIG. 3). That is, as the shielding member 27 rotates in the positive direction X1 from the initial position, the area where the shielding member 27 shields the heated region α increases, and the area of the heated region α decreases. Note that the initial position is a position where the shielding member 27 has moved to the maximum in the X2 direction, so the shielding member 27 does not move in the X2 direction beyond the initial position. In the present embodiment, while the shielding member 27 moves between the initial position shown in FIG. 12A and the position shown in FIG. 12B, the shielding area α of the heated region α by the shielding member 27 is small. It is configured to be substantially zero. Then, if the shielding member 27 is rotated in the positive direction X1 even slightly from the position shown in FIG. 12B, the area of the heated region α is reduced, and the shielding member 27 is stopped at each shielding position, thereby being heated. The area α can be reduced in stages.

  In FIG. 12, the convex pattern of the encoder unit 61 is shown in white, and the concave pattern between the convex patterns is shown in black. As shown in FIG. 12A, in the state where the shielding member 27 is disposed at the initial position, the convex pattern 61 a on the one end side of the encoder section 61 is disposed at the detection position of the initial position detection sensor 63. ing. At this time, the initial position detection sensor 63 generates a Low output signal. On the other hand, as shown in FIG. 12B, when the convex pattern 61a on the one end side is not at the detection position of the initial position detection sensor 63, the output signal of the initial position detection sensor 63 becomes High. Yes. When the slide member 41 moves in the X2 direction from the state shown in FIG. 12B and the convex pattern 61a on the one end side reaches the detection position of the initial position detection sensor 63, the output signal becomes Low. Become. It is determined that the shielding member 27 is disposed at the initial position at the timing when the output signal of the initial position detection sensor 63 switches from High to Low. In the state where the shielding member 27 is disposed at the initial position, the output signal of the rotation angle control sensor 64 is High.

  When the shielding member 27 moves in the X1 direction from the initial position shown in FIG. 12A, as shown in FIG. 12B, the convex pattern 61b on the other end side of the encoder part 61 is used for rotation angle control. The detection position of the sensor 64 is reached, and the output signal of the rotation angle control sensor 64 is switched from High to Low. Further, when the shielding member 27 moves in the X1 direction, the convex pattern and the concave pattern alternately pass through the detection positions of the rotation angle control sensor 64, so that high and low output signals are repeatedly generated. By counting the number of repetitions of High and Low of the output signal and stopping the motor 42 when the target number of times is reached, the shielding member 27 can be placed at the target position (see FIG. 12C). ).

  As described above, in the present embodiment, unlike the example shown in FIG. 14, the position of the slide member 41 that holds the shielding member 27 is directly detected, and the movement of the shielding member 27 is controlled by feeding back the position information. Therefore, the shielding member 27 is caused by the variation in the length of the connecting member 400 shown in FIG. 14, the angular accuracy error of the filler 200, the positional accuracy error of the filler 200, and the backlash between the rotation center of the filler 200 and the support portion. There is no position variation. For this reason, in this embodiment, the shielding member 27 can be arrange | positioned to the target position with high precision.

  Further, in the present embodiment, since the initial position detection sensor 63 is provided, the shielding member 27 can be quickly returned to the initial position as compared with the configuration in which the initial position detection sensor 63 is not provided. This will be described in detail below.

  Even if the shielding member is controlled to return to the initial position after the fixing process is finished, the shielding member is used when the image forming apparatus stops during operation due to a paper jam or other abnormality, or when the fixing apparatus is detached or attached. May not have been returned to the initial position. In such a case, it is necessary to perform an operation of returning the shielding member to the initial position when the image forming apparatus is started up.

  For example, as shown in FIG. 15, when the filler 200 is stationary at a position between the initial position B and the sensor 300 in a configuration that does not include the initial position detection sensor 63, first, the position of the shielding member 27. In order to grasp this, it is necessary to once rotate the shielding member 27 in the positive direction X1. Then, after the filler 200 is detected by the sensor 300, the shielding member 27 is rotated in the reverse direction X2 by the pulse control of the stepping motor and moved to the initial position. However, once the shielding member 27 is moved in the positive direction X1 in this way, the time required to return the shielding member 27 to the initial position is increased accordingly. Therefore, there is a problem that the warm-up time at startup (the time required from the normal temperature state to a predetermined printable temperature (reload temperature) such as when the power is turned on) becomes long.

  On the other hand, in the case of the present embodiment, it is assumed that the printer stops during operation due to some abnormality or the shielding member 27 stops at a position different from the initial position by detaching the fixing device from the printer main body. Also, after the cause is eliminated, when the shielding member 27 is rotated in the reverse direction X2 during the startup operation of the printer, the initial position detecting sensor 63 can detect that the shielding member 27 has returned to the initial position. . When returning to the initial position, since it is not necessary to move the shielding member 27 in the positive direction X1, the time required to return the shielding member 27 to the initial position is shortened, and the warm-up during the start-up operation of the image forming apparatus is shortened. It is possible to shorten the up time.

  In this embodiment, since the shielding member 27 is moved based on the position information of the pattern of the encoder unit 61 detected by the sensors 63 and 64, it is not necessary to use a stepping motor as a driving source, and the configuration is inexpensive. it can.

  Furthermore, in this embodiment, since at least one of the gears that transmits the driving force to the shielding member 27 (the rotating shaft of the motor 42 shown in FIG. 6) is a worm gear, the worm gear self-locking function enables the holding power of the driving source. It is possible to hold the stop position of the shielding member 27 without consuming it.

  The shielding position of the shielding member 27 can be set in a plurality of stages. In this case, the shielding position at which the shielding member 27 is arranged can be determined based on the temperature information in the non-sheet passing area detected by the temperature sensor 28 shown in FIG. For example, when repeatedly printing on paper of the same size, in the initial state where the temperature of the non-sheet passing region is low, the shielding member 27 is disposed at a shielding position where the area of the heated region becomes large, and then the non-sheet passing region. It can be considered that the shielding member 27 is moved stepwise in the forward direction so that the area of the heated region decreases as the temperature rises. The position of each shielding position in the circumferential direction and the temperature at which the shielding member 27 is moved may be varied depending on the paper size.

  Since the number of temperature sensors 28 is limited, the temperature sensor 28 cannot be arranged in the non-sheet passing area depending on the paper size, and the temperature of the non-sheet passing area may not be measured. In that case, the shielding member 27 can be controlled to move to a different shielding position according to the accumulated time from the start of printing. The shielding position can be changed not only according to the accumulated time but also according to the number of printed sheets and the accumulated lighting time of the halogen heater 23 (duty accumulation). It is also possible to determine the shielding position by appropriately combining two or more of these conditions.

  In addition to the temperature of the non-sheet passing area detected by the temperature sensor 28, the shielding position of the shielding member 27 is determined in consideration of the heat storage state of the entire fixing device (elapsed time since the previous printing, the ambient temperature of the fixing device, etc.). You can also. This heat storage state can be determined based on temperature information from a temperature sensor 29 (see FIG. 2) that measures the temperature of the pressure roller 22, for example.

  Further, when continuous paper feeding or the like is performed, the temperature of the shielding member 27 itself may increase. In this case, if the continuous sheet passing time exceeds a certain time, the shielding member 27 is temporarily moved to the non-heated region β to reduce productivity and combine the control for promoting the heat radiation of the shielding member 27. You can also.

Hereinafter, an operation sequence of each part of the fixing device until image formation is started will be described.
When the control device of the image forming apparatus receives the image formation start signal, it is determined whether or not the shielding member 27 is in the initial position. At this time, as described above, if the initial position detection sensor 63 is LOW (reflected light receiving state) and the rotation angle control sensor 64 is High (reflected light not received), it is determined that the shielding member 27 is in the initial position. Is done. Further, the nip portion N is switched from the depressurized state to the pressurized state. After this switching is completed, the halogen heater 23 is turned on, and heating of the fixing belt 21 by the halogen heater 23 is started.

  After the halogen heater 23 is turned on, the shielding member 27 is rotated in the positive direction X1, and the motor 42 is driven until the number of convex patterns detected by the rotation angle control sensor 64 (low detection number) reaches the target number. Then, the shielding member 27 is moved to the target shielding position. Thereafter, as indicated by an arrow A1 in FIG. 2, the sheet P is fed into the nip portion N with the unfixed toner image T facing the fixing belt 21 side. Then, the paper P is heated and pressed by the fixing belt 21 and the pressure roller 22, whereby the toner image T is fixed, and the image formation is completed.

  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 operation sequence of each part of the fixing device after image formation has been completed normally will be described.
At the timing when the trailing edge of the last sheet out of the nip portion N out of one or a plurality of sheets printed based on the image forming command, the shielding member 27 is rotated in the reverse direction X2, and the shielding member 27 is moved to the initial position. Return to. The halogen heater 23 is turned off simultaneously with or slightly before the start of the movement of the shielding member 27 in the reverse direction X2. If the output signal from the initial position detection sensor 63 of the position detection means confirms that the shielding member 27 has moved to the initial position, the rotation of the fixing belt 21 is stopped.

  FIG. 13 shows an example of a specific control flow of the shielding member 27 described above. In the figure, the shielding position (i) is the position where the area of the heated region is the maximum (100%), the shielding position (ii) is the position where the area of the heated region is 66%, and the shielding position (iii) The position represents a position where the area of the heated region becomes 33%, and the shielding position (iv) represents a position where the area of the heated region becomes 0%.

  In this control flow, it is first determined whether or not the temperature of the pressure roller 22 measured by the temperature sensor 29 as the second temperature detecting means exceeds 80 ° C. If this temperature is 80 ° C. or lower, the shielding member 27 is placed at the shielding position (start position) (i), and if it exceeds 80 ° C., the shielding member 27 is placed at the shielding position (start position) (ii). Deploy. Thereafter, printing is started. When the temperature of the non-sheet passing region of the fixing belt 21 exceeds 190 ° C., the shielding member 27 is moved to the shielding position (stop position) of (iii), and when it exceeds 200 ° C., the shielding member 27 is moved. Is placed at the shielding position (stop position) of (iv).

  In this control flow, when the shielding member 27 is moved to the next-stage shielding position, a maintenance time is set for each shielding position, and the shielding member 27 is moved to that position for a predetermined time (for example, about 3 seconds). To stop. Thereby, frequent forward / reverse rotation of the shielding member 27 can be prevented, and the operation of the shielding member 27 can be stabilized.

  As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention can add a various change in the range which is not restricted to the above-mentioned embodiment and does not deviate from the summary of this invention. For example, as the fixing member, a hollow (cylindrical) or solid fixing roller may be used instead of the fixing belt. 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.

20 Fixing device 21 Fixing belt (fixing member)
22 Pressure roller (opposing member)
23 Halogen heater (heating source)
27 Shielding member 28 Temperature sensor (first temperature detecting means)
29 Temperature sensor (second temperature detection means)
40 Flange member 41 Slide member (holding member)
42 Motor (drive source)
47 Power transmission mechanism 61 Encoder unit 61a Pattern 61b Pattern 63 Sensor (position detection means, initial position detection sensor)
64 sensors (position detection means, rotation angle control sensor)

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

Claims (7)

A rotatable fixing member, a heating source that heats the fixing member, an opposing member that abuts an outer peripheral surface of the fixing member to form a nip portion, and a forward direction and a reverse direction between the fixing member and the heating source. A shielding member capable of moving in the direction and capable of changing the area of the heated region heated by the heating source of the fixing member, a holding member holding the shielding member movably, and a drive source In a fixing device comprising a power transmission mechanism that transmits power from the power to the shielding member to move the shielding member,
A position detecting means for directly detecting the position of the holding member;
A fixing device that controls movement of the shielding member based on positional information of the holding member detected by the position detection means. An encoder unit comprising a predetermined pattern provided on the holding member so as to be arranged in the moving direction of the holding member, and a sensor for detecting the pattern of the encoder unit,
The fixing device according to claim 1, wherein the shielding member is moved based on position information of a pattern of the encoder unit detected by the sensor.   The fixing device according to claim 1, wherein the holding member is a slide member that is slidable along a flange member that holds both ends of the fixing member. The power transmission mechanism has a gear train composed of a plurality of gears;
The fixing device according to any one of claims 1 to 3, wherein at least one of the gears constituting the gear train is a worm gear. First temperature detecting means for detecting the temperature of the fixing member;
The fixing device according to claim 1, wherein a stop position of the shielding member is determined based on temperature information from the first temperature detection unit. A second temperature detecting means for detecting the temperature of the facing member;
The fixing device according to claim 1, wherein a start position of the shielding member at the start of image formation is determined based on temperature information from the second temperature detection unit.   An image forming apparatus comprising the fixing device according to claim 1.

Images