JP2014059332A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of reducing time required to return a shield member to an initial position.SOLUTION: A fixing device comprises: a rotatable fixing member; a heat source that heats the fixing member with radiation heat; an opposing member that comes into contact with the outer peripheral surface of the fixing member to form a nip part; and a shield member 27 that shields the heat from the heat source. The shield member 27 is configured to be movable between a preset initial position and a position different from the initial position according to a width size of a recording medium passing through the nip part, and includes initial position detection means 54 and 55 for detecting the initial position of the shield member 27.

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. Further, 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. A heating area corresponding to the above can be secured.

  Note that the fixing device described in Patent Document 4 uses an electromagnetic induction heating method in which the fixing member is heated by generating a magnetic flux. Here, the magnetic flux shielding member that shields the magnetic flux depends on the paper size. Thus, the heating area corresponding to the sheet width can be secured.

  As described above, in the configuration in which the shielding member is movable, it may be considered that the shielding member is temporarily returned to the initial position after the printing operation (fixing process) is completed in order to control the position of the shielding member. However, if the image forming apparatus stops in the middle of operation due to an abnormality or if the fixing device is removed, the shielding member may not be returned to the initial position. It is necessary to perform an operation for returning the shielding member to the initial position. However, at that time, if it takes time to return the shielding member to the initial position, the printing operation (fixing process) cannot be performed during that time, so that there is a problem that the waiting time of the user or the like becomes long.

  In view of such circumstances, an object of the present invention is to provide a fixing device capable of shortening the time for returning the shielding member to the initial position, and an image forming apparatus including the fixing device.

  In order to solve the above-mentioned problem, the present invention according to claim 1 forms a nip portion by contacting a rotatable fixing member, a heating source for heating the fixing member by radiant heat, and an outer peripheral surface of the fixing member. In the fixing device including an opposing member and a shielding member that shields heat from the heating source, the shielding member includes an initial position set in advance according to a width size of the recording medium that passes through the nip portion, and Is configured to be movable between different positions, and includes an initial position detecting means for detecting an initial position of the shielding member.

  According to the first aspect of the invention, since the initial position of the shielding member can be directly detected by the initial position detecting means, the time required to return the shielding member to the initial position can be shortened.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic configuration diagram of a fixing device mounted on the image forming apparatus. It is a figure which shows the state which moved the shielding member to the retracted position. It is a perspective view of the fixing device. It is a figure which shows the support structure of a shielding member. It is a figure 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 position detection means to detect the position of a shielding member. It is a figure for demonstrating the operation | movement which returns a shielding member to an initial position. It is a figure which shows the position detection means of a comparative example. It is a figure for demonstrating the operation | movement which returns the shielding member at the time of using the position detection means of a comparative example to an initial position.

  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.

  In addition, when there is no elastic layer, the heat capacity is reduced and the fixability is improved, but when the unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image, and uneven glossiness is formed on the solid portion of the image. 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 member having a heat-resistant temperature of 200 ° C. or more, prevents deformation of the nip forming member 24 due to heat in the toner fixing temperature region, and ensures a stable state of the nip portion N for output. Stabilizes image quality. Examples of the material of the base pad 241 include polyether sulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyether nitrile (PEN), polyamide imide (PAI), and polyether ether ketone (PEEK). A general heat resistant resin can be used.

  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 base pad 241 is also preferably made of a material that is hard to some extent to ensure strength. As a material for the base pad 241, a resin such as a liquid crystal polymer (LCP), a metal, a ceramic, or the like can be used.

  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 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 in the circumferential direction of the fixing belt 21 as necessary. 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 are non-direct heating regions where members (reflecting member 26, stay 25, nip forming member 24, etc.) intervene, but when it is necessary to shield heat, shield member 27 is directly heated region as shown in FIG. It is arranged at the shielding position on the 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 retracted position on the non-direct heating region side, and the shielding member 27 is retracted to the back side of the reflecting member 26 and the stay 25. Is possible. Moreover, 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 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 supported via an arcuate slide member 41 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. The slide member 41 is provided with a convex portion 41b, and the convex portion 41b is inserted into an arcuate groove portion 40a provided in the flange member 40, whereby the guide 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 unit of the shielding member.
As shown in FIG. 6, in the present embodiment, as a driving unit for the shielding member 27, a motor 42 that is a driving source and a gear train including a plurality of transmission gears 43, 44, and 45 are provided. In the gear train, the gear 43 on one end side is connected to the motor 42, and the gear 45 on the other end side is connected to a gear portion 41 c provided in the circumferential direction of the slide member 41. Thus, when the motor 42 is driven, the driving force is transmitted to the slide member 41 via the gear train, and the shielding member 27 is rotated.

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 on which the shielding member 27 is rotationally moved 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 toward the shielding side Y. 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. 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.

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 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 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. 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.

  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.

  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 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. 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.

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 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 48 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 on 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 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.

  By the way, in order to dispose the shielding member at an appropriate position according to the paper size, it is necessary to provide a position detection means for detecting the rotational position of the shielding member and to manage the rotational position. As the position detection means, for example, as shown in FIG. 13, there are those provided with a filler 200 as a detected part interlocked with the shielding member 100 and a photo interrupter 300 as a detection sensor for detecting the position of the filler 200. Can be mentioned. In this case, with the rotation of the shielding member 100, the filler 200 is interposed between the light emitting portion and the light receiving portion of the photo interrupter 300 and is shielded from light so that the shielding member 100 is indicated by a solid line in the figure (initial position). It is detected that the position indicated by the two-dot chain line in FIG. In this case, when the printing operation (fixing process) is completed, the shielding member 100 is returned to the initial position.

  However, when the image forming apparatus stops in the middle of operation due to a paper jam or other abnormality, or when the fixing device is detached, the shielding member may not be returned to the initial position. In such a case, for example, it is necessary to perform an operation of returning the shielding member to the initial position during the start-up operation of the image forming apparatus. However, if the time required to return the shielding member to the initial position becomes long at that time, the warm-up time at the time of start-up (the time required from the normal temperature state to the printable temperature (reload temperature) such as when the power is turned on) ) Will be long.

  Specifically, as shown in FIG. 14, when the filler 200 is stationary at a position between the initial position and the photo interrupter 300, first, in order to grasp the position of the shielding member 100, the shielding member is temporarily used. It is necessary to rotate 100 to the photo interrupter 300 side opposite to the initial position. Then, after the filler 200 is detected by the photo interrupter 300, the shielding member 100 is moved to the initial position by pulse control of the stepping motor or the like. However, once the shielding member 100 is moved to the side opposite to the initial position in this way, it takes extra time.

Therefore, in the present invention, measures are taken so that the shielding member can be quickly returned to the initial position.
Hereafter, the characteristic part of this invention is demonstrated.

FIG. 11 is a diagram showing the position detecting means of the shielding member in the embodiment of the present invention.
Here, as the position detection means, one filler 54 which is a detected part and two photo interrupters 55 and 56 which are detection sensors for detecting the position of the detected part are provided. In addition, you may use things other than a filler and a photo interrupter as a position detection means.

  The filler 54 is formed in a substantially sector shape, and is configured to be rotatable around a fulcrum 54 a attached to the support plate 57. Further, the filler 54 is configured to be interlocked with the shielding member 27 via the link member 58. Specifically, both end portions of the link member 58 are connected to a protrusion 54 b provided on the filler 54 and a protrusion 41 d provided on the slide member 41. Thereby, when the slide member 41 holding the shielding member 27 rotates along the flange member 40, the filler 54 rotates around the fulcrum 54a. In addition, the filler 54 and the photo interrupters 55 and 56 can be disposed in the vicinity of the shielding member 27 and the slide member 41 in the layout by adopting a configuration in which the filler 54 is linked via the link member 58 in this way. Even if it is not possible, it will be possible to cope.

  Further, the support plate 57 is formed with two guide portions 57a and 57b formed of arc-shaped grooves along the rotation paths of the filler 54 and the projections 54b and 41d of the slide member 41. When the filler 54 and the slide member 41 rotate, the protrusions 54b and 41d move along the guide portions 57a and 57b, so that the filler 54 and the slide member 41 are stably linked.

  The two photo interrupters 55 and 56 are fixed to a frame (not shown) of the printer body. As with the above, each of the photo interrupters 55 and 56 has a light emitting unit that emits light and a light receiving unit that receives the light. Then, when the end portion of the filler 54 enters between the light emitting portion and the light receiving portion and blocks light, or when the end portion of the filler 54 comes out from between the light emitting portion and the light receiving portion and light is transmitted, the light is blocked. The mechanism is such that it is detected that the member 27 has reached a predetermined rotational position.

  In the present embodiment, one of the two photo interrupters 55 and 56 (the upper side in FIG. 11) is used as an initial position detecting unit that detects the initial position of the shielding member 27. When returning the shielding member 27 to the initial position such as when the printing operation (fixing process) is completed, the filler 54 is detected by the photo interrupter 55 for the initial position.

  The other (lower side in FIG. 11) photointerrupter 56 is used as a check position detecting means for detecting the position of the shielding member 27 at a position different from the initial position. Basically, the rotational position of the shielding member 27 is controlled by adjusting the pulse amount of a stepping motor (not shown). However, by using the photo interrupter 56 for checking, the position recognition reliability of the shielding member 27 is reliable. Improves sex. A DC motor or the like may be used instead of the stepping motor.

  Further, when the printer stops in the middle of operation due to some abnormality or when the fixing device is detached from the printer main body, the operation of returning the shielding member 27 to the initial position is performed during the startup operation of the printer. At this time, if the shielding member 27 is stationary at an arbitrary position other than the initial position, the shielding member 27 is directly moved to the initial position side, and the filler 54 is detected by the photo interrupter 56 for the initial position.

  For example, as shown in FIG. 12, even if the intermediate portion in the circumferential direction of the filler 54 is interposed between the photointerrupters 56 for checking, the filler 54 is placed on the photointerrupter 55 side for the initial position (in the drawing). The shield member 27 is moved directly to the initial position. That is, in this case, it is not necessary to move the shielding member 27 to the side opposite to the initial position (below the arrow J in the figure) in order to once detect the end portion 540 of the filler 54 with the photo interrupter 56 for check.

  Thus, according to the present invention, even when the shielding member is stationary at an arbitrary position due to an abnormality or the like, the initial position detecting means does not detect the position of the shielding member once by another position detecting means. Can be detected directly. As a result, the time required to return the shielding member to the initial position is shortened, so that the warm-up time during the start-up operation of the image forming apparatus can be shortened.

  Further, the position to be set as the initial position may be determined as appropriate according to the configuration of the printer, the usage mode, and the like, but in this embodiment, the initial position corresponds to the sheet passing width that is predicted to be used most frequently Let me set.

  For example, in the embodiment (see FIG. 7) in which each of the shielding portions has one step portion, the width (passage of the double letter size paper in the vertical direction or the letter size paper in the horizontal direction). (Paper width 279.4 mm) is the paper passing width predicted to be the most frequently used. Therefore, in this case, when the double letter size paper is passed in the vertical direction or the letter size paper is passed in the horizontal direction, the shielding position where the shielding member 27 is disposed is set as the initial position.

  In the embodiment in which each of the shielding portions has two step portions (see FIG. 9), the width when passing A3 size paper in the vertical direction or A4 size paper in the horizontal direction (paper passing width). 297 mm) is the sheet passing width that is predicted to be the most frequently used. Therefore, in this case, when the A3 size paper is passed in the vertical direction or the A4 size paper is passed in the horizontal direction, the shielding position where the shielding member 27 is disposed is set as the initial position.

  Thus, by setting the initial position to a position corresponding to the sheet passing width that is predicted to be used most frequently, the frequency of moving the shielding member can be reduced, and the warm-up time at the start-up and the first It is possible to shorten the printing time (the time from when a print request is received to when the printing operation is performed and the paper discharge is completed after completion of printing preparation).

  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)
24 nip forming member 27 shielding member 54 filler (detected portion)
55 Photo interrupter (detection sensor)
58 Link member P Paper (recording medium)

Japanese Patent No. 4130898 JP 2008-58833 A JP 2008-139779 A JP 2006-71960 A

Claims (7)

A rotatable fixing member; a heating source that heats the fixing member by radiant heat; an opposing member that abuts an outer peripheral surface of the fixing member to form a nip; and a shielding member that shields heat from the heating source. In a fixing device comprising:
The shielding member is configured to be movable between a preset initial position and a position different from the initial position according to the width size of the recording medium passing through the nip portion,
A fixing device comprising an initial position detecting means for detecting an initial position of the shielding member. The fixing member is an endless fixing belt;
The fixing device according to claim 1, further comprising a nip forming member fixedly supported on an inner peripheral surface side of the fixing belt and abutting the opposing member via the fixing belt.   The initial position is a position where the shielding member is disposed when an A3 size recording medium passes through the nip portion in the vertical direction or an A4 size recording medium in the horizontal direction. Fixing device.   The initial position is a position where the shielding member is disposed when the double letter size recording medium is passed through the nip portion in the vertical direction or the letter size recording medium in the horizontal direction. The fixing device described.   5. The fixing device according to claim 1, wherein the initial position detection unit includes a detected portion that interlocks with the shielding member, and a detection sensor that detects a position of the detected portion.   The fixing device according to claim 5, wherein the detected part is connected to the shielding member via a link member.   An image forming apparatus comprising the fixing device according to claim 1.

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