JP2013178316A - Fixing device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that prevents an increase in size of the device, keeps a warm-up time short, and reliably reduces an increase in temperature of a non-paper feed area, even in the case where a heater and a reflection member are provided inside a fixing rotating body; and an image forming apparatus.SOLUTION: A reflection member 24 provided with a reflection surface that reflects light emitted from a heater 25 that is fixedly provided to an inner peripheral surface side of a fixing rotating body 21 to extend in a width direction, toward the inner peripheral surface of the fixing rotating body 21 is installed facing the heater 25. The reflection member 24 has a reflection surface that is formed to be partially switchable to an absorption surface 23a that absorbs all or a part of light emitted from the heater 25 and made incident on the absorption surface 23a.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof, and a fixing device installed therein.

2. Description of the Related Art Conventionally, in image forming apparatuses such as copiers and printers, fixing apparatuses that have a short warm-up time and first print time and are less likely to cause poor fixing even when the apparatus is speeded up are known (for example, (See Patent Documents 1 to 3.)
In such a fixing device, a heater that emits light in the infrared region such as a halogen heater, a nichrome heater, or a ceramic heater is used as a heater as a heat source for heating the fixing rotating body. In particular, halogen heaters are widely used as heat sources for fixing devices because of their excellent temperature rise and fall characteristics.

Specifically, the fixing device of Patent Document 1 includes a fixing belt as a fixing rotating body, a substantially cylindrical metal member (opposing member) fixed so as to face part or all of the inner peripheral surface of the fixing belt, In order to heat the metal member, a heater provided in the metal member, a pressure roller as a pressure rotating body that presses against the fixing belt to form a nip portion, and the like are configured.
The fixing belt is heated by the metal member heated by the heater, and the toner image on the recording medium conveyed toward the nip portion is fixed on the recording medium by receiving heat and pressure at the nip portion. It will be.

  Patent Document 1 discloses a fixing device in which a fixing member (first opposing member) that presses against a pressure roller via a fixing belt to form a nip portion and a reinforcing member that reinforces the fixing member are installed. It is disclosed. Furthermore, a technique is disclosed in which part or all of the surface of the reinforcing member facing the heater is mirror-finished to use infrared light from the heater toward the reinforcing member for heating the metal member as a reflecting member.

The fixing device of Patent Document 2 includes a fixing belt as a fixing rotating body, a heater provided in the fixing belt for directly heating the fixing belt, and a pressure rotating body that presses against the fixing belt to form a nip portion. It is composed of a pressure roller, two pressure rollers that form a nip portion in pressure contact with the pressure roller via a fixing belt, and the like.
FIG. 9 of Patent Document 2 discloses a technique in which a reflector is provided between the heater and the pressing roller, and infrared light from the heater toward the pressing roller is used for heating on the fixing belt side.

The fixing device of Patent Document 3 is a fixing belt as a fixing rotator, a heater provided in the fixing belt for directly heating the fixing belt, and a pressure rotator that presses against the fixing belt to form a nip portion. It is composed of a pressure roller, a fixing member that forms a nip portion in pressure contact with the pressure roller via a fixing belt, and the like.
Patent Document 3 discloses a technique in which a reflector is provided between the heater and the fixing member, and infrared light from the heater toward the fixing member is used for heating on the fixing belt side. Furthermore, a technique is disclosed in which the fixing member is formed of a metal material, thereby performing heat transfer in the width direction to reduce the temperature rise that occurs in the non-sheet passing region.

  Since the fixing devices described in Patent Documents 1 to 3 and the like described above are provided with the reflecting member at a position facing the heater, red toward the members other than the fixing belt (fixing member, pressing roller, and the like) from the heater. The light in the outer region can be used for heating the fixing belt, and the effect of improving the heating efficiency of the fixing belt can be expected.

Here, for example, in an image forming apparatus capable of passing paper up to A4 size (210 mm × 297 mm), the range of the fixing belt heated by the heater is set to about 210 mm corresponding to the short size of A4 size. However, when a small-sized recording medium such as a postcard is passed through such an image forming apparatus, the fixing belt does not take heat away from the recording medium in a range where the recording medium does not pass (non-sheet passing area). There has been a problem that the temperature rises (hereinafter, referred to as “non-paper passing region temperature rise” as appropriate).
Such a problem is particularly noticeable in a fixing device having a short warm-up time as in Patent Documents 1 to 3 because heat movement in the width direction of the fixing belt is difficult to occur.

In order to solve such a temperature increase in the non-sheet passing region, a technique is known in which a plurality of heaters having different heat generation widths according to the size of the recording medium are provided. In such a case, the fixing device is increased in size. It will cause a long warm-up time.
There is also known a technique of providing a light shielding plate between the heater and the inner peripheral surface of the fixing belt. In this case, however, the fixing device becomes larger or the warm-up time becomes longer. Become. Furthermore, if the light shielding plate itself continues to be heated by the heater, the light shielding plate may rise in temperature and may be thermally damaged.
In Patent Document 3, the fixing member is made of a metal material to uniform the temperature distribution in the width direction. However, if the fixing member is made of a metal material having a large heat capacity, the heat of the fixing belt is easily lost. As a result, the warm-up time may be significantly increased.

  The present invention has been made to solve the above-described problems. Even when the heater and the reflecting member are installed in the fixing rotating body, the warm-up is short without increasing the size of the apparatus. An object of the present invention is to provide a fixing device and an image forming apparatus in which the time is maintained and the temperature rise in the non-sheet-passing area is surely reduced.

  In the fixing device according to the first aspect of the present invention, a fixing rotating body that travels in a predetermined direction to heat and melt a toner image, and a recording medium is conveyed in pressure contact with an outer peripheral surface of the fixing rotating body. A pressure rotator forming a nip portion, a heater fixed to extend in the width direction on the inner peripheral surface side of the fixing rotator, and light emitted from the heater facing the heater A reflecting member that has a reflecting surface that reflects toward the inner peripheral surface of the fixing rotator, and the reflecting member includes a part of the reflecting surface that is emitted from the heater and is incident on all of the incident light. Or it is formed so that it can switch to the absorption surface which absorbs a part.

In the present application, the “sheet passing area” is defined as a range in the width direction of the recording medium to be passed by the fixing device (image forming apparatus), and the “non-sheet passing area” is defined as “passing area”. It is defined as an area outside the range of “paper area”. Therefore, when a recording medium having a different size in the width direction is passed, the size of the “sheet passing area” and the size of the “non-sheet passing area” vary depending on the size.
Further, in the present application, the “width direction” is defined as a direction orthogonal to the paper passing direction of the recording medium.

  According to the present invention, even when the heater and the reflection member are installed in the fixing rotating body, a part of the reflection surface of the reflection member is switchable to an absorption surface that absorbs light emitted from the heater. Therefore, it is possible to provide a fixing device and an image forming apparatus in which a short warm-up time is maintained and an increase in the non-sheet-passing area temperature is reliably reduced without increasing the size of the apparatus.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a configuration diagram illustrating a fixing device installed in the image forming apparatus of FIG. 1. FIG. 3 is a view of the fixing device of FIG. 2 as viewed in the width direction. It is an enlarged view which shows the vicinity of a reflective member and a nip part. It is a figure which shows the structure and operation | movement of a reflection member. 6 is a graph showing a temperature change of the fixing belt at a position of a temperature sensor. It is a schematic perspective view which shows a reflection member and a reinforcement member as a 1st modification. It is a schematic perspective view which shows a reflection member and a reinforcement member as a 2nd modification. It is a schematic perspective view which shows a reflection member and a reinforcement member as a 3rd modification. It is a block diagram which shows the fixing device as a 4th modification.

Embodiment.
Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
As shown in FIG. 1, the image forming apparatus 1 in the present embodiment is a tandem color printer. Four bottles 102Y, 102M, 102C, and 102K corresponding to the respective colors (yellow, magenta, cyan, and black) are detachably (replaceable) installed in the bottle housing portion 101 above the image forming apparatus main body 1. ing.
An intermediate transfer unit 85 is disposed below the bottle housing portion 101. Image forming units 4Y, 4M, 4C, and 4K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 78 of the intermediate transfer unit 85.

  Photosensitive drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively. Further, around each of the photosensitive drums 5Y, 5M, 5C, and 5K, a charging unit 75, a developing unit 76, a cleaning unit 77, a charge eliminating unit (not shown), and the like are disposed. Then, an image forming process (charging process, exposure process, development process, transfer process, cleaning process) is performed on each of the photoconductive drums 5Y, 5M, 5C, and 5K. An image of each color is formed on 5K.

The photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven in a clockwise direction in FIG. 1 by a drive motor (not shown). Then, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging unit 75 (a charging process).
Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser light L emitted from the exposure unit 3, and electrostatic latent images corresponding to the respective colors are formed by exposure scanning at this position. (It is an exposure process.)

Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the developing device 76, and the electrostatic latent image is developed at this position to form toner images of each color (developing process). .)
Thereafter, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach the positions facing the intermediate transfer belt 78 and the first transfer bias rollers 79Y, 79M, 79C, and 79K, and at these positions, the photoconductive drums 5Y, 5M. The toner images on 5C and 5K are transferred onto the intermediate transfer belt 78 (this is a primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drums 5Y, 5M, 5C, and 5K.

Thereafter, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, and untransferred toner remaining on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position. 77 is mechanically collected by a cleaning blade (cleaning process).
Finally, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing a neutralization unit (not shown), and the residual potential on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position. The
Thus, a series of image forming processes performed on the photosensitive drums 5Y, 5M, 5C, and 5K is completed.

Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are transferred onto the intermediate transfer belt 78 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 78.
Here, the intermediate transfer unit 85 includes an intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning unit 80. , Etc. The intermediate transfer belt 78 is stretched and supported by the three rollers 82 to 84 and is endlessly moved in the direction of the arrow in FIG.

The four primary transfer bias rollers 79Y, 79M, 79C, and 79K sandwich the intermediate transfer belt 78 with the photosensitive drums 5Y, 5M, 5C, and 5K, respectively, thereby forming primary transfer nips. Then, a transfer bias reverse to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K.
The intermediate transfer belt 78 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K. In this way, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, and 5K are primarily transferred while being superimposed on the intermediate transfer belt 78.

Thereafter, the intermediate transfer belt 78 onto which the toner images of the respective colors are transferred in an overlapping manner reaches a position facing the secondary transfer roller 89. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between the secondary transfer roller 89 and forms a secondary transfer nip. The four color toner images formed on the intermediate transfer belt 78 are transferred onto the recording medium P conveyed to the position of the secondary transfer nip. At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 78.
Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, the untransferred toner on the intermediate transfer belt 78 is collected.
Thus, a series of transfer processes performed on the intermediate transfer belt 78 is completed.

Here, the recording medium P transported to the position of the secondary transfer nip is transported from the paper feeding unit 12 disposed below the apparatus main body 1 via the paper feeding roller 97 and the registration roller pair 98. It is a thing.
Specifically, a plurality of recording media P such as transfer paper are stored in the paper supply unit 12 in an overlapping manner. When the paper feed roller 97 is rotationally driven in the counterclockwise direction in FIG. 1, the uppermost recording medium P is fed between the rollers of the registration roller pair 98.

  The recording medium P conveyed to the registration roller pair 98 is temporarily stopped at the position of the roller nip of the registration roller pair 98 that has stopped rotating. Then, the registration roller pair 98 is rotationally driven in synchronization with the color image on the intermediate transfer belt 78, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing unit 20. At this position, the color image transferred on the surface is fixed on the recording medium P by heat and pressure generated by the fixing belt 21 and the pressure roller 31.
Thereafter, the recording medium P is discharged out of the apparatus through a pair of paper discharge rollers 99. The recording medium P discharged out of the apparatus by the discharge roller pair 99 is sequentially stacked on the stack unit 100 as an output image.
Thus, a series of image forming processes in the image forming apparatus is completed.

Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS.
As shown in FIGS. 2 to 4, the fixing device 20 includes a fixing belt 21 (fixing member) as a fixing rotator, a fixing member 26, a metal member 22 (heating member), a reinforcing member 23, a reflecting member 24, and a heating unit. Heater 25 (heat source), pressure roller 31 as a pressure rotator, two temperature sensors 40A and 40B, heat insulating member 27, stay member 28, and the like.

Here, the fixing belt 21 as a fixing rotator is a thin and flexible endless belt, and rotates (runs) in an arrow direction (counterclockwise) in FIG. The fixing belt 21 has a base material layer, an elastic layer, and a release layer sequentially laminated from the inner peripheral surface 21a (sliding contact surface with the fixing member 26) side, and its total thickness is 1 mm or less. Is set to
The base material layer of the fixing belt 21 has a layer thickness of 30 to 50 μm and is formed of a metal material such as nickel or stainless steel or a resin material such as polyimide.
The elastic layer of the fixing belt 21 has a layer thickness of 100 to 300 μm and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber. By providing the elastic layer, minute irregularities on the surface of the fixing belt 21 in the nip portion are not formed, and heat is uniformly transmitted to the toner image T on the recording medium P, thereby suppressing the generation of a scum skin image.
The release layer of the fixing belt 21 has a layer thickness of 10 to 50 μm, and includes PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, PES ( Polyether sulfide) and the like. By providing the release layer, the releasability (peelability) for the toner T (toner image) is secured.

Further, the diameter of the fixing belt 21 is set to be 15 to 120 mm. In the present embodiment, the inner diameter of the fixing belt 21 is set to 30 mm.
A fixing member 26, a heater 25 (heating means), a metal member 22, a reinforcing member 23, a reflecting member 24, a heat insulating member 27, a stay member 28, and the like are fixedly installed inside the fixing belt 21 (inner peripheral surface side). ing.
Here, the fixing member 26 is fixed so as to be in sliding contact with the inner peripheral surface 21 a of the fixing belt 21. The fixing member 26 is pressed against the pressure roller 31 via the fixing belt 21 to form a nip portion where the recording medium P is conveyed. Referring to FIG. 3, both ends of the fixing member 26 in the width direction are fixedly supported by the side plates 43 of the fixing device 20. The configuration of the fixing member 26 will be described in detail later.

Referring to FIG. 2, the metal member 22 (heating member) is formed so as to face the inner peripheral surface of the fixing belt 21 at a position excluding the nip portion, and the fixing member is interposed via the heat insulating member 27 at the position of the nip portion. 26 is a substantially cylindrical body formed so as to hold 26. Referring to FIG. 3, both ends of the metal member 22 in the width direction are fixedly supported by the side plates 43 of the fixing device 20. Further, at both ends of the metal member 22, stopper flanges 29 for restricting the shift of the fixing belt 21 (movement in the width direction) are inserted.
The metal member 22 formed in a substantially pipe shape is heated by infrared light emitted from the heater 25 to heat the fixing belt 21 (transmits heat). That is, the metal member 22 is directly heated by the heater 25, and the fixing belt 21 is indirectly heated by the heater 25 through the metal member 22. In order to maintain the heating efficiency of the fixing belt 21 favorably, the thickness of the metal member 22 is preferably set to 0.1 mm or less.
As a material of the metal member 22, a metal heat conductor (a metal having heat conductivity) such as stainless steel, nickel, aluminum, and iron can be used. X Ferrite stainless steel having a relatively small specific heat) is preferred. In the present embodiment, SUS430 that is a ferritic stainless steel is used as the material of the metal member 22. Further, the thickness of the metal member 22 is set to 0.1 mm.

  The heater 25 (heat source) is a halogen heater fixed so as to extend in the width direction on the inner peripheral surface side of the metal member 22 (fixing belt 21), and both ends thereof are formed on the side plate 43 of the fixing device 20. It is fixed (see FIG. 3). The metal member 22 is heated by the light in the infrared region of the heater 25 whose output is controlled by the power supply unit of the apparatus body 1. Further, the fixing belt 21 is entirely heated by the metal member 22 at a position excluding the nip portion, and heat is applied to the toner image T on the recording medium P from the surface of the heated fixing belt 21. The output control of the heater 25 is performed based on the detection result of the belt surface temperature by the temperature sensor 40A facing the surface of the fixing belt 21. Further, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature by such output control of the heater 25.

  As described above, both ends of the metal member 22 are fixedly supported on the side plate 43 of the fixing device 20. Therefore, at the time of warm-up (when the fixing device 20 is heated from room temperature to a desired temperature), heat easily escapes from both ends of the metal member 22 to the side plate 43 that is a support member. However, there is a problem that the temperature at both ends does not rise to a desired temperature. In the present embodiment, such a problem is solved, and the light distribution at both ends of the heater 25 is about 10% as compared with the central portion so that the temperature in the width direction of the metal member 22 immediately after the warm-up becomes uniform. It is getting bigger.

In the present embodiment, one of the two temperature sensors described above is a first temperature sensor 40A serving as a first temperature detecting means for detecting the surface temperature of the central portion in the width direction of the fixing belt 21, and the other is the other. Is a second temperature sensor 40B as second temperature detecting means for detecting the surface temperature of the end portion in the width direction of the fixing belt 21 (see FIG. 5). As the two temperature sensors 40A and 40B, a contact temperature sensor such as a thermistor can be used, or a non-contact temperature sensor such as a thermopile can be used.
The output control of the heater 25 described above is performed mainly based on the detection result of the belt surface temperature by the first temperature sensor 40A. Further, the switching control of the reflecting member 24 is performed based on the detected temperatures detected by the two temperature sensors 40A and 40B, which will be described in detail later.

  As described above, in the fixing device 20 in the present embodiment, not only a part of the fixing belt 21 is locally heated, but the fixing belt 21 is almost entirely heated in the circumferential direction by the metal member 22. For this reason, even when the speed of the apparatus is increased, the fixing belt 21 is sufficiently heated, and the occurrence of fixing failure can be suppressed. That is, since the fixing belt 21 can be efficiently heated with a relatively simple configuration, the warm-up time and the first print time are shortened, and the size of the apparatus is reduced.

Here, the substantially pipe-shaped metal member 22 is fixed so as to face the inner peripheral surface (the position excluding the nip portion) of the fixing belt 21 with a clearance. A clearance amount A between the fixing belt 21 and the metal member 22 (a gap at a position excluding the nip portion) is set to be greater than 0 mm and equal to or less than 1 mm (0 mm <A ≦ 1 mm). As a result, the area in which the metal member 22 and the fixing belt 21 are in sliding contact with each other is increased, and the problem that the wear of the fixing belt 21 is accelerated is suppressed, and the metal member 22 and the fixing belt 21 are separated too much and the fixing belt 21 is heated. Inconveniences that reduce efficiency can be suppressed. Furthermore, since the metal member 22 is provided close to the fixing belt 21, the circular posture of the flexible fixing belt 21 is maintained to some extent, so that deterioration and breakage due to deformation of the fixing belt 21 can be reduced. .
Further, in order to reduce the wear of the fixing belt 21 even if the metal member 22 and the fixing belt 21 are in sliding contact with each other, the inner circumferential surface of the fixing belt 21 has fluorine grease or the like between the members 21 and 22. The lubricant is applied.
In the present embodiment, the cross-sectional shape of the metal member 22 is formed to be substantially circular. However, the cross-sectional shape of the metal member 22 may be formed to be a polygon, or the circumference of the metal member 22 may be formed. A slit can also be provided on the surface.

Here, in the present embodiment, the reinforcing member 23 that reinforces the strength of the fixing member 26 that forms the nip portion is fixed to the inner peripheral surface side of the fixing belt 21. Referring to FIG. 3, the reinforcing member 23 is formed so that the length in the width direction is equal to that of the fixing member 26, and both end portions in the width direction are fixedly supported by the side plates 43 of the fixing device 20. . The reinforcing member 23 abuts against the pressure roller 31 via the fixing member 26 and the fixing belt 21, thereby preventing a problem that the fixing member 26 is greatly deformed by the pressure applied by the pressure roller 31 in the nip portion. ing.
Here, in order to satisfy the functions described above, the reinforcing member 23 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron.
In the present embodiment, the reinforcing member 23 is a plate-like member disposed so as to divide the inside of the metal member 22 into two spaces.
The configuration / operation of the reinforcing member 23 will be described in more detail later.

In the present embodiment, the reflecting surface that reflects the infrared light emitted from the heater 25 so as to face the heater 25 toward the inner peripheral surface of the metal member 22 (in other words, fixing via the metal member 22). A reflecting member 24 having a reflecting surface that reflects toward the inner peripheral surface of the belt 21 is provided on the reinforcing member 23. Infrared light traveling from the heater 25 toward the reinforcing member 23 is reflected by the reflecting surface of the reflecting member 24 and used for heating the metal member 22, so that the heating efficiency of the fixing belt 21 (metal member 22). Will be further improved.
The configuration and operation of the reflecting member 24 will be described in more detail later.

  Referring to FIG. 2, a pressure roller 31 as a pressure rotating body that abuts on the outer peripheral surface of the fixing belt 21 at the position of the nip portion has a diameter of 30 mm, and an elastic layer on a hollow core metal 32. 33 is formed. The elastic layer 33 of the pressure roller 31 (pressure rotator) is formed of a material such as foamable silicone rubber, silicone rubber, or fluororubber. A thin release layer made of PFA, PTFE or the like can be provided on the surface layer of the elastic layer 33. The pressure roller 31 is pressed against the fixing belt 21 to form a desired nip portion between both members. Referring to FIG. 3, the pressure roller 31 is provided with a gear 45 that meshes with a drive gear of a drive mechanism (not shown), and the pressure roller 31 is in the direction of the arrow (clockwise) in FIG. Driven by rotation. Further, both ends of the pressure roller 31 in the width direction are rotatably supported by the side plates 43 of the fixing device 20 via bearings 42. A heat source such as a halogen heater can be provided inside the pressure roller 31.

Note that when the elastic layer 33 of the pressure roller 31 is formed of a sponge-like material such as foamable silicone rubber, the pressure applied to the nip portion can be reduced. Further reduction can be achieved. Furthermore, since the heat insulation of the pressure roller 31 is enhanced and the heat of the fixing belt 21 is difficult to move to the pressure roller 31 side, the heating efficiency of the fixing belt 21 is improved.
In this embodiment, the diameter of the fixing belt 21 is formed so as to be almost equal to the diameter of the pressure roller 31, but the diameter of the fixing belt 21 is formed smaller than the diameter of the pressure roller 31. You can also In that case, since the curvature of the fixing belt 21 in the nip portion is smaller than the curvature of the pressure roller 31, the recording medium P sent out from the nip portion is easily separated from the fixing belt 21.

Referring to FIG. 4, the fixing member 26 that is in sliding contact with the inner peripheral surface 21a of the fixing belt 21 has a surface layer 26a formed on a base layer 26b. The fixed member 26 is formed in a concave shape so that the surface (sliding contact surface) facing the pressure roller 31 follows the curvature of the pressure roller 31. Thereby, since the recording medium P is sent out from the nip portion so as to follow the curvature of the pressure roller 31, the problem that the recording medium P after the fixing process is not attracted to the fixing belt 21 and separated is suppressed. be able to.
In the present embodiment, the shape of the fixing member 26 that forms the nip portion is formed in a concave shape, but the shape of the fixing member 26 that forms the nip portion can also be formed in a flat shape. That is, the sliding contact surface of the fixing member 26 (the surface facing the pressure roller 31) can be formed in a planar shape. As a result, the shape of the nip portion is substantially parallel to the image surface of the recording medium P, and the adhesion between the fixing belt 21 and the recording medium P is increased, so that the fixing property is improved. Further, since the curvature of the fixing belt 21 on the exit side of the nip portion is increased, the recording medium P sent from the nip portion can be easily separated from the fixing belt 21.

In addition, as a material for forming the base layer 26b of the fixing member 26, a material having a certain degree of rigidity (for example, a high-rigidity metal or ceramic so as not to bend greatly even when applied with pressure by the pressure roller 31). Etc.).
Since the thickness of the substantially pipe-shaped metal member 22 formed by bending a metal plate can be reduced, the warm-up time can be shortened. However, since the rigidity of the metal member 22 itself is small, the metal member 22 may bend or deform without resisting the pressure applied by the pressure roller 31. If the pipe-shaped metal member 22 is deformed, a desired nip width cannot be obtained and the fixing property is deteriorated. On the other hand, in the present embodiment, since the high-rigidity fixing member 26 is installed separately from the thin metal member 22 to form the nip portion, such a problem can be prevented from occurring. can do.

In this embodiment, a heat insulating member 27 is installed between the fixing member 26 and the heater 25 (heating means). Specifically, the heat insulating member 27 is installed between the fixing member 26 and the metal member 22 so as to cover the surface of the fixing member 26 excluding the sliding contact surface. As a material of the heat insulating member 27, sponge rubber having excellent heat insulating properties, ceramic having an empty package, or the like can be used.
In the present embodiment, since the fixing belt 21 and the metal member 22 are close to each other over almost the entire circumference, the fixing belt 21 can be heated in the circumferential direction without temperature unevenness even when waiting for heating (when waiting for a printing operation). Therefore, after receiving a print request, a print operation can be performed promptly. At this time, in a conventional on-demand type fixing device (see, for example, Japanese Patent No. 2884714), if heat is applied while the pressure roller is deformed during heating standby at the nip portion, the rubber of the pressure roller Depending on the material, heat deterioration may cause the life of the pressure roller to be shortened or compression set to be generated on the pressure roller. Increased by joining.) When compression set is generated in the pressure roller, a part of the pressure roller is indented, and a desired nip width cannot be obtained. Therefore, fixing failure occurs or abnormal noise occurs during rotation. To do.
On the other hand, in the present embodiment, since the heat insulating member 27 is installed between the fixing member 26 and the metal member 22, the heat of the metal member 22 does not easily reach the fixing member 26 during heating standby. Therefore, the problem of being heated at a high temperature in a state where the pressure roller 31 is deformed at the time of heating standby can be reduced, and the above-described problems can be prevented from occurring.

Further, the lubricant applied between the two members in order to reduce the frictional resistance between the fixing member 26 and the fixing belt 21 is deteriorated by use under a high temperature condition in addition to the high pressure condition in the nip portion. There is a possibility that problems such as slippage may occur.
In contrast, in the present embodiment, since the heat insulating member 27 is installed between the fixing member 26 and the metal member 22, the heat of the metal member 22 does not easily reach the lubricant in the nip portion. Therefore, deterioration due to high temperature of the lubricant is reduced, and the above-described problems can be prevented from occurring.

  Further, in this embodiment, since the heat insulating member 27 is installed between the fixing member 26 and the metal member 22, the fixing member 26 is thermally insulated, and the fixing belt 21 is not actively heated in the nip portion. It will be. For this reason, the temperature of the recording medium P fed into the nip portion is lowered when it is sent out from the nip portion. That is, at the exit of the nip portion, the temperature of the toner image fixed on the recording medium P is lowered, the viscosity of the toner is lowered, and the toner adhesive force to the fixing belt 21 is reduced. Separated from the fixing belt 21. Therefore, the problem that the recording medium P immediately after the fixing process is wound around the fixing belt 21 and jamming is prevented, and toner adhesion to the fixing belt 21 is also suppressed.

In the present embodiment, referring to FIG. 4, a stay member 28 that holds the concave portion of the metal member 22 in which the fixing member 26 is inserted from the inner peripheral surface side is provided.
The substantially pipe-shaped metal member 22 is formed by bending a stainless steel plate having a thickness of 0.1 mm. Therefore, even if it is going to process a stainless steel plate into a desired pipe shape by bending, it will open in the direction where a diameter becomes large with a spring back, and a desired pipe shape cannot be formed. If the metal member 22 is opened by the spring back, it contacts the inner peripheral surface of the fixing belt 21 and damages the fixing belt 21 or causes uneven heating of the fixing belt 21 due to uneven contact with the fixing belt 21. Resulting in. In the present embodiment, in order to prevent the occurrence of such a problem, the recess (bending portion) in which the opening of the metal member 22 is formed is fixed by the stay member 28, whereby the spring back of the metal member 22 is performed. Deformation due to is suppressed. Specifically, the stay member 28 is press-fitted into the recess from the inner peripheral surface side of the metal member 22 while maintaining the shape of the metal member 22 that has been bent so as to resist the springback force.

Here, in order to increase the heating efficiency of the metal member 22, the thickness of the metal member 22 is preferably set to 0.2 mm or less.
As described above, since the thickness of the substantially pipe-shaped metal member 22 formed by bending a metal plate can be reduced, the warm-up time can be shortened. However, since the rigidity of the metal member 22 itself is small, when the pressing force of the pressure roller 31 acts on the metal member 22, the metal member 22 cannot be fully resisted and is bent or deformed. When the pipe-shaped metal member 22 is deformed, a desired nip width cannot be obtained, and a problem that the fixing property is deteriorated occurs. On the other hand, in the present embodiment, the thin metal member 22 is provided with a recess (a portion where the fixing member 26 is inserted) so as to be separated from the nip portion, and the pressing force of the pressure roller 31 is increased. Therefore, it is possible to prevent such a problem from occurring.

Hereinafter, the operation of the fixing device 20 configured as described above will be briefly described.
When a print signal is given to the apparatus main body 1, electric power is supplied to the heater 25, and rotation driving of the pressure roller 31 in the direction of the arrow in FIG. 2 is started (warm-up is started). Thereby, the fixing belt 21 is also driven (rotated) in the direction of the arrow in FIG. 2 by the frictional force with the pressure roller 31. When the temperature of the fixing belt 21 reaches a temperature at which fixing can be performed (fixable temperature), the warm-up is ended, and the temperature of the fixing belt 21 is maintained at the fixing possible temperature while controlling the heater 25 on and off.
Thereafter, the recording medium P is fed from the paper supply unit 12, and an unfixed color image is carried (transferred) on the recording medium P at the position of the secondary transfer roller 89. The recording medium P carrying the unfixed image T (toner image) is conveyed in the direction of arrow Y10 in FIG. 2 while being guided by a guide plate (not shown), and the fixing belt 21 and the pressure roller 31 that are in a pressure contact state. It is fed into the nip part.
The toner image is formed on the surface of the recording medium P by the heating by the fixing belt 21 heated by the metal member 22 (heater 25) and the pressing force of the fixing member 26 reinforced by the reinforcing member 23 and the pressure roller 31. T is fixed. Thereafter, the recording medium P delivered from the nip portion is conveyed in the direction of arrow Y11.
Note that, when the recording medium P is passed (during the passing operation), the switching control of the reflecting member 24 is appropriately performed. This will be described in detail below.

Hereinafter, a characteristic configuration and operation of the fixing device 20 according to the present embodiment will be described in detail.
FIG. 4 is an enlarged view showing the vicinity of the reflecting member 24 and the nip portion. FIG. 5 is a schematic view of the reflecting member 24 as viewed from the direction A in FIG. 4 and shows the configuration and operation of the reflecting member 24.
Referring to FIGS. 2, 4, etc., fixing device 20 in the present exemplary embodiment includes a reflective surface that reflects infrared light emitted from heater 25 toward the inner peripheral surface of metal member 22. The reflecting member 24 is installed on the reinforcing member 23.

The reinforcing member 23 is formed of a metal material having high mechanical strength such as stainless steel or iron in order to suppress a problem that the fixing member 26 is greatly deformed by the pressure applied by the pressure roller 31. In the present embodiment, a metal material having a thickness of about 3 mm is used as the reinforcing member 23 in order to ensure the strength of the reinforcing member 23.
In addition, the reinforcing member 23 is subjected to a black plating process on a surface (absorbing surface 23 a) facing the heater 25 through the reflecting member 24. The surface subjected to the black plating process has a low reflectivity with respect to the light in the infrared region emitted from the heater 25 and thus functions as an absorption surface that absorbs (absorbs heat) in the infrared region. Further, the reinforcing member 23 on which the absorbing surface 23 a is formed functions as an absorbing member (heat absorbing member) having a larger heat capacity than the heat capacity of the reflecting member 24.

In the present embodiment, the reinforcing member 23 is black-plated, but otherwise, the reflectance is lowered by applying black DLC (diamond-like carbon) treatment, rough surface treatment, oxidation treatment, or the like. Thus, it is possible to form the absorption surface 23a that easily absorbs light in the infrared region. Here, the “absorptive surface” absorbs a part of the incident light (light in the infrared range) emitted from the heater 25, even if not all (a reflectance lower than the reflectance of the reflecting member 24). In the present invention, the “absorbing surface” will be referred to.
In the present embodiment, only a part of the reinforcing member 23 (the surface facing the heater 25 via the reflecting member 24) is subjected to black plating, but the entire reinforcing member 23 is subjected to black plating. Can also be applied. In that case, it is possible to prevent a problem that the absorption surface 23a is installed so as to be located on the opposite side (opposite the surface facing the heater 25 via the reflection member 24) due to an assembly error. it can.

Here, in the present embodiment, the reflecting member 24 is formed such that a part of the reflecting surface facing the heater 25 can be switched to the absorbing surface 23a.
Specifically, with reference to FIGS. 4 and 5, the reflecting member 24 is installed so that the reflecting plate 24 a functioning as a fixed plate and the movable plate 24 b moving in the left-right direction in FIG. 5 overlap. . The reflector 24a is installed on the side facing the heater 25, and a plurality of openings 24a1 are formed at both ends in the width direction. The movable plate 24b is installed at a position sandwiched between the reflecting plate 24a and the reinforcing member 24 (absorbing surface 23a), a plurality of openings 24b1 are formed at both ends in the width direction, and moved to the end in the width direction. A long hole 24b2 that fits into the mechanisms 51 to 53 is formed. Each of the reflecting plate 24a and the movable plate 24b is a highly reflective aluminum plate having a thickness of about 0.2 mm, and has a reflectance of 90% or more with respect to light (radiant heat) emitted from the heater 25 and incident. Is formed. Therefore, the movable plate 24b has a surface directly facing the heater 25, similarly to the reflector 24a (when the surface faces the heater 25 through the opening 24a1 of the reflector 24a). ), And functions as a reflector (second reflector).

  In addition, as a highly reflective aluminum plate used as a material for the reflecting plate 24a and the movable plate 24b, "MIRO" (manufactured by Alanod) in which an increased reflection film made of a metal oxide is formed on an aluminum plate, and a silver layer are further included. “MIROsilver” (manufactured by alanod) can be used. Further, as the material of the reflecting plate 24a and the movable plate 24b, a material obtained by vapor deposition or plating on a substrate made of metal or glass can be used.

Referring to FIG. 5A, the reflector 24a is fixedly supported by the reinforcing member 23, and has a non-sheet passing area of a postcard size recording medium P having a width direction size of 100 mm and a width direction size. A plurality of openings 24a1 (substantially rectangular through holes) are formed at positions corresponding to the non-sheet passing area of the 148 mm A5 vertical size recording medium P.
The movable plate 24b (second reflecting plate) is divided into two in the width direction, and both are installed so as to be slidable between the reinforcing member 23 and the reflecting plate 24a in the left-right direction (width direction) in the figure. ing.
In the present embodiment, the reflecting member 24 is formed such that both end portions in the width direction can be switched to the absorbing surface 23a, and the central portion in the width direction cannot be switched to the absorbing surface 23a, and only the reflecting surface 24a faces. Is formed.

  Further, the movable plate 24b has a plurality of openings 24b1 (substantially rectangular through holes) at positions shifted inward with respect to the openings 24a1 of the reflecting plate 24a in the reference state shown in FIG. Is formed. The plurality of openings 24b1 are reflectors corresponding to non-sheet passing regions of the recording medium P when the movable plate 24b is slid by the moving mechanisms 51 to 53 according to the size of the recording medium P to be passed. The absorbing surface 23a (hatched surface in FIG. 5) of the reinforcing member 23 is formed so as to be exposed so as to overlap with the opening 24a1 of 24a.

Specifically, when the recording medium P of A4 vertical size (the size in the width direction is 210 mm), which is the maximum size in the present embodiment, is passed, the movable plate 24b is moved by the moving mechanisms 51-53. It is moved so as to be located at the position shown in FIG. At this time, all of the plurality of openings 24b1 of the movable plate 24b are in positions that do not coincide with the plurality of openings 24a1 of the reflecting plate 24a, and the absorbing surface 23a of the reinforcing member 23 is not exposed. That is, in the state of FIG. 5A, only the reflective surface of the reflective member 24 (the reflective surface of the reflective plate 24a and the reflective surface of the movable plate 24b) is opposed to the heater 25. The absorbing surface 23a of the reinforcing member 23 is not opposed.
Further, when the recording medium P of A5 vertical size (the size in the width direction is 148 mm) is passed, the movable plate 24b is positioned at the position shown in FIG. To be moved. At this time, a part of the plurality of openings 24b1 of the movable plate 24b is in a position corresponding to a part of the plurality of openings 24a1 of the reflecting plate 24a so as to correspond to the non-sheet passing region of A5 vertical size. The absorbing surface 23a of the reinforcing member 23 is exposed at those positions. That is, in the state shown in FIG. 5B, only the reflecting surface of the reflecting member 24 is opposed to the heater 25 in the A5 vertical size paper passing area, and the absorbing surface 23a is not opposed. In the non-sheet-passing region, the absorbing surface 23a is opposed to the reflecting member 24 through the openings 24a1 and 24b1.
When a postcard-sized recording medium P (size in the width direction is 100 mm) is fed, the movable plate 24b is positioned at the position shown in FIG. Moved to. At this time, all of the plurality of openings 24b1 of the movable plate 24b are aligned with all of the plurality of openings 24a1 of the reflecting plate 24a so as to correspond to the post-size non-sheet passing region, and reinforcement is performed at those positions. The absorbing surface 23a of the member 23 is exposed. That is, in the state of FIG. 5C, only the reflection surface of the reflection member 24 is opposed to the heater 25 in the postcard-size paper passing region, and the absorption surface 23a is not opposed, and the postcard-size non-printing region is not opposed. In the sheet passing region, the absorbing surface 23a is opposed to the reflecting member 24 through the openings 24a1 and 24b1.
In the present embodiment, the state (position) of the movable plate 24b shown in FIG. 5A is set so that the switching control (slide movement control) is performed as the reference state (reference position).
Further, the above-described switching control of the reflecting plate 24 (sliding movement control of the movable plate 24b) is performed based on the information regarding the size of the recording medium P input to the control unit. It may be based on information detected by a size detection sensor that directly detects the size of the recording medium P in the conveyance path from the paper unit 12 or the paper supply unit 12 to the fixing device 20, or may be operated by a user through an operation panel. It may be based on the information of the recording medium P input from (not shown).

Here, in the present embodiment, the moving mechanism for sliding the movable plate 24b is composed of a lever 51, a cam 52, a spring 53, etc., and is installed on each of the movable plates 24b divided into two in the width direction. ing.
The lever 51 is supported by the casing of the fixing device 20 so as to be rotatable about the support shaft 51a. Further, a pin that fits into the long hole 24b2 of the movable plate 24b is provided on one end side of the lever 51 (the side away from the support shaft 51a).
The cam 52 is formed so that the cam surface abuts on the lever 51. The cam 52 can be switched between three rotational positions (positions that are 120 ° out of phase) by a motor (not shown).
Further, one end of the spring 53 is installed at the center in the longitudinal direction of the lever 51, and urges the lever 51 so as to contact the cam 52.
By the moving mechanism 51 to 53 configured as described above, the rotation position of the cam 52 is controlled in three stages by the control unit, so that the movable plate 24b is brought to a desired position in FIGS. It will slide.
Since the moving mechanisms 51 to 53 configured as described above can relatively reduce the sliding amount of the reflecting plate 24b, it is possible to perform the switching control of the reflecting member 24 in a relatively small space.

In the present embodiment, referring to FIG. 5A, the first temperature sensor 40A serving as a first temperature detecting means for detecting the surface temperature of the central portion in the width direction of the fixing belt 21, and the fixing belt 21 A second temperature sensor 40B is installed as a second temperature detecting means for detecting the surface temperature of the end portion in the width direction.
The position in the width direction where the first temperature sensor 40A is installed is a position where switching to the absorption surface 23a is not performed even if the movable plate 24b is slid to any position by the moving mechanisms 51-53. On the other hand, in the position in the width direction where the second temperature sensor 40B is installed, the movable plate 24b is slid to the position shown in FIG. 5B or the position shown in FIG. However, it is a position (A5 vertical size non-sheet passing area) where switching to the absorbing surface 23a is performed. During the sheet passing, the heater 25 is on / off controlled so that the temperature detected by the first temperature sensor 40A is constant.
Note that the two temperature sensors 40A and 40B illustrated in FIG. 5A are illustrated to facilitate understanding of the positional relationship with the reflecting member 24, and as shown in FIG. The temperature sensors 40 </ b> A and 40 </ b> B are disposed at positions facing the outer peripheral surface of the fixing belt 21.

Thus, in the present embodiment, the reflecting member 24 is switched so that the absorption surface 23a faces the position corresponding to the non-sheet passing area when the recording medium P is passed, and the size in the width direction is changed. When a different recording medium P is passed, the range of the absorbing surface 23a (the range in the width direction) can be varied in accordance with the fluctuation of the non-sheet passing area.
With such a configuration, a part of the light of the heater 25 is absorbed by the reinforcing member 23 (absorbing surface 23a) in the non-sheet passing region, so that the fixing belt 21 (metal member 22) is hardly heated in the non-sheet passing region. As a result, the temperature increase in the non-sheet passing region is surely reduced. At that time, a short warm-up time is maintained. That is, even when the switching control to the absorption surface 23a is performed, the warm-up time does not become long.
In addition, the reinforcing member 23 is formed to have a relatively large mass in order to ensure strength, and has a heat capacity larger than the heat capacity of the reflecting member 24, so that light absorbed from the absorbing surface 23 a ( The temperature does not increase greatly due to heat. Therefore, the problem that the reinforcing member 23 that functions as an absorbing member that absorbs heat is thermally damaged is less likely to occur.

Here, the switching operation of the reflecting member 24 in conjunction with the operation of the fixing device 20 described above will be briefly described.
When the warm-up of the fixing device 20 is started and the size of the recording medium P to be passed is determined, the slide movement of the movable plate 24b to the position corresponding to the size of the recording medium P is performed after the warm-up is completed. (Move to any position in FIGS. 5A to 5C). Thereafter, when the movable plate 24b is slid, the sheet passing operation is performed in that state. At this time, since the fixing belt 21 is not easily heated in the non-sheet-passing area, the temperature rise of the fixing belt 21 in the non-sheet-passing area becomes moderate.

FIG. 6 shows the surface temperature of the fixing belt 21 (the surface temperature at the position of the first temperature sensor 40A and the position of the second temperature sensor 40B) when the postcard-sized recording medium P is passed. It is a graph which shows a change. As shown in FIG. 6, the heater 25 is on / off controlled so that the temperature detected by the first temperature sensor 40a is constant during the sheet passing.
As shown in FIG. 6, when the switching control of the reflection member 24 is not performed as in the conventional case (when the postcard is passed in the state of FIG. 5A), the fixing belt 21 is widened by the heater 25. It can be seen that the surface temperature of the fixing belt 21 suddenly rises in the non-sheet passing region because it is heated throughout the entire direction. At this time, the temperature detected by the second temperature sensor 40B rises with an increase in the number of sheets to be passed, eventually reaches the heat resistance temperature of the fixing belt 21, and the sheet passing is interrupted for control purposes.
On the other hand, when the switching control of the reflecting member 24 is performed as in the present embodiment (when the postcard is passed in the state of FIG. 5C), the absorbing surface 23a in the non-sheet passing area. Is exposed and absorbs the light (heat) of the heater 25, so that the temperature rise in the non-sheet passing region becomes moderate. Therefore, it is possible to increase the number of sheets that pass until the temperature of the fixing belt 21 reaches the heat resistant temperature in the non-sheet passing area.
In the present embodiment, the switching control of the reflecting member 24 (sliding control of the movable plate 24b) is performed after the warm-up is completed and before the paper passing operation is started. It is also possible to do it.

Here, in the fixing device 20 in the present embodiment, the temperature detected by the second temperature sensor 40B (second temperature detection means) is changed to the temperature detected by the first temperature sensor 40A (first temperature detection means). On the other hand, when it becomes higher than a predetermined value, it controls so that the width direction both ends of the reflection member 24 may be switched to the absorption surface 23a.
Specifically, when the largest A4 vertical size recording medium P is passed, the reflection member 24 is controlled to be switched to the state shown in FIG. 5A as described above. Then, the heater 25 is on / off controlled so that the temperature detected by the first temperature sensor 40A becomes a desired temperature. However, since the heater 25 is formed such that the light distribution is larger at both ends in the width direction than at the center in the width direction, the temperature at both ends in the width direction of the fixing belt 21 is increased when continuous paper is passed. It will rise slowly. Therefore, in the present embodiment, when the detected temperature of the second temperature sensor 40B is 10 ° C. or higher than the detected temperature of the first temperature sensor 40A, the reflecting member 24 is in the state of FIG. Switching control is performed so that That is, the movable plate 24b is controlled to slide so that the absorption surface 23a is exposed at both ends in the width direction. Further, when the detected temperature of the second temperature sensor 40B is lower than 10 ° C. with respect to the detected temperature of the first temperature sensor 40A, the reflection member 24 is switched so as to return to the state of FIG. I have control.
By performing such control, it is possible to prevent a problem that the temperature increases at both ends in the width direction of the fixing belt 21 when the maximum size recording medium P is continuously fed.
In the present embodiment, when the temperature detected by the second temperature sensor 40B reaches the heat resistance temperature of the fixing belt 21, the sheet passing is interrupted and the heater 25 is turned off.

Hereinafter, four modified examples of the fixing device 20 in the present embodiment will be described.
FIG. 7 shows a first modification, and is a schematic perspective view showing the reflecting member 24 and the reinforcing member 23 (an exploded perspective view showing the three members 24a, 24b, and 23 separated from each other). is there.
As shown in FIG. 7, the reflecting member 24 according to the first modified example is that the movable plate 24 b is formed with a plurality of absorbing surfaces 24 b 10 instead of the plurality of openings 24 b 1. It is very different from the one. Specifically, on the opposing surface of the movable plate 24b (the surface facing the reflecting plate 24a), in addition to the reflecting surface, a plurality of absorbing surfaces 24b10 (heat resistant paints) corresponding to the non-sheet passing regions of each size. Is painted black). On the other hand, unlike the embodiment, the reinforcing member 23 is not subjected to black plating.
Even in such a configuration, the movable plate 24b is controlled to slide in the same manner as in the above-described embodiment, so that the absorption surface 24b10 faces the position corresponding to the non-sheet passing area of the recording medium P. Therefore, the same effect as that of the present embodiment is exhibited.
In the first modification, the movable plate 24b itself on which the absorption surface 24b10 is formed has a small heat capacity, but the reinforcing member 23 that is in surface contact with the movable plate 24b has a large heat capacity and functions as an absorption member (heat absorption member). Therefore, the problem that the movable plate 24b is excessively heated and damaged by heat is suppressed.

FIG. 8 shows a second modification, and is a schematic perspective view showing the reflecting member 24 and the reinforcing member 23 (an exploded perspective view showing the three members 24a, 24b, and 23 separated from each other). is there.
As shown in FIG. 8, in the reflecting member 24 according to the second modification, the reflecting plate 24a is formed with a width of 100 mm in accordance with the minimum postcard size, and the movable plate 24b divided into two has a width of 60 mm. It is formed with. Further, neither the reflecting plate 24a nor the movable plate 24b is provided with the openings 24a1 and 24b1 as in the above-described embodiment. Although not shown, the movable plate 24b divided into two and configured to be slidable in the direction of the double arrow is overlapped with each other so that the back surface of the reflector 24a matches the width of the reflector 24a. It is possible to move so as to be hidden behind (the surface not facing the heater 25). Each of the two movable plates 24b is configured to be movable so as to be exposed within a range of 0 to 55 mm from the end of the reflecting plate 24a. On the other hand, similar to the above embodiment, the reinforcing member 23 is subjected to a black plating process to form an absorption surface 23a.
Even in such a configuration, by controlling the sliding movement of the movable plate 24b, it is possible to adjust the absorption surface 23a to face the position corresponding to the non-sheet passing area of the recording medium P. The same effect as that of will be demonstrated. Particularly, in the second modified example, although the sliding amount of the movable plate 24b is increased, the area of the heat absorbing surface 23a in the non-sheet passing region can be increased, so that the effect of suppressing the temperature rise in the non-sheet passing region is large. Become.

FIG. 9 shows a third modification, and is a schematic perspective view showing the reflecting member 24 and the reinforcing member 23 (an exploded perspective view showing the three members 24a, 24b, and 23 separated from each other). is there.
As shown in FIG. 9, in the reflecting member 24 according to the third modification, the reflecting plate 24a is formed with a maximum size of 210 mm, and the movable plate 24b is also formed with a maximum size of 210 mm. Further, neither the reflecting plate 24a nor the movable plate 24b is provided with the openings 24a1 and 24b1 as in the above-described embodiment. Further, unlike the above-described embodiment, the movable plate 24b is configured to slide in a direction orthogonal to the width direction, and is not divided into two, and both ends in the width direction are in the width direction. It is formed in a substantially U-shape so as to protrude in the slide movement direction as compared with the central portion. Further, the opposing surface of the movable plate 24b (the surface facing the reflecting plate 24a) is black-plated on the entire surface to form an absorbing surface 24b10. On the other hand, unlike the embodiment, the reinforcing member 23 is not subjected to black plating.
Even in such a configuration, by sliding the movable plate 24b upward in the drawing, the absorption surface 23a can be made to face the position corresponding to the non-sheet passing area of the recording medium P. The same effect as the thing will be exhibited. In particular, in the third modified example, although the area of the reflector 24a is not changed, the absorption surface 24b10 moves so as to be exposed to an area other than the area of the reflector 24a. The suppressing effect will be exhibited. Even in the case where the absorbing surface is exposed in a region other than the region of the reflecting plate as in the third modification, the ratio between the reflecting surface and the absorbing surface is varied in the non-sheet passing region. It is included in a mode in which a part of the reflecting surface is switched to the absorbing surface.

FIG. 10 shows a fourth modification and is a configuration diagram showing the fixing device 20.
As shown in FIG. 10, the fixing device 20 according to the fourth modification differs from that of the present embodiment in that the metal member 22 is not installed and the fixing belt 21 is directly heated by the heater 25. It is configured as follows. In the fixing device 20, a flange member for holding the circular posture of the fixing belt 21 in contact with the inner peripheral surface of the fixing belt 21 is inserted into the side plate 43. Further, the reinforcing member 23 is formed in a substantially W shape, and the reflecting member 24 is installed on the facing surface (the surface facing the heater 25). And the reflective member 24 is formed so that a part can be switched to an absorption surface like the thing of the said embodiment (or the thing of the modifications 1-3).
Even in such a configuration, the same effect as that of the present embodiment can be obtained by controlling the sliding movement of the movable plate 24b as in the case of the present embodiment. In particular, the fixing device 20 according to the fourth modified example is configured such that the fixing belt 21 is directly heated by the heater 25, so that the warm-up time can be further shortened.

  As described above, in the present embodiment, even if the heater 25 and the reflection member 24 are installed in the fixing belt 21 (fixing rotating body), a part of the reflection surface of the reflection member 24 is not provided. Further, since the absorption surface 23a that absorbs the light emitted from the heater 25 is formed so as to be switchable, a short warm-up time is maintained without increasing the size of the fixing device 20, and the non-sheet-passing region temperature rises. It can be certainly reduced.

In this embodiment, the fixing belt 21 having a multilayer structure is used as the fixing rotator. However, an endless fixing film made of polyimide, polyamide, fluororesin, metal, or the like may be used as the fixing rotator. A fixing roller in which an elastic layer, a surface layer, etc. are laminated on a hollow cored bar can also be used as a fixing rotating body.
In the present embodiment, the pressure roller 31 is used as the pressure rotator, but an endless pressure belt can also be used as the pressure rotator.
In these cases, the same effect as in the present embodiment can be obtained.

In the present embodiment, as described with reference to FIGS. 5A to 5C, the reflection member 24 (movable plate 24b) is switched in three stages corresponding to the three types of recording media P. It was configured to allow control. However, the type of the size of the recording medium P is not limited to this, and the reflecting member 24 (movable plate 24b) is provided in a plurality of stages corresponding to the number of recording media P of two types or four or more sizes. It is also possible to configure so that switching control can be performed.
Further, in the present embodiment, the present invention is applied to the fixing device 20 in which one heater 25 is installed on the inner peripheral surface side of the fixing belt 21. In contrast, the present invention can also be applied to the fixing device 20 in which a plurality of heaters 25 are arranged in parallel on the inner peripheral surface side of the fixing belt 21. Furthermore, the present invention can also be applied to the fixing device 20 in which the heater 25 is installed on the inner peripheral surface side of the fixing belt 21 so as to extend in the width direction.
In these cases, the same effect as in the present embodiment can be obtained.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 image forming apparatus body (apparatus body),
20 fixing device,
21 fixing belt (fixing rotating body),
22 metal member (heating member),
23 Reinforcing member (absorbing member),
23a absorbing surface,
24 reflective member,
24a Reflector (fixed plate),
24a1 opening,
24b movable plate,
24b1 opening, 24b2 oblong hole,
25 heater,
26 fixing member,
31 Pressure roller (pressure rotating body),
40A 1st temperature sensor (1st temperature detection means),
40B 2nd temperature sensor (2nd temperature detection means),
P Recording medium.

Japanese Patent No. 2008-158482 Japanese Patent No. 2009-42305 Japanese Patent No. 2010-32625

Claims (7)

A fixing rotator that travels in a predetermined direction to heat and melt the toner image;
A pressure rotator that forms a nip portion that is pressed against the outer peripheral surface of the fixing rotator to convey the recording medium; and
A heater fixed to extend in the width direction on the inner peripheral surface side of the fixing rotating body;
A reflective member having a reflective surface that faces the heater and reflects light emitted from the heater toward the inner peripheral surface of the fixing rotating body;
With
The fixing device is characterized in that a part of the reflection surface of the reflection member is switchable to an absorption surface that absorbs all or a part of incident light emitted from the heater.   The reflection member is switched so that the absorption surface faces a position corresponding to a non-sheet passing area when the recording medium is passed, and is not used when a recording medium having a different size in the width direction is passed. The fixing device according to claim 1, wherein the fixing device is formed so that a range of the absorbing surface can be changed in accordance with a change in a sheet passing region. First temperature detecting means for detecting the surface temperature of the central portion in the width direction of the fixing rotating body;
Second temperature detecting means for detecting the surface temperature of the end portion in the width direction of the fixing rotating body;
With
The reflection member is formed such that a width direction end portion can be switched to the absorption surface, and a width direction central portion cannot be switched to the absorption surface,
When the temperature detected by the second temperature detecting means is higher than a predetermined value by the temperature detected by the first temperature detecting means, the widthwise end of the reflecting member is used as the absorbing surface. The fixing device according to claim 1, wherein the fixing device is switched.   The fixing device according to claim 1, wherein the absorption surface is formed on an absorption member having a heat capacity larger than a heat capacity of the reflection member. A fixing member fixed on the inner peripheral surface side of the fixing rotator and forming the nip portion by pressing against the pressure rotator via the fixing rotator;
A reinforcing member fixed on the inner peripheral surface side of the fixing rotator and contacting the fixing member to reinforce the fixing member;
With
The absorbing member is the reinforcing member,
The fixing device according to claim 4, wherein the reflecting member is installed on the reinforcing member. A pipe that is fixed at the position excluding the nip portion so as to face the inner peripheral surface of the fixing rotator to heat the fixing rotator and is heated by the heater fixed at the inner peripheral surface side A metal member having a shape,
The said reflecting member is installed in the inner peripheral surface side of the said metal member, and reflects the light inject | emitted from the said heater toward the inner peripheral surface of the said metal member, The Claims 1-5 characterized by the above-mentioned. The fixing device according to any one of the above.   An image forming apparatus comprising the fixing device according to claim 1.

Images