JP5354385B2 - Fixing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device and an image forming apparatus with short warming up time and first printing time, without an occurrence of a fixing failure in a fixed image and sufficiently carrying out heat accumulation in a pressing rotary body during standby time without accelerating deterioration by wear in a fixing belt or a fixed member. <P>SOLUTION: The fixing device is provided with the pressing rotary body 31 forming a nip section by being brought into press contact with the fixing member 26 through the fixing belt 21 which is rotated and driven in a prescribed direction and a heating member 22 for heating the fixing belt 21 by being fixed to face an inner periphery surface of the fixing belt 21. Then, the pressing rotary body 31 is indirectly heated through the fixing belt 21 by heating the heating member 22 by the heating means 25 while carrying out rotary drive of the pressing rotary body 31 in a state of having the pressing rotary body 31 brought into contact with the fixing belt 21 and in a state of having the travelling of the fixing belt 21 stopped during the standby time. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

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 and 2.)

Specifically, the fixing device disclosed in Patent Documents 1 and 2 includes a fixing belt as a fixing member, a substantially cylindrical heating member fixed so as to face part or all of the inner peripheral surface of the fixing belt, and a heating member. A heater (heating means) provided in the heating member to heat the pressure member, a pressure roller as a pressure rotator that presses against a fixing member (contact member) via a fixing belt to form a nip portion, etc. It consists of
The fixing belt is heated by the heating 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. In such a fixing device, the pressure roller is rotationally driven by the driving means, so that the fixing belt pressed against the pressure roller at the position of the nip portion is driven to rotate by frictional resistance.

  On the other hand, Patent Document 3 discloses a fixing device in which a ceramic heater (heating body) as a fixing member is pressed against a pressure rotating body via a fixing belt (endless belt) to form a nip portion.

  In the fixing devices described in Patent Documents 1 and 2 and the like, since the driving of the device is stopped during the standby of the device, even if the fixing belt is heated, the entire circumferential direction of the pressure rotator from the fixing belt. However, there is a problem in that the heat of the pressurizing rotating body is greatly lowered or temperature unevenness occurs because heat is not sufficiently transmitted. When such a problem occurs, the fixing belt and the pressure rotator are heated to a predetermined temperature (a good fixed image is output) when the paper passing operation (fixing step) is performed again after the standby state is finished. The control temperature of the heat-up time and the first print time will be prolonged for heating evenly.

  In order to solve such problems, the fixing belt is heated and pressurized from the fixing belt while the fixing belt and the pressure rotator are rotationally driven without stopping the driving of the apparatus during standby of the apparatus. A measure for transferring heat over the entire circumferential direction of the rotating body is conceivable. However, in that case, there is a high possibility that the fixing member that is in sliding contact with the inner peripheral surface of the fixing belt and the inner peripheral surface of the fixing belt are worn out and deteriorated at an early stage.

  Such a problem is also common to an apparatus in which a ceramic heater as a fixing member is pressed against a pressure rotating body via a fixing belt to form a nip portion as in the fixing apparatus of Patent Document 3 or the like. Is. That is, even when the fixing belt and the pressure rotator are driven to rotate while the apparatus is on standby, the fixing belt is heated with a ceramic heater to heat the pressure rotator, and the apparatus is slid on the inner peripheral surface of the fixing belt. There is a problem that the ceramic heater (fixing member) in contact with the inner peripheral surface of the fixing belt is quickly worn out.

  The present invention has been made to solve the above-described problems. The warm-up time and the first print time are short, and the fixing belt and the fixing member are quickly worn out without causing a fixing defect in the fixed image. Another object of the present invention is to provide a fixing device and an image forming apparatus in which heat is sufficiently stored in the pressure rotating body during standby.

  According to a first aspect of the present invention, there is provided a fixing device that travels in a predetermined direction to heat and melt a toner image, and has an endless fixing belt having flexibility, and an inner peripheral surface of the fixing belt. A fixing member fixed on the side, and a pressure rotator which is pressed against the fixing member via the fixing belt to form a nip portion where the recording medium is conveyed, and is rotated in a predetermined direction by a driving unit And a heating member that is fixed so as to face the inner peripheral surface of the fixing belt and heats the fixing belt, and is heated by a heating means, and the sheet feeding operation of the recording medium in the nip portion is performed In a standby state where the pressure rotator is in contact with the fixing belt and the travel of the fixing belt is stopped, the driving means rotates the pressure rotator. No while, is to indirectly heat the pressure rotating body via the fixing belt to heat the heating member by the heating means.

  According to a second aspect of the present invention, there is provided a fixing device according to the first aspect of the present invention, further comprising a pressure reducing mechanism for reducing a pressure contact force between the fixing belt and the pressure rotator, and the nip during the standby. The pressure contact force is smaller than the pressure contact force when the recording medium is passed through the recording unit, and the frictional rotational torque of the pressure rotator is smaller than the static frictional torque of the fixing belt. The decompression mechanism is controlled.

  According to a third aspect of the present invention, there is provided the fixing device according to the second aspect, wherein the pressure rotator includes a first pressure portion formed at a central portion in the width direction and an end portion in the width direction. And a second pressurizing part formed on the outer peripheral surface of the first pressurizing part. The second pressurizing part is formed such that the friction coefficient of the outer peripheral face of the second pressurizing part is larger than that of the outer peripheral face of the first pressurizing part At the same time, the outer diameter of the second pressurizing unit is formed to be smaller than the outer diameter of the first pressurizing unit, and the decompression mechanism is configured to perform a sheet feeding operation of the recording medium in the nip unit. The first pressure unit and the second pressure unit are moved so that the pressure member is pressed against the fixing member via the fixing belt. While being separated from the fixing belt, only the first pressure unit is moved forward through the fixing belt. Wherein in pressure-contact with the fixing member is for moving the pressure rotating body.

  According to a fourth aspect of the present invention, there is provided the fixing device according to any one of the first to third aspects, wherein the first temperature detecting means for detecting the temperature of the fixing belt, and the pressure rotation. Second temperature detecting means for detecting the temperature of the body, and when the temperature detected by the second temperature detecting means is equal to or lower than a first predetermined value during the standby, the temperature is second. When the temperature detected by the second temperature detecting means becomes equal to or higher than the second predetermined value, the driving means rotates the pressure rotating body until the predetermined value is reached. The rotational driving of the pressure rotator is stopped.

  According to a fifth aspect of the present invention, in the fixing device according to the fourth aspect, the predetermined time elapses after the sheet feeding operation of the recording medium in the nip portion is completed in the standby state. Is to rotate the pressurizing rotator by the driving means regardless of the temperature value detected by the second temperature detecting means.

  A fixing device according to a sixth aspect of the present invention is the fixing device according to any one of the first to fifth aspects, wherein the heating member has an inner peripheral surface of the fixing belt at a position excluding the nip portion. A pipe-shaped metal member fixed so as to oppose to the heating member, further comprising a reinforcing member fixed on the inner peripheral surface side of the heating member and abutting the fixing member to reinforce the fixing member Is.

  An image forming apparatus according to a seventh aspect of the present invention includes the fixing device according to any one of the first to sixth aspects.

  In the present application, “waiting” means that the recording apparatus does not perform the sheet feeding operation (fixing process) at the nip portion, but waits for the sheet feeding operation (fixing process) to be performed next by the fixing device. It is defined as being in the state of being. Therefore, in addition to when waiting for the next sheet passing operation (fixing step) after the sheet passing operation (fixing step) is completed, the warm-up is performed after the image forming apparatus main body is turned on. Time is also included in “standby”.

  In the present application, the state in which the fixing member, the heating member, or the reinforcing member is “fixed” is a state in which the fixing member, the heating member, or the reinforcing member is held in a non-rotating manner without being driven to rotate. It is defined as Therefore, for example, even when the fixing member is biased toward the nip portion by a biasing member such as a spring, the fixing member is “fixed” if the fixing member is held non-rotating. It becomes a state.

  According to the present invention, in a standby state, the heating member is heated and fixed while rotating the pressure rotator while the pressure rotator is in contact with the fixing belt and the traveling of the fixing belt is stopped. The pressure rotator is indirectly heated via the belt. As a result, the warm-up time and the first print time are short, fixing defects do not occur in the fixed image, and the heat storage of the pressure rotating body during standby is sufficiently performed without accelerating the wear deterioration of the fixing belt and the fixing member. A fixing device and an image forming apparatus can be provided.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 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 expanded sectional view showing the neighborhood of a nip part. It is a figure which shows the fixing device at the time of standby. FIG. 6 is a view of the fixing device of FIG. 5 as viewed in the width direction. It is a graph which shows the relationship between the amount of biting in a nip part, and the friction rotation torque of a pressure roller. It is a flowchart which shows the control at the time of standby. It is a block diagram which shows the fixing device in Embodiment 2 of this invention. It is a block diagram which shows the fixing device of another form.

  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.

Embodiment 1 FIG.
The first embodiment of the present invention will be described in detail with reference to FIGS.
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 according to the first embodiment is a tandem type 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 transferred P discharged from 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.
2 to 4, the fixing device 20 includes a fixing belt 21 (belt member) as a fixing member, a fixing member 26, a heating member 22 (metal member), a reinforcing member 23, and a heater 25 (heating means). Heat source), a pressure roller 31 as a pressure rotator, a first temperature sensor 40 as a first temperature detection means, a second temperature sensor 55 as a second temperature detection means, a decompression mechanism 51-53 (moving mechanism), The heat insulation member 27, the stay member 28, etc. are comprised.

Here, the fixing belt 21 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 first embodiment, the inner diameter of the fixing belt 21 is set to 30 mm.
A fixing member 26, a heater (heating means), a heating member 22 (metal member), a reinforcing member 23, a heat insulating member 27, a stay member 28, and the like are fixed inside the fixing belt 21 (inner peripheral surface side). Yes. Although not shown, a lubricant is applied between the fixing belt 21 and the heating member 22.
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 heating member 22 is formed so as to face the inner peripheral surface of the fixing belt 21 at a position excluding the nip portion, and holds the fixing member 26 via the heat insulating member 27 at the position of the nip portion. This is a substantially cylindrical metal member formed as described above. With reference to FIG. 3, both ends of the heating 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 heating member 22, stopper flanges 29 for restricting the shift of the fixing belt 21 (movement in the width direction) are inserted.
The heating member 22 formed in a substantially pipe shape is heated by the radiant heat of the heater 25 to heat the fixing belt 21 (transmits heat). That is, the heating member 22 is directly heated by the heater 25, and the fixing belt 21 is indirectly heated by the heater 25 through the heating member 22. In order to maintain the heating efficiency of the fixing belt 21 well, it is preferable to set the thickness of the heating member 22 to 0.1 mm or less.
As a material of the heating member 22, a metal heat conductor (a metal having heat conductivity) such as stainless steel, nickel, aluminum, and iron can be used, and among them, a heat capacity ratio (density) of unit volume. X Ferrite stainless steel having a relatively small specific heat) is preferred. In the first embodiment, SUS430 that is ferritic stainless steel is used as the material of the heating member 22. Further, the thickness of the heating member 22 is set to 0.1 mm.

  The heater 25 as a heating means is a halogen heater (or carbon heater), and both ends thereof are fixed to the side plate 43 of the fixing device 20 (see FIG. 3). The heating member 22 is heated by the radiant heat of the heater 25 (heating means) whose output is controlled by the power supply unit of the apparatus body 1. Further, the fixing belt 21 is entirely heated by the heating 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 first temperature sensor 40 (first temperature detecting means) such as a thermistor 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, in the fixing device 20 according to the first 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 heating member 22. Therefore, 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 heating 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 δ between the fixing belt 21 and the heating 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 <δ ≦ 1 mm). As a result, the area in which the heating 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 heating member 22 and the fixing belt 21 are too far apart to heat the fixing belt 21. Inconveniences that reduce efficiency can be suppressed. In addition, since the heating member 22 is placed close to the fixing belt 21, the circular posture of the fixing belt 21 having flexibility is maintained to some extent, so that deterioration / breakage due to deformation of the fixing belt 21 can be reduced. .
Further, in order to reduce wear of the fixing belt 21 even if the heating 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 both members 21 and 22. A lubricant such as silicone oil is applied.
In the first embodiment, the heating member 22 is formed to have a substantially circular cross-sectional shape, but the heating member 22 may be formed to have a polygonal cross-sectional shape.

  Here, in the first 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. In the first embodiment, the reinforcing member 23 is a plate-like member arranged so that the inside of the heating member 22 is roughly divided into two spaces.

In order to satisfy the above-described function, the reinforcing member 23 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron.
In addition, a heat insulating member can be provided on a part or all of the surface of the reinforcing member 23 facing the heater 25, or a mirror surface treatment can be performed. As a result, the heat from the heater 25 toward the reinforcing member 23 (heat for heating the reinforcing member 23) is used for heating the heating member 22, and thus the heating efficiency of the fixing belt 21 (heating member 22) is further improved. Will do.
In the first embodiment, the reinforcing member 23 is formed in a flat plate shape, but the shape of the reinforcing member 23 is not limited to this, and various shapes such as a T-shape are used. be able to.

2 and 3, a pressure roller 31 as a pressure rotator that abuts the outer peripheral surface of the fixing belt 21 at the position of the nip portion is formed on a hollow cored bar 34 with a first pressure portion. 32 and the 2nd pressurizing part 33 are formed, respectively. In the pressure roller 31, the first pressure unit 32 is formed in a sheet passing region at the center in the width direction, and the second pressure unit 33 is formed in a non-sheet passing region at both ends in the width direction.
In the present application, the “sheet passing area” is defined as a range in the width direction (direction perpendicular to the sheet passing direction) of the maximum size recording medium to be passed by the image forming apparatus. The “non-sheet passing area” is defined as an area outside the range of the “sheet passing area”.

The first pressure part 32 of the pressure roller 31 (pressure rotator) is a main part that forms a nip part through which the recording medium P is conveyed, and is made of an elastic material having a diameter of 30 mm (core). It is an elastic layer formed on the gold 34.) The first pressure portion 32 (elastic layer) of the pressure roller 31 is formed of a material such as foamable silicone rubber, silicone rubber, or fluorine rubber. Note that a thin release layer made of PFA, PTFE, or the like may be provided as a surface layer on the first pressure unit 32 (elastic layer). The pressure roller 31 (first pressure unit 32) is in pressure contact with the fixing belt 21 to form a desired nip portion between both members.
In addition, the 2nd pressurization part 33 provided in the width direction both ends (non-sheet passing area | region) of the pressure roller 31 is a foaming silicone rubber, a silicone rubber, a fluorine rubber, etc. similarly to the 1st pressurization part 32. Made of elastic material. The second pressurizing part 33 is formed so that the frictional resistance of the outer peripheral surface thereof is larger than the frictional resistance of the outer peripheral surface of the first pressurizing part 32 and has an outer diameter (28 mm). Is smaller than the outer diameter (30 mm) of the first pressure member 32. The second pressure unit 33 of the pressure roller 31 will be described in detail later.

When the elastic layer 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. Can be reduced. 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 the first embodiment, the diameter of the fixing belt 21 is formed so as to be approximately equal to the diameter of the pressure roller 31, but the diameter of the fixing belt 21 is smaller than the diameter of the pressure roller 31. It can also be formed. 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. 3, the pressure roller 31 is provided with a gear 45 that meshes with a drive gear of a drive means (drive mechanism) (not shown). The pressure roller 31 is driven by the drive means in FIG. It is rotationally driven in the direction of the arrow (clockwise).
Further, both ends of the pressure roller 31 in the width direction are rotatably supported via a bearing 42 with respect to the pressure lever 51 that is rotatably supported by the side plate 43 of the fixing device 20. The pressure roller 31 is moved in the left-right direction in FIG. 2 at a predetermined timing by the pressure-reducing mechanisms 51 to 53 (contact / separation mechanism) including the pressure lever 51 (positions in FIGS. 2 and 3). And the position between FIG. 5 and FIG.
The configuration and operation of the decompression mechanisms 51 to 53 (contact / separation mechanism) will be described in detail later.

  In the first embodiment, a second temperature sensor 55 such as a thermistor is installed as a second temperature detection means for detecting the surface temperature of the pressure roller 31 (first pressure unit 32). The standby control is performed based on the detection result of the second temperature detection sensor 55, which will be described in detail later.

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 first 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 substantially pipe-shaped heating member 22 formed by bending a metal plate can be thinned, the warm-up time can be shortened. However, since the rigidity of the heating member 22 itself is small, it may be bent or deformed without resisting the pressure applied by the pressure roller 31. If the pipe-shaped heating member 22 is deformed, a desired nip width cannot be obtained, and there is a problem that the fixing property is deteriorated. On the other hand, in the first embodiment, since the high-rigidity fixing member 26 is installed separately from the thin-walled heating member 22 to form the nip portion, it is possible to prevent such a problem from occurring. Can be prevented.

  Further, the surface layer 26a of the fixing member 26 is formed of a coarse sheet-like low friction material. The surface layer 26a is impregnated with a lubricant in advance. As a result, the fixing member 26 is in a state where the lubricant is held on the surface in contact with the fixing belt 21. Therefore, the problem that both the members 21 and 26 are worn due to the sliding contact between the fixing member 26 and the fixing belt 21 is reduced.

In the first embodiment, the 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 heating 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 first embodiment, since the fixing belt 21 and the heating 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 during heating standby (standby for 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 first embodiment, since the heat insulating member 27 is installed between the fixing member 26 and the heating member 22, the heat of the heating 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.
On the other hand, in the first embodiment, since the heat insulating member 27 is installed between the fixing member 26 and the heating member 22, the heat of the heating 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.

  In the first embodiment, since the heat insulating member 27 is installed between the fixing member 26 and the heating member 22, the fixing member 26 is thermally insulated, and the fixing belt 21 is actively heated in the nip portion. Will not 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 first embodiment, referring to FIG. 4, a stay member 28 that holds the concave portion of the heating member 22 into which the fixing member 26 is inserted from the inner peripheral surface side is provided.
The substantially pipe-shaped heating 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 heating 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 first embodiment, in order to prevent such a problem from occurring, the recess of the heating member 22 in which the opening is formed (bending portion) is fixed by the stay member 28, whereby the spring of the heating member 22 is fixed. Deformation due to back is suppressed. Specifically, the stay member 28 is press-fitted into the recess from the inner peripheral surface side of the heating member 22 while maintaining the shape of the heating member 22 that has been bent so as to resist the springback force.

Here, in order to increase the heating efficiency of the heating member 22, the thickness of the heating member 22 is preferably set to 0.2 mm or less.
As described above, since the thickness of the substantially pipe-shaped heating member 22 formed by bending a metal plate can be reduced, the warm-up time can be shortened. However, since the rigidity of the heating member 22 itself is small, when the pressing force of the pressure roller 31 acts on the heating member 22, the pressing member 31 may bend or deform without resisting the pressing force. Then, if the pipe-shaped heating 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 first embodiment, the thin heating 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. Since the pressure is configured not to directly act on the heating member 22, it is possible to prevent such a problem from occurring.

The normal operation of the fixing device 20 configured as described above will be briefly described below.
When the power switch of the apparatus main body 1 is turned on, power is supplied to the heater 25, and rotation driving of the pressure roller 31 in the direction of the arrow in FIG. 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.
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.
Then, by the heating by the fixing belt 21 heated by the heating member 22 (heater 25) and the pressing force of the fixing member 26 reinforced by the reinforcing member 23 and the pressure roller 31 (first pressure unit 32), The toner image T is fixed on the surface of the recording medium P. Thereafter, the recording medium P delivered from the nip portion is conveyed in the direction of arrow Y11.

Hereinafter, a characteristic configuration and operation of the fixing device 20 according to the first embodiment will be described in detail.
The fixing device 20 according to the first exemplary embodiment is in a state where the pressure roller 31 is in contact with the fixing belt 21 and is stopped by the driving means (driving mechanism) while the traveling of the fixing belt 21 is stopped during standby. While rotating the roller 31, the heating member 22 is heated by the heater 25 to indirectly heat the pressure roller 31 via the fixing belt 21.
Specifically, referring to FIGS. 2 and 5, the fixing device 20 according to the first exemplary embodiment reduces the pressure contact force between the fixing belt 21 and the pressure roller 31 (the pressure contact force at the nip portion). Mechanisms 51 to 53 are provided. In the pressure reducing mechanisms 51 to 53 (contact / separation mechanisms), the pressure contact force at the nip portion is smaller than that at the time of paper feeding (during the fixing process) during standby, and the static friction torque of the fixing belt 21 is reduced. Thus, the frictional rotation torque of the pressure roller 31 is controlled to be small.

  More specifically, the pressure reducing mechanism (contact / separation mechanism) includes a pressure lever 51, a cam 52, a tension spring 53, and the like (installed at both ends in the width direction). The pressure lever 51 is installed on the side plate 43 so as to be rotatable about a support shaft 51a. A shaft portion of the cored bar 34 of the pressure roller 31 is rotatably held at one end side of the pressure lever 51 via a bearing 42, and one end of a tension spring 53 is connected to the other end side. Although not shown, the other end of the tension spring 53 is connected to the side plate 43. A cam 52 connected to a drive motor (not shown) is rotatably installed on the side plate 43 of the fixing device 20. Then, the cam 52 is rotationally controlled so as to come in contact with and separate from the pressure lever 51, so that the state during paper passing (the state shown in FIGS. 2 and 3) and the state during standby (FIG. , And the state of FIG. 6).

Specifically, when the posture in the rotational direction is controlled so that the cam 52 does not contact the pressure lever 51, the pressure lever 51 fixes the pressure roller 31 by the spring force of the tension spring 53. The urging is performed in a direction approaching the belt 21. Accordingly, as shown in FIGS. 2 and 3, the first pressure unit 32 and the second pressure unit 33 of the pressure roller 31 are respectively brought into pressure contact with the fixing belt 21 to form a nip portion. Become. When the driving means (not shown) operates in this state, the pressure roller 31 is rotationally driven by transmission of the driving force from the driving means to the gear 45, and the first pressure unit 32 and the second pressure unit 33 Due to this frictional resistance, the fixing belt 21 is also driven to rotate counterclockwise in FIG. In this state, the above-described fixing process (sheet feeding operation of the recording medium P) is performed.
On the other hand, when the posture in the rotational direction is controlled so that the cam 52 contacts the pressure lever 51, the pressure lever 51 pressurizes so as to resist the spring force of the tension spring 53. The roller 31 is rotated in a direction away from the fixing belt 21. As a result, as shown in FIGS. 5 and 6, the second pressure portion 33 (whose outer diameter is smaller than the outer diameter of the first pressure portion 32) is separated from the fixing belt 21. Only the first pressure part 32 is pressed against the fixing belt 21 to form a nip part (the pressure contact force is smaller than the state shown in FIGS. 2 and 3). In this state, the frictional rotation torque of the pressure roller 31 is smaller than the static friction torque of the fixing belt 21. Therefore, when a driving unit (not shown) is operated in this state, the pressure roller 31 is rotated by transmission of driving force from the driving unit to the gear 45, but the frictional resistance with the first pressing unit 32 is small. For this reason, the fixing belt 21 stops without being driven to rotate. In such a state, electric power is supplied to the heater 25 (heating means). As a result, the heating member 22 is heated, and heat is efficiently transmitted from the fixing belt 21 heated by the heating member 22 to the pressure roller 31 that rotates in the direction of the arrow in FIG. Such an operation is performed as a standby operation of the apparatus (an operation in preparation for the next fixing step).

As described above, in the pressure roller 31 according to the first embodiment, the outer diameter of the first pressure unit 32 (the outer diameter in the no-load state) is set to 30 mm, and the second pressure unit The outer diameter of 33 (the outer diameter in an unloaded state) is set to 28 mm. Further, the outer diameter of the fixing belt 21 is set to 30 mm.
In the state at the time of paper passing (the state shown in FIGS. 2 and 3), the distance between the rotation center of the fixing belt 21 and the rotation center of the pressure roller 31 (hereinafter referred to as “distance between axes”). Both members 21 and 31 are pressure-contacted by the pressure-reducing mechanisms 51 to 53 (contact / separation mechanism) so as to be 28 mm. Accordingly, in the state during paper feeding, the amount of biting of the first pressure unit 32 with respect to the fixing belt 21 becomes 2 mm (corresponding to a nip width of 6 to 7 mm), and the second pressure unit 33 with respect to the fixing belt 21 has a biting amount. The amount of biting is 1 mm.
On the other hand, in the standby state (the state shown in FIGS. 5 and 6), the pressure reducing mechanisms 51 to 53 (so that the center distance between the fixing belt 21 and the pressure roller 31 is 29.5 mm. The members 21 and 31 are pressed against each other by the contact / separation mechanism. Therefore, in the standby state, the amount of biting of the first pressure unit 32 with respect to the fixing belt 21 is 0.5 mm (corresponding to a nip width of 1 to 2 mm), and the second pressure is applied to the fixing belt 21. The part 33 is in a separated state (the gap B between the members 21 and 33 is about 0.875 mm).

FIG. 7 is a graph showing the relationship between the amount of biting (horizontal axis) at the nip portion and the frictional rotational torque (vertical axis) of the pressure roller 31 in the fixing device 20 according to the first embodiment.
As shown in FIG. 7, when the amount of biting of the pressure roller 31 (first pressure portion 32) with respect to the fixing belt 21 at the nip portion is 2.0 mm, the frictional rotational torque of the pressure roller 31 is 0.6 N · m. When the biting amount is reduced to 1.0 mm, the second pressure unit 33 is separated from the fixing belt 21, and the frictional rotational torque of the pressure roller 31 is 0.4 N · m to 0.3 N · m. Drop to. Here, since the static friction torque of the fixing belt 21 in the first embodiment is 0.2 N · m, the traveling of the fixing belt 21 is stopped when the biting amount is 0.75 mm or less. In the first embodiment, as described above, since the amount of biting of the first pressure unit 32 with respect to the fixing belt 21 during standby is set to 0.5 mm, the pressure roller 31 is driven to rotate. The fixing belt 21 does not travel.

  In the fixing device 20 configured as described above, the decompression mechanisms 51 to 53 are controlled so as to be in the state of FIGS. 2 and 3 at the time of paper passing (during the fixing process), and in the state of FIGS. It is controlled to become. Further, at the time of standby, the driving means is controlled to rotate and drive the pressure roller 31 and the heater 25 (heating means) is controlled to heat the heating member 22 in the same manner as at the time of passing the paper. Power is supplied to the heater 25). However, at the time of standby, as described above, the pressure contact force in the nip portion is reduced by the pressure reducing operation by the pressure reducing mechanisms 51 to 53, and therefore the pressure roller 31 is in contact with the fixing belt 21, but the fixing is performed. The belt 21 will not run.

Thereby, the heat storage of the pressure roller 31 during standby can be sufficiently performed without accelerating the wear deterioration of the fixing belt 21 and the fixing member 26. That is, since the pressure roller 31 is heated while being in contact with the fixing belt 21 while rotating the pressure roller 31 during standby, the pressure roller 31 is efficiently heated over the entire circumferential direction. . At this time, since the travel of the fixing belt 21 is stopped and the sliding between the fixing belt 21 and the fixing member 26 does not occur, even if the pressure roller 31 is rotationally driven during standby, The wear deterioration with the fixing member 26 is not accelerated.
In the first embodiment, the pressure roller 31 and the fixing belt 21 rub against each other during standby, but the first pressure unit 32 during standby is provided by providing the second pressure unit 33. Since the pressure contact force between the fixing belt 21 and the fixing belt 21 can be set to be extremely small, even when the standby control is performed, the wear deterioration of both the members 21 and 31 is not greatly affected.
Further, in order to reduce the influence of the rubbing between the pressure roller 31 and the fixing belt 21 at the time of standby as described above, the rotational speed of the pressure roller 31 at the time of standby may be decreased with respect to that at the time of paper. it can. Specifically, it is preferable to decelerate and set the linear velocity of the pressure roller 31 during standby (the linear velocity at the nip portion) to about 40 to 60 mm / second.

In the first embodiment, the following control is further performed during standby.
During standby, when the temperature detected by the second temperature sensor 55 (second temperature detection means) is equal to or lower than a first predetermined value (in the first embodiment, it is set to 80 ° C.). The pressure roller 31 is rotationally driven by the driving means until the temperature reaches a second predetermined value (in the first embodiment, it is set to 100 ° C.). Then, when the temperature detected by the second temperature sensor 55 becomes equal to or higher than a second predetermined value (in the first embodiment, it is set to 100 ° C.), the pressure roller 31 by the driving means Stop rotation drive.
Furthermore, when performing such control, a predetermined time (60 seconds is set in the first embodiment) after the sheet feeding operation of the recording medium P in the nip portion is completed during standby. Until this is done, the pressure roller 31 is forcibly driven by the driving means regardless of the temperature value detected by the second temperature sensor 55.

This will be specifically described with reference to the flowchart of FIG.
First, when the sheet passing operation (printing operation) is finished and the apparatus is in a standby state (steps S1 and S2), the temperature detected by the first temperature sensor 40 (first temperature detecting means) (the surface temperature of the fixing belt 21). Is controlled at 150 ° C., the output control of the heater 25 is performed (step S3). Further, the pressure reducing mechanisms 51 to 53 are controlled to reduce the pressure contact force of the pressure roller 31 to the fixing belt 21 to the state shown in FIGS. 5 and 6 (step S4). Immediately thereafter, the pressure roller 31 is rotationally driven by the driving means at a predetermined rotational speed (linear velocity at the nip portion is 40 to 60 mm / second) (step S5). And it is discriminate | determined whether the rotational drive of the pressure roller 31 in the pressure reduction state was performed for 60 seconds (step S6).
As a result, if it is determined that the rotation of the pressure roller 31 in the reduced pressure state has been performed for 60 seconds, the rotation of the pressure roller 31 is temporarily stopped assuming that the frequency of print requests is low ( Step S7). And it is discriminate | determined whether the temperature of the pressure roller 31 detected by the 2nd temperature sensor 55 is 80 degrees C or less (step S8).

As a result, when it is determined that the temperature of the pressure roller 31 is 80 ° C. or higher, the driving of the pressure roller 31 is continuously stopped, and it is determined that the temperature of the pressure roller 31 is 80 ° C. or lower. If so, the driving of the pressure roller 31 is resumed (step S9). And it is discriminate | determined whether the temperature of the pressure roller 31 detected by the 2nd temperature sensor 55 is 100 degreeC or more (step S10).
As a result, when it is determined that the temperature of the pressure roller 31 is 100 ° C. or less, the driving of the pressure roller 31 is continued and it is determined that the temperature of the pressure roller 31 is 100 ° C. or more. If this happens, the driving of the pressure roller 31 is stopped again.
Such control is performed until a print request signal is received.

By performing such control, when the heat storage state of the pressure roller 31 is sufficient, the pressure roller 31 is not rotationally driven, and the pressure roller 31 is rotationally driven intermittently. Therefore, unnecessary sliding contact between the pressure roller 31 and the fixing belt 21 can be reduced during standby.
Immediately after the end of the printing operation (paper passing operation), the intermittent rotation driving of the pressure roller 31 described above is not performed immediately, and the predetermined time (in the first embodiment, 60 seconds). ), The pressure roller 31 is forcibly rotated regardless of the temperature of the pressure roller 31. Therefore, it is possible to further shorten the start-up of the apparatus when the next printing operation by the user is performed immediately.

  As described above, in the first embodiment, in the standby state, the pressure roller 31 (pressure rotator) is in contact with the fixing belt 21 and the traveling of the fixing belt 21 is stopped. While rotating the pressure roller 31, the heating member 22 is heated to indirectly heat the pressure roller 31 via the fixing belt 21. As a result, the warm-up time and the first print time are short, fixing defects do not occur in the fixed image, and the heat storage of the pressure roller 31 during standby is sufficiently performed without accelerating the wear deterioration of the fixing belt 21 and the fixing member 26. Can be done.

In the first embodiment, the pressure roller 31 is provided with the second pressure unit 33 so that the pressure reducing mechanisms 51 to 53 can switch between the state during paper passing and the state during standby. . That is, when the driving means is operated (when the pressure roller 31 is rotated), the fixing belt 21 travels in a predetermined direction when the paper is being passed (the state shown in FIGS. In the state (the state of FIGS. 5 and 6), the fixing belt 21 is configured to stop running.
On the other hand, the outer diameter and material of the pressure roller 31 (first pressure unit 32), the movement range of the decompression mechanisms 51 to 53, and the like are optimized without providing the second pressure unit 33 on the pressure roller 31. Only by making it possible, the state at the time of passing the paper and the state at the time of waiting can be switched. In such a case, the same effect as in the first embodiment can be obtained.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 9 is a configuration diagram illustrating the fixing device according to the second embodiment, and corresponds to FIG. 2 according to the first embodiment. The fixing device according to the second embodiment is different from that according to the first embodiment in that the heating member 22 is heated by electromagnetic induction.

As shown in FIG. 9, the fixing device 20 according to the second embodiment also has a fixing belt 21, a fixing member 26, a substantially pipe-shaped heating member 22, a reinforcing member 23, a heat insulating member, as in the first embodiment. The member 27, the pressure roller 31 (heating rotator), the first temperature sensor 40, the second temperature sensor 55, the pressure reducing mechanisms 51 to 53, and the like are configured. Also, the pressure roller 31 in the second embodiment is also formed with a first pressure portion 32 at the center in the width direction and second pressure portions at both ends in the width direction, as in the first embodiment. 33 is formed. Further, the decompression mechanisms 51 to 53 allow the first pressurizing unit 32 to be separated from the fixing belt 21 by separating the second pressurizing unit 33 from the state during paper passing (the state illustrated in FIG. 9) and the standby state (the state illustrated in FIG. 9). Only is in pressure contact state)). During standby, while the pressure roller 31 (first pressure unit 32) is in contact with the fixing belt 21 and the traveling of the fixing belt 21 is stopped, the pressure roller 31 is rotated and driven. The heating member 22 is heated to indirectly heat the pressure roller 31 via the fixing belt 21.
Here, in the fixing device 20 according to the second embodiment, an induction heating unit 50 is installed as a heating unit instead of the heater 25. And the heating member 22 in this Embodiment 2 is heated by the electromagnetic induction by the induction heating part 50 unlike the thing of the said Embodiment 1 heated by the radiant heat of the heater 25. FIG.

  The induction heating unit 50 includes an exciting coil, a core, a coil guide, and the like. The exciting coil is formed by extending a litz wire, which is a bundle of thin wires, in the width direction (in the direction perpendicular to the plane of FIG. 9) so as to cover a part of the fixing belt 21. The coil guide is made of a resin material having high heat resistance and holds the exciting coil and the core. The core is a semi-cylindrical member made of a ferromagnetic material such as ferrite (having a relative permeability of about 1000 to 3000), and in order to form an efficient magnetic flux toward the heating member 22, A side core is provided. The core is installed so as to face the exciting coil extending in the width direction.

The fixing device 20 configured as described above operates as follows.
When the pressure roller 31 is rotationally driven in the direction of the arrow in FIG. 9, the fixing belt 21 is also driven to rotate in the direction of the arrow. The fixing belt 21 is heated at a position facing the induction heating unit 50. Specifically, the magnetic lines of force are formed alternately around the heating member 22 by passing a high-frequency alternating current through the exciting coil. At this time, an eddy current is generated on the surface of the heating member 22, and Joule heat is generated by the electric resistance of the heating member 22 itself. Due to the Joule heat, the heating member 22 is heated by electromagnetic induction, and the fixing belt 21 is heated by the heated heating member 22.
In order to efficiently perform electromagnetic induction heating of the heating member 22, the induction heating unit 50 is preferably configured to face the entire circumferential direction of the heating member 22. Moreover, as a material of the heating member 22, nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, an alloy made of a plurality of these metals, or the like can be used. .

  As described above, also in the second embodiment, the fixing belt 21 and the fixing member can be fixed without causing a fixing defect in the fixed image because the warm-up time and the first print time are short as in the above embodiments. The heat storage of the pressure roller 31 during standby can be sufficiently performed without accelerating the wear deterioration of 26.

In the second embodiment, the heating member 22 is heated by electromagnetic induction heating. However, as shown in FIG. 10, the heating member 62 is a resistance heating element (a planar heating element such as a ceramic heater). The fixing belt 21 can also be heated by the heat of the heating member 62 itself. Specifically, the heating member 62 as a resistance heating element has both ends in the width direction connected to the power supply unit 61 via electrodes (not shown). When power is supplied from the power supply unit 61 to the heating member 62 and a current flows through the heating member 62, the heating member 62 is heated by the electrical resistance of the heating member 62 itself. Further, the fixing belt 21 is heated by the radiant heat of the heating member 62.
Furthermore, as in Patent Document 3, the present invention can also be applied to a fixing device in which a ceramic heater as a fixing member is pressed against a pressure rotating body via a fixing belt to form a nip portion. . In this case, the ceramic heater has a function as a heating means, a function as a heating member, and a function as a fixing member.
Also in these cases, the same effect as in the second embodiment can be obtained by configuring the pressure roller 31 and the pressure reducing mechanisms 51 to 53 in the same manner as in the second embodiment and performing the standby control in the same manner. be able to.

  In each of the above embodiments, the fixing belt 21 having a multilayer structure is used as the fixing belt. However, an endless fixing film made of polyimide, polyamide, fluororesin, metal, or the like may be used as the fixing belt. In this case, the same effects as those of the above embodiments can be obtained.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 image forming apparatus body (apparatus body),
20 fixing device,
21 fixing belt (fixing member),
22 Heating member (metal member),
23 reinforcing members,
25 heater (heating means),
26 fixing member,
31 Pressure roller (pressure rotating body),
32 1st pressurizing part,
33 second pressure part,
40 1st temperature sensor (1st temperature detection means),
51 Pressure lever (pressure reduction mechanism),
52 cam (pressure reduction mechanism),
53 Tension spring (pressure reduction mechanism),
55 Second temperature sensor (second temperature detecting means), P recording medium.

Japanese Patent No. 2009-3410 Japanese Patent No. 2008-158482 Japanese Patent No. 2002-6656

Claims (7)

An endless fixing belt having flexibility and running in a predetermined direction to heat and melt the toner image;
A fixing member fixed to the inner peripheral surface side of the fixing belt;
A pressure rotator that is pressed against the fixing member via the fixing belt to form a nip portion on which a recording medium is conveyed, and is rotated in a predetermined direction by a driving unit;
A heating member fixed to the inner peripheral surface of the fixing belt to heat the fixing belt and heated by a heating unit;
With
In a standby state where the recording medium does not pass through the nip portion, the driving unit is configured to stop the travel of the fixing belt while the pressure rotator is in contact with the fixing belt. A fixing device that heats the heating member by the heating means and indirectly heats the pressure rotator through the fixing belt while rotating the pressure rotator. A pressure reducing mechanism for reducing the pressure contact force between the fixing belt and the pressure rotator,
At the time of the standby, the pressure contact force is smaller than the pressure contact force when the recording medium is passed through the nip portion, and the friction rotation torque of the pressure rotator with respect to the static friction torque of the fixing belt. The fixing device according to claim 1, wherein the pressure-reducing mechanism is controlled so as to be small. The pressure rotator is
A first pressurizing part formed at the center in the width direction, and a second pressurizing part formed at the end in the width direction,
The friction coefficient of the outer peripheral surface of the second pressurizing unit is formed to be larger than the friction coefficient of the outer peripheral surface of the first pressurizing unit, and the outer diameter of the first pressurizing unit is larger than the outer diameter of the first pressurizing unit. It is formed so that the outer diameter of the second pressurizing part becomes small,
The pressure reducing mechanism is configured so that the first pressurizing unit and the second pressurizing unit are pressed against the fixing member via the fixing belt when a recording medium passing operation is performed in the nip unit. The pressure rotator is moved so that the second pressurizing unit is separated from the fixing belt during the standby, and only the first pressurizing unit is in pressure contact with the fixing member via the fixing belt. The fixing device according to claim 2, wherein the pressure rotator is moved. First temperature detecting means for detecting the temperature of the fixing belt;
Second temperature detecting means for detecting the temperature of the pressure rotating body;
With
When the temperature detected by the second temperature detection means becomes equal to or lower than a first predetermined value during the standby, the drive means rotates the pressure rotating body until the temperature reaches a second predetermined value. Rotation driving is performed, and when the temperature detected by the second temperature detection means becomes equal to or higher than the second predetermined value, the rotation driving of the pressure rotator by the driving means is stopped. The fixing device according to claim 1.   During the standby period, until the predetermined time elapses after the recording medium passing operation at the nip portion is completed, the driving means increases the temperature regardless of the temperature value detected by the second temperature detecting means. The fixing device according to claim 4, wherein the pressure rotator is rotationally driven. The heating member is a pipe-like metal member fixed so as to face the inner peripheral surface of the fixing belt at a position excluding the nip portion,
The reinforcing member which is fixedly provided on the inner peripheral surface side of the heating member and abuts on the fixing member to reinforce the fixing member. Fixing device.   An image forming apparatus comprising the fixing device according to claim 1.

Images