JP2016085276A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that can avoid delay in paper feed in the subsequent job due to an increase in temperature of a fixing belt while saving heating energy.SOLUTION: A fixing device includes: a heating member that is a rotor to be heated by a heat source; a fixing member that is a rotor in contact with the heating member; a pressure member that is a rotor applied with pressure by the fixing member to form a nip part with the fixing member; a sensor that detects the temperature of the fixing member; a contact force changing mechanism that changes a contact force between the fixing member and heating member; a stopper that breaks the rotation of the heating member; and a control part that causes the contact force changing mechanism to change the contact force between the fixing member and heating member on the basis of an output from the sensor and causes the stopper to break the rotation of the heating member.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a fixing device and an image forming apparatus.

  In a fixing device using heat and pressure, a pressure member is pressed against a fixing member including a heat source therein, and a transfer sheet on which an unfixed toner image is placed is passed between the fixing member and the pressure member. The mainstream is a technique for fixing toner to a recording medium.

  Of these, those using a silicone rubber seamless belt (hereinafter referred to as a fixing belt) as a fixing member have many achievements.

  In this configuration, a fixing roller made of silicone rubber and a heating roller as a heating source are provided inside the fixing belt, and a nip portion is formed by pressing the pressure roller and the fixing roller outside the fixing belt between them. In this embodiment, the transfer paper on which the unfixed toner image is placed is passed and fixed.

  In this system, a form in which a plurality of heat pipes are mounted on the heating roller in the axial direction can be seen. This is because an effect of reducing the thermal deviation in the axial direction can be obtained by using the heat pipe. When the heat distribution of the heater in the heating roller is uniform in the roller width direction, if a transfer paper shorter than the roller width is passed, the part where the transfer paper does not pass is not deprived of heat by the transfer paper. The temperature will rise. If the number of sheets passed per time is large, the temperature rise may exceed the allowable temperature of the fixing belt. However, by using this heat pipe, the temperature in the axial direction can be reduced, and the fixing belt can be protected.

  The use of a heat pipe has the above advantages, but the following problems also exist.

  In order to mount the heat pipe, the thickness of the heating roller is necessary, and the heat capacity is increased by increasing the thickness and volume of the heating roller. During continuous paper feeding, the fixing belt is controlled to a temperature suitable for fixing to the transfer paper, but the heating roller is at a temperature several tens of degrees higher than the fixing belt in order to transfer heat to the fixing belt. Since the fixing belt is not particularly deprived of heat after the paper is passed, the heat of the heating roller flows and the temperature rises. When the next job is issued in such a state, when the temperature is higher than the appropriate temperature range of the transfer paper of the next job, the fixing belt temperature is waited for to be lowered, and the job starts late.

  In the case of a heating roller equipped with a heat pipe, since the heat capacity is large, it takes a long time to decrease.

  In order to solve such problems, some have a belt cooling fan. However, it is not possible to efficiently cool the belt cooling fan alone.

  In this regard, a fixing device that can change the distance between a heat source for heating the fixing belt and the fixing belt has been proposed (for example, Patent Document 1 and Patent Document 2).

  However, these techniques have been developed to efficiently heat the fixing belt, and the cooling efficiency is not good enough to solve the above problem.

  In view of the above problems, an object of the present invention is to provide a fixing device capable of avoiding delay in passing a next job due to an increase in the temperature of the fixing belt while saving heating energy.

  In order to solve the above problems, the present invention provides a heating member that is a rotating body that is heated by a heat source, a fixing member that is a rotating body that is in contact with the heating member, and a pressure applied to the fixing member so that the fixing member and the nip portion are A pressure member that is a rotating body to be formed, a sensor that detects the temperature of the fixing member, a contact force changing mechanism that changes the contact force between the fixing member and the heating member, a stopper that brakes the rotation of the heating member, There is provided a fixing device including a control unit that changes a contact force between a fixing member and a heating member by a contact force changing mechanism based on an output, and controls rotation of the heating member by a stopper.

  According to the present invention, it is possible to provide a fixing device capable of avoiding delay in passing a next job due to an increase in the temperature of the fixing belt while saving heating energy.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus. FIG. 3 is a diagram illustrating a configuration of a fixing device. It is a figure which shows the state which the tension | pulling spring tension change mechanism weakened the tension | tensile_strength of the fixing belt. FIG. 6 is a diagram illustrating a relationship between a transition of a print job and a fixing belt temperature. FIG. 6 is a diagram illustrating a state of the fixing device when the contact width of the fixing belt to the heating roller is large. FIG. 4 is a diagram illustrating a state of the fixing device when the contact width of the fixing belt to the heating roller is small. FIG. 6 is a diagram illustrating a relationship between a transition of a print job and a fixing belt temperature. It is a figure which shows the state which the pressure roller is pressing completely. It is a figure which shows the state which the pressure roller is spaced apart completely and is depressurizing. It is a figure which shows the state of a pressure roller intermediate | middle of a depressurization and pressurization. FIG. 6 is a diagram illustrating a relationship between a transition of a print job and a fixing belt temperature.

  Hereinafter, a fixing device and an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus 100 to which the present invention is applied. In the figure, a tandem intermediate transfer type image forming apparatus main body as the image forming apparatus 100 and a paper feed table 200 on which the image forming apparatus 100 is placed are shown. Further, inside the image forming apparatus 100, a tandem intermediate transfer type image forming unit 20 in which a plurality of image forming units 18Y, 18M, 18C, and 18K are arranged in parallel is provided. Subscripts Y, M, C, and K attached to the above symbols indicate yellow, magenta, cyan, and black colors, respectively. The image forming apparatus 100 is provided with an endless belt intermediate transfer member (hereinafter referred to as an intermediate transfer belt 10) near the center. The intermediate transfer belt 10 is wound around a driving roller 14, a plurality of support rollers 15, 15 ', a secondary transfer counter roller 16, and the like, and can be rotated and conveyed clockwise in the drawing.

  In the example of FIG. 1, a cleaning device 17 for the intermediate transfer belt is provided on the left side of the secondary transfer counter roller 16. The cleaning device 17 removes residual toner remaining on the intermediate transfer belt 10 after image transfer.

  Four images of yellow (Y), magenta (M), cyan (C), and black (K) are arranged on the intermediate transfer belt 10 stretched between the driving roller 14 and the support roller 15 along the conveying direction. The tandem-type image forming unit 20 is configured by arranging the forming units 18Y, 18M, 18C, and 18K side by side. The image forming units 18Y, 18M, 18C, and 18K of the tandem-type image forming unit 20 are photosensitive drums 40Y, 40M, and 40C as image carriers that support toner images of yellow, magenta, cyan, and black, respectively. , 40K.

  On the tandem type image forming unit 20, two exposure devices 21 are provided as shown in FIG. The two exposure devices 21 correspond to two image forming units (18Y and 18M, 18C and 18K), respectively. The exposure apparatus 21 includes, for example, an optical scanning type exposure apparatus that includes two light source devices, a coupling optical system, a common optical deflector (polygon mirror, etc.), two scanning imaging optical systems, and the like. For example, a semiconductor laser, a semiconductor laser array, or a multi-beam light source is used as the light source device. The exposure device 21 exposes the photosensitive drums 40Y, 40M, 40C, and 40K according to the image information of each color of yellow, cyan, magenta, and black to form an electrostatic latent image.

  Prior to the exposure described above, the photosensitive drums 40Y, 40M, 40C, and 40K are uniformly charged around the photosensitive drums 40Y, 40M, 40C, and 40K of the image forming units 18Y, 18M, 18C, and 18K. A charging device, a developing device that develops the electrostatic latent image formed by the exposure device 21 with toner of each color, and a photoconductor cleaning device that removes transfer residual toner on the photoconductor drums 40Y, 40M, 40C, and 40K. Is provided. Further, at the primary transfer position where the toner image is transferred from the photosensitive drums 40Y, 40M, 40C, and 40K to the intermediate transfer belt 10, the photosensitive drums 40Y, 40M, 40C, and 40K are opposed to each other with the intermediate transfer belt 10 interposed therebetween. Thus, primary transfer rollers 62Y, 62M, 62C, and 62K are provided as components of the primary transfer means.

  Of the plurality of support rollers that support the intermediate transfer belt 10, the drive roller 14 is a drive roller that rotationally drives the intermediate transfer belt 10, and is connected to the motor via a drive transmission mechanism (gear, pulley, belt, etc.) not shown. Has been. When a black single color image is formed on the intermediate transfer belt 10, the supporting rollers 15, 15 'other than the driving roller 14 are moved by a moving mechanism (not shown), and the yellow, magenta, and cyan photosensitive drums are moved. 40Y, 40M, and 40C can be separated from the intermediate transfer belt 10.

  The image forming apparatus 100 includes a secondary transfer device 22 on the side opposite to the tandem image forming unit 20 with the intermediate transfer belt 10 interposed therebetween. In the illustrated example, the secondary transfer device 22 applies a transfer electric field by pressing the secondary transfer roller 16 ′ against the secondary transfer counter roller 16, thereby transferring the image on the intermediate transfer belt 10 as a transfer medium. Is transferred onto a recording medium.

  In addition, the image forming apparatus 100 includes a fixing device 25 that fixes a transfer image on a recording medium beside the secondary transfer device 22.

  The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is a rotating body of an endless belt. The fixing belt 26 is wound around two support rollers, and at least one of the rollers is provided with heating means (not shown) (a heater, a lamp, an electromagnetic induction heating device, or the like).

  The recording medium on which the image is transferred by the secondary transfer device 22 is transported to the fixing device 25 by the transport belt 24 supported by the two rollers 23. Of course, the conveyance belt 24 may be a fixed guide member, a conveyance roller, a conveyance roller, or the like.

  In the illustrated example, the image forming apparatus 100 records images on both sides of the recording medium under the secondary transfer device 22 and the fixing device 25 in parallel with the tandem image forming unit 20 described above. A sheet reversing device 28 that reverses and conveys the recording medium is provided.

  The image forming apparatus 100 includes a paper feed unit 43 in the paper feed table 200. The paper feed unit 43 has a paper cassette 44 on which recording media are stacked and stored. The paper feed unit 43 further includes a pickup roller 42 that takes out recording media from the paper cassette 44 one by one, and a paper feed roller 45 that conveys the taken out recording medium. The paper feed unit 43 includes a conveyance path 46 and a conveyance roller 47 for conveying the recording medium.

  In addition to the paper feed unit 43, the image forming apparatus 100 includes a manual feed tray 51 and a manual feed tray pickup roller 50 that takes out a recording medium from the manual feed tray 51.

  The image forming apparatus 100 conveys either the recording medium from the manual feed tray 51 via the first conveyance path 53 or the recording medium from the paper feed unit 43 via the second conveyance path 48 to the registration roller 49.

  The registration roller 49 corrects the skew of the recording medium and delivers the recording medium to the secondary transfer device 22.

  In the image forming apparatus 100, the recording medium on which the developer image is fixed by the fixing device 25 is discharged to a discharge tray 57 by a discharge roller 56.

  FIG. 2 is a diagram illustrating a configuration of the fixing device 25. As shown in FIG. 2, the fixing device 25 includes a fixing belt 26 that is a fixing member of the rotating body, a pressure roller 27 that is a pressing member of the rotating body, and a sensor 25 </ b> S that detects the temperature of the fixing belt 26. And a control unit 101. The fixing belt 26 has a belt shape.

  The fixing device 25 includes a tension spring tension changing mechanism 34 that is a contact force changing mechanism.

  The fixing belt 26 is an endless belt having a multilayer structure in which an elastic layer such as silicone rubber and a release layer are sequentially laminated on a base layer made of PI (polyimide) resin and having a layer thickness of 90 μm.

  The elastic layer of the fixing belt has a thickness of about 200 μm and is formed of an elastic material such as silicone rubber, fluorine rubber, or foamable silicone rubber. The release layer of the fixing belt has a layer thickness of about 20 μm, and is formed of PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), or the like. The By providing a release layer on the surface layer of the fixing belt, the releasability to the developer or developer image, that is, the releasability is secured, the recording medium having the developer image is well fixed, and the paper is fixed to the fixing belt. 26 can be well separated.

  The fixing belt 26 includes a fixing roller 29 and a heating roller 31 as a heating member on the inner side. The fixing roller 29 is formed by coating a cored bar with a silicone rubber layer having a thickness of 5 to 30 mm. The silicone rubber layer is pressed against the pressure roller 27 via the fixing belt 26 to form a nip portion. Is done. A bearing 30 and a bearing bracket 32 are provided at both ends of the heating roller 31.

  The heating roller 31 is formed of a metal such as aluminum, SUS, or copper. The heating roller 31 has a heat source 31A inside. As the heat source 31A, a halogen heater, an IH heating device, or the like can be used. In the case where the heat source is a halogen heater, the halogen heater is disposed inside the heat source 31A.

  Further, a heat pipe may be press-fitted into the heating roller 31 for the purpose of equalizing the temperature in the axial direction.

  The tension spring tension changing mechanism 34 which is a contact force changing mechanism includes a tension spring 33. The tension spring tension changing mechanism 34 is attached to an axis positioned in parallel with the axis of the heating roller 31, and the urging force of the tension spring 33 changes as the axis rotates.

  The tension spring 33 is installed to urge the heating roller 31 in the direction in which the fixing belt 26 is tensioned.

  For example, when the heating roller 31 is mounted with play so that it can be displaced with respect to the fixing roller 29, the tension spring 33 is connected to the bearing bracket 32.

  Alternatively, the heating roller 31, the driving unit that drives the heating roller 31, the transmission that changes the rotation of the driving unit and transmits the rotation to the heating roller 31, and the frame are formed in one unit. It can also be configured to be displaced with respect to the fixing roller 29. In this case, the tension spring 33 is connected to the frame of this unit.

  Accordingly, when the tension spring tension changing mechanism 34 rotates to pull the tension spring 33, the heating roller 31 is displaced away from the fixing roller 29, and the tension of the fixing belt 26 becomes the standard tension which is the default tension. When the tension spring tension changing mechanism 34 rotates to return the tension spring 33, the heating roller 31 is displaced so as to approach the fixing roller 29, and the tension of the fixing belt 26 is reduced.

  The fixing device 25 further includes a cooling fan 35 that blows cooling air to the pressure roller 27. The cooling fan 35 can cool the temperature of the pressure roller 27 by applying cooling air to the pressure roller 27. In this embodiment, the cooling air is applied to the pressure roller 27. However, a fan that applies the cooling air to the fixing belt 26 may be provided.

  The heating roller 31 further includes a stopper 31S that brakes the rotation of the heating roller 31. The configuration of the stopper 31S is not limited as long as the tension spring tension changing mechanism 34 can brake the rotation of the heating roller 31 at the timing when the tension of the fixing belt 26 is weakened.

  For example, the stopper 31S can employ a mechanism that locks the heating roller 31 when the tension spring tension changing mechanism 34 weakens the tension of the fixing belt 26, and brakes the rotation of the heating roller 31.

  Alternatively, the stopper 31S may further include a stopper driving unit that operates the stopper, and the stopper driving unit may be configured to brake the rotation of the heating roller 31 by a frictional force or the like when the control unit 101 operates.

  The sensor 25 </ b> S desirably detects the temperature of the fixing belt 26 without contacting the fixing belt 26. For example, an infrared sensor can be used as the sensor 25S. The output of the sensor 25S is input to the control unit 101.

  Next, the operation of the fixing device 25 will be described.

  Based on the output of the sensor 25S, the control unit 101 changes the contact force between the fixing roller 29 as the fixing member and the heating roller 31 as the heating member by the tension spring tension changing mechanism 34 as the contact force changing mechanism, and stops the stopper 31S. To brake the rotation of the heating member.

  FIG. 2 shows a case where the tension of the fixing belt 26 is a standard tension. When the temperature of the fixing belt 26 detected based on the output of the sensor 25S is lower than the threshold, the control unit 101 sets the tension of the fixing belt 26 to the standard tension by the tension spring tension changing mechanism 34.

  When the tension spring tension changing mechanism 34 rotates in the direction indicated by the arrow X1, the tension spring 33 is pulled, and the tension of the fixing belt 26 becomes the standard tension.

  When the tension of the fixing belt 26 becomes the standard tension, the surface pressure of the fixing belt 26 with respect to the heating roller 31 increases to a predetermined value, so that the heat of the heating roller 31 is easily transmitted to the fixing belt, and the temperature of the fixing belt 26 increases.

  Conversely, when the temperature of the fixing belt 26 detected based on the output of the sensor 25S is higher than the threshold value, the control unit 101 weakens the tension of the fixing belt 26 by the tension spring tension changing mechanism 34.

  FIG. 3 is a view showing a state where the tension spring tension changing mechanism 34 weakens the tension of the fixing belt 26. As shown in FIG. 3, when the tension spring tension changing mechanism 34 rotates in the direction indicated by the arrow X3 opposite to the arrow X1, the tension spring 33 is pushed, and the tension of the fixing belt 26 is weakened. When the tension of the fixing belt 26 is weakened, the surface pressure of the fixing belt 26 against the heating roller 31 is lowered, so that the heat of the heating roller 31 is not easily transmitted to the fixing belt, and the temperature of the fixing belt 26 is lowered.

  The control unit 101 operates in a mode in which the normal tension is applied to the fixing belt 26 and the pressure roller 27 during normal warm-up or image formation. During image formation, the heating roller 31 is at a higher temperature than the fixing belt 26 and has a large heat capacity, so it is slow to cool down. When the image formation is completed and the next print job is received, the control unit 101 needs to optimize the temperature of the fixing belt 26 in accordance with the type of the recording medium. Therefore, the heating roller 31 is rotated in the direction indicated by the arrow X2. As a result, the fixing belt 26 starts to rotate. At this time, if heat is stored in the heating roller 31 by the previous print job, the temperature of the fixing belt 26 becomes high, and it is necessary to wait until it is cooled to an appropriate temperature.

  In order to prevent this waiting time from occurring, the control unit 101 performs a fixing belt cooling operation. After the image formation, the control unit 101 rotates the tension spring tension changing mechanism 34 in the direction of the arrow X3 to weaken the tension, that is, the tension on the heating roller 31 and the fixing belt 26.

  Further, normally, the heating roller 31 rotates following the rotation of the fixing belt 26, and the fixing belt 26 rotates following the pressure roller 27. Even when the tension is weak, when the fixing belt 26 rotates, the heating roller 31 also rotates, and the temperature of the heating roller 31 moves to the fixing belt 26.

  Therefore, the control unit 101 operates the stopper 31S that prevents the heating roller 31 from rotating when the tension of the fixing belt 26 is weak. Then, the heating roller 31 stops rotating, the fixing belt 26 and the heating roller 31 slide, and the heat of the heating roller 31 can be prevented from moving to the fixing belt 26 due to the contact of the fixing belt 26, so that the fixing can be performed efficiently. The temperature of the belt 26 can be lowered. The surface of the heating roller 31 is subjected to a treatment for reducing the sliding resistance such as Teflon (registered trademark) coating so that the sliding resistance is small.

  Further, the control unit 101 keeps the tension on the heating roller 31 and the fixing belt 26 weak until the next print job comes. When the next print job comes, the control unit 101 waits until the temperature of the fixing belt 26 falls below the appropriate temperature range for fixing the next recording medium.

  The control unit 101 uses a cooling fan 35 in order to make the decrease in the fixing belt temperature efficient. The control unit 101 drives the cooling fan 35 to bring the pressure roller 27 into contact with the fixing belt 26.

  Here, when the wind of the cooling fan 35 is also applied to the fixing belt 26, it is not necessary to bring the pressure roller 27 into contact with the fixing belt 26.

  As described above, the control unit 101 executes the fixing belt cooling operation to lower the temperature of the fixing belt 26, and when the temperature of the fixing belt 26 falls below the temperature range suitable for the next print job, The mode shifts to a mode in which a strong tension is applied to the pressure roller 27. In this case, the control unit 101 performs control so as to release the stopper 31S. Since the heat roller 31 is still storing heat, the temperature of the fixing belt 26 rises when it comes into contact with the heating roller 31 and becomes a temperature range suitable for fixing the recording medium. At that timing, the sheet feeding of the recording medium to the fixing device 25 is started.

  FIG. 4 is a diagram showing the relationship between the transition of the print job and the temperature of the fixing belt 26. The vertical axis represents the temperature of the fixing belt 26, and the horizontal axis represents time. As shown in a graph 501 in FIG. 4, the control unit 101 maintains a state where the tension of the fixing belt 26 is strong during execution of a print job. The temperature of the fixing belt 26 temporarily exceeds the range of the appropriate fixing temperature when the previous job is finished. During this job, the control unit 101 maintains a state where the tension of the fixing belt 26 is weak.

  When the tension of the fixing belt 26 is weakened, the contact area between the fixing belt 26 and the heating roller 31 is reduced, so that the heat transfer from the heating roller 31 to the fixing belt 26 is reduced. Accordingly, the fixing belt 26 is cooled.

  When the next job is started with the fixing belt 26 cooled, the control unit 101 drives the heat source 31A to heat the heating roller 31 to an appropriate fixing temperature.

  As described above, the fixing device 25 according to the present embodiment includes the tension spring tension changing mechanism 34 that is a tension changing member that changes the tension of the fixing belt 26, and the control unit 101 fixes the tension between the print jobs using the tension changing member. The tension of the belt 26 is weakened.

  Therefore, according to the embodiment of the present invention, there is an effect that it is possible to provide a fixing device capable of avoiding delay in passing a next job due to an increase in the temperature of the fixing belt 26 while saving heating energy. is there.

(Second Embodiment)
The configuration of the image forming apparatus 100 of this embodiment is the same as that of the image forming apparatus 100 of the first embodiment except for the fixing device 25.

  FIG. 5 is a diagram showing a configuration of the fixing belt 26 of the present embodiment. As shown in FIG. 5, the fixing device 25 includes a fixing belt 26, a pressure roller 27, a heating roller 31, a tension spring 33, a tension spring tension changing mechanism 34, a sensor 25S, a control unit 101, Is provided.

  The fixing device 25 further includes a contact width changing member 26 </ b> A that changes the contact width of the fixing belt 26 to the heating roller 31.

  The configurations of the fixing belt 26, the pressure roller 27, the heating roller 31, the tension spring 33, and the tension spring tension changing mechanism 34 are the same as those in the first embodiment.

  The contact width changing member 26 </ b> A is controlled by the control unit 101. The contact width changing member 26A includes, for example, a reciprocating mechanism that is disposed outside the fixing belt 26 and has a roller at the tip.

  FIG. 5 shows the state of the fixing device 25 when the contact width of the fixing belt 26 to the heating roller 31 is large. The contact width changing member 26 </ b> A increases the winding width of the fixing belt 26 around the heating roller 31 by pressing the fixing belt 26 from the outer peripheral side to the inner peripheral side of the fixing belt 26.

  The tension spring tension changing mechanism 34 can also weaken the tension of the tension spring 33 so as to weaken the tension when the tension of the fixing belt 26 is increased by the contact width changing member 26A pressing the fixing belt 26. Accordingly, it is possible to prevent an excessive tension from being applied to the fixing belt 26.

  Next, the operation of the fixing device 25 will be described.

  When the temperature of the fixing belt 26 detected based on the output of the sensor 25S is lower than the threshold value, the control unit 101 increases the tension of the fixing belt 26 by the tension spring tension changing mechanism 34 and also fixes the fixing belt by the contact width changing member 26A. 26 so that the width of contact with the heating roller 31 is increased.

  When the tension spring tension changing mechanism 34 rotates in the direction indicated by the arrow X1, the tension spring 33 is pulled, and the tension of the fixing belt 26 becomes the default standard tension.

  When the tension of the fixing belt 26 becomes the standard tension, the surface pressure of the fixing belt 26 with respect to the heating roller 31 increases, so that the heat of the heating roller 31 is easily transmitted to the fixing belt, and the temperature of the fixing belt 26 increases.

  In addition, the control unit 101 changes the contact width of the fixing belt 26 to the heating roller 31 by the contact width changing member 26A so that the temperature of the fixing belt 26 is more quickly heated to a specified temperature. Is possible.

  On the contrary, when the temperature of the fixing belt 26 detected based on the output of the sensor 25S is higher than the threshold value, the control unit 101 weakens the tension of the fixing belt 26 by the tension spring tension changing mechanism 34 and the contact width changing member 26A. Thus, the width of contact of the fixing belt 26 with the heating roller 31 is changed.

  FIG. 6 is a diagram illustrating a state of the fixing device 25 when the contact width of the fixing belt 26 to the heating roller 31 is small. As shown in FIG. 6, the contact width changing member 26 </ b> A reduces the winding width of the fixing belt 26 around the heating roller 31 by releasing the pressing of the fixing belt 26 from the outer peripheral side to the inner peripheral side of the fixing belt 26. Let

  At this time, when the tension of the fixing belt 26 is weakened when the contact width changing member 26A releases the pressing of the fixing belt 26, the tension spring tension changing mechanism 34 adjusts the tension spring 33 so that the tension becomes the standard tension. Strengthen the pulling force. Therefore, the fixing belt 26 can maintain a predetermined tension.

  As described above, when heat is stored in the heating roller 31 by the previous print job, the temperature of the fixing belt 26 becomes high, and it is necessary to wait until it is cooled to an appropriate temperature. In order to prevent this waiting time from occurring, the control unit 101 performs a fixing belt cooling operation.

  After the image formation, the control unit 101 rotates the tension spring tension changing mechanism 34 in the direction of the arrow X5 to increase the tension, that is, the tension on the heating roller 31 and the fixing belt 26. Simultaneously with this operation, the control unit 101 causes the contact width changing member 26A to release the pressing of the fixing belt 26. As a result, the contact width of the fixing belt 26 to the heating roller 31 is reduced, and the temperature of the heating roller 31 is hardly transmitted to the fixing belt 26.

  Further, when the contact width of the fixing belt 26 is narrow, the control unit 101 operates a stopper 31S that prevents the heating roller 31 from rotating. Then, the heating roller 31 stops rotating, the fixing belt 26 and the heating roller 31 slide, and the heat of the heating roller 31 can be prevented from moving to the fixing belt 26 due to the contact of the fixing belt 26, so that the fixing can be performed efficiently. The temperature of the belt 26 can be lowered.

  FIG. 7 is a diagram illustrating a relationship between the transition of the print job and the temperature of the fixing belt 26. The vertical axis represents the temperature of the fixing belt 26, and the horizontal axis represents time. As shown in a graph 701 in FIG. 7, the control unit 101 maintains a state where the contact width of the fixing belt 26 to the heating roller 31 is wide during execution of the print job. The temperature of the fixing belt 26 temporarily exceeds the range of the appropriate fixing temperature when the previous job is finished. During this job, the control unit 101 maintains a state where the contact width of the fixing belt 26 to the heating roller 31 is narrow.

  When the contact width of the fixing belt 26 to the heating roller 31 is narrowed, the heat transfer from the heating roller 31 to the fixing belt 26 is reduced. Accordingly, the fixing belt 26 is cooled.

  When the next job is started with the fixing belt 26 cooled, the control unit 101 drives the heat source 31A to heat the heating roller 31 to an appropriate fixing temperature.

  As described above, the fixing device 25 of this embodiment includes the tension spring tension changing mechanism 34 that is a tension changing member that changes the contact width of the fixing belt 26 to the heating roller 31 and the contact width changing member 26A. Prepare. The controller 101 weakens the tension of the fixing belt 26 by the tension spring tension changing mechanism 34 between print jobs, and narrows the contact width of the fixing belt 26 to the heating roller 31 by the contact width changing member 26A.

  Therefore, according to the embodiment of the present invention, it is possible to provide a fixing device that can avoid delaying the passing of the next job due to an increase in the temperature of the fixing belt 26 while further saving heating energy. There is.

(Third embodiment)
A third embodiment of the present invention will be described with reference to FIGS. The configuration of the image forming apparatus 100 according to the present embodiment is the same as the configuration of the image forming apparatus 100 according to the first embodiment. In the present embodiment, for example, as shown in FIG. 8, the fixing device 25 further includes a displacement mechanism 27 </ b> A that is a pressing force changing member that changes the pressing force of the pressure roller 27 to the fixing roller 29.

  For example, the pressure roller 27 is a pressure roller 27, a pressure roller drive unit such as a motor that drives the pressure roller 27, and a rotation that transmits the rotation of the pressure roller drive unit to the pressure roller 27 while changing speed. The pressure roller transmission unit and the frame can be configured as one pressure roller unit.

  In this case, the displacement mechanism 27 </ b> A changes the pressure applied to the fixing roller 29 by the pressure roller 27 by displacing the pressure roller unit with respect to the fixing roller 29 by the control unit 101.

  The fixing device 25 may further include a link mechanism 102 that links, that is, interlocks, the displacement mechanism 27A and the tension spring tension changing mechanism 34. This link mechanism 102 eliminates the need to provide independent power (such as a motor) for the two mechanisms, and allows an inexpensive configuration.

  In the link mechanism 102, the tension spring tension changing mechanism 34 generates a strong tension on the fixing belt 26 when the pressure roller 27 and the fixing roller 29 are completely depressurized or completely pressurized. In addition, when the pressure roller 27 and the fixing roller 29 are in the intermediate state of the depressurization or pressurization, the tension spring tension changing mechanism 34 weakens the tension of the fixing belt 26.

  Next, the operation of the fixing device 25 will be described.

  In the case of this configuration, after the image formation, the control unit 101 reduces the tension from the heating roller 31 to the fixing belt 26 by setting the pressure roller 27 to an intermediate state between depressurization and pressure. When the next print job comes, the control unit 101 detects the temperature of the fixing belt 26 from the output of the sensor 25S.

  The control unit 101 keeps the tension of the fixing belt 26 weak until the temperature of the fixing belt 26 detected based on the output of the sensor 25S becomes lower than the appropriate temperature range of the next printing paper.

  A cooling fan 35 is used to make the temperature reduction of the fixing belt 26 efficient. When the pressure roller 27 comes into contact with the fixing roller 29 in the intermediate state of the pressure roller 27 depressurizing or pressing, the fixing belt 26 can be cooled by applying air to the pressure roller 27. When the pressure roller 27 does not contact the fixing roller 29, the cooling fan 35 is blown against the fixing belt 26.

  In this way, the control unit 101 reduces the temperature of the fixing belt 26, and when the temperature of the fixing belt 26 falls below the fixing temperature of the next print job, the standard that is the default tension for the fixing belt 26 and the heating roller 31 is used. Set the mode to apply tension.

  Since the heat roller 31 is still storing heat, the temperature of the fixing belt 26 rises when it comes into contact with the heat roller 31, and becomes an appropriate temperature range of the printing paper. Paper feeding starts at that timing.

  The control unit 101 is configured to change the pressure applied to the fixing roller 29 of the pressure roller 27 by the displacement mechanism 27A based on the output of a paper sensor (not shown) that detects the entry of the recording medium into the fixing device 25. You can also.

  The paper sensor is disposed upstream (near side) and / or downstream of the nip formed by the pressure roller 27 and the fixing roller 29 via the fixing belt 26, and outputs the presence / absence of a recording medium to the control unit 101. To do.

  The control unit 101 controls the tension of the fixing belt 26 to the standard tension by the tension spring tension changing mechanism 34 when the paper sensor detects the paper passing, and reduces the tension of the fixing belt 26 when the paper passing is not detected.

  FIG. 8 is a diagram showing a state where the pressure roller 27 is completely pressurized. As shown in FIG. 8, in a state where the pressure roller 27 is completely pressurized, the tension spring tension changing mechanism 34 rotates in the direction of the arrow X1 and pulls the tension spring 33 so that the tension of the fixing belt 26 is increased. Use standard tension.

  FIG. 9 is a view showing a state where the pressure roller 27 is completely separated and released. As shown in FIG. 9, in a state where the pressure roller 27 is completely depressurized, the tension spring tension changing mechanism 34 rotates in the direction of the arrow X1 and pulls the tension spring 33 so that the tension of the fixing belt 26 is increased. Use standard tension.

  FIG. 10 is a view showing a state in which the pressure roller 27 is in the middle of the depressurization and the pressurization. As shown in FIG. 10, when the pressure roller 27 is in the intermediate state between the depressurization and pressurization, the tension spring tension changing mechanism 34 rotates in the direction of the arrow X3 and returns the tension spring 33 to the fixing belt 26. Reduce the tension.

  FIG. 11 is a diagram illustrating a relationship between the transition of the print job and the temperature of the fixing belt 26. The vertical axis represents the temperature of the fixing belt 26, and the horizontal axis represents time. As shown in the graph 1101 of FIG. 11, the control unit 101 completely presses the pressure roller 27 against the fixing roller 29 by the displacement mechanism 27A and executes the tension spring 33 by the tension spring tension changing mechanism 34 during execution of the print job. By pulling, the tension of the fixing belt 26 is maintained strong. The temperature of the fixing belt 26 temporarily exceeds the range of the appropriate fixing temperature when the previous job is finished. During this job, the control unit 101 completely releases the pressure roller 27 from the fixing roller 29 by the displacement mechanism 27A, returns the tension spring 33 by the tension spring tension changing mechanism 34, and the tension of the fixing belt 26 is weak. To maintain.

  When the tension of the fixing belt 26 is weakened, heat transfer from the heating roller 31 to the fixing belt 26 is reduced. Accordingly, the fixing belt 26 is cooled.

  When the next job is started with the fixing belt 26 cooled, the control unit 101 drives the heat source 31A to heat the heating roller 31 to an appropriate fixing temperature.

  As described above, the fixing device 25 of this embodiment includes the tension spring tension changing mechanism 34 that is a tension changing member that changes the contact width of the fixing belt 26 to the heating roller 31, and the fixing roller 29 of the pressure roller 27. And a displacement mechanism 27A for changing the pressure applied to the control unit 101. The control unit 101 places the pressure roller 27 in an intermediate state between the depressurization and the pressure by the displacement mechanism 27A between print jobs, and the tension spring tension change mechanism 34. The tension of the fixing belt 26 is weakened.

  Therefore, according to the embodiment of the present invention, it is possible to provide a fixing device that can more efficiently avoid delaying the passing of the next job due to the temperature of the fixing belt 26 rising while further saving heating energy. There is an effect that can be done.

25: fixing device 25S: sensor (temperature detection sensor)
26: fixing belt (fixing member)
26A: contact width changing member 27: pressure roller 27A: pressure changing member 29: fixing roller 31: heating roller 31A: heat source 33: tension spring 34: tension spring tension changing mechanism 35: cooling fan 100: image forming apparatus 101: Control unit

JP 2014-112174 A Japanese Patent No. 4728059

Claims (9)

A heating member which is a rotating body heated by a heat source;
A fixing member which is a rotating body in contact with the heating member;
A pressure member that is a rotating body that is pressurized to the fixing member to form a nip portion with the fixing member;
A sensor for detecting the temperature of the fixing member;
A contact force changing mechanism for changing a contact force between the fixing member and the heating member;
A stopper for braking rotation of the heating member;
A control unit configured to change a contact force between the fixing member and the heating member by the contact force changing mechanism based on an output of the sensor and brake rotation of the heating member by the stopper;
A fixing device.   2. The fixing device according to claim 1, wherein when the temperature of the fixing member detected based on the output of the sensor is higher than a threshold, the control unit weakens the tension of the belt-shaped fixing member by the contact force changing mechanism. . A cooling fan for cooling the pressure member;
The fixing device according to claim 2, wherein the control unit operates the cooling fan when the contact force between the fixing member and the heating member is weakened by the contact force changing mechanism.   The control unit weakens the tension of the fixing member by the contact force changing mechanism when there is no recording medium in the nip portion and the temperature of the fixing member detected based on the output of the sensor is higher than a threshold value. 3. The fixing device according to 2. A pressing force changing member that changes the pressing force of the pressing member to the fixing member;
A link mechanism for interlocking the pressing force changing member and the contact force changing mechanism;
The fixing device according to claim 1, further comprising: A contact width changing member that changes a contact width of the fixing member to the heating member;
The controller changes the contact force between the fixing member and the heating member by the contact force changing mechanism based on the output of the sensor, brakes the rotation of the heating member by the stopper, and the contact width changing member. The fixing device according to claim 1, wherein a contact width of the fixing member to the heating member is changed.   The fixing device according to claim 1, wherein a surface of the heating member is subjected to a process for reducing a sliding resistance.   The fixing device according to claim 1, wherein the heating member is a roller. An image forming apparatus comprising the fixing device according to claim 1.

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