JP2013195862A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device and an image forming apparatus, which effectively prevent a failure due to a local increase in a surface temperature of a fixing roller after transporting a sheet, causing an abnormal image such as hot-offset to a fixed image on a recording medium in the following series of transport actions.SOLUTION: If a detected temperature detected by temperature detection means exceeds a predetermined threshold when a series of sheet transport actions are finished, an idle rotation mode of rotating a fixing roller and a pressure roller is executed in the state of stopping heating the fixing roller with heating means (a step S7). Further, the executing time of the idle rotation mode is varied (steps S14, 16, 17, 19, 21, and 22) on the basis of information of a recording medium related to the series of transporting actions (a step S2) and information of the recording medium related to a following series of transporting actions (a step S10).

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, there is known a fixing device in which an image forming apparatus such as a copying machine and a printer has a short warm-up time and a first print time and hardly causes a fixing failure (see, for example, Patent Document 1).

Specifically, the fixing device described in FIG. 2, FIG. 4 and the like of Patent Document 1 is a pipe-shaped fixing device that is fixed so as to face the inner peripheral surface of the fixing belt except for the fixing belt (reference numeral 21) and the nip portion. A heating member (reference numeral 22), a heater (reference numeral 25) provided in the heating member for heating the heating member, and a pressure roller (reference numeral 31) via a fixing belt to form a nip portion A fixing member (reference numeral 26) installed inside the fixing belt, a substantially plate-shaped reinforcing member (reference numeral 23) that abuts the fixing member and reinforces the fixing member, and the like.
Then, the fixing belt is heated by the pipe-shaped heating member heated by the heater, and the toner image on the recording medium conveyed toward the nip portion receives heat and pressure at the nip portion and is received on the recording medium. It will be fixed.

  On the other hand, in Patent Document 2, when the temperature sensor detects that the temperature of the fixing roller (fixing rotator) has exceeded a predetermined temperature after the fixing operation (paper passing operation) of the apparatus is completed. A technique is disclosed in which the fixing roller is cooled by idling the apparatus for a predetermined time (idle driving).

  In the fixing device described in Patent Document 1 and the like, if the operation of the apparatus is stopped immediately after a series of paper feeding operations (recording medium conveyance operations) is completed, a portion of the fixing belt that is close to the heater is removed. The heater was locally heated by the remaining heat of the heater that was de-energized along with the operation stop, and the temperature was raised. In such a state, if the next fixing step (paper feeding operation) is performed, an abnormal image such as a hot offset is added to the fixed image on the recording medium fixed by the locally heated portion of the fixing belt. Sometimes occurred.

In order to solve such a problem, the state in which the surface temperature of the fixing belt exceeds a predetermined temperature after a series of conveying operations (sheet feeding operations) is completed by applying the technique of Patent Document 2 is a temperature. When detected by the detection means, a method of idling the device for a predetermined time can be considered. However, in that case, a series of sheet passing operations performed in the next process is performed after the idle rotation of the apparatus for a predetermined time is completely completed, and accordingly, a waiting time corresponding thereto is generated.
On the other hand, as a result of repeated research, the inventor of the present application performs the type of recording medium (paper passing condition) passed through a series of paper passing operations performed before the idling rotation and after the idling rotation. Depending on the combination of the type of recording medium (passing conditions) that is passed through a series of pass-through operations, the degree and position of the fixing belt locally increases, which affects the pass-through operation of the next process. I knew that there were things I didn't.

  In addition, such a problem is noticeable in a fixing device with a short warm-up time and first print time and good start-up characteristics (temperature rise characteristics) and cannot be ignored, but is stretched around a plurality of roller members as a fixing rotating body. This can occur in the same manner even in a fixing device using a fixing belt and a fixing device using a fixing roller as a fixing rotating body.

  The present invention has been made in order to solve the above-described problems, and after the end of paper passing, the surface temperature of the fixing rotator is locally increased, and recording in a series of transport operations to be performed next is performed. It is an object of the present invention to provide a fixing device and an image forming apparatus that can efficiently prevent a problem that an abnormal image such as a hot offset occurs in a fixed image on a medium.

  The fixing device according to the first aspect of the present invention is heated by a heating unit, rotated in a predetermined direction to heat and melt a toner image, and rotated in a predetermined direction. A pressure rotator that forms a nip portion that is pressed against the fixing rotator to convey the recording medium; and a temperature detection unit that detects a temperature of the surface of the fixing rotator, and the recording medium to the nip portion. When the detected temperature detected by the temperature detection means exceeds a predetermined threshold when the series of transport operations is completed, the fixing rotator is stopped in a state where heating of the fixing rotator by the heating means is stopped. And an idle rotation mode for rotating the pressurizing rotator, and the idle rotation mode includes information on the recording medium related to the series of transport operations and the recording medium related to the series of transport operations to be performed next. And distribution, based on, in which the execution time is variable.

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

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

  The present invention relates to the execution time of the idling mode that is executed when the detected temperature detected by the temperature detection unit exceeds a predetermined threshold when the series of transport operations is completed. It is varied based on information on the recording medium and information on the recording medium related to a series of transport operations to be performed next. As a result, the surface temperature of the fixing rotator locally rises after the end of paper passing, and an abnormal image such as a hot offset occurs in the fixed image on the recording medium in the next series of transport operations. A fixing device and an image forming apparatus that can be efficiently prevented can be provided.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. 2 is a configuration diagram illustrating a fixing device. FIG. (A) The side view which looked at the fixing device in the width direction, and (B) The schematic diagram which looked at two heaters in the width direction, respectively. It is an enlarged view which shows the vicinity of a nip part. FIG. 4 is a cross-sectional side view showing a state where the fixing belt is held by a holding member. 3 is a schematic front view showing a state in which a fixing belt and a reinforcing member are held by a holding member. FIG. It is (A) side view and (B) bottom view which show the fixing member in the state in which the sheet-like member was installed. In FIG. 7A, (A) a schematic cross-sectional view showing the X1-X1 cross section, (B) a schematic cross-sectional view showing the X2-X2 cross section, and (C) a schematic cross-sectional view showing the X3-X3 cross section. is there. They are (A) top view, (B) side view, and (C) bottom view showing a fixing member. It is an expanded view which shows a sheet-like member. It is a top view which shows a plate-shaped member. It is a flowchart which shows the control which concerns on idling mode. It is a block diagram which shows the fixing device in Embodiment 2 of this invention.

  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.
A 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 photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, and untransferred toner remaining on the photosensitive 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 fed with a paper feed roller 97, a registration roller pair 98 (timing roller pair), and the like from a paper feed unit 12 disposed below the apparatus main body 1. It was transported via.
Specifically, a plurality of recording media P such as transfer paper are stored in the paper supply unit 12 in an overlapping manner. When the paper feed roller 97 is rotationally driven in the counterclockwise direction in FIG. 1, the uppermost recording medium P is fed between the rollers of the registration roller pair 98.

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

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

Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS.
2 to 4 and the like, the fixing device 20 includes a fixing belt 21 (belt member) as a fixing rotating body, a fixing member 26 (nip portion forming member), a reinforcing member 23, a heater 25A as heating means, 25B (heat source), pressure roller 31 as a pressure rotator, temperature sensors 40A and 40B as temperature detection means, sheet-like member 22 (lubricant supply member), plate-like member 28 (fixed plate), reflecting member 27 , Etc.

Here, the fixing belt 21 (fixing member) as a fixing rotating body is a thin and flexible endless belt, and rotates (runs) in the direction of the arrow (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 5 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.
Inside the fixing belt 21 (inner peripheral surface side), a fixing member 26, two heaters (first heater 25A and second heater 25B), a reinforcing member 23, a reflecting member 27, a sheet-like member 22, Double-sided tape 49 (sticking means), screws 24, plate-like member 28 (fixing plate), and the like are fixed.
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. 3 and 5, both ends of the fixing member 26 in the width direction are rotatably held by flanges 29 (holding members) fixedly supported by the side plates 43 of the fixing device 20. The configuration of the fixing member 26 and the flange 29 will be described in more detail later.
The fixing belt 21 is directly heated by radiant heat (infrared light) of heaters 25A and 25B (heating means) installed therein.

  The two heaters 25A and 25B as heating means are both halogen heaters (or carbon heaters), and both end portions thereof are fixed to the side plate 43 of the fixing device 20 (see FIG. 3). . Then, due to the radiant heat of the heaters 25A and 25B (heating means) whose output is controlled by the power supply unit of the apparatus main body 1, the opposed surface of the fixing belt 21 excluding the nip portion and opposed to the heaters 25A and 25B is heated. The Further, 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 heaters 25A and 25B is performed based on the detection result of the belt surface temperature by the temperature sensors 40A and 40B (temperature detection means) such as a thermopile facing the surface of the fixing belt 21. Further, the temperature (fixing temperature) of the fixing belt 21 can be set to a desired temperature by such output control of the heaters 25A and 25B.

Here, in the first embodiment, two heaters 25 </ b> A and 25 </ b> B are arranged in parallel on the inner peripheral surface side of the fixing belt 21.
Specifically, as shown in FIG. 3 (B), in the first heater 25A, the light emitting portion 25A1 serving as the heater portion is in the width direction (the horizontal direction in FIG. 3 and the vertical direction in FIG. 2). It is installed in the range M of the central part. This range M is 200 to 220 mm, and corresponds to the paper passing area of the recording medium P of A4 vertical size. On the other hand, in the second heater 25B, the light emitting portions 25B1 serving as the heater portions are respectively installed at both ends in the width direction (the range N is a range excluding the range M). Here, the range N is 300 to 330 mm, and the margin (with respect to the end of the light-emitting portion) with respect to the sheet passing area of the A3 vertical size recording medium P (non-sheet passing area of the A4 vertical size recording medium P). The light emission intensity of the portion is weakened to prevent the temperature of the end portion from dropping.) Is added. Such two heaters 25A and 25B can be controlled separately, and when the A3 vertical size recording medium P is fed (conveyed), the two heaters 25A and 25B are turned on. When the A4 vertical size recording medium P is passed (conveyed), it is controlled to turn on only the first heater 25A, thereby preventing an excessive temperature rise in the non-sheet passing area of the fixing belt 21. it can.
In the first embodiment, two heaters 25A and 25B are installed on the inner peripheral surface side of the fixing belt 21, but only one heater can be installed on the inner peripheral surface side of the fixing belt 21. .

Further, in the first embodiment, two temperature sensors 40A and 40B (temperature detection means) that respectively detect temperatures at positions that face the heaters 25A and 25B through the fixing belt 21 and that differ in the width direction. ) Is installed.
Specifically, as shown in FIG. 3A, the first temperature sensor 40A can detect the surface temperature of the center portion in the width direction (in the range M) of the fixing belt 21 corresponding to the first heater 25A. It is arranged. On the other hand, the second temperature sensor 40B can detect the surface temperature of the end portion in the width direction of the fixing belt 21 (the range except the range M in the range N) corresponding to the second heater 25B. It is arranged. The first heater 25A can be turned on / off based on the temperature detected by the first temperature sensor 40A, and the second heater 25B can be controlled on / off based on the temperature detected by the second temperature sensor 40B.
The two temperature sensors 40A and 40B are installed so as to face positions where the fixing belt is directly heated by the heaters 25A and 25B. By installing the temperature sensors 40A and 40B at such positions, the surface of the fixing belt 21 is heated by the residual heat of the heaters 25A and 25B that are de-energized when the operation of the apparatus is stopped (when the rotation of the fixing belt 21 is stopped). It becomes easy to detect temperature.

Thus, 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 heated over a relatively wide range in the circumferential direction. 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.
In particular, since the fixing device 20 according to the first embodiment is configured such that the fixing belt 21 is directly heated by the heaters 25A and 25B (heating means), the heating efficiency of the fixing belt 21 is further improved. At the same time, the fixing device 21 can be further reduced in cost and size.

With reference to FIGS. 5 and 6, the two flanges 29 as the holding members are formed of a heat-resistant resin material or the like, and are fitted into the side plates 43 at both ends in the width direction of the fixing device 20. The flange 29 has a guide portion 29a for holding the fixing belt 21 while maintaining the circular posture of the fixing belt 21, a stopper portion 29b for restricting the movement of the fixing belt 21 in the width direction (belt shift), and the like. Is provided.
In the fixing device 20 in the present embodiment, low friction and heat resistance such as PEEK, PPS, PAI, and PTFE are used to reduce wear at the end of the fixing belt 21 at the position of the stopper portion 29b of the flange 29. A slipping member (ring-shaped member) made of a material can be installed as a separate member from the flange 29.

  Here, since both ends in the width direction of the fixing belt 21 are held by the flanges 29, the circular posture of the fixing belt 21 is maintained to some extent, but depending on the rigidity of the fixing belt 21, a certain amount is present in the central portion in the width direction during traveling. There is a possibility of fluttering. Accordingly, when the fixing belt 21 has a relatively high rigidity so that the fixing belt 21 does not come into contact with other components (the reinforcing member 23, the reflecting member 27, etc.) even if the fixing belt 21 flutters. Is preferably set so as to ensure a separation distance of 0.02 mm or more from other constituent members and to ensure a separation distance of 3 mm or more from other constituent members when the rigidity of the fixing belt 21 is relatively low. .

  Further, the inner circumferential surface 21a of the fixing belt 21 is surrounded by a sliding portion (indicated by a broken line in FIG. 5) at both ends in the width direction (the left-right direction in FIG. 5) with the guide portion 29a of the flange 29. The low-friction portion 21a1 is formed to reduce the sliding resistance. Specifically, the low friction part 21a1 is formed by coating the surface of the base material layer with a low friction material such as a fluororesin. With such a configuration, even if the fixing belt 21 and the flange 29 (guide portion 29a) are in sliding contact with each other due to the rotation (running) of the fixing belt 21, the fixing belt 21 and the flange 29 (guide portion 29a) are not easily deteriorated by wear. .

In the first embodiment, the members that contact the inner peripheral surface 21a of the fixing belt 21 are only the flanges 29 at both ends in the width direction and the fixing member 26. In addition, the members contact the inner peripheral surface 21a. Thus, there is no member (belt guide) that guides the rotation of the fixing belt 21.
As described above, the fixing device 20 according to the first exemplary embodiment further improves the heating efficiency of the fixing belt 21 and reduces the cost of the device as compared to the conventional fixing device (the fixing device disclosed in Patent Document 1). For the purpose of downsizing and the like, a configuration is adopted in which the pipe-shaped heating member is removed and the fixing belt 21 is directly heated by the heating means (heaters 25A and 25B) without using the pipe-shaped heating member. . Specifically, a configuration in which the inner peripheral surface 21 a of the fixing belt 21 is held by the flange 29 is employed.

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 held by the flange 29 (holding member) of the fixing device 20. Has been. Specifically, the position of the reinforcing member 23 is determined so as to be sandwiched between the flange 29 and the fixing member 26. In the first embodiment, as shown in FIG. 4, the end surfaces (reference surface 23b) of the two standing portions 23c of the reinforcing member 23 (the portions rising in the direction away from the facing surface 23a). Is in contact with the holding portion 29c (see FIG. 6) of the flange 29 so that the reinforcing member 23 is held. On the other hand, the reinforcing member 23 can be held in contact with the side plate 43 instead of the holding portion 29c of the flange 29.
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 substantially U-shaped plate-like member formed so that the concave portion faces the side where the heaters 25A and 25B are located. 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.
The configuration of the reinforcing member 23 will be described in more detail later.

In the first embodiment, the reflecting member 27 (reflecting plate) is fixed on the side of the reinforcing member 23 facing the heater 25. As a result, heat from the heaters 25 </ b> A and 25 </ b> B toward the reinforcing member 23 (heat for heating the reinforcing member 23) is reflected by the reflecting member 27 and used for heating the fixing belt 21. Efficiency will be further improved. In addition, as a material of the reflecting member 27, aluminum, stainless steel, or the like can be used.
The same effect can be obtained even when a part of or the entire surface of the reinforcing member 23 facing the heaters 25A and 25B is mirror-finished or provided with a heat insulating member.

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

  Here, in the first embodiment, a third temperature sensor 41 such as a thermistor is installed so as to contact the outer peripheral surface of the pressure roller 31. Then, it is possible to perform control so as not to start printing when the surface temperature of the pressure roller 31 detected by the third temperature sensor 41 does not reach a predetermined value when the apparatus is started up. Further, when a heat source such as a halogen heater is provided inside the pressure roller 31, the heat source is operated based on the temperature detected by the third temperature sensor 41 (for example, heater on / off control). )can do.

Although not shown, the pressure roller 31 is moved in a direction away from the fixing belt 21 to the fixing device 20 according to the first embodiment to reduce the pressure contact force of the pressure roller 31 against the fixing belt 21. A decompression mechanism (contact / separation mechanism) can be installed.
In such a case, the pressure reducing mechanism is controlled by the control unit when the sheet is not fed, and the pressure roller 31 is moved in the separation direction to reduce the pressure contact force in the nip portion. As a result, the pressure contact state continues for a long time, and the problem that the fixing belt 21 and the pressure roller 31 are distorted by the pressure contact force at the nip portion is reduced.
Further, when a paper jam (jam) occurs in the recording medium P in the nip portion, the pressure reducing mechanism is controlled by the control unit (or the pressure reducing mechanism is manually operated), and the pressure roller 31 moves in the separation direction. The pressure at the nip is reduced. As a result, the operation of removing the recording medium P jammed in the nip portion can be easily performed.

When the elastic layer 33 of the pressure roller 31 is formed of a sponge-like material such as foamable silicone rubber, the pressure applied to the nip portion can be reduced. 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. 4, fixing member 26 slidably in contact with inner peripheral surface 21 a of fixing belt 21 has a concave shape so that the surface (sliding contact surface) facing pressure roller 31 follows the curvature of pressure roller 31. Is formed. 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.

  As a material for forming the fixing member 26, a resin material or a metal material can be used. However, the material has a rigidity that does not bend greatly even if it is subjected to a pressure applied by the pressure roller 31. Resin materials (liquid crystal polymer (LCP), polyamideimide (PAI), polyethersulfone (PES), polyphenylene sulfide (PPS), polyethernitrile (PEN), polyetheretherketone (PEEK), etc. .) Is preferred. In the first embodiment, a liquid crystal polymer (LCP) is used as the material of the fixing member 26.

The fixing member 26 is covered with a sheet-like member 22 made of a low friction material such as PTFE in order to reduce sliding resistance with the fixing belt 21. Specifically, the sheet-like member 22 is fixed around the fixing member 26 (fixed as seen in a cross section as shown in FIG. 4) so as to be interposed across the width direction between the fixing member 26 and the fixing belt 21 at the nip portion. Around the member 26). Further, the sheet-like member 22 in the first embodiment is formed of a fiber material (a cloth member made of a fluororesin such as PTFE) impregnated with a lubricant such as silicone oil. As a result, the lubricant is held on the surface where the fixing member 26 and the fixing belt 21 abut. 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.
Here, referring to FIG. 4, FIG. 8, FIG. 9, etc., the sheet-like member 22 is positioned at the nip portion position and the upstream side in the circumferential direction (the upstream side in the running direction of the fixing belt 21 with respect to the nip portion position). Corresponding position) is fixed (adhered) to the fixing member 26 through the double-sided tape 49 in the width direction. As a result, even if the fixing belt 21 rotates counterclockwise in FIG. 4, the problem that the sheet-like member 22 peels off from the fixing member 26 along the rotation is reliably prevented.

Here, in the first embodiment, the reinforcing member 23 (and the reflecting member 27) is installed so as to isolate the space between the fixing member 26 and the heaters 25A and 25B (heating means).
In the first embodiment, the heaters 25A and 25B are installed so as to face a relatively wide range in the circumferential direction of the fixing belt 21 (inner peripheral surface 21a). Also, the fixing belt 21 can be heated in the circumferential direction without temperature unevenness. 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.
In contrast, in the first embodiment, the reinforcing member 23 (and the reflecting member 27) is installed between the fixing member 26 and the heaters 25A and 25B so as to block the heat of the heaters 25A and 25B. Therefore, it becomes difficult for heat to reach the fixing member 26 during the heating standby. Therefore, the problem of being heated at a high temperature in a state where the pressure roller 31 is deformed at the time of heating standby can be reduced, and the above-described problems can be prevented from occurring.

Further, the lubricant applied between the two members in order to reduce the frictional resistance between the fixing member 26 and the fixing belt 21 is deteriorated by use under a high temperature condition in addition to the high pressure condition in the nip portion. There is a possibility that problems such as slippage may occur.
In contrast, in the first embodiment, the reinforcing member 23 (and the reflecting member 27) is installed between the fixing member 26 and the heaters 25A and 25B so as to block the heat of the heaters 25A and 25B. Therefore, the heat of the heaters 25A and 25B hardly reaches 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, the reinforcing member 23 (and the reflecting member 27) is installed between the fixing member 26 and the heaters 25A and 25B so as to block the heat of the heaters 25A and 25B. Since the fixing member 26 is insulated, the fixing belt 21 is not positively heated in the nip portion. 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.

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 heaters 25A and 25B, and the rotational driving of the pressure roller 31 in the direction of the arrow in FIG. Accordingly, 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 in the nip portion.
Thereafter, the recording medium P is fed from the paper supply unit 12, and an unfixed color image is carried (transferred) on the recording medium P at the position of the secondary transfer roller 89. The recording medium P carrying the unfixed image T (toner image) is conveyed in the direction of arrow Y10 in FIG. 2 while being guided by a guide plate (not shown), and the fixing belt 21 and the pressure roller 31 that are in a pressure contact state. It is fed into the nip part.
The toner image T is fixed on the surface of the recording medium P by the heating by the fixing belt 21 heated by the heaters 25A and 25B and the pressing force of the fixing member 26 reinforced by the reinforcing member 23 and the pressure roller 31. Is done. 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.
Here, as described above, in the fixing device 20 according to the first embodiment, the nip is fixed to the inner peripheral surface side of the fixing belt 21 and pressed against the pressure roller 31 via the fixing belt 21. And a reinforcing member 23 fixed to the inner peripheral surface side of the fixing belt 21 and abutting against the fixing member 26 from the inside of the fixing belt 21 to reinforce the fixing member 26. Yes.
In the first embodiment, as shown in FIG. 4, the protrusions 26 a and 26 b that protrude toward the opposing surface 23 a of the reinforcing member 23 so as to contact the reinforcing member 23 are provided on the fixing member 26. A plurality of rows are provided along the P conveying direction (or the rotation direction of the fixing belt 21). Specifically, as a plurality of rows of protrusions, an upstream protrusion 26a that protrudes toward the opposing surface 23a of the reinforcing member 23 so as to abut on the reinforcing member 23 on the upstream side in the conveyance direction of the recording medium P, and a recording medium A downstream projecting portion 26b projecting toward the facing surface 23a of the reinforcing member 23 is formed so as to contact the reinforcing member 23 on the downstream side with respect to the conveying direction of P. In other words, the fixed member 26 has two rows of protruding portions 26a and 26b (the distance between the upstream end portion and the downstream end portion) that are spaced apart in the transport direction on the side facing the reinforcing member 23. ), And these two rows of protrusions 26a and 26b come into surface contact with the opposing surface 23a of the reinforcing member 23, respectively.

With such a configuration, the fixing member 26 in a state where the reinforcing member 23 is in pressure contact is held in a well-balanced manner even when a pipe-shaped heating member for fitting and fixing the fixing member 26 is not installed. Inconvenience that the 26 falls down is suppressed. Then, a desired nip is formed with high accuracy, and a fixing failure occurs in the output image or a conveyance failure of the recording medium occurs, thereby preventing problems.
That is, when the fixing member 26 is biased toward the upstream side in the transport direction or downstream in the transport direction and contacts the reinforcing member 23, or when the contact width (distance B) of the fixing member 26 that contacts the reinforcing member 23 is narrow. In this case, the fixing member 26 that has received the pressing force at the nip portion is likely to rotate (easily fall down) clockwise or counterclockwise in FIG. 4 with the contact portion with the reinforcing member 23 as a fulcrum. . On the other hand, in the present embodiment, the fixing member 26 is not biased toward the upstream side in the transport direction or the downstream side in the transport direction and is not in contact with the reinforcing member 23, but the contact width ( Since the distance B) is set to be sufficiently large, the fixing member 26 that has received the pressing force at the nip portion is supported in a balanced manner by the reinforcing member 23, and the fixing member 26 falls with the contact portion with the reinforcing member 23 as a fulcrum. It becomes difficult.

  Furthermore, in the first embodiment, since only the portion of the fixing member 26 divided into the upstream protruding portion 26a and the downstream protruding portion 26b is in contact with the reinforcing member 23, the upstream of the fixing member 26 Since the contact area between the reinforcing member 23 and the fixing member 26 can be reduced as compared with the case where one flat surface formed in a wide range from the side to the downstream side is in contact with the reinforcing member 23, the fixing member 26 can be reduced. Heat is difficult to be transferred to That is, heat transmitted from the fixing belt 21 through the fixing member 26 toward the reinforcing member 26 at the nip portion can be reduced (amount of heat escaping from the fixing belt 21 to the reinforcing member 23 via the fixing member 26). Can be reduced.) In particular, when the thickness of the fixing belt 21 is reduced (for example, when the thickness is set to 160 μm or less) or when the nip width is set wide, the amount of heat easily moves from the fixing belt 21 to the fixing member 26. Therefore, a configuration in which the contact area between the reinforcing member 23 and the fixing member 26 is reduced as in the first embodiment is useful.

Here, referring to FIG. 7 and FIG. 9, the fixing member 26 according to the first embodiment has a plurality of rows of protrusions (upstream protrusions 26 a and downstream protrusions 26 b). It is divided into a plurality of pieces with a gap in the width direction (the left-right direction in FIGS. 7 and 9). Specifically, in the first embodiment, eight upstream protrusions 26a and eight downstream protrusions 26b are formed at approximately equal intervals in the width direction. With such a configuration, the contact area between the reinforcing member 23 and the fixing member 26 can be further reduced, so that the above-described effects are more reliably exhibited.
In the first embodiment, the plurality of rows of protrusions 26a and 26b are configured to come into surface contact with the opposing surface 23a of the reinforcing member 23. However, in order to further ensure the above-described effect, a plurality of rows of protrusions 26a and 26b are configured. The projecting portions 26a and 26b may be configured to make line contact or point contact (or contact in a state close thereto) to the facing surface 23a of the reinforcing member 23, respectively. In the first embodiment, two rows of protruding portions, that is, the upstream protruding portion 26a and the downstream protruding portion 26b are provided as a plurality of rows of protruding portions. However, three or more rows of protruding portions are provided as the plurality of rows of protruding portions. Can also be provided.

Further, in the first embodiment, referring to FIG. 4, when the fixing member 26 is viewed in a cross section orthogonal to the width direction, an imaginary straight line passing through the center of the conveyance direction in the nip portion and orthogonal to the conveyance direction (see FIG. 4 is a straight line indicated by a one-dot chain line).
With such a configuration, the fixing member 26 that has received the pressure contact force at the nip portion is more easily supported by the reinforcing member 23, and the fixing member 26 is more unlikely to fall down.

Further, in the first embodiment, as shown in FIG. 4, the length of the nip portion (nip width) with respect to the conveyance direction of the recording medium is A, and the fixing member 26 and the reinforcing member 23 are in contact with each other on the upstream side in the conveyance direction. The length from the contacting upstream contact portion to the downstream contact portion where the fixing member 26 and the reinforcing member 23 abut on the downstream side in the transport direction is defined as B, and the opposing surface of the reinforcing member 23 facing the fixing member 26 in the transport direction. When the length of the surface 23a is C,
A <B <C
The relationship is established.
Further, the range of the nip portion (the range of A in FIG. 4) with respect to the conveyance direction is the range (the range of B in FIG. 4) from the upstream contact portion to the downstream contact portion. ) And the range from the upstream contact portion to the downstream contact portion (the range of B in FIG. 4) is the range of the facing surface 23a of the reinforcing member 23 (the range of C in FIG. 4). It is formed to be included in.
In other words, the range of the nip width is included in the range of the conveying direction (the vertical direction in FIG. 4) of the fixing member 26 that contacts the reinforcing member 23. Further, the range in the conveyance direction of the fixing member 26 that contacts the reinforcement member 23 is included in the range in the conveyance direction of the facing surface 23 a of the reinforcing member 23.
With such a configuration, the fixing member 26 that has received the pressure contact force at the nip portion is more easily supported by the reinforcing member 23, and the fixing member 26 is more unlikely to fall down.

Here, as described above, in the fixing device 20 according to the first embodiment, the fixing member 26 is interposed between the fixing member 26 and the fixing belt 21 in the width direction at the position of the nip portion. A sheet-like member 22 (made of a low friction material and impregnated with a lubricant) is covered along the circumferential direction.
The sheet-like member 22 is a lubricant (silicone oil) having a thickness set within a range of 150 to 500 μm, formed of a fiber material made of a fluororesin such as PTFE, and having a viscosity set within a range of 50 to 1000 cs. Etc.) is impregnated in the fiber.

  Thus, by forming the sheet-like member 22 with a fiber material, the lubricant can easily penetrate into the eyes of those fibers, so that the retention of the lubricant is improved. Further, since the sheet-like member 22 is formed of a fluororesin fiber material that is a low friction material, even if the lubricant held on the sheet-like member 22 is exhausted, the fixing member 26 and The sliding resistance at the nip portion with the fixing belt 21 can be lowered to some extent.

With reference to FIGS. 7 to 11, the sheet-like member 22 is formed with a plurality of holes 22 b that fit into a plurality of rows of protrusions (upstream protrusions 26 a and downstream protrusions 26 b). Has been. And the sheet-like member 22 is installed so that it may closely_contact | adhere to the fixing member 26 along the circumferential direction in the position except multiple rows of protrusion parts 26a and 26b.
Specifically, as shown in FIG. 10, the sheet-like member 22 has a rectangular shape when deployed as a single component. At both ends of the rectangular sheet-like member 22, a plurality of hole portions 22a and 22b (hole portions that fit into the protruding portions 26a and 26b) and screw hole portions 22c (screws of the screws 24) are provided. Is a hole for inserting the part.).
When the sheet-like member 22 is covered with the fixing member 26, the both ends of the rectangle are overlapped and overlapped between the upstream-side protruding portions 26a and the downstream-side protruding portions 26b (between the plurality of rows of protruding portions). A portion (a region surrounded by a broken line in FIG. 8 and a hatched region in FIG. 10) is formed.
Then, as shown in FIG. 8, a plate-like member 28 (fixed plate) is fixed to the fixing member 26 with a plurality of screws 24 so as to sandwich the overlapping portion of the sheet-like member 22. Specifically, the plate-like member 28 is placed on the fixing member 26 via the overlapping portion so as to sandwich the overlapping portion of the sheet-like member 22, and a screw hole 28 c of the plate-like member 28 (see FIG. 11 can be referred to). ) And the screw hole portion 22c of the sheet-like member 22, and the screw portion of the screw 24 is screwed into the female screw portion 26c of the fixing member 26 (see FIG. 9C). Here, the plurality of screws 24 are formed such that the heights of the screw heads exceed the heights of the protruding portions 26 a and 26 b and do not contact the reinforcing member 23.

Thus, the sheet-like member 22 is fixedly held on the fixing member 26 at the time of unfolding, the end corresponding to the upstream side in the transport direction and the end corresponding to the downstream side in the transport direction. Therefore, in addition to the case where the sheet-like member 22 receives a frictional force with the fixing belt 21 traveling toward the downstream side (during a normal fixing step), the sheet-like member 22 faces the upstream side. Even when the frictional force is received between the belt and the fixing belt 21 that travels (the fixing belt 21 and the pressure roller 31 are manually rotated in reverse during the jam processing), the sheet-like member 22 is used. This causes a problem that a gap or a wrinkle is generated between the fixing member 26 and the fixing member 26.
In particular, in the first embodiment, the overlapping portion of the sheet-like member 22 is sandwiched between the plate-like members 28, and the plate-like member 28 is fastened to the fixing member 26 with a plurality of screws 24 arranged substantially evenly in the width direction. Therefore, as compared with other fixing and holding methods (for example, when the overlapping portion is bonded with an adhesive, or when the overlapping portion is hook-shaped and hooked on the protruding portions 26a and 26b), the fixing member is used. The sheet-like member 22 can be stably and firmly fixed to the member 26.

Further, the hole portions 22a and 22b of the sheet-like member 22 are fitted into the protruding portions 26a and 26b of the fixing member 26, and the plate-like member 28 and the screw 24 are placed between the protruding portions 26a and 26b (central portion in the conveying direction). Since it is installed, the fixing member 26 in a state where the sheet-like member 22 is installed is made compact.
Further, since the fixing member 26 in a state where the sheet-like member 22 is installed can be managed in units of one sub-assembled part, the parts manageability and assemblability at the time of manufacturing and maintenance are improved. be able to.
In addition, since the sheet-like member 22 is fitted and held in a plurality of protrusions 26a and 26b that are divided at substantially equal intervals in the width direction, a plurality of holes are provided even if the sheet-like member 22 receives a sliding contact force. It is easy to apply force equally to 22a and 22b, and the trouble that the sheet-like member 22 is damaged by local stress concentration can be reduced.

Hereinafter, characteristic control performed by the fixing device 20 according to the first embodiment will be described in detail with reference to FIG.
In the first embodiment, when a series of conveyance operations of the recording medium P to the nip portion (a series of sheet feeding operations, which is an image forming process continuously performed in one job) is completed. The surface temperature of the fixing belt 21 is detected by the temperature sensors 40A and 40B (temperature detection means). When the detected temperature detected by the temperature sensors 40A and 40B exceeds a predetermined threshold, heating of the fixing belt 21 (fixing rotator) by the idling mode (heaters 25A and 25B (heating means) is stopped. In this state, the fixing belt 21 and the pressure roller 31 are rotated. By performing such an idling mode, the fixing belt 21 stops rotating immediately after the end of the series of sheet passing operations, and the portions close to the heaters 25A and 25B are locally heated by the residual heat of the heaters 25A and 25B. Therefore, it is possible to prevent a problem that the temperature rises and to prevent occurrence of abnormal images such as hot offset.

In the first embodiment, the idling mode is information on the recording medium P related to a series of transport operations (information on the recording medium P related to a job (previous process) immediately before the idling mode is executed). )) And information on the recording medium related to a series of transport operations to be performed next (information on the recording medium P related to the job (next process) immediately after the idling mode is executed). The execution time (the time during which the idling mode is executed) is varied.
Here, the information on the recording medium P acquired in the previous process and the next process is information on the size (in particular, the size in the width direction) and the thickness (paper thickness) of the recording medium P, Can be obtained based on the result of direct detection by installing a known size detection sensor or thickness detection sensor in the conveyance path from the unit 12 or the sheet feeding unit 12 to the fixing device 20. It can also be acquired based on the information of the recording medium P input to one operation panel (not shown).
As described above, by changing the execution time of the idling mode based on the information on the recording medium P in the previous process and the information on the recording medium P in the next process, it is possible to efficiently eliminate the problem that an abnormal image such as a hot offset occurs. Can be prevented. That is, the occurrence of an abnormal image such as a hot offset can be suppressed without causing a useless waiting time when the next process is passed. This is because the fixing belt 21 depends on the combination of the type of recording medium P passed in the previous process (paper passing condition) and the type of recording medium P passed in the next process (paper passing condition). This is because the degree and position of the local temperature increase are different and may not affect the sheet passing operation in the next process.

  For example, when a recording medium P having a paper thickness larger than that of the recording medium P in the previous process is passed in the next process, the amount of heat transferred from the fixing belt 21 to the recording medium P increases, and hot offset is unlikely to occur. Therefore, the execution time of the idling mode can be set short. Further, even when a recording medium P having a size larger than that of the recording medium P in the previous process is passed in the next process, the amount of heat transferred from the fixing belt 21 to the recording medium P is increased, so that hot offset does not easily occur. Therefore, the execution time of the idling mode can be set short. Further, in the next process, when the recording medium P having a smaller size in the width direction than the recording medium P in the previous process is passed, the portion corresponding to the non-sheet passing area of the recording medium P is overheated. In such a case, the excessive temperature rise does not affect the recording medium P and the hot offset does not occur. Therefore, it is possible to set the execution time of the idling mode to be short, Can be stopped (suspended) immediately.

Here, in the first embodiment, the above-described threshold value (the detected temperature value serving as a reference for determining whether or not to execute the idling mode) is varied according to the information of the recording medium P in the previous process. It is controlled so that
For example, when a recording medium P (thick paper) having a large paper thickness is passed in the previous process, the amount of heat transferred from the fixing belt 21 to the recording medium P increases, so that the threshold value can be set low. In addition, when the recording medium P (thin paper) having a small paper thickness is passed in the previous process, the amount of heat transferred from the fixing belt 21 to the recording medium P becomes small, so that the threshold can be set high.
Thereby, the idling mode can be executed efficiently.

In the first embodiment, the position of the temperature sensor in the width direction at which the detected temperature exceeds the threshold value among the two temperature sensors 40A and 40B (temperature detection means) is passed through the recording medium P in the next process. In the non-sheet passing area, the execution of the idling mode is immediately stopped (suspended). Specifically, when the A3 vertical size recording medium P is passed in the previous process and the A4 vertical size recording medium P is passed in the next process, the first temperature sensor 40A exceeds the threshold. If the second temperature sensor 40B detects an excessive temperature rise exceeding the threshold value without detecting the excessive temperature rise, the excessive temperature rise does not affect the recording medium P in the next process, and a hot offset occurs. Since the condition does not occur, the idling mode can be stopped (interrupted) immediately.
Thereby, the idling mode can be executed efficiently.

Hereinafter, an example of control related to the idling mode described above will be described with reference to FIG.
First, when paper feeding is started in the previous process, information on the recording medium P related to the paper feeding is acquired (steps S1 to S2). Based on the information of the recording medium P, a threshold value in the idling mode is determined (step S3). Then, when the paper feeding in the previous process is completed (step S4), it is determined whether the detected temperatures of the two temperature sensors 40A and 40B are larger than the threshold values set in step S3 (step S5).
As a result, if it is determined that the detected temperatures of the two temperature sensors 40A and 40B are both lower than the threshold value, it is determined that the fixing belt 21 is not overheated, and the idling mode is performed. The process ends as it is (step S6).
On the other hand, if it is determined that one of the detected temperatures of the two temperature sensors 40A and 40B is higher than the threshold value, it is assumed that the fixing belt 21 is overheated. The idling mode is started (step S7).

Then, during execution of the idling mode (or before that), it is determined whether there is a print command for the next process (step S8). As a result, if there is no print command for the next process, the idle rotation mode is performed for the set execution time as a standard, and then the process is terminated (step S9).
On the other hand, if there is a print command for the next process, information about the recording medium P to be passed to the next process is acquired (step S10), and the information and the recording medium for the previous process acquired in step S2 are acquired. Information regarding P is compared (step S11).

Then, it is determined whether the paper thickness of the recording medium P in the next process is thicker than the paper thickness of the recording medium P in the previous process (step S12).
As a result, when it is determined that the paper thickness of the recording medium P in the next process is equal to or less than the paper thickness of the recording medium P in the previous process, the size of the recording medium P in the next process is further increased. It is determined whether it is smaller than the size of the recording medium P (step S13). As a result, if it is determined that the size of the recording medium P in the next process is equal to or larger than the size of the recording medium P in the previous process, an offset image may be generated as it is. The idle rotation mode is performed for the execution time set as a standard (step S14), and then the paper feeding operation of the next process is performed.

On the other hand, if it is determined in step S13 that the size of the recording medium P in the next process is smaller than the size of the recording medium P in the previous process, the next threshold is exceeded. It is determined whether it is only the non-sheet passing area of the recording medium P in the process (step S15). Specifically, the temperature exceeding the threshold value among the detected temperatures of the two temperature sensors 40A and 40B is specified.
As a result, if it is determined that it is not only the non-sheet passing area of the recording medium P in the next process that exceeds the threshold value, it is assumed that an offset image may be generated as it is. Only the execution time set as standard is performed (step S16), and then the paper feeding operation of the next process is performed. On the other hand, if it is determined that only the non-sheet passing area of the recording medium P in the next process exceeds the threshold, there is no possibility that an offset image is generated in the sheet passing area. The idling mode is immediately stopped (step S17), and then the paper feeding operation of the next process is performed.

  On the other hand, if it is determined in step S12 that the paper thickness of the recording medium P in the next process is thicker than the paper thickness of the recording medium P in the previous process, the size of the recording medium P in the next process is further increased. It is determined whether it is smaller than the size of the recording medium P (step S18). As a result, if it is determined that the size of the recording medium P in the next process is equal to or larger than the size of the recording medium P in the previous process, The mode is shortened from the execution time set as standard (step S19), and then the paper feeding operation of the next process is performed.

On the other hand, if it is determined in step S18 that the size of the recording medium P in the next process is smaller than the size of the recording medium P in the previous process, the next threshold is exceeded. It is determined whether it is only the non-sheet passing area of the recording medium P in the process (step S20).
As a result, when it is determined that it is not only the non-sheet passing area of the recording medium P in the next process that exceeds the threshold, it is assumed that the offset image is unlikely to occur, and the idle rotation mode is set as a standard. The execution time is set to be shorter than the set execution time (step S21), and then the paper feeding operation of the next process is performed. On the other hand, if it is determined that only the non-sheet passing area of the recording medium P in the next process exceeds the threshold, there is no possibility that an offset image is generated in the sheet passing area. The idling mode is immediately stopped (step S22), and then the next sheet passing operation is performed.

In the first embodiment, a speed variable unit that varies the rotational speeds of the fixing belt 21 and the pressure roller 31 is installed, and when the idling mode is executed, the speed variable unit causes the fixing belt 21 and It can also be controlled to increase the rotation speed of the pressure roller 31.
Specifically, in the first embodiment, a variable speed type drive motor is used as the drive motor that rotationally drives the pressure roller 31. When the idling mode is executed, the rotational speed of the pressure roller 31 (and the fixing belt 21) is increased by the drive motor.
By increasing the rotation speeds of the fixing belt 21 and the pressure roller 31 in this way, the heat of the fixing belt 21 is transferred to the pressure roller 31 in a short time, so that the efficiency of the idling mode is increased. Can do. That is, the execution time of the idling mode can be set short.

  As described above, in the first embodiment, it is executed when the detected temperature detected by the temperature sensors 40A and 40B (temperature detecting means) exceeds a predetermined threshold when a series of transport operations is completed. The execution time of the idle rotation mode is varied based on the information of the recording medium P related to the series of transport operations and the information of the recording medium P related to the series of transport operations performed next. As a result, the surface temperature of the fixing belt 21 (fixing rotator) locally rises after the end of paper passing, and a hot offset or the like is added to the fixed image on the recording medium P in the next series of transport operations. It is possible to efficiently prevent problems that cause abnormal images.

  In Embodiment 1, 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 effect as that of 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. 13 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 fixing belt 21 is heated by electromagnetic induction.

As shown in FIG. 13, the fixing device 20 according to the second embodiment also has a fixing belt 21 (belt member), a fixing member 26, a reinforcing member 23, and a pressure roller 31 (as in the first embodiment). Heating rotary body), temperature sensors 40A and 40B, sheet-like member 22, double-sided tape 49, screw 24, plate-like member 28 (fixed plate), and the like.
Also in the second embodiment, as in the first embodiment, the idling mode is executed after the end of paper feeding.

  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 heaters 25A and 25B. The fixing belt 21 in the second embodiment is heated by electromagnetic induction by the induction heating unit 50, unlike the first embodiment in which the fixing belt 21 is heated by the radiant heat of the heaters 25A and 25B.

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. 13) 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 fixing belt 21, A side core is provided. The core is installed so as to face the exciting coil extending in the width direction.
On the other hand, in addition to the base material layer, the elastic layer, and the release layer described in the first embodiment, the fixing belt 21 includes a heat generating layer (for example, an elastic layer and a release layer) that is electromagnetically heated by the induction heating unit 50. The base material layer can be used as a heat generating layer). As a material for the heat generating layer, nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, an alloy composed of a plurality of these metals, or the like can be used.

The fixing device 20 configured as described above operates as follows.
When the fixing belt 21 is rotationally driven in the arrow direction in FIG. 13, the fixing belt 21 is heated at a position facing the induction heating unit 50. More specifically, the magnetic field lines are alternately switched around the fixing belt 21 by flowing a high-frequency alternating current through the exciting coil. At this time, an eddy current is generated on the surface of the heat generating layer of the fixing belt 21, and Joule heat is generated by the electric resistance of the heat generating layer itself. Due to this Joule heat, the heat generating layer is heated by electromagnetic induction, and the fixing belt 21 is heated.
Here, also in the second embodiment, since the induction heating unit 50 is installed so as to face a part of the outer peripheral surface of the fixing belt 21, the temperature of the fixing belt 21 is locally increased after the sheet is passed. A malfunction may occur. Therefore, in order to prevent such inconvenience, the idling mode is executed based on a predetermined condition after the end of paper passing, as in the first embodiment.

  As described above, also in the second embodiment, the detected temperature detected by the temperature sensors 40A and 40B (temperature detecting means) when the series of transport operations is completed is the same as in the above embodiments. The execution time of the idling mode that is executed when the threshold value is exceeded, information on the recording medium P related to the series of transport operations, information about the recording medium P related to the series of transport operations performed next, Variable based on As a result, the surface temperature of the fixing belt 21 (fixing rotator) locally rises after the end of paper passing, and a hot offset or the like is added to the fixed image on the recording medium P in the next series of transport operations. It is possible to efficiently prevent problems that cause abnormal images.

In the second embodiment, the fixing belt 21 is heated by electromagnetic induction heating. However, the fixing belt 21 can be heated by the heat of the resistance heating element. Specifically, the resistance heating element is brought into contact with a part of the inner peripheral surface or the outer peripheral surface of the fixing belt 21. The resistance heating element is a planar heating element such as a ceramic heater, and a power supply unit is connected to both ends thereof. When a current is passed through the resistance heating element, the resistance heating element is heated by the electric resistance of the resistance heating element itself, and the fixing belt 21 in contact with the heating element is heated.
Even in such a case, as in the second embodiment, the same effect as in the second embodiment can be obtained by executing the idling mode based on a predetermined condition after the passing of the paper. .

In each of the embodiments described above, the fixing belt 21 having the fixing member 26 provided therein is used as the fixing rotating body. However, a fixing belt stretched and supported by a plurality of roller members may be used as the fixing rotating body. It is also possible to use a fixing roller in which an elastic layer, a surface layer, etc. are laminated on a hollow cored bar as a fixing rotating body.
In each of the above embodiments, the pressure roller 31 is used as the pressure rotator. However, an endless pressure belt may be used as the pressure rotator.
In these cases, the same effects as those in 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 rotating body),
22 sheet-like members,
25A 1st heater (heating means),
25B 2nd heater (heating means),
25A1, 25B1 light emitting part,
26 fixing member,
26a upstream protrusion, 26b downstream protrusion,
28 plate-like member (fixed plate),
29 Flange (holding member),
31 Pressure roller (pressure rotating body),
40A 1st temperature sensor (temperature detection means),
40B 2nd temperature sensor (temperature detection means).

Japanese Patent No. 2010-96782 Japanese Patent No. 2005-77700

Claims (7)

A fixing rotator that is heated by a heating unit and that rotates in a predetermined direction to heat and melt the toner image;
A pressure rotator that rotates in a predetermined direction and forms a nip portion in which a recording medium is conveyed in pressure contact with the fixing rotator;
Temperature detecting means for detecting the temperature of the surface of the fixing rotating body;
With
When the detection temperature detected by the temperature detection unit exceeds a predetermined threshold when a series of conveying operations of the recording medium to the nip portion is finished, heating of the fixing rotator by the heating unit is stopped. In this state, an idle rotation mode is performed in which the fixing rotator and the pressure rotator are rotated.
The idle rotation mode is characterized in that the execution time thereof is variable based on the information on the recording medium related to the series of transport operations and the information on the recording medium related to the series of transport operations performed next. Fixing device to do.   The fixing device according to claim 1, wherein the information on the recording medium is information on a size or / and a thickness of the recording medium.   The fixing device according to claim 1, wherein the threshold value is varied in accordance with information on a recording medium related to the series of transport operations. A speed variable means for varying the rotation speed of the fixing rotator and the pressure rotator;
4. The rotation speed of the fixing rotator and the pressure rotator is increased by the speed variable unit when the idling mode is executed. 5. Fixing device. The temperature detecting means is a plurality of temperature detecting means for detecting temperatures at positions different from each other in the width direction at positions facing the heating means via the fixing rotator,
When the position in the width direction of the temperature detection means in which the detected temperature exceeds the threshold among the plurality of temperature detection means is in a non-sheet passing region of the recording medium related to the series of transport operations performed next, The fixing device according to claim 1, wherein execution of the idling mode is stopped. The fixing rotator is an endless fixing belt having flexibility,
A fixing member fixed on the inner peripheral surface side of the fixing belt and forming a nip portion for conveying a recording medium in pressure contact with the pressure rotator via the fixing belt;
A reinforcing member fixed on the inner peripheral surface side of the fixing belt and abutting the fixing member from the inside of the fixing belt to reinforce the fixing member;
A holding member for holding both ends in the width direction of the fixing belt;
The fixing device according to claim 1, further comprising:   An image forming apparatus comprising the fixing device according to claim 1.

Images