JP5377194B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that detects that a recording medium is wound around a heating means, without heating the heating means in a fixing device. <P>SOLUTION: The image forming apparatus includes: a paper detection sensor 17 for detecting that conveyance of paper P fails in the fixing device 12; and first and second temperature detection sensors 26a and 26b for detecting a surface temperature of a non-paper passing region and a paper passing region of a first heating roller 21 of the fixing device 12. A control part 35 stops the rotation and heating of the first heating roller 21 urgently when the paper detection sensor 17 detects a conveyance failure, and determines that the paper P is wound around the first heating roller 21 when the first detection temperature of the first temperature detection sensor 26a after the urgent stop increases, and the second detection temperature of the second temperature detection sensor 26b decreases. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus equipped with a fixing device that inserts a sheet carrying an unfixed toner image, heats and melts the unfixed toner, and fixes the sheet on the sheet, such as an electrophotographic copying machine, a facsimile machine, or a printer. .

  In an electrophotographic image forming apparatus, a heat source is built in at least one roller (heating roller) of a roller pair forming a nip to serve as a heating unit, and unfixed toner is formed in a nip portion of the roller pair heated by the heat source. A heat roller fixing method is used in which toner is fixed to a sheet by inserting a sheet (recording medium) carrying an image.

  As the heat roller fixing method, an endless fixing belt is stretched between the fixing roller and the heating roller to form a heating means, the fixing belt generates heat by the heat source of the heating roller, and the fixing roller is A system in which an unfixed toner image is fixed on a sheet at a nip portion with a pressure roller is also used.

  For example, in the heat roller fixing system described above, a fluorine-based coating or tube is provided on the surface layer of the heating roller in order to improve the releasability of the toner from the heating roller. Further, a separation member is provided on the downstream side of the heating roller for the purpose of peeling the paper from the heating roller.

  However, if the paper adheres strongly to the heating roller, the paper may be wound around the heating roller without being separated by the separating member. In particular, when a paper having a small stiffness, such as a recycled paper containing thin paper or recycled paper, is used, winding around the heating roller is likely to occur. When such wrapping occurs, it is not easy to remove the paper, and if the user cannot handle it, it is necessary to call a service person. In addition, when the user does not notice the winding, the heating roller is heated while the paper is wound, and if the wound paper is heated, there is a risk of a safety and disaster prevention problem.

  Therefore, a method for detecting the occurrence of such winding has been proposed. For example, Patent Document 1 includes first and second temperature detecting means for detecting the surface temperatures of the fixing member (heating roller) within the sheet passing range and outside the sheet passing range, respectively, and the fixing member is heated by a heat source to fix the fixing member (heating roller). When the surface temperature of the member reaches a predetermined set temperature, the difference between the detected temperatures of the first and second temperature detecting means is compared with a reference value to detect the winding of the paper (recording medium), and the winding occurs. In such a case, a method is disclosed in which energization (heating) to a heat source is stopped to easily and surely detect a winding jam or a paper jam and to prevent the paper jam from recurring.

  Japanese Patent Laid-Open No. 2004-228867 determines whether the recording material is wound by comparing the output state of the non-contact temperature detecting means when there is no recording material (recording medium) on the heating member (heating roller) and when there is no recording material. Thus, there is disclosed a method that can quickly cope with a paper jam and that can reliably detect the remaining paper and avoid troubles such as flames caused by the remaining paper.

JP 2002-156868 A JP 2002-296953 A

  However, in Patent Document 1, when printing is performed in a state where paper of an irregular size or paper having different size widths is mixed, there is a possibility that the temperature difference between the paper passing area and the non-paper passing area cannot be accurately detected. There is. In Patent Document 2, a normal value measured in advance and a detected value are compared. However, if the measurement time is different, the power supply circumstances such as the input voltage, the ambient temperature, the temperature of the pressure roller, and the like are different. Since the temperature rise curve of the sensor changes, the detection accuracy may be lowered.

  Further, in Patent Documents 1 and 2, since it is necessary to heat the heating roller by turning on the heat source in order to detect winding, when the power is turned on while the recording medium is wound around the heating roller, the paper is heated, There is a risk that scorching may cause smoke and off-flavors. Further, such a winding problem can occur in the same manner even when a fixing belt is used.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of detecting winding of a recording medium around a heating unit without heating the heating unit in the fixing device.

  In order to achieve the above object, the present invention comprises a conveyance path for conveying a recording medium, a rotatable heating unit, and a pressure unit that abuts against the heating unit to form a nip portion. A fixing device for fixing a toner image on the recording medium by inserting the recording medium conveyed along the path into the nip portion while the heating means rotates in a predetermined direction; and a non-passing area of the recording medium on the surface of the heating means Based on the first and second detected temperatures by the first temperature detecting means, the second temperature detecting means for detecting the temperature of the passage region, and the first and second temperature detecting means. And a control unit capable of controlling the surface of the heating unit to a predetermined fixing temperature at the time of fixing. In the image forming apparatus, the conveyance path detects a conveyance failure of the recording medium in the fixing device. Fault detection means are provided The control unit executes heating and rotation stop of the heating unit when the conveyance failure detection unit detects the conveyance failure, and the first and second detected temperatures after the stop with respect to the fixing time. Based on the difference in change, it is determined whether or not the recording medium is wound around the heating unit.

  Further, according to the present invention, when the predetermined detection time elapses from the stop time and the first detection temperature rises and the second detection temperature decreases with respect to the fixing time, the winding is performed. It is characterized by judging that it occurred.

  Further, the present invention is characterized in that the predetermined time is set from the time of the stop until the rise of the first detected temperature reaches a peak.

  Further, the present invention is characterized in that the second temperature detection means is disposed at a position where the temperature of the passage area can be detected with a recording medium wound around the heating means interposed therebetween.

  Further, the present invention is characterized in that a display means is provided, and when the control means determines that the winding has occurred, the occurrence of the winding is displayed on the display means.

  Further, the present invention is characterized in that when the control means determines that the winding has occurred, the heating means is rotated in a direction opposite to that during the fixing.

  Further, the present invention is characterized in that the heating means is a first heating roller having a first heat source therein.

  Further, according to the present invention, the heating unit includes a second heating roller having a second heat source therein, a fixing roller, a fixing belt that is rotatable around the second heating roller and the fixing roller. The pressurizing means abuts on the fixing roller through the fixing belt to form the nip portion.

  In the invention, it is preferable that the pressure unit is a pressure roller.

  According to the first configuration of the present invention, the conveyance path is provided with a conveyance failure detection unit that detects a conveyance failure of the recording medium in the fixing device, and the control unit detects when the conveyance failure detection unit detects the conveyance failure. By performing heating and rotation stop of the heating means, and determining whether or not the recording medium is wound around the heating means based on the difference in change of the first and second detection temperatures after the stop with respect to fixing. It is possible to determine whether the recording medium is wound around the heating unit without heating the heating unit in the fixing device.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, the control unit increases the first detected temperature with respect to the fixing time after the elapse of a predetermined time from the stop time, and the second By determining that winding has occurred when the detected temperature of the recording medium decreases, the difference in change between the first and second detected temperatures at the time of fixing becomes clearer. Can be judged more reliably.

  According to the third configuration of the present invention, in the image forming apparatus having the second configuration, the predetermined time is set between the stop time and the rise of the first detected temperature reaches the peak, Since the difference in change between the first and second detection temperatures with respect to fixing becomes clear at an early stage, the presence or absence of winding of the recording medium can be determined in a shorter time and with certainty.

  According to the fourth configuration of the present invention, in the image forming apparatus having any one of the first to third configurations, the second temperature detection unit is configured such that the temperature of the passage region sandwiches the recording medium wound around the heating unit. By arranging at a position where can be detected, the temperature detection accuracy by the second temperature detection means can be increased.

  According to the fifth configuration of the present invention, in the image forming apparatus having any one of the first to fourth configurations, when the display unit is provided and the control unit determines that the winding has occurred, the winding is generated. By displaying on the display means, it is possible to reliably notify the user of the occurrence of winding, so that the user can quickly start the work of taking out the recording medium wound, and the workability can be improved.

  According to the sixth configuration of the present invention, in the image forming apparatus having any one of the first to fifth configurations, when the control unit determines that the winding has occurred, the heating unit is moved in the direction opposite to that at the time of fixing. By rotating the recording medium, the rear end of the recording medium can be protruded to the upstream side of the fixing device in the conveyance direction of the recording medium, so that the user can easily take out the recording medium wrapped around the recording medium and improve workability. it can.

  According to the seventh configuration of the present invention, in the image forming apparatus having any one of the first to sixth configurations, the heating unit is a first heating roller having a first heat source therein. This is effective because the entire surface is formed of a curved surface and it can be determined whether or not the recording medium is wound around the heating roller that is likely to be wound.

  According to the eighth configuration of the present invention, in the image forming apparatus having any one of the first to sixth configurations, the heating unit includes a second heating roller having a second heat source therein, a fixing roller, The second heating roller and the fixing belt which is stretched around the fixing roller and is rotatable, and the pressure means rotates by contacting the fixing roller via the fixing belt to form a nip portion. Even when a fixing belt in which a flat portion and a curvature portion coexist in the trajectory is used, the presence or absence of winding of the recording medium around the fixing belt can be determined, which is effective.

  According to the ninth configuration of the present invention, in the image forming apparatus having any one of the first to eighth configurations, the pressure unit is a pressure roller, thereby affecting the damage or rotation of the heating unit. Can be reduced.

FIG. 1 is a schematic sectional view showing an image forming apparatus according to a first embodiment of the present invention. FIG. 1 is a schematic cross-sectional view showing a fixing device used in the image forming apparatus according to the present embodiment. FIG. 3 is a schematic perspective view showing the arrangement of first and second temperature detection sensors in a fixing device used in the image forming apparatus according to the present embodiment. FIG. 2 is a block diagram showing an example of a control mechanism of the image forming apparatus according to the present embodiment. FIG. 6 is a diagram schematically showing a time transition of detected temperatures by the first and second temperature detection sensors due to an emergency stop when no wrapping occurs in the fixing device in the image forming apparatus according to the present embodiment. FIG. 4 is a schematic cross-sectional view showing a state in which the paper is wound around the first heating roller. Is a plan view seen from the direction A in FIG. FIG. 6 is a diagram schematically illustrating a time transition of detected temperatures by the first and second temperature detection sensors due to an emergency stop when winding occurs in the fixing device in the image forming apparatus according to the present exemplary embodiment. FIG. 3 is a flowchart showing an example of a control procedure of the image forming apparatus according to the present embodiment. FIG. 3 is a schematic cross-sectional view showing a fixing device used in an image forming apparatus according to a second embodiment of the present invention. FIG. 6 is a graph showing the time transition of the detected temperature by the first and second temperature detection sensors due to an emergency stop when winding occurs in the fixing device in the image forming apparatus of the present embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic sectional view showing an image forming apparatus according to the first embodiment of the present invention. The image forming apparatus (for example, a printer) 100 includes an image forming unit 2, a paper feed mechanism 10, a transport unit (transport path) 11, a fixing device 12, a paper discharge unit 13, and the like. The image forming unit 2 includes a photosensitive drum 3, a charging unit 4, an exposure unit (laser scan unit) 5, a developing unit 6, a cleaning device 7, a toner container 8, and a transfer roller 9.

  The photosensitive drum 3 is formed by laminating a photosensitive layer such as an amorphous silicon layer (a-Si) or an organic photosensitive layer (OPC) on an aluminum drum, for example. An electrostatic latent image with the charge being attenuated is formed on the surface that has received the laser beam from 5.

  The charging unit (charging charger) 4 charges the surface of the photosensitive drum 3 by discharging (for example, corona discharge), and the exposure unit (LSU) 5 is based on the image data. Laser beam) is applied to the photosensitive drum 3 to form an electrostatic latent image on the surface of the photosensitive drum 3. Note that the image data is transmitted from a personal computer (not shown), for example.

  The developing unit 6 is for attaching toner to the electrostatic latent image on the photosensitive drum 3 to form a toner image. Examples of the developer accommodated in the developing unit 6 include a one-component developer composed of a styrene-acrylic magnetic one component and a two-component developer composed of a toner component and a carrier. When the toner in the unit 6 is insufficient, toner is supplied from the toner container 8. Further, the transfer roller 9 moves (transfers) the toner image formed on the surface of the photosensitive drum 3 onto the sheet (recording medium) P being conveyed by the conveying unit 11 without disturbing the toner image.

  The cleaning device 7 removes toner (residual toner) remaining on the surface of the photosensitive drum 3 after the toner image is transferred to the sheet, and is a rubbing roller that makes line contact with the longitudinal direction of the photosensitive drum 3. And a cleaning blade (not shown). The paper feed mechanism 10 accommodates the paper P on which an image (toner image) is printed, and feeds the paper P to the transport unit 11 that is a path of the paper P from the paper feed mechanism 10 to the paper discharge unit 13. It is.

  The fixing device 12 converts the toner image transferred to the paper P in the housing 12a into a stable permanent image, and melts the powder toner image by applying energy such as heat and pressure. Fix on the paper P. Details of the fixing device 12 will be described later. The paper discharge unit 13 accommodates the paper P that has passed through the fixing device 12, that is, the paper P on which a permanent image is printed.

  Then, the exposure unit 5 emits a laser beam on the photosensitive drum 3 based on image data input in advance, thereby forming an electrostatic latent image based on the image data on the surface of the photosensitive drum 3. Thereafter, toner is attached to the electrostatic latent image by the developing unit 6 (a toner image is formed), and the toner image is transferred onto the paper P by the transfer roller 9. Next, heat and pressure are applied to the paper P on which the toner image has been transferred by the fixing device 12 to form a permanent image.

  In the transport unit 11, a paper detection sensor (transport failure detection unit) 17 including an actuator is provided near the downstream side of the fixing device 12. The paper detection sensor 17 detects the passage of the paper P. Then, an output signal is transmitted to the control unit 35 described later. If the paper detection sensor 17 does not detect the passage of the paper P at a preset timing, the paper P does not pass through the fixing device 12 downstream, and a jam or paper jam occurs in the fixing device 12. And the detection result is transmitted to the control unit 35. The sheet detection sensor 17 can be provided on the upstream side of the fixing device 12 or on the upstream side and the downstream side.

  FIG. 2 is a schematic cross-sectional view showing a fixing device used in the image forming apparatus according to the present embodiment. FIG. 3 shows first and second temperatures in the fixing device used in the image forming apparatus according to the present embodiment. It is a model perspective view which shows arrangement | positioning of a detection sensor. In FIGS. 2 and 3, the housing 12a is omitted. The housing 12a (see FIG. 1) of the fixing device 12 is mainly provided with a first heating roller (first heating roller, heating means) 21 and a pressure roller 23.

  The first heating roller 21 has an elastic layer made of silicon rubber or the like formed on a cored bar made of Al (aluminum), Fe (iron), SUS (stainless steel) or the like having excellent thermal conductivity, for example. The surface of this elastic layer is covered with a resin having excellent releasability such as a fluororesin. Moreover, as a core metal, the thing of the low heat capacity which is easy to produce temperature changes, such as a temperature rise and fall, is preferable, and the one where the thickness of a metal core is smaller is preferable. The thickness of the metal core can be 0.2 mm to 1.5 mm. In addition, the warm-up time can be shortened by reducing the thickness of the cored bar.

  Here, the core of the first heating roller 21 is an aluminum core having an outer diameter of 26 mm and a thickness of 1 mm, and the elastic layer is a silicon rubber layer having a thickness of 0.3 mm, and PFA is formed on the surface of the silicon rubber layer. A (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) layer was provided. A first heat source (first heat source) 21a such as a halogen heater is provided inside the cored bar. The first heating roller 21 is driven so as to be able to rotate forward and backward by a driving device 51 (see FIG. 4) composed of a motor or the like, and at the time of fixing, the sheet P is transported downstream (in the direction of the white arrow). Rotate clockwise to convey the Further, the rotation speed is the same as the conveyance speed of the paper P.

  The pressure roller 23 has an elastic layer made of silicon rubber or the like formed on a metal core made of stainless steel, for example, and the surface of the elastic layer is covered with a resin having excellent releasability such as a fluororesin. . The pressure roller 23 contacts the first heating roller 21 to form a nip portion through which the paper P carrying the toner T is inserted. Further, the pressure roller 23 contacts the first heating roller 21 and rotates according to the rotation of the first heating roller 21. Here, the pressure roller 23 is formed of a stainless steel core and an elastic layer of a silicon rubber layer, and the outer diameter of the roller is 25 mm.

  Note that, similarly to the first heating roller 21, a heat source such as a halogen heater can be provided in the core of the pressure roller 23. In addition, since the pressure roller 23 is used in the present embodiment, the influence on the damage and rotation of the first heating roller 21 can be reduced, but other examples of the pressure unit include a fixing member and a belt-shaped member. However, it is not particularly limited to this embodiment.

  A first temperature detection sensor (first temperature detection means) 26a for detecting the surface temperature of the first heating roller 21 and a second temperature detection sensor (second temperature detection) are provided on the outer peripheral surface of the first heating roller 21. Means) 26b. The first temperature detection sensor 26a is composed of a contact type thermistor, abuts against the non-passing area (non-passing area) of the paper P at both longitudinal ends of the first heating roller 21, and determines the surface temperature of the non-passing area. Detect.

  The second temperature detection sensor 26 b is formed of a non-contact type thermistor, and is disposed at a position facing the paper passing area (passing area) of the paper P at a substantially central portion in the longitudinal direction of the first heating roller 21. It is provided at a predetermined interval from the surface of the first heating roller 21 so that the wound paper P can pass therethrough. Thereby, the second temperature detection sensor 26b detects the surface temperature of the paper passing area. The first detection temperature by the first temperature detection sensor 26a and the second detection temperature by the second temperature detection sensor 26b are sent to the control unit 35 to be described later, and based on the detection result, the control unit 35 The energization of the heating roller 21 to the first heat source 21a is turned on / off, and the fixing temperature is adjusted to a preset temperature.

  A separation member 27 is provided adjacent to the first heating roller 21 on the downstream side (left side in FIG. 2) in the conveyance direction of the paper P with respect to the nip portion between the first heating roller 21 and the pressure roller 23. The separation member 27 is formed of a substantially L-shaped plate member, and a substantially central portion of the L shape is rotatably supported by a housing 12a (see FIG. 1) of the fixing device 12. Further, the downstream end of the separating member 27 is urged downstream by the tension spring 29, and the separating member 27 is rotated by the urging force, and the upstream (right side) end is the first heating roller. 21 is close to the surface.

  Here, a gap of 0.3 mm was formed between the separating member 27 and the first heating roller 21. The separation member 27 can separate the paper P from the first heating roller 21 by peeling the leading edge of the paper P from the first heating roller 21. The gap between the separation member 27 and the first heating roller 21 is not particularly limited as long as the paper P can be separated from the first heating roller 21, and the separation member 27 contacts the surface of the first heating roller 21. It can also be made.

  As described above, during normal printing, the sheet P is separated from the first heating roller 21 by the separating member 27, so that the sheet P is interposed between the second temperature detection sensor 26 b and the surface of the first heating roller 21. Instead, the second temperature detection sensor 26b appropriately detects the surface temperature of the first heating roller 21 in the sheet passing area.

  FIG. 4 is a block diagram illustrating an example of a control mechanism of the image forming apparatus according to the present embodiment. Portions common to FIGS. 1 to 3 are denoted by the same reference numerals and description thereof is omitted. The image forming apparatus 100 includes an image forming unit 2, a fixing device 12, a paper detection sensor 17, an image input unit 32, an AD conversion unit 33, a storage unit 34, a control unit 35, and an operation panel (display unit) 36. .

  When the image forming apparatus 100 is a copying machine, the image input unit 32 includes a scanning optical system equipped with a scanner lamp that illuminates the document during copying and a mirror that changes the optical path of reflected light from the document, and reflected light from the document. 1 is an image reading unit (not shown) including a condensing lens that collects and forms an image and a CCD that converts the imaged image light into an electrical signal. In the case of a printer as shown, it is a receiving unit that receives image data transmitted from a personal computer or the like. The image signal input from the image input unit 32 is sent to the control unit 35, appropriately performs image processing such as gradation processing, and after being converted into a digital signal by the AD conversion unit 33, an image in the storage unit 34 to be described later. It is sent to the memory 40.

  The image forming unit 2 includes a photosensitive drum 3, a charging unit 4, an exposure unit 5, a developing unit 6, a transfer roller 9, and the like. Based on the image data converted by the AD conversion unit 33 and stored in the image memory 40. Then, an electrostatic latent image is formed on the photosensitive drum 3. The photosensitive drum 3, the transfer roller 9 and the like are rotationally driven by a main motor (not shown), and the control unit 35 transmits a control signal to the main motor to control the rotation and stop of the photosensitive drum 3 and the transfer roller 9. .

  The storage unit 34 includes an image memory 40, a RAM 41, and a ROM 42, and the image memory 40 stores an image signal input by the image input unit 32 and digitally converted by the AD conversion unit 33, and is stored in the control unit 35. Send it out. The RAM 41 and ROM 42 store an image processing program, processing contents, and the like of the control unit 35. The storage unit 34 also maintains a program for controlling image formation in the image forming unit 2, a program for controlling the conveyance of the paper P, and the surface temperature of the first heating roller 21 at a predetermined fixing temperature. In order to do so, a program for controlling energization of the first heat source 21a, parameters necessary for detecting a conveyance failure by the paper detection sensor 17, a monitoring time Tm described later, and detection of the first and second temperature detection sensors 26a and 26b Parameters that relate the temperature and the occurrence of the winding of the paper P around the first heating roller 21 are also stored.

  The control unit 35 is, for example, a central processing unit (CPU), and generally controls the image input unit 32, the image forming unit 2, the fixing device 12, conveyance of the paper P, and the like according to a set program, and the image input unit. The image signal input from 32 is converted into image data by scaling processing or gradation processing as necessary. The exposure unit 5 irradiates a laser beam based on the processed image data to form a latent image on the photosensitive drum 3. Further, the control unit 35 also controls each part of the image forming apparatus such as the image input unit 32, the charging unit 4, the exposure unit 5, and the developing unit 6 in accordance with the set program.

  Further, the control unit 35 receives an output signal indicating that the conveyance failure of the paper P in the fixing device 12 has occurred from the paper detection sensor 17, and turns on the first heating roller 21 and energizes the first heat source 21a. It has a function to stop (emergency stop). At this time, the control unit also stops driving the image forming unit 2 and transporting the paper P in the transport unit 11. In addition, the control unit 35 measures the time elapsed from the emergency stop and determines whether or not the monitoring time Tm has elapsed, and the first and second temperature detection sensors 26a after the monitoring time Tm has elapsed since the emergency stop. , 26b, and a function of determining whether or not the paper P is wound around the first heating roller 21 based on the parameters stored in the storage unit 34. In addition, the control unit 35 has a function of displaying on the operation panel 36 that a conveyance failure has occurred when the paper P has not been wound, and when the winding has occurred, or when the winding has occurred. The first heating roller 21 has a function of rotating in the direction opposite to that at the time of fixing.

  When the image forming apparatus 100 is a copying machine, the operation panel 36 includes an operation unit composed of a plurality of operation keys and a display unit (none of which is shown) for displaying setting conditions, the state of the apparatus, and the like. For example, when the image forming apparatus 100 has a facsimile function, the facsimile transmission destination is registered in the storage unit 34, and the registered transmission destination is read out. It is also used for various settings such as rewriting and rewriting. When the image forming apparatus 100 is the printer shown in FIG. 1, the operation panel 36 is composed of an input unit displayed on a personal computer (not shown). Further, the operation panel 36 receives a signal from the control unit 35, and when the paper P is not wrapped around the first heating roller 21 at the time of an emergency stop, a winding failure has occurred and a winding has occurred. If so, this is displayed.

  Next, winding detection of the image forming apparatus according to the present embodiment will be described. FIG. 5 is a diagram schematically illustrating a time transition of detected temperatures by the first and second temperature detection sensors due to an emergency stop when no wrapping occurs in the fixing device in the image forming apparatus according to the present embodiment. FIG. 6 is a schematic cross-sectional view showing a state in which the paper is wound around the first heating roller, FIG. 7 is a plan view seen from the direction A in FIG. 6, and FIG. In the image forming apparatus according to the present invention, when the winding occurs in the fixing device, it is a diagram schematically showing a time transition of the detected temperature by the first and second temperature detection sensors due to the emergency stop. Portions common to those in FIGS. 1 to 4 are denoted by common reference numerals and description thereof is omitted.

  First, as described above, during normal printing, the energization of the first heat roller 21 to the first heat source 21a is turned on / off based on the detected temperatures of the first and second temperature detection sensors 26a and 26b, thereby fixing the image. The temperature is controlled to be substantially constant. Further, a paper detection sensor 17 provided in the vicinity of the downstream side of the fixing device 12 in the transport unit 11 detects the occurrence of a transport failure such as a jam or a paper jam in the fixing device 12. Note that such a conveyance failure includes a conveyance failure caused by the winding of the paper P around the first heating roller 21.

  When the sheet detection sensor 17 detects a conveyance failure of the sheet P in the fixing device 12, the detection result is transmitted to the control unit 35, and the control unit 35 that has received the detection result forcibly in the fixing device 12. The rotation of the first heating roller 21 and the energization (heating) to the first heat source 21a are stopped (emergency stop). At this time, the control unit 35 also stops the conveyance of the paper P, the drive of the image forming unit 2, and the like.

  When the conveyance failure of the paper P occurs in the fixing device 12 as described above, the heating of the first heating roller 21 is stopped, but at the same time, the rotation of the first heating roller 21 is stopped. The heat generated on the surface is not taken away by contact with the pressure roller 23 or the paper P. For this reason, heat continues to accumulate on the surface of the first heating roller 21, and the surface temperature continues to rise for a while after the heating of the first heating roller 21 is stopped. Therefore, if the paper P does not wrap around the first heating roller 21, the first and second detected temperatures of the first and second temperature detection sensors 26a and 26b after the emergency stop are as shown in FIG. Both are higher than those at the time of fixing (see the upper right arrow in the figure).

  Thereafter, when the heat accumulated on the surface of the first heating roller 21 is released into the air, the surface temperature is lowered. Accordingly, as shown in FIG. 5, the first and second detection temperatures of the first and second temperature detection sensors 26a and 26b are substantially constant during printing (during fixing), but an emergency stop (broken line in the figure). After that, the detected temperature rises and then decreases with time.

  However, when the adhesion between the paper P and the surface of the first heating roller 21 due to toner is strong, such as when there is little margin at the leading edge of the paper P, the paper P remains attached to the first heating roller 21 and the separating member. In some cases, the paper P passes through it against the urging force of 27, and the paper P is wound as shown in FIGS. Even when such wrapping occurs, the paper detection sensor 17 does not detect the passage of the paper P, so that it is detected that a conveyance failure has occurred in the fixing device 12, and the control unit 35 that has received the detection result executes an emergency stop. .

  When the emergency stop due to the occurrence of winding of the paper P is executed in this way, as shown in FIG. 7, the first temperature detection sensor 26a detects the temperature of the non-sheet passing region on the surface of the first heating roller 21, The surface temperature can be detected without being disturbed by the paper P. However, the second temperature detection sensor 26b is disposed in the sheet passing area, and the sheet P (see the hatched area in FIG. 7) interposed between the sensor and the first heating roller 21 serves as a heat insulating material. Since the temperature transmission from the first heating roller 21 is blocked, the surface temperature of the first heating roller 21 cannot be sufficiently detected.

  As a result, as shown in FIG. 8, after the emergency stop (the emergency stop time is indicated by a broken line), the first detection temperature of the first temperature detection sensor 26a rises higher than during printing (during fixing) (right The second detection temperature of the second temperature detection sensor 26b is lower than that during printing (during fixing) (see the right downward arrow).

  Therefore, in the present invention, when the sheet detection sensor 17 detects a conveyance failure, the control unit 35 performs an emergency stop, and the first detection temperature of the first temperature detection sensor 26a after the emergency stop changes with respect to the fixing time. The presence or absence of winding around the first heating roller 21 is determined based on the difference between the second temperature detection sensor 26b and the change in the second detection temperature at the time of fixing.

  In the present embodiment, when the first detection temperature of the first temperature detection sensor 26a after the emergency stop increases (changes) and the second detection temperature of the second temperature detection sensor 26b decreases (changes), It is determined that the paper P is wound around the one heating roller 21. As a result, after an emergency stop, the difference between the first detection temperature and the second detection temperature increases with respect to the fixing time, and the second detection temperature decreases with respect to the fixing time.

  In addition, the detection temperatures of the first and second temperature detection sensors 26a and 26b are compared after a predetermined monitoring time Tm elapses from the time of emergency stop until the time Th when the first detection temperature reaches the peak. It was. That is, after the monitoring time Tm has elapsed since the emergency stop, if the temperature detected by the first temperature detection sensor 26a is higher than that at the time of fixing and the temperature detected by the second temperature detection sensor 26b is lower than that at the time of fixing, 1 It was decided that the winding of the heating roller 21 occurred. Thereby, after an emergency stop, while the 1st detection temperature continues rising, the difference with the 2nd detection temperature can be compared.

  Further, when the paper P is wound, the first heating roller 21 is rotated in the direction opposite to that at the time of fixing (counterclockwise in FIG. 6). As a result, the trailing edge of the wrapped paper P can be protruded upstream of the fixing device 12 in the conveyance direction of the paper P, and the user can easily confirm and grasp the trailing edge of the paper P.

  Further, when the paper P is wound, the control unit 35 displays the occurrence of the winding on the operation panel 36. Thereby, it is possible to reliably notify the user that the winding of the paper P has occurred. The user who has confirmed the display can open the cover (not shown) of the apparatus main body arranged to face the fixing device 12 and remove the wrapped paper P.

  On the other hand, when the paper P is not wound, the fact that the conveyance failure has occurred is displayed on the operation panel 36. As a result, it is possible to reliably notify the user that a conveyance failure has occurred. Further, it can be notified that the conveyance failure is not caused by the winding of the paper P. Further, the user who has confirmed the display can open the cover and remove the paper P that has caused the conveyance failure.

  FIG. 9 is a flowchart illustrating an example of a control procedure of the image forming apparatus according to the present embodiment. This control will be described according to the steps in FIG. 9 with reference to FIG.

  First, the power of the image forming apparatus 100 is turned on, and printing conditions such as the paper size, the number of printed sheets, and the printing magnification are manually set by an input operation by the user from the operation panel 36 or a personal computer, and the paper size is manually set by the input operation. Alternatively, when a print start instruction (print signal) is input by a start button ON after being automatically set by the original reading operation (start), detection of a paper P conveyance failure by the paper detection sensor 17 is started (step) S1), temperature detection of the surface of the first heating roller 21 by the first and second temperature detection sensors 26a and 26b is started (step S2), and printing is started (step S3).

  When the conveyance failure in the fixing device 12 is detected by the paper detection sensor 17 during printing, the control unit 35 drives the image forming unit 2 and conveys the paper P in the conveyance unit 11, as well as the first in the fixing device 12. The emergency stop which stops rotation and heating of 1 heating roller 21 is performed (step S4). At this time, the first and second temperature detection sensors 26a and 26b continue to detect the temperature of the surface of the first heating roller 21, and the control unit 35 determines whether or not the monitoring time Tm has elapsed since the emergency stop. (Step S5).

  If the monitoring time Tm has not elapsed, the process waits in step S5 until Tm has elapsed. On the other hand, if the monitoring time Tm has elapsed, it is determined whether or not the second detection temperature of the second temperature detection sensor 26b is lower than that during fixing (step S6). If the second detection temperature has decreased in step S6, the control unit 35 next determines whether or not the first detection temperature of the first temperature detection sensor 26a has increased (step S7).

  If the first detection temperature is increased in step S7, the control unit 35 determines that the paper P is wound around the first heating roller 21 (step S8), and the first heating roller 21 is fixed. And the rear end of the paper P wound around the first heating roller 21 is sent out so as to protrude to the upstream side of the fixing device 12 (step S9). After the reverse rotation, the control unit 35 displays that the wrapping has occurred on the operation panel 36 (step S10), and then ends. The user who has confirmed the display can start printing again after removing the wound paper P.

  On the other hand, when the second detection temperature of the second temperature detection sensor 26b has not decreased in step S6 and when the first detection temperature of the first temperature detection sensor 26a has not increased in step S7, the control unit No. 35 determines that the paper P has not been wrapped around the first heating roller 21 (step S11), displays that the conveyance failure has occurred on the operation panel 36 (step S12), and ends. The user who has confirmed such a display can start printing again after removing the paper P that has caused the conveyance failure.

  As described above, in the present embodiment, the sheet P for the first heating roller 21 is based on the difference in change of the first and second temperature detection sensors 26a and 26b after the emergency stop with respect to the fixing time. Therefore, it is possible to detect the occurrence of winding of the paper P around the first heating roller 21 without heating the first heating roller 21. Thereby, since the paper P is not heated, the fire from the paper P can be prevented, and it becomes safe in terms of disaster prevention.

  Further, since the presence or absence of winding can be determined by simply comparing the first and second detection temperatures of the first and second temperature detection sensors 26a and 26b, the occurrence of winding of the paper P can be easily detected. Further, since it is not compared with a reference value set in advance, the occurrence of winding is not affected by environmental factors such as a difference in power supply conditions (input power supply), the temperature of the pressure roller 23, the temperature around the fixing device 12, and the like. Can be detected. Further, even when paper P having different sizes and widths is mixedly loaded, the winding of the paper P can be detected without being affected by the type and size of the paper P.

  Further, in the present embodiment, when the first detection temperature of the first temperature detection sensor 26a after the emergency stop increases and the second detection temperature of the second temperature detection sensor 26b decreases, the sheet for the first heating roller 21 Since it is determined that the winding of P has occurred, the difference in change between the first and second detection temperatures with respect to fixing becomes clearer, and the presence or absence of winding of the paper P can be more reliably determined.

  However, the determination method is not particularly limited as long as it is possible to determine whether or not the paper P is wound based on the difference between the first and second detection temperatures after the emergency stop from the fixing time. Depending on the type, fixing temperature, environmental conditions, etc., it can be set as appropriate by preliminary experiments or the like. For example, after the emergency stop, the paper P is wound when the temperature detected by the first temperature detection sensor 26a rises from the time of fixing and the temperature detected by the second temperature detection sensor 26b is substantially the same as that at the time of fixing. It can also be judged.

  In the present embodiment, the monitoring time Tm from the emergency stop is set between the emergency stop and the time Th when the first detection temperature of the first temperature detection sensor 26a reaches the peak. While the first detection temperature continues to rise, the difference from the second detection temperature can be compared. As a result, the difference between the two changes at the time of fixing becomes clearer, and it is possible to determine whether or not the paper P has been wound in a shorter time and more reliably. However, the monitoring time Tm is not particularly limited as long as the difference in change between the first and second detection temperatures with respect to fixing can be determined, and can be set as appropriate through preliminary experiments or the like.

  In the present embodiment, since the second temperature detection sensor 26b is disposed at a position where the surface temperature of the sheet passing area of the first heating roller 21 can be detected with the sheet P wound around the first heating roller 21 interposed therebetween, The temperature detection accuracy of the temperature detection sensor 26b can be increased. In addition, since the first and second temperature detection sensors 26a and 26b are arranged along the width direction of the first heating roller 21 (perpendicular to the rotation direction), the surface temperature of the non-sheet passing region and the sheet passing region can be further increased. It can be detected with high accuracy.

  However, the arrangement of the first and second temperature detection sensors 26a and 26b detects the surface temperature of the first heating roller 21 at the time of printing and enables control to a predetermined fixing temperature. The position is not particularly limited as long as the winding of the paper P can be detected, and may be set as appropriate according to the type of toner, the material and curvature of the release layer of the first heating roller 21, and other device configurations. it can.

  When the paper P that has passed through the separation member 27 adheres to the first heating roller 21 and rotates together with the first heating roller 21, the leading edge of the paper P is in the nip with the pressure roller 23 with respect to the rotation direction of the first heating roller 21. As the sheet P moves to the downstream side, the sheet P warps and curves, so the sheet P may be peeled off from the first heating roller 21 in the middle.

  Accordingly, in consideration of such a viewpoint, the arrangement of the second temperature detection sensor 26b can be set according to the curvature of the surface of the first heating roller 21, the stiffness of the wound paper P, and the like. One heating roller 21 may be disposed in the vicinity of the downstream side of the separation member 27 with respect to the rotation direction of the heating roller 21. Accordingly, it is possible to more reliably determine whether or not the paper P is wound.

  Further, the first temperature detection sensor 26 a and the second temperature detection sensor 26 b do not have to be arranged along the width direction of the first heating roller 21, and both are different positions with respect to the rotation direction of the first heating roller 21. It can also be arranged. Further, in the present embodiment, since such a first heating roller 21 is used, it is possible to determine whether or not the sheet P is wound around the first heating roller 21 where the entire surface is a curved surface and the winding is likely to occur. Is.

  Further, in this embodiment, when the paper P is wound, the first heating roller 21 is rotated in the direction opposite to that at the time of fixing, so that the trailing end of the wound paper P is transported by the paper P rather than the fixing device 12. Projecting upstream in the direction, the user can easily confirm and grasp the trailing edge of the paper P. Thereby, it becomes easy for the user to take out the paper P wrapped around, and workability can be improved.

  As for the time required for the reverse rotation, the trailing edge of the wound paper P protrudes from the housing 12a of the fixing device 12 to the upstream side, so that the user can check the trailing edge of the paper P, grasp the trailing edge and pull it out. There is no particular limitation as long as it is fixed, and it can be set as appropriate in accordance with the length in the conveyance direction of the paper P being fixed (printed).

  Further, considering the ease of confirmation and the ease of taking out the trailing edge of the rolled paper P by the user, the first heating is performed until the trailing edge of the paper P hangs from the fixing device 12 by about 10 cm to 20 cm. It is preferable to reversely rotate the roller 21. In addition, the structure which reversely rotates the 1st heating roller 21 is not an essential component of this invention, and can also be set as the structure which does not reversely rotate.

  In the present embodiment, when the paper P is wound, the control unit 35 displays the occurrence of the winding on the operation panel 36, so that the user can be sure that the paper P has been wound. I can let you know. As a result, the user can quickly start the work of taking out the paper P that is wound, and the workability can be improved. Such display can be performed simultaneously with the reverse rotation of the first heating roller 21 or can be performed before and after the reverse rotation.

  Further, in the present embodiment, when the paper P is not wound, the fact that the conveyance failure has occurred is displayed on the operation panel 36, so that the user is surely notified that the conveyance failure has occurred. At the same time, it is possible to notify that the conveyance failure is not caused by the wrapping of the paper P, and it is possible to assist the investigation of the cause of the conveyance failure.

  In this embodiment, the fixing device 12 having the first heating roller 21 and the pressure roller 23 is used. However, the fixing device used in the image forming apparatus according to the present invention is particularly limited to the fixing device 12. It is not something.

  FIG. 10 is a schematic cross-sectional view showing a fixing device used in an image forming apparatus according to the second embodiment of the present invention. Portions common to those in FIG. 2 are denoted by common reference numerals and description thereof is omitted. The image forming apparatus 100 according to the present embodiment includes the fixing device 12 illustrated in FIG. 10 in the image forming apparatus 100 illustrated in FIG. 1.

  As shown in FIG. 10, the fixing device 12 is provided with a fixing roller 41, a second heating roller (second heating roller) 43, a fixing belt 45, and a pressure roller 23. In the fixing roller 41, for example, an elastic layer made of silicon rubber or the like is formed on a cylindrical cored bar made of aluminum. Here, the fixing roller 41 is formed of a stainless metal core and an elastic layer of a sponge-like silicon rubber layer, and the outer diameter of the roller is 32 mm.

  The fixing roller 41 is driven by a driving device 51 (see FIG. 4) so as to be able to rotate in the forward and reverse directions. At the time of fixing, the fixing roller 41 is transported downstream in the transport direction (in the direction of the white arrow). Rotate clockwise. Further, the rotation speed is the same as the conveyance speed of the paper P. With the rotation of the fixing roller 41, a fixing belt 45 and a second heating roller 43, which will be described later, rotate.

  The second heating roller 43 is made of a metal core formed of, for example, Al (aluminum), Fe (iron), SUS (stainless steel), or the like having excellent thermal conductivity. Moreover, as a core metal, the thing of the low heat capacity which is easy to produce temperature changes, such as a temperature rise and fall, is preferable, and the one where the thickness of a metal core is smaller is preferable. The thickness of the metal core can be 0.2 mm to 1.5 mm.

  Here, the second heating roller 43 is an aluminum cored bar having an outer diameter of 21.5 mm and a thickness of 0.7 mm. That is, the outer diameter of the second heating roller 43 is smaller than the outer diameter of the fixing roller 41. A second heat source (second heat source) 43a such as a halogen heater is provided inside the cored bar. Further, when the fixing roller 41 rotates, the second heating roller 43 is rotated by receiving a rotational driving force from a fixing belt 45 described later.

  The fixing belt 45 is an endless belt. For example, an elastic layer made of silicon rubber, fluorine resin, or the like is formed on the surface of a rolled metal substrate such as Ni (nickel) or SUS (stainless steel). The surface of this elastic layer is covered with a resin having excellent releasability such as a fluororesin. Here, for the fixing belt 45, a silicon rubber layer having a thickness of 0.3 mm was formed on a Ni substrate having an outer diameter of 55 mm, and a PFA layer was provided on the surface of the silicon rubber layer.

  The fixing belt 45 is wound between the fixing roller 41 and the second heating roller 43 (heating means), is given a predetermined tension, and rotates with the rotation of the fixing roller 41. Further, the pressure roller 23 contacts the fixing roller 41 with the fixing belt 45 interposed therebetween, thereby forming a nip portion through which the paper P is inserted. Here, the pressure roller 23 is formed of a stainless steel core and an elastic layer of a silicon rubber layer, and the outer diameter of the roller is 35 mm.

  Further, first and second temperature detection sensors 26a and 26b are provided in the vicinity of the upstream side of the central portion in the belt rotation direction in the portion of the fixing belt 45 that contacts the second heating roller 43, and the first temperature detection. The sensor 26a is in contact with the non-sheet passing area of the paper P at both ends in the belt width direction on the surface of the fixing belt 45, and the second temperature detection sensor 26b is opposed to the paper passing area of the paper P at a substantially central part in the belt width direction. The positions are arranged at predetermined intervals.

  Further, the separating member 27 is provided on the downstream side (left side in the drawing) of the sheet P with respect to the nip portion between the fixing roller 41 and the pressure roller 23 and adjacent to the fixing belt 45, and the first embodiment. Similarly, the downstream end is biased by the tension spring 29 so that the upstream end is close to the surface of the fixing belt 45, whereby the paper P can be separated from the fixing belt 45. It can be done. Here, a gap of 0.3 mm was formed between the separating member 27 and the fixing belt 45 as described above. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  When the conveyance failure in the fixing device 12 is detected by the sheet detection sensor 17 (see FIG. 1), the control unit 35 (see FIG. 4) causes the sheet in the conveyance unit 11 to be the same as in the first embodiment. At the same time as the conveyance of P and the driving of the image forming unit 2 are stopped, the rotation of the fixing roller 41 in the fixing device 12 and the energization (heating) of the second heating roller 43 to the second heat source 43a are stopped (emergency stop).

  At this time, as shown in FIG. 10, if the paper P is wound around the fixing belt 45, the first temperature detection sensor 26 a after the emergency stop has the first detection temperature as in the first embodiment. In the second temperature detection sensor 26b, the sheet P interposed between the surface of the fixing belt 45 serves as a heat insulating material, and the temperature transmission from the fixing belt 45 is shielded, so that the second detection temperature decreases. .

  This will be described in detail with reference to FIG. FIG. 11 is a graph showing the time transition of the temperature detected by the first and second temperature detection sensors due to an emergency stop when winding occurs in the fixing device in the image forming apparatus of this embodiment. FIG. 11 shows changes in the first and second detection temperatures of the first and second temperature detection sensors 26a and 26b when the fixing belt 45 is wound on the first printed sheet.

  For this reason, unlike FIG. 8 described above, the second detection temperature of the second temperature detection sensor 26b is higher than the first detection temperature of the first temperature detection sensor 26a during printing. Even in such a case, as the number of printed sheets increases, the first detection temperature becomes higher than the second detection temperature, and the same behavior as in FIG. 8 is exhibited.

  As shown in FIG. 11, before the start of printing, the fixing temperature of the surface of the fixing belt 45 is controlled by the control unit 35 (see FIG. 4) so that the sheet passing area is approximately 160.degree. At this time, the non-sheet passing area is approximately 180 ° C. In FIG. 11, the printing start time is set to 0 msec. When printing (fixing) in the fixing device 12 is started (indicated by the alternate long and short dash line in the figure), the surface of the fixing belt 45 is deprived of heat by contact with the pressure roller 23 and the paper P. The temperature detected by the two temperature detection sensors 26a and 26b temporarily decreases, but then returns to the fixing temperature during printing under the control of the control unit 35.

  Then, at the time of fixing the first sheet of printing, after about 24500 msec from the start of printing, the paper P is wound around the fixing belt 45, and the paper detection sensor 17 detects the occurrence of a conveyance failure in the fixing device 12. Then, the control unit 35 performs an emergency stop (indicated by a broken line in the figure).

  After the emergency stop, the first detection temperature of the first temperature detection sensor 26a continues to rise (see the upper right arrow in the figure) from the emergency stop to about 8500 msec (see the upper right arrow in the figure), and then from about 8500 msec. The maximum temperature (peak) is shown up to 39000 msec (approximately 63500 msec from the start of printing). That is, the time Th when the first detected temperature reaches the peak is approximately 8500 msec from the emergency stop. Thereafter, although the first detection temperature decreased, the first detection temperature was higher than that at the time of printing (at the time of fixing) within the time shown in FIG.

  On the other hand, in the second temperature detection sensor 26b, the second detection temperature decreases after the emergency stop (see the right downward arrow in the figure). Although the temperature once rises at about 8000 msec to about 9000 msec from the time of emergency stop (about 32500 msec to about 43500 msec from the start of printing), the second detected temperature is higher than that at the time of printing within the time shown in FIG. Was low.

  As a result, the winding of the paper P around the fixing belt 45 occurs, whereby when the paper detection sensor 17 detects a conveyance failure and the controller 35 performs an emergency stop, the first temperature detection sensor 26a performs the first stop after the emergency stop. 1 detection temperature rose and 2nd detection temperature of the 2nd temperature detection sensor 26b fell.

  In addition, the monitoring time Tm is set from the time of emergency stop until the time Th (approximately 8500 msec) when the first detection temperature of the first temperature detection sensor 26a reaches the peak, and the first and second temperature detection sensors. It has been found that the occurrence of winding of the paper P around the fixing roller 41 can be detected in a shorter time and more reliably by comparing the first and second detection temperatures of 26a and 26b. The monitoring time Tm can be set to, for example, 3000 msec from FIG.

  As described above, also in the present embodiment, after the emergency stop, the sheet P with respect to the fixing belt 45 is based on the difference between the first and second temperature detection sensors 26a and 26b when the first and second detection temperatures are fixed. It is possible to determine the presence or absence of winding. When such winding is detected, the fixing belt 45 is rotated in the reverse direction to that during printing (during fixing) in the same manner as in the first embodiment, so that the paper P is conveyed in the conveyance direction (the direction of the white arrow in FIG. 10). On the other hand, the rear end of the paper P can be projected upstream of the fixing device 12 (see FIG. 1).

  Also in the present embodiment, as in the first embodiment, the arrangement of the first and second temperature detection sensors 26a and 26b is not particularly limited as long as it can detect whether or not the paper P has been wound. However, in this embodiment, since the fixing belt 45 is stretched between the fixing roller 41 and the second heating roller 43, the second temperature detection sensor 26b is connected to the first fixing belt 45 from the viewpoint of accurately controlling the fixing temperature. 2 It is preferable to arrange at a position facing the contact portion with the heating roller 43.

  The sheet P that has passed through the separating member 27 is downstream of the fixing roller 41 and upstream of the second heating roller 43 (left side in FIG. 10) with respect to the rotation direction of the fixing belt 45 (clockwise direction in FIG. 10). , Since it adheres to a substantially flat portion of the fixing belt 45, it is relatively difficult to peel off from the fixing belt 45. However, when the contact portion between the fixing belt 45 and the second heating roller 43 is reached, the outer diameter of the second heating roller 43 is smaller than that of the fixing roller 41, that is, the curvature is larger. It becomes easy to peel off.

  Therefore, in view of such a viewpoint, when the fixing belt 45 is used, as shown in the present embodiment, the arrangement of the second temperature detection sensor 26b is set so that the contact portion of the fixing belt 45 with the second heating roller 43 is in contact. Among these, it is preferable that the fixing belt 45 is disposed so as to face the upstream side of the central portion in the rotation direction. Further, it is more preferable that the contact portion is disposed at a position facing the vicinity of the upstream end portion in the rotation direction of the fixing belt 45.

  In this embodiment, since the fixing belt 45 is used as described above, whether or not the paper P is wound around the fixing belt 45 even if the fixing belt 45 in which a flat portion and a curvature portion coexist in the rotation locus are used. Since it can be judged, it is effective.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, a contact type thermistor is used as the first temperature detection sensor 26a. However, the first temperature detection sensor 26a may be a non-contact type thermistor. In the above embodiment, since the separation member 27 is provided, the detection of the winding of the paper P becomes more effective. However, the separation member depends on how easily the paper P adheres to the first heating roller 21 or the fixing belt 45. 27 may be omitted.

  The image forming apparatus to which the present invention can be applied can be applied to various image forming apparatuses such as a digital copying machine, an analog copying machine, and a laser beam printer, regardless of whether it is for color or monochrome.

  In the present invention, a conveyance failure detection unit that detects a conveyance failure of the recording medium in the fixing device is provided in the conveyance path, and when the conveyance failure detection unit detects the conveyance failure, the control unit detects the heating and rotation of the heating unit. The stop is executed, and the presence or absence of occurrence of winding of the recording medium around the heating unit is determined based on the difference in change between the first and second detected temperatures after the stop.

  As a result, it is possible to detect the occurrence of winding of the recording medium around the heating means without heating the heating means in the fixing device. it can. Further, after the predetermined time has elapsed since the stop, when the first detection temperature rises and the second detection temperature decreases with respect to the fixing time, it is determined that winding has occurred, so that the recording medium with respect to the heating unit is detected. Winding can be detected more reliably, and by setting the predetermined time from the stop to the time when the first detected temperature rises at the time of fixing reaches the peak, the winding of the recording medium can be performed in a shorter time and It can be detected reliably.

  Further, by arranging the second temperature detection means at a position where the surface temperature of the passage area can be detected with the recording medium wound around the heating means interposed therebetween, the temperature detection accuracy by the second temperature detection means can be improved. it can. In addition, when the display unit is provided and the control unit determines that the winding has occurred, the occurrence of the winding is displayed on the display unit, thereby improving the workability of the user. In addition, when the control unit determines that the winding has occurred, the workability of the user can be improved by rotating the heating unit in the direction opposite to that at the time of fixing.

  Moreover, it becomes effective by making a heating means into the 1st heating roller which has a 1st heat source inside. Further, the heating means includes a second heating roller having a second heat source therein, a fixing roller, and a fixing belt which is stretched around the second heating roller and the fixing roller and is rotatable. The pressure means is effective by contacting the fixing roller via the fixing belt to form a nip portion. Further, by using the pressure roller as the pressure roller, it is possible to reduce the influence on the damage and rotation of the heating device.

11 Transport section (transport path)
12 Fixing device 17 Paper detection sensor (conveyance failure detection means)
21 1st heating roller (1st heating roller, heating means)
21a First heat source (first heat source)
23 Pressure roller (Pressure means)
26a First temperature detection sensor (first temperature detection means)
26b 2nd temperature detection sensor (2nd temperature detection means)
27 Separating member 29 Tension spring 34 Storage unit 35 Control unit (control means)
36 Operation panel (display means)
41 Fixing roller (heating means)
43 Second heating roller (second heating roller, heating means)
43a Second heat source (second heat source)
45 Fixing belt (heating means)
51 Driving Device 100 Image Forming Device

Claims (7)

A transport path for transporting the recording medium;
A heating unit that is rotatable, and a pressurizing unit that abuts on the heating unit to form a nip portion, and the nip portion A fixing device for fixing the toner image to the recording medium by being inserted into the recording medium;
A first temperature detecting means for detecting the temperature of the non-passing area of the recording medium on the surface of the heating means; a second temperature detecting means for detecting the temperature of the passing area;
An image forming apparatus comprising: control means capable of controlling the surface of the heating means at a predetermined fixing temperature during fixing based on the first and second detected temperatures by the first and second temperature detecting means; In
The conveyance path is provided with a conveyance failure detection means for detecting a conveyance failure of the recording medium in the fixing device.
The control unit executes heating and rotation stop of the heating unit when the conveyance failure detection unit detects the conveyance failure, and after a predetermined time has elapsed from the stop time, the first control unit performs the first operation with respect to the fixing time. When the detection temperature rises and the second detection temperature decreases, it is determined that the winding has occurred ,
The image forming apparatus according to claim 1, wherein the predetermined time is set from the time of the stop to the time when the rise of the first detected temperature reaches a peak . The image forming apparatus according to claim 1, wherein the second temperature detection unit is disposed at a position where the temperature of the passage region can be detected with a recording medium wound around the heating unit interposed therebetween. 3. The image forming apparatus according to claim 1, further comprising: a display unit configured to display the occurrence of the winding on the display unit when the control unit determines that the winding has occurred. Said control means, when with the winding is determined to have occurred, the image forming apparatus according to any one of claims 1 to 3, characterized in that rotating the heating means in the opposite direction as when the fixing. It said heating means, the image forming apparatus according to any one of claims 1 to 4, characterized in that a first heating roller having a first internal heat source. The heating means includes a second heating roller having a second heat source therein, a fixing roller, and a fixing belt that is stretched around the second heating roller and the fixing roller and is rotatable.
The pressurizing means, the image forming apparatus according to any one of claims 1 to 4, characterized in that to form the nip portion in contact with the fixing roller via the fixing belt. The pressurizing means, the image forming apparatus according to any one of claims 1 to 6, characterized in that a pressure roller.

Images