JP6507831B2 - Fixing device and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus. More particularly, the present invention relates to a fixing device and an image forming apparatus for fixing a toner image on a sheet by applying heat and pressure.

  Conventionally, in an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine including these functions in combination, an image is formed on a sheet by fixing a toner image transferred onto the sheet by a fixing device. doing. The fixing device passes a sheet to a fixing nip formed by pressing a pair of fixing members and performs fixing processing by heating and pressing the sheet in the passing state. For this reason, the fixing device is provided with a heating source for heating the fixing nip to a fixing temperature at which the fixing process is performed.

  In addition, some fixing devices are provided with a current interruption unit such as a thermostat to prevent the heating temperature by the heat source from excessively rising above the fixing processing temperature at which the fixing processing is performed. . That is, when the heating unit causes overheating due to the heat source and the heat sensitive unit of the current interruption unit rises to the operating temperature or higher, the power interruption unit shuts off the power supply to the heating source. Thereby, the temperature of the heating source is prevented from rising excessively. In addition, it is preferable that the power interruption unit can stop power supply to the heating source as early as possible when overheating occurs due to the heating source.

  For example, Patent Document 1 discloses a technology in which the distance between the current blocking portion and the fixing roller heated by the heating source is different according to the environmental temperature of the current blocking portion. In other words, Patent Document 1 describes a technique for moving the current-blocking portion away from the fixing roller as the environmental temperature of the current-blocking portion is higher. As a result, even if the temperature of the fixing roller is not sufficiently increased, the supply of electricity to the heating source can be promptly stopped by the energization interrupting unit when overheating occurs due to the heating source. ing.

JP 2008-076912 A

  By the way, in recent years, the temperature rise rate by heating of a heat source is required to be higher. The purpose is to shorten the warm-up time and the time for raising the fixing member to the fixing processing temperature. Along with this, it is necessary to stop the heating by the heating source earlier when the heating by the heating source occurs.

  However, the degree of temperature rise of the current interruption part becomes gentler than the heat source. This is because the temperature rise of the current interruption part is delayed from the temperature rise of the heat source by the time when the heat is transferred from the heat source to the fixing member and the heat is transferred from the fixing member to the current interruption part. Further, in the technology as described in Patent Document 1 described above, a gap is provided between the current blocking portion and the fixing roller. As a result, the time for the heat to move from the fixing roller to the current interruption portion tends to be long. For this reason, it is not easy to shorten the time from the temperature of the heat source to reach the operating temperature until the temperature of the de-energizer to reach the operating temperature.

  Further, in the technology as described in Patent Document 1 described above, when the configuration for moving the current interruption unit does not function due to a failure or the like, overheating of the heating source occurs in a state where the temperature of the fixing roller is not sufficiently increased. In such a case, there is a risk that the power interruption unit does not function properly. Therefore, when the overheating | superheat by a heat source arises, there existed a case where the heating by a heat source could not be stopped appropriately by the electricity supply interruption part.

  The present invention has been made for the purpose of solving the problems of the above-mentioned prior art. That is, it is an object of the present invention to provide a fixing device and an image forming apparatus capable of appropriately suppressing overheating due to a heating source.

The fixing device of the present invention, which has been made for the purpose of solving this problem, performs fixing processing of fixing a toner image on a sheet by passing a sheet carrying unfixed toner through a fixing nip of a pair of fixing members. The apparatus includes a fixing heating unit that receives power supply and heats at least one of the pair of fixing members during fixing processing, and a heat sensing unit provided toward the fixing member that receives heating by the fixing heating unit. In addition, when the temperature of the heat-sensitive unit is equal to or higher than a predetermined operating temperature, the distance between the heat-sensitive unit and the power-off unit that shuts off the power supply path to the fixing heating unit is shorter than that of the fixing heating unit. A thermal-sensitive heating unit that heats the thermal-sensitive unit within a temperature range lower than the operating temperature; a thermal-heating determination unit that performs determination control to determine whether or not the thermal-sensitive heating unit operates normally ; temperature And the heat-sensitive temperature output unit for outputting a thermal temperature index value index, the power mode for supplying power to the heat-fixing unit, and the normal mode for supplying a normal power for heating the fixing member to a fixing heating unit, a fixing heating The fixing power control unit switches the normal mode to the initialization mode, and the thermal control unit is normal by the determination control. If it is determined that the state is the case , and if the heat-sensitive temperature index value output by the heat-sensitive temperature output unit falls under at least one of the predetermined threshold values , the normal mode is maintained, and judgment control is performed. it is determined that the heat-sensitive heating section is not normal state, and, when the heat-sensitive temperature index value output from the heat-sensitive temperature output section is less than the threshold value, switches from the normal mode to the limitation mode A fixing device, characterized in that the shall.

In the fixing device of the present invention, in the normal mode, the temperature rise rate of the heat sensitive portion can be increased by heating by the heat sensitive heating portion. As a result, it is possible to shorten the time from the temperature of the heat source to reach the operating temperature until the temperature of the de-energizer to reach the operating temperature. In the limit mode, for example, the heating by the fixing heating unit can be stopped to suppress the overheating of the fixing heating unit. Alternatively, in the limit mode, heating by the fixing heating unit is performed so as to lower the rate of temperature rise, and the temperature rise can be appropriately followed even by the thermosensitive section when there is no heating by the heat sensitive heating section. Therefore, in the fixing device of the present invention, overheating by the heat source can be appropriately suppressed. Furthermore, when the heat sensitive temperature index value outputted by the heat sensitive temperature output unit is equal to or more than a predetermined threshold value, the normal mode is maintained regardless of whether the heat sensitive heating unit is in the normal state. This is because, when the temperature of the heat sensitive part is high to some extent, the temperature of the heat sensitive part can appropriately follow the temperature rise of the fixing heating part in the normal mode even if there is no heating by the heat sensitive heating part. is there.

  Further, in the fixing device described above, the heat sensitive heating unit receives power to generate heat, and the heat sensitive heating judgment unit supplies power during a power supply period in which power is supplied to the heat sensitive heating unit. While having a power index value output unit that detects and outputs a power index value that indexes the power being supplied, and the power index value output by the power index value output unit is within a predetermined normal range, the normal state If the power index value is out of the normal range, it may be determined that the state is not normal.

  Preferably, in the fixing device described above, the fixing power control unit does not supply power to the fixing heating unit in the limit mode. By stopping heating by the fixing heating unit, it is possible to suppress overheating of the fixing heating unit.

  In the fixing device described above, it is preferable that the fixing power control unit supplies less power to the fixing heating unit in the limit mode than in the normal mode. This is because heating by the fixing heating unit can be performed so that the temperature rise rate becomes low, and the temperature rise can be appropriately followed even by the heat sensitive unit when there is no heating by the heat sensitive heating unit. In addition, the fixing process can be continued even in the limit mode.

  The fixing device described above further includes a fixing temperature output unit for outputting a fixing temperature index value indicating a temperature of the fixing member heated by the fixing heating unit, and the fixing power control unit performs fixing in the limit mode. When the temperature of the fixing temperature index value output by the temperature output unit is high, power is supplied to the fixing heating unit so that the temperature increase rate of the fixing heating unit is lower than that in the normal mode. Is preferred. That is, by lowering the temperature rise rate of the fixing heating unit as the temperature of the fixing member increases, the temperature can be raised in a short time until the fixing processing temperature. When the fixing heating unit is overheated, the temperature of the fixing heating unit can be suppressed from rising.

  Further, according to the present invention, a conveyance unit for conveying a sheet, an image forming unit for forming a toner image and transferring the formed toner image onto the sheet, and a downstream side of the image forming unit in the sheet conveyance direction The present invention also extends to an image forming apparatus characterized by including the fixing device described above.

  According to the present invention, there are provided a fixing device and an image forming apparatus capable of appropriately suppressing overheating due to a heating source.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 2 is a schematic view of a control configuration of the image forming apparatus according to the embodiment. FIG. 1 is a schematic configuration view of a fixing device according to an embodiment. FIG. 2 is a schematic view of a control configuration of the fixing device according to the embodiment. FIG. 6 is a diagram for explaining temperature transition when overheating of the fixing heater occurs. It is a flowchart which shows the procedure of switching with the normal mode and restriction | limiting mode which concern on a 1st reference form . It is a timing chart which shows the time of normal concerning a 1st reference form . It is a timing chart which shows the time of abnormality concerning the 1st reference form . It is a flowchart which shows the procedure of switching with the normal mode and restriction | limiting mode which concern on a 2nd reference form . FIG. 7 is a diagram for explaining temperature transition when overheating of the fixing heater occurs in a state where the temperature at the heating start time is high. It is a flowchart which shows the procedure of switching with the normal mode which concerns on a 1st form , and a restriction mode. It is a flowchart which shows the procedure of switching with the normal mode which concerns on a 2nd form , and a restriction mode. FIG. 17 is a diagram for explaining temperature transition when overheating of the fixing heater occurs in the limit mode according to the second embodiment .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. This embodiment is an embodiment of the present invention in an electrophotographic printer.

[ First embodiment ]
FIG. 1 shows a schematic configuration of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 is a so-called tandem type color printer having an intermediate transfer belt 30. The intermediate transfer belt 30 is an endless belt member having conductivity, and both ends in FIG. 1 are supported by rollers 31 and 32. At the time of image formation, the roller 31 on the right side in FIG. 1 is rotationally driven counterclockwise. As a result, the intermediate transfer belt 30 and the roller 32 on the left side in FIG. 1 are each driven to rotate in the direction indicated by the arrow in the figure.

  A secondary transfer roller 40 is provided on the outer peripheral surface of a portion of the intermediate transfer belt 30 supported by the roller 31 on the right side in FIG. The secondary transfer roller 40 is pressed against the intermediate transfer belt 30 in a direction (leftward in FIG. 1) perpendicular to the axis. At a portion where the intermediate transfer belt 30 and the secondary transfer roller 40 are in contact with each other, a transfer nip N1 for transferring the toner image on the intermediate transfer belt 30 to the sheet P is formed. During image formation, the secondary transfer roller 40 is driven to rotate by the frictional force caused by pressure contact with the rotating intermediate transfer belt 30.

  Further, a belt cleaner 41 is provided on the outer peripheral surface of a portion of the intermediate transfer belt 30 supported by the roller 32 on the left side in FIG. The belt cleaner 41 is in pressure contact with the outer peripheral surface of the intermediate transfer belt 30. Further, a recovery area 42 for recovering residual transfer toner not transferred to the sheet P at the transfer nip N1 is formed by the portion in contact by the pressure contact.

  The lower portion of the intermediate transfer belt 30 in FIG. 1 in the order from left to right, yellow (Y), magenta (M), cyan (C), and black (K) image forming portions 10Y, 10M, 10C, 10K is arranged. Each of the image forming units 10Y, 10M, 10C, and 10K is for forming a toner image of the corresponding color and transferring it onto the intermediate transfer belt 30. The image forming units 10Y, 10M, 10C, and 10K all have the same configuration. For this reason, in FIG. 1, the image forming unit 10Y is represented by a symbol.

  The image forming units 10Y, 10M, 10C, and 10K include the photosensitive member 11 which is a cylindrical electrostatic latent image carrier, and the charger 12, the developing device 14, and the photosensitive member cleaner 16 disposed around the photosensitive member. doing. Further, a primary transfer roller 15 is disposed at a position opposite to the photosensitive member 11 with the intermediate transfer belt 30 interposed therebetween. Further, an exposure device 13 is disposed below the image forming units 10Y, 10M, 10C, and 10K of the respective colors in FIG.

  The charger 12 is for charging the surface of the photosensitive member 11 uniformly. The exposure device 13 is for irradiating the surface of each photosensitive member 11 with a laser beam based on image data to form an electrostatic latent image. The developing device 14 is for applying the toner contained therein to the surface of the photosensitive member 11.

  The primary transfer roller 15 is pressed against the intermediate transfer belt 30 in the direction perpendicular to the axis (downward in FIG. 1). As a result of this pressure contact, primary transfer nips for transferring the toner images on the photosensitive members 11 of the respective colors onto the intermediate transfer belt 30 are formed at the portions where the intermediate transfer belt 30 and the photosensitive members 11 are in contact. There is. The photoconductor cleaner 16 is for collecting the toner not transferred onto the intermediate transfer belt 30 from the photoconductor 11.

  Although FIG. 1 shows a roller charging system having a roller shape as the charger 12, the present invention is not limited to this. A corona discharge type charger, a blade-shaped charging member, or a brush-shaped charging member may be used. In addition, although the plate-like photosensitive member cleaner 16 is shown in which one end is in contact with the outer peripheral surface of the photosensitive member 11, the present invention is not limited to this. Other cleaning members may be used, such as fixed brushes, rotating brushes, rollers or combinations of several of these. Alternatively, if a cleanerless method is employed in which the non-transferred toner on the photosensitive member 11 is collected by the developing device 14, the photosensitive member cleaner 16 may not be necessary.

  Further, hoppers 17Y, 17M, 17C, and 17K containing toners of respective colors are disposed above the intermediate transfer belt 30 in FIG. The toners of the respective colors stored in these are appropriately supplied to the developing device 14 of the corresponding color.

  A density sensor for detecting the image density of the toner image transferred onto the intermediate transfer belt 30 at a position downstream of the image forming unit 10K in the rotational direction of the intermediate transfer belt 30 and upstream of the transfer nip N1. 20 are provided. The density sensor 20 uses the outer peripheral surface of the intermediate transfer belt 30 as a detection position. The density sensor 20 has, for example, a light emitting unit used to adjust the image density, which emits light toward the detection position, and a light receiving unit that receives the reflected light.

  A removable paper feed cassette 51 is attached to the lower part of the image forming apparatus 1. A conveying path 50 is provided upward from the right side of the sheet feeding cassette 51 in FIG. Then, the sheets P stored in the sheet feeding cassette 51 by being stacked are sent out by the sheet feeding roller 52 to the conveyance path 50 one by one from the uppermost sheet.

  A pair of registration rollers 53, a transfer nip N1, a fixing device 60, and a sheet discharge roller 54 are disposed in this order in the conveyance path 50 of the sheet P fed by the sheet feed roller 52. A paper discharge unit 55 is provided on the upper surface of the image forming apparatus 1 which is further downstream of the conveyance path 50. The registration roller 53 is for adjusting the timing at which the sheet P is fed to the transfer nip N1. The fixing device 60 is for performing fixing processing of the toner image transferred to the sheet P by heating and pressing the sheet P at the fixing nip N2.

  Next, an example of a normal image forming operation by the image forming apparatus 1 of the present embodiment will be briefly described. The following description is an example of the image forming operation in the case of forming a color image on a sheet P stored in the sheet feeding cassette 51 using four color toners.

  At the time of forming a color image, first, the intermediate transfer belt 30 and the photosensitive members 11 of respective colors are respectively rotated at a predetermined circumferential speed in the direction indicated by the arrows in FIG. The outer peripheral surface of the photosensitive member 11 is substantially uniformly charged by the charger 12. A light corresponding to the image data is projected by the exposure device 13 on the outer peripheral surface of the charged photosensitive member 11 to form an electrostatic latent image. Subsequently, the electrostatic latent image is developed by the developing device 14, and a toner image is formed on the photosensitive member 11.

  The toner image formed on each photosensitive member 11 is transferred (primary transfer) onto the intermediate transfer belt 30 by the primary transfer roller 15. As a result, toner images of yellow, magenta, cyan and black are superimposed on the intermediate transfer belt 30 in this order. Then, the four color toner images superimposed are conveyed to the transfer nip N1 by the rotation of the intermediate transfer belt 30. Further, the transfer residual toner which is not transferred to the intermediate transfer belt 30 and remains on the photosensitive member 11 after passing the primary transfer roller 15 is scraped off by the photosensitive member cleaner 16 and removed from the photosensitive member 11 Be done.

  On the other hand, the sheets P stored in the sheet feeding cassette 51 are pulled out one by one to the conveyance path 50 from the uppermost sheet. The pulled out sheet P is transported to the transfer nip N1 along the transport path 50. The entry timing of the sheet P into the transfer nip N1 is adjusted by the registration roller 53 so as to coincide with the entry timing of the toner image on the intermediate transfer belt 30 into the transfer nip N1. As a result, the four color toner images superimposed on each other are transferred (secondary transfer) onto the sheet P at the transfer nip N1.

  The sheet P on which the toner image has been transferred is further transported to the downstream side of the transport path 50. That is, after the toner image is fixed by the fixing device 60, the sheet P is discharged to the sheet discharge unit 55 by the sheet discharge roller 54. The transfer residual toner remaining on the intermediate transfer belt 30 after passing through the transfer nip N1 is collected by the belt cleaner 41 in the collection area 42. Thus, the intermediate transfer belt 30 is removed.

  FIG. 2 shows an outline of a control configuration of the image forming apparatus 1. The image forming apparatus 1 includes an engine unit 2 and a controller unit 3 in order to control each unit. The engine unit 2 has a CPU 4 that performs overall control processing, and a non-volatile memory 5 attached to the main body.

  The non-volatile memory 5 stores various values for performing image formation and the like of the image forming apparatus 1. For example, values known in design, such as the distance on the transport path 50 from the sheet feeding cassette 51 to the fixing nip N2, the system speed which is the speed at which the sheet P and the formed toner image are transported, are stored. In addition, a fixing processing temperature at which the toner image can be appropriately fixed to the sheet P by the fixing processing by the fixing device 60 is also stored.

  The CPU 4 controls each part of the image forming apparatus 1 based on the value stored in the non-volatile memory 5. For example, by adjusting the timing of the start of formation of electrostatic latent images by the respective exposure devices 13, a color toner image having no misalignment is formed on the intermediate transfer belt 30. In addition, by adjusting the timing at which the image forming units 10Y, 10M, 10C, and 10K form an image and the timing at which the sheet P is fed from the sheet feeding cassette 51, the rushing timing to the transfer nip N1 matches Control.

  Further, the CPU 4 of this embodiment has a fixing heater control unit 8 and a bimetal heater control unit 9. The fixing heater control unit 8 and the bimetal heater control unit 9 are for controlling the fixing device 60 so that the fixing process is appropriately performed by the fixing device 60. The fixing heater control unit 8 and the bimetal heater control unit 9 will be described in detail later.

  The engine unit 2 controls various units 6 included in the image forming apparatus 1 and performs writing and reading of nonvolatile memories 7 attached to the various units. The various units 6 include, for example, an imaging unit. Then, for the non-volatile memory 7 attached to various units, for example, the number of images formed by the imaging unit is stored in the memory attached to the imaging unit.

  The controller unit 3 is connected to an external personal computer or the like to receive an instruction input. For example, an image forming job is generated in the image forming apparatus 1 by receiving an image forming command from a personal computer. Further, various information such as dot counter values are exchanged between the engine unit 2 and the controller unit 3.

  Next, the fixing device 60 of this embodiment will be described. FIG. 3 is a cross-sectional view showing a schematic configuration of the fixing device 60 of the image forming apparatus 1. The fixing device 60 includes a pressure roller 61, a fixing pad 62, a fixing belt 63, and a fixing heater 64. The fixing pad 62 and the pressure roller 61 are both long members in the depth direction in FIG. 3 and are arranged in parallel to each other.

  The fixing pad 62, the fixing belt 63, and the fixing heater 64 are disposed on the side of the sheet P carrying the toner image of the sheet P passing through the fixing nip N2. The fixing pad 62, the fixing belt 63, and the fixing heater 64 have a heating side configuration for heating the sheet P passing through the fixing nip N2.

  On the other hand, the pressure roller 61 on the pressure side facing the configuration on the heating side and the transport path 50 is pressed against the fixing belt 63 in the direction perpendicular to the axis. Thus, the endless fixing belt 63 is sandwiched between the fixing pad 62 and the pressure roller 61. A fixing nip N2 for performing a fixing process on the sheet P is formed at a pressure contact position between the fixing belt 63 and the pressure roller 61.

  Further, when the fixing process is performed, the pressure roller 61 is rotationally driven in the direction shown by the arrow in FIG. As a result, the fixing belt 63 is also driven to rotate by the frictional force due to the pressure contact of the pressure roller 61 rotating during the fixing process.

  The fixing heater 64 is disposed on the inner peripheral side of the fixing belt 63 and is for heating the fixing belt 63. A reflecting plate 65 is provided between the fixing heater 64 and the fixing nip N2. The reflection plate 65 is for suppressing direct heating of the fixing nip N2 by the fixing heater 64.

  That is, in the fixing device 60 of this embodiment, the portion on the left side in FIG. 3 other than the vicinity of the fixing nip N2 of the fixing belt 63 faces the fixing heater 64. Therefore, the portion of the fixing belt 63 other than the vicinity of the fixing nip N 2 is directly heated by the fixing heater 64. Therefore, the fixing device 60 of this embodiment is configured to have a short warm-up time and a short time of temperature rise up to the fixing processing temperature.

  Further, as shown in FIG. 3, the fixing device 60 of this embodiment has a temperature sensor 66. The temperature sensor 66 is, for example, a non-contact infrared sensor or the like, and can detect the surface temperature of the fixing belt 63.

  Further, as shown in FIG. 3, the fixing device 60 of the present embodiment has a current interruption unit 70. The current interruption unit 70 is provided in the vicinity of the fixing belt 63 with an interval. That is, since the current blocking portion 70 is not in contact with the fixing belt 63, the surface of the fixing belt 63 is not scratched. Further, when the temperature becomes equal to or higher than the operating temperature, the power interruption unit 70 can shut off the supply of power to the fixing heater 64. The energization interrupting unit 70 will be described in detail with reference to FIG.

  FIG. 4 shows an outline of a control configuration of the fixing device 60 of this embodiment. As described above, the CPU 4 includes the fixing heater control unit 8 and the bimetal heater control unit 9. Further, FIG. 4 shows the fixing belt 63, the fixing heater 64, the temperature sensor 66, and the current interruption unit 70 in the configuration of the fixing device 60. Further, FIG. 4 shows a fixing heater power supply 67 which is a power supply for supplying power to the fixing heater 64.

  The fixing heater control unit 8 controls the fixing heater power supply 67 so that the temperature of the fixing belt 63 detected by the temperature sensor 66 becomes the predetermined fixing processing temperature at the time of fixing processing. The temperature of the fixing belt 63 detected by the temperature sensor 66 is output by a temperature output unit 68 provided in the CPU 4.

  For example, the fixing heater control unit 8 according to the present embodiment determines the heating start time for starting the supply of power to the fixing heater 64 from the fixing heater power supply 67. The heating start time can be determined by the fixing rise time in which the temperature of the fixing belt 63 at the fixing nip N2 rises to the fixing processing temperature by the heating of the fixing heater 64. That is, the heating start time can be determined as the timing before the fixing rise time or more before the time when the sheet P fed from the sheet feeding cassette 51 reaches the fixing nip N2. As the fixing rise time, for example, the time obtained by conducting an experiment in advance may be stored in the non-volatile memory 5 attached to the main body, and the stored value may be used. Therefore, the fixing heater control unit 8 can determine the heating start time based on the image forming job input to the image forming apparatus 1.

  Furthermore, the fixing heater control unit 8 according to the present embodiment controls the power supplied from the fixing heater power supply 67 to the fixing heater 64 while switching between the normal mode and the restriction mode. The fixing heater control unit 8 sets the initial setting mode to the normal mode. More specifically, in the normal mode, the fixing heater control unit 8 supplies the fixing heater power supply 67 with the normal power required for the fixing heater 64 to heat the fixing belt 63. In the normal mode, the fixing heater control unit 8 supplies power to the fixing heater power supply 67 so that the temperature of the fixing belt 63 rises to the fixing processing temperature in as short time as possible. On the other hand, in the limit mode, the fixing heater control unit 8 according to the present embodiment prevents power from being supplied to the fixing heater 64 from the fixing heater power supply 67. The switching between the normal mode and the limit mode will be described in detail later.

  In addition, as shown in FIG. 4, the current interruption unit 70 of this embodiment includes a bimetal 71, a contact unit 72, and a bimetal heater 73. The shape of the bimetal 71 is different between the operating temperature of the electric current interruption unit 70 and the operating temperature of the electric current interruption unit 70 or higher. That is, the bimetal 71 is deformed when heated from below the operating temperature to at least the operating temperature, and returns to its original shape when cooled from above the operating temperature to below the operating temperature. The operating temperature at which the bimetal 71 is deformed is a temperature higher than the fixing processing temperature.

  The contact portion 72 of the energization blocking portion 70 is provided in the middle of a circuit in which the fixing heater power supply 67 and the fixing heater 64 are connected. The contact portion 72 can take an energized position shown by a solid line in FIG. 4 and a cut-off position shown by a two-dot chain line. Specifically, the contact portion 72 is in a state in which the fixing heater power supply 67 can supply power to the fixing heater 64 at the energized position.

  On the other hand, the contact portion 72 can be in a state where power is not supplied to the fixing heater 64 by the fixing heater power supply 67 at the blocking position. When the temperature of the bimetal 71 is less than the operating temperature, the contact portion 72 takes the energized position, and when the temperature of the bimetal 71 becomes higher than the operating temperature and deforms, the contact portion 72 takes the blocking position due to the deformation of the bimetal 71. Is configured. That is, the current interruption unit 70 of the present embodiment is a mechanical thermostat based on the deformation of the bimetal 71.

  When the bimetal 71 is lower than the operating temperature of the bimetal 71, the energization blocking unit 70 according to the present embodiment brings the fixing heater 64 into a heatable state in which heating can be performed. On the other hand, the current interruption unit 70 operates when the bimetal 71 is at the operating temperature or more, and sets the fixing heater 64 in a non-heatable state where heating can not be performed.

  In addition, the current blocking unit 70 is provided with the bimetal 71 facing the fixing belt 63. For this reason, the energization cutoff unit 70 is activated when the fixing belt 64 is heated to a temperature higher than the operating temperature by the fixing heater 64 and the fixing heater 64 is rendered unheatable. Can.

  The bimetal heater 73 provided in the energization blocking unit 70 of the present embodiment can generate heat under the control of the bimetal heater control unit 9. The bimetal heater 73 is provided at a position where the distance between the bimetal heater 73 and the bimetal 71 is shorter than the distance between the fixing heater 64 and the bimetal 71. That is, the bimetal heater 73 is a heater for heating the bimetal 71 provided in the vicinity of the bimetal 71. In addition, the bimetal heater 73 can heat the bimetal 71 at a temperature lower than the operating temperature when heat is generated. The bimetal heater 73 of this embodiment heats the bimetal 71 at a temperature lower than the fixing processing temperature.

  In this embodiment, as the bimetal heater 73, a resistive heating element that generates heat by the supply of power is used. For this reason, the bimetal heater 73 has a power supply for supplying power. As a power supply of the bimetal heater 73, a fixing heater power supply 67 may be used. Alternatively, a power supply different from the fixing heater 64 can be used.

  Further, in the bimetal heater 73 of the present embodiment, the resistance value rises as the temperature rises. Furthermore, the bimetal heater 73 of this embodiment has a characteristic that the temperature does not rise any further due to the increase of the resistance value when the upper limit temperature is reached. And, in the present embodiment, the upper limit temperature of the bimetal heater 73 is a temperature lower than the operating temperature. For this reason, the current interruption unit 70 operates by heating only the bimetal heater 73, and the fixing heater 64 will not be in a non-heatable state.

  Here, when the fixing heater 64 is overheated in the fixing device 60, it is preferable that the fixing heater 64 be made into a non-heatable state promptly. When the fixing heater 64 is overheated, the fixing heater 64 may not be properly controlled by the fixing heater control unit 8. Furthermore, as described above, the fixing device 60 is of a specification that can raise the temperature of the fixing belt 63 in a short time. For this reason, in the present embodiment, when overheating occurs due to the fixing heater 64, it is preferable to stop the heating due to the fixing heater 64 earlier.

  Further, heat generated by the heat generated by the fixing heater 64 is transferred to the bimetal 71 via the fixing belt 63. Further, in the present embodiment, the bimetal 71 is disposed with a gap between the bimetal 71 and the fixing belt 63. Therefore, the rate of increase of the temperature of the bimetal 71 due to the heating of the fixing heater 64 is lower than the rate of increase of the temperature of the fixing heater 64. In particular, when the temperature of the bimetal 71 is low, the rate of increase of the temperature of the bimetal 71 tends to be lower than the rate of increase of the temperature of the fixing heater 64.

  FIG. 5 shows the temperature transition when the fixing heater 64 is overheated. In FIG. 5, the horizontal axis represents time, and the vertical axis represents temperature. Further, in FIG. 5, the temperature transition of the fixing belt 63 is indicated by a two-dot chain line, and the temperature transition of the bimetal 71 is indicated by a solid line and a broken line. The solid line shows the temperature transition of the bimetal 71 when the bimetal 71 is heated by the bimetal heater 73. On the other hand, the broken line shows the temperature transition of the bimetal 71 when the heating by the bimetal heater 73 is not performed. The two-dot chain line in FIG. 5 indicates the temperature transition when overheating occurs when heating by the fixing heater 64 is performed in the normal mode.

  In FIG. 5, the temperature of the fixing belt 63 rises from room temperature Ta from the heating start time t1, and reaches the fixing processing temperature Tc at time t3 when the fixing rise time has elapsed. Further, the temperature of the fixing belt 63 continues to rise after time t3 in FIG. 5 where the fixing heater 64 is overheated.

  The temperature of the bimetal 71 in the presence of the heating of the bimetal heater 73 indicated by the solid line is slightly later than the temperature of the fixing belt 63 indicated by the two-dot chain line, but rises at almost the same temperature rise rate as the fixing belt 63. ing. The temperature of the bimetal 71 when the bimetal heater 73 is heated reaches the operating temperature Td at time t4. Therefore, when the bimetal heater 73 is heated, the fixing heater 64 is incapable of heating at time t4. The temperature of the fixing belt 63 is the temperature Te at time t4 at which the fixing heater 64 can not be heated.

  On the other hand, the temperature of the bimetal 71 when heating of the bimetal heater 73 shown by a broken line is not performed is rising behind the temperature of the fixing belt 63 shown by a two-dot chain line. That is, when the bimetal heater 73 is not heated, the temperature of the bimetal 71 hardly rises until the time t2 at which the temperature Tb is reached after the heating start time t1, as shown in FIG. For this reason, when the bimetal heater 73 is not heated, the temperature of the bimetal 71 can not properly follow the rise of the temperature of the fixing belt 63.

  The temperature of the bimetal 71 when the bimetal heater 73 is not heated rises at almost the same rate as the temperature rise rate of the fixing belt 63 after time t2 when the temperature Tb is reached. The temperature of the bimetal 71 when the bimetal heater 73 is not heated reaches the operating temperature Td at time t5. Therefore, when the bimetal heater 73 is not heated, the fixing heater 64 is incapable of heating at time t5.

  When the bimetal heater 73 is not heated, the fixing heater 64 can not be heated at time t5, which is later than the time when the bimetal heater 73 is heated, the fixing heater 64 can not be heated. is there. Further, since the fixing heater 64 is overheated, the temperature of the fixing belt 63 continues to rise also from time t4 to time t5. Therefore, temperature Tf at time t5 when fixing heater 64 can not be heated when bimetal heater 73 is not heated is the temperature at time t4 when fixing heater 64 is not heated when bimetal heater 73 is heated. It is a temperature higher than Te.

  That is, in the fixing device 60 of this embodiment, as shown in FIG. 5, the bimetal 71 is heated by the bimetal heater 73 to increase the temperature increase rate of the bimetal 71. As a result, the temperature of the bimetal 71 can appropriately follow the rise of the temperature of the fixing heater 64. In the fixing device 60, even if the temperature of the bimetal 71 is low, the temperature of the bimetal 71 reaches the operating temperature after the temperature of the fixing heater 64 reaches the operating temperature when the fixing heater 64 is overheated. The time to get to is supposed to be short. Therefore, even if the fixing heater 64 is overheated, it can be made unheatable before the fixing heater 64 becomes so hot.

  Further, as shown in FIG. 4, the CPU 4 of the fixing device 60 of the present embodiment has a power index value output unit 74. The power index value output unit 74 of this embodiment can detect and output an index value that indicates the power supplied to the bimetal 71 during a power supply period in which power is supplied to the bimetal 71. is there.

  Specifically, the power index value output unit 74 of this embodiment can detect and output the current value of the power supplied to the bimetal 71 during the power supply period. The power index value output unit 74 may detect and output the voltage value of the power supplied to the bimetal 71 during the power supply period.

  Furthermore, the bimetal heater control unit 9 of the present embodiment can perform determination control to determine whether or not the bimetal heater 73 is in a normal state of operating normally. The bimetal heater control unit 9 according to the present embodiment performs determination control based on the power index value output from the power index value output unit 74.

  Specifically, in the determination control, the bimetal heater control unit 9 determines whether the power index value output by the power index value output unit 74 is within a predetermined normal range. Then, when the power index value is within the normal range, it is determined that the bimetal heater 73 is in the normal state. On the other hand, when the power index value is out of the normal range, it is determined that the bimetal heater 73 is in an abnormal state where it can not operate normally. As an abnormal state of the bimetal heater 73, disconnection in a circuit supplying power to the bimetal heater 73, disconnection of a connector, failure of the bimetal heater 73, and the like can be considered.

  Next, switching between the normal mode and the limit mode at the time of fixing processing by the fixing heater control unit 8 of the present embodiment will be described using the flowchart shown in FIG. First, when an image forming job is input to the image forming apparatus 1, the CPU 4 outputs an instruction to start heating to the fixing heater control unit 8 and the bimetal heater control unit 9 (S101).

  In response to the instruction to start heating, the bimetal heater control unit 9 starts heating the bimetal 71 by the bimetal heater 73 (S102). Subsequently, in response to the instruction to start heating, the fixing heater control unit 8 starts heating the fixing belt 63 by the fixing heater 64 (S103). The fixing heater control unit 8 starts heating by the fixing heater 64 in the normal mode which is the initial setting mode.

  Next, the bimetal heater control unit 9 performs determination control (S104). That is, the bimetal heater control unit 9 determines whether the bimetal heater 73 is in the normal state or the abnormal state based on the power index value of the bimetal heater 73 output from the power index value output unit 74.

  If it is determined in the determination control that the state is normal (S104: YES), the fixing heater control unit 8 maintains the normal mode which is the initial setting mode (S105). Then, the fixing heater control unit 8 determines whether the temperature of the fixing belt 63 output from the temperature sensor 66 is equal to or higher than the fixing processing temperature (S106).

  When the temperature of the fixing belt 63 becomes equal to or higher than the fixing processing temperature (S106: YES), the CPU 4 outputs an instruction to end the heating to the fixing heater control unit 8 and the bimetal heater control unit 9 (S108). The bimetal heater control unit 9 receives the instruction to finish the heating, and finishes the heating of the bimetal 71 by the bimetal heater 73 (S109). Further, the fixing heater control unit 8 receives an instruction to finish heating, and ends the heating of the fixing belt 63 by the fixing heater 64 (S109). Further, the sheet P to which the toner has been transferred is conveyed so as to pass through the fixing nip N2 when the fixing belt 63 is in the state of being at the fixing processing temperature or higher.

  On the other hand, when it is determined in the determination control that there is an abnormal state (S104: NO), the fixing heater control unit 8 switches from the normal mode to the restriction mode (S107). When the mode is switched to the limit mode, the CPU 4 outputs an instruction to end heating to the fixing heater control unit 8 and the bimetal heater control unit 9 (S108). The bimetal heater control unit 9 receives the instruction to finish the heating, and finishes the heating of the bimetal 71 by the bimetal heater 73 (S109). Further, the fixing heater control unit 8 receives an instruction to finish heating, and ends the heating of the fixing belt 63 by the fixing heater 64 (S109). In addition, when the CPU 4 of the present embodiment is switched to the restriction mode, the execution of the image forming job is also ended.

  When the bimetal heater 73 is in an abnormal state, as described above, disconnection in a circuit supplying power to the bimetal heater 73, disconnection of a connector, failure of the bimetal heater 73, and the like can be considered. Therefore, when it is determined by the determination control that the bimetal heater 73 is in the abnormal state, the user may be warned that the bimetal heater 73 is in the abnormal state. The warning can be performed, for example, by providing a display panel or a lamp in the image forming apparatus 1.

  FIG. 7 shows a timing chart in the normal state where the bimetal heater 73 is in the normal state. That is, when normal, as shown in FIG. 7, an instruction to start heating is issued at time t11, and the bimetal heater 73 starts heating at time t12. When the bimetal heater 73 in the normal state starts heating, the power index value output unit 74 starts output of the power index value within the normal range.

  Subsequently, at time t1, the fixing heater 64 starts heating. Further, in the determination control performed at time t13, the abnormality is not detected because the bimetal heater 73 is in the normal state. Thereafter, at time t3 when the fixing belt 63 has reached the fixing processing temperature or higher, an instruction to finish heating is issued, and at time t6, the fixing heater 64 and the bimetal heater 73 finish heating.

  On the other hand, FIG. 8 shows a timing chart in the abnormal state where the bimetal heater 73 is in the abnormal state. That is, when abnormal, as shown in FIG. 8, an instruction to start heating is issued at time t11, and the bimetal heater 73 starts heating at time t12. When the bimetal heater 73 in an abnormal state starts heating, the power index value is out of the normal range. FIG. 8 shows the case where the power index value is 0 due to disconnection.

  Subsequently, at time t1, the fixing heater 64 starts heating. In addition, in the determination control performed at time t13, an abnormality is detected because the bimetal heater 73 is in an abnormal state. Therefore, at time t14, an instruction to finish heating is issued, and at time t15, the fixing heater 64 and the bimetal heater 73 finish heating. The time 15 when the fixing heater 64 and the bimetal heater 73 finish heating is earlier than the time t3 when the fixing belt 63 becomes the fixing processing temperature or more when the heating by the fixing heater 64 is continued.

  That is, when it is determined that the bimetal heater 73 is in the normal state by the determination control, the fixing device 60 of the present embodiment maintains the normal mode. Then, an image forming job is executed in the normal mode. On the other hand, when the initial setting mode is not maintained because the determination control determines that the bimetal heater 73 is in the abnormal state, the mode is switched to the restriction mode.

  When the bimetal heater 73 is in the normal state, the fixing process is appropriately performed in the normal mode. Further, when the bimetal heater 73 is in the normal state, when the fixing heater 64 is overheated, the fixing heater 64 can be appropriately made into the heating impossible state by the current interruption unit 70. This is because the bimetal 71 is appropriately heated by the bimetal heater 73.

  On the other hand, in the case where the bimetal heater 73 is in an abnormal state, when the fixing heater 64 is overheated, there is a possibility that the fixing heater 64 can not be appropriately heated by the energization blocking unit 70. This is because the temperature rise rate of the bimetal 71 may be low due to the bimetal heater 73 being in an abnormal state. Therefore, in the present embodiment, when the bimetal heater 73 is in an abnormal state, the fixing heater 64 is prevented from being overheated by stopping the supply of power to the fixing heater 64.

  As a result, in the fixing device 60 of this embodiment, overheating of the fixing heater 64 is appropriately suppressed regardless of whether the bimetal heater 73 is in the normal state or in the abnormal state.

[ Second embodiment ]
Next, the second embodiment will be described. Also in this embodiment, the configuration of the image forming apparatus is the same as that of the first embodiment . Specifically, the configuration of the fixing device of the image forming apparatus, the normal mode and the limit mode controlled by the fixing heater control unit 8, and the determination control by the bimetal heater control unit 9 are the same as those of the first embodiment. It is. In the present embodiment, the procedure for switching between the normal mode and the limit mode at the time of fixing processing is different from that of the first embodiment .

  The switching between the normal mode and the limit mode at the time of fixing processing by the fixing heater control unit 8 of the present embodiment will be described using a flowchart shown in FIG. First, also in this embodiment, when an image forming job is input to the image forming apparatus 1, the CPU 4 outputs an instruction to start heating (S201). In response to the instruction to start heating, the bimetal heater control unit 9 starts heating the bimetal 71 by the bimetal heater 73 (S202).

Next, unlike the first embodiment, the bimetal heater control unit 9 of this embodiment performs determination control (S203). That is, the bimetal heater control unit 9 determines whether the bimetal heater 73 is in the normal state or the abnormal state based on the power index value of the bimetal heater 73 output from the power index value output unit 74. If it is determined in the determination control that the state is normal (S203: YES), the fixing heater control unit 8 maintains the normal mode which is the initial setting mode (S204).

  Subsequently, the fixing heater control unit 8 receiving the instruction to start heating starts heating the fixing belt 63 by the fixing heater 64 (S205). Since the fixing heater control unit 8 maintains the initial setting mode, heating by the fixing heater 64 is started in the normal mode. Then, the fixing heater control unit 8 determines whether the temperature of the fixing belt 63 output from the temperature sensor 66 is equal to or higher than the fixing processing temperature (S206).

  When the temperature of the fixing belt 63 becomes equal to or higher than the fixing processing temperature (S206: YES), the CPU 4 outputs an instruction to end the heating to the fixing heater control unit 8 and the bimetal heater control unit 9 (S207). In response to the instruction to finish heating, the fixing heater control unit 8 ends the heating of the fixing belt 63 by the fixing heater 64 (S208). Further, the bimetal heater control unit 9 receives the instruction to finish the heating, and finishes the heating of the bimetal 71 by the bimetal heater 73 (S210). Further, the sheet P to which the toner has been transferred is conveyed so as to pass through the fixing nip N2 when the fixing belt 63 is in the state of being at the fixing processing temperature or higher.

  On the other hand, when it is determined in the determination control that there is an abnormal state (S203: NO), the fixing heater control unit 8 switches from the normal mode to the limit mode (S203). When the mode is switched to the limit mode, the bimetal heater control unit 9 ends the heating of the bimetal 71 by the bimetal heater 73 (S210). When the CPU 4 is switched to the restriction mode, the CPU 4 also ends the execution of the image forming job.

  Also in this embodiment, when it is determined by the determination control that the bimetal heater 73 is in the abnormal state, the user may be warned that the bimetal heater 73 is in the abnormal state.

That is, also in the fixing device 60 of this embodiment, when it is determined that the bimetal heater 73 is in the normal state by the determination control, the normal mode is maintained. Then, an image forming job is executed in the normal mode. On the other hand, when the initial setting mode is not maintained because the determination control determines that the bimetal heater 73 is in the abnormal state, the mode is switched to the restriction mode. Thus, in the fixing device 60 of the present embodiment, overheating of the fixing heater 64 is appropriately suppressed as in the first embodiment , regardless of whether the bimetal heater 73 is in the normal state or in the abnormal state. .

[ First embodiment ]
Next, the first embodiment will be described. Also in this embodiment, the configuration of the image forming apparatus is the same as the above embodiment. Specifically, the configuration of the fixing device of the image forming apparatus, the normal mode and the limit mode controlled by the fixing heater control unit 8, and the determination control by the bimetal heater control unit 9 are the same as those in the above embodiment. . In this embodiment, when the temperature of the bimetal is high, the normal mode is maintained regardless of whether or not the bimetal heater is in a normal state, unlike the above embodiment.

  FIG. 10 shows the temperature transition when the fixing heater 64 is overheated. However, FIG. 10 is different from FIG. 5 when heating is started in the state where the temperature of the fixing device 60 is high. That is, FIG. 10 shows, for example, the case where the time of the fixing device 60 has not dropped since the time has not passed so much after the end of the previous image forming job. Therefore, the heating of the fixing heater 64 is started with the temperature of the fixing belt 63 and the bimetal 71 not decreasing so much after the previous image formation.

  Further, in FIG. 10, the temperature transition of the fixing belt 63 is indicated by a two-dot chain line, and the temperature transition of the bimetal 71 is indicated by a solid line. Further, in FIG. 10, the solid line indicates the temperature transition of the bimetal 71 when the heating by the bimetal heater 73 is not performed.

  In FIG. 10, the temperature in the fixing device 60 at the heating start time t1 is indicated by the temperature Tg. That is, in FIG. 10, the temperatures of both the fixing belt 63 and the bimetal 71 at the heating start time t1 are the temperature Tg. The temperature of the fixing belt 63 rises from the temperature Tg from the heating start time t1, and continues to increase because the fixing heater 64 is overheated even after the time t3 when the fixing processing temperature Tc is reached. .

  Further, in FIG. 10, the temperature of the bimetal 71 indicated by a solid line is almost the same as that of the fixing belt 63 although the bimetal heater 73 does not heat it. This is because the temperature Tg in the fixing device 60 at the heating start time t1 is high.

  As described above with reference to FIG. 3, when the temperature of the bimetal 71 of this embodiment is equal to or higher than the temperature Tb, the rate of increase is almost the same as the rate of temperature increase of the fixing belt 63 even when heating by the bimetal heater 73 is not performed. The temperature rises. As described above, a thermosensitive part such as a thermostat generally has a characteristic that the responsiveness to temperature rise is improved when the temperature is higher than a certain level.

  And, as shown in FIG. 10, the temperature Tg of the bimetal 71 at the heating start time t1 is higher than the temperature Tb at which the responsiveness to the temperature rise of the bimetal 71 is improved. Therefore, in FIG. 10, the temperature of the bimetal 71 which is not heated by the bimetal heater 73 appropriately follows the rise of the temperature of the fixing heater 64.

  Then, as shown in FIG. 10, the temperature of the bimetal 71 indicated by the solid line has reached the operating temperature Td at time t51. Therefore, at time t51, the fixing heater 64 is in a non-heatable state. Further, in FIG. 10, the temperature Th of the fixing belt 63 at time t51 at which the fixing heater 64 is incapable of heating is not so large because the temperature of the bimetal 71 appropriately follows the temperature increase of the fixing heater 64. It is not expensive.

  Therefore, in the case where the temperature of the bimetal 71 is equal to or higher than the temperature Tb, the fixing device 60 of the present embodiment maintains the normal mode regardless of whether the bimetal heater 73 is in a normal state. When the temperature of the bimetal 71 is equal to or higher than the temperature Tb, even if the heating by the bimetal heater 73 is not properly performed, when the fixing heater 64 is overheated, heating can not be performed before the fixing heater 64 becomes so hot. It is because it can be in the state.

  Next, switching between the normal mode and the limit mode at the time of fixing processing by the fixing heater control unit 8 of the present embodiment will be described using the flowchart shown in FIG. First, also in this embodiment, when an image forming job is input to the image forming apparatus 1, the CPU 4 outputs an instruction to start heating (S301).

  Next, in the present embodiment, the fixing heater control unit 8 acquires the initial temperature detected by the temperature sensor 66 from the temperature output unit 68 (S302). The initial temperature is a temperature before both the fixing heater 64 and the bimetal heater 73 start heating. The temperature sensor 66 can detect the temperature of the fixing belt 63, and the detected temperature is a temperature indicative of the temperature of the bimetal 71 provided in the vicinity of the fixing belt 63. That is, the initial temperature is an index of the temperature of the bimetal 71.

  Next, the bimetal heater control unit 9 starts the heating of the bimetal 71 by the bimetal heater 73 (S303). Further, the fixing heater control unit 8 starts the heating of the fixing belt 63 by the fixing heater 64 (S304). The fixing heater control unit 8 starts heating by the fixing heater 64 in the normal mode which is the initial setting mode.

  Subsequently, the fixing heater control unit 8 determines whether the initial temperature is equal to or higher than a predetermined temperature threshold (S305). Specifically, the fixing heater control unit 8 according to this embodiment sets the temperature Tb as a temperature threshold and determines whether the initial temperature is equal to or higher than the temperature Tb.

  If the initial temperature is equal to or higher than the temperature threshold (S305: YES), the fixing heater control unit 8 maintains the normal mode which is the initial setting mode (S306). Then, when the temperature of the fixing belt 63 becomes equal to or higher than the fixing processing temperature (S307: YES), the CPU 4 outputs an instruction to end the heating (S310). Therefore, the fixing heater control unit 8 ends the heating by the fixing heater 64 (S311). Further, the bimetal heater control unit 9 ends the heating by the bimetal heater 73 (S311). Further, the sheet P to which the toner has been transferred is conveyed so as to pass through the fixing nip N2 when the fixing belt 63 is in the state of being at the fixing processing temperature or higher.

  In addition, even if the initial temperature is less than the temperature threshold (S305: NO), it is determined that the bimetal heater 73 is in the normal state by the determination control by the bimetal heater control unit 9, even if the initial temperature is less than the temperature threshold. (S308: YES), the normal mode is maintained (S306). And the procedure of step S307, step S310, and step S311 is performed similarly to the above.

  On the other hand, when the initial temperature is less than the temperature threshold (S305: NO) and it is determined that the determination control is abnormal (S308: NO), the fixing heater control unit 8 switches from the normal mode to the limit mode. Switch (S309). When the mode is switched to the limit mode, the CPU 4 outputs an instruction to end the heating (S310). Thus, the fixing heater control unit 8 ends the heating by the fixing heater 64 (S311). Further, the bimetal heater control unit 9 ends the heating by the bimetal heater 73 (S311). When the CPU 4 is switched to the restriction mode, the CPU 4 also ends the execution of the image forming job.

  Also in this embodiment, when it is determined by the determination control that the bimetal heater 73 is in the abnormal state, the user may be warned that the bimetal heater 73 is in the abnormal state.

  As described with reference to FIG. 11, when the initial temperature indicating the temperature of the bimetal 71 is equal to or higher than the temperature threshold, the fixing device 60 according to this embodiment maintains the normal mode regardless of the determination control. Then, an image forming job is executed in the normal mode. That is, even if the bimetal heater 73 is in an abnormal state, the fixing device 60 according to this embodiment can perform the fixing process while appropriately suppressing the overheating of the fixing heater 64 when the temperature of the bimetal 71 is high. .

  Also in this embodiment, when the initial temperature indicating the temperature of the bimetal 71 is less than the temperature threshold, determination control is performed. Then, if it is determined that the bimetal heater 73 is in the normal state by the determination control, the normal mode is maintained. Then, an image forming job is executed in the normal mode. On the other hand, when the initial setting mode is not maintained because the determination control determines that the bimetal heater 73 is in the abnormal state, the mode is switched to the restriction mode. As a result, in the fixing device 60 of this embodiment as well, even if the bimetal heater 73 is in either the normal state or the abnormal state, overheating by the fixing heater 64 is appropriately suppressed as in the above embodiment.

[ Second form ]
Next, the second embodiment will be described. Also in this embodiment, the configuration of the image forming apparatus is the same as the above embodiment. Specifically, the configuration of the fixing device of the image forming apparatus, the normal mode by the fixing heater control unit 8 and the determination control by the bimetal heater control unit 9 are the same as those in the above embodiment. In the present embodiment, the limitation mode by the fixing heater control unit 8 is different from the above embodiment.

  The switching between the normal mode and the limit mode at the time of fixing processing by the fixing heater control unit 8 of the present embodiment will be described using a flowchart shown in FIG. First, also in this embodiment, when an image forming job is input to the image forming apparatus 1, the CPU 4 outputs an instruction to start heating (S401).

Next, in the present embodiment, the fixing heater control unit 8 acquires the initial temperature detected by the temperature sensor 66 from the temperature output unit 68 (S402). The initial temperature is a temperature before both the fixing heater 64 and the bimetal heater 73 start heating. The initial temperature is an index of the temperature of the bimetal 71 in the present embodiment as in the first embodiment .

  Next, the bimetal heater control unit 9 starts the heating of the bimetal 71 by the bimetal heater 73 (S403). Further, the fixing heater control unit 8 starts the heating of the fixing belt 63 by the fixing heater 64 (S404). The fixing heater control unit 8 starts heating by the fixing heater 64 in the normal mode which is the initial setting mode.

Subsequently, the fixing heater control unit 8 determines whether the initial temperature is equal to or higher than a predetermined temperature threshold (S405). Specifically, also in the fixing heater control unit 8 of this embodiment, as in the first embodiment , the temperature Tb is used as a temperature threshold, and it is determined whether the initial temperature is equal to or higher than the temperature Tb.

  If the initial temperature is equal to or higher than the temperature threshold (S405: YES), the fixing heater control unit 8 maintains the normal mode which is the initial setting mode (S406). Because the temperature of the bimetal 71 is high, overheating of the fixing heater 64 can be appropriately suppressed even if the bimetal heater 73 is in an abnormal state.

  Then, when the temperature of the fixing belt 63 becomes equal to or higher than the fixing processing temperature (S410: YES), the CPU 4 outputs an instruction to end the heating (S411). Therefore, the fixing heater control unit 8 ends the heating by the fixing heater 64 (S412). Further, the bimetal heater control unit 9 ends the heating by the bimetal heater 73 (S412). Further, the sheet P to which the toner has been transferred is conveyed so as to pass through the fixing nip N2 when the fixing belt 63 is in the state of being at the fixing processing temperature or higher.

In addition, even if the initial temperature is less than the temperature threshold (S405: NO), it is determined that the bimetal heater 73 is in the normal state by the determination control by the bimetal heater control unit 9, in the present embodiment. (S407: YES), the normal mode is maintained (S406). And the procedure of step S410, step S411, and step S412 is performed similarly to the above. That is, also in this embodiment, the case where the initial temperature is equal to or higher than the temperature threshold and the case where the bimetal heater 73 is in the normal state even if the initial temperature is less than the temperature threshold are the same as the first embodiment .

  On the other hand, when the initial temperature is less than the temperature threshold (S405: NO) and it is determined that the determination control is in an abnormal state (S407: NO), the fixing heater control unit 8 switches from the normal mode to the limit mode. Switch (S408). When the fixing heater control unit 8 of the present embodiment switches to the limit mode, the temperature increase rate of the fixing heater 64 is reduced compared to that in the normal mode (S409). Specifically, in the limit mode, the fixing heater control unit 8 reduces the power supplied from the fixing heater power supply 67 to the fixing heater 64 as compared to that in the normal mode.

  Then, in the limit mode of the present embodiment, the fixing process is performed while the temperature increase rate of the fixing heater 64 is lower than that in the normal mode. That is, in the limit mode, the fixing belt 63 is heated while decreasing the temperature increase rate of the fixing heater 64, and the CPU 4 ends the heating when the temperature of the fixing belt 63 becomes equal to or higher than the fixing processing temperature (S410: YES). Output instruction (S411).

  Therefore, the fixing heater control unit 8 ends the heating by the fixing heater 64 (S412). Further, the bimetal heater control unit 9 ends the heating by the bimetal heater 73 (S412). Further, the sheet P to which the toner has been transferred is conveyed so as to pass through the fixing nip N2 when the fixing belt 63 is in the state of being at the fixing processing temperature or higher. That is, in this embodiment, even when the mode is switched to the restriction mode, the job of image formation can be continued.

  Also in this embodiment, when it is determined by the determination control that the bimetal heater 73 is in the abnormal state, the user may be warned that the bimetal heater 73 is in the abnormal state.

  FIG. 13 shows the temperature transition when the fixing heater 64 is overheated. However, unlike FIG. 5, FIG. 13 shows the temperature transition when the fixing heater 64 is overheated in the limit mode of this embodiment.

  In FIG. 13, a solid line indicates the temperature transition of the fixing belt 63 when the switching to the limit mode occurs, and a broken line indicates the temperature transition of the bimetal 71. 13 shows the temperature transition of the fixing belt 63 when overheating occurs in the normal mode, which is the same as the temperature transition shown by the two-dot chain line in FIG. 5 by the two-dot chain line. Further, the broken line represents the temperature transition of the bimetal 71 when the heating by the bimetal heater 73 is not performed, as in the broken line shown in FIG.

  As shown in FIG. 13, the temperature of the fixing belt 63 indicated by the solid line rises from room temperature Ta from the heating start time t1, and reaches the fixing processing temperature Tc at time t31. Here, time t13 between heating start time t1 and time t31 is a time when switching from the normal mode to the limit mode occurs. Therefore, the temperature rise of the fixing belt 63 shown by the solid line is lowered by switching to the limit mode. Therefore, time t31 is later than time t3 at which the temperature of the fixing belt 63 in the normal mode reaches the fixing processing temperature Tc. As indicated by the solid line, the temperature of the fixing belt 63 continues to increase because the fixing heater 64 is overheated even after the fixing processing temperature Tc is reached.

  Further, as shown in FIG. 13, the temperature of the bimetal 71 without the heating of the bimetal heater 73 hardly rises until the time t2 when the temperature Tb is reached after the heating start time t1. However, the temperature of the bimetal 71 when the bimetal heater 73 is not heated rises at a higher rate than before the time t2 after the time t2 when the temperature Tb is reached. The temperature of the bimetal 71 when the bimetal heater 73 is not heated reaches the operating temperature Td at time t5. Therefore, when the bimetal heater 73 is not heated, the fixing heater 64 is incapable of heating at time t5.

  Then, as shown in FIG. 13, the temperature Ti of the fixing belt 63 when the mode is switched to the limit mode at time t5 when the fixing heater 64 is in the non-heatable state is higher than the temperature Tf when the normal mode remains. It is a low temperature. In the limit mode, the temperature rise rate of the fixing heater 64 is lower than that in the normal mode. Also, the temperature Ti is not much higher than the operating temperature Td. Therefore, in the present embodiment, even if the bimetal heater 73 is in an abnormal state, the fixing heater 64 can be appropriately made unable to heat when the fixing heater 64 is overheated by switching to the restriction mode. There is.

  Also in this embodiment, when the initial temperature indicating the temperature of the bimetal 71 is less than the temperature threshold, determination control is performed. Then, if it is determined that the bimetal heater 73 is in the normal state by the determination control, the normal mode is maintained. Then, an image forming job is executed in the normal mode. On the other hand, when the initial setting mode is not maintained because the determination control determines that the bimetal heater 73 is in the abnormal state, the mode is switched to the restriction mode. Then, an image forming job is executed in the restriction mode. As a result, in the fixing device 60 of this embodiment as well, even if the bimetal heater 73 is in either the normal state or the abnormal state, overheating by the fixing heater 64 is appropriately suppressed as in the above embodiment.

  Further, in the present embodiment, as shown in FIG. 12, determination control is performed when the initial temperature is less than the temperature threshold. However, the determination control may be performed without performing the determination based on the initial temperature. In that case, step S402 and step S405 may not be performed in FIG. That is, after heating of the fixing heater 64 is started (S404), determination control may be performed (S407).

  Further, in the present embodiment, the temperature increase rate of the fixing heater 64 is decreased only once after switching to the limit mode. However, in the limit mode, the temperature increase rate of the fixing heater 64 may be reduced a plurality of times. In this case, when the temperature of the fixing belt 63 output from the temperature output unit 68 is high, the temperature increase rate of the fixing heater 64 is lower than that in the normal mode than when the temperature is low. The power supplied to the fixing heater 64 from the control unit 67 may be controlled.

  When the temperature rise rate is to be reduced, the degree to which the temperature rise rate is to be decreased can be determined in advance. Then, by decreasing the temperature rise rate as the temperature of the fixing belt 63 increases, the temperature of the fixing belt 63 can be raised to the fixing processing temperature more quickly. Furthermore, when the fixing heater 64 is overheated, the temperature rise rate is low, so that the temperature when the heating can not be performed can be reduced.

  As described above in detail, the image forming apparatus 1 of the present embodiment has the fixing device 60. The fixing device 60 has a fixing heater 64 which is a heating source for heating the fixing belt 63 at the time of fixing processing, and a current interruption unit 70. The current interruption unit 70 includes a bimetal 71, a contact portion 72, and a bimetal heater 73. The contact portion 72 can shut off the power supply to the fixing heater 64 when the temperature of the bimetal 71 which is the heat sensitive portion becomes equal to or higher than the operation temperature. Further, the fixing heater control unit 8 sets the normal mode to the initial setting mode, and when it is determined that the bimetal heater 73 is in the normal state by the determination control performed by the bimetal heater control unit 9, the normal mode is maintained. On the other hand, when the normal mode is not maintained, the normal mode is switched to the limit mode. As a result, a fixing device and an image forming apparatus capable of appropriately suppressing overheat by the fixing heater 64 as a heating source are realized.

  The present embodiment is merely an example and does not limit the present invention. Accordingly, the present invention is naturally capable of various improvements and modifications within the scope of the subject matter of the present invention. For example, the present invention is applicable not only to color printers, but also to image forming apparatuses that transmit and receive print jobs via a public line, for example.

  Further, for example, the fixing device of the image forming apparatus 1 may be configured differently from the fixing device 60 described above. That is, the present invention can be applied to fixing devices of other configurations such as a fixing device of an electromagnetic induction heating system. Further, for example, a thermostat other than a bimetal type can also be used as the current interruption unit 70. Alternatively, a temperature fuse may be used as the current interruption unit 70, which melts and breaks the heat sensitive part when the heat sensitive part reaches the operating temperature.

In the first and second embodiments , the detection value of the temperature sensor 66 is used as an initial temperature indicative of the temperature of the bimetal 71. However, values other than the detection value of the temperature sensor 66 can be used as a value indicating the temperature of the bimetal 71. For example, a temperature detection sensor may be provided at a position closer to the bimetal 71 than the temperature sensor 66, and the detection value of the temperature detection sensor may be used as a value indicating the temperature of the bimetal 71.

  Alternatively, when a bimetal heater 73 having a different resistance value depending on the temperature is used as a value indicating the temperature of the bimetal 71, the power index value output by the power index value output unit 74 can be used. This is because the power index value has a correlation with the resistance value of the bimetal heater 73. In addition, the bimetal heater 73 is disposed at a position close to the bimetal 71. In this case, first, the relationship between the power index value of the bimetal heater 73 and the temperature is obtained in advance by experiment or the like, and the relationship is stored in the non-volatile memory 5 attached to the main body. The temperature of the bimetal heater 73 can be determined by detecting the power index value in the meantime while supplying current to the bimetal heater 73 and referring to the nonvolatile memory 5 based on the detected power index value.

  Further, as the initial temperature of the bimetal 71, the previous heating time in which heating by the fixing heater 64 was performed at the previous fixing process, and the time from the end of the previous fixing process to the start of the current fixing process It is also possible to estimate by the pause time.

  When the previous heating time of the fixing heater 64 in the previous fixing process is long, it is considered that the temperature of the bimetal 71 is sufficiently increased. Furthermore, when the previous heating time is long and the pause time until the current fixing process is started is short, it can be estimated that the temperature of the bimetal 71 sufficiently raised at the previous fixing process is not so lowered It is from. On the other hand, when the previous heating time is short, it is considered that the temperature of the bimetal 71 has not risen so much. Further, when the pause time is long, it is considered that the temperature of the bimetal 71 has decreased by the start of the fixing process this time.

  Therefore, when the previous heating time is long and the rest time is short, it is possible to estimate that the temperature of the bimetal heater 73 is equal to or higher than the heating execution temperature at the start of the fixing process this time. Therefore, when the previous heating time is longer than the predetermined threshold for the previous heating time, and when the pause time is shorter than the predetermined threshold for the pause time, it is determined that the initial temperature of the bimetal 71 is the temperature threshold or more. can do. On the other hand, when the previous heating time is short or the rest time is long, it can be determined that the initial temperature of the bimetal 71 is less than the temperature threshold.

  Furthermore, the temperature of the bimetal 71 can be estimated as the previous heating time using the time during which the heating by the bimetal heater 73 was performed during the previous fixing process. Also in this case, it is the same as the above case using the time when the heating by the fixing heater 64 was performed at the previous fixing process as the previous heating time.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10Y, 10M, 10C, 10K Image forming unit 8 Fixing heater control unit 9 Bimetal heater control unit 60 Fixing device 61 Pressure roller 62 Fixing pad 63 Fixing belt 64 Fixing heater 70 Conduction blocking unit 71 Bimetal 72 Contact unit 73 Bimetal heater 74 Power index value output part N2 Fixing nip P Paper

Claims (6)

In a fixing device that performs a fixing process for fixing a toner image on a sheet by passing a sheet carrying unfixed toner through a fixing nip of a pair of fixing members,
A fixing heating unit configured to receive power supply to heat at least one of the pair of fixing members during the fixing process;
A heat sensing portion provided toward the fixing member to be heated by the fixing heating portion, and a path for supplying power to the fixing heating portion when the temperature of the heat sensing portion is equal to or higher than a predetermined operation temperature A power cut-off unit that cuts off the
A heat-sensitive heating unit provided at a position closer to the heat-sensitive unit than the fixing-heating unit and heating the heat-sensitive unit within a temperature range lower than the operating temperature;
A thermal heating determination unit that performs determination control to determine whether or not the thermal heating unit is in a normal state in which the thermal heating unit operates normally;
A thermosensitive temperature output unit for outputting a thermosensitive temperature index value indicative of a temperature of the thermosensitive unit;
About the power mode for supplying power to the fixing heating unit,
A normal mode for supplying normal power to the fixing heating unit to heat the fixing member;
And a fixing power control unit for switching between a limit mode for limiting the power supplied to the fixing heating unit more than that in the normal mode;
The fixing power control unit
Set the normal mode to the initial setting mode,
It was determined that at least one of the case where the thermal control unit was determined to be in the normal state by the determination control , and the thermal temperature index value output by the thermal temperature output unit is at least a predetermined threshold value. when the maintains the normal mode,
When it is determined by the determination control that the heat-sensitive heating unit is not in the normal state and the heat-sensitive temperature index value output by the heat-sensitive temperature output unit is less than the threshold , the normal mode is switched to the limit mode A fixing device characterized by switching. In the fixing device according to claim 1,
The heat-sensitive heating unit generates heat when supplied with power,
The heat-sensitive heating determination unit
A power index value output unit that detects and outputs a power index value that indicates the supplied power during a power supply period in which power is supplied to the thermal heating unit;
When the power index value output by the power index value output unit is within a predetermined normal range, it is determined that the state is the normal state,
The fixing device is characterized in that when the power index value is out of the normal range, it is determined that the state is not the normal state. In the fixing device according to claim 1 or 2 ,
The fixing power control unit
In the limiting mode, no power is supplied to the fixing heating unit. In the fixing device according to claim 1 or 2 ,
The fixing power control unit
The fixing device is characterized in that less electric power is supplied to the fixing and heating unit in the limit mode than in the normal mode. In the fixing device according to claim 4 ,
A fixing temperature output unit that outputs a fixing temperature index value that indicates the temperature of the fixing member that is heated by the fixing heating unit;
The fixing power control unit
In the restricted mode,
When the temperature of the fixing temperature index value output by the fixing temperature output unit is high, the fixing heating unit is set such that the temperature increase rate of the fixing heating unit is lower than that in the normal mode. Power supply to the fixing device. A conveyance unit for conveying a sheet;
An image forming unit that forms a toner image and transfers the formed toner image to a sheet;
An image forming apparatus comprising the fixing device according to any one of claims 1 to 5 , provided downstream of the image forming unit in the sheet conveyance direction.

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