JP6572599B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming equipment. More particularly, it relates to an image forming equipment for fixing by pressing while heating the toner image on the sheet.

  Conventionally, in an image forming apparatus such as a copier, printer, facsimile, or a multi-function machine having a combination of these functions, an image is formed on a sheet by fixing the toner image transferred on the sheet with a fixing device. doing. The fixing device performs a fixing process by passing a sheet through a fixing nip formed by press-contacting a pair of fixing members and applying pressure while heating the passing sheet. For this reason, the fixing device is provided with a heating source for heating the fixing nip to a fixing temperature for performing the fixing process.

  Some fixing devices are provided with a power-off unit such as a thermostat in order to prevent the heating temperature of the heating source from excessively exceeding the fixing processing temperature for performing the fixing processing. . That is, the energization interrupting unit interrupts the power supply to the heating source when overheating occurs due to the heating source and the heat sensitive part of the energizing interrupting unit rises to the operating temperature or higher. This prevents the temperature of the heating source from rising excessively. In addition, it is preferable that the energization cutoff unit can stop the power supply to the heating source as soon as possible when the heating source overheats.

  For example, Patent Document 1 discloses a technique in which the distance between the energization cut-off unit and the fixing roller heated by the heating source differs according to the environmental temperature of the energization cut-off unit. In other words, Patent Document 1 describes a technique in which the energization cutoff unit is further away from the fixing roller as the environmental temperature of the energization cutoff unit is higher. As a result, even when the temperature of the fixing roller is not sufficiently increased, when the heating source overheats, the supply of power to the heating source can be quickly stopped by the energization cutoff unit. ing.

JP 2008-076912 A

  By the way, in recent years, the rate of temperature increase due to heating of the heating source has become higher. This is to shorten the warm-up time and the time for raising the fixing member to the fixing processing temperature. Accordingly, when overheating by the heating source occurs, it is necessary to stop heating by the heating source at an earlier stage.

  However, the degree of temperature rise in the energization interrupting part is more gradual than that of the heating source. This is because the temperature rise of the energization cut-off unit is delayed from the temperature rise of the heating source by the time when the heat moves from the heating source to the fixing member and further the heat moves from the fixing member to the energization cut-off unit. Further, in the technique as described in Patent Document 1 described above, a gap is provided between the energization cutoff unit and the fixing roller. As a result, the time for the heat to move from the fixing roller to the energization cutoff part tends to be long. For this reason, it is not easy to shorten the time from when the temperature of the heating source reaches the operating temperature until the temperature of the energization cutoff unit reaches the operating temperature.

The present invention has been made for the purpose of solving the problems of the prior art described above. That it is an issue, when the heating by source occurs is to provide an image forming equipment which can be quickly stopped the heating by the heating source.

An image forming apparatus according to the present invention for solving the problem includes an image forming unit that forms a toner image and transfers the formed toner image onto a sheet, and a sheet on which the toner image is transferred by the image forming unit. Is passed through a fixing nip of a pair of fixing members to fix the toner image on the sheet, and a fixing device that performs a fixing process. A heating source that heats at least one of the fixing members, and a heat-sensitive portion that is provided toward the fixing member that is heated by the heating source, and the heating source when the temperature of the heat-sensitive portion is equal to or higher than a predetermined operating temperature. An energization cut-off unit that cuts off the supply of power to the heater and the distance to the heat sensitive part are located closer to the heating source, and the temperature of the heat sensitive part is a preheating temperature that is set to a temperature lower than the operating temperature. Sea urchin, a preheating unit for heating the heat-sensitive portion, and the heating start timing output section which heating source for outputting a heating start timing is a timing for starting the heating of the fixing member, the temperature of the fixing member, heating by the heating source is started After that, the fixing rise time output unit that outputs the fixing rise time that rises to the preheating temperature, and the preheating required time for the temperature of the heat sensitive part to rise to the preheating temperature after the heating by the preheating portion is started are output. preheating time required output unit, and a preheating start timing output section for outputting the preheating start timing is a timing for starting the heating of the heat-sensitive part by preheating section, preheating start timing output section, fixing rise time from heating start timing timing older than the preheating time required than the timing but have passed, to output the result as a preheating start timing, the preheating unit, preheating opens The preheating start timing timing output section outputs an image forming apparatus, characterized in that for starting heating of the heat-sensitive part.

  In the image forming apparatus of the present invention, the preheating unit performs preheating to heat the heat sensitive part so that the heat sensitive part reaches the preheating temperature before the fixing member heated by the heating source reaches a temperature higher than the preheating temperature. Is called. Due to the preheating, the heat sensitive part has risen to the preheating temperature, so that the time from when the fixing member rises to the operating temperature until the heat sensitive part rises to the operating temperature is shorter than when the temperature is lower than the preheating temperature. Can be. Therefore, when overheating by the heating source occurs, heating by the heating source can be stopped quickly.

  In the image forming apparatus described above, it is preferable that the preheating start timing output unit outputs a timing before the heating start timing as the preheating start timing. This is because preheating can be performed so that the heat sensitive portion reaches the preheating temperature before the fixing member reaches a temperature higher than the preheating temperature.

  In the image forming apparatus described above, the heating start timing output unit may determine the heating start timing based on the input image formation instruction information and output the determined heating start timing.

  Further, the image forming apparatus described above has a power state output unit that outputs the presence / absence of power supplied to the heating source, and the heating start timing output unit has no power supply to the heating source. There may be a timing that outputs the timing as the heating start timing.

  In the image forming apparatus described above, the preheating unit generates heat when supplied with electric power, and has a characteristic that the resistance value increases as the temperature rises, so that the temperature does not rise above the upper limit temperature. In addition, it is preferable that the heat sensitive part can be brought to the preheating temperature by heating the heat sensitive part at the upper limit temperature. This is because it is not necessary to provide a control unit for performing control to maintain the preheating unit at the preheating temperature. That is, preheating can be performed with an inexpensive configuration.

According to the present invention, when the heating by the heat source occurs, an image forming equipment which can be quickly stopped the heating by the heating source is provided.

1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. 2 is a schematic diagram of a control configuration of the image forming apparatus according to the present embodiment. FIG. 1 is a schematic configuration diagram of a fixing device according to an embodiment. It is a schematic diagram of a control configuration of a fixing device according to the present embodiment. It is the figure which showed the temperature transition of the bimetal when a preheating heater starts preheating before the heating by a fixing heater is started. It is the figure which showed the temperature transition of the bimetal different from FIG. 5 at the time of a preheating heater starting preheating before the heating by a fixing heater is started. It is the figure which showed the temperature transition of the bimetal when the preheating heater starts preheating after the heating by the fixing heater is started. It is the figure which showed the temperature transition of the bimetal different from FIG. 7 at the time of a preheating heater starting preheating after the heating by a fixing heater was started. It is the figure which showed the temperature transition when a preheating heater heats a bimetal to preheating temperature, before the heating by a fixing heater is started.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is embodied in an electrophotographic printer.

  FIG. 1 shows a schematic configuration of an image forming apparatus 1 of the present embodiment. The image forming apparatus 1 is a so-called tandem 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 driven to rotate 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 drawing.

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

  Also, a belt cleaner 41 is provided on the outer peripheral surface of the portion of the intermediate transfer belt 30 supported by the left roller 32 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 transfer residual toner and the like that has not been transferred to the paper P in the transfer nip N1 is formed by a portion that is in contact with the pressure contact.

  In the lower part of the intermediate transfer belt 30 in FIG. 1, the image forming units 10Y, 10M, 10C for yellow (Y), magenta (M), cyan (C), and black (K) are sequentially arranged from left to right. 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 10 </ b> Y is represented by a reference numeral.

  Each of the image forming units 10Y, 10M, 10C, and 10K includes a photosensitive member 11 that is a cylindrical electrostatic latent image carrier, and a charger 12, a developing device 14, and a photosensitive member cleaner 16 disposed around the photosensitive member. doing. A primary transfer roller 15 is disposed at a position facing the photoconductor 11 with the intermediate transfer belt 30 therebetween. Further, an exposure device 13 is disposed below the image forming units 10Y, 10M, 10C, and 10K for each color in FIG. The charger 12 is for uniformly charging the surface of the photoconductor 11. The exposure device 13 is for irradiating the surface of each photoconductor 11 with laser light based on image data to form an electrostatic latent image. The developing device 14 is for applying the contained toner to the surface of the photoreceptor 11.

  The primary transfer roller 15 is pressed against the intermediate transfer belt 30 in a direction perpendicular to the axis (downward in FIG. 1). As a result of this pressure contact, a primary transfer nip for transferring the toner image on the photoreceptor 11 of each color onto the intermediate transfer belt 30 is formed at the portion where the intermediate transfer belt 30 and each photoreceptor 11 are in contact with each other. Yes. The photoconductor cleaner 16 is for collecting toner that has not been transferred from the photoconductor 11 to the intermediate transfer belt 30.

  Although FIG. 1 shows a roller charging type charging device 12 having a roller shape, the present invention is not limited to this. A corona discharge charging charger, a blade charging member, a brush charging member, or the like may be used. Further, although the photosensitive member cleaner 16 is a plate and has one end portion in contact with the outer peripheral surface of the photosensitive member 11, the present invention is not limited to this. Other cleaning members, for example, a fixed brush, a rotating brush, a roller, or a combination of a plurality of them can be used. Alternatively, if a cleaner-less system in which the untransferred toner on the photoconductor 11 is collected by the developing device 14, the photoconductor cleaner 16 is not necessary.

  Further, hoppers 17Y, 17M, 17C, and 17K that store toners of the respective colors are disposed above the intermediate transfer belt 30 in FIG. The toner of each color accommodated in these is appropriately replenished 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 is located downstream of the image forming unit 10K in the rotation direction of the intermediate transfer belt 30 and upstream of the transfer nip N1. 20 is provided. The density sensor 20 uses the outer peripheral surface of the intermediate transfer belt 30 as a detection position. The density sensor 20 includes, for example, a light projecting unit that irradiates light toward a detection position and a light receiving unit that receives the reflected light, which are used for adjusting the image density.

  A detachable paper feed cassette 51 is mounted at the bottom of the image forming apparatus 1. A conveyance path 50 is provided above the right side in FIG. Then, the sheets P stored in the sheet feeding cassette 51 by stacking are sent out one by one from the uppermost one to the conveying path 50 by the sheet feeding roller 52. Further, the image forming apparatus 1 of the present embodiment has a paper type input unit 56. The paper type input unit 56 is used by the user to input the type of paper P stored in the paper feed cassette 51.

  A pair of registration rollers 53, a transfer nip N 1, a fixing device 60, and a paper discharge roller 54 are arranged in this order on the transport path 50 of the paper P delivered by the paper feed roller 52. A paper discharge unit 55 is provided on the upper surface of the image forming apparatus 1 further downstream of the transport path 50. The registration roller 53 is for adjusting the timing of feeding the paper P to the transfer nip N1. The fixing device 60 is for fixing the toner image transferred to the paper P by heating and pressurizing the paper P in the fixing nip N2.

  Next, an example of a normal image forming operation by the image forming apparatus 1 of this embodiment will be briefly described. The following description is an example of an image forming operation when a color image is formed on the paper P stored in the paper feed cassette 51 using four colors of toner.

  When forming a color image, first, the intermediate transfer belt 30 and the photoconductors 11 of the respective colors are rotated at a predetermined peripheral speed in the directions indicated by arrows in FIG. The outer peripheral surface of the photoconductor 11 is charged almost uniformly by the charger 12. Light corresponding to the image data is projected onto the outer peripheral surface of the charged photoconductor 11 by the exposure device 13 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 photoreceptor 11.

  The toner image formed on each photoconductor 11 is transferred (primary transfer) onto the intermediate transfer belt 30 by the primary transfer roller 15. As a result, yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 30 in this order. Then, the superimposed four color toner images are conveyed to the transfer nip N <b> 1 by the rotation of the intermediate transfer belt 30. Further, the transfer residual toner that is not transferred to the intermediate transfer belt 30 and remains on the photoconductor 11 after passing the primary transfer roller 15 is scraped off by the photoconductor cleaner 16 and removed from the photoconductor 11. Is done.

  On the other hand, the paper P stored in the paper feed cassette 51 is pulled out one by one from the uppermost one to the transport path 50. The drawn paper P is transported along the transport path 50 to the transfer nip N1. The entry timing of the paper 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 superimposed four color toner images are transferred (secondary transfer) onto the paper P in the transfer nip N1.

  The paper P on which the toner image has been transferred is further conveyed downstream of the conveyance path 50. That is, the paper P is discharged to the paper discharge section 55 by the paper discharge roller 54 after the toner image is fixed by the fixing device 60. Note that the transfer residual toner remaining on the intermediate transfer belt 30 even after passing through the transfer nip N1 is collected by the belt cleaner 41 in the collection area 42. As a result, the intermediate transfer belt 30 is removed.

  FIG. 2 shows an outline of the 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 includes a CPU 4 that performs overall control processing and a nonvolatile memory 5 attached to the main body.

  The nonvolatile memory 5 stores various values for performing image formation of the image forming apparatus 1 and the like. For example, values known in design such as a distance on the conveyance path 50 from the paper feed cassette 51 to the fixing nip N2, a system speed that is a speed for conveying the paper P and the formed toner image, and the like are stored. Further, a fixing processing temperature at which the toner image can be appropriately fixed on the paper 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 values stored in the nonvolatile memory 5. For example, a color toner image without deviation is formed on the intermediate transfer belt 30 by adjusting the timing of starting the formation of the electrostatic latent image by each exposure device 13. Further, by adjusting the timing at which an image is formed by the image forming units 10Y, 10M, 10C, and 10K and the timing at which the paper P is fed from the paper feed cassette 51, the timing of entering the transfer nip N1 can be matched. To control.

  Further, the CPU 4 of this embodiment has a fixing heater control unit 8 and a preheating heater control unit 9. The fixing heater control unit 8 and the preheating heater control unit 9 are for controlling the fixing device 60 so that the fixing device 60 can appropriately perform the fixing process. The fixing heater control unit 8 and the preheating 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 the nonvolatile memory 7 attached to the various units. The various units 6 include, for example, an imaging unit. For the non-volatile memory 7 attached to the various units, for example, the memory attached to the imaging unit stores the number of images formed by the imaging unit.

  The controller unit 3 is connected to an external personal computer or the like and receives 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 illustrating 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. Both the fixing pad 62 and the pressure roller 61 are members that are long 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 surface carrying the toner image of the paper P that passes through the fixing nip N2. The fixing pad 62, the fixing belt 63, and the fixing heater 64 are configured on the heating side for heating the paper P passing through the fixing nip N2.

  On the other hand, the pressure-side pressure roller 61 facing the heating-side configuration and the conveyance path 50 is pressed against the fixing belt 63 in a direction perpendicular to the axis. As a result, the endless fixing belt 63 is sandwiched between the fixing pad 62 and the pressure roller 61. A fixing nip N <b> 2 for fixing the paper P is formed at the press contact portion between the fixing belt 63 and the pressure roller 61.

  Further, the pressure roller 61 is rotationally driven in the direction indicated by the arrow in FIG. 3 when the fixing process is performed. As a result, the fixing belt 63 is also driven to rotate by the frictional force generated by the pressure contact of the pressure roller 61 that rotates during the fixing process.

  The fixing heater 64 is disposed on the inner peripheral side of the fixing belt 63 and heats the fixing belt 63. A reflective plate 65 is provided between the fixing heater 64 and the fixing nip N2. The reflection plate 65 is for suppressing the fixing nip N2 from being directly heated by the fixing heater 64.

  That is, in the fixing device 60 of the present embodiment, the left portion in FIG. 3 other than the vicinity of the fixing nip N 2 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 N2 is directly heated by the fixing heater 64. For this reason, the fixing device 60 of the present embodiment has a configuration in which the warm-up time and the temperature rise time to the fixing processing temperature are short.

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

  Further, the fixing device 60 of the present embodiment has an energization interrupting section 70 as shown in FIG. The energization cutoff unit 70 is provided in the vicinity of the fixing belt 63 while being spaced from the fixing belt 63. That is, since the energization interruption unit 70 is not in contact with the fixing belt 63, the surface of the fixing belt 63 is not damaged. The energization cut-off unit 70 can cut off the supply of electric power to the fixing heater 64 when the temperature exceeds the operating temperature. The energization cutoff unit 70 will be described in detail in the next FIG.

  FIG. 4 shows an outline of a control configuration of the fixing device 60 of the present embodiment. As described above, the CPU 4 has the fixing heater control unit 8 and the preheating heater control unit 9. FIG. 4 shows a fixing belt 63, a fixing heater 64, a temperature sensor 66, and an energization cutoff unit 70 in the configuration of the fixing device 60. Further, FIG. 4 shows a fixing heater power source 67 which is a power source for supplying power to the fixing heater 64.

  The fixing heater control unit 8 controls the fixing heater power source 67 so that the temperature of the fixing belt 63 detected by the temperature sensor 66 becomes a predetermined fixing processing temperature during the fixing processing. That is, the fixing heater control unit 8 can maintain the temperature of the fixing belt 63 at the fixing processing temperature by controlling the power supplied from the fixing heater power source 67 to the fixing heater 64 during the fixing processing.

  For example, the fixing heater control unit 8 of this embodiment determines the heating start time at which the fixing heater power supply 67 starts supplying power to the fixing heater 64. The heating start time can be determined by the fixing rise time during which the temperature of the fixing belt 63 in the fixing nip N2 rises to the fixing processing temperature due to the heating of the fixing heater 64. That is, the heating start time can be determined at a timing more than the fixing rise time before the time when the paper P delivered from the paper feed cassette 51 reaches the fixing nip N2. As the fixing rise time, for example, the time acquired by conducting an experiment in advance can be stored in the nonvolatile memory 5 attached to the main body, and the stored value can 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.

  In addition, as shown in FIG. 4, the energization cutoff unit 70 of this embodiment includes a bimetal 71, a contact part 72, and a preheating heater 73. The shape of the bimetal 71 is different between the temperature lower than the operating temperature of the energization cutoff unit 70 and the temperature higher than the operation temperature of the energization cutoff unit 70. That is, the bimetal 71 has a characteristic of deforming when heated from below the operating temperature to above the operating temperature and returning 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 higher than the fixing processing temperature.

  The contact portion 72 of the energization interruption unit 70 is provided in the middle of the circuit to which the fixing heater power source 67 and the fixing heater 64 are connected. The contact portion 72 can take an energized position indicated by a solid line in FIG. 4 and a blocking position indicated by a two-dot chain line. Specifically, the contact portion 72 is in a state where the fixing heater power source 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 source 67 at the blocking position. The contact portion 72 takes an energized position when the temperature of the bimetal 71 is lower than the operating temperature, and takes an interrupted position due to the deformation of the bimetal 71 when the temperature of the bimetal 71 is deformed above the operating temperature. It is configured. That is, the energization cut-off unit 70 of this embodiment is a mechanical thermostat that is formed by deformation of the bimetal 71.

  Then, when the bimetal 71 is lower than the operating temperature, the energization cut-off unit 70 of this embodiment sets the fixing heater 64 in a heatable state in which heating can be performed. On the other hand, the energization cut-off unit 70 operates when the bimetal 71 is at an operating temperature or higher, and makes the fixing heater 64 unable to heat and unable to heat.

  In addition, the energization cutoff unit 70 is provided with the bimetal 71 facing the fixing belt 63. For this reason, the energization cut-off section 70 operates when the fixing heater 64 is heated to a temperature equal to or higher than the operating temperature by the fixing heater 64, and makes the fixing heater 64 unheatable. Can do.

  The preheating heater 73 provided in the energization cutoff unit 70 of the present embodiment can generate heat under the control of the preheating heater control unit 9. The preheater 73 is provided at a position where the distance between the preheater 73 and the bimetal 71 is shorter than the distance between the fixing heater 64 and the bimetal 71. That is, the preheating heater 73 is a heater for heating the bimetal 71 provided in the vicinity of the bimetal 71.

  The preheater 73 is for preheating the bimetal 71. That is, the preheating heater 73 can heat the bimetal 71 to the preheating temperature when heat is generated. The preheating temperature is a temperature lower than the operating temperature of the energization cutoff unit 70.

  In this embodiment, a resistance heating element that generates heat by supplying electric power is used as the preheating heater 73. For this reason, a power source for supplying power to the preheating heater 73 is provided. As a power source for the preheating heater 73, a fixing heater power source 67 may be used. Alternatively, a power source different from the fixing heater 64 can be used.

  In addition, the preheating heater 73 of this embodiment is such that the resistance value increases as the temperature increases. Furthermore, the preheating heater 73 of this embodiment has a characteristic that when the upper limit temperature is reached, the temperature does not increase any more due to the increase in resistance value. In this embodiment, the upper limit temperature of the preheating heater 73 is the preheating temperature of the bimetal 71 heated by the preheating heater 73. Since the preheating temperature is lower than the operating temperature, the energization interrupting unit 70 operates by heating only the preheating heater 73 and does not make the fixing heater 64 unheatable.

  Here, when the fixing heater 64 is overheated, it is preferable that the fixing heater 64 is quickly brought into an unheatable state. This is because when the fixing heater 64 is overheated, the fixing heater 64 may not be properly controlled by the fixing heater control unit 8. Further, as described above, the fixing device 60 has a specification that can raise the temperature of the fixing belt 63 in a short time. For this reason, in this embodiment, when overheating by the fixing heater 64 occurs, it is preferable to stop heating by the fixing heater 64 earlier.

  Therefore, the preheating heater 73 of this embodiment can quickly make the fixing heater 64 unheatable if the fixing heater 64 is overheated by preheating the bimetal 71 to the preheating temperature. Specifically, the preheating heater control unit 9 turns on the bimetal 71 before the temperature of the fixing belt 63 heated by the fixing heater 64 becomes higher than the preheating temperature after the power of the image forming apparatus 1 is turned on. The preheater 73 is controlled so that becomes the preheat temperature.

  Therefore, the preheating heater control unit 9 of this embodiment can determine the preheating start time for causing the preheating heater 73 to start preheating. The preheating start time can be determined by, for example, the heating start time by the fixing heater 64, the fixing rise time of the fixing belt 63, and the preheating required time required to raise the temperature of the bimetal 71 to the preheating temperature. Specifically, the preheating start time can be determined at a timing that is more than the preheating required time before the timing at which the fixing rise time has elapsed from the heating start time. Therefore, the preheating heater control unit 9 of this embodiment can acquire the heating start time by the fixing heater 64 and the fixing rise time of the fixing belt 63 from the fixing heater control unit 8. For the preheating time, for example, the time acquired by conducting an experiment in advance can be stored in the nonvolatile memory 5 attached to the main body, and the stored value can be used.

  By setting the temperature of the bimetal 71 as the preheating temperature, the heating by the fixing heater 64 can be stopped earlier when the fixing heater 64 is overheated than when the temperature is lower than the preheating temperature. This is because the bimetal 71 at the preheating temperature requires less heat to rise to the operating temperature than when it is below the preheating temperature.

  5 to 9 show the temperature transition when the fixing heater 64 is overheated. 5 to 9, the horizontal axis represents time and the vertical axis represents temperature. 5 to 9 show the temperature transition of the fixing belt 63 by a two-dot chain line. Further, the solid line shows the temperature transition of the bimetal 71 when preheating is performed by the preheating heater 73 according to this embodiment. On the other hand, unlike the present embodiment, the broken line shows the temperature transition of the bimetal 71 when the preheating by the preheating heater 73 is not performed.

  5 to 9 are different from each other in temperature transition of the bimetal 71 when there is preheating indicated by a solid line according to the present embodiment. That is, in FIG. 5 to FIG. 9, solid lines indicate cases where the preheating start time by the preheating heater 73 and the temperature rise of the bimetal 71 due to preheating of the preheating heater 73 are different. On the other hand, in FIGS. 5 to 9, the temperature transition of the fixing belt 63 indicated by a two-dot chain line and the temperature transition of the bimetal 71 when there is no preheating indicated by the broken line are the same.

  Further, specifically, FIGS. 5 and 6 show a temperature transition when the preheating heater 73 starts preheating the bimetal 71 before the heating by the fixing heater 64 is started. 7 and 8 show a temperature transition when the preheating heater 73 starts preheating the bimetal 71 after the heating by the fixing heater 64 is started. FIG. 9 shows a temperature transition when the preheating heater 73 heats the bimetal 71 to the preheating temperature before the heating by the fixing heater 64 is started.

  First, FIG. 5 shows a temperature transition when the preheating heater 73 starts preheating the bimetal 71 before the heating by the fixing heater 64 is started as described above. The vertical axis in FIG. 5 shows the room temperature Ta, the preheating temperature Tb by the preheating heater 73, and the operating temperature Tc of the energization cutoff unit 70. Before the heating and preheating are started, the temperatures of the fixing belt 63 and the bimetal 71 are both room temperature Ta.

  The horizontal axis in FIG. 5 shows the preheating start time t1 by the preheating heater 73 and the heating start time t2 by the fixing heater 64. As described above, the preheating start time t1 is a timing determined by the preheating heater control unit 9. The heating start time t2 is a timing determined by the fixing heater control unit 8.

  In FIG. 5, the preheating start time t1 is a timing before the heating start time t2. For this reason, the temperature of the bimetal 71 when there is preheating indicated by the solid line is the room temperature Ta until the preheating start time t1, and starts to rise from the preheating start time t1. Further, the temperature of the fixing belt 63 indicated by a two-dot chain line is room temperature Ta until the heating start time t2, and starts to rise from the heating start time t2. Further, the temperature of the bimetal 71 when there is no preheating indicated by a broken line is also the room temperature Ta until the heating start time t2, and starts to rise from the heating start time t2.

  In FIG. 5, at time t3, the temperature of the bimetal 71 when there is preheating indicated by the solid line rises to the preheating temperature Tb. That is, in the energization cutoff unit 70 according to FIG. 5, the time from the preheating start time t1 to the time t3 is the required preheating time of the bimetal 71.

  In addition, the temperature of the fixing belt 63 indicated by a two-dot chain line rises to the preheating temperature Tb at time t4 after time t3. Therefore, in the fixing device 60 according to FIG. 5, the time from the heating start time t2 to the time t4 is the fixing rising time of the fixing belt 63.

  As shown in FIG. 5, the preheating heater 73 in the case where there is preheating indicated by the solid line indicates that the bimetal 71 is heated to the preheating temperature before the fixing belt 63 heated by the fixing heater 64 reaches a temperature higher than the preheating temperature Tb. Preheating is performed so that Tb is obtained. On the other hand, the temperature of the bimetal 71 when there is no preheating indicated by a broken line is a temperature lower than the preheating temperature Tb even at time t4. The temperature of the bimetal 71 when there is no preheating indicated by the broken line is increased only by the movement of heat from the fixing belt 63 heated by the fixing heater 64. For this reason, the rate of temperature increase is lower than that of the fixing belt 63.

  The temperature of the bimetal 71 in the case where there is preheating indicated by the solid line increases as the temperature of the fixing belt 63 heated by the fixing heater 64 increases from time t4. Note that the rate of increase in the temperature of the bimetal 71 after the time t4 is lower than the rate of increase in the temperature of the fixing belt 63. This is because the temperature of the bimetal 71 is increased by the transfer of heat from the fixing belt 63 heated by the fixing heater 64.

  Then, the temperature of the bimetal 71 in the case where there is preheating indicated by the solid line reaches the operating temperature Tc of the energization cutoff unit 70 at time t5. Therefore, when preheating is performed by the preheating heater 73 as in the present embodiment, heating by the fixing heater 64 is stopped at time t5. Note that the temperature of the fixing belt 63 at the time t5 is the temperature Td.

  On the other hand, the temperature of the bimetal 71 when there is no preheating indicated by the broken line also increases with the temperature increase of the fixing belt 63 heated by the fixing heater 64 after time t4. And the temperature of the bimetal 71 when there is no preheating shown with a broken line has reached the operating temperature Tc of the electricity interruption | blocking part 70 in the time t6 after the time t5.

  Therefore, unlike the present embodiment, when the preheating by the preheating heater 73 is not performed, the heating by the fixing heater 64 is stopped at time t6. The temperature Te of the fixing belt 63 at time t6 is higher than the temperature Td. This is because when the preheating by the preheating heater 73 is not performed, the fixing belt 63 is heated by the fixing heater 64 from time t5 to time t6.

  Therefore, as shown in FIG. 5, when there is preheating by the preheating heater 73 according to the present embodiment, heating by the fixing heater 64 is stopped earlier after overheating by the fixing heater 64 than when there is no preheating. Can be made. Therefore, even when overheating by the fixing heater 64 occurs, heating by the fixing heater 64 can be stopped before the temperature of the fixing belt 63 becomes so high.

  FIG. 6 shows a case where the rate of increase in the temperature of the bimetal 71 due to preheating of the preheating heater 73 is lower than in the case of FIG. Also in FIG. 6, the preheating start time t1 by the preheating heater 73 and the heating start time t2 by the fixing heater 64 are the same as those in FIG.

  FIG. 6 shows a case where the rate of temperature increase of the bimetal 71 due to preheating is lower than in the case of FIG. 5 as described above. That is, in the energization cutoff unit 70 according to FIG. 6, the time from the preheating start time t1 to the time t4 is the preheating required time of the bimetal 71, and the preheating required time is longer than the case of FIG. However, the temperature of the bimetal 71 when there is preheating indicated by the solid line is the preheating temperature Tb at time t4 when the temperature of the fixing belt 63 becomes the preheating temperature Tb. That is, also in FIG. 6, before the fixing belt 63 heated by the fixing heater 64 reaches a temperature higher than the preheating temperature Tb, the preheating by the preheating heater 73 is performed so that the bimetal 71 reaches the preheating temperature Tb. .

  Also in FIG. 6, the temperature of the bimetal 71 when there is preheating indicated by the solid line reaches the operating temperature Tc at time t5. Time t5 is before time t6 when the temperature of the bimetal 71 when there is no preheating indicated by a broken line reaches the operating temperature Tc. Therefore, also in FIG. 6, when there is preheating by the preheating heater 73 according to the present embodiment, heating by the fixing heater 64 is stopped earlier after overheating by the fixing heater 64 than when there is no preheating. Can do. Therefore, even when overheating by the fixing heater 64 occurs, heating by the fixing heater 64 can be stopped before the temperature of the fixing belt 63 becomes so high.

  Next, FIG. 7 shows the temperature transition when the preheating heater 73 starts preheating the bimetal 71 after the heating by the fixing heater 64 is started as described above. Also in FIG. 7, the vertical axis indicates the room temperature Ta, the preheating temperature Tb, and the operating temperature Tc.

  FIG. 7 shows a heating start time t11 by the fixing heater 64 and a preheating start time t12 by the preheating heater 73. In FIG. 7, the preheating start time t12 is a timing after the heating start time t11.

  As shown in FIG. 7, the temperature of the bimetal 71 when there is preheating indicated by a solid line, the temperature of the fixing belt 63 indicated by a two-dot chain line, and the temperature of the bimetal 71 when there is no preheating indicated by a broken line are all the heating start times. From t11, it starts to rise from room temperature Ta. At this time, the temperature rise rate of the bimetal 71 when there is preheating indicated by a solid line and the temperature of the bimetal 71 when there is no preheating indicated by a broken line are both higher than the rate of temperature increase of the fixing belt 63 indicated by a two-dot chain line. It is low.

  Further, as shown in FIG. 7, the rate of increase in the temperature of the bimetal 71 when there is preheating indicated by the solid line between the preheating start time t12 and the time t13 is the temperature of the bimetal 71 when there is no preheating indicated by the broken line. It is higher than the rate of increase. This is because preheating is performed by the preheating heater 73. In FIG. 7, the temperature of the bimetal 71 when there is preheating indicated by a solid line rises to the preheating temperature Tb at time t <b> 13 after the preheating start time t <b> 12 by the preheating heater 73.

  In FIG. 7, the temperature of the fixing belt 63 indicated by a two-dot chain line rises to the preheating temperature Tb at time t14 after time t13. That is, the preheating heater 73 shown by the solid line in FIG. 7 is also preheated so that the bimetal 71 reaches the preheating temperature Tb before the fixing belt 63 heated by the fixing heater 64 reaches a temperature higher than the preheating temperature Tb. It is carried out. On the other hand, the temperature of the bimetal 71 when there is no preheating indicated by a broken line is a temperature lower than the preheating temperature Tb even at time t14.

  In FIG. 7, the temperature of the bimetal 71 when there is preheating indicated by a solid line reaches the operating temperature Tc at time t15. Time t15 is before time t16 when the temperature of the bimetal 71 when there is no preheating indicated by a broken line reaches the operating temperature Tc. Therefore, also in FIG. 7, when there is preheating by the preheating heater 73 according to this embodiment, heating by the fixing heater 64 is stopped earlier after overheating by the fixing heater 64 than when there is no preheating. Can do. Therefore, even when overheating by the fixing heater 64 occurs, heating by the fixing heater 64 can be stopped before the temperature of the fixing belt 63 becomes so high.

  FIG. 8 shows a case where the rate of increase in the temperature of the bimetal 71 due to preheating of the preheating heater 73 is lower than that in FIG. Also in FIG. 8, the heating start time t11 by the fixing heater 64 and the preheating start time t12 by the preheating heater 73 are the same as those in FIG.

  FIG. 8 shows a case where the rate of temperature increase of the bimetal 71 due to preheating is lower than in the case of FIG. 7 as described above. That is, in the energization cutoff unit 70 according to FIG. 8, the required preheating time is longer than that in the case of FIG. However, the temperature of the bimetal 71 when there is preheating indicated by a solid line is the preheating temperature Tb at time t14 when the temperature of the fixing belt 63 becomes the preheating temperature Tb. That is, also in FIG. 8, preheating is performed by the preheating heater 73 so that the bimetal 71 reaches the preheating temperature Tb before the fixing belt 63 heated by the fixing heater 64 reaches a temperature higher than the preheating temperature Tb. .

  Also in FIG. 8, the temperature of the bimetal 71 when there is preheating indicated by the solid line reaches the operating temperature Tc at time t15. Time t15 is before time t16 when the temperature of the bimetal 71 when there is no preheating indicated by a broken line reaches the operating temperature Tc. Therefore, also in FIG. 8, when there is preheating by the preheating heater 73 according to this embodiment, heating by the fixing heater 64 is stopped earlier after overheating by the fixing heater 64 occurs than when there is no preheating. Can do. Therefore, even when overheating by the fixing heater 64 occurs, heating by the fixing heater 64 can be stopped before the temperature of the fixing belt 63 becomes so high.

  Next, FIG. 9 shows a temperature transition when the preheating heater 73 heats the bimetal 71 to the preheating temperature before the heating by the fixing heater 64 is started as described above. Also in FIG. 9, the vertical axis indicates room temperature Ta, preheating temperature Tb, and operating temperature Tc.

  FIG. 9 shows a preheating start time t21 by the preheating heater 73 and a heating start time t23 by the fixing heater 64. Note that the temperature of the bimetal 71 when there is preheating indicated by the solid line rises to the preheating temperature Tb at the time t22 before the heating start time t23.

  In FIG. 9, both the temperature of the fixing belt 63 indicated by the two-dot chain line and the temperature of the bimetal 71 when there is no preheating indicated by the broken line are starting to rise from the room temperature Ta from the heating start time t23. Note that the increase rate of the temperature of the bimetal 71 when there is no preheating is lower than the increase rate of the temperature of the fixing belt 63 indicated by a two-dot chain line.

  In FIG. 9, the temperature of the fixing belt 63 indicated by a two-dot chain line rises to the preheating temperature Tb at time t24 after time t22. That is, the preheating heater 73 shown by the solid line in FIG. 9 is also preheated so that the bimetal 71 reaches the preheating temperature Tb before the fixing belt 63 heated by the fixing heater 64 reaches a temperature higher than the preheating temperature Tb. It is carried out. On the other hand, the temperature of the bimetal 71 when there is no preheating indicated by a broken line is a temperature lower than the preheating temperature Tb even at time t24.

  In FIG. 9, the temperature of the bimetal 71 when there is preheating indicated by the solid line reaches the operating temperature Tc at time t <b> 25. Time t25 is before time t26 when the temperature of the bimetal 71 when there is no preheating indicated by a broken line reaches the operating temperature Tc. Therefore, also in FIG. 9, when there is preheating by the preheating heater 73 according to this embodiment, heating by the fixing heater 64 is stopped earlier after overheating by the fixing heater 64 occurs than when there is no preheating. Can do. Therefore, even when overheating by the fixing heater 64 occurs, heating by the fixing heater 64 can be stopped before the temperature of the fixing belt 63 becomes so high.

  That is, in any of the cases indicated by the solid lines in FIGS. 5 to 9 described above, the bimetal 71 is heated to the preheating temperature Tb before the fixing belt 63 heated by the fixing heater 64 reaches a temperature higher than the preheating temperature Tb. Preheating by the preheating heater 73 is performed so that it becomes. Thereby, in this embodiment, when the temperature of the fixing belt 63 rises to the operating temperature Tc due to overheating of the fixing heater 64, heating by the fixing heater 64 can be stopped quickly.

  Further, as described above, in this embodiment, the preheater 73 has a characteristic that the resistance value increases as the temperature rises, and when the temperature reaches the upper limit temperature, the temperature does not further increase due to the increase in the resistance value. Used. For this reason, the control etc. for maintaining the temperature of the preheating heater 73 in the preheating temperature are unnecessary for the preheating heater control part 9 of this form. Therefore, preheating by the preheating heater 73 can be performed with an inexpensive configuration.

  Further, it is preferable that the preheating start time by the preheating heater 73 is a timing before the heating start time by the fixing heater 64. That is, preheating is preferably performed as shown in FIGS. 5, 6, and 9 in FIGS. 5 to 9. The preheating time may become longer due to, for example, the temperature in the vicinity of the bimetal 71 or the air flow. That is, the earlier the preheating start time is, the more reliably preheating can be performed so that the bimetal 71 reaches the preheating temperature Tb before the fixing belt 63 reaches a temperature higher than the preheating temperature Tb. However, it is not preferable that the preheating start time is too early. This is because power consumption increases.

  In the present embodiment, the preheating heater control unit 9 acquires the heating start time determined by the fixing heater control unit 8 from the fixing heater control unit 8. However, the preheating heater control unit 9 can also acquire the heating start time by detecting that power is supplied from the fixing heater power source 67 to the fixing heater 64. Therefore, for example, a detection unit that detects the presence or absence of power supplied to the fixing heater 64 may be provided in a circuit to which the fixing heater power source 67 and the fixing heater 64 are connected. A voltmeter or an ammeter can be used as a detection unit for detecting the presence or absence of supplied power. Then, the timing when the detection state of the detection unit becomes “no” may be set as the heating start time.

  In the above-described embodiment, the preheating heater control unit 9 is provided in the CPU 4 of the image forming apparatus 1. However, the preheating heater control unit 9 can also be provided in the fixing device 60.

As described in detail above, the image forming apparatus 1 of the present embodiment has the fixing device 60. The fixing device 60 includes a fixing heater 64 that is a heating source for heating the fixing belt 63 during the fixing process, and an energization interrupting unit 70. The energization cutoff unit 70 includes a bimetal 71, a contact point 72, and a preheating heater 73. The contact portion 72 can cut off the power supply to the fixing heater 64 when the temperature of the bimetal 71 that is the heat sensitive portion becomes equal to or higher than the operating temperature. The preheater 73 preheats the bimetal 71 to a preheat temperature lower than the operating temperature. Further, the preheating heater 73 performs preheating so that the bimetal 71 reaches the preheating temperature before the fixing belt 63 reaches a temperature higher than the preheating temperature. Thus, when the heating by the heat source occurs, an image forming equipment which can be quickly stopped the heating by the heating source is realized.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the present invention is not limited to a color printer, and can be applied to an image forming apparatus that transmits and receives a print job 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. In other words, the present invention can be applied to a fixing device having other configurations such as an electromagnetic induction heating type fixing device. In addition, for example, a thermostat other than the bimetal type can be used as the energization cutoff unit 70.

  The preheating may be performed so that the bimetal 71 reaches the preheating temperature Tb before the fixing belt 63 becomes higher than the preheating temperature Tb. For example, the preheating is started when the power of the image forming apparatus 1 is turned on. It is good to do. Also, for example, preheating may be started when an image forming job is input. Alternatively, preheating can be started when heating by the fixing heater 64 is started.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10Y, 10M, 10C, 10K Image forming part 8 Fixing heater control part 9 Preheating heater control part 60 Fixing apparatus 61 Pressing roller 62 Fixing pad 63 Fixing belt 64 Fixing heater 70 Energization interruption part 71 Bimetal 72 Contact part 73 Preheating heater N2 Fixing nip P Paper

Claims (5)

An image forming unit that forms a toner image and transfers the formed toner image onto a sheet;
An image forming apparatus having a fixing device that performs a fixing process for fixing a toner image on a sheet by passing the sheet on which the toner image is transferred by the image forming unit through a fixing nip of a pair of fixing members.
During the fixing process, a heating source that receives power supply and heats at least one of the pair of fixing members;
A heat-sensitive part provided toward the fixing member that is heated by the heat source is provided, and power supply to the heat source is cut off when the temperature of the heat-sensitive part is equal to or higher than a predetermined operating temperature. A current interrupting section;
A preheating unit that heats the heat sensitive part so that the distance to the heat sensitive part is closer to the heating source and the temperature of the heat sensitive part is a preheating temperature that is predetermined to a temperature lower than the operating temperature; ,
A heating start timing output unit for outputting a heating start timing which is a timing at which the heating source starts heating the fixing member;
A fixing rising time output unit for outputting a fixing rising time in which the temperature of the fixing member rises to the preheating temperature after heating by the heating source is started;
A preheating time output unit that outputs a preheating time in which the temperature of the heat sensitive part rises to the preheating temperature after heating by the preheating part is started;
A preheating start timing output unit for outputting a preheating start timing which is a timing for starting heating of the heat sensitive unit by the preheating unit ,
The preheating start timing output unit is
Outputting the timing more than the required preheating time before the timing when the fixing rising time has elapsed from the heating start timing as the preheating start timing,
The preheating part is
The image forming apparatus , wherein heating of the heat sensitive part is started at the preheat start timing output by the preheat start timing output part . The image forming apparatus according to claim 1 ,
The preheating start timing output unit is
The image forming apparatus according to claim 1, wherein a timing before the heating start timing is output as the preheating start timing. The image forming apparatus according to claim 1 or claim 2,
The heating start timing output unit is
An image forming apparatus characterized in that the heating start timing is determined from input image formation instruction information, and the determined heating start timing is output. The image forming apparatus according to claim 1 ,
A power status output unit that outputs the presence or absence of power supplied to the heating source;
The heating start timing output unit is
An image forming apparatus characterized in that a timing when there is no supply of power to the heating source is output as the heating start timing. The image forming apparatus according to any one of claims 1 to 4,
The preheating part is
It generates heat when supplied with electric power, and the resistance value increases as the temperature rises, so that the temperature does not rise above the upper limit temperature.
An image forming apparatus, wherein the heat sensitive part can be set to the preheating temperature by heating the heat sensitive part at the upper limit temperature.

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