JP5995141B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a fixing device that performs a heat fixing process in which an image formed on a recording material is thermally fixed to the recording material by applying heat of a heating rotator.

  In image forming apparatuses such as copiers, printers, facsimiles, and multifunction peripherals thereof, in recent years, there has been a strong market demand for shortening the first print time. The first print time means the time required from when a print request (image formation command) is received to when the image forming operation is performed through the image forming preparation operation and the first recording material on which the image is formed is discharged. To do. In an image forming apparatus provided with a fixing device that performs heat fixing processing for fixing an image formed on a recording material to the recording material by heat, in order to shorten the first print time, the warm-up time of the fixing device Is required to be shortened. The warm-up time referred to here is required to raise the temperature of the heating rotator that applies heat to the image on the recording material to the target temperature (target fixing temperature) at which heat fixing processing can be performed when returning from the standby state. It means time.

  On the other hand, if the temperature of the heating rotator is kept at the target fixing temperature during the standby state, not only wasteful power is consumed, but also the heat deterioration of the heating rotator is promoted. Conventionally, in order to shorten the warm-up time while suppressing such problems, in the standby state, the temperature of the heating rotator is lower than the target fixing temperature and higher than the environmental temperature (room temperature), and a predetermined target standby temperature (Patent Document 1, Patent Document 2, etc.). By this control, wasteful power consumption is less than in the case where the fixing temperature of the heating rotator is kept at the target fixing temperature during the standby state, and the promotion of thermal deterioration of the heating rotator can be suppressed. Furthermore, the warm-up time can be shortened as compared with the case where the heating rotator is heated to the target fixing temperature from the state cooled to the environmental temperature.

  In such a standby state, the heating rotator of the fixing device is normally in a state where the rotation is stopped. Therefore, in the standby state, heating control for maintaining the target standby temperature is performed on the heating rotator in the rotation stopped state. However, conventionally, the heating rotator may rotate even during the standby state. For example, in a fixing device that forms a fixing nip by pressing the pressure member against the heating rotator to form a fixing nip, the same portion of the heating rotator heated to the target standby temperature is deformed for a long time. If left untouched, the part cannot be restored and may be permanently deformed. In such a fixing device, there is a case where control is performed to prevent permanent deformation of the heating rotator by periodically rotating the heating rotator temporarily during the standby state. Further, for example, when the heating rotator of the fixing device and the paper feed mechanism of the image forming apparatus are connected to a common drive source, an operation of inserting and removing the paper feed cassette in the standby state is performed. The paper feed mechanism moves, and the heating rotator of the fixing device may rotate in conjunction with this. For example, when the image forming operation is shifted to a standby state after the completion of the image forming operation, the temperature of the heating rotator may overshoot when the rotation of the heating rotator of the fixing device is stopped for some reason. . In such a case, in order to rapidly cool the temperature of the heating rotator, there is a case where control is performed to rotate the heating rotator in a standby state.

  In the standby state, when the heating control is performed to maintain the non-rotating heating rotator at the target standby temperature, when the heating rotator rotates, the heating rotator is rapidly cooled by the rotation. Therefore, since the temperature of the heating rotator rapidly decreases, the heating rotator is heated in order to recover the temperature of the heating rotator to the target standby temperature by the heating control. At this time, since the heating rotator is in the rotating state, more heat escapes from the heating rotator than in the non-rotating state, and the temperature of the heating rotator gradually rises. However, the rotation of the heating rotator that occurs during the standby state is temporary and stops immediately. For this reason, the rotation of the heating rotator often stops before the temperature of the heating rotator that has started rotating returns to the target standby temperature. When the rotation of the heating rotator is stopped, the amount of heat escaping from the heating rotator is less than that in the rotating state, so that the temperature of the heating rotator rapidly increases. As a result, overshoot occurs in which the temperature of the heating rotator rises to a temperature that greatly exceeds the target standby temperature. When such an overshoot occurs, the heating rotator becomes an unexpectedly high temperature, causing thermal degradation of the heating rotator and causing problems such as shortening the life of the heating rotator.

  The present invention has been made in view of the above problems, and an object of the present invention is to suppress overshooting of the temperature of the heating rotator that occurs when the heating rotator of the fixing device temporarily rotates during the standby state. An image forming apparatus is provided.

  In order to achieve the above object, the present invention provides an image formed on a recording material by the image forming means using an image forming means for forming an image on the recording material and a heating rotator heated to a target fixing temperature. A fixing means for performing heat fixing processing for fixing the recording material to the recording material, and normal standby control for maintaining the temperature of the heating rotator within a target standby temperature range while stopping the rotation of the heating rotator during the standby state. In the image forming apparatus including the standby control unit that performs the above, the standby control unit determines whether or not a special standby control transition condition including a necessary condition that the heating rotating body rotates during the normal standby control is satisfied. If the special standby control transition condition is not satisfied, the normal standby control is continued. If the special standby control transition condition is satisfied, the heating rotor is heated and a predetermined heating end timing is determined. But If the temperature of the heating rotator is within the target standby temperature range, the heating rotator is finished heating until the predetermined non-heating end timing arrives. It is characterized by carrying out a special standby control that does not heat.

  According to the present invention, when the heating rotator rotates during normal standby control and the special standby control transition condition is satisfied, the special standby control is started, and first, heating of the heating rotator is started. Thereby, the temperature fall of the heating rotator rapidly cooled by the rotation can be quickly suppressed, and further the temperature of the heating rotator can be promptly recovered. And, when the heating rotator is heated until a predetermined heating end timing comes, regardless of whether the temperature of the heating rotator is within the target standby temperature range, until the non-heating end timing comes, The heating rotor is not forcibly heated. By providing such a forced non-heating period, the temperature of the heating rotator is overshooted as compared with the conventional configuration in which the heating rotator is continuously heated until the temperature of the heating rotator falls within the target standby temperature range. Can be suppressed.

  As described above, according to the present invention, it is possible to obtain an excellent effect that it is possible to suppress the overshoot of the temperature of the heating rotator that has occurred when the heating rotator of the fixing device temporarily rotates during the standby state.

1 is a schematic configuration diagram illustrating a configuration of a printer according to an embodiment. FIG. 2 is a schematic diagram illustrating a schematic configuration of a process cartridge of the printer. 1 is a schematic configuration diagram illustrating an example of a fixing device that can be used in an embodiment. It is a schematic block diagram which shows the other example of the fixing device which can be used by embodiment. It is explanatory drawing which shows an example of the structure of the temperature sensor in embodiment. FIG. 10 is an explanatory diagram showing a temperature change of a fixing belt when the fixing belt is temporarily rotated during a standby state in the conventional configuration. It is a flowchart which shows the flow of the heater control in the standby state in embodiment. In the embodiment, it is an explanatory diagram showing a temperature change of the fixing belt when the fixing belt is temporarily rotated during the standby state. 10 is a flowchart showing a flow of heater control during a standby state in Modification 1. 10 is a table showing an example of a table used when a control unit in Modification 1 determines a heater lighting duty to be used when a heater is turned on during special standby control. FIG. 9 is an explanatory diagram illustrating a temperature change of a fixing belt when the fixing belt is temporarily rotated during a standby state in Modification 1. 10 is a flowchart showing a flow of heater control during a standby state in Modification 2. FIG. 10 is an explanatory diagram showing a temperature change of the fixing belt when the fixing belt is temporarily rotated during a standby state when the specified number of times in Modification 2 is set to two. FIG. 10 is an explanatory diagram illustrating a temperature change of the fixing belt when the fixing belt is temporarily rotated during a standby state when the specified number of times in Modification 2 is set to 3 or more. 10 is a flowchart showing a flow of heater control during a standby state in Modification 3. FIG. 10 is an explanatory diagram illustrating a temperature change of the fixing belt when the fixing belt temporarily rotates during a standby state when a resistance abnormality occurs in the central temperature sensor. FIG. 10 is an explanatory diagram for explaining a method of detecting an abnormal temperature increase of the fixing belt. It is the graph which showed the detection temperature of the central temperature sensor 46a after implementing one special standby control in order to demonstrate an example of the determination method of subtraction temperature. FIG. 10 is an explanatory diagram showing a temperature change of a fixing belt when a subtraction temperature in Modification 3 is set to 20 ° C.

Hereinafter, an embodiment in which the present invention is applied to an electrophotographic printer as an image forming apparatus will be described.
First, a basic configuration of the printer 100 according to the present embodiment will be described.
FIG. 1 is a schematic configuration diagram illustrating a configuration of the printer 100.
The printer 100 constitutes a tandem image forming unit in which four toner image forming units of yellow, cyan, magenta, and black are arranged in the endless moving direction of the intermediate transfer belt 1 that is an intermediate transfer member. In the tandem image forming unit, toner image forming units 101Y, 101C, 101M, and 101K, which are individual toner image forming units, are arranged in order from the left in the drawing. Here, the suffixes Y, C, M, and K of the respective symbols indicate members for yellow, magenta, cyan, and black, respectively.

  Each of the toner image forming units 101Y, 101C, 101M, and 101K includes a charging device, a developing device 10Y, 10C, 10M, and 10K around a drum-shaped photosensitive member 21Y, 21C, 21M, and 21K as a latent image carrier. A photoconductor cleaning device and the like are provided. At the top of the printer 100, toner bottles 2Y, 2C, 2M, and 2K filled with yellow, cyan, magenta, and black color toners are arranged. Then, each color toner is supplied from the toner bottles 2Y, 2C, 2M, and 2K to the developing devices 10Y, 10C, 10M, and 10K of the respective colors by a predetermined supply amount through a conveyance path (not shown).

  An optical writing unit 9 as a latent image forming unit is provided below the tandem image forming unit. The optical writing unit 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each of the photoreceptors 21Y, 21C, 21M, and 21K while scanning the laser beam based on image data. It is configured as follows.

  In addition, a transfer unit including an endless belt-like intermediate transfer belt 1, a primary transfer device, a secondary transfer roller, and the like as an intermediate transfer member is provided immediately above the tandem image forming unit. The intermediate transfer belt 1 is wound around support rollers 1a and 1b, and a drive motor (not shown) serving as a drive source is connected to the rotation shaft of the drive roller 1a among the support rollers. When this drive motor is driven, the intermediate transfer belt 1 rotates counterclockwise in the figure and the followable support roller 1b rotates. Inside the intermediate transfer belt 1, primary transfer devices 11Y, 11C, 11M, and 11K for transferring the toner images formed on the photoreceptors 21Y, 21C, 21M, and 21K onto the intermediate transfer belt 1 are provided. Yes.

  A secondary transfer roller 5 as a secondary transfer device is provided downstream of the primary transfer devices 11Y, 11C, 11M, and 11K in the endless movement direction of the intermediate transfer belt 1. A support roller 1b is disposed on the opposite side of the secondary transfer roller 5 and the intermediate transfer belt 1, and functions as a pressing member. In addition, a paper feed cassette 8 that houses transfer paper P as a recording material, a paper feed roller 7, a registration roller 6 and the like are provided. Further, a fixing device 4 for fixing the image on the transfer paper P and a discharge roller 3 are provided at the downstream portion of the secondary transfer roller 5 with respect to the traveling direction of the transfer paper P on which the toner image is transferred by the secondary transfer roller 5. I have.

Next, the operation of the printer 100 will be described.
The photoreceptors 21Y, 21C, 21M, and 21K are rotated by the individual toner image forming units 101Y, 101C, 101M, and 101K, and the charging devices 17Y, 17C, and 17M are first rotated along with the rotation of the photoreceptors 21Y, 21C, 21M, and 21K. , 17K uniformly charge the surfaces of the photoreceptors 21Y, 21C, 21M, and 21K. Next, based on the image data, laser light from the optical writing unit 9 is irradiated to form electrostatic latent images on the photosensitive members 21Y, 21C, 21M, and 21K. Thereafter, toner is attached by the developing devices 10Y, 10C, 10M, and 10K, and the electrostatic latent images are visualized to form yellow, cyan, magenta, and black on the photoreceptors 21Y, 21C, 21M, and 21K, respectively. A monochromatic image is formed. Further, the drive roller 1a is driven to rotate by a drive motor (not shown), the other driven roller 1b and the secondary transfer roller 5 are driven to rotate, the intermediate transfer belt 1 is rotated and conveyed, and the visible image is transferred to the primary transfer device. The images are sequentially transferred onto the intermediate transfer belt 1 by 11Y, 11C, 11M, and 11K. As a result, a composite color image is formed on the intermediate transfer belt 1. The surface of the photoconductors 21Y, 21C, 21M, and 21K after image transfer is cleaned by removing residual toner with a photoconductor cleaning device to prepare for image formation again.

  In accordance with the timing of image formation described above, the transfer paper P is fed from the paper feed cassette 8 by the paper feed roller 7 and conveyed to the registration rollers 6 and temporarily stops. Then, the sheet is conveyed between the secondary transfer roller 5 and the intermediate transfer belt 1 while taking timing with the image forming operation. Here, the intermediate transfer belt 1 and the secondary transfer roller 5 form a so-called secondary transfer nip across the transfer paper P, and the secondary transfer roller 5 transfers the toner image on the intermediate transfer belt 1 onto the transfer paper P. Secondary transfer to.

  The transfer paper P onto which the unfixed image has been transferred is sent to the fixing device 4, where the fixing device 4 applies heat and pressure to fix the unfixed image, and is discharged outside the apparatus. On the other hand, the intermediate transfer belt 1 after the image transfer is removed by the intermediate transfer body cleaning device 12 to remove residual toner remaining on the intermediate transfer belt 1 after the image transfer, so that the tandem image forming unit prepares for another image formation.

  The toner image forming units 101Y, 101C, 101M, and 101K for each color are integrally formed and are detachable process cartridges that can be attached to and detached from the main body. These integral process cartridges can be pulled out to the near side of the printer 100 main body along a guide rail (not shown) fixed to the printer 100 main body. Further, the toner image forming units 101Y, 101C, 101M, and 101K can be loaded at predetermined positions by pushing the process cartridge into the back side of the printer 100 main body.

FIG. 2 is a schematic diagram illustrating a schematic configuration of a process cartridge that is the toner image forming units 101Y, 101C, 101M, and 101K.
Since the process cartridges of the toner image forming units 101Y, 101C, 101M, and 101K perform the same configuration and operation, the subscripts Y, C, M, and K are appropriately omitted below. .
In FIG. 2, a charging roller 17 as a charging device, a developing device 10, a fur brush 36 as a photosensitive member cleaning device, a cleaning blade 33, and the like are sequentially arranged around a photosensitive member 21 that rotates clockwise in the drawing. . The charging roller 17 is disposed vertically below the photoconductor 21. Further, below the charging roller 17, there is provided a cleaner roller 18 as a charging cleaning roller for cleaning by contacting the surface of the charging roller 17 so as to rotate around. The photoconductor cleaning device also includes a fur brush 36, a cleaning blade 33, and a waste toner conveying coil 34 that discharges waste toner scraped off from the photoconductor 21 to the outside of the process cartridge.

FIG. 3 is a schematic configuration diagram illustrating an example of a fixing device that can be used in this embodiment.
A fixing device 4 shown in FIG. 3 is an example of a belt-type fixing device. In this fixing device 4, a fixing belt 42, which is a heating rotator, is bridged between a fixing roller 43 and a heating roller 44 including a heater 45 composed of, for example, a halogen heater. Is pressed against the fixing roller 43 via the fixing belt 42. A temperature sensor 46 serving as a temperature detection unit is provided at a location facing the outer peripheral surface portion of the fixing belt 42 wound around the heating roller 44. Based on the detection result of the temperature sensor 46, the heater 45 is controlled.

  The transfer paper P carrying an unfixed image made of unfixed toner T is guided by an entrance guide 47 and is fed into a fixing nip N formed by the portion of the fixing belt 42 wound around the fixing roller 43 and the pressure roller 41. enter in. In the fixing nip N, the unfixed toner T is fixed on the transfer paper P by heat and pressure. Further, in order to prevent the transfer paper P that has passed through the fixing nip N from being wound around the fixing belt 42, a paper separating means 49 such as a separating plate or a separating claw is provided.

FIG. 4 is a schematic configuration diagram illustrating another example of a fixing device that can be used in this embodiment.
The fixing device 4 shown in FIG. 4 is an example of a roller type fixing device. In this fixing device 4, instead of the fixing belt 42, the fixing roller 43, and the heating roller 44 described above, a fixing roller 48, which is a heating rotator provided with a heater 45 such as a halogen heater, is disposed. In the fixing device 4, the fixing nip N is formed by adopting a configuration in which the pressure roller 41 is pressed against the fixing roller 48. In the fixing device 4, a temperature sensor 46 that is a temperature detection unit is provided at a location facing the outer peripheral surface of the fixing roller 48, and the heater 45 is controlled based on the detection result of the temperature sensor 46. .

  The fixing device that can be used in this embodiment is not limited to that shown in FIGS. 3 and 4, and other configurations may be adopted. In the following description, the belt type fixing device shown in FIG. 3 will be described as an example.

FIG. 5 is an explanatory diagram showing an example of the configuration of the temperature sensor 46 in the present embodiment.
The temperature sensor 46 of the present embodiment includes a central temperature sensor 46a serving as a central temperature detecting unit that detects a temperature in a substantially central region of the fixing belt 42 in the fixing belt rotation axis direction (the rotation axis direction of the heating roller 44), and a fixing belt. It comprises an end temperature sensor 46b as end temperature detecting means for detecting the temperature of the end region of the fixing belt 42 in the rotation axis direction. The temperature of the fixing belt portion that comes into contact with the transfer paper P during the fixing process can be detected by the central temperature sensor 46a. Further, the temperature of the fixing belt portion that does not come into contact with the transfer paper P during the fixing process can be detected by the end temperature sensor 46b.

  When the image forming operation (print job) related to the input image data is finished, the printer 100 according to the present embodiment shifts to an image forming operation standby state, and stops the rotation of the fixing belt 42 while targeting the fixing belt 42. The standby state is maintained in a predetermined target standby temperature range lower than the fixing temperature. In the present embodiment, control for maintaining the temperature of the fixing belt 42 within the target standby temperature range during the standby state is realized by controlling the heater 45 on / off. More specifically, when the central temperature of the fixing belt 42 detected by the temperature sensor 46a falls below the lower limit value of the target standby temperature range, the heater 45 is turned on (on) to heat the fixing belt 42. When the center temperature of the fixing belt 42 detected by the temperature sensor 46a exceeds the lower limit value of the target standby temperature range, the heater 45 is turned off (off) and heating of the fixing belt 42 is stopped. Such on / off control of the heater 45 is an advantageous heater control method for satisfying the flicker standard of the heater (flicker standard) because the state of the heater 45 is controlled by binary values of on and off.

FIG. 6 is an explanatory diagram showing a temperature change of the fixing belt 42 when the fixing belt 42 temporarily rotates during the standby state in the conventional configuration.
FIG. 6 also shows the heater lighting duty indicating the amount of heating by the heater 45 along with the temporal change of the temperature at the center of the fixing belt 42 and the temperature at the center of the pressure roller 41 in the fixing belt rotation axis direction. The heater lighting duty is determined every time the predetermined control cycle T0 [s], from the temperature detection value of the central temperature sensor 46a and the lower limit value of the target standby temperature range, the heating amount of the heater 45 in the next control cycle, It is determined according to the amount of heating. The heater lighting duty is indicated by the ratio between the heater lighting time T1 [s] and the control period T0 [s] within one control period T0 [s]. As the difference between the temperature detection value of the central temperature sensor 46a and the lower limit value of the target standby temperature range is larger, the heater lighting duty is set larger.

  In the control shown in FIG. 6, when the temperature of the non-rotating fixing belt 42 is controlled during the standby state (normal standby control), the heater is turned on when the temperature falls below the lower limit (for example, 160 ° C.) of the target standby temperature range. Control is performed to turn off the light when exceeding. In this case, the temperature ripple can be reduced to about 159 to 180 ° C., and the temperature of the fixing belt 42 can be maintained within the target standby temperature range (159 to 180 ° C.).

  However, in the present embodiment, a drive source that applies a rotational driving force to the fixing roller 43 that is a drive roller of the fixing belt 42 is shared with the drive source of the paper feed cassette 8. Therefore, for example, when the user moves the paper feed cassette 8 during the standby state and the drive source of the paper feed cassette 8 rotates, the fixing belt 42 rotates in conjunction with this. In FIG. 6, the rotation of the fixing belt 42 occurs at the time of 200 [s]. When such a rotation of the fixing belt 42 occurs, the fixing belt 42 is rapidly cooled, and the central temperature of the fixing belt 42 detected by the central temperature sensor 46a rapidly decreases, and the lower limit (160 ° C.) of the target standby temperature range is greatly increased. It will be less than.

  In response to this, in the temperature control of the fixing belt 42, the heater 45 is controlled so as to restore the temperature of the fixing belt 42 to the target standby temperature range. At this time, the temperature detection value of the central temperature sensor 46a and the target standby temperature are controlled. The difference from the lower limit of the range is very large. Therefore, until the difference between the temperature detection value of the central temperature sensor 46a and the lower limit value of the target standby temperature range becomes small, the heater lighting duty of each control cycle T0 [s] continues to be set to the maximum value of 100%. Here, while the fixing belt 42 is rotating, the amount of heat that escapes from the fixing belt 42 is large. Therefore, even if the heater lighting duty of the control cycle T0 [s] is 100%, the temperature of the fixing belt 42 is relatively high. It will recover slowly. However, the rotation of the fixing belt 42 described above is temporary, and the rotation immediately stops as shown in FIG. For this reason, while the heater lighting duty is 100% and the temperature control of the heater 45 is being performed, the rotation of the fixing belt 42 is stopped, whereby the amount of heat escaping from the fixing belt 42 is greatly reduced, and as a result, fixing is performed. The temperature of the belt 42 increases rapidly. As a result, as shown in FIG. 6, the temperature of the fixing belt 42 overshoots to about 230 ° C.

  Since the fixing belt 42 of this embodiment begins to deteriorate at about 240 ° C. or higher, it is important to extend the life of the fixing belt 42 so that the maximum temperature that the fixing belt 42 can take is as low as possible. is there. For this purpose, it is necessary to suppress the above-described overshoot.

FIG. 7 is a flowchart showing a flow of control of the heater 45 in the standby state in the present embodiment.
In the present embodiment, after shifting to the standby state (S1), the normal standby control described above is performed (S2), and the heater is used to maintain the fixing belt 42 within the target standby temperature range while stopping the rotation of the fixing belt 42. 45 is controlled. When the return condition that a new print job is input is satisfied (Yes in S3), an image forming operation is performed according to the print job (S11). In this example, the return condition from the standby state illustrates the condition that a new print job is input, but other return conditions may be used.

  If the rotation of the fixing belt 42 is detected during the standby state (Yes in S4), the control unit (not shown) first checks whether or not the temperature of the fixing belt 42 is maintained within the target standby temperature range. . Specifically, the temperature Ta in the central region of the fixing belt 42 is detected by the central temperature sensor 46a (S5), and it is determined whether the temperature Ta is equal to or higher than the lower limit value Tmin of the target standby temperature range (S6). . In this determination, if it is determined that the temperature Ta in the central region of the fixing belt 42 is equal to or higher than the lower limit value Tmin of the target standby temperature range (Yes in S6), the normal standby control is continued (S2). On the other hand, if it is determined that the temperature Ta in the central region of the fixing belt 42 is lower than the lower limit value Tmin of the target standby temperature range (No in S6), the process proceeds to special standby control.

  When shifting to the special standby control, the control unit first turns on the heater 45 for a predetermined lighting time W [s] determined in advance (S7, S8). The specified lighting time W [s] can be set as appropriate. For example, when the fixing belt 42 rotates for a minimum rotation duration assumed when the fixing belt 42 that is in the target standby temperature range rotates during the standby state, this is performed by one special standby control. Can be set on the basis of the minimum heater lighting time required to recover the temperature within the target standby temperature range.

  As a method for detecting the rotation of the fixing belt 42, known detection means for detecting the rotation of the fixing belt 42 can be widely used. When the control unit performs drive control for rotating the fixing belt 42 in the standby state, it can be determined that the fixing belt 42 has been rotated when the drive control is performed.

  When a predetermined lighting time W [s] determined in advance after the heater 45 is turned on (Yes in S8), the control unit forcibly turns off the heater 45 for a predetermined blacking-off time X [s]. (S9, S10). Specifically, the heater 45 is turned off regardless of whether or not the temperature of the fixing belt 42 has returned to the target standby temperature range when the specified lighting time W [s] has elapsed since the heater was turned on. Thereby, generation | occurrence | production of the overshoot mentioned above can be suppressed by setting the regulation lighting time W [s] appropriately.

  In this way, after the heater 45 is turned off, after the specified turn-off time X [s] has elapsed (Yes in S10), the routine may proceed to normal standby control as it is. However, in the present embodiment, the specified lighting time W [s] is set to a relatively short time. Therefore, when the rotation time of the fixing belt 42 is relatively long, the heater is lit for the specified lighting time W [s]. In many cases, it is difficult to return the temperature of the fixing belt 42 to the target standby temperature range.

  Therefore, in the present embodiment, it is confirmed whether or not the temperature of the fixing belt 42 has returned to the target standby temperature range after the lapse of the specified turn-off time X [s] from the heater turn-off (Yes in S10). Specifically, as in the case of the normal standby control, the temperature Ta in the central region of the fixing belt 42 at the time when the specified turn-off time X [s] has elapsed from the heater turn-off is detected by the central temperature sensor 46a (S5). It is determined whether the temperature Ta is equal to or higher than the lower limit value Tmin of the target standby temperature range (S6). In this determination, if it is determined that the temperature Ta in the central region of the fixing belt 42 is equal to or higher than the lower limit value Tmin of the target standby temperature range (Yes in S6), the routine proceeds to normal standby control (S2). On the other hand, if it is determined that the temperature Ta in the central region of the fixing belt 42 is lower than the lower limit value Tmin of the target standby temperature range (No in S6), special standby control is executed again (S7 to S10).

  Therefore, in this embodiment, the special standby control in which the forced heater turn-off time is provided is repeated until the temperature Ta in the central region of the fixing belt 42 becomes equal to or higher than the lower limit value Tmin of the target standby temperature range. Thereby, the temperature of the fixing belt 42 can be returned to the target standby temperature range without causing an overshoot.

FIG. 8 is an explanatory diagram showing a temperature change of the fixing belt 42 when the fixing belt 42 temporarily rotates during the standby state in the present embodiment.
In FIG. 8, when the fixing belt 42 rotates during the standby state, the temperature of the fixing belt 42 is rapidly decreased. Therefore, the temperature Ta in the central region of the fixing belt 42 becomes less than the lower limit value Tmin of the target standby temperature range, and the process shifts to special standby control. First, in the first special standby control, the heater is turned on for the specified lighting time W1 (= 2 [s]) and the heater is forcibly turned off for the specified light-off time X1 (= 10 [s]).

  At the time when the specified turn-off time X1 has elapsed, the temperature Ta in the central region of the fixing belt 42 is not equal to or higher than the lower limit value Tmin of the target standby temperature range. Therefore, the second special standby control is performed, and the heater is turned on for the specified lighting time W2 (= 2 [s]) and the heater is forcibly turned off for the specified lighting time X2 (= 10 [s]). In the example of FIG. 8, the temperature Ta in the central region of the fixing belt 42 is equal to or higher than the lower limit value Tmin of the target standby temperature range during the second specified turn-off time X2. Therefore, the temperature Ta in the central region of the fixing belt 42 detected by the central temperature sensor 46a when the specified turn-off time X2 has elapsed is equal to or higher than the lower limit value Tmin of the target standby temperature range. As a result, thereafter, the process shifts to the normal standby control, and the temperature of the fixing belt 42 is stably maintained within the target standby temperature range.

  The specified lighting time W and the specified turn-off time X may be different between the first special standby control and the second and subsequent special standby controls.

[Modification 1]
Next, a modified example of heater control in the standby state in the above embodiment (hereinafter, this modified example is referred to as “modified example 1”) will be described.
In the above embodiment, when the fixing belt 42 is rotating and the special standby control transition condition that the temperature Ta in the central region of the fixing belt 42 is lower than the lower limit value Tmin of the target standby temperature range is satisfied, the special standby control is performed. It was an example to move to. On the other hand, in the first modification, after detecting the rotation of the fixing belt 42, the temperature Ta in the central region of the fixing belt 42 is less than the lower limit value Tmin of the target standby temperature range, and the fixing belt within a predetermined period. When the special standby control transition condition that the temperature Ta in the central region of 42 has decreased is an example, the process shifts to special standby control. In addition, in this modification 1, the description about the location similar to the said embodiment is abbreviate | omitted.

FIG. 9 is a flowchart showing a flow of control of the heater 45 in the standby state in the first modification.
In the first modification, when the rotation of the fixing belt 42 is detected during the standby state (Yes in S4), the control unit first detects the temperature Ta1 in the central region of the fixing belt 42 by the central temperature sensor 46a (S21). . Thereafter, when a predetermined period has elapsed (S22), the temperature Ta2 in the central region of the fixing belt 42 is again detected by the central temperature sensor 46a (S23). The current temperature Ta2 detected at this time is less than the lower limit value Tmin of the target standby temperature range, and the value obtained by subtracting the previous temperature Ta1 detected at the time of detecting the rotation of the fixing belt 42 from the current temperature Ta2 is less than zero. It is determined whether or not the special standby control transition condition of small is satisfied (S24). In this determination, if it is determined that the special standby control shift condition is not satisfied, the normal standby control is continued (S2). If it is determined that the special standby control shift condition is satisfied, the process shifts to the special standby control (S7 to S7). S10).

FIG. 10 is a table showing an example of a table used when the controller in the first modification determines the heater lighting duty used when the heater is on during the special standby control.
In the first modification, the special standby control is repeated while the special standby control transition condition described above is satisfied. The heater lighting duty when the heater is on during the special standby control is set to 100%.

FIG. 11 is an explanatory diagram showing a temperature change of the fixing belt 42 when the fixing belt 42 rotates temporarily during the standby state in the first modification.
From FIG. 11, also in the first modification, even if the fixing belt 42 rotates during the standby state, the temperature of the fixing belt 42 can be returned to the target standby temperature range without causing overshoot.

[Modification 2]
Next, another modified example of the heater control in the standby state in the above embodiment (hereinafter, this modified example is referred to as “modified example 2”) will be described.
In the above embodiment, after the transition to the special standby control, the special standby control in which the forced heater turn-off time is provided until the temperature Ta in the central region of the fixing belt 42 becomes equal to or higher than the lower limit value Tmin of the target standby temperature range. Will repeat. In the second modification, when the number of executions N of the special standby control is equal to or greater than the specified number Nc, the process shifts to the normal standby control. In the second modification, description of the same parts as those in the above embodiment is omitted.

FIG. 12 is a flowchart showing a flow of control of the heater 45 in the standby state in the second modification.
In the second modification, when the rotation of the fixing belt 42 is detected during the standby state (Yes in S4), and the temperature Ta in the central region of the fixing belt 42 is less than the lower limit value Tmin of the target standby temperature range, a special 1 is added to the count value N indicating the number of times of execution of standby control (S31). The count value N is reset to zero when shifting from the special standby control to the normal standby control (S33), and N = 1 at the first special standby control. In the second modification, after the first special standby control is performed (S7 to S10), it is determined whether or not the count value N is equal to or greater than the specified number Nc (S32). The specified number of times Nc can be set as appropriate.

FIG. 13 is an explanatory diagram showing a temperature change of the fixing belt 42 when the fixing belt 42 temporarily rotates during the standby state when the specified number of times Nc in the second modification is set to two.
In the second modification, unlike the example in FIG. 8 and the example in FIG. 11 described above, the input voltage of the image forming apparatus is reduced to 70% of the rated voltage. For example, when a plurality of energizing devices other than the printer 100 are connected to the power source, the input voltage may decrease. When the input voltage is low, the power consumption of the heater 45 decreases, and the power consumption is about 1.4th power of the voltage ratio to the rated voltage. Therefore, when the input voltage is 70% of the rated voltage (for example, when the input voltage is 70V with respect to the rated voltage of 100V), the power consumption decreases to about 60% of the rated power.

  In the example of FIG. 8, the temperature of the fixing belt 42 recovered to the target standby temperature range by the second special standby control. However, in the example of FIG. 13, since the input voltage has decreased, the second special standby control is performed. Even if the operation is performed, the temperature of the fixing belt 42 does not recover to the target standby temperature range. Even if the normal standby control is performed in this state, the difference between the fixing belt temperature and the lower limit value of the target standby temperature range is small due to the execution of the special standby control twice. It is suppressed. However, as shown in FIG. 13, even in this case, since the fixing belt 42 is heated to about 190 ° C., it is desirable to suppress such a small overshoot.

FIG. 14 is an explanatory diagram showing a temperature change of the fixing belt 42 when the fixing belt 42 temporarily rotates during the standby state when the specified number of times Nc in the second modification is set to 3 or more.
As shown in FIG. 14, by performing the third special standby control, the temperature Ta in the central region of the fixing belt 42 becomes equal to or higher than the lower limit value Tmin of the target standby temperature range during the third specified turn-off time X3. . Therefore, after that, the routine proceeds to normal standby control, and the temperature of the fixing belt 42 is stably maintained within the target standby temperature range.

[Modification 3]
Next, still another modified example of the heater control in the standby state in the above embodiment (hereinafter, this modified example is referred to as “modified example 3”) will be described.
In the third modification, in the second modification described above, when the central temperature sensor 46a causes a resistance abnormality and falls into an abnormal state in which the temperature in the central area of the fixing belt 42 is detected lower than the actual temperature, Control is performed.

FIG. 15 is a flowchart showing a flow of control of the heater 45 in the standby state in the third modification.
In the third modification, when the rotation of the fixing belt 42 is detected during the standby state (Yes in S4), it is determined whether or not the temperature Ta in the central region of the fixing belt 42 is equal to or higher than the lower limit value Tmin of the target standby temperature range. (S5, S6). At this time, in the third modification, even when it is determined that the temperature Ta is equal to or higher than the lower limit value Tmin of the target standby temperature range, the normal standby control is not continued, but the control shifts to the special standby control. It has become.

  More specifically, when the rotation of the fixing belt 42 is detected during the standby state, the first special standby control is always performed (S41). However, the first special standby control is performed when the temperature Ta detected by the central temperature sensor 46a when the rotation of the fixing belt 42 is detected is equal to or higher than the lower limit value Tmin of the target standby temperature range (Yes in S6, Yes in S41). Then, the heater is not turned on for the specified lighting time W1, and the heater is turned off for the specified turn-off time X1 (S9, S10). On the other hand, when the temperature Ta detected by the central temperature sensor 46a when the rotation of the fixing belt 42 is detected is less than the lower limit value Tmin of the target standby temperature range, the specified lighting time W1 is also used in the first special standby control as described above. After the heater is turned on (S7, S8), the heater is turned off forcibly during the specified turn-off time X1 (S9, S10).

FIG. 16 is an explanatory diagram showing a temperature change of the fixing belt 42 when the fixing belt 42 temporarily rotates during the standby state when the central temperature sensor 46a has a resistance abnormality.
In the example illustrated in FIG. 16, the image forming operation for continuously forming 20 images is performed, and then the standby state is entered. However, since the fixing belt 42 is in the non-rotating state, the temperature of the fixing belt 42 is increased. It shows a rising situation. When the temperature of the non-rotating fixing belt 42 rises to a specified temperature (206 ° C. in this case) during the standby state, fixing belt cooling control is performed in which the fixing belt 42 is rotationally driven to lower the temperature of the fixing belt 42. .

  When the fixing belt 42 rotates by this fixing belt cooling control, special standby control is performed. At this time, since the detected temperature Ta of the central temperature sensor 46a is equal to or higher than the lower limit value Tmin of the target standby temperature range, in the first special standby control, the heater is not turned on for the specified lighting time W1, and the heater is set for the specified lighting time X1. It will be forcibly turned off.

  Here, in the example of FIG. 16, when the temperature of the fixing belt 42 is suddenly lowered by the fixing belt cooling control, the central temperature sensor 46a causes a resistance abnormality, and the temperature Ta detected by the central temperature sensor 46a shows a low value. It has become. Therefore, the temperature Ta detected by the central temperature sensor 46a of the resistance abnormality is less than the lower limit value Tmin of the target standby temperature range when the specified turn-off time X1 in the first special standby control has elapsed. As a result, the second special standby control is performed, and the heater is lit for the specified lighting time W2 (S7, S8). Furthermore, even when the specified turn-off time X2 in the second special standby control has elapsed, the temperature Ta detected by the central temperature sensor 46a having the resistance abnormality is less than the lower limit value Tmin of the target standby temperature range. The heater is turned on for a specified lighting time W3 (S7, S8).

  However, as shown in FIG. 16, the actual temperature of the fixing belt 42 has already become abnormal in the lower limit value Tmin of the target standby temperature range when the specified turn-off time X1 in the first special standby control has elapsed. Therefore, when the second and third special standby controls are performed, the actual temperature of the fixing belt 42 rises beyond the target standby temperature range as shown in FIG.

  When the third special standby control is completed, the normal standby control is resumed. If the control shifts to the normal standby control, the abnormal temperature rise countermeasure control for dealing with the resistance abnormality of the central temperature sensor 46a is performed. Therefore, the heater 45 is not heated after this point, and the temperature rise of the fixing belt 42 is prevented. Stops. However, because of the resistance abnormality in the central temperature sensor 46a, even if the actual temperature of the fixing belt 42 has risen above the target standby temperature range, the special standby control is repeatedly performed up to Nc times, which is the maximum number of times. In such a case, as shown in FIG. 16, the temperature of the fixing belt 42 rises to about 305 ° C. at the maximum.

  Here, the abnormal temperature rise control of the central temperature sensor 46a in the present embodiment will be described with reference to FIG. In the abnormal temperature rise control, the abnormal temperature rise of the individual fixing belts 42 is determined based on the detected temperatures acquired independently from the center temperature sensor 46a and the end temperature sensor 46b. Therefore, even when the resistance abnormality occurs in the central temperature sensor 46a and proper temperature detection cannot be performed, appropriate abnormal temperature rise control can be performed based on the temperature detection result of the end temperature sensor 46b.

In the abnormal temperature rise control, as shown in FIG. 17, two-stage detection of a first stage and a second stage is performed.
In the first stage detection, when the detection temperature of the central temperature sensor 46a or the end temperature sensor 46b reaches the first stage detection start temperature, the temperature (temperature rise amount) that rises during a predetermined detection time is When it is equal to or higher than the temperature rise threshold, it is determined that the temperature is abnormally high. Here, in the first stage detection based on the temperature detected by the end temperature sensor 46b, a condition that the heater lighting duty is continued at 100% during the detection period is further added.
In the second stage detection, when the detected temperature of the central temperature sensor 46a or the end temperature sensor 46b reaches the second stage detection start temperature, the second stage detection start temperature or higher continues for a predetermined detection time. Is detected, it is determined that the temperature is abnormally high.

  In such an abnormal temperature rise control, since it is not possible to make a sufficient determination by turning on a short heater during the special standby control, the abnormal temperature rise response control is performed during the normal standby control as described above. Therefore, as described above, when the number of repetitions of the special standby control exceeds the specified number, the abnormal temperature rise of the fixing belt 42 can be dealt with by returning to the normal standby control. However, after shifting to the normal standby control, a certain amount of time is required to determine the abnormal temperature rise of the fixing belt 42. Therefore, as shown in FIG. 16, even after the special standby control is repeated Nc times and returned to the normal standby control, the fixing belt 42 is heated for a while and the temperature of the fixing belt 42 rises. As a result, the temperature of the fixing belt 42 rises up to about 305 ° C. as shown in FIG.

  Therefore, in the third modification, the temperature Ta in the central region of the fixing belt 42 is detected by the central temperature sensor 46a when the specified turn-off time X in the special standby control has elapsed (S42). Then, it is determined whether or not the normal standby control transition condition that the temperature Ta is less than a value obtained by subtracting the predetermined subtraction temperature α from the lower limit value Tmin of the target standby temperature range is determined (S43). In this determination, when the normal standby control transition condition is satisfied, the routine proceeds to normal standby control, and abnormal temperature rise control is performed.

FIG. 18 illustrates the central temperature sensor 46a after performing one special standby control (the heater is turned on at the specified lighting time W and the heater is turned off at the specified lighting time X) in order to explain an example of a method for determining the subtraction temperature α. It is the graph which showed detected temperature of. This graph shows the results when the input voltage and the heater end light distribution are changed.
Under the condition where the input voltage is high, the temperature is higher than the lower limit value Tmin (= 160 ° C.) of the target standby temperature range by performing the special standby control once, but the condition where the input voltage is low (for example, 70 [V]) Then, the temperature is lower than the lower limit value Tmin of the target standby temperature range. Based on this, a temperature lower than the temperature detected by the central temperature sensor 46a when the special standby control is performed only once at the lower limit voltage considered in actual operation is set, and this temperature and the lower limit value of the target standby temperature range The difference from Tmin is set as the subtraction temperature α. In this case, when special standby control at a low voltage is performed, it is possible to suppress erroneous transition to the normal standby state.

FIG. 19 is an explanatory view showing a temperature change of the fixing belt 42 when the subtraction temperature α is set to 20 ° C. in the third modification.
In the third modification, the normal standby control transition condition that the detected temperature Ta of the central temperature sensor 46a is less than (Tmin−α) is satisfied at the elapse of the specified turn-off time X2 in the second special standby control. The process shifts to standby control, and abnormal temperature rise control is performed. In the example shown in FIG. 16, since the special standby control is repeated three times and then the normal standby control is performed and the abnormal temperature rise countermeasure control is performed, the temperature of the fixing belt 42 has increased to 305 ° C. On the other hand, according to the third modification, as shown in FIG. 19, after the special standby control is repeated twice, the control shifts to the normal standby control and the abnormal temperature rise control is performed. The temperature rise of 42 could be suppressed to 245 ° C.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
By using the image forming unit such as a tandem image forming unit or a transfer unit for forming an image on a recording material such as transfer paper P, and a heating rotator such as a fixing belt 42 heated to a target fixing temperature, A fixing unit such as a fixing device 4 for performing a heat fixing process for thermally fixing an image formed on the recording material to the recording material; and a temperature of the heating rotator while stopping the rotation of the heating rotator during a standby state. In the image forming apparatus including a standby control unit such as a control unit that performs normal standby control that maintains the temperature within the target standby temperature range, the standby control unit rotates the heating rotator during the normal standby control. It is determined whether or not the special standby control transition condition including the necessary condition is satisfied. When the special standby control transition condition is not satisfied, the normal standby control is continued, and when the special standby control transition condition is satisfied The When the heating rotator is heated and a predetermined heating end timing arrives, heating of the heating rotator is terminated regardless of whether or not the temperature of the heating rotator is within the target standby temperature range. A special standby control is implemented in which the heating rotator is not heated until a predetermined non-heating end timing arrives.
According to this, it is possible to suppress the overshoot of the temperature of the heating rotator that occurred when the heating rotator of the fixing device temporarily rotates during the standby state.

(Aspect B)
In the aspect A, the special standby control transition condition includes a condition that a temperature of the heating rotator when the heating rotator rotates is below a target standby temperature range.
According to this, when the temperature of the heating rotator is within the target standby temperature range or exceeding the target standby temperature range, the special rotator control is not performed, and the heating rotator is not heated by the special standby control. Therefore, it is possible to prevent the heating rotator from being excessively heated by the special standby control.

(Aspect C)
In the aspect A or B, the special standby control transition condition includes a condition that a temperature of the heating rotator is decreased with time within a predetermined period after the heating rotator rotates. To do.
According to this, when the temperature of the heating rotator is decreased due to the rotation of the heating rotator, special standby control can be performed to suppress the temperature decrease of the heating rotator, and the temperature of the heating rotator. Can be recovered.

(Aspect D)
In any of the above aspects A to C, the standby control means determines whether or not the special standby control transition condition is satisfied when the special standby control is finished, and satisfies the special standby control transition condition. If not, the normal standby control is performed. If the special standby control transition condition is satisfied, the special standby control is performed again.
According to this, the heating time of the heating rotator during one special standby control can be shortened by repeatedly executing the special standby control transition condition. Thereby, it becomes possible to suppress effectively the overshoot of the temperature of a heating rotary body.

(Aspect E)
In the aspect D, the special standby control transition condition includes a condition that the temperature of the heating rotator when the heating rotator rotates is lower than a target standby temperature range. Determining whether or not an abnormal condition is satisfied, including a condition that the temperature of the heating rotator is lower than a threshold temperature that is lower than a predetermined temperature such as a subtracted temperature α determined in advance from a target standby temperature range; When it is determined that the condition is satisfied, predetermined abnormality response control is performed.
According to this, as described in Modification 3 above, even when the temperature of the heating rotator cannot be properly detected, the abnormality response control can be performed more quickly, and the heating is performed by repeating the special standby control. A situation where the temperature of the rotating body is excessively increased can be suppressed.

(Aspect F)
In the aspect E, the specified temperature is set to a value larger than a difference between a minimum temperature that the heating rotator can take when the special standby control is performed and a lower limit value of the target standby temperature range. It is characterized by.
According to this, when the heating rotating body during the special standby control is insufficiently heated, such as when the input voltage is lowered, it is possible to prevent the abnormality handling control from being erroneously performed.

(Aspect G)
In the aspect E or F, the central temperature detecting means such as the central temperature sensor 46a for detecting the temperature in the substantially central region in the rotation axis direction of the heating rotator, and the temperature in the end region in the rotation axis direction of the heating rotator are detected. Normal temperature control performed by the standby control means specifies the temperature of the heating rotator from the detection result of the central temperature detection means, and the end temperature detection means such as the end temperature sensor 46b. The temperature of the heating rotator specified by is maintained within the target standby temperature range, and the abnormal condition is that the detection result of the end temperature detection means exceeds a predetermined threshold such as the first stage detection start temperature. And the condition that the temperature rise detected by the end temperature detecting means within a predetermined time is not less than a predetermined width is included.
According to this, it is possible to suppress a situation in which the heating rotator is excessively heated due to a detection abnormality of the central temperature detection means.

(Aspect H)
In the aspect D, the central temperature detecting means such as the central temperature sensor 46a for detecting the temperature in the substantially central region in the rotation axis direction of the heating rotator, and the end for detecting the temperature in the end region in the rotation axis direction of the heating rotator. Normal standby control performed by the standby control means is to specify the temperature of the heating rotator from the detection result of the central temperature detection means, and to thereby specify The temperature of the heated rotating body is maintained within a target standby temperature range, and the standby control means has a detection result of the end temperature detection means exceeding a predetermined threshold value during the normal standby control. In addition, it is determined whether or not an abnormal condition that the temperature increase detected by the end temperature detecting means is equal to or greater than a predetermined width within a predetermined time is satisfied. Anomaly response system Further, the standby control means includes a transition to normal standby control including a condition that the temperature of the heating rotator is below a threshold temperature that is lower than a target standby temperature range by a predetermined temperature that is predetermined. It is determined whether or not the condition is satisfied, and when the normal standby control transition condition is satisfied, the normal standby control is performed.
According to this, it is possible to suppress a situation in which the heating rotator is excessively heated due to a detection abnormality of the central temperature detection means.

DESCRIPTION OF SYMBOLS 1 Intermediate transfer belt 4 Fixing device 8 Paper feeding cassette 9 Optical writing unit 10 Developing device 17 Charging device 21 Photoconductor 41 Pressure roller 42 Fixing belt 43 Fixing roller 44 Heating roller 45 Heater 46a Central temperature sensor 46b End temperature sensor 47 Entrance guide 48 Fixing roller 49 Paper separating means 100 Printer

Japanese Patent No. 343057 JP 2007-133247 A

Claims (8)

Image forming means for forming an image on a recording material;
A fixing means for performing a heat fixing process for thermally fixing an image formed on the recording material by the image forming means to the recording material using a heating rotator heated to a target fixing temperature;
In an image forming apparatus comprising standby control means for performing normal standby control to stop the rotation of the heating rotator while maintaining the temperature of the heating rotator within a target standby temperature range during a standby state,
The standby control means determines whether or not a special standby control transition condition including a necessary condition that the heating rotating body has rotated during the normal standby control is satisfied, and if the special standby control transition condition is not satisfied, When the normal standby control is continued and the special standby control transition condition is satisfied, the heating rotator is heated, and when the predetermined heating end timing is reached, the temperature of the heating rotator is within the target standby temperature range. Regardless of whether or not the heating rotator is heated, the heating rotator is heated, and a special standby control is performed in which the heating rotator is not heated until a predetermined non-heating end timing comes. Image forming apparatus. The image forming apparatus according to claim 1.
The special standby control transition condition includes an image forming apparatus characterized in that a temperature of the heating rotator when the heating rotator rotates is below a target standby temperature range. The image forming apparatus according to claim 1 or 2,
The special standby control transition condition includes a condition that a temperature of the heating rotator is decreased with time within a predetermined period after the heating rotator is rotated. The image forming apparatus according to any one of claims 1 to 3,
The standby control means determines whether or not the special standby control transition condition is satisfied when the special standby control is completed.If the special standby control transition condition is not satisfied, the normal standby control is performed. When the special standby control transition condition is satisfied, the special standby control is performed again. The image forming apparatus according to claim 4.
The special standby control transition condition includes a condition that the temperature of the heating rotator when the heating rotator rotates is below the target standby temperature range,
The standby control means determines whether or not an abnormal condition including a condition that the temperature of the heating rotator is lower than a threshold temperature that is lower than a target standby temperature range by a predetermined temperature that is predetermined, An image forming apparatus that performs predetermined abnormality response control when it is determined that the condition is satisfied. The image forming apparatus according to claim 5.
The specified temperature is set to a value larger than the difference between the minimum temperature that the heating rotator can take when the special standby control is performed and the lower limit value of the target standby temperature range. An image forming apparatus. The image forming apparatus according to claim 5 or 6,
A central temperature detecting means for detecting a temperature in a substantially central region in the rotation axis direction of the heating rotating body;
End temperature detection means for detecting the temperature of the end region in the rotation axis direction of the heating rotator,
The normal standby control performed by the standby control means specifies the temperature of the heating rotator from the detection result of the central temperature detection means, and maintains the temperature of the heating rotator specified thereby within the target standby temperature range. Is,
The abnormal condition is a condition that the detection result of the end temperature detection means exceeds a predetermined threshold value, and the temperature increase detected by the end temperature detection means within a predetermined time is equal to or greater than a predetermined width. An image forming apparatus comprising: The image forming apparatus according to claim 4.
A central temperature detecting means for detecting a temperature in a substantially central region in the rotation axis direction of the heating rotating body;
End temperature detection means for detecting the temperature of the end region in the rotation axis direction of the heating rotator,
The normal standby control performed by the standby control means specifies the temperature of the heating rotator from the detection result of the central temperature detection means, and maintains the temperature of the heating rotator specified thereby within the target standby temperature range. Is,
The standby control means is configured such that during the normal standby control, the detection result of the end temperature detection means exceeds a predetermined threshold value, and the temperature rise detected by the end temperature detection means within a predetermined time. Is determined whether or not the abnormal condition that is equal to or greater than a predetermined width, and if it is determined that the abnormal condition is satisfied, predetermined abnormality response control is performed,
Further, the standby control means satisfies a condition that when the special standby control is repeatedly performed a predetermined number of times, the temperature of the heating rotator is below a threshold temperature that is lower than a target standby temperature range by a predetermined temperature that is predetermined. An image forming apparatus comprising: determining whether or not a normal standby control transition condition is satisfied, and performing the normal standby control when the normal standby control transition condition is satisfied.

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