JP2014228677A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that controls the lighting of heating means on the basis of image information, and suppresses the occurrence of temperature deviation in the longitudinal direction of a fixing member; and an image forming apparatus using the fixing device.SOLUTION: A thermal head 23 includes heating areas R divided in a direction orthogonal to a recording material conveyance direction. Heating control means 26 individually controls the heating areas according to an image area having an unfixed image formed on the recording material, stores the cumulative time of the energization to the heating areas R by going back from the present time, and controls to adjust the energization time in the allocated heating areas R so that one heating area R has the difference between the maximum value and minimum value of the energization cumulative time in a fixed time smaller than a threshold compared with the other allocated heating area R.

Description

  The present invention relates to a fixing device and an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine having at least two functions thereof.

  In the image forming apparatus of the above-mentioned type, an unfixed toner image is formed on a recording medium sheet, printing paper, photosensitive paper, electrostatic recording by an image transfer method or a direct method by an image forming process such as electrophotographic recording, electrostatic recording, and magnetic recording. It is formed on a recording medium such as paper. As a fixing device for fixing an unfixed toner image, a heat roller system is widely used from the viewpoint of safety, compatibility with high speed machines, and the like.

  However, in the heat roller system, since the core of the fixing roller is made of metal and has a large heat capacity, it takes several minutes to reach a predetermined fixing temperature. For this reason, there is a problem that energy consumption is high due to standby heat that maintains the fixing roller at a certain temperature even when not in use.

  A belt and film system is often used as a fixing device for realizing energy saving. For example, Patent Document 1 discloses a fixing device configured to apply a plate-shaped heating unit that contacts a thin-walled cylindrical heat-resistant film and a recording material that is sandwiched between the film and the recording material with a pressure roller, and applies heat energy to the recording material. Have been described. In such a fixing device, since the film is as thin as about 100 μm, it is only necessary to raise the temperature of the plate-like heating means having a small heat capacity, so that the rise time can be shortened and the preheating power can be reduced.

  Furthermore, the fixing device of Patent Document 1 can save energy by changing the control temperature and heating area of the heating means in accordance with the image formed on the recording material and reducing the energy supply to the non-image area. The structure to perform is disclosed.

  Japanese Patent Application Laid-Open No. 2004-228561 is configured to measure the temperature of each element of the heating element of the thermal head and supply appropriate heat so that the influence of the ambient temperature is taken into consideration and only the toner portion on the paper is heated. Is disclosed.

  Patent Document 3 discloses a fixing device having means for varying the heating rate of the heating means based on image information for the purpose of reducing excess energy during paper feeding and reducing running costs. Such a fixing device has the advantage that the rise time is short and the energy loss is small compared to the internal heating method in which the entire fixing roller is heated by melting the toner with the heat stored near the fixing roller surface layer by heating from the outside. is there. Further, in Patent Document 3, a heating unit is divided in a direction orthogonal to the conveyance direction of the recording material, and each heating unit has a fixing set temperature and a low temperature setting temperature lower than that, and the non-image portion has a low temperature setting temperature. The structure which reduces energy by controlling by is disclosed.

  In such a technique, an image area is selectively heated using a fixing member, and energy is saved by lowering the temperature of the non-image area. However, in the case of image information that is asymmetric with respect to the center in the longitudinal direction, which is the width direction of the fixing member, an asymmetric amount of heat is supplied in the longitudinal direction of the fixing member that is selectively heated based on the image information. For this reason, there has been a problem that a deviation occurs in the heat accumulation in the right and left of the fixing member in the longitudinal direction. When such a deviation increases, there is a problem in that the fixing member moves toward one of the longitudinal directions due to the temperature deviation.

  The present invention solves the above-described conventional problems, and provides a fixing device in which a temperature deviation in the longitudinal direction of a fixing member hardly occurs in addition to lighting of a heating unit based on image information, and an image forming apparatus using the fixing device. It is a problem.

  In order to solve the above problems, the present invention provides a fixing member that contacts and rotates with an unfixed image, a pressure member that forms a fixing nip between the fixing member, and the fixing member is heated by energization. A fixing device having a heating means and a heating control means for controlling the heating means, and fixing the sheet-like recording material carrying an unfixed image through the fixing nip, wherein the heating means is a recording material The heating control means has a plurality of heating areas divided in the direction orthogonal to the conveying direction and having the same heating capacity, and the heating control means determines each heating area according to an image area where the unfixed image is formed on the recording material. In the fixing device that controls the temperature of the fixing member by independently controlling the temperature of the fixing member that contacts the image area, and controls the temperature of the fixing member that contacts the non-image area to be low. Energized In addition, each accumulated time is stored, and one of the heating areas is compared with another assigned heating area so that the difference between the maximum value and the minimum value of the energized accumulation time within the predetermined time is below a certain threshold value. The present invention proposes a fixing device having a control for adjusting the energization time in the assigned heating region.

  According to the present invention, it is possible to solve the problem that a deviation occurs in the accumulation of heat in the longitudinal direction of the fixing member while realizing energy saving by turning on the heating means based on image information.

FIG. 1 is a schematic view showing an example of a printer as an image forming apparatus in which the fixing device of the present invention is used. 1 is a cross-sectional explanatory view of a fixing device showing an embodiment of the present invention. It is explanatory drawing explaining the heating means of the fixing device. FIG. 6 is a diagram illustrating a basic operation of control of the fixing device according to the present invention. FIG. 4 is a diagram illustrating an image forming pattern in which an image area and a non-image area exist on a sheet. FIG. 6 is a diagram for explaining a target temperature during basic operation during control of the fixing device. It is explanatory drawing which shows another embodiment of the fixing device which concerns on this invention. FIG. 8 is an explanatory diagram illustrating a modified example of a fixing device including the fixing belt of FIG. 7. It is explanatory drawing explaining the heating means of this invention. It is a perspective view explaining the lighting control system of each heating area of the fixing device according to the present invention. It is a figure explaining the lighting control system of each heating area | region of the fixing device which concerns on this invention. It is explanatory drawing explaining the timing which performs lighting control of each heating area | region of this invention. It is explanatory drawing explaining the lighting system by Example 2 of this invention. It is explanatory drawing explaining lighting of each heating area | region of this invention. It is explanatory drawing explaining the lighting control system of each heating area | region by Example 3 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic view showing an example of a printer as an image forming apparatus in which the fixing device of the present invention is used. The printer shown here includes a photoconductive drum 1 as an image carrier, and around the photoconductive drum 1 is a charging unit, an optical writing unit, a developing unit, a transfer unit, a cleaning unit in order of rotation in the clockwise direction. Means and the like are arranged. When the photosensitive drum 1 is driven to rotate clockwise by a driving unit (not shown), the surface is uniformly charged by a charging roller 2 as a charging unit. When this charged portion reaches the optical writing section 3, exposure light (not shown) irradiates exposure light through the mirror 3a, and an electrostatic latent image corresponding to the image to be created is formed. When the formed electrostatic latent image reaches the developing position, it is visualized by the developing means 4 provided with the developing roller 4a to become a toner image. Then, the toner image arrives at a position where the transfer means 5 provided with the transfer charger 5a faces. The transfer means 5 is not limited to the transfer charger 5a, and a transfer roller, a transfer brush, a transfer belt, or the like can be used.

  In the present embodiment, a sheet feeding means 10 is disposed below the photosensitive drum 1. The sheet feeding means 10 separates the sheet feeding tray 11 in which sheets P as sheet-like recording materials are accommodated in a stacked state and the sheet P accommodated in the sheet feeding tray 11 one by one from the top. It has a paper feed roller 12 to be sent out.

  The paper P delivered by the paper supply roller 12 is conveyed to the photosensitive drum 1 via a pair of timing conveying rollers 13 (hereinafter referred to as timing rollers). At that time, the paper P is abutted against the timing roller 13 and temporarily stopped. After the posture deviation is corrected, the paper P is sent out at a timing synchronized with the rotation of the photosensitive drum 1. That is, the timing roller 13 sends the toner image formed on the photosensitive drum 1 to the transfer unit at a timing when the leading end of the toner image coincides with a predetermined position at the leading end of the sheet P in the transport direction.

  In the transfer portion, the image is transferred onto the paper P entering the same portion by applying a transfer bias by the transfer means 5. The paper P on which the toner image has been transferred is conveyed toward the fixing device 20 and is fixed by the fixing device 20, and then discharged and stacked on a paper discharge tray (not shown). On the other hand, it is inevitable that toner remains on the photosensitive drum 1 after the transfer, and this residual toner is scraped off by the cleaning blade 15 while passing through the cleaning means 14 as the photosensitive drum 1 rotates. To be cleaned. Thereafter, the residual potential on the photosensitive drum 1 is removed by a neutralizing unit (not shown) and prepared for the next image forming process.

FIG. 2 is an explanatory cross-sectional view of a fixing device showing an embodiment of the present invention, and FIG. 3 is an explanatory diagram for explaining a heating unit of the fixing device.
In FIG. 2, the fixing device 20 of the present embodiment is provided with a fixing roller 21 as a fixing member, and a pressing member as a pressure member that is disposed in opposition to the fixing device fixing device and is pressed to form a fixing nip SN. A pressure roller 22. Further, the fixing device 20 includes a heating unit configured as a thermal heater 23 that heats the fixing roller 21 from the outside.

  As shown in FIG. 3, the thermal heater 23 has a heating region R composed of a plurality of (seven in this embodiment) heaters arranged in the width direction of the paper P, and each heater is independently provided. The fixing roller 21 can be heated. The fixing roller 21 is provided with a thermistor 24 as temperature detecting means for detecting the surface temperature downstream of the fixing nip SN in the rotation direction and upstream of the thermal heater 23, and further provided with a thermistor 25 for detecting the temperature of the thermal heater 23. ing. Detection information of the thermistors 24 and 25 is sent to a heating control unit 26 provided outside, and the heating control unit 26 energizes the thermistors 24 and 25 of the power supply 27 based on the detection information of the thermistors 24 and 25. To control. The heating control unit 26 of this example is a microcomputer including a CPU, ROM, RAM, I / O interface, and the like.

The fixing roller 21 has an aluminum cored bar 21a having an outer diameter of 40 mm and a thickness of 1 mm, and a heat insulating layer 21b coated on the surface of the cored bar 21a. The heat insulating layer 21b is made of silicon rubber and has a thickness of 3 mm. The heat insulating layer 21b may be formed of foamed silicon rubber with less heat escape in order to further enhance its heat insulating function. A good heat conductive layer 21c made of nickel is formed on the heat insulating layer 21b of the fixing roller 21. The good heat conductive layer 21c is not limited to nickel, but an iron-based alloy such as stainless steel, aluminum, copper, or the like. It is sufficient that the thermal conductivity of the metal system, graphite sheet, etc. is at least as high as that of the heat insulating layer 21b. By forming the good heat conductive layer 21 c on the fixing roller 21, local temperature unevenness of the surface temperature of the fixing roller 21 due to uneven heat generation of the thermal heater 23 is reduced. Further, the temperature of the region slightly larger than the region heated by the thermal heater 23 is raised by the function of the good heat conductive layer 21c, so that there is an advantage that a slight deviation from the image can be compensated.
In other words, there is an advantage that the degree of freedom in design is large in setting the size and interval of each heater constituting the thermal heater 23. Further, in order to enhance the durability of the fixing roller 21 and ensure the releasability, a release layer having a thickness of 5 to 30 μm made of a fluorine-based resin such as PFA or PTFE may be formed on the surface of the heat insulating layer 21b.

  The pressure roller 22 has an iron cored bar 22a having an outer diameter of 40 mm and a thickness of 2 mm, and an elastic layer 22b covered on the surface of the cored bar 22a. The elastic layer 22b is made of silicon rubber and has a thickness of 5 mm. It is desirable to form a fluororesin layer having a thickness of about 40 μm on the surface of the elastic layer 22b in order to improve the releasability. The pressure roller 22 is pressed against the fixing roller 21 by an urging means (not shown). The thermal heater 23 is also pressed against the surface of the fixing roller 21 by an urging means (not shown).

Next, a control method of the thermal heater 23 that can realize energy saving will be described.
FIG. 4 is a diagram for explaining the basic operation of the control of the fixing device 20 according to the present invention. FIG. 5 is an image region c on the paper P in the longitudinal direction which is the width direction of the fixing roller 21 perpendicular to the transport direction. An image forming pattern in which a non-image area d exists is shown.

The heating control unit 26 changes the heating rate of the thermal heater 23 based on image information for forming an image on the paper P, and an example of the control operation is shown below.
FIG. 4 shows an image forming pattern in which a vertical image area a, a vertical non-image area b, and a vertical image area c exist on the paper P in order from the leading end side in the transport direction. Fixing is required in the vertical image area a and the vertical image area a ′, but fixing is not necessary in the vertical non-image area b because there is no toner to be fixed.

  Image information of the above pattern is input to the heating control unit 26 from an image processing apparatus (not shown). Then, the heating control unit 26 controls the thermal heater 23 so that the temperature of the part of the fixing roller 21 corresponding to the non-image area b is lower than the temperature of the part of the fixing roller 21 corresponding to the vertical image areas a and a ′. Control.

  Here, “corresponding to an image region or a non-image region” means a position that is in close contact with the fixing roller 21, and is hereinafter also expressed as close contact as appropriate. That is, in FIG. 4A, electric power for obtaining the fixing temperature is supplied to the entire area of the thermal heater 23 in the part corresponding to the vertical image area a, and the supplied electric power is reduced in the part corresponding to the non-image area b. In the portion corresponding to the vertical image area a 'at the rear end of the paper, the electric power for obtaining the fixing temperature is supplied again. Further, in FIG. 4B, the power for obtaining the fixing temperature is supplied to the entire area of the thermal heater 23 at the portion corresponding to the vertical image region a, and thereafter, the power supply is reduced because only the vertical non-image region b is used.

  At this time, the actual supply power is provided with a preheating region SH that is input so as to preliminarily heat the portion before the image region enters the nip portion, as indicated by the hatched portion in the figure. Such a preheating region SH is an indispensable region mainly because the heating length in the circumferential direction of the heating member and the heating element itself requires a temperature raising time, but it is made as small as possible from the viewpoint of energy saving. It is desirable.

  FIG. 5 shows an image forming pattern in which a horizontal image area c and a horizontal non-image area d exist on the paper P in the longitudinal direction of the fixing roller 21 perpendicular to the transport direction. In the case of FIG. 5A as well, in the same manner as the above control, the heating control unit 26 determines that the temperature of the portion of the fixing roller 21 corresponding to the horizontal non-image area d is the temperature of the portion of the fixing roller 21 corresponding to the horizontal image area c. The heating roller 32 is controlled to be lower. In other words, the power corresponding to the fixing temperature is supplied to the heating member 56 at the portion corresponding to the horizontal image region c, and the supplied power is reduced at the portion corresponding to the horizontal non-image region d. This also requires the preheating region SH in the shaded area as described above.

  In FIG. 5B, a horizontal region e and a horizontal region f are set in the longitudinal direction of the fixing roller 21 perpendicular to the transport direction, and in the horizontal region e, images exist in the vertical regions g and h in the transport direction. . However, in the horizontal region f, an image exists in the vertical region g in the transport direction, but no image exists in the vertical region h. For this reason, in the regions e and f, the vertical region g is supplied with electric power to obtain a fixing temperature, the vertical region h is controlled so as to supply electric power in the horizontal region e, and the horizontal region f is reduced in electric power.

  In this manner, energy saving can be realized by controlling the amount of power supplied in accordance with the image area. In this control, the power supply may be completely stopped (off) at the portions corresponding to the non-image areas c and d. However, if the temperature is excessively lowered, the fixing temperature in the next image area is reached. Rise may not be in time. For this reason, as shown in FIG. 6, it is possible to perform control so that the fixing roller 21 temperature is maintained at a second target temperature that is lower than the first target temperature corresponding to the image area but is equal to or higher than the room temperature. desirable.

  In the present embodiment, the heating unit is configured by the thermal heater 23 that is brought into contact with the surface of the fixing roller 21 and heated. However, the heating unit may be configured by a coil and an inverter, and may be a non-contact heating method based on the IH method. In the IH system, a configuration in which a large number of heating coils are arranged, or a configuration in which a heating region and a heating amount are controlled by positioning a number of members that cancel magnetic flux may be used.

FIG. 7 is an explanatory diagram showing another embodiment of the fixing device according to the present invention.
In FIG. 7, the fixing device 30 has a fixing belt 31 as a fixing member instead of a roller configuration. The fixing belt 31 includes a SUS base 31a having an outer diameter of 40 mm and a thickness of 40 μm, and an elastic layer 31b coated on the surface of the base 31a. The elastic layer 31b is made of silicon rubber and has a thickness of 100 μm. On the surface of the fixing belt 31, a release layer 31 c having a thickness of 5 to 50 μm is formed by a fluorine-based resin such as PFA or PTFE in order to enhance durability and ensure release properties. The base 31a of the fixing belt 31 may be polyimide, and the fixing member may be a fixing film instead of the fixing belt.

  Inside the fixing belt 31, a heating unit configured as a support member 32 and a thermal head 33 is provided. A pressing member 34 is installed at a position where the pressure roller 22 as a pressing member and the nip SN are formed, and is connected to an external member (not shown) to support the fixing member.

  In the fixing device 30 according to the present embodiment, the thermal head 33 forms a resistance heating element on a plate-like substrate, and is arranged inside the belt and raises the temperature of the belt with the heat, thereby the nip portion. The unfixed image conveyed to the SN is heated and fixed. The thermistor 24 is disposed on the fixing belt 31 downstream of the fixing nip SN in the rotation direction and upstream of the thermal head 33, and further, a thermistor 25 for detecting the temperature of the thermal head 33 is provided. Detection information of the thermistors 24 and 25 is sent to the heating control unit 26, and the heating control unit 26 controls a power source 27 that supplies power to the heating control unit 26 based on the detection information of the thermistors 24 and 25.

  As shown in FIG. 9, the thermal head 33 has a heating region R that is divided into a plurality of portions in the direction perpendicular to the paper conveyance direction. In this example, ten heating regions R are provided. That is, ten thermal heads 33 are arranged in a straight line in a direction orthogonal to the paper transport direction. The heating means may be a ceramic heater in which a resistance heating element is formed on a plate-like substrate instead of the thermal head 33.

  FIG. 8 is a modified example of the fixing device 30 including the fixing belt 31 of FIG. 7, and is different from that of FIG. 7 in that the thermal head 33 is provided as a pressing member that forms the nip portion SN. Therefore, the pressing member shown in the fixing device 30 in FIG. 8 is not necessary, and the configuration can be simplified and the device can be made compact.

  Since the fixing device 30 shown in FIGS. 7 and 8 also has the plurality of heating regions R described above, energy saving can be realized by controlling lighting of each heater according to the image.

FIG. 10 and FIG. 11 are diagrams for explaining the lighting control method of each heating region of the fixing device 30 according to the present invention.
Although the temperature of the fixing device 30 according to the present invention is normally controlled as shown in FIG. 6, the temperature of the fixing belt 31 is increased by the heat of the thermal head 33 arranged inside the film, so that it is conveyed to the nip portion SN. The unfixed image to be fixed is heated and fixed. At this time, as shown in FIG. 10, the unfixed image formed on the recording material is rarely formed symmetrically with respect to the center line of the recording material, and the fixing belt 31 heated by the thermal head 33 has left and right images. Temperature deviation is born.

  The left-right temperature deviation of the fixing belt 31 causes various problems. For example, a deviation occurs due to the left-right deviation employing the fixing belt or the fixing film, and stable running may not be obtained.

  Therefore, the heating means is controlled as follows in order to prevent the lateral deviation of the fixing member such as the fixing belt 31.

FIG. 11 is an explanatory diagram for explaining the control of the first embodiment of the present invention.
In FIG. 11, the thermal head 33 has heating areas R1, R2, R3, R4, R5, R6, R7, and R8 having the same heating capability, and the recording material P is a part of the paper divided into 32 parts. Set when there is an image in. The unfixed image portion on the recording material P in FIG. 11 is non-mirror symmetrical with respect to the center line CL that is the width direction of the fixing belt 31. For this reason, when the fixing belt 31 is heated in this state, the temperature on the left side of the fixing belt where the number of lighting of the heating region R is large increases, and a temperature deviation on the left and right occurs on the fixing belt 31.

  Therefore, in the present invention, each accumulated time energized in each heating region is stored retroactively from the present time or a certain point in time, and each heating region is compared, and the difference between the maximum value and the minimum value of the accumulated current time within a certain time The energization time in the assigned heating area is adjusted so that it is below a certain threshold. Specifically, the lighting time of each heating region is stored from the start-up time to the cool-down time, and the heating regions that are mirror-symmetric with respect to the center in the longitudinal direction are compared. In the case of FIG. 11, there is no difference between the comparative symmetry R2 and R6, R3 and R7, and there is a difference between R1 and R8, and R4 and R5. Therefore, the above-described problem can be solved by controlling the lighting of each heating region during the sheet passing so that the difference between the respective cumulative lighting times is equal to or less than the threshold value. That is, when the difference in the cumulative lighting time exceeds the time set as appropriate in the heating region to be compared, control is performed so that the heating means in the heating region on the side with less lighting is turned on to reduce the difference.

Here, a case where the one lighting time of the heating region is always constant, the number of lighting times is used instead of the lighting time, and the threshold value is zero will be described as an example.
In the case of the unfixed image on the recording material in FIG. 11, the heating region R5 is not lit when the image in the second row is heated, so that a difference occurs in the cumulative number of lighting times with the heating region R4. For this reason, the heating region R5 is turned on and the heating region is controlled so that the number of times of lighting is 0 or less when the fourth row that is not scheduled to be lit is heated so that the difference in the number of times of lighting is zero. As a result, it is possible to reduce the left-right temperature deviation occurring in the fixing belt 31 and to prevent the fixing belt 31 from being shifted.

  FIG. 12 illustrates the timing for performing lighting control of each heating region of the present invention. In the above embodiment, lighting control is performed to reduce the temperature deviation of the fixing belt 31 when the paper is passed. The lighting control of the present invention may be performed not only at the time of paper passing but also at the time of start-up shown in FIG. That is, the lighting control of the present invention may be continuously performed from the start of operation of the fixing device to the stop of operation.

FIG. 13 is an explanatory diagram for explaining a lighting method according to the second embodiment of the present invention.
In this example, the heating means is not controlled to be lit by the number of times each of the heating areas divided into eight as shown in FIG. 10, but a plurality (two) of heating areas are divided into four groups RG1, Separated as RG2, RG3, and RG4. Then, the lighting control may be performed by comparing the number of times of lighting in the group with the number of times of lighting of another heating region group in the mirror symmetrical position. In the example of FIG. 13, the heating region group, RG1 and RG4, and RG2 and RG3 are compared, and control is performed so that the threshold value is equal to or less than a predetermined value.

  Specifically, in the case of the image on the recording material in FIG. 13, the heating region RG3 group does not light up to the second row, but the RG2 group lights twice during that time, and there is a difference in the number of times of lighting. Has occurred. In order to eliminate the temperature deviation due to the number of lighting on the record, the temperature deviation can be eliminated by lighting each heating region in the RG3 group twice.

  Similar to the lighting control described above, the same lighting control may be performed not only at the time of paper passing but also at the time of start-up, paper interval, and cool-down.

14 and 15 are explanatory diagrams for explaining the lighting control method of each heating region according to the third embodiment of the present invention.
In the lighting method shown in FIG. 10 or FIG. 13, lighting control of the heating region is performed by detecting the difference in the cumulative number of lightings between the heating regions.

On the other hand, in the present invention, control is performed so that the heating region is always lit in a mirror-symmetric manner with respect to the longitudinal center without considering another heating region as a comparison target.
For example, when the corresponding heating area is controlled to be turned on in order to heat an unfixed image (image portion) on a recording material as shown in FIG. 14, it is symmetric with respect to the longitudinal center as shown in FIG. As described above, the heating area is controlled to be additionally lit separately from the image. By doing so, it is possible to prevent a left-right temperature deviation that occurs in a fixing member such as a fixing belt.

  In the case of this lighting control method, the energy-saving effect is reduced because intentionally unnecessary heating is performed, but the fixing belt can be reliably prevented from shifting, and unlike the above-described lighting control method, the fixing member can be stably driven. Sex can be maintained.

20, 30 Fixing device 21 Fixing roller 22 Pressure roller 23 Thermal heater 26 Heating control means 31 Fixing belt 33 Thermal head P Recording medium

JP-A-6-95540 JP 2005-181946 A JP 2001-343860 A

Claims (9)

A fixing member that contacts and rotates with an unfixed image, a pressure member that forms a fixing nip with the fixing member, a heating unit that heats the fixing member by energization, and heating that controls the heating unit A fixing device having a control unit and fixing a sheet-like recording material carrying an unfixed image through the fixing nip;
The heating means has a plurality of heating regions having the same heating ability divided in a direction orthogonal to the recording material conveyance direction,
The heating control means controls the temperature of the fixing member by independently controlling each heating area in accordance with the image area where the unfixed image is formed on the recording material, and the fixing member that contacts the image area In the fixing device for controlling the temperature of the fixing member that is in contact with the non-image area to be low,
Each cumulative time energized in each heating area is stored,
One of the heating regions is compared with another assigned heating region so that the difference between the maximum value and the minimum value of the energized cumulative time within the predetermined time is equal to or less than a certain threshold value. A fixing device having control for adjusting energization time.   2. The fixing device according to claim 1, wherein the assigned heating region to be compared is set to be mirror-symmetric with respect to a center line in a direction orthogonal to a recording material conveyance direction of the fixing member. A fixing device characterized by the above.   3. The fixing device according to claim 1, wherein a difference in the number of times of heating due to a certain energization time is compared with each heating region of the heating unit, and the difference in the number of times is controlled to be equal to or less than a certain threshold value. A fixing device.   4. The fixing device according to claim 1, wherein the heating area is compared for each area or for each heating area group including two or more areas.   4. The fixing device according to claim 1, wherein the control is continuously performed from the start of operation of the fixing device to the stop of operation.   4. The fixing device according to claim 1, wherein the control is performed only when no recording material is interposed in the fixing nip.   4. The fixing device according to claim 1, wherein the control is performed only between sheets.   8. The fixing device according to claim 1, wherein a heating region set to be pre-mirror symmetrical is always mirror-symmetric with respect to a center line in a direction orthogonal to the recording material conveyance direction of the fixing member. Fixing device characterized by controlling to turn on   An image forming apparatus comprising the fixing device according to claim 1.

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