JP4012685B2 - Thermal fixing device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat fixing device mounted on an image forming apparatus such as a printer, a facsimile machine, and a copying machine.
[0002]
[Prior art]
In the image forming apparatus, as the sheets on which image information is to be recorded, not only regular sizes such as A row, B row, and letter row, but also various types of sheets up to irregular size sheets are targeted. However, it is configured to allow paper to pass. Correspondingly, even in the heat fixing device, the surface temperature of the fixing roller is controlled so as to be kept efficient and uniform even if any of all the paper sizes are continuously fed. Is required. Therefore, it has been proposed and realized to provide a plurality of heaters to be incorporated in the fixing roller.
[0003]
By the way, in recent years when the demand for energy saving is routine, the zero energy standby mode (ZESM) in which the fixing unit of the image forming apparatus reaches a zero energy consumption state when the apparatus is not in operation. ) Is being adopted. In this ZESM, as in the conventional standby mode, the image forming apparatus can copy or copy instantaneously or almost instantaneously upon receiving an operation instruction. In other words, in the state of ZESM, only a minimum amount of energy for maintaining electronic functions such as a timer, a counter, and a memory function is consumed. In a so-called “future copying machine”, the ZESM is equivalent to the sleep mode .
[0004]
[Problems to be solved by the invention]
In such a ZESM-compatible thermal fixing apparatus, the thickness of the fixing roller is extremely thin in order to shorten the startup time. For example, in the case of a φ40 mm roller, heat conduction is accelerated by about 0.3 mm when made of an iron material and around 0.4 mm when made of an aluminum material. As for the heater (heat source), since other parts are not operating in the stationary state at the time of start-up, the heater having the maximum effective output (for example, 1200 W) allowed by the apparatus is used. In this case, the maximum effective output (for example, 860 W) allowed in the operating state is used by thinning out the lighting rate.
[0005]
However, a configuration in which different ranges of the fixing roller are heated by two built-in heaters as in the prior art and the light distribution is divided by each heater (the first and second heaters have the same output per unit length, and A4 (Measures for separating the vertical width as a boundary) When a small size paper such as A5 vertical or B5 vertical is continuously passed, the temperature of the roller portion outside the paper size area immediately rises, and the end side The temperature rise state is transmitted to the range of the temperature detection means, and there is a risk that abnormal temperature will be detected on the end side, or the roller may be welded due to abnormal temperature rise. If a large size paper that spans the entire width of the paper is continuously fed, the temperature drop in the paper area is large and the temperature is lower than that required for fixing. This tends to become more prominent as the ability of the heat fixing device to pass paper increases (for example, in the experiment, it is remarkable from the case where A4 paper can be passed at a speed of 40 sheets / min or more). In addition, a temperature difference occurs in the roller inner peripheral surface portion that is shaded with respect to each heater as compared with the other portions, and from the characteristic surface of both heaters, the temperature of the end heating heater is lower, In the area shaded on the roller end side by the heater for the central area, a difference of, for example, about 60 ° C. is generated compared to the high area on the opposite side. Detection is slow and dull, and ZESM cannot be achieved, and there is a risk that the member will melt on the opposite side. Furthermore, when controlling the heater based on the detection of the roller surface temperature, a delay in response (time lag) from the surface temperature detection to the heater control also exists in the case of a thin fixing roller, and in particular, heating is performed at full lighting. When starting up, if you wait until the target detection temperature is detected, the start-up time until the paper can be passed will be out of the target time (designed start-up time), or the heater off timing Due to the delay, the roller surface may be melted by overshoot.
[0006]
It is an object of the present invention to solve the above-described problems in the ZESM-compatible thermal fixing device.
[0007]
[Means for Solving the Problems]
The above object is achieved according to the present invention, there is provided a ZESM corresponding heat fixing device constituted by a two heat sources incorporated in the fixing roller and the roller, the sheet passing range roller longitudinal direction and main sheet passing range It is divided into a secondary paper passing range which is the other region, and one heat source is a first heat source for heating the main paper passing range, and the other heat source is for heating the secondary paper passing range. In a heat fixing device that is a second heat source and that has temperature detection means installed for each heat source and individually controls the driving of each heat source based on the detection result of the detection means, the main sheet passing range is heated. The heating range by the first heat source is divided into an end area near the heating range by the second heat source that heats the secondary paper passing range and other central heating areas, and the heating intensity in the end heating area is divided into the central heating area. 30-50% of the heating intensity of By limiting the, it can be solved.
[0008]
The distribution of the outputs of the first heat source and the second heat source is preferably set to a ratio of first heat source: second heat source = 6.25: 3.75 to 5: 5 in a fully lit state. Further, the heating range by the first heat source and the heating range by the second heat source are overlapped, and the heating range by the second heat source is divided into an end area close to the heating range by the first heat source and other central heating areas. If the heating intensity at the overlapping portion can be adjusted to 30 to 50% of the maximum heating intensity, it is more effective.
[0009]
An output control of the heat source, and variable in the time of start-up time and the feed, also in the case the paper size for sheet passing size according only to the heat target area of the first heat source, the heat target area of both of the heat source In the case of such a size, it is more preferable that the configuration is such that the output of each heat source is changed. If the paper size is the size of the heating target area of both heat sources, the output of each heat source is changed after a certain period of time, or the paper size is applied only to the heating target area of the first heat source, and If it does not reach the full width of the heating target area, the fixing control temperature is lowered by a predetermined temperature from the initial fixing control value immediately or after a certain period of time when the paper is passed, and further, the fixing control temperature is gradually increased during continuous paper feeding. It is better to lower the value.
[0010]
If each heat source and each temperature detection means are arranged so that the interval between the second heat source and the temperature detection means for the second heat source is shorter than the distance between the first heat source and the temperature detection means for the first heat source, Is preferred. In order to ensure such an arrangement, the fitting holes of the support for fitting and holding the heat source end portions are formed in different diameters in accordance with the end portion diameters of the respective heat sources. Further, the overheat prevention device attached to each heat source is set so that the distance between the first heat source and the overheat prevention device is equal to the distance between the second heat source and the overheat prevention device. , Good to arrange.
[0011]
When starting up, based on the temperature rise gradient during the temperature rise, if the gradient is equal to or greater than a certain level, it is preferable to allow paper to pass after a certain time. If the temperature rise gradient does not reach a certain value, the paper is not allowed to pass, or the roller temperature after a certain time is further detected, and if the detected temperature is equal to or greater than a certain value, the paper feeding is started. On the other hand, the heat source drive may be continued until the fixing set temperature is reached. When the fixing roller is switched from the rotation state to the stop state, it is more preferable to turn off the heat source for a predetermined time and then control the temperature again.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The details of the present invention will be described based on examples shown in the drawings.
First, an image forming apparatus according to the present invention will be described. The configuration of the entire image forming apparatus is basically the same as that of the conventional one. In FIG. 1, a charging for charging the surface of the drum around the photosensitive drum 21 which is an electrostatic latent image carrier. Charger 22, writing unit (multi-beam writing) 23 for forming a latent image on a uniformly charged surface, developing device 24 for forming a toner image by attaching charged toner to the latent image on the drum surface A transfer device (transfer conveyor belt unit) 25 for transferring the toner image on the drum to the recording sheet, a cleaning device 27 for removing the residual toner on the drum, and a static elimination device 28 for removing the residual potential on the drum. Are arranged in order. In such a configuration, when image formation is performed at N / P (negative positive), the photosensitive member 21 whose surface is uniformly negatively charged by the charging charger 22 is formed with an electrostatic latent image by the writing unit 23. Then, a toner image is formed by the developing device 24. The toner image is transported from the surface of the photosensitive drum 21 by a transfer device 25 including a transfer belt 29 or the like from a paper feed bank 26 or a horizontal paper feed tray formed by combining a tandem tray, a universal tray, a fixed tray, and the like at the bottom of the device. Transferred to the recorded sheet. The recording sheet electrostatically attached to the photosensitive drum 21 during the transfer is separated from the photosensitive drum 21 by the separation claw. The toner image on the unfixed recording sheet is fixed on the recording sheet by the fixing device 30. On the other hand, the toner remaining on the photosensitive drum 21 without being transferred is removed and collected by the cleaning device 27. The photosensitive drum 21 from which the residual toner has been removed is initialized by the charge eliminating lamp 28 and used for the next image forming process.
[0013]
Next, the fixing device 30 according to the present invention will be described with reference to FIG. In the following description, the sheet passing reference is described as being in the center in the longitudinal direction of the roller. However, the present invention can be easily applied to those using the end as a reference. As shown, two heaters 2a and 2b are built in the fixing roller 1 to which the pressure roller 4 is pressed. The surface of the fixing roller 1 is provided with two thermistors 3a and 3b corresponding to the two heaters, in addition to the separation claw 5 for preventing the paper from being wound when the paper is discharged. Furthermore, thermostats 6a and 6b, which are overheat prevention devices, are also arranged so as to contact the surface of the fixing roller 1 so as to correspond to two heaters. A thermal fuse may be used instead of the thermostat.
[0014]
As can be understood from FIG. 3, the two heaters are a first heater 2a for a central region corresponding to a main sheet passing range and a second heater 2b for an end region corresponding to a sub sheet passing range. The two thermistors are a center region thermistor 3a and an end region thermistor 3b. The thermostats are also a central region thermostat 6a and an end region thermostat 6b. As is well known, power supply control to each heater is performed from a control circuit (not shown) via each solid state relay (SSR). In FIG. 4 for clarifying the positional relationship of each heater, thermistor, and thermostat in the roller circumferential direction, the central region thermistor 3a and the end region thermistor 3b are overlapped at the same position in the roller circumferential direction. In other words, the end region thermistor 3b is more than the distance between the center region thermistor 3a and the first heater 2a with respect to the heater built in the fixing roller 1 and arranged in a fixed state regardless of roller rotation. The two heaters 2b are positioned so as to have a contact point with the fixing roller. As for the thermostat, the distance between the first heater 2a and the center region thermostat 6a is equal to the distance between the second heater 2b and the end region thermostat 6b, and each of the two heaters arranged in parallel and each thermostat. Is placed at an equal distance, the thermostat is placed at a position where the original radiant heat is not hindered by the presence of a heater other than the heater to be sensed.
[0015]
In order to correctly hold a plurality of heaters in the fixing roller, as shown in FIG. 5, the diameters of the insulator portions at the ends of the central first heater 2a and the end second heater 2b are φd ₁ and φd, respectively. ₂ (φd ₁ ≠ φd ₂ , in the example shown, φd ₁ <φd ₂ ). Further, the diameters of the fitting holes of the heater bracket 8 for fitting and holding the lever parts are also φD ₁ and φD ₂ (φD ₁ ≠ φD ₂ , φD ₁ <φD _{2 in} the illustrated example) corresponding to φd ₁ and φd _2. It has become. For this reason, each fitting hole can be fitted and installed only by a heater corresponding to 1 to 1. In order to correctly maintain the positional relationship between the fixing roller 1 and the heaters 2a and 2b, the heater bracket 8 is naturally directly or indirectly attached to the roller bearing.
[0016]
As can be recognized in FIG. 3, the first heater 2a and the second heater 2b are each divided into three sections, and the second heater 2b has a light emitting part (that is, a heating part) only in a length range of 55 mm at both ends. The heater 2a has a light emitting portion in the central length range of 210 mm excluding both ends, but as shown in FIG. 6, the light emission intensity (that is, the heating intensity) in the central length range of 150 mm of the first heater 2a. ), The emission intensity is suppressed to about 30% to 50% in the length range of 30 mm at each end of the light emission portion having a length range of 210 mm at the center. By performing such light distribution, it is possible to avoid an excessive temperature rise at both ends of the light emitting portion of the first heater 2a even when continuous passing of small size paper is performed.
[0017]
With the first heater 2a and the second heater 2b configured as described above, the output distribution of each heater is 6.25: 3.75 in the first heater: second heater according to the length ratio of the light emitting section. 5: 5 is set to achieve a more uniform temperature distribution. For example, when the lighting rate is 1.0 (when starting up) and the total output of both heaters is 1200 W, the temperature ranges from 750 W for the first heater and 450 W for the second heater, so that both heaters are 600 W each. Set so that the distribution is uniform. As an example, the first heater for the central area is set to 650 W, the second heater for the end area is set to 550 W, and as shown in FIG. If the size is applied to both the first heater 2a and the second heater 2b, for example, A3 or A4 size, the lighting rate is 0.72, that is, the first heater 468W and the second heater 396W, and the detected paper size is In the case where only the first heater 2a is applied, control is performed so that the combination of output ratios can be switched so that the lighting rate of the first heater is 553 W of 0.85 and the lighting rate of the second heater is 308 W of 0.56. To do.
[0018]
In addition, when the lighting rate is set to 0.72 and paper is passed by the first heater 468W and the second heater 396W, the time from the low temperature after the start of paper feeding to the return to the appropriate temperature can be shortened. If the ratio remains the same, the fixing temperature will not be uniform. If paper continues to pass for a certain period of time (equivalent to Time out 2 in FIG. 7), it is corrected. In order to achieve this, the switching temperature distribution of the ZESM fixing device is changed by switching the combination of the lighting rate of the first heater to an output ratio of 553 W of 0.85 and the lighting rate of the second heater of 308 W of 0.56. It becomes possible to stabilize.
[0019]
When the detected paper size is applied only to the first heater, as described above, the output ratio is switched to the output ratio of the first heater 553W and the second heater 308W. In the case of a sheet narrower than the width of the first heater 2a, the fixing set temperature is controlled to be lowered by 10 degrees at both the center and the end. With such control, temperature rise outside the paper area at the time of small size (postcard, A6, B5T, etc.) is suppressed, abnormal temperature is detected on the end side, or the roller is welded due to actual abnormal temperature. To prevent.
[0020]
Further, in any paper type, when the paper continues to pass for a certain period of time (corresponding to after Time out 3 and 4 in FIG. 7), the fixing set temperature is further controlled to be lowered at both the center and the edge. With such control, temperature rise outside the paper area during continuous paper feeding is suppressed, and problems such as resin deterioration, meltdown, and bearing lock due to high temperatures are prevented.
[0021]
On the other hand, in the above configuration, temperature control for avoiding a delay in response to temperature detection will be described below. In the flowchart of FIG. 8, t = 0 when the power is turned on (S1), the surface temperature T1 after t1 seconds is detected (S2), the temperature T2 after t2 seconds is detected (S3), and T2-T1 is set. If it is determined that the temperature gradient is constant (eg, 20 degrees) or more (S4), copying is allowed after a certain time (Time out, S5) (S6), and response delay is avoided. In the determination of T2-T1, if the temperature gradient is not equal to or greater than a certain level, an error is notified and copying is not possible (S7), so that problems such as heater disconnection can be detected early.
[0022]
In order to avoid malfunctions related to abnormality detection when the startup in the ZESM mode is difficult in advance, such as when the heater power is insufficient due to voltage fluctuation of the power supply or when the room temperature is extremely low, In the flowchart, when the temperature gradient between the temperature T1 after t1 seconds and the temperature T2 after t2 seconds is not more than a certain level based on the power-on time, the temperature T3 after t3 seconds is further detected (S7), and a constant temperature (example) : 160 ° C.) (S8), copy is permitted (S9). If the temperature has not reached a certain temperature, an error is notified and copying is disabled (S10).
[0023]
In addition, when the copy operation is started and the fixing roller is rotated at the time of passing the paper, the fixing operation is finished and the roller is stopped. Is supplied to the roller, and if the roller stops as it is and the heater OFF timing is delayed, a rapid temperature rise occurs. Therefore, as shown in FIG. 10, after the fixing is completed, the fixing control temperature value is once lowered to room temperature (for example, 20 ° C.) so that the heater does not have to be turned on, and the fixing is performed again after a certain time (for example, 0.5 seconds). Control to return the control temperature to the original state. As a result, it is possible to avoid problems such as surface melting due to overshoot due to temperature rise when the fixing roller stops rotating after completion of paper passing.
[0024]
In addition to suppressing the emission intensity at the end of the first heater for the central region, the emission intensity of the end region on the boundary side with the first heater is also suppressed for the second heater for the end region. However, the light emission intensity suppression region overlaps with the first heater end light emission region, so that the temperature at the boundary between both heaters can be supplemented and the temperature can be easily maintained in that range. At that time, as shown in FIG. 11, the emission intensity in the overlapping range (diagonal grid line portion) is adjusted from 30% to 50% of the maximum emission intensity to obtain the improved type of the example shown in FIG. 6. Is good. In order to form an overlapping range, the light emitting portion of the second heater is extended from 55 mm in the first example to, for example, 70 mm, and the extended range is set as a light emission intensity suppression region. Such a configuration is particularly preferably applied to an apparatus that forms an image with about 35 sheets or less of A4 size paper per minute. In experiments, with such a configuration, it is easier to keep the temperature of the roller surface uniform even when various sheets of paper are continuously passed. A result more preferable than that of the configuration was obtained .
[0025]
【The invention's effect】
According to the present invention, the heating range by the first heat source for heating the main sheet passing range in the longitudinal direction of the roller, the end area close to the heating range by the second heat source for heating the following sheet passing range, and others Since the heating intensity in the end heating area is limited to 30 to 50% of the heating intensity in the central heating area, even in a ZESM-compatible heat fixing device, various different sizes are available. Even if the paper is continuously passed, the surface temperature of the fixing roller can be kept uniform, the temperature rises outside the paper area, and the temperature rises to around the temperature detection means for the second heat source. Or problems such as roller welding for abnormal temperature rise can be solved.
[0026]
The distribution of each output of the second heat source of the first heat source is in a fully lit state, and the ratio of the first heat source: second heat source = 6.25: 3.75 to 5: 5 makes the roller temperature distribution uniform. It is an ideal heat source output distribution for holding. In addition, the heating range by the first heat source and the heating range by the second heat source have an overlapping portion, the heating range by the second heat source is divided into an end area close to the heating range by the first heat source and other central heating areas, When the heating intensity at the overlapping portion is adjusted to be 30 to 50% of the maximum heating intensity, for example, in an image forming apparatus having a thin fixing roller compatible with ZESM, a sheet passing speed of 35 sheets or less per minute can be achieved. In such a case, it will effectively act on the temperature drop at the boundary portion particularly when the roller width is full size.
[0027]
An output control of the heat source, and variable in the time of start-up time and the feed, also in the case the paper size for sheet passing size according only to the heat target area of the first heat source, the heat target area of both of the heat source In the case of such a size, by configuring the output of each heat source to be changed, it is possible to avoid problems due to the sheet passing size while realizing ZESM. In the case where the paper size is the size applied to the heating target area of both heat sources, the output of each heat source is further changed after a certain period of paper passing, or the paper size is applied only to the heating target area of the first heat source, and If it does not reach the full width of the heating target area, the fixing control temperature is lowered from the initial fixing control value by a predetermined temperature immediately or after a certain period of time, and further, fixing control is performed step by step during continuous paper feeding. by so gradually lowering the temperature still be followed by the sheet passing it is possible to keep the surface temperature of the fixing roller uniformly.
[0028]
If each heat source and each temperature detection means are arranged so that the interval between the second heat source and the temperature detection means corresponding thereto is shorter than the interval between the first heat source and the temperature detection means corresponding thereto, the startup time can be reduced. Melt down due to a temperature increase beyond the schedule due to delay or response delay can be avoided. If the overheat prevention device attached to each heat source has the same distance between the first heat source and the overheat prevention device relative to the first heat source and the overheat prevention device relative to the second heat source, Variations in operating time can be minimized, and smoke and fire can be avoided during abnormal conditions.
[0029]
When starting up, if the slope is above a certain level, if the slope is above a certain level, it is possible to pass the paper after a certain period of time. Can be prevented, and a safer and more stable ZESM compatible machine can be provided. When the temperature rise gradient does not reach a certain value, it is possible to detect problems such as disconnection of the heat source at an early stage by disabling paper feeding, and further detect the roller temperature after a certain time and detect the detected temperature. If the value is equal to or greater than a certain value, paper feeding is started, while the heat source driving is continued until the fixing set temperature is reached. Even under conditions in which it is difficult to start up in the ZESM state, malfunctions in abnormality detection can be avoided. When the fixing roller is switched from the rotation state to the stop state, the heat source is turned off for a predetermined time, and then the temperature is controlled again. The trouble can be solved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a configuration of an image forming apparatus according to the present invention.
FIG. 2 is a schematic cross-sectional view showing a configuration of a thermal fixing apparatus according to the present invention.
FIG. 3 is a schematic diagram for explaining a heating area of a first heater and a second heater.
FIG. 4 is a diagram showing a positional relationship of each thermistor and each heater in a cross section of the fixing roller.
FIG. 5 is a partial schematic perspective view showing an example of attaching a heater end.
FIG. 6 is a graph showing a light emission distribution as a first example.
FIG. 7 is a flowchart illustrating a configuration in which the output of each heat source and the fixing control temperature are variable during start-up and continuous sheet passing.
FIG. 8 is a flowchart illustrating a control for enabling copying based on a temperature rise gradient at the time of startup.
FIG. 9 is a flowchart for explaining control for extracting a copy-ready state safely while avoiding malfunction of abnormality detection even when the temperature rise gradient at startup is not a constant value.
FIG. 10 is a flowchart illustrating a control for avoiding a problem when a roller stops rotating after the end of paper passing.
FIG. 11 is a graph showing a light emission distribution as a second example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fixing roller 2a 1st heater 2b 2nd heater 3a, 3b Thermistor 4 Heating roller 5 Separation claw

Claims (17)

A ZESM-compatible heat fixing device comprising a fixing roller and two heat sources built in the roller, wherein the paper passing area is the main paper passing area and the other area in the longitudinal direction of the roller. is divided into a paper range, a first heat source for one of the heat source heats the main sheet passing range, a second heat source for the other heat source for heating the minor sheet passing range, each heat source On the other hand, in the thermal fixing device in which the temperature detection means is installed and the drive of each heat source is individually controlled based on the detection result by the detection means,
The heating range by the first heat source that heats the main sheet passing range is divided into an end area near the heating range by the second heat source that heats the sub sheet passing range and other central heating areas, The heat fixing device is characterized in that the heating intensity is limited to 30 to 50% of the heating intensity in the central heating area.   2. The distribution of outputs of the first heat source and the second heat source is adjusted to a ratio of first heat source: second heat source = 6.25: 3.75 to 5: 5, according to claim 1. Thermal fixing device.   The heating range by the first heat source and the heating range by the second heat source are overlapped, and the heating range by the second heat source is divided into an end area close to the heating range by the first heat source and other central heating areas. The heat fixing device according to claim 1, wherein the heating intensity at the overlapping portion is adjusted to be 30 to 50% of the maximum heating intensity. The output control of each heat source can be made variable at the time of start-up and paper passing , and the paper size at the time of paper passing is a size that only affects the heating target area of the first heat source, and the heating target of both heat sources The thermal fixing device according to any one of claims 1 to 3, wherein the output of each heat source is changed depending on the size of the region. 5. The thermal fixing device according to claim 4, wherein, when the paper size is a size corresponding to the heating target area of both heat sources, the output of each heat source is further changed after a certain period of time during which the paper is passed. When the paper size is applied only to the heating target area of the first heat source and does not reach the entire width of the heating target area, the fixing control temperature is changed from the initial fixing control value to a predetermined temperature immediately or after a certain period of time when the paper is passed. The thermal fixing device according to claim 4, wherein the thermal fixing device is lowered only by a distance.   The thermal fixing device according to any one of claims 4 to 6, wherein the fixing control temperature is lowered stepwise during continuous paper feeding.   Each heat source and each temperature detection means are arranged so that the interval between the second heat source and the temperature detection means corresponding thereto is shorter than the interval between the first heat source and the temperature detection means corresponding thereto. The thermal fixing device according to claim 1.   9. The heat fixing apparatus according to claim 8, wherein the fitting holes of the support body for fitting and holding the heat source end portions are formed in different diameters in accordance with the end portion diameters of the respective heat sources.   The overheat prevention device attached to each heat source is such that the distance between the first heat source and the overtemperature prevention device is equal to the distance between the second heat source and the overtemperature prevention device relative thereto. The thermal fixing device according to claim 8, wherein the thermal fixing device is disposed.   When starting up, based on a temperature increase gradient during temperature rise, if the gradient is equal to or greater than a certain level, the sheet can be passed after a certain time. Thermal fixing device.   The thermal fixing device according to claim 11, wherein when the temperature increase gradient does not reach a certain value, the sheet cannot be passed. When the temperature rise gradient does not reach a certain value, the roller temperature after a certain time is further detected. If the detected temperature is equal to or greater than a certain value, the paper feeding is started and the fixing set temperature is reached. The heat fixing device according to claim 11, wherein the heat source driving is continued until the heat fixing device is turned on.   The heat fixing according to any one of claims 1 to 3, wherein when the fixing roller is switched from the rotating state to the stopped state, the heat source is turned off for a predetermined time and then the temperature is controlled again. apparatus. 2. The heat fixing according to claim 1, wherein when the core metal of the fixing roller is an iron material, the thickness of the core metal is about 0.3 mm, and when the core metal is an amyl material, the thickness of the core metal is about 0.4 mm. apparatus. An image forming apparatus having a thermal fixing device according to any one of claims 1 to 15. The image forming apparatus according to claim 16, wherein the sheet can be passed at a speed of 40 sheets or more on a side of A4 size paper per minute.

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