JP2004198528A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a fixing roller incorporating a main heater for mainly heating the middle portion of the fixing roller and sub-heaters for mainly heating both ends of the fixing roller from causing fixing failure due to low temperature, by speedily and accurately detecting the surface temperature of the middle portion of the fixing roller with a thermister provided in a paper non-passage area when switching takes place from a fixing process using a main heater and a sub-heater to a fixing process using only a main heater. <P>SOLUTION: When switching takes place from the fixing process using the main heater H<SB>1</SB>and the sub-heater H<SB>2</SB>to the fixing process using only the main heater H<SB>1</SB>, supply of power to the main heater H<SB>1</SB>and the sub-heater H<SB>2</SB>is stopped for a predetermined length of time after the switching of the control state. Also, feed of paper to the fixing roller 61 is stopped. When a temperature difference between the detected temperature of the thermister 63 after the lapse of a predetermined time and second set temperature is equal to or lower than a predetermined value, a control part 64 controls the supply of power to the main heater H<SB>1</SB>and starts to feed the paper to the fixing roller 61. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus including a fixing device having a fixing roller and a pressure roller, and more specifically, image formation in which temperature detection of a fixing roller is performed using a temperature detection unit provided in a non-sheet passing region. It relates to the device.
[0002]
[Prior art]
In an electrophotographic image forming apparatus, a fixing roller having a built-in heater and a pressure roller are pressed against each other, and a paper carrying an unfixed toner image is passed between the rollers to fix the toner onto the paper. A roller type fixing device has been widely used.
[0003]
In this heat roller type fixing device, from the viewpoint of energy saving, two or more heaters are built in the fixing roller so that the surface temperature of the fixing roller can be partially increased, and the roller passes only in the region through which the paper passes. Fixing is also performed by raising the surface temperature. For example, in the case of an apparatus that performs document alignment at the center of the document mounting table, a main heater that mainly heats the axial center of the fixing roller and a sub-heater that mainly heats both ends in the axial direction are built in the fixing roller, and the paper When the toner is conveyed in the vertical direction (narrow direction), only the main heater is turned on to perform toner fixing processing to save power.
[0004]
By the way, in order to keep the surface temperature of the fixing roller constant, a temperature detecting means such as a thermistor thermometer (hereinafter sometimes referred to as “thermistor”) is attached to the surface of the fixing roller, and the fixing roller is based on the detected temperature of the thermistor. It is generally performed to control on / off of a heater built in the heater. In order to accurately detect the surface temperature of the fixing roller, it is preferable to attach a thermistor to an area through which the paper passes. However, if the thermistor is attached to the surface of the fixing roller, the surface of the fixing roller is scratched by rubbing with the thermistor, and the releasability of the fixing roller is reduced, or unfixed toner adheres to the thermistor, and the copy image becomes dirty. May occur or the temperature detection accuracy may decrease. Therefore, in order to prevent such a problem, a temperature detection unit is being provided in a sheet passing area (non-sheet passing area) where the sheet does not pass through the fixing roller (for example, Patent Document 1).
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-311581 (Claims, FIG. 1)
[0006]
[Problems to be solved by the invention]
By the way, in the fixing device in which two or more heaters are built in the fixing roller and the thermistor is provided in the non-sheet passing area, when fixing is performed using the entire fixing roller (temperature control with the main heater and the sub heater), When fixing using only the central part of the fixing roller (temperature control using only the main heater), the former temperature is set to the temperature detected by the thermistor, taking into account the length of the distance from the heater heating part to the thermistor installation position. Lower than the latter. Here, when the set temperature of the detected temperature is changed from a high value to a low value, that is, when the fixing process using the entire fixing roller is changed to the fixing process using only the central portion of the fixing roller, the fixing roller Since the distance from the center to the thermistor installation position is long, even if the fixing process starts at the center of the fixing roller and the surface temperature of the center of the fixing roller decreases, the temperature detected by the thermistor is higher than the set temperature due to residual heat There was sometimes a value. For this reason, there is a problem that the main heater is not turned on, the surface temperature of the center portion of the fixing roller is rapidly lowered, and a low-temperature fixing failure is caused.
[0007]
The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an image forming apparatus in which a means for detecting the surface temperature of the fixing roller is provided in a non-sheet passing region. When the entire fixing process is changed to a fixing process using only the central part of the fixing roller, the surface temperature of the central part of the fixing roller is quickly and accurately detected by a thermistor. The object is to prevent the surface temperature from rapidly decreasing and fixing failure.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the image forming apparatus of the present invention incorporates a first heating element that mainly heats the central part in the roller axial direction and a second heating element that mainly heats both end parts in the roller axial direction. A fixing roller, a pressure roller in pressure contact with the fixing roller, a temperature detecting means for detecting a surface temperature of the fixing roller provided in a non-sheet passing area of the surface of the fixing roller, and a temperature detected by the temperature detecting means And a control unit that controls energization of the first heating element and the second heating element based on the first heating element, and the control unit maintains the first set temperature so that the detected temperature is maintained at the first set temperature. And the first state for controlling energization to the second heat generating element and the energization to the second heat generating element are stopped so that the detected temperature is maintained at the second set temperature lower than the first set temperature. With the first heating element And when the control state is changed from the first state to the second state, the first heating element and the second heating element are energized for a predetermined time after the change of the control state. If the temperature difference between the detected temperature after the lapse of the predetermined time and the second set temperature is equal to or smaller than a predetermined value, the control unit performs the energization control in the second state. When the temperature difference is larger than a predetermined value, the energization of the first heating element and the second heating element and the sheet feeding to the fixing roller are further stopped for a predetermined time. And it was set as the structure which repeats this until the said temperature difference becomes below the said predetermined value.
[0009]
Here, the control unit further includes a third state in which energization of the first heating element and the second heating element is controlled such that the detected temperature is maintained at a third setting temperature lower than the second setting temperature. The control state may be changed from the first state to the second state immediately via the third state.
[0010]
The predetermined time for stopping energization of the first heating element and the second heating element and passing the paper to the fixing roller is preferably in the range of 1 to 10 seconds.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
A major feature of the image forming apparatus according to the present invention is that when the set temperature of the temperature detected by the temperature detecting unit is changed from a high temperature (first state) to a lower temperature (second state), the second state is set. The temperature difference between the temperature detected by the temperature detection means and the set temperature in the second state (second set temperature) is predetermined after the energization to the heating means and the paper feeding to the fixing roller are stopped for a predetermined time after the change. It is to determine whether to start energizing the heating means and passing the paper to the fixing roller depending on whether the value is less than the value. According to such a configuration, the temperature detection unit can quickly detect a temperature drop in the center portion of the fixing roller due to the fixing process, and a low-temperature fixing failure in the fixing process using the center portion of the fixing roller can be prevented.
[0012]
The image forming apparatus of the present invention will be described below with reference to the drawings. The present invention is not limited to these embodiments.
[0013]
FIG. 1 is a schematic configuration diagram of a copying machine which is an embodiment of an image forming apparatus of the present invention. The main body housing 1 includes an upper housing 11, a lower housing 13, and a connection housing 12 positioned therebetween. On the upper housing 11, the document conveying unit 2 placed so as to be freely opened and closed is attached.
[0014]
The document transport unit 2 includes a document feed tray 21, a document transport unit body 22, a document discharge tray 23, and a document cover 24. The document discharge tray 23 is integrally formed as a part of the upper surface of the document cover 24. A document feed tray 21 is disposed at the upstream end on the extension of the document transport path d, and a document discharge tray 23 is disposed at the downstream end. A pickup roller 22a, a conveyance roller pair 22b, a registration roller pair 22c, and a discharge roller pair 22d are provided in order from the upstream side in the document conveyance direction in the document conveyance path d in the document conveyance unit main body 22. An image reading unit 25 is provided between the registration roller pair 22c and the discharge roller pair 22d. An image document (not shown) set on the document feed tray 21 with its image surface facing upward is conveyed along the conveyance path d by the rollers when a copy start button (not shown) is turned on, and an intermediate image reading unit. At 25, an image is read by the exposure unit 3.
[0015]
The exposure unit 3 is built in the upper housing 11. The exposure unit 3 includes an exposure lamp 31 and a reflecting plate 32, a first mirror 33, a second mirror 34, a third mirror 35, a condenser lens 36, and an image sensor (for example, a line type CCD) 37. The exposure lamp 31 and the first mirror 33 are mounted on a first carriage (not shown), and the second mirror 34 and the third mirror 35 are mounted on a second carriage (not shown). When reading a document image by a so-called sheet-through method, the first carriage moves directly below the image reading unit 25, and the light irradiation light from the exposure lamp 31 exposes the moving document. Irradiation light reaches the CCD 37 through the first mirror 33, the second mirror 34, the third mirror 35, and the condenser lens 36, and is read out as an electric signal through a photoelectric conversion process. On the other hand, when the original image is read by the original fixing method, the original image placed on the original placement plate 26 is subjected to reading scanning by the exposure unit 3 to be reduced and imaged on the CCD 37 and subjected to photoelectric conversion processing. After that, it is read to become an electric signal.
[0016]
In the lower housing 13, the paper feeding unit 4, the image forming unit 5, and the fixing device 6 are built. The paper feed unit 4 will be described first. A paper feed cassette 41 containing paper P is disposed below the lower housing 13, and the paper P is sent out one by one by a roller 42 to the conveyance path. Further, an openable / closable paper feed tray 43 is provided at the lower left portion of the lower housing 13, and the paper P is placed on the lower tray 13 so that the paper is transported one by one by the rollers 44 in the same manner as described above. Sent to the road.
[0017]
Next, the image forming unit will be described. The image forming unit 5 includes a photosensitive drum 51 and a charger 52, an optical scanning unit 53, a developing device 54, a transfer roller 55, and a cleaning device 56 disposed around the photosensitive drum 51. The photosensitive drum 51 rotates clockwise. First, the surface of the photosensitive drum 51 is uniformly charged by the charger 52. Next, the surface of the photosensitive drum 51 is irradiated with laser light from the optical scanning unit 53, the charge corresponding to the image portion or the background portion is erased, and an electrostatic latent image is formed on the surface of the photosensitive drum 51. . Then, the developing device 54 supplies toner to the electrostatic latent image on the photosensitive drum 51, and the electrostatic latent image is visualized.
[0018]
When the photosensitive drum 51 further rotates and the toner image comes to a position facing the transfer roller 55, the paper P is conveyed between the photosensitive drum 51 and the transfer roller 55 accordingly. At this time, the toner image on the photosensitive drum 51 is transferred onto the paper P by applying a voltage having a polarity opposite to the charging polarity of the toner to the transfer roller 55. Residual toner that has not been transferred onto the photosensitive drum 51 is removed from the photosensitive drum 51 by the cleaning device 56. On the other hand, the paper P onto which the toner image has been transferred is conveyed to a fixing unit 6 which will be described later, where the toner image is heated and pressurized to be fixed on the paper, and discharged to the paper discharge trays 7a and 7b through the paper discharge path. Is done.
[0019]
Next, the fixing device will be described. The fixing device 6 includes a fixing roller 61 and a pressure roller 62 that are in pressure contact with each other. FIG. 2 shows an enlarged configuration diagram of the fixing device 6. A thermistor (temperature detection means) 63 for detecting the surface temperature of the fixing roller 61 is provided in the non-sheet passing region of the fixing roller 61. The fixing roller 61 includes a main heater H ₁ (first heating element) and a sub-heater H ₂ (second heating element). Note that specific configurations of the fixing roller 61 and the pressure roller 62 will be described in the following embodiments.
[0020]
FIG. 3 shows an example of a heat distribution pattern of these heaters H ₁ and H ₂ . As understood from this figure, the main heater H ₁ is set so as to mainly heat the central portion of the fixing roller 61, and the sub heater H ₂ is set so as to mainly heat both ends of the fixing roller 61. Further, the heat generation pattern are combined so that the surface temperature distribution in the axial direction of the fixing roller is constant when the lit both main heater H ₁ and sub-heater H _2. The length of the central portion of the fixing roller in this fixing device is about 210 mm, which matches the sheet passing area when A4 paper (297 mm × 210 mm) is conveyed in the vertical direction. Both the main heater H ₁ and the sub heater H _{2 have} a total length of 310 mm, and the A4 sheet is covered even when the A4 sheet is conveyed in the horizontal direction. In FIG. 3, the left side is the front side of the image forming apparatus, and the right side is the back side of the image forming apparatus.
[0021]
Figure 2 Oite, the surface temperature of the fixing roller 61 detected by the thermistor 63 is transmitted to the control unit 64, on-off control of the main heater H ₁ and sub-heater H ₂ is made based on the detected temperature. The control unit 64 specifically, when the sheet passing area of the paper is wider than the central portion of the fixing roller 61, the main heater so that the detected temperature by the thermistor 63 maintains the first set temperature H ₁ and the sub heater H ₂ is controlled (first state). On the other hand, when the paper passing area is the same as or narrower than the central portion of the fixing roller 61, the sub-heater H is set so that the temperature detected by the thermistor 63 is maintained at the second set temperature lower than the first set temperature. controlling the energization of the main heater H ₁ in a state of stopping the power supply to the ₂ (second state).
[0022]
The set temperature of the temperature detected by the thermistor 63 is changed between the first state and the second state in consideration of the distance between the installation position of the thermistor 63 and the heater heating unit. When only the central part is heated, the second set temperature is set lower than the first set temperature because the amount of heat conducted to the installation position of the thermistor 63 is small. Control unit 64 from the viewpoint of energy saving is also, when the image forming process is completed, controls the power supply to the main heater H ₁ and sub-heater H ₂ to maintain the third set temperature lower than the second predetermined temperature (the 3 states).
[0023]
In such fixing device control, when the control state is changed from the first state to the second state, or when the change of the control state is immediately changed from the first state to the second state via the third state. In the present invention, the energization to the main heater H ₁ and the sub heater H ₂ is stopped for a predetermined time after the control state is changed to the second state, and the sheet feeding to the fixing roller 61 is stopped. If the temperature difference between the detected temperature and the second set temperature after the lapse of the predetermined time is equal to or smaller than a predetermined value, the control unit 64 performs the energization control in the second state and starts passing the paper to the fixing roller 61. On the other hand, if the temperature difference is larger than the predetermined value, the energization to the main heater H ₁ and the sub heater H ₂ and the sheet passing to the fixing roller 61 are further stopped for a predetermined time, and the temperature difference becomes the predetermined value or less. Repeat until this. Thereby, the deviation of the temperature change between the temperature detected by the thermistor 63 and the central portion of the fixing roller 61 is suppressed to be small, and problems such as low-temperature fixing failure are effectively prevented. Hereinafter, based on an Example, this invention is demonstrated in detail.
[0024]
Using the fixing device shown in FIG. 1 and FIG. 2, changes with time in the surface temperature of the center portion of the fixing roller and the temperature detected by the thermistor were examined. The surface temperature at the center of the fixing roller was measured using another thermistor. The used fixing roller 61 has a 25 μm-thick PTFE (polytetrafluoroethylene) layer 61 b formed on the surface of an aluminum roller body 61 a having an outer diameter of 37 mm and a wall thickness of 1 mm. In the pressure roller 62, an elastic layer 62b having a thickness of 5 mm is formed on the surface of an iron core bar 62a having an outer diameter of 20 mm, and a PFA (tetrafluoroethylene-per-fluoroalkylvinylether copolymer) having a thickness of 50 μm is further formed on the surface. Combined) A tube layer 62c is formed. The elastic layer 62b is a foam of silicon rubber having an Asuka C hardness of 55 degrees. The fixing roller 61 is driven and rotated with the photosensitive drum 51 (shown in FIG. 1) at a constant peripheral speed of 178 mm / sec, and the pressure roller 62 is in pressure contact with the fixing roller 61 and is driven to rotate.
[0025]
FIG. 4 is a diagram showing the temporal change of the surface temperature of the fixing roller center portion and the temperature detected by the thermistor, and the timings of turning on / off the main heater and sub heater, and on / off of the driving rotation of the fixing roller. In the first state in which the A4 sheet is fixed in the horizontal direction, the main heater and the sub heater are controlled on and off so that the temperature detected by the thermistor (broken line in FIG. 4) is 180 ° C. (first set temperature). ing. As a result, the surface temperature (solid line in the figure) at the center of the fixing roller is maintained in the range of 190 to 200 ° C. Then, immediately after the fixing process of the A4 sheet in the horizontal direction is completed, when the start signal for the fixing process in the vertical direction of the A4 sheet is input, the main heater H ₁ and the sub heater H ₂ are energized, and the fixing roller 61 is supplied. Paper passing is stopped for 8 seconds. During this time, the surface temperature of the non-sheet-passing area where the thermistor 63 of the fixing roller is installed gradually decreases as in the central portion of the fixing roller. As a result, the temperature detected by the thermistor 63 and the temperature change at the center of the fixing roller 61 show the same tendency. Since the temperature difference between the detected temperature detected by the thermistor 63 after 8 seconds and the second set temperature (167 ° C.) is about 2 ° C. and a predetermined value (10 ° C.) or less, the control unit 64 is connected to the thermistor. performs energization control of the main heater H ₁ so that the detected temperature is 167 ° C., to initiate the sheet passing the fixing roller 61. As a result, the surface temperature of the central portion of the fixing roller once lowered to 180 ° C. or less gradually increases, and the range of 190 to 200 ° C., which is a good fixing temperature range, is maintained.
[0026]
In this embodiment, the temperature difference between the detected temperature detected by the thermistor and the second set temperature becomes equal to or smaller than a predetermined value after 8 seconds. However, if the temperature difference is larger than the predetermined value even after 8 seconds. The energization of the main heater H ₁ and the sub-heater H ₂ and the passage of paper to the fixing roller 61 are further stopped for 8 seconds, and this is repeated until the temperature difference becomes a predetermined value or less.
[0027]
The time to stop the sheet passing between the energization of the main heater H ₁ and the sub heater H ₂ to the fixing roller 61, there the deviation of temperature change between the central portion and the non-paper passing area of the fixing roller can be time resolved There is no particular limitation, and it may be appropriately determined from the power of the heater, the length of the fixing roller, the heat capacity, and the like. Generally, the range of 1 to 10 seconds is preferable. Further, as the predetermined value of the temperature difference between the temperature detected by the thermistor 63 and the second set temperature, the temperature difference can be eliminated as long as the temperature difference between the central portion of the fixing roller and the non-sheet passing region is the same as described above. There is no limitation in particular, and generally the range of 1-10 degreeC is preferable.
[0028]
On the other hand, using the same fixing device as described above, after the fixing process of the A4 sheet in the horizontal direction is completed, when the start signal for the fixing process in the vertical direction of the A4 sheet is input, the fixing process is immediately started. Under the same conditions as in the example, changes with time in the surface temperature of the center portion of the fixing roller and the temperature detected by the thermistor were examined. FIG. 5 is a diagram showing temporal changes in the surface temperature of the fixing roller center portion and the temperature detected by the thermistor, and the timings of turning on / off the main and sub heaters and driving the fixing roller.
[0029]
As is apparent from FIG. 5, in the first state where the fixing process of the A4 sheet in the horizontal direction is performed, the main heater is set so that the temperature detected by the thermistor (broken line in FIG. 5) is 180 ° C. (first set temperature). • The sub-heater is on / off controlled. As a result, the surface temperature (solid line in the figure) at the center of the fixing roller is maintained in the range of 190 to 200 ° C. Then, after the fixing process for the A4 sheet in the horizontal direction is completed, when a start signal is input for the fixing process for the A4 sheet in the vertical direction, the fixing process is started immediately unlike the above. As a result, the surface temperature at the center of the fixing roller is suddenly lowered due to the heat taken by the paper. On the other hand, the detected temperature at the thermistor located away from the central portion was higher than the second set temperature (167 ° C.) due to residual heat. For this reason, although the surface temperature at the center of the fixing roller suddenly decreased, the main heater did not light up, and a low-temperature fixing failure occurred.
[0030]
In the present invention, as the fixing roller main body 61a (see FIG. 2), a metal material such as iron, copper, nickel, and stainless steel can be used in addition to aluminum. The thickness of the fixing roller body is not particularly limited, but is preferably in the range of 0.5 mm to 3 mm. When the release layer 61b is provided on the surface of the fixing roller body, in addition to PTFE, a PFA layer, a fluororesin such as PVF (polyvinyl fluoride), ECTFE (ethylene-chlorotrifluoroethylene copolymer), or the like is used. be able to. The thickness of the releasable layer is preferably from 10 to 100 μm.
[0031]
Further, the pressure roller used in the present invention is preferably one in which the elastic layer 62b is provided on the surface of the core metal 62a, and the thickness of the elastic layer 62b is preferably in the range of 2 to 15 mm. The elastic layer 62b is preferably an elastic rubber having an Asuka C hardness of 5 to 90 degrees. When the release layer 62c is provided on the surface of the elastic layer 62b, a fluororesin such as PVF or ECTFE can be used in addition to PTFE. The thickness of the releasable layer 62c is preferably in the range of 20 to 100 μm.
[0032]
As the heating element used in the present invention, a conventionally known heating element can be used. Among them, a halogen heater is preferable because it can provide instantaneous warming. As the temperature detecting means used in the present invention, a conventionally known means can be used.
[0033]
【The invention's effect】
In the image forming apparatus of the present invention, from the first state in which the energization to the main heater and the sub heater is controlled so that the detected temperature of the thermistor maintains the first set temperature, the detected temperature of the thermistor is lower than the first set temperature. 2 When the control state is changed to the second state in which the energization only to the main heater is controlled so as to maintain the set temperature, the energization to the main heater and the sub-heater and the sheet passing to the fixing roller are changed after the control state is changed. Since it is stopped for a predetermined time, a decrease in the surface temperature of the center portion of the fixing roller due to the state change from the first state to the second state can be detected quickly and accurately by the thermistor, and the occurrence of poor fixing at low temperatures can be prevented.
[0034]
The control unit further includes a third state for controlling energization to the main heater and the sub heater so that the temperature detected by the thermistor is maintained at a third set temperature lower than the second set temperature. Even when the state is immediately changed to the second state via the third state, the same effect as described above can be obtained.
[0035]
If the time to stop energization of the main heater and sub heater and the passage of paper to the fixing roller is in the range of 1 to 10 seconds, the deviation of the temperature change between the surface temperature of the fixing roller center and the detected temperature of the thermistor is further ensured. Can be prevented.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention.
FIG. 2 is a schematic configuration diagram of a fixing device used in the image forming apparatus of FIG.
FIG. 3 is a diagram illustrating a heat distribution of a heater of a fixing roller and a sheet passing area.
FIG. 4 is a diagram showing temporal changes in the surface temperature of the fixing roller central portion and the detected temperature of the thermistor, and the timings of turning on / off the main and sub heaters and driving the fixing roller.
FIG. 5 is a diagram showing temporal changes in the surface temperature of the fixing roller central portion and the detected temperature of the thermistor, and timings of turning on / off of the main and sub heaters and driving of the fixing roller.
[Explanation of symbols]
H ₁ main heater (first heating element)
H ₂ sub-heater (second heating element)
61 Fixing roller 62 Pressure roller 63 Thermistor (temperature detection means)
64 Control unit

Claims (3)

A fixing roller including a first heating element that mainly heats the central portion in the roller axial direction and a second heating element that mainly heats both ends in the roller axial direction; and a pressure roller in pressure contact with the fixing roller; The temperature detecting means for detecting the surface temperature of the fixing roller provided in the non-sheet passing area on the surface of the fixing roller, and the first heating element and the second heating element based on the temperature detected by the temperature detecting means. And a control unit for controlling energization of
The control unit controls the energization of the first heating element and the second heating element so that the detected temperature maintains the first set temperature, and the detected temperature is the first set temperature. A second state for controlling energization to the first heating element in a state in which energization to the second heating element is stopped so as to maintain a lower second set temperature.
When the control state is changed from the first state to the second state, the energization to the first heating element and the second heating element is stopped for a predetermined time after the change of the control state, and the sheet is fed to the fixing roller. If the temperature difference between the detected temperature and the second set temperature after the lapse of the predetermined time is equal to or smaller than a predetermined value, the control unit performs the energization control in the second state and passes the paper to the fixing roller. On the other hand, if the temperature difference is larger than a predetermined value, the energization of the first heat generating element and the second heat generating element and the paper passing to the fixing roller are further stopped for a predetermined time, and the temperature difference is the predetermined value. An image forming apparatus that repeats this until the following is satisfied. The control unit further includes a third state in which energization to the first heating element and the second heating element is controlled so that the detected temperature maintains a third setting temperature lower than the second setting temperature,
The image forming apparatus according to claim 1, wherein the control state is changed from the first state to the second state immediately through the third state. 3. The image forming apparatus according to claim 1, wherein the predetermined time for stopping energization of the first heating element and the second heating element and passing of the paper to the fixing roller is in a range of 1 to 10 seconds.

Images