JP5867292B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device for fixing an unfixed image on a recording sheet while the recording sheet on which the unfixed image is formed passes through a fixing nip formed by pressure contact between a heating rotator and a pressure rotator. The present invention also relates to an image forming apparatus having such a fixing device.

In an image forming apparatus such as a printer that forms a toner image by an electrophotographic method, a toner image transferred to a recording sheet is usually fixed on the recording sheet by a fixing device.
In the fixing device, a heating rotator such as a heating roller and a fixing belt and a pressure body such as a pressure roller are pressed to form a fixing nip, and a toner image on a recording sheet passing through the fixing nip is displayed. The recording sheet is fixed by heating and pressing. The recording sheet passing through the fixing nip is heated by, for example, a heater lamp.

  When performing the heat fixing operation in the fixing device, first, warm-up is performed by heating the heating rotator to a target temperature (about 160 ° C.) or higher with a heater lamp, and when the warm-up is completed, the print job is started. The recording sheet is conveyed to the fixing nip. During the execution of the job, the heater lamp is turned off when the temperature of the heating rotator exceeds the target temperature, and is turned on again when the temperature of the heating rotator falls below the target temperature.

  When the temperature of the heating rotator is in a low state such as about room temperature at the start of warm-up, the pressure member that is in pressure contact with the temperature may be in a low temperature state such as about room temperature. In this case, after the warm-up is started, the heating rotator is heated by the heat of the heater lamp, and a part of the heat of the heating rotator moves to the pressure rotator through the fixing nip. In order to suppress a delay in the temperature rise of the heating rotator due to such heat transfer, a heater lamp having a large calorific value per unit time is used.

  When a heater lamp having a large calorific value per unit time is used, the temperature of the heating rotator is increased quickly, and warm-up can be completed quickly, so that the start of the print job can be accelerated.

JP 2010-96969 A

However, if the heater lamp is repeatedly turned on and off during a job that continuously conveys multiple recording sheets, the temperature of the heating rotator does not stabilize at the target temperature, and a temperature ripple that fluctuates up and down occurs. It becomes easy.
In other words, at the end of warm-up, even if the surface temperature of the heating rotator has risen to near the target temperature, even if the warm-up is completed if the pressure body is at a low temperature at the start of warm-up, The inside of the pressure body is in a low temperature state, and the heat transfer from the heating rotator to the pressure body is often continued after the warm-up is completed until the heat reaches the inside of the pressure body. When the job is started in such a state, the heat of the heating rotator is taken away by both the recording sheet passing through the fixing nip and the pressure member pressed by the fixing nip. Even if the heating by the heater lamp having a large calorific value is continued, the temperature of the heating rotator greatly decreases every time the recording sheet passes through the fixing nip, and until the next recording sheet reaches the fixing nip, The temperature of the heating rotator rises greatly.

  In addition, when heat is accumulated inside the pressurizer due to the passage of time from the start of the job, there is almost no transfer of heat from the heating rotator to the pressurizer, and most of the heat from the heater lamp is To the recording sheet. In this case, the amount of heat generated from the heater lamp per unit time is substantially constant while the heater lamp is on, and the amount of heat per unit time taken by the recording sheet passing through the fixing nip is also the recording sheet. If the size and the conveyance speed are constant, they are substantially constant during job execution.

  Therefore, if the heat deprived by the pressurizing body is reduced, heat transfer from the heater lamp to the recording sheet is almost eliminated even if the heat from the heater lamp is deprived by the recording sheet. Due to the heating of the heater lamp having a large amount, the temperature of the heating rotator rapidly increases and exceeds the target temperature in a relatively short time (overshoot). Moreover, immediately after the overshoot, when the heater lamp with a large calorific value is turned off, the heat capacity of the heating rotator is small, so the temperature of the heater lamp heating rotator falls below the target temperature in a relatively short time, The heater lamp is turned on. As a result, even when the pressurizing body is in a heat storage state, the heater lamp is likely to be frequently turned on and off in a short cycle, and a temperature ripple with a large temperature change may occur.

In a configuration using a heater lamp, normally, the temperature of the heating rotator is detected by a sensor, and power is supplied to the heater lamp (on) based on the detected temperature of the sensor so that the temperature of the heating rotator stabilizes at the target temperature. And a circuit configuration in which stop (off) is switched by a switch.
In such a circuit that switches between supply and stop of electric power with a switch, there is a considerable response delay from sensor temperature detection to switch switching, and this response delay may further increase the temperature ripple of the heating rotor. .

In particular, in recent years, in order to shorten the time required for warm-up as much as possible, a heating rotator with a low heat capacity is used. However, the lower the heat capacity, the higher the rate of temperature rise and fall. As the temperature rise and fall periods become shorter and the peak values of the upper and lower temperatures become larger, it becomes easier to perform heat fixing stably.
Moreover, the resistance value of the heater lamp depends on the temperature, and it is known that when electric power is supplied with the resistance value of the heater lamp being low, a large current (inrush current) is temporarily supplied to the heater lamp. It has been.

  For this reason, as described above, if the power supply to and the stop of the heater lamp are repeated in a short time, the number of occurrences of inrush current increases, so that the power consumption of the heater lamp increases and the energy saving performance may be impaired. There is. Further, since the surface temperature of the heating rotator temporarily rises due to the occurrence of the inrush current, the temperature change of the surface of the heating rotator may also become large.

Note that the above-described problems occur not only when the heater lamp is used, but also when other electric-heat conversion heating means are used.
The present invention has been made in view of such a problem, and can suppress a temperature change of the heating rotator when a plurality of recording sheets continuously pass through the fixing nip, and can further reduce power consumption. An object of the present invention is to provide a fixing device capable of reducing the above.

  Another object of the present invention is to provide an image forming apparatus using such a fixing device.

  In order to achieve the above object, the fixing device according to the present invention is provided on the recording sheet when the recording sheet passes through the fixing nip secured between the heating rotator and the pressure member pressed against the heating rotator. A fixing device for thermally fixing an unfixed image, wherein a plurality of heating means for heating the heating rotator, a detection means for detecting a temperature of the heating rotator, and one of the plurality of heating means or One power capacity selected from among different power capacities obtained by a plurality of combinations is set as a reference mode, and the detection means during the heat fixing operation for a plurality of recording sheets passing through the fixing nip continuously Control means for heating the heating rotator in a reference mode when the detected temperature is lower than a target temperature, and stopping heating of the heating rotator when the temperature exceeds the target temperature. After the heating rotator is heated in the mode, the heating rotator is overheated with respect to the target temperature by stopping the heating of the heating rotator, and rises to a predetermined upper limit temperature higher than the target temperature. In this case, the reference mode is updated to a power capacity smaller than the previously set power capacity.

  In addition, another fixing device according to the present invention has an indeterminate state on a recording sheet by heating when the recording sheet passes through a fixing nip secured between the heating rotator and a pressure body pressed against the heating rotator. A fixing device for fixing a received image, wherein a plurality of heating means for heating the heating rotator, a detection means for detecting a temperature of the heating rotator, and one or more of the plurality of heating means One power capacity selected from among the power capacities obtained by the combination is set as a reference mode, and the temperature detected by the detecting means during the heat fixing operation for a plurality of recording sheets continuously passing through the fixing nip. Control means for heating the heating rotator in a reference mode when the temperature is lower than a target temperature, and stopping heating of the heating rotator when the temperature exceeds the target temperature. When the temperature of the heating rotator overshoots the target temperature due to the heating of the heating rotator after the rotator is heated, the time required to fall below the target temperature is a predetermined time or more. The reference mode is updated to a power capacity smaller than the previously set power capacity.

  Furthermore, an image forming apparatus according to the present invention includes the fixing device.

  In the fixing device of the present invention, when the heating rotator overheats to the target temperature and rises to the upper limit temperature when the heating rotator is stopped after heating the heating rotator in the reference mode, the reference mode is changed to the previous time. The power capacity is updated to be smaller than the set power capacity. As a result, while the heat fixing operation is being performed, as the heat storage amount of the pressurizing body or the like increases as the heat of the heating rotary body moves to the pressurizing body or the like, The capacity is updated and heated.

  Therefore, even when the heating rotator overshoots the target temperature during heating of the heating rotator, it is possible to suppress an increase to the upper limit temperature. As a result, it is possible to suppress the occurrence of a temperature ripple with a large temperature change in the heating rotator. Moreover, by heating the heating rotator in the reference mode in which the power capacity is reduced, the power consumption during heating can be reduced.

  In another fixing device of the present invention, when the heating rotator overshoots the target temperature when heating of the heating rotator is stopped after heating the heating rotator in the reference mode, a predetermined time or more is required until the temperature falls below the target temperature. In short, the reference mode is updated to a power capacity smaller than the power capacity set last time. As a result, while the heat fixing operation is being performed, as the heat storage amount of the pressurizing body or the like increases as the heat of the heating rotary body moves to the pressurizing body or the like, The capacity is updated and heated.

  Therefore, also in this case, when the heating rotator is heated, the heating rotator can be prevented from overshooting the target temperature and rising to the upper limit temperature. As a result, it is possible to suppress the occurrence of a temperature ripple with a large temperature change in the heating rotator. Moreover, by heating the heating rotator in the reference mode in which the power capacity is reduced, the power consumption during heating can be reduced.

Preferably, the control means sets the reference mode to be larger than the previously set power capacity when the detection temperature of the detection means falls below a predetermined lower limit temperature lower than the target temperature during heating of the heating rotator. After the update to the power capacity, the heating rotator is heated in the updated reference mode.
Preferably, the control means updates the reference mode to the maximum power capacity when the temperature falls below the lower limit temperature.

Preferably, the control means sets the reference mode to a maximum power capacity at the start of the thermal fixing operation, and heats the heating rotator in the set reference mode.
Preferably, the control unit raises the heating rotator to a predetermined temperature lower than the target temperature during a standby state after the heating rotator is heated to the target temperature until the thermal fixing operation is instructed. When the heat fixing operation is instructed in the power saving mode, the reference mode is set to the power capacity selected based on the elapsed time in the standby state. The heating rotator is heated to raise the temperature in a set reference mode.

Preferably, the control unit sets the reference mode to the maximum power capacity until the elapsed time of the standby state reaches a threshold, and if the elapsed time exceeds the threshold, the control mode is set to be higher than the maximum power capacity. It is characterized by setting to a small power capacity.
Preferably, at the start of the thermal fixing operation, the control unit sets the reference mode to a power capacity selected based on a temperature detected by the detection unit, and the heating rotator is set with the set power capacity. Is heated.

Preferably, the control unit sets the reference mode to the maximum power capacity when the detection temperature of the detection unit at the start of the thermal fixing operation is lower than a threshold temperature set lower than the target temperature. When the temperature is equal to or higher than the threshold temperature, the reference mode is set to a power capacity smaller than the maximum power capacity.
In the fixing device according to another aspect of the invention, it is preferable that the control unit is in a lowered state between the target temperature and a predetermined lower limit temperature lower than the target temperature. When the heating rotator is heated in the reference mode and the temperature is changed from the lowered state to the raised state between the target temperature and the lower limit temperature, the power capacity set in the reference mode is also small. The heating rotator is heated by switching to power capacity.

  Furthermore, in another fixing device according to the present invention, preferably, the control unit updates the reference mode to the maximum power capacity when the detection temperature of the detection unit falls below the lower limit temperature, The heating rotator is heated with a power capacity.

1 is a schematic diagram illustrating a schematic configuration of a tandem type color printer which is an example of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view for explaining a configuration of a fixing device provided in the color printer. FIG. 3 is a block diagram illustrating a configuration of a control system provided in the fixing device. 6 is a table for explaining first to fourth power modes set in a fixing control unit. 5 is a flowchart illustrating an example of fixing temperature control executed in a fixing control unit. 6 is a graph showing a change in power supplied to the first heater lamp and a change in surface temperature of the heating roller after the reference mode is switched to the fourth power mode in the fixing temperature control of the present embodiment. (A) is a graph showing a change in the surface temperature of the fixing belt in the fixing temperature control of the comparative example, and (b) is a time chart of a control signal when heating the fixing belt in the comparative example. It is a table | surface which shows the average value of the power supply (power consumption) with respect to the 1st heater lamp in the graph shown by FIG. 6, and a print TEC value. 6 is a flowchart illustrating another example of fixing temperature control executed in the fixing control unit. 10 is a flowchart showing still another example of fixing temperature control executed in the fixing controller. 10 is a flowchart showing still another example of fixing temperature control executed in the fixing controller. 10 is a table for explaining another example of the power mode set in the fixing control unit. Each of (a) to (e) is a relationship between the power mode set as the reference mode and the power mode for heating the fixing belt in still another example of the fixing temperature control executed in the fixing controller. It is a table | surface which shows. 10 is a flowchart showing still another example of fixing temperature control executed in the fixing controller. FIG. 15 is a flowchart showing a fixing temperature control processing procedure following the flowchart of FIG. 14. FIG. (A) is a graph showing an example of a change in the surface temperature of the fixing belt in the fixing temperature control in Embodiment 5, and (b) is a graph showing a change in the power mode for heating the fixing belt in the fixing temperature control. is there. (A) is a graph which shows an example of the change of the surface temperature of the fixing belt in a comparative example, (b) is a graph which shows the electric power mode in that case. 10 is a table for explaining conditions for fixing temperature control in another comparative example. (A) is a graph showing a change in the surface temperature of the heating rotator when the fixing temperature control is executed under the conditions shown in the table of FIG. 18, and (b) is a graph showing a change in the supplied power in that case. .

Hereinafter, embodiments of an image forming apparatus according to the present invention will be described.
<Configuration of image forming apparatus>
FIG. 1 is a schematic diagram illustrating a schematic configuration of a tandem color printer (hereinafter simply referred to as “printer”) which is an example of an image forming apparatus according to an embodiment of the present invention. This printer forms a toner image by a well-known electrophotographic method based on image data input from an external terminal device via a network (for example, LAN), and feeds a sheet from a lower sheet feeding cassette 22 to a sheet conveyance path 21. The toner image is transferred to the recording sheet P conveyed along the direction. The recording sheet P to which the toner image is transferred is conveyed to the fixing device 30, and the toner image is fixed to the recording sheet P in the fixing device 30.

  An intermediate transfer belt 18 having an orbital movement area that is elongated along the horizontal direction is provided at a substantially central portion in the vertical direction of the printer. The intermediate transfer belt 18 moves (runs) in the direction indicated by the arrow X. Below the intermediate transfer belt 18, image forming units 10Y, 10M, 10C, and 10K are provided. The image forming units 10Y, 10M, 10C, and 10K face the lower belt running portion of the intermediate transfer belt 18 and are arranged in that order along the running direction.

  In each of the image forming units 10Y, 10M, 10C, and 10K, below the belt running portion on the lower side of the intermediate transfer belt 18, a photoconductor disposed so as to be rotatable in the arrow Z direction in a state of facing the intermediate transfer belt 18. Drums 11Y, 11M, 11C, and 11K are provided. Yellow (Y), magenta (M), cyan (C), and black (K) are provided using the photosensitive drums 11Y, 11M, 11C, and 11K, respectively. A toner image of each color is formed.

Each of the image forming units 10Y, 10M, 10C, and 10K has substantially the same configuration except that only the color of the toner used for forming the toner image is different. Only the configuration of 10Y will be described in detail, and detailed description of the configuration of the other image forming units 10M, 10C, and 10K will be omitted.
The image forming unit 10Y has a charger 12Y disposed to face the lower part of the photosensitive drum 11Y. The surface of the photosensitive drum 11Y is uniformly charged by the charger 12Y. An exposure device 13Y is disposed below the image forming units 10Y, 10M, 10C, and 10K, and an electrostatic latent image is formed on the surface of the charged photosensitive drum 11Y by the laser light emitted from the exposure device 13Y. Is formed.

The photosensitive drums 11M, 11C, and 11K in the other image forming units 10M, 10C, and 10K are also irradiated with the laser beam emitted from the exposure device 13, and the surfaces of the photosensitive drums 11M, 11C, and 11K. An electrostatic latent image is formed.
The electrostatic latent image formed on the surface of the photoreceptor drum 11Y is developed with Y-color toner by the developing device 14Y. As a result, a Y-color toner image is formed on the surface of the photosensitive drum 11Y.

A primary transfer roller 15 </ b> Y that faces the photosensitive drum 11 </ b> Y with the intermediate transfer belt 18 interposed therebetween is disposed in an area inside the circumferential movement area of the intermediate transfer belt 18. The toner image formed on the photoreceptor drum 11Y is primarily transferred onto the intermediate transfer belt 18 by the action of an electric field by the primary transfer roller 15Y to which a transfer bias voltage is applied.
Primary transfer rollers 15M, 15C, and 15K facing the respective photosensitive drums 11M, 11C, and 11K with the intermediate transfer belt 18 interposed therebetween are also provided above the other image forming units 10M, 10C, and 10K. The toner images formed on the surfaces of the photosensitive drums 11M, 11C, and 11K are respectively transferred onto the intermediate transfer belt 18 by the action of an electric field by the primary transfer rollers 15M, 15C, and 15K to which a transfer bias voltage is applied. Primary transfer.

  In the case of forming a full-color image, each toner image formed on each of the photoconductive drums 11Y, 11M, 11C, and 11K is transferred to the same area on the intermediate transfer belt 18 in a multiple transfer manner. The timings of the image forming operations of the image forming units 10Y, 10M, 10C, and 10K are shifted. On the other hand, in the case of forming a monochrome image, only one selected image forming unit (for example, the image forming unit 10K for K toner) is driven, and a photosensitive drum provided in the image forming unit. The toner image formed thereon is transferred onto a predetermined area on the intermediate transfer belt 18.

  A driving roller 17 that makes the intermediate transfer belt 18 circulate around the downstream end portion (the right end portion in FIG. 1) in the traveling direction of the lower belt traveling portion on which the toner image is formed. Has been placed. A secondary transfer roller 19 is brought into pressure contact with the intermediate transfer belt 18 wound around the drive roller 17, and a transfer nip Nt is formed at a portion where they are in pressure contact with each other.

  The recording sheet P conveyed through the sheet conveyance path 21 is conveyed to the transfer nip Nt. The toner image transferred onto the intermediate transfer belt 18 is recorded on the recording sheet P by the action of an electric field formed by the transfer bias voltage applied to the secondary transfer roller 19 while the recording sheet P passes through the transfer nip Nt. Secondary transferred on top. The recording sheet S on which the toner image is secondarily transferred is conveyed to the fixing device 30 disposed above the secondary transfer roller 19.

The recording sheet S is heated to a predetermined fixing temperature while passing through the fixing device 30, and the toner image on the recording sheet S is fixed on the recording sheet S. A specific configuration of the fixing device 30 will be described later.
The recording sheet P on which the toner image is fixed is discharged onto the paper discharge tray 23 by the paper discharge roller 24.

<Configuration of fixing device>
FIG. 2 is a schematic cross-sectional view for explaining the configuration of the fixing device 30. As shown in FIG. 2, the fixing device 30 includes a fixing belt 33 that is wound around the heating roller 31 and the fixing roller 32 and moves around (runs) in the direction of arrow F, and a fixing belt 33 that is wound around the fixing roller 32. And a pressure roller 34 for pressing.

The fixing roller 32 is rotatably supported by a side plate (not shown). The heating roller 31 is biased in a direction away from the fixing roller 32 by a tension mechanism (not shown) using a spring or the like. As a result, a tension is applied to the fixing belt 33 wound around the fixing roller 32 and the heating roller 31.
The pressure roller 34 is pressed against the fixing belt 33 at a predetermined pressure by a pressure mechanism (not shown) using a spring or the like, and a fixing nip Nf is secured between the two. The recording sheet P to which the toner image has been transferred is conveyed to the fixing nip Nf with the image surface directed toward the fixing belt 33 and passes through the fixing nip Nf. In this embodiment, the nip load of the fixing nip Nf The nip width (the length along the circumferential direction of the fixing belt 33) is 8 mm, and the nip length (the length along the width direction orthogonal to the running direction of the fixing belt 33) is 50 to 500 N. It is 320 mm.

  The heating roller 31 is formed in a hollow cylindrical shape, and includes therein a first heater lamp 35, a second heater lamp 36, and a third heater lamp 37 that heat the heating roller 31 by an electric-heat conversion method. A heating means is provided. When the heating roller 31 is heated by any one or more of the first to third heater lamps 35 to 37, the fixing belt 33 that is wound around the heating roller 31 and heated is heated, and the fixing belt heated. The recording sheet P passing through the fixing nip Nf is heated by 33.

Each of the first heater lamp 35, the second heater lamp 36, and the third heater lamp 37 is constituted by, for example, a halogen heater lamp, and each has a constant radius around the axis of the heating roller 31. Are arranged along the axial center of the heating roller 31 with an equal interval in the circumferential direction.
The rated power (power capacity) of each of the first heater lamp 35, the second heater lamp 36, and the third heater lamp 37 is different, the rated power of the first heater lamp 35 is 700 W, and the rated power of the second heater lamp 36. Is 500 W, and the rated power of the third heater lamp 37 is 300 W.

  Each of the first heater lamp 35, the second heater lamp 36, and the third heater lamp 37 enters a lighting (heat generation) state when power is supplied, and the heating roller 31 has a heat generation amount approximately proportional to the supplied power. Heat. Accordingly, the first heater lamp 35 with the rated power of 700 W has the maximum heat generation amount, and then the second heater lamp 36 with the rated power of 500 W has the large amount of heat generation, and the third heater lamp 37 with the rated power of 300 W. Is the minimum calorific value.

  Each of the first to third heater lamps 35 to 37 has the same length of 290 mm, and the fixing property at each end on both sides of the fixing belt 33 in the width direction (direction orthogonal to the running direction) is improved. In order to ensure, the light distribution (corresponding to light intensity and heating intensity) at each end on both sides in the longitudinal direction is larger than the light distribution in the central part in the longitudinal direction. In the present embodiment, the light distribution of the 20 mm long portions at the ends on both sides of each of the first to third heater lamps 35 to 37 is distributed at the central portion of the length 250 mm other than the ends on both sides. If the light is 100%, each is 115%.

The pressure roller 34 is rotated at a predetermined surface speed (165 mm / s in this embodiment) by a drive motor (not shown). As a result, the fixing roller 32 that is in pressure contact with the pressure roller 34 with the fixing belt 33 interposed therebetween rotates following the pressure roller 34, and the fixing belt 33 is integrated with the fixing roller 32. And run.
A temperature sensor 38 that detects the surface temperature of the fixing belt 33 wound around the heating roller 31 is provided in the vicinity of the heating roller 31. The temperature sensor 38 is disposed so as to face the upstream portion of the fixing belt 33 wound around the heating roller 31 in the traveling direction. As the temperature sensor 38, a non-contact thermistor is used in this embodiment.

In the heating roller 31, for example, a PTFE coat 31b is laminated on the outer peripheral surface (surface) of a cylindrical cored bar 31a, and the outer diameter is 25 mm. The cored bar 31a is made of an aluminum plate having a thickness of 0.5 mm. The heating roller 31 having such a configuration has a relatively small heat capacity.
The fixing roller 32 includes a cored bar 32a having an outer diameter of 18 mm made of iron having a thickness of 0.5 mm, an elastic layer 32b stacked on the outer peripheral surface (surface) of the cored bar 32a, and an elastic layer 32b. And an elastic layer 32c laminated on the outer peripheral surface (surface). The outer diameter of the fixing roller 32 is 30 mm. The elastic layer 32b is made of a 4 mm thick silicone rubber, and the elastic layer 32c is made of a 2 mm thick silicone sponge. The fixing roller 32 has a hardness of 30 °. The fixing roller 32 having such a configuration has a relatively large heat capacity.

  The fixing belt 33 includes a base material 33a configured in a cylindrical shape having an outer diameter of 50 mm with nickel having a thickness of 35 μm, an elastic layer 33b stacked on the surface (outer peripheral surface) of the base material 33a, and an elastic layer 33b. And a release layer 33c laminated on the surface (outer peripheral surface). The fixing belt 33 is formed in an oval shape along the horizontal direction by being wound around the heating roller 31 and the fixing roller 32 with a predetermined tension.

The elastic layer 33b of the fixing belt 33 is made of 200 μm thick silicone rubber, and the release layer 32c is made of 20 μm thick PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer tube). The fixing belt 33 having such a configuration has a relatively small heat capacity.
The pressure roller 34 includes an iron (thickness 2.5 mm) cored bar 34a configured in a cylindrical shape with an outer diameter of 30 mm, an elastic layer 34b stacked on the outer peripheral surface (surface) of the cored bar 34a, And a release layer 34c laminated on the outer peripheral surface (surface) of the layer 34b. The elastic layer 34b is made of, for example, silicone rubber having a thickness of 1.0 mm. The release layer 34c is made of, for example, a PFA tube having a thickness of 30 μm. The hardness of the pressure roller 34 is, for example, 80 °. As described above, the pressure roller 34 is configured to have high rigidity by including the iron cored bar 34 a having a thickness of 2.5 mm, and has a larger heat capacity than the fixing belt 33.

<Fixing device control system>
FIG. 3 is a block diagram illustrating a configuration of a control system provided in the fixing device 30. The fixing device 30 is provided with a fixing control unit 52 having a CPU, a RAM, a ROM, and the like. The fixing device 30 is supplied with the output of the temperature sensor 38 for measuring the surface temperature of the fixing belt 33 described above. Yes.

  Each of the first heater lamp 35, the second heater lamp 36, and the third heater lamp 37 provided in the fixing device 30 is supplied with electric power supplied from the power supply unit 51 as a first relay 55 provided as a switching element. It is supplied via the second relay 56 and the third relay 57. Each of the first relay 55, the second relay 56, and the third relay 57 is controlled by the fixing control unit 52 to the power supply (on) state and the power supply stop (off) state.

When the fixing controller 52 heats the fixing belt 33, one or more halogen heaters selected from the first heater lamp 35, the second heater lamp 36, and the third heater lamp 37 are turned on (heat generation). In addition, the relay selected from each of the first relay 55, the second relay 56, and the third relay 57 is controlled to an on state and an off state.
The fixing controller 52 controls the surface temperature Ts of the fixing belt 33 detected by the temperature sensor 38 so as to become a preset target temperature Tu when a continuous print job is instructed to the printer. Perform temperature control.

In the present embodiment, one heater lamp or a combination of a plurality of heater lamps used for heating the fixing belt 33 is set in advance so that the power capacity for heating the fixing belt 33 in the fixing temperature control is different. Yes.
The fixing controller 52 measures, by the temperature sensor 38, one power capacity selected when the fixing belt 33 is heated in the fixing temperature control (hereinafter, the selected one power capacity is set as a reference mode). Updating is performed based on a change in the surface temperature Ts of the fixing belt 33.

In the present embodiment, four different power capacities are stored in the ROM of the fixing control unit 52 as the first power mode M1, the second power mode M2, the third power mode M3, and the fourth power mode M4. FIG. 4 is a table for explaining each of the first to fourth power modes M1 to M4 stored in the ROM of the fixing control unit 52 in the present embodiment.
In the present embodiment, the maximum allowable power of the entire printer is 1500 W, and the maximum allowable capacity (maximum power capacity) of the fixing device 30 is 1200 W. For this reason, in the first power mode M1 having the maximum power capacity, the first heater lamp 35 having a rated power of 700 W and the rated power of 500 W are set so that the power capacity of 1200 W, which is the maximum power capacity in the fixing device 30, is obtained. The second heater lamp 36 is used to heat the fixing belt 33 via the heating roller 31.

In the second power mode M2, the fixing belt 33 is heated by using both the first heater lamp 35 having a rated power of 700 W and the third heater lamp 37 having a rated power of 300 W. The capacity is 1000W.
In the third power mode M3, the fixing belt 33 is heated using the second heater lamp 36 having a rated power of 500 W and the third heater lamp 37 having a rated power of 300 W, and the power capacity is 800 W. It has become.

In the fourth power mode M4, only the first heater lamp 35 having a rated power of 700 W is used to heat the fixing belt 33, and thus the power capacity is 700 W.
In addition, the resistance value of the 1st-3rd heater lamps 35-37 is dependent on temperature, and resistance value becomes low, so that the temperature of each heater lamp 35-37 becomes low. For this reason, when electric power is supplied in a state where the resistance values of the heater lamps 35 to 37 are low, a large current (rush current) is temporarily supplied to the heater lamps 35 to 37.

<Fixing temperature control by fixing controller>
Next, a fixing temperature control processing procedure executed in the fixing controller 52 when a continuous print job is instructed will be described based on the flowchart of FIG.
When a continuous print job is instructed to the printer, the fixing control unit 52 performs warm-up to heat the surface temperature Ts of the fixing belt 33 to the target temperature Tm. In this embodiment, the target temperature Tm is set to about the fixing temperature (160 ° C.) required when fixing the toner image on the recording sheet P.

In the following, the power mode set for heating the fixing belt 33 is represented by the reference mode Mn, and an index value n (n = 1 to 4) indicating the power mode set as the reference mode Mn. ) Is the mode reference value.
The fixing control unit 52 sets the mode reference value n to “1” in order to execute heating of the fixing belt 33 during warm-up in the first power mode M1 having the maximum power capacity (n = 1, FIG. 5 step S11). Thereby, the first power mode M1 is set as the reference mode Mn.

  Next, the fixing controller 52 heats the fixing belt 33 in the set reference mode Mn (first power mode M1) (step S12). In order to heat the fixing belt 33 in the first power mode M1, the fixing control unit 52 turns on both the first relay 55 and the second relay 56 and turns on the 700 W first heater lamp 35 and the 500 W second heater. Power is supplied to both lamps 36.

  As a result, both the first heater lamp 35 with a rated power of 700 W and the second heater lamp 36 with a rated power of 500 W are turned on (heat generation), and the heating roller 31 Heated by both second heater lamps 36. When the heating roller 31 is heated, the heat applied to the heating roller 31 is transmitted to the fixing belt 33 and the temperature of the fixing belt 33 rises.

In this case, since 1200 W of electric power equal to the maximum allowable power in the fixing device 30 is supplied to both the first heater lamp 35 and the second heater lamp 36 for heating the heating roller 31, the heating roller 31 is supplied to the heating roller 31. The surface temperature Ts of the wound fixing belt 33 is quickly raised to the target temperature Tm.
When the temperature sensor 38 detects that the surface temperature Ts of the fixing belt 33 is equal to or higher than the target temperature Tm, the printing operation by the printer is started. As a result, the fixing device 30 also starts the heat fixing operation, and heats the recording sheet P that passes through the fixing nip Nf continuously.

The fixing controller 52 executes the fixing temperature control in the first power mode M1 set as the set reference mode Mn at the beginning of the heat fixing operation. In this case, since the first power mode M1 has already been set as the reference mode Mn, the set state is maintained.
When the heat fixing operation is started, the fixing controller 52 sets the surface temperature Ts of the fixing belt 33 detected by the temperature sensor 38 to be higher than the target temperature Tm by a predetermined temperature (3 ° C. in this embodiment). It is confirmed whether the temperature exceeds the upper limit temperature Tu (Tm + 3 ° C.) (step S13).

The upper limit temperature Tu is such that a control signal for turning off the relay that has been turned on by the fixing control unit 52 in order to stop the heating of the fixing belt 33 when the surface temperature Ts of the fixing belt 33 exceeds the target temperature Tm. Even if it is output, it occurs due to overshoot when heating of the fixing belt 33 is continued due to a delay in response of the relay or the like.
If the surface temperature Ts of the fixing belt 33 does not exceed the upper limit temperature Tu (“NO” in step S13), the process proceeds to step S14 to check whether the instructed continuous print job is completed. When the continuous print job is completed (“YES” in step S14), the fixing temperature control by the fixing control unit 52 is also ended in order to end the printing operation by the printer. Thereby, the electric power supply with respect to all the heater lamps 35-37 is stopped.

  In step S14, if the instructed continuous print job has not ended (“NO” in step S14), the surface temperature Ts of the fixing belt 33 detected by the temperature sensor 38 exceeds the target temperature Tm. Is confirmed (step S15). When the surface temperature Ts of the fixing belt 33 is higher than the target temperature Tm (“YES” in step S15), by stopping the power supply to both the first heater lamp 35 and the second heater lamp 36, Heating of the heating roller 31 is stopped (step S16), and the process returns to step S13.

If the surface temperature of the fixing belt 33 detected by the temperature sensor 38 does not exceed the target temperature Tm in step S15 (“NO” in step S15), the fixing belt 33 is heated in the set reference mode Mn. (Step S17). Thereafter, the process returns to step S13.
The pressure roller 34 that is pressed against the fixing belt 33 to form the fixing nip Nf and the fixing roller 32 wound around the fixing belt 33 have a heat capacity larger than that of the fixing belt 33, and thus the heat fixing operation starts. Initially, the amount of heat stored in the pressure roller 34 and the fixing roller 32 is small.

In this state, when the recording sheet P passes through the fixing nip Nf, a large amount of heat of the fixing belt 33 moves to the recording sheet P. As a result, the surface temperature Ts of the fixing belt 33 having a relatively small heat capacity rapidly decreases, and the surface temperature Ts of the fixing belt 33 decreases to the target temperature Tm or less in a relatively short time.
When the surface temperature Ts of the fixing belt 33 falls below the target temperature Tm, the fixing belt 33 is heated in the reference mode Mn. In this case, the heat fixing operation is started and the heating is performed in the reference mode Mn set to the first power mode M1 having the maximum power capacity. Accordingly, a large amount of heat is applied to the fixing belt 33 by the first heater lamp 35 having a rated current of 700 W and the second heater lamp 36 having a rated current of 500 W, and the surface temperature Ts of the fixing belt 33 is relatively short. It becomes higher than the target temperature Tm.

When the surface temperature Ts of the fixing belt 33 exceeds the target temperature Tm, the heating of the fixing belt 33 is stopped and, as described above, the surface temperature Ts of the fixing belt 33 becomes equal to or lower than the target temperature Tm. The fixing belt 33 is heated in the first power mode M1 set as Mn.
As a result, the surface temperature Ts of the fixing belt 33 is repeatedly higher and lower than the target temperature Tm in a relatively short cycle, and power is supplied to the first heater lamp 35 and the second heater lamp 36. And the stop of the power supply is repeated with a relatively short cycle. Therefore, when supply of electric power to the first heater lamp 35 and the second heater lamp 36 is started, an inrush current occurs relatively frequently, and the surface temperature Ts of the fixing belt 33 generates a temperature ripple with a large temperature change.

  In this case, part of the amount of heat applied to the fixing belt 33 also moves to the pressure roller 34 and the fixing roller 32, and the amount of heat stored in the pressure roller 34 and the fixing roller 32 with the passage of time from the start of the job. Gradually increases. In addition, since the fixing belt 33 is heated in the first power mode M1 having the maximum power capacity, the amount of heat stored in the pressure roller 34 and the fixing roller 32 increases at a relatively large rate.

  As the amount of heat stored in the pressure roller 34 and the fixing roller 32 increases, a decrease in the surface temperature Ts of the fixing belt 33 when the recording sheet P passes through the fixing nip Nf is suppressed. As a result, even if it is detected that the surface temperature Ts of the fixing belt 33 has exceeded the target temperature Tm and the control signal for turning off the first relay 55 and the second relay 56 is output from the fixing control unit 52, the first When power supply to the first heater lamp 35 and the second heater lamp 36 is continued due to a response delay of the relay 55 and the second relay 56, the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu due to overshoot. There is.

For this purpose, in step S13, it is confirmed whether the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu. If the surface temperature Ts of the fixing belt 33 does not exceed the upper limit temperature Tu (“NO” in step S13), the process proceeds to step S14.
When the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu (“YES” in step S13), the process proceeds to step S21, and the mode reference value n is changed to “n + 1” (n + 1 → n). As a result, the reference mode Mn for heating the fixing belt 33 is switched to a power mode in which the power capacity (corresponding to power consumption) of the heater lamp used for heating the fixing belt 33 is reduced by one step (update). )

  It is considered that the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu because heating of the fixing belt 33 with a large amount of heat is continued due to a response delay of a relay or the like. For this reason, when the reference mode Mn is switched to the second power mode M2 in which the power capacity is set to be smaller by one level, the fixing belt 33 is heated in the second power mode M2 thereafter, so that the fixing belt 33 is heated. Temperature rise due to overshoot in can be suppressed.

  When the mode reference value n is changed, the process proceeds to step S22 to check whether the mode reference value n is “4”, and the changed reference mode Mn is the fourth power mode in which the power capacity is the minimum level. Check if it is set to M4. When the mode reference value n is not “4” (“NO” in step S23), the process returns to step S13, and thereafter, until the surface temperature Ts of the heating roller 31 reaches the upper limit temperature Tu (“YES” in step S13). ) Or until the instructed print job is completed (“YES” in step S14), the fixing temperature control for heating the fixing belt 33 in the changed reference mode Mn is executed (steps S13 to S17).

If the changed reference mode Mn is the fourth power mode M4 (n = 4, “YES” in step S22), the process proceeds to step S14, and thereafter, the instructed print job is completed. Until ("NO" in step S14), the fixing temperature control for heating the fixing belt 33 in the fourth power mode M4 is executed (steps S13 to S17).
As described above, since the reference mode Mn is the first power mode M1 at the beginning of the heat fixing operation, the reference mode Mn is changed to the second power mode M2 in step S21. When the fixing belt 33 is heated in the second power mode M2, the first relay 55 and the third relay 57 are turned on, the first heater lamp 35 having a rated power of 700 W, and the third relay having a rated power of 300 W. Electric power is supplied to both heater lamps 37. When the heating of the heating roller 31 is stopped, the first relay 55 and the third relay 57 are turned off.

  As described above, the fixing temperature control in the state where the second power mode M2 is set as the reference mode Mn is other than using the first heater lamp 35 and the third heater lamp 37 to heat the fixing belt 33. The processing procedure is the same as that in the case of fixing temperature control in the state where the first power mode M1 is set as the reference mode Mn. Therefore, when the fixing belt 33 is heated in the second power mode M2, 1000 W in total is supplied to the first heater lamp 35 and the third heater lamp 37. The power consumption during heating of the fixing belt 33 is reduced by about 200 W compared to the time during heating in the first power mode M1 (about 1200 W).

  When the reference mode Mn is switched to the second power mode M2, the amount of heat stored in the pressure roller 34 and the fixing roller 32 increases compared to when the fixing temperature control is started in the state where the first power mode M1 is set. Therefore, the decrease in the surface temperature Ts of the fixing belt 33 due to the recording sheet P continuously passing through the fixing nip Nf becomes gentle. As a result, the period in which the fixing belt 33 is heated when the surface temperature Ts of the fixing belt 33 falls below the target temperature Tm is longer than when the fixing temperature control is performed in the first power mode M1.

  As a result, the number of times the heater lamp is turned on / off is reduced, and accordingly, the number of times that the power consumption rapidly increases due to the inrush current generated during heating is reduced. Moreover, in the second power mode M2, the total rated current (1000 W) of the first heater lamp 35 and the third heater lamp 37 is smaller than the power capacity when heating the fixing belt 33 in the first power mode M1. Therefore, since the current value at the time of occurrence of the inrush current is also reduced, the change in the surface temperature Ts of the fixing belt 33 due to overshoot can be suppressed.

  Even in the fixing temperature control in the state where the second power mode M2 is set as the reference mode Mn, the surface temperature Ts of the fixing belt 33 is increased by the heating of the fixing belt 33 before the instructed print job is completed. If it exceeds Tu (“YES” in step S13), the process proceeds to step S21, the reference mode Mn is switched from the second power mode M2 to the third power mode M3, and the process returns to step S13 (steps S21 to S22). Accordingly, after that, the fixing temperature control for heating the fixing belt 33 in the reference mode Mn set in the third power mode M3 is performed until the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu, or the designated printing is performed. Runs until the job is finished.

  In the fixing temperature control in the state where the third power mode M3 is set as the reference mode Mn, when the fixing belt 33 is heated, the second relay 56 and the third relay 57 are turned on, and the rated power is 500 W. Electric power is supplied to both the second heater lamp 36 and the third heater lamp 37 having a rated power of 300 W. When the heating of the fixing belt 33 is stopped, both the second relay 56 and the third relay 57 are turned off.

Except for this, the processing procedure of the fixing temperature control in the state where the second power mode M2 is set as the reference mode Mn is the same. Therefore, the power consumption when the fixing belt 33 is heated in the third power mode M3 is reduced by about 200 W compared to the heating time (1000 W) in the second power mode M2.
At the start of fixing temperature control in the third power mode M3, the amount of heat stored in the pressure roller 34 and the fixing roller 32 is higher than that at the start of fixing temperature control when the second power mode M2 is set as the reference mode Mn. Therefore, the heating period of the fixing belt 33 due to the surface temperature Ts of the fixing belt 33 being lower than the target temperature Tm is longer than that at the time of executing the fixing temperature control in the second power mode M2. As a result, the rapid increase in power consumption due to a temporary inrush current equal to or greater than the sum of the rated currents of the second heater lamp 36 and the third heater lamp 37 (800 W) is suppressed.

In addition, even if a temperature ripple occurs in the fixing belt 33 due to overshoot due to the inrush current, the change in the surface temperature Ts generated in the fixing belt 33 is suppressed more than when the fixing belt 33 is heated in the second power mode M2. be able to.
Also in the fixing temperature control in the third power mode M3, when the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu before the instructed print job is finished (“YES in step S13). ”), The process proceeds to step S21, and the reference mode Mn is switched from the third power mode M3 to the fourth power mode M4.

In this case, since the mode reference value n becomes “4”, “YES” is determined in the step S22, and the process proceeds to the step S14. Thereafter, the fixing belt is operated in the reference mode Mn set in the fourth power mode M4. The fixing temperature control for heating 33 is executed until the instructed print job is completed.
In the fixing temperature control in a state where the reference mode Mn is set to the fourth power mode M4, when the fixing belt 33 is heated, the first relay 55 is turned on, and the first heater lamp 35 having a rated power of 700 W is applied. In contrast, power is supplied. When the heating of the fixing belt 33 is stopped, the first relay 55 is turned off.

  As described above, in the fixing temperature control in the state where the fourth power mode M4 is set as the reference mode Mn, the reference mode Mn is used except that only the first heater lamp 35 is used to heat the fixing belt 33. This is the same as the fixing temperature control processing procedure in the state where the third power mode M3 is set. Therefore, the power consumption (about 700 W) when heating the fixing belt 33 in the fourth power mode M4 is reduced by about 100 W compared to the power consumption (about 800 W) in the third power mode M3.

  When the fixing temperature control is started in the state where the fourth power mode M4 is set as the reference mode Mn, the pressurization is higher than in the case where the fixing temperature control is started when the third power mode M3 is set as the reference mode Mn. The amount of heat stored in the roller 34 and the fixing roller 32 has increased, and the decrease in the surface temperature Ts of the fixing belt 33 due to the recording sheet P passing through the fixing nip Nf becomes gentle. As a result, when the heating of the fixing belt 33 is started by the surface temperature Ts of the fixing belt 33 being lowered to the target temperature Tm or less, the period (heating time) until the heating of the fixing belt 33 is stopped thereafter. It becomes longer than the third power mode M3.

In this case, the power consumption when heating the fixing belt 33 in the fourth power mode M4 is as low as about 700 W, and even if the heating time of the fixing belt 33 is increased, the fixing belt 33 is moved in the third power mode M3. Power consumption is suppressed as compared with the case of heating.
Thereafter, when the surface temperature Ts of the fixing belt 33 exceeds the target temperature Tm, the heating of the fixing belt 33 only by the first heater lamp 35 is stopped. In this case, since the increase in the surface temperature Ts of the fixing belt 33 is moderate, even if the surface temperature Ts exceeds the target temperature Tm, the temperature difference with respect to the target temperature Tm is small and there is no possibility of reaching the upper limit temperature Tu. When the heating of the fixing belt 33 is stopped, the temperature is lowered to the target temperature Tm or less in a relatively short time, and the heating of the fixing belt 33 is resumed.

  When heating of the fixing belt 33 is started, an inrush current is generated in the first heater lamp 35. However, in the fourth power mode M4 in which the power capacity is 700 W, the current value of the generated inrush current is smaller than that in the third power mode M3 in which the power capacity is 800 W. Power consumption is suppressed. In addition, since the inrush current becomes smaller, the temperature change of the fixing belt 33 due to the inrush current becomes smaller than that in the third power mode M3.

Hereinafter, until the instructed print job is completed, heating of the fixing belt 33 with a low power consumption of 700 W for a relatively long time and heating of the fixing belt 33 for a relatively short time are repeated.
Thus, in the fixing temperature control in the fourth power mode M4, it is possible to reduce power consumption required to control the fixing belt 33 to the target temperature Tm. In addition, since the number of occurrences of inrush current before the end of the print job can be reduced, an increase in power consumption due to inrush current can be suppressed, and the temperature ripple of a large temperature change in the fixing belt 33 can be suppressed. Can also be prevented.

FIG. 6 shows changes in the power supplied to the first heater lamp 35 and changes in the surface temperature of the heating roller 31 during execution of the fixing temperature control after the setting of the reference mode Mn is switched to the fourth power mode M4. It is a graph shown, respectively.
Since the heating roller 31 is directly heated by the first heater lamp 35, the surface temperature of the heating roller 31 is about 2 to 3 ° C. higher than the surface temperature of the fixing belt 33. When 31 is about 163 ° C., the surface temperature of the fixing belt 33 is about 160 ° C.

  For comparison, the fixing belt 33 has the same configuration as the fixing device 30 of the above embodiment except that only one heater lamp with a rated power of 1000 W is used to heat the fixing belt 33. The change in power supplied to the 1000 W heater lamp in the case where the fixing temperature control is executed so that the surface temperature becomes 160 ° C. is indicated by a broken line in FIG. Further, the change in the surface temperature of the heating roller 31 in this case is also indicated by a broken line in FIG.

  In the present embodiment, in the fixing temperature control in the reference mode set in the fourth power mode M4, when the surface temperature of the fixing belt 33 is lower than 160 ° C., the first heater lamp 35 with a rated power of 700 W is used. Due to the heating of the heating roller 31, the surface temperature of the heating roller 31 rises gently. As a result, the surface temperature of the fixing belt 33 similarly gradually increases, and power supply to the first heater lamp 35 is continued for a relatively long time until the surface temperature of the fixing belt 33 reaches 160 ° C.

Thereafter, when the surface temperature of the fixing belt 33 reaches 160 ° C., the power supply to the first heater lamp 35 is stopped, and the surface temperature of the fixing belt 33 decreases. When the surface temperature of the fixing belt 33 becomes lower than 160 ° C., power supply to the first heater lamp 35 is started.
An inrush current is generated at the start of power supply to the first heater lamp 35. However, since the electric power supplied to the first heater lamp 35 is relatively small as 700 W, the current value of the inrush current is relatively small, and the heating roller 31 The overshoot is suppressed, and the heating roller 31 does not generate a temperature ripple due to a large temperature change. Thereafter, power supply to the first heater lamp 35 continues for a relatively long time.

  In contrast, in the comparative example in which the heating roller is heated by a heater lamp with a rated power of 1000 W, every time the recording sheet passes through the fixing nip Nf even if the surface temperature of the fixing belt reaches the target temperature Tm. Each time the temperature drops below the target temperature Tm, power is supplied to the heater lamp. In this case, even if the surface temperature Ts of the fixing belt 33 reaches the target temperature Tm, a response delay occurs until the power is supplied to the heater lamp.

FIG. 7 is an explanatory diagram of a response delay that occurs between the surface temperature Ts of the fixing belt 33 reaching the target temperature Tm and the power supply to the heater lamp, and FIG. 7A shows the surface temperature Ts of the fixing belt. FIG. 7B is a time chart of a control signal output from the control unit.
As shown in FIG. 7A, when the temperature sensor detects that the surface temperature of the fixing belt has become lower than the target temperature Tm, as shown in FIG. 7B, a control signal for turning on the relay. (ON signal) is output from the control unit. In this case, the heating of the fixing belt 33 is delayed by the time t due to the response delay of the relay, the control unit, etc., and the surface temperature Ts of the fixing belt 33 is relatively lowered with respect to the target temperature Tm.

Thereafter, when the fixing belt is heated by the heater lamp, the surface temperature Ts of the fixing belt 33 becomes higher than the target temperature Tm, and a control signal (off signal) for turning off the relay is output from the control unit. Also in this case, the surface temperature Ts of the fixing belt 33 rises relatively large with respect to the target temperature Tm due to a response delay of the relay or the control unit.
In addition, since the power supplied to the heater lamp is as large as 1000 W, the inrush current generated when power is supplied to the heater lamp is increased. Thereby, the temperature ripple of the big temperature change has generate | occur | produced in the heating roller. In addition, since a large inrush current is generated, the amount of power consumption is increased as compared with the case of the present embodiment.

FIG. 8 is a table showing an average value of power supplied to the first heater lamp 35 (power consumption: converted to 36 sheets) and a print TEC value (Typical Electricity Consumption: converted to 36 sheets) in the graph shown in FIG. is there. Table 7 also shows the average value of power consumption and the print TEC value in the case of the comparative example shown in FIG.
In the present embodiment using the first heater lamp 35 with a rated power of 700 W, the average power is 619.1 W, whereas in the case of a comparative example using a heater lamp with a rated power of 1000 W, the average power Was 681.4W. Therefore, in this embodiment, the average power was reduced by 62.3 W compared to the comparative example. In the present embodiment, the TEC value is 825.5 Wh, whereas in the comparative example, the TEC value is 908.6 Wh, and the TEC value in the present embodiment is 83. It was reduced by 1 Wh.

  As described above, in the present embodiment, in the fixing temperature control of the continuous print job, when the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu, the reference mode Mn when the fixing belt 33 is heated is changed to the power capacity. Since the power mode is set to a smaller value, the period for heating the fixing belt 33 becomes longer. Thereby, the frequency | count of heating the fixing belt 33 can be reduced.

For this reason, even when a response delay occurs in the fixing control unit 52 that controls the power supply to any of the first to third heater lamps 35 to 37, the first to third relays 55 to 57, etc., Since the number of times the fixing belt 33 is heated is reduced, it is possible to suppress a large change in the surface temperature Ts of the fixing belt 33 due to the response delay.
Further, since the number of times of power supply to any one of the first to third heater lamps 35 to 37 is reduced, the number of occurrences of inrush current is also reduced, so that the surface temperature Ts of the fixing belt 33 changes greatly. This can be further suppressed. Moreover, an increase in power consumption due to the inrush current can be suppressed by reducing the number of occurrences of the inrush current.

Further, as the number of recording sheets P passing through the fixing nip Nf increases, the amount of power used to heat the fixing belt 33 is reduced, thereby effectively reducing the amount of power consumed in a continuous print job. it can.
Further, at the time of warm-up, since the heating roller 31 is heated by the first power mode M1 having a large power capacity, the surface temperature Ts of the fixing belt 33 can be quickly raised to the target temperature Tm. it can.

  In the present embodiment, when the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu, the reference mode for heating the fixing belt 33 is the power mode with a power capacity smaller than the set power capacity. However, the present invention is not limited to such a configuration. For example, when the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu for a predetermined time or longer, the reference mode may be switched to a power mode with a small power capacity.

[Embodiment 2]
In the present embodiment, a lower limit temperature Td that is lower than the target temperature Tm by a predetermined temperature (3 ° C. in the present embodiment) is preset.
The lower limit temperature Td is output from the fixing control unit 52 to turn on a predetermined relay to heat the fixing belt 33 when it is detected that the surface temperature Ts of the fixing belt 33 is lower than the target temperature Tm. In this case, the temperature is the lower limit of the permissible range of undershoot due to the heating stop of the fixing belt 33 being continued due to a delay in response of the relay. When the fixing belt 33 reaches the lower limit temperature Td, the surface of the fixing belt 33 can be heated even if the fixing belt 33 is heated without switching the power mode set as the reference mode to the power mode with a small power capacity. It takes a long time for the temperature Ts to exceed the target temperature Tm, which may lead to a fixing failure or the like.

Next, the processing procedure of the fixing temperature control of the present embodiment executed in the fixing controller 52 will be described based on the flowchart of FIG.
Note that steps S11 to S14 in the flowchart shown in FIG. 9 are the same as steps S11 to S14 in the flowchart of the first embodiment shown in FIG. 5, and any of the first mode M1 to the fourth mode M4 is used as the reference mode Mn. The fixing temperature control is executed in a state where is set. During execution of such fixing temperature control, it is confirmed whether the surface temperature Ts of the fixing belt 33 is lower than the lower limit temperature Td in a state where the surface temperature Ts of the fixing belt 33 is heated below the target temperature. (Step S18 in the flowchart of FIG. 9).

  When the surface temperature Ts of the fixing belt 33 is lower than the lower limit temperature Td (“YES” in step S18), the mode reference value n is changed to “1” (step S19). Thereby, even if the reference mode Mn is set to any of the first to third power modes M1 to M4, the reference mode Mn is switched to the first power mode M1 set to the maximum power capacity.

  Thus, when the surface temperature Ts of the fixing belt 33 is lower than the lower limit temperature Td, the fixing control unit 52 heats the fixing belt 33 in the reference mode Mn set in the first power mode M1. The first relay 55 and the second relay 56 are turned on to supply power to the first heater lamp 35 and the second heater lamp 36. As a result, the fixing belt 33 is heated by the first heater lamp 35 and the second heater lamp 36 whose power consumption is about 1200 W, and the surface temperature Ts of the fixing belt 33 quickly rises above the lower limit temperature Td. .

Thereafter, the process returns to step S13, and fixing temperature control for heating the fixing belt 33 in the reference mode Mn set in the first power mode M1 is executed. Thereafter, as described in the first embodiment, the fixing belt 33 Each time the surface temperature Ts exceeds the upper limit temperature Tu, the reference mode Mn is switched to the power mode in which the power capacity is set to one level lower.
Therefore, for example, during the execution of the heat fixing operation on the low-temperature recording sheet P, the large size recording sheet P, etc., the fourth power mode M4 is set as the reference mode Mn, and the fixing belt 33 is in the fourth power mode M4. Even in the heated state, if the surface temperature Ts of the fixing belt 33 falls below the lower limit temperature Td, the fixing belt 33 is heated in the first power mode M1. As a result, the surface temperature Ts of the fixing belt 33 can be raised to the target temperature Tm or higher in a short time.

In the present embodiment, when the fourth power mode M4 is set as the reference mode Mn, the surface temperature Ts of the fixing belt 33 falls below the lower limit temperature Td, so that the reference mode Mn is changed to the second power mode M2. It is good also as a structure changed into.
In the present embodiment, the first lower limit temperature Td1 (= 157 ° C.) that is lower than the target temperature Tm by a predetermined temperature (eg, 3 ° C.) and the predetermined temperature (eg, 2 ° C.) that is lower than the first lower limit temperature Td1. When the second lower limit temperature Td2 (for example, 155 ° C. lower by 5 ° C. than the target temperature Tm) is set in advance, and the third power mode M3 or the fourth power mode M4 is set as the reference mode Mn When the surface temperature Ts of the fixing belt 33 falls below the first lower limit temperature Td1, the reference mode Mn is switched to the second power mode M2, and when the surface temperature Ts of the fixing belt 33 falls below the second lower limit temperature Td2, the reference mode It is good also as a structure which switches Mn to the 1st electric power mode M1.

  As described above, when the surface temperature Ts of the fixing belt 33 is lower than the target temperature Tm, the fixing belt 33 can be appropriately heated in the power mode corresponding to the lowered state of the surface temperature Ts. Accordingly, when the surface temperature Ts of the fixing belt 33 is relatively slowly decreased, the surface temperature Ts of the fixing belt 33 is surely prevented from exceeding the target temperature Tm and exceeding the upper limit temperature Tu. be able to.

[Embodiment 3]
In the present embodiment, when the printer is activated, the fixing control unit 52 executes the start-up control in which the surface temperature Ts of the fixing belt 33 detected by the temperature sensor 38 is heated to the target temperature Tm, and then the printing is performed. During the standby state until the job is instructed, for example, power is supplied only to the third heater lamp 37 so as not to exceed a predetermined temperature (for example, 100 ° C.) lower than the target temperature Tm. It becomes power saving mode to heat. In the start-up control, for example, the fixing belt 33 is heated in the first power mode as in the above-described warm-up.

  In such a configuration, in this embodiment, when the transition to the power saving mode standby state after the start-up control ends, the elapsed time in the standby state (power saving mode) is measured, and the first time after the start-up control When a continuous print job is designated as the print job, the reference mode Mn is set to an appropriate power mode based on the elapsed time in the standby state. This is due to the following reason.

  That is, in the standby state, since the fixing belt 33 is heated in the power saving mode, the heat storage amount in the pressure roller 34 and the fixing roller 32 increases as the elapsed time in the standby state becomes longer. In such a state, even if the recording sheet P passes through the fixing nip Nf, there is no possibility that the surface temperature Ts of the fixing belt 33 is greatly reduced. For this reason, in this embodiment, the reference mode Mn is set to a power mode with a smaller power capacity as the elapsed time in the standby state becomes longer.

  Hereinafter, the processing procedure of the fixing temperature control executed in the fixing controller 52 of the present embodiment will be described based on the flowchart of FIG. When it is confirmed that the first print job instruction after the start-up control executed when the fixing device 30 is started is a continuous print job, the fixing control unit 52 proceeds to step S31 in FIG. When the continuous print job is instructed, it is confirmed whether the elapsed time of the standby state measured by the timer is 5 minutes or more.

  When the elapsed time in the standby state is less than 5 minutes (“YES” in step S31), since the elapsed time in the standby state after the start-up control is completed is relatively short, It is determined that the amount of heat stored in the pressure roller 34 and the fixing roller 32 is small, and the mode reference value n is set to “1” (step S32). Thereby, the reference mode Mn is set to the first power mode M1 in which the power capacity is set to the maximum. Then, the fixing belt 33 is heated in the set first power mode M1 (step S33). In this case, electric power is supplied to both the 700 W first heater lamp 35 and the 500 W second heater lamp 36.

  Thereafter, as in the first embodiment shown in the flowchart of FIG. 5, when the surface temperature Ts of the fixing belt 33 reaches the target temperature Tm, the printing operation by the printer is started, and the fixing nip Nf is continuously recorded on the recording sheet. P passes. In this case, the fixing control unit 55 performs the fixing temperature control in a state where the first power mode M1 is set as the reference mode Mn (steps S13 to S17). In steps S21 to S23, the reference mode Mn is switched.

  In step S31, if the elapsed time in the standby state measured by the timer is 5 minutes or longer (“NO” in step S31), it is confirmed whether the elapsed time in the standby state is 30 minutes or less. (Step S34). When the elapsed time in the standby state is 30 minutes or less (“YES” in step S34), the mode reference value n is set to “2” (step S35), and the reference mode Mn is set to be more power than the first power mode M1. The second power mode M2 is set to have a small capacity. Then, the fixing belt 33 is heated in the reference mode Mn set in the second power mode M2 (step S33). In this case, power is supplied to both the 700 W first heater lamp 35 and the 300 W third heater lamp 37.

  As described above, when the elapsed time in the standby state is 5 minutes or more and 30 minutes or less, it is assumed that a relatively large amount of heat is accumulated in the pressure roller 34 and the fixing roller 32 during the standby state. The mode Mn is set to the second power mode M2, and the fixing belt 33 is heated in the reference mode Mn set to the second power mode M2. Thereafter, the fixing temperature control in steps S13 to S17 is executed in the reference mode Mn set in the second power mode M2, and the reference mode Mn is switched in steps S21 to S23.

  In step S34, when the standby state time measured by the timer is longer than 30 minutes (“NO” in step S34), the mode reference value n is set to “3” (step S36), and the reference mode Mn is set to the third power mode M3 in which the power capacity is smaller than that of the second power mode M2. Then, in order to heat the fixing belt 33 in the set third power mode M3, power is supplied to the 700 W first heater lamp 35 (step S33). Thereafter, the fixing temperature control in steps S13 to S17 is executed in the reference mode Mn set in the third power mode M3, and the reference mode Mn is switched in steps S21 to S23.

  Thus, when the time of the standby state measured by the timer is longer than 30 minutes, a considerable amount of heat is accumulated in the pressure roller 34 and the fixing roller 32 during the standby state. Then, the reference mode Mn is set to the third power mode M3 in which the power capacity is smaller than that of the second power mode M2. Then, the fixing belt 33 is heated in the reference mode Mn set in the third power mode M3. In this case, the surface temperature Ts of the fixing belt 33 can be raised to the target temperature Tm in a relatively short time.

  As described above, when a continuous print job is instructed in the standby state in the power saving mode after the start-up control is finished, the power mode is set to an appropriate power mode according to the heat storage state of the pressure roller 34 and the fixing roller 32. The fixing belt 33 is heated in the reference mode Mn. In addition, also in the subsequent fixing temperature control, the fixing belt 33 is heated in the reference mode Mn set to an appropriate power mode. Therefore, it is possible to prevent wasteful consumption of power when the fixing belt 33 is heated, and appropriate power consumption can be achieved.

Note that this embodiment is not limited to when the main switch of the printer is turned on from the off state, but is also applied when, for example, the print job is finished and the printer enters the power saving mode standby state. Can do. In this case, the reference mode Mn is set to an appropriate power mode that is selected based on the elapsed time in the standby state.
[Embodiment 4]
In the present embodiment, for example, when the continuous print job is instructed, or when the thermal fixing operation is resumed after the paper jam processing in the middle of the continuous print job is completed, the fixing belt 33 detected by the temperature sensor 38 is detected. The reference mode Mn is set to an appropriate power mode based on the surface temperature.

  Hereinafter, a control processing procedure in the fixing control unit 52 in this case will be described with reference to a flowchart of FIG. The fixing control unit 52 is instructed when a continuous print job is instructed, or when the heat fixing operation is resumed after the continuous heat fixing operation is interrupted by the instruction of the continuous print job (usually heat fixing due to occurrence of a paper jam). In the case where the thermal fixing operation is resumed after the operation is interrupted and the paper jamming process is completed), the process proceeds to step S41 in FIG. 11, and first the surface temperature of the fixing belt 33 detected by the temperature sensor 38 is 50 ° C. Check if it is less.

  When the surface temperature of the fixing belt 33 is less than 50 ° C. (“YES” in step S41), the mode reference value n is set to “1” (step S42). Thereby, the reference mode Mn is set to the first power mode M1 in which the power capacity is set to the maximum. Then, the fixing belt 33 is heated in the set first power mode M1 (step S43). In this case, electric power is supplied to both the 700 W first heater lamp 35 and the 500 W second heater lamp 36. Thereafter, the fixing temperature control in steps S13 to S17 is executed in the third power mode M3 set as the reference mode Mn, and the reference mode Mn is switched in steps S21 to S23.

  If the surface temperature of the fixing belt 33 detected by the temperature sensor 38 is 50 ° C. or higher in step S41 (“NO” in step S41), the surface temperature of the fixing belt 33 detected by the temperature sensor 38. It is confirmed whether Ts is 100 degrees C or less (step S44). When the surface temperature of the fixing belt 33 is 100 ° C. or less (“YES” in step S44), the mode reference value n is set to “2” (step S45), and the reference mode Mn is set to have power higher than that of the first power mode M1. The second power mode M2 having a reduced capacity is set. Then, in order to heat the fixing belt 33 in the reference mode Mn set in the second power mode M2, power is supplied to both the 700 W first heater lamp 35 and the 300 W third heater lamp 37 ( Step S43).

  As described above, when the surface temperature Ts of the fixing belt 33 is 50 ° C. or more and 100 ° C. or less, the continuous heat fixing operation according to the instruction of the print job has already been executed, and the pressure roller 34 and the fixing roller Therefore, the fixing belt 33 is heated by setting the reference mode Mn to the second power mode M2 in which the power capacity is set smaller than that of the first power mode M1. Like to do.

Thereafter, the fixing temperature control in steps S13 to S17 described above is executed in the second power mode M2 set as the reference mode Mn, and the reference mode Mn is switched in steps S21 to S23.
In step S44, when the surface temperature Ts of the fixing belt 33 detected by the temperature sensor 38 is 100 ° C. or more (“NO” in step S44), the mode reference value n is set to “3” (step S46), and the reference The mode Mn is set to the third power mode M3 whose power capacity is smaller than that of the second power mode M2. Then, in order to heat the fixing belt 33 in the reference mode Mn set to the third power mode M3, power is supplied to the 700 W first heater lamp 35 (step S43).

  As described above, when the surface temperature Ts of the fixing belt 33 is 100 ° C. or higher, the amount of heat stored in the pressure roller 34 and the fixing roller 32 is large, so that the power capacity is the second power as the reference mode Mn. The third power mode M3, which is smaller than the mode M2, is set, and the fixing belt 33 is heated by the set third power mode M3. In this case, the surface temperature Ts of the fixing belt 33 can be raised to the target temperature Tm in a relatively short time even though the power consumption is reduced.

Thereafter, the fixing temperature control in steps S13 to S17 is executed in the third power mode M3 set as the reference mode Mn, and the reference mode Mn is switched in steps S21 to S23.
With such a configuration, when a continuous print job is instructed, or when a paper jam process at the time of continuous print job execution is completed, an appropriate reference according to the heat storage state of the pressure roller 34 and the fixing roller 32 The fixing belt 33 can be heated by the mode Mn, and also in the fixing temperature control, the fixing belt 33 can be heated in the power mode appropriately set as the reference mode Mn. Therefore, it is possible to prevent wasteful consumption of power when the fixing belt 33 is heated, and appropriate power consumption can be achieved.

[Embodiment 5]
In the present embodiment, the fixing controller 52 samples the surface temperature Ts of the fixing belt 33 detected by the temperature sensor 38 at a predetermined interval of 1 second or less, and the surface temperature Ts of the fixing belt 33 is determined as the fixing temperature. The fixing temperature control is executed so that the lower limit temperature Td is set lower by 2 ° C. than Tf and the upper limit temperature (corresponding to the target temperature) Tu is set higher by 3 ° C. than the fixing temperature Tf.

In such fixing temperature control, the surface temperature Ts of the fixing belt 33 does not greatly decrease from the vicinity of the upper limit temperature Tu, and repeats up and down fluctuations in the vicinity of the upper limit temperature Tu (with an upper limit sticking), and the lower limit temperature. Each of the states (with a lower limit sticking) that does not greatly decrease from Td and repeats vertical fluctuations in the vicinity of the lower limit temperature Td is prevented.
For this reason, in the present embodiment, first to sixth power modes M1 to M6 are set as power modes for heating the fixing belt 33.

FIG. 12 shows one heater lamp or a plurality of heater lamps used for heating the fixing belt 33 in each of the first to sixth power modes M1 to M6 set in the fixing controller 52 in the present embodiment. It is a table | surface for demonstrating a combination.
The first to fourth power modes M1 to M4 shown in FIG. 12 are the same as the first to fourth power modes M1 to M4 of the first embodiment shown in FIG. The fifth power mode M5 in FIG. 12 is set to use only the second heater lamp 36 having a rated power of 500W. Therefore, the power capacity of the fifth power mode M5 is 500W. The sixth power mode M6 is set to use only the third heater lamp 37 having a rated power of 300W. Therefore, the power capacity of the sixth power mode M6 is 300W.

  In this embodiment, when a continuous print job is instructed, the reference mode Mn is set to the first power mode M1, and warm-up is performed in the first power mode M1 set as the reference mode Mn. In the subsequent fixing temperature control, when the surface temperature Ts of the fixing belt 33 exceeds a preset upper limit temperature Tu, the heating is stopped. As a result, when the surface temperature Ts of the fixing belt 33 decreases and then decreases below the upper limit temperature Tu, the fixing belt 33 is heated in the power mode set as the reference mode Mn.

  Thereafter, when the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu and the state continues for a predetermined time or longer (1 second or longer in this embodiment), the reference mode Mn is set to a level where the power capacity is decreased by one step. Switch to the power mode set to. Thereafter, similarly, every time the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu and the state continues for a predetermined time or more, the reference mode Mn is changed to a power mode in which the power capacity is set to a level smaller by one level. Switch.

  However, the switching of the reference mode Mn is performed up to the fifth power mode M5, and the sixth power mode M6 is not set as the reference mode Mn. For this reason, when the fifth power mode M5 is set as the reference mode Mn, when the surface temperature Ts of the fixing belt 33 falls below the upper limit temperature Tu and the descending state is continued, the reference mode Mn is set. The fixing belt 33 is heated in the fourth power mode M4 in which the power capacity is larger than that in the fifth power mode M5.

When the surface temperature Ts of the fixing belt 33 is lower than the lower limit temperature Td, the first power mode M1 is switched regardless of whether the reference mode Mn is set to the second power mode M2 to the fifth power mode M5.
Further, when each of the first power mode M1 to the fifth power mode M5 is set as the reference mode Mn, the surface temperature Ts of the fixing belt 33 increases in an appropriate temperature range from the lower limit temperature Td to the upper limit temperature Tu. When the state is reached, the fixing belt 33 is heated in the power mode in which the power capacity is smaller than the power mode set as the reference mode Mn.

13A to 13E show the surface temperature Ts of the fixing belt 33 when each of the first power mode M1 to the fifth power mode M5 is set as the reference mode in the fixing temperature control of the present embodiment. 4 is a table showing a relationship between the power mode when the fixing belt 33 is heated.
As shown in FIGS. 13A to 13E, the surface temperature Ts of the fixing belt 33 is the upper limit regardless of which of the first power mode M1 to the fifth power mode M5 is set as the reference mode Mn. When the temperature Tu is exceeded, heating of the fixing belt 33 is stopped (OFF, power supply 0 W), and even if one second or more has elapsed since the heating of the fixing belt 33, the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu. If so, the reference mode Mn is switched to a power mode in which the power capacity is set to a level one step smaller.

  Further, as shown in FIGS. 13A to 13E, the surface temperature Ts of the fixing belt 33 is the same regardless of which of the first power mode M1 to the fifth power mode M5 is set as the reference mode Mn. When the temperature falls below the lower limit temperature Td, the basic mode Mn is switched to the first power mode M1 (if the first power mode M1 is set as the reference mode Mn, the setting of the first power mode M1 is maintained. ), The fixing belt 33 is heated in the first power mode M1, which is the switched reference mode Mn.

  Furthermore, as shown in FIGS. 13A to 13D, when each of the first power mode M1 to the fourth power mode M4 is set as the reference mode Mn, the surface of the fixing belt 33 is used. When the temperature Ts rises in an appropriate temperature range between the lower limit temperature Td and the upper limit temperature Tu, the fixing belt 33 is in the power mode M (n + 3) in which the power capacity is three levels lower than the power mode set as the reference mode Mn. Each is heated. In this case, the power mode set as the reference mode Mn is not changed.

As shown in FIG. 13E, when the fifth power mode M5 is set as the reference mode Mn, the surface temperature Ts of the fixing belt 33 is an appropriate temperature between the lower limit temperature Td and the upper limit temperature Tu. When the range is raised, heating of the fixing belt 33 is stopped. Also in this case, the power mode set as the reference mode Mn is not changed.
Further, as shown in FIGS. 13A to 13D, when each of the first power mode M1 to the fourth power mode M4 is set as the reference mode Mn, the surface temperature of the fixing belt 33 is set. When Ts falls in an appropriate temperature range between the lower limit temperature Td and the upper limit temperature Tu, the fixing belt 33 is heated in the power mode set as the reference mode Mn. Also in this case, the power mode set as the reference mode Mn is not changed.

  As shown in FIG. 13E, when the fifth power mode M5 is set as the reference mode Mn, the surface temperature Ts of the fixing belt 33 is an appropriate temperature between the lower limit temperature Td and the upper limit temperature Tu. When in the range, the fixing belt 33 is heated in the fourth power mode M4 in which the power capacity is set to one level larger than the fifth power mode M5 set as the reference mode. Also in this case, the power mode set as the reference mode Mn is not changed.

FIG. 14 is a flowchart showing a processing procedure of fixing temperature control executed in the fixing controller 52 of the present embodiment.
When the continuous print job is instructed, the fixing control unit 52 sets the mode reference value n to “1” in order to set the reference mode Mn to the first power mode M1 (step S61 in FIG. 14). Thereby, the reference mode Mn is set to the first power mode M1 (n = 1).

Next, the fixing belt 33 is heated in the first power mode M1 set as the reference mode Mn (step S62). In this case, the first and second relays 55 and 56 are turned on to supply power to the first and second heater lamps 35 and 36 used in the first power mode M1, respectively.
When the surface temperature Ts of the fixing belt 33 becomes equal to or higher than the fixing temperature Tf due to the heating (warm-up) of the fixing belt 33 in the first power mode M1, the printing operation by the printer is started and the fixing nip Nf is continuously continued. The recording sheet P passes through. As a result, the surface temperature Ts of the fixing belt 33 in a heated state is lowered.

When the printing operation is started, the fixing controller 52 starts fixing temperature control for controlling the surface temperature Ts of the fixing belt 33 from the lower limit temperature Td to the upper limit temperature Tu.
For this purpose, the fixing controller 52 first checks in step S63 whether the instructed continuous print job is completed. When the instructed continuous print job is completed (“YES” in step S63), the fixing temperature control by the fixing control unit 52 is also ended in order to end the printing operation by the printer. Thereby, all the 1st-3rd relays 55-57 are turned off, and the power supply with respect to a heater lamp is stopped.

If the instructed print job is not completed in step S63 (“NO” in step S63), the surface temperature Ts of the fixing belt 33 detected by the temperature sensor 38 at intervals of 1 second or less is the upper limit temperature. It is confirmed whether it is higher than Tu (step S64).
In step S64, when the surface temperature Ts of the fixing belt 33 is higher than the upper limit temperature Tu (“YES” in step S64), the process proceeds to step S65, and all the relays 55 to 57 are turned off. The power supply to all the heater lamps 35 to 37 is stopped, and the heating of the fixing belt 33 is stopped.

It should be noted that the surface temperature Ts of the fixing belt 33 measured by the temperature sensor 38 is measured at a predetermined sampling period of 1 second or less in Step S64 while the heat fixing operation is continuously performed. And the obtained surface temperature Ts of the fixing belt 33 is held until the next surface temperature Ts is obtained.
At the beginning of the printing operation, since the heat storage amounts of the pressure roller 34 and the fixing roller 32 are relatively small, the surface temperature Ts of the fixing belt 33 is relatively abrupt when the recording sheet P passes through the fixing nip Nf. However, when the fixing belt 33 is heated in the first power mode M1 in which the power capacity is set to the maximum, the heat storage amount of the pressure roller 34 and the fixing roller 32 is gradually increased, and the surface temperature is increased. The decrease in temperature at Ts is also gradually suppressed.

In this state, when the surface temperature Ts of the fixing belt 33 becomes higher than the upper limit temperature Tu, and the heating of the fixing belt 33 in the first power mode M1 is stopped, the surface temperature Ts of the fixing belt 33 is Descend.
When the heating of the fixing belt 33 is stopped, the process proceeds to step S66, and whether the surface temperature Ts of the fixing belt 33 has fallen below the upper limit temperature Tu until one second has passed after the heating of the fixing belt 33 was stopped. Confirm. If the surface temperature Ts of the fixing belt 33 is equal to or lower than the upper limit temperature Tu until 1 second elapses (“NO” in step S66 and “YES” in step S64), step S71 is performed. Proceed to

  As described above, when the surface temperature Ts of the fixing belt 33 falls below the upper limit temperature Tu before one second has elapsed from the stop of heating of the fixing belt 33 due to the surface temperature Ts of the fixing belt 33 exceeding the upper limit temperature Tu. It is considered that the heat storage amount of the pressure roller 34 and the fixing roller 32 is small. For this reason, the reference mode Mn is not changed to the set first power mode M1.

If the surface temperature Ts of the fixing belt 33 does not fall below the upper limit temperature Tu even after one second has passed since the heating of the fixing belt 33 was stopped (“NO” in step S64, and step S66) "YES"), the process proceeds to step S67 assuming that the heat storage amounts of the pressure roller 34 and the fixing roller 32 are relatively large.
In this case, first, it is confirmed whether or not the mode reference value n is “4” or less (step S67). When the mode reference value n is “4” or less (“YES” in step S67), the process proceeds to step S68, and the mode reference value n is changed to “n + 1”. Thereafter, the process returns to step S63.

In step S67, when the mode reference value n is not “4” or less (“NO” in step S68), the reference mode Mn is set to the fifth power mode M5. In this case, it is set. The process returns to step S63 without changing the reference mode Mn (fifth power mode M5).
In the present embodiment, the reference mode Mn is not set to the sixth power mode M6 having a power capacity smaller than that of the fifth power mode M5. This is because when the surface temperature Ts of the fixing belt 33 is lower than the upper limit temperature Tu and continues to be lowered, the fixing belt 33 is heated in the sixth power mode M6 in which the power capacity is smaller than that in the fifth power mode M5. This is because, since the amount of heat applied to the fixing belt 33 is small, the surface temperature Ts of the fixing belt 33 may be rapidly lowered by the recording sheet P passing through the fixing nip Nf.

  In step S64, if the surface temperature Ts of the fixing belt 33 does not exceed the upper limit temperature Tu (“NO” in step S64), the process proceeds to step S71, where the surface temperature Ts of the fixing belt 33 is lower than the lower limit temperature Td (Tm). -2 ° C) is confirmed. If the surface temperature Ts of the fixing belt 33 is lower than the lower limit temperature Td (“YES” in step S71), the process proceeds to step S72.

  In step S72, it is confirmed whether or not the mode reference value n is “1”. When the mode reference value n is “1” (“YES” in step S72), since the reference mode Mn is set to the first power mode M1, step S73 is skipped and the process proceeds to step S74. The fixing belt 33 is continuously heated in the first power mode M1 set as the reference mode Mn.

  If the mode reference value n is not “1” in step S72 (“NO” in step S72), the process proceeds to step S73 because the reference mode Mn is not the first power mode M1, and the mode reference value n is set to “ 1 ”and the reference mode Mn is switched to the first power mode M1. Then, the fixing belt 33 is heated in the first power mode M1 set as the reference mode Mn (step S74). Thereafter, the process returns to step S63.

Thus, when the surface temperature Ts of the fixing belt 33 is lower than the lower limit temperature Td, the reference mode Mn is set to the first power mode M1 set to the maximum power capacity, and the first power mode M1 is set. The fixing belt 33 is heated. Thereby, the surface temperature Ts of the fixing belt 33 can be quickly raised to the lower limit temperature Td or higher.
Thereafter, when the surface temperature Ts of the fixing belt 33 becomes equal to or higher than the lower limit temperature Td (“NO” in step S71), the process proceeds to step S81 in FIG.

  In step S81 of FIG. 15, the surface temperature Ts of the fixing belt 33 is not less than the lower limit temperature Td and not more than the upper limit temperature Tu. In such an appropriate temperature range, the surface temperature Ts of the fixing belt 33 is in the rising state and the falling state. In order to confirm which is the latest detection surface temperature Ts2 which is the latest detection result of the temperature sensor 38 and the previous detection surface temperature Ts1 which is the previous detection result of the latest detection result, It is confirmed whether the latest detected surface temperature Ts2 is higher than the previous detected surface temperature Ts1 (Ts1 <Ts2) (step S81).

If the latest detected surface temperature Ts2 is higher than the previous detected surface temperature Ts1 (“YES” in step S81), it is determined that the surface temperature Ts of the fixing belt 33 is in the rising state in the appropriate temperature range, and the fixing belt It is confirmed whether or not the temperature raising flag Fu indicating that 33 is heated in the predetermined power mode is in the set state (Fu = 1) (step S82).
If the temperature increase flag Fu is not in the set state (“NO” in step S82), the heating of the fixing belt 33 in the predetermined power mode has not been executed, so the mode reference value n becomes “3” or less. (Step S83).

When the mode reference value n is “3” or less (“YES” in step S83), the power mode M (with a power capacity of three levels lower than the power capacity of the power mode set as the reference mode Mn ( In step n84, the fixing belt 33 is heated (step S84).
That is, when the reference mode Mn is the first power mode M1, the fourth power mode M4, when the reference mode is the second power mode M2, the fifth power mode M5, and when the reference mode is the third power mode M3. Respectively heats the fixing belt 33 in the sixth power mode M6. In this case, the mode reference value n is not changed, and therefore the power mode set as the reference mode Mn is not changed.

  As described above, the fixing belt 33 that has been heated in the appropriate temperature range from the lower limit temperature Td to the upper limit temperature Tu has a power capacity set to a level that is three steps lower than the power mode set as the reference mode Mn. By heating in mode M (n + 3), there is no possibility that the surface temperature Ts of the fixing belt 33 that is in a temperature rising state will be rapidly heated. As a result, when the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu and the heating of the fixing belt 33 is stopped, the surface temperature Ts of the fixing belt 33 is prevented from significantly increasing beyond the upper limit temperature Tu. it can.

When the fixing belt 33 is heated in the predetermined power mode in step S84, the temperature raising flag Fu is then set (Fu = 1) (step S84), and the process returns to step S63.
In step S83, when the mode reference value n is not “3” or less (“NO” in step S83), the process proceeds to step S86 to check whether the mode reference value n is “4”. When the mode reference value n is “4” (“YES” in step S86), the fixing belt 33 is heated in the sixth power mode M6 set to the smallest power capacity (step S87).

  As described above, when the fourth power mode M4 is set as the reference mode Mn, the heat storage amount in the pressure roller 34 and the fixing roller 32 is relatively large, but the recording sheet P passes through the fixing nip Nf. Even if the toner passes continuously, the surface temperature Ts of the fixing belt 33 is increased. Therefore, it is considered that the heat storage amount in the pressure roller 34 and the fixing roller 32 is not sufficient. For this reason, the fixing belt 33 is heated in the sixth power mode M6 in which the power capacity is set to be the smallest.

Since the sixth power mode M6 has the minimum power capacity, even when the fourth power mode M4 is set as the reference mode Mn, the fixing belt 33 is heated by the sixth power mode M6. There is no possibility that the surface temperature Ts of the fixing belt 33 greatly exceeds the upper limit temperature Tu.
When the fixing belt 33 is heated in the sixth power mode M6, the temperature raising flag Fu is set (Fu = 1) (step S84), and the process returns to step S63. Also in this case, the mode reference value n is not changed (n = 4), and the reference mode Mn is maintained in the fourth power mode M4.

  If the mode reference value n is not “4” in step S86 (“NO” in step S86), the mode reference value n is “5”, and the reference mode Mn is set to the fifth power mode M5. Has been. In this case, since the fixing belt 33 is in a heated state even though the fixing belt 33 is heated with relatively small power consumption by only the second heater lamp 36 of 500 W, the fixing belt 33 is heated. If this heating is continued, the surface temperature Ts of the fixing belt 33 may exceed the upper limit temperature Tu, and the temperature may increase significantly. For this purpose, heating of the fixing belt 33 is stopped (step S88).

Thereafter, the temperature raising flag Fu is set (Fu = 1) (step S84), and the process returns to step S63.
As described above, when the temperature rising state of the fixing belt 33 continues even when the fixing belt 33 is heated or stopped in the predetermined power mode (“YES” in step S81), the temperature rising flag Fu is set. By being in the set state (Fu = 1) (“YES” in step S82), heating of the fixing belt 33 in the predetermined power mode or heating stop of the fixing belt 33 is maintained, and the process returns to step S63. Become.

In step S81, when the surface temperature Ts of the fixing belt 33 is not in the rising state (“NO” in step S81), the process proceeds to step S91, where the latest detected surface temperature Ts2 is compared with the previous detected surface temperature Ts1. It is confirmed whether the latest detected surface temperature Ts2 is lower than the previously detected surface temperature Ts1 (Ts2 <Ts1).
If the latest detected surface temperature Ts2 is lower than the previous detected surface temperature Ts1 (“YES” in step S91), it is assumed that the surface temperature Ts of the fixing belt 33 has been lowered, and the fixing belt 33 is It is confirmed whether or not the temperature drop flag Fd indicating heating in the power mode is in the set state (Fd = 1) (step S92).

  If the temperature drop flag Fd is not in the set state (“NO” in step S92), it is confirmed whether the mode reference value n is “4” or less (step S93). When the mode reference value n is “4” or less (“YES” in step S93), since the heating of the fixing belt 33 in the predetermined power mode is not executed, the power mode set as the reference mode Mn. In step S94, the fixing belt 33 is heated. In this case, the mode reference value n is not changed, and the power mode set as the reference mode Mn is not changed.

  As described above, when the fixing belt 33 is in the temperature lowered state within the appropriate temperature range between the lower limit temperature Td and the upper limit temperature Tu, the pressure roller 34 is used to heat the fixing belt 33 in the set reference mode Mn. The fixing belt 33 is heated with an amount of heat corresponding to the amount of heat stored in the fixing roller 32. As a result, the surface temperature Ts of the fixing belt 33 is gradually lowered or not lowered.

  In particular, even if the surface temperature Ts of the fixing belt 33 falls due to the surface temperature Ts of the fixing belt 33 exceeding the upper limit temperature Tu and the heating of the fixing belt 33 is stopped, the upper limit temperature Tu continues for 1 second or more. In this case, if the lowering state continues even if the temperature falls below the upper limit temperature Tu, the fixing belt is heated in the reference mode Mn switched to the voltage mode corresponding to the heat storage state of the pressure roller 34 and the fixing roller 32. become. Accordingly, the surface temperature Ts of the fixing belt 33 is in a relatively gradual lowering state, and there is no possibility that the surface temperature Ts of the fixing belt 33 is significantly lower than the upper limit temperature Tu and lower than the lower limit temperature Td.

Thereafter, the temperature decrease flag Fd is set (Fd = 1) (step S95), and the process returns to step S63.
If the mode reference value n is not “4” in step S93 (“NO” in step S93), the mode reference value n is “5”, and the reference mode Mn is set to the fifth power mode M5. Yes. In this case, the fixing belt 33 is heated in the fourth power mode M4 (step S96).

  When the reference mode Mn is set to the fifth power mode M5 having a small power capacity, the amount of heat stored in the pressure roller 34 and the fixing roller 32 is large. Therefore, the fixing belt 33 is used in the fifth power mode M5. Is heated, there is a possibility that the temperature lowering state of the fixing belt 33 cannot be effectively suppressed. Therefore, the fixing belt 33 is heated in the fourth power mode M4 whose power capacity is one level larger than that of the fifth power mode M5.

Thereafter, the temperature decrease flag Fd is set (Fd = 1) (step S95), and the process returns to step S63.
When the surface temperature Ts of the fixing belt 33 is in the temperature rising state within the appropriate temperature range (“YES” in step S81), the fixing belt 33 is neither in the temperature rising state nor in the temperature lowering state due to heating or heating stop. Then (“NO” in step S81 and “NO” in step S91), the heating state or the heating stop state of the fixing belt 33 is maintained.

Similarly, when the surface temperature Ts of the fixing belt 33 is in the temperature-decreasing state within the appropriate temperature range (“YES” in step S91), the fixing belt 33 is heated to enter a state that is neither the temperature rising state nor the temperature lowering state. (“NO” in step S81 and “NO” in step S91), the heating state of the fixing belt 33 is maintained.
When the instructed continuous print job is completed while the above fixing temperature control is being executed (“YES” in step S63), the fixing temperature control by the fixing controller 52 is ended.

  FIG. 16A is a graph showing an example of a change in the surface temperature Ts of the fixing belt 33 in the fixing temperature control of the present embodiment, and FIG. 16B is a graph of the fixing belt 33 shown in FIG. 6 is a graph showing a change in a power mode for heating the fixing belt 33 due to a change in the surface temperature Ts. In the graph of FIG. 16B, the first heater lamp 35, the second heater lamp 36, and the third heater lamp 37 are denoted as a first HL 35, a second HL 36, and a third HL 37, respectively.

In the graph of FIG. 16A, when the continuous printing is instructed, the reference mode Mn is set to the first power mode M1, and the heat fixing operation is performed with the fixing belt 33 heated in the first power mode M1. 3 shows a change in the surface temperature Ts after the surface temperature Ts of the fixing belt 33 falls below the upper limit temperature Tu after the start of.
In this case, since the recording sheet P continuously passes through the fixing nip Nf, the surface temperature Ts of the fixing belt 33 continues to decrease even when the surface temperature Ts falls below the upper limit temperature Tu. Accordingly, the fixing control unit 52 continues heating the fixing belt 33 in the first power mode M1 (700 W first heater lamp 35 and 500 W second heater lamp 36) set as the reference mode Mn.

  At the beginning of the heat fixing operation, since the heat accumulation amount in the pressure roller 34 and the fixing roller 32 is small, the fixing belt 33 is heated in the first power mode M1 in which the power capacity is set to 1200 W. As the recording sheet P continuously passes through the fixing nip Nf, the surface temperature Ts continues to decrease. In this case, when the fixing belt 33 is heated in the first power mode M1, the heat storage amounts of the pressure roller 34 and the fixing roller 32 also gradually increase, and the decrease in the surface temperature Ts of the fixing belt 33 gradually gradually. Become.

Thereafter, when the surface temperature Ts of the fixing belt 33 becomes equal to or lower than the lower limit temperature Td, the heating of the fixing belt 33 in the first power mode M1 is continued because the reference mode Mn is set to the first power mode M1. . As a result, even if the recording sheet P continuously passes through the fixing nip Nf, the surface temperature Ts of the fixing belt 33 starts to rise in a relatively short time.
Due to the heating of the fixing belt 33 in the first power mode M1, the surface temperature Ts of the fixing belt 33 exceeds the lower limit temperature Td and continues to rise thereafter. Accordingly, the surface temperature Ts of the fixing belt 33 rises in an appropriate temperature range, and the fixing control unit 52 sets the power capacity to be lower by three steps than the first power mode M1 set as the reference mode Mn. The fixing belt 33 is heated in the four power mode M4 (using only the 700 W first heater lamp 35). In this case, the setting of the reference mode Mn is not changed, and the setting of the first power mode M1 is maintained.

When the fixing belt 33 is heated in the fourth power mode M4, the surface temperature Ts of the fixing belt 33 is in a moderately higher state than when heated in the first power mode M1.
Thereafter, when the surface temperature Ts of the fixing belt 33 reaches the upper limit temperature Tu, the fixing control unit 52 outputs a signal for turning off the first relay 55 in order to stop the heating of the fixing belt 33. In this case, the supply stop of power to the first heater lamp 35 is delayed due to a response delay of the first relay 55, and the surface temperature Ts of the fixing belt 33 overshoots the upper limit temperature Tu. However, since the fixing belt 33 is heated in the fourth power mode M4 in which the power capacity is smaller than that in the first mode in which the power capacity is set as the reference mode Mn, the increase in the surface temperature Ts is moderated. Therefore, it is possible to suppress the surface temperature Ts of the fixing belt 33 from exceeding the upper limit temperature Tu and greatly rising.

When the heating of the fixing belt 33 is stopped, the surface temperature Ts of the fixing belt 33 continues to rise above the upper limit temperature Tu and then changes to a lowered state.
In this case, the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu even after one second has elapsed since the fixing control unit 52 outputs a signal to turn off the first relay 55, and the fixing control unit 52 The setting of the reference mode Mn is switched from the first power mode M1 to the second power mode M2.

Thereafter, the surface temperature Ts of the fixing belt 33 continues to decrease, and the decreasing state continues even when the temperature falls below the upper limit temperature Tu. As a result, the fixing controller 52 heats the fixing belt 33 in the second power mode M2 (using the 700 W first heater lamp 35 and the 300 W third heater lamp 37) newly set as the reference mode Mn.
In this case, since the heat storage amounts in the pressure roller 34 and the fixing roller 32 are increased from the beginning of the heat fixing operation, the second power mode in which the power capacity is set to a level smaller than that in the first power mode M1. By heating the fixing belt 33 with M2, the decrease in the surface temperature Ts of the fixing belt 33 is suppressed, and the surface temperature Ts decreases relatively slowly.

Thereafter, the surface temperature Ts of the fixing belt 33 rises without lowering to the lower limit temperature Td. In such a state, the fixing belt 33 has a fifth power mode M5 (500 W second heater lamp) in which the power capacity is set to a level three steps smaller than the second power mode M2 set as the reference mode Mn. Use only 36).
As described above, the surface temperature Ts is increased by heating the fixing belt 33 in the second power mode M2 in a state where the surface temperature Ts of the fixing belt 33 is decreasing in an appropriate temperature range of the lower limit temperature Td to the upper limit temperature Tu. If the fixing belt 33 continues to be heated in the second power mode M2 in the case of turning to, the surface temperature Ts may increase rapidly.

  From this, when the surface temperature Ts of the fixing belt 33 is changed from the lowered state to the raised state in the appropriate temperature range, the heating of the fixing belt 33 is performed more than the second power mode M2 set as the reference mode Mn. This is performed in the fifth power mode M5 in which the capacity is set to a level that is three steps smaller, and the surface temperature Ts is raised relatively slowly. Also in this case, the reference mode Mn maintains the state set to the second power mode M2.

  Thereafter, when the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu, the fixing control unit 52 outputs a signal for turning off the third relay 57 in order to stop the heating of the fixing belt 33. In this case, even if the power stop for the third heater lamp 37 is delayed due to a response delay of the third relay 57 and the surface temperature Ts of the fixing belt 33 overshoots the upper limit temperature Tu, the surface temperature Ts of the fixing belt 33 is reached. Since the lowering of the temperature is relatively gradual, the surface temperature Ts of the fixing belt 33 is suppressed from exceeding the upper limit temperature Tu and greatly rising.

When the heating of the fixing belt 33 is stopped, the surface temperature Ts of the fixing belt 33 continues to rise above the upper limit temperature Tu and then changes to a lowered state.
In this case, if the surface temperature Ts of the fixing belt 33 is higher than the upper limit temperature Tu even after 1 second has passed since the fixing control unit 52 outputs a signal for turning off the first relay 55, the fixing control is performed. The unit 52 switches the setting of the reference mode Mn from the second power mode M2 to the third power mode M3.

Thereafter, the surface temperature Ts of the fixing belt 33 continues to fall even if the surface temperature Ts falls below the upper limit temperature Tu. As a result, the fixing controller 52 heats the fixing belt 33 in the third power mode M3 (using the 500 W second heater lamp 36 and the 300 W third heater lamp 37) newly set as the reference mode Mn.
In this case, the amount of heat stored in the pressure roller 34 and the fixing roller 32 is further increased, and the fixing belt 33 is used in the reference mode set in the third power mode M3 having a lower power capacity than the second power mode M2. By heating, the surface temperature Ts of the fixing belt 33 falls relatively slowly.

Thereafter, since the amount of heat taken away from the fixing belt 33 by the recording sheet P continuously passing through the fixing nip Nf is large, even when the fixing belt 33 is heated in the third power mode M3, the surface of the fixing belt 33 is The temperature Ts continues to decrease and falls below the lower limit temperature Td.
In such a state, the fixing control unit 52 switches the reference mode Mn from the third power mode M3 to the first power mode M1. Then, in order to heat the fixing belt 33 in the switched first power mode M1, a signal for turning on the first relay 55 and the second relay 56 is output.

  In this case, when the power supply to the first heater lamp 35 and the first heater lamp 36 is delayed due to the response delay of the first relay 55 and the second relay 56, the surface temperature Ts of the fixing belt 33 is lower than the lower limit temperature Td. Shoot. However, since the surface temperature Ts of the fixing belt 33 is in a gently decreasing state, the surface temperature Ts of the fixing belt 33 is suppressed from greatly decreasing below the lower limit temperature Td.

  After that, when the fixing belt 33 is heated in the first power mode M1, the surface temperature Ts of the fixing belt 33 continues to decrease below the lower limit temperature Td and then goes up, and increases even if the temperature exceeds the lower limit temperature Td. Continue state. In such a state, the fixing control unit 52 heats the fixing belt 33 in the fourth power mode M4 (using only the first heater lamp 35 of 700 W). In this case, the setting of the reference mode Mn is not changed, and the state set to the first power mode M1 is maintained.

Thereafter, similarly, the fixing belt 33 is heated in an appropriate power mode corresponding to the temperature change of the surface temperature Ts of the fixing belt 33.
As described above, in the present embodiment, the upper limit is suppressed by preventing the surface temperature Ts of the fixing belt 33 from increasing to a level higher than the upper limit temperature Tu and from decreasing to a level lower than the lower limit temperature Td. Sticking and lower limit sticking are prevented. Accordingly, the surface temperature Ts of the fixing belt 33 repeatedly increases and decreases in an appropriate temperature range between the lower limit temperature Td and the upper limit temperature Tu, and is controlled to a temperature within a small temperature difference range with respect to the fixing temperature Tf. .

FIG. 17A is a graph showing a change in the surface temperature Ts of the fixing belt 33 after the third power mode M3 is set as the reference mode Mn in the fixing temperature control of the present embodiment, and FIG. 5 is a graph showing a change in power mode in the fixing temperature control.
As shown in FIG. 17A, when the surface temperature Ts of the fixing belt 33 falls in an appropriate temperature range from the lower limit temperature Td to the upper limit temperature Tu, the third power mode M3 (rated rating) set as the reference mode Mn. The fixing belt 33 is heated by using a second heater lamp 36 having a power of 500 W and a third heater lamp 37 having a rated power of 300 W. As a result, the surface temperature Ts of the fixing belt 33 decreases relatively slowly.

Thereafter, when the surface temperature Ts of the fixing belt 33 rises before the temperature falls below the lower limit temperature Td, the sixth power mode M6 (rated power) set to a power capacity that is two steps smaller than the power capacity in the third power mode M3. The fixing belt 33 is heated by using only the 300 W third heater lamp 37).
As a result, the fixing belt 33 rises relatively slowly, the surface temperature Ts of the fixing belt 33 is lowered before reaching the upper limit temperature Tu, and the fixing belt 33 is heated in the third power mode M3.

Thereafter, the surface temperature Ts of the fixing belt 33 repeatedly rises and falls in an appropriate temperature range from the lower limit temperature Td to the upper limit temperature Tu, and is maintained within a temperature range of a small temperature difference with respect to the fixing temperature Tf.
As described above, in this embodiment, the surface temperature Ts of the fixing belt 33 is suppressed from falling below the lower limit temperature Td, and the number of times the fixing belt 33 is heated in the first power mode M1 is reduced. As a result, an increase in power consumption due to heating of the fixing belt 33 in the first power mode M1 in which the power capacity is set to the maximum can be suppressed.

Further, since the number of heating times of the fixing belt 33 is reduced, the number of occurrences of inrush current can also be reduced. As a result, it is possible to suppress the increase in power consumption due to the occurrence of the inrush current and the occurrence of a temperature ripple with a large temperature change in the fixing belt 33.
For comparison, a continuous heat fixing operation is performed by a fixing device having the same configuration as the fixing device 30 of the above embodiment, except that the fixing belt 33 is heated using one heater lamp with a rated power of 1200 W. When executed, the fixing temperature control was executed under the conditions shown in the table of FIG. FIG. 19A is a graph showing the temperature change of the surface temperature Ts of the fixing belt 33 in such fixing temperature control, and FIG. 19B is the power supplied when heating the fixing belt in the fixing temperature control. It is a graph which shows the change of.

In this case, as shown in the table of FIG. 18, when the surface temperature Ts of the fixing belt 33 exceeds the upper limit temperature Tu, the supply of power to the heater lamp with a rated power of 1200 W is stopped (OFF), and the fixing belt 33 When the heating is stopped and the temperature falls below the lower limit temperature Td, electric power is supplied to the heater lamp (ON), and the fixing belt 33 is heated.
Further, when the surface temperature Ts of the fixing belt 33 rises in an appropriate temperature range between the lower limit temperature Td and the upper limit temperature Tu, the power supply to the heater lamp is stopped (OFF) to stop the heating of the fixing belt 33. When the temperature is lowered in the appropriate temperature range, power is supplied (ON) to the heater lamp to heat the fixing belt 33.

In such fixing temperature control, since the rated power of the heater lamp is as large as 1200 W and the amount of heat applied to the fixing belt 33 is large, heating of the fixing belt 33 is stopped by stopping the power supply to the heater lamp. As a result, the surface temperature Ts of the fixing belt 33 rises relatively rapidly.
In the state where the heating of the fixing belt 33 is stopped, the recording sheet P continuously passes through the fixing nip Nf, whereby the increase in the surface temperature Ts of the fixing belt 33 is gradually suppressed and the surface temperature Ts of the fixing belt 33 is suppressed. Falls after exceeding the upper limit temperature Tu due to overshoot.

  Thereafter, when the surface temperature Ts of the fixing belt 33 falls below the upper limit temperature Tu and continues to be lowered, the fixing belt 33 is heated by the heater lamp. In this case, since the amount of heat applied to the fixing belt 33 by the heater lamp is large, the surface temperature Ts of the fixing belt 33 is changed to a rising state without falling below the lower limit temperature Td. As a result, the heater lamp is turned off and heating of the fixing belt 33 is stopped, but the surface temperature Ts of the fixing belt 33 continues to rise due to a response delay of a relay or the like.

  The off state of the heater lamp continues even when the surface temperature Ts of the fixing belt 33 becomes equal to or higher than the upper limit temperature Tu, and thereafter, the surface temperature Ts of the fixing belt 33 turns to a lowered state. If the descending state continues even if the surface temperature Ts of the fixing belt 33 falls below the upper limit temperature Tu, the heater lamp is turned on. As a result, the lowering of the surface temperature Ts of the fixing belt 33 is suppressed, and thereafter the state is changed to the rising state. As described above, the heater lamp is turned off. Due to the response delay, it overshoots above the upper limit temperature Tu.

Thereafter, such an operation is repeated, and the surface temperature Ts of the fixing belt 33 repeatedly rises and falls in the vicinity of the upper limit temperature Tu (with an upper limit sticking).
When such an upper limit is applied, the surface temperature Ts of the fixing belt 33 frequently becomes equal to or higher than the upper limit temperature Tu. Accordingly, there is a possibility that the heat fixing operation cannot be stably performed on the recording sheet P passing through the fixing nip Nf. Moreover, if high temperature more than upper limit temperature Tu generate | occur | produces frequently, useless energy consumption will generate | occur | produce.

In this embodiment, the surface temperature Ts of the fixing belt 33 is not likely to frequently exceed the upper limit temperature Tu as described above, and the heat fixing operation is stably performed on the recording sheet P passing through the fixing nip Nf. Can do.
In the present embodiment, the surface temperature Ts of the fixing belt 33 is changed between the lower limit temperature Td and the upper limit temperature Tu when the fixing belt 33 is lowered and when the surface temperature Ts is raised. Although the power mode for heating is changed, the configuration is not limited to this.

  For example, even when the surface temperature Ts of the fixing belt 33 is in the rising state in the appropriate temperature range between the lower limit temperature Td and the upper limit temperature Tu, heating is performed in the reference mode Mn as in the lowering state. It is good also as a structure. With such a configuration as well, it is possible to reduce power consumption during heating of the fixing belt 33, and it is possible to suppress the surface temperature Ts of the fixing belt 33 from fluctuating greatly.

<Modification>
In the above embodiment, as the means for heating the heating roller 31, the first heater lamp 35 having a rated power of 700W, the second heater lamp 36 having a rated power of 500W, and the third heater lamp 37 having a rated power of 300W. However, the number of heater lamps, the rated power, and the like can be appropriately changed depending on the configuration of the fixing device.

  Moreover, it is good also as a structure which uses not only the structure which uses a heater lamp but electric heaters, such as a nichrome wire heater. Electric heaters such as heater lamps and nichrome wire heaters are not limited to being arranged inside the heating roller 31, but may be arranged outside the heating roller 31 to directly heat the fixing belt 33. Further, the fixing nip may be formed by the heating roller 31 and the pressure roller 34 without providing the fixing belt 33. Further, instead of the pressure roller 34, a configuration using a pressure belt, a configuration using a pressure body fixedly arranged so as not to rotate, or the like may be used.

  According to the present invention, when a recording sheet on which an unfixed image is formed passes through a fixing nip formed by pressure contact between a heating rotator and a pressure body, the recording sheet is heated and pressed to form an unfixed image. In a fixing device for fixing, it is useful as a technique for reducing the power consumption in the continuous heat fixing operation and suppressing the temperature change of the heating rotator.

10Y, 10M, 10C, 10K Image forming unit 30 Fixing device 31 Heating roller 32 Fixing roller 33 Fixing belt 34 Pressure roller 35 First heater lamp 36 Second heater lamp 37 Third heater lamp 38 Temperature sensor 52 Fixing control unit 55 First 1 relay 56 2nd relay 57 3rd relay

Claims (12)

A fixing device for thermally fixing an unfixed image on a recording sheet when the recording sheet passes through a fixing nip secured between a heating rotator and a pressure member pressed against the heating rotator,
A plurality of heating means for heating the heating rotator;
Detecting means for detecting the temperature of the heating rotor;
One power capacity selected from different power capacities obtained by one or a combination of the plurality of heating means is set as a reference mode, and a plurality of recordings that pass through the fixing nip continuously are recorded. Control means for heating the heating rotator in a reference mode when the detection temperature of the detection means falls below a target temperature during a heat fixing operation on the sheet, and stopping heating of the heating rotator when the temperature exceeds the target temperature. With
The control unit is configured such that the temperature of the heating rotator overshoots the target temperature by stopping the heating of the heating rotator after the heating rotator is heated in the reference mode, and is higher than the target temperature. A fixing device that updates a reference mode to a power capacity smaller than a previously set power capacity when the temperature rises to a predetermined upper limit temperature.   The control means sets the reference mode to a power capacity larger than the previously set power capacity when the temperature detected by the detection means falls below a predetermined lower limit temperature lower than the target temperature during heating of the heating rotator. The fixing device according to claim 1, wherein after the update, the heating rotator is heated in the updated reference mode.   The fixing device according to claim 2, wherein the control unit updates the reference mode to a maximum power capacity when the temperature falls below the lower limit temperature.   The control unit according to claim 1, wherein at the start of the heat fixing operation, the reference mode is set to a maximum power capacity and the heating rotator is heated in the set reference mode. The fixing device according to claim 1. The control means raises the heating rotator above a predetermined temperature lower than the target temperature during a standby state until the heat fixing operation is instructed after the heating rotator is heated to the target temperature. It becomes power saving mode to heat so as not to
When the thermal fixing operation is instructed in the power saving mode, the reference mode is set to a power capacity selected based on the elapsed time in the standby state, and the heating rotator is heated in the set reference mode. The fixing device according to claim 1, wherein the temperature is increased by heating.   The control means sets the reference mode to the maximum power capacity until the elapsed time in the standby state reaches a threshold value, and if it is equal to or greater than the threshold value, sets the reference mode to a power capacity smaller than the maximum power capacity. The fixing device according to claim 5, wherein the fixing device is set as follows.   The control means sets the reference mode to a power capacity selected based on the temperature detected by the detection means at the start of the heat fixing operation, and heats the heating rotator with the set power capacity. The fixing device according to claim 1, wherein   The control means sets the reference mode to the maximum power capacity when the detection temperature of the detection means at the start of the heat fixing operation is lower than a threshold temperature set lower than a target temperature, The fixing device according to claim 7, wherein when the temperature is equal to or higher than the threshold temperature, the reference mode is set to a power capacity smaller than a maximum power capacity. A fixing device that fixes an unfixed image on a recording sheet by heating when the recording sheet passes through a fixing nip secured between a heating rotator and a pressure member pressed against the heating rotator,
A plurality of heating means for heating the heating rotator;
Detecting means for detecting the temperature of the heating rotor;
A plurality of recording sheets passing through the fixing nip continuously by setting one power capacity selected from among power capacities obtained by one or a combination of the plurality of heating means as a reference mode When the temperature detected by the detection means falls below the target temperature during the heat fixing operation, the heating rotator is heated in a reference mode, and when the temperature exceeds the target temperature, the control means stops heating the heating rotator. With
The control means is less than the target temperature when the temperature of the heating rotator overshoots the target temperature due to the stop of heating of the heating rotator after the heating rotator is heated in the reference mode. A fixing device that updates a reference mode to a power capacity that is smaller than a previously set power capacity when a time required until the time reaches a predetermined time or more.   The control means heats the heating rotator in a reference mode when the detection temperature of the detection means is in a lowered state between the target temperature and a predetermined lower limit temperature lower than the target temperature. When the temperature is changed from the lowered state to the raised state between the target temperature and the lower limit temperature, the heating capacity is set by switching the power capacity set in the reference mode to a smaller power capacity to heat the heating rotator. The fixing device according to claim 9.   When the detected temperature of the detecting means falls below the lower limit temperature, the control means updates the reference mode to the maximum power capacity and heats the heating rotator with the updated power capacity. The fixing device according to claim 10.   An image forming apparatus comprising the fixing device according to claim 1.

Images