JP7456158B2 - Image forming device, control method and program - Google Patents

Description

The present invention relates to an image forming apparatus equipped with a fixing device having a plurality of heaters, and a control method and program for the image forming apparatus.

Conventionally, an image forming apparatus performs continuous energization control in which alternating current is continuously applied to each of two heaters within a control cycle, and phase control in which the phase angle is changed before and after the continuous energization control. There are known devices that do this (see Patent Document 1). In this technique, generation of harmonic current is suppressed by energizing so that the phase control execution period for one heater does not overlap with the phase control execution period for the other heater.

Japanese Patent Application Publication No. 2010-096969

By the way, in the conventional technology, there may be a time interval between continuous energization control for one heater and continuous energization control for the other heater within a control period. In this case, after an instantaneous voltage drop that causes flicker occurs in one continuous energization control, an instantaneous voltage drop may occur in the other continuous energization control. In other words, there is a possibility that instantaneous voltage drops may occur twice within the control period.

Therefore, an object of the present invention is to reduce the frequency of occurrence of instantaneous voltage drops within a control period.

In order to solve the above problems, an image forming apparatus according to the present invention includes a developer image forming section that forms a developer image on a sheet, and a fixing device that fixes the developer image formed by the developer image forming section on the sheet. The apparatus includes a device and a control section.
The fixing device includes a heating section, a first heater that has an output peak in a first region of the heating section, and a first heater that heats the heating section, and a second region of the heating section that has an output peak that is different from the first region. a second heater that has a peak and heats the heating section; a pressure section that sandwiches the sheet between the heating section; and a first temperature detection section that detects the temperature of at least a portion of the first region; and a second temperature detection section that detects the temperature of at least a portion of the second region.
The control unit includes a first continuous energization control that continuously supplies a first alternating current to the first heater, and a second continuous energization control that continuously supplies a second alternating current to the second heater. It is possible to control the first heater based on the energization pattern determined for each control cycle from the first detected temperature detected by the first temperature detecting section and the second detected temperature detected by the second temperature detecting section. and controlling the energization to the second heater, and assuming that the control period is T, the period for executing the first continuous energization control is T1, and the period for executing the second continuous energization control is T2, a period of T1+T2<T is determined. If one condition is satisfied, the second continuous energization control is started immediately after the first continuous energization control ends.

According to this configuration, by starting the second continuous energization control immediately after the end of the first continuous energization control, the first continuous energization control and the second continuous energization control are performed continuously within the control period, and the control period Since continuous energization control is performed once within the control period, the instantaneous voltage drop that occurs within the control period can be suppressed to once.

The control unit may also perform a second start phase control performed before the second continuous energization control, which energizes the second heater in a part of the sine wave of the second alternating current. Start phase control can be executed, and the second start phase control may be executed while the first continuous energization control is being executed.

Further, when the first condition is satisfied, the control unit may start the second start phase control simultaneously with the start of the first continuous energization control.

Further, the control unit may perform a first end phase control performed after the first continuous energization control, and perform a first end phase control in which the first heater is energized in a part of the sine wave of the first alternating current. If time phase control is executable and the first condition is satisfied, energization may be stopped after the first continuous energization control without executing the first termination phase control.

According to this, when the first condition is satisfied, the first termination phase control is not executed after the first continuous energization control, so it is possible to suppress the peak of the composite current in the second continuous energization control. .

Moreover, the peak of the current in the energization in the second continuous energization control may be larger than the peak in the current in the energization in the first continuous energization control.

According to this, the second region of the heating section can be quickly heated.

Further, the first condition may be a condition that does not include a condition regarding an execution period of the second start phase control.

Further, in the second start time phase control, the control unit energizes so that a composite value of the first alternating current and the second alternating current is equal to or less than a peak of the second alternating current. Good too.

According to this, the peak of the composite current can be suppressed when the first continuous energization control and the second starting phase control are executed simultaneously.

Moreover, the control unit may gradually increase the amount of current per half wave of the second alternating current by changing the phase angle in the second start phase control.

According to this, since the amount of current per half wave of the second alternating current is gradually increased in the second start phase control, it is possible to suppress a sudden change in the current flowing through the second heater.

The control unit may also execute a first start phase control before the first continuous current control, in which current is applied to the first heater at a portion of the sine wave of the first AC current, and the phase angle may be kept constant in the first start phase control.

The control unit may also perform a first termination phase control performed after the first continuous energization control, in which the first heater is energized in a part of the sine wave of the first alternating current. time phase control; and a second end phase control performed after the second continuous energization control, the second end phase control in which the second heater is energized in a part of the sine wave of the second alternating current. control, and in at least one of the first end phase control and the second end phase control, the amount of energization per half wave of the alternating current is gradually reduced by changing the phase angle. It's okay.

According to this, the amount of current per half wave of alternating current is gradually reduced in at least one of the first end phase control and the second end phase control, so that sudden changes in the current flowing through a predetermined heater can be prevented. Can be suppressed.

The control method according to the present invention includes a developer image forming unit that forms a developer image on a sheet, a fixing device that fixes the developer image formed by the developer image forming unit to the sheet, and a control unit, the fixing device having a heating unit, a first heater that has an output peak in a first region of the heating unit and heats the heating unit, a second heater that has an output peak in a second region different from the first region of the heating unit and heats the heating unit, a pressure unit that sandwiches a sheet between the heating unit and the pressure unit, a first temperature detection unit that detects the temperature of at least a part of the first region, and a second temperature detection unit that detects the temperature of at least a part of the second region, and the control unit supplies a first AC current to the first heater. A control method by the control unit in an image forming apparatus capable of executing a first continuous current control in which current is continuously supplied to the second heater, and a second continuous current control in which current is continuously supplied to the second heater, the control method controls current to the first heater and the second heater based on a current pattern determined for each control cycle from the first detected temperature detected by the first temperature detection unit and the second detected temperature detected by the second temperature detection unit, the control cycle is T, the period during which the first continuous current control is executed is T1, and the period during which the second continuous current control is executed is T2, and when a first condition of T1+T2<T is satisfied, the second continuous current control is started immediately after the end of the first continuous current control.

Further, the program according to the present invention includes a developer image forming section that forms a developer image on a sheet, a fixing device that fixes the developer image formed by the developer image forming section on the sheet, and a control section. The fixing device includes a heating section, a first heater having an output peak in a first region of the heating section and heating the heating section, and a second region of the heating section different from the first region. a second heater that has an output peak at and heats the heating section; a pressure section that sandwiches the sheet between the heating section; and a first temperature detector that detects the temperature of at least a portion of the first region. and a second temperature detection section that detects the temperature of at least a portion of the second area, the program for operating the control section, the program comprising: means for executing a first continuous energization control for continuously supplying a first alternating current to the second heater; means for executing a second continuous energization control for continuously supplying a second alternating current to the second heater; Based on the energization pattern determined for each control cycle from the first detected temperature detected by the first temperature detection section and the second detected temperature detected by the second temperature detection section, the first heater and the second heater are a means for controlling energization; a first condition that T1+T2<T is satisfied, where the control period is T, the period for executing the first continuous energization control is T1, and the period for executing the second continuous energization control is T2; In this case, it functions as means for starting the second continuous energization control immediately after the first continuous energization control ends.

According to the control method or program described above, by starting the second continuous energization control immediately after the end of the first continuous energization control, the first continuous energization control and the second continuous energization control are performed continuously within the control period. Since continuous energization control is performed once within the control period, the instantaneous voltage drop that occurs within the control period can be suppressed to one time.

According to the present invention, it is possible to reduce the frequency of occurrence of instantaneous voltage drops within a control period.

FIG. 1 is a diagram showing a laser printer according to the present embodiment. FIG. 3 is a diagram showing a fixing device. It is a graph showing the output of each heater. FIG. 3 is a block diagram showing the configuration of a control section. FIG. 3 is a diagram showing a table for determining an energization pattern. FIG. 6 is a diagram showing energization patterns within a column surrounded by a frame X in FIG. 5. FIG. FIG. 6 is a diagram showing a current flow pattern within a section surrounded by a frame Y in FIG. 5 . They are a diagram (a) showing energization control in pattern III, a diagram (b) showing a composite waveform in the first start phase control, and a diagram (c) showing an enlarged view of the last half wave of the composite waveform. 3 is a diagram showing energization control in pattern I. FIG. 5 is a flowchart showing the operation of the control section. FIG. 7 is a diagram showing a form in which the execution period of the first end phase control and the execution period of the second end phase control overlap.

Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.
As shown in FIG. 1, a laser printer 1 is an example of an image forming apparatus that forms an image on a sheet S, and includes a main body housing 2, a sheet supply section 3, and a process section as an example of a developer image forming section. The image forming apparatus includes a PR, a fixing device 8, and a control section 100.

The sheet supply section 3 is a mechanism for supplying the sheet S to the process section PR, and is provided at the lower part of the main body casing 2. The sheet supply section 3 includes a supply tray 31 that accommodates the sheets S, a sheet pressing plate 32, and a supply mechanism 33. The supply mechanism 33 includes a pickup roller 33A, a separation roller 33B, a first conveyance roller 33C, and a registration roller 33D. In the sheet supply section 3, the sheet S in the supply tray 31 is brought to a pickup roller 33A by a sheet pressing plate 32, and is sent to a separation roller 33B by the pickup roller 33A. The sheet S is separated into one sheet by the separation roller 33B, and is transported by the first transport roller 33C. The registration roller 33D aligns the leading edge of the sheet S and then transports the sheet S toward the process section PR. Here, the direction in which the sheet S is conveyed is the conveyance direction, and the direction perpendicular to the conveyance direction within the plane of the sheet S is the width direction.

The process section PR has a function of forming a developer image on the sheet S. The process section PR includes an exposure device 4 and a process cartridge 5.

The exposure device 4 is disposed in the upper part of the main body housing 2, and includes a laser light source (not shown), a polygon mirror, a lens, a reflecting mirror, etc., which are shown without reference numerals. In the exposure device 4, the surface of the photoreceptor drum 61 is exposed by scanning the surface of the photoreceptor drum 61 with laser light based on image data emitted from a laser light source.

The process cartridge 5 is disposed below the exposure device 4 and is removable from the main body casing 2 through an opening created when a front cover 21 provided on the main body casing 2 is opened. The process cartridge 5 includes a drum unit 6 and a developing unit 7.

The drum unit 6 includes a photosensitive drum 61, a charger 62, and a transfer roller 63. The developing unit 7 is removably attached to the drum unit 6 and includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, a developer accommodating section 74 that accommodates a developer that is dry toner, and an agitator 75. It is equipped with

In the process cartridge 5, the surface of the photoreceptor drum 61 is uniformly charged by the charger 62 and then exposed to laser light from the exposure device 4, thereby forming an image on the photoreceptor drum 61 based on the image data. A latent image is formed. Further, the developer in the developer storage section 74 is supplied to the developing roller 71 via the supply roller 72 while being agitated by the agitator 75, and as the developing roller 71 rotates, the developing roller 71 and the layer thickness regulating blade 73 and is carried on the developing roller 71 as a thin layer with a constant thickness.

The developer carried on the developing roller 71 is supplied from the developing roller 71 to the electrostatic latent image formed on the photoreceptor drum 61 . As a result, the electrostatic latent image is visualized, and a developer image is formed on the photoreceptor drum 61. Thereafter, the sheet S supplied from the sheet supply section 3 is conveyed between the photoreceptor drum 61 and the transfer roller 63, so that the developer image formed on the photoreceptor drum 61 is transferred onto the sheet S. Ru.

The fixing device 8 is a device that fixes the developer image formed by the process section PR onto the sheet S. The fixing device 8 includes a heating section 81 that heats the sheet S, and a pressure section 82 that sandwiches the sheet S between the heating section 81 and the heating section 81 .

The heating unit 81 is a rotatable cylindrical heating roller made of metal or the like. A first heater H1 and a second heater H2 that heat the heating section 81 are provided inside the heating section 81. The pressure unit 82 is a rotatable pressure roller, and has an elastic layer made of elastically deformable rubber or the like on its surface. In the fixing device 8, the sheet S to which the developer image has been transferred is conveyed between a heating section 81 and a pressing section 82, so that the developer image is thermally fixed onto the sheet S. The sheet S on which the developer image is thermally fixed is discharged onto the discharge tray 22 by the second conveyance roller 23 and discharge roller 24 .

As shown in FIG. 2, the fixing device 8 includes the heating section 81, the first heater H1, and the second heater H2 described above, and further includes a first temperature detection section ST1 and a second temperature detection section ST2. There is.

The first heater H1 is a halogen lamp, and has an output peak in a first region 81A that includes the widthwise central portion of the heating section 81 (see FIG. 3). The first heater H1 includes a glass tube H11 and a filament H12 provided within the glass tube H11. In the filament H12, the light-emitting portions are concentrated at the center portion in the width direction than at each end portion in the width direction.

The second heater H2 is a halogen lamp, and has an output peak in second regions 81B and 81C that are closer to the ends than the first region 81A of the heating section 81 (see FIG. 3). The second heater H2 includes a glass tube H21 and a filament H22 provided within the glass tube H21. In the filament H22, the light emitting parts are concentrated at each end in the width direction compared to the center part in the width direction.

Here, the width direction of the heating section 81 refers to the direction along the rotational axis of the heating section 81, and means the same direction as the width direction of the sheet S. The first region 81A of the heating section 81 is a range including the center in the width direction of the heating section 81, and the second region 81B on one end side of the heating section 81 is a range that includes the edge 81D on the one end side of the heating section 81 and the first region 81A on the one end side of the heating section 81. This is the range between the area 81A and the area 81A. The second region 81C on the other end side of the heating section 81 is a range between the edge 81E on the other end side of the heating section 81 and the first region 81A.

As shown by the solid line in FIG. 3, the output of the first heater H1 has a distribution in which the output is highest at the center in the width direction and gradually decreases toward both ends in the width direction. Thereby, in the first heater H1, the heating capacity of the heating unit 81 for the first region 81A is larger than the heating capacity for the second regions 81B and 81C. As shown by the broken line, the output of the second heater H2 has a higher distribution at the end than at the center in the width direction. As a result, the second heater H2 has a heating ability for the second regions 81B and 81C of the heating section 81 that is greater than the heating ability for the first region 81A. The range where the output of the first heater H1 is maximum and the range where the output of the second heater H2 is maximum are set so as not to overlap.

The output in the second region 81B, 81C of the first heater H1 is 30% or less of the output in the first region 81A, and the output in the first region 81A of the second heater H2 is 80% of the output in the second region 81B, 81C. % or less.

Note that, as a method for detecting the output of each of the heaters H1 and H2, for example, a method of arranging an optical sensor that detects the light of the heater at a predetermined distance from the heater and detecting the amount of light can be mentioned. Here, the predetermined distance is the distance from the heater to the inner peripheral surface of the heating section 81.

As shown in FIG. 2, the first temperature detection section ST1 is a sensor that detects the temperature of at least a portion of the first region 81A of the heating section 81. The first temperature detection section ST1 is not in contact with the heating section 81. Specifically, the first temperature detection section ST1 is arranged at a distance from the outer circumferential surface of the heating section 81.

The second temperature detection section ST2 is a sensor that detects the temperature of at least a portion of the second region 81B on one end side of the heating section 81. The second temperature detection section ST2 is in contact with the second region 81B of the heating section 81. The second temperature detection section ST2 is shifted from the largest area SW of the sheet S that can be fixed by the fixing device 8 toward the edge 81D on one end side.

Note that, for example, a thermistor or the like can be used as the first temperature detection section ST1 and the second temperature detection section ST2.

As shown in FIG. 4, the control unit 100 includes an ASIC 110 and an energization circuit 120. ASIC 110 includes a CPU 111 and a heater controller 112. The energizing circuit 120 is a circuit including a switching circuit that switches the input AC voltage between a energized state and a non-energized state, and is connected to each heater H1, H2 and the ASIC 110.

The CPU 111 is implemented as a function within the ASIC 110. The CPU 111 outputs to the heater controller 112 a first target temperature that is the target temperature of the first region 81A and a second target temperature that is the target temperature of the second region 81B. Each target temperature is a command value in feedback processing when the heater controller 112 executes energization control to the first heater H1 and the second heater H2.

The heater controller 112 is a function or circuit built into the ASIC 110, and controls each heater by controlling the energizing circuit 120 so that the detected temperature in each temperature detection section ST1, ST2 becomes the respective target temperature. Power is being supplied to H1 and H2. Specifically, the heater controller 112 determines the duty ratio of the alternating current voltage applied to each of the heaters H1 and H2 based on the detected temperature and the target temperature, and performs a feedback process to control the energization circuit 120 with the determined duty ratio. . Note that the feedback processing performed by the heater controller 112 may be implemented in a chip outside the ASIC 110 or may be executed by the CPU 111.

The control unit 100 receives print commands output from an external computer, detected temperatures detected by the first temperature detection unit ST1 and second temperature detection unit ST2, and programs stored in storage units such as ROM 113 and RAM 114. Control is executed by performing various calculation processes based on the data. In other words, the control unit 100 functions as a means for executing various controls by operating according to a program.

The control unit 100 controls the first energization pattern based on the energization pattern P determined for each control period T from the first detected temperature detected by the first temperature detection unit ST1 and the second detected temperature detected by the second temperature detection unit ST2. It has a function of controlling energization to the heater H1 and the second heater H2. Here, the control period T is a predetermined unit time in which the energization pattern of the heaters H1 and H2 is set. The control unit 100 generates a first deviation D1 that is the deviation between the first target temperature and the first detected temperature, a second deviation D2 that is the deviation between the second target temperature and the second detected temperature, and a table shown in FIG. The energization pattern P is selected based on the following.

The table shown in FIG. 5 is a table set in advance through experiments, simulations, etc., and is stored in the ROM 113 or RAM 114. Here, the magnitude relationship of the numerical values a to i shown in FIG. 5 is a<b<c<d<e<f<g<i. Further, the magnitude relationship of the numerical values j to r is j<k<l<m<n<o<p<q<r.

The energization pattern P is a pattern indicating execution periods of various energization controls to be executed for each heater H1 and H2 within the control period T. As the energization pattern P, a plurality of types of patterns are set, such as pattern I, pattern II, pattern III, pattern IV, pattern V, and pattern VI. Although FIG. 5 shows some of the energization patterns P out of the plurality of types, there are also other energization patterns P that can be applied to at least one of the heaters H1 and H2 from the beginning to the end of the control period T. Patterns for stopping power supply, etc. are set.

As shown in FIGS. 6 and 7, the energization pattern P includes a first energization pattern P1 for controlling energization to the first heater H1 and a second energization pattern for controlling energization to the second heater H2. P2. Here, FIG. 6 shows the energization patterns P (I to IV) in the column surrounded by the broken line frame X in FIG. Further, FIG. 7 shows the energization patterns P (I to III, V) in the column surrounded by the broken line frame Y in FIG.

In the first energization pattern P1, periods T1, T11 to T13 are selectively set within the control period T, during which a plurality of types of energization control are executed for the first heater H1. Hereinafter, the period T1 will also be referred to as the "first full lighting period T1," the period T11 as the "first starting period T11," the period T12 as the "first ending period T12," and the period T13 as the "first non-lighting period T13."

The first start period T11 is a period during which first start phase control, which will be described later, is executed. The first full lighting period T1 is a period during which first continuous energization control, which will be described later, is executed. The first end period T12 is a period during which first end phase control, which will be described later, is executed. The first light-off period T13 is a period in which power supply to the first heater H1 is stopped. The first full lighting period T1 is set to a longer period as the first deviation D1 is larger. Note that the relationship between the first full lighting period T1 and the first deviation D1 is not limited to the frame X in FIG. 5, but is the same in the vertical columns.

In the second energization pattern P2, periods T2, T21 to T23 are selectively set within the control period T, during which a plurality of types of energization control are executed for the second heater H2. Hereinafter, the period T2 will also be referred to as the "second full lighting period T2," the period T21 as the "second start period T21," the period T22 as the "second end period T22," and the period T23 as the "second light-off period T23."

As shown in FIG. 7, the second start period T21 is a period during which second start phase control, which will be described later, is executed. The second full lighting period T2 is a period during which second continuous energization control, which will be described later, is executed. The second end period T22 is a period during which second end phase control, which will be described later, is executed. The second light-off period T23 is a period in which power supply to the second heater H2 is stopped. As shown in FIG. 7, the second full lighting period T2 is set to a longer period as the second deviation D2 is larger. Note that the relationship between the second full lighting period T2 and the second deviation D2 is not limited to the frame Y in FIG. 5, but is the same in the horizontal columns.

As shown in FIG. 6, pattern I is a pattern in which the first full lighting period T1 and the second full lighting period T2 do not overlap. Specifically, in pattern I, the second full lighting period T2 starts immediately after the first full lighting period T1.

In the first energization pattern P1 of pattern I, a first start period T11, a first full lighting period T1, and a first light-off period T13 are set, and a first end period T12 is not set. In the second energization pattern P2 of pattern I, all the above-mentioned periods T2, T21 to T23 are set.

In the first energization pattern P1 of pattern I, each period T11, T1, T13 is set in the order of the first full lighting period T1 after the first starting period T11, and the first non-lighting period T13 after the first full lighting period T1. has been done. In the second energization pattern P2 of pattern I, the second start period T21 occurs after the second lights-out period T23, the second full lighting period T2 after the second starting period T21, and the second end period T22 after the second full lighting period T2. Periods T23, T21, T2, and T22 are set in this order.

In pattern I, the start time of the first start period T11 and the start time of the second lights-out period T23 coincide with the start time of the control cycle T. In pattern I, the start time of the first full lighting period T1 and the start time of the second start period T21 match. In pattern I, the end point of the first light-off period T13 and the end point of the second end period T22 coincide with the end point of the control cycle T.

That is, the energization pattern P of pattern I corresponds to a prescribed energization pattern in which the first start phase control is started at the start of the control period T, and the second end phase control is ended at the end of the control period T.

Pattern II, like pattern I, is a pattern in which the second full lighting period T2 starts immediately after the first full lighting period T1. Specifically, pattern II is a pattern obtained by removing the second end period T22 from pattern I. In pattern II, the end point of the second full lighting period T2 coincides with the end point of the control cycle T.

Pattern III is a pattern in which the first full on period T1 and the second full on period T2 overlap. Specifically, pattern III is a pattern in which the first end period T12 is added to pattern I. In pattern III, the first end period T12 is set between the first full on period T1 and the first off period T13. In pattern III, the start point of the second full on period T2 is set after the start point of the first full on period T1 and before the end point of the first full on period T1. In pattern III, the end point of the second full on period T2 coincides with the end point of the first end period T12.

Furthermore, in pattern III, as in pattern I, the start time of the first start period T11 coincides with the start time of the control cycle T, and the end time of the second end period T22 coincides with the end time of the control cycle T. We are doing so. Therefore, the energization pattern P of pattern III also corresponds to the above-mentioned prescribed energization pattern.

Pattern IV, like pattern III, is a pattern in which the first full lighting period T1 and the second full lighting period T2 overlap, and is a pattern in which the first full lighting period T1 is set to the period from the start to the end of the control cycle T. It is. Specifically, pattern IV is a pattern obtained by removing the first start period T11, the first light-off period T13, and the second light-off period T23 from pattern I.

In pattern IV, the start time of the first full lighting period T1 and the start time of the second start period T21 coincide with the start time of the control cycle T. In pattern IV, the end point of the first full lighting period T1 and the end point of the second end period T22 coincide with the end point of the control cycle T.

As shown in FIG. 7, pattern V, like pattern III, is a pattern in which the first full lighting period T1 and the second full lighting period T2 overlap, and the second full lighting period T2 ends from the start of the control cycle T. This is the pattern set for the period up to. Specifically, pattern V is a pattern obtained by removing the first light-off period T13, the second start period T21, the second end period T22, and the second light-off period T23 from pattern III.

In pattern V, the start time of the second full lighting period T2 coincides with the start time of the control cycle. In pattern V, the end point of the first end period T12 and the end point of the second full lighting period T2 coincide with the end point of the control cycle T.

Pattern VI is not shown in the figure, but is a pattern in which the first full lighting period T1 and the second full lighting period T2 are set to the period from the start to the end of the control cycle T.

The control unit 100 is capable of performing first continuous energization control, second continuous energization control, and phase control based on the energization pattern P. As shown in FIG. 8A, the first continuous energization control C1 is a control in which the first alternating current A1 is continuously energized to the first heater H1. The second continuous energization control C2 is a control that continuously energizes the second heater H2 with the second alternating current A2. Here, although the waveform shown in FIG. 8(a) is a waveform corresponding to pattern III, individual controls such as the first continuous energization control and the second continuous energization control are performed in the same way in any pattern. , the individual controls will be explained using the waveforms shown in FIG. 8(a).

The peak of the second alternating current A2 is larger than the peak of the first alternating current A1. That is, the peak of the current in the energization in the second continuous energization control C2 is larger than the peak in the current in the energization in the first continuous energization control C1.

Phase control is control in which electricity is applied in a part of the sine wave of alternating current. Specifically, the phase control is a control in which current is applied in a portion less than a half wave of a sine wave (the second half of the half wave). In phase control, the control unit 100 supplies alternating current to the heaters H1 and H2 based on the target phase angle θt.

Here, the phase angle is defined as 0° at the end point of a predetermined half-wave, and 180° at the start point of a predetermined half-wave. In other words, within a given half-wave, the position where the current value is 0 after the absolute value of the current value tends to decrease is defined as a phase angle of 0°, and the phase angle gradually increases from this position toward the starting point of the given half-wave. The range of the phase angle is set to 0 to 180°. Further, the range of phase angle used for control is 0 to 90°.

The control unit 100 performs intermittent energization by changing or fixing the target phase angle θt to a constant value during the phase control execution period. The control unit 100 can execute, as phase control, a first start phase control C11, a first end phase control C12, a second start phase control C21, and a second end phase control C22. ing.

The first starting phase control C11 is a phase control that is performed before the first continuous energization control C1, and is a phase control that energizes the first heater H1 during a part of the sine wave of the first AC current A1. . For example, when executing the first starting phase control C11 in pattern I shown in FIG. 9 or pattern III shown in FIG. 8, the control unit 100 keeps the target phase angle θt constant. That is, when the first start period T11 can only be set to a very short time as in patterns I to III, the target phase angle θt is kept constant. Here, the target phase angle θt in the case of keeping the target phase angle θt constant is set to a value less than 90° and larger than 0°.

Note that when executing the first start phase control C11 in the pattern V shown in FIG. Increase gradually. That is, when the time of the first start period T11 can be set to a sufficiently long time as in pattern V, the target phase angle θt is changed.

Specifically, the control unit 100 gradually increases the target phase angle θt from 0° toward 90° so that the absolute value of the current peak in each half-wave gradually increases from a state where the current value is 0 toward the peak of the first AC current A1. Note that examples of a method for gradually increasing the target phase angle θt include a method for proportionally increasing the target phase angle θt by adding a predetermined amount from 0°, and a method for logarithmically or exponentially increasing the target phase angle θt. In addition, examples of a method for increasing the target phase angle θt by a predetermined amount include a method for dividing a phase angle of 90° by the number of half-waves that fall within the execution period (T11) of the first start phase control C11, and setting the value as the predetermined amount.

The first end phase control C12 is a phase control performed after the first continuous current control C1, and is a phase control in which current is applied to the first heater H1 during part of the sine wave of the first AC current A1. When the control unit 100 executes the first end phase control C12 in pattern III shown in FIG. 8, for example, the control unit 100 gradually reduces the amount of current per half wave of the first AC current A1 by changing the target phase angle θt. In other words, when the time of the first end period T12 can be set to a sufficiently long time as in pattern III, the target phase angle θt is changed.

Specifically, the control unit 100 gradually changes the target phase angle θt from 90° to 0° so that the absolute value of the current peak in each half wave from the peak of the first AC current A1 gradually decreases. Make it smaller. Note that the method of gradually decreasing the target phase angle θt includes a method of decreasing the target phase angle θt proportionally, a method of decreasing the target phase angle θt logarithmically or exponentially, similar to the above-mentioned increasing method. can be mentioned.

Furthermore, when executing the first termination phase control C12 in pattern V shown in FIG. 7, the control unit 100 keeps the target phase angle θt constant. Note that in the first end phase control C12 in pattern V, the target phase angle θt may be changed so that the amount of energization per half wave gradually decreases.

The second start phase control C21 is a phase control performed before the second continuous energization control C2, and is a phase control in which the second heater H2 is energized in a part of the sine wave of the second AC current A2. be. The second starting phase control C21 is the same control as the first starting phase control C11. The control unit 100 changes the target phase angle θt or fixes it to a constant value depending on the length of the second start period T21.

For example, when executing the second start phase control C21 in pattern I shown in FIG. 9 or pattern III shown in FIG. The amount of current per half wave of current A2 is gradually increased. Specifically, the control unit 100 sets the target phase angle θt to 0 so that the absolute value of the current peak in each half wave gradually increases from the state where the current value is 0 to the peak of the second AC current A2. Gradually increase from °. Note that the method for gradually increasing the target phase angle θt may be the same method as the first starting phase control C11.

FIG. 8(b) is an enlarged diagram showing the first alternating current A1, the second alternating current A2, and the combined waveform in the second start period T21. FIG. 8(c) is an enlarged view of the last half wave of the composite waveform of FIG. 8(b). As shown in FIGS. 8(b) and 8(c), in the second start phase control C21, the control unit 100 determines that the composite value A12 of the first alternating current A1 and the second alternating current A2 is the second alternating current The current is applied so that the peak PK of A2 is lower than the peak PK of A2. Specifically, the control unit 100 determines a final phase angle θe at which the current value is the same as the peak PK of the second AC current A2 in the last half wave of the composite value A12, and uses this final phase angle θe as the second starting point. The final target phase angle θt of the time phase control C21 is set. Then, the control unit 100 calculates the target phase angle θt of each half-wave by sequentially subtracting a predetermined amount from the final phase angle θe from the last half-wave to the first half-wave of the second starting phase control C21. Set to .

As shown in FIG. 8(a), the second termination phase control C22 is a phase control performed after the second continuous energization control C2, and is a phase control performed after the second continuous energization control C2, in which a sine wave of the second AC current A2 is applied to the second heater H2. This is phase control in which electricity is applied to a portion of the system. The second end phase control C22 is substantially the same control as the first end phase control C12. The control unit 100 changes the target phase angle θt or fixes it to a constant value depending on the length of the second end period T22.

For example, when executing the second termination phase control C22 in pattern I shown in FIG. 9 or pattern III shown in FIG. The amount of current per half wave of current A2 is gradually reduced. Specifically, the control unit 100 gradually reduces the target phase angle θt from 90° so that the amount of energization per half wave gradually decreases, using a method substantially similar to the first end phase control C12.

Here, the energization patterns P of patterns I and III are the aforementioned prescribed energization patterns. The prescribed energization pattern is the first peak current value β in the first starting phase control C11 and the last peak of the combination of the first AC current A1 and the second AC current A2 at the end of the second ending phase control C22. The current value α is set to match the current value α. In this embodiment, the execution periods of the phase controls C11, C12, C21, and C22 are set so that they do not overlap, so when the second end phase control C22 ends, the energization to the first heater H1 is stopped. Therefore, the first alternating current A1 is zero. Therefore, in the present embodiment, the last peak current value α of the second AC current A2 in the control period T is the composite value of the first AC current A1 and the second AC current A2 at the end of the second end phase control C22. It becomes.

When the first condition expressed by the following formula (1) is satisfied, the control unit 100 starts the second continuous energization control C2 immediately after the first continuous energization control C1 ends, as shown in FIG. do.
T1+T2<T...(1)
T: Control cycle T1: First full lighting period T2: Second full lighting period

More specifically, in this embodiment, the minimum period required to execute the first start phase control C11 is defined as T11 _min , and the condition shown in the following equation (2) is defined as the first condition.
_T11min + T1 + T2 < T ... (2)

In other words, the first condition does not include conditions regarding the first end period T12, the second start period T21, and the second end period T22.

Further, if the first condition is satisfied, the control unit 100 stops the energization after the first continuous energization control C1 without executing the first ending phase control C12. When the first condition is satisfied, the control unit 100 starts the second start-time phase control C21 at the same time as the start of the first continuous energization control C1.

The first condition is satisfied when patterns I and II are selected based on the deviations D1 and D2. In other words, the first condition means that the first and second detected temperatures are at temperatures at which patterns I and II are selected.

As shown in FIG. 8, when the second conditions having the following equations (3) and (4) are satisfied, the control unit 100 controls the second Continuous energization control C2 is started.
T1+T2≧T...(3)
T1>T2...(4)

Specifically, in this embodiment, the minimum period required to execute the first start phase control C11 is set as T11 _min , and the condition expressed by the following equation (4) is set as the second condition.
T11 _min +T1+T2>T...(4)

If the second condition is satisfied and T1<T, the control unit 100 executes the first termination phase control C12 after the first continuous energization control C1. If the second condition is satisfied and T1<T, the control unit 100 stops energizing the first heater H1 after the first end phase control C12 ends. If the second condition is satisfied and T1<T, the control unit 100 executes the second end phase control C22 immediately after the first end phase control C12 ends.

Note that the case where the second condition is satisfied means the case where patterns III and VI are selected based on the respective deviations D1 and D2. In other words, the second condition means that the first detected temperature and the second detected temperature have become temperatures at which patterns III and VI are selected.

Furthermore, the case where the second condition is satisfied and T1<T means the case where pattern III is selected based on the respective deviations D1 and D2. In other words, the case where the second condition is satisfied and T1<T means that the first detected temperature and the second detected temperature have reached the temperature at which pattern III is selected.

Next, the operation of the control section 100 will be explained with reference to the flowchart shown in FIG. When the control unit 100 receives a printing command, it repeatedly executes the process shown in FIG. 10 at a control cycle T until printing is completed.

In the process shown in FIG. 10, the control unit 100 first obtains temperatures from the first temperature detection unit ST1 and the second temperature detection unit ST2 (S1). After step S1, the control unit 100 selects the energization pattern P based on each detected temperature acquired from each temperature detection unit ST1, ST2 and the table of FIG. 5 (S2). Specifically, in step S2, the control unit 100 calculates the first deviation D1 and the second deviation D2 from each detected temperature and the target temperature, and selects the energization pattern P from each deviation D1, D2 and the table.

After step S2, the control unit 100 sets the wave number and target phase angle for each phase control based on each start period T11, T21 and each end period T12, T22 set in the energization pattern P (S3 ). After step S3, the control unit 100 executes energization control based on the energization pattern P (S4), and ends this process.

Next, a specific example of the operation of the control unit 100 will be described.
As shown in FIG. 5, when the deviation conditions are j≦D1<k and d≦D2<e, the control unit 100 selects pattern I as the energization pattern P. As shown in FIG. 6, pattern I includes a first start period T11, a first full lighting period T1, a first lights out period T13, a second lights out period T23, a second starting period T21, a second full lighting period T2, and A second end period T22 is set.

The control unit 100 fixes the target phase angle to a predetermined value for the first start phase control C11 executed during the first start period T11. For the second start phase control C21 executed in the second start period T21 and the second end phase control C22 executed in the second end period T22, the control unit 100 calculates the wave number from the length of each period, and calculates the wave number. Set the target phase angle in each half-wave based on .

Thereafter, the control unit 100 executes energization control based on pattern I, as shown in FIG. Specifically, the control unit 100 first starts the first start phase control C11 while stopping the power supply to the second heater H2. At this time, the control unit 100 keeps the target phase angle constant and executes the first starting phase control C11.

After executing the first starting phase control C11 for the first starting period T11, the control unit 100 ends the first starting phase control C11, and then starts the first continuous energization control C1 and the second starting phase control C21. start at the same time. In addition, in the second start phase control C21, the control unit 100 gradually increases the peak of the current per half wave by gradually increasing the target phase angle. Specifically, the control unit 100 gradually increases the target phase angle so that the combined peak current value of the first alternating current A1 and the second alternating current A2 gradually approaches the peak current value of the second alternating current A2. do.

The control unit 100 executes the first continuous energization control C1 and the second start phase control C21 for a predetermined time (T1, T21), and then ends the first continuous energization control C1 and the second start phase control C21. . After the first continuous energization control C1 and the second starting phase control C21 are completed, the control unit 100 stops energizing the first heater H1 and starts the second continuous energization control C2.

After executing the second continuous current control C2 for the second full lighting period T2, the control unit 100 starts the second end phase control C22. In the second end phase control C22, the control unit 100 gradually reduces the target phase angle, thereby gradually reducing the peak current per half wave. In detail, the control unit 100 gradually reduces the peak current per half wave so that the peak current value α of the last half wave of the second end phase control C22 becomes a predetermined value (the same value as the first peak current value β in the first start phase control C11). This makes it possible to match the peak current value at the end of the current control by the current current pattern P with the first peak current value of the current control by the next current pattern P when the next current pattern P to be selected is one of patterns I to III.

After executing the second termination phase control C22 for the second termination period T22, the control unit 100 selects the next energization pattern P (for example, pattern I) and performs energization control using the selected energization pattern P.

As shown in FIG. 5, when the deviation conditions are o≦D1<p and d≦D2<e, the control unit 100 selects pattern III as the energization pattern P. As shown in FIG. 6, in pattern III, in addition to each period set in pattern I, a first end period T12 is set. For the first end phase control C12 to be executed during the first end period T12, the control unit 100 determines the wave number from the length of the period and sets the target phase angle based on the wave number. Note that other phase controls are set in the same way as when pattern I is selected.

Thereafter, the control unit 100 executes energization control based on pattern III, as shown in FIG. In addition, in the following description, the description of the same operation as in the case of executing the energization control based on pattern I will be omitted.

The control unit 100 ends the second start phase control C21 while the first continuous current control C1 is being executed, and starts the second continuous current control C2. The control unit 100 ends the first continuous current control C1 while the second continuous current control C2 is being executed, and starts the first end phase control C12. In the first end phase control C12, the control unit 100 gradually decreases the target phase angle so that the peak current per half wave gradually decreases toward zero.

The control unit 100 simultaneously ends the first ending phase control C12 and the second continuous energization control C2 after the first ending period T12 has elapsed from the start of the first ending phase control C12. After the first termination phase control C12 and the second continuous energization control C2 are completed, the control unit 100 stops energizing the first heater H1 and starts the second termination phase control C22.

As described above, the following effects can be obtained in this embodiment.
When patterns I and II are selected as the current supply pattern P, the second continuous current supply control C2 is started immediately after the first continuous current supply control C1 is terminated, so that the first continuous current supply control C1 and the second continuous current supply control C2 are performed continuously within the control period T, and one continuous current supply control is performed within the control period T. Therefore, the momentary voltage drop that occurs within the control period T can be limited to one time.

When the first condition is met, the first end phase control C12 is not executed after the first continuous current control C1, so that the peak of the combined current can be suppressed in the second continuous current control C2.

Since the peak of current during energization in the second continuous energization control C2 is made larger than the peak of current in energization in the first continuous energization control C1, it is possible to quickly heat the second regions 81B and 81C of the heating section 81. can.

In the second start phase control C21, energization is performed so that the combined value of the first AC current A1 and the second AC current A2 is equal to or less than the peak of the second AC current A2, so the first continuous energization control C1 The peak of the composite current can be suppressed when the second start phase control C21 and the second start phase control C21 are executed simultaneously.

Since the energization amount per half wave of the second AC current A2 is gradually increased in the second start phase control C21, it is possible to suppress a sudden change in the current flowing through the second heater H2.

In the first end phase control C12 and the second end phase control C22, the amount of current per half wave of alternating current is gradually reduced, so that it is possible to suppress sudden changes in the current flowing through each heater H1, H2. can.

If the energization pattern P is determined to be the prescribed energization pattern (for example, I, III) in both the predetermined control period T and the control period T following the predetermined control period T, then in the predetermined control period T. The final peak current value α of the combination of the first AC current A1 and the second AC current A2 at the end of the second end phase control C22 is the first peak current value α of the synthesis of the first AC current A1 and the second AC current A2 at the end of the second end phase control C22. It matches the peak current value β. Therefore, sudden changes in the current used in the fixing device 8 when switching the energization pattern P can be suppressed.

When the second condition is satisfied and T1<T, the first end phase control C12 is executed after the first continuous energization control C1, so that sudden changes in the current flowing through the first heater H1 can be prevented. Can be suppressed.

Note that the present invention is not limited to the embodiments described above, and can be utilized in various forms as exemplified below. In the following description, controls and the like that are substantially similar to those in the embodiment described above are denoted by the same reference numerals, and the description thereof will be omitted.

In the embodiment described above, the energization pattern P is set so that the execution periods of each phase control do not overlap, but the present invention is not limited to this, and as shown in FIG. 11, for example, in energization control in pattern III, The execution period (T12) of the first end phase control C12 and the execution period (T22) of the second end phase control C22 may overlap.

Specifically, in the energization control in pattern III, the first end phase control C12 may be executed until the end of the control period T. In this case, the control unit 100 generates a value that is the sum of the peak current value α1 of the last half wave in the first end phase control C12 and the peak current value α2 of the last half wave in the second end phase control C22. However, the final target phase angle θt may be set so as to match the first peak current value β in the first start phase control C11, and the second end phase control C22 may be executed.

In the embodiment, the energization pattern P is determined using the table shown in FIG. 5, but the present invention is not limited to this, and for example, the energization pattern may be determined using a function or the like.

In the embodiment, the first region 81A is a region including the central portion in the width direction of the heating section 81, and the second regions 81B and 81C are regions on the end side of the first region 81A of the heating section 81. However, the present invention is not limited thereto, and the first region and the second region may be regions having different positions in the width direction.

In the above embodiment, the amount of current flowing per half-wave of the AC current is gradually reduced in both the first end phase control and the second end phase control, but the present invention is not limited to this, and the amount of current flowing per half-wave of the AC current may be gradually reduced in either the first end phase control or the second end phase control.

In the embodiment, the second start phase control is started simultaneously with the start of the first continuous energization control, but the present invention is not limited to this, and the second start phase control is started while the first continuous energization control is being executed. All you have to do is execute it. Specifically, the second start phase control may be started after the first continuous energization control is started.

The sheet S may be paper such as cardboard, postcard, or thin paper, or may be an OHP sheet.

The developer image forming section is arbitrarily configured. For example, it may be a developer image forming section that exposes a photosensitive drum using an LED head.

In the embodiment described above, a heating roller is used as an example of the heating section, but the present invention is not limited thereto. It may also be a fixing belt sandwiched between the two.

In the embodiment, a halogen lamp is used as an example of the heater, but the present invention is not limited thereto, and the heater may be a solid heating element such as a carbon heater.

In the embodiment, a thermistor is used as an example of the temperature detection section, but the present invention is not limited to this, and any sensor that detects temperature may be used.

In the embodiment, the first temperature detection section ST1 is not in contact with the heating section 81, but the present invention is not limited thereto, and the first temperature detection section may be in contact with the heating section. Further, the second temperature detection section may be made non-contact with the heating section.

In the above embodiment, the present invention is applied to the laser printer 1, but the present invention is not limited to this, and the present invention may be applied to other image forming apparatuses, such as color printers, copying machines, multifunction devices, etc. .

In the embodiment, the phase angle is set so that the phase angle gradually increases from the end point to the start point of a predetermined half wave, but the present invention is not limited to this. The phase angle may be set so that the phase angle gradually increases toward the target. That is, the phase angle at the start point of a predetermined half wave may be defined as 0°, and the phase angle at the end point may be defined as 180°. In this case, if the range of phase angles used for control is 90° to 180°, the increase and decrease of the phase angle in each control may be reversed from the above embodiment.

The elements described in the embodiments and modifications described above may be implemented in any combination.

1 Laser printer 8 Fixing device 81 Heating section 81A First region 81B, 81C Second region 82 Pressure section 100 Control section A1 First alternating current A2 Second alternating current C1 First continuous energization control C2 Second continuous energization control H1 First 1 heater H2 2nd heater P Energization pattern PR Process section S Sheet ST1 1st temperature detection section ST2 2nd temperature detection section T Control period

Claims (11)

a developer image forming section that forms a developer image on the sheet;
a fixing device that fixes the developer image formed by the developer image forming section to a sheet;
comprising a control unit;
The fixing device includes:
a heating section;
a first heater that has an output peak in a first region of the heating section and heats the heating section;
a second heater that has an output peak in a second region different from the first region of the heating section and heats the heating section;
a pressure section that sandwiches the sheet between the heating section;
a first temperature detection section that detects the temperature of at least a portion of the first region;
a second temperature detection section that detects the temperature of at least a portion of the second region;
The control unit includes:
first continuous energization control that continuously energizes the first heater with the first alternating current by energizing the first heater with the entire sine wave of the first alternating current ;
a second continuous energization control that continuously energizes the second heater with a second alternating current by energizing the second heater with the entire sine wave of the second alternating current ;
a second start phase control performed before the second continuous energization control, which energizes the second heater during a part of the sine wave of the second alternating current; is feasible and
The first heater and the second heater are controlled based on the energization pattern determined for each control cycle from the first detected temperature detected by the first temperature detector and the second detected temperature detected by the second temperature detector. controls the energization to the
The control period is T, the period for performing the first continuous energization control is T1, and the period for performing the second continuous energization control is T2,
If the first condition T1+T2<T is satisfied, the second start phase control is executed during the first continuous energization control, and the second start phase control is executed immediately after the first continuous energization control ends. An image forming apparatus characterized by starting two consecutive energization control. 2. The image forming apparatus according to claim 1 , wherein a peak of current in energization in the second continuous energization control is larger than a peak in current in energization in the first continuous energization control. The control unit includes:
Image formation according to claim 1 or 2, characterized in that when the first condition is satisfied, the second start phase control is started simultaneously with the start of the first continuous energization control. Device. The control unit is
a first end phase control that is performed after the first continuous current control, the first end phase control being capable of performing a first end phase control in which current is applied to the first heater during a part of a sine wave of a first AC current;
4. The image forming apparatus according to claim 1, wherein when the first condition is satisfied, after the first continuous current control, current supply is stopped without executing the first end phase control. 5. The image forming apparatus according to claim 1 , wherein the first condition does not include a condition regarding an execution period of the second start phase control. The control unit is characterized in that, in the second start phase control, the control unit energizes so that a composite value of the first alternating current and the second alternating current is equal to or less than the peak of the second alternating current. The image forming apparatus according to any one of claims 1 to 5 . 7. The image forming apparatus according to claim 1 , wherein the control unit, in the second start phase control, gradually increases the amount of current per half wave of the second AC current by changing a phase angle. The control unit is
a first start phase control is executed before the first continuous energization control within the control period , the first start phase control being executed to energize the first heater during a part of a sine wave of a first AC current;
In the case where the first start-up phase control is executed, a period during which the first start-up phase control is executed is defined as T11,
T11+T1+T2<T
8. The image forming apparatus according to claim 1, wherein the first condition is : The control unit includes:
a first termination phase control performed after the first continuous energization control, the first termination phase control in which the first heater is energized during a part of the sine wave of the first alternating current;
A second termination phase control performed after the second continuous energization control, in which the second heater is energized during a part of the sine wave of the second alternating current. It is possible and
From claim 1, wherein in at least one of the first end phase control and the second end phase control, the amount of current per half wave of alternating current is gradually reduced by changing the phase angle. The image forming apparatus according to claim 8 . a developer image forming section that forms a developer image on the sheet;
a fixing device that fixes the developer image formed by the developer image forming section to a sheet;
comprising a control unit;
The fixing device
a heating section;
a first heater that has an output peak in a first region of the heating section and heats the heating section;
a second heater that has an output peak in a second region different from the first region of the heating section and heats the heating section;
a pressure section that sandwiches the sheet between the heating section;
a first temperature detection section that detects the temperature of at least a portion of the first region;
a second temperature detection section that detects the temperature of at least a portion of the second region;
The control section,
first continuous energization control that continuously energizes the first heater with the first alternating current by energizing the first heater with the entire sine wave of the first alternating current ;
a second continuous energization control that continuously energizes the second heater with a second alternating current by energizing the second heater with the entire sine wave of the second alternating current ;
a second start phase control performed before the second continuous energization control, which energizes the second heater during a part of the sine wave of the second alternating current; A control method by the control unit in an image forming apparatus that is executable, the method comprising:
The first heater and the second heater are controlled based on the energization pattern determined for each control cycle from the first detected temperature detected by the first temperature detector and the second detected temperature detected by the second temperature detector. controls the energization to the
The control period is T, the period for performing the first continuous energization control is T1, and the period for performing the second continuous energization control is T2,
If the first condition T1+T2<T is satisfied, the second start phase control is executed during the first continuous energization control, and the second start phase control is executed immediately after the first continuous energization control ends. A control method characterized by starting two consecutive energization control. a developer image forming section that forms a developer image on the sheet;
a fixing device that fixes the developer image formed by the developer image forming section to a sheet;
comprising a control unit;
The fixing device
a heating section;
a first heater that has an output peak in a first region of the heating section and heats the heating section;
a second heater that has an output peak in a second region different from the first region of the heating section and heats the heating section;
a pressure section that sandwiches the sheet between the heating section;
a first temperature detection section that detects the temperature of at least a portion of the first region;
A program for operating the control unit in an image forming apparatus including a second temperature detection unit that detects a temperature of at least a portion of the second area, the program comprising:
The control section,
means for executing a first continuous energization control in which the first heater is continuously energized with the first alternating current by energizing the first heater in the entire sine wave of the first alternating current ;
means for executing second continuous energization control that continuously energizes the second heater with the second alternating current by energizing the second heater with the entire sine wave of the second alternating current ;
A second start phase control performed before the second continuous energization control, in which the second heater is energized during a part of the sine wave of the second alternating current. means and
The first heater and the second heater are controlled based on the energization pattern determined for each control cycle from the first detected temperature detected by the first temperature detector and the second detected temperature detected by the second temperature detector. means for controlling energization to;
The control period is T, the period for performing the first continuous energization control is T1, and the period for performing the second continuous energization control is T2,
If the first condition T1+T2<T is satisfied, the second start phase control is executed during the first continuous energization control, and the second start phase control is executed immediately after the first continuous energization control ends. A program characterized in that it functions as a means for starting two-continuous energization control.

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