JP7187946B2 - Heater control device and image forming apparatus - Google Patents

Description

The present invention relates to controlling multiple heaters.

2. Description of the Related Art Conventionally, there is an image forming apparatus provided with a plurality of heaters as a heat source for a heat fixing device that heats a sheet on which a toner image is formed (for example, Japanese Laid-Open Patent Publication No. 2002-100000). The image forming apparatus disclosed in Patent Document 1 repeatedly controls power supply to a plurality of heaters at a control cycle. The image forming apparatus performs control so that periods during which power is supplied to each of the plurality of heaters do not overlap within each control cycle. For example, the image forming apparatus supplies power to heaters with high power consumption for a predetermined power supply time from the beginning of the control cycle, and supplies power to heaters with low power consumption from the end of the control cycle for the predetermined power supply time. Power is supplied until the end of the control period from the point at which the time is subtracted.

JP 2009-069623 A

In the image forming apparatus described above, the power supply order and the power supply time for supplying power to each heater are set by paying attention to the power consumption of each heater. Therefore, for example, even if the heater to which power supply is started first reaches the target temperature, power continues to be supplied until the end of the power supply time, and there is a risk that the temperature will rise. Further, the heater to which power is supplied later is not supplied with power until the end of the power supply time during which power supply is started first, and there is a risk that the temperature of the heater may drop. Therefore, the temperature ripple of each heater could increase.

SUMMARY OF THE INVENTION An object of the present application is to provide a heater control device and an image forming apparatus that can suppress the temperature ripple of the heater.

In this specification, a first heater supplied with power from an AC power supply, a second heater supplied with power from the AC power supply, and a first temperature which is a temperature that varies according to the heat generation state of the first heater and a second temperature, which is a temperature that fluctuates according to the heat generation state of the second heater; A first ON period, which is a period in which power is supplied to one heater, is controlled, and power is supplied from the AC power supply to the second heater in the predetermined control period based on the detected second temperature. a control device for controlling a second ON period that is a period, wherein the control device starts one ON period of the first ON period and the second ON period, and then starts the other ON period. power is supplied to the heater, of the first heater and the second heater, to which power has been supplied in response to the first temperature or the second temperature reaching the control temperature during the period until the and start supplying power to the heater to which power supply has been stopped.

Further, the contents of the present disclosure are effective not only when implemented as a heater control device, but also when implemented as an image forming apparatus in which the first and second heaters are heated by the heater control device.

According to the heater control device and the like according to the present application, the temperature ripple of the heater can be suppressed.

1 is a cross-sectional view of a printer according to this embodiment; FIG. It is a circuit diagram of a heater control device. 4 is a time chart of signals related to control of energization of heaters; 4 is a flowchart showing details of a heater control process; 4 is a flowchart showing details of a heater control process; It is a figure which shows the control pattern of a table. It is a figure which shows the control pattern of a table. FIG. 5 is a diagram showing changes in temperature in control between the present embodiment and comparative examples 1 and 2; FIG. 5 is a diagram showing changes in temperature in control between the present embodiment and comparative examples 1 and 2; FIG. 10 is a diagram showing changes in temperature in heater control processing of another example; FIG. 10 is a diagram showing changes in temperature in heater control processing of another example;

(1. Configuration of Printer)
An embodiment of the present application will be described below with reference to the drawings. FIG. 1 shows a cross-sectional view of a printer 1 that is an embodiment of an image forming apparatus according to the present application. The printer 1 is a monochrome laser printer, and includes a main body casing 2, a tray 4 for accommodating sheets 3 (paper, OHP sheets, etc.), an image forming section 5, a fixing device 7, and the like. The printer 1 forms a toner image in the image forming section 5 on the sheet 3 supplied from the tray 4 arranged in the lower part of the main body casing 2 . The printer 1 heats the toner image formed on the sheet 3 by the fixing device 7 to fix it on the sheet 3 . Discharge. In the following description, as shown in FIG. 1, the right side of the paper surface of FIG. Description will be made using the directions of front and back, left and right, and up and down.

The image forming section 5 has a scanner section 11, a developing cartridge 13, a photosensitive drum 17, a charger 18, a transfer roller 19, and the like. The scanner unit 11 is arranged in the upper part of the main body casing 2, and directs laser light emitted from a laser light emitting unit (not shown) to a photosensitive drum 17 via a polygon mirror, a reflecting mirror, a lens, etc. (not shown). The surface is illuminated in a fast scan.

The developer cartridge 13 is detachable from the main body of the printer 1, and contains toner therein. The developing cartridge 13 also has a developing roller 21 and a supply roller 23 . The developing roller 21 and the supply roller 23 are provided facing each other in the front-rear direction. Further, the developing roller 21 is arranged facing the photosensitive drum 17 in the front-rear direction. The toner in the developing cartridge 13 is supplied to the developing roller 21 by the rotation of the supply roller 23 and carried by the developing roller 21 .

A charger 18 is arranged above the rear side of the photosensitive drum 17 with a space therebetween. A transfer roller 19 is arranged below the photosensitive drum 17 so as to face the photosensitive drum 17 . The surface of the photosensitive drum 17 is uniformly charged, for example, positively by the charger 18 while rotating. Then, an electrostatic latent image is formed on the surface of the photosensitive drum 17 by laser light from the scanner section 11 . After that, the toner carried on the developing roller 21 rotating in contact with the photosensitive drum 17 is supplied to the electrostatic latent image on the surface of the photosensitive drum 17 and carried thereon, whereby the toner on the surface of the photosensitive drum 17 is A toner image is formed on the The formed toner image is transferred to the sheet 3 by a transfer bias applied to the transfer roller 19 while the sheet 3 is passed between the photosensitive drum 17 and the transfer roller 19 .

(2. Configuration of heater control device)
The fixing device 7 is arranged on the downstream side (rear side) of the sheet 3 conveying direction with respect to the image forming section 5 , and includes a fixing roller 27 , a pressure roller 29 that presses the fixing roller 27 , and a heater that heats the fixing roller 27 . 31, 32 and so on. FIG. 2 shows a circuit diagram of a heater control device 30 that controls power supplied to the heaters 31 and 32. As shown in FIG. The heaters 31 and 32 are, for example, halogen heaters. Note that the heater of the present application is not limited to the halogen heater, and may be other heat-generating elements, devices, and the like.

The heaters 31 and 32 are energized and controlled by a control device 33 of the heater control device 30 . The heater 31 is arranged inside the fixing roller 27 , for example, near the center of the fixing roller 27 in the axial direction. Further, the heaters 32 are arranged inside the fixing roller 27 at both ends in the axial direction of the fixing roller 27, for example. As a result, for example, for a sheet 3 having a large size, the fixing roller 27 is heated not only by the heater 31 but also by the heater 32 , so that the print fixability at the edge of the sheet 3 can be improved. Note that the arrangement of the heaters 31 and 32 described above is an example. The fixing roller 27 rotates in response to driving of an electric motor (not shown) controlled by the control device 33 of the heater control device 30 , heats the toner transferred to the sheet 3 , and fixes the toner onto the sheet 3 . , apply a conveying force to the sheet 3 . On the other hand, the pressure roller 29 is driven to rotate while pressing the sheet 3 toward the fixing roller 27 side.

As shown in FIG. 2, the heater control device 30 includes an AC/DC converter 34, a DC/DC converter 35, a zero-cross detection circuit 36, a current sensor 37, a relay 42, in addition to the heaters 31 and 32 and the control device 33 described above. , heater control circuits 43 and 44, and the like. The control device 33 is composed of, for example, a computer having a CPU as a main body, and controls other devices by executing programs with the CPU. Note that the control device 33 may be configured by dedicated hardware such as ASIC, for example. Alternatively, the control device 33 may be configured to operate using both software processing and hardware processing, for example. The control device 33 also has a memory 33A for storing information relating to control and processing. The memory 33A has, for example, RAM, ROM, flash memory, and the like. The memory 33A stores a control program PG for executing heater control processing (see FIGS. 4 and 5), which will be described later, and a table TB to be referred to when executing the control program PG. In the following description, the names of the control devices 33 and the like that execute the control program PG may be indicated by device names. For example, the description that "the control device 33 performs control based on the temperatures of the heaters 31 and 32" means that "the control device 33 controls the temperature of the heaters 31 and 32 by executing the control program PG with the CPU." "execute control based on The memory 33A also stores target temperatures and required temperatures of the heaters 31 and 32 used in the heater control process.

The heaters 31 and 32 generate heat when the AC power supply 101 is energized. The heater 32 is connected in parallel with the heater 31 . A temperature sensor 31A is provided near the heater 31 . The temperature sensor 31A outputs the value of the detected temperature of the heater 31 (hereinafter sometimes referred to as "first temperature") to the controller 33 as a temperature detection signal Sa1. A temperature sensor 32A is provided near the heater 32 . The temperature sensor 32A outputs the value of the detected temperature of the heater 32 (hereinafter sometimes referred to as "second temperature") to the controller 33 as a temperature detection signal Sa2. Thereby, the control device 33 performs control based on the temperatures of the heaters 31 and 32 . The temperature sensors 31A and 32A are composed of, for example, thermistors, thermocouples, and the like.

The AC power supply 101 is, for example, a commercial power supply that supplies an AC voltage of 100V. The printer 1 has a power cord connectable to the AC power supply 101 . The AC/DC converter 34 converts, for example, a 100V AC voltage supplied from the AC power supply 101 into a 24V DC voltage, and outputs it to the DC/DC converter 35 and other devices. The DC/DC converter 35 converts the DC voltage of 24V into a DC voltage of 3.3V and supplies it to the control device 33 and the like. A current sensor 37 is connected in series with the heaters 31 and 32 . The current sensor 37 outputs to the control device 33 a current value signal Sig1 that is a signal corresponding to the magnitude of the current flowing from the AC power supply 101 to the heater 31 and/or the current flowing to the heater 32 . Thereby, the control device 33 can perform control according to the magnitude of the current flowing through the heater 31 and the like. Relay 42 switches whether to electrically connect AC power supply 101 and heaters 31 and 32 according to relay control signal Sig<b>2 output from control device 33 .

Zero-cross detection circuit 36 outputs zero-cross signal Sig3, which is a pulse signal, to control device 33 when detecting zero-cross timing ZC (see FIG. 3) of AC power supply 101 . Specifically, the zero-cross detection circuit 36 has a diode bridge 51, a photocoupler PH21, resistors R21 and R22, a transistor Tr1 which is an NPN bipolar transistor, and the like. The power of the AC power supply 101 is full-wave rectified by the diode bridge 51 and applied to the LED of the photocoupler PH21. A collector terminal of the phototransistor of the photocoupler PH21 is connected to a 24V DC power supply via a resistor R21, and an emitter terminal is grounded. A base terminal of the transistor Tr1 is connected through a resistor R22 to a connection point between the resistor R21 and the phototransistor of the photocoupler PH21. A collector terminal of the transistor Tr1 is connected to the control device 33 . The emitter terminal of transistor Tr1 is grounded. The wiring connecting the collector terminal of the transistor Tr1 and the control device 33 is pulled up to the power supply voltage inside the control device 33 .

FIG. 3 shows a time chart of signals relating to control of energization to the heater. In addition, in FIG. 3, only the energized state of the heater 31 is illustrated. The LED of the photocoupler PH21 included in the zero-cross detection circuit 36 of FIG. 2 emits light with an amount of light emission corresponding to the applied power. For example, when the voltage value of the input voltage V (see FIG. 3) of the AC power supply 101 decreases, the voltage applied to the LED of the photocoupler PH21 decreases and the ON resistance of the phototransistor of the photocoupler PH21 increases. As a result, the base voltage of transistor Tr1 increases. When the base voltage of the transistor Tr1 exceeds the threshold (for example, when the absolute value of the input voltage V shown in FIG. 3 becomes equal to or less than the threshold Vt), the transistor Tr1 is turned on and the zero cross signal Sig3 becomes low level. Therefore, as shown in FIG. 3, the zero-cross signal Sig3 output by the zero-cross detection circuit 36 is low for a predetermined time Tw1 (time during which the absolute value of the input voltage V is equal to or less than the threshold Vt) before and after the zero-cross timing ZC of the input voltage V. level pulse signal. The control device 33 can specify the zero-cross timing ZC of the input voltage V, for example, based on the low-level pulse width (predetermined time Tw1) of the input zero-cross signal Sig3.

As shown in FIG. 2, the heater control circuit 43 has a triac TA1, a phototriac coupler PH1, resistors R1 and R2, and the like. The heater control circuit 44 has a triac TA11, a phototriac coupler PH11, resistors R11 and R12, and the like. The triac TA1 has a T2 terminal connected to one pole of the AC power supply 101 and a T1 terminal connected to the other pole of the AC power supply 101 via the heater 31 and the relay 42 . The gate terminal of the triac TA1 and the T1 terminal are connected via a resistor R1. The T2 terminal of the triac TA1 and the gate terminal are connected via the triac of the phototriac coupler PH1 and the resistor R2. A heater control signal Sig4 output from the control device 33 is input to the anode terminal of the LED of the phototriac coupler PH1. A cathode terminal of the LED of the phototriac coupler PH1 is grounded. The controller 33 controls energization of the heater 31 by a heater control signal Sig4. The heater control circuit 44 has the same configuration as the heater control circuit 43 . A heater control signal Sig5 output from the control device 33 is input to the anode terminal of the LED of the phototriac coupler PH11 of the heater control circuit 44 . The controller 33 controls energization of the heater 32 by the heater control signal Sig5. That is, the controller 33 can control the heater 31 and the heater 32 separately.

For example, as shown in FIG. 3, when energizing the heater 31, the controller 33 switches the heater control signal Sig4 from low level to high level, and switches from high level to low level after a predetermined time has elapsed. That is, the controller 33 outputs a heater control signal Sig4, which is a pulse signal with a predetermined pulse width, to the heater control circuit 43. FIG. As a result, the triac TA1 is turned on and the heater 31 is energized. As shown in FIG. 3, the heater voltage Vh (see FIG. 3) is supplied to the heater 31 only for the time that the heater control signal Sig4 is maintained at the high level, for example. When the heater control signal Sig4 is set to low level, the triac TA1 is turned off at the first zero cross timing ZC after the heater control signal Sig4 is set to low level, and the heater 31 is de-energized. Further, the control device 33 switches the energization state of the heater 32 by switching the signal level (high level or low level) of the heater control signal Sig5, similarly to the heater 31 .

In the following description, the period during which power is supplied to the heater 31 after the control device 33 outputs the high-level heater control signal Sig4 is referred to as an ON period Ton. Similarly, the period during which power is supplied to the heater 32 after the controller 33 outputs the high-level heater control signal Sig5 is referred to as an ON period Ton. When the on-period Ton of the heater 31 and the heater 32 are separately described, the on-period Ton of the heater 31 will be referred to as the on-period Ton1, and the on-period Ton of the heater 32 will be referred to as the on-period Ton2. . As described above, even if the heater control signal Sig4 is set to low level, the triac TA1 is not turned off until the first zero cross timing ZC after the heater control signal Sig4 is set to low level, and the heater 31 is energized. Since such a period is in an energized state in which electric power is supplied to the heater 31, it can be considered as an ON period Ton. Also, a period during which power is not supplied to both the heaters 31 and 32, that is, a period corresponding to neither of the on-periods Ton1 and Ton2 will be referred to as an off-period Toff.

In the example shown in FIG. 3, the control device 33 keeps the heater control signal Sig4 at a high level and continuously applies the heater voltage Vh to the heater 31 during the ON period Ton. However, the controller 33 may perform phase control and wave number control on the sinusoidal heater voltage Vh during the ON period Ton to intermittently apply the heater voltage Vh to the heater 31 . The phase control referred to here means, for example, that the power supply to the heater 31 in the half cycle of the input voltage V of the AC power supply 101 is performed at the timing after a predetermined time has elapsed from the zero cross timing ZC at the start of the half cycle and the phase of the input voltage V. This control is started at a timing corresponding to the angle and is performed until the zero cross timing ZC at the end of the half cycle. The wave number control increases or decreases the number of half cycles (wave number) in which power is supplied to the heater 31 in the half cycle of the input voltage V from the zero cross timing ZC at the start of the half cycle to the zero cross timing ZC at the end of the half cycle. It is a control that changes Therefore, the controller 33 may intermittently output the heater control signal Sig4 (for example, a pulse signal with a pulse width shorter than half the cycle of the input voltage V) during the ON period Ton based on the zero-cross signal Sig3. . As a result, heater voltage Vh is applied to heater 31 with a specific phase and wave number. That is, the on-period in the present application is not limited to the period in which the heater voltage Vh is continuously applied to the heaters 31 and 32, and is not limited to the period during which the heater voltage Vh is temporarily stopped. Any period for the purpose of applying the heater voltage Vh may be used.

Further, the control device 33 of the present embodiment controls the ON period Ton and the OFF period Toff of the heaters 31 and 32 in a predetermined control cycle. As shown in FIG. 3, the control device 33 sets the control cycle Tc, for example, with the zero-cross timing ZC of the input voltage V as a starting point. The length of one cycle of the control cycle Tc is not particularly limited, but can be set to a value of several hundred milliseconds to several seconds, for example. Also, the length of one cycle of the control cycle Tc is appropriately changed according to the resistance values of the heaters 31 and 32, the voltage value of the heater voltage Vh applied to the heater 31 and the like, and the like.

The control device 33 may change the length of the control period Tc according to the operating state of the printer 1, for example. Here, the operating state is, for example, a state in which the heaters 31 and 32 are warmed when the printer 1 is started, and a state in which the image forming section 5 executes print processing. Alternatively, the operating state may be a standby state in which the temperatures of the heaters 31 and 32 are maintained at a constant temperature when temporarily waiting until the next print instruction is received after completing the printing process. The control device 33 may change the length of the control period Tc according to such an operating state.

In addition, the control device 33 controls the ON periods Ton of the heaters 31 and 32 so as not to overlap as much as possible in the control period Tc. As shown in FIG. 2, the memory 33A of the control device 33 stores a control pattern CP (see FIGS. 6 and 7) for controlling the ON period Ton1 of the heater 31 and the ON period Ton2 of the heater 32, as will be described later. ) is stored. The control device 33 selects a control pattern CP from this table TB, and controls the ON periods Ton1 and Ton2 within the control period Tc based on the selected control pattern CP. For example, the control device 33 compares the target temperature set in each operating state with the temperatures of the heaters 31 and 32 detected based on the temperature detection signals Sa1 and Sa2, and selects a control pattern CP from among the control patterns CP included in the table TB. Select an appropriate control pattern CP.

(3. Heater control processing)
Next, the details of the heater control process executed by the control device 33 will be described. 4 and 5 are flowcharts showing the details of the heater control process. 6 and 7 are diagrams showing control patterns CP of the table TB. In the following description, the temperature of heater 31 detected by temperature sensor 31A is referred to as temperature TR1, and the temperature of heater 32 detected by temperature sensor 32A is referred to as temperature TR2. Further, the target temperature of the heater 31 will be referred to as a target temperature T1, and the target temperature of the heater 32 will be referred to as a target temperature T2.

For example, when receiving a print instruction, the control device 33 starts heater control processing shown in FIGS. 4 and 5 . The control device 33 executes the heater control process, for example, by executing the control program PG stored in the memory 33A with the CPU. Note that the timing of starting the heater control process is not limited to when a print instruction is received, and may be other times when energization of the heaters 31 and 32 is controlled. For example, the control device 33 may execute the heater control process of FIGS. 4 and 5 when the printer 1 is powered on and the system is activated to heat the heater 31 and the like. Alternatively, the control device 33 executes the heater control process of FIGS. 4 and 5 in a standby state in which the temperature of the heater 31 or the like is maintained at a constant temperature until the next print instruction is received because the print instruction has not been received for a certain period of time. You can

When the heater control process is started, the control device 33 detects the temperature TR1 of the heater 31 based on the temperature detection signal Sa1 of the temperature sensor 31A in step 11 of FIG. 4 (hereinafter simply referred to as "S"). . Further, the control device 33 detects the temperature TR2 of the heater 32 based on the temperature detection signal Sa2 of the temperature sensor 32A (S11).

Next, the control device 33 selects a control pattern CP from the table TB read from the memory 33A based on the temperatures TR1 and TR2 detected in S11 (S13). As shown in FIGS. 6 and 7, a plurality of control patterns CP are set in the table TB. The leftmost columns in FIGS. 6 and 7 show the temperature difference between the target temperature T1 and the temperature TR1. Also, the top rows of FIGS. 6 and 7 show the temperature difference between the target temperature T2 and the temperature TR2. In the following description, as shown in FIGS. 6 and 7, for example, a control pattern CP in which rows of CPX and columns of CPY intersect will be referred to as a control pattern CPXY using the CP number. If it is the control pattern CP in the second row (CP1) and the third column (CP2), it will be referred to as a control pattern CP12. When the control patterns CP00 to CP98 are collectively described, they will be referred to as the control pattern CP.

In FIGS. 6 and 7, as an example, a total of 90 control patterns CP of 10 rows and 9 columns are illustrated. A hatched square in each control pattern CP indicates the ON period Ton1 of the heater 31 . A dotted square indicates the ON period Ton2 of the heater 32 . Further, the horizontal width of the frame of each control pattern CP, that is, the width of each column indicates one period of the control period Tc. Therefore, the horizontal width of the hatched or dotted squares shown in the frame of the control pattern CP indicates the respective lengths of the on-periods Ton1 and Ton2.

A white square indicates the soft start period Ts that is set first of the on-periods Ton1 and Ton2. The soft start period Ts referred to here is a period in which the application time of the heater voltage Vh is gradually increased by, for example, phase control to increase the duty ratio of the heater control signal Sig4 and the heater control signal Sig5 stepwise. is. As a result, the inrush currents flowing through the heaters 31 and 32 can be reduced, and voltage fluctuations at the start of the on-periods Ton1 and Ton2 can be suppressed. Note that the control pattern CP may not have the soft start period Ts. A period that does not correspond to any of the soft start period Ts, the ON period Ton1, and the ON period Ton2 is an OFF period Toff in which the energization of both the heaters 31 and 32 is stopped.

In S13, the control device 33 specifies a row for selecting the control pattern CP from each row of the table TB shown in FIGS. 6 and 7 based on the temperature difference between the temperature TR1 and the target temperature T1. As shown in FIGS. 6 and 7, each row of the table TB corresponds to the temperature difference between the temperature TR1 and the target temperature T1. A control pattern CP is set in the first row (CP0 row) when the temperature TR1 is equal to or higher than the target temperature T1. In the second and subsequent rows (rows CP1 to CP9), control patterns CP are set in which the temperature TR1 decreases by 1° C. from the target temperature T1 in order from top to bottom.

Similarly, each column of table TB corresponds to the temperature difference between temperature TR2 and target temperature T2. A control pattern CP is set in the first column (column of CP0) when the temperature TR2 is equal to or higher than the target temperature T2. Further, in the second and subsequent columns (columns CP1 to CP8), control patterns CP are set in which the temperature TR2 decreases by 1° C. from the target temperature T2 in order from left to right.

For example, when the control device 33 determines that the temperature TR1 is equal to or higher than the target temperature T1, it specifies the first line (the line of CP0) as the line for selecting the control pattern CP. When the temperature TR1 is equal to or higher than the target temperature T1, there is no need to heat the heater 31 further, so the ON period Ton1 is not set in the control patterns CP00 to CP08 of the first row.

Further, for example, when the temperature TR1 is lower than the target temperature T1 by 1° C., the control device 33 specifies the second line (the line of CP1) as the line for selecting the control pattern CP. Further, when the temperature TR1 is lower than the target temperature T1 by 9° C. or more, the control device 33 specifies the 10th row as the row for selecting the control pattern CP. The temperature TR1 decreases from top to bottom in each row of the table TB, and the temperature difference between the temperature TR1 and the target temperature T1 increases. On the other hand, the on-period Ton1 of the heater 31 becomes longer from the top to the bottom of the table TB in proportion to the increase in the temperature difference.

Similarly, control device 33 specifies a column for selecting control pattern CP from each column of table TB based on the temperature difference between temperature TR2 and target temperature T2. As shown in FIGS. 6 and 7, in each column of the table TB, the temperature TR2 decreases from left to right, and the temperature difference between the temperature TR2 and the target temperature T2 increases. The ON period Ton2 of the heater 32 increases from left to right on the table TB.

In S13 of FIG. 4, for example, when the temperature TR1 is 2° C. lower than the target temperature T1 and the temperature TR2 is 3° C. lower than the target temperature T2, the control device 33 selects the control pattern CP23 in the third row and fourth column. As a result, the control device 33 can select a control pattern CP with a longer ON period Ton as the temperature difference between the actual temperature of the heater and the target temperature increases. In other words, the control device 33 of the present embodiment lengthens the ON period Ton1 according to an increase in the temperature difference obtained by subtracting the temperature TR1 from the target temperature T1 (hereinafter sometimes referred to as the first difference). Further, the control device 33 lengthens the ON period Ton2 in accordance with an increase in the temperature difference obtained by subtracting the temperature TR2 from the target temperature T2 (hereinafter sometimes referred to as the second difference). As described above, the term "temperature difference from the target temperature" is used in the present application to have the same meaning as "the difference obtained by subtracting the detected temperature from the target temperature".

In S15 following S13, the control device 33 determines whether or not the control pattern CP selected in S13 is a control pattern CP in which the ON period Ton1 is started before the ON period Ton2, that is, the heater 31 is turned on first. to judge whether

Here, as shown in FIGS. 6 and 7, all of the control patterns CP included in the table TB of the present embodiment are such that, of the on-periods Ton1 and Ton2, the short-period on-periods are preceded by the long-period on-periods. A period is set to start. In other words, all of the control patterns CP included in the table TB are set so that the ON period Ton having a large duty ratio starts before the ON period Ton having a small duty ratio with respect to the control cycle Tc. there is Specifically, the ratio of the ON period Ton1 to the control period Tc is defined as the duty ratio DT1. Also, the ratio of the ON period Ton2 to the control period Tc is defined as a duty ratio DT2. The ON period Ton1 of the control pattern CP shown in FIGS. 6 and 7 increases from top to bottom of the table TB. Therefore, the ratio of the duty ratio DT1 increases from the top to the bottom of the table TB. Similarly, the ON period Ton2 of each control pattern CP increases from left to right in the table TB. Therefore, the ratio of the duty ratio DT2 increases from left to right in the table TB.

In the control pattern CP of the table TB shown in FIGS. 6 and 7, for example, the duty ratio increases by 10% each time the detected temperature is 1° C. lower than the target temperature. The duty ratio DT1 of each of the control patterns CP00, CP10, CP20, . . . CP90 increases from 0%, 10%, 20%, . Similarly, the duty ratio DT2 of each of the control patterns CP00, CP01, CP02, .

For example, in the control pattern CP21 (third row and second column), the duty ratio DT1 is 20% and the duty ratio DT2 is 10%. In this case, the duty ratio DT1 is larger than the duty ratio DT2, and the ON period Ton1 is longer than the ON period Ton2. Therefore, the ON period Ton1 is set to start before the shorter ON period Ton2. The ON period Ton1 of the control pattern CP21 is a period that starts continuously at the end of the first soft start period Ts of the control period Tc. Also, the on-period Ton2 of the control pattern CP21 is a period that starts continuously after the end of the on-period Ton1.

On the other hand, for example, in the control pattern CP13 (second row and fourth column name), the duty ratio DT1 is 10% and the duty ratio DT2 is 30%. In this case, the duty ratio DT2 is larger than the duty ratio DT1. Therefore, the ON period Ton2 is set to start before the shorter ON period Ton1. The ON period Ton2 of the control pattern CP13 is a period that starts continuously at the end of the first soft start period Ts of the control period Tc. Also, the ON period Ton1 of the control pattern CP13 is a period that starts continuously at the end of the ON period Ton2.

Further, in each control pattern CP of the table TB of the present embodiment, for example, like the control pattern CP11, when the duty ratio DT1 and the duty ratio DT2 are the same ratio (for example, 10%), that is, the ON period When Ton1 and Ton2 have the same length, the ON period Ton1 is set to start earlier than the ON period Ton2. Each control pattern CP described above is an example. For example, the control pattern CP may be a control pattern in which a shorter ON period Ton starts before a longer ON period Ton. Also, the ON period Ton1 and the ON period Ton2 may be discontinuous periods with an OFF period Toff interposed therebetween, instead of continuous periods. Also, the on-period Ton1 and the on-period Ton2 may have overlapping periods that overlap each other.

As described above, the control device 33 can use the table TB to select the control pattern CP, so that the ON period Ton, which has a long time, that has a large duty ratio, can be started first. The controller 33 of the present embodiment performs control to lengthen the ON period Ton as the temperature difference from the target temperature increases. In other words, of the heaters 31 and 32, the ON period Ton of the heater having a large temperature difference from the target temperature is lengthened. As a result, the heater with the longer ON period Ton is energized first within the control cycle Tc.

Returning to S15 of FIG. 4, in S15, when the control device 33 determines that the control pattern CP selected in S13 is the control pattern CP that turns on the heater 31 first (S15: YES), S17 and subsequent steps are executed. Based on the control pattern CP, the control device 33 first controls the heater control signal Sig4 to turn on the heater 31 (S17), and then executes the determination process of S19. In S19, the control device 33 continues to energize the heater 31 until the condition that the temperature TR1 of the heater 31 rises to the target temperature T1 or the condition that the ON period Ton1 ends is satisfied (S19: NO). Therefore, the controller 33 monitors the temperature of the heater 31 during the ON period Ton1.

When one of the above two conditions is satisfied (S19: YES), the controller 33 turns off the heater 31 and turns on the heater 32 (S21). Therefore, the controller 33 turns off the heater 31 and turns on the heater 32 when the temperature TR1 of the heater 31 that was turned on earlier is increased to the target temperature T1. If the temperature TR1 does not rise to the target temperature T1, the control device 33 continues to energize the heater 31 until the end of the ON period Ton1, turns off the heater 31, and turns on the heater 32. FIG. It should be noted that the control device 33 sets the soft start period Ts before the ON period Ton1, and when executing the soft start, starts the soft start period Ts before the temperature TR1 of the heater 31 rises to the target temperature T1. (See FIG. 8).

Next, in S23, similarly to S19, the controller 33 controls the heater 32 until the condition that the temperature TR2 of the heater 32 rises to the target temperature T2 or the condition that the ON period Ton2 ends is satisfied (S23: NO). continue to energize the Therefore, the controller 33 monitors the temperature of the heater 32 during the ON period Ton2.

When one of the above two conditions is met (S23: YES), the controller 33 turns off the heater 32 (S25 in FIG. 5). Therefore, the control device 33 turns off the heater 32 when the temperature TR2 of the heater 32 turned on later is increased to the target temperature T2. Further, when the temperature TR2 does not rise to the target temperature T2, the control device 33 continues to energize the heater 32 until the end of the ON period Ton2 and turns off the heater 32 .

Next, in S27, the control device 33 turns on the heater 31 again if the temperature TR1 of the heater 31 that was previously turned on in S17 and turned off in S21 falls below the target temperature T1 and the control period Tc has not ended. . The control device 33 continues to energize the heater 31 until the condition for increasing the temperature TR1 to the target temperature T1 or the condition for ending the control period Tc is satisfied. Note that, when the temperature TR1 is raised to the target temperature T1, the control device 33 may turn off the heater 31 and wait until the end of the control period Tc. Alternatively, the control device 33 may repeat the same process of warming the heater 32 to the target temperature T2. Also, the reference temperature for monitoring the decrease in the temperature TR1 of the heater 31 in S27 is not limited to the target temperature T1, and may be, for example, a temperature (an example of a predetermined temperature) that is lower than the target temperature T1 by a predetermined temperature. In this case, the control device 33 turns on the heater 31 again when the temperature TR1 is lower than the target temperature T1 by a predetermined temperature.

Further, in S27, if the temperature TR1 of the heater 31 is not lower than the target temperature T1 or if the control period Tc has ended, the control device 33 does not turn on the heater 31 and executes next S29. .

Further, in S15 of FIG. 4, when the control device 33 determines that the control pattern CP selected in S13 is the control pattern CP in which the heater 32 is turned on first (S15: NO), the processing of S37 to S47 is executed. . Since the processing contents of S37 to S47 are the same as those of S17 to S27 described above, detailed description thereof will be omitted. In the processing of S37 to S47, the control device 33 turns ON the heater 32 first, monitors the temperature TR2 during the ON period Ton2, and executes control to switch ON/OFF of the heaters 31 and 32 .

After executing S27 or S47, the control device 33 executes S29 in FIG. In S29, the controller 33 determines whether to continue the heater control process. For example, when all printing processes are completed, the control device 33 determines not to continue the heater control process (S19: NO), and ends the heater control process shown in FIGS. Further, for example, when all printing processes have not been completed, the control device 33 determines to continue the heater control process (S29: YES), and executes the processes from S11 again.

The control device 33 of the present embodiment executes the processes of S11 to S29 described above every control cycle Tc. Specifically, for example, after S15, the control device 33 executes the determination process of S29 in parallel while executing energization based on the control pattern CP selected in S13. While executing the energization control from S15 onward, the control device 33 executes the processes of S11 and S13 if the process of S29 executed in parallel results in affirmative determination (S29: YES), and performs the processes of S11 and S13, and A control pattern CP to be used is selected in advance. The control device 33 starts the processing of the next control cycle Tc (energization control after S15) using the preselected control cycle Tc in accordance with the end of the previous control cycle Tc (energization control after S15). Similarly, the control device 33 executes the determination process of S29 in parallel while starting the energization control after S15. In addition, the control device 33, while executing the energization control after S15, if the process of S29 executed in parallel results in a negative determination (S29: NO), in accordance with the end of the control cycle Tc, FIG. 4 and FIG. 5 ends the heater control process.

In this way, the control device 33 repeatedly executes the energization control using the control pattern CP and the selection process of the control pattern CP to be executed in the next control period Tc every control period Tc. Thereby, the controller 33 can maintain the temperatures TR1 and TR2 at the desired target temperatures T1 and T2. In addition, when at least one of the heaters 31 and 32 rises to the target temperature, the control device 33 can switch between on and off of the two heaters. Note that the control device 33 does not have to execute the process of selecting the control pattern CP from the table TB every control period Tc. For example, the control device 33 may use the once-selected control pattern CP continuously for two or more control cycles Tc. Further, the control device 33 may change the length of the control period Tc each time the control pattern CP is selected, for example.

FIG. 8 shows changes in temperatures TR1 and TR2 in the control of this embodiment and the control of Comparative Examples 1 and 2. FIG. In the example shown in FIG. 8, the horizontal axis represents the control period Tc, and one period of the control period Tc is divided into 10 equal parts. FIG. 8 illustrates a case where the ON period Ton2 is longer than the ON period Ton1. In this case, in the present embodiment, the ON period Ton2 starts before the ON period Ton1. On the other hand, Comparative Example 1 shows an example in which the short ON period Ton1 is started before the long ON period Ton2. Comparative Example 2 exemplifies a case where the ON/OFF switching of the heater is not performed even if the temperature TR2 of the heater 32 that has been turned on earlier is raised to the target temperature T2. Accordingly, Comparative Example 2 is an example in which the control of energizing until the end of the ON periods Ton1 and Ton2 determined before the start of the control period Tc is executed regardless of the rise in the temperatures TR1 and TR2.

A thick solid line graph W1 in FIG. 8 indicates a change in the temperature TR1 of the heater 31 in the first comparative example. A thin solid line graph W4 indicates changes in the temperature TR2 of the heater 32 in the first comparative example. A line graph W2 of wavy lines with wide intervals indicates changes in the temperature TR1 of the heater 31 in the second comparative example. A line graph W5 of wavy lines with narrow intervals indicates changes in the temperature TR2 of the heater 32 in the second comparative example. A two-dot chain line graph W3 indicates changes in the temperature TR1 of the heater 31 in this embodiment. A dashed-dotted line graph W6 indicates a change in the temperature TR2 of the heater 32 in this embodiment. Also, in FIG. 8, the target temperature T1 and the target temperature T2 are shown as the same temperature for the sake of easy understanding. Further, the required temperatures shown in FIG. 8 are, for example, temperatures TR1 and TR2 required to maintain good fixability of the toner onto the sheet 3 .

As described above, the controller 33 lengthens the ON period Ton as the temperature difference from the target temperature increases. Therefore, with two heaters set to the same target temperature, the temperature of the heater with the longer ON period Ton is lower than the temperature of the heater with the shorter ON period Ton at the start of the control period Tc. As shown in FIG. 8, the temperature TR2 of the heater 32 with the long ON period Ton is lower than the temperature TR1 at the start of the control period Tc.

From the viewpoint of suppressing voltage fluctuation, it is preferable to energize the two heaters one by one without overlapping the ON period Ton1 and the ON period Ton2 within the control period Tc. When such control is executed to avoid overlapping of the on-periods Ton of the two heaters, while one heater is energized, the other heater is not energized and the temperature is lowered. As indicated by line graphs W1 to W6 in FIG. 8, the temperature TR2 of the heater 32 decreases during the ON period Ton1 of the heater 31. As shown in FIG. Similarly, the temperature TR1 of the heater 31 decreases during the ON period Ton2 of the heater 32 .

As in Comparative Example 1, for example, regardless of the length of the ON period Ton, it is assumed that the ON period Ton1 is uniformly started first, and then the ON period Ton2 is started. In this case, although the temperature TR2 of the heater 32 is lower than the temperature TR1 of the heater 31 at the start of the control cycle Tc, it decreases until the ON period Ton2 starts (see line graph W4). As a result, the temperature TR2 is likely to fall below the required temperature required for the printing process (see minimum value MIN1 in FIG. 8).

On the other hand, in Comparative Example 2 and the present embodiment, control is executed to start the ON period Ton with the longest time first of the two ON periods Ton. As a result, as shown by line graphs W5 and W6 in FIG. 8, the ON period Ton2 can be started at an early stage in the control period Tc, and the temperature TR2 can be prevented from falling below the required temperature. Therefore, the temperature ripple (temperature drop) of the temperature TR2 can be suppressed by the earlier start of the ON period Ton2. By executing such control, the controller 33 of the present embodiment can prevent both the temperatures TR1 and TR2 from falling below the required temperature. As a result, the required temperature can be ensured, and the fixability of the toner to the sheet 3 can be maintained satisfactorily.

Further, in the comparative example 2 and the present embodiment, the temperature TR2 of the heater 32 reaches the target temperature T2 at the time t1 within the control period Tc. In Comparative Example 2, even if the temperature TR2 rises to the target temperature T2, the heater 32 continues to be energized during the ON period Ton2 determined before the start of the control cycle Tc (line graph W5). As a result, the temperature TR2 of Comparative Example 2 rises from the time t1 at which the target temperature T2 is reached to the time t2 at which the ON period Ton2 ends, and exceeds the target temperature T2 (see maximum value MAX1 in FIG. 8).

On the other hand, in the control device 33 of the present embodiment, as shown in FIGS. 4 and 5, when the temperature TR2 rises to the target temperature T2 (S39: YES), the heater 32 is turned off and the heater 31 is turned on (S41). ). As shown in FIG. 8, the ON period Ton2 of this embodiment ends at time t1 when the temperature TR2 reaches the target temperature T2. As a result, it is possible to prevent the temperature TR2 from overshooting the target temperature T2 (see the maximum value MAX2). Also, the ON period Ton1 starts at time t1 consecutively to the end of the ON period Ton2. As a result, the line graph W3 of the temperature TR1 of the present embodiment begins to rise from the minimum temperature value MIN3 higher than the minimum value MIN2 of the line graph W2. As a result, the drop in temperature TR1 of heater 31 can be suppressed.

Further, as shown in FIG. 8, the ON period Ton1 of the present embodiment starts when the temperature TR2 reaches the target temperature T2. Therefore, the ON period Ton1 of the present embodiment starts at time t1 earlier than the time t2 at which the ON period Ton1 of Comparative Example 2 starts, and ends at time t3 earlier. The controller 33 determines that the ON period Ton1 ends at time t3 (S43: YES), and turns off the heater 31 (S45). Although not shown, the controller 33 turns off the heater 31 (S45) even if the temperature TR1 rises to the target temperature T1 (S43: YES). As a result, it is possible to repeatedly suppress the temperature TR1 from exceeding the target temperature T1 within the control period Tc.

At the time t3 when the heater 31 is turned off in S45, the temperature TR2 of the heater 32, which was previously turned on in S37 and turned off in S41, is lower than the target temperature T2, and the control period Tc has not ended. 32 is turned on again (S47). The controller 33 turns on the heater 32 until the temperature TR2 reaches the target temperature T2, and turns off the heater 32 when the temperature TR2 rises to the target temperature T2 (S47). Thereby, the temperature TR2 can be raised to the target temperature T2 again, and the temperature TR2 can be prevented from exceeding the target temperature T2.

Temperature ripples WR1 to WR6 are illustrated on the right side of FIG. Temperature ripples WR1 to WR6 indicate temperature differences between the maximum and minimum values of line graphs W1 to W6 within control cycle Tc in order from left to right. The temperature difference of the temperature ripple WR3 of this embodiment is smaller than that of the temperature ripple WR1 of the first comparative example. Further, among the temperature ripples WR4 to WR6 of the temperature TR2, the temperature difference of the temperature ripple WR6 of this embodiment is the smallest. Therefore, the control device 33 of the present embodiment can more effectively suppress the temperature ripple by switching the heater on and off while comparing the temperatures TR1 and TR2 with the target temperatures T1 and T2.

FIG. 9 shows a case where the slopes of the temperatures TR1 and TR2 are made larger than those in FIG. In other words, this shows the case where the heaters 31 and 32 have higher temperature rise and fall rates. In this case, in Comparative Example 1, the start of the ON period Ton2 is delayed, so that the minimum value MIN1 becomes a lower temperature than in the case of FIG. 8 and is below the required temperature. Further, in Comparative Example 2, by continuing the ON period Ton2, the maximum value MAX1 becomes a higher temperature than in the case of FIG. 8 and exceeds the target temperature T2. Therefore, by executing the above-described control of the present embodiment, specifically, the control of starting the one with the longer ON period Ton first, and the control of switching the heater on and off based on the target temperature, the temperature rise rate The temperature ripple can be suppressed more effectively in heater control with a higher rate of decrease. That is, the temperature ripple can be suppressed more as the rate of temperature rise or fall increases.

Further, in the control of the embodiment shown in FIG. 8, the soft start period Ts is started prior to the temperature TR2 reaching the target temperature T2, and the ON period Ton1 is advanced from the time t1 at which the temperature TR2 reaches the target temperature T2. started. Then, the ON period Ton1, which was started ahead of schedule, was executed for the time set before the start of the control cycle Tc. That is, the length of the ON period Ton1 that starts later was not changed. On the other hand, as in the control of the present embodiment shown in FIG. 9, the ON period Ton1 that is started ahead of time from time t1 may be extended beyond the time set before the start of the control period Tc. For example, as shown in the line graph W3 in FIG. 9, the ON period Ton1 started later may be extended until the temperature TR1 reaches the target temperature T1.

Further, in the examples shown in FIGS. 8 and 9 described above, the control device 33 determines whether or not the temperatures TR1 and TR2 rise to the target temperatures T1 and T2, but the present invention is not limited to this. The control device 33 may determine whether the temperatures TR1 and TR2 are below the target temperatures T1 and T2. FIG. 10 shows changes in temperatures TR1 and TR2 in another heater control process.

As shown in FIG. 10, for example, at time t1, the temperature TR2 reaches the target temperature T2, so the controller 33 switches the heaters 31 and 32 on and off. For example, depending on the control method, even if the heater control signal Sig5 (see FIG. 2) is set to low level at the end of the ON period Ton2, the triac TA11 will not be turned off until the zero cross timing ZC, and the heater 32 will be energized. In some cases. As a result, the temperature TR2 may rise even after the ON period Ton2 ends, exceeding the target temperature T2 and reaching the maximum value MAX2. Temperature TR2 falls below target temperature T2 at time t4. Therefore, at time t5 when the temperature TR2 falls below the target temperature T2, the controller 33 may switch the heaters 31 and 32 on and off again.

Therefore, in the example shown in FIG. 10, the control device 33 turns off the heater 32 (time t1) in response to the temperature TR2 of the heater 32 that was previously turned on rising to the target temperature T2. In addition, when the temperature TR2 of the heater 32 that was turned on first falls below the target temperature T2, the control device 33 turns off the heater 31 that was turned on later (time t5). That is, when the temperature of the heater that was previously turned on rises to the target temperature, but when the heater is turned off, the temperature falls below the target temperature again, the heater is turned on and off. The controller 33 resumes energization of the heater 32 that was previously turned on (time t5). Thereby, it is possible to monitor whether or not the temperature is below the target temperature, and if the temperature is below the target temperature, the heater can be turned on again to bring the temperature closer to the target temperature. Further, for example, when priority is given to the temperature control of either the heater 31 or the heater 32, by monitoring whether the temperature of the heater with priority is lower than the target temperature, the temperature of the heater with priority can be adjusted to the target temperature. can be maintained with

Further, in the above-described embodiment, control is performed using the target temperatures T1 and T2 as the control temperatures of the present application, but the present invention is not limited to this. For example, other control temperatures that can be used to control the heater may be used. For example, the required temperature may be used as the control temperature. FIG. 11 shows changes in temperatures TR1 and TR2 when the required temperature is used. As shown in FIG. 11, for example, at time t6, the temperature TR1 has decreased to the target temperature T1, so the controller 33 switches the heaters 31 and 32 on and off. The temperature TR1 is prevented from falling below the required temperature by changing from falling to rising. The controller 33, for example, turns on the heater 31 until the temperature TR1 reaches the target temperature T1. Therefore, the control device 33 may switch the heater on and off when the temperature TR1 of the heater 31 to be turned on later drops to the required temperature. As a result, the temperature drop of the heater that is turned on later can be suppressed.

Incidentally, the heater 31 is an example of a first heater. The heater 32 is an example of a second heater. The target temperatures T1 and T2 and the required temperature are examples of control temperatures. The ON period Ton1 is an example of a first ON period. The ON period Ton2 is an example of a second ON period. Temperature TR1 is an example of a first temperature. Temperature TR2 is an example of a second temperature. Target temperature T1 is an example of a first target temperature. Target temperature T2 is an example of a second target temperature.

(5. Effect)
As described above, according to the present embodiment described above, the following effects can be obtained.
(1) The heater control device 30 of the present embodiment includes a heater 31 to which power is supplied from the AC power supply 101, a heater 32 to which power is supplied from the AC power supply 101, and a temperature control device that varies according to the heat generation state of the heater 31. and a temperature TR2 that fluctuates according to the heat generation state of the heater 32, and the temperature sensors 31A and 32A that detect the temperature TR1 and the temperature TR2 that varies according to the heat generation state of the heater 32. is a period during which power is supplied to the heater 31 from the AC power supply 101 to the heater 31, and based on the detected temperature TR2, a period during which power is supplied from the AC power supply 101 to the heater 32 in a predetermined control cycle Tc. and a control device 33 that controls the period Ton2. The control device 33 controls the temperature TR1 or the temperature TR2 to be the control temperature (the target temperatures T1, T2 or In response to reaching the required temperature), the power supply to the heater to which power has been supplied among the heaters 31 and 32 is stopped, and the power supply to the heater to which power supply has been stopped is stopped. Start.

According to this, the control device 33 controls the on/off of the heater from the start of one of the two on-periods Ton until the other on-period Ton is started. The controller 33 switches between on and off of the two heaters when the temperature TR1 of the heater 31 or the temperature TR2 of the heater 32 reaches a predetermined control temperature. As a result, the heater is switched on and off according to the arrival of the control temperature used for heater control such as the target temperatures T1 and T2 and the required temperature, and the heater temperature rises above the target temperature or drops below the required temperature. can be suppressed. Therefore, it is possible to suppress an increase in the temperature difference obtained by subtracting the minimum temperature from the maximum temperature of each heater within the control cycle Tc, that is, it is possible to suppress the temperature ripple.

(2) In addition, the control device 33 switches the power of the two heaters when the temperature TR1 rises to the target temperature T1 or the temperature TR2 rises to the target temperature T2 (S19: YES, S39: YES). The power supply to the heater that has been supplied is stopped, and the power supply to the heater that has been stopped is started (S21, S41). According to this, the control device 33 switches the heater on and off in response to the temperature TR1 or the temperature TR2 rising to the target temperature. As a result, the heater to which power is being supplied, that is, the heater whose temperature has reached the target temperature is turned off, thereby suppressing the temperature of the heater from rising beyond the target temperature. In addition, as the heater that is turned on first rises to the target temperature, power supply to the heater that is turned on later is started. As a result, it is possible to suppress the temperature drop of the heater that is turned on later. As a result, temperature ripple can be suppressed.

(3) In addition, when the control device 33 stops power supply to the heater whose power supply is started in response to the temperature TR1 rising to the target temperature T1 or the temperature TR2 rising to the target temperature T2, , power to the heater whose power supply is stopped in response to the temperature TR1 or the temperature TR2 rising to the target temperature in response to the temperature TR1 or the temperature TR2 rising to the target temperature falling below a predetermined temperature; is resumed at a predetermined control period Tc (S27, S47, time t3 in FIG. 8). According to this, when the power supply to the heater to which the power supply is started later is stopped (when the target temperatures T1 and T2 are reached or when the ON period Ton ends), the target temperature is set before the heater is turned on and off. If the temperature TR1 or the temperature TR2 that has risen to the temperature is lower than a predetermined temperature (for example, a target temperature), power supply to the heater that has been turned off is resumed. As a result, the temperature TR1 or the temperature TR2, which has been once raised to the target temperature, can be brought closer to the target temperature again.

(4) In addition, the controller 33 stops supplying power to the heaters 31 and 32 to which power has been supplied in response to the temperature TR1 dropping to the required temperature (an example of the control temperature). and start supplying power to the heater to which power supply has been stopped (see FIG. 11). According to this, the control device 33 switches ON/OFF of the heater in response to the temperature TR1 or the temperature TR2 dropping to the required temperature. As a result, it is possible to turn on the heater whose power supply has been stopped, that is, whose temperature has dropped to the required temperature, and to prevent the temperature of the heater from dropping below the required temperature. Therefore, the temperature drop of the heater can be suppressed.

(5) In addition, the controller 33 supplies power to the heaters 31 and 32 to which power has been supplied in response to the temperature TR1 reaching the target temperature T1 or the temperature TR2 reaching the target temperature T2. When the supply of power is stopped, the supply of power to the heater to which the power supply has been stopped is started.

According to this, by turning on one heater in response to turning off the other heater, the two on-periods Ton can be continued so that the other starts at the timing when one ends. Transition from a state in which power is supplied to at least one of the two heaters to a state in which the supply of power to both heaters is stopped (off period Toff), or from a state in which power supply to both heaters is stopped (off period Toff). can reduce the number of occurrences of transitions such as transitions to states that start That is, it is possible to reduce the number of transitions from the ON period Ton to the OFF period Toff or from the OFF period Toff to the ON period Ton. Thereby, fluctuations in the voltage supplied to the heaters 31 and 32 can be suppressed. As a result, it is possible to suppress the influence of flicker that occurs in other electronic devices that use the same AC power supply 101 as the heater control device 30 .

(6) In addition, the control device 33 starts the ON period Ton with the short time after starting the ON period Ton with the long time among the ON periods Ton1 and Ton2. According to this, by starting the long ON period Ton first, it is possible to start supplying power earlier to the heater having a large difference between the target temperature and the actual temperature. It is possible to suppress an increase in the temperature difference between the temperatures. As a result, temperature ripple can be suppressed.

(7) In addition, the control device 33 lengthens the ON period Ton1 according to an increase in the first difference obtained by subtracting the temperature TR1 from the target temperature T1, and increases the second difference obtained by subtracting the temperature TR2 from the target temperature T2. The ON period Ton2 is lengthened according to the increase. According to this, by lengthening the ON periods Ton1 and Ton2 in accordance with an increase in the temperature difference between the target temperatures T1 and T2 and the temperatures TR1 and TR2, the temperatures TR1 and TR2 are adjusted to the target temperatures T1 and T2. can be maintained at a constant temperature difference.

(8) Further, the control device 33 creates a table TB having a plurality of control patterns CP in which the ON period Ton1 and the ON period Ton2 are set corresponding to the first difference and the second difference in one control cycle Tc. are used to control the on-periods Ton1 and Ton2 based on the control pattern CP corresponding to the first difference and the second difference selected from the table TB. The control pattern CP of the table TB is set such that the long ON period Ton starts earlier than the short ON period Ton (see FIGS. 6 and 7). According to this, the control device 33 refers to the table TB, selects and executes the control pattern CP according to the temperature difference, and can start the long ON period Ton earlier.

(6. Others)
It goes without saying that the present invention is not limited to the above-described embodiments, and that various improvements and modifications are possible without departing from the gist of the present invention.
For example, in the embodiment described above, the control device 33 determines the control pattern CP by selecting the control pattern CP from the table TB shown in FIGS. On the other hand, for example, a first difference that is a value obtained by subtracting the temperature TR1 from the target temperature T1 and a second difference that is a value obtained by subtracting the temperature TR2 from the target temperature T2 are compared to determine the control pattern CP. You can decide. For example, the control device 33 may first start the ON period Ton in which the value of the temperature difference is greater between the first difference and the second difference. For example, when the first difference is greater than or equal to the second difference, the control device 33 may perform control to start the ON period Ton1 earlier than the ON period Ton2. Moreover, when the table TB is not used, the method for setting the length of the ON period Ton is not particularly limited. For example, the control device 33 may calculate the ON period Ton1 by multiplying the value of the first difference by a predetermined coefficient.

Here, for example, the larger the difference between the target temperature and the actual temperature, the longer the ON period Ton is not necessarily, due to differences in the structure of the heaters, differences in the temperature rise rate of each heater, and differences in the target temperature. . For example, a heater with a high rate of temperature rise with respect to energization time can raise the temperature in a shorter ON period Ton than a heater with a low rate of temperature rise. Therefore, the proportional relationship between the first difference and the ON period Ton1 may not be the same as the proportional relationship between the second difference and the ON period Ton2. Depending on the structure or the like of the heater control device 30, the ON period Ton1 may be shorter than the ON period Ton2 even though the first difference is greater than the second difference. Therefore, as described above, focusing on the difference between the first and second temperatures, that is, the temperature difference with respect to the target temperature, priority may be given to energizing heaters having a large temperature difference. As a result, it is possible to start supplying power to the heater having a large difference between the target temperature and the actual temperature first, suppress an increase in the temperature difference between the target temperature and the actual temperature, and suppress the temperature ripple. .

Alternatively, the control device 33 may calculate the on-periods Ton1 and Ton2 for each control cycle Tc, compare the calculated on-periods Ton1 and Ton2, and adjust the relationship between them. The controller 33 calculates the ON periods Ton1 and Ton2, for example, based on the temperatures TR1 and TR2 detected before starting the control period Tc. A method for calculating the on-periods Ton1 and Ton2 is not particularly limited. For example, the controller 33 may calculate the ON period Ton1 by multiplying the value of the temperature TR1 by a predetermined coefficient. Then, the control device 33 may calculate the on-periods Ton1 and Ton2 for each control period Tc, and execute control to start the long-time on-period Ton first. According to this, while comparing the on-periods Ton1 and Ton2 calculated based on the actual temperatures (temperatures TR1 and TR2), power supply can be started earlier to the heater having the longer on-period Ton. Generally, if the temperature difference between the target temperature and the actual temperature increases, there is a high possibility that the ON period Ton will be lengthened. That is, there is a proportional relationship between the temperature difference and the length of the ON period. Therefore, by prioritizing the start of the long ON period Ton, it is possible to suppress an increase in the temperature difference between the actual temperature of the heater and the target temperature, thereby suppressing the temperature ripple.

In addition, the table TB may have control patterns CP whose on-periods Ton1 and Ton2 are discontinuous or overlapping control patterns CP.
Further, although the heater control circuits 43 and 44 have the triacs TA1 and TA11, the heater control circuits 43 and 44 may have other semiconductor elements such as FETs instead of the triacs.
Moreover, in the above embodiment, the heaters 31 and 32 are used as an example of the first heater and the second heater of the present application, but the present invention is not limited to this. The first heater and the second heater of the present application may be heaters having the same shape, or may be heaters arranged at completely different positions.
Further, the heater control device 30 of the present application is not limited to a device that controls two heaters (first and second heaters), and may be a device that controls three or more heaters. That is, the heater control device 30 may control each heater using two tables in which the ON periods Ton for each of three or more heaters are arranged.
Further, the heater control device 30 of the present application is not limited to a device that controls heaters provided in an image forming apparatus such as the printer 1 . For example, the heater control device 30 may be a device that controls heaters used in sewing machines and machine tools.

In the above-described embodiments, the printer 1, which is a monochrome laser printer, is used as an example of the image forming apparatus of the present application. However, the present invention is not limited to this. A so-called compound machine can be employed. In the case of an inkjet printer, the heater control device may control a heater or the like that is used to speed up the drying of jetted ink.

1 Printer (Image Forming Apparatus) 3 Sheet 5 Image Forming Unit 7 Fixing Device 30 Heater Control Device 31 Heater (First Heater) 31A, 32A Temperature Sensor 32 Heater (Second Heater) 33 Control Device , 101 AC power supply, TR1 temperature (first temperature), TR2 temperature (second temperature), T1 target temperature (first target temperature), T2 target temperature (second target temperature), Ton ON period, Ton1 ON period (second 1 ON period), Ton2 ON period (second ON period), Tc Control cycle.

Claims (5)

a first heater powered by an AC power supply;
a second heater supplied with power from the AC power supply;
a temperature sensor for detecting a first temperature that varies according to the heat generation state of the first heater and a second temperature that varies according to the heat generation state of the second heater;
Based on the detected first temperature, a first ON period, which is a period during which power is supplied from the AC power supply to the first heater, is controlled in a predetermined control cycle, and based on the detected second temperature. a control device for controlling a second ON period, which is a period during which power is supplied from the AC power supply to the second heater in the predetermined control period;
with
The control device is
Before the start of the predetermined control cycle, based on the first temperature and the second temperature, the first ON period and the second ON period in the control cycle do not overlap and the first ON period When the period and the second ON period are set to be continuous,
After the start of the predetermined control cycle, during the period from when one of the first ON period and the second ON period is started to when the other ON period is started, the first heater and the second heater are controlled. When the first temperature or the second temperature corresponding to the heater being supplied with power among the two heaters rises to the control temperature, the supply of power to the heater being supplied with power is set. stop without execution until the end of the ON period, and start supplying power to the heater to which the supply of power was stopped in line with ending the supply of power to the heater to which power was being supplied; heater controller. The control device is
The heater to which power is being supplied in response to the first temperature or the second temperature corresponding to the heater to which power is being supplied, among the first heater and the second heater, rising to the control temperature. The power supply to the heater is stopped without being executed until the end of the set ON period, and the power supply to the heater to which the power supply has been stopped is started after starting the power supply to the heater. is stopped again, and when the predetermined control cycle has not ended, the first temperature or the second temperature that has risen to the control temperature is lower than the predetermined temperature. 2. The heater control device according to claim 1, wherein power supply to the heater, to which the power supply has been stopped in response to the first temperature or the second temperature rising to the control temperature, is resumed in the predetermined control period. . The control device is
The greater the difference between the control temperature and the first temperature, the longer the first ON period within the control cycle. Lengthen the second ON period,
3. The heater control device according to claim 1, wherein, of said first ON period and said second ON period, a longer ON period is started and then a shorter ON period is started. The control device is
setting a soft start period before the first ON period and the second ON period;
stepwise increasing a duty ratio of energization from the AC power supply to the first heater during the soft start period set before the first ON period by phase control;
stepwise increasing a duty ratio of energization from the AC power supply to the second heater during the soft start period set before the second ON period by phase control;
4. The heater control device according to any one of claims 1 to 3, wherein the soft start period is set so as to overlap with the preceding ON period. A heater control device according to any one of claims 1 to 4;
an image forming unit that forms an image on a sheet;
a fuser that heats the imaged sheet;
with
The fixing device
An image forming apparatus comprising the first heater and the second heater.

Images