JP6919191B2 - Image forming device - Google Patents

Description

The present invention relates to a technique for controlling energization of a plurality of heaters built in a fixing portion by PWM (Pulse Width Modulation) in an image forming apparatus.

In the image forming apparatus, the toner particles are fixed on the paper by heating by the fixing portion having a built-in heater.
In Patent Document 1, when the fixing unit includes one heater, a control signal that repeats on and off at a predetermined duty ratio and a predetermined switching frequency is generated, and the input current is generated by a switching element using this control signal. It switches and supplies the drive current to the heater. In addition, the duty ratio and switching frequency of the control signal are set so that the supply of the drive current in the next cycle is not started in the middle of the drive current flowing through the heater, which drops due to the switching off and reaches zero. .. This is because if the drive current is not zero at the time of cycle switching, a recovery current flows through the reflux element included in the chopper circuit, which causes noise to increase.

Further, the fixing portion described in Patent Document 2 includes a plurality of heaters, generates a control signal that repeats on and off for each heater, and uses each control signal to input current by a switching element corresponding to each heater. Is switched and supplied to the heater.

Japanese Unexamined Patent Publication No. 2016-92887 Japanese Unexamined Patent Publication No. 11-73057

When the fixing portion includes a plurality of heaters, there is a problem that noise is generated due to the current flowing through each heater.
An object of the present invention is to provide an image forming apparatus capable of suppressing the generation of noise when a plurality of heaters are built in the fixing portion.

In order to achieve the above object, the present invention is an image forming apparatus, comprising a first heating element and a second heating element having a rated current smaller than that of the first heating element, and a toner image formed on a paper. The fixing means that fixes by heating, the control means that outputs the first control signal and the second control signal that repeat on and off in synchronization with the same duty ratio, and the full-wave rectified input current are the first control signal. The first chopper circuit that generates the first drive current by switching using the above and supplies the generated first drive current to the first heating element, and the second input current that has been full-wave rectified. It is provided with a second chopper circuit that generates a second drive current by switching using a control signal and supplies the generated second drive current to the second heating element, and changes in the second drive current are provided. , Compared with the change of the first drive current, and at each cycle of the second control signal, between the time when the second control signal is turned off and the time when the second control signal is turned on next. The second time constant in the second chopper circuit and the second heating element is set so that the second drive current decreases to zero.

Here, the first chopper circuit includes a first switching element that switches the input current that has been full-wave rectified, a first inductance element that is connected in series with the first heating element, and a first recirculation that is connected in parallel. The second chopper circuit having an element includes a second switching element that switches the input current that has been full-wave rectified, a second inductance element that is connected in series with the second heating element, and a second that is connected in parallel. It may have a bicirculation element.

Here, the second time constant determined by the inductance of the second inductance element and the resistance value of the second heating element is determined by the inductance of the first inductance element and the resistance value of the first heating element. It may be larger than the first temporary constant.
Further, the present invention is an image forming apparatus, comprising a first heating element and a second heating element having a rated power smaller than that of the first heating element, and fixing a toner image formed on a paper by heating. The means, the control means that outputs the first control signal and the second control signal that repeat on and off in synchronization with the same duty ratio, and the change in the second drive current are compared with the change in the first drive current. Then, the current flowing through the second heating element becomes slow and the current flowing through the second heating element is generated between the time when the second control signal is turned off and the time when the second control signal is turned on next every cycle of the second control signal. A signal generation circuit that generates a control signal with a slow rise of the second control signal and a full-wave rectified input current are switched using the first control signal so that the current drops to zero. The first chopper circuit that generates the first drive current and supplies the generated first drive current to the first heating element and the full-wave rectified input current are switched by using the control signal. It is characterized by including a second chopper circuit that generates a second drive current and supplies the generated second drive current to the second heating element.

Further, the present invention is an image forming apparatus, comprising a first heating element and a second heating element having a rated power smaller than that of the first heating element, and fixing a toner image formed on a paper by heating. The means, the control means for outputting the first control signal and the second control signal that repeat on and off in synchronization with the same duty ratio, and the control signal by delaying the second control signal from the first control signal. The signal generation circuit that generates the The first chopper circuit supplied to the device and the full-wave rectified input current are switched using the control signal to generate a second drive current, and the generated second drive current is sent to the second heating element. It is characterized in that it is provided with a first chopper circuit to be supplied.

Here, the signal generation circuit may generate the control signal that changes from off to on after the first drive current flowing through the first heating element becomes steady.
Here, the frequencies of the first control signal and the second control signal may both be out of the audible range.
Here, the fixing means includes a fixing member in contact with the paper, the first heating element heats the central portion of the fixing member, and the second heating element heats the end portion of the fixing member. Further, the control means includes a first temperature detecting means arranged at a position facing the central portion of the fixing member and a second temperature detecting means arranged at a position facing the end portion of the fixing member. The duty ratios of the first control signal and the second control signal are determined so that the temperature detected by the first temperature detecting means and the temperature detected by the second temperature detecting means reach the target temperature, respectively. May be good.

Here, the control means may output the first control signal and the second control signal having a duty ratio corresponding to the mode in the case of the print operation mode or the power saving mode.

According to the above configuration, it is possible to suppress the generation of noise when the fixing portion incorporates a plurality of heaters.

It is a figure which shows the main structure of the image forming apparatus 10 as an embodiment. It is a figure which shows the schematic structure of the heating roller 35 which incorporates a heater 101, 102a, 102b. The relationship between the operation mode in the image forming apparatus 10 and the energization control for the heater is shown. It is a figure which shows the structure of the main control part 40. It is a circuit diagram which shows the structure of the drive circuit 100 and the circuit around it. The upper row shows the current flowing through the heater 101 during the on period of the switching element 131, and the lower row shows the current flowing through the heater 101 during the off period of the switching element 131. The waveform of the current flowing through the heater 101 when the duty ratio is low is shown. The waveform of the current flowing through the heater 101 when the duty ratio is high is shown. Waveforms F1 to F3 and F5 to F7 of the flowing current at each position on the circuit shown in FIG. 5 are shown. As a modification (1), waveforms F1 to F3 and F5 to F7 of the flowing current are shown at each position on the circuit shown in FIG. As a modification (2), it is a circuit diagram which shows the structure of the drive circuit 100a and the circuit around it. The waveforms F1 to F7 of the flowing current at each position on the circuit shown in FIG. 11 are shown. As a modification (3), it is a circuit diagram which shows the structure of the drive circuit 100b and the circuit around it. The waveforms F1 to F7 of the flowing current at each position on the circuit shown in FIG. 13 are shown. As a modification (4), waveforms F1 to F7 of the flowing current are shown at each position on the circuit shown in FIG.

1 Embodiment Hereinafter, the image forming apparatus 10 as the embodiment according to the present invention will be described with reference to the drawings.
1.1 Configuration of the image forming apparatus 10 FIG. 1 is a diagram showing a main configuration of the image forming apparatus 10.

As shown in FIG. 1, the image forming apparatus 10 is a so-called tandem type color printer apparatus. The image forming units 21Y, 21M, 21C and 21K included in the image forming apparatus 10 are toners of each color of Y (yellow), M (magenta), C (cyan) and K (black) under the control of the main control unit 40. Form an image.
For example, in the image processing unit 21Y, the peripheral surface of the photoconductor drum is uniformly charged by the charging device, and light writing is performed on the peripheral surface of the photoconductor drum by the optical writing unit to form an electrostatic latent image. Toner is supplied to the peripheral surface of the photoconductor drum by a developing device to develop (visualize) an electrostatic latent image. The primary transfer roller electrostatically transfers (primary transfer) the toner image from the photoconductor drum to the intermediate transfer belt 31.

Similarly, the toner images of the M, C, and K colors formed by the image forming portions 21M, 21C, and 21K are primarily transferred onto the intermediate transfer belt 31 so as to overlap each other. The color toner image formed by the primary transfer is conveyed to the secondary transfer roller 32 by the intermediate transfer belt 31 orbiting in the arrow X direction.
The paper feed unit 60 includes paper feed cassettes 61, 62, 63 for accommodating papers of different sizes, and pickup rollers 64, 65, 66 for feeding these papers from each paper feed cassette to a transport path. For example, the paper S supplied from the paper cassette 61 is conveyed to the secondary transfer roller 32.

The secondary transfer roller 32 electrostatically transfers (secondary transfer) the toner image on the intermediate transfer belt 31 onto the paper S. The paper S on which the toner image is transferred is conveyed to the fixing unit 34.
The heater control unit 48, which is included in the main control unit 40 and will be described later, generates a first control signal and a second control signal that repeat on and off at a predetermined duty ratio and a predetermined switching frequency, and the generated first control signal. And the second control signal is supplied to the drive circuit 100.

The drive circuit 100 switches the full-wave rectified input current using the first control signal to generate the first drive current, and the generated first drive current is used as the heater 101 (which heats the heating roller 35). It will be supplied to (described later). Further, the drive circuit 100 switches the full-wave rectified input current using the second control signal to generate a second drive current, and transfers the generated second drive current to the heaters 102a and 102b (described later). Supply to.

In the fixing portion 34, the heating roller 35 and the pressure roller 36 come into contact with each other to form a nip. The pressure roller 36 rotates under the control of the main control unit 40. The heating roller 35 rotates in accordance with the rotation of the pressure roller 36.
As shown in FIG. 2, the heating roller (fixing member) 35 has a heater 101 (first heating element) built in the central portion of the tubular core metal, and is provided at both end portions of the core metal, respectively. , The heaters 102a and 102b are built-in. The heaters 101, 102a, and 102b are, for example, halogen heaters, respectively. The heater 101 heats the central portion of the heating roller 35 in the axial direction (left-right direction in FIG. 2), and the heaters 102a and 102b heat the end portions in the axial direction. The heater 102a and the heater 102b are electrically connected in series to form one heater 102 (second heating element). The heater 101 is turned on by the first drive current supplied from the drive circuit 100. The heater 102 is turned on by the second drive current supplied from the drive circuit 100. The rated power of the heater 102 is smaller than the rated power of the heater 101. Here, the rating refers to the specifications, performance, usage limits, etc. of equipment, devices, parts, etc. under specified conditions, and indicates the specifications of the equipment and the proper usage method according to the standard or by the manufacturer. It is a number.

Further, the temperature sensor 134 is arranged at a position facing the central portion of the heating roller 35, and the temperature sensor 144a and the temperature sensor 144b are arranged at a position facing both end portions of the heating roller 35. In the following, the temperature sensor 144a and the temperature sensor 144b may be referred to as the temperature sensor 144 as a representative. The temperature sensors 134, 144a, 144b detect the temperature of the central portion and the end portions on both sides of the heating roller 35, respectively. The temperature sensors 134, 144a, and 144b each output the detected temperature to the heater control unit 48.

Returning to FIG. 1, when the paper S is fed into the nip, the paper S is pressurized by the pressurizing roller 36 and the heating roller 35, and is also heated by the heating roller 35. As a result, the toner particles are fixed on the paper S. After that, the paper S is sent out toward the output tray 37.
An operation panel 47 is provided on the upper part of the image forming apparatus 10. The operation panel 47 receives an instruction to start copying, a setting of the number of copies, a setting of copy conditions, and the like from the user, and conveys the accepted contents to the main control unit 40.

As shown in FIG. 3, the image forming apparatus 10 shifts in the order of initial timing mode, warm-up mode, power saving mode, and printing operation mode after the main power is turned on by the user. After that, the power saving mode and the printing operation mode are repeated. For example, in the power saving mode, when a print job is received, the image forming apparatus 10 shifts from the power saving mode to the printing operation mode. After that, if the print job is not received for a certain period of time, the image forming apparatus 10 shifts from the print operation mode to the power saving mode.

In the power saving mode, the duty ratio of the first control signal and the second control signal is, for example, 30% or a value in the vicinity thereof, and the switching frequency is, for example, 35 kHz. As a result, the temperature of the heating roller 35 is set low. On the other hand, in the print operation mode, the duty ratio of the first control signal and the second control signal is, for example, 70% or a value in the vicinity thereof, and the switching frequency is, for example, 25 kHz. As a result, the temperature of the heating roller 35 is set high. The duty ratio and switching frequency are not limited to those described above.

1.2 Main control unit 40
The configuration of the main control unit 40 will be described.
FIG. 4 is a diagram showing the configuration of the main control unit 40.
As shown in this figure, the main control unit 40 includes a RAM 41, a ROM 42, a CPU 43, a network I / F unit 44, a printer control unit 45, an image memory 46, and the like. The printer control unit 45 includes a heater control unit (control means) 48.

The printer control unit 45 controls the operation of each part of the image forming apparatus 10, and uniformly controls the feeding operation from the paper cassette 61 and the like and the image forming operation of the image forming units 21Y to 21K. , The image forming operation is executed. The printer control unit 45 has a CPU and a ROM inside, and executes each control based on a control program stored in the ROM.
The RAM 41 temporarily stores various control variables, the number of copies set by the operation panel 47, and the like, and provides a work area when the program is executed by the CPU 43.

The ROM 42 stores a control program for executing various jobs such as a copy operation.
The network I / F unit 44 receives a print job from an external terminal device such as a PC (personal computer) via a network such as a LAN.
The CPU 43 controls the network I / F unit 44, the printer control unit 45, and the like. For example, when the network I / F unit 44 accepts a print job, the CPU 43 instructs the printer control unit 45 to execute an image forming operation based on the data of the print job.

The image memory 46 temporarily stores image data such as a print job.
1.3 Heater control unit 48
As shown in FIG. 5, the heater control unit 48 includes a control circuit 49 and an AND circuit 50. The control circuit 49 generates a first control signal that repeats on and off at a predetermined duty ratio and a predetermined switching frequency according to the operation mode of the image forming apparatus 10. As shown in FIG. 3, when the image forming apparatus 10 is in the power saving mode, the duty ratio of the first control signal is, for example, 30% or a value in the vicinity thereof, and the switching frequency of the first control signal is, for example, , 35 kHz. On the other hand, when the image forming apparatus 10 is in the print operation mode, the duty ratio of the first control signal is, for example, 70% or a value in the vicinity thereof, and the switching frequency of the first control signal is, for example, 25 kHz.

The control circuit 49 generates a third control signal indicating the timing at which the heater 102 is first turned on only once. The third control signal is turned on once and then continues to be turned on.
The AND circuit 50 performs an AND operation on the first control signal and the third control signal to generate a second control signal. Since the second control signal is generated by performing an AND operation on the first control signal and the third control signal, it is the same signal as the first control signal.

The heater control unit 48 outputs the first control signal and the second control signal to the terminals 167 and 168 of the drive circuit 100, respectively.
An example of the waveforms F1, F2, and F3 of the first control signal, the third control signal, and the second control signal, respectively, is shown in FIG. In this figure, the horizontal axis represents the passage of time, and the vertical axis of each waveform represents the current value.

As shown in the waveform F1, the first control signal is turned on at time t1 and turned off at time t2. Further, it is turned on at time t3 and turned off at time t4. The same applies thereafter. In this way, the first control signal repeats on and off.
Further, as shown in the waveform F2, the third control signal is turned on at time t1. After that, it keeps on.

Further, as shown in the waveform F3, the second control signal is turned on at time t1 and turned off at time t2. Further, it is turned on at time t3 and turned off at time t4. The same applies thereafter. In this way, the second control signal repeats on and off. As shown in FIG. 9, the waveform F3 of the second control signal is the same as the waveform F1 of the first control signal.

The heater control unit 48 receives the detected temperature from the temperature sensors 134, 144a and 144b. The heater control unit 48 determines the duty ratios of the first control signal and the second control signal, respectively, so that the temperature detected by the temperature sensors 134, 144a, 144b becomes the target temperature.
1.4 Drive circuit 100
(1) Configuration of Drive Circuit 100 As shown in FIG. 5, the drive circuit 100 is composed of a rectifier circuit 111, a noise filter 112, a chopper circuit 113, and a chopper circuit 114. Further, the drive circuit 100 includes terminals 161, 162, 163, 164, 165, 166, 167, 168 for connecting to an external circuit or the like.

The drive circuit 100 is connected to the commercial power supply 11 via terminals 161 and 162, is connected to the heater 101 via terminals 163 and 164, is connected to the heater 102 via terminals 165 and 166, and is connected to terminal 167. It is connected to the heater control unit 48 via 168.
(Rectifier circuit 111)
The rectifier circuit 111 is connected to the commercial power supply 11 via terminals 161 and 162 on the input side, and is connected to the noise filter 112 via nodes 171 and 173 on the output side. The rectifier circuit 111 full-wave rectifies the single-phase alternating current supplied from the commercial power supply 11, and supplies the full-wave rectified current to the noise filter 112. Specifically, the rectifier circuit 111 is a bridge-type rectifier circuit configured by combining four rectifier elements 111a, 111b, 111c, and 111d. The cathode of the rectifying element 111a and the anode of the rectifying element 111c are connected to the terminal 161 and the cathode of the rectifying element 111b and the anode of the rectifying element 111d are connected to the terminal 162. Further, the anode of the rectifying element 111a and the anode of the rectifying element 111b are connected to the node 173, and the cathode of the rectifying element 111c and the cathode of the rectifying element 111d are connected to the node 171.

(Noise filter 112)
The noise filter 112 is connected to the rectifier circuit 111 via the nodes 171 and 173 on the input side, and is connected to the chopper circuit 113 and the chopper circuit 114 via the nodes 172 and 173 on the output side. The noise filter 112 reduces the noise so that the noise generated in the image forming apparatus 10 does not propagate to the commercial power supply 11 side. Specifically, the noise filter 112 is, for example, a π-type filter, which is composed of a coil 122, capacitors 121, and 123. The first end of the coil 122 and the first end of the capacitor 121 are connected to the node 171 and the second end of the coil 122 and the first end of the capacitor 123 are connected to the node 172. Further, the second end of the capacitor 121 and the second end of the capacitor 123 are connected to the node 173.

(Chopper circuit 113)
The chopper circuit 113 is connected to the noise filter 112 via nodes 172 and 173 on the input side, and is connected to the heater 101 via terminals 163 and 164 on the output side. The chopper circuit 113 is, for example, a step-down chopper circuit, which is composed of a reactor (coil) 133, a reflux element 132, and a switching element 131.

The reflux element 132 is, for example, a diode. Further, the switching element 131 is, for example, an IGBT (Insulated Gate Bipolar Transistor) or a MOS-FET (Metal-Oxide-Semiconductor Field-Effect Transistor).
The first end of the reactor 133 and the cathode of the reflux element 132 are connected to the node 172. Further, the second end of the reactor 133 is connected to the terminal 163, and the anode of the reflux element 132 is connected to the node 174 (that is, the terminal 164). The collector of the switching element 131 is connected to node 174, the emitter is connected to node 173, and the gate is connected to terminal 167.

The switching element 131 repeats on and off according to a first control signal that repeats on and off at a predetermined duty ratio and a predetermined switching frequency.
(Chopper circuit 114)
The chopper circuit 114 is connected to the noise filter 112 via nodes 172 and 173 on the input side, and is connected to the heater 102 via terminals 165 and 166 on the output side. The chopper circuit 114 has the same configuration as the chopper circuit 113. The chopper circuit 114 is, for example, a step-down chopper circuit, which is composed of a reactor (coil) 143, a reflux element 142, and a switching element 141.

The reflux element 142 is, for example, a diode. Further, the switching element 141 is, for example, an IGBT or a MOS-FET.
The first end of the reactor 143 and the cathode of the reflux element 142 are connected to node 175 (ie, node 172). Further, the second end of the reactor 143 is connected to the terminal 165, and the anode of the reflux element 142 is connected to the node 176 (that is, the terminal 166). The collector of the switching element 141 is connected to the node 176, the emitter is connected to the node 173, and the gate is connected to the terminal 168.

The switching element 141 repeats on and off according to a second control signal that repeats on and off at a predetermined duty ratio and a predetermined switching frequency.
(2) Operation of Chopper Circuit 113 The operation of the chopper circuit 113 will be described. Since the operation of the chopper circuit 114 is the same as the operation of the chopper circuit 113, the description thereof will be omitted.

The switching element 131 repeats on and off according to a first control signal that repeats on and off at a predetermined duty ratio and a predetermined switching frequency.
When the switching element 131 is turned on, as shown by the arrow A in the upper part of FIG. 6, a full-wave rectified current generated by the rectifier circuit 111 flows through the reactor 133 and the heater 101 via the switching element 131. During this time, the reactor 133 stores a part of the current flowing through itself as magnetic energy.

On the other hand, when the switching element 131 is turned off, as shown by the arrow B in the lower part of FIG. 6, the magnetic energy stored in the reactor 133 while the switching element 131 is on is released as a current and starts to flow to the heater 101. This current returns to reactor 133 via the freewheeling element 132 as a regenerative diode.
FIG. 7 shows the waveform WF1 of the current flowing through the heater 101 in the power saving mode, and FIG. 8 shows the waveform WF2 of the current flowing through the heater 101 in the printing operation mode. In FIGS. 7 and 8, the horizontal axis represents the passage of time and the vertical axis represents the current value, respectively.

In the power saving mode, the target temperature of the heater 101 is set lower than the target temperature during the printing operation (that is, during the printing job execution). Therefore, in the PWM control under the power saving mode, the switching frequency is relatively high, for example, 35 kHz, that is, a predetermined short period C is maintained and the duty ratio is set during the power saving mode. , For example, set relatively small, such as about 30%. At this time, as shown in FIG. 7, the waveform WF1 of the current flowing through the heater 101 repeats rising (A) and falling (B), and the time during which the current value becomes a certain value or more (12A or more in FIG. 7) is , Is getting shorter. As a result, the temperature of the heater 101 can be lowered. Here, A of the waveform WF1 corresponds to the current indicated by the arrow A in the upper row of FIG. 6, and B of the waveform WF1 corresponds to the current indicated by the arrow B in the lower row of FIG. Further, in the waveform WF1, the current value continuously becomes zero in the time zone from when the current value indicated by the arrow B in the lower part of FIG. 6 becomes zero until the switching element 131 is turned on. (Current discontinuous mode). That is, the currents shown in the waveform WF1 are discontinuous. This is because the switching frequency is set high, such as 35 kHz, but the duty ratio is set low, for example, about 30%.

On the other hand, in the print operation mode, the target temperature of the heater 101 is set higher than the target temperature in the power saving mode. Therefore, in the PWM control under the print operation mode, the switching frequency is relatively low, for example, 25 kHz, during the period of the print operation mode, that is, a predetermined long period D is maintained and the duty ratio is set. , For example, set relatively large, such as about 70%. At this time, as shown in FIG. 8, the waveform WF2 of the current flowing through the heater 101 repeats rising (A) and falling (B), and the time during which the current value becomes a certain value or more (12A or more in FIG. 8) is , Compared to WF1 shown in FIG. 7, it is longer. Thereby, the temperature of the heater 101 can be raised. Here, A of the waveform WF2 corresponds to the current indicated by the arrow A in the upper row of FIG. 6, and B of the waveform WF2 corresponds to the current indicated by the arrow B in the lower row of FIG. Further, in the waveform WF2, the current value continuously becomes zero in the time zone from when the current value indicated by the arrow B in the lower part of FIG. 6 becomes zero until the switching element 131 is turned on. (Current discontinuous mode). That is, the currents shown in the waveform WF2 are discontinuous. This is because the duty ratio is set large, for example, about 70%, but the switching frequency is set relatively low, such as 25 kHz, so that the current is generated after the switching element 131 is turned off. This is because sufficient time is secured before it decreases.

Here, it is desirable that the switching frequency is not set to 20 kHz or less. When the switching frequency falls into the audible range of 20 kHz or less, the reactor 133 vibrates, and as a result, there arises a problem that noise is generated from the image forming apparatus 10. Therefore, both the switching frequencies of the first control signal and the second control signal are out of the audible range.
Further, as described above, both the current shown in the waveform WF1 and the current shown in the waveform WF2 are discontinuous. This current discontinuity is important for suppressing the generation of noise.

If, in the print operation mode, the switching frequency is set relatively high, for example, 35 kHz, and the duty ratio is set relatively large, for example, about 70%, 12 A or more shown in FIG. 7 or more. Since the rise of the next current of A starts until the current of B shown in FIG. 7 drops to 0, a time occurs in which both the current of A and the current of B flow. sell. Therefore, when the cycle is switched, the current value does not become zero (current continuous mode), a recovery current flows through the recirculation element 132, and recovery noise tends to increase. Further, if the switching element 131 is turned on while a current is flowing through the recirculation element 132, a switching loss occurs and the temperature of the switching element 131 rises.

(3) Circuit time constant The time constant τ1 of the chopper circuit 113 and the heater 101, and the time constant τ2 of the chopper circuit 114 and the heater 102 are expressed as follows.
τ1 = L1 / R1
τ2 = L2 / R2
Here, the inductance L1 (H) of the reactor 133 of the chopper circuit 113, the inductance L2 (H) of the reactor 143 of the chopper circuit 114, the resistance value R1 (Ω) of the heater 101, and the heater 102 so as to satisfy τ2> τ1. The resistance value R2 (Ω) is defined.

In this case, it is necessary to reduce the first drive current to zero for each cycle of the first control signal between the time when the first control signal is turned off and the time when the first control signal is turned on next. There is. That is, it is necessary to prevent the supply of the first drive current in the next cycle from being started before the first drive current becomes zero. This is because if the first drive current of the next cycle is supplied before the first drive current becomes zero, the current continuous mode is set and the above-mentioned problem occurs.

Therefore, the inductance L1 (H), the inductance L2 (H), the resistance value R1 (Ω), and the resistance value R2 (Ω) are determined so as not to enter the current continuous mode and satisfy τ2> τ1.
(4) Currents flowing through the heater 101 and the heater 102 FIG. 9 shows examples of waveforms F5 and F6 of the first drive current flowing through the heater 101 and the second drive current flowing through the heater 102. Further, an example of the waveform F7 (F5 + F6) of the current at which the first drive current and the second drive current merge is shown.

As shown in the waveform F5, the first drive current turns on at time t1 and rises with a predetermined inclination. Further, the first drive current is turned off at time t2 and decreases by a predetermined inclination. The same applies to the following.
Further, as shown in the waveform F6, the second drive current turns on at time t1 and rises more gently than the slope of the first drive current. Further, the second drive current turns off at time t2, and falls gently below the slope of the first drive current. The same applies to the following.

Further, as shown in the waveform F7 (F5 + F6), the current at which the first drive current and the second drive current merge is turned on at time t1 and rises with a predetermined inclination. Further, the merged current turns off at time t2 and drops by a predetermined inclination. The same applies to the following.
In this way, when the timing of changing from off to on overlaps or the timing of changing from on to off overlaps between the first control signal and the second control signal, the second drive current is the first drive current. It changes more slowly.

Here, from the viewpoint of cost and manufacturing of the drive circuit 100, if the chopper circuit 114 is the same circuit as the chopper circuit 113, that is, the inductance L1 of the reactor 133 of the chopper circuit 113 and the reactor of the chopper circuit 114. The waveform F6'of the second drive current flowing through the heater 101 when the inductance L2 of 143 is the same is shown together with the waveform F6 in this figure. Further, in this figure, the waveform F7'shown together with the waveform F7 is a composite of the waveform F5 and the waveform F6'.

In this case, L1 = L2, so if R1 <R2, then
τ1 = L1 / R1> τ2 = L2 / R2.
Therefore, the waveform F6'turns on at time t1 and rises sharply from the first drive current. Further, the waveform F6'turns off at time t2 and drops sharply from the first drive current. The same applies to the following.

Further, the waveform F7'turns on at time t1 and rises steeper than the waveform F7. Further, the waveform F7'turns off at time t2 and drops sharply from the waveform F7. The same applies to the following.
Therefore, even when comparing the case of the present embodiment and the case where the chopper circuit 114 is the same circuit as the chopper circuit 113, the first control signal and the second control signal are switched from off to on. When the timings of change overlap or the timings of changing from on to off overlap, it is suppressed that the current at which the first drive current and the second drive current merge suddenly changes.

Further, in FIG. 9, the waveform G1 shown together with the waveform F6 is a waveform of the drive current in the case of the current continuous mode. The waveform G1 gradually decreases from the time t2, but at the time t3, the drive current does not become zero without being steady-stated. In such a continuous current mode, the above-mentioned problem occurs. Therefore, in the present embodiment, the time constant τ2 is set so as not to be the continuous current mode.

1.5 Effect of Embodiment In this embodiment, the inductance L1 (H) of the reactor 133, the inductance L2 (H) of the reactor 143, and the resistance value R1 of the heater 101 so as to satisfy the time constant τ2> the time constant τ1. (Ω) and the resistance value R2 (Ω) of the heater 102 are defined.
here,
τ1 = L1 / R1,
τ2 = L2 / R2
Is.

By setting the time constant in this way, the change in the drive current flowing through the heater 102 having a rated power smaller than that of the heater 101 is made slower than the change in the drive current flowing through the heater 101.
As a result, when the timing of changing from off to on overlaps or the timing of changing from on to off overlaps between the first control signal and the second control signal, the second drive current is compared with the first drive current. As a result, the generation of harmonics, which are noise components, can be suppressed.

Further, at each cycle of the second control signal, the time constant τ2 is set so that the second drive current decreases to zero between the time when the second control signal is turned off and the time when the second control signal is turned on next. By determining the inductance L2 while satisfying the time constant τ1, the heater 102 can be set to the current discontinuous mode. As a result, the heater 102 does not enter the continuous current mode, prevents the recovery current from flowing, and regulates the change of the second drive current so as not to be too slow. As a result, it is also possible to prevent the change of the current at which the first drive current and the second drive current merge from becoming too slow. As a result, the generation of harmonics, which are noise components, can be suppressed.

When the rated powers of the heater 101 and the heater 102 are predetermined, the inductance L1 in the chopper circuit 113 is set to an appropriate value for the current discontinuous mode in the heater 101 while suppressing noise generation. The chopper circuit 114 so that the constant τ2> the time constant τ1 is satisfied, and the second drive current drops to zero between the time when the second control signal changes off and the time when the second control signal changes to the next on. By determining the inductance L2, the heater 102 can be set to the current discontinuous mode while suppressing the generation of noise. In this way, it is possible to prevent the recovery current from flowing in both the heaters 101 and 102 without entering the current continuous mode. As a result, the generation of harmonics, which are noise components, can be suppressed.

(summary)
As described above, since the time constant is set so that the change in the second drive current is slower than the change in the first drive current, the second drive current does not change suddenly. As a result, the generation of noise can be suppressed. In addition, since the time constant is set so that the second drive current becomes zero between the time when the second control signal turns off and the time when it turns on next, the generation of recovery current is prevented. At the same time, it prevents the change of the second drive current from becoming too slow. As a result, the generation of noise can be suppressed.

2 Modification example (1)
A modified example (1) of the embodiment will be described.
The image forming apparatus of the modified example (1) has a configuration similar to that of the image forming apparatus 10 of the embodiment. Here, the differences will be mainly described.
(1) Circuit time constant As described above, the time constant τ1 of the chopper circuit 113 and the heater 101, and the time constant τ2 of the chopper circuit 114 and the heater 102 are expressed as follows.

τ1 = L1 / R1
τ2 = L2 / R2
Here, in the modification (1), the inductance L1 (H) of the reactor 133 of the chopper circuit 113 and the inductance L2 (H) of the reactor 143 of the chopper circuit 114 are satisfied so that τ2 = τ1 is satisfied instead of τ2> τ1. The resistance value R1 (Ω) of the heater 101 and the resistance value R2 (Ω) of the heater 102 are defined.

(2) Drive current flowing through the heater 101 and the heater 102 Examples of waveforms F1, F2, and F3 of the first control signal, the third control signal, and the second control signal are shown in FIG. Further, examples of waveforms F5 and F6 of the first drive current flowing through the heater 101 and the second drive current flowing through the heater 102 are shown in this figure. Further, an example of the waveform F7 (F5 + F6) of the current at which the first drive current and the second drive current merge is shown. In this figure, the horizontal axis represents the passage of time, and the vertical axis of each waveform represents the current value. Here, the waveforms F1, F2, and F3 shown in FIG. 10 are the same as the waveforms F1, F2, and F3 shown in FIG. 9, respectively.

As shown in the waveform F5, the first drive current turns on at time t11 and rises with a predetermined inclination. Further, the first drive current is turned off at time t12 and decreases by a predetermined inclination. The same applies to the following.
Further, as shown in the waveform F6, the second drive current turns on at time t11 and rises with a slope substantially equal to that of the first drive current. Further, the second drive current turns off at time t12 and decreases with a slope substantially equal to that of the first drive current. The same applies to the following.

By setting the time constant as described above, the change in the drive current flowing through the heater 102 having a rated power smaller than that of the heater 101 is made to be substantially the same as the change in the drive current flowing through the heater 101. Therefore, it is possible to suppress the generation of harmonics, which are noise components.
As shown in the waveform F7 (F5 + F6), the current at which the first drive current and the second drive current merge is turned on at time t11 and rises with a predetermined inclination. Further, the merged current turns off at time t12 and drops by a predetermined inclination. The same applies to the following.

Here, in FIG. 10, the waveform F6'shown together with the waveform F6 is the waveform of the second drive current flowing through the heater 102 when the chopper circuit 114 is the same circuit as the chopper circuit 113, as described above. Is shown. The waveform F6'in FIG. 10 is the same as the waveform F6' in FIG.
The waveform F6'turns on at time t11 and rises sharply from the first drive current. Further, the waveform F6'turns off at time t12 and drops sharply from the first drive current. The same applies to the following.

Further, in FIG. 10, the waveform F7'shown together with the waveform F7 is a composite of the waveform F5 and the waveform F6'. The waveform F7'turns on at time t11 and rises steeper than the waveform F7. Further, the waveform F7'turns off at time t12 and drops sharply from the waveform F7. The same applies to the following.
Therefore, when comparing the case of the modification (1) and the case where the chopper circuit 114 is the same circuit as the chopper circuit 113, the first control signal and the second control signal are switched from off to on. When the timings of change overlap or the timings of changing from on to off overlap, it is suppressed that the current at which the first drive current and the second drive current merge suddenly changes. As a result, the generation of harmonics, which are noise components, can be suppressed.

Further, also in the modification (1), the inductance L1 (H), the inductance L2 (H), the resistance value R1 (Ω), and the resistance value R2 so as not to be in the current continuous mode and to satisfy τ2 = τ1. Determine (Ω). Therefore, it is possible to suppress the generation of harmonics, which are noise components.
3 Modification example (2)
A modified example (2) of the embodiment will be described.

The image forming apparatus of the modified example (2) has a configuration similar to that of the image forming apparatus 10 of the embodiment. Here, the differences will be mainly described.
The image forming apparatus of the modification (2) includes the driving circuit 100a shown in FIG. 11 instead of the driving circuit 100 of the image forming apparatus 10 of the embodiment.
The drive circuit 100a differs from the drive circuit 100 in that an RC circuit 105 is provided between the gate of the switching element 141 and the terminal 168. Further, from the viewpoint of cost and manufacturing of the drive circuit 100a, the chopper circuit 113 and the chopper circuit 114 included in the drive circuit 100a are the same circuit.

The RC circuit 105 is composed of a resistor 151, a capacitor 152, and a ground 153. The first end of the resistor 151 is connected to the gate of the switching element 141, and the second end of the resistor 151 is connected to the terminal 168 and the first end of the capacitor 152. Further, the first end of the capacitor is connected to the second end of the resistor 151 and the terminal 168, and the second end of the capacitor is connected to the ground 153.

As the second control signal supplied from the heater control unit 48 passes through the RC circuit 105, the change from off to on becomes gradual, and the change from off to on becomes gradual. Here, the control signal that has passed through the RC circuit 105 is referred to as a fourth control signal.
An example of the waveforms F1, F2, F3, and F4 of the first control signal, the third control signal, the second control signal, and the fourth control signal is shown in FIG. Further, examples of waveforms F5 and F6 of the first drive current flowing through the heater 101 and the second drive current flowing through the heater 102 are shown in this figure. Further, an example of the waveform F7 (F5 + F6) of the current at which the first drive current and the second drive current merge is shown in this figure.

In this figure, the horizontal axis represents the passage of time, and the vertical axis of each waveform represents the current value. The waveforms F1, F2, and F3 shown in FIG. 12 are the same as the waveforms F1, F2, and F3 shown in FIG. 9, respectively.
As shown in the waveform F4, the fourth control signal turns on at time t21 and rises slowly. Further, the fourth control signal is turned off at time t22 and gradually decreases. The same applies to the following.

Further, as shown in the waveform F5, the first drive current turns on at time t21 and rises from a predetermined inclination. Further, the first drive current is turned off at time t22 and falls below a predetermined inclination. The same applies to the following.
Further, as shown in the waveform F6, the second drive current turns on at time t21 and rises more gently than the slope of the first drive current. Further, the second drive current turns off at time t22, and falls gently below the slope of the first drive current. The same applies to the following.

Further, as shown in the waveform F7 (F5 + F6), the current at which the first drive current and the second drive current merge is turned on at time t21 and rises with a predetermined inclination. Further, the merged current turns off at time t22 and drops by a predetermined inclination. The same applies to the following.
In this way, when the timing of changing from off to on overlaps or the timing of changing from on to off overlaps between the first control signal and the second control signal, the second drive current becomes the first drive current. It suppresses sudden changes in comparison. Therefore, it is possible to suppress the generation of harmonics, which are noise components.

Here, in FIG. 12, the waveform F6'shown together with the waveform F6 shows the waveform of the second drive current flowing through the heater 102 when the RC circuit 105 is not provided.
The waveform F6'turns on at time t21 and rises sharply from the first drive current. Further, the waveform F6'turns off at time t22 and drops sharply from the first drive current. The same applies to the following.

Further, in this figure, the waveform F7'shown together with the waveform F7 is a composite of the waveform F5 and the waveform F6'. The waveform F7'turns on at time t21 and rises steeper than the waveform F7. Further, the waveform F7'turns off at time t22 and drops sharply from the waveform F7. The same applies to the following.
Therefore, even when comparing the case of the modification (2) and the case where the RC circuit 105 is not provided, when the timing of changing from off to on overlaps between the first control signal and the second control signal. Alternatively, when the timings of changing from on to off overlap, it is suppressed that the current at which the first drive current and the second drive current merge suddenly changes. Therefore, it is possible to suppress the generation of harmonics, which are noise components.

Further, also in the modification (2), the resistance value of the resistor 151 of the RC circuit 105 and the capacitance of the capacitor 152 are set so as not to enter the current continuous mode. Therefore, it is possible to suppress the generation of harmonics, which are noise components.
4 Modification example (3)
A modified example (3) of the embodiment will be described.

The image forming apparatus of the modified example (3) has a configuration similar to that of the image forming apparatus 10 of the embodiment. Here, the differences will be mainly described.
The image forming apparatus of the modification (3) includes the driving circuit 100b shown in FIG. 13 instead of the driving circuit 100 of the image forming apparatus 10 of the embodiment.
The drive circuit 100b differs from the drive circuit 100 in that a delay circuit 105a is provided between the gate of the switching element 141 and the terminal 168. Further, from the viewpoint of cost and manufacturing of the drive circuit 100b, the chopper circuit 113 and the chopper circuit 114 included in the drive circuit 100b are the same circuit.

The delay circuit 105a delays the input control signal by a predetermined delay time, and outputs the delayed control signal. The delay circuit 105a is, for example, a delay type inverter or a delay line.
The second control signal supplied from the heater control unit 48 is delayed by passing through the delay circuit 105a. Here, the control signal that has passed through the delay circuit 105a is referred to as a fifth control signal.

An example of the waveforms F1, F2, F3, and F4 of the first control signal, the third control signal, the second control signal, and the fifth control signal is shown in FIG. Further, examples of waveforms F5 and F6 of the first drive current flowing through the heater 101 and the second drive current flowing through the heater 102 are shown in this figure. Further, an example of the waveform F7 (F5 + F6) of the current at which the first drive current and the second drive current merge is shown in this figure.

In this figure, the horizontal axis represents the passage of time, and the vertical axis of each waveform represents the current value. The waveforms F1, F2, and F3 shown in FIG. 14 are the same as the waveforms F1, F2, and F3 shown in FIG. 9, respectively.
As shown in the waveform F3, the second control signal is turned on at time t31 and turned off at time t33. The same applies to the following.

Further, as shown in the waveform F4, the fifth control signal is turned on at the time t32 and turned off at the time t34. The same applies to the following. That is, the fifth control signal is delayed by the delay time (= time t32-time t31) as compared with the second control signal.
As shown in the waveform F5, the first drive current turns on at time t31 and rises with a predetermined inclination. Further, the first drive current is turned off at time t33 and decreases by a predetermined inclination. The same applies to the following.

Further, as shown in the waveform F6, the second drive current turns on at time t32 and rises steeper than the slope at the time of rising of the first drive current. Further, the second drive current is turned off at time t34, and the second drive current drops steeper than the slope when the first drive current drops. The same applies to the following. As described above, the waveform F6 is delayed by the delay time (= time t32-time t31) as compared with the waveform F5.

Here, the delay time is set so that the second drive current is turned on before the first drive current becomes steady.
As shown in the waveform F7 (F5 + F6), the current at which the first drive current and the second drive current merge is turned on at time t31 and rises with the same inclination as the first drive current. Next, the merged current rises at time t32 with a slope similar to that of the second drive current. Further, the merged current decreases at time t33 due to the same inclination as the first drive current, and further decreases at time t34 due to the same inclination as the second drive current. The same applies to the following.

As described above, in the modification (3), the delay time is set so that the second drive current is turned on before the first drive current becomes steady, and the first drive current and the second drive current are set. It suppresses the sudden change of the merged current. Therefore, it is possible to suppress the generation of harmonics, which are noise components.
Further, also in the modification (3), the time constant is set so as not to be in the current continuous mode. Therefore, it is possible to suppress the generation of harmonics, which are noise components.

5 Modification example (4)
A modified example (4) of the embodiment will be described.
The image forming apparatus of the modified example (4) has a configuration similar to that of the image forming apparatus of the modified example (3). Here, the differences will be mainly described.
The delay time due to the delay circuit of the modification (4) is different from the delay time due to the delay circuit 105a of the modification (3).

In the modification (3), the delay time is set so that the second drive current is turned on before the first drive current becomes steady.
On the other hand, in the modified example (4), the delay time is set so that the second drive current is turned on during the steady state after the first drive current is steady. That is, the delay circuit of the modified example (4) generates and outputs a fifth control signal in which the second control signal is delayed so that the second drive signal is turned on after the first drive signal has become stationary. do.

Further, from the viewpoint of cost and manufacturing of the drive circuit 100b, the chopper circuit 113 and the chopper circuit 114 included in the drive circuit 100b are the same circuit.
An example of the waveforms F1, F2, F3, and F4 of the first control signal, the third control signal, the second control signal, and the fifth control signal is shown in FIG. Further, examples of waveforms F5 and F6 of the first drive current flowing through the heater 101 and the second drive current flowing through the heater 102 are shown in this figure. Further, an example of the waveform F7 (F5 + F6) of the current at which the first drive current and the second drive current merge is shown in this figure.

In this figure, the horizontal axis represents the passage of time, and the vertical axis of each waveform represents the current value. The waveforms F1, F2, and F3 shown in FIG. 15 are the same as the waveforms F1, F2, and F3 shown in FIG. 9, respectively.
As shown in the waveform F1, the first control signal turns on at time t41 and turns off at time t43. The same applies to the following.

Further, as shown in the waveform F4, the fifth control signal is turned on at time t42 and turned off at time t45. The same applies to the following. That is, the fifth control signal is delayed by the delay time (= time t42-time t41) as compared with the first control signal. When the fifth control signal is turned on at time t42, the first drive signal shown in the waveform F5 is stationary.

As shown in the waveform F5, the first drive current turns on at time t41 and rises with a predetermined inclination. Further, the first drive current is turned off at time t43 in a state where the second drive current is steady, and is lowered by a predetermined inclination. The same applies to the following.
Further, as shown in the waveform F6, the second drive current turns on at time t42 in a steady state of the first drive current, and rises steeper than the inclination of the first drive current at the time of rising. Further, at time t45, the second drive current is turned off in a state where the first drive current is steady, and the second drive current drops steeper than the slope when the first drive current drops. The same applies to the following.

As described above, the waveform F6 is delayed by the delay time (= time t42-time t41) as compared with the waveform F5.
As shown in the waveform F7 (F5 + F6), the current at which the first drive current and the second drive current merge is turned on at time t41 and rises with the same inclination as the first drive current. Next, the merged current rises at time t42 with a slope similar to that of the second drive current. Further, the merged current decreases at time t43 with the same inclination as the first drive current, and further rises at time t44 with the same inclination as the first drive current. Next, the merged current drops at time t45 due to the same inclination as the second drive current.

In this way, the current at which the first drive current and the second drive current merge repeatedly increases and decreases after the time t42. This reduces noise.
Further, also in the modification (4), the time constant is set so as not to be in the current continuous mode. Therefore, it is possible to suppress the generation of harmonics, which are noise components.
6 Other Modifications The present invention has been described based on the above embodiments and modifications, but is not limited to the above description. It may be as shown below.

(1) In the above-described embodiment and modification, the heating roller 35 has a heater 101 built in the central portion of the tubular core metal, and the heater 102a, respectively, at both end portions of the core metal. It has a built-in 102b. However, this configuration is not limited to this.
The heating roller has one first heater built in the first end and the center of the tubular core, and the second end in the core has a smaller rated power than the first heater. Two second heaters may be built in. This arrangement method is effective when a printing method is adopted so that one side of the paper passes through the first end side.

Further, the shape of the heating roller as the fixing member is not limited to the roller shape, and for example, a pad shape fixedly pressed by the pressure roller can be applied.
(2) The above-described embodiment and the above-described modification may be combined.

The image forming apparatus according to the present invention can suppress the generation of noise when a plurality of heaters are built in the fixing portion, and is useful as a technique for controlling energization of the plurality of heaters by PWM.

10 Image forming device 11 Commercial power supply 34 Fixing unit 35 Heating roller 36 Pressurizing roller 40 Main control unit 45 Printer control unit 48 Heater control unit 49 Control circuit 50 AND circuit 100, 100a, 100b Drive circuit 101, 102, 102a, 102b Heater 105 RC circuit 105a Delay circuit 111 Rectifier circuit 111a, 111b, 111c, 111d Rectifier element 112 Noise filter 113, 114 Chopper circuit 121, 123, 152 Capacitor 122 Coil 131, 141 Switching element 132, 142 Refrigeration element 133, 143 Reactor 151 Resistor 153 ground

Claims (7)

It is an image forming device
A fixing means provided with a first heating element and a second heating element having a rated power smaller than that of the first heating element, and fixing a toner image formed on paper by heating.
A control means that outputs a first control signal and a second control signal that repeat on and off in synchronization with the same duty ratio, and
A first chopper circuit that switches the full-wave rectified input current using the first control signal to generate a first drive current, and supplies the generated first drive current to the first heating element. ,
A second chopper circuit that switches the full-wave rectified input current using the second control signal to generate a second drive current, and supplies the generated second drive current to the second heating element. With and
The change in the second drive current becomes slower than the change in the first drive current, and after each cycle of the second control signal, the second control signal changes to off, and then next. It is characterized in that the second time constant in the second chopper circuit and the second heating element is set so that the second drive current drops to zero before it is turned on. Image forming device. The first chopper circuit includes a first switching element that switches the input current that has been full-wave rectified, a first inductance element that is connected in series with the first heating element, and a first recirculation element that is connected in parallel. death,
The second chopper circuit has a second switching element that switches the input current that has been full-wave rectified, a second inductance element that is connected in series with the second heating element, and a second return element that is connected in parallel. The image forming apparatus according to claim 1. The said second said second time constant determined by the resistance value of the inductance and the second heating element inductance element has has is that Sadama by resistance inductance and the first heating element the first inductance element has has The image forming apparatus according to claim 2, wherein the image forming apparatus is larger than a temporary constant. It is an image forming device
A fixing means provided with a first heating element and a second heating element having a rated power smaller than that of the first heating element, and fixing a toner image formed on paper by heating.
A control means that outputs a first control signal and a second control signal that repeat on and off in synchronization with the same duty ratio, and
The change in the second drive current is slower than the change in the first drive current, and at each cycle of the second control signal, the second control signal is turned off and then turned on. A signal generation circuit that generates a control signal with a slow rise of the second control signal so that the current flowing through the second heating element decreases to zero before the change.
A first chopper circuit that switches the full-wave rectified input current using the first control signal to generate a first drive current, and supplies the generated first drive current to the first heating element. ,
A second chopper circuit that switches the full-wave rectified input current using the second control signal to generate a second drive current, and supplies the generated second drive current to the second heating element. An image forming apparatus comprising the above. It is an image forming device
A fixing means provided with a first heating element and a second heating element having a rated power smaller than that of the first heating element, and fixing a toner image formed on paper by heating.
A control means that outputs a first control signal and a second control signal that repeat on and off in synchronization with the same duty ratio, and
A signal generation circuit that generates a control signal by delaying the second control signal from the first control signal.
The input current is full-wave rectified by switching with the first control signal to generate a first drive current, the first chopper circuit supplies the generated first drive current to the first heating element When,
The input current is full-wave rectified by switching using the control signal to generate a second drive current, and a second chopper circuit supplies the generated second drive current to the second heating element Prepare,
The signal generation circuit is an image forming apparatus, characterized in that the control signal that changes from off to on is generated after the first drive current flowing through the first heating element becomes steady. It is an image forming device
A first heating element and a second heating element having a rated power smaller than that of the first heating element are provided on paper.
A fixing means for fixing the toner image formed in the above by heating,
A control means that outputs a first control signal and a second control signal that repeat on and off in synchronization with the same duty ratio, and
A signal generation circuit that generates a control signal by delaying the second control signal from the first control signal.
A first chopper circuit that switches the full-wave rectified input current using the first control signal to generate a first drive current, and supplies the generated first drive current to the first heating element. ,
A second chopper circuit that switches the full-wave rectified input current using the control signal to generate a second drive current, and supplies the generated second drive current to the second heating element.
With
An image forming apparatus characterized in that both the frequencies of the first control signal and the second control signal are outside the audible range. It is an image forming device
A first heating element and a second heating element having a rated power smaller than that of the first heating element are provided on paper.
A fixing means for fixing the toner image formed in the above by heating,
A control means that outputs a first control signal and a second control signal that repeat on and off in synchronization with the same duty ratio, and
A signal generation circuit that generates a control signal by delaying the second control signal from the first control signal.
A first chopper circuit that switches the full-wave rectified input current using the first control signal to generate a first drive current, and supplies the generated first drive current to the first heating element. ,
A second chopper circuit that switches the full-wave rectified input current using the control signal to generate a second drive current, and supplies the generated second drive current to the second heating element.
With
The image forming apparatus is characterized in that, in the case of a print operation mode or a power saving mode, the control means outputs the first control signal and the second control signal having a duty ratio corresponding to the mode.

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