JP6984260B2 - Image forming device - Google Patents

Description

The present disclosure relates to an image forming apparatus.

Conventionally, there is PWM control as one of the power control methods for the purpose of controlling the temperature of a heater or the like. Patent Document 1 discloses an image forming apparatus including a fixing device including a heater. In this image forming apparatus, in the control means for controlling the amount of electric power supplied to the heater by PWM controlling the current flowing through the heater, the frequency of the PWM signal is constantly changed to suppress the generation of terminal noise.

Japanese Unexamined Patent Publication No. 2007-86352

In the conventional image forming apparatus, since the frequency of PWM control is only spread spectrum, the noise level cannot be sufficiently reduced.

The present disclosure has been conceived in view of such circumstances, and an object thereof is to provide an image forming apparatus capable of sufficiently reducing a noise level.

According to a certain aspect of the present disclosure, a fixing unit including a heater for fixing an unfixed image on paper and a control unit that controls the amount of electric power supplied to the heater by PWM controlling the current flowing through the heater. The control unit is provided by an image forming apparatus that executes frequency processing for adjusting the drive frequency width of the PWM control to a frequency width corresponding to the amount of electric power supplied in one cycle of the PWM control. Will be done.

Preferably, the control unit corrects the duty ratio in one cycle in which the frequency processing is executed to the duty ratio in one cycle in which the frequency processing is not executed. Preferably, the control unit executes a process for reducing the drive frequency width of the PWM control as the frequency process as the amount of electric power supplied in one cycle of the PWM control is smaller.

Preferably, in a state in which an unfixed image is formed on the sheet, further comprising a conveying unit to convey the the paper to the fixing unit, the heater heats the region of both ends in the direction of the conveyance of the paper The control unit controls the amount of electric power supplied to the first heater by PWM-controlling the current flowing through the first heater, which includes a first heater and a second heater that heats a central region of the paper. Further, the image forming apparatus further includes a switching unit for switching whether or not a current flows through the second heater when a current is flowing through the first heater, and the control unit drives the PWM control. the frequency width, performs frequency processing to a frequency width corresponding to the total amount of the amount of power supplied to the electric energy and the second heater supplied to the first heater in one period in the PWM control.

According to the present disclosure, the noise level can be sufficiently reduced.

It is a figure for demonstrating the configuration example of the image forming apparatus. It is a figure for demonstrating the hardware configuration example of the image forming apparatus. It is a figure for demonstrating the fixing device. It is a figure for demonstrating the jitter processing. It is a figure for demonstrating a jitter control table. It is a figure for demonstrating the processing related to a jitter control. It is a figure for demonstrating the 1st sine wave and the 1st triangular wave. It is a figure for demonstrating the 2nd sine wave and the 2nd triangular wave. It is a figure for demonstrating the 1st heater and the 2nd heater. It is a figure for demonstrating the effect of 1st Embodiment. It is a figure for demonstrating the relationship between the power supply to a heater, and a standard value margin. It is a figure for demonstrating a current waveform and the like. It is a figure for demonstrating the fixing device. It is a figure for demonstrating a jitter control table.

Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the following description, the same parts and components are designated by the same reference numerals. Their names and functions are the same. Therefore, these explanations will not be repeated.

<Embodiment 1>
[Structure of image forming apparatus]
The image forming apparatus of this embodiment will be described. FIG. 1 is a diagram for explaining the image forming apparatus 1501. The image forming apparatus 1501 according to the embodiment is provided with an intermediate transfer belt 1502 as a belt member in a substantially central portion inside the image forming apparatus 1501.

Below the lower horizontal part of the intermediate transfer belt 1502, four image-forming units 1506Y, 1506M, 1506C, 1506K corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Are arranged side by side along the intermediate transfer belt 1502.

The image forming units 1506Y, 1506M, 1506C, and 1506K have photoconductor drums 1507Y, 1507M, 1507C, and 1507K, respectively. Around each photoconductor drum 1507Y, 1507M, 1507C, 1507K, a charger 1508, a print head portion 1509, a developer 1510, and an intermediate transfer belt 1502 are sandwiched in order along the rotation direction of each photoconductor. Primary transfer rollers 1511Y, 1511M, 1511C, 1511K facing the drums 1507Y, 1507M, 1507C, 1507K are arranged, respectively.

The secondary transfer roller 1503 is pressure-welded to the portion of the intermediate transfer belt 1502 supported by the intermediate transfer belt drive roller 1505, and the nip portion between the secondary transfer roller 1503 and the intermediate transfer belt 1502 is a secondary transfer region. It is 1530. A fixing device 100 is arranged at a downstream position of the transport path 1541 on the wake side of the secondary transfer region 1530.

A paper cassette 1517 is detachably arranged at the lower part of the image forming apparatus 1501. The paper P loaded and accommodated inside the paper cassette 1517 is sent out one by one from the uppermost one to the transport path 1540 by the rotation of the paper feed roller 1518. An image density (AIDC) sensor 1519 that also serves as a resist sensor is installed between the image forming unit 1506K on the most downstream side of the intermediate transfer belt 1502 and the secondary transfer region 1530.

Next, the schematic operation of the image forming apparatus 1501 having the above configuration will be described. An image signal is input from an external device (for example, a personal computer) to an image signal processing unit (not shown) of the image forming device 1501. The image signal processing unit to which the image signal is input creates a digital image signal in which the image signal is color-converted into yellow, cyan, magenta, and black. The printhead unit 1509 of each image forming unit 1506Y, 1506M, 1506C, 1506K emits light based on a digital image signal, and exposes each photoconductor drum 1507Y, 1507M, 1507C, 1507K.

The electrostatic latent image formed on each of the photoconductor drums 1507Y, 1507M, 1507C, and 1507K is developed by each developer 1510 to become a toner image of each color. The toner images of each color are sequentially superimposed on the intermediate transfer belt 1502 moving in the direction of arrow A by the action of the primary transfer rollers 1511Y, 1511M, 1511C, and 1511K, and are primary transferred.

The toner image formed on the intermediate transfer belt 1502 reaches the secondary transfer region 1530 as the intermediate transfer belt 1502 moves. In the secondary transfer region 1530, the superimposed color toner images are collectively secondary transferred to the paper P by the action of the secondary transfer roller 1503.

The paper P on which the toner image is secondarily transferred (paper P on which the unfixed image is formed) is conveyed to the fixing device 100 by the conveying device (CPU 301 in FIG. 2) via the conveying path 1541. In the fixing device 100, the toner image is fixed on the paper P.

FIG. 2 is a diagram showing a hardware configuration of the image forming apparatus 1501. With reference to FIG. 2, the image forming apparatus 1501 includes a CPU (Central Processing Unit) 101 for executing a program, a ROM (Read Only Memory) 302 for storing data non-volatilely, and a RAM for storing data volatilely. (Random Access Memory) 303, a flash memory 304, a touch screen 305, and a speaker 306 are provided.

The touch screen 305 includes a display 3051 as a display device and a touch panel 3052 as an input device. Specifically, the touch screen 305 is realized by positioning and fixing the touch panel 3052 on the display 3051 (for example, a liquid crystal display). The touch screen is also referred to as a touch panel display, a display with a touch panel, or a touch panel monitor. In the touch screen 305, for example, a resistance film method or a capacitance method can be used as a method for detecting the touch position.

The flash memory 304 is a non-volatile semiconductor memory. The flash memory 304 stores an operating system executed by the CPU 301, various programs, various contents, and data. Further, the flash memory 304 volatilely stores various data such as data generated by the image forming apparatus 1501 and data acquired from an external device of the image forming apparatus 1501.

The speaker 306 generates sound in response to a command from the CPU 301. The CPU 301 specifies an input position based on the output from the touch panel 3052, and displays a screen based on the specified input position.

The processing in the image forming apparatus 1501 (fixing apparatus 100) is realized by the software executed by each hardware and the CPU 301. Such software may be stored in the flash memory 304 in advance. Each component constituting the image forming apparatus 1501 shown in the figure is general. Therefore, it can be said that an essential part of the present invention is software stored in a flash memory 304, a memory card or other storage medium, or software that can be downloaded via a network. Since the operation of each hardware of the image forming apparatus 1501 is well known, detailed description thereof will not be repeated.

[Fixing device configuration]
Next, the configuration of the fixing device 100 will be described. FIG. 3 is a diagram for explaining the fixing device 100. The fixing device 100 includes a rectifier circuit 102, a first chopper circuit 104, a second chopper circuit 106, a fixing unit 109, a control unit 114, and the like. The fixing unit 109 includes a first heater 108, a second heater 110, and a temperature sensor 112. Further, both the first heater 108 and the second heater 110 are halogen heaters. As a modification, at least 1 of the first heater 108 and the second heater 110 may be another heater. For example, other heaters are carbon heaters, ceramic heaters, and the like. Further, the configuration of FIG. 3 actually includes a noise filter and the like. Further, the control unit 114 may be a control unit of the image forming apparatus 1501 or a dedicated control unit of the fixing apparatus 100.

The rectifier circuit 102 rectifies the AC (alternating current) current from the AC power supply 2 into a DC (Direct Current) current. The first chopper circuit 104 and the second chopper circuit are arranged after the rectifier circuit 102. The first chopper circuit 104 and the second chopper circuit are composed of switching elements such as a reactor, a recirculation element, and an IGBT (Insulated Gate Bipolar Transistor). Hereinafter, the first chopper circuit 104 and the second chopper circuit are collectively referred to as a “chopper circuit”.

The first chopper circuit 104 is connected to the first heater 108. The second chopper circuit 106 is connected to the second heater 110. The temperature sensor 112 detects the temperature of the fixing unit 109, and the detected temperature is transmitted to the control unit 114. The control unit 114 determines the power supply to the fixing unit 109 based on the transmitted temperature. The control unit 114 determines the duty ratio of the first chopper circuit 104 and the duty ratio of the second chopper circuit 106 based on the determined power supply. The control unit 114 repeats ON (transmission) or OFF (non-transmission) of the first PWM signal to the first chopper circuit 104 based on the duty ratio of the first chopper circuit 104. Further, the control unit 114 repeats ON (transmission) or OFF (non-transmission) of the second PWM signal to the second chopper circuit 106 based on the duty ratio of the second chopper circuit 106. When the PWM signal is output from the control unit 114 to the chopper circuit, the chopper circuit (switching element) is turned on for a time of a ratio corresponding to the determined duty ratio. As a result, power corresponding to the duty ratio (and the rated power of the heater) is supplied to the heater connected to the chopper circuit.

In this way, the control unit 114 controls the amount of electric power supplied to the first heater 108 by PWM controlling the current flowing through the first heater 108. Further, the control unit 114 controls the amount of electric power supplied to the second heater 110 by PWM controlling the current flowing through the second heater 110.

In the present embodiment, the PWM signal that controls the chopper circuit is controlled at a PWM frequency of 20 kHz or higher. The PWM frequency is the frequency of the pulse of the PWM signal, and is the frequency of the chopping control when the PWM signal is ON. If the PWM frequency is 20 kHz or less, the product operating sound becomes loud because it is in the human audible frequency range, and there is a problem that the user is concerned about the product operating sound. Further, if the PWM frequency is raised too much, the number of operation of the IGBT increases by that amount and the switching loss becomes large. In the present embodiment, in view of these circumstances, the image forming apparatus of the present embodiment has a PWM frequency of 20 kHz or more and does not raise the PWM frequency too much.

Further, in general, switching noise of a 20 kHz chopper circuit (IGBT) deteriorates EMC (electromagnetic compatibility: emission), so noise countermeasures are required. As measures against this noise, measures such as adjusting the gate resistance value of the IGBT, adding a snubber circuit, and adding ferrite beads can be considered. Further, as a noise countermeasure, a noise filter is used at the input section such as a normal mode coil, a common mode choke coil, an X capacitor, a Y capacitor, and a ferrite core added to the AC bundle wire between the AC2 power supply and the rectifier circuit 102. Countermeasures are also conceivable. However, these measures are not useful measures because they cause deterioration of loss, large size of the substrate, cost increase, and the like.

[About jitter control]
In this embodiment, jitter control is executed as a noise countermeasure for the image forming apparatus. Jitter control is a control for setting the PWM frequency width (drive frequency width) of PWM control to a frequency width corresponding to the amount of electric power (or duty ratio) supplied in one cycle in PWM control. Further, this jitter control is executed for each of the first chopper circuit 104 (first heater 108) and the second chopper circuit 106 (second heater 110).

FIG. 4 is a diagram for explaining a waveform of a PWM signal by PWM control of the present embodiment. Regarding FIGS. 4A to 4C, “ON” indicates the ON time of the chopper circuit, and “OFF” indicates the OFF time of the chopper circuit. Further, FIG. 4 shows an intermediate portion of the 4th cycle together with the 1st cycle, the 2nd cycle, and the 3rd cycle in the PWM cycle. FIG. 4A is a diagram showing a case where jitter control is not executed. Since the PWM frequency in this case is 20 kHz, it is assumed that all the PWM cycles including the first cycle to the fourth cycle are 50 μsec.

In FIG. 4A, it is assumed that the duty ratio in the first cycle is 20%. In this case, the time for outputting the PWM signal (hereinafter referred to as ON time) is 10 μsec. Further, it is assumed that the duty ratio in the second cycle is 50%. The ON time in this case is 25 μsec. Further, it is assumed that the duty ratio in the third cycle is 70%. The ON time in this case is 35 μsec.

FIG. 4B is a diagram showing a case where jitter control is executed. As shown in the portion corresponding to the first cycle in FIG. 4B, when the duty ratio is 20%, the jitter control is not executed in this embodiment. As shown in the portion corresponding to the second cycle in FIG. 4B, when the duty ratio is 50%, it is changed (modulated) to 21 kHz by adding 1 kHz to the PWM frequency of 20 kHz. Further, as shown in the portion corresponding to the third cycle in FIG. 4B, when the duty ratio is 70%, it is changed (modulated) to 23 kHz by adding 3 kHz to the PWM frequency of 20 kHz. ).

FIG. 5 schematically shows a jitter control table used in jitter control. The jitter control table of FIG. 5 is stored in, for example, the ROM 302. The leftmost column in FIG. 5 shows the PWM ratio in one cycle (PWM cycle) when the jitter control is not performed. Further, the parentheses indicate the electric power supplied to the heater in the one cycle. For example, when the duty ratio is 30% or less, it indicates that the power supplied is 0 to 390 W. Further, the jitter control table of FIG. 5 is applied to the PWM control for the first heater 108 and the PWM control for the second heater 110, respectively.

The column on the right side shows the jitter setting of the PWM cycle. The amount of jitter in FIG. 5 means the width of the PWM frequency after the change. In other words, the amount of jitter means the difference between the maximum value and the minimum value of the changed PWM frequency. The amount of jitter is also called the degree of modulation.

For example, a duty ratio of 30% or less is associated with "none" as the amount of jitter. Therefore, when the duty ratio is 30% or less, the PWM cycle is not changed and remains at 20 kHz (see the corresponding portion of the first cycle in FIG. 4B).

Further, the duty ratio larger than 30% and less than 60% is associated with "small" as the amount of jitter. In the example of FIG. 5, the small amount of jitter is set to "1 kHz". This indicates that any frequency of 0 to 1 kHz is added to the PWM frequency. Therefore, when the duty ratio is larger than 30% and less than 60%, the PWM frequency after the change (after adding the frequency) is any of 20 to 21 kHz. In the corresponding part of the second cycle of FIG. 4C, the case where the changed PWM frequency is 21 kHz is shown.

Further, the duty ratio of 60% or more is associated with "large" as the amount of jitter. In the example of FIG. 5, the large amount of jitter is set to "3 kHz". This indicates that any frequency of 0 to 3 kHz is added to the PWM frequency. Therefore, when the duty ratio is larger than 30% and less than 60%, the PWM frequency after the change (after frequency addition) is any of 20 to 23 kHz. In the corresponding part of the third cycle of FIG. 4C, the case where the changed PWM frequency is 23 kHz is shown.

Next, a flowchart of processing related to jitter control will be described. This process is a timer interrupt process executed by the control unit 114 at predetermined time intervals. FIG. 6 is a diagram showing this flowchart.

As shown in S2, the control unit 114 increments the counter value n by 1. Here, the counter value n is a value indicating the number of times the PWM signal is transmitted. That is, the counter value is a value that is incremented by 1 every time 1 PWM cycle elapses.

Next, in S4, the control unit 114 acquires the duty ratio. Here, the control unit 114 acquires the duty ratio based on the temperature of the fixing unit 109 detected by the temperature sensor 112.

In S6, the control unit 114 determines whether or not the duty ratio is ≦ 30%. If YES is determined in S6, the PWM frequency is not changed as described in FIG. 5, and the process is terminated.

If NO is determined in S6, the process proceeds to S8. In S8, it is determined whether or not 30% <Duty ratio <60%. If YES is determined in S8, the process proceeds to S10. In S10, the control unit 114 acquires the counter value.

Next, in S12, the PWM frequency is specified based on the first sine wave and the counter value acquired in S10. Then, the frequency is changed to the specified PWM frequency. FIG. 7A is a diagram showing an example of a first sine wave.

In FIG. 7A, the horizontal axis shows the counter value, and the vertical axis shows the PWM frequency (the changed PWM frequency). The first sine wave in FIG. 7A is a part of the sine wave. When the counter value is 0 or N, the PWM frequency is set to 20 kHz, and when the counter value is N / 2, the PWM frequency is set to 23 kHz.

Here, N is the maximum value of the counter value. In the increment process of S2 in FIG. 6, when the counter value reaches N, the counter value is initialized (set to 0). In S12, the frequency corresponding to the counter value acquired in S10 is specified based on the sine wave of FIG. 7A. For example, Y = AsinX, which is an equation showing the sine wave of FIG. 7A (hereinafter referred to as a first sine wave equation), may be used. Here, X indicates a counter value on the horizontal axis, Y indicates a frequency on the vertical axis, and A indicates a constant. The control unit 114 assigns the acquired counter value to X of the first sine wave type to specify the PWM frequency. Then, the control unit 114 changes to the specified PWM frequency. The control unit 114 executes PWM control so as to have the changed PWM frequency.

Further, in S12, the control unit 114 may specify the frequency by using the triangular wave (hereinafter referred to as the first triangular wave) shown in FIG. 7B instead of using the first sine wave. For example, the control unit 114 may specify the PWM frequency by using an equation (hereinafter referred to as a triangular wave equation) showing the first triangular wave of FIG. 7B.

If NO is determined in S8, the process proceeds to S14. In S14, the control unit 114 acquires a counter value.

Next, in S16, the PWM frequency is specified based on the first sine wave and the counter value acquired in S14. Then, the frequency is changed to the specified PWM frequency. FIG. 8A is a diagram showing an example of a second sine wave.

In FIG. 8A, the horizontal axis shows the counter value, and the vertical axis shows the PWM frequency (the changed PWM frequency). The second sine wave in FIG. 8 (A) is a part of the sine wave. When the counter value is 0 or N, the PWM frequency is set to 20 kHz, and when the counter value is N / 2, the PWM frequency is set to 21 kHz. In S16, the frequency corresponding to the counter value acquired in S14 is specified based on the sine wave of FIG. 8A. For example, Y = BsinX, which is an equation showing the sine wave of FIG. 8A (hereinafter referred to as a second sine wave equation), may be used. Here, X indicates a counter value on the horizontal axis, Y indicates a frequency on the vertical axis, and B indicates a constant. The control unit 114 assigns the acquired counter value to X of the second sinusoidal wave type to specify the PWM frequency. Then, the control unit 114 changes to the specified PWM frequency. The control unit 114 executes PWM control so as to have the changed PWM frequency.

Further, in S16, the control unit 114 may specify the frequency by using the triangular wave (hereinafter referred to as the second triangular wave) shown in FIG. 8B instead of using the second sine wave. For example, the control unit 114 may specify the PWM frequency by using an equation (hereinafter referred to as a triangular wave equation) showing the second triangular wave of FIG. 7B.

Further, as a modification, the PWM frequency may be specified by using another formula instead of using the sine wave type or the triangular wave type. Further, as a modification, a table in which the counter value and the PWM frequency are associated with each other may be used instead of the sine wave type or the triangular wave type in S12 and S16. For example, the first table used in S12 and the second table used in S16 are created in advance and stored in a predetermined area (for example, ROM 302). The control unit 114 may specify the PWM frequency in S12 with reference to the first table. Further, the control unit 114 may specify the PWM frequency in S16 with reference to the second table.

[1st heater and 2nd heater]
Next, the heating regions of the first heater 108 and the second heater 110 will be described. FIG. 9 is a diagram for explaining a heating region of the first heater 108 and the second heater 110. In FIG. 9, the arrow α indicates the transport direction of the fixing device 100. Further, in FIG. 9, the first paper and the second paper are shown, and it is assumed that the first paper is A3 size paper and the second paper is A4 size paper.

The first heater 108 heats the regions B at both ends of the first sheet in the transport direction α. The second heater 110 heats the central region A of the second paper in the transport direction α. Region A and region B are different regions from each other.

By having the first heater 108 and the second heater 110, for example, when the fixing process is performed on A4 paper, the fixing device 100 does not perform heating by the first heater 108, but the second heater 110. Perform heating by. Further, when the fixing process is performed on the A3 paper, both the heating by the first heater 108 and the heating by the second heater 110 are executed. Therefore, fine fixing processing can be performed according to the size of the paper.

As the first heater 108 and the second heater 110, heaters that are proportional to the area and heat capacity of the respective heating regions are used.

[Effect of this embodiment]
Next, the effect of this embodiment will be described. High-frequency chopper control using a chopper circuit has less deterioration of power factor and generation of harmonics, but has a large EMC noise (power supply noise: noise terminal voltage), and requires a large-scale noise filter and a snubber circuit with a large loss. It caused the deterioration, deterioration of loss, and cost increase. In the present embodiment, jitter control that intentionally gives jitter to the PWM frequency is executed for a period in which the duty ratio is larger than 30%. As a result, the noise level can be reduced by spreading the EMC noise energy generated at 20 kHz in a spread spectrum while not increasing the device size and reducing the component cost.

FIG. 10 is a diagram for explaining the effect of the present embodiment. The horizontal axis of each of FIGS. 10A and 10B shows the frequency based on the PWM frequency, and the vertical axis shows the standard value margin. FIG. 10A shows a case where the jitter control is not executed, and FIG. 10B shows a case where the jitter control is executed. In the jitter control in FIG. 10B, the modulation degree (jitter amount) is 1 kHz, and the first triangular wave equation (FIG. 7B) is used as the equation for obtaining the PWM frequency. Further, it is assumed that the period of the first triangular wave (variable period in FIG. 10B) is 1 kHz.

As is clear from FIGS. 10 (A) and 10 (B), when the jitter control is executed, the margin QP value is improved by about 5 dB as compared with the case where the jitter control is not executed. The margin CISPR-AV value was improved by about 7 dB.

Further, the control unit 114 executes frequency processing (jitter processing) for adjusting the width of the PWM frequency of the PWM control to the frequency width corresponding to the electric energy (duty ratio) supplied in one cycle of the PWM control. Here, as shown in FIG. 5 and the like, the smaller the amount of power (Duty ratio) supplied in one cycle of PWM control, the smaller the frequency width (jitter amount) of the PWM control drive frequency. Is executed. The effect of this process will be described.

As described above, the PWM frequency is set to 20 kHz in order to exclude it from the human audible frequency range. When the amount of jitter is applied, the frequency is also controlled to be larger than 20 kHz in order to exclude it from the audible frequency region. Increasing the PWM frequency is synonymous with increasing the number of switching times of the IGBT (chopper circuit). Then, the switching loss in the IGBT increases and the energy efficiency of the entire device decreases (hereinafter, referred to as “switching loss”). Since a decrease in energy efficiency in an image forming apparatus in recent years means a decrease in product competitiveness, it is necessary to suppress a decrease in product energy efficiency due to jitter control.

The EMC noise energy correlates with the heater input power, and the smaller the heater input power, the smaller the EMC noise energy. FIG. 11 is a diagram for explaining this correlation. FIG. 11 shows a heater of 1300 W, the horizontal axis shows the power supply (duty ratio) to the heater, and the vertical axis shows the standard value margin. As shown in FIG. 11, it can be seen that there is a phenomenon that the EMC noise level is lowered as the heater supply power is made smaller (the duty ratio is lowered).

In view of this phenomenon, the image forming apparatus of the present embodiment executes jitter control based on the table shown in FIG. In FIG. 5, since the EMC noise is large when the duty ratio is 60% or more, the spread spectrum can be widened and the noise suppression effect can be enhanced by setting a large jitter amount (+3 kHz). Further, since the EMC noise level is also small at the duty ratio of 30% to 60%, the EMC noise suppression and the switching loss suppression are both set by setting the jitter amount to be small (+ 1 kHz). Further, since the EMC noise level becomes even smaller when the duty ratio is 30% or less, the setting is set so that the switching loss is not increased without performing jitter control.

In this way, since the jitter processing for adjusting the PWM frequency to the frequency width corresponding to the amount of electric power supplied in one cycle in the PWM control is executed, the suppression of EMC noise and the suppression of switching loss are taken into consideration. Control can be performed.

<Embodiment 2>
Next, the second embodiment will be described. As also described in FIG. 4B, when jitter is applied to the PWM frequency, the ON time fluctuates. For example, when the PWM frequency is 20 kHz (PWM cycle is 50 μsec), the ON time is 25 μsec when controlling the duty ratio of one cycle at 50%. When the PWM frequency of 20 kHz is changed to 21 kHz (PWM cycle is 47 μsec), the duty ratio becomes 53%, and the duty ratio fluctuates. When the duty ratio fluctuates, the productivity of the image forming apparatus decreases.

FIG. 12 is a diagram showing that the productivity of the image forming apparatus is reduced. The upper figure of FIGS. 12A and 12B shows the PWM frequency, and the lower figure shows the current waveform. The PWM frequency in the upper figure shows the change from 20 kHz, shows the current passed through the heater when the solid line duty ratio in the lower figure is 100%, and the broken line shows the current flowing through the heater according to the set duty ratio. Indicates the current applied. The thickness of the vertical line in the curve indicates the PWM frequency. That is, a thick vertical line indicates that the PW frequency is high, and a thin vertical line indicates that the PW frequency is low.

As shown in FIG. 12A, when the PWM frequency is constant (for example, 20 kHz), the power factor is improved because the current waveform shown by the broken line is not distorted. On the other hand, as shown in FIG. 12B, when the PWM frequency fluctuates periodically, the current waveform shown by the broken line is distorted, and the power factor deteriorates.

When the PWM frequency is periodically changed by the jitter control in this way, the current level supplied to the heater also changes periodically as shown in FIG. 12B, so that the SIN wave-shaped current waveform is distorted. It occurs and the power factor deteriorates. When the power factor deteriorates, a larger current is required for the heat generation amount of the heater, which lowers the productivity of the image forming apparatus.

Therefore, in the present embodiment, in order to prevent the decrease in productivity, the duty ratio in one cycle in which the jitter processing is executed is corrected to the duty ratio in one cycle in which the jitter processing is not executed. .. This correction process is executed by the correction unit 1142 (see FIG. 3).

This correction process will be described with reference to FIG. 4 (C). Since the jitter control is not executed in the first cycle, the correction unit 1142 does not execute the correction process. Since the jitter control is executed in the second cycle, the correction unit 1142 executes the correction process.

First, the correction unit 1142 acquires the duty ratio in two cycles when the jitter control is not executed. The duty ratio is 50%. The second period after jitter control is 47 μsec, and the duty ratio is 53%. The correction unit 1142 corrects the duty ratio, which is 53%, so that the duty ratio becomes 50% in the second cycle after the jitter control. For example, the correction unit 1142 can correct the duty ratio, which is 53%, to 50% by setting the ON time to 23.5 μsec. The control unit 114 transmits a PWM signal based on the set ON time.

Next, the third cycle will be described. First, the correction unit 1142 acquires the duty ratio in three cycles when the jitter control is not executed. The duty ratio is 70%. The third period after the jitter control is 43 μsec, and the duty ratio is 81%. The correction unit 1142 corrects the duty ratio, which is 81%, so that the duty ratio becomes 70% in the third cycle after the jitter control. For example, the correction unit 1142 can correct the duty ratio, which is 81%, to 70% by setting the ON time to 30 μsec. The control unit 114 transmits a PWM signal based on the set ON time.

In the process of FIG. 6, after the process of S12, the correction unit 1142 corrects the duty ratio as the process of S13 shown by the broken line. Further, after the processing of S16, the correction unit 1142 corrects the duty ratio as the processing of S17 shown by the broken line.

As described above, the correction unit 1142 corrects the duty ratio in one PWM cycle in which the jitter control is executed to the duty ratio in one PWM cycle in which the jitter control is not executed. Therefore, the waveform of the current shown in FIG. 12B (waveform of the broken line) is the same as the waveform of the current shown in FIG. 12A (waveform of the broken line), or is shown in FIG. 12A. It can be a waveform close to the current waveform (waveform of a broken line). Therefore, since the distortion generated by the current waveform (broken line waveform) is eliminated or reduced, deterioration of the power factor can be prevented.

<Embodiment 3>
Next, the third embodiment will be described. FIG. 13 is a diagram for explaining the fixing device 150 of the third embodiment. Comparing FIG. 13 and FIG. 3, FIG. 3 has two chopper circuits (first chopper circuit 104 and second chopper circuit 106), whereas FIG. 13 has one chopper circuit 204 and a cutoff. Both drawings differ in that they include a portion 206. The blocking unit 206 is configured by using a switching element such as a triac or a thyristor. Further, an inrush current prevention element and a short-circuit means may be installed after the cutoff portion 206. The inrush current prevention element is composed of, for example, an NTC (Negative Temperature Coefficient) thermistor.

The chopper circuit 204 is installed in the subsequent stage of the cutoff portion 206. The chopper circuit 204 is connected to the second heater 110, and the cutoff portion 206 is connected to the first heater 108.

The control unit 124 can execute PWM control by transmitting a PWM signal to the chopper circuit 204. Further, the control unit 124 can switch between heating and non-heating of the first heater 108 by transmitting a switching signal to the cutoff unit 206. Further, when the second heater 110 is energized and the cutoff portion 206 is turned on, the second heater 110 is energized.

Since the configuration of FIG. 13 supplies power to the two heaters with one chopper circuit, there is an advantage that the size of the fixing device can be made smaller and the component cost can be reduced as compared with the configuration of FIG. However, in the configuration of FIG. 13, the table shown in FIG. 5 cannot be applied. For example, in the case of executing the control with the duty ratio set to 60%, when the power is supplied only to the first heater 108 by the PWM control (hereinafter, referred to as "the first case"), the first is performed by the PWM control. The actual heater supply power differs depending on whether power is supplied to both the heater 108 and the second heater 110 (hereinafter, referred to as “second case”). Therefore, the EMC noise level differs between the first case and the second case, and the table of FIG. 3 does not determine a setting that can achieve both EMC noise suppression and switching loss suppression.

Therefore, in the present embodiment, when the second heater 110 connected to the chopper circuit 204 is energized, whether or not the first heater 108 is energized (whether it is energized or not energized). ) To make the table different in the amount of jitter.

FIG. 14 schematically shows the jitter control table of the present embodiment. In the example of FIG. 14, the condition that the second heater 110 is energized and the first heater 108 is not energized is the first condition. The second condition is that the first heater 108 and the second heater 110 are energized. Under the first condition, the total amount of the electric power of the first heater 108 in one PWM cycle (= 0 W because it is not energized) and the electric energy of the second heater 110 having a duty ratio of 100%. Is 870W. Further, under the first condition, the electric energy of the first heater 108 in one PWM cycle (= 0 W because it is not energized) and the electric energy of the second heater 110 having a duty ratio of 70%. The total amount of is 609W.

Further, under the second condition, the total amount of the electric energy of the second heater 110 in which the duty ratio in one PWM cycle is 100% and the electric energy of the first heater 108 in one PWM cycle is the total amount. It will be 1300W. Further, under the second condition, the total amount of the electric energy of the second heater 110 in which the duty ratio in one PWM cycle is 70% and the electric energy of the first heater 108 in one PWM cycle is , 910W.

Then, in the example of FIG. 14, when the total amount of electric power of the two heaters is smaller (that is, when the first condition is satisfied), the amount of jitter is set to "small (1 kHz)". Further, when the total amount of electric power of the two heaters is larger (that is, when the second condition is satisfied), the amount of jitter is set to "large (3 kHz)".

Further, the control unit 124 may be provided with the function of the correction unit 1142 described in the second embodiment.

According to the configuration of the third embodiment, when two heaters (first heater 108 and second heater 110) are provided, PWM control is performed for one heater and PWM control is performed for the other heater. It can be configured to perform different controls (eg, switching controls). Therefore, there is an advantage that the size of the fixing device can be reduced and the cost of parts can be reduced as compared with the fixing device that executes PWM control for each of the two heaters.

Further, even in the configuration of the present embodiment 3, the width of the PWM frequency of the PWM control, the amount of power supplied to the first heater 108 to 1 cycle of the PWM control and the amount of power supplied to the second heater 110 Jitter processing is executed to obtain the frequency width (jitter amount) according to the total amount. Therefore, the noise level can be appropriately reduced.

[others]
In the first embodiment, it has been described that the number of heaters subject to PWM control is two. However, the number of heaters subject to PWM control may be one or three. Further, in the third embodiment, it has been described that the number of heaters subject to PWM control is one, and the number of heaters subject to control different from PWM control is also one. However, the number of heaters subject to PWM control may be 2 or more. When the number of heaters subject to PWM control is 2 or more, for example, the table of FIG. 14 is applied to the PWM control of each of the 2 or more heaters.

Further, when the number of heaters to be controlled different from the PWM control is two or more, the heater to be energized may be selected based on the job input from the user or the like.

In addition, it should be considered that each embodiment disclosed this time is exemplary in all respects and is not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims. Further, the inventions described in the embodiments and the modifications thereof are intended to be carried out alone or in combination as much as possible.

102 Rectifier circuit, 104 1st chopper circuit, 106 2nd chopper circuit, 108 1st heater, 109 fixing unit, 110 2nd heater, 112 temperature sensor, 114, 124 control unit.

Claims (4)

A fixing part including a heater for fixing an unfixed image on paper,
It is provided with a control unit that controls the amount of electric power supplied to the heater by PWM controlling the current flowing through the heater.
The control unit is an image forming apparatus that executes frequency processing for adjusting the drive frequency width of the PWM control to a frequency width corresponding to the amount of electric power supplied in one cycle of the PWM control. The image forming apparatus according to claim 1, wherein the control unit corrects the duty ratio in one cycle in which the frequency processing is executed to the duty ratio in one cycle in which the frequency processing is not executed. 1. Item 2. The image forming apparatus according to item 2. Further, a transport unit for transporting the paper to the fixing portion in a state where an unfixed image is formed on the paper is provided.
The heater includes a first heater that heats the regions at both ends of the paper in the transport direction and a second heater that heats the central region of the paper.
The control unit controls the amount of electric power supplied to the first heater by PWM controlling the current flowing through the first heater.
The image forming apparatus further includes a switching unit for switching whether or not a current flows through the second heater when a current is flowing through the first heater.
Wherein the control unit, the driving frequency of the PWM control, the frequency width corresponding to the total amount of the amount of power supplied to the electric energy and the second heater supplied to the first heater in one period of the PWM control The image forming apparatus according to any one of claims 1 to 3, wherein the frequency processing for performing the above-mentioned is performed.

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