Fixing device and image forming apparatus

Abstract

To provide a fixing device that can freely adjust the amount of supplied power.SOLUTION: A fixing device comprises: a fixing roller 171 and a pressure roller 174 that are provided rotatably; a heat source 172a that heats the fixing roller 171; and a control unit 50 that controls AC power supplied to the heat source 172a, and the fixing device fixes an unfixed image onto a sheet that is sandwiched and conveyed by the fixing roller 171 and the pressure roller 174. The control unit 50 performs energization including an energization waveform in which a phase angle is different for every half wave in a preset control period.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a fixing device that fixes an unfixed image on a sheet of paper and an image forming apparatus. [Background technology]

[0002] Conventionally, in a fixing device used in an electrophotographic image forming apparatus such as a copying machine or a printer, a toner image is fixed by applying pressure and heat to a sheet on which an unfixed toner image (unfixed image) is formed. In a heater provided in the fixing device, if the power supply is large, an inrush current becomes excessive, which may cause a voltage fluctuation flicker in the power supply system. To reduce this, there is a method of controlling the heater using phase control (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-268447 A [Patent Document 2] JP 2004-191710 A [Patent Document 3] Japanese Patent Application Publication No. 10-162935 Summary of the Invention [Problem to be solved by the invention]

[0004] The electrophotographic apparatus (image forming apparatus) described in Patent Document 1 includes a heater, an AC power source, and a control unit. When power is supplied to the heater, the heater is first maintained at a designated phase angle for a certain period of time, and then a control for maintaining a phase angle greater than the designated phase angle for a certain period of time is repeated multiple times before the heater is fully turned on. When power is turned off, the heater is first maintained at a designated phase angle for a certain period of time, and then a control for maintaining a phase angle smaller than the designated phase angle for a certain period of time is repeated multiple times before the heater is fully turned off.

[0005] The image forming apparatus described in Patent Document 2 includes a heater, a fixing member, a temperature detection means, and a control means. When the heater is turned on, the control means performs phase control of the AC power using a soft start method, and continues the phase control at a predetermined duty ratio for a predetermined time, and then switches to half-wave control with a duty ratio equal to the predetermined duty ratio.

[0006] The image forming apparatus described in Patent Document 3 is equipped with a phase control means that presets a voltage-time change curve based on the electrical resistance value of the heater when it is initially energized, and outputs a phase control signal so that the voltage actually applied to the heater falls within a predetermined allowable voltage range, and a voltage application means that applies a voltage to the heater based on the phase control signal.

[0007] In recent years, image forming apparatuses are installed in various places such as offices, homes, and stores, but voltage fluctuations synchronized with the on / off of heaters can affect other installed devices. For example, in lighting equipment (hereinafter referred to as lighting), voltage fluctuations can change the illuminance, causing flickering that can be unpleasant for users. In addition, in a control method in which a control cycle is set, voltage fluctuations also occur when changing the power when the control cycle is switched, etc.

[0008] The above-mentioned Patent Documents 1 to 3 do not mention combining half-wave waveforms with adjusted phase angles during a control cycle, and there is a problem that the amount of power supplied cannot be precisely adjusted. In addition, frequent use of waveforms with large phase angles increases harmonic noise, and particularly when there are a lot of high-order harmonic components, there is a risk of serious effects such as malfunctions and burning of peripheral devices.

[0009] The present invention has been made to solve the above-mentioned problems, and has an object to provide a fixing device and an image forming apparatus that are capable of freely adjusting the amount of power supplied. [Means for solving the problem]

[0010] A fixing device according to the present invention includes a rotatably provided fixing member and pressure member, a heat source for heating the fixing member, and a control unit for controlling AC power supplied to the heat source, and fixes an unfixed image on a sheet of paper that is sandwiched and conveyed between the fixing member and the pressure member, and the control unit applies current including a current waveform that differs in phase angle in half-wave units during a preset control period. The energization waveforms are classified into any one of a plurality of groups in which non-overlapping phase angle ranges are set, and the control unit provides a group in which the energization waveforms belonging to different groups are consecutively arranged during the control period. It is characterized by:

[0011] In the fixing device according to the present invention, the control section may be configured to make the energization waveform continuous at a joint between the control cycle and the adjacent control cycle.

[0012] In the fixing device according to the present invention, the control section may be configured to make the energization waveform continuous during the control period.

[0014] In the fixing device according to the present invention, the phase angle of the current waveform may be configured to be a low phase angle when it is 90 degrees or less, a medium phase angle when it is more than 90 degrees and less than 120 degrees, and a high phase angle when it is more than 120 degrees and less than 180 degrees.

[0015] In the fixing device according to the present invention, the control section may be configured to set a difference in effective voltage between adjacent ones of the energized wave forms at a joint between the control cycle and the adjacent control cycle to a predetermined value or less.

[0016] In the fixing device according to the present invention, the control unit may be configured to control the effective voltage for each control cycle, and to set the difference between the effective voltage for the entire current control cycle and the effective voltage for the entire next control cycle to a predetermined value or less.

[0017] The image forming apparatus according to the present invention is characterized by including the fixing device according to the present invention. Effect of the Invention

[0018] According to the present invention, by including multiple current waveforms with different phase angles in one control period, the amount of power supplied can be freely adjusted, and harmonic noise caused by waveform distortion can be suppressed while avoiding the occurrence of extreme voltage differences. [Brief description of the drawings]

[0019] [Figure 1] 1 is a schematic side view showing an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic side view illustrating a main part of the fixing device. [Diagram 3] 1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention; [Figure 4] 2 is an explanatory diagram showing a relationship between AC power supplied to an image forming apparatus and lighting in an installation location. [Diagram 5] FIG. 4 is an explanatory diagram showing a change in voltage in phase control. [Figure 6] FIG. 4 is an explanatory diagram showing a current supply pattern in phase control. [Figure 7] FIG. 11 is an explanatory diagram showing a change in voltage in conventional duty control. [Figure 8] FIG. 4 is an explanatory diagram showing an example of a first voltage control in the image forming apparatus according to the embodiment of the present invention. [Figure 9] 6 is an explanatory diagram showing an example of a second voltage control in the image forming apparatus according to the embodiment of the present invention. FIG. [Figure 10] FIG. 4 is a flow diagram showing a control flow in the image forming apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus and a fixing device according to an embodiment of the present invention will now be described with reference to the drawings.

[0021] FIG. 1 is a schematic side view showing an image forming apparatus according to an embodiment of the present invention.

[0022] The image forming apparatus 1 forms multi-color and monochrome images on a specified sheet of paper in accordance with image data transmitted from outside, and is configured to include an exposure device 11, a developing device 12, a photosensitive drum 13, a cleaner device 14, a charger 15, an intermediate transfer belt device 16, a fixing device 17, a paper feed cassette 18, and a paper output tray 19.

[0023] Image data handled by the image forming apparatus 1 corresponds to a color image using each of the colors black (K), cyan (C), magenta (M), and yellow (Y). Therefore, four developing devices 12, photoconductor drums 13, chargers 15, and cleaner devices 14 are provided so as to form four types of latent images corresponding to each color, and are set to black, cyan, magenta, and yellow, respectively, forming four image stations.

[0024] The photoconductor drum 13 is disposed approximately in the center of the image forming apparatus 1. The charger 15 uniformly charges the surface of the photoconductor drum 13 to a predetermined potential. The exposure device 11 exposes the surface of the photoconductor drum 13 to light to form an electrostatic latent image. The development device 12 develops the electrostatic latent image on the surface of the photoconductor drum 13 to form a toner image on the surface of the photoconductor drum 13. Through the above-mentioned series of operations, a toner image of each color is formed on the surface of each photoconductor drum 13. The cleaner device 14 removes and collects residual toner on the surface of the photoconductor drum 13 after development and image transfer.

[0025] The intermediate transfer belt device 16 is disposed above the photosensitive drum 13, and includes an intermediate transfer belt 21, an intermediate transfer belt drive roller 22, an intermediate transfer belt driven roller 23, an intermediate transfer roller 24, an intermediate transfer belt cleaning device 25, and a tension roller 26. Four intermediate transfer rollers 24 are provided corresponding to the image stations for each color of YMCK.

[0026] The intermediate transfer belt drive roller 22, the intermediate transfer belt driven roller 23, the intermediate transfer roller 24, and the tension roller 26 are configured to tension the intermediate transfer belt 21 and move the surface of the intermediate transfer belt 21 in a predetermined direction (the direction of the arrow C in the figure).

[0027] The intermediate transfer belt 21 rotates in the direction of arrow C, and residual toner is removed and collected by the intermediate transfer belt cleaning device 25. The toner images of each color formed on the surface of each photosensitive drum 13 are sequentially transferred and superimposed to form a color toner image on the surface of the intermediate transfer belt 21.

[0028] A nip area is formed between the transfer roller 27a of the secondary transfer device 27 and the intermediate transfer belt 21, and the paper P conveyed through the sheet conveying path S is sandwiched in the nip area and conveyed. When the paper P passes through the nip area, the toner image on the surface of the intermediate transfer belt 21 is transferred to the paper P.

[0029] The paper feed cassette 18 is a cassette for storing paper P to be used for image formation, and is provided below the exposure device 11. The paper discharge tray 19 is provided above the image forming unit 1a, and is a tray for placing paper P on which an image has been formed.

[0030] In the image forming apparatus 1, the paper P in the paper feed cassette 18 is sent to the paper discharge tray 19 through the sheet transport path S, the secondary transfer device 27, and the fixing device 17. Along the sheet transport path S, a paper feed roller 31, a registration roller 32, a pre-registration roller 33, the fixing device 17, and a paper discharge roller 34 are arranged.

[0031] The paper feed roller 31 is provided near an end of the paper feed cassette 18, and supplies the paper P one sheet at a time from the paper feed cassette 18 to the sheet transport path S. The registration roller 32 temporarily holds the paper P being transported from the paper feed cassette 18, and transports the paper P to the transfer roller 27a at a timing when the leading edge of the toner image on the photosensitive drum 13 and the leading edge of the paper P are aligned. The pre-registration roller 33 is a small roller for assisting in the transport of the paper P.

[0032] The fixing device 17 is a belt fixing type fixing device, and a fixing belt 173 (an example of a fixing member) is wound around a plurality of rollers (here, a fixing roller 171 and a heating roller 172). The fixing belt 173 is adapted to transfer heat from the heating roller 172 to the fixing roller 171. In the fixing device 17, a pressure roller 174 (an example of a pressure member) is pressed against the fixing roller 171 via the fixing belt 173. The fixing device 17 receives the paper P on which an unfixed toner image is formed, and conveys the paper P by sandwiching it between the fixing belt 173 and the pressure roller 174. A temperature detection unit 60 is provided near the fixing belt 173. The paper P after fixing is discharged onto the paper discharge tray 19 by the paper discharge roller 34. The fixing device 17 will be described in detail with reference to FIG. 2, which will be described later.

[0033] In the present embodiment, the fixing device 17 is a fixing device of a belt fixing type, but is not limited to this, and may be a type in which the pressure roller 174 directly presses the fixing roller 171, or a type in which a fixing pad that does not rotate, instead of the fixing roller 171, presses the fixing belt 173 against the pressure roller 174. In the former type, the fixing member described above corresponds to the fixing roller 171, and in the latter type, it corresponds to the fixing belt 173.

[0034] Next, a fixing device according to an embodiment of the present invention will be described with reference to the drawings.

[0035] Fig. 2 is a schematic side view showing the main part of the fixing device. Note that Fig. 1 shows the image forming apparatus 1 from the front side, whereas Fig. 2 shows the image forming apparatus 1 from the rear side, so the left and right are reversed.

[0036] In this embodiment, the pressure roller 174 is configured to be switchable between a pressed state in contact with the fixing roller 171 and a released state in which it is separated from the fixing roller 171. The heating roller 172 contains a heat source 172a, such as a heater, inside. The heating roller 172 and the fixing belt 173 are warmed by the heat generated by the heat source 172a. The fixing belt 173 moves with the rotation of the fixing roller 171, and the portion close to the heat source 172a gradually shifts, so that the entire fixing belt 173 is warmed. The temperature detection unit 60 is a non-contact temperature sensor, and is provided near the heating roller 172 and facing the fixing belt 173.

[0037] Fig. 3 is a schematic diagram showing an image forming apparatus according to an embodiment of the present invention. In Fig. 3, only a part of the members related to the fixing device 17 of the image forming apparatus 1 is shown, and other members may be included.

[0038] The image forming apparatus 1 further includes a control unit 50 in addition to the above-mentioned fixing roller 171, pressure roller 174, heat source 172a, and temperature detection unit 60. The control unit 50 controls the AC power supplied to the heat source 172a. The image forming apparatus 1 is supplied with AC power from a power source used in the installation location, such as an ordinary home or office, in the same manner as lighting. Next, the relationship between the AC power supplied to the image forming apparatus 1 and the lighting in the installation location will be described with reference to FIG. 4.

[0039] FIG. 4 is an explanatory diagram showing the relationship between AC power supplied to an image forming apparatus and lighting in the installation location.

[0040] In Fig. 4, the voltage waveform corresponding to the AC power supplied to the image forming apparatus 1 is shown in the upper row, the illumination illuminance of the lighting in the installation location is shown in the middle row, and the heater signal corresponding to the instruction from the control unit 50 to the heat source 172a is shown in the lower row. In Fig. 4, the horizontal axis indicates the passage of time, and the vertical axis indicates the value corresponding to each item. Specifically, the upper row indicates the AC voltage value, which increases in the positive or negative direction as it moves away from the reference line indicating 0. The middle row indicates that the illuminance increases as it moves upward from the reference line indicating 0. The lower row indicates the switching between on (ON) and off (OFF) of the heater signal.

[0041] During the period from time T0 to time T1, the voltage waveform has a large amplitude, the illumination illuminance is bright, and the heater signal is OFF. At time T1, the heater signal turns ON and is maintained until time T2. As the heat source 172a turns ON, the voltage drops and the amplitude of the voltage waveform becomes smaller. In addition, the illumination illuminance becomes darker. At time T2, the heater signal turns OFF and is maintained until time T3. Since the heater signal is OFF during the period from time T2 to time T3, the state is the same as that during the period from time T0 to time T1, and the illumination illuminance becomes brighter. After that, at time T3, the heater signal turns ON and returns to the same state as that of time T1. In other words, the control period SP from time T1 to time T3 is repeated.

[0042] In the image forming apparatus 1, it is desirable to keep the fixing roller 171 and the like at a desired temperature during image formation, and they are periodically heated by the heat source 172a. As the heat source 172a is repeatedly turned on and off, the illumination changes, that is, the illumination becomes darker and brighter. Although the level at which this illumination change is felt as being uncomfortable varies depending on the type of illumination, the lighting method, the power supply environment, the reflection conditions of the walls, ceiling, and floor around the illumination, the arrangement of the person and the illumination, and individual differences, the human eye often feels intense flickering when there is an illumination change of 400 Lux or more in a short period of time, although this depends on the period of the illumination change. On the other hand, an illumination change of about 100 to 200 Lux hardly causes discomfort. Therefore, in the image forming apparatus 1, phase control is performed to reduce the voltage fluctuation so that the illumination change is not felt as being uncomfortable.

[0043] FIG. 5 is an explanatory diagram showing a change in voltage during phase control.

[0044] In FIG. 5, the horizontal axis indicates the passage of time, and the vertical axis indicates the voltage value, as in the voltage waveform column shown in FIG. 4. In the AC power supplied to the image forming apparatus 1, the voltage gradually rises from a point where the voltage is 0 (zero cross point, time ST1 in FIG. 5) like a sine wave, and gradually drops after reaching a positive maximum value (time ST2 in FIG. 5). After that, it passes through a zero cross point (time ST3 in FIG. 5), reaches a negative maximum value, and then rises again. In FIG. 5, the dashed line indicates the change in voltage when the output is set to 100%, and the solid line indicates the change in voltage when phase control is performed. Note that, for the sake of explanation, the voltage waveform from one of the zero cross points (for example, time ST1) to the next zero cross point (for example, time ST3) may be referred to as a half-wave waveform.

[0045] In phase control, the output voltage is controlled by changing the ratio of on-time in each cycle of AC power. Specifically, in FIG. 5, the period from time ST1 to time ST2 is set as off-time, and the voltage is zero. Also, the period from time ST2 to time ST3 is set as on-time, and the voltage changes in the same way as when the output is at 100%. In the phase control shown in FIG. 5, the phase angle PA corresponds to the off-time with respect to the timing of switching from off to on. Also, the conduction angle CA corresponds to the on-time. In FIG. 5, the phase angle PA is set to 90 degrees. In phase control, the value of the voltage is determined by the area of ​​the on-time period.

[0046] FIG. 6 is an explanatory diagram showing a current supply pattern in phase control.

[0047] Fig. 6 shows an example of a current conduction pattern in phase control, and shows a voltage waveform in which the phase angle PA is changed, and hereinafter, five half-wave waveforms (first half-wave SW1 to fifth half-wave SW5) among the current conduction patterns shown in Fig. 6 will be described. The phase angle (first angle ω1) in the first half-wave SW1 is set to 30 degrees, the phase angle (second angle ω2) in the second half-wave SW2 is set to 60 degrees, the phase angle (third angle ω3) in the third half-wave SW3 is set to 90 degrees, the phase angle (fourth angle ω4) in the fourth half-wave SW4 is set to 120 degrees, and the phase angle (fifth angle ω5) in the fifth half-wave SW5 is set to 150 degrees.

[0048] In the conventional image forming apparatus, duty control may be performed when adjusting the output voltage. Next, the voltage waveform in the duty control will be described with reference to FIG.

[0049] FIG. 7 is an explanatory diagram showing a change in voltage in conventional duty control.

[0050] In conventional duty control, one control cycle is repeated that combines a current-carrying time TK and a non-current-carrying time HK. The current-carrying time TK is considered to be an on-time, during which normal AC power is supplied. The non-current-carrying time HK is considered to be an off-time, during which the supply of power is stopped. In duty control, the strength of the output power is adjusted by changing the ratio of the current-carrying time TK to the non-current-carrying time HK. In other words, as the ratio of the current-carrying time TK increases, the output increases, and as the ratio of the non-current-carrying time HK increases, the output decreases.

[0051] In conventional duty control, switching is performed between energized time TK and non-energized time HK, which causes large increases and decreases in voltage, resulting in flickering of the lighting.

[0052] In contrast, in the present invention, the voltage fluctuation is reduced by adopting phase control. Next, the first voltage control and the second voltage control in the image forming apparatus according to the embodiment of the present invention will be described with reference to FIGS. 8 and 9.

[0053] FIG. 8 is an explanatory diagram showing an example of the first voltage control in the image forming apparatus according to the embodiment of the present invention.

[0054] In the first voltage control, one control cycle is repeated, which combines a full wave time P1 and a phase control time P2. In the full wave time P1, the phase angle is 0 degrees, and a full wave Wa that is always on is output. Next, in the phase control time P2, a phase wave Wb with a predetermined phase angle is output. The phase angle of the phase wave Wb can be changed according to the effective voltage in the phase control time P2. As shown in FIG. 5, increasing the phase angle reduces the effective voltage, and decreasing the phase angle increases the effective voltage. Note that, in the phase control time P2, the phase angle of the phase wave Wb is constant, but the phase angle of some of the phase waves Wb may be made different.

[0055] In the image forming apparatus 1, the full wave time P1 and the phase control time P2 are combined to control the effective voltage in one control cycle, and the heating amount of the heat source 172a is determined. In this way, by performing continuous energization including an energization waveform with a different phase angle in half-wave units during a control cycle, the amount of power supplied can be freely adjusted, and harmonic noise due to waveform distortion can be suppressed while avoiding the occurrence of an extreme voltage difference. That is, in this embodiment, since there is no non-energization time HK during which power is not output, as in the conventional duty control, the heating amount can be finely changed while the heat source 172a is continuously turned on. In addition, the ratio of the full wave time P1 and the phase control time P2 in one control cycle may be appropriately changed, and the phase angle may be adjusted accordingly. Specifically, by making the phase control time P2 longer, the effective voltage in the control cycle can be sufficiently reduced even if the phase angle is reduced. By reducing the phase angle, the waveform of the phase wave Wb approaches the waveform of the full wave Wa, and the distortion of the waveform can be reduced, and harmonic noise can be suppressed.

[0056] FIG. 9 is an explanatory diagram showing an example of the second voltage control in the image forming apparatus according to the embodiment of the present invention.

[0057] In the second voltage control, one control cycle is repeated in which multiple half waves with different phase angles are combined. In FIG. 9, the second wave W2 to the eighth wave W8 are included in one control cycle. The first wave W1 is included in the previous control cycle and is the half wave immediately before the second wave W2. The ninth wave W9 is included in the next control cycle and is the half wave immediately after the eighth wave W8.

[0058] In this embodiment, a plurality of groups are set, each consisting of a plurality of phase angle ranges divided so as not to overlap with each other. The energization waveform is classified into one of the plurality of groups depending on the range of the phase angle. Specifically, the phase angle of the energization waveform (half wave) is determined as a low phase angle when it is 90 degrees or less, as a medium phase angle when it is more than 90 degrees and less than 120 degrees, and as a high phase angle when it is more than 120 degrees and less than 180 degrees. A half wave with a low phase angle is classified into a first group, a half wave with a medium phase angle is classified into a second group, and a half wave with a high phase angle is classified into a third group.

[0059] In the example shown in FIG. 9, the first wave W1, the seventh wave W7, and the ninth wave W9 correspond to low phase angles, the fourth wave W4 and the eighth wave W8 correspond to medium phase angles, and the second wave W2, the third wave W3, and the sixth wave W6 correspond to high phase angles. The fifth wave W5 is a full wave with a phase angle PA of 0 degrees, and corresponds to a low phase angle. The successive first wave W1 and the second wave W2 are a combination of a low phase angle and a high phase angle. The successive third wave W3, the fourth wave W4, and the fifth wave W5 are a combination of a low phase angle, a medium phase angle, and a high phase angle. In the second voltage control, a group is provided in which current waveforms belonging to different groups are consecutively connected. In this way, by providing a certain degree of difference in the phase angles of adjacent current waveforms, the amount of power can be flexibly set. In addition, by not consecutively connecting current waveforms with large phase angles, the generation of harmonic noise can be avoided. Furthermore, by making the energization waveform continuous at joints between control cycles or within a control cycle, it is possible to eliminate sections where the energization is interrupted and reduce voltage fluctuations.

[0060] Combinations that are less likely to worsen harmonic noise are not limited to those mentioned above, but include "high phase angle + low phase angle," "high phase angle + medium phase angle," "low phase angle + medium phase angle," "low phase angle + high phase angle + medium phase angle," "low phase angle + high phase angle + low phase angle," and "medium phase angle + high phase angle + medium phase angle."

[0061] Next, the control flow in the image forming apparatus will be described with reference to FIG.

[0062] FIG. 10 is a flow diagram showing a control flow in the image forming apparatus.

[0063] In step S01, the temperature detection unit 60 detects the temperature.

[0064] In step S02, the control unit 50 determines whether heating is necessary based on the detection result of the temperature detection unit 60. The temperature of the heat source 172a may be controlled taking into consideration the set value and the rate of increase, and may be appropriately adjusted to prevent overshooting or the like. The control unit 50 may also determine whether heating is necessary by taking into consideration the timing at which the control cycle switches, or may control the temperature at predetermined intervals. If the control unit 50 determines that heating is necessary (step S01: Yes), the process proceeds to step S03. On the other hand, if heating is not necessary (step S01: No), the process returns to step S01.

[0065] In step S03, the control unit 50 refers to the effective voltage. The effective voltage may refer to the entire previous control cycle, or the last half wave in the previous control cycle. For the next control cycle, the control unit 50 estimates the effective voltage based on the amount of heat calculated by the control unit 50.

[0066] In step S04, the control unit 50 determines whether the difference in effective voltage between the previous control cycle and the next control cycle exceeds a predetermined value, here a first threshold value. In this embodiment, the first threshold value is set to 30 V. As a result, if the difference in effective voltage exceeds the first threshold value (step S04: Yes), the process proceeds to step S06. On the other hand, if the difference in effective voltage does not exceed the first threshold value (step S04: No), the process proceeds to step S05.

[0067] In step S05, the control unit 50 applies a phase angle at which the effective voltage changes in one step for the first two half waves (two waves) of the control cycle. The control unit 50 changes the phase angle stepwise for the first two half waves of the control cycle. That is, the voltage is changed so that the phase angle changes stepwise in the order of the previous half wave, the first two half waves, and the subsequent half waves. In this way, at the joint between control cycles, the difference in effective voltage between adjacent half waves is set to a predetermined value or less to reduce the voltage fluctuation, thereby suppressing the flickering of the lighting while combining waveforms that conduct electricity in a combination pattern of phase angles that do not increase harmonics, thereby suppressing harmonic noise. Note that when the difference in effective voltage is 30V or less, although it depends on the type of lighting, the illuminance change is small under most conditions and is within about 100 Lux, so that flickering is not easily felt.

[0068] Regarding the voltage control, either the first voltage control or the second voltage control described above may be used, and in either case, the required effective voltage can be obtained by adjusting the phase angle of the half wave. In the first voltage control and the second voltage control, a table may be provided in which the phase angle of each half wave to be turned on is set in advance, and the control unit 50 may select the phase angle according to the amount of heating from the table. In the above-mentioned table, the phase angle may be set so that the duty ratio is changed in 1% increments.

[0069] In step S06, the control unit 50 determines whether the difference in effective voltage between the previous control cycle and the next control cycle exceeds a second threshold. In this embodiment, the second threshold is set to 60 V. As a result, if the difference in effective voltage exceeds the second threshold (step S06: Yes), the process proceeds to step S08. On the other hand, if the difference in effective voltage does not exceed the second threshold (step S06: No), the process proceeds to step S07.

[0070] In step S07, the control unit 50 applies a phase angle at which the effective voltage changes in one step to the first three half waves (three waves) of the control cycle. The control unit 50 changes the phase angle in stages for the first three half waves of the control cycle. That is, the voltage is gradually changed by changing the phase angle in stages from the immediately preceding half wave, to the first three half waves, and then to the subsequent half waves.

[0071] Specifically, when the effective voltage difference is between 30V and 60V, a single switching causes a large voltage fluctuation, but by increasing the number of waves from 2 half waves to 3 half waves and smoothing the change, it becomes difficult to recognize it as flickering. In other words, it is also possible to switch in stages, in units of several half waves or in blocks of multiple half waves.

[0072] In step S08, the control unit 50 applies a phase angle at which the effective voltage changes in two stages. The control unit 50 changes the phase angle in stages for the first two half waves of the control cycle. That is, the voltage is gradually varied by changing the phase angle in stages from the immediately preceding half wave, to one of the first two half waves, to the other of the first two half waves, and to the subsequent half waves.

[0073] After steps S05, S07, and S08, the process returns to step S01 and is repeated.

[0074] In steps S05, S07, and S08, the phase angles of the first two or three half waves of the control cycle are changed stepwise, but the present invention is not limited to this, and the effective voltage may be changed stepwise in units of control cycles. In other words, if the difference in effective voltage between the current control cycle and the next control cycle exceeds a predetermined value, the next control cycle is set so that the difference in effective voltage from the immediately preceding control cycle is equal to or less than a predetermined value, and the subsequent control cycle is set to a desired effective voltage. In other words, when heating is performed to a large extent, heating is performed in stages, thereby making it possible to reduce voltage fluctuations while ensuring a sufficient amount of heating.

[0075] The embodiments disclosed herein are illustrative in all respects, including numerical values, and are not intended to be a basis for restrictive interpretation. The present invention can be implemented not only in image forming apparatuses equipped with heat sources, but also in lighting devices, air conditioners equipped with compressors, and refrigerators, as long as the device requires AC power with high power consumption. The present invention can be applied to control of illuminance in lighting devices, and to control of compressor capacity, i.e., control of air conditioning intensity in air conditioners. Therefore, the technical scope of the present invention is not interpreted only by the above-described embodiments, but is defined based on the claims. In addition, all modifications within the meaning and scope equivalent to the claims are included. [Explanation of symbols]

[0076] 1. Image forming device 17 Fixing device 171 Fixing roller (an example of a fixing member) 172a Heat source 174 Pressure roller (an example of a pressure member) 50 Control section 60 Temperature detection unit

Claims

1. a fixing member and a pressure member that are rotatably provided; a heat source for heating the fixing member; a control unit for controlling AC power supplied to the heat source, A fixing device that fixes an unfixed image on a sheet of paper that is sandwiched and conveyed between the fixing member and the pressure member, The control unit applies current including a current waveform having a phase angle that differs in half-wave units during a preset control period, The energization waveforms are classified into any one of a plurality of groups having mutually non-overlapping phase angle ranges, The control unit provides a group of the energization waveforms each belonging to a different group in succession during the control period. A fixing device comprising:

2. 2. The fixing device according to claim 1, The control unit continues the energization waveform at a joint between the control cycle and an adjacent control cycle. A fixing device comprising:

3. 3. The fixing device according to claim 1, The control unit causes the energization waveform to be continuous during the control period. A fixing device comprising:

4. 2. The fixing device according to claim 1, The phase angle of the current waveform is determined as a low phase angle when it is 90 degrees or less, a medium phase angle when it is more than 90 degrees and less than 120 degrees, and a high phase angle when it is more than 120 degrees and less than 180 degrees. A fixing device comprising:

5. The fixing device according to any one of claims 1 to 4, The control unit controls a difference in effective voltage of the adjacent energization waveforms at a joint between the control cycle and the adjacent control cycle to be equal to or less than a predetermined value. A fixing device comprising:

6. The fixing device according to any one of claims 1 to 5, The control unit controls the effective voltage for each control period, and keeps a difference between the effective voltage over the current control period and the effective voltage over the next control period equal to or less than a predetermined value. A fixing device comprising:

7. 7. An image forming apparatus comprising the fixing device according to claim 1.

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