Image forming apparatus

Abstract

The present invention discloses an image forming apparatus. The image forming apparatus includes a fixing unit, a switching element, and a controller. The controller controls the switching element in units of a half cycle of an alternating current. A period during which power is supplied to the heater in a half cycle period of the alternating current is divided into at least one first power supply period and a second power supply period longer than one first power supply period. The sum of the lengths of the at least one first power supply periods is from 1 / 6000 to 1 / 40 of the length of one cycle of the alternating current. The sum of the power supplied in the at least one first power supply period and the power supplied in the second power supply period is determined according to the difference between the temperature of the fixing unit and a target temperature.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including an image heating device as an image fixing unit. Background Art

[0002] The image heating device of an image forming apparatus fixes an unfixed image (toner image) formed on a transfer paper by an image forming unit using electrophotographic processing or the like. As a type thereof, a film heating type using a heater represented by a ceramic heater as a heat source is known. Generally, the heater is connected to an AC power supply through a switching element such as a triac (hereinafter referred to as a triac), and electric power (electric power) is supplied from this AC power supply. When power is supplied to a high-output heater and temperature control of the heater is performed, phase control is often performed in many cases to achieve a quick response of control. On the other hand, when a high-output heater (that is, a heater having a low resistance value) is subjected to phase control, harmonic currents increase. As a countermeasure against this problem, a method of moderating a sharp current change per unit time has been considered and has been proposed, for example, in Japanese Patent Application Laid-Open No. 2018-073048.

[0003] However, as in the conventional method, when moderating a sharp current change, there is a possibility that the switching element generates heat. Summary of the Invention

[0004] The present invention has been made in the above circumstances, and a main object of the present invention is to reduce harmonic currents while suppressing the influence on the switching element.

[0005] According to one aspect of the present invention, there is provided an image forming apparatus for forming a toner image on a recording material, including: a fixing unit configured to heat and fix the toner image on the recording material, the fixing unit including a heater; a switching element configured to switch between an on state and an off state, in the on state, power from an AC power supply is supplied to the heater, and in the off state, the supply of power to the heater is cut off; and a controller configured to control the switching element to maintain the temperature of the fixing unit at a target temperature, the controller controlling the switching element in units of a half cycle of alternating current so that power determined according to the difference between the temperature of the fixing unit and the target temperature is supplied to the heater, wherein a period during which power is supplied to the heater within a half cycle period of the alternating current is divided into at least one first power supply period and a second power supply period longer than one first power supply period, wherein the sum of the lengths of the at least one first power supply periods is from 1 / 6000 to 1 / 40 of the length of one cycle of the alternating current, and wherein the sum of the power supplied in the at least one first power supply period and the power supplied in the second power supply period is determined according to the difference between the temperature of the fixing unit and the target temperature.

[0006] Further features of the present invention will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a schematic diagram for illustrating an image forming apparatus according to Embodiments 1 to 3.

[0008] Figure 2 is a cross-sectional view of an image heating apparatus in Embodiments 1 to 3.

[0009] Figure 3 is a schematic diagram of a heater control circuit using an FET (field effect transistor) in Embodiment 1.

[0010] Figure 4 Parts (a) to (c) of are schematic diagrams each showing a heater current waveform and a control signal in Embodiment 1.

[0011] Figure 5 Parts (a) to (c) of are schematic diagrams each showing a heater current waveform and a control signal in Embodiment 1.

[0012] Figure 6 is a schematic diagram showing a heater current waveform and a control signal in a case where Embodiment 1 is not executed.

[0013] Figure 7 Parts (a) and (b) are diagrams respectively showing the measurement results of harmonic currents in Example 1.

[0014] Figure 8 is a schematic diagram of the power supply device in Example 2.

[0015] Figure 9 Parts (a) and (b) are schematic diagrams respectively showing the heater current waveform and control signal in Example 2, and Figure 9 part (c) is a diagram showing the measurement result of harmonic current in Example 2.

[0016] Figure 10 is a schematic diagram of the heater control circuit using a triac in Example 3.

[0017] Figure 11 is a schematic diagram showing the heater current waveform and control signal in Example 3. Detailed Description of the Invention

[0018] Hereinafter, embodiments for implementing the present invention will be specifically described with reference to the accompanying drawings. The following embodiments are examples of the present invention, and the technical scope of the present invention is not intended to be limited thereto.

[0019] [Example 1]

[0020] [Image Forming Apparatus]

[0021] Figure 1 is a cross-sectional view of an image forming apparatus 100 using electrophotographic recording technology. When a print signal is generated, the scanner unit 21 emits laser light modulated according to image information, so that the photosensitive drum 19 charged to a predetermined polarity by the charging roller 16 is scanned with the laser. Thus, an electrostatic latent image is formed on the photosensitive drum 19. Toner is supplied from the developing device 17 to this electrostatic latent image, so that a toner image according to the image information is formed on the photosensitive drum 19. On the other hand, the recording paper P stacked on the paper (sheet) feed cassette 11 is fed one by one by the pickup roller 12 and conveyed toward the alignment roller pair 14 by the roller pair 13. Then, in synchronization with the moment when the toner image on the photosensitive drum 19 reaches the transfer position formed by the photosensitive drum 19 and the transfer roller 20, the recording paper P is transferred from the alignment roller pair 14 to the transfer position. During the recording paper P passing through the transfer position, the toner image on the photosensitive drum 19 is transferred onto the recording paper P.

[0022] Thereafter, the recording paper P is heated by the heater 201 in the image heating device 200, so that the (unfixed) toner image is thermally fixed on the recording paper P. The recording paper P carrying the fixed toner image is discharged onto a tray above the image forming device 100 by the roller pair 26 and 27. Incidentally, the cleaner 18 cleans the photosensitive drum 19. The paper feed tray (manual feed tray) 28 is a tray including a pair of recording paper regulating plates (not shown), and the pair of recording paper regulating plates can adjust the width of the recording paper P according to the size of the recording paper P. Incidentally, the width refers to the length of the recording paper P in a direction substantially perpendicular to the feeding direction of the recording paper P. The paper feed tray 28 is provided to also accommodate the recording paper P having a size other than the conventional size. The pickup roller pair 29 is a roller pair for feeding the recording paper P from the paper feed tray 28. The motor 30 is a motor for driving the image heating device 200 and the like. The power circuit 302 connected to the commercial AC power supply 301 supplies electric power (electric power) to the motor 30. Through the control of the control circuit 303 connected to the AC power supply 301, electric power is supplied to the heater 201 in the image heating device 200. The photosensitive drum 19, the charging roller 16, the scanner unit 21, the developing device 17, and the transfer roller 20 described above constitute an image forming portion for forming an (unfixed) toner image on the recording paper P. Incidentally, hereinafter, the image heating device 200, the AC power supply 301, the power circuit 302, and the control circuit 303 are also referred to as the peripheral portion 300.

[0023] [Image heating device]

[0024] Figure 2 is a cross-sectional view of the image heating device 200 in Embodiment 1. The image heating device 200 includes a film 203, a heater 201, a pressure roller 208, and a thermistor 202. The film 203 is configured as an endless belt in the form of a cylindrical film. The heater 201 contacts the inner surface of the film 203. The pressure roller 208 as a clamping forming member forms a fixing clamping portion N in cooperation with the heater 201 through the film 203. The thermistor 202 as a temperature detection portion is a temperature detection element for detecting the temperature of the heater 201.

[0025] The material of the base layer of the film 203 is, for example, a heat-resistant resin material such as polyimide or a metal such as stainless steel. In addition, as the surface layer of the film 203, an elastic layer such as heat-resistant rubber can also be provided. The pressure roller 208 includes, for example, a core metal 209 made of a material such as iron or aluminum and an elastic layer 210 made of a material such as silicone rubber. The heater 201 is held by a holding member 205 made of a heat-resistant resin material. The holding member 205 also has a guiding function for guiding the rotation of the film 203. The support column 204 is a support column made of metal for applying the pressure of a spring (not shown) to the holding member 205. The pressure roller 208 rotates in the arrow direction (counterclockwise direction) by receiving power from a motor (not shown). By the rotation of the pressure roller 208, the film 203 rotates in the arrow direction (clockwise direction). The recording paper P on which a (non-fixed) toner image is carried is clamped and fed in the fixing clamping portion N while being heated and subjected to a fixing process. In Figure 2 , the recording paper P is fed from the right hand side (also the upstream side) to the left hand side (also the downstream side), and this direction is hereinafter referred to as the feeding direction.

[0026] [Heater drive circuit]

[0027] Figure 3 An example of the control circuit 303 of the heater 201 in the first embodiment and its peripheral portion 300 is shown. The peripheral portion 300 shows a circuit for supplying the power supplied from the AC power supply 301 to the heating element H1 of the heater 201 through the relay 304 by the conduction (hereinafter referred to as ON) of the field effect transistors (hereinafter referred to as FETs) 305 and 306.

[0028] By controlling the conduction state / non-conduction state (hereinafter referred to as ON / OFF) of the FETs 305 and 306 which are switch elements connected in parallel with the heating element H1, the power supply (hereinafter referred to as energization) / power cut-off of the heating element H1 is performed. The ON / OFF of each of the FETs 305 and 306 is performed by controlling the voltage applied to the gate terminal of each of the FETs 305 and 306. First, the voltage supplied from the AC power supply 301 is supplied to the parallel-connected power supply circuit 302 and control circuit 303. The power supply circuit 302 includes a power supply device 307 for driving the motor 30, etc., and includes a zero-cross detection circuit 308 which is a zero-cross detection part for detecting the zero-cross point and for outputting a zero-cross signal ( Figure 3 "ZEROX" in

[0029] The voltage supplied to the control circuit 303 is rectified by diodes 309 and 310. The rectified voltage is divided by resistors 311 and 312, and the divided voltage is supplied to the electrolytic capacitor 314 via diode 313, so that a DC voltage Vcc (also referred to as the power supply voltage Vcc hereinafter) is generated. Then, the power supply voltage Vc charged in the electrolytic capacitor 314 supplies current to the base terminal of the transistor 317 via resistor 315 and optocoupler 316.

[0030] A drive signal ON1 of the heater 201 output by the operation of the CPU 324, which is a controller described later, causes current to flow through the base terminal of the transistor 321 via resistor 319. Thereby, current is supplied from a 3.3V power supply to the light-emitting diode 316d of the optocoupler 316 via resistor 322. When current is supplied to the light-emitting diode 316d of the optocoupler 316, the phototransistor 316t of the optocoupler 316 turns on. The drive signal ON1 (also referred to as the ON1 signal hereinafter) is connected to ground (referred to as GND hereinafter) via resistor 320. With the above configuration, current consistent with the switching of the drive signal ON1 is supplied to the base terminal of the transistor 317.

[0031] Current is supplied from the electrolytic capacitor 314 to the base terminal of the transistor 317 synchronously with the drive signal ON1. During the time when the current is supplied, the transistor 317 turns on, so that voltage is supplied from the electrolytic capacitor 314 to the gate terminals of the FETs 305 and 306. Then, a potential difference is generated between the gate and source of each of the FETs 305 and 306 through the resistor 341 between the gate and source shared by the FETs 305 and 306, so that the FETs 305 and 306 turn on. Thereby, current flows through the heating element H1. Incidentally, the supply of the DC voltage Vcc to the electrolytic capacitor 314 can also be performed by supply from, for example, an external power supply, or can also be performed from a switching transformer (not shown) of the power supply device 307.

[0032] [CPU 324]

[0033] The CPU 324 of the controller 303 outputs an ON1 signal for driving the heater 201 to the control circuit 303. The CPU 324 outputs an RLON signal to the relay 304 to control the connected state or non-connected state of the relay 304. A TH signal indicating the temperature of the heater 201 as a detection result of the thermistor 202 and a ZEROX signal output from the zero-crossing detection circuit 308 are input to the CPU 324. In the CPU 324, the actual temperature of the heater 201 obtained based on the input TH signal and the target temperature of the heater 201 set inside the CPU 324 are compared with each other. As a result of the comparison, the CPU 324 determines the supply duty ratio for each of the control cycles (cycle periods) required for the temperature of the heater 201 to reach the target temperature. Here, each control cycle is, for example, an integer multiple of the zero-crossing cycle. In addition, the supply duty ratio refers to the ratio of the power (power ratio) to be supplied within the control cycle in order to make the temperature of the heater 201 reach the target temperature, and is hereinafter referred to as the first power (electric power). Based on the first power determined based on the TH signal and based on the ZEROX signal as a timing signal, the CPU 324 outputs a drive signal ON1 for driving the heater 201.

[0034] [Control Method of Heater Current]

[0035] A control method of the heater current during the printing operation in Embodiment 1 will be described. The feature of Embodiment 1 is that phase control is performed and the heater is turned on multiple times within a half cycle of the AC power supply 301, in other words, within a single half-wave of the AC voltage. In the following description, the frequency of the AC power supply 301 is, for example, 50 Hz, and one cycle is 20 ms (a single half-wave is 10 ms). At this time, when 100% of the power is supplied within a single half-wave, the time for performing energization (hereinafter referred to as the energization time) is 10 ms.

[0036] Figure 4 Each of parts (a) to (c) shows the waveform of the heater current (hereinafter referred to as the harmonic current waveform) in Embodiment 1 and the waveform of the ON1 signal as a control signal. In Figure 4In each of the diagrams of parts (a) to (c), starting from the leftmost column, the supplied power (%), the energization period (ms) in the first power supply period described later, the number of energizations in the first power supply period (hereinafter referred to as the number of energizations), the heater current waveform, and the ON1 signal waveform are shown. In any of the diagrams, a case where the power supplied in one control period is 50% when the supplied power under full energization is 100% is shown. Incidentally, each of t1 to t18 represents a time point (or moment), and hereinafter, t1 etc. means the time point t1 (or moment t1) etc. Also, for example, t1 to t2 etc. means the time (or period) from time point t1 to time point t2 etc.

[0037] In Figure 4 In part (a), in a single half-wave of the AC voltage, current is made to flow through the heater 201 in the periods from t1 to t2 and from t3 to t4, and this control is repeated. Incidentally, for example, based on the rise (or fall) of the ZEROX signal input from the zero-crossing detection circuit 308, the CPU 324 executes control to set the ON1 signal to high level at t1 or t3 by referring to a timer (not shown) etc. included therein. Also, for example, based on the rise (or fall) of the ZEROX signal input from the zero-crossing detection circuit 308, the CPU 324 executes control to set the ON1 signal to low level at t2 or t4 by referring to a timer (not shown) etc. Further, in the following description, the CPU 324 executes similar control and thus executes control of the ON1 signal and the heater current.

[0038] (Definition of period)

[0039] The period from t1 to t2 is set to a time in the range from 1 / 40 times (e.g., 0.5 ms) to 1 / 6000 times (e.g., 0.003 ms) of one cycle time (e.g., 20 ms) at a predetermined frequency of the AC power supply 301. The period from t1 to t2 is hereinafter referred to as the first power supply period or the first energization period. Incidentally, the first energization period refers to the energization period in the first power supply period, and in Figure 4In part (a), the first power-on period is the period from t1 to t2. Therefore, the first power-on period is the same period as the first power supply period. On the other hand, the period from t3 to t4 is set so that power corresponding to the difference between "the first power determined by the CPU" and "the power supplied during the first power supply period" is supplied. The period from t3 to t4 refers to the second power supply period. In addition, the period from t2 to t3 is set to be within the range of 1 / 40 times to 1 / 6000 times of one cycle time at the predetermined frequency of the AC power supply 301. The period from t2 to t3 is the period between the first power supply period and the second power supply period, and is hereinafter referred to as the power supply interruption period. As a result, the number of power-on times is two in a single half-wave.

[0040] Figure 4 Part (a) shows the case where the supplied power is 50%. Each of the first power supply period from t1 to t2 and the power supply interruption period from t2 to t3, which is the period between the first power supply period and the second power supply period, is set to 0.1 ms. The second power supply period from t3 to t4 is set to 4.9 ms. That is, the first power supply period from t1 to t2 is a shorter time than the second power supply period from t3 to t4. The power supply interruption period from t2 to t3 is a time that is substantially the same as the first power supply period from t1 to t2 and shorter than the second power supply period from t3 to t4.

[0041] In Figure 4 In part (b), current is applied to the heater 201 in each of the periods from t5 to t6, from t7 to t8, and from t9 to t10. Figure 4 Part (b) shows Figure 4 the waveforms of the heater current and the control signal in the case where, compared with the case of part (a), the number of first power-on periods (number of power-on times) in the range of 1 / 40 times to 1 / 6000 times of one cycle time of the frequency is changed. In Figure 4 Part (b), the first power supply period is the period from t5 to t8, and the second power supply period is the period from t9 to t10. In the first power supply period from t5 to t8, the period from t5 to t6 is the first power-on period, and the period from t7 to t8 is the second power-on period. Each of the periods from t5 to t6, from t6 to t7, from t7 to t8, and from t8 to t9 is set to 0.1 ms. The period from t9 to t10 is set to 4.8 ms. As a result, the number of power-on times is three.

[0042] In Figure 4In part (c), current is applied to the heater 201 in each of the time periods from t11 to t12, t13 to t14, t15 to t16, and t17 to t18. Figure 4 Part (c) shows that Figure 4 compared with the cases of parts (a) and (b), when the number of energization periods (number of energization times) in the range of 1 / 40 times to 1 / 6000 times the period time of the frequency of the AC power supply 301 is changed, the waveforms of the heater current and the control signal. In Figure 4 part (c), the first power supply period is the period from t11 to t16, and the second power supply period is the period from t17 to t18. In the first power supply period from t11 to t16, the period from t11 to t12 is the first energization period, the period from t13 to t14 is the second energization period, and the period from t15 to t16 is the third energization period. Each of the periods from t11 to t12, t12 to t13, t13 to t14, t14 to t15, t15 to t16, and t16 to t17 is set to 0.1 ms. The period from t17 to t18 is set to 4.7 ms. As a result, the number of energization times is four. In the above, the waveforms in the case where the number of energization times of energization in the range of 1 / 40 times to 1 / 6000 times the period time of the frequency of the AC power supply 301 is changed are described. In Figure 4 parts (a) to (c), the CPU 324 executes control at least once during the first power supply period, where the FETs 305 and 306 are placed in the conducting state for, for example, up to 0.1 ms (which is the first time).

[0043] As Figure 4 shown in parts (a) to (c), the CPU 324 controls the conducting state or non-conducting state of the FETs 305 and 306 so that the period of supplying power to the heater 201 in a single half-wave is divided into at least two periods and power is supplied to the heater 201. In addition, the CPU 324 divides the period of supplying power to the heater 201 into at least one first power supply period and a second power supply period longer than one first power supply period. In addition, the length of the sum of all power supply periods is in the range of 1 / 6000 to 1 / 40 of a cycle of the AC power supply 301. In addition, the sum of the power supplied in all first power supply periods and the power supplied in the second power supply period is the power determined according to the difference between the temperature of the fixing part and the target temperature.

[0044] [Change of energization period]

[0045] Next, the waveforms in the case of changing the energization period while fixing the number of energization times of energization will be described. Compared with Figure 4The situations of parts (a) to (c) are similar. Figure 5 Each of parts (a) to (c) shows a case of supplying 50% of the power during full power-on. Figure 5 Parts (a) to (c) are Figure 4 figures similar in constitution to Figure 5 Parts (a) to (c). Similarly, in the control of each of parts (a) to (c), the number of power-on times in the range of 1 / 40 times to 1 / 6000 times of one cycle time of the frequency of the AC power supply 301 is fixed at once. For this reason, in this control, the power-on period in the first power supply period is only the first power-on period. In addition, the number of power-on times in a single half-wave is fixed at twice. In addition, the first power-on period (i.e., the first power supply period) and the power supply interruption period between the first power supply period and the second power supply period are changed.

[0046] In Figure 5 Part (a), the first power supply period (in other words, the first power-on period) is the period from t1 to t2, and the second power supply period is the period from t3 to t4. In Figure 5 Part (a), each of the first power supply period from t1 to t2 and the power supply interruption period from t2 to t3 is set to 0.107 ms. The second power supply period from t3 to t4 is set to 4.893 ms. The number of power-on times of the power-on is twice as described above.

[0047] In Figure 5 Part (b), the first power supply period (in other words, the first power-on period) is the period from t5 to t6, and the second power supply period is the period from t7 to t8. In Figure 5 Part (b), each of the first power supply period from t5 to t6 and the power supply interruption period from t6 to t7 is set to 0.115 ms. The second power supply period from t7 to t8 is set to 4.885 ms. The number of power-on times of the power-on is twice as described above.

[0048] In Figure 5 Part (c), the first power supply period (in other words, the first power-on period) is the period from t9 to t10, and the second power supply period is the period from t11 to t12. In Figure 5In part (c), each of the first power supply period from t9 to t10 and the power supply interruption period from t10 to t11 is set to 0.123 ms. The second power supply period from t11 to t12 is set to 4.877 ms. The number of energizations is two as described above. In the above, the energization period and the change in the waveform in the case of the change in the period between the first power supply period and the second power supply period are described. In Figure 5 In parts (a) to (c), during the first power supply period, the CPU 324 changes the first time when the FETs 305 and 306 are placed in the conduction state.

[0049] (Harmonic current reduction effect 1)

[0050] Figure 6 is a schematic diagram showing the heater current waveform and the ON1 signal waveform when supplying 50% power without performing the control of Embodiment 1, and includes diagrams similar to Figure 4 parts (a) to (c) of Figure 5 and diagrams similar to parts (a) to (c) of Figure 6 are shown for comparative study with the control of Embodiment 1 below. Figure 7 Part (a) of Figure 6 and Figure 4 is a diagram showing the measurement results of harmonic current when the heater current waveform of each of parts (a) to (c) of Figure 4 is controlled, where the abscissa represents the order of the harmonic current, and the ordinate represents the ratio of the magnitude of the harmonic current of each order to the standard value of the harmonic current of the associated order (current value / standard value). The standard value refers to the value defined for Class A equipment according to IEC 61000-6-3. The case of executing the control of Figure 4 part (a) is represented by ● and a broken line, the case of executing the control of Figure 4 part (b) is represented by ■ and a dotted line, and the case of executing the control of Figure 6 part (c) is represented by ▲ and a solid line. In addition, the case of not executing the control of Embodiment 1

[0051] It is understood that compared with the result of the case of not executing the control of Embodiment 1 ( Figure 6 the waveform), the case of executing the control of Embodiment 1 ( Figure 4The results of parts (a) to (c) (variation in the number of energizations) of the waveform are reduced in harmonic current. This is because: due to the presence of an energization period within the range of 1 / 40 times to 1 / 6000 times the period of the frequency of the AC power supply 301, the order of the enhanced harmonic current shifts to a higher order side of 40 (orders) or more. Additionally, from Figure 4 the results of parts (a) to (c), it is understood that the harmonic current reduction effect varies depending on the order of the harmonic current. For example, near the 30th order in part (a) (number of energizations: once) of Figure 4 , near the 20th order in part (b) (number of energizations: twice) of Figure 4 , and near the 10th order in part (c) (number of energizations: three times) of Figure 4 , the harmonic current reduction effect is 50% or less. This indicates that the order of the enhanced harmonic current changes due to the different number of energizations within the range of 1 / 40 times to 1 / 6000 times the period of the frequency of the AC power supply 301. Therefore, the order of the reduced harmonic current changes. Depending on the order of the harmonic current to be reduced as intended, it is necessary to change the number of energizations within the range of 1 / 40 times to 1 / 6000 times the period of the frequency of the AC power supply 301.

[0052] Incidentally, in parts (a) to (c) of Figure 4 , during the first power supply period, the length of the energization period within the range of 1 / 40 times to 1 / 6000 times the period of the frequency of the AC power supply 301, the length of the period between the previous period and the subsequent period, and the length of the power supply interruption period are set to 0.1 ms. However, depending on the order of the harmonic current to be reduced as intended, it is also possible to change each of the length of the energization period within the range of 1 / 40 times to 1 / 6000 times the period of the frequency of the AC power supply 301, the length of the period between the previous period and the subsequent period, and the length of the power supply interruption period.

[0053] (Harmonic current reduction effect 1)

[0054] Figure 7 Part (b) of Figure 5 and Figure 6 is a graph showing the measurement results of the harmonic current of the heater current waveform for each of parts (a) to (c) of Figure 5 , where the abscissa represents the order of the harmonic current, and the ordinate represents the ratio of the magnitude of the harmonic current of each order to the standard value of the harmonic current associated with that order (current value / standard value). The case where the control of part (a) of Figure 5 is executed is indicated by ● and a broken line, the case where the control of part (b) ofFigure 5 The controlled situation of part (c) is indicated by ▲ and solid lines. Additionally, the Figure 6 situation where the control of Example 1 was not executed is indicated by x and solid lines.

[0055] It is understood that, compared with the result of the situation where the control of Example 1 was not executed ( Figure 6 the waveform), the result of the situation where the control of Example 1 was executed ( Figure 5 the waveforms of parts (a) to (c)) shows a reduction in harmonic current. This is because: through the first energization period, the order of the enhanced harmonic current shifts to the higher-order side of 40 (orders) or greater. Additionally, from Figure 5 the results of parts (a) to (c), it is understood that the harmonic current reduction effect varies according to the order of the harmonic current. For example, around the 35th order in Figure 5 part (a) (energization period: 0.107 ms), the harmonic current reduction effect is 40% or less. Additionally, around the 30th order in Figure 5 part (b) (energization period: 0.115) and around the 25th order in Figure 5 part (c) (energization period: 0.123), the harmonic current reduction effect is 20% or less. This indicates that the order of the enhanced harmonic current changes due to the difference in the length of the first energization period or the length of the power supply interruption period, and thus, the harmonic current reduction effect is different. For this reason, according to the order of the harmonic current intended to be reduced, it is necessary to change the length of the first energization period or the length of the power supply interruption period. In Figure 5 parts (a) to (c), the first energization period and the power supply interruption period are made equal to each other. Here, these periods are set to 0.107 ms in Figure 5 part (a), to 0.115 ms in Figure 5 part (b), and to 0.123 ms in Figure 5 part (c). However, according to the order of the harmonic current intended to be reduced, the length of the first energization period and the length of the power supply interruption period can also be changed.

[0056] In Embodiment 1, the first power was limited to 50% and described. However, it is not required that the first power be limited to 50%, but Embodiment 1 can also be applied even when the value of the first power is another value. In the case where the first power changes, the first energization period, the number of energizations within a range of 1 / 40 times to 1 / 6000 times the period of the frequency of the AC power supply 301, or the length of the power supply interruption period is not limited to those in Embodiment 1. These numbers and periods change according to the supply duty ratio. Additionally, a single second power supply period was adopted, but the second power supply period can also be divided into two or more second power supply periods. As described in Embodiment 1, the order of harmonic current generation is shifted to the higher-order side, such that harmonic currents from the 3rd order to the 39th order can be reduced.

[0057] As described above, according to Embodiment 1, harmonic currents can be reduced while suppressing the influence on the switching elements.

[0058] [Embodiment 2]

[0059] (Power supply circuit)

[0060] Figure 8 is a schematic diagram showing the circuit configuration of a power supply device 307 (power supply) connected in parallel with a control circuit 303 for controlling an image heating device 200. The AC voltage of the AC power supply 301 is input to a diode bridge 901. The AC voltage undergoes full-wave rectification through the diode bridge 901 and is thus smoothed by a smoothing capacitor 902. The smoothed voltage is input to a switching power supply 903 serving as a DC-DC capacitor, and the switching power supply 903 outputs a secondary (side) voltage. As the switching power supply 903, an isolation transformer 903t is used to ensure insulation between the primary side and the secondary side. The smoothing capacitor 904 is a capacitor for outputting the secondary voltage from the switching power supply 903. The current It flowing out from the AC power supply 301 is branched into a current Ic flowing through the power supply device 307 and a current Ih flowing through the image heating device 200 via the control circuit 303.

[0061] (Control method)

[0062] Figure 9 Parts (a) and (b) thereof are schematic diagrams respectively showing the current Ic flowing through the power supply device 307 and the current Ih flowing through the image heating device 200 under the control of the control circuit 303. The current indicated by the dotted line is the current Ic flowing through the power supply device 307, and the current indicated by the solid line shows the current Ih flowing through the image heating device 200. Figure 9Part (a) shows the waveform when the control of Embodiment 2 is not executed. It is understood that the current Ic and the current Ih overlap with each other in time near a phase angle of 90°. Therefore, when the current Ic and the current Ih overlap with each other in time, the influence of the combined current of the current Ic and the current Ih on the harmonic current increases.

[0063] On the other hand, Figure 9 Part (b) shows the waveform when Embodiment 2 is executed. Figure 9 The total current of the current Ih in part (b) is not different from Figure 9 the total current of the current Ih in part (a). In Embodiment 2, the CPU 324 controls the current Ih so that the current Ic and the current Ih do not overlap with each other in time. In addition, the CPU 324 performs the control of providing the first power supply period and the second power supply period as described in Embodiment 1. Here, the first power supply period is a period including an energization period within a range of 1 / 40 times to 1 / 6000 times of one cycle time of the frequency of the AC voltage. The second power supply period is a period for supplying the difference in power between "the first power determined by the CPU 324" and "the power supplied during the first power supply period". Specifically, in Figure 9 part (b), the first power supply period is the period from t3 to t8, and specifically includes the first energization period from t3 to t4, the second energization period from t5 to t6, and the third energization period from t7 to t8. The periods from t4 to t5 and from t6 to t7, which are periods of non-energization between the previous energization period and the subsequent energization period in the first power supply period respectively, are set to different times. In addition, the second power supply period includes the period from t1 to t2 and the period from t9 to t10. Therefore, in Embodiment 2, the second power supply period is divided into two periods. For this reason, the power supply interruption periods also include two periods from t2 to t3 and from t8 to t9, and the lengths of these (two) power supply interruption periods may be the same or different from each other. Thus, in Figure 9 part (b), the second power supply period of the current Ih is arranged not to overlap with the current Ic of the power supply device 307 in time (or in terms of phase). Therefore, it is only necessary to set the control method and order of each period in a single half-wave according to the current Ic of the power supply device 307.

[0064] Through the above, the CPU 324 makes the current Ic and the current Ih not overlap with each other in time and subjects the current Ic flowing through the image heating device 200 to the control of Embodiment 2. Thus, compared with Figure 9 the harmonic current of the combined current of the current Ic and the current Ih in part (a), Figure 9The harmonic current of the combined current of the current Ic and the current Ih in part (b) is reduced.

[0065] (Confirmation of harmonic current reduction effect)

[0066] Figure 9 Part (c) shows Figure 9 the measurement results of the harmonic current in part (a) of Figure 9 and the measurement results of the harmonic current in part (b) of Figure 9 where the abscissa represents the order of the harmonic current and the ordinate represents the ratio of the magnitude of the harmonic current of each order to the standard value of the harmonic current of the associated order (current value / standard value). The case where the control of part (a) of Figure 9 is executed is indicated by ● and a solid line, and the case where the control of part (b) of

[0067] When Figure 9 the results of part (a) are confirmed, it is understood that the harmonic current due to the power supply device 307 is generated at the 3rd and 5th orders. Here, the orders of the harmonic current intended to be reduced in Embodiment 2 are determined to be the 3rd and 5th orders. In addition, an optimal first power supply period, an optimal number of energizations in the range of 1 / 40 times to 1 / 6000 times the period of the AC voltage frequency, and an optimal power supply interruption period are set. By making the above settings, the waveform of part (b) of Figure 9 is prepared, where the first power is the same as the power in the waveform of part (a) of Figure 9 of

[0068] In Figure 9 the waveform of part (b), the first power supply period is the period from t3 to t8, and the second power supply period includes the periods from t1 to t2 and from t9 to t10. The period from t1 to t2 is set to 2.2631 ms. Each of the periods from t2 to t3 and from t3 to t4 is set to 0.101 ms. The period from t4 to t5 is set to 2.6849 ms. Each of the periods from t5 to t6, from t6 to t7, from t7 to t8, and from t8 to t9 is set to 0.1176 ms. The period from t9 to t10 is set to 4.3796 ms. Incidentally, the second power supply period is controlled (arranged) so that the AC current amount is near a small phase angle of 0° (or 180°). For this reason, by performing control using the millisecond numbers as the above values, Figure 9 the total current amount of the current Ih in part (b) of Figure 9The total amount of current Ih in part (a). Additionally, in Example 1, the second power supply period occurs once within the time of one cycle of the frequency of the AC voltage. However, in Example 2, the second power supply period is divided into two periods (twice) to satisfy the first power. When Figure 9 the result of part (c) is confirmed, it can be confirmed that, compared with the result of the waveform of part (a) of Figure 9 where the control of Example 2 is not executed, in the result of the waveform of part (b) of Figure 9 where the control of Example 2 is executed, the harmonic current decreases. Specifically, in the case of Figure 9 part (b), the ratio (current value / standard value) is 40% or less in the 3rd order and in the 5th order.

[0069] When the first power changes, the first power supply period or the number of energization times within the range of 1 / 40 times to 1 / 6000 times the time of one cycle of the frequency of the AC voltage changes, not limited to those in Example 2. Additionally, the period between the energization period and the adjacent energization period in the first power supply period or the number of divisions of the second power supply period changes, not limited to those in Example 2. As described above in Example 2, the order of the generated harmonic current shifts to the higher order side, and even when considering the synthetic current of the charging current entering the input capacitor of the switching power supply, the harmonic current can be reduced.

[0070] As described above, according to Example 2, the harmonic current can be reduced while suppressing the influence on the switching element.

[0071] [Example 3]

[0072] (Circuit configuration in which two triac elements are connected in parallel with each other)

[0073] Figure 10An example of the control circuit 303 of the heater 201 in Embodiment 3 and its peripheral part 300 is shown. In Embodiment 1, power is supplied to the heating element H1 by using FETs (305 and 306). In Embodiment 3, as switching elements, triac (hereinafter referred to as triode alternating current switch) 1201 and 1202 are used and subjected to ON / OFF control so as to perform energization and cut-off of the energization. ON / OFF of the triode alternating current switch 1201 as the first triac is performed by controlling the current flowing through the light-emitting diode 1203d of the optotriac 1203. The triode alternating current switch 1201 is serially connected to the heater 201. The capacitor 1206 is serially connected to the triode alternating current switch 1201. ON / OFF of the triode alternating current switch 1202 as the second triac is performed by controlling the current flowing through the light-emitting diode 1204d of the optotriac 1204. The triode alternating current switch 1202 is connected in parallel to the triode alternating current switch 1201 and the capacitor 1206, and the triode alternating current switch 1201 and the capacitor 1206 are serially connected to each other.

[0074] First, the voltage supplied from the AC power supply 301 to the control circuit 303 is supplied to the capacitor 1206 and the triode alternating current switch 1202 via the capacitor C600 and the inductor 1205. The charging current entering the capacitor 1206 supplies power to the heating element H1 in synchronization with the turning-on of the triode alternating current switch 1201. When the optotriac 1203 is turned on, current flows to the gate terminal of the triode alternating current switch 1201 via the resistor 1210. The current via the resistor 1210 flows through the heating element H1 via the resistor 1211. By turning on the optotriac 1203, the triode alternating current switch 1201 is turned on. The optotriac 1203 is turned on by energization of the light-emitting diode 1203d. In synchronization with the base current of the transistor 1207, current flows from the 3.3V power supply to the cathode terminal of the light-emitting diode 1203d of the optotriac 1203 via the resistor 1219. The switching of the base current of the transistor 1207 is synchronized with the control signal ON2 (hereinafter also referred to as ON2 signal) via the resistor 1208. The control signal ON2 is connected to GND via the resistor 1209. The control signal ON2 is output from the CPU 324. Through the above, the triode alternating current switch 1201 is turned on by the control signal ON2.

[0075] The supply of power from the triac 1201 to the heating element H1 is performed only by the amount of charge stored in the capacitor 1206. The amount of charge stored in the capacitor 1206 can be set to a value smaller than the total power supplied to the heating element H1. Therefore, the first power supply period in the first embodiment can be constituted by the amount of charge stored in the capacitor 1206. Synchronously with the charging time of the capacitor 1206, the turn-off control signal ON2 is output. Since the charging is completed, the triac 1201 can be turned off.

[0076] Similarly to the control of the triac 1201 described above, the voltage supplied to the triac 1202 is turned on and off by using the control signal ON3 (hereinafter also referred to as the ON3 signal) output from the CPU 324 and supplied to the heating element H1. When the opto-triac 1204 is turned on, current flows through the resistor 1216 to the gate terminal of the triac 1202. The current flowing through the resistor 1216 flows through the heating element H1 via the resistor 1217. By turning on the opto-triac 1204, the triac 1202 is turned on. The opto-triac 1204 is turned on by energizing the light-emitting diode 1204d. Synchronously with the base current of the transistor 1215, current flows from the 3.3V power supply through the resistor 1212 to the cathode terminal of the light-emitting diode 1204d of the opto-triac 1204. The switching of the base current of the transistor 1215 is synchronized with the control signal ON3 via the resistor 1213. The control signal ON3 is connected to GND via the resistor 1214. Through the above, the triac 1202 is turned on by the control signal ON3. The supply of power from the triac 1202 to the heating element H1 provides a dominant ratio in the total power supplied to the heating element H1, and thus can constitute the second power supply period in the first embodiment. The other configurations are similar to those in Figure 3 those, and thus will be omitted from the description.

[0077] [Control of the Third Embodiment]

[0078] Figure 11 shows Figure 10The waveforms of the heater current, ON2 signal, and ON3 signal in the circuit. The case where 50% of the full power supply is supplied is shown. In the heater current waveform, the waveform formed by the turn-on of the triac element 1201 is the part indicated by the dotted line and constitutes the first power supply period in Embodiment 1. The waveform formed by the turn-on of the triac element 1202 is the part indicated by the solid line and constitutes the second power supply period in Embodiment 1. The number of similar power-on times is two. Other configurations are similar to those of Embodiment 1 and will be omitted from the description.

[0079] In Embodiment 3, two triac elements 1201 and 1202 are connected in parallel with each other, and a single capacitor 1206 is connected to the single triac element 1201, so as to constitute the first power supply period in Embodiment 1. On the other hand, the other triac element 1202 constitutes the second power supply period in Embodiment 1, indicating that the control described in Embodiment 1 can be achieved. Incidentally, even when performing the control shown in each of parts (b) and (c) of Figure 4 and Figure 5 as well as Figure 9 each shown in part (b) of

[0080] it may only be necessary to turn on the triac element 1201 connected in parallel with the capacitor 1206 in the first power supply period and turn on the triac element 1202 in the second power supply period.

[0081] Incidentally, in the above embodiments, the image heating device 200 including a single heating element H1 is described, but the control of each of the embodiments is also applicable to the case of using two or more heating elements and achieves a similar effect.

[0082] Although the present invention has been described with reference to the exemplary embodiments, it is to be understood that the present invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to cover all such modifications as well as equivalent structures and functions.

Claims

1. An image forming apparatus for forming a toner image on a recording material, comprising: A fixing unit configured to heat and fix the toner image on the recording material, the fixing unit including a heater; A switching element configured to switch between an on-state and an off-state, in the on-state, power from an AC power source is supplied to the heater, and in the off-state, the supply of power to the heater is cut off; And A controller configured to control the switching element to maintain the temperature of the fixing unit at a target temperature, the controller controlling the switching element in units of a half-cycle of an alternating current so that power determined based on the difference between the temperature of the fixing unit and the target temperature is supplied to the heater, Wherein, in a period of a half-cycle of the alternating current, the period of supplying power to the heater is divided into at least one first power supply period and a second power supply period longer than one first power supply period, Wherein, the sum of the lengths of the at least one first power supply period is from 1 / 6000 to 1 / 40 of the length of one cycle of the alternating current, and Wherein, the sum of the power supplied in the at least one first power supply period and the power supplied in the second power supply period is determined based on the difference between the temperature of the fixing unit and the target temperature.

2. The image forming apparatus according to claim 1, wherein, The controller controls the switching element such that the first power supply period appears multiple times in a half-cycle of the alternating current, and Wherein, all of the first power supply periods have the same length.

3. The image forming apparatus according to claim 1, wherein, The controller controls the switching element such that the at least one first power supply period appears only once in a half-cycle of the alternating current, and Wherein, depending on the power determined based on the difference between the temperature of the fixing unit and the target temperature, the lengths of the at least one first power supply period are different from each other.

4. The image forming apparatus according to claim 1, wherein, The switching element is a field effect transistor serially connected to the heater.

5. The image forming apparatus according to claim 1, wherein, The switching element is a triac.

6. The image forming apparatus according to claim 5, further comprising: A first triac serially connected to the heater; A capacitor serially connected to the first triac; And A second triac connected in parallel to the first triac and the capacitor, the first triac and the capacitor being serially connected to each other, Wherein, the controller performs control by using the first triac when supplying power to the heater in the at least one first power supply period, and performs control by using the second triac when supplying power to the heater in the second power supply period.

7. The image forming apparatus according to claim 1, further comprising a power supply connected to the AC power source, Among them, The controller controls the switching element such that the second power supply period does not overlap with the period when current flows through the power supply.

8. An image forming apparatus for forming a toner image on a recording material, comprising: A fixing unit configured to heat and fix the toner image on the recording material, the fixing unit including a heater; A switching element configured to switch between an on state and an off state, in the on state, power from an AC power supply is supplied to the heater, and in the off state, the supply of power to the heater is cut off; And A controller configured to control the switching element to maintain the temperature of the fixing unit at a target temperature, the controller controlling the switching element in units of a half cycle of an alternating current so that power determined according to the difference between the temperature of the fixing unit and the target temperature is supplied to the heater, Wherein, a period during which power is supplied to the heater within a period of a half cycle of the alternating current is divided into at least one first power supply period and a second power supply period, the second power supply period being a period corresponding to power obtained by subtracting the power supplied in the at least one first power supply period from the power determined according to the difference between the temperature of the fixing unit and the target temperature, Wherein, the sum of the lengths of the at least one first power supply period is from 1 / 6000 to 1 / 40 of the length of one cycle of the alternating current, and Wherein, the sum of the power supplied in the at least one first power supply period and the power supplied in the second power supply period is determined according to the difference between the temperature of the fixing unit and the target temperature.

9. The image forming apparatus according to claim 8, wherein, The controller controls the switching element such that the first power supply period appears multiple times within a half cycle of the alternating current, and Wherein, all of the first power supply periods have the same length.

10. The image forming apparatus according to claim 8, wherein, The controller controls the switching element such that the at least one first power supply period appears only once within a half cycle of the alternating current, and Wherein, depending on the power determined according to the difference between the temperature of the fixing unit and the target temperature, the lengths of the at least one first power supply period are different from each other.

11. The image forming apparatus according to claim 8, wherein, The switching element is a field effect transistor serially connected to the heater.

12. The image forming apparatus according to claim 8, wherein, The switching element is a triac.

13. The image forming apparatus according to claim 12, further comprising: A first triac serially connected to the heater; A capacitor serially connected to the first triac; And A second triac connected in parallel to the first triac and the capacitor, the first triac and the capacitor being serially connected to each other, Wherein, the controller performs control by using the first triac when power is supplied to the heater in the at least one first power supply period, and performs control by using the second triac when power is supplied to the heater in the second power supply period.

14. The image forming apparatus according to claim 8 further includes a power supply connected to the AC power supply, Among them, wherein the controller controls the switching element such that the second power supply period does not overlap with the period during which current flows through the power supply.

Images