Image forming apparatus

Abstract

To provide an image forming device capable of suppressing harmonics, flicker and temperature ripple.SOLUTION: Disclosed are waveform patterns of currents flowing through a first heat generation group and a second heat generation group controlled by a control part, which differ from each other in at least one same phase in a period of one control cycle. In the period of one control cycle, a ratio of overlap between a period of phase control of the first heat generation group and a period of phase control of the second heat generation group is 50% or less.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a printer or a copier using an electrophotographic method.

Background Art

[0002] In order to achieve both reduction of harmonics generated from the current flowing from a commercial AC power supply and reduction of flicker in a fixing unit mounted in an image forming apparatus, control of the waveform pattern of the current flowing through a heating element has been performed. In Patent Document 1, control has been proposed in which phase control is adopted for at least one half-wave in a control period that is an integer multiple of one half-wave of the commercial frequency, and frequency control in which full conduction or non-conduction is performed for each of the remaining half-waves is adopted.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0007] Furthermore, the present invention relates to an image forming apparatus that can switch the heat distribution of the heater in the longitudinal direction of the fixing apparatus, wherein the combined resistance of the first heating group to which the first switch element of the at least two switch elements is connected is the smallest combined resistance of the first heating group to which the combined resistance of the at least two heating groups is connected, and the combined resistance of the first heating group to which the first switch element of the at least two switch elements is connected is the smallest combined resistance of the first heating group to which the combined resistance of the at least two heating groups is connected, and the combined resistance of the first heating group to which the first switch element of the at least two switch elements is connected is the smallest combined resistance of the first heating group to which the first switch element of the at least two switch elements is connected, and the combined resistance of the heater in the longitudinal direction of the fixing apparatus is switched, wherein the combined resistance of the first heating group to which the first switch element of the at least two switch elements is connected is the smallest combined resistance of the first heating group to which the first switch element of the at least two switch elements is connected, and two The combined resistance of the second heating group to which the second switching element among the switching elements is connected is the second smallest, the waveform patterns of the current flowing through the first heating group and the second heating group controlled by the control unit are different waveform patterns with the same phase at least once during the period of one control cycle, the overlapping ratio of the phase control period of the first heating group and the phase control period of the second heating group during the period of one control cycle is 50% or less, and for both the first heating group and the second heating group, the proportion of the phase control period in the period of one control cycle is higher than 50%, and at least one period of the AC is a wavenumber control pattern. [Effects of the Invention]

[0008] As described above, the present invention makes it possible to suppress current harmonics, flicker, and temperature ripple. [Brief explanation of the drawing]

[0009] [Figure 1] Schematic diagram of an image forming apparatus [Figure 2] Cross-sectional view of the anchoring section [Figure 3] Heater configuration diagram [Figure 4] Heater control circuit diagram [Figure 5] Waveform pattern diagram [Figure 6] Waveform pattern diagram [Figure 7] Overall view of the waveform pattern in Example 1 [Figure 8] Modified heater control circuit [Figure 9] Overall view of the waveform pattern in Example 2 [Modes for carrying out the invention]

[0010] The embodiments for carrying out this invention will be described in detail below with reference to the drawings, based on examples. However, the dimensions, materials, shapes, and relative arrangements of the components described in these embodiments should be appropriately modified depending on the configuration of the device to which the invention is applied and various conditions. In other words, the scope of this invention is not intended to be limited to the following embodiments.

[0011] (Example 1) Figure 1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention, which uses electrophotographic recording technology. Examples of image forming apparatuses to which the present invention can be applied include photocopiers and printers that utilize electrophotographic or electrostatic recording methods. Here, we will describe the case in which the present invention is applied to a laser printer that forms an image on recording paper P as a recording material using the electrophotographic method.

[0012] The image forming apparatus 100 comprises a video controller 120 and a control unit 113. The video controller 120 is an acquisition unit that acquires image information formed on a recording material, and receives and processes image information and print instructions transmitted from an external device such as a personal computer. The control unit 113 is connected to the video controller 120 and controls each part of the image forming apparatus 100 in accordance with instructions from the video controller 120. When the video controller 120 receives a print instruction from an external device, image forming is performed in the following operation.

[0013] When the image forming apparatus 100 receives a print signal, the scanner unit 21 emits a laser beam modulated according to the image information and scans the surface of the photosensitive drum 19, which has been charged to a predetermined polarity by the charging roller 16. This forms an electrostatic latent image on the photosensitive drum 19. Toner is supplied to this electrostatic latent image from the developing roller 17, and the electrostatic latent image on the photosensitive drum 19 is developed as a toner image. Meanwhile, the recording material (recording paper) P loaded in the paper feed cassette 11 is fed one sheet at a time by the pickup roller 12 and transported toward the registration roller pair 14 by the transport roller pair 13. Furthermore, the recording material P is transported from the registration roller pair 14 to the transfer position in time with the timing when the toner image on the photosensitive drum 19 reaches the transfer position formed by the photosensitive drum 19 and the transfer roller 20. As the recording material P passes through the transfer position, the toner image on the photosensitive drum 19 is transferred to the recording material P. After that, the recording material P is heated in the fixing unit 200, and the toner image is heat-fixed to the recording material P. The recording material P, which carries the fixed toner image, is discharged to a tray at the top of the image forming apparatus 100 by transport roller pairs 26 and 27. The drum cleaner 18 cleans the toner remaining on the photosensitive drum 19. The paper feed tray 28 (manual feed tray), which has a pair of recording material regulating plates whose width can be adjusted according to the size of the recording material P, is provided to accommodate recording material P of sizes other than standard sizes. The pickup roller 29 feeds the recording material P from the paper feed tray 28. The image forming apparatus 100 has a motor 30 that drives the fixing unit 200 and the like.

[0014] The control circuit 400, which serves as a power control unit connected to a commercial AC power supply 401, supplies power to the fixing unit 200. The photosensitive drum 19, charging roller 16, scanner unit 21, developing roller 17, and transfer roller 20, as described above, constitute an image forming unit that forms an unfixed image on the recording material P. Also, in this embodiment, a developing unit including the photosensitive drum 19, charging roller 16, and developing roller 17, and a cleaning unit including the drum cleaner 18 are configured to be detachable from the apparatus main body of the image forming apparatus 100 as the process cartridge 15. Further, the fixing unit 200 is also configured to be detachable from the image forming apparatus 100.

[0015] FIG. 2 is a cross-sectional view of the fixing unit 200 of this embodiment. The fixing unit 200 includes a cylindrical fixing film (hereinafter referred to as film) 202, a heater 300 disposed in the internal space of the film 202, a pressure roller 208 that forms a fixing nip portion N together with the heater 300 via the film 202, and a metal stay 204.

[0016] The film 202 is a heat-resistant film formed in a cylindrical shape also referred to as an endless belt or endless film. The material of the base layer is a heat-resistant resin such as polyimide or a metal such as stainless steel. Also, an elastic layer such as heat-resistant rubber may be provided on the surface of the film 202. The pressure roller 208 has 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 300 is held by a holding member 201 made of heat-resistant resin. The holding member 201 also has a guide function for guiding the rotation of the film 202. 204 is a metal stay for applying the pressure of a spring (not shown) to the holding member 201. The pressure roller 208 rotates in the direction of the arrow receiving power from the motor 30. When the pressure roller 208 rotates, the film 202 rotates passively. The recording paper P carrying the unfixed toner image is heated and fixed while being sandwiched and conveyed at the fixing nip portion N.

[0017] The heater 300 is heated by heating elements (heating resistors) 302a and 302b provided on a ceramic substrate 305, which will be described later. A protection element 212 (Fig. 4) is in contact with the heater 300. The protection element 212 is an example of a thermoswitch, a temperature fuse, etc., and operates when the heater 300 generates abnormal heat to cut off the power supplied to the heater 300. Also, a thermistor T1 (T1-1 to T1-4, T1-7, see Fig. 3(B)) is installed on the sliding surface side of the heater 300 with respect to the film 202.

[0018] Using Fig. 3, the configuration of the heater 300 according to this embodiment will be described. Fig. 3(A) is a cross-sectional view of the heater 300, and Fig. 3(B) is a plan view of each layer of the heater 300. Fig. 3(B) shows the conveyance reference position X0 of the recording material P in the image forming apparatus 100 of this embodiment. The conveyance reference in this embodiment is the center reference, and the recording material P is conveyed such that the center line in the direction orthogonal to its conveyance direction follows the conveyance reference position X0. Also, Fig. 3(A) is a cross-sectional view of the heater 300 at the conveyance reference position X0.

[0019] As shown in Fig. 3(A), the heater 300 has a conductor 301 and a conductor 303 on the substrate 305. The conductor 301 is separated into a conductor 301a arranged on the upstream side in the conveyance direction of the recording material P and a conductor 301b arranged on the downstream side. Further, the heater 300 has a heating element 302 that generates heat by the power supplied through the conductor 301 and the conductor 303, and the heating element 302 is provided between the conductor 301 and the conductor 303 on the substrate. This heating element 302 is separated into a heating element 302a arranged on the upstream side in the conveyance direction of the recording material P and a heating element 302b arranged on the downstream side. Also, an electrode E3 is provided for power supply. Further, on the back surface layer 2, an insulating surface protection layer (protective glass) 308 covers the area other than the electrode E3. The heater 300 (substrate 305) is arranged such that its longitudinal direction is orthogonal to the conveyance direction of the recording material P.

[0020] As shown in Figure 3(B), the back layer 1 of the heater 300 has seven heating blocks (HB1 to HB7) arranged along the longitudinal direction of the heater 300, each consisting of a conductor 301, a conductor 303, a heating element 302, and an electrode E3. To indicate the correspondence with these seven heating blocks HB1 to HB7, the components constituting each heating block are numbered according to the heating block, for example, heating element 302a-1 to 302a-7, with the number corresponding to the heating block at the end of each symbol. The same applies to heating element 302b, conductors 301a and 301b, conductor 303, and electrode E3.

[0021] The surface protective layer 308 of the back layer 2 of the heater 300 is formed to expose electrodes E3-1 to E3-7, E4, and E5, and is configured to allow connection of electrical contacts (not shown) from the back side of the heater 300. This allows each heating block to be supplied with power independently and controlled independently. By dividing it into seven heating blocks in this way, four paper feeding areas can be formed, such as AREA1 to AREA4. In this embodiment, AREA1 is for A5 paper, AREA2 for B5 paper, AREA3 for A4 paper, and AREA4 for Letter paper. Since the seven heating blocks can be controlled independently, the heating block to be supplied with power can be selected according to the size of the recording paper P. However, in this embodiment, as shown in the circuit diagram in Figure 4, the seven heating blocks are driven by five triacs (switching elements). Note that the number of heating areas and heating blocks are not limited to the number in this embodiment. Furthermore, the heating elements 302a-1 to 302a-7 and 302b-1 to 302b-7 within each heating block are not limited to a continuous pattern as described in this embodiment, but may also be strip-shaped patterns with gaps between them.

[0022] On the sliding surface layer 1 of the heater 300 (on the surface of the substrate 305 opposite to the surface on which the heating element is provided), thermistors T1-1 to T1-4 and T1-7 are installed as temperature sensing elements for detecting the temperature of each heating block of the heater 300. Thermistors T1-1 to T1-4 and T1-7 are mainly used for temperature control of each heating block and are therefore placed in each heating block. As will be described later in Figure 4, heating elements 302-3 and 302-5 are electrically connected, so no temperature sensing element is provided in the position corresponding to heating block HB5. Similarly, heating elements 302-2 and 302-6 are electrically connected, so no temperature sensing element is provided in the position corresponding to heating block HB6. One end of thermistors T1-1 to T1-4 and T1-7 is connected to conductors ET1-1 to ET1-4 and ET1-7, respectively, for detecting the resistance value of the thermistors, while the other end is commonly connected to conductor EG9.

[0023] The sliding surface layer 2 of the heater 300 has a surface protection layer 309 made of a sliding glass coating. The surface protection layer 309 is provided except at both ends of the heater 300 in order to provide electrical contacts for each conductor of the sliding surface layer 1.

[0024] Figure 4 is a circuit diagram showing the control circuit 400 of the heater 300 in Embodiment 1. A commercial AC power supply 401 is connected to the image forming apparatus 100. Power supply voltages Vcc1 and Vcc2 are DC power supplies generated by an AC / DC converter (not shown) connected to the AC power supply 401. The AC power supply 401 is connected to the heater 300 via relays 430 and 440 and triacs 441 to 444 and 447. Relays 430 and 440 are turned on / off by the control signal RLON from the CPU 420, and each signal is connected to transistors 433 and 435 via gate resistors 434 and 436. Triacs 441 to 444 and 447 are turned on / off by control signals FUSER1 to FUSER4 and FUSER7 from the CPU 420. The drive circuits for triacs 441 to 444 and 447 are omitted from the illustration. By selectively controlling the triacs 441-444 and 447, which are multiple semiconductor elements, the energization of multiple heating elements can be selectively controlled, and multiple heating regions divided in the longitudinal direction can be individually and selectively heated.

[0025] The thermistor temperature sensing circuit is described below. Conductor EG9 is connected to ground potential. Then, all thermistors T1-1 to T1-4 and T1-7, as described in Figure 3, are divided by resistors 451 to 454 and 457, which are pulled up to Vcc1. The divided voltages are detected by the CPU 420 as temperature signals Th1-1 to Th1-4 and Th1-7, and the temperature is detected by converting the voltage to temperature using information pre-set in the CPU 420's internal memory.

[0026] The CPU 420 calculates the power to be supplied, for example, by PI control, based on the set temperature (target temperature) and the temperatures detected by thermistors T1-1 to T1-4 and T1-7. The ON timing of the FUSER 1 to 4 and 7 signals is generated by the CPU 420 based on the ZEROX timing signal, which is synchronized with the zero potential of the AC power supply 401 generated by the zero-cross detection unit 421. Since heating elements 302-3 and 302-5 are electrically connected, the FUSER 3 signal can control the power supplied to heating elements 302-3 and 302-5. Similarly, since heating elements 302-2 and 302-6 are electrically connected, the FUSER 2 signal can control the power supplied to heating elements 302-2 and 302-6. The power calculated by CPU420 is converted to a duty cycle as shown in Table 1, and triacs 441-444 and 447 are controlled by the phase angle corresponding to the duty cycle (=FUSER1-4, 7 signals). A table as shown in Table 1 is set up within CPU420, and when performing phase control where current is supplied from the middle of a half-cycle of AC, FUSER1-4, 7 signals are output based on this table. When performing wavenumber control where current is supplied or not supplied for the entire half-cycle of AC, control is performed with two values: full wave energization (100% duty cycle) or current cutoff (0% duty cycle).

[0027] [Table 1]

[0028] Figures 5, 6(a), and 6(b) show the waveform patterns flowing through the heater 300 when the CPU 420 supplies control signals FUSER1 to FUSER4 and FUSER7 to triacs 441 to 444 and 447. The CPU 420 updates the power supplied to the heater 300 every four cycles (four full waves) of the commercial AC waveform. These four cycles (four full waves) of the AC waveform are defined as the control update cycle (control cycle).

[0029] As can be seen by referring to Figure 5, when the triac 444 (first switching element) is driven based on the control signal FUSER 4, the waveform pattern of the current flowing through the heating element 302-4 is a phase-controlled pattern in the first and third periods. On the other hand, in the second and fourth periods, it is a wavenumber-controlled pattern (shown as OFF in Figure 5). Similarly, when the triac 443 (second switching element) is driven based on the control signal FUSER 3, the waveform pattern of the current flowing through the heating elements 302-3 and 302-5 is a wavenumber-controlled pattern in the first and third periods (shown as OFF in Figure 5). On the other hand, in the second and fourth periods, it is a phase-controlled pattern.

[0030] Here, heating element 302-1, to which triac 441 is connected, is designated as heating group G441, and heating elements 302-2 and 302-6, to which triac 442 is connected, are designated as heating group G442. Heating elements 302-3 and 302-5, to which triac 443 (second switching element) is connected, are designated as heating group G443 (second heating group). Heating element 302-4, to which triac 444 (first switching element) is connected, is designated as heating group G444 (first heating group). Heating element 302-4, to which triac 447 is connected, is designated as heating group G447. Comparing the combined resistance of heating groups G441-G444 and G447, heating group G444 has the smallest combined resistance, followed by heating group G443. When the current flowing through a heating group with a small combined resistance is large, harmonics, flicker, and temperature ripple worsen.

[0031] Therefore, in this embodiment, as shown in Figure 5, among the five heating groups G441-G444 and G447, the relationship between the waveform patterns flowing through heating group G444, which has the smallest combined resistance, and heating group G443, which has the second smallest combined resistance, has been carefully designed. Specifically, the waveform patterns are set so that the current waveforms flowing through heating group G444 and heating group G443 are different from each other at least one phase (timing) during the period of one control cycle (Rule 1). The remaining heating groups G441, G442, and G447 have a larger combined resistance compared to heating groups G444 and G443, so they have a lower influence on harmonics, flicker, and temperature ripple. In addition, the waveform patterns used in the five heating groups G441-G444 and G447 have been simplified to two types. For this reason, the five heating groups G441-G444 and G447 are divided into two large groups so that the difference in the total value of the combined resistance is smallest. In this embodiment, heat generation group G444 is classified into the first major group to which it belongs, and heat generation groups G441 to G443 and G447 are classified into the second major group to which heat generation group G443 belongs. Therefore, in this embodiment, the waveform patterns of heat generation groups G441, G442, and G447 are always the same (the phase is also the same) as the waveform pattern of heat generation group G443. Note that heat generation group G444, which has the smallest combined resistance, and heat generation group G443, which has the second smallest combined resistance, can be classified into different major groups, and the other heat generation groups G441, G442, and G447 can each belong to either of the two major groups. For example, heat generation groups G441 and G447 may belong to the same first major group as heat generation group G444, and heat generation group G442 may belong to the same second major group as heat generation group G443.

[0032] Furthermore, as shown in Figure 5, the percentage of time during one control cycle when the phase control period of heat generation group G444 and the phase control period of heat generation group G443 overlap (at the same timing) is 50% or less (0% in Figure 5) (Rule 2). This is because if the phase control waveforms overlap in phase (at the same timing), harmonics, flicker, and temperature ripple will worsen.

[0033] Figures 6(a) and 6(b) show the waveform patterns of heat-generating groups G444 and G443. The waveform patterns of the other heat-generating groups G441, G442, and G447 are the same as those of heat-generating group G443 and are therefore omitted. In Figure 6(a), the waveform pattern flowing through heat-generating group G444 is a phase-controlled pattern in the first, second, and third periods, and a wavenumber-controlled (OFF) pattern in the fourth period. On the other hand, the waveform pattern flowing through heat-generating group G443 is a phase-controlled pattern in the second, third, and fourth periods, and a wavenumber-controlled (OFF) pattern in the first period. Also, as with Figure 5, it can be seen that rules 1 and 2 are applied in Figure 6(a). In Figure 6(a), under rule 2, the overlapping period of phase control is 50%. On the other hand, in Figure 6(a), each waveform pattern is a phase-controlled pattern for a proportion higher than 50% of one control period. Specifically, in both the waveform patterns flowing through heat generation group G444 and the waveform patterns flowing through heat generation group G443, the proportion of the phase control period within one control cycle is 3 / 4. In addition, at least one cycle of the AC is controlled by wavenumber. Thus, in this example, the proportion of the phase control period is higher than 50%, and at least one cycle of the AC is controlled by wavenumber (Rule 3). In this way, temperature ripple can be suppressed by increasing the proportion of phase control within one control cycle, and harmonics can be further suppressed by providing wavenumber control for at least one cycle of the AC.

[0034] In Figure 6(b), the waveform pattern flowing through heat-generating group G444 is a phase-controlled pattern in the 0.5, 1.5, 2, 2.5, 3, and 4th periods, and a wavenumber-controlled (OFF) pattern in the 1st and 3.5th periods. On the other hand, the waveform pattern flowing through heat-generating group G443 is a phase-controlled pattern in the 0.5, 1.0, 1.5, 2.0, 3, and 3.5th periods, and a wavenumber-controlled (OFF) pattern in the 2.5 and 4th periods. Similar to Figure 6(a), it can be seen that rules 1, 2, and 3 are applied in Figure 6(b). However, in Figure 6(b), the wavenumber-controlled periods are distributed so that they do not continue for a period longer than half a cycle of AC (rule 4). Specifically, in the waveform pattern flowing through heat-generating group G444, the wavenumber-controlled periods are distributed between the 1st and 3.5th periods. The waveform pattern flowing through the heat generation group G443 has the wavenumber control period distributed between the 2.5th and 4th periods. This rule 4 can further suppress flicker.

[0035] The waveform patterns of the currents flowing through the five heat generation groups G441-G444 and G447 satisfy at least rules 1 and 2 described above. Rules 1-4 can be summarized as follows: Rule 1: The waveform patterns of the current flowing through the heat-generating group with the smallest combined resistance (first heat-generating group) and the second smallest heat-generating group (second heat-generating group) are different from each other and have at least one same phase during the duration of one control cycle (Rule 1). Rule 2: Within one control cycle, the overlap between the phase control period of the first heat generation group and the phase control period of the second heat generation group must be 50% or less (Rule 2). Rule 3: For both the first and second heating groups, the proportion of the phase control period to the duration of one control cycle is greater than 50%, and at least one cycle of the AC is a wavenumber control pattern (Rule 3). Rule 4: In both the first and second heat generation groups, the wavenumber control period is distributed so that it does not continue for a period longer than half a cycle of the AC within the duration of one control period (Rule 4).

[0036] Figure 7 shows the waveform patterns flowing through heat-generating groups G444 and G443 at each input power ratio (input power level). The waveform patterns for heat-generating groups G441, G442, and G447, other than G444 and G443, are omitted because either pattern can be selected.

[0037] When the input power is between 0% and 75%, the phase angle of each phase control is adjusted according to the power using the waveform pattern described in Figure 6(b). When the input power is between 75% and 100%, the power of the wavenumber control is set to 100% (ON), and the waveform pattern of the phase control is similarly adjusted according to the power. In the example in Figure 7, the waveform satisfies all rules 1 to 4 in both the case when the input power is between 0% and 75% and the case when the input power is between 75% and 100%. However, when using a heater having at least three heating groups driven by at least three switch elements, as in this example, it is sufficient to satisfy at least rules 1 and 2. A waveform pattern that satisfies rules 1 to 3 is more preferable, and a waveform pattern that satisfies all rules 1 to 4 is most preferable.

[0038] On the other hand, as shown in the modified example in Figure 8, we will explain the case where the heater 300 has only two heat-generating groups G442 and G444 (combined resistance of heat-generating group G444 < combined resistance of heat-generating group G442). In this case, a waveform pattern that satisfies at least rules 1 to 3 is preferred, and a waveform pattern that satisfies all of rules 1 to 4 is most preferred.

[0039] When the input power changes due to PID control, by selecting a waveform pattern that satisfies rules 1 to 4, harmonics, flicker, and temperature ripple can be improved, respectively.

[0040] (Example 2) Figure 9 shows the waveform patterns of Example 2 for each power input ratio when using the control circuit 400 of the heater 300 shown in Figure 4.

[0041] The waveform pattern shown in Figure 9 differs in that a portion of the input power does not apply rules 1 to 4 as shown in Example 1.

[0042] For input power of 0-25%, phase control is selected for the entire duration of the control cycle. While this waveform pattern has the disadvantage of generating harmonic noise, it is advantageous in terms of temperature ripple and flicker. When the voltage of the commercial AC power supply is high, the power supplied to the heating element increases, so the proportion of input power required to supply the predetermined power during temperature control decreases. Also, the power of one cycle of AC increases, making it easier for temperature ripple to occur. Therefore, by selecting phase control as the waveform pattern for a low input power ratio of 0-25%, temperature ripple can be suppressed.

[0043] For input power of 25-50%, a waveform pattern is selected that applies all of the rules 1 to 4 shown in Example 1.

[0044] When the input power is between 50% and 100%, the waveform pattern is one in which rules 1 and 2 of the rules 1 to 4 shown in Example 1 are applied. This waveform is unfavorable to temperature ripple but favorable to harmonics and flicker. Since the heater 300 is temperature-controlled to maintain the target temperature, when power is supplied to the heating element, the heater 300 gradually reaches a state of thermal saturation, and the supplied power settles below a certain level. Levels with a large percentage of input power, such as between 50% and 100%, are mainly used during the warm-up period before the heater 300 reaches thermal saturation, so a waveform pattern favorable to flicker is selected.

[0045] Thus, when the ratio of input power changes due to PID control, you may choose which of the following is more important: suppressing harmonics, suppressing flicker, or suppressing temperature ripple, and selectively apply rules 1 to 4.

[0046] Finally, the typical configurations disclosed in this application are summarized below. Note that some elements in the following configuration examples are denoted by reference numerals, which indicate their correspondence to the elements described in the above-mentioned embodiments. However, this correspondence is merely an example for reference, and the elements described below are not limited to the configurations of the elements in the above-mentioned embodiments.

[0047] <<Configuration Example A1>> An image forming unit that forms a toner image on a recording material, A fixing unit for heating and fixing a toner image formed on a recording material, the fixing unit having a heater having at least three heating groups that generate heat by power supplied from an AC power source, At least three switch elements are provided in each power supply path from the AC power source to each of the at least three heat-generating groups, A control unit that controls the power supplied to at least three heat-generating groups by controlling at least three switch elements, wherein multiple continuous cycles of the AC power supply are defined as one control cycle, and the control unit controls the power for each of the control cycles, An image forming apparatus having a heater that can switch the heat distribution of the heater in the longitudinal direction of the fixing section, Of the combined resistances of each of the at least three heat-generating groups, the combined resistance of the first heat-generating group to which the first switch element of the at least three switch elements is connected is the smallest, and the combined resistance of the second heat-generating group to which the second switch element of the at least three switch elements is connected is the second smallest. The waveform patterns of the currents flowing through the first heating group and the second heating group, controlled by the control unit, The waveforms are at least one waveform with the same phase but different from each other during the duration of the control cycle, An image forming apparatus characterized in that, during the period of one control cycle, the proportion of overlap between the phase control period of the first heat generation group and the phase control period of the second heat generation group is 50% or less.

[0048] <<Configuration example A2>> The image forming apparatus according to Configuration Example A1, wherein the waveform pattern controlled by the control unit is further characterized in that, for both the first heating group and the second heating group, the proportion of the phase control period to the duration of one control cycle is higher than 50%, and at least the duration of one AC cycle is a wavenumber control pattern.

[0049] <<Configuration Example A3>> The image forming apparatus according to configuration example A2, characterized in that the waveform patterns controlled by the control unit are further distributed such that, for both the first heating group and the second heating group, the period of wavenumber control is longer than the period of half a cycle of the AC within the period of one control cycle.

[0050] <<Configuration example A4>> The image forming apparatus according to any one of the configuration examples A1 to A3, characterized in that, among the at least three heat-generating groups, the waveform pattern of the current flowing through the heat-generating groups other than the first heat-generating group and the second heat-generating group is the same as either the waveform pattern of the current flowing through the first heat-generating group or the waveform pattern of the current flowing through the second heat-generating group.

[0051] <<Configuration Example A5>> The image forming apparatus according to configuration example A4, characterized in that the difference in combined resistance between the first major group to which the first heat generation group belongs and the second major group to which the second heat generation group belongs is minimized, and heat generation groups other than the first major group and the second major group are classified into the first major group or the second major group.

[0052] <<Configuration example A6>> The image forming apparatus according to any one of configuration examples A1 to A3, characterized in that the waveform pattern of the current flowing through the first heating group and the second heating group, controlled by the control unit, is set at a predetermined power level or lower.

[0053] <<Configuration example A7>> The image forming apparatus according to any one of the configuration examples A1 to A3, characterized in that the heater has a substrate on which the at least three heat-generating groups are provided.

[0054] <<Configuration Example A8>> The image forming apparatus according to Configuration Example 7, characterized in that the at least three heat-generating groups are arranged in the longitudinal direction.

[0055] <<Configuration example A9>> The image forming apparatus according to configuration example A8, characterized in that each of the three heating groups comprises two conductors arranged along the longitudinal direction and a heating element connected between the two conductors.

[0056] <<Configuration Example A10>> The image forming apparatus according to Configuration Example 9, characterized in that the fixing section comprises a cylindrical film and a roller that contacts the outer surface of the film, the heater is arranged in the internal space of the film, the film is sandwiched between the heater and the roller, and a fixing nip section is formed between the film and the roller to sandwich and transport the recording material.

[0057] <<Configuration Example B1>> An image forming unit that forms a toner image on a recording material, A fixing unit for heating and fixing a toner image formed on a recording material, the fixing unit having a heater having at least two heating groups that generate heat by power supplied from an AC power source, At least two switch elements are provided in each power supply path from the AC power source to each of the at least two heat-generating groups, A control unit that controls the power supplied to at least two heat-generating groups by controlling at least two switch elements, wherein a control unit controls power for each control cycle, with multiple continuous cycles of the AC power supply being defined as one control cycle, An image forming apparatus having a heater that can switch the heat distribution of the heater in the longitudinal direction of the fixing section, Of the combined resistances of the two heat-generating groups, the combined resistance of the first heat-generating group to which the first switch element of the at least two switch elements is connected is the smallest, and the combined resistance of the second heat-generating group to which the second switch element of the at least three switch elements is connected is the second smallest. The waveform patterns of the currents flowing through the first heating group and the second heating group, controlled by the control unit, The waveforms are at least one waveform with the same phase but different from each other during the duration of the control cycle, During the period of the aforementioned control cycle, the overlap between the phase control period of the first heat generation group and the phase control period of the second heat generation group is 50% or less. The image forming apparatus is characterized in that, in both the first heating group and the second heating group, the proportion of the phase control period to the duration of one control cycle is higher than 50%, and at least the duration of one AC cycle is a wavenumber control pattern.

[0058] <<Configuration example B2>> The image forming apparatus according to configuration example B1, characterized in that the waveform patterns controlled by the control unit are further distributed such that, for both the first heating group and the second heating group, the period of wavenumber control is longer than the period of half a cycle of the AC within the period of one control cycle.

[0059] <<Configuration Example B3>> The image forming apparatus according to configuration example B1 or B2, characterized in that the heater has a first heating group and heating groups other than the second heating group, and the waveform pattern of the current flowing through the first heating group and the heating groups other than the second heating group is the same as either the waveform pattern of the current flowing through the first heating group or the waveform pattern of the current flowing through the second heating group.

[0060] <<Configuration Example B4>> The image forming apparatus according to configuration example B1 or B2, characterized in that the waveform pattern of the current flowing through the first heating group and the second heating group, controlled by the control unit, is set to a power input level below a predetermined level.

[0061] <<Example Configuration B5>> The image forming apparatus according to configuration example B1 or B2, characterized in that the heater has a substrate on which at least two heat-generating groups are provided.

[0062] <<Configuration example B6>> The image forming apparatus according to configuration example B5, characterized in that the at least two heat-generating groups are arranged in the longitudinal direction.

[0063] <<Configuration Example B7>> The image forming apparatus according to configuration example B6, characterized in that each of the two heating groups comprises two conductors arranged along the longitudinal direction and a heating element connected between the two conductors.

[0064] <<Configuration example B8>> The image forming apparatus according to configuration example B7, characterized in that the fixing section comprises a cylindrical film and a roller that contacts the outer surface of the film, the heater is arranged in the internal space of the film, the film is sandwiched between the heater and the roller, and a fixing nip section is formed between the film and the roller for sandwiching and conveying the recording material. [Explanation of symbols]

[0065] 100 Image forming apparatus 302 Heating element 420 CPU 441-444, 447 Triac

Claims

1. An image forming unit that forms a toner image on a recording material, A fixing unit for heating and fixing a toner image formed on a recording material, the fixing unit having a heater having at least three heating groups that generate heat by power supplied from an AC power source, At least three switch elements are provided in each power supply path from the AC power source to each of the at least three heat-generating groups, A control unit that controls the power supplied to at least three heat-generating groups by controlling at least three switch elements, wherein multiple continuous cycles of the AC power supply are defined as one control cycle, and the control unit controls the power for each of the control cycles, An image forming apparatus having a heater that can switch the heat distribution of the heater in the longitudinal direction of the fixing section, Of the combined resistances of each of the at least three heat-generating groups, the combined resistance of the first heat-generating group to which the first switch element of the at least three switch elements is connected is the smallest, and the combined resistance of the second heat-generating group to which the second switch element of the at least three switch elements is connected is the second smallest. The waveform patterns of the currents flowing through the first heating group and the second heating group, controlled by the control unit, The waveforms are at least one waveform with the same phase but different from each other during the duration of the control cycle, During the period of the aforementioned control cycle, the overlap between the phase control period of the first heat generation group and the phase control period of the second heat generation group is 50% or less. The image forming apparatus is characterized in that, in both the first heating group and the second heating group, the proportion of the phase control period to the duration of one control cycle is higher than 50%, and at least the duration of one cycle of the AC is a wavenumber control pattern.

2. The image forming apparatus according to claim 1, characterized in that the waveform patterns controlled by the control unit are further distributed such that, for both the first heating group and the second heating group, the period of wavenumber control is longer than the period of half a cycle of the AC within the period of one control cycle.

3. The image forming apparatus according to claim 1 or 2, characterized in that, among the at least three heat-generating groups, the waveform pattern of the current flowing through the heat-generating groups other than the first heat-generating group and the second heat-generating group is the same as the waveform pattern of the current flowing through the first heat-generating group and the waveform pattern of the current flowing through the second heat-generating group.

4. The image forming apparatus according to claim 3, characterized in that the difference in the combined resistance between the first major group to which the first heat generation group belongs and the second major group to which the second heat generation group belongs is minimized, and the heat generation groups other than the first major group and the second major group are classified into the first major group or the second major group.

5. The image forming apparatus according to claim 1 or 2, characterized in that the waveform patterns of the currents flowing through the first heating group and the second heating group, which are controlled by the control unit, are set according to the input power level.

6. The image forming apparatus according to claim 1 or 2, characterized in that the heater has a substrate on which the at least three heating groups are provided.

7. The image forming apparatus according to claim 6, characterized in that the at least three heat-generating groups are arranged in the longitudinal direction.

8. The image forming apparatus according to claim 7, characterized in that each of the three heating groups comprises two conductors arranged along the longitudinal direction and a heating element connected between the two conductors.

9. The image forming apparatus according to claim 8, wherein the fixing section comprises a cylindrical film and a roller that contacts the outer surface of the film, the heater is arranged in the internal space of the film, and the film is sandwiched between the heater and the roller, forming a fixing nip section that sandwiches and conveys the recording material between the film and the roller.

10. An image forming unit that forms a toner image on a recording material, A fixing unit for heating and fixing a toner image formed on a recording material, the fixing unit having a heater having at least two heating groups that generate heat by power supplied from an AC power source, At least two switch elements are provided in each power supply path from the AC power source to each of the at least two heat-generating groups, A control unit that controls the power supplied to at least two heat-generating groups by controlling at least two switch elements, wherein a control unit controls power for each control cycle, with multiple continuous cycles of the AC power supply being defined as one control cycle, An image forming apparatus having a heater that can switch the heat distribution of the heater in the longitudinal direction of the fixing section, Of the combined resistances of the at least two heat-generating groups, the combined resistance of the first heat-generating group to which the first switch element of the at least two switch elements is connected is the smallest, and the combined resistance of the second heat-generating group to which the second switch element of the at least two switch elements is connected is the second smallest. The waveform patterns of the currents flowing through the first heating group and the second heating group, controlled by the control unit, The waveforms are at least one waveform with the same phase but different from each other during the duration of the control cycle, During the period of the aforementioned control cycle, the overlap between the phase control period of the first heat generation group and the phase control period of the second heat generation group is 50% or less. The image forming apparatus is characterized in that, in both the first heating group and the second heating group, the proportion of the phase control period to the duration of one control cycle is higher than 50%, and at least the duration of one cycle of the AC is a wavenumber control pattern.

11. The image forming apparatus according to claim 10, characterized in that the waveform patterns controlled by the control unit are further distributed such that, for both the first heating group and the second heating group, the period of wavenumber control is longer than the period of half a cycle of the AC within the period of one control cycle.

12. The image forming apparatus according to claim 10 or 11, characterized in that the heater has a heating group other than the first heating group and the second heating group, and the waveform pattern of the current flowing through the heating group other than the first heating group and the second heating group is the same as the waveform pattern of the current flowing through the first heating group and the waveform pattern of the current flowing through the second heating group.

13. The image forming apparatus according to claim 10 or 11, characterized in that the waveform patterns of the currents flowing through the first heating group and the second heating group, controlled by the control unit, are set according to the input power level.

14. The image forming apparatus according to claim 10 or 11, characterized in that the heater has a substrate on which at least two heat-generating groups are provided.

15. The image forming apparatus according to claim 14, characterized in that the at least two heat-generating groups are arranged in the longitudinal direction.

16. The image forming apparatus according to claim 15, characterized in that each of the two heating groups comprises two conductors arranged along the longitudinal direction and a heating element connected between the two conductors.

17. The image forming apparatus according to claim 16, wherein the fixing section comprises a cylindrical film and a roller that contacts the outer surface of the film, the heater is arranged in the internal space of the film, and the film is sandwiched between the heater and the roller, forming a fixing nip section that sandwiches and conveys the recording material between the film and the roller.

Images