Heating apparatus and image forming apparatus

Abstract

Even when the heater resistance is reduced to increase the available power supply, the flicker in wavenumber control should be improved. [Solution] The wavenumber control pattern includes a first pattern that has a control period of 14 half-waves, which is a number greater than or equal to 2, and satisfies the positive / negative symmetry, and a second pattern that has a control period of 16 half-waves, which is a number greater than or equal to 2 and divisible by 4, and satisfies the positive / negative symmetry. The CPU 32 sets the second pattern when the input power duty cycle is the first duty cycle (50%) (S103YES~S108), and sets the first pattern for the second duty cycle (42.9%, 57.1%), which is one step larger or one step smaller than the first duty cycle (S103NO~S108), and performs wavenumber control (S109~S113).

Description

Technical Field

[0001] The present invention relates to a heating device and an image forming apparatus, and more particularly to a method for controlling a fixing heater of an image forming apparatus using an electrophotographic process.

Background Art

[0002] In a conventional image heating device (hereinafter referred to as a fixing device) of an image forming apparatus using an electrophotographic process, an unfixed image (toner image) formed on a transfer paper by an image forming means such as an electrophotographic process is fixed on the transfer paper. The fixing device includes a heat roller type heat fixing device using a halogen heater as a heat source, a film heating type heat fixing device using a ceramic surface heater as a heat source, and the like. Generally, the heater is connected to an AC power supply via a switching element such as a triac, and power is supplied by controlling the triac. In heater control by a triac, for example, as described in Patent Document 1, wave number control is performed to turn on and off the triac near the zero cross point of the AC voltage. Thereby, a power supply control method has been proposed that reduces the harmonic current and reduces the noise when turning on the current flowing through the heater. Since the noise is reduced by changing the heater power supply control method to wave number control, the filter can be simplified and the size of the device can be reduced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, image forming machines have become faster. Such high-speed image forming machines require a significant amount of power to heat and fix the toner image formed on the paper. To supply sufficient power to the heater for this purpose, the heater's resistance needs to be reduced. However, reducing the heater's resistance in wavenumber control systems presents a challenge: increased flicker. Therefore, even when reducing the heater's resistance, there is a need to improve the flicker issue in wavenumber control systems and increase the available power supply.

[0005] This invention was made under such circumstances and aims to improve flicker in wavenumber control even when the heater resistance is reduced in order to increase the available power supply. [Means for solving the problem]

[0006] To solve the above-mentioned problems, the present invention has the following configuration.

[0007] (1) A heating element connected to an AC power source; a switch element provided between the AC power source and the heating element, which switches between a conductive state that allows power from the AC power source to be supplied to the heating element and a non-conductive state that prevents power from the AC power source from being supplied to the heating element; a control means that controls the power supplied to the heating element by switching the switch element between the conductive state and the non-conductive state for each half wave, with a control period of a plurality of consecutive half waves in the waveform of the AC voltage of the AC power source; and a detection means for detecting the temperature of the heating element, wherein the control means determines the input power duty cycle, which is the ratio of power supplied to the heating element within the control period, based on the temperature of the heating element detected by the detection means and the target temperature of the heating element, and determines whether or not to supply power to each half wave within the control period according to the determined input power duty cycle. A heating device that sets a power control pattern and performs wavenumber control according to the set power control pattern, wherein the number of positive half-waves in which the switch element is in the conductive state within the control period is equal to the number of negative half-waves in which the switch element is in the conductive state within the control period is called positive-negative symmetry, the power control pattern includes a first pattern that satisfies positive-negative symmetry with a first number of half-waves which is a number of 2 or more as the control period, and a second pattern that satisfies positive-negative symmetry with a second number of half-waves which is a number of 2 or more and divisible by 4 as the control period, and the control means sets the second pattern when the input power duty cycle is a first duty cycle, and sets the first pattern for a second duty cycle which is an input power duty cycle that is one step larger or one step smaller than the first duty cycle, and performs wavenumber control.

[0008] (2) A heating element connected to an AC power supply; a switch element provided between the AC power supply and the heating element, which switches between a conductive state that allows power from the AC power supply to be supplied to the heating element and a non-conductive state that prevents power from the AC power supply from being supplied to the heating element; a control means that controls the power supplied to the heating element by switching the switch element between the conductive state and the non-conductive state for each half wave, with a control period of a plurality of consecutive half waves in the waveform of the AC voltage of the AC power supply; and a detection means for detecting the temperature of the heating element, wherein the control means controls the input power duty cycle, which is the ratio of power supplied to the heating element within the control period, based on the temperature of the heating element detected by the detection means and the target temperature of the heating element. A heating device that determines the input power duty cycle, sets a power control pattern that defines whether or not to supply power to each half-wave within the control cycle according to the determined input power duty cycle, and performs wavenumber control according to the set power control pattern, wherein the power control pattern includes a first pattern in which the control cycle is a first number of half-waves which is a number of 2 or more, and a second pattern in which the control cycle is a second number of half-waves which is a number greater than the first number, and the control means sets the second pattern when the input power duty cycle is the first duty cycle, sets the first pattern for the second duty cycle which is an input power duty cycle that is one step larger or one step smaller than the first duty cycle, and performs wavenumber control.

[0009] (3) An image forming apparatus for forming an image on a recording material, comprising: forming means for forming a toner image on the recording material; and a heating device according to (1) or (2) above for heating and fixing the toner image. [Effects of the Invention]

[0010] According to the present invention, even when the heater resistance is reduced to increase the available power supply, the flicker in wavenumber control can be improved. [Brief explanation of the drawing]

[0011] [Figure 1] Diagram showing the configuration of the image forming apparatuses of Examples 1 to 3 [Figure 2] Diagram showing the configuration of the fixing device of Examples 1 to 3 [Figure 3] Diagram showing the heater drive circuit applied to Examples 1 to 3 [Figure 4] Diagram showing the input power pattern of Example 1 [Figure 5] Diagram showing the relationship between the heater resistance value and the Pst value of Example 1 [Figure 6] Diagram showing the input power pattern of Example 1 [Figure 7] Diagram showing the input power pattern of Example 1 [Figure 8] Diagram showing the input power pattern applied to Example 1 [Figure 9] Diagram showing the effect of the input power pattern applied to Example 1 [Figure 10] Flowchart showing the power supply control of Example 1 [Figure 11] Diagram showing the input power pattern of Example 2 [Figure 12] Diagram showing the input power pattern applied to Example 2 [Figure 13] Diagram showing the effect of the input power pattern applied to Example 2 [Figure 14] Flowchart showing the power supply control of Example 2 [Figure 15] Diagram showing the input power pattern and the PST value at the 8 half-wave control cycles of Example 3 [Figure 16] Diagram showing the input power pattern and the effect applied to Example 3 [Figure 17] Diagram showing the input power pattern and the effect applied to Example 3 [Figure 18] Diagram showing the input power pattern and the effect applied to Example 3

Mode for Carrying Out the Invention

Examples

[0012] Hereinafter, with reference to the drawings, embodiments of the present invention implemented in an image forming apparatus will be described. FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus using an electrophotographic process. In Example 1, a laser beam printer will be described as an example of the image forming apparatus, but an image forming apparatus such as a copier, a facsimile machine, or a multifunction machine incorporating these may also be used.

[0013] [Image Forming Apparatus] The laser beam printer main body 100 shown in FIG. 1 (hereinafter referred to as the main body 100) has a paper feed cassette 104 for storing paper 21 as a recording material. The main body 100 has a paper feed roller 141 for feeding out the paper 21 from the paper feed cassette 104, a pair of conveyance rollers 142, a top sensor 143 for detecting the leading edge of the paper 21 downstream of the pair of conveyance rollers 142, and a pair of registration rollers 144 for synchronously conveying the paper 21. The main body 100 has a cartridge unit 105 for forming a toner image on the paper 21 based on the laser light from the laser scanner 106 downstream of the pair of registration rollers 144. The cartridge unit 105 includes a photosensitive drum 148 as an image carrier, a charging roller 147, a developing roller 146, etc., which are necessary for a known electrophotographic process, and forms a toner image on the paper 21 together with the transfer roller 145. The members contributing to the formation of the toner image on the paper 21 correspond to forming means. And the main body 100 has a fixing device 103 (fixing apparatus, heating apparatus) for thermally fixing the unfixed toner image formed on the paper 21 downstream of the cartridge unit 105. The fixing device 103 has a fixing film 149, a pressure roller 150, a heater 102 disposed inside the fixing film 149, and a thermistor 109 disposed near the heater 102 so as to detect the temperature of the heater 102 within the fixing film 149. The thermistor 109 is a detecting means for detecting the temperature of the heater 102. The main body 100 has a pair of discharge rollers 151 downstream of the fixing device 103, and discharges the paper 21 after heat fixing the toner image formation.

[0014] The power supply unit 120 (details to be described later), which functions as a power supply device, can output a voltage of 24V or 10V as appropriate, and generates a voltage of 24V in print mode or standby mode. The power supply unit 120 supplies a voltage of 24V to a high-voltage power supply (not shown) for supplying high voltage to drive units (not shown) such as motors and clutches, and to the cartridge unit 105, via the engine controller 123 described later. The power supply unit 120 also supplies a voltage of 24V as the drive system voltage to the rotating multi-face mirror drive unit (not shown) of the laser scanner 106, etc., via the engine controller 123 described later.

[0015] The cooling fan 125 is a fan for cooling the power supply unit 120, and cools the power supply unit 120 by blowing air onto it. The cooling fan 125 can only blow air when the power supply unit 120 is outputting a voltage of 24V.

[0016] The engine controller 123 controls the main unit 100. The engine controller 123 controls the transport of the paper 21 by operating each roller through the drive unit (not shown). At the same time, the engine controller 123 controls the laser scanner 106, cartridge unit 105, fuser 103, etc. to perform image formation (hereinafter referred to as printing) operations. The engine controller 123 also has a DC-DC converter 121, which will be described later, and generates a voltage of 3.3V mainly used in the control system based on the voltage supplied from the power supply unit 120. The voltage of 3.3V is supplied to the control system circuits, including the control circuit (not shown) inside the engine controller 123, the video controller 131 (described later), the laser light-emitting part of the laser scanner 106 (not shown), the top sensor 143, etc. The video controller 131 is connected to the engine controller 123 via the engine interface 133, and is also connected to an external device 132 such as a personal computer via a general-purpose external interface 134 (USB, etc.).

[0017] The power supply unit 120 detects the zero-crossing timing of the AC power supply 50 (see Figure 3), which will be described later, and transmits a detection signal (not shown) to the engine controller 123. The engine controller 123 appropriately controls a switch element (not shown) so that the power from the AC power supply 50 matches the duty cycle of the wavenumber in synchronization with the detection signal, or in other words, the zero-crossing timing. As a result, the engine controller 123 controls the heater 102, which is connected in parallel with the AC power supply 50, to reach a predetermined temperature.

[0018] The video controller 131 receives print information (number of copies, various settings, etc.) and print data from the external interface 134. The video controller 131 has an internal image control unit (not shown) that converts the print data into image data that can actually be printed. Subsequently, the engine controller 123 receives the image data from the video controller 131 via the engine interface 133 at a predetermined timing and sends it to the laser scanner 106.

[0019] [Fuser] Figure 2(a) is a cross-sectional model of the fuser 103 of Example 1. The paper 21 is transported from right to left in Figure 2(a), and this transport direction will be referred to as Dr below. The fuser 103 is a heating device of the pressure roller driven type film heating method, using, for example, an endless film (cylindrical film), and has the following general configuration. The fuser 103 has a heater 102, a semi-circular trough-shaped heater holder 101 with heat resistance and rigidity that fixes and holds the heater 102, and a cylindrical thin heat-resistant film (fixing film) 149 that is loosely fitted onto the heater holder 101 to which the heater 102 is attached. The fuser 103 has a pressure roller 150 as a rotatable pressurizing body that presses against the heater 102 with the fixing film 149 in between to form a fixing nip portion N, and a thermistor 109 that is arranged so that its heat-sensitive surface is in contact with the surface of the heater 102.

[0020] The pressure roller 150 is driven to rotate at a predetermined peripheral speed in the counterclockwise direction indicated by the arrow in the figure by a driving means (not shown). Due to the pressure friction force at the fixing nip portion N, which is the contact point between the outer surface of the pressure roller 150 and the fixing film 149, the rotational force of the pressure roller 150 acts on the cylindrical fixing film 149, causing the fixing film 149 to rotate in a driven state. The fixing film 149 rotates around the outer surface of the heater holder 101 in the clockwise direction indicated by the arrow in the figure, while its inner surface is in close contact with the downward surface of the heater 102 and sliding.

[0021] Power is supplied to the heater 102, causing it to heat up to a predetermined temperature (target temperature) and the temperature is controlled. In this temperature-controlled state, the paper 21 carrying the unfixed toner image Tt in the fixing nip section N is transported. In the fixing nip section N, the toner image-carrying side of the paper 21 adheres closely to the outer surface of the fixing film 149, and the fixing nip section N is clamped and transported together with the fixing film 149. During the clamping and transport process, heat from the heater 102 is applied to the paper 21 via the fixing film 149, and the unfixed toner image Tt on the paper 21 is heated and pressurized, causing it to melt and fix. After passing through the fixing nip section N, the paper 21 is separated from the fixing film 149 by curvature.

[0022] Figure 2(b) is an enlarged cross-sectional view of heater 102. Heater 102 is a back-heating type ceramic heater. Heater 102 has a ceramic insulating substrate 110 made of SiC, AlN, Al2O3, etc., heating elements 111a and 111d formed on the insulating substrate 110 by paste printing or the like, and a protective layer 113 made of glass or the like that protects the two heating elements 111a and 111d. In some cases, a glass layer is formed on the side facing the insulating substrate 110 on which the heating elements 111a and 111d are printed in order to improve sliding properties.

[0023] Figure 2(c) is a plan view of the heater 102. The heater 102 has two heating elements 111a and 111d, electrodes 111c and 111f, a conductive part 111b connecting heating element 111a and electrode 111c, and a conductive part 111e connecting heating element 111a and heating element 111d. Power is supplied via electrodes 111c and 111f, causing heating elements 111a and 111d to generate heat. Power is supplied via a power supply connector 114. Hereinafter, heating elements 111a and 111d will be collectively referred to as heating element 111.

[0024] [Heater drive circuit] Figure 3 is a circuit diagram illustrating the heater drive circuit of Embodiment 1, and shows the power supply circuit in the present invention. The AC power supply 50 is a power supply to which the image forming apparatus is connected, and AC power is supplied to the image forming apparatus via the inlet 51. The power supply circuit generally consists of a primary side directly connected to the AC power supply 50 and a secondary side non-contactly connected to the AC power supply 50.

[0025] Power input from the AC power supply 50 is supplied to the heating element 111 via the inlet 51, causing the heating element 111 to generate heat. The power supply unit 120 receives power from the AC power supply 50 via the AC filter 52 and outputs a predetermined voltage to the secondary load. The engine controller 123 is equipped with a CPU 32. The CPU 32 is also used for heater drive control, etc., and consists of various input / output ports (PA1, PA2, AN0), ROM 32a, RAM 32b, etc. The CPU 32 is a control means that performs wavenumber control, which controls the power supplied to the heating element 111 by switching the triac 61 (described later) between a conductive state and a non-conductive state for each half wave, using a control period of multiple consecutive half waves in the waveform of the AC voltage of the AC power supply 50. The CPU 32 determines the input power duty cycle, which is the ratio of power supplied to the heater 102 within the control period, based on the temperature of the heater 102 detected by the thermistor 109 and the target temperature of the heater 102. The CPU32 sets a power control pattern that defines whether or not to supply power to each half-wave within the control cycle, according to the determined power duty cycle, and performs wavenumber control according to the set power control pattern. Hereinafter, the power control pattern will be referred to as the wavenumber control pattern. Further details of wavenumber control will be described later.

[0026] In the image forming apparatus, on the primary side of the power supply circuit, the heating element 111 of the fuser 103 and the power supply unit 120 for supplying power to the secondary side are directly connected to the AC power supply 50 to receive power. On the secondary side of the power supply circuit, a high-voltage power supply (not shown) for supplying high voltage to drive units (not shown) such as motors and clutches, and the cartridge unit 105, are connected non-contact to the AC power supply 50 to receive power. The rotating multi-face mirror drive unit (not shown) of the laser scanner 106 is also connected non-contact to the AC power supply 50 to receive power.

[0027] The heating element 111 is supplied with a predetermined amount of power by the wavenumber control circuit 60. The thermistor 109, located on the back surface of the heater 102, has one end connected to ground and the other end connected to resistor 55, and is further connected to the analog input port AN0 of the CPU 32 via resistor 56. The thermistor 109 has the characteristic of decreasing resistance when it gets hot. The CPU 32 detects the temperature of the heater 102 by converting the voltage from the divided voltage between the thermistor 109 and resistor 55 to a preset temperature table (not shown) stored in ROM 32a.

[0028] Meanwhile, the power from the AC power supply 50 is input to the zero-crossing generation circuit 57 (ZEROX generation circuit) via the AC filter 52. The zero-crossing generation circuit 57 outputs a high-level signal when the AC voltage is below a certain threshold voltage near 0V, and outputs a low-level signal otherwise. A pulse signal (hereinafter referred to as the ZEROX signal) with a period approximately equal to the period of the AC voltage from the AC power supply 50 is input to the CPU 32 via the resistor 58 to port PA1. The CPU 32 detects the edge where the ZEROX signal changes from high level to low level and uses it for timing control of wavenumber control. The CPU 32 determines the timing for driving the wavenumber control circuit 60 (hereinafter referred to as the "lighting timing") based on the temperature detected by the thermistor 109, and outputs a drive signal (Drive1) from the output port PA2.

[0029] (Wavenumber control circuit) The wavenumber control circuit 60 is described below. When the output port PA2 becomes high level at a predetermined lighting timing, the transistor 65 is turned on via the base resistor 67. The base resistor 67 is connected to the base terminal of the transistor 65. When the transistor 65 is turned on, the phototriac coupler 62 is turned on. The phototriac coupler 62 is a device that ensures the creepage distance between the primary and secondary, and the resistor 66 is a resistor that limits the current flowing to the light-emitting diode 62d inside the phototriac coupler 62. When the transistor 65 is turned on, current flows from the power supply Vcc1 via the resistor 66 and the light-emitting diode 62d lights up.

[0030] Resistors 63 and 64 are bias resistors for the bidirectional thyristor (hereinafter referred to as triac) 61, and the triac 61 conducts when the phototriac coupler 62 is turned on. The triac 61 is a switching element installed between the AC power supply 50 and the heater 102, and switches between a conductive state that allows power from the AC power supply 50 to be supplied to the heater 102 and a non-conductive state that prevents power from the AC power supply 50 from being supplied to the heater 102.

[0031] If the phototriac coupler 62 is a zero-crossing type, the triac 61 conducts when the AC voltage of the AC power supply 50 is below a predetermined voltage and the transistor 65 is ON. In Embodiment 1, a zero-crossing type phototriac coupler is used, and the CPU 32 turns on the transistor 65 near the zero-crossing timing based on the signal generated by the zero-crossing generation circuit 57. This configuration allows for accurate wavenumber control even when frequency fluctuations occur, but the system is not limited to this configuration. For example, wavenumber control may be performed using a zero-crossing type phototriac coupler without a zero-crossing generation circuit 57. Alternatively, for example, a non-zero-crossing type phototriac coupler may be used, and the transistor 65 may be turned on near the zero-crossing timing based on the signal generated by the zero-crossing generation circuit 57.

[0032] [Power supply through wavenumber control] The wavenumber control method used by the CPU 32 to supply power to the heater 102 using the wavenumber control circuit 60 will be explained with reference to Figure 4. Figure 4(a) shows wavenumber control pattern A, and Figure 4(b) shows pattern B. As explained in Figure 3, in wavenumber control, the heater 102 can only be turned ON / OFF near the zero-cross timing, so the power supplied in each half-wave can only be selected as either 100% or 0%. In other words, the control is either to supply power (100%) or not to supply power (0%) in one half-wave of the waveform, which is half a period of the AC voltage of the AC power supply 50.

[0033] As shown in Figures 4(a) and 4(b), wavenumber control determines the power duty cycle in a control period by how many half-waves (hereinafter referred to as wavenumber) of the control period are turned ON for the heater 102. In Figure 4, the control period for wavenumber control is set to 14 half-waves. Also, one control period starts with a positive half-wave of the AC voltage waveform. Therefore, within one control period, odd-numbered half-waves are positive half-waves, and even-numbered half-waves are negative half-waves. The number of half-waves included in a control period is sometimes called the wavenumber length.

[0034] As shown in Figures 4(a) and (b), when the power duty cycle for one control cycle is set to 0%, the power supplied for all half-waves from the 1st half-wave to the 14th half-wave is 0% in both pattern A and pattern B. On the other hand, when the power duty cycle for one control cycle is set to 35.7%, in pattern A, the values ​​for half-waves from the 1st half-wave to the 14th half-wave are 100%, 0%, 0%, 100%, 0%, 0%, 0%, 100%, 0%, 0%, 100%, 0%, 0%, 100%, 0%, 100%, 0%. Also, when the power duty cycle for one control cycle is set to 35.7%, in pattern B, the values ​​for half-waves from the 1st half-wave to the 14th half-wave are 100%, 0%, 0%, 100%, 0%, 0%, 0%, 100%, 0%, 0%, 0%, 0%, 0%, 100%, 0%, 0%, 100%. A wavenumber control pattern is information such as pattern A or pattern B that specifies 0% or 100% power input for multiple half-waves included in the control cycle in order to achieve a predetermined power duty cycle (%). The wavenumber control pattern is stored as a pattern table in ROM32a, for example.

[0035] The power input duty cycle is calculated by the CPU 32 using, for example, PID control, based on the temperature detected by the thermistor 109 and a preset target temperature. For each control cycle, the CPU 32 selects the optimal power input duty cycle from the wavenumber control patterns shown in Figure 4(a) or Figure 4(b). In the wavenumber control patterns of Figures 4(a) and 4(b), the power input duty cycle increases by 7.1% (≒(1÷14)×100%) for every half-wave increase in the number of half-waves supplied with 100% power within a 14-half-wave control cycle. This allows power to be adjusted in 15 steps of power input duty cycle from 0% to 100%. Figures 4(a) and 4(b) also show the number of half-waves supplied with 100% power and the number of half-waves supplied with 0% power (no power supplied), respectively. In Figures 4(a) and 4(b), for the sake of simplicity, the detailed patterns for input power duty cycles of 7.1% to 28.6% and 71.4% to 92.9% are omitted.

[0036] In controlling the power of heater 102, positive-negative symmetry of the power supply pattern is required. Here, positive-negative symmetry means that the number of positive half-waves in which the triac 61 is in a conductive state within the control period is equal to the number of negative half-waves in which the triac 61 is in a conductive state within the control period. Figures 4(a) and 4(b) also show the positive-negative symmetry of each input power duty cycle. As shown in Figures 4(a) and 4(b), patterns in which the number of 100% is odd (such as the 35.7% mentioned above) do not satisfy positive-negative symmetry on their own. Conversely, in patterns in which the number of 100% is even, positive-negative symmetry is satisfied on their own.

[0037] In the case of asymmetry, pattern A, shown in Figure 4(a), is a pattern with one extra positive half-wave (hereinafter referred to as the positive side). On the other hand, in the case of asymmetry, pattern B, shown in Figure 4(b), is a pattern with one extra negative half-wave (hereinafter referred to as the negative side). For example, in the case of an input power duty cycle of 35.7%, pattern A has 13 half-waves at 100%, which is one extra positive half-wave, while pattern B has 14 half-waves at 100%, which is one extra negative half-wave.

[0038] Figure 4(c) shows the transitions (I-IV) selected between pattern A and pattern B in wavenumber control. As shown in Figure 4(c), if the output wavenumber is even, the original pattern is output again. On the other hand, if the output wavenumber is odd, the control is such that if the original was pattern A, the next output will be pattern B, and if the original was pattern B, the next output will be pattern A.

[0039] For example, if the number of half-waves supplying 100% power is even in the power duty cycle selected in pattern A, the positive-negative symmetry is satisfied, and the power duty cycle will be selected from pattern A again in the next control cycle (transition I). On the other hand, if the number of half-waves supplying 100% power is odd in the power duty cycle selected in pattern A, the positive-negative symmetry is not satisfied, and in order to satisfy the positive-negative symmetry, the power duty cycle will be selected from pattern B again in the next control cycle (transition II). If the number of half-waves supplying 100% power is even in the power duty cycle selected in pattern B, the positive-negative symmetry is satisfied, and the power duty cycle will be selected from pattern B again in the next control cycle (transition III). On the other hand, if the number of half-waves supplying 100% power is odd in the power duty cycle selected in pattern B, the positive-negative symmetry is not satisfied, and in order to satisfy the positive-negative symmetry, the power duty cycle will be selected from pattern A again in the next control cycle (transition IV). The engine controller 123 satisfies positive-negative symmetry by performing this type of control. By performing this type of control, it becomes possible to control power without reducing power resolution while satisfying positive-negative symmetry.

[0040] [Flicka] Next, Figure 5 shows the relationship between the input power duty cycle (%) and the Pst value (short-term flicker index) when the resistance value of heater 102 is changed (shaken). In Figure 5, the horizontal axis shows the input power duty cycle (%), and the vertical axis shows the Pst value for each resistance value of heater 102. The thick solid line shows the Pst value of heater 102 with a resistance value of 8.9Ω, the thin solid line shows the Pst value of heater 102 with a resistance value of 9.5Ω, the dotted line shows the Pst value of heater 102 with a resistance value of 10.3Ω, and the dashed line shows the Pst value of heater 102 with a resistance value of 11.07Ω.

[0041] The Pst value is the short-term flicker value (voltage fluctuation value), and the larger the value, the greater the fluctuation and the greater the impact of the flicker. As shown in Figure 5, the Pst value is larger when the resistance value of heater 102 is small. Also, for any resistance value, the Pst value when the power duty cycle is 50% is higher than the Pst value at other power duty cycles. In order to reduce the resistance value in order to increase the power supplied to heater 102, it is necessary to improve the flicker, especially when the power duty cycle is 50%.

[0042] [Wavenumber control pattern when input power duty cycle is 50%] Figures 6(a) and 6(b) show four types of wavenumber control patterns (patterns 1-4) with a 50% power duty cycle for 14 half-wave periods, and Figure 6(c) shows the Pst values ​​for patterns 1-4. Figure 6(a) shows pattern A, and Figure 6(b) shows pattern B. The Pst values ​​shown are for when the resistance of heater 102 is 10.3Ω. Areas in each pattern where the background is gray indicate two or more consecutive values ​​of 0%. Areas in each pattern where the background is black indicate two or more consecutive values ​​of 100%. Note that the 14 half-waves of pattern A and the 1 half-wave of pattern B are continuous, and the 14 half-waves of pattern B and the 1 half-wave of pattern A are continuous during wavenumber control.

[0043] Figure 6(c) shows the number of consecutive occurrences of 100% and 0% for each pattern. In Pattern 1, there are 3 consecutive occurrences of 2 for both 100% and 0%; in Pattern 2, there is 1 consecutive occurrence of 2 for both 100% and 0%; and in Pattern 3, there are 2 consecutive occurrences of 2 for both 100% and 0%. Among Patterns 1 to 3, Pattern 2, which has the fewest consecutive occurrences of 2 for both 100% and 0%, has the lowest Pst value (1.12), while Pattern 1, which has the most consecutive occurrences of 2 for both 100% and 0%, has the highest Pst value (2.64). Furthermore, compared to Patterns 1 to 3, Pattern 4, which has the most consecutive occurrences of 3 or more for both 100% and 0%, has the highest Pst value (4.55).

[0044] Therefore, it is possible to reduce the Pst value by preventing consecutive occurrences of the same 100% and 0% patterns. With a control period of 14 half-waves and an input power duty cycle of 50%, flicker can be significantly reduced by decreasing the number of consecutive occurrences of the same 100% and 0% pattern, such as pattern 2.

[0045] [Wavenumber control pattern when the input power duty cycle is around 50%] Figure 7(a) shows the wavenumber control pattern and Pst value when repeating the A and B patterns of Pattern 2 with an input power duty cycle of 50% as explained in Figure 6, and the pattern with an input power duty cycle of 42.9%, which is one step lower. Figure 7(b) shows the wavenumber control pattern and Pst value when repeating the A and B patterns of Pattern 2 with an input power duty cycle of 50% and the pattern with an input power duty cycle of 57.1%, which is one step higher.

[0046] The power duty cycle is determined by PID control or similar methods based on the temperature detected by thermistor 109 and a preset target temperature. Therefore, temperature control is not always performed with a fixed power duty cycle; it often alternates between adjacent power duty cycles. For this reason, the wavenumber control pattern must be designed to ensure that the Pst value remains low even when operating with adjacent power duty cycles.

[0047] As shown in Figure 7(a), when pattern A with a 50% power duty cycle and pattern A with a 42.9% power duty cycle are repeated, the Pst value is 2.2. On the other hand, when pattern B with a 50% power duty cycle and pattern B with a 42.9% power duty cycle are repeated, the Pst value is 1.51. In pattern A with a 50% power duty cycle (pattern 2), the 1st and 14th half-waves are 100%, and in pattern A with a 42.9% power duty cycle, the 1st and 14th half-waves are also 100%. Therefore, the flicker effect is greatly increased because 100% occurs twice in a row at the timing of switching the power duty cycle.

[0048] As shown in Figure 7(b), when pattern A with a 50% power duty cycle and pattern A with a 57.1% power duty cycle (pattern 2) are repeated, the Pst value is 1.89. On the other hand, when pattern B with a 50% power duty cycle and pattern B with a 57.1% power duty cycle are repeated, the Pst value is 1.63. In pattern A with a 50% duty cycle, the 1st and 14th half-waves are 100%, and in pattern A with a 57.1% power duty cycle, the 1st and 14th half-waves are also 100%. Therefore, the flicker effect is greatly increased because 100% occurs twice in a row at the timing of switching the power duty cycle.

[0049] As explained above, in a 14-half-wave input power duty cycle of 50%, the number of times 100% power is supplied is odd, so both pattern A and pattern B are necessary to satisfy positive and negative symmetry. In this case, when switching from pattern A to an adjacent input power duty cycle, the effect of flicker becomes significant. Therefore, it is necessary to create a wavenumber control pattern that does not cause a significant effect of flicker even in adjacent input power duty cycles.

[0050] [Wavenumber control pattern of Example 1] The wavenumber control pattern of Example 1 includes a first pattern that satisfies positive-negative symmetry and uses a first half-wave, which is a number greater than or equal to 2, as the control period, and a second pattern that satisfies positive-negative symmetry and uses a second half-wave, which is a number greater than or equal to 2 and divisible by 4, as the control period. Here, in Example 1, the second number is greater than the first number. The CPU 32 sets the second pattern when the input power duty cycle is the first duty cycle, and sets the first pattern for the second duty cycle, which is the input power duty cycle adjacent to the first duty cycle, and performs wavenumber control. It can also be said that the second duty cycle is an input power duty cycle that is one step larger or one step smaller than the first duty cycle. For example, the first duty cycle is an input power duty cycle of 50%. In Example 1, the second number is 16 (control period of 16 half-waves) and the first number is 14 (control period of 14 half-waves), as described below. The second duty cycle is an input power duty cycle of 42.9% and an input power duty cycle of 57.1%.

[0051] Figure 8 shows the wavenumber control pattern of Example 1. Figure 8(a) shows the input power duty cycle of pattern A of the wavenumber control pattern of Example 1 from 0% to 100%, and Figure 8(b) shows the input power duty cycle of pattern B of the wavenumber control pattern of Example 1 from 0% to 100%. Note that the input power duty cycles of 7.1% to 28.6% and 71.4% to 92.9% are omitted in both figures. The information for the input power duty cycles of patterns A and B shown in Figure 8 from 0% to 100% is stored in advance as a pattern table in ROM 32a.

[0052] In pattern A of Figure 8(a) and pattern B of Figure 8(b), the wavenumber control patterns with input power duty cycles of 42.9% and 57.1% correspond to the first pattern described above. Also, in pattern A of Figure 8(a) and pattern B of Figure 8(b), the wavenumber control pattern with an input power duty cycle of 50% corresponds to the second pattern described above.

[0053] The main difference from the wavenumber control pattern explained in Figure 4 is the 50% input power duty cycle. Only when the input power duty cycle is 50% is the control period changed to 16 half-waves. The wavenumber control pattern in Example 1 is a common pattern for both Pattern A and Pattern B, and the positive / negative symmetry is satisfied with either one of the patterns. In Figure 8(b), the hatched areas are half-waves that have the same supplied power as Pattern A. In the wavenumber control pattern for a 50% input power duty cycle in Example 1, the control period is 16 half-waves, and the number of half-waves supplied with 100% power is 8 in both patterns, thus satisfying the positive / negative symmetry. Furthermore, by using a common pattern for Pattern A and Pattern B, it is possible to solve the problem of the Pst value becoming large when switching the input power duty cycle, as explained in Figure 7.

[0054] [Comparison of Example 1 with a Conventional Example] Figure 9(a) shows the relationship between the input power duty cycle and the Pst value in the conventional example and Example 1 described in Figure 4. Example 1 is shown with a solid line, and the conventional example is shown with a dashed line. Looking at the input power duty cycle of 50%, it can be seen that a significant improvement has been made, from the Pst value of 2.5 in the conventional example to the Pst value of 1.9 in Example 1.

[0055] Figure 9(b) shows the Pst values ​​when the input power duty cycle was switched from 50% to 42.9% and 57.1% in the conventional example and Example 1. From left to right on the horizontal axis, it shows the case when the input power duty cycle was switched from 50% to 42.9% in pattern A, and the case when the input power duty cycle was switched from 50% to 42.9% in pattern B. Furthermore, it shows the case when the input power duty cycle was switched from 50% to 57.1% in pattern A, and the case when the input power duty cycle was switched from 50% to 57.1% in pattern B.

[0056] When switching the power duty cycle from 50% to 42.9%, the Pst value improved from 2.2 to 1.4 in pattern A, which had the highest value. Similarly, when switching the power duty cycle from 50% to 57.1%, the Pst value also improved from 1.89 to 1.49 in pattern A, which had the highest value.

[0057] As described above, in Example 1, the control period of the wavenumber control pattern with an input power duty cycle of 50% is set to a number that satisfies positive-negative symmetry, i.e., a control period divisible by 4. For example, the control period of the wavenumber control pattern is set to 16 half-waves, which is divisible by 4. This makes it possible to significantly improve flicker and to reduce the resistance value, thereby increasing the power that can be supplied to the heater 102.

[0058] [Heater power supply control] Figure 10 is a flowchart illustrating the power supply control (power on sequence) to the heater 102 in Example 1. In step (hereinafter referred to as S) 101, the CPU 32 initializes counter Nc, which counts the number of wavenumbers, and counter C, which counts the number of half-waves that receive 100% power during the control cycle (number of 100% power on cycles) (N=0, C=0). In S102, the CPU 32 calculates the power on duty cycle based on the target temperature in temperature control and the current temperature detected by the thermistor 109.

[0059] In S103, the CPU 32 determines whether the input power duty cycle calculated in S102 is 50% or not. If the CPU 32 determines in S103 that the input power duty cycle is 50%, it proceeds to S104; otherwise, it proceeds to S105. In S104, the CPU 32 sets the control period T to a control period divisible by 4, for example, the 16 half-waves mentioned above (T=16), and proceeds to S106. In S105, the CPU 32 sets the control period T to a control period not divisible by 4, for example, the 14 half-waves mentioned above (T=14), and proceeds to S106.

[0060] In S106, the CPU 32 determines whether it has detected the falling edge or rising edge of the ZEROX signal received from the zero-crossing generation circuit 57. If the CPU 32 determines in S106 that it has detected the falling edge or rising edge of the ZEROX signal received from the zero-crossing generation circuit 57, it proceeds to S107; otherwise, it returns to S106. In S107, the CPU 32 increments the counter Nc (N=N+1). In S108, the CPU 32 selects the power supply Dn for the half-wave (Nc half-wave) at counter Nc from the pattern table pre-stored in ROM 32a, based on the input power duty cycle calculated in S102 and the counter Nc. For example, if the input power duty cycle is 50% and counter Nc=1, it is the first half-wave, and if it is pattern A, the power supply Dn is 0% (Figure 8(a)), and if it is pattern B, the power supply Dn is 100% (Figure 8(b)).

[0061] In S109, the CPU 32 outputs the supplied power Dn for the half-wave (Nc half-wave) in counter Nc. If the supplied power Dn is 0%, there is no power supply. In S110, the CPU 32 determines whether the supplied power Dn for the half-wave (Nc half-wave) in counter Nc is 100% or not. In S110, the CPU 32 determines that the supplied power Dn is 100% (Dn=100%), and proceeds to S111. If it determines that the supplied power Dn is not 100% (Dn=0%), it proceeds to S112. In S111, the CPU 32 increments counter C (C=C+1). This allows the CPU 32 to count the number of times 100% power is supplied within the control cycle, in other words, the number of waves (half-waves) that received 100% power.

[0062] In S112, the CPU 32 determines whether the counter Nc is equal to the control period T. In other words, the CPU 32 determines whether one control period of the power duty cycle calculated in S102 has ended. If the CPU 32 determines in S112 that the counter Nc is equal to the control period T, it proceeds to S113. If it determines that they are not equal, it returns to S106 and executes the processes in S106 to S111. In S113, the CPU 32 determines whether the power supply to the heater 102 has ended. If the CPU 32 determines in S113 that the power supply has not ended, it proceeds to S114.

[0063] In S114, the CPU 32 determines whether counter C is odd or not. If the CPU 32 determines in S114 that counter C is odd, it proceeds to S115; otherwise, it proceeds to S116. In S115, the CPU 32 decides to use a different pattern table than the one used in the current control cycle for the next control cycle, and returns to S101. For example, if pattern A was used in the current control cycle, the CPU 32 will use pattern B in the next control cycle. In S116, the CPU 32 decides to use the same pattern table as the one used in the current control cycle, and returns to S101. For example, if pattern A was used in the current control cycle, the CPU 32 will use pattern A in the next control cycle as well. The processing from S114 to S116 is the control described in Figure 4(c).

[0064] The wavenumber control patterns include a third pattern in which the half-wave of the first number is used as the control period and the positive-negative symmetry is not satisfied. In the example in Figure 8, the first number is 14 (control period is 14 half-waves). The third pattern includes a fourth pattern in which the number of positive half-waves in which the triac 61 is conducting is greater than the number of negative half-waves in which it is conducting, and a fifth pattern in which the number of negative half-waves in which it is conducting is greater than the number of positive half-waves in which it is conducting. For example, in pattern A of Figure 8(a), wavenumber control patterns with input power duty cycles of 35.7% and 64.3% correspond to the third and fourth patterns. Also, in pattern B of Figure 8(b), wavenumber control patterns with input power duty cycles of 35.7% and 64.3% correspond to the third and fifth patterns. If the CPU32 performs wavenumber control using the fourth pattern, it will perform wavenumber control using the fifth pattern in the next control cycle, and if it performs wavenumber control using the fifth pattern, it will perform wavenumber control using the fourth pattern in the next control cycle (S114 YES~116) (Figure 4(c) transitions II, IV).

[0065] In this way, the CPU 32 supplies power to the heater 102 while changing the power duty cycle for each control cycle by repeating steps S114-S116 and S101-S112 until it determines in S113 that the power supply has ended. Finally, when the CPU 32 determines in S113 that the power supply has ended, such as due to the end of the print sequence, the power supply sequence in Figure 10 ends.

[0066] The above sequence allows control periods for input power duty cycles of 42.9% and 57.1% to be set to an arbitrary wavenumber length of 14 half-waves, while satisfying positive and negative symmetry by setting the control period for an input power duty cycle of 50% to a wavenumber length divisible by 4. This improves flicker when switching between adjacent input power duty cycles. By improving flicker, the resistance value of heater 102 can be reduced, and the power that heater 102 can supply can be increased.

[0067] As described above, according to Example 1, even when the heater resistance is reduced to increase the available power, the flicker in wavenumber control can be improved. [Examples]

[0068] Example 1 describes an example in which flicker was improved by changing the control period for a 50% power duty cycle from 14 half-waves to 16 half-waves, which satisfies positive and negative symmetry. Example 2 describes examples of shortening the power duty cycle and control period other than 50%.

[0069] [Power input duty cycle other than 50%] Figure 11 shows the wavenumber control patterns (Pattern A and Pattern B) and their respective Pst values ​​when the input power duty cycle is 35.7% and 42.9%. The Pst values ​​are shown for the case where the resistance of heater 102 is 10.3Ω, as in Example 1. As shown in Figure 11, the Pst value is 1.96 when the input power duty cycle is 35.7%, and the Pst value is 1.87 when the input power duty cycle is 42.9%. The wavenumber control pattern with an input power duty cycle of 35.7% cannot satisfy positive-negative symmetry because it supplies 100% power in 5 out of 14 half-waves. Therefore, Pattern A and Pattern B are necessary to satisfy positive-negative symmetry. As explained in Example 1, it is necessary to consider the effects of flicker during pattern switching between the 14th half-wave with a power duty cycle of 35.7% and the 1st half-wave with a power duty cycle of 42.9%, and between the 14th half-wave with a power duty cycle of 42.9% and the 1st half-wave with a power duty cycle of 35.7%.

[0070] [Wavenumber control pattern of Example 2] The wavenumber control pattern of Example 2 includes a first pattern that satisfies positive-negative symmetry and uses a first half-wave, which is a number greater than or equal to 2, as the control period, and a second pattern that satisfies positive-negative symmetry and uses a second half-wave, which is a number greater than or equal to 2 and divisible by 4, as the control period. Here, in Example 2, the second number is smaller than the first number. The CPU 32 sets the second pattern when the input power duty cycle is the first duty cycle, and sets the first pattern for the second duty cycle, which is the input power duty cycle adjacent to the first duty cycle, and performs wavenumber control. For example, the first duty cycle is an input power duty cycle of 33.3%. In Example 2, the second number is 12 (control period of 12 half-waves) and the first number is 14 (control period of 14 half-waves), as described below. The second duty cycle is an input power duty cycle of 42.9%.

[0071] Figure 12 shows the wavenumber control pattern of Example 2. Figure 12(a) shows the input power duty cycle of pattern A of the wavenumber control pattern of Example 2 from 0% to 100%, and Figure 12(b) shows the input power duty cycle of pattern B of the wavenumber control pattern of Example 2 from 0% to 100%. Note that the input power duty cycles of 7.1% to 28.6% and 71.4% to 92.9% are omitted in both figures. The information for the input power duty cycles of patterns A and B shown in Figure 12 from 0% to 100% is stored in advance as a pattern table in ROM 32a.

[0072] In pattern A of Figure 12(a) and pattern B of Figure 12(b), the wavenumber control pattern with an input power duty cycle of 42.9% corresponds to the first pattern described above. Also, in pattern A of Figure 12(a) and pattern B of Figure 12(b), the wavenumber control pattern with an input power duty cycle of 33.3% corresponds to the second pattern described above.

[0073] A distinctive feature of Example 2 is the change in the input power duty cycle from 35.7% to 33.3%. Originally, with an input power duty cycle of 35.7%, the pattern was such that 5 out of 14 halfwaves supplied 100% power. By changing this pattern to a 33.3% pattern where 4 out of 12 halfwaves supplied 100% power, the positive and negative symmetry can be satisfied with 12 halfwaves. In other words, in Example 2, the wavenumber length of one control period is shortened from 14 halfwaves to 12 halfwaves. When the input power duty cycle is determined to be 35.7%, the positive and negative symmetry among 12 halfwaves is satisfied in pattern A, so pattern B can be the same as pattern A. In Figure 12(b), the hatched areas are halfwaves that have the same supply power as pattern A.

[0074] [Comparison of Example 2 with the Conventional Example] Figure 13(a) shows the relationship between the input power duty cycle and the Pst value in the conventional example and Example 2. Looking at the input power duty cycle around 30%, although the input power duty cycle differs slightly between the conventional example and Example 2, it can be seen that the Pst value has improved significantly from 1.9 to 1.45. Figure 13(b) shows the Pst values ​​when the input power duty cycle is switched from around 30% (35.72% in the conventional example and 33.3% in Example 2) to 42.9% in the conventional example and Example 2. From the left on the horizontal axis, it shows when the input power duty cycle is switched from 35.72% or 33.3% to 42.9% in Pattern A, and when the input power duty cycle is switched from 35.72% or 33.3% to 42.9% in Pattern B. Regarding the Pst value when the input power duty cycle is switched to 42.9%, Pattern B, which has the largest Pst value, shows an improvement from 2.16 to 1.45.

[0075] As described above, by setting the control period of the input power pattern to a control period divisible by 4, which satisfies the positive-negative symmetry, a significant improvement in flicker is possible even when the input power duty cycle and control period are shortened to values ​​other than 50%. Furthermore, it becomes possible to use a heater 102 with a lower resistance value, thereby increasing the amount of power that can be supplied.

[0076] [Heater power supply control] Figure 14 is a flowchart illustrating the power-on sequence of Example 2. Note that in the flowchart of Figure 14, the same steps as in Figure 10 are assigned the same step numbers (in the 100s). The following explanation will primarily focus on the steps in the 200s.

[0077] If CPU32 determines in S103 that the input power duty cycle is not 50%, it proceeds to S201. In S201, CPU32 determines whether the input power duty cycle is 33.3% or not. If CPU32 determines in S201 that the input power duty cycle is 33.3%, it proceeds to S202. In S202, CPU32 sets the control period T to 12 half-waves (T=12) and proceeds to S106. If CPU32 determines in S201 that the input power duty cycle is not 33.3%, it proceeds to S105.

[0078] The above sequence allows for a significant improvement in flicker by setting the control period for the input power duty cycle of 33.3% to a 12-half-wave control period that satisfies positive and negative symmetry, thereby reducing the resistance of heater 102 and increasing the power that heater 102 can supply.

[0079] As described above, according to Example 2, even when the heater resistance is reduced to increase the available power, the flicker in wavenumber control can be improved.

[0080] <Other Embodiments> The present invention can also be realized by supplying a program that implements one or more of the functions of the above embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions. [Examples]

[0081] Example 1 describes an example of improving flicker by changing the control period for a 50% power duty cycle from 14 half-waves to 16 half-waves, which satisfies positive and negative symmetry. Example 2 describes examples of shortening the control period for power duty cycles other than 50%. In this example, an example of extending the control period for duty cycles where flicker improvement is necessary is described. In heater power control, generally, shortening the control period allows for checking the target temperature and the actual temperature in a shorter period and reflecting this in the power duty cycle applied, thereby improving controllability in temperature control and preventing overshoot. Therefore, it is necessary to determine the control period in the power input pattern considering the controllability due to flicker and control period as described above. In the case of wavenumber control, a short control period results in low resolution of the power duty cycle, so in this example, the control period is described as 8 half-waves or more, but if there are no problems with controllability and flicker, 2 half-waves or more is sufficient, and it is not limited to this example.

[0082] Figure 15(a) shows the control patterns for this embodiment with an 8-half-wave control period when the input power duty cycle is 25%, 37.5%, 50%, 62.5%, and 75%. Figure 15(b) is a graph with the input power duty cycle on the horizontal axis and the PST value on the vertical axis when the control period is 8-half-wave. In this embodiment, the acceptable PST value is set to 2.0, and with an 8-half-wave control period, as shown in Figures 15(a) and (b), the PST values ​​for input power duty cycles of 37.5% and 62.5% are 1.63, which is below the acceptable PST value. On the other hand, the PST values ​​for input power duty cycles of 25%, 50%, and 75% are greater than the acceptable PST value. For input power duty cycles that satisfy the acceptable PST value with an 8-half-wave control period, the control period is set to 8-half-wave from the viewpoint of controllability. In this embodiment, we will explain in detail an example of improving the PST value by extending the control period for input power duty cycles that do not satisfy these acceptable PST values.

[0083] Figures 16(a) and 16(b) show control patterns for 8, 16, 20, and 24 half-waves at power input duty cycles of 25% and 75%. These patterns were designed to minimize the PST value for each control cycle. Figures 16(c) and 16(d) show the PST values ​​for each control cycle when power is applied using the control patterns described in Figures 16(a) and 16(b). It can be seen that the PST value improves as the control cycle lengthens, regardless of whether the power input duty cycle is 25% or 75%. The PST value at 24 half-waves is below the acceptable PST value (2.0) in this embodiment.

[0084] As shown in Figures 16(a) and 16(b), the longer the control period, the lower the frequency of power supply changes that cause flicker, and therefore the PST value, which is an index for evaluating flicker, also improves. Figure 17(a) shows control patterns for 8, 10, 12, 14, 16, 18, 20, 22, and 24 half-waves at a power supply duty cycle of 50%. These patterns are control patterns that were designed to reduce the PST value for each control period. Figure 17(b) shows the PST value for each control period when power is supplied using the control patterns described in Figure 17(a). As shown in Figure 17(b), it can be seen that the longer the control period, the better the PST value becomes. The PST values ​​for 16 half-waves are 1.95, for 18 half-waves they are 1.64, for 20 half-waves they are 1.40, and for 22 half-waves they are 1.21. Thus, for control periods of 16 half-waves or more, all values ​​are below the acceptable PST value (2.0) in this embodiment.

[0085] Figure 18(a) shows the control pattern incorporating the results of improving the PST value by lengthening the control period for input power duty cycles of 25%, 75%, and 50%, as described above. The control pattern in Figure 18(a) is a variation of the control pattern described in Figure 15(a), where the control period is changed to 24 half-waves for input power duty cycles of 25% and 75%, and to 22 half-waves for an input power duty cycle of 50%. The shorter the control period, the better the controllability. As explained above, the longer the control period, the better the PST value and flicker. In this control pattern, the control period was determined for each input power duty cycle to achieve a balance between controllability and PST value and flicker. In this embodiment, the control period for an input power duty cycle of 50% is set to 22 half-waves, but the control period may be shorter than 22 half-waves as long as the PST value is below the acceptable PST value, and is not limited to this embodiment. By lengthening the control cycle as needed for each power duty cycle, it becomes possible to improve the PST value and flicker while minimizing the deterioration of controllability. Note that the PST values ​​shown in Figures 15 to 18 are all values ​​when the resistance of heater 102 is 10.3Ω. In the PST judgment, a "○" was used if the PST value was less than or equal to the acceptable value (2.0).

[0086] As described above, according to Example 3, even when the heater resistance is reduced to increase the available power, the flicker in wavenumber control can be improved. [Explanation of symbols]

[0087] 32 CPU 61 Triac 102 Heater 103 Fuser 109 Thermistor

Claims

1. A heating element connected to an AC power supply, A switch element is provided between the AC power supply and the heating element, and switches between a conductive state that allows power from the AC power supply to be supplied to the heating element and a non-conductive state that prevents power from the AC power supply from being supplied to the heating element. A control means for performing wavenumber control, which controls the power supplied to the heating element by switching the switch element between the conductive state and the non-conductive state for each half-wave, using a control period of multiple consecutive half-waves in the waveform of the AC voltage of the AC power supply, A detection means for detecting the temperature of the heating element, Equipped with, The control means determines the input power duty cycle, which is the ratio of power supplied to the heating element within the control cycle, based on the temperature of the heating element detected by the detection means and the target temperature of the heating element; sets a power control pattern that defines whether or not power is supplied to each half-wave within the control cycle according to the determined input power duty cycle; and performs the wavenumber control according to the set power control pattern, wherein the control means determines the input power duty cycle, which is the ratio of power supplied to the heating element within the control cycle; sets a power control pattern that defines whether or not power is supplied to each half-wave within the control cycle; and performs the wavenumber control according to the set power control pattern, When the number of positive half-waves in which the switch element is in the conductive state within the control period is equal to the number of negative half-waves in which the switch element is in the conductive state within the control period, this is called positive-negative symmetry. The power control pattern includes a first pattern that satisfies positive-negative symmetry and has a first half-wave that is a number of 2 or more as the control period, and a second pattern that satisfies positive-negative symmetry and has a second half-wave that is a number of 2 or more and divisible by 4 as the control period. The control means sets the second pattern when the input power duty cycle is the first duty cycle, and sets the first pattern for the second duty cycle which is one step larger or one step smaller than the first duty cycle, and performs the wavenumber control. A heating device characterized by the following features.

2. The aforementioned first duty cycle is 50%. The heating apparatus according to feature 1.

3. The second number is greater than the first number. The heating apparatus according to feature 2.

4. The aforementioned first duty cycle is 33.3%. The heating apparatus according to feature 1.

5. The second number is smaller than the first number. The heating apparatus according to feature 4.

6. The power control pattern includes a third pattern in which the first half-wave is the control period and the positive / negative symmetry is not satisfied. The heating apparatus according to feature 1.

7. The third pattern includes a fourth pattern in which the number of positive half-waves in a conducting state is greater than the number of negative half-waves in a conducting state, and a fifth pattern in which the number of negative half-waves in a conducting state is greater than the number of positive half-waves in a conducting state. The heating apparatus according to feature 6.

8. If the wavenumber control is performed using the fourth pattern, the control means will perform the wavenumber control using the fifth pattern in the next control cycle, and if the wavenumber control is performed using the fifth pattern, it will perform the wavenumber control using the fourth pattern in the next control cycle. The heating apparatus according to feature 7.

9. A heating element connected to an AC power supply, A switch element is provided between the AC power supply and the heating element, and switches between a conductive state that allows power from the AC power supply to be supplied to the heating element and a non-conductive state that prevents power from the AC power supply from being supplied to the heating element. A control means for performing wavenumber control, which controls the power supplied to the heating element by switching the switch element between the conductive state and the non-conductive state for each half-wave, using a control period of multiple consecutive half-waves in the waveform of the AC voltage of the AC power supply, A detection means for detecting the temperature of the heating element, Equipped with, The control means determines the input power duty cycle, which is the ratio of power supplied to the heating element within the control cycle, based on the temperature of the heating element detected by the detection means and the target temperature of the heating element; sets a power control pattern that defines whether or not power is supplied to each half-wave within the control cycle according to the determined input power duty cycle; and performs the wavenumber control according to the set power control pattern, wherein the control means determines the input power duty cycle, which is the ratio of power supplied to the heating element within the control cycle; sets a power control pattern that defines whether or not power is supplied to each half-wave within the control cycle; and performs the wavenumber control according to the set power control pattern, The power control pattern includes a first pattern in which the control period is a first half-wave that is a number greater than or equal to two, and a second pattern in which the control period is a second half-wave that is a number greater than the first. The control means sets the second pattern when the input power duty cycle is the first duty cycle, and sets the first pattern for the second duty cycle which is one step larger or one step smaller than the first duty cycle, and performs the wavenumber control. A heating device characterized by the following features.

10. When the number of positive half-waves in which the switch element is in the conductive state within the control period is equal to the number of negative half-waves in which the switch element is in the conductive state within the control period, this is called positive-negative symmetry. The first pattern satisfies the positive-negative symmetry, The heating apparatus according to feature 9.

11. When the number of positive half-waves in which the switch element is in the conductive state within the control period is equal to the number of negative half-waves in which the switch element is in the conductive state within the control period, this is called positive-negative symmetry. The second pattern satisfies the positive-negative symmetry, The heating apparatus according to feature 9.

12. The aforementioned first duty cycle is 50%. The heating apparatus according to feature 9.

13. The power control pattern includes a third pattern in which the first half-wave is the control period and the positive / negative symmetry is not satisfied. The heating apparatus according to feature 1.

14. The third pattern includes a fourth pattern in which the number of positive half-waves in a conducting state is greater than the number of negative half-waves in a conducting state, and a fifth pattern in which the number of negative half-waves in a conducting state is greater than the number of positive half-waves in a conducting state. The heating apparatus according to feature 13.

15. If the wavenumber control is performed using the fourth pattern, the control means will perform the wavenumber control using the fifth pattern in the next control cycle, and if the wavenumber control is performed using the fifth pattern, it will perform the wavenumber control using the fourth pattern in the next control cycle. The heating apparatus according to feature 14.

16. An image forming apparatus that forms an image on a recording material, A forming means for forming a toner image on the recording material, A heating device according to any one of claims 1 to 15 for heating and fixing the toner image, Equipped with, An image forming apparatus characterized by the following:

Images