Image forming apparatus

Abstract

To stably electrically conduct a bidirectional thyristor while preventing an increase in cost.SOLUTION: A bidirectional thyristor controls whether to supply power supplied from an AC power source to heating means. A DC voltage source supplies a control signal to a gate terminal of the bidirectional thyristor. Acquisition means acquires a state parameter including at least either one of the temperature of the bidirectional thyristor, AC voltage supplied from the AC power source, or the history of operation of the DC voltage source. Control means controls the number of times of output of control signals output from the DC voltage source to the gate terminal in a half period of the AC voltage.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] In an electrophotographic fixing device, toner is melted by the heat of a heater energized with alternating current, and a toner image is fixed on a sheet. According to Patent Document 1, it is described that the supply of alternating current to the heater is controlled using a bidirectional thyristor (triac).

[0003] According to Patent Document 1, a trigger current (gate trigger current) supplied to the gate terminal to turn on the bidirectional thyristor is generated by the discharge of a capacitor. This capacitor is charged in the first half cycle (half wave) of the alternating current and generates a gate trigger current in the next half cycle. Further, Patent Document 1 also proposes outputting the gate trigger current a plurality of times during a half cycle as a countermeasure against waveform distortion of the alternating current supplied from an alternating current power source.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the gate trigger current is output multiple times during a half cycle, the voltage across the capacitor gradually decreases during that half cycle. When the voltage across the capacitor decreases, the gate trigger current decreases, and eventually, the bidirectional thyristor stops conducting. The gate trigger current required to turn on the bidirectional thyristor increases as the temperature of the junction (Tj) of the bidirectional thyristor decreases. Also, due to aging, the capacitance of the capacitor decreases. Therefore, the gate trigger current that the capacitor can generate also decreases. Further, when the AC voltage fluctuates and the voltage across the capacitor decreases, the gate trigger current also decreases. Accordingly, an object of the present invention is to stably turn on the bidirectional thyristor while suppressing cost increase. Means for Solving the Problem

[0006] The present invention is, for example, heating means for applying heat to a toner image formed on a sheet to fix the toner image on the sheet; a bidirectional thyristor for controlling whether to supply power supplied from an AC power source to the heating means; a DC voltage source for supplying a control signal to the gate terminal of the bidirectional thyristor; acquisition means for acquiring a state parameter including at least one of the temperature of the bidirectional thyristor, the AC voltage supplied from the AC power source, or the operation history of the DC voltage source; control means for controlling the number of output times of the control signal output from the DC voltage source to the gate terminal during a half cycle of the AC voltage according to the state parameter; and provides an image forming apparatus having the same. Advantages of the Invention

[0007] According to the present invention, it is possible to stably turn on the bidirectional thyristor while suppressing cost increase. Brief Description of the Drawings

[0008]

Figure 1

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Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are assigned the same reference numerals, and duplicate explanations are omitted.

[0010] <Example 1> [Image forming apparatus] As shown in FIG. 1, the image forming apparatus 100 is an electrophotographic laser beam printer. The photosensitive drum 1 is a photoreceptor and an image carrier having a photosensitive layer formed on its surface. The charging roller 2 charges the surface layer of the photosensitive drum 1. The laser scanner 3 is an exposure device or an optical scanning device that irradiates the surface layer of the photosensitive drum with laser light according to an image signal to form an electrostatic latent image. The developing roller 4 develops the electrostatic latent image using the toner 5 housed in the toner container to form a toner image. The transfer roller 6 is a roller that supplies transfer charges to the sheet 7. The transfer roller 6 transfers the toner image from the photosensitive drum 1 to the sheet 7 passing through the transfer nip portion formed by the photosensitive drum 1 and the transfer roller 6. Thereafter, the sheet 7 is conveyed to the fixing device 30.

[0011] The fixing device 30 has a cylindrical fixing film 9 and a heater 11 disposed in the internal space of the fixing film 9. The heater 11 generates heat by the electric power supplied from the power source 50. The power source 50 supplies alternating current supplied from an AC power source to the heater 11. The pressure roller 10 contacts the outer peripheral surface of the fixing film 9 and forms a fixing nip portion by pressing the fixing film 9. The sheet 7 and the toner image 8 are heated by the heater 11 via the fixing film 9. Further, the sheet 7 and the toner image 8 are pressed at the fixing nip portion. The heater 11 is, for example, a heater having a ceramic base material, a heat generating layer, and a protective layer. The stay 12 is a holding member that holds the heater 11. The reinforcing member 13 is a member that reinforces and supports the stay 12.

[0012] The thermistor 14 is a temperature sensor that detects the temperature of the heater 11. The detection result of the thermistor 14 is used for feedback control to maintain the temperature of the heater 11 at the target temperature. Thereafter, the sheet 7 is discharged from the fixing nip portion to the discharge tray 16 of the image forming apparatus 100 through the discharge port.

[0013] The feed roller 17 is a roller that feeds the sheet 7. The conveyance rollers 18 and 19 are rollers that convey the sheet 7 along the conveyance path. The CPU 15 is a processor or controller that controls various operations of the image forming apparatus 100. CPU is an abbreviation for central processing unit. The CPU 15 may incorporate a memory 22 and a timer 23. The memory 22 has a non-volatile storage area (ROM area) and a volatile storage area (RAM area). ROM is an abbreviation for read only memory. RAM is an abbreviation for random access memory. The timer 23 can be realized by a real-time clock (RTC) or a counter circuit. The temperature sensor 20 is connected to the CPU 15 and detects the temperature inside the image forming apparatus 100. The motor 21 rotationally drives the photosensitive drum 1, the developing roller 4, the transfer roller 6, the pressure roller 10, the feed roller 17, etc. at a predetermined speed based on an instruction from the CPU 15.

[0014] [Heater power source] (1) Circuit configuration FIG. 2 is a circuit diagram of a power supply 50 that operates as a heater power supply. The bidirectional thyristor 202 is a control element that controls the power supply from the AC power supply 201 to the heater 11. The drive circuit that drives the bidirectional thyristor 202 has, for example, transistors Tr3, Tr5, a photocoupler 204, and resistors R6, R7, R8, R9. The base of the transistor Tr3 is connected to the output port of the CPU 15. The emitter of the transistor Tr3 is grounded. The collector of the transistor Tr3 is connected to the cathode of the light-emitting diode (LED) in the photocoupler 206. The anode of the light-emitting diode in the photocoupler 206 is connected to the reference power supply Vcc via the resistor R6. The collector of the phototransistor in the photocoupler 204 is connected to one end of the resistor R7. The emitter of the phototransistor in the photocoupler 204 is connected to one end of the resistor R8 and the base of the transistor Tr6. The other end of the resistor R7 and one end of the resistor R9 are connected to the gate terminal of the thyristor 403. The other end of the resistor R9 is connected to the collector of the transistor Tr5. The emitter of the transistor Tr5 is connected to the other end of the resistor R8, one end of the capacitor C20, one end of the resistor R21, and the anode of the Zener diode D19.

[0015] The other end of the resistor R21 is connected to the anode of the diode D22. The cathode of the diode D22 is connected to one end of the heater 11 and the N pole of the AC power supply 201. Note that the Zener diode D19, the capacitor C20, the resistor R21, and the diode D22 form a DC voltage source 218.

[0016] The L pole of the AC power supply 201 is connected to one end of the coil L1. The other end of the coil L1 is connected to the cathode of the Zener diode D19, the other end of the capacitor C20, and the T1 terminal of the bidirectional thyristor 402.

[0017] The T2 terminal of the bidirectional thyristor 402 is connected to one end of the protection element 210. The other end of the protection element 210 is connected to the other end of the heater 11. The protection element 210 is an element (e.g., temperature fuse, thermostat) that suppresses excessive temperature rise of the heater 11.

[0018] A zero-cross detection circuit 220 for detecting the zero-cross of the AC voltage supplied from the AC power supply 201 is connected to the input port of the CPU 15. The input port of the CPU 15 is connected to one end of the resistor R16. The other end of the resistor R16 is connected to one end of the capacitor C17, one end of the resistor R15, and the collector of the phototransistor in the photocoupler 214. The other end of the resistor R15 is connected to the reference power supply Vcc. The emitter of the phototransistor in the photocoupler 214 is grounded. The anode of the light-emitting diode in the photocoupler 214 is connected to the L pole via the resistor R12. The cathode of the light-emitting diode in the photocoupler 214 is connected to the N pole. The cathode of the diode D13 is connected to the anode of the light-emitting diode in the photocoupler 214. The anode of the diode D13 is connected to the cathode of the light-emitting diode in the photocoupler 214.

[0019] (2) Circuit operation When the CPU 15 outputs a control signal in the High state (hereinafter referred to as the FSRD signal) to the base of the transistor Tr3, the transistor Tr3 becomes conductive. When the transistor Tr3 becomes conductive, current flows from the reference power supply Vcc through the resistor R6, and the photocoupler 204 becomes conductive. As a result, current flows through the resistors R7 and R8, and the transistor Tr5 becomes conductive. A gate trigger voltage is applied between the T1 terminal and the gate terminal of the bidirectional thyristor 202 from the capacitor C20, and a gate trigger current flows through the gate terminal. As a result, the bidirectional thyristor 202 becomes conductive between the T1 terminal and the T2 terminal, and power is supplied from the AC power supply 201 to the heater 11. At this time, the CPU 15 executes control in a control cycle with half a wave of the AC voltage of the AC power supply 201 as a unit.

[0020] The temperature sensor 20 may be, for example, a chip-type NTC thermistor. NTC is an abbreviation for Negative Temperature Coefficient. That is, the resistance value of the temperature sensor 20 decreases / increases in response to an increase / decrease in temperature. The reference voltage supplied from the reference power supply Vcc is divided by a voltage dividing circuit formed by the resistor R23 and the internal resistance of the temperature sensor 20. The divided voltage is input to the CPU 15 via the resistor R24 and the capacitor C25. The CPU 15 detects the temperature based on the input voltage. The temperature sensor 20 is disposed at a position where it can measure a temperature correlated with the temperature (hereinafter, Tj) of the junction of the bidirectional thyristor 202. The CPU 15 uses the temperature sensor 20 to detect, measure, or estimate the temperature Tj. Hereinafter, the measured value or estimated value of the temperature Tj is referred to as the Tj estimated value.

[0021] The coil L1 suppresses the switching noise generated at the start of conduction of the bidirectional thyristor 202 from being emitted outside the image forming apparatus 100.

[0022] In the zero-cross detection circuit 220, when power is supplied from the L pole of the AC power supply 201, current flows through the light emitting diode of the photocoupler 214 via the resistor R12, and the light emitting diode emits light. When the photocoupler 214 emits light, light enters the phototransistor of the photocoupler 214, and current flows through the phototransistor. That is, current flows from the reference power supply Vcc connected via the resistor R15, through the phototransistor of the photocoupler 214, to the frame ground (GND). Then, the capacitor C17 is charged, and a zero-cross signal (hereinafter, ZEROX signal) is output to the CPU 15 via the resistor R16. At this time, the zero-cross detection circuit 220 outputs a ZEROX signal in a High state or a Low state to the CPU 15 according to the voltage waveform of the AC power supply 201. The CPU 15 outputs the FSRD signal in synchronization with the ZEROX signal, that is, in synchronization with the detection result of the zero-cross detection circuit 220. Thereby, the bidirectional thyristor 202 can be made conductive near the zero-cross point of the AC power supply 201.

[0023] (3) Charge and discharge operation of capacitor C20 (3-1) Charge operation When current flows through the path of current loop LP1 from the L pole of AC power supply 201, the capacitor C20 is charged with electric charge. The upper limit voltage applied across both ends of the capacitor C20 is limited by the Zener voltage Vz of the Zener diode D19 (hereinafter referred to as the Vz voltage). Therefore, the capacitor C20 is charged so that the upper limit value of the voltage across both ends becomes the Vz voltage. When current is supplied from the N pole of the AC power supply 201, a reverse bias is applied to the diode D22. As a result, the current trying to flow through the capacitor C20 via the current loop LP1 is restricted, and no charging current flows through the capacitor C20.

[0024] (3-2) Discharge operation When current is supplied from the L pole or N pole of the AC power supply 201, during the period when the CPU 15 outputs the FSRD signal in the High state, the capacitor C20 discharges the electric charge and allows a gate trigger current to flow through the bidirectional thyristor 202. There may be a case where the capacitor C20 conducts the bidirectional thyristor 202 during the period when current is supplied from the L pole of the AC power supply 201. In this case, the capacitor C20 is charged by the AC power supply 201 while discharging the electric charge. As a result, a gate trigger current flows through the bidirectional thyristor 202. There may also be a case where the capacitor C20 conducts the bidirectional thyristor 202 during the period when current is supplied from the N pole of the AC power supply 201. In this case, the capacitor C20 discharges the electric charge and a gate trigger current flows through the bidirectional thyristor 202.

[0025] (4) Gate trigger current of bidirectional thyristor 202 As shown in FIG. 2, the DC voltage source 218 is composed of a Zener diode D19 and a capacitor C20. At this time, when the CPU 15 sets the FSRD signal to the High state, the capacitor C20 discharges the charge. Therefore, the current loop LP2 is in the forward direction, that is, the gate trigger current flows through the bidirectional thyristor 202, and the T1 terminal and the T2 terminal of the bidirectional thyristor 202 are turned on. When the CPU 15 sets the FSRD signal to the Low state, the transistors Tr3 and Tr5 are turned off, and the gate trigger current stops flowing.

[0026] On the other hand, the gate trigger current (current value) required for the T1 terminal and the T2 terminal to conduct changes depending on the temperature Tj of the bidirectional thyristor 202.

[0027] FIG. 3 is a graph showing the characteristics between the temperature of the junction of the bidirectional thyristor 202 and the gate trigger current. Here, the potential of the T1 terminal of the bidirectional thyristor 202 is the reference potential. In FIG. 3, the characteristics of the three trigger modes i, ii, and iii are shown respectively. The horizontal axis represents the temperature Tj of the bidirectional thyristor 202. The vertical axis represents the ratio of the gate trigger current with respect to Tj = 25°C as a reference. As shown in FIG. 3, as the temperature Tj of the bidirectional thyristor 202 decreases, the required gate trigger current increases.

[0028] The amount of charge that the capacitor C20 can store is finite. Therefore, according to the temperature Tj of the bidirectional thyristor 202, the output frequency N of the FSRD signal (gate trigger current) output within a half cycle needs to be adjusted. That is, the CPU 15 may reduce the output frequency N as the temperature Tj of the bidirectional thyristor 202 decreases. If the output frequency N is maintained despite the low temperature Tj, problems will occur. For example, due to the waveform distortion of the AC voltage Vac supplied from the AC power source 201, the bidirectional thyristor 202 turns off, and the power supply to the heater 11 stops. As a result, the heat generation of the heater 11 becomes unstable, and the fixing performance of the toner image may deteriorate.

[0029] On the one hand, according to Embodiment 1, the CPU 15 adjusts the number of output times N according to the temperature Tj of the bidirectional thyristor 202. As a result, the heat generation of the heater 11 is stabilized, and the fixing performance of the toner image is maintained.

[0030] (5) Gate trigger signal FIG. 4 shows a table 400 stored in the memory 22 of the CPU 15. The table 400 shows the correspondence between the estimated value of Tj of the bidirectional thyristor 202 and the number of output times N of the High state of the FSRD signal in one half-wave of the AC power supply 201.

[0031] (5-1) When the estimated value of Tj is 25°C or higher When the estimated value of Tj is 25°C or higher, the number of output times N is 3 times. FIG. 5(A) shows the waveform of the AC voltage supplied from the AC power supply 201. FIG. 5(B) shows the waveform of the FSRD signal output from the CPU 15. FIG. 5(C) shows the current waveform of the bidirectional thyristor 202. FIG. 5(D) shows the waveform of the voltage across the capacitor C20.

[0032] V1 in FIG. 5(D) is the voltage across the capacitor C20 that can generate the gate trigger current required to turn on the bidirectional thyristor 202 when Tj is 25°C. V2 is the voltage value across the capacitor C20 that can generate the gate trigger current required to turn on the bidirectional thyristor 202 when the Tj of the bidirectional thyristor 202 is 0°C.

[0033] The periods from timing T1 to T7 and from T13 to T19 are the charging intervals of the capacitor C20. The period from T7 to T13 is the non-charging interval.

[0034] As shown in Fig. 5(A), waveform distortion occurs in the AC voltage Vac of the AC power supply 201 during the period from T10 to T11. As a result, the AC voltage Vac becomes 0 [V]. Accordingly, as shown in Fig. 5(C), the current flowing through the bidirectional thyristor 202 also becomes 0 [A]. However, as shown in Fig. 5(B) and Fig. 5(C), when the FSRD signal becomes High at T11, a gate trigger current flows through the bidirectional thyristor 202, and conduction starts again.

[0035] As shown in Fig. 5(B), the FSRD signal becomes High during a predetermined period. The predetermined period includes the period from T1 to T2, the period from T3 to T4, the period from T5 to T6, the period from T7 to T8, the period from T9 to T10, the period from T11 to T12, the period from T13 to T14, the period from T15 to T16, and the period from T17 to T18. Thus, a gate trigger current flows through the bidirectional thyristor 202 multiple times in a half cycle. As a result, the conduction failure of the bidirectional thyristor 202 due to the waveform distortion of the AC power supply 201 is suppressed. On the other hand, since the capacitor C20 discharges to flow the gate trigger current, the voltage across the capacitor C20 decreases. The capacitor C20 is charged during the period from T2 to T3, the period from T4 to T5, the period from T6 to T7, the period from T14 to T15, the period from T16 to T17, and the period from T18 to T19. The lower limit value of the voltage across the capacitor C20 is V4 at T2 and T14. As shown in Fig. 5(D), V4 > V1. Therefore, when the Tj of the bidirectional thyristor 202 is 25°C or higher, the output number N is set to 3 times. Thereby, no matter when the waveform distortion occurs, the capacitor C20 can flow a gate trigger current to the bidirectional thyristor 202.

[0036] In FIG. 5(D), V3 is the voltage across capacitor C20 when the estimated Tj value is 0° C. and the output count N is maintained at 3. In this case, the voltage V3 across the capacitor during the period from T12 to T13 is lower than V2. That is, the capacitor C20 cannot turn on the bidirectional thyristor 202. Therefore, FIG. 5(D) suggests that the output count N should be set to 2 or less when the estimated Tj value is 0° C.

[0037] (5-2) When the estimated Tj value is lower than 25° C. As an example, assume that the estimated Tj value is 0° C. The CPU 15 refers to the table 400 and determines that the output count N is 2 times when the estimated Tj value is 0° C. FIG. 6(A) shows the waveform of the AC voltage supplied from the AC power supply 201. FIG. 6(B) shows the waveform of the FSRD signal. FIG. 6(C) shows the waveform of the gate trigger current of the bidirectional thyristor 202. FIG. 6(D) shows the waveform of the voltage across the capacitor C20.

[0038] In FIG. 6(D), the definitions of V1 and V2 are as described in relation to FIG. 5(D). The periods from T1 to T5 and from T9 to T13 are the charging intervals of the capacitor C20. The period from T5 to T9 is the non-charging interval.

[0039] As shown in FIG. 6(A), waveform distortion occurs in the AC voltage Vac supplied from the AC power supply 201 during the period from T6 to T7. As a result, the AC voltage Vac becomes 0 [V]. As shown in FIG. 6(C), the current of the bidirectional thyristor 202 also becomes 0 [A]. However, as shown in FIGS. 6(B) and 6(C), since the FSRD signal becomes High at T7, a gate trigger current flows through the bidirectional thyristor 202 and the bidirectional thyristor 202 conducts again.

[0040] During the period from T1 to T2, the period from T3 to T4, the period from T5 to T6, the period from T7 to T8, the period from T9 to T10, and the period from T11 to T12, as shown in FIG. 6(B), the FSRD signal becomes High. Therefore, a gate trigger current flows through the bidirectional thyristor 202, and the influence of waveform distortion is reduced. On the other hand, the capacitor C20 discharges, and the voltage across its both ends decreases. During the period from T2 to T3, the period from T4 to T5, the period from T10 to T11, and the period from T12 to T13, the capacitor C20 is charged. Further, during the period from T4 to T5 and the period from T12 to T13, the voltage across the both ends of the capacitor C20 reaches the Zener voltage Vz of the Zener diode D19.

[0041] The lower limit value of the voltage across the capacitor C20 is V5 at T2 and T10. As shown in FIG. 6(D), since V5 > V2, even when the temperature Tj of the bidirectional thyristor 202 is 0°C, the capacitor C20 can pass a gate trigger current.

[0042] According to the first embodiment, the CPU 15 adjusts the output frequency N of the FSRD signal based on the Tj estimated value obtained by the temperature sensor 20. The output frequency N can be set to the maximum value as long as the bidirectional thyristor 202 can be stably turned on even when waveform distortion occurs. Thereby, since the heater 11 is stably supplied with power, the defect of the temperature rise of the fixing device 30 is reduced.

[0043] In the first embodiment, when the Tj estimated value of the bidirectional thyristor 202 is 25°C or higher, the output frequency N is set to 3 times. When the Tj estimated value is lower than 25°C, the output frequency N is set to 2 times. However, this is only an example. The correspondence between the Tj estimated value of the bidirectional thyristor 202 and the output frequency N of the FSRD signal may be other relationships. That is, this correspondence is determined according to the capacity of the heater 11 and the temperature-dependent characteristics of the capacitor C20.

[0044] In Example 1, the temperature sensor 20 is assumed to be a chip-type NTC thermistor, but this is just an example. Any temperature sensor that can measure or estimate the temperature Tj of the bidirectional thyristor 202 can be adopted.

[0045] <Example 2> In Example 1, the junction temperature Tj of the bidirectional thyristor 202 was adopted as the state parameter that affects the gate trigger current supply capacity. However, there are other parameters that affect the gate trigger current supply capacity. Therefore, in Example 2, the operation history of the image forming apparatus 100 is considered as the state parameter. Note that the number of state parameters may be plural. Therefore, in Example 2, a combination of the Tj estimated value and the operation history (hereinafter, the integrated energization time) is adopted as the state parameter. The CPU 15 adjusts the output frequency N according to these. Note that the description of matters common to Example 1 in Example 2 is incorporated by reference to the description of Example 1.

[0046] As described in Example 1, the capacitor C20 functions as a DC voltage source for supplying a gate trigger current to the bidirectional thyristor 202. The current I flowing through the capacitor C20 is expressed by the following equation.

[0047] I = C·V / t ····· Eq1 Here, C is the capacitance of the capacitor C20. V is the voltage across the capacitor C20. t is time. As shown by Equation Eq1, when the capacitance C of the capacitor C20 decreases, the current I flowing through the capacitor C20 decreases. That is, as described in Example 1, the current flowing along the current loop LP1 and charging the capacitor C20 decreases.

[0048] On the other hand, as shown in FIG. 7, the capacitor C20 has a characteristic that its capacitance decreases according to the integrated energization time (aging deterioration). In FIG. 7, the horizontal axis represents the integrated energization time [h] of the image forming apparatus 100. The vertical axis represents the capacitance change rate [%] of the capacitor C20.

[0049] For example, when the integrated energization time is 800 h, the capacitance change rate of the capacitor C20 is -10%. That is, when the integrated energization time is 800 h, the capacitance of the capacitor C20 decreases by about 10% from the capacitance of the capacitor C20 when the energization time is 0 h.

[0050] FIG. 8 shows a table 800 that holds the number of output times N corresponding to combinations of the Tj estimated value of the bidirectional thyristor 202 and the integrated energization time of the image forming apparatus 100. This table 800 is stored in the memory 22 of the CPU 15. The integrated energization time is measured, for example, by the timer 23 for the time (integrated drive time) during which the CPU 15 rotationally drives the motor 21, and the integrated energization time of the image forming apparatus 100 is calculated based on the measured value. The integrated energization time may be stored and held, for example, in the memory 22 of the CPU 15. The integrated energization time may be replaced with the number of drive pulses input to the motor 21 or the number of pulses (count value) output from the motor 21.

[0051] The table 800 holds four control patterns P1 to P4. When the Tj estimated value is 25° C. or higher and the integrated energization time is shorter than 800 [h], the number of output times N is determined to be 5 times (pattern P1). When the Tj estimated value is 25° C. or higher and the integrated energization time is 800 [h] or longer, the number of output times N is determined to be 4 times (pattern P2). When the Tj estimated value is lower than 25° C. and the integrated energization time is shorter than 800 [h], the number of output times N is determined to be 3 times (pattern P3). When the Tj estimated value is lower than 25° C. and the integrated energization time is 800 [h] or longer, the number of output times N is determined to be 2 times (pattern P4).

[0052] According to the second embodiment, the CPU 15 refers to the table 800 based on the combination of the Tj estimated value and the integrated energization time, and adjusts the number of output times N. For example, the number of output times N may be set to the largest possible value. Thereby, even when waveform distortion occurs in the AC voltage, it becomes possible to stably turn on the bidirectional thyristor 202. As a result, the power supply to the heater 11 becomes stable, and defects in the temperature rise of the fixing device 30 are reduced.

[0053] In Embodiment 2, the CPU 15 estimates the integrated energization time (operation history) of the image forming apparatus 100 from the integrated drive time of the motor 21. However, this is only an example. For example, the CPU 15 may use the memory 22 or the like to count the integrated number of printed sheets (printing sheets). The CPU 15 may calculate the integrated energization time from this count result, or use the count result instead of the integrated energization time. In any case, any parameter correlated with the integrated energization time of the capacitor C20 can be used to adjust the number of outputs N.

[0054] <Embodiment 3> In Embodiment 3, as the state parameter, the maximum value (peak value) of the AC voltage Vac supplied from the AC power supply 201 is considered. The CPU 15 adjusts the number of outputs N according to the combination of the Tj estimated value and the peak value. Note that the peak value may be adopted alone as the state parameter.

[0055] FIG. 9 shows the voltage waveform of the AC power supply 201. The horizontal axis represents time. The vertical axis represents the voltage value. The frequency of the AC voltage is 60 [Hz]. The effective value is 120 [V]. The peak value is 120√2 [V].

[0056] FIG. 10 shows the power supply 50 of Embodiment 3. Compared with FIG. 2, in FIG. 10, a voltage detection circuit 1001 is connected between the L pole and the N pole of the AC power supply 201. The voltage detection circuit 1001 may be realized by at least two voltage dividing resistors that divide the AC voltage Vac into a voltage (detection voltage Vsns) that can be input to the CPU 15, for example. The detection voltage Vsns is proportional to the AC voltage Vac and indicates the AC voltage Vac. The output of the voltage detection circuit 1001 is connected to the input port of the CPU 15 with an A / D converter. The CPU 15 monitors the AC voltage Vac detected by the voltage detection circuit 1001.

[0057] As described in Example 1, when power is supplied from the L pole of the AC power supply 201, current flows along the current loop LP1, and charges are accumulated in the capacitor C20. The current I flowing through the capacitor C20 is expressed by the following equation.

[0058] I = Vac / √(R^2 + (1 / ωC)^2) ····· Eq2 Here, Vac is the voltage value of the AC power supply 201. R is the resistance value of the resistor R21. C is the capacitance of the capacitor C20. ω is the angular frequency [rad / s] of the AC voltage.

[0059] From Equation Eq2, it can be seen that when the AC voltage Vac decreases, the current value I flowing through the capacitor C20 also decreases. This means that, as described in Example 1, the current flowing along the path of the current loop LP1 to charge the capacitor C20 decreases.

[0060] Figure 11 shows the table 1100 stored in the memory 22. The table 1100 holds the number of output times N corresponding to the combination of the Tj estimated value and the AC voltage Vac (detected voltage Vsns). In this example, there are four control patterns P5 to P8.

[0061] As shown in Figure 11, when the AC voltage Vac is 100 [V] or more and the Tj estimated value is 25 °C or more, the CPU 15 determines the number of output times N to be 4 times (pattern P5). When the AC voltage Vac is 100 [V] or more and the Tj estimated value is lower than 25 °C, the CPU 15 determines the number of output times N to be 2 times (pattern P6). When the AC voltage Vac is lower than 100 [V] and the Tj estimated value is 25 °C or more, the CPU 15 determines the number of output times N to be 3 times (pattern P7). When the AC voltage Vac is lower than 100 [V] and the Tj estimated value is lower than 25 °C, the CPU 15 determines the number of output times N to be 2 times (pattern P8).

[0062] According to Example 3, the output count N is adjusted based on the combination of the estimated Tj value and the AC voltage Vac. Here, the output count N may be set to the maximum value as long as the bidirectional thyristor 202 conducts stably. Thereby, even if waveform distortion occurs in the AC voltage Vac, the heater 11 will generate heat stably, and temperature defects in the fixing device 30 will be reduced.

[0063] In Example 3, it is assumed that the frequency of the AC voltage Vac is 60 [Hz], the effective value is 120 [V], and the peak value is 120√2 [V]. Also, as shown in FIG. 11, the threshold value of the AC voltage Vac is assumed to be 100 [V]. However, these numerical values are merely examples. The parameters regarding the AC voltage Vac are appropriately changed according to the specifications of the commercial AC power supply for each destination of the image forming apparatus 100.

[0064] In Example 3, the voltage value of the AC voltage Vac is directly detected by the voltage detection circuit 1001. However, this is merely an example. Other physical parameters useful for estimating the AC voltage Vac may be detected.

[0065] <Example 4> In Example 1, the temperature of the bidirectional thyristor 202 (e.g., the estimated Tj value) is adopted as the state parameter. In Example 2, a combination of the temperature of the bidirectional thyristor 202 (e.g., the estimated Tj value) and the integrated energization time of the capacitor C20 is adopted as the state parameter. In Example 3, a combination of the temperature of the bidirectional thyristor 202 (e.g., the estimated Tj value) and the voltage value (peak value) of the AC voltage Vac is adopted as the state parameter. However, these are merely examples.

[0066] As a state parameter, the integrated energization time of capacitor C20 may be used alone. As a state parameter, the AC voltage Vac may be used alone. Further, as a state parameter, a combination of the integrated energization time of capacitor C20 and the AC voltage Vac may be adopted. Further, as a state parameter, a combination of the temperature of the bidirectional thyristor 202 (e.g., Tj estimated value), the integrated energization time of capacitor C20, and the AC voltage Vac may be adopted. In any case, a table, mathematical formula, or program module for converting the state parameter into the output count N is stored in the memory 22 and referred to by the CPU 15. Also, instead of a table, a mathematical formula or program module may be adopted.

[0067] <Example 5> (1) Functions realized by the CPU FIG. 12 shows functions realized by the CPU 15 executing the program 1209. The zero-cross detection unit 1201 detects or recognizes the zero-cross of the AC voltage Vac based on the ZEROX signal output from the zero-cross detection circuit 220. Each time the zero-cross detection unit 1201 recognizes a zero-cross, it outputs a detection signal to the signal generator 1208.

[0068] The acquisition unit 1202 acquires the state parameter. The temperature detection unit 1203 detects or estimates the temperature (Tj estimated value) of the junction of the bidirectional thyristor 202 based on the detection signal output by the temperature sensor 20. The operation history recording unit 1204 uses the timer 23 to record the cumulative operation time of the motor 21 (the integrated energization time of the capacitor C20) and stores the cumulative operation time in the ROM area of the memory 22. As described above, the cumulative number of printed sheets may be recorded in the memory 22. The voltage detection unit 1205 detects or estimates the AC voltage Vac based on the detection voltage Vsns output from the voltage detection circuit 1001.

[0069] The output frequency adjustment unit 1206 adjusts the output frequency N according to the state parameter acquired by the acquisition unit 1202. At this time, the output frequency adjustment unit 1206 may refer to tables 400, 800, 1100, etc., and determine the output frequency N corresponding to the state parameter.

[0070] The signal setting unit 1207 determines the period ton during which the FSRD signal is in the High state and the period toff during which the FSRD signal is in the Low state based on the output frequency N, and sets them in the signal generator 1208. For example, the signal setting unit 1207 measures the time (half cycle) from the preceding zero cross to the subsequent zero cross, and obtains the sum of ton and toff by dividing the half cycle by N. Assume that the ratio of ton and toff (duty ratio) is stored in the memory 22 in advance. The signal setting unit 1207 refers to this ratio and determines ton and toff. Each time a zero cross is detected by the zero cross detection unit 1201, the signal generator 1208 outputs an FSRD signal with the output frequency N. That is, the signal generator 1208 outputs a pulsed FSRD signal based on the period ton during which the FSRD signal is in the High state and the period toff during which the FSRD signal is in the Low state.

[0071] (2) Flowchart FIG. 13 shows a control method executed by the CPU 15 according to the program 1209.

[0072] In S1301, the CPU 15 (acquisition unit 1202) acquires a state parameter. The state parameter includes at least one of the temperature of the bidirectional thyristor 202 (e.g., Tj estimated value), the integrated energization time of the capacitor C20, and the AC voltage Vac.

[0073] In S1302, the CPU 15 (output frequency adjustment unit 1206) determines the output frequency N corresponding to the acquired state parameter. For example, the output frequency adjustment unit 1206 may refer to tables 400, 800, 1100, and acquire the output frequency N corresponding to the state parameter.

[0074] In S1303, the CPU 15 (zero-cross detection unit 1201) determines whether a zero-cross of the AC voltage Vac has been detected. When a zero-cross is detected, the CPU 15 proceeds from S1303 to S1304.

[0075] In S1304, the CPU 15 (signal setting unit 1207, signal generator 1208) outputs a pulsed FSRD signal according to the output count N.

[0076] In S1305, the CPU 15 determines whether the end condition of the control method is satisfied. The end condition may be, for example, that image formation on the sheet 7 in the image forming apparatus 100 is completed and no next print job is input even after waiting for a predetermined time. If the end condition is not satisfied, the CPU 15 returns from S1305 to S1303 and continues to supply power to the heater 11. When the end condition is satisfied, the CPU 15 stops supplying power to the heater 11.

[0077] <Technical idea derived from the embodiment> (Item 1) Heating means for applying heat to a toner image formed on a sheet to fix the toner image on the sheet; A bidirectional thyristor for controlling whether to supply power supplied from an AC power source to the heating means; A DC voltage source for supplying a control signal to the gate terminal of the bidirectional thyristor; Acquisition means for acquiring state parameters including at least one of the temperature of the bidirectional thyristor, the AC voltage supplied from the AC power source, or the operation history of the DC voltage source; Control means for controlling the number of output times of the control signal output from the DC voltage source to the gate terminal in a half cycle of the AC voltage according to the state parameters; An image forming apparatus having the above. The heater 11 functions as a heating means for applying heat to the toner image formed on the sheet and fixing the toner image on the sheet. The bidirectional thyristor 202 controls whether to supply the power supplied from the AC power supply 201 to the heating means. The CPU 15 and the acquisition unit 1202 acquire state parameters including at least one of the temperature (Tj estimated value) of the bidirectional thyristor 202, the AC voltage Vac supplied from the AC power supply 201, or the operation history of the DC voltage source (e.g., capacitor C20). The CPU 15 controls the number of output times N of the control signal (gate trigger current depending on the FSRD signal) output from the DC voltage source to the gate terminal G in a half cycle of the AC voltage Vac according to the state parameters. Thereby, it is possible to stably turn on the bidirectional thyristor 202 while suppressing cost increase. As a result, the heat generation of the heater 11 is stabilized and the fixing performance of the fixing unit 30 is also maintained. (Item 2) Temperature The acquisition means is configured to acquire a measured value or an estimated value of the temperature of the bidirectional thyristor. The control means controls the number of output times of the control signal using, as the state parameter, the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means, according to Item 1 of the image forming apparatus described. The acquisition unit 1202 may be configured to acquire a measured value or an estimated value of the temperature Tj of the bidirectional thyristor 202. As described in the first embodiment, the CPU 15 may control the number of output times N of the control signal using, as the state parameter, the measured value or the estimated value of the temperature Tj of the bidirectional thyristor 202. Thereby, the number of output times N is adjusted according to the temperature Tj of the junction of the bidirectional thyristor 202, and it is possible to stably turn on the bidirectional thyristor 202. (Item 3) Temperature The apparatus further includes storage means for storing in advance the correspondence relationship between the measured value or the estimated value of the temperature of the bidirectional thyristor and the number of output times of the control signal. The image forming apparatus according to item 2, wherein the control means determines the number of output times of the control signal corresponding to the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means by referring to the correspondence relationship stored in the storage means. The memory 22 and the table 400 function as storage means for storing in advance the correspondence relationship between the measured value or the estimated value of the temperature Tj of the bidirectional thyristor 202 and the number of output times N of the control signal. The CPU 15 may determine the number of output times N of the control signal corresponding to the temperature Tj of the bidirectional thyristor 202 by referring to the correspondence relationship stored in the storage means. (Item 4) Alternating voltage The acquisition means includes a measurement circuit that measures an alternating voltage supplied from the AC power supply. The image forming apparatus according to any one of items 1 to 3, wherein the control means controls the number of output times of the control signal according to the alternating voltage measured by the measurement circuit as the state parameter. The acquisition unit 1202 may include a measurement circuit (for example, the voltage detection circuit 1001) that measures the alternating voltage Vac supplied from the AC power supply 201. The CPU 15 may control the number of output times N of the control signal according to the alternating voltage Vac measured by the measurement circuit as the state parameter. When the alternating voltage Vac decreases, the voltage across the capacitor C20 also decreases, so the gate trigger current also decreases. Therefore, by adjusting the number of output times N according to the alternating voltage Vac, it is possible to stably turn on the bidirectional thyristor 202. (Item 5) Alternating voltage The apparatus further includes storage means for storing in advance the correspondence relationship between the alternating voltage and the number of output times of the control signal. The image forming apparatus according to item 4, wherein the control means determines the number of output times of the control signal corresponding to the alternating voltage acquired by the measurement circuit by referring to the correspondence relationship stored in the storage means. The memory 22 and the table 1100 function as storage means for pre-storing the correspondence relationship between the AC voltage Vac and the number of output times N. The CPU 15 may determine the number of output times N of the control signal corresponding to the AC voltage Vac acquired by the measurement circuit by referring to the correspondence relationship stored in the memory 22. (Item 6) Operating history The acquisition means has holding means for holding the operating history of the DC voltage source. The control means controls the number of output times of the control signal according to the operating history held by the holding means as the state parameter, in the image forming apparatus according to any one of Items 1 to 5. The memory 22 and the operation history recording unit 1204 function as holding means for holding the operation history (for example, the integrated energization time of the image forming apparatus 100) of the DC voltage source (for example, the capacitor C20). The CPU 15 may control the number of output times N of the control signal according to the operation history held by the holding means as the state parameter. As illustrated in FIG. 7, the capacitance of the capacitor C20 decreases according to the integrated energization time. This means that the ability of the capacitor C20 to store electric charge, that is, the ability to generate a gate trigger current deteriorates over time. Therefore, by determining the number of output times N in consideration of the operation history of the DC voltage source, it becomes possible to stably turn on the bidirectional thyristor 202. (Item 7) Operating history It further has storage means for pre-storing the correspondence relationship between the operating history of the DC voltage source and the number of output times of the control signal. The control means determines the number of output times of the control signal corresponding to the operating history of the DC voltage source held by the holding means by referring to the correspondence relationship stored in the storage means, in the image forming apparatus according to Item 6. The memory 22 and the table 800 may function as storage means for pre-storing the correspondence relationship between the operating history of the DC voltage source and the number of output times N of the control signal. The CPU 15 may determine the number of output times N of the control signal corresponding to the operating history of the DC voltage source by referring to the correspondence relationship stored in the memory 22. Thereby, it becomes possible to stably turn on the bidirectional thyristor 202. (Item 8) Temperature + AC Voltage The acquisition means is means for acquiring a measured value or an estimated value of the temperature of the bidirectional thyristor, a measurement circuit for measuring the AC voltage supplied from the AC power supply, and has The control means uses, as the state parameter, the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means and the AC voltage measured by the measurement circuit to control the output frequency of the control signal. The image forming apparatus according to any one of Items 1 to 7. The CPU 15 and the temperature detection unit 1203 function as means for acquiring a measured value or an estimated value of the temperature Tj of the bidirectional thyristor 202. As described in the third embodiment, the CPU 15 may control the output frequency N of the control signal using, as the state parameter, the measured value or the estimated value of the temperature Tj of the bidirectional thyristor 202 and the AC voltage Vac. (Item 9) Temperature + AC Voltage further includes storage means for storing in advance the correspondence between the combination of the measured value or the estimated value of the temperature of the bidirectional thyristor and the AC voltage and the output frequency of the control signal, The control means determines the output frequency of the control signal corresponding to the combination of the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means and the AC voltage measured by the measurement circuit by referring to the correspondence stored in the storage means. The image forming apparatus according to Item 8. The memory 22 and the table 1100 function as storage means for storing in advance the correspondence between the combination of the temperature Tj of the bidirectional thyristor 202 and the AC voltage Vac and the output frequency N of the control signal. The CPU 15 may determine the output frequency N of the control signal corresponding to the combination of the temperature Tj of the bidirectional thyristor 202 and the AC voltage Vac by referring to the correspondence stored in the memory 22. (Item 10) Temperature + Operation History The acquisition means is Means for acquiring a measured value or an estimated value of the temperature of the bidirectional thyristor; Holding means for holding the operation history of the DC voltage source; and The control means uses, as the state parameter, the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means and the operation history held by the holding means to control the output frequency of the control signal. The image forming apparatus according to any one of Items 1 to 9. (Item 11) Temperature + Operation history The apparatus further includes storage means for storing in advance the correspondence between the combination of the measured value or the estimated value of the temperature of the bidirectional thyristor and the operation history, and the output frequency of the control signal. The control means refers to the correspondence stored in the storage means to determine the output frequency of the control signal corresponding to the combination of the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means and the operation history held by the holding means. The image forming apparatus according to Item 10. The memory 22 and the table 800 function as storage means for storing in advance the correspondence between the combination of the temperature Tj of the bidirectional thyristor 202 and the operation history, and the output frequency N of the control signal. The CPU 15 may determine the output frequency N of the control signal corresponding to the combination of the temperature Tj of the bidirectional thyristor 202 and the operation history by referring to this correspondence. (Item 12) AC voltage + Operation history The acquisition means includes a measurement circuit for measuring the AC voltage supplied from the AC power source, holding means for holding the operation history of the DC voltage source, and The control means uses, as the state parameter, the AC voltage acquired by the measurement circuit and the operation history held by the holding means to control the output frequency of the control signal. The image forming apparatus according to any one of Items 1 to 11. As described in Example 4, the CPU 15 may control the output frequency N of the control signal using the AC voltage Vac and the operation history as state parameters. (Item 13) AC voltage + operation history It further has storage means for storing in advance the correspondence between the combination of the AC voltage and the operation history and the output frequency of the control signal. The control means determines the output frequency of the control signal corresponding to the combination of the AC voltage acquired by the measurement circuit and the operation history held by the holding means by referring to the correspondence stored in the storage means. The image forming apparatus according to item 12. As described in Example 4, the memory 22 may function as storage means for storing in advance the correspondence between the combination of the AC voltage Vac and the operation history and the output frequency N of the control signal. The CPU 15 may determine the output frequency N of the control signal corresponding to the combination of the AC voltage Vac and the operation history by referring to the correspondence stored in the memory 22. (Item 14) Temperature + AC voltage + operation history The acquisition means Means for acquiring the measured value or estimated value of the temperature of the bidirectional thyristor, A measurement circuit for measuring the AC voltage supplied from the AC power supply, Holding means for holding the operation history of the DC voltage source, And has The control means controls the output frequency of the control signal using, as the state parameters, the measured value or estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means, the AC voltage measured by the measurement circuit, and the operation history of the DC voltage source held by the holding means. The image forming apparatus according to any one of items 1 to 13. As described in Example 4, the CPU 15 may control the output frequency N of the control signal using, as state parameters, the temperature Tj of the bidirectional thyristor 202, the AC voltage Vac (e.g., maximum value), and the operation history. (Item 15) Temperature + AC voltage + operation history Further comprising storage means for storing in advance the correspondence between the measured value or the estimated value of the temperature of the bidirectional thyristor, the AC voltage, and the combination of the operation history and the number of times the control signal is output. The control means determines the number of times the control signal is output corresponding to the combination of the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means, the AC voltage measured by the measurement circuit, and the operation history held by the holding means by referring to the correspondence stored in the storage means. The image forming apparatus according to item 14. As described in the fourth embodiment, the memory 22 may function as storage means for storing in advance the correspondence between the combination of the temperature Tj of the bidirectional thyristor 202, the AC voltage Vac, and the operation history and the number of output times N. The CPU 15 may determine the number of output times N corresponding to the combination of the temperature Tj of the bidirectional thyristor 202, the AC voltage Vac, and the operation history by referring to the correspondence stored in the memory 22. (Item 16) Circuit configuration The DC voltage source A capacitor (e.g., C20) having one end connected to the first terminal (e.g., L pole) of the AC power source and the T1 terminal of the bidirectional thyristor, Connected between the other end of the capacitor and the second terminal of the AC power source, allowing an AC current from the AC power source to flow so that the capacitor is charged in the first half cycle of the AC voltage, and blocking the AC current so that the charging of the capacitor is stopped in the second half cycle of the AC voltage. A rectifying element (e.g., diode D22). The capacitor, the bidirectional thyristor, a discharge resistor (e.g., resistor R9) having one end connected to the gate terminal of the bidirectional thyristor, and a switch element (e.g., transistor Tr5) connected between the other end of the discharge resistor and the other end of the capacitor form a discharge path (e.g., current loop LP22) of the capacitor. The control means causes the DC voltage source to generate the control signal (e.g., the gate trigger current depending on the FSRD signal) by controlling the switching element to discharge the capacitor along the discharge path in the second half cycle, in the image forming apparatus according to any one of items 1 to 15. (Item 17) further comprising detection means (e.g., zero-cross detection circuit 220) for detecting a zero-cross of the AC voltage, The control means recognizes the first half cycle and the second half cycle based on the zero-cross detected by the detection means, in the image forming apparatus according to item 16. The CPU 15 may recognize the boundary (zero-cross) between two consecutive half cycles based on the detection signal output from the zero-cross detection circuit 220. (Item 18) The operation history includes information regarding the energization time of the image forming apparatus, in the image forming apparatus according to any one of items 1 to 17. As described above, the operation history may include any one of the integrated energization time of the image forming apparatus 100, the integrated operation time, the integrated drive time of the motor 21, and the integrated energization time of the capacitor C20. (Item 19) The operation history includes information regarding the number of printed sheets of the image forming apparatus, in the image forming apparatus according to any one of items 1 to 18. The number of printed sheets of the image forming apparatus 100 will also be useful for estimating the integrated energization time of the capacitor C20.

[0078] The invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, claims are attached to disclose the scope of the invention.

Explanation of Reference Numerals

[0079] 11…heater, 202…bidirectional thyristor, 15…CPU

Claims

1. heating means for applying heat to a toner image formed on a sheet to fix the toner image on the sheet; a bidirectional thyristor for controlling whether to supply power supplied from an AC power supply to the heating means; a DC voltage source for supplying a control signal to the gate terminal of the bidirectional thyristor; acquisition means for acquiring state parameters including at least one of the temperature of the bidirectional thyristor, the AC voltage supplied from the AC power supply, or the operation history of the DC voltage source; control means for controlling the number of output times of the control signal output from the DC voltage source to the gate terminal in a half cycle of the AC voltage according to the state parameters; An image forming apparatus having the above.

2. The acquisition means is configured to acquire a measured value or an estimated value of the temperature of the bidirectional thyristor, The control means controls the number of output times of the control signal using the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means as the state parameter. The image forming apparatus according to claim 1.

3. further comprising storage means for storing in advance the correspondence between the measured value or the estimated value of the temperature of the bidirectional thyristor and the number of output times of the control signal, The control means determines the number of output times of the control signal corresponding to the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means by referring to the correspondence stored in the storage means. The image forming apparatus according to claim 2.

4. The acquisition means has a measurement circuit for measuring the AC voltage supplied from the AC power supply, The control means controls the number of output times of the control signal according to the AC voltage measured by the measurement circuit as the state parameter. The image forming apparatus according to claim 1.

5. further comprising storage means for storing in advance the correspondence between the AC voltage and the number of output times of the control signal, The control means determines the number of output times of the control signal corresponding to the AC voltage acquired by the measurement circuit by referring to the correspondence stored in the storage means. The image forming apparatus according to claim 4.

6. The acquisition means has holding means for holding the operation history of the DC voltage source, The image forming apparatus according to claim 1, wherein the control means controls the number of output times of the control signal according to the operation history held by the holding means as the state parameter.

7. The apparatus further comprises storage means for storing in advance a correspondence relationship between the operation history of the DC voltage source and the number of output times of the control signal. The control means determines the number of output times of the control signal corresponding to the operation history of the DC voltage source held by the holding means by referring to the correspondence relationship stored in the storage means, according to claim 6 of the image forming apparatus.

8. The acquisition means includes means for acquiring a measured value or an estimated value of the temperature of the bidirectional thyristor, and a measurement circuit for measuring an AC voltage supplied from the AC power source. The image forming apparatus according to claim 1, wherein the control means controls the number of output times of the control signal by using, as the state parameter, the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means and the AC voltage measured by the measurement circuit.

9. The apparatus further comprises storage means for storing in advance a correspondence relationship between a combination of the measured value or the estimated value of the temperature of the bidirectional thyristor and the AC voltage, and the number of output times of the control signal. The control means determines the number of output times of the control signal corresponding to a combination of the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means and the AC voltage measured by the measurement circuit by referring to the correspondence relationship stored in the storage means, according to claim 8 of the image forming apparatus.

10. The acquisition means includes means for acquiring a measured value or an estimated value of the temperature of the bidirectional thyristor, and holding means for holding the operation history of the DC voltage source. The image forming apparatus according to claim 1, wherein the control means controls the number of output times of the control signal by using, as the state parameter, the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means and the operation history held by the holding means.

11. The apparatus further comprises storage means for storing in advance a correspondence relationship between a combination of the measured value or the estimated value of the temperature of the bidirectional thyristor and the operation history, and the number of output times of the control signal. ​ ​ The control means determines the number of output times of the control signal corresponding to the combination of the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means and the operation history held by the holding means by referring to the correspondence relationship stored in the storage means. The image forming apparatus according to claim 10.

12. The acquisition means A measurement circuit that measures the AC voltage supplied from the AC power supply, A holding means that holds the operation history of the DC voltage source, has, The control means controls the number of output times of the control signal by using, as the state parameter, the AC voltage acquired by the measurement circuit and the operation history held by the holding means. The image forming apparatus according to claim 1.

13. It further has a storage means for storing in advance the correspondence relationship between the combination of the AC voltage and the operation history and the number of output times of the control signal, The control means determines the number of output times of the control signal corresponding to the combination of the AC voltage acquired by the measurement circuit and the operation history held by the holding means by referring to the correspondence relationship stored in the storage means. The image forming apparatus according to claim 12.

14. The acquisition means Means for acquiring a measured value or an estimated value of the temperature of the bidirectional thyristor, A measurement circuit that measures the AC voltage supplied from the AC power supply, A holding means that holds the operation history of the DC voltage source, has, The control means controls the number of output times of the control signal by using, as the state parameter, the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means, the AC voltage measured by the measurement circuit, and the operation history of the DC voltage source held by the holding means. The image forming apparatus according to claim 1.

15. It further has a storage means for storing in advance the correspondence relationship between the combination of the measured value or the estimated value of the temperature of the bidirectional thyristor, the AC voltage, and the operation history and the number of output times of the control signal, The control means determines the number of output times of the control signal corresponding to a combination of the measured value or the estimated value of the temperature of the bidirectional thyristor acquired by the acquisition means, the AC voltage measured by the measurement circuit, and the operation history held by the holding means, by referring to the correspondence relationship stored in the storage means. The image forming apparatus according to claim 14.

16. The DC voltage source A capacitor having one end connected to the first terminal of the AC power supply and the T1 terminal of the bidirectional thyristor, Connected between the other end of the capacitor and the second terminal of the AC power supply, allowing an alternating current from the AC power supply to flow so that the capacitor is charged in the first half cycle of the AC voltage, and blocking the alternating current so that the charging of the capacitor is stopped in the second half cycle of the AC voltage. The image forming apparatus according to claim 1, further comprising a rectifying element. The capacitor, the bidirectional thyristor, a discharge resistor having one end connected to the gate terminal of the bidirectional thyristor, and a switching element connected between the other end of the discharge resistor and the other end of the capacitor form a discharge path for the capacitor. The control means generates the control signal in the DC voltage source by controlling the switching element to discharge the capacitor along the discharge path in the second half cycle. The image forming apparatus according to claim 1.

17. Further comprising detection means for detecting the zero cross of the AC voltage, The control means recognizes the first half cycle and the second half cycle based on the zero cross detected by the detection means. The image forming apparatus according to claim 16.

18. The operation history includes information regarding the energization time of the image forming apparatus. The image forming apparatus according to any one of claims 1 to 17.

19. The operation history includes information regarding the number of printed sheets of the image forming apparatus. The image forming apparatus according to any one of claims 1 to 17.

Images