Heater control device and image forming apparatus

Abstract

To provide a heater control unit that can switch to a current limiting resistor that can withstand input of a high voltage pulse during phase control of a heater, and can switch to a resistor that is easily disconnected in an abnormal condition during entire energization control of the heater.SOLUTION: A heater control unit D1 comprises: a triac Q2 that is connected in series between an AC power supply 32 and a heater 14; a phototriac coupler PTC1 that transmits a heater trigger signal to a gate electrode G of the triac Q2; resistors R13, R14 that are two resistors each connected in series with the phototriac coupler PTC1 and used for current limiting different in rated power and easiness of disconnection according to a phase controllable signal representing the period of phase control; and a resistor selection unit 36 that selects one resistor of the resistors R13, R14 being the two resistors and connects the selected resistor to a second main electrode T2 of the triac Q2.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a heater control device and an image forming apparatus. [Background technology]

[0002] A known conventional heater control device has a circuit configuration as shown in FIG. Conventionally, in heater control using a triac, a phototriac coupler PTC100 and a resistor R100 are connected in series between the gate terminal G and T2 terminal of the triac Q100 on a circuit board, as shown in Figure 12. When the triac is turned on, this resistor R100 serves to limit the current flowing through the phototriac coupler. Incidentally, if the terminals (G, T1, T2) of the triac Q100 are not connected to the wiring pattern on the circuit board and are left floating, an AC current will flow directly through the resistor R100 used to limit the current and the phototriac coupler PTC100, which may result in smoke or fire. Therefore, in order to prevent smoke and fire, it is already known to use a fuse resistor, which is prone to breaking immediately when an overvoltage / overcurrent is applied during abnormal operation, as resistor R100 to limit the current.

[0003] Patent Document 1 discloses a method in which a current limiting resistor is configured with two resistors having different disconnection characteristics in order to reduce the voltage applied to a fuse resistor. Specifically, Patent Document 1 reports a triac drive circuit having a triac connected between an AC power supply and a load, and a phototriac coupler that transmits signals to the triac, with the aim of minimizing damage to the phototriac coupler with an inexpensive configuration. In this triac drive circuit, the phototriac coupler, a first resistive element, and a second resistive element are connected in series to the gate terminal of the triac, and the first resistive element and the second resistive element have different susceptibilities to breakage.

[0004] In Patent Document 1, it is possible to prevent the fuse resistor from blowing out during normal operation, but the problem of instantaneous blowing during abnormal operation remains unresolved.

[0005] However, in conventional heater control devices using fuse resistors, there is a discrepancy in the time it takes for the triac to turn on after the phototriac coupler turns on. As shown in Figure 13, when phase control is performed in phase F100, a high-voltage pulse is suddenly applied. This can cause the fuse resistor to blow even during normal operation. Increasing the rated power of the fuse resistor to prevent this increases component costs and makes the fuse resistor less likely to blow during abnormal operation.

[0006] Therefore, there is a strong demand for a heater control device that can switch to a current-limiting resistor that can withstand high-voltage pulse input when controlling the heater phase, and can switch to a resistor that is prone to breakage in the event of an abnormality when controlling full current flow to the heater.

[0007] It is also desirable to provide a heater control device that can suppress the voltage peak occurring in the current limiting resistor during phase control. Summary of the Invention [Problem to be solved by the invention]

[0008] One embodiment of the present invention has been made in view of the above, and its purpose is to provide a heater control device that can switch to a current-limiting resistor that can withstand high-voltage pulse input when controlling the phase of the heater, and can switch to a resistor that is prone to breakage in the event of an abnormality when controlling full current flow to the heater. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention of claim 1 is characterized by comprising: a triac connected in series between an AC power supply and a heater; a phototriac coupler that transmits a heater trigger signal to the gate electrode of the triac; two resistors that are connected in series to the phototriac coupler and are used for current limiting and have different rated powers and breakage susceptibility depending on a phase controllable signal that indicates the phase control period; and a resistor selection unit that selects one of the two resistors and connects the selected resistor to a second main electrode of the triac. [Effects of the Invention]

[0010] According to the present invention, a heater control device can be provided that can switch to a current-limiting resistor that can withstand high-voltage pulse input when controlling the phase of the heater, and can switch to a resistor that is prone to breakage in the event of an abnormality when controlling full current flow to the heater. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating a printer as an example of an image forming apparatus incorporating a heater control device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a circuit diagram showing an example of a system control unit included in the heater control device according to the embodiment of the present invention. [Figure 3] FIG. 2 is a circuit diagram showing an example of a zero-cross detection unit provided in the heater control device according to the embodiment of the present invention. [Figure 4] 1 is a circuit diagram including a functional configuration showing an example of a heater control device according to a first embodiment of the present invention. [Figure 5] 4 is a timing chart showing the operation of the heater control device according to the first embodiment of the present invention. [Figure 6] FIG. 6 is a circuit diagram including a functional configuration showing an example of a heater control device according to a second embodiment of the present invention. [Figure 7] 6 is a timing chart showing the operation of a heater control device according to a second embodiment of the present invention. [Figure 8]FIG. 10 is a circuit diagram including a functional configuration showing an example of a heater control device according to a third embodiment of the present invention. [Figure 9] 10 is a timing chart showing the operation of a heater control device according to a third embodiment of the present invention. [Figure 10] FIG. 10 is a circuit diagram including a functional configuration showing an example of a heater control device according to a fourth embodiment of the present invention. [Figure 11] 10 is a timing chart showing the operation of a heater control device according to a fourth embodiment of the present invention. [Figure 12] FIG. 1 is a circuit diagram including a functional configuration showing an example of a heater control device according to a conventional technique. [Figure 13] 1 is a timing chart showing the operation of a heater control device according to the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below with reference to the embodiments shown in the drawings. The present invention has the following configuration to switch to a current-limiting resistor that can withstand high-voltage pulse input during phase control of the heater, and to switch to a resistor that is prone to breakage in the event of an abnormality during full-power control of the heater. That is, the heater control device of the present invention is characterized by comprising: a triac connected in series between an AC power supply and a heater; a phototriac coupler that transmits a heater trigger signal to the gate electrode of the triac; two resistors that are connected in series to the phototriac coupler and are used for current limiting and have different rated powers and susceptibility to breakage depending on a phase controllable signal that indicates the phase control period; and a resistor selection unit that selects one of the two resistors and connects the selected resistor to the second main electrode of the triac. With the above configuration, when the heater is under phase control, the resistor can be switched to a current limiting resistor that can withstand high voltage pulse input, and when the heater is under full current control, the resistor can be switched to a resistor that is prone to breakage in the event of an abnormality. The features of the present invention described above will be explained in detail with reference to the following drawings. However, unless otherwise specified, the components, types, combinations, shapes, relative arrangements, etc. described in the embodiments are merely illustrative examples and do not limit the scope of the present invention. The above-mentioned features of the present invention will be described in detail below with reference to the drawings.

[0013] <Image forming device> Fig. 1 is a schematic diagram showing a printer as an example of an image forming apparatus incorporating a heater control device according to an embodiment of the present invention. The image forming apparatus shown in Fig. 1 is an image forming apparatus that forms a toner image on recording paper using an electrostatic photographic method.

[0014] Recording paper supplied from the paper feed tray 2 or multi-tray 4 is transported by a series of transport rollers to the toner image forming unit 6. In the toner image forming unit 6, an electrostatic latent image is formed on the photosensitive drum 8. The electrostatic latent image is developed with toner into a toner image, and the toner image is transferred onto the recording paper.

[0015] The recording paper with the toner image transferred thereon is transported to a fixing device 9. The fixing device 9 has a fixing roller 10 and a pressure roller 12. A heater 14 is built into the fixing roller 10, which heats the fixing roller to a predetermined temperature. As the recording paper passes between the fixing roller 10 and the pressure roller 12, the toner image transferred to the recording paper is heated by the fixing roller 10 and pressed by the pressure roller 12, thereby being fixed onto the recording paper. After the toner image has been fixed, the recording paper is ejected from the top or front side of the image forming apparatus 1 by a series of rollers.

[0016] In the image forming apparatus 1 configured as described above, a heater control device according to the present invention is used to control the energization of the heater 14 incorporated in the fixing roller 10. A control unit 34 (FIG. 4) that controls the energization of the heater 14 using the heater control method according to the present invention is provided on a control board 16 made of a printed circuit board provided inside the main body of the image forming apparatus 1.

[0017] The heater 14 of the image forming apparatus 1 requires a relatively large amount of power to rapidly heat the fixing roller 10. When the image forming apparatus 1 is powered on, the internal electronic components and motors are started, resulting in a large amount of power consumption. Therefore, if a large amount of power is supplied to the heater 14 in a short period of time, the power supply voltage may fluctuate, potentially affecting electrical equipment around the image forming apparatus 1. Therefore, the power supply to the heater is typically controlled using a soft start method to gradually increase the voltage supplied to the heater.

[0018] <System Control Unit> FIG. 2 is a circuit diagram showing an example of a system control unit included in the heater control device according to the embodiment of the present invention. The system control unit includes a CPU 21, a ROM 22, a timer 23, a RAM 24, various input / output circuits I / O 25, a nonvolatile memory (NVRAM) 26, and the like, all of which are connected to one another via a system bus. The CPU 21 controls the power supply to the heater 14 by phase-controlling the triac Q2 (FIG. 4) on the control board 16 using a heater trigger signal, using a control program and parameters stored in the ROM 22. The CPU 21 also has the function of controlling the entire image forming apparatus, including sequence control of the photosensitive member and its surrounding components such as charging, exposure, development, and transfer, and transfer paper transport control. Here, the function of the CPU 21 as a control unit related to the control of the heater 14 will be described. The timer 23 includes a plurality of counters that count clock signals. If the counters are, for example, 16-bit counters, they can count up to a maximum of 65,536, and divide the clock signals to adjust the count cycle.

[0019] <Zero-cross detection section> FIG. 3 is a circuit diagram showing an example of a zero-cross detection unit provided in the heater control device according to the embodiment of the present invention. The heater control device includes a power supply unit, and the power supply unit is further provided with a zero-cross detection unit 30. As shown in Figure 3, the zero-crossing detector 30 full-wave rectifies AC power 32 supplied from a commercial power source in a diode bridge BR1 via a circuit consisting of resistors R1 and R2, which function as a low-pass filter and current limiter, and a capacitor C1. The full-wave rectified pulsating current signal is transmitted in isolation through a photocoupler PC1, which is composed of a light-emitting diode (LED) and a phototransistor (PT), and is input to a hysteresis inverter IC1, which generates a heater trigger signal (zero-crossing signal). Resistors R3 and R4 are pull-up resistors for applying a positive voltage. The heater trigger signal detected (generated) by the zero-cross detection unit 30 is supplied to, for example, the gate terminal of the transistor Q1 shown in FIG. 4, and its waveform is a square wave as shown in FIG.

[0020] First Embodiment <Heater control device> FIG. 4 is a circuit diagram including a functional configuration showing an example of a heater control device D1 according to the first embodiment of the present invention. The heater control device D1 includes a triac Q2, a phototriac coupler PTC1, resistors R13 and R14, a resistor selection unit 36, and a transistor Q1. The triac Q2 is connected in series between the AC power supply 32 and the heater 14. The phototriac coupler PTC1 transmits a heater trigger signal to the gate electrode G of the triac Q2. Resistors R13 and R14 are connected in series to the phototriac coupler PTC1 and are used for current limiting with different rated power and susceptibility to breakage depending on the phase controllable signal that indicates the phase control period. The resistor selection unit 36 ​​selects one of the two resistors R13 and R14, and connects the selected resistor to the second main electrode T2 of the triac Q2.

[0021] The heater control device D1 includes two resistors: a resistor R13 connected in series with the phototriac coupler PTC1, and a resistor R14 connected in series with the phototriac coupler PTC1, which has a different rated power and susceptibility to breakage than the resistor R13. The resistor selection section 36 includes a switch circuit SW1 that selects and connects either the resistor R13 or the resistor R14.

[0022] The heater control device D1 includes a control unit . The control unit 34 generates a phase controllable signal that indicates the period of the phase control. The resistor selection section 36 selects a resistor in response to a phase controllable signal supplied from the control section 34 .

[0023] The image forming apparatus 1 includes a heater control device D1 and a fixing device 9 incorporating a heater 14 controlled by the heater control device D1.

[0024] In FIG. 4, a commercial AC power supply (AC power supply) 32 and a heater 14 are connected via terminals T1 and T2 of a triac Q2. The power supplied to the heater 14 is controlled by turning on / off the triac Q2. When the light-emitting diode in the phototriac coupler PTC1, which ensures electrical insulation between the primary and secondary, is energized, the triac Q2 turns on. The resistor R11 is a resistive element for limiting the current of the light-emitting diode in the phototriac coupler PTC1. The transistor Q1 turns on / off the phototriac coupler PTC1 in accordance with the heater trigger signal. That is, the gate terminal of the transistor Q1 is connected to the zero-crossing detector 30, and the transistor Q1 operates in accordance with the heater trigger signal output from the zero-crossing detector 30. Resistor R12, resistor R13, and resistor R14 connected to phototriac coupler PTC1 each function as a bias resistor for driving triac Q2.

[0025] The resistor selection unit 36 ​​selects one of the two resistors R13 and R14, and connects the selected resistor to the second main electrode T2 of the triac Q2. The resistor selection section 36 includes a switch circuit SW1. One end of the resistor R13 and one end of the resistor R14 are commonly connected to one end of the phototriac coupler PTC1, the other end of the resistor R13 is connected to a first contact a of the switch circuit SW1, and the other end of the resistor R14 is connected to a second contact b of the switch circuit SW1. A phase controllable signal is supplied to the control terminal c of the switch circuit SW1 from the control unit 34, and when the phase controllable signal is in a high state (a voltage value of approximately Vcc), the first contact a of the switch circuit SW1 is selected, and the other end of the resistor R13 is connected via the output terminal d of the switch circuit SW1 to the second main electrode T2 of the triac Q2 and the heater 14. On the other hand, when the phase controllable signal is in a low state (a voltage value of approximately the ground on the control board 16), the second contact b of the switch circuit SW1 is selected, and the other end of the resistor R14 is connected via the output terminal d of the switch circuit SW1 to the second main electrode T2 of the triac Q2 and the heater 14.

[0026] When performing phase control on the heater 14, the resistor selection unit 36 ​​selects the resistor R13 (first resistor) by the switch circuit SW1 and connects the resistor R13 (first resistor) in series with the phototriac coupler PTC1. On the other hand, when performing full power supply control for the heater 14, the resistor selection unit 36 ​​selects the resistor R14 (second resistor) using the switch circuit SW1 and connects the resistor R14 (second resistor) in series with the second main electrode T2 of the triac Q2.

[0027] 4, transistor (FET) Q1 turns on / off depending on the voltage level of the heater trigger signal supplied from zero-cross detection unit 30, thereby energizing / de-energizing the photodiode of phototriac coupler PTC1 from Vcc. That is, when the heater trigger signal is at a high level, the photodiode of phototriac coupler PTC1 is energized and emits light, while when the heater trigger signal is at a low level, the photodiode of phototriac coupler PTC1 is de-energized and extinguished. The heater control device D1 shown in FIG. 4 is characterized in that, during phase control, a current limiting resistor (resistor R13) to be connected to the second main electrode T2 of the triac Q2 is selected in accordance with a phase controllable signal supplied from the control unit 34. For example, during phase control, the phase control signal is high and the switch circuit SW1 selects resistor R13, whereas during full conduction control, the phase control signal is low and the switch circuit SW1 selects resistor R14.

[0028] <Regarding resistors R13 and R14> Here, resistor R13 is a resistor that can withstand the input of a high voltage pulse (for example, a metal oxide film resistor), while resistor R14 is a fuse resistor that is prone to breaking in the event of an abnormality such as an overcurrent. The fuse resistor is a resistor that normally functions as a resistive element and, in the event of an abnormality, safely melts down the resistor to cut off the circuit current. When the heater 14 is fully energized, the voltage applied to resistor R14 increases slowly at the slope of the input AC voltage. Therefore, triac Q2 turns on before the voltage reaches a high level, preventing the voltage applied to resistor R14 from becoming too high. This allows a fuse resistor with a low rated power to be used as a resistor that is prone to breaking. In the event of an abnormality such as an overcurrent, the same voltage as during full-energization control is applied to resistor R14, so a fuse resistor with a low rated power will easily break.

[0029] On the other hand, metal oxide film resistors have a much higher pulse resistance than fuse resistors at the same rated power, and their component costs are significantly lower than fuse resistors.Moreover, metal oxide film resistors can maintain (withstand) a conductive state without breaking even when a high-voltage pulse is input at a low rated power. For example, in design, resistor R13 may be a metal oxide film resistor with a rated power of 0.1 W. On the other hand, a fuse resistor with a rated power of 0.25W can be used as resistor R14.

[0030] <Operation timing> FIG. 5 is a timing chart showing the operation of the heater control device D1 according to the first embodiment of the present invention. FIG. 5 shows an example in which the phase controllable signal is in a high state during phase control and in a low state otherwise (for example, during full power control). Hereinafter, the operation of the heater control device D1 shown in FIG. 4 will be described with reference to the timing chart shown in FIG. For example, at times t1 and t2, when the heater trigger signal switches from a low state to a high state, the triac Q2 turns on and becomes conductive until the AC voltage of the AC power supply 32 reaches 0 V, and the heater drive signal i1 flows to the heater 14. During phase control, triac Q2 is turned on at any phase of the AC voltage from t0 to t6, and conducts until the AC voltage reaches 0V. During phase control, the voltage rises rapidly from 0V to the AC voltage at that point. When phototriac coupler PTC1 turns on, current i2 also increases rapidly in line with this sudden increase in voltage until triac Q2 turns on. On the other hand, during full-power control, triac Q2 is turned on at times t6 to t9 when the AC voltage of AC power supply 32 reaches 0 V. During full-power control, the voltage rises slowly in line with the AC voltage, so even if there is a time lag between when phototriac coupler PTC1 turns on and when triac Q2 turns on, current i2 does not increase suddenly.

[0031] Second Embodiment FIG. 6 is a circuit diagram including a functional configuration showing an example of a heater control device D2 according to a second embodiment of the present invention. The heater control device D2 includes two resistors: a resistor R13 connected in series with the phototriac coupler PTC1, and a resistor R14 connected in series with the phototriac coupler PTC1, which has a different rated power and susceptibility to breakage than the resistor R13. The resistor selection unit 36a includes a photocoupler PC3 connected in series with a resistor R13, and a photocoupler PC4 connected in series with a resistor R14. When performing phase control on the heater 14, i.e., when the phase controllable signal is in a high state, the resistor selection unit 36a turns on the photocoupler PC3 and connects the resistor R13 and the second main electrode T2 of the triac Q2 in series with the phototriac coupler PTC1. On the other hand, when full current control is performed on the heater 14, that is, when the phase controllable signal is in a low state, the resistor selection unit 36a turns on the photocoupler PC4 and connects the resistor R14 and the second main electrode T2 of the triac Q2 in series with the phototriac coupler PTC1.

[0032] The heater control device D2 includes a control unit . The control unit 34 generates a phase controllable signal that indicates the period of the phase control. The resistor selection unit 36a selects a resistor in response to a phase controllable signal supplied from the control unit 34.

[0033] The image forming apparatus 1 includes a heater control device D2 and a fixing device 9 incorporating a heater 14 controlled by the heater control device D2.

[0034] In the second embodiment, two sets of resistors and photocouplers connected in series are provided as the resistor selection unit 36a. That is, a photocoupler PC1 is provided which operates when the phase controllable signal is in a high state (approximately the voltage value of Vcc) during phase control, and a photocoupler PC2 is provided which operates when the phase controllable signal is in a low state (approximately the voltage value of ground on the control board 16) during full power control, and the path and resistance value during phase control are changed.

[0035] The resistor R11 is a resistive element for limiting the current of the light-emitting diode provided in the phototriac coupler PTC1. The gate terminal of the transistor Q5 receives a heater trigger signal output from the zero-cross detection unit 30. The transistor Q5 turns the phototriac coupler PTC1 on and off in accordance with the heater trigger signal. The phase controllable signal output from the control unit 34 is connected to the light emitting diode of the photocoupler PC3 and further to GND via a resistor R15. The collector of the phototransistor of the photocoupler PC3 is connected to the phototriac coupler PTC1 via a resistor R13, and the emitter is connected to the heater 14. The phase controllable signal output from the control unit 34 is connected to the light emitting diode of the photocoupler PC4 via an inverter INV1 and is further connected to GND via a resistor R16. The collector of the phototransistor of the photocoupler PC4 is connected to the phototriac coupler PTC4 via a resistor R14, and the emitter is connected to the heater 14.

[0036] <Operation timing> FIG. 7 is a timing chart showing the operation of the heater control device D2 according to the second embodiment of the present invention. <During phase control> When the phase controllable signal output from the control unit 34 is in a high state, the light emitting diode of the photocoupler PC3 is grounded to GND via resistor R15, and the light emitting diode emits light, turning on the phototransistor of the photocoupler PC3. When the phototransistor turns on, R13 is connected to the heater 14 via the collector and emitter of the phototransistor. At this time, the heater trigger signal output from the zero-cross detector 30 turns the transistor Q5 on and off. During phase control, the phototransistor of photocoupler PC3 is turned on and the path of resistor R13 is used. As mentioned above, resistor R13 can be a resistor that can withstand the input of a high voltage pulse (for example, a metal oxide film resistor).

[0037] <During full power control> When the phase control signal output from the control unit 34 is in the low state, the output of the inverter INV1 goes to the high state, and the light-emitting diode of the photocoupler PC4 is grounded to GND via the resistor R16, causing the light-emitting diode to emit light, turning on the phototransistor of the photocoupler PC4. When the phototransistor turns on, the resistor R14 is connected to the heater 14 via the collector and emitter of the phototransistor. At this time, the heater trigger signal output from the zero-cross detector 30 turns the transistor Q5 on and off. During full-power control, the phototransistor of photocoupler PC4 is turned on and the path of resistor R14 is used. As mentioned above, resistor R14 can be a fuse resistor or the like that is prone to breaking in the event of an abnormality such as an overcurrent.

[0038] <Third embodiment> FIG. 8 is a circuit diagram including a functional configuration showing an example of a heater control device D3 according to a third embodiment of the present invention. The heater control device D3 includes a triac Q2, a phototriac coupler PTC2, a resistor R21, a phototriac coupler PTC3, a resistor R22, and a selection driver . The resistor R11 is a resistive element for limiting the current of each light-emitting diode provided in the phototriac coupler PTC2 and the phototriac coupler PTC3.

[0039] The triac Q2 is connected in series between the AC power supply 32 and the heater 14. The phototriac coupler PTC2 transmits a heater trigger signal to the gate electrode G of the triac Q2. Resistor R21 is used to limit current and is connected in series between the second main electrode T2 of triac Q2 and phototriac coupler PTC2. The phototriac coupler PTC3 transmits a heater trigger signal to the gate electrode G of the triac Q2. Resistor R22 is connected in series between the second main electrode T2 of triac Q2 and phototriac coupler PTC3, and is used for current limiting, having a different rated power and susceptibility to breakage from resistor R21. The selection driver 38 selects and drives one of the phototriac couplers PTC2 and PTC3.

[0040] The phototriac coupler PTC2 is turned on and off by the transistor Q3. The transistor Q3 turns the phototriac coupler PTC2 on and off in accordance with a signal input to its gate terminal. In the selection driver 38, the gate terminal of the transistor Q3 is connected to the output terminal of an AND gate G1, one input terminal of which is connected to the heater trigger signal of the zero-cross detector 30. The other input terminal of the AND gate G1 is connected to the phase controllable signal of the controller 34.

[0041] On the other hand, the transistor Q4 turns the phototriac coupler PTC3 on and off in accordance with a signal input to the gate terminal. In the selective drive unit 38, the gate terminal of the transistor Q4 is connected to the output terminal of an AND gate G2, one input terminal of which is connected to the heater trigger signal of the zero-cross detection unit 30. The other input terminal of the AND gate G2 is connected to the phase controllable signal of the control unit 34 via an inverter INV2.

[0042] When performing phase control on the heater 14, the selective drive unit 38 turns on the phototriac coupler PTC2 and connects a resistor R21 in series with the phototriac coupler PTC2.

[0043] The image forming apparatus 1 includes a heater control device D3 and a fixing device 9 incorporating a heater 14 controlled by the heater control device D3.

[0044] The third embodiment is characterized by the provision of two sets of phototriac couplers and resistors. That is, a logic circuit is provided that can handle combinations of the level states (logical values) of the heater trigger signal and the level states (logical values) of the phase controllable signal, and the path and resistance value during phase control can be changed.

[0045] <Operation timing> FIG. 9 is a timing chart showing the operation of the heater control device D3 according to the third embodiment of the present invention. <During phase control> When the phase controllable signal of the control unit 34 is in a high state, the other input terminal of the AND gate G1 is in a high state, and therefore the heater trigger signal output from the zero-cross detection unit 30 turns the transistor Q3 on / off via the AND gate G1. During phase control, the phototriac coupler PTC2 is turned on / off, and the path through resistor R21, which can withstand high-voltage pulse input, is made conductive.

[0046] <During full power control> When the phase controllable signal of the control unit 34 is in a low state, the output of the inverter INV2 becomes a high state, and the other input terminal of the AND gate G2 becomes a high state, so that the heater trigger signal output from the zero-cross detection unit 30 turns the transistor Q4 on / off via the AND gate G2. During full current control, the phototriac coupler PTC3 is turned on / off, and the path of resistor R22, which uses a fuse resistor that is prone to breaking in the event of an abnormality such as an overcurrent, is made conductive.

[0047] <Fourth embodiment> FIG. 10 is a circuit diagram including a functional configuration showing an example of a heater control device D4 according to a fourth embodiment of the present invention. In Patent Document 1, two fuse resistors are connected in series to a phototriac coupler, and are further connected to the second main electrode of the triac, thereby reducing the voltage applied to the fuse resistors. In contrast to this, the heater control device D4 according to the fourth embodiment includes a triac Q2, a phototriac coupler PTC5, resistors R24 and R25, and a voltage peak value suppression circuit 40. The triac Q2 is connected in series between the AC power supply 32 and the heater 14. The phototriac coupler PTC5 transmits a heater trigger signal to the gate electrode G of the triac Q2. Resistors R24 and R25 are two resistors connected in series between the phototriac coupler PTC5 and the second main electrode T2 of the triac Q2. The voltage peak value suppression circuit 40 suppresses the voltage peak occurring at the connection point 39 of the two resistors R24 and R25 in response to a phase controllable signal that indicates the period of phase control.

[0048] The voltage peak value suppression circuit 40 includes a capacitor C2 and a photocoupler PC5. One end of the capacitor C2 is connected to a junction 39 between two resistors, resistor R24 ​​and resistor R25. The photocoupler PC5 is connected to the other end of the capacitor C2. When performing phase control on the heater 14, the voltage peak value suppression circuit 40 turns on the transistor of the photocoupler PTC5 and grounds the capacitor C2 connected to the connection point 39, thereby forming a low-pass filter circuit.

[0049] The image forming apparatus 1 includes a heater control device D4 and a fixing device 9 incorporating a heater 14 controlled by the heater control device D4.

[0050] Furthermore, the voltage peak value suppression circuit 40 suppresses the voltage peaks occurring across the resistors R24 and R25 in accordance with the phase control signal indicating the period of phase control.

[0051] The voltage peak value suppression circuit 40 includes a capacitor C2 connected to a connection point 39 between two resistors, resistors R24 and R25, and a photocoupler PC5 connected to the capacitor C2. When phase control is performed on the heater 14, the photocoupler PTC5 is turned on and the capacitor C2 connected to the connection point 39 is grounded, thereby forming a low-pass filter circuit. The voltage peak value suppression circuit 40 is characterized in that it suppresses the rise of the voltage applied to the resistor during phase control in response to a phase controllable signal supplied from the control unit 34. During phase control, for example, a low-pass filter circuit is configured to make the rise of the voltage applied to the resistor gentler when the triac Q2 is turned on.

[0052] One end of a capacitor C2 is connected to a connection point 39 between resistors R24 (first resistor) and R25 (second resistor) connected in series, and in the voltage peak value suppression circuit 40 shown in FIG. 10, the other end of the capacitor C2 is grounded during phase control in response to a phase controllable signal supplied from the control unit 34. This allows the resistor R24 ​​(first resistor) and capacitor C2 to form a low-pass filter circuit, and the voltage applied to the connection point 39 between the resistor R24 ​​(first resistor) and the resistor R25 (second resistor) can be reduced (the rise can be made gentler) at the time when the triac is turned on (t31 in Figure 11).

[0053] <Operation timing> FIG. 11 is a timing chart showing the operation of the heater control device D4 according to the fourth embodiment of the present invention. The timing chart shown in FIG. 11 shows, from top to bottom, (1) heater drive signal i1, (2) current i2 that flows through the current limiting resistor (resistor R100) during phase control in the prior art, and (3) current i2 that flows through the current limiting resistors (resistors R24 and R25) after passing through the voltage peak value suppression circuit 40. * is shown.

[0054] As shown in FIG. 11, at times t30 and t31, when the heater drive signal i1 switches from a low state to a high state, the triac Q2 turns on and becomes conductive until the AC voltage of the AC power supply 32 reaches 0 V, and the heater drive signal i1 flows to the heater 14.

[0055] Between timings t30 and t31, the time until the phototriac coupler PTC5 turns on is assumed to be short, for example, about 1 usec. Also, assume that the time it takes for the triac Q2 to turn on is slow, for example, about 10 usec.

[0056] At timings t31 and t32, the peak value of the current i2 flowing through the current limiting resistor R100 during phase control in the prior art (FIG. 12) is compared with the current i2 after passing through the voltage peak value suppression circuit 40 of the present invention. * The peak value can be reduced to approximately 1 / 3 to 1 / 2. By adopting the voltage peak value suppression circuit 40 of the present invention, it is possible to use a fuse resistor with a lower rated power than when two resistors are connected in series as in the configuration of Patent Document 1. Because the rated power is low, it is also easier for the resistor to break in the event of an abnormality.

[0057] <Summary of the functions and effects of the exemplary embodiment> <First aspect> The heater control device D1 of this embodiment is characterized by including: a triac Q2 connected in series between an AC power supply 32 and a heater 14; a phototriac coupler PTC1 that transmits a heater trigger signal to a gate electrode G of the triac Q2; two resistors R13 and R14 that are connected in series with the phototriac coupler PTC1 and are used for current limiting and have different rated powers and susceptibility to breakage in response to a phase controllable signal that indicates the phase control period; and a resistor selection unit 36 ​​that selects one of the two resistors R13 and R14 and connects the selected resistor to a second main electrode T2 of the triac Q2. According to this aspect, the resistor selection section 36 can select one of the two resistors R13 and R14 and connect the selected resistor to the second main electrode T2 of the triac Q2. This makes it possible to provide a heater control device that can switch to a current-limiting resistor (resistor R13) that can withstand high-voltage pulse input when controlling the heater phase, and can switch to resistor R14, which is prone to breaking in the event of an abnormality, when controlling the heater to full power.

[0058] <Second mode> In the heater control device D1 according to the first aspect, the two resistors include a resistor R13 (first resistor) connected in series with the phototriac coupler PTC1, and a resistor R14 (second resistor) connected in series with the phototriac coupler PTC1 and having a rated power and susceptibility to breakage different from those of the resistor R13 (first resistor), and the resistor selection unit 36 ​​includes a switch circuit SW1 that selects and connects either the resistor R13 (first resistor) or the resistor R14 (second resistor). According to this embodiment, when performing phase control on the heater 14, the resistor selection unit 36 ​​can select the resistor R13 (first resistor) using the switch circuit SW1 and connect the resistor R13 (first resistor) in series with the phototriac coupler PTC1. This makes it possible to provide a heater control device that can switch to a current-limiting resistor (resistor R13) that can withstand high-voltage pulse input when controlling the heater phase, and can switch to resistor R14, which is prone to breaking in the event of an abnormality, when controlling the heater to full power.

[0059] <Third aspect> In the heater control device D2 according to the first aspect, the two resistors include a resistor R13 (first resistor) connected in series with the phototriac coupler PTC1, and a resistor R14 (second resistor) connected in series with the phototriac coupler PTC1 and having a rated power and a susceptibility to breakage different from those of the resistor R13 (first resistor), and the resistor selection unit 36a selects a photocoupler PC3 (first photocoupler) connected in series with the resistor R13 (first resistor) and a resistor R14 (second resistor) connected in series with the resistor R14 (second resistor). The resistor selection unit 36a is characterized in that it has a photocoupler PC3 connected to it, and a photocoupler PC4 (second photocoupler) connected to it, and when performing phase control on the heater 14, it turns on the photocoupler PC3 and connects a resistor R13 (first resistor) in series with the phototriac coupler PTC1, and when performing full current control on the heater 14, it turns on the photocoupler PC4 (second photocoupler) and connects a resistor R14 (second resistor) in series with the phototriac coupler PTC1. According to this aspect, when performing phase control on the heater 14, the resistor selection unit 36a can turn on the photocoupler PC3 and connect the resistor R13 (first resistor) in series with the phototriac coupler PTC1, while when performing full current control on the heater 14, the resistor selection unit 36a can turn on the photocoupler PC4 and connect the resistor R14 (second resistor) in series with the phototriac coupler PTC1. This makes it possible to provide a heater control device that can switch to a current-limiting resistor (resistor R13) that can withstand high-voltage pulse input when controlling the heater phase, and can switch to resistor R14, which is prone to breaking in the event of an abnormality, when controlling the heater to full power.

[0060] <Fourth aspect> The heater control device according to any one of the first to third aspects includes a control unit 34 that generates a phase controllable signal that indicates a period of phase control, and a resistor selection unit 36 ​​that selects a resistor in accordance with the phase controllable signal supplied from the control unit 34. According to this aspect, the resistor selection section 36 can select a resistor in accordance with the phase controllable signal supplied from the control section 34. This makes it possible to provide a heater control device that can switch to a current-limiting resistor that can withstand high-voltage pulse input when controlling the heater phase, and can switch to a resistor that is more likely to break in the event of an abnormality when controlling full current flow to the heater.

[0061] <Fifth aspect> The heater control device D3 of this embodiment is characterized by comprising: a triac Q2 connected in series between the AC power supply 32 and the heater 14; a phototriac coupler PTC2 (first phototriac coupler) that transmits a heater trigger signal to the gate electrode G of the triac Q2; a resistor R21 (first resistor) used for current limiting that is connected in series between the second main electrode T2 of the triac Q2 and the phototriac coupler PTC2; a phototriac coupler PTC3 (second phototriac coupler) that transmits the heater trigger signal to the gate electrode G of the triac Q2; a resistor R22 (second resistor) used for current limiting that is connected in series between the second main electrode T2 of the triac Q2 and the phototriac coupler PTC3 and has a rated power and a susceptibility to breakage different from those of the resistor R21 (first resistor); and a selection drive unit 38 that selects and drives either the phototriac coupler PTC2 (first phototriac coupler) or the phototriac coupler PTC3. According to this embodiment, the selective drive unit 38 can select and drive either the phototriac coupler PTC2 or the phototriac coupler PTC3, so that one of the resistor R21 (first resistor) and the second resistor R22 can be connected in series with the phototriac coupler. This makes it possible to provide a heater control device that can switch to a current-limiting resistor (resistor R21) that can withstand high-voltage pulse input when controlling the heater phase, and can switch to resistor R22 that is prone to breaking in the event of an abnormality when controlling full current to the heater.

[0062] <Sixth aspect> In the heater control device D3 of the fifth aspect, when performing phase control on the heater 14, the selective drive unit 38 turns on the phototriac coupler PTC2 (first phototriac coupler) and connects a resistor R21 (first resistor) in series with the phototriac coupler PTC2. According to this aspect, when performing phase control on the heater 14, the selective drive unit 38 can turn on the phototriac coupler PTC2 and connect the resistor R21 (first resistor) in series with the phototriac coupler PTC2. This makes it possible to provide a heater control device that can switch to a current-limiting resistor (resistor R21) that can withstand high-voltage pulse input when controlling the heater phase, and can switch to resistor R22 that is prone to breaking in the event of an abnormality when controlling full current to the heater.

[0063] <Seventh aspect> The heater control device D4 of this embodiment is characterized by comprising: a triac Q2 connected in series between the AC power supply 32 and the heater 14; a phototriac coupler PTC5 that transmits a heater trigger signal to the gate electrode G of the triac Q2; two resistors R24 and R25 connected in series between the second main electrode T2 of the triac Q2 and the phototriac coupler PTC5; and a voltage peak value suppression circuit 40 that suppresses the voltage peak generated at a connection point 39 between the two resistors R24 and R25 in response to a phase controllable signal that indicates the phase control period. According to this aspect, the voltage peak value suppression circuit 40 can suppress the voltage peak occurring at the connection point 39 between the resistors R24 and R25 in accordance with the phase controllable signal indicating the period of phase control. This makes it possible to suppress the voltage peak occurring at the connection point 39 between the resistor R24 ​​and the second resistor R25, thereby suppressing a sudden increase in voltage or current during phase control, and even if fuse resistors that are prone to blow in the event of an abnormality are used for the resistors R24 and R25, they can be prevented from blowing during normal operation. That is, it is possible to suppress the peak of the voltage generated in the current limiting resistor (resistors R24 and R25) formed by the resistor R24 ​​and the second resistor R25 in response to the phase controllable signal.

[0064] <Eighth aspect> The voltage peak value suppression circuit 40 of the heater control device D4 according to the seventh aspect includes a capacitor C2 connected to a connection point 39 between two resistors, resistors R24 and R25, and a photocoupler PC5 connected to the capacitor C2. When performing phase control on the heater 14, the photocoupler PTC5 is turned on and the capacitor C2 connected to the connection point 39 is grounded, thereby forming a low-pass filter circuit. According to this embodiment, when performing phase control on the heater 14, a low-pass filter circuit can be formed by turning on the photocoupler PTC5 and grounding the capacitor C2 connected to the connection point 39 between the resistors R24 and R25. This allows a low-pass filter circuit to be configured when performing phase control on the heater 14, so that a sudden increase in voltage or current during phase control can be suppressed with a simple circuit including resistors and capacitors.

[0065] <Ninth aspect> The image forming apparatus 1 of this embodiment is characterized by including the heater control device according to any one of the first to eighth embodiments, and a fixing device 9 incorporating a heater controlled by the heater control device. According to this aspect, it is possible to provide an image forming apparatus 1 that includes a heater control device described in any one of the first to eighth aspects and a fixing device 9 that incorporates a heater controlled by the heater control device. [Explanation of symbols]

[0066] 1...image forming apparatus, 2...paper feed tray, 4...multi-tray, 6...toner image forming section, 7...zero cross detection section, 8...photosensitive drum, 9...fixing device, 10...fixing roller, 12...pressure roller, 14...heater, 16...control board, 21...CPU, 22...ROM, 23...timer, 24...RAM, 30...zero cross detection section, 32...AC power supply, 34...control section, 36...resistance selection section, 36a...resistance selection section, 38...selection drive section, 39...connection point, 40...voltage peak value suppression circuit, C2...capacitor, D1...heater control device, D2...heater control device, D3...heater control device, D4...heater control device, G1...AND gate, G2...AND gate, IC1...hysteresis inverter , INV1...inverter, INV2...inverter, PC1...photocoupler, PC2...photocoupler, PC3...photocoupler, PC4...photocoupler, PC5...photocoupler, PTC1...phototriac coupler, PTC2...phototriac coupler, PTC3...phototriac coupler, PTC4...phototriac coupler, PTC5...phototriac coupler, Q1...transistor, Q2...triac, Q3...transistor, Q3...transistor, R11...resistor, R12...resistor, R13...resistor, R14...resistor, R15...resistor, R16...resistor, R21...resistor, R22...resistor, R24...resistor, R25...resistor, SW1...switch circuit [Prior art documents] [Patent documents]

[0067] [Patent Document 1] JP 2019-133848 A

Claims

1. a triac connected in series between the AC power supply and the heater; a phototriac coupler for transmitting a heater trigger signal to a gate electrode of the triac; two resistors used for current limiting, each connected in series to the phototriac coupler, and having different rated power and breakability depending on a phase controllable signal indicating a period of phase control; a resistor selection section that selects one of the two resistors and connects the selected resistor to a second main electrode of the triac.

2. The two resistors are: a first resistor connected in series with the phototriac coupler; a second resistor connected in series with the phototriac coupler and having a rated power and a susceptibility to breakage different from those of the first resistor, 2. The heater control device according to claim 1, wherein the resistor selection unit includes a switch circuit that selects and connects either the first resistor or the second resistor.

3. The two resistors are: a first resistor connected in series with the phototriac coupler; a second resistor connected in series with the phototriac coupler and having a rated power and a susceptibility to breakage different from those of the first resistor, The resistor selection unit a first photocoupler connected in series with the first resistor; a second photocoupler connected in series with the second resistor; 2. The heater control device according to claim 1, wherein the resistor selection unit turns on the first photocoupler and connects the first resistor in series with the phototriac coupler when performing phase control on the heater, and turns on the second photocoupler and connects the second resistor in series with the phototriac coupler when performing full current control on the heater.

4. a control unit that generates a phase controllable signal that indicates a period of the phase control; 4. The heater control device according to claim 1, wherein the resistor selection section selects a resistor in response to the phase controllable signal supplied from the control section.

5. a triac connected in series between the AC power supply and the heater; a first phototriac coupler for transmitting a heater trigger signal to a gate electrode of the triac; a first resistor used for current limiting, connected in series between the second main electrode of the triac and the first phototriac coupler; a second phototriac coupler for transmitting a heater trigger signal to the gate electrode of the triac; a second resistor used for current limiting, the second resistor being connected in series between a second main electrode of the triac and the second phototriac coupler, the second resistor having a rated power and a tendency to break different from those of the first resistor; a selection drive unit that selects and drives one of the first phototriac coupler and the second phototriac coupler.

6. 6. The heater control device according to claim 5, wherein the selective drive unit, when performing phase control on the heater, turns on the first phototriac coupler and connects the first resistor in series with the first phototriac coupler.

7. The heater control device according to any one of claims 1 to 6, an image forming apparatus comprising: a fixing device having a built-in heater controlled by the heater control device;

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