JP2012053171A - Image heating device - Google Patents

Abstract

In an image heating apparatus having a power supply circuit for supplying power to a heater, an image heating apparatus capable of suppressing damage to a switch element provided in the power supply circuit with a simple configuration is provided.
An image heating apparatus including a switch element driving circuit 45 for switching on and off of first and second switch elements 41 and 43 capable of interrupting power supply to a heater 120 is configured by a capacitor and a resistor. By transmitting on / off signals to the first and second switch elements 41 and 43 via the delay means, the first and second switch elements 41 and 43 are prevented from being simultaneously turned on and off.
[Selection] Figure 4

Description

  The present invention relates to an image heating apparatus for heating an image on a sheet material.

  An image heating apparatus including a heater that generates heat when electric power is supplied is known. The image heating apparatus is provided with a power supply circuit for supplying power from a commercial power source to the heater, and the power supply circuit is provided with a plurality of switch elements capable of interrupting power supply to the heater. Yes. Further, the image heating apparatus is provided with a switch element driving circuit (also referred to as a safety circuit) for switching on / off of these switch elements. According to this configuration, when the heater temperature is abnormally increased, the switch element is turned off by the safety circuit, so that the image heating apparatus can be prevented from being thermally damaged. A related technique is disclosed in Patent Document 1.

JP 2008-209718 A

  However, the conventional image heating apparatus has the following problems. When the switch elements are turned off to cut off the power supply to the heater when the heater temperature becomes higher than a preset value, if all the switch elements are turned off at the same time, an arc is generated at each switch element. Discharging occurs and causes damage to the switch element. Similarly, when turning on the switch elements to increase the temperature of the heater during driving, if all the switch elements are turned on at the same time, arc discharge occurs in each of the switch elements, resulting in damage to the switch elements. If the switch element is damaged in this manner, for example, when the temperature of the heater is abnormally increased, there is a possibility that the switch element cannot be reliably turned off, and the image heating apparatus may be thermally damaged.

  Accordingly, the present invention provides an image heating apparatus having a power supply circuit for supplying power to a heater, and capable of suppressing damage to a switch element provided in the power supply circuit with a simple configuration. For the purpose.

In order to achieve the above object, the present invention provides:
A heating member having a heater that generates heat by electric power supplied from a commercial power source; a pressure member that presses the heating member to form a heating nip; and a power supply circuit that supplies electric power from the commercial power source to the heater. The first and second switch elements provided between the commercial power supply and the heater in the power supply circuit and capable of shutting off the power supply to the heater, and the temperature of the heater become a target temperature, In an image heating apparatus comprising a switch element drive circuit that switches on and off of the first and second switch elements, when the temperature of the heater is higher than a target temperature while power is supplied to the heater, In the switch element driving circuit, a signal for turning off the first switch element and the second switch element is output, so that these switch elements are turned off. If the temperature of the heater is lower than the target temperature when the image heating apparatus is being driven and the first switch element and the second switch element are turned off, the switch element drive circuit By outputting a signal for turning on the first switch element and the second switch element, these switch elements are turned on,
When turning off the first switch element and the second switch element, these switch elements are not turned off at the same time, and when turning on the first switch element and the second switch element, these switch elements are turned on simultaneously. It is characterized by not turning on.

  According to the present invention, in an image heating apparatus having a power supply circuit for supplying power to a heater, an image heating apparatus capable of suppressing damage to a switch element provided in the power supply circuit with a simple configuration is provided. It becomes possible to do.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. 1 is a schematic configuration diagram of an image heating apparatus according to a first embodiment. The schematic block diagram of the electric power supply circuit in 1st Embodiment. The schematic block diagram of the switch element drive circuit in 1st Embodiment. The chart figure of the on sequence in 1st Embodiment, and an off sequence. The schematic block diagram of the switch element drive circuit in 2nd Embodiment. The chart of the on sequence in 2nd Embodiment, and an off sequence.

[First embodiment]
(1-1: Schematic configuration of image forming apparatus)
In this embodiment, a case where an image heating apparatus is used as a fixing device of an image forming apparatus will be described. With reference to FIG. 1, an image forming apparatus according to the present embodiment will be described. The image forming apparatus in this embodiment is a laser printer using an electrophotographic process.

  The laser printer main body 1101 (hereinafter, main body 1101) has a cassette 1102 for storing the sheet material S. The presence / absence of the sheet material S in the cassette 1102 is detected by a cassette presence / absence sensor 1103, and the size of the stored sheet material S is detected by a size detection sensor 1104 configured by a plurality of micro switches. When the sheet material S is fed, the sheet material S is fed by the feeding roller 1105 and conveyed to the nip portion of the registration roller pair 1106.

  An image forming unit 1108 that forms a toner image on the sheet material S based on the laser beam from the laser scanner unit 1107 is provided downstream of the registration roller pair 1106. Further, a fixing device 109 (image heating device) that thermally fixes the toner image formed on the sheet material S is provided downstream of the image forming unit 1108. Further, downstream of the fixing device 109, a discharge roller 1111 for discharging the sheet material S, a stacking tray 1112 for stacking the discharged sheet material S, and a discharge sensor 1113 for detecting a discharge state by the discharge roller 1111 are provided. Yes.

  A laser scanner unit 1107 includes a laser unit 1120 that emits laser light modulated based on an image signal (VDO signal) sent from an external device 1131, a polygon motor 1114 that scans the laser light, an imaging lens 1115, and a folding mirror. 1116. The image forming unit 1108 includes a photosensitive drum 1117, a charging roller 1119, a developing device 1118, a transfer roller 1145, a cleaner 1146, and the like necessary for a known electrophotographic process.

  The main motor 1123 applies a driving force to the feeding roller 1105 via a feeding roller clutch 1147 and to the registration roller pair 1106 via a registration roller clutch 1125. Further, a driving force is also applied to each unit of the image forming unit 1108 including the photosensitive drum 1117, the fixing device 109, and the discharge roller 1111.

  The image forming apparatus is provided with an engine controller 126 as a control unit. The engine controller 126 performs control of the electrophotographic process by the laser scanner unit 1107, the image forming unit 1108, and the fixing device 109, and conveyance control of the sheet material S in the main body 1101. In addition, a video controller 1127 is connected to the engine controller 126 via a connection cable 1128. The video controller 1127 is connected to an external device 1131 such as a personal computer via a general-purpose interface (Centronics, RS232C, etc.) 1132. The image information sent from the general-purpose interface 1132 is expanded into bit data, and the bit data is sent to the engine controller 126 as a VDO signal.

  With the above-described configuration, when an image is formed on the sheet material S, first, toner is supplied from the developing device 1118 to the electrostatic latent image formed by scanning exposure on the photosensitive drum 1117, and the toner Develop as an image. Thereafter, a toner image is transferred at the nip portion between the photosensitive drum 1117 and the transfer roller 1145 to the sheet material S conveyed at a timing from the registration roller pair 1106. The toner image transferred onto the sheet material S is fixed on the sheet material S by being heated and pressurized in the fixing device 109. The sheet material S on which the image is formed in this manner is discharged onto the stacking tray 1112 by the discharge roller 1111.

(1-2: Schematic configuration of fixing device)
A schematic configuration of the fixing device 109 will be described with reference to FIG. FIG. 2A shows a schematic configuration of the heater provided in the fixing device 109, and FIG. 2B is a schematic cross-sectional view of the fixing device 109.

  As shown in FIG. 2B, the fixing device 109 includes a heat-resistant fixing sleeve 100 (heating member) having a heater 120 inside, and a pressure contact member that presses against the fixing sleeve 100 so as to sandwich the fixing sleeve 100 together with the heater 120. And a pressure roller 150 (pressure member). Further, inside the fixing sleeve 100, a guide member 140 that fits the fixing sleeve 100 and guides the rotation of the fixing sleeve 100 and a heater holder 130 that holds the heater 120 are provided. The heater 120 and the fixing sleeve 100 are provided. The inner peripheral surface is in direct contact.

  The sheet material is conveyed to a heating nip formed by the fixing sleeve 100 and the pressure roller 150, and the toner image is heated and pressure-fixed at the heating nip. The fixing sleeve 100 has flexibility and is driven to rotate by a pressure roller 150 that is rotationally driven by a driving source (not shown). According to such a configuration, since the inner peripheral surface of the fixing sleeve 100 and the heater 120 slide directly, the heat generated by the heater 120 can be efficiently transmitted to the sheet material at the heating nip portion.

  A thermistor 120b as a temperature detection element and a thermo switch 120a as a temperature protection element are provided on the back surface of the heater 120 (the surface opposite to the heating nip portion). The thermistor 120b detects the temperature of the heater 120, and outputs the detection result to a control unit (not shown). The thermo switch 120a protects the device when the heater 120 abnormally increases in temperature. It is for cutting off the power supply to.

A schematic configuration of the heater 120 will be described with reference to FIG. FIG. 2A shows a schematic configuration of the back surface of the heater 120. As shown in the figure, a ceramic substrate 155 made of SiC, AlN, Al ₂ O ₃ or the like is used as the substrate for the heater 120. On the ceramic substrate 155, two heating resistors 121 and 122 (both have resistance values) R (Ω)) is paste printed. These heating resistors 121 and 122 generate heat when electric power is supplied from a commercial power supply via a power supply circuit. The surfaces of the heating resistors 121 and 122 are covered with a protective layer 154 made of insulating glass or the like.

  The heating resistor 121 is connected to the electrode parts 121a and 153, and the heating resistor 122 is connected to the electrode parts 122a and 153. These electrode portions are electrically connected to terminals of a commercial power source. Specifically, the electrode portion 153 that is a common electrode is connected to a hot-side terminal of a commercial power source, and the other electrode portions are connected to a neutral-side terminal of the commercial power source. Although the back surface of the heater 120 has been described here, the surface of the heater 120 may be covered with a glass layer or the like in order to improve the slidability with the fixing sleeve 100. Furthermore, sliding grease or the like may be applied to the surface.

(1-3: Schematic configuration of power supply circuit)
With reference to FIG. 3, the power supply circuit in this embodiment is demonstrated. The fixing device 109 is provided with a power supply circuit that supplies power to the heater 120 from a commercial power source. In the figure, reference numeral 1 denotes a commercial power source (AC power source). By supplying power from the commercial power source 1 to the heating resistors 121 and 122 of the heater 120 via the AC filter 2 and relays 41 and 43 (switch elements). The heating resistors 121 and 122 can generate heat. Here, for the sake of clarity, the relay 41 is described as the first switch element and the relay 43 is the second switch element. However, the combination of the first and second switch elements is not limited to this, and vice versa. It may be. A plurality of relays may be provided.

  Supply of electric power to the heating resistor 121 is controlled by an engine controller 126 as a control unit switching on / off of energization to the triac 4 (drive element). Note that the relays 41 and 43 are provided between the commercial power source 1 and the heater 120 so that the power supply to the heater 120 can be cut off.

  The resistors 5 and 6 are bias resistors of the triac 4, and the phototriac coupler 7 is a device for securing a creepage distance between the primary and secondary. The triac 4 can be turned on by energizing the light emitting diode provided in the phototriac coupler 7. The resistor 8 is a resistor for limiting the current of the phototriac coupler 7, and the phototriac coupler 7 is switched on and off by a transistor 9. The transistor 9 operates based on the ON1 signal from the engine controller 126 via the resistor 10.

  Supply of electric power to the heating resistor 122 is controlled by an engine controller 126 as a control unit switching on / off of energization to the triac 13. The resistors 14 and 15 are bias resistors for the triac 13, and the phototriac coupler 16 is a device for securing a creepage distance between the primary and secondary. The triac 13 can be turned on by energizing the light emitting diode of the phototriac coupler 16. The resistor 17 is a resistor for limiting the current of the phototriac coupler 16, and the phototriac coupler 16 can be switched on and off by the transistor 18. The transistor 18 operates based on an ON2 signal from the engine controller 126 input via the resistor 19.

The power output from the AC power source 1 is input to the zero cross detection circuit 12 via the AC filter 2. In the zero cross detection circuit 12, when the voltage of the commercial power source 1 becomes a voltage equal to or lower than a certain threshold value, this is notified by outputting a pulse signal to the engine controller 126. Hereinafter, this signal output to the engine controller 126 is referred to as a ZEROX signal. The engine controller 126 detects the edge of the pulse of the ZEROX signal, and switches the triac 4 or 13 on and off by phase control or wave number control.
The power supply to the heater 120 is controlled.

  The heater current supplied to the heating resistors 121 and 122 is converted into a voltage by the current transformer 25 and input to the current detection circuit 27 via the bleeder resistor 26. In the current detection circuit 27, the heater current waveform converted into a voltage is converted into an average value or an effective value, and A / D is input to the engine controller 126 as an HCRRT signal.

  The thermistor 120b is disposed via an insulator having a withstand voltage so that an insulation distance can be secured with respect to the heating resistors 121 and 122 on the heater 120. The temperature detected by the thermistor 120b is detected as a partial pressure between the resistor 22 and the thermistor 120b, and A / D is input to the engine controller 126 as a TH signal.

  The temperature of the heater 120 is monitored by the engine controller 126 as a TH signal. When controlling the power supplied to the heater 120, the power ratio to be supplied to the heating resistors 121 and 122 is calculated by comparing with the set temperature of the heater 120 set in the engine controller 126. . Then, the calculated power ratio is converted into a corresponding phase angle (phase control) or wave number (wave number control), whereby the engine controller 126 sends an ON1 signal to the transistor 9 or an ON2 signal to the transistor 18. To do. When controlling the supply power, an upper limit power ratio is calculated based on the HCRRT signal notified from the current detection circuit 27, and control is performed so that power equal to or less than the upper limit power ratio is energized. For example, in the case of phase control, data shown in the following table is stored in the engine controller 11 in advance, and supply power is controlled based on this data.

  In addition, the fixing device 109 is provided with a “relay driving unit and safety circuit unit 45” (hereinafter referred to as a safety circuit 45) as a “switch element driving circuit”. In the figure, reference numerals 42 and 44 denote diodes for preventing damage to the relays 41 and 43 due to the counter electromotive force. The safety circuit 45 is configured to be able to turn off the relays 41 and 43 in order to cut off the power supply to the heater 120 when the thermistor 120b reaches or exceeds a predetermined temperature (target temperature). Hereinafter, the safety circuit 45 will be described.

(1-4: Schematic configuration of safety circuit)
With reference to FIG. 4, the schematic configuration and operation of the safety circuit 45 in the present embodiment will be described. In normal operation, when a print request command is input to the engine controller 126 by the user (the image heating process starts), the relays 41 and 43 are turned on to supply power to the heater 120. When turning on relays 41 and 43, engine controller 126 outputs relay drive signal / RLD to safety circuit 45. When the relay drive signal / RLD is input from the engine controller 126, the safety circuit 45 turns off the transistor 103. When the transistor 103 is turned off, current is supplied to the bases of the transistors 107, 110, and 122 through the resistor 102, so that the transistors 107, 110, and 122 are turned on.

  The transistor 116 is turned on before the print request command is received via the resistor 112. Accordingly, the transistor 119 is also turned on. Therefore, the plurality of transistors are turned on, the relays 41 and 43 are turned on, and power supply to the heater 120 is enabled.

  The safety circuit 45 has a comparator such as a comparator as a signal output unit that outputs a signal for switching the relays 41 and 43 on and off depending on whether the temperature of the heater 120 is higher or lower than the target temperature. 125 is provided. A voltage value is input to the inverting input terminal of the comparator 125 via the thermistor 120 b disposed on or near the heater 120 and the voltage dividing resistor 22. That is, the comparator 125 can compare the detected temperature of the heater 120 with the target temperature and output a signal according to the magnitude relationship. Hereinafter, this point will be described in detail.

  In general, the thermistor 120b has NTC characteristics, so that the resistance value decreases as the temperature rises. Therefore, as the temperature of the heater 120 rises, the voltage value input to the inverting input terminal of the comparator 125 decreases. A predetermined reference voltage value is input to the non-inverting input terminal of the comparator 125 via the resistors 123 and 124. The reference voltage value corresponds to a temperature (target temperature) that is equal to or lower than a temperature at which the heater 120 is not damaged and is equal to or higher than a temperature necessary for normal printing operation. That is, it is possible to detect whether the temperature of the heater 120 is higher or lower than the target temperature by comparing the voltage value input to the comparator 125 with this reference voltage value. In the normal printing operation, since the temperature is used at a temperature corresponding to a reference voltage value or higher, the output of the comparator 125 is at a low level, and thus the transistor 128 is turned off.

  Next, the “off sequence” will be described. If any abnormality occurs in the power supply circuit during driving, and power supply to the heater 120 cannot be controlled, the heater 120 may be heated abnormally. Therefore, in the present embodiment, when the temperature of the heater 120 becomes higher than the target temperature during driving, the relays 41 and 43 are turned off to supply power to the heater 120 in order to protect the heater 120 and the fixing device 109. Execute “off sequence” to shut off.

  The off sequence is performed when the power supply to the heater 120 becomes uncontrollable, the temperature of the heater 120 rises, and the non-inverting input terminal voltage of the comparator 125 becomes equal to or lower than the reference voltage value. When the non-inverting input terminal voltage of the comparator 125 becomes equal to or lower than the reference voltage value, the comparator 125 first outputs a high level, and the transistor 128 is turned on. When the transistor 128 is turned on, the transistors 110 and 122 are immediately turned off. At the same time, the relay 41 is turned off.

However, at this time, the transistors 107 and 116 are connected to the capacitors 105 and 114 and the resistor 1
Due to the time constants of 06 and 115, it takes time for the time constant to turn off. Thus, a time difference can be generated between the timing when the transistors 110 and 122 and the transistors 107 and 116 are turned off. Since the relay 43 is configured not to be turned off unless both the transistors 107 and 110 are turned off, a time difference is generated between the timings when the relays 41 and 43 are turned off. Further, this time difference is characterized in that it is set to a length equal to or longer than a half cycle of the commercial power supply (AC voltage) by setting the capacitance of the capacitor 105 and the resistance value of the resistor 106. Note that the capacitor 105, the resistor 106, or the combination of the capacitor 114 and the resistor 115 corresponds to the “delay unit” in the present embodiment, and it is sufficient that the “delay unit” is provided for at least one of the relays. .

  As described above, in the “off sequence”, the relay 41 is turned off and the relay 43 is turned off after a predetermined time difference, that is, the relays are not turned off at the same time. Furthermore, the time difference when the relays 41 and 43 are sequentially turned off is longer than a half cycle of the AC voltage. After the first relay 41 is turned off and before the next relay 43 is turned off, the waveform of the AC voltage always passes the zero cross point. Since arc discharge does not occur at the zero cross point, at least the relay 43 can be prevented from being damaged by arc discharge if the relay 43 is turned off at this timing (timing to pass the zero cross point).

  Next, the “on sequence” will be described. When the “off sequence” is executed and then printing is performed again, it is necessary to raise the temperature of the heater 120 that has become lower than the target temperature to a printable temperature. That is, it is necessary to turn on the relays 41 and 43 that have been turned off again to start supplying power to the heater 120. When performing the “on sequence”, first, the comparator 125 outputs the Low level again to turn off the transistor 128. In that state, the transistors 110 and 122 are turned on almost simultaneously.

  When the transistor 110 is turned on, the relay 43 is turned on almost simultaneously. At this time, the relay 41 is not turned on yet. At this time, the transistors 107 and 116 require time constants until they are turned off by the time constants of the capacitors 105 and 114 and the resistors 106 and 115. Therefore, a time difference is generated at the timing when the transistors 110 and 112 and the transistors 107 and 116 are turned on.

  Since the relay 41 is configured not to be turned on unless both the transistors 119 and 122 are turned on, a time difference is generated between the timing when the relay 41 and the relay 43 are turned on. This time difference is characterized in that it is set to a length equal to or longer than a half cycle of the commercial power supply (AC voltage) by setting the capacitance of the capacitor 114 and the resistance value of the resistor 115. Thus, even in the “on sequence”, since all the relays are not turned on at the same time, as described in the “off sequence”, at least the relay 43 can be prevented from being damaged by arc discharge.

(1-5: Overview of off sequence and on sequence)
The outline of the off sequence and the on sequence will be described with reference to FIG. First, when a print request command is input to the engine controller 126, the engine controller 126 outputs a relay drive signal. That is, when the relay drive signal is input to the safety circuit 45, the relays 41 and 43 are simultaneously turned on.

  Next, when power supply control to the heater 120 becomes impossible for some reason, such as a triac failure, the temperature of the heater 120 continues to rise, and the voltage value of the inverting input terminal of the comparator 125 based on the detected temperature of the thermistor 120b. Is lower than the reference voltage value as described above. Thereby, the relays 41 and 43 are turned off, and the power supply to the heater 120 is cut off.

  However, at this time, since all the relays are turned off after a time difference, the relay 43 is turned off after the relay 41 is turned off. Thereby, only the relay 41 can generate arc discharge when it is off. Furthermore, this time difference is set to a length equal to or longer than a half cycle of the AC voltage. Therefore, the relay 43 can be turned off at a timing when the relay 41 is completely turned off and no arc discharge occurs.

  When the power supply to the heater 120 is completely cut off by the relays 41 and 43 being turned off, the temperature of the heater 120 decreases. As a result, the voltage value input to the inverting input terminal portion of the comparator 125 based on the detected temperature of the thermistor 120b again exceeds the reference voltage value. Then, the relays 41 and 43 are turned on again to start supplying power to the heater 120. At this time, the relays are turned on in the order of the relays 43 and 41 after a time difference of more than a half cycle of the AC voltage. It occurs only in 41. Therefore, the relay 43 can be protected.

(1-6: Effects of this embodiment)
According to the present embodiment, by providing a delay circuit with a simple configuration in the safety circuit, the relays 41 and 43 can be turned on and off with a time difference, so that all the relays are arced and damaged. Can be prevented. In addition, since the time difference is set to a length of more than a half cycle of the AC voltage, turning on and off the subsequent relay at the zero-cross timing of the AC waveform prevents arcing from occurring in the subsequent relay. it can.

  In addition, the relay that is turned off first in the off sequence and the relay that is turned on last in the on sequence are the same relay (in this embodiment, the relay 41), so that the relay affected by the arc discharge becomes one relay. It can be limited. Therefore, it becomes possible to protect other relays.

  Also, at the stage of starting printing (step of starting printing by turning on the fixing device switch), all the relays are simultaneously turned on. Therefore, in the normal print sequence, the first printout time is not unnecessarily delayed.

  As described above, according to the present embodiment, in the image heating apparatus having the power supply circuit that supplies power to the heater, an image that can suppress damage to the switch element provided in the power supply circuit with a simple configuration. A heating device can be provided.

[Second Embodiment]
An image heating apparatus according to a second embodiment to which the present invention can be applied will be described with reference to FIGS. In addition, description is abbreviate | omitted about the structure same as 1st Embodiment, and only a structure different from 1st Embodiment is demonstrated here.

(2-1: Schematic configuration of safety circuit)
With reference to FIG. 6, a schematic configuration of the safety circuit in the present embodiment will be described. In normal operation, when a print request command is input to the engine controller 126 by the user (the image heating process starts), the relays 41 and 43 are turned on to supply power to the heater 120.

  When turning on relays 41 and 43, engine controller 126 outputs relay drive signal / RLD to safety circuit 45. When the relay drive signal / RLD is input from the engine controller 126, the safety circuit 45 turns off the transistor 203. When the transistor 203 is turned off, current is supplied to the bases of the transistors 209 and 215 via the resistor 202, so that the transistors 209 and 215 are turned on.

  The transistors 222 and 229 are turned on before the print request command is received. Accordingly, the transistors 206 and 212 are also turned on. Therefore, the plurality of transistors are turned on, the relays 41 and 43 are turned on, and power can be supplied to the heater 120.

  The safety circuit 45 also includes comparators 218 and 225 as signal output units that output signals for switching the relays 41 and 43 on and off depending on whether the temperature of the heater 120 is higher or lower than the target temperature. Is provided. These comparators are provided corresponding to the respective relays, the comparator 225 is a first signal output unit that outputs a signal to the relay 41, and the comparator 218 outputs a signal to the relay 43. It is a signal output unit. The non-inverting input terminals of the comparators 218 and 225 are inputted with voltage values via the thermistor 120 b disposed on or near the heater 120 and the voltage dividing resistor 22.

  Specifically, a predetermined reference voltage value is input to the inverting input terminal of the comparator 218 via the resistors 216 and 217. A predetermined reference voltage value is input to the inverting input terminal of the comparator 225 via the resistors 223 and 224. Further, as described above, these reference voltage values are set based on the temperature below the temperature at which the heater 120 is not damaged and above the temperature necessary for the normal printing operation. In addition, the reference voltage value is set differently. Since the operation of the thermistor 120b and the operation of the comparator based on the detected temperature of the thermistor 120b have been described in the first embodiment, description thereof is omitted here.

  In the normal printing operation, since the heater temperature corresponding to the reference voltage value or higher is used, the outputs of the comparators 218 and 225 become High level, and the transistors 222 and 229 are turned on. Accordingly, the transistors 206 and 215 are turned on. Thereafter, in the “off sequence”, first, the non-inverting input terminal voltage of the comparator 225 becomes equal to or lower than the reference voltage value, the comparator 225 outputs a low level, and the transistor 229 is turned off. At this time, the relay 41 is turned off and the power supply to the heater 120 is cut off.

  However, even after the power supply to the heater 120 is cut off, the temperature of the heater 120 continues to rise further due to the temperature overshoot for a predetermined period. Then, since the non-inverting input terminal voltage of the comparator 218 becomes equal to or lower than the reference voltage value constituted by the resistors 216 and 217, the comparator 218 outputs a low level and the transistor 222 is turned off. As a result, the relay 43 is turned off.

  Thus, in the “off sequence”, the comparators 218 and 225 are provided corresponding to the respective relays, and the reference voltage value is made different for each comparator, so that the relays are turned off from the comparators exceeding the target temperature. The signal for this is output. Therefore, the relays 41 and 43 are sequentially turned off after a time difference without being turned off at the same time. Furthermore, this time difference is set so as to be longer than a half cycle of the commercial power supply (AC voltage) by appropriately changing the resistance values of the resistors 216 and 217 and the resistors 223 and 224.

  Next, the “on sequence” will be described. When the temperature of the heater 120 falls, the voltage input to the comparator 218 first becomes equal to or higher than the reference voltage value. Then, the comparator 218 outputs the High level again, and the transistor 222 is turned on. The relay 43 is turned on when the transistors 222 and 206 are turned on. At this time, the relay 41 is not turned on yet.

When the temperature of the heater 120 further decreases, the voltage input to the comparator 225 becomes equal to or higher than the reference voltage value. Then, the comparator 225 outputs the High level again, and the transistor 229 is turned on. The relay 41 is turned on when the transistors 212 and 229 are turned on. Thus, also in the “on sequence”, the relays 43 and 41 can be turned on in this order after a time difference.

(2-2: Outline of off sequence and on sequence)
The outline of the off sequence and the on sequence will be described with reference to FIG. First, when a print request command is input to the engine controller 126 by the user, the engine controller 126 outputs a relay drive signal. That is, when the relay drive signal is input to the safety circuit 45, the relays 41 and 43 are simultaneously turned on.

  Next, when power supply control to the heater 120 becomes impossible for some reason, such as a triac failure, the temperature of the heater 120 continues to rise and an “off sequence” is performed. That is, first, the voltage value input to the comparator 225 is lower than the reference voltage value (corresponding to the target temperature A ° C.). As a result, the relay 41 is turned off and the power supply to the heater 120 is interrupted.

  However, immediately after the power supply is cut off, the temperature does not drop suddenly due to the effect of temperature overshoot. Then, the voltage value input to the comparator 218 next falls below the reference voltage value (corresponding to the set temperature B ° C.). As a result, the relay 43 is turned off. As described above, since a time difference of more than a half cycle of the AC voltage is provided after the relay 41 is turned off until the relay 43 is turned off, it is possible to prevent arc discharge from occurring when the relay 43 is turned off. .

  Thereafter, when the power supply to the heater 120 is completely cut off by the relays 41 and 43 being turned off, the temperature of the heater 120 decreases. As a result, the voltage value input to the comparator 218 again exceeds the reference voltage value (corresponding to the target temperature B ° C.). Therefore, the relay 43 is turned on. In this state, since the electric power is not yet supplied to the heater 120, the temperature of the heater 120 continues to decrease. Eventually, the voltage value input to the comparator 225 again exceeds the reference voltage value (corresponding to the target temperature A ° C.), and the relay 41 is turned on. Thereby, power supply to the heater 120 is started.

(2-3: Effects of the present embodiment)
According to this embodiment, a comparator corresponding to each relay is provided for a plurality of relays, and the reference voltage value (corresponding to the target temperature of the heater) set in the comparator is different for each comparator. Therefore, the relay can be turned on and off after a time difference. Therefore, it is possible to prevent arc discharge from occurring in all the relays with a simple configuration. In addition, since the time difference is set to a length longer than a half cycle of the AC voltage, turning on and off the subsequent relay at the zero cross timing of the AC waveform reliably prevents arcing from occurring in the subsequent relay. be able to.

  In addition, the relay that is turned off first in the off sequence and the relay that is turned on last in the on sequence are the same relay (in this embodiment, the relay 41), so that the relay affected by the arc discharge becomes one relay. It can be limited. Therefore, it becomes possible to protect other relays.

  Also, at the stage of starting the printer (step of starting printing by turning on the fuser switch), all the relays are simultaneously turned on. Therefore, in the normal print sequence, the first printout time is not unnecessarily delayed.

As described above, according to the present embodiment, in the image heating apparatus having the power supply circuit that supplies power to the heater, an image that can suppress damage to the switch element provided in the power supply circuit with a simple configuration. A heating device can be provided.

[Other embodiments]
In the first embodiment, the delay unit is configured by the capacitor and the resistor, but the configuration of the delay unit is not limited to this. That is, any other form may be used as long as it is a means capable of delaying and transmitting an on / off signal to at least one of a plurality of relays provided.

  In the first and second embodiments, the surf type fixing device in which the inner surface of the fixing sleeve and the heater slide directly has been described. However, the form of the image heating apparatus according to the present invention is not limited to this, and a heat roller type fixing device using a fixing roller having a heating element such as a halogen lamp inside may be used.

  In the first and second embodiments, the fixing device that heats and presses and fixes the unfixed toner image on the sheet material has been described. However, the form of the image heating device according to the present invention is not limited to this, and a gloss applying device that adds gloss to the toner image by heating and pressurizing the sheet material carrying the fixed toner image again. It may be.

41, 43 ... Relay (switch element) 45 ... Safety circuit 105, 106, 114, 115 ... Delay means 120 ... Heater 125 ... Comparator

Claims (7)

A heating member having a heater that generates heat by electric power supplied from a commercial power source;
A pressure member that presses against the heating member to form a heating nip; and
A power supply circuit for supplying power from the commercial power source to the heater;
First and second switch elements provided between the commercial power supply and the heater in the power supply circuit, and capable of interrupting power supply to the heater;
A switch element drive circuit for switching on and off of the first and second switch elements so that the heater temperature becomes a target temperature;
In an image heating apparatus comprising:
When power is supplied to the heater and the heater temperature is higher than a target temperature, a signal for turning off the first switch element and the second switch element is output in the switch element drive circuit. These switch elements are turned off,
When the image heating apparatus is being driven and the first switch element and the second switch element are turned off and the temperature of the heater is lower than the target temperature, the switch element drive circuit uses the first heating element. By outputting a signal for turning on the switch element and the second switch element, these switch elements are turned on,
When turning off the first switch element and the second switch element, these switch elements are not turned off at the same time, and when turning on the first switch element and the second switch element, these switch elements are turned on simultaneously. An image heating apparatus that is not turned on. In the switch element driving circuit,
A signal output unit that outputs a signal for switching on and off of the first and second switch elements according to whether the temperature of the heater is higher or lower than a target temperature;
Provided between at least one of the signal output unit and the first switch element and between the signal output unit and the second switch element, and transmits the signal output from the signal output unit with a delay. A delay means, and
When turning off the first switch element and the second switch element,
The signal output unit outputs a signal for turning off these switch elements, and the output signal is transmitted through the delay means, so that these switch elements are not turned off at the same time,
When turning on the first switch element and the second switch element,
The signal output unit outputs a signal for turning on these switch elements, and the output signal is transmitted through the delay means, so that these switch elements do not turn on simultaneously. The image heating apparatus according to claim 1. In the switch element driving circuit,
A first signal output unit that outputs a signal for switching on / off to the first switch element according to whether the temperature of the heater is higher or lower than a target temperature;
A second signal output unit that outputs a signal for switching on / off to the second switch element according to whether the temperature of the heater is higher or lower than a target temperature;
Is provided,
The image heating apparatus according to claim 1, wherein a target temperature of the heater set in the first signal output unit is different from a target temperature of the heater set in the second signal output unit.   The first switch element and the second switch element are turned off at different timings, or the time difference when turning on is set to a length of a half cycle or more of the AC voltage used in the commercial power supply. The image heating apparatus according to any one of claims 1 to 3. When turning off the first switch element and the second switch element, the first switch element is turned off first,
5. The image heating apparatus according to claim 1, wherein when the first switch element and the second switch element are turned on, the first switch element is turned on last. 6. The switch element driving circuit includes:
6. The apparatus according to claim 1, wherein when the image heating process is started in the heating nip portion, the first switch element and the second switch element are simultaneously turned on. 6. Image heating device.   The heating member has a flexible fixing sleeve, the inner surface of the fixing sleeve and the heater are in contact with each other, and the pressure member presses against the fixing sleeve so as to sandwich the fixing sleeve together with the heater. The image heating apparatus according to claim 1, wherein the heating nip portion is formed.

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