JP5793927B2 - Induction heating apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an induction heating device used as, for example, a heating source of a fixing device of an image forming apparatus, and an image forming apparatus using the induction heating device.

  For example, image forming apparatuses such as copiers, printers, facsimiles, and the like, and multifunction digital image forming apparatuses called MFP (Multi Function Peripherals) that integrate the functions of these apparatuses include a fixing roller in the fixing apparatus. There is one in which an induction heating device is used as a heating source for heating.

  As such an induction heating device, for example, a commercial AC voltage is full-wave rectified and converted into a direct current and applied to a coil for induction heating, for example, and an insulated gate bipolar transistor connected in series with the coil for induction heating, for example 2. Description of the Related Art Conventionally, a method of controlling power supplied to a heating roller by controlling on / off of a switching element made of (IGBT: Insulated Gate Bipolar Transistor) has been used.

  In addition, as a fixing device, a device having a small heat capacity is demanded in order to shorten the warm-up time for the image forming apparatus and to save energy. The fixing device having a small heat capacity can be rapidly heated, but has a feature that the temperature is rapidly lowered. Therefore, in order to keep the temperature constant with a fixing device having a small heat capacity, fine power control of the heating induction device is required.

  By the way, when a surge voltage is input to a commercial input AC (50/60 Hz) during the operation of the induction heating device, an excessive voltage is applied to the switching element that switches the induction heating coil, and the switching element It can be destroyed. In addition, when the input voltage fluctuates abnormally, the switching element may be destroyed, but the surge voltage is generated once, whereas the abnormal fluctuation voltage tends to be repeated regularly. It is in.

  Therefore, a circuit for detecting the surge voltage and abnormal fluctuation voltage as described above is provided, and when these abnormal voltages occur, the operation of the induction heating device is generally stopped. It is not easy to distinguish whether the voltage is due to surge voltage or abnormal voltage fluctuation. For this reason, conventionally, even in the case of a surge voltage, a relatively long stop time for determining whether the voltage is an abnormal fluctuation voltage has been secured.

  In Patent Document 1, a heater is disposed so as to be locally heated, and a fixing roller is rotated during warm-up in order to prevent an excessive temperature rise in a locally heated portion. An apparatus is disclosed.

JP 2002-40871 A

  However, when the stop time of the induction heating device is long, the temperature of the fixing device is lowered, which may affect the fixing performance.

  In particular, in the case of a fixing device having a small heat capacity as described above, when the power supply from the induction heating device is stopped, the temperature of the fixing roller is instantaneously lowered, so that an unfixed image is easily generated. There was a problem of becoming defective.

  Such a problem cannot be solved by the technique described in Patent Document 1.

  The present invention has been made in view of such a technical background, and is an induction heating apparatus that can suppress the stoppage of the apparatus as much as possible when an abnormal voltage such as a surge voltage or an abnormal input fluctuation voltage is detected. And an image forming apparatus using the induction heating device.

The above problem is solved by the following means.
(1) A rectifier circuit that rectifies an AC voltage from an AC power source into DC, a DC voltage obtained by the rectifier circuit, a coil for induction heating of a heated object, and a series of the coils A connected switching element; power control means for controlling power supplied to the heated object by controlling on / off of the switching element; abnormal voltage detection means for detecting abnormal voltage; and Zero cross detection means for detecting zero cross, and time measuring means for counting the time from the zero cross detected by the zero cross detection means to the abnormal voltage detected by the abnormal voltage detection means, the power control means, When an abnormal voltage is detected by the abnormal voltage detection means, power supply to the heated body is temporarily stopped and the zero cross detection is performed. The power supply is restarted at the timing of the zero cross detected by the means, and the time from the zero cross to the abnormal voltage when the abnormality is detected again is within a certain range with the time from the zero cross to the abnormal voltage at the previous abnormal voltage detection Then, the induction heating apparatus is characterized in that the power supply to the heated object is completely stopped.
(2) Counting means for counting the number of occurrences of the abnormal voltage is provided, and even when the number of occurrences of the abnormal voltage counted by the counting means within a unit time is more than a certain value, the power control means 2. The induction heating device according to item 1, wherein power supply to the body is completely stopped.
(3) In the power control means, the count value of the time from the zero cross to the abnormal voltage when the abnormality is detected again is the same as the count value of the time from the zero cross to the abnormal voltage at the time of the previous abnormal voltage detection. 3. The induction heating device according to item 1 or 2, wherein the power supply to the object to be heated is completely stopped when the value can be regarded as being.
(4) An image forming apparatus, wherein the induction heating device according to any one of items 1 to 3 is used as a heating source of a fixing device.

  According to the invention described in the preceding paragraph (1), when an abnormal voltage is detected, the power supply to the heated body is temporarily stopped, the power supply is restarted at the zero cross timing of the AC voltage, and the abnormality is again detected. When the time from the zero cross to the abnormal voltage when detected is within a certain range with the time from the zero cross at the previous abnormal voltage detection to the abnormal voltage, the power supply to the heated object is completely stopped and fixed If it is not within the range, the power supply does not stop. Therefore, since the power supply is not completely stopped for irregular and one-time abnormal voltages such as surge voltage, the power supply stop time when the abnormal voltage is detected can be reduced accordingly.

  According to the invention described in item (2) above, since the power supply to the heated object is completely stopped even when the number of occurrences of the abnormal voltage within the unit time is more than a certain value, there is a risk of destruction of the switching element. Can be reliably avoided.

  According to the invention described in (3) above, the power supply is not completely stopped for irregular and one-time abnormal voltages such as surge voltages, and accordingly, the fixing device when the abnormal voltage is detected accordingly. As a result of reducing the heating stop time, it is possible to prevent the temperature of the fixing roller from decreasing and to prevent the occurrence of an unfixed image.

1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. (A) shows a state where a surge voltage is input to an AC voltage of a commercial power supply, and (B) shows a state where both positive and negative peak voltages exceed the level of damage to the switching element due to abnormal fluctuations in the AC voltage. FIG. It is a figure for demonstrating the process at the time of abnormal voltage detection. It is a figure for demonstrating the other process at the time of abnormal voltage detection. It is a flowchart which shows the process at the time of abnormal voltage detection. It is a flowchart of a zero cross interruption process. It is a flowchart which shows the process at the time of the conventional abnormal voltage detection.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of an induction heating apparatus according to an embodiment of the present invention. In this embodiment, the induction heating device 10 is mounted on the image forming apparatus 1 such as the MFP described above, and heats the fixing roller 30 as a heated body in the fixing unit.

  The induction heating device 10 includes a commercial power supply 101, a full-wave rectifier circuit 102, an induction heating coil (inductor) 103, a capacitor 104, a switching element 105, an IGBT drive circuit 106, a power control unit 107, An abnormal voltage detection circuit 108, an input voltage detection circuit 109, a zero-cross detection circuit 110, and an input current detection circuit 111 are provided.

  The commercial power source 11 is a 50/60 Hz 100V AC power source, and the full-wave rectification circuit 12 performs full-wave rectification of the commercial power source 11's 100V AC voltage to convert it into direct current.

  The coil 13 receives the output voltage of the full-wave rectifier circuit 12 and induction-heats the fixing roller 30 as a heated body magnetically coupled.

  The capacitor 104 is connected in parallel with the coil 103, and forms a resonance circuit 112 with the coil 103.

  The switching element 105 is connected in series with the coil 103 and forms a closed loop from the full wave rectifier circuit 12 to the full wave rectifier circuit 102 through the resonance circuit 112 and the switching element 105. The type of the switching element 105 is not limited, but in this embodiment, the above-described insulated gate bipolar transistor (IGBT) is used.

  The IGBT drive circuit 106 performs high-frequency switching drive of the switching element 105 by turning on and off the switching element 105 based on an instruction from the power control unit 107.

  The power control unit 107 controls the power supplied to the fixing roller by controlling on / off of the switching element 105 via the IGBT drive circuit 106, and includes a CPU, ROM, RAM, and the like (not shown). ing.

  The abnormal voltage detection circuit 108 detects an abnormal voltage such as a surge voltage or an abnormal fluctuation voltage input to the commercial power supply 101 with quick response. Although the configuration of the abnormal voltage detection circuit 108 is not limited, for example, an AC voltage of the commercial power supply 101 is divided and compared with a reference value, and an abnormal voltage detection signal is output when the divided voltage exceeds the reference value. Can do.

  The input voltage detection circuit 109 detects a voltage input from the commercial power supply 101 to the coil 103 via the full-wave rectification circuit 102, and the input current detection circuit 111 similarly detects the input current, and is a power control unit. Reference numeral 107 receives detection results from the input voltage detection circuit 109 and the input current detection circuit 111 and stabilizes the power supplied to the fixing roller 30 that is a heated body. Note that the input voltage detection circuit 109 may be less responsive than the abnormal voltage detection circuit 108.

  The zero cross detection circuit 110 is a circuit that detects a zero cross of the AC voltage of the commercial power supply 101 and outputs a zero cross signal.

  The power control unit 107 receives a set value of power supplied to the fixing roller 30 and an instruction to start control from the control circuit 21 in the main body control unit 20 of the image forming apparatus 1, and becomes an instructed power output value. As described above, the switching element 105 is controlled to be turned on / off via the IGBT drive circuit 106.

  Furthermore, the power control unit 107 receives detection signals from the abnormal voltage detection circuit 108 and the zero cross detection circuit 110, and controls the power output of the switching element 105 as follows.

  First, a conventional control method will be described with reference to FIG.

  FIG. 2A shows a state where the surge voltage Vs is input to the AC voltage V of the commercial power supply 101 at time T1. The AC voltage V has both positive and negative peak voltages Vp smaller than the damage level Vt of the switching element 105, and the surge voltage Vs exceeds the damage level ± Vt.

  When the surge voltage Vs is detected at time T1, the power control unit 107 immediately stops the switching control for the switching element 105 and stops the power supply (also referred to as power output) to the fixing roller 30, but the surge voltage Vs is It occurs only once and irregularly.

  FIG. 2B shows a state where both positive and negative peak voltages Vp exceed the damage level ± Vt of the switching element 105 due to abnormal fluctuation of the AC voltage V. When an abnormal fluctuation voltage is detected at time T <b> 2, the power control unit 107 immediately stops switching control on the switching element 105 and stops power output to the fixing roller 30. Since this abnormal fluctuation voltage is repeated, the power output to the fixing roller 30 is stopped until it is determined as an abnormal fluctuation voltage, and when it is determined as an abnormal fluctuation voltage, it is completely stopped and checked. It is supposed to do.

  On the other hand, since it is not easy to distinguish between a surge voltage and an abnormal fluctuation voltage, the surge voltage Vs shown in FIG. As in the case of (B), the power output to the fixing roller 30 was stopped until it was determined that the voltage was not an abnormal fluctuation voltage.

  Next, a control method according to this embodiment will be described with reference to FIGS.

  FIG. 3A shows a state where the surge voltage Vs is input to the AC voltage V of the commercial power supply 101 at time T3. The AC voltage V has both positive and negative peak voltages Vp smaller than the damage level Vt of the switching element 105, and the surge voltage Vs exceeds the damage level ± Vt.

  When the surge voltage Vs is detected at time T3, the power control unit 107 immediately stops switching control for the switching element 105 and temporarily stops power output to the fixing roller 30, but at the timing T4 of the next zero cross signal, Restart switching control. Since the AC voltage is low at zero crossing, the power output can be resumed without damaging the switching element 105.

  Further, since the surge voltage Vs is generated only once and irregularly, the power output is continued as it is.

  FIG. 3B shows a state where both positive and negative peak voltages Vp exceed the failure level ± Vt of the switching element 105 due to abnormal fluctuations in the AC voltage V.

  When an abnormal fluctuation voltage is detected at time T5, the power control unit 107 immediately stops switching control for the switching element 105 and temporarily stops power output to the fixing roller 30, but at the timing T6 of the next zero cross signal. The switching control for the switching element 105 is resumed.

  Next, when an abnormal fluctuation voltage is detected at time T7, the power control unit 107 immediately stops switching control for the switching element 105. Then, the power control unit 107 counts the time from the zero-cross timing T6 to the timing T7 when the abnormal voltage is detected, in other words, the most recent on-time of the switching element 105, and after holding the result, Switching control for the switching element 105 is resumed at timing T8.

  Next, when an abnormal voltage is detected at time T <b> 9, the power control unit 107 immediately stops switching control for the switching element 105. The power control unit 107 counts the time from the zero cross timing T8 to the time T9 when the abnormal fluctuation voltage is detected, and then compares this count value with the count value at the time of detecting the previous abnormal voltage.

  If both count values are the same, it judges that it is not a surge voltage but an abnormal fluctuation voltage, and stops switching control. Therefore, the power output to the fixing roller 30 is completely stopped, and the cause is investigated.

  It should be noted that the same count value does not mean completely the same, and the difference between the two may be within a predetermined range. Alternatively, the abnormal fluctuation voltage may be detected three or more times, and when the same count value continues twice or more, it may be determined as abnormal and the power output to the fixing roller 30 may be completely stopped.

  In addition, when a single surge voltage is frequently input or when an irregular fluctuation voltage occurs, an abnormality may not be detected by the method shown in FIG.

  Therefore, in this embodiment, the number of abnormal voltage detections per unit time is counted, and when a preset threshold value is reached, it is determined that there is an abnormality, switching control for the switching element 105 is stopped, and The power output is completely stopped.

  For example, as shown in FIG. 4A, when the surge voltage Vs is generated at time T11, the switching control for the switching element 105 is immediately stopped to stop the power output, and then restarted at the next zero-crossing timing T12. . After that, when the surge voltage Vs is generated again at time T14, the power output is stopped. However, when the number of occurrences within the unit time reaches the threshold value, it is determined as abnormal and the power output is restarted at the next zero cross. Without stopping.

  Further, as shown in FIG. 4B, voltage fluctuations occur irregularly. For example, when an abnormal voltage is generated at time T18 and further an abnormal voltage is generated at time T20, the former and the latter from zero crossing. The time is (T18-T17) in the former and (T20-T19) in the latter, and the time from the zero cross is different. For this reason, although it is not determined to be abnormal by the method of FIG. 3, if the number of occurrences within a unit time when an abnormal voltage occurs at time T20 reaches a threshold value, it is determined as abnormal and power is output at the next zero cross. Without restarting, the system is set to the stopped state.

  As described above, even when the number of occurrences of the abnormal voltage within the unit time is equal to or greater than a certain value, the power output to the heated body is completely stopped. it can.

  FIG. 5 is a flowchart for explaining the operation of the power control unit 107.

  In step S01, a power control instruction including a set value of supply power and a control start instruction is received from the control circuit 21 of the main body control unit 20 in the image forming apparatus 1, and based on this, a power output is output to the IGBT drive circuit 106. And switching control of the switching element 105 is performed.

  In step S02, it is determined from the output of the abnormal voltage detection circuit 108 whether or not an abnormal voltage has been detected. If not detected (NO in step S02), the process returns to step S01 to continue the power output. When an abnormal voltage is detected (YES in step S02), power output is stopped in step S03, and then in step S04, an abnormal voltage detection timer is started, zero cross interrupt processing is started, and the number of abnormal voltage detections is counted. The number of detections is set in the abnormality counter.

  FIG. 6 shows the zero cross interrupt processing.

  In step S041, whether or not a zero cross signal is detected is checked from the output of the zero cross detection circuit 110. If not detected (NO in step S041), the process waits until it is detected (YES in step S041), and in step S042 Start after resetting the zero cross timer. Also, the power output is resumed.

  Next, in step S043, it is determined whether or not an abnormal voltage has been detected. If not (NO in step S043), the process returns. If an abnormal voltage is detected (YES in step S043), the abnormality counter is incremented by 1 in step S044, and the time from the zero cross detected in step S041 to the abnormality detection (zero cross timer value) is stored, and then the process returns. .

  Returning to FIG. 5, in step S05, it is checked whether or not the count value of the abnormality counter has reached the threshold (YES in step S05), the process proceeds to step S09, and it is determined that there is an abnormality. In this case, the power output is completely stopped. If the threshold value has not been reached (NO in step S05), it is checked in step S06 whether the zero-cross timer value stored at the time of the previous occurrence of abnormal voltage is the same as the current zero-cross timer value (whether it is within a certain range).

  If they are the same (YES in step S06), the process proceeds to step S09 to determine that there is an abnormality. If not the same (NO in step S06), it is determined in step S07 whether or not the abnormal voltage detection timer has expired. If not completed (NO in step S07), the process returns to step S05. If completed (YES in step S07), the zero cross interrupt process is terminated in step S08.

  Incidentally, FIG. 7 shows a conventional process when an abnormal voltage is detected.

  In step S <b> 21, a power control instruction including a set value of supply power and a control start instruction is received from the control circuit 21 of the main body control unit 20 in the image forming apparatus 1, and based on this, a power output is output to the IGBT drive circuit 106. And switching control of the switching element 105 is performed.

  In step S22, it is determined whether an abnormal voltage is detected. If not detected (NO in step S22), the process returns to step S21 to continue the power output. If detected (YES in step S22), the power output is stopped in step S23, and then the stop timer is started in step S24.

  Next, in step S25, it is determined whether or not the set time by the stop timer has ended. If not (NO in step S25), the process waits until the end. If completed (YES in step S25), the abnormal voltage detection timer is started and the power output is restarted in step S26.

  Next, in step S27, it is checked whether or not an abnormal voltage is detected again. If detected (YES in step S27), it is determined in step S29 that it is abnormal. If not detected (NO in step S27), it is determined in step S28 whether or not the abnormal voltage detection timer has expired. If not (NO in step S28), the process returns to step S26. If completed (YES in step S28), the process is terminated.

  As mentioned above, although one Embodiment of this invention was shown, this invention is not limited to the said embodiment.

  For example, although detection of abnormal voltage, detection of zero crossing, and the like are performed on the induction heating device 10 side, the control circuit 21 of the main body control unit 20 may perform the detection.

  Moreover, although the case where the induction heating apparatus 10 was used for the image forming apparatus 1 was shown, the use of the induction heating apparatus 1 is not limited.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Induction heating apparatus 20 Main body control part 21 Control circuit 30 Fixing coil 101 Commercial power supply 102 Full wave rectifier circuit 103 Coil 104 Capacitor 105 Switching element 107 Power control part 108 Abnormal voltage detection circuit 110 Zero cross detection circuit

Claims (4)

AC power supply,
A rectifier circuit for rectifying an alternating voltage from the alternating current power source into a direct current;
A DC voltage obtained by the rectifier circuit is applied, and a coil for inductively heating an object to be heated;
A switching element connected in series to the coil;
Power control means for controlling power supplied to the object to be heated by controlling on / off of the switching element;
Abnormal voltage detection means for detecting abnormal voltage;
Zero-cross detection means for detecting a zero-cross of the AC voltage;
Time counting means for counting the time from the zero cross detected by the zero cross detecting means to the abnormal voltage detected by the abnormal voltage detecting means;
With
When an abnormal voltage is detected by the abnormal voltage detection unit, the power control unit temporarily stops power supply to the heated body and supplies power at the timing of the zero cross detected by the zero cross detection unit. When the time from the zero cross when the abnormality is detected again to the abnormal voltage is within a certain range with the time from the zero cross at the previous abnormal voltage detection to the abnormal voltage, the power to the object to be heated An induction heating device characterized in that supply is completely stopped. Comprising a counting means for counting the number of occurrences of the abnormal voltage;
2. The induction heating according to claim 1, wherein the power control unit completely stops the power supply to the heated object even when the number of occurrences of the abnormal voltage counted by the counting unit within a unit time is equal to or greater than a predetermined value. apparatus. The power control means is such that the time count value from the zero cross to the abnormal voltage when the abnormality is detected again is the same value as the time count value from the zero cross to the abnormal voltage at the previous abnormal voltage detection. The induction heating apparatus according to claim 1, wherein when the power is, the power supply to the heated body is completely stopped. An image forming apparatus, wherein the induction heating device according to claim 1 is used as a heating source of a fixing device.

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