JP4585803B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that ensures safety by stopping energization of a heater when an abnormally high temperature of a fixing heater occurs.

  In an electrophotographic image forming apparatus such as a copying apparatus, a printer apparatus, and a facsimile apparatus, an electrostatic latent image is formed on a photosensitive member by light modulated based on image information, and the photosensitive member on which the electrostatic latent image is formed. The toner is attached to the body and developed. The image forming apparatus transfers the toner attached to the photosensitive member to a transfer sheet, and the pressure roller is pressed against the fixing roller and the fixing roller heated by the fixing heater of the fixing unit. And the transfer paper is heated and pressed by a fixing roller and a pressure roller to fix the toner onto the transfer paper.

  Conventionally, this fixing device employs a heating method using a halogen heater as a heat source as a fixing heater, and a representative of a thermistor is used to control the temperature of the fixing roller heated by the fixing heater. The temperature control element is brought into contact with a protective film such as polyimide. The image forming apparatus supplies power to the halogen heater by an AC power supply circuit including a safety device such as an AC power source, a triac, a thermal fuse, and an electric wire connecting them, and raises the temperature of the fixing roller to a predetermined fixing temperature. Yes.

  As a heat source for the fixing device of the image forming apparatus, a radiation heater called a halogen heater in which a halogen substance that is an indirect heating type radiation heat source is enclosed is widely used because of its low cost and high safety. Yes.

  However, in recent years, radiation heaters that do not enclose halogen substances and radiation heaters that use carbon as a filament to obtain infrared radiation have been developed due to environmental problems.

  Further, in an image forming apparatus that is fixed by a fixing device, ensuring the safety of the fixing device is an important problem.

  Therefore, conventionally, a circuit having a memory function for detecting a temperature abnormality of the fixing heater and forcibly turning off the fixing heater, but maintaining the off state, can only release a predetermined soft setting sequence. A heater control circuit and an image forming apparatus provided have been proposed (see Patent Document 1).

  Conventionally, image formation in which the cause of an abnormality can be easily recognized by temporarily holding each output signal of a plurality of abnormality detection units by hardware corresponding to the cause of the abnormality in a register. An apparatus has been proposed (see Patent Document 2).

  Various proposals have been made for a fixing device using a radiant heater and an image forming apparatus using the fixing device (see Patent Document 3, etc.).

  In addition, an image forming apparatus that uses a DC power supply and reduces the influence on the power supply environment such as power supply voltage fluctuation and shortens the rise time has been conventionally proposed (see Patent Document 4).

JP 2004-077755 A JP 2000-122489 A JP 2002-139939 A JP 2002-278352 A

However, an image forming apparatus having a fixing unit using a radiant heater driven by a DC power source as a fixing heater has conventionally existed. However, in the above-described conventional technique, a technique in consideration of safety of heater driving is known. Is not disclosed, and there is a demand for the development of an image forming apparatus including a fixing unit including a radiation heater that is driven by an efficient DC power source while improving safety and having a quick start-up.
Therefore, the present invention detects an abnormally high temperature before the thermal fuse is blown, and stops the drive of the radiant heater in a hardware (electrical circuit), preventing the occurrence of a fire or the like even in the case of malfunction or erroneous detection. An object of the present invention is to provide an image forming apparatus that ensures safety and suppresses damage in the event of an abnormality.

In order to achieve the above object, the present invention provides an image forming apparatus including a fixing unit that heats and fixes a sheet onto which a developer has been transferred using a fixing roller heated by a radiant heater. Temperature detection means for detecting the power supply, power supply means for supplying DC power to the radiation heater, and supply power control means for controlling DC power supplied from the power supply means to the radiation heater based on the detection result of the temperature detection means If, when the temperature detecting means detects a predetermined abnormally high temperature, it causes an abnormality stop signal and an abnormal power stopping means for stopping the supply of the DC power to the radiant heater from the power supply unit, the abnormality The power stop means latches the abnormal stop signal, generates a delay by the zero cross signal from the zero cross signal output means, and then outputs the heater drive signal. Include a latching means for sealed, is connected to the AC power supplied to the power supply unit detects a zero-cross point of the AC power supply, and the zero cross signal output means for outputting the latch circuit to generate a zero cross signal, the It is characterized by .
In this case, when the abnormal power supply stopping means stops supplying DC power from the power supply means to the radiant heater by detecting the abnormally high temperature, the abnormality occurrence information is displayed on the display means. When the abnormal power supply stopping means stops the supply of DC power from the power supply means to the radiant heater by detecting the abnormally high temperature, the voice output is provided. An alarm sound indicating that an abnormality has occurred in the means can be output.

By the present invention lever, when an abnormally high temperature occurred in the fixing heater, reliably stop the energization of the heater it is possible to ensure safety, Ru can be suppressed damage abnormality.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, since the Example described below is a suitable Example of this invention, various technically preferable restrictions are attached | subjected, However, The scope of the present invention limits this invention especially in the following description. As long as there is no description of the effect, it is not restricted to these aspects.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus of the present invention. FIG. 1 is a block diagram of a DC fixing heater driving unit 1 of the image forming apparatus to which an embodiment of the image forming apparatus of the present invention is applied. FIG. The DC fixing heater driving unit 1 determines the maximum DC voltage supplied to the radiation heater 8 according to the system configuration of the image forming apparatus, and controls the heater power by varying the control voltage within the range of the maximum DC voltage. have.

  In FIG. 1, a DC fixing heater driving unit 1 controls driving of a DC fixing unit DCT of an image forming apparatus such as a copying machine that forms an image by an electrophotographic method, and includes a noise filter 2, an input relay 3, a zero cross circuit 4, and a switch. Element 22, diode bridge 6, step-up chopper circuit 7, radiation heater 8, temperature fuse 9, temperature detection circuit 10, engine control circuit 11, high temperature detection circuit 12, latch circuit 13, AND circuits 14 and 15, NAND circuit 16 and buffer 17 etc.

  The step-up chopper circuit (power supply means) 7 is connected between the diode bridge 6 and the radiant heater 8, and includes the inductor 21, the switch element 22, the drive circuit 23, the rectifier diode 24, the smoothing capacitor 25, the output voltage detection circuit 26, and the above-mentioned. A switch element 5 and the like are provided.

  The engine control circuit 11 includes a microcomputer (not shown) that controls the system of the image forming apparatus main body and peripheral devices to which the DC fixing heater driving unit 1 is applied, a control voltage calculation block 31, a heater. A temperature control block 32, a connection detection block 33, a non-volatile memory 34, and the like are provided. The connection detection block 33 includes, for example, an additional paper feed unit 41, a duplex unit 42, a paper discharge sorter unit 43, a connection operation unit 44, and a buzzer. 45 etc. are connected.

  An external AC power supply 50 is connected to the noise filter 2, and the noise filter 2 performs full-wave rectification of the AC power supply 50 and supplies it to the diode bridge 6 via the input relay 3. The generated high frequency noise is attenuated to attenuate the outflow to the AC power supply 50 and the inflow of the high frequency noise from the AC power supply 50 to the boost chopper circuit 7.

  The zero cross circuit 4 is connected to an AC power source supplied to the diode bridge 6, detects a zero cross point of the AC power source, generates a zero cross signal, and outputs the zero cross signal to the latch circuit 13.

  The diode bridge 6 performs full-wave rectification on the input AC power supply and supplies it to the boost chopper circuit 7.

  The boost chopper circuit 7 has an inductor 21 connected to the diode bridge 6, and the inductor 21 includes an output signal of the heater temperature control block 32 of the engine control circuit 11, a switch element 22 driven by the drive circuit 23, and a rectifier diode 24. It is connected to the. Further, the rectified output of the rectifier diode 24 is output to the smoothing capacitor 25 and the radiation heater 8, and the output voltage detection circuit 26 detects the voltage across the smoothing capacitor 25, that is, the output voltage to the radiation heater 8, and the engine. This is output to the heater temperature control block 32 of the control circuit 11. The switch element 22 is usually a transistor, FET (Field Effect Transistor), or GTIB, and is driven by the drive circuit 23 at a high frequency of, for example, 20 kHz or more.

  The drive circuit 23 drives the switch element 22 according to the output signal of the heater temperature control block 32 of the engine control circuit 11. That is, when the output signal of the heater temperature control block 32 of the engine control circuit 11 becomes high, the drive circuit 23 turns on the switch element 22 and charges the inductor 21 with energy. At this time, no current flows through the rectifier diode 24 and the smoothing capacitor 25. Next, when the output signal of the heater temperature control block 32 of the engine control circuit 11 becomes low, the drive circuit 23 stops charging the inductor 21 and the voltage at the connection point between the inductor 21 and the switch element 22. Increases due to the self-inductance of the inductor 21 and becomes equal to or higher than the forward voltage of the rectifier diode 24 plus the voltage of the smoothing capacitor 25, the rectifier diode 24 becomes conductive and rectified, and the smoothing capacitor 25 is charged and smoothed. Is done. The voltage of the smoothing capacitor 25 is almost direct current. The magnitude of the DC voltage of the smoothing capacitor 25 can be varied by the duty ratio when the load impedance is constant, when the switch element 22 is driven by the fixed frequency method, and when the frequency modulation method is used. Can be varied in its on or off period. Specifically, in the fixed frequency method, the on-duty and the output voltage are proportional, and in the frequency modulation method, the on-cycle and the output voltage are proportional when the off-period is constant, and when the on-period is constant, the off-duty is off. The period and output voltage are inversely proportional. As the switch element 22, a triac, a thyristor or the like is usually used.

  The DC voltage of the step-up chopper circuit 7 is controlled to be a value calculated by the control voltage calculation block 31 of the engine control circuit 11, and this DC voltage is supplied to the radiation heater 8 and the thermal fuse 9, and the radiation heater 8 Heats the fixing roller of the DC fixing unit DCT (not shown). The temperature detection circuit (temperature detection means) 10 is disposed in the vicinity of the fixing roller that is the heating target of the radiation heater 8, detects the temperature of the fixing roller, and outputs a detection signal to the heater temperature control block of the engine control circuit 11. 32 and the high temperature detection circuit 12.

  The radiant heater 8 is, for example, a radiant heater excellent in thermal responsiveness, in which a tungsten filament is enclosed in a glass tube together with an inert gas.

  The temperature fuse 9 has an operation set temperature that is set higher than a set temperature of a fixing roller (not shown). When the temperature fuse 9 reaches an operation set temperature due to some abnormality, the temperature fuse 9 is cut off and power supply to the radiation heater 8 is stopped. Let

  The detected temperature signal from the temperature detection circuit 10 is input to the control voltage calculation block 31 and the heater temperature control block 32 of the engine control circuit 11, and the control voltage calculation block 31 is based on the detected temperature signal. The DC voltage of the boost chopper circuit 7 is controlled by controlling the drive of the boost chopper circuit 7 through the heater temperature control block 32 so that the temperature of the fixing roller becomes a predetermined fixing temperature.

  The heater temperature control block 32 outputs the drive control signal to the drive circuit 23 via the AND circuit 14 according to the output voltage detection signal detected by the output voltage detection circuit 26 under the control of the control voltage calculation block 31. In addition, an ON / OFF control signal is output to the switch element 5 via the AND circuit 15, and an ON / OFF control signal is output to the input relay 3 via the NAND circuit 16 and the buffer 17.

  The high temperature detection circuit 12 uses, for example, a comparison circuit (comparator) and compares the detection temperature of the fixing roller input from the temperature detection circuit 10 with a preset high temperature abnormality detection level that is an abnormally high temperature. When the detected temperature exceeds the high temperature abnormality detection level (abnormally high temperature), an abnormal stop signal is generated and output to the latch circuit 13.

  Further, as described above, the zero-cross signal is input from the zero-cross circuit 4 to the latch circuit (latch means) 13. When the zero-cross signal is input from the zero-cross circuit 4, the latch circuit 13 receives the high-temperature detection circuit 12. Are latched and output to the AND circuits 14 and 15 and the NAND circuit 16. That is, the latch circuit 13 generates a delay from the abnormal stop signal from the high temperature detection circuit 12 by the zero cross signal from the zero cross circuit 4, and then outputs it to the AND circuits 14 and 15 and the NAND circuit 16 to control the heater temperature. The output of the drive signal from the block 32 is stopped, and the voltage output to the radiation heater 8 is stopped. That is, if the high temperature detection circuit 12 determines that the temperature detection circuit 10 that detects the temperature of the radiant heater 8 has detected an abnormally high temperature, an abnormal stop signal is output to the latch circuit 13, and the latch circuit 13 delays based on the zero cross signal. , The AND circuit 14 is closed, and the drive control signal output from the heater temperature control block 32 is stopped, whereby the drive of the switch element 22 by the drive circuit 23 is stopped, and the direct current to the radiation heater 8 is stopped. The supply of voltage is cut off, and the switch element 5 is turned off and the input relay 3 is turned off.

  Then, as described above, the DC fixing heater driving unit 1 delays the abnormal stop signal output from the high temperature detection circuit 12 by the latch circuit 13 based on the zero cross signal from the zero cross circuit 4, whereby the input relay 3. The relay off signal for turning off the signal is generated at a timing including a delay corresponding to the time (half cycle or more) when the switch element 5 is turned off to prevent welding to the relay contact portion.

  The high-temperature detection circuit 12, the latch circuit 13, the AND circuits 14 and 15, the NAND circuit 16, the switch element 5, and the input relay 3 function as an abnormal power supply stop unit as a whole.

  The control voltage calculation block 31 of the engine control circuit 11 receives the temperature signal detected by the temperature detection circuit 10 and calculates the control maximum voltage and the control set voltage as shown below. Therefore, the control voltage calculation block 31 and the heater temperature control block 32 function as supply power control means as a whole.

  That is, the maximum control voltage is determined by the signal of the connection detection block 33 of the engine control circuit 11. The connection detection block (system configuration detection means) 33 is, for example, an image forming apparatus to which the DC fixing heater driving unit 1 is applied. In the case of a copying machine, this is a circuit for detecting optional connection of an additional paper feeding unit 41, a duplex unit 42, a paper discharge sorter unit 43, etc., and is usually attached to an image forming apparatus. Then, when the system configuration of the image forming apparatus is detected by the connection detection block 33, the maximum control power voltage can be recognized from the maximum power consumption of the heater power in the detected system configuration. A maximum control voltage is determined.

  For example, assuming that the maximum power in the full system of the image forming apparatus is Ws1, the heater power is Wh1, and the load power other than the radiation heater 8 is Wo1, the maximum power Ws1 = Wh1 + Wo1. When the electric power Wh1 of the radiant heater 8 is determined, and the resistance value of the radiant heater 8 is Z, the maximum value Vh1 of the control voltage is determined by Vh1 = Wh1 / Z. Next, assuming that load power other than one option of the image forming apparatus, for example, the radiation heater 8 when the paper discharge sorter unit 43 is not connected is Wo2, Wo1> Wo2. This is because the power of the entire image forming apparatus can be used up to Ws1 even when the paper discharge sorter unit 43 is not connected. Therefore, assuming that the power of the radiation heater 8 in this system is Wh2, Wh2 = Wh1 + Wo1-Wo2. Can be. The power Wh2 of the radiant heater 8 in this system is larger than the power Wh1 of the radiant heater 8 in the full system by the capacity Wo1-Wo2, so if the maximum value of the control voltage of the radiant heater 8 is Vh2, Vh2 = Wh2 / Z, Vh2> Vh1, and the power of the radiation heater 8 can be increased.

  The control set voltage is calculated as follows, for example. That is, the control set voltage is calculated by the following equations (1), (2), and (3) from the detected value and target temperature that are provided around the radiation heater 8 and that detects the temperature of the fixing roller. It is determined.

A = B + α (1)
_{α = a (t a-1} -t a) + b (2 × t a-1 -t a -t a-2) + c (T-t a) ··· (2)
A ≦ Vhmax (3)
Here, T: target temperature, t _a : measurement temperature, t _a-1 : previous detection temperature, t _a-2 : previous detection temperature, a / b / c: coefficient, A: control set voltage, B: initial value , Α: increase / decrease amount, Vhmax: maximum control voltage (value determined by the system configuration of the image forming apparatus). The coefficient a / b / c is determined by the operating environment temperature, the heater capacity, the response time of the power supply circuit, and the like.

  The control set voltage can be set at an arbitrary time. For example, in the case of the value determined by the above formulas (1) to (3), at the time of warm-up, the control with almost no overshoot of the roller temperature, the roller temperature Even when an image with a large change in temperature is formed, control with small temperature ripple becomes possible.

  Next, the operation of this embodiment will be described. The DC fixing heater driving unit 1 according to the present embodiment controls the DC voltage supplied from the step-up chopper circuit 7 to the radiation heater 8 based on the temperature detected by the temperature detection circuit 10 to control the temperature of the DC fixing unit DCT. When the temperature detection circuit 10 detects an abnormally high temperature, the energization from the step-up chopper circuit 7 to the radiation heater 8 is stopped to ensure safety.

  That is, the DC fixing heater driving unit 1 reduces the high frequency noise of the AC power supply 50 with the noise filter 2 and supplies the AC power supply 50 to the diode bridge 6 via the input relay 3 and the switch element 5. It is detected by the zero cross circuit 4 and a zero cross signal is output to the latch circuit 13.

  The DC fixing heater driving unit 1 performs full-wave rectification of the AC power supply 50 with the diode bridge 6 and applies it to the inductor 21 of the step-up chopper circuit 7, and connects the switch element 22 connected to the inductor 21 via the AND circuit 14. Then, the drive circuit 23 performs on / off drive at a high frequency of, for example, 20 KHz or more by a drive signal from the heater temperature control block 32. That is, the heater temperature control block 32 of the engine control circuit 11 sets the output signal to high, thereby causing the drive circuit 6 to turn on the switch element 22 and charging the inductor 21 with energy. At this time, no current flows through the rectifier diode 24 and the smoothing capacitor 25. Next, the heater temperature control block 32 of the engine control circuit 11 stops the charging of the inductor 21 by setting the output signal to low, and the voltage at the connection point between the inductor 21 and the switch element 22 is changed to the inductor. When the voltage at the connection point between the inductor 21 and the switch element 22 becomes equal to or higher than the voltage obtained by adding the voltage of the smoothing capacitor 25 to the forward voltage of the rectifier diode 24, the rectifier diode 24 conducts and rectifies. Then, the smoothing capacitor 25 is charged and smoothed.

  The DC fixing heater driving unit 1 controls the DC voltage of the boost chopper circuit 7 so as to be a value calculated by the control voltage calculation block 31, and supplies this DC voltage to the radiation heater 8 and the thermal fuse 9 for radiation. A fixing roller (not shown) is heated by the heater 8.

  The temperature detection circuit 10 detects the temperature of the fixing roller heated by the radiation heater 8 that is heated by the DC voltage from the boost chopper circuit 7, and the engine control circuit 11 is based on the detected temperature of the temperature detection circuit 10. The temperature of the fixing roller is controlled by controlling the driving of the driving circuit 23 of the step-up chopper circuit 7 and controlling the on / off of the switch element 22.

  When the high temperature detection circuit 12 detects that the temperature detection circuit 10 has detected a predetermined abnormal high temperature, the DC fixing heater driving unit 1 causes the high temperature detection circuit 12 to latch an abnormal stop signal. When the zero cross signal from the zero cross circuit 4 is input, the latch circuit 13 outputs the latched abnormal stop signal to the AND circuits 14 and 15 and the NAND circuit 16 to drive the drive circuit 23. At the same time, the switch element 5 is turned off and the input relay 3 is turned off.

  Therefore, energization from the boost chopper circuit 7 to the radiation heater 8 is stopped, and safety is ensured.

  As described above, the DC fixing heater driving unit 1 according to this embodiment includes the DC fixing unit DCT that heats and fixes the sheet onto which the developer has been transferred using the fixing roller heated by the radiation heater 8. When the heater temperature control block 32 controls the DC power supplied from the step-up chopper circuit 7 to the radiation heater 8 based on the temperature detection circuit 10 that detects the temperature of the current, the temperature detection circuit 10 detects a predetermined abnormally high temperature. The high temperature detection circuit 12 generates an abnormal stop signal to stop the supply of DC power from the boost chopper circuit 7 to the radiation heater 8.

  Therefore, before the thermal fuse 9 is blown, an abnormally high temperature can be detected and the driving of the radiation heater 8 can be stopped in a hardware (electrical circuit) manner. It can prevent and secure safety, and can suppress damage at the time of abnormality.

  Further, in the DC fixing heater driving unit 1 of this embodiment, the heater temperature control block 32 supplies the maximum power and the control maximum voltage supplied to the radiation heater 8 according to the system configuration of the image forming apparatus detected by the connection detection block 33. The control voltage that can be set to any value within the range of the maximum control voltage is calculated from the difference between the detected temperature of the fixing roller and the target temperature detected by the temperature detection circuit 10 and the temperature change rate of the fixing roller. The DC power source is controlled based on the control voltage.

  Accordingly, even when the power supply to the radiation heater 8 is controlled based on the maximum power and the control maximum voltage according to the system configuration, the abnormal heater is detected and the radiation heater is driven before the thermal fuse 9 is blown. Can be stopped by hardware (electrical circuit), and it is possible to prevent the occurrence of a fire, etc., and to ensure safety in the event of a malfunction or error detection, and to suppress damage in the event of an abnormality. it can.

  Further, when the high temperature detection circuit 12 detects an abnormally high temperature, the DC fixing heater driving unit 1 outputs an abnormal stop signal to the latch circuit 13 and the latch circuit 13 holds the abnormal stop signal. Yes. The DC fixing heater driving unit 1 does not cancel the output of the drive stop signal from the latch circuit 13 to the drive circuit 23, the switch element 5, and the input relay 3 unless the operator performs an operation such as power off / on. In addition, the heater re-lighting operation is prevented, and continuous operation such as fixing high temperature detection is prevented.

  Therefore, even when the energization to the radiation heater 8 is stopped and the temperature of the fixing roller is lowered to the steady temperature, the latch circuit 13 outputs the latched abnormal stop signal to the AND circuits 14 and 15 and the NAND circuit 16. Subsequently, the drive of the drive circuit 23 is continuously stopped and the switch element 5 and the input relay 3 are continuously turned off.

  As a result, even if the temperature detected by the temperature detection circuit 10 returns to normal or the apparatus power is turned on / off, the heater drive is not returned until the safety of the operation of the image forming apparatus is confirmed. By stopping the operation, it is possible to prevent the temperature abnormality of the fixing roller from being repeated, thereby further ensuring safety.

  Further, the DC fixing heater driving unit 1 stores an abnormal stop signal that has detected an abnormally high temperature in the nonvolatile memory 34 of the engine control circuit 11, and the history of performing abnormality detection even when the image forming apparatus is turned off / on. And the fixing heater control may be stopped based on the presence or absence of abnormality processing when the power is turned on again.

  For example, the DC fixing heater driving unit 1 performs the cancellation based on the abnormality detection flag data on the nonvolatile memory 34, and cancels the abnormality mode only by rewriting the abnormality detection flag data only from the SP mode or the like and performing a clear process. By enabling the fixing heater control, if there is no operation such as power off / on by the operator, the abnormal mode is not canceled and the heater re-lighting operation is prevented, and the fixing high temperature detection and the like are continuously performed. You may make it prevent operation | movement.

  Therefore, even if the temperature detected by the temperature detection circuit 10 returns to normal or the apparatus power is turned on / off, the heater is driven until the operator deletes the abnormal high temperature detection history information in the nonvolatile memory 34. By stopping without returning, it is possible to prevent the temperature abnormality of the fixing roller from being repeated, thereby further ensuring safety.

  Furthermore, when the high temperature detection circuit 12 detects the abnormally high temperature detected by the temperature detection circuit 10, the DC fixing heater driving unit 1 causes the engine control block 11 to display an abnormality occurrence message on the display of the connection operation unit 44. Further, the occurrence of abnormality may be notified by sound such as sounding the buzzer 45, and the user may be immediately notified of abnormality information of the image forming apparatus.

  If it does in this way, a user can be able to respond appropriately and usability and safety can be secured further.

  The invention made by the present inventor has been specifically described based on the preferred embodiments. However, the present invention is not limited to the above, and various modifications can be made without departing from the scope of the invention. Needless to say.

  It is possible to provide an image forming apparatus including a DC fixing heater driving unit that reliably stops energization to the radiant heater at an abnormally high temperature of the fixing unit to ensure safety.

1 is a block configuration diagram of a DCDC fixing heater driving unit of an image forming apparatus to which an embodiment of the image forming apparatus of the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC fixing heater drive part 2 Noise filter 3 Input relay 4 Zero cross circuit 22 Switch element 6 Diode bridge 7 Boost chopper circuit 8 Radiation heater 9 Thermal fuse 10 Temperature detection circuit 11 Engine control circuit 12 High temperature detection circuit 13 Latch circuit 14, 15 AND Circuit 16 NAND circuit 17 Buffer 21 Inductor 22 Switch element 23 Drive circuit 24 Rectifier diode 25 Smoothing capacitor 26 Output voltage detection circuit 31 Control voltage calculation block 32 Heater temperature control block 33 Connection detection block 34 Non-volatile memory 41 Additional paper feed unit 42 Duplex unit 43 Discharge sorter unit 44 Connection operation section 45 Buzzer 50 AC power supply DCT DC fixing section

Claims (3)

In an image forming apparatus provided with a fixing unit that heats and fixes a sheet onto which a developer has been transferred using a fixing roller heated by a radiation heater,
Temperature detecting means for detecting the temperature of the fixing roller;
Power supply means for supplying DC power to the radiation heater;
Supply power control means for controlling a DC power supplied from the power supply means to the radiation heater based on a detection result of the temperature detection means;
When the temperature detecting means detects a predetermined abnormally high temperature, an abnormal power stop means for generating an abnormal stop signal and stopping the supply of DC power from the power supply means to the radiation heater;
Equipped with a,
The abnormal power stop means is
Latch means for latching the abnormal stop signal, generating a delay by the zero cross signal from the zero cross signal output means, and then stopping the output of the heater drive signal;
An image forming system comprising: zero cross signal output means connected to an AC power source supplied to the power source means, detecting a zero cross point of the AC power source, generating a zero cross signal, and outputting the zero cross signal to a latch circuit. apparatus. Provided with a predetermined display means, and when the abnormal power supply stop means stops the supply of DC power from the power supply means to the radiation heater upon detection of the abnormally high temperature, the abnormality occurrence information is displayed on the display means. the image forming apparatus according to claim 1, wherein the cause. A predetermined audio output means, and when the abnormal power supply stop means stops the supply of DC power from the power supply means to the radiant heater by detecting the abnormally high temperature, the audio output means that an abnormality has occurred the image forming apparatus according to claim 1 or 2, wherein the to output an alarm sound.

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