JP2006276276A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely and inexpensively prevent a malfunction in the case of excessive rise of fixing temperature and when noise is generated to fixing thermistor output and to detect a relay failure. <P>SOLUTION: Since a zero cross signal is generated independently of on/off of a main heating element shielding means 11, there is no timing in which a fixing double monitor circuit is disabled and the failure of the main heating element shielding means 11 is detected. Namely, since a frequency detection means 12 for outputting the zero cross signal is arranged at a prestage of the main heating element shielding means 11 by using no zero cross signal for abnormality detection of the main heating element shielding means 11, the fixing double monitor circuit is constituted at low cost and a clock of fixed cycle is inputted in a noise elimination means 17. Thus, the malfunction in the case of excessive rise of the fixing temperature and when the noise is generated to the fixing thermistor output is surely and inexpensively prevented and the relay failure of the main heating element shielding means 11 is detected. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or the like provided with a fixing device for fixing an unfixed image formed with toner or the like on a recording medium.

  2. Description of the Related Art Thermal fixing devices for fixing an unfixed image formed with toner or the like on a recording medium in an image forming apparatus such as a copying machine, a printer, or a facsimile are well known. In an image forming apparatus provided with such a thermal fixing device, a fixing temperature monitoring mechanism is provided in order to prevent an accident when the fixing temperature rises above a set temperature. In general, temperature detection means such as a thermistor is provided to detect the fixing temperature, and this is monitored by control means mainly composed of a microprocessor such as a CPU (Central Processing Unit). That is, as shown in FIG. 4, the CPU controls the fixing control corresponds to this. In FIG. 4, the fixing temperature slightly increases immediately after the fixing heater is turned off, and conversely, the fixing temperature slightly decreases immediately after the fixing heater is turned on is due to overshoot and undershoot, respectively.

  However, if the CPU breaks down or goes out of control for some reason, the fixing device is not only damaged, but it may lead to an ignition accident of the image forming apparatus. In order to prevent such an accident, a device having a double fixing temperature monitoring mechanism has been proposed.

  As a conventional dual monitoring mechanism of the fixing temperature, there is a mechanism that monitors the fixing temperature with a comparator or the like and gates an ON signal of the fixing heater based on the output in addition to the CPU. That is, the gate is turned on and the fixing heater is energized only when both the CPU and the comparator issue a command (signal) for turning on the fixing heater.

  In this configuration, the gate is turned off only when the fixing temperature exceeds the abnormality detection temperature, that is, the gate is turned on again when the fixing temperature falls below the abnormality detection temperature. Therefore, as shown in FIG. Repeats on / off. As a result, the fixing heater is turned on / off at the fixing relay contact, which may cause relay welding.

  Therefore, in Patent Document 1, in order to prevent welding of the fixing relay contact, a storage unit is provided in the fixing double monitoring mechanism, and once the fixing double monitoring mechanism detects an overtemperature, the state is stored and the fixing temperature is detected abnormally. The gate is kept off even when the temperature falls below (see FIG. 6).

  However, according to the technique disclosed in Patent Document 1, safety is ensured by providing the storage means, but there is a possibility of malfunction in normal operation. If noise occurs in the fixing thermistor output and a voltage lower than the reference voltage is input to the comparator as the fixing thermistor output, and the comparator outputs a state indicating the fixing temperature overheating, the storage means is in an extremely short temperature overheating state. However, since the state is stored, there is a possibility that the fixing heater cannot be turned on even though there is no problem with the fixing temperature control.

  Therefore, Patent Document 2 proposes a configuration using a flip-flop and using a zero-cross signal as its clock. According to this, since the additional component is only one flip-flop and the zero cross signal input as the clock is the signal originally used in the fixing heater control, it is possible to prevent malfunction due to noise on the fixing thermistor output. Can be realized at a cost.

  In addition, a heating device that incorporates a capacitor (capacitor) as an auxiliary power supply device and achieves energy saving and rise time reduction has been proposed (see, for example, Patent Document 3).

  Specifically, in addition to the power supplied from the main power supply device (usually commercial power supply) provided in the same manner as in the past, the power supplied from the auxiliary power supply device configured with a capacitor is also supplied to the heating device. It is. With this configuration, it is possible to supply a large amount of power to the heating device without the input from the commercial power supply exceeding 100V15A, which is the rating of a general commercial power supply in Japan. (1) Rise time Shortening and (2) energy saving by eliminating the low power mode can be achieved.

Japanese Patent Laid-Open No. 10-307514 Japanese Patent Laid-Open No. 11-30927 JP 2000-315567 A

  However, the configuration disclosed in Patent Document 2 as described above is a configuration that can prevent malfunction due to noise on the fixing thermistor output at a low cost, but this is disclosed in Patent Document 3. When an image forming apparatus equipped with a simple capacitor as an auxiliary power source is deployed, there is a problem in safety.

  More specifically, the fixing double monitoring mechanism of Patent Document 2 uses a zero-cross signal as a clock input of a flip-flop for preventing malfunction (noise removal), but does not generate a zero-cross signal (when the AC heater relay is off) Or, when the commercial power supply is not applied to the zero cross detection circuit such as when the AC heater relay is open, the clock input is fixed to H and the comparator output cannot be latched. It becomes impossible to forcibly turn off. When conventional fixing heater power is supplied only from a commercial power source, no zero cross signal is synonymous with AC heater relay off, that is, the power supply to the fixing heater is shut off. However, in the image forming apparatus in which the capacitor is mounted as an auxiliary power source, there is a power supply path from the capacitor to the fixing heater even when the AC heater relay is off.

  The present invention has been made in view of the above, and it is possible to reliably and inexpensively prevent malfunction when the fixing temperature rises and noise occurs on the fixing thermistor output, and to detect a relay failure. Objective.

  In order to solve the above-described problems and achieve the object, the invention according to claim 1 includes a main heating element that generates heat by electric power supplied from a commercial power supply and an auxiliary heating element that generates heat by electric power supplied from an auxiliary power supply device. Image forming apparatus comprising a fixing double monitoring mechanism for monitoring the temperature of the heating section having a control means and an overtemperature detecting means, and using a zero cross signal as a clock input of the noise removing means in the fixing double monitoring mechanism In the apparatus, a temperature detection means for detecting the temperature of the heating unit, a main heating element cutoff means provided at a subsequent stage of the frequency detection means, for cutting off power supply from the commercial power source to the main heating element, and the temperature And an abnormality occurrence determining means for performing a failure diagnosis of the main heating element blocking means based on the output change degree of the detecting means.

  According to the first aspect of the present invention, since the zero cross signal is generated regardless of whether the main heating element blocking means is turned on or off, there is no timing for disabling the fixing double monitoring mechanism, and the main heating element blocking means Fault detection is possible. That is, by not using the zero cross signal for detecting the abnormality of the main heating element blocking means, the frequency detection means can be arranged in front of the main heating element blocking means, so that the fixing double monitoring mechanism is configured at low cost. In addition, it is possible to input a clock having a fixed period to the noise removing means for removing noise using the output of the frequency detecting means of the fixing double monitoring mechanism. As a result, it is possible to reliably and inexpensively prevent malfunction when the fixing temperature rises and noise occurs on the fixing thermistor output, and it is possible to detect a relay failure of the main heating element cutoff means.

  Exemplary embodiments of an image forming apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings.

  An embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram in which only the fixing heater related part in the image forming apparatus according to the embodiment of the present invention is extracted. An image forming apparatus 100 illustrated in FIG. 1 includes a heating unit 1, an auxiliary power supply device 2, a main heating element driving unit 3, an auxiliary heating element driving unit (capacitor heater driving circuit) 4, and a control unit 5.

  The heating unit 1 includes a main heating element (AC heater) 7 that generates heat by electric power supplied from a commercial power source 6, an auxiliary heating element (capacitor heater) 8 that generates heat by electric power supplied from the auxiliary power supply device 2, and a heating unit. 1 has a temperature detecting means (thermistor) 9 for detecting the temperature in 1.

  The auxiliary power supply device 2 has a chargeable / dischargeable power storage device (for example, an electric double layer capacitor).

  The main heating element driving unit 3 includes a main heating element driving unit 10 that controls power supply from the commercial power supply 6 to the main heating element 7 and a main heating element cutoff that interrupts power supply from the commercial power supply 6 to the main heating element 7. Means (AC heater relay) 11. In addition, in the present embodiment, frequency detection means (zero cross) for detecting the frequency of the commercial power supply 6 between the commercial power supply 6 and the main heating element cutoff means (AC heater relay) 11 of the main heating element drive unit 3. Detection circuit) 12 is provided.

  The auxiliary heating element driving unit 4 includes auxiliary heating element driving means 13 for controlling power supply from the auxiliary power supply device 2 to the auxiliary heating element 8, and auxiliary heat generation for cutting off power supply from the auxiliary power supply device 2 to the auxiliary heating element 8. A body shut-off means (capacitor heater relay) 14.

  The control unit 5 includes an overtemperature detection unit (comparator) 15 that detects an overtemperature of the heating unit 1, and an overtemperature storage unit (flip-flop) that stores the overtemperature information detected by the overtemperature detection unit 15. 2) Noise removal means (flip-flop 1) 17 provided between 16 and overtemperature detection means 15 and overtemperature storage means 16 for removing noise using the output of frequency detection means 12, and temperature The main heating element forced-off means (gate) 18 forcibly turns off the main heating element control signal of the main heating element 7 by the output of the overheating storage means 16 and the auxiliary heating element 8 by the output of the overheating storage means 16. An auxiliary heating element forced-off means (gate) 19 for forcibly turning off the auxiliary heating element control signal and a CPU (Central Processing Unit) 20 that is a control means for controlling the image forming apparatus 100 are included.

  Here, the commercial power supply 6 includes a charger 22 for charging the auxiliary power supply device 2 via the main switch 21 and a PSU (Power Supply Unit) (not shown) that generates a DC power supply necessary for the operation of the image forming apparatus 100. And supplied to.

  Further, the commercial power source 6 is input to the AC heater driving circuit 3 without passing through the main switch 21. The main switch 21 can be arranged on a common path of the AC heater driving circuit 3, the PSU, and the charger 22 (before the commercial power supply 6 is input to the image forming apparatus 100 and branched). If configured, the current of the AC heater 7 is also supplied to the main switch 21 and the main switch 21 having a very large rated current must be selected. Therefore, the main switch 21 is separated from the power supply path of the AC heater driving circuit 3. It is common to do.

  The PSU rectifies and steps down the commercial power supply 6 to generate a power supply used in the image forming apparatus 100. The power supply generated by the PSU is mainly two systems, one system is Vcc mainly used in the control system, and the other system is Vaa mainly used in the drive system.

  The fixing roller (not shown) disposed in the fixing unit 1 is provided with an AC heater 7 and a capacitor heater 8 which are heat generating members. The AC heater 7 is on / off controlled by the AC heater driving circuit 3 using the commercial power source 6 as a power source. The capacitor heater 8 is on / off controlled by the capacitor heater drive circuit 4 using the power charged in the auxiliary power supply 2 as a power source. The auxiliary power supply 2 is charged by the charger 22. The commercial power source 6 is input to the charger 22 via the main switch 21, and charging is controlled by a control signal (not shown) from the control unit 5 of the image forming apparatus 100.

  In the vicinity of the fixing roller, a thermistor (hereinafter referred to as a fixing thermistor) 9 is provided as an overtemperature detecting means (temperature detecting means) for detecting the surface temperature (overtemperature) of the fixing roller. The controller 5 detects the surface temperature of the fixing roller when the resistance value 9 changes with temperature. As the fixing thermistor 9, a thermistor having a negative characteristic (a resistance value decreases as the temperature rises) is generally used.

  The capacitor heater drive circuit 4 cuts off the power supply to the FET (field effect transistor) 13 as an auxiliary heating element drive means used for on / off control of the capacitor heater 8 at the normal time and the capacitor heater 8 at the time of abnormality. The capacitor heater relay 14 is configured to be configured. The FET 13 and the capacitor heater relay 14 are both turned on / off by the control unit 5.

  The AC heater driving circuit 3 includes a triac 10 as a main heating element driving unit used for on / off control of the AC heater 7 in a normal state, and an AC heater relay 11 that cuts off power supply to the AC heater 7 in an abnormal state. Consists of. The triac 10 and the AC heater relay 11 are both turned on / off by the control unit 5.

  The frequency detection means (zero cross detection circuit) 12 for detecting the zero cross point of the commercial power supply 6 is provided between the commercial power supply 6 and the main heating element cutoff means (AC heater relay) 11 of the main heating element drive unit 3. . A zero-cross signal that is an output of the zero-cross detection circuit 12 is input to the control unit 5 and used for phase control of the fixing heater and the like. Since the phase control is irrelevant to the present invention, detailed description thereof is omitted.

  The control unit 5 controls the image forming apparatus 100, a fixing double monitoring mechanism for forcibly turning off the AC heater 7 and the capacitor heater 8 regardless of the I / O port output of the CPU 20 when the fixing temperature is abnormal, and AC The AC heater drive circuit 3 and the capacitor heater drive circuit 4 output the heater relay 11 on / off signal, the capacitor heater relay 14 on / off signal, the AC heater 7 on / off signal, and the capacitor heater 8 on / off signal. And drivers 23 to 26 for the purpose.

  The fixing double monitoring mechanism includes a comparator 15, a flip-flop 1 (17), a flip-flop 2 (16), gates 18 and 19, and the like.

  The comparator 15 uses the output of the fixing thermistor 9 to determine whether or not the fixing unit 1 is overheated. A reference voltage generated by dividing the voltage Vcc generated by the PSU by the two resistors R1 and R2 is input to the inverting input (−) of the comparator 15. A voltage generated by dividing the voltage Vcc generated by the PSU by the resistor R3 and the fixing thermistor 9 is input to the non-inverting input (+) of the comparator 15. By setting the resistance values of the resistors R1 and R3 to the same value, the output of the comparator 15 is determined depending on whether the resistance value of the fixing thermistor 9 is larger or smaller than the resistance value of the resistor R2.

  When the resistance value of the fixing thermistor 9 is larger than the resistance value of the resistor R2, the voltage of the non-inverted input (+) becomes higher, so H (“1” logic level) is output, and the resistance value of the fixing thermistor 9 is When the resistance value is smaller than the resistance value of the resistor R2, the voltage of the inverting input (+) becomes higher, so that L (“0” logic level) is output. The fixing temperature excessive detection temperature is determined by the resistance value of the resistor R2.

  For example, when the detection temperature rise detection temperature is set to 200 ° C., the resistance value of the fixing thermistor 9 at 200 ° C. is set as the resistance value of the resistor R2. Further, the voltage generated by voltage division by the resistor R3 and the fixing thermistor 9 is also connected to the A / D input of the CPU 20 and used for fixing temperature control by the CPU 20.

  The output of the comparator 15 is connected to the data input (D) of the flip-flop 1 (17) for the purpose of noise removal. A zero cross signal is connected to the clock input of the flip-flop 1 (17), and the data input is latched at every rising edge of the zero cross signal. Here, FIG. 2 is an explanatory view showing a generation state of the zero cross signal. As shown in FIG. 2, since the zero cross signal is one cycle for each half wave of the commercial power source 6, if the frequency of the commercial power source 6 is 50 Hz as in the eastern Japan region, the frequency of the zero cross signal is 100 Hz, and the western Japan region. Thus, if the frequency of the commercial power supply 6 is 60 Hz, the frequency of the zero cross signal is 120 Hz.

  Here, the noise removal effect will be described by taking the case where the image forming apparatus 100 is used in the East Japan region as an example. The data input of the flip-flop 1 (17) is latched at every rising edge of the zero cross signal. In other words, the data input is not latched except for a short time when the zero cross signal rises. Even if noise is superimposed on the output of the fixing thermistor 9 at a fixed timing, the noise will not be erroneously latched. Further, since the zero cross signal is a relatively low speed signal of 100 Hz, the data latching interval is relatively long and is a suitable clock input for achieving noise removal.

  The output (Q) of the flip-flop 1 (17) is connected to the reset input (R, active L) of the flip-flop 2 (16) for the purpose of storing overheating information. The output of the comparator 15 becomes H when the fixing temperature rise is not detected and becomes L when the fixing temperature rise is detected, and is latched in the flip-flop 1 (17) by the rising edge of the zero cross signal. The reset input of group 2 (16) becomes L. When the flip-flop 2 (16) is reset, the inverted output (-Q) becomes H. When the fixing temperature falls after the detection of excessive fixing temperature, the output of the comparator 15 becomes H, the output of the flip-flop 1 (17) becomes H, and the reset input of the flip-flop 2 (16) becomes H, but the reset is released. However, the inverted output continues to hold H unless the over-rise detection cancel signal that is the clock input of the flip-flop 2 (16) is output.

  The inverted output of the flip-flop 2 (16) is connected to the gates 18 and 19. By gating the AC heater relay trigger and capacitor heater relay trigger output by the CPU 20 with this signal, each relay is turned off regardless of the output of the I / O port of the CPU 20 when overheating is detected.

  Here, a specific action in the present embodiment will be described. Conventionally, if the zero cross detection circuit is arranged after the AC heater relay and the AC heater relay is normal, the zero cross signal is detected when the AC heater relay is on, and the zero cross signal is not detected when the AC heater relay is off. The abnormality of the AC heater relay was detected using. In the present embodiment, a frequency detection means (zero cross detection circuit) 12 is provided between the commercial power supply 6 and the main heating element cutoff means (AC heater relay) 11, and the main heating element cutoff means (AC heater relay) 11 is provided. Abnormality detection is performed based on the temperature detection result of the fixing thermistor 9.

  Here, FIG. 3 is a flowchart showing a flow of abnormality detection of the main heating element blocking means (AC heater relay) 11 based on the temperature detection result of the fixing thermistor 9. As shown in FIG. 3, when the controller 5 acquires the surface temperature (temp1) of the fixing roller detected by the fixing thermistor 9 (step S1), the controller 5 controls the main heating element blocking means (AC heater relay) 11 to be turned off. The AC heater relay trigger output by the CPU 20 is turned on (step S2).

  Then, after the lapse of the specified time (step S3), the control unit 5 acquires the surface temperature (temp2) of the fixing roller detected by the fixing thermistor 9 (step S4), and the temperature difference between temp2 and the previously acquired temp1 is obtained. It is determined whether the temperature is within the specified temperature (α) (step S5).

  When the control unit 5 determines that the temperature difference between temp2 and the previously acquired temp1 is within the specified temperature (α) (Y in step S5), the main heating element blocking means (AC heater relay) 11 is turned on. In addition to the on-control, the AC heater relay trigger output by the CPU 20 is controlled to be off (step S6), and after the lapse of a specified time (step S7), the surface temperature (temp3) of the fixing roller detected by the fixing thermistor 9 is acquired (step 3). S8), it is determined whether or not the temperature difference between temp3 and the previously acquired temp2 exceeds the specified temperature (β) (step S9).

  When the control unit 5 determines that the temperature difference between temp3 and the previously acquired temp2 exceeds the specified temperature (β) (Y in step S9), the main heating element blocking means (AC heater relay) 11 It is determined that there is no abnormality detection in, and the process ends.

  On the other hand, when it is determined that the temperature difference between temp2 and the previously acquired temp1 exceeds the specified temperature (α) (N in step S5), the temperature rise of the fixing roller disposed in the fixing unit 1 is increased. If it is larger, the failure flag 1 (welding failure) of the main heating element cutoff means (AC heater relay) 11 is turned on (step S10: abnormality occurrence determination means). If it is determined that the temperature difference between temp3 and temp2 acquired previously is within the specified temperature (β) (N in step S9), the temperature rise of the fixing roller arranged in the fixing unit 1 is small. Then, the failure flag 2 (open failure) of the main heating element blocking means (AC heater relay) 11 is turned on (step S11: abnormality occurrence determination means).

  As described above, according to the present embodiment, since the zero cross signal is generated regardless of whether the main heating element blocking means (AC heater relay) 11 is turned on or off, there is no timing at which the fixing double monitoring circuit is invalidated. In addition, it is possible to detect a failure of the main heating element blocking means (AC heater relay) 11. That is, the frequency detection means (zero cross detection circuit) 12 that outputs a zero cross signal is used as the main heating element cutoff means (AC heater relay) 11 by not using the zero cross for the abnormality detection of the main heating element cutoff means (AC heater relay) 11. Therefore, it is possible to construct a fixing double monitoring circuit at a low cost, and a noise removing means (flip-flop) that performs noise removal using the output of the frequency detecting means 12 of the fixing double monitoring circuit. A clock with a fixed period can be input to the group 1) 17. Accordingly, it is possible to reliably and inexpensively prevent malfunction when the fixing temperature rises and noise occurs on the fixing thermistor output, and to detect a relay failure of the main heating element cutoff means (AC heater relay) 11. Can do.

FIG. 3 is a block diagram illustrating only a portion related to the fixing heater in the image forming apparatus according to the embodiment of the present invention. It is explanatory drawing which shows the generation | occurrence | production state of a zero cross signal. 6 is a flowchart showing a flow of AC heater relay abnormality detection based on a temperature detection result of a fixing thermistor. It is explanatory drawing which shows the relationship between operation | movement of a relay, a triac, a fixing heater, and fixing temperature. It is explanatory drawing which shows the relationship between operation | movement of a relay, a triac, a fixing heater, and fixing temperature. It is explanatory drawing which shows the relationship between operation | movement of a relay, a triac, a fixing heater, and fixing temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating part 2 Auxiliary power supply device 6 Commercial power supply 7 Main heating element 8 Auxiliary heating element 9 Temperature detection means 11 Main heating element cutoff means 12 Frequency detection means 15 Overtemperature detection means 17 Noise removal means 20 Control means 100 Image forming apparatus

Claims (1)

Fixing for monitoring the temperature of a heating unit having a main heating element that generates heat by electric power supplied from a commercial power source and an auxiliary heating element that generates heat by electric power supplied from an auxiliary power supply device by a control means and an overtemperature detection means In an image forming apparatus comprising a double monitoring mechanism and using a zero cross signal output from a frequency detection means as a clock input of a noise removal means in the fixing double monitoring mechanism,
Temperature detecting means for detecting the temperature of the heating unit;
A main heating element blocking means provided at a subsequent stage of the frequency detection means, for blocking power supply from the commercial power source to the main heating element;
Based on the output change degree of the temperature detection means, an abnormality occurrence determination means for performing a failure diagnosis of the main heating element blocking means,
An image forming apparatus comprising:

Images