JP2007226151A - Fixing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing apparatus capable of performing the temperature control of an object to be measured with high accuracy, and to provide an image forming apparatus. <P>SOLUTION: The power supply voltage v1 of a power source V1, that supplies power to a first thermistor 511 for detecting the detection temperature, is set lower than the power supply voltage v2 of a power source V2 that supplies power to a second thermistor 512 for detecting the compensation temperature, and also, the power supply voltage v1 is generated by using the power supply voltage v2 of the power source V2 by a power supply voltage generation circuit 46. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device that performs a fixing process for fixing a toner image transferred onto a transfer material in an image forming apparatus, and an image forming apparatus including the fixing device.

  2. Description of the Related Art Conventionally, a fixing device mounted on an image forming apparatus such as a copying machine is installed on the downstream side of an image forming unit, and a toner image transferred on a sheet (transfer material) in the image forming unit is heated on the sheet. A fixing process for fixing is performed. Such a fixing device is provided with a fixing roller heated by a heat source (heater) and a pressure roller pressed against the fixing roller.

  Then, the transfer-finished paper is supplied toward the nip formed between the pressure roller and the fixing roller rotating around the axis, and the fixing roller heats the paper passing through the nip. The toner is melted by supplying the toner, and the fixing process is performed by fixing the molten toner to the paper surface.

  In such a fixing device, for example, if an abnormal temperature rise occurs in the fixing roller, the fixing device may be damaged or broken, and therefore it is necessary to appropriately control the temperature of the fixing roller. Therefore, conventionally, a temperature sensor is disposed at a position opposite to a predetermined position on the peripheral surface of the fixing roller, and when an abnormal temperature rise occurs in the fixing roller, a process of stopping power supply to the fixing roller is performed.

  By the way, a non-contact type infrared temperature sensor may be employed for detecting the temperature of the fixing roller. This infrared temperature sensor includes two thermistors and an infrared film, and one thermistor detects the temperature of a measurement object such as a fixing roller (hereinafter referred to as a detection temperature) via the infrared film. On the other hand, the other thermistor detects, for example, the temperature of the casing of the infrared temperature sensor (hereinafter referred to as compensation temperature), and outputs the temperature derived based on these detection outputs as the temperature of the measurement object. It is configured.

  However, in the infrared temperature sensor, there may be a plurality of combinations of detection temperature and compensation temperature corresponding to the output of the same infrared temperature sensor, so that the actual temperature of the measurement object and the predetermined reference value When the method of determining the stop of the power supply to the fixing roller based on the comparison result is employed, it is assumed that a certain reference value is set as the predetermined reference value. Even if the output of the temperature sensor is obtained, the combination of the detected temperature and the compensation temperature corresponding to this output is not uniquely derived, and it is considered that the power supply to the measurement object cannot be stopped accurately. It is done.

In Patent Document 1 below, for such a problem, in a temperature detection circuit including an infrared detection thermistor and a temperature compensation thermistor, a resistance element connected in series to the temperature compensation thermistor is added, and the temperature of the object is predetermined. A method has been proposed in which the output value of the temperature detection circuit is constant when the temperature is reached.
Japanese Patent Laid-Open No. 2003-302288

  However, in Patent Document 1, since the output signal of the thermistor has a very low signal level, if a resistance element is added to the temperature detection portion, the signal level further decreases and the S / N deteriorates. As a result, the temperature detection accuracy of the thermistor is lowered, and as a result, the temperature of the fixing roller may not be properly managed.

  SUMMARY An advantage of some aspects of the invention is that it provides a fixing device and an image forming apparatus that can perform temperature management of a measurement object with high accuracy.

  According to the first aspect of the present invention, by supplying heat to at least one of a pair of rollers that are in contact with each other on a cylindrical peripheral surface, toner adhering to the sheet conveyed between the pair of rollers is transferred to the sheet. A heating means for fixing the heating means, a power supply means for generating heat by supplying power to the heating means, and a temperature of a predetermined measurement object to which heat is supplied by the heating means And a second sensor for detecting a temperature of an object different from the measurement object as a compensation temperature, and the temperature based on the outputs of the first and second sensors is The temperature detection means that outputs the temperature of the object to be measured and the differential value of the outputs of the first and second sensors are compared with a predetermined reference value, and power is supplied to the heating means based on the comparison result. Power interruption to cut off A first power supply means for supplying power to the stage, a circuit relating to the first sensor, and a circuit relating to the second sensor at a voltage different from a supply voltage by the first power supply means. And a second power supply means for supplying the fixing device.

  According to the present invention, since the voltage supplied to the circuit related to the first sensor is different from the voltage supplied to the circuit related to the second sensor, the voltage supplied to the circuit related to the first and second sensors is supplied. Compared to the case where the voltages are the same, the differential value can be increased, and the temperature detection range can be expanded.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the power supply means having the lower supply voltage of the first and second power supply means supplies the power in the direction of the higher supply voltage. The supply voltage is generated using the voltage generated by the means.

  According to the present invention, the power supply means with the lower supply voltage generates the supply voltage using the voltage generated by the power supply means with the higher supply voltage. The output error can be reduced.

  According to a third aspect of the present invention, in the fixing device according to the second aspect, the power supply unit having the lower supply voltage includes a voltage follower connected to the power supply unit having the higher supply voltage. It is characterized by being comprised.

  According to the present invention, the power supply means with the lower supply voltage is configured to include the voltage follower connected to the power supply means with the higher supply voltage, so the lower supply with a simple and inexpensive circuit. A voltage can be generated.

  According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, an abnormality detection unit that detects an abnormality in the fixing device based on outputs of the first and second sensors. It is characterized by comprising.

  According to the present invention, since the abnormality detecting means for detecting an abnormality in the fixing device based on the outputs of the first and second sensors is provided, the temperature in the fixing device is not reduced without causing a decrease in temperature detection accuracy. It is possible to detect disconnection of circuit elements and power transmission lines.

  According to a fifth aspect of the present invention, in the fixing device according to any one of the first to fourth aspects, the predetermined measurement object detected by the first sensor is one of the pair of rollers. The temperature of the roller, and the object whose temperature is detected by the second sensor is the temperature of the casing of the temperature detecting means.

  According to this invention, the first sensor detects the temperature of one of the pair of rollers, and the second sensor detects the temperature of the casing of the temperature detecting means. The effect | action by the invention in any one of claim | item 1 thru | or 4 is acquired.

  According to a sixth aspect of the present invention, there is provided an image forming unit that performs an image forming operation on a sheet based on predetermined image data, and a toner that adheres to the sheet with respect to the sheet after the image forming operation by the image forming unit. An image forming apparatus comprising: the fixing device according to claim 1, wherein the fixing device is fixed to the paper.

  According to the present invention, in the image forming apparatus, the action according to any one of the first to fifth aspects can be obtained.

  According to the present invention, since the temperature detection range can be expanded, the correspondence between the temperature of the measurement object and the differential value can be set in detail. Therefore, when the differential value becomes the differential value corresponding to the threshold value for the temperature of the object to be measured, the power supply to the heating means is cut off. The temperature error of the object can be reduced and the temperature can be made substantially constant. As a result, the temperature of the measurement object can be managed with high accuracy.

  The image forming apparatus according to the present invention will be described below. FIG. 1 is a diagram illustrating an internal configuration of the first embodiment of the image forming apparatus.

  As shown in FIG. 1, the image forming apparatus 1 includes a sheet supply unit 2 positioned below the apparatus 1, an image forming unit 3 positioned above the sheet supply unit 2, and a downstream side of the image forming unit 3. And a discharge unit 5 positioned above the image forming unit 3.

  The paper supply unit 2 includes paper cassettes 6 to 8 configured to be able to replenish paper P by being pulled out from a main body frame (not shown) of the image forming apparatus 1. 8 are sent to the outlet side (right side in FIG. 1) of the paper feed cassettes 6-8 by the rotation operation of the paper feed rollers 9-11, and the uppermost by the retard rollers 12-14. The paper P at the position is fed to the first paper transport unit 15 one by one.

  The first paper transport unit 15 transports the paper P fed from the paper supply unit 2 toward the image forming unit 3. The first paper transport unit 15 includes a registration sensor 16 in which a pair of reflective photosensors are disposed at both ends in a direction (main scanning direction) orthogonal to the paper surface of FIG. 1, and the paper P is the registration sensor 16. When the toner image is conveyed to the position of the sheet P, a registration roller 17 disposed on the downstream side of the registration sensor 16 aligns a toner image formed on the surface of the photosensitive drum 18 described later with the leading end position of the sheet P. In this way, the sheet is conveyed between the photosensitive drum 18 and the transfer roller 22 after the conveyance timing is taken.

  The image forming unit 3 includes a photoconductive drum 18 rotatably supported on a photoconductive drum, and a charger 19, a laser scanning unit 20, and a developing unit around the photoconductive drum 18 along the rotation direction. 21, a transfer roller 22 and a cleaning unit 23, and a predetermined toner image is formed on the photosensitive drum 18 by an electrophotographic process, and the toner image is transferred to the paper P.

  The charger 19 charges the peripheral surface of the photosensitive drum 18 with a certain polarity (in this embodiment, positive polarity).

  Although not shown in detail, the laser scanning unit 20 includes a laser emitter, a polygon mirror, and a reflecting mirror, and responds to image data of an original obtained from an image input device (not shown) such as an externally connected personal computer or scanner. The laser beam with the intensity is output from a laser emitter and irradiated to the exposure area of the positively charged photosensitive drum 18 through a polygon mirror and a reflecting mirror. By this irradiated laser light, the surface potential of the photosensitive drum 18 is decreased according to the image, and an electrostatic latent image corresponding to the document image data is formed on the surface of the photosensitive drum 18. This light irradiation is repeatedly scanned in the width direction of the rotating photosensitive drum 18 (the direction perpendicular to the paper surface in FIG. 1) to the exposure area between the charger 19 and the developing unit 21 by the rotation of the polygon mirror. The

  The developing unit 21 includes a developing roller 24 disposed opposite to the photosensitive drum 18 and a toner container 25 storing toner, and the positive charge on the photosensitive drum 18 is reduced (the potential is reduced) by the laser beam. The toner having the same polarity in the developing region, that is, positively charged toner is attached to the portion of the electrostatic latent image by using the developing roller 24. As a result, the electrostatic latent image formed on the photosensitive drum 18 is developed with toner, and a toner image is formed on the surface of the photosensitive drum 18 as a visible image.

  The transfer roller 22 is disposed to face the photoconductive drum 18 in a non-contact state, and is formed on the photoconductive drum 18 by performing negative corona discharge from the back surface of the paper P in the transfer area of the photoconductive drum 18. The transferred toner image is electrostatically transferred onto the paper P.

  The cleaning unit 23 has a cleaning blade (not shown) formed to have a length substantially the same as the width direction dimension of the photosensitive drum 18, and the front end of the cleaning blade is exposed to the biasing force of a biasing means (not shown). By urging the surface of the body drum 18, the residual toner adhering to the surface of the photoreceptor drum 18 after the transfer is scraped off.

  The fixing unit 4 performs a fixing process for fixing the toner transferred onto the paper by pressurizing and heating the paper on which the toner image is transferred. The heat shielding box 26 and the heat shielding box 26 A fixing roller 27 disposed in the upper part of the heat shield box 26; and a pressure roller 28 disposed in pressure contact with the fixing roller 27 in the lower part of the heat shielding box 26. The fixing roller 27 includes a heater 42 (see FIG. 2), and is normally set at a constant temperature. When the sheet comes into contact with the fixing roller 27, the sheet is heated.

  The discharge unit 5 is formed, for example, on the upper surface of the main body frame of the image forming apparatus 1, and sequentially accumulates the sheets after the fixing process conveyed from the fixing unit 4 through the second sheet conveying unit 29. . The operation input unit 30 is used to input operations such as an instruction to start an image forming operation by the image forming apparatus 1 and designation of the type of paper P. The control unit 31 includes a microcomputer having a built-in storage unit including, for example, a ROM that stores a control program and a RAM that temporarily stores data, and associates driving of each member in the image forming apparatus 1 described above with each other. It is something to control.

  FIG. 2 is a block diagram illustrating a circuit configuration of the fixing unit 4. As shown in FIG. 2, the fixing unit 4 includes a temperature detection unit 41, a heater 42, a differential amplifier circuit 43, an AD conversion circuit 44, and a hard cut circuit 45. In addition, the control part 31 in a figure is corresponded to the above-mentioned control part 31. FIG.

  In the fixing unit 4, the temperature detection unit 41 generates two temperature signals Vs and Vd (hereinafter also referred to as voltages Vs and Vd), and the temperature signals Vs and Vd are supplied to the differential amplifier circuit 43. The differential amplifier circuit 43 amplifies the signal level difference (Vd−Vs) of these signals by a predetermined coefficient γ. The differential amplification signal Vb (= γ · (Vd−Vs)) is input to the AD conversion circuit 44. After the amplification signal Vb is AD converted by the AD conversion circuit 44, the AD conversion value is controlled. Input to the unit 31. Note that one of the temperature signals Vd generated by the temperature detection unit 41 is also input to the AD conversion circuit 44.

  The hard cut circuit 45 is supplied with an instruction signal for supplying power to the heater 42 from the control unit 31 and normally supplies power to the heater 42 (when an abnormal temperature rise of the measurement object has not occurred). . The hard cut circuit 45 takes in the differential amplification signal input from the differential amplification circuit 43 and supplies power to the heater 42 according to the magnitude of the signal level of the differential amplification signal Vb and a predetermined reference value. Shut off (stop).

  FIG. 3 is a diagram illustrating a circuit configuration of the temperature detection unit 41 and the differential amplifier circuit 43.

  As shown in FIG. 3, the temperature detection unit 41 includes an infrared temperature sensor 51, operational amplifiers 411 and 412, resistance elements R1 to R5, and a capacitor C1. The infrared temperature sensor 51 includes a first thermistor 511, a second thermistor 512, and an infrared film (not shown). The first and second thermistors 511 and 512 have negative resistance values that decrease in resistance as the temperature increases. NTC (Negative Temperature Coefficient Thermistor) thermistor having a temperature coefficient of

  The first thermistor 511 detects the temperature of the infrared film that receives and absorbs the infrared radiation radiated from the measurement object (the fixing roller 27 in the present embodiment) (hereinafter referred to as a detection temperature), while the second thermistor 512 is The temperature of another infrared film isolated from the infrared ray radiated from the measurement object (the fixing roller 27 in this embodiment) (hereinafter referred to as compensation temperature) is detected.

  The compensation temperature detected by the second thermistor 512 corresponds to, for example, the temperature of the casing of the infrared temperature sensor 51 or the ambient temperature, and the resistance value of the first thermistor 511 is the temperature of the casing of the infrared temperature sensor 51. Therefore, the second thermistor 512 detects, for example, the temperature of the casing of the infrared temperature sensor 51 and the atmospheric temperature in order to detect the degree of the influence and eliminate the influence.

  The first thermistor 511 is connected in series with the resistor element R1, and this series circuit is connected in parallel between the power supply Vp1 and the ground. The second thermistor 512 is connected in series with a series circuit of resistance elements R3, R4, and R5, and this series circuit is connected in parallel between the power supply Vp2 and the ground. Here, the power supply voltage v1 of the power supply V1 and the power supply voltage v2 of the power supply V2 are set to different values. This will be described later.

  The non-inverting input terminal of the operational amplifier 411 is connected to the connection point a between the resistance element R1 and the first thermistor 511, while the inverting input terminal is connected to the output terminal of the operational amplifier 411 via the resistance element R5. Yes. Note that the power supply V3 is connected to the + power supply terminal of the operational amplifier 411, while the-power supply terminal is connected to the ground. A capacitor C1 is connected in parallel with the operational amplifier 411 between the power supply V3 and the ground.

  The non-inverting input terminal of the operational amplifier 412 is connected to the connection point b between the resistance element R2 and the second thermistor 512, while the inverting input terminal is connected to the output terminal of the operational amplifier 412 via the resistance element R6. Yes. The output terminal of the operational amplifier 412 is connected to the output terminal T2 of the temperature detection unit 41 via the resistance element R12, and the output of the operational amplifier 412 is directed from the output terminal T2 to the AD conversion circuit 44 as the compensation temperature signal Vs. Is output.

  The temperature detector 41 outputs the outputs of the operational amplifiers 411 and 412 to the differential amplifier circuit 43 and the like as temperature signals Vs and Vd. Hereinafter, the temperature signal Vs is referred to as a detection temperature signal Vs, and the temperature signal Vd is referred to as a compensation temperature signal Vd.

  The differential amplifier circuit 43 amplifies the signal level difference between the detected temperature signal Vs and the compensation temperature signal Vd output from the temperature detector 41, and includes an operational amplifier 431, resistance elements R7 to R11, and capacitors C2 and C3. With.

  The inverting input terminal of the operational amplifier 431 is connected to the output terminal of the operational amplifier 411 in the temperature detection unit 41 via the resistor element R7, and the temperature signal Vs is input thereto, while the non-inverting input terminal is connected to the resistor element R8. Is connected to the output terminal of the operational amplifier 412 in the temperature detection unit 41, and the temperature signal Vd is input thereto.

  Further, a parallel circuit of a resistor element R10 and a capacitor C3 is connected between the inverting input terminal and the output terminal of the operational amplifier 431, and the non-inverting input terminal of the operational amplifier 431 is connected via the resistor element R9. Connected to ground. A capacitor C2 is connected in parallel to the resistor element R9.

  The output terminal of the operational amplifier 431 is connected to the output terminal T1 of the differential amplifier circuit 43 via the resistance element R11. The output of the operational amplifier 431 is converted from the output terminal T1 to the AD converter circuit 44 and the hardware as the differential amplification signal Vb. It is output toward the cut circuit 45.

  Returning to FIG. 2, the AD conversion circuit 44 AD-converts the output value of the differential amplifier circuit 43 and outputs the output value after the AD conversion to the control unit 31. The control unit 31 instructs the hard cut circuit 45 to supply power to the heater 42. The heater 42 is installed in the fixing roller 27 and heats the fixing roller 27.

  The hard cut circuit 45 is a circuit that switches between permitting / cutting off the power supply to the heater 42 and compares the level between a predetermined threshold value (reference value) and the differential amplified signal Vb to determine the differential amplified signal Vb. A comparator (not shown) that cuts off (stops) the power supply to the heater 42 when the signal level is higher than a predetermined threshold (reference value) is provided.

  By the way, in the present embodiment, the power supply voltage v1 of the power supply V1 is set smaller than the power supply voltage v2 of the power supply V2, and is generated by the power supply voltage generation circuit 46 shown in FIG. 4 using the power supply voltage v2 of the power supply V2. Is done. As shown in FIG. 4, the power supply voltage generation circuit 46 includes an operational amplifier 461, resistance elements R21 to R23, and a capacitor C11.

  A series circuit of a resistor element R21 and a resistor R22 is connected between the power supply V2 that supplies power to the second thermistor 512 and the ground, and the operational amplifier 461 is connected to a connection point c between the resistor element R21 and the resistor R22. Non-inverting input terminal is connected. A capacitor C11 is connected between the connection point c and the ground.

  The operational amplifier 461 functions as a voltage follower, the inverting input terminal of the operational amplifier 461 is connected to the output terminal of the operational amplifier 461 via the resistor element R23, and the output of the operational amplifier 461 is the power supply voltage v1 of the power supply V1. Is output.

  Thus, by making the power supply voltage v1 of the power supply V1 different from the power supply voltage v2 of the power supply V2, the differential value is increased and the temperature detection range is expanded as compared with the case where they are the same. The fixing roller 27 for each combination of the signal level (voltage) of the compensation temperature signal Vs and the signal level (voltage) of the detected temperature signal Vd and then the signal level (voltage) of the differential amplification signal Vb. The temperature can be set. For example, as shown in FIG. 5, a table in which the differential value corresponding to the temperature of the measurement object is set more can be generated.

  The table shown in FIG. 5 shows the differential amplification signal Vb for each combination of the compensation temperature detected by the second thermistor 512 and the corresponding compensation output (the signal level of the compensation temperature signal Vs) and the temperature of the fixing roller 27. It is an example of the table which set the signal level (voltage).

  According to this table, the circuit in the fixing unit 4 according to the present embodiment, for example, when the temperature of the fixing roller 27 is 0 (° C.), the compensation output is 3.185 (V) and the differential amplification signal Vb. When the temperature of the fixing roller 27 is 260 (° C.), the compensation output is 3.185 (V) and the signal level of the differential amplification signal Vb is 3.123. As shown in (V), each combination of the compensation output and the signal level of the differential amplified signal Vb is associated with the temperature of the fixing roller 27.

  In this case, when the signal level of the differential amplification signal Vb reaches a voltage of, for example, 3.12 (V), when the power supply to the heater 42 is cut off (stopped), the compensation temperature (° C.) And the roller temperature (° C.) have a correlation as shown in FIG.

  As can be seen from FIG. 6, when the reference value to be compared with the signal level of the differential amplification signal Vb is set to a voltage of, for example, 3.12 (V), the fixing roller 27 is 250 (° C.) although there is a slight error. ) It is detected that the temperature is around.

  That is, in this embodiment, even if the compensation temperature (compensation output) changes, the detected temperature of the fixing roller 27 is a substantially constant temperature.

  Therefore, by setting a reference value generated based on the table as a reference value for level comparison with the differential amplification signal Vb in the hard cut circuit 45, the hard cut circuit 45 supplies power to the heater 42. The temperature of the fixing roller 27 at the time of switching between permissible / shutoff becomes substantially constant, and the switching accuracy of permissible / shutoff of power supply by the hard cut circuit 45 can be improved.

  The power supply voltage v1 of the power supply V1 (first thermistor 511 for detecting the detected temperature) set to be smaller than the power supply voltage v2 of the power supply V2 (voltage for supplying power to the second thermistor 512 for detecting the compensation temperature). Is generated using the power supply voltage v2 of the power supply V2, so that the output error of the first thermistor 511 is smaller than when the power supply voltage v1 is generated using a regulator. can do.

  FIG. 7A shows the first embodiment in which the power supply voltage v1 is generated using the power supply voltage v2 of the power supply V2 using the output (compensation output) of the second thermistor 512 and the temperature of the fixing roller 27 as parameters. FIG. 7B is a graph showing the output error of the first thermistor 511 when the power supply voltage v1 is generated using a regulator. FIG. 7A is a graph showing the output error of the first thermistor 511. When the graph shown in FIG. 7 is compared with the graph shown in FIG. 7B, it can be seen that the output error of the first thermistor 511 is small in this embodiment.

  Further, in this embodiment, the configuration for generating the power supply voltage v1 of the power supply V1 using the power supply voltage v2 of the power supply V2 is realized by a voltage follower using an operational amplifier, so that the power supply voltage v2 can be obtained with a simple and inexpensive circuit. Can be generated.

  Further, in the present embodiment, by making the power supply voltage v1 of the power supply V1 different from the power supply voltage v2 of the power supply V2, it is possible to detect a failure of an element installed in the fixing unit 4 or a disconnection of the transmission line. .

  FIG. 8 is a table obtained by converting the signal level (voltage) of the differential amplification signal Vb in the table shown in FIG. 5 into the detection output of the first thermistor 511.

  As can be seen from FIG. 8, the compensation output is the maximum value that 3.185 (V) can be taken at the estimated temperature (0 (° C.) to 260 (° C.)) of the fixing roller 27, and the error is taken into consideration. However, an output value of 3.3 (V) or higher cannot be taken. Similarly, the detected output is the maximum value that 2.903 (V) can be taken at the assumed temperature (0 (° C.) to 260 (° C.)) of the fixing roller 27. An output value greater than 0 (V) cannot be taken.

  Therefore, when the compensation output becomes 3.3 (V) continuously for a predetermined time (for example, 1 second), or with reference to the table shown in FIG. .185 (V), when the state of approximately 1.7 (V) or less, which substantially corresponds to the detection output 3 (V), continues for a predetermined time (for example, 1 second) continuously, an abnormality in the fixing unit 4 (element It is possible to determine that a failure or a disconnection of the transmission line has occurred.

  In this determination, the control unit 31 is equipped with a function as an abnormality detection unit 311 (see FIG. 1) for detecting the abnormality, and the voltage of 3.3 (V) or about 1.7 (V). The abnormality detection process may be performed based on an AD conversion value corresponding to the voltage.

1 is a diagram illustrating an internal configuration of a first embodiment of an image forming apparatus. 2 is a block diagram illustrating a circuit configuration of a fixing unit. FIG. It is a figure which shows the circuit structure of a temperature detection part and a differential amplifier circuit. It is a figure which shows the circuit structure of a power supply voltage generation circuit. The signal level (voltage) of the differential amplification signal Vb is set for each combination of the compensation temperature detected by the second thermistor and the corresponding compensation output (the signal level of the compensation temperature signal Vs) and the temperature of the fixing roller. It is a figure which shows an example of a table. When the signal level of the differential amplification signal Vb reaches a voltage of, for example, 3.12 (V), when the power supply to the heater is cut off (stopped), the compensation temperature (° C.) and the roller temperature (° C.) It is a graph which shows correlation of these. (A) is an output of the first thermistor in the present embodiment in which the power supply voltage v1 is generated using the power supply voltage v2 of the power supply V2 using the output (compensation output) of the second thermistor and the temperature of the fixing roller as parameters. It is a graph which shows an error, (b) is a graph which shows the output error of the 1st thermistor at the time of producing | generating the said power supply voltage v1 using a regulator. It is a figure which shows the table which converted the signal level (voltage) of the differential amplification signal Vb in the table shown in FIG. 5 into the detection output of the 1st thermistor.

Explanation of symbols

4 fixing unit 27 fixing roller 28 pressure roller 31 control unit 41 temperature detection unit 42 heater 43 differential amplification circuit 45 hard cut circuit 46 power supply voltage generation circuit 51 infrared temperature sensor 311 abnormality detection unit 461 power supply voltage generation circuits 511 and 512 thermistor

Claims (6)

Heating means for fixing toner adhering to the paper conveyed between the pair of rollers by supplying heat to at least one of the pair of rollers in contact with each other on the cylindrical peripheral surface;
Power supply means for generating heat by supplying power to the heating means; and
A first sensor for detecting a temperature of a predetermined measurement object to which heat is supplied by the heating unit; and a second sensor for detecting a temperature of an object different from the measurement object as a compensation temperature. Temperature detection means for outputting a temperature based on the outputs of the first and second sensors as the temperature of the measurement object;
A power cutoff means for comparing the differential value of the outputs of the first and second sensors with a predetermined reference value and shutting off the power supply to the heating means based on the comparison result;
First power supply means for supplying power to a circuit according to the first sensor;
A fixing device comprising: a circuit according to the second sensor; and a second power supply unit that supplies power at a voltage different from a supply voltage by the first power supply unit.   The power supply means with the lower supply voltage of the first and second power supply means generates the supply voltage using the voltage generated by the power supply means with the higher supply voltage. The fixing device according to claim 1.   The fixing device according to claim 2, wherein the power supply unit having the lower supply voltage includes a voltage follower connected to the power supply unit having the higher supply voltage.   4. The fixing device according to claim 1, further comprising an abnormality detection unit configured to detect an abnormality in the fixing device based on outputs of the first and second sensors.   The predetermined measurement object whose temperature is detected by the first sensor is the temperature of one of the pair of rollers, and the object whose temperature is detected by the second sensor is the temperature detection The fixing device according to claim 1, wherein the fixing device is a temperature of a housing of the means. Image forming means for performing an image forming operation on a sheet based on predetermined image data;
An image comprising: the fixing device according to claim 1, wherein a toner attached to the paper is fixed to the paper after the image forming operation by the image forming unit. Forming equipment.