JP4389685B2 - Heating device - Google Patents

Description

  The present invention relates to a heating apparatus, for example, a heating apparatus suitable for use in an image forming apparatus that thermally fixes a toner image on a sheet.

  Conventionally, various techniques for preventing a heating roll from being excessively heated have been proposed for laser printers that thermally fix a toner image. Patent Document 1 discloses a temperature detection method for detecting an excessive temperature rise only with hardware when a thermistor type non-contact temperature detection device is used.

  In this temperature detection method, there is a non-comprising film composed of a film that absorbs infrared rays from the heating means, an infrared detection thermistor element that detects the temperature of the film, and a temperature compensation thermistor element that detects the temperature of the holding body that holds the film. Contact temperature detection means is used.

The detection circuit includes a first output voltage of a series circuit of the infrared detection thermistor element and one or more resistance elements, and a second output of a series circuit of the temperature compensation thermistor element and one or more resistance elements. When the heating means is at a predetermined temperature, the third output voltage that outputs the difference between the first output voltage and the second output voltage is substantially constant. Thereby, the temperature of the heating means is detected by the third output voltage.
JP 2003-302288 A

  In Patent Document 1, a temperature detection circuit is configured with priority given to abnormality detection. For this reason, the output change (ΔV / ΔT) with respect to the temperature is reduced, and the resolution is reduced. In addition, the number of parts constituting the temperature detection circuit is increased, and the cumulative tolerance is increased. For these reasons, the temperature detection method of Patent Document 1 has a problem that the temperature detection accuracy is greatly reduced.

  The present invention has been proposed to solve the above-described problems, and an object of the present invention is to provide a heating device that can accurately detect a temperature abnormality of a heating body and can heat the heating body safely. To do.

The heating device according to the present invention detects the temperature of a heating means for heating the heating body and the temperature of an infrared absorber disposed at a distance from the heating body and changing in temperature by infrared rays radiated from the heating body as a detection temperature. a sensing element, the compensating element for detecting the temperature of the sensor or near the compensation temperature, the non-contact temperature sensor with, the compensation voltage output and the detection voltage output from the sensing element from the compensation element The differential voltage, which is differential, has a first threshold value obtained by multiplying the compensation voltage by a first constant, a second threshold value that is a predetermined second constant, and a difference between the circuit applied voltage and the compensation voltage. When the value of any one of the third threshold values multiplied by a third constant is exceeded, or when the compensation voltage is greater than or equal to a fourth threshold value that is a predetermined fourth constant. High temperature to detect high temperature abnormality of the heating element A normally detecting means, when the abnormally high temperature of the heating member is detected by said high temperature abnormality detecting means, and a heating stop means for stopping the heating of the heating means.

  The heating element may be a roll, a film, a belt, or the like, and is not particularly limited. The heating means is not limited as long as it heats the heating body.

  The non-contact temperature sensor is arranged so as not to contact the heating body and includes a detection element and a compensation element. A detection element detects the detection temperature according to the radiant heat of a heating body. The compensation element detects a compensation temperature in or near the sensor that is not affected by the radiant heat of the heating element.

The high temperature abnormality detection means has a first threshold value obtained by multiplying a compensation voltage by a first constant, a differential voltage that is a difference between the detection voltage output from the detection element and the compensation voltage output from the compensation element , in advance. A second threshold value that is a determined second constant, a third threshold value obtained by multiplying the difference between the circuit applied voltage and the compensation voltage by a third constant, or any one of the values, or When the compensation voltage is equal to or higher than a fourth threshold that is a predetermined fourth constant, a high temperature abnormality of the heating element is detected. As a result, the high temperature abnormality detection means effectively monitors the temperature detection accuracy of the non-contact temperature sensor and uses a compensation voltage or a differential voltage to monitor whether the heating body is abnormal in high temperature from two directions. it can. The heating stop means forcibly stops heating of the heating means when a high temperature abnormality of the heating body is detected.

  The high temperature abnormality detection means may detect the high temperature abnormality when at least one of the compensation voltage and the differential voltage exceeds a predetermined threshold. The high temperature abnormality detection means may detect a high temperature abnormality when the differential voltage exceeds a threshold value determined according to the compensation voltage. Here, the threshold value may be expressed as a function of the compensation voltage and the differential voltage, for example, or may have a linear characteristic.

The heating device calculates the temperature of the heating body based on the detection voltage, the differential voltage, and the compensation voltage, and controls the heating temperature of the heating unit based on the calculated temperature. A temperature control means may be further provided. Thus, since the heating device is provided with the heating temperature control means and the high temperature abnormality detection means separately, even if a problem such as a failure occurs in the heating temperature control means, the high temperature abnormality can be detected reliably and safely. The heating body can be heated.

  The heating device may further include holding means for holding a heating stop state by the heating stop means. Thereby, it can prevent returning from a heating stop state to the original state before safety is confirmed.

  A heating device according to the present invention includes a compensation voltage output from a compensation element of a non-contact temperature sensor, a differential voltage that is a difference between the detection voltage output from the detection element of the non-contact temperature sensor and the compensation voltage. Based on at least one of the above, the temperature detection accuracy of the non-contact temperature sensor is made effective by detecting the high temperature abnormality of the heating body and stopping the heating of the heating means when the high temperature abnormality of the heating body is detected. Since it can be utilized to detect a high temperature abnormality of the heating element, the heating element can be heated safely.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a cross-sectional view showing a main part of a heating device according to an embodiment of the present invention. The heating device detects the temperature of the heating roll 2 provided in the fixing device (Fuser) 1 of the image forming apparatus with a non-contact temperature sensor (NC sensor) 10 and controls the heating lamp 3 in the heating roll 2. . Thereby, the heating roll 2 can heat the unfixed toner image on the paper and fix it on the paper.

  The NC sensor 10 is disposed within the sheet passing range of the image forming apparatus. Although FIG. 1 illustrates the heating lamp 3 that obtains heat generation energy of 650 W and 835 W, either one may be used. The 835 W heating lamp 3 is configured such that its heating range is longer in the axial direction of the heating roll 2 than the 650 W heating lamp 3.

  The heating lamp 3 is arranged in a direction from the rotation axis of the heating roll 2 to the NC sensor 10 and at a position shifted by 4 mm from the rotation axis of the heating roll 2 toward the NC sensor 10. Here, the reason why the temperature is shifted by 4 mm is to detect a high temperature abnormality earlier by monitoring the portion where the temperature is highest at the circumferential position of the heating roll 2 with the NC sensor 10. The amount is not limited, and naturally the amount of deviation may be zero.

  When there are a plurality of heating lamps 3, the heating lamp 3 having the highest heat generation energy per unit length at the end of the heating roll 2 away from the NC sensor 10 may be disposed closer to the NC sensor 10. Thereby, in the position away from the NC sensor 10, since the influence by the heating lamp 3 which makes the heating roll 2 the highest temperature can be reliably detected, the heating roll 2 can be heated safely.

  The heating target of the heating lamp 3 is exemplified by the heating roll 2 in the present embodiment, but may be a belt or a film. Further, in the present embodiment, the heater lamp (quartz lamp) 3 is taken as an example of a heater for heating the heating roll 2, but other heaters may be used.

  FIG. 2 is a diagram showing a circuit configuration of the heating device according to the embodiment of the present invention.

  The heating device includes a non-contact temperature sensor 10 that detects a temperature of a heating roll that is a temperature measurement target, a differential amplifier circuit 20 that obtains a differential output Vamp, and a high temperature that detects a high temperature abnormality of the heating roll. An abnormality detection circuit 30, 40, 50, 60, a latch circuit 70 that holds a predetermined state, a reset circuit 80 that resets the latch circuit 70 when the power is turned on, a relay operation circuit 90 that operates the relay 100, and a heating roll The relay 100 which turns on / off the heating lamp to heat, and CPU110 which performs a predetermined | prescribed process based on the voltage value output from each circuit are provided.

  Although not shown, the CPU 110 performs an analog / digital (A / D) conversion on the voltage input to the analog signal input terminals (Vd, Vamp, Vc), and a D / A conversion of the calculation result. And a D / A converter for outputting via an analog signal output terminal (I / O).

  The NC sensor 10 includes a housing (not shown), a film-like absorber (not shown) that is supported by the housing and absorbs infrared rays from a temperature measurement target and changes its temperature, and the temperature of the film-like absorber is a first temperature. A detection element 11 for detecting (detection temperature), and a compensation element 12 for detecting the casing temperature, the ambient temperature of the casing, or the temperature of the hollow portion inside the casing as the second temperature (compensation temperature). Yes.

  With such a configuration of the NC sensor 10, the detection element 11 detects the temperature of the film-like absorber whose temperature is changed by infrared rays radiated from the temperature measurement target. On the other hand, the compensation element 12 can detect the compensation temperature that is the temperature inside the sensor without being affected by the infrared rays emitted from the temperature measurement target.

  Here, the internal resistances of the detection element 11 and the compensation element 12 have negative temperature-dependent characteristics that become smaller as the temperature rises. One terminal of the detection element 11 and the compensation element 12 is grounded. A voltage Vref (for example, 3.3 [V]) is applied to the other terminal (output terminal) of the detection element 11 via the resistor R5 of the differential amplifier circuit 20. The voltage at the output terminal of the detection element 11 is Vd. The voltage Vref is applied to the other terminal (output terminal) of the compensation element 12 via the resistor R6 of the differential amplifier circuit 20. The voltage at the output terminal of the compensation element 12 is Vc.

(Principle of detection by NC sensor 10)
FIG. 3 is a diagram showing a circuit configuration for explaining the principle that the temperature of the heating roll can be detected based on the detection results of the detection element 11 and the compensation element 12 of the NC sensor 10. The resistor R and the CPU 200 are different from those in FIG.

  The resistance values of the sensing element 11 and the compensation element 12 have negative temperature dependent characteristics as described above. The CPU 200 sequentially reads the voltage values of the detection element 11 and the compensation element 12 as the temperatures of the detection element 11 and the compensation element 12 change due to the radiant heat from the heating roll, and obtains the temperature of the heating roll based on these voltage values. .

  Assume that the output voltage of the detection element 11 is a detection voltage Vd, the output voltage of the compensation element 12 is a compensation voltage Vc, and the output voltage of the amplifier 210 is a differential output Vamp. When the A / D conversion values of the compensation voltage Vc and the differential output Vamp are respectively ADc and ADamp, the following equations (1) and (2) are established (note that the A / D conversion accuracy is 10 bits (= 1024). ).)

From these voltage values, the resistance value r _C of the compensation element 12 and the resistance value r _d of the sensing element 11 are expressed by the following equations (3) and (4).

  Note that α is an amplifier magnification and satisfies Expression (5).

  From the above resistance values, the compensation temperature Tc of the compensation element 12 and the detection temperature Td of the detection element 11 can be calculated as in the following formulas (6) and (7).

Note that r ₀ [kΩ] and B [K] are element characteristic values. From the temperature of the detection element 11 and the compensation element 12, the temperature T _{ROLL of the} heating roll is logically obtained by the equation (8). Note that F [K ⁻³ ] is a proportionality constant determined by the field of view (shape) of the NC sensor 10.

  As described above, the CPU 200 can detect the temperature of the heating roll based on the temperature detected by the detection element 11 and the compensation element 12 of the NC sensor 10.

(Circuit configuration of the heating device)
The differential amplifier circuit 20 illustrated in FIG. 2 includes an operational amplifier OP1 and an operational amplifier OP2. The inverting input terminal of the operational amplifier OP1 is grounded through the resistor r1. The inverting input terminal is connected to the output terminal via a resistor r2. The non-inverting input terminal of OP1 is connected to the output terminal (Vd line) of the sensing element 11.

  The inverting input terminal of the operational amplifier OP2 is connected to the output terminal of the operational amplifier OP1 through the resistor r3, and is further connected to its own output terminal through the resistor r4. The non-inverting input terminal of the operational amplifier OP2 is connected to the output terminal (Vc line) of the compensation element 12.

  Thereby, the differential output Vamp output from the differential amplifier circuit 20 becomes a voltage having a value (a predetermined number of times the differential) corresponding to the differential between the voltage Vc and the voltage Vd.

  Further, the differential output Vamp has a condition of Expression (9).

  In the present embodiment, the maximum differential output Vamp is specifically 3.3 [V].

(Configuration of high temperature abnormality detection circuit)
The high temperature abnormality detection circuits 30, 40, 50, 60 can detect that the heating roll has become abnormally high temperature based on at least one of the differential output Vamp and the compensation output Vc.

FIG. 4 is a diagram illustrating a threshold voltage Vo for determining a high temperature abnormality. In the present embodiment, each threshold voltage Vo is
Threshold voltage Vo1: Vamp = a · Vc
Threshold voltage Vo2: Vamp = b
Threshold voltage Vo3: Vamp = c · (Vref−Vc)
Threshold voltage Vo4: Vc = d
And has a linear characteristic.

  The threshold voltage Vo1 is a differential output Vamp representing a high temperature abnormality detection boundary according to the compensation temperature when the compensation temperature is relatively high. The threshold voltage Vo3 is a differential output Vamp representing a high temperature abnormality detection boundary according to the compensation temperature when the compensation temperature is relatively low. The threshold voltage Vo4 is a compensation output Vc representing a high temperature abnormality detection boundary when the compensation temperature is relatively low. The threshold voltage Vo2 is a differential output Vamp representing a high temperature abnormality detection boundary without being affected by the compensation temperature when the compensation temperature is between the threshold voltage Vo1 and the threshold voltages Vo3 and Vo4.

  Here, the high temperature abnormality detection circuit 30 uses the threshold voltage Vo3, the high temperature abnormality detection circuit 40 uses the threshold voltage Vo1, the high temperature abnormality detection circuit 50 uses the threshold voltage Vo2, and the high temperature abnormality detection circuit 60 uses the threshold voltage Vo4. Detect high temperature abnormalities.

  Note that it is not limited which threshold voltage Vo1 to Vo4 is used to detect a high temperature abnormality of the heating roll 2 (which one of the high temperature abnormality detection circuits 30, 40, 50, and 60 is provided) is arbitrary. It is.

(High temperature abnormality detection circuit 30)
The high-temperature abnormality detection circuit 30 includes an operational amplifier OP3 that functions as a buffer, an operational amplifier OP4 that outputs a threshold voltage Vo3, a comparator COM1 that compares the differential output Vamp and the threshold voltage Vo3, and is turned on according to the comparison result of the comparator COM1. Transistor TR1 to be turned off.

  The inverting input terminal of the operational amplifier OP4 is connected to the Vc line via the resistor R1 and the operational amplifier OP3, and is connected to the output terminal via the resistor R2. The non-inverting input terminal of the operational amplifier OP4 is grounded via the resistor R2 'and the voltage Vref is applied via the resistor R1'. Note that the resistance values are R1 = R1 ′ and R2 = R2 ′. Thereby, the operational amplifier OP4 outputs the threshold voltage Vo3 of Expression (10).

  The comparator COM1 compares the threshold voltage Vo3 and the differential output Vamp, outputs an H signal when the differential output Vamp exceeds the threshold voltage Vo3, and when the differential output Vamp does not exceed the threshold voltage Vo3 Outputs an L signal. The transistor TR1 is turned on / off according to the output result of the comparator COM1, turned on when the comparator COM1 outputs an H signal, and turned off when the L signal is output.

  Therefore, when the differential output Vamp exceeds the threshold voltage Vo3 corresponding to the compensation temperature, the transistor TR1 is turned on. When the differential output Vamp does not exceed the threshold voltage Vo3 corresponding to the compensation temperature, the transistor TR1 is turned off.

  The collector of the transistor TR1 is connected to the gate of the MOSFET 91 of the relay operation circuit 90 via the latch circuit 70. The emitter of the transistor TR1 is grounded. A voltage Vref is applied to the collector of the transistor TR1 through a resistor. The transistors TR2, TR3, TR4 of the high temperature abnormality detection circuits 40, 50, 60 are also connected to the latch circuit 70 and the relay operation circuit 90 in the same manner as the transistor TR1.

  FIG. 5 is a diagram for explaining a settable range of the threshold voltage Vo3. The high temperature abnormality detection circuit 30 can set the threshold voltage Vo3 within the following range. It is assumed that the differential output Vamp and the compensation output Vc are both 0 to 3.3 [V].

  Since the maximum value of the compensation output Vc is 3.3 [V], it is assumed that the expression (10) passes (3.3, 0) on the compensation output Vc axis. At this time, if Vref = 3.3 [V], then the intercept of equation (10) is D = 3.3 (R2 / R1). For the intercept D, it is necessary to satisfy the condition of Expression (11).

  However, Vr is a voltage that needs to be prepared separately.

(High temperature abnormality detection circuit 40)
The high temperature abnormality detection circuit 40 is turned on according to the comparison result of the operational amplifier OP5 functioning as a buffer, the operational amplifier OP6 that outputs the threshold voltage Vo1, the comparator COM2 that compares the differential output Vamp and the threshold voltage Vo1, and the comparator COM2. Transistor TR2 to be turned off.

  The inverting input terminal of the operational amplifier OP6 is grounded via a resistor R3 and is connected to its own output terminal via a resistor R4. The non-inverting potential terminal of the operational amplifier OP6 is connected to the Vc line via the resistor R3 'and the operational amplifier OP5. The non-inverting input terminal is grounded via a resistor R4 '. Note that the resistance values are R3 = R3 ′ and R4 = R4 ′. Thereby, the operational amplifier OP6 outputs the threshold voltage Vo1 of Expression (12).

  The operations of the comparator COM2 and the transistor TR2 are the same as those of the high temperature abnormality detection circuit 30. Therefore, when the differential output Vamp exceeds the threshold voltage Vo1 corresponding to the compensation temperature, the transistor TR2 is turned on. When the differential output Vamp does not exceed the threshold voltage Vo1 corresponding to the compensation temperature, the transistor TR2 is turned off.

  FIG. 6 is a diagram for explaining a settable range of the threshold voltage Vo1. The high temperature abnormality detection circuit 40 can set the threshold voltage Vo1 within the following range.

  Since the minimum value of the compensation output Vc is 0 [V], Equation (12) is assumed to pass through the origin. However, the intercept D may be given to Expression (12) as necessary. For the intercept D, the condition of Expression (13) needs to be satisfied.

  However, Vr is a voltage that needs to be prepared separately.

(High temperature abnormality detection circuit 50, 60)
The high temperature abnormality detection circuit 50 includes a comparator COM3 that compares the differential output Vamp and the threshold voltage Vo2 (= [R6 / (R5 + R6)] · Vref), and a transistor TR3 that is turned on / off according to the comparison result of the comparator COM3. ,have.

  The comparator COM3 outputs an H signal when the differential output Vamp exceeds the threshold voltage Vo2, and outputs an L signal when the differential output Vamp does not exceed the threshold voltage Vo2. The transistor TR3 is turned on when the comparator COM3 outputs an H signal, and turned off when the L signal is output.

  Therefore, regardless of the compensation output Vc, the transistor TR3 is turned on when the differential output Vamp exceeds the threshold voltage Vo2 (constant), and the transistor TR3 is turned off when the differential output Vamp does not exceed the threshold voltage Vo2. become.

  The high temperature abnormality detection circuit 60 includes a comparator COM4 that compares the voltage Vc and the threshold voltage Vo4 (= [R8 / (R7 + R8)] · Vref), and a transistor TR4 that is turned on / off according to the comparison result of the comparator COM4. Have. The operations of the comparator COM4 and the transistor TR4 are the same as those of the high temperature abnormality detection circuit 50.

  Therefore, regardless of the differential output Vamp, the transistor TR4 is turned on when the compensation output Vc exceeds the threshold voltage Vo4 (constant), and the transistor TR4 is turned off when the compensation output Vc does not exceed the threshold voltage Vo4. Become.

(Latch circuit 70)
The latch circuit 70 is a circuit that holds the state of the relay operation circuit 90 in accordance with the detection state of the high temperature abnormality detection circuits 30, 40, 50, 60.

  Here, each collector of the transistors TR <b> 1 to TR <b> 4 is connected to the gate of the MOSFET 91 of the relay operation circuit 90 via the latch circuit 70. The Vref is applied to the gate of the MOSFET 91 via a resistor, and the MOSFET 91 is at the H level.

  When none of the high temperature abnormality detection circuits 30, 40, 50, 60 detect a high temperature abnormality (none of the transistors TR1 to TR4 is ON), the latch circuit 70 sets the gate of the MOSFET 91 to the H level (active) state. Keep it. Further, the latch circuit 70 is configured such that when any of the high temperature abnormality detection circuits 30, 40, 50, 60 detects a high temperature abnormality (any one of the transistors TR1 to TR4 is turned on), the gate of the MOSFET 91 is grounded. Is maintained (L level).

  When the power is turned on, the gate of the MOSFET 91 of the relay operation circuit 90 is grounded. Therefore, when the latch circuit 70 maintains this state, the relay 100 (heating lamp 3) is not turned on. Therefore, the reset circuit 80 resets the latch circuit 70 when the power is turned on. Thereby, the latch circuit 70 maintains the state where the gate of the MOSFET 91 of the relay operation circuit 90 is changed from the L level to the H level and the relay 100 is turned on.

  Of course, the circuit configuration of the latch circuit 70 and the reset circuit 80 is not particularly limited as long as they have the functions described above.

  The relay operation circuit 90 includes a transistor TR <b> 5 whose on / off is controlled by the CPU 110 and a MOSFET 91 that turns on / off the relay 100. Note that the present invention is not limited to the MOSFET 91, and a transistor may be used instead. The collector of the transistor TR5 is connected to the gate of the MOSFET 91 through a resistor, and the emitter thereof is grounded. The drain of the MOSFET 91 is connected to the relay 100, and its source is grounded. Further, the gate of the MOSFET 91 is at the H level (active) by the voltage Vref via the resistor r90.

  Therefore, normally, the MOSFET 91 is turned on, the relay 100 is also turned on, and the heating lamp 3 is also turned on. Thereby, the heating roll 2 is heated by the heating lamp 3.

  On the other hand, when any of the high temperature abnormality detection circuits 30, 40, 50, 60 detects a high temperature abnormality as described above, one of the transistors TR1 to TR4 is turned on and the MOSFET 91 is turned off. As a result, the relay 100 is turned off and the heating lamp 3 stops heating. Further, the CPU 110 can forcibly turn off the heating lamp 3 by directly turning off the transistor TR5.

  Note that when controlling the heating temperature of the heating lamp 3, the CPU 110 turns on / off the heating lamp 3 not through the relay 100 but through another circuit (not shown).

The CPU 110 constantly monitors the voltages Vd, Vamp, and Vc, and calculates the detected temperature Td, the compensation temperature Tc, and the temperature T _ROLL of the heating roll 2 based on the equations (1) to (8). Then, the CPU 110 controls the temperature of the heating lamp 3 via a circuit (not shown). Note that the CPU 110 may obtain the temperature T _ROLL of the heating roll 2 using a predetermined table instead of the equations (1) to (8). Further, the CPU 110 may forcibly turn on the transistor TR5 and turn off the heating lamp 3 as necessary.

(Setting example of threshold voltage Vo)
The heating apparatus configured as described above can detect the high temperature abnormality of the heating roll and control the heating lamp 3 in various manners by adjusting the setting of the threshold voltage Vo.

(First setting example)
In the first setting example, the heating device detects a high temperature abnormality of the heating roll 2 by comparing the differential output Vamp with the threshold voltages Vo1, Vo2, and Vo3.

  FIG. 7A is a diagram illustrating threshold voltages Vo1, Vo2, and Vo3 on the graph of the differential output Vamp with respect to the compensation output Vc, and FIG. 7B is a threshold voltage Vo1 on the graph of the differential output Vamp with respect to the compensation temperature. , Vo2 and Vo3. FIG. 5B is a diagram in which the compensation output in FIG. 4A is converted into compensation temperature, and FIGS. 4A and 4B are equivalent.

Here, Vref = 3.3V, R5 = R6 = 200 kΩ, and the magnification of the amplifier (differential amplifier circuit 20) is 37 times. High temperature abnormality detection condition is
Threshold voltage Vo1: Vamp> 1.8 · Vc
Threshold voltage Vo2: Vamp> 3.0
Threshold voltage Vo3: Vamp> 5.4 · (Vref−Vc)
It becomes.

  7A and 7B also show temperature characteristics of the differential output Vamp with respect to the compensation output Vc (or compensation temperature). The temperature characteristic of the differential output with respect to the compensation output linearly increases from the vicinity of the origin to the right at any point of 0 to 380 ° C., reaches a peak near Vc = 2 [V], and then decreases linearly. . In addition, FIG. 8 thru | or FIG. 11 mentioned later shows the said temperature characteristic similarly.

  The threshold voltages Vo1, Vo2, Vo3 of the first setting example are set so as to substantially match the temperature characteristics when the heating roll 2 is 240 ° C. Thereby, the heating apparatus can detect the high temperature abnormality of the heating roll 2 when the heating roll 2 reaches about 240 ° C.

(Second setting example)
In the second setting example, the heating device detects a high temperature abnormality of the heating roll 2 by comparing the differential output Vamp, the threshold voltages Vo1, Vo2, and the compensation outputs Vc, Vo4.

  FIG. 8A is a diagram showing threshold voltages Vo1, Vo2, and Vo4 on the graph of the differential output Vamp with respect to the compensation output Vc, and FIG. 8B is a threshold voltage Vo1 on the graph of the differential output Vamp with respect to the compensation temperature. , Vo2 and Vo4.

Here, Vref = 3.3V, R5 = R6 = 300 kΩ, and the magnification of the amplifier (differential amplifier circuit 20) is 33 times. High temperature abnormality detection condition is
Threshold voltage Vo1: Vamp> 1.8 · Vc
Threshold voltage Vo2: Vamp> 3.0
Threshold voltage Vo4: Vc> 2.76
It becomes.

  The threshold voltages Vo1, Vo2, Vo4 of the second setting example are set so as to substantially match the temperature characteristics when the heating roll 2 is 240 ° C. However, when the compensation temperature is about −10 ° C. or lower, an abnormality is detected regardless of the value of the differential output Vamp.

(Third setting example)
In the third setting example, the heating device detects a high temperature abnormality of the heating roll 2 by comparing the differential output Vamp and the threshold voltages Vo1 and Vo3.

FIG. 9A is a diagram showing the threshold voltages Vo1 and Vo3 on the graph of the differential output Vamp with respect to the compensation output Vc. FIG. 9B is a diagram showing the threshold voltages Vo1 and Vo3 on the graph of the differential output Vamp with respect to the compensation temperature. FIG. Here, Vref = 3.3V, R5 = R6 = 400 kΩ, and the magnification of the amplifier (differential amplifier circuit 20) is 24 times. High temperature abnormality detection condition is
Threshold voltage Vo1: Vamp> 1.45 · Vc
Threshold voltage Vo3: Vamp> 2.9 · (Vref−Vc)
It becomes.

(Fourth setting example)
In the fourth setting example, the heating device detects a high temperature abnormality of the heating roll 2 by comparing the differential output Vamp with the threshold voltages Vo2 and Vo3.

FIG. 10A is a diagram showing the threshold voltages Vo2 and Vo3 on the graph of the differential output Vamp with respect to the compensation output Vc, and FIG. 10B is a threshold voltage Vo2 and Vo3 on the graph of the differential output Vamp with respect to the compensation temperature. FIG. Here, Vref = 3.3V, R5 = R6 = 33 kΩ, and the magnification of the amplifier (differential amplifier circuit 20) is 63 times. High temperature abnormality detection condition is
Threshold voltage Vo2: Vamp> 3.0
Threshold voltage Vo3: Vamp> 9.5 · (Vref−Vc)
It becomes.

(Fifth setting example)
In the fifth setting example, the heating device detects a high temperature abnormality of the heating roll 2 by comparing the differential output Vamp and the threshold voltage Vo2, and further the compensation output Vc and the threshold voltage Vo4.

FIG. 11A shows the threshold voltages Vo2 and Vo4 on the graph of the differential output Vamp with respect to the compensation output Vc, and FIG. 11B shows the threshold voltages Vo2 and Vo4 on the graph of the differential output Vamp with respect to the compensation temperature. FIG. Here, Vref = 3.3V, R5 = R6 = 100 kΩ, and the magnification of the amplifier (differential amplifier circuit 20) is 44 times. High temperature abnormality detection condition is
Threshold voltage Vo2: Vamp> 3.0
Threshold voltage Vo4: Vc> 3.1
It becomes.

  Of the first to fifth setting examples in the present embodiment, the first setting example is preferable. However, it is not particularly limited which of threshold voltages Vo1 to Vo4 is used to detect a high temperature abnormality. Further, the numerical values in the first to fifth setting examples are merely examples, and it is needless to say that the numerical values are not limited thereto.

  As described above, the heating device according to the first embodiment of the present invention determines whether or not the heating roll 2 is at an abnormally high temperature based on the output voltages of the detection element 11 and the compensation element 12 of the NC sensor 10. Detecting and turning off the heating lamp 3 when detecting an abnormally high temperature. Thereby, the heating roll 2 can be heated safely without sacrificing the temperature detection accuracy of the NC sensor 10.

  Specifically, the heating device obtains the compensation output Vc of the compensation element 12 and the differential output Vamp of the detection element 11 and the compensation element 12, and becomes a threshold for detecting a high temperature abnormality based on the obtained compensation output Vc. The differential output (threshold voltage Vo) is determined. When the differential output Vamp exceeds the threshold voltage Vo, a high temperature abnormality is detected and the heating lamp 3 is turned off.

  In other words, the heating device determines the high temperature abnormal region (outside the region surrounded by the plurality of threshold voltages Vo in FIGS. 7 to 11) two-dimensionally, and the operating points of the differential output Vamp and the compensation output Vc are this. It detects whether or not it is in a high temperature abnormal region. Thereby, compared with the case where it is determined whether one voltage value exceeded a certain threshold value as in the prior art, it is possible to detect a high temperature abnormality with higher accuracy.

  In addition, when a failure occurs in any of the high temperature abnormality detection circuits 30, 40, 50, and 60 and a hardware problem occurs, the CPU 110 can also detect the failure. That is, the CPU 110 can detect whether the high temperature abnormality detection circuits 30, 40, 50, 60 are faulty by constantly monitoring the voltages Vd, Vamp, Vc.

  Specifically, the CPU 110 monitors whether the differential output Vamp is a predetermined multiple of the differential between the voltage Vd and the compensation output Vc (or a voltage value within a predetermined range including this value). When the differential output Vamp does not reach the above value, the CPU 110 determines that a failure has occurred in any of the high temperature abnormality detection circuits 30, 40, 50, 60, and the relay operation circuit 90 The transistor TR5 is turned on. At this time, the MOSFET 91 and the relay 100 are turned off.

  Thus, the heating device according to the present embodiment can detect whether or not a failure has occurred in any of the high temperature abnormality detection circuits 30, 40, 50, 60 without increasing the cost. When a crab failure occurs, the heating lamp 3 can be turned off to prohibit the operation of the entire heating device.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the circuit same as 1st Embodiment, and the description which overlaps with 1st Embodiment is abbreviate | omitted.

  The heating device according to the second embodiment can detect a high temperature abnormality of the heating roll 2 even when the compensation temperature is high.

  For example, in FIG. 7B, the threshold voltage Vo1 is an index for determining whether or not the heating roll 2 has reached a predetermined temperature (for example, 240 ° C.). However, as the compensation temperature increases (100 ° C. or higher), the threshold voltage Vo1 becomes larger than the 240 ° C. temperature characteristic. In other words, the relationship between the threshold voltage Vo1 and the 240 ° C. temperature characteristic is such that when the compensation temperature is 100 ° C. or higher, the value obtained by differentiating the threshold voltage Vo1 with the compensation temperature is greater than the value obtained by differentiating the 240 ° C. temperature characteristic with the compensation temperature. End up. For this reason, when the compensation temperature is high, even if the heating roll 2 actually reaches 240 ° C., there is a possibility that a high temperature abnormality will not be detected.

  Here, as an example in which a high temperature abnormality may not be detected when the compensation temperature is high, the relationship between the threshold voltage and the temperature characteristic in FIG. 7 has been described. However, the present embodiment is not limited to the relationship between the threshold voltage and the temperature characteristic in FIG. For example, the circuit functions effectively when a circuit corresponding to FIGS. 9, 10, and 11 is used or when a configuration other than this is used.

  FIG. 12 is a flowchart showing a high temperature abnormality detection routine by the CPU 110. CPU110 performs the process shown in FIG. 12 in order to avoid said problem.

  In step ST1, the CPU 110 determines whether or not the compensation output Vc <predetermined value. If the determination is affirmative, the CPU 110 proceeds to step ST2, and if the determination is negative, the process ends. The predetermined value here is, for example, a compensation temperature range (for example, a temperature difference between the differential output Vamp when the heating roll 2 is actually 240 ° C. and the threshold voltage Vo1 may not be detected). The compensation output Vc in a state of being 100 ° C. or higher) is shown.

  CPU 110 may determine whether compensation temperature> predetermined abnormal temperature (for example, 100 ° C.) instead of determining whether compensation output Vc <predetermined value.

  In step ST2, the CPU 110 turns on the transistor TR5 and ends the process. At this time, MOSFET 91 shown in FIG. 2 is turned off, relay 100 is turned off, and heating lamp 3 is also turned off. Thereby, when it will be in the above states, CPU110 can avoid high temperature abnormality by forcibly turning off the heating lamp 3. FIG.

  CPU 110 repeatedly executes step ST1.

  As described above, in the heating device according to the second embodiment, the gradient of the temperature characteristic of the differential output Vamp with respect to the compensation output Vc is larger than the gradient of the threshold voltage Vo1, and the compensation temperature is equal to or higher than a predetermined temperature. If it is, the heating lamp 3 is turned off. As a result, the heating device stops heating the heating roll 2 with software before entering the compensation temperature range where the high temperature abnormality of the heating roll 2 cannot be detected by hardware, so that the safety of the entire apparatus can be ensured. it can.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the circuit same as embodiment mentioned above, and the overlapping description is abbreviate | omitted.

  The heating device according to the third embodiment can reliably prevent overheating of the heating roll 2 even when the compensation temperature is high.

  For example, in FIG. 7B, the threshold voltage Vo1 is an index for determining whether or not the heating roll 2 has reached a predetermined temperature or higher (eg, 240 ° C.). However, as the compensation temperature increases (100 ° C. or higher), the threshold voltage Vo1 becomes larger than the 240 ° C. temperature characteristic. In other words, the relationship between the threshold voltage Vo1 and the 240 ° C. temperature characteristic is such that when the compensation temperature is 100 ° C. or higher, the value obtained by differentiating the threshold voltage Vo1 with the compensation temperature is greater than the value obtained by differentiating the 240 ° C. temperature characteristic with the compensation temperature. End up. For this reason, when the compensation temperature is high, even if the heating roll 2 actually reaches 240 ° C., there is a possibility that a high temperature abnormality will not be detected.

  In the present embodiment, an overheat prevention device such as a thermostat or a temperature fuse is provided in the vicinity of the heating lamp 3, and this is connected in series between the power supply device and the heating lamp 3. In a state where the compensation temperature is high such that a high temperature abnormality may not be detected, the thermostat or the temperature fuse has already been heated. Therefore, when the heating roll 2 becomes abnormally hot, the power supply from the power supply device to the heating lamp 3 can be shut off even if it is a thermostat or temperature fuse with low responsiveness, and this can be dealt with sufficiently. .

  Further, in this embodiment, since it is not necessary to detect a high temperature abnormality at all compensation temperatures, it becomes possible to select a relatively simple circuit (for example, as shown in FIG. 11), and to reduce the cost of the circuit. There is also a merit such as reduction of the base area.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the circuit same as embodiment mentioned above, and the overlapping description is abbreviate | omitted. In the fourth embodiment, a case where a contact-type temperature sensor that detects the temperature of the heating roll 2 in addition to the NC sensor 10 is used will be described.

  FIG. 13 is a diagram illustrating the heat energy distribution in the axial direction of the heating roll 2 when heated by one of the plurality of heating lamps 3 (650 W and 835 W). The 650 W heating lamp 3 is configured such that the heat generation energy is reduced at the end of the heating roll 2. On the other hand, the heating lamp 3 of 835 W is configured so that the heat generation energy is maximized at the end of the heating roll 2.

  As shown in FIG. 13, when the NC sensor 10 is disposed near the center of the heating roll 2 in the axial direction, the NC sensor 10 can detect the maximum value of heat generation energy when heated at 650 W. Although it is possible, the maximum value of the heat generation energy when heated at 835 W cannot be detected.

  In other words, when the axial position of the heating roll 2 of the NC sensor 10 is different from the axial position where the heat generation energy per unit length is the highest (in the case of 835 W), the NC sensor 10 is the maximum value of the heat generation energy. Cannot be detected.

  Therefore, in the above case, a contact-type temperature sensor 120 that detects the temperature by contacting the end of the heating roll 2 may be provided at the position shown in the figure. Note that the contact-type temperature sensor 120 is preferably arranged in a non-sheet passing portion in order to prevent image defects.

  Thereby, the heating apparatus should just detect the high temperature abnormality of the heating roll 2, when the temperature detected with the contact-type temperature sensor exceeds predetermined temperature. Thereby, irrespective of the structure of the heating lamp 3, the heating roll 2 can be heated safely.

  It should be noted that the present invention is not limited to the first to fourth embodiments, and can of course be applied to those modified in design within the scope described in the claims. It is.

  For example, the heating device according to the present invention is not limited to being used in a fixing device of an image forming apparatus as in the above-described embodiment, and can be applied to, for example, a heating cooker.

It is sectional drawing which shows the principal part of the heating apparatus which concerns on embodiment of this invention. It is a figure which shows the circuit structure of the heating apparatus which concerns on embodiment of this invention. It is a figure which shows the circuit structure for demonstrating the principle which can detect the temperature of a heating roll based on the detection result of the detection element of a NC sensor, and a compensation element. It is a figure which shows the threshold voltage Vo for determining high temperature abnormality. It is a figure for demonstrating the settable range of threshold voltage Vo3. It is a figure for demonstrating the settable range of threshold voltage Vo1. (A) is a diagram showing threshold voltages Vo1, Vo2, and Vo3 on the graph of the differential output Vamp with respect to the compensation output Vc, and (B) is a threshold voltage Vo1, Vo2 on the graph of the differential output Vamp with respect to the compensation temperature. , Vo3. (A) is a diagram showing threshold voltages Vo1, Vo2, Vo4 on the graph of the differential output Vamp with respect to the compensation output Vc, and (B) is a threshold voltage Vo1, Vo2 on the graph of the differential output Vamp with respect to the compensation temperature. , Vo4. (A) is a diagram showing the threshold voltages Vo1 and Vo3 on the graph of the differential output Vamp with respect to the compensation output Vc, and (B) is a diagram showing the threshold voltages Vo1 and Vo3 on the graph of the differential output Vamp with respect to the compensation temperature. FIG. (A) is a diagram showing the threshold voltages Vo2 and Vo3 on the graph of the differential output Vamp with respect to the compensation output Vc, and (B) is a diagram showing the threshold voltages Vo2 and Vo3 on the graph of the differential output Vamp with respect to the compensation temperature. FIG. (A) is a diagram showing the threshold voltages Vo2 and Vo4 on the graph of the differential output Vamp with respect to the compensation output Vc, and (B) is a diagram showing the threshold voltages Vo2 and Vo4 on the graph of the differential output Vamp with respect to the compensation temperature. FIG. It is a flowchart which shows the high temperature abnormality detection routine by CPU. It is a figure which shows the heat_generation | fever energy distribution of the axial direction of a heating roll when it heats by 650W and 835W.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing device 2 Heating roll 3 Heating lamp 10 NC sensor 11 Detection element 12 Compensation element 20 Differential amplification circuit 30,40,50,60 High temperature abnormality detection circuit 70 Latch circuit 80 Reset circuit 90 Relay operation circuit 100 Relay 110 CPU
120 Contact temperature sensor

Claims (3)

Heating means for heating the heating element;
A detection element that is arranged apart from the heating body and detects the temperature of an infrared absorber whose temperature changes with infrared rays emitted from the heating body as a detection temperature, and a temperature in or near the sensor is detected as a compensation temperature. A non-contact temperature sensor having a compensation element;
A differential voltage that is a difference between the detection voltage output from the detection element and the compensation voltage output from the compensation element is a first threshold value obtained by multiplying the compensation voltage by a first constant, a predetermined first value. A second threshold that is a constant of 2, a third threshold obtained by multiplying a difference between the circuit applied voltage and the compensation voltage by a third constant, or the compensation voltage. High temperature abnormality detection means for detecting a high temperature abnormality of the heating body when becomes equal to or greater than a fourth threshold that is a predetermined fourth constant,
A heating stop means for stopping heating of the heating means when a high temperature abnormality of the heating body is detected by the high temperature abnormality detection means;
Heating device with. A heating temperature control means for calculating the temperature of the heating body based on the detection voltage, the differential voltage, and the compensation voltage, and controlling the heating temperature of the heating means based on the calculated temperature. The heating device according to claim 1 further provided. The heating apparatus according to claim 1, further comprising holding means for holding a heating stop state by the heating stop means.

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