JP2017102326A - Fixing device and abnormality detection method for temperature sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of detecting the abnormality of a temperature sensor, before the driving of a heat source is started.SOLUTION: The fixing device includes a control part 10, a heating member 61, a heat source 63 for heating the heating member 61, and a temperature sensor 64 for measuring the temperature of the heating member 61. When a first signal is inputted, the control part 10 stops the driving of the heat source 63. When the first signal is inputted, the control part 10 acquires a first temperature on the basis of output from the temperature sensor 64. When a second signal is inputted after the first signal is inputted, the control part 10 acquires a second temperature on the basis of the output from the temperature sensor 64. When a temperature change from the first temperature to the second temperature satisfies a first condition, the control part 10 determines that the temperature sensor 64 is abnormal. When the temperature change satisfies a second condition, the control part 10 drives the heat source 63.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fixing device and a temperature sensor abnormality detection method.

  An electrophotographic image forming apparatus, which is a type of image forming apparatus, includes a fixing device and fixes a toner image on a sheet. The fixing device includes a heating member and a pressure member. The heating member is heated by a heat source such as a halogen heater or an IH coil provided in the fixing device. The pressure member is provided to face the heating member and forms a fixing nip with the heating member. The sheet is heated and pressed by passing through the fixing nip. As a result, the toner image is fixed on the sheet.

  Further, the fixing device includes a temperature sensor. The temperature sensor measures the temperature of the heating member. The heat source is controlled so that the heating member has a predetermined temperature based on the temperature measured by the temperature sensor. On the other hand, if an abnormality occurs in the temperature sensor, the temperature of the heating member cannot be controlled. As a result, the temperature of the heating member may exceed a predetermined temperature. Therefore, various techniques for detecting abnormality of the temperature sensor have been disclosed. For example, Patent Document 1 discloses a technique for detecting an abnormality of a temperature sensor based on an output from a temperature sensor (thermistor) after starting to supply power to a heat source.

JP 2007-025010 A

  However, the technique disclosed in Patent Document 1 cannot detect an abnormality of the temperature sensor unless the supply of electric power to the heat source is started and the heat source is driven.

  In view of the above problems, an object of the present invention is to provide a fixing device and a temperature sensor abnormality detection method capable of detecting an abnormality of a temperature sensor before starting to drive a heat source.

  The fixing device of the present invention includes a fixing unit and a control unit that controls a heating operation by the fixing unit. The fixing unit includes a heat source, a heating member, and a temperature sensor. The heating member is heated by the heat source. The temperature sensor measures the temperature of the heating member. The control unit includes a drive unit, a temperature acquisition unit, and an abnormality determination unit. The drive unit drives the heat source. When the first signal is input to the control unit, the temperature acquisition unit acquires a first temperature based on an output from the temperature sensor. When the second signal is input after the first signal is input to the control unit, the temperature acquisition unit acquires a second temperature based on an output from the temperature sensor. The abnormality determination unit determines an abnormality of the temperature sensor based on a temperature change from the first temperature to the second temperature and a first condition. The drive unit stops driving the heat source when the first signal is input to the control unit. The abnormality determination unit determines that the temperature sensor is abnormal when the temperature change satisfies the first condition. The driving unit drives the heat source when the temperature change satisfies a second condition different from the first condition.

  The temperature sensor abnormality detection method of the present invention is a temperature sensor abnormality detection method for measuring the temperature of the heating member provided in the fixing unit. The temperature sensor abnormality detection method includes the following steps. When the first signal is generated, the driving of the heat source for heating the heating member is stopped, and the first temperature is acquired based on the output from the temperature sensor. Acquiring a second temperature based on an output from the temperature sensor when a second signal is generated after the first signal is generated; Determining that the temperature sensor is abnormal when a temperature change from the first temperature to the second temperature satisfies a first condition; Driving the heat source when the temperature change satisfies a second condition different from the first condition;

  According to the present invention, it is possible to detect abnormality of the temperature sensor before starting to drive the heat source.

1 is a diagram illustrating a configuration of an image forming apparatus including a fixing device according to an embodiment of the present invention. 2 is a diagram illustrating a configuration of a fixing unit according to an embodiment of the present invention. 1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. It is a flowchart which shows the abnormality detection method of the thermistor which concerns on embodiment of this invention. It is a flowchart which shows the 1st abnormality determination process which concerns on embodiment of this invention. It is a flowchart which shows the 2nd abnormality determination process which concerns on embodiment of this invention. It is a figure which shows the change of the measurement temperature of the thermistor which concerns on embodiment of this invention.

  Hereinafter, an image forming apparatus including a fixing device according to an embodiment of the present disclosure and a temperature sensor abnormality detection method will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof is not repeated.

  First, an image forming apparatus 1 including a fixing device according to the present embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating a configuration of an image forming apparatus 1 including a fixing device. In the present embodiment, the image forming apparatus 1 is an electrophotographic multifunction machine.

  As shown in FIG. 1, the image forming apparatus 1 includes a power switch 2, an operation unit 3, a paper feeding unit 4, an image forming unit 5, a fixing unit 6, a discharge unit 7, and a transport unit L.

  The power switch 2 switches between starting and stopping the supply of power to the image forming apparatus 1. When the power switch 2 is turned on, supply of power to the image forming apparatus 1 is started. On the other hand, when the power switch 2 is turned off, the supply of power to the image forming apparatus 1 is stopped.

  The operation unit 3 receives an input operation by a user. The operation unit 3 includes a touch panel 31 and a plurality of operation keys 32. The touch panel 31 displays various processing results. The operation keys 32 include, for example, a numeric keypad and a start key. The image forming apparatus 1 starts an image forming operation when the operation unit 3 receives an input operation for starting the operation.

  The conveyance unit L conveys the sheet S from the paper supply unit 4 to the discharge unit 7 via the image forming unit 5 and the fixing unit 6. The paper feed unit 4 feeds the sheets S one by one to the transport unit L. The discharge unit 7 discharges the sheet S outside the apparatus.

  The image forming unit 5 forms an image on the sheet S fed from the sheet feeding unit 4. The image forming unit 5 includes an exposure device 51, a developing device 52, a photosensitive drum 53, and a transfer device 54. The exposure device 51 irradiates the photosensitive drum 53 based on the image data. Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 53. The developing device 52 supplies toner to the photosensitive drum 53 and develops the electrostatic latent image formed on the photosensitive drum 53 to form a toner image.

  The transfer device 54 transfers the toner image formed on the photosensitive drum 53 to the sheet S. The sheet S on which the toner image is transferred is conveyed to the fixing unit 6.

  The fixing unit 6 includes a heating roller 61 that is an example of a heating member, a pressure roller 62 that is an example of a pressure member, and a halogen heater 63 that is an example of a heat source. The heating roller 61 and the pressure roller 62 are arranged to face each other and form a fixing nip. The halogen heater 63 is disposed inside the heating roller 61 and heats the heating roller 61. The halogen heater 63 radiates infrared rays toward the inner peripheral surface of the heating roller 61 when electric power is supplied. As a result, the heating roller 61 is heated. The sheet S conveyed from the image forming unit 5 is heated and pressed by passing through the fixing nip. As a result, the toner image is fixed on the sheet S.

  Next, the configuration of the fixing unit 6 will be described with reference to FIG. FIG. 2 is a diagram illustrating a configuration of the fixing unit 6.

  As shown in FIG. 2, the fixing unit 6 further includes a thermistor 64 that is an example of a temperature sensor.

  The thermistor 64 is disposed so as to contact a part of the outer peripheral surface of the heating roller 61. The thermistor 64 measures the temperature of the outer peripheral surface (surface) of the heating roller 61 and outputs a signal corresponding to the measured temperature.

  Next, the configuration of the image forming apparatus 1 will be described in detail with reference to FIG. FIG. 3 is a block diagram illustrating a configuration of the image forming apparatus 1.

  As shown in FIG. 3, the image forming apparatus 1 further includes a storage unit 9 and a control unit 10. In the present embodiment, the storage unit 9 also serves as a storage unit of the fixing device. The control unit 10 also serves as a control unit of the fixing device.

  The storage unit 9 includes an HDD (Hard Disk Drive), a RAM (Random Access Memory), and a ROM (Read Only Memory). The storage unit 9 stores a control program.

  The control unit 10 includes a heater driving circuit 11, a real time clock unit 12, and a processing unit 13 that are examples of the driving unit. In the present embodiment, the processing unit 13 receives an ON signal when the power switch 2 is turned on. The processing unit 13 receives an OFF signal when the power switch 2 is turned off. The ON signal is an example of a second signal, and the OFF signal is an example of a first signal.

  The heater drive circuit 11 supplies electric power to the halogen heater 63 to drive the halogen heater 63. In the present embodiment, when the OFF signal is input to the processing unit 13, the operation of the heater drive circuit 11 is stopped. As a result, the supply of electric power to the halogen heater 63 is stopped, and the driving of the halogen heater 63 is stopped.

  The real time clock unit 12 measures the current time. The real-time clock unit 12 is always supplied with power.

  The processing unit 13 includes a CPU (Central Processing Unit) and an ASIC (Application Specific Integrated Circuit). The processing unit 13 functions as the heater control unit 130, the temperature acquisition unit 131, the time acquisition unit 132, and the sensor abnormality determination unit 133 by executing the control program stored in the storage unit 9. The processing unit 13 controls the operation of each unit of the image forming apparatus 1 by executing a control program stored in the storage unit 9.

  The heater control unit 130 controls the heating operation by the halogen heater 63 via the heater drive circuit 11 based on the signal output from the thermistor 64. Specifically, the heater control unit 130 controls the operation of the heater drive circuit 11 so that the measured temperature of the thermistor 64 becomes a predetermined temperature. In the present embodiment, when an OFF signal is input to the processing unit 13, the heater control unit 130 stops driving the heater driving circuit 11. As a result, the supply of power to the halogen heater 63 is stopped.

  The temperature acquisition unit 131 acquires the temperature based on the signal output from the thermistor 64. Specifically, the temperature acquisition unit 131 acquires a temperature corresponding to a signal (voltage value) output from the thermistor 64 from the temperature conversion table. The temperature conversion table is stored in the storage unit 9 in advance. The temperature conversion table associates voltage values with temperatures. In the present embodiment, when an OFF signal is input to the processing unit 13, the temperature acquisition unit 131 acquires a temperature (first temperature) corresponding to the signal output from the thermistor 64 from the temperature conversion table. Further, when the ON signal is input to the processing unit 13, the temperature acquisition unit 131 acquires the temperature (second temperature) corresponding to the signal output from the thermistor 64 from the temperature conversion table. The temperature acquisition unit 131 stores the acquired temperature in the storage unit 9.

  When the OFF signal is input to the processing unit 13, the time acquisition unit 132 acquires the time (first time) indicated by the real-time clock unit 12. Further, when the ON signal is input to the processing unit 13, the time acquisition unit 132 acquires the time (second time) indicated by the real-time clock unit 12.

The processing unit 13 executes an abnormality determination process. In the present embodiment, the abnormality determination process includes a first abnormality determination process, a second abnormality determination process, and a third abnormality determination process. In the first abnormality determination process, the sensor abnormality determination unit 133 detects the abnormality of the thermistor 64 based on the temperature change per unit time from the first temperature to the second temperature in the period from the first time to the second time. judge. Specifically, the sensor abnormality determination unit 133 calculates the downward slope of the temperature change (temperature change per unit time) based on the first temperature, the second temperature, the first time, and the second time stored in the storage unit 9. calculate. The descending slope α of the temperature change is calculated by the following (Equation 1).
α = | (k2−k1) / p | (° C./min) (Formula 1)
In (Expression 1), k1 represents the first temperature, k2 represents the second temperature, and p represents the length of the period from the first time to the second time.

  The sensor abnormality determination unit 133 determines the abnormality of the thermistor 64 based on the calculated downward inclination α, the first condition, the second condition, and the third condition. In the present embodiment, the first condition is a condition that the downward inclination α is larger than the first inclination threshold TL (α> TL), and the second condition is that the downward inclination α is equal to or greater than the second inclination threshold TS. The third condition is a condition that the downward inclination α is smaller than the second inclination threshold TS (α <TS). The first inclination threshold value TL is an example of a first threshold value, and the second inclination threshold value TS is an example of a second threshold value. The first inclination threshold TL and the second inclination threshold TS are thresholds set for the downward inclination α. The first inclination threshold value TL and the second inclination threshold value TS are stored in the storage unit 9 in advance. The first inclination threshold value TL has a value larger than the second inclination threshold value TS. The first inclination threshold value TL is, for example, | −51 (° C./min) |. The second inclination threshold value TS is, for example, | −5 (° C./min) |.

  The sensor abnormality determination unit 133 determines whether or not the downward inclination α is larger than the first inclination threshold TL. The sensor abnormality determination unit 133 determines that the thermistor 64 is abnormal when it is determined that the downward inclination α is larger than the first inclination threshold TL. When the sensor abnormality determination unit 133 determines that the thermistor 64 is abnormal, the processing unit 13 notifies an error. In the present embodiment, the processing unit 13 causes the touch panel 31 to display a message indicating that an error has occurred. On the other hand, if the sensor abnormality determination unit 133 determines that the downward slope α is not greater than the first slope threshold TL, that is, if the downward slope α is equal to or less than the first slope threshold TL, the downward slope α is the second slope. It is determined whether it is smaller than the threshold value TS. The sensor abnormality determination unit 133 determines that the thermistor 64 is not abnormal when it is determined that the downward inclination α is not smaller than the second inclination threshold value TS, that is, when the downward inclination α is greater than or equal to the second inclination threshold value TS. To do. That is, it is determined that the thermistor 64 is normal. On the other hand, when it is determined that the downward inclination α is smaller than the second inclination threshold value TS, a second abnormality determination process is executed.

  In the second abnormality determination process, the sensor abnormality determination unit 133 determines the abnormality of the thermistor 64 based on the length p of the period and the second temperature k2. Specifically, the sensor abnormality determination unit 133 determines whether or not the period length p is equal to or greater than the period threshold value Pt. If the sensor abnormality determination unit 133 determines that the length p of the period is equal to or greater than the period threshold value Pt (p ≧ Pt), the sensor abnormality determination unit 133 determines whether the second temperature k2 is greater than the temperature threshold value Kt. The sensor abnormality determination unit 133 determines that the thermistor 64 is abnormal when it is determined that the second temperature k2 is higher than the temperature threshold Kt (k2> Kt). As a result, the error is notified by the processing unit 13. In the present embodiment, the processing unit 13 causes the touch panel 31 to display a message indicating that an error has occurred.

  On the other hand, if the sensor abnormality determination unit 133 determines that the period length p is not greater than or equal to the period threshold value Pt, that is, if the period length p is smaller than the period threshold value Pt (p <Pt), the third abnormality Judgment processing is executed. When the sensor abnormality determination unit 133 determines that the second temperature k2 is not greater than the temperature threshold Kt, that is, when the second temperature k2 is equal to or lower than the temperature threshold Kt (k2 ≦ Kt), the third abnormality determination Processing is executed.

  The period threshold value Pt and the temperature threshold value Kt are stored in the storage unit 9 in advance. The period threshold value Pt is 30, for example, and the temperature threshold value Kt is 100, for example. The period threshold value Pt is an example of a third threshold value, and the temperature threshold value Kt is an example of a fourth threshold value. The period threshold value Pt is set so that the temperature of the halogen heater 63 is sufficiently low when the period indicated by the period threshold value Pt has elapsed since the driving of the halogen heater 63 has stopped. Further, the temperature threshold Kt is set to a temperature at which the heating roller 61 does not immediately exceed a predetermined temperature even when the driving of the halogen heater 63 is started.

  In the third abnormality determination process, the heater control unit 130 drives the halogen heater 63 cp for a certain period via the heater drive circuit 11. The sensor abnormality determination unit 133 determines abnormality of the thermistor 64 based on the output from the thermistor 64 after the halogen heater 63 has been cp driven for a certain period. Specifically, the temperature acquisition unit 131 acquires the third temperature k3 after the lapse of a certain period cp from the start of driving of the halogen heater 63. The sensor abnormality determination unit 133 calculates a temperature change rising slope β (temperature change per unit time) by dividing a value obtained by subtracting the second temperature k2 from the third temperature k3 by a certain period cp. To do. When the calculated value of the rising slope β is a value within a predetermined range, the sensor abnormality determination unit 133 determines that the thermistor 64 is not abnormal. On the other hand, when the value of the rising slope β is not within the predetermined range, it is determined that the thermistor 64 is abnormal. When the sensor abnormality determination unit 133 determines that the thermistor 64 is abnormal, the processing unit 13 notifies an error. In the present embodiment, the processing unit 13 causes the touch panel 31 to display a message indicating that an error has occurred.

  Next, a method for detecting an abnormality of the thermistor 64 in the image forming apparatus 1 will be described with reference to FIG. FIG. 4 is a flowchart showing an abnormality detection method for the thermistor 64.

  As shown in FIG. 4, when an OFF signal is input to the processing unit 13 (step S102), the heater control unit 130 stops driving the halogen heater 63 (step S104). Next, the temperature acquisition unit 131 acquires the first temperature k1 corresponding to the signal output from the thermistor 64 (step S106). And the time acquisition part 132 acquires 1st time (step S108). When the ON signal is input to the processing unit 13 (step S110), the temperature acquisition unit 131 acquires the second temperature k2 (step S112). Then, the time acquisition unit 132 acquires the second time (step S114). Next, an abnormality determination process for the thermistor 64 is executed (step S116). Note that the order of step S104, step S106, and step S108 can be interchanged. Moreover, the order of step S112 and step S114 can be interchanged.

  Next, the first abnormality determination process will be described with reference to FIG. FIG. 5 is a flowchart showing the first abnormality determination process. The first abnormality determination process is started when the temperature acquisition unit 131 acquires the second temperature k2 and the time acquisition unit 132 acquires the second time.

  As shown in FIG. 5, first, the sensor abnormality determination unit 133 calculates a downward gradient α of the temperature change (Step S202). Next, the sensor abnormality determination unit 133 determines whether or not the downward inclination α is larger than the first inclination threshold TL (step S204). If the sensor abnormality determination unit 133 determines that the downward inclination α is larger than the first inclination threshold TL (step S204: Yes), the sensor abnormality determination unit 133 determines that the thermistor 64 is abnormal (step S206). Next, the processing unit 13 notifies an error (step S208).

  On the other hand, if the sensor abnormality determination unit 133 determines that the downward inclination α is not greater than the first inclination threshold TL (step S204: No), the sensor abnormality determination unit 133 determines whether the downward inclination α is smaller than the second inclination threshold TS. (Step S210). If the sensor abnormality determination unit 133 determines that the downward inclination α is not smaller than the second inclination threshold TS (step S210: No), the sensor abnormality determination unit 133 determines that the thermistor 64 is not abnormal (step S212). As a result, the heater control unit 130 starts driving the halogen heater 63 so that the heating roller 61 reaches a predetermined temperature (step S214). On the other hand, when the sensor abnormality determination unit 133 determines that the downward inclination α is smaller than the second inclination threshold TS (step S210: Yes), a second abnormality determination process is executed (step S216).

  Next, the second abnormality determination process will be described with reference to FIG. FIG. 6 is a flowchart showing the second abnormality determination process.

  As illustrated in FIG. 6, the sensor abnormality determination unit 133 determines whether or not the period length p is equal to or greater than the period threshold value Pt (step S302). If it is determined that the period length p is not equal to or greater than the period threshold value Pt (step S302: No), the process proceeds to step S310. On the other hand, if the sensor abnormality determination unit 133 determines that the period length p is equal to or greater than the period threshold value Pt (step S302: Yes), the sensor abnormality determination unit 133 determines whether the second temperature k2 is greater than the temperature threshold value Kt ( Step S304). When it is determined that the second temperature k2 is not greater than the temperature threshold Kt (step S304: No), the process proceeds to step S310. On the other hand, if the sensor abnormality determination unit 133 determines that the second temperature k2 is greater than the temperature threshold Kt (step S304: Yes), the sensor abnormality determination unit 133 determines that the thermistor 64 is abnormal (step S306). Next, the processing unit 13 notifies an error (step S308).

  In step S310, the processing unit 13 executes a third abnormality determination process. Specifically, the sensor abnormality determination unit 133 determines whether or not the rising slope β is within a predetermined range. When the rising slope β is within a predetermined range, the heater control unit 130 starts driving the halogen heater 63 so that the heating roller 61 reaches a predetermined temperature. On the other hand, when the rising slope β is not within the predetermined range, the processing unit 13 notifies an error.

  Then, with reference to FIG. 7, the change of the measured temperature of the thermistor 64 is demonstrated. FIG. 7 is a diagram showing changes in the measured temperature of the thermistor 64. Specifically, FIG. 7 shows a change in measured temperature when the thermistor 64 is normal. In FIG. 7, the vertical axis indicates the measurement temperature (° C.), and the horizontal axis indicates time (minutes). In FIG. 7, curve C shows the change in the measured temperature of the thermistor 64. In FIG. 7, the first time t1 indicates the time when the OFF signal is input to the processing unit 13 and the driving of the halogen heater 63 is stopped. The third time t3 indicates the time when 2 minutes have elapsed from the first time t1, and the fourth time t4 indicates the time when 30 minutes have elapsed from the first time t1.

  In the example shown in FIG. 7, the measured temperature is approximately 200 ° C. while the halogen heater 63 is driven. When the OFF signal is input to the processing unit 13 and the driving of the halogen heater 63 is stopped, the measured temperature changes suddenly and becomes approximately 100 ° C. at the third time t3. Thereafter, the measured temperature changes slowly and reaches approximately 50 ° C. at the fourth time t4.

  In the example shown in FIG. 7, the temperature change from the first time t1 to the third time t3 is −100 (° C.). The length of the period from the first time t1 to the third time t3 is 2 minutes. Therefore, when the downward slope α is calculated with reference to (Equation 1), the downward slope α is 50 (° C./minute). The temperature change from the first time t1 to the fourth time t4 is −150 (° C.). The length of the period from the first time t1 to the fourth time t4 is 30 minutes. Therefore, when the downward slope α is calculated with reference to (Equation 1), the downward slope α is 5 (° C./minute).

  The first slope threshold TL is set for the downward slope α from the first time t1 to the third time t3. The second slope threshold TS is set for the downward slope α from the first time t1 to the fourth time t4. Preferably, the first inclination threshold TL is set to a value slightly larger than the maximum value of the downward inclination α when the thermistor 64 is normal. In the present embodiment, 51 is set as the first inclination threshold TL, and 5 is set as the second inclination threshold TS. Thereby, when the downward slope α is 5 (° C./min) or more and 51 (° C./min) or less, it can be determined that the thermistor 64 is normal. On the other hand, when the downward slope α is larger than 51 (° C./min), the measured temperature changes more rapidly than when the thermistor 64 is normal. Therefore, it can be determined that the thermistor 64 is abnormal. Further, when the downward inclination α is smaller than 5 (° C./minute), there is a possibility that the temperature change is gradually changed as compared with the case where the thermistor 64 is normal. Therefore, there is a possibility that an abnormality has occurred in the thermistor 64. Therefore, in the present embodiment, the second abnormality determination process is executed.

  In the second abnormality determination process, the sensor abnormality determination unit 133 determines abnormality of the thermistor 64 based on the temperature threshold value Kt and the period threshold value Pt. In the example shown in FIG. 7, the measured temperature after 30 minutes from the first time t1 is sufficiently lower than 100 ° C. Therefore, when the measured temperature after 30 minutes or more from the first time t1 is higher than 100 ° C., it can be determined that the thermistor 64 is abnormal. For this reason, by setting 30 as the period threshold value Pt and setting 100 as the temperature threshold value Kt, the processing unit 13 can detect the abnormality of the thermistor 64.

  Further, when the length p of the period is smaller than the period threshold value Pt, or when the second temperature k2 is equal to or lower than the temperature threshold value Kt, there is a possibility that the thermistor 64 is abnormal. For this reason, the processing unit 13 drives the halogen heater 63 to execute the third abnormality determination process.

  The present embodiment has been described above. According to the present embodiment, when the downward inclination α is larger than the first inclination threshold TL, it is possible to determine that the thermistor 64 is abnormal without driving the halogen heater 63.

  Further, when the downward inclination α is smaller than the second inclination threshold value TS, an abnormality may have occurred in the thermistor 64. According to the present embodiment, when the downward inclination α is smaller than the second inclination threshold value TS, the processing unit 13 executes a second abnormality determination process and a third abnormality determination process. Thus, it is possible to suppress the heating roller 61 from exceeding a predetermined temperature by repeatedly performing the process of determining the abnormality of the thermistor 64.

  The embodiment of the present invention has been described above with reference to the drawings (FIGS. 1 to 7). However, the present invention is not limited to the above-described embodiment, and can be implemented in various modes without departing from the gist thereof.

  For example, in the embodiment of the present invention, the case where the contact type thermistor 64 is used as the temperature sensor has been described as an example, but the present invention is not limited to this. For example, a non-contact thermistor and a compensation ambient temperature sensor may be used as the temperature sensor. In this case, the temperature acquisition unit 131 acquires the difference between the temperature measured by the non-contact type thermistor and the temperature measured by the compensation ambient temperature sensor as the temperature of the surface of the heating roller 61. The compensation ambient temperature sensor is provided in the fixing unit 6 and acquires the temperature of air in the fixing unit 6.

  In the embodiment of the present invention, the example in which the present invention is applied to the roller type fixing unit 6 has been described, but the present invention is not limited to this. For example, the present invention can also be applied to a belt-type fixing unit 6.

  In the embodiment of the present invention, the case where the halogen heater 63 that emits infrared rays is used as the heat source has been described as an example. However, the present invention is not limited to this. The heat source can be, for example, an IH coil that heats the heating member by electromagnetic induction.

  Further, in the embodiment of the present invention, the case where the present invention is applied to a multifunction machine has been described as an example, but the present invention is not limited to this. The present invention is also applicable to a printer.

  The present invention is useful for an electrophotographic image forming apparatus.

6 Fixing unit 61 Heating roller 63 Halogen heater 64 Thermistor 131 Temperature acquisition unit 132 Time acquisition unit 133 Sensor abnormality determination unit

Claims (10)

A fixing device comprising: a fixing unit; and a control unit that controls a heating operation by the fixing unit,
The fixing unit includes:
A heat source,
A heating member heated by the heat source;
A temperature sensor for measuring the temperature of the heating member, and
The controller is
A drive unit for driving the heat source;
When the first signal is input to the control unit, the first temperature is acquired based on the output from the temperature sensor, and the second signal is input after the first signal is input to the control unit. A temperature acquisition unit that acquires a second temperature based on an output from the temperature sensor;
An abnormality determination unit that determines an abnormality of the temperature sensor based on a temperature change from the first temperature to the second temperature and a first condition;
The drive unit, when the first signal is input to the control unit, to stop driving the heat source,
The abnormality determination unit determines that the temperature sensor is abnormal when the temperature change satisfies the first condition,
The driving unit drives the heat source when the temperature change satisfies a second condition different from the first condition.
The control unit further includes a time acquisition unit that acquires a first time when the first signal is input to the control unit, and acquires a second time when the second signal is input to the control unit. ,
The fixing device according to claim 1, wherein the abnormality determination unit acquires a temperature change per unit time in a period from the first time to the second time as the temperature change.
The first condition is a condition that the temperature change per unit time is larger than a first threshold value,
The fixing device according to claim 2, wherein the second condition is a condition that a temperature change per unit time is not less than a second threshold value and not more than the first threshold value.
When the temperature change per unit time is smaller than the second threshold, the abnormality determination unit is based on the length of the period from the first time to the second time and the second temperature. The fixing device according to claim 3, wherein abnormality of the temperature sensor is determined.
The abnormality determination unit determines that the temperature sensor is abnormal when the length of the period from the first time to the second time is equal to or greater than a third threshold and the second temperature is greater than a fourth threshold. The fixing device according to claim 4, wherein the determination is made.
A temperature sensor abnormality detection method for measuring the temperature of a heating member provided in a fixing unit,
When the first signal is generated, the driving of the heat source for heating the heating member is stopped, and the first temperature is acquired based on the output from the temperature sensor;
Obtaining a second temperature based on an output from the temperature sensor when a second signal is generated after the first signal is generated;
Determining that the temperature sensor is abnormal when a temperature change from the first temperature to the second temperature satisfies a first condition;
And a step of driving the heat source when the temperature change satisfies a second condition different from the first condition.
Obtaining a first time when obtaining the first temperature;
Obtaining a second time when obtaining the second temperature;
The temperature sensor abnormality detection method according to claim 6, further comprising: acquiring, as the temperature change, a temperature change per unit time in a period from the first time to the second time.
The first condition is a condition that the temperature change per unit time is larger than a first threshold value,
The temperature sensor abnormality detection method according to claim 7, wherein the second condition is a condition that a temperature change per unit time is not less than a second threshold and not more than the first threshold.
When the temperature change per unit time is smaller than the second threshold value, the abnormality of the temperature sensor is determined based on the length of the period from the first time to the second time and the second temperature. The temperature sensor abnormality detection method according to claim 8, further comprising a step of:
  The temperature sensor determines that the temperature sensor is abnormal when a length of a period from the first time to the second time is equal to or greater than a third threshold and the second temperature is greater than a fourth threshold. An abnormality detection method for the temperature sensor described in 1.

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