Image forming device

Abstract

To provide an image forming apparatus that performs correction processing suitable for a thermopile sensor.SOLUTION: A fixing unit 10 comprises, as temperature sensors, thermopile sensors (main thermopile sensor 141 and sub thermopile sensor 142) that detect the temperature of a paper-feeding area in a fixing member 12, and a contact thermistor 143. Output signals from these temperature sensors are input to a control microcomputer 31 through an operational amplifier. The control microcomputer 31 executes correction processing of determining a correction value of the thermopile sensors in the initial period of an image forming apparatus. In the correction processing, an output voltage from the thermopile sensors corresponding to a temperature detected by the contact thermistor 143 is defined as a thermopile reference voltage, and a voltage detected by the control microcomputer 31 from the thermopile sensors as a thermopile detection voltage. A correction value of the thermopile sensors is determined based on the voltage difference value between the thermopile reference voltage and the thermopile detection voltage (S5, 6).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus equipped with a fixing device. [Background technology]

[0002] In a fixing device provided in an image forming apparatus, the temperature of a fixing member (fixing belt or fixing roller) is detected by a temperature sensor, and temperature control is performed by feedback control based on the detection result. The output signal (voltage value) of the temperature sensor is input to a control unit via an operational amplifier and a protection circuit. At this time, a correction process (calibration) is required to reduce errors generated in the operational amplifier. Patent Document 1 discloses a method of correction process when a non-contact thermistor is used as a temperature sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-167259 A Summary of the Invention [Problem to be solved by the invention]

[0004] In addition to non-contact thermistors, thermopile sensors are also available as types of temperature sensors that can detect temperature without contact. However, when using a thermopile sensor as a temperature sensor, a different correction process is required than when using a non-contact thermistor.

[0005] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide an image forming apparatus that performs correction processing suitable for a thermopile sensor. [Means for solving the problem]

[0006] In order to solve the above problems, the image forming apparatus of the present invention is an image forming apparatus equipped with a fixing device, and is equipped with a first temperature sensor that detects the temperature of a paper passing area of ​​a fixing member of the fixing device and uses a thermopile sensor, a second temperature sensor other than the first temperature sensor that is equipped in the image forming apparatus, and a control unit to which output signals of the first temperature sensor and the second temperature sensor are input via an operational amplifier, and the control unit performs a correction process to obtain a correction value of the first temperature sensor immediately after the image forming apparatus is turned on and at an initial time when the temperatures of the paper passing area of ​​the fixing member are equal, and in the correction process, an output voltage of the first temperature sensor corresponding to the detected temperature of the second temperature sensor is calculated, the calculated output voltage of the first temperature sensor is set as a thermopile reference voltage, a voltage detected by the control unit from the first temperature sensor is set as a thermopile detected voltage, and the correction value of the first temperature sensor is obtained based on a voltage difference value between the thermopile reference voltage and the thermopile detected voltage.

[0007] According to the above configuration, the control unit can obtain a correction value for the first temperature sensor, which is a thermopile sensor. In this correction process, a voltage correction value is obtained based on a voltage difference (voltage difference value) between a thermopile reference voltage and a thermopile detection voltage, and by correcting the voltage value, the correction process can be applied to the entire operating temperature range of the first temperature sensor. In addition, this correction process can perform a correction specialized for a large offset voltage of the operational amplifier, and a simple mechanism that does not require complicated processing or steps can prevent major malfunctions.

[0008] In addition, in the above image forming apparatus, a minimum correction value based on a measurement error of the first temperature sensor is set, and the control unit can be configured to set the correction value to a value obtained by subtracting the minimum correction value from the voltage difference value.

[0009] According to the above configuration, when the thermopile detection voltage is not irregular, it is possible to eliminate the influence of measurement errors that may occur due to the influence of variations in the reference voltage from the correction value.

[0010] In addition, in the image forming apparatus, the control unit can be configured to compare the correction value with a maximum correction value, and if the correction value exceeds the maximum correction value, change the correction value to the maximum correction value.

[0011] According to the above configuration, when the correction value exceeds the maximum correction value, the correction value is determined to be an abnormal value, and the correction value is changed to the maximum correction value, thereby performing irregular rounding processing.

[0012] The image forming apparatus may be configured to display an error or restrict the operation of the image forming apparatus when the correction value exceeds the maximum correction value a predetermined number of times or more.

[0013] In addition, in the above image forming device, the first temperature sensor includes a main thermopile sensor that detects the temperature of a central region of the paper passing section and a sub-thermopile sensor that detects the temperature of an end region of the paper passing section, and the control unit compares a main / sub temperature difference, which is the temperature difference between the temperature detected by the main thermopile sensor and the temperature detected by the sub-thermopile sensor, with a predetermined temperature threshold, and if the main / sub temperature difference exceeds the temperature threshold a predetermined number of times or more, displays an error or restricts the operation of the image forming device.

[0014] According to the above configuration, when the main / sub temperature difference exceeds the threshold temperature, it can be determined that an abnormality such as poor contact has occurred in either the main thermopile sensor or the sub thermopile sensor, and based on this abnormality determination, an error can be displayed or the operation of the image forming device can be restricted.

[0015] In the image forming apparatus, the first temperature sensor may be disposed outside the fixing device, and the second temperature sensor may be disposed inside the fixing device.

[0016] The thermopile sensor of the first temperature sensor needs to be at a distance from the object to be measured in terms of heat resistance, so if it is to be placed inside the fixing device, a certain amount of space is required. By placing it outside the fixing device, the required space can be reduced, making it possible to make the fixing device more compact. Effect of the Invention

[0017] The image forming apparatus of the present invention has an advantageous effect of being able to appropriately determine a voltage correction value for a thermopile sensor based on a thermopile reference voltage, a thermopile detected voltage, and a voltage difference value. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic diagram showing a schematic configuration of a temperature control mechanism in an image forming apparatus to which the present invention is applied; [Diagram 2] 6 is a flowchart showing a correction process for a first temperature sensor and a second temperature sensor. [Diagram 3] 13 is a sub-flowchart showing a method for calculating a correction value of a thermopile sensor. [Figure 4] 13 is a sub-flowchart showing a main / sub temperature difference check. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] [First embodiment] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. An image forming apparatus according to this embodiment includes a fixing unit and a temperature control mechanism for controlling the temperature of the fixing unit. FIG. 1 is a schematic diagram showing a general configuration of the temperature control mechanism. As shown in FIG. 1, this temperature control mechanism includes a fixing unit (fixing device) 10, a heater driver unit 20, and a power control unit 30.

[0020] The fixing unit 10 has a fixing member 12 and a pressure roller 13 inside a unit housing 11. Inside the fixing member 12, a main heater 121 for heating a central region of a paper passage portion and sub-heaters 122, 123 for heating end regions are provided. As temperature sensors for detecting the temperatures of the members inside the fixing unit 10, a main thermopile sensor (first temperature sensor) 141, a sub-thermopile sensor (first temperature sensor) 142, a contact thermistor (second temperature sensor) 143, and a non-contact thermistor 144 are provided. The fixing member 12 may be a fixing belt or a fixing roller. In addition, when a heating roller for bridging the fixing belt and a fixing roller are provided, the main heater 121 and the sub-heaters 122, 123 are provided inside the heating roller.

[0021] The main thermopile sensor 141 measures the temperature of the central region of the paper passing portion of the fixing member 12 in a non-contact manner. The sub-thermopile sensor 142 measures the temperature of the edge region of the paper passing portion of the fixing member 12 in a non-contact manner. Note that the main thermopile sensor 141 and the sub-thermopile sensor 142 are not actually included in the fixing unit 10, but are installed in the image forming apparatus main body outside the fixing unit 10, and measure the temperature of the fixing member 12 through a window (opening) provided in the unit housing 11. The contact thermistor 143 measures the temperature of the edge region of the fixing member 12. The non-contact thermistor 144 measures the temperature of the central region of the pressure roller 13.

[0022] Heater driver unit 20 includes a heater driver 21 that drives main heater 121 and sub-heaters 122, 123. Power control unit 30 includes a control microcomputer (control unit) 31 that receives output signals from main thermopile sensor 141, sub thermopile sensor 142, contact thermistor 143, and non-contact thermistor 144 and feedback controls heater driver 21. Power control unit 30 also includes operational amplifiers and protection circuits for main thermopile sensor 141, sub thermopile sensor 142, contact thermistor 143, and non-contact thermistor 144, respectively, and inputs output signals from these temperature sensors to control microcomputer 31 via the operational amplifiers and protection circuits.

[0023] This temperature control mechanism obtains a correction value (machine offset correction value) for reducing detection errors for the thermopile sensors (main thermopile sensor 141 and sub thermopile sensor 142). Figure 2 is a flowchart showing the correction process for obtaining this correction value.

[0024] When the image forming apparatus is powered on, first, the temperature sensors detect the temperature (S1), and the output signals of the temperature sensors are input to the control microcomputer 31 (S2). As described above, the output signals of the temperature sensors are input to the control microcomputer 31 via operational amplifiers and protection circuits, and the control microcomputer 31 obtains the output signals of the temperature sensors as voltage values.

[0025] The control microcomputer 31 converts the acquired voltage value into a temperature value (S3). The control microcomputer 31 has a lookup table or a conversion formula that has been experimentally obtained in advance, and converts the voltage value into a temperature value using this table or formula.

[0026] After S3, an initial determination is made (S4). The correction process by this temperature control mechanism is performed immediately after the image forming apparatus is powered on, more specifically, when a sufficient amount of time has passed since the previous power off and the temperatures of the central region and the end region of the fixing member 12 are equal. In the initial determination, it is determined whether or not the correction process is in a state in which it is possible to execute the correction process (for example, whether or not a predetermined time has passed since the previous power off). If the initial determination determines that the correction process is possible (YES in S4), the correction process for the thermopile sensor is started. If the initial determination determines that the correction process is not possible (NO in S4), the correction process for the thermopile sensor is not executed.

[0027] In this correction process, first, the detected temperature of contact thermistor 143 is set as a reference temperature, and the voltage difference between the thermopile reference voltage corresponding to this reference temperature and the actually detected thermopile detection voltage (=thermopile detection voltage-thermopile reference voltage: hereinafter, voltage difference value) is calculated (S5).

[0028] The reference temperature by contact thermistor 143 is acquired as a reference current temperature in order to obtain a reference voltage, which is an output value that does not include an error of the thermopile sensor. In the above example, the temperature detected by contact thermistor 143 is used as the reference temperature, but it is preferable that the reference temperature is the temperature of an object (e.g., a fixing belt) from which the thermopile sensor receives infrared rays, and any temperature within fixing unit 10 may be used as the reference temperature as long as fixing unit 10 is sufficiently adapted to room temperature.

[0029] The thermopile reference voltage and the thermopile detection voltage are determined individually for each of the main thermopile sensor 141 and the sub thermopile sensor 142. The thermopile reference voltage here is determined from a lookup table or conversion formula that has been experimentally determined in advance. That is, the above-mentioned reference temperature is input to the lookup table or conversion formula, and the thermopile reference voltage is obtained as the output. The thermopile detection voltage is a voltage value that is input to the control microcomputer 31 via an operational amplifier and a protection circuit.

[0030] After the voltage difference value is calculated, a correction value for the thermopile sensor is calculated based on this voltage difference value (S6). The correction values ​​for the thermopile sensor are calculated individually for each of the main thermopile sensor 141 and the sub thermopile sensor 142, and are calculated in accordance with the subflow in FIG.

[0031] In the subflow of FIG. 3, first, a value obtained by subtracting a minimum correction value from a voltage difference value is set as a correction value (correction value=voltage difference value-minimum correction value: S61). Furthermore, the correction value calculated in S61 is compared with a maximum correction value (S62). If the correction value is equal to or less than the maximum correction value (correction value≦maximum correction value: YES in S62), the correction value calculated in S61 becomes the final correction value (i.e., machine offset correction value) as it is. On the other hand, if the correction value exceeds the maximum correction value (correction value>maximum correction value: NO in S62), the final correction value is changed to the maximum correction value (correction value=maximum correction value) and the first counter value α (initial value is 0) is incremented by 1 (S63). The first counter value α is stored in the memory of the control microcomputer 31.

[0032] The maximum correction value here is a threshold value for determining whether the thermopile detection voltage is irregular or not, and is set based on the maximum cumulative value of error factors occurring in the operational amplifier and protection circuit. If the voltage difference value exceeds the maximum correction value, the thermopile detection voltage is determined to be an abnormal value, and the correction value is set to the maximum correction value to perform irregularity rounding processing. On the other hand, the minimum correction value is a measurement error that may occur due to the influence of variations in the reference voltage, and by using the value obtained by subtracting the minimum correction value from the voltage difference value as the correction value, it is possible to eliminate the influence of errors and variations in the reference voltage from the correction value when the thermopile detection voltage is not irregular. However, it is not essential to use the minimum correction value in calculating the correction value, and in the calculation of S61, the voltage difference value may be used as the correction value as it is.

[0033] After the correction value of the thermopile sensor is calculated in S6, the temperature difference between the temperatures detected by the main thermopile sensor 141 and the sub thermopile sensor 142 is checked (S7). This main / sub temperature difference check is performed according to the procedure in the subflow of FIG.

[0034] 4, the temperature difference (main / sub temperature difference) between the temperature detected by main thermopile sensor 141 (main temperature) and the temperature detected by sub thermopile sensor 142 (sub temperature) is compared with a predetermined threshold temperature (S71). If the main / sub temperature difference exceeds the threshold temperature (YES in S71), it is determined whether the magnitude relationship between the main temperature and the sub temperature has changed compared to the previous time when the main / sub temperature difference exceeded the threshold temperature (S72).

[0035] If the magnitude relationship between the main temperature and the sub temperature has not changed (NO in S72), it is determined that an abnormality such as poor contact has occurred in either the main thermopile sensor 141 or the sub thermopile sensor 142 due to the main / sub temperature difference exceeding the threshold temperature, and the second counter value β (initial value is 0) is incremented by 1 (S73). If the magnitude relationship between the main temperature and the sub temperature has changed (YES in S72), the second counter value β is decremented by 1 (S74). However, the minimum value of the second counter value β is set to 0, and if the second counter value β is 0, the subtraction in S74 is not performed. The second counter value β is stored in the memory of the control microcomputer 31. Furthermore, if the main / sub temperature difference does not exceed the threshold temperature (NO in S71), no particular process is performed and the main / sub temperature difference check is terminated.

[0036] In the above explanation, the main / sub temperature difference check is performed based on the temperature difference between the main temperature and the sub temperature, but the present invention is not limited to this, and may be performed based on the voltage difference (main / sub voltage difference) between the detection voltage (main voltage) of main thermopile sensor 141 before temperature conversion and the detection voltage (sub voltage) of sub thermopile sensor 142. In this case, the main / sub voltage difference is compared with a predetermined threshold voltage. The predetermined threshold voltage is set from the maximum value of the accumulated individual difference error of the constituent elements of the thermopile.

[0037] Returning to the main flow of FIG. 2, after the main / sub temperature difference check in S7, it is determined whether the first counter value α or the second counter value β has reached a predetermined count number (e.g., 3) (S8). If both the first counter value α and the second counter value β have not reached the predetermined count number (NO in S8), the thermopile voltage is corrected based on the correction value calculated in S6 (S9). That is, the calculated correction value is added to the thermopile detection voltage input to the control microcomputer 31 to obtain a corrected thermopile voltage. Note that the predetermined count number used in the determination in S8 may be different values ​​for each of the first counter value α and the second counter value β.

[0038] On the other hand, if either the first counter value α or the second counter value β has reached a predetermined count number (YES in S8), it is determined that there is an abnormality in the main thermopile sensor 141 or the sub thermopile sensor 142, and error processing is performed (S10). Here, the determination in S8 is performed in order to avoid erroneous detection due to noise, etc.

[0039] In error handling, for example, Main heater 121 and sub heaters 122, 123 are OFF Stopping control by the control microcomputer 31 -Error display on the operation display unit of the image forming device - Operational restrictions on image forming devices The error display may be different when the first counter value α reaches a predetermined count number and when the second counter value β reaches a predetermined count number. When the error process is performed, the first counter value α and the second counter value β are reset to their initial values.

[0040] Through the above correction processing, control microcomputer 31 can obtain corrected thermopile voltages for each of main thermopile sensor 141 and sub thermopile sensor 142. Thereafter, control microcomputer 31 converts the corrected thermopile voltages into temperatures using a look-up table or a conversion formula, and performs feedback control of main heater 121 and sub-heaters 122 and 123 based on the temperatures.

[0041] The above-mentioned correction process for the thermopile sensor has the advantage that it does not require predetermined heating unintentionally by the user for main thermopile sensor 141 and sub thermopile sensor 142, and also does not require a special calibration circuit. In addition, since the correction process is performed each time a predetermined condition is satisfied when the image forming apparatus is started up, the user is not aware of this correction process, and it is possible to prevent problems (such as temperature unevenness) caused by erroneous temperature detection.

[0042] Furthermore, the above-mentioned correction process does not obtain a temperature correction value based on the temperature difference between a reference temperature and the temperature detected by the thermopile sensor, but obtains a voltage correction value based on the voltage difference (voltage difference value) between the thermopile reference voltage and the thermopile detection voltage. Since most errors occurring in the detection value of the thermopile sensor are errors that shift the voltage, such as the offset error of an operational amplifier, by correcting the voltage difference, it is possible to apply the correction process over the entire operating temperature range of the thermopile sensor.

[0043] In addition, the offset voltage of the differential amplifier's op-amp affects the detection voltage of the thermopile sensor as the product of the amplification factor (for example, 5 times), and its impact on the detection temperature of the thermopile sensor is orders of magnitude larger than other factors. The above-mentioned correction process performs correction specifically for this large offset voltage, and is a simple mechanism that does not require complex processing or steps, making it possible to prevent major problems before they occur.

[0044] [Embodiment 2] In the above-mentioned embodiment 1, the machine offset correction value of the thermopile sensor is obtained by the correction process performed immediately after the power supply of the image forming apparatus is turned on. In the present embodiment 2, the board offset correction value obtained in the inspection process during the production of the image forming apparatus will be described.

[0045] The substrate offset correction value is obtained by performing an offset measurement on the PCU substrate which becomes the power control unit 30. The offset measurement is performed on the PCU substrate alone using a measurement tool equipped with a dedicated circuit. At this time, the thermopile sensor is not connected to the PCU substrate, but a predetermined voltage is input to the input terminal for connecting the thermopile sensor instead of the sensor output. Then, the voltage difference between the input predetermined voltage and the voltage after AD conversion via the operational amplifier and protection circuit of the PCU substrate is obtained as the substrate offset correction value. The obtained substrate offset correction value is stored in the memory of the control microcomputer 31.

[0046] As for the substrate offset correction value, similarly to the machine offset correction value, the voltage difference between the predetermined voltage and the voltage after AD conversion may not be used as the substrate offset correction value as it is, but may be obtained by subtracting the minimum correction value from the voltage difference between the predetermined voltage and the voltage after AD conversion. If the voltage difference between the predetermined voltage and the voltage after AD conversion exceeds the maximum correction value, the maximum correction value may be used as the substrate offset correction value. Alternatively, if the voltage difference between the predetermined voltage and the voltage after AD conversion exceeds the maximum correction value, it may be regarded as an abnormality, and the PCU substrate may be sent to another check process. The minimum and maximum correction values ​​for the substrate offset correction value may be different from the minimum and maximum correction values ​​for the machine offset correction value.

[0047] When the substrate offset correction value is stored in the image forming apparatus, after the machine offset correction value is detected, the substrate offset correction value is compared with the machine offset correction value, and the one with the larger absolute value is set as the final correction value. Also, when the substrate offset correction value and the machine offset correction value have opposite signs and the absolute values ​​are the same, it is preferable to select the machine offset correction value in which the accumulated error has been corrected as the final correction value. However, even in this case, when the reliability of the machine offset correction value is low, such as when there is a large variation in the reference temperature or thermopile voltage, the substrate offset correction value may be selected as the final correction value.

[0048] Third Embodiment After the image forming apparatus is powered on and the machine offset correction value is found by the above-mentioned correction process, the temperature rise rate is measured by the thermopile sensor during the first warm-up of the fixing unit 10 (when the main heater 121 and the sub-heaters 122, 123 are turned on) to determine an error. During the first warm-up of the fixing unit 10, there is a period during which the main heater 121 and the sub-heaters 122, 123 for heating the fixing member 12 are turned on simultaneously and continuously, and during that period, the temperature rise rates of the main thermopile sensor 141 and the sub-thermopile sensor 142 are measured.

[0049] At this time, the fixing member 12 being warmed up is heated from an initial state where the temperatures of the central region and the end region are equal, and the temperature rises at a prescribed heating rate under normal circumstances. Therefore, if a temperature difference of a prescribed temperature or more occurs with respect to the prescribed heating rate in each of the measured main temperature and sub-temperature, an error message is displayed indicating that there is an abnormality in the detection by the thermopile sensor, and the operation of the machine can be restricted.

[0050] In this case, the abnormality of the thermopile sensor that can be detected is, for example, an abnormality caused when a foreign object adheres to the lens surface of the thermopile sensor. In the initial state in which the fixing member 12 is not heated, it is difficult to determine whether such an abnormality exists because there is little change in the amount of infrared light received. However, if the fixing member 12 is being heated, a difference occurs in the amount of infrared light received, making it possible to detect the abnormality.

[0051] Furthermore, during temperature adjustment of the fixing unit 10 (during feedback control of the main heater 121 and the sub-heaters 122 and 123), since there is no reference temperature to compare with, it is difficult to determine whether or not there is an abnormality as described above. However, during heating from the initial state, the heater is continuously energized at a specified maximum power, so that the heating conditions are constant and it is possible to determine whether or not there is an abnormality by using the specified heating rate as a reference.

[0052] In this way, in the above-mentioned abnormality judgment during warm-up, by comparing with a specified temperature rise rate as a reference, an abnormality in the thermopile sensor can be detected before paper is passed without the user being aware of it. Also, in order to more simply judge an abnormality during warm-up, the temperature rise rate difference between the main temperature detected by main thermopile sensor 141 and the main temperature detected by sub thermopile sensor 142 can be compared with a predetermined value, and if the temperature rise rate difference is equal to or greater than the predetermined difference, an error message can be displayed and the operation of the machine can be restricted.

[0053] <Example 1> In the above-mentioned first embodiment, a method for detecting a machine offset correction value based on the voltage difference (voltage difference value) between the thermopile reference voltage and the thermopile detected voltage, the minimum correction value, and the maximum correction value has been described.

[0054] The voltage difference value is generated by machine-specific errors such as the offset error of the operational amplifier, leakage current, and AD conversion error, and the maximum cumulative value of these machine-specific errors is set as the maximum correction value. The minimum correction value is set taking into consideration measurement errors such as variations in the output voltage of the thermopile sensor and variations in the reference voltage, and for example, 3σ (three times the standard deviation) of the measurement error distribution is set as the minimum correction value.

[0055] Here, the following (Case 1) to (Case 4) show examples of calculation of the machine offset correction value when the minimum correction value is 15 mV and the maximum correction value is 20 mV.

[0056] (Case 1): When the voltage difference is 18mV Since the voltage difference value-minimum correction value=3 mV<maximum correction value, the machine offset correction value is 3 mV.

[0057] (Case 2): When the voltage difference is -25mV If the voltage difference value is negative, the minimum correction value is also subtracted as a negative value. Also, the comparison with the maximum correction value is performed in absolute value. Since the voltage difference value-minimum correction value=-25 mV-(-15 mV)=-10 mV and 10 mV<maximum correction value, the machine offset correction value is-10 mV.

[0058] (Case 3): When the voltage difference is 40mV Since voltage difference value-minimum correction value=25 mV>maximum correction value, the machine offset correction value becomes the maximum correction value of 20 mV.

[0059] (Case 4): When the voltage difference is 32mV Since the voltage difference value-minimum correction value=17 mV<maximum correction value, the machine offset correction value is 17 mV.

[0060] <Example 2> In the above-mentioned second embodiment, a method for detecting a substrate offset correction value by a voltage difference between a predetermined voltage and a voltage after AD conversion, a minimum correction value, and a maximum correction value has been described. Here, the following (Case 5) to (Case 7) show examples of calculation of a substrate offset correction value when the minimum correction value is 6 mV and the maximum correction value is 10 mV.

[0061] (Case 5): Voltage difference is 10mV Since voltage difference-minimum correction value=4 mV<maximum correction value, the substrate offset correction value is 4 mV.

[0062] (Case 6): Voltage difference is -12mV Regarding the substrate offset correction value, when the voltage difference is negative, the minimum correction value is also subtracted as a negative value. Also, the comparison with the maximum correction value is performed in absolute value. Since voltage difference-minimum correction value=-12mV-(-6mV)=-6mV and 6mV<maximum correction value, the substrate offset correction value is-6mV.

[0063] (Case 7): When the voltage difference is 17mV Since voltage difference value−minimum correction value=11 mV>maximum correction value, the machine offset correction value becomes the maximum correction value of 10 mV.

[0064] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present invention is not interpreted solely by the above-described embodiments, but is defined by the claims. Also, all modifications within the scope and meaning equivalent to the claims are included. [Explanation of symbols]

[0065] 10 Fixing unit (fixing device) 11 Unit chassis 12 Fixing member 121 Main heater 122,123 Sub heater 13 Pressure roller 141 Main thermopile sensor (first temperature sensor) 142 Sub-thermopile sensor (first temperature sensor) 143 Contact thermistor (second temperature sensor) 144 Non-contact thermistor 20 Heater driver unit 21 Heater driver 30 Power control unit 31 Control microcomputer (control unit)

Claims

1. An image forming apparatus including a fixing device, a first temperature sensor that detects a temperature of a paper passing area of ​​a fixing member of the fixing device, the first temperature sensor using a thermopile sensor; a second temperature sensor other than the first temperature sensor, the second temperature sensor being provided in the image forming apparatus; a control unit to which output signals from the first temperature sensor and the second temperature sensor are input via an operational amplifier, the control unit performs a correction process to obtain a correction value of the first temperature sensor immediately after a power source of the image forming apparatus is turned on and at an initial time when a temperature of a paper passing area of ​​the fixing member is uniform; In the correction process, calculating an output voltage of the first temperature sensor corresponding to the detected temperature of the second temperature sensor, and setting the calculated output voltage of the first temperature sensor as a thermopile reference voltage; a voltage detected by the control unit from the first temperature sensor is defined as a thermopile detection voltage; determining a correction value for the first temperature sensor based on a voltage difference value between the thermopile reference voltage and the thermopile detection voltage; an output voltage of the first temperature sensor being corrected by adding the correction value to the output voltage of the first temperature sensor;

2. 2. The image forming apparatus according to claim 1, a correction minimum value based on a measurement error of the first temperature sensor is set; The image forming apparatus according to claim 1, wherein the control unit sets the correction value as a value obtained by subtracting the minimum correction value from the voltage difference value.

3. 3. The image forming apparatus according to claim 1, The control unit compares the correction value with a maximum correction value, and if the correction value exceeds the maximum correction value, changes the correction value to the maximum correction value.

4. 4. The image forming apparatus according to claim 3, When the correction value exceeds the maximum correction value a predetermined number of times or more, an error is displayed and / or an operation of the image forming apparatus is restricted.

5. 5. The image forming apparatus according to claim 1, the first temperature sensor includes a main thermopile sensor that detects a temperature in a central region of the sheet passing portion and a sub thermopile sensor that detects a temperature in an end region of the sheet passing portion; The control unit of this image forming apparatus compares a main / sub temperature difference, which is the temperature difference between the temperature detected by the main thermopile sensor and the temperature detected by the sub thermopile sensor, with a predetermined temperature threshold, and if the main / sub temperature difference exceeds the temperature threshold a predetermined number of times or more, displays an error or restricts the operation of the image forming apparatus.

6. 6. The image forming apparatus according to claim 1, 2. An image forming apparatus, comprising: a fixing device that fixes an image to a surface of the image forming apparatus; a fixing unit that fixes an image to the surface of the image forming apparatus;

Images