Non-contact temperature measuring device and image forming apparatus equipped with the same

Abstract

To provide a non-contact type temperature measurement device which can effectively prevent erroneous offset correction from being performed by false recognition in a case where offset correction should not be performed like a case where a measurement object is heated for a short time at correction timing at which a prescribed offset correction condition may be established, and provide an image formation apparatus having the same.SOLUTION: A non-contact type temperature measurement device 300 is configured to perform offset correction under a prescribed offset correction condition for performing offset correction, uses a detection temperature Ts detected by using a detection temperature detection element 75s as the offset correction condition, and performs offset correction when the detection temperature Ts detected by using the detection temperature detection element 75s is equal to or less than a prescribed threshold Th.SELECTED DRAWING: Figure 7A

Description

[Technical Field]

[0001] The present disclosure relates to a non-contact temperature measuring device that measures the temperature of an object without contact, and to an image forming apparatus such as a copier, multifunction device, printer, or facsimile machine that includes the same. [Background technology]

[0002] Non-contact temperature measurement devices that measure the temperature of an object to be measured while spaced apart from the object to be measured include, for example, those that have a non-contact temperature sensor that includes a detection temperature detection element (e.g., a detection thermistor) that detects the measured temperature of the object to be measured non-contactly, and a compensation temperature detection element (e.g., a compensation thermistor) that detects the environmental temperature (the ambient temperature of the surrounding area that is not affected by heat from the object to be measured).

[0003] Such non-contact temperature measuring devices are widely used because they can measure the temperature of an object to be measured non-contact based on the output change of the detection temperature detecting element in response to the measured temperature of the object to be measured and the output change of the compensation temperature detecting element in response to the ambient temperature.

[0004] Fig. 8A is a three-sided view showing an example of a non-contact temperature sensor 75 including a detection temperature detection element 75s and a compensation temperature detection element 75c. Fig. 8B is a cross-sectional view showing the detection temperature detection element 75s and the compensation temperature detection element 75c in the non-contact temperature sensor 75 shown in Fig. 8A.

[0005] As shown in Figures 8A and 8B, in the non-contact temperature sensor 75, the detection temperature detection element 75s detects radiant heat due to infrared rays IR from the object to be measured 400, and the compensation temperature detection element 75c, which is provided inside the housing 75a so as not to be directly exposed to the radiant heat, detects the environmental temperature (ambient temperature).

[0006] The measured temperature T of the measurement object 400 requires various temperature corrections of the detected temperature Ts detected using the detecting temperature detection element 75s in accordance with the ambient temperature around the detecting temperature detection element 75s at the time of measurement. Specifically, the measured temperature T can be calculated by converting the detected temperature Ts detected using the detecting temperature detection element 75s and the ambient temperature (compensated temperature Tc) detected using the compensating temperature detection element 75c using a conversion method such as a conversion formula and / or conversion table that follows the physical laws of radiant heat and actual measurements. For example, in a non-contact temperature measurement device, the measured temperature T of the measurement object 400 is measured as follows: First, the detection output (detected voltage converted from the thermistor resistance) from the detecting temperature detection element 75s corresponding to the measured temperature T of the measurement object 400 and the compensation output (compensated voltage converted from the thermistor resistance) from the compensating temperature detection element 75c corresponding to the compensation temperature Tc of the measurement object 400 are obtained, and the difference between these outputs (voltage difference) is calculated. Next, the analog signals of the obtained output difference and compensation output are converted into digital data by an AD converter (not shown). Next, the output difference and compensation output converted into digital data are used to perform a predetermined calculation process, thereby measuring the measured temperature T of the measurement object 400.

[0007] This will be further explained using the example of measuring the measured temperature T of a fixing member using a non-contact temperature measuring device in an image forming apparatus equipped with a fixing device having a fixing member (e.g., a fixing member such as a fixing belt, a heating roller, or a fixing roller) for heat-fixing an unfixed toner image to a sheet.

[0008] In recent image forming apparatuses, the need for rapid heating due to shorter warm-up times has led to an increase in the temperature rise rate of the fixing member, necessitating faster response from non-contact temperature measurement devices. Faster response from non-contact temperature measurement devices is primarily achieved by miniaturizing the detection element. However, as the detection element becomes smaller, the detection area (amount of infrared light IR received) of the temperature detection element 75s that detects radiant heat tends to become smaller, resulting in a smaller output difference (voltage difference). Therefore, to accurately measure the measured temperature T of the measurement object 400 from a small output difference, an operational amplifier (op-amp) is typically used, along with an increased number of AD conversion bits, to amplify the output difference.

[0009] Incidentally, operational amplifiers have their own offset value (offset voltage), which is a source of error in the differential output obtained by amplifying the output difference with the operational amplifier.

[0010] <Relationship between differential input and output of an operational amplifier> 9A is a graph showing an example of the relationship between the differential input (input voltage) of an operational amplifier, the ideal output (ideal voltage), and the actual output (output voltage). In FIG. 9A, the gain of the operational amplifier is 5 (5 times amplification), and the offset voltage is 100 mV (the offset voltage when the gain is 1 is 20 mV).

[0011] As shown in Figure 9A, op-amps have an inherent offset voltage. If the voltage difference is amplified with a gain of, say, 5 (5 times), the offset voltage will also be amplified by 5 times. In this example, when the offset voltage is 20 mV, the output voltage = (input voltage + offset voltage 20 mV) × 5, meaning that an offset voltage of 100 mV is added to the output voltage.

[0012] Although designers can check the rated value (maximum value) of the offset value (offset voltage) from the data sheet of an operational amplifier, the offset value differs for each operational amplifier. Also, because the offset value of an operational amplifier may change due to environmental changes or over time, it is preferable to repeatedly perform offset correction at correction intervals when predetermined offset correction conditions for performing offset correction can be met.

[0013] <Relationship between differential input and output of an operational amplifier> 9B is a graph showing an example of the relationship between the compensation output (compensation voltage) and differential output (differential voltage) and the measured temperature when the compensation temperature Tc is 25°C. Fig. 9B shows the differential voltage of an ideal operational amplifier (offset voltage is 0 mV) and the differential voltage of an actual operational amplifier (offset voltage before amplification is 20 mV) to which an offset voltage of 100 mV (20 mV × gain = 5) has been added. It also shows the temperature error between the measured temperature of the object 400 measured using the ideal operational amplifier and the measured temperature of the object 400 measured using the actual operational amplifier.

[0014] Although FIG. 9B shows an example where the compensation temperature Tc is 25° C., even if the compensation temperature Tc changes, the offset value (offset voltage) does not change.

[0015] In this way, in the operational amplifier, when measuring the measurement temperature T of the measurement object 400, the offset value (offset voltage) needs to be offset corrected.

[0016] In this regard, offset correction can be performed as follows, using the differential output when the heat source (not shown) that heats the object 400 is not operating as the offset correction value.

[0017] That is, the detection temperature detection element 75s and the compensation temperature detection element 75c are designed to have the same temperature characteristics by being mounted in close proximity to each other on the board, or by selecting elements with similar characteristics. Therefore, when the detection temperature detection element 75s and the compensation temperature detection element 75c detect the same temperature for the measurement object 400, the differential output is essentially 0.

[0018] Generally, the offset voltage is added to the output voltage at a constant value regardless of the input voltage. The differential voltage (see * in Figure 9B) when the environmental temperature (compensated temperature Tc) and the measurement temperature T are the same indicates the offset voltage itself.

[0019] From this perspective, the correction time when a specified offset correction condition can be met is the initial state when the detection temperature detection element 75s and the compensation temperature detection element 75c can detect the same temperature for the object to be measured 400, that is, when the heat source is not operating and in a heat source inactive state (specifically, when the power switch is on and power is being supplied but the heat source is not operating), in which case the differential output is acquired as a measured offset correction value, and the acquired measured offset correction value is considered to be the offset correction value of the operational amplifier, and the offset correction value when the heat source is in an inactive state is subtracted from the differential output when the object to be measured 400 is being measured to cancel the influence of the offset value (see, for example, Patent Document 1).

[0020] The conditions required for the specified offset correction, i.e., the conditions for obtaining the offset correction value, are that the object to be measured 400 (e.g., a fixing member such as a fixing belt, a heating roller, or a fixing roller) and the non-contact temperature sensor 75 must be at the same temperature, and therefore the heat source (e.g., a heater lamp) must be in an inactive state.

[0021] Conventionally, when the heat source is not operating, the offset correction condition is the end temperature detected by an end temperature sensor (temperature sensor for detecting the sheet non-conveying area) provided at the end of the object to be measured 400 (the sheet non-conveying area of ​​the fixing member such as the fixing belt, heating roller, fixing roller, etc.), and the offset correction is performed when the end temperature detected by the end temperature sensor 74 is below a predetermined threshold value (specifically, 30°C). [Prior art documents] [Patent documents]

[0022] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-4758 Summary of the Invention [Problem to be solved by the invention]

[0023] However, if the object to be measured 400 is heated for only a short time, such as when the heat source (heater lamp) stops generating heat (the power switch of the image forming apparatus is turned off) immediately after generating heat (after the power switch of the image forming apparatus is turned on and the heat source is energized), the temperature within the heated area of ​​the object to be measured 400 will rise because the object to be measured 400 is heated for only a short time, but the temperature at the end of the object to be measured 400 will not rise because the amount of heat near the boundary of the heated area is small and the temperature does not rise easily due to heat transfer to the end of the object to be measured 400.As a result, the end temperature detected by the end temperature sensor (temperature sensor for detecting the sheet non-conveying area) will be below the threshold value of the offset correction condition (specifically, 30°C), and offset correction will be performed when the heat source is in an inactive state, which is the time for correction. That is, the compensation temperature Tc detected using the compensation temperature detection element 75c barely rises because the heating is short, but the temperature in the heated area that has risen despite the short time is quickly detected by the detection temperature detection element 75s, and an output difference (voltage difference) due to heating occurs between the compensation output from the compensation temperature detection element 75c and the detection output from the detection temperature detection element 75s. Non-contact temperature measurement devices erroneously recognize this output difference as an offset value (offset voltage), and perform erroneous offset correction even though offset correction should not be performed, which is a problem.

[0024] Therefore, the present disclosure aims to provide a non-contact temperature measuring device and an image forming apparatus equipped with the same that can effectively prevent erroneous offset correction from being performed due to misrecognition when offset correction should not be performed, such as when the object to be measured is heated for only a short time at a correction time when specified offset correction conditions can be met. [Means for solving the problem]

[0025] In order to solve the above problem, the temperature measuring device of the present disclosure is a non-contact temperature measuring device comprising a non-contact temperature sensor including a detection temperature detecting element that detects the measured temperature of an object to be measured non-contactly and a compensation temperature detecting element that detects the ambient temperature, and an operational amplifier that amplifies the output difference between the output of the detection temperature detecting element and the output of the compensation temperature detecting element, measures an offset value contained in a differential output obtained by amplifying the output difference with the operational amplifier, and performs offset correction to remove the offset from the differential output based on the measured offset value, and is configured to perform the offset correction when predetermined offset correction conditions for performing the offset correction are met, characterized in that the detected temperature detected using the detection temperature detecting element is used as the offset correction condition, and the offset correction is performed when the detected temperature detected using the detection temperature detecting element is below a predetermined threshold.

[0026] In addition, the image forming apparatus according to the present disclosure is characterized in that it comprises the temperature measuring device according to the present disclosure and a fixing device having a fixing member for heat-fixing an unfixed toner image to a sheet, and the object to be measured is the fixing member. [Effects of the Invention]

[0027] According to the present disclosure, it is possible to effectively prevent erroneous offset correction due to misrecognition when offset correction should not be performed, such as when the object to be measured is heated for only a short time at a correction time when specified offset correction conditions may be met. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus including a non-contact temperature measuring device according to an embodiment of the present disclosure, as viewed from the front; [Figure 2] 2 is a schematic cross-sectional view showing a fixing device in the image forming apparatus shown in FIG. [Figure 3]FIG. 2 is a perspective view of the pressure roller, fixing belt, heat source, end temperature sensor, first and second non-contact temperature sensors in the non-contact temperature sensor, fixing roller, and heating roller in the fixing device, viewed obliquely from above. [Figure 4] FIG. 2 is a schematic block diagram showing a control configuration for measuring a measurement object. [Figure 5] FIG. 2 is a schematic diagram showing the positional relationship of an end temperature sensor, a first non-contact temperature sensor, and a second non-contact temperature sensor in a non-contact temperature sensor with respect to an object to be measured. [Figure 6] FIG. 1 is a circuit diagram illustrating a temperature measurement circuit showing a non-contact temperature sensor electrically connected to an operational amplifier. [Figure 7A] 10 is a flowchart showing the first half of an example of a control operation for offset correction according to the present embodiment. [Figure 7B] 10 is a flowchart showing an example of an intermediate part of an example of a control operation for offset correction according to the present embodiment. [Figure 7C] 10 is a flowchart showing another example of the intermediate part of the control operation example of the offset correction according to the present embodiment. [Figure 7D] 10 is a flowchart showing the second half of an example of a control operation for offset correction according to the present embodiment. [Figure 8A] 1A and 1B are three-view diagrams showing an example of a non-contact temperature sensor including a detection temperature detection element and a compensation temperature detection element. [Figure 8B] 8B is a cross-sectional view showing the detection temperature detection element and the compensation temperature detection element portion of the non-contact temperature sensor shown in FIG. 8A. FIG. [Figure 9A] 1 is a graph showing an example of the relationship between the differential input of an operational amplifier and the ideal output and the actual output. [Figure 9B] 10 is a diagram showing an example of the relationship between the compensation output and the differential output and the measurement temperature when the compensation temperature is 25° C. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. The names and functions of the components are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0030] 1 is a schematic cross-sectional view of an image forming apparatus 100 equipped with a non-contact temperature measuring device 300 according to an embodiment of the present disclosure, viewed from the front. In the figure, the symbol X indicates the width direction (depth direction), the symbol Y indicates the left-right direction perpendicular to the width direction X, and the symbol Z indicates the up-down direction.

[0031] 1 is an image forming apparatus that forms a monochrome image on a sheet P such as recording paper by electrophotography in accordance with image data read by an image reading device 10 or image data transmitted from an external device. Note that the image forming apparatus 100 may also be a color image forming apparatus that forms multicolor and monochrome images.

[0032] The image forming apparatus 100 includes an image reading device 10 and an image forming apparatus main body 110, and the image forming apparatus main body 110 is provided with an image forming section 101 and a sheet conveying system .

[0033] The image forming section 101 includes an exposure device 1 (exposure unit), a development device 2 (development unit), a photosensitive drum 3, a photosensitive drum cleaning device 4, a charging device 5, a transfer device 6 (transfer unit), and a fixing device 7 (fixing unit). The sheet transport system 102 includes a paper feed tray 8 and a discharge tray 9.

[0034] An original placement glass 11 and an original reading glass 12 are provided at the top of the image forming apparatus main body 110, and an image reading device 10 for reading an image of an original (not shown) is provided below the original placement glass 11 and the original reading glass 12. The original placement glass 11 is an original placement table on which an original is placed. In addition, an original transport device 13 is disposed above the original placement glass 11 and the original reading glass 12. The original reading glass 12 is provided at a position where it reads an original transported by the original transport device 13. The image of the original read by the image reading device 10 is sent to the image forming apparatus main body 110 as image data, and an image formed based on the image data in the image forming apparatus main body 110 is formed (printed) on a sheet P.

[0035] In the image forming apparatus 100, when forming an image (printing), a sheet P is supplied from a paper feed tray 8 and conveyed to registration rollers 15 by conveyance rollers 14a provided along a sheet conveyance path S. Next, the sheet P is conveyed in a timed manner to align the sheet P with the toner image on the photosensitive drum 3, and the transfer device 6 transfers the toner image on the photosensitive drum 3 onto the sheet P. Thereafter, the fixing device 7 melts and fixes unfixed toner on the sheet P with heat, and the sheet is discharged onto a discharge tray 9 via conveyance rollers 14b and discharge rollers 16a. Furthermore, in the image forming apparatus 100, when forming an image (printing) on ​​the back side of the sheet P in addition to the front side, the sheet P is conveyed in the reverse direction from discharge rollers 16b to a reversing path Sr, inverted, and guided again to the registration rollers 15. The toner image is fixed on the back side of the sheet P in the same manner as on the front side, and the sheet is discharged onto a discharge tray 9. In this way, the image forming apparatus 100 completes a series of printing operations. The sheet P is conveyed along the sheet conveying path S in the direction of the rotation axis of the photosensitive drum 3 (width direction X) with the center of the image forming apparatus main body 110 as the reference (center reference).

[0036] <Fixing device> FIG. 2 is a schematic cross-sectional view of the fixing device 7 in the image forming apparatus 100 shown in FIG. 1. FIG. 3 is a perspective view of the pressure roller 71, fixing belt 72, heat source 73, end temperature sensor 74, first non-contact temperature sensor 751 and second non-contact temperature sensor 752 in the non-contact temperature sensor 75, fixing roller 76, and heating roller 77 in the fixing device 7, viewed obliquely from above. FIG. 4 is a schematic block diagram showing a control configuration for measuring the measurement object 400 (72). FIG. 5 is a schematic diagram showing the positional relationship of the end temperature sensor 74 and the first non-contact temperature sensor 751 and second non-contact temperature sensor 752 in the non-contact temperature sensor 75 relative to the measurement object 400 (72). FIG. 6 is a circuit diagram showing a temperature measurement circuit showing the non-contact temperature sensor 75 (751, 752) electrically connected to the operational amplifier 310.

[0037] Next, an example in which the non-contact temperature measuring device 300 according to this embodiment is applied to a fixing device 7 of a belt fixing type will be described below.

[0038] The display unit 51 is provided on an operation panel 50 on the front side (front side in the width direction X) of the image reading device 10 of the image forming apparatus main body 110 shown in FIG.

[0039] (First embodiment) The fixing device 7 includes a pressure roller 71, a fixing belt 72 which is an example of the measurement object 400, a heat source 73, an edge temperature sensor 74, and a non-contact temperature sensor 75. The image forming apparatus 100 further includes a control unit 60 (see FIGS. 2 and 4). The pressure roller 71 is supported by a main body frame 70 (see FIG. 2) of the fixing device 7 so as to be rotatable about a rotation axis δ. The fixing belt 72 faces the pressure roller 71 and nip and conveys the sheet P together with the pressure roller 71.

[0040] In this example, the fixing device 7 is of a belt fixing type, and a fixing belt 72 is wound around multiple rollers (in this example, a fixing roller 76 and a heating roller 77). The fixing belt 72 is capable of transferring heat from the heating roller 77 to the fixing roller 76. The fixing belt 72 and the pressure roller 71 are rotated by the fixing roller 76 being driven to rotate. In the fixing device 7, the pressure roller 71 is pressed against the fixing roller 76 via the fixing belt 72, and the sheet P on which an unfixed toner image is formed is sandwiched between the fixing belt 72 and the pressure roller 71 and conveyed.

[0041] 4, the control unit 60 has a processing unit 60a consisting of a computer such as a CPU (Central Processing Unit), and a storage unit 60b including a non-volatile memory such as a ROM (Read Only Memory) and a volatile memory such as a RAM (Random Access Memory). The control unit 60 controls the operation of various components by having the processing unit 60a load a control program stored in advance in the ROM of the storage unit 60b onto the RAM of the storage unit 60b and execute the program.

[0042] The display unit 51 displays predetermined display information. The display unit 51 is electrically connected to the output system of the control unit 60. This allows the control unit 60 to transmit display control data processed by the processing unit 60a to the display unit 51, thereby causing the display unit 51 to display a message, which will be described later.

[0043] The non-contact temperature measuring device 300 includes a non-contact temperature sensor 75, operational amplifiers (310, 320), and a control unit 60, and performs offset correction.

[0044] In the image forming apparatus 100, power to the control unit 60 is supplied from a power source E via a power switch 80. That is, when the power switch 80 is turned on, the control unit 60 operates, and if an offset correction condition, which will be described later, is met, offset correction is performed, after which the heat source 73 operates, the measurement object 400 (in this example, the fixing belt 72) is heated, and the measurement temperature T of the measurement object 400 (72) is measured. On the other hand, if the offset correction condition is not met, the heat source 73 operates, the measurement object 400 (72) is heated, and the measurement temperature T of the measurement object 400 (72) is measured without performing offset correction.

[0045] As shown in FIG. 5, the edge temperature sensor 74 is provided so as to come into contact with an edge region (in this example, a sheet non-conveying region α2 where the sheet P is not conveyed) in the width direction X of the measurement object 400 (72), and detects the edge temperature of the edge region (α2) in the width direction X of the measurement object 400 (72). The edge temperature sensor 74 is electrically connected to the input system of the control unit 60 (see FIG. 4). This allows the edge temperature sensor 74 to send a signal related to the edge temperature of the edge region (α2) of the measurement object 400 (72) to the control unit 60.

[0046] The non-contact temperature sensors 75 (751, 752) are provided at a distance from a central region in the width direction X of the measurement object 400 (72) (in this example, the sheet conveying region α1 through which the sheet P is conveyed), and detect the temperature of the central region (α1) in the width direction X of the measurement object 400 (72). The non-contact temperature sensors 75 (751, 752) are electrically connected to the input system of the control unit 60 (see FIG. 4). This allows the non-contact temperature sensors 75 (751, 752) to transmit a signal related to the temperature of the central region (α1) of the measurement object 400 (72) to the control unit 60.

[0047] In detail, the first non-contact temperature sensor 751 and the second non-contact temperature sensor 752 are provided at a distance from the center and one end of the sheet transport area α1 of the measurement object 400 (72), and detect the temperature of the center and one end of the sheet transport area α1 of the measurement object 400 (72).

[0048] The non-contact temperature sensors 75 (751, 752) include a detection temperature detection element 75s (detection temperature detection thermistor) and a compensation temperature detection element 75c (compensation temperature detection thermistor), and are electrically connected to the input system of the control unit 60. The detection temperature detection element 75s detects the measurement temperature T of the measurement object 400 (72) in a non-contact manner. In this example, the compensation temperature detection element 75c detects the environmental temperature (compensation temperature Tc) in a non-contact manner. Note that the compensation temperature detection element 75c may detect the environmental temperature while in contact with a member capable of measuring the environmental temperature, such as a housing. The configuration of the non-contact temperature sensor 75 is the same as that shown in FIG. 8B described above, and therefore a description thereof will be omitted here.

[0049] The operational amplifier 310 amplifies the output difference (voltage difference Vd) between the output (detection voltage Vs) of the detection temperature detection element 75s and the output (compensation voltage Vc) of the compensation temperature detection element 75c with a gain G1 (5 times) and outputs a differential output (differential voltage AVd). The operational amplifier 320 outputs the compensated output (compensation voltage Vc) of the compensation temperature detection element 75c with a gain G2 (1 times).

[0050] In the offset correction, the non-contact temperature measurement device 300 measures an offset value F (see FIG. 4) contained in a differential voltage AVd obtained by amplifying the voltage difference Vd using an operational amplifier 310, and performs offset correction to remove the offset from the differential output AVd based on the measured offset value F.

[0051] The non-contact temperature measuring device 300 further includes a DC power supply D, a sensing resistor Rs, and a compensation resistor Rc.

[0052] 6, a detection temperature detection element 75s and a detection resistor Rs connected in series are connected to a DC power supply D, and similarly, a compensation temperature detection element 75c and a compensation resistor Rc connected in series are also connected to the DC power supply D. The gain G1 of the differential operational amplifier 310 is 5 (5 times amplification), and the gain G2 of the compensation operational amplifier 320 is 1 (1 time amplification). A connection C1 between the detection temperature detection element 75s and the detection resistor Rs is connected to one input terminal 311 of the differential operational amplifier 310, and a connection C2 between the compensation temperature detection element 75c and the compensation resistor Rc is connected to the other input terminal 312 of the differential operational amplifier 310 and an input terminal 321 of the compensation operational amplifier 320.

[0053] In the non-contact temperature measuring device 300 according to this embodiment, the measurement temperature T of the measurement object 400 (72) is measured by first obtaining a detection voltage Vs (a voltage converted from the resistance value of the thermistor) from the detection temperature detecting element 75s corresponding to the measurement temperature T of the measurement object 400 (72) and a compensation voltage Vc (a voltage converted from the resistance value of the thermistor) from the compensation temperature detecting element 75c corresponding to the compensation temperature Tc of the measurement object 400 (72), and then calculating the voltage difference Vd (= Vc - Vs) between these voltages. More specifically, the detection temperature detecting element 75s and the compensation temperature detecting element 75c are elements whose resistances change in response to temperature changes, so the detection voltage Vs and the compensation voltage Vc, which are voltage-divided by a known detection resistor Rs and a known compensation resistor Rc, are obtained, respectively.

[0054] Here, the voltage difference Vd between the compensation voltage Vc and the detection voltage Vs tends to become smaller as the response speed of the non-contact temperature sensor 75 increases (see the description of the background art).

[0055] Therefore, in order to accurately detect the voltage difference Vd, the differential operational amplifier 310 is used to amplify the voltage difference Vd between the compensation voltage Vc and the detection voltage Vs to obtain a differential voltage AVd. The compensation voltage Vc is then input to the compensation operational amplifier 320 to obtain the compensation voltage Vc. The obtained differential voltage AVd and compensation voltage Vc are input to the control unit 60. Here, the compensation operational amplifier 320 also has an offset voltage, but because the gain G2 of the compensation operational amplifier 320 is 1, the offset voltage of the compensation operational amplifier 320 is at a negligible level.

[0056] Next, the control unit 60 receives the compensation voltage Vc and the differential voltage AVd as analog values ​​and converts the analog signals of the compensation voltage Vc and the differential voltage AVd into digital data using an AD converter (not shown). The detection voltage Vs can be calculated from the compensation voltage Vc and the voltage difference Vd (Vs = Vc - AVd / gain G1 of the operational amplifier 310).

[0057] Next, the measured temperature T of the measurement object 400 (72) is measured by performing a predetermined calculation using the differential output (differential voltage AVd) and the compensation output (compensation voltage Vc) converted into digital data. Specifically, the temperature-voltage relationship is unique to each non-contact temperature sensor 75, so the detected temperature Ts can be calculated from the detected voltage Vs and the compensation temperature Tc can be calculated from the compensation voltage Vc according to the individual sensor characteristics. Then, the measured temperature T can be calculated from the detected temperature Ts and the compensation temperature Tc using a predetermined conversion means H (see FIG. 4) pre-stored in the memory unit 60b. For example, the measured temperature T may be calculated using an approximation formula based on the compensation voltage Vc and the differential voltage AVd. Alternatively, the measured temperature T may be calculated from the compensation voltage Vc and the differential voltage AVd using a predetermined two-dimensional table.

[0058] Incidentally, in the operational amplifier 310, when measuring the temperature T of the measurement object 400 (72), the offset voltage needs to be offset corrected.

[0059] In this regard, the non-contact temperature measuring device 300 performs offset correction at a correction time when a predetermined offset correction condition can be met, using the differential voltage AVd when the heat source 73 that heats the measurement object 400 (72) is not operating as the offset correction value F. Here, the correction time is the initial state when the detection temperature detecting element 75s and the compensation temperature detecting element 75c can detect the same temperature for the measurement object 400 (72), that is, when the heat source 73 is not operating (specifically, when the power switch 80 is turned on and power is supplied but the heat source 73 is not operating). The differential voltage AVd at this time is obtained as the measured offset correction value Fm, and the obtained measured offset correction value Fm is considered to be the offset correction value F of the operational amplifier 310. The offset correction value F when the heat source is not operating is subtracted from the differential voltage AVd when measuring the measurement object 400 (72), thereby canceling the influence of the offset value.

[0060] The predetermined offset correction conditions for performing offset correction, i.e., the conditions necessary for obtaining the offset correction value F, are that the object to be measured 400 (72) and the non-contact temperature sensor 75 must be at the same temperature, and therefore the heat source 73 (in this example, a heater lamp) must be in an inactive state.

[0061] Conventionally, when the heat source is not operating, the offset correction condition is the end temperature detected by an end temperature sensor 74 (temperature sensor for detecting the sheet non-conveying area) provided at the end of the measurement object 400 (72) (the sheet non-conveying area α2 in the fixing belt 72), and the offset correction is performed when the end temperature detected by the end temperature sensor 74 is below a predetermined threshold value (specifically, 30°C).

[0062] However, the compensation temperature Tc detected by the compensation temperature detection element 75c barely rises because the heating is short, but the temperature in the heated area (sheet conveying area α1) that rose in a short time is quickly detected by the detection temperature detection element 75s, and a voltage difference Vd due to heating occurs between the compensation output from the compensation temperature detection element 75c and the detection output from the detection temperature detection element 75s. The non-contact temperature measurement device 300 erroneously recognizes this voltage difference Vd as an offset voltage and performs erroneous offset correction even though offset correction should not be performed.

[0063] In this regard, in this embodiment, the control unit 60 includes a temperature detection control unit 61, a first determination control unit 62, and an offset correction control unit 63. The temperature detection control unit 61 detects the detected temperature Ts of the measurement object 400 (72) using a signal related to the detected temperature Ts output from the temperature detection element 75s for detection. The first determination control unit 62 determines whether the detected temperature Ts detected by the temperature detection control unit 61 is equal to or lower than a predetermined threshold value (e.g., 30°C) using the detected temperature Ts as an offset correction condition. The offset correction control unit 63 performs offset correction when the first determination control unit 62 determines that the detected temperature Ts detected by the temperature detection control unit 61 is equal to or lower than the threshold value (e.g., 30°C). The differential output (differential voltage AVd) at this time is stored in the storage unit 60b as an offset correction value F. Thereafter, the heat source 73 is operated, and the ideal or nearly ideal differential output (AVd) can be obtained by subtracting the offset correction value F stored in the memory unit 60b from the differential output (AVd) when measuring the measurement object 400 (72) heated by the heat source 73. In this way, an accurate measured temperature can be obtained, eliminating the influence of the offset value.

[0064] According to this embodiment, the control unit 60 uses the detected temperature Ts detected using the detection temperature detecting element 75s as the offset correction condition, and performs offset correction when the detected temperature Ts is equal to or lower than a predetermined threshold (specifically, 30°C), so that the detection temperature detecting element 75s can respond immediately to a temperature rise of the measurement object 400 (72). For example, if the measurement object 400 (72) that has been heated for only a short time rises in temperature above the threshold of the offset correction condition (specifically, 30°C), the detection temperature detecting element 75s can be used to detect a detected temperature Ts of the measurement object 400 (72) that exceeds the threshold of the offset correction condition, so that offset correction is not performed.

[0065] Therefore, it is possible to effectively prevent erroneous offset correction due to misrecognition when offset correction should not be performed, such as when the measurement object 400 (72) is heated for only a short time at the correction time when specified offset correction conditions can be met.

[0066] In this embodiment, the first determination control unit 62 determines whether at least one of the detected temperature Ts of the center detected using the detection temperature detection element 75s in the first non-contact temperature sensor 751 and the detected temperature Ts of one end detected using the detection temperature detection element 75s in the second non-contact temperature sensor 752 is below a predetermined threshold (e.g., 30°C), and the offset correction control unit 63 may perform offset correction when the first determination control unit 62 determines that at least one of the detected temperature Ts of the center and the detected temperature Ts of one end is below the predetermined threshold.

[0067] In this case, if there is temperature unevenness or temperature gradient in the heating area (sheet conveying area α1), the offset correction condition may not be established accurately based on the detected temperature Ts detected by the temperature detecting element 75s for detection.

[0068] Therefore, the following configuration may be adopted. That is, the temperature detection control unit 61 calculates the temperature difference between the detected temperature Ts of the center portion detected by the detection temperature detecting element 75s of the first non-contact temperature sensor 751 in the sheet conveying region α1 and the detected temperature Ts of one end portion detected by the detection temperature detecting element 75s of the second non-contact temperature sensor 752. The first determination control unit 62 determines whether the temperature difference between the detected temperature Ts of the center portion and the detected temperature Ts of the one end portion is smaller than a predetermined temperature difference threshold (e.g., 5°C). The offset correction control unit 63 performs offset correction when the first determination control unit 62 determines that at least one of the detected temperature Ts of the center portion and the detected temperature Ts of the one end portion is equal to or lower than a predetermined threshold (e.g., 30°C) and that the temperature difference between the detected temperature Ts of the center portion and the detected temperature Ts of the one end portion calculated by the temperature detection control unit 61 is smaller than the temperature difference threshold. As a result, even if at least one of the detected temperature Ts at the central portion and the detected temperature Ts at one end portion is equal to or lower than a predetermined threshold, if the temperature difference between the detected temperature Ts at the central portion and the detected temperature Ts at one end portion is equal to or higher than the temperature difference threshold, offset correction is not performed. Therefore, the offset correction condition can be accurately established based on the detected temperature Ts (detected temperatures Ts, Ts at the central portion and one end portion) detected using the detection temperature detecting element 75s (detection temperature detecting elements 75s, 75s in the first non-contact temperature sensor 751 and the second non-contact temperature sensor 752).

[0069] Alternatively / additionally, the control unit 60 may detect the on-time interval from the time when the power switch 80 was last turned on to the time when it is turned on this time, and perform offset correction when it determines that the detected temperature Ts is equal to or lower than the threshold value and the on-time interval is greater than a predetermined reference on-time interval.

[0070] Alternatively / furthermore, from the viewpoint that offset correction may not be performed accurately when the ambient temperature changes suddenly, the control unit 60 may detect the temperature change rate per unit time of the ambient temperature (compensated temperature Tc), and perform offset correction when it determines that the detected temperature Ts is below a threshold value and the temperature change rate is below a predetermined change rate.

[0071] In the present embodiment, the threshold value of the offset correction condition is preferably set to a value equal to or lower than the recommended upper limit temperature of the image forming apparatus 100 (the rated upper limit temperature for use, e.g., 30°C). If the threshold value of the offset correction condition exceeds the recommended upper limit temperature of the image forming apparatus 100, there is a risk that an erroneous offset correction will be performed due to a misidentification when offset correction should not be performed, such as when the measurement object 400 (72) is heated for only a short time. On the other hand, even if the threshold value of the offset correction condition is within the recommended temperature range of the image forming apparatus 100 (the rated upper limit temperature for use, e.g., 10°C to 30°C), if the threshold value is too low, there is a risk that the detected temperature Ts detected using the temperature detection element 75s for detection will continuously exceed the threshold value or will exceed the threshold value more frequently when offset correction should be performed, and as a result, offset correction may not be performed.

[0072] (Second embodiment) Incidentally, if the differential output (differential voltage AVd) is equal to or greater than a predetermined abnormal output threshold (abnormal voltage threshold), it is possible that some kind of abnormality has occurred in the temperature measuring device 300. Here, the abnormal output threshold can be, for example, a value of the differential output (AVd) at which some kind of abnormality may occur in the temperature measuring device 300. For example, in an abnormal state such as when the leakage current in the temperature measuring circuit of the temperature measuring device 300 increases and the potential changes, accurate temperature measurement cannot be performed.

[0073] In this regard, in the second embodiment, the control unit 60 in the first embodiment has a second determination control unit 64 that determines whether the differential output (AVd) is equal to or greater than a predetermined abnormal output threshold, and an alarm control unit 65 that, when performing offset correction, if the second determination control unit 64 determines that the differential output (AVd) is equal to or greater than the predetermined abnormal output threshold, issues an alarm indicating that there may be an abnormality in the temperature measuring device 300. For example, the display unit 51 of the operation panel 50 and / or a sound generating unit (not shown) may be configured to display a message and / or issue a sound such as "There may be an abnormality in the temperature measuring circuit. Call a service technician."

[0074] This allows the user to recognize that measuring the temperature of the measurement object 400 (72) in an abnormal state will prevent accurate temperature measurement.

[0075] (Third embodiment) However, there is a possibility that offset correction may never be performed, for example, if the ambient temperature (e.g., 35°C) of the installation environment of the measurement object 400 (72) always exceeds the threshold value (e.g., 30°C) of the offset correction condition.

[0076] In this regard, in the third embodiment, in the first or second embodiment, for example, the first offset correction (before shipping from the factory) is performed in the production process at the factory, and an initial offset correction value, which is the offset correction value of the offset correction performed in the production process, is stored in advance in the storage unit 60b. If the detected temperature Ts detected using the temperature detection element 75s for detection continuously exceeds a threshold value (e.g., 30°C) after the initial offset correction value is stored in the storage unit 60b, the offset correction control unit 63 uses the initial offset correction value stored in advance in the storage unit 60b.

[0077] By doing this, even if the environmental temperature (e.g., 35°C) of the environment in which the measurement object 400 (72) is installed after shipping from the factory continuously exceeds the threshold value of the offset condition (e.g., 30°C), offset correction can be performed using the differential output (AVd) of the offset correction performed during the factory production process or at the time of shipping from the factory.

[0078] Here, once the detected temperature Ts detected using the detecting temperature detecting element 75s falls below the threshold, the offset correction value F obtained by the offset correction performed when the detected temperature Ts detected using the detecting temperature detecting element 75s falls below the threshold can be used instead of the initial offset correction value previously stored in the storage unit 60b during the production process. Thus, even if the detected temperature Ts exceeds the threshold after it has fallen below the threshold, the offset correction value F obtained when the detected temperature Ts fell below the threshold can be used. In this case, as in the present embodiment, the storage area of ​​the storage unit 60b that stores the initial offset correction value during the production process and the storage area of ​​the storage unit 60b that stores the offset correction value F when the detected temperature Ts falls below the threshold can be made the same. Therefore, the initial offset correction value stored in the production process can be rewritten in the storage unit 60b with the offset correction value F obtained when the detected temperature Ts falls below the threshold. This eliminates the need for a control unit 60 to determine whether the detected temperature Ts has fallen below the threshold.

[0079] (Fourth embodiment) Incidentally, the differential output (AVd) normally contains noise, but even if the differential output (AVd) contains noise, if it is below a predetermined lower limit threshold that can be regarded as not being 0, it is preferable to regard the differential output (AVd) as 0.

[0080] In this regard, in the fourth embodiment, in any one of the first to third embodiments, the second determination control unit 64 determines whether the differential output (AVd) is below a predetermined lower threshold. When performing offset correction, if the second determination control unit 64 determines that the differential output (AVd) is below the predetermined lower threshold, the offset correction control unit 63 sets the measured offset correction value Fm to 0 and rewrites the offset correction value F in the storage unit 60b to the measured offset correction value Fm(0). Here, the lower threshold can be a value approximately equal to the noise level.

[0081] By doing so, the differential output (AVd) below the lower threshold can be regarded as noise, and thus offset correction can be performed with the offset value set to zero.

[0082] (Fifth embodiment) In the fifth embodiment, in any one of the first to fourth embodiments, when performing offset correction, if the second judgment control unit 64 judges that the differential output (AVd) is below the abnormal output threshold, the offset correction control unit 63 sets the differential output (AVd) as a measured offset correction value Fm, and rewrites the offset correction value F in the memory unit 60b to the measured offset correction value Fm [differential output (AVd)].

[0083] By doing so, it is possible to reliably update the offset correction value F to the newly acquired measured offset correction value Fm every time offset correction is performed in the storage unit 60b.

[0084] Incidentally, when the differential output (AVd) is equal to or greater than the lower limit threshold, it can be considered that the differential output (AVd) is not 0 even if it contains noise.

[0085] In this regard, in the present embodiment, when performing offset correction, if the second judgment control unit 64 determines that the differential output (AVd) is equal to or greater than the lower threshold, the offset correction control unit 63 sets the differential output (AVd) as the measured offset correction value Fm, and rewrites the offset correction value F in the memory unit 60b to the measured offset correction value Fm [differential output (AVd)].

[0086] In this case, the offset correction value F may simply be rewritten as the measured offset correction value Fm [differential output (AVd)], or the lower limit threshold may be regarded as noise and the measured offset correction value Fm may be set to the differential output (AVd) minus the lower limit threshold. By doing so, every time offset correction is performed in the storage unit 60b, the offset correction value F can be accurately updated to the measured offset correction value Fm, which is the differential output (AVd) minus the lower limit threshold regarded as noise.

[0087] In this embodiment, the second determination control unit 64 determines whether the measured offset correction value Fm is different from the offset correction value F stored in the storage unit 60b. When performing offset correction, the offset correction control unit 63 may rewrite the offset correction value F in the storage unit 60b to the measured offset correction value Fm if the second determination control unit 64 determines that the measured offset correction value Fm is different from the offset correction value F stored in the storage unit 60b.

[0088] By doing so, it is possible to omit the operation of rewriting the storage unit 60b when the measured offset correction value Fm is equal to the offset correction value F stored in the storage unit 60b.

[0089] In this embodiment, the second determination control unit 64 determines whether the measured offset correction value Fm is less than the offset correction value F stored in the storage unit 60b. When the second determination control unit 64 determines that the measured offset correction value Fm is less than the offset correction value F stored in the storage unit 60b in performing offset correction, the offset correction control unit 63 sets the measured offset correction value Fm to the offset correction value F stored in the storage unit 60b, and rewrites the offset correction value F in the storage unit 60b to the measured offset correction value Fm (the offset correction value F stored in the storage unit 60b), or may leave it as is.

[0090] In this way, even if the measured offset correction value Fm falls below the offset correction value F stored in the storage unit 60b, the offset correction value F can be maintained at the offset correction value F stored in the storage unit 60b. This is particularly effective when another offset factor not caused by the operational amplifier 310 is added to the offset value.

[0091] In this embodiment, when performing offset correction, if the second judgment control unit 64 determines that the measured offset correction value Fm is equal to or greater than the offset correction value F stored in the memory unit 60b, the offset correction control unit 63 may rewrite the offset correction value F in the memory unit 60b to the measured offset correction value Fm.

[0092] By doing this, when the measured offset correction value Fm becomes equal to or greater than the offset correction value F stored in the memory unit 60b, the offset correction value F stored in the memory unit 60b can be updated to the measured offset correction value Fm.

[0093] In this embodiment, the second determination control unit 64 determines whether the differential output (AVd) is below a predetermined upper threshold that is greater than the lower threshold. When performing offset correction, the offset correction control unit 63 may rewrite the offset correction value F in the storage unit 60b to a measured offset correction value Fm if the second determination control unit 64 determines that the differential output (AVd) is equal to or greater than the predetermined lower threshold and is less than the predetermined upper threshold.

[0094] In this way, the offset correction value F can be reliably updated to the appropriate measured offset correction value Fm.

[0095] In this embodiment, when performing offset correction, the offset correction control unit 63 may set the measured offset correction value Fm to the upper limit threshold and rewrite the offset correction value F in the storage unit 60b to the measured offset correction value Fm (upper limit threshold) if the second determination control unit 64 determines that the differential output (AVd) is equal to or greater than a predetermined upper limit threshold. Here, the upper limit threshold can be set to a value that is lower than the abnormal output threshold and is smaller by a predetermined amount than a value that may suddenly occur due to a leak or the like.

[0096] This ensures that the offset correction value F is updated to the measured offset correction value Fm, which is kept at the upper limit threshold, without exceeding the upper limit threshold. This is particularly effective when the differential output (AVd) suddenly exceeds the upper limit threshold due to a leak or the like.

[0097] (Sixth embodiment) However, the offset value of the operational amplifier 310 usually changes over time. Therefore, if the offset value changes over time after offset correction, it will be impossible to accurately measure the temperature of the measurement object 400 (72). Therefore, it is preferable to repeatedly perform offset correction at correction intervals when predetermined offset correction conditions can be met.

[0098] In this regard, in the sixth embodiment, in any one of the first to fifth embodiments, the offset correction control unit 63 performs offset correction whenever the heat source 73 that heats the object to be measured 400 (72) is in a heat source inactive state (in this example, whenever the power switch 80 is turned on), and when the detected temperature Ts detected using the detection temperature detection element 75s is below the threshold value.

[0099] By doing this, offset correction can be performed on the offset value of the operational amplifier 310, which has changed over time, each time the heat source is inactive, so that the measurement object 400 (72) can be measured accurately even if the offset value changes.

[0100] (Seventh embodiment) In the seventh embodiment, in any one of the first to sixth embodiments, the control unit 60 stores a history of the differential output (AVd) in the storage unit 60b each time the heat source 73 is in a heat source inactive state (in this example, each time the power switch 80 is turned on), and includes an increase trend value calculation unit 66 that calculates an increase trend value that indicates the increase trend of the differential output (AVd). The second determination control unit 64 determines whether the increase trend value calculated by the increase trend value calculation unit 66 is equal to or greater than a predetermined abnormal trend value.

[0101] Here, an example of the abnormal tendency value is an increasing tendency value that indicates a high possibility that some abnormality will occur in the temperature measuring device 300. An example of an increasing tendency value that indicates an increasing tendency of the differential output (AVd) is a differential output (AVd) whose difference from the previous differential output (AVd) is positive and whose differential output ratio is equal to or greater than a reference ratio, which is obtained by storing a history of the differential output (AVd) in the memory unit 60b each time the heat source is in an inoperative state (each time the power switch 80 is turned on in this example). The differential output ratio can be the ratio of the differential output (AVd) to a predetermined abnormal output threshold. The reference ratio is not limited to this, but can be, for example, a ratio of approximately 70% to 80% or more of the abnormal output threshold.

[0102] When the second determination control unit 64 determines that the increasing tendency value is equal to or greater than a predetermined abnormal tendency value, the alarm control unit 65 issues an alarm indicating that it is necessary to check the operating state of the temperature measuring device 300. For example, the alarm control unit 65 may be configured to display a message and / or sound such as a warning or error on the display unit 51 of the operation panel 50 and / or to issue a sound such as "There is a high possibility that the temperature measurement circuit will become abnormal."

[0103] In this way, the second judgment control unit 64 recognizes that even though the differential output (AVd) does not exceed the abnormal output threshold, it has increased from the previous differential output (AVd) and is approaching the abnormal output threshold, and the alarm control unit 65 issues an alarm indicating that the operating status of the temperature measuring device 300 needs to be checked.By doing so, measures can be taken, such as having a service technician or other worker check the temperature measuring circuit in advance (for example, checking the output voltage, etc.), and breakdowns in the temperature measuring device 300 can be prevented.

[0104] (Eighth embodiment) However, if the differential output (AVd) is equal to or greater than the abnormal output threshold, accurate temperature measurement cannot be performed, which may result in poor fixing in the image forming apparatus 100. For this reason, it is desirable to stop the image forming operation.

[0105] In this regard, in the eighth embodiment, in any one of the first to seventh embodiments, the control unit 60 has an operation stop control unit 67 that stops the image forming operation when the second judgment control unit 64 judges that the differential output (AVd) is equal to or greater than a predetermined abnormal output threshold when performing offset correction.

[0106] This makes it possible to avoid poor fixing in the image forming apparatus 100. Then, a service technician or other worker can take measures such as repairing or replacing the temperature measurement circuit board, and after confirming that it is working properly, can start image formation operations.

[0107] <Example of offset correction control> 7A to 7D are flowcharts showing the first half, an example of the middle part, another example of the middle part, and the second half of an example of the control operation for offset correction according to this embodiment, respectively.

[0108] Prior to performing the control operations of the offset correction shown in FIGS. 7A to 7D, the first offset correction is performed in the production process at the factory, and the initial offset correction value Fi of the offset correction performed in the production process is stored in advance in the memory unit 60b.

[0109] 7A to 7D, first, as shown in FIG. 7A, when the power switch 80 is turned on (S1), the control unit 60 determines whether the edge temperature Te of the sheet non-conveying region α2 of the measurement object 400 (72) detected by the edge temperature sensor 74, the detected temperature Ts of the center of the sheet conveying region α1 of the measurement object 400 (72) detected by the first non-contact temperature sensor 751, and the detected temperature Ts of one edge of the sheet conveying region α1 of the measurement object 400 (72) detected by the second non-contact temperature sensor 752 are equal to or lower than the threshold value Th (30°C in this example) (S2). Next, if the control unit 60 determines that at least one of the edge temperature Te, the detected temperature Ts of the center, and the detected temperature Ts of the one edge exceeds the threshold value Th (S2: No), the control unit 60 assigns the initial offset correction value Fi stored in the storage unit 60b in advance during the production process to the offset correction value F, and proceeds to S19 shown in FIG. 7D. On the other hand, if all of the temperatures Te, the detected temperature Ts at the center, and the detected temperature Ts at one end are equal to or lower than the threshold value Th (S2: Yes), the control unit 60 acquires the differential voltage AVd (S4) and determines whether the differential voltage AVd is equal to or higher than the abnormal voltage threshold value Va (S5). If the control unit 60 determines that the differential voltage AVd is lower than the abnormal voltage threshold value Va (S5: No), it determines whether the differential voltage AVd is lower than the lower threshold value Vmin (S6). If the control unit 60 determines that the differential voltage AVd is lower than the lower threshold value Vmin (S6: Yes), it assigns 0 to the measurement offset correction value Fm (S7) and proceeds to S13 shown in FIG. 7B or S13a shown in FIG. 7C. If the control unit 60 determines that the differential voltage AVd is equal to or higher than the lower threshold value Vmin (S6: No), it determines whether the differential voltage AVd is higher than the upper threshold value Vmax (S8). If the control unit 60 determines that the differential voltage AVd exceeds the upper threshold Vmax (S8: Yes), it assigns the upper threshold Vmax to the measured offset correction value Fm (S9) and proceeds to S13 shown in Fig. 7B or S13a shown in Fig. 7C. If the control unit 60 determines that the differential voltage AVd is equal to or smaller than the upper threshold Vmax (S8: No), it assigns (differential voltage AVd - lower threshold Vmin) to the measured offset correction value Fm (S10) and proceeds to S13 shown in Fig. 7B or S13a shown in Fig. 7C.In S10, the differential voltage AVd may be substituted for the measured offset correction value Fm.

[0110] On the other hand, if the control unit 60 determines that the differential voltage AVd is equal to or greater than the abnormal voltage threshold Va (S5: Yes), it displays a message on the display unit 51 indicating that there may be an abnormality in the temperature measuring device 300 (S11), stops the image forming operation of the image forming apparatus 100 (S12), and ends the processing.

[0111] Next, in the example shown in FIG. 7B, the control unit 60 determines whether the measured offset correction value Fm is different from the offset correction value F stored in the memory unit 60b (S13). If it is determined that they are different (S13: Yes), the control unit 60 assigns the measured offset correction value Fm to the offset correction value F (S14) and proceeds to S15 shown in FIG. 7D. On the other hand, if it is determined that they are equal (S13: No), the control unit 60 proceeds directly to S15 shown in FIG. 7D.

[0112] In the example shown in FIG. 7C, the control unit 60 determines whether the measured offset correction value Fm is less than the offset correction value F stored in the memory unit 60b (S13a). If it is determined that the measured offset correction value Fm is less than the offset correction value F (S13a: Yes), the control unit 60 substitutes the offset correction value F stored in the memory unit 60b for the offset correction value F (S14a) and proceeds to S15 shown in FIG. 7D. On the other hand, if it is determined that the measured offset correction value Fm is greater than or equal to the offset correction value F (S13a: No), the control unit 60 substitutes the measured offset correction value Fm for the offset correction value F (S14) and proceeds to S15 shown in FIG. 7D.

[0113] Next, as shown in FIG. 7D, the control unit 60 stores the offset correction value F in the memory unit 60b (S15) (updates the offset correction value F), stores the history of the differential voltage AVd in the memory unit 60b, and calculates the increase tendency value K (S16).

[0114] Next, the control unit 60 determines whether the increase tendency value K is equal to or greater than the abnormal tendency value Ka (S17), and if it determines that it is below the abnormal tendency value Ka (S17: No), it proceeds to S19, whereas if it determines that it is equal to or greater than the abnormal tendency value Ka (S17: Yes), it displays a message on the display unit 51 indicating that the operating status of the temperature measuring device 300 needs to be checked (S18), and proceeds to S19.

[0115] Next, the control unit 60 activates the heat source 73 (S19), measures the temperature T of the measurement object 400 (72) (S20), and acquires the compensation voltage Vc and the differential voltage AVd (S21, S22).

[0116] Next, the control unit 60 substitutes (the acquired differential voltage Vc-offset correction value F) for the appropriate appropriate differential voltage RAVd (S23), and obtains the measured temperature T from the acquired compensation voltage Vc and the appropriate differential voltage RAVd (S24).

[0117] The present disclosure is not limited to the above-described embodiments, but can be implemented in various other forms. Therefore, the embodiments are merely examples in all respects and should not be interpreted as being limiting. The scope of the present disclosure is defined by the claims and is not bound by the text of the specification. Furthermore, all modifications and variations within the equivalent scope of the claims are within the scope of the present disclosure. [Explanation of symbols]

[0118] 100 Image forming device 300 Temperature measuring device 310 Differential Op-Amp (Example of Op-Amp) 320 Compensation Op-Amp 400 Measurement Objects 51 Display section 60 Control Unit 60a Processing section 60b Storage section 61 Temperature detection control section 62 First determination control unit 63 Offset correction control section 64 Second determination control section 65 Alarm control section 66 Increase trend value calculation section 67 Operation stop control section 7 Fixing device 72 Fixing belt (example of measurement object) 73 Heat source 74 Edge temperature sensor 75 Non-contact temperature sensor 751 First Non-Contact Temperature Sensor 752 Secondary Non-Contact Temperature Sensor 75c Compensation temperature detection element 75s temperature detection element 80 Power switch AVd differential voltage D DC power supply E power supply F Offset correction value Fi Initial offset correction value Fm measurement offset correction value H conversion means IR Infrared K increasing trend value Ka abnormal trend value P-sheet RAVd Appropriate differential voltage Rc compensation resistor Rs Sensing resistor T Measurement temperature Tc compensation temperature Te end temperature Th threshold Ts detection temperature Va Abnormal voltage threshold Vc Compensation voltage Vd voltage difference Vmax upper threshold Vmin Lower Threshold Vs detection voltage X Width direction α1 sheet transport area α2 Sheet non-transport area

Claims

1. a non-contact temperature sensor including a detection temperature detection element that detects the temperature of the object to be measured in a non-contact manner and a compensation temperature detection element that detects the environmental temperature; an operational amplifier that amplifies an output difference between the output of the detection temperature detection element and the output of the compensation temperature detection element; a non-contact temperature measurement device that measures an offset value included in a differential output obtained by amplifying the output difference by the operational amplifier, and performs offset correction to remove the offset from the differential output based on the measured offset value, The offset correction is performed under a predetermined offset correction condition for performing the offset correction, A temperature measurement device characterized in that the detected temperature detected using the detection temperature detection element is used as the offset correction condition, and the offset correction is performed when the detected temperature detected using the detection temperature detection element is below a predetermined threshold.

2. 2. The temperature measurement device according to claim 1, When performing the offset correction, if the differential output is equal to or greater than a predetermined abnormal output threshold, an alarm is issued indicating that there may be an abnormality in the temperature measuring device.

3. 2. The temperature measurement device according to claim 1, an initial offset correction value, which is the offset correction value obtained by the offset correction, is stored in a storage unit in advance; A temperature measuring device characterized in that, when the detected temperature detected using the detection temperature detection element continuously exceeds the threshold value after the initial offset correction value is stored in the memory unit, the initial offset correction value stored in the memory unit is used.

4. 2. The temperature measurement device according to claim 1, When performing the offset correction, if the differential output falls below a predetermined abnormal output threshold, the differential output is set as a measured offset correction value, and the offset correction value is rewritten to the measured offset correction value in a memory unit.

5. 2. The temperature measurement device according to claim 1, A temperature measuring device characterized in that the offset correction is performed when the detected temperature detected using the detection temperature detection element is below the threshold value each time the heat source that heats the object to be measured is in a heat source inactive state.

6. 2. The temperature measurement device according to claim 1, A temperature measuring device characterized by calculating an increase trend value indicating an increase trend of the differential output each time a heat source that heats the object to be measured is not operating, and if the increase trend value is equal to or greater than a predetermined abnormal trend value, issuing an alarm indicating that the operating status of the temperature measuring device needs to be checked.

7. A temperature measuring device according to any one of claims 1 to 6; a fixing device having a fixing member for heat-fixing an unfixed toner image onto a sheet; The image forming apparatus, wherein the object to be measured is the fixing member.

8. 8. The image forming apparatus according to claim 7, When performing the offset correction, if the differential output is equal to or greater than a predetermined abnormal output threshold, an alarm is issued indicating that there may be an abnormality in the temperature measuring device, and the image forming operation is stopped.

Images