Fixing device, image forming apparatus, and control method

Abstract

To enable a temperature detection sensor to detect a correct temperature by correcting a resistance value of the temperature detection sensor changed with time.SOLUTION: A fixing device 4 includes a heat member 4a provided with a heat source, a temperature detection sensor 46 for changing a resistance value according to the temperature of the heat member 4a, a heat control part 72 for detecting the temperature of the heat member 4a by calculating the resistance value of the temperature detection sensor 46, and heat controlling the heat source, and a resistance compensation part 73 for calculating a correction coefficient K for correcting the resistance value of the temperature detection sensor 46 based on the voltage outputted from the temperature detection sensor 46 when a predetermined compensation condition is satisfied. The heat control part 73 corrects the resistance value of the temperature detection sensor 46 by using the correction coefficient K calculated by the resistance compensation part 73 when detecting the temperature of the 4a part of the heat member.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a fixing device, an image forming apparatus, and a control method. [Background technology]

[0002] An image forming apparatus that forms an image using an electrophotographic method includes a fixing device for fixing an image transferred onto a sheet such as printing paper. The fixing device forms a nip by bringing a heating member and a pressure member into contact with each other, and applies heat and pressure to the sheet by sandwiching the sheet in the nip, thereby fixing the image onto the sheet. The fixing device includes a temperature sensor that detects the temperature of the heating member, and controls the temperature based on the temperature detected by the temperature sensor. It has been proposed to use a non-contact temperature sensor including a detection temperature detection element and a compensation temperature detection element in this type of fixing device (see, for example, Patent Document 1).

[0003] The temperature detection element changes its resistance value in response to the temperature of the object to be measured, thereby changing its output voltage, so that the fixing device can detect the temperature of the heating member based on the output voltage of the temperature detection element.

[0004] However, the resistance value of the temperature detection element changes over time. If the resistance value changes over time, it will be impossible to accurately detect the temperature of the heating element. Therefore, it is possible to compare the temperature detected by the output voltage of the temperature detection element with the temperature detected by another temperature sensor, and calculate a correction coefficient to correct the temperature detected by the temperature detection element.

[0005] However, the method of calculating a correction coefficient for correcting the temperature and correcting the temperature detected by the temperature detection element based on the correction coefficient has the problem that the correct temperature cannot be detected outside the temperature range when the correction coefficient was calculated. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2023-183799 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve the above-mentioned problems of the conventional art, and aims to provide a fixing device, an image forming apparatus, and a control method that can detect the correct temperature by correcting the resistance value that has changed over time. [Means for solving the problem]

[0008] In order to achieve the above object, the invention of claim 1 is a fixing device comprising: a heating element provided with a heat source; a temperature detection sensor that changes its resistance value according to the temperature of the heating element; a control unit that calculates the resistance value of the temperature detection sensor based on the output voltage of the temperature detection sensor to detect the temperature of the heating element and control the heating of the heat source; and a resistance compensation unit that calculates a correction coefficient for correcting the resistance value of the temperature detection sensor based on the output voltage of the temperature detection sensor when a predetermined compensation condition is met, wherein the control unit corrects the resistance value of the temperature detection sensor using the correction coefficient calculated by the resistance compensation unit when detecting the temperature of the heating element.

[0009] The invention of claim 2 is characterized in that, in the fixing device of claim 1, the temperature detection sensor has a measurement detection element that detects the surface temperature of the heating member and a compensation detection element that detects the ambient temperature, and the resistance compensation unit calculates the correction coefficient when there is a difference between the output voltage of the measurement detection element and the output voltage of the compensation detection element.

[0010] The invention of claim 3 is a fixing device of claim 2, wherein when there is a difference between the output voltage of the measurement detection element and the output voltage of the compensation detection element, the resistance compensation unit calculates a first resistance value, which is the resistance value of the measurement detection element, from the output voltage of the measurement detection element, and calculates a second resistance value, which is the resistance value of the compensation detection element, from the output voltage of the compensation detection element, and calculates the ratio of the first resistance value to the second resistance value as the correction coefficient.

[0011] The invention of claim 4 is characterized in that, in the fixing device of claim 2, the temperature detection sensor has a casing that holds the measurement detection element and the compensation detection element, and the casing is open at a position corresponding to the measurement detection element to guide radiant heat from the heating element to the measurement detection element, while covering a position corresponding to the compensation detection element to block radiant heat from the heating element.

[0012] The invention of claim 5 is characterized in that, in the fixing device of claim 1, the resistance compensation unit calculates the correction coefficient when a predetermined time has elapsed since the control unit has finished controlling the heating of the heat source.

[0013] The invention of claim 6 is characterized in that in the fixing device of claim 1, the resistance compensation unit calculates the correction coefficient before the control unit starts warming up the heat source.

[0014] The invention of claim 7 is a fixing device of claim 1, further comprising an internal temperature measuring sensor that measures the temperature inside the fixing device, and the resistance compensation unit is configured to calculate the correction coefficient when the temperature measured by the internal temperature measuring sensor is below a predetermined value.

[0015] The invention of claim 8 is a fixing device of claim 1, further comprising an internal temperature measuring sensor that measures the internal temperature inside the fixing device and an external temperature measuring sensor that measures the external temperature outside the fixing device, and is characterized in that the resistance compensation unit calculates the correction coefficient when the temperature difference between the internal temperature and the external temperature is less than a predetermined value.

[0016] The invention of claim 9 is characterized in that, in the fixing device of claim 1, the resistance compensation unit estimates the internal temperature of the heating member and calculates the correction coefficient when it estimates that the internal temperature of the heating member is below a predetermined temperature.

[0017] The invention of claim 10 is characterized in that, in the fixing device of claim 9, the resistance compensation unit estimates the internal temperature of the heating element based on the control time during which the control unit performed the previous heating control on the heat source and the elapsed time since the previous heating control ended.

[0018] The invention of claim 11 is an image forming apparatus comprising an image forming section that forms an image on a sheet and a fixing device of any one of claims 1 to 10, characterized in that the sheet on which the image has been formed in the image forming section is transported to the fixing device, and the image is fixed to the sheet in the fixing device.

[0019] The invention of claim 12 is a control method for a fixing device equipped with a heating element provided with a heat source and a temperature detection sensor that changes its resistance value depending on the temperature of the heating element, comprising: a control step of calculating the resistance value of the temperature detection sensor based on the output voltage of the temperature detection sensor to detect the temperature of the heating element and control the heating of the heat source; and a resistance compensation step of calculating a correction coefficient for correcting the resistance value of the temperature detection sensor based on the output voltage of the temperature detection sensor when a predetermined compensation condition is met, wherein the control step corrects the resistance value of the temperature detection sensor using the correction coefficient calculated by the resistance compensation step when detecting the temperature of the heating element. [Effects of the Invention]

[0020] According to the present invention, the resistance value that has changed over time is corrected when a predetermined compensation condition is met, thereby enabling the correct temperature to be detected. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 illustrates an example of the configuration of an image forming apparatus. [Figure 2] FIG. 2 is a diagram illustrating a detailed configuration of a fixing device. [Figure 3] FIG. 2 is a perspective view showing a heating member and a pressure member of the fixing device. [Figure 4] FIG. 2 is a diagram illustrating an example of a configuration of a temperature detection sensor. [Figure 5] FIG. 2 is a block diagram showing the functional configuration of a control unit. [Figure 6] FIG. 10 is a diagram illustrating an example of TR characteristic information. [Figure 7] 10 is a flowchart showing an example of a processing procedure performed by a CPU of a control unit. [Figure 8] 10 is a flowchart showing an example of a detailed processing procedure of heating control. [Figure 9] 10 is a flowchart illustrating an example of a detailed processing procedure of a resistance compensation process. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Elements common to the embodiments described below are designated by the same reference numerals, and redundant description thereof will be omitted.

[0023] (Embodiment) 1 is a diagram showing an example of the configuration of an image forming apparatus 1 according to one embodiment of the present invention. This image forming apparatus 1 forms and outputs an image on a sheet 9 such as printing paper using an electrophotographic method. The image forming apparatus 1 has a paper feed conveyance section 2, an image forming section 3, and a fixing device 4 inside a device main body 1a.

[0024] The paper feed conveyance unit 2 conveys the sheet 9 along a conveyance path 13 formed inside the apparatus main body 1a. The paper feed conveyance unit 2 includes a paper feed cassette 11, a paper feed roller 12, a timing roller 14, a secondary transfer roller 15, and a paper discharge roller 16. The paper feed cassette 11 stores a stack of sheets 9. The paper feed roller 12 picks up the topmost sheet 9 from the stack of sheets 9 stored in the paper feed cassette 11 and sends it to the conveyance path 13. The timing roller 14 sends the sheet 9 sent by the paper feed roller 12 to the secondary transfer roller 15 in synchronization with the operation of the image forming unit 3. That is, the timing roller 14 temporarily stops the conveyance of the sheet 9 sent to the conveyance path 13 by the paper feed roller 12. The timing roller 14 is driven in synchronization with the timing at which the image formed by the image forming unit 3 is conveyed to the position of the secondary transfer roller 15, and sends the sheet 9 toward the secondary transfer roller 15.

[0025] The image forming unit 3 forms an image to be transferred onto the sheet 9 conveyed by the paper feed conveying unit 2. The image forming unit 3 has an intermediate transfer belt 24 that is stretched over a drive roller 20 and driven rollers 21 and 22. The intermediate transfer belt 24 is an endless belt that circulates clockwise as the drive roller 20 rotates. The image forming unit 3 has imaging units 30K, 30Y, 30M, and 30C below the intermediate transfer belt 24 that form images of each color, such as black (K), Y (yellow), M (magenta), and C (cyan).

[0026] The imaging units 30K, 30Y, 30M, and 30C generate toner images of each color based on the image to be printed, and perform primary transfer of the toner images onto the intermediate transfer belt 24. Each of the imaging units 30K, 30Y, 30M, and 30C has a photosensitive drum 31, a charger 32, an exposure device 33, a developing device 34, a primary transfer roller 35, and a cleaner 36. The charger 32, the exposure device 33, the developing device 34, the primary transfer roller 35, and the cleaner 36 are arranged around the photosensitive drum 31.

[0027] The charger 32 uniformly charges the surface of the photoconductor drum 31 to a predetermined charge. The exposure unit 33 is controlled by the exposure control unit 28. The exposure unit 33 exposes the surface of the photoconductor drum 31 to light according to image data for each color, forming an electrostatic latent image on the surface of the photoconductor drum 31. The developer 34 applies a developer containing toner to the surface of the photoconductor drum 31, developing the electrostatic latent image with toner. This forms a toner image on the surface of the photoconductor drum 31. The primary transfer roller 35 brings the intermediate transfer belt 24 into contact with the surface of the photoconductor drum 31, and by applying a predetermined voltage, performs primary transfer of the toner image on the photoconductor drum 31 to the intermediate transfer belt 24. The cleaner 36 neutralizes the surface of the photoconductor drum 31 after primary transfer and removes any toner remaining on the surface of the photoconductor drum 31.

[0028] Each of the imaging units 30K, 30Y, 30M, and 30C performs primary transfer, superimposing the toner images of each color onto the same position on the circulating intermediate transfer belt 24. As a result, a color image is formed on the surface of the intermediate transfer belt 24 when it passes the imaging unit 30C located at the most downstream position.

[0029] The image that has been primarily transferred onto the intermediate transfer belt 24 comes into contact with the surface of the sheet 9 being conveyed by the paper feed conveyance unit 2 when the intermediate transfer belt 24 passes the position of the secondary transfer roller 15. At this time, a predetermined voltage is applied to the secondary transfer roller 15. Therefore, the image carried on the intermediate transfer belt 24 is secondarily transferred onto the surface of the sheet 9 by the electrostatic force from the secondary transfer roller 15. As a result, the image is transferred onto the surface of the sheet 9.

[0030] After the secondary transfer, the toner remaining on the surface of the intermediate transfer belt 24 is removed from the surface of the intermediate transfer belt 24 by a cleaner 25 provided near the driven roller 21 .

[0031] The sheet 9 onto which the image has been transferred by the secondary transfer roller 15 is transported along a transport path 13 and guided to a fixing device 4. The fixing device 4 fixes the image transferred onto the sheet 9 onto the sheet 9. For example, the fixing device 4 includes a heating member 4a and a pressure member 4b. The heating member 4a and the pressure member 4b come into contact with each other to form a nip portion. As the sheet 9 passes through the nip portion, a fixing process including a heating process and a pressure process is performed on the sheet 9. The image is fixed onto the sheet 9 by the fixing process. The sheet 9 onto which the image has been fixed in the fixing device 4 is then discharged by a paper discharge roller 16 to a paper discharge tray 17 provided on the side of the apparatus main body 1a.

[0032] The image forming apparatus 1 is provided with a control unit 27 that performs overall control of the above-mentioned operations. When a print job is executed in the image forming apparatus 1, the control unit 27 controls the driving of the above-mentioned paper feed conveyance unit 2, image forming unit 3, and fixing device 4. In addition, when a print job is not executed, the control unit 27 also performs processing to transition the image forming apparatus 1 to a power saving mode.

[0033] Fig. 2 is a diagram showing a detailed configuration of the fixing device 4. Fig. 3 is a perspective view showing a heating member 4a and a pressure member 4b of the fixing device 4. The heating member 4a includes a heating roller 40, a heating belt 41, a heating pad 42, heaters 43a and 43b, and a support member 44. The pressure member 4b includes a pressure roller 45.

[0034] Heaters 43a and 43b are disposed inside heating roller 40 and are heat sources that heat heating roller 40 from the inside, and are constituted by, for example, halogen lamps. As shown in Fig. 3, heater 43a is a long heater that is provided inside heating roller 40 and extends over the entire axial area of ​​heating roller 40. Heater 43b is a short heater that is provided inside heating roller 40 only in the center of heating roller 40 in the axial direction.

[0035] The heating belt 41 is an endless belt that is stretched between the heating roller 40 and the heating pad 42. The heating pad 42 is supported by a support member 44 in a position that allows it to come into contact with the pressure roller 45. For example, the heating pad 42 is made of an elastic material such as rubber or sponge, and a sliding sheet is attached to its surface. The heating belt 41 is stretched in contact with the sliding sheet, and therefore moves in a circular motion as the heating roller 40 rotates.

[0036] The pressure roller 45 is provided at a position facing the heating pad 42 and applies a predetermined pressure to the heating belt 41 stretched over the heating pad 42 .

[0037] The fixing device 4 is equipped with a control unit 60 that controls the operation of the heating member 4a and the pressure member 4b. The control unit 60 controls the operation of the fixing process in the fixing device 4. For example, the control unit 60 controls the rotation of the heating roller 40 and the pressure roller 45. The control unit 60 also controls the on / off of heaters 43a and 43b, which are heat sources. When heating the entire axial area of ​​the heating roller 40, the control unit 60 turns on the heater 43a. On the other hand, when heating only the center of the axial direction of the heating roller 40, the control unit 60 turns on the heater 43b.

[0038] The fixing device 4 is equipped with a temperature detection sensor 46 and a temperature measurement sensor 47. The temperature detection sensor 46 detects the surface temperature of the heating belt 41 at a position diagonally below the heating roller 40. The temperature detection sensor 46 is provided at the center position in the axial direction of the heating roller 40. The temperature measurement sensor 47 is provided as an internal temperature measurement sensor and measures the internal temperature of the fixing device 4. As shown in FIG. 3 , the temperature measurement sensor 47 is equipped with two temperature sensors 47a and 47b arranged above the heating roller 40. The temperature sensor 47a is provided above an end of the heating roller 40 and measures the temperature above the end of the heating roller 40. The temperature sensor 47b is provided above the center of the heating roller 40 and measures the temperature above the center of the heating roller 40.

[0039] The control unit 60 controls the surface temperature of the heating belt 41 to a predetermined temperature based on the surface temperature of the heating belt 41 detected by the temperature detection sensor 46. For example, when a print job is executed in the image forming apparatus 1, the control unit 60 controls the surface temperature of the heating belt 41 to a target temperature for the fixing process based on the temperature detected by the temperature detection sensor 46. For example, the target temperature for the fixing process is 155°C. When the fixing device 4 is maintained in a warm-up state while no print job is being executed in the image forming apparatus 1, the control unit 60 controls the surface temperature of the heating belt 41 to a target temperature for the warm-up state. Even when the fixing device 4 is maintained in the warm-up state, the control unit 60 detects the surface temperature of the heating belt 41 based on the temperature detected by the temperature detection sensor 46. The target temperature for the warm-up state may be the same as or lower than the target temperature for the fixing process. For example, the target temperature for the warm-up state is preset to a temperature within a range of 135°C to 155°C.

[0040] Furthermore, the control unit 60 can adjust the temperature balance between the center and ends of the heating roller 40 in the axial direction while a print job is being executed. For example, assume that when an image is formed on a sheet 9 of a specific size, the sheet 9 passes over almost the entire area of ​​the heating roller 40 in the axial direction. In this case, the sheet 9 of the specific size passes over the entire area of ​​the nip formed by the heating member 4a and the pressure member 4b. Therefore, when an image is formed on a sheet 9 of the specific size, a temperature difference is unlikely to occur in the longitudinal direction of the heating roller 40. In this case, the control unit 60 controls the heater 43a on and off to maintain the entire heating belt 41 at a constant temperature.

[0041] In contrast, when an image is formed on a sheet 9 smaller than the specific size, the sheet 9 passes only through the center of the nip formed by the heating member 4a and the pressure member 4b, and does not pass through the edge regions. In this case, heat is absorbed from the center of the heating belt 41 by the sheet 9, but heat is not absorbed from the edge regions of the heating belt 41 by the sheet 9. This causes a temperature difference in the longitudinal direction of the heating roller 40, with the temperature at the edge being higher than the temperature at the center. This temperature difference is detected by the temperature sensors 47a and 47b. Therefore, when the temperature sensors 47a and 47b detect a temperature difference, the control unit 60 controls the heater 43b on and off to heat only the center of the heating roller 40 and eliminate the temperature difference in the longitudinal direction of the heating roller 40.

[0042] Furthermore, the control unit 60 is connected to a temperature measurement sensor 49 that is provided outside the fixing device 4 and inside the device body 1a of the image forming apparatus 1. The temperature measurement sensor 49 is an external temperature measurement sensor that measures the external temperature of the fixing device 4. The control unit 60 can detect the external temperature of the fixing device 4 by acquiring the temperature measured by the temperature measurement sensor 49.

[0043] 4 is a diagram showing an example of the configuration of the temperature detection sensor 46. The temperature detection sensor 46 includes a substrate 50, a measurement detection element 51, a compensation detection element 52, and a casing 53. The measurement detection element 51 is an element that detects the surface temperature of the heating member 4a and is configured, for example, by a thermistor. The compensation detection element 52 is an element that detects the environmental temperature in the installation environment of the measurement detection element 51 and is configured, for example, by a thermistor. The measurement detection element 51 and the compensation detection element 52 are mounted on one substrate 50. The casing 53 is arranged to cover the surface of the substrate 50 on which the measurement detection element 51 and the compensation detection element 52 are mounted.

[0044] The casing 53 has an opening 53a at a position corresponding to the detection surface of the measurement detection element 51. The casing 53 guides radiant heat from the heating member 4a to the detection surface of the measurement detection element 51 through the opening 53a. Therefore, the measurement detection element 51 detects the temperature of the heating member 4a based on the radiant heat from the heating member 4a. On the other hand, the casing 53 does not have an opening at a position corresponding to the detection surface of the compensation detection element 52, and covers the compensation detection element 52. Therefore, the casing 53 blocks the radiant heat from the heating member 4a without directing it to the compensation detection element 52. Therefore, the compensation detection element 52 detects the environmental temperature of the environment in which the measurement detection element 51 is installed.

[0045] The control unit 60 controls the temperature of the heating member 4a based on the temperature detected by the temperature detection sensor 46. Figure 5 is a block diagram showing the functional configuration of the control unit 60. The measurement detection element 51 and compensation detection element 52 of the temperature detection sensor 46 each have a resistor whose resistance value changes with temperature. The control unit 60 detects the change in the resistance value and measures the temperature of the heating member 4a.

[0046] As shown in Fig. 5, the resistance value of the measurement detection element 51 is Ra, and the resistance value of the compensation detection element 52 is Rb. However, the measurement detection element 51 and the compensation detection element 52 are configured from the same element. Pull-up resistors 54, 55 are connected to one end of the measurement detection element 51 and the compensation detection element 52, and are connected to a power supply voltage 56 via the pull-up resistors 54, 55. The resistance value of the pull-up resistors 54, 55 is Rc. The other end of the measurement detection element 51 and the compensation detection element 52 is connected to ground.

[0047] The resistance value Ra of the measurement detection element 51 changes depending on the surface temperature of the heating member 4a. Therefore, the voltage Va at the junction between the measurement detection element 51 and the pull-up resistor 54 is a voltage that depends on the surface temperature of the heating member 4a. The measurement detection element 51 outputs the voltage Va as an output voltage.

[0048] The resistance value Rb of the compensation detection element 52 changes depending on the ambient temperature of the environment in which the temperature detection sensor 46 is installed. Therefore, the voltage Vb at the junction between the compensation detection element 52 and the pull-up resistor 55 is a voltage that corresponds to the ambient temperature of the temperature detection sensor 46. The compensation detection element 52 outputs this voltage Vb as an output voltage. The control unit 60 calculates the resistance value of the temperature detection sensor 46 based on these output voltages Va and Vb, and detects the surface temperature of the heating member 4a. The control unit 60 then controls the heating of the heaters 43a and 43b, which are heat sources, based on the surface temperature of the heating member 4a.

[0049] The control unit 60 includes a differential amplifier 61, AD converters 62 and 63, an input / output interface 64, a CPU 65, and a memory 66. The CPU 65 is a hardware processor that reads and executes a program 68 stored in the memory 66. The memory 66 is a non-volatile storage device configured with a ROM or the like. The program 68 to be executed by the CPU 65 is stored in advance in the memory 66. The memory 66 also stores TR characteristic information 69 related to the measurement detection element 51 and the compensation detection element 52. The TR characteristic information 69 is information that defines the relationship between the temperature and resistance value of the measurement detection element 51 and the compensation detection element 52. The input / output interface 64 connects the control unit 27, the temperature measurement sensor 47, and the temperature measurement sensor 49 to the CPU 65.

[0050] The differential amplifier 61 outputs a differential voltage Vc between the output voltage Va of the measurement detection element 51 and the output voltage Vb of the compensation detection element 52. For example, the differential voltage Vc is Vc=Vb−Va.

[0051] The AD converter 62 converts the differential voltage Vc output from the differential amplifier 61 into a digital signal with a predetermined number of bits and outputs it to the CPU 65. The AD converter 63 converts the output voltage Vb of the compensation detection element 52 into a digital signal with a predetermined number of bits and outputs it to the CPU 65.

[0052] The CPU 65 executes the program 68 to function as a temperature detection unit 71 , a heating control unit 72 , and a resistance compensation unit 73 .

[0053] The temperature detection unit 71 detects the surface temperature of the heating member 4a based on the differential voltage Vc and output voltage Vb output from the AD converters 62 and 63. For example, the temperature detection unit 71 calculates the output voltage Va of the measurement detection element 51 based on the differential voltage Vc and output voltage Vb, and determines the resistance value Ra of the measurement detection element 51. For example, the resistance value Ra can be determined by the calculation Ra = Rc·Va / (Vd-Va). After determining the resistance value Ra, the temperature detection unit 71 reads the TR characteristic information 69 from the memory 66 and detects the temperature of the heating member 4a based on the TR characteristic information 69.

[0054] Fig. 6 is a diagram showing an example of TR characteristic information 69. As shown in Fig. 6, the resistance value Ra of the measurement detection element 51 decreases as the temperature of the object to be measured increases. The TR characteristic of the compensation detection element 52 is similar. The temperature detection unit 71 detects the temperature of the heating member 4a corresponding to the resistance value Ra by referring to the TR characteristic information 69 as shown in Fig. 6.

[0055] The heating control unit 72 controls the heaters 43a and 43b based on the temperature of the heating member 4a detected by the temperature detection unit 71 so that the surface temperature of the heating member 4a reaches a predetermined target temperature. For example, the heating control unit 72 constantly monitors the operating state of the image forming apparatus 1 by communicating with the control unit 27. When a print job is executed in the image forming apparatus 1, the heating control unit 72 controls the temperature of the heating member 4a so that it reaches the target temperature for the fixing process. Furthermore, when the image forming apparatus 1 is in a warm-up state, the heating control unit 72 controls the temperature of the heating member 4a so that it reaches the target temperature for the warm-up state. Furthermore, when the image forming apparatus 1 transitions to a power-saving mode, the control unit 60 turns off the heaters 43a and 43b to reduce power consumption in the power-saving mode.

[0056] The resistance values ​​Ra and Rb of the measurement detection element 51 and the compensation detection element 52 change over time. If the resistance values ​​Ra and Rb change over time, the temperature detection unit 71 will no longer be able to correctly detect the temperature of the heating member 4a. To prevent this, the CPU 65 activates the resistance compensation unit 73.

[0057] The resistance compensating unit 73 compensates for changes over time in the resistance values ​​Ra and Rb of the measurement detecting element 51 and the compensation detecting element 52. For example, when a deviation occurs between the resistance value Ra of the measurement detecting element 51 and the resistance value Rb of the compensation detecting element 52 due to changes over time, the resistance compensating unit 73 performs a process to compensate for the deviation.

[0058] When the heating control of the heaters 43a and 43b is being performed, the temperatures detected by the measurement detection element 51 and the compensation detection element 52 are different. Therefore, even if compensation processing is performed when the heating control of the heaters 43a and 43b is being performed, the discrepancy between the resistance values ​​Ra and Rb cannot be eliminated. Furthermore, even when the heating control of the heaters 43a and 43b is not being performed, if the heating member 4a has not yet cooled down sufficiently, the discrepancy between the resistance values ​​Ra and Rb cannot be eliminated even if compensation processing is performed.

[0059] Therefore, the resistance compensator 73 performs compensation processing when a predetermined compensation condition is met. The compensation condition for performing compensation processing is that the heating element 4a is sufficiently cooled down and the measurement detection element 51 and the compensation detection element 52 are in the same temperature environment. However, it is not possible to directly determine whether the heating element 4a is sufficiently cooled down. Therefore, the resistance compensator 73 determines that the compensation condition is met when, for example, any of the following first to sixth conditions is met.

[0060] The first condition is the timing immediately after power is turned on to the image forming apparatus 1. Immediately after power is turned on to the image forming apparatus 1, it is highly likely that the heating member 4a has cooled down to the same level as the surrounding environment. Therefore, when the first condition is met, the resistance compensation unit 73 determines that the compensation condition is met and executes the compensation process.

[0061] The second condition is the timing before the start of warm-up of the fixing device 4. Before the start of warm-up of the fixing device 4, the heating member 4a may be completely cooled. Therefore, when the second condition is met, the resistance compensation unit 73 determines that the compensation condition is met and executes the compensation process.

[0062] The third condition is that a predetermined time or more has elapsed since the control unit 60 ended the heating control of the heaters 43a, 43b. If a predetermined time or more has elapsed since the heating control of the heaters 43a, 43b ended, the heating member 4a may have cooled down completely. Therefore, when the third condition is met, the resistance compensator 73 determines that the compensation condition is met and executes the compensation process.

[0063] The fourth condition is that the internal temperature of the fixing device 4 detected by the temperature measurement sensor 47 is equal to or lower than a predetermined value. The temperature measurement sensor 47 measures the internal temperature of the fixing device 4 at a position above the heating member 4a. If the temperature above the heating member 4a is equal to or lower than the predetermined value, it is highly likely that the heating member 4a has cooled down. Therefore, when the fourth condition is met, the resistance compensation unit 73 determines that the compensation condition is met and executes compensation processing.

[0064] The fifth condition is that the temperature difference between the internal temperature of fixing device 4 detected by temperature measurement sensor 47 and the external temperature of fixing device 4 detected by temperature measurement sensor 49 is equal to or less than a predetermined value. If the temperature difference between the internal and external temperatures of fixing device 4 is equal to or less than the predetermined value, there is a high possibility that heating member 4a is completely cooled. Therefore, when the fifth condition is met, resistance compensation unit 73 determines that the compensation condition is met and executes compensation processing.

[0065] The sixth condition is that the resistance compensation unit 73 estimates the internal temperature of the heating member 4a and the estimated internal temperature is equal to or lower than a predetermined value. For example, the resistance compensation unit 73 estimates the internal temperature of the heating member 4a based on the control time during which the heating control unit 72 performed the previous heating control on the heaters 43a and 43b and the time elapsed since the previous heating control ended. If the resistance compensation unit 73 estimates that the internal temperature of the heating member 4a is equal to or lower than the predetermined value, it is highly likely that the heating member 4a has cooled down. Therefore, when the estimated internal temperature of the heating member 4a is equal to or lower than the predetermined value, the resistance compensation unit 73 determines that the compensation condition is met and executes compensation processing.

[0066] The resistance compensation unit 73 may determine that the compensation conditions are met when a plurality of conditions selected from the first to sixth conditions described above are met simultaneously.

[0067] Furthermore, even if it is determined that the compensation conditions are met, the resistance compensation unit 73 may not execute the compensation process if a predetermined period of time has not elapsed since the previous compensation process. The predetermined period is set in advance to, for example, one week or one month. By setting such a predetermined period of time, it is possible to prevent the resistance compensation unit 73 from executing the compensation process too frequently.

[0068] When the resistance compensation unit 73 determines that the compensation conditions are met, it executes compensation processing and calculates a correction coefficient for correcting the resistance value of the temperature detection sensor 46. In other words, the resistance compensation unit 73 calculates a correction coefficient for correcting the resistance value when the heating member 4a is sufficiently cooled.

[0069] If the resistance values ​​Ra and Rb of the measurement detection element 51 and the compensation detection element 52 have not changed over time, the two resistance values ​​Ra and Rb will be equal when the heating element 4a has cooled down sufficiently. However, if the resistance values ​​Ra and Rb of the measurement detection element 51 and the compensation detection element 52 have changed over time, a difference will arise between the two resistance values ​​Ra and Rb when the heating element 4a has cooled down sufficiently. In the compensation process, the resistance compensation unit 73 calculates a correction coefficient to correct the difference between the two resistance values ​​Ra and Rb. The compensation process will be described in detail below.

[0070] When the compensation condition is met, the resistance compensation unit 73 determines whether the differential voltage Vc output from the AD converter 62 is greater than 0. If the differential voltage Vc is 0, this means that the two resistance values ​​Ra and Rb are equal. On the other hand, if the differential voltage Vc is greater than 0, this means that there is a difference between the two resistance values ​​Ra and Rb. Therefore, the resistance compensation unit 73 determines whether it is necessary to calculate a correction coefficient based on the differential voltage Vc output from the differential amplifier 61.

[0071] When it is necessary to calculate a correction coefficient, the resistance compensation unit 73 calculates the output voltage Va of the measurement detection element 51 based on the differential voltage Vc and output voltage Vb output from the AD converters 62 and 63, and calculates the resistance value Ra of the measurement detection element 51. For example, the resistance value Ra is calculated by Ra = Rc · Va / (Vd - Va). Furthermore, the resistance compensation unit 73 calculates the resistance value Rb of the compensation detection element 52 based on the output voltage Vb output from the AD converter 63. For example, the resistance value Rb is calculated by Rb = Rc · Vb / (Vd - Vb).

[0072] After calculating the resistance values ​​Ra and Rb, the resistance compensation unit 73 calculates a correction coefficient K based on these resistance values ​​Ra and Rb. For example, the resistance compensation unit 73 calculates the ratio between the resistance values ​​Ra and Rb as the correction coefficient K. For example, the correction coefficient K is K=Rb / Ra. When compensation processing is not performed, the correction coefficient K is held at a value of "1" as an initial value. After calculating the correction coefficient K through compensation processing, the resistance compensation unit 73 updates the correction coefficient K to the calculated value.

[0073] Furthermore, the resistance compensation unit 73 may limit the range of the correction coefficient K to a predetermined range. For example, if the calculated correction coefficient K is less than 1, the resistance compensation unit 73 sets the correction coefficient K to 1. For example, if the calculated correction coefficient K exceeds a predetermined upper limit value (e.g., 1.08), the resistance compensation unit 73 sets the correction coefficient K to the upper limit value (e.g., 1.08). By limiting the range of the correction coefficient K in this way, the resistance compensation unit 73 can prevent excessive correction from being performed.

[0074] The updated correction coefficient K is used when the temperature detection unit 71 subsequently detects the temperature of the heating member 4a. That is, after calculating the output voltage Va of the measurement detection element 51 to determine the resistance value Ra of the measurement detection element 51, the temperature detection unit 71 corrects the resistance value Ra with the correction coefficient K. For example, the temperature detection unit 71 corrects the resistance value Ra by multiplying the calculated resistance value Ra by the correction coefficient K. The temperature detection unit 71 then detects the temperature of the heating member 4a using the corrected resistance value Ra. This allows the temperature detection unit 71 to accurately detect the temperature of the heating member 4a.

[0075] Next, an example of a processing procedure performed by the CPU 65 of the control unit 60 will be described. Figures 7 to 9 are flowcharts showing an example of a processing procedure performed by the CPU 65 of the control unit 60. This processing is executed by the CPU 65 when the image forming apparatus 1 is powered on.

[0076] When the CPU 65 starts the processing based on the flowchart, it puts the resistance compensation unit 73 into operation and determines whether the above-described compensation conditions are met (step S10). That is, the resistance compensation unit 73 determines whether the compensation conditions are met by determining whether the above-described first to sixth conditions are met. If the compensation conditions are met (YES in step S10), the resistance compensation unit 73 executes resistance compensation processing (step S11). Details of this resistance compensation processing will be described later. If the compensation conditions are not met (NO in step S10), the resistance compensation unit 73 does not execute resistance compensation processing.

[0077] Next, CPU 65 determines whether or not the image forming apparatus 1 is in the power saving mode (step S12). If the image forming apparatus 1 is not in the power saving mode (NO in step S12), CPU 65 activates the temperature detection unit 71 and the heating control unit 72 to start warming up the fixing device 4 (step S13). For example, immediately after the image forming apparatus 1 is powered on, the image forming apparatus 1 is not in the power saving mode. Therefore, CPU 65 determines that the image forming apparatus 1 is not in the power saving mode and starts warming up.

[0078] If the image forming apparatus 1 is in the power saving mode (YES in step S12), the CPU 65 determines whether it is time to return from the power saving mode (step S14). The timing for returning from the power saving mode may be, for example, when the image forming apparatus 1 receives a print job via the network. If it is not time to return from the power saving mode (NO in step S14), the processing by the CPU 65 returns to step S10.

[0079] If it is time to return from the power saving mode (YES in step S14), the CPU 65 activates the resistance compensation unit 73. The resistance compensation unit 73 then determines whether the above-described compensation conditions are met (step S15). That is, the resistance compensation unit 73 determines whether the compensation conditions are met by determining whether the above-described first to sixth conditions are met. If the compensation conditions are met (YES in step S15), the resistance compensation unit 73 executes resistance compensation processing (step S16). Details of this resistance compensation processing will be described later. If the compensation conditions are not met (NO in step S15), the resistance compensation unit 73 does not execute resistance compensation processing. The CPU 65 then activates the temperature detection unit 71 and the heating control unit 72 to start warming up the fixing device 4 (step S13).

[0080] After starting the warm-up of the fixing device 4, the CPU 65 determines whether or not the control unit 27 will start executing a print job (step S17). If the control unit 27 will start executing a print job (YES in step S17), the CPU 65 executes heating control of the heaters 43a and 43b (step S18).

[0081] 8 is a flowchart showing an example of a detailed processing procedure of the heating control (step S18). When the CPU 65 starts the heating control, it first activates the temperature detection unit 71. The temperature detection unit 71 first acquires the differential voltage Vc (step S30). Next, the temperature detection unit 71 acquires the output voltage Vb (step S31). Then, the temperature detection unit 71 calculates the resistance value Ra of the measurement detection element 51 based on the differential voltage Vc and the output voltage Vb (step S32).

[0082] After calculating the resistance value Ra, the temperature detection unit 71 reads out the current correction coefficient K (step S33). Then, the temperature detection unit 71 corrects the calculated resistance value Ra with the correction coefficient K (step S34). Note that if the correction coefficient K is 1, the resistance value Ra is not corrected in step S34.

[0083] Next, the temperature detection unit 71 reads out the TR characteristic information 69 from the memory 66 (step S35). Then, the temperature detection unit 71 identifies the temperature corresponding to the resistance value Ra of the measurement detection element 51, and detects the identified temperature as the temperature of the heating member 4a (step S36).

[0084] Next, the CPU 65 activates the heating control unit 72. The heating control unit 72 determines the control amount of the heaters 43a, 43b based on the temperature of the heating member 4a detected by the temperature detection unit 71. This control amount is, for example, a duty ratio for controlling the on / off of the heaters 43a, 43b. The heating control unit 72 controls the heaters 43a, 43b based on the control amount (step S38).

[0085] Returning to the flowchart of Fig. 7, the temperature detection unit 71 and the heating control unit 72 repeatedly execute the heating control process (step S18) as described above until the execution of the print job is completed (step S19). When the execution of the print job is completed (YES in step S19), the temperature detection unit 71 and the heating control unit 72 transition the fixing device 4 to a warm-up state (step S20). Thereafter, the process by the CPU 65 returns to step S10.

[0086] On the other hand, if execution of a print job is not started (NO in step S17), CPU 65 determines whether or not control unit 27 will transition to power saving mode (step S21). For example, if a predetermined time has passed without a print job being executed, control unit 27 will initiate processing to transition to power saving mode. CPU 65 determines whether or not control unit 27 will perform processing to transition to power saving mode. If transition to power saving mode is not being executed (NO in step S21), processing by CPU 65 returns to step S17, and the device enters a state of waiting for execution of a print job.

[0087] When the control unit 27 performs the process of transitioning to the power saving mode (YES in step S21), the CPU 65 ends the warm-up of the fixing device 4 (step S22). This stops the heating process of the heating member 4a. Therefore, after the warm-up ends, the temperature of the fixing device 4 gradually drops. Thereafter, the process by the CPU 65 returns to step S10, and the above-mentioned process is repeated.

[0088] In the above process, the CPU 65 determines whether or not a predetermined compensation condition is met each time (steps S10 and S15). As a result, if the predetermined compensation condition is met (YES in step S10 or S15), the CPU 65 executes the resistance compensation process (steps S11 and S16). For example, the CPU 65 executes the resistance compensation process (S11 and S16) when the heating member 4a is sufficiently cooled.

[0089] 9 is a flowchart showing an example of a detailed processing procedure of the resistance compensation process (steps S11 and S16). When the CPU 65 starts the resistance compensation process, it puts the resistance compensation unit 73 into operation. The resistance compensation unit 73 acquires the differential voltage Vc (step S40). The resistance compensation unit 73 determines whether the acquired differential voltage Vc is greater than 0 (step S41). If the differential voltage Vc is not 0 when the heating member 4a is sufficiently cooled, it means that a difference has occurred between the resistance values ​​Ra and Rb due to changes over time. On the other hand, if the differential voltage Vc is 0, it means that the resistance values ​​Ra and Rb have not changed over time.

[0090] If the differential voltage Vc is not greater than 0 (NO in step S41), the resistance compensation unit 73 determines that there is no need to compensate for the resistance value, and in this case, the resistance compensation process ends.

[0091] If the differential voltage Vc is greater than 0 (YES in step S41), the resistance compensator 73 acquires the output voltage Vb (step S42). Then, the resistance compensator 73 calculates the resistance value Ra of the measurement detection element 51 based on the differential voltage Vc and the output voltage Vb (step S43). The resistance compensator 73 also calculates the resistance value Rb of the compensation detection element 52 based on the output voltage Vb (step S44).

[0092] After calculating the resistance values ​​Ra and Rb, the resistance compensation unit 73 calculates a correction coefficient K (step S45). Then, the resistance compensation unit 73 updates the correction coefficient K (step S46). When the correction coefficient K is read out in the subsequent heating process (step S18), the correction coefficient K updated in step S46 is read out.

[0093] As described above, the fixing device 4 of this embodiment includes a heating control unit 72 that calculates the resistance value of the temperature detection sensor 46 based on the output voltage of the temperature detection sensor 46, detects the temperature of the heating member 4a, and controls the heating of the heaters 43a and 43b, which are heat sources. When a predetermined compensation condition is met, the fixing device 4 executes a resistance compensation process to correct the resistance value of the temperature detection sensor 46 based on the output voltage of the temperature detection sensor 46, and calculates a correction coefficient K. When detecting the temperature of the heating member 4a, the heating control unit 72 corrects the resistance value of the temperature detection sensor 46 using the correction coefficient K calculated by the resistance compensation process. According to this fixing device 4, even if the resistance value of the temperature detection sensor 46 changes over time, the resistance value of the temperature detection sensor 46 can be corrected using the correction coefficient K calculated by the resistance compensation process. Therefore, the fixing device 4 can perform heating control while detecting the correct temperature of the heating member 4a, even if the resistance value of the temperature detection sensor 46 changes over time.

[0094] (Variation) Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible.

[0095] For example, in the above embodiment, the control unit 60 that controls the heaters 43a and 43b, which are heat sources, is provided in the fixing device 4. However, the above-described control unit 60 is not limited to being provided in the fixing device 4. For example, the control unit 60 may be provided outside the fixing device 4, in the device main body 1a of the image forming apparatus 1.

[0096] In the above embodiment, the heating member 4a is described as including the heating roller 40 and the heating belt 41. However, the heating member 4a is not limited to such a configuration. For example, the heating member 4a may be configured to include only the heating roller 40. In this case, the heating roller 40 forms a nip portion with the pressure roller 45. [Explanation of symbols]

[0097] 1. Image forming device 3 Image forming unit 4 Fixing device 4a Heating element 4b Pressure member 9 sheets 43a, 43b Heater (heat source) 46 Temperature detection sensor 47 Temperature measurement sensor (internal temperature measurement sensor) 49 Temperature measurement sensor (external temperature measurement sensor) 51 Measuring detector element 52 Compensation detection element 53 Casing 60 Control Unit 65 CPU 71 Temperature detection unit 72 Heating control section 73 Resistance compensation section

Claims

1. a heating element provided with a heat source; a temperature detection sensor that changes its resistance value in response to the temperature of the heating member; a control unit that calculates a resistance value of the temperature detection sensor based on an output voltage of the temperature detection sensor, detects the temperature of the heating element, and controls heating of the heat source; a resistance compensation unit that calculates a correction coefficient for correcting a resistance value of the temperature detection sensor based on an output voltage of the temperature detection sensor when a predetermined compensation condition is met; Equipped with The fixing device according to claim 1, wherein the control unit corrects the resistance value of the temperature detection sensor using the correction coefficient calculated by the resistance compensation unit when detecting the temperature of the heating member.

2. the temperature detection sensor has a measurement detection element that detects the surface temperature of the heating member and a compensation detection element that detects the environmental temperature, 2. The fixing device according to claim 1, wherein the resistance compensator calculates the correction coefficient when there is a difference between the output voltage of the measurement detection element and the output voltage of the compensation detection element.

3. 3. The fixing device according to claim 2, wherein, when there is a difference between the output voltage of the measurement detection element and the output voltage of the compensation detection element, the resistance compensation unit calculates a first resistance value, which is the resistance value of the measurement detection element, from the output voltage of the measurement detection element, and calculates a second resistance value, which is the resistance value of the compensation detection element, from the output voltage of the compensation detection element, and calculates the ratio of the first resistance value to the second resistance value as the correction coefficient.

4. the temperature detection sensor has a casing that holds the measurement detection element and the compensation detection element, The fixing device according to claim 2, wherein the casing has an opening at a position corresponding to the measurement detection element to guide radiant heat from the heating member to the measurement detection element, while covering a position corresponding to the compensation detection element to block radiant heat from the heating member.

5. 2. The fixing device according to claim 1, wherein the resistance compensating section calculates the correction coefficient when a predetermined time has elapsed since the control section finished controlling the heating of the heat source.

6. 2. The fixing device according to claim 1, wherein the resistance compensator calculates the correction coefficient before the controller starts warming up the heat source.

7. an internal temperature measurement sensor for measuring the temperature inside the fixing device; Further provided with 2. The fixing device according to claim 1, wherein the resistance compensator calculates the correction coefficient when the temperature measured by the internal temperature sensor is equal to or lower than a predetermined value.

8. an internal temperature measuring sensor for measuring an internal temperature inside the fixing device; an external temperature measuring sensor for measuring an external temperature outside the fixing device; Further provided with 2. The fixing device according to claim 1, wherein the resistance compensator calculates the correction coefficient when the temperature difference between the internal temperature and the external temperature is equal to or smaller than a predetermined value.

9. 2. The fixing device according to claim 1, wherein the resistance compensator estimates an internal temperature of the heating member, and calculates the correction coefficient when it estimates that the internal temperature of the heating member is equal to or lower than a predetermined temperature.

10. The fixing device according to claim 9, wherein the resistance compensation unit estimates the internal temperature of the heating member based on the control time during which the control unit performed the previous heating control on the heat source and the elapsed time since the previous heating control ended.

11. an image forming unit that forms an image on a sheet; a fixing device according to any one of claims 1 to 10; Equipped with an image forming apparatus, wherein a sheet on which an image has been formed in the image forming section is conveyed to the fixing device, and the image is fixed on the sheet in the fixing device;

12. a heating element provided with a heat source; a temperature detection sensor that changes its resistance value in response to the temperature of the heating member; A method for controlling a fixing device comprising: a control step of calculating a resistance value of the temperature detection sensor based on an output voltage of the temperature detection sensor, detecting a temperature of the heating element, and controlling heating of the heat source; a resistance compensation step of calculating a correction coefficient for correcting a resistance value of the temperature detection sensor based on an output voltage of the temperature detection sensor when a predetermined compensation condition is met; and The control method is characterized in that the control step corrects the resistance value of the temperature detection sensor using the correction coefficient calculated in the resistance compensation step when detecting the temperature of the heating member.

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