JP6303855B2 - Fixing apparatus and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus including a first rotating body heated by a heating device and a second rotating body pressed against the first rotating body.

  2. Description of the Related Art An electrophotographic image forming apparatus includes a fixing device that fixes a toner image transferred onto a printing paper (transfer sheet) onto the printing paper. The fixing device includes a heating roller (first rotating body) and a pressure roller (second rotating body), and these rollers are rotatably supported while being pressed against each other. When the printing paper is passed between the heating roller and the pressure roller, heat is transmitted from the heating roller at that time, whereby the toner constituting the toner image is melted to the printing paper. The image is fixed.

  In order to melt the toner, it is necessary to control the heating by the heating device and maintain the heating roller at an appropriate temperature (fixing temperature). For this reason, the fixing device is provided with a non-contact type temperature sensor (hereinafter abbreviated as a non-contact sensor) that detects the temperature of the heating roller, and the detected temperature of the non-contact sensor becomes the fixing temperature. Thus, the temperature of the heating roller is controlled.

  A radiation temperature sensor such as a thermopile is known as the non-contact sensor. The radiation temperature sensor measures the temperature of the object by measuring the intensity of the electromagnetic wave emitted from the object. In the radiation temperature sensor, when the input window to which electromagnetic waves are input becomes dirty or the emissivity from the object changes, the detection temperature is distorted. Therefore, conventionally, a contact type temperature sensor (hereinafter abbreviated as a contact sensor) that detects the temperature of the non-sheet passing region of the heating roller is separately provided in the fixing device, and the detection of the non-contact sensor based on the detection temperature of the contact sensor. The temperature is corrected (see Patent Document 1).

JP 2007-316169A

  However, in the conventional temperature correction, the temperature of the non-sheet passing area on the heating roller is detected by a contact sensor, and the temperature of the sheet passing area on the heating roller is detected by a non-contact sensor. The paper passing area is an area where the temperature is deprived due to the passing of printing paper, but the non-paper passing area is not an area where the temperature is deprived by passing the printing paper. As described above, the temperature state in each region differs between the region with a temperature drop and the region without a temperature drop. For this reason, even if the non-contact sensor that detects the temperature of the other region is corrected based on the temperature of one region having different temperature conditions, there is a possibility that sufficient correction is not performed. Further, even if the temperature detected by the non-contact sensor is corrected in consideration of the temperature gradient between the non-sheet passing area and the sheet passing area, the temperature gradient changes due to dirt or deterioration of the sheet passing area. Therefore, the correction cannot be performed accurately due to the change in the temperature gradient itself.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fixing device capable of correcting a temperature detected by a non-contact type temperature detection unit with high accuracy and an image forming apparatus including the same. It is to provide.

  A fixing device according to one aspect of the present invention includes a first rotating body, a second rotating body, a first temperature detecting unit, and a second temperature detecting unit. The first rotating body is heated by a heating device, and is configured to be able to contact the transfer sheet. The second rotating body is configured to be capable of forming a nip portion that is pressed against the first rotating body and can pass through the transfer sheet. The first temperature detector is used for temperature control of the first rotating body by the heating device. The first temperature detection unit is a non-contact type that detects a temperature of a first detection point in a contact area of the first rotating body with which the transfer sheet contacts. The second temperature detector is used to correct the first temperature detected by the first temperature detector. The second temperature detector is a contact type that detects the temperature of a second detection point defined on the circumference of the first rotating body that passes through the first detection point.

  An image forming apparatus according to another aspect of the present invention includes the fixing device.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to correct | amend the temperature detected by the non-contact-type temperature detection part with high precision.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a configuration of a fixing device according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration of a heating roller of the fixing device illustrated in FIG. 2. FIG. 2 is a block diagram illustrating a configuration of a control unit included in the image forming apparatus illustrated in FIG. 1. It is a flowchart which shows the procedure of the temperature correction process performed by the control part shown in FIG.

  Embodiments of the present invention will be described below with reference to the drawings as appropriate. In addition, the following embodiment is only an example which actualized this invention, and does not limit the technical scope of this invention.

[Image forming apparatus 10]
FIG. 1 is a schematic diagram illustrating a schematic configuration of an image forming apparatus 10 (an example of an image forming apparatus) according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 10 is a so-called tandem color image forming apparatus, and includes a plurality of image forming units 1 to 4, an intermediate transfer belt 5, a resist detection sensor 6, and a driving roller 7A. A driven roller 7B, an exposure device 14, a secondary transfer device 15, a fixing device 16 (an example of a fixing device), a control unit 8, a paper feed tray 17, and a paper discharge tray 18. . A specific example of the image forming apparatus 10 according to the embodiment of the present invention is, for example, a printer, a copying machine, a facsimile, or a multifunction machine having these functions. The image forming apparatus 10 can form a color image. However, the image forming apparatus of the present invention may be configured to form a monochrome image.

  The image forming units 1 to 4 form toner images of different colors on each of the plurality of photosensitive drums 21 arranged in parallel by a so-called electrophotographic system, and the toner images are transferred to the intermediate transfer belt 5 that is running (moving). Sequentially superimpose and transfer. In the example shown in FIG. 1, in order from the downstream side in the moving direction (arrow 19 direction) of the intermediate transfer belt 5, an image forming unit 1 for black, an image forming unit 2 for yellow, an image forming unit 3 for cyan, The magenta image forming units 4 are arranged in a line in that order.

  Each of the image forming units 1 to 4 includes a photosensitive drum 21 that carries a toner image, a charging device 22, a developing device 23, a primary transfer device 24, and the like. The exposure device 14 forms an electrostatic latent image by exposing the surface of the charged photosensitive drum 21 and scanning the light. The developing device 23 develops the electrostatic latent image with toner. Then, the toner image on the photosensitive drum 21 is transferred to the intermediate transfer belt 5 by the primary transfer device 24.

  The intermediate transfer belt 5 is an endless annular belt in which an elastic layer such as polyimide resin or urethane rubber and a release layer such as fluorine resin are laminated. The intermediate transfer belt 5 is supported by a driving roller 7A and a driven roller 7B so as to be rotationally driven. By being supported by the driving roller 7 </ b> A and the driven roller 7 </ b> B, the intermediate transfer belt 5 can move while its surface is in contact with the surface of each photosensitive drum 21. Then, when the surface of the intermediate transfer belt 5 passes between the photosensitive drums 21 and the primary transfer device 24, the toner images are sequentially superimposed and transferred from the photosensitive drums 21.

  The secondary transfer device 15 transfers the toner image transferred to the intermediate transfer belt 5 onto the printing paper (an example of a transfer sheet) conveyed from the paper feed tray 17. The printing paper on which the toner image is transferred is conveyed to the fixing device 16 by a conveyance unit (not shown).

[Fixing device 16]
Hereinafter, the fixing device 16 will be described with reference to FIGS. 1 to 3. Here, FIG. 3 is a diagram showing the arrangement positions of the heating roller 71 and the temperature sensors 78A and 78B.

  As shown in FIG. 2, the fixing device 16 includes a heating roller 71 (an example of a first rotating body), a pressure roller 72 (an example of a second rotating body), and a first temperature sensor 78A (first temperature detection). Part) and a second temperature sensor 78B (an example of the second temperature detection part). Further, the fixing device 16 includes a displacement portion 95 (an example of a displacement portion) that displaces the second temperature sensor 78B. Hereinafter, the first temperature sensor 78A and the second temperature sensor 78B may be collectively referred to as temperature sensors 78A and 78B.

  The heating roller 71 has a roller body 71A formed in a cylindrical shape. The outer peripheral surface (roller surface) of the roller body 71A is brought into contact with the transfer surface (the surface on which the toner image is attached) of the printing paper at the time of fixing. The roller body 71A is made of a material having high thermal conductivity, and is made of a metal such as aluminum, for example. Support shafts 71B (see FIG. 3) are attached to both ends of the roller main body 71A as rotation shafts during rotation. The support shaft 71B is rotatably supported by a frame (not shown) of the fixing device 16. Thereby, the heating roller 71 becomes rotatable. As shown in FIG. 1, the heating roller 71 is disposed closer to the intermediate transfer belt 5 than the printing paper conveyance path (the path indicated by the broken line arrow in FIG. 1), and the outer peripheral surface of the roller body 71A is printed. It is arranged at a position where it can come into contact with the transfer surface of the paper.

  As shown in FIG. 2, the heating roller 71 includes a main heater 75 and a sub heater 76. The main heater 75 and the sub heater 76 are an example of a heating device. The main heater 75 and the sub heater 76 are provided inside the heating roller 71. The roller main body 71A of the heating roller 71 is heated from the inside by the main heater 75 and the sub heater 76. The main heater 75 is for heating the central portion 80C of the roller body 71A. The sub-heater 76 is for heating the end portion 80E (see FIG. 3) on the outer side in the axial direction from the central portion 80C (see FIG. 3) of the roller body 71A. Each of the main heater 75 and the sub heater 76 has a heat generating part such as a halogen lamp arranged corresponding to a region to be heated. In addition, the said heating apparatus is not restricted to what consists of the main heater 75 and the sub heater 76, You may consist only of one heater.

  The roller body 71 </ b> A is formed to have a length that can be contacted with the maximum width printing paper that can be fixed by the fixing device 16. In this embodiment, A3 size (420 mm × 297 mm) printing paper can be fixed by the fixing device 16, and the roller body 71 </ b> A is formed to be longer than the A3 size short dimension (297 mm). For this reason, the outer peripheral surface (roller surface) of the roller body 71A has a contact area R1 (see FIG. 3) where the printing paper is contacted during fixing, and a non-contact area R2 (see FIG. 3) where the printing paper is not contacted during fixing. And exist.

  The pressure roller 72 is disposed to face the heating roller 71. The pressure roller 72 is parallel to the heating roller 71 and is rotatably supported in a state of being pressed against the surface of the heating roller 71. The pressure roller 72 has a support shaft 72 </ b> A at the center, and the support shaft 72 </ b> A is rotatably supported by a frame (not shown) of the fixing device 16. Thereby, the pressure roller 72 can be rotated. The pressure roller 72 is connected to a motor 67 (see FIG. 4) that is driven and controlled by a motor driver 66 (see FIG. 4) of the control unit 8 via a drive transmission mechanism (not shown). When the motor 67 is rotationally driven, the pressure roller 72 is transmitted with the rotational driving force and rotates in a predetermined direction. In the present embodiment, the pressure roller 72 is rotated in the clockwise direction (the direction of the arrow 47) in FIG. The support shaft 72A of the pressure roller 72 is provided with a cylindrical elastic portion 72B made of elastic silicon or porous rubber. The pressure roller 72 is elastically biased toward the heating roller 71 by a spring (not shown) and is pressed against the heating roller 71. As a result, the elastic portion 72B is elastically deformed by the roller body 71A to form a nip portion 82 that is recessed in a curved shape. The printing paper is conveyed while being nipped in the nip portion 82. That is, the nip portion 82 is configured to allow printing paper to pass therethrough.

  In the fixing device 16, the printing paper is conveyed so as to pass through the nip portion 82 from the bottom to the top. A frictional force is generated in the nip portion 82 by the pressure contact of the pressure roller 72 that is rotationally driven. Due to this frictional force, the heating roller 71 is driven to rotate counterclockwise (in the direction of the arrow 46) in FIG. For this reason, the printing paper that has entered the nip portion 82 is conveyed upward while being supplied with heat from the heating roller 71 while being sandwiched between the heating roller 71 and the pressure roller 72. At this time, the heat supplied from the heating roller 71 melts the toner image on the printing paper and fixes it on the printing paper.

  The temperature sensors 78A and 78B are for detecting the surface temperature of the heating roller 71. Specifically, the temperature sensors 78A and 78B are used to detect the temperature of the contact region R1 (see FIG. 3) on the outer peripheral surface of the roller body 71A. The temperature sensors 78A and 78B are provided around the heating roller 71. The first temperature sensor 78 </ b> A is attached to a bracket 79 provided below the heating roller 71. The second temperature sensor 78 </ b> B is attached to the bracket 79 via the displacement portion 95. The temperature sensors 78 </ b> A and 78 </ b> B are disposed upstream of the nip portion 82, which is a contact portion between the heating roller 71 and the pressure roller 72, as indicated by an arrow 46. Accordingly, the temperature sensors 78A and 78B can detect the surface temperature of the heating roller 71 before the heat is removed from the printing paper at the nip portion 82.

  The first temperature sensor 78A is a non-contact temperature sensor. As shown in FIG. 3, the first temperature sensor 78 </ b> A is disposed at the center in the axial direction of the heating roller 71. A non-contact type temperature sensor detects the surface temperature of an object by measuring electromagnetic waves such as infrared rays emitted from the object (detection target), and is, for example, a thermopile. The first temperature sensor 78A is arranged so that the sensor head 87 for detecting the infrared rays faces the outer peripheral surface of the roller body 71A. The sensor head 87 is provided with a condensing lens for condensing the infrared light, and detects the infrared light through the condensing lens. The sensor signal output from the first temperature sensor 78A is sent to the sensor processing unit 69 of the control unit 8, and the control unit 8 calculates the surface temperature of the roller body 71A based on the sensor signal. The calculated temperature is used for temperature control of the heating roller 71 by the main heater 75 and the sub heater 76 (S20 in FIG. 5). The first temperature sensor 78A may be of any type as long as it is a non-contact type used for detecting the surface temperature of the heating roller 71.

  The second temperature sensor 78B is a contact type temperature sensor. As shown in FIG. 3, the second temperature sensor 78 </ b> B is disposed at the center in the axial direction of the heating roller 71. The contact-type temperature sensor includes a contact portion 88 including a thermal element that is brought into contact with an object (detection target), and the contact portion of the object is changed based on the change in resistance of the thermal element upon receiving heat. The temperature is detected, for example, a thermistor, a resistance temperature detector, a thermocouple, or the like. The second temperature sensor 78B is attached to the bracket 79 with the contact portion 88 in contact with the outer peripheral surface of the roller body 71A. The sensor signal output from the second temperature sensor 78B is sent to the sensor processing unit 69 of the control unit 8, and the control unit 8 calculates the surface temperature of the roller body 71A based on the sensor signal. The temperature calculated in this way is used for correction of the temperature calculated using the first temperature sensor 78A (S19 in FIG. 5). The second temperature sensor 78B can be of any type as long as it is a contact type used for detecting the surface temperature of the heating roller 71.

  The first temperature sensor 78 </ b> A is arranged so as to be able to detect the temperature of the first detection point 91 defined on the outer peripheral surface of the roller body 71 </ b> A of the heating roller 71. In the present embodiment, as shown in FIG. 2, the first detection point 91 is a position vertically below the center of the roller main body 71A on the outer peripheral surface of the roller main body 71A (a position where the center line and the outer peripheral surface are within tolerance). ) Is set. More specifically, as shown in FIG. 3, the first detection point 91 is located in the contact region R1 on the outer peripheral surface of the roller body 71A and at the center of the roller body 71A in the axial direction. Yes.

  The second temperature sensor 78B is arranged so as to be able to detect the temperature of the second detection point 92 defined on the outer peripheral surface of the roller body 71A of the heating roller 71. In the present embodiment, as shown in FIG. 2, the second detection point 92 is set on the same circumference of the roller body 71A passing through the first detection point 91 on the outer peripheral surface of the roller body 71A. More specifically, as shown in FIG. 3, the second detection point 92 is on the same circumference passing through the first detection point 91, and the rotation direction of the heating roller 71 from the first detection point 91 (arrow 46). Is set at a position spaced a predetermined distance D to the upstream side in the direction of

  Here, the distance D is a distance such that the second temperature sensor 78B does not interfere with temperature detection by the first temperature sensor 78A. The smaller the interval D, the smaller the post-temperature measurement difference caused by the interval D, so that the temperature correction described later is performed with high accuracy. Therefore, it is desirable that the first detection point 91 and the second detection point 92 are close to each other on the same circumference. However, the distance D between the first detection point 91 and the second detection point 92 is affected by the viewing angle of the first temperature sensor 78A, the emissivity at the first detection point 91, and the like. Therefore, the interval D is preferably set to the minimum interval that does not interfere most, based on the viewing angle and emissivity.

  As described above, the fixing device 16 is provided with the displacement portion 95. As shown in FIG. 2, the displacement portion 95 is fixed to the bracket 79. The displacement unit 95 is, for example, a solenoid in which the plunger 96 is displaced in the axial direction on condition that a drive signal is input. A second temperature sensor 78B is fixed to the tip of the plunger 96. For this reason, when the plunger 96 is displaced, the second temperature sensor 78 </ b> B is also displaced to a position corresponding to the position of the plunger 96. Specifically, the displacement part 95 displaces the 2nd temperature sensor 78B to the separation position shown with a broken line in FIG. 2, and the contact position shown with the continuous line in FIG. The separation position is a position where the contact portion 88 is separated from the second detection point 92 and away from the contact region R1. The contact position is a position where the contact portion 88 contacts the second detection point 92. The displacement part 95 is drive-controlled by the control part 8 so that it may mention later. In the present embodiment, when the heating roller 71 is rotated (rotation state) by the drive control by the control unit 8, the displacement unit 95 sets the second temperature sensor 78B to the separation position. Further, when the heating roller is not rotating and is in a stopped state (non-rotating state), the displacement unit 95 brings the second temperature sensor 78B to the contact position.

[Control unit 8]
The control unit 8 controls the image forming apparatus 10 in an integrated manner. As shown in FIG. 4, the control unit 8 includes a CPU 61, a ROM 62, and a RAM 63, a motor driver 66, a PID control unit 65, and correction control. Part 68, sensor processing part 69, and the like. The calculation unit 64 executes various processes according to a predetermined program stored in the ROM 62 by the CPU 61. In addition, the PID control unit 65 receives the control signal from the calculation unit 64 and thereby drives the main heater 75 and the sub heater 76 to control the surface temperature of the heating roller 71, which will be described later. The temperature control unit of the present invention is realized by the calculation unit 64 and the PID control unit 65 of the control unit 8. The correction control unit 68 receives the control signal from the calculation unit 64 and corrects the temperature (calculation result) calculated based on the output of the first temperature sensor 78A in the sensor processing unit 69. The calculation unit 64 and the correction control unit 68 implement the correction control unit of the present invention.

  In the present embodiment, data used for a temperature correction process (see FIG. 5) described later is stored in the ROM 62. For example, the ROM 62 stores threshold values such as the duty ratio of the drive current used in the temperature control (PID control) in step S20 and the set temperature used in step S12 in the flowchart of FIG.

  The motor driver 66, the sensor processing unit 69, and the correction control unit 68 are configured by an electronic circuit such as an integrated circuit (ASIC) or an internal memory, for example. The motor driver 66 and the sensor processing unit 69 are not limited to those configured by an electronic circuit such as an integrated circuit (ASIC), and may be realized by executing a predetermined program by the CPU 61, for example.

  The motor driver 66 is electrically connected to the motor 67. The motor driver 66 drives and controls the motor 67 based on the instruction signal from the calculation unit 64. Thereby, the rotational drive of the pressure roller 72 is controlled.

  The sensor processing unit 69 converts the sensor signal input from the temperature sensors 78A and 78B into a digital signal, and calculates a temperature value corresponding to each signal based on the converted signal. Specifically, the temperature values of the surface temperatures of the first detection point 91 and the second detection point 92 of the heating roller 71 detected using the temperature sensors 78A and 78B are calculated. Hereinafter, the temperature value calculated as the surface temperature of the first detection point 91 is referred to as a first temperature T1. Further, the temperature value calculated as the surface temperature of the second detection point 92 is referred to as a second temperature T2. The calculated temperature information is sent to the calculation unit 64.

  The correction control unit 68 corrects the first temperature T1 based on the second temperature T2 calculated by the sensor processing unit 69. Specifically, when there is a positive temperature difference ΔT obtained by subtracting the first temperature T1 from the second temperature T2, a correction is performed to add the temperature difference ΔT to the first temperature T1.

  The PID control unit 65 is electrically connected to the calculation unit 64. The temperature control of the heating roller 71 using the main heater 75 and the sub heater 76 by the PID control unit 65 is performed by a control signal from the calculation unit 64. The calculation unit 64 sends the target temperature used for PID control by the PID control unit 65, the duty ratio used for PID control, and the like to the PID control unit 65 as the control signal. Here, the target temperature is a temperature that can be fixed by the fixing device 16 (so-called fixing temperature). The PID control unit 65 performs the temperature control based on the first temperature T1 corrected by the correction control unit 68. Specifically, the PID control unit 65 controls the temperature of the heating roller 71 by controlling the main heater 75 and the sub heater 76 so that the first temperature T1 becomes the target temperature.

  The control unit 8 is electrically connected to the displacement unit 95. The control unit 8 drives and controls the displacement unit 95 by sending a drive signal to the displacement unit 95. For example, when the displacement part 95 is a solenoid, the plunger 95 is displaced according to the output or stop of the drive signal.

[Temperature correction processing]
Next, an example of a temperature correction process performed by the control unit 8 will be described with reference to the flowchart of FIG. In the figure, S11, S12,... Represent processing procedure (step) numbers. Processing in each step is performed by the control unit 8, more specifically, when the CPU 61 of the calculation unit 64 executes a program in the ROM 62, by the PID control unit 65, or by the correction control unit 68.

  When a print job is input from the outside, the control unit 8 shifts to a normal operation mode, controls driving of the heaters 75 and 76 of the heating roller 71, and starts temperature control. On the other hand, when the print job is not input for a predetermined time, the driving of the heaters 75 and 76 is stopped and the mode is shifted to the power saving mode. In the present embodiment, in step S11, the control unit 8 determines whether it is a predetermined temperature correction timing in any operation mode. The temperature correction timing is, for example, when a predetermined number of prints have been performed, when a predetermined time has elapsed, or when shifting from the power saving mode to the normal operation mode, when a predetermined number of images are formed with a density exceeding the threshold value. When it is performed continuously, it can be considered. These timings are timings at which the sensor head 87 of the first temperature sensor 78A may have been contaminated to such an extent that the temperature detection accuracy is lowered, or the contact region R1 of the roller body 71A is deteriorated. This is the timing that may have occurred. That is, this timing is a timing for determining whether or not it is necessary to correct the first temperature T1 in step S19 described later.

  In the next step S12, the control unit 8 calculates the first temperature T1, and determines whether or not the first temperature T1 is equal to or higher than a preset temperature. The set temperature is, for example, a temperature that can be fixed in the fixing device 16 (so-called fixing temperature), and is the target temperature. The first temperature sensor 78A is used for temperature control so that the temperature of the heating roller 71 becomes the fixing temperature, and a sensor having high resolution near the fixing temperature is employed. For this reason, the determination process in step S12 is performed in order to perform a temperature correction described later near the fixing temperature. The set temperature is not limited to the fixing temperature, and may be any temperature that allows accurate temperature correction to be described later.

  If it determines with 1st temperature T1 being less than the said preset temperature in step S12, it will progress to step S13 and the temperature increase control which raises the temperature of the heating roller 71 to the said preset temperature will be performed. Specifically, the control unit 8 causes the PID control unit 65 to control the heating of the heaters 75 and 76 until the first temperature T1 reaches the set temperature.

  If it is determined in step S12 that the first temperature T1 is equal to or higher than the set temperature, the process proceeds to step S14. In step S14, the control unit 8 determines whether or not the heating roller 71 is stopped. When the heating roller 71 is not stopped (when rotating), the driving of the heating roller 71 is stopped (S15). The process proceeds to step S16. On the other hand, when the heating roller 71 is stopped, the process proceeds to step S16. Whether the heating roller is rotating or stopped can be determined based on whether rotation driving control is being performed, or based on a rotation sensor (not shown) such as a rotary encoder provided on the heating roller 71.

  In step S <b> 16, the control unit 8 causes the contact portion 88 of the second temperature sensor 78 </ b> B to contact the second detection point 92. Specifically, the control unit 8 drives the displacement unit 95 to displace the second temperature sensor 78B from the separated position to the contact position. Thereby, the contact part 88 contacts the 2nd detection point 92, and the 2nd temperature sensor 78B becomes possible [detecting the temperature of the 2nd detection point 92]. That is, the control unit 8 can calculate the temperature of the second detection point 92 based on the second temperature sensor 78B.

  In the next step S17, the control unit 8 calculates the first temperature T1 and the second temperature T2 based on detection signals from the temperature sensors 78A and 78B.

  Thereafter, in step S18, the temperature difference ΔT is calculated by subtracting the first temperature T1 from the second temperature T2. And the control part 8 determines whether the temperature difference (DELTA) T is more than a predetermined threshold value. Here, the threshold value is used to determine whether or not the temperature difference ΔT is such that the first temperature T1 needs to be corrected. If the temperature difference ΔT is less than the threshold value, the control unit 8 proceeds to step S20 without performing temperature correction, assuming that the temperature difference ΔT is a small difference that does not require correction of the first temperature T1. On the other hand, if the temperature difference ΔT is greater than or equal to the threshold value, the process proceeds to step S19 to perform temperature correction.

  In step S19, the control unit 8 corrects the first temperature T1 calculated in step S17 based on the second temperature T2 calculated in step S17. Specifically, when the temperature difference ΔT is positive, the control unit 8 adds the temperature difference ΔT to the first temperature T1 and corrects the new first temperature T1. Here, the new first temperature T1 after correction corresponds to the corrected temperature according to the present invention.

  In step S20, the controller 8 controls the surface temperature of the heating roller 71 with the new first temperature T1 after correction. Specifically, the control unit 8 controls the temperature by causing the PID control unit 65 to control the driving of the heaters 75 and 76 so that the new first temperature T1 becomes the fixing temperature. Note that the temperature control in step S20 may be performed only when a print job is input.

  Since the temperature correction process is performed by the control unit 8 in this way, the first temperature T1 is corrected based on the second temperature T2 of the second detection point 92 on the same circumference close to the first detection point 91. Therefore, even if the first detection point 91 becomes dirty or deteriorates and the detection accuracy by the first temperature sensor 78A decreases, or the condenser lens of the sensor head 87 becomes dirty and the detection by the first temperature sensor 78A. Even when the accuracy is lowered, the first temperature T1 is corrected with high accuracy.

  In the above-described embodiment, the example in which the first detection point 91 and the second detection point 92 are set at the center in the axial direction of the roller body 71A has been described. However, the present invention is not limited to this. The first detection point 91 and the second detection point 92 may be on the same circumference in the contact region R1.

  Moreover, although the above-mentioned embodiment demonstrated the structure by which the main heater 75 and the sub heater 76 were incorporated in the heating roller 71, this invention is not limited to this. For example, the structure which heats the surface of the heating roller 71 from the outside may be sufficient. Further, the main heater 75 and the sub heater 76 are examples of a heating device, and various heating devices can be applied instead. For example, the main heater 75 and the sub heater 76 may be configured to be heated by an induction heating method using electromagnetic induction.

  In the above-described embodiment, the solenoid is exemplified as the displacement unit 95. However, the displacement unit 95 may be configured to obtain the driving force from a driving unit such as a motor other than the solenoid to displace the second temperature sensor 78B. Good. Further, a driving force for rotating the pressure roller 72 may be transmitted through a transmission mechanism, and the second temperature sensor 78B may be displaced by the driving force.

8: Control unit 10: Image forming device 16: Fixing device 64: Calculation unit 65: PID control unit 68: Correction control unit 71: Heating roller 72: Pressure roller 75: Main heater 76: Sub heater 78A: First temperature sensor 78B: Second temperature sensor

Claims (5)

A first rotating body capable of contacting the transfer sheet;
A main heater that is provided inside the first rotating body and that heats a central portion of the surface of the first rotating body; and a sub-heater that heats an axially outer end portion of the surface of the first rotating body. A heating device;
A second rotator that is pressed against the first rotator to form a nip that can pass through the transfer sheet;
It is used for temperature control of the first rotating body by the heating device, and is defined in the axial center of the first rotating body within the contact area of the first rotating body with which the transfer sheet contacts. A first non-contact first temperature detection unit for detecting the temperature of the first detection point;
It is used for correction of the first temperature detected by the first temperature detection unit, and is on the circumference of the first rotating body passing through the first detection point, and from the first detecting point to the first rotating body. A contact-type second temperature detection unit that detects the temperature of the second detection point that is set at a position spaced a predetermined distance upstream in the rotation direction of
A correction controller that corrects the first temperature detected by the first temperature detector based on the second temperature detected by the second temperature detector;
The first temperature detector is a radiation temperature sensor;
The second detection point is set at a position close to the first detection point on the circumference, and the predetermined interval is a viewing angle of the first temperature detection unit and radiation at the first detection point. The fixing device in which the second temperature detection unit is set to a minimum interval that does not interfere with temperature detection by the first temperature detection unit based on the rate .   The second temperature detection unit is separated from the second detection point when the first rotating body is in a rotating state, and the second temperature detecting unit is detected as the second detection when the first rotating body is in a non-rotating state. The fixing device according to claim 1, further comprising a displacement unit that displaces the second temperature detection unit so as to contact the point. Wherein the correction control unit by claim 1 or 2, wherein the first temperature is further provided with a temperature control unit for controlling the heating by the heating device so that the target temperature corrected temperature is predetermined after correction Fixing device. The correction control unit corrects the first temperature at a predetermined timing when the first rotating body is in a non-rotating state,
The fixing device according to claim 3 , wherein the displacement unit brings the second temperature detection unit into contact with the second detection point when correction is performed by the correction control unit. An image forming apparatus including a fixing device according to any one of claims 1 to 4.

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