JP2020052309A - Temperature detector and image heating device using the same - Google Patents

Abstract

To provide a temperature detector and an image heating device using the same that can detect temperature of a rotating body heated by electromagnetic induction in good responsiveness, and that can deal with winding of a recording material.SOLUTION: A temperature detector detecting surface temperature of a rotating body used in an image heating device that comprises a cylindrical rotating body comprising a heating layer, and magnetic field generation means that is inserted through the rotating body, that forms alternate magnetic field in a rotation axis direction of the rotating body by flowing AC current, and that generates induction current in a circumferential direction of the rotating body comprises: magnetic path formation means that intersects with a first cross section in the circumferential direction in which the induction current is formed and that forms a magnetic path in a second cross section surrounding a position of the induction current; and acquisition means that acquires a current value corresponding to the surface temperature of the rotating body in a third cross section which intersects with the second cross section and which surrounds a portion of the magnetic path.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a temperature detecting device used in an electromagnetic induction heating type image heating device used for a copying machine, a printer, or the like as an electrophotographic image forming device, and an image heating device using the same.

  2. Description of the Related Art In recent years, a fixing device has been proposed as an image heating device of an electromagnetic induction heating type that can directly generate heat in a heating layer of a heating rotator. In Patent Literature 1, an exciting coil and a magnetic core are arranged inside a heating rotator, an alternating magnetic field is generated in an axial direction of the heating rotator, and a current (circulating current) generated in a circumferential direction of the heating rotator is used. A fixing device that generates heat is disclosed.

JP 2014-26267A

  Here, in the case of an image heating apparatus using a rotating body heated by electromagnetic induction, the temperature of the rotating body rises faster than that of other types of image heating apparatuses. It is desirable to be able to handle recording materials. Incidentally, the contact-type thermistor is generally widely used temperature detecting means, but its response is slightly inferior. Further, although the non-contact thermopile is excellent in responsiveness, accurate temperature detection cannot be performed when the recording material is wound around the rotating body.

  SUMMARY OF THE INVENTION It is an object of the present invention to provide a temperature detecting device which can detect the temperature of a rotating body heated by electromagnetic induction with good responsiveness and can cope with winding of a recording material, and an image heating device using the same. is there.

  In order to achieve the above object, a temperature detecting device according to the present invention includes a cylindrical rotating body having a heat generating layer, and an alternating magnetic field that is inserted through the rotating body and allows an alternating current to flow in a rotation axis direction of the rotating body. A magnetic field generating means for generating an induced current in a circumferential direction of the rotating body, used for an image heating device, a temperature detecting device for detecting a surface temperature of the rotating body, wherein the induced current A magnetic path forming means intersecting with the first section in the circumferential direction in which a magnetic path is formed in a second section surrounding the position of the induced current, intersecting with the second section, Acquiring means for acquiring a current value corresponding to a surface temperature of the rotating body in a third section surrounding a part of the magnetic path.

  Further, another temperature detecting device according to the present invention is a cylindrical rotating body having a heating layer, and is inserted into the rotating body, and forms an alternating magnetic field in the rotation axis direction of the rotating body by passing an alternating current. A magnetic field generating means for generating an induced current in a circumferential direction of the rotating body, a temperature detecting device for detecting a surface temperature of the rotating body, wherein the induced current is formed. Magnetic path forming means for forming a magnetic path in a second cross section which intersects the first cross section in the circumferential direction and surrounds the position of the induced current, the magnetic path forming means being provided outside the rotating body. Magnetic path forming means including: a first magnetic core and a second magnetic core disposed inside the rotating body; and a third magnetic path intersecting the second cross section and surrounding a part of the magnetic path. A current value corresponding to the surface temperature of the rotating body A acquiring unit, and having a an acquisition unit having a detection coil wound around the first magnetic core or said second magnetic cores.

  Further, an image heating device according to the present invention includes the above-mentioned temperature detecting device.

  According to the present invention, it is possible to provide a temperature detecting device capable of detecting the temperature of a rotating body subjected to electromagnetic induction heating with good responsiveness and capable of coping with winding of a recording material, and an image heating device using the same. it can.

FIG. 2 is a cross-sectional view illustrating an entire configuration of an image forming apparatus equipped with the image heating device according to the embodiment. Cross-sectional side view of a main part of the fixing device A as an image heating device Perspective view of main parts of fixing device A Perspective view of the excitation core Conceptual diagram showing the moment when the current is increasing in the exciting coil Explanatory drawing of the measurement principle of a CT type current sensor Sectional view showing the configuration of a current sensor as temperature detecting means Perspective view showing that magnetic flux Φ is generated in a magnetic path formed by outer and inner magnetic cores Perspective view when no magnetic flux is generated in the magnetic core Layout diagram when I-shaped core is adopted as outer and inner magnetic cores Layout diagram when a U-shaped core is used for one of the outer and inner magnetic cores Layout when U-shaped cores are used as the outer and inner magnetic cores Layout when the outer and inner magnetic cores are shifted in the axial direction (longitudinal direction) Layout when the detection coil is placed in the center of the magnetic core Layout when the detection coil is placed at the end of the magnetic core Layout diagram when crank-shaped magnetic cores are used as the outer and inner magnetic cores Layout when the detection coil is placed on a crank-shaped magnetic core Relationship between fixing film temperature and current sensor output Relationship between fixing film temperature and fixing film resistance Cross-sectional side view of a fixing device using a contact thermistor as a comparative example Diagram showing the detected temperature responsiveness of a contact thermistor as a comparative example FIG. 5 is a diagram illustrating a detected temperature response of the current sensor according to the embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

<< 1st Embodiment >>
(Image forming device)
FIG. 1 is a cross-sectional view showing the overall configuration of a color laser beam printer (hereinafter, printer) as an image forming apparatus equipped with a fixing device as an image heating device according to an embodiment of the present invention.

  At the lower part of the printer 1, a cassette 2 is housed so as to be able to be pulled out. The cassette 2 stores sheets P as recording materials. Sheets P from the cassette 2 are separated one by one by separation rollers 3 and fed to registration rollers 4. The printer 1 includes an image forming unit 5 as image forming means in which image forming stations 5Y, 5M, 5C, and 5K corresponding to respective colors of yellow, magenta, cyan, and black are arranged in a row.

  The image forming section 5Y is provided with a photosensitive drum 6Y as an image carrier and a charging unit 7Y for uniformly charging the surface of the photosensitive drum 6Y. Further, a scanner unit 8 is provided below the image forming unit 5Y. The scanner unit 8 irradiates a laser beam, which is input from an external device such as a computer (not shown) based on image information, and irradiates a laser beam on / off-modulated according to a digital image signal generated by the image processing means, An electrostatic latent image is formed on 6Y.

  Further, a developing unit 9Y for attaching toner to the electrostatic latent image and developing it as a toner image (toner image), and a primary transfer unit 11Y for transferring the toner image on the photosensitive drum 6Y to the electrostatic transfer belt 10 are provided. I have. The toner image of the electrostatic transfer belt 10 to which the toner image has been transferred by the primary transfer unit 11Y is superimposed on the electrostatic transfer belt 10 through the same process in the image forming unit 5M, the image forming unit 5C, and the image forming unit 5K. The image is transferred to the sheet P by the secondary transfer unit 12. Thereafter, the toner image on the sheet P passes through the fixing device A and is fixed as a fixed image. Further, the sheet P passes through the discharge conveyance section 13 and is discharged and stacked on the stacking section 14.

  In FIG. 1, M is a storage unit described later in detail, and stores a function for associating the surface temperature of the fixing film in the fixing device A with the current value of the current sensor.

(Image heating device)
In the present embodiment, the fixing device A as an image heating device is a fixing device of an electromagnetic induction heating type. FIG. 2 is a cross-sectional side view of a main part of the fixing device A according to the present embodiment, and FIG. 3 is a perspective view. Here, regarding the members constituting the fixing device A, the longitudinal direction is a direction orthogonal to the conveying direction of the recording material and the thickness direction of the recording material.

  The fixing film 20 is a flexible cylindrical rotating body having a heating layer 20b serving as a heating element provided on a base layer 20a and an elastic layer 20c and a release layer 20d formed thereon. The base layer 20a is made of an insulating heat-resistant resin such as polyimide, polyamideimide, PEEK, and PES. In this embodiment, a cylindrical base layer 20a having an inner diameter of 30 mm, a longitudinal length of 240 mm, and a thickness of about 60 μm was manufactured by molding a polyimide resin.

  The following materials are preferable for the heat generating layer 20b. That is, it is made of iron, copper, silver, aluminum, nickel, chromium, tungsten, an alloy containing SUS304 or nichrome containing them, or a conductor such as CFRP (carbon fiber reinforced plastic) or carbon nanotube resin, and has an absolute temperature resistance coefficient. A material with a large value. As a forming method, there are means such as coating, plating, sputtering and vapor deposition. In this embodiment, nickel is formed to a thickness of about 5 μm by an electroless plating method.

  The elastic layer 20c is preferably made of a material having excellent heat resistance and thermal conductivity, such as silicone rubber, fluorine rubber, or fluorosilicone rubber. In this embodiment, it is formed of silicone rubber having a thickness of about 200 μm.

  As the release layer 20d, it is preferable to select a material having good releasability and heat resistance, such as PFA, PTFE, and FEP. In this embodiment, it is formed by covering a PFA resin tube having a thickness of about 15 μm.

  The pressing roller 21 as a pressing member facing the fixing film 20 includes a core metal 21a, and an elastic layer 21b formed and coated concentrically and integrally around the core metal in a roller shape. 21c is provided. The elastic layer 21b is preferably made of a material having good heat resistance such as silicone rubber, fluorine rubber, fluorosilicone rubber, or the like. Both ends in the longitudinal direction of the cored bar 21a are rotatably held between unillustrated chassis-side sheet metal of the apparatus via conductive bearings.

  As shown in FIG. 3, compression springs 24a and 24b are respectively contracted between both ends of the press stay 22 in the longitudinal direction and the spring receiving members 23a and 23b on the apparatus chassis side, so that compression is performed. A pressing force is applied to the pressing stay 22. In the fixing device A of this embodiment, a pressing force of a total pressure of about 100 N to 300 N (about 10 kgf to about 30 kgf) is applied.

  As a result, the lower surface of the sleeve guide member 25 made of heat-resistant resin PPS or the like and the upper surface of the pressure roller 21 are pressed against each other with the fixing film 20 being a cylindrical rotating body interposed therebetween, so that the fixing nip portion N having a predetermined width is formed. It is formed. The sleeve guide member 25 functions together with the pressure roller 21 as a nip portion forming member that forms a nip portion that sandwiches and conveys a recording material carrying a toner image via the fixing film 20.

  The pressure roller 21 is rotationally driven in a counterclockwise direction by a driving unit (not shown), and a clockwise rotational force is applied to the fixing film 20 by a frictional force with the outer surface of the fixing film 20.

  FIG. 4 is a perspective view showing the longitudinal direction of the magnetic core 26 shown in FIG. An exciting coil 27 is wound around the outer periphery of a magnetic core 26 inserted into a hollow portion of the fixing film 20 which is a cylindrical rotating body. The magnetic core 26 has a columnar shape, and is disposed substantially at the center of the fixing film 20 by fixing means (not shown).

  The magnetic core 26 provided inside the exciting coil 27 guides the magnetic field lines (magnetic flux) of the alternating magnetic field generated by the exciting coil 27 into the heat generating layer 20b of the fixing film 20 to form a path (magnetic path) for the magnetic field lines. There is a role to do. The material of the magnetic core 26 is preferably a material having a small hysteresis loss and a high relative magnetic permeability, for example, a ferromagnetic material having a high magnetic permeability such as fired ferrite or ferrite resin. The cross-sectional shape of the magnetic core 26 may be any shape as long as it can be accommodated in the hollow portion of the fixing film 20, and need not be circular, but is preferably a shape that allows the cross-sectional area to be as large as possible. In the present embodiment, the diameter of the magnetic core 26 is 10 mm, and the length in the longitudinal direction is 280 mm.

  The excitation coil 27 was formed by winding a copper wire (single conductor) having a diameter of 1 to 2 mm (single conductor) coated with heat-resistant polyamideimide in a spiral shape around the magnetic core 26 with 20 turns. The exciting coil 27 is wound around the magnetic core 26 in a direction crossing the axial direction of the fixing film 20. Therefore, when a high-frequency current is applied to the exciting coil 27, an alternating magnetic field is generated in a direction parallel to the axial direction, and an induced current flows through the heat generating layer 20b of the fixing film 20 according to a principle described later to generate heat.

  Here, the temperature sensor for detecting the surface temperature of the fixing film 20 in the present embodiment is the current sensor 30. Details of the configuration and principle of the current sensor 30 will be described later. The temperature of the fixing film 20 is measured as an electric signal by the current sensor 30, and the electric temperature information is input to a control circuit unit (not shown), and the temperature of the fixing film 20 is controlled to be a predetermined temperature.

(Heating principle)
FIG. 5 is a conceptual diagram illustrating the moment when the current increases in the direction of the arrow I1 in the exciting coil 27. The excitation coil 27 is inserted into the fixing film 20, and forms an alternating magnetic field in the rotation axis direction of the fixing film 20 by passing an alternating current to function as a magnetic field generating unit that generates an induced current in the circumferential direction of the fixing film 20. . The magnetic core 26 functions as a member that guides the lines of magnetic force generated by the exciting coil 27 and forms a magnetic path.

  S in the figure is a diagram of a circuit simulating only a part of the fixing film 20. The heat generation principle of the fixing film 20 follows Faraday's law. Faraday's law states that, when a magnetic field in a circuit S is changed, an induced electromotive force that causes a current to flow in the circuit is generated, and the induced electromotive force is proportional to the time change of a magnetic flux that vertically passes through the circuit. I do. "

  It is assumed that the circuit S is placed at the center in the longitudinal direction of the magnetic core 26 shown in FIG. When a high-frequency alternating current flows, an alternating magnetic field is formed inside the magnetic core 26. At that time, the induced electromotive force generated in the circuit S is proportional to the time change of the magnetic flux penetrating vertically according to the following equation.

V: Induced electromotive force N: Number of coil turns ΔΦ / Δt: Change in magnetic flux vertically penetrating the circuit in a minute time Δt Due to the induced electromotive force V, a circulating current (induced current) I is generated in the heating layer 20 b of the fixing film 20. It flows and generates Joule heat. In this method based on such a heating principle, since the fixing film 20 itself generates heat, the temperature rises faster than in a fixing device of another method. Therefore, in order to perform stable temperature control, a system having excellent responsiveness is required as the temperature detecting means.

(Principle and configuration of temperature detecting means in the present embodiment)
1) Principle of Temperature Detecting Unit Hereinafter, the principle of the temperature detecting unit in the present embodiment will be described in detail. Since the heat generating layer 20b of the fixing film 20 is formed of a conductor, its resistance generally has temperature dependency. Therefore, if the change in the resistance value can be detected, the temperature of the fixing film 20 can be estimated. As described above, since the circulating current I due to the induced electromotive force V flows through the heating layer 20b, if the values of the induced electromotive force V and the circulating current I can be obtained, the resistance value R of the fixing film 20 is calculated from the ratio. Becomes possible.

  Here, a method of obtaining the induced electromotive force will be described. The induced electromotive force is proportional to the time change of the magnetic flux Φ generated by the exciting coil 26 as in the above-described equation. Since the magnetic flux Φ is proportional to the amount of current of the exciting coil 26, the induced electromotive force V can be obtained by connecting a general current measuring circuit to the exciting coil 26 and measuring it.

  On the other hand, the circulating current I flowing through the heating layer 20b cannot be measured by connecting a general current measuring circuit. Therefore, as described later, in the present embodiment, the principle of a CT-type current sensor, which is a type of non-contact current sensor, is applied. FIG. 6 is an explanatory diagram of the measurement principle of the CT type current sensor. The magnetic flux Φ1 is generated in the magnetic core by the alternating current I1 flowing through the measurement conductor. A magnetic flux Φ2 is generated in the winding so as to cancel the generated magnetic flux Φ1, and a secondary current I2 according to the turns ratio flows to generate a voltage across the shunt resistor. Since this voltage is proportional to the alternating current I1 flowing through the measurement conductor, the amount of the current can be determined.

  Here, when the induced electromotive force V is constant, in estimating the temperature of the fixing film 20, a change in the resistance value of the fixing film is captured, and a change in the circulating current of the fixing film related to the reciprocal of the resistance value is determined. Capturing has the same technical meaning. That is, by using a non-contact current detection sensor (an acquisition unit for acquiring a current value corresponding to the surface temperature of the fixing film) applying the principle of the CT type current sensor shown in FIG. 6, the surface temperature of the fixing film is responded. It can be detected well.

  Although a non-contact thermopile having a different measurement principle from that of the present embodiment has excellent responsiveness, accurate temperature detection cannot be performed when the recording material is wound around the rotating body. On the other hand, since the temperature detecting means according to the present embodiment is an electromagnetic induction method, accurate temperature detection can be performed even when the recording material is wound around the rotating body.

2) Configuration of Temperature Detector Next, the configuration of the temperature detector in the present embodiment will be described in detail. FIG. 7 and FIG. 8 are cross-sectional views showing the configuration of the current sensor 30 as the temperature detecting means in the present embodiment.

  In this embodiment, a cross section in the circumferential direction of the fixing film 20 where the induced current is formed is referred to as a first cross section. As a section crossing the first section, a section surrounding the position of the induced current is defined as a second section. Then, a magnetic path is formed in the second section by the magnetic path forming means. As a cross section that intersects the second cross section, a cross section surrounding a part of the magnetic path in the second cross section is referred to as a third cross section. Then, a current value corresponding to the surface temperature of the fixing film 20 in the third section is obtained by an obtaining unit that obtains a current value.

  As a magnetic path forming means, as shown in FIG. 8 (FIG. 7), a magnetic core 30a as a first detection magnetic core is provided outside the fixing film 20 with the fixing film 20 interposed therebetween, and a magnetic core 30a is provided inside the fixing film 20. The magnetic core 30b as the second detection magnetic core is disposed. The magnetic cores are the same, but the magnetic cores 30a and 30b relate to temperature detection of the fixing film 20, while the magnetic core 26 relates to heating of the fixing film 20.

  The magnetic cores 30a and 30b may have a shape (A shape) parallel to the longitudinal direction of the fixing film 20, as shown in FIG. Alternatively, as shown in FIG. 12, a device having a shape (B shape) having a first region parallel to the longitudinal direction of the fixing film 20 and a second region crossing the longitudinal direction of the fixing film 20 is also provided. good. Alternatively, one of the magnetic cores 30a and 30b may have an A shape and the other may have a B shape.

  Thus, at least one of the magnetic cores 30a and 30b may have an A shape, or at least one of the magnetic cores 30a and 30b may have a B shape.

  In the present embodiment, a U-shaped magnetic core 30a is used, and an I-shaped magnetic core 30b is used. Then, the detection coil 30c was wound around the magnetic core 30a. Compared with the above-described CT type current sensor, the configuration of the present embodiment has a configuration in which the magnetic core portion is divided. In the present embodiment, although the detection coil 30c is formed on the magnetic core 30a, the detection coil 30c may be formed on the magnetic core 30b in principle.

  As a current detecting means, a detection coil 30c is formed on the magnetic core 30a, and shunt resistors 30d are connected to both ends of the detection coil 30c. According to the principle of the CT type current sensor described above, an alternating current according to the turns ratio of the detection coil 30c flows through the detection coil 30c so as to cancel the generated magnetic flux, and a voltage is generated across the shunt resistor 30d. Since this voltage is proportional to the circulating current flowing through the fixing film 20, the circulating current amount can be determined by measuring the voltage value output across the shunt resistor 30d with a general voltmeter.

  FIG. 8 is a perspective view showing that a magnetic flux Φ is generated in a magnetic path formed by the magnetic core 30a and the magnetic core 30b by the circulating current I flowing through the fixing film 20. According to the principle of the CT type current sensor described above, an alternating current according to the turns ratio of the detection coil 30c flows through the detection coil 30c so as to cancel the generated magnetic flux, and a voltage is generated across the shunt resistor 30d. Since this voltage is proportional to the circulating current flowing through the fixing film 20, the amount of circulating current can be determined by measuring a voltage value output across the shunt resistor 30d with a general voltmeter.

  In order to generate a large magnetic flux in the magnetic core 30a and the magnetic core 30b, the relationship between the direction of the circulating current flowing through the fixing film 20 and the direction of each magnetic core is important. As shown in FIG. 9, when the magnetic core 30a and the magnetic core 30b are arranged in parallel with respect to the circumferential direction of the fixing film 20, almost no magnetic flux is generated, and almost no current flows through the detection coil 30c.

  In order to generate a large magnetic flux in the magnetic core 30a and the magnetic core 30b, it is preferable that the gap between the magnetic core 30a and the magnetic core 30b is narrow. That is, the magnetic core 30a and the magnetic core 30b are preferably closer to the fixing film 20. This is because if the gap between the magnetic core 30a and the magnetic core 30b is wide, a large amount of magnetic flux leaks from the gap, and the magnetic flux generated in the detection coil 30c becomes small.

  However, the magnetic core 30a and the magnetic core 30b need to be arranged at positions so as not to contact the fixing film 20. The detection coil 30c wound around the magnetic core also needs to be arranged so as not to contact the fixing film 20 (distance H in FIG. 10). That is, it is necessary to secure a distance H from the surface of the fixing film 20 to the detection coil 30c from the viewpoint of mechanical tolerance and the like. As described above, when the detection coil 30c is wound using the I-shaped core as the magnetic core 30a, the magnetic core 30a needs to be separated from the fixing film surface by the thickness of the detection coil 30c. Becomes g1.

  On the other hand, as shown in FIG. 11, a U-shaped core is adopted as a magnetic core around which the detection coil 30c is wound, and a U-shaped core having legs longer than the thickness of the detection coil 30c is used. It can be arranged without considering the thickness. Thereby, the gap between the magnetic core 30a and the magnetic core 30b can be reduced to g2. Although it is the same as being arranged at the closest position not in contact with the fixing film 20, since g1> g2, it is possible to generate a larger magnetic flux when the U-shaped core is adopted, It can be said that this is a more desirable shape.

  In order to narrow the gap between the magnetic cores 30a and 30b, not only the distance from the fixing film 20 but also the positional relationship between the magnetic cores 30a and 30b in the plane direction of the fixing film 20 is important. As shown in FIG. 12, when U-shaped cores are used as the magnetic cores 30a and 30b, the end faces 30a1, 30a2, 30b1, and 30b2 of the magnetic cores serve as the entrance / exit of the magnetic flux.

  As shown in FIG. 13, when the respective magnetic cores are displaced in the axial direction (longitudinal direction) of the fixing film 20, the gap between the magnetic core 30a and the magnetic core 30b increases, and the magnetic flux does not easily increase. It goes without saying that the magnetic flux is not likely to be increased not only in the case of displacement in the axial direction but also in the case of displacement in the circumferential direction.

  When an I-shaped magnetic core is employed as the magnetic core 30a as shown in FIG. 14, the position of the detection coil 30c is also important. For example, if the detection coil 30c is wound around the end of the magnetic core 30a as shown in FIG. 15, the exit / entrance of the magnetic flux on the side where the detection coil 30c is wound will be an I-shaped end face 30a3. For this reason, the gap between the magnetic cores is substantially wide, and the magnetic flux is unlikely to increase.

  On the other hand, when the detection coil 30c is formed at the center of the magnetic core 30a as shown in FIG. 14, the exit / entrance of the magnetic flux is near the magnetic core side surface 30a5 close to the fixing film 20 surface. It becomes an apparent gap, and the magnetic flux tends to increase.

  From the viewpoint that the magnetic flux inlets / outlets of the magnetic cores 30a and 30b are close and the gap can be narrowed, a magnetic core 30a having a shape as shown in FIG. 16 may be employed. That is, a shape (C shape) having a shape different from FIG. 12 and having a first region parallel to the longitudinal direction of the fixing film 20 and a second region crossing the longitudinal direction of the fixing film 20 is provided. Is also good.

  FIG. 17 is a view of the magnetic core 30a shown in FIG. When the detection coil 30c is wound around the center part of the crank shape, the direction of the detection coil 30c becomes parallel to the current flowing through the fixing film 20. However, there is no problem because the magnetic path itself is formed by the magnetic core 30a and the magnetic core 30b.

  Next, an experiment was performed to obtain a relationship between the surface temperature of the fixing film 20 and the output of the current sensor 30 in the present embodiment (corresponding to the secondary current I2 in FIG. 6). While a constant current is applied to the exciting coil 27 (FIG. 4), the surface temperature of the fixing film 20 is measured by an infrared thermography camera (TVS-8500 manufactured by Nippon Avionics), and the current value flowing to the current sensor 30 in the present embodiment is monitored. (FIG. 18).

  Since the current flowing through the exciting coil 27 is constant, the generated magnetic flux is also constant. The experiment was performed in an environment at an ambient temperature of 25 ° C. Since the current continued to flow through the excitation coil 27, the surface temperature of the fixing film 20 increased with time, and the current flowing through the current sensor 30 decreased as the temperature increased. Note that the output of the current sensor 30, which is the vertical axis in FIG. 18, is normalized by the value when the surface temperature of the fixing film 20 is 25 ° C.

  The function shown in FIG. 18 (the function for associating the surface temperature of the fixing film in the fixing device A with the current value of the current sensor) in which the horizontal axis is the surface temperature of the fixing film 20 and the vertical axis is the output of the current sensor 30 is: It can be stored in the storage means M (FIG. 1).

  FIG. 19 shows the temperature dependence of the resistance value of the fixing film 20 based on FIG. The vertical axes of FIGS. 18 and 19 show the current value and the resistance value when the voltage value of the fixing film is kept constant. In FIGS. 18 and 19, if one increases with the temperature of the fixing film, the other decreases. Shows the relationship.

  Then, based on the data in FIG. 19, the fixing film resistance with respect to the temperature of the fixing film is determined (for example, 2 as the value on the vertical axis in FIG. 19), and the output value of the current sensor 30 becomes a predetermined value (vertical in FIG. 18). The amount of current to the exciting coil is controlled so that the value of the axis becomes the reciprocal of 0.5). That is, when the value of the sensor output on the vertical axis of FIG. 18 is 0.5, the fixing film is at a controlled temperature, and when the value of the sensor output is different from 0.5, the fixing film is at a temperature different from the controlled temperature. Will be detected. Thus, the surface temperature of the fixing film 20 can be controlled to a predetermined temperature.

3) Comparison of temperature detection responsiveness In order to confirm the improved responsiveness in this configuration, a comparison was made with a configuration (comparative example) in which a contact thermistor was employed as the temperature detection means. FIG. 20 is a sectional view of a fixing device having a configuration (comparative example) in which a contact thermistor is employed as temperature detecting means for detecting the temperature of the fixing film 20. Other configurations are the same except that the temperature detecting means is changed from the current sensor 30 to the contact thermistor 40.

  In FIG. 20, the contact thermistor 40 is fixedly installed on the sleeve guide member 25. The contact-type thermistor 40 includes a spring plate 40a as a support member having spring elasticity extending toward the inner surface of the fixing film 20, and a thermistor element 40b as a temperature detecting element installed at the tip of the spring plate 40a. Consists of

  The surface of the thermistor element 40b is covered with a 50 μm thick polyimide tape in order to ensure electrical insulation. Then, the thermistor element 40b is pressed against the inner surface of the fixing film 20 by the spring elasticity of the spring plate 40a and is kept in a contact state. The thermistor element 40b measures the inner surface temperature of the fixing film 20 as an electric signal, and the electric temperature information is input to a control circuit (not shown) so that the temperature of the fixing film 20 is controlled to a predetermined temperature. .

  Here, the alternating current flowing through the exciting coil 27 is controlled to check the surface temperature of the fixing film 20 with an infrared thermography camera, and the current sensor 30 is used as the temperature detecting means and the contact type thermistor 40 is used. The state of temperature detection was compared. FIG. 21 shows an experimental result when a contact thermistor 40 is employed as a comparative example. The horizontal axis is time, and the vertical axis is temperature. The dotted line is the measurement result with the infrared thermography camera, and the solid line is the measurement result with the contact thermistor 40.

  The measurement result using the contact thermistor 40 as a comparative example has a time delay from the measurement result of the infrared thermography camera, and it can be said that the response speed is slow. On the other hand, FIG. 22 shows an experimental result when the current sensor 30 according to the embodiment of the present invention is employed. The dotted line is the measurement result with the infrared thermography camera, and the solid line is the measurement result with the current sensor 30. Unlike the case of the contact thermistor 40, the measurement result almost coincides with the measurement result of the infrared thermography camera, and it was confirmed that the response speed when the current sensor 30 of the present embodiment was adopted was fast.

  In the above-described embodiment, a preferred embodiment of the present invention has been described, but the present invention is not limited to this, and various modifications can be made within the scope of the present invention.

  In the above-described embodiment, an example was described in which the principle of a CT-type current sensor having a magnetic core was applied as the temperature detecting means. However, the present invention is not limited to this, and in principle, Rogowski without a magnetic core was used. Measurement is also possible with the coil method. Further, it is needless to say that the measurement can be performed by a Hall element type current sensor instead of the CT type, and a hybrid type current sensor combining a Hall element and a detection coil can also be measured.

20 fixing film, 27 exciting coil, 30 current sensor, 30a, 30b magnetic core, 30c detecting coil

Claims (9)

A cylindrical rotating body having a heat generating layer, and an alternating magnetic field is inserted through the rotating body, and an alternating current is applied to form an alternating magnetic field in a rotation axis direction of the rotating body, thereby generating an induced current in a circumferential direction of the rotating body. Magnetic field generating means, and used in an image heating device comprising: a temperature detection device for detecting the surface temperature of the rotating body,
Magnetic path forming means intersecting with the first section in the circumferential direction where the induced current is formed, and forming a magnetic path in a second section surrounding the position of the induced current;
Acquiring means for acquiring a current value corresponding to a surface temperature of the rotating body in a third cross section which intersects the second cross section and partially surrounds the magnetic path;
A temperature detecting device comprising: A cylindrical rotating body having a heat generating layer, and an alternating magnetic field is inserted through the rotating body, and an alternating current is applied to form an alternating magnetic field in a rotation axis direction of the rotating body, thereby generating an induced current in a circumferential direction of the rotating body. Magnetic field generating means, and used in an image heating device comprising: a temperature detection device for detecting the surface temperature of the rotating body,
Magnetic path forming means for forming a magnetic path in a second cross section that intersects the first cross section in the circumferential direction where the induced current is formed and surrounds the position of the induced current, Magnetic path forming means, comprising: a first magnetic core disposed on a first magnetic core; and a second magnetic core disposed inside the rotating body.
Acquiring means for acquiring a current value corresponding to a surface temperature of the rotating body in a third cross section which intersects the second cross section and partially surrounds the magnetic path, wherein the first magnetic core or Acquisition means comprising a detection coil wound around the second magnetic core;
A temperature detecting device comprising:   The temperature detecting device according to claim 2, wherein at least one of the first magnetic core and the second magnetic core has a shape parallel to a longitudinal direction of the rotating body.   At least one of the first magnetic core and the second magnetic core has a first region parallel to a longitudinal direction of the rotator and a second region intersecting the longitudinal direction of the rotator. The temperature detecting device according to claim 2, comprising a shape.   The temperature detecting device according to claim 4, wherein the shape is a U-shape.   The temperature detection device according to claim 1, further comprising a storage unit configured to store a function that associates the current value with a surface temperature of the rotating body. A cylindrical rotating body having a heating layer,
A magnetic field generating unit that is inserted into the rotating body, forms an alternating magnetic field in the rotation axis direction of the rotating body by flowing an alternating current, and generates an induced current in a circumferential direction of the rotating body;
An opposing body facing the rotating body,
A nip portion forming member that forms a nip portion that sandwiches and conveys a recording material carrying a toner image via the rotating body,
A temperature detection device according to any one of claims 1 to 6,
An image heating device comprising:   The image heating apparatus according to claim 7, wherein the magnetic field generating unit includes an exciting coil and a magnetic core disposed inside the exciting coil.   The image heating apparatus according to claim 8, wherein a current flowing through the exciting coil is controlled such that the current value becomes a current value corresponding to the temperature control temperature.