Patent Grant
11429044
The present disclosure relates to a fixing apparatus used in an image forming apparatus of an electrophotographic system or the like, and to an image forming apparatus including the fixing apparatus.
In recent years, a fixing apparatus of an induction heating system that causes a heat-generation layer provided in a heating member to directly generate heat by electromagnetic induction is proposed. Japanese Patent Laid-Open No. 2015-118232 discloses a fixing apparatus of a system in which an energizing coil and a magnetic core are disposed inside a cylindrical rotary member, an alternating magnetic field is generated in a rotation axis direction of the rotary member, and thus heat is generated in the heat-generation layer by a circulating current generated in the circumferential direction of the rotary member.
In addition, a fixing apparatus of a thermal fixation system includes a temperature detecting element capable of detecting an abnormal temperature for blocking supply of power to a heating mechanism from the viewpoint of safety in the case where the temperature of a heating member reaches the abnormal temperature which is out of a normal use range.
The heat-generation layer of the rotary member disclosed in the document described above is formed from a heat-generation pattern made up of a plurality of regions divided in the rotation axis direction. Therefore, if a conduction failure in the circumferential direction occurs in one of the regions constituting the heat-generation pattern, the circulating current does not flow in that region and therefore heat is not generated in that region. Further, if the conduction failure occurs at a position corresponding to the position of the temperature detecting element that detects the abnormal temperature, the temperature detected by the temperature detecting element does not rise even though heat is generated in the other regions of the heat-generation layer, and therefore there is a risk that the supply of power is not blocked even when the temperature of the rotary member is raised to the abnormal temperature.
An aspect of the present disclosure provides a fixing apparatus and an image forming apparatus in which abnormal temperature rise can be more reliably suppressed
According to one aspect of the disclosure, a fixing apparatus is configured to heat a toner image on a recording material and fix the toner image to the recording material. The fixing apparatus includes a rotary member that is cylindrical, includes a heat-generation layer, and is configured to come into contact with the recording material, the heat-generation layer being conductive and including a plurality of rings each continuous in the circumferential direction of the rotary member, the plurality of rings being electrically separated from one another in a rotation axis direction of the rotary member, a magnetic field generator disposed on an inner circumferential side of the rotary member and configured to, by being supplied an alternating current, generate an alternating magnetic field to induce a circulating current flowing in the circumferential direction in each of the plurality of rings of the heat-generation layer, a temperature detecting portion configured to detect a temperature of the rotary member, a conduction detecting unit configured to detect a conduction failure in an opposing ring that is one of the plurality of rings of the heat-generation layer and that opposes the temperature detecting portion, and a controller configured to control supply and interruption of power to the magnetic field generator on a basis of detection results of the temperature detecting portion and the conduction detecting unit. The conduction detecting unit includes a first magnetic core disposed on an outer circumferential side of the rotary member, a second magnetic core disposed on the inner circumferential side of the rotary member and configured to form, together with the first magnetic core, a magnetic path surrounding the circulating current flowing in the opposing ring, and a current detecting portion that includes a detection coil wound around one of the first magnetic core and the second magnetic core and that is configured to output a signal corresponding to the circulating current flowing in the opposing ring. A length in the rotation axis direction of the one of the first magnetic core and the second magnetic core around which the detection coil is wound is smaller than a length in the rotation axis direction of another of the first magnetic core and the second magnetic core around which the detection coil is not wound.
Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An exemplary embodiment of the present disclosure will be described below with reference to drawings.
Image Forming Apparatus
The printer 1 includes an image forming portion 5 serving as an image forming unit in which image forming stations 5Y, 5M, 5C, and 5K respectively corresponding to yellow, magenta, cyan, and black and arranged in parallel in the lateral direction. The image forming station 5Y includes a photosensitive drum 6Y, which is an electrophotographic photosensitive member, i.e., an image bearing member, and a charging roller 7Y serving as a charging member that uniformly charges the surface of the photosensitive drum 6Y. Further, scanner units 8 are provided in a lower portion of the image forming portion 5. The scanner units 8 irradiate the photosensitive drum 6Y with a laser beam that is on/off-modulated in accordance with a digital image signal generated by an image processing portion from image information input from an external device such as an unillustrated computer, and thus forms an electrostatic latent image on the photosensitive drum 6Y. Further, the image forming station 5Y includes a developing roller 9Y serving as a developing member that develops the electrostatic latent image on the photosensitive drum 6Y into a toner image by applying toner thereto, and a primary transfer portion 11Y that transfers the toner image on the photosensitive drum 6Y onto an intermediate transfer belt 10.
Toner images formed in the other image forming stations 5M, 5C, and 5K in substantially the same processes with the image forming station 5Y are transferred so as to be superimposed on the toner image on the intermediate transfer belt 10 transferred at the primary transfer portion 11Y, and thus a full-color toner image is formed on the intermediate transfer belt 10. The full-color toner image is transferred onto a sheet P by a secondary transfer portion 12 serving as a transfer member. Then, the toner image on the sheet P serving as a recording material passes through a fixing apparatus 15, and is fixed as a fixed image. Then, the sheet P is discharged onto a supporting portion 14 via a discharge conveyance portion 13 and is supported on the supporting portion 14.
To be noted, the image forming portion 5 described above is merely an example of an image forming unit. For example, a direct transfer system in which a toner image is directly transferred from an image bearing member onto the sheet P may be employed, and a monochromatic system in which only toner of one color is used may be employed.
Fixing Apparatus
The fixing apparatus 15 of the present embodiment is a fixing apparatus of an induction heating system serving as an image heating apparatus.
The fixing apparatus 15 includes a fixing film 20, a film guide 25, a pressurizing roller 21, a pressurizing stay 22, a magnetic core 26, an energizing coil 27 illustrated in
The fixing film 20 is a flexible rotary member having a cylindrical shape (i.e., tubular shape) and includes a base layer 20a, a heat-generation layer 20b serving as a heat-generation member, an elastic layer 20c, and a mold releasing layer 20d in this order from the inner circumferential side to the outer circumferential side. The base layer 20a is formed from a heat-resistant insulating resin such as polyimide, polyamide-imide, polyether ether ketone: PEEK, or polyethersulfone: PES. In the present embodiment, the base layer 20a having a cylindrical shape of an inner diameter of 30 mm, a length in the longitudinal direction X1 of 240 mm, and a thickness of about 60 μm was made by molding a polyimide resin.
The heat-generation layer 20b is formed into a heat-generation pattern in which heat-generation rings 201 illustrated in
Preferable examples of the material for the heat-generation layer 20b include materials having good electrical conductivity such as iron, copper, silver, aluminum, nickel, chromium, tungsten, alloys including these such as SUS304 (18Cr-8Ni stainless steel) and nichrome, carbon fiber-reinforced plastics: CFRP, and carbon nanotube resin. Examples of methods for forming the heat-generation pattern include printing, plating, sputtering, and vapor deposition, and in the present embodiment, the heat-generation rings 201 each had a width of 3 mm in the longitudinal direction X1 were arranged at intervals of 0.1 mm. In addition, these heat-generation rings 201 were formed as a nickel layer having a thickness of about 5 μm by electroless plating.
The elastic layer 20c is preferably formed from a material having high heat resistance and high thermal conductivity such as silicone rubber, fluorine rubber, or fluorosilicone rubber. In the present embodiment, the elastic layer 20c having a thickness of about 300 μm was formed from silicone rubber.
It is preferable that a material having high mold releasability and high heat resistance such as polyfluoroalkyl alkane: PFA, polytetrafluoroethylene: PTFE, or fluorinated ethylene propylene: FEP is selected. In the present embodiment, the mold releasing layer 20d having a thickness of about 15 μm was formed by covering the elastic layer 20c with a PFA resin tube. Here, PFA is a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, and FEP is a copolymer of tetrafluoroethylene and hexafluoropropylene.
The pressurizing roller 21, which is a pressurizing member serving as an opposing member opposing the fixing film 20 includes a core metal 21a, an elastic layer 21b formed coaxially to and around the core metal 21a in a roller shape to cover the core metal 21a, and a mold releasing layer 21c serving as a surface layer. The elastic layer 21b is preferably formed from a material having high heat resistance such as silicone rubber, fluorine rubber, or fluorosilicone rubber. Further, end portions of the core metal 21a in the longitudinal direction X1 are rotatably held by unillustrated chassis side metal plates of the apparatus via conductive bearings.
In addition, as illustrated in
The pressurizing roller 21 is rotationally driven in a clockwise direction in
The magnetic core 26 provided inside the energizing coil 27 induces magnetic field lines, that is, a magnetic flux of an alternating magnetic field generated by the energizing coil 27 on the inner circumferential side of the heat-generation layer 20b of the fixing film 20, and thus, forms a path of magnetic field lines, that is, a magnetic path. The magnetic core 26 is preferably formed from a material having a small hysteresis loss and high relative magnetic permeability, for example, a soft magnetic material having high magnetic permeability such as sintered ferrite or ferrite resin. The sectional shape of the magnetic core 26 may be any shape as long as the magnetic core 26 can be accommodated in the hollow portion of the fixing film 20, and although the sectional shape does not have to be circular, a shape whose sectional area is as large as possible is preferred. In the present embodiment, the magnetic core 26 had a diameter of 10 mm and a length in the longitudinal direction X1 of 280 mm.
The energizing coil 27 was formed by winding a copper wire coated with heat-resistant polyamide-imide and having a diameter of 1 to 2 mm around the magnetic core 26 about 20 times. The copper wire is an example of a wire made of a single conductive material. The energizing coil 27 is wound around the magnetic core 26 in a direction intersecting with the rotation axis direction of the fixing film 20. Therefore, when an alternating current of high frequency is supplied to the energizing coil 27, an alternating magnetic field is generated in a direction parallel to the rotation axis direction, and therefore, an induced current, which is a circulating current, flows in each heat-generation ring 201 of the heat-generation layer 20b of the fixing film 20 by the principle of electromagnetic induction as described later, and heat is generated.
As illustrated in
The thermistor 40 is fixed to the film guide 25 so as to be positioned at approximately the center of the fixing film 20 in the longitudinal direction X1. Further, the thermistor element 40b is pressed against and is held in a contacted state with the inner circumferential surface of the fixing film 20 by the spring elasticity of the spring plate 40a. To be noted, the thermistor 40 may be disposed on the outer circumferential side of the fixing film 20.
The current sensor 30 constituting a conduction monitoring device that monitors the conduction in the circumferential direction of the heat-generation layer 20b is disposed at the same position as the thermistor 40 in the longitudinal direction X1 of the fixing apparatus 15. That is, the current sensor 30 monitors the conduction state of a heat-generation ring 201 provided at a position where the thermistor element 40b is in contact with the fixing film 20. The principle and configuration of the current sensor 30 will be described in detail later.
Heating Principle
A heating principle of the fixing film 20 in the fixing apparatus 15 of an induction heating system will be described.
When an alternating magnetic field is formed by the energizing coil 27, the induced current I according to Faraday's law flows in each heat-generation ring 201 of the heat-generation layer 20b of the fixing film 20. Faraday's law states that “when a magnetic field in a circuit is changed, an induced electromotive force that acts to generate a current in the circuit is generated, and the induced electromotive force is proportional to temporal change of a magnetic flux perpendicularly passing through the circuit”.
The induced current I that flows in a heat-generation ring 201c in the case where an alternating current of a high frequency is supplied to the energizing coil 27 is assumed. The heat-generation ring 201c is positioned at a center portion in the longitudinal direction X1 of the magnetic core 26 illustrated in
V: induced electromotive force
N: number of turns of coil
ΔΦ/Δt: temporal change of magnetic flux perpendicularly passing through the circuit (heat-generation ring 201c) in a minute time Δt
This induced electromotive force V generates the induced current I, that is a circulating current that circulates in the heat-generation ring 201c, and the heat-generation ring 201c generates heat as Joule heat generated by the induced current I. However, in the case where there is a breakage within the heat-generation ring 201c, the induced current I does not flow and the heat-generation ring 201c does not generate heat.
Abnormal Temperature Rise Suppression Control
The thermistor 40 is connected to a temperature detecting portion 50. The temperature detecting portion 50 detects an inner surface temperature of the fixing film 20 as an electric signal input from the thermistor 40, and this electric temperature information is input to an engine controller 51. The engine controller 51 calculates power to be input to the fixing apparatus 15, and supplies a high-frequency current to the energizing coil 27 from an energizing circuit 53 via a power controller 52. In this manner, the temperature of the fixing film 20 is adjusted to and maintained at a predetermined target temperature. The target temperature is normally set within a range of about 150° C. to 200° C.
Further, in the case where information indicating that the temperature of the fixing film 20 is equal to or higher than a predetermined temperature higher than the setting range of the target temperature, for example, equal to or higher than 220° C., is input to the engine controller 51 from the temperature detecting portion 50, the engine controller 51 determines that the fixing film 20 is in an abnormal temperature rise state. In this case, the engine controller 51 serving as a controller or a blocking portion prohibits supply of power to the fixing apparatus 15, that is, blocks a driving voltage supplied from the energizing circuit 53 to the energizing coil 27, and emergency-stops the image forming operation.
Here, the current sensor 30 is disposed at a position corresponding to the position of the thermistor 40 in the longitudinal direction X1 of the fixing apparatus 15, that is, the rotation axis direction of the fixing film 20. For example, the difference between the center position of an outer magnetic core 30a, which will be described later, in the longitudinal direction X1 and the center position of the thermistor element 40b in the longitudinal direction X1 is preferably smaller than the width of the heat-generation ring 201, and is more preferably smaller than a half of the width of the heat-generation ring 201. In the present embodiment, the current sensor 30 and the thermistor 40 are provided at the same position in the longitudinal direction X1 provided that the influence of inevitable positional deviation caused by component tolerance, assembly tolerance, and so forth is ignored.
Therefore, the output signal of the current sensor 30 has correlation with the magnitude of the circulating current flowing in the circumferential direction in the heat-generation ring 201c opposing the thermistor 40, i.e., opposing ring in the present embodiment, among the plurality of heat-generation rings 201 constituting the heat-generation layer 20b of the fixing film 20. The output signal of the current sensor 30 is input to a detection result comparing portion 54 as information related to the magnitude of the circulating current flowing in the heat-generation ring 201c. In the case where the amount of current obtained as the detection result of the current sensor 30 is equal to or less than a threshold value, the detection result comparing portion 54 determines that a conduction failure in the circumferential direction has occurred in the heat-generation ring 201c opposing the thermistor 40, and transmits a conduction failure detection signal to the engine controller 51. The engine controller 51 that has received the conduction failure detection signal prohibits supply of power to the fixing apparatus 15, and emergency-stops the image forming operation.
By prohibiting the supply of power to the fixing apparatus 15 in the case where a conduction failure is detected in the heat-generation ring 201c, occurrence of abnormal temperature rise of the fixing film 20, as a result of the temperature detected by the thermistor 40 not reflecting the fixing film 20, can be suppressed. That is, when a conduction failure occurs in the heat-generation ring 201c opposing the thermistor 40, which is one of the ring-shaped regions (plurality of rings) constituting the heat-generation layer 20b, the circulating current does not flow and therefore heat is not generated in that region. In this case, the temperature detected by the thermistor 40 does not rise even though the other heat-generation rings 201 generate heat, and therefore there is a possibility that suppressing the abnormal temperature rise of the fixing film 20 is failed if detection of the abnormal temperature rise depends only on the thermistor 40. In contrast, in the present embodiment, the supply of power to the fixing apparatus 15 is prohibited, that is, blocked even in the case where the heat-generation ring 201c does not generate heat, and therefore the abnormal temperature rise of the fixing film 20 can be more reliably suppressed.
Here, in the case where a conduction failure occurs in a heat-generation ring 201 other than the heat-generation ring 201c opposing the thermistor 40, the temperature of a part of the fixing film 20 corresponding to the heat-generation ring other than the heat-generation ring 201c becomes lower than that of the surroundings thereof, and there is a possibility that a streak-shaped image defect occurs. However, since the temperature of the fixing film 20 is managed in a state in which at least the heat-generation ring 201c opposing the thermistor 40 is generating heat normally, there is no need to prohibit supply of power to the fixing apparatus 15 for suppressing the abnormal temperature rise of the fixing film 20.
Principle and Configuration of Conduction Monitoring Device
(1) Principle of Conduction Monitoring Device
The principle of the conduction monitoring device serving as a conduction detecting unit of the present embodiment will be described below. As described above, a circulating current generated by an induced electromotive force flows in the heat-generation layer 20b of the fixing film 20. The induced electromotive force is proportional to the temporal change of a magnetic flux Φ generated by the energizing coil 27 as expressed by the formula 1 described above. Since the magnetic flux Φ is proportional to the amount of current in the energizing coil 27, the induced electromotive force that acts on the heat-generation layer 20b can be obtained by measuring the current by connecting a typical current measurement circuit to the energizing coil 27. In contrast, the circulating current flowing in the heat-generation layer 20b cannot be measured by connecting a typical current measurement circuit.
Therefore, in the present embodiment, the principle of a current sensor of a current transformer: CT type, which is a non-contact current sensor, is applied in the present embodiment.
(2) Configuration of Conduction Monitoring Device
Next, a configuration of the conduction monitoring device according to the present embodiment will be described in detail.
In the present embodiment, a section taken along a circumferential direction in which an induced current flows in the fixing film 20, for example, a section viewed in the longitudinal direction X1 will be referred to as a first section. As a section intersecting with the first section, a section transverse to the induced current, for example, a section of
Further, by detecting the change in the magnetic flux crossing the third section by a winding wound around the magnetic path transverse to the third section, which corresponds to the winding illustrated in
As the magnetic path forming portion, as illustrated in
In the present embodiment, the outer magnetic core 30a has a U shape with right-angled corners, and the inner magnetic core 30b has an I shape, that is, a linear shape. The outer magnetic core 30a includes a first portion a1 extending in the longitudinal direction X1, a second portion a2 extending from a first end of the first portion a1 toward the fixing film 20, and a third portion a3 extending from a second end of the first portion a1 toward the fixing film 20. To be noted, among the magnetic cores included in the fixing apparatus 15, whereas the outer magnetic core 30a and the inner magnetic core 30b are provided for detecting breakage in the heat-generation layer 20b of the fixing film 20, the magnetic core 26 described above is related to induction heating of the fixing film 20.
As the current detecting portion or an obtaining portion, the detection coil 30c is wound around the outer magnetic core 30a, a shunt resistor 30d is connected to both ends of the detection coil 30c, and the potential difference, that is, the voltage between the both ends of the shunt resistor 30d is obtained as an output signal. Compared with the basic configuration of the CT current sensor illustrated in
(3) Width and Detection Sensitivity of Detection Magnetic Core
One important element related to the configuration of the outer magnetic core 30a around which the detection coil 30c is wound is the positional relationship between the circulating current flowing in the fixing film 20 and positions of a magnetic flux entrance 30a_in and a magnetic flux exit 30a_out illustrated in
However, the outer magnetic core 30a needs to have a certain length for providing a region for winding the detection coil 30c therearound, and therefore can be larger than the width of the heat-generation ring 201c in some cases. In this case, the outer magnetic core 30a is configured to monitor a plurality of heat-generation rings 201, and the change in the current at the time of breakage of the heat-generation ring 201c opposing the thermistor 40 is small. That is, a plurality of heat-generation rings 201 are included in a region surrounded by the magnetic path formed by the outer magnetic core 30a and the inner magnetic core 30b in the second section. Therefore, the contribution rate of the circulating current of the heat-generation ring 201c to the total current value of the circulating current intersecting with the magnetic path in the region surrounded by the magnetic path becomes low. As a result of this, in some cases, it is difficult to secure the detection sensitivity of the current sensor 30 appropriate for determining the conduction failure of the heat-generation ring 201c opposing the thermistor 40.
Therefore, in the present embodiment, a length W3 of the outer magnetic core 30a in the longitudinal direction X1 and a length W4 of the inner magnetic core 30b in the longitudinal direction X1 are set to be different, and the length of one magnetic core among these two around which the detection coil 30c is not wound, that is, the inner magnetic core 30b, is set to be shorter. More preferably, the length W4 of the inner magnetic core 30b in the longitudinal direction X1 is set to be smaller than the inner width W2 of the outer magnetic core 30a. As a result of this, the detection sensitivity of the current sensor 30 can be secured even in the case where, for example, it is difficult to set the length W3 of the outer magnetic core 30a to be smaller than the width W1 of the heat-generation ring 201.
To confirm the relationship between the lengths of the outer magnetic core 30a and the inner magnetic core 30b in the longitudinal direction X1 and the detection sensitivity, an experiment was conducted in conditions shown in Table 1. In this experiment, the heat-generation ring 201c opposing the thermistor 40 was intentionally broken, and the change rate of the output signal of the current sensor 30 in the breakage was calculated. The number of turns of the detection coil 30c was set to 100, and the resistance of the shunt resistor 30d was set to 10 kΩ. In addition, the inner width W2 of the outer magnetic core 30a was set to 3 mm in all examples.
The measurement described above was performed and the decrease rate of the output signal of the current sensor 30 was obtained for respective configurations of Comparative Example 1, Example 1, Comparative Example 2, and Example 2 shown in Table 1. The results are shown in Table 2.
As can be seen from Table 2, in the case where the inner magnetic core 30b was shortened, that is, where the core width of the inner magnetic core 30b was reduced, the decrease rate of output signal of the current sensor 30 increased. This can be seen from comparison between Example 1 and Comparative Example 1 and comparison between Example 2 and Comparative Example 2. That is, by setting the inner magnetic core 30b to be shorter than the outer magnetic core 30a in the longitudinal direction X1, the detection sensitivity of the current sensor 30 was improved, and the breakage detection performance of the conduction monitoring device including the current sensor 30 was improved. Further, as can be seen from the fact that the improvement rate of Example 2 from Comparative Example 2, which is 40/15, is higher than the improvement rate of Example 1 from Comparative Example 1, which is 50/45, setting the inner magnetic core 30b to be shorter in the longitudinal direction X1 is particularly effective in the case where the width of the heat-generation patter is small.
Here, the decrease rate of the output signal at the time of breakage is supposed to be approximately 100% if the current sensor 30 monitors only the heat-generation ring 201c that is broken. However, the decrease rate is about 50% at highest in the examples and comparative examples described above. The reason for this can be considered that the detection coil 30c received the influence of an excess magnetic flux generated by a circulating current flowing in heat-generation rings 201 that were not broken and were adjacent to the heat-generation ring 201c that was broken.
That is, in the present embodiment, unlike a normal CT current sensor illustrated in
Therefore, the measurement was performed again for a configuration in which a shielding member that surrounds the outer magnetic core 30a is additionally provided such that the detection coil 30c is not influenced by the excess magnetic flux generated by a source different from the heat-generation ring 201c as much as possible.
From the viewpoint of shielding the outer magnetic core 30a by absorbing an excess magnetic flux, a soft magnetic material having high magnetic permeability, for example, a soft magnetic metal material such as ferrite, permalloy, or silicon steel is preferably used as a material for the magnetic shield 30e. Therefore, a magnetic shield having a thickness of 2 mm and formed from ferrite was used this time.
To confirm the effect of the magnetic shield 30e, as shown in Table 3, the decrease rate of the output signal of the current sensor 30 at the time of breakage was calculated in the same conditions as in the case described above where the magnetic shield 30e was not provided. That is, the number of turns of the detection coil 30c was 100, and the resistance of the shunt resistor 30d was 10 kΩ. In addition, the inner width W2 of the outer magnetic core 30a was set to 3 mm in all examples.
The decrease rate of the output signal of the current sensor 30 was obtained by performing measurement for the respective configurations of Comparative Example 3, Example 3, Comparative Example 4, and Example 4 in substantially the same manner as in Table 2. The results are shown in Table 4.
As can be seen from Table 4, it was confirmed that as a result of the addition of the magnetic shield 30e, the decrease rate of the output signal at the time of breakage further increased, that is, the breakage detection performance of the conduction monitoring device was greatly improved as compared with Examples 1 and 2 described above in which the magnetic shield 30e was not provided. Further, it was also confirmed that the effect of setting the width of the inner magnetic core 30b to be short also increased.
In the embodiment described with reference to
In addition, although an I-shaped magnetic core is used as the inner magnetic core 30b in the embodiment described above, the configuration is not limited to this. For example, also in the case where the shape of the inner magnetic core 30b is set to the U shape employed for the outer magnetic core 30a, a similar effect can be obtained by setting the length thereof in the longitudinal direction X1 to be small and setting the inner width to be small.
In addition, although the detection coil 30c is formed on the outer magnetic core 30a in the embodiment described above, in principle, a similar effect can be obtained also by forming the detection coil 30c on the inner magnetic core 30b. However, the inner magnetic core 30b needs to be larger for forming the detection coil 30c thereon, and the diameter of the fixing film 20 needs to be increased for disposing the inner magnetic core 30b therein. In addition, the diameter of the fixing film 20 needs to be increased similarly in the case where a U-shaped inner magnetic core 30b is employed. From the viewpoint of miniaturizing the apparatus, it is preferable that the detection coil 30c is formed on the outer magnetic core 30a disposed on the outside of the fixing film 20, and it is preferable that an I-shaped inner magnetic core 30b is employed.
In addition, although an example in which a thermistor is used as the temperature detecting portion to block supply of power when an abnormal temperature is detected has been described in the embodiment above, the temperature detecting portion is not limited to this. A similar effect can be obtained by using a thermo switch having a mechanism of blocking a current by inversion of a bi-metallic strip at a predetermined temperature, a thermal fuse that blocks a current by operation of a spring mechanism caused by fusion of a pellet, or the like.
In addition, although the fixing film 20 formed from a flexible film material has been described as an example of a cylindrical rotary member having a heat-generation layer in the embodiment described above, a stiff cylindrical rotary member may be also used.
To be noted, although the width W1 of the heat-generation ring 201 illustrated in
While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of priority from Japanese Patent Application No. 2020-010967, filed on Jan. 27, 2020, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2020-010967 | Jan 2020 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20160026132 | Hirai | Jan 2016 | A1 |
| 20160313683 | Nishizawa | Oct 2016 | A1 |
| 20190018350 | Usui | Jan 2019 | A1 |
| 20200103800 | Nishizawa | Apr 2020 | A1 |
| 20210003948 | Isono | Jan 2021 | A1 |
| Number | Date | Country |
|---|---|---|
| 2015118232 | Jun 2015 | JP |
| 2017223820 | Dec 2017 | JP |
| 2018066808 | Apr 2018 | JP |
| 2018066810 | Apr 2018 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20210232073 A1 | Jul 2021 | US |
