JP2005148649A - Fixing device using induction heating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of exactly detecting that a heating member reaches an abnormal temperature and uniformly maintaining the temperature in the rotating direction of the heating member. <P>SOLUTION: The fixing device has the heating member heated by induction heating, a pressurization member for providing the heating member with a prescribed pressure and an induction heating mechanism for providing the heating member with a prescribed magnetic field. The device detects the temperature in a region having a possibility of being heated most by the induction heating mechanism among the outer peripheral surfaces of the heating member, for example, in the neighborhood where the outer peripheral surface of the heating member and the induction heating mechanism approach each other. If the detected temperature is within the range of the set abnormal temperature, the fixing device shuts off the electric power to be supplied to the induction heating mechanism. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device that is mounted on an image forming apparatus such as a copying machine or a printer and fixes a developer image on a sheet.

  An image forming apparatus, for example, an electronic copying machine, has a fixing device that fixes a developer image melted by heating to a sheet by applying pressure.

  There is an induction heating method as a method of heating the heating member of the fixing device. The induction heating method is a method in which a predetermined electric power is supplied to a coil to generate a magnetic field, and predetermined heat is generated in a heating member by Joule heat generated by an eddy current generated by the magnetic field.

  For example, an induction heating method in which a coil arranged opposite to a heating area where a heating member and a sheet contact area are divided is divided into a predetermined number of coils according to the size of the sheet and arranged outside the heating member. There is disclosed a fixing device using the above (see Patent Document 1).

  Also, fixing using an induction heating method that has a plurality of excitation coils and controls the amount of current supplied to excitation coils other than the first excitation coil in accordance with the amount of current supplied to the first excitation coil. An apparatus is disclosed (see Patent Document 2).

  Furthermore, it has several coils arrange | positioned facing the heating area | region which is arrange | positioned on the outer side of a heating member, and the area | region where a heating member and a paper contact is divided according to the size of the paper heated by a heating member. A fixing device using an induction heating system that supplies current to each of the plurality of coils independently is disclosed (see Patent Document 3).

  In the fixing device using the induction heating method as described in the above three publications, a heating member having a very high heat generation efficiency has a very fast temperature rise. There is a possibility that the vicinity facing the coil may locally generate heat.

  In addition, a fixing device having a fixing belt heated by a heating roller that generates heat by an induction heating method and a detecting unit that detects movement of the fixing belt in the rotational direction is disclosed (see Patent Document 4).

Further, in the fixing device in which the position heated by the heating member and the position providing a predetermined pressure to the sheet together with the pressure member are separated from the belt in contact with the passing sheet, It is disclosed that induction heating by a heating member is started (see Patent Document 5).
Japanese Patent Laid-Open No. 2001-235932 Japanese Patent Laid-Open No. 2000-206913 JP 7-295414 A JP 2002-40839 A JP 2002-82549 A

  Thus, the detection means for detecting that the heating member has risen to an abnormal temperature is required to be able to detect the temperature at a predetermined position where there is a possibility of local heat generation by the exciting coil.

  However, in the fixing device in which the exciting coil and the detecting means for detecting abnormal temperature cannot be arranged inside because the inside of the heating member is buried, for example, a predetermined position where there is a possibility of locally generating heat, for example, the coil and the heating member In the meantime, it is physically difficult to arrange the temperature detecting means.

  Further, in the fixing device using the heating member clogged inside, the abnormal temperature detecting means for detecting the abnormal temperature is arranged in the vicinity of the exciting coil, so that the magnetic field is uniformly provided from the exciting coil to the heating roller. However, there is a problem that the temperature is not maintained uniformly in the rotation direction of the heating member.

  An object of the present invention is to provide a fixing device that can accurately detect that a heating member has reached an abnormal temperature and can maintain a uniform temperature in the rotation direction of the heating member.

  According to the present invention, a cylindrical heating member that generates heat when a predetermined magnetic field is supplied, a pressurizing member that supplies a predetermined pressure to the heating member, an outer side of the heating member, and a predetermined electric power An induction heating mechanism that provides the predetermined magnetic field to the heating member by being supplied, and the induction heating mechanism includes at least one coil having a window portion in which no electric wire is arranged at the center, A parallel electric wire portion made of electric wires arranged on both sides of the window portion and parallel to the axial direction of the heating member, and a folded electric wire portion connecting the parallel electric wire portions arranged to face each other across the window portion. The abnormal temperature detection mechanism is provided in the window portion of the coil, and provides a fixing device that cuts off the electric power supplied to the coil when the temperature of the heating member reaches the abnormal temperature.

  The present invention also includes a cylindrical heating member that generates heat when a predetermined magnetic field is provided, a pressure member that supplies a predetermined pressure to the heating member, and a predetermined distance from the heating member. And an induction heating mechanism that provides the predetermined magnetic field to the heating member by supplying predetermined electric power, and the induction heating mechanism is arranged in a row in the axial direction of the heating member outside the heating member. Are arranged side by side and include at least two coils that provide the predetermined magnetic field to the heating member by supplying predetermined electric power, and are arranged in a joint region between the coil and the coil outside the heating member, It is an object of the present invention to provide a fixing device having an abnormal temperature detection mechanism that cuts off power supplied to the coil when the temperature of a heating member reaches an abnormal temperature.

  The present invention further includes a cylindrical heating member that generates heat when supplied with a predetermined magnetic field, a pressurizing member that supplies a predetermined pressure to the heating member, and an outer side of the heating member. An induction heating mechanism that provides the predetermined magnetic field to the heating member by supplying electric power, and the induction heating mechanism applies the predetermined magnetic field to the heating member by supplying predetermined electric power. Including a coil to be provided, a temperature detection unit that detects a temperature between the outer peripheral surface of the heating member and the coil, a heat pipe unit that transmits heat of the temperature detection unit, and heat from the heat pipe unit The temperature detection unit has an abnormal temperature detection mechanism that can detect at a position away from the heating member by a predetermined distance and cuts off the power supplied to the coil when the abnormal temperature of the heating member is reached based on the detection result. , There is provided a fixing device characterized in that it is arranged close to or in contact with the said heating element.

  As described above, the fixing device of the present invention can make the temperature distribution in the longitudinal direction of the heating roller uniform by preventing the temperature drop at the joint portion of the coil of the heating roller. Thereby, a good image can be obtained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows an example of a fixing device of the present invention. 2A and 2B and FIGS. 3A and 3B show examples of a coil body (induction heating mechanism) and an abnormal temperature detection mechanism provided in the fixing device. Further, FIG. 4 shows a configuration of an induction heating control circuit applicable to this fixing device.
As shown in FIG. 1, the fixing device can come into contact with the transfer material, that is, the surface of the paper P on which the toner T adheres, and the heating member (heating roller) 2 for heating the toner T and the paper P, and the heating And a pressure member (pressure roller) 3 that applies a predetermined pressure to the roller 2.

  The heating roller 2 includes a metal core (2a) that is a metallic (high rigidity) shaft that does not deform under a predetermined pressure, a foam rubber layer (sponge) 2b that is sequentially disposed around the metal core 2a, and a metal conductive layer 2c. And a solid rubber layer 2d and a release layer 2e. The foamed rubber layer (sponge) 2b is 5 mm thick, the metal conductive layer 2c is 40 μm thick, the solid rubber layer 2d is 200 μm thick and the release layer 2e is 30 μm thick, and the heating roller 2 is about 40 mm in diameter. Is preferred. The metal conductive layer 2c is formed of a conductive material (for example, nickel, stainless steel, aluminum, copper, a composite material of stainless steel and aluminum, or the like).

The pressure roller 3 includes a metal core 3a that is a metallic (high rigidity) shaft that does not deform with a predetermined pressure, and a silicon rubber 3b, a fluorine rubber 3c, and the like provided around the metal core 3a, and has a diameter of 40 mm. Preferably there is.
The pressure roller 3 receives a pressure from the pressure mechanism 4 to provide a predetermined pressure to the heating roller 2. The heating roller 2 that is in contact with the pressure roller 3 while maintaining a constant nip width by this pressure is rotated in the arrow direction (CW) by a drive motor (not shown). As the heating roller 2 rotates, the pressure roller 3 is rotated in the arrow direction (CCW).

Outside the heating roller 2, coil bodies (induction heating mechanisms) 5 and 6 that provide a predetermined magnetic field to the metal conductive layer 2 c of the heating roller 2 have a predetermined distance from the outer peripheral surface outside the heating roller 2. Are arranged.
When a predetermined current or voltage is supplied to the coil bodies 5 and 6, a predetermined magnetic field is generated. Due to the magnetic field from the coil bodies 5 and 6, an eddy current is generated in the metal conductive layer 2c of the heating roller 2 and Joule heat is generated. The toner T melted by the heat from the heating roller 2 passes through the contact portion (nip portion) between the heating roller 2 and the pressure roller 3 on the sheet P to which the toner T adheres, and is predetermined by the pressure roller 3. Is applied to the paper P by applying a pressure of.

Around the heating roller 2, a peeling blade 7 for peeling the paper P from the heating roller 3 in order of rotation from the contact position (nip portion) between the heating roller 2 and the pressure roller 3, and the heating roller 2. A release agent coating apparatus 8 for applying a release agent (for example, silicone oil) for preventing offset is disposed on the peripheral surface. Further, thermistors 9 a and 9 b for detecting the temperature in the vicinity of the peripheral surface of the heating roller 2 are arranged at predetermined positions in the longitudinal direction of the heating roller 2. In this embodiment, two thermistors 9a and 9b are used, but three or more may be used.
In the vicinity of the coil bodies 5 and 6, an abnormal temperature detection mechanism (thermostat) 10 is arranged that interrupts the current or voltage supplied to the coils 5 and 6 when the temperature of the heating roller 2 reaches the abnormal temperature.

Next, an example of coil bodies (induction heating mechanisms) 5 and 6 and an abnormal temperature detection mechanism applicable to the fixing device shown in FIG. 1 will be described with reference to FIGS.
2A is a view as seen from the direction of arrow P in FIG. 1, and FIG. 2B is a view as seen from the direction of arrow Q in FIG.
As shown in FIGS. 2A and 2B, the coil body 5 is disposed at a position facing the central area of the heating roller 2 (area where the paper P passes frequently), and the coil body 6 is a coil In a state in which the body 5 and the heating roller 2 are arranged in a line in the axial direction, the body 5 and the heating roller 2 are arranged at positions facing both end regions of the heating roller 2. The coil body 6 includes a coil body 61 disposed at one end of the heating roller 2 and a coil body 62 disposed at the other end of the heating roller 2, and the coil bodies 61 and 62 are connected in series. It is electrically one coil. Therefore, hereinafter, when describing both the coil bodies 61 and 62, they will be described as the coil body 6, and the same constituent elements will be described with the same alphabets and the like.

  The coil body 5 includes an exciting coil 5a formed in a predetermined shape (for example, a donut shape) by winding an electric wire around an imaginary shaft, and a magnetic core 5b disposed on the electric wire of the exciting coil 5a. A space portion (hereinafter referred to as a window portion) 5c where no electric wire exists is formed in the central portion of the exciting coil 5a including the imaginary shaft, and the magnetic core 5b is not disposed. That is, as shown in FIG. 2A, the exciting coil 5a includes a parallel electric wire portion made of electric wires extending in parallel with the magnetic core 5b, one parallel electric wire portion and an imaginary shaft (window portion 5c). ) And a folded electric wire portion that connects to another parallel electric wire portion arranged on the opposite side.

  Similarly, the coil bodies 61 and 62 (coil body 6) are respectively formed by exciting coils 61a and 62a (excitation coil 6a) in which electric wires are wound around an imaginary shaft and formed into a predetermined shape (for example, donut shape). The magnetic cores 61b and 62b are disposed on the electric wires of the exciting coils 61a and 62a, respectively. Space portions (window portions) 61c and 62c in which no electric wire exists are formed in the central portions of the exciting coils 61a and 62a including the imaginary shaft. That is, as shown in FIG. 2 (a), the exciting coils 61a and 62a include a parallel electric wire portion composed of electric wires extending in parallel with the magnetic cores 61b and 62b, one parallel electric wire portion and an aerial shaft, etc. And a folded electric wire portion connecting other parallel electric wire portions arranged on the opposite side across (window portions 61c, 62c). In addition, the magnetic cores 61b and 62b can be arrange | positioned in a parallel electric wire part except the window parts 61c and 62c similarly to the magnetic body core 5b.

  In addition, as the electric wires of the exciting coils 5a and 6a, litz wires obtained by bundling a plurality of electric wires whose surfaces are insulated are used. The exciting coils 5a and 6a formed by the litz wires can effectively generate a magnetic field even when an alternating current is supplied. In this embodiment, a litz wire in which 16 copper wires having a diameter of 0.5 mm whose surface is insulated with heat-resistant polyamideimide is bundled is used.

  Further, the number of windings of the exciting coils 5a, 61a, 62a can be reduced by providing the magnetic cores 5b, 61b, 62b. The coil bodies 5 and 6 are formed in the shape as described above, so that magnetic flux can be generated intensively, and a predetermined region of the heating roller 2 can be locally heated.

  When the exciting coils 5a and 6a are arranged such that the imaginary shafts intersect perpendicularly with the outer peripheral surface of the heating roller 2, the electric wires of the exciting coils 5a and 6a are spaced apart from each other on the outer peripheral surface of the heating roller 2. Area (hereinafter referred to as a coil area) 2-5a, 2-61a, 2-62a and windows 5c, 61c, 62c in which no electric wires are arranged are located and electric wires are arranged around 2-5c, 2-61c, and 2-62c (hereinafter referred to as window region) are formed. Therefore, when the heating roller 2 is viewed from the direction as shown in FIG. 2A, no electric wires are arranged in the window regions 2-5c, 2-61c, and 2-62c, so that the surface of the heating roller 2 can be seen.

  In this window area 2-5c, the temperature of the heating roller 2 is detected, and when the detected temperature reaches the abnormal temperature, the abnormal temperature detection for cutting off the power supplied to the exciting coils 5a, 61a, 62a. A mechanism (thermostat) 10 is arranged with a predetermined interval. The abnormal temperature is higher than the temperature range (normal temperature) required for fixing, and other members mounted on the fixing device malfunction, or the heating roller 2 and the pressure roller 3 are It is defined as the upper limit temperature when the current stops and the current continues to be supplied to the exciting coil.

  Therefore, the thermostat 10 can detect the heat generated from the window region 2-5c of the heating roller 2 by the magnetic field provided from the surrounding excitation coil 5a. Moreover, the heat from the coil area | region 2-5a which generate | occur | produces heat with the magnetic field provided from the exciting coil 5a is transmitted to the window part area | region 2-5c. For this reason, even if the heating roller 2 stops and the coil area 2-5a generates heat locally and reaches an abnormal temperature, a temperature close to the coil area 2-5a having the highest temperature is obtained. It can be detected.

  When the thermostat 10 detects this abnormal temperature, the thermostat 10 cuts off the electric power supplied to the exciting coils 5a and 6a.

  Moreover, the thermostat 10 may have the magnetic field shielding material 10A which prevents that the magnetic field from the surrounding excitation coil 5a is provided as FIG.3 (a) shows. With this magnetic shielding material 10A, for example, the thermostat 10 can be prevented from malfunctioning due to the influence of the magnetic field from the exciting coil 5a and the temperature rising due to induction heating (induction current), making it impossible to detect the true value. . As shown in FIG. 3B, the magnetic field shielding material 10 </ b> A has a shape that covers the surface of the thermostat 10 that faces the excitation coil except for the portion where the thermostat 10 and the outer peripheral surface of the heating roller 2 face each other. It is preferable.

  Thus, by arranging the abnormal temperature detection mechanism (thermostat 10) in the coil window, the space of the abnormal temperature detection mechanism can also be used as the space of the exciting coil, and the space around the outside of the heating roller 2 can be used effectively. it can.

  In the example shown in FIG. 2A, the thermostat 10 is arranged in the window portion 5c of the excitation coil 5a. However, the present invention is not limited to this, and the window portions 61c and 62c of the excitation coils 61a and 62a. It may be arranged in any one of these. Moreover, two thermostats may be provided in the window parts 5c and 61c or the window part 5c.

  Next, referring to FIG. 4, the configuration of an induction heating control circuit applicable to the fixing device shown in FIG. 1 and a method of operating this fixing device will be described. The induction heating control circuit includes a coil current control circuit 200, a rectifier circuit 25, a commercial AC power supply 26, an input power monitor 27, a CPU 28, and thermistors 31 and 32. The commercial AC power supply 26 is a power supply that provides power for operating the fixing device of the present invention, and is a part of power supplied to a copying machine or the like equipped with the fixing device.

  The coil current control circuit 200 includes the excitation coils 5a, 61a, 62a described above.

  The first resonance circuit includes an exciting coil 5a and a resonance capacitor 21 connected in parallel. Further, the first inverter circuit includes a first resonance circuit and a switching element 23 connected in series.

  The second resonance circuit includes an exciting coil 6a connected in parallel and a resonance capacitor 22. The exciting coil 6a is an electrically single coil in which exciting coils 61a and 62a are connected in series. is there. Further, the second inverter circuit includes a second resonance circuit and a switching element 24 connected in series. As the switching elements 23 and 24, IGBTs or MOS-FETs that can be used with a high breakdown voltage and a large current are used.

  The first and second inverter circuits are supplied with a direct current from a commercial alternating current power supply 26 smoothed by the rectifier circuit 25. In addition, between the rectifier circuit 25 and the commercial AC power supply 26, an input power monitor 27 for monitoring the input power PI that is a product of the current and voltage provided from the thermostat 10 and the commercial AC power supply 26 is connected. Yes.

  The input power monitor 27 includes a transformer (transformer) 27a connected to the commercial AC power supply 26, and an input power detection circuit 27b that detects input power PI transmitted from the transformer 27a. The input power detection circuit 27b is connected to the CPU 28, and information on the input power PI detected by the transformer 27a is fed back.

  The CPU 28 is connected to the drive circuits 29 and 30, the drive circuit 29 is connected to the control terminal of the switching element 23, and the drive circuit 30 is connected to the control terminal of the switching element 24. When the drive circuits 29 and 30 are operated by the CPU 28, a high frequency current flows through the exciting coils 5a and 6a to generate a predetermined magnetic field. When this predetermined magnetic field is provided to the heating roller 2, an eddy current is generated in the heating roller 2, and the excitation coil 5a causes a predetermined area 2A (center area) of the heating roller 2 and an excitation coil 6a to Heat is generated from each of the predetermined regions 2B (end regions). Thermistors 31 and 32 for detecting the surface temperature of the heating roller 2 are disposed in the vicinity of the predetermined areas 2A and 2B of the heating roller 2.

  The thermistors 31 and 32 output the detected surface temperature of the heating roller 2 to the CPU 28 as a temperature detection signal (voltage value). In response to the temperature detection signal, the CPU 28 can selectively switch the drive circuits 29 and 30 to be operated. For example, when the temperature of the thermistor 31 is lower than the temperature of the thermistor 32 by a predetermined temperature, the drive circuit 29 to which the excitation coil 5a is connected is driven to heat the heating roller central portion 2A. When the temperature of the thermistor 32 becomes lower than the temperature of the thermistor 31 by a predetermined temperature, the drive circuit 30 to which the exciting coil 6a is connected is driven to heat the heating roller end 2B. Therefore, the center region 2A and the end region 2B of the heating roller 2 are alternately heated.

  The thermistors 31 and 32 may be disposed in the windows 5c, 61c, and 62c. In addition, the induction heating control circuit for generating heat from the heating roller 2 shown in FIG. 4 is not limited to the configuration described above, but a half that independently changes the frequency of the drive voltage supplied to the switching elements 23 and 24. A bridge die circuit, a quasi-E class circuit, or the like, or a PWM (pulse width modulation) may be used as a drive circuit.

  Next, an example of a method for operating the fixing device will be described with reference to the induction heating control circuit shown in FIG.

  The CPU 28 drives the drive circuits 29, 30 so as to alternately supply current or voltage (hereinafter referred to as coil output power, which is the product of the current and voltage) to the exciting coils 5a, 6a alternately at a predetermined ratio (time ratio). To instruct. For example, the time when power is supplied to the excitation coil 5a by the drive circuit 29 is 2, and the time when power is supplied to the excitation coil 6a by the drive circuit 30 is 1, and the central portion of the heating roller 2 through which the sheet P passes more. Increase the time ratio at which is heated. The drive circuits 29 and 30 alternately supply a drive voltage as an ON / OFF signal to the control terminals of the switching elements 23 and 24 at a predetermined timing and frequency specified by the CPU 28.

  For example, when one switching element 23 supplied with the driving voltage is turned ON, the other switching element 24 not supplied with the driving voltage is turned OFF.

  When the switching element 23 is turned on, predetermined power corresponding to the frequency of the drive voltage is supplied from the rectifier circuit 25 to the exciting coil 5a (including a high-frequency current in the frequency range of 20 to 50 kHz in this embodiment). The The exciting coil 5a generates a magnetic field according to the supplied power. By providing this magnetic field, an eddy current flows through the predetermined region 2A of the heating roller 2 near the exciting coil 5a, and the heating roller 2 generates heat due to Joule heat. Similarly, when the switching element 24 is turned on by the drive circuit 30, the predetermined region 2B of the heating roller 2 generates heat.

  However, when an abnormality such as the heating roller 2 stops in the fixing device, the coil region 2-5a on the outer peripheral surface of the heating roller 2 facing the electric wire of the exciting coil 5a may locally rise to an abnormal temperature. .

  As described above, the thermostat 10 can detect the temperature of the outer peripheral surface of the heating roller 2 that generates heat by the magnetic field provided from the surrounding excitation coil 5a.

  Therefore, the thermostat 10 can detect the temperature of the region close to the coil region 2-5a having the highest temperature in the outer peripheral surface of the heating roller 2 generated by the exciting coil 5a. That is, the thermostat 10 can detect the temperature of the heating roller 2 by heat conduction at a response speed as fast as the response speed for detecting the temperature of the coil region 2-5a.

  When the heating roller 2 generates heat to an abnormal temperature, the thermostat 10 detects the abnormal temperature of the heating roller and cuts off the electric power supplied from the commercial AC power supply 26 to the rectifier circuit 25.

  The operation method of the fixing device is not limited to this. For example, the exciting coil 5a disposed in the central region of the heating roller 2 according to the size of the paper P passing between the heating roller 2 and the pressure roller 3 The surface of the heating roller 2 can be heated uniformly by selectively switching the timing of supplying power to 6a arranged in the end region of the heating roller 2.

  Specifically, when the longer side such as A4 size or A3 size is passed in parallel to the longitudinal direction of the heating roller 2, one side having the same length as the sheet passing area in the longitudinal direction of the heating roller 2 is used. In the case where the full-size paper has been passed, electric power is supplied to the exciting coil 5a located at the center of the heating roller 2 and the exciting coil 6a located at the end at approximately the same rate.

  On the other hand, when a small size paper such as a postcard is passed, or when the shorter side of A4 size is passed parallel to the longitudinal direction of the heating roller 2, power is supplied to the coil 5a located in the center. The ratio to be increased is larger than the ratio at which power is supplied to the coil 6a located at the end.

  For example, when changing the maximum value of the coil output power (the product of the current and voltage supplied to both the coils 5a and 6a) supplied to the coils 5a and 6a according to the operation mode, the switching elements 23 and 24 are changed. The coil output power can be changed in the range of 700 W to 1500 W by controlling the frequency of the drive voltage supplied to the power source in the range of 20 to 50 kHz.

  Further, by providing a rotation detection mechanism in the induction heating control circuit shown in FIG. 4, it is possible to prevent the heating roller from generating heat to an abnormal temperature, and to further improve the safety of the fixing device.

  As shown in FIG. 5, a rotation detection mechanism 33 that can detect the rotation of the heating roller 2 is disposed at a predetermined position of the heating roller 2.

  For example, the rotation detection mechanism 33 indicates that a pulse plate (FG plate) 33a fixed to the metal core 2a (shaft) of the heating roller 2 is rotated by the heating roller 2 as the predetermined rotation of the fixing device 1 is performed. The rotation of the heating roller 2 can be detected by detecting with the photosensor 33b fixed at the position. Note that the rotation detection mechanism 33 is not limited to this, and the marking at a predetermined position on the outer peripheral surface of the heating roller 2 may detect the rotation of the heating roller 2 using a light detection unit or the like.

  The rotation detection mechanism 33 has an output terminal connected to an input terminal of an AND circuit 34 connected to the drive circuit 29 and an output terminal connected to an input terminal of an AND circuit 35 connected to the drive circuit 30. The AND circuits 34 and 35 are further connected to the CPU 28 on the input terminal side.

  Therefore, the AND circuit 34 receives the rotation detection signal output from the rotation detection mechanism 33 and the instruction signal (hereinafter referred to as an excitation control signal) for driving the drive circuit 29 output from the CPU 28. A signal for driving 29 (hereinafter referred to as a drive signal) is output. The drive circuit 29 to which this drive signal is input turns on the switching element 23, and predetermined power is supplied to the exciting coil 5a.

  Similarly, when the rotation detection signal output from the rotation detection mechanism 33 and the excitation control signal for driving the drive circuit 30 output from the CPU 28 are input, the AND circuit 35 generates a drive signal for driving the drive circuit 30. Output. The drive circuit 30 to which the drive signal is input turns on the switching element 24, and predetermined power is supplied to the exciting coils 61a and 62a.

  That is, power is supplied to the excitation coils 5a, 61a, 62a when the heating roller 2 is rotating, and no power is supplied when the heating roller 2 is stopped.

  Therefore, even if a trouble occurs in the CPU 28 or the thermistors 9a and 9b, the rotating roller 2 is not heated by the exciting coils 5a and 6a unless accompanied by rotation. Therefore, it is possible to prevent the outer peripheral surface of the heating roller 2 from locally generating heat to an abnormal temperature, and the safety of the fixing device 1 is greatly increased as compared with the conventional case.

  In order to further improve safety, a temperature detection mechanism (thermistor) 36 that detects the temperature of the pressure roller 3 may be provided at a predetermined position close to the outer peripheral surface of the pressure roller 3. When the rotation detection signal and the excitation control signal are input to either the AND circuit 34 or the AND circuit 35, the temperature of the pressure roller 3 is within a predetermined range due to heat conduction from the rotating heating roller 2. Rise. That is, based on the information on the temperature of the pressure roller 3 from the thermistor 36, when the temperature of the pressure roller 3 output from the thermistor 36 has risen to a predetermined range, the heating roller 2 is rotating. If the temperature of the pressure roller 3 does not rise, it can be determined that the heating roller 2 is not rotating.

  Due to this, the CPU 28 is set so that the excitation control signal is output to either the AND circuit 34 or the AND circuit 35 only when the temperature of the pressure roller 3 rises to a predetermined range. To do. As a result, for example, even if the rotation detection signal is input to the AND circuit 31 or the AND circuit 32 even though the heating roller 2 is not rotating, the excitation control signal is output. Therefore, no power is supplied to the exciting coils 5a, 61a, 62a.

  Therefore, even if a trouble occurs in the rotation detection mechanism 33 or the thermistors 9a and 9b, the heating roller 2 is not heated by the excitation coils 5a and 6a unless it is rotating. Therefore, it is possible to prevent the outer peripheral surface of the heating roller 2 from locally generating heat to an abnormal temperature.

  Further, the rotation detection mechanism 33 may detect the rotation speed of the heating roller 2. By feeding back the detection result, the CPU 28 can keep the rotation speed of the heating roller 2 constant. Therefore, an appropriate image is formed on the sheet passing between the heating roller 2 and the pressure roller 3.

  Next, different examples of the coil bodies 5 and 6 described with reference to FIGS. 2A and 2B and the thermostat 10 will be described with reference to FIG. 6 is a view seen from the direction of arrow P in FIG. Detailed descriptions of the same configurations as those in FIGS. 2A and 2B are omitted.

  As shown in FIG. 6, on the outside of the heating roller 2, a coil body 105 that heats the central region of the heating roller 2 (region where the paper P passes frequently) and both end regions of the heating roller 2 are provided. The coil bodies 106 (161, 162) to be heated are arranged in a line in the axial direction of the heating roller 2.

  The coil body 105 includes an exciting coil 105a in which an electric wire is wound around an imaginary shaft and formed in a predetermined shape, and a magnetic core 105b disposed on the exciting coil 105a and covering the window portion 105c.

  Similarly, coil bodies 161 and 162 (coil body 106) are arranged on excitation coils 161a and 162a (excitation coil 106a) in which electric wires are wound around an imaginary shaft, respectively, and excitation coils 161a and 162a. And have magnetic cores 161b and 162b that cover the windows 161c and 162c, respectively.

  When the imaginary shafts of the exciting coils 105a and 106a are arranged so as to intersect perpendicularly with the outer peripheral surface of the heating roller 2, the surface of the heating roller 2 is placed in a predetermined region of the joint region W11 between the exciting coils 5a and 61a. A region is formed where is visible. An abnormal temperature detection mechanism that cuts off the electric power supplied to the exciting coils 105a, 161a, and 162a when the temperature detected by detecting the temperature of the heating roller 2 reaches the abnormal temperature at a predetermined position of the joint region W11. A (thermostat) 110 is arranged.

  Similarly, a region where the surface of the heating roller 2 can be seen is formed in the joint region W12 between the exciting coils 5a and 62a, and the thermostat 111 can be arranged at a predetermined position of the joint region W12. Note that the thermostats 110 and 111 are preferably arranged close to the exciting coil.

  Therefore, the thermostats 110 and 111 can detect the temperature of the heating roller 2 by heat conduction at a faster response speed. This is because, for example, the thermostats 110 and 111 are arranged in the vicinity of a region where a magnetic field is continuously provided, such as between the electric wire of the exciting coil 105a and the heating roller 2, so that the response speed is appropriately secured. It is. Therefore, even if the heating roller 2 stops and generates heat locally, an abnormality in the temperature rise in the region where the temperature is highest on the outer peripheral surface of the heating roller 2 can be detected.

  Further, by providing two thermostats 110 and 111, even if one of them does not function due to a failure or the like, the other one can detect an abnormal temperature. Needless to say, even if only one of them is detected, an abnormality in temperature rise in the region of the outer peripheral surface of the heating roller 2 where the temperature is highest can be detected.

  Further, the magnetic field shielding material 110A that prevents the thermostat 110 from being provided with the magnetic field from the excitation coils 5a and 61a, and the magnetic field shielding material 111A that prevents the thermostat 111 from being provided with the magnetic field from the excitation coils 5a and 62a. May be provided.

  Next, further different examples of the coil bodies 5 and 6 and the thermostat 10 described with reference to FIGS. 2A and 2B will be described with reference to FIG. 7 is a view seen from the direction of arrow P in FIG. Detailed descriptions of the same configurations as those in FIGS. 2A and 2B are omitted.

  As shown in FIG. 7, outside the heating roller 2, a coil body 205 that heats the central area of the heating roller 2 (an area where the paper P passes frequently) and both end areas of the heating roller 2 are provided. The coil bodies 206 (261, 262) to be heated are arranged in a line in the axial direction of the heating roller 2.

  The coil body 205 includes an exciting coil 205a formed in a predetermined shape (for example, a trapezoidal shape) by winding an electric wire around an imaginary shaft, and a magnetic core 205b disposed on the exciting coil 205a. For example, as shown in FIG. 7, the exciting coil 205 a is provided with a magnetic core 205 b, and includes a parallel electric wire portion made of electric wires extending in parallel to the axial direction of the heating roller 2, one parallel electric wire portion and an imaginary shaft. And a folded electric wire portion connecting the other parallel electric wire portion arranged on the opposite side between the two. The folded electric wire portion includes first and second straight portions that intersect the parallel electric wire portion at a predetermined angle (that is, the non-parallel sides of the trapezoid).

  The coil body 261 includes an excitation coil 261a having a third linear portion formed in accordance with one folded wire portion of the excitation coil 205a adjacent to one end, that is, the first linear portion, and the excitation coil 261a. Including a magnetic core 261b. Similarly, the coil body 262 includes an excitation coil 262a having a fourth straight line portion formed in accordance with the other one folded electric wire portion adjacent to one end, that is, the second straight line portion. The magnetic core 262b is disposed on the exciting coil 262a. The excitation coil 205a is not limited to a trapezoidal shape as shown in FIG. 7, and may be formed in a parallelogram shape in which the first and second straight portions are parallel, for example.

  The excitation coil 261a is disposed with a distance L1 between the excitation coil 205a. Between the exciting coils 205a and 261a, the temperature of the heating roller 2 is detected. When the detected temperature reaches an abnormal temperature, a thermostat 210 that cuts off the electric power supplied to the exciting coils 205a, 261a, and 262a. Is placed. Similarly, the excitation coil 262a is arranged with a distance L2 between the excitation coil 205a. A thermostat 211 is disposed between the exciting coils 205a and 262a. Note that the thermostats 210 and 211 are preferably arranged close to the exciting coil.

  Accordingly, the thermostats 210 and 211 are disposed in the vicinity of a region where a magnetic field is continuously provided, for example, between the electric wire of the exciting coil 205a and the heating roller 2, so that the temperature of the heating roller 2 can be increased with a faster response speed. Can be detected by heat conduction. Therefore, even if the heating roller 2 stops and generates heat locally, an abnormality in temperature rise in the region where the temperature is highest can be detected.

  Further, for example, even in a fixing device including a heating roller 2 as shown in FIG. 1 in which an excitation coil cannot be arranged, a space where an abnormal temperature detection mechanism is arranged (occupation of an excitation coil arranged outside the heating roller 2) The area) can be suppressed to a predetermined area divided in the axial direction of the heating roller 2 used by the exciting coils arranged in a row.

  Of the regions divided in the direction orthogonal to the axial direction, the region where the magnetic field is provided from the exciting coils 205a and 261a is supplied to the joint portion W21 of the exciting coil when a predetermined power is supplied to the exciting coil. Including. Similarly, the joint portion W22 of the exciting coil includes a region where a magnetic field is provided from the exciting coils 205a and 262a when predetermined power is supplied to the exciting coil.

  Therefore, in the joint portions W21 and W22 of the coils, the regions where the magnetic fields are provided from the adjacent exciting coils are overlapped (overlapped), so that temperature reduction can be prevented, and the longitudinal direction of the heating roller 2 can be prevented. The temperature distribution can be made uniform.

  The thermostats 210 and 211 may be provided with magnetic field shielding materials 210A and 211A, respectively. Further, when the thermostat 211 is removed using the thermostat 210 as the abnormal temperature detection mechanism, the exciting coils 205a and 262a are preferably arranged close to each other.

  Furthermore, different examples of the coil bodies 5 and 6 and the thermostat 10 described with reference to FIGS. 2A and 2B will be described with reference to FIGS. 8A, 8B, and 8C. 8A is a schematic diagram showing the relationship between the heating roller 2 and the abnormal temperature detection mechanism, and FIG. 8B is a view seen from the direction of arrow P in FIG. 8A. FIG.8 (c) is the figure seen from the arrow Q direction of Fig.8 (a). Detailed descriptions of the same configurations as those in FIGS. 2A and 2B are omitted.

  As shown in FIG. 8B, outside of the heating roller 2, both the coil body 305 that heats the central region of the heating roller 2 (the region where the paper P passes frequently) and the heating roller 2 are provided. Coil bodies 306 (361, 362) for heating the end regions are arranged.

  The coil body 361 that heats one end region of the heating roller 2 has a part of the region R1 through which the paper P passes in the longitudinal direction of the heating roller 2 and the paper P does not pass in the longitudinal direction of the heating roller 2. A coil body 362 that is arranged to face a part of the region (non-sheet passing region) R2 and heats the other end region is a part of the region R1 through which the paper P passes in the longitudinal direction of the heating roller 2. The heating roller 2 is disposed so as to face a part of a region (non-sheet passing region) R3 where the paper P does not pass in the longitudinal direction of the heating roller 2.

  The coil body 305 has an exciting coil 305a formed in a predetermined shape (for example, a donut shape) by winding an electric wire around an imaginary shaft, and a magnetic core 305b disposed on the exciting coil 305a. The coil bodies 361 and 362 (coil bodies 306) include excitation coils 361a and 362a (excitation coils 306a) in which electric wires are wound around an imaginary shaft and formed in a predetermined shape (for example, donut shape), and the excitation coils. The magnetic cores 361b and 362b are disposed on the 361a and 362a, respectively.

  A part of the abnormal temperature detection mechanism (heat pipe type) 310 is disposed close to or in contact between the exciting coil 362a and the non-sheet passing region R3.

  The abnormal temperature detection mechanism 310 includes a first conductive member 311 disposed between the outer peripheral surface of the heating roller 2 and the electric wire of the excitation coil 362a in proximity to or in contact with the outer peripheral surface of the heating roller 2, and the first conductive member 311. A heat pipe 312 for transferring heat from the conductive member 71 to a position away from the heating roller 2, a second conductive member 313 for transferring heat from the heat pipe 312, and the second conductive member 313. When the detected temperature reaches the abnormal temperature, the abnormal temperature detection unit 314 that cuts off the power supplied to the exciting coils 305a, 361a, and 362a is provided.

  The first conductive member 311 is made of a material having high thermal conductivity (for example, a material containing copper, aluminum, silver, or the like). Further, the first conductive member 311 may include a material that does not easily generate heat by induction heating for generating heat from the heating roller 2, that is, a material that has a deep penetration depth of magnetic flux generated from an excitation coil used for induction heating. Good. Accordingly, since a large amount of magnetic flux from the excited coil passes through the first conductive member 311, the first conductive member 311 does not generate heat.

  The second conductive member 313 is made of a material that has very high thermal conductivity and does not generate heat due to the magnetic field from the exciting coil 362a (for example, a material containing copper, aluminum, silver, or the like).

  Note that the first conductive member 311, the heat pipe 312, and the second conductive member 313 can be integrally formed.

  When predetermined power is supplied to the exciting coils 305a, 361a, and 362a and the heating roller 2 generates heat, the first conductive member 311 is heated to a temperature substantially equal to the surface of the heating roller 2 by the radiant heat from the heating roller 2. Is done. The second conductive member 313 disposed at a predetermined position where the abnormal temperature detector 314 can be disposed holds the temperature of the first conductive member 311 by heat transfer using the heat pipe 312. Therefore, the abnormal temperature detection unit 314 to which the radiant heat from the second conductive member 313 is provided is the temperature of the first conductive member 311, that is, the outer periphery of the heating roller 2, even at a position away from the heating roller 2. A temperature substantially equal to the surface can be detected.

  Therefore, the abnormal temperature detection unit 314 does not need to be disposed in the vicinity of the heating roller 2, and the abnormal temperature detection unit 314 and the excitation coils 305a, 361a, and 362a are not limited in their respective locations.

  Here, when the heating roller 2 generates heat to an abnormal temperature, the first conductive member 311 disposed between the heating roller 2 and the exciting coil 362a can detect the temperature of the heating roller 2 at a faster response speed. This temperature is detected by the abnormal temperature detector 314 through the heat pipe 312 and the second conductive member 313. The abnormal temperature detection unit 314 that has detected the abnormal temperature cuts off the power supplied to the exciting coils 305a, 361a, and 362a.

  Therefore, even if the heating roller 2 is stopped, the abnormal temperature detection unit 314 can detect a temperature substantially equal to the temperature of the first conductive member 311 that is close to the heating roller 2 at a fast response speed. Therefore, it is possible to prevent the heating roller 2 from locally generating heat.

  When the first conductive member 311 is brought into contact with the heating roller 2, the first conductive member 311 can detect the surface temperature of the heating roller 2 with an earlier response time.

  Further, the arrangement position of the first conductive member 311 is not limited to this, and may be, for example, the region R1 through which the paper P passes. In this case, it is preferable that the first conductive member 311 does not contact the outer peripheral surface of the heating roller 2.

  Further, when the response time of the abnormal temperature detection unit 314 is shifted due to a delay in heat transfer, the power supplied to the exciting coils 305a, 361a, and 362a can be cut off when the heating roller 2 reaches the abnormal temperature. The temperature lower than the abnormal temperature of the heating roller 2 may be set to a temperature level at which the abnormal temperature detection unit 314 blocks the abnormal temperature.

  Next, different examples of the abnormal temperature detection method applicable to the fixing device of the present invention will be described.

  FIG. 9 shows different examples of induction heating control circuits applicable to the fixing device of the present invention.

  As shown in FIG. 9, the induction heating control circuit includes a coil body 405 disposed opposite to the central region of the heating roller 2 on the outside of the heating roller 2 and the heating roller 2, as in the example described above. The coil bodies 406 (461, 462) disposed at positions facing both end regions of the two are connected. The coil bodies 405, 461, and 462 have excitation coils 405a, 461a, and 462a, respectively.

  Similar to the induction heating control circuit shown in FIG. 4, the coil current control circuit 300 including the exciting coils 405a, 461a, and 462a includes the capacitor 21 and the switching element 23, and a third inverter that supplies power to the exciting coil 405a. The circuit includes a capacitor 22 and a switching element 24, and includes a fourth inverter circuit that supplies power to the exciting coils 461a and 462a. The third and fourth inverter circuits are connected to drive circuits 29 and 30, respectively.

  Further, the coil current control circuit 300 is connected to the commercial AC power supply 26 via the rectifier circuit 25 and is connected to the CPU 28 that can drive the drive circuit based on the input from the input power monitor 27 or the thermistors 31 and 32.

  In addition, the structure of this induction heating control circuit removes the abnormal temperature detection mechanism 10 from the circuit of FIG. 4, and detailed description is abbreviate | omitted.

  The third and fourth inverter circuits are self-excited oscillation circuits that efficiently use the resonance by the respective excitation coils and capacitors to efficiently supply a high-frequency current to the excitation coils.

  The operation of this self-excited oscillation circuit will be described below.

  FIGS. 11A, 11B, 11C, and 11D show an equivalent circuit EC of the third inverter circuit, and are diagrams for explaining a current flowing through the equivalent circuit EC. FIGS. 10A and 10B are reference diagrams showing the relationship between the current flowing through the equivalent circuit EC of the third inverter circuit and time.

  As shown in FIGS. 10A and 10B, the equivalent circuit EC of the third inverter circuit has a length of the ON time (OP time) of the switching element 23 that is turned ON / OFF by the CPU 28. A current having a predetermined frequency corresponding thereto flows. In this frequency, one period is time OR.

  As shown in FIG. 11A, the current from the power source PW flows through the switching element 23 and the exciting coil 405a in the ON state as indicated by an arrow A at time OP. When the switching element 23 is turned OFF, the current flowing through the switching element 23 flows to the resonance capacitor 21 as shown by an arrow B as shown in FIG. 11B, and the resonance capacitor 21 is charged at time PQ. .

  The charged resonance capacitor 21 starts discharging as shown in FIG. A reverse current as indicated by an arrow C flows through the resonant capacitor 21 in the discharged state, and the voltage becomes zero when the time QR has elapsed. However, this reverse current does not stop suddenly, flows into the diode 23a of the switching element 23, and flows as indicated by the arrow D in FIG. 11D for a time RS.

  When the switching element 23 is turned on again, a predetermined current flows through the exciting coil 405a. By repeating this cycle OS, the heating roller 2 is provided with a predetermined magnetic field and generates heat. At time P, the value X1 of the current flowing through the exciting coil 405a is a peak current value. The peak current value X1 can be calculated by feeding back the input power PI monitored by the input power monitor 27 described above to the CPU. The input power PI is determined based on the heat output (W) of the heating roller 2 that generates heat by the magnetic field provided from the exciting coil 405a.

  The heat output of the heating roller 2 is thermal energy when the heating roller 2 through which eddy current flows is generated by a magnetic field generated according to a predetermined value of current flowing through the exciting coil 405a. This is defined as energy obtained by subtracting predetermined energy wasted due to induction heating from input power PI monitored by the monitor 27.

  Therefore, by monitoring the input power PI, the peak current value X1 of the exciting coil 405a is calculated, and the temperature of the heating roller 2 based on the energy when the heating roller 2 generates heat can be detected.

  The exciting coil 405a and the heating roller 2 have predetermined magnetic characteristics (magnetic coupling), and the peak current value X1, the frequency and the voltage of the current supplied to the exciting coil 405a are determined by this magnetic characteristic. Yes. This magnetic characteristic is initially determined by the magnetic permeability and resistivity of the heating roller 2, the number of turns (number of turns) of the exciting coil 405a, the arrangement position of the magnetic core 405b, and the like.

  However, when the heating roller 2 is raised to an abnormal temperature, the exciting coil 405a is heated to a predetermined temperature by the radiant heat from the heating roller 2, and the magnetic characteristics of the heated exciting coil 405a are the same as before heating. Change to different magnetic properties. That is, this magnetic characteristic has temperature dependence.

  FIG. 10B shows the relationship between the current flowing through the exciting coil 405a whose magnetic characteristics have changed due to the heating roller 2 generating heat to an abnormal temperature and time. 10 (a) and 10 (b) show the relationship between the current flowing through the exciting coil 405a and time when the heat output of the heating roller 2 to be set is 900W.

  As shown in FIG. 10B, a current having a peak current value X2 larger than the peak current value X1 flows through the exciting coil 405a whose magnetic characteristics have changed due to the heating roller 2 having risen to an abnormal temperature. The frequency of this current also changes to one period O′-S ′ that is longer than the period OS. That is, the frequency decreases.

  Therefore, the CPU 28 sets the input power PI fed back from the input power monitor 27, that is, the peak current value, within a predetermined range based on the set value set according to the value of the frequency of the predetermined current supplied to the exciting coil 405a. If it is not held, it can be determined that the heating roller 2 has risen to an abnormal temperature. The set value (threshold value) is a frequency and a peak current value having a predetermined range corresponding to the magnetic characteristics of the exciting coil 405a and the heating roller 2, and is stored in the storage unit of the CPU 28. For example, when the heat output of the heating roller 2 is 700 W, the peak current value of the current flowing through the exciting coil 405 a is 55 A, the frequency is 26 kHz, and when the heat output is 900 W, the peak current value is 60 A, the frequency is 23 kHz, and the heat output is 1200 W. The peak current value is 65 A and the frequency is 21 kHz.

  For example, when the set heat output of the heating roller 2 is 900 W and the temperature of the heating roller 2 is about 150 degrees, as shown in FIG. 10A, the exciting coil 405a has a peak current value of the flowing current. X1 is 50A. However, when the heating roller 2 rises to an abnormal temperature (for example, 300 degrees) and the magnetic characteristics change, a current with a peak current value X2 of 60 A flows through the exciting coil 405a. The change in the peak current value is calculated from the input power PI fed back from the input power monitor 27, and the frequency shown in FIG. 10B has decreased, that is, the heat output supplied to the heating roller 2 has increased. CUP 28 can find out.

  When the increase in the heat output supplied to the heating roller 2 is found, the CPU 28 stops the power supplied to the exciting coil 405a.

  Also, as shown in FIGS. 10A and 10B, the frequency of the current supplied to the exciting coil 405a can be calculated by detecting the ON time of the switching element 23. This frequency is defined by a value obtained by combining the ON time of the switching element 23 and the resonance time of the resonance capacitor 21.

  The CPU 28 is connected to a timer 28b for detecting the ON time of the switching element 23. The storage unit 28a connected to the CPU 28 stores thresholds for setting the ON time of the switching element 23 and the resonance time of the resonance capacitor 21 according to the magnetic characteristics of the exciting coil 405a and the magnetic core 405b. ing.

  Therefore, the CPU 28 compares the detected ON time of the switching element 23 with a preset threshold value, and can determine that the frequency has decreased when the ON time is longer than the threshold value. When this frequency becomes equal to or lower than the set value as described above, for example, the CPU 28 cuts off the power for heating the heating roller 2 supplied to the exciting coil 405a to an abnormal temperature.

  Therefore, even when the heating roller 2 is stopped, power for raising the heating roller 2 to an abnormal temperature is not supplied to the exciting coil 405a, so that the heating roller 2 can be prevented from generating heat locally.

  Further, the abnormality of the heating roller 2 can be detected without using the abnormal temperature detection mechanism, and the safety of the fixing device 1 can be greatly improved as compared with the conventional case.

  Needless to say, the same abnormal temperature detection method can be applied to the exciting coil 406a.

  Further, in this embodiment, the abnormal temperature detection method using the fact that the magnetic cores 405b and 406b holding the exciting coils 405a and 406a are heated by the radiant heat of the heating roller 2 to change the magnetic characteristics. Can be applied.

  The magnetic cores 405b and 406b are configured using a core material whose magnetic characteristics change because the magnetic roller saturates when passing through a predetermined Curie point when the heating roller 2 generates heat to an abnormal temperature.

  The Curie point is used to evaluate the temperature of the magnetic cores 405b and 406b when the heating roller 2 exceeds the normal temperature range so that it does not pass when the heating roller 2 generates heat within the normal temperature range. However, the temperature is preferably slightly higher than the temperature range of the magnetic cores 405b and 406b.

  When the temperature of the heating roller 2 exceeds the set normal temperature range, the magnetic characteristics of the magnetic cores 405b and 406b passing through the Curie point and magnetically saturated with the exciting coils 405a and 406a change. As a result, the value of current flowing through the exciting coils 405a and 406a (peak current value) changes. This change in the current value is detected by the CPU 28 by referring to the input power PI fed back from the input power monitor 27 as described above with the set value as described above.

  When the change in the magnetic characteristics of the exciting coil 405a and the magnetic core 405b due to the change in the current value is found, the CPU 28 stops the power supplied to the exciting coil 405a.

  Therefore, even when the heating roller 2 is stopped, power for raising the heating roller 2 to an abnormal temperature is not supplied to the exciting coil 405a, so that the heating roller 2 can be prevented from generating heat locally.

  Further, the abnormality of the heating roller 2 can be detected without using the abnormal temperature detection mechanism, and the safety of the fixing device 1 can be greatly improved as compared with the conventional case.

  Note that the fixing device, the excitation coil provided in the fixing device, and the control method of the fixing device as described above can be arbitrarily combined.

  As described above, the fixing device according to the present invention can prevent a temperature drop at the joint portion of the coil of the heating roller, thereby making the temperature distribution in the longitudinal direction of the heating roller uniform and obtaining a good image.

1 is a schematic diagram illustrating a fixing device to which an embodiment of the present invention can be applied. Schematic explaining an example of the induction heating mechanism provided in the fixing device shown in FIG. Schematic explaining another example of the induction heating mechanism provided in the fixing device shown in FIG. FIG. 2 is a schematic diagram illustrating a configuration of an induction heating control circuit applicable to the fixing device illustrated in FIG. 1. Schematic explaining the structure of the other induction heating control circuit applicable to the fixing device shown in FIG. Schematic explaining another example of the induction heating mechanism provided in the fixing device shown in FIG. Schematic explaining another example of the induction heating mechanism provided in the fixing device shown in FIG. Schematic explaining another example of the induction heating mechanism provided in the fixing device shown in FIG. Schematic explaining the structure of the other induction heating control circuit applicable to the fixing device shown in FIG. FIG. 10 is a reference diagram showing a relationship between current flowing through an equivalent circuit of the inverter circuit shown in FIG. 9 and time. The figure explaining the electric current which flows into the equivalent circuit of the inverter circuit shown by FIG.

Explanation of symbols

  2 ... heating roller, 3 ... pressure roller, 5, 6 ... induction heating mechanism, 9a, 9b ... thermistor, 10 ... thermostat, 28 ... main control mechanism (CPU), 33 ... rotation detection mechanism, 34, 35 ... heating induction Control mechanism, 310, 314 ... abnormal temperature detection mechanism, 311 ... temperature detection unit, 312, 313 ... heat pipe unit.

Claims (5)

A cylindrical heating member that generates heat by being supplied with a predetermined magnetic field;
A pressure member for supplying a predetermined pressure to the heating member;
An induction heating mechanism that is disposed outside the heating member and that supplies the predetermined magnetic field to the heating member by supplying predetermined electric power;
The induction heating mechanism includes at least one coil having a window portion where no electric wire is arranged at the center,
The coil is arranged on both sides of the window part, and a folded electric wire part that connects a parallel electric wire part made of an electric wire parallel to the axial direction of the heating member and a parallel electric wire part arranged to face each other across the window part. Including
The abnormal temperature detection mechanism is disposed in the window portion of the coil, and cuts off the electric power supplied to the coil when the temperature of the heating member reaches the abnormal temperature. The fixing device according to claim 1, wherein the heating member includes a heat insulating foam layer on an inner side and an elastic layer and a release layer on an outer side. A rotation detection mechanism that detects that the heating member is rotating and outputs a rotation detection signal;
A main control mechanism for outputting an instruction signal for supplying predetermined power to the coil;
The fixing device according to claim 1, further comprising a heating induction control mechanism that supplies predetermined power to the coil when the rotation detection signal and the instruction signal are input. A cylindrical heating member that generates heat by providing a predetermined magnetic field;
A pressure member that supplies a predetermined pressure to the heating member; and an induction heating that is disposed at a predetermined interval from the heating member and that supplies the predetermined magnetic field to the heating member by being supplied with a predetermined power. A mechanism,
The induction heating mechanism is arranged outside the heating member in a line in the axial direction of the heating member, and is provided with at least two or more coils for supplying the predetermined magnetic field to the heating member by supplying predetermined power. Including
A fixing device comprising an abnormal temperature detection mechanism which is disposed in a joint region between the coil and the coil outside of the heating member, and cuts off power supplied to the coil when the temperature of the heating member reaches an abnormal temperature. apparatus. A cylindrical heating member that generates heat by being supplied with a predetermined magnetic field;
A pressure member for supplying a predetermined pressure to the heating member;
An induction heating mechanism that is disposed outside the heating member and that supplies the predetermined magnetic field to the heating member by supplying predetermined electric power;
The induction heating mechanism includes a coil that provides the predetermined magnetic field to the heating member when predetermined electric power is supplied;
A temperature detection unit that detects a temperature between the outer peripheral surface of the heating member and the coil, a heat pipe unit that transmits heat of the temperature detection unit, and heat from the heat pipe unit at a predetermined distance from the heating member It can be detected at a remote position, and has an abnormal temperature detection mechanism that cuts off the power supplied to the coil when the abnormal temperature of the heating member is reached based on the detection result,
The fixing device, wherein the temperature detection unit is disposed in proximity to or in contact with the heating member.

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