JP2007078989A - Image heating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image heating apparatus capable of appropriately shutting off electric power supply to a magnetic flux generating means even in case an electric power supply to the magnetic flux generating means is runaway while a belt is not rotated, and being therefore very safe. <P>SOLUTION: A thermo-switch 108 is disposed in contact with the internal face of the fixing belt 101. An excitation coil is disposed opposite the thermo-switch so that the area of contact with the thermo-switch 108 is the area where heat is generated. The electric power supply to the coil is runaway while the fixation belt is not rotated, the fixing belt is prevented from being thermally damaged. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image heating apparatus for heating an image on a recording material. This image heating device can be used, for example, as a fixing device that fixes an unfixed image on a recording material or a gloss increasing device that increases the glossiness of an image that is supposedly attached to the recording material.

  2. Description of the Related Art Conventionally, in an image forming apparatus employing an electrophotographic method, various types of fixing devices have been proposed as a fixing device that heats and fixes an unfixed toner image.

  In the fixing device, an electromagnetic induction heating method that directly generates heat from a heating target is attracting attention from the viewpoint of energy saving.

  As one of the electromagnetic induction heating type fixing devices, a fixing device is devised in which a coil is disposed opposite to a suspension roller via a fixing belt, and the suspension roller generates heat together with the fixing belt by a magnetic flux from the coil (for example, Patent Document 1).

  Since the fixing belt itself generates heat in this way, the temperature of the fixing belt can quickly reach the desired fixing temperature. That is, there is an advantage that the thermal responsiveness of the fixing belt used for fixing the image formed on the recording material can be improved.

  In addition, since the suspension roller itself generates heat by effectively using the leakage magnetic flux that has passed through the fixing belt, the temperature of the suspension roller having a large heat capacity can be increased more quickly. As a result, it is possible to shorten the warm-up time of the fixing device.

Further, in this fixing device, a thermo switch is disposed in the coil unit in order to cope with a case where energization to the coil runs away due to some abnormality of the device. This thermoswitch has a function of cutting off the power supply to the coil by itself deforming as the temperature rises.
JP 2004-279661 A

  However, according to the above-described prior art, there are the following problems. In the fixing device of Patent Document 1, since the thermo switch is arranged in the coil unit, the portion of the fixing belt facing the thermo switch is not a heat generating area.

  Therefore, if energization of the coil runs out of control with the fixing belt stopped, the temperature of the fixing belt facing the coil will rise abnormally before this thermoswitch is activated. You will receive heat damage.

  On the other hand, if you try to prevent the thermal damage to the fixing belt by setting the operating temperature of the thermo switch lower, the thermo switch will malfunction even if the temperature of the fixing belt fluctuates slightly higher during normal fixing operation. There is a risk that.

  As described above, in the fixing device of Patent Document 1, there is no way to deal with the case where energization of the coil runs away in a state where the rotation of the fixing belt is stopped.

  That is, with such a thermoswitch arrangement, the true safety of the fixing device cannot be guaranteed.

  Accordingly, an object of the present invention is to provide an image heating apparatus with high safety.

  It is a further object of the present invention to provide an image heating apparatus that can properly cut off the energization to the magnetic flux generation means even when the energization to the magnetic flux generation means goes out of control while the rotation of the belt is stopped. is there.

  According to the present invention, the above object can be achieved.

The present invention relates to an endless belt that heats an image on a recording material at a nip portion, a guide member that guides the inner surface of the belt, magnetic flux generating means that generates a magnetic flux that induces heat generation of the belt and the guide member, and the belt is abnormal. In an image heating apparatus having an interruption element for interrupting energization to the magnetic flux generating means when the temperature is reached,
The interrupting element is arranged in contact with the inner surface of the belt or separated by a small distance, and the magnetic flux generating means has an exciting coil at a position facing the guide member and a position facing the interrupting element via the belt. .

  According to the present invention, a highly safe image heating apparatus can be provided.

  Furthermore, according to the present invention, it is possible to properly cut off the energization of the coil even when the energization of the magnetic flux generating means goes out of control while the rotation of the belt is stopped.

  Hereinafter, the present invention will be described more specifically with reference to working examples.

  Although the following Examples 1 and 2 are the best modes according to the present invention, various configurations described in the following Examples 1 and 2 can be appropriately changed within the scope of the idea of the present invention.

  Before describing a fixing device as an image heating device according to the present invention, the overall configuration and function of an image forming apparatus including the fixing device will be briefly described first.

  The image forming apparatus shown in FIG. 1 is a copier that can form a full-color image. In the following, the constituent elements related to the image formation of each color of yellow, magenta, cyan, and black are expressed by adding Y, M, C, and K after the number. In addition, when these constituent elements are simply represented by numbers, the constituent elements in the respective colors are indicated in common.

  In FIG. 1, a photosensitive drum 1 as an image carrier is rotatably provided and is rotated by a driving force of a driving motor (not shown). The rotation direction of the photosensitive drum 1 during the image forming operation is clockwise (counterclockwise) in FIG.

  A charging roller 12 is disposed in pressure contact with the photosensitive drum 1, and the charging roller 12 rotates following the photosensitive drum 1. A DC voltage of −600 V is applied to the charging roller 12 as a charging bias. The surface of the photosensitive drum 1 is uniformly charged by this bias voltage, and its value is slightly lower than the DC value of the charging bias, and is about −550V.

  Next, when image exposure is performed by the laser 3 in accordance with the image information of the document read by the document reading device, the surface potential of the photosensitive drum 1 at that portion decreases to about −200V. As a result, an electrostatic latent image corresponding to the image information is formed on the photosensitive drum 1.

  The electrostatic latent image formed on the photosensitive drum 1 is developed with toner by the developing device 4.

  The developing device 4 contains a two-component developer in which a nonmagnetic toner and a magnetic carrier are mixed, and a developing sleeve 8 in which a magnet roller 9 is built is rotatably provided.

  The two-component developer accommodated in the developing device 4 is sucked and carried on the surface of the developing sleeve 8 by the magnetic force of the magnet roller 9 and is conveyed to a portion facing the photosensitive drum 1 as the developing sleeve 8 rotates. The developer on the developing sleeve is raised by the magnetic field of the magnet roller 9 at the opposing portion, so that the toner moves and adheres when it contacts the electrostatic latent image on the photosensitive drum.

  In addition to the DC voltage of −400 V as the developing bias, an AC voltage of 1800 V with a peak-to-peak value is superimposed and applied to the developing sleeve 8. Since the toner is negatively charged, it does not adhere to the non-image portion (non-exposed portion) of −550V, but becomes an electrostatic latent image by attaching to the image portion (exposed portion) of −200V. The

  Here, the two-component developer of this embodiment will be described. As the toner, a spherical toner (polymerized toner) produced by a suspension polymerization method in which a monomer composition obtained by adding a colorant and a charge control agent to a styrene acrylic monomer is subjected to suspension polymerization in an aqueous medium was used. . Further, as the developing carrier, a ferrite particle coated with a silicon resin was used. By appropriately selecting the internal additive added to the toner resin, the external additive added to the toner, and the internal additive of the silicon resin coating agent of the development carrier, the toner is stably negatively (negatively) charged.

  Through the above process, the yellow, magenta, cyan, and black toner images formed on the photosensitive drum in each image forming unit are sequentially transferred onto the intermediate transfer belt 10 by the primary transfer rollers 5. The At this time, a primary transfer bias of +200 V is applied to each primary transfer roller 5.

  On the other hand, the recording material accommodated in the paper feed cassette is conveyed so as to match the toner image on the intermediate transfer belt 10, and the toner images on the intermediate transfer belt 10 are transferred collectively by the secondary transfer roller 11. At this time, a secondary transfer bias of 1 KV is applied to the secondary transfer roller.

  Thereafter, the recording material onto which the toner image has been transferred is conveyed to the fixing device A. The unfixed toner image formed on the recording material in the fixing device A is fixed on the recording material by being heated / pressurized.

  The recording material after fixing is discharged out of the apparatus by a transport mechanism (not shown).

  Note that the transfer residual toner remaining on the photosensitive drum 2 in the primary transfer process changes to a positive polarity due to the influence of the primary transfer bias. The transfer residual toner is negatively charged again by the charging bias applied to the charging roller 12 when passing between the charging roller 12 and the photosensitive drum 1, and is developed by the developing bias when passing through the developing region. 4, the toner returns to the developing sleeve 8 side in the non-image portion and adheres to the photosensitive drum 1 in the image portion.

  As described above, in this example, the developing device 4 is provided with a motor for collecting the transfer residual toner, thereby realizing a cleaner-less system that eliminates the conventional cleaner.

  FIG. 2 is a cross-sectional view of a fixing device A as an image heating device.

  The fixing device A includes an endless fixing belt 101, a heating roller 102 and a fixing roller 103 as guide members for guiding the inner surface of the fixing belt 101, a coil unit 110 disposed on the outer surface side of the fixing belt, and a pressure contact with the fixing belt. Thus, a pressure roller for forming a fixing nip is provided. As will be described later, the heat generating roller 102 has a function of generating electromagnetic induction heat by a coil, and the fixing roller 103 has a function of receiving a rotational force from a driving motor via a driving gear train and transmitting this to the belt. is doing.

  The fixing belt has a base layer made of nickel manufactured by electroforming, and has an inner diameter of 34 mm and a thickness of 50 μm. That is, the fixing belt is substantially cylindrical before the tension is applied by the rollers 2 and 3. On the outer periphery of the base layer, a heat-resistant silicone rubber layer is laminated as an elastic layer of 100 to 1000 μm.

  As the base layer of the fixing belt 101, iron alloy, copper, silver or the like can be appropriately selected in addition to the above nickel. In addition, the thickness of the base layer (metal layer) may be adjusted according to the frequency of the high-frequency current applied to the exciting coil, which will be described later, and the permeability / conductivity of the base layer, and should be set between about 5 to 200 μm. .

  In this example, the thickness of the silicone rubber layer is set to 300 μm in consideration of reducing the heat capacity of the fixing belt to shorten the warm-up time and obtaining a suitable fixed image when fixing a color image. ing. The silicone rubber has a hardness (JIS-A) of 20 degrees and a thermal conductivity of 0.8 W / mK.

  Note that the warm-up time refers to the time required from when the main switch of the image forming apparatus is turned on until the image formation can be started (the fixing operation can be started).

  Further, a fluororesin layer (for example, PFA or PTFE) is laminated on the outside of the elastic layer as a surface release layer having a thickness of 30 μm.

  When a pressure pad for forming a fixing nip is provided on the inner surface of the fixing belt, fluororesin or polyimide as a low friction layer is formed on the inner surface of the base layer in order to reduce sliding friction with the pressure pad. 10 to 50 μm may be provided. In this example, since no pressure pad is provided, such a resin layer is not provided.

  When the rollers 2 and 3 that are in contact with the inner surface of the fixing belt are conductive, an electrical insulating layer is provided on the inner surface of the fixing belt in order to appropriately generate eddy currents in the base layer (metal layer) of the fixing belt. Is desirable.

  In this example, since the fixing belt generates heat by the action of magnetic flux from the coil, it has a high thermal response and is advantageous in shortening the warm-up time.

  Here, the minimum curvature radius of the fixing belt 101 is 5 mm or more, preferably 8 mm or more. This is because if the radius of curvature is too small, the rigidity of the nickel base layer of the fixing belt 101 is so high that the nickel base layer breaks over time or the rotational driving load of the fixing belt via the fixing roller 103 increases. Because.

  The hollow heat generating roller 102 as a guide member is an iron cored bar having a diameter of 20 mm and a thickness of 1 mm, and is configured to generate electromagnetic induction heat by a magnetic flux from a coil. Further, the heat roller 102 also plays a role of giving a tension of 5 kgf to the fixing belt 101.

  The fixing roller 103 is provided with a rubber layer as an elastic layer on an iron cored bar.

  The fixing belt 101 is rotated by driving the fixing roller 103 by a motor (not shown), and the fixing belt 101 is rotated by friction between the rubber surface layer of the fixing roller 103 and the inner surface of the fixing belt 101.

  In the pressure roller 104, a silicone rubber layer is provided on a core bar made of an iron alloy having an outer diameter of 20 mm, a diameter in the longitudinal central portion of 18 mm, and a diameter of both ends of 17 mm. The surface is provided with a fluororesin layer (for example, PFA or PTFE) as a release layer with a thickness of 30 μm.

  The hardness at the central portion in the longitudinal direction of the pressure roller 104 is 80 degrees (Asker C hardness).

  The pressure roller 104 distorts the fixing belt 101 and the rubber layer of the fixing roller so that the recording material on which the toner image is formed can be easily peeled off from the fixing belt 101 at 20 kgf to the fixing belt 101. It is pressed. The width in the rotation direction of the fixing nip portion for fixing the recording material while nipping and conveying the recording material between the fixing belt 101 and the pressure roller 104 is about 10 mm.

  A magnetic core 106 is installed in the vicinity of the exciting coil 105 as a magnetic flux generating means for inductively heating the fixing belt 101 so that the generated magnetic flux is effectively directed to the fixing belt 101 side.

  The exciting coil 105 is integrally molded so as to be covered with an electrically insulating resin together with the magnetic core 106 and is unitized (hereinafter referred to as a coil unit).

  The gap between the fixing belt 101 and the coil unit is approximately 1 mm to maintain electrical insulation, and the distance between the fixing belt 101 and the exciting coil 105 is 3 mm (the distance between the resin mold surface of the coil unit and the fixing belt surface is 2 mm). ). The gap is configured to be substantially uniform in the rotation direction and the width direction of the fixing belt 101. As a result, the fixing belt is heated almost uniformly regardless of the position.

  The length in the width direction of the excitation coil 105 is set to be longer than the sheet passing width of the maximum size recording material used for image formation.

  As shown in the block diagram of FIG. 3, a power source for applying a high frequency current of 20 to 50 kHz is connected to the excitation coil 105 described above.

  The temperature sensor 107 is disposed in contact with the heat generating area of the fixing belt 101 by the exciting coil 105 and on the inner surface of the belt. This temperature sensor is connected to the controller as shown in the block diagram.

  If the temperature sensor 107 is arranged as in this example, the belt temperature is detected in the heat generation region of the fixing belt 101 by the excitation coil 105 and in the region where the heat capacity not suspended by the rollers 2 and 3 is small (when the rotation of the belt is stopped). Therefore, the belt temperature can be detected with good responsiveness.

  The control unit (CPU) is configured to control energization to the exciting coil based on the temperature detection result of the temperature sensor. That is, the control unit controls the electric power supplied from the power source to the exciting coil.

  The control unit is also connected to a drive motor that drives the fixing belt, and starts energizing the excitation coil upon receiving an input of a signal indicating “normally rotating” from the drive motor. It is the composition to do. However, in the unlikely event that the drive gear train between the drive motor and the fixing roller is damaged, it is possible that the rotation of the fixing belt stops although the motor rotates normally.

  Specifically, the control unit changes the frequency of the high-frequency current applied from the power supply based on the temperature detected by the temperature sensor 107 so that the temperature of the fixing belt 101 substantially maintains a predetermined fixing temperature of 170 ° C. The power supplied to the exciting coil 105 is controlled by such a method.

  The fixing belt 101 is rotationally driven at a predetermined peripheral speed in the direction of arrow X in FIG. 1 by a drive motor at least during image formation. The fixing belt 101 is set to a circumferential speed that is substantially the same as the conveyance speed of the recording material P carrying the unfixed toner image conveyed from the secondary transfer unit.

  In the case of this example, the fixing belt 101 is configured to rotate at a peripheral speed of 160 mm / sec. As a result, if it is an A4 size recording material, 40 full-color images can be fixed per minute. it can.

  In the state where the temperature of the fixing belt 101 is substantially maintained at a predetermined fixing temperature, heat is applied from the fixing belt 101 when the recording material P having the unfixed toner image T passes through the fixing nip portion, and Fixing is performed under pressure applied by the pressure roller. At this time, the recording material is introduced into the fixing nip so that the side on which the toner image is carried contacts the fixing belt 101.

  Thereafter, the recording material P is naturally separated at the portion where the curvature on the fixing nip exit side is deformed, and is conveyed outside the fixing device.

  The pressure roller 104 can take a state of being in contact with the fixing belt 101 or a state of being separated from the fixing belt 101 by a contact / separation mechanism. By this contact / separation mechanism, the pressure roller 104 is separated from the fixing belt 101 except during the fixing operation.

  In addition, since the fixing belt 101 is pressed with a relatively light pressure by the pressure roller, even if the fixing belt 101 is in a rotating state, the shifting force in the width direction is small. That is, the force for shifting the fixing belt 101 in the width direction is small. For this reason, a flange portion against which the end portion of the fixing belt 101 abuts may be provided at the end portion of the heat generating roller 102 or the fixing roller 103 as a means for regulating the deviation in the width direction of the belt. In this example, the heating roller 102 is provided.

  Next, safety measures for the fixing device of this embodiment will be described. This is to provide a safety measure that can appropriately cope with a case where energization of the exciting coil runs away due to some abnormality of the apparatus. In particular, in this example, an attempt is made to provide a safety measure that can appropriately cope with even a worst case situation in which the energization to the exciting coil goes out of control even though the rotation of the fixing belt is stopped. Is. In the configuration of this example, when a situation occurs in which the energization to the excitation coil runs away, the energization to the excitation coil can be forcibly cut off even during an image forming job. .

  In this example, first, as a first-stage safety measure, a software measure using a temperature sensor and a control unit is taken. Specifically, when the detected temperature of the belt by the temperature sensor (blocking element) used for temperature control of the fixing belt reaches an abnormal temperature (for example, 200 ° C.), the control unit receives this and the exciting coil It is configured to forcibly cut off the energization to.

  The abnormal temperature refers to a temperature higher than a temperature that can be detected by a temperature sensor during a normal fixing operation. When this abnormal temperature is detected, the power supply is immediately turned off to stop the fixing device, and the image formation in the image forming apparatus is stopped (interrupted if the image forming job is in progress). In this example, the fixing temperature, which is the target temperature of the fixing belt, is set to 170 ° C., and the abnormal temperature is set to 200 ° C. in consideration of the normal temperature fluctuation of the fixing belt.

  In this example, when this situation occurs, the control unit displays a notification of “error” on the operation unit (liquid crystal display unit) provided at the top of the image forming apparatus. By this notification, the operator recognizes that an abnormality has occurred in the apparatus, and calls a service man as necessary.

  On the other hand, when the image forming apparatus is connected to a personal computer as a host computer via a LAN cable and used as a “printer”, the control unit notifies the personal computer of an “error” via the network.

  Specifically, the control unit outputs a control signal to the personal computer so that “error” is displayed on the monitor connected to the personal computer.

  Note that the display content “error” may be changed as appropriate as long as the operator can be notified that a problem has occurred.

  In this example, the temperature sensor is installed in the vicinity of the heat generating area of the fixing belt, similarly to a thermoswitch described later, and can quickly detect an abnormality at a position where the heat responsiveness of the fixing belt is high. Therefore, it is possible to cut off the energization to the exciting coil before the fixing belt is thermally damaged.

  Next, as a second safety measure, a hardware measure using a thermo switch 108 as a shut-off element that cuts off the energization to the exciting coil regardless of the temperature detected by the temperature sensor is taken. More specifically, the thermo switch 108 is configured to forcibly cut off the energization to the exciting coil when the thermo switch 108 raises the temperature of the fixing belt with an abnormal temperature increase. The thermo switch 108 is disposed at a substantially central portion in the width direction of the fixing belt, and is connected to a current-carrying circuit from the power source to the exciting coil.

  The thermo switch 108 has a bimetal disposed therein, and when the bimetal temperature reaches a predetermined operating temperature, the bimetal is thermally deformed, and the energization circuit is opened (cut) using this deformation to energize. Is to shut off.

  Therefore, in this example, the bimetal operating temperature is set to 200 ° C. so that the bimetal in the thermoswitch operates when the fixing belt becomes abnormally heated due to the energization of the exciting coil running out of control. .

  As described above, by using the thermoswitch, even when the control unit or the temperature sensor fails, the energization to the exciting coil 105 can be immediately cut off when the operating temperature is reached.

  Although the thermo switch has been described as an example of the interrupting element, for example, a thermal fuse 1108 can be used. The thermal fuse 1108 is configured to melt and break when a predetermined operating temperature is reached, and the energization circuit can be opened, that is, the energization of the exciting coil can be interrupted, similarly to the thermoswitch. In the present invention, the thermal phenomenon that occurs when the thermoswitch or the thermal fuse 1108 reaches the operating temperature is collectively referred to as “the breaking element is thermally deformed”.

  In this example, the position where the above-described temperature sensor and thermo switch 108 are installed is a characteristic point. Hereinafter, the thermo switch 108 will be described as an example, but the same applies to a temperature sensor.

  That is, when the energization to the exciting coil runs away due to some abnormality in the apparatus, the abnormal temperature rise of the fixing belt is severe (the temperature rising speed of only the fixing belt not suspended by the rollers 2 and 3 is fast). As described above, the fixing belt rotation is stopped.

  On the other hand, as described above, in the fixing device of this example, the heat capacity is reduced (thinned) in order to quickly reach the desired fixing temperature of the fixing belt. On the other hand, the roller 2 is designed to have a high heat capacity in order to suppress temperature fluctuations (temperature reduction) of the fixing belt caused by the fixing belt taking heat away from the recording material during continuous copying.

  However, in such a configuration, since the magnetic flux generated from the exciting coil passes through the fixing belt and leaks to the roller 2 side, in this example, the power factor will be increased by effectively utilizing this leakage magnetic flux. It is said. That is, the temperature of the roller 2 having a large heat capacity can be increased more quickly by effectively utilizing the leakage magnetic flux to generate the heat of the roller 2 itself. That is, the temperature reduction of the fixing belt during continuous copying can be suppressed, and further, the warm-up time of the fixing device can be shortened.

  In such a configuration, when the energization of the exciting coil goes out of control while the rotation of the fixing belt is stopped, it is required to cope with the fixing belt before thermal damage occurs.

  Therefore, in this example, as shown in FIG. 2, the thermo switch 108 is provided in contact with the inner surface of the fixing belt, and the region where the thermo switch is in contact (when the rotation of the belt is stopped) is the heat generation region. An exciting coil is disposed opposite the thermo switch via the fixing belt.

  That is, the exciting coil is provided so as to extend from a position facing the heat generating roller 102 via the fixing belt toward a position facing the thermo switch 108 via the fixing belt. In this example, the exciting coil is formed by winding one litz wire.

  In this manner, in the fixing belt region (when rotation is stopped) in contact with the thermo switch 108, only the fixing belt 101 having a small heat capacity generates heat, so that the temperature increase rate in that region of the fixing belt is very fast. . Accordingly, in consideration of safety when the rotation of the fixing belt is stopped, it is preferable to place the thermo switch 108 at this position. That is, the energization to the exciting coil can be cut off before the fixing belt is thermally damaged.

  Although it is conceivable that a thermo switch is disposed in contact with the inner surface of the heat generating roller 102 (on the side close to the exciting coil in the circumferential direction of the roller), the thermal responsiveness is poor as in the above-mentioned Patent Document 1, so that the fixing belt is used. It is inevitable that heat damage will occur.

  Although it is conceivable to arrange the thermo switch 108 in a region between the exciting coil and the outer surface of the fixing belt, it is not a preferable configuration for the following reason.

  In other words, when the thermo switch 108 is installed in this region, an installation space for that is required, and the distance between the exciting coil and the outer surface of the fixing belt is increased, so that the magnetic flux from the exciting coil acts on the fixing belt efficiently. It is because it becomes impossible to make it.

  As described above, with the configuration of this example, even when the energization to the exciting coil runs away when the rotation of the fixing belt stops, it can be quickly and appropriately dealt with. That is, it is possible to prevent thermal damage to the fixing belt.

  In the above description, the example in which the thermo switch 108 is disposed in contact with the inner surface of the fixing belt has been described. In this case, the thermo switch 108 may be provided separately from the fixing belt. In this example, considering that the thickness of the heat generating roller is 1 mm, if the thermo switch 108 is installed within 500 μm from the inner surface of the fixing belt, the above relationship is satisfied. It is preferable to place 108 in contact with the inner surface of the fixing belt.

  In the above description, the example in which the exciting coil is formed by one litz wire (the litz wire is formed by twisting a plurality of strands) is not limited to this. For example, the first excitation coil disposed at a position facing the heat generating roller 102 via the fixing belt and the second excitation coil disposed at a position facing the thermo switch 108 via the fixing belt are separated from each other by a litz wire. It does not matter if it is formed by. In this case, when an abnormality occurs, it is preferable that the energization of both the first excitation coil and the second excitation coil be cut off by the above-described safety mechanism such as a temperature sensor or a thermo switch.

  In the above example, the rollers 2 and 3 have been described as examples of the member for guiding the inner surface of the fixing belt. However, the present invention is not limited to this configuration. For example, in the configuration that guides the running of the inner surface of the fixing belt, a guide member that is substantially non-rotatable (during the fixing operation) can be used in place of the rollers 2 and 3.

  Next, the configuration of the second embodiment according to the present invention will be described with reference to FIG. Since the basic configuration of the fixing device of this example is the same as that of the first embodiment except for a part of the configurations described later, a detailed description is omitted. Of course, the configuration of the image forming apparatus is the same as that of the first embodiment, and a detailed description thereof is omitted.

  In this example, an attempt is made to properly cope with a case where the fixing belt is torn for some reason or partially cut. That is, it is a characteristic point in this example that the thermo switch 109 as another interruption element is arranged in addition to the thermo switch 108 as the interruption element described in the first embodiment.

  If the fixing belt breaks for some reason, the fixing belt 101 that has generated electromagnetic induction heat does not exist from the opposite portion of the thermo switch 108.

  In such a situation, if energization to the exciting coil runs out of control, the temperature of the thermo switch 108 does not rise, and the thermo switch 108 does not operate until forever. That is, since energization to the exciting coil cannot be interrupted, the fixing belt is thermally damaged.

  Therefore, in this example, the thermoswitch 109 is provided on the outer surface side of the fixing belt and at the position facing the heat generating roller 102 by using a configuration in which the heat generating roller 102 generates heat by electromagnetic induction. Here, the operating temperature of the bimetal of the thermo switch 108 is 200 ° C. as in the first embodiment, and the operating temperature of the bimetal of the thermo switch 109 is set to 170 ° C. lower than that of the thermo switch 108. This is because the thermo switch 109 is arranged in a non-contact manner with respect to the fixing belt 101. Note that, similarly to the thermo switch 108, the thermo switch 109 is disposed so as to face the center portion of the fixing belt in the width direction.

  As a result, even when the fixing belt is broken, the temperature of the thermo switch 109 is increased, so that the energization to the exciting coil 105 can be forcibly cut off.

  The thermo switch 109 is disposed in a non-contact state on the outer surface of the fixing belt 101 because the outer surface of the fixing belt is damaged.

  If the thermo switch 109 is arranged in a non-contact manner with respect to the fixing belt, the thermal response of the thermo switch when the temperature of the heat generating roller 102 is abnormally increased is somewhat slow, but the heat capacity of the heat generating roller 102 is larger than that of the fixing belt 101. There is no problem.

  Further, FIG. 5 is a configuration in which the safety before and after the belt breakage is the highest by combining all of the first embodiment and the second embodiment. That is, in FIG. 5, the first thermo switch 108 for preventing abnormal temperature rise when the belt is not broken and the temperature sensor 107 are provided in contact with the inner surface of the fixing belt, and the thermo switch 108 and the temperature sensor 107 are provided. The exciting coil is disposed opposite to the thermo switch via the fixing belt so that the region where the belt contacts (when the rotation of the belt is stopped) becomes the heat generating region. In FIG. 5, a second thermo switch 109 for preventing belt breakage is provided on the outer surface side of the fixing belt and facing the heat generating roller 102. With the above configuration, when the belt is not broken, the temperature sensor 107 and the first thermo switch 108 are used to provide a double safety measure, and when the belt is broken, the second thermo switch 109 can prevent abnormal temperature rise. .

  In this example, the thermoswitch is described as an example of the interruption element. However, as in the first embodiment, a thermal fuse 1108 may be used instead of the thermoswitch.

  According to the example described above, even if the fixing belt 101 is broken for some reason, it is possible to properly cut off the energization to the exciting coil. That is, it is to provide a fixing device with high safety.

  In the first and second embodiments, the fixing device is described as an example of the image heating device. However, the present invention is not limited to this.

  For example, it can be used as a gloss increasing device that increases the glossiness of an image by heating an image that has already been assumed on the recording material.

  In addition, it cannot be overemphasized that the various structure demonstrated in the above-mentioned Example 1, 2 can be changed into another well-known structure within the range of the thought of this invention.

Schematic sectional view of the image forming apparatus Sectional view of the fixing device of Example 1 Control block diagram of fixing device Sectional view of the fixing device of Example 2 Cross-sectional view of a conventional fixing device Cross-sectional view of a conventional fixing device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing belt 3 Fixing roller 4 Pressure roller 5, 15 Excitation coil 6, 16 Ferrite core 8, 18 Thermo switch 9, 19 Thermo switch

Claims (5)

A belt that heats an image on the recording material at a nip; a guide member that guides the inner surface of the belt; a magnetic flux generating means that generates a magnetic flux that heats the guide member together with the belt; and the belt reaches an abnormal temperature. In the image heating apparatus having a blocking element for cutting off the energization to the magnetic flux generating means when
The blocking element is arranged in contact with the belt circumferential surface or separated by a minute distance,
The image heating apparatus according to claim 1, wherein the magnetic flux generating means includes an exciting coil at a position facing the guide member via the belt and a position facing the blocking element via the belt.   2. The image heating apparatus according to claim 1, wherein the interrupting element is connected in an energization circuit to the magnetic flux generating means and opens the energization circuit by its own thermal deformation.   A temperature detection element for detecting the temperature of the belt; and an energization control means for controlling energization to the magnetic flux generation means based on an output of the temperature detection element, wherein the temperature detection element is brought into contact with the inner surface of the belt. The image heating apparatus according to claim 1, wherein the image heating apparatus is disposed at a position facing the exciting coil via the belt.   2. A separate blocking element that is disposed to face the guide member via the belt and cuts off the power supply to the magnetic flux generating means when the guide member reaches an abnormal temperature. The image heating apparatus of any one of thru | or 3. A belt for heating the image on the recording material at the nip portion, a guide member for guiding the inner surface of the belt, a magnetic flux generating means for generating a magnetic flux for generating heat with the belt, and detecting the temperature of the belt. In an image heating apparatus comprising: a temperature detection element; and an energization control unit that interrupts energization to the magnetic flux generation unit based on an output of the temperature detection element.
The temperature sensing element is arranged in contact with the belt circumferential surface or separated by a minute distance,
The image heating apparatus according to claim 1, wherein the magnetic flux generation means includes an exciting coil at a position facing the guide member via the belt and a position facing the temperature detection element via the belt.

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