JP4254533B2 - Abnormal temperature rise prevention element and abnormal temperature rise prevention device using the same - Google Patents

Description

  The present invention relates to an abnormal temperature rise prevention element used for preventing a surface of a movable body heated by a heating device while controlling the temperature of the surface from being abnormally overheated, and a recording medium. The present invention relates to an abnormal temperature rise prevention device for preventing a surface temperature of a fixing rotator from being overheated abnormally in a fixing device for visualizing a formed unfixed toner image.

  In general, in the step of fixing an unfixed toner image in an image forming apparatus using powdery toner, an unfixed toner image is electrostatically transferred to the surface of a recording medium, and then this is heated and pressed. A method is widely used in which a non-fixed toner image is heated and melted and pressed onto a recording medium in the previous period. Here, a rotating body such as a roller or an endless belt is used for the heating member or the pressure member. For example, the former heating member is referred to as a fixing roller or a fixing belt (in the present invention). These are collectively referred to as “fixing rotators”).

  Generally, in a fixing device, a thermistor is provided on an outer peripheral surface or an inner peripheral surface of a fixing rotator, and a control device that controls a power supply circuit that supplies power to a heater for heating the fixing rotator. The surface temperature of the fixing rotator is maintained within a predetermined fixing temperature range (for example, 150 ° C. to 200 ° C.) by controlling on / off of energization to the heater.

  Furthermore, as a safety device when the surface temperature of the fixing rotator rises abnormally due to thermal runaway caused by a failure of the control device, etc., it is detected that the surface temperature of the fixing rotator has reached a predetermined abnormal temperature. A temperature fuse that blows off and cuts off the current is provided opposite to the peripheral surface of the fixing rotator, so that when the temperature rises abnormally, the power supply circuit is cut off and the power supply to the heater is stopped. A prevention device is generally provided.

  Incidentally, as means for heating a member to be heated such as a fixing rotator, Patent Document 1 and Patent Document 2 disclose a method in which a conductive layer is provided on the member to be heated and the conductive layer generates heat by electromagnetic induction heating. Has been. In the electromagnetic induction heating, an exciting coil that generates a variable magnetic field is disposed close to a conductive layer, and heat is generated by an eddy current generated in the conductive layer. According to this electromagnetic induction heating, the member to be heated can be directly heated, the range of the high temperature is extremely limited, and the member to be heated can be heated to a predetermined temperature in a short time. Also in this method, the same safety device as that described above is generally applied as a safety device when the surface temperature of the member to be heated rises abnormally.

  However, if the object to be detected is a moving object such as a fixing rotator, the surface will move, and even if it tries to approach it, it must be separated by the amount of movement and may interfere with other members. There is. If it is attempted to follow, the position of the thermal fuse moves, and there is a possibility that the thermal fuse contacts with a member other than the fixing rotating body.

  In the conventional fixing device, since the heat sensitive surface of the thermal fuse is exposed, if it comes into contact with a member other than the fixing rotating body to be detected, heat may be taken away. As a result, the fixing rotator is abnormally heated without being operated at the temperature at which it should be operated, and there is a problem that peripheral members in the image forming apparatus are damaged. In particular, in the case of an electromagnetic induction heating type fixing device, members other than the fixing rotator may be a member in the vicinity of the fixing rotator, even if it is not very high temperature, The heat taken away is great.

  On the other hand, the lead terminal (feeding terminal) connected to the thermal fuse is generally made of a material having a high heat conductivity such as copper as a main component, and the heat transferred to the corner temperature fuse is directly connected to the lead. There was a problem that the thermal fuse was blunted due to conduction through the terminal and the thermal fuse's response.

Japanese Patent Laid-Open No. 10-254263 JP 11-352804 A JP-A-10-275548 JP 2000-323308 A

  Accordingly, it is an object of the present invention to provide an abnormal temperature rise prevention element and an abnormal temperature rise prevention apparatus using the same, which are provided with a countermeasure against abnormal high temperature without malfunction and having a fast thermal response speed.

The above object is achieved by the present invention described below.
That is, the abnormal temperature rise prevention element of the present invention includes an energization interruption member that interrupts electrical connection at a predetermined temperature, a pair of power supply terminal portions protruding from both ends thereof, and one end of the power supply terminal portion electrically and physically. And a pair of elongated holding members having a function of abutting the temperature sensitive part on the surface of the movable body to be detected while holding the current-carrying-off member.
The shape of the periphery of the end connected to the power supply terminal portion of the holding member, as viewed from the extended line of the power supply terminal portion, excludes the temperature-sensitive portion or its periphery, and is perpendicular to the extension line of the energization cutoff member With respect to the cross-sectional shape, at least in part, the power supply terminal part or its extension line is projected outward as an axis,
At the end which holds the current blocking member in the holding member, on the opposite side of the temperature-sensitive portion about an axis passing through both ends of the current blocking member, the portion of the holding member is characterized in that it does not exist .

According to the abnormal temperature rise prevention element of the present invention, the temperature sensitive portion of the energization blocking member is brought into contact with the surface of the movable body to be detected, so that the temperature of the movable body surface is directly transmitted to the energization blocking member. Can do.
Further, with the power supply terminal part or its extension line as an axis, the periphery of the end part connected to the power supply terminal part of the holding member is more than the current-carrying interruption member (excluding the temperature-sensitive part or its periphery), Since at least a portion projects outward, the member other than the movable body first comes into contact with the projecting portion of the holding member (hereinafter also referred to as “protective shape portion”). There is no worry of contact with the current-carrying member.

  In other words, the protective shape portion has a function of protecting the energization blocking member from contact with other members. For this reason, there is no concern that the energization interrupting member comes into contact with other members, and there is no concern that the temperature difference from the surface of the movable body will be widened. It becomes a thing with a quick thermal response speed without worry.

  It is desirable that the holding member be connected to the energization blocking member only through the power supply terminal portion both electrically and physically. Since the connection between the energization interruption member and the holding member is made only through the power supply terminal portion, the energization interruption member and the holding member are not in direct contact with each other. Heat does not escape from the member, the heat capacity of the energization blocking member can be reduced, and the temperature difference between the energization blocking member and the movable body surface can be minimized.

Particularly in this case, even if the number of contact points is small, the heat conduction from the intervening power supply terminal portion is relatively large. Therefore, in order to suppress this heat conduction as much as possible, the connection between the holding member and the power supply terminal is limited. It is preferable that the contact be close to point contact regardless of welding or mechanical caulking.
In the abnormal temperature rise prevention element of the present invention, the holding member can have a function of supplying power to the power supply terminal.

In the abnormal temperature rise prevention element of the present invention, it is also a preferable aspect that at least a part of the outer surface of the energization cutoff member and / or the holding member is covered with a thin film.
The material of the temperature-sensitive portion in the energization interruption member is preferably aluminum nitride (AlN). Aluminum nitride has a very high thermal conductivity (specifically, 150 W / m · K), and by using this for a temperature-sensitive part, a part having a current-cut-off function in the current-cut-off member (so-called “fuse element”) It is possible to improve the heat transfer speed to the heat transfer speed.

On the other hand, the abnormal temperature rise prevention device of the present invention comprises a fixing rotator heated by a heat source and controlled in a predetermined fixing temperature range, and a pressure roller that presses against the fixing rotator to form a nip portion, and the nip portion An abnormal temperature rise prevention device applied to a fixing device that inserts a recording medium carrying an unfixed toner image into and heat-fixes,
An abnormal temperature rise prevention element of the present invention according to the present invention, wherein an energization blocking member is disposed in contact with the front or back surface of the fixing rotating body, and is wired so as to block energization to the heat source when the temperature exceeds a predetermined temperature. It is characterized by including.

The abnormal temperature rise prevention element of the present invention is preferably applied to a fixing rotator in a fixing device that performs heat fixing like the abnormal temperature rise prevention device of the present invention. In particular, when the heat source is a heating means based on an electromagnetic induction heating method, it effectively solves the problem caused by the heat conduction member coming into contact with the peripheral member held at a relatively low temperature and the heat escaping. It can be said that this is a preferred embodiment.
The fixing rotator is an endless fixing belt that is driven to rotate in a direction perpendicular to the shaft of the current-carrying-off member disposed in contact with the inner peripheral surface thereof, and is perpendicular to the surface of the fixing belt. It can be configured such that the abnormal temperature rise prevention element can be moved so that the energization blocking member can move following the displacement.
In this case, the fixing belt includes a conductive layer,
An electromagnetic induction heating device which is a heating means by an electromagnetic induction heating method as the heat source is disposed apart from the outer peripheral surface of the fixing belt,
A magnetic body that collects magnetic flux from the electromagnetic induction heating device that has passed through the fixing belt is provided at a position facing the electromagnetic induction heating device across the fixing belt and spaced from the inner peripheral surface of the fixing belt. ,
The abnormal temperature rise prevention element may be arranged between the fixing belt and the magnetic body so that the energization blocking member is positioned apart from the magnetic body.

According to the abnormal temperature rise prevention element of the present invention, the temperature sensitive portion of the energization blocking member is brought into contact with the surface of the movable body to be detected, so that the temperature of the movable body surface is directly transmitted to the energization blocking member. In addition, the presence of the protective portion prevents the energization cutoff member from coming into contact with a member other than the movable body, so that the obtained heat is less likely to escape, and there is no risk of malfunction. The response speed is fast.
The abnormal temperature rise prevention device of the present invention can be preferably applied to a fixing rotating body in a fixing device that performs heat fixing.

Hereinafter, the present invention will be described in detail with reference to preferred embodiments.
FIG. 1 is a plan view showing an embodiment of an abnormal temperature rise prevention element as an exemplary embodiment of the abnormal temperature rise prevention element of the present invention, and FIG. 2 is a right side view thereof.
The abnormal temperature rise prevention element of this embodiment is in contact with the surface of a movable body such as a fixing rotating body (fixing roll, fixing belt, etc.) in the fixing device, and detects a temperature fuse (energization) that detects the abnormal temperature of the surface of the movable body. The one end is electrically and physically connected to the lead terminals 4a and 4b and the pair of lead terminals (feed terminal portions) 4a and 4b protruding from both ends of the thermal fuse 2 and the thermal fuse 2 A pair of long metal spring plates (holding members) 6a, 6b having a function of bringing a part of the outer periphery (temperature-sensitive portion) into contact with the surface of the movable body to be detected while holding Composed. Although not shown, of the ends of the metal spring plates 6a and 6b, the end opposite to the side holding the temperature fuse 2 or the like is fixedly supported by an appropriate fixing support member (described later).

  In the present invention, the energization interrupting member corresponding to the thermal fuse 2 is not particularly limited as long as it has a function of interrupting electrical connection at a predetermined temperature, but as an example, a pair of electrodes (or leads) There is a thermal fuse (hereinafter, simply referred to as a “fusible alloy type thermal fuse”) that is electrically bridged by a fuse element made of a fusible alloy that melts at a predetermined temperature. In the present embodiment, a cylindrical fusible alloy type thermal fuse is used.

  FIG. 3 is a longitudinal sectional view of a cylindrical fusible alloy type thermal fuse in the present embodiment. As shown in FIG. 3, in the thermal fuse (energization interruption member) 2, a pair of leads 4 a and 4 b having a circular tip end portion and a cross section are arranged in a state where the tip end portions having electrode functions are opposed to each other. . Both ends and both ends of a fuse element 12 made of a low-melting point alloy having a circular cross section are fixed to the opposite ends of the pair of leads 4a and 4b by welding or the like, and covered with a flux 16 from above. Furthermore, this is inserted into the cylindrical insulating case 10, and the openings at both ends of the insulating case 10 are sealed with the insulating sealing material 18.

The insulating case 10 is for protecting the fuse element 12 and the material thereof is not particularly limited, but of course heat resistance as a thermal fuse is required. From this viewpoint, aluminum nitride, alumina ceramics and heat resistant It is preferable that it consists of molded objects, such as resin. In this embodiment, aluminum nitride is used. Aluminum nitride has a very high thermal conductivity (specifically, 150 W / m · K), and by using this as a material for the insulating case 10 including the temperature-sensitive portion, a portion having a current-cut-off function in the current-cut-off member. The heat transfer rate to the so-called “fuse element” can be improved and the thermal response rate can be increased. Of course, the above effect can also be obtained by using aluminum nitride only in the temperature-sensitive portion.
In this example, the shape is a cylindrical shape, but in the present invention, the shape may be a simple cylindrical shape in terms of function.

  Since the outer periphery of the insulating case 10 is a contact surface pressed against the surface of the movable body to be detected, the contact surface is a thin film according to various purposes such as wear resistance, slidability, and heat resistance. It is preferable to coat the film. For the purpose of achieving insulation from the surface of the movable body, it is also preferable to coat a thin film. The thin film may be selected according to the purpose, and a fluororesin film and a polyimide film are preferable. In the present embodiment, a 50 μm thick polyimide film coated with an adhesive material is provided for the purpose of improving slidability. The entire outer periphery of the insulating case 10 may be covered, or only the region that can be the contact surface may be covered.

  The fuse element 12 has a circular shape at both ends and a cross section, and may be made of a fusible alloy generally used as an element material of a fusible alloy type thermal fuse, and melts at a predetermined temperature. In addition, a material having an appropriate composition is selected. Specific examples of the material include alloys of metals such as tin, lead, and the like, and the melting temperature can be controlled by the composition ratio thereof. In the case where the heating rotator of the fixing device in the electrophotographic apparatus is to be detected, the melting temperature (“predetermined temperature” in the present invention) is selected from a range of about 180 to 220 ° C.

  The leads 4a and 4b also function as electrodes of the thermal fuse 2 in the present embodiment. Therefore, the end portion is circular, and both ends of the fuse element 12 are fixed by welding or the like. There is no restriction | limiting in particular in the material of lead | read | reed 4a, 4b, The thing of a general material is used as a lead | read, and copper or nickel is used suitably. In this embodiment, a lead tin-plated on copper is used.

  The insulating sealing material 18 is not particularly limited as long as it is an insulator that can seal the openings at both ends of the insulating case 10, but of course heat resistance as a thermal fuse is required. In this embodiment, an epoxy resin is used because of its compatibility with the flux resin near the operating temperature.

In the case of a fusible alloy type thermal fuse, when the temperature of an object to be detected abnormally generates heat for some reason during operation and the temperature of the fuse element 12 reaches a predetermined temperature (for example, 187 ° C.), the fuse element 12 is melted. start. When the fuse element 12 is sufficiently melted, the fuse element 12 is disconnected halfway, and the electrical connection between the leads 4a and 4b (and between the metal spring plates 6a and 6b) is interrupted.
In the present invention, when a fusible alloy type thermal fuse is used, it is not limited to the cylindrical one as described above. For example, a pair of electrodes is provided on the surface of the insulating substrate, and the gap between the pair of electrodes is It may be of a substrate type that is electrically bridged by such fuse elements. In this case, the surface of the substrate on which the electrode or the like is not provided is a temperature-sensitive portion that contacts the movable body surface.

The material of the metal spring plates 6a and 6b is not particularly limited, and is selected from various metal materials generally used as a spring plate. Specifically, it is stainless steel (particularly, 0.07 mm to 0.15 mm in thickness). Are preferably used. In this embodiment, the metal spring plates 6a and 6b are formed by etching using a stainless plate having a thickness of 100 μm.
The metal spring plates 6a and 6b also have a function of giving a bending reaction force and a function of a conductor that forms a disconnection control circuit (not shown).

  In the present embodiment, the metal spring plates 6a and 6b are arranged at the end portion on the side holding the temperature fuse 2 or the like as shown in FIG. In the department). Of course, since a part of the outer peripheral surface of the thermal fuse 2 is a part (temperature-sensitive part) that contacts the movable body to be detected, the metal spring plate 6a (on the right side in FIG. 2) 6b) is retreating.

  In this way, the metal spring plate (holding member) 6a (6b) as viewed from the extension line of the lead (feeding terminal portion) 4a (4b) (that is, as viewed from the rear side in FIG. 2). The shape of the periphery of the end connected to the lead 4a (4b) is a cross-sectional shape perpendicular to the extension line of the thermal fuse (energization interruption member) 2 excluding the temperature-sensitive portion or its periphery (that is, a cross-section). The feature of the present embodiment and the present invention is that the lead 4a (4b) or its extension line projects outwardly. Such a shape is hereinafter referred to as “protective shape” as appropriate, and the shape portion is referred to as “protective shape portion X” (see FIGS. 1 and 2).

In the present invention, as the “protective shape”, it is not required that all of the protective portion (the temperature sensitive portion or the portion excluding the periphery thereof) is “extending outward”, and at least a part of the protective portion is covered. It suffices if a portion that may hit a peripheral member other than the movable member that is a detection target is “projected outward”, and this case is also included in the scope of the present invention.
The action or effect of this protective shape portion X, preferred modes, and the like will be described later.

  In the present invention, the holding member that contacts the metal spring plates 6a and 6b is not particularly required to be made of metal, and various elastomers can be used, for example. In this case, the lead 4a, Since a configuration for establishing electrical connection with 4b (for example, wiring inside) is required, it is preferable to use a metal spring plate that is easy to mold and has good conductivity. Further, in the holding member, the region rubbed with the movable member or its periphery is preferably covered with a thin film according to various purposes such as wear resistance, slidability, and heat resistance. For the purpose of achieving insulation from the surface of the movable body, it is also preferable to coat a thin film. A preferred embodiment of the thin film is the same as the thin film that covers the outer periphery of the insulating case 10.

  In the present invention, it is essential that the holding member is a pair, but a pair of plate-like portions connected to the thermal fuse via the lead is sufficient, and wiring and insulation are prevented so as not to be electrically short-circuited. As long as the countermeasure is performed by a known means such as the above, the two may be integrated in the middle (that is, one may be provided in a portion fixed to the fixing support member 46 described later). .

The abnormal temperature rise prevention element of this embodiment and the abnormal temperature rise prevention device using the same are suitably used for, for example, a fixing device in an electrophotographic image forming apparatus. Hereinafter, taking this case as an example, the operation and effect of the abnormal temperature rise prevention element of the present embodiment will be described.
First, an example of an image forming apparatus to which the abnormal temperature rise prevention element of this embodiment is applied will be described.

FIG. 4 is a schematic configuration diagram illustrating an example of an image forming apparatus to which the abnormal temperature rise prevention element of the present embodiment is applied.
The image forming apparatus shown in FIG. 4 has a cylindrical drum in which a latent image due to a difference in electrostatic potential is formed on the surface by irradiating image light after uniform charging, and a photosensitive drum 101 that rotates in the direction of arrow A. A charging device 102 that uniformly charges the surface of the photosensitive drum 101 around the photosensitive drum 101; and an exposure device that irradiates the photosensitive drum 101 with image light to form a latent image on the surface. 103, a developing unit 104 that selectively transfers toner to a latent image on the surface of the photosensitive drum 101 and forms a toner image, and an endless belt-like shape that faces the photosensitive drum 101 and is supported so that its peripheral surface can rotate. An intermediate transfer member 105, a cleaning device 106 that removes toner remaining on the photosensitive drum 101 after the transfer of the toner image, and a static elimination exposure device 107 that neutralizes the surface of the photosensitive drum 101. To have.

  Further, inside the intermediate transfer member 105, a transfer charger 108 that primarily transfers the toner image formed on the surface of the photosensitive drum 101 to the intermediate transfer member 105, two support rolls 109a and 109b, and secondary transfer are performed. A transfer counter roll 110 for performing the transfer is disposed, and the intermediate transfer member 105 is stretched around these in a direction of an arrow B by these. At a position facing the transfer counter roll 110, a transfer roll 111 for secondary transfer of the toner image primarily transferred to the outer peripheral surface of the intermediate transfer body 105 via the intermediate transfer body 105 onto the recording paper P is disposed. The recording paper P is fed in the direction of arrow C from a paper tray (not shown) to the pressure contact portion between the transfer facing roll 110 and the transfer roll 111. Then, the recording paper P on which the toner image is secondarily transferred on the surface at the press contact portion is conveyed in the direction of the arrow C as it is.

  On the downstream side of the recording paper P conveyance direction (arrow C direction), a fixing device 112 is arranged to heat and melt the toner image on the surface of the recording paper P, and press and fix it on the recording paper P. It is sent via the guide 114. A cleaning device 113 that removes toner remaining on the surface of the intermediate transfer member 105 is provided at a position along the downstream direction of the rotation of the intermediate transfer member 105 (in the direction of arrow B).

The fixing device 112 is a fixing device using an electromagnetic induction heating method, and the above-described abnormal temperature rise prevention element of the present embodiment is applied to the fixing device 112. First, the configuration of the fixing device using the electromagnetic induction heating method in the state where the abnormal temperature rise prevention element of this embodiment is not provided will be described.
FIG. 5 is a schematic configuration diagram illustrating an example of a general electromagnetic induction heating type fixing device that does not include the abnormal temperature rise prevention element of the present embodiment.

  The fixing device shown in FIG. 5 mainly includes an endless fixing belt 30 rotating in the direction of arrow A, an electromagnetic induction heating device 32 supported at a position facing the peripheral surface of the fixing belt 30, and the fixing belt 30. A pressure roll 34 that is in pressure contact with the pressure belt 34, a pressure opposing member 36 that is disposed inside the fixing belt 30 and that presses against the pressure roll 34 while sandwiching the pressure roller 34 via the fixing belt 30 to form a nip portion; And a peeling member 38 supported in the vicinity of the downstream side in the rotation direction (arrow A direction) of the fixing belt 30. A temperature detection device 40 that measures the temperature of the inner peripheral surface of the fixing belt 30 is provided on the upstream side of the nip portion.

  The electromagnetic induction heating device 32 is formed in a shape that follows the outer peripheral surface of the fixing belt 30, and is disposed so that the gap with the outer peripheral surface is 1 to 3 mm, and heats the conductive layer of the fixing belt 30. It is. The electromagnetic induction heating device 32 includes a magnetic core 32b made of ferrite or the like supported by a pedestal 32a, an excitation coil 32c wound around the magnetic core 32b, and an alternating current supplied to the excitation coil 32c. The main part is composed of the excitation circuit 32d.

  The pressure facing member 36 includes an elastic member 36a having a contact surface curved in a shape along the peripheral surface of the pressure roll 34, and a support member 36b that supports the elastic member 36a and is fixedly supported at both ends. The main portion is constituted by a belt traveling guide (not shown) supported by the support member 36b, abutted against the inner peripheral surface at both ends in the width direction of the fixing belt 30, and regulating the position of the fixing belt 30. ing. In addition, a magnetic body 44 that collects magnetic flux that has passed through the fixing belt 30 including a conductive layer (not shown) is provided at a portion of the pressure facing member 36 that faces the electromagnetic induction heating device 32. As the material of the magnetic body 44, ferrite or the like is used. The support member 36 b and the magnetic body 44 are supported and fixed to the fixing member 42.

  The elastic member 36 a is in pressure contact with the pressure roll 34 and has a concave shape following the circumferential surface of the pressure roll 34, so that a sufficient nip width is obtained between the elastic member 36 a and the pressure roll 34 via the fixing belt 30. be able to. In addition, a low friction layer is provided on the surface of the elastic member 36 a and is configured to reduce friction with the inner peripheral surface of the fixing belt 30.

  The release member 38 includes a support portion 38 a that is fixedly supported at one end, and a release sheet 38 b that is supported by the support member 38 a, and is arranged so that the leading end of the release sheet 38 b approaches or contacts the fixing belt 30. As a result, the release sheet 38 b enters between the recording paper P that has passed through the nip portion and the fixing belt 30, and the recording paper P is released from the surface of the fixing belt 30.

  The temperature detection device 40 is in contact with the inner peripheral surface of the fixing belt 30 and detects the temperature thereof, and supports the temperature sensor 40 a and presses the temperature sensor 40 a against the inner peripheral surface of the fixing belt 30. 40b, and one side of the metal spring plate 40b is supported and fixed to a fixed support member 46. The amount of power supplied from the exciting circuit 32d to the exciting coil 32c is controlled by the detection value of the temperature sensor 40a, so that the surface temperature of the fixing belt 30 is maintained at a desired temperature.

As described above, one end of the metal spring plate 40b is fixed to the fixed support member 46, and the temperature sensor 40a attached to the distal end side of the metal spring plate 40b is fixed by the elastic repulsive force of the curved metal spring plate 40b. It is pressed against the inner peripheral surface of the belt 30.
The position where the temperature sensor 40a exists can be moved in the substantially normal direction from the center when the fixing belt 30 is regarded as a circle by the elastic repulsive force of the metal spring plate 40b. It follows the displacement of 30.

The temperature sensor 40 a included in the temperature detection device 40 is in contact with the inner peripheral surface of the fixing belt 30 so as to detect the temperature of the fixing belt 30, but instead of this temperature detection device 40 or in this temperature detection device. In addition, a temperature detection device 48 that detects the surface temperature of the pressure roll 34 may be provided.
Next, operations of the image forming apparatus and the fixing device 112 will be described.

  First, the surface of the photosensitive drum 101 is charged almost uniformly by the charging device 102, and then image light is irradiated from the exposure device 103 to form a latent image on the surface of the photosensitive drum 101 due to the difference in electrostatic potential. When the photosensitive drum 101 rotates in the direction of arrow A, the photosensitive drum 101 moves to a position facing one developing device 104a of the developing unit 104, and the first color toner is transferred from the developing device 104a, and the toner is transferred to the surface of the photosensitive drum 101. An image is formed. This toner image is conveyed to a position facing the intermediate transfer member 105 by the rotation of the photosensitive drum 101 in the direction of arrow A, and is electrostatically primarily transferred onto the surface of the intermediate transfer member 105.

On the other hand, the toner remaining on the surface of the photosensitive drum 101 after the primary transfer is removed by the cleaning device 106, and the cleaned surface of the photosensitive drum 101 is potentialally initialized by the charge eliminating exposure device 107, and again with the charging device 102. Move to the opposite position.
Thereafter, the three developing devices 104b, 104c, and 104d of the developing unit 104 sequentially move to positions facing the photosensitive drum 101, and similarly, the second, third, and fourth color toner images are sequentially formed, and the four colors are changed. When they overlap, they are transferred onto the surface of the intermediate transfer member 105 in a lump.

The toner image T superimposed on the intermediate transfer body is conveyed to a position where the transfer roll 111 and the transfer counter roll 110 face each other by the circular movement of the intermediate transfer body 105 in the direction of arrow B, and from a paper tray (not shown). It is brought into contact with the fed recording paper P. A transfer bias voltage is applied between the transfer roll 111 and the intermediate transfer member 105, and the toner image T is secondarily transferred onto the surface of the recording paper P.
The recording paper P carrying the unfixed toner image T is transported to the fixing device 112 via the transport guide 114 and sent to the nip portion between the fixing belt 30 and the pressure roll 34 included in the fixing device 112. It is.

  In the fixing device 112, electromagnetic induction heating is performed almost at the same time or immediately after the pressure roll 34 starts to rotate in the direction of arrow E and the fixing belt 30 is driven to rotate in the direction of arrow D. An alternating current is supplied from the excitation circuit 32d included in the device 32 to the excitation coil 32c. When an alternating current is supplied to the exciting coil 32c, the magnetic flux indicated by the arrow H around the exciting coil 32c repeats generation and disappearance. When the magnetic flux H crosses the conductive layer (not shown) included in the fixing belt 30, an eddy current is generated in the conductive layer so that a magnetic field that prevents the change in the magnetic field is generated. Heat is generated in proportion to the skin resistance and the magnitude of the current flowing through the conductive layer. On the other hand, the magnetic flux penetrating the conductive layer forms a closed path toward the magnetic body 44.

The recording paper P sent to the fixing device is heated and pressed by the fixing belt 30 heated to a predetermined temperature by the electromagnetic induction heating device 32 and the pressure roll 34, and the toner image T is applied to the surface of the recording paper P. It is melt-bonded. When the recording paper P is fed out from the nip portion between the pressure roll 34 and the elastic member 36a, the recording paper P tends to go straight in the fed-out direction due to its rigidity, and is easily peeled off from the fixing belt 30 that is bent. Then, it is peeled off from the fixing belt 30 by the peeling member 38.
The abnormal temperature rise prevention element of this embodiment is juxtaposed in the same shape next to the temperature detection device 40 in the fixing device of FIG. 5 described above.

  FIG. 6 is a schematic configuration diagram illustrating an example of an electromagnetic induction heating type fixing device including the abnormal temperature rise prevention element of the present embodiment. The fixing device shown in FIG. 6 is obtained by adding the abnormal temperature rise prevention element 20 of this embodiment as it is to the fixing device shown in FIG. However, the temperature detection device 40 is not shown in FIG. 6 from the viewpoint of avoiding the complication of the drawing and simplifying the description. Moreover, since members other than the configuration related to the abnormal temperature rise prevention element 20 are the same as the configuration shown in FIG. 5, the description thereof is omitted. FIG. 7 is an enlarged cross-sectional view illustrating part of members in the corresponding region in order to explain the arrangement around the abnormal temperature rise prevention element 20 in the fixing device shown in FIG.

  In this example, as shown in FIG. 7, the metal spring plate opposite to the side on which the thermal fuse 2 is held in the abnormal temperature rise prevention element 20 of the present embodiment shown in FIG. 1 and FIG. The ends of 6a and 6b are fixed to the fixed support member 46, and the thermal fuse 2 is pressed against the inner peripheral surface of the fixing belt 30 by the elastic repulsive force of the curved metal spring plates 6a and 6b. As shown in the figure, the metal spring plate 6 a (6 b) is greatly curved, and the thermal repulsive force based on the restoring force enables the thermal fuse 2 to advance and retreat, and can follow the displacement of the fixing belt 30. It can be done.

  As shown in FIG. 7, in this example, the position where the thermal fuse 2 exists is movable in a substantially normal direction from the center when the fixing belt 30 is regarded as a circle. At this time, depending on the movement of the fixing belt 30, the thermal fuse 2 may approach the magnetic body 44 and eventually come into contact. At this time, if the thermal fuse 2 comes into contact with another member, the heat is rapidly lost and the function as the thermal fuse is degraded.

On the other hand, in the present embodiment, in order to prevent the thermal fuse 2 from being deprived of heat due to contact with other members, the end portions of the metal spring plates 6a and 6b are shown in FIG. As shown, an integrally formed protective shape portion X is provided. Therefore, the protective member X first contacts the peripheral member such as the magnetic body 44, and an air layer exists between the thermal fuse 2 and the peripheral member, so that the thermal fuse 2 and the peripheral member are in direct contact with each other. Can be prevented. Therefore, there is no fear of causing a deviation from the actual temperature due to the thermal fuse 2 being deprived of heat by contacting the peripheral member, and the temperature detection accuracy is improved.
The shape of the protective shape portion X is not particularly limited in the present invention as long as it is a protective shape suitable for the purpose of the present invention. For example, even if the end portion has a corner as in the present embodiment. It may be a shape with rounded corners.

  In this embodiment, the metal spring plates 6a and 6b are electrically and physically connected to the thermal fuse 2 only via the leads 4a and 4b. Therefore, since the thermal fuse 2 has a structure that is not in direct contact with the metal spring plates 6a and 6b, heat does not escape from the metal spring plates 6a and 6b, and the thermal capacity of the thermal fuse 2 is reduced. The temperature difference between the thermal fuse and the movable body surface can be minimized.

  Further, in the present embodiment, the connection between the metal spring plates 6a and 6b and the leads 4a and 4b is made by fitting as shown in FIG. The contact point between them is a point where heat from the thermal fuse 2 escapes, and since the leads 4a and 4b are made of metal, the heat conduction from this part is relatively large, so contact such as welding or mechanical caulking Rather than a joining method with many points, it is preferable that the fitting is close to point contact. In the joining by fitting, since the contact portion is close to point contact, the escape of heat can be suppressed to a minimum, and the factors that hinder the increase in the thermal response can be suppressed. In addition, in the joining by fitting, it is possible to reliably establish an electrical connection, and there is an advantage that the joining is simple although the joining situation is simple.

  Joining by this fitting means that the lead 4a (4b) is fitted into the U-shaped groove 8 provided at the tip end portion (the side having the protective shape portion X) of the metal spring plates 6a, 6b, thereby connecting the both. It is a method of joining and fixing. In this embodiment, the inner wall of the U-shaped groove 8 is literally U-shaped with nothing provided, but a groove is formed so that the distance between the walls becomes narrower toward the entrance, It may be possible to ensure the fixing of both by providing a convex portion or the like. Of course, as in this embodiment, even if these measures are not taken, there is no problem in fixing as long as both are firmly fitted.

In the application example of the abnormal temperature rise prevention element of FIG. 6 and the abnormal temperature rise prevention device using the same, a mechanism for expressing the abnormal temperature rise prevention function is shown in FIG. I will explain it.
The heat source is used in a fixing device that heats and fixes an unfixed toner image formed in the image forming apparatus on the recording paper P. In this example, an electromagnetic induction heating type heat source is used. Specifically, the exciting coil (magnetic field generating means) 32c, the control device (power supply monitoring means, output permission means) 50, the exciting circuit 32d (high frequency power supply), the temperature fuse 2 in the abnormal temperature rise prevention element 20, and A relay 54 is provided. In FIG. 8, reference numeral 30 indicated by a broken line is an electromagnetic induction heat-generating fixing belt.

  The exciting coil 32c generates a magnetic field in cooperation with a magnetic core (32b in FIG. 6). The control device 50 includes a voltage monitoring circuit that receives a heating permission signal (pulse signal) of the fixing device from the outside (for example, a pulse input circuit) and monitors the DC power supply voltage supplied to the excitation circuit 32d. . The thermal fuse 2 detects the inner peripheral surface temperature of the fixing belt (electromagnetic induction heating member) 30 of the fixing device 112 in the image forming apparatus. The excitation circuit 32d includes a voltage resonance inverter circuit (switching inverter circuit) for supplying high frequency power to the excitation coil 32c when electric power is supplied via the contact of the relay 54 upon receiving AC input.

  Here, the relay 54 is supplied with DC power to its drive winding via the thermal fuse 2 that detects the inner peripheral surface temperature of the fixing belt 30. If the inner peripheral surface temperature of the fixing belt 30 exceeds a predetermined temperature and the temperature rises abnormally, the temperature fuse 2 also rises as described above, the fuse element 12 inside thereof melts and breaks, and the relay 54 By the operation (or the non-operation from the operation state), the AC power supply for supplying the voltage to the excitation circuit 32d is cut off, and the safety of the fixing device 112 is ensured from the thermal runaway.

  As described above, the overheat prevention element on the surface of the movable body and the overheat prevention device using the same have been described by way of example, but the present invention is not limited to these configurations. The present invention has no problem as long as it has essential constituent requirements, and those skilled in the art can make various modifications based on known knowledge.

  For example, in the present embodiment, the fixing device is described by taking an electromagnetic induction heating type as an example, but the overheat prevention element of the movable body surface of the present invention and the overheat prevention device using the same are described. However, it is not essential to be applied to such a fixing method, and can be applied to a heater such as a general halogen heater or other various heating methods. Of course, it is most suitable to apply the present invention to an electromagnetic induction heating type fixing device having no space in the fixing rotating body.

Further, as a configuration of the fixing device to be applied, in this embodiment, a fixing rotator is an endless belt, and a pressure rotator that presses oppositely is a roll, and a so-called belt-roll nip type fixing device is taken as an example. However, the present invention can be applied to all types of fixing devices such as a general two-roll system, a roll-fixing rotator and a belt-roll nip system in which a pressure rotator is a belt, a two-belt system, and the like.
The overheat prevention element on the surface of the movable body of the present invention is not limited to the fixing device and may be any detection target as long as the surface is heated and the purpose is to prevent an abnormal temperature rise of the moving movable body. It can also be applied to.

It is a top view which shows the temperature rise prevention element which is an example of the temperature rise prevention element of this invention. FIG. 2 is a right side view of the overheat prevention element shown in FIG. 1. It is a longitudinal cross-sectional view of the fusible alloy type thermal fuse of the overheat prevention element shown in FIG. It is a schematic block diagram which shows an example of the image forming apparatus to which the overheat prevention element shown in FIG. 1 is applied. It is a schematic block diagram which shows an example of the fixing device by the general electromagnetic induction heating system which is not provided with the overheat prevention element. It is a schematic block diagram which shows an example of the fixing device by the electromagnetic induction heating system provided with the overheat prevention element shown in FIG. 1 and FIG. FIG. 7 is an enlarged cross-sectional view illustrating a part of members in the corresponding region in order to explain the arrangement around the abnormal temperature rise prevention element in the fixing device illustrated in FIG. 6. FIG. 7 is a circuit diagram or a block diagram showing only a configuration that serves as a core of the mechanism for expressing the abnormal temperature rise prevention function in the fixing device shown in FIG. 6.

Explanation of symbols

  2: fusible alloy type thermal fuse (energization interruption member), 4a, 4b: lead (power supply terminal part), 6a, 6b: metal spring plate (holding member), 8: U-shaped groove, 10: insulating case, 12 : Fuse element, 16: flux, 18: insulating sealing material, 20: abnormal temperature rise prevention element, 30: fixing belt, 32: electromagnetic induction heating device, 32a: pedestal, 32b: magnetic core, 32c: excitation coil, 32d: Excitation circuit, 34: Pressure roll, 36: Pressure facing member, 36a: Elastic member, 36b: Support member, 38: Release member, 38a: Support part, 38b: Release sheet, 40: Temperature detection device, 40a : Temperature sensor, 40b: Metal spring plate, 42: Fixed member, 44: Magnetic body, 46: Fixed support member, 48: Temperature detection device, 50: Control device, 5 : Relay, 101: Photoconductor drum, 102: Charging device, 103: Exposure device, 104: Development unit, 104a: Development device, 104b, 104c, 104d: Development device, 105: Intermediate transfer member, 106: Cleaning device, 107 : Static elimination exposure device, 108: Transfer charger, 109a, 109b: Support roll, 110: Transfer counter roll, 111: Transfer roll, 112: Fixing device, 113: Cleaning device, 114: Transport guide, P: Recording paper, T : Toner image, X: Protection shape

Claims (10)

A current-carrying member that cuts off the electrical connection at a predetermined temperature, a pair of power supply terminal portions projecting from both ends thereof, and one end of the power supply terminal portion that is electrically and physically connected to hold the current-carrying member However, it comprises a pair of elongated holding members having a function of bringing the temperature-sensitive part into contact with the surface of the movable body to be detected,
The shape of the periphery of the end connected to the power supply terminal portion of the holding member, as viewed from the extended line of the power supply terminal portion, excludes the temperature-sensitive portion or its periphery, and is perpendicular to the extension line of the energization cutoff member With respect to the cross-sectional shape, at least in part, the power supply terminal part or its extension line is projected outward as an axis,
At the end which holds the current blocking member in the holding member, on the opposite side of the temperature-sensitive portion about an axis passing through both ends of the current blocking member, the portion of the holding member is characterized in that it does not exist An element that prevents abnormal temperature rise on the surface of movable bodies. 2. The abnormal temperature rise prevention element according to claim 1, wherein the holding member is electrically and physically connected to the energization cutoff member only through the power supply terminal portion. The abnormal temperature rise prevention element according to claim 2, wherein the connection between the holding member and the power supply terminal is by fitting. The abnormal temperature rise prevention element according to claim 1, wherein the holding member also has a function of supplying power to the power supply terminal. The abnormal temperature rise prevention element according to claim 1, wherein at least a part of the outer surface of the energization interrupting member and / or the holding member is covered with a thin film. The abnormal temperature rise prevention element according to claim 1, wherein the temperature-sensitive portion of the energization cutoff member is made of aluminum nitride. A fixing rotating body heated by a heat source and controlled in a predetermined fixing temperature range, and a pressure roller that presses against the fixing rotating body to form a nip portion, and a recording medium carrying an unfixed toner image in the nip portion. An abnormal temperature rise prevention device applied to a fixing device that is inserted and heat-fixed,
2. The abnormal temperature rise prevention element according to claim 1, wherein a current cut-off member is disposed in contact with the front surface or the back surface of the fixing rotating body, and is wired so as to cut off the power supply to the heat source when the temperature exceeds a predetermined temperature. An abnormal temperature rise prevention device comprising: The abnormal temperature rise prevention device according to claim 7, wherein the heat source is a heating unit using an electromagnetic induction heating method. The fixing rotator is an endless fixing belt that is driven to rotate in a direction perpendicular to the shaft of the current-carrying-off member disposed in contact with the inner peripheral surface thereof, and is displaced in a direction perpendicular to the surface of the fixing belt. The abnormal temperature rise prevention device according to claim 7, wherein the abnormal temperature rise prevention element is arranged so that the energization cutoff member can follow and move. The fixing belt includes a conductive layer;
  An electromagnetic induction heating device that is a heating means by an electromagnetic induction heating method as the heat source is disposed apart from the outer peripheral surface of the fixing belt,
  A magnetic body that collects magnetic flux from the electromagnetic induction heating device that has passed through the fixing belt is provided at a position facing the electromagnetic induction heating device across the fixing belt and spaced from the inner peripheral surface of the fixing belt. ,
  10. The abnormal temperature rise prevention element is disposed between the fixing belt and the magnetic body so that the energization cutoff member is positioned apart from the magnetic body. An abnormal temperature rise prevention device.

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