JP5556268B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that fixes a formed image on a recording medium at a nip between an endless belt-shaped fixing member and a pressure rotating member, and an image forming apparatus including the fixing device.

  Conventionally, various image forming apparatuses using an electrophotographic system have been devised as image forming apparatuses such as copying machines and printers, and are well known in the art. In the image forming process, an electrostatic latent image is formed on the surface of the photosensitive drum as an image carrier, and the electrostatic latent image on the photosensitive drum is developed with a toner as a developer to be visualized and developed. This is established by a process in which the transferred image is transferred onto a recording paper (also referred to as a paper or a recording medium) by a transfer device to carry the image, and a toner image on the recording paper is fixed by a fixing device using pressure or heat.

  In this fixing device, a fixing member and a pressure member constituted by opposing rollers or belts or a combination thereof are arranged so as to contact each other to form a nip portion, and a recording sheet is sandwiched in the nip portion, Heat and pressure are applied to fix the toner image on the recording paper.

  As an example of the fixing device, a technique using a fixing belt stretched around a plurality of roller members as a fixing member is known (for example, see Patent Document 1). An apparatus using such a fixing belt is provided in a fixing belt (endless belt) as a fixing member, a plurality of roller members that stretch and support the fixing belt, and one of the plurality of roller members. And a heater, a pressure roller (pressure member), and the like. The heater heats the fixing belt via the roller member. Then, the toner image on the recording medium conveyed toward the nip formed between the fixing belt and the pressure roller is fixed on the recording medium by receiving heat and pressure at the nip. Belt fixing method).

Further, in the fixing device used in the image forming apparatus described above, there is a fixing device having a fixing member that is in sliding contact with the inner surface of a fixing member that is a rotating body.
For example, in Patent Document 2, a fixing nip portion is formed by sandwiching a heat-resistant film (fixing film) between a ceramic heater as a heating element and a pressure roller as a pressure member. A recording material on which an unfixed toner image to be image-fixed is formed and supported is introduced between the film and the pressure roller, and is nipped and conveyed together with the film. A film heating type fixing device is disclosed in which an unfixed toner image is fixed to a surface of a recording material by a pressure applied to a recording material through a fixing nip portion. This film heating type fixing device can be configured as an on-demand type device using a ceramic heater and a member having a low heat capacity as a film, and energizes the ceramic heater as a heat source only when the image forming apparatus performs image formation. Thus, it is only necessary to generate heat at a predetermined fixing temperature, the waiting time from the power-on of the image forming apparatus to the image forming executable state is short (quick start property), and the power consumption during standby is greatly reduced ( There are advantages such as (power saving).

  In Patent Documents 3 and 4, a rotatable heat-fixing roll whose surface is elastically deformed, an endless belt (pressure belt) that can run while being in contact with the heat-fixing roll, and a non-rotation inside the endless belt The endless belt is placed in pressure contact with the heat fixing roll, a belt nip is provided between the endless belt and the heat fixing roll to allow recording paper to pass, and the surface of the heat fixing roll is elastic. A pressure belt type image fixing device having a pressure pad to be deformed has been proposed. According to this fixing method, the lower pressure member is used as a belt, and the contact area between the paper and the roll is widened to greatly improve the heat conduction efficiency, and it is possible to reduce the energy consumption and at the same time realize the miniaturization. It has become.

  However, although the fixing device described in Patent Document 1 described above is suitable for speeding up the device as compared with a device using a fixing roller, it is a warm-up time (a time required to reach a printable temperature). In addition, there is a limit to shortening the first print time (the time from when a print request is received until the print operation is performed and the paper discharge is completed).

On the other hand, the fixing device described in Patent Document 2 can reduce the warm-up time and the first print time by reducing the heat capacity, and also reduce the size of the device. However, the fixing device described in Patent Document 2 has a problem of durability and a problem of belt temperature stability. In other words, the wear resistance due to sliding between the ceramic heater, which is a heat source, and the inner surface of the belt is inadequate, and the surface that repeats continuous friction is roughened when operated for a long time, increasing the frictional resistance and making the belt run unstable. Or, a phenomenon such as an increase in the driving torque of the fixing device occurs, and as a result, the transfer paper forming the image slips and the image shifts, or the stress on the driving gear increases, causing damage to the gear. (Problem 1).
In the film heating type fixing device, since the belt is locally heated at the nip portion, when the rotating belt returns to the nip entrance, the belt temperature becomes the coldest state (especially at high speed rotation). , There was a problem that fixing failure was likely to occur (Problem 2).

  On the other hand, in Patent Document 3, a glass fiber sheet (PTFE-impregnated glass cloth) impregnated with PTFE as a low friction sheet (sheet-like sliding material) on the surface layer of the pressure pad is used, and the slidability of the belt inner surface and the fixing member is improved. Means for improving the problem are disclosed. However, such a pressure belt type fixing device (Patent Documents 3 and 4) has a problem that it takes a long time to warm up because the heat capacity of the fixing roller is large and the temperature rise is slow. (Problem 3).

  With respect to the above problems 1 to 3, in Patent Documents 5 and 6, a substantially pipe-shaped counter member (metal thermal conductor) disposed on the inner peripheral side of the endless fixing belt, and the counter member By providing a resistance heating element such as a ceramic heater that is disposed on the inner peripheral side and heats the opposing member, the entire fixing belt can be warmed, the warm-up time and the first print time can be shortened, and There has been proposed a fixing device that can solve the shortage of heat during high-speed rotation. However, there may be a part where the flexible fixing belt is largely separated from the metal heat conductor during rotation, and heat transfer is not performed at the part. There was a problem that burns occurred and the rotational torque of the fixing belt increased.

  In Patent Document 7, an endless fixing belt, a pressure roller that presses against the fixing belt to form a nip portion on which a recording medium is conveyed, and an inner peripheral surface of the fixing belt are fixed. A resistance heating element that heats the fixing belt, and the resistance heating element is disposed in a minute gap so as not to be in pressure contact with the inner peripheral surface of the fixing belt, and heats the entire fixing belt with radiant heat. A device has been proposed. As a result, even when the warm-up time and the first print time are shortened and the apparatus is speeded up, it is possible to prevent problems such as defective fixing and wear and damage of the fixing member and the resistance heating element. It is supposed to be.

  However, in the fixing device described in Patent Document 7, since the fixing belt and the resistance heating element are disposed close to each other in order to suppress a decrease in heating efficiency, the flexible fixing belt rotates. In some cases, it may partially come into contact with the resistance heating element, and the fixing belt may be heated non-uniformly due to heat transfer at the contact portion, resulting in temperature unevenness.

  In the fixing device described in Patent Document 7, stress due to rotation and vibration of the pressure roller repeatedly acts on the resistance heating element, and the resistance heating element is repeatedly bent. Since the heating element is made of a metal material, the fixing belt may not be heated properly due to disconnection due to fatigue failure due to repeated bending.

  By the way, in the fixing device, the temperature of the fixing member is detected by the temperature sensor, and the heating unit is controlled based on the detection result. However, the temperature sensor cannot detect the temperature accurately for some reason. When the control circuit is faulty, overheating due to the heating means may occur. In Patent Document 8, when an excessively high temperature prevention means is provided on the outer peripheral surface of a roller on which a fixing belt of a roller having a heating source is not wound, and the excessive temperature rise prevention means detects an abnormally high temperature, The operation of the excessive temperature rise prevention means cuts off the supply of electric power to the heating source and can reliably prevent an unexpected accident.

  However, Patent Document 8 is based on the premise that the fixing belt is wound around two rollers, and like the fixing device described in the fixing device 7, resistance heat is generated so as not to press against the inner peripheral surface of the fixing belt. It is difficult to apply the structure in which the body is arranged with a minute gap.

  The present invention has been made in view of the above-described problems in the prior art, and in a fixing device that locally heats an endless belt-shaped fixing member, the fixing member can be rotated or not rotated. It is an object of the present invention to provide a fixing device capable of preventing abnormal heating when heating control is not effective, and an image forming apparatus including the fixing device.

The present invention provided to solve the above problems is as follows.
[1] A fixing member (fixing sleeve 21) of a rotating endless belt, a pressure member (pressure roller 31) in contact with the outer peripheral surface of the fixing member, and an inner peripheral side of the fixing member, A contact member (contact member 26) that forms a nip portion by contacting the pressure member via a fixing member, and a heating mechanism portion (planar heating element 22) that heats a predetermined region in the circumferential direction of the fixing member. , The heating element support member 23, the halogen heater 22h, the heating member 27A), and the fixing member at a position corresponding to a predetermined area where the heating mechanism heats the fixing member on the outer peripheral side of the fixing member. A first overheating prevention device (first overheating prevention device 32) that stops the power supply to the heating mechanism by a mechanical operation when it is detected in a non-contact manner that the temperature is higher than the temperature; The heating mechanism unit is on the outer peripheral side and the fixing unit In a position corresponding to an area other than the predetermined area where the material is heated, when it is detected in a non-contact manner that the fixing member has reached a predetermined temperature or higher, power supply to the heating mechanism is stopped by a mechanical operation. A temperature rise prevention device (second over temperature rise prevention device 33) , wherein the first over temperature rise prevention device indicates that the fixing member has reached a predetermined temperature or higher when the fixing member is not rotating. And detecting power supply to the heating mechanism, and the second overheat prevention device detects that the fixing member has reached the predetermined temperature or more during rotation of the fixing member. A fixing device (fixing device 20, FIGS. 10 and 15) characterized by controlling power supply to a mechanism unit .
[2] The heating mechanism is disposed on the inner peripheral side of the fixing member, and heats a heating member (heating member 27A) that contacts the fixing member and heats the fixing member, and heats a predetermined region of the heating member. The fixing device according to [1] (FIG. 15), comprising heating means (halogen heater 22h).
[3] The fixing device according to [2], wherein the heating unit is any one of a planar heating element, a halogen heater, and an electromagnetic induction heating mechanism.
[4] The heating mechanism is disposed on the inner peripheral side of the fixing member, and is formed on a planar heating element (planar heating element 22) for heating a predetermined region of the fixing member, and on the inner peripheral side of the fixing member. The fixing device according to [1], further comprising: a heating element support member (heating element support member 23) that is disposed and supports the planar heating element from the side opposite to the fixing member. 10).
[5] Any one of [1] to [4], wherein a plurality of the first overheat prevention devices and / or the second overheat prevention devices are arranged in the axial direction of the fixing member. The fixing device according to claim 1 (FIG. 12).
[6] The plurality of first overheat prevention devices are arranged such that a sensor surface is arranged away from the fixing member as it goes from an end to a center in the axial direction of the fixing member. 5] (FIG. 12).
[7] The plurality of first overheat prevention devices are arranged such that a sensor surface facing the fixing member is inclined with respect to the axial direction from the center to the end in the axial direction of the fixing member. The fixing device as described in [6] above (FIG. 13).
[8] The plurality of first overheat prevention devices and / or the plurality of second overheat prevention devices are arranged in the axial direction of the fixing member corresponding to the heating distribution in the axial direction of the heating mechanism. The fixing device according to any one of [5] to [7], wherein:
[9] The fixing according to [8], wherein the plurality of second excessive temperature rise prevention devices are arranged in an axial direction of the fixing member corresponding to a size of a recording medium to be passed. apparatus.
[10] Any one of [1] to [9], wherein the second overheat prevention device is disposed on an outer peripheral side of the fixing member and on a side opposite to a direction of gravity acceleration. (FIG. 10, FIG. 15).
[11] The fixing device according to any one of [1] to [10], wherein the first overheat prevention device and / or the second overheat prevention device is a thermostat.
[12] An image forming apparatus (image forming apparatus 1, FIG. 14) comprising the fixing device (fixing device 20) according to any one of [1] to [11].

According to the fixing device of the present invention, the first overheating prevention device that detects abnormal heating from the heating state in the heating region of the fixing member and the second that detects abnormal heating from the heating state in regions other than the heating region of the fixing member. Since the excessive temperature rise prevention devices are appropriately arranged, abnormal heating when the heating control is not effective can be prevented both when the fixing member is not rotated and when it is rotated.
According to the image forming apparatus of the present invention, since the fixing device of the present invention is provided, the abnormal heating when the heating control is not effective can be prevented both when the fixing member is not rotated and when the fixing member is rotated. The warm-up time and first print time are short, and appropriate image formation can be performed.

FIG. 3 is a cross-sectional view illustrating a configuration of a reference example which is a premise of the fixing device according to the present invention. FIG. 3 is a schematic diagram illustrating an axial direction and a circumferential direction of a fixing sleeve. FIG. 2 is a cross-sectional view illustrating a configuration of a heat generating sheet used in the fixing device of FIG. 1. It is a figure which shows the structural example (1) of the planar heating element used with the fixing device of FIG. FIG. 3 is a top view showing a configuration example (2) of a planar heating element used in the fixing device of FIG. 1. It is a figure which shows the structural example (3) of the planar heating element used with the fixing device of FIG. FIG. 6 is a top view showing a configuration example (4) of a planar heating element used in the fixing device of FIG. 1. It is a perspective view which shows the structure of the rotation support member used with the fixing device of FIG. FIG. 2 is a schematic diagram illustrating a configuration of an internal mechanism unit on a fixing sleeve side in the fixing device of FIG. 1. 2 is a cross-sectional view illustrating a configuration example of a fixing device according to the present invention. FIG. It is a conceptual diagram which shows the relationship between the distance from the fixing sleeve of the excessive temperature rise prevention apparatus used by this invention, and a detection level. It is the schematic which shows arrangement | positioning of the axial direction of the 1st overheating prevention apparatus and the 2nd overheating prevention apparatus in the fixing device of this invention. It is the schematic which shows the arrangement | positioning relationship between a 1st overheating prevention apparatus and the outer peripheral surface of a fixing sleeve. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to the present invention. FIG. 6 is a cross-sectional view illustrating another configuration example of the fixing device according to the present invention.

First, a reference example which is a premise of the fixing device according to the present invention will be described.
FIG. 1 is a cross-sectional view showing a configuration of a reference example which is a premise of a fixing device according to the present invention.
As shown in FIG. 1, the fixing device 50 includes a fixing member (fixing sleeve 21 (also referred to as a fixing rotating body)) composed of a rotating endless belt, and a pressing member (pressurizing) that contacts the outer peripheral surface of the fixing member. A roller 31 (also referred to as a pressure rotator) and an abutting member (abutting member) that is disposed on the inner peripheral side of the fixing member and forms a nip portion by abutting the pressure member via the fixing member. 26), a sheet heating element (sheet heating element 22) that is disposed in contact with the fixing member on the inner peripheral side of the fixing member and heats the fixing member, and a sheet heating element on the inner peripheral side of the fixing member. A heating element support member (heating element support member 23) which is disposed so as to sandwich the planar heating element between the fixing member and supports the planar heating element at a predetermined position, and an inner peripheral side of the fixing sleeve 21. A pipe-shaped rotation support member (supporting the rotating fixing sleeve 21 provided) A rolling support member 27), a heat insulating support member (heat insulating support member 29) provided on the H-shaped outer surface of the core holding member 28 so as to be disposed on the inner peripheral side of the rotation support member 27 and downstream of the nip portion, Is provided.

  Here, the fixing sleeve 21 is a pipe-shaped endless belt having a length corresponding to the width of the recording medium P through which the paper is passed in the axial direction and having flexibility, for example, a thickness of 30 to 50 μm. At least a release layer is formed on a base material made of the above metal material, and the outer diameter is 30 mm. Hereinafter, the pipe longitudinal direction of the fixing sleeve 21 is referred to as an axial direction as shown in FIG. 2A, and the pipe circumferential direction of the fixing sleeve 21 is referred to as a circumferential direction as shown in FIG.

  As a material for forming the base material of the fixing sleeve 21, a metal material having good heat conductivity such as iron, cobalt, nickel, or an alloy thereof can be used.

  The release layer of the fixing sleeve 21 is obtained by coating a fluorine compound such as PFA in a tube shape, and its thickness is 50 μm. The release layer is for enhancing the toner release property on the surface of the fixing sleeve 21 with which the toner image (toner) T on the recording medium P is in direct contact.

  The pressure roller 31 is formed by sequentially forming a heat-resistant elastic layer such as silicone rubber (solid rubber) and a release layer on a metal core made of a metal material such as aluminum or copper, and has an outer diameter of 30 mm. It has become. The elastic layer is formed to have a thickness of 2 mm to 3 mm. The release layer is coated with a PFA tube and is formed to have a thickness of 50 μm. Further, a heating element such as a halogen heater may be incorporated in the cored bar as necessary. The pressure roller 31 is pressed against the contact member 26 via the fixing sleeve 21 by a pressing means (not shown), and the pressure contact portion forms a nip portion where the fixing sleeve 21 side is recessed. Then, the recording medium P is conveyed to the nip portion.

  Further, the pressure roller 31 is rotationally driven by a driving mechanism (not shown) while being in pressure contact with the fixing sleeve 21 (rotates in the clockwise direction in FIG. 1), and the fixing sleeve 21 is rotated along with the rotation of the pressure roller 31. It will rotate (rotating counterclockwise in FIG. 1).

  The contact member 26 has a length in the axial direction of the fixing sleeve 21, and at least a portion in pressure contact with the pressure roller 31 through the fixing sleeve 21 is made of an elastic body having heat resistance such as fluorine rubber. In addition, the core holding member 28 is fixed in a state of being held at a predetermined position on the inner peripheral side of the fixing sleeve 21. Further, the portion of the contact portion 26 that contacts the inner peripheral surface of the fixing sleeve 21 is preferably made of a material having excellent sliding properties and wear resistance, such as a Teflon (registered trademark) sheet.

  The core holding member 28 is a rigid member having a length corresponding to the axial length of the fixing sleeve 21 and having an H-shaped cross section. It is arranged at a substantially central portion on the circumferential side.

  The core holding member 28 holds various members arranged on the inner peripheral side of the fixing sleeve 21 at predetermined positions. For example, one of the H-shaped core holding members 28 (the side facing the pressure roller 31). The abutting member 26 is housed and held in the recessed portion of (), and is supported from the side opposite to the nip portion so that the abutting member 26 is not greatly deformed even when pressed by the pressure roller 31. The core holding member 28 holds the contact member 26 so as to slightly protrude from the core holding member 28 toward the pressure roller 31, so that the core holding member 28 does not contact the fixing sleeve 21 at the nip portion. Is arranged.

  In addition, a concave portion of the other of the H shapes of the core holding member 28 (the side opposite to the pressure roller 31 side) has a length corresponding to the axial length of the fixing sleeve 21 and has a T-shaped cross section. A terminal block stay 24 having a shape and a power supply line 25 that extends on the terminal block stay 24 and supplies electric power from the outside are housed and held. Further, the heating element support member 23 is held on the H-shaped outer surface of the core holding member 28. In FIG. 1, the heating element support member 23 is held in a region corresponding to a lower half circumference of the fixing sleeve 21 (a half circumference on the entry side of the nip portion). At this time, the heating element support member 23 and the core holding member 28 may be bonded in consideration of assembly. Alternatively, in order to prevent heat transfer from the heating element support member 23 side to the core holding member 28 side, both may be non-bonded.

  The core holding member 28 holds the end portion of the pipe-shaped rotation support member 27 formed by cutting the pipe peripheral surface in the axial direction before and after the nip portion in the circumferential direction. Holding. Note that both ends of the rotation support member 27 in the axial direction are held by side plates constituting a frame of the fixing device 50.

  The heating element support member 23 supports the planar heating element 22 in order to place the planar heating element 22 in contact with the inner peripheral surface of the fixing sleeve 21. Therefore, the heating element support member 23 has an outer peripheral surface having a predetermined arc length along the inner peripheral surface of the fixing sleeve 21 having a circular cross-sectional shape.

  Further, the heating element support member 23 has heat resistance sufficient to withstand the heat generation of the sheet heating element 22, and the sheet heating element 22 is not deformed when the rotating fixing sleeve 21 contacts the sheet heating element 22. It is preferable to have strength sufficient to support the heat and heat insulation so that the heat of the sheet heating element 22 is transmitted to the fixing sleeve 21 side without being transmitted to the core holding member 28 side. A molded body is preferred. When the sheet heating element 22 is in contact with the inner peripheral surface of the fixing sleeve 21, the force that the fixing sleeve 21 that rotates rotates pulls the sheet heating element 22 toward the nip portion acts on the sheet heating element 22. Therefore, the heating element support member 23 needs to have sufficient strength to support the planar heating element 22 without being deformed. In this case as well, a polyimide resin foam molded body is suitable. In addition, a solid resin member may be supplementarily provided inside the polyimide resin foam to improve the rigidity.

  As shown in FIG. 3, the sheet heating element 22 includes a resistance heating layer 22b in which conductive particles are dispersed in a heat-resistant resin on an insulating base layer 22a, and power to the resistance heating layer 22b. An electrode layer 22c to be supplied, and has a heat generating sheet 22s having a predetermined width and length corresponding to the axial direction and the circumferential direction of the fixing sleeve 21 and exhibiting flexibility. On the base layer 22a, an insulating layer 22d is provided that insulates between the resistance heating layer 22b and an electrode layer 22c of another power feeding system adjacent to the base layer 22a or between an edge portion of the heating sheet 22s and the outside. The planar heating element 22 includes an electrode terminal 22e (not shown, described later) that is connected to the electrode layer 22c at the end of the heating sheet 22s and supplies power supplied from the power supply line 25 to the electrode layer 22c. .

  Further, the thickness of the heat generating sheet 22s is about 0.1 to 1 mm, and is flexible enough to be wound around at least the outer peripheral surface of the heat generating element support member 23.

  Here, the base layer 22a is an elastic film made of a resin having a certain degree of heat resistance, such as PET or polyimide resin, and among them, a film member made of polyimide resin is preferable. Thereby, heat resistance, insulation, and a certain amount of flexibility (flexibility) are provided.

  The resistance heating layer 22b is a conductive thin film in which conductive particles such as carbon particles and metal particles are uniformly dispersed in a heat-resistant resin such as polyimide resin. It is configured to generate heat. Such a resistance heating layer 22b may be formed by applying a coating material in which conductive particles such as carbon particles and metal particles are dispersed in a precursor of a heat resistant resin such as polyimide resin on the base layer 22a.

  The resistance heating layer 22b is formed by first forming a thin conductive layer made of carbon particles or metal particles on the base layer 22a, and then laminating an insulating thin film made of a heat resistant resin such as polyimide resin on the conductive layer. It may be integrated.

  The carbon particles used for the resistance heating layer 22b may be ordinary carbon black powder, but may be carbon nanoparticles composed of at least one of carbon nanofibers, carbon nanotubes, and carbon microcoils.

  Further, the metal particles are particles made of Ag, Al, Ni, etc., and the shape thereof may be granular or may be a filament shape.

  The insulating layer 22d may be formed by applying an insulating material made of the same heat resistant resin as the base layer 22a such as polyimide resin.

  The electrode layer 22c may be formed by applying a conductive paste such as conductive ink or Ag, or may be formed by bonding a metal foil or a metal net.

Since the heat generating sheet 22s constituting the sheet heating element 22 is a thin sheet, its heat capacity is small and rapid heating is possible. The amount of heat generated can be arbitrarily set by the volume resistivity of the resistance heat generating layer 22b. . That is, the heat generation amount can be adjusted by the constituent material, shape, size, dispersion amount, etc. of the conductive particles constituting the resistance heat generation layer 22b. For example, the heat generation amount per unit area is 35 W / cm ² , It is possible to realize the planar heating element 22 that can output about 1200 W of electric power. In this case, the heat generating sheet 22s has a size of about 20 cm in width (axial direction) and 2 cm in length (circumferential direction), for example.

  Further, when a sheet heating element made of a metal filament such as stainless steel is used, the surface of the sheet heating element is uneven due to the presence of the filament. When sliding with the peripheral surface, the surface is easily worn, but the heat generating sheet 22s used in the present invention is flat with no unevenness as described above. Excellent durability against sliding. Furthermore, it is preferable to coat the surface of the resistance heating layer 22b of the heating sheet 22s with a fluororesin because durability against contact with the inner peripheral surface of the fixing sleeve 21 is further improved.

  In addition, as an arrangement | positioning area | region in the fixing sleeve 21 internal peripheral surface of 22 s of heat_generation | fever sheets, you may arrange | position in arbitrary positions from the position on the inner peripheral surface of the fixing sleeve 21 on the opposite side to the nip part.

Next, a detailed configuration of the heat generating sheet 22s in the sheet heating element 22 used in the present invention will be described.
That is, the heat generating sheet 22s may have the resistance heat generating layer 22b formed on the entire main surface of the base layer 22a or a certain region, but in each of a plurality of regions arbitrarily divided on the main surface of the base layer 22a. The resistance heating layer 22b is preferably formed so as to be able to generate heat independently. An example of the configuration is shown in FIGS.

  FIG. 4A is a top view showing a configuration example (1) of the planar heating element 22. Here, a state in which the planar heating element 22 is unfolded on a flat surface and viewed from above is shown before being attached to the heating element support member 23. Further, the horizontal direction in the figure is the width direction corresponding to the axial direction of the fixing sleeve 21, and the vertical direction is the length direction corresponding to the circumferential direction of the fixing sleeve 21.

  In FIG. 4A, the heat generating sheet 22s is roughly divided into three in the width direction (axial direction) and further divided into two in the length direction (circumferential direction) on its main surface. ing. Here, when viewing the six divided regions as a matrix matrix in which the length direction (circumferential direction) is composed of row components and the width direction (axial direction) is composed of column components (FIG. 4B), (1,2) A resistance heating layer 22b1 having a predetermined width and length is formed in a divided region of the component (a region corresponding to the central portion in the axial direction of the fixing sleeve 21), and a divided region of the (2, 1) component and the (2, 3) component. A resistance heating layer 22b2 having a predetermined width and length is formed in each of the regions corresponding to both axial ends of the fixing sleeve 21.

  In addition, an electrode layer 22c connected to the resistance heating layer 22b1 is formed in the divided region of the (1,1) component and the (1,3) component, and each of the electrode layers 22c has a heating sheet 22s. An electrode terminal 22e1 extending from one side (lower side in the figure) is provided to form a first heat generating circuit.

  In addition, an electrode layer 22c that connects the two resistance heating layers 22b2 is formed in the (2, 2) component divided region, and the length direction of the heating sheet 22s ( The electrode layer 22c extending in the circumferential direction and extending toward the one side (the lower side in the figure) is connected, and each electrode layer 22c has an electrode terminal 22e2 extending from the one side of the heat generating sheet 22s. A second heat generation circuit is formed.

  In addition, an insulating layer 22d is provided between the first heat generating circuit and the second heat generating circuit to prevent short circuit therebetween.

  In the planar heating element 22 having the configuration shown in FIG. 4A, when the electrode terminal 22e1 is energized, it generates heat as Joule heat due to the internal resistance of the resistance heating layer 22b1, and the electrode layer 22c does not generate heat due to low resistance. Only the divided region of the (1, 2) component of the heat generating sheet 22s generates heat, and the central portion in the axial direction of the fixing sleeve 21 can be heated.

  Further, when energized from the electrode terminal 22e2, heat is generated as Joule heat due to the internal resistance of the resistance heating layer 22b2, and the electrode layer 22c does not generate heat due to low resistance. Therefore, the (2, 1) component and (2 3) Only the divided region of the component generates heat, and both axial end portions of the fixing sleeve 21 can be heated.

  Therefore, when a small-size (narrow width) recording medium P is passed through the fixing device 50, only the electrode terminal 22e1 is energized to heat only the central portion in the axial direction of the fixing sleeve 21 and to widen the width. When the recording medium P is passed, the electrode terminals 22e1 and 22e2 are energized to heat the entire width in the axial direction of the fixing sleeve 21, thereby suppressing the energy consumption and appropriately depending on the width of the recording medium P. Fixing is possible. Further, since the amount of heat generated by the sheet heating element 22 can be controlled in accordance with the size of the recording medium P, the temperature of the non-sheet passing portion does not rise excessively even if small size paper is continuously fed. It is possible to prevent the device from being stopped for protection and the productivity from being lowered. Further, by providing the positional relationship of the different heat generating portions with the integrated planar heat generating element 22, a heat generating element having a smaller temperature deviation in the axial direction than that formed by a separate heat generating element can be obtained.

  In addition, in the heat generating sheet 22s, the heat generation amount tends to decrease due to the outflow of heat to the insulating layer 22d and the electrode layer 22c having a relatively high thermal conductivity at the ends of the respective resistance heat generating layers 22b1 and 22b2. It is in. Therefore, as shown in FIG. 4A, in the width direction (axial direction) of the heat generating sheet 22s, the boundary between the resistance heating layer 22b1 at the center and the resistance heating layer 22b2 at the end is the same surface. When the currents 22e1 and 22e2 were energized, the temperature distribution in the axial direction of the fixing sleeve 21 caused a temperature drop at the boundary between the resistance heating layer 22b1 and the resistance heating layer 22b2, and an abnormal image such as a fixing failure was generated. Accordingly, it is preferable to adopt the configuration shown in FIG. 5 or 6 to improve this problem.

FIG. 5 is a top view showing a configuration example (2) of the planar heating element 22.
The basic configuration of the planar heating element 22 shown in FIG. 5 is the same as that shown in FIG. 4A, but a part of the resistance heating layer 22b1 and the resistance heating layer 22b2 is in the width direction of the heating sheet 22s. The difference is that they overlap in the (axial direction) to form an overlap region. Thereby, it is possible to prevent a temperature drop at the boundary between the resistance heating layer 22b1 and the resistance heating layer 22b2 when the electrode terminals 22e1 and 22e2 are energized.

FIG. 6 is a top view showing a configuration example (3) of the planar heating element 22.
The basic structure of the planar heating element 22 shown in FIG. 6 is the same as that shown in FIG. 5, but in the overlapping region of the resistance heating layer 22b1 and the resistance heating layer 22b2, the resistance heating layers 22b1 and 22b2 and the electrodes respectively. The difference is that the boundary line with the layer 22c is inclined in different directions with respect to the length direction (circumferential direction) to adjust the overlapping amount of the resistance heating layers 22b1 and 22b2.

  This is because the area ratio of the overlapping regions of the resistance heating layers 22b1 and 22b2 is constant in the width direction (axial direction) in the configuration of FIG. However, in the configuration of FIG. 6, the area ratio in the overlapping region of the resistance heating layers 22b1 and 22b2 changes at a constant rate in the width direction (axial direction) to reduce the influence of adjustment of heat generation distribution and component variations. Thus, the temperature uniformity in the entire axial direction is improved, and the problem caused by the configuration of FIG. 5 is improved.

  In the heat generating sheet 22s having the configuration shown in FIGS. 4 to 6 described above, first, only the regions corresponding to the resistance heating layers 22b1 and 22b2 on the main surface of the base layer 22a are exposed to form the resistance heating layers 22b1 and 22b2 by coating. Next, an insulating layer 22d made of only a heat-resistant resin is formed by application in a state where only the region corresponding to the insulating layer 22d is exposed, then only the region corresponding to the electrode layer 22c is exposed, and a conductive paste is applied to expose the electrode layer 22c. This is possible by forming Therefore, the resistance heating layers 22b1 and 22b2 having an arbitrary shape can be formed by adjusting the exposed shape of the region corresponding to the resistance heating layers 22b1 and 22b2.

  Further, the sheet heating element 22 used in the fixing device 50 is formed by laminating a plurality of heating sheets 22s, and the plurality of heating sheets 22s is formed in a resistance heating layer in an arbitrary region on the main surface of each base layer 22a. It is preferable that 22b is formed so that it can generate heat independently. FIG. 7 shows a specific configuration thereof.

FIG. 7 is an exploded perspective view showing a configuration example (4) of the planar heating element 22.
In FIG. 7, a planar heating element 22 is formed by laminating a first heating sheet 22s, an insulating sheet made of an insulating layer 22d, and a second heating sheet 22s in this order from the top.

  Here, the main surface of the first heat generating sheet 22s is divided into three in the width direction (axial direction), the resistance heat generating layer 22b1 is formed in the central divided region, and the resistance is formed in each of the divided regions on both sides thereof. An electrode layer 22c connected to the heat generating layer 22b1 is formed. The main surface of the second heat generating sheet 22s is divided into five in the width direction (axial direction), and the resistance heat generating layer 22b2 is formed in the second and fourth divided regions in the width direction (axial direction). An electrode layer 22c connected to the resistance heating layer 22b2 is formed in each of the remaining divided regions.

  The first heat generating sheet 22s and the second heat generating sheet 22s are stacked with an insulating sheet made of an insulating layer 22d interposed therebetween, and an independent first heat generating circuit is formed on the first heat generating sheet 22s. An independent second heat generating circuit is formed on the second heat generating sheet 22s.

  As a result, when the first heat generating circuit is energized, heat is generated as Joule heat by the internal resistance of the resistance heat generating layer 22b1, and only the central region in the width direction (axial direction) of the first heat generating sheet 22s generates heat. The central portion of the sleeve 21 in the axial direction can be heated. When the second heat generating circuit is energized, heat is generated as Joule heat by the internal resistance of the resistance heat generating layer 22b2, and only the both end regions in the width direction (axial direction) of the second heat generating sheet 22s generate heat. Both axial ends of the sleeve 21 can be heated.

  Like the planar heating element 22 shown in FIG. 4 to FIG. 6, the area of the entire planar heating element 22 is increased in order to secure a necessary amount of heat when it is divided up to the length direction (circumferential direction), In some cases, the fixing sleeve 21 having a small diameter cannot be used. Accordingly, as shown in FIG. 7, the heat generation sheets 22 s having different heat generation portions are stacked in the thickness direction of the sheet heating element 22, thereby different heat generation distributions as in the sheet heating element 22 illustrated in FIGS. 4 to 6. It is possible to achieve a high output while saving space (reducing the size) while realizing the planar heating element 22 that can be obtained.

  By the way, in the fixing device 50, during rotation, the fixing roller 21 is pulled by the pressure roller 31 at the nip portion, so that the fixing sleeve 21 on the upstream side of the nip portion becomes a tensioned side, and the inner peripheral surface of the fixing sleeve 21 is It slides on the sheet heating element 22 while being in pressure contact with the heating element support member 23. On the other hand, the tension is not applied to the fixing sleeve 21 on the downstream side of the nip portion, and the fixing sleeve 21 is in a relaxed state. If an attempt is made to increase the speed of the apparatus in this state, the fixing sleeve 21 on the downstream side of the nip portion. As a result, the degree of slackening of the fixing sleeve 21 becomes serious, and the rotational running stability of the fixing sleeve 21 is hindered.

  Therefore, the fixing device 50 is preferably provided with a rotation support member 27 that supports the rotation state of the fixing sleeve 21 on the inner peripheral side of the fixing sleeve 21 and at least on the downstream side of the nip portion.

  The rotation support member 27 has a pipe shape made of, for example, a thin metal such as iron or stainless steel having a thickness of 0.1 to 1 mm, and the outer diameter thereof is about 0.5 to 1 mm in diameter than the inner diameter of the fixing sleeve 21. It is small. Further, on the circumference of the pipe of the rotation support member 27, the inner peripheral surface of the fixing sleeve 21 is in contact with the outer peripheral surface of the rotation support member 27 at least from the position opposite to the nip portion and in the vicinity of the entrance of the nip portion. Further, the nip portion side is cut and opened in the axial direction on the outer peripheral surface of the rotation support member 27, and the end portion thereof is folded into the core holding member 28 side so as not to contact the nip portion.

  Further, as shown in FIG. 8, the rotation support member 27 is provided with an opening 27a by removing an outer peripheral surface of a certain region on the upstream side of the nip portion. As a result, as shown in FIG. 9, when the internal mechanism portion of the fixing sleeve 21 is configured, the entire surface of the sheet heating element 22 is exposed from the opening 27 a and the surface of the sheet heating element 22 is the rotation support member 27. The outer peripheral surface of the rotation support member 27 is slightly protruded from the outer peripheral surface of the rotation support member 27, and the planar heating element 22 contacts the inner peripheral surface of the fixing sleeve 21. become.

  Accordingly, the sheet heating element 22 (heating sheet 22s) is supported by the heating element support member 23 and is disposed in contact with the inner peripheral surface of the fixing sleeve 21, so that the fixing sleeve 21 can be efficiently heated. It is.

  As described above, the rotation support member 27 not only ensures the rotational running stability of the fixing sleeve 21 but also the fixing sleeve 21 can be supported by the rigid metal rotation support member 27, so that handling in assembly is easy. It is.

  The heat insulating support member 29 has a heat resistance sufficient to withstand the heat of the fixing sleeve 21 via the rotation support member 27 and a heat outflow (loss) from the rotation support member 27 in contact with the fixing sleeve 21 on the exit side of the nip portion. It has a heat insulating property to prevent, and a strength sufficient to support the rotating support member 27 so that the rotating fixing sleeve 21 does not deform when it contacts the rotating support member 27, and a heating element support member 23 is preferably the same foamed molded body of polyimide resin as 23.

  With the above configuration, the fixing device 50 can shorten the warm-up time and the first print time while saving energy. Further, since the heat generating sheet 22s in the sheet heating element 22 is a resin-based sheet, the stress caused by the rotation and vibration of the pressure roller 31 repeatedly acts on the heat generating sheet 22s, and the heat generating sheet 22s is repeatedly bent. Even if it breaks, it will not be damaged by fatigue and can be operated for a long time. In addition to this, by providing the rotation support member 27 (the heat insulation support member 29 as necessary), the rotational running stability of the fixing sleeve 21 can be improved, and the speed can be increased. Further, the heat support in the axial direction of the fixing sleeve 21 in the rotation support member 27 can assist the temperature uniformity in the axial direction of the fixing sleeve 21, so that it is possible to cope with a higher speed apparatus. Become.

  In the fixing device 50, the temperature at a predetermined position in the fixing sleeve 21 is detected by a temperature sensor, and heating control is performed by adjusting the power supply to the planar heating element 22 based on the detection result.

  Here, in the fixing device 50, when the temperature sensor is broken or an abnormality occurs in the mechanism or control software of the heating control system, the heating control is runaway and excessive power is supplied to the planar heating element 22. Is performed, and the sheet heating element 22 is abnormally heated, causing a failure of the apparatus.

  Therefore, the inventors have caused abnormal heating of the planar heating element 22 even when the temperature sensor is broken or the heating control system mechanism or control software becomes abnormal and the heating control becomes a runaway state. The device to prevent was examined. At this time, since there is no space for installing such a device in the fixing sleeve 21 in the fixing device 50, the sheet heating element 22 is detected by detecting the heating state of the fixing sleeve 21 from the outer peripheral side of the fixing sleeve 21. We examined the configuration with an overheat prevention device that detects abnormal heat generation.

At this time, in order to prevent the outer peripheral surface of the fixing sleeve 21 from being damaged (in order to ensure image quality), it is necessary to install an overheat prevention device in a non-contact manner with respect to the fixing sleeve 21, and the fixing device 50. Is a configuration in which the fixing sleeve 21 is locally heated at a location where the sheet heating element 22 (heating body) is in contact with the fixing sleeve 21 (fixing member) in a sliding state, and therefore, an excessive temperature rise is prevented. Devise was necessary for the installation of the equipment. That is, when the apparatus is started up, the heat generation control of the planar heating element 22 is performed in a state where the fixing sleeve 21 is not rotating (non-rotating state). At this time, the planar heating element 22 is out of the circumferential direction of the fixing sleeve 21. The internal members (the rotation support member 27 and the heating element support member 23), which are members on the inner peripheral side of the fixing sleeve 21, are heated only in the contact area, and local thermal expansion occurs. The amount of thermal deformation of the internal member is different, and the internal member and the fixing sleeve 21 have a banana shape in which the amount of deformation becomes maximum near the center in the axial direction. Therefore, in consideration of the deformation amount of the thermal expansion of the internal member in the axial direction, it is necessary to provide an installation position of the excessive temperature rise prevention device so that the internal member does not come into contact with the fixing sleeve 21 even if the internal member is thermally expanded. On the other hand, when the fixing process is performed after the apparatus is started up, the heat generation control of the sheet heating element 22 is performed while rotating the fixing sleeve 21, so that the heat of the sheet heating element 22 is heated by the rotation of the fixing sleeve 21. Therefore, the difference in deformation due to thermal expansion in the axial direction as described above is eliminated. Here, in order to accurately detect the heating state of the fixing sleeve 21, it is desired to install the overheat prevention device as close as possible to the fixing sleeve 21, and as described above, the installation position of the overheat prevention device is changed in the axial direction. In the configuration described above, the distance from the fixing sleeve 21 is particularly long in the central portion in the axial direction, and the accuracy of detecting excessive temperature rise is lowered, so that the abnormal heat generation of the planar heating element 22 cannot be detected with high accuracy.
The present invention has been made on the basis of the above-described concept, and it is possible to safely and reliably overheat the fixing member and its internal member both when the fixing member (fixing sleeve 21) is not rotated and when it is rotated. It is something to prevent.

Hereinafter, the fixing device according to the present invention will be described.
FIG. 10 is a cross-sectional view showing the configuration of the fixing device according to the present invention.
As shown in FIG. 10, the fixing device 20 includes a rotating endless belt fixing member (fixing sleeve 21), a pressure member (pressure roller 31) in contact with the outer peripheral surface of the fixing member, and the fixing member. An abutting member (abutting member 26) that is disposed on the inner peripheral side of the sheet and abuts against the pressure member via the fixing member to form a nip portion, and heats a predetermined region in the circumferential direction of the fixing member. At a position corresponding to a heating mechanism (planar heating element 22, heating element support member 23) and a predetermined area (heating area) where the heating mechanism heats the fixing member on the outer peripheral side of the fixing member. A first overheat prevention device (first overheat prevention device 32) that stops power supply to the heating mechanism by a mechanical operation when it is detected in a non-contact manner that the fixing member has reached a predetermined temperature or more; And the heating mechanism portion on the outer peripheral side of the fixing member. When it is detected in a non-contact manner that the fixing member has reached a predetermined temperature or higher in a position corresponding to an area other than a predetermined area (heating area) for heating the member, power supply to the heating mechanism is stopped by a mechanical operation. A second excessive temperature rise prevention device (second excess temperature rise prevention device 33).

  Here, the fixing sleeve 21, the sheet heating element 22, the heating element support member 23, the terminal block stay 24, the power supply line 25, the contact member 26, the rotation support member 27, the core holding member 28, the heat insulation support member 29, and the pressurization The roller 31 is the same as that constituting the fixing device 50 shown in FIG. 1 and is different from the fixing device 50 in that it includes a first overheat prevention device 32 and a second overheat prevention device 33. The rotation support member 27 and the heat insulation support member 29 may be omitted.

Hereinafter, the two excessive temperature rise prevention devices 32 and 33 forming the basis of the present invention will be described.
First, the first excessive temperature rise prevention device 32 and the second excessive temperature rise prevention device 33 are both arranged in a non-contact manner with respect to the fixing sleeve 21 and are sensors for detecting the heating state of the fixing sleeve 21 and a power source ( A circuit component incorporated in a circuit related to power feeding from the external power source or the power storage device) to the planar heating element 22, and when detecting that the fixing sleeve 21 has reached a predetermined temperature or more, the planar heating element that is a heating mechanism section The power supply to 22 is stopped by a mechanical operation. Thereby, since a control circuit and control software are not required, even if the temperature sensor is broken in the fixing device 20 or an abnormality occurs in the mechanism and control software of the heating control system, the sheet heating element is not affected. 22 abnormal heat generation can be prevented.

  The first overheat prevention device 32 and the second overheat prevention device 33 are preferably thermostats, and in particular, a mechanical detection type thermostat using a bimetal or a shape memory alloy is suitable. The first excessive temperature rise prevention device 32 and the second excessive temperature rise prevention device 33 have a surface with a predetermined area that receives the radiant heat from the detection target (fixing sleeve 21) and detects the heating state of the detection target. When the fixing sleeve 21 receives radiant heat at the time of passing paper (solid line in FIG. 11), the power supply stop operation does not occur, and the sheet heating element 22 generates abnormal heat and the fixing sleeve 21 is abnormally heated. When receiving radiant heat at a temperature just before the temperature (the one-dot chain line in FIG. 11), the power supply stopping operation is caused (dotted line in FIG. 11 (overheat prevention device detection level)). Further, since the first excessive temperature rise prevention device 32 and the second excessive temperature rise prevention device 33 are arranged in a non-contact manner with respect to the fixing sleeve 21, the distance from the fixing sleeve 21 is important, and the fixing sleeve 21. If it is too close, it is unsuitable because the power supply is stopped even if the temperature rises slightly, and if it is too far, the detection accuracy is deteriorated. A suitable distance L1 from the fixing sleeve 21 is, for example, 0.7 mm.

The first overheat prevention device 32 is disposed on the outer peripheral side of the fixing sleeve 21 in the circumferential direction and at a position corresponding to a predetermined region (heating region) in which the planar heating element 22 heats the fixing sleeve 21. In FIG. 10, it is disposed below the fixing sleeve 21.
The first excessive temperature rise prevention device 32 is for preventing abnormal heat generation of the sheet heating element 22 when the fixing sleeve 21 is not rotated. Note that the time when the fixing sleeve 21 is not rotated is an initial time when the fixing device 20 is started up or a standby time such as waiting for the next print job.

  Further, it is preferable that a plurality of the first excessive temperature rise prevention devices 32 are arranged in the axial direction of the fixing sleeve 21. For example, as shown in FIG. 12, the first overheat prevention device 32a is disposed at the axial center of the fixing sleeve 21, and the first overheat prevention device 32b is disposed at the axial end. This is effective when heat generation control is performed using a plurality of temperature sensors in the axial direction of the fixing sleeve 21.

  These are arranged in the axial direction of the fixing sleeve 21 corresponding to the heating distribution (heat generation control region) in the axial direction of the planar heating element 22 which is a heating mechanism portion. That is, the plurality of first overheat prevention devices 32 are formed on the resistance heating layer 22b formed on the main surface of the heat generating sheet 22s so as to be able to generate heat independently in each of a plurality of regions divided arbitrarily in the axial direction. For example, when the heating sheet 22s shown in FIGS. 4 to 7 is used, the first overheat prevention device 32a is arranged corresponding to the resistance heating layer 22b1, and the resistance heating layer 22b2. Corresponding to the first overheat prevention device 32b is arranged.

  At this time, the plurality of first overheat prevention devices 32 may be arranged such that the sensor surfaces are separated from the fixing sleeve 21 in the axial direction of the fixing sleeve 21 from the end to the center. This is suitable for accurately detecting an excessive temperature rise without contacting the fixing sleeve 21 whose shape changes when the apparatus is started up by performing heat generation control of the sheet heating element 22 with the fixing sleeve 21 being non-rotating. This is to arrange them at intervals. That is, as shown in FIG. 12, in the area where the planar heating element 22 is disposed (the lower area in the figure), the heating control of the planar heating element 22 is performed while the fixing sleeve 21 is not rotated. When the apparatus is started up, the internal members of the fixing sleeve 21 (the rotation support member 27 and the heating element support member 23) are only in the area (heating area) in the circumferential direction of the fixing sleeve 21 where the planar heating element 22 is in contact. Is heated, and the local thermal expansion occurs, and the amount of thermal deformation of the internal member differs in the axial direction. Therefore, the planar heating element 22 and the fixing sleeve 21 are pushed most by the internal member at the central portion in the axial direction. The protrusions protrude outward and are hardly deformed at the end (the line during thermal expansion in FIG. 12), and the first overheat prevention devices 32a and 32b with respect to the outer peripheral surface of the fixing sleeve 21 in this state. They are arranged at suitable intervals to raise the temperature detection. Note that in the region where the planar heating element 22 is arranged (the lower region in the figure) before the heating control of the planar heating element 22 such as when the apparatus is cold before starting the apparatus (that is, the rotation support member 27 and Before the heating element support member 23 is thermally expanded), since the outer peripheral surface of the heating element support member 23 is flat in the axial direction, the planar heating element 22 and the fixing sleeve 21 are also flat in the axial direction ( Line before thermal expansion in FIG. 12). Since the fixing sleeve 21 travels about 0.6 mm at the center in the axial direction and about 0.1 mm at the end compared to before the thermal expansion at the time of thermal expansion, the specifics of the first overheat prevention devices 32a and 32b are specific. As an arrangement example, the fixing sleeve 21 before thermal expansion may be separated by 1.3 mm at the central portion in the axial direction and 0.8 mm at the end portion.

  In the fixing device 20, the rotation support member 27 and the heating element support member 23 are not fixed to the frame (side plate 20 f) of the fixing device 20 at both ends in the axial direction. This is also applicable in the case of this state. That is, in any state, when the apparatus is started up by performing heat generation control of the sheet heating element 22 while the fixing sleeve 21 is not rotated, the rotation support member 27 or This is because local heat expansion of the heat generating member support member 23 occurs, and the planar heat generating member 22 and the fixing sleeve 21 are deformed so as to protrude to the outermost side in the axial central portion and become convex. However, when the rotation support member 27 and the heating element support member 23 are fixed to the frame (side plate 20f) of the fixing device 20 at both axial ends, the planar heating element 22 and the fixing sleeve 21 are axially central. The present invention is more effective because the convex deformation is more conspicuous.

  Further, since the outer peripheral surface of the fixing sleeve 21 at the time of thermal expansion tends to be inclined toward the end in the axial direction as shown in FIG. 13, the plurality of first overheat prevention devices 32 include the fixing sleeve. In the axial direction of 21, it is preferable that the sensor surface facing the fixing sleeve 21 is inclined with respect to the axial direction from the center to the end. In FIG. 13, the sensor surface of the first excessive temperature rise prevention device 32 a at the axial center is arranged in parallel to the axial direction (for example, the rotation center axis of the fixing sleeve 21), and the first excessive temperature at the axial end portion. The sensor surface of the temperature preventing device 32b is disposed so as to be inclined with respect to the axial direction so as to be parallel to the outer peripheral surface of the fixing sleeve 21 during thermal expansion. Accordingly, each of the first excessive temperature rise prevention devices 32a and 32b can accurately detect the excessive temperature increase of the fixing sleeve 21.

  The second excessive temperature rise prevention device 33 corresponds to a region other than a predetermined region (heating region) where the sheet heating element 22 heats the fixing sleeve 21 on the outer peripheral side in the circumferential direction of the fixing sleeve 21. Placed in position (FIG. 10). The second excessive temperature rise prevention device 33 is for preventing abnormal heat generation of the sheet heating element 22 when the fixing sleeve 21 rotates. Note that the time when the fixing sleeve 21 rotates is when the fixing device 20 is started up in the latter half or when a sheet is passed.

  Since the heat generation control of the sheet heating element 22 is performed while rotating the fixing sleeve 21 when the fixing sleeve 21 rotates, the heat of the sheet heating element 22 is made uniform around the entire circumference of the fixing sleeve 21 by the rotation of the fixing sleeve 21. The inner member expands evenly in the axial direction, and there is no difference in the amount of deformation that protrudes outward between the central portion and the end portion. For this reason, the first overheat prevention device 32 (particularly, the first overheat prevention device 32a) at this time is separated from the outer peripheral surface of the fixing sleeve 21 by a distance that accurately detects overheat rise. The excessive temperature rise of 21 cannot be detected with high accuracy. Therefore, the second excessive temperature rise prevention device 33 is arranged at a distance that accurately detects the excessive temperature rise from the outer peripheral surface of the fixing sleeve 21 that has been thermally expanded uniformly in the axial direction. It is possible to prevent overheating of the fixing sleeve 21 during 21 rotations, that is, abnormal heat generation of the planar heating element 22.

  At this time, it is preferable that the second excessive temperature rise prevention device 33 is disposed on the outer peripheral side of the fixing sleeve 21 and on the opposite side to the direction of gravity acceleration as shown in FIG. As a result, the second excessive temperature rise prevention device 33 is arranged in a region where the hot air rises and the ambient temperature easily rises, and it is possible to detect the excessive temperature rise of the fixing sleeve 21 with higher accuracy. If the configuration is such that the temperature is highest at the outer peripheral side of the fixing sleeve 21 other than the direction opposite to the gravitational acceleration direction by airflow control or the like, the second excessive temperature rise prevention is provided at that position. The device 33 may be arranged.

  Further, it is preferable that a plurality of second excessive temperature rise prevention devices 33 are arranged in the axial direction of the fixing sleeve 21. For example, as shown in FIG. 12, the second overheat prevention device 33a is arranged at the axial center of the fixing sleeve 21, the second overheat prevention device 32c is arranged at the axial end, and the middle of them. The second overheat prevention device 33b is disposed at the position. This is effective when heat generation control is performed using a plurality of temperature sensors in the axial direction of the fixing sleeve 21.

  In addition, as in the case of the first excessive temperature rise prevention device 32, they correspond to the axial distribution of the fixing sleeve 21 corresponding to the heating distribution (heat generation control region) in the axial direction of the planar heating element 22 that is the heating mechanism. Is to be placed. For example, the second excessive temperature rise prevention devices 33a and 33c are based on this concept.

  Furthermore, it is preferable that the plurality of second excessive temperature rise prevention devices 33 are arranged at predetermined positions in the axial direction of the fixing sleeve 21 corresponding to the size of the recording medium P to be passed. In the nip portion, heat is taken away by the recording medium P in the area where the recording medium P to be passed through the fixing sleeve 21 contacts, but heat is not taken away outside the recording medium P in the axial direction. It is easy to become. Therefore, the second excessive temperature rise prevention device 33 is disposed at a position outside the axial direction (width direction) end of the recording medium P having a size to be passed through the fixing sleeve 21, thereby It is possible to accurately prevent excessive temperature rise and, in turn, abnormal heat generation of the planar heating element 22. For example, the second excessive temperature rise prevention device 33b is based on this concept.

The fixing device 20 configured as described above operates as follows.
First, when the image forming apparatus receives an output signal (for example, when there is a print request to the image forming apparatus by operation of a user's operation panel or communication from a personal computer), in the fixing device 20, the pressure roller 31 is moved to the fixing sleeve 21. Is pressed by the contact member 26 to form a nip portion.
Next, when the pressure roller 31 is driven to rotate in the clockwise direction in FIG. 10 by a driving device (not shown), the fixing sleeve 21 is also rotated in the clockwise direction. At this time, the heating sheet 22 s of the sheet heating element 22 is in a state of sliding with respect to the inner peripheral surface of the fixing sleeve 21.
In synchronism with this, power is supplied to the sheet heating element 22 from the external power source or the internal power storage device, and the heating sheet 22s generates heat. At this time, the heat generating sheet 22s generates heat with a predetermined width corresponding to the width of the recording medium P to be passed, and the fixing sleeve 21 efficiently transfers heat from the heat generating sheet 22s in an area corresponding to the width. To be heated. Here, the surface on the upstream side of the nip portion so that the nip portion has a predetermined temperature by a temperature detected by a temperature sensor (not shown) arranged in contact with or non-contact with the fixing sleeve 21. Heating control is performed by the heating element 22 and the temperature is raised to a temperature necessary for fixing. At this time, even if the temperature control is broken or the heating control system mechanism or control software becomes abnormal and the heating control becomes in a runaway state, the first overheat prevention device 32 causes the surface heat generation. The power supply to the body 22 (heat generating sheet 22s) is stopped, and the abnormal heat generation is appropriately prevented.
The operation of the driving device and the heating by the sheet heating element 22 do not need to be started at the same time, but may be started with an appropriate time difference.

  Next, the fixing sleeve 21 is heated to a temperature necessary for fixing and then held, and the recording medium P starts to pass. At this time, even when the temperature sensor is broken or the heating control system mechanism or control software is abnormal and the heating control is in a runaway state, the second overheat prevention device 33 causes the planar heating element. The power supply to 22 (heat generation sheet 22s) is stopped, and the abnormal heat generation is appropriately prevented.

  As described above, in the fixing device of the present invention, the heat capacity of the fixing sleeve 21 and the sheet heating element 22 is small, so that it is possible to shorten the warm-up time and the first print time while saving energy. Further, since the heat generating sheet 22s in the sheet heating element 22 is a resin-based sheet, the stress caused by the rotation and vibration of the pressure roller 31 repeatedly acts on the heat generating sheet 22s, and the heat generating sheet 22s is repeatedly bent. Even if it breaks, it will not be damaged by fatigue and can be operated for a long time. Furthermore, the fixing sleeve 21 is heated only in the area corresponding to the width of the recording medium P scheduled to be passed. In addition, abnormal heating when the heating control is lost can be prevented both when the fixing sleeve 21 is not rotated and when the fixing sleeve 21 is rotated.

  When there is no output signal to the image forming apparatus, the pressure roller 31 and the fixing sleeve 21 are normally not rotated and the sheet heating element 22 is not energized in order to reduce power consumption. When re-outputting is to be started (returned), the sheet heating element 22 can be energized even when the pressure roller 31 and the fixing sleeve 21 are not rotated. In this case, the sheet heating element 22 is energized to keep the entire fixing sleeve 21 warm.

Next, the image forming apparatus according to the present invention will be described.
FIG. 14 is an overall configuration diagram showing the configuration of the image forming apparatus according to the present invention.
As shown in FIG. 14, the image forming apparatus 1 is a tandem type color printer. Four bottles 102Y, 102M, 102C, and 102K corresponding to the respective colors (yellow, magenta, cyan, and black) are detachably (replaceable) installed in the bottle housing portion 101 above the image forming apparatus main body 1. ing.
An intermediate transfer unit 85 is disposed below the bottle housing portion 101. Image forming units 4Y, 4M, 4C, and 4K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 78 of the intermediate transfer unit 85.

  Photosensitive drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively. Further, around each of the photosensitive drums 5Y, 5M, 5C, and 5K, a charging unit 75, a developing unit 76, a cleaning unit 77, a charge eliminating unit (not shown), and the like are disposed. Then, an image forming process (charging process, exposure process, development process, transfer process, cleaning process) is performed on each of the photoconductive drums 5Y, 5M, 5C, and 5K. An image of each color is formed on 5K.

The photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven in a clockwise direction in FIG. 14 by a drive motor (not shown). Then, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging unit 75 (a charging process).
Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser light L emitted from the exposure unit 3, and electrostatic latent images corresponding to the respective colors are formed by exposure scanning at this position. (It is an exposure process.)

Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the developing device 76, and the electrostatic latent image is developed at this position to form toner images of each color (developing process). .)
Thereafter, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach the positions facing the intermediate transfer belt 78 and the first transfer bias rollers 79Y, 79M, 79C, and 79K, and at these positions, the photoconductive drums 5Y, 5M. The toner images on 5C and 5K are transferred onto the intermediate transfer belt 78 (this is a primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drums 5Y, 5M, 5C, and 5K.

Thereafter, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, and untransferred toner remaining on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position. 77 is mechanically collected by a cleaning blade (cleaning process).
Finally, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing a neutralization unit (not shown), and the residual potential on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position. The
Thus, a series of image forming processes performed on the photosensitive drums 5Y, 5M, 5C, and 5K is completed.

Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are transferred onto the intermediate transfer belt 78 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 78.
Here, the intermediate transfer unit 85 includes an intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning unit 80. , Etc. The intermediate transfer belt 78 is stretched and supported by three rollers 82 to 84 and is endlessly moved in the direction of the arrow in FIG.

The four primary transfer bias rollers 79Y, 79M, 79C, and 79K sandwich the intermediate transfer belt 78 with the photosensitive drums 5Y, 5M, 5C, and 5K, respectively, thereby forming primary transfer nips. Then, a transfer bias reverse to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K.
The intermediate transfer belt 78 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K. In this way, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, and 5K are primarily transferred while being superimposed on the intermediate transfer belt 78.

Thereafter, the intermediate transfer belt 78 onto which the toner images of the respective colors are transferred in an overlapping manner reaches a position facing the secondary transfer roller 89. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between the secondary transfer roller 89 and forms a secondary transfer nip. The four color toner images formed on the intermediate transfer belt 78 are transferred onto the recording medium P conveyed to the position of the secondary transfer nip. At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 78.
Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, the untransferred toner on the intermediate transfer belt 78 is collected.
Thus, a series of transfer processes performed on the intermediate transfer belt 78 is completed.

Here, the recording medium P transported to the position of the secondary transfer nip is transported from the paper feeding unit 12 disposed below the apparatus main body 1 via the paper feeding roller 97 and the registration roller pair 98. It is a thing.
Specifically, a plurality of recording media P such as transfer paper are stored in the paper supply unit 12 in an overlapping manner. When the paper feed roller 97 is driven to rotate counterclockwise in FIG. 14, the uppermost recording medium P is fed between the rollers of the registration roller pair 98.

  The recording medium P conveyed to the registration roller pair 98 is temporarily stopped at the position of the roller nip of the registration roller pair 98 that has stopped rotating. Then, the registration roller pair 98 is rotationally driven in synchronization with the color image on the intermediate transfer belt 78, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing device 20. At this position, the color image transferred to the surface is fixed on the recording medium P by heat and pressure generated by the fixing sleeve 21 and the pressure roller 31.
Thereafter, the recording medium P is discharged out of the apparatus through a pair of paper discharge rollers 99. The transferred P discharged from the apparatus by the discharge roller pair 99 is sequentially stacked on the stack unit 100 as an output image.
Thus, a series of image forming processes in the image forming apparatus is completed.

  As described above, since the image forming apparatus of the present invention includes the fixing device 20 described above, an abnormality occurs when the heating control is not effective when the fixing sleeve 21 is not rotated or rotated. Heating can be prevented, warm-up time and first print time are short, and appropriate image formation can be performed.

  Although the present invention has been described with the embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. Can be changed within the range that can be conceived, and any embodiment is included in the scope of the present invention as long as the effects and advantages of the present invention are exhibited.

  For example, in FIG. 10, the planar heating element 22 and the heating element support member 23 are configured to heat by directly contacting the fixing sleeve 21 as a heating mechanism, but the present invention is not limited to this. The mechanism portion is disposed on the inner peripheral side of the fixing sleeve 21, and includes a pipe-shaped heating member that contacts the fixing sleeve 21 and heats the fixing sleeve 21, and a heating unit that heats a predetermined region of the heating member. It may be. In other words, the heating unit locally heats a predetermined region of the heating member, and the heating region of the heating member contacts the fixing sleeve 21 to heat the fixing sleeve 21.

  The heating means is preferably any of a planar heating element, a halogen heater, and an electromagnetic induction heating mechanism. FIG. 15 shows the configuration of the fixing device when the heating means is a halogen heater.

  As shown in FIG. 15, the fixing device 20 is disposed on a fixing sleeve 21 of a rotating endless belt, a pressure roller 31 in contact with an outer peripheral surface of the fixing sleeve 21, and an inner peripheral side of the fixing sleeve 21. An abutting member 26 that abuts against the pressure roller 31 through the fixing sleeve 21 to form a nip portion, and is disposed on the inner peripheral side of the fixing sleeve 21, and abuts on the fixing sleeve 21 to heat the fixing sleeve 21. A heating mechanism portion that includes a pipe-shaped heating member 27A and a halogen heater 22h that heats a predetermined area of the heating member 27A, and that heats a predetermined area in the circumferential direction of the fixing sleeve 21; Then, in a position corresponding to a predetermined region (heating region) in which the heating mechanism heats the fixing sleeve 21, it is detected in a non-contact manner that the fixing sleeve 21 has exceeded a predetermined temperature. Then, the first excessive temperature rise prevention device 32 that stops the power supply to the heating mechanism part by a mechanical operation, and a predetermined region (on the outer peripheral side of the fixing sleeve 21 where the heating mechanism part heats the fixing sleeve 21). Second overheating prevention in which the power supply to the heating mechanism is stopped by a mechanical operation when it is detected in a non-contact manner that the fixing sleeve 21 has reached a predetermined temperature or higher at a position corresponding to a region other than the heating region). And a device 33. Further, the contact member 26 is supported from the back by a reinforcing member 28A, and the reinforcing member 28A defines a heating region of the heating member 27A by the halogen heater 22h.

  Here, the components other than the heating mechanism are the same as those constituting the fixing device 20 shown in FIG. Therefore, in the fixing device 20 as well, the first excessive temperature rise prevention device 32 and the second excessive temperature rise prevention device 33 make it impossible to control the heating when the fixing sleeve 21 is not rotating or rotating. It becomes possible to prevent abnormal heating at the time.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 3 Exposure part 4Y, 4M, 4C, 4K Image formation part 5Y, 5M, 5C, 5K Photosensitive drum 12 Paper feed part 20,50 Fixing apparatus 20f Side plate (frame)
21 fixing sleeve 22 sheet heating element 22a base layer 22b, 22b1, 22b2 resistance heating layer 22c electrode layer 22d insulating layer 22e, 22e1, 22e2 electrode terminal 22s heating sheet 22h halogen heater 23 heating element support member 24 terminal block stay 25 power supply line 26 Contact member 27 Rotation support member 27a Opening 27A Heating member 28 Core holding member 28A Reinforcing member 29 Heat insulation support member 31 Pressure roller 32, 32a, 32b First excessive temperature rise prevention device 33, 33a, 33b, 33c Temperature rise prevention device 75 Charging unit 76 Developing unit 77 Cleaning unit 78 Intermediate transfer belt 79Y, 79M, 79C, 79K First transfer bias roller 80 Intermediate transfer cleaning unit 82 Secondary transfer backup roller 83 Cleaning backup roller 84 Tension roller Roller 89 Secondary transfer roller 85 Intermediate transfer unit 97 Paper feed roller 98 Registration roller pair 99 Paper discharge roller pair 100 Stack part 101 Bottle storage part 102Y, 102M, 102C, 102K Toner bottle L Laser light P Recording medium T Toner

Japanese Patent Laid-Open No. 11-2982 JP-A-4-44075 JP-A-8-262903 Japanese Patent Laid-Open No. 10-213984 JP 2007-334205 A JP 2008-154822 A JP 2008-216928 A JP 2007-212579 A

Claims (12)

A fixing member for a rotating endless belt;
A pressure member in contact with the outer peripheral surface of the fixing member;
An abutting member disposed on an inner peripheral side of the fixing member and abutting the pressure member via the fixing member to form a nip portion;
A heating mechanism for heating a predetermined region in the circumferential direction of the fixing member;
When it is detected in a non-contact manner that the fixing member has reached a predetermined temperature or more at a position corresponding to a predetermined region where the heating mechanism heats the fixing member on the outer peripheral side of the fixing member, the heating mechanism A first overheating prevention device that stops the power supply of the machine by mechanical operation;
When it is detected in a non-contact manner that the fixing member has reached a predetermined temperature or higher at a position corresponding to a region other than the predetermined region where the heating mechanism heats the fixing member, on the outer peripheral side of the fixing member. A second excessive temperature rise prevention device for stopping power feeding to the mechanism part by a mechanical operation;
Equipped with a,
The first excessive temperature rise prevention device detects that the fixing member has reached a predetermined temperature or more during non-rotation of the fixing member and controls power supply to the heating mechanism unit,
The second overheat prevention device detects that the fixing member has reached the predetermined temperature or more during rotation of the fixing member, and controls power supply to the heating mechanism. apparatus.   The heating mechanism section is disposed on the inner peripheral side of the fixing member, and includes a heating member that contacts the fixing member and heats the fixing member, and a heating unit that heats a predetermined region of the heating member. The fixing device according to claim 1.   The fixing device according to claim 2, wherein the heating unit is any one of a planar heating element, a halogen heater, and an electromagnetic induction heating mechanism.   The heating mechanism is disposed on the inner peripheral side of the fixing member, and is disposed on the inner peripheral side of the fixing member, and the sheet heating element is disposed on the inner peripheral side of the fixing member. The fixing device according to claim 1, further comprising a heating element support member that is supported from a side opposite to the fixing member.   5. The fixing device according to claim 1, wherein a plurality of the first overheating prevention devices and / or the second overheating prevention devices are arranged in the axial direction of the fixing member. .   6. The plurality of first excessive temperature rise prevention devices are arranged such that a sensor surface is separated from the fixing member as it goes from an end portion toward a central portion in the axial direction of the fixing member. Fixing device.   The plurality of first overheat prevention devices are arranged such that a sensor surface facing the fixing member is inclined with respect to the axial direction from the center to the end in the axial direction of the fixing member. The fixing device according to claim 6.   The plurality of first excessive temperature rise prevention devices and / or the plurality of second excessive temperature rise prevention devices are arranged in the axial direction of the fixing member corresponding to the heating distribution in the axial direction of the heating mechanism section. The fixing device according to claim 5, wherein:   9. The fixing device according to claim 8, wherein the plurality of second excessive temperature rise prevention devices are arranged in an axial direction of the fixing member in accordance with a size of a recording medium to be passed.   The fixing device according to claim 1, wherein the second excessive temperature rise prevention device is disposed on an outer peripheral side of the fixing member and on a side opposite to a direction of gravity acceleration.   The fixing device according to claim 1, wherein the first overheat prevention device and / or the second overheat prevention device is a thermostat. An image forming apparatus comprising the fixing device according to claim 1.

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