JP2014142402A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of improving cooling efficiency of an induction coil (excitation coil) with a simple configuration at low costs.SOLUTION: An induction heating unit 50 includes a case 55 in which an excitation coil 51 is installed, and a cover 56 arranged at an upper part of the case. A rectifying member 57 that divides an air stream flowed into the unit into two is provided between an excitation coil installation surface of the case 55 and an inner surface of the cover 56 that faces the installation surface, and at an inside part of the excitation coil 51. A cooling air stream is divided into two by the rectifying member 57, and flows along the excitation coil 51. With this configuration, the flow rate of the cooling air stream in the vicinity of the excitation coil is increased to improve cooling efficiency.

Description

  The present invention relates to an electromagnetic induction heating type fixing device.

  2. Description of the Related Art Image forming apparatuses such as copying machines and printers that use an electromagnetic induction heating type fixing device are widely known for the purpose of reducing energy consumption by reducing the rise time of the apparatus.

  For example, Japanese Patent Laying-Open No. 2006-350054 (Patent Document 1) discloses a fixing roller stretched between a support roller (heating roller) as a heating element, a fixing auxiliary roller (fixing roller), and a supporting roller and a fixing auxiliary roller. An electromagnetic induction heating type fixing device including an induction heating unit (induction heating means) facing the support roller via a fixing belt, a pressure roller contacting the fixing auxiliary roller via the fixing belt, and the like is disclosed. ing.

  The induction heating means includes a coil portion (excitation coil) wound in the longitudinal direction, a core (coil core) disposed around the coil portion, and the like. The fixing belt is heated at a position facing the induction heating unit. The heated fixing belt heats and fixes the toner image on the recording medium conveyed to the positions of the auxiliary fixing roller and the pressure roller. Specifically, when a high-frequency alternating current is passed through the coil portion, an alternating magnetic field is formed around the coil portion, and an eddy current is generated near the surface of the support roller. When an eddy current is generated in the support roller (heating element), Joule heat is generated by the electric resistance of the support roller itself. The fixing belt wound around the support roller is heated by the Joule heat.

  In such an electromagnetic induction heating type fixing device, since the heating element is directly heated by electromagnetic induction, the heat conversion efficiency is higher than that of the conventional halogen heater method, etc., and the startup time is short with less energy consumption. It is known that the surface temperature (fixing temperature) of the fixing belt can be raised to a desired temperature.

  However, in the induction heating type fixing device, since a high-frequency alternating current flows through the coil portion as described above, the problem is that the temperature of the exciting coil rises due to Joule heat generation due to the electric resistance of the exciting coil. There is a concern that safety standards such as UL certification cannot be observed or the exciting coil is disconnected due to an increase in coil temperature. In order to solve this problem, a technique for cooling the exciting coil using a cooling fan is considered and already known.

  However, in the induction heating type fixing device, the coil temperature is higher than the conventional one due to an increase in paper passing time due to use in a high-speed device of 60 cpm (copy per minute) or higher, and a high power input for a short temperature increase. It tends to rise. The current countermeasure is to increase the output of the cooling fan in order to increase the cooling efficiency, and there is a problem that there is a concern about an increase in cost, an increase in power consumption, and an increase in noise.

  The present invention provides a fixing device and an image forming apparatus that solve the above-described problems in an induction heating type fixing device, and that can improve the cooling efficiency of an induction coil (excitation coil) with a simple configuration at low cost. This is the issue.

  In order to solve this problem, the present invention provides a rotatable fixing member, a pressure member that is pressed against the fixing member and forms a nip portion between the fixing member, and a heating source that heats the fixing member. In the fixing device including the induction heating unit, the induction heating unit bisects the flow of air flowing into the unit between the exciting coil installation surface and the surface facing the installation surface, and inside the excitation coil. A rectifying member is provided.

  According to the present invention, in the induction heating unit, the flow of air flowing into the unit between the exciting coil installation surface and the surface facing the installation surface, and on the inner part (inner peripheral part) of the excitation coil, By providing the rectifying member that bisects, the flow velocity of the cooling airflow in the vicinity of the exciting coil can be increased and the cooling efficiency can be improved. Since the cooling efficiency can be increased without increasing the output of the cooling fan, it is energy saving, and the lower the coil temperature, the higher the heating efficiency of the exciting coil. Therefore, it is possible to realize a low cost and high heat generating efficiency fixing device. it can. In addition, since a high cooling efficiency can be obtained with a simple configuration in which a rectifying member is provided, an increase in cost can be suppressed as much as possible.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus including a fixing device according to the present invention. 2 is a cross-sectional view illustrating a configuration of a fixing device according to the present invention. FIG. 3 is a cross-sectional view illustrating a configuration of a fixing belt. It is sectional drawing which shows the structure of an induction heating unit. It is a schematic diagram for demonstrating the structure of an exciting coil. It is a perspective view which shows the specific shape of the exciting coil arrangement | positioning part in an Example. It is a perspective view for demonstrating the rectification | straightening member arrange | positioned at the inner part of the exciting coil. It is sectional drawing of the induction heating unit in the intermediate part of a unit longitudinal direction. It is a schematic diagram for demonstrating the effect | action of a baffle member. It is a schematic diagram which shows the flow of the airflow in the conventional structure which is not provided with the rectifying member. It is a graph which shows the result of having compared embodiment of invention and the conventional structure in the heating experiment. It is a schematic diagram which shows the curved part vicinity of the exciting coil in an Example and a comparative example. It is a graph which shows the experimental result which compared the Example and the comparative example. It is a figure which shows the example of a preferable structure of a baffle member. It is a figure which shows the rectification | straightening member with the square shape which a front-end | tip protrudes toward an upstream. It is a schematic diagram explaining a design aim and a molded product in the prior art. It is a mimetic diagram explaining a design aim and a molded article in an embodiment. It is a figure which shows 2nd Embodiment which applied this invention to the fixing apparatus of a heat roll system.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view illustrating a schematic configuration in the vicinity of an image forming unit in an example of an image forming apparatus including a fixing device according to the present invention. First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.

  The illustrated image forming apparatus employs an electrophotographic system, and includes four sets (10Y, 10M) of image forming units 10 centering on a photosensitive drum 1 (1Y, 1M, 1C, 1Bk) which is an image carrier. , 10C, 10Bk) and a printer capable of forming a full-color image with toners of four colors of yellow (Y), magenta (M), cyan (C), and black (Bk). However, the configuration of the image forming apparatus is not limited to the illustrated example. For example, the illustrated printer is of a direct transfer system that directly transfers a toner image onto a sheet (recording medium), but an indirect transfer system that transfers a toner image onto a sheet via an intermediate transfer member may be employed. Is possible. Further, the number of colors, the color order, and the like can be changed as appropriate. Furthermore, the printer is not limited to a copier, a facsimile machine, or a multifunction machine having a plurality of functions.

  As shown in FIG. 1, the four image forming units 10Y, 10M, 10C, and 10Bk are juxtaposed along the upper side of the conveyor belt 20 to form a tandem image forming unit. The conveyor belt 20 is stretched around a driving roller 26 and a driven roller 27, and rotates in a direction indicated by an arrow in the drawing. A paper tray 21 for storing the paper P as a recording medium is disposed below the transport belt 20, and the paper P sent out by the paper feed roller 22 is guided by a pair of transport rollers 23, 24 by a guide member (not shown). It is guided and transported. The transported paper P is fed to the upper side of the transport belt 20 from the receiving portion where the bias roller 25 faces the driven roller 27, and is electrostatically attracted to the transport belt 20 and transported. The toner images are sequentially transferred from the color image forming units 10Y, 10M, 10C, and 10Bk of the tandem image forming unit onto the paper P that is transported by the transport belt 20. The paper carrying the unfixed toner image is fed from the transport belt 20 to the fixing device 40, where the toner image is fixed on the paper by heat and pressure.

  The four image forming units 10Y, 10M, 10C, and 10Bk have the same structure, and here, the yellow image forming unit 1Y located on the most upstream side in the paper transport direction will be described as a representative. In order to avoid complication of the drawing, the reference numerals of the elements constituting the image forming unit are omitted except for the yellow image forming unit 1Y. In the following description, subscripts indicating colors are also omitted.

  The image forming unit 10 is configured around the photosensitive drum 1 that is in rolling contact with the conveyance belt 20. Around the photosensitive drum 1, a charging device 2 that charges the surface of the photosensitive drum 1 to a predetermined potential, the charged drum surface is exposed based on the color-separated image signal, and the drum surface is electrostatically charged. An exposure device 3 that forms a latent image, a developing device 4 that supplies toner to the electrostatic latent image formed on the drum surface and develops it, and transfers the developed toner image onto a sheet that is conveyed via a conveyance belt 20 A transfer roller 5 (transfer device) that performs transfer, a cleaner 6 that removes residual toner that remains on the drum surface without being transferred, and a static elimination lamp (not shown) that removes charge remaining on the drum surface. They are arranged in order along the rotation direction.

Next, an embodiment of a fixing device according to the present invention will be described in detail with reference to the drawings.
FIG. 2 is a cross-sectional view showing a schematic configuration of an induction heating type fixing device according to the present invention, which can be used as the fixing device 40 in the printer of FIG. The fixing device shown in FIG. 2 includes a heating roller 41, a fixing roller 42, a fixing belt 43, a pressure roller 44, an induction heating unit 50, and the like.

  It is necessary to select a material and a thickness for the heating roller 41 so as to have rigidity capable of withstanding a load applied when the fixing belt 43 is stretched. Therefore, metals such as stainless steel, aluminum and iron can be used. Moreover, the material which does not affect induction heating can also be used by comprising a metal core layer with nonmagnetic and insulating materials, such as a ceramic. The core metal thickness can be about 0.2 to 1 mm.

  In the embodiment, the heating roller 41 is made of nonmagnetic SUS (stainless steel) and has a core metal thickness of about 0.2 to 1 mm. On the surface of the metal core, Cu (copper) is formed to a thickness of about 3 to 15 μm as a heat generation layer to enhance the heat generation efficiency. In this case, it is also preferable to apply Ni (nickel) plating to the Cu surface layer for the purpose of rust prevention.

  As another example, a magnetic shunt alloy having a Curie point of about 160 to 220 ° C. can be used. At this time, the magnetic shunt alloy may be used as a heat generating layer, or Cu may be formed on the surface of the magnetic shunt alloy as a heat generating layer with a thickness of about 3 to 15 μm. An aluminum member is disposed inside the magnetic shunt alloy, which makes it possible to stop the temperature rise near the Curie point.

  The fixing roller 42 includes a metal core 42a made of, for example, stainless steel or carbon steel, and an elastic member 42b in which a heat resistant silicone rubber or the like is solid or foamed and covered with the core. Then, a contact portion (fixing nip portion N) having a predetermined width is formed between the pressure roller 44 and the fixing roller 42 by the pressing force from the pressure roller 44. The outer diameter of the roller is about 30 to 40 mm, and the elastic member 42b has a thickness of about 3 to 10 mm and a hardness of about 10 to 50 ° (JIS-A).

The fixing belt 43 as a fixing member will be described in detail with reference to the cross-sectional view of FIG.
As shown in FIG. 3, in the fixing belt 43 of the embodiment, an elastic layer 43b and a release layer 43c are laminated on a base material 43a.

  The properties required for the base material 43a include mechanical strength when the belt is stretched, flexibility, and heat resistance that can withstand use at a fixing temperature. In the present invention, since the heat generating member (in this embodiment, the heating roller 41) is induction-heated, the base 43a of the fixing belt 43 stretched around the heat roller 41 that is the heat generating member has an insulating heat resistant resin material, Polyimide, polyimide amide, PEEK, PES, PPS, fluororesin and the like are suitable. The thickness is preferably 30 to 200 μm from the relationship between heat capacity and strength.

  The elastic layer 43b is formed for the purpose of giving flexibility to the belt surface in order to obtain a uniform image without uneven glossiness, and the rubber hardness is preferably 5 to 50 ° (JIS-A) and the thickness is preferably 50 to 500 μm. Also, from the viewpoint of heat resistance at the fixing temperature, silicone rubber, fluorosilicone rubber or the like is used as the material.

  Materials used for the release layer 43c include tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), and tetrafluoroethylene / hexafluoropropylene copolymer. Examples thereof include fluorine resins such as (FEP), mixtures of these resins, and heat-resistant resins in which these fluorine-based resins are dispersed.

  When the release layer 43c covers the elastic layer 43b, toner release properties and prevention of paper dust adhesion can be achieved without using silicone oil or the like (oilless). However, these resins having releasability generally do not have elasticity like a rubber material. Therefore, if a release layer is formed thickly on the elastic layer, the flexibility of the belt surface is impaired and gloss unevenness occurs. In order to achieve both releasability and flexibility, the film thickness of the release layer 43c is 5 to 50 μm, preferably 10 to 30 μm.

Moreover, a primer layer may be provided between each layer as needed, and a layer for improving durability during sliding may be provided on the inner surface of the base material 43a.
It is also preferable that the base material 43a has a heat generating layer. For example, it is possible to form a Cu layer of 3 to 15 μm on a base layer made of polyimide or the like and use it as a heat generating layer.

  The pressure roller 44 includes a metal core 44a made of a metal cylindrical member, a highly heat-resistant elastic layer 44b, and a release layer 44c, and presses the fixing roller 42 via the fixing belt 43 to fix the fixing nip. Part N is formed. The pressure roller 44 has an outer diameter of about 30 to 40 mm, and the elastic layer 44b has a thickness of about 0.3 to 5 mm and a hardness of about 20 to 50 ° (Asker hardness). Since the material needs heat resistance, silicone rubber is used. Further, in order to improve the releasability at the time of double-sided printing, a release layer 44c using a fluororesin is formed on the elastic member 44b by about 10 to 100 μm.

  By making the hardness of the pressure roller 44 harder than that of the fixing roller 42, the pressure roller 44 bites into the fixing roller 42 (and the fixing belt 43). It has a curvature that cannot be along the surface of the recording medium, and can improve the releasability of the recording material.

The operation of the fixing device configured as described above will be described.
The fixing belt 43 rotates in the direction of the arrow in FIG. 2 (counterclockwise in the figure). The heating roller 41 is heated by the induction heating unit 50. More specifically, when a high frequency alternating current of 10 kHz to 1 MHz is passed through the exciting coil 51, the magnetic field lines are alternately switched in both directions in the loop of the exciting coil 51. By forming an alternating magnetic field in this way, an eddy current is generated in the heating roller 41, Joule heat is generated, and induction heating is performed. The fixing belt 43 is heated by the heat generated from the heating roller 41 in this way, and the conveyed paper P and the fixing belt 43 come into contact with each other at the nip portion N to heat and melt the toner image on the paper.

  When the heat generation efficiency of induction heating is improved, the temperature of the surface layer of the fixing belt 43 is quickly raised, and the start-up characteristics are very good. The start-up characteristic means a short heating time up to a temperature required for the fixing belt 43 to fix the toner, and the shorter the heating time is, the better the image forming apparatus is for the user.

Further, when the heat generation efficiency is improved, less power is required for passing paper, which means that the user can save energy.
When the heating roller is heated, a high frequency alternating current is passed through the exciting coil 51, so that the coil itself generates heat due to Joule heat, and the temperature of the exciting coil 51 rises. In the configuration of the embodiment, the excitation coil 51 is installed as close as possible to the heating roller 41 in order to improve the heat generation efficiency. However, the temperature of the excitation coil 51 is increased by receiving radiant heat from the heating roller 41. To do.

  Here, when the temperature of the exciting coil rises, the electric resistance of the exciting coil increases due to the relationship between the electric resistance of the metal and the temperature coefficient, and the heat generation efficiency decreases. Therefore, in the electrophotographic apparatus, when the operation time becomes longer from the beginning of the operation, the temperature of the exciting coil increases, and the heat generation efficiency gradually decreases. In order to prevent this reduction in efficiency and for safety to prevent accidents such as disconnection of the excitation coil, the excitation coil is cooled by an air current using a cooling fan or the like. Also in this embodiment, a cooling fan 61 is provided as described later, and a cooling airflow is sent into the induction heating unit 50 to cool the excitation coil 51. The present invention is characterized in that the cooling efficiency of the exciting coil by the cooling airflow is improved, which will be described in detail later.

  FIG. 4 is a diagram illustrating a configuration of the induction heating unit 50. This figure is a cross-sectional view near the end in the unit longitudinal direction (axial direction of the heating roller 41), and shows a cross section viewed from the axial direction of the heating roller 41. 4 is a cross section taken along the line AA shown in FIG. 7 to be described later.

  As shown in this figure, the induction heating unit 50 of this example includes an exciting coil 51, an arch core 52, a center core 53, a side core 54, a case 55, a cover 56, and a rectifying member 57. The case 55 also functions as a coil holding member that installs and holds the exciting coil 51.

The core member composed of the arch core 52, the center core 53, and the side core 54 forms a magnetic path that concentrates the magnetic flux generated from the exciting coil 51 on the heat generating member (heating roller 41).
A plurality of arch cores 52 are installed at appropriate intervals in the longitudinal direction so that the temperature distribution in the longitudinal direction of the heating roller 41 is uniform (see FIG. 6).

  The magnetic core is preferably a soft magnetic material having a small coercive force and a high magnetic permeability and a high electrical resistivity. In addition to ferrite, materials such as permalloy are listed. As the material of each core member, Mn—Zn ferrite, Ni—Zn ferrite, or the like is used. Further, in order to increase the surface of the side core 54 facing the heating roller 41, the side core 54 is disposed obliquely.

  The exciting coil 51 is formed by winding a litz wire obtained by twisting about 50 to 500 conductive wires having a diameter of about 0.05 to 0.2 mm and having an insulating coating 5 to 15 times. The surface of the litz wire is provided with a fusion layer, and the fusion layer is solidified by heating in an electric heating or thermostatic bath, and the shape of the wound coil can be maintained. Alternatively, it is possible to give a shape by winding a coil using a litz wire that does not hold the fusion layer and press-molding it. Since the Litz wire needs to have a heat resistance equal to or higher than the fixing temperature, a resin having both heat resistance and insulation properties, such as polyamideimide and polyimide, is used for the insulation coating material of the strand. In addition, according to this invention, since the cooling efficiency of the exciting coil 51 goes up, the utilization possibility of polyester and polyester imide with lower heat resistance than before is also considered.

  The exciting coil 51 that has been wound is adhered to the case 55 using a silicone adhesive or the like. Since the case 55 needs to have heat resistance equal to or higher than the fixing temperature, PET, liquid crystal polymer, or the like, which is a resin having high heat resistance, is used. In the examples, a liquid crystal polymer was used.

  The case 55 is covered with a cover 56 to prevent the user from touching the components in the induction heating unit 50 by mistake. Since the cover 56 also needs heat resistance, if a resin is used, PET, a liquid crystal polymer, or the like, which is a resin having high heat resistance, is used. In the embodiment, the cover 56 is made of an aluminum material so as to serve as an electromagnetic shield for preventing leakage of a magnetic field generated from the coil.

The configuration of the exciting coil 51 will be described in more detail with reference to FIG.
As described above, the exciting coil 51 is formed by winding a litz wire with an insulating coating, and is wound in a rectangular shape extending in the axial direction of the heating roller 41 as shown in FIG. Curved along the outer periphery of the roller 41 in an arc shape (when viewed from the axial direction of the heating roller 41). In the present embodiment, the center cores 53 and 53 are arranged along the axial direction of the heating roller 41 in a portion corresponding to the inside of the rectangle.

5 schematically shows the exciting coil 51 wound in a rectangular shape, the specific shape of the embodiment is shown in the perspective view of FIG.
In FIG. 6, a rectangular excitation coil 51 with rounded corners is bonded and disposed on the upper surface of a case 55 that also serves as a coil holding member. The upper surface of the case 55 is exposed at the inner portion of the exciting coil 51. Two center cores 53, 53 are arranged in the inner part of the exciting coil 51 so as to extend in the axial direction of the heating roller 41 as described above. Further, side cores 54, 54 are arranged outside the exciting coil 51 along the two long sides of the rectangular shape so as to extend in the axial direction of the heating roller 41. Further, the plurality of arch cores 52 are arranged at intervals from each other so as to cover the exciting coil 51 from above in the drawing.

  In the present embodiment, a total of three bosses 58 for screwing the cover 56 to the case 55 are provided in the inner portion of the exciting coil 51 in the vicinity of both ends in the longitudinal direction and in the substantially central portion. In this example, the boss 58 is provided integrally with the case 55. A circular window (notch) for arranging a temperature sensor (not shown) for measuring the temperature of the heating roller 41 in a non-contact manner is provided in the case 55 in the substantially central portion in the longitudinal direction of the inner portion of the exciting coil 51. 60 is provided. A cylindrical protective wall 59 is provided around the notch 60. In this example, the protective wall 59 is provided integrally with the case 55.

  Furthermore, as shown in FIG. 7, a rectifying member 57, which is a feature of the present invention, is disposed on the inner portion of the exciting coil 51 so as to extend in the longitudinal direction (the axial direction of the heating roller 41). In this embodiment, the rectifying member 57 is provided integrally with the case 55 erected from the case 55, but may be a separate member from the case 55. The rectifying member 57 of this example is provided in a wall shape, and has a rectangular shape in which both end portions in the longitudinal direction are rounded when viewed from directly above. The rectifying member 57 is not shown in FIGS. 5 and 6. In FIG. 7, the boss 58, the protective wall 59, and the like are not shown. Also, the bosses 58 at both ends can be provided integrally with the rectifying member 57. In this example, the central boss 58 and the protective wall 59 are disposed on the inner side of the rectifying member 57.

  As described above, the rectifying member 57 in the illustrated example is provided in a wall shape, and in FIG. 4, which is a cross-sectional view at the position of the AA line near the longitudinal end of the induction heating unit, The outer end face of 57 is seen as a rectangle. In the case of a cross section of the wall portion of the rectifying member 57, for example, a cross section at the position of the line BB in the figure, the rectifying member 57 is shown as two members with diagonal lines as shown in FIG.

  As can be seen from FIG. 4, the rectifying member 57 divides the space formed between the exciting coil installation surface of the case 55 and the inner surface of the cover 56 facing the coil installation surface into two (left and right in the figure). Be placed. In the case of the embodiment, the rectifying member 57 is provided integrally with the case 55 (standing from the upper surface of the case), and there is no gap between the rectifying member 57 and the case 55. Further, when the cover 56 is screwed to the case 55, the cover 56 comes into contact with the upper end of the rectifying member 57, and there is no gap between the rectifying member 57 and the cover 56.

  Thus, by providing the rectifying member 57 so that the space in which the exciting coil 51 is installed is divided into two by the rectifying member 57 in the induction heating unit 50, one end in the longitudinal direction of the induction heating unit is provided. When the cooling air is sent from the section, the air flow is divided into two by the rectifying member 57.

For the rectifying member 57, PET, liquid crystal polymer, or the like, which is a resin having high heat resistance, is used. In the example, the same liquid crystal polymer as the case material was used (provided integrally with the case 55).
As will be described later, since the rectifying member adjusts the flow of the air flow inside the induction heating unit to increase the cooling efficiency, it may be formed of a material having good thermal conductivity. Heat dissipation can be promoted. Moreover, in order to reduce fluid resistance, it is desirable that the surface of the rectifying member is smooth. Therefore, as the rectifying member 57, in addition to the material of the embodiment, a metal such as aluminum, copper, or iron, a resin having a smooth surface, or the like can be used.

FIG. 9 is a view for explaining the operation of the rectifying member 57.
In FIG. 9, a cooling fan 61 for sending a cooling air flow into the induction heating unit is arranged on one side in the longitudinal direction of the induction heating unit 50 (the cover 56 is omitted in the figure). In the embodiment, the cooling fan 61 is mounted on the side surface of the induction heating unit 50. However, the cooling fan 61 and the induction heating unit 50 are connected by a flow path such as a duct and a cooling airflow is sent through the flow path. It may be.

  As shown by a thick arrow in FIG. 9, the cooling airflow sent into the unit by the cooling fan 61 is first a curved portion that is a short side of the exciting coil 51 (a curved portion that connects two linear portions of the exciting coil 51). ) Is cooled, hits the flow straightening member 57, and is divided into two flows. The bisected airflow flows through the straight portion (long side portion) of the exciting coil 51. The airflow flows outside the rectifying member 57 (two members with hatching) in the cross-sectional view of FIG. 8, and the cooling airflow flows along the exciting coil 51. At this time, air current does not flow inside the rectifying member 57 (two members with hatching), that is, inside the exciting coil 51 where no coil conducting wire exists.

FIG. 10 is a schematic diagram illustrating the flow of airflow in a conventional configuration that does not include a rectifying member, for comparison.
In the conventional configuration, as indicated by a thick arrow in the figure, the cooling airflow sent into the unit by the cooling fan flows straight as it is and passes through the unit. The airflow also flows through the inner portion of the exciting coil 51 where no coil conductor exists. There are few obstacles that block the airflow, such as the arch coil 52, inside the exciting coil 51, and a lot of wind flows.

  What is desired to be cooled in the induction heating unit is an exciting coil. By reducing the temperature of the exciting coil, safety can be ensured, and the coil resistance can be lowered to improve the heat generation efficiency. According to the present invention, the air flow is concentrated near the exciting coil 51 by the rectifying member 57, thereby increasing the flow velocity and improving the cooling efficiency of the exciting coil 51.

On the other hand, in the conventional configuration, the cooling airflow flowing in the unit flows in the same degree in both the coil conductor part and the central part without the coil conductor, so that the cooling efficiency is inferior to that of the present invention.
The reason why the cooling efficiency increases as the flow velocity increases is that the heat transfer coefficient between the exciting coil 51 and the air flow increases, and the amount of heat released to the air increases.

  By the way, it is preferable that the distance between the rectifying member and the exciting coil bending portion is smaller on the cooling fan 61 side (upstream side of cooling airflow) than on the opposite side (downstream side of cooling airflow). That is, in FIG. 9, the distance between the rectifying member 57 and the exciting coil 51 curved portion is the distance upstream of the cooling airflow: L1 <the distance downstream of the cooling airflow: L2. The reason is that, on the upstream side, the end of the rectifying member 57 is brought close to the exciting coil 51 curved portion, so that the air current divided by the rectifying member flows along the coil curved portion and the coil curved portion is efficiently cooled. is there.

  On the other hand, on the downstream side of the cooling airflow, since a certain distance is required for the airflow divided by the rectifying member 57 to merge, if the end of the rectifying member is close to the coil bending portion, it is difficult to cool. By taking a larger distance than the upstream side, the coil bending portion can be efficiently cooled by the airflow merged downstream of the rectifying member 57.

  The result of comparing the embodiment of the invention and the above-described conventional configuration in a heating experiment is shown in the graph of FIG. The configuration used for the comparative experiment is that described in FIGS. 2 to 9 for this embodiment (Example 1), the conventional configuration is FIG. 10 (Comparative Example 1), and only the presence or absence of the rectifying member 57 is different. The configuration is the same. In the experiment, power is applied to the excitation coil 51 and the surface temperature of the fixing belt 43 is raised to a set temperature of 170 ° C., and then the temperature is maintained at 170 ° C., and the temperature of the excitation coil 51 when continuous paper feeding is performed. It was measured. The temperature of the exciting coil 51 was measured at the outlet portion of the airflow where the temperature was highest. In the conventional configuration, the temperature of the exciting coil 51 rose to 220 ° C., whereas in the embodiment, it remained at 200 ° C. It has been found that the temperature rise is suppressed by 20 ° C. and the cooling efficiency is improved in this embodiment compared to the conventional configuration.

  That is, according to the present invention, it is possible to provide a fixing device having a simple configuration and good coil cooling characteristics. As a result, it is possible to reduce the output of the cooling fan within the range of safety standards, and it is also expected to reduce costs, save power, and reduce noise. Further, if the heat generation efficiency of the coil is improved by cooling the exciting coil, less power is required for passing the paper.

  The rectifying member should be inside (inner peripheral part) of the exciting coil. This is because if the rectifying member is arranged outside the exciting coil, the curved portion at the coil end is hardly cooled. This point will be described with reference to FIGS.

  FIG. 12A shows the vicinity of the coil bending portion in the embodiment of the invention (Example 1). Moreover, FIG.12 (b) shows the comparative example (comparative example 2) which has arrange | positioned the rectification | straightening member also to the outer side of the exciting coil. A, B, C, and D in FIG. 12 represent the positions of the exciting coil 51, and the transition of the temperature at each position during heating is indicated by the curves A, B, C, and D in the graph of FIG. Yes.

  By placing the rectifying member 157 on the outside of the exciting coil 51, the airflow has flowed through the linear portion of the exciting coil 51 from an early stage. Therefore, although the cooling efficiency of C is slightly higher than A, the airflow does not flow. The temperature of the curved portion D at the coil end is very difficult to be cooled.

  Even if the excitation coil overheats partially, a disconnection of the coil or the like occurs. Therefore, in order to cool the entire excitation coil, it is preferable that the rectifying member is on the inner side (inner periphery) of the excitation coil.

  In the first embodiment, the end surface of the rectifying member 57 facing the curved portion of the coil end portion has a curved surface shape (curved shape protruding toward the upstream side). This is to reduce the fluid resistance of the rectifying member 57 against the airflow. When the fluid resistance decreases, the speed of the airflow increases and the cooling efficiency can be further increased.

  Therefore, as shown in FIG. 14, it is not preferable to create a wall that faces the air flow and increase the fluid resistance. In addition, as in the rectifying member 57B shown in FIG. 15, a square shape in which the tip (tip of the airflow facing surface) protrudes toward the upstream side is also a preferable shape because the fluid resistance becomes small. If the tip angle is acute, the fluid resistance can be further reduced.

In the embodiment, the rectifying member 57 is integrally formed with the case 55 and also serves as a rib for increasing the case strength.
FIGS. 16 and 17 are schematic diagrams for explaining design objectives and molded products in the prior art and the embodiment. FIG. 16 shows a configuration according to the prior art, and FIG. 17 shows a case of the embodiment. In the figure, the induction heating unit is viewed with the unit longitudinal direction faced in front.

  As shown in FIG. 16, in the configuration of the prior art that does not include a rectifying member that also serves as a rib, a “sledge” may appear when molded against the designed aim. If the warpage occurs, the distance between the exciting coil (not shown) and the heating roller 41 becomes long, and the heat generation efficiency decreases. If the thickness of the case 55 is increased in order to increase the strength, the distance between the exciting coil and the heating roller 41 is also increased, and the heat generation efficiency is lowered.

  On the other hand, in the embodiment shown in FIG. 17, the rectifying member 57 on the inner circumference of the exciting coil conducting wire portion is formed as a rib integrally formed with the case 55, so that the rib enters the central portion in the case longitudinal direction. Strength can be increased. If the strength is increased by the rib, the warpage is reduced. Moreover, the thickness of the wall of the other part of a case can be made thin. Since the induction heating unit can be brought closer to the heating roller 41 by reducing warpage or reducing the wall thickness, the heat generation efficiency of induction heating is increased.

Note that the present invention is not limited to a belt fixing device, and can also be applied to a heat roll method. A second embodiment in which the present invention is applied to a heat roll type fixing device will be described below.
The fixing device of the second embodiment shown in FIG. 18 has a configuration in which the fixing roller 45 is used as a fixing member, and the fixing roller 45 is heated by the induction heating unit 50. Except that the fixing member is a fixing roller 45, the configuration is the same as that of the fixing device shown in FIG. In the configuration of the second embodiment, the fixing roller 45 is not only a fixing member but also a heat generating member (a member that generates heat when heated by the induction heating unit 50).

The configuration and operation of the induction heating unit 50 are the same as those in the first embodiment described above, and include the rectifying member 57, and redundant description is omitted.
The fixing roller 45 in the second embodiment has an outer diameter of about 30 to 40 mm, and an elastic layer 45b, a heat generating layer 45c, a release layer (not shown) and the like are laminated on the cored bar 45a. It is configured. The fixing roller 45 rotates in the direction of the arrow (counterclockwise in the drawing), and the fixing roller 45 heated by induction heating heats and melts the toner image on the conveyed recording paper.

  As described in the above two embodiments, according to the fixing device of the present invention, the inside of the induction heating unit 50, between the excitation coil installation surface and the surface facing the installation surface, and the inner portion of the excitation coil ( By providing a rectifying member that bisects the flow of air that has flowed into the unit in the inner peripheral portion, the flow velocity of the cooling airflow in the vicinity of the exciting coil can be increased, and the cooling efficiency can be improved. Since the cooling efficiency can be increased without increasing the output of the cooling fan, it is energy saving, and the lower the coil temperature, the higher the heating efficiency of the exciting coil. Therefore, it is possible to realize a low cost and high heat generating efficiency fixing device. it can. In addition, since a high cooling efficiency can be obtained with a simple configuration in which a rectifying member is provided, an increase in cost can be suppressed as much as possible.

  Further, the rectifying member extends in the longitudinal direction of the unit so as to flow the bisected air flow along the long side portion (in the embodiment, a straight portion) of the exciting coil. The long side portion of the large exciting coil can be efficiently cooled.

  Further, the end face on the upstream side (upstream side of the air flow) of the rectifying member is formed into a curved shape or a rectangular shape protruding toward the upstream side, thereby reducing the fluid resistance of the rectifying member and further increasing the cooling efficiency. be able to.

  In addition, the distance between the rectifying member and the exciting coil bending portion is such that the upstream side of the air flow is made smaller than the downstream side, and on the upstream side, the air stream divided by the rectifying member flows along the coil bending portion, The coil bending portion can be efficiently cooled. Further, on the downstream side, the airflow merged downstream of the rectifying member can be flowed along the coil bending portion, and the coil bending portion can be efficiently cooled.

Moreover, since the rectifying member is formed of a material having excellent thermal conductivity, heat dissipation of the exciting coil during operation can be promoted.
Further, the configuration in which the rectifying member is also used as the reinforcing rib of the unit can increase the strength of the case for holding the exciting coil, reduce warpage (deformation), and reduce the thickness of the case.

  Although the present invention has been described based on the illustrated examples, the present invention is not limited to this and can be appropriately changed within the scope of the present invention. In the induction heating means, the size and shape of the rectifying member can be appropriately set according to the invention. For example, the rectangular shape in FIG. 15 of the rectifying member has been described as an embodiment in which the tip is closed and the airflow is divided into two, but the airflow can substantially flow (bisected) into the exciting coils on both sides. For example, even if the square tip is somewhat divided and as a result the airflow is not completely divided into two, it is within the scope of the present invention. In addition, an appropriate material can be used for the flow regulating member.

  As the fixing device and the image forming apparatus, any configuration can be adopted as long as the present invention is applicable. The image forming apparatus is not limited to a copying machine or a printer, but may be a facsimile machine or a multifunction machine having a plurality of functions.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 10 Image forming unit 40 Fixing apparatus 41 Heating roller 42 Fixing roller 43 Fixing belt (fixing member)
44 Pressure roller 45 Fixing roller (fixing member)
DESCRIPTION OF SYMBOLS 50 Induction heating unit 51 Excitation coil 52 Arch core 53 Center core 54 Side core 55 Case 56 Cover 57 Rectification member 61 Cooling fan

JP 2006-350054 A

Claims (8)

In a fixing device comprising: a rotatable fixing member; a pressure member that is pressed against the fixing member to form a nip portion between the fixing member; and an induction heating unit as a heating source for heating the fixing member.
The induction heating unit is provided with a rectifying member that bisects the flow of air flowing into the unit between the exciting coil installation surface and the surface facing the installation surface, and on the inner part of the excitation coil. A fixing device characterized.   2. The fixing according to claim 1, wherein the rectifying member is provided so as to extend in a longitudinal direction of the unit so that the divided air flow flows along a long side portion of the exciting coil. 3. apparatus.   The fixing device according to claim 1, wherein an upstream end surface of the air flow of the rectifying member is provided in a curved shape or a square shape protruding toward the upstream side.   The distance between the rectifying member and the longitudinal end of the excitation coil is smaller on the upstream side of the air flow than on the downstream side. Fixing device.   The fixing device according to claim 1, wherein the rectifying member is also used as a reinforcing rib of the unit.   The fixing device according to claim 1, wherein the rectifying member is integrally formed with a coil holding member that holds the exciting coil.   The fixing device according to claim 1, wherein the rectifying member is formed of a material having excellent thermal conductivity. An image forming apparatus comprising the fixing device according to claim 1.

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