JP2007041198A - Fixing device and image forming apparatus having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate oscillation control in a high-frequency power source in a fixing device accommodated in a heating roller by an induction heating unit that generates heat by an electromagnetic induction action, and to make the temperature distribution of the heating roller uniform. Improve the heat generation efficiency and improve the rise characteristics.
SOLUTION: An induction heating unit 25 accommodated in a heating roller 21 includes a plurality of excitation coils 32 arranged in series in the axial direction, and a plurality of magnetisms provided in each of the plurality of excitation coils. It is assumed that the plurality of magnetic cores are sequentially provided at different arrangement angles from the magnetic cores adjacent in the axial direction. In particular, it is assumed that the magnetic core includes a pair of protrusions that protrude from the base extending inside the excitation coil to the outside of the excitation coil and that have tips that are close to the inner peripheral surface of the heating roller.
[Selection] Figure 3

Description

  The present invention relates to a fixing device in which an induction heating unit that heats a heating roller by electromagnetic induction action is housed in the heating roller, and an image forming apparatus including the fixing device.

  In an image forming apparatus (such as a printer, a facsimile machine, a copying machine, and a multi-function machine) that forms an image on recording paper by an electrophotographic process, unfixed toner transferred from the photosensitive member onto the recording paper is recorded by heat and pressure. There is provided a fixing device for fixing the toner. In this fixing device, in recent years, an electromagnetic induction heating method in which a heating medium such as a heating roller is heated by Joule heat generated by an eddy current generated by electromagnetic induction has attracted attention from the viewpoint of energy saving.

In such an electromagnetic induction heating type fixing device, the induction heating unit including the exciting coil, the magnetic core, and the holding members thereof is arranged opposite to the outer peripheral side of the heating roller, and the induction heating unit is disposed inside the heating roller. Is known (see Patent Documents 1 and 2). Thus, the structure which accommodated the induction heating unit in the inside of a heating roller is convenient when aiming at space saving.
JP 2001-242727 A JP 2002-229360 A

  However, in the conventional technique, in the configuration in which the exciting coil is provided so as to extend over substantially the entire length of the heating roller, there is a problem that the oscillation control in the high-frequency power source is difficult because the length of the magnetic flux passing through the heating roller becomes long. .

  On the other hand, in the configuration in which a plurality of exciting coils are arranged in the axial direction, the length of magnetic flux passing through the heating roller is shortened, so that oscillation control in a high-frequency power source is facilitated. However, simply arranging a plurality of exciting coils in the axial direction generates an area where no heat is generated between adjacent exciting coils, which is not desirable from the viewpoint of uniformizing the temperature distribution of the heating roller.

  Further, in the configuration in which a plurality of magnetic cores are arranged in the axial direction, the length of magnetic flux passing through the heating roller is shortened, similarly to the above configuration, so that oscillation control in a high frequency power supply is facilitated. However, even in this configuration, since the distance that the magnetic flux passes through the air with low permeability is long, the magnetic flux density at the heating roller is low, and a sufficiently high heat generation efficiency cannot be achieved. It takes time to raise the temperature of the heating roller to a temperature suitable for fixing, and there is a problem in terms of rising characteristics.

  The present invention has been devised to solve such problems of the prior art, and its main purpose is to facilitate oscillation control in a high-frequency power source and to make the temperature distribution of the heating roller uniform. It is an object of the present invention to provide a fixing device configured to be able to perform the above and an image forming apparatus including the fixing device. Another object of the present invention is to provide a fixing device configured to improve heat generation efficiency and improve start-up characteristics, and an image forming apparatus including the same.

  In order to solve such a problem, in the present invention, as shown in claim 1, in a fixing device in which an induction heating unit for generating heat by an electromagnetic induction action is housed in the heating roller, The induction heating unit has a plurality of exciting coils provided in series in the axial direction, and a plurality of magnetic cores provided in each of the plurality of exciting coils. The magnetic cores adjacent to each other in the axial direction were sequentially provided with a circumferential arrangement angle shifted.

  According to this, since the length of the magnetic flux passing through the heating roller is shortened, the oscillation control in the high frequency power source becomes easy. Moreover, since the heat generation area formed around the axial center position of the magnetic core can be formed without gaps in the axial direction, the temperature distribution in the axial direction can be made uniform.

  In this case, the magnetic core may be configured to be arranged so as to partially overlap the magnetic core adjacent in the axial direction at different arrangement angles.

  Moreover, it is preferable that a plurality of magnetic cores be arranged at equal intervals in the circumferential direction at the same axial position. According to this, it is possible to shorten the time from the start of rotation of the heating roller to the transition to a state where the circumferential temperature distribution is uniform.

  In the fixing device, as shown in claim 2, the magnetic core is protruded to the outside of the exciting coil from a base portion that extends to the inside of the exciting coil, and a tip is formed on the inner peripheral surface of the heating roller. It can be set as the structure provided with a pair of protrusion part which adjoins. According to this, since the tip of the projecting portion serving as a magnetic pole in the magnetic core is close to the inner peripheral surface of the heating roller, the distance that the magnetic flux passes through the air having a low magnetic permeability is shortened. The density is increased and the heat generation efficiency is improved.

  In this case, the magnetic core can have various cross-sectional shapes such as a U-shape, a U-shape, and a C-shape, but a portion from the base portion to the protruding portion in order to avoid spreading the magnetic flux in an unnecessary direction. Is preferably formed into a circular arc shape.

  In the fixing device, as shown in claim 3, the induction heating unit includes a core member that extends in a center line direction of the heating roller and holds the exciting coil and the magnetic core on an outer periphery thereof. The core material is formed in a pipe shape with a non-magnetic material having high thermal conductivity, and cooling the excitation coil and the magnetic core through the cooling air from the air blowing means through the core material. It can be set as the structure made into. According to this, an exciting coil and a magnetic body core can be cooled, without inhibiting induction heating.

  In this case, aluminum is suitable as a material for forming the core material.

  The core material may be formed in a polygonal cross section having an even number of sides such as a quadrangular shape, a hexagonal shape, and an octagonal shape so as to conform to the arrangement form of the magnetic core.

  In the fixing device, as shown in claim 4, a through-hole into which the magnetic core is fitted is formed in a peripheral wall of the core material, and cooling air passing through the core material is directly supplied to the magnetic core. It can be set as the structure made to hit. According to this, the cooling efficiency can be further increased.

  As described above, according to the present invention, the oscillation control in the high-frequency power source can be facilitated, the temperature distribution of the heating roller can be made uniform, the heat generation efficiency is improved, the rising characteristics are improved, and the heating roller is Since the temperature can be raised efficiently and uniformly in a short time, and the rotation of the heating roller can be stopped until just before the paper is passed, a great effect can be obtained in saving power.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a copying machine to which the present invention is applied. The copying machine (image forming apparatus) includes an original reading unit 1 that reads an image of an original, an image forming unit 2 that forms an image of the original read here on a recording paper (image forming medium) with toner, A fixing unit (fixing device) 3 that fixes a toner image formed on the recording paper. The recording paper is supplied from the paper supply unit 4 to the image forming unit 2, and the fixing unit 3 finishes the fixing process. The paper is discharged to the paper discharge unit 5.

  In the image forming unit 2, the photosensitive drum 12 uniformly charged by the charging roller 11 is irradiated with laser light from the laser scanning unit 13 to form an electrostatic latent image on the image forming surface of the photosensitive drum 12. After that, the toner in the developing unit 14 is supplied to the photosensitive drum 12 through the developing roller 15 to develop the electrostatic latent image on the image forming surface, and the toner image formed thereby is transferred. The image is transferred onto the recording paper by the roller 16.

  FIG. 2 is a cross-sectional view showing a main part of the fixing unit shown in FIG. The fixing unit 3 includes a heating roller 21 that thermally melts the toner image on the recording paper (image forming medium) S, and a pressure roller 22 that is urged in a direction in which the toner image is pressed against the heating roller 21 by a spring (not shown). The recording paper S is fed into the nip portion between the heating roller 21 and the pressure roller 22, and the toner on the recording paper S is fixed to the recording paper S by the action of heat and pressure.

  The heating roller 21 has a hollow cylindrical roller body 24 made of a magnetic metal material such as iron, nickel, copper, and chromium, and a release layer 26 made of fluorine resin or the like is formed on the surface of the roller body 24. Is formed. Further, an electromagnetic induction heating unit 25 is accommodated in the roller body 24, and this electromagnetic induction heating unit 25 is driven by a high frequency power source 27.

  The pressure roller 22 includes a metal core 28 made of an aluminum alloy material and an elastic layer 29 made of a sponge material such as foamed silicone rubber formed around the metal core 28.

  3 is a cross-sectional view of the heating roller shown in FIG. The electromagnetic induction heating unit 25 housed in the heating roller 21 includes a plurality of exciting coils 32 provided in series in the axial direction, and a magnetic core 33 provided individually in the plurality of exciting coils 32. In order to hold the exciting coil 32 and the magnetic core 33, a core member (holding member) 34 extending in the axial direction is formed.

  The exciting coil 32 is coaxially formed with the heating roller 21 by a conducting wire 36 wound around the center line of the heating roller 21, and a plurality of insulated copper wires are bundled on the conducting wire 36. Litz wire is used. Each of the exciting coils 32 is provided with a plurality (two in this case) of magnetic cores 33 at symmetrical positions around the center line of the heating roller 21.

  The core material 34 is formed in a pipe shape with a non-magnetic material having high thermal conductivity such as aluminum, and the cooling air from a fan (air blowing means) 36 is circulated inside the core material 34 to be excited. The coil 32 and the magnetic core 33 are cooled. Cooling air generated by the fan 36 is introduced into the core member 34 from one end 38 of the core member 34 through the duct 37 and discharged from the other end 39 side of the core member 34.

  FIG. 4 is a cross-sectional view showing a magnetic flux generation state by the magnetic core shown in FIG. The magnetic core 33 is formed of a ferromagnetic material such as ferrite, protrudes from the base 41 extending inside the exciting coil 32 to the outside of the exciting coil 32, and the tip is the inner peripheral surface of the roller body 24. Is provided with a pair of protrusions 42 close to each other. The front end surface of the protruding portion 42 is formed so as to be substantially orthogonal to the radial direction, and faces the inner peripheral surface of the roller body 24. A portion extending from the base 41 to the protruding portion 42 is formed in an arcuate cross-sectional shape in order to prevent the magnetic flux from traveling in a useless direction.

  The magnetic flux generated by the exciting coil 32 is guided by the magnetic core 33 and proceeds from the front end surface of the projecting portion 42 in a substantially radial direction, and enters in a direction substantially orthogonal to the inner peripheral surface of the roller body 24. Since the tip end surface of the projecting portion 42 is close to the inner peripheral surface of the roller body 24 and the distance through which the magnetic flux passes through the air having a low magnetic permeability is short, the roller 42 enters the roller body 24 with a high magnetic flux density.

  FIG. 5 is a perspective view showing the electromagnetic induction heating unit shown in FIG. Two magnetic cores 33 are arranged at the same axial position, and one exciting coil 32 is formed by winding a conducting wire 36 around the pair of magnetic cores 33. In addition, the magnetic core 33 and the magnetic cores 33 adjacent to each other in the axial direction are shifted from each other by 90 degrees in the circumferential direction with respect to the center line of the heating roller 21.

  The core material 34 is formed in a quadrangular cross section so as to conform to the arrangement form of the magnetic core 33, and the base portion 41 is in a state where the protruding portion 42 of the magnetic core 33 is directed radially outward. It is bonded and fixed to the flat surface of the core material 34.

  FIG. 6 shows a heat generation state of the heating roller shown in FIG. The magnetic core 33 is arranged so as to partially overlap the magnetic core 33 adjacent in the axial direction at different arrangement angles in the axial direction. Thereby, since the heat generation area formed around the axial center position of the magnetic core 33 is formed without gaps in the axial direction, the temperature distribution in the axial direction can be made uniform. The overlapping range between the magnetic cores 33 is preferably 10 to 20% of the axial length of the magnetic cores 33, for example.

  FIG. 7 shows the temperature distribution in the axial direction of the heating roller shown in FIG. Here, (A) shows a cross section of the heating roller 21 cut along a plane orthogonal to the center line, and (B-1) shows a cross section of the heating roller 21 cut along the line BB in (A). , (C-1) shows a cross section of the heating roller 21 cut along line CC in (A). (B-2) shows the temperature distribution when the heating roller 21 stops at the cut surface shown in (B-1), and (C-2) shows the temperature distribution at the cut surface shown in (C-1). The temperature distribution when the heating roller 21 is stopped is shown, and (D) shows the temperature distribution when the heating roller 21 rotates.

  As shown in (B-2) and (C-2), in the heating roller 21, the temperature is highest at the axial center position of the magnetic core 33, and the magnetic cores 33 adjacent in the axial direction at the same arrangement angle. The temperature is lowest at the intermediate position. Further, since the magnetic core 33 shown in cross section in (C-1) is located at the axial center position between adjacent magnetic cores 33 shown in cross section in (B-1), (B-2) In the case of (C-2) and the case of (C-2), the temperature distribution state becomes reverse characteristics, and when the heating roller 21 rotates, the temperature distribution state is averaged and the axial direction of the heating roller 21 as shown in (D). Temperature fluctuation is reduced.

  FIG. 8 is a sectional view showing another example of the induction heating unit according to the present invention. FIG. 9 is a perspective view showing an exploded state of the induction heating unit shown in FIG. In this induction heating unit 51, as in the above example, each of a plurality of exciting coils 52 arranged in series in the axial direction is provided with a magnetic core 53 as a pair. Although the coil 52 and the magnetic core 53 are supported by the core material 54 extending in the axial direction, unlike the above example, a through hole 56 in which the magnetic core 53 is fitted on the peripheral wall of the core material 54 is opened. Thus, the base 57 of the magnetic core 53 is embedded in the peripheral wall of the core material 54, whereby the cooling air passing through the core material 54 is directly applied to the magnetic core 53 to increase the cooling efficiency. it can.

  FIG. 10 is a sectional view showing another example of the induction heating unit according to the present invention. Here, around the core member 61, three magnetic cores 62 are arranged at equal intervals in the circumferential direction at the same axial position, and the mounting angle with the adjacent magnetic cores 62 in the axial direction is circumferential. It is shifted 60 degrees in the direction. The core member 61 is formed in a hexagonal cross section so as to conform to the arrangement form of the magnetic core 62. As in the example shown in FIG. 5, an exciting coil is formed around a set of three magnetic cores 62 at the same axial position by winding a conducting wire.

  FIG. 11 is a sectional view showing another example of the induction heating unit according to the present invention. Here, around the core 71, four magnetic cores 72 are arranged at equal intervals in the circumferential direction at the same axial position, and the mounting angle with the adjacent magnetic cores 72 in the axial direction is circumferential. It is shifted 45 degrees in the direction. The core material 71 is formed in an octagonal cross section so as to conform to the arrangement form of the magnetic core 72. As in the example shown in FIG. 5, an exciting coil is formed around a set of four magnetic cores 72 at the same axial position by winding a conducting wire.

  In this way, increasing the number of magnetic cores arranged in the circumferential direction at the same axial position is convenient for making the temperature distribution in the circumferential direction uniform, and the heating roller 21 starts rotating. It is possible to further shorten the time from the transition to the state where the temperature distribution in the circumferential direction becomes uniform.

  In the above example, the configuration in which the pressure roller is brought into pressure contact with the heating roller in which the induction heating unit is accommodated and the recording paper is passed through the nip formed between the two is described. In order to improve the characteristics, a configuration using a heating belt having a smaller heat capacity than that of the roller can be similarly applied. In this case, an endless belt-shaped heating belt is wound around the heating roller and the fixing roller in which the induction heating unit is accommodated, and a pressure roller disposed opposite to the fixing roller and a portion where the heating belt is wound around the fixing roller. By passing the recording paper between them, the toner on the recording paper is fixed to the recording paper by the action of heat and pressure.

  The fixing device according to the present invention and the image forming apparatus including the same facilitate the oscillation control in the high-frequency power supply, make the temperature distribution of the heating roller uniform, further improve the heat generation efficiency, and improve the start-up characteristics. An induction heating unit that has a heating roller by electromagnetic induction action is useful as a fixing device housed in the heating roller and an image forming apparatus including the fixing device.

Schematic sectional view showing a schematic configuration of a copying machine to which the present invention is applied Sectional drawing which shows the principal part of the fixing | fixed part shown in FIG. Sectional view of the heating roller shown in FIG. Sectional drawing which shows the generation | occurrence | production state of the magnetic flux by the magnetic body core shown in FIG. The perspective view which shows the electromagnetic induction heating unit shown in FIG. The figure which shows the heat_generation | fever condition of the heating roller shown in FIG. The figure which shows the temperature distribution of the axial direction of the heating roller shown in FIG. Sectional drawing which shows another example of the induction heating unit by this invention The perspective view which shows the decomposition | disassembly state of the induction heating unit shown in FIG. Sectional drawing which shows another example of the induction heating unit by this invention Sectional drawing which shows another example of the induction heating unit by this invention

Explanation of symbols

3 Fixing part (fixing device)
21 Heating roller 24 Roller body 25 Electromagnetic induction heating unit 32 Excitation coil 33 Magnetic core 34 Core material (holding member)
36 Fan (Blowing means)
36 Conductor 41 Base 42 Projection 51 Induction Heating Unit 52 Excitation Coil 53 Magnetic Core 54 Core Material 56 Through Material 61/71 Core Material 62/72 Magnetic Material Core

Claims (5)

An induction heating unit that generates heat from the heating roller by electromagnetic induction is a fixing device housed in the heating roller,
The induction heating unit has a plurality of exciting coils provided in series in the axial direction, and a plurality of magnetic cores provided in each of the plurality of exciting coils. A fixing device, wherein the magnetic cores adjacent to each other in the axial direction are sequentially provided with a circumferential arrangement angle being shifted.   The magnetic core includes a pair of protrusions that protrude from the base extending inside the excitation coil to the outside of the excitation coil and have tips that are close to the inner peripheral surface of the heating roller. The fixing device according to claim 1.   The induction heating unit includes a core material that extends in the center line direction of the heating roller and holds the exciting coil and the magnetic core on the outer periphery, and the core material is nonmagnetic and has high thermal conductivity. The material according to claim 1, wherein the exciting coil and the magnetic core are cooled by passing cooling air from an air blowing means into the core material. Fixing device.   The through-hole which the said magnetic body core fits was opened in the surrounding wall of the said core material, The cooling air which passes through the inside of the said core material was directly applied to the said magnetic body core, The Claim 3 characterized by the above-mentioned. The fixing device described.   An image forming apparatus comprising the fixing device according to claim 1.

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