JP2002006659A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve heating efficiency by a simple structure. SOLUTION: A coil 15 is disposed on an outer portion of a heat roll which is cylindrically formed from a conductive member and rotatably held around an axis 16. Caps 17 are fitted on both ends of the heat roll 11. High frequency power is supplied to the coil 15 to generate eddy current. The roll 11 is consequently heated. A toner image formed on transfer paper is fixed to the transfer paper by the heated roll.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art In general, in an electrophotographic image forming apparatus, a toner image formed by an image forming unit including a photoreceptor is transferred by a transfer unit onto a transfer sheet carried from a paper feeding unit to a photoreceptor position. After the toner image is fixed on the transfer paper by the fixing unit, the toner image is discharged out of the apparatus.

As a fixing unit, a heat roller fixing system composed of a heating roller and a pressure roller is often used recently in terms of speeding up. In the heat roller fixing method,
The pressure roller is pressed against the heating roller with a predetermined pressure, and the transfer paper on which the toner image has been transferred is passed between the heating roller and the pressure roller, and is heated by the heat from the heating roller and the pressure of the pressure roller. The toner image is fixed on the transfer paper.

[0004] Many conventional heating rollers incorporate a heater such as a halogen lamp and heat the roller surface by radiant heat from the heater.

On the other hand, a core around which a coil is wound is provided inside or outside a heating roller formed of a conductive member, and high-frequency power is supplied to the coil. An induction heating type fixing device has been proposed in which an induced eddy current is generated in a roller by a magnetic field interlinking the roller, and the heating roller is heated by Joule heat generated by the eddy current and the resistance of the roller. (Japanese Unexamined Patent Publication No. 54-39645, Japanese Unexamined Patent Publication No.
295414, JP-A-9-258586).

In the induction heating type fixing device, since the roller itself is heated, it is more efficient than a system in which the roller is heated indirectly by a heater, and the temperature rise in portions other than the roller can be reduced. Therefore, it is expected that the time required for raising the temperature to the fixing-possible temperature can be shortened and the energy saving of the apparatus can be realized.

[0007]

However, if the coil is arranged inside the heating roller, the coil itself is heated by the radiant heat from this roller. Then, the characteristics such as the resistance value and the inductance value of the coil change, the efficiency decreases, the coil wire itself melts, causing dielectric breakdown,
As a result, there is a possibility that the power supply for supplying power to the coil is greatly affected. For this reason, it is necessary to forcibly cool the coil using a fan or the like, which is inefficient, such as cooling while heating. In the case of forcible cooling, the opening of the roller must be large, and the temperature drop at both ends of the roller is accelerated.

On the other hand, even if the coil is arranged outside the heating roller, although the forced cooling of the coil is not necessary, since the air flows in and out from both ends of the roller and natural cooling by heat conduction, the coil is naturally cooled. In this case as well, it is inefficient to cool while heating, and the temperature drop at both ends of the roller is remarkable.

In any case, since the temperature drop at both ends of the roller impairs uniform fixing properties over the entire length of the roller, conventionally, the number of windings of the coil is higher at the roller end side than at the roller center side. Or a complicated configuration, such as splitting the coils and controlling each independently.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem and to provide an induction heating type fixing device capable of further improving the heating efficiency with a simple structure.

[0011]

According to the first aspect of the present invention,
A coil is disposed in the vicinity of a hollow roller that is rotatably held around a central axis in a cylindrical shape formed by a conductive member, and high-frequency power is supplied to the coil to generate an eddy current in the hollow roller. Heating the hollow roller by causing the toner image formed on the transfer paper to be fixed to the transfer paper using the heated hollow roller. In addition to being disposed outside the hollow roller, lids are provided at both ends of the hollow roller.

According to this configuration, since the coil is disposed outside the hollow roller, the coil is naturally cooled and the roller is only heated. Therefore, the inefficiency of cooling the roller while heating it is eliminated. In addition, since the lids are provided at both ends of the coil, natural cooling due to the inflow and outflow of air from both ends of the roller is almost eliminated, and the heating efficiency is improved.

If the conductive member is made of a ferromagnetic material as in the second aspect of the present invention, efficient induction heating is performed, so that the heating efficiency is further improved.

If the lid is made of a heat-insulating material as in the third aspect of the present invention, the heat dissipation from the end of the roller is reduced, and the heating efficiency is further improved.

If the lid has an air hole as in the invention according to the fourth aspect, the pressure increase due to air expansion in the roller is prevented.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a main part of an embodiment of a copying machine to which a fixing device according to the present invention is applied.

In the copying machine 1, the photoconductor 3 is uniformly charged by the charging unit 2, and the photoconductor 3 is irradiated with light from the exposure unit 4 based on a document image read by a document reading unit 90 (see FIG. 3). An electrostatic latent image is formed thereon, and toner adheres to the electrostatic latent image by the developing unit 5 to form a toner image. On the other hand, the transfer paper 7 is conveyed from the paper supply unit 70 (see FIG. 3) to the photoconductor 3, and the toner image on the surface of the photoconductor 3 is transferred to the transfer paper 7 by the transfer unit 6.

The transfer paper 7 separated from the photoreceptor 3
Is conveyed to a fixing unit 8, and after the toner image is fixed on the transfer paper 7 in the fixing unit 8, the transfer paper 7
Is discharged to a discharge section (not shown).

The fixing unit 8 includes a heating roller 11 and a pressure roller 12, and the fixing unit 1 fixed to the copying machine main body.
3.

The heating roller 11 is a cylindrical hollow roller having a diameter of about 40 mm formed of a conductive member, and is as thin as possible so as to be quickly heated. A release layer made of rubber is provided. A core 14 made of ferrite or the like is provided at a predetermined position outside the roller 11.
5 are wound. As the conductive member, iron, nickel, or the like, which is a ferromagnetic material, is preferable from the viewpoint of dielectric heating efficiency. For example, stainless steel represented by SUS430 is more preferable from the viewpoint of corrosion resistance. However, a weak magnetic material or a non-magnetic material may be used as needed.

The heating roller 11 has a central shaft 16 (FIG. 2).
Reference) is held by the fixing unit 13 rotatably around,
A drive gear (not shown) is attached to one end, and is rotatably driven by a motor (not shown) connected to the drive gear.

On the other hand, the pressure roller 12 has a surface slightly softer than the surface of the heating roller 11 and is made of, for example, silicon rubber. The pressure roller 12 comes into contact with the heating roller 11 and is pressed by a predetermined pressure to be rotatably held by the fixing unit 13. It is configured to be driven by rotation of the heating roller 11.

When the transfer paper 7 is conveyed between these rollers 11 and 12, the transfer paper 7 is sandwiched by both rollers, and the toner image transferred to the transfer paper 7 is heated and fixed to the transfer paper 7. . At this time, the transfer paper 7 after fixing may be wrapped around the heating roller 11 and not peeled off. Therefore, in order to forcibly remove the transfer paper 7, a section-shaped separating member 20 is disposed downstream of the contact position of the heating roller 11. Has been established.

FIG. 2 is a perspective view showing the configuration of the coil and the heating roller. The same elements as those in FIG. 1 are denoted by the same reference numerals.

The core 14 around which the coil 15 is wound is disposed outside the heating roller 11 while maintaining a predetermined gap between the core 14 and the heating roller 11, and is fixed to the fixing unit 13 so as not to rotate. ing. The core 14 and the coil 15 are insulated from the heating roller 11 by the gap.

The core 14 is disposed parallel to the heating roller 11, and has a rectangular cross section perpendicular to the central axis 16, in which two parallel grooves are formed on the side facing the heating roller 11. Is slightly smaller than the roller diameter.
The coil 15 is made of one copper wire, and the core 1
4 is ideally wound in a single-stage spiral shape in the parallel groove, but may be wound in a plurality of stages. In the illustrated example, the coils 15 are wound so as to be accommodated in a three-fold manner in the parallel grooves. However, actually, the coils 15 are wound so as to be further multiplexed and accommodated. With such a configuration, the magnetic field generated around the wound coil 15 can be strengthened.

In FIG. 2, the core 14 is
The copier 1 of the present embodiment is arranged on the upper right side of the
Is such that when the A3 size transfer paper 7 (see FIG. 1) is conveyed in the long side direction and copied, the transfer paper 7 can contact and fix over the entire length of the heating roller 11. I have.

In this embodiment, both ends of the heating roller 11 are closed with caps (lids) 17. The cap 17 includes a cylindrical guide portion 17a that can be fitted to the inner surface of the heating roller 11 to a predetermined depth, a disc-shaped flange portion 17b that regulates the predetermined depth and closes one end of the guide portion 17a, Heating roller 11 outside of 17b
1 is formed coaxially with a cylindrical rotary shaft portion 17c having a diameter of approximately 20 mm.
Is rotatably supported by the fixing unit 13. The heating roller 11 is fixed by the flange portion 17b of the cap 17
The air exchange between the inside and the outside is shut off, and the temperature at the end of the heating roller 11 is prevented from lowering, so that the heating efficiency can be improved.

The guide portion 17a of the cap 17
The flange portion 17b and the rotating shaft portion 17c are made of a resin, metal, ceramic, or the like as a material to be used.
Above all, those having excellent heat resistance, being hardly induced by the coil 15 for induction heating, hardly transmitting heat to the bearing portion 18, and having high impact resistance are preferable. For example, heat-resistant resins such as PBT and phenol, and SUS304, which is a weak magnetic material and a metal having relatively low thermal conductivity, are examples of suitable constituent materials.
Thereby, the heating efficiency can be further improved while protecting the bearing portion 18 from the heat of the heating roller 11.

Further, the flange portion 17b of the cap 17
In the center of the through hole (air hole) 1 to 2 mm or less in diameter
9 are provided. This is because the air confined inside the roller by providing the cap 17 is thermally expanded when the heating roller 11 is heated and the internal pressure of the roller is increased, thereby preventing the cap 17 from dropping or jumping out. . Providing the through-holes 19 also has an advantage that the press-fitting of the cap 17 becomes easy even in the assembling process. In addition, only the bearing portion 18 can be reduced in size, which is effective in reducing the sliding load of the bearing portion 18 and the cost of the bearing member.

In the present embodiment, the core 14 around which the coil 15 is wound is disposed outside the heating roller 11.
Is limited to only the upstream portion of the heating roller 11 as close as possible to the contact portion. The reason is that the contact between the heating roller 11 and the pressure roller 12 is not actually line contact, but
The fixing is performed within a range having a width of 10 mm to 10 mm. In order to perform heat fixing between them, the coil 15 is disposed as close as possible to the upstream portion of the contact portion, and the coil 15 is placed on the transfer paper 7 conveyed here. This is because the transferred toner image needs to be quickly melted.

On the other hand, a separation member 20 for peeling off the transfer paper 7 after fixing is provided at a downstream portion of the contact portion of the heating roller 11. This is because it is necessary to cool the toner image once melted by lowering the temperature as much as possible to surely fix the toner image onto the transfer paper 7. For this reason, in the present embodiment, the coil 15 is not provided in the downstream portion of the contact portion of the heating roller 11.

FIG. 3 is a block diagram showing a main part of an electric configuration of the copying machine 1. As shown in FIG. The same elements as those in FIGS. 1 and 2 are denoted by the same reference numerals.

In FIG. 3, a resonance circuit is formed by connecting a resonance capacitor C1 in parallel to a coil 15 (copper wire), and a switching element 31 is connected between one end of the resonance circuit and ground to form an inverter circuit. 41 are configured.

The switching element 31 is a power semiconductor element having a high withstand voltage and a large current. When a predetermined level of drive voltage is applied to the control terminal, the switching element 31 conducts one end of each resonance circuit to the ground. As the switching element 31, for example, an IGBT, a MOS-FET, or the like can be employed.

The other end of the resonance circuit is a bridge diode 5
0 is connected to one DC output terminal 51. The other DC output terminal 52 of the bridge diode 50 is grounded, and the AC input terminals 53 and 54 are connected to the AC
It can be connected to a 100 V AC power supply 56.

The AC input terminal 5 of the bridge diode 50
A primary coil of a current transformer 57 is interposed between the power transformer 4 and the connection portion 55. A resistor 58 having a predetermined resistance value is connected in parallel to a secondary coil of the current transformer 57. The power supplied from the AC power supply 56 by the voltage between both ends, that is, the total power consumption in the inverter circuit 41 can be detected. The bridge diode 50 and the AC power supply 56 constitute a DC power supply that supplies DC power to the inverter circuit 41. A drive circuit 61 is connected to a control terminal of the switching element 31, and a control IC 63 is connected to the drive circuit 61.
The control IC 63 is connected to the CPU 65.

The drive circuit 61 operates at a predetermined level (for example, 24
V) is applied to the control terminal of the switching element 31 to turn on the switching element 31. The control IC 63 outputs a pulse voltage signal having a frequency equal to or higher than a predetermined frequency (for example, 20 kHz to 50 kHz) to the drive circuit 61 in order to indicate the application timing of the drive voltage applied to the switching element 31 from the drive circuit 61. Control I
The frequency of the pulse voltage signal output from C63 is
65.

The CPU 65 is connected to a paper feed unit 70, an operation unit 80, and a document reading unit 90. Paper feed section 7
Reference numeral 0 denotes transfer papers 7 of various sizes, and a paper transport unit including a pair of rollers for transporting the respective transfer papers 7 toward the photoconductor 3 (see FIG. 1) and a motor for driving the pair of rollers. 71 are provided.

In the present embodiment, for example, A3 size, B4 size, and A4 size transfer sheets 7 are accommodated in the sheet feeding section 70 in the transport direction. The operation unit 80 includes a print key for instructing the start of a copying operation, a copy number setting key for setting the number of copies for each document, and the like.
A transfer paper selection key 81 for selecting a transfer paper 7 to be used for copying from among them, and a magnification setting key 82 for setting a copy magnification are provided.

The document reading section 90 reads a document image and sends the image data to the exposure section 4 (see FIG. 1).
An original size detecting unit 91 for detecting the size of the set original is provided.

When the print key is operated, the CPU 65 reads the document image by the document reading section 90,
The operation of the entire copying machine 1 is controlled, for example, by transferring the transfer paper 7 from the paper supply unit 70 and starting a copying operation.

With such a configuration, when high-frequency power (high-frequency current) is supplied to the coil 15, a high-frequency magnetic field is generated. For example, in FIG. 1, a high-frequency current is applied to the coil 15 accommodated in the upper groove in a direction toward the rear of the paper,
Assuming that a high-frequency current is applied to the coil 15 accommodated in the lower groove in a direction toward the front of the drawing, a high-frequency magnetic field is generated around the coil 15 in accordance with the right-hand screw rule.

The high-frequency magnetic field interlinks with a portion of the heating roller 11 facing the coil, and an eddy current is generated in the heating roller 11. The heating roller 11 is heated by Joule heat generated by the eddy current, and thereby the toner The fixing of the image to the transfer paper 7 is suitably performed.

At this time, according to the present embodiment, the coil 1
5 is disposed outside the heating roller 11, the coil 1
5 is allowed to cool naturally, while the heating roller 11 is only heated. Therefore, the inefficiency of cooling while heating the heating roller 11 is eliminated. Further, since the caps 17 are provided at both ends of the heating roller 11, natural cooling due to the inflow and outflow of air from both ends of the heating roller 11 is almost eliminated, and the heating efficiency is improved. Further, the density of the coil 15 may be uniform over the entire length of the heating roller 11, and it is not necessary to divide the coil 15 and control each of them separately, so that a very simple configuration is sufficient.

In the above embodiment, the heating roller 11
Although both ends are closed by separate caps 17, the heat roller 11 and the cap 17 may be integrally formed, and a heat insulating material may be attached to the cap 17. In that case, the configuration becomes simpler. Further, the through hole 19 does not need to be formed in the center of the flange portion 17b of the cap 17, and it is not necessary to provide the through hole 19 in both the caps 17 at both ends of the heating roller 11. Any material that allows air to enter and exit from at least one end of the heating roller 11 may be used.

In the above embodiment, the core 14 has a rectangular cross section perpendicular to the central axis 16 of the heating roller 11. However, the core 14 has a curved shape (saddle-shaped shape) along the outer surface of the heating roller 11. ). In this case, since the gap between the coil 15 wound around the core 14 and the surface of the heating roller 11 can be made constant, the heating efficiency can be further improved.

Although the above embodiment has been described using a copying machine, the present invention is not limited to this, and the present invention can be applied to an electrophotographic image forming apparatus such as a facsimile or a printer.

[0049]

According to the first aspect of the present invention, the inefficiency of heating and cooling the roller is eliminated, and natural cooling due to the inflow and outflow of air from both ends of the roller is almost eliminated. Can be improved.

According to the second aspect of the present invention, the heating efficiency can be further improved by performing efficient induction heating.

According to the third aspect of the invention, heat radiation due to heat conduction from the roller ends is reduced, and the heating efficiency can be further improved.

According to the fourth aspect of the present invention, it is possible to prevent pressure rise due to air expansion in the roller and to prevent the lid from falling off or jumping out of the roller. There is also an advantage that the press-fitting of the lid to the roller is facilitated in the assembling process.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a main part of an embodiment of a copying machine to which a fixing device according to the present invention is applied.

FIG. 2 is a perspective view showing a configuration of a coil and a heating roller.

FIG. 3 is a block diagram showing a main part of an electric configuration of the copying machine.

[Explanation of symbols]

 8 Fixing Unit 11 Heating Roller (Hollow Roller) 14 Core 15 Coil 16 Center Shaft 17 Cap (Lid) 17a Guide 17b Flange 17c Rotating Shaft 18 Bearing 19 Through Hole (Air Hole) 20 Separating Member

Continued on the front page (72) Inventor Naofumi Miyake 1-2-28 Tamazo, Chuo-ku, Osaka City Inside Kyocera Mita Corporation (72) Inventor Haruya Osaka 1-2-28 Tamazo, Chuo-ku, Osaka City Kyocera Mita Corporation F-term (reference) 2H033 BA25 BE06 3K059 AA08 AB04 AC07 AD05 CD44

Claims (4)

[Claims] A coil is disposed in the vicinity of a hollow roller formed of a conductive member and rotatably held around a central axis, and a coil is provided. An induction heating type fixing device in which the hollow roller is heated by causing an eddy current to flow, and the toner image formed on the transfer paper is fixed on the transfer paper using the heated hollow roller. Wherein the coil is disposed outside the hollow roller and lids are provided at both ends of the hollow roller. 2. The fixing device according to claim 1, wherein the conductive member is a ferromagnetic material. 3. The fixing device according to claim 1, wherein the lid is formed of a heat insulating material. 4. The fixing device according to claim 1, wherein the lid has an air hole.