JP2001100579A - Inductively heated fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a inductively heated fixing device which is made light- weight and low-cost. SOLUTION: In a core 17 forming a closed magnetic circuit, an insertion part 17b forming the core material of a coil 14 is constituted of an iron core, and parts (a return part 17a and a connection part 17c) which do not contribute to heat generation of a fixing roller 12 are constituted of a sintered magnetic body like ferrite.

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 for, for example, an electrophotographic copying machine, a printer, a facsimile, and the like, and more particularly, to a fixing device for fixing a toner image to a recording medium using induction heating. About.

[0002]

2. Description of the Related Art An image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile includes a fixing device for fixing a toner image held on a sheet such as recording paper or a transfer material as a recording medium onto the sheet. Is provided.

There are various types of fixing devices, and a general heat roller type fixing device includes a fixing roller for thermally melting toner on a sheet, and a pressure roller for pressing and holding the sheet by pressing the fixing roller. And a roller. The fixing roller is formed in a hollow cylindrical shape, and a heat source for heating the fixing roller is provided inside the fixing roller. By this heat source, the fixing roller is heated to a predetermined fixing temperature required for fixing by fusing the toner by heat.

As a heat source in the heat roller fixing device, a tubular heater such as a halogen lamp is generally used. This halogen lamp is arranged on the center axis of the fixing roller, and the fixing roller is heated by radiant heat of the halogen lamp. . Such a halogen lamp heating type fixing device is
Although it is inexpensive in terms of cost, it has the drawback of low thermal efficiency and large energy loss due to heating by radiant heat.

In order to solve these drawbacks and respond to recent demands for energy saving, a fixing device of an induction heating system has been proposed.

For example, Japanese Patent Publication No. 4-73155 discloses that
An induction heating fixing device is described in which a coil formed by spirally winding a coil is formed through a core forming a closed magnetic path inside a conductive fixing roller and concentrically arranged inside the fixing roller. In this fixing device, the coil is energized to generate a magnetic flux in the core, and the magnetic flux induces an induced current in the fixing roller, thereby causing the fixing roller to generate Joule heat. For the core, a silicon steel sheet having high magnetic permeability is usually used, and a laminated iron core having a laminated structure is used to reduce energy loss due to eddy current.

A fixing device using such induction heating is:
Since the heating element, such as the fixing roller, is heated directly by electromagnetic induction, the heat conversion efficiency is higher and the power of the fixing roller surface is quickly raised to the fixing temperature with less power compared to the halogen lamp heating method. It is possible to meet the demand for energy saving. In particular, those having a core forming a closed magnetic path as described in the above publication have almost no leakage of magnetic flux and can efficiently generate a secondary current in the fixing roller, so that the energy saving effect is high.

[0008]

However, in the conventional induction heating fixing device, since the whole of the core forming the closed magnetic circuit is composed of a laminated iron core, the weight of the core increases and the cost of the core increases. There is a problem that increases.

Further, the increase in the core weight causes an increase in the weight of the fixing device and, consequently, an increase in the weight of the image forming apparatus. Further, as the weight increases, the structure supporting the fixing device must be made heavy, which may increase the cost of the image forming apparatus.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems associated with the prior art, and it is an object of the present invention to provide an induction heating fixing device capable of achieving weight reduction and cost reduction.

[0011]

According to the present invention, there is provided an induction heating fixing apparatus, comprising: a fixing member having a hollow shape formed of a conductive member; and a recording medium holding toner. A pressing body sandwiched between the fixing member, a core partially inserted into the hollow portion of the fixing member and forming a closed magnetic path, and a coil wound around the core and induction heating the fixing member. Wherein at least a portion of the core, which forms the core material of the coil, is made of an iron core, and the other portion is made of a magnetic material having a lower specific gravity than the iron core. is there.

Further, the coil is arranged in the hollow portion of the fixing member.

As a magnetic material having a specific gravity smaller than that of an iron core, a sintered magnetic material such as ferrite or a powder magnetic material molded product obtained by solidifying a magnetic material powder with a resin is used.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a copying machine as an image forming apparatus incorporating the induction heating fixing device according to the present invention.

As shown in the figure, the copying machine 100 includes an image scanner unit 101 for reading an original, a signal processing unit 102 for performing signal processing, and an image corresponding to the original image read by the image scanner unit 101 as a recording medium. And a casing 104 for arranging or storing these units.

In the image scanner section 101, a document placed on a platen glass 105 is pressed by a platen cover 106. When an automatic document feeder (not shown) is mounted, an automatic document feeder is used instead of the platen cover 106. Is attached. Platen glass 1
The original on the original 05 is irradiated by a lamp 107, and the light reflected by the original passes through mirrors 108a, 108b, 108c and a condenser lens 109, and the CCD line image sensor 11
The image is converted to image information and sent to the signal processing unit 102. In addition, by driving the scanner motor 111, the first slider 112
The slider 113 mechanically moves at V / 2 in the vertical direction (sub-scanning direction) with respect to the electrical scanning direction (main scanning direction) of the line sensor, and scans the entire original.

The signal processing unit 102 includes a line sensor 110
Process the signals read by the printer unit 103
Send to

The printer unit 103 includes a laser generator 115
And a photosensitive drum 116 as an image carrier,
Around the rotating photosensitive drum 116, a charging roller 117 as a charging device, a developing device 118, a transfer roller 119 as a transfer device, a charge elimination needle 120 as a device for removing and separating the sheet 10, and a photosensitive member And a cleaning device 121 that removes residual toner on the drum 116. The laser generator 115 includes the signal processing unit 1
The drive modulation of the semiconductor laser is performed according to the level of the image signal sent from the device 02. The laser beam is applied to the photosensitive drum 116 at a position between the charging roller 117 and the developing device 118 via a polygon mirror (not shown), an f-θ lens, a return mirror, and the like. Photoconductor drum 1
The electrostatic latent image formed on 16 is developed with toner in developing device 118.

On the other hand, a sheet cassette 125 detachably attached to the casing 104 has a plurality of sheets 1.
0 are stored in a stacked state. Paper cassette 12
The sheet 10 in the sheet 5 is separated and fed one by one by a feed roller 126, and the photosensitive drum 116 and the transfer roller 11 are separated by a timing roller 127 at a predetermined timing.
9 is transferred toward the transfer position between the transfer positions 9 and 9. The image developed on the photosensitive drum 116 is transferred to the sheet 10 by the transfer roller 119. The sheet 10 after the transfer is separated from the photosensitive drum 116, and is conveyed by the conveying belt 129 toward the fixing device 128. The unfixed toner transferred onto the sheet 10 is fixed in the fixing device 128, and the sheet 10 on which the toner is fixed is discharged to a discharge tray 130. Note that the fixing device 128 according to the embodiment of the present invention is based on an induction heating method, and the configuration will be described later.

When the transfer to the sheet 10 is completed by the transfer roller 119, the photosensitive drum 116 is charged to a negative polarity by a charger (not shown) before the cleaner, and
The residual toner is removed by the cleaning device 121, and the residual charge is removed by the eraser. Thereafter, the toner is charged again by the charging roller 117, receives a latent image formed by the laser beam, is developed by the developing device 118, and the charge in the non-development area is removed by a pre-transfer eraser (not shown).

FIG. 2 is a sectional view schematically showing a main part of the induction heating fixing device shown in FIG. 1, and FIGS. 3 and 4 are a sectional view and a side view schematically showing the structure of the fixing device.

The induction heating fixing device 128 has a hollow cylindrical fixing roller (corresponding to a fixing member) 12 formed from a conductive member, and a sheet holding toner 10 between the fixing roller 12. It has a pressure roller (corresponding to a pressure member) 13, a core 17 forming a closed magnetic path for eliminating leakage magnetic flux, and a coil 14 wound around the core 17 and inductively heating the fixing roller 12. Fixing roller 12
Are provided so as to be rotatable in the direction of arrow a in FIG. A part of the core 17 is inserted into the hollow portion 12 a in the fixing roller 12. The illustrated coil 14 is disposed in the hollow portion 12 a of the fixing roller 12.

The fixing roller 12 is formed of a conductive member such as a carbon steel tube, a stainless alloy tube or an aluminum tube, and iron. The fixing roller 12 is formed so as to have a sufficient mechanical strength against a pressing force from the pressure roller 13 and a thickness sufficient to secure a heat capacity. Further, the outer peripheral surface of the roller is coated with a fluororesin to facilitate separation of the sheet 10,
A release layer having good release properties and heat resistance with respect to the toner is formed.

The pressure roller 13 comprises a shaft core 15 and a silicone rubber layer 16 formed around the shaft core 15. The silicon rubber layer 16 covers the sheet 1 from the surface.
0 is a rubber layer having releasability and heat resistance as well as easy release. In the illustrated embodiment, a halogen lamp 28 is incorporated in the shaft core 15. The pressure roller 13 is pressed in a direction toward the fixing roller 12 by a spring material (not shown).

The core 17 is provided in the hollow portion 12 of the fixing roller 12.
a, a return portion 17a facing the surface of the fixing roller 12, and a connecting portion 17c connecting the insertion portion 17b and the return portion 17a.

The coil 14 is formed by spirally winding a winding 18. The coil 14 is inserted into the insertion portion 1 of the core 17.
7b, and are arranged concentrically inside the fixing roller 12. Therefore, a part of the insertion portion 17 b of the core 17 forms the core of the coil 14. As the winding 18, an ordinary single conductor having a fusion layer and an insulating layer on the surface is used.

In the present embodiment, of the core 17, the insertion portion 17b, which is a portion forming the core material of the coil 14, is made of an iron core used for a normal transformer, and the return portion 17a, which is another portion, is provided. The connecting portion 17c is made of a magnetic material having a lower specific gravity than the iron core. Insertion part 17
As the iron core constituting b, one having a high magnetic permeability such as a laminated iron core made of a silicon steel plate is used. In addition, other parts 1
As a magnetic material having a small specific gravity constituting 7a and 17c,
A sintered magnetic material such as ferrite is used.

The weight per unit volume of ferrite is about 1/2 (specific gravity, about 4.5) of silicon steel sheet or iron (specific gravity, about 7.9). Therefore, the return unit 1
When the core 7a and the connecting portion 17c are made of ferrite, the weight of the return portion 17a and the connecting portion 17c is reduced to about 1/2 compared to the case where the whole core is made of a silicon steel sheet laminated iron core. Lighter weight.

As shown in FIG. 3, both ends of the fixing roller 12 are fitted with stepped tubular sleeves 20 and penetrate through mounting holes 22 provided in a metal support frame 21. The core 17 also passes through the support frame 21.
A bearing 23 is arranged between the sleeve 20 and the mounting hole 22. Further, a fixing ring 24 for regulating the axial position of the fixing roller 12 is fitted into a ring groove 25 formed at an end of the fixing roller 12. The cylindrical sleeve 20, the support frame 21, the bearing 23, and the fixing ring 24 form a roller support structure 26 that rotatably supports the fixing roller 12. In addition,
The fixing roller 12 has a driving gear (not shown) fixed to one end thereof, and is rotatably driven by a driving source (not shown) such as a motor connected to the driving gear.

On the other hand, both ends of the pressure roller 13 penetrate through holes 27 provided in the support frame 21 and are rotatably held via bearings (not shown). The halogen lamp 28 is attached to the support frame 21 via a holding plate 29.

In the fixing operation, first, an alternating current of about 50 to 60 Hz is applied to the coil 14 from a power supply circuit (not shown), and the temperature of the fixing roller 12 is adjusted to a temperature suitable for fixing by induction heating (for example, 150 to 200 ° C.). ) Until heated. Sheet 10 holding unfixed toner 11
Is conveyed from the left as shown by the arrow b in FIG. 2 and is sent to a nip 19 which is a contact portion between the fixing roller 12 and the pressure roller 13. The sheet 10 is conveyed while being nipped by the nip 19 while the heated heat of the fixing roller 12 and the pressure roller 13 and the pressure applied from the pressure roller 13 are applied. As a result, the unfixed toner 11 is fixed on the sheet 10, and a fixed toner image is formed on the sheet 10. The toner 11 is applied to the sheet 1
0 is held on the side that comes into contact with the fixing roller 12 among the two surfaces. The sheet 10 that has passed through the nip 19 is naturally separated from the fixing roller 12 by a curvature according to the strength of the sheet itself, and is conveyed rightward in FIG. This sheet 10
The sheet is conveyed by a sheet discharge roller and discharged onto a sheet discharge tray 130.

The basic operation principle of the induction heating fixing device is the same as that of a transformer. The coil 14 corresponds to an input-side primary coil (N windings), and the fixing roller 12 corresponds to an output-side secondary coil (N winding). 1 turn). When an AC voltage V1 of about 50 to 60 Hz is applied to the primary coil (coil 14), a current I1 flows through the primary coil. The resulting magnetic flux φ flows through the core 17 forming a closed magnetic path,
The magnetic flux φ generates an induced electromotive force V2 in the secondary coil (fixing roller 12), and a current I2 flows along the circumferential direction of the fixing roller 12. Since the closed magnetic path is formed by the core 17, there is no leakage magnetic flux in principle, and the primary energy V1 × I1 and the secondary energy V2 × I2 are substantially equal.

The first part of the system in which the induction heating is performed is as follows. First, heat generation of the coil due to copper loss in the copper wire of the primary coil, that is, heat of the coil 14,
Heat generation of the coil due to copper loss in the copper wire of the secondary coil, that is, heat generation of the fixing roller 12, and thirdly, heat generation of the core 17 due to Joule heat loss and hysteresis loss generated inside the core. In the induction heating fixing device, the first and third heats are energy losses, so that these heats are suppressed as much as possible, while the second copper loss is used to heat the fixing roller 12. It is.

Here, in the present embodiment, of the core 17 forming the closed magnetic circuit, the insertion portion 17b serving as the core material of the coil 14 which directly affects the magnetic flux density of the fixing roller 12
Is formed from a silicon steel sheet laminated core while the fixing roller 12
The other portions 17a and 17c, which do not relatively contribute to the heat generation, are formed from ferrite. For this reason, the fixing roller 12
Is heated by induction heating in the same manner as in the prior art. Also,
In the other portions 17a and 17c, no leakage magnetic flux is generated by the ferrite core.

Sintered magnetic materials such as ferrite are generally
It is cheaper and lighter in weight per unit volume than silicon steel sheets. Therefore, according to the core 17 in which the portion other than the core material of the coil 14 is made of a sintered magnetic material, the core 17 can be manufactured at a lower cost and the core weight can be reduced as compared with the case where the whole core is made of a silicon steel plate. Can be lightened.
By reducing the weight of the core 17, it is possible to reduce the weight of the fixing device 128 and thus the entire image forming apparatus. In addition, the structure supporting the fixing device 128 can be simplified with the weight reduction, and in this respect, the cost of the image forming apparatus can be reduced.

Further, since ferrite has no conductivity, no eddy current loss occurs and energy loss is small. Therefore, unlike the case of the silicon steel sheet, it is not necessary to form a laminated structure. From this point, the core 17 can be manufactured more inexpensively and easily as compared with the case where the entire core is formed of a laminated iron core made of a silicon steel plate.

Moreover, ferrite has an excellent property that it can be formed into a desired shape by die molding. Therefore, the core 17 can be easily reduced in size and weight, and the cost of the core 17 can be further reduced.

In the above-described embodiment, other portions of the core 17 other than the portion forming the core of the coil 14 are formed of ferrite, but may be formed of another sintered magnetic material.

"A magnetic material having a specific gravity smaller than that of an iron core"
Is not limited to the sintered magnetic material of the embodiment,
For example, a magnetic powder solidified with a resin is also included.
In this case, the magnetic powder and the resin compound serving as an insulating and bonding material are compression-molded in a mold and heat-treated to form other parts than the part constituting the core of the coil 14 from the powder magnetic molded article.

Further, although the case where the coil 14 is disposed in the hollow portion 12a of the fixing roller 12 is shown, since the closed magnetic path is formed by the core 17, the coil 14 is inserted through the return portion 17a of the core 17. However, the fixing roller 12 can be heated by induction heating.

The fixing member is not limited to the fixing roller 12, but may be, for example, a fixing belt formed of a conductive member. The fixing belt is stretched between a pair of rollers to form a hollow shape.

In the core 17, the portion composed of the iron core and the portion composed of the sintered magnetic material such as ferrite or the molded product of the powder magnetic material may be divided into separate parts, or they may be integrated. May be formed.

[0044]

As described above, according to the present invention, among the cores forming the closed magnetic circuit, the portion forming the core material of the coil is constituted by the iron core, while the portion which does not relatively contribute to the heat generation of the fixing member is formed. Since the core is made of a magnetic material having a specific gravity smaller than that of the iron core, it is possible to reduce the weight and size of the induction heating fixing device, and to achieve a reduction in cost, by reducing the weight, size and cost of the core. Becomes Further, in the case of a sintered magnetic material or a powder magnetic material molded article, since no eddy current loss occurs, it is possible to reduce energy loss and increase heat generation efficiency of the fixing member.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a copying machine as an image forming apparatus incorporating an induction heating fixing device according to the present invention.

FIG. 2 is a configuration diagram schematically showing a main part of the induction heating fixing device shown in FIG. 1;

FIG. 3 is a sectional view showing the induction heating fixing device.

FIG. 4 is a side view showing the induction heating fixing device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Sheet (recording medium) 11 ... Toner 12 ... Fixing roller (fixing member) 13 ... Pressure roller (Pressing body) 14 ... Coil 17 ... Core 17a ... Return part (other part among cores) 17b ... Penetration Part (the part of the core that forms the core material of the coil) 17c... Connection part (the other part of the core)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H033 AA21 AA32 BA25 BB12 BB28 BE06 3K059 AD03 CD44 CD64 CD66

Claims (2)

[Claims] 1. An induction heating fixing device, comprising: a hollow fixing member formed of a conductive member; a pressure member for sandwiching a recording medium holding toner between the fixing member; A core partially inserted into the hollow portion and forming a closed magnetic circuit; and a coil wound around the core and induction-heating the fixing member, at least a core material of the coil among the core The induction heating fixing device is characterized in that a portion that forms the following is made of an iron core, and the other portion is made of a magnetic material having a lower specific gravity than the iron core. 2. The induction heating fixing device according to claim 1, wherein the coil is disposed in the hollow portion of the fixing member.