JP2001109289A - Fixing device with induction heating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device with induction heating capable of preventing the occurrence of fixing defect, the low temperature offset, and the high temperature offset by adjusting the heat generation distribution in a fixing member. SOLUTION: The fixing belt 30 as the fixing member, is provided with distributing means 40 for adjusting the heat generation distribution the belt. This distributing means, is constituted by forming plural areas S1, S2, S3 and S4 respectively provided with different resistance value on the fixing belt. The areas S2 and S3 respectively provided with the lower resistance value, is arranged on both end part areas where the temperature falling is easier than the center area on the fixing belt.

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, for example, an electrophotographic copying machine, a printer, a facsimile, and the like. More specifically, the present invention uses a low-frequency induction heating to fix a toner image on a recording medium. It relates to a fixing device.

[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 Application Laid-Open No. H10-207265 discloses a hollow fixing member supported by a guide plate and formed of a conductive member, a part of which is inserted into a hollow portion of the fixing member, and a magnetic field is closed. An induction heating fixing device having a core forming a path and an induction coil wound so as to link the core is described. The fixing member has a thin film shape and also has a function of conveying a sheet by moving along a guide board. 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 member, thereby causing the fixing member to generate Joule heat.

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

[0008]

However, since the fixing member to be induction-heated is relatively thin and has a small heat capacity, the toner or sheet is apt to lose heat when the sheet passes. Further, in the end region in the width direction orthogonal to the moving direction of the fixing member, heat is significantly released to the atmosphere even when the sheet is not passed. For this reason, the temperature of the end region is lower than that of the central region of the fixing member. With this temperature drop,
In the end region of the fixing member, there is a possibility that a fixing defect or a low-temperature offset occurs.

It is conceivable to set the temperature of all the regions of the fixing member slightly higher in anticipation of the temperature drop in the end region. However, not only does this contradict the demand for energy saving but also has the following problems. In other words, when a sheet having a size smaller than the maximum size that can be passed is continuously passed, the temperature of the end area where the sheet is not passed becomes too high, and then the sheet having a larger size is passed. There is a possibility that high-temperature offset occurs when the paper is made.

The low temperature offset refers to a phenomenon in which the heat of the fixing member is not sufficiently transmitted to the interface between the toner and the sheet, and the toner on the sheet is transferred to the fixing member. The high-temperature offset refers to a phenomenon in which toner is separated on both sides of the fixing member and the sheet due to excessive supply of heat to the toner, lowering the viscosity of the toner, and reducing the cohesive force between the toners.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems associated with the above-mentioned prior art, and is capable of adjusting the distribution of heat generation in a fixing member and preventing the occurrence of defective fixing, low-temperature offset and high-temperature offset. It is intended to provide a device.

[0012]

The present invention for achieving the above object is constituted as follows.

(1) A hollow fixing member formed of a conductive member, a pressure member for sandwiching a recording medium holding toner between the fixing member, and a part in a hollow portion of the fixing member Is inserted and forms a closed magnetic path, and a coil wound around the core and induction-heats the fixing member, wherein the fixing member is configured to generate heat in the fixing member. The induction heating fixing device is characterized by having a distribution means for adjusting the temperature.

(2) The induction heating fixing device according to the above (1), wherein the distribution unit is formed by forming at least two regions having different resistance values on the fixing member. .

(3) The area having the smaller resistance value among the at least two areas is disposed in a portion of the fixing member where the temperature is more likely to drop than in other portions. 2. An induction heating fixing device according to (1).

(4) The induction heating fixing device according to any one of (1) to (3), wherein the fixing member has a belt shape.

[0017]

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 an 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 structural view showing the induction heating fixing device shown in FIG. 1, and FIG. 3 is a sectional view showing a main part of the identification attaching device.

The induction heating fixing device 128 nips a moving hollow fixing belt (corresponding to a fixing member) 30 formed of a conductive member and the sheet 10 holding toner between the fixing belt 30. 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 belt 30 are provided. Fixing belt 30
Is provided so as to be movable in the direction of arrow a in FIG.
It also functions as a conveying member for conveying 0. Pressure roller 1
Reference numeral 3 rotates following the movement of the fixing belt 30 and the sheet 10.

On the outer peripheral surface of the fixing belt 30, a sheet 1
In order to easily separate 0, a release layer having good release properties and heat resistance to the toner is formed by coating with a fluororesin.

Inside the fixing belt 30, a hollow guide board 34 is arranged. Both ends of the guide panel 34
It is fixed to a frame of a fixing unit (not shown).
The fixing belt 30 is wound around the outer peripheral surface of the guide board 34, and a driving roller (not shown) is in contact with the fixing belt 30. The fixing belt 30 is rotated and moved along the outer peripheral surface of the guide board 34 by a driving source (not shown) such as a motor connected to the driving roller.

The guide plate 34 in the illustrated example is formed in a rectangular shape, and the fixing belt 30 moving along the guide plate 34
A flat portion 35 is formed in a portion facing the pressure roller 13. The flat portion 35 enlarges a nip region N for nipping the sheet 10 between the fixing belt 30 and the pressure roller 13. The guide board 34 is formed of an insulating material such as a heat-resistant resin or glass so as not to generate an induced current. Even if the guide plate 34 is formed in a triangular shape, for example, the flat portion 35 can be formed on the fixing belt 30 at a portion facing the pressure roller 13.

The pressure roller 13 includes a shaft core 15 and a silicon 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. The pressure roller 13 is pressed in a direction toward the fixing belt 30 by a spring material (not shown).

The core 17 has a rectangular shape, and a part of the core 17 has a hollow portion 30 a in the fixing belt 30 and the guide plate 3.
4 penetrates the hollow part. The core 17 is an iron core used for an ordinary transformer or the like, and preferably has a high magnetic permeability such as a laminated iron core made of a silicon steel plate.

The coil 14 is formed by spirally winding a winding 18. The coil 14 is inserted through the core 17 and disposed inside the fixing belt 30. Coil 1
When a current flows through the fixing belt 4, a magnetic flux that generates an induced current in the fixing belt 30 along the circumferential direction is generated. As the winding 18,
An ordinary single conductor having a fusion layer and an insulating layer on the surface is used. In addition, the heat insulation layer 22 is provided in the coil 14,
The heat generated by the fixing belt 30 and the coil 14 is not transmitted to the core 17.

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 belt 30 is adjusted to a temperature suitable for fixing by low frequency induction heating (for example, 150 to 150 Hz). (200 ° C.). The sheet 10 holding the unfixed toner 11 is conveyed from the right as indicated by an arrow b in FIG. 2 and is sent toward a nip 19 which is a contact portion between the fixing belt 30 and the pressure roller 13. The sheet 10 is conveyed while being nipped by the nip 19 while the heat of the heated fixing belt 30 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 held on the side of the sheet 10 that contacts the fixing belt 30. The sheet 10 that has passed through the nip 19 is naturally separated from the fixing belt 30 by the strength of the sheet itself, and is conveyed leftward in FIG. The sheet 10 is conveyed by a discharge roller and discharged onto a discharge tray 130.

The basic operation principle of the induction heating fixing device is the same as that of the transformer. The coil 14 corresponds to the primary coil on the input side (N windings), and the fixing belt 30 corresponds to the secondary coil on the output side. 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 belt 30), and a current I2 flows along the circumferential direction of the fixing belt 30. 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.

In the system in which the induction heating is performed, the first part generates heat, namely, heat of the coil due to copper loss in the copper wire of the primary coil, that is, heat of the coil 14, and second,
Heat generation of the coil due to copper loss in the copper wire of the secondary coil, that is, heat generation of the fixing belt 30, and thirdly, heat generation of the core 17 due to Joule heat loss and hysteresis loss generated inside the core. The induction heating fixing device suppresses the heat generation as much as possible because the first and third heats cause an energy loss, while causing the fixing belt 30 to generate heat using the second copper loss. It is.

The hollow fixing member, in which an induced current is generated, has a small heat capacity due to its relatively thin thickness, and further has a remarkable heat radiation from an end portion in the width direction. The temperature of the part area is likely to drop.

Therefore, in the present embodiment, as shown in FIG. 3, the fixing belt 30 has distribution means 40 for adjusting the heat distribution in the fixing belt 30. The distribution means 40 includes a plurality of areas S1, S2 having different resistance values.
2, S3 is formed on the fixing belt 30. Among the plurality of regions S1, S2, S3, the regions S2, S3 having a smaller resistance value are arranged in a portion of the fixing belt 30 where the temperature tends to drop more than other portions. By the distribution means 40, the temperature distribution in the fixing belt 30 can be arbitrarily adjusted or set.

More specifically, the fixing device 12 shown in FIG.
Numeral 8 conveys the sheet 10 with reference to the center in the width direction of the fixing belt 30 (the direction along the arrow W in FIG. 3).
That is, regardless of the sheet size, the conveyance center of the sheet 10 coincides with the center in the width direction of the fixing belt. As shown in FIG. 3, the fixing belt 30 includes a first region S1 located at the center along the width direction, and second and third regions S2 and S3 located on both left and right sides of the first region S1 in the drawing. It is divided into three areas. The portion of the fixing belt 30 where the temperature is easier to drop than other portions is the second, located at the end,
These are the third areas S2 and S3. Second and third regions S2, S3
Is smaller than the first region S1.

When the sheet 10 is conveyed on the basis of one end of the fixing belt in the width direction regardless of the sheet size, the fixing belt may be divided into only two areas.

By changing the thickness of the conductive member,
The resistance value of each area in the fixing belt 30 can be different. However, in such a configuration, it is difficult to make the nip pressure uniform along the nip portion 19. Therefore, in the present embodiment, the thickness of each of the first to third regions S1 to S3 is made uniform, and the type of the conductive member that is a material for forming each region is changed, so that the resistance value of each of the regions S1 to S3 is changed. Are different. Specifically, for example, nickel (Ni) is used for a conductive member that is a material for forming the first region S1,
For example, a stainless alloy (SUS) is used as a conductive member that is a material for forming the third regions S2 and S3. Each area S1
The conductive member, which is a material for forming S3, is connected by means such as rolling to be formed on one fixing belt 30. The resistance of nickel is Ra, the resistance of stainless steel is Rb
When represented by, the relationship of Ra> Rb is established in terms of physical properties. For example, the resistance value Ra is about 7 mΩ, and the resistance value Rb is about 3 mΩ.

FIG. 4 is an equivalent circuit diagram of the induction heating fixing device according to the embodiment.

As shown in the drawing, it is assumed that the induction heating fixing apparatus according to the present embodiment has three loops forming a closed loop one turn at a time on the secondary side. Since each loop is one turn, the secondary voltage V2 = (primary voltage V1) / (induction coil N)
(V) secondary voltage V2 is generated in each loop.

Then, the following Ia, I
A current b flows.

Ia = V2 / Ra and Ib = V2 / Rb.

The copper loss that causes the fixing belt 30 to generate heat is as follows: Pa = Ia ² · Ra (W) = V ^{2 2} / Ra Pb = Ib ² · Rb (W) = V ^{2 2} / Rb

In order to raise the temperatures of the second and third regions S2 and S3 more than the first region S1, the distribution of heat generation in the fixing belt 30 may be adjusted so that Pa <Pb.
Therefore, if the resistance value Rb of the second and third regions S2 and S3 is smaller than the resistance value Ra of the first region S1, the power distribution to the end region increases, and the temperature of the end region becomes higher than that of the central region. It rises slightly. As a result, an excessive temperature drop in the end region of the fixing belt 30 does not occur.

Accordingly, even in the fixing belt 30 in which the temperature in the end portion region is apt to decrease due to the thin shape,
Since it is desired that the temperature of the end region is excessively lowered with respect to the center region, fixing failure and low-temperature offset do not occur in the end region.

Further, since it is not necessary to set the temperature of the central region slightly higher in anticipation of the temperature drop in the end region, it meets the demand for energy saving. In addition, even if a sheet having a size smaller than the maximum size that can be passed is continuously passed, the temperature of the end region does not become too high. Therefore, even if a large-size sheet is subsequently passed, no high-temperature offset occurs in the end region.

As described above, in the induction heating fixing device 128 according to this embodiment, the distribution of heat generation can be adjusted by changing the resistance value at a desired portion of the fixing belt 30.
The temperature distribution of the fixing belt 30 can be arbitrarily adjusted, and it is possible to prevent the occurrence of defective fixing, low-temperature offset, and high-temperature offset.

The combination of the conductive members is not limited to the combination of the above-described embodiments. For example, carbon steel, aluminum, iron, or the like may be used as long as a plurality of regions having different resistance values can be formed. can do.

Further, the fixing belt is not limited to the form wound around the guide board 34, but may be a form wound around a drive roller and a plurality of guide rollers instead of the guide board 34. In this case, the rotation of the driving roller moves the fixing belt.

Further, the fixing member is not limited to the fixing belt 30, but the present invention can be applied to a hollow fixing roller formed of a conductive member.

Although the form in which the fixing member moves is shown, the present invention is also applicable to a fixed fixing member.
In this case, a movable belt may be interposed between the fixing member and the pressure roller. The conveyor belt is preferably formed of an insulating material so that no induced current is generated.

As described above, the induction heating fixing device can take various forms. Here, by taking into account the difference in the temperature rise characteristic and the temperature drop of the fixing member and selecting the area, location, value, etc. of the region in which the resistance value is changed, the temperature distribution in the fixing member can be changed in each form (fixing). By adjusting the distribution to an optimum distribution according to the system, it is possible to prevent the occurrence of fixing failure, low-temperature offset and high-temperature offset. The fact that the present invention can be applied to a wide range of induction heating fixing devices is one of the features of the present invention.

[0055]

As described above, according to the induction heating fixing device of the present invention, the distribution of heat in the fixing member can be arbitrarily adjusted by adjusting the distribution of heat generated in the fixing member by the distribution means, thereby making it possible to adjust the temperature distribution of the fixing member. It is possible to prevent the occurrence of offset and high-temperature offset.

In particular, when the fixing member has a belt shape, the above effect is remarkably exhibited because the fixing member is thin, has a small heat capacity, and has a large heat radiation in the end region.

[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 showing the induction heating fixing device shown in FIG. 1;

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

FIG. 4 is an equivalent circuit diagram of the induction heating fixing device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Sheet (recording medium) 11 ... Toner 13 ... Pressure roller (Pressure body) 14 ... Coil 17 ... Core 30 ... Fixing belt (fixing member) 40 ... Distribution means S1 ... 1st area | region of fixing belt S2, S3 ... Second and third areas of fixing belt (area with smaller resistance value)

Claims (4)

[Claims] 1. A fixing member having a hollow shape formed of a conductive member, a pressure member for sandwiching a recording medium holding toner between the fixing member, and a part in a hollow portion of the fixing member. In an induction heating fixing device having a core inserted and forming a closed magnetic path, and a coil wound around the core and induction-heating the fixing member, the fixing member distributes heat generated in the fixing member. An induction heating fixing device comprising a distribution unit for adjusting. 2. The induction heating fixing device according to claim 1, wherein the distribution unit is configured by forming at least two regions having different resistance values on the fixing member. 3. The fixing member according to claim 2, wherein a region having a smaller resistance value among the at least two regions is disposed in a portion of the fixing member where the temperature is more likely to drop than other portions. Induction heating fixing device. 4. The induction heating fixing device according to claim 1, wherein the fixing member has a belt shape.