JP2001051531A - Fixing device with induction heating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fixing device with induction heating capable of appropriately securing the temperature of a conductive member coming in contact with a passing sheet necessary for melting toner and restraining temperature drop caused by the passing of the sheet without making supply power higher even when the conductive member coming in contact with the sheet is comparatively thin in thickness by making the conductive member coming in contact with the sheet generate heat of quantity enough to melt the toner simultaneously with increasing the heat capacity by providing plural conductive members formed in hollow shape. SOLUTION: By providing a 1st temperature rise member 12 and a 2nd temperature rise member 20 arranged on the outside of the member 12 and coming in contact with the sheet 10 as plural conductive members, the heat capacity is increased. By adding a resistor 25 to the member 12, the resistance value of the member 12 is changed so as to adjust the distribution of Joule heat generated in the temp. rise members 12 and 20.

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 is provided with a fixing device for fixing a toner image held on a sheet such as paper or transfer material as a recording medium to the sheet. Have been.

There are various types of fixing devices. In order to meet the recent demand for energy saving, an induction heating type fixing device having higher conversion efficiency than a fixing device using a halogen lamp as a heat source has been proposed.

In the field of a conventional induction heating type fixing device, for example, as shown in Japanese Patent Laid-Open No. 10-207265, a guide plate fixed in a non-rotating state and having a hollow shape, and supported by the guide plate. In addition, a conductive member having a hollow shape that can be fixed or moved, a part of the conductive member is inserted through the hollow portion of the conductive member, and a closed magnetic circuit core that forms a closed magnetic circuit, and wound around the closed magnetic circuit core An induction coil,
Having a current flowing through the induction coil, thereby generating a magnetic flux that generates an induced current along the circumferential direction in the conductive member,
Thus, an induction heating fixing device has been proposed in which the conductive member is induction heated.

[0005]

By the way, in the above-described conventional induction heating fixing device, the conductive member having a hollow shape having a function of contacting a sheet and conveying the sheet is as follows.
Generally, the sheet has a relatively thin shape, and therefore has a problem that the heat capacity is small, heat is taken off when the sheet passes, and the temperature drop is remarkable. Therefore, when a large number of sheets are continuously passed through the fixing device at a high speed, it becomes difficult for the conductive member to maintain a temperature required for securing the fixing quality.

On the other hand, in order to compensate for the temperature drop of the conductive member, there is a method of increasing the power supplied to the induction coil. However, increasing the power would be contrary to the demand for energy saving. .

Accordingly, an object of the present invention is to increase the heat capacity by providing a plurality of conductive members having a hollow shape,
By increasing the amount of heat generated in the conductive member in contact with the sheet to be passed, sufficient to melt the toner, even if the conductive member in contact with the sheet has a relatively thin shape, the supply power can be increased. Another object of the present invention is to provide an induction heating fixing device capable of appropriately securing a temperature required for melting a toner of a conductive member in contact with a sheet and suppressing a temperature drop due to sheet passing.

[0008]

The object of the present invention is achieved by the following means.

(1) A plurality of hollow conductive members that are fixed or moved, a pressing member that directly or indirectly adheres a recording medium holding a toner to the conductive members, A part is inserted into a hollow portion in the conductive member, a closed magnetic circuit core forming a closed magnetic circuit, and wound so as to interlink with the closed magnetic circuit core, and induces an induced current along the circumferential direction in the conductive member. An induction coil that generates a magnetic flux to be generated, a power supply that supplies AC power to the induction coil, and a resistance value changing unit that changes a resistance value of at least one conductive member of the plurality of conductive members. An induction heating fixing device comprising:

(2) The plurality of conductive members include a first conductive member, and a second conductive member disposed outside the first conductive member and in contact with the recording medium. The induction heating fixing device according to the above (1), wherein:

(3) The resistance value changing means is provided in the first
A resistor having a predetermined resistance value added to the conductive member, wherein the resistance value of the first conductive member is increased by adding the resistor. The induction heating fixing device according to the above (2).

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described.

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, a copying machine 100 includes an image scanner unit 101 for reading a document, a signal processing unit 102 for performing signal processing, and an image corresponding to the document 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 document 05 is illuminated 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. By driving the scanner motor 111, the first slider 112 and the second slider 113 mechanically move in the direction (sub-scanning direction) perpendicular to the electrical scanning direction (main scanning direction) of the line image sensor 110, Scans the entire original. At this time, the first slider 112 moves at the speed v, and the second slider 113 moves at the speed v.
/ 2.

The signal processing unit 102 includes a line sensor 109
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 contains 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 129. Note that the fixing device 12 of the present embodiment is
Reference numeral 8 denotes a low-frequency induction heating system, the configuration of which will be described later.

When the transfer to the sheet 10 is completed by the transfer roller 119, the surface of 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. After that, the photosensitive drum 116 is charged again by the charging roller 117, receives a latent image by laser light, and
And the charge in the non-development area is removed by a pre-transfer eraser (not shown).

FIG. 2 is a sectional view showing an induction heating fixing device.
FIG. 3 is a cross-sectional view illustrating a main part of the identification attachment device, and FIG. 4 is a diagram illustrating a circuit configuration of the identification attachment device.

The induction heating fixing device 128 heats and melts the toner 11 held on the sheet 10 to heat and melt the sheet 10.
The present embodiment particularly has a plurality of hollow conductive members that are fixed or moved. The plurality of conductive members are arranged on a first temperature-raising member (corresponding to a first conductive member) 12 fixed in a non-rotating state, and outside the first temperature-raising member 12. A second temperature-raising member (corresponding to a second conductive member) 20 that comes into contact with the second temperature-raising member.

The induction heating fixing device 128 is provided with a pressure roller (pressing member) for bringing the sheet 10 holding the toner into indirect contact with the first temperature raising member 12 and directly with the second temperature raising member 20. 13) and an induction coil (hereinafter simply referred to as a coil) 14 for induction heating the heating members 12 and 20.
And Here, the second temperature raising member 20 also functions to convey the sheet 10 by being interposed between the fixed first temperature raising member 12 and the pressure roller 13.

The second temperature raising member 20 is provided so as to be movable in the direction of arrow a in FIG. 2, and the pressing roller 13 is moved in the direction of arrow c in FIG. It rotates following.

The first temperature raising member 12 is a conductive hollow pipe made of, for example, a carbon steel pipe, a stainless alloy pipe or an aluminum pipe, iron, or the like, and has a sufficient pressing force from the pressing roller 13. It is formed within a range in which mechanical strength can be ensured and with a thickness that can ensure heat capacity. Both ends of the first temperature raising member 12 are fixed to a frame of a fixing unit (not shown). In particular, the first temperature raising member 12 is formed in a rectangular shape, and the surface facing the pressure roller 13 is a flat portion 21. The flat portion 21 allows the sheet 10 to move between the heating members 12 and 20 and the pressure roller 13.
The nip width or the nip area N that sandwiches is increased.

Further, the induction heating fixing device 12 of this embodiment
In particular, 8 has resistance value changing means for changing the resistance value of the first temperature raising member 12. This resistance value changing means includes:
A resistor 25 having a predetermined resistance value added to the first temperature raising member 12. As shown in FIGS. 2 and 3, the resistor 25 has a band shape along the axial direction of the first temperature raising member 12, and is provided above the first temperature raising member 12 in FIG. 2. The fixing of the resistor 25 to the first temperature raising member 12 is performed by, for example, welding. The resistance value of the first temperature raising member 12 is increased by adding the resistor 25.

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. The pressure roller 13 is pressed in a direction toward the first temperature raising member 12 by a spring material (not shown).

The second temperature raising member 20 is a conductive belt, and is formed in a thin shape by using, for example, a carbon steel pipe, a stainless alloy pipe, an aluminum pipe, iron, nickel or the like. This second heating member 20
Is wound around the outer peripheral surface of the first heating member 12 having a rectangular shape, and a driving roller (not shown) is in contact therewith. By a drive source (not shown) such as a motor connected to the drive roller, the second temperature raising member 20 rotates while using the first temperature raising member 12 as a guide plate. Further, on the outer peripheral surface of the second temperature raising member 20, a release layer coated with a fluororesin to facilitate separation of the sheet 10 and having good release properties and heat resistance to the toner is provided. Is formed.

The induction heating fixing device 128 further has a rectangular core 17 (corresponding to a closed magnetic core) forming a closed magnetic circuit.
Penetrates the inside hollow portion 23. The core 17 is a so-called iron core used for an ordinary transformer or the like, and preferably has a high magnetic permeability such as a silicon steel sheet laminated iron core.

The coil 14 is inserted by the core 17,
It is arranged inside the temperature raising members 12 and 20. Further, the coil 14 is formed by spirally winding a winding 18, and a normal single conducting wire having a fusion layer and an insulating layer on the surface is used for the winding 18. The heat insulating layer 2 is provided in the coil 14.
2 is provided so that heat generated in the temperature raising members 12 and 20 and the coil 14 is not transmitted to the core 17.

The basic operation of such a fixing device is as follows. First, from the power supply 50, for example, 50 to 60
When alternating current power of about Hz is applied to the coil 14 and energized, a magnetic flux is generated in the core 17 to generate an induced current in the temperature raising members 12 and 20 along the circumferential direction. As a result, the temperature raising members 12 and 20 are heated until the surface in contact with the sheet 10 reaches a temperature suitable for fixing (for example, 150 to 200 ° C.).
Heated by low frequency induction. The sheet 10 holding the unfixed toner 11 is conveyed from the right as shown by an arrow b in FIG.
Is fed toward the nip 19 which is a contact portion with the nip.
The sheet 10 has the heat of the heated temperature raising members 12 and 20,
The sheet is conveyed while being nipped by the nip 19 while the pressure acting from the pressure roller 13 is applied. As a result, the unfixed toner 11 is fixed on the sheet 10. Toner 1
1 is held on the side of the sheet 10 that contacts the second temperature-raising member 20. The sheet 10 that has passed through the nip 19 is subjected to the second heating member 2 by the strength of the sheet itself.
It is naturally separated from 0 and transported to the left in FIG. The sheet 10 is conveyed by a discharge roller and discharged onto a discharge tray 129.

The principle of operation of the induction heating fixing device constructed as described above is the same as that of the transformer, and the coil 14 corresponds to the primary coil (N windings) on the input side.
Reference numeral 20 corresponds to a secondary coil (one turn) on the output side. When an AC voltage V1 is applied to the primary coil (coil 14), a current I1 flows through the primary coil. The magnetic flux φ generated by this flows into the core 17 forming the closed magnetic circuit, and the magnetic flux φ causes the secondary coil (the temperature raising members 12 and 20)
, An induced electromotive force V2 is generated, and a current I2 flows along the circumferential direction of the temperature raising members 12, 20. Since the closed magnetic circuit 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 approximately equal.

In the system in which the induction heating is performed, the first part generates heat. The first part is heat generation of the coil due to copper loss in the copper wire of the primary coil, that is, the heat of the coil 14 itself. Heat generation of the coil due to copper loss in the copper wire of the coil, that is, heat generation due to induction heating of the temperature raising members 12 and 20, 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, since the first and third heats are energy losses, these heats are suppressed as much as possible, while the second copper loss is used to heat the temperature raising member 12. Things.

The induction heating fixing device 128 of this embodiment is
As described above, since the first heating member 12 and the second heating member 20 as a plurality of conductive members are provided, both of the heating members 12 and 20 are induction-heated. Of the fixing device. Therefore, since the heat capacity of the entire temperature-raising member is increased, even if the sheet 10 passes and some heat is taken from the second temperature-raising member 20, the first temperature-raising member 12 is also induction-heated. It is possible to suppress a temperature drop of the contacting second temperature raising member 20. For this reason,
In a copying machine capable of high-speed print output, the induction heating fixing device 128 of the present embodiment can sufficiently follow the sheet even if the sheet conveyance speed increases and the heat taken by the sheet from the heating member increases.

As shown in FIG. 2, the first temperature-raising member 12 usually has a low resistance value due to its relatively large thickness, and the second temperature-raising member 20 has a relatively small thickness. The resistance value increases. That is, assuming that the resistance value of the portion of the first temperature raising member 12 excluding the resistor 25 is R1, and the resistance value of the second temperature raising member 20 is R2, the relationship of R1 <R2 is established.

If the resistor 25 is neglected, as described above, the induced electromotive force V2 is generated at both of the heating members 12 and 20, and the induced electromotive force V2 is generated along the circumferential direction of the heating members 12 and 20, respectively. Currents I21 and I22 (I2 = I21 + I22) flow.

Therefore, the first and second temperature raising members 12,
The Joule heats J21 and J22 generated respectively at 20 are as follows: J21 = I2 ² · R1 (2) J22 = I2 ² · R2 (3)

Here, I22 = (R1 / R2) .I21 (4) is expressed as J21> J22 (5) in consideration of the above equation (1).

As described above, the Joule heat generated by the first temperature raising member 12 becomes large, while the Joule heat generated by the second temperature raising member 20 becomes relatively small. There is a possibility that the amount of heat applied to the toner on the sheet in contact with the member 20 becomes less than the amount of heat that can melt the toner.

Therefore, according to the present invention, by adding a resistor 25 to the heating member 12, the resistance value of the heating member 12 is changed, and the distribution of Joule heat generated in each of the heating members 12, 20 is distributed. It is intended to be adjusted.

That is, as shown in the circuit diagram of FIG. 4, the first and second heating members 12,
The Joule heats J21 'and J22' respectively generated at 20
, When the resistance value of the resistor 25 and ^{R, J21 '= I21' 2} · (R1 + R) ...... (6) J22 '= I22' 2 · R2 ...... (7) , and the addition I22 '= ((R1 + R ) / R2) · I21 ′ (8)

As can be seen from the above equations (6) to (8),
With the addition of the resistor 25 having the resistance value R, the Joule heat generated in the second temperature-raising member 20 becomes an amount of heat capable of melting the toner on the sheet in contact with the second temperature-raising member 20. It is possible to adjust the distribution of Joule heat generated by the temperature raising members 12 and 20. Further, the degree of freedom in designing the fixing device is increased.

As described above, according to this embodiment, the heat capacity can be increased by providing the first and second temperature raising members 12 and 20 as a plurality of hollow conductive members, and furthermore, the heat capacity can be increased. By adding a resistor 25 to the first heating member 12, the resistance value of the heating member 12 is changed,
By adjusting the distribution of Joule heat generated in each of the temperature raising members 12 and 20, it is possible to generate a sufficient amount of heat to melt the toner in the second temperature raising member 20 that contacts the sheet.

Therefore, even if the second temperature-raising member 20 in contact with the sheet has a relatively thin shape, the temperature required for melting the toner of the second temperature-raising member 20 in contact with the sheet can be maintained without increasing power supply. And the temperature drop due to the sheet passing can be suppressed. As a result, power saving can be achieved, and it is possible to sufficiently cope with high-speed printing of a copying machine.

FIG. 5 is a sectional view showing an induction heating fixing device according to another embodiment.

The induction heating fixing device 128a includes a rotating metal roller (corresponding to a first conductive member) 12a as a plurality of conductive members, and is stretched over the metal roller 12a and the support roller 27 to form a sheet. And a metal belt (corresponding to a second conductive member) 20a that comes into contact with the metal belt. The metal roller 12a has a resistor 2
5a is added. The sheet 10 is supported by the support rollers 27.
Metal belt 20a and pressure roller 13
Is to be sent between. Members common to those shown in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted.

Also with this induction heating fixing device 128a, the metal roller 12a and the metal belt 20a are induction heated at the same time, so that the heat capacity is increased and the metal roller 12a
Since the resistor 25a is separately added to the metal roller 1,
The heat distribution in the 2a and the metal belt 20a can be adjusted, and the same effect as in the above-described embodiment can be obtained.

The present invention is not limited to the above embodiment, and it is needless to say that those skilled in the art can appropriately change the technical scope of the present invention.

For example, as the resistance value changing means for changing the resistance value of the first temperature raising member 12, a belt-shaped resistor 25 is added to the first temperature raising member 12, but the shape and size of the resistor 25 are changed. It can be changed. Further, for example, the method of adding the resistor 25 to the first temperature raising member 12 is not limited to welding, but may be a mechanical connection or a first temperature raising member 1.
Various methods can be adopted, such as providing a hole or a concave groove in 2, and melting and filling the resistor 25. Furthermore, it is also possible to change the resistance value by providing a cutout such as a concave groove in the first temperature raising member 12 and changing the cross-sectional area.

Also, a description has been given of a case where two conductive members are simultaneously subjected to induction heating. However, a configuration may be employed in which three or more conductive members are simultaneously subjected to induction heating.

[0050]

As described above, according to the present invention,
By providing a plurality of hollow conductive members,
The heat capacity can be increased, and the resistance value changing means changes the resistance value of the conductive member, and adjusts the distribution of Joule heat generated in each of the plurality of conductive members,
It is possible to generate a sufficient amount of heat to melt the toner in the conductive member in contact with the sheet to be passed.

Therefore, even if the conductive member in contact with the sheet has a relatively thin shape, the temperature required for melting the toner of the conductive member in contact with the sheet can be appropriately secured without increasing power supply. In addition, a temperature drop due to sheet passing can be suppressed. As a result, power saving can be achieved, and it is possible to sufficiently cope with high-speed printing of a copying machine.

[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 sectional view showing the induction heating fixing device.

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

FIG. 4 is a diagram showing a circuit configuration of the induction heating fixing device.

FIG. 5 is a cross-sectional view illustrating an induction heating fixing device according to another embodiment.

[Explanation of symbols]

 Reference Signs List 10: sheet (recording medium), 11: toner, 12, 12a: first heating member (first conductive member), 13: pressure roller (pressure member), 14: induction coil, 17: core ( Closed magnetic circuit core), 20, 20a: second heating member (second conductive member), 23: hollow portion, 25, 25a: resistor (resistance changing means), 50: power supply, 128, 128a: fixing apparatus.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Ryo Takasu, Inventor F-term (reference) 2H033 AA32 BA11 BA25 BE03 BE06 3K059 AA08 AB00 AB19 AB23 AB28 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka International Building Minolta Co., Ltd. AC09 AC10 AC37 AC44 AC73 AD02 AD03 AD07 AD15 BD21 CD14 CD73 CD77

Claims (3)

[Claims] A plurality of conductive members having a hollow shape that are fixed or movable; a pressing member that directly or indirectly adheres a recording medium holding a toner to the conductive members; A part is inserted into the hollow part in the conductive member, and a closed magnetic path iron core forming a closed magnetic path is wound so as to interlink with the closed magnetic path iron core to generate an induced current along the circumferential direction in the conductive member. An induction coil that generates a magnetic flux to be applied, a power supply that supplies AC power to the induction coil, and a resistance value changing unit that changes a resistance value of at least one of the plurality of conductive members. An induction heating fixing device, characterized in that: 2. The plurality of conductive members include a first conductive member, and a second conductive member disposed outside the first conductive member and in contact with the recording medium. The induction heating fixing device according to claim 1, wherein: 3. The resistance change means is a resistor having a predetermined resistance value added to the first conductive member, and the first conductive member is provided with the resistor. The induction heating fixing device according to claim 2, wherein the resistance value is increased by doing so.