JPH0863022A - Induction heating and fixing device - Google Patents

Abstract

PURPOSE: To make the temperature distribution uniform along the rotation axis of the fixing roller and to realize uniform fixability along the fixing roller even if a gap is installed between coils by disposing a coil so as to produce a magnetic flux in the direction opposite to that of the magnetic flux produced by another coil neighboring with the coil. CONSTITUTION: When a high-frequency current is made to flow in the coil 22, a magnetic flux 31a orthogonal to the longitudinal axial direction of the fixing roller 10 is produced from the core 23. The magnetic flux 31b having reached the fixing roller 10 made of conductive material bends along the fixing roller 10 and becomes magnetic flux 31c which passes inside the peripheral face of the fixing roller 10 with a proportion depending on the relative permeability of the conductor. The magnetic flux concentrated on the peripheral face of the fixing roller 10 has a maximum density in the part which opposes the coil 22. Affected by this concentrated magnetic flux 31c, an induced eddy current which generates a magnetic flux being opposite to the direction of the magnetic flux 31c and disturbing the flux 31c is generated inside the wall face of the fixing roller. This induced current is converted into Joule heat by the skin resistance of the fixing roller 10 to generate heat in the fixing roll 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying machine,
The present invention relates to a fixing device used in printers, facsimiles, and the like, and more specifically, to a fixing device that fixes a toner image on a recording medium by using dielectric heating.

[0002]

2. Description of the Related Art An electrophotographic copying machine or the like is provided with a fixing device for fixing a toner image transferred onto a sheet such as recording paper or a transfer material as a recording medium onto the sheet. This fixing device has, for example, a fixing roller that heat-melts the toner on the sheet, and a pressure roller that presses the fixing roller to sandwich the sheet. The fixing roller is formed in a cylindrical shape, and a heating element is held by a holding means on the central axis of the fixing roller. The heating element is composed of, for example, a halogen lamp or the like, and generates heat when a predetermined voltage is applied. Since this heating element is located on the central axis of the fixing roller, the heat generated from the heating element is radiated uniformly to the inner wall of the fixing roller, and the temperature distribution of the outer wall of the fixing roller becomes uniform in the circumferential direction. The outer wall of the fixing roller is heated until its temperature reaches a temperature suitable for fixing (for example, 150 to 200 ° C.).
In this state, the fixing roller and the pressure roller rotate in opposite directions while slidingly contacting each other, and sandwich the sheet to which the toner is attached. At the sliding contact portion (hereinafter referred to as a nip portion) between the fixing roller and the pressure roller, the toner on the sheet is melted by the heat of the fixing roller and is fixed on the sheet by the pressure applied from both rollers. After the toner is fixed, the sheet is conveyed by the discharge rollers and discharged onto the discharge tray as the fixing roller and the pressure roller rotate.

In the above fixing device provided with a heating element composed of a halogen lamp or the like, after the power is turned on,
It took a relatively long time for the temperature of the fixing roller to reach a predetermined temperature suitable for fixing. During that time, the user cannot use the copying machine and is forced to wait for a long time. On the other hand, when the heat capacity of the fixing roller is increased in order to shorten the waiting time and improve the operability for the user, the power consumption of the fixing device increases, which causes a problem of energy saving. .

Therefore, in order to increase the value of a product such as a copying machine, energy saving (low power consumption) of the fixing device is performed.
At the same time, it has become more important and more important to achieve both the improvement of user operability (quick print). Along with this, it has become necessary to improve not only the toner fixing temperature and the heat capacity of the fixing roller, which have been conventionally performed, but also the electric-heat conversion efficiency.

An induction heating type fixing device has been proposed as a device satisfying such a request (Japanese Patent Laid-Open No. 58-17).
8385). In this apparatus, an open magnetic circuit iron core in which coils are concentrically wound is arranged inside a fixing roller made of a metal conductor. Then, a high-frequency current is passed through the coil close to the inner surface of the fixing roller, an induced eddy current is generated in the fixing roller by the high-frequency magnetic field generated thereby, and the fixing roller itself causes Joule heat generation by the skin resistance of the fixing roller itself. Has become.

This induction heating has the following advantages over other heating methods. First of all, the temperature rises faster than indirect heating such as near-infrared heating of a halogen lamp, and less heat is generated and transferred to parts other than the fixing roller. Further, there is no loss corresponding to the light leakage of the halogen lamp. Second, rather than surface heating with a solid resistance heating element on the surface of the fixing roller,
Due to the skin effect peculiar to electromagnetic induction, heat generation efficiency is good,
Further, since there is no sliding contact, the reliability of the fixing device is high for a long time. Third, there is less heat transfer loss due to contact resistance than heating with a film belt and solid resistance heating element,
Further, since the temperature of the heat generating surface can be easily detected, the temperature controllability is excellent.

In recent years, development of low fixing temperature toner has progressed, and due to the spread and cost reduction of inverter circuit switching elements in high frequency power supplies for home appliances, it has become possible to realize an induction heating fixing device having the above characteristics. is there.

[0008]

In the conventional general induction heating fixing device, as described in JP-A-59-33785 and JP-A-59-33788, the fixing roller is built in the fixing roller. As a coil for generating an induced current in the roller, a single coil long in the direction along the rotation axis of the fixing roller has been used. However, it has not been easy to manufacture a long single coil.

Here, in consideration of facilitating the manufacture of the coils, it is possible to arrange a plurality of short coils along the direction of the rotation axis of the fixing roller, but if there is a gap between adjacent coils. However, that portion or area becomes a non-heat generating portion or area, and there is a possibility that the fixing property along the rotation axis direction of the fixing roller cannot be made uniform. Therefore, in order to make the fixing property uniform, it is necessary to suppress the gap between the coils. However, if only the gap is made small, the length of the coil is lengthened and the manufacturing is facilitated. The result will be contrary.

Therefore, the present invention is an induction heating fixing device in which a plurality of coils for generating an induction current in a fixing roller are arranged along the rotation axis direction of the fixing roller in consideration of facilitating manufacture of the coil. Therefore, even if a certain gap is provided between the coils, the temperature distribution along the rotation axis direction of the fixing roller can be made uniform, and therefore, the uniform fixing property can be realized along the rotation axis direction of the fixing roller. An object is to provide a heat fixing device.

[0011]

The present invention for achieving the above object is a fixing device for fixing a toner image formed on a recording medium to the recording medium, the fixing device being formed of a conductive member. A roller and a plurality of coils arranged inside the fixing roller along the rotation axis direction to generate an induced current in the fixing roller, and at least one coil of the plurality of coils is The induction heating fixing device is arranged so as to generate a magnetic flux in the opposite direction to the magnetic flux generated by another coil adjacent to the coil.

[0012]

In the induction heating fixing device constructed as described above, when an alternating current is applied to the coil, an induction current is generated in the fixing roller to heat the fixing roller.

Further, since at least one coil in the fixing roller generates a magnetic flux in the opposite direction to the other coils, a new magnetic flux is generated between these adjacent coils in accordance with the Coulomb law regarding magnetic poles. . This magnetic flux generates an induced current in the fixing roller, so that a new heat generating portion or area is generated between the coils, and the fixing roller generates heat. Therefore, even if a certain amount of gap is provided between the coils, it is possible to suppress the generation of non-heat generating points or regions, and to make the temperature distribution along the rotation axis direction of the fixing roller uniform, thereby preventing the deterioration of the fixing property. As a result, it is possible to realize uniform fixability along the rotation axis direction of the fixing roller.

Further, since a plurality of coils are arranged in parallel in the rotation axis direction, the coil can be manufactured more easily than when one coil long in the rotation axis direction is used.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An induction heating fixing device according to an embodiment of the present invention will be described below with reference to the drawings. 1 is a sectional view showing an induction heating fixing device to which the present invention is applied, FIG. 2 is a perspective view showing the fixing roller shown in FIG. 1, and FIG. 3 is a perspective view showing coils and cores in the fixing roller. FIG. 4 is an exploded perspective view showing the internal structure of the holder unit, and FIG. 5 is a perspective view showing the coil assembly.

As shown in FIG. 1, an induction heating fixing device incorporated in a printer or the like has a fixing roller 10 rotatably driven in the direction of arrow a, and a fixing roller provided in pressure contact with the fixing roller 10. The pressure roller 11 is driven to rotate with the rotation of 10. As shown in FIG.
The fixing roller 10 is a hollow conductor pipe, and a plurality of coil assemblies 12 for generating an induced current in the fixing roller 10 are arranged inside the fixing roller 10 along the rotation axis direction (cylindrical axis direction). It is set up. In particular, in this embodiment, the coil assemblies 12 are arranged so that the magnetic flux generating directions of the adjacent coil assemblies 12 are opposite to each other. Each coil assembly 12 has a holder 24
The holder unit 13 is held by the.

As shown in FIG. 2, the fixing roller 10 has sliding bearings 10a formed at both ends thereof and is rotatably attached to a fixing unit frame (not shown).
Further, the fixing roller 10 has a drive gear (not shown) fixed to one end thereof, and is rotationally driven by a drive source (not shown) such as a motor connected to the drive gear. Further, the holder unit 13 is housed inside the fixing roller 10 with a minimum gap of a predetermined dimension maintained between the holder unit 13 and the inner peripheral surface of the fixing roller 10. The holder unit 13 is fixed to the fixing unit frame and is non-rotating.

The sheet 14 to which the unfixed toner image is transferred is conveyed from the left side in FIG. 1, and is fed toward the nip portion between the fixing roller 10 and the pressure roller 11. The sheet 14 is conveyed through the nip portion while the heat of the fixing roller 10 heated by the principle described later and the pressure applied from both rollers 10 and 11 are applied. As a result, the unfixed toner is fixed, and a fixed toner image is formed on the sheet 14. Sheet 1 that passed through the nip
4 is naturally separated from the fixing roller 10, or
As shown in FIG. 1, the separation claws 15 and the separation guides provided so that the front ends of the fixing rollers 10 are in sliding contact with each other are forcibly separated from the fixing roller 10 and are conveyed rightward in FIG. The sheet 14 is conveyed by a paper discharge roller (not shown) and discharged onto the paper discharge tray.

A temperature sensor 16 for detecting the temperature of the fixing roller 10 is provided above the fixing roller 10. The temperature sensor 16 is in pressure contact with the surface of the fixing roller 10 so as to face the side surface of the coil 22 across the fixing roller 10. The temperature sensor 16 is composed of, for example, a thermistor. While the temperature of the fixing roller 10 is detected by the thermistor 16, the energization of the coil 22 is controlled so that the temperature of the fixing roller 10 becomes the optimum temperature.

A thermostat 17 is further provided above the fixing roller 10 as a safety mechanism when the temperature rises abnormally. This thermostat 17 is used for the fixing roller 1.
It is pressed against the surface of No. 0, and when the temperature reaches a preset temperature, the contact is opened and the coil 22 is de-energized. This prevents the fixing roller 10 from reaching a temperature higher than a predetermined temperature.

The fixing roller 10 is formed of a conductive member such as a carbon steel pipe, a stainless alloy pipe, or an aluminum alloy pipe, and the outer peripheral surface thereof is coated with a fluororesin, and a heat-resistant release layer is formed on the surface. . The fixing roller 10 is more preferably formed of a conductive magnetic member. The pressure roller 11 has a silicon rubber layer 19, which is a surface-releasing heat-resistant rubber layer, formed around a shaft core 18. The sliding bearing 10a and the separating claw 15 are made of heat resistant sliding engineering plastic or the like.

As shown in FIG. 5, the coil assembly 12 has a square-shaped bobbin 20 having a through hole 20a formed in the center thereof, and a copper wire 21 is quasi-aligned around the bobbin 20. The coil 22 is formed by winding a plurality of continuous windings (terminal treatment and connection can be omitted). A core 23 is inserted into the through hole 20 a of the bobbin 20 so as to be orthogonal to the copper wire 21 of the coil 22. The bobbin 20 may be formed of, for example, ceramic or heat-resistant insulating engineering plastic, and the coil 22 is preferably a single or litz copper wire having a fusion layer and an insulating layer on the surface. The core 23 is, for example, a ferrite core or a laminated core.

As shown in FIG. 3, the coil assembly 1
2 is such that the copper wire 21 wound around the bobbin 20 is along a plane parallel to the rotation axis of the fixing roller 10, so that a magnetic flux is generated in a direction orthogonal to the rotation axis direction of the fixing roller 10, that is, The core 23 is arranged in a direction orthogonal to the rotation axis.

Further, in this embodiment, FIGS.
And a plurality of coil assemblies 1 as shown in FIG.
2 is a holder 24 such that the core 23 is substantially parallel to the conveying direction of the sheet 14 and the coil 22 is substantially opposite to the pressure roller 11.
Are arranged side by side in the axial direction of the fixing roller 10. An insulating film 28 is arranged on the outer peripheral surface of the coil 22. The insulating film 28 is made of, for example, a heat-resistant insulating resin such as polyimide or polyphenylene sulfide. The holder 24 has a holder stay 24a and a holder cover 24b attached to the holder stay 24a, and each is made of heat-resistant insulating engineering plastic. As shown in FIG. 4, the holder stay 24 a and the holder cover 24
A recess 29 for holding the coil assembly 12 and the like is formed on the inner surface of b, and fitting portions 25 for fixing to the fixing unit frame are provided at both ends.
In the holder unit 13, for example, the coil 22 is inserted into the recess 29 provided in the holder stay 24a, the core 23 is inserted into the through hole 20a of the bobbin 20, the insulating film 28 is arranged on the outer peripheral surface of the coil 22, and the holder cover 24b is provided. Is attached to the holder stay 24a to be assembled. The plurality of coils 22 are connected in series in the holder 24, and the coils 22 are connected to both ends (or one end) of the holder unit 13.
A connector terminal 30 to which the terminal is connected is provided, and is connected to a high frequency power source 35, which will be described later, which supplies a high frequency current through the terminal 30. The holder unit 13 has an outer diameter slightly smaller than the inner diameter of the fixing roller 10 so that a gap is formed between the holder unit 13 and the inner wall of the fixing roller 10.

FIG. 6 is an explanatory view for explaining the heating principle of the fixing roller 10 in the induction heating fixing device to which the present invention is applied. High frequency (several kHz to several tens of kHz) in the coil 22
When the current is applied, a magnetic flux 31a orthogonal to the longitudinal axis direction of the fixing roller 10 is generated from the core 23, as shown in the figure, in accordance with "Ampere's right-hand screw law". This magnetic flux 31a is also a high frequency magnetic flux.

Magnetic flux 3 reaching the fixing roller 10 made of a conductor
1b is a magnetic flux 31c that bends along the fixing roller 10 and passes through the circumferential surface of the fixing roller 10 at a ratio depending on the relative magnetic permeability of the conductor. The magnetic flux 31c concentrated on the peripheral surface of the fixing roller 10 has the maximum density in the portion facing the coil 22.

Due to the action of the concentrated magnetic flux 31c, a vortex-shaped induced current is generated in the wall surface of the fixing roller 10 according to the "Lenz's law" so as to generate a magnetic flux in the opposite direction to the magnetic flux 31c that obstructs the magnetic flux 31c. To do. This induced current is converted into Joule heat by the skin resistance of the fixing roller 10, so that the fixing roller 10 generates heat.

In this structure, the magnetic flux density in the circumferential surface becomes maximum at points P and R of the fixing roller 10, and conversely,
It becomes minimum at points Q and S. Therefore, the induced current density also has a similar tendency, so that the heat generation of the fixing roller 10 is not uniform in the circumferential surface, and the portions 32a, 3 surrounded by the two-dot chain line are shown.
2b locally generates heat. This locally heated portion 3
2a and 32b are fixing rollers 10 as shown in FIG.
Corresponding to the upper and lower regions of. Therefore, the nip portion and one heat generating portion (area) overlap at least in part. Further, the thermistor 16 is in contact with the other heat generating portion (region), and the thermostat 17 is also arranged so as to be in contact with or close to it. The thermistor 1
The mounting position of 6 may be either the upper part or the lower part of the fixing roller 10, but in the illustrated embodiment, it is mounted outside the upper part. If the thermistor 16 is small, it may be mounted inside the upper part or the lower part of the fixing roller 10.

FIG. 7 is a block diagram of a circuit for controlling the temperature of the fixing roller 10 by supplying a high frequency current to the induction heating coil 22, and FIG. 8 is a block diagram showing an inverter circuit.

The high-frequency current is generated by rectifying the alternating current of the commercial power source 35 by the rectifying circuit 36 and converting it into a high frequency by the self-excited inverter circuit 37. The current to the induction heating coil 22 is supplied through the thermostat 17 pressed against the surface of the fixing roller 10, and when the surface temperature of the fixing roller 10 reaches a preset abnormal temperature, the thermostat 17 causes the current path to flow. It is supposed to be disconnected.
The control circuit 38 is composed of a microprocessor, a memory and the like, and outputs an ON / OFF signal to the drive circuit 40 in the inverter circuit 37 while monitoring the temperature of the fixing roller 10 based on the potential of the thermistor 16 to control the temperature. I do. The inverter circuit 37 frequency-converts the direct current from the rectifier circuit 36 into a high frequency current and supplies the high frequency current to the coil 22.

As shown in FIG. 8, an inverter circuit 37
Is a control signal (heating signal) issued from the control circuit 38.
When is turned on, the drive circuit 40 first turns on the switching element 41 including, for example, a transistor, an FET, or an IGBT, whereby a current flows through the induction heating coil 22. On the other hand, the current detection circuit 42 sends a signal to the drive circuit 40 so as to turn off the switching element 41 when detecting that the predetermined current value IP has been reached. The waveform of the drain current ID detected by the current detection circuit 42 is shown in FIG. When the switching element 41 is turned off, the induction heating coil 22 and the resonance capacitor 44
Resonant current flows between and. Then, the voltage detection circuit 43
Detects that the drain voltage VD on the induction heating coil 22 side of the switching element 41 has dropped to around 0 V due to resonance, and sends a signal to the drive circuit 40 to turn on the switching element 41 again. Hereinafter, by repeating this switching cycle, a high frequency current is passed to the induction heating coil 22. The waveform of the voltage VD detected by the voltage detection circuit 43 is shown in FIG. 9A, and the ON / OFF signal of the switching element 41 (for example, the gate ON / OFF signal in the case of FET) is shown in FIG. 9C. Show.

Next, the arrangement of the coil 22 will be described.

Before explaining the arrangement state in the present embodiment, first, the arrangement state in the comparative example will be described with reference to FIGS. In this comparative example, FIG. 10 and FIG.
As shown in FIGS. 1 (A) and 1 (B), a fixing roller 10 made of a conductor is used.
A plurality of coils 22 for generating induced currents are arranged or connected so as to generate magnetic flux in the same direction.
If the magnetic flux generated in this case is illustrated, the magnetic flux 31d, 3
It becomes 1e. Here, the magnetic flux 31d is the same as the magnetic flux 31a shown in the principle of heat generation, and finally relates to heat generation of the fixing roller 10 and becomes heat generation points or regions 32c and 32d. On the other hand, as shown in FIG. 12, the magnetic flux 31e does not contribute to the heat generation of the fixing roller 10 because it hardly becomes the in-plane magnetic flux of the fixing roller 10. In addition, the adjacent coil 22
When the coil gap portion 33 is provided between them, the fixing roller 10 does not have a heat generating region in the gap portion 33. Therefore, when the coil gap portion 33 is increased, the temperature distribution along the rotation axis direction of the fixing roller 10 becomes non-uniform, and the fixability along the rotation axis direction of the fixing roller 10 cannot be made uniform, which adversely affects the fixing performance. Will bring.

Next, FIG. 1 shows the arrangement state in this embodiment.
It demonstrates based on 3 to 15. In this embodiment, FIG.
As shown in FIGS. 14A and 14B, the coils 22b and 22d of the plurality of coils 22 are replaced by the other coils 22.
They are arranged or connected so as to generate a magnetic flux in the opposite direction to a and 22c. If the magnetic flux generated in this case is illustrated,
The magnetic flux becomes 31f and 31g. Here, the magnetic flux 31g is "Coulomb's law regarding magnetic poles", which is different from the above-mentioned magnetic flux 31e.
That is, the direction of the magnetic flux and the magnetic flux density are different. According to "Coulomb's law regarding magnetic poles", N and S of the magnet attract each other, N and N or S and S repel each other, and a force inversely proportional to the square of the distance between both magnetic poles acts.

As shown in FIG. 15, the magnetic flux 31g becomes a component in the direction of the magnetic flux in the rotation axis plane of the fixing roller 10, so that the fixing roller 10 has a new heat generation region 32.
e and 32f are generated. Further, the magnetic flux 31g is higher than the magnetic flux 31d with respect to the magnetic flux density.

As described above, like the configuration of this embodiment,
By making the directions of the magnetic fluxes generated by the adjacent coils 22 to be opposite to each other, compared to the case where the magnetic fluxes are in the same direction,
In the range of the coil gap portion 33 where "Coulomb's law regarding magnetic poles" is established, the heat generation regions 32e and 32f are newly added to the fixing roller 10.

FIG. 16 is a graph showing the results of measuring the magnetic flux density in the direction of the rotation axis of the fixing roller 10. The horizontal axis is
It is the position of the fixing roller 10 in the rotation axis direction, and the vertical axis is the maximum magnetic flux density of the X and Z direction components at the position of the fixing roller 10 in the rotation axis direction. The current supplies a direct current. The white circles in the graph represent the absolute value of the magnetic flux density of the X-axis direction component, and the black circles represent the absolute value of the magnetic flux density of the Z-axis direction component. Regarding the X, Y, and Z axis directions, FIG.
3 is shown.

As is apparent from this graph, when the coils 22 are arranged as in this embodiment, the adjacent coils 22 are
The X-axis direction component magnetic flux is generated in the coil gap portions 33 formed between each other, and the Z-axis direction component magnetic flux density is higher in the vicinity of the coil gap portion 33 than in the central portion of the coil 22. It was revealed.

FIG. 17 is a graph showing the results of measuring the fixing peel strength of the fixing roller 10 in the rotation axis direction. The abscissa axis represents the image position of the fixing roller 10 in the rotation axis direction (main scanning direction), and the ordinate axis represents the fixing peel strength of the embodiment in comparison with the rotation axis direction position of the fixing roller 10.

As is apparent from this graph, when the coil 22 is arranged as in this embodiment, the coil gap portion 3
In No. 3 and its vicinity, the fixing peel strength was improved, and uniform fixing properties could be obtained along the rotation axis direction of the fixing roller 10.

As described above, in this embodiment, the coil assembly 12 is arranged such that the core 23 is substantially parallel to the sheet passing direction, that is, the coil 22 is an axis orthogonal to the rotation axis of the fixing roller 10. Since it is arranged so as to be wound around the center of the fixing roller 10, it is possible to locally generate heat at a specific portion on the peripheral surface of the fixing roller 10, and the local heating portion is brought into contact with the pressure roller 11. It is possible to perform heating with good thermal efficiency by associating with a neighboring portion to be heated. Since a plurality of coil assemblies 12 of the same size are arranged in parallel in the rotation axis direction, one coil assembly 1 long in the rotation axis direction is used.
As compared with the case where 2 is used, manufacturing of the coil becomes easier.

Further, in this embodiment, the adjacent coils 2
2 has a simple structure in which a plurality of coils 22 are arranged in the fixing roller 10 so that the directions of the magnetic fluxes generated by the magnetic fluxes 2 are opposite to each other. Between the adjacent coils 22, a new heat generating portion or area 32e of the fixing roller 10 is formed.
2f, and the coil gap portion 3 to some extent
Even if 3 is provided between the coils 22, the temperature distribution on the surface of the fixing roller 10 along the rotation axis direction can be made uniform, and thus uniform fixing property can be realized along the rotation axis direction of the fixing roller 10. I was able to.

Moreover, even if the width of the coil gap portion 33 is increased by reducing the lengths of the coil 22 and the core 23, the temperature distribution in the rotation axis direction of the fixing roller 10 can be made uniform. It is possible to achieve both improvement of heating efficiency and cost reduction.

In the illustrated embodiment, 22b and 2b of the coils 22a to 22d in which the copper wire 21 is wound in the same direction are used.
Only the 2d is reversed but the adjacent coil 22
Other methods may be used as long as the magnetic poles between them are opposite to each other.

Further, the shape or structure of the coil assembly 12 is not limited to the shape and the like of the above-described embodiment, and the same effects as those of the above-described embodiment can be obtained even if various modifications are made.

18 and 19 are cross-sectional views of essential parts according to an embodiment in which the cross-sectional shape of the coil of the coil assembly is modified.

The coil 22 for generating an induced current in the fixing roller 10 is preferably close to the fixing roller 10 in a wide range with a minimum gap in order to apply a high magnetic flux to the fixing roller 10. In view of this, in the coil assembly 12 shown in FIG. 18, the cross-sectional shape of the coil 22e is reduced so that the number of coil rows at the end of winding is smaller than that at the beginning of winding and the overall shape is convex. In addition, the coil shown in FIG.
In the assembly 12, two coils 22f having an ordinary cross-sectional shape are combined so as to have a cross-shaped cross-sectional shape.

20A and 20B are perspective views according to an embodiment in which the coil assembly is modified to have a coreless structure.

The core 23 of the coil 22 for generating an induced current in the fixing roller 10 is used for increasing the magnetic flux generated by the coil 22 and forming a magnetic path for guiding the magnetic flux to the fixing roller 10. In the above-described embodiment, the case where the core 23 is used so as to form a pair with all the coils 22 is shown. However, as shown in FIG. 20 (A), a form in which a part of the core 23 is removed, or FIG. As shown in (B), the core 23 may be entirely removed.

21 to 25 are sectional views of essential parts according to an embodiment in which the sectional shape of the core of the coil assembly is modified.

The core 23 of the coil 22 is, as described above,
It is used for increasing the magnetic flux generated by the coil 22 and for forming a magnetic path for guiding the magnetic flux to the fixing roller 10. Therefore, it is desirable that the core 23 be close to the fixing roller 10 in a wide range with a minimum gap. Therefore, in the coil assembly 12 shown in FIG.
Both end surfaces 50, 50 of 3a are not flat surfaces but the fixing roller 1
It is formed in an arc surface corresponding to the inner surface shape of 0. Also,
In the coil assembly 12 shown in FIG. 22, the core 23b
Both end surfaces 50, 51 of the fixing roller 1 are formed in an arcuate surface corresponding to the inner surface shape of the fixing roller 10, and one end surface 51 is formed larger than the other end surface 50 to fix the fixing roller 1 in a wide range.
It is close to 0. Further, in the coil assembly 12 shown in FIG. 23, the two core bodies 23c and 23d are
The core 23e is assembled, and both end surfaces 51, 51 are formed into arcuate surfaces corresponding to the inner surface shape of the fixing roller 10, and both end surfaces 51, 51 are formed larger than the end surface 50 of the core 23a shown in FIG. Fixing roller 10 in a wide range
To be close to. Further, in the coil assembly 12 shown in FIG. 24, the core 23f is arranged only above the coil 22 in the figure, and the end surface 51 of the core 23f is formed into an arc surface corresponding to the inner surface shape of the fixing roller 10 and has a wide range. And is close to the fixing roller 10.
Further, in the coil assembly 12 shown in FIG. 25, the cores 23g and 23h are arranged both above and below the coil 22 in the drawing,
The end surfaces 51 of the cores 23g and 23h are formed into arcuate surfaces corresponding to the inner surface shape of the fixing roller 10 and are arranged to be close to the fixing roller 10 in a wide range.

FIGS. 26 and 27 are cross-sectional views of essential parts according to an embodiment in which the cross-sectional shape of the core of the coil assembly is further modified.

The core 23 of the coil 22 is, as described above,
It is used for increasing the magnetic flux generated by the coil 22 and for forming a magnetic path for guiding the magnetic flux to the fixing roller 10. The magnetic flux passing through the core 23 is concentrated on the skin of the core 23 due to the skin effect of electromagnetic induction. Therefore, when the diameter of the fixing roller 10 is large and the core 23 is thick, or when the frequency of the high frequency current is high, the central portion of the core 23 may not contribute to the function. Therefore, in the coil assembly 12 shown in FIG. 26, the through hole 53 is formed in the core 23i,
An air gap 54 is formed in the center of the core 23i. Further, in the coil assembly 12 shown in FIG. 27,
Blind holes 55 are formed from both ends of the core 23j, and an air gap 54 is formed in the center of the core 23j.

[0054]

As described above, according to the induction heating fixing device of the present invention, an induction current is generated in the fixing roller formed of a conductive member along the rotation axis direction. The "Coulomb's law regarding magnetic poles" has a simple structure in which at least one of the plurality of coils is arranged so as to generate a magnetic flux in a direction opposite to the magnetic flux generated by another coil adjacent to the coil. By generating new magnetic flux in accordance with the above, it is possible to make the space between the coils a new heat generation point or region of the fixing roller. Even if a certain coil gap is provided between the coils, the direction of the rotation axis of the fixing roller It is possible to make the temperature distribution along the axis uniform, and to realize uniform fixing properties along the direction of the rotation axis of the fixing roller.

Further, since a plurality of coils are arranged in parallel in the rotation axis direction, the coil can be manufactured more easily than when one coil long in the rotation axis direction is used. Further, even if the width of the coil gap portion is increased by reducing the length of the coil or the core, the temperature distribution on the surface of the fixing roller along the rotation axis direction can be made uniform, so that the efficiency of induction heating is improved. It is possible to achieve both cost reduction and cost reduction.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an induction heating fixing device to which the present invention is applied.

FIG. 2 is a perspective view showing a fixing roller shown in FIG.

FIG. 3 is a perspective view showing a coil and a core in a fixing roller.

FIG. 4 is an exploded perspective view showing an internal structure of a holder unit.

FIG. 5 is a perspective view showing a coil assembly.

FIG. 6 is an explanatory diagram illustrating a heating principle of the fixing roller 10 in the induction heating fixing device to which the present invention is applied.

FIG. 7 is a block diagram of a circuit that controls the temperature of the fixing roller 10 by applying a high-frequency current to the induction heating coil 22.

FIG. 8 is a block diagram showing an inverter circuit.

9A is a waveform diagram of a voltage detected by the voltage detection circuit shown in FIG. 8, and FIG. 9B is a waveform diagram of a current detected by the current detection circuit shown in FIG. 8C is a waveform diagram of the ON / OFF signal of the switching element shown in FIG.

FIG. 10 is a perspective view showing an arrangement state of coils in a comparative example.

11A and 11B are explanatory diagrams for explaining the generation of magnetic flux and the heat generation points of the fixing roller in the comparative example shown in FIG. 10, and are a plan view and a side view of FIG. 10, respectively. It is a corresponding figure.

12 is an enlarged view showing a magnetic flux generated in an air gap portion in the comparative example shown in FIG.

FIG. 13 is a perspective view showing an arrangement state of coils in one embodiment of the present invention.

14A and 14B are explanatory diagrams for explaining the generation of magnetic flux and the heat generation points of the fixing roller in the embodiment shown in FIGS. 14A and 14B, respectively, corresponding to the plan view and side view of FIG. is there.

FIG. 15 is an enlarged view showing a magnetic flux generated in an air gap portion in the embodiment shown in FIG.

FIG. 16 is a graph showing the results of measuring the magnetic flux density in the rotation axis direction of the fixing roller.

FIG. 17 is a graph showing the results of measuring the fixing peel strength in the rotation axis direction of the fixing roller.

FIG. 18 is a cross-sectional view of essential parts according to an example in which the cross-sectional shape of the coil of the coil assembly is modified.

FIG. 19 is a cross-sectional view of essential parts according to another embodiment in which the cross-sectional shape of the coil of the coil assembly is modified.

20 (A) and (B) are perspective views according to an embodiment in which the coil assembly is modified to have a coreless structure.

FIG. 21 is a cross-sectional view of essential parts according to an example in which the cross-sectional shape of the core of the coil assembly is modified.

FIG. 22 is a cross-sectional view of essential parts according to another embodiment in which the cross-sectional shape of the core of the coil assembly is modified.

FIG. 23 is a main-portion cross-sectional view according to still another embodiment in which the cross-sectional shape of the core of the coil assembly is modified.

FIG. 24 is a cross-sectional view of a main part according to still another embodiment in which the cross-sectional shape of the core of the coil assembly is modified.

FIG. 25 is a fragmentary cross-sectional view according to still another embodiment in which the cross-sectional shape of the core of the coil assembly is modified.

FIG. 26 is a main-portion cross-sectional view according to still another embodiment in which the cross-sectional shape of the core of the coil assembly is modified.

FIG. 27 is a main-portion cross-sectional view according to still another embodiment, in which the cross-sectional shape of the core of the coil assembly is modified.

[Explanation of symbols]

 10 ... Fixing roller 11 ... Pressure roller 12 ... Coil assembly 14 ... Sheet (recording medium) 22 ... Coil 23 ... Core

Front page continuation (72) Inventor Takeshi Kato 2-3-13 Azuchi-cho, Chuo-ku, Osaka Osaka International Building Minolta Co., Ltd. (72) Inventor Eiji Okabayashi 2-3-13 Azuchi-cho, Chuo-ku, Osaka Kokusai Building Minolta Co., Ltd.

Claims (1)

[Claims] 1. A fixing device for fixing a toner image formed on a recording medium onto the recording medium, comprising: a fixing roller formed of a conductive member; and inside the fixing roller along a rotation axis direction. A plurality of coils arranged to generate an induced current in the fixing roller, and at least one coil of the plurality of coils,
An induction heating fixing device arranged so as to generate a magnetic flux in a direction opposite to the magnetic flux generated by another coil adjacent to the coil.