JP3448017B2 - Fixing device - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Generally, in an electrophotographic image forming apparatus, a toner image formed by an image forming section made of a photoconductor or the like is transferred by a transfer section to a transfer sheet carried from a paper feed section to a photoconductor position. Then, the toner image is fixed on the transfer paper by the fixing unit and then discharged to the outside of the apparatus.

In recent years, a heat roller fixing system composed of a heating roller and a pressure roller is often used as the fixing unit in terms of speeding up and safety. In the heat roller fixing method, the pressure roller is pressed against the heat roller with a predetermined pressure, and the transfer paper on which the toner image is transferred is passed between the heat roller and the pressure roller to remove heat from the heat roller. The toner image is fixed on the transfer paper by the pressure of the pressure roller.

In many conventional heating rollers, a heater such as a halogen lamp is built in, and the surface of the roller is heated by radiant heat from the heater.

On the other hand, a core around which a coil is wound is arranged inside a heating roller formed of a conductive member, and AC power of a predetermined frequency is supplied to this coil, which is generated by this AC power. An induction heating type fixing device has been proposed in which an alternating eddy current is linked to the roller to generate an induced eddy current in the roller, and the roller is heated by Joule heat generated by the eddy current and the resistance of the roller. . Since the roller itself is heated in this induction heating type fixing device, it is more efficient than the method of indirectly heating with a heater, and there is an advantage that the temperature rise in parts other than the roller can be reduced. Therefore, it is expected that the time required to rise to the fixable temperature and the energy saving of the apparatus will be realized.

On the other hand, generally, since the heat radiation amount at both ends is larger than that at the central portion in the central axis direction of the roller (direction orthogonal to the transfer paper conveying direction), conventionally, if the roller is uniformly heated, it is necessary to fix the fixing nip. Since there is a problem that a uniform temperature distribution cannot be obtained in some parts, an induction heating type fixing device that solves this problem has been proposed (Japanese Patent Laid-Open No. 10-171).
279). In this fixing device, by arranging a plurality of cores of different sizes in the central axis direction and changing the shape of the core in the central axis direction, the cross-sectional area of the core is changed between the central portion and both end portions. The temperature rise in the central part is suppressed and the temperature distribution in both ends and the central part is made uniform.

[0007]

However, in the apparatus described in the above-mentioned Japanese Patent Laid-Open No. 10-171279, a uniform temperature distribution can be obtained when a large-sized transfer paper extending across both ends is used. However, when small-sized transfer paper that passes only through the center of the heating roller is continuously conveyed, the temperature rise at both ends becomes excessive and uniform temperature distribution cannot be obtained, so proper fixing is performed. Will not be done. Further, if the temperature distribution becomes non-uniform, the roller is deformed due to the expansion of the high temperature portion, so that there is a risk of causing conveyance failure of the transfer paper such as oblique conveyance and generation of wrinkles.

Further, when a plurality of cores of different sizes are arranged in the central axis direction, there arises a problem that the manufacturing process becomes complicated and the loss in the magnetic coupling portion between the cores increases.

The present invention solves the above problem and provides an induction heating type fixing device capable of making the surface temperature distribution of a heating roller uniform irrespective of the size of a transfer sheet being conveyed. To aim.

[0010]

According to a first aspect of the present invention, a coil is provided in the vicinity of a hollow roller which is formed of a conductive member and is rotatably held around a central axis.
An eddy current is generated in the hollow roller by an AC magnetic field generated by supplying AC power to the coil to heat the hollow roller, and the toner image formed on the transfer paper is transferred by using the heated hollow roller. In an induction heating type fixing device for fixing to transfer paper, a plurality of cores formed of materials having different frequency characteristics of loss and arranged in the vicinity of the coil, and AC power supplied to the coil. And a discriminating means for discriminating the width dimension of the transfer paper in the central axis direction, wherein the frequency control means is the width dimension of the transfer paper discriminated by the discriminating means. The frequency is changed according to the above.

According to this structure, a plurality of cores formed of materials having different frequency characteristics of loss are arranged in the vicinity of the coil, and the degree of each core contributing to the generation of the AC magnetic field in the coil is It depends on the frequency of the AC power supplied to the coil. Therefore, the width dimension of the transfer paper in the central axis direction is determined, and by changing the frequency of the AC power according to the determined width dimension, the optimum core for the transfer paper width dimension is used to generate the AC magnetic field. This makes it possible to make the temperature distribution of the hollow roller uniform regardless of the size of the transfer paper.

The loss includes iron loss such as eddy current loss and hysteresis loss, and copper loss.

According to a second aspect of the invention, in the fixing device according to the first aspect, the plurality of cores have different shapes from each other, and the cross-sectional areas in the planes orthogonal to the central axis are along the central axis. It is characterized by changing.

According to this structure, in the hollow roller,
Since the heating amount of the region facing the portion having a large cross-sectional area in the plane orthogonal to the central axis of each core having a different shape is increased, the frequency of the AC power is changed according to the width dimension of the transfer paper. As a result, the amount of heating of the area corresponding to the size of the transfer paper is increased, and the temperature distribution of the hollow roller can be made uniform.

According to a third aspect of the present invention, in the fixing device according to the second aspect, the plurality of cores include a first core in which the cross-sectional areas of both end portions are slightly larger than the central portion in the central axis direction. It is characterized by being.

According to this structure, the contribution of the first core to the generation of the AC magnetic field in the coil is increased by changing the frequency of the AC power supplied to the coil so that the loss of the first core is reduced. As a result, since the heating amount of both end portions where the heat radiation amount is large becomes larger than that of the central portion, the hollow roller is heated substantially uniformly in the facing regions of the both ends of the first core and the facing region of the central portion. Become.

According to a fourth aspect of the invention, in the fixing device according to the third aspect, the first core is such that the cross-sectional area of the central portion is substantially constant along the central axis. I am trying.

According to this structure, by changing the frequency so that the loss of the first core becomes low, the heating amount of the central portion becomes substantially uniform in the central axis direction, and the both end portions with large heat radiation amount. As a result, the hollow roller is heated substantially uniformly from the facing region at one end of the first core to the facing region at the other end.

According to a fifth aspect of the present invention, in the fixing device according to any one of the second to fourth aspects, the plurality of cores have a cross-sectional area significantly larger at both end portions than at the central portion in the central axis direction. It is characterized by including a small second core.

According to this structure, since both ends of the second core hardly contribute to the generation of the magnetic flux in the coil, the frequency of the AC power supplied to the coil should be changed so that the loss of the second core becomes low. As a result, only the region of the hollow roller facing the central portion of the second core is heated.

According to a sixth aspect of the present invention, in the fixing device according to the third or fourth aspect, the plurality of cores are second cores in which the cross-sectional areas of both end portions are significantly smaller than the central portion in the central axis direction. The dimension of the central portion of the second core in the central axis direction is shorter than the dimension of the first core in the central axis direction.

According to this structure, the frequency of the AC power supplied to the coil is changed to a frequency at which the loss of the first core is reduced, thereby increasing the contribution of the first core to the generation of the AC magnetic field in the coil. As a result, the heating amount at both ends where the heat radiation amount is large becomes larger than that at the central part, so that the hollow roller is heated uniformly in the facing region at the central part and the facing region at both ends of the first core. .

On the other hand, by changing the frequency of the AC power supplied to the coil so that the loss of the second core becomes low, only the region of the hollow roller facing the central portion of the second core is heated. It will be. Here, since the dimension of the central portion of the second core in the central axis direction is shorter than the dimension of the first core in the central axis direction, by changing the frequency of the AC power supplied to the coil,
It is possible to change the heating range of the hollow roller.

According to a seventh aspect of the present invention, in the fixing device according to the sixth aspect, the frequency control means determines the width dimension of the transfer paper from the dimension of the central portion of the second core by the determination means. When it is determined that it is large, the frequency is changed so that the loss of the first core is low, and when it is determined that the width dimension of the transfer paper is equal to or smaller than the dimension of the central portion, the frequency is set to the first frequency. It is characterized in that it is modified so that the loss of two cores is reduced.

According to this structure, the width of the transfer paper is the second dimension.
When it is determined that the size of the central portion of the core is larger than the above-mentioned size, the frequency of the AC power is changed so that the loss of the first core is reduced. Thus, the toner image is uniformly heated in the opposing area of the sheet, and the toner image is appropriately fixed on the transfer paper.

On the other hand, when it is determined that the width of the transfer paper is equal to or smaller than the above-mentioned size of the central portion of the second core, the frequency of the AC power is changed so that the loss of the second core is reduced, so that the hollow roller is changed. Only the area of the second core facing the central portion of the second core is heated, so that the toner image can be favorably fixed on the transfer sheet and the power consumption can be reduced.

[0027]

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

In the copying machine 1, the photoconductor 3 is uniformly charged by the charging unit 2, and the photoconductor 3 is exposed by the light from the exposure unit 4 based on the document image read by the document reading unit 62 (see FIG. 3). An electrostatic latent image is formed on the electrostatic latent image, and toner is attached to the electrostatic latent image by the developing unit 5 to form a toner image. On the other hand, the transfer paper is transported toward the photoconductor 3 by the paper transport unit 64 (see FIG. 3), and the toner image on the surface of the photoconductor 3 is transferred to the transfer paper by the transfer unit 6.

Then, the transfer paper 7 separated from the photoconductor 3
Is conveyed to a fixing unit 8, and after the toner image is fixed on the transfer paper 7 in the fixing unit 8, the transfer paper 7 is discharged to a discharge unit (not shown) by a discharge roller pair 9.

The fixing unit 8 includes a heating roller 11 and a pressure roller 12, and is arranged in a fixing unit 13 fixed to the main body of the copying machine.

The heating roller 11 is a cylindrical hollow roller formed of a conductive member such as stainless steel, and has a release layer formed of, for example, fluororesin on its surface. The heat roller 11 is covered with a heat insulating material 14, and a first core 15 and a second core 16 are integrally provided inside the heat roller 11. The first and second cores 15 and 16 have For example, a coil 17 made of copper wire is wound.

The first and second cores 15 and 16 are fixed to the fixing unit 13 by a stay 18 formed of a metal material such as aluminum while maintaining a gap of a predetermined size between the first and second cores 15 and 16. ing. Coil 17
May be, for example, a litz wire obtained by bundling a plurality of insulating coated conductors in parallel or a single-core insulating coated fine wire, and the first and second cores 15, 15 may be provided a predetermined number of times so as to obtain a predetermined inductance. It is wound around 16.

The heating roller 11 has a central shaft 19 (see FIG. 2).
(See (e)) It is rotatably held by the fixing unit 13, and a drive gear (not shown) is attached to one end of the fixing unit 13. The motor is connected to the drive gear (not shown) so that the motor is rotated. It has become.

On the other hand, the surface of the pressure roller 12 is made slightly softer than the surface of the heating roller 11, for example, made of silicone rubber, and is pressed against the heating roller 11 with a predetermined pressure and rotatably held by the fixing unit 13. And is configured to be driven by the rotation of the heating roller 11.

The temperature sensor 20 is disposed in contact with the end of the heating roller 11 at a position where it does not hinder the conveyance of the transfer sheet, and detects the surface temperature of the heating roller 11. It consists of a thermistor.

FIG. 2 is a diagram showing the shape of the core, in which (a) is the first
Front view of the core, (b) is a side view of the first core, (c) is a front view of the second core, (d) is a side view of the second core, (e) is a right sectional view of the heating roller. . The same parts as those in FIG. 1 are designated by the same reference numerals.

The first core 15 has a substantially rectangular shape when viewed from the front as shown in FIG. 2 (a), and has a predetermined dimension in the direction of the central axis 19 of the heating roller 11 as shown in FIG. 2 (b) (e). It has a long length. In the direction of the central axis 19, the cross-sectional area in the plane orthogonal to the central axis 19 is formed so as to be slightly larger at both end portions 22 and 22 than at the central portion 21. Further, the dimension in the direction of the central axis 19 is significantly longer in the central portion 21 than in the both end portions 22 and 22, and the cross-sectional area of the central portion 21 is substantially constant along the central axis 19 and the central line The line 23 is formed line-symmetrically. As the first core 15, a material having a low loss over a high frequency range, for example, ferrite such as Ni—Zn ferrite is used.

The second core 16 has a substantially rectangular shape in a front view as shown in FIG. 2 (c), and has a predetermined dimension in the direction of the central axis 19 of the heating roller 11 as shown in FIGS. 2 (d) (e). It has a long length. In the direction of the central axis 19, the cross-sectional area in the plane orthogonal to the central axis 19 is formed so as to be much smaller at both end portions 24, 24 than at the central portion 25. , Is substantially constant along the central axis 19, and is formed in line symmetry with respect to the central line 26. As the second core 16, a material having a lower loss in the low frequency range than that of the first core 15, such as a silicon steel plate, is used.

That is, the shapes of the first and second cores 15 and 16 are as shown in FIG.
The cross-sectional areas at 2 and 22 are slightly larger than those at the central portion 21, whereas only the cross-sectional area at the central portion 25 of the second core 16 is large and both end portions 24 function as cores to generate magnetic flux. It makes little contribution to.

The loss includes iron loss such as eddy current loss and hysteresis loss, and copper loss.

As shown in FIG. 2 (e), the first and second cores 1
The width dimension in the direction of the central axis 19 of 5, 5 is D1, and the second
The width dimension of the central portion 25 of the core 16 in the direction of the central axis 19 is D
2, in the present embodiment, for example, D1 = 297 mm (A3
The short side dimension of the size is set to D2 = 210 mm (the short side dimension of the A4 size). Further, the dimension of the heating roller 11 in the direction of the central axis 19 is set to be slightly larger than D1, and the copying machine 1 of the present embodiment conveys A3 size transfer paper in the long side direction for copying. Is possible.

With such a configuration, when AC power is supplied to the coil 17, an AC magnetic field is generated, and this AC magnetic field interlinks with the portion of the heating roller 11 facing the coil 17 and causes an eddy current to the heating roller 11. The heating roller 11 is heated by the Joule heat generated by the eddy current and the resistance of the roller itself, and the toner image is appropriately fixed on the transfer paper.

FIG. 3 is a block diagram showing the essential parts of the electrical construction of the copying machine 1. The same components as those in FIGS. 1 and 2 are designated by the same reference numerals.

In FIG. 3, a resonance capacitor 31 is connected in parallel to the coil 17 to form an LC resonance circuit,
The semiconductor switch element 32 is connected between one end of the LC resonance circuit and the ground. Semiconductor switch element 32
Is a high-voltage and large-current power semiconductor element, which electrically connects one end of the LC resonance circuit to the ground when a drive voltage of a predetermined level is applied to the control terminal.
Uses IGBT. Other semiconductor switch elements such as MOS-FET may be used.

The other end of the LC resonance circuit is connected to one DC output terminal 41 of the bridge diode 40. The other DC output terminal 42 of the bridge diode 40 is grounded, and the AC input terminals 43 and 44 are
It is connectable to a C100V AC power supply 46.

AC input terminal 4 of bridge diode 40
A primary coil of a current transformer 47 is interposed between the connection coil 4 and the connection portion 45, and a resistor 48 having a predetermined resistance value is connected in parallel to the secondary coil of the current transformer 47. The electric power supplied from the AC power supply 46 can be detected by the voltage at both ends. The bridge diode 40 and the AC power supply 46 constitute a DC power supply.

The drive circuit 51 is connected to the control terminal of the semiconductor switch element 32, and the zero-cross detection circuit 53 is connected to the line 52 connecting the LC resonance circuit and the semiconductor switch element 32. Further, a control IC 54 is connected to the drive circuit 51 and the zero-cross detection circuit 53, a control unit 55 is connected to the control IC 54, and an operation unit 61, a document reading unit 62, an image forming unit 63, and a sheet conveying unit are connected to the control unit 55. The part 64 is connected.

The drive circuit 51 has a predetermined level (for example, DC
The semiconductor switch element 32 is turned on by applying a drive voltage of 20 V) to the control terminal of the semiconductor switch element 32, and the drive voltage is applied in synchronization with the timing control signal from the control IC 54.

In the zero-cross detection circuit 53, the voltage across the semiconductor switch element 32, which has risen as the semiconductor switch element 32 is turned off and the energy stored in the coil 17 is released through the capacitor 31, returns to near zero. The zero cross is detected, and a predetermined detection signal is sent to the control IC 54 each time the zero cross is detected.

The control IC 54 sends to the drive circuit 51 a timing control signal instructing the application timing when the drive circuit 51 applies the drive voltage to the semiconductor switch element 32. This timing control signal is made up of a pulse voltage signal, and is generated so that ON of the semiconductor switch element 32 is synchronized with detection of a zero cross and OFF is synchronized with a control signal from the control unit 55. That is, the switching frequency of the semiconductor switch element 32 is controlled by the controller 55.

The operation section 61 selects a transfer sheet to be used for copying from a print key 71 for instructing the start of a copy operation and a transfer sheet of each size accommodated in the sheet feeding section 65 of the sheet conveying section 64. A paper selection key 72, a copy number setting key 73 for setting the number of copies for each original, and a magnification setting key 74 for setting the copy magnification are provided.

The document reading section 62 reads the document image and also has a function of detecting the size of the set document. The image forming unit 63 is composed of a charging unit 2, a photoconductor 3, an exposure unit 4 (FIG. 1), and the like, and performs copying to form a document image on a transfer sheet.

The sheet conveying section 63 conveys the transfer sheet of the size designated by the control signal of the control section 55 from the sheet feeding section 65 in which the transfer sheets of various sizes are accommodated toward the photoconductor 3 (FIG. 1). And a heating roller 11 (FIG. 1) for driving the roller to rotate.

In the present embodiment, for example, A3 size, B4 size, A4 size, and B5 size transfer papers are accommodated in the paper feeding unit 65. Transfer papers of A3 size, B4 size, and B5 size are stored so as to be transported along the long side direction, and transfer papers of A4 size are stored so as to be transported along the long side direction. Some are stored and some are stored so as to be transported along the short side direction.

The control unit 55 is composed of a CPU, etc., and controls the overall operation of the copying machine 1 such as carrying a transfer sheet from the paper feeding unit 65 in response to an operation on the operation unit 61 to start a copying operation. It has the following functions.

A function as a size discriminating section for discriminating the width dimension of the transfer sheet selected by the transfer sheet selection key 72 in the direction orthogonal to the conveying direction (the direction of the central axis 19 of the heating roller 11). Instead of the transfer paper selection key 72, the width size of the transfer paper may be determined based on the document size detected by the document reading unit 62 and the copy magnification set by the magnification setting key 74.

A function as a switch controller for controlling the switching frequency of the semiconductor switch element 32 according to the determined width dimension. Here, the width dimension is D2 (A
When the width is less than D2, the switching frequency is set to a high frequency f1 (for example, f1 = 50 kHz in the present embodiment) when it is larger than the 4th size (short side). For example, f2 = 50Hz)
And

The AC power supplied from the AC power supply 46 is detected by detecting the voltage across the resistor 48 connected in parallel to the secondary coil of the current transformer 47. When this AC power exceeds a predetermined level, the semiconductor switch element is detected. Three
Function as a power limiter that turns off 2.

A function as an overheat preventing portion for turning off the semiconductor switch element 32 when the surface temperature of the heating roller 11 detected by the temperature sensor 20 exceeds a predetermined level.

Next, the heating operation of the heating roller 11 will be described with reference to FIGS.

As described above, the first core 15 and the second core 16 are made of different materials. Therefore, since the cores interfere with each other, the magnetic flux generated in the coil 17 concentrates on the core that is more likely to pass through (the one with lower loss).

When the width of the transfer paper is larger than D2,
Since the switching frequency of the semiconductor switch element 32 is set to the high frequency f1, the magnetic flux generated in the coil 17 concentrates on the first core 15 having good high frequency characteristics. Therefore, the heating roller 11 is heated over the region facing the width dimension D1 of the first core 15.

Since the heat radiation amount is large at both end portions of the heating roller 11, the heating efficiency is low, and the first portion is correspondingly correspondingly.
By increasing the cross-sectional areas of both end portions 22, 22 of the core 15 as compared with the central portion 21, the heating amount at both end portions of the heating roller 11 is increased.
The temperature distribution is made uniform over the central axis 19 direction.

On the other hand, when the width dimension of the transfer paper is D2 or less, the switching frequency of the semiconductor switch element 32 is set to the low frequency f2, so that the magnetic flux generated in the coil 17 has the second loss which is low in the low frequency range. Focus on the core 16. Therefore, in the heating roller 11, only the portion facing the width dimension D2 of the central portion 25 of the second core 16 is heated.

As described above, according to this embodiment, the first core 15 is made of a material having a low loss in a high frequency range such as ferrite and is formed to have the width dimension D1, and the second core 16 is made of a silicon steel plate or the like. It is made of a material with low loss in the low frequency range and the width dimension D of the central portion 25
When the width dimension of the transfer paper is larger than D2, the heating frequency of the semiconductor switch element 32 is set to the high frequency f1 and the heating roller 11 is heated by the first core 15 over the width dimension D1. The heating roller 11 can be heated appropriately over the entire range of the transfer paper.

Further, since the cross-sectional areas of the two end portions 22, 22 of the first core 15 are made slightly larger than that of the central portion 21, the heating amount of the both end portions 22, 22 having a larger heat radiation amount is set to the central portion 21. In comparison, the temperature distribution can be made substantially uniform over the entire region of the heating roller 11 facing the first core 15.

If the temperature distribution is not uniform, the roller is deformed due to the expansion of the high temperature portion, which may cause the conveyance failure of the transfer paper such as the oblique conveyance and the generation of wrinkles.
Such a situation can be prevented in advance, and the transfer sheet transfer accuracy can be improved.

Further, according to the present embodiment, when the width of the transfer paper is D2 or less, the switching frequency of the semiconductor switch element 32 is set to the low frequency f2 and the second core 16 heats only the central portion of the heating roller 11. Therefore, it is possible to prevent a situation in which both ends of the heating roller 11 through which the transfer paper does not pass are heated and the temperature rises excessively. Further, when the width dimension of the transfer paper is D2 or less, only the necessary portion is heated, so that the power consumption can be reduced.

The present invention is not limited to the above embodiment, but the following modifications can be adopted.

(1) The shape and number of the first and second cores 15 and 16 are not limited to those shown in FIG. 2 of the above embodiment.

FIGS. 4A and 4B show the first and second cores 15 and 16.
6A and 6B are views showing another configuration example of FIG. 3A, in which FIG.

In FIG. 2, the first and second cores 15 and 16 are arranged side by side, while in FIG. 4, the first and second cores 15 and 16 are arranged.
The cores 15 and 16 are laminated vertically. As shown in FIG. 4B, also in this configuration example, as in the above embodiment,
The first core 15 has both end portions 82, 82 compared to the central portion 81.
Has a large cross-sectional area, and the second core 16 has both end portions 8
The cross-sectional area of the central portion 81 is formed larger than those of Nos. 2 and 82.

According to the configuration of FIG. 4, when the switching frequency of the semiconductor switch element 32 is the high frequency f1, the first
The core 15 heats the entire width dimension D1 and the second core 16 heats only the portion of the central portion 81 facing the width dimension D2 at the low frequency f2. The effect can be obtained.

FIG. 5 is a view showing an example in which a third core 83 is provided in addition to the first and second cores 15 and 16, (a) is a front view,
(b) is a side view of the first core 15, (c) is a side view of the third core 83, and (d) is a side view of the second core 16.

As shown in FIG. 5B, the first core 15 has the same shape as that of the above embodiment. As shown in FIG. 5D, in the second core 16, the width dimension D3 of the central portion 25 is shorter than that in the above embodiment (for example, D3 = 120 mm <D2).
It has a shape.

As shown in FIG. 5C, the third core 83 is
The same shape as the second core 16 in FIG. 2, that is, the central portion 84.
Has a larger cross-sectional area than both end portions 85, 85, and the width dimension of the central portion 84 is set to D2. The third core 83 is formed of a material having slightly better high frequency characteristics than the second core 16, for example, carbonyl iron dust.

The controller 55 sets the switching frequency to the high frequency f1 (eg, f1 = 200 kHz) when the size of the transfer sheet in the width direction is larger than D2, and sets the size of the transfer sheet in the width direction to D3 or less (eg, envelope. ), The switching frequency is set to a low frequency f2 (for example, f2 = 50 Hz), and when the size in the width direction of the transfer paper is larger than D3 and is D2 or less, the switching frequency is set to an intermediate frequency f3 (for example, f3 = 20 kHz).
z).

According to the embodiment of FIG. 5, the heating roller 11 is
When the switching frequency is the high frequency f1, the first core 1
5, the width dimension D1 is heated over the entire length, and at the intermediate frequency f3, the width dimension D of the central portion 84 is increased by the third core 83.
2 is heated, and at the low frequency f2, the second core 16 heats only the portion facing the width dimension D3 of the central portion 24.

As described above, instead of the two kinds of cores, the cores formed of three or more kinds of materials having different frequency characteristics of loss are combined, so that the heating roller 11 can be more finely adjusted according to the size of the transfer paper. Temperature control can be performed. Further, regarding the switching frequency, by providing the intermediate frequency f3 in accordance with the type of the core, it is possible to perform finer temperature control of the heating roller 11, and thereby to make the surface temperature of the heating roller 11 more uniform. it can. In addition, power consumption can be reduced.

As shown in FIG. 5A, the first, third, and second cores 15, 83, 16 are arranged in order from the left, but the arrangement position of each core is not limited to this. I can't.

FIG. 6 is a view showing an example in which the shape of the first core 15 is different, (a) is a front view, (b) is a side view of the first core 15,
(c) is a side view of the second core 16.

In FIG. 6A, the first core 15 has a U-shaped cross section, and the second core 1 is provided inside the first core 15 surrounded by the first core 15.
6 and the coil 17 are arranged. Also in this form,
It is possible to obtain the same effect as that of the above-described embodiment.

FIG. 7 is a side view showing another example of the shape of the second core 16. In FIG. 7, both end portions 24, 2 of the second core 16 are
4, the cross-sectional area of only the portion near the end is slightly increased. According to this aspect, even when continuous copying is performed on a small-sized transfer sheet, the end portion of the heating roller 11 can be heated to some extent, so that the temperature decrease of the end portion is suppressed. Therefore, even when continuous copying is performed on a small-sized transfer sheet and then copying is performed on a large-sized transfer sheet, the temperature of the edge portion reaches the required temperature immediately,
It is possible to preferably perform copying on a large-sized transfer sheet without requiring a large waiting time.

In the above embodiment and this modification (1), since a plurality of cores made of different materials are used,
The interference of the cores, that is, the phenomenon that the magnetic flux concentrates on one core depending on the frequency is inevitable. Therefore, it is necessary to design the shape of each core as a combination of the respective characteristics to some extent, unlike the case where the cores are used alone.

(2) As shown by the broken lines in FIGS. 1 and 3, a temperature sensor 91 may be further provided. The temperature sensor 91 is arranged in contact with the center of the heating roller 11 at a position where it does not hinder the transfer sheet from being conveyed. The temperature sensor 91 detects the surface temperature of the heating roller 11, and a thermistor or the like. Consists of.

In this embodiment, the controller 55 further controls the temperature T1 at the center of the heating roller 11 detected by the temperature sensor 91 and the temperature T2 at the end of the heating roller 11 detected by the temperature sensor 20. Difference ΔT = | T1-T2
Based on |, it has a function of adjusting the switching frequency of the semiconductor switch element 32.

For example, when the switching frequency of the semiconductor switch element 32 is the high frequency f1 (for example, f1 = 50 kHz) and the temperature difference ΔT is less than the predetermined value, the switching frequency is not changed.

When the temperature T1 at the central portion decreases and the temperature difference ΔT becomes a predetermined value ΔT1 (eg, ΔT1 = 5K) or more, most (eg, 90%) of the predetermined unit time is set to the high frequency f1. The heating of the central portion of the heating roller 11 is increased by setting the low frequency f2 (for example, f2 = 50 Hz) for the remaining time.

When the temperature T1 of the central portion further decreases and the temperature difference ΔT becomes a predetermined value ΔT2 (for example, ΔT2 = 10K) or more, the switching frequency is set to the low frequency f2 to maximize the heating of the central portion. To do.

According to this aspect, since the switching frequency is adjusted according to the actual temperature of the heating roller 11,
The heating roller 11 can be heated so that the surface temperature becomes uniform even when the temperature, moisture absorption, paper quality, or ambient temperature of the transfer paper changes.

When the temperature difference ΔT is greater than or equal to the predetermined value ΔT1 and less than the predetermined value ΔT2 (for example, 5K ≦ ΔT <10K),
The switching frequency is set to the intermediate frequency f3 (for example, f3 = 1k
Hz) may be used. Also in this case, since the switching frequency is smaller than that of the high frequency f1, the contribution of the second core 16 to heating is increased as compared with the case of the high frequency f1, so that the heating of the central portion can be increased. .

Further, the ratio of the high frequency f1 and the low frequency f2 per unit time (90% and 10% in the above) and the intermediate frequency f3 (f3 = 1 kHz in the above) are set in multiple steps according to the temperature difference ΔT. It may be changed. Thereby, the surface temperature of the heating roller 11 can be controlled more finely.

Thus, the central shaft 19 of the heating roller 11 is
The controller 55 includes a temperature sensor (first temperature detecting means) 20 and a temperature sensor (second temperature detecting means) 91 for detecting the temperatures of the end portion and the central portion in the direction of, respectively.
By changing the switching frequency according to the difference between the temperatures detected by the temperature sensors 20 and 91, for example, the central portion of the heating roller 11 in the direction of the central axis 19 has a lower temperature than the end portion. When the temperature becomes lower than the predetermined value, the frequency is changed so that the heating amount of the central portion increases, so that the temperature distribution of the heating roller 11 can be made more uniform.

(3) In the above embodiment, the first and second cores 15 and 16 and the coil 17 are separate bodies, but instead of this, one of the cores is made integral with an insulating material. It may be molded by molding.

Further, the molded magnetic body may be configured as a core by molding the coil 17 with a plurality of materials each including a ferromagnetic material having different frequency dependence of loss.

(4) In the above embodiment, each core 15, 1
Although 6 is arranged inside the heating roller 11, it is not limited to this and may be arranged near the outside of the heating roller 11. In this case, it may be arranged at a position apart from the fixing nip portion so as not to hinder the fixing on the transfer paper.

(5) In the above embodiment, a copying machine is used for explanation, but the present invention is not limited to this, and the present invention can be applied to a fixing unit in an electrophotographic image forming apparatus such as a facsimile or a printer. it can.

[0098]

As described above, according to the first aspect of the present invention, a plurality of cores made of materials having different frequency characteristics of loss are arranged in the vicinity of the coil, and the width of the transfer paper is adjusted. Since the frequency of the AC power supplied to the coil is changed according to the determined width dimension, the optimum core for the width dimension of the transfer paper is made to contribute to the generation of the AC magnetic field. Therefore, the temperature distribution of the hollow roller can be made uniform regardless of the size of the transfer paper.

Further, according to the invention of claim 2, the plurality of cores have different shapes from each other, and the cross-sectional areas in the planes orthogonal to the central axis change along the central axis, so that in the hollow roller. , The heating amount of the area facing the portion having a large cross-sectional area in the plane orthogonal to the central axis of each core having a different shape is increased, and the frequency of the AC power is changed according to the width dimension of the transfer paper. As a result, the heating amount of the area corresponding to the size of the transfer paper can be increased, and the temperature distribution of the hollow roller can be made uniform.

According to the third aspect of the present invention, the plurality of cores include the first cores having the cross-sectional areas of the both ends slightly larger than the central part in the central axis direction. Therefore, the plurality of cores are supplied to the coil. By changing the frequency of the AC power to a frequency such that the loss of the first core is low, the heating amount at both ends where the heat radiation amount is large becomes larger than that at the central part, so that the hollow roller is placed at both end portions of the first core. It can be heated almost uniformly in the central part.

Further, according to the invention of claim 4, since the cross-sectional area of the central portion of the first core is substantially constant along the central axis, the loss of the first core is reduced. By changing the frequency, the heating amount of the central portion becomes substantially uniform along the central axis direction, and the heating amount of both end portions with large heat radiation amount becomes large.
The core can be heated almost uniformly from one end to the other end.

Further, according to the invention of claim 5, the plurality of cores include the second core, in which the cross-sectional areas of both end portions are significantly smaller than the central portion in the central axis direction.
Since both ends of the core contribute little to the generation of magnetic flux in the coil, by changing the frequency of the AC power supplied to the coil so that the loss of the second core is reduced,
Only the area of the hollow roller facing the central portion of the second core can be heated.

Further, according to the invention of claim 6, the plurality of cores include the second core whose cross-sectional area at both end portions is significantly smaller than the central portion in the central axis direction.
Since the dimension of the central part of the core in the central axis direction is shorter than the dimension of the first core in the central axis direction, the frequency of the AC power supplied to the coil is reduced so that the loss of the first core is low. By changing the frequency, the hollow roller can be heated uniformly at the center and both ends of the first core, while the frequency of the AC power supplied to the coil is reduced so that the loss of the second core becomes low. By changing it, only the region of the hollow roller facing the central portion of the second core can be heated. Here, since the dimension of the central portion of the second core in the central axis direction is shorter than the dimension of the first core in the central axis direction, the heating range of the hollow roller can be changed by changing the frequency of the AC power. Can be changed.

Further, according to the invention of claim 7, when it is judged that the width dimension of the transfer paper is larger than the above-mentioned dimension of the central portion of the second core, the frequency is changed so that the loss of the first core becomes low. Therefore, the hollow roller can be heated uniformly in the facing area at the central portion and the facing areas at both ends of the first core, while it is determined that the width dimension of the transfer paper is equal to or smaller than the above-described dimension of the central portion. Since the frequency is changed so that the loss of the second core becomes low when it is heated, only the region of the hollow roller facing the central portion of the second core can be heated. In any case, The toner image can be suitably fixed on the transfer paper. In addition, when heating only the region facing the central portion of the second core, it is possible to reduce power consumption and prevent unnecessary deterioration of the device by preventing heating to both end portions. it can.

[Brief description of drawings]

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

2A and 2B are views showing the shape of the core, where FIG. 2A is a front view of the first core, FIG. 2B is a side view of the first core, FIG. 2C is a front view of the second core, and FIG. A side view of the two cores, (e) is a right side sectional view of the heating roller.

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

4A and 4B are views showing another configuration example of the first and second cores, FIG. 4A is a front view, and FIG. 4B is a perspective view.

FIG. 5 is a diagram showing an example including a third core in addition to the first and second cores, (a) is a front view, (b) is a side view of the first core,
(c) is a side view of a 3rd core, (d) is a side view of a 2nd core.

FIG. 6 is a diagram showing an example in which the shape of the first core is different, (a) is a front view, (b) is a side view of the first core, and (c) is a side view of the second core.

FIG. 7 is a side view showing another example of the shape of the second core.

[Explanation of symbols]

8 fixing section 11 Heating roller (hollow roller) 15 1st core 16 Second core 17 coils 20,91 Temperature sensor 32 Semiconductor switch element 40 bridge diode 46 AC power supply 55 Control unit (frequency control means, discrimination means) 61 Operation part 62 Document reading section 72 Transfer paper selection key 74 Magnification setting key 83 Third Core

Claims (7)

(57) [Claims] 1. An AC magnetic field generated by arranging a coil in the vicinity of a hollow roller, which is a cylindrical shape formed of a conductive member and rotatably held around a central axis, and supplies AC power to the coil. To heat the hollow roller by generating an eddy current in the hollow roller, and fix the toner image formed on the transfer paper to the transfer paper by using the heated hollow roller. In the apparatus, a plurality of cores formed of materials having different frequency characteristics of loss and arranged in the vicinity of the coil, frequency control means for controlling the frequency of AC power supplied to the coil, and the transfer paper. And a determining means for determining a width dimension in the central axis direction of the transfer paper, wherein the frequency control means determines the width dimension of the transfer paper determined by the determining means. Fixing apparatus characterized in that to change the wave number. 2. The fixing device according to claim 1, wherein the plurality of cores have different shapes from each other, and cross-sectional areas in a plane orthogonal to the central axis change along the central axis. Characterizing fixing device. 3. The fixing device according to claim 2, wherein the plurality of cores include a first core in which the cross-sectional areas of both end portions are slightly larger than the central portion in the central axis direction. apparatus. 4. The fixing device according to claim 3, wherein the cross-sectional area of the central portion of the first core is substantially constant along the central axis. 5. The fixing device according to any one of claims 2 to 4, wherein the plurality of cores include a second core in which the cross-sectional areas of both end portions are significantly smaller than the central portion in the central axis direction. A fixing device characterized by being installed. 6. The fixing device according to claim 3 or 4, wherein the plurality of cores include a second core in which the cross-sectional areas of both end portions are significantly smaller than the central portion in the central axis direction. The fixing device, wherein the size of the central portion of the two cores in the central axis direction is shorter than the size of the first core in the central axis direction. 7. The fixing device according to claim 6, wherein when the frequency control unit determines that the width dimension of the transfer sheet is larger than the dimension of the central portion of the second core by the determination unit. The frequency is changed so that the loss of the first core is low, and when it is determined that the width dimension of the transfer paper is equal to or less than the dimension of the central portion, the frequency is reduced and the loss of the second core is low. A fixing device characterized by being modified as follows.