JP2001312178A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize the surface temperature distribution of a heating roller regardlessly of the size of transfer paper. SOLUTION: A CPU 65 discriminates the size in a width direction orthogonal to the carrying direction of the transfer paper selected by a transfer paper selection key 81. The CPU 65 outputs a pulse signal having a specified on/off duty ratio to control ICs 63 and 64 with specified frequency or more, so that switching elements 31 and 32 are turned on/off with the specified frequency or more. Bp controlling the frequency and the on/off duty ratio, at such a time, supply power to coils 151 and 152 and a coil 153 is changed in accordance with the dimension in the width direction orthogonal to the carrying direction of the transfer paper.

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 In general, in an electrophotographic image forming apparatus, a toner image formed by an image forming unit including a photoreceptor is transferred by a transfer unit onto a transfer sheet carried from a paper feeding unit to a photoreceptor position. After the toner image is fixed on the transfer paper by the fixing unit, the toner image is discharged out of the apparatus.

As a fixing unit, a heat roller fixing system composed of a heating roller and a pressure roller has recently been often used 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 has been transferred is passed between the heat roller and the pressure roller, and the heat from the heat roller is removed. The toner image is fixed on the transfer paper by the pressure of the pressure roller.

[0004] Many conventional heating rollers incorporate a heater such as a halogen lamp and heat the roller surface by radiant heat from the heater.

On the other hand, a core around which a coil is wound is provided inside a heating roller formed of a conductive member, and high-frequency power is supplied to the coil, and a high-frequency magnetic field generated by the high-frequency power is generated. An induction heating type fixing device has been proposed in which an induced eddy current is generated in a roller by interlinking with the roller, and the heating roller is heated by Joule heat generated by the eddy current and the resistance of the roller. JP-A-54-39645, JP-A-9-2585
No. 86).

In the induction heating type fixing device, since the roller itself is heated, it is more efficient than a system in which the roller is heated indirectly by a heater, and the temperature rise in portions other than the roller can be reduced. Therefore, it is expected that the time required for raising the temperature to the fixing-possible temperature can be shortened and the energy saving of the apparatus can be realized.

[0007]

Generally, transfer papers of various sizes are used depending on the specifications of the image forming apparatus. The heating roller is designed to be able to fix the maximum width of the transfer paper used in the apparatus, but if a transfer paper having a width smaller than the maximum width is fixed, the portion of the heat roller where the transfer paper does not pass, that is, the heating roller The temperature at both ends increases. This is because there is no heat absorption by the paper only in that part. Therefore, if a large amount of transfer paper is fixed immediately after the transfer paper having a small width is fixed, a problem such as a high-temperature offset in which toner adheres to a high-temperature portion of the roller may occur.

Therefore, in the case of the above-described fixing device using a heater, for example, two halogen lamps having different light distributions are incorporated in the heating roller, and each lamp is turned on / off according to the width of the transfer paper to be fixed. Thus, the surface temperature of the heating roller is made uniform for various widths of the transfer paper.

However, the above-mentioned conventional Japanese Patent Application Laid-Open No. 54-396
No. 45 or JP-A-9-258586 does not disclose any control of energization of a coil according to the size of a transfer sheet to be fixed.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide an induction heating type fixing device capable of making the surface temperature distribution of a heating roller uniform regardless of the size of a transfer sheet.

[0011]

According to a first aspect of the present invention, a coil is disposed inside a hollow roller which is formed of a conductive member and has a cylindrical shape and is rotatably held around a central axis.
The hollow roller is heated by supplying high-frequency power to the coil to generate an eddy current in the hollow roller,
In the fixing device of the induction heating type, in which the toner image formed on the transfer paper is fixed to the transfer paper by using the heated hollow roller, the fixing device is arranged inside the hollow roller along the central axis. N (n is an integer of 2 or more) cores provided in a direction orthogonal to the central axis, n coils wound around each of the cores, and electric power from a power supply unit to each of the coils. K (k is an integer equal to or less than n) switching means for turning on and off the supply, and the switching means are turned on and off at a predetermined frequency or more, and the on / off duty ratio is changed to supply the power from the power supply unit to each of the coils. Control means for controlling power; and discriminating means for discriminating the dimension of the transfer paper in the central axis direction, wherein the control means supplies power to each of the coils in accordance with a discrimination result by the discriminating means. It is characterized in that to vary the force.

According to this configuration, the n cores are arranged inside the hollow roller along the central axis and provided in a direction orthogonal to the central axis, and the coils are wound around the respective cores. The k switching means for turning on and off the power supply from the power supply unit to each coil are turned on and off at a predetermined frequency or more, and the power supply from the power supply unit to each coil is controlled by changing the on / off duty ratio. You. At this time, the size of the transfer paper in the central axis direction is determined, and the power supply to each coil is changed according to the determination result. It becomes possible to make it uniform.

According to a second aspect of the present invention, in the fixing device according to the first aspect, the control unit is configured to control, among the n coils, the coil through which the transfer paper passes in a region facing the coil. It is characterized in that power is supplied only to this.

According to this configuration, since power is supplied only to the coil of the n coils through which the transfer paper passes in the area facing the coil, the transfer paper is used when the transfer paper is small. Unnecessary portions for fixing the toner image are not heated, and the power consumption is reduced.

According to a third aspect of the present invention, in the fixing device according to the second aspect, the control means is arranged so that each of the coils is opposed to the corresponding one of the coils when compared with a case where the transfer paper passes through the entire opposed area of each of the coils. When the transfer paper passes through a part of the area, power supplied to each of the coils is reduced.

According to this configuration, the amount of heat absorbed by the transfer paper is lower when the transfer paper passes through a part of the opposing area of each coil than when the transfer paper passes through the entire opposing area. Since the temperature reduction width of the roller is small, if the supply power to each coil is reduced at this time, the temperature distribution of the hollow roller is maintained uniformly.

According to a fourth aspect of the present invention, in the fixing device of the first aspect, the m-th (m is an integer of 1 ≦ m ≦ n / 2) core and the other end side from one end side of the center shaft. And the m-th core are set to the same size as each other,
The coils wound around the m-th core are set to have the same number of turns, respectively, and the control means supplies the same power to the coil wound around the m-th core. It is characterized by having.

According to this configuration, the m-th core from one end and the m-th core from the other end of the central axis are set to the same size, and wound around each m-th core. The coils are set to the same number of turns with each other,
The same power is supplied to the coil wound around each m-th core. Therefore, the core is arranged symmetrically with respect to the center of the hollow roller in the center axis direction, and the position and intensity of the high-frequency magnetic field generated by the coil are also symmetrical, so that the center of the transfer paper in the center axis direction coincides with the center of the hollow roller. By doing so, the toner image is suitably fixed on transfer paper of various sizes.

According to a fifth aspect of the present invention, in the fixing device according to the fourth aspect, the coils wound around the respective m-th cores are respectively connected in series with each other, and wound around the respective m-th cores. Switching means for turning on and off the power supply to each of the turned coils is shared by one switching means.

According to this configuration, the coils wound around each m-th core are connected in series with each other, and
The switching means for turning on and off the power supply to each coil wound on the third core is shared by one switching means, so that the high-frequency magnetic field generated in the coil maintains a symmetrical state while the switching is performed. Since the number of means is reduced, the number of parts constituting the apparatus can be reduced.

According to a sixth aspect of the present invention, in the fixing device according to any one of the first to fifth aspects, the power supply section comprises an AC power supply and a rectifying means connectable to the AC power supply. DC power obtained by rectifying AC power output from an AC power supply by the rectifier is supplied to the n coils.

According to this configuration, when the rectifier is connected to the AC power supply, the AC power output from the AC power supply is rectified, and the rectified DC power is supplied to the n coils. Since the rectifiers are shared by the n coils, it is possible to supply DC power to each coil with a simple configuration.

According to a seventh aspect of the present invention, in the fixing device according to the sixth aspect, when the AC power supply is connected to the rectification means, the power supplied from the AC power supply to the rectification means is detected. Means, wherein the control means controls the on / off duty ratio of the k switching means based on the detection result by the detection means.

According to this configuration, when the AC power supply is connected to the rectifier, the power supplied from the AC power supply to the rectifier is detected, and based on the detection result, the on / off duty ratios of the k switching means are changed. Controlled. For example, when the detected power increases, the on / off duty ratio of each switching unit is reduced at the same ratio, and when the detected power decreases, the on / off duty ratio of each switching unit increases at the same ratio. Thereby, appropriate power is supplied to each coil, and the surface temperature of the hollow roller becomes uniform.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a main part 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 irradiated with light from the exposure unit 4 based on the document image read by the document reading unit 90 (see FIG. 3). An electrostatic latent image is formed thereon, and toner adheres to the electrostatic latent image by the developing unit 5 to form a toner image. On the other hand, the transfer paper is conveyed from the paper supply unit 70 (see FIG. 3) toward the photoconductor 3, and the toner image on the surface of the photoconductor 3 is transferred to the transfer paper by the transfer unit 6.

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

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

The heating roller 11 is a cylindrical hollow roller formed of a conductive member such as stainless steel, and has a release layer formed on its surface, for example, of Teflon (registered trademark) rubber. A core 14 made of ferrite or the like is provided inside the heating roller 11.
A coil 15 made of, for example, a copper wire is wound around 4.

The heating roller 11 has a central shaft 16 (FIG. 2).
Reference) is held by the fixing unit 13 rotatably around,
A drive gear (not shown) is attached to one end, and is rotatably driven by a motor (not shown) connected to the drive gear.

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

FIG. 2 is a view showing the structure of the heating roller.
FIG. 2 is a perspective view of a heating roller, and FIG. 2B is a transparent perspective view showing an internal configuration of a coil holding unit. The same components as those in FIG. 1 are denoted by the same reference numerals.

The core 14 around which the coil 15 is wound is formed of an insulating material such as a hard synthetic resin, and is housed in a hollow coil holding portion 21 having a cylindrical shape. The coil holding portion 21 is housed inside the heating roller 11 while maintaining a predetermined gap between the coil holding portion 21 and the heating roller 11, and is fixed to the fixing unit 13 so as not to rotate. The core 14 and the coil 15 are insulated from the heating roller 11 by the coil holding unit 21.

The core 14 has a central shaft 16 of the heating roller 11.
, And three cores 141, 142, 143 provided in a direction orthogonal to the central axis 16, and the coils 15 are wound around the cores 141, 142, 143, respectively. , 153.

In FIG. 2, the core 141 is a heating roller 1
1, the core 142 is disposed on the right end side of the heating roller 11, the core 143 is disposed at the center of the heating roller 11, and the core 141 and the core 142 are set to the same size. I have.

In this embodiment, for example, the cores 141, 14
2, the dimension D1, D2 = 50 mm in the direction of the central axis 16 and the core 14
The dimension D3 in the direction of the central axis 16 of D.3 is set to 210 mm (the short side dimension of the A4 size), and the copying machine 1 of this embodiment is
Is capable of copying A3 size transfer paper by conveying it in the long side direction.

The coils 151 and 152 are formed of one copper wire 22 and the number of turns is set to be the same. The coil 153 is formed of another copper wire 23.

With such a configuration, the coils 151, 1
When a high-frequency electric power (high-frequency current) is supplied to the heating rollers 1 and 52, a high-frequency magnetic field is generated.
1 and the heating roller 11
The heating roller 11 is heated by Joule heat generated by the eddy current, so that the toner image is appropriately fixed on the transfer paper.

FIG. 3 is a block diagram showing a main part of an electric configuration of the copying machine 1. As shown in FIG. 1 and 2 are denoted by the same reference numerals.

In FIG. 3, a resonance capacitor C1 is connected in parallel to coils 151 and 152 (copper wire 22) to form a resonance circuit, and a switching element 31 is connected between one end of the resonance circuit and the ground. Inverter circuit 4
1 is configured. Also, the coil 153 (copper wire 23)
A resonance capacitor C2 is connected in parallel to a resonance circuit, and a switching element 32 is connected between one end of the resonance circuit and the ground to form an inverter circuit 42.

The switching elements 31 and 32 have a high withstand voltage.
When a predetermined level of drive voltage is applied to the control terminal, a large current power semiconductor element conducts between one end of each resonance circuit and the ground.
For example, IGBT, MOS-FET, or the like can be used as 2.

The other ends of the resonance circuits are connected to each other, and one DC output terminal 5
1 connected. The other DC output terminal 52 of the bridge diode 50 is grounded, and AC input terminals 53, 54
Can be connected to an AC power supply 56 of AC 100 V via a connection unit 55.

AC input terminal 5 of bridge diode 50
A primary coil of a current transformer 57 is interposed between the power transformer 4 and the connection portion 55. A resistor 58 having a predetermined resistance value is connected in parallel to a secondary coil of the current transformer 57. The power supplied from the AC power supply 56 by the voltage between both ends, that is, the total power consumption in the inverter circuits 41 and 42 can be detected.

Bridge diode 50 and AC power supply 5
6 constitutes a DC power supply that supplies DC power to the inverter circuits 41 and 42.

Driving circuits 61 and 62 are connected to the control terminals of the switching elements 31 and 32, respectively.
Control ICs 63 and 64 are connected to the control ICs 1 and 62, respectively. The control ICs 63 and 64 are connected to the CPU 65.

The drive circuits 61 and 62 apply a drive voltage of a predetermined level (for example, 24 V) to the switching element 3.
The switching elements 31,
32 is turned on. Control ICs 63 and 64
Outputs a pulse voltage signal having a frequency equal to or higher than a predetermined value (for example, 20 kHz to 50 kHz) to the drive circuits 61 and 62 in order to indicate the application timing of the drive voltage applied to the switching elements 31 and 32 from the drive circuits 61 and 62, respectively. Is what you do. As described later, the frequency and the on / off duty ratio of the pulse voltage signals output from the control ICs 63 and 64 are controlled by the CPU 65.

The CPU 65 is connected to a paper feed unit 70, an operation unit 80, and a document reading unit 90. Paper feed section 7
Reference numeral 0 denotes transfer papers of various sizes, and a paper transport unit 71 including a pair of rollers for transporting each transfer paper toward the photoconductor 3 (see FIG. 1) and a motor for driving the pair of rollers. Have.

In the present embodiment, for example, A3 size, B4 size, and A4 size transfer sheets are accommodated in the sheet feeding section 70. A3 size and B4 size transfer papers are accommodated so as to be transported along the long side direction (hereinafter, referred to as “A3R” and “B4R”, respectively). Further, A4 size transfer paper is accommodated so as to be transported along the long side direction (hereinafter, referred to as “A4R”), and is accommodated so as to be transported along the short side direction (hereinafter, referred to as “A4R”). "A4T"
That. ).

The operation unit 80 includes a print key for instructing the start of a copying operation, a copy number setting key for setting the number of copies for each document, and the like. A transfer paper selection key 81 for selecting a transfer paper to be used for copying is provided, and a magnification setting key 82 for setting a copy magnification.

The document reading section 90 reads a document image and sends the image data to the exposure section 4 (see FIG. 1).
An original size detecting unit 91 for detecting the size of the set original is provided.

When the print key is operated, the CPU 65 reads the document image by the document reading section 90,
The operation of the entire copying machine 1 is controlled, for example, by transferring a transfer sheet from the paper supply unit 70 and starting a copying operation. The CPU 65 has the following functions (1) to (3).

(1) A function as a size discriminating unit for discriminating a dimension in a width direction (direction of the center axis 16 of the heating roller 11) orthogonal to the transfer direction of the transfer paper selected by the transfer paper selection key 81. Instead of the transfer paper selection key 81, the size of the transfer paper to be conveyed is determined based on the document size detected by the document size detection unit 91 and the copy magnification set by the magnification setting key 82. Is also good.

(2) A function as a switch control unit that outputs a pulse signal having a predetermined ON / OFF duty ratio at a predetermined frequency or higher to the control ICs 63 and 64 and turns the switching elements 31 and 32 ON and OFF at a predetermined frequency or higher. At this time, by controlling the frequency and the on / off duty ratio, the coil 15 can be adjusted in accordance with the dimension in the width direction (the direction of the central axis 16 of the heating roller 11) orthogonal to the transfer direction of the transfer sheet.
1, 152 and the power supplied to the coil 153 are changed. As a result, the surface temperature distribution of the heating roller 11 in the area of the transfer paper passing through the fixing unit 8 is made uniform. The details of this control will be described later.

(3) The voltage between both ends of the resistor 58 connected in parallel to the secondary coil of the current transformer 57 is determined, and the AC power supplied from the AC power supply 56 is detected.
When controlling the power supplied to the coils 152 and 153, the detection results are used to control the on / off frequency of the switching elements 31 and 32 so that the total power supplied to the coils 151 to 153 is maintained at a constant value. And a function to adjust the duty ratio.

FIG. 4 is a diagram showing the surface temperature distribution of the heating roller 11 when the power supplied to the coils 151, 152 and 153 is changed by the CPU 65 according to the size of the transfer paper.

In this embodiment, as described above, since the A3 size, B4 size, and A4 size transfer papers are stored in the paper supply unit 70 (FIG. 3), the heating roller 1 of the fixing unit 8 is used.
The maximum value in the width direction of the transfer paper passing through No. 1 (in the direction of the central axis 16 of the heating roller 11) is the size A3R,
When the transfer paper of A4T is conveyed, the next largest value is when the transfer paper of size B4R is conveyed, and the minimum value is when the transfer paper of size A4R is conveyed.

FIG. 4 shows a case where transfer paper of size A3R, A4T is conveyed. In this case, 400 W, 6 W is applied to the coils 151, 152 and 153.
00 W of electric power is supplied. Indicates a case where a transfer sheet of size B4R is conveyed. In this case,
20 for the coils 151 and 152 and the coil 153
0 W and 800 W of electric power are supplied, respectively. Also, indicates a case where transfer paper of size A4R is conveyed. In this case, since the transfer paper only passes through the portion facing the coil 153, power is not supplied to the coils 151 and 152. Only the coil 153 is supplied with 1000 W of power.

That is, as the size of the transfer paper 7 in the width direction decreases, the power supplied to the central coil 153 in the direction of the central axis 16 of the heating roller 11 increases.
As a result, as shown in FIG. 4, the temperature is approximately 180 ° C. over the entire range where the transfer paper 7 passes on the heating roller 11 in any of the cases (1), (2), (3), and a substantially uniform temperature distribution is obtained. Have been.

As described above, according to the present embodiment, the power supplied to the coils 151, 152 and 153 is changed according to the size of the transfer paper 7 in the width direction (the direction of the central axis 16 of the heating roller 11). Therefore, the temperature distribution can be made substantially uniform over the entire range of the heating roller 11 through which the transfer paper 7 passes.

According to the present embodiment, when the transfer paper 7 does not pass through the area facing the coils 151 and 152, the power supply to the coils 151 and 152 is stopped.
Power consumption can be reduced.

According to the present embodiment, the coil 151
153, the supply power to the coil 153 increases as the width of the transfer paper 7 decreases. For example, when the transfer paper of size B4R is conveyed compared to the case where the transfer paper of size A3R and A4T is conveyed, the power supplied to the coil 153 is reduced.
It has increased from 600W to 800W. That is, the ratio of the power supplied to the coil 153 to the power supplied to the coils 151 and 152 is changed according to the size of the transfer paper 7 in the width direction. Accordingly, even when transfer paper of an intermediate size such as the size B4R is conveyed, the temperature distribution of the heating roller 11 can be made uniform without increasing the number of cores and coils.

Since the total power supplied to the coils 151, 152 and 153 is maintained at a constant value, energy efficiency can be improved and power consumption can be reduced.

Since one bridge diode 50 is provided and a circuit for supplying DC power to the inverter circuits 41 and 42 is shared, the number of components such as bridge diodes and current transformers can be reduced.

The present invention is not limited to the above-described embodiment, but can employ the following modified embodiments.

(1) In the above embodiment, the cores 141 to 1
43 and three coils 151 to 153, respectively, but are not limited thereto. For example, heating roller 1
N (n is an integer of 2 or more) cores provided side by side along the central axis 16 inside the one coil holding portion 21 and provided in a direction orthogonal to the central axis 16, and wound around each core It may be configured with the n coils set as described above.

The above n is an odd number of 5 or more, and the m-th core (m is an integer of 1 ≦ m ≦ (n−1) / 2) from one end of the central axis 16 and the m-th core from the other end. And the coil wound around the m-th core from one end side and the coil wound around the m-th core from the other end side are respectively constituted by the same conductor, Switching means for turning on and off the power supply to each coil wound around the m-th core may be shared by one switching means.

According to this embodiment, by controlling the power supplied to each coil, the surface temperature distribution of the heating roller 11 can be made uniform in the range where each transfer sheet passes for transfer sheets of various sizes. Can be achieved.

(2) In the above embodiment, a circuit for supplying DC power to the inverter circuits 41 and 42 is shared. However, the present invention is not limited to this. A DC power supply circuit is individually provided, and a current is supplied to each circuit. A transformer may be provided. According to this aspect, the power supply can be individually detected by each current transformer, so that the power supply to each coil can be more finely controlled.

(3) In the above embodiment, the current transformer 57 is provided, and the total power consumption is detected based on the current transformer 57. However, the present invention is not limited to this.
The ON time of the switching elements 31 and 32 may be integrated by the PU 65, and the power consumption may be calculated based on the integrated time. According to this embodiment, the current transformer can be omitted, and the number of components can be reduced.

(4) The power supplied to each coil in FIG. 4 of the above embodiment is not limited to the above numerical values. In accordance with the material of the heating roller 11 and the surface temperature suitable for fixing, electric power for obtaining a desired surface temperature may be supplied to each coil.

Although the total power supplied to each coil is set to a constant value of 1000 W as shown in FIGS. 4A to 4C, the present invention is not limited to this. For example, when power is supplied only to the coil 153 as shown in FIG.
If the temperature of the heating roller 11 is maintained at a desired temperature (for example, 180 ° C. in the figure) even at 900 W), the coil 153
It is sufficient to reduce the power supplied to the power supply.

In this case, a temperature sensor composed of a thermistor or the like may be arranged on the surface of the heating roller 11, and the power supplied to the coil may be increased or decreased according to the surface temperature detected by the temperature sensor.

(5) Although the above embodiment has been described using a copying machine, the present invention is not limited to this, and the present invention can be applied to an electrophotographic image forming apparatus such as a facsimile or a printer.

[0074]

As described above, according to the first aspect of the present invention, the n cores are arranged along the central axis inside the hollow roller and provided in a direction perpendicular to the central axis, and Are wound around each of the cores, and k switching means for turning on and off the power supply from the power supply unit to each coil are turned on and off at a frequency equal to or higher than a predetermined frequency, and the on / off duty ratio is changed to change the on / off duty ratio. The power supplied to the coil is controlled. At this time, the size of the transfer paper in the central axis direction is determined, and the power supplied to each coil is changed according to the determination result. The surface temperature distribution of the hollow roller can be made uniform with respect to paper.

According to the second aspect of the present invention, the power is supplied only to the coil, of the n coils, through which the transfer paper passes in the area facing the coil. When the image is small, for example, unnecessary portions for fixing the toner image on the transfer paper are not heated, so that the power consumption can be reduced.

According to the third aspect of the present invention, when the transfer paper passes through a part of the opposing area of each coil, compared to when the transfer paper passes through the entire opposing area of each coil, each coil The power supply to the hollow roller is reduced, so that the temperature distribution of the hollow roller can be maintained more uniformly.

According to the fourth aspect of the present invention, the m-th core from one end and the m-th core from the other end of the central axis are set to the same size, and each m-th core has Since the wound coils are set to the same number of turns and the same power is supplied to the coils wound around each m-th core, the center of the hollow roller in the center axis direction is Are symmetrically arranged, and the position and intensity of the high-frequency magnetic field generated by the coil are also symmetrical.
By aligning the center of the transfer sheet in the center axis direction with the center of the hollow roller, a toner image can be suitably fixed on transfer sheets of various sizes.

According to the fifth aspect of the present invention, the coils wound around each m-th core are connected in series with each other, and power is supplied to each coil wound around each m-th core. Since the switching means to be turned on and off is shared by one switching means, the number of the switching means is reduced while maintaining a symmetric state of the high-frequency magnetic field generated by the coil. Points can be reduced.

According to the sixth aspect of the present invention, the AC power supply and the rectifying means connectable to the AC power supply constitute a power supply unit, and the AC power output from the AC power supply is rectified by n DC powers. To supply the coil
Since one rectifier is shared by n coils, it is possible to supply DC power to each coil with a simple configuration.

According to the seventh aspect of the present invention, when an AC power supply is connected to the rectifying means, the power supplied from the AC power supply to the rectifying means is detected, and k is determined based on the detection result.
Since the on / off duty ratio of the switching means is controlled, appropriate power is supplied to each coil,
The surface temperature of the hollow roller can be made uniform.

[Brief description of the drawings]

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

FIGS. 2A and 2B are diagrams showing a configuration of a heating roller. FIG. 2A is a perspective view of the heating roller, and FIG. 2B is a transparent perspective view showing an internal configuration of a coil holding unit.

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

FIG. 4 is a diagram illustrating a surface temperature distribution of a heating roller when a power supply to a coil is changed by a CPU according to a transfer sheet size.

[Explanation of symbols]

 8 Fixing Unit 11 Heating Roller (Hollow Roller) 141-143 Core 151-153 Coil 31, 32 Switching Means 50 Bridge Diode (Power Supply) 56 AC Power Supply (Power Supply) 65 CPU (Determination Unit, Control Unit) 81 Transfer Paper Selection Key

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H05B 6/44 H05B 6/44

Claims (7)

[Claims] A coil is disposed inside a hollow roller formed of a conductive member and rotatably held about a central axis, and a high-frequency power is supplied to the coil to supply the coil with the coil. An induction heating type fixing device that heats the hollow roller by generating an eddy current and fixes the toner image formed on the transfer paper to the transfer paper using the heated hollow roller, It is juxtaposed along the central axis inside the hollow roller,
N (n is an integer of 2 or more) cores provided in a direction orthogonal to the central axis, n coils wound on each of the cores, and power supply from a power supply unit to each of the coils Turn on / off
(K is an integer equal to or less than n) switching means, and control for turning on / off each of the switching means at a predetermined frequency or more, and changing the on / off duty ratio to control power supplied from the power supply unit to each of the coils. Means, and discriminating means for discriminating the dimension of the transfer paper in the central axis direction, wherein the control means changes power supplied to each of the coils according to the discrimination result by the discriminating means. A fixing device. 2. The fixing device according to claim 1, wherein the control unit supplies power only to the coil, of the n coils, through which the transfer paper passes in a region facing the coil. A fixing device. 3. The fixing device according to claim 2, wherein the control unit transfers a part of the opposing area of each coil to the transfer area as compared with when the transfer paper passes through the entire opposing area of each coil. When the paper passes, the fixing device reduces the power supplied to each of the coils. 4. The fixing device according to claim 1, wherein an m-th core from one end of the central axis (m is an integer of 1 ≦ m ≦ n / 2) and an m-th core from the other end are The coils wound around the m-th core are set to the same number of turns, respectively, and the control means controls the coil wound around the m-th core. A fixing device for supplying the same electric power. 5. The fixing device according to claim 4, wherein the coils wound around the respective m-th cores are connected in series with each other, and the coils wound around the respective m-th cores are connected to each other. The switching means for turning on and off the power supply includes:
A fixing device characterized by being shared by one switching means. 6. The fixing device according to claim 1, wherein the power supply unit includes an AC power supply and a rectifying unit connectable to the AC power supply, and the AC power output from the AC power supply. A fixing device, wherein DC power obtained by rectifying power by the rectifier is supplied to the n coils. 7. The fixing device according to claim 6, further comprising: a detection unit configured to detect power supplied from the AC power supply to the rectification unit when the AC power supply is connected to the rectification unit; Is a device for controlling the on / off duty ratio of said k switching means based on the detection result of said detection means.