JP3637956B2 - Fixing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fixing device that fixes a toner image transferred onto a recording medium by electromagnetic induction heating in an image forming apparatus such as a copying machine, a printer, a fax machine, or the like that uses electrophotography.
[0002]
[Prior art]
In the image forming apparatus, an electrostatic latent image is formed on an image carrier such as a photosensitive member, the electrostatic latent image is developed into a toner image, and then the toner image is transferred onto a recording medium. The toner image transferred above is fixed by a fixing device. Conventionally, various fixing methods using electromagnetic induction heating have been proposed as the fixing device. For example, Japanese Patent No. 2616433 proposes a method in which the magnetic field generating means is arranged in an arc shape along the outer periphery excluding the contact portion between the fixing roller and the pressure roller.
[0003]
[Problems to be solved by the invention]
However, in the conventional fixing device, in order to increase the heating efficiency, the gap between the fixing roller and the magnetic field generating means is set small, so that the excitation coil is heated by heat transfer from the heated fixing roller, There is a problem that the magnetic field generation efficiency decreases due to the temperature rise of the coil, and as a result, the heating efficiency decreases. In addition, the coil temperature rise causes a problem that the insulating material of the coil and the holding member of the coil are thermally deteriorated and the durability is lowered.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described conventional problems, and to provide a fixing device capable of preventing a temperature rise of a magnetic field generating unit, improving heating efficiency, and improving durability. To do.
[0005]
[Means for Solving the Problems]
Therefore, the fixing device of the present invention is a fixing device for fixing toner on a recording medium by electromagnetic induction heating, a fixing roller made of a magnetic material, a pressure roller pressed against the fixing roller, and an outer periphery of the fixing roller. And a magnetic field generating means disposed in the air passage, and an air passage is formed in a central portion of the magnetic field generating means.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram showing an example of an image forming apparatus to which the present invention is applied. This image forming apparatus is a color electrophotographic printer capable of forming a full-color image with four color toners, but the present invention is not limited to this, and is applicable to all image forming apparatuses using electrophotography. Applicable.
[0007]
The photosensitive member 1 has a thin cylindrical conductive substrate and a photosensitive layer formed on the surface thereof, and is driven to rotate in the direction of the arrow shown by a driving unit (not shown). Around the photoconductor 1, a charging device 2 for uniformly charging the photoconductor 1 along the rotation direction, an exposure device 3 for forming an electrostatic latent image on the photoconductor 1, a static A rotary developing device 4 for developing an electrostatic latent image, an intermediate transfer drum 5 and a primary transfer device 6 for transferring a monochromatic toner image formed on the photosensitive member 1, and an intermediate transfer drum 5 are provided. 2 is a secondary transfer device 7 for transferring a four-color full-color image formed on the intermediate transfer drum 5 onto a recording medium (paper or the like), and for fixing the toner image transferred onto the recording medium. A fixing device 9 is provided. In addition, 10 is a paper feed tray for storing a recording medium, and 11 is a recording medium conveyance path.
[0008]
The rotary developing device 4 is configured such that a yellow developing device 4Y, a cyan developing device 4C, a magenta developing device 4M, and a black developing device 4K can be rotated, and these developing devices 4Y, 4C, 4M, and 4K. In this configuration, only the developing roller of one developing device can be brought into contact with the photosensitive member 1 selectively for each rotation of the photosensitive member 1. Each developing device is provided with a toner container 12 (only one tank is shown in the figure) in which each toner is stored.
[0009]
The operation of the image forming apparatus having the above configuration will be described. When an image forming signal is input from a computer (not shown), the photosensitive member 1, the developing roller of the developing device 4, and the intermediate transfer drum 5 are rotationally driven. First, the outer peripheral surface of the photosensitive member 1 is uniformly charged by the charging device 2, and the outer peripheral surface of the uniformly charged photosensitive member 1 is subjected to image information of the first color (for example, yellow) by the exposure device 3. Selective exposure is performed to form a yellow electrostatic latent image.
[0010]
The yellow developing unit 4Y is rotated on the photosensitive member 1 and the developing roller comes into contact therewith, whereby a yellow electrostatic latent image toner image is formed on the photosensitive member 1. The primary transfer device 6 is applied with a primary transfer voltage having a polarity opposite to the charging polarity of the toner, and the toner image formed on the photoreceptor 1 is transferred onto the intermediate transfer drum 5. At this time, the secondary transfer device 7 is separated from the intermediate transfer drum 5. The toner remaining on the photosensitive member 1 is removed by a photosensitive member cleaning device (not shown), and then the outer peripheral surface of the photosensitive member 1 is discharged by a discharging means (not shown).
[0011]
In response to the second color, the third color, and the fourth color of the image formation signal, the above processing is repeated to form a latent image, develop, and transfer by one rotation of the photosensitive member 1 and the intermediate transfer drum 5, and the image formation is performed. Four color toner images corresponding to the contents of the signals are superimposed on the intermediate transfer drum 5 and transferred. Then, at the timing when this full-color image reaches the secondary transfer device 7, the recording medium is supplied from the transport path 11 to the secondary transfer device 7, and at this time, the secondary transfer device 7 is pressed against the intermediate transfer drum 5. A secondary transfer voltage is applied, and the full-color toner image on the intermediate transfer drum 5 is transferred onto the recording medium. The toner image transferred onto the recording medium is fixed by being heated and pressed by the fixing device 9.
[0012]
The present invention relates to the fixing device 9. FIGS. 2 to 5 show one embodiment of the fixing device of the present invention, FIG. 2 is a sectional view of the fixing device, and FIG. FIG. 4 is a side view showing a partially broken section viewed from the X direction in FIG. 2, FIG. 5 (A) is a plan view of the magnetic field generating means, and FIG. 5 (B) is FIG. FIG. In the following description, the same components may be denoted by the same reference numerals in the drawings, and description thereof may be omitted.
[0013]
In FIG. 2, the fixing device 9 includes a cylindrical fixing roller 13 made of a magnetic material, and a pressure roller 14 is in contact with and pressed against the fixing roller 13. The pressure roller 14 includes a cylindrical rotary shaft 15 and an elastic layer 16 such as silicon rubber on the outer periphery thereof. When the fixing roller 13 and the pressure roller 14 rotate as indicated by the arrows in the drawing, the elastic layer 16 is fixed. A nip (pressure surface) N is formed by being pressed by the roller 13. On the outer periphery of the fixing roller 13, magnetic field generating means 17 is disposed with a predetermined gap from the fixing roller 13. The pressure roller 14, the fixing roller 13, and the magnetic field generating means 17 are accommodated in a case 21 made of a nonmagnetic material.
[0014]
2 to 5, the magnetic field generating means 17 has a coil holding member 19 made of an insulating material, and this coil holding member 19 is fixed to a case 21 by an attachment member 22. The coil holding member 19 is composed of two supports 19a and 19b disposed with a predetermined gap and spaced apart from the fixing roller 13, and the supports 19a and 19b are connected by a plurality of connecting pieces 19c. ing. As a result, a long hole-shaped air passage 23 is formed in the central portion of the coil holding member 19. The exciting coil 20 is held so that a loop is formed between the two supports 19a and 19b.
[0015]
An intake hole 21a is formed below the case 21, an exhaust hole 21b is formed at the top of the case 21, and a cooling fan device 24 is attached at a position facing the exhaust hole 21b. The cooling fan device 24 may not be provided and may be cooled by natural ventilation. A peeling claw 25 for peeling the recording medium from the fixing roller 13 is disposed on the outer periphery of the fixing roller 13 on the downstream side in the rotation direction of the nip N. Reference numeral 26 denotes a recording medium conveyance guide, and 27 denotes a recording medium conveyance roller.
[0016]
In FIG. 3, the fixing roller 13 and the pressure roller 14 are rotatably mounted on the case 21 by rotating shafts 29 and 30, respectively. A driving gear 31 is fixed to the rotation shaft 29 of the fixing roller 13, and the driving gear 31 is driven by an electric motor (not shown).
[0017]
In the magnetic field generating means 17, the exciting coil 20 is held in a loop shape on a coil holding member 19, and the magnetic field generating means 17 is substantially parallel along the outer peripheral surface of the fixing roller 13 and is in the axial direction of the fixing roller 13. It is wound along the outer periphery of a long rectangle or ellipse. As a result, the lines of magnetic force perpendicular to the coil forming surface are captured almost perpendicularly on the surface of the fixing roller 13, and an eddy current that circulates around the surface of the fixing roller 13 is generated to generate heat. A uniform temperature rise over a wide range of directions can be realized.
[0018]
Moreover, in order to make each exciting coil 20 hard to receive a magnetic loss, by making it a strand of a plurality of coated thin wires, a large current can be totally flowed, and even a small coil can be heated more efficiently. In addition, by using a stranded wire, the rigidity of the wire is increased and the coil can be easily created.
[0019]
Further, each turn of the exciting coil 20 is formed in one layer in the radial direction of the fixing roller 13 so as to be located in the same plane. If the coil line wound several times overlaps in the radial direction of the fixing roller, the magnetic field on the far side is canceled out by the magnetic force of the coil on the side close to the roller. Since the roller receives the magnetic lines of force generated by any of them, the heat generation efficiency can be improved. In addition, each turn of the exciting coil 20 is equivalent to winding the coils densely without gaps, thereby forming a thick wire coil, enabling efficient heat generation and eliminating portions where magnetic field lines cancel each other. Uniform heat generation on the roller surface facing the coil can be realized.
[0020]
Furthermore, since the ventilation path 32 can be formed in the central portion of the magnetic field generating means 17, the exciting coil 20 is cooled, and a decrease in heat generation due to an increase in coil temperature can be prevented. The coil holding member 19, the case 21, the transport guide 26, etc. are all made of a nonmagnetic material. If there is a magnetic material other than the fixing roller 13 around the magnetic field generating means 17, the magnetic force concentrates on the magnetic material and the temperature becomes partially high. However, by forming the adjacent member of the magnetic field generating means 17 with a nonmagnetic material. In addition, abnormal magnetic force concentration can be prevented, and the fixing roller 13 can be efficiently heated with uniform heating and no heating of other members.
[0021]
The operation of the present invention having the above configuration will be described. When an exciting current is supplied to the exciting coil 20 by an exciting circuit (not shown), an alternating magnetic field is generated between the exciting coil 20 and the fixing roller 13, and an electromagnetic induction action is applied to the magnetic fixing roller 13 placed in the alternating magnetic field. As a result, an eddy current flows, Joule heat is generated by the current and the resistance of the metal itself, the fixing roller 13 itself is self-heated, and its temperature rises. When the temperature of the fixing roller 13 is increased while the fixing roller 13 is rotated and the temperature of the fixing roller 13 is detected to be a predetermined temperature by the output of the temperature sensor 24, the surface temperature of the fixing roller 13 is thereafter set to the predetermined temperature. Controlled to maintain. When the recording medium is moved to the fixing roller 13, the recording medium is guided between the fixing roller 13 and the pressure roller 14 and heated and pressed by both rollers, so that the toner is placed on the recording medium. It is fixed. At this time, the air sucked from the intake hole 21a is exhausted from the exhaust hole 21b through the air passage 23 around the coil 20 and the central part of the coil 20 as shown by the dotted arrows in FIG. Can be effectively cooled.
[0022]
FIG. 6 is a plan view showing a modification of the magnetic field generating means according to the present invention. In addition, the same number is attached to the same structure as FIG. 5, and description is abbreviate | omitted. In this example, notches 19d are formed in the supports 19a and 19b so as to expose the coil 20, and the cooling effect is further enhanced.
[0023]
Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications are possible. For example, in the above-described embodiment, the fixing roller 13 and the pressure roller 14 are arranged in a substantially horizontal direction, and the conveyance direction Y of the recording medium is set to a substantially vertical direction from bottom to top. 13 and the pressure roller 14 may be arranged in a substantially vertical direction, and the recording medium conveyance direction Y may be a substantially horizontal direction.
[0024]
【The invention's effect】
As is apparent from the above description, according to the present invention, since the air passage is formed in the central portion of the magnetic field generating means, the exciting coil can be effectively cooled, and the temperature of the magnetic field generating means is prevented from rising. Heating efficiency can be improved. In addition, the coil insulating material and the coil holding member can be kept at a low temperature, thereby preventing thermal deterioration and improving its durability.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing an example of an image forming apparatus to which the present invention is applied.
FIG. 2 is a cross-sectional view showing an embodiment of a fixing device of the present invention.
FIG. 3 is a perspective view showing a state where a case is removed in FIG. 2;
4 is a side view showing a partially broken section viewed from the X direction in FIG. 2; FIG.
5A is a plan view of the magnetic field generating means, and FIG. 5B is a side view of FIG. 5A.
FIG. 6 is a plan view showing a modification of the magnetic field generating means.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 13 ... Fixing roller 14 ... Pressure roller 17 ... Magnetic field generation means 19 ... Coil holding member 19a, 19b ... Support body 19c ... Connection piece 20 ... Excitation coil 23 ... Airflow path

Claims (2)

In a fixing device for fixing toner on a recording medium by electromagnetic induction heating, a fixing roller made of a magnetic material, a pressure roller pressed against the fixing roller, and a magnetic field generating means disposed on an outer periphery of the fixing roller And a ventilation path formed in the center of the magnetic field generating means. The magnetic field generating means has a coil holding member for holding an exciting coil, and the coil holding member is composed of two supports that are arranged at a predetermined gap from the fixing roller and spaced from each other. The fixing device according to claim 1, wherein the support is connected by a plurality of connecting pieces, and an air passage is formed in a central portion of the coil holding member.

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