JP3545996B2 - Fixing device - Google Patents

Description

[0001]
TECHNICAL 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]
[Prior art]
Generally, in an electrophotographic image forming apparatus, a toner image formed by an image forming unit composed of a photoconductor or the like is transferred by a transfer unit to transfer paper conveyed from a paper feed unit to a photoconductor position, and is transferred by a fixing unit. After the toner image is fixed on the transfer paper, the toner image is discharged out of the apparatus.
[0003]
As a fixing unit, a heat roller fixing method including a heating roller and a pressure roller is often used recently in terms of speeding up. 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.
[0005]
On the other hand, a core around which a coil is wound is disposed inside or outside a heating roller formed of a conductive member, and high-frequency power is supplied to the coil. 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 (Japanese Patent Application Laid-Open No. H11-163873). See JP-A-54-39645, JP-A-7-295414, and JP-A-9-258586.
[0006]
Since the induction heating type fixing device heats the roller itself, it is more efficient than a method 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]
[Problems to be solved by the invention]
However, if the coil is arranged inside the heating roller, the coil itself will be heated by the radiant heat from this roller. Then, the characteristics of the coil, such as the resistance value and the inductance value, change and the efficiency decreases, and the coil wire itself melts to cause dielectric breakdown, which may have a great effect on the power supply for supplying power to the coil. there were. For this reason, it is necessary to forcibly cool the coil using a fan or the like, which is inefficient such as cooling while heating. In the case of forcible cooling, the opening of the roller must be large, and the temperature drop at both ends of the roller is accelerated.
[0008]
On the other hand, even if a coil is arranged outside the heating roller, although forced cooling of the coil is not required, natural cooling by air inflow and outflow from both ends of the roller and heat conduction is also required. However, the heating and cooling are inefficient, and the temperature at both ends of the roller is remarkably reduced.
[0009]
In any case, since the temperature drop at both ends of the roller impairs uniform fixing performance over the entire length of the roller, conventionally, the number of windings of the coil is made closer at the roller end side than at the roller center side, A complicated configuration was inevitable, such as splitting the coils and controlling each one independently.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above problem and to provide an induction heating type fixing device capable of further improving heating efficiency with a simple configuration.
[0011]
[Means for Solving the Problems]
According to the first aspect of the present invention, a coil is disposed close to a hollow roller which is formed of a ferromagnetic material and is rotatably held around a central axis, and high-frequency power is supplied to the coil. An induction heating type fixing method in which the hollow roller is heated by generating an eddy current in the hollow roller, and the toner image formed on the transfer paper is fixed on the transfer paper using the heated hollow roller. A device, wherein the coil is disposed outside the hollow roller, and a cover made of resin or a weak magnetic material is provided at both ends of the hollow roller, and the cover can be fitted to a predetermined depth on the inner surface of the hollow roller. Cylindrical guide part, a disc-shaped flange part that regulates the predetermined depth and closes one end of the guide part, and is formed coaxially with the hollow roller outside the flange part and rotates on the bearing part of the hollow roller. Possible And it is characterized in that it is composed of a rotation shaft and which is supported.
[0012]
According to this configuration, since the coil is disposed outside the hollow roller, the coil is naturally cooled while the roller is only heated. Therefore, the inefficiency of cooling while heating the roller is eliminated. In addition, lids made of resin or a weak magnetic material are provided at both ends of the coil, and the lid regulates the cylindrical guide portion which can be fitted to the inner surface of the hollow roller to a predetermined depth, and regulates the predetermined depth. Since it is composed of a disk-shaped flange portion closing one end of the guide portion, and a rotary shaft portion formed coaxially with the hollow roller outside the flange portion and rotatably supported by the bearing portion of the hollow roller . Thus, natural cooling due to the inflow and outflow of air from both ends of the roller is almost eliminated, and the heating efficiency is improved.
[0013]
In addition , since efficient induction heating is performed, the heating efficiency is further improved.
[0014]
If the lid is made of a heat-insulating material as in the second aspect of the invention, heat dissipation from the roller ends due to heat conduction is reduced, and the heating efficiency is further improved.
[0015]
If the lid has an air hole as in the third aspect of the present invention, pressure increase due to air expansion in the roller is prevented.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a configuration diagram showing a main part of an embodiment of a copying machine to which a fixing device according to the present invention is applied.
[0017]
In the copying machine 1, the photoconductor 3 is uniformly charged by the charging unit 2, and is stuck on the photoconductor 3 by 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, 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 7 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 7 by the transfer unit 6.
[0018]
Then, the transfer paper 7 separated from the photoreceptor 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 by a discharge roller pair 9 (not shown). Is discharged to the department.
[0019]
The fixing unit 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.
[0020]
The heating roller 11 is a cylindrical hollow roller having a diameter of about 40 mm and formed of a conductive member, and is as thin as possible so as to be quickly heated. A layer is provided. A core 14 made of ferrite or the like is provided at a predetermined position outside the roller 11, and a coil 15 made of, for example, a copper wire is wound around the heating core 14. As the conductive member, iron, nickel, or the like, which is a ferromagnetic material, is suitable from the viewpoint of dielectric heating efficiency, and stainless steel represented by, for example, SUS430 is more preferable from the viewpoint of corrosion resistance. However, a weak magnetic material or a non-magnetic material may be used as needed.
[0021]
The heating roller 11 is rotatably held by a fixing unit 13 around a central shaft 16 (see FIG. 2), and a drive gear (not shown) is attached to one end of the heat roller 11, and a motor ( (Not shown).
[0022]
On the other hand, the pressure roller 12 has a surface slightly softer than the surface of the heating roller 11 and is made of, for example, silicon rubber, is brought into contact with the heating roller 11, is pressed with a predetermined pressure, and is rotatably held by the fixing unit 13. , Driven by the rotation of the heating roller 11.
[0023]
When the transfer paper 7 is conveyed between the rollers 11 and 12, the transfer paper 7 is sandwiched by the two rollers, and the toner image transferred to the transfer paper 7 is heated and fixed to the transfer paper 7. At this time, since the transfer paper 7 after fixing may be wound around the heating roller 11 and not peeled off, a section-shaped separating member 20 is disposed downstream of the contact position of the heating roller 11 so as to forcibly remove the paper. Is established.
[0024]
FIG. 2 is a perspective view showing the configuration of the coil and the heating roller. The same elements as those in FIG. 1 are denoted by the same reference numerals.
[0025]
The core 14 around which the coil 15 is wound is arranged outside the heating roller 11 while maintaining a predetermined gap between the core 14 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 this gap.
[0026]
The core 14 is arranged parallel to the heating roller 11, and has a rectangular cross section perpendicular to the central axis 16 in which two parallel grooves are formed on the side facing the heating roller 11. Is slightly smaller than The coil 15 is formed of a single copper wire, and is ideally wound in a single-step spiral shape in the parallel groove of the core 14, but may be wound in a plurality of steps. In the illustrated example, the coils 15 are wound so as to be accommodated in the parallel grooves in a three-fold manner. However, in practice, the coils 15 are wound so as to be further multiplexed and accommodated. With such a configuration, the magnetic field generated around the wound coil 15 can be strengthened.
[0027]
In FIG. 2, the core 14 is disposed on the upper right side of the heating roller 11 and is set to have substantially the same size as the longitudinal direction of the heating roller 11, and the copying machine 1 of the present embodiment is an A3-size transfer sheet. When the transfer roller 7 (see FIG. 1) is conveyed in the long side direction and is copied, the transfer paper 7 can be brought into contact and fixed over the entire length of the heating roller 11.
[0028]
In the present embodiment, both ends of the heating roller 11 are closed with caps (lids) 17. The cap 17 includes a cylindrical guide portion 17a that can be fitted to the inner surface of the heating roller 11 to a predetermined depth, a disc-shaped flange portion 17b that regulates the predetermined depth and closes one end of the guide portion 17a, A cylindrical rotary shaft portion 17c having a diameter of about 20 mm formed coaxially with the heating roller 11 outside the heating roller 17b. The rotary shaft portion 17 is fitted into a bearing portion 18 of the heating roller 11 by fitting. , And rotatably supported by the fixing unit 13 in FIG. The air exchange between the inside and outside of the heating roller 11 is blocked by the flange portion 17b of the cap 17, so that the temperature at the end of the heating roller 11 is prevented from lowering, and the heating efficiency can be improved.
[0029]
The guide portion 17a, the flange portion 17b, and the rotary shaft portion 17c of the cap 17 include, for example, resins, metals, and ceramics as materials to be used. It is difficult to transmit heat to the bearing portion 18 and the impact resistance is high. For example, a heat-resistant resin such as PBT or phenol, or SUS304, which is a weak magnetic material and a metal having a relatively low thermal conductivity, can be cited as suitable constituent materials. Thereby, the heating efficiency can be further improved while protecting the bearing portion 18 from the heat of the heating roller 11.
[0030]
Further, a through hole (air hole) 19 having a diameter of 2 to 3 mm or less is provided at the center of the flange portion 17b of the cap 17. This is because the air confined inside the roller by providing the cap 17 is thermally expanded when the heating roller 11 is heated, and the internal pressure of the roller is increased, so that the cap 17 is prevented from dropping or jumping out. . Providing the through holes 19 also has an advantage that the cap 17 can be easily press-fitted in the assembling process. In addition, only the bearing portion 18 can be made smaller, which is effective in reducing the sliding load of the bearing portion 18 and the cost of the bearing member.
[0031]
By the way, in the present embodiment, the core 14 around which the coil 15 is wound is disposed outside the heating roller 11, but the disposing position is as close as possible to the contact portion between the heating roller 11 and the pressure roller 12. Is limited only to the upstream part of. The reason is that the contact between the heating roller 11 and the pressure roller 12 is not actually a line contact, but is performed in a range having a width of about 8 to 10 mm. This is because it is necessary to dispose the coil 15 at a position near the upstream portion of the printer and quickly melt the toner image transferred onto the transfer paper 7 conveyed here.
[0032]
On the other hand, a separation member 20 for peeling off the transfer paper 7 after fixing is provided in a downstream portion of the contact portion of the heating roller 11, but the temperature is as low as possible before the separation by the separation member 20. This is because it is necessary to cool the toner image once melted and to reliably fix the toner image on the transfer paper 7 by lowering the temperature. For this reason, in the present embodiment, the coil 15 is not provided in the downstream portion of the contact portion of the heating roller 11.
[0033]
FIG. 3 is a block diagram showing a main part of an electric configuration of the copying machine 1. As shown in FIG. The same elements as those in FIGS. 1 and 2 are denoted by the same reference numerals.
[0034]
In FIG. 3, a resonance capacitor C1 is connected in parallel to a coil 15 (copper wire) to form a resonance circuit, and a switching element 31 is connected between one end of the resonance circuit and ground to form an inverter circuit 41. Have been.
[0035]
The switching element 31 is a power semiconductor element having a high withstand voltage and a large current. When a predetermined level of drive voltage is applied to the control terminal, one end of each resonance circuit is electrically connected to the ground. For example, an IGBT, a MOS-FET, or the like can be employed.
[0036]
The other end of the resonance circuit is connected to one DC output terminal 51 of the bridge diode 50. The other DC output terminal 52 of the bridge diode 50 is grounded, and the AC input terminals 53 and 54 can be connected to an AC power supply 56 of 100 V AC via a connection 55.
[0037]
A primary coil of a current transformer 57 is interposed between the AC input terminal 54 of the bridge diode 50 and the connection portion 55, and 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, that is, the total power consumption in the inverter circuit 41, can be detected by the voltage across the resistor 58. The bridge diode 50 and the AC power supply 56 constitute a DC power supply that supplies DC power to the inverter circuit 41. A drive circuit 61 is connected to a control terminal of the switching element 31, and a control IC 63 is connected to the drive circuit 61, and the control IC 63 is connected to a CPU 65.
[0038]
The drive circuit 61 turns on the switching element 31 by applying a driving voltage of a predetermined level (for example, 24 V) to the control terminal of the switching element 31. The control IC 63 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 circuit 61 in order to indicate the application timing of the drive voltage applied to the switching element 31 from the drive circuit 61. The frequency of the pulse voltage signal output from the control IC 63 is controlled by the CPU 65.
[0039]
The CPU 65 is connected with a paper feed unit 70, an operation unit 80, and a document reading unit 90. The paper feed unit 70 accommodates transfer papers 7 of various sizes, and includes a roller pair for transporting each transfer paper 7 toward the photoconductor 3 (see FIG. 1), a motor for driving the roller pair, and the like. A paper transport unit 71 is provided.
[0040]
In the present embodiment, for example, A3 size, B4 size, and A4 size transfer papers 7 are accommodated in the paper supply unit 70 in the transport direction. 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 the transfer paper 7 used for copying and a magnification setting key 82 for setting a copy magnification are provided.
[0041]
The document reading unit 90 reads a document image and sends the image data to the exposure unit 4 (see FIG. 1), and includes a document size detection unit 91 that detects the size of the set document.
[0042]
When the print key is operated, the CPU 65 reads the original image by the original reading unit 90 and controls the entire operation of the copying machine 1 such as starting the copying operation by transporting the transfer paper 7 from the paper feeding unit 70. is there.
[0043]
With such a configuration, when high-frequency power (high-frequency current) is supplied to the coil 15, a high-frequency magnetic field is generated. For example, in FIG. 1, a high-frequency current is applied to the coil 15 accommodated in the upper groove in a direction toward the rear of the paper, and a high-frequency current is applied to the coil 15 accommodated in the lower groove in a direction toward the front of the paper. Then, a high-frequency magnetic field centering on the coil 15 is generated in accordance with the right-hand screw rule.
[0044]
The high-frequency magnetic field links to a portion of the heating roller 11 facing the coil, and an eddy current is generated in the heating roller 11. The heating roller 11 is heated by Joule heat generated by the eddy current, thereby transferring the toner image. Fixing to the paper 7 is suitably performed.
[0045]
At this time, according to the present embodiment, since the coil 15 is disposed outside the heating roller 11, the coil 15 is allowed to cool naturally while the heating roller 11 is only heated. Therefore, the inefficiency of cooling the heating roller 11 while heating it is eliminated. In addition, since the caps 17 are provided at both ends of the heating roller 11, natural cooling due to the inflow and outflow of air from both ends of the heating roller 11 is almost eliminated, and the heating efficiency is improved. Further, the density of the coil 15 may be uniform over the entire length of the heating roller 11, and it is not necessary to divide the coil 15 and control each of them separately, so that a very simple configuration is sufficient.
[0046]
In the above embodiment, both ends of the heating roller 11 are closed with the separate caps 17. However, the heating roller 11 and the cap 17 may be integrally formed, and a heat insulating material may be attached to the cap 17. . In that case, the configuration becomes even simpler. Further, the through hole 19 does not need to be formed at the center of the flange portion 17 b of the cap 17, and need not be provided at both the caps 17 at both ends of the heating roller 11. What is necessary is just to allow air to enter and exit from at least one end of the heating roller 11.
[0047]
In the above embodiment, the core 14 has a rectangular cross section perpendicular to the central axis 16 of the heating roller 11. However, the core 14 may have a curved shape (saddle shape) along the outer surface of the heating roller 11. Good. In this case, since the gap between the coil 15 wound around the core 14 and the surface of the heating roller 11 can be made constant, the heating efficiency can be further improved.
[0048]
Further, in the above-described embodiment, the description has been made using a copying machine. However, 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.
[0049]
【The invention's effect】
According to the first aspect of the present invention, the inefficiency of cooling while heating the roller is eliminated, and natural cooling due to the inflow and outflow of air from both ends of the roller is almost eliminated, thereby improving the heating efficiency. it can.
[0050]
Further, it is possible to further improve the heating efficiency by performing efficient induction heating.
[0051]
According to the second aspect of the present invention, heat radiation from the roller end due to heat conduction is reduced, and the heating efficiency can be further improved.
[0052]
According to the third aspect of the present invention, it is possible to prevent pressure rise due to air expansion in the roller and prevent the lid from falling off or jumping out of the roller. There is also an advantage that the lid can be easily pressed into the roller in the assembling process.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a main part of an embodiment of a copying machine to which a fixing device according to the present invention is applied.
FIG. 2 is a perspective view showing a configuration of a coil and a heating roller.
FIG. 3 is a block diagram showing a main part of an electric configuration of the copying machine.
[Explanation of symbols]
8 Fixing unit 11 Heating roller (hollow roller)
14 Core 15 Coil 16 Center shaft 17 Cap (lid)
17a Guide part 17b Flange part 17c Rotation shaft part 18 Bearing part 19 Through hole (air hole)
20 Separation member

Claims (3)

A coil is disposed in proximity to a hollow roller rotatably held around a central axis in a cylindrical shape formed of a ferromagnetic material, and high-frequency power is supplied to this coil to generate an eddy current in the hollow roller. Heating the hollow roller by causing the toner image formed on the transfer paper to be fixed to the transfer paper using the heated hollow roller, wherein the induction coil is fixed. Along with being provided outside the hollow roller, lids made of resin or a weak magnetic material are provided at both ends of the hollow roller, and the lid has a cylindrical guide portion that can be fitted to a predetermined depth on the inner surface of the hollow roller; A disk-shaped flange portion that regulates the predetermined depth and closes one end of the guide portion; and a rotary shaft formed coaxially with the hollow roller outside the flange portion and rotatably supported by a bearing portion of the hollow roller. Department Fixing apparatus characterized by being configured. The lid fixing apparatus according to claim 1, characterized in that formed in the heat-insulating material. The lid fixing apparatus according to claim 1 or 2, characterized in that with an air hole.

Images