JP3548724B2 - Fixing device and image forming apparatus using the same - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fixing device for fixing an unfixed toner image transferred on a recording sheet and an image forming apparatus using the fixing device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus includes, for example, a photoconductor, a developing device, a transfer device, and a fixing device. The fixing device generally includes a pair of fixing rollers. The pair of fixing rollers include, for example, a heat roller heated to a predetermined fixing temperature and a pressure roller pressed against the heat roller at a predetermined fixing pressure. The recording paper on which the toner image has been transferred by the photoconductor passes between these pairs of fixing rollers, whereby the toner particles are melted and fixed.
[0003]
One of the heating methods of the heat roller is an IH (Induction Heating) method. FIG. 6 is a schematic diagram for explaining the magnetic flux 42 generated from the conventional induction heating coil 20A, and the heat roller 11 is heated by the IH method.
The heat roller 11 is, for example, cylindrical and formed of a ferromagnetic material such as iron or stainless steel. The heat roller 11 extends in a horizontal direction orthogonal to the sheet conveying direction, and an induction heating coil 20A extends in the inside thereof in the axial direction.
[0004]
The induction heating coil 20A includes a cylindrical bobbin 21 and a coil wire 22 wound (radially wound) around an axis on the outer peripheral surface of the bobbin 21. The coil wire 22 is made of, for example, a copper wire, and generates a high-frequency magnetic field when a high-frequency current is applied. The high-frequency magnetic field generates an induced eddy current in the heat roller 11, and the heat roller 11 itself generates Joule heat due to the material specific resistance of the heat roller 11 itself.
[0005]
In the bobbin 21, one core 41 made of, for example, ferrite, which does not easily generate heat and easily transmits magnetic flux, extends in the axial direction.
[0006]
[Problems to be solved by the invention]
However, as shown in FIG. 6, the entry points of the magnetic flux 42 to the heat roller 11 become non-uniform in the axial direction, and the magnetic flux 42 is coarse at both ends of the heat roller 11 and dense at the center. Since the heat generated by the IH method is proportional to the density of the magnetic flux 42 penetrating the heat roller 11, there is a problem that the temperature at both ends of the heat roller 11 decreases, and temperature unevenness occurs in the axial direction.
[0007]
In addition, as shown in FIG. 6, the magnetic flux 42 penetrates the heat roller 11 from one end to the other end, so that the magnetic flux 42 penetrates the heat roller 11 long. Therefore, there is a problem that the magnetic resistance is large, the oscillation waveform is easily attenuated, and it becomes difficult to control the oscillation on the high frequency power supply side. As measures against this problem, it is conceivable to increase the cross-sectional area of the coil wire 22 or increase the magnetic force generated by increasing the number of turns of the coil wire 22. In any case, the outer shape of the induction heating coil 20A is reduced. It gets bigger. In this case, a sufficient cooling space cannot be secured between the heat roller 11 and the induction heating coil 20A.
[0008]
The induction heating coil 20 </ b> A is heated by radiant heat from the heat roller 11. By sending air from outside the device to the cooling space, the induction heating coil 20A can be air-cooled. The heat roller 11 is controlled so that its surface temperature becomes a predetermined fixing temperature (for example, 190 ° C.), whereas the heat-resistant temperature of the induction heating coil 20A is, for example, 200 ° C., and a sufficient cooling space is secured. There must be.
[0009]
Although it is conceivable to increase the diameter of the heat roller 11 in order to secure a cooling space, in this case, the heat capacity of the heat roller 11 increases, and it takes time to heat the heat roller 11 to a predetermined temperature.
The present invention has been made in view of such a background, and an object of the present invention is to provide a fixing device capable of reducing temperature unevenness in the axial direction of a fixing roller and an image forming apparatus using the fixing device.
[0010]
It is another object of the present invention to provide a fixing device that facilitates oscillation control on the high frequency power supply side and an image forming apparatus using the same.
[0011]
Means for Solving the Problems and Effects of the Invention
According to an aspect of the present invention, there is provided a fixing roller for fixing a toner image to a recording sheet by conveying the recording sheet carrying an unfixed toner image while heating and pressing the recording sheet, and the fixing roller. A coil that is formed by spirally winding a coil wire around the axis of the fixing roller, and that generates a magnetic field for induction heating the fixing roller; and a coil that extends along the axis of the fixing roller. A plurality of cores provided so as to insert the coil and arranged so that the axial positions thereof partially overlap with each other, and an induction heating area by the coil is provided in a paper passing area of the recording sheet conveyed by the fixing roller. as the corresponding, characterized in that the core disposed at an end of the axial line direction among the plurality of cores and a core driving mechanism for displacing the said axial direction It is wearing equipment.
[0012]
According to this configuration, since a magnetic flux is generated from each of the plurality of cores provided along the axis in the coil, the magnetic flux density can be made uniform at both ends and the center of the fixing roller. Therefore, temperature unevenness in the axial direction of the fixing roller can be reduced.
Further, since the magnetic flux generated from each core passes through the fixing roller, the length of the magnetic flux passing through the fixing roller can be shortened. Accordingly, since the magnetic resistance can be reduced and the oscillation waveform can be suppressed from attenuating, it is possible to provide a fixing device in which the oscillation control on the high frequency power supply side is easy.
When the recording sheet is continuously conveyed, the heat of the fixing roller in the portion where the recording sheet is conveyed is taken away by the recording sheet. To compensate for this, control is performed so that more current flows through the coil.
According to the configuration of the present invention, the core disposed at the end of the coil is displaced in the axial direction so that the induction heating area by the coil corresponds to the paper passing area of the recording sheet conveyed by the fixing roller. Accordingly, it is possible to prevent the surface temperature of the portion where the recording sheet is not conveyed at both ends of the fixing roller from rising.
[0013]
In the invention according to claim 2, the plurality of cores are arranged in two rows along the axis of the fixing roller, and the axial positions of the adjacent cores in the axial direction of the fixing roller partially overlap. The fixing device according to claim 1, wherein the fixing devices are arranged alternately in one row and the other row.
According to this configuration, a magnetic flux is generated from each of the plurality of cores arranged in two rows along the axis in the coil.
[0014]
The length of the portion where the axial positions of the adjacent cores overlap in the axial direction of the fixing roller is preferably 10 to 20% of the length of the corresponding core. In this case, the magnetic flux density can be suitably made uniform at both ends and the center of the fixing roller.
[0016]
If the coil is wound so that the winding density at the end is higher than the winding density at the center, the magnetic flux passing through both ends of the fixing roller can be increased. Thus, it is possible to prevent the temperature at both ends of the fixing roller from decreasing and the temperature from being uneven in the axial direction.
Further, the core disposed at the end of the coil can increase the magnetic flux passing through both ends of the fixing roller even if the cross-sectional area is formed larger than the cross-sectional areas of the other cores. Thus, it is possible to prevent the temperature at both ends of the fixing roller from decreasing and the temperature from being uneven in the axial direction.
[0017]
According to a third aspect of the present invention, an unfixed toner image is formed on a recording sheet by developing the electrostatic latent image formed on the surface of the photoreceptor into a toner image and transferring the toner image to a recording sheet. an image forming unit, an image forming apparatus which comprises a fixing device according to claim 1 or 2, wherein for fixing on the recording sheet the unfixed toner image.
According to this configuration, it is possible to provide an image forming apparatus using the fixing device having the above effects.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of a main part showing an internal configuration of an image forming apparatus 1 to which a fixing device 8 according to an embodiment of the present disclosure is applied. The image forming apparatus 1 is, for example, a digital copying machine, and the surface of the photosensitive drum 3 is uniformly charged by the main charger 2 and an LSU (laser scanning unit) based on an image read by an image reading unit (not shown). The surface of the photosensitive drum 3 is selectively exposed by 4, and a so-called electrostatic latent image is written on the surface of the photosensitive drum 3. Thereafter, the developing device 5 develops the electrostatic latent image into a toner image, and the transfer device 6 transfers the toner image to recording paper. The recording paper is guided to the transfer device 6 at a predetermined timing from a paper supply unit (not shown).
[0019]
The main charger 2, the photosensitive drum 3, the LSU 4, the developing device 5, and the transfer device 6 constitute a series of image forming units.
The recording paper 7 after the transfer of the toner image is guided to a fixing device 8. The fixing device 8 includes a pair of fixing rollers 11 and 12 arranged vertically. The pair of fixing rollers 11 and 12 include, for example, a heat roller 11 heated to a predetermined fixing temperature and a pressure roller 12 pressed against the heat roller 11 at a predetermined fixing pressure. As the recording paper 7 passes between the fixing roller pairs 11 and 12, the toner particles transferred to the recording paper 7 are heated and pressed to be melted and fixed on the recording paper 7.
[0020]
The recording paper 7 that has been subjected to the fixing process by the fixing device 8 is discharged to the outside of the image forming apparatus 1 through the discharge roller pair 9.
FIG. 2 is a schematic side view illustrating the configuration of the fixing device 8. The heat roller 11 has a cylindrical shape and is formed of a ferromagnetic material such as iron or stainless steel. The heat roller 11 extends in a horizontal direction perpendicular to the paper transport direction A, and an induction heating coil 20 extends in the inside thereof in the axial direction.
[0021]
The induction heating coil 20 includes a cylindrical bobbin 21 and a coil wire 22 wound (radially wound) around the axis on the outer peripheral surface of the bobbin 21. The coil wire 22 is made of, for example, a copper wire, and is configured to generate a high-frequency magnetic field when a high-frequency current is applied. The high-frequency magnetic field generates an induced eddy current in the heat roller 11, and the heat roller 11 itself generates Joule heat due to the material specific resistance of the heat roller 11 itself.
[0022]
The heat roller 11 is held so as to be rotatable around its axis. The heat roller 11 is connected to a motor via, for example, a plurality of gears (not shown), and is driven to rotate in a direction indicated by an arrow in FIG. The induction heating coil 20 is held separately from the heat roller 11, so that the induction heating coil 20 does not rotate even if the heat roller 11 is driven to rotate.
The pressure roller 12 has, for example, a cylindrical shape and extends parallel to the heat roller 11. The pressure roller 12 is held so as to be rotatable around its axis, and its outer peripheral surface is pressed against the outer peripheral surface of the heat roller 11 at a predetermined fixing pressure. 2 in the direction shown by the arrow in FIG. In the present embodiment, the induction heating coil 20 is not provided inside the pressure roller 12, but the induction heating coil 20 may be provided inside the pressure roller 12 similarly to the heat roller 11.
[0023]
On the downstream side of the heat roller 11 in the sheet conveying direction, a peeling claw 23 for peeling off the recording sheet adhered to the heat roller 11 from the heat roller 11 is provided. The peeling claw 23 is rotatably held by a rotating shaft 25 fixed to the mounting frame 24, and its tip 23 a is slidably contacted with the outer peripheral surface of the heat roller 11 with an appropriate pressure by, for example, a spring (see FIG. (Not shown).
A thermistor 26 for detecting the surface temperature of the heat roller 11 is in contact with the outer peripheral surface of the heat roller 11. The detection result of the thermistor 26 is sent to a control unit (not shown), and the control unit adjusts the current applied to the coil wire 22 based on the detection result. Thus, the surface temperature of the heat roller 11 is controlled so as to reach a predetermined fixing temperature (for example, 190 ° C.).
[0024]
The induction heating coil 20 is heated by radiant heat from the heat roller 11. A cooling space is provided between the heat roller 11 and the induction heating coil 20, and the induction heating coil 20 can be air-cooled by sending air from outside the apparatus into the cooling space. While the heat roller 11 is controlled to have a temperature of 190 ° C., the heat-resistant temperature of the induction heating coil 20 is, for example, 200 ° C., so that a sufficient cooling space needs to be secured.
[0025]
FIG. 3 is a cross-sectional view illustrating the internal configuration of the induction heating coil 20. In the bobbin 21, a plurality of cores 27 made of, for example, ferrite, which does not easily generate heat and easily transmit magnetic flux, are arranged in two rows (for example, three in each row) in the axial direction. Each core 27 has, for example, the same rectangular parallelepiped shape, and has a length of, for example, 65 mm. The cores 27 in each row are arranged side by side at a predetermined interval B (for example, 45 mm).
[0026]
The cores 27 in one row and the cores 27 in the other row are arranged so as to alternately overlap by a predetermined length C (for example, 10 mm) in plan view. The predetermined length C is preferably set to be 10 to 20% of the length of the core 27.
The material, shape and number of the cores 27 are not limited to the above-described embodiments. Further, the numerical values of the predetermined interval B and the predetermined length C are not limited to the above numerical values.
[0027]
FIG. 4 is a schematic diagram for explaining a magnetic flux 39 generated from the induction heating coil 20. In this induction heating coil 20, a magnetic flux 39 is generated from each core 27. Thereby, the magnetic flux density becomes uniform at both ends and the center of the heat roller 11. Therefore, temperature unevenness in the axial direction of the heat roller 11 can be reduced.
Further, the magnetic flux 39 generated from each core 27 passes through the heat roller 11. As a result, the length of the magnetic flux 39 penetrating the heat roller 11 can be reduced, so that the magnetic resistance can be reduced and the oscillation waveform can be suppressed from attenuating. Therefore, it is possible to provide the fixing device 8 in which the oscillation control on the high frequency power supply side is easy.
[0028]
Referring again to FIG. 3, cores 27 a disposed at both ends of bobbin 21 among the plurality of cores 27 are capable of being displaced in the axial direction according to the size of the recording paper being conveyed. FIG. 3A shows a case where the size of the recording paper is large (for example, A4 horizontal (297 mm)), and FIG. 3B shows a case where the size of the recording paper is small (for example, A4 vertical ( 210 mm)).
When the recording paper is continuously conveyed, the heat of the heat roller 11 in the portion where the recording paper is conveyed is taken away by the recording paper. Therefore, in order to compensate for this, the current is controlled so that more current flows through the coil wire 22. In the present embodiment, the cores 27a disposed at both ends of the bobbin 21 are displaced so that the induction heating area by the induction heating coil 20 corresponds to the sheet passing area of the recording paper conveyed by the heat roller 11. Accordingly, it is possible to prevent the surface temperature of the portions of the heat roller 11 at both ends where the recording paper is not conveyed from rising.
[0029]
With reference to FIGS. 2 and 3, a core driving mechanism for displacing the cores 27a disposed at both ends of the bobbin 21 will be described.
A partition plate 28 extends in the bobbin 21 in the axial direction. A flat surface 29 is formed in the bobbin 21, and the partition plate 28 is fitted in a housing recess 30 formed in the flat surface 29.
The cores 27 in each row are arranged with a partition plate 28 interposed therebetween. A pair of holding members 31 for holding the plurality of cores 27 are arranged in the bobbin 21 with the partition plate 28 interposed therebetween.
[0030]
The holding member 31 has, for example, a substantially L-shaped cross section, and includes a lower plate 32 and a side plate 33 protruding upward from one side of the lower plate 32. The plurality of cores 27 are respectively fitted between the partition plate 28 and the respective holding members 31, and the lower surfaces thereof are held by the lower plate 32. The lower surface of the lower plate 32 of the holding member 31 is slidable on the flat surface 29 in the sheet width direction (the left-right direction shown in FIG. 3) orthogonal to the sheet conveyance direction A. Projections 34 protrude outward from the upper end of each side plate 33, and the tips of these projections 34 contact the inner peripheral surface of the bobbin 21, so that each holding member 31 can be displaced only in the paper width direction. Has become.
[0031]
Of the plurality of cores 27, the cores 27b other than the cores 27a disposed at both ends of the bobbin 21 have their both ends sandwiched by engagement projections 35 projecting outward from the partition plate 28, and cannot be displaced in the sheet width direction. It has become. On the other hand, the core 27a has both ends sandwiched by engagement projections 36 projecting inward from the side plate 33 of the holding member 31, and together with the holding member 31 sliding in the paper width direction. In the paper width direction.
[0032]
A rack 37 is formed inside one end of each holding member 31. A pinion 38 corresponding to the rack 37 is arranged between the pair of holding members 31, and the rack 37 of each holding member 31 is engaged with the pinion 38.
FIG. 5 is a schematic diagram for explaining a driving mechanism of the pinion 38. The pinion 38 is connected to a drive shaft 48 of a motor M rotatable in forward and reverse directions, and is rotatable in forward and reverse directions depending on the rotation direction of the motor M.
[0033]
The rotational drive of the motor M is controlled by a control unit 46 provided in the image forming apparatus 1. The control unit 46 includes, for example, a signal from a sheet size detection sensor for detecting the size of a recording sheet provided in the image forming apparatus 1 and a sheet size to an operation panel provided on the upper surface of the image forming apparatus 1. The paper size information 47 is provided by an input signal or the like based on the input. The control unit 46 rotates the pinion 38 by a predetermined amount in a predetermined direction via the motor M based on the sheet size information 47.
[0034]
Referring to FIG. 3 again, by rotating pinion 38 in the direction indicated by the arrow in FIG. 3A, one holding member 31a is displaced to the right and the other holding member 31b is displaced to the left. As a result, the cores 27a held by the holding members 31a and 31b are respectively displaced inward, and the state shown in FIG.
In order to return the state shown in FIG. 3B to the state shown in FIG. 3A again, the pinion 38 may be rotated in the opposite direction.
[0035]
The mechanism for displacing the core 27a is not limited to the mechanism described above, and may be another mechanism.
The present invention is not limited to the contents of the above embodiments, and various modifications can be made within the scope of the claims. For example, the winding density of the coil wire 22 at both ends of the bobbin 21 may be increased, or the cross-sectional area of the cores 27a disposed at both ends of the bobbin 21 may be increased. In this case, since the magnetic flux 39 penetrating the both ends of the heat roller 11 can be increased, it is possible to prevent the temperature of the both ends of the heat roller 11 from lowering and to cause temperature unevenness in the axial direction.
[0036]
The recording paper may be conveyed so as to be aligned with, for example, the left end or the right end of the heat roller 11 in each size. In this case, only one of the cores 27a disposed at both ends of the bobbin 21 needs to be displaced.
The image forming apparatus to which the present invention can be applied is not limited to a digital copying machine, but may be, for example, an analog copying machine or a laser beam printer.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a main part showing an internal configuration of an image forming apparatus to which a fixing device according to an embodiment of the present disclosure is applied.
FIG. 2 is a schematic side view illustrating a configuration of a fixing device.
FIG. 3 is a sectional view showing an internal configuration of the induction heating coil.
FIG. 4 is a schematic diagram for explaining a magnetic flux generated from an induction heating coil.
FIG. 5 is a schematic diagram for explaining a pinion drive mechanism.
FIG. 6 is a schematic diagram for explaining a magnetic flux generated from a conventional induction heating coil.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image forming apparatus 3 Photoreceptor 7 Recording paper 8 Fixing device 11 Heat roller 20 Induction heating coil 22 Coil wire 27 Core 27a Core

Claims (3)

A fixing roller that fixes the toner image to the recording sheet by conveying the recording sheet carrying the unfixed toner image while heating and pressing the recording sheet;
A coil that is provided inside the fixing roller, is formed by spirally winding a coil wire around the axis of the fixing roller, and generates a magnetic field for inductively heating the fixing roller;
A plurality of cores provided so as to penetrate the coil along the axis of the fixing roller, and arranged so that their axial positions partially overlap ;
Of the plurality of cores, the core arranged at the end in the axial direction is moved in the axial direction so that the induction heating area by the coil corresponds to the paper passing area of the recording sheet conveyed by the fixing roller. And a core driving mechanism for displacing the fixing device. The plurality of cores are arranged in two rows along the axis of the fixing roller, and one of the cores and the other are arranged so that the axial positions of adjacent cores in the axial direction of the fixing roller partially overlap. The fixing device according to claim 1, wherein the fixing devices are alternately arranged in a row. Developing an electrostatic latent image formed on the photoreceptor surface into a toner image and transferring the toner image to a recording sheet, thereby forming an unfixed toner image on the recording sheet;
An image forming apparatus comprising a fixing device according to claim 1 or 2, wherein for fixing the unfixed toner image on the recording sheet.

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