JP2010002813A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device of an electromagnetic heating system, which prevents fixing unevenness from occurring by maintaining accuracy of the positional relationship between an exciting coil and a magnetic core and, at the same, allows the cost thereof to be reduced. <P>SOLUTION: The exciting coil 62 is retained by a coil retention member 61 made by injection-molding a liquid crystal polymer and a plurality of main cores are retained by a core retention member 63 leaving a constant interval in the longitudinal direction on the position facing the exciting coil 62. The core retention member 63 is made by injection-molding a polyester-based resin, has a plurality of slits 631 formed therein and extended in the direction vertical to the longitudinal direction, and hence has a rigidity in the longitudinal direction considerably lowered as compared to that of the coil retention member 61 and, as the result, by fixing the base part of the core retention member 63 to the base part of the coil retention member 61, the warping of the core retention member 63 is corrected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus using the fixing device, and in particular, in a fixing device that heats a rotating body to be heated by induction heating provided with an exciting coil, while suppressing occurrence of uneven fixing and cost reduction. It is related with the technology to plan.

In recent years, image forming apparatuses such as printers have begun to employ an electromagnetic induction heating type fixing device that can save energy and shorten warm-up time compared to a fixing device that uses a halogen heater as a heat source (for example, Patent Documents). 1).
In such a fixing device, for example, a heat generating layer is formed on the outer peripheral portion of the fixing roller, and an exciting coil unit extending in parallel with the axial direction is arranged along the peripheral surface of the fixing roller. The

In general, an exciting coil unit includes a coil bobbin, an exciting coil wound around the coil bobbin, a plurality of magnetic cores that guide the magnetic flux generated by the exciting coil in the fixing roller direction, and the plurality of magnetic cores in the axial direction of the fixing roller. It consists of a core holding member that holds at a predetermined interval and at the same distance from the exciting coil.
If the dimensional accuracy of the coil bobbin and the core holding member is poor, the relative positional relationship between the exciting coil and the magnetic core varies in the axial direction, resulting in magnetic flux unevenness, and the heat generation state of the fixing roller is not uniform in the axial direction. The image may be deteriorated due to the above.

Therefore, conventionally, the coil bobbin and the core holding member have been manufactured by injection molding a liquid crystal polymer resin. This liquid crystal polymer resin is excellent in heat resistance and insulation, and hardly deforms during cooling after injection molding. By assembling the excitation coil unit with the material, the relative position relationship between the excitation coil and the magnetic core is improved. Since it can be made constant in the longitudinal direction (direction perpendicular to the sheet passing direction), the occurrence of uneven fixing can be prevented.
JP 2005-17705 A

However, the liquid crystal polymer resin is relatively expensive and hinders cost reduction of the apparatus.
The present invention has been made in view of the above circumstances, and in an electromagnetic induction heating type fixing device, while maintaining the accuracy of the positional relationship between the exciting coil and the magnetic core so as not to cause uneven fixing, the cost can be reduced. It is an object of the present invention to provide a fixing device capable of realizing the above and an image forming apparatus using the same.

  In order to achieve the above object, a fixing nip is formed by pressing the peripheral surface of the second rotating body on the peripheral surface of the first rotating body, and the first rotating body is induction-heated by the magnetic flux generated by the exciting coil. And a fixing device for passing the sheet on which the unfixed image is formed to the fixing nip and thermally fixing the unfixed image, wherein the excitation coil extends along the peripheral surface of the first rotating body. A plurality of magnetic cores that guide the magnetic flux generated by the exciting coil in the direction of the first rotating body, and a direction perpendicular to the sheet passing direction of the sheet. A core holding member that is held along the longitudinal direction of the exciting coil, and a rigid member that is larger in rigidity than the core holding member and extends in parallel with the longitudinal direction of the exciting coil. By fixing to the member The corrected shape of the core holding member, a plurality of magnetic cores and said exciting coil held thereto is characterized by being configured such that the positional relationship of the normal.

  In this way, the magnetic core holding member is fixed to a rigid member having a rigidity higher than that and extending in parallel with the longitudinal direction of the exciting coil to correct the shape of the core holding member, and a plurality of magnetic cores held by the magnetic core holding member. And the exciting coil are in a proper positional relationship, it is possible to prevent the occurrence of uneven fixing even if an inexpensive resin that is easily deformed during injection molding is used for the core holding member. We can plan down.

Here, the core holding member may be made of a polyester resin.
Here, it is desirable that the core holding member includes a plurality of elongated holes extending in the longitudinal direction in a direction substantially orthogonal to the longitudinal direction at a location where the core is not located.
Furthermore, each said long hole is good also as being divided | segmented into 2 or more in the direction substantially orthogonal to the said longitudinal direction.

A coil holding member for holding the exciting coil in a state in which a distance from the peripheral surface of the first rotating body is uniform in the longitudinal direction, the coil holding member holding the rigid member; It may be combined.
Here, the coil holding member is preferably made of a liquid crystal polymer resin.
The core holding member is a metal that holds the plurality of magnetic cores on a surface facing the exciting coil and covers a surface of the core holding member opposite to the side holding the magnetic core. A frame may be provided, and the metal frame may also serve as the rigid member.

Here, the metal frame is preferably made of a nonmagnetic metal.
Further, the metal frame may form a duct with the core holding member, and may include cooling means for blowing air into the duct to cool it.
The present invention may also be an image forming apparatus provided with the fixing device.

Hereinafter, an embodiment of an image forming apparatus including a fixing device according to the present invention will be described by taking a tandem type color printer (hereinafter simply referred to as “printer”) as an example.
(1) Overall Configuration of Printer FIG. 1 is a diagram showing the overall configuration of the printer 1.
As shown in FIG. 1, the printer 1 forms an image by an electrophotographic method or the like. The printer 1 includes an image process unit 2, a transfer belt unit 3, a paper feed unit 4, a fixing unit 5 and a control unit 7. I have.

The image processing unit 2 includes image forming units 20Y, 20M, 20C, and 20K corresponding to the reproduction colors of yellow (Y), magenta (M), cyan (C), and black (K), an optical unit 21, and the like. Consists of.
The transfer belt unit 3 is configured so that the intermediate transfer belt 30 is stretched by a drive roller 31, a driven roller 32, and a tension roller 33, and is circulated and driven in the direction of arrow B. The image forming units 20Y, A primary transfer roller 24 is disposed at positions corresponding to 20M, 20C, and 20K.

Each of the image forming units 20Y to 20K includes a photosensitive drum, a charging roller, a developing device, and the like, and is arranged in a row from the upstream side to the downstream side in the belt running direction so as to face the intermediate transfer belt 30.
The optical unit 21 includes a print head 22, four reflection mirrors 23, and the like. The print head 22 has four laser diodes inside and deflects the laser beam emitted from each laser diode to expose and scan the surface of the photosensitive drum of each of the image forming units 20Y to 20K in the main scanning direction. A polygon mirror and a scanning lens are provided.

  The paper feeding unit 4 feeds the recording sheets S fed out, the paper feeding cassettes 41 and 42 that store the recording sheets S, the feeding rollers 43 and 44 that feed out the recording sheets S in the paper feeding cassettes 41 and 42 one by one. A pair of conveying rollers 45, a timing roller pair 46 for taking the timing of sending the recording sheet S to the secondary transfer position 48, and a secondary transfer pressed against the driving roller 31 with the intermediate transfer belt 30 sandwiched at the secondary transfer position 48. A roller 47 is provided.

The fixing unit 5 includes a fixing roller and a pressure roller, and heats and presses the recording sheet S at a predetermined fixing temperature to fix the toner image.
The control unit 7 includes a CPU, a ROM, a RAM, a communication interface, and the like. The control unit 7 adds necessary processing to the image data related to the print job received via the LAN, A smooth print job is executed by controlling the operation of the belt unit 3, the sheet feeding unit 4, and the like.

In such a configuration, when the control unit 7 receives a print job from an external terminal via the LAN, it converts the received image data into image data of each reproduction color, and a laser diode for each reproduction color. Drive signal is generated.
Each laser diode of the optical unit 21 is driven by the generated drive signal, and an electrostatic latent image is formed on the photosensitive drums of the corresponding image forming units 20Y to 20K. This electrostatic latent image is developed by a developing device and visualized as a toner image. The images are sequentially superimposed and transferred onto the intermediate transfer belt 30. At this time, the image forming operations for the respective colors are executed at different timings so that the toner images are superimposed and transferred at the same position on the intermediate transfer belt 30. The full-color toner image formed on the intermediate transfer belt 30 moves to the secondary transfer position 48 as the intermediate transfer belt 30 travels.

The recording sheet S is fed from the sheet feeding unit 4 via the timing roller 46 in accordance with the movement timing of each color toner image on the intermediate transfer belt 30, and the recording sheet S is secondly transferred at the secondary transfer position 48. The toner images of each color on the intermediate transfer belt 30 are secondarily transferred to the recording sheet S electrostatically by the action of an electric field by the next transfer roller 47.
The recording sheet S that has passed through the secondary transfer position 48 is conveyed to the fixing unit 5 where the toner image is heated and pressed against the recording sheet S and then fixed to the recording sheet S. The paper is discharged onto a paper discharge tray 83 outside the apparatus.
(2) Configuration of Fixing Unit FIG. 2 is a schematic sectional view showing the configuration of the fixing unit 5.

  As shown in the figure, in the fixing unit 5, a fixing roller 52 and a pressure roller 53 are arranged in parallel at a predetermined distance in a housing 51, and the pressure roller 53 is rotated by a drive motor (not shown). . The fixing roller 52 is formed with an elastic layer 521 made of silicone sponge or the like on the peripheral surface of the shaft core 520, and further provided with an electromagnetic induction heat generating layer 522 made of a Ni electroformed sleeve on the outer periphery thereof. It is configured to generate heat by electromagnetic induction by an alternating magnetic flux generated by the exciting coil 62 of the exciting coil unit 6 disposed close to the peripheral surface.

The pressure roller 53 is pressed against the fixing roller 52 side by a pressure contact mechanism (not shown), whereby the elastic layer 521 of the fixing roller 52 is mainly deformed to secure a nip width necessary for fixing.
In the figure, reference numeral 55 denotes a metal roller that contacts the peripheral surface of the pressure roller 53 so that the temperature in the axial direction becomes uniform, and is called a soaking roller.

Reference numeral 56 denotes a cleaning brush for cleaning the peripheral surface of the soaking roller 55.
Further, an infrared sensor 57 for detecting the surface temperature in the substantially central portion in the axial direction of the peripheral surface in a non-contact manner is disposed near the peripheral surface of the fixing roller 52, and the control unit 7 receives this detection signal. The energization of the exciting coil 62 in the exciting coil unit 6 is controlled to control the fixing roller 52 to a predetermined fixing temperature.

(3) Configuration of Excitation Coil Unit 6 The excitation coil unit 6 includes an excitation coil 62, a main core 641, a center core 642, skirt cores 643 and 644, and a coil holding member (coil bobbin) 61 and a core for holding them. A holding member 63 is provided.
The exciting coil 62 is held by the coil holding member 61. The exciting coil 62 is connected to a high-frequency inverter (not shown) and is supplied with high-frequency power of 10 to 100 [kHz] and 100 to 2000 [W]. Therefore, a litz bundled with thin wires covered with a heat-resistant resin. It is desirable to form by winding a wire.

The main core 641 is bent in a trapezoidal shape so as to cover the exciting coil 62, and the core is held at a constant interval in a direction parallel to the axial direction of the fixing roller 52 (hereinafter simply referred to as “longitudinal direction”). It is held by the member 63.
The number of main cores 641 is sufficient as long as the efficiency of the magnetic circuit from the exciting coil 62 is saturated, and it is not necessary to provide more than that.

The center core 642 and the skirt cores 643 and 644 as auxiliary magnetic cores are formed in a long shape extending in parallel with the axial direction of the fixing roller 52 (see FIG. 3), and the coil holding member 61 is made of silicon. It is fixed with a heat-resistant adhesive such as an adhesive.
Further, a duct member 64 having an L-shaped cross section is provided so as to cover the outside of the core holding member 63, and the exciting coil 62 is blown from the fan device 65 through the slit-like vent hole 645 to the inside of the duct. In addition, the main magnetic core 641 is cooled to prevent the main magnetic core 641 from being damaged when the temperature exceeds the heat resistant temperature.

Here, the coil holding member 61 is formed by injection molding a liquid crystal polymer resin, and the core holding member 63 is formed by injection molding a polyester resin.
Examples of the liquid crystal polymer resin include a polycondensate of ethylene terephthalate and parahydroxybenzoic acid and a polycondensate of phenol, phthalic acid and parahydroxybenzoic acid.

Moreover, as a polyester-type resin, a polyethylene terephthalate (PET) is typical, for example. The most mass-produced polyester resin and the unit price is low.
The duct member 64 is preferably made of metal from the viewpoint of heat dissipation. Furthermore, it is desirable to have a magnetic shielding effect, and from this point of view, a nonmagnetic metal such as aluminum is used.

  The coil holding member 61, the core holding member 63, and the duct member 64 are fixed by bolts 661 and nuts 662 at both skirts in the circumferential direction. The bolts and nuts are fixed at at least three locations, ie, both ends and the center in the longitudinal direction (see FIG. 5). This is because the warp in the longitudinal direction of the core holding member 63 is corrected by the coil holding member 61 and the duct member 64. The fixing means is not limited to bolts and nuts, and rivets or the like can be used in some cases.

3 is a perspective view showing a configuration of a main part of the fixing unit 5, FIG. 4 is an external perspective view of only the core holding member 63, and FIG. 5 is an external perspective view of the exciting coil unit 6 as a whole. Note that the exciting coil unit 6 of FIG. 3 is shown partially cut in the longitudinal direction so that the internal configuration can be easily understood.
As shown in FIGS. 3 and 4, the core holding member 63 includes a plurality of core holding portions 632 arranged in the longitudinal direction, and both ends of each core holding portion 632 are connected by skirt portions 633 and 634. The shapes of the end portions 635 and 636 are mountain-shaped so as to match the edges of both ends of the duct member 64.

6A is a front view of the core holding member 63, and FIG. 6B is a plan view.
As described above, the slit 631 is formed between the core holding portions 632, so that the rigidity in the longitudinal direction is sufficiently lower than that of the coil holding member 61.
The polyester resin used as the material of the core holding member 63 has heat resistance and insulating properties, and is less expensive than the liquid crystal polymer resin. However, deformation (warping) tends to occur particularly in the longitudinal direction during injection molding. There are drawbacks.

  However, since the core holding member 63 is configured so that the rigidity in the longitudinal direction is low as described above, it is assumed that warping occurs in the P or Q direction during molding as shown in FIG. Also, by fixing this at the skirts 633 and 634 between the skirts 613 and 614 (see FIG. 3) of the coil holding member 61 and the skirts 646 and 647 (see FIG. 5) of the duct member 64, The coil holding member 61 is corrected to follow the longitudinal direction.

  Since the coil holding member 61 is formed of a liquid crystal polymer resin as described above, there is almost no deformation after injection molding, the dimensional accuracy is high, and the core holding member 63 is deformed so as to follow the coil holding member 61. By doing so, the warpage is corrected, and the positional relationship between the plurality of main cores 641 held by this and the exciting coil 62 held by the coil holding member 61 can be made uniform in the longitudinal direction. .

According to such a configuration, it is possible to prevent uneven fixing while using an inexpensive polyester-based resin for the core holding member 63, and thus the manufacturing cost of the exciting coil unit 6 can be reduced. In addition, the amount of resin material used can be reduced by the amount of the slit 631, and the cost can be further reduced.
FIG. 7 is a partial cross-sectional view taken along line XX of the core holding member 63 of FIG. As shown in the figure, the core holding portion 632 in the core holding member 63 has a U-shaped cross section so as to cover three surfaces except the lower surface of the main core 641, and is heat resistant such as a silicon-based adhesive. 632 is fixed by the adhesive. Thus, the core holding portion 632 has a U-shaped cross section and is bent along the outer contour of the main core 641 when viewed from the longitudinal direction (FIG. 2). The rigidity in the direction perpendicular to the longitudinal direction in this portion can be increased, the main core 641 can be securely held to increase its positioning accuracy, and the serviceman can pass the fingertip through the opening 631 during maintenance. Even if it is inserted, the main core 641 is prevented from being directly touched.

<Modification>
As described above, the present invention has been described based on the embodiment. However, the content of the present invention is not limited to the above embodiment, and for example, the following modifications can be implemented.
(1) In the above embodiment, the slits 631 of the core holding member 63 are provided between all adjacent core holding parts 632, but may be provided between adjacent ones of the core holding parts 632.

In addition, the length of the slit 631 along the circumferential direction of the fixing roller 52 is desirably within a range of 40% to 100% of the entire length in the circumferential direction excluding the skirt portions 633 and 634.
As shown in the plan view of the core holding member 63 in FIG. 8, a bridging portion 6311 where adjacent core holding portions 632 are connected to each other at the center position may be provided, thereby dividing the slit 631 in the circumferential direction. . According to this configuration, it is easy to flow the molten resin material using the bridge portion 6311 portion as a flow path at the time of injection molding, and molding is performed by providing a gas vent hole in the vicinity of one of the bridge portions 6311. Since the gas at that portion is sometimes released, the yield can be increased. Note that the number of the bridging portions 6311 in the circumferential direction of each slit 631 is not limited to one, and may be plural.

  (2) In the above embodiment, a plurality of slits 631 orthogonal to the longitudinal direction are provided so that the rigidity in the longitudinal direction is lower than that of the coil holding member 61. The method of lowering the rigidity of is not limited to providing a slit. For example, it can be realized by reducing the thickness of the core holding member 63 within a range in which insulation can be secured, or by using a more flexible resin material. However, even in this case, in order to sufficiently obtain the cooling effect of the exciting coil 62 by the fan device 65, it is desirable to provide the core holding member 63 with some opening through which air from the fan device 65 flows.

In a small printer, the fan device 65 may not necessarily be provided in this portion. Even in this case, it is preferable to obtain a magnetic shield effect and / or a heat dissipation effect by attaching a non-magnetic metal frame having substantially the same shape instead of the duct member 64.
(3) In the above embodiment, the core holding member 63 is formed of only a polyester resin, but other heat-resistant and insulating resins can be used as long as they are less expensive than the liquid crystal polymer.

Moreover, high flame retardance is securable by including glass fiber etc. in resin.
(4) In the above embodiment, the deformation of the core holding member 63 during molding is corrected by sandwiching and fixing the skirt of the core holding member 63 between the skirt of the coil holding member 61 and the duct member 64. However, since the rigidity of the metal duct member 64 is the highest, the coil holding member 61 is also made of a polyester resin or the like like the core holding member 63. If the coil holding member 61 and the core holding member 63 are combined so that the rigidity in the longitudinal direction is lower than that of the duct member 64, and both of these are fixed to the duct member 64 and corrected accordingly, the cost can be further reduced. It is possible to go down.

(5) The configuration of the fixing unit 5 is not limited to the configuration having the fixing roller 52 shown in FIG. 2, but is a configuration in which a fixing belt is circulated instead of another rotating body, for example, the fixing roller 52. In short, any fixing device of an electromagnetic induction heating type using an exciting coil unit may be used.
(6) The excitation coil unit 6 may be provided with a known degaussing coil.

  That is, the demagnetizing coil is disposed in an overlapping manner on a portion of the excitation coil 62 corresponding to a portion (non-sheet passing portion) other than a sheet passing portion of a sheet of a specific size (for example, A4 vertical size) that is normally used. The temperature of the non-sheet passing portion is detected, and the demagnetizing coil is short-circuited by the control unit 7 before the non-sheet passing portion of the fixing roller 52 is overheated by heating by the exciting coil 62, or the exciting coil A configuration may be adopted in which energization is performed so as to generate a magnetic flux in a direction opposite to the magnetic flux generated by 62 to prevent excessive temperature rise in the non-sheet passing portion.

  (7) In the above embodiment, the tandem type color printer has been described. However, the present invention is not limited to this, and may be, for example, a monochrome printer, and a composite having functions such as a copying machine and a fax machine. It may be a machine.

  The present invention can be widely applied to an image forming apparatus including an electromagnetic induction heating type fixing device using an exciting coil unit.

1 is a schematic cross-sectional view of a tandem type color printer according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating a configuration of a fixing unit in the printer. FIG. 3 is a partial cross-sectional perspective view showing a configuration of the fixing unit. It is an external appearance perspective view of the core holding member in an exciting coil unit. It is an external appearance perspective view of the whole exciting coil unit after an assembly. (A) is a front view of a core holding member, (b) is a top view of a core holding member. It is a figure which shows a part of arrow cross section in the XX line of FIG.6 (b). It is a top view which shows the shape of the core holding member which concerns on a modification.

Explanation of symbols

1 Printer 5 Fixing Unit 6 Excitation Coil Unit
52 Fixing roller 53 Pressure roller 55 Heat equalizing roller 61 Coil holding member 62 Excitation coil 63 Core holding member 64 Duct member 65 Fan device 631 Slit 632 Core holding portion

Claims (10)

A fixing nip is formed by pressing the peripheral surface of the second rotating body on the peripheral surface of the first rotating body, and the first rotating body is induction-heated by the magnetic flux generated by the exciting coil, thereby A fixing device for passing the formed sheet through the fixing nip and thermally fixing the unfixed image,
The excitation coil is disposed along a circumferential surface of the first rotating body with a direction perpendicular to the sheet passing direction of the sheet as a longitudinal direction,
A plurality of magnetic cores for guiding the magnetic flux generated by the exciting coil in the direction of the first rotating body;
A core holding member for holding the plurality of magnetic cores along a longitudinal direction of the exciting coil;
A rigidity member having a rigidity greater than that of the core holding member and extending in parallel with a longitudinal direction of the excitation coil,
By fixing the core holding member to the rigid member, the shape of the core holding member is corrected, and a plurality of magnetic cores held by the core holding member and the excitation coil are configured in a normal positional relationship. A fixing device characterized by the above.   The fixing device according to claim 1, wherein the core holding member is made of a polyester resin.   3. The fixing device according to claim 1, wherein the core holding member includes a plurality of elongated holes extending in a direction substantially orthogonal to the longitudinal direction at a location where the core is not positioned. .   The fixing device according to claim 3, wherein each of the elongated holes is divided into two or more in a direction substantially orthogonal to the longitudinal direction. A coil holding member for holding the exciting coil in a state in which the distance from the peripheral surface of the first rotating body is uniform in the longitudinal direction;
The fixing device according to claim 1, wherein the coil holding member also serves as the rigid member.   The fixing device according to claim 5, wherein the coil holding member is made of a liquid crystal polymer resin. The core holding member holds the plurality of magnetic cores on the surface facing the exciting coil,
A metal frame that covers a surface of the core holding member opposite to the side holding the magnetic core;
The fixing device according to claim 1, wherein the metal frame also serves as the rigid member.   The fixing device according to claim 7, wherein the metal frame is made of a nonmagnetic metal. The metal frame forms a duct with the core holding member,
The fixing device according to claim 7, further comprising a cooling unit that blows air into the duct to cool the duct.   An image forming apparatus comprising the fixing device according to claim 1.

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