JP3843076B2 - Fixing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fixing device that is mounted on an image forming apparatus such as a copying machine or a printer and fixes a developer image on a sheet.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image forming apparatus using digital technology, such as an electronic copying machine, has a fixing device that fixes a developer image onto a sheet by heating in a pressurized state.
For example, in an electronic copying machine, a document table on which a document is placed is exposed, and reflected light from the document is guided to a photoelectric conversion element such as a CCD (charge coupled device). The CCD outputs an image signal corresponding to the original image. Laser light corresponding to the image signal is irradiated onto the photosensitive drum, and an electrostatic latent image is formed on the peripheral surface of the photosensitive drum. This electrostatic latent image is visualized by the adhesion of developer (toner). A sheet is sent to the photosensitive drum in time with the rotation of the photosensitive drum, and a visible image (developer image) on the photosensitive drum is transferred to the sheet. The sheet on which the developer image is transferred is sent to a fixing device.
[0003]
The fixing device includes a heating roller and a pressure roller that rotates with the heating roller while being in contact with the heating roller in a pressurized state. The developer image on the paper is fixed by heat.
As a heat source for the heating roller of the fixing device, there is induction heating. This is because a coil is placed in a heating roller, a capacitor is connected to the coil to form a resonance circuit, and the resonance circuit is excited at one frequency with respect to one resonance circuit. A high-frequency magnetic field is generated from the coil to generate an eddy current in the heating roller by the high-frequency magnetic field, and the heating roller self-heats by Joule heat generated by the eddy current.
[0004]
Furthermore, in recent years, shortening warm-up has become a technical issue as an energy-saving technology, but as a countermeasure, the thickness of the heating roller can be reduced.
However, since the heat capacity becomes smaller as the thickness of the heating roller is thinner, it is difficult to keep the heat distribution on the heating roller uniform. For example, when the heating roller is heated by a coil wound coaxially with the heating roller, the heat distribution on the heating roller is uneven if the distance between the heating roller and the coil is not constant.
[0005]
For example, in a fixing device having an induction heating unit composed of a coil bobbin that holds a coil coaxial with a heating roller and a holding member that holds the coil bobbin, in order to maintain a predetermined gap between the heating roller and the coil. In addition, high precision is required in forming the coil bobbin and the holding member. Accordingly, there is a demand for a coil bobbin and a holding member that have high fitting accuracy and satisfy various conditions in each molding. Further, in the fixing device, the developer is fixed on the sheet at a high temperature, and therefore the induction heating unit becomes a high temperature. For this reason, the said coil bobbin and the said holding member which have the precision of high fitting even under high temperature are desired.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-312165.
[0007]
[Problems to be solved by the invention]
The present invention takes the above-mentioned circumstances into consideration, and its object is to provide induction heating consisting of a coil bobbin and a holding member that have high fitting accuracy even when used at high temperatures and satisfy various conditions in molding. It is an object of the present invention to provide a fixing device having a section.
[0008]
[Means for Solving the Problems]
The fixing device according to the present invention fixes a developer on an image forming medium by a heated member that generates heat due to an eddy current generated by a change in a magnetic field generated by a coil, and is a hollow around which an electric wire forming a coil is wound. The coil bobbin and an inner shape of the coil bobbin, and a holding member for holding the coil bobbin in a predetermined position. The holding member is formed by compression molding, and the coil bobbin It is formed by injection molding.
[0009]
In the fixing device according to the present invention, a developer is fixed on an image forming medium by a heated member that generates heat due to an eddy current generated by a change in a magnetic field generated by a coil, and an electric wire forming the coil is wound around the fixing device. The coil bobbin has an induction heating means that has a shape that fits into the shape of the inside of the coil bobbin and holds the coil bobbin in a predetermined position, and the coil bobbin and the holding member It is characterized by being molded using a material having a difference in expansion coefficient within a predetermined allowable range.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an internal configuration of a composite electronic copying machine as an image forming apparatus. First, a transparent document table (glass plate) 2 for placing a document is provided on the upper surface of the main body 1, and the exposure lamp 5 provided on the carriage 4 is turned on to place the document on the document table 2. The placed document D is exposed.
[0011]
Reflected light by this exposure is projected onto a photoelectric conversion element, for example, a CCD (charge coupled device) 10 to output an image signal. The image signal output from the CCD 10 is converted into a digital signal. The digital signal is appropriately processed and then supplied to the laser unit 27. The laser unit 27 emits a laser beam B according to an input signal.
[0012]
A control panel for setting operating conditions (not shown) is provided on the upper surface of the main body 1 at a position where the automatic document feeding unit 40 is not covered. The control panel includes a touch panel type liquid crystal display, a numeric keypad for inputting numerical values, a copy key, and the like.
[0013]
On the other hand, a photosensitive drum 20 is rotatably provided at a substantially central portion in the main body 1. Around the photosensitive drum 20, a charger 21, a developing unit 22, a transfer unit 23, a peeling unit 24, a cleaner 25, and a static eliminator 26 are sequentially arranged. The photosensitive drum 20 is formed by a known process method. A toner (developer) image is formed thereon, the toner image is transferred onto a sheet, and the toner on the sheet is heated and pressure-fixed by a fixing device 100 described later.
[0014]
FIG. 2 shows a schematic configuration of the fixing device 100.
In FIG. 2, the fixing device 100 is provided with a heating roller 101 and a pressure roller 102 at a position sandwiching the conveyance path of the copy paper S up and down. The pressure roller 102 is in pressure contact with the peripheral surface of the heating roller 101 by a pressure mechanism (not shown). The contact portions of these rollers 101 and 102 have a constant nip width.
[0015]
The heating roller 101 is formed by forming a conductive material, for example, iron into a cylindrical shape, and coating the outer peripheral surface of the iron with, for example, a fluororesin such as a tetrafluoroethylene resin. The heating roller 101 is rotationally driven in the right direction in the figure by a drive motor (not shown). The pressure roller 102 rotates in the left direction in the figure in response to the rotation of the heating roller 101. When the copy sheet S passes through the contact portion between the heating roller 101 and the pressure roller 102 and the copy sheet receives heat from the heating roller 101, the developer image T on the copy sheet S is applied to the copy sheet S. It is fixed.
[0016]
Around the heating roller 101, there are an isolation claw 103 for peeling the copy paper S from the heating roller 101, a cleaning member 104 for removing toner and paper dust remaining on the heating roller 101, and the heating roller 101. An application roller 105 for applying a release agent to the surface is disposed.
[0017]
An induction heating unit 110 for induction heating is accommodated inside the heating roller 101. The induction heating unit 110 includes a coil bobbin 110A around which a wire serving as the coil 111 is wound, and a holding member 110B that holds the coil bobbin 110A. When the coil 111 includes a plurality of coils (111a,...), The coil bobbin 110A includes a plurality of coil bobbins 110A (110Aa,...) Corresponding to the number of coils. The induction heating unit 110 is supplied with high frequency power from a high frequency circuit described later, and generates a high frequency magnetic field for induction heating. When this high frequency magnetic field is generated, an eddy current is generated in the heating roller 101, and the heating roller 101 self-heats due to Joule heat generated by the eddy current.
[0018]
FIG. 3 shows a control circuit of the composite electronic copying machine. That is, the main CPU 50 is connected to the scan CPU 70, the control panel CPU 80, and the print CPU 90.
The main CPU 50 controls the scan CPU 70, the control panel CPU 80, and the print CPU 90 in an integrated manner. The main CPU 50 controls the copy mode according to the operation of the copy key, and responds to the image input to the network interface 59. The printer mode control means and the facsimile mode control means according to the image reception by the FAX transmission / reception unit 60 are provided.
[0019]
The main CPU 50 includes a control program storage ROM 51, a data storage RAM 52, a pixel counter 53, an image processing unit 55, a page memory controller 56, a hard disk unit 58, a net interface 59, and a FAX transmission / reception unit 60. It is connected.
[0020]
The page memory controller 56 controls writing and reading of image data with respect to the page memory 57. The image processing unit 55, the page memory controller 56, the page memory 57, the hard disk unit 58, the net interface 59, and the FAX transmission / reception unit 60 are connected to each other via the image data bus 61. .
[0021]
The network interface 59 functions as an input unit for a printer mode to which an image (image data) transmitted from an external device is input. The network interface 59 is connected to a communication network 201 such as a LAN or the Internet, and external devices such as a plurality of personal computers 202 are connected to the communication network 201. These personal computers 202 include a controller 203, a display 204, an operation unit 205, and the like.
The FAX transmission / reception unit 60 is connected to a telephone line 210 and functions as a reception unit for a facsimile mode that receives an image (image data) transmitted by facsimile via the telephone line 210.
[0022]
The scan CPU 70 includes a ROM 71 for storing a control program, a RAM 72 for storing data, a signal processing unit 73 that processes the output of the CCD 10 and supplies it to the image data bus 61, a CCD driver 74, a scan motor driver 75, and an exposure lamp 5 The automatic document feeder 40 and a plurality of document sensors 11 are connected.
[0023]
The CCD driver 74 drives the CCD 10. The scan motor driver 75 drives a scan motor 76 for driving the carriage. The automatic document feeder 40 has a document D set on a tray 41 and a document sensor 43 for detecting the size of the document D.
[0024]
Connected to the control panel CPU 80 are a touch panel type liquid crystal display unit 14, a numeric keypad 15, an all reset key 16, a copy key 17, and a stop key 18 of the control panel.
[0025]
Connected to the print CPU 90 are a control program storage ROM 91, a data storage RAM 92, a print engine 93, a paper transport unit 94, a process unit 95, and a fixing device 100. The print engine 93 includes the laser unit 27 and its drive circuit. The paper transport unit 94 includes a paper transport mechanism from the paper feed cassette 30 to the tray 38, a drive circuit thereof, and the like. The process unit 95 includes the photosensitive drum 20 and its peripheral part.
A print unit that prints the image processed by the image processing unit 55 on the paper P is mainly configured by the print CPU 90 and its peripheral configuration.
[0026]
FIG. 4 shows a configuration example of the electric circuit of the fixing device 100.
Here, it is assumed that the induction heating unit 110 accommodated in the heating roller 101 includes a coil 111 including a plurality of coils (111a, 111b, 111c). That is, in the example shown in FIG. 4, the coil 111 is divided into three coils 111a, 111b, and 111c. In the example shown in FIG. 4, the coil 111 a constitutes a first coil and exists at the center of the heating roller 101. The coils 111b and 111c constitute a second coil and are located on both sides of the heating roller 101 with the coil 111a interposed therebetween. These coils 111a, 111b, and 111c are connected to the high frequency generation circuit 120.
[0027]
A temperature sensor 112 is provided at the center of the heating roller 101. The temperature sensor 112 detects the temperature at the center of the heating roller 101. A temperature sensor 113 is provided at one end of the heating roller 101. The temperature sensor 113 detects the temperature of one end of the heating roller 101. These temperature sensors 112 and 113 are connected to the print CPU 90 together with a drive unit 160 for rotationally driving the heating roller 101.
[0028]
In addition to the function of controlling the drive unit 160, the print CPU 90 operates as a first resonance circuit (output power P1), which will be described later, having the coil 111a as the first coil as a component, and as the second coil. The function of issuing a P1 / P2 switching signal for designating the operation of a second resonance circuit (output power P2) to be described later using the coils 111b and 111c as constituent elements, the output power of each resonance circuit, and the detection of the temperature sensors 112 and 113 It has a function to control according to temperature.
[0029]
The high frequency generation circuit 120 generates high frequency power for generating a high frequency magnetic field, and includes a rectifier circuit 121 and a switching circuit 122 connected to an output terminal of the rectifier circuit 121. The rectifier circuit 121 rectifies the AC voltage of the commercial AC power supply 130. In the switching circuit 122, a coil 111a forms a first resonance circuit, and coils 111b and 111c form a second resonance circuit.
Further, the first resonance circuit and the second resonance circuit are selectively excited by a switching element (not shown) provided in the switching circuit 122 (for example, a transistor such as an FET).
[0030]
The coils 111b and 111c constituting the second coil are connected in parallel to the switching circuit 122. Similarly, when the first coil or the second coil is composed of a plurality of coils in the induction heating unit 110, each coil is connected in parallel to the switching circuit 122.
[0031]
The first resonance circuit has a resonance frequency f1 determined by the inductance of the coil 111a and the capacitance of a capacitor (not shown) in the switching circuit 122. The second resonance circuit has a resonance frequency f2 determined by the inductances of the coils 111b and 111c, the capacitance of a capacitor (not shown) in the switching circuit 122, and the like.
[0032]
The switching circuit 122 is turned on and off by the controller 140 in accordance with a P1 / P2 switching signal from the print CPU 90. The controller 140 includes an oscillation circuit 141 and a CPU 142. The oscillation circuit 141 generates a drive signal having a predetermined frequency for the switching circuit 122. The CPU 142 controls the oscillation frequency (frequency of the drive signal) of the oscillation circuit 141. The CPU 142 has, for example, the following means (1) and (2) as main functions.
[0033]
(1) When the operation of the first resonance circuit (using only the coil 111a) is designated by the P1 / P2 switching signal from the print CPU 90, the CPU 142 sets the first resonance circuit in the vicinity of the resonance frequency f1. For example, (f1−Δf), (f1 + Δf), and a control means for exciting them sequentially (alternately).
[0034]
(2) When the operation of the first and second resonance circuits (use of all the coils 111a, 111b, 111c) is specified by the P1 / P2 switching signal from the print CPU 90, the CPU 142 determines that the first and second resonance circuits Control means for sequentially exciting the two resonance circuits at a plurality of frequencies in the vicinity of the resonance frequencies f1 and f2, for example, (f1−Δf), (f1 + Δf), (f2−Δf), and (f2 + Δf) .
[0035]
Next, the operation of the electric circuit of the fixing device 100 configured as described above will be described.
When a drive signal having the same frequency (or a nearby frequency) as the resonance frequency f1 of the first resonance circuit is emitted from the oscillation circuit 141, the switching circuit 122 is turned on / off by the drive signal, and the first resonance circuit is Excited. By this excitation, a high frequency magnetic field is generated from the coil 111a, an eddy current is generated in the axial central portion of the heating roller 101 by the high frequency magnetic field, and the axial central portion of the heating roller 101 is self-heated by Joule heat due to the eddy current. .
[0036]
When a drive signal having the same frequency (or a nearby frequency) as the resonance frequency f2 of the second resonance circuit is emitted from the oscillation circuit 141, the switching circuit 122 is turned on / off by the drive signal, and the second resonance circuit is turned on. Excited. By this excitation, high frequency magnetic fields are generated from the coils 111b and 111c, and eddy currents are generated on both sides in the axial direction of the heating roller 101 due to the high frequency magnetic fields. To do.
[0037]
FIG. 5 shows the relationship between the output power P1 of the first resonance circuit and the frequency for exciting the first resonance circuit, and the relationship between the output power P2 of the second resonance circuit and the frequency for exciting the second resonance circuit. FIG.
[0038]
As shown in FIG. 5, the output power P1 of the first resonance circuit reaches a peak level when excited at the same frequency as the resonance frequency f1 of the first resonance circuit, and the excited frequency is separated from the resonance frequency f1. The pattern gradually decreases according to the mountain.
Similarly, the output power P2 of the second resonance circuit becomes a peak level when excited at the same frequency as the resonance frequency f2 of the second resonance circuit, and becomes a peak as the excited frequency goes away from the resonance frequency f2. The pattern gradually decreases.
[0039]
When fixing a large size sheet S, both the first and second resonance circuits are excited, and high frequency magnetic fields are emitted from all the coils 111a, 111b, and 111c. An eddy current is generated in the entire heating roller 101 by the high-frequency magnetic field, and the entire heating roller 101 self-heats due to Joule heat generated by the eddy current. In this case, a drive signal having two frequencies (f1−Δf) and (f1 + Δf) separated by a predetermined value Δf in the vertical direction around the resonance frequency f1 of the first resonance circuit is sequentially output from the oscillation circuit 141, and then Drive signals having two frequencies (f2−Δf) and (f2 + Δf) that are separated by a predetermined value Δf in the vertical direction around the resonance frequency f2 of the second resonance circuit are sequentially output from the oscillation circuit 141.
[0040]
By these drive signals, the first resonance circuit is sequentially excited at two frequencies (f1−Δf) and (f1 + Δf) that sandwich the resonance frequency f1, and then the second resonance circuit has two frequencies that sandwich the resonance frequency f2. Sequential excitation is performed at (f2−Δf) and (f2 + Δf). The excitation for each frequency is repeated.
[0041]
As shown in FIG. 5, the output power P1 of the coil 111a in the first resonance circuit is a value P1a slightly lower than the peak level P1c when excited at the frequency (f1−Δf), and excited at the frequency (f1 + Δf). Even at this time, the value P1b is slightly lower than the peak level P1c.
[0042]
The output power P2 of the coils 111b and 111c in the second resonance circuit has a value P2a that is slightly lower than the peak level P2c when excited at the frequency (f2−Δf), and the peak level P2c also when excited at the frequency (f2 + Δf). The value P2b is slightly lower than that.
[0043]
Next, the configuration of the induction heating unit 110 will be described.
In the induction heating unit 110, in order to arrange a plurality of coils to be connected in parallel to the high-frequency generation circuit 120, connection of individual coils becomes complicated. For this reason, in this Embodiment, the one coil bobbin which wound the electric wire as one coil is used as one coil unit, A plurality of coil units are held by one holding member 110B, and the induction heating part 110 is formed. Shall be.
[0044]
Each coil unit configured as described above is fixed at a predetermined position by a holding member 110B for holding each coil coaxially with the heating roller 101. The holding member 110B is combined inside the coil bobbins 110A of the coil units. Further, the holding member 110B and each coil bobbin 110A are fixed by fitting recesses and projections (not shown) so that each coil unit does not rotate with respect to the holding member 110B.
[0045]
6 and 7 are diagrams illustrating a configuration example of the induction heating unit 110. FIG.
In the example shown in FIG. 6, the induction heating unit 110 includes three coils 111a, 111b, and 111c. The coil 111a is constituted by an electric wire wound around the coil bobbin 110Aa, the coil 111b is constituted by an electric wire wound around the coil bobbin 110Ab, and the coil 111c is constituted by an electric wire wound around the coil bobbin 110Ac. That is, the induction heating unit 110 shown in FIG. 6 has a configuration in which the coil bobbins Aa, Ab, and Ac wound with three coils 111a, 111b, and 111c are held by the holding member 110B.
[0046]
In the example shown in FIG. 7, the induction heating unit 110 includes 12 coils (a1 to a6, b1 to b3, and c1 to c3). Each coil is constituted by an electric wire wound around an independent coil bobbin. In the induction heating unit 110 shown in FIG. 7, the coils a1 to a6 correspond to the coil 111a, the coils b1 to b3 correspond to the coil 111b, and the coils c1 to c3 correspond to the coil 111c.
[0047]
In addition, as shown in FIG. 7, when the first coil and the second coil are composed of a plurality of coils, each coil in the induction heating unit 110 is, for example, a high frequency generating circuit as shown in FIG. 120 is connected in parallel. That is, the coils a1 to a6 corresponding to the coil 111a are connected in parallel to the switching circuit 122 in the portion of the coil 111a of the high frequency generation circuit 120. The coils b1 to b3 corresponding to the coil 111b are connected in parallel to the switching circuit 122 in the coil 111b portion of the high frequency generation circuit 120. The coils c1 to c3 corresponding to the coil 111c are connected in parallel to the switching circuit 122 in the portion of the coil 111c of the high frequency generation circuit 120.
[0048]
6 and 7, the induction heating unit 110 as a whole has a configuration in which a plurality of coils 111a wound around a plurality of coil bobbins 110Aa are held by a holding member 110B. That is, in the induction heating unit 110 as a whole, the number of coil bobbins (coil units) around which coils are wound is required to be at least the number to be controlled. In the fixing device according to the present embodiment, since a plurality of coils are controlled, the induction heating unit 110 needs to be configured with at least the number of coil units equal to or greater than the number of coils to be controlled. Furthermore, for example, as shown in FIG. 7, each coil to be controlled can be configured by a plurality of coil units.
[0049]
FIG. 8 is a view showing the relationship between the coil bobbin 110A and the holding member 110B.
As shown in FIG. 8, each coil bobbin (coil holding part) 110A is configured by a hollow cylindrical shape. In addition, the holding member 110B has a shape that fits inside each coil bobbin 110A and fits with the shape inside the coil bobbin 110A.
[0050]
That is, the entire induction heating unit 110 is configured such that a plurality of coil bobbins 110A are held by one holding member 110B. Each coil bobbin 110 </ b> A has flange portions 190 a and 190 b for guiding an electric wire wound as the coil 111 at both ends. The coil bobbin 110A and the holding member 110B are made of plastic, ceramic, or the like. For example, PEEK (polyether ether ketone) material, phenol material, unsaturated polyester, or the like can be used.
[0051]
Next, features of the coil bobbin 110A and the holding member 110B will be described.
In the induction heating unit 110 configured as described above, the distance (gap) between each coil 111 of each coil unit and the heating roller 101 as the member to be heated greatly affects the heat distribution on the heating roller 101. That is, when the power applied to the coil 111 is the same, the narrower the gap between the coil 111 and the heating roller 101, the higher the temperature of the heating roller 101, and the wider the gap, the lower the temperature of the heating roller.
[0052]
Further, since the coil bobbin 110A has a cylindrical shape, for example, if the coil bobbin 110A is eccentric, the heat distribution on the heating roller 101 is uneven. The heating roller 101 of the fixing device used in the image forming apparatus needs to have a uniform temperature distribution at least in a region where the paper passes in order to prevent poor fixing of the developer onto the paper. Therefore, the gap between the coil 111 of the induction heating unit 110 used in the fixing device and the heating roller 101 needs to be a constant distance.
[0053]
From the above, the specifications and accuracy shown below are required for the coil bobbin 110A and the holding member 110B used in the fixing device.
The coil bobbin 110A is required to be accurate in the following points.
(1) Cylindricity (to eliminate eccentricity and maintain a constant distance between the heating roller and the coil)
(2) Hard to generate burrs (because burrs etc. do not damage the wire as a coil)
(3) Formability (because many pieces are required)
(4) Heat resistance (for use at high temperatures)
(5) Insulation (to insulate the coil)
Further, the holding member 110B is required to be accurate in the following points.
(6) Less warpage (to maintain a certain gap from the heating roller)
(7) Heat resistance (for use at high temperatures)
(8) Insulation (to insulate the coil and the wiring from the coil to the high frequency generation circuit).
[0054]
The above points (1), (2), (3), and (6) are realized by the accuracy in the molding process.
In order to satisfy the accuracy in these points, in this embodiment, the holding member 110B is formed by compression molding, and the coil bobbin 110A is formed by injection molding.
[0055]
If the holding member 110B is formed by compression molding, the holding member 110B can be less likely to warp. As a result, it is possible to form a holding member that is less likely to warp. Further, if the coil bobbin 110A is formed by injection molding, burrs are not easily generated, and a large number can be easily formed. Thereby, it is difficult to generate burrs while maintaining a predetermined cylindricity, and a large number can be easily produced.
[0056]
As described above, according to the present embodiment, the holding member is molded by compression molding, and the coil bobbin is molded by injection molding. Accordingly, a large number of coil bobbins that are less likely to generate burrs can be easily manufactured, and a holding member that is less likely to warp can be manufactured.
[0057]
Next, a material for forming the coil bobbin 110A and a material for forming the holding member 110B will be described.
The heat resistance and insulation as shown in the above (4), (5), (7) and (8) are satisfied by the material for molding the coil bobbin 110A and the holding member 110B. Since the holding member 110B is used by being fitted at a high temperature in the fixing device, it is necessary to use a material having substantially the same coefficient of thermal expansion.
[0058]
Therefore, the coil bobbin 110A and the holding member 110B are preferably molded using, for example, the same grade material (same material) that can be compression molded and injection molded.
Further, the coil bobbin 110A and the holding member 110B may be molded using materials having substantially the same coefficient of thermal expansion, not necessarily the same grade of material. As a specific example, a material that satisfies the following conditions can be used.
[0059]
That is, the coil bobbin 110 </ b> A and the holding member 110 </ b> B are required to maintain part accuracy by fitting at the maximum temperature used.
Here, a linear expansion coefficient of a material for molding the holding member 110B by compression molding (hereinafter referred to as compression molding material) is α1, and a material for molding the coil bobbin 110A by injection molding (hereinafter, referred to as compression molding material). The linear expansion coefficient of the injection molding material) is α2. In this case, at the maximum use temperature (T degrees), in order to make the difference between the compression molding material of length L and the injection molding material to be D or less,
D ≧ (α2−α1) × (T−20) × L (where α2> α1)
It is necessary that the compression molding material and the injection molding material satisfy the requirements.
[0060]
For example, when the maximum use temperature T = 240 ° C., L = 4 mm, and D = 50 μm, α1 = 1.1 × 10^-FiveThe linear expansion coefficient α2 of the injection molding material with respect to the compression molding material is α2 ≦ 4.33 × 10.^-Five
It is necessary to satisfy.
[0061]
Therefore, the linear expansion coefficient is 1.5 × 10^-FiveFor the following compression molding materials:
α2 / α1 ≦ 4 or less
That is, it is necessary to use an injection molding material having a linear expansion coefficient within 4 times the linear expansion coefficient of the compression molding material.
[0062]
As described above, the compression molding material and the injection molding material whose difference in accuracy at the maximum use temperature is not more than a predetermined allowable value are easily determined based on the linear expansion coefficient of the compression molding material and the linear expansion coefficient of the injection molding material. it can. In addition, by selecting a material suitable for compression molding and a material suitable for injection molding satisfying the above conditions, it is easy to mold the coil bobbin and the holding member that maintain a predetermined component accuracy at a predetermined high temperature. can do.
[0063]
【The invention's effect】
As described above in detail, according to the present invention, there is provided a fixing device having an induction heating portion including a coil bobbin and a holding member that have high fitting accuracy even when used at high temperatures and satisfy various conditions in molding. it can.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus having a fixing device according to an embodiment of the present invention.
FIG. 2 is a diagram showing a schematic configuration of a fixing device according to an embodiment of the present invention.
FIG. 3 is a block diagram illustrating a control circuit of the image forming apparatus.
FIG. 4 is a diagram illustrating a configuration of an electric circuit for a fixing device.
FIG. 5 is a diagram illustrating a relationship between output power of each resonance circuit in the fixing device and a frequency for exciting each resonance circuit.
FIG. 6 is a diagram illustrating a configuration example of an induction heating unit.
FIG. 7 is a diagram illustrating a configuration example of an induction heating unit.
FIG. 8 is a view showing a relationship between a coil bobbin and a holding member.
[Explanation of symbols]
S: Copy paper (image forming medium), T: Toner (developer), 100: Fixing device, 101 ... Heating roller (heated member), 102 ... Pressure roller, 110 ... Induction heating unit, 110A ... Coil bobbin, 110B ... Holding member, 111 (111a, 111b, 111c, a1-a3, b1-b6, c1-c3) ... Coil

Claims (4)

In a fixing device that fixes a developer on an image forming medium by a heated member that generates heat due to an eddy current generated by a change in a magnetic field generated by a coil.
Inductive heating means comprising a hollow coil bobbin around which an electric wire forming a coil is wound, and a holding member that holds the coil bobbin in a predetermined position, and has a shape that fits inside the coil bobbin.
The fixing device, wherein the holding member is molded by compression molding, and the coil bobbin is molded by injection molding. The fixing device according to claim 1, wherein the coil bobbin and the holding member are formed using the same material. The fixing device according to claim 1, wherein the coil bobbin and the holding member are formed using a material having a difference in thermal expansion coefficient within a predetermined allowable range. The holding member is formed of a compression molding material having insulation and heat resistance suitable for compression molding, the coil bobbin is molded of an injection molding material having insulation and heat resistance suitable for injection molding, and the compression molding is further performed. The fixing device according to claim 1, wherein a difference between a linear expansion coefficient of the material and a linear expansion coefficient of the injection molding material is within a predetermined allowable range.

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