JP5923865B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly to a fixing device using an electromagnetic induction heating method and an image forming apparatus using the same.

In recent years, there has been an increasing demand for energy saving in the field of image forming apparatuses, and electromagnetic induction heating type fixing devices having high energy efficiency have been attracting attention.
The electromagnetic induction heating type fixing device includes a fixing roller, a fixing belt (hereinafter collectively referred to as a “fixing rotating body”), an exciting coil, a demagnetizing coil, and the like. The exciting coil is disposed along the axial direction of the fixing rotator and generates an alternating magnetic field by energizing an alternating current to inductively heat the fixing rotator. The fixing rotating body heated by induction heat-fixes the toner image of the recording sheet that has been passed.

  The degaussing coil is disposed in a non-sheet passing area where the recording sheet of the fixing rotator is not passed. By connecting both ends of the winding to form a closed loop (hereinafter referred to as “turning on the demagnetizing coil”). )), A magnetic flux is generated in a direction that cancels out the magnetic flux that is going to pass through the degaussing coil among the magnetic flux generated by the exciting coil, thereby suppressing the temperature rise of the fixing rotator in the non-sheet-passing region, thereby fixing rotation. Prevent thermal degradation of body and other peripheral members.

When recording sheets of a plurality of sizes are used, for example, the sheet width size of each recording sheet (hereinafter, “paper width size” is simply referred to as “size”) varies depending on the range of the non-sheet passing area. A demagnetizing coil having a size is sequentially stacked on the exciting coil to cope with it (Patent Document 1).
FIG. 13 is a perspective view illustrating a configuration of a main part of the fixing device disclosed in Patent Document 1.

As shown in FIG. 13, the fixing device 800 includes a fixing rotator 801, an exciting coil 802, demagnetizing coils 803 and 803, and degaussing coils 804 and 804 (a pair of demagnetizing coils is given the same reference numeral). The same shall apply hereinafter.)
The exciting coil 802 is disposed along the rotation axis J direction (hereinafter referred to as “longitudinal direction”) of the outer peripheral surface of the fixing rotator 801, and the degaussing coil 803 is disposed at both ends in the longitudinal direction of the exciting coil 802. Degaussing coils 804 are stacked in this order.

  The lengths of the degaussing coils 803 and 804 in the longitudinal direction are set to the lengths corresponding to the non-sheet passing regions when the size C and size B recording sheets are passed, respectively. When passing paper, the degaussing coils 803 and 803 are turned on, and when passing a size B recording sheet, the degaussing coils 804 and 804 are turned on. Further, when a size A recording sheet is passed, both the degaussing coils 803 and 803 and the degaussing coils 804 and 804 are turned off.

JP 2008-139475 A JP 2009-145421 A JP 2009-271154 A

However, it is generally known that the efficiency with which the degaussing coil cancels the magnetic field of the exciting coil (hereinafter referred to as “demagnetizing efficiency”) is extremely reduced when the degaussing coil is separated from the exciting coil even a little.
In the conventional fixing device 800 shown in FIG. 13, each demagnetizing coil 804 is superimposed on the corresponding demagnetizing coil 803 and separated from the exciting coil 802 by that amount. If a large number of size B recording sheets are continuously printed, the excessive temperature rise in the non-sheet passing portion cannot be suppressed, and the fixing rotator 801 and the like may be thermally deteriorated.

In order to improve the decrease in the demagnetization efficiency as described above, for example, it is conceivable to increase the number of turns of the demagnetizing coil 804 stacked thereon. However, in this case, the demagnetizing coil 804 becomes large, which causes a problem that the fixing device is enlarged.
In FIG. 13, the demagnetizing coils are only doubled, but the problem of increasing the size of the apparatus is even more pronounced when the degaussing coils are tripled in preparation for recording sheet passing through different sizes. become.

  On the other hand, for example, as in the fixing device 900 shown in FIG. 14, the degaussing coils 903 and 903 and the demagnetizing coils 904 and 904 are arranged in the longitudinal direction at both ends of the exciting coil 902, and all the degaussing coils are arranged as exciting coils. A configuration in which it is arranged close to 902 is also conceivable. In this case, the demagnetizing coils 904 and 904 are turned on when the size B recording sheet is passed, and the degaussing coils 904 and 904 and the degaussing coils 903 and 903 are turned on when the size C recording sheet is passed. Will respond.

  However, the degaussing efficiency of the degaussing coil is different between the coil winding part and the coil loop, and it is known that the winding part is extremely lower than the inside of the loop. When paper is applied, the demagnetization efficiency is lowered in the wide areas Ra and Rb in which the folded portions 903a, 904a and 903b and 904b of the demagnetizing coils 903 and 904 are arranged in the longitudinal direction. Even if the demagnetization efficiency is improved, the decrease in the demagnetization efficiency in the regions Ra and Rb cannot be compensated, and when a large number of recording sheets are fixed, an excessive temperature rise may occur in this portion.

  The present invention has been made in view of the above-described problems, and even when a plurality of sizes of recording sheets are passed, overheating in a non-sheet passing area is not caused without increasing the size of the apparatus. It is an object of the present invention to provide a fixing device that can be effectively suppressed and an image forming apparatus using the same.

In order to achieve the above object, a fixing device according to the present invention heats a fixing rotator electromagnetically by an excitation coil arranged along the rotation axis direction, and includes a peripheral surface of the fixing rotator, a pressing member, and the like. A fixing device for fixing a non-fixed image by passing a recording sheet through a fixing nip formed between the fixing rotator and the fixing rotor when the recording sheet of a specific size passes through the exciting coil. In each of the areas corresponding to the non-sheet passing areas existing on both outer sides of the paper area, the plurality of degaussing coils arranged along the rotation axis direction and the plurality of degaussing according to the width of the recording sheet to be passed through Operation control means for controlling the operation of the coil, and the plurality of degaussing coils are arranged such that adjacent demagnetization coils and folded portions in the rotation axis direction overlap each other, and one of the plurality of demagnetization coils Wrapping However, the degaussing coil that is overlaid on the folding part of the adjacent degaussing coil is arranged in a posture inclined with respect to the rotation axis so that the other folding part approaches the excitation coil, and The thickness of each degaussing coil is 1 to 2 [mm] .

According to the fixing device having the above structure, a plurality of degaussing coils arrayed in the rotational axis direction of the fixing rotary body, together with the superimposed mutually folded portion between adjacent degaussing coil rotation axis direction, among the plurality of demagnetizing coils The demagnetizing coil having one folded portion overlying the folded portion of the adjacent degaussing coil is arranged in a posture inclined with respect to the rotation axis so that the other folded portion approaches the excitation coil. Therefore, as in the fixing device shown in FIG. 13, the entire specific degaussing coil is not overlapped with another degaussing coil and separated from the excitation coil, and the degaussing efficiency of the specific degaussing coil is greatly reduced. Can be avoided.

Further, by overlapping the folded portions of the adjacent demagnetizing coils, the width in the longitudinal direction of the low demagnetizing efficiency region corresponding to the folded portions of the demagnetizing coil is reduced to about half that of the fixing device shown in FIG. It can be made small, and the influence on the demagnetization efficiency reduction of the folded portion can be suppressed.
Accordingly, it is possible to provide a fixing device that is less likely to cause an excessive temperature rise in a non-sheet passing region in a plurality of size recording sheets without increasing the size of the device by increasing the number of turns of each degaussing coil.

Further, each demagnetizing coil has a folded portion on the side farther from the sheet passing center in the rotation axis direction over the folded portion of another adjacent demagnetizing coil, and the folded portion on the side closer to the sheet passing center is It is desirable that the rotor is disposed in an inclined posture with respect to the rotating shaft so as to approach the exciting coil.

Also, the present invention may be an image forming apparatus having a fixing device configured as described above, thereby obtaining the same effect as the fixing device configured as described above.

1 is a schematic diagram illustrating a configuration of a printer according to a first embodiment of the present invention. FIG. 2 is an exploded perspective view illustrating a configuration of a main part of a fixing unit in the printer. FIG. 3 is a cross-sectional view illustrating a configuration of a fixing unit in FIG. 2. FIG. 4 is a diagram for explaining a laminated structure of fixing rollers. (A) is a top view for demonstrating the positional relationship of a demagnetizing coil and an exciting coil, (b) is a schematic part when the demagnetizing coil and exciting coil in (a) are cut | disconnected by DD line | wire. It is sectional drawing. It is a figure which shows the structure of an excitation circuit and a demagnetizing circuit. It is the graph which compared the degaussing efficiency of the degaussing coil between an Example and a prior art example. It is the figure which compared the planar shape of the degaussing coil which concerns on this Embodiment with the prior art example. It is the schematic which shows the overlap state of the return part of the degaussing coil in the fixing part which concerns on the 2nd Embodiment of this invention. It is the schematic which shows the modification of the lamination | stacking state of a degaussing coil. It is the schematic which shows another modification of the lamination | stacking state of a degaussing coil. It is the schematic which shows another modification of the overlapping state of a degaussing coil. FIG. 10 is a schematic perspective view illustrating a configuration of a main part of a fixing device according to a conventional example. It is a schematic perspective view which shows an example of the structure which has arrange | positioned the several degaussing coil side by side in the longitudinal direction on an exciting coil.

<First Embodiment>
Hereinafter, a first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings by taking a tandem type full color printer (hereinafter simply referred to as “printer”) as an example.
(1) Overall Configuration of Printer FIG. 1 is a schematic diagram showing the configuration of the printer 1 according to the present embodiment.

  As shown in FIG. 1, the printer 1 includes an image process unit 3, a paper feed unit 4, a fixing unit 5, and a control unit 60. When the printer 1 is connected to a network (for example, a LAN) and receives a print job execution instruction from an external terminal device (not shown), each of the colors of yellow, magenta, cyan, and black is received based on the instruction. After a toner image is formed and these are multiplex-transferred to form a full-color image, a printing process on a recording sheet is executed.

Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are represented as Y, M, C, and K, and Y, M, C, and K are added as subscripts to the numbers of the components related to the reproduction colors.
The image processing unit 3 includes image forming units 3Y, 3M, 3C, and 3K corresponding to each of Y to K colors, an optical unit 10, an intermediate transfer belt 11, and the like.
The image forming unit 3Y includes a photosensitive drum 31Y, a charger 32Y, a developing unit 33Y, a primary transfer roller 34Y, a cleaner 35Y for cleaning the photosensitive drum 31Y, and the like disposed around the photosensitive drum 31Y. A Y-color toner image is formed on the drum 31Y. The other image forming units 3M to 3K have the same configuration as the image forming unit 3Y, and the reference numerals are omitted in FIG.

The intermediate transfer belt 11 is an endless belt, and is stretched around the driving roller 12 and the driven roller 13 to circulate in the direction of arrow A.
The optical unit 10 includes a light emitting element such as a laser diode. The optical unit 10 emits laser light L for forming images of Y to K colors according to a drive signal from the control unit 60, and exposes and scans the photosensitive drums 31Y to 31K.

By this exposure scanning, electrostatic latent images are formed on the photosensitive drums 31Y to 31K charged by the chargers 32Y to 32K.
The electrostatic latent images are developed by developing units 33Y to 33K, and Y to K color toner images are formed on the photosensitive drums 31Y to 31K.
Each of the formed toner images is primarily transferred onto the intermediate transfer belt 11 by an electrostatic force generated by a voltage applied to the primary transfer rollers 34Y to 34K. At this time, the image forming operation in the image forming units 3Y, 3M, 3C, and 3K is performed by the intermediate transfer belt 11 so that the toner images of the respective colors are transferred to the same position on the intermediate transfer belt 11 that is traveling. It is executed with the timing shifted from the upstream side to the downstream side.

After the primary transfer, the toner image on the intermediate transfer belt 11 is collectively transferred onto the recording sheet P conveyed from the paper feeding unit 4 by the electrostatic force generated by the voltage applied to the secondary transfer roller 45. Is done.
The paper feeding unit 4 stores the recording sheet P, the feeding roller 42 that feeds the recording sheet P in the paper feeding cassette 41 one by one onto the transport path 43, and the fed recording sheet P as a secondary. A timing roller pair 44 and the like for taking the timing of sending to the transfer position 46 are provided. The recording sheet P is conveyed from the paper feeding unit 4 to the secondary transfer position 46 in accordance with the timing of the toner image on the intermediate transfer belt 11.

The recording sheet P on which the toner image (unfixed image) is formed by the secondary transfer is further conveyed to the fixing unit 5. In the fixing unit 5, the toner image on the recording sheet P is heated and pressed to be thermally fixed. Thereafter, the recording sheet P is discharged onto the discharge tray 72 by the discharge roller pair 71.
The control unit 60 controls the operations of the image processing unit 3, the paper feeding unit 4, and the fixing unit 5.

(2) Configuration of Fixing Unit Next, the configuration of the fixing unit 5 will be described with reference to FIGS. 2 and 3.
FIG. 2 is an exploded perspective view showing the configuration of the main part of the fixing unit 5, and FIG. 3 is a cross-sectional view showing the configuration of the fixing unit 5. 3 corresponds to a cross section viewed from the Y ′ direction when cut along the virtual plane V of FIG.

The fixing unit 5 is based on an electromagnetic induction heating method, and includes a fixing roller 51 that is a fixing rotating body, a pressure roller 52, a magnetic flux generation unit 53, and the like.
The fixing roller 51 and the pressure roller 52 are arranged in parallel, and the pressure roller 52 is pressed against the fixing roller 51 by a pressure mechanism (not shown). As a result, a fixing nip portion N (see FIG. 3) for passing the recording sheet is formed between the fixing roller 51 and the pressure roller 52.

The pressure roller 52 is rotationally driven through a power transmission mechanism such as a gear or belt using a motor (not shown) as a power source. The fixing roller 51 is driven to rotate following the rotation of the pressure roller 52 and interlocks with each other. The pressure roller 52 rotates in the arrow C direction, and the fixing roller 51 rotates in the arrow B direction.
Hereinafter, each component in the fixing unit 5 will be described in detail.

(Fixing roller)
The fixing roller 51 includes a roller body 51a in which a heat insulating layer 512 is formed around a long and cylindrical cored bar 511, and a heat generating belt 51b that is externally fitted to the roller body 51a.
The cored bar 511 is made of, for example, a nonmagnetic material such as aluminum, and has axial portions 511a, which are rotatably supported by bearing portions provided in a housing (not shown) of the fixing portion 5 at both axial ends thereof. 511b.

The heat insulating layer 512 is made of a material having high heat resistance and high heat insulating properties, such as a foamed elastic body such as silicone rubber or fluororubber.
As shown in the partial sectional view of FIG. 4, the heat generating belt 51b is formed by laminating a metal heat generating layer 513, an elastic layer 514, and a release layer 515 in this order from the heat insulating layer 512 side of the roller body 51a.
The metal heating layer 513 is made of a magnetic material such as Ni, SUS, or Fe. The elastic layer 514 is made of a rubber material or a resin material having heat resistance, elasticity and insulation, for example, silicone rubber. By providing the elastic layer 514, the toner image is prevented from being crushed or the toner image is not uniformly melted, and image noise is prevented from being generated. The release layer 515 is a layer for enhancing the releasability from the recording sheet P after fixing, and is made of an insulating resin having heat resistance and excellent releasability. As the insulating resin, for example, a fluororesin such as PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer) can be used.

Here, the outer diameter of the core metal 511 (excluding the shaft portions 511a and 511b) is about 18 [mm], and the thickness of the heat insulating layer 512 is about 10 [mm]. The thickness of each layer of the heat generating belt 51b is 10 to 100 [μm] for the metal heat generating layer 513, 10 to 800 [μm] for the elastic layer 514, and 5 to 100 [μm] for the release layer 515. The thickness of each layer is uniform over the entire circumference.
The outer diameter of the fixing roller 51 combined with these is set to about 30 [mm].

The length excluding the shaft portions 511a and 511b of the fixing roller 51 is set to a dimension larger than the maximum sheet passing width of the recording sheet P (here, A3 longitudinal length).
(Pressure roller)
2 and 3, the pressure roller 52 has an elastic layer 522 and a release layer 523 laminated in this order around a long and cylindrical cored bar 521.

  The metal core 521 is made of, for example, aluminum, and has axial portions 521a and 521b that are rotatably supported by bearing portions provided in a housing (not shown) of the fixing portion 5 at both axial ends. ing. The elastic layer 522 is made of, for example, silicone rubber, and the release layer 523 is made of, for example, a fluorine-based resin such as PFA. By providing the elastic layer 522, the pressure roller 52 and the fixing roller 51 are in elastic contact so that the contact pressure is as small as possible and the contact state is improved. The thickness of the elastic layer 522 is preferably 1 to 20 [mm], and the thickness of the release layer 523 is preferably 10 to 50 [μm].

Here, the outer diameter of the cored bar 521 (excluding the shaft portions 521a and 521b) is about 30 [mm], and the thickness of the elastic layer 522 is about 3 [mm]. Further, the length of the pressure roller 52 excluding the shaft portions 521a and 521b is set to be larger than the maximum sheet passing width (A3 lengthwise) of the recording sheet P.
(Temperature detector)
A temperature detection sensor 54 (see FIG. 3) is held by a frame (not shown) so as to detect the surface temperature at the central portion of the fixing roller 51 in the rotation axis direction.

The temperature sensor 54 is composed of, for example, a non-contact type infrared sensor, and the controller 60 determines that the surface temperature of the sheet passing area of the fixing roller 51 is a predetermined fixing temperature (for example, 170) based on the detection result of the temperature sensor 54. The electric power supplied to the exciting coil 80 is controlled so as to be at (° C).
(Magnetic flux generator)
As shown in FIG. 2, the magnetic flux generator 53 includes an exciting coil 80, three pairs of demagnetizing coils 81, 81, 82, 82, 83, 83, a coil bobbin 84, a main core 85, and hem cores 86a and 86b. Have. In FIG. 2, in order to avoid complication, the winding of each coil is not shown, and only the outer diameter is shown.

The coil bobbin 84 holds the exciting coil 80 and the three pairs of demagnetizing coils 81, 81, 82, 82, 83, 83, and the cores 85, 86 a, 86 b, and the rotation axis J direction of the outer peripheral surface of the fixing roller 51. It is arranged along.
The cross-sectional shape of the portion of the coil bobbin 84 that faces the outer peripheral surface of the fixing roller 51 is curved in an arc shape along the outer peripheral surface of the fixing roller 51. The coil bobbin 84 is fixed to a frame (not shown) such that a gap between the arc-shaped surface and the fixing roller 51 is a predetermined interval, for example, about 1.5 [mm].

The exciting coil 80 is formed by winding a litz wire along the direction of the rotation axis J of the fixing belt 51 and placing it on the inner surface of the arcuately curved portion of the coil bobbin 84. The cross-sectional shape of the coil 80 is a shape along the circumferential direction of the fixing roller 51.
The length of the exciting coil 80 in the longitudinal direction is set to be larger than the maximum sheet passing width of the recording sheet (here, A3 lengthwise).

The exciting coil 80 receives supply of high frequency power and generates an alternating magnetic flux that causes the metal heat generating layer 513 of the fixing roller 51 to generate heat.
Three pairs of demagnetizing coils 81, 81, 82, 82, 83, 83 are held on the upper surface of the exciting coil 80. Details of this arrangement will be described later.
Each of the demagnetizing coils 81 to 83 is also formed by winding a litz wire along the rotation axis J direction, and each cross section is formed in an arc shape along the upper surface of the exciting coil 80.

The main core 85 and the bottom cores 86a and 86b are made of a magnetic material having a high magnetic constant and low loss, for example, an alloy such as ferrite or permalloy.
The main core 85 is composed of a plurality of members bent in a trapezoidal shape so as to cover the outer surface of the exciting coil 80. Each of the trapezoidal members is disposed at a predetermined interval in the rotation axis J direction of the fixing roller 51, and both ends thereof are attached to long hem cores 86a and 86b extending in parallel to the rotation axis J direction. Yes. The hem cores 86a and 86b are fixed to the coil bobbin 84 with, for example, a silicone adhesive.

By providing the main core 85 and the skirt cores 86a and 86b, the fixing roller 51 is efficiently induction-heated so that the magnetic flux generated by the exciting coil 80 does not leak from the side opposite to the fixing roller 51 side. I can do it.
(Arrangement of degaussing coil)
Next, details of the arrangement of the degaussing coil pairs 81 to 83 will be described.

5A is a plan view for explaining the positional relationship between each demagnetizing coil pair 81-83 and the exciting coil 80. FIG. 5B shows only the exciting coil 80 and the demagnetizing coils 81-83. FIG. 6 is a diagram schematically showing a front view when cut along a line D-D in FIG.
Regions N1 and N2 shown in FIG. 5A are regions corresponding to non-sheet passing regions when a recording sheet of a specific size (here, size D) of the exciting coil 80 is passed through the fixing unit 5. Thus, in each of the regions N1 and N2, the demagnetizing coils 81, 82, and 83 are turned from the inner side to the outer side in the rotation axis J direction of the fixing roller 51. They are lined up so as to overlap each other.

  That is, as shown in FIG. 5B, the folded portion 82b of the degaussing coil 82 is overlapped on the folded portion 81a of the demagnetizing coil 81 via an insulating resin (not shown). Similarly, the folded portion 83b of the degaussing coil 83 is also superimposed on the folded portion 82a of the demagnetizing coil 82 via an insulating resin (not shown). And each of the demagnetizing coils 81 to 83 is tilted so as to approach the exciting coil 80 as it goes from the inner side to the outer side in the rotation axis J direction, and a heat resistant adhesive (not shown) interposed in each gap. It is fixed to the exciting coil 80.

However, the innermost demagnetizing coil 81 does not need to be tilted and may be fixed in close contact with the exciting coil 80.
In FIG. 5 (b), the overlapping portions of the folded portions and the gap between the folded portions and the surface of the exciting coil 82 are exaggerated and drawn for easy understanding. The adhesive layer is very thin compared to the thickness of each coil and is negligible (the same applies to other side views).

  In this way, each of the demagnetizing coils 81 to 83 is inclined so that it is closer to the exciting coil 80 than a position overlapping the other folded part except at least a part overlapping the folded part of the other demagnetizing coil. Therefore, as shown in FIG. 13 in the related art, it is possible to sufficiently suppress the demagnetization efficiency of each degaussing coil as compared with the case where all of the specific degaussing coils are separated from the excitation coil.

Moreover, by overlapping the folded portions 81a and 82b of the degaussing coils 81 to 83, the low demagnetization region R has a lower demagnetization efficiency than the case where the folded portions are arranged in the rotation axis J direction as shown in FIG. The range in the longitudinal direction can be halved, and the demagnetization efficiency can be improved as a whole.
The “specific size” that is the narrowest sheet passing width is specifically determined for each model. In the present embodiment, the size D (for example, A5 size longitudinal) is used, but this specific size is not necessarily the minimum size that can be used in the image forming apparatus. This is because if the frequency of use of the minimum size is extremely low, providing a degaussing coil corresponding to it will only increase the cost.

(Excitation circuit and demagnetization circuit)
FIG. 6 is a diagram illustrating a configuration example of the excitation circuit 90 that drives the excitation coil 80 and the demagnetization circuits 91 to 93 that operate the degaussing coil pairs 81 to 83.
As shown in FIG. 6, the excitation circuit 90 is formed by connecting an excitation coil 80, a high frequency power supply 94 and a switching relay 95 in series.

The high frequency power supply 94 outputs high frequency power (for example, 10 to 100 [kHz], 100 to 2000 [W]) supplied to the exciting coil 80. The switching relay 95 includes a known relay switch, and performs on / off control of power supply to the exciting coil 80 based on a control signal from the control unit 60.
The demagnetizing circuit 91 is formed by connecting a demagnetizing coil pair 81 and a switching relay 96 in series. The switching relay 96 performs on / off control of the operation of the degaussing coil pair 81 based on a control signal from the control unit 60.

By turning on the switching relay 96 and closing the demagnetizing circuit 91, a magnetic field is generated in each demagnetizing coil 81 in a direction that prevents the magnetic flux of the alternating magnetic field generated by the exciting coil 80. Conversely, by turning off the switching relay 96 and opening the demagnetizing circuit 91, each demagnetizing coil 81 does not operate, and the alternating magnetic field of the exciting coil 80 is not reduced.
Similarly, the degaussing circuit 92 includes a demagnetizing coil pair 82 and a switching relay 97, and the degaussing circuit 93 includes a demagnetizing coil pair 83 and a switching relay 98.

Further, the control unit 60 transmits a control signal to the switching relay 95 so that the temperature of the sheet passing area of the fixing roller 51 becomes the fixing temperature based on the detection result of the temperature detection unit 54, and drives the excitation coil 80. To control.
When the control unit 60 receives a print job from an external terminal, the control unit 60 extracts information on the user-specified sheet size included in the header of the print job data, and based on that information, the control unit 60 determines the size of the size at the time of image formation. A recording sheet is fed and an input signal is transmitted to the switching relays 96 to 98 to control operations of the degaussing coil pairs 81 to 83. Here, when the recording sheet of the paper feed cassette 41 is not the specified size, the control unit 60 returns error information to the external terminal that has transmitted the print job. When a recording sheet of a specified size is set in the sheet feeding cassette 41, the control unit 60 feeds the recording sheet and transmits an input signal to the switching relays 96 to 98 to set the demagnetizing coil pairs 81 to 83. Control the behavior. Note that the size of the recording sheet stored in the paper feed cassette 41 can be obtained by detecting with a known size detection sensor, or by inputting from the operation panel by the user when the recording sheet is set in the paper feed cassette. It is done.

  Here, if there are a plurality of paper feed cassettes that the printer 1 has, and recording sheets of different sizes are accommodated in the respective paper cassettes, the control unit 60 applies the information according to information on the sheet size of the print job. A configuration in which a sheet feeding cassette in which a recording sheet is stored is selected to feed a recording sheet at the time of image formation, and an input signal is transmitted to the switching relays 96 to 98 to control the operation of each demagnetizing coil pair 81 to 83. Taken. Even in this case, if the corresponding recording sheet is not stored in any of the sheet feeding cassettes, the control unit 60 returns error information to the external terminal that has transmitted the print job, and the corresponding recording sheet is fed. It will wait for it to be set in the cassette.

  In the present embodiment, in the recording sheet of size D or smaller, all three demagnetizing coil pairs 81 to 83 arranged in this way are turned on. Further, by turning on two pairs of the degaussing coil pairs 82 and 83, it corresponds to a size C recording sheet, and by turning on only the demagnetizing coil pair 83, it corresponds to a size B recording sheet. . In the case of a recording sheet of size A, the demagnetizing coil pairs 81 to 83 are not operated while being kept off.

When each of the demagnetizing coils 81 to 83 is turned on, the magnetic flux generated in the exciting coil 80 is generated in a direction that cancels the magnetic flux passing through the demagnetizing coil, so that the metal heating layer 513 of the fixing roller 51 is generated. The magnetic flux for induction heating is reduced to suppress the temperature rise in the non-sheet passing region.
(Verification by experiment)
In FIG. 7, a recording sheet of size B (here, B4 size longitudinal) is passed between the fixing unit 5 (example) of the present embodiment and the fixing device 800 (conventional example) of FIG. When the degaussing coil corresponding to the non-sheet passing region (the outermost degaussing coil, corresponding to the degaussing coil 83 in FIG. 5 in the embodiment and the second-stage degaussing coil 804 in FIG. 13) is measured. It is the graph which compared. In this experiment, the demagnetizing coils 83 and 804 have the same number of turns and the same thickness for comparison. Specifically, a degaussing coil in which 114 strands of strands having a strand diameter of 0.17 are wound for 10 turns and having a coil thickness of 2.8 [mm] is used. .

In FIG. 7, the vertical axis represents the demagnetization efficiency [%], and the horizontal axis represents the distance [mm] from the sheet passing center in the rotation axis J direction of the fixing roller 51. A line 101 indicates the demagnetizing efficiency of the embodiment, and a line 102 indicates the demagnetizing efficiency of the conventional example.
As shown in the graph of FIG. 7, when a recording sheet of size B is passed, the boundary between the sheet passing area and the non-sheet passing area is at a position 128.5 [mm] from the sheet passing center, and the boundary The demagnetizing coil 83 according to the embodiment and the folded portion of the degaussing coil 804 according to the conventional example are arranged in a region from about 10 to 15 mm. Therefore, within that range, the demagnetization efficiency is low in both the example and the conventional example, but outside the configuration, the configuration of this example greatly improves the demagnetization efficiency than the configuration of the conventional example. Is easily understood.

  In this experiment, compared with the demagnetizing coil in the second stage as a conventional example, in order to cope with a recording sheet of a different size with the conventional configuration, the degaussing coils are stacked in three stages and four stages. On the other hand, according to the present embodiment, all the degaussing coils can be provided as close to the excitation coil as much as the size is increased. An improvement in demagnetization efficiency can be expected.

(Coil shape)
In the present embodiment, since one folded portion of the degaussing coil is overlapped with the folded portion of the adjacent degaussing coil, a gap with the exciting coil is generated accordingly. Therefore, the inventors of the present application tried to further improve the demagnetization efficiency by suppressing the thickness of the degaussing coil itself to reduce the gap and thereby reducing the inclination of the degaussing coil and bringing it as close to the exciting coil 80 as possible.

FIG. 8 shows a demagnetizing coil 81 (82, 83) according to the embodiment in this case (hereinafter, the shape of the “example product” in a plan view and a side view is shown as a conventional demagnetization coil (hereinafter “conventional product”). FIG.
The conventional product uses a degaussing coil 880 formed by winding 114 strands of strands having a strand diameter of 0.17 and wound for 10 turns, and its thickness T2 is 2.8 [mm]. .

On the other hand, in the example product, a litz wire formed by twisting 20 strands having a strand diameter of 0.17 is wound by 19 turns, and the thickness T1 is suppressed to 1.0 [mm].
Further, in the conventional product, the folded portion is greatly curved in plan view, whereas in the example product, the coil winding shape is generally rectangular in plan view, and the folded portion is curved. It is getting smaller. By reducing the curvature of the folded portion in this way, most of the folded portions overlap when folded on the folded portions of the adjacent degaussing coils, so that the low demagnetization region R can be further reduced. is there.

  In the example product, the number of twists of the litz wire is significantly smaller than that of the conventional product, so the cancellation magnetic flux generated is less and the demagnetization efficiency seems to be lower than that of the conventional product. When the embodiment having a thickness of 1.0 mm is arranged as shown in FIG. 5, the demagnetization efficiency of an average of 63% can be obtained in the region where the embodiment product exists. It was. Incidentally, when the average demagnetization efficiency was measured in the same manner as described above with the thickness of the example product set to 2.0 mm and 2.8 mm, the folded portion and the exciting coil overlapped with the folded portion of the adjacent demagnetizing coil as the thickness increased. The average demagnetization efficiency was reduced, and the former was 57% and the latter was 50%.

Recently, a high-speed machine that has a processing capacity of 75 sheets / minute in the A4 size has also appeared, and in this case, even when a large amount of continuous printing is performed, an excessive temperature rise in the non-sheet passing area is effectively prevented. For this purpose, it is empirically known that the degaussing efficiency of the degaussing coil is preferably 55% or more. From this viewpoint, the thickness of the degaussing coil is preferably 2 mm or less.
On the other hand, in order to prevent excessive heat generation of the coil itself, there is a limit to reducing the fineness of the strands and the number of twisted litz wires, and the lower limit of the thickness of the coil is desirably 1 [mm] or more.

Therefore, it can be said that the thickness T1 of the demagnetizing coil is more preferably 1 to 2 [mm].
<Second Embodiment>
Next, a second embodiment of the present invention will be described.
The fixing unit of the second embodiment and the fixing unit 5 of the first embodiment are different in the shape of the demagnetizing coil and the configuration for bringing the degaussing coil close to the exciting coil.

Other configurations are basically the same as those in the first embodiment. Therefore, only the above differences will be described below, and descriptions of other configurations will be omitted. In addition, the same reference numerals are used for the same components as those of the fixing unit 5 of the first embodiment.
FIG. 9A is a cross-sectional view illustrating the shape of the demagnetizing coils 181 to 183 included in the fixing unit 150 according to the second embodiment in a side view. FIG. 9B is a perspective view showing the shape of the degaussing coil 182 of which only the external shape is shown, and the litz wire is not shown.

In FIG. 9A, only one side from the sheet passing center in the rotation axis J direction of the fixing roller 51 is shown.
As shown in FIG. 9A, among the demagnetizing coils 181 to 183 arranged in the direction of the rotation axis J, the shape of the demagnetizing coil 181 is linear when viewed from the side, and is close to the fixing roller 51. Arranged in parallel, the degaussing coils 182 and 183 are formed so that one of the folded portions is in a step.

That is, in the demagnetizing coil 182, a step is provided so that the other parallel portion 182c and the folded portion 182a are close to the exciting coil 80 in a state where the folded portion 182b is superimposed on the folded portion 181a of the demagnetizing coil 181. It has been.
Here, the parallel portion 182c is a portion between the folded portions 182a and 182b of the degaussing coil 182 and in which the litz wires constituting the coil are parallel along the rotation axis J direction. Similarly, in the demagnetizing coil 183, a step is provided so that the other parallel portion 183c and the folded portion 183a are close to the exciting coil 80 in a state where the folded portion 183b is superimposed on the folded portion 182a of the demagnetizing coil 182. It has been.

Such a shape can be easily formed by pressing a coil body wound in a flat shape.
Since the demagnetizing coils 182 and 183 are provided with steps as described above, the parallel portions 182c and 183c can be brought into close contact with the exciting coil 80, so that the demagnetizing coils 81 to 83 of the first embodiment. As described above, the demagnetization efficiency can be further improved as compared with the first embodiment in which each is inclined and close to the exciting coil 80. Thereby, the excessive temperature rise in the non-sheet passing region can be more effectively suppressed.
[Modification]
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications can be implemented.

(1) The number and arrangement of the demagnetizing coils are not limited to the above embodiment, and can be appropriately selected according to the specifications of the fixing roller and the fixing unit.
(1-1) FIG. 10 is a modified example of the first embodiment, in which each of the demagnetizing coils 281 to 283 increases from the outer side to the inner side in the rotation axis J direction of the fixing roller 51. It is arrange | positioned with the attitude | position which inclines so that it may adjoin. That is, the demagnetizing coils 81 to 83 of the first embodiment are opposite to the tilting direction. In this case, the degaussing coils 281 to 283 are close to the exciting coil near the boundary between the paper passing area and the non-paper passing area of the corresponding paper passing width size. The demagnetization efficiency in the vicinity of the boundary of the paper region can be increased as compared with the first embodiment.

(1-2) FIGS. 11 and 12 show modifications of the second embodiment. In FIG. 11, the demagnetizing coils 381 and 382 are turned back in the direction of the rotation axis J of the fixing roller 51. 382a is overlaid on the folded portions 382b and 383b of the adjacent demagnetizing coils 382 and 383, respectively.
In FIG. 12, two folded portions 482a and 482b of the degaussing coil 482 are overlaid on the folded portions 481a and 483b of the adjacent demagnetizing coils 481 and 483, respectively.

  (2) In the above embodiment, the configuration using the fixing roller 51 in which the heat generating belt 51b having the metal heat generating layer 513 is fitted on the outer periphery of the roller main body 51a is shown as the fixing rotating body. It is not a thing. For example, a fixing belt having a metal heating layer may be used, and a roller body may be loosely or tightly fitted on the inside thereof. When the fixing belt is used, a long pressing member that receives the pressing force from the pressure roller 52 may be disposed inside the fixing belt instead of the roller body.

  (3) In the above embodiment, the configuration of the heat generating belt 51b in which the metal heat generating layer 513, the elastic layer 514, and the release layer 515 are laminated in this order is shown, but the present invention is not limited to this. For example, a low resistance layer made of a low resistance material such as Cu, Ag, or Au can be interposed between the metal heating layer 513 and the elastic layer 514. In this case, however, the thickness of the low-resistance layer is preferably about several [μm] to several tens [μm], and even better heat generation efficiency can be obtained by inserting the low-resistance layer.

(4) In the above embodiment, the main core 85 and the skirt cores 86a and 86b are configured to form a magnetic circuit together with the exciting coil 80 and the fixing roller 51. Further, both ends in the longitudinal direction in the loop of the exciting core 80 are shown. You may arrange | position a core member (end part core) to a part.
Since both ends of the fixing roller 51 in the direction of the rotation axis are not easily accessible by the alternating magnetic field of the exciting coil and are also easy to dissipate heat from the side to the outside, the end core is arranged so that the magnetic flux at both ends By increasing the density, it is possible to prevent fixing defects at both ends in the width direction when the maximum size A is passed.

  (5) In the above embodiment, since the demagnetizing coil is configured so that the other part of the degaussing coil is closer to the exciting coil than the part overlapped with the folded part of the adjacent degaussing coil, the degaussing coil is inclined (first Embodiment), a step portion is provided (second embodiment), but the position of any folded portion where at least other portions of the respective demagnetizing coils overlap each other among the overlapped folded portions If it is arranged in a posture closer to the exciting coil side, it may be possible to improve the demagnetization efficiency at least as compared with the conventional case.

(6) In the above embodiment, a tandem full-color printer has been described as the image forming apparatus. However, the scope of the present invention is not limited to this, and a copying machine having a fixing unit using a resistance heating element, The present invention can be applied to a facsimile machine, a printer, and the like.
Further, the contents of the above-described embodiment and modification examples may be combined as much as possible.

  The present invention is suitable as a technique for preventing an excessive temperature rise in a non-sheet passing region in an electromagnetic induction type fixing device.

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 4 Paper feed part 5 Fixing part 10 Optical part 11 Intermediate transfer belt 31 Photosensitive drum 32 Charger 33 Developer 51 Fixing belt 51 Fixing roller 51a Roller body 51b Heat generating belt 52 Pressure roller 53 Magnetic flux generation part 54 Temperature detection unit 54a Infrared sensor 60 Control unit 80 Excitation coil 81, 82, 83 Demagnetization coil 81a, 81b, 82a, 82b, 83a, 83b Folding unit 90 Excitation circuit 91, 92, 93 Demagnetization circuit 150 Fixing unit 181, 182, 183 Degaussing coil 513 Metal heating layer N1, N2 area (area corresponding to non-paper passing area of degaussing coil)
T1 thickness (demagnetizing coil)

Claims (3)

The fixing rotator is heated by electromagnetic induction by an excitation coil arranged along the rotation axis direction, and a recording sheet is passed through a fixing nip formed between the peripheral surface of the fixing rotator and the pressing member. A fixing device for fixing an unfixed image,
In each region corresponding to the non-sheet passing region existing on both outer sides of the sheet passing region of the fixing rotator when the recording sheet of a specific size is passed through the exciting coil, the exciting coil is arranged along the rotation axis direction. A plurality of degaussing coils;
Operation control means for controlling the operations of the plurality of degaussing coils according to the width of the recording sheet to be passed;
With
The plurality of degaussing coils are:
A degaussing coil in which an adjacent demagnetizing coil and a folded portion in the direction of the rotation axis are overlapped with each other, and one of the plurality of degaussing coils overlaps with a folded portion of the adjacent demagnetizing coil. The other folded portion is disposed in a posture inclined with respect to the rotating shaft so as to approach the exciting coil, and the thickness of each demagnetizing coil is 1 to 2 [mm]. A fixing device characterized. Each demagnetizing coil has a folded portion on the side farther from the sheet passing center in the rotation axis direction over the folded portion of another adjacent demagnetizing coil, and a folded portion on the side closer to the sheet passing center is the excitation coil. The fixing device according to claim 1, wherein the fixing device is disposed in a posture inclined with respect to the rotation shaft so as to approach the rotation axis . An image forming apparatus comprising the fixing device according to claim 1 or 2.

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