JP5439754B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus using the fixing device, and more particularly to a technique for shortening a warm-up time in a fixing device using an induction heating fixing belt.

In recent years, in the field of image forming apparatuses such as printers and copiers, those equipped with a fixing device of an electromagnetic induction heating method having a higher power saving effect than a fixing device using a halogen heater as a heat source are becoming widespread (for example, patent documents). 1).
FIG. 10 is a cross-sectional view showing the configuration of the electromagnetic induction heating type fixing device in Patent Document 1.

As shown in the figure, in the fixing device, a fixing roller 302 is disposed on the inner side of the circulation path of the fixing belt 301, and on the outer side of the circulation path, at a position facing the fixing roller 302 with the fixing belt 301 interposed therebetween. A pressure roller 303 is disposed, and the pressure roller 303 is urged toward the fixing belt 301 to form a fixing nip 310.
The pressure roller 303 receives a driving force from a driving motor (not shown) and rotates in the arrow Q direction. This driving force is transmitted to the fixing roller 302 and the fixing belt 301 via the fixing nip 310, whereby the fixing roller 302 and the fixing belt 301 are driven to rotate in the direction of arrow P.

  In addition, a magnetic flux generator 304 that generates a magnetic flux for generating heat from the heat generating layer included in the fixing belt 301 is disposed outside the circumference of the fixing belt 301 and on the opposite side of the pressure roller 303. Is done. A regulation plate 305 that contacts the back surface of the fixing belt 301 and regulates the circulation position is disposed at a position facing the magnetic flux generation unit 304 inside the circulation path. This stabilizes the relative position with the magnetic flux generation unit 304 even during the rotation of the fixing belt 301, so that the heat generation of the fixing belt 301 due to electromagnetic induction does not vary.

In such a configuration, when the magnetic flux is generated from the magnetic flux generation unit 304 while the fixing belt 301 is driven to rotate, the portion of the heat generation layer in the fixing belt 301 that mainly faces the magnetic flux generation unit 304 generates heat, and the sheet S When the toner image formed thereon passes through the fixing nip 310, it is heated and pressurized and thermally fixed to the sheet S.
According to such a configuration, the heat capacity of the fixing belt 301 can be sufficiently reduced and the heat efficiency is excellent, so that the warm-up time can be shortened.
JP 2007-264421 A

  In the configuration such as the fixing device described above, the regulation plate 305 plays an important role in order to stabilize the circular orbit of the fixing belt 301 particularly in the portion facing the magnetic flux generation unit 304 and prevent the variation in heat generation. The heat is transferred from the portion in contact with the fixing belt 301 to the regulation plate 305, which is an obstacle to further shortening the warm-up time of the fixing belt 301.

  An object of the present invention is to further reduce the warm-up time in a fixing device configured to guide a fixing belt with a regulating plate.

In order to achieve the above-described object, the present invention presses a first roller disposed on the inside of a circulation path of a belt that circulates with a second roller from the outside of the circulation path via the belt, thereby A fixing nip is formed between the two rollers, and a heat generation layer included in the belt is caused to generate heat by electromagnetic induction, and a sheet on which an unfixed image is formed is passed through the fixing nip to thermally fix the unfixed image. A fixing device, disposed on the inner side of the belt circulation path, in sliding contact with the back surface of the belt that circulates and guides the belt in the circulation direction;
An excitation coil disposed at a position opposite to the regulation plate across the belt, and is cut along a plane perpendicular to the rotation axis of the first roller. C is the center of curvature of the orbit in the region guided by the regulation plate, P and Q are the positions of the upstream and downstream edges of the belt in the circumferential direction of the belt, and the belt of the excitation coil When the positions of the end portions on the upstream side and the downstream side in the circumferential direction are R and S, respectively, the edge portions P and Q of the regulation plate are configured to be located within a range sandwiched between the line segment CR and the line segment CS. In addition , at least one end portion of the restriction plate on the upstream side and the downstream side in the circumferential direction of the belt has a thick portion that is thicker than the central portion .

By defining the upper limit of the position and length of the regulating plate in the circumferential direction of the belt as described above, the heat capacity can be reduced within a necessary range, and the belt warm-up time can be shortened.
Here, the thick portion may be formed by folding the end portion of the restriction plate 180 °.
In the present invention, the first roller disposed on the inner side of the circulation path of the belt that circulates is pressed from the outer side of the circulation path by the second roller via the belt, so that the gap between the belt surface and the second roller is reached. A fixing device that forms a fixing nip, heats a heat generation layer included in the belt by electromagnetic induction, passes a sheet on which an unfixed image is formed, through the fixing nip, and thermally fixes the unfixed image. A regulating plate that is disposed on the inner side of the belt's circulation path and is in sliding contact with the back surface of the belt that circulates and guides the belt in the circulation direction, and the belt is disposed outside the belt's circulation path with the belt interposed therebetween. An excitation coil disposed at a position facing the restriction plate, and when cut by a plane perpendicular to the rotation axis of the first roller, C is the center of curvature of the orbit in the region to be generated, P and Q are the positions of the upstream and downstream edges of the belt in the circumferential direction of the regulation plate, and the upstream and downstream of the excitation coil in the circumferential direction of the belt. When the positions of the end portions on the side are R and S, respectively, the edge portions P and Q of the restriction plate are configured to be located within a range sandwiched between the line segment CR and the line segment CS, and the restriction plate plate, at least one end of the upstream side and downstream side of the rotating direction of the belt, have a bent portion bent in a direction away from the belt, and the regulating plate is magnetic shunt alloy layer and the low-resistance conductive layer And the magnetic shunt alloy layer is located closer to the belt than the low resistance conductive layer .
Here, in the case of cutting along a plane perpendicular to the rotation axis of the first roller, if the winding center of the coil is M, at least the edge portions P and Q of the restriction plate have the line segment MC interposed therebetween. It is desirable that the belt is located on the upstream side and the downstream side in the circumferential direction of the belt.

This is because the main magnetic flux is considered to flow on the line MC, and it is desirable that the belt is stably guided by the restriction plate in this portion.
Here, it is preferable that a magnetic shunt alloy layer is included in the regulation plate or on the regulation plate side of the heating layer of the belt.
The automatic temperature control of the magnetic shunt alloy layer can suppress the excessive temperature rise in the non-sheet passing portion.

Here, if a low friction layer is formed on at least one of the inner peripheral surface of the belt and the rubbing surface of the regulating plate with the belt, the durability is increased.
The present invention also relates to a belt that has a heat generating layer and circulates, an excitation coil that generates heat by electromagnetic induction, an arcuate plate that faces the excitation coil via the belt, and the belt. A pressure rotator that forms a fixing nip in contact therewith, heats the heat generation layer included in the belt by electromagnetic induction, passes the sheet on which the unfixed image is formed, through the fixing nip, and the unfixed image The width of the arc-shaped plate is narrower than the width of the exciting coil in the circumferential traveling direction of the belt, and the fixing device is configured to fix both ends of the exciting coil in the circumferential traveling direction of the belt. The arc-shaped plate is located between the at least one end of the arc-shaped plate on the upstream side and the downstream side in the circumferential direction of the belt. Characterized in that it has a have thick portion.
Furthermore, the present invention provides a belt that has a heat generating layer and circulates, an excitation coil that generates heat by electromagnetic induction, an arc-shaped plate that faces the excitation coil via the belt, and the belt A pressure rotator that forms a fixing nip in contact with the belt, heats a heat generation layer included in the belt by electromagnetic induction, passes a sheet on which an unfixed image is formed, through the fixing nip, and A fixing device that thermally fixes a received image, wherein the width of the arc-shaped plate is narrower than the width of the excitation coil in the circumferential running direction of the belt, and the excitation coil in the circumferential running direction of the belt. The arc-shaped plate is positioned between both ends, and at least one end of the arc-shaped plate on the upstream side and the downstream side in the circumferential direction of the belt is far from the belt. Have a bent portion bent mow direction, it said and a regulation plate shunt alloy layer and the low-resistance conductive layer, said magnetic shunt alloy layer is located on the belt side of the low-resistance conductive layer It may be a feature.
The present invention can also be an image forming apparatus including the fixing device.

Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described by taking as an example a case where it is applied to a tandem type color digital printer (hereinafter simply referred to as “printer”).
(1) Overall Configuration of Printer FIG. 1 is a schematic cross-sectional view showing the overall configuration of the printer 1.
As shown in the figure, the printer 1 includes an image processing unit 3, a paper feeding unit 4, a fixing unit 5, and a control unit 60. The printer 1 is connected to a network (for example, a LAN) and is connected to an external terminal device (not connected). When a print job execution instruction is received from the figure, a toner image of each color of yellow, magenta, cyan, and black is formed based on the instruction, and a full color image formation is executed by multiple transfer of these toner images.

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, 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, and a cleaner 35Y for cleaning the photosensitive drum 31Y disposed around the photosensitive drum 31Y. A Y-color toner image is formed on the photosensitive drum 31Y. The other image forming units 3M to 3K have the configuration of the chargers 32M to 32K as in the image forming unit 3Y except that the toner color is different. However, in order to prevent the figure from becoming complicated, The sign of is not shown.

The intermediate transfer belt 11 is an endless belt, is stretched around a driving roller 12 and a driven roller 13, and is driven to rotate in the direction of arrow C.
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 superimposed on the same positions on the intermediate transfer belt 11 and primarily transferred onto the photosensitive drums 31Y to 31K. It is executed at different timings.
The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 11 by the electrostatic force acting on the primary transfer rollers 34Y to 34K to form a full-color toner image, and further move toward the secondary transfer position 46.

  On the other hand, the paper feed unit 4 includes a paper feed cassette 41 that accommodates the paper S, a feed roller 42 that feeds the paper S in the paper feed cassette 41 one by one onto the transport path 43, and a secondary feed of the fed paper S. A timing roller pair 44 and the like are provided for timing to send the toner to the transfer position 46, and the paper S is fed from the paper supply unit 4 to the secondary transfer position in accordance with the movement timing of the toner image on the intermediate transfer belt 11. The toner images on the intermediate transfer belt 11 are secondarily transferred onto the sheet S all at once by the action of electrostatic force by the secondary transfer roller 45.

The sheet S that has passed the secondary transfer position 46 is further conveyed to the fixing unit 5, and the toner image (unfixed image) on the sheet S is fixed on the sheet S by heating and pressurization in the fixing unit 5. The paper is discharged onto a discharge tray 72 via a discharge roller pair 71.
(2) Configuration of Fixing Unit FIG. 2 is a partial cross-sectional perspective view showing the configuration of the fixing unit 5, and FIG. 3 (a) is a cross-sectional view of the main part thereof.

As shown in FIG. 2, the fixing unit 5 includes a fixing roller 150, a fixing belt 155, a regulation plate 156, a pressure roller 160, and a magnetic flux generation unit 170.
The fixing roller 150 is formed by covering the periphery of a long and cylindrical cored bar 152 with an elastic body layer 153, and is arranged inside the circulation path of the fixing belt 155.
The cored bar 152 is a cylindrical body having an outer diameter of about 20 mm made of, for example, aluminum, iron, stainless steel, or the like.

The elastic layer 153 has a thickness of about 10 mm, for example, and the outer diameter of the fixing roller 150 is about 40 mm, for example. The material is a foamed elastic body such as silicone rubber or fluororubber, and a material having high heat resistance and heat insulation is desired.
The pressure roller 160 is formed by laminating a release layer 163 around a cylindrical cored bar 161 with an elastic body layer 162 interposed therebetween, and is disposed outside the circumference path of the fixing belt 155, and from the outside of the fixing belt 155. A fixing nip 155n having a predetermined width in the circumferential direction is formed between the surface of the fixing belt 155 by pressing the fixing roller 150 through the fixing belt 155.

The metal core 161 is made of, for example, aluminum, the elastic layer 162 is made of silicon sponge rubber, and the release layer 163 is made of PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) or PTFE (polyethylene). Tetrafluoroethylene) coat or the like.
The outer diameter of the pressure roller 160 is, for example, about 35 mm.

  The fixing roller 150 and the pressure roller 160 are rotatably supported at both ends in the axial direction of the core bars 152 and 161 on a bearing portion of a frame (not shown), and the pressure roller 160 is driven by a drive motor (not shown). Is driven to rotate in the direction of arrow B. As the pressure roller 160 rotates, the fixing belt 155 and the fixing roller 150 are driven to rotate in the direction of arrow A.

The fixing belt 155 is a cylindrical belt, and as shown in FIG. 3B, a release layer 1551, an elastic layer 1552, a heat generating layer 1553, and a magnetic shunt alloy layer 1554 are formed from the outer peripheral surface side. These are stacked in this order.
As the fixing belt 155, a belt that can stand independently and hold a cylindrical shape is used. The belt width direction (corresponding to the rotation axis direction of the fixing roller 150) of the fixing belt 155 is longer than the width direction length of the maximum size sheet.

The release layer 1551 is a cylindrical body made of PFA or the like, and its thickness is determined as appropriate from the range of 30 μm to 40 μm based on experience.
The elastic body layer 1552 is made of silicone rubber having a thickness of about 200 μm.
In addition to this, fluorine rubber or the like may be used.
The heat generation layer 1553 is made of nickel or the like having a thickness of about 40 μm, and generates heat by the magnetic flux generated from the magnetic flux generation unit 170.

The magnetic shunt alloy layer 1554 is made of, for example, an alloy of nickel and iron and has a thickness of about 30 μm. The magnetic shunt alloy layer 1554 is a ferromagnetic material at a normal temperature but becomes non-magnetic when the Curie temperature is exceeded. This Curie temperature can be adjusted by the mixing ratio of nickel and iron. In this embodiment, the Curie temperature is set to a temperature approximately 20 ° C. higher than the temperature suitable for fixing (target temperature).
In addition, an alloy such as nickel, iron, and chromium may be used.

  Returning to FIG. 2, the magnetic flux generator 170 has a coil bobbin 171, a hem core 172, an exciting coil 173, a main core 174, and a cover 175, and is outside the circulation path of the fixing belt 155. With reference to a position facing the pressure roller 160 with the 155 interposed therebetween, the fixing belt 155 is disposed along the width direction of the fixing belt 155 slightly upstream in the circumferential direction.

  The exciting coil 173 generates a magnetic flux for heating the heat generating layer 1553 included in the fixing belt 155, and is wound around the coil bobbin 171. The coil bobbin 171 has a winding surface of the excitation coil 173 placed on the surface of the virtual cylinder substantially concentric with respect to the center of curvature C (see FIG. 4) of the portion guided by the restriction plate 156 of the fixing belt 155. Thus, the direction of the magnetic flux generated by the exciting coil 173 is directed toward the curvature center C as a whole so that the generated magnetic flux effectively acts on the fixing belt 156. It has become.

  The alternating magnetic flux generated from the exciting coil 173 is guided to the fixing belt 155 by the main core 174 and the bottom core 172, and mainly in the magnetic flux generation unit 170 of the heat generating layer 1553 (see FIG. 3B) of the fixing belt 155. The fixing belt 155 is heated by penetrating the opposing portions, generating an eddy current in this portion to generate heat in the heat generating layer 1553 itself. As the fixing belt 155 is heated, the temperature of the pressure roller 160 in contact with the fixing belt 155 is also increased.

A sensor for detecting the surface temperature of the center portion in the width direction of the fixing belt 155 is separately provided (not shown), and the controller 60 determines that the temperature of the fixing belt 155 is based on the detection signal of the sensor. The power supply to the exciting coil 173 is controlled so as to be maintained at (about 180 ° C.).
When the sheet S passes through the fixing nip 155n while the fixing nip 155n is maintained at the target temperature, an unfixed toner image on the sheet S is heated and pressed to be thermally fixed on the sheet S.

The regulation plate 156 is a long plate made of a non-magnetic and low-resistance conductive material and arranged in parallel with the axis of the fixing roller 150, and has a substantially arc-shaped cross section. The guide surface is rubbed against the back surface of the fixing belt 155 to restrict the circular trajectory to an arc shape.
In addition, the low-resistance conductive material is specifically copper, and in addition to this, aluminum, and in some cases, gold or silver can be used.

The restriction plate 156 is supported at both ends in the longitudinal direction by a frame (not shown).
In such a configuration, due to the interaction between the magnetic shunt alloy layer 1554 in the fixing belt 155 and the low-resistance conductive layer in the regulating plate 156, a portion where the sheet of the fixing roller 150 is not passed (hereinafter referred to as “non-sheet passing portion”). The effect that the excessive temperature rise in the above is automatically suppressed is obtained.

That is, the fixing belt 155 has a temperature at the central portion (sheet passing portion) in the axial direction through which the sheet is passed, and the temperature is lowered due to the heat being taken away by the sheet, but at a non-sheet passing portion on both ends where the sheet does not pass. Since the temperature remains high, if power is supplied to the magnetic flux generator 170 in order to maintain the sheet passing portion at the target temperature necessary for fixing, the temperature of the non-sheet passing portion further increases.
At that time, a portion corresponding to the non-sheet passing portion of the magnetic shunt alloy layer 1554 included in the fixing belt 155 is heated to a temperature higher than the Curie temperature, and is changed from a ferromagnetic material to a non-magnetic material. The magnetic flux that has been used as the circulation path in 1554 now passes through the magnetic shunt alloy layer 1554 and reaches the regulation plate 156.

This magnetic flux generates an eddy current in the regulating plate 156. However, since it has a low resistance, it generates a magnetic flux in a direction that cancels the magnetic flux rather than generating heat as an eddy current loss. It decreases rapidly and the temperature rise is alleviated.
As described above, according to the configuration of the fixing unit 5 according to the present embodiment, the fixing belt 155 itself generates heat, so that it has excellent thermal efficiency. Further, due to the interaction between the magnetic shunt alloy layer 1554 and the regulating plate 156, the fixing belt 155. The temperature can be automatically controlled so as not to overheat the non-sheet passing portion (hereinafter referred to as “magnetizing effect”).

(3) Length and Position of Restriction Plate 156 in Belt Circulation Direction FIG. 4 is a diagram for explaining conditions such as dimensions of the restriction plate 156. In this figure, the cross-sectional view of the fixing unit in FIG. 3A is simplified, and the magnetic flux generation unit 170 shows only the bottom core 172, the excitation coil 173, and the main core 174.
Now, the upstream and downstream edges (hereinafter simply referred to as “upstream side” and “downstream side”) of the regulation plate 156 in the rotation direction of the fixing belt 155 are denoted by P and Q, respectively, and are guided by the regulation plate 156. Let C be the center of curvature of the area of the fixing belt 155. Further, if the upstream and downstream ends of the exciting coil 173 are R and S, respectively, the restriction plate 156 has its edges P and Q positioned within a range sandwiched between the line segment CR and the line segment CS. It is set to such a length.

That is, the angle β formed by the line connecting the both edges of the restriction plate 156 and the center of curvature C is included in the angle α formed by the line connecting the both ends of the excitation coil 173 and the center of curvature C (β <α ).
By doing so, the total heat capacity of the fixing belt 155 and the regulating plate 156 in the region where the fixing belt 155 is mainly induction-heated (the region facing the exciting coil 173 of the magnetic flux generator 170) is smaller than that in the past. (As shown in FIG. 10, in the conventional fixing device, the relation of β> α is established), and the warm-up time can be further shortened.

As described above, the restriction plate 156 has two functions: (a) the function of stabilizing the circulation path of the fixing belt 155 and (b) the function of suppressing excessive temperature rise due to the magnetic shunt effect. Originally, the fixing belt 155 itself has a rigidity sufficient to maintain a cylindrical shape in a natural state (in a state where it is not driven in a circular motion). Therefore, there is no necessity that α ≦ β in particular. In order to cancel the magnetic flux from the exciting coil 173 toward the center of curvature C at 156, it is meaningless even if it is wider than the angle α in the range where the exciting coil 173 exists. In order to shorten the warm-up time, The range in which the excitation coil 173 of the magnetic flux generator 170 covers the fixing belt 155 in the circumferential direction, that is, the angle α in FIG. Since the heat capacity of the belt 155 itself is not increased as much as possible, the diameter thereof cannot be increased so much that the temperature of the peripheral surface is changed along the peripheral surface within a limited diameter range of the fixing belt 155. If a temperature sensor for detection, a sheet passing guide, a sheet separation claw, and the like are provided, there is a certain upper limit on the size of β. In this embodiment, it is set to 90 °.

On the other hand, when the winding center of the exciting coil 173 is M (hereinafter referred to as “coil center M”), it is considered that the main magnetic flux passes through this portion, and therefore the exciting coil 173, the coil center M and the curvature center C. It is at least necessary to be present on the line segment MC connecting.
Therefore, the regulating plate 156 is arranged symmetrically with respect to the line segment MC, and the angle β indicating the existence range of the regulating plate 156 is changed from 40 ° to 90 °, so that the magnetic shunt effect (the regulating plate 156 is curie). The rate of heat generation (Q2) of the fixing belt 155 when it becomes non-magnetic after the passage of temperature decreases from the previous heat generation amount (Q1) at room temperature (100 × (Q1-Q2) / Q1 [ %]) Using a finite element method, a result as shown in G1 of FIG. 5 was obtained.

At this time, α = 90 ° (angle 30 ° between the left and right coil portions 173a and 173b (FIG. 4)), the fixing belt 155 has a diameter of 40 mm, the fixing roller 150 has a diameter of 36 mm, and the regulation plate 156 has a thickness of 0.5 mm. Yes.
As shown by the curve G1 in FIG. 5, the magnetic shunt effect decreases as the angle β of the restricting plate 156 decreases.

When the curve G1 indicating the change of the magnetic shunt effect with respect to the angle β is differentiated, it is found that an inflection point T exists as shown by the curve G2 when β is about 60 °. This is just equal to the angle γ (see FIG. 4) formed by the circumferential central portions of the left and right coil cross sections 173a and 173b (the central angle of each width of 30 °) of the exciting coil 173.
If the value of β is less than or equal to this inflection point, the rate of reduction of the magnetic shunt effect increases (see curve G2). From this point of view, β ≧ 60 ° is desirable. More specifically, it is considered desirable that ∠PCM ≧ 30 ° and ∠QCM ≧ 30 °. Note that the minimum value of the magnetic shunt effect that is actually required is the model in which the fixing device is installed (high speed or low speed machine), the number of sheets that can be stored in the paper cassette (that is, the maximum number of continuous prints), and others. In the range necessary for preventing the non-sheet passing portion from being overheated depending on the presence or absence of the excessive temperature rise suppression function, for example, whether there is a combined use of a known degaussing coil, etc. The minimum angle α of the restriction plate 156 can be specified based on data obtained in advance as shown in FIG.
<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 regulation plate 156 is formed with a uniform thickness over the entire length in the circumferential direction (the length is L0), but as shown in FIGS. 6 (a) and 6 (b), The total length (L0) is the same, and the folded portions 1571 and 1572 may be provided by folding back 180 degrees by the lengths of the ends L1 and L2.
FIG. 7 shows the result of simulation showing the effect in this case. At this time, the inner diameter of the fixing belt 155 is set to φ40 mm, the fixing roller 160 is set to φ36 mm, the thickness of the regulating plate 157 is set to 0.5 mm, and L1 and L2 are set to 1 mm.

As shown in the table, by providing folding at both ends of the restriction plate 157, the belt heat generation amount of the fixing belt 155 increases by 0.3%, and the heat generation amount of the restriction plate 157 other than the fixing belt 155 is the Curie temperature. Less than -3.1% and above the Curie temperature -4.2%.
As described above, the reason why the amount of heat generated by the restriction plate 157 is reduced by providing the folded portions at both ends of the belt rotation direction of the restriction plate 157 is estimated as follows.

  That is, the frequency of the alternating magnetic flux generated in the exciting coil 173 is high (about 40000 Hz), and the eddy current generated in the regulating plate 157 is also high in frequency, so that the current tends to concentrate on the surface of the end portion of the regulating plate 157 due to the skin effect. It seems to have become. And it is assumed that the current density at the time of eddy current generation is reduced and induction heating is suppressed by folding the end portion where the current concentrates in this way and providing a thick portion with a large thickness. .

Note that specific dimensions such as L1 and L2 can be determined by those skilled in the art based on the model to be applied (whether it is a high-speed machine or a low-speed machine) and other design contents based on the above disclosure. .
In addition, as a method of thickening the end portion, a metal plate having an originally thick end portion may be used in addition to folding the end portion having a uniform thickness as described above.

According to the present modification, the temperature of the regulation plate can be increased particularly after the magnetic shunting effect is activated without greatly affecting the warm-up time by increasing the thickness of both ends of the regulation plate in the belt circulation direction. It is possible to obtain an effect of suppressing the deformation of the restriction plate itself due to heat.
The thickness of the thick part provided at both ends of the restriction plate and the length in the circumferential direction are based on experiments so that the rate of decrease in the amount of heat generated by the restriction plate after activation of the magnetic shunt effect is greater than that of the conventional product. It may be determined as appropriate.

Moreover, it is not necessary to provide the folding | turning (thick part) in each of the both ends in the belt surrounding direction of a control plate, and it should just be provided in at least any one. In this case, the folding portion can be provided at the upstream end to reduce friction with the back surface of the fixing belt 155.
(2) Further, the end of the regulation plate 156 may not be completely folded back by 180 °, but may be folded away from the fixing belt 155.

FIG. 6C shows an example of the regulation plate 158 according to such a modification.
As shown in the figure, the upstream end portion of the regulating plate 158 is bent inward by a length L3 to form a bent portion 1582. According to such a configuration, the area directly contacting the fixing belt 155 can be reduced while maintaining the effect of canceling the magnetic flux after the magnetic shunt effect is activated by the low-resistance conductive material, and the fixing belt 155 to the regulation plate 158 can be reduced. The heat transfer efficiency can be lowered, which contributes to shortening the warm-up time.

The size of the bending angle of the bent portion 1582 is appropriately determined.
The folded portion 1581 may be eliminated, and the folded portion 1582 may be provided at both ends, or only the folded portion may be provided at one side. Also in this case, the friction with the back surface of the fixing belt 155 can be reduced by providing at the upstream end.
(3) In order to reduce wear on the rubbing surfaces of the fixing belt 155 and the regulating plate 156 and increase durability, the surfaces of the fixing belt 155 and the regulating plate 156 facing each other are reduced as shown in the laminated structure diagram of FIG. It is desirable to provide friction layers 1555 and 1563. Moreover, you may provide only in any one surface.

This low friction layer is formed by coating heat-resistant PFA or the like with a thickness of 10 [μm], for example. Since the thickness of the low friction layer is extremely thin, it hardly affects the shortening of the warm-up time.
(4) In the above embodiment, the magnetic shunt alloy layer 1554 (see FIG. 3B) is provided on the fixing belt 155 side. However, as shown in the laminated structure diagram of FIG. It may be provided on the surface facing the fixing belt 155.

As a result, the magnetic shunt effect may be slightly reduced, but the heat capacity of the fixing belt 155 itself is reduced, which further contributes to shortening of the warm-up time.
(5) Although the tandem type color printer has been described in the above embodiment, the present invention is not limited to this, and may be a monochrome printer, for example, and has additional functions such as a copying machine and a fax machine. In short, the present invention may be applied to all image forming apparatuses including a fixing device that uses a fixing belt and a regulating plate that guides the fixing belt in a rotating direction.

  The present invention is an electromagnetic induction heating method, and can be widely applied to a fixing device using a fixing belt and a regulating plate that guides the belt in a rotating direction, and an image forming apparatus using the fixing device.

1 is a schematic cross-sectional view of a tandem color digital printer according to an embodiment of the present invention. FIG. 3 is a partial cross-sectional perspective view of a fixing unit according to an embodiment of the present invention. (A) is a cross section which shows the structure of the principal part of the fixing part which concerns on embodiment of this invention, (b) is a schematic diagram which shows the laminated structure of a fixing belt and a control plate. It is a figure which shows the correlation of an exciting coil and a control plate. It is a figure which shows the simulation result which shows the relationship between the magnetic shunt effect and the angle of the range where a control plate exists. (A) (b) is a figure which shows the shape of the control plate in the 1st modification of the fixing part which concerns on this invention, (c) is the shape of the control plate which concerns on the 2nd modification of a fixing part. FIG. It is a table | surface which shows the effect in the said 1st modification. It is a schematic diagram which shows the laminated structure of the control plate and fixing belt of the fixing part which concern on the 3rd modification of this invention. It is a schematic diagram which shows the laminated structure of the control plate and fixing belt in the fixing part which concerns on the 4th modification of this invention. FIG. 10 is a cross-sectional view illustrating a configuration of a conventional fixing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 3Y, 3M, 3C, 3K Image creation part 4 Paper feed part 5 Fixing part 10 Optical part 150 Fixing roller 152 Core metal 153 Elastic body layer 155 Fixing belt 1551 Release layer 1552 Elastic body layer 1553 Heat generation layer 1554 Magnetic shunt alloy layer 155n Fixing nip 156, 157, 158 Regulating plate 160 Pressure roller 161 Core metal 162 Elastic body layer 163 Release layer 170 Magnetic flux generator 171 Coil bobbin 172 Bottom core 173 Excitation coil 174 Main core 175 Cover 1571, 1572 , 1581 Folding part 1572 Folding part

Claims (9)

A first roller disposed on the inner side of the circulation path of the belt traveling around the belt is pressed by the second roller through the belt from the outer side of the circulation path to form a fixing nip between the belt surface and the second roller. A fixing device that heats a heat generation layer included in the belt by electromagnetic induction, passes a sheet on which an unfixed image is formed, through the fixing nip, and thermally fixes the unfixed image;
A regulating plate that is disposed on the inside of the circulation path of the belt, is in sliding contact with the back surface of the belt that circulates, and guides the belt in the circulation direction;
An excitation coil disposed at a position facing the regulation plate across the belt, on the outer side of the belt circulation path;
With
In the case of cutting along a plane perpendicular to the rotation axis of the first roller,
The center of curvature of the orbit in the region guided by the restriction plate of the belt is C, the positions of the upstream and downstream edges of the restriction plate in the circulation direction of the belt are P, Q, and the excitation coil Assuming that the positions of the upstream and downstream ends of the belt in the circumferential direction are R and S, respectively, the edges P and Q of the regulating plate are positioned within the range sandwiched between the line segment CR and the line segment CS. As it is configured ,
The fixing device according to claim 1 , wherein at least one end portion of the restriction plate on the upstream side and the downstream side in the circumferential direction of the belt has a thick portion thicker than a central portion thereof . The fixing device according to claim 2 , wherein the thick portion is formed by folding back an end portion of the regulating plate by 180 °. A first roller disposed on the inner side of the circulation path of the belt traveling around the belt is pressed by the second roller through the belt from the outer side of the circulation path to form a fixing nip between the belt surface and the second roller. A fixing device that heats a heat generation layer included in the belt by electromagnetic induction, passes a sheet on which an unfixed image is formed, through the fixing nip, and thermally fixes the unfixed image;
A regulating plate that is disposed on the inside of the circulation path of the belt, is in sliding contact with the back surface of the belt that circulates, and guides the belt in the circulation direction;
An excitation coil disposed at a position facing the regulation plate across the belt, on the outer side of the belt circulation path;
With
In the case of cutting along a plane perpendicular to the rotation axis of the first roller,
The center of curvature of the orbit in the region guided by the restriction plate of the belt is C, the positions of the upstream and downstream edges of the restriction plate in the circulation direction of the belt are P, Q, and the excitation coil Assuming that the positions of the upstream and downstream ends of the belt in the circumferential direction are R and S, respectively, the edges P and Q of the regulating plate are positioned within the range sandwiched between the line segment CR and the line segment CS. As it is configured,
The regulation plate, at least one end of the upstream side and downstream side of the rotating direction of the belt, have a bent portion bent in a direction away from said belt,
The fixing device, wherein the regulating plate includes a magnetic shunt alloy layer and a low resistance conductive layer, and the magnetic shunt alloy layer is located on the belt side with respect to the low resistance conductive layer . In the case of cutting along a plane perpendicular to the rotation axis of the first roller,
When the winding center of the coil is M, at least the edge portions P and Q of the restriction plate are positioned on the upstream side and the downstream side in the circumferential direction of the belt with the line segment MC interposed therebetween. Item 4. The fixing device according to any one of Items 1 to 3 . The regulating plate or fixing device according to claim 1 or 2, characterized in that it contains magnetic shunt alloy layer on the regulating plate side than the heat generating layer of the belt. The inner peripheral surface of the belt, and on at least one surface of the rubbing surface between the regulating plates of the belt fixing device according to any one of claims 1 to 5, characterized in that the low friction layer is formed . A belt having a heating layer and running around,
An exciting coil for generating heat by electromagnetic induction in the heating layer;
An arcuate plate facing the excitation coil via the belt;
A pressure rotator that contacts the belt and forms a fixing nip; and
A fixing device that heats a heat generation layer included in the belt by electromagnetic induction, passes a sheet on which an unfixed image is formed, through the fixing nip, and thermally fixes the unfixed image;
The width of the arc-shaped plate is narrower than the width of the excitation coil in the circumferential running direction of the belt, and the arc-shaped plate is located between both ends of the excitation coil in the circumferential running direction of the belt,
The arcuate plate has a thick portion at a thickness larger than its central portion at at least one of the upstream side and the downstream side in the circumferential direction of the belt.
A fixing device. A belt having a heating layer and running around,
An exciting coil for generating heat by electromagnetic induction in the heating layer;
An arcuate plate facing the excitation coil via the belt;
A pressure rotator that contacts the belt and forms a fixing nip; and
A fixing device that heats a heat generation layer included in the belt by electromagnetic induction, passes a sheet on which an unfixed image is formed, through the fixing nip, and thermally fixes the unfixed image;
The width of the arc-shaped plate is narrower than the width of the excitation coil in the circumferential running direction of the belt, and the arc-shaped plate is located between both ends of the excitation coil in the circumferential running direction of the belt,
It said arcuate plate, at least one end of the upstream side and downstream side of the rotating direction of the belt, have a bent portion bent in a direction away from said belt,
The fixing device, wherein the regulating plate includes a magnetic shunt alloy layer and a low resistance conductive layer, and the magnetic shunt alloy layer is located on the belt side with respect to the low resistance conductive layer . An image forming apparatus comprising: a fixing device according to any one of claims 1 to 8.

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