JP6658128B2 - Fixing device and image forming device - Google Patents

Description

  The present invention relates to a fixing device for fixing a toner image on paper and an image forming apparatus using the fixing device. More specifically, the present invention relates to a fixing device using induction heating as a heat source for fixing and an image forming apparatus using the same.

  As a conventional image forming apparatus that uses induction heating as a heat source for fixing, an image forming apparatus described in Patent Document 1 can be mentioned. In the fixing device in the image forming apparatus of the document, as shown in FIG. 7 of the document, the cooling fan “57” is moved from one end to the other end in the longitudinal direction of the coil holding member “54”. Flows the airflow “F”. Further, an aluminum cover "55" facing the coil holding member is provided to define an air flow path. The shape of the aluminum cover allows the flow path to temporarily narrow at the center in the longitudinal direction. Thereby, the speed of the airflow in the central portion in the longitudinal direction is increased.

JP 2014-145896 A

  However, the above-mentioned conventional technology has the following problems. It is impossible to cope with the case where the degaussing coil is partially overlapped with the exciting coil. The degaussing coil is a coil for preventing overheating of a portion outside the paper passing range when the small size paper is passed, by eliminating magnetic flux. Patent Document 1 does not consider providing a degaussing coil. For this reason, when the technique of Patent Document 1 is applied to a fixing device having a degaussing coil, the temperature distribution of the exciting coil and the degaussing coil is not always appropriate. In particular, if there is a location where the temperature is locally high, the fusion layer of the coil is softened at that location, and the shape of the coil may be different from the initial shape. If this happens, the temperature distribution in the heating roller is also affected, and the originally expected fixing characteristics cannot be obtained.

  The present invention has been made in order to solve the problems of the above-described conventional technology. That is, the problem is that the fixing device has a degaussing coil in addition to the exciting coil, and performs appropriate cooling in accordance with the arrangement of the degaussing coil with respect to the exciting coil, thereby preventing local overheating of the coil and the fixing device. To provide an image forming apparatus using the same.

  A fixing device according to one aspect of the present invention includes a heating member having a built-in conductive heating member, a pressing member forming a fixing nip together with the heating member, and a magnetic flux generating device for generating a magnetic flux applied to the heating member. A fixing device for fixing the toner image to the paper by passing the paper carrying the toner image through the fixing nip, and having a cooling unit for sending cooling air to the magnetic flux generator to cool the magnetic flux generator. Is disposed at a position where a non-sheet passing area may be provided depending on a sheet size in the axial direction of the heating member and an excitation coil provided over the entire heating member in the axial direction, and the excitation coil cancels magnetic flux applied to the heating member. A degaussing coil is provided. The cooling capacity of the magnetic flux generator by the cooling unit is superimposed on the exciting coil in the degaussing area where the degaussing coil is not superimposed on the exciting coil. In which has a stronger construction than the demagnetizing area being.

  In the fixing device according to the above aspect, the heat generating member of the heating member generates heat by induction heating when the exciting coil of the magnetic flux generating device generates magnetic flux. Due to this heat generation, the heating member and the pressing member fix the toner image on the paper. Here, by using the degaussing coil, heating can be turned off for a part of the heating member in the axial direction. This is for handling small size paper. Apart from induction heating of the heating member of the heating member, the exciting coil and the degaussing coil themselves also generate Joule heat. For this reason, by sending cooling air from the cooling unit to the magnetic flux generator, the magnetic flux generator is cooled. Here, in the magnetic flux generator, the heat capacity of the non-demagnetized area is smaller than that of the degaussed area. This is because the degaussing coil is not superimposed on the exciting coil in the non-gaussing region, whereas the degaussing coil is superimposed on the exciting coil in the degaussing region. To that extent, the non-demagnetized region is easier to use in terms of temperature than the degaussed region. However, on the contrary, the cooling capacity of the cooling unit is configured to be stronger in the non-demagnetized area than in the demagnetized area. As a result, overheating of the non-demagnetizing region is prevented.

  It is desirable that the cooling unit in the fixing device of the above aspect has a configuration in which cooling air is sent to the non-demagnetizing region in the magnetic flux generating device. With this configuration, the non-demagnetizing region of the magnetic flux generator is cooled by the cooling air just sent from the cooling unit. The cooling air that has cooled the non-demagnetized area then turns to the degaussed area in the magnetic flux generator, and cools the degaussed area. As a result, the cooling capacity is higher in the non-demagnetized area than in the demagnetized area.

  The fixing device in this case further has a shielding plate for shielding the opposite side of the heating member in the magnetic flux generating device, the shielding plate having an inlet provided at least partially facing the non-demagnetizing region, An outlet provided at a location different from the inlet is formed, and the cooling unit preferably feeds cooling air from the inlet into the space inside the magnetic flux generator. By arranging the inflow port and the outflow port in this way, the cooling air supplied from the cooling section first flows into the non-demagnetizing area, and cools the non-demagnetizing area strongly. Then, the cooling air flows to the degaussing area, cools the degaussing area mildly, and is discharged through the outlet.

  When the degaussing coils are provided at both ends in the axial direction of the heating member, the outlets are provided to face the degaussing areas at both ends where the degaussing coils are superimposed on the exciting coils. Is desirable. In this way, the cooling air that has cooled the non-demagnetized area is divided in two directions, cools each demagnetized area, and is discharged from the outlet.

  Alternatively, when the degaussing coil is provided at both ends in the axial direction of the heating member, the inflow port is provided so as to straddle the non-gaussing region and the first degaussing region where one of the degaussing coils is superimposed on the exciting coil. The outlet may be provided so as to face a second degaussing area in which the other degaussing coil is superimposed on the exciting coil. Even with such an inlet and outlet arrangement, the non-demagnetized area is first cooled strongly, and the demagnetized areas on both sides are cooled more mildly.

  In this case, a flow path regulating wall located between the shielding plate and the exciting coil and guiding the cooling air sent from the inlet to the flow path on the exciting coil side is further provided in an area between the inlet and the outlet. It is desirable to have. By having such a flow path regulating wall, the flow path of the cooling air is limited to a narrow range near the exciting coil in a region between the inlet and the outlet. For this reason, in this area, the cooling air flows at a high flow velocity concentrated near the exciting coil. For this reason, the degaussing coil in the non-gaussing area is more strongly cooled.

  According to another aspect of the present invention, there is provided an image forming unit that forms an image on a sheet by applying a toner image to a sheet, and a fixing unit that fixes the toner image on the sheet to which the toner image has been given by the image forming unit. And the fixing unit is the fixing device according to any one of the above-described embodiments.

  According to this configuration, a fixing device that has a degaussing coil in addition to the exciting coil and performs appropriate cooling in accordance with the arrangement of the degaussing coil with respect to the exciting coil, thereby preventing local overheating of the coil and a fixing device using the same. Image forming apparatus is provided.

FIG. 1 is a cross-sectional view illustrating an entire configuration of an image forming apparatus according to an embodiment. FIG. 2 is a cross-sectional view illustrating a schematic configuration of a fixing device according to the exemplary embodiment. It is a schematic diagram which shows arrangement with respect to the whole axial direction of an exciting coil and a degaussing coil. FIG. 2 is a cross-sectional view illustrating a detailed configuration of a fixing device according to the exemplary embodiment and its periphery. It is a perspective view of the magnetic flux generation device in an embodiment. It is a perspective view of the shielding board in an embodiment. It is a perspective view in the state where the shielding board was attached to the magnetic flux generator in an embodiment. It is sectional drawing of the magnetic flux generation device in embodiment. It is a front view for explaining the flow of the cooling wind in a magnetic flux generating device. It is a perspective view of the shielding board in a 2nd form. It is a front view explaining the flow of the cooling air when the flow path regulating wall in the second mode is provided. It is sectional drawing (the 1) which shows arrangement | positioning of the flow-path regulating wall in 2nd form. It is sectional drawing (the 2) which shows arrangement | positioning of the flow-path regulating wall in 2nd form. It is a graph which shows the measurement result of the coil temperature in a 2nd form.

[First form]
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to the image forming apparatus 1 shown in FIG. The image forming apparatus 1 of the present embodiment shown in FIG. 1 is a so-called tandem type image forming apparatus. The image forming apparatus 1 includes an intermediate transfer belt 2 and image forming units 3Y to 3K of respective colors arranged along the intermediate transfer belt 2. Each of the image forming units 3Y to 3K has a photoconductor 4. Around each photoconductor 4, a charger 5, an exposure head 6, a developing device 7, a primary transfer roller 8, and a cleaner 9 are provided.

  In addition, the image forming apparatus 1 includes a paper feed cassette 10, a secondary transfer roller 11, and a fixing device 12 in addition to the above. As a result, a toner image is formed on the intermediate transfer belt 2, and the toner image is transferred to the sheet supplied from the sheet feeding cassette 10 by the secondary transfer roller 11. Then, the sheet on which the toner image has been transferred is passed through the fixing device 12, so that the toner image is fixed on the sheet. Further, the image forming apparatus 1 is provided with toner bottles 41Y to 41K for replenishing toner.

  The fixing device 12 in the image forming apparatus 1 according to the present embodiment is an electromagnetic induction heating type fixing device having a magnetic flux generator 15 in addition to the heating roller 13 and the pressure roller 14. The schematic configuration of the fixing device 12 will be further described with reference to FIG. The heating roller 13 in the fixing device 12 shown in FIG. The conductive layer 16 is a portion that generates Joule heat by an induced current in response to the application of magnetic flux by the magnetic flux generator 15. The conductive layer 16 exists in the entire axial direction of the heating roller 13 (the direction perpendicular to the plane of FIG. 1 and FIG. 2; hereinafter, simply referred to as the axial direction) and in all circumferential directions. Further, a temperature sensor 23 is provided near the heating roller 13 in FIG.

  Although the magnetic flux generator 15 is shown in FIG. 1 very simply, it is actually composed of a number of components as shown in FIG. The magnetic flux generator 15 has a main core 17, an end core 18, and a skirt core 19 as cores serving as magnetic flux paths. Although these appear to be present separately in FIG. 2, they are actually connected and constitute one core. These cores are formed by molding and firing ferrite made of permalloy or the like.

  The magnetic flux generator 15 further includes an excitation coil 20 as a magnetic flux generation source and a degaussing coil 21 for canceling the magnetic flux. The exciting coil 20 and the degaussing coil 21 are held on a bobbin 22. The bobbin 22 is formed of a heat-resistant insulating resin (LCP, PPS, PET, or the like). The order of stacking the exciting coil 20 and the degaussing coil 21 is such that the exciting coil 20 is closer to the degaussing coil 21 when viewed from the conductive layer 16 of the heating roller 13. Each of the exciting coil 20 and the degaussing coil 21 is formed of a litz wire in which several tens of fine wires covered with a heat-resistant resin fusion layer are bundled. Although not shown, a heat-resistant insulating sheet (such as polyamide fiber) is interposed between the exciting coil 20 and the degaussing coil 21.

  Further, the fixing device 12 is provided with a high frequency power supply circuit 24. The high-frequency power supply circuit 24 is a circuit that supplies high-frequency power (about 20 to 90 kHz, about 100 to 2000 W) to the exciting coil 20 and the degaussing coil 21. The high-frequency power supply circuit 24 is provided with a control circuit 25, a switching relay 26, and a switching relay 27. The switching relay 27 is a relay that turns on and off the application of power to the exciting coil 20. The switching relay 26 is a relay that turns on and off the application of power to the degaussing coil 21. The control circuit 25 is a circuit that controls the switching relay 26 and the switching relay 27. A detection signal is input to the control circuit 25 from the temperature sensor 23.

  FIG. 3 shows the arrangement of the exciting coil 20 and the degaussing coil 21 with respect to the entire axial direction. As shown in FIG. 3, the excitation coil 20 is provided over the entire heating roller 13 in the axial direction. On the other hand, the degaussing coils 21 are provided only in the areas at both ends in the axial direction that may become non-sheet passing areas depending on the sheet size. That is, near the center of the heating roller 13 in the axial direction, there is an area where the excitation coil 20 exists but the degaussing coil 21 does not overlap. This region is called a non-demagnetizing region 28. In addition, regions where the degaussing coil 21 is superimposed on the exciting coil 20 at both ends in the axial direction are referred to as degaussing regions 29 and 30.

  The exciting coil 20 and the degaussing coil 21 have substantially the same thickness in FIG. 2 and the same heat capacity per unit length in the axial direction. Therefore, the total heat capacity of the exciting coil 20 and the degaussing coil 21 is smaller in the non-gaussing region 28 than in the degaussing regions 29 and 30. The relationship between the coil heat capacities affects the temperature distribution of the exciting coil 20 and the degaussing coil 21 during the heating operation. That is, the temperature of the exciting coil 20 tends to increase in the non-demagnetizing region 28 having a small heat capacity. On the other hand, in the degaussing regions 29 and 30 having a large heat capacity, the temperatures of the exciting coil 20 and the degaussing coil 21 are less likely to rise than in the non-degaussing region 28. In other words, the temperature distribution in the excitation coil 20 and the degaussing coil 21 is different from the temperature distribution of the heating roller 13 to be heated.

  FIG. 4 shows the configuration of the fixing device 12 and its periphery. In the image forming apparatus 1 of the present embodiment, the duct 31 is provided in the fixing device 12. The duct 31 is provided with a blower fan 32. The cooling air A is sent to the magnetic flux generator 15 of the fixing device 12 by the blower fan 32 and the duct 31. This is because, apart from the above-described induction heating of the conductive layer 16, the exciting coil 20 and the degaussing coil 21 themselves also generate Joule heat by their own current. Further, the fixing device 12 is provided with a shielding plate 33 on a side opposite to the heating roller 13. The shielding plate 33 is for shielding magnetic flux generated by the magnetic flux generating device 15 to prevent leakage to the outside. The shielding plate 33 is formed with an inflow port, which will be described later, so that the cooling air A can flow into the magnetic flux generator 15. The sheet that has passed through the fixing device 12 advances as indicated by an arrow B in FIG.

  FIG. 5 is a perspective view of the magnetic flux generator 15. The magnetic flux generator 15 in FIG. 5 is a state where the magnetic flux generator 15 in FIG. 4 is viewed from the left. However, FIG. 5 shows the magnetic flux generator 15 with the shielding plate 33 removed. As shown in FIG. 5, in the magnetic flux generating device 15, the main core 17 and the skirt core 19 form a ladder shape. The exciting coil 20 and the degaussing coil 21 can be seen in those gaps. Therefore, also in FIG. 5, the non-demagnetizing area 28 exists at the center in the left-right direction, and the demagnetizing areas 29 and 30 exist on both sides thereof. The bobbin 22 has an outer shape at a portion of the magnetic flux generator 15 on the back side in FIG.

  FIG. 6 shows a perspective view of the shielding plate 33. The shielding plate 33 is made of a thin metal plate such as aluminum. The shielding plate 33 has an upper surface portion 34 that covers an upper portion in FIG. 5 of the magnetic flux generator 15 and a front surface portion 35 that covers a front portion. The shielding plate 33 is further formed with an inflow port 36 and outflow ports 37 and 38. Each of the inlet 36 and the outlets 37 and 38 is an opening in which a part of the shielding plate 33 is hollowed out. The inflow port 36 is an opening for receiving the cooling air A from the duct 31 shown in FIG. On the other hand, the outlets 37 and 38 are openings for finally discharging the cooling air A received from the inlet 36. In FIG. 6, the inflow port 36 is formed in the front face 35, and the outflow ports 37 and 38 are formed in the top face 34.

  FIG. 7 is a perspective view showing a state where the shielding plate 33 of FIG. The viewing direction in FIG. 5 and the viewing direction in FIG. 7 are substantially the same. In the magnetic flux generator 15 in the state shown in FIG. 7, as shown in the cross-sectional view of FIG. 8, the shielding plate 33 on the front side and the bobbin 22 on the back side in FIG. That is, in the state of FIG. 7, the exciting coil 20, the degaussing coil 21, the main core 17, the skirt core 19, and the like are accommodated in a space partitioned by the shielding plate 33 and the bobbin 22. More specifically, the main core 17 exists around the middle between the shielding plate 33 and the bobbin 22, as viewed in the cross-sectional view of FIG. An exciting coil 20 and a degaussing coil 21 exist between the main core 17 and the bobbin 22. Note that the shielding plate 33 also has a role of restricting warpage of the bobbin 22 by being fixed to the bobbin 22.

  Furthermore, in the left-right direction in FIG. 7 (the axial direction of the heating roller 13), the inflow port 36 is provided in the non-demagnetizing area 28. That is, the inflow port 36 is arranged in a region where the heat capacity of the coil is small. On the other hand, the outlets 37 and 38 are provided in the demagnetizing regions 29 and 30. That is, the outlets 37 and 38 are arranged in a region where the heat capacity of the coil is large.

  As a result, a flow of the cooling air C as shown in FIG. 9 is generated in the magnetic flux generator 15 by operating the blower fan 32 shown in FIG. That is, the cooling air A shown in FIG. 4 flows into the magnetic flux generator 15 via the inlet 36 of the shielding plate 33. There is a non-demagnetizing area 28 in the magnetic flux generator 15, which is a central part in the axial direction. The inflowing air is separated from the left and right in FIG. 9 toward both ends in the axial direction (cooling air C). Then, the magnetic flux reaches the demagnetizing regions 29 and 30 from the non-magnetizing region 28, and goes out of the magnetic flux generator 15 via the outlets 37 and 38 there (arrow D).

  That is, fresh cool air just supplied from the duct 31 of FIG. 4 first cools the exciting coil 20 in the non-demagnetizing area 28. Although this region is a region where the coil heat capacity is small and the temperature easily rises as described above, excessive cooling of the exciting coil 20 is prevented by cooling with the fresh cool air. That is, softening and deformation due to excessive temperature rise of the exciting coil 20 are prevented. Then, the cool air that has cooled the non-demagnetizing area 28 is supplied to the demagnetizing areas 29 and 30 as cooling air C. Therefore, the temperature of the cool air supplied to the demagnetizing regions 29 and 30 has risen to some extent, and the cooling capacity has decreased. However, as described above, the demagnetizing regions 29 and 30 are regions where the heat capacity of the coil is large and the temperature is hardly excessively increased, so that it is sufficient.

  Thus, in the image forming apparatus 1 of the present embodiment, due to the arrangement of the inflow port 36 and the outflow ports 37 and 38 in the shielding plate 33, the degaussing area 28 is located upstream with respect to the flow of the cool air in the magnetic flux generator 15 so that the degaussing is performed. The regions 29 and 30 are located downstream. In this way, the cooling capacity in the non-demagnetizing area 28 is made stronger than the cooling capacity in the demagnetizing areas 29 and 30. Thereby, sufficient cooling performance can be obtained without increasing the size of the blower fan 32.

[Second embodiment]
The second embodiment to be described next is another example regarding the arrangement of the inflow port 36 and the outflow ports 37 and 38 in the above-mentioned shielding plate 33, and other portions are basically the same as the first embodiment. . In this embodiment, a shield plate 43 shown in FIG. 10 is used instead of the shield plate 33 shown in FIG. The difference between the shield plate 43 of FIG. 10 and the shield plate 33 of FIG. 6 lies in the positions of the inlet and the outlet. That is, in the shield plate 43 of FIG. Further, the outlet 38 in the shield plate 33 in FIG. 6 is not provided in the shield plate 43 in FIG. The outlet 37 is provided in the shielding plate 33 of FIG. 6 as well as in the shielding plate 43 of FIG.

  In the magnetic flux generator 15 using the shield plate 43 of FIG. 10 instead of the shield plate 33 of FIG. 6, fresh cool air from the duct 31 is supplied to the vicinity of the boundary between the non-demagnetizing region 28 and the degaussing region 30. It will be. The cool air flows therefrom toward the demagnetizing region 29 and is discharged from the outlet 37. For this reason, focusing on the non-demagnetizing area 28 and the demagnetizing area 29, the non-demagnetizing area 28 is located upstream of the airflow, and the cooling capacity is high. Further, since a part of the cool air circulates in the degaussing area 30, the cooling capacity of the non-gaussing area 28 is higher than that of the degaussing area 30. Therefore, also in the present embodiment, similar to the case where the shielding plate 33 of FIG. 6 is used, sufficient cooling performance can be obtained without increasing the size of the blower fan 32. When the first and second embodiments are considered together, it can be said that the inlets 36 and 46 need only be at least partially opposed to the non-demagnetizing region 28.

  In the second embodiment, the cooling ability of the non-demagnetizing area 28 can be further increased by providing the flow path regulating wall in the magnetic flux generator 15. This will be described with reference to FIG. That is, in the magnetic flux generator 15 using the shielding plate 43 in FIG. 10, two types of flow path regulating walls 39 and 40 can be provided as shown in FIG. 11, the flow path regulating wall 39 is located between the inlet 46 and the main core 17 adjacent to the non-demagnetizing area 28 side. Further, the flow path regulating wall 40 is provided at a position between the main cores 17 within a range between the inflow port 46 and the outflow port 37.

  The flow path regulating wall 39 is arranged so as to close the gap between the shielding plate 43 and the main core 17 as shown in FIG. This prevents the cooling air A flowing from the duct 31 via the inflow port 46 from diffusing in the gap between the shielding plate 43 and the main core 17. For this reason, the cooling air A enters the region E between the main core 17 and the exciting coil 20 or the degaussing coil 21 and can change its direction in the axial direction only there.

  The flow path regulating wall 40 is disposed so as to substantially overlap the main core 17 as shown in FIG. For this reason, in the place where the flow path regulating wall 40 exists, the air in the area E between the main core 17 and the exciting coil 20 or the degaussing coil 21 moves to the area F between the shielding plate 43 and the main core 17. Can not do.

  That is, within the range between the inflow port 46 and the outflow port 37 in FIG. 11, the range in the cross-sectional view through which the cooling air C in the axial direction can flow is limited to only the region E in FIG. . In other words, in this range, the cross-sectional area of the flow path through which the cooling air C in the axial direction can flow is reduced due to the existence of the flow path regulating walls 39 and 40. Then, the excitation coil 20 exists within the limited range. That is, in the range where the flow path is limited by the flow path regulating walls 39 and 40, the cooling air C flows intensively near the excitation coil 20. In addition, the flow rate should be high because the flow path is limited. Therefore, the cooling capacity in the non-demagnetizing area 28 is further enhanced by the existence of the flow path regulating walls 39 and 40.

  FIG. 14 shows actual measurement results of the coil temperature during operation in the magnetic flux generator 15 of the second embodiment. In this actual measurement test, thermocouples were arranged on the coil surface at various locations in the axial direction in the magnetic flux generator 15 provided with the flow path regulating walls 39 and 40 described above. The thermocouple was arranged on the excitation coil 20 in the non-demagnetization area 28 and was arranged on the demagnetization coil 21 in the demagnetization areas 29 and 30. Further, as a comparative example, one having a configuration in which cooling air was caused to flow uniformly from one axial end to the other axial end was prepared, and a thermocouple was similarly arranged in this comparative example.

  Then, the demagnetizing coil 21 is turned off with the short side direction of the A4 size paper as the transport direction (that is, the long side direction is the axial direction), and 300 or more sheets are continuously fed, and each thermocouple at the time when the coil temperature is saturated is reached. FIG. 14 plots the measured temperatures. Looking at the “comparative example” in FIG. 14, it can be seen that the coil temperature in the non-demagnetizing region 28 is nearly 100 ° C. higher than the coil temperature in the demagnetizing regions 29 and 30. This is considered to be a manifestation of the small heat capacity of the non-demagnetizing region 28 as described above. On the other hand, in the present embodiment, the coil temperature in the non-demagnetizing region 28 is lower by about 30 to 40 ° C. than in the “comparative example”. In addition, the temperature difference between the non-demagnetizing region 28 and the demagnetizing regions 29 and 30 in the present embodiment is about 20 to 30 ° C., which is much smaller than in the comparative example. As a result, even in the non-demagnetizing region 28, an excessive temperature increase that causes a problem of coil deformation does not occur. This is considered to be due to the arrangement of the inflow port 46 and the effects of the flow path regulating walls 39 and 40 as described above.

  The coil temperature in FIG. 14 is an example. This is because the heat-resistant temperature of the fusion layer of the excitation coil 20 and the demagnetization coil 21 differs depending on the material of the fusion layer and the processing method. The example shown in FIG. 14 is a case where a high heat-resistant material is used as the type of the fusion layer. Therefore, the actual required cooling temperature differs depending on the type of the fusion layer.

  In the above description, the flow path regulating wall 40 overlaps with the main core 17 in the cross-sectional view of FIG. For this reason, the flow path regulating walls 40 are arranged in the respective gaps between the main cores 17 as viewed in FIG. However, other configurations are possible. For example, the flow path regulating wall 40 may be arranged along the surface of the main core 17 on the side of the shield plate 43 when viewed in the sectional view of FIG. In this case, as shown in FIG. 11, it can be continuous without being separated by the main core 17. Further, the flow path regulating wall 39 may be combined with the flow path regulating wall 40 to be integrally formed on the inner surface side of the shielding plate 43. Such a form may be used. In this case, the flow path regulating wall 39 may be inclined.

  As described above in detail, according to the fixing device 12 according to the present embodiment, the inlets 36 and 46 of the cooling air A from the duct 31 to the magnetic flux generator 15 are at least partially opposed to the non-demagnetizing region 28. Is provided. The outflow ports 37 and 38 are provided to face at least one of the demagnetization areas 29 and 30. Thus, the cooling air supplied from the duct 31 cools the non-demagnetizing area 28 first, and then cools the demagnetizing areas 29 and 30. Thus, the cooling capacity of the non-demagnetizing area 28 is made stronger than the cooling capacity of the demagnetizing areas 29 and 30. Thus, the fixing device 12 in which the coil temperature does not excessively increase even in the non-demagnetizing region 28 having a small heat capacity and the image forming apparatus 1 using the same are realized. As a result, the fixing characteristics of the fixing device 12 are maintained as originally designed for a long period of time. Furthermore, in particular, by providing the flow path regulating walls 39 and 40 in the second embodiment, the cooling capacity of the non-demagnetizing area 28 is further improved.

  Note that the present embodiment is merely an example and does not limit the present invention in any way. Therefore, naturally, the present invention can be variously modified and modified without departing from the gist thereof. For example, the overall configuration of the image forming apparatus 1 is a color machine or a monochrome machine, a single-function printer, a multifunction machine with a scanner function, a double-sided machine, or a single-sided machine. Is optional. Further, the degaussing coil 21 may have a multilayer structure.

  In the above-described embodiment, the cooling capacity of the non-demagnetizing area 28 and the cooling capacity of the demagnetizing areas 29 and 30 are made different depending on the flow direction of the cooling air in the magnetic flux generator 15. However, the present invention is not limited to this. The cooling capacity supplied may be different between the non-demagnetizing area 28 and the demagnetizing areas 29 and 30 so as to provide different cooling air. For example, a plurality of sets of ducts are provided, one of which introduces outside air and supplies it to the non-demagnetizing area 28, and the other duct extracts air inside the machine (for example, around the toner bottles 41Y to 41K) and sucks air therefrom. , 30 may be supplied. In this case, since the temperature of the outside air is usually lower than that of the air in the apparatus, the cooling capacity of the non-demagnetized region 28 supplied with the outside air is stronger. Nevertheless, the in-flight ventilation can be achieved.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Intermediate transfer belts 3Y to 3K Image forming section 11 Secondary transfer roller 12 Fixing device 13 Heating roller 15 Magnetic flux generating device 16 Conductive layer 17 Main core 20 Exciting coil 21 Degaussing coil 28 Non-gaussable area 29, 30 Degaussing area 31 duct 32 blowing fans 33, 43 shielding plate 36 inflow port 37, 38 outflow port 39, 40 flow regulating wall A, C cooling air

Claims (7)

A heating member having a built-in conductive heating member;
A pressure member that forms a fixing nip with the heating member;
A magnetic flux generator for generating a magnetic flux applied to the heating member,
A fixing device for fixing a toner image to a sheet by passing a sheet carrying a toner image through the fixing nip,
A cooling unit that sends cooling air to the magnetic flux generator to cool the magnetic flux generator;
The magnetic flux generator includes:
An excitation coil provided over the entire axial direction of the heating member;
A demagnetizing coil disposed at a position where a non-sheet passing area may be formed depending on a sheet size in the axial direction of the heating member, wherein the exciting coil cancels a magnetic flux applied to the heating member;
A configuration in which the cooling capacity of the magnetic flux generator by the cooling unit is stronger in a non-demagnetizing area where the degaussing coil is not superimposed on the exciting coil than in a degaussing area where the degaussing coil is superimposed on the exciting coil. A fixing device, comprising: The fixing device according to claim 1, wherein the cooling unit includes:
The fixing device according to claim 1, wherein the magnetic flux generator is configured to send cooling air to the non-demagnetizing region. 3. The fixing device according to claim 2, wherein
A shielding plate for shielding the opposite side of the heating member in the magnetic flux generator,
The shielding plate has
An inflow port provided at least partially facing the non-demagnetizing area;
An outlet provided at a location different from the inlet,
The fixing device according to claim 1, wherein the cooling unit sends cooling air from the inlet to a space inside the magnetic flux generator. The fixing device according to claim 3, wherein
The degaussing coils are provided at both ends in the axial direction of the heating member.
The fixing device according to claim 1, wherein the outflow ports are provided to oppose demagnetizing regions at both ends where the demagnetizing coil is superimposed on the exciting coil. The fixing device according to claim 3, wherein
The degaussing coils are provided at both ends in the axial direction of the heating member.
The inflow port is provided across the non-demagnetizing region and a first demagnetizing region in which one of the degaussing coils is superimposed on the exciting coil,
The fixing device according to claim 1, wherein the outlet is provided to face a second degaussing area where the other degaussing coil is superimposed on the exciting coil. The fixing device according to claim 5, wherein
A flow path regulating wall, which is located between the shielding plate and the exciting coil and guides the cooling air sent from the inlet to the flow path on the exciting coil side, is provided between the inlet and the outlet. A fixing device provided in a region. An image forming unit for forming an image on a sheet by applying a toner image to the sheet;
A fixing unit for fixing the toner image on the sheet to which the toner image has been provided by the image forming unit;
The image forming apparatus according to claim 1, wherein the fixing unit is the fixing device according to claim 1.

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