JP6024959B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device used in an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, and a copying machine.

  In an electrophotographic image forming apparatus, an electrostatic latent image is formed by irradiating light corresponding to a document or electronic data onto the surface of a photoconductor uniformly charged by a charging device. Toner is attached to the latent image and developed to create a toner image. Then, after the toner image is transferred to the paper, the toner image is heated and pressurized to be melted and fixed on the paper.

  As a fixing device that heats and pressurizes a toner image, a device that melts and fixes a toner image by passing a sheet on which an unfixed toner image is formed through a nip portion between a fixing rotator and a pressure rotator is widely used. Has been. In the fixing device having such a configuration, the temperature of the fixing rotator tends to be excessively increased in a non-sheet passing region where the sheet does not pass as compared with a sheet passing region through which the sheet passes. When such excessive temperature rise occurs, there arises a problem that the life of the elastic layer constituting the fixing rotator is shortened. Further, when switching from a small size paper to a large size paper, uneven glossiness may occur in the toner image due to temperature unevenness in the rotation axis direction of the fixing rotator.

  Therefore, in Patent Document 1, for example, the air blowing port for sending air toward the fixing nip part is partially shielded by a movable shielding plate, and the shielding plate is at a position showing the highest temperature in the non-sheet passing region. A technique is disclosed in which the moving speed is slowed down to enhance cooling and suppress temperature unevenness.

JP 2009-237203 A

  FIG. 16 shows an example of the temperature distribution of the fixing rotator. Usually, the surface temperature of the fixing rotator becomes the highest temperature at a position K3 at substantially the center of the non-sheet passing region (solid line in FIG. 16). Therefore, in the technique disclosed in Patent Document 1, the moving speed of the shielding plate is the slowest speed when passing through the position K3 of the non-sheet passing area. However, at this time, wind does not hit between the position K3 and the position K3 of the shielding plate where the blower opening is fully opened, and thereafter the maximum temperature is reached at the position K4 on the inner side in the rotation axis direction than the position K3 ( (Broken line in FIG. 16). And when passing the position K4, the moving speed of a shielding board becomes the slowest speed. Then, this time, the position K3 becomes the highest temperature, and the moving speed of the shielding plate becomes the slowest speed when passing through the position K3 again. Such an operation is repeated and temperature unevenness is not suppressed.

  An object of the present invention is to provide a fixing device capable of suppressing temperature rise and temperature unevenness in a non-sheet passing region of a fixing rotator.

According to the present invention, the non-transferred toner has a fixing rotator having a heat generating member and a pressure rotator that presses against the fixing rotator to form a nip portion, and allows a sheet to pass through the nip portion. A fixing device that melts and fixes an image on a sheet, and is provided with a plurality of size detection units that detect a length in a direction perpendicular to the sheet conveyance direction and a rotation axis direction that detects the temperature of the fixing rotator. and a temperature detecting means, a cooling means for cooling by blowing the fixing rotator, and a cooling zone varying means for varying the cooling zone by the cooling means, control means for controlling the cooling zone and cooling time by the cooling zone varying means And when the cooling means cools the fixing rotator, the control means detects the whole cooling mode for cooling the entire non-sheet passing area by the cooling area variable means and the temperature detection means. Non-paper passing A fixing device is provided, characterized in that repeated to the local cooling mode for cooling the region including the hot spot of the pass alternately at predetermined time intervals.

  The control means is configured such that, after the cooling of the fixing rotator is started by the cooling means, the difference between the maximum detected temperature and the minimum detected temperature by the plurality of temperature detecting means is greater than or equal to a predetermined value in the non-sheet passing region, If the detected temperature is detected in the local cooling area, increase the cooling time ratio in the local cooling mode.If the detected temperature is detected outside the local cooling area, increase the cooling time ratio in the overall cooling mode. You may make it high.

  Alternatively, after the cooling of the fixing rotator by the cooling unit, the control unit has a difference between the maximum detected temperature and the minimum detected temperature by the plurality of temperature detecting units in a non-sheet passing region is a predetermined value or more, and If the maximum detected temperature is detected in the local cooling area, the cooling area in the local cooling mode is narrowed. If the maximum detected temperature is detected outside the local cooling area, the cooling area in the local cooling mode is You may make it wide.

  As the cooling region variable means, a pair of shielding plates provided so as to be movable in the direction of the rotation axis are used for the air outlets from which the air blown from the cooling means blows out, and the blowout position of the air blow is obtained by moving the pair of shielding plates. Further, the opening degree may be adjusted.

  In the fixing device of the present invention, the non-sheet passing area of the fixing rotating body is cooled alternately and repeatedly in the whole cooling mode and the local cooling mode every predetermined time, so that the temperature rise and temperature unevenness in the non-sheet passing area are effective. Can be suppressed.

1 is a schematic diagram illustrating an example of an image forming apparatus equipped with a fixing device of the present invention. 1 is a schematic perspective view showing an example of a fixing device of the present invention. 1 is a schematic cross-sectional view showing an example of a fixing device of the present invention. The fragmentary sectional view which shows the laminated structure of a heat generating belt. FIG. 3 is a schematic diagram illustrating an example of a cooling configuration of a fixing rotator. FIG. 6 is a view when the blower opening is fully opened in the fixing device shown in FIG. 5. FIG. 6 is a diagram when the blower opening is partially closed in the fixing device illustrated in FIG. 5. FIG. 6 is a diagram when the air blowing port is fully closed in the fixing device illustrated in FIG. 5. The figure explaining the relationship between the non-sheet passing area and the air blowing port in the whole cooling mode when fixing a small size sheet. The figure explaining the relationship between the non-sheet passing area and the air blowing port in the local cooling mode when fixing a small-size sheet. The figure explaining the relationship between the non-sheet passing area and the air blowing port in the whole cooling mode when fixing a large size sheet. The figure explaining the relationship between the non-sheet passing area and the air blowing port in the local cooling mode when fixing a large size sheet. 6 is a flowchart showing an example of operation control of the fixing device of the present invention. 6 is a flowchart showing another operation control example of the fixing device of the present invention. FIG. 4 is a temperature distribution diagram of a fixing rotator in the fixing device of the present invention. FIG. 6 is a temperature distribution diagram of a fixing rotator in a conventional fixing device.

  Hereinafter, the fixing device of the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a schematic view showing an example of an image forming apparatus D equipped with the fixing device of the present invention. The image forming apparatus D is a so-called tandem color printer. In the image forming apparatus D, an endless intermediate transfer belt 21 that is hung on rollers 22 and 23 is provided at a substantially central portion. The roller 22 is rotated counterclockwise by a motor (not shown), whereby the intermediate transfer belt 21 and the roller 23 in contact therewith are driven to rotate. A secondary transfer roller 24 is in pressure contact with the outside of the belt portion supported by the roller 22. The toner image formed on the intermediate transfer belt 21 at the nip portion (secondary transfer region N2) between the secondary transfer roller 24 and the intermediate transfer belt 22 is secondarily transferred to the conveyed paper P.

  A belt cleaning unit 25 for cleaning the surface of the intermediate transfer belt 21 is provided outside the belt portion supported by the roller 23. The belt cleaning unit 25 removes and collects untransferred toner on the intermediate transfer belt 21.

  Below the intermediate transfer belt 21, four image forming units 10Y, 10M, yellow (Y), magenta (M), cyan (C), and black (K) are sequentially formed from the upstream side in the rotation direction of the intermediate transfer belt 21. 10C and 10K (hereinafter collectively referred to as “image forming unit 10”) are detachably arranged with respect to the apparatus main body. In these image forming units 10, toner images of different colors are generated.

  In the image forming unit 10, a charging device, an exposure device, a developing device, a primary transfer roller, and a cleaning device are arranged around a cylindrical photosensitive member 20 in the rotation direction (clockwise direction). Yes. The primary transfer roller is in pressure contact with the photosensitive member with the intermediate transfer belt 21 interposed therebetween to form a nip portion (primary transfer region) N1. Since this configuration is the same regardless of the image forming unit 10, only the primary transfer region of the image forming unit 10Y is denoted by reference numeral N1 in FIG.

  As shown in FIG. 1, a paper feeding cassette 71 is detachably disposed as a paper feeding device at the lower part of the image forming unit 10. The sheets P stacked and accommodated in the sheet feeding cassette 71 are sent out one by one to the transport path in order from the uppermost sheet by the rotation of the sheet feeding roller 72 disposed in the vicinity of the sheet feeding cassette 71. The paper P sent out from the paper feed cassette 71 is conveyed to the registration roller pair 73 and is sent out to the secondary transfer area N2 at a predetermined timing.

  A color image forming operation will be briefly described. First, in each image forming unit 10, the outer peripheral surface of the photoconductor 20 that is rotationally driven at a predetermined peripheral speed is uniformly charged by a charging device. Next, light corresponding to image information is projected from the exposure device on the surface of the charged photoconductor to form an electrostatic latent image. Subsequently, the electrostatic latent image is visualized with toner as a developer supplied from the developing device. When the toner images of the respective colors formed on the surface of the photoreceptor in this way reach the primary transfer area by the rotation of the photoreceptor, yellow, magenta, cyan, and black are sequentially transferred from the photoreceptor to the intermediate transfer belt 21. Transfer (primary transfer) to be overlaid.

  Residual toner remaining on the photoreceptor without being transferred to the intermediate transfer belt 21 is scraped off by a cleaning device and removed from the outer peripheral surface of the photoreceptor 20.

  The superimposed toner images of four colors are conveyed to the secondary transfer region N2 by the intermediate transfer belt 21. On the other hand, the paper P is conveyed from the registration roller pair 73 to the secondary transfer region N2 in accordance with the timing. Then, the four-color toner images are transferred (secondary transfer) from the intermediate transfer belt 21 to the paper P in the secondary transfer region N2, and then conveyed to the fixing device 3. In the fixing device 3, the paper P passes through a nip portion N3 between a heat generating belt and a pressure roller, which will be described later. During this time, the toner image on the paper P is melted and fixed by being heated and pressurized. The paper P on which the toner image is fixed is discharged to a paper discharge tray 75 formed on the upper surface of the apparatus by a pair of discharge rollers 74.

  The fixing device 3 will be described with reference to FIGS. The fixing device 3 is intended to reduce the heat capacity of the heating unit from the viewpoint of energy saving and responsiveness, and includes a fixing rotator 34 and a pressure roller (pressure rotator) 35. The fixing rotator 34 includes an endless belt-like heat generating belt (heat generating member) 31 and an elastic roller 32 that is disposed inside the heat generating belt 31 and presses against the pressure roller 35 with the heat generating belt interposed therebetween. The pressure roller 35 is formed by laminating an elastic layer and a release layer (not shown) on the outer periphery of the core metal, and is pressed against the fixing rotating body 34 by an urging member (not shown) to form a nip portion N3. . The inner diameter of the heat generating belt 31 is larger than the outer diameter of the elastic roller 32. Thereby, the contact portion between the heat generating belt 31 and the elastic roller 32 is reduced, and the amount of heat transfer from the heat generating belt 31 to the elastic roller 32 is reduced.

  FIG. 3 shows a schematic diagram of the cooling means 4 for air-cooling the fixing rotator 34. The cooling unit 4 includes a blower fan 41 and a duct 42, and cools the fixing rotator 34 by sending air to both ends of the fixing rotator 34 in the rotation axis direction. In the middle of the duct 42, the cooling zone varying means 5 is provided. The cooling region varying means 5 will be described later. The air sent from the blower fan 41 takes heat from the fixing rotator 34 and is then exhausted from the outlet 43.

  As shown in FIG. 4, the heat generating belt 31 includes a heat generating layer 311, a reinforcing layer 312, an elastic layer 313, and a release layer 314 in order from the inside, and electrodes 315 </ b> L are provided at both ends in the width direction of the belt. , 315R (hereinafter sometimes referred to as electrode 315). As shown in FIG. 2, the electrode 315 comes into contact with the power supply members 38 </ b> L and 38 </ b> R (hereinafter sometimes referred to as the power supply member 38), and electricity flows through the heat generation layer 311, so that the heat generation layer 311 generates heat. Then, the surface temperature of the heat generating belt 31 is detected at a plurality of points from the central portion to the end portion in the rotation axis direction by two temperature detecting means 61L and 61R (hereinafter also referred to as temperature detecting means 61). . As the temperature detection means 61, for example, a thermistor, a thermopile, a multi-array thermopile, or the like can be used, but a multi-array thermopile that can measure temperatures at a plurality of locations is suitable.

  The heat generating layer 311 is adjusted to a predetermined electrical resistivity by dispersing a conductive filler in the resin. As the resin, a heat resistant resin such as PI, PPS, and PEEK can be used, but PI is preferable from the viewpoint of heat resistance. As the conductive filler, metal powders such as silver, copper, aluminum, magnesium, and nickel, and carbon compound powders such as graphite, carbon black, carbon nanofibers, and carbon nanotubes are desirable, and a plurality of types may be mixed and dispersed. The shape is preferably a fibrous form with a small content so as to increase the contact probability between fillers and facilitate percolation. The conductive filler to be dispersed in the heat resistant resin is preferably 40 to 50% by volume if it is a carbon compound. If the amount of filler to be dispersed is large, the resistance may be lowered and the power supply allowable range on the power feeding side may be exceeded. If the amount is small, the resistance becomes high and the desired power cannot be supplied. Therefore, the filler amount for obtaining a desired resistance value is selected. The thickness of the heat generating layer 311 is arbitrary, but is preferably about 30 to 150 μm.

  The electrical resistivity varies depending on the thickness of the heat generating layer 311, the diameter and the axial length of the heat generating belt 31, and even if conductive particles such as a metal alloy or an intermetallic compound are appropriately blended in consideration of conditions on the power feeding side. Good. Further, glass fiber, whisker, titanium oxide, potassium titanate or the like may be added from the viewpoint of mechanical strength, or aluminum nitride, alumina or the like may be added from the viewpoint of thermal conductivity. Furthermore, an imidizing agent, a coupling agent, a surfactant, and an antifoaming agent may be added in view of production stability. The heat generating layer 311 is manufactured by uniformly dispersing a conductive filler in a polyimide varnish obtained by polymerizing an aromatic tetracarboxylic dianhydride and an aromatic diamine in an organic solvent, and then applying it to a mold and converting the imide. .

  The reinforcing layer 312 serves to reinforce the decrease in the strength of the heat generating layer 311 due to the conductive filler dispersion. If the strength of the heat generating layer 311 is sufficient, the insulating layer may not be provided. As a material for the insulating layer, the same kind of resin may be used to ensure contact with the heat generating layer 311, or a heat resistant resin such as PI, PPS, or PEEK, which is a different base material from the heat generating layer 311, may be used. The thickness is preferably about 5 to 100 μm.

  The elastic layer 313 is provided to prevent uneven gloss of the color image. As the material, a rubber material having a high body heat property such as silicon rubber or fluorine rubber is used. The thickness is preferably about 100 μm to 300 μm.

  The release layer 314 is preferably configured to have release properties such as fluorine tubes such as PFA, PTFE, and ETFE and fluorine coating, and may be conductive. Although thickness is arbitrary, about 5-100 micrometers is desirable. Examples of fluorine-based tubes include PFA350-J, 451HP-J, and 951HP Plus manufactured by Mitsui DuPont Fluorochemical Co., Ltd. The contact angle with water is 90 degrees or more, preferably 110 degrees or more. The surface roughness Ra is desirably about 0.01 μm to 50 μm.

  The electrode 315 can be made of metal such as copper, aluminum, nickel, stainless steel, brass, phosphor bronze, etc., but nickel, stainless steel, aluminum, etc. having low electrical resistivity and excellent heat resistance and oxidation resistance can be used. desirable. The thickness of the electrode layer is desirably 20 μm to 80 μm.

  Electric power is supplied to the electrode 315 from a power supply member 38 such as a carbon brush made of copper graphite or carbon graphite. The power supply member 38 is pressed against the electrode 315 with a predetermined force. The length of the electrode 315 in the axial direction of the heat generating belt 31 is equal to or longer than the length of the power supply member 38 in the axial direction. Set arbitrarily within the range that does not exceed the allowable current density of the brush. The shape of the contact surface is preferably along the curved surface of the belt because the contact area is large and the current density is lowered. Electric power is supplied to the power supply member 38 via a harness.

  Next, the pressure roller 35 will be described. The outer diameter of the pressure roller 35 is desirably 20 mm to 100 mm. The release layer of the pressure roller 35 preferably has a release property such as a fluorine-based tube such as PFA and PTFE and fluorine-based coating, and may be conductive, and the thickness is 5 μm to 100 μm. The elastic layer is preferably made of a material having high heat resistance such as silicon rubber or fluorine rubber, and has a thickness of 1 mm to 20 mm. The core metal is preferably a metal such as aluminum or iron, and may have a pipe shape with a thickness of 0.1 mm to 10 mm, or a solid shape or a cross-sectional shape such as a three-headed shape.

  The cooling control in the fixing device of the present invention will be described below with reference to FIGS. FIG. 5 shows a state diagram in which the sheet P is nipped and conveyed by the nip portion between the fixing rotator 34 and the pressure roller 35. In the figure, the members arranged symmetrically are distinguished from each other by adding “L” to the left member and “R” to the right member. In the following description, “L” and “R” may be omitted to describe the member.

  By driving the blower fans 41L and 41R, air is blown to the both ends of the fixing rotating body 34 from the blower ports 44L and 44R through the ducts 42L and 42R. At this time, the temperature of the fixing rotator 34 is measured by the temperature detectors 61L and 61R. The temperature detectors 61L and 61R measure not only the non-sheet passing area but also the temperature of the sheet passing area. In this embodiment, the two blower fans 41L and 41R are used. However, a single blower fan may be used, and the duct may be branched halfway to blow out from the two blower ports 44L and 44R.

  The size of the paper P is detected by the size detection means 62L and 62R, and the detection result is sent to the control device 64. Here, the non-sheet passing area in the fixing rotator 34 is calculated. The size of the paper P may be recognized by user input or detection data when stored in the paper feed cassette 71. Alternatively, since the temperature of the heat generating belt 31 decreases in the range in which the paper P has passed, the temperature may be measured by the temperature detecting unit 61 to detect the paper size.

  6 to 8 show the shielding plate 52 and shielding plate 55 that constitute the cooling region varying means 5, and the moving mechanism thereof. FIGS. 6 to 8 are views of the direction of the cooling region varying means 5 from the fixing rotator 34. In the following description, “L” and “R” meaning left and right will be omitted.

  Air blowing ports 44 are formed at both ends of the substrate 51 in the axial direction. A shield plate 52 and a shield plate 55 are respectively provided in the air outlet 44 so as to be movable in the axial direction. The shielding plate 52 is held by a support rod 53 on which a rack gear 53G is formed. The two support rods 53 are arranged substantially in parallel at a predetermined distance, and the rack gears 53G of the two support rods 53 mesh with the pinion gears 54 arranged between the support rods 53, respectively. When the pinion gear 54 rotates counterclockwise in FIG. 6, the shielding plate 52 moves from the center side in a direction to close the air outlet 44. On the other hand, the shielding plate 55 is held by a support rod 56 on which a rack gear 56G is formed. The two support rods 56 are arranged substantially parallel to each other at a predetermined distance, and the rack gears 56G of the two support rods 56 mesh with the pinion gears 57 arranged between the support rods 56, respectively. When the pinion gear 57 rotates clockwise in FIG. 6, the shielding plate 56 moves from the end side in a direction to close the air blowing port 44. The pinion gear 54 and the pinion gear 57 can be independently driven by motors 58 and 59 (shown in FIG. 5).

  FIG. 6 shows a fully open state in which the shielding plate 52 and the shielding plate 55 do not block the air blowing port 44. FIG. 7 shows a state in which the pinion gear 54 is slightly rotated counterclockwise, the pinion gear 57 is slightly rotated clockwise, and the air outlet 44 is slightly closed from the left and right. FIG. 8 shows a state in which the pinion gear 54 and the pinion gear 57 are rotated and the air outlet 44 is all closed. 6 to 8 show the case where the pinion gear 54 and the pinion gear 57 rotate at the same time, the pinion gear 54 and the pinion gear 57 can be individually rotated. For example, either one of the pinion gears 57 can be rotated. Can be rotated to move one of the shielding plate 52 and the shielding plate 55 to block a part of the blower port 44.

  Information on the non-sheet passing area based on the temperature of the fixing rotator 34 and the size information of the paper P is sent to the control device 64 (shown in FIG. 5). The blower fan 41 and the motors 58 and 59 are driven by the control device 64. Further, the power supply to the heat generating layer 311 of the heat generating belt 31 is performed by the control device 64 so as to reach the optimum fixing temperature based on the signal from the temperature detecting means 61.

  9 to 12 are diagrams for explaining the paper size, the non-sheet passing area of the fixing rotator 34, and the cooling area by the blower fan. 9 and 10 show a case where a fixing process for a small-sized sheet (sheet width: W1) is performed. The non-sheet passing area is a distance (X1) from both ends of the sheet to the electrode 315 of the fixing rotator 34. In the fixing device shown in FIG. 9, the width Y1 of the air blowing port 44 is equal to the non-sheet passing region X1, and in the entire cooling mode, the air blowing port 44 is fully opened and the entire non-sheet passing region X1 is cooled. On the other hand, in the local cooling mode, as shown in FIG. 10, the shielding plates 52 and 55 are moved, and a part of the non-sheet passing region X1 including the high temperature portion is intensively cooled.

  11 and 12 show a case where a fixing process is performed on a large-sized sheet (sheet width: W2). The non-sheet passing area is a distance (X2) from both ends of the sheet to the electrode 315 of the fixing rotator 34. In the whole cooling mode, the shielding plate 52 moves and the air blowing port 44 is connected to the non-sheet passing area X2. The width is equal to Z1. On the other hand, in the local cooling mode, as shown in FIG. 12, the shielding plates 52 and 55 are moved so that the air blowing port 44 is narrowed to the horizontal width Z2, and a partial region including the high temperature portion of the non-sheet passing region X2 Cooled intensively. As described above, the cooling region varying means 5 can appropriately change the width of the air outlet 44 and the position thereof according to the size of the non-sheet passing region and the position where the high temperature is generated.

  The opening degree of the air blowing port 44 in the whole cooling mode is controlled by calculating a non-sheet passing region in the fixing rotating body 34 by the control device 64 from the size of the paper P detected by the size detecting means 62L, 62R. The opening degree of the air blowing port 44 is adjusted by the movement of the shielding plates 52 and 55. At this time, from the viewpoint of preventing a temperature drop in the sheet passing area, the position of the outer end of the shielding plate 52 is preferably positioned about 0 to 10 mm outside the boundary between the non-sheet passing area and the sheet passing area.

  On the other hand, the opening position of the air blowing port 44 in the local cooling mode first determines the center of the cooling region. The center of the cooling area can be calculated and determined from the width of the non-sheet passing area or the like, but is preferably the highest temperature position detected by the temperature detecting means 61. The width of the local cooling area (the opening degree of the blower opening) may be set to a width set in advance according to the size of the paper P. Table 1 shows an example of the width of the local cooling area with respect to the paper size. As can be understood from Table 1, the smaller the size of the sheet, the wider the non-sheet passing area of the fixing rotator 34. Therefore, the width of the local cooling area is set wider.

  From the viewpoint of more efficiently suppressing a partial temperature rise in the non-sheet passing area, the cooling in the local cooling mode may be performed in a narrower area during the cooling. Table 2 shows an example of the width of the narrower local cooling area with respect to the paper size.

  The cooling of the non-sheet passing area is performed by alternately repeating the entire cooling mode and the local cooling mode. The cooling time in the overall cooling mode is preferably in the range of 5 to 10 seconds, and the cooling time in the local cooling mode is preferably in the range of 3 to 7 seconds. The ratio of the cooling time in the whole cooling mode and the local cooling mode may be changed as appropriate so that a high temperature region higher than a predetermined temperature does not occur from the detected temperature in the non-sheet passing region.

  FIG. 13 is a flowchart showing an example of cooling control for the non-sheet passing area. When the printing operation starts, the size of the paper P is detected by the size detection means 62, and a non-sheet passing area is determined (step S1). Next, temperatures at a plurality of axial positions in the non-sheet passing area are detected (step S2). If the detected maximum temperature exceeds the allowable temperature (for example, 200 ° C.) (step S3), the position where the maximum temperature is detected is determined as the center of the cooling region in the local cooling mode (step S4), and the paper P The width of the local cooling zone is determined from the size of

  Next, the blower fan 41 is driven (step S5), and cooling in the local cooling mode is started (step S6). And after predetermined time progress (step S7), it replaces with local cooling mode and cooling by the whole cooling mode is started (step S8). After a predetermined time has elapsed (step S9), the temperature at a plurality of axial positions in the non-sheet passing area is detected (step S10), and when the detected maximum temperature exceeds an allowable temperature (for example, 200 ° C.) (step S11). Further, it is determined whether or not the difference (temperature unevenness) between the detected maximum temperature and the minimum temperature exceeds an allowable temperature (for example, 10 ° C.) (step S12). When the temperature unevenness exceeds the allowable temperature, it is determined whether or not the position showing the maximum temperature is within the local cooling region (step S13). When the position showing the maximum temperature is within the local cooling region, the time ratio of the local cooling mode is increased (step S14), and when the position showing the maximum temperature is not within the local cooling region, the time of the whole cooling mode is set. After the ratio is increased (step S15), the process returns to step S6, and cooling in the local cooling mode and the overall cooling mode is alternately repeated.

  On the other hand, when the detected maximum temperature does not exceed the allowable temperature (step S11), the blower fan 41 is stopped (step S16). If the printing operation has not been completed, the process returns to step S10, and the temperatures at a plurality of axial positions in the non-sheet passing area are detected. If the temperature unevenness does not exceed the allowable temperature (step S12), the process returns to step S6, and the cooling in the local cooling mode and the whole cooling mode is alternately repeated.

  FIG. 14 shows another example in the case of changing the cooling conditions in the overall cooling mode and the local cooling mode. The flowchart shown in this figure is the same as the flowchart of FIG. 13 except for step S18 and step S19, so the description of the same part is omitted and only the different part will be described below. When the position showing the maximum temperature in step S13 is within the local cooling region, the local cooling region is narrowed and cooling is performed more intensively (step S18). For example, the local cooling region is changed from the region shown in Table 1 to the region shown in Table 2. On the other hand, when the position where the maximum temperature is detected is outside the local cooling region, the local cooling region is widened (step S19). This shortens the distance between the local cooling region and the maximum temperature detection position, increases the heat transfer from the maximum temperature detection position to the local cooling region, and decreases the temperature outside the local cooling region.

  As described above, in the fixing device of the present invention, the entire cooling mode for cooling the entire non-sheet passing region and the local cooling mode for cooling a predetermined range centering on the position showing the maximum temperature are alternately repeated, thereby Occurrence of partial high temperature portions and temperature unevenness in the paper passing area is prevented. FIG. 15 shows the measurement result of the temperature distribution in the fixing rotator 34. As understood from this figure, in the fixing device of the present invention, as a result of repeating the whole cooling mode for cooling the whole T1 of the non-sheet-passing area and the local cooling mode for cooling a part T2 therein, The non-sheet passing area was kept at the same temperature.

  The fixing device of the present invention is useful because it can effectively suppress temperature rise and temperature unevenness in the non-sheet passing region.

3 Fixing Device 4 Cooling Means 5 Cooling Area Variable Means P Paper 31 Heating Belt
32 Elastic roller 34 Fixing rotator 35 Pressure roller (Pressure rotator)
44 Air outlet 52 Shield plate 55 Shield plate 58, 59 Motor 61 Temperature detection means 62 Size detection means 64 Control device

Claims (4)

A fixing rotator having a heat generating member, and a pressure rotator that presses against the fixing rotator to form a nip portion. By passing the paper through the nip portion, the untransferred toner image is melted and fixed on the paper. In the fixing device to be
Size detection means for detecting the length in the direction perpendicular to the paper transport direction;
A plurality of temperature detection means provided in the direction of the rotation axis for detecting the temperature of the fixing rotator;
Cooling means for cooling the fixing rotator by blowing air;
A cooling zone varying means for varying the cooling zone by the cooling means;
Control means for controlling the cooling zone and the cooling time by the cooling zone variable means,
When the fixing unit is cooled by the cooling unit, the control unit cools the entire non-sheet passing region by the cooling region changing unit, and the non-sheet passing region detected by the temperature detecting unit. A fixing device, wherein a local cooling mode for cooling a region including a high temperature portion is alternately and repeatedly performed every predetermined time. The control means, after the cooling means starts cooling the fixing rotator, in the non-sheet passing region, the difference between the maximum detected temperature and the minimum detected temperature by the plurality of temperature detecting means is a predetermined value or more and the maximum If the detected temperature is detected in the local cooling area, increase the cooling time ratio in the local cooling mode.If the detected temperature is detected outside the local cooling area, increase the cooling time ratio in the overall cooling mode. The fixing device according to claim 1, wherein the fixing device is raised.   The control means, after the cooling means starts cooling the fixing rotator, in the non-sheet passing region, the difference between the maximum detected temperature and the minimum detected temperature by the plurality of temperature detecting means is a predetermined value or more and the maximum If the detected temperature is detected in the local cooling area, the cooling area in the local cooling mode is narrowed. If the maximum detected temperature is detected outside the local cooling area, the cooling area in the local cooling mode is widened. The fixing device according to claim 1.   The cooling region varying means is a pair of shielding plates provided at the air outlet through which the air blown from the cooling means blows so as to be movable in the direction of the rotation axis, and blowing the air by moving the pair of shielding plates. The fixing device according to claim 1, wherein a position and an opening degree are adjusted.