JP6043699B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that fixes a toner image on a recording medium, and an image forming apparatus including the fixing device.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses such as copying machines and printers include a fixing device that fixes a toner image on a recording medium. For this fixing device, a “heat roller method” is widely used from the viewpoint of thermal efficiency and safety. The hot roller method is a method of forming a fixing nip using a pair of rollers. On the other hand, in recent years, the “belt method” has attracted attention due to demands for shortening the warm-up time and energy saving. The belt method is a method of forming a fixing nip using a fixing belt.

  For example, Patent Document 1 discloses a pressure member that forms a fixing nip between a fixing belt (see “Endless Belt 6” in Patent Document 1) and the fixing belt (see “Heating Roll 20” in Patent Document 1). A pressing member that presses the fixing belt toward the pressing member (see “Pad Cap 9” in Patent Document 1), and a guide member that makes the outer peripheral surface contact the inner peripheral surface of the fixing belt (“Belt Travel” in Patent Document 1). And a fixing device including the guide 13 ").

  In the fixing device having such a configuration, normally, when the fixing belt rotates with respect to the pressing member and the guide member, the fixing belt, the pressing member, and the guide member rub against each other. In particular, since the fixing belt is pressed toward the pressing member by the pressure member, the fixing belt and the pressing member rub violently. Therefore, the fixing belt may be worn with the rotation of the fixing belt, and the fixing belt may be damaged. Therefore, in Patent Document 1, the unevenness surface is formed on the surface of the pressing member that contacts the fixing belt, and the lubricant is held on the uneven surface, thereby suppressing the wear of the fixing belt.

JP 2004-198655 A

  However, in Patent Document 1, although the lubricant can be moved in the rotation direction of the fixing belt as the fixing belt rotates, it is difficult to move the lubricant in the rotation axis direction (longitudinal direction) of the fixing belt. is there. For this reason, if there is unevenness in the amount of lubricant in the rotation axis direction of the fixing belt, this unevenness cannot be eliminated, and the lubricant is thin between the fixing belt and the pressing member or between the fixing belt and the guide member. Part (part with weak lubrication) will occur. As a result, the fixing belt is locally worn in the thin portion of the lubricant, and the fixing belt is damaged from the worn portion, so that the life of the fixing belt may be shortened.

  Accordingly, in consideration of the above circumstances, the present invention moves the lubricant in the direction of the rotation axis of the fixing belt, thereby making the amount of the lubricant uniform in the direction of the rotation axis of the fixing belt as much as possible and extending the life of the fixing belt. The purpose is to plan.

  The fixing device according to the present invention is disposed rotatably on a fixing belt provided around a rotation shaft, and is disposed on the outer diameter side of the fixing belt so as to be in pressure contact with the fixing belt to form a fixing nip. A pressure member; a pressing member that is disposed on an inner diameter side of the fixing belt and presses the fixing belt toward the pressure member; and a guide member that makes an outer peripheral surface contact the inner peripheral surface of the fixing belt. In the outer peripheral surface of the guide member, a holding groove for holding a lubricant is provided along a direction inclined with respect to the rotation direction of the fixing belt.

  By adopting such a configuration, it becomes possible to move the lubricant along a direction inclined with respect to the rotation direction of the fixing belt, and accordingly, the amount of the lubricant in the rotation axis direction of the fixing belt. Can be made as uniform as possible. Therefore, it is possible to prevent a thin portion of the lubricant from being generated between the fixing belt and the pressing member or between the fixing belt and the guide member. Along with this, it is possible to avoid local wear of the fixing belt, and it is possible to prevent the fixing belt from being damaged and to prolong the life of the fixing belt.

  The holding grooves are arranged in the direction of the rotation axis, and a first area and a second area formed on the outer peripheral surface of the guide member on the outer side in the rotation axis direction than the first area. The holding groove forming interval in the second region may be shorter than the holding groove forming interval in the first region.

  By adopting such a configuration, the function of holding the lubricant by the holding groove formed in the second region can be enhanced. Along with this, it is possible to prevent the lubricant from leaking to the outer side in the rotational axis direction than the guide member.

  The width of the holding groove in the rotation axis direction may be gradually narrowed from the upstream side to the downstream side in the rotation direction of the fixing belt.

  By adopting such a configuration, it is possible to promote the movement of the lubricant in the holding groove.

  The holding groove may be inclined inward in the rotation axis direction from the upstream side to the downstream side in the rotation direction of the fixing belt.

  By adopting such a configuration, it becomes possible to bring the lubricant inward in the rotational axis direction. Along with this, it is possible to prevent the lubricant from leaking to the outer side in the rotational axis direction than the guide member.

  The fixing device further includes an exciting coil that is disposed on an outer diameter side of the fixing belt and heats the fixing belt, and the guide member faces the exciting coil with the fixing belt interposed therebetween, and the exciting coil It may be formed of a material that generates heat by a magnetic field generated by.

  By adopting such a configuration, the fixing belt can be efficiently heated.

  The image forming apparatus of the present invention includes any one of the fixing devices described above.

  According to the present invention, by moving the lubricant in the direction of the rotation axis of the fixing belt, it is possible to make the amount of the lubricant uniform in the direction of the rotation axis of the fixing belt as much as possible and to extend the life of the fixing belt. .

1 is a schematic diagram illustrating an outline of a configuration of a color printer according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a fixing device according to an embodiment of the present invention. 1 is a perspective view showing a fixing device according to an embodiment of the present invention. 1 is a perspective view showing an inner diameter side of a fixing belt in a fixing device according to an embodiment of the present invention. In the fixing device according to the embodiment of the present invention, (a) is a side view showing a guide member, and (b) is an enlarged view of a portion surrounded by a dashed line A in (a).

  First, the overall configuration of the color printer 1 (image forming apparatus) will be described with reference to FIG.

  The color printer 1 includes a box-shaped printer main body 2, a paper feed cassette 3 that stores paper (recording medium) is provided in the lower part of the printer main body 2, and a paper discharge tray is provided in the upper part of the printer main body 2. 4 is provided.

  An intermediate transfer belt 6 is installed between a plurality of rollers in the center of the printer main body 2, and an exposure device 7 composed of a laser scanning unit (LSU) is disposed below the intermediate transfer belt 6. Yes. Below the intermediate transfer belt 6, four image forming units 8 are provided for each toner color (for example, four colors of magenta, cyan, yellow, and black). Each image forming unit 8 is rotatably provided with a photosensitive drum 9, and around the photosensitive drum 9, a charger 10, a developing unit 11, a primary transfer unit 12, and a cleaning device 13 are provided. The static eliminator 14 is arranged in the order of the primary transfer process. Above the developing unit 11, a toner container 15 corresponding to each image forming unit 8 is provided for each toner color.

  A paper transport path 16 is provided on one side (right side in the drawing) of the printer body 2. A paper feed unit 17 is provided at the upstream end of the conveyance path 16, and a secondary transfer unit 18 is provided at one end (right end in the drawing) of the intermediate transfer belt 6 at a middle portion of the conveyance path 16, and downstream of the conveyance path 16. A fixing device 19 is provided in the section, and a paper discharge port 20 is provided at the downstream end of the transport path 16.

  Next, an image forming operation of the color printer 1 having such a configuration will be described. When the color printer 1 is turned on, various parameters are initialized, and initial settings such as temperature setting of the fixing device 19 are executed. When image data is input from a computer or the like connected to the color printer 1 and an instruction to start printing is given, an image forming operation is executed as follows.

  First, after the surface of the photosensitive drum 9 is charged by the charger 10, an electrostatic latent image is formed on the surface of the photosensitive drum 9 by laser light (see arrow P) from the exposure device 7. Next, the electrostatic latent image is developed into a toner image of a corresponding color by the developing device 11 with the toner supplied from the toner container 15. This toner image is primarily transferred to the surface of the intermediate transfer belt 6 in the primary transfer portion 12. Each image forming unit 8 sequentially repeats the above operation, whereby a full-color toner image is formed on the intermediate transfer belt 6. Note that the toner and charge remaining on the photosensitive drum 9 are removed by the cleaning device 13 and the static eliminator 14.

  On the other hand, the paper taken out from the paper feed cassette 3 by the paper feed unit 17 is conveyed to the secondary transfer unit 18 in synchronism with the above-described image forming operation. The full-color toner image is secondarily transferred to the paper. The sheet on which the toner image has been secondarily transferred is conveyed downstream in the conveyance path 16 and enters the fixing device 19, where the toner image is fixed on the sheet. The sheet on which the toner image is fixed is discharged from the discharge port 20 onto the discharge tray 4.

  Next, the fixing device 19 will be described. Arrows Fr attached to FIGS. 3, 4, and 5 (a) indicate the front side (front side) of the fixing device 19. An arrow I in FIGS. 5A and 5B indicates an inner side in the front-rear direction, and an arrow O in FIGS. 5A and 5B indicates an outer side in the front-rear direction.

  As shown in FIG. 2, the fixing device 19 includes a fixing belt 21, a pressure roller 22 (pressure member) disposed on the right side (outer diameter side) of the fixing belt 21, and a left side (outside) of the fixing belt 21. The IH fixing unit 23 arranged on the radial side), the support member 24 arranged on the inner diameter side of the fixing belt 21, the pressing member 25 arranged on the right side of the support member 24 on the inner diameter side of the fixing belt 21, and fixing. Magnetic shielding plates 26 disposed on the upper and lower sides and the left side of the support member 24 on the inner diameter side of the belt 21, and guide members 27 disposed on the upper and lower sides and the left side of the magnetic shielding plate 26 on the inner diameter side of the fixing belt 21. I have.

  As shown in FIG. 3, the fixing belt 21 is an endless belt, and has a substantially cylindrical shape that is long in the front-rear direction. The fixing belt 21 is provided so as to be rotatable in the rotation direction Y about a rotation axis X extending in the front-rear direction. That is, in the present embodiment, the front-rear direction is the rotation axis direction of the fixing belt 21.

  The fixing belt 21 includes, for example, a base material layer, an elastic layer provided around the base material layer, and a release layer that covers the elastic layer. The base material layer of the fixing belt 21 is formed by, for example, plating or rolling a metal such as nickel or copper, and has conductivity. The elastic layer of the fixing belt 21 is made of, for example, silicon rubber. The release layer of the fixing belt 21 is formed of a fluorine resin such as PFA, for example. In each figure, each layer (base material layer, elastic layer, release layer) of the fixing belt 21 is displayed without being particularly distinguished.

  The pressure roller 22 has a substantially cylindrical shape that is long in the front-rear direction. As shown in FIG. 2 and the like, the pressure roller 22 is in pressure contact with the fixing belt 21, and a fixing nip 34 is formed between the fixing belt 21 and the pressure roller 22 along the paper conveyance path 16. ing.

  As shown in FIG. 3 and the like, the pressure roller 22 includes, for example, a cylindrical core material 36, an elastic layer 37 provided around the core material 36, and a release layer ( (Not shown).

  The core material 36 of the pressure roller 22 is formed of a metal such as stainless steel or aluminum. At both front and rear ends of the core material 36 of the pressure roller 22, mounting cylinder portions 30 are provided. A front bearing 31 is mounted on the front mounting cylinder 30. A rear bearing 32 is mounted on the rear mounting cylinder 30. The front bearing 31 and the rear bearing 32 are attached to a fixing frame (not shown). Thereby, the pressure roller 22 is rotatable in the rotation direction Z. A driving gear 33 is fixed to the rear mounting cylinder 30 on the rear side of the rear bearing 32. The drive gear 33 is connected to a drive source (not shown).

  The elastic layer 37 of the pressure roller 22 is formed of, for example, silicon rubber or silicon sponge. The release layer of the pressure roller 22 is formed of, for example, a fluorine resin such as PFA.

  As shown in FIG. 2, the IH fixing unit 23 includes a case member 38, an excitation coil 40 (heat source) housed in the case member 38 and provided in an arc shape along the outer periphery of the fixing belt 21, and a case member. 38, and an arch core 41 provided along the outer periphery of the exciting coil 40. The IH fixing unit 23 is not shown in FIG.

  The exciting coil 40 is disposed on the left side (outer diameter side) of the fixing belt 21. The exciting coil 40 is connected to an AC power source (not shown). The excitation coil 40 is configured to generate a magnetic field by applying an AC voltage to the excitation coil 40 by an AC power source.

  The support member 24 is formed by combining a pair of sheet metal members 42 having a substantially L-shaped cross section, and has a rectangular tube shape that is long in the front-rear direction. The support member 24 includes an upper wall portion 43, a lower wall portion 44, a left wall portion 45 and a right wall portion 46. Fixed pieces 48 (see FIGS. 3 and 4) are fixed to the front end portion and the rear end portion of the support member 24. Each fixing piece 48 is fixed to a fixing frame (not shown).

  As shown in FIG. 2, the cross section of the pressing member 25 has a substantially vertically long rectangular shape. The pressing member 25 has a shape that is long in the front-rear direction. The pressing member 25 is fixed to the right wall portion 46 of the support member 24. The pressing member 25 is in contact with the inner peripheral surface of the fixing belt 21 and presses the fixing belt 21 to the right side (pressure roller 22 side). The pressing member 25 is in contact only with the right portion (the portion on the fixing nip 34 side) of the inner peripheral surface of the fixing belt 21.

  The magnetic shielding plate 26 is fixed to the support member 24. The magnetic shielding plate 26 is made of a nonmagnetic and highly conductive material such as oxygen-free copper, for example. The magnetic shielding plate 26 includes a side plate 50 that covers the left side of the support member 24, and upper and lower plates 51 that are bent rightward from both upper and lower ends of the side plate 50, and has a substantially U-shaped cross section. ing. The magnetic shielding plate 26 prevents the magnetism from the exciting coil 40 from penetrating the support member 24.

  The guide member 27 is made of a material that generates heat by a magnetic field generated by the exciting coil 40 (for example, a magnetic shunt metal such as an Fe—Ni alloy). The guide member 27 includes an upper attachment portion 52 and a lower attachment portion 53, and a curved portion 54 that connects the upper attachment portion 52 and the lower attachment portion 53.

  As shown in FIG. 4 and the like, the upper mounting portion 52 is provided at the front end portion, the rear end portion, and the front-rear direction center portion of the guide member 27. The upper attachment portion 52 is attached to the upper plate 51 of the magnetic shielding plate 26 by screws 55. The lower attachment portion 53 (see FIG. 2 and the like) is attached to the lower plate 51 of the magnetic shielding plate 26.

  As shown in FIG. 2 and the like, the curved portion 54 is curved in an arc shape toward the left side (side away from the fixing nip 34). The curved portion 54 faces the exciting coil 40 with the fixing belt 21 interposed therebetween. The outer peripheral surface of the curved portion 54 is in contact with the inner peripheral surface of the fixing belt 21 and guides (stretches) the fixing belt 21 from the inner diameter side. As a result, the rotation trajectory of the fixing belt 21 is stabilized.

  As shown in FIG. 4 and the like, holding grooves 56 are arranged in the front-rear direction on the outer peripheral surface of the bending portion 54. Each holding groove 56 holds a lubricant for lubricating the inner peripheral surface of the fixing belt 21. This lubricant is composed of, for example, fluorine grease, silicon grease, silicon oil, or the like.

  As shown in FIG. 5A, the outer peripheral surface of the bending portion 54 is provided with a first region R1 and a second region R2 formed on the outer side in the front-rear direction than the first region R1. It has been. The formation interval P1 of each holding groove 56 in the first region R1 is, for example, 30 mm to 50 mm. In the first region R1, the positions of the holding grooves 56 in the front-rear direction do not overlap. The formation interval P2 of each holding groove 56 in the second region R2 is, for example, 10 mm to 20 mm. The formation interval P2 of each holding groove 56 in the second region R2 is shorter than the formation interval P1 of each holding groove 56 in the first region R1. In the second region R2, the positions of the holding grooves 56 in the front-rear direction partially overlap.

  As shown in FIG. 5B and the like, each holding groove 56 has a trapezoidal shape that is long in the vertical direction. Each holding groove 56 is provided along a direction inclined with respect to the rotation direction Y of the fixing belt 21. Specifically, each holding groove 56 is inclined inward in the front-rear direction from the upper side (upstream side in the rotation direction Y of the fixing belt 21) to the lower side (downstream side in the rotation direction Y of the fixing belt 21). . The width d in the front-rear direction of each holding groove 56 gradually decreases from the upper side (upstream side in the rotation direction Y of the fixing belt 21) to the lower side (downstream side in the rotation direction Y of the fixing belt 21).

  In the fixing device 19 configured as described above, when the toner image is fixed on the paper, the pressure roller 22 is rotated by a drive source (not shown) (see arrow Z in FIG. 2). When the pressure roller 22 is thus rotated, the fixing belt 21 that is in pressure contact with the pressure roller 22 is driven to rotate in the opposite direction to the pressure roller 22 (see arrow Y in FIG. 2). Accordingly, the fixing belt 21 slides with respect to the pressing member 25 and the curved portion 54 of the guide member 27.

  Further, when fixing the toner image on the paper, an AC power source (not shown) applies an AC voltage to the exciting coil 40. Along with this, the exciting coil 40 generates a magnetic field, and this magnetic field generates an eddy current in the fixing belt 21 and the fixing belt 21 generates heat. That is, the fixing belt 21 is induction-heated by the exciting coil 40. Further, when the exciting coil 40 generates a magnetic field as described above, an eddy current is generated in the guide member 27 by this magnetic field, and the guide member 27 generates heat. That is, the guide member 27 is induction-heated by the exciting coil 40. Along with this, the fixing belt 21 is heated by heat transfer from the guide member 27. In this state, when the paper passes through the fixing nip 34, an unfixed toner image is heated and pressurized and fixed on the paper.

  When the fixing belt 21 rotates as described above, the fixing belt 21 and the pressing member 25 rub against each other, and the fixing belt 21 and the curved portion 54 of the guide member 27 rub against each other. In particular, since the fixing belt 21 is pressed to the left side (the pressing member 25 side) by the pressure roller 22, the fixing belt 21 and the pressing member 25 are rubbed violently. Therefore, the fixing belt 21 may be worn with the rotation of the fixing belt 21, and the fixing belt 21 may be damaged. Therefore, in this embodiment, the lubricant is supplied to the inner peripheral surface of the fixing belt 21 to suppress wear of the fixing belt 21.

  The lubricant is held in each holding groove 56 provided on the outer peripheral surface of the curved portion 54 of the guide member 27. For example, when each holding groove 56 is provided in parallel with the rotation direction Y of the fixing belt 21, the lubricant held in each holding groove 56 is rotated in the rotation direction Y of the fixing belt 21 as the fixing belt 21 rotates. Will only move to.

  In contrast, in the present embodiment, as described above, each holding groove 56 is provided along a direction inclined with respect to the rotation direction Y of the fixing belt 21. Therefore, as shown in FIG. 5B, the lubricant F held in the holding grooves 56 is inclined with respect to the rotation direction Y of the fixing belt 21 in the direction F (the vector component f1 in the rotation direction of the fixing belt 21). It is possible to move along the direction (with the vector component f2 in the front-rear direction). Along with this, the amount of lubricant can be made as uniform as possible in the front-rear direction, and a thin portion of lubricant between the fixing belt 21 and the pressing member 25 and between the fixing belt 21 and the curved portion 54 of the guide member 27. Can be prevented from occurring. Therefore, local wear of the fixing belt 21 can be avoided, and damage to the fixing belt 21 can be suppressed, and the life of the fixing belt 21 can be extended.

  In particular, when a toner image is continuously fixed on a small-size sheet, heat is intensively taken away by the sheet at the central part in the front-rear direction of the fixing belt 21, and thus the temperature distribution of the fixing belt 21 in the front-rear direction. Tends to be non-uniform, and the deterioration of the lubricant is likely to be promoted. However, in this embodiment, as described above, the amount of the lubricant can be made uniform in the front-rear direction as much as possible, so that deterioration of the lubricant can be kept to a minimum.

  The formation interval P2 of each holding groove 56 in the second region R2 of the guide member 27 is shorter than the formation interval P1 of each holding groove 56 in the first region R1 of the guide member 27. By adopting such a configuration, it is possible to enhance the lubricant holding function of the second region R2 of the guide member 27. Along with this, it is possible to prevent the lubricant from leaking to the outside in the front-rear direction than the guide member 27.

  Further, the width d in the front-rear direction of each holding groove 56 gradually decreases from the upper side (upstream side in the rotation direction Y of the fixing belt 21) to the lower side (downstream side in the rotation direction Y of the fixing belt 21). . By adopting such a configuration, it is possible to promote the movement of the lubricant in each holding groove 56.

  Each holding groove 56 is inclined inward in the front-rear direction from the upper side (upstream side in the rotation direction Y of the fixing belt 21) to the lower side (downstream side in the rotation direction Y of the fixing belt 21). By adopting such a configuration, the lubricant can be brought inward in the front-rear direction. Along with this, it is possible to prevent the lubricant from leaking to the outside in the front-rear direction than the guide member 27.

  The guide member 27 has a curved portion 54 that faces the excitation coil 40 with the fixing belt 21 interposed therebetween, and is formed of a material that generates heat by a magnetic field generated by the excitation coil 40. By adopting such a configuration, the fixing belt 21 can be efficiently heated.

  In the present embodiment, the case where the front and rear positions of the holding grooves 56 do not overlap in the first region R1 of the guide member 27 has been described. On the other hand, in other different embodiments, the positions of the holding grooves 56 in the front-rear direction may partially overlap in the first region R1 of the guide member 27.

  In the present embodiment, the case where the positions in the front-rear direction of the holding grooves 56 partially overlap in the second region R2 of the guide member 27 has been described. On the other hand, in other different embodiments, the positions of the holding grooves 56 in the front-rear direction may not overlap in the second region R2 of the guide member 27.

  In this embodiment, the case where the base material layer of the fixing belt 21 is made of metal has been described. However, in another different embodiment, the base material layer of the fixing belt 21 may be made of a resin such as polyimide. .

  In the present embodiment, the case where the exciting coil 40 is used as a heat source has been described. However, in other different embodiments, a heater such as a halogen heater or a ceramic heater may be used as a heat source.

  In the present embodiment, the case where the configuration of the present invention is applied to the fixing device 19 in which the fixing belt 21 slides with respect to the pressing member 25 arranged on the inner diameter side of the fixing belt 21 has been described. On the other hand, in another different embodiment, the configuration of the present invention may be applied to a fixing device in which one or a plurality of rollers arranged on the inner diameter side of the fixing belt 21 rotate together with the fixing belt 21.

  In this embodiment, the case where the configuration of the present invention is applied to the color printer 1 has been described. However, in other different embodiments, the present invention is applied to other image forming apparatuses such as a monochrome printer, a copier, a facsimile machine, and a multifunction machine. A configuration may be applied.

1 Color printer (image forming device)
19 Fixing Device 21 Fixing Belt 22 Pressure Roller (Pressure Member)
25 Pressing member 27 Guide member 34 Fixing nip 40 Excitation coil 56 Holding groove X (Fixing belt) Rotating shaft Y (Fusing belt) Rotating direction R1 First region R2 Second region

Claims (4)

A fixing belt provided rotatably around a rotation axis;
A pressure member that is disposed on the outer diameter side of the fixing belt, is pressed against the fixing belt to form a fixing nip, and is rotatably provided;
A pressing member disposed on the inner diameter side of the fixing belt on the fixing nip side of the rotating shaft, and pressing the fixing belt toward the pressing member;
A guide member that makes the outer peripheral surface contact the inner peripheral surface of the fixing belt on the opposite side of the fixing nip across the rotation shaft,
A holding groove for holding a lubricant is provided on the outer peripheral surface of the guide member along a direction inclined with respect to the rotation direction of the fixing belt,
The width of the holding groove in the rotation axis direction is gradually narrowed from the upstream side to the downstream side in the rotation direction of the fixing belt ,
The holding grooves are arranged in a row in the rotation axis direction,
The outer peripheral surface of the guide member is provided with a first region and a second region formed on the outer side in the rotation axis direction than the first region,
The holding groove forming interval in the second region is shorter than the holding groove forming interval in the first region,
In the first region, adjacent positions of the holding groove do not overlap with each other in the direction of the rotational axis, and adjacent portions of the holding groove overlap in the direction of the rotational axis. The fixing device is characterized in that the fixing device is disposed . The fixing device according to claim 1 , wherein the holding groove is inclined inward in the rotation axis direction from an upstream side to a downstream side in a rotation direction of the fixing belt. An excitation coil disposed on an outer diameter side of the fixing belt and heating the fixing belt;
3. The fixing device according to claim 1, wherein the guide member is formed of a material that is opposed to the excitation coil across the fixing belt and generates heat by a magnetic field generated by the excitation coil. . An image forming apparatus characterized in that it comprises a fixing device according to any one of claims 1-3.

Images