JP2009271297A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which avoids increases in the size and cost of the device, eliminates the need for, in particular, highly precise components, prevents excessive partial temperature rise even when small size sheets of paper are successively passed through, and is highly productive, and to provide an image forming apparatus. <P>SOLUTION: The fixing device 1 has a fixing belt 11 and a pressure belt 12 and passes a sheet through a nip between both belts, thereby fixing a toner image on the sheet. The fixing belt 11 has a conductive heat generating layer which generates heat by receiving a magnetic flux. A magnetic flux generating section 13 is disposed over the widthwise maximum dimension of a passing sheet and applies a magnetic flux to the fixing belt 11. A part including at least one of widthwise ends of the magnetic flux generating section 13 is disposed so as to be rotatable within a plane facing an area of the fixing belt 11, the area being subject to the application of a magnetic flux. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine and a printer, and a fixing device used therefor. More specifically, the present invention relates to a fixing device and an image forming apparatus using electromagnetic induction heating.

  2. Description of the Related Art Conventionally, some fixing devices of image forming apparatuses have a heating device using an electromagnetic induction heating method. In particular, a configuration in which a magnetic flux generated by an exciting coil is guided to a conductive heat generating layer by a magnetic core such as a ferrite core is often used. The electromagnetic induction heating type heating device has a higher heat conversion efficiency than the halogen heater type, and with this configuration, a compact and efficient fixing device can be obtained.

  In order to shorten the warm-up time of the fixing device, it is desirable to reduce the heat capacity of the conductive heat generating layer that is a heating member. However, when the heat capacity of the conductive heat generating layer is reduced, another problem arises that overheating tends to occur outside the sheet passing range, for example, when small-size paper is continuously printed. On the other hand, Patent Document 1 discloses a fixing device that is provided with a demagnetizing coil to control the heat generation distribution. When printing on small-size paper, an excessive temperature rise in the non-sheet passing region is prevented by causing an induced current to flow through the degaussing coils provided at both ends in the axial direction.

Patent Document 2 discloses a fixing device in which an exciting coil and a magnetic core are fixed to a holding member and can swing with the holding member. In the apparatus described in this document, a hinge is provided at the longitudinal end of the holding member and the other end is lifted substantially perpendicular to the inner surface of the fixing roller. Accordingly, the end of the coil or core can be moved to a position away from the inner surface of the fixing roller, and the amount of heat generated in the non-sheet passing region at the end in the longitudinal direction can be reduced.
JP 2001-60490 A JP 2000-188178 A

  However, when a degaussing coil is used as in the fixing device described in Patent Document 1, it is necessary to provide various types of degaussing coils in order to cope with various types of paper sizes. This is not preferable because it causes an increase in size and cost of the apparatus.

  Further, in the case of changing the distance between the coil or core and the fixing roller (heating member) as in the apparatus described in Patent Document 2, there is a problem that the change in heat generation distribution with respect to the distance is very large. For example, if the distance is moved by 0.1 mm, a difference in calorific value of about 1 ° C. occurs. Therefore, in order to precisely control the heat generation distribution, there is a problem that high-precision parts and mechanisms are required.

  The present invention has been made to solve the above-described problems of the prior art. In other words, the problem is that there is no partial increase in temperature even when small-sized paper is continuously fed without increasing the size and cost of the device, and without using particularly high-precision parts. It is an object of the present invention to provide a fixing device and an image forming apparatus that do not generate a toner and have high productivity.

  The fixing device of the present invention, which has been made for the purpose of solving this problem, has a pair of fixing members, and fixes the toner image on the sheet by passing the sheet through the nip between the pair of fixing members. , One of the pair of fixing members has a conductive heat generating layer that generates heat upon receiving the magnetic flux, and applies the magnetic flux to one of the pair of fixing members, and the magnetic flux provided over the maximum dimension in the width direction of the passing sheet. A part of the magnetic flux applying member including at least one end in the width direction is provided so as to be rotatable in a plane facing a portion where the magnetic flux is applied in one of the pair of fixing members. It is what.

  According to the fixing device of the present invention, one conductive heat generating layer of the pair of fixing members generates heat by receiving the magnetic flux from the magnetic flux applying member. A part of the magnetic flux applying member including at least one end in the width direction is rotatable. That is, the state of the magnetic flux applied to the conductive heat generating layer is changed by the rotation of a part of the magnetic flux applying member. In the present invention, this rotation is performed in a plane facing a portion to which the magnetic flux is applied in one of the pair of fixing members. That is, the rotation is in a plane that does not include a portion that receives the application of magnetic flux. This is, for example, rotation in a direction that changes the angle with respect to the width direction of the sheet in a plane that forms the fixing nip or a plane that is parallel to the paper surface when passing through the nip. For example, in the case of a long-type magnetic flux applying member, if it is rotated from a direction perpendicular to the nip, the effective width in the width direction of the sheet is reduced or it is out of the range of the nip. Thereby, the range of the width direction in which heat is generated in the conductive heat generating layer can be changed.

  Furthermore, since it is a part including the edge part of the width direction that can be rotated, the heat-generation condition of an edge part changes especially. For example, the end portion in the width direction of the conductive heat generating layer can be prevented from generating heat. Therefore, even when printing on a small size paper, it is possible to prevent an excessive temperature rise at the edge. In this direction of rotation, the magnetic flux application member does not change greatly in distance with respect to one of the pair of fixing members, so that highly accurate control is not required. As a result, there is no increase in the size and cost of the device, and there is no partial overheating even when small-size paper is continuously fed without using highly accurate parts. It is a fixing device with good productivity.

Further, in the present invention, one of the pair of fixing members has a flat portion, the magnetic flux applying member is disposed to face the flat portion, and the rotatable surface is a surface parallel to the flat portion. desirable.
If it is such, it can be rotated without changing the distance to one of the pair of fixing members. Therefore, more accurate control can be performed.

Further, in the present invention, the magnetic flux applying member is divided into a plurality of members adjacent to each other in the width direction, and among the plurality of members, a part of the members is fixed and the rest is rotatably provided. It is desirable that the rotation shaft of the rotatable member is in a position where no gap is generated between adjacent members even when the rotatable member is rotated.
In such a case, there is no possibility that the magnetic flux is reduced or interrupted in the middle of the magnetic flux applying member in which a part thereof is moved by the rotation. Therefore, a substantially uniform heating state can be obtained within the heating range.

Further, in the present invention, it is desirable that the magnetic flux applying member has an exciting coil, and the exciting coil is rotated.
In such a case, the angular position of the exciting coil that generates magnetic flux is changed. It is easy to rotate the exciting coil, and therefore control to change the heating width is easy.

Further, in the present invention, it is desirable that the magnetic flux applying member has an exciting coil and a magnetic core, and at least one of the exciting coil or the magnetic core is rotated.
In such a case, the angular position of the exciting coil that generates magnetic flux or the magnetic core that collects the generated magnetic flux is changed. Therefore, it is easy to control the amount of magnetic flux supplied to the conductive heat generating layer.

Furthermore, the present invention has a control unit that controls the rotational drive of the magnetic flux application member, and the control unit controls the rotation angle of the magnetic flux application member so that the heating width corresponds to the width of the passing sheet. It is desirable to be.
If this is the case, the heating width can be set according to the width of the sheet. Therefore, there is no possibility of overheating the range where the sheet is not passed.

  The present invention further includes an image forming portion that forms a toner image on a sheet and a pair of fixing members at least one of which rotates, and the sheet carrying the toner image formed by the image forming portion is connected to a nip between the pair of fixing members. An image forming apparatus having a fixing device for fixing a toner image on a sheet by passing between them, the fixing device having a conductive heating layer in which one of a pair of fixing members receives heat and generates heat A magnetic flux applying member configured to apply a magnetic flux to one of the pair of fixing members and provided over the maximum dimension in the width direction of the passing sheet, and including at least one end of the magnetic flux applying member in the width direction. However, a part of the image forming apparatus also extends to an image forming apparatus provided so as to be rotatable in a plane facing a portion that receives application of magnetic flux in one of the pair of fixing members.

  According to the fixing device and the image forming apparatus of the present invention, even when small-sized paper is continuously passed without increasing the size and cost of the apparatus and without using particularly high-precision parts. No excessive overheating occurs and productivity is improved.

"First form"
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to an image forming apparatus having an electromagnetic induction heating type fixing device.

  The image forming apparatus 100 of the present embodiment is a so-called tandem color printer having an intermediate transfer belt 101 as schematically shown in FIG. The intermediate transfer belt 101 is an endless belt member, and both ends in the figure are supported by rollers 102 and 103. Along the lower portion of the intermediate transfer belt 101 in the drawing, yellow (Y), magenta (M), cyan (C), and black (K) image forming units 104Y, 104M, 104C, and 104K and an image density sensor 105 are provided. Has been placed. The image density sensor 105 also has a function as a registration sensor.

  The image forming units 104Y, 104M, 104C, and 104K for each color have the same configuration. Each includes a photosensitive drum 106 and a charging device 107, an exposure device 108, a developing device 109, and a cleaner device 110 arranged around the photosensitive drum 106. A primary transfer device 111 is disposed at a position facing the photosensitive drum 106 with the intermediate transfer belt 101 interposed therebetween. In FIG. 1, the image forming unit 104Y is representatively shown.

  1 shows a paper feeding device 112 that accommodates the paper P. A paper feed roller 113 that feeds the paper P is provided above the paper feed device 112. The paper P is sent upward from the paper feeding device 112 along the transport path 114. A secondary transfer device 115 is disposed at a position facing the roller 103 with the conveyance path 114 interposed therebetween. Further, a fixing device 1 is disposed on the downstream side (upper side in the drawing). The fixing device 1 includes a fixing belt 11, a pressure belt 12, and a magnetic flux generator 13. The fixing device 1 will be described in detail later. A paper discharge roller 116 and a paper discharge tray 117 are arranged further downstream of the conveyance path 114 from the fixing device 1.

  Next, the operation of the image forming apparatus 100 of this embodiment will be briefly described. When the image forming apparatus 100 receives an image formation instruction, the image forming apparatus 100 generates image data of each color from the image signal. The generated image data of each color is sent to the corresponding image forming units 104Y, 104M, 104C, and 104K. The image forming units 104Y, 104M, 104C, and 104K for each color form electrostatic latent images by charging and exposing the respective photosensitive drums 106 based on the image data. Further, the formed electrostatic latent image is developed to form a toner image.

  The formed toner images are sequentially transferred to the intermediate transfer belt 101 by the primary transfer device 111 and superimposed. The toner image superimposed on the intermediate transfer belt 101 is transferred onto the paper P by the secondary transfer device 115. The sheet P carrying the toner image is further conveyed and reaches the fixing device 1 where it is heated and pressurized by the fixing device 1. As a result, the toner image is fixed on the paper P. The paper P on which the toner image is fixed is discharged to a paper discharge tray 117 by a paper discharge roller 116.

  As shown in FIG. 1, the fixing device 1 according to this embodiment is configured such that a fixing belt 11 and a pressure belt 12 are spanned between two internal rollers 14. Therefore, both the fixing belt 11 and the pressure belt 12 have an oval cross section, and there are flat portions on both side surfaces. These internal rollers 14 are pressed against each other to form a fixing nip between the fixing belt 11 and the pressure belt 12.

  The fixing nip of this embodiment includes a pressure contact portion between the inner rollers 14 and a contact portion between the flat portions of the fixing belt 11 and the pressure belt 12 formed between them. Further, the fixing belt 11 is provided with a substantially flat magnetic flux generating portion 13 facing the plane portion opposite to the fixing nip. Note that the fixing device 1 of the present embodiment is of a central paper passing type. That is, the recording material passes through the central portion in the longitudinal direction of the fixing device 1.

  As shown in FIG. 2, the inner roller 14 of the fixing belt 11 includes a cored bar 21 and a heat insulating layer 22 from the inner side (lower side in the figure). A fixing belt 11 having a three-layer structure including a heating element layer 24, an elastic layer 25, and a release layer 26 is in close contact with the outer peripheral side.

  The cored bar 21 is a support that supports the entire inner roller 14 and needs to have sufficient heat resistance and strength. In this embodiment, a solid aluminum rod within a range of φ6 to 30 mm, preferably φ9 to 17 mm is used. Although it is not impossible to use a magnetic material such as iron, a non-magnetic material is preferable in order to prevent the core metal 21 from generating heat. Further, if the strength can be secured, a heat resistant resin such as PPS (polyphenylene sulfide) can be used.

  The heat insulating layer 22 is for preventing the heat generated in the fixing belt 11 from escaping to the cored bar 21. Therefore, a sponge material (heat insulation structure) made of a rubber material or a resin material having low thermal conductivity, heat resistance and elasticity is preferable. With such a configuration, the deflection of the fixing belt 11 can be allowed and the nip width can be kept large. In addition, the hardness of the internal roller 14 can be reduced to improve the fixing property and paper passing property. The heat insulating layer 22 may be a rubber solid material or a two-layer structure of a rubber solid material and a sponge body as long as it has a low thermal conductivity. In this embodiment, when a resin sponge is used as the heat insulating layer 22, a layer having a thickness of 1 to 6 mm, more preferably 2 to 3 mm is used. The heat insulation layer 22 has a hardness of 20 to 60 degrees, more preferably 30 to 50 degrees, as measured by a hardness Asker rubber hardness meter.

  The heating element layer 24 of the fixing belt 11 is a layer that receives heat generated by the magnetic flux generator 13 and induces an induced current, thereby generating heat. Therefore, a magnetic material having a high relative permeability and a moderately large volume resistivity is used. For example, nickel, magnetic stainless steel, permalloy and the like are preferable. Here, an endless nickel electroformed belt having a thickness of 10 to 100 μm, more preferably 20 to 50 μm is used. The heating element layer 24 may be made of a conductive non-magnetic material such as metal made into a thin film and laminated with nickel, permalloy, SUS, PI (polyimide), or the like.

  Further, as the heating element layer 24, particles of magnetic material such as nickel or permalloy may be dispersed in a resin. Alternatively, a resin material may be coated with these magnetic materials. If a resin-based material is used as the heating element layer 24, the flexibility of the fixing belt 11 as a whole is further increased, and the paper separation property can be improved. In such a case, external conductivity may not be obtained, but eddy current can pass. Such a layer is also included in the conductive layer of the present invention.

  The elastic layer 25 is for enhancing the close contact between the recording material and the fixing belt 11. For the elastic layer 25, a rubber material or a resin material having heat resistance and elasticity is used. As the material, for example, heat-resistant elastomers such as silicon rubber and fluorine rubber that can withstand use at the fixing temperature are suitable. Further, the above materials may be mixed with various fillers for the purpose of thermal conductivity and reinforcement. Of these, examples of particles filled for improving thermal conductivity include silver, copper, aluminum, iron, and glass. Practically, silica, alumina, magnesium oxide, boron nitride, beryllium oxide and the like are preferable.

  The elastic layer 25 has a thickness in the range of 10 to 800 μm, more preferably in the range of 100 to 300 μm. If the thickness of the elastic layer 24 is less than 10 μm, it is difficult to obtain sufficient elasticity in the thickness direction. On the other hand, if the thickness exceeds 800 μm, it is difficult to cause the heat generated in the heating element layer 24 to reach the outer peripheral surface of the fixing belt 11, which is not preferable because the thermal efficiency is poor.

  The elastic layer 25 has a JIS hardness of 1 to 80 degrees, more preferably 5 to 30 degrees. If the hardness is within this range, it is possible to ensure a stable fixing property while preventing a decrease in the strength and adhesion of the elastic layer 25. Examples of silicon rubber having a hardness within this range include, for example, one-component, two-component, or three-component or more silicone rubber, LTV (Low Temperature Vulcanizable) type, RTV (Room Temperature Vulcanizable) Sulfur) type, HTV (High Temperature Vulcanizable) type silicon rubber, condensation type or addition type silicon rubber, or the like can be used. In this embodiment, silicon rubber having a JIS hardness of 10 degrees and a thickness of 200 μm is used.

  The release layer 26 is the outermost layer of the fixing belt 11 and is for improving the release property between the fixing belt 11 and the paper. As the release layer 26, a layer that can withstand use at a fixing temperature and has excellent release properties with respect to toner is used. For example, silicon rubber, fluorine rubber, PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer), PTFE (tetrafluoroethylene), FEP (tetrafluoroethylene / hexafluoroethylene copolymer), PFEP Fluorine resins such as (tetrafluoroethylene / hexafluoropropylene copolymer) are preferred. Alternatively, a mixture of these may be used.

  The thickness of the release layer 26 is 5 to 100 μm, more preferably 10 to 50 μm. Further, in order to improve the adhesive force between the release layer 26 and the elastic layer 25, an adhesion treatment with a primer or the like may be performed. In addition, a conductive material, an abrasion resistant material, a good heat conductive material, or the like may be added as a filler to the release layer 26 as necessary.

  The pressure belt 12 is the same as the fixing belt 11. However, since the toner image of the recording material does not contact the pressure belt 12, the elastic layer may not be provided. Further, the heating element layer is not necessarily a heating element. Note that the size of the fixing belt 11 and the pressure belt 12 in the circumferential direction is, for example, about 25 to 65 mm, preferably about 30 to 50 mm. Further, the nip load applied to the internal roller 14 is 10 to 500 N, preferably 20 to 200 N. Note that the pressure contact load of the internal roller 14 on the upstream side in the sheet passing direction is preferably set smaller than that on the downstream side. In this embodiment, the upstream side is 20N and the downstream side is 50N.

  Further, as shown in FIG. 3, the magnetic flux generator 13 of the fixing device 1 faces the outer periphery of the fixing belt 11 and is arranged in parallel with the flat portion of the fixing belt 11. The magnetic flux generator 13 has three exciting coils 41 a, 41 b, 41 c, a large number of magnetic cores 42, a coil bobbin 43, and a rotating shaft 44.

  The exciting coils 41 a to 41 c are coils wound in an oval shape along the longitudinal direction of the fixing belt 11, and are respectively held by the coil bobbins 43. In this embodiment, the three exciting coils 41a to 41c are connected in series. In addition, as the winding of the exciting coil 41, a wire made of litz wires obtained by bundling several tens to several hundreds of thin wires is used. The exciting coil 41 generates heat when energized. Even in such a case, the winding is coated with a heat-resistant resin so that insulation can be maintained.

  In this embodiment, as shown in FIG. 3, three substantially identical three-turn exciting coils 41 a to 41 c are arranged along the longitudinal direction of the fixing belt 11. Each exciting coil 41 a to 41 c has a size in the direction perpendicular to the longitudinal direction of the fixing belt 11, which is about the same as the planar portion of the fixing belt 11. At least the excitation coils 41 a and 41 c are larger in the longitudinal direction of the fixing belt 11 than in the direction perpendicular to the longitudinal direction of the fixing belt 11.

  The exciting coil 41 b arranged in the center is fixed so as to face the central portion of the fixing belt 11. The exciting coils 41a and 41c arranged on both sides of the exciting coils 41a and 41c are rotatably locked by a rotating shaft 44 provided at one location near the center. Thereby, the exciting coils 41 a and 41 c can rotate in a plane facing the flat portion of the fixing belt 11. Specifically, the fixing belt 11 is rotatable in a plane parallel to the plane portion.

  Note that at least the ends near the center of the exciting coils 41a and 41c are formed in a semicircular shape. And the rotating shaft 44 is arrange | positioned in the center position of the semicircle. In the fixing device described in Patent Document 2, the rotating surfaces of the exciting coil and the magnetic core are in a plane including a portion of the fixing roller that receives the application of magnetic flux. This is an arrangement different from the rotation surfaces of the exciting coils 41a and 41c in this embodiment.

  The magnetic core 42 is for increasing the efficiency of the magnetic circuit and for magnetic shielding. In this embodiment, the magnetic core 42 is formed by arranging a plurality of rectangular parallelepiped plates in a range substantially corresponding to the size of the flat surface portion of the fixing belt 11. The magnetic core 42 is made of a material having high magnetic permeability and low loss of eddy current. Since this embodiment uses high frequency, the loss of eddy current in the core tends to increase. In addition, when a core made of a high permeability alloy such as Permalloy is used, the loss of eddy current tends to increase. Therefore, when such a material is used, it is desirable to use a core having a structure in which thin plates are laminated.

  In addition, when the magnetic shielding of the magnetic circuit portion by the exciting coils 41a to 41c and the magnetic core 42 can be sufficiently performed by other means, the core may not be provided (air core). Furthermore, as the magnetic core 42, a resin material in which magnetic powder is dispersed can be used. Although this material has a slightly low magnetic permeability, it has the advantage that the shape can be set freely.

  Further, in this embodiment, as shown in FIG. 4, a thermistor 45, a high frequency inverter 46, a rotation drive unit 47, and a control unit 48 are provided. The thermistor 45 is disposed in contact with the surface of the fixing belt 11 and detects the surface temperature of the fixing belt 11. Further, the detected surface temperature is input to the control unit 48. A plurality of thermistors 45 exist and are arranged at different positions in the longitudinal direction of the fixing belt 11.

  The high frequency inverter 46 is for supplying high frequency power of 10 to 100 kHz and 100 to 2000 W to the three exciting coils 41a to 41c. Thereby, the magnetic flux is induced by the alternating current flowing through the exciting coils 41 a to 41 c, and the magnetic flux is guided to the magnetic core 42. Further, the magnetic flux exits from the end of the magnetic core 42 and passes through the inside of the heating element layer 24 of the fixing belt 11. Thereby, an eddy current flows through the heating element layer 24 and the heating element layer 24 is heated by Joule heat. That is, the fixing belt 11 receives the magnetic flux generated by the magnetic flux generator 13 to induce an induced current, thereby generating heat.

  The rotation drive unit 47 is for controlling the rotation positions of the excitation coils 41a and 41c arranged on both sides. In this embodiment, as shown in FIG. 5, only the exciting coils 41a and 41c are rotated. None of the magnetic cores 42 and the exciting coils 41b arranged in the center are rotated. The exciting coils 41a and 41c are rotated at the same angle. The direction of rotation is preferably on the same side as shown, but may be reversed. Here, an arrangement parallel to the longitudinal direction of the fixing belt 11 is set to a rotation angle of 0 degree, and the rotational position is controlled within a range from here to a rotation angle of 90 degrees perpendicular to the longitudinal direction of the fixing belt 11.

  In this embodiment, since the rotation shaft 44 is located at the center of the semicircular shape at the ends of the excitation coils 41a and 41c, even if it is rotated up to 90 degrees, it is almost between the center excitation coil 41b. There is no gap. Further, as shown in FIG. 5, the thermistor 45 is arranged at positions (45p, 45q, 45r, 45s) corresponding to the respective paper sizes in the width direction. Here, four locations are shown, but it may be more or less.

  The control unit 48 is for controlling the high-frequency inverter 46 so that the surface temperature of the fixing belt 11 falls within an appropriate fixing temperature range. The rotation drive unit 47 is controlled according to the width of the paper to be printed to adjust the rotation angle of the excitation coils 41a and 41c. Alternatively, the detection value of each thermistor 45 may be used for the control. An appropriate fixing temperature is set in advance according to the type of toner. Further, the detection of the surface temperature of the fixing belt 11 is not limited to the thermistor 45 and may be performed by a non-contact type temperature sensor.

  As described above, the distribution of the amount of heat generated in each part when the exciting coils 41a and 41c are rotated changes as shown in FIG. First, as shown in FIG. 3, when all the exciting coils 41a to 41c are arranged in parallel to the longitudinal direction of the fixing belt 11 (rotation angle 0 degree), all the portions of the exciting coils 41a to 41c are , Facing the magnetic core 42 and the fixing belt 11. Accordingly, almost all of the magnetic flux generated in the exciting coils 41a to 41c enters the magnetic core 42 and contributes to heat generation in the entire range. The solid line L1 in FIG. 6 shows the distribution of the amount of heat generated when the rotation angle is 0 degree, and the heat generation is almost uniformly 100% within the range of the fixing belt 11.

  On the other hand, when the exciting coils 41 a and 41 c are rotated around the rotation shaft 44, their ends (both ends in the longitudinal direction of the fixing belt 11) face the magnetic core 42 and the fixing belt 11. The position is out of range. Therefore, the magnetic flux generated at the end cannot enter the magnetic core 42 or the fixing belt 11 straight. Since the magnetic flux concentrates in the effective direction, the magnetic flux generated at the edge that has become out of position also gathers at a location near the center. Therefore, not all the magnetic flux generated at the point of departure is wasted.

  That is, when the exciting coils 41a and 41c are rotated, the magnetic flux does not pass through both ends of the fixing belt 11 in the longitudinal direction. Therefore, both ends of the fixing belt 11 hardly generate heat. This non-heat-generating range varies depending on the rotation angle of the exciting coils 41a and 41c. A solid line L2 in FIG. 6 indicates the distribution of heat generation when the exciting coils 41a and 41c are rotated up to 10 degrees. Solid lines L3 and L4 indicate the distribution of heat generation when the exciting coils 41a and 41c are rotated to 20 degrees and 90 degrees, respectively.

  On the other hand, since the position of the exciting coil 41b does not change in the central portion in the longitudinal direction of the fixing belt 11, the amount of heat generation hardly changes in that range. There is no difference from the case where the rotation angle is 0 degree. If the width of the minimum size paper that can be passed and the width of the exciting coil 41b (or the heat generation width when the rotation angle is 90 degrees) are set to be approximately the same, even the minimum size paper can be fixed reliably. Further, the relationship between the rotation angle and the range of paper width that can be fixed at that time may be grasped and stored in advance by experiments.

  In this way, for example, in the case of the color printer 1 capable of printing from A5 vertical size paper to A3 vertical size paper, A3 vertical size printing is performed at a rotation angle of 0 degree. Then, B4 vertical size printing may be performed at a rotation angle of 10 degrees, A4 vertical size printing may be performed at a rotation angle of 20 degrees, and A5 vertical size printing may be performed at a rotation angle of 90 degrees. In either case, the rotation angle is adjusted so that the heated range matches the width in the direction perpendicular to the paper passing direction of the printing paper. Further, when a sheet having an intermediate size is used, the rotation angle may be adjusted more finely according to the sheet size.

  In this embodiment, the three exciting coils 41a to 41c are connected in series. However, at least the exciting coils 41a and 41c and the exciting coil 41b may be able to supply power separately. In this way, the supply of power to the exciting coils 41a and 41c can be stopped, and only the range of the exciting coil 41b can contribute to heat generation. A broken line L5 in FIG. 6 shows, for reference, the distribution of the amount of heat generated when power is supplied only to the excitation coil 41b and power is not supplied to the excitation coils 41a and 41c. It is.

  Next, a fixing process operation by the fixing device 1 of the present embodiment will be described. In the fixing device 1 of the present embodiment, the fixing rollers 11 and the pressure belt 12 are pressed against each other to form a fixing nip therebetween. During the fixing process, the internal roller 14 of the fixing belt 11 is rotationally driven, and the pressure belt 12 is driven and rotated by the frictional force generated by the pressure contact with the fixing belt 11. Note that the relationship between the driving and the driven may be reversed, or both belts may be driven together.

  In the magnetic flux generator 13, high frequency power is supplied to the exciting coil 41 by the high frequency inverter 46. The magnetic flux generated thereby passes through the inside of the magnetic core 42. The magnetic flux exits outside at the end of the magnetic core 42 and penetrates the heating element layer 24 of the fixing belt 11. Thereby, an eddy current flows through the heating element layer 24 and the heating element layer 24 generates heat due to Joule heat. As a result, the fixing belt 11 is heated.

  The heat thus generated is transmitted to the surface of the fixing belt 11 through the elastic layer 25 bonded to the heating element layer 24. In this embodiment, the heating element layer 24 that contributes to heat generation and through which an eddy current flows is a very thin layer, and therefore has a small heat capacity. Further, since the heat of the heating element layer 24 is thermally insulated and held by the heat insulating layer 22, it is difficult to escape to the core metal 21 side, and the elastic layer 25 and the release layer 26 on the surface layer side of the fixing belt 11 are rapidly heated.

  Then, the high frequency inverter 46 is controlled by the controller 48 so that the surface of the fixing belt 11 has an appropriate fixing temperature. The paper P carrying the toner image is inserted into the nip between the fixing belt 11 and the pressure belt 12 with the surface on which the toner image is placed facing the fixing belt 11 side. Then, the toner is melted and fixed on the paper P while passing through the nip between the fixing belt 11 and the pressure belt 12 from the bottom to the top in FIG.

  Due to the fixing process of the paper P, heat is removed from the surface of the fixing belt 11 by the paper P and the toner. Therefore, the surface temperature of the fixing belt 11 decreases in the range where the paper P is passed in the axial direction of the fixing belt 11. The control unit 48 controls the high frequency inverter 46 in response to the detection result of the surface temperature of the fixing belt 11 by the thermistor 45. That is, the controller 48 increases or decreases the high-frequency power supplied from the high-frequency inverter 46 to the excitation coil 41 so that the next sheet P is transported to the fixing nip so as to be within an appropriate fixing temperature range. .

  In this embodiment, since the heat capacity of the fixing belt 11 is small and the surface thereof can be rapidly heated to the fixing temperature, the supply of heat can catch up even if heat is taken away by the fixing process. Furthermore, the control unit 48 controls the rotation angle of the excitation coils 41 a and 41 c by the rotation driving unit 47 according to the size of the printing paper. As a result, only the necessary and sufficient width portion of the fixing belt 11 is heated.

  As described above in detail, according to the fixing device 1 of the present embodiment, the exciting coils 41a, 41b, and 41c are divided into three, and two at both ends are rotatable. Therefore, only the necessary and sufficient range of the fixing belt 11 can be heated according to the size of the paper to be printed. Further, since the movement is caused by rotation, no space is required outside the fixing device 1 in the axial direction. As a result, even when small-size paper is continuously fed, partial overheating does not occur and the productivity is improved.

"Second form"
Next, a second embodiment of the present invention will be described in detail with reference to the accompanying drawings. This embodiment is different from the first embodiment only in the configuration of the exciting coil, and the same members are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 7, the exciting coil 51 of the fixing device 2 of this embodiment is formed in a single oval shape. The whole is housed in a coil bobbin 52, and a rotating shaft 53 is provided at the center of the coil bobbin 52. In this embodiment, the rotation shaft 53 is rotated by the rotation drive unit 47, and the angular position of the excitation coil 51 with respect to the fixing belt 11 is changed as shown in FIG. By this rotation, the distance between the excitation coil 51 and the fixing belt 11 does not change so much in the vicinity of the rotation shaft 53, but greatly changes at both ends in the axial direction.

  FIG. 9 shows the rotation angle of the exciting coil 51 according to this embodiment and the distribution of the heat generation amount at that time. The solid line L6 in the figure is the case where the rotating shaft 53 is not rotated from the state shown in FIG. 7 (rotation angle 0 degree), and the heat generation of 100% is almost uniform over the entire longitudinal range of the fixing belt 11. The amount is obtained. When printing on the maximum size paper that can be handled, the exciting coil 51 is stopped at this position. For example, in an image forming apparatus capable of printing on A3 vertical size paper, printing on A3 vertical size paper is performed at a rotation angle of 0 degree.

  In FIG. 9, the solid line L7 is the distribution of heat generation at a rotation angle of 5 degrees, and is used for printing on, for example, B4-size paper. A solid line L8 is a distribution of heat generation at a rotation angle of 10 degrees, and is used for printing on, for example, A4 portrait paper. A solid line L9 is a distribution of heat generation at a rotation angle of 15 degrees, and is used for printing on, for example, A5 portrait paper. A solid line L10 is a distribution of heat generation at a rotation angle of 30 degrees, and is used for printing on, for example, A6 portrait paper.

  Since the apparatus of this embodiment has only one rotating shaft 53, angle adjustment is easy. Further, in this embodiment, since there is no range in which a uniform heat generation amount can be obtained as compared with the first embodiment, a certain temperature gradient is generated even in the sheet passing area. However, from the effect of leveling the temperature in the fixing belt 11 due to heat transfer in the longitudinal direction of the fixing belt 11, the surface temperature distribution can be within about ± 4 ° C. in the sheet passing region. Therefore, the fixing property and glossiness are not adversely affected by this embodiment as well, and excessive temperature rise at the end can be prevented.

  As described in detail above, even with the image forming apparatus of this embodiment, as in the first embodiment, even when small-size paper is continuously fed, partial overheating does not occur, and productivity is improved. It is a good image forming apparatus.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, in the above embodiment, only the exciting coil is rotated, but substantially the same effect can be obtained even if the exciting coil is fixed and the magnetic core is rotated. Alternatively, both the exciting coil and the magnetic core may be rotated. Further, for example, the shape of the magnetic core and the exciting coil is not limited to the above. Of the three-part excitation coils, the size and shape can be different between those at both ends and those at the center. Moreover, it is good also as a two-part excitation coil without a central thing.

  Further, the position of the rotating shaft does not necessarily have to be the center position of the exciting coil in the sheet passing direction. However, the shape is such that there is no gap between the central exciting coil and the ones at both ends when rotating. Furthermore, by devising the shape, it is possible to prevent the heat generation efficiency from dropping so much at the boundary between the divided excitation coils. Moreover, as long as the rotation range of the excitation coils at both ends is not disturbed, the shape of the central excitation coil is arbitrary.

  Further, the shape and arrangement of the fixing belt 11 and the pressure belt 12 are not limited to those described above. For example, a cylindrical pressure belt may be used. In that case, the fixing belt 11 may be pressed against a flat surface portion on the side where the magnetic flux generation unit 13 is not disposed, or may be pressed against the inner roller 14 of the fixing belt 11. . Further, by adjusting the size and arrangement, the magnetic flux generator 13 can be arranged on the inner peripheral side of the fixing belt 11.

  Further, in the above description, the exciting coils 41 are connected in series. However, they may be connected in parallel or controlled independently. For example, if high frequency power can be independently supplied to the central excitation coil and the ones at both ends, it is easy to obtain the heat generation distribution indicated by the broken line L5 in FIG. Further, a separation claw may be provided at the fixing nip outlet. Further, for example, although the color printer is used in this embodiment, the present invention can be applied to a single-color printer, a copier, a FAX machine, etc. having only one color image forming unit.

1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. FIG. 3 is an explanatory diagram illustrating a layer configuration of a fixing belt. 1 is a schematic perspective view of a fixing device according to a first embodiment. 1 is a schematic configuration diagram of a fixing device according to a first embodiment. It is explanatory drawing which shows the state which the excitation coil rotated. It is a graph which shows the difference in distribution of the emitted-heat amount by the rotation angle of an exciting coil. FIG. 6 is a schematic perspective view of a fixing device according to a second embodiment. It is explanatory drawing which shows the state which the excitation coil which concerns on a 2nd form rotated. It is a graph which shows the difference in distribution of the emitted-heat amount by the rotation angle of an exciting coil.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing device 11 Fixing belt 12 Pressure belt 13 Magnetic flux generation part 100 Image forming apparatus

Claims (7)

In a fixing device having a pair of fixing members and fixing a toner image on a sheet by passing the sheet through a nip between the pair of fixing members,
One of the pair of fixing members has a conductive heat generating layer that generates heat by receiving magnetic flux,
A magnetic flux applying member that applies a magnetic flux to the one of the pair of fixing members, and that is provided over the maximum dimension in the width direction of a passing sheet;
A part of the magnetic flux applying member including at least one end in the width direction is provided rotatably in a plane facing a portion where the magnetic flux is applied to the one of the pair of fixing members. A fixing device characterized by the above. The fixing device according to claim 1,
The one of the pair of fixing members has a flat surface;
The magnetic flux applying member is disposed to face the flat portion;
The fixing device according to claim 1, wherein the rotatable surface is a surface parallel to the flat portion. The fixing device according to claim 1 or 2,
The magnetic flux applying member is divided into a plurality of members adjacent to each other in the width direction;
Among the plurality of members, some of the members are fixed and the rest are rotatably provided,
The fixing device according to claim 1, wherein the rotation shaft of the rotatable member is in a position where no gap is generated between adjacent members even when the rotatable member is rotated. In the fixing device according to any one of claims 1 to 3,
The magnetic flux applying member has an exciting coil;
A fixing device in which the exciting coil is rotated. In the fixing device according to any one of claims 1 to 3,
The magnetic flux applying member has an exciting coil and a magnetic core;
A fixing device in which at least one of the exciting coil and the magnetic core is rotated. In the fixing device according to any one of claims 1 to 5,
A control unit for controlling the rotational drive of the magnetic flux applying member;
The fixing device is characterized in that the controller controls a rotation angle of the magnetic flux applying member so as to have a heating width corresponding to a width of a sheet passing therethrough. An image forming unit that forms a toner image on a sheet and a pair of fixing members that rotate at least one of the sheets, and a sheet carrying the toner image formed by the image forming unit is passed between the nips of the pair of fixing members In an image forming apparatus having a fixing device for fixing a toner image on a sheet,
The fixing device includes:
One of the pair of fixing members has a conductive heat generating layer that generates heat by receiving magnetic flux,
A magnetic flux applying member that applies a magnetic flux to the one of the pair of fixing members, and that is provided over the maximum dimension in the width direction of a passing sheet;
A part of the magnetic flux applying member including at least one end in the width direction is provided rotatably in a plane facing a portion where the magnetic flux is applied to the one of the pair of fixing members. An image forming apparatus.

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