JP2007108213A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device constituted so that it may be adaptable to various sheet sizes, and also, energy loss is reduced, and excessive temperature rise in a non-paper passing area is suppressed. <P>SOLUTION: The fixing device 100 includes: a fixing roller 1; a pressure roller 2; a magnetic flux generating part 3 equipped with an exciting coil 31 and a degaussing coil 34; and a heat uniformizing roller 8 arranged so as to come in press contact with or separate from the pressure roller 2. The degaussing coil 34 is arranged in a position as the non paper passing area above the axial direction of the fixing roller 1 when a large-sized paper passes through. In the fixing apparatus 100, when passing a small-sized sheet through, the degaussing coil 34 is turned on, and the heat uniformizing roller 8 is separated from the pressure roller 2. In passing a recording sheet smaller than the small-sized sheet through, the degaussing coil 34 is turned on, and also, the heat uniformizing roller 8 is brought in press contact with the pressure roller 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electromagnetic induction heating type fixing device that heat-fixes a toner image on a recording medium. More specifically, the present invention relates to a fixing device in which a magnetic flux generator such as an excitation coil is disposed outside a heating roller.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus is provided with a fixing device that fixes a toner image onto a recording sheet. As a fixing device, a roller system that includes a roller pair composed of a heating roller (fixing roller) and a pressure roller and that fixes a toner image by passing a recording sheet through a nip portion of the roller pair is widely adopted. Yes. In this roller type fixing device, the surface layer of the fixing roller is heated by a heat source such as a halogen heater, and the toner image is fixed on the recording paper by the heat and the pressure of the roller.

  In addition, electromagnetic induction heating type fixing devices have been proposed from the viewpoint of reducing power consumption and starting time. In the electromagnetic induction heating type fixing device, heat generation in the electromagnetic induction heat generating layer in the fixing roller is promoted by the magnetic flux from the magnetic flux generation unit. In addition, the electromagnetic induction heating type fixing device can be configured such that the heat capacity of the fixing member is smaller than that of the halogen heater due to the feature that the heat generating layer can be directly heated. Thereby, it becomes possible to improve thermal efficiency. In recent years, there has been proposed an electromagnetic induction heating type fixing device in which the heat capacity is reduced by reducing the thickness of the heat generating layer in order to further increase efficiency and start-up speed (for example, Patent Document 1 and Patent Document 2). ).

  In the electromagnetic induction heating type fixing device, the heat generation layer has a small heat capacity. Therefore, the following problems occur when small-sized recording sheets are continuously fed. That is, heat is transmitted to the recording paper in the area where the recording paper passes (paper passing area) and is conveyed, whereas heat is accumulated in the area where the recording paper does not pass (non-paper passing area). Therefore, the temperature difference between the paper passing area and the non-paper passing area becomes large. In the fixing device, since the sheet passing area is normally maintained at a predetermined fixing temperature, the non-sheet passing area is excessively heated. When such an excessive temperature rise occurs, for example, the surface of the fixing roller deteriorates due to heat, and there is a problem that a difference in gloss occurs when a large size recording paper is passed immediately after passing a small size recording paper continuously. Arise. In addition, when silicon rubber is used in the vicinity of the induction heating element, the upper limit of the heat resistant temperature may be exceeded.

As a fixing device paying attention to this problem, for example, a coil (excitation coil) serving as a heating source is provided for each size of recording paper and the magnetic flux generation range is switched between small size paper and large size paper has been put into practical use. . Further, for example, in Patent Document 1, a cancel coil (demagnetizing coil) for canceling the magnetic flux formed by the exciting coil is provided in the non-sheet passing region, and the magnetic flux in the non-sheet passing region is canceled as necessary. As a result, excessive temperature rise in the non-sheet passing area is suppressed. For example, in Patent Document 2, an excessive temperature rise is suppressed by pressing a pressure roller with an external roller for heat equalization (heat equalization roller) to equalize the temperature.
JP 2001-60490 A JP 2002-55552 A

  However, the conventional electromagnetic induction heating type fixing device has the following problems. That is, there are various types of recording paper sizes such as A5T, B5T, A4T, and B5Y. For this reason, in the fixing device that suppresses the excessive temperature rise by dividing the excitation coil, it is necessary to provide an excitation coil for each size of the recording paper. However, in an electromagnetic induction heating type fixing device with a small heat capacity of the heat generating layer, since the heat smoothing effect is small, the excessive temperature rise has not been sufficiently suppressed. In addition, as the size types increase, the arrangement of the exciting coils becomes more difficult. This problem also applies to a fixing device that suppresses excessive temperature rise by a degaussing coil.

  Further, in the fixing device using the heat leveling roller, it is possible to suppress excessive temperature rise even if the paper size is different. However, even if the excessive temperature rise is suppressed by the heat leveling roller, it takes time to warm up the temperature leveling roller. For this reason, the advantages of the electromagnetic induction heating method that the warm-up time is short cannot be fully utilized. Further, once the heat is generated and then the heat of the abnormally high temperature portion is taken and cooled, as a result, the power for generating heat is wasted. Therefore, energy efficiency is low.

  The present invention has been made to solve the problems of the conventional fixing device described above. That is, an object of the present invention is to provide a fixing device that can cope with various types of paper sizes, has little energy loss, and suppresses an excessive temperature rise in a non-sheet passing region.

  A fixing device for solving this problem is an electromagnetic induction heating type fixing device for fixing an image on a recording medium to a recording medium, and includes a heating rotating body having a heat generating layer that generates electromagnetic induction heat, A pressure roller that is in pressure contact with the rotating body, a heat leveling roller that is opposed to the pressure roller in the longitudinal direction and that can be pressed and separated, and is disposed along the axial direction of the heating rotating body An excitation coil and a degaussing coil that is disposed in an area on the axis of the heating rotator so that the recording medium does not pass when the first-size recording medium passes, and that generates a magnetic field opposite to the excitation coil; If the size of the recording medium is equal to or smaller than the first size, power is supplied to the degaussing coil, and the size of the recording medium is equal to or smaller than the second size, which is smaller than the first size. , Pressurizing the heat leveling roller It is characterized in that to be pressed against the over La.

  That is, the fixing device of the present invention forms a nip portion between the fixing roller and the pressure roller, and conveys the recording medium to the nip portion to melt and fix the unfixed image. The fixing device according to the present invention is of an electromagnetic induction heating type, and an exciting coil is disposed along the axial direction of the heating rotator. The heating rotator may be a roller member or a belt member. In the fixing device of the present invention, a magnetic field is generated by supplying power to the exciting coil. An eddy current is generated in the heat generating layer (electromagnetic induction heat generating layer) of the heating rotator by the generation of the magnetic field, and the heat generating layer is heated.

  Further, in the fixing device of the present invention, a demagnetizing coil is disposed at the axial end of the heating rotator to generate a magnetic field opposite to the exciting coil. Specifically, the degaussing coil is disposed at a position that becomes a non-sheet passing region when the first size recording medium is passed. As a result, the magnetic field in the non-paper passing area can be extinguished.

  In the fixing device of the present invention, a heat leveling roller is attached to the pressure roller forming the heating rotator and the nip portion. The heat leveling roller is provided so as to be capable of being pressed and separated from the pressure roller. Then, the pressure of the pressure roller and the heating roller that forms the nip portion with the pressure roller can be made uniform by pressing the pressure roller.

  When the recording medium is passed, the degaussing coil and the heat leveling roller are operated as follows. First, if the size of the recording medium is equal to or smaller than the first size, power is supplied to the degaussing coil. For example, if the first size is “B4T”, when passing recording paper of B4T or less (for example, A4T paper), the magnetic field in the non-sheet passing area when the B4T paper is passed by the demagnetizing coil. Extinguish. As a result, the generation of heat in the non-sheet passing region can be suppressed, and the excessive temperature rise can be suppressed without heat loss.

  At this time, the heat leveling roller is separated from the pressure roller. For this reason, there is no heat loss due to heat transfer to the heat leveling roller. In addition, since there is little heat loss, the number of sheets that can be continuously fed does not decrease even if large-size paper is passed.

  Further, if the size of the recording medium is equal to or smaller than the second size, in addition to supplying power to the degaussing coil, the heat leveling roller is brought into pressure contact with the pressure roller. The second size is smaller than the first size. For example, assuming that the second size is “A4T”, the heat leveling roller is brought into pressure contact when recording paper (for example, B5T paper) of A4T or less is passed. As a result, the heat of the heating rotating body is leveled in the axial direction via the heat leveling roller, and excessive temperature rise in the non-sheet passing area is suppressed. In particular, the heat generated in the non-sheet passing area, which is not covered by the degaussing coil, moves to the heat leveling roller, and excessive temperature rise in the area is suppressed. Further, even a recording paper having a size smaller than that of B5T paper can be handled. Therefore, even when a recording medium having a different size is passed, it is possible to suppress overheating of the heating rotator.

  At this time, since electric power is supplied to the degaussing coil, the magnetic flux generated by the exciting coil concentrates on the sheet passing area of the recording medium. That is, the thermal energy in the paper passing area increases. For this reason, even if the heat leveling roller is pressed, the number of sheets that can be continuously fed does not decrease.

  In the fixing device of the present invention, it is better to arrange the exciting coil and the degaussing coil outside the heating rotator. That is, the diameter of the heating rotator can be reduced by disposing the magnetic flux generator outside the heating rotator. In addition, the heat capacity can be reduced and the warm-up time is shortened.

  According to the present invention, the excessive temperature rise is suppressed by the degaussing coil, so that energy loss is small. In addition, excessive temperature rise in a region where the degaussing coil cannot be covered is suppressed by a heat equalizing roller. As a result, it is possible to cope with various types of paper sizes while suppressing energy loss. Therefore, it is possible to realize a fixing device that can cope with various types of paper sizes, has little energy loss, and suppresses excessive temperature rise in the non-sheet passing region.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to an electromagnetic induction heating type fixing device provided in an electrophotographic printer.

  The image forming apparatus according to the present embodiment is an electrophotographic laser printer. As shown in FIG. 1, a laser oscillator 102, a polygon mirror 103, and a reflecting mirror 104 are arranged in an optical system, and a photoconductor is provided in an image processing unit. A drum 101, a charging charger 105, a developing device 106, a transfer charger 107, and a cleaning blade 108 are disposed. In addition, a paper feed roller 109, a paper discharge roller 115, a paper feed sensor 110, a paper discharge sensor 114, a fixing device 100, and the like are disposed in the transport unit.

  Next, the operation of the laser printer configured as described above will be briefly described. The photosensitive drum 101 rotates in the direction of the arrow in FIG. 1, and the surface is uniformly charged by the charging charger 105. Further, the laser light is modulated and emitted from the laser oscillator 102 based on the image signal. This laser beam is scanned in the main scanning direction by the polygon mirror 103, reflected by the reflection mirror 104, and incident on the photosensitive drum 101. Thereby, an electrostatic latent image is formed on the photosensitive drum 101. This electrostatic latent image is developed by the developing device 106 to become a toner image. The toner image is transferred onto the recording paper P fed by the paper feed roller 109 by a transfer charger 107 disposed opposite to the photosensitive drum 101. Thereafter, the recording paper P onto which the toner image has been transferred is heated in the fixing device 100, and the toner image is melted and fixed on the recording paper P by the heat. After the image is fixed, the recording paper P is discharged out of the apparatus by a paper discharge roller 115. With the above operation, printing for one sheet is performed.

  Next, the configuration of the fixing device 100 provided in the laser printer of this embodiment will be described. The fixing device 100 is an electromagnetic induction heating type fixing device. As shown in FIG. 2, the fixing device 100 includes a fixing roller 1, a pressure roller 2, a magnetic flux generator 3, a temperature sensor 4, and a heat leveling roller 8. Have.

  The fixing roller 1 and the pressure roller 2 are arranged in parallel in the longitudinal direction (axial direction). The pressure roller 2 is rotationally driven at a predetermined speed by a drive mechanism such as a motor. The pressure roller 2 is biased toward the fixing roller 1 by a biasing member such as a spring, and forms a nip portion with the fixing roller 1. Further, the fixing roller 1 is provided so as to be driven to rotate by the rotation of the fixing roller 1 by a pressure frictional force with the pressure roller 2.

  As shown in FIG. 3, in the fixing roller 1, a heat insulating layer 12, an electromagnetic induction heat generating layer 13, an elastic layer 14, and a release layer 15 are sequentially laminated on a cored bar 11. The roller hardness is set, for example, in the range of 30 to 90 degrees as Asker C hardness.

  The core metal 11 as the support layer is an aluminum pipe having a thickness of about 3 mm. The core metal 11 may be made of a heat resistant resin such as iron or PPS (polyphenylene sulfide). In order to prevent the metal core 11 from generating heat, it is preferable to use a nonmagnetic material that is less affected by electromagnetic induction heating.

  The heat insulating layer 12 is a layer for insulatingly holding the electromagnetic induction heat generating layer 13, and a sponge body of a member having heat resistance or elasticity (for example, rubber material or resin material) is applied. In addition, when a sponge member made of a rubber material or a resin material is used, the electromagnetic induction heat generating layer 13 can be insulated and held, and the electromagnetic induction heat generating layer 13 can be allowed to be bent to increase the nip width. Further, it is possible to reduce the roller hardness and improve the paper discharge performance and the recording paper separation performance. For example, when a silicon sponge material is applied to the heat insulating layer 12, the thickness is in the range of 2 mm to 10 mm, preferably 3 mm to 10 mm, and the hardness is 20 degrees to 60 degrees with the Asker rubber hardness meter, preferably 30 degrees. Each is set within a range of ˜50 degrees.

  Further, if a two-layer structure of a solid rubber layer as a lower layer and a sponge rubber layer as a surface layer is used instead of the heat insulating layer 12, durability can be improved. A roller having such a structure is used when it is used under relatively severe conditions such as high load and high-speed rotation, or when the heat insulating layer 12 is set thick to secure a nip width, or soft. Rubber breakage can be prevented when using a sponge layer.

  The electromagnetic induction heat generating layer 13 is a layer that generates Joule heat by excitation by the magnetic flux generator 3, and is a nickel electroformed belt layer having a thickness in the range of 10 μm to 100 μm, preferably 20 to 50 μm. The electromagnetic induction heating layer 13 may be made of a material having a high magnetic permeability such as a magnetic metal such as magnetic stainless steel and having an appropriate resistivity. Moreover, it is possible to use a non-magnetic material or a thin film of a conductive material such as metal. Further, a resin in which exothermic particles are mixed may be used. By using a resin-based material for the electromagnetic induction heat generating layer 13, it is possible to improve the separability.

  An eddy current flows through the electromagnetic induction heat generating layer 13 due to excitation by a magnetic flux generator 3 described later. Since the electromagnetic induction heat generating layer 13 has a small heat capacity and is in contact with the heat insulating layer 12, it quickly heats the elastic layer 14 or the release layer 15 located on the surface layer side of the fixing roller 1. Therefore, the surface temperature of the fixing roller 1 can be quickly reached to a desired temperature, and the necessary heat can be supplied immediately even if the recording paper is deprived of heat when the paper is passed.

  The elastic layer 14 is a layer for enhancing the adhesion between the recording paper and the surface of the fixing roller 1, and a member having heat resistance or elasticity (for example, a rubber material or a resin material) is applied. Specifically, heat-resistant elastomers such as silicon rubber and fluorine rubber that can withstand use at the fixing temperature can be used. Various fillers may be mixed in the elastic layer 14 for the purpose of thermal conductivity, reinforcement, and the like. Examples of thermally conductive particles include diamond, silver, copper, aluminum, marble, and glass. In addition, silica, alumina, magnesium oxide, boron nitride, beryllium oxide, and the like can be used.

  The thickness of the elastic layer 14 is set in the range of 10 μm to 800 μm, preferably 100 μm to 300 μm. If the thickness of the elastic layer 14 is less than 10 μm, it is difficult to obtain elasticity in the thickness direction. On the other hand, if the thickness of the elastic layer 14 exceeds 800 μm, the heat from the electromagnetic induction heat generating layer 13 hardly reaches the surface of the fixing roller 1 and the thermal efficiency is deteriorated.

  The elastic layer has a JIS hardness of 1 to 80 degrees, preferably 5 to 30 degrees. If it is within this range, it is possible to suppress poor toner fixability while suppressing a decrease in strength and poor adhesion of the elastic layer 14. As the silicone rubber, one-component, two-component or three-component or more silicone rubber, LTV type, RTV type or HTV type silicone rubber, condensation type or addition type silicone rubber can be used. In this embodiment, the silicon rubber layer has a JIS hardness of 10 degrees and a thickness of 200 μm.

  The release layer 15 is a layer for improving the release property of the surface, and a material that can withstand use at the fixing temperature is used. For example, fluororesins such as silicon rubber, fluororubber, PFA, PTFE, FEP, and PFEP are used. The thickness of the release layer 15 is 5 μm to 100 μm, desirably 10 μm to 50 μm. Moreover, in order to improve an interlayer adhesive force, you may perform the adhesion process by a primer etc. In addition, you may add a electrically conductive material, an abrasion-resistant material, a good heat conductive material etc. in the mold release layer 15 as needed.

  In the pressure roller 2, as shown in FIG. 4, a silicon sponge layer 22 and a release layer 25 are sequentially laminated on a cored bar 21. The pressure roller 2 is pressed against the fixing roller 1 with a load of 300 N to 500 N, and the width of the nip portion is in the range of 5 mm to 15 mm. The load may be changed depending on the type of recording paper.

  The cored bar 21 as a support layer is an aluminum pipe having a thickness of about 3 mm. The core metal 21 may be made of a heat resistant resin such as iron or PPS. In order to prevent the metal core 21 from generating heat, it is preferable to use a nonmagnetic material that is less affected by electromagnetic induction heating. The thickness of the silicon sponge layer 22 is designed in accordance with the use conditions within a range of 3 mm to 10 mm. Although a solid rubber layer can be used instead of the silicon sponge layer 22, a material having a low thermal conductivity is desirable so that heat transmitted from the fixing roller 1 through the nip portion is not lost. The release layer 25 is a layer for improving the surface releasability similarly to the fixing roller 1 and has a thickness of 10 μm to 50 μm and is made of a material that can withstand use at a fixing temperature. For example, fluororesins such as silicon rubber, fluororubber, PFA, PTFE, FEP, and PFEP are used.

  Further, if a two-layer structure having a solid rubber layer as a lower layer and a sponge rubber layer as a surface layer is used instead of the silicon sponge layer 22, durability can be improved. A roller having such a structure is used in a particularly severe condition such as a high load or high-speed rotation, or when the thickness of the silicon sponge layer 22 is set to be thick in order to secure a nip width, When using a soft sponge layer, the rubber can be prevented from breaking.

  The magnetic flux generation unit 3 includes an exciting coil 31, a magnetic core 32, a coil bobbin 33, and a degaussing coil 34. The magnetic flux generator 3 is located outside the fixing roller 1 and is disposed along the longitudinal direction so as to face the fixing roller 1. Further, a high frequency inverter 5 (excitation circuit) and a control circuit 6 are connected to the magnetic flux generation unit 3.

  The magnetic core 32 is a long member having a substantially E-shaped cross section and a length corresponding to the longitudinal dimension of the fixing roller 1. The magnetic core 32 is provided with a portion projecting toward the fixing roller at the center portion so as to have a substantially E shape, thereby improving the heat generation efficiency. As the material of the magnetic core 32, a material having high permeability and low loss (for example, ferrite) is used. In the case of an alloy such as permalloy, the eddy current loss in the core increases in the high frequency region, so a laminated structure is preferable.

  The magnetic core 32 has both functions of increasing the efficiency of the magnetic circuit and magnetic shielding. If there is a means capable of sufficient magnetic shielding, an air core (no core) may be used. In addition, if a core material made of a resin material mixed with magnetic powder is used, the design flexibility of the shape is increased.

  The exciting coil 31 has a structure in which a conducting wire is wound along the long magnetic core 32 in the longitudinal direction. The exciting coil 31 is connected to the high-frequency inverter 5 and is supplied with high-frequency power of 100 W to 2000 W. For this reason, a thin wire bundled within a range of several tens to several hundred wires is used as a litz wire. In consideration of the case where heat is transferred to the winding, it is covered with heat-resistant resin.

  Further, an alternating current of 10 kHz to 100 kHz is applied to the excitation coil 31 by the high frequency inverter 5. The magnetic flux induced by the alternating current passes through the ferrite core 32 without leaking outside, and further passes through the electromagnetic induction heat generating layer 13 of the fixing roller 1. The protrusion of the magnetic core 32 leaks to the outside of the magnetic core 32 and penetrates the electromagnetic induction heat generating layer 13 of the fixing roller 1. And when an eddy current flows through the electromagnetic induction heat generating layer 13, the electromagnetic induction heat generating layer 13 itself generates Joule heat. As a result, the fixing roller 1 is heated.

  As shown in FIG. 5, the degaussing coil 34 has a structure in which a conducting wire is wound around both ends in the longitudinal direction. The degaussing coil 34 is also connected to the high frequency inverter 5 and supplied with high frequency power of 100 W to 2000 W. Further, the degaussing coil 34 is appropriately turned on and off by the control circuit 6. When the demagnetizing coil 34 is turned on by the control circuit 6, a magnetic field opposite to that of the exciting coil 31 is generated, and the magnetic field in the region where the demagnetizing coil 34 is disposed decreases. Thereby, generation | occurrence | production of Joule heat is suppressed. Details of the on / off control of the degaussing coil 34 will be described later.

  The temperature sensor 4 is for detecting the surface temperature of the fixing roller 1 and is disposed in the vicinity of the nip portion between the fixing roller 1 and the pressure roller 2. As the temperature sensor 4, for example, a thermistor can be used. A detection signal of the temperature sensor 4 is input to the control circuit 6.

  The control circuit 6 performs control of the high-frequency inverter 5 (that is, control of the exciting coil 31 and the demagnetizing coil 34) and control of a press-contact / separation mechanism 81 described later. The control circuit 6 controls the high frequency inverter 5 based on the detection signal of the temperature sensor 4 to increase or decrease the power supply to the exciting coil 31 and the degaussing coil 34. That is, automatic control is performed so that the surface temperature of the fixing roller 1 is constant.

  The heat leveling roller 8 is disposed so as to face the pressure roller 2 in the entire longitudinal direction, and is provided so as to be capable of being pressed and separated by a pressure contact / separation mechanism 81. Further, the heat leveling roller 8 is configured to be driven and rotated by the pressure roller 2 when being brought into pressure contact with the pressure roller 2. When the heat leveling roller 8 comes into pressure contact with the pressure roller 2, heat moves in the axial direction of the heat leveling roller 8, and the temperature distribution in the axial direction of the pressure roller 2 is made uniform. Further, the temperature distribution of the fixing roller 1 that is in pressure contact with the pressure roller 2 to form the nip portion is also made uniform.

  As the material of the heat leveling roller 8, a metal material having good thermal conductivity is desirable. The thermal conductivity is at least 12 W / (m · K) or more, preferably 100 W / (m · K) or more, more preferably 200 W / (m · K) or more. Specifically, a material having high strength such as aluminum, iron, and SUS material is desirable. In particular, it is desirable to use aluminum material with high thermal conductivity.

  Further, when the heat leveling roller 8 has a small heat capacity per unit length, the heat is radiated without moving in the axial direction. Therefore, in order to obtain the effect of soaking, it is necessary to set the heat capacity per unit length of the heat soaking roller 8 to a predetermined value or more. On the other hand, if the heat capacity is too large, heat is absorbed by the heat equalizing roller 8, so that the effect of temperature equalization is reduced. Therefore, the heat capacity per unit length is preferably 200 to 1000 J / (m · K), more preferably 250 to 500 J / (m · K). Specifically, when the diameter of the heat equalizing roller is 15 mm to 30 mm, the thickness is 2 mm to 5 mm for aluminum, and 1 mm to 3 mm for iron or SUS material. Is preferred.

  The heat leveling roller 8 is urged toward the pressure roller 2 by the action of the solenoid and spring of the pressure contact / separation mechanism 81, and forms a nip portion with the pressure roller 2. The pressure contact / separation mechanism 81 is operated by an on / off signal from the control circuit 6. In this embodiment, the pressure contact state is turned on and the separated state is turned off.

  The heat leveling roller 8 is pressed against the pressure roller 2 with a load of 80 N to 120 N, and the width of the nip portion is in the range of 2 mm to 5 mm. The width of the nip portion may be adjusted by appropriately changing the load according to various conditions.

  The heat leveling roller 8 may incorporate a heating source such as a heater lamp or a resistance heating element. Incorporating a heating source has the effect of assisting the temperature rise of the pressure roller 2 and making the temperature constant. Further, the temperature rise in the non-sheet passing region can be further prevented by press-contacting with the heat source turned off during the sheet passing. That is, the heat in the non-sheet passing area of the fixing roller 1 can be moved to the low temperature sheet passing area via the pressure roller 2 and the heat leveling roller 8.

  Next, a fixing operation in the fixing device 100 of this embodiment will be described. First, as a warm-up operation, the pressure roller 2 is rotationally driven, and the fixing roller 1 is also rotated in accordance with this. The electromagnetic induction heat generating layer 13 of the fixing roller 1 generates heat due to the action of the magnetic flux generated by the magnetic flux generating unit 3. At this time, power supply to the degaussing coil 34 is turned off, and power is supplied only to the excitation coil 31. Then, the surface temperature of the fixing roller 1 is automatically controlled so as to become a predetermined temperature. Since the electromagnetic induction heat generating layer 13 has a small heat capacity and is insulated and held by the heat insulating layer 12, the elastic layer 14 or the release layer 15 located on the surface layer side of the fixing roller 1 is rapidly heated. In other words, the surface of the fixing roller 1 quickly reaches the fixable temperature.

  After the warm-up operation is completed, the recording paper P carrying an unfixed toner image is conveyed to the nip portion between the fixing roller 1 and the pressure roller 2 (see FIGS. 2 and 5). At that time, the toner image on the recording paper P faces the fixing roller 1. The recording paper P introduced into the nip portion is nipped and conveyed through the nip portion and heated by heat from the fixing roller 1. As a result, the unfixed toner image is melted and fixed on the recording paper P.

  The recording paper P after the fixing process at the nip portion is separated from the fixing roller 1 and carried out. At that time, even if the recording paper P is stuck on the surface of the fixing roller 1 by a separation claw or the like arranged in contact with the surface of the fixing roller 1, it is forcibly separated. As a result, jamming in the fixing device 100 is prevented.

  Next, the temperature control of the fixing roller 1 at the time of paper passing will be described based on the flowchart of FIG. First, the demagnetizing coil 34 and the heat leveling roller 8 are set to an initial state. That is, the demagnetizing coil 34 is turned off, and the heat equalizing roller 8 is turned off (S1). Of course, the exciting coil 31 is on.

  Next, it is determined whether or not the size of the paper to be passed is equal to or smaller than a predetermined size (hereinafter referred to as “first size”, specifically, “B4T size” in the present embodiment) (S2). . If the paper size is larger than the first size (S2: NO), the degaussing coil 34 is turned off (S4), and the process proceeds to S8. On the other hand, when the paper size is equal to or smaller than the first size (S2: YES), the degaussing coil 34 is turned on (S3), and the process proceeds to S5.

  Next, it is determined whether or not the size of the paper to be passed is smaller than the first size (hereinafter referred to as “second size”, specifically, “A4T size” in this embodiment). (S5). If the paper size is larger than the second size (S5: NO), the heat leveling roller 8 is turned off (S7), and the process proceeds to S8. On the other hand, when the paper size is equal to or smaller than the second size (S5: YES), the heat leveling roller 8 is turned on (S6), and the process proceeds to S8. When the heat leveling roller 8 is turned on, heat moves in the axial direction in a region in contact with the heat leveling roller 8, and the temperature is made uniform.

  Next, it is determined whether or not all sheets have been passed (S8). If not finished (S8: NO), the process returns to S2, and the processes after S2 are repeated. If completed (S8: YES), this control is terminated.

  In the temperature control of this embodiment, if the paper size is B4T or less, the demagnetizing coil 34 is turned on to suppress excessive temperature rise at the end of the fixing roller. That is, by supplying power to the degaussing coil 34, the magnetic field disappears in the regions at both ends in the axial direction, and the generation of Joule heat is suppressed.

  FIG. 7 shows the temperature distribution of the fixing roller 1. When the paper size is larger than B4T, that is, when large-size paper is continuously printed, the entire heating area becomes the paper-passing area, and thus no excessive temperature rise occurs (at the time of large-size continuous printing in FIG. 7). On the other hand, when the paper size is B4T, that is, when continuous printing is performed on small-size paper, if the degaussing coil 34 is left off, an excessive temperature rise occurs in the non-sheet passing regions at both ends (when the degaussing coil is OFF in FIG. 7). . Therefore, the demagnetizing coil 34 located on the non-sheet passing area is turned on to eliminate the magnetic field in the non-sheet passing area, thereby suppressing heat generation in the non-sheet passing area. As a result, excessive temperature rise at the end of continuous printing of small-size paper is suppressed (when the demagnetizing coil is ON in FIG. 7).

  In the temperature control of the present embodiment, if the paper size is A4T or less, the heat leveling roller 8 is turned on to suppress an excessive temperature increase in a non-paper passing area where the magnetic field is not lost by the degaussing coil 34. To do. That is, by bringing the heat leveling roller 8 into pressure contact with the pressure roller 2, the heat generated by the fixing roller 1 moves in the axial direction via the heat leveling roller 8, and the temperature of the fixing roller 1 is uniform in the axial direction. It becomes.

  FIG. 8 shows the flow of heat in the fixing roller 1. As shown in FIG. 8, when the heat leveling roller 8 is pressed, heat generated mainly in a non-sheet passing area and not affected by the demagnetization coil 34 moves. Therefore, if the paper is smaller than the small size paper, partial overheating of the fixing roller 1 is suppressed without specifying the paper size. When the demagnetizing coil 34 is turned on, the magnetic flux generated from the exciting coil 31 is concentrated in the center. As a result, the thermal energy in the center increases. For this reason, even when the heat leveling roller 8 is pressed, the heat can be made uniform without decreasing the number of continuous sheets.

  Note that when the recording paper having a size larger than the second size is passed, the heat leveling roller 8 is separated from the pressure roller 2. Therefore, there is no increase in heat capacity and heat radiation area. Therefore, the sheet passing interval may be short, and the continuous sheet passing number is not reduced.

  As described above in detail, the fixing device 100 of this embodiment is an electromagnetic induction heating type fixing device, and the exciting coil 31 is provided outside the fixing roller 1 along the axial direction thereof. Further, a demagnetizing coil 34 is provided on both ends of the fixing roller 1 in the axial direction. If the size of the recording paper is equal to or smaller than the first size, that is, if the small-size paper is passed, the degaussing coil 34 is turned on. As a result, the magnetic field in the non-sheet passing area disappears, and excessive temperature rise in the non-sheet passing area of the fixing roller 1 is suppressed. At this time, the heat leveling roller 8 is separated and the heat loss is small.

  Further, the fixing roller 100 of this embodiment is provided with a heat leveling roller 8 that can be pressed against and separated from the pressure roller 2. If the size of the recording paper is equal to or smaller than the second size, that is, if the recording paper is smaller than the small size paper, the demagnetizing coil 34 is turned on and the heat leveling roller 8 is set to the pressure roller. 2 and press. As a result, the heat in the non-sheet passing region where the magnetic field has not disappeared moves in the axial direction via the heat leveling roller 8. That is, the temperature of the fixing roller 1 is made uniform. For this reason, even when a recording sheet having a smaller size than a small-size sheet is passed, an excessive temperature rise of the fixing roller 1 is suppressed. At this time, since the magnetic flux is concentrated in the central portion, the thermal energy in the central portion is large. Therefore, a fixing device that can cope with various types of paper sizes, has a small energy loss, and suppresses an excessive temperature rise in the non-sheet passing region is realized.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, in the embodiment, the present invention is applied to a laser printer, but the present invention is not limited to this. That is, even a copying machine, scanner, FAX, word processor, or the like can be applied as long as it has a fixing device. Moreover, it is not limited to color but may be dedicated to monochrome images. Further, a tandem method or a four-cycle method may be used.

  Further, the on / off control of the demagnetizing coil 34 and the heat leveling roller 8 may be performed not only by the paper size but also by the paper thickness, basis weight, paper temperature, paper passing speed, etc., or a combination thereof. For example, an on / off combination may be determined based on a list of paper sizes and basis weights, and correction processing may be performed based on the temperature of the paper or the temperature of the end of the fixing roller 1.

  Further, the magnetic flux generation unit 3 may be outside or inside the heating roller 1. When arranged outside as in the embodiment, the heat capacity can be reduced and the warm-up time is shortened. That is, when the magnetic flux generating unit 3 is built in, the built-in material also becomes a factor for increasing the heat capacity. Therefore, a low heat capacity material such as a sponge roller can be placed inside the heating roller 1 by providing the magnetic flux generator 3 on the outside.

  In the embodiment, the fixing roller is heated. However, the present invention is not limited to this. For example, a type in which a fixing belt heated by a magnetic flux generation unit is provided and the fixing belt and a pressure roller are arranged to face each other may be used.

1 is a diagram illustrating a schematic configuration of a printer according to an embodiment. 1 is a diagram illustrating a schematic configuration of a fixing device according to an embodiment. 2 is a cross-sectional view illustrating a schematic configuration of a fixing roller. FIG. It is sectional drawing which shows schematic structure of a pressure roller. It is sectional drawing which shows schematic structure of each coil in a magnetic flux generation part. It is a flowchart which shows control of a degaussing coil. 3 is a graph showing a temperature distribution of a fixing roller. FIG. 3 is a diagram illustrating a heat flow of the fixing device.

Explanation of symbols

1 Fixing roller (heated rotating body)
2 Pressure roller (Pressure roller)
3 Magnetic flux generator 31 Excitation coil (Excitation coil)
32 Magnetic core 33 Coil bobbin 34 Demagnetizing coil (demagnetizing coil)
4 Temperature sensor 5 High frequency inverter 6 Control circuit 8 Heat equalizing roller (heat equalizing roller)
100 Fixing device (fixing device)

Claims (2)

In an electromagnetic induction heating type fixing device for fixing an image on a recording medium to the recording medium,
A heating rotator with a heat generating layer that generates electromagnetic induction heat;
A pressure roller in pressure contact with the heating rotator;
A heat-equalizing roller which is disposed so as to face the pressure roller along the longitudinal direction and to be capable of being pressed and separated;
An exciting coil disposed along the axial direction of the heating rotor;
A demagnetizing coil that is disposed in an area on the axis of the heating rotator so that the recording medium does not pass when the recording medium of the first size passes, and that generates a magnetic field opposite to the excitation coil. And
If the size of the recording medium is less than or equal to the first size, power is supplied to the degaussing coil,
A fixing device, wherein if the size of a recording medium is equal to or smaller than a second size that is smaller than the first size, the heat leveling roller is pressed against the pressure roller. The fixing device according to claim 1,
The fixing device according to claim 1, wherein the exciting coil and the degaussing coil are located outside the heating rotator.

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