JP4353120B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device that heats and fixes a toner image on a recording medium. More specifically, the present invention relates to a fixing device that achieves both shortening of warm-up time and suppression of overheating of the fixing rotating body.

  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 including a 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 used. In this roller type fixing device, a heat source is provided in at least one of the roller pair, and the toner image is fixed on the recording paper by the heat and the pressure of the roller.

  In the fixing device, the following problems occur when a sheet is continuously passed by a fixing roller having a low heat capacity (for example, an electromagnetic induction heating method). That is, in the fixing roller having a small heat capacity, the excessive temperature rise in the non-sheet passing region becomes conspicuous during continuous passing of recording paper. Specifically, when the recording paper is supplied and conveyed to the fixing device, in the paper passing area where the fixing roller and the recording paper are in contact with each other, the heat of the fixing roller is removed and the surface temperature is lowered. For this reason, the heating source is controlled so that the surface temperature does not fall below the predetermined fixing temperature. On the other hand, in the non-sheet passing area where the fixing roller and the recording sheet do not contact each other, the heat continues to be generated in accordance with the temperature control of the sheet passing area even though the heat is not taken away. For this reason, the surface temperature of the fixing roller exceeds the fixing temperature, resulting in excessive temperature rise.

  When the temperature of the fixing roller is excessively high, not only does the material of the fixing roller itself change, but also the pressure roller, separation claw, cleaning member, support frame, etc. It will cause damage and deformation. In order to solve this problem, for example, a fixing device (for example, Patent Document 1) is disclosed in which an external heating roller that heats only the central portion of the fixing roller is detachable.

  Further, in the fixing device, it is required to shorten the warm-up time. That is, when a fixing roller having a low heat capacity is used, only the surface layer of the roller can be positively heated. However, if both rollers are rotated for pre-rotation after the power is turned on, most of the heat of the fixing roller is taken away by the pressure roller that has been cooled until then. Therefore, it takes a long time for the fixing roller to rise to the set temperature, that is, until the warm-up is completed.

Therefore, an auxiliary heating method has been proposed in which a heating unit is attached to the fixing roller or the pressure roller, and heating is performed in parallel by the heating unit (for example, Patent Document 2). In this system, each roller can be heated quickly by an external heating roller heated by a halogen lamp or the like, which contributes to shortening the warm-up time.
JP 2003-45638 A Japanese Patent Laid-Open No. 3-180883

  However, the conventional fixing device described above has the following problems. That is, it is impossible to achieve both shortening of the warm-up time and suppression of overheating of the fixing roller. That is, even when the fixing roller is heated by the external heating roller as in Patent Document 1 at the time of warming up, the effect of shortening the warming up is small. On the other hand, even if the pressure roller is always heated by the external heating roller as in Patent Document 2, the problem of overheating of the fixing roller is not solved.

  Further, when an external heating roller that can be contacted and separated as in Patent Document 1 is provided, the mechanical configuration becomes complicated. In addition, the number of parts for realizing the mechanism that enables contact and separation increases, resulting in an increase in cost.

  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 achieves both a reduction in warm-up time and suppression of excessive temperature rise of the fixing rotating body with a simple device configuration.

A fixing device for solving this problem is a fixing device for fixing an image on a recording medium to the recording medium. The fixing device fixes the image on the recording medium by a first heating source in a region having a width equal to the passing width of the large size recording paper. A fixing rotator that is heated in a certain heating region, a pressure rotator that is in contact with the fixing rotator and forms a nip for conveying a recording medium, and a second heating source at least on the axial direction of the fixing rotator An area whose position is equal to the heating area of the fixing rotator is heated, is in contact with the pressure rotator, and has an auxiliary rotator having high thermal conductivity . The auxiliary rotator is energized by the second heating source during warm-up. is turned on, at the time of paper passing, energization of the second heat source is turned on when the size of the recording sheet of large size, when the size of the recording sheet is smaller smaller size than large size energization of the second heat source Is turned off There.

  In the fixing device of the present invention, a nip portion is formed by a fixing rotator and a pressure rotator, and a recording medium is conveyed through the nip portion to fix an image. The fixing device of the present invention includes an auxiliary rotator that contacts the pressure rotator. A roller member and a belt member correspond to the fixing rotating body. As the fixing rotator, for example, a belt heating type or an electromagnetic induction heating type is suitable. By using such a fixing rotator with a low heat capacity, the warm-up time can be shortened.

  The auxiliary rotating body operates differently when warming up and when passing paper. That is, on / off control of energization of the second heating source is performed according to the operation state of the fixing device. Specifically, at the time of warming up, the energization of the second heating source is turned on to heat the pressure rotator. That is, it acts as a heating source for the pressure rotating body. This shortens the warm-up time.

  On the other hand, when the paper is passed, the energization of the second heating source is turned off, and the temperature becomes low. Therefore, when the non-sheet passing area of the fixing rotator becomes a high temperature state due to continuous passing of small size paper, heat moves from the non-sheet passing area through the pressure rotator. That is, the auxiliary rotator acts as a heat leveling member. As a result, the surface temperature of the fixing rotator is smoothed, so that the material quality of the fixing rotator itself is altered, and damage or deformation of the pressure rotator is suppressed.

  In the auxiliary rotating body of the present invention, the energization of the second heating source may be turned on during warm-up, and the on / off of energization of the second heating source may be selected depending on the size of the recording paper to be passed. . Alternatively, a temperature detection unit for detecting the surface temperature of the non-sheet passing area is provided, and the second heating source is turned on during warming-up, and the second heating source is turned on / off according to the detection value of the temperature detecting unit during sheet feeding. It may be done.

  That is, the auxiliary rotator not only simply turns off the power supply of the second heating source when passing paper, but also turns on and off the power supply of the second heat source depending on the size of the recording medium to be passed and the surface temperature of the fixing rotator. Switch. Thereby, finer temperature control can be performed.

  According to the present invention, the heating source of the auxiliary rotator that is in contact with the pressure rotator is on / off controlled. Thereby, the auxiliary rotator has both a function as a heating source for the pressure rotator and a function as a heat leveling member for the fixing rotator. Further, the auxiliary rotator remains in contact with the pressure rotator and does not require a contact / separation mechanism. Accordingly, there is provided a fixing device that achieves both a shortening of warm-up time and suppression of excessive temperature rise of the fixing rotating body with a simple device configuration.

  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.

[First embodiment]
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. The 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 roller 1, the pressure roller 2, the magnetic flux generator 3, the temperature sensors 41 and 42, the external heating roller 5, and the like. have.

  The fixing roller 1 and the pressure roller 2 are arranged in parallel in the longitudinal direction (axial direction). The fixing roller 1 is rotationally driven at a predetermined speed by a driving 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 pressure roller 2 is provided so as to be driven to rotate by the rotation of the fixing roller 1 by the frictional force of contact with the fixing roller 1.

  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. Therefore, 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 7 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.

  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.

  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 preferably has a JIS hardness of 1 to 80 degrees, preferably 5 to 30 degrees. Within this range, it is possible to suppress the toner fixing property failure while suppressing the strength reduction and adhesion failure 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 releasability of the surface of the fixing roller 1, and a material that can withstand use at a 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. 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. The release layer 25 is a layer for improving the surface releasability like the fixing roller 1, 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 magnetic flux generation unit 3 includes an excitation coil 31, a magnetic core 32, and a coil bobbin 33. 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. In addition, a drive circuit 34 and a control circuit 9 are connected to the magnetic flux generator 3.

  The magnetic core 32 is a long member having a length corresponding to the length of the fixing roller 1 in the longitudinal direction. 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.

  Further, the effective width W of the magnetic flux guide of the magnetic core 32 is substantially the same as the paper passing width of the large size paper P1, as shown in FIG. That is, the heating area is almost the same as the sheet passing width of the large size paper P1. Furthermore, the magnetic flux in the magnetic core 32 is substantially uniform in the longitudinal direction. For this reason, the heat generation amount of the fixing roller 1 is also substantially uniform in the longitudinal direction.

  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 a high-frequency converter 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 a high frequency converter (drive circuit 34). 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.

  The temperature sensor 41 is for detecting the surface temperature of the end portion in the longitudinal direction of the fixing roller 1, that is, the portion that becomes a non-sheet passing region when small-size paper is passed, and the fixing roller 1 and the pressure roller 2. It is arrange | positioned in the vicinity of the nip part. The temperature sensor 42 is for detecting the surface temperature of the central portion in the longitudinal direction of the fixing roller 1, that is, the portion that becomes a sheet passing area when a small size sheet is passed. It is disposed in the vicinity of the nip portion between the roller 1 and the pressure roller 2. As the temperature sensor 41 and the temperature sensor 42, for example, a thermistor can be used.

  The temperature control of the fixing roller 1 is performed by the control circuit 9 based on the detection signal of the temperature sensor 42. That is, the control circuit 9 controls the drive circuit 34 based on the detection signal from the temperature sensor 42 and controls the power supply from the drive circuit 34 to the excitation coil 31. Thereby, the surface temperature of the fixing roller 1 is automatically controlled so as to become a predetermined temperature.

  The external heating roller 5 includes a heater lamp 51 as a heating source. The material of the external heating roller 5 may be a material having high thermal conductivity. For example, aluminum material can be applied. The external heating roller 5 is urged toward the pressure roller 2 by an urging means such as a spring, and is in contact with the entire area in the longitudinal direction of the pressure roller 2 as shown in FIG. The external heating roller 5 is rotatably provided so as to follow the pressure roller 2. In addition, a drive circuit 52 and a control circuit 9 are connected to the heater lamp 51.

  Next, a fixing operation in the fixing device 100 of this embodiment will be described. First, as a warm-up operation, the fixing roller 1 is rotationally driven, and the pressure roller 2 is also rotated in accordance with this. Then, the energization to the exciting coil 31 of the magnetic flux generator 3 is turned on. As a result, the electromagnetic induction heating layer 13 of the fixing roller 1 generates heat. 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 positioned on the surface layer side of the fixing roller 1 is rapidly heated.

  Further, during the warm-up operation, energization of the heater lamp 51 of the external heating roller 5 is also turned on. As a result, the external heating roller 5 is heated, and the heat is propagated to the pressure roller 2 to quickly warm the surface layer of the pressure roller 2. Since the surface layer of the pressure roller 2 is warmed, the propagation of heat from the fixing roller 1 to the pressure roller 2 is suppressed. Therefore, the surface temperature of the fixing roller 1 quickly reaches a predetermined temperature, and the warm-up operation is completed in a short time.

  After the warm-up operation is completed, the recording paper P carrying the unfixed toner image is conveyed to the nip portion between the fixing roller 1 and the pressure roller 2 (see FIG. 2). 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.

  In the fixing process, the power supply to the heater lamp 51 of the external heating roller 5 is turned off. Thereby, the supply of heat from the external heating roller 5 is cut off, and the surface temperatures of the external heating roller 5 and the pressure roller 2 are lowered. For this reason, for example, during continuous passage of small-size paper, even if the heat supply on the fixing roller 1 side becomes excessive in the non-sheet passing region, the excessively supplied heat is externally heated via the pressure roller 2. Move to roller 5. That is, the external heating roller 5 removes heat from the excessive temperature rise portion of the fixing roller 1, and the surface temperature of the fixing roller 1 is smoothed. Thereby, the excessive temperature rise of the fixing roller 1 is suppressed.

  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 sticks to 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. That is, jamming in the fixing device 100 is prevented.

  Note that on / off control of energization to the heater lamp 51 is performed by the control circuit 9. Further, by performing on / off control of energization to the heater lamp 51 based on the size of the recording paper and the surface temperature of the fixing roller 1, more detailed temperature adjustment can be performed.

  For example, when the on / off control is performed according to the size of the recording paper, the on / off is switched depending on whether or not the size of the recording paper is equal to the heating area of the fixing roller 1. That is, if the size of the recording paper is a large size paper P1 (see FIG. 5) equal to the heating area, the energization to the heater lamp 51 is turned on. Thereby, the surface of the pressure roller 2 is warmed, and unfixed toner images are suppressed. On the other hand, for the small size paper P2, the energization of the heater lamp 51 is turned off. As a result, the heat of the non-sheet passing area of the fixing roller 1 is taken away, and the excessive temperature rise of the fixing roller 1 is suppressed. That is, more precise temperature control can be performed.

  Further, when the on / off control is performed according to the surface temperature of the fixing roller 1, the on / off is switched depending on whether or not the temperature of the temperature sensor 41 that detects the temperature of the non-sheet passing region is equal to or higher than a threshold value. In addition, on / off may be switched depending on the difference between the detection value of the temperature sensor 41 in the non-sheet passing area and the detection value of the temperature sensor 42 in the sheet passing area. In other words, if the non-sheet passing area is excessively heated, the external heating roller 5 is caused to function as a heat leveling member, and if the non-sheet passing area is not excessively heated, the external heating roller 5 is caused to function as a heating member.

  Next, the measurement result of the temperature distribution of the fixing roller when continuously passing small-size paper will be described. In this experiment, the temperature of the fixing roller was adjusted so that the surface temperature of the fixing roller was 170 ° C., and 100 small-size sheets were continuously fed. FIG. 7 shows the temperature distribution of the fixing roller when the external heating roller is brought into contact with the pressure roller and continuously passes small size paper. FIG. 8 shows the small size without bringing the external heating roller into contact with the pressure roller. The temperature distribution of the fixing roller when the paper is continuously fed is shown.

  When the external heating roller was brought into contact with the pressure roller (FIG. 7), the peak value in the non-sheet passing area was about 190 ° C., and the temperature difference from the sheet passing area was about 30 ° C. On the other hand, when the external heating roller is not brought into contact with the pressure roller (FIG. 8), the peak value in the non-sheet passing area exceeds 220 ° C., and the temperature difference from the sheet passing area is 70 ° C. or more. became. From this experimental result, it was found that excessive temperature rise in the non-sheet passing region can be suppressed by contacting the external heating roller.

  As described in detail above, the fixing device 100 according to the present embodiment includes the external heating roller 5 that is in pressure contact with the pressure roller 2. The external heating roller 5 is energized by the heater lamp 51 when warming up. Therefore, heat is supplied to the pressure roller 2. As a result, the pressure roller 2 is heated early and the movement of heat from the fixing roller 1 to the pressure roller 2 is suppressed, and the warm-up time is shortened.

  Also, the heat lamp 51 is turned off when the paper is passed. Therefore, when the non-sheet passing area in the fixing roller 1 becomes a high temperature state due to continuous passing of small size paper, heat is transferred from the non-sheet passing area to the external heating roller 5 via the pressure roller 2. . Thereby, the surface temperature of the fixing roller 1 is smoothed. Therefore, it is possible to prevent deterioration of the material of the fixing roller 1 itself, and damage or deformation of the pressure roller 2, the separation claw, the cleaning member, the support frame, or the like disposed in contact with or adjacent to the fixing roller 1.

  The external heating roller 5 is always in pressure contact with the pressure roller 2. Therefore, no contact / separation mechanism is required. Therefore, with a simple structure, it is possible to achieve both shortening of the warm-up time and suppression of overheating of the fixing roller 1.

[Second form]
The fixing device 200 is a belt heating type fixing device, and includes a fixing body 6, a pressure body 7, and an external heating roller 5 as shown in FIG. 9. Further, the fixing body 6 includes an endless fixing belt 61, a pad member 62, a heater lamp 63, a guide member 64, and a temperature sensor 4.

  The fixing body 6 and the pressure body 7 are arranged in parallel in the longitudinal direction (axial direction). The fixing belt 61 is rotationally driven at a predetermined speed by a driving mechanism such as a motor. Further, the fixing member 6 and the pressure member 7 are pressed against each other by the pad member 62 included in the fixing member 6, and a nip portion is formed between the fixing member 6 and the pressure member 7. Further, the fixing body 6 is provided to rotate following the rotation of the pressure body 7. The pressure contact force of the pressing body 7 to the pad member 62 is in the range of 100N to 400N as a whole, depending on the system speed.

  Further, the external heating roller 5 incorporating the heater lamp 51 is in contact with the pressurizing body 7 and is provided to rotate following the rotation of the pressurizing body 7. The pressure contact force of the external heating roller 5 to the pressure body 7 is in the range of 50N to 200N depending on the system speed.

  As shown in FIG. 10, the fixing belt 61 has an elastic layer having a thickness of 50 μm to 400 μm on a base 611 made of resin (for example, polyimide) or metal (for example, nickel or stainless steel) having a thickness of 30 μm to 120 μm. 612 (for example, silicon rubber) and a release layer 613 (for example, fluororesin) are sequentially laminated. A carbon resin may be dispersed in the resin base 611 and the elastic layer 612 to increase the heat absorption efficiency. Further, the inner diameter of the fixing belt 61 is in the range of 25 mm to 65 mm.

  As shown in FIG. 11, the pad member 62 has an elastic layer 622 (for example, silicon rubber) having a thickness of 0.5 mm to 5 mm and a thickness on a metal support frame 621 having a thickness of 2 mm to 10 mm. A low friction layer 623 (for example, fluorine-containing glass cloth) having a thickness of about 0.1 mm is sequentially laminated. The low friction layer 623 serving as the surface layer does not need to be integrated with the pad member 62 and may be a separate member as a sliding sheet member.

  As shown in FIG. 12, the pressure member 7 is formed on a metal core 71 (eg, aluminum) having a thickness of 0.3 mm to 3 mm and an elastic layer 72 (eg, having a thickness of 0.2 mm to 3 mm). Silicon rubber) and a release layer 73 (for example, fluororesin) having a thickness of 10 μm to 50 μm are sequentially laminated. Moreover, the internal diameter of the pressurizing body 7 is in the range of 20 mm to 60 mm.

  The temperature sensor 4 is for detecting the temperature of the fixing belt 61 and is included in the fixing belt 61. Heating and temperature control of the fixing belt 61 are performed by a control circuit based on a detection signal of the temperature sensor 4. That is, the control circuit controls the drive circuit based on the detection signal of the temperature sensor 4 and controls the power supply from the drive circuit to the heater lamp 65. Thereby, the temperature of the fixing belt 61 is automatically controlled so as to become a predetermined temperature.

  The external heating roller 5 includes a heater lamp 51 as a heating source. The external heating roller 5 is the same as the external heating roller 5 of the first embodiment and has high thermal conductivity. The external heating roller 5 is urged toward the pressure body 7 by an urging means such as a spring, and is in contact with the entire area of the pressure body 7 in the longitudinal direction. The heater lamp 51 is connected to a drive circuit and a control circuit.

  Even in the belt-type fixing device 200 configured as described above, the overheating of the fixing belt 61 is suppressed by performing on / off control of energization to the heater lamp 51 in the same manner as the fixing device 100 of the first embodiment. it can. For example, when warming up, power to the heater lamp 51 is turned on to increase the speed of warming up. On the other hand, when the paper is passed, the heater lamp 51 is turned off to make the surface temperature of the fixing belt 61 uniform. Thereby, both shortening of the warm-up time and suppression of overheating of the fixing belt 61 can be achieved.

  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.

1 is a cross-sectional view illustrating a schematic configuration of a printer according to an embodiment. 1 is a cross-sectional view illustrating a schematic configuration of a fixing device according to a first 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 a schematic diagram which shows the positional relationship of a magnetic flux generation | occurrence | production part and a paper passing area | region. It is a schematic diagram which shows the positional relationship of an external heating roller and a pressure roller. 6 is a graph showing the temperature distribution of the fixing roller when small-size paper is continuously fed with an external heating roller in contact therewith. 6 is a graph showing a temperature distribution of a fixing roller when small-size paper is continuously passed without contacting an external heating roller. It is sectional drawing which shows schematic structure of the fixing device concerning a 2nd form. FIG. 2 is a cross-sectional view illustrating a schematic configuration of a fixing belt. It is sectional drawing which shows schematic structure of a pad member. It is sectional drawing which shows schematic structure of a pressurization body.

Explanation of symbols

1 Fixing roller (fixing rotating body)
2 Pressure roller (Pressure rotating body)
3 Magnetic flux generator (first heating source)
31 Excitation coil 32 Magnetic core 33 Coil bobbin 34 Drive circuit 41 Temperature sensor (temperature detection unit)
42 Temperature sensor 5 External heating roller (auxiliary rotating body)
51 Heater lamp (second heating source)
9 Control circuit 100 Fixing device (fixing device)

Claims (4)

In a fixing device for fixing an image on a recording medium to the recording medium,
A fixing rotator in which a heating area, which is an area having a width equal to the width of a large-size recording sheet, is heated by a first heating source;
A pressure rotator that is in contact with the fixing rotator and forms a nip for conveying the recording medium;
The second heating source heats at least a region where the axial direction of the fixing rotator is equal to the heating region of the fixing rotator , contacts the pressure rotator, and has an auxiliary rotator having high thermal conductivity ; With
The auxiliary rotor is
When warming up, the energization of the second heating source is turned on,
At the time of paper feeding, the energization of the second heating source is turned on when the size of the recording paper is the large size, and the second heating source is turned on when the size of the recording paper is smaller than the large size . A fixing device in which energization is turned off. In a fixing device for fixing an image on a recording medium to the recording medium,
A fixing rotator in which a heating area, which is an area having a width equal to the width of a large-size recording sheet, is heated by a first heating source;
A pressure rotator that is in contact with the fixing rotator and forms a nip for conveying the recording medium;
The second heating source heats at least a region where the axial direction of the fixing rotator is equal to the heating region of the fixing rotator , contacts the pressure rotator, and has an auxiliary rotator having high thermal conductivity ; ,
The surface temperature of the fixing rotator is disposed at a position that is an end portion in the axial direction of the fixing rotator and becomes a non-sheet-passing region when a small-sized recording paper smaller than the large-sized recording paper is passed. A temperature detection unit for detecting
The auxiliary rotor is
When warming up, the energization of the second heating source is turned on,
At the time of passing the paper, it is determined whether or not the non-sheet passing area in the heating area of the fixing rotating body is overheated based on the detection value by the temperature detecting unit. The fixing device is characterized in that energization of the second heating source is turned off and energization of the second heating source is turned on when it is not determined that the temperature is excessively high. In the fixing device according to claim 1 or 2,
The fixing rotator is a roller member that generates electromagnetic induction heat. In the fixing device according to claim 1 or 2,
The fixing device, wherein the fixing rotator is an endless belt member.

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